HIGH RESISTANCE STEEL SHEET AND HIGH RESISTANCE GALVANIZED STEEL SHEET FOR SHAPE FIXABILITY, AND MET

专利摘要:
patent summary: "high strength steel plate and high strength galvanized steel plate excellent in shape fixability, and production method thereof". The present invention relates to a high strength steel plate excellent in shape fixability. the high strength steel sheet contains c, si, mn, p, s, al, n, and the predetermined contents, in which a retained austenite phase of 5 to 20% by volume fraction is contained, an amount of The solid solution c contained in the retained austenite phase is 0.80 to 1.00% by weight, wsi? is it 1.10 times or more wsi *, wmn? is 1,10 times or more wmn *, and when the frequency distribution is measured, with respect to a sum of a ratio between wsi and wsi *, and a ratio between wal and wal *, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more. 20351453v1
公开号:BR112014002026B1
申请号:R112014002026-4
申请日:2012-07-27
公开日:2019-03-26
发明作者:Akinobu Minami；Hiroyuki Kawata；Akinobu Murasato；Yuji Yamaguchi；Natsuko Sugiura；Takuya Kuwayama；Naoki Muruyama；Takamasa Suzuki
申请人:Nippon Steel & Sumitomo Metal Corporation；
IPC主号:

专利说明:

Invention Patent Descriptive Report for HIGH-RESISTANCE STEEL SHEET AND HIGH-RESISTANCE GALVANIZED STEEL SHEET IN SHAPE FIXABILITY, AND METHOD OF PRODUCTION OF THE SAME.
TECHNICAL FIELD [001] The present invention relates to a high-strength steel sheet and a high-strength galvanized steel sheet in form fixability, and to a method of producing them. This application is based on and claims the priority benefit of previous Japanese Patent Application No. 2011-167689, filed on July 20, 2011, the total contents of which are hereby incorporated by reference.
BACKGROUND TECHNIQUE [002] In recent years, a demand for high-strength steel plates used for automobiles and the like has been increased, and high-strength steel plates having a maximum tensile strength of 900 MPa or more are also being used .
[003] These high strength steel sheets are formed in large quantities, and in an inexpensive manner, through stamping similar to light steel sheets, and are provided as members. However, according to a rapid acceleration of high reinforcement in recent years, there has been a problem that in a high strength steel plate having a maximum tensile strength of 900 MPa or more, an elastic return is caused after pressing formation, and it is difficult to form a target mold.
[004] As a technique to improve a fixability of the shape of a conventional high-strength steel plate, a hot-dip galvanized steel plate with high resistance and high ductility can be mentioned, in shape fixability, being a plate of steel containing, in mass%, C: 0.0001 to 0.3%, Al: 0.001
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2/107 to 4%, Μη: 0.001 to 3%, Mo: 0.001 to 4%, P: 0.0001 to 0.3%, and S: 0.01% or less, having a coating layer containing Al: 0.001 to 0.5%, Mn: 0.001 to 2%, Fe: less than 20%, and a remainder composed of Zn and unavoidable impurities, containing ferrite or ferrite and bainite from 50 to 97% in total in fraction of volume as a main phase, containing austenite of 3 to 50% in total in volume fraction as a second phase, and having a yield ratio of 0.7 or less (refer to Patent Document 1, for example).
[005] Also, as a technique to improve a fixability of the shape of a conventional high strength steel plate, a steel plate of high resistance in operability and shape fixability can be cited having a structure that contains, in mass% , each of C: 0.06 to 0.6%, Si + Al: 0.5 to 3%, Mn: 0.5 to 3%, P: 0.15% or less (0% is not included) , and S: 0.02% or less (including 0%), contains tempered martensite of 15% or more in an area ratio to the total structure, contains ferrite of 5 to 60% in an area ratio to the total structure, contains a retained austenite phase of 5% or more in a volume ratio to the total structure, and may additionally contain bainite and / or martensite, in which a proportion of retained austenite phase, but of the austenite phase retained, which turns into martensite by applying a pressure of 2% is 20 to 50% (refer to Patent Document 2, for example).
[006] Additionally, as a technique for improving a fixability of the shape of a conventional high-strength steel sheet, a method of producing a cold-rolled high-strength steel sheet in terms of impact property and fixability can be mentioned. form in which a plate having a composition of C: 0.08 to 0.18% by weight, Si: 1.00 to 2.0% by weight, Mn: 1.5 to 3.0% by weight, P: 0.03% by mass or less, S: 0.005% by mass or less, and T.AI: 0.01 to 0.1% by mass, and having a degree of segregation
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3/107 Mn with respect to a 1.05 to 1.10 molten plate is hot rolled, the resultant is additionally cold rolled, the resultant is then heated for a retention time of 60 seconds or more in a two-phase region or a single-phase region at 750 to 870Ό on a continuous annealing line, cooling is then carried out in a temperature region of 720 to 600Ό at an average cooling rate of 100 / s or less, cooling is then carried out until the temperature reaches 350 to 460Ό at an average cooling rate of 100 / s or more, retention is carried out for 30 seconds to 20 minutes, and cooling is then carried out until the temperature reaches a temperature environment to obtain a five-phase structure of polygonal ferrite, acicular ferrite, bainite, retained austenite phase, and martensite (refer to Patent Document 3, for example).
[007] In addition, as a technique for improving the fixability of the shape of a conventional high-strength steel plate, a high-strength steel plate in formability and fixability in a characterized manner in which it is mainly formed of a ferrite phase of 20 to 97% by volume fraction, and a retained austenite phase of 3% or more by volume fraction, in which a proportion of one part other than the ferrite phase having an aspect ratio of crystal grains of 2.5 or less is 50 to 95%, and the steel plate preferably contains C: 0.05 to 0.30% by weight, Si: 2.0% by weight or less, Mn: 0, 8 to 3.0% by weight, P: 0.003 to 0.1% by weight, S: 0.01% by weight or less, Al: 0.01 to 2.50% by weight, and N: 0.007% by weight mass or less, where Si and Al satisfy a Si + Al ratio ^Λ 0.50 mass% (refer to Patent Document 4, for example).
[008] Additionally, the present applicant discloses a steel sheet of high strength in ductility and stretch flangeability,
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4/107 containing predetermined components, and having a steel plate structure composed of, in fraction of volume, a 10 to 50% ferrite phase, a 10 to 50% tempered martensite phase, and a remaining hard phase ( refer to Patent Document 5, for example).
BACKGROUND DOCUMENT
PATENT DOCUMENT [009] Patent Document 1: Japanese Patent Publication No. [0010] 253386 [0011] Patent Document 2: Japanese Patent Publication No.
[0012] 218025 [0013] Patent Document 3: Japanese Patent Publication No.
[0014] 2004-300452 [0015] Patent Document 4: Japanese Patent Publication
No.2007-154283 [0016] Patent Document 5: International Publication WO2012 / 036269A1
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION [0017] However, in Patent Document 1, there is a problem that a production cost is increased, since it is essential to add a large amount of expensive Mo.
[0018] In addition, in Patent Document 2, the production steps become complicated, since the annealing step after hot rolling is carried out in two divided steps, and, however, it was difficult to ensure the fixability in a stable manner. on high-strength steel sheet having a maximum tensile strength of 900 MPa or more.
[0019] Additionally, in Patent Document 3, it is required to carry out processing to control the casting conditions for
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5/107 reduce a central secretion of Mn in the plate when producing the plate, and there is a possibility of reducing production efficiency. [0020] Additionally, in Patent Document 4, the steel plate structure and the aspect ratio of the crystal grains are specified to improve shape fixability, but no specification is made to ensure ductility and resistance to stress , so that the fastening of the high-strength steel sheet with the maximum tensile strength of 900 MPa or more was unstable. In addition, the shape fixability in the region of high strength of 900 MPa or more, as above, is insufficient, and, therefore, it has been desired to further improve the shape fixability.
[0021] Additionally, in Patent Document 5, it is basically required to have the martensite phase tempered by 10 to 50%, so that there is an interest that the operability becomes inferior.
[0022] Consequently, the present invention was produced in view of such circumstances, and an objective of the same is to provide a high strength steel sheet and a high strength galvanized steel sheet having fixability of form and operability, while ensuring a high tensile strength of 900 MPa or more, and a method of producing them.
MEANS TO SOLVE THE PROBLEMS [0023] The present inventors conducted rigorous studies to solve the problems described above. As a result of these, they found that it is possible to obtain a steel sheet having fixability of form and operability with a large amount of hardening operation in an initial formation stage, while ensuring a high resistance to maximum stress of 900 MPa or moreover, by the production of a steel plate microstructure to be a microstructure having a retained austenite phase, and by Si and Mn concentration in the retained austenite phase.
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6/107 [0024] The purpose of the present invention to solve the problems described above is as follows.
(1) [0025] A steel sheet of high strength in form fixability, contains, in mass%, C: 0.075 to 0.300%; Si: 0.30 to 2.5%; Mn: 1.3 to 3.50%; P: 0.001 to 0.030%; S: 0.0001 to 0.0100%; Al: 0.080 to 1.500%; N: 0.0001 to 0.0100; O: 0.0001 to 0.0100; and a remainder of Fe and unavoidable impurities, in which a steel plate structure contains a 5 to 20% austenite phase retained in volume fraction in a range of 1/8 thickness to 3/8 thickness of the plate of steel; an amount of solid solution C contained in the retained austenite phase is 0.80 to 1.00% by weight%; Wsíy defined as an amount of solid Si solution contained in the retained austenite phase is 1.10 times or more a Wsr defined as an average amount of Si in the range of 1/8 thickness to 3/8 thickness of the steel plate ; WwinY defined as an amount of solid Mn solution contained in the retained austenite phase is 1.10 times or more WMn * defined as an average amount of Mn in the range of 1/8 thickness to 3/8 thickness of the steel plate; and when the frequency distribution is measured, by adjusting a plurality of measurement regions, each having a diameter of 1 pm or less in the range of 1/8 thickness to 3/8 thickness of the steel plate, with respect to to a sum of a ratio between WSi defined as a measured value of an amount of Si in each of the plurality of measurement regions and Wsr being the average amount of Si, and a ratio between Wai defined as a measured value of an amount of Si Al in each of the plurality of measurement regions, and Wai * being an average amount of Al, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more.
(2)
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7/107 [0026] In the high strength steel plate in form fixability, according to (1), the steel plate structure additionally contains a ferrite phase of 10 to 75% in volume fraction, and any or both of a bainitic ferrite phase and a 10 to 50% bainite phase in total, a tempered martensite phase is limited to less than 10% by volume fraction, and a “fresh” martensite phase is limited to 15 % or less in fraction of volume.
(3) [0027] The steel sheet of high strength in form of fixability additionally contains, in% by mass, one or two or more of Ti: 0.005 to 0.150%, Nb: 0.005 to 0.150%, V: 0.005 to 0.150 %, and B: 0.0001 to 0.0100%.
(4) [0028] The steel sheet of high strength in form fixability, according to (1) additionally contains, in mass%, one or two or more of Mo: 0.01 to 1.00%, W : 0.01 to 1.00%, Cr: 0.01 to 2.00%, Ni: 0.01 to 2.00%, and Cu: 0.01 to 2.00%.
(5) [0029] The steel sheet of high strength in form fixability, according to (1) additionally contains, in mass%, one or two or more of Ca, Ce, Mg, Zr, Hf, and REM from 0.0001 to 0.5000% in total.
(6) [0030] A galvanized steel sheet of high strength in form fixability has the steel sheet of high strength according to (1) having a galvanized layer formed on its surface.
(7) [0031] In galvanized steel sheet of high strength in form fixability, according to (6), a coating film produced from a compound oxide containing a phosphorus oxide and / or
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8/107 phosphorus is formed on a surface of the galvanized layer.
(8) [0032] A method of producing a highly resistant steel sheet in form fixability includes: a hot rolling step being a heating step of a plate containing, in mass%, C: 0.075 to 0.300 %, Si: 0.30 to 2.5%, Mn: 1.3 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.080 to 1.500%, N : 0.0001 to 0.0100, O: 0.0001 to 0.0100, and a remainder of Fe and unavoidable impurities at 1100Ό or more, hot lamination on the plate in a temperature region where a higher temperature high between 850Ό and an Ar 3 temperature is set to a lower limit temperature, performing a first cooling of cooling performance in a range from a rolling completion to a beginning of winding at a rate of 100 / second or more on average , carrying out winding in a winding temperature range of 600 to 750Ό, and carrying out a second cooling of the coiled steel sheet in a coiling temperature range a (coiling temperature - 100) Ό at a rate of 10 ° / hour or less on average; and a continuous annealing step to perform annealing on the steel sheet at a maximum heating temperature (Aci + 40) Ό at 1000Ό after the second cooling, then performing a third cooling at an average cooling rate of 1.0 to 10.OO / following a range of maximum heating temperature at 700Ό, then performing a fourth cooling at an average cooling rate of 5.0 to 200.0'C / second in a range from 700Ό to 500Ό, and then carrying out the retention process of retention of the steel plate after being subjected to the fourth cooling for 30 to 1000 seconds in a range of 350 to 450Ό.
(9)
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9/107 [0033] The method of production of the high strength steel sheet in form fixability, according to (8), includes a cold rolling step of stripping and then cold rolling at a reduction rate of 30 to 75%, between the hot rolling step and the continuous annealing step.
(10) [0034] The method of production of the high strength steel sheet in form fixability, according to (8), includes a tempering lamination step of performing lamination on the steel sheet at a rate of reduction of less than 10% after the continuous annealing step.
(11) [0035] A method of producing a galvanized steel sheet of high strength in form fixability, includes forming, after carrying out the retention process when producing the high strength steel sheet in the production method according to (8), of a galvanized layer on a steel plate surface by conducting electroplating.
(12) [0036] A method of producing a highly resistant galvanized steel sheet in form fixability includes forming, between the fourth cooling and the retention process, or after the retention process when producing the steel sheet from high resistance in the production method according to (8), of a galvanized layer on a steel sheet surface by immersing the steel sheet in a galvanizing bath.
(13) [0037] In the production method of the galvanized steel sheet of high strength in form fixability, according to (12), the steel sheet after being immersed in the galvanizing bath is reheated to 460 a
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10/107
600Ό, and held for two seconds or more to make the galvanized layer turn on.
(14) [0038] In the production method of the galvanized steel sheet of high strength in form fixability, according to (11), after the galvanized layer is formed, a coating film produced from a composite oxide containing either or both of a phosphorus oxide and phosphorus is added to a surface of the galvanized layer.
(15) [0039] In the production method of the high-strength galvanized steel sheet in form fixability, according to (13), after the galvanized layer is bonded, a coating film produced from a composite oxide containing either or both of a phosphorus oxide and phosphorus is given to an alloyed galvanized layer surface.
EFFECT OF THE INVENTION [0040] Each of a high strength steel sheet and a high strength galvanized steel sheet of the present invention contains predetermined chemical components, and when a frequency distribution is measured, in a 1/8 range of thickness to 3/8 of thickness of the steel plate, with respect to a sum of a ratio between a measured value of Si quantity and an average quantity of Si, and a ratio between a measured value of quantity Al and an average quantity of Al, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more, so that it is possible to create a distribution state where either Si or Al exists in an amount being an amount equal to or greater than an average amount in the total area of the steel sheet. Consequently, an iron-based carbide generation is suppressed, and C can be prevented from being
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11/107 consumed as carbide. For this reason, it is possible to stably maintain a retained austenite phase, resulting in that form fixability, ductility and resistance to tension, can be greatly improved.
[0041] Additionally, in each of the high strength steel sheet and the high strength galvanized steel sheet of the present invention, the retained austenite phase occupies 5 to 20% in volume fraction, an amount of Si contained in the phase of retained austenite is 1.10 times or more an average amount of Si, an amount of Mn contained in the retained austenite phase is 1.10 times or more an average amount of Mn, and an amount of C contained in the retained austenite phase it is 0.80 to 1.00% by weight%, so that it is possible to obtain a steel sheet having fixability of form and operability, while ensuring a high strength of 900 MPa or more than a resistance to maximum stress.
[0042] Additionally, in a method of producing a steel sheet of the present invention, a step of producing a sheet containing predetermined chemical components to be a hot rolled coil includes a first cooling step in which a cooling rate of when hot rolling is completed when winding is conducted, it is set at 10 ° C / second or more, a steel sheet production combining step to be a 600 to 700Ό coil, and a second step cooling rate in which an average cooling rate of a coiling temperature a (the coiling temperature -100) Ό, is adjusted to 10 / hour or less, so that Si of solid solution and Al of solid solution inside the plate of steel can be distributed in a symmetrical manner, namely, an amount of Al is reduced to a portion where an amount of Si is large, and a portion where Si of solid solution is concentrated, and a portion where Mn solid solution
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12/107 is concentrated can be adjusted to the same.
[0043] Additionally, in the steel sheet production method of the present invention, a steel sheet production step passes through a continuous annealing line, includes an annealing step at a maximum heating temperature (Ac1 + 40) Ό at 1000Ό, a third cooling stage for cooling the steel plate from the maximum heating temperature at 700Ό at 1.0 to 1060 / sec on average, a fourth cooling stage of the plate cooling steel after being subjected to the third cooling step from 700Ό to 500Ό at 5.0, 200 to 200.0'C / sec on average, and a steel plate retention step after being subjected to the fourth cooling step for 30 to 1000 seconds in a range of 350 to 450Ό, so that a microstructure of the steel sheet contains the 5 to 20% retained austenite phase, and Si, Mn, and C having predetermined concentrations can be dissolved solid in the retained austenite phase , resulting in a plate high strength steel, or a high strength galvanized steel sheet capable of ensuring a high strength of 900 MPa or more of the maximum tensile strength and having fixability of form and operability, can be obtained.
MODE FOR CARRYING OUT THE INVENTION [0044] Hereinafter, a high-strength steel sheet and a high-strength galvanized steel sheet in form-fixability, and a method of producing them of the present invention will be described in detail.
HIGH-RESISTANCE STEEL SHEET [0045] A high-strength steel plate of the present invention is a steel plate that contains, in mass%, each of C: 0.075 to 0.300%, Si: 0.30 to 2, 5%, Mn: 1.3 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.080 to 1.500%, N: 0.0001 to 0.0100, O : 0.0001
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13/107 to 0.0100, and a remainder of Fe and unavoidable impurities, in which a steel plate structure contains an austenite phase retained from 5 to 20% in volume fraction in a range of 1/8 thickness at 3/8 thickness of the steel plate, an amount of solid solution C contained in the retained austenite phase is 0.80 to 1.00% by mass%, WSiY defined as an amount of solid Si solution contained in the phase of retained austenite is 1.10 times or more Wsr defined as an average amount of Si in the range of 1/8 thickness to 3/8 thickness of the steel plate, WMnY defined as an amount of solid Mn solution contained in the phase of retained austenite is 1.10 times or more WMn * defined as an average amount of Mn in the range of 1/8 thickness to 3/8 thickness of the steel plate, and when the frequency distribution is measured, by adjusting a plurality of measurement regions, each having a diameter of 1 pm or less in the range of 1/8 thickness to 3 / 8 thickness of the steel plate, with respect to a sum of a ratio between Wsí defined as a measured value of an amount of Si in each of the plurality of measurement regions and Wsr being the average amount of Si, and a ratio between Wai defined as a measured value of an amount of Al in each of the plurality of measurement regions, and Wai * being an average amount of Al, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 5.00 or more.
[0046] Hereinafter, reasons for limiting the steel plate structure and chemical components (composition) in the present invention will be described. Note that the notation of% means fraction of volume related to the structure, and means mass% related to the composition, unless otherwise noted.
[0047] The steel plate structure of the high strength steel plate of the present invention contains predetermined chemical components, in which, in the range of 1/8 thickness to 3/8
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14/107 steel sheet thickness, the austenite phase retained from 5 to 20% by volume fraction is contained, the amount of solid solution C in the retained austenite phase is 0.80 to 1.00% by weight% , WMnY / WMn * being the ratio between WMnY being the amount of solid Mn solution in the retained austenite phase, and WMn * being the average amount of Mn in the range of 1/8 thickness to 3/8 thickness of the plate. steel is 1.10 or more, and Wsíy / Wsr being the ratio between the amount of solid solution Si Wsíy in the retained austenite phase, and Wsr being the average amount of Si in the range of 1/8 of thickness to 3/8 of steel sheet thickness is 1.10 or more, so that the steel sheet having fixability of form and operability, while ensuring a high strength of 900 MPa or more of tensile strength, is obtained.
[0048] Note that it is desirable that the austenite phase retained from 5 to 20% in volume fraction is contained in the total steel sheet structure. However, a metal structure in the range of 1/8 thickness to 3/8 thickness with 1/4 of the steel plate thickness being the center representing the total steel plate structure. Therefore, if austenite retained from 5 to 20% in volume fraction is contained in the range of 1/8 thickness to 3/8 thickness of the steel plate, it can be related that austenite retained from 5 to 20% in fraction of volume is substantially contained in the total steel sheet structure. For this reason, in the present invention, a range of volume fraction of austenite retained in the range of 1/8 thickness to 3/8 thickness of the base steel plate, is defined.
[0049] With respect to the volume fraction of the retained austenite phase, an X-ray analysis is conducted by adjusting a surface parallel to and at a thickness of 1/4 from the sheet surface of the steel sheet as an observation surface to calculate a fraction of area, and a result of the calculation can be related to the fraction of volume.
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15/107 [0050] Note that a microstructure in the range of 1/8 thick to 3/8 thick has high homogeneity, and if measurement is performed in a sufficiently large region, even when the measurement is performed in any position in the range of 1/8 of thickness to 3/8 of thickness, a fracture of microstructure representing the range of 1/8 of thickness to 3/8 of thickness can be obtained.
[0051] An X-ray diffraction test is performed on an arbitrary surface parallel to and in 1/8 thickness to 3/8 thickness from the surface of the steel plate sheet to calculate a fraction of the austenite phase area retained, and a calculation result can be related to the volume fraction in the range of 1/8 thickness to 3/8 thickness. Concretely, it is preferable to perform the X-ray diffraction test on a surface parallel to and at a thickness of 1/4 from the surface of the steel plate sheet in a range of 250,000 mm square or more.
[0052] Hereinafter, elements of solid solution and quantities of solid solution elements dissolved solid in the retained austenite phase, will be described in detail.
RETENTED AUSTENITE PHASE [0053] Quantities of solid elements dissolved in the retained austenite phase determine a stability of the retained austenite phase, and change the amount of pressure required when the retained austenite phase is transformed into hard martensite. For this reason, it is possible to control an operating hardening behavior by controlling the quantities of solid solution elements in the retained austenite phase, resulting in that the shape fixability, ductility and stress resistance can be greatly improved.
[0054] The solid solution of C in the retained austenite phase is an element that increases the stability of the retained austenite phase, and
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10/167 increases a transformed martensite resistance. If the amount of solid C solution is less than 0.80%, it is not possible to sufficiently achieve the effect of improving the ductility obtained by retained austenite, so that in the present embodiment, a lower limit of the amount of solid C solution is adjusted to 0.80%. It is noted that in order to sufficiently increase ductility, the amount of solid solution of C is preferably 0.85% or more, and is more preferably 0.90% or more. On the other hand, if the amount of solid C solution exceeds 1.00%, the strength of transformed martensite is increased much more, and the martensite acts as a starting point of destruction with respect to processing where a high pressure is locally applied as strain flange deformation, which only deteriorates formability, so that an upper limit on the amount of solid C solution is set to 1.00% or less. From this point of view, the amount of solid C solution is preferably 0.98% or less, and is more preferably 0.96% or less.
[0055] Note that the amount of solid C (Cg) solution in the retained austenite phase can be determined using the following equation (1) by conducting an X-ray diffraction test under the same conditions as those of the measurement of the fraction of area of the retained austenite phase to determine a lattice constant to that of the retained austenite phase.
Mathematical equation 1 (a - 0.3556) 12.01
C = ^y -------- '· * «D ⁷ 0.00095 55.84 [0056] Mn of solid solution in the retained austenite phase is an element that increases the stability of the retained austenite phase. If an amount of solid Mn solution in the retained austenite phase is
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17/107 adjusted for WMng, and an average amount of Mn in the range of 1/8 thickness to 3/8 thickness of the steel plate is adjusted for Wm ^, a lower limit of WMng / Wmr * being a ratio of both the amounts are adjusted to 1.1 or more in the present embodiment. It is noted that in order to increase the stability of the retained austenite phase, the WMng / WMn * is preferably 1.15 or more, and is more preferably 1.20 or more.
[0057] Additionally, the solid Si solution in the retained austenite phase is an element that moderately destabilizes the retained austenite phase, increases an operating hardening performance, and increases the form fixability in a low pressure region. Specifically, by the Si concentration in the retained austenite phase, it is possible to give a moderate instability to the retained austenite phase, so that it is possible to cause easy transformation when applying a pressure, and to cause sufficient operational hardening at an early stage processing time. On the other hand, the solid Si solution in the retained austenite phase is an element that increases the stability of the retained austenite phase, and contributes to a local ductility in a region of high resistance.
[0058] In the present embodiment, by adjusting Wsig / Wsr being a ratio between Wsig defined as an amount of solid Si solution in the retained austenite phase, and Wsr defined as an average amount of Si in the 1/8 thickness range at 3/8 thickness of the steel plate to 1.10 or more, the influence of Si solution described above is obtained. Note that Wsig / Wsr is preferably 1.15 or more, and is more preferably 1.20 or more.
[0059] Additionally, the amount of solid Mn solution and the amount of solid Si solution in the retained austenite phase are obtained by first collecting a sample by adjusting a thick cross section parallel to a lamination direction of the plate. steel like
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18/107 an observation surface, in the range of 1/8 thickness to 3/8 thickness of the steel plate. Then, an analysis of ΕΡΜΑ is performed in the range of 1/8 thick to 3/8 thick with 1/4 thick being the center for measuring quantities of Mn and Si. The measurement is performed while a probe diameter is set to 0.2 to 1.0 æm, and a one-point measurement time is set to 10 ms or more, and the amounts of Mn and Si are measured at 2500 points or more, based on an area analysis, to thereby create Si and Mn concentration maps.
[0060] Here, in the measurement results described above, a point at which the concentration of Mn exceeds three times an added Mn concentration can be considered to be a point at which an inclusion, such as Mn sulfide, is measured. In addition, a point at which the Mn concentration is less than 1/3 times the added Mn concentration can be considered to be a point at which an inclusion, such as Al oxide, is measured. Since the Mn concentrations in these inclusions do not affect a phase transformation behavior in the base iron almost entirely, the measurement resulting from the inclusions is adjusted to be excluded from the measurement results described above. Note that the Si measurement results are also processed in a similar manner, and the inclusion measurement results are adjusted to be excluded from the measurement results described above.
[0061] Additionally, the region analyzed either before or after the ΕΡΜΑ analysis described above is observed using an EBSD analysis method, distributions of FCC iron (retained austenite phase) and BCC iron (ferrita) are mapped, the obtained map is superimposed with the Si and Mn concentration maps, and quantities of Si and Mn in a region superimposed with an FCC iron region, namely, retained austenite, are read. Consequently, the amount of solid solution of
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Si and the amount of solid Mn solution in the retained austenite phase can be determined.
[0062] The solid Si solution in the retained austenite phase is the element that moderately destabilizes the retained austenite phase, increases the performance of the operating hardening, and increases the form fixability in the low pressure region, and is the element that it increases the stability of the retained austenite phase, and contributes to local ductility in the high strength region, as described above, and, in addition to this, it is also an element of suppression of an iron-based carbide generation.
[0063] Normally, when Si is only concentrated in the retained austenite phase, the iron-based carbide is generated in a portion where Si is not concentrated, and C being an austenite stabilizing element is consumed as a carbide, resulting in that the retained austenite phase cannot be sufficiently secure and the fixability of shape is deteriorated, which is a problem.
[0064] Consequently, in the present embodiment, Al being an iron-based carbide suppression element, similar to Si, is added in an appropriate amount, and processing is carried out based on a predetermined thermal history in the lamination step a resulting in that Si can be efficiently concentrated in the retained austenite. Additionally, at this time, Al exhibits the concentration distribution opposite to the Si concentration distribution, so that a region with low Si concentration has a higher amount of Al.
[0065] For this reason, in retained austenite, it is possible to suppress the generation of iron-based carbide by Si in a region with a high concentration of Si, and in a region with a low concentration of Si, the generation of carbide based on Si iron can be suppressed by Al, instead
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20/107 of Si. Consequently, it is possible to prevent C from being consumed as a carbide in the retained austenite phase, resulting in the retained austenite phase being efficiently obtained. Additionally, the generation of coarse iron-based carbide that becomes a starting point of destruction at the moment of processing can be suppressed, which contributes to the improvement of shape fixability, ductility and resistance to tension.
[0066] Si is the element that destabilizes austenite, and, generally, Mn is concentrated in the retained austenite phase, and Si is concentrated in the ferrite. However, in the present invention, Al is added, and through predetermined production conditions, Al is concentrated in ferrite, and Si is concentrated in the retained austenite phase.
[0067] Additionally, when a thick cross-section parallel to the rolling direction of the steel sheet, according to the present embodiment, a frequency distribution (histogram) of F (Wsí, Wai) = Wsí / Wsr + Wai / Wai * being a sum of a ratio between Wsí defined as a measured value of an amount of Si in each of the measurement regions at 1/8 thickness to 3/8 thickness with 1/4 thickness being the center, and Wsr defined as an average amount of Si in 1/8 thickness to 3/8 thickness, and the ratio between Wai defined as a measured value of an amount Al in each of the measurement regions at 1/8 thickness at 3 / 8 thick with 1/4 thick being the center, and Wai * defined as an average amount of Al at 1/8 thick at 3/8 thick, is created, a mode value is adjusted to fall within a range from 1.95 to 2.05, and a K kurtosis of the histogram defined by the following equation (2) is adjusted to 2.00 or more s. Note that the measurement region is adjusted to have a diameter of 1 pm or less, and a plurality of such measurement regions are adjusted to measure the amount of Si and the amount of Al.
[0068] By creating a distribution state as described
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21/107 above where either Si or Al exists in an amount being an amount equal to or greater than an average amount in the total area of the steel plate, the generation of iron-based carbide is suppressed, so that it is possible to hold stably the retained austenite phase, resulting in that shape fixability, ductility, and stress resistance, can be greatly improved.
[0069] In either case where the mode value becomes less than 1.95, a case where the mode value exceeds 2.05, and a case where the K kurtosis becomes less than 2.00, there is a region where iron-based carbide generation suppression performance is small in the measurement range, and there is a possibility that fixability of sufficient shape, formability and / or resistance cannot be achieved. From this point of view, kurtosis K is preferably 2.50 or more, and is more preferably 3.00 or more.
[0070] Here, kurtosis K is a number determined by the following equation (2) of data, and is a numerical value evaluated by comparing a frequency distribution of data with a normal distribution. When kurtosis is a negative number, this represents that a data frequency distribution curve is relatively flat, and it is significant that the higher an absolute value is, the more the frequency distribution is deviated from the normal distribution.
[0071] Note that Fi in the following equation (2) indicates a value of F (W _S i, W _A i) at measurement point i, F * indicates an average value of F (W _S i, W _A i ), s * indicates a standard deviation of F (Wsí, W _A i), and N indicates a number of measurement points in the histogram obtained.
Mathematical equation 2
3ÇV-1) ² ₍ TV-2) (# - 3) [0072] Note that the method of measuring the quantities of
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22/107 C, Mn, Si and Al solid solution is not limited to the method described above. For example, an EMA method, or direct observation using a three-dimensional atom probe (3D-AP), can be performed to measure the concentrations of the various elements. MICRO-STRUCTURE [0073] It is preferred that the steel plate structure of the high strength steel plate of the present invention contains, in addition to the austenite phase described above, a ferrite phase of 10 to 75% by volume fraction, and either or both of a bainitic ferrite phase, and a 10 to 50% bainite phase in total by volume fraction, a tempered martensite phase is limited to less than 10% by volume fraction, and a martensite phase “Fresh” is limited to 15% or less in fraction of volume. When the high strength steel sheet of the present invention has the steel sheet structure as described above, it becomes a steel sheet having additionally form, fixability and formability.
Ferrite phase [0074] The ferrite phase is an effective structure for improving ductility, and is preferably contained in the steel plate structure in an amount of 10 to 75% by volume fraction. The volume fraction of the ferrite phase contained in the steel sheet structure is, more preferably, 15% or more, and is still, more preferably, 20% or more from a ductility point of view. In addition, in order to sufficiently increase the tensile strength of the steel plate, the volume fraction of the ferrite phase contained in the steel plate structure is, more preferably, adjusted to 65% or less, and is, even more preferably, adjusted to 50% or less. When the volume fraction of the ferrite phase is less than 10%, there is a chance that sufficient ductility cannot be achieved. On the other hand, the ferrite phase is a soft structure, so that when the volume fraction
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23/107 of it exceeds 75%, sufficient strength may not be obtained.
Bainitic ferrite phase and / or bainite phase [0075] Bainitic ferrite and / or bainite are / are necessary structure (s) to efficiently obtain the retained austenite phase, and preferably contained in the steel plate structure in an amount of 10 to 50% in total in fraction of volume. In addition, the bainitic ferrite phase and / or bainite phase are / is microstructure (s) having a resistance that is on average a resistance of a soft ferrite phase and hard martensite phase, tempered martensite phase and austenite phase retained, and the bainitic ferrite phase and / or bainite phase is / are more preferably contained in an amount of 15% or more, and, even more preferably, contained in an amount of 20% or more, from a point view of stretch flangeability. On the other hand, it is not preferable that the volume fraction of the bainitic ferrite phase and / or the bainite phase exceeds 50%, as there is a problem that a yield stress is excessively increased and the fixability of the shape is deteriorated.
Tempered martensite phase [0076] The tempered martensite phase is a structure for improving the resistance to tension. However, martensite is preferably generated by consumption of untransformed austenite with a high Si content, so there is a tendency for a steel sheet containing a large amount of tempered martensite to have a small amount of austenite retained with a high content of Si. Additionally, it is not preferable that a quantity of tempered martensite is 10% or more, since there is a problem that the yield stress is excessively increased, and the fixability of the shape is deteriorated. For this reason, in the present invention, tempered martensite is limited to less than 10% by volume fraction. The tempered martensite phase is preferably 8%
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24/107 or less, and is more preferably 6% or less.
“Fresh” martensite phase [0077] The “fresh” martensite phase greatly improves stress resistance, but on the other hand, it becomes a starting point of destruction to deteriorate the stretch flangeability. Additionally, martensite is generated by preferential consumption of untransformed austenite with a high Si content, so there is a tendency for a steel sheet containing a large amount of "fresh" martensite to have a small amount of austenite retained with a large Si content. From the point of view of stretching flangeability and shape fixability, the “fresh” martensite phase in the steel plate structure is preferably limited to 15% or less in volume fraction. In order to further increase the stretch flangeability, the volume fraction of "fresh" martensite is most preferably set to 10% or less, and is even more preferably set to 5% or less. Other microstructures [0078] It is also possible that the steel plate structure of the high strength steel plate of the present invention contains a structure other than the above, such as perlite and / or coarse cementite. However, when an amount of coarse perlite and / or cementite is increased in the steel plate structure of the high strength steel plate, the ductility is deteriorated. For this reason, a volume fraction of coarse perlite and / or cementite contained in the steel sheet structure is preferably 10% or less in total, and is more preferably 5% or less in total.
[0079] The volume fraction of each structure contained in the steel plate structure of the high strength steel plate of the present invention can be measured by a method described below, for example.
[0080] Regarding the volume fractions of ferrite, bainitic ferrite,
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25/107 bainite, tempered martensite and “fresh” martensite contained in the steel plate structure of the high strength steel plate of the present invention, a sample is collected, while a thick cross section perpendicular to the lamination direction of the plate steel is fitted as an observation surface, the observation surface is polished and subjected to nital etching, and a strip of 1/8 thickness to 3/8 thickness with 1/4 of the plate thickness being the center is observed with FE-SEM (Field Emission Scanning Electron Microscope) to measure area fractions, and the measurement results can be related to the volume fractions.
[0081] As described above, the microstructure fractions, except the retained austenite phase, can be measured by performing the observation with the electron microscope at an arbitrary position at 1/8 thick at 3/8 thickness. Concretely, an observation with the electron microscope is performed in three or more fields of vision adjustment, on a surface that is perpendicular to the surface of the base steel plate sheet, and parallel to the rolling direction, while providing a gap 1 mm or more between them in the range of 1/8 thick to 3/8 thick, to calculate a fraction of the area of each structure in a range where the observation area is 5000 mm square or more in total, and a The result of the calculation can be related to the volume fraction in the range of 1/8 thickness to 3/8 thickness.
[0082] Ferrite is a mass of crystal grains, and it is a region in which no iron-based carbide with a axis greater than 100 nm or more exists inside it. Note that the volume fraction of ferrite is a sum of a volume fraction of ferrite remaining at the maximum heating temperature and a volume fraction of ferrite recently generated in a transformation temperature region.
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26/107 of ferrite.
[0083] Bainitic ferrite is an aggregation of crystal grains in the form of a slat, and does not contain, inside the slat, an iron-based carbide with a larger axis of 20 nm or more.
[0084] Bainite, which is an aggregation of clapboard crystal grains, contains, inside the clapboard, a plurality of iron-based carbides with a larger axis of 20 nm or more, and those carbides belonging to a variant simple, namely, an iron-based carbide group that stretches in the same direction. Here, the carbide group based on iron stretching in the same direction means one having a difference of 5 or less in ^the direction of stretch carbide iron-based group.
[0085] The tempered martensite, which is an aggregation of crystal grains in the form of a slat, contains, inside the slat, a plurality of iron-based carbides with a greater axis of 20 nm or more, and those carbides belonging to a plurality of variants, namely, a plurality of a group of iron-based carbides stretching in different directions.
[0086] It is noted that bainite and tempered martensite can be easily distinguished by looking at iron-based carbide inside the slat-shaped crystal grain using FE-SEM and examining its stretching direction.
[0087] Additionally, the “fresh” martensite and retained austenite are not sufficiently corroded by the nital engraving.
Consequently, “fresh” martensite and retained austenite are clearly distinguished from the aforementioned structures (ferrite, bainite ferrite, bainite, tempered martensite) in the observation with FE-SEM.
[0088] Therefore, the volume fraction of “fresh” martensite is obtained as a difference between a fraction of area of a region not
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Corroded 27/107 observed with FE-SEM, and a fraction of retained austenite area measured with X-rays.
CHEMICAL COMPONENTS [0089] Next, the chemical components (composition) of the high-strength steel sheet of the present invention will be described. Note that in the description below, [%] indicates [% in mass%]. C: 0.075 to 0.300% [0090] C is contained to increase the strength of the high strength steel sheet. However, if a C content exceeds 0.300%, weldability becomes insufficient. From a weldability point of view, the C content is preferably 0.250% or less, and is more preferably 0.220% or less. On the other hand, if the C content is less than 0.075%, the resistance is lowered, and it is not possible to ensure the maximum tensile strength of 900 MPa or more. In order to increase the strength, the C content is preferably 0.090% or more, and is more preferably 0.100% or more.
Si: 0.30 to 2.50% [0091] Si is an element required to suppress the generation of iron-based carbide in an annealing step to obtain a predetermined amount of retained austenite. However, if the Si content exceeds 2.50%, the steel sheet becomes brittle, and the ductility is deteriorated. From a ductility point of view, the Si content is preferably 2.20% or less, and is more preferably 2.00% or less. On the other hand, if the Si content is less than 0.30%, a large amount of iron-based carbides is generated in the annealing step, resulting in that a sufficient amount of retained austenite phase cannot be obtained, and it is not possible to achieve both of the maximum tensile strength of 900 MPa or more and form fixability. In order to increase the fixability of form, a lower limit value of Si is preferably 0.50% or more, and is, more
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28/107 preferably 0.70% or more.
Mn: 1.30 to 3.50% [0092] Mn is added to the steel sheet of the present invention to increase the strength of the steel sheet. However, if an Mn content exceeds 3.50%, a concentrated portion of coarse Mn is generated in a central portion in the sheet thickness of the steel plate, embrittlement occurs easily, and a problem such as breaking a molten plate occurs easily. . Additionally, if the Mn content exceeds 3.50%, weldability is also impaired. Therefore, it is required to adjust the Mn content to 3.50% or less. From a weldability point of view, the Mn content is preferably 3.20% or less, and is more preferably 3.00% or less. On the other hand, if the Mn content is less than 1.30%, a large amount of soft structures is formed during cooling after annealing, which makes it difficult to ensure a maximum tensile strength of 900 MPa or more, so it is required to adjust the Mn content to 1.30% or more. In order to increase the strength, the Mn content is preferably 1.50% or more, and is more preferably 1.70% or more.
P: 0.001 to 0.030% [0093] P tends to be added in the central portion in the sheet thickness of the steel plate, and weakens the weld zone. If a P content exceeds 0.030%, significant weakness of the weld zone occurs, so that the P content is limited to 0.030% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the P content, 0.001% is adjusted as a lower limit value, as production costs increase greatly when the P content is adjusted to less than 0.001 %.
S: 0.0001 to 0.0100% [0094] S has an adverse effect on weldability and manufacturability during casting and hot rolling. For this
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29/107 reason, an upper limit value of S content is set to 0.0100% or less. In addition, S couples with Mn to form coarse MnS and lowers stretch ductility and flangeability, so that the S content is preferably adjusted to 0.0050% or less, and is more preferably adjusted to 0.0025 % or less. Although the effect of the present invention is exhibited without particularly setting a lower limit on the S content, 0.0001% is adjusted as a lower limit value, as production costs increase greatly when the S content is adjusted below than 0.0001%.
Al: 0.080% to 1.500% [0095] Al is an element that suppresses the generation of iron-based carbide to make it easy to obtain the retained austenite phase. In addition, by adding an appropriate amount of Al, it is possible to increase an amount of solid solution of Si in the retained austenite phase to increase the form fixability. However, if an Al content exceeds 1,500%, weldability worsens, so that an upper limit on the Al content is adjusted to 1,500%. From this point of view, the Al content is preferably adjusted to 1,200% or less, and is more preferably adjusted to 0.900% or less. On the other hand, if the Al content is less than 0.080%, the effect of increasing the amount of solid Si solution in the retained austenite phase is insufficient, and it is not possible to ensure sufficient fixability. When Al is increased, Si is easily concentrated in the retained austenite phase, so that the Al content is preferably 0.100% or more, and is more preferably 0.150% or more.
N: 0.0001 to 0.0100% [0096] N forms a coarse nitride and deteriorates ductility and stretch flangeability, so that an added amount of this is required to be suppressed. If an N content exceeds
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10/30
0.0100%, this trend becomes evident, so that a range of N content is adjusted to 0.0100% or less. In addition, since N causes a generation of spiracles during welding, the N content is preferably small. Although the effect of the present invention is exhibited without particularly setting a lower limit on the N content, 0.0001% is adjusted as a lower limit value, as production costs increase greatly when the N content is adjusted below than 0.0001%.
O: 0.0001 to 0.0100% [0097] O forms an oxide and deteriorates ductility and stretch flangeability, so that an added amount of this is required to be suppressed. If an O content exceeds 0.0100%, the deterioration of stretch flangeability becomes noticeable, so that an upper limit on the O content is set to 0.0100% or less. The O content is preferably 0.0080% or less, and is more preferably 0.0060% or less. Although the effect of the present invention is exhibited without particularly setting a lower limit on the O content, 0.0001% is set as the lower limit, as production costs increase greatly when the O content is set to less than 0 , 0001%.
[0098] The high-strength steel sheet of the present invention can additionally contain the following elements as needed.
Ti: 0.005 to 0.150% [0099] Ti is an element that contributes to increase the strength of the steel sheet by stiffening the precipitate, stiffening the fine grain by suppressing the growth of ferrite crystal grains, and displacement of the stiffness through the suppression of recrystallization. However, if a Ti content exceeds 0.150%, carbonitrite precipitation increases, and formability is deteriorated,
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31/107 so that the Ti content is preferably 0.150% or less. From a formability point of view, the Ti content is more preferably 0.100% or less, and is, even more preferably, 0.070% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the Ti content, in order to sufficiently obtain the effect of increasing the resistance provided by the Ti, the Ti content is preferably 0.005% or more. In order to increase the strength of the steel sheet, the Ti content is more preferably 0.010% or more, and is even more preferably 0.015% or more.
Nb: 0.005 to 0.150% [00100] Nb is an element that contributes to increase the strength of the steel sheet by stiffening the precipitate, stiffening the fine grain by suppressing the growth of ferrite crystal grains, and stiffening the displacement through suppression recrystallization. However, if the Mb content exceeds 0.150%, the precipitation of carbonitrites increases, and the formability is deteriorated, so that the Mb content is preferably 0.150% or less. From a formability point of view, the Mb content is more preferably 0.100% or less, and is even more preferably 0.060% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the Mb content, in order to sufficiently obtain the effect of increasing the resistance provided by the Nb, the Mb content is preferably 0.005% or more. In order to increase the strength of the steel sheet, the Mb content is more preferably 0.010% or more, and is even more preferably 0.015% or more.
V: 0.005 to 0.150% [00101] Ο V is an element that contributes to increase the strength of the steel sheet by stiffening the precipitate, stiffening the fine grain by suppressing the growth of grains of
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32/107 ferrite crystal, and stiffening of the displacement through suppression of recrystallization. However, if a V content exceeds 0.150%, the carbonitride precipitation increases, and formability is deteriorated, so that the V content is preferably 0.150% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the V content, in order to sufficiently obtain the effect of increasing the strength provided by V, the V content is preferably 0.005% or more.
B: 0.0001 to 0.0100% [00102] B is an effective element to increase resistance, and can be added instead of a part of C and / or Mn. If a B content exceeds 0.0100%, operability during hot operation is impaired and productivity is lowered, so that the B content is preferably 0.0100% or less. From a productivity point of view, the B content is, more preferably, 0.0050% or less, and is, even more preferably, 0.0030% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the B content, in order to sufficiently increase the strength with the use of B, the B content is preferably adjusted to 0.0001% or more. To increase strength, the B content is, more preferably, 0.0003% or more, and is, even more preferably, 0.0005% or more.
Mo: 0.01 to 1.00% [00103] Mo is an effective element to increase resistance, and can be added instead of a part of C and / or Mn. If a Mo content exceeds 1.00%, operability during hot operation is impaired and productivity is lowered, so that the Mo content is preferably 1.00% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the MO content, in order to sufficiently increase the resistance with the use of
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10/33
Mo, the MO content is preferably 0.01% or more.
W: 0.01 to 1.00% [00104] W is an effective element to increase resistance, and can be added instead of C and / or Mn. If the W content exceeds 1.00%, operability during hot operation is impaired and productivity is lowered, so that the W content is preferably 1.00% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the W content, in order to sufficiently increase the resistance with the use of W, the W content is preferably 0.01% or more.
Cr: 0.01 to 2.00% [00105] Cr is an effective element to increase resistance, and can be added instead of C and / or Mn. If a Cr content exceeds 2.00%, operability during hot operation is impaired, and productivity is lowered, so that the Cr content is preferably 2.00% or less. Although the effect of the present invention is exhibited without particularly determining a lower Cr content limit, in order to sufficiently increase the strength with the use of Cr, the Cr content is preferably 0.01% or more.
Ni: 0.01 to 2.00% [00106] Ni is an effective element to increase resistance, and can be added instead of a part of C and / or Mn. If an N content exceeds 2.00%, weldability is impaired, so that the N content is preferably 2.00% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the N content, in order to sufficiently increase the resistance with the use of Ni, the N content is preferably 0.01% or more.
Cu: 0.01 to 2.00% [00107] Cu is an element that exists in steel as a fine particle to increase strength, and can be added instead of a
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34/107 part of C and / or Mn. If a Cu content exceeds 2.00%, weldability is impaired, so that the Cu content is preferably 2.00% or less. Although the effect of the present invention is exhibited without particularly determining a lower Cu content limit, in order to sufficiently increase the strength with the use of Cu, the Cu content is preferably 0.01% or more.
One or two or more of Ca, Ce, Mg, Zr, Hf, and REM of 0.0001 to 0.5000% in total [00108] Ca, Ce, Mg, and REM are effective elements to improve formability, and one or two or more of these can be added. However, if a total content of one or two or more of Ca, Ce, Mg and REM exceeds 0.5000%, the ductility may be impaired, on the contrary, so that the total content of the respective elements is preferably 0, 5000% or less. Although the effect of the present invention is exhibited without particularly determining a lower limit of the content of one or two or more of Ca, Ce, Mg and REM, in order to sufficiently achieve the effect of perfecting the formability of the steel sheet, the total content of the respective elements is preferably 0.0001% or more. From a formability point of view, the total content of one or two or more of Ca, Ce, Mg and REM is, more preferably, 0.0005% or more, and is, even more preferably, 0.0010% or more .
[00109] Note that REM supports Rare Earth Metal, and represents an element belonging to the lanthanoid series. In the present invention, REM and Ce are often added in metal misch, and there is a case where the elements in the lanthanoid series are contained in a complex form, in addition to La and Ce. Even if these elements in the lanthanoid series other than La and Ce are contained as unavoidable impurities, the effect of the present invention is exhibited. In addition, the effect of the present invention is exhibited even if metal La and Ce are added.
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35/107 [00110] Additionally, the high-strength steel sheet of the present invention can be configured as a high-strength galvanized steel sheet by forming a galvanized layer, or a galvanized layer with an alloy on a surface thereof. By forming the galvanized layer on the surface of the high-strength steel sheet, the high-strength steel sheet becomes one with corrosion resistance. Additionally, by forming the galvanized layer with alloy on the surface of the high-strength steel sheet, the high-strength steel sheet becomes one with corrosion resistance and with coating adhesion. In addition, the galvanized layer or the alloyed galvanized layer may contain Al as an impurity.
[00111] The alloyed galvanized layer may contain one or two or more of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, Sr, I, Cs, and REM, or one or two or more of the elements can be mixed in the alloyed galvanized layer. Even if the alloyed galvanized layer contains one or two or more of the elements described above, or one or two or more of the elements is (are) mixed in the alloyed galvanized layer, the effect of the present invention is not impaired, and there is sometimes a preferable case where corrosion resistance and operability are improved, depending on the content of the element.
[00112] A coating weight of the galvanized layer or the galvanized layer with alloy is not particularly limited, but 20 g / m ² or more from a corrosion resistance standpoint is desirable, and is desirably 150 g / m ² or less from an economic efficiency point of view. In addition, an average thickness of the galvanized layer or the galvanized layer with alloy is adjusted to not less than 1.0 mm, nor more than 50 mm. If the average thickness is less than 1.0 mm, it is not possible to achieve sufficient corrosion resistance. The average thickness is preferably adjusted to 2.0
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36/107 mm or more. On the other hand, adjusting the average thickness to more than 50.0 mm is not economical, and impairs the strength of the steel sheet, and therefore is not preferable. From a raw material cost point of view, the thinner the thickness of the galvanized layer or the galvanized layer with alloy is, the more favorable it is, and therefore the thickness is preferably 30.0 mm or less. [00113] Regarding the average thickness of the coating layer, a thick cross section parallel to the rolling direction of the steel sheet is finished to be a mirror surface, and observed with FE-SEM, coating layer thicknesses are measured at five points on a front surface, and at five points on a rear surface, namely 10 points in total steel sheet, and an average thickness value is adjusted as the coating layer thickness.
[00114] Note that when performing alloy treatment, an iron content in the galvanized layer with alloy is adjusted to 8.0% or more, and is preferably 9.0% or more, to ensure good strength flanking. In addition, the iron content in the alloyed galvanized layer is adjusted to 12.0% or less, and is preferably 11.0% or less, to ensure good spray resistance.
[00115] Additionally, in the high-strength steel plate of the present invention, a coating film produced from a composite oxide containing a phosphorus and / or phosphorus oxide, can be formed on a surface of the galvanized layer. Consequently, the coating film can be operated as a lubricant when carrying out processing on the steel sheet, resulting in that the galvanized layer formed on the surface of the steel sheet can be protected.
HIGH STEEL SHEET PRODUCTION METHOD
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RESISTANCE [00116] Next, a method of producing the high-strength steel sheet of the present embodiment will be described.
[00117] The method of producing the high-strength steel sheet of the present embodiment includes: a hot rolling step being a heating step of a plate containing the chemical components mentioned above at 1100Ό or more, carrying out hot rolling in the plate in a temperature region where a higher temperature between 850Ό and an Ar3 temperature is set to a lower limit temperature, first cooling performance of cooling performance in a range from a lamination completion to a winding start to a rate of 10000 / second or more on average, winding in a winding temperature range of 600 to 750Ό, and second cooling of the steel sheet winding in a winding temperature range of 100Ό at winding temperature a rate of 15Ό / hour or less on average; and a continuous annealing step to perform annealing on the steel sheet at a maximum heating temperature (Aci + 40) Ό at 1000 segundo after the second cooling, then performing a third cooling at an average cooling rate of 1.0 at 10 OO / second in a range of maximum heating temperature to 700Ό, then performing a fourth cooling at an average cooling rate of 5.0 to 200.0'C / second in a range of 700Ό to 500Ό, and , then, holding the retention process of the steel plate after being subjected to the fourth cooling for 30 to 1000 seconds in a range of 350 to 450Ό.
[00118] Hereafter, reasons for limiting the production conditions described above will be described.
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38/107 [00119] In order to produce the high-strength steel plate of the present embodiment, a plate containing the chemical components described above (composition) is first melted.
[00120] Depending on the plate subjected to hot rolling, it is possible to use a continuously fused plate or a plate manufactured by a thin plate melter or similar. The production method of the high strength steel plate of the present invention is compatible with a process similar to direct continuous casting (CC-DR) where hot rolling is performed after casting.
HOT LAMINATION STEP [00121] In the hot rolling step, a plate heating temperature is required to be set to 1100X3 or more. If the plate heating temperature is excessively low, a finishing lamination temperature is below an Ar3 temperature, two-stage lamination of ferrite and austenite is performed, a hot-rolled sheet structure becomes a duplex grain structure heterogeneous, and the heterogeneous structure remains even after being subjected to cold rolling and annealing steps, resulting in ductility and curvatures being deteriorated. In addition, lowering the finish rolling temperature causes an excessive increase in the rolling load, and there is a problem that the rolling may become difficult to perform or a shape of the rolled steel sheet may be defective, so that plate heating temperature is required to be set to 1100X3 or more. Although the effect of this invention is exhibited without particularly determining an upper plate heating temperature limit, it is desirable to set the upper plate heating temperature limit to 1350Ό or less, since it is not economically preferable to adjust the heating temperature.
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39/107 heating to an excessively high temperature.
[00122] Note that the temperature of Ar ₃ is calculated based on the following equation.
Ar3 = 901 - 325 x C + 33 x Si - 92 x (Mn + Ni / 2 + Cr / 2 + Cu / 2 + Mo / 2) + 52 x Al [00123] In the above equation, C, Si, Mn, Ni, Cr, Cu, Mo, and Al represent contents [% by mass] of the respective elements. An element that is not contained is calculated as 0.
[00124] A lower limit of the finishing laminating temperature being a hot rolling finishing temperature is set to a higher temperature between 850Ό and the Ar ₃ temperature. If the finish laminating temperature is less than 850Ό, the laminating load during finishing laminating increases, and there is a problem that hot rolling can become difficult to do, or the shape of the rolled steel sheet The heat obtained after hot rolling can be defective. In addition, if the finishing rolling temperature is lower than the Ar3 temperature, the hot rolling becomes two-stage rolling of ferrite and austenite, and the structure of the hot-rolled steel sheet sometimes becomes a heterogeneous duplex grain structure.
[00125] On the other hand, although the effect of the present invention is exhibited without particularly determining an upper limit of the finishing laminating temperature, when the finishing laminating temperature is set to an excessively high temperature, it is necessary to adjust the heating temperature excessively high temperature to ensure the finishing laminating temperature.
[00126] For this reason, it is desirable to adjust the temperature of the upper limit of the finishing laminating temperature to 1000Ό or
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40/107 less.
[00127] Then, the first cooling of cooling in a range from the completion of rolling to the beginning of winding at a rate of 100 / second or more on average is conducted, and winding is carried out in a temperature range of winding from 600 to 750Ό. In addition, the second cooling of the coiled steel sheet cooling in a coiling temperature to coiling temperature range - 100Ό at a rate of 10 ° / hour or less on average is conducted.
[00128] The reason why the winding condition after hot rolling and the cooling conditions before and after winding, which are defined as above, will be described in detail.
[00129] In the present embodiment, the winding step after hot rolling and the first and second cooling steps before and after the winding step, are very important stages of Si, Mn and Al distribution.
[00130] In the present embodiment, in order to control the distributions of concentrations of Si, Mn, and Al in the base iron at 1/8 thick at 3/8 thick steel plate, it is required that the volume fraction of austenite is 50% or more at 1/8 thick to 3/8 thick after the steel sheet is wound. If the volume fraction of austenite 1/8 thick to 3/8 thick is less than 50%, austenite disappears after winding, due to a phase transformation progress, so that the Si and Mn do not proceed sufficiently, resulting in that the distribution distributions of elements of solid solution of the steel sheet, according to the present embodiment, as described above, cannot be obtained. In order to effectively facilitate the distribution of Mn, the volume fraction of austenite is preferably
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70% or more, and is more preferably 80% or more. On the other hand, even if the volume fraction of austenite is 100%, the phase transformation proceeds after winding, ferrite is generated, and the Mn distribution is started, so that an upper limit of the volume fraction of austenite is not it is particularly proportionate.
[00131] As described above, in order to increase the austenite fraction when winding the steel sheet, it is required to adjust the cooling rate in the first cooling in the temperature range from the completion of hot rolling for WC winding. / second or more, on average. If the average cooling rate in the first cooling is less than WC / second, the transformation of ferrite proceeds during cooling, and there is a possibility that the volume fraction of austenite during winding becomes less than 50%. In order to increase the volume fraction of austenite, the cooling rate is preferably ISO / second or more, and is more preferably 10 / second or more. Although the effect of the present invention is exhibited without particularly setting an upper limit on the cooling rate, the cooling rate is preferably set to 200'C / second or less, since a special facility is required to obtain the cooling rate more than 200'C / second, and production costs increase significantly.
[00132] If the steel sheet is wound at a temperature exceeding 800Ό after the first cooling, an oxide thickness formed on the surface of the steel sheet increases excessively, and the stripping capacity is deteriorated, so that the winding temperature is adjusted to 750 “C or less. In order to increase the pickling capacity, the coiling temperature is preferably 720Ό or less, and is more preferably 700Ό or less. On the other hand, if the winding temperature is lower
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42/107 than 600Ό, an alloying element distribution is insufficient, so the winding temperature is adjusted to 600Ό or more. In addition, in order to increase the austenite fraction after winding, the winding temperature is preferably set to 615Ό or more, and is most preferably set to 630Ό or more.
[00133] Note that since it is difficult to directly measure the volume fraction of austenite during production, to determine the volume fraction of austenite at the time of winding in the present invention, a small piece is cut from the plate before hot rolling, the small part is rolled or compressed at a temperature, and a reduction ratio, the same as that in the finishing lamination (final pass) of the hot rolling, the resulting one is cooled with water after being cooled at a rate cooling, the same as that over a period of time from the completion of hot rolling to the completion of winding, phase fractions of the small part are then measured, and a sum of the volume fractions of extinct martensite, tempered martensite and retained austenite phase, is adjusted as a fraction of austenite volume during winding.
[00134] The second cooling being the cooling step for the coiled steel sheet is an important step for controlling the distribution of Si, Mn and Al elements.
[00135] In the present embodiment, the conditions of the first cooling described above are controlled to adjust the austenite fraction during winding to 50% or more, and then slow cooling is conducted over a range of winding temperature to winding - 100Ό at a rate of wool / hour or less. By conducting the slow cooling after winding as described above, the steel sheet structure
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43/107 can be adjusted to have a two-phase ferrite and austenite structure, and, in addition, it is possible to obtain the Si, Mn and Al distributions of the present invention.
[00136] Since the distribution of Mn after winding is more likely to proceed as the temperature becomes higher, it is required to adjust the cooling rate of the steel sheet to 10 / hour or less, particularly over a temperature range winding temperature (winding temperature - 100Ό).
[00137] Additionally, in order to make the distribution of Mn from ferrite to austenite proceed to obtain the distribution of Mn, as described above, it is required to create a state where two phases of ferrite and austenite coexist, and retain this state for a long period of time. If the cooling rate from the winding temperature to the winding temperature - 100Ό exceeds 10o / hour, the phase transformation proceeds excessively, and the austenite in the steel plate can disappear, so that the cooling rate from the temperature winding temperature the winding temperature 100Ό is set to õO / hour or less. In order to make the Mn distribution of austenite ferrite proceed, the cooling rate from the winding temperature to the winding temperature - 100 temperatura is preferably adjusted to MO / hour or less, and is most preferably adjusted to ISO / hour or less. Although the effect of the present invention is exhibited without particularly setting a lower limit on the cooling rate, it is preferable to set the limit below 1 “C / hour or more, as long as it is required to perform heat retention for a long period of time. to adjust the cooling rate to less than 1 “C / hour, and production costs increase significantly.
[00138] Additionally, there is no problem if the steel sheet is reheated after winding within a range of satisfaction of the
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44/107 average cooling rate of the second cooling.
[00139] The pickling is carried out on the hot-rolled steel plate produced as above. An oxide on the surface of the steel plate can be removed by pickling, so pickling is important to perfect a conversion property of the cold-rolled high-strength steel plate as a final product, and a hot-dip palatability of the cold rolled steel sheet for hot-dip galvanized steel sheet, or bonded hot-dip galvanized steel sheet. In addition, stripping can be carried out once, or a plurality of times separately.
[00140] It is also possible to perform cold rolling on the hot rolled steel plate after being subjected to pickling, for the proposal of adjusting the plate thickness and shape correction. When performing cold rolling, a reduction ratio is adjusted to fall within a range of 30 to 75%. If the reduction ratio is less than 30%, it is difficult to maintain the flat shape, and the ductility of the final product becomes poor, so the reduction ratio is adjusted to 30% or more. In order to simultaneously increase strength and ductility, it is effective to recrystallize ferrite during temperature rise, and to reduce grain diameters. From this point of view, the reduction ratio is preferably 40% or more, and is more preferably 45% or more.
[00141] On the other hand, in cold rolling where the reduction ratio exceeds 75%, a cold rolling load is increased much more, resulting in it becoming difficult to perform cold rolling. For this reason, an upper limit of the reduction ratio is adjusted to 75%. From a cold rolling load point of view, the reduction ratio is preferably 70% or less.
CONTINUOUS RECOVERY STEP [00142] Then, the steel sheet is passed through a
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45/107 continuous annealing line to carry out a continuous annealing step, thereby producing the cold-rolled high-strength steel plate.
[00143] First, annealing is carried out by adjusting that a maximum heating temperature is (Aci + 40) Ό to 1000Ό. Such a temperature range is a range in which two phases of ferrite and austenite coexist, and it is possible to additionally facilitate the distributions of Si, Mn, and Al, as described above.
[00144] If the maximum heating temperature is less than (Ac1 + 40) Ό, a large number of coarse iron-based carbides remain in the steel sheet in an insoluble state, and the formability is significantly deteriorated, so that the maximum heating temperature is set to (Ac1 + 40) Ό or more. From a formability point of view, the maximum heating temperature is preferably set to (Aci + 50) Ό or more, and is most preferably set to (Aci + 60) Ό or more. On the other hand, if the maximum heating temperature exceeds 1000Ό, an atom diffusion is facilitated, and the distributions of Si, Mn, and Al are reduced, so that the maximum heating temperature is adjusted to 1000Ό or less. In order to control the amounts of Si, Mn, and Al in the retained austenite phase, the maximum heating temperature is preferably the temperature Ac3 or less.
[00145] Then, a third cooling of the steel plate is carried out from the maximum heating temperature to 700Ό described above. In the third, then if an average cooling rate exceeds 10.OO / second, a fraction of ferrite in the steel plate becomes easily non-uniform, and formability is deteriorated, so that an upper limit on the average cooling rate is set to 10 OO / second. On the other hand, if the average cooling rate is less than I.OO / second, a large
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46/107 amount of ferrite and perlite is generated, and it is not possible to obtain the retained austenite phase, so that a lower limit of the average cooling rate is set to 1 .OO / second. In order to obtain the retained austenite phase, the average cooling rate is preferably adjusted to 2.0 'C / second or more, and is more preferably adjusted to S.OO / second or more.
[00146] After the third cooling, a fourth cooling of the steel plate from 700Ό to 500Ό is additionally performed.
In the fourth cooling, if an average cooling rate becomes less than õ.OO / second, a large amount of iron-based perlite and / or carbide is generated, and the retained austenite phase is not maintained, so that a lower limit of the average cooling rate is set to õ.OO / second or more. From this point of view, the average cooling rate is preferably 7.0 ° C / second or more, and is more preferably e.OO / second or more. On the other hand, although the effect of the present invention is exhibited without particularly determining an upper limit on the average cooling rate, the upper limit on the average cooling rate is adjusted to 200.0'C / second from a cost point of view, since a special facility is required to obtain the average cooling rate of more than 200 ^< C / second.
[00147] Note that a cooling cessation temperature in the fourth cooling is preferably adjusted to Ms 20Ό or more. This is because, if the cooling cessation temperature is greatly below a point Ms, untransformed austenite is transformed into martensite, and it is not possible to obtain sufficiently retained austenite in which Si is concentrated. From this point of view, the cooling cessation temperature is most preferably adjusted to the point Ms or more.
[00148] The Ms point is calculated based on the following equation.
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Point Ms [Ό] = 541 - 474C / (1 - VF) - 15Si - 35Mn - 17Cr -17Ni + 19AI [00149] In the above equation, VF represents a fraction of ferrite volume, and C, Si, Mn, Cr, Ni, and Al represent added amounts [% by mass] of the respective elements. Note that since it is difficult to directly measure the volume fraction of ferrite during production, to determine the Ms point in the present invention, a small piece of the cold-rolled steel sheet before the steel sheet is passed through the continuous annealing line, is cut and annealed, based on a temperature history, the same as when the small part is passed through the continuous annealing line, a change in the ferrite volume in the small part is measured, and a value numeric calculated using the measurement result is adjusted as the volume fraction VF of ferrite.
[00150] Additionally, in order to make the bainite transformation proceed to obtain the retained austenite phase, a retention process is carried out in which the steel plate is retained in a range of 350 to 450Ό for 30 to 1000 seconds after the fourth cooling. If a retention time is short, the transformation of bainite does not proceed, resulting in the concentration of C in the retained austenite phase becoming insufficient, and a sufficient amount of retained austenite cannot be maintained. From this point of view, a lower limit on the retention time is set to 30 seconds. The retention time is preferably 40 seconds or more, and is more preferably 60 seconds or more. On the other hand, if the retention time is too long, iron-based carbide is generated, C is consumed as the iron-based carbide, and a sufficient amount of retained austenite phase cannot be obtained, so the retention time is set to 1000 seconds or less. From this point of view, the retention time is preferably 800 seconds or less, and is, more
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48/107 preferably 600 seconds or less.
[00151] Additionally, in order to adjust the tempered martensite to less than 10%, the average cooling rate in the fourth cooling is preferably adjusted to 10 to 190 ° C / s according to the production method. In addition, in the retention process after the fourth cooling, the retention time is preferably adjusted to 50 to 600 seconds.
[00152] Note that by performing cooling without reheating conduction above 600 de as in the present application, the concentration of Si concentrated in the retained austenite phase can be maintained as it is. If the temperature exceeds 600 ° C, a diffusion rate of the alloying element becomes very fast, and a redistribution of Si is caused between retained austenite and a microstructure on the periphery of retained austenite, resulting in the concentration of Si in the austenite is lowered.
[00153] Additionally, in the present invention, it is also possible to form a high-strength galvanized steel sheet by performing electro-galvanization, after the above described retention process, on the high-strength steel sheet obtained by causing the steel sheet to pass through the continuous annealing line using the method mentioned above.
[00154] Additionally, in the present invention, it is also possible to produce a high strength galvanized steel sheet using the following method by using the high strength steel sheet obtained by the method described above.
[00155] Specifically, the high strength galvanized steel sheet can be produced in a manner similar to the case where the hot rolled steel sheet or cold rolled steel sheet described above is passed through the continuous annealing line, except that the high-strength steel sheet contained is immersed in a
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49/107 galvanizing bath between the fourth cooling and the retention process, or after the retention process.
[00156] Consequently, it is possible to obtain a high strength galvanized steel sheet having a galvanized layer formed on a surface thereof, and having high ductility and high stretch flangeability.
[00157] Additionally, it is also possible to perform an alloy treatment in which the steel plate after being immersed in the galvanizing bath is reheated to 460Ό to 600Ό, and is retained for two seconds or more, in order to produce the layer coating on the surface to be bonded.
[00158] By carrying out such an alloy treatment, the Zn-Fe alloy formed by the alloy of the galvanized layer is formed on the surface, resulting in a high strength galvanized steel sheet having the layer galvanized with alloy on one surface thereof, is obtained.
[00159] The plating bath is not particularly limited, and even if one or two or more of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi , Sr, I, Cs, and REM, are (are) mixed (s) in the galvanizing bath, the effect of the present invention is not impaired, and there is sometimes a preferable case where corrosion resistance and operability are depending on the content of the element. In addition, Al can also be contained in the galvanizing bath. In this case, it is preferable to adjust an Al concentration in the bath to not less than 0.05%, or more than 0.15%.
[00160] Additionally, a temperature in the alloy treatment is preferably 480 to 560 °, and a retention time in the alloy treatment is preferably 15 to 60 seconds.
[00161] In addition, there is no problem if a coating film produced from a compound oxide containing an oxide of
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50/107 phosphorus and / or phosphorus is given to a surface layer of each of these galvanized steel sheets.
[00162] It is noted that the present invention is not limited to the examples described above.
[00163] For example, in the production method of the high-strength galvanized steel sheet of the present invention, it is also possible to perform coating with one type or a plurality of selected types of Ni, Cu, Co, and Fe, on the steel sheet before being subjected to annealing, in order to improve the coating adhesiveness.
[00164] Additionally, in the present embodiment, there is no problem if tempering lamination is carried out on the steel sheet after being subjected to annealing, for the proposal of shape correction. However, when a reduction ratio after annealing exceeds 10%, operating hardness of the soft ferrite part is caused and the ductility is greatly deteriorated, so that the reduction ratio is preferably adjusted to less than 10%.
[00165] With the use of the high strength steel plate, according to the present invention, as described above, since Mn is concentrated in the retained austenite phase, it is possible to stabilize the retained austenite phase, and increase the resistance to tension.
[00166] Additionally, in the high strength steel plate, according to the present invention, since Si is also concentrated in the retained austenite phase, similar to Mn, it is possible to moderately destabilize the retained austenite phase, easily causing the transformation when applying a pressure, and causing sufficient operating trouble in the initial stage of processing time in the low pressure region. As a result of this, it is possible to achieve form fixability. On the other hand, in the high strength region, it is possible to increase the stability of the austenite phase
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51/107 retained, and make Si contribute to local ductility.
[00167] Additionally, in the high-strength steel plate, according to the present invention, Al being an element of suppression of the generation of iron-based carbide is added in an appropriate amount, and processing is carried out based on a thermal history predetermined in the hot rolling stage, resulting in that Si can be efficiently concentrated in retained austenite. Additionally, at this time, Al exhibits the concentration distribution opposite to the Si concentration distribution, so that it is possible to create a distribution state where either Si or Al exists in an amount being an amount equal to or greater than an average amount in the total area of the steel sheet. Consequently, the generation of iron-based carbide is suppressed, and C can be prevented from being consumed as a carbide, so that it is possible to stably maintain the retained austenite phase, resulting in that form fixability, ductility, and resistance to tension, can be greatly improved.
[00168] Additionally, in the production method of the high-strength steel sheet, according to the present invention, by controlling the winding step after hot rolling and the first and second cooling steps before and after the winding step , it is possible to ensure sufficient retained austenite phase, and to distribute Si, Mn and Al on the steel plate.
EXAMPLES [00169] Hereinafter, the effect of the present invention will be described based on the examples, but the present invention is not limited to the conditions employed in the following examples.
[00170] Plates containing chemical components (composition) from A to AD presented in Tables 1 and 2 were melted, hot rolling was carried out under conditions (heating temperature of
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52/107 plate, hot rolling completion temperature) presented in Tables 3 to 5 after casting, cooling was carried out under conditions of average cooling rate in the first cooling from the completion of hot rolling to the beginning of winding presented in Tables 3 to 5, winding was carried out at winding temperatures shown in Tables 3 to 5, cooling was carried out under conditions of average cooling rate in the second cooling after winding shown in Table 2, and then stripping was carried out. Note that experimental examples 6, 49, and 87 were left as they were after pickling, and the other experimental examples were subjected to cold rolling in reduction ratios described in Tables 3 to 5, and subjected to annealing under conditions presented in Tables 6 to 8, in order to obtain steel sheets of experimental examples 1 to 93.
[00171] Additionally, after cooling the steel plate after being subjected to annealing to room temperature, cold rolling at a reduction rate of 0.15% was performed in experimental examples 9 to 28, and cold rolling at a ratio reduction of 0.55% was carried out in experimental examples 47 to 67.
[00172] Then, in each of the experimental examples 15 and 85, a coating film produced from a compound oxide containing P was given to a surface layer of a galvanized steel sheet.
[00173] Note that Ac1, and Ac3 in Tables 6 to 8 were calculated based on the following empirical formulas.
Ac [Ό] = 723 - 10.7Mn + 19.1 Si + 29.1 Al -16.9Ni + 16.9Cr
Ac3 [Ό] = 910 - 203 VC + 44.7Si - 30Mn + 200AI - 20Ni - 10Cr [00174] The annealing conditions presented in Tables 6 to 8 include the maximum heating temperature step
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53/107 heating, the average cooling rate in the third cooling stage where cooling is performed from the maximum heating temperature at 700Ό, the average cooling rate in the fourth cooling stage where cooling is performed from 700Ό to 500Ό, and the retention time in the retention process in a range of 350Ό to 450Ό for the production of the bainite transformation proceeds. [00175] Additionally, a CR-type steel shown in Tables 6 to 8 indicates a cold-rolled steel sheet obtained by carrying out cold rolling after blasting, an HR-type steel indicates a hot-rolled steel sheet being the steel that is left as it is after pickling, a steel type Gl indicates a hot-dip galvanized steel sheet obtained by performing hot-dip galvanizing on a surface of the steel sheet, a steel type GA indicates a hot-dip galvanized alloy steel obtained by performing alloy treatment after hot-dip galvanizing, and an EG-type steel indicates an electrogalvanized steel sheet obtained by electrogalvanizing on a surface of the steel sheet. Note that an alloy temperature when performing the alloy treatment was adjusted to a temperature shown in Table 3, and a retention time on the alloy was adjusted to 25 seconds.
[00176] Additionally, when the electrogalvanized steel sheet (EG) was produced, alkaline degreasing, water washing, pickling, and water washing were carried out in order as electrocoating pre-processing on the steel plate after being subjected to annealing. Then, electrolytic treatment was carried out on the steel plate after being subjected to pre-processing using an electrocoating device of the liquid circulation type with a coating bath containing zinc sulfate, sodium sulfate, and sulfuric acid, at a density current of 100
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A / dm ² until a predetermined coating thickness was obtained, and galvanization was carried out.
Table 1
EXAMPLE OFCOMPOSITION Ç Si Mn P s Al N 0 PASTA% PASTA% PASTA% PASTA% PASTA% PASTA% PASTA% %INPASTA THE 0.198 1.22 2.45 0.003 0.0010 0.101 0.0100 0.0013 B 0.220 1.45 1.84 0.008 0.0043 0.094 0.0052 0.0022 Ç 0.183 1.22 2.00 0.004 0.0020 0.122 0.0030 0.0017 D 0.282 0.61 2.49 0.005 0.0003 0.802 0.0021 0.0012 AND 0.150 0.85 2.84 0.009 0.0031 0.902 0.0012 0.0011 j F 0.121 1.87 2.28 0.011 0.0022 0.153 0.0026 0.0017 G 0.080 1.98 2.89 0.008 0.0013 0.203 0.0043 0.0029 H 0.168 1.11 2.33 0.009 0.0025 0.302 0.0044 0.0007 1 0.200 1.62 1.47 0.013 0.0019 0.401 0.0080 0.0041 J 0.120 1.64 1.35 0.017 0.0022 0.605 0.0047 0.0028 K 0.210 0.94 2.82 0.014 0.0007 1.403 0.0076 0.0015 L 0.187 1.49 1.61 0.018 0.0020 0.903 0.0027 0.0013 M 0.197 1.29 1.46 0.021 0.0025 0.550 0.0057 0.0052 N 0.201 0.41 2.61 0.008 0.0030 0.221 0.0039 0.0071 0 0.131 1.76 2-47 0.022 0.0013 0.133 0.0048 0.0027 P 0.151 1.97 2.33 0.014 0.0033 0.141 0.0031 0.0015 Q 0.176 1.78 2.93 0.010 0.0005 0.451 0.0013 0.0028 R 0.156 1.65 2.83 0.018 0.0037 0.105 0.0022 0.0009 s 0.142 2.08 1.95 0.013 0.0042 0.203 0.0101 0.0008 T 0.093 2.42 2.14 0.016 0.0007 0.155 0.0017 0.0006 u 0.211 2.30 2.48 0.030 0.0016 0.173 0.0044 0.0015 V 0.201 1.86 1.83 0.016 0.0011 0.128 0.0028 0.0015 w 0.242 2.02 1.98 0.010 0.0044 0.304 0.0026 0.0012 X 0.198 1.73 1.51 0.011 0.0020 0.142 0.0041 0.0030 Y 0.135 1.61 3.37 0.010 0.0023 0.152 0.0022 0.0020 z 0.210 2.15 2.65 0.019 0.0017 0.118 0.0040 0.0017 AA 0.003 0.98 2.29 0.007 0.0017 0.254 0.0028 0.0008 AB 0.172 0.08 2.23 0.006 0.0018 0.251 0.0027 0.0009 B.C 0.170 0.90 0.54 0.005 0.0017 0.251 0.0028 0.0009 AD 0.173 0.94 2.21 0.005 0.0017 0.003 0.0027 0.0008
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Table 2
EBFIO DE (mçio You Nb B GrM Ass Mo V 1 Here Ce Me ht Hf REM% Inpasta % inpasta % inpasta % in large scale % in large scale % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpastaTHE EBFIODAGIFTINVENTION B EBFIODAGIFTINVENTION Ç0.0020EBFIODA PRESENT INVENTION D 0.0021 EXANPLEOF PRESENT · INVENTION AND 0.0017 EBFIODA PRESENT INVENTION F 0.0021 EBFIODA PRESENT INVENTION G 1.73 EBFIODA PRESENT INVENTION H EBFIODAGIFTINVENTION 1 0.0005 EBFIODA PRESENT INVENTION J 0.710.0015EBFIODA PRESENT INVENTION K 0.20 ο, οου EBFIODA PRESENT INVENTION L 0.068 EBFIODA PRESENT INVENTION M 0.0420.0013 0.0013 EBFIODA PRESENT INVENTION N 0.0160.0034 0.0012EBFIODA PRESENT INVENTION 0 0.050 0.070 0.0038 EBFIODAGIFTINVENTION P0.029EBFIODA
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B0RD DECOHOSÇÃO YOU Nb B Gr Ni Ass Mo V 1 Here Ce Me Ix Hf REM% Inpasta % inpasta % inpasta % in large scale % in large scale % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpasta % inpastaPHESENIEINVENTION 0 0/44 0.47 0.0012EEIPLOCAPHESENIEINVENTION R 0.55 0.0014 EXEWLODA PHESENIE INVENTION s 0.057 EXEWLODAPHESENIEINVENTION T 0.00730.150.0009 EXEWLODA PHESENIE INVENTION u 1.22 0.83EXEWLODA PHESENIE INVENTION V 0.143 0.050EXEWLODA PHESENIE INVENTION H EXEWLODA PHESENIE INVENTION X 0.04 0.0017 EXEWLODAPHESENIEINVENTION Y EXEWLODAPHESENIEINVENTION z 0.144 EXEWLODAPHESENIEINVENTION AA EXAMPLECOMPARATIVE AB EXAMPLECOMPARATIVE B.C EXAMPLECOMARATVO AD EXAMPLECOMPARATVO
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Table 3
EXAMPLEEXPERIENCEMENTAL EXAMPLE OFCOMPOSITION PLATE HEATING TEMPERATURE POINT OFTRANSFOR APPLICATIONAr3 TEMPERATURECOMPLETION OFHOT lamination AVERAGE TAXADERFRIEND TO THE START OFCOILING TEMPERATUR ACOILTO COOLING RATETO AVERAGE AFTER COILING REASON FOR REDUCING LAMINATION TOCOLD° c ° c ° C ° C / SECOND ° c ° C / HOUR % 1 THE 1152 662 882 34 643 15 48 EXAMPLE OFPRESENT INVENTION 2 THE 1172 662 893 38 658 6 47 EXAMPLE OFPRESENT INVENTION 3 THE 1201 662 896 17 623 10 55 EXAMPLE OFPRESENT INVENTION 4 THE 1152 662 702 33 630 8 48 EXAMPLECOMPARATIVE 5 B 1189 715 891 27 674 11 52 EXAMPLE OFPRESENT INVENTION 6 B 1169 715 913 27 696 7 0 EXAMPLE OFPRESENT INVENTION 7 B 1155 715 916 37 670 13 60 EXAMPLE OFPRESENT INVENTION 8 B 1203 715 883 31 452 15 52 EXAMPLECOMPARATIVE 9 ç 1203 704 912 23 689 12 61 EXAMPLE OFPRESENT INVENTION 10 ç 1204 704 925 24 713 15 60 EXAMPLE OFPRESENT INVENTION 11 ç 1214 704 944 25 692 9 45 EXAMPLE OFPRESENT INVENTION 12 ç 1194 704 878 21 656 42 61 EXAMPLECOMPARATIVE 13 D 1238 651 923 25 635 12 69 EXAMPLE OFPRESENT INVENTION 14 D 1219 651 934 24 657 12 42 EXAMPLE OFPRESENT INVENTION 15 D 1227 651 935 19 645 7 43 EXAMPLE OFPRESENT INVENTION 16 D 1211 651 954 24 671 5 69 EXAMPLECOMPARATIVE 17 AND 1297 668 954 24 648 12 58 EXAMPLE OFPRESENT INVENTION 18 AND 1270 668 964 18 671 8 54 EXAMPLE OFPRESENT INVENTION 19 AND 1298 668 962 18 637 12 46 EXAMPLE OFPRESENT INVENTION 20 AND 1287 668 964 17 646 7 58 EXAMPLECOMPARATIVE 21 F 1182 727 874 18 673 13 62 EXAMPLE OFPRESENT INVENTION
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22 F 1190 727 885 18 686 9 59 EXAMPLE OFPRESENT INVENTION 23 F 1175 727 873 20 659 7 43 EXAMPLE OFPRESENT INVENTION 24 F 1192 727 860 27 685 7 62 EXAMPLE COMPARATIVE25 G 1192 612 867 54 659 8 46 EXAMPLE OFPRESENT INVENTION 26 G 1201 612 891 57 682 10 41 EXAMPLE OFPRESENT INVENTION 27 G 1197 612 874 55 640 7 52 EXAMPLE OFPRESENT INVENTION 28 G 1243 612 866 56 710 12 46 EXAMPLE COMPARATIVE29 H 1242 688 892 68 661 12 53 EXAMPLE OFPRESENT INVENTION 30 H 1210 688 908 46 686 9 58 EXAMPLE OFPRESENT INVENTION
Table 4
EXAMPLEEXPERIENCEMENTAL EXAMPLE OFCOMPOSITION TEMPERA-TURE OFHEATING POINT OFTRANS-FORM- TEMPERATURECOMPLETION OFLAMINATION A RATE OFCOOLINGAVERAGE TO COILING TEMPERATURE RATE OFCOOL-MENT REASON FORREDUCTIONIN MENT OFBOARD AODEAü HOT COILING START NTO AVERAGE AFTER COIL-MENT BLADE-TIONACOLD υ tTC / SECÜHOUR %31 H 1212 688 925 66 673 14 44 EXAMPLE OF THE PRESENT INVENTION 32 H 1232 688 921 48 637 11 53 EXAMPLECOMPARATIVE0 33 1 1263 776 888 49 693 10 69 EXAMPLE OF THE PRESENT INVENTION 34 1 1240 776 907 49 713 10 45 AND PLEFPREET
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INVENTION 35 1 1254 776 918 42 684 14 40 E plE f pre eNTINVENTION 36 1 1242 776 913 41 674 7 69 EXAMPLECOMPARATIVE 37 J 1172 794 919 66 647 9 47 EXAMPLE OFGIFTINVENTION 38 J 1194 794 936 52 668 6 59 EXAMPLE OFGIFTINVENTION 39 J 1205 794 947 62 634 8 58 EXAMPLE OFGIFTINVENTION 40 J 1182 794 958 60 682 15 47 XEMPLOCOMPARATIVE 41 K 1182 668 934 25 697 11 59 EXAMPLE OFGIFTINVENTION 42 K 1194 668 958 21 720 15 54 EXAMPLE OFGIFTINVENTION 43 K 1178 668 971 28 712 11 43 EXAMPLE OFGIFTINVENTION 44 L 1163 787 952 23 659 10 62 EXAMPLE OFGIFTINVENTION 45 L 1174 787 966 24 675 6 52 EXAMPLE OFGIFTINVENTION
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46 L 1196 787 976 23 655 10 52 EXAMPLE OFGIFTINVENTION 47 M 1172 777 974 24 663 9 55 INVENTION 48 M 1192 777 997 21 674 13 60 EXAMPLE OFGIFTINVENTION 49 M 1181 777 850 26 645 5 0 EXAMPLE OFGIFTINVENTION 50 N 1211 626 928 23 682 9 60 AND PLEFPRE AND TINVENTION 51 N 1205 626 947 24 700 13 48 EXAMPLE OFGIFTINVENTION 52 N 1215 626 929 24 689 14 55 EXAMPLE OFGIFTINVENTION 53 0 1209 701 918 21 691 8 58 EXAMPLE OFGIFTINVENTION 54 0 1229 701 942 23 712 10 49 EXAMPLE OFGIFTINVENTION 55 0 1246 701 956 25 698 6 51 AND PLEFPRE AND TINVENTION 56 P 1211 711 922 17 673 11 52 EXAMPLE OFGIFTINVENTION 57 P 1232 711 937 21 629 10 59 EXAMPLE OF
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GIFTINVENTION 58 P 1216 711 937 17 664 7 49 EXAMPLE OFGIFTINVENTION 59 Q 1293 620 892 17 666 12 47 EXAMPLE OFGIFTINVENTION 60 Q 1273 620 913 28 678 8 44 AND PLEFPREETINVENTION
Table 5
EXAMPLE EXAMPLE OF TEMPE- POINT OF TEMPE- RATE OF TEMPE RATE OF REASONEXPERIENCE COMPOSITION RATURE TRANS- RATURE COOL- RATUR COOL- RE-MENTALFROM A- FORMATION OF COM- MENT ADE ΑΜΕΝΓΟ DUÇÂO WANTED- DEAr ₃ PLETA- AVERAGE TO COIL AVERAGE HER- MENTÇÂODE BEGINNING OF MENT AFTER MINING PLATEBLADE- COIL-COIL- THE COLDÇÂOA MENTMENT HOT0 ° C / SECUND° C / HOUR % 0 61 0 1249 620 902 24 673 9 50 ET INVENTION 62 R 1173 630 948 23 654 13 59 EXAMPLE OF THE PRESENT INVENTION 63 R 1193 630 972 20 673 14 59 EXAMPLE OF THE PRESENT INVENTION
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64 R 1184 630 988 17 641 13 45 EXAMPLEGIVESGIFTINVENTION 65 s 1164 757 873 26 682 7 49 EXAMPLEGIVESGIFTINVENTION 66 s 1172 757 883 17 705 10 58 EXAMPLEGIVESGIFTINVENTION 67 s 1195 757 890 25 687 5 60 EXAMPLEGIVESGIFTINVENTION 68 T 1183 766 883 37 688 7 62 EXAMPLEGIVESGIFTINVENTION 69 T 1153 766 905 27 701 9 46 EXAMPLEGIVESGIFTINVENTION 70 T 1135 766 901 34 685 13 59 EXAMPLEGIVESGIFTINVENTION 71 u 1177 605 897 20 691 8 58 EXAMPLEGIVESGIFTINVENTION
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72 U 1182 605 922 25 630 12 44 EXAMPLE OF THE PRESENT INVENTION 73 U 1186 605 939 23 693 10 54 EXAMPLE OF THE PRESENT INVENTION 74 V 1257 736 874 28 686 9 61 EAPLEFPREETINVENTION 75 V 1237 736 888 23 701 15 53 EXAMPLE OF THE PRESENT INVENTION 76 V 1251 736 889 24 677 10 59 EPLEFPREETINVENTION 77 W 1283 730 921 34 672 13 45 EXAMPLE OF THE PRESENT INVENTION 78 w 1253 730 942 31 610 6 50 EXAMPLE OF THE PRESENT INVENTION 79 w 1281 730 932 27 668 12 51 EXAMPLE OF THE PRESENT INVENTION 80 X 1184 762 947 38 661 8 44 EXAMPLEGIVES
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GIFTINVENTION 81 X 1192 762 971 28 679 10 57 PLePREENT INVENTION 82 X 1168 762 957 28 675 13 55 EXAMPLEGIVESGIFTINVENTION 83 Y 1173 610 878 18 659 8 47 EXAMPLEGIVESGIFTINVENTION 84 Y 1153 610 888 23 680 11 42 PLePREENT INVENTION 85 Y 1171 610 904 17 651 10 43 EXAMPLEGIVESGIFTINVENTION 86 Z 1223 669 869 17 682 15 62 EXAMPLEGIVESGIFTINVENTION 87 z 1204 669 886 28 614 6 0 EXAMPLEGIVESGIFTINVENTION 88 z 1218 669 905 17 686 12 rr EXAMPLEGIVESGIFTINVENTION
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89 AA 1224 735 919 32 693 12 58 EXAMPLECOMPARATIGRANDFATHER 90 AB 1253 656 922 37 694 7 54 EXAMPLECOMPARATIGRANDFATHER 91 B.C 1155 839 883 35 673 8 57 EXAMPLECOMPARATIGRANDFATHER 92 AD 1196 673 887 30 664 15 62 EXAMPLECOMPARATIGRANDFATHER 93 D 1207 651 903 23 625 13 50 EXAMPLECOMPARATIGRANDFATHER 94 D 1189 651 915 1 683 12 50 EXAMPLECOMPARATIyo
Table 6
EXPERIMENTAL EXAMPLE COMPOSITION EXAMPLE STEEL TYPE ACi ACi +40 AC3 MAXIMUM HEATING TEMPERATURE THIRD R COOLING STEP FOURTH COOLING STEP PROC ESSO OF RETENTION ALLOY TREATMENTAVERAGE COOLING RATE AVERAGE COOLING RATE HAVE RE POTENDOG TEMP ERATU RA DETURNS ON Ç Ç Ç ç WITH SECOND WITH SECOND MONOF ç 1 THE CR 723 763 822 815 5 113 420EXAMPLE OFPRESENT INVENTION 2 THE CR 723 763 910 820 5 103 420EXAMPLE OFPRESENT INVENTION
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3 THE GA 723 763 880 776 5 66 364 516 EXAMPLE OFGIFTINVENTION 4 THE CR 723 763 822 821 5 108 299 - EXAMPLECOMPARATIVE 5 B CR 733 773 842 805 3 113 421 - EXAMPLE OFGIFTINVENTION 6 B HR 733 773 842 808 3 95 421 - EXAMPLE OFGIFTINVENTION 7 B Gl 733 773 842 811 3 60 133 - EXAMPLE OFGIFTINVENTION 8 B CR 733 773 842 815 3 75 431 - EXAMPLECOMPARATIVE 9 Ç CR 728 768 917 826 5 34 201 - EXAMPLE OFGIFTINVENTION 10 ç CR 728 768 917 836 9 58 201 - EXAMPLE OFGIFTINVENTION 11 ç EG 728 768 917 901 9 62 61 - EXAMPLE OFGIFTINVENTION 12 ç CR 728 768 917 858 5 57 56 - EXAMPLECOMPARATIVE 13 D CR 732 772 963 815 8 69 91 - EXAMPLE OFGIFTINVENTION 14 D CR 732 772 963 893 3 30 91 - EXAMPLE OFGIFT
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INVENTION 15 D GA 732 772 963 824 3 45 185 482 EXAMPLE OFGIFTINVENTION 16 0 CR 732 772 963 1052 8 45 268 - EXAMPLECOMPARATIVE 17 AND CR 735 775 884 861 10 68 276 - EXAMPLE OFGIFTINVENTION 18 AND CR 735 775 884 819 7 119 276 - EXAMPLE OFGIFTINVENTION 19 AND Gl 735 775 884 852 9 43 346EXAMPLE OFGIFTINVENTION 20 AND CR 735 775 884 654 10 95 461 - EXAMPLECOMPARATIVE 21 F CR 738 778 877 827 9 191 297 - EAPLE FPREENTINVENTION 22 F CR 738 778 877 801 10 73 297EXAMPLE OFGIFTINVENTION 23 F EG 738 778 877 840 1 91 222EXAMPLE OFGIFTINVENTION 24 F CR 738 778 877 824 0.1 22 89 - EXAMPLECOMPARATIVE 25 6 CR 764 804 868 844 6 65 94EXAMPLE OFGIFTINVENTION 26 G CR 764 804 868 831 2 25 94EXAMPLE OF
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GIFTINVENTION 27 G GA 764 804 868 856 1 34 371 481 EXAMPLE OFGIFTINVENTION 28 G CR 764 804 868 862 20 13 205 - EXAMPLECOMPARATIVE 29 H CR 728 768 927 787 8 85 332ETINVENTION 30 H CR 728 768 927 909 5 75 332Example ofgiftinvention
Table 7
EXAMPLE EXAMPLE TYPEAC1 +40 AC3 TEMPE THIRD QUAR PROCE TRATEXPERIENCE IN OF STEEL RAYUR THE STAGE OF OK SSO OF LOVE NMENTAL COMPOSI ADE RESFRIAME STEP OF RETEN TO DOG AQUEC NTO RESFRIA DOG IN IMENTTURNS ON MENT MAXIMUM THE RATE OF RATE TIME HAS COOL- IN IN PER THE AVERAGE MENT- RESFRIA RETEN TUR DOG THE DAY MENT INAVERAGETURNS ON Ç ° C Ç Ç ° C / SECOND  C / SEGU SECOND NDO 0 31 H Gl 728 768 927 780 5 84 73 - EXAMPLE OF GIFT INVENTION 32 H CR 728 768 927 872 8 2 211EXAMPLE
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COMPARATIGRANDFATHER 33 1 CR 750 790 985 858 7 21 576 EXAMPLE OFGIFTINVENTION 34 1 CR 750 790 985 835 6 102 576 EXAMPLE OFGIFTINVENTION 35 1 EG 750 790 985 848 8 14 235 EXAMPLE OFGIFTINVENTION 36 t CR 750 790 985 849 7 88 12 EXAMPLECOMPARATIGRANDFATHER 37 J CR 769 809 1053 878 4 72 382 EXAMPLE OFGIFTINVENTION 38 J CR 769 809 1053 882 5 22 382 EMPLOYE OFGIFTINVENTION 39 J GA 769 809 1053 The wire3u9 1 23 228 546 EMPLOYE OFGIFTINVENTION 40 J CR 769 809 1053 937 4 29 3072 EXAMPLECOMPARATIGRANDFATHER 41 K CR 751 791 1017 938 5 113 191 EMPLOYE OFGIFTINVENTION 42 K CR 751 791 1017 878 4 68 191 EPLEFPRE ENTINVENTION
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43 K Gl 751 791 1017 595 7 70 363 - EXAMPLE OFGIFTINVENTION 44 L CR 759 799 942 553 2 48 261 - EXAMPLE OFGIFTINVENTION 45 L CR 759 799 942 565 1 185 261 - EXAMPLE OFGIFTINVENTION 46 L EG 759 799 942 545 9 12 594 EXAMPLE OFGIFTINVENTION 47 M CR 747 757 505 503 7 53 161 EXAMPLE OFGIFTINVENTION 48 M CR 747 757 505 300 2 49 161 EMPLOYE OFGIFTINVENTION 49 M HR-GA 747 757 505 797 5 63 167 529EX MPLO DAGIFTINVENTION 50 N CR 710 750 567 304 5 48 52EXAMPLE OFGIFTINVENTION 51 N CR 710 750 567 303 3 84 52EXAMPLE OFGIFTINVENTION 52 N Gl 710 750 567 503 3 109 521EXAMPLE OFGIFTINVENTION 53 0 CR 734 774 575 792 5 24 66EXAMPLE OFGIFT
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INVENTION 54 0 CR 734 774 875 793 10 59 66EXAMPLE OFGIFTINVENTION 55 0 EG 734 774 875 871 10 55 500XAMPLE OFPRESENTINVENTION 56 P CR 739 779 896 818 4 86 518EXAMPLE OFGIFTINVENTION 57 P CR 739 779 896 890 2 14 518EXAMPLE OFGIFTINVENTION 58 P GA 739 779 896 825 3 34 67 472 XAMPLE OFPRESENTINVENTION 59 Q CR 731 771 835 834 3 185 303PLEFPREETINVENTION 60 Q CR 731 771 835 781 1 165 303PLE F PREETINVENTION
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Table 8
EXAMPLEEXPERIENCEMENTAL COMPOSITION EXAMPLE TYPEOF STEEL ACi ACi +40 B.C3 TEMPE RATUR ADE MAXIMUM HEATING A THIRD STAGE OF RESTRAINTING FOURTH STAGE OF COOLINGMENT PROC AND SSOINRETE NDOG TREATMENTNTODETURNS ONRATE OFAVERAGE COOLING AVERAGE COOLING RATE RETENTION TIME TEMPER ALLOY TURA WITH SECOND WITH SE GUN DO FOLLOWNDO61 0 Gl 731 771 835 814 8 94 310 - EXAMPLE OFGIFTINVENTION 62 R CR 736 776 906 809 9 80 432 - EXAMPLE OFGIFTINVENTION 63 R CR 736 776 906 861 7 39 432 - EXAMPLE OFGIFTINVENTION 64 R EG 736 776 906 894 6 65 73 - EXAMPLE OFGIFTINVENTION 65 s CR 747 787 923 829 8 61 130 - EXAMPLE OFGIFTINVENTION 66 s CR 747 787 923 865 8 69 130EXAMPLE OF
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GIFTINVENTION 67 s GA 747 787 923 876 7 56 82 508 EXAMPLE OFGIFTINVENTION 68 T CR 751 791 858 833 6 27 361 - EPLEETINVENTION 69 T CR 751 791 858 810 3 63 361 - EXAMPLE OFGIFTINVENTION 70 T Gl 751 791 858 806 1 78 277 - EXAMPLE OFGIFTINVENTION 71 u CR 726 766 871 799 5 57 366 - EXAMPLE OFGIFTINVENTION 72 u CR 726 766 871 782 6 14 366 - EXAMPLE OFGIFTINVENTION 73 u EG 726 766 871 829 4 78 213 - EXAMPLE OFGIFTINVENTION 74 V CR 742 782 903 881 7 174 528 - EXAMPLE OFGIFTINVENTION 75 V CR 742 782 903 860 10 54 528 - EXAMPLE OFGIFTINVENTION 76 V GA 742 782 903 884 2 48 343 522 EXAMPLE OFGIFTINVENTION
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77 W CR 750 790 879 848 10 67 287 - EXAMPLE OFGIFTINVENTION 78 W CR 750 790 879 806 4 75 287 - EXAMPLE OFGIFTINVENTION 79 w Gl 750 790 879 870 6 34 444 - EXAMPLE OFGIFTINVENTION 80 X CR 743 783 836 818 4 94 71 - EXAMPLE OFGIFTINVENTION 81 X CR 743 783 836 808 3 86 71EXAMPLE OFGIFTINVENTION 82 X EG 743 783 836 804 5 107 92EXAMPLE OFGIFTINVENTION 83 Y CR 722 762 856 845 3 38 175 - EXAMPLE OFGIFTINVENTION 84 Y CR 722 762 856 817 3 116 175EXAMPLE OFGIFTINVENTION 85 Y GA 722 762 856 850 7 56 286 493 EXAMPLE OFGIFTINVENTION 86 z CR 739 779 925 883 8 26 365EXAMPLE OFGIFTINVENTION 87 z HR 739 779 925 854 4 47 365HEYINVENTION
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88 Z Gl 739 779 925 856 7 115 274 - EXAMPLE OFGIFTINVENTION 89 AA CR 725 765 853 776 6 120 455 - EXAMPLECOMPARATIVE 90 AB CR 708 748 901 869 5 119 456 - EXAMPLECOMPARATIVE 91 B.C CR 742 782 802 794 4 108 81 - EXAMPLECOMPARATIVE 92 AD CR 717 757 910 775 8 59 576 - EXAMPLECOMPARATIVE 93 D CR 732 772 963 1030 25 82 409 - EXAMPLECOMPARATIVE 94 D CR 732 772 963 846 4 53 352 z EXAMPLECOMPARATIVE
[00177] Tables 9 to 11 represent the results of analysis of microstructures. The results were obtained by measuring, on each of the steel plates of experimental examples 1 to 93, of the microstructure fractions when a surface parallel to and 1/4 of a thickness of a steel plate surface was adjusted as an observation surface. Out of the microstructure fractions, an amount of austenite phase retained (retained g) was measured based on X-ray analysis, and the fractions of ferrite (F), bainite (B), bainitic ferrite (BF), tempered martensite (TM ) and “fresh” martensite (M), the other microstructures being obtained by cutting a thick cross section parallel to the lamination direction, carrying out nital engraving on the polished cross section to be a mirror surface, and observing the cross section using FESEM (field emission scanning electron microscope).
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Table 9
EXAMPLEEXPERIENCEMENTAL COMPOSITION EXAMPLE KIND OFSTEEL RESULT OF MICRO-OBSERVATIONOSTRUCTURETHEVOLUME FRACTION F B BF TH M RETIDAy OUTRAT % % % % % % % 1 THE CR 42 3 38 1 4 10 2 EXAMPLE OFGIFTINVENTION 2 THE CR 40 5 37 2 3 13 0 EXAMPLE OFGIFTINVENTION 3 THE GA 32 3 44 4 1 13 3 EXAMPLE OFGIFTINVENTION 4 THE CR 47 3 36 0 0 12 2 EXAMPLE COMPARATIVE 5 6 CR 50 4 31 6 0 8 1 EXAMPLE OFGIFTINVENTION 6 B HR 41 6 39 5 0 6 3 EXAMPLE OFGIFTINVENTION 7 B Gl 36 4 44 5 2 7 2 EXAMPLE OFGIFTINVENTION 8 B CR 42 10 38 0 0 9 1 EXAMPLE COMPARATIVE
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9 Ç CR 36 4 35 0 3 19 2 EXAMPLE OFGIFTINVENTION 10 Ç CR 42 9 32 0 3 14 0 EXAMPLE OFGIFTINVENTION 11 Ç EG 44 4 36 0 3 11 2 EXAMPLE OFGIFTINVENTION 12 Ç CR 36 3 45 2 1 10 3 EXAMPLE COMPARATIVE 13 D CR 31 7 41 4 3 12 2 EXAMPLE OFGIFTINVENTION 14 D CR 34 7 39 5 2 13 0 EXAMPLE OFGIFTINVENTION 15 D GA 39 0 46 0 4 10 1 EXAMPLE OFGIFTINVENTION 16 D CR 0 4 56 23 5 11 1 EXAMPLE COMPARATIVE 17 AND CR 43 0 46 0 1 8 2 EXAMPLE OFGIFTINVENTION 18 AND CR 41 5 40 0 1 9 4 EXAMPLE OFGIFTINVENTION 19 AND Gl 39 9 39 0 3 9 1 EXAMPLE OFGIFTINVENTION 20 AND CR 79 0 0 0 0 0 21 EXAMPLE
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COMPARATIVE 21 F CR 49 2 35 0 2 9 3 EXAMPLE OFGIFTINVENTION 22 F CR 48 8 33 0 2 8 1 EXAMPLE OFGIFTINVENTION 23 F EG 47 5 39 0 1 8 0 EXAMPLE OFGIFTINVENTION 24 F CR 78 0 0 0 4 0 18 EXAMPLE COMPARATIVE 25 G CR 20 2 45 15 2 14 2 EXAMPLE OFGIFTINVENTION 26 G CR 28 4 46 10 2 10 0 EXAMPLE OFGIFTINVENTION 27 G GA 33 2 54 0 0 10 1 EXAMPLE OFGIFTINVENTION 28 G CR 5 1 63 10 5 13 3 EXAMPLE COMPARATIVE 29 H CR 35 10 36 4 3 11 1 EXAMPLE OFGIFTINVENTION 30 H CR 40 6 37 2 3 11 1 EXAMPLE OFGIFTINVENTION
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Table 10
EXAMPLEEXPERIENCEMENTAL EXAMPLEINCOMPOSIDOG KIND OFSTEEL MI OBSERVATION RESULTCROESTRUCTUREFRA ( TO DEVO LUME F B BF TH M RET IDA ^y OUTRAS % % % % % % % 31 M Gl 47 5 37 1 0 9 1 EXAMPLE OFPRESENT INVENTION 32 H CR 65 8 6 0 3 6 12 EXAMPLECOMPARATIVE 33 1 CR 33 0 49 0 2 14 2 EXAMPLE OFPRESENT INVENTION 34 1 CR 37 7 41 0 2 13 0 EXAMPLE OFPRESENT INVENTION 35 1 EG 35 5 47 0 2 6 5 EXAMPLE OFPRESENT INVENTION 36 1 CR 35 5 22 8 24 4 2 COMPARATIVE EXAMPLE 37 J CR 38 1 48 0 2 9 2 EXAMPLE OFPRESENT INVENTION 38 J CR 32 11 43 0 2 8 4 EXAMPLE OF THISINVENTION 39 J GA 37 2 46 0 3 10 2 EXAMPLE OF THISINVENTION 40 J CR 42 39 14 0 0 2 3 EXAMPLECOMPARATIVE
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41 K CR 21 7 38 18 1 13 2 EXAMPLE OFPRESENT INVENTION 42 K CR _29 | 8 42 11 1 9 0 EXAMPLE OFPRESENT INVENTION 43 K Gl 31 9 32 16 2 8 2 EXAMPLE OFPRESENT INVENTION 44 L CR 34 3 44 5 4 8 2 EXAMPLE OFPRESENT INVENTION 45 L CR 32 7 42 4 4 10 1 EXAMPLE OFPRESENT INVENTION 46 L EG 27 2 38 25 1 7 0 EXAMPLE OFPRESENT INVENTION 47 M CR 34 2 42 0 2 19 1 EXAMPLE OFPRESENT INVENTION 48 M CR 38 8 39 0 2 12 1 EXAMPLE OFPRESENT INVENTION 49 M HR-GA 37 10 40 0 0 11 2 EXAMPLE OFPRESENT INVENTION 50 N CR 44 16 25 0 3 10 2 EXAMPLE OFPRESENT INVENTION 51 N CR 48 12 26 0 3 11 0 EXAMPLE OFPRESENT INVENTION 52 N Gl 53 14 16 0 2 12 3 EXAMPLE OFPRESENT INVENTION 53 0 CR 41 4 40 0 3 11 1 EXAMPLE OFPRESENT INVENTION 54 0 CR 47 5 36 0 3 9 0 EXAMPLE OFPRESENT INVENTION 55 0 EG 46 1 42 0 0 9 2 EXAMPLE OFPRESENT INVENTION 56 P CR 29 8 47 0 0 16 0 EXAMPLE OFPRESENT INVENTION 57 P CR 34 8 48 0 0 10 0 EXAMPLE OF
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PRESENT INVENTION 58 P GA 32 11 48 0 1 8 0 EXAMPLE OFPRESENT INVENTION 59 Q CR 35 9 38 0 1 15 2 EXAMPLE OFPRESENT INVENTION 60 QCR 38 8 37 0 1 15 1 EXAMPLE OFPRESENT INVENTION
Table 11
EXAMPLE EXAMPLE OF KIND OF RESULT OF MICROSES OBSERVATIONEXPERIMENTAL COMPOSITION STEEL STRUCTUREVOLUME FRACTION F 6 BF TM M RETENTION yOTHERS % % % % % % %61 Q Gl 35 4 45 0 3 10 3 EMPLOYE OFGIFTINVENTION 62 R CR 28 4 53 0 4 9 2 MPLO DAGIFTINVENTION 63 R CR 32 8 43 0 4 13 0 MPLO DAGIFTINVENTION 64 R EG 36 10 41 0 0 13 0 MPLO DAGIFTINVENTION 65 s CR 27 10 44 0 2 16 1 MPLO DAGIFTINVENTION
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66 s CR 25 2 63 0 2 6 2 MPLO DAGIFTINVENTION 67 s GA 23 6 58 0 1 10 2 MPLO DAGIFTINVENTION 68 T CR 22 8 60 0 3 6 1 MPLO DAGIFT
INVENTION 69 T CR 29 8 52 0 3 8 0 MPLO DAGIFTINVENTION 70 T Gl 24 11 52 0 0 9 4 MPLO DAGIFTINVENTION 71 u CR 42 2 14 32 0 9 1 MPLO DAGIFTINVENTION 72 u CR 43 1 18 27 0 9 2 MPLO DAGIFTINVENTION 73 u EG 41 0 22 25 1 11 0 MPLO DAGIFTINVENTION 74 V CR 25 12 48 0 1 12 2 MPLO DAGIFTINVENTION 75 V CR 37 5 49 0 1 7 1 PRESENT MPLOINVENTION 76 V GA 41 2 46 0 1 8 2 PRESENT MPLOINVENTION
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77 W CR 29 2 62 0 1 5 1 PRESENT MPLOINVENTION 78 W CR 35 7 49 0 1 8 0 PRESENT MPLOINVENTION 79 W Gl 31 12 45 0 3 9 0 PRESENT MPLOINVENTION 80 | X CR 41 6 44 0 2 7 0 PRESENT MPLOINVENTION 81 X CR 45 6 38 0 2 9 0 PRESENT MPLO INVENTION 82 X EG 45 1 38 0 4 10 2 PRESENT MPLOINVENTION 83 Y CR 48 3 38 0 1 9 1 GIFT IPLOINVENTION 84 Y CR 45 7 35 0 3 10 0 EXAMPLE OFGIFTINVENTION 85 Y GA 42 4 43 0 0 8 3 EXAMPLE OFGIFTINVENTION 86 z CR 32 9 38 0 4 17 0 EXAMPLE OFGIFTINVENTION 87 z HR 46 6 34 0 4 9 1 GIFT IPLOINVENTION 88 z Gl 41 3 41 0 1 11 3 GIFT IPLOINVENTION 89 AA CR 98 0 0 0 0 0 2 EXAMPLE COMPARATIVE 90 AB CR 62 17 5 0 16 0 0 EXAMPLE COMPARATIVE
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91 B.C CR 84 1 10 0 0 5 0 EXAMPLE COMPARATIVE 92 AD CR 63 1 22 0 0 14 0 EXAMPLE COMPARATIVE 93 D CR 12 6 41 12 2 27 0 EXAMPLE COMPARATIVE 94 D CR 36 12 24 18 0 10 0 EXAMPLE COMPARATIVE
[00178] Tables 12 to 14 represent results of analysis of components in the steel sheets obtained. Out of the component analysis results, an amount of solid carbon solution (C _g ) in the retained austenite phase was determined based on the X-ray analysis.
[00179] An amount of solid Mn solution in the retained austenite phase was determined in the following way.
[00180] First, a thick cross section parallel to the rolling direction was cut from each of the steel sheets obtained in a range from 1/8 thickness to 3/8 thickness of the steel plate, an analysis of ΕΡΜΑ was A polished cross section was performed to be a mirror surface to create a Mn concentration map, and an average amount of Mn (WMn *) was determined. In addition, in the same range, a retained austenite phase distribution was mapped using an EBSD analysis device provided together with FE-SEM, the resultant was superimposed with the Mn concentration map, and only the result of the component analysis in the retained austenite phase it was extracted, to thereby determine the amount of solid solution Mn (WMng) in the retained austenite phase.
[00181] An amount of Si solid solution in the retained austenite phase was also determined in a manner similar to that of
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[00182] First, análise analysis and analytical research were conducted to determine a Si concentration map, an average amount of Si (Wsí *), and an amount of solid solution of Si (Wsig) in the retained austenite.
[00183] An amount of solid Al solution in the retained austenite phase was also determined in a manner similar to that of the amount of solid Mn solution.
[00184] First, the ΕΡΜΑ analysis was conducted to determine an Al concentration map, and an average amount of Al (Wai *). [00185] Note that representing the amount of solid solution of C, the amount of solid solution of Mn, and the amount of solid solution of Si in experimental examples 89 and 90, indicates that the measurement was impossible to be performed. This is because the volume fraction of the retained austenite phase was 0% in both of the experimental examples 89 and 90, as shown in Tables 9 to 11, and, consequently, it was impossible to measure an amount of any solid solution element.
[00186] Then, from the resultados analysis results, a sum (F) of normalized amounts of Si (Wsí / Wsí *) and normalized amounts of Al (Wai / Wai *) at each measurement point was determined, a histogram of this was created, and a mode value and K kurtosis were determined.
The results of these are presented in Tables 12 to 14.
EXAMPLEEXPERIENCEMENTAL EXAMPLE OFCOMPOSITION0 KIND OFSTEEL COMPONENT ANALYSIS RESULTCY WMn r / WMnX Wsí τΛΔ / Si x VALUEOF MODE KURTOSEK % IN
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PASTA1 THE CR 0.92 1.25 1.48 1.96 3.91 EX EMPLOYE OFGIFTINVENTION 2 THE CR 0.96 1.12 1.36 1.97 4.04 EX MPLO DAGIFTINVENTION 3 THE GA 0.96 1.46 1.41 1.97 4.17 EX MPLO DAGIFTINVENTION 4 THE CR 0.95 1.31 1.24 2.04 5.21 COMPARATIVEAND EXAMPLE 5 B CR 0.94 1.35 1.43 2.02 4.70 MPLO DAGIFT
INVENTION 6 B HR 0.95 1.40 1.48 1.96 3.24 EMPLOYE OFGIFTINVENTION 7 B Gl 0.96 1.33 1.31 2.05 5.78 EMPLOYE OFGIFTINVENTION 8 B CR 0.95 1.06 0.97 1.93M 1.95 COMPARATIVE EXAMPLE 9 Ç CR 0.94 1.45 1.21 1.96 4.74 MPLO DAGIFTINVENTION 10 Ç CR 0.95 1.37 1.39 1.97 3.00 MPLO DAGIFTINVENTION 11 Ç EG 0.96 1.49 1.45 1.95 5.76 MPLO DAGIFT
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INVENTION 12 Ç CR 0.93 1.07 0.88 1.90 1.90 COMPARATIVE 13 D CR 0.95 1.30 1.45 2.03 3.11 EXAMPLE 14 D CR 0.95 1.42 1.37 1.97 3.29 MPLO DAGIFTINVENTION 15 D GA 0.93 1.20 1.46 2.00 3.45 MPLO DAGIFTINVENTION 16 D CR 0.94 1.06 1.07 1.97 4.93 COMPARATIVE
EXAMPLE 17 AND CR 0.91 1.29 1.33 2.00 3.22 MPLO DAGIFTINVENTION 18 AND CR 0.93 1.21 1.40 1.96 4.46 MPLO DAGIFTINVENTION 19Gl 0.96 1.50 1.19 1.95 5.97 MPLO DAGIFTINVENTION 20CR 0.93 1.38 1.46 2.03 3.94 COMPARATIVEEXAMPLE 21CR 0.90 1.48 1.13 2.01 3.80 MPLO DAGIFTINVENTION 22CR 0.93 1.49 1.20 1.99 3.15 MPLO DAGIFTINVENTION 23EG 0.95 1.40 1.24 1.95 4.71 MPLO DAGIFTINVENTION
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24CR 0.96 1.50 1.26 2.05 3.33 COMPARATIVE EXAMPLE 25 G CR 0.93 1.42 1.51 1.98 3.62 MPLO DAGIFTINVENTION 26 G CR 0.92 1.46 1.38 2.02 2.38 MPLO DAGIFTINVENTION
27 G GA 0.95 1.41 1.36 1.99 5.66 MPLOGIFTINVENTION GIVES 28 G CR 0.94 1.25 1.37 2.00 5.60 COMPARATIVEEXAMPLE29 H CR 0.95 1.33 1.49 1.99 5.55 MPLOGIFTINVENTION GIVES 30 H CR 0.96 1.47 1.34 2.03 3.71 MPLOGIFTINVENTION GIVES
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Table 13
EXAMPLEEXPERIENCEMENTAL EXAMPLE OFCOMPOSITION 0 KIND OFSTEEL COMPONENT ANALYSIS RESULTCY WMn r / WMn x Wsl r / WSi x VALUEINMODE KURTO SEK % IN LARGE SCALE 31 H Gl 0.93 1.48 1.37 2.03 5.62 PRESENT MPLOINVENTION 32 H CR 0.93 1.40 1.43 2.02 3.62 IPARATIVE MPLE 33 1 CR 0.88 1.49 1.38 2.05 4.41 PRESENT MPLOINVENTION 34 1 CR 0.95 1.30 1.29 1.97 5.89 PRESENT MPLOINVENTION 35 1 EG 0.92 1.31 1.20 2.00 5.28 PRESENT MPLOINVENTION 36 1 CR 0.65 1.35 1.28 1.98 3.51 COMPARATIVE MPLO 37 J CR 0.91 1.23 1.45 2.00 3.18 PRESENT MPLOINVENTION 38 J CR 0.93 1.32 1.39 1.99 3.09 PRESENT MPLOINVENTION 39 J GA 0.93 1.50 1.27 1.97 4.81 PRESENT EMPLOYEINVENTION 40 J CR 0.95 1.30 1.47 2.02 3.32 COMPARATIVE EXAMPLE 41 K CR 0.94 1.31 1.39 2.04 4.22 PRESENT EMPLOYEINVENTION
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42 K CR 0.94 1.24 1.33 1.98 3.15 PRESENT EMPLOYEINVENTION 43 K Gl 0.96 1.45 1.40 1.97 4.17 PRESENT EMPLOYEINVENTION 44 L CR 0.95 1.46 1.39 1.98 4.08 PRESENT EMPLOYEINVENTION 46 L CR 0.95 1.20 1.12 2.04 5.46 PRESENT EMPLOYEINVENTION 46 L EG 0.86 1.34 1.22 1.98 5.62 PRESENT EMPLOYEINVENTION 47 M CR 0.96 1.31 1.24 2.01 2.51 EXAMPLE OFPRESENT INVENTION 48 M CR 0.96 1.45 1.45 2.04 3.88 EXAMPLE OFGIFTINVENTION 49 M HR-GA 0.92 1.20 1.36 1.95 4.25 EXAMPLE OFGIFTINVENTION 50 N CR 0.93 1.20 1.23 1.99 3.56 EXAMPLE OFGIFTINVENTION 51 N CR 0.96 1.35 1.30 1.95 3.99 EXAMPLE OFGIFTINVENTION 52 N Gl 0.94 1.17 1.41 2.05 5.57 EXAMPLE OFGIFTINVENTION 53 0 CR 0.92 1.35 1.30 2.03 5.15 EXAMPLE OFGIFTINVENTION 54 0 CR 0.95 1.30 1.21 2.04 4.74 EXAMPLE OF
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GIFTINVENTION 55 0 EG 0.93 1.45 1.42 1.99 3.92 EXAMPLE OFGIFTINVENTION 56 P CR 0.85 1.44 1.36 1.97 4.44 EXAMPLE OFGIFTINVENTION 57 P CR 0.92 1.31 1.21 1.96 4.13 EXAMPLE OFGIFTINVENTION 58 P GA 0.96 1.27 1.22 1.96 3.31 EXAMPLE OFGIFTINVENTION 59 0 CR 0.93 1.43 1.49 1.96 5.57 EXAMPLE OFGIFTINVENTION 60 0 CR 0.95 1.25 1.25 2.03 3.22 EXAMPLE OFPPRESENTINVENTION
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92/107 Abela 14
Cy WMn r / WMn x Wsí r / WsiX VALUEINMODE KURTOSEK % INPASTA61 Q Gl 0.83 1.41 1.24 1.96 4.79 EMPLOYE OFGIFTINVENTION 62 R CR 0.91 1.29 1.37 2.04 3.37 EMPLOYE OFGIFTINVENTION 63 R CR 0.94 1.46 1.40 1.99 4.05 EMPLOYE OFGIFTINVENTION 64 R EG 0.95 1.49 1.44 1.99 4.75 EMPLOYE OFGIFTINVENTION 65 s CR 0.91 1.34 1.35 1.97 4.14 EX MPLO DAGIFTINVENTION 66 s CR 0.87 1.46 1.35 1.96 2.73 EX MPLO DAGIFTINVENTION 67 s GA 0.94 1.45 1.27 2.00 3.61 EXE MPLO DAGIFTINVENTION 68 T CR 0.95 1.40 1.49 2.02 5.15 EX EMPLOYE OFGIFTINVENTION 69 T CR 0.96 1.37 1.22 1.95 3.70 AMPLE OF
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PRESENT,INVENTION 70 T Gl 0.95 1.31 1.50 1.99 5.14 MPLO DAGIFTINVENTION 71 u CR 0.92 1.38 1.40 1.96 4.06 EXE MPLO DAGIFTINVENTION 72 u CR 0.94 1.15 1.50 2.04 4.01 EX MPLO DAGIFTINVENTION 73 u EG 0.96 1.34 1.38 1.96 5.71 EXE MPLO DAGIFTINVENTION 74 V CR 0.94 1.36 1.30 2.00 3.33 EXE MPLO DAGIFTINVENTION 75 V CR 0.92 1.34 1.33 2.04 4.49 EXE MPLO DAGIFTINVENTION 76 V GA 0.93 1.21 1.38 1.99 5.55 EX MPLO DAGIFTINVENTION 77 w CR 0.95 1.45 1.34 1.98 5.03 EXE MPLO DAGIFTINVENTION 78 w CR 0.92 1.33 1.20 2.03 3.21 EX MPLO DAGIFTINVENTION 79 w Gl 0.92 1.33 1.37 2.00 3.18 MPLO DAGIFTINVENTION
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80 X CR 0.88 1.36 1.37 1.96 5.66 EMPLOYEGIFTINVENTION GIVES 81 X CR 0.87 1.40 1.25 1.98 4.64 EMPLOYEGIFTINVENTION GIVES 82 X EG 0.84 1.20 1.48 1.95 4.76 EMPLOYEGIFTINVENTION GIVES 83 Y CR 0.94 1.28 1.46 2.01 3.86 EMPLOYEGIFTINVENTION GIVES 84 Y CR 0.92 1.45 1.42 1.99 3.60 EMPLOYEGIFTINVENTION GIVES 85 Y GA 0.96 1.31 1.34 1.99 3.38 EMPLOYEGIFTINVENTION GIVES 86 z CR 0.93 1.42 1.28 1.99 3.56 MPLOGIFTINVENTION GIVES 87 Z HR 0.94 1.43 1.26 1.98 3.45 MPLOGIFTINVENTION GIVES 88 Z Gl 0.94 1.47 1.21 2.01 3.89 EXAMPLEGIFTINVENTION GIVES 89 AA CR - - - 2.11 1 AC1.45 EXAMPLECOMPARATIVE90 AB CR - - - 2.14 1 76 EXAMPLECOMPARATIVE
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91 B.C CR 0.91 1.05 1.24 2.01 1 84 EXAMPLE COMPARATIVE 92 AD CR 0.95 1.23 0.95 2.09 1.70 EXAMPLE COMPARATIVE 93 D CR 0.91 1.27 1.23 2.03 4.01 EXAMPLE COMPARATIVE 94 D CR 0.97 1.04 1.06 2.10 1.85 EXAMPLE COMPARATIVE
00187] Next, the results of the steel sheet property evaluation of experimental examples 1 to 93 are shown in Tables 15 to 17.
[00188] Part stress test pieces based on JIS Z 2201 were collected from the steel sheets of experimental examples 1 to 93, and a stress test was conducted based on JIS Z 2241 to measure a yield resistance (YS ), a tensile strength (TS), and a total elongation (EL).
[00189] Additionally, a hole expansion test to assess the stretch flangeability was conducted based on JFST1001, to determine a hole expansion limit value (1) without an index of the stretch flangeability.
[00190] Additionally, in order to assess the shape fixability, a 90 degree V-bend test was conducted. A 35 mm x 100 mm test piece was cut from each of the steel sheets in experimental examples 1 to 92, a shear cut surface was mechanically polished, and the bending test was conducted, while a bending radius was adjusted to double the
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96/107 sheet thickness of each [00191] one of the steel sheets, in which an angle produced by the test piece after forming was measured, and a 90 ° return angle was measured.
[00192] Note that the test example having X in the test results in Tables 15 to 17 has conditions in which a fracture and / or tapering was (was) observed in an edge line of the test piece, and the training cannot be carried out.
[00193] Note that as a method of evaluating properties, the example having the tensile strength of less than 900 MPa, the example having the total elongation of less than 10%, the example having the limit value of bore expansion of less than 20%, and the example having shape fixability of more than 3.0 degrees, were assessed as flawed.
[00194] Note that the underlined numeric value and symbol in Tables 1 to 17 indicate a range outside the present invention.
Table 15
EXAMPLE OFCOMPOSITION STEEL TYPE MATERIAL MEASUREMENT RESULTYS TS EL THE FIXABILIDE OFFORM MPa MPa % % DEGREE THE CR 686 1082 22 35 0.4 EXAMPLE OF THISINVENTION THE CR 655 1003 25 45 2.7 EXAMPLE OF THISINVENTION THE GA 619 1109 21 32 0.5 EXAMPLE OF THISINVENTION THE CR 700 1088 7 20 X COMPARATIVE EXAMPLE B CR 539 1051 25 45 1.7 EXAMPLE OF THIS
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INVENTION B HR 570 1056 24 55 0.4 EXAMPLE OF THISINVENTION
B Gl 667 1074 26 42 0.6 EXAMPLE OF THE PRESENT INVENTION B CR 555 1049 26 44 4.5 COMPARATIVE EXAMPLE Ç CR 487 1022 22 42 2.3 EXAMPLE OF THE PRESENT INVENTION Ç CR 514 1038 20 49 0.8 EXAMPLE OF THE PRESENT INVENTION ç EG 581 1041 23 31 0.8 EXAMPLE OF THE PRESENT INVENTION ç CR 531 1032 19 49 5.2 COMPARATIVE EXAMPLE D CR 623 1048 19 43 2.7 EXAMPLE OF THE PRESENT INVENTION D CR 537 1029 18 41 1.6 EXAMPLE OF THE PRESENT INVENTION D GA 538 1030 21 42 2.7 EXAMPLE OF THE PRESENT INVENTION D CR 1058 1202 9 15 X COMPARATIVE EXAMPLE AND CR 510 994 24 52 1.0 EXAMPLE OF THE PRESENT INVENTION AND CR 649 1045 22 52 1.7 EXAMPLE OF THE PRESENT INVENTION AND Gl 572 1059 25 33 1.1 EXAMPLE OF THE PRESENT INVENTION AND CR 485 558 14 17 X COMPARATIVE EXAMPLE F CR 469 984 26 46 91 EXAMPLE OF THE PRESENT INVENTION F CR 593 998 23 49 2.4 EXAMPLE OF THE PRESENT INVENTION F EG 601 1012 26 53 0.1 EXAMPLE OF THE PRESENT INVENTION F CR 496 705 23 27 X COMPARATIVE EXAMPLE G CR 622 1018 18 35 2.9 EXAMPLE OF THE PRESENT INVENTION
INVENTION G CR 673 1049 14 37 0.6 EXAMPLE OF THISINVENTION G GA 573 1062 15 40 2.9 EXAMPLE OF THISINVENTION G CR 1086 1199 8 22 X COMPARATIVE EXAMPLE H CR 614 1034 21 60 0.3 EXAMPLE OF THISINVENTION
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H CR 571 1024 17 53 1.1 EXAMPLE OF THISINVENTION
Table 16
EXAMPLE EX-PERIMENTAL EXAMPLE OFCOMPOSITION STEEL TYPE MATERIAL MEASUREMENT RESULTYS TS EL THE FIXABILI DADE DEFORM MPa MPa % % DEGREE 31 H Gl 540 1035 20 40 1.6 EXAMPLE OF THISINVENTION 32 H CR 479 861 19 23 2.7 EXAMPLE COMPARATIVE 33 I CR 665 1102 22 56 0.1 EXAMPLE OF THISINVENTION 34 1 CR 595 1120 19 57 0.4 EXAMPLE OF THISINVENTION 35 1 EG 561 1133 22 65 1.9 EXAMPLE OF THISINVENTION 36 1 CR 500 1516 5 3 X EXAMPLE COMPARATIVE 37 J CR 555 1121 20 53 2.8 EXAMPLE OF
PRESENT INVENTION 38 J CR 564 1140 19 50 1.7 EXAMPLEPRESENT INVENTION GIVES 39 J GA 585 1160 20 52 1.6 EXAMPLEPRESENT INVENTION GIVES 40 J CR 866 1054 13 42 X EXAMPLECOMPARATIVE 41 K CR 799 1252 21 65 2.8 EXAMPLE GIVES
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PRESENT INVENTION 42 K CR 827 1320 17 70 1.2 EXAMPLEPRESENT INVENTION GIVES 43 K Gl 840 1326 18 39 0.0 EXAMPLEPRESENT INVENTION GIVES 44 L CR 711 1316 17 47 1.9 EXAMPLEPRESENT INVENTION GIVES 45 L CR 715 1203 15 48 0.3 EXAMPLEPRESENT INVENTION GIVES 46 L EG 605 1222 18 49 1.3 EXAMPLEPRESENT INVENTION GIVES 47 M CR 619 1206 28 33 0.5 EXAMPLEPRESENT INVENTION GIVES 48 M CR 716 1205 24 53 2.4 EXAMPLEPRESENT INVENTION GIVES 49 If HR-GA 672 1104 30 66 2.8 EXAMPLEPRESENT INVENTION GIVES 50 N CR 650 1084 27 53 2.8 EXAMPLEPRESENT INVENTION GIVES 51 N CR 772 1143 23 47 2.2 EXAMPLEPRESENT INVENTION GIVES 52 N Gl 759 1158 26 46 0.5 EXAMPLEPRESENT INVENTION GIVES 53 0 CR 646 1196 24 46 0.6 EXAMPLE OF PRESENT INVENTION 54 0 CR 790 1254 23 39 0.8 EXAMPLEPRESENT INVENTION GIVES 55 0 EG 784 1245 24 70 0.3 EXAMPLEPRESENT INVENTION GIVES 56 P CR 691 1324 21 37 0.4 EXAMPLEPRESENT INVENTION GIVES 57 P CR 666 1345 17 32 1.4 EXAMPLE GIVES PRESENT INVENTION
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58 P GA 745 1357 19 48 0.0 EXAMPLEPRESENT INVENTION GIVES 59 0 CR 600 1234 21 40 0.5 EXAMPLEPRESENT INVENTION GIVES 60 0 CR 676 1274 17 32 2.5 EXAMPLEPRESENT INVENTION GIVES
Table 17
EXPERIMENT EXAMPLEIMENTAL EXAMPLE OFCOMPOSITION KIND OFSTEEL MATERIAL MEASUREMENT RESULTYS TS EL THE FIXABILITY ANDOF FORM MPa MPa % % DEGREE 61 Q Gl 700 1255 20 49 0.1 EXAMPLE OFPRESENT INVENTION 62 R CR 705 1327 17 43 0.8 EXAMPLE OFPRESENT INVENTION 63 R CR 731 1269 16 35 2.7 EXAMPLE OFPRESENT INVENTION
64 R EG 792 1276 19 41 2.1 EXAMPLE OFPRESENT INVENTION 65 s CR 745 1314 21 31 1.6 EXAMPLE OFPRESENT INVENTION 66 s CR 856 1258 19 34 1.8 EXAMPLE OFPRESENT INVENTION 67 s GA 813 1368 16 42 2.4 EXAMPLE OFPRESENT INVENTION 68 T CR 781 1295 16 42 1.5 EXAMPLE OFPRESENT INVENTION 69 T CR 690 1393 12 46 1.9 EXAMPLE OF
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PRESENT INVENTION 70 T G! 770 1402 13 32 0.6 EXAMPLE OFPRESENT INVENTION 71 u CR 686 1183 21 52 2.6 EXAMPLE OFPRESENT INVENTION 72 u CR 801 1256 19 58 0.5 EXAMPLE OFPRESENT INVENTION 73 u EG 774 1248 22 40 1.5 EXAMPLE OFPRESENT INVENTION 74 V CR 686 1212 18 53 1.4 EXAMPLE OF THIS
INVENTION 75 V CR 841 1283 15 53 1.4 EXAMPLE OFPRESENT INVENTION 76 V GA 915 1274 18 28 0.7 EXAMPLE OFPRESENT INVENTION 77 w CR 682 1286 19 39 1.2 EXAMPLE OFPRESENT INVENTION 78 w CR 845 1214 18 29 2.5 EXAMPLE OFPRESENT INVENTION 79 w Gl 875 1296 19 40 0.9 EXAMPLE OFPRESENT INVENTION 80 X CR 820 1294 20; 51 2.7 EXAMPLE OFPRESENT INVENTION 81 X CR 870 1234 19 49 2.0 EXAMPLE OF THISINVENTION 82 X EG 974 1246 20 38 2.7 EXAMPLE OF THISINVENTION 83 Y CR 658 1279 22 46 2.6 EXAMPLE OF THISINVENTION 84 Y CR 895 1284 20 55 0.3 EXAMPLE OF THISINVENTION
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85 Y GA 912 1269 22 53 1.8 EXAMPLE OFGIFTINVENTION 86 Z CR 706 1409 21 35 0.4 EXAMPLE OF THISINVENTION 87 Z HR 882 1432 19 29 2.9 EXAMPLE OF THISINVENTION 88 z Gt 956 1417 16 41 0.6 EXAMPLE OF THISINVENTION 89 AA CR 284 383 33 56 0.2 COMPARATIVEEXAMPLE 90 AB CR 351 930 12 2 X COMPARATIVE EXAMPLE 91 B.C CR 423 712 27 32 3.8 COMPARATIVE EXAMPLE 92 AD CR 592 958 19 42 4.2 COMPARATIVEEXAMPLE 93 D CR 618 1339 28 9 2.3 COMPARATIVE EXAMPLE 94 D CR 735 1029 21 39 3.6 COMPARATIVEEXAMPLE
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103/107 [00195] Experimental examples 6 and 87 are examples of the present invention in which hot rolling and coiling were conducted based on the conditions according to the present invention, and annealing processing was carried out. Additionally, experimental example 49 is an example of the present invention in which hot rolling and coiling were conducted based on the conditions according to the present invention, the steel sheet was immersed in a zinc bath during cooling in the annealing step , and the alloy treatment of the coating layer was additionally conducted. The experimental example satisfies the production conditions of the present invention, and shows form fixability, ductility, and formability.
[00196] Additionally, experimental examples 11, 23, 35, 46, 55, 64, 73, and 82 are examples of the present invention in which the respective hot rolling, winding, cold rolling and annealing processes have been conducted based on the conditions according to the present invention, and electrocoating processing was then conducted to obtain the high strength galvanized steel sheets. These experimental examples satisfy the production conditions of the present invention, and show fixability of shape, ductility, and formability.
[00197] Additionally, experimental examples 7, 19, 31, 43, 52, 61, 70, 79, and 88 are examples of the present invention in which hot rolling, coiling and cold rolling were conducted based on the conditions according to the present invention, and the steel sheets were then immersed in a zinc bath in the middle of cooling in the annealing step, to thereby obtain the high-strength hot-dip galvanized steel sheets . These experimental examples satisfy the production conditions of the present invention, and show form fixability,
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104/107 ductility, and formability.
[00198] Additionally, experimental examples 3, 15, 27, 39, 58, 67, 76, and 85 are examples of the present invention in which hot rolling, coiling and cold rolling were conducted based on the conditions according to with the present invention, the steel sheets were then immersed in a zinc bath in the cooling medium in the annealing step, and the alloy treatment of the coating layer was additionally conducted to thereby obtain the sheet high strength alloy galvanized steel by hot dipping. These experimental examples satisfy the production conditions of the present invention, and show fixability of shape, ductility, and formability. [00199] Additionally, experimental examples 15 and 85 are examples in which a coating film produced from an oxide compound containing P was given to a surface of the alloyed galvanized layer, and obtained good properties.
[00200] Examples of the present invention other than the above are examples in which hot rolling and coiling were conducted based on the conditions according to the present invention, the steel sheets were cooled to 100Ό or less, the surfaces were subjected to pickling, cold rolling was carried out at the reduction ratios described, and then annealing processing was carried out. Each of the examples of the present invention shows form fixability, ductility, and formability.
[00201] In experimental example 89, the amount of C added is small, and it is not possible to obtain bainite, bainitic ferrite, tempered martensite and "fresh" martensite, being hard microstructures, so that the resistance is lower.
[00202] In experimental example 90, the added amount of Si
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105/107 is small, and the retained austenite phase cannot be achieved, so that the shape fixability is lower.
[00203] In the experimental example 91, bainite, bainitic ferrite, tempered martensite and "fresh" martensite being hard microstructures cannot be obtained sufficiently since the added amount of Mn is small, and since the amount of solid Mn solution in the phase of retained austenite is small, the strength and form fixability are lower.
[00204] In experimental example 92, the added amount of Al is small, so that Si cannot be sufficiently concentrated in the retained austenite phase, and distributions of Si and Al concentrations are not predetermined distributions, resulting in the fixability of shape is inferior.
[00205] Experimental example 4 is an example in which the temperature of completion of the hot lamination is low, and since the microstructure becomes a heterogeneous microstructure in which the structure stretches in one direction, the ductility and the fixability of form are inferior.
[00206] Experimental example 8 is an example in which the temperature at which the steel sheet is wound in a coil after hot rolling is low, and since Mn and Si are not sufficiently concentrated in the retained austenite phase, the shape fixability is inferior.
[00207] Experimental example 12 is an example in which the cooling rate after hot rolling and after winding is low, and since Mn and Si are not sufficiently concentrated in the retained austenite phase, the form fixability is lower .
[00208] Experimental example 16 is an example where the maximum heating temperature in the annealing step is high, and since the volume fraction of soft ferrite is small, the ductility,
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106/107 the stretch flangeability and shape fixability are inferior.
[00209] On the other hand, experimental example 20 is an example in which the maximum heating temperature in the annealing step is low, and since a large number of coarse iron-based carbide to be a starting point of destruction is remained in an insoluble state, bainite, bainitic ferrite, tempered martensite and “fresh” martensite, being hard microstructures, and retained austenite, cannot be sufficiently obtained, resulting in ductility, stretch flangeability and shape fixability. lower. [00210] In experimental example 24, the average cooling rate in the third cooling stage up to 700Ό is low, a large number of carbide based on coarse iron and ferrite is generated, and bainite, bainitic ferrite, tempered martensite and "fresh martensite" ”Being hard microstructures cannot be obtained sufficiently, resulting in the resistance being lower.
[00211] On the other hand, in experimental example 28, the average cooling rate in the third cooling step up to 700Ό is high, and the volume fraction of soft ferrite is small, so that the ductility and the fixability of shape are lower .
[00212] In experimental example 32, the cooling rate in the fourth cooling stage from 700Ό to 500Ό is low, a large number of carbide based on coarse iron is generated, and bainite, bainitic ferrite, tempered martensite, and martensite “ fresh ”being hard microstructures, cannot be obtained sufficiently, resulting in lower resistance.
[00213] In experimental example 36, since the retention time of 450Ό to 350Ό is short, C is not sufficiently concentrated in the retained austenite phase, and the retained austenite phase cannot be sufficiently maintained, and, provided that a big
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107/107 amount of martensite to be a starting point of destruction is contained, the ductility, the stretch flangeability and the form fixability, are inferior.
[00214] On the other hand, in experimental example 40, since the retention time from 450Ό to 350Ό is long, the iron-based carbide is generated during the retention process, and the volume fraction of austenite phase retained it is small, so that ductility and form fixability are inferior.
[00215] Experimental example 93 is an example where the maximum heating temperature in the annealing step is high, and the average cooling rate in the third cooling step after the annealing step is high, and provided that the volume fraction of soft ferrite is small, the stretch flangeability is lower.
[00216] Experimental example 94 is an example in which the average cooling rate in the first cooling from the completion of hot rolling to the beginning of winding is low, and since the ferrite transformation proceeds excessively, the distributions of Mn , Si, and Al cannot be carried out after winding, and the amounts of Mn, Si, and Al in the retained austenite phase obtained in the annealing step are outside the range of the present invention, so that the shape fixability is bottom.

权利要求:
Claims (14)
[1]
1. Highly resistant steel sheet in form fixability, characterized by the fact that it comprises:
in mass%,
C: 0.075 to 0.300%;
Si: 0.30 to 2.5%;
Mn: 1.3 to 3.50%;
P: 0.001 to 0.030%;
S: 0.0001 to 0.0100%;
Al: 0.080 to 1.500%;
N: 0.0001 to 0.0100%;
O: 0.0001 to 0.0100%; and a remainder of Fe and unavoidable impurities, where:
a steel plate structure contains an austenite phase retained from 5 to 20% in volume fraction in a range of 1/8 thickness to 3/8 thickness of the steel plate;
an amount of solid solution C contained in the retained austenite phase is 0.80 to 1.00% by weight%;
Wsíy defined as an amount of solid Si solution contained in the retained austenite phase is 1.10 times or more Wsr defined as an average amount of Si in the range of 1/8 thickness to 3/8 thickness of the steel plate;
WMnY defined as an amount of solid Mn solution contained in the retained austenite phase is 1.10 times or more WMn * defined as an average amount of Mn in the range of 1/8 thickness to 3/8 thickness of the steel plate ; and when the frequency distribution is measured by adjusting a plurality of measurement regions, each having a diameter of 1 pm or less in the range of 1/8 thickness to 3/8 thickness of
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[2]
2/6 steel plate, with respect to a sum of a ratio between Wsí defined as a measured value of an amount of Si in each of the plurality of measurement regions and Wsi * being the average amount of Si, and a ratio between Wai defined as a measured value of an amount of Al in each of the plurality of measurement regions, and Wai * defined as an average amount of Al, a mode value of the frequency distribution is 1.95 to 2.05, and a kurtosis is 2.00 or more.
2. Highly resistant steel sheet in form fixability according to claim 1, characterized by the fact that:
the steel sheet structure additionally contains a 10 to 75% ferrite phase by volume fraction, and either or both of a bainitic ferrite phase and a 10 to 50% bainite phase in total; and a tempered martensite phase is limited to less than 10% by volume fraction, and a "fresh" martensite phase is limited to 15% or less by volume fraction.
[3]
3. Highly resistant steel sheet in form fixability according to claim 1, characterized by the fact that it additionally comprises:
in mass%, one or two or more than
Ti: 0.005 to 0.150%,
Nb: 0.005 to 0.150%,
V: 0.005 to 0.150%,
B: 0.0001 to 0.0100%,
Mo: 0.01 to 1.00%,
W: 0.01 to 1.00%,
Cr: 0.01 to 2.00%,
Ni: 0.01 to 2.00%, and
Cu: 0.01 to 2.00%, and / or
Petition 870180163908, of 12/17/2018, p. 116/121
3/6 one or two or more of Ca, Ce, Mg, Zr, Hf, and REM from 0.0001 to 0.5000% in total.
[4]
4. Galvanized steel sheet of high strength in form fixability, characterized by the fact that it comprises the high strength steel sheet as defined in claim 1, having a galvanized layer formed on its surface.
[5]
5. Galvanized steel sheet of high strength in fixability of form according to claim 4, characterized in that a coating film produced from a composite oxide containing a phosphorous oxide and / or phosphorus is formed on a surface of the galvanized layer .
[6]
6. Method of production of a sheet of high-strength steel in form fixability, characterized by the fact that it comprises:
a hot rolling step being a step of heating a plate comprising:
in mass%,
C: 0.075 to 0.300%;
Si: 0.30 to 2.5%;
Mn: 1.3 to 3.50%;
P: 0.001 to 0.030%;
S: 0.0001 to 0.0100%;
Al: 0.080 to 1.500%;
N: 0.0001 to 0.0100;
O: 0.0001 to 0.0100; and a remainder of Fe and unavoidable impurities at 1100Ό or more, hot lamination on the plate in a temperature region where a higher temperature between 850Ό and an Ar3 temperature is set to a lower limit temperature, realization of first cooling of cooling performance in
Petition 870180163908, of 12/17/2018, p. 117/121
4/6 a range from a rolling completion to a start of winding at a rate of WC / second or more on average, winding in a winding temperature range of 600 to 750Ό, and conducting a second cooling cooling of the steel sheet coiled in a coiling temperature range a (the coiling temperature - 100) Ό at a rate of 1 õO / hour or less on average; and a continuous annealing step of annealing steel sheet at a maximum heating temperature (Aci + 40) Ό to 1000Ό after the second cooling, followed by a third cooling at an average cooling rate of 1, 0 to 10 OO / second in a range of maximum heating temperature to 700Ό, then performing a fourth cooling at an average cooling rate of 5.0 to 200.0'C / second in a range of 700Ό to 500Ό , and then, a process of retaining the fixability of the steel plate after being subjected to the fourth cooling for 30 to 1000 seconds in a range of 350 to 450Ό.
[7]
7. Method of producing a high-strength steel sheet in form fixability according to claim 6, characterized by the fact that the plate comprises:
in mass%, one or two or more than
Ti: 0.005 to 0.150%,
Nb: 0.005 to 0.150%,
V: 0.005 to 0.150%, and
B: 0.0001 to 0.0100%,
Mo: 0.01 to 1.00%,
W: 0.01 to 1.00%,
Cr: 0.01 to 2.00%,
Petition 870180163908, of 12/17/2018, p. 118/121
5/6
Ni: 0.01 to 2.00%, and
Cu: 0.01 to 2.00%, and / or one or two or more of Ca, Ce, Mg, Zr, Hf, and REM from 0.0001 to 0.5000% in total.
[8]
8. Method of production of high-strength steel sheet in form fixability according to claim 6, characterized by the fact that it additionally comprises:
a cold laminating step of stripping and then cold rolling at a reduction rate of 30 to 75% between the hot rolling step and the continuous annealing step.
[9]
9. Method of production of high-strength steel sheet in form fixability according to claim 6, characterized by the fact that it additionally comprises:
a tempering lamination step of rolling steel sheet at a reduction rate of less than 10%, after the continuous annealing step.
[10]
10. Method of production of a galvanized steel sheet of high strength in fixability of form according to claim 6, characterized by the fact that it comprises:
formation, after carrying out the retention process when producing the high-strength steel sheet in the method of producing a galvanized layer on a surface of the steel sheet by conducting electroplating.
[11]
11. Method of production of a galvanized steel sheet of high strength in form fixability according to claim 6, characterized by the fact that it comprises:
formation, between the fourth cooling and the retention process, or after the retention process when producing high strength steel sheet in the production method, of a
Petition 870180163908, of 12/17/2018, p. 119/121
6/6 layer galvanized on a steel sheet surface by immersing the steel sheet in a galvanizing bath.
[12]
12. Method of production of high strength galvanized steel sheet in form fixability according to the claim
11, characterized by the fact that:
the steel sheet after being immersed in the galvanizing bath is reheated to 460 to 600Ό, and retained for two seconds or more to cause the galvanized layer to be formed by alloy.
[13]
13. Production method of high-strength galvanized steel sheet in form fixability according to claim 10, characterized by the fact that:
after the galvanized layer is formed, a coating film produced from a composite oxide containing one or both of a phosphorus and phosphorus oxide is given to a surface of the galvanized layer.
[14]
14. Production method of high-strength galvanized steel sheet in form fixability according to the claim
12, characterized by the fact that:
after the galvanized layer is formed by alloy, a coating film produced from a composite oxide containing one or both of a phosphorus and phosphorus oxide is given to a surface of the alloyed galvanized layer.

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同族专利:

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US9988700B2|2018-06-05|

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EP2738278B1|2019-11-13|

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TWI488976B|2015-06-21|

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CN103703157B|2015-12-02|

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JPWO2013018741A1|2015-03-05|

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EP2738278A1|2014-06-04|

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PL2738278T3|2020-05-18|

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KR20140043156A|2014-04-08|

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ZA201401402B|2015-04-29|

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CA2842800A1|2013-02-07|

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CN103703157A|2014-04-02|

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RU2014107494A|2015-09-10|

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TW201313913A|2013-04-01|

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ES2766756T3|2020-06-15|

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KR101598309B1|2016-02-26|

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BR112014002026A2|2017-02-21|

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US20140242414A1|2014-08-28|

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WO2013018741A1|2013-02-07|

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法律状态:
2018-05-15| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|

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2018-09-18| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|

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2019-01-22| B09A| Decision: intention to grant|

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2019-03-26| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 27/07/2012, OBSERVADAS AS CONDICOES LEGAIS. |

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2019-11-19| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

优先权:

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申请号 | 申请日 | 专利标题

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JP2011167689|2011-07-29|

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JP2011-167689|2011-07-29|

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PCT/JP2012/069262|WO2013018741A1|2011-07-29|2012-07-27|High-strength steel sheet having excellent shape-retaining properties, high-strength zinc-plated steel sheet, and method for manufacturing same|

---