HOT PRESSED COMPONENT FROM STEEL PLATE, HOT PRESS STEEL PLATE, AND METHOD FOR PRODUCING HOT PRESSED

专利摘要:

公开号:BR112012003763B1
申请号:R112012003763-3
申请日:2010-08-19
公开日:2018-04-17
发明作者:Kobayashi Akio；Funakawa Yoshimasa；Seto Kazuhiro；Kageyama Nobuyuki；Yamamoto Tetsuo；Hoshi Toru；Yokota Takeshi
申请人:Jfe Steel Corporation；
IPC主号:

专利说明:

(54) Title: HOT PRESSED COMPONENT FROM STEEL PLATE, STEEL SHEET FOR HOT PRESSING, AND METHOD FOR PRODUCTION OF HOT PRESSED COMPONENT FROM STEEL PLATE (51) Int.CI .: C22C 38 / 60; B21D 22/20 (30) Unionist Priority: 08/05/2010 JP 2010-175850, 08/21/2009 JP 2009-191573 (73) Holder (s): JFE STEEL CORPORATION (72) Inventor (s): AKIO KOBAYASHI ; YOSHIMASA FUNAKAWA; KAZUHIRO SETO; NOBUYUKI KAGEYAMA; TETSUO YAMAMOTO; TORU HOSHI; TAKESHI YOKOTA
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Invention Patent Descriptive Report for
HOT PRESSED COMPONENT FROM STEEL SHEET, STEEL SHEET FOR HOT PRESSING, AND METHOD FOR PRODUCTION OF HOT PRESSED COMPONENT FROM STEEL SHEET.
TECHNICAL FIELD [001] The present invention relates to a component hot pressed from steel sheet, whose strength is increased by working the heated steel sheet in a metal mold including a mold and a stamping core simultaneously quickly cooling the steel sheet. In particular, the present invention relates to a hot-pressed component from steel sheet that has a tensile strength (LRT) limit (Tensile Strengh (TS)) from 980 to 2130 MPa and in which the decrease in hardness surface is small, to a hot pressed steel plate, and to a method for producing the hot pressed component from steel plate.
BACKGROUND OF THE TECHNIQUE [002] Up until now, structural members used in automobiles and the like have been produced by pressing a steel plate with the desired strength. Recently, based on the need to reduce the weight of automobile bodies, for example, a high strength steel plate having a thickness of about 1.0 to 4.0 mm has been desired as a steel plate material. However, with the increase in strength of the steel sheet, the working capacity of the steel sheet decreases and it becomes difficult to work the steel sheet on a member having the desired shape.
[003] Consequently, as described in Patent Literature 1, a method for producing a structural member has attracted attention, the method being called hot pressing or
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2/59 die hardening, in which a high resistance is achieved by working a steel sheet heated in a metallic mold and simultaneously cooling the steel sheet quickly. This production method was used practically to produce some members that require a tensile strength limit (LRT) of 1.0 to 1.5 GPa. In this method, since the steel sheet is heated to about 950 ° C and it is then worked at a high temperature, the problem in terms of working capacity in cold pressing can be reduced. In addition, this method is advantageous in that since the rapid cooling is performed with a water-cooled metal mold, the strength of the member can be increased using a transformation structure, and the amount of connecting elements added steel plate material can be reduced. [LIST OF CITATIONS] [PATENT LITERATURE] [004] [PTL 1] Great Britain Patent Application n ° 1490535 SUMMARY OF THE INVENTION
TECHNICAL PROBLEM [005] However, in a hot-pressed component from steel sheet described in Patent Literature 1, the surface hardness decreases significantly, which can often result in deterioration of wear resistance or the like.
[006] An objective of the present invention is to provide a hot-pressed component from steel sheet that has a tensile strength limit (LRT) of 980 to 2130 Mpa and in which the decrease in surface hardness is small, a hot-pressed steel plate, and a method for producing a hot-pressed component from steel plate. Note that here the tensile strength limit (LRT) of a component hot-pressed from sheet steel refers to the tensile strength limit (LRT)
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3/59 of the steel plate that constitutes the member after hot pressing. SOLUTION TO THE PROBLEM [007] As a result of intensive studies conducted to achieve the above objective, the inventors of the present invention discovered the following:
i) One cause of the decrease in surface hardness is the decarburized layer having a thickness of several tens of micrometers to several hundred micrometers, the decarburized layer being formed in a portion of the surface layer of a steel plate while the steel plate it is heated before hot pressing and is then cooled by a series of hot pressing treatments.
ii) To avoid the formation of such a decarburized layer, it is effective to add Sb to the steel plate for hot pressing in an amount of 0.002% to 0.03% by mass.
[008] The present invention was made on the basis of that discovery and provides a hot-pressed component from steel sheet having a composition containing, in mass%, C: 0.09% to 0.38%, Si: 0 , 05% to 2.0%, Mn: 0.5% to 3.0%, P: 0.05% or less, S: 0.05% or less, Al: 0.005% to 0.1%, N : 0.01% or less, Sb: 0.002% to 0.03%, and the balance being Fe and the inevitable impurities, where the limit of tensile strength (LRT) is 980 to 2130 Mpa.
[009] The hot-pressed component from the steel sheet of the present invention may also contain, in% by weight, at least one element selected from Ni: 0.01% to 5.0%, Cu: 0.01% at 5.0%, Cr: 0.01% to 5.0%, and Mo: 0.01% to 3.0%. The hot-pressed component from the steel sheet of the present invention may also contain, in% by weight, at least one element selected from Ti: 0.005% to 3.0%, Nb: 0.005% to 3.0%, V : 0.005% to 3.0%, and W: 0.005% to 3.0%; B: 0.0005% to 0.05%; or at least one sePetition element 870170086905, of 11/10/2017, p. 9/71
4/59 taught between REM: 0.0005% to 0.01%, Ca: 0.0005% to 0.01%, and Mg: 0.0005% to 0.01% separately or at the same time.
[0010] According to the hot-pressed component from the steel sheet of the present invention, the range of the selected C content varies between, in mass%, C: 0.34% to 0.38%, C : 0.29% or more and less than 0.34%; C: 0.21% or more and less than 0.29%, C: 0.09% or more and less than 0.14%, it is possible to obtain hot-pressed steel plate members at the desired strength levels, ie , resistance levels from 1960 to 2130 MPa, 1220 MPa or more and less than 1960 MPa, 1470 MPa or more and less than 1770 MPa, 1180 MPa or more and less than 1470 MPa, and 980 MPa or more and less than 1180 MPa , respectively, corresponding to the respective contents of C. [0011] In this case, in a component hot pressed from steel sheet having a C content of C: 0.14% or more and less than 0.21% or C: 0.21% or more and less than 0.29% in Sb content is preferably 0.002% to 0.01% from the point of view of fatigue properties.
[0012] The present invention also provides a hot pressed steel plate having the above composition.
[0013] A hot-pressed component from steel sheet at a desired strength level corresponding to the above C content range can be produced by a method including heating a hot-pressed steel sheet of the present invention having a carbon content selected from, in mass%, C: 0.34% to 0.38%, C: 0.29% or more and less than 0.34%, C: 0.21% or more and less 0.29%, C: 0.14% or more and less than 0.21%, and 0.09% or more and less than 0.14% at a heating rate of 1 ° C / s or more, keep the steel sheet in a temperature range from the transformation point Ac3 to (transformation point Ac3 + 150 ° C) for 1 to 600 seconds, and then start the hot pressing
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5/59 over a temperature range of 550 ° C or greater, and bringing cooling to an average cooling rate of 3 ° C / s or more up to 200 ° C.
[0014] In this case, after hot pressing, preferably, the member is removed from a metal mold and cooled with a liquid or gas.
ADVANTAGE EFFECTS OF THE INVENTION [0015] In accordance with the present invention, it is possible to produce a hot-pressed component from steel sheet that has a tensile strength limit (LRT) of 980 to 2130 MPa and in which the decrease in surface hardness is small. The hot-pressed component from the steel sheet of the present invention is suitable for structural members to ensure safety at the time of the collision, such as door protection, a side member, and an automobile central pillar.
DESCRIPTION OF THE CONFIGURATION [0016] The present invention will now be described specifically. Note that the% notation for compositions represents% by mass unless otherwise stated.
[0017] Composition of the hot-pressed component from C steel sheet: 0.09 to 0.38% [0018] Carbon (C) is an element that improves the strength of a steel. To achieve a tensile strength limit (LRT) of a hot-pressed component from steel sheet of 980 MPa or more, it is necessary to adjust the C content to 0.09% or more. On the other hand, when the C content exceeds 0.38%, it is difficult to reach a tensile strength limit (LRT) of 2,130 MPa or less. Consequently, the C content is adjusted to 0.09% to 0.38%. In particular, to obtain a tensile strength limit (LRT) from 1960 to 2130 MPa, the
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The C content is preferably adjusted to 0.34% to 0.38%. To obtain a tensile strength limit (LRT) of 1770 MPa or more and less than 1960 MPa, the C content is preferably adjusted to 0.29% or more and less than 0.34%. To obtain a tensile strength limit (LRT) of 1470 MPa or more and less than 1770 MPa, the C content is preferably adjusted to 0.21% or more and less than 0.29%. To obtain a tensile strength limit (LRT) of 1470 MPa or more and less than 1770 MPa, the C content is preferably adjusted to 0.21% or honeys and less than 0.29%. To obtain a tensile strength limit (LRT) of 1180 MPa or more and less than 1470 MPa, the C content is preferably adjusted to 0.14% or more and less than 0.21%. To obtain a tensile strength limit (LRT) of 980 MPa or more and less than 1180 MPa, the C content is preferably adjusted to 0.09% or more and less than 0.14%.
Si: 0.05% to 2.0% [0019] Silicon (Si) is an element that improves the strength of a steel similar to C. To reach a limit of tensile strength (LRT) of a hot-pressed component from steel sheet of 980 MPa or more, it is necessary to adjust the Si content to 0.05% or more. On the other hand, when the Si content exceeds 2.0%, during hot rolling, the generation of a surface defect called red scale increases significantly, the rolling load increases, and the ductility of the hot rolled steel sheet resultant decreases. Consequently, the Si content is adjusted to 0.05% to 2.0%.
Mn: 0.5% to 3.0% [0020] Manganese (Mn) is an element that is effective in improving the hardening capacity. In addition, since Mn decreases the transformation point Ac ₃ , Mn is an element that is also effective in decreasing the heating temperature before pressing
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7/59 hot. To present these effects, it is necessary to adjust the Mn content to 0.5% or more. On the other hand, when the Mn content exceeds 3.0%, the Mn secretes, resulting in a decrease in the uniformity of the properties of the steel plate material and the hot-pressed component from the steel plate. Consequently, the Mn content is adjusted to 0.5% to 3.0%.
P: 0.05% or less [0021] When the P content exceeds 0.05%, the P secretes, resulting in a decrease in the uniformity of the properties of the steel plate material and the hot-pressed component from steel plate. steel, and toughness also decreases significantly. Consequently, the P content is adjusted to 0.05% or less. Note that an excessive dephosphoration treatment causes an increase in cost, and so the P content is preferably adjusted to 0.001% or more.
S: 0.05% or less [0022] When the S content exceeds 0.05%, the toughness of a hot-pressed component from steel plate decreases. Consequently, the S content is adjusted to 0.05% or less.
Al: 0.005% to 0.1% [0023] Aluminum (Al) is added as a deoxidizing element in steel. To show this effect, it is necessary to adjust the Al content to 0.005% or more. On the other hand, an Al content exceeding 0.1% decreases the stamping work capacity and the hardening capacity of the steel sheet material. Consequently, the Al content is adjusted to 0.005% to 0.1%.
N: 0.01% or less [0024] When the N content exceeds 0.01%, N forms an AlN nitride during hot rolling and heating to perform the hot pressing, and decreases the working capacity of 870170086905, of 10/11/2017, p. 13/71
8/59 capping and hardening capacity of steel sheet material. Consequently, the N content is adjusted to 0.01% or less.
Sb: 0.002% to 0.03% [0025] Antimony is the most important element of the present invention, and has the effect of suppressing an unburdened layer formed on a surface layer portion of a steel sheet while the steel sheet is heated before hot pressing and is then cooled by a series of hot pressing treatments. To show this effect, it is necessary to adjust the Sb content to 0.002% or more. Most preferably, the Sb content is 0.003% or more. On the other hand, an Sb content exceeding 0.03% results in an increase in the rolling load, thus decreasing productivity. Consequently, the Sb content is adjusted to 0.002% to 0.03%.
[0026] The hot-pressed component from the steel sheet of the present invention is mainly applied to structural members to ensure safety at the time of the collision, such as door protection, a side member, and a central car pillar. In particular, for a component hot pressed from sheet steel at a strength level of 1180 Mpa or more and less than 1470 Mpa or 1470 Mpa or more and less than 1770 Mpa, that is, preferably, for a component hot pressed from steel sheet having a content of C: 0.14% or more and less than 0.21% or C: 0.21% or more and less than 0.29%, excellent fatigue properties are also frequently needed. Therefore, in a hot-pressed component from steel sheet having this C content, the Sb content is preferably adjusted to 0.002% to 0.01%. This is because when the Sb content exceeds 0.01%, the fatigue properties tend to decrease.
[0027] The balance is Fe and wing inevitable impurities. However,
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9/59 reasons described below, it is preferable to incorporate at least one element selected from Ni: 0.01% to 5.0%, Cu: 0.01% to 5.0%, Cr: 0.01% to 5.0 %, and Mo: 0.01% to 3.0%; at least one element selected from Ti: 0.005% to 3.0%, Nb: 0.005% to 3.0%, V: 0.005% to 3.0%, and W: 0.005% to 3.0%; B: 0.0005% to 0.05%; or at least one element selected from REM: 0.0005% to 0.01%, Ca: 0.0005% to 0.01%, and Mg: 0.0005% to 0.01% separately or at the same time.
Ni: 0.01% to 5.0% [0028] Nickel (Ni) is an element that is effective in increasing the strength of a steel plate and improving its hardening capacity. To show these effects, the NI content is preferably adjusted to 0.01% or more. On the other hand, a Ni content exceeding 5.0% results in a significant increase in cost, and thus the upper limit of the Ni content is preferably adjusted to 5.0%.
Cu: 0.01% to 5.0% [0029] Copper (Cu) is an element that is effective in increasing the strength of a steel and improving the hardening capacity similar to Ni. To show these effects, the Cu content is preferably adjusted to 0.01% or more. On the other hand, a Cu content exceeding 5.0% results in a significant increase in cost, and thus the upper limit of the Cu content is preferably adjusted to 5.0%.
Cr: 0.01% to 5.0% [0030] Chromium (Cr) is an element that is effective in increasing the strength of a steel and in improving the hardening capacity similar to Cu and Ni. To show these effects, the Cr content is preferably adjusted to 0.01% or more. On the other hand, a Cr content exceeding 5.0% results in a significant increase in cost, and thus the upper limit the Cr content is preferably adjusted to 5.0%.
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Mo: 0.01% to 3.0% [0031] Molybdenum (Mo) is an element that is effective in increasing the strength of a steel and in improving the hardening capacity similar to Cu, Ni and Cr. Molybdenum also has the effect of suppressing the growth of crystal grains to improve toughness by refining the grain. To exhibit these effects, the Mo content is preferably adjusted to 0.01% or more. On the other hand, an Mo content in excess of 3.0% results in a significant increase in cost, and thus the upper limit of the Mo content is preferably adjusted to 3.0%.
Ti: 0.005% to 3.0% [0032] Titanium (Ti) is an element that is effective in increasing the strength of a steel and improving the toughness by refining the grain. In addition, Ti is an element that is effective in inhibiting the effect of improving the hardening capacity due to solute B by the formation of a nitride, preferably to the B described below. To present these effects, the Ti content is preferably adjusted to 0.005% or more. On the other hand, when the Ti content exceeds 3.0%, the rolling load during hot rolling increases significantly, and the toughness of a hot-pressed component from steel plate decreases. Consequently, the upper limit of the Ti content is preferably adjusted to 3.0%.
Nb: 0.005% to 3.0% [0033] Niobium (Nb) is an element that is effective in increasing the strength of a steel and improving the toughness for grain refining similar to Ti. To present these effects, the content of Nb is preferably adjusted to 0.005% or more. On the other hand, when the Nb content exceeds 3.0%, the precipitation of carbonitrides increases, and the ductility and resistance to delayed fracture decrease. Consequently, the upper limit of Nb is preferably adjusted to 3.0%.
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V: 0.005% to 3.0% [0034] Vanadium (V) is an element that is effective in increasing the strength of a steel and improving the toughness for grain refining similarly to Ti and Nb. In addition, the V precipitates as a precipitate or a crystal, which functions as a hydrogen trapping site, which improves resistance to hydrogen embrittlement. To show these effects, the V content is preferably adjusted to 0.005% or more. On the other hand, when the V content exceeds 3.0%, the precipitation of carbonitrides becomes significant, and the ductility decreases significantly. Consequently, the upper limit of the V content is preferably adjusted to 3.0%.
W: 0.005% to 3.0% [0035] Tungsten (W) is an element that is effective in increasing the strength of a steel, improving toughness, and improving resistance to hydrogen embrittlement similarly to V. To present these For this purpose, the W content is preferably adjusted to 0.005% or more. On the other hand, when the W content exceeds 3.0%, the ductility decreases significantly. Consequently, the upper limit of the W content is preferably adjusted to 3.0%.
B: 0.0005% to 0.05% [0036] Boron (B) is an element that is effective in improving the hardening capacity during hot pressing and improving toughness after hot pressing. To show these effects, the B content is preferably adjusted to 0.0005% or more. On the other hand, when the B content exceeds 0.05%, the rolling load during hot rolling increases significantly, and the martensite and bainite phases are formed after hot rolling, resulting in the formation of fractures and the like on the steel plate. Consequently, the upper limit of the B content is preferably adjusted to 0.05%.
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REM: 0.0005% to 0.01% [0037] A rare earth metal (REM) is an element that is effective in controlling the shape of inclusions, and contributes to an improvement in ductility and resistance to hydrogen embrittlement. To show these effects, the REM content is preferably adjusted to 0.0005% or more. On the other hand, a REM content in excess of 0.01% deteriorates the hot work capacity, and thus the upper limit of the REM content is preferably set to 0.01%.
Ca: 0.0005% to 0.01% [0038] Calcium (Ca) is an element that is effective in controlling the shape of inclusions, and contributes to an improvement in ductility and resistance to hydrogen embrittlement similarly to REMs. To show these effects, the Ca content is preferably adjusted to 0.0005% or more. On the other hand, a Ca content exceeding 0.01% deteriorates the hot workability, and thus the upper limit of the Ca content is preferably adjusted to 0.01%.
Mg: 0.0005% to 0.01% [0039] Magnesium (Mg) is also an element that is effective in controlling the shape of inclusions, improves ductility, and contributes to an improvement in resistance to hydrogen embrittlement by formation of a compound precipitate or a compound crystal with other elements. To show these effects, the Mg content is preferably adjusted to 0.0005% or more. On the other hand, when the Mg content exceeds 0.01%, crude oxides and sulfides are formed, thus decreasing ductility. Consequently, the upper limit of the Mg content is preferably adjusted to 0.01%.
[0040] The microstructure of the hot-pressed component from the steel sheet of the present invention can be a cooled microstructure obtained by normal hot-pressing, and is not particularly limited. In general, in hot pressing, a steel plate
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The heated 13/59 is worked in a metal mold and is simultaneously cooled quickly. Consequently, a cooled microstructure composed mainly of a martensite phase tends to be formed in the composition range of the present invention.
[0041] In addition, for some hot-pressed steel plate members, although not for all members, after forming by pressing, for example, drilling and grinding work can be performed in a specific position of the members, and a cut tapping to secure with a screw can be performed. In the event that such grinding work is performed, from the point of view of providing it with a good working capacity, the microstructure is preferably close to a single phase microstructure. From this point of view, the microstructure is preferably a close microstructure. of a single martensitic phase, and the area ratio of the martensitic phase to the total microstructure is preferably controlled to be 90% or more. This is because when the area ratio of the martensite phase is less than 90%, a tensile strength limit (LRT) of 980 MPa or more cannot be achieved at low C levels.
[0042] As described above, the area ratio of the martensite phase is preferably 90% or more from the point of view of the grinding work capacity, a stable realization of the resistance, and the reduction in cost achieved by reaching the strength required by adding components in as small an amount as possible. The area ratio of the martensite phase is more preferably 96% or more, and can be 100%. Microstructures other than the martensite phase can be various microstructures, such as a bainite phase, a retained austenite phase, a cementite phase, a perlite phase, and a ferrite phase.
[0043] The area ratio of the martensite phase or other phases in miPetição 870170086905, of 10/11/2017, p. 19/71
14/59 croestructure can be determined by image analysis of a microstructure photograph.
[0044] A decarburized layer is formed on a surface layer of a steel plate together with the scale when the heat treatment is conducted in an oxidizing atmosphere such as air. In this case, the edges of the crystal grains become the preferred atom diffusion path, if compared to the interior of the crystal grains. Consequently, oxidation proceeds easily at the grain edges, is formed and a corrosion pit called the oxidized part of the grain edge. It is believed that the Sb is concentrated in the surface layer of the steel plate at the same time as the generation of scale, thus suppressing oxidation and decarburization. The formation and growth of the oxidized part of the grain edge described above are also suppressed by the concentration of Sb. As in the case of fatigue fracture, in the case where stress is repeatedly applied, fractures are easily formed in abnormal portions such as a portion having a different hardness and a pit of a steel plate that forms a member. Consequently, it is effective to reduce these abnormal portions to improve fatigue properties. It is believed that once the formation of pits due to erosion by oxidation is suppressed by the addition of Sb, the source of fracture formation is reduced, thus improving the fatigue properties. However, since the atomic size of Sb is larger than that of iron, the concentrated Sb portion is hardened. In the case where Sb is excessively concentrated, repeated stress is concentrated in part of the concentration of Sb which can become a source of fracture formation. Therefore, in the case where fatigue properties are also necessary, it is preferable to suppress the formation of a part with excessive concentration of Sb in a surface layer of a steel plate before hot pressing.
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15/59 [0045] Here, the concentration of Sb can be assessed by the following method.
[0046] Sb concentration evaluation method: the amount of Sb concentration in a surface layer of a steel plate before hot pressing can be measured by analyzing the line in which an electron beam is scanned linearly in the layer surface area of the steel plate or an analysis of the area in which an electron beam is scanned in a square shape using an electronic probe micro analyzer (EPMA) with x-ray dispersive energy spectroscopy (EDS) to measure the x-ray energy inherent to the elements or X-ray dispersive wavelength spectroscopy (WDS) to measure its wavelength. In that case, although measurement conditions such as voltage acceleration are equipment dependent, it is sufficient that the amount of Sb count detected with the above detector is set to 20 or more. For example, in the case where the measurement time is reduced, it is sufficient that the length of the electron beam scan in the line analysis is set to 15 mm or more in total, and that the scan area in the area analysis is adjusted to a quadrangle having a side of 2 mm or more. The Sb-maximum / Sb-average ratio of the maximum Sb-maximum intensity to the average Sb-average intensity of Sb in the measurement area is used as an evaluation index of the Sb concentration. When the Sb-maximum / Sb-average ratio is 5 or less, the propagation of fractures at the time of fatigue can be suppressed in a surface layer of a steel plate after hot pressing.
STEEL SHEET FOR HOT PRESSING [0047] Steel sheets such as a hot-rolled steel sheet, a cold-rolled steel sheet having a microstructure composed of a cold-rolled microstructure, and a laPetition 870170086905 steel sheet, of 10 / 11/2017, p. 21/71
16/59 cold mined annealed after cold rolling, all of which have the composition of the hot-pressed component from the steel sheet described above, can be used as the hot-pressed steel sheet of the present invention.
[0048] Steel sheets produced under the usual conditions can be used for these steel sheets. For example, as a hot-rolled steel plate, it is possible to use a steel plate obtained by hot-rolling a steel plate having the above composition at a temperature of the finish laminate inlet side of 1100 ° C or less and at a temperature on the output side of the finishing laminate in the range from transformation point Ac ₃ to (transformation point Ac3 + 50 ° C), the resulting hot-rolled steel plate being cooled under a normal cooling condition, and winding the steel sheet at a normal winding temperature. As a cold rolled steel sheet, a steel sheet obtained by cold rolling the hot rolled steel sheet above can be used. In that case, the reduction in lamination in cold rolling is preferably 30% or more, and more preferably 50% or more to prevent overgrowth of the grains during heating before hot pressing and during subsequent annealing. The upper limit of the lamination reduction is preferably 85% because the lamination load increases, thereby decreasing productivity. In addition, as a cold-rolled steel sheet annealed after cold rolling, it is preferable to use a steel sheet obtained by annealing the cold-rolled steel sheet described above at an annealing temperature of the transformation point Ac ₁ or less in a continuous annealing line. The steel sheet obtained by annealing at an annealing temperature greater than the transformation point Ac1 can also be used. However, care must be taken because a second hard phase such as a martensite phase, a
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17/59 bainite, or a pearlite phase is formed in the microstructure after annealing, and then the strength of the steel sheet can become excessively high.
[0049] To improve the fatigue properties, it is preferable to avoid excessive concentration on a surface layer of a steel sheet after hot rolling. For this purpose, the following method is effective: Specifically, at the time of hot rolling which is performed continuously after heating a plate, in addition to the flaking which is usually performed immediately before rolling to prevent scratches from being formed when the scale is pressed on a steel plate by lamination, peeling is performed repeatedly after lamination three times or more to a lamination reduction of 15% or more in a high temperature range of 1000 ° C or more in which scale formation occurs significantly. That is, it is effective to repeat lamination and peeling three times or more. Here the reason why the peeling is carried out at a lamination reduction of 15% or more is as follows. In the case where flaking is performed in a state where the scale is broken to some extent by lamination to a lamination reduction of 15% or more, the scale is effectively removed and an excessive concentration of Sb is avoided to achieve homogenization. Note that, in this case, it is sufficient that the collision pressure of the water stream at the flaking is 5 MPa or more. HOT PRESSING CONDITIONS [0050] The conditions for hot pressing that are usually conducted can be used as hot pressing conditions. As described above, from the point of view of obtaining a microstructure close to a single martensite phase, that is, a microstructure having 90% or more of a martensite phase in terms of area ratio, the following hot pressing conditions are
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18/59 preferable. In the case of the hot pressing conditions described below, a hot pressed component from steel sheet at a desired strength level can be easily produced by adjusting the C content range. For example, to obtain a limit of tensile strength (LRT) from 1960 to 2130 MPa, the C content is adjusted to be 0.34% to 0.38%. To obtain a tensile strength limit (LRT) of 1770 MPa or more and less than 1960 MPa, the C content is adjusted to be 0.29% or more and less than 0.34%. To obtain a tensile strength limit (LRT) of 1470 MPa or more and less than 1770 MPa, the C content is adjusted to be 0.21% or more and less than 0.29%. To obtain a tensile strength limit (LRT) of 1180 MPa or more and less than 1470 MPa, the C content is adjusted to be 0.14% or more and less than 0.21%. To obtain a tensile strength limit (LRT) of 980 MPa or more and less than aa80MPa, the C content is adjusted to be 0.09% or more and less than 0.14%. Thus, a hot-pressed component from steel sheet at any of the desired strength levels can be stably obtained. A preferred production method for obtaining a microstructure having 90% or more of the martensite phase in terms of area ratio will now be described having, as an example, a case in which a hot-pressed component is produced from steel sheet at a desired level of resistance corresponding to the C content range above. Specifically, a hot-pressed steel plate of the present invention having a carbon content selected from, in mass%, C: 0.34% to 0.38%, C: 0.29% or more and less than 0 , 34%, C: 0.21% or more and less than 0.29%, C: 0.14% or more and less than 0.21%, and 0.09% or more and less than 0.14% is heated at a heating rate of 1 ° C / s or more, and maintained in a temperature range of the transformation point Ac3, in which the microstructure becomes a single austenite phase, up to (transformation point Ac3 +
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150 ° C) for 1 to 600 seconds, hot pressing is then started over a temperature range of 550 ° C or more, and cooling is conducted at an average cooling rate of 3 ° C / s or more up to 200 ° C / s.
[0051] The reason why the heating rate is set to 1 ° C / s or more is that when the heating rate is less than 1 ° C / s, productivity decreases, and the auste nita grains cannot be refined during heating, resulting in a decrease in the toughness of the limb after cooling, from the point of view of refining the grains of the anterior austenite of the limb, the heating rate is preferably high and more preferably 3 ° C / s or more. The heating rate is even more preferably 5 ° C / s or more.
[0052] The reason why the heating temperature is adjusted to a temperature range from the transformation point Ac ₃ to (transformation point Ac ₃ + 150 ° C) is as follows. When the heating temperature is lower than the transformation point Ac3, a ferrite phase is formed after cooling and the resulting steel sheet becomes soft, and thus a desired tensile strength limit (LRT) corresponding to each of the bands C content cannot be obtained. On the other hand, when the heating temperature is higher than (transformation point Ac ₃ + 150 ° C), this condition is disadvantageous in terms of thermal efficiency and the amount of scale formed on the surface of the steel plate increases, resulting in an increase in the load of a subsequent scale removal treatment such as shot blasting. To increase thermal efficiency and reduce the amount of scale formed as much as possible, the temperature range from transformation point Ac3 to (transformation point Ac ₃ + 100 ° C) is preferable, and a temperature range from transformation point Ac3 up to (transformation point Ac3 + 50 ° C) is more preferable.
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20/59 [0053] Note that the transformation point Ac ₃ can be determined without causing a practical problem by the following empirical formula: [0054] Transformation point Ac ₃ = 881 - 206C + 53Si - 15Mn 20Ni = 1Cr - 27Cu + 41Mo [ 0055] where the symbols of the elements represent the contents (% by mass) of the respective elements.
[0056] The reason why the retention time is set to 1 to 600 seconds is as follows. When the retention time is less than 1 second, a sufficient amount of austenite phase is not formed during heating, and the area ratio of the martensite phase after cooling decreases. Thus, a desired tensile strength limit (LRT) corresponding to each of the C content ranges cannot be obtained. When the holding time exceeds 600 seconds, this condition is disadvantageous in terms of thermal efficiency and the amount of scale formed on the surface of the steel plate increases, resulting in an increase in the load of a subsequent scale removal treatment such as sandblasting. shot. In the event that the retention time is excessively long, the effect of preventing the formation of a decarburized layer, the effect being caused by Sb, becomes insufficient. In addition, the concentration of Sb on the surface becomes irregular. Consequently, the retention time is more preferably 1 to 300 seconds.
[0057] The reason why the temperature at which hot pressing is started is set to 550 ° C or more is as follows. When the temperature is below 550 ° C, a soft ferrite phase or a bainite phase is formed excessively during the cooling process and it becomes difficult to reach a desired tensile strength limit (LRT) corresponding to each of the content ranges from C.
[0058] After the start of hot pressing, the steel sheet is shaped to have the shape of a member, and cooled in a mold
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21/59 metal for hot pressing. Alternatively, after the steel sheet is shaped to have the shape of a member, the member is removed from the metal mold either immediately or in the course of cooling in the metal mold, and cooled. To guarantee the area ratio of the martensite phase, it is necessary that the cooling after the start of the hot pressing be conducted at an average cooling rate of 3 ° C / s or more up to 200 ° C. As for the cooling method, for example, a stamping tap is kept in the bottom neutral for 1 to 60 seconds during hot pressing, and the member is cooled using the mold and the stamping tap. Alternatively, the member can be cooled by air cooling in combination with the above cooling. In addition, from the point of view of an improvement in productivity and the achievement of a desired tensile strength limit (LRT) corresponding to each of the C content ranges, it is preferable to remove the metal mold member after hot pressing. , and cool the limb with a liquid or a gas. Note that the cooling rate is preferably about 400 ° C / s or less from the point of view that the production cost is not excessively increased.
EXAMPLE 1 [0059] The steel sheet members hot - pressed paragraphs 1 to 22 having a hat shape were prepared driving by heating, retention, hot pressing and cooling under the hot pressing conditions shown in Table 2 using steel plates of the paragraphs a to P shown in Table 1. Note that the Ac3 transformation point shown in Table 1 was determined by the above empirical formula.
[0060] A metal mold used in hot processing has a pit width of 70 mm, a pit edge of R4 mm, a mold edge of R4 mm, and a forming depth of 30
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22/59 mm. The heating was conducted using either an infrared heating oven or an atmosphere heating oven according to the rate of heating in an atmosphere of 95% by volume of N ₂ + 5% by volume of O ₂ . Cooling was conducted from the pressing temperature (starting) to 150 ° C combining cooling in a state in which the steel sheet was sandwiched between the pit and the mold with air cooling in the mold after the state of release was released. press. In this step, the cooling rate was adjusted by varying the time during which the melt core was kept at the bottom dead center in the range from 1 to 60 seconds. One of the members (member No. 20) was removed from the metal mold immediately after forming by hot pressing, and subjected to accelerated cooling with air. In this case, the cooling rate in the above cooling was determined as the average cooling rate from the start pressure temperature up to 200 ° C. The temperature was measured in a position at the bottom of the hat with a thermocouple.
[0061] A JIS No. 5 tensile test specimen was prepared from a position of the bottom of the hat of each of the members hot-pressed steel plates prepared so that the direction parallel to the rolling direction of the plate. steel corresponded to the direction of traction. A tensile test was conducted according to JIS Z 2241 to measure the tensile strength limit (LRT). In the preparation of the tensile test specimen, after the specimen was finished by normal machining, parallel portions and R portions (edge portions) were polished with paper from # 300 to # 1500, and grinding was also carried out with a diamond paste to remove the damage due to machining. The reason for this is as follows. In the case where the tensile strength limit (LRT) is at an ultra high strength level as in the present invention, when normal machining is
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23/59 performed simply, early fractures occur at the same time as the tensile test from a damaged portion (such as a small scratch) due to machining. Consequently, the original tensile strength limit (LRT) cannot be assessed. In addition, the microstructure close to a portion from which the tensile test specimen was cut was examined by the following method.
[0062] A small strip was cut from the portion close to the portion from which the tensile test specimen was cut. The small strip was blasted to remove the scale on its surface. The Vickers hardness of the surface was then measured according to JIS Z 2244 at a load of 10 kgf (98.07 N). The number of measuring points was ten, and the average of these measuring points was determined. To clarify the degree of decrease in surface hardness, the cross section of the small strip in the direction of the thickness of the steel plate was polished, and the Vickers hardness of a central portion in the direction of the thickness of the steel plate was measured according to JIS Z 2244 at a load of 2 kgf (19.61 N). The number of measuring points was 5, and the average of these measuring points was determined. [0063] In addition, a small strip was cut from a portion close to the portion from which the tensile test specimen was cut. The cross section of the small strip in the direction of the thickness of the steel plate was polished, and corroded with nital. Images from a two-field electron scanning microscope (SEM) were taken in a position located about 1/4 of the edge of the steel sheet in the direction of its thickness to examine whether the microstructure was a martensite phase or a structure different from a martensite phase. The area ratio of the martensite phase was measured by image analysis. In this case, the area ratio was defined as the average of the fields of view.
[0064] Table 2 shows the results. The pressed component
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24/59 hot from steel plate No. 10 corresponds to a case in which the C content exceeds the upper limit of the C content of the present invention, and has a limit of tensile strength (LRT) exceeding the desired 2130 MPa. Consequently, there is a concern that since ductility is extremely insufficient, a fragile fracture occurs when a car collides, and the necessary amount of collision energy absorption cannot be obtained. The hot pressed component from steel plate No. 11 has a Sb content lower than the lower limit of the range of the present invention, and the decrease in the surface hardness of this hot pressed component from steel plate is more significant than that of the hot-pressed component from steel plate No. 4 which had substantially the same composition and was produced under substantially the same production conditions. Hot-pressed steel plate members other than those above are examples of the present invention. It is found that these hot-pressed steel sheet members each have a tensile strength limit (LRT) in the range of 980 to 2130 MPa, and the decrease in surface hardness is also small. In particular, the steel sheet members hot - pressed No 1, 4, 5, 8 and 12 to 22, which were produced under the preferred hot pressing conditions described above using steel plates for hot pressing of this invention having a C content of 0.34% to 0.38%, it is found that the desired tensile strength limit (LRT): 1960 to 2130 MPa corresponding to the C content range: 0.34% to 0, 38% is obtained as described above and the decrease in surface hardness is also small.
Petition 870170086905, of 11/10/2017, p. 30/71 [TABLE 1]
Steel sheet n ° Composition (% by mass) Ac3 transformation point (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.37 0.81 1.83 0.02 0.003 0.042 0.004 0.004 820 hot rolled steel sheet 2.3 in the range of the invention B 0.35 0.12 2.36 0.02 0.003 0.049 0.004 0.006 780 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention Ç 0.36 0.19 2.41 0.02 0.005 0.038 0.004 0.010 781 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention D 0.34 0.15 1.42 0.01 0.007 0.037 0.005 0.027 798 cold rolled steel sheet 1.2 in the range of the invention AND 0.31 0.19 1.37 0.01 0.005 0.035 0.003 0.006 807 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention F 0.40 0.26 1.45 0.02 0.004 0.041 0.003 0.005 791 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention G 0.34 0.15 1.41 0.01 0.004 0.034 0.004 <0.001 798 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention H 0.34 0.27 1.86 0.01 0.005 0.036 0.004 0.007 Ni: 1.1Cu: 0.2 770 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention I 0.36 0.22 1.31 0.02 0.006 0.044 0.004 0.006 Cr: 0.7Mo: 0.3 810 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention J 0.36 0.25 1.45 0.01 0.004 0.046 0.005 0.004 Ti: 0.04Nb: 0.05 798 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention K 0.35 0.18 1.45 0.01 0.003 0.034 0.003 0.014 V: 0.06W: 0.04 797 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 31/71 [TABLE 1] CONTINUED
Steel sheet n ° Composition (% by mass) Ac3 transformation point (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others L 0.37 0.18 1.82 0.02 0.006] 0.026 0.004 0.004 B: 0.0018 789 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention M 0.35 0.12 1.68 0.02 0.005 0.043 0.004 0.007 Sc (REM): 0008 790 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention N 0.34 0.16 1.43 0.01 0.005 0.031 0.003 0.006 Ca: 0.0016Mg: 0.0017 798 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention O 0.35 0.19 1.33 0.01 0.004 0.052 0.004 0.007 799 cold rolled sheet. (reduction: 50%) 1.2 in the range of the invention P 0.35 0.23 1.24 0.02 0.005 0.036 0.005 0.011 802 cold rolled sheet. (reduction: 44%) 1.8 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 32/71 [TABLE 2]
Table 2 hot pressing conditions toughness Area ratio of the mar-strained (%) Grades Hot pressed steel plate member n ° Steel sheet n ° heating rate (° C / s) heating temperature (° C) retention time (s) pressing start temperature (° C) cooling rate (° C / s) Tensile strength limit (LRT) (MPa) surfacecie center of the plate thickness 1 THE 15 930 120 650 60 2120 620 655 100 Ex. Inv. 2 15 780 120 650 60 1892 544 586 70 Ex. Inv, 3 15 880 0 650 60 1927 553 592 75 Ex. Inv, 4 B 15 860 120 650 60 2023 598 624 100 Ex. Inv, 5 Ç 15 840 120 650 60 2004 603 617 100 Ex. Inv, 6 15 850 120 350 60 1931 580 596 75 Ex. Inv, 7 15 840 120 650 1 1916 578 593 85 Ex. Inv, 8 D 15 860 120 650 60 1967 593 607 100 Ex. Inv, 9 AND 15 900 120 650 60 1883 557 583 100 Ex. Inv, 10 F 15 890 120 650 60 2160 640 668 100 Ex;Comp. 11 G 15 860 120 650 60 1965 479 605 100 Ex.Comp. 12 H 15 840 120 650 60 1967 579 602 100 Ex. Inv. 13 I 15 890 120 650 60 2069 610 636 100 Ex. Inv. 14 J 15 880 120 650 60 2058 600 635 100 Ex. Inv. 15 K 15 890 120 650 60 2004 608 620 100 Ex. Inv. 16 L 15 900 120 650 60 2091 613 648 100 Ex. Inv. 17 M 15 890 120 650 60 1972 586 609 100 Ex. Inv.
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Petition 870170086905, of 11/10/2017, p. 33/71 [TABLE 2] CONTINUED
Table 2 hot pressing conditions toughness Area ratio of the mar-strained (%) Grades Hot pressed steel plate member n ° Steel sheet n ° heating rate (° C / s) heating temperature (° C) retention time (s) press start temperature (fC) cooling rate (° C / s) Tensile strength limit (LRT) (MPa) surfacecie center of the plate thickness 18 N 15 880 120 650 60 1964 581 607 100 Ex. Inv. 19 O 15 890 540 650 60 2058 610 633 100 Ex. Inv. 20 15 870 120 650 15 2043 609 634 100 Ex. Inv. 21 2 860 120 650 60 2061 609 633 100 Ex. Inv. 22 P 15 910 120 650 60 1968 595 609 100 Ex. Inv.
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EXAMPLE 2 [0065] Members steel sheets hot - pressed paragraphs 1 to 22 having a hat shape leading were prepared by heating, retention, hot pressing, and cooling under the hot pressing conditions shown in Table 4 using- n is ^the steel plates a to P shown in Table 3.
[0066] The same tests as in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of a surface and the central portion in the direction of the thickness of the steel plate, and the area ratio of a martensite phase of each of the hot-pressed steel plate members.
[0067] Table 4 shows the results. The hot pressed component from steel plate No. 11 has a Sb content lower than the lower limit of the range of the present invention, and the decreased surface hardness of this pressed component. hot pressing from steel plate is more significant than that of the hot pressed component from steel plate No. 4 which had substantially the same composition and was produced under substantially the same production conditions. Hot-pressed steel plate members other than the above are examples of the present invention. It is found that these hot-pressed steel plate members each have a tensile strength limit (LRT) in the range of 980 to 2130 MPa, and the decrease in surface hardness is also small. In particular, the steel sheet members hot - pressed No 1, 4, 5, 8, and 12 to 22, which were produced under the aforementioned conditions of hot pressing Preferred using steel plates for hot pressing of present invention having a C content of 0.29% or more and less than 0.34%, it is found that the desired limit of tensile strength (LRT): 1770 MPa or more and less than 1960 MPa corresponding to the content range of C: 0.29% or more and
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0.34% or less is obtained as described above and the decrease in surface hardness is also small.
Petition 870170086905, of 11/10/2017, p. 36/71 [TABLE 3]
Steel sheet n ° Composition (% by mass) AC3 transformation point(° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.33 1.03 1.71 0.01 0.004 0.034 0.004 0.003 842 hot rolled steel sheet 2.3 in the range of the invention B 0.30 0.14 2.88 0.02 0.005 0.036 0.003 0.006 786 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention Ç 0.31 0.23 2.43 0.01 0.004 0.037 0.004 0.011 793 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention D 0.30 0.21 1.30 0.01 0.005 0.041 0.005 0.029 811 cold rolled steel sheet 1.2 in the range of the invention AND 0.26 0.15 1.49 0.02 0.006 0.042 0.004 0.004 813 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention F 0.35 0.18 1.34 0.01 0.003 0.049 0.003 0.007 795 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention G 0.29 0.14 1.40 0.03 0.003 0.033 0.003 <0.001 808 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention H 0.31 0.21 1.82 0.02 0.004 0.038 0.004 0.006 Ni: 1.2 Cu: 0.4 766 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention I 0.30 0.20 1.52 0.02 0.004 0.037 0.004 0.005 Cr: 0.6 Mo: 0.5 827 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention J 0.32 0.19 1.43 0.01 0.005 0.037 0.005 0.007 Ti: 0.06 Nb: 0.04 804 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention K 0.29 0.16 1.56 0.02 0.003 0.029 0.003 0.008 V: 0.06 W: 0.04 806 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 37/71 [TABLE 3] CONTINUED
Steel sheet n ° Composition (% by mass) transformation point AC3 (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others L 0.30 0.18 1.37 0.01 0.005 0.048 0.004 0.014 B: 0.0016 808 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention M 0.30 0.12 1.49 0.02 0.006 0.048 0.003 0.012 Sc(REM): 0.007 803 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention N 0.31 0.13 1.67 0.01 0.004 0.042 0.005 0.005 Ca: 0.0026Mg: 0.0023 799 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention O 0.29 0.17 1.35 0.03 0.007 0.052 0.003 0.007 810 cold rolled sheet. (reduction: 50%) 1.2 in the range of the invention P 0.30 0.18 1.49 0.02 0.006 0.045 0.005 0.010 806 cold rolled sheet. (reduction: 44%) 1.8 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 38/71 [TABLE 4]
Pressed steel plate memberhot n ° hot pressing conditions Limit oftensile strength (LRT)(MPa) toughness Reason forarea ofphasemartensi-OK(%) Grades Steel sheetn ° heating rate(° C / s) heating temperature(° C) time toretention(s) pressing start temperature(° C) rate ofcool-ment(° C / s) surfacecie center ofplate thickness 1 THE 15 960 120 650 60 1928 560 596 100 Ex. Inv. 2 15 810 120 650 60 1720 492 535 80 Ex. Inv, 3 15 920 0 650 60 1713 489 529 80 Ex. Inv, 4 B 15 840 120 650 60 1864 552 574 100 Ex. Inv, 5 Ç 15 850 120 650 60 1846 563 575 100 Ex. Inv, 6 15 860 120 350 60 1742 525 539 75 Ex. Inv, 7 15 850 120 650 1 1749 529 540 80 Ex. Inv, 8 D 15 860 120 650 60 1806 543 555 100 Ex. Inv, 9 AND 15 890 120 650 60 1874 489 519 100 Ex. Inv, 10 F 15 880 120 650 60 2022 605 624 100 Ex. Inv, 11 G 15 900 120 650 60 1779 439 547 100 Ex. Comp. 12 H 15 840 120 650 60 1840 550 572 100 Ex. Inv.
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Petition 870170086905, of 11/10/2017, p. 39/71 [TABLE 4] CONTINUED
Pressed steel plate memberhot n ° hot pressing conditions Limit oftensile strength (LRT)(MPa) toughness Reason forarea ofphasemartensi-OK(%) Grades Steel sheetn ° heating rate(° C / s) heating temperature(° C) time toretention(s) pressing start temperature(° C) rate ofcool-ment(° C / s) super-surface center ofthickness ofplate 13 I 15 890 120 650 60 1805 529 553 100 Ex. Inv. 14 J 15 880 120 650 60 1934 579 598 100 Ex. Inv. 15 K 15 880 120 650 60 1783 531 548 100 Ex. Inv. 16 L 15 870 120 650 60 1863 561 573 100 Ex. Inv. 17 M 15 880 120 650 60 1845 555 567 100 Ex. Inv. 18 N 15 890 120 650 60 1875 556 580 100 Ex. Inv. 19 15 910 540 650 60 1800 539 558 100 Ex. Inv. 20 O 15 890 120 650 15 1786 535 556 100 Ex. Inv. 21 2 870 120 650 60 1806 536 556 100 Ex. Inv. 22 P 15 870 120 650 60 1825 546 558 100 Ex. Inv.
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EXAMPLE 3 [0068] The steel sheet members hot pressed paragraphs 1 to 22 having a medium were prepared up leading-heating, retention, hot pressing, and cooling under the hot pressing conditions shown in Table 6 using up the steel sheet of ^the n to P shown in Table 5.
[0069] The same tests as the tests in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of a surface and the central portion in the direction of the thickness of the steel sheet, and the area ratio from the martensite phase of each of the members hot-pressed steel plates.
[0070] Table 6 shows the results. The hot pressed component from steel plate No. 11 has a Sb content lower than the lower limit of the range of the present invention, and the decrease in the surface hardness of this hot pressed component from steel plate is more significant than that of the hot-pressed component from steel plate No. 4 which had substantially the same composition and was produced under substantially the same production conditions. Hot-pressed steel plate members other than the above are examples of the present invention. It is found that these hot-pressed steel plate members each have a tensile strength limit (LRT) in the range of 980 to 2130 MPa, and the decrease in surface hardness is also small. In particular, the steel sheet members hot - pressed No 1, 4, 5, 8 and 12 to 22, which were produced under the preferred conditions for the hot pressing as described above using steel plates for hot pressing of this invention having a C content of 0.21% or more and less than 0.29%, it is found that the desired tensile strength limit (LRT): 1470 MPa or more and less than 1770 MPa corresponding to the C: 0.21% or more and less than
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0.29% is obtained as described above and the decrease in surface hardness is also small.
Petition 870170086905, of 11/10/2017, p. 42/71 [TABLE 5]
Steel sheet n ° Composition (% of mass) transformation point Ac ₃ (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.27 0.64 1.74 0.02 0.004 0.038 0.004 0.003 833 hot rolled steel sheet 2.3 in the range of the invention B 0.23 0.09 2.42 0.02 0.003 0.039 0.003 0.005 802 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention Ç 0., 23 0.18 2.68 0.02 0.004 0.044 0.004 0.010 802 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention D 0.22 0.11 1.46 0.01 0.005 0.042 0.004 0.027 820 cold rolled steel sheet 1.2 in the range of the invention AND 0.18 0.21 1.44 0.02 0.004 0.036 0.003 0.005 833 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention F 0.31 0.28 1.37 0.02 0.003 0.039 0.003 0.005 811 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention G 0.21 0.11 1.48 0.01 0.005 0.041 0.003 <0.001 822 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention
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Petition 870170086905, of 11/10/2017, p. 43/71 [TABLE 5] CONTINUED
Steel sheet n ° Composition (% of mass) transformation point Ac3 (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others H 0.26 0.23 1.77 0.01 0.004 0.040 0.004 0.004 Ni: 1.1Cu: 0.4 780 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention I 0.24 0.20 1.42 0.02 0.003 0.042 0.005 0.008 Cr: 0.3Mo: 0.5 841 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention J 0.25 0.25 1.43 0.01 0.004 0.039 0.003 0.007 Ti: 0.08Nb: 0.04 821 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention K 0.28 0.20 1.82 0.01 0.005 0.037 0.004 0.018 V: 0.09W: 0.05 810 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention L 0.22 0.18 1.42 0.02 0.005 0.029 0.003 0.008 B: 0.0015 824 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention M 0.26 0.12 1.64 0.01 0.003 0.048 0.005 0.009 Sc (REM): 0007 809 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention N 0.23 0.14 1.37 0.01 0.004 0.052 0.004 0.007 Ca: 0.0022Mg: 0.0015 820 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention O 0.23 0.19 1.39 0.02 0.006 0.037 0.005 0.006 823 cold rolled sheet. (reduction: 50%) 1.2 in the range of the invention P 0.24 0.13 1.41 0.01 0.004 0.034 0.003 0.011 817 cold rolled sheet. (reduction: 44%) 1.8 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 44/71
TABLE 6]
Member platehot pressed steel n ° Steel sheet n ° hot press conditions Tensile strength limit (LRT) (MPa) toughness Reason forarea ofphasemartensite(%) Grades heating rate (° C / s) heating temperature (° C) retention time (s) start temperaturepressing(° C) cooling rate (° C / s) surface center ofplate thickness 1 THE 15 950 120 650 60 1694 495 525 100 Ex. Inv. 2 15 780 120 650 60 1423 406 443 70 Ex. Inv, 3 15 900 0 650 60 1451 411 445 85 Ex. Inv, 4 B 15 870 120 650 60 1516 446 466 100 Ex. Inv, 5 Ç 15 870 120 650 60 1584 479 489 100 Ex. Inv, 6 15 870 120 350 60 1415 428 440 75 Ex. Inv, 7 15 860 120 650 1 1432 434 445 80 Ex. Inv, 8 D 15 860 120 650 60 1495 454 464 100 Ex. Inv, 9 AND 15 900 120 650 60 1340 400 418 100 Ex. Inv, 10 F 15 900 120 650 60 1823 542 562 100 Ex. Inv, 11 G 15 890 120 650 60 1471 361 451 100 Ex. Comp. 12 H 15 840 120 650 60 1699 498 523 100 Ex. Inv. 13 I 15 900 120 650 60 1610 481 499 100 Ex. Inv. 14 J 15 880 120 650 60 1655 496 512 100 Ex. Inv. 15 K 15 890 120 650 60 1733 526 536 100 Ex. Inv. 16 L 15 900 120 650 60 1492 449 463 100 Ex. Inv. 17 M 15 900 120 650 60 1632 499 510 100 Ex. Inv. 18 N 15 880 120 650 60 1535 457 473 100 Ex. Inv.
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Petition 870170086905, of 11/10/2017, p. 45/71
TABLE 6] CONTINUED
Member platehot pressed steel n ° Steel sheet n ° hot press conditions Tensile strength limit (LRT) (MPa) toughness Reason forarea ofphasemartensite(%) Grades heating rate (C / s) heating temperature (C) retention time (s) start temperaturepressing(Ç) cooling rate (C / s) surfacecie center ofplate thickness 19 O 15 900 540 650 60 1535 456 474 100 Ex. Inv. 20 15 910 120 650 15 1524 453 473 100 Ex. Inv. 21 2 870 120 650 60 1560 464 483 100 Ex. Inv. 22 P 15 890 120 650 60 1642 500 510 100 Ex. Inv.
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EXAMPLE 4 [0071] The steel sheet members hot - pressed paragraphs 1 to 9 having a hat shape were prepared driving by heating, retention, hot pressing, and cooling under the pressing conditions Hot shown in Table 8 using If the steel plates paragraphs a to I shown in Table 7. Here, the steel sheets paragraphs a to C and E to I in addition to shedding prior to lamination, peeling was repeatedly conducted immediately after the lamination a high temperature range of 1000 ° C or more. At a lamination reduction of 15% or more, and a water current collision pressure of 5 MPa or more. The number of times for this peeling is shown in Table 7. On steel plate No. D, this last peeling has not been performed.
[0072] The same tests as those in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of a surface and the central portion in the direction of the thickness of the steel plate, and the area ratio of the martensite phase of each member hot-pressed steel plates. The degree of Sb concentration was assessed by line analysis in terms of maximum Sb / average Sb using an EPMA equipped with an EDS by the method described above. In addition, a plurality of fatigue test specimens were prepared from the bottom position of the hat of each member of hot-pressed steel plates, and a fatigue test under pulsating tension was conducted. The mean of the maximum stress at which the test specimen does not fracture even after a load is applied repeatedly 10 ⁷ times was defined as fatigue strength, and the fatigue strength ratio (= fatigue strength / tensile strength limit ( LRT)) has been determined. In general, the fatigue strength ratio of a steel sheet having a tensile strength limit (LRT) of more than 1180 MPa and composed of a single martensite phase is about 0.55. Consequently, in the present invention, in the case where the fatigue strength ratio exceeded 0.58, the specimen was evaluated as having an excellent fatigue strength property.
[0073] Table 8 shows the results. In steel sheets hot - pressed members ^Nos 1 to 4 and 6 to 9 as described above, a threshold
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42/59 desired tensile strength (LRT): 1470 MPa or more and less than 1770 MPa corresponding to the C content range: 0.21% u more and less than 0.29% is obtained and the decrease in surface hardness is small. In the hot-pressed component from steel plate No. 5 having a low Sb content, which is outside the range of the present invention, a significant decrease in surface hardness is observed.
[0074] The ratio of the fatigue strength of each steel sheet members hot - pressed is equal to or greater than that of the standard material, in particular, steel sheet members hot - pressed No 1, 2, 4 and 6 to 9, which have a Sb content in the range of 0.002% to 0.01%, have a fatigue strength ratio of 0.58 or more, indicating that these members have excellent fatigue properties. In the hot-pressed component from steel plate No. 3 composed of steel plate No. C, which had a Sb content of 0.015%, and which was obtained by conducting, in addition to the usual flaking before rolling, a flaking immediately after rolling in a high temperature range of 1000 ° C or more at a rolling reduction of 15% or more, a fatigue strength ratio substantially the same as that of normal material was obtained. Moreover, the steel sheet members hot - pressed paragraphs 1, 2 and 7 to 9 composed of steel sheets A, B, G, H and I, respectively, were obtained leading to flaking three times immediately after rolling in a temperature range of 1000 ° C or more, the average Sb Maximo / Sb ratio was 5 or less and particularly good fatigue strength ratios were obtained.
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TABLE 7
Steel sheet n ° Composition (% by mass) transformation point Ac3 (° C) Peeling condition in hot rolled (number of times) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.21 0.64 1.16 0.02 0.004 0.038 0.004 0.003 Cr: 0.24Ti: 0.012B: 0.0010 854 3 hot rolled steel sheet 2.3 in the range of the invention B 0.21 0.20 1.18 0.01 0.005 0.042 0.004 0.006 Ti: 0.0015 831 3 cold rolled steel sheet 1.2 in the range of the invention Ç 0.21 0.21 1.20 0.02 0.004 0.036 0.003 0.015 831 1 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention D 0.22 0.28 1.20 0.02 0.003 0.039 0.003 0.005 B: 0.0024 833 0 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention AND 0.22 0.11 1.37 0.01 0.005 0.041 0.003 <0.001 821 1 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention F 0.22 0.23 1.45 0.01 0.004 0.040 0.004 0.004 Cr: 0.22Ti: 0.025 828 2 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention G 0.23 0.20 1.42 0.02 0.003 0.042 0.005 0.006 Mo: 0.5 843 3 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention H 0.25 0.20 1.27 0.01 0.005 0.037 0.004 0.009 Ni: 0.02Nb: 0.02 821 3 cold rolled steel sheet 1.6 in the range of the invention I 0.28 0.35 0.85 0.01 0.004 0.052 0.004 0.007 829 3 hot rolled steel sheet 3.2 in the range of the invention
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TABLE 8
Hot pressed steel plate member n ° Steel sheet n ° hot press conditions Limitintensile strength (LRT) (MPa) toughness Area ratio of the martensite phase(%) Maximum Sb / Average Sb fatigue resistance ratio Grades heating rate (° C / s) heating temperature (° C) retention time (s) pressing start temperature (° C) cooling rate (° C / s) surface center of the plate thickness 1 THE 15 950 120 650 60 1477 439 452 100 4.1 0.6 Ex. Inv. 2 B 15 870 120 700 60 1481 436 451 100 3.4 0.61 Ex. Inv, 3 Ç 15 870 120 650 50 1477 434 452 100 5.9 0.56 Ex. Inv, 4 D 15 860 150 650 65 1571 471 481 100 15.9 0.58 Ex. Inv, 5 AND 15 860 150 650 65 1519 394 465 100 0.53 Ex. Comp. 6 F 15 860 150 650 65 1523 457 467 100 6.4 0.59 Ex. Inv, 7 G 15 890 120 650 60 1558 470 477 100 3.4 0.61 Ex. Inv, 8 H 15 840 180 650 55 1584 470 485 100 3 0.62 Ex. Inv, 9 I 15 900 120 750 60 1707 520 523 100 3.3 0.62 Ex. Inv,
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EXAMPLE 5 [0075] Members steel sheets hot - pressed paragraphs 1 to 22 having a hat shape leading were prepared by heating, retention, hot pressing, and cooling under the hot pressing conditions shown in Table 10 using- if the steel plates paragraphs a to P shown in Table 9.
[0076] The same tests as the tests in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of a surface and a central portion in the direction of the thickness of the steel sheet, and the area ratio from the martensite phase of each of the members hot-pressed steel plates.
[0077] Table 10 shows the results. The hot pressed component from steel plate No. 11 has a Sb content lower than the lower limit of the range of the present invention, and the decrease in the surface hardness of this hot pressed component from steel plate is more significant than that of the hot-pressed component from steel plate No. 4 which had substantially the same composition and was produced under substantially the same production conditions. Hot-pressed steel plate members other than the above are examples of the present invention. It is found that these hot-pressed steel sheet members each have a tensile strength limit (LRT) in the range of 980 to 2130 MPa, and the decrease in surface hardness is also small. In particular, the plate members steel ^Nos 1, 4, 5, 8, and 12 to 22, which were produced under the same conditions for hot pressing Preferred described above using steel plates for hot pressing of the invention having a C content of 0.14% or more and less than 0.21%, it is found that the desired tensile strength limit (LRT): 1180 MPa or more and less than 1470 MPa corresponding to the C content ranges : 0.14% or more and less than 0.21% is obtained as described above and the decrease in surface hardness is also small.
Petition 870170086905, of 11/10/2017, p. 51/71 [TABLE 9]
Steel sheet n ° Composition (% by mass) transformation point Ac3 (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.19 0.65 1.54 0.01 0.004 0.046 0.004 0.004 - 864 hot rolled steel sheet 2.3 in the range of the invention B 0.16 0.11 2.48 0.03 0.003 0.035 0.004 0.004 - 817 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention Ç 0.15 0.12 2.58 0.02 0.003 0.039 0.004 0.010 - 818 cold rolled sheet. (reduction: 50%) 1.5 in the range of the invention D 0.15 0.22 1.44 0.02 0.005 0.037 0.005 0.026 - 840 cold rolled steel sheet 1.2 in the range of the invention AND 0.12 0.30 1.49 0.02 0.006 0.036 0.003 0.004 - 850 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention F 0.22 0.19 1.28 0.01 0.007 0.042 0.004 0.005 - 827 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention G 0.15 0.11 1.67 0.01 0.008 0.048 0.005 <0.001 - 832 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention H 0.14 0.25 1.94 0.02 0.005 0.045 0.003 0.008 Ni: 1.3 Cu: 0.5 797 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention I 0.18 0.18 1.54 0.02 0.003 0.041 0.004 0.004 Cr: 0.6 Mo: 0.5 850 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention J 0.17 0.19 1.82 0.01 0.003 0.038 0.005 0.006 Ti: 0.05 Nb: 0.04 829 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention K 0.16 0.21 1.73 0.02 0.003 0.037 0.003 0.014 V: 0.06 W: 0.04 833 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 52/71 [TABLE 9] CONTINUED
Steel sheet n °
Si
Mn
0.17
0.18
1.24
0.14
0.11
1.58
0.15
0.18
1.47
0.20
0.21
1.78
0.16
0.20
1.35
Composition (% by mass)
0.01
0.02
0.01
0.01
0.01
Al
On other AC3 transformation point (° C)
Type of steel sheet
Thickness (mm)
Note
0.004
0.039
0.005
0.006
B: 0.0014
836 cold rolled sheet. (reduction: 50%)
1.6 in the range of the invention
0.005
0.044
0.005
0.010
Sç (REM): 0,005
835 cold rolled sheet. (reduction: 50%)
1.6 in the range of the invention
0.006
0.049
0.004
0.005
Ca: 0.0018
Mg: 0.0015
838 cold rolled sheet. (reduction: 50%)
1.6 in the range of the invention
0.007
0.008
0.041
0.051
0.004
0.009
825 cold rolled sheet. (reduction: 53%)
1.2 in the range of the invention
0.005
0.011
838 cold rolled sheet. (reduction: 44%)
1.8 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 53/71 [TABLE 10]
Hot-pressed component from steel plate no. Steel sheet n ° hot press conditions Limit oftensile strength (LRT)(MPa) toughness Reason forarea ofmar- phasestrained(%) Grades heating rate (° C / s) heating temperature (° C) retention time (s) start temperaturepressing(° C) cooling rate(° C / s) surface center ofplate thickness 1 THE 15 940 120 650 60 1442 428 448 100 Ex. Inv. 2 15 800 120 650 60 1132 327 354 80 Ex. Inv, 3 15 900 0 650 60 1151 329 353 80 Ex. Inv, 4 B 15 850 120 650 60 1249 365 385 100 Ex. Inv, 5 Ç 15 870 120 650 60 1267 388 396 100 Ex. Inv, 6 15 860 120 350 60 1144 345 355 75 Ex. Inv, 7 15 870 120 650 1 1131 345 354 85 Ex. Inv, 8 D 15 920 120 650 60 1206 363 371 100 Ex. Inv, 9 AND 15 900 120 650 60 1137 333 353 100 Ex. Inv, 10 F 15 900 120 650 60 1504 452 468 100 Ex. Inv, 11 G 15 900 120 650 60 1189 285 357 100 Ex. Comp. 12 H 15 850 120 650 60 1198 357 372 100 Ex. Inv.
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Petition 870170086905, of 11/10/2017, p. 54/71 [Table 10] continued
Hot-pressed component from steel plate no. Steel sheet n ° hot press conditions Limit oftensile strength (LRT)(MPa) toughness Reason forarea ofmar- phasestrained(%) Grades heating rate (° C / s) heating temperature (° C) retention time (s) start temperaturepressing(° C) cooling rate(° C / s) surface center ofplate thickness 13 I 15 910 120 650 60 1424 424 444 100 Ex. Inv. 14 J 15 900 120 650 60 1380 415 430 100 Ex. Inv. 15 K 15 900 120 650 60 1224 368 376 100 Ex. Inv. 16 L 15 900 120 650 60 1346 405 420 100 Ex. Inv. 17 M 15 900 120 650 60 1185 360 368 100 Ex. Inv. 18 N 15 850 120 650 60 1265 377 393 100 Ex. Inv. 19 O 15 880 540 650 60 1441 438 447 100 Ex. Inv. 20 15 890 120 650 15 1402 424 435 100 Ex. Inv. 21 2 880 120 650 60 1464 433 443 100 Ex. Inv. 22 P 15 890 120 650 60 1269 387 395 100 Ex. Inv.
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50/59
EXAMPLE 6 [0078] Members steel sheets hot - pressed paragraphs 1 to 8 having a hat shape leading were prepared by heating, retention, hot pressing, and cooling under the hot pressing conditions shown in Table 12 using- if the steel plates paragraphs a to H shown in Table 11. Here, in each of the steel plates, in addition to shedding prior to lamination, peeling running in the laminating step of the production of hot steel plate, flaking was repeatedly conducted immediately after lamination in a high temperature range of 1000 ° C or more, to a lamination reduction of 15% or more, and a water current collision pressure of 5 MPa or more. The number of times for this peeling is shown in Table 11. [0079] The same tests used in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of a surface and the central portion in the direction of thickness of the steel sheet, and the area ratio of the martensite phase of each of the members hot-pressed steel sheets. The maximum Sb / average Sb ratio and the fatigue strength ratio were also determined as in Example 4.
[0080] Table 12 shows the results, the steel plate members hot - pressed paragraphs 1 to 3 and 5 to 8 as described above, the tensile strength limit (TRL) desired: 1180 MPa or more and less than 1470 MPa corresponding to the C content range: 0.14% or more and less than 0m21% is obtained and the decrease in surface hardness is small. In the hot-pressed component from steel plate No. 4 having a low Sb content, which is outside the range of the present invention, a significant decrease in the surface hardness is observed.
[0081] The reason for the fatigue resistance of each member
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51/59 hot-pressed steel sheets is equal to or greater than that of normal material. In particular, steel sheets hot - pressed members paragraphs 1 to 3 and 5 to 7, having an Sb content in the range of 0.002% to 0.01%, have a fatigue strength ratio of 0.58% or more, indicating that these members have excellent fatigue properties. In the hot-pressed component from steel plate No. 8 composed of steel plate No. H which has a Sb content of 0.021%, and which was obtained by conducting, in addition to the usual flaking before rolling, a flaking once immediately after rolling in a high temperature range of 1000 ° C or more at a rolling reduction of 15% or more, a fatigue strength ratio was obtained being substantially the same as that of normal material. Moreover, the steel sheet materials hot - pressed No 1, 3 and 7 compounds of steel sheets in A, C and G, respectively, were obtained leading to flaking three times immediately after rolling in a range of high temperatures of 1000 ° C or greater at a rolling reduction of 15% or more, the maximum Sb / average Sb ratio was 5 or less and particularly good fatigue strength ratios were obtained.
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TABLE 11
Steel sheet n ° Composition (% by mass) transformation point Ac3 (° C) Peeling condition in hot rolled (number of times) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.14 0.64 1.74 0.02 0.004 0.038 0.004 0.008 860 3 hot rolled steel sheet 2.3 in the range of the invention B 0.15 0.20 0.96 0.01 0.005 0.042 0.004 0.003 Cr: 0.22Ti: 0.015 846 2 cold rolled steel sheet 1.2 in the range of the invention Ç 0.18 0.28 1.20 0.02 0.003 0.039 0.003 0.005 B: 0.0024 841 3 cold rolled sheet. (reduction: 50%) 1.5 in the range of the invention D 0.18 0.11 1.37 0.01 0.005 0.041 0.003 <0.001 829 3 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention AND 0.19 0.23 1.45 0.01 0.004 0.040 0.004 0.004 Cr: 0.22Ti: 0.025 832 2 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention F 0.20 0.20 1.27 0.01 0.005 0.037 0.004 0.009 Ni: 0.02 Nb: 0.02 831 1 cold rolled steel sheet 1.6 in the range of the invention G 0.20 0.35 0.85 0.01 0.004 0.052 0.004 0.007 Cr: 0.18B: 0.0015 845 3 hot rolled steel sheet 2.3 in the range of the invention H 0.20 0.13 1.34 0.01 0.004 0.034 0.003 0.021 827 1 cold rolled steel sheet 2 in the range of the invention
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Petition 870170086905, of 11/10/2017, p. 58/71 [TABLE 12]
Com-nentehot pressed from steel plate n ° Steel sheet n ° hot pressing conditions Tensile strength limit (LRT) (MPa) toughness Area ratio of the martensite phase (%) Maximum Sb / Average Sb fatigue resistance ratio Grades heating rate (° C / s) heating temperature (° C) retention time (s) pressing start temperature(° C) cooling rate (° C / s) super-surface center of the plate thickness 1 THE 15 910 60 650 40 1188 349 362 100 3.2 0.62 Ex. Inv. 2 B 15 870 120 800 120 1229 365 375 100 7.1 0.61 Ex. Inv, 3 Ç 15 870 120 650 50 1353 406 414 100 3.5 0.62 Ex. Inv, 4 D 15 880 90 650 65 1380 345 417 100 - 0.53 Ex.Comp. 5 AND 15 880 90 650 65 1394 421 427 100 6.3 0.61 Ex. Inv, 6 F 15 860 150 650 65 1435 432 439 100 7.3 0.60 Ex. Inv, 7 G 15 890 120 650 60 1413 419 433 100 3.2 0.64 Ex. Inv, 8 H 15 840 180 650 55 1441 437 439 100 5.2 0.54 Ex. Inv,
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54/59
EXAMPLE 7 [0082] Members steel sheets hot - pressed paragraphs 1 to 22 having a hat shape leading were prepared by heating, retention, hot pressing, and cooling under the hot pressing conditions shown in Table 14 using- if the steel plates paragraphs a to P shown in Table 13.
[0083] The same tests as those in Example 1 were conducted to measure the tensile strength limit (LRT), the Vickers hardness of the surface and the central portion in the direction of the thickness of the steel sheet, and the area ratio of a martensite phase of each member hot-pressed steel plates.
[0084] Table 14 shows the results. In the hot pressed part from sheet steel paragraphs 2, 3, 6, 7, and 9, the tensile strength limit (TRL) does not reach the target of 980 MPa. The hot pressed component from steel plate No. 11 has a Sb content lower than the lower limit of the range of the present invention and the decrease in the surface hardness of this steel plate member is more significant than that of the pressed component at hot from steel plate No. 4 which had substantially the same composition and was produced under substantially the same production conditions. Hot-pressed steel plate members other than the above are examples of the present invention. It is found that these hot-pressed steel sheet members each have a tensile strength limit (LRT) in the range of 980 to 2130 MPa, and the decrease in surface hardness is also small. In particular, the steel sheet members hot - pressed No 1, 4, 5, 8 and 12 to 22, which were produced under the preferred conditions for the hot pressing as described above using steel plates for hot pressing of this invention having a C content of 0.09% or more and less than 0.14%, it is discovered that the limit of tensile strength (LRT) desires Petition 870170086905, of 10/11/2017, p. 60/71
55/59 do: 980 MPa or more and less than 1180 MPa corresponding to the C content range: 0.09% or more and less than 0.14% is obtained as described above and the decrease in surface hardness is also small .
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TABLE 13
Steel sheet n ° Composition (% by mass) transformation point Ac3 (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others THE 0.13 0.97 1.62 0.02 0.005 0.043 0.005 0.003 - 881 hot rolled steel sheet 2.3 in the range of the invention B 0.10 0.10 2.53 0.01 0.004 0.045 0.004 0.005 - 828 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention Ç 0.10 0.14 2.51 0.01 0.003 0.041 0.005 0.011 - 830 cold rolled sheet. (reduction: 50%) 1.5 in the range of the invention D 0.09 0.17 1.32 0.02 0.006 0.038 0.004 0.025 - 852 cold rolled steel sheet 1.2 in the range of the invention AND 0.07 0.23 1.58 0.01 0.007 0.033 0.004 0.005 - 855 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention F 0.15 0.22 1.33 0.01 0.006 0.040 0.003 0.004 - 842 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention G 0.09 0.13 1.42 0.02 0.006 0.046 0.004 <0.001 - 848 cold rolled sheet. (reduction: 50%) 1.6 out of the range of the invention H 0.11 0.22 1.71 0.01 0.006 0.039 0.003 0.005 Ni: 1.4 Cu: 0.3 808 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention I 0.12 0.21 1.45 0.01 0.005 0.036 0.005 0.005 Cr: 0.4 Mo: 0.4 862 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention J 0.11 0.21 1.42 0.02 0.003 0.037 0.004 0.006 Ti: 0.05 Nb: 0.03 845 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention K 0.10 0.23 1.55 0.02 0.004 0.028 0.004 0.013 V: 0.07 W: 0.03 849 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention
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TABLE 13 (CONTINUED)
Steel sheet n ° Composition (% by mass) transformation point Ac3 (° C) Type of steel sheet Thickness(mm) Note Ç Si Mn P s Al N Sb others L 0.10 0.15 1.31 0.01 0.01 0.039 0.004 0.005 B: 0.0013 849 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention M 0.11 0.13 1.65 0.01 0.004 0.040 0.005 0.010 Sc (REM): 0.008 840 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention N 0.12 0.16 1.39 0.02 0.007 0.051 0.003 0.004 Ca: 0.0020Mg: 0.0011 844 cold rolled sheet. (reduction: 50%) 1.6 in the range of the invention O 0.10 0.20 1.47 0.01 0.006 0.042 0.005 0.008 - 849 cold rolled sheet. (reduction: 53%) 1.2 in the range of the invention P 0.10 0.19 1.43 0.02 0.005 0.044 0.004 0.012 - 849 cold rolled sheet. (reduction: 44%) 1.8 in the range of the invention
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TABLE 14
Hot-pressed component from steel plate no. Steel sheet n ° hot pressing conditions TENSION RESISTANCE LIMIT (LRT)(MPa) toughness Reason forarea ofmartensite phase (%) Grades heating rate (° C / s) heating temperature (° C) retention time(s) start temperaturepressing(° C) rate ofcooling (° C / s) surface center ofthicknessof the plate 1 15 950 120 650 60 1153 340 358 100 Ex. Inv. 2 THE 15 800 120 650 60 932 264 289 75 Ex.Comp, 3 15 900 0 650 60 948 273 294 85 Ex.Comp, 4 B 15 850 120 650 60 1017 306 318 100 Ex. Inv, 5 15 860 120 650 60 1030 316 322 100 Ex. Inv, 6 Ç 15 860 120 350 60 958 292 300 70 Ex.Comp, 7 15 860 120 650 1 966 292 299 85 Ex.Comp, 8 D 15 860 120 650 60 984 298 304 100 Ex. Inv, 9 AND 15 900 120 650 60 913 270 282 100 Ex.Comp, 10 F 15 900 120 650 60 1218 364 379 100 Ex. Inv,
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Hot-pressed component from steel plate no. Steel sheet n ° hot pressing conditions TENSION RESISTANCE LIMIT (LRT)(MPa) toughness Reason forarea ofmartensite phase (%) Grades heating rate (° C / s) heating temperature (° C) retention time(s) start temperaturepressing(° C) rate ofcooling (° C / s) surface center ofthicknessof the plate 11 G 15 900 120 650 60 986 247 301 100 Ex.Comp. 12 H 15 850 120 650 60 1070 322 334 100 Ex. Inv. 13 I 15 880 120 650 60 1111 330 342 100 Ex. Inv. 14 J 15 880 120 650 60 1055 315 325 100 Ex. Inv. 15 K 15 880 120 650 60 1031 312 318 100 Ex. Inv. 16 L 15 880 120 650 60 1016 300 312 100 Ex. Inv. 17 M 15 880 120 650 60 1084 327 333 100 Ex. Inv. 18 N 15 880 120 650 60 1122 329 344 100 Ex. Inv. 19 15 900 540 650 60 1015 310 317 100 Ex. Inv. 20 O 15 880 120 650 15 1003 309 314 100 Ex. Inv. 21 2 860 120 650 60 1026 312 318 100 Ex. Inv. 22 P 15 900 120 650 60 1012 307 313 100 Ex. Inv.
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1/2

权利要求:
Claims (10)
[1]
1. Hot pressed component from steel plate, characterized by having a composition containing, in% by weight, C: 0.09% to 0.38%, Si: 0.05% to 2.0%, Mn : 0.5% to 3.0%, P: 0.05% or less, S: 0.05% or less, Al: 0.005% to 0.1%, N: 0.01% or less, Sb: 0.002% to 0.03%, and optionally containing, in mass%, at least one element selected from Ni: 0.01% to 5.0%, Cu: 0.01% to 5.0%, Cr: 0 , 01% to 5.0%, Mo: 0.01% to 3.0%, Ti: 0.005% to 3.0%, Nb: 0.005% to 3.0%, V: 0.005% to 3.0% , W: 0.005% to 3.0%, B: 0.0005% to 0.05%, REM: 0.0005% to 0.01%, Ca: 0.0005% to 0.01%, and Mg: 0.0005% to 0.01%, and the balance being Fe and the inevitable impurities, where the limit of tensile strength (LRT) is 980 to 2130 MPa, where the ratio of Sb-maximum / Sb-average is 5 or less in the case where the average intensity of Sb in the measurement area is defined as Sb-average and the maximum intensity of Sb in the measurement area is defined as Sb-maximum.
[2]
2/2
0.21% by mass.
2. Hot-pressed component from steel sheet according to claim 1, characterized by the fact that carbon is contained in an amount of 0.34% to 0.38% by weight.
[3]
3. Hot-pressed component from steel sheet according to claim 1, characterized by the fact that carbon is contained in an amount of 0.29% or more and less than 0.34% by weight.
[4]
4. Hot-pressed component from steel sheet according to claim 1, characterized by the fact that carbon is contained in an amount of 0.21% or more and less than 0.29% by weight.
[5]
5. Hot-pressed component from steel sheet according to claim 1, characterized by the fact that the carbon is contained in an amount of 0.14% or more and less than
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[6]
6. Hot-pressed component from steel sheet according to claim 1, characterized by the fact that the carbon is contained in an amount of 0.09% or more and less than 0.14% by weight.
[7]
7. Hot-pressed component from steel sheet according to claim 4 or 5, characterized by the fact that the antimony is contained in an amount of 0.002% to 0.01% by weight.
[8]
Steel plate for hot pressing, characterized in that it has the composition as defined in any one of claims 2 to 7.
[9]
9. Method for the production of a hot-pressed component from steel plate, characterized in that it comprises heating the steel plate for hot pressing as defined in claim 8 at a heating rate of 1 ° C / s or more, maintaining the steel plate in a temperature range from transformation point Ac ₃ to (transformation point Ac ₃ + 150 ° C) for 1 to 600 seconds, and then start hot pressing in a temperature range of 550 ° C or more, and conduct cooling at an average cooling rate of 3 ° C / s or more up to 200 ° C.
[10]
10. Method for producing a hot-pressed component from steel sheet according to claim 9, characterized by the fact that, after hot pressing, the member is removed from the metal mold and cooled with a liquid or a gas.
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类似技术:

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BR112020003351A2|2020-08-18|steel with a high content of mn and production method for the same

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JPWO2020162560A1|2021-02-18|Hot-dip galvanized steel sheet and its manufacturing method

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BR112021001434A2|2021-04-27|steel with a high manganese content and production method

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同族专利:

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公开号 | 公开日

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EP2468911A1|2012-06-27|

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JP2011063877A|2011-03-31|

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CN102482750B|2014-02-19|

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EP2468911A4|2014-07-09|

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EP2468911B1|2015-11-11|

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US8628630B2|2014-01-14|

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KR101291010B1|2013-07-30|

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AU2010285619A1|2012-02-16|

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CA2770585A1|2011-02-24|

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CA2770585C|2014-04-08|

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CN102482750A|2012-05-30|

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AU2010285619B2|2014-03-06|

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JP4766186B2|2011-09-07|

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BR112012003763A2|2016-04-12|

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MX2012002200A|2012-03-16|

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US20120216925A1|2012-08-30|

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WO2011021724A1|2011-02-24|

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KR20120035940A|2012-04-16|

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法律状态:
2017-08-15| B07A| Application suspended after technical examination (opinion) [chapter 7.1 patent gazette]|

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2018-02-14| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2018-04-17| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|

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2021-06-22| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 11A ANUIDADE. |

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2021-10-13| B24J| Lapse because of non-payment of annual fees (definitively: art 78 iv lpi, resolution 113/2013 art. 12)|Free format text: EM VIRTUDE DA EXTINCAO PUBLICADA NA RPI 2633 DE 22-06-2021 E CONSIDERANDO AUSENCIA DE MANIFESTACAO DENTRO DOS PRAZOS LEGAIS, INFORMO QUE CABE SER MANTIDA A EXTINCAO DA PATENTE E SEUS CERTIFICADOS, CONFORME O DISPOSTO NO ARTIGO 12, DA RESOLUCAO 113/2013. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2009-191573|2009-08-21|

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JP2009191573|2009-08-21|

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JP2010-175850|2010-08-05|

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JP2010175850A|JP4766186B2|2009-08-21|2010-08-05|Hot pressed member, steel plate for hot pressed member, method for manufacturing hot pressed member|

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PCT/JP2010/064432|WO2011021724A1|2009-08-21|2010-08-19|Hot pressed member, steel sheet for hot pressed member, and method for producing hot pressed member|

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