cold rolled steel sheet and method of production thereof

专利摘要:
Cold rolled steel sheet and method of production thereof. The present invention relates to a cold rolled steel sheet which includes,% by weight, c: 0.02% to 0.4%, bs: 0.001% to 2.5%, mn: 0.001% to 4. , 0%, and al: 0.001% to 2.0%. the sum of the self content and the al content is 1.0% to 4.5%. an average pole density of an orientation group of {100} <011> to {223} <110> is 1.0 to 6.5, and a pole density of a crystal orientation {332} <113> is 1.0 to 5.0. A microstructure includes, for 1 or 1% area ratio, 5% to 80% ferrite, 5% to 80% bainite, and 2% to 30% retained austenite. In microstructure, by a% area ratio, martensite is limited to 20% or less, pearlite is limited to 10% or less, and tempered martensite is limited to 60% or less.
公开号:BR112013025015B1
申请号:R112013025015-1
申请日:2012-03-28
公开日:2018-11-06
发明作者:Takayuki Nozaki；Manabu Takahashi；Nobuhiro Fujita；Hiroshi Yoshida；Shinichiro Watanabe；Takeshi Yamamoto
申请人:Nippon Steel & Sumitomo Metal Corporation；
IPC主号:

专利说明:

(54) Title: COLD LAMINATED STEEL PLATE AND SAME PRODUCTION METHOD (51) IntCI .: C22C 38/06; C22C 38/58; C21D 8/02; C21D 9/46.
(30) Unionist Priority: 03/28/2011 JP 2011/070725.
(73) Holder (s): N1PPON STEEL & SUMITOMO METAL CORPORATION.
(72) Inventor (s): TAKAYUKI NOZAKI; MANABU TAKAHASHI; NOBUHIRO FUJITA; HIROSHI YOSHIDA; SHINICHIRO WATANABE; TAKESHI YAMAMOTO.
(86) PCT Application: PCT JP2012058199 of 28/03/2012 (87) PCT Publication: WO 2012/133563 of 10/04/2012 (85) Date of the Beginning of the National Phase: 27/09/2013 (57) Summary: COLD LAMINATED STEEL SHEET AND THE SAME PRODUCTION METHOD. The present invention relates to a cold rolled steel sheet that includes,% by mass, C: 0.02% to 0.4%, Si: 0.001% to 2.5%, Mn: 0.001% to 4 , 0%, and Al: 0.001% to 2.0%. The sum of the Si content and the Al content is 1.0% to 4.5%. An average pole density of an orientation group of (100) 011> to {223} 110> is 1.0 to 6.5, and a pole density of a {332} 113> crystal orientation is 1.0 to 5.0. A microstructure includes, by 10% an area proportion, 5% to 80% ferrite, 5% to 80% bainite, and 2% to 30% retained austenite. In the microstructure, for a% of area ratio, martensite is limited to 20% or less, pearlite is limited to 10% or less, and tempered martensite is limited to 60% or less.
1/71
Descriptive Report of the Invention Patent for COLD LAMINATED STEEL SHEET AND THE SAME PRODUCTION METHOD.
Technical field [001] The present invention relates to a high-strength cold-rolled steel sheet that is excellent in ductility and orifice expandability, and a method of producing it. In particular, the present invention relates to a steel sheet using a TRIP (Transformation Induced Plasticity) phenomenon.
[002] The priority is claimed in Japanese Patent Application No. 2011-70725, filed on March 28, 2011, the content of which is incorporated here by reference.
Background of the Technique [003] The high increase in the mechanical strength of a steel sheet that is a raw material is in progress in order to achieve compatibility between a weight saving of a body, components and the like of a vehicle and safety. Generally, when the strength of the steel plate increases, the ductility decreases, and thus the plasticity is impaired. Therefore, a balance of strength and ductility is necessary in order to use the high strength steel plate for vehicle members. For this requirement, until now, a so-called TRIP steel sheet has been suggested, in which the plasticity induced by the retained austenite transformation is used (for example, it refers to Patent Document 1 and Patent Document 2).
[004] However, the TRIP sheet has characteristics where the strength and ductility are excellent, but generally, the local deformability such as orifice expansion is low. In addition, in order to progress the weight savings of the vehicle body, it is necessary to increase the level of resistance of use of the high-strength steel plate in addition to the related technique. So, for example,
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2/71 In order to use the high strength steel plate for components in the less part of the body, it is necessary to improve the local deformability as well as the expandability of the hole.
Citation List
Patent Literature [005] [Patent Document 1] Unexamined Japanese Patent Application, First Publication No. S61-217529 [006] [Patent Document 2] Unexamined Japanese Patent Application, First Publication No. H5-59429
Summary of the Invention
Problem to be solved by the invention [007] Therefore, the present invention is an object to provide a cold rolled high strength steel plate, in which the ductility and expandability of the orifice are also improved in TRIP steel, and a method of production.
Means for Solving Problems [008] The present inventors have found that in the TRIP plate, a cold rolled steel plate, in which the pole density of a predetermined crystal orientation is controlled, has excellent strength, ductility, orifice expansion, and balance between them. In addition, the present inventors have been successful in producing a steel sheet that is excellent in strength, ductility, and orifice expandability by optimizing the chemical components and production conditions of TRIP steel in order to control a microstructure of the steel sheet. The essence of the present invention is as follows.
[009] (1) In accordance with an aspect of the present invention, a cold-rolled steel sheet is provided which has a chemical composition including, by weight, from C: 0.02% to 0.4%, Si: 0.001% to 2.5%, Mn: 0.001% to 4.0%, Al: 0.001% to 2.0%, and P: limited to 0.15%
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3/71 or less, S: limited to 0.03% or less, N: limited to 0.01% or less, O: limited to 0.01% or less, and the balance consisting of Fe and unavoidable impurities. In the chemical composition of the steel sheet, a sum of the Si content and the Al content is 1.0% to 4.5%. In a central portion of the plate thickness within a range of 5/8 to 3/8 of a plate thickness, an average pole density of an orientation group from {100} <011> to {223} <110> , which is a pole density expressed by an arithmetic mean of pole densities of the respective crystal orientations {100} <011>, {116} <110>, {114} <110>, {112} <110>, and {223} <110>, is 1.0 to 6.5, and a pole density of a crystal orientation {332} <113> is 1.0 to 5.0. A plurality of grains are in a microstructure of the steel sheet. The microstructure of steel includes, by an area ratio, 5% to 80% of ferrite, 5% to 80% of bainite, and 2% to 30% of retained austenite, and in the microstructure, martensite is limited to 20% or less , pearlite is limited to 10% or less, and tempered martensite is limited to 60% or less. rC which is a Lankford value in a direction orthogonal to a rolling direction is 0.70 to 1.10, and r30 which is a Lankford value in a direction forming an angle of 30 ° with the rolling direction is 0, 70 to 1.10.
[0010] (2) In the cold-rolled steel plate according to (1), the chemical composition of the steel plate may also include,% by weight, one or more selected from the group consisting of Ti: 0.001% to 0, 2%, Nb: 0.005% to 0.2%, B: 0.0001% to 0.005%, Mg: 0.0001% to 0.01%, REM: 0.0001% to 0.1%, Ca: 0 , 0001% to 0.01%, Mo: 0.001% to 1.0%, Cr: 0.001% to 2.0%, V: 0.001% to 1.0%, W: 0.001% to 1.0%, Ni : 0.001% to 2.0%, Cu: 0.001% to 2.0%, Co: 0.0001% to 1.0%, Sn: 0.0001% to 0.2%, Zr: 0.0001% to 0.2%, and As: 0.0001% to 0.5%.
[0011] (3) In cold rolled steel sheet according to (1) or (2), an average volume diameter in the grains can be from 2 gm to 15
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4/71 μΓΠ.
[0012] (4) In cold rolled steel sheet according to any one of (1) to (3), the average pole density of the orientation group from {100} <011> to {223} <110> it can be 1.0 to 5.0, and the pole density of the {332} <113> crystal orientation can be 1.0 to 4.0.
[0013] (5) In cold rolled steel sheet according to any one of (1) to (4), among the plurality of grains, a proportion of the grains area that exceeds 35 μίτι can be limited to 10% or any less.
[0014] (6) In cold rolled steel plate according to any one of (1) to (5), among the plurality of grains, a proportion of grains, in which a value obtained by dividing a length of a grain in the lamination direction for a length of a grain in the direction of sheet thickness is 3.0 or less, it can be 50% to 100%.
[0015] (7) In cold rolled steel sheet according to any of (1) to (6), a Vickers hardness of bainite can be 180 HV or more, and an average concentration of C in the austenite residual can be 0.9% or more.
[0016] (8) In cold rolled steel sheet according to any of (1) to (7), rL which is a Lankford value in the rolling direction can be from 0.70 to 1.10, and r60 which is a Lankford value in the direction forming an angle of 60 ° with the rolling direction can be from 0.70 to 1.10.
[0017] (9) In cold-rolled steel sheet according to any of (1) to (8), a hot-dip galvanized layer or a galvannealed annealed layer can be provided on a surface of the steel sheet.
[0018] (10) According to another aspect of the present invention, a method of producing a cold rolled steel sheet is provided. The method includes: a first hot rolling process to perform a hot rolling with respect to steel, in order to adjust
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5/71 an average austenite grain size of steel to 200 μίτι or less, under a condition so that a pass is carried out with a rolling reduction ratio of 40% or more at least once, in a temperature range from 1,000 ° C to 1,200 ° C, and the chemical composition of steel includes,% by mass, C: 0.02% to 0.4%, Si: 0.001% to 2.5%, Mn: 0.001% to 4, 0%, Al: 0.001% to 2.0%, and P: limited to 0.15% or less, S: limited to 0.03% or less, N: limited to 0.01% or less, O: 0 , 01% or less, and the balance consisting of Fe and unavoidable impurities, and in which a sum of the Si content and the Al content can be 1.0% to 4.5%; a second hot rolling process of carrying out a hot rolling with respect to steel, under the condition that a large rolling reduction passes with a rolling reduction ratio of 30% or more over a temperature range of T1 + 30 ° C to T1 + 200 ° C when the temperature calculated by Expression 1 below is set to T1 ° C, a cumulative lamination reduction ratio in the temperature range from T1 + 30 ° C to T1 + 200 ° C is 50% or more, a cumulative lamination reduction ratio over a temperature range, which is greater than or equal to Ar3 ° C and less than T1 + 30 ° C, is limited to 30% or less when Ar3 ° C is calculated Expression 4 below, and a lamination termination temperature is greater than or equal to that of Ar3 ° C, which is calculated by Expression 4 below; a first cooling process to perform a cooling with respect to the steel, in such a way that a waiting time t second, which is adjusted as a time from the conclusion of a final passage between the great reduction of rolling becomes a beginning cooling, meets Expression 2 below; a winding process to perform winding with respect to steel in a temperature range of 650 ° C or less; a pickling process with respect to steel; a cold rolling process to perform a
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6/71 cold rolling with respect to the plate in a rolling reduction ratio of 30% to 90%; a two-stage heating process to carry out two-stage heating with respect to steel, where an average heating rate HR1 in a temperature range from ambient temperature to 650 ° C is 0.3 ° C / s or more, and an average heating rate HR2 over a temperature range from greater than 650 ° C to Aci ° C, when Aci ° C is calculated by Expression 5 below, is 0.5 x HR1 or less, unit is ° C / s; a retention process to perform a retention with respect to steel within a temperature range of Aci ° C to 900 ° C for 1 second to 300 seconds; a cooling process to perform cooling with respect to steel up to a temperature range of 580 ° C to 780 ° C, at an average cooling rate of 1 ° C / s to 20 ° C / s; a cooling process to perform a cooling with respect to steel to a temperature Toa, which is within a temperature range of 350 ° C to 500 ° C, and an average cooling rate of 5 ° C / s to 200 ° C / s; and a retention process to carry out a retention with respect to the steel in order to obtain a steel plate, the steel is retained within the temperature range of 350 ° C to 500 ° C for a time of 11 seconds or more, which is calculated by Expression 6 below, at 1,000 seconds or less, or the steel sheet is further cooled to a temperature of 350 ° C or less, when the steel is reheated to a temperature range of 350 ° C to 500 ° C, and the plate is retained within the temperature range of 350 ° C to 500 ° C for the time of 10 seconds or more, which is calculated by Expression 6 below, at 1,000 seconds or less.
T1 = 850 + 10 x ([C] + [N]) x [Mn] ... (Expression 1) [0019] here, [C], [N], and [Mn] represent mass percentages of the C, N content, and Mn content in steel, respectively, t <2.5 x t1 ... (Expression 2) [0020] here, t1 is expressed by Expression 3 below,
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7/71 t1 = 0.001 x ((Tf-T1) x P1 / 100) ² - 0.109 x ((Tf-T1) x P1 / 100) + 3.1 ... (Expression 3) [0021] here, Tf represents a temperature in Celsius of the steel at the time of completion of the final pass, and P1 represents a percentage of the rolling reduction ratio during the final pass,
Ar ₃ = 879.4 - 516.1 x [c] - 65.7 x [Mn] + 38.0 x [Si] + 274.7 x [P] ... (Expression 4)
Aci = 723 - 10.7 x [Mn] - 16.9 x [Ni] + 29.1 x [Si] + 16.9 x [Cr] + 290 x [As] + 6.38 x [W]. .. (Expression 5) [Mathematical Expression 1]
OA ... (Expression 6) [0022] (11) In the production method of a cold rolled steel sheet according to (10), the production method may have, in which the chemical composition of the steel may also include ,% by mass, one or more selected from the group consisting of Ti: 0.001% to 0.2%, Nb: 0.005% to 0.2%, B: 0.0001% to 0.005%, Mg: 0.0001% to 0.01%, REM: 0.0001% to 0.1%, Ca: 0.0001% to 0.01%, Mo: 0.001% to 1.0%, Cr: 0.001% to 2.0%, V : 0.001% to 1.0%, W: 0.001% to 1.0%, Ni: 0.001% to 2.0%, Cu: 0.001% to 2.0%, Co: 0.0001% to 1.0% , Sn: 0.0001% to 0.2%, Zr: 0.0001% to 0.2%, and As: 0.0001% to 0.5%, and a temperature calculated by Expression 7 below in place of calculated temperature Expression 1 can be set as T1 ° C.
T1 = 850 + 10 x ([C] + [N]) x [Mn] + 350 x [Nb] + 250 x [Ti] + 40 x [B] + 10 x [Cr] + 100 x [Mo] + 100 χ [V] ... (Expression 7) [0023] here, [C], [N], [Mn], [Nb], [Ti], [B], [Cr], [Mo], and [V] represent mass percentages of C, N, Mn, Nb, Ti, B, Cr, Mo, and V in steel, respectively, [0024] (12) In the method of producing a sheet steel sheet
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8/71 of the cold according to (10) or (11), the waiting time t second can satisfy Expression 8 below using t1.
<t <t1 ... (Expression 8) [0025] (13) In the method of producing a cold rolled steel sheet according to (10) or (11), the waiting time t second can satisfy the Expression 9 to follow using t1.
t1 <t <2.5 x t1 ... (Expression 9) [0026] (14) In the method of producing a cold rolled steel sheet according to any of (10) to (13), in the first cooling, a variation in the cooling temperature which is a difference between a temperature of the steel at the time of the start of cooling and a temperature of the steel at the time of the end of cooling can be from 40 ° C to 140 ° C, and the temperature of the plate at the end of cooling it can be T1 + 100 ° C or less.
[0027] (15) In the method of producing a cold rolled steel sheet according to any one of (10) to (14), the first hot rolling may include a passage that has a rolling reduction ratio of 40% or more at least one or more times, and an average austenite grain size of steel can be 100 μίτι or less.
[0028] (16) In the method of producing a cold-rolled steel sheet according to any of (10) to (15), the second cooling can be started within 10 seconds after passing through a rolling support end and after the end of the first cooling.
[0029] (17) In the method of producing a cold rolled steel sheet according to any of (10) to (16), in the second hot rolling, an increase in the temperature of the steel between the respective passages in the strip temperature range from T1 + 30 ° C to T1 + 200 ° C can be adjusted to 18 ° C or less.
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9/71 [0030] (18) In the method of producing a cold rolled steel sheet according to any of (10) to (17), the first cooling can be carried out between the rolling supports.
[0031] (19) In the method of producing a cold rolled steel sheet according to any one of (10) to (18), a hot dip galvanized layer or an annealed layer after galvanizing can be formed in a steel sheet surface. Advantage of the Invention [0032] In accordance with the aspects of the present invention, it is possible to provide a high strength steel sheet which is excellent in ductility and expandability of the orifice, and a production method. When steel sheet is used, in particular, vehicle weight savings and vehicle collision safety can be compatible with each other, and thus an industrial contribution is very significant. Brief Description of the Drawings [0033] Figure 1 is a diagram illustrating a relationship between an average density of pole D1 of an orientation group from {100} <011> to {223} <110> and TS x resistance limit orifice expansion ratio λ.
[0034] Figure 2 is a diagram illustrating a relationship between an average density of pole D1 of an orientation group from {100} <011> to {223} <110> and TS resistance limit x EL elongation. [0035] Figure 3 is a diagram illustrating a relationship between a pole density D2 of an orientation {332} <113> and resistance limit TS x orifice expansion ratio λ.
[0036] Figure 4 is a diagram illustrating a relationship between a pole density D2 of an orientation {332} <113> and resistance limit TS x EL elongation.
[0037] Figure 5 is a diagram illustrating a relationship between a number of rolling times of 40% or more in rolling mills.
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10/71 well and an average austenite grain size after draft lamination.
[0038] Figure 6 is a diagram illustrating a relationship between TS resistance limit and orifice expansion λ in examples and comparative examples.
[0039] Figure 7 is a diagram illustrating a relationship between strength limit TS and EL elongation in examples and comparative examples.
[0040] Figure 8 is a flow chart illustrating the outline (the first half) of a method of producing a cold rolled steel sheet related to a modality of the present invention.
[0041] Figure 9 is a flow chart illustrating the outline (the last half) of a method of producing a cold rolled steel sheet related to a modality of the present invention.
Description of Modalities [0042] In TRIP steel sheet which is one of the technologies to increase ductility, during an annealing process, as long as C in austenite is concentrated, and thus an amount of austenite retained or the C content in austenite retained increase. In this way, the resistance limit is improved.
[0043] The present inventors found that in the steel plate TRIP, optimizing the steel components or a microstructure during production, by starting a cooling that is initiated from a temperature range of a region of two phases of ferrite and austenite or a single-phase region of austenite, controlling a cooling (two-stage cooling) in a predetermined temperature range, and retaining the steel sheet in that temperature range, a steel sheet in which the balance between resistance, ductility, and Orifice expandability is excellent can be obtained.
[0044] From now on, a cold rolled steel plate related
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11/71 nothing to an embodiment of the present invention will be described in detail.
[0045] First, a pole density of a crystal orientation of a cold rolled steel sheet will be described.
[0046] Pole Density (D1 and D2) of Crystal Orientation:
[0047] In the cold-rolled steel plate related to the modality, such as pole densities of two types of crystal orientations, with respect to a thickening cross-section of the plate, which is parallel to a rolling direction, in a central portion of the thickening of the plate within a range of 5/8 to 3/8 of thickening of the plate (that is, a range distant from a surface of the steel plate by a distance of 5/8 to 3/8 thickness of the plate in a direction of thickening of the daughter (depth direction) of the steel plate), an average density of pole D1 of an orientation group from {100} <011> to {223} <110> (hereinafter, can be abbreviated as an average pole density), and a D2 pole density of a {332} <113> crystal orientation are controlled.
[0048] In the modality, the average pole density is a characteristic (a degree of orientation integration, a degree of texture development) of a particularly important texture (the crystal orientation of a grain in a microstructure). In addition, the average pole density is a pole density expressed by an arithmetic mean of pole densities of the respective crystal orientation {100} <011>, {116} <110>, {114} <110>, {112 } <110>, and {223} <110>.
[0049] In figures 1 and 2, with respect to a cross section in a central portion of plate thickness within a range of 5/8 to 3/8 of plate thickness, X-ray diffraction is performed to obtain proportion of intensity of X-ray diffraction intensities of the respective orientations for a random sample, and the
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12/71 mean pole density of an orientation group from {100} <011> to {223} <110> can be obtained from the respective intensity proportions.
[0050] As shown in figures 1 and 2, when the average pole density of the orientation group from {100} <011> to {223} <110> is 6.5 or less, a steel plate can satisfy properties (TS χ λ and TS x EL indices to be described later) that have recently become required for processing body components. That is, how the properties, TS strength limit, orifice expansion ratio λ, and EL elongation can satisfy TS χ λ> 30,000 (see figure 1), and TS x EL> 14,000 (see FIGURE 2). In a case of further increase in the TS χ λ and TS χ EL indices, it is preferable that the average pole density is 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less.
[0051] In addition, when the average pole density exceeds 6.5, anisotropy in the mechanical properties of a steel plate increases significantly. As a result, the orifice expandability in one specific direction is improved, but the orifice expandability in other directions, other than the specific direction, deteriorates significantly. Thus, in this case, with regard to the properties that are necessary for processing the body components, the steel sheet does not satisfy TS χ λ> 30,000 and TS x EL> 14,000.
[0052] On the other hand, when the average pole density is less than 1.0, there is a concern that will deteriorate the orifice expansiveness. In this way, it is preferable that the average pole density is 1.0 or more.
[0053] Furthermore, for the same reason, the pole density of the crystal orientation {332} <113> in the central portion of the plate thickness within a range of 5/8 to 3/8 of the plate thickness is es
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13/71 set to 5.0 or less. Similarly to figures 1 and 2, figures 3 and 4 show a relationship between the pole density of the crystal orientation {332} <113> which is obtained by X-ray diffraction and the respective indices (TS χ λ and TS x EL ). As shown in figures 3 and 4, the pole density can be set to 5.0 or less in order to sufficiently hold the respective indices. That is, when the crystal orientation pole density {332} <113> is 5.0 or less, with respect to the properties that have recently become required for processing body components, the steel sheet can satisfy TS χ λ > 30,000 and TS x EL> 14,000. In case of further increasing the TS χ λ and TS x EL indices, it is preferable that the pole density is 4.0 or less, and more preferably 3.0 or less. In addition, when the pole density of the {332} <113> crystal orientation exceeds 5.0, anisotropy in the mechanical properties of a steel plate increases significantly. As a result, the expansiveness of the orifice in a specific direction is improved, but the expansiveness of the orifice in directions other than the specific direction deteriorates significantly. Thus, in this case, with regard to the properties that are necessary for processing the body components, the steel sheet does not satisfy TS χ λ> 30.000 and TS x EL> 14.000.
[0054] On the other hand, when the pole density of the {332} <113> crystal orientation is less than 1.0, there is a concern that it will deteriorate the orifice expansiveness. Thus, it is preferable that the pole density of the {332} <113> crystal orientation is 1.0 or more.
[0055] The reason why the pole density of the crystal orientation described above is important for the shape retention properties during the elongation and expansion process of the orifice is not necessarily clear, but it is assumed that the reason has a re
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14/71 with the sliding movement of a crystal during a process of expanding the orifice.
[0056] The pole density has the same meaning as a proportion of the random X-ray intensity. The proportion of the random X-ray intensity is a numerical value obtained by dividing the diffraction intensity of a sample material by the diffraction intensity of a sample. standard sample not having integration in a specific orientation. The diffraction intensity (X-ray or electron) of the standard sample, and the diffraction intensity of the sample material can be obtained by measuring using an X-ray diffraction method and the like under the same conditions. The pole density may be able to be measured using X-ray diffraction, EBSD (Electron Back Scattering Diffraction), or channeling electron. For example, the pole density of the orientation group from {100} <011> to {223} <110> can be obtained as follows. The pole densities of the respective crystal orientation {100} <011>, {116} <110>, {114} <110>, {112} <110>, and {223} <110> are obtained from a three-dimensional texture (ODF) calculated by a series expansion method using a plurality of pole figures between the pole figures {110}, {100}, {211}, and {310} measured by the methods, and those pole densities they are arithmetically measured to obtain the pole density of the orientation group from {100} <011> to {223} <110>.
[0057] With respect to the sample that is provided for X-ray diffraction, EBSD, and electron channeling, the thickness of the steel plate can be reduced by mechanical polishing or similar to a predetermined plate thickness, subsequently to the while being able to remove a strain by chemical polishing, electrolytic polishing, or the like, the sample can be adjusted in order to an appropriate surface including a range from 5/8 to 3/8 of the plate thickness to be a measuring surface, and the density of
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15/71 pole can be measured according to the methods described above. With respect to a plate width direction, it is preferable that the sample is collected in the vicinity in 1/4 or 3/4 of the plate thickness position (a position away from the final surface of the steel plate by a distance that is 1/4 the width of a sheet of steel plate).
[0058] With respect not only to the central portion of the plate thickness, but also to as many plate thickness positions as possible, when the steel plate satisfies the pole density described above, the expandability of the orifice is further improved.
[0059] However, the integration of the central portion of the sheet thickness orientation described above has the greatest influence on the anisotropy of the steel sheet, and thus the material quality of the central sheet thickness portion is generally to represent material properties of the sheet. the entire steel sheet. In this way, the average pole density of the orientation group from {100} <011> to {223} <110> and the pole density of the crystal orientation {332} <113> in the range 5/8 to 3/8 of the central thickness portion of the plate are specified.
[0060] Here, {hkl} <uvw> represents that when the sample is collected by the method described above, a normal direction of a plate surface is parallel to <hkl>, and a laminating direction is parallel to <uvw>. In addition, with respect to a crystal orientation, an orientation that is orthogonal to the plate surface is commonly expressed by (hkl) or {hkl}, and an orientation that is parallel to the lamination direction is expressed by [uvw] or < uvw>. {hkl} <uvw> collectively represents equivalent planes, and (hkl) [uvw] represents individual crystal planes. That is, in the modality, since a centered body cubic structure (bcc structure) is a target, for example, respective planes (111), (-111), (1-11), (11-1), ( -1-11), (-11-1), (1-1-1), and (-1
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16/71
1-1) are equivalent, and thus are not distinguishable. In this case, these guidelines are collectively called the {111} plan. The expression ODF is also used to express orientation of other crystal structures having a low symmetric property, and thus the expression ODF, an individual orientation is generally expressed by (hkl) [uvwj. However, in the modality, {hkl} <uvw> and (hkl) [uvw] have the same meaning.
[0061] Next, a value of r (Lankford value) of the steel sheet will be described. In this modality, in order to further improve the local deformability, r values in the respective directions (rL which is a value of r in a rolling direction to be described later, r30 which is a value of r in one direction forming an angle of 30 ° with the rolling direction, r60 which is a value of r in one direction forming an angle of 60 ° with the rolling direction, and rC which is a value of r in a direction orthogonal to the rolling direction) can be established within a predetermined range. These r values are important in the modality. As a result of the intensive investigation by the present inventors, it has been proven that when the respective pole densities described above are properly controlled, and those r values are properly controlled, additional excellent orifice expansion can be obtained.
[0062] Value of r (rC) in the Orthogonal Direction for the Lamination Direction:
[0063] that is, as a result of intensive investigation by the present inventors, they found that when the respective pole densities, which are described above, are established within the range described above, at that time, the rC is set to 0.70 or more, good orifice expandability can be obtained. In this way, rC is set to 0.70 or more.
[0064] The upper limit of rC can be 1.10 or less to obtain
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17/71 additional excellent orifice expandability.
[0065] The value of r (r30) in the Direction Formation Angle of 30 ° with Lamination Direction:
[0066] As a result of intensive research by the present inventors, they found that when the respective pole densities, which are described above, are established within the ranges described above, and r30 is set to 1.10 or less, good orifice expandability can be obtained. In this way, r30 is set to 1.10 or less.
[0067] The lower limit of r30 can be 0.70 or more to obtain additional excellent orifice expandability.
[0068] The r (rL) value in the Lamination Direction, and the r (r60) value in the 60 ° Direction Formation Angle with Lamination Direction:
[0069] Furthermore, as a result of intensive research by the present inventors, they found that when the respective pole densities, which are described above, rC, and r30 are established within the ranges described above, at the same time, and rL and r60 satisfy rL> 0.70 and r60 <1.10, respectively, excellent TS x λ additional is able to be obtained. In this way, rL can be 0.70 or more, and r60 can be 1.10 or less.
[0070] With respect to the upper limit of rL and the lower limit of r60, which are described above, rL can be 1.10 or less, and r60 can be 0.70 or more in order to obtain additional excellent orifice expandability.
[0071] Each r value described above is evaluated by a tensile test using a JIS No. 5 tensile test specimen. In consideration of a common high strength steel plate, the r value can be evaluated within a range in that the tensile strain is within a range of 5% to 15% and within a range that corresponds to the length of Petition 870180072452, of 17/08/2018, p. 20/86
18/71 uniform development.
[0072] However, it is generally known that the texture and the value of r have a correlation with each other, but in the cold-rolled steel plate related to the modality, as already mentioned, the limitation for the density of the pole crystal orientation and the limitation for the value of r are different from each other. In this way, when both limitations are met concurrently, still excellent local deformability can be obtained.
[0073] Next, a microstructure of the cold rolled steel sheet related to the modality will be described.
[0074] A basic microstructure of the cold rolled steel sheet related to the modality includes ferrite, bainite, and retained austenite. In the modality, in addition to the basic components of the microstructure (in place of a part of ferrite, bainite, and retained austenite), one or more types between pearlite, martensite, and tempered martensite can also be included in the microstructure as a selective component of the microstructure. when necessary or in an unavoidable way. In addition, in the modality, an individual microstructure is evaluated by a proportion of area.
[0075] Concentrate C of ferrite and bainite in the retained austenite, and thus ferrite and bainite are necessary to improve the elongation by the effect of TRIP. In addition, ferrite and bainite also contribute to improving the orifice expandability. The ferrite fraction and the bainite fraction can be left to vary depending on a resistance level that is a development goal, but when ferrite is set at 5% to 80% and bainite is set at 5% to 80%, ductility excellent and excellent orifice expandability can be obtained. In this way, ferrite is set to 5% to 80%, and bainite is set to 5% to 80%.
[0076] Retained austenite is a structure that increases ductilide
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19/71 of, in particular, uniform elongation by induced transformation plasticity, and it is necessary for the retained austenite to be 2% or more in terms of an area ratio. In addition, the retained austenite is transformed into martensite by processing, and also contributes to the improvement of strength. The higher the proportion of the area of austenite retained, the more preferable it is. However, it is necessary to increase the C and Si content in order to guarantee retained austenite exceeding 30% in terms of an area ratio, in which case, weldability or surface qualities deteriorate. In this way, the upper limit of the proportion of the retained austenite area is set at 30% or less. Furthermore, in the case where it is still necessary to increase uniform elongation, it is preferable that the retained austenite is 3% or more, more preferably 5% or more, and even more preferably 8% or more.
[0077] When martensite is generated to a certain degree during cooling before the start of the bainitic transformation, an effect to promote the bainitic transformation or an effect to stabilize retained austenite can be obtained. The martensite is tempered by reheating, so that the tempered martensite can be included in the microstructure when necessary. However, when tempered martensite exceeds 60% in terms of area proportion, ductility decreases, and thus tempered martensite is limited to 60% or less in terms of area proportion.
[0078] In addition, the microstructure can include pearlite within a range of 10% or less and martensite within a range of 20% or less when necessary, respectively. When the amount of pearlite and the amount of martensite increase, the viability or local deformability of the steel plate decreases, or a C utilization rate that generates a retained austenite, decreases. Thus, in the microstructure, pearlite is limited to 10% or less, and martensite is limited. Petition 870180072452, of 17/08/2018, p. 22/86
20/71 gives 20% or less.
[0079] Here, the proportion of the austenite area can be determined from the diffraction intensity that can be obtained by performing X-ray diffraction with respect to a plane, which is parallel to the plate's surface, around 1/4 plate thickness position.
[0080] In addition, the proportion of the area of ferrite, pearlite, bainite, and martensite can be determined from an image that can be obtained by looking within a range of 1/8 to 3/8 thickness of the plate (this ie, a plate thickness range in which 1/4 of the plate thickness position becomes the center) using a FE-SEM (Field Emission Scanning Electron Microscope). In FE-SEM observation, a sample is collected in such a way that a cross-section of the sheet thickness parallel to the rolling direction of the steel sheet becomes an observation surface, and the polishing of a Nital etching is carried out with respect to observation surface.
[0081] Furthermore, with regard to the direction of the thickness of the sheet, around the surface of the sheet steel and around the center of the sheet steel, the microstructure (components) of the sheet steel can be largely different from other portions due to decarburization and precipitation of Mn. In this way, in the modality, the observation of the microstructure is performed in 1/4 of the thickness position of the plate, which is the reference.
[0082] Furthermore, in case of still improving the elongation, the grain size in the microstructure, particularly an average diameter of the volume can become thin. Furthermore, by refining the average diameter of the volume, fatigue properties (proportion of the fatigue limit) that are required for steel sheets for vehicles are improved.
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21/71 [0083] The number of coarse grains has a greater influence on elongation compared to fine grains, and thus elongation has a close correlation to an average volume diameter calculated as a heavy average volume compared to a diameter of average number. In this way, In case of obtaining the effect described above, the average volume diameter can be from 2 μίτι to 15 μίτι, and more preferably from 2 μίτι to 9.5 μίτι.
[0084] Furthermore, when the average diameter of the volume decreases, the concentration of local strain that occurs in an order of micrometer is suppressed, and thus the strain during local deformation can be dispersed. In this way, it is considered that the stretching, particularly, uniform stretching is improved. In addition, when the average diameter of the volume decreases, a grain boundary, which is serving as a displacement movement barrier, can be appropriately controlled. In addition, the grain boundary acts on repetitive plastic deformation (fatigue phenomenon) that occurs due to the displacement movement, and in this way the fatigue properties are improved.
[0085] In addition, the diameter of an individual grain (grain unit) can be determined as follows.
[0086] Pearlite is specified by observing the structure using an optical microscope. In addition, ferrite, austenite, bainite, martensite, and tempered martensite grain units are specified by EBSD. When a crystal structure of a region that is determined by EBSD is a centered face cubic structure (fcc structure), that region is determined as austenite. In addition, when a crystal structure of a region that is determined by EBSD is a centered body cubic structure (bcc structure), this region is determined as any of ferrite, bainite, martensite, and tempered martensite. Ferrite, bainite, martensite, and marten
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22/71 tempered site can be distinguished using a KAM method (Kernel Mean Monitoring) which is equipped for EBSP-OIM (registered trademark, Electron Back Scatter Diffraction PatternOrientation Image Microscopy). In the KAM method, a difference in orientation between the respective pixels is calculated in a first approximation (total of seven pixels) in which an arbitrary regular hexagonal pixel (central pixel) between measurement data, six pixels that are adjacent to the pixel are used , in a second approximation (total 19 pixels) in which 12 pixels still outside the six pixels are also used, or a third approximation (total 37 pixels) in which 18 pixels still outside the 12 pixels are also used. Then, an average value that is obtained is determined as a central pixel value, and this operation is performed with respect to the totality of pixels. When the calculation according to the KAM method is performed without exceeding a grain limit, a map, which is expressing a variation of intragranular orientation, can be created. This map shows a distribution of strains based on the variation of the local intragranular orientation.
[0087] In the modality, the difference in orientation between adjacent pixels is calculated by the third approximation in EBSP-OIM (registered trademark). The grain size of ferrite, bainite, martensite, and austenite can be obtained as follows. For example, the orientation measurement described above is performed in a measurement step 0.5 μΐιι below with a magnification of 1500 times, a position where the difference in orientation between measurement points, which are adjacent to each other, exceeds 15 ° is determined as a grain boundary (this grain boundary may not be a general grain boundary), and an equivalent circle diameter is calculated to obtain the grain size. In a case where pearlite is included in the microstructure, with respect to an image obtained by an optical microscope, the
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23/71 pearlite grain size can be calculated by applying an image processing method such as binarization processing and an interceptor method.
[0088] In the grain (grain unit) defined as described above, in the case where an equivalent circle radius (an average value of the equivalent circle diameter) is set to r, the volume of an individual grain can be obtained by 4χπχΓ ^3/3 , and an average volume diameter can be obtained by a heavy volume average.
[0089] In addition, a fraction of coarse grain to be described below can be obtained by dividing the proportion of the coarse grain area, which is obtained by the method, by an area of an object to be measured.
[0090] Furthermore, an equiaxial grain fraction to be described below can be obtained by dividing the proportion of the equiaxial grain area, which is obtained by the method, by an area of an object to be measured. [0091] Furthermore, in the case of still improving the expandability of the orifice, with respect to the total components of the microstructure, a proportion of an area (fraction of coarse grain) occupied by a grain (coarse grain) having a grain size , which exceeds 35 μΐη dust, a unit area may be limited to 10% or less. When a grain having a large grain size increases, the strength limit decreases, and thus the local deformability also decreases. In this way, it is preferable to make the grains as fine as possible. Furthermore, when all grains are uniformly and equivalently received from a strain, the orifice expandability is improved. In this way, the local grain strain can be suppressed by limiting the amount of coarse grains.
[0092] The present inventors continued an investigation for greater local deformability. As a result, they discovered the following fact. In the event that the respective pole densities, which
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24/71 are described above, (and r values) satisfy the conditions described above, and when equiaxial properties of the grains are excellent, directional dependence on an orifice expansion process is small, and local deformability is further improved. Thus, in the case of still improving the local deformability, the fraction of equiaxial grain, which is an index indicating the equiaxial properties, can be established from 50% to 100%. When the equiaxial grain fraction is 50% or more, the deformability in an L direction, which is a rolling direction, and deformability in a C direction, which is orthogonal to the rolling direction, becomes relatively uniform, and thus the local deformability is improved. In addition, the equiaxial grain fraction represents a proportion of a grain (equiaxial grain), which has excellent equiaxial properties, between grains (for example, total grains) in the microstructure of the steel plate, where a value (dL / dt ) obtained by dividing the length dL of the grain in the rolling direction by the length dt of the grain in the direction of plate thickness is 3.0 or less.
[0093] Vickers hardness of bainite has an influence on the strength limit. Along with the progress of bainitic transformation, the retained austenite stabilizes and the retained austenite contributes to improving the elongation. Furthermore, when bainite hardness is 180 HV or more, the strength limit and expandability of the hole can be further improved. In order to achieve a good balance between strength limit and orifice expansion, and a good balance between strength limit and elongation, the Vickers hardness of bainite can be set to 180 HV or more. In addition, Vickers hardness is measured using a microVickers measuring device.
[0094] C (average C concentration) in retained austenite largely contributes to the stability of retained austenite. When the concen
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25/71 average C traction in retained austenite is 0.9% or more, sufficient stability of retained austenite can be obtained. In this way, the TRIP effect can be effectively obtained, and in this way the elongation is improved. In this way, the average concentration of C in the retained austenite can be 0.9% or more.
[0095] The average concentration of C in the retained austenite is obtained by X-ray diffraction. That is, in X-ray analysis using CuKa rays, a lattice constant a (angstrom unit) is obtained from a reflection angle of a plane (200), a plane (220), and a plane (311) of austenite, and according to Expression 10 below, a concentration of carbon Cy in retained austenite can be calculated.
Cy = (a-3,572) / 0.033 ... (Expression 10) [0096] Next, the reason why the chemical components (chemical elements) of the cold rolled steel sheet related to the modality are limited will be described. Here,% in the content of the respective chemical components represents% by mass.
C: 0.02% to 0.4% [0097] C it is necessary to guarantee high resistance and retained austenite. In order to obtain a sufficient amount of austenite retained, it is preferable that the C content, which is included in the steel, is 0.02% or more. On the other hand, when the steel sheet excessively includes C, the weldability deteriorates, and thus the upper limit of the C content is set at 0.4%. In the case of still improving strength and elongation, it is preferable that the C content is 0.05% or more, more preferably 0.10% or more, and even more preferably 0.12% or more. In addition, in the case of still improving weldability, it is preferable that the C content is 0.38% or less, and more preferably 0.36% or less.
Si: 0.001% to 2.5%
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26/71 [0098] Si is a deoxidizer, and it is preferable that the Si content, which is included in steel, is 0.001% or more. In addition, Si stabilizes ferrite during annealing, and suppresses cementite precipitation during bainitic transformation (during retention within a predetermined temperature range). In this way, Si increases the concentration of C in austenite, and contributes to the safety of retained austenite. The more the Si content, the additional effect increases. However, when Si is added excessively to steel, surface qualities, paintability, weldability and the like deteriorate. In this way, the upper limit of the Si content is set at 2.5%. In the event that an effect of obtaining stable retained austenite is sufficiently exhibited by Si, it is preferable that the Si content is 0.02% or more, more preferably 0.50% or more, and even more preferably 0.60% or more. In addition, in the case of still holding surface qualities, paintability, weldability, and the like, it is preferable that the Si content is 2.2% or less, and more preferably 2.0% or less.
Mn: 0.001% to 4.0% [0099] Mn is an element that stabilizes austenite, and increases temperability. In order to guarantee sufficient hardenability, it is preferable that the Mn content, which is included in the steel, is 0.001% or more. On the other hand, when Mn is excessively added to the steel, the ductility deteriorates, and thus the upper limit of the Mn content is set at 4.0%. In the case of insuring additional higher temperability, it is preferable that the Mn content is 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more. In addition, in the case of ensuring additional higher ductility, it is preferable that the Mn content is 3.8% or less, and more preferably 3.5% or less.
P: 0.15% or less
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27/71 [00100] P is an impurity, and when P is excessively included in steel, ductility or weldability deteriorates. In this way, the upper limit of the P content is set at 0.15%. In addition, P operates as a solid solution hardening element, but P is inevitably included in steel. In this way, it is not particularly necessary to limit the lower limit of the P content, and the lower limit is 0%. In addition, when considering recent general refinement (including secondary refinement), the lower limit of the P content can be 0.001%. In the case of further increase in ductility and weldability, it is preferable that the P content is 0.10% or less, and more preferably 0.05% or less.
S: 0.03% or less [00101] S is an impurity, and when S is excessively contained in the steel, MnS which is extended by hot rolling is generated. In this way, formability such as ductility and expandability of the orifice deteriorates. In this way, the upper limit of the S content is set at 0.03%. In addition, since S is inevitably included in steel, it is not necessary to particularly limit the lower limit of the S content, and the lower limit is 0%. In addition, when considering recent general refinement (including secondary refinement), the lower limit of the S content can be 0.0005%. In the case of ductility and orifice expansion still increasing, it is preferable that the S content is 0.020% or less, and more preferably 0.015% or less.
N: 0.01% or less [00102] N is an impurity, and when the N content exceeds 0.01%, the ductility deteriorates. In this way, the upper limit of the N content is set to 0.01% or less. In addition, since N is inevitably included in steel, it is not particularly necessary to limit the lower limit of the N content, and the lower limit is 0%. In addition, when
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28/71 of the recent general refinement (secondary refinement), the lower limit of the N content can be 0.0005%. In the case of an additional ductility of increase, it is preferable that the N content is 0.005% or less.
Al: 0.001% to 2.0% [00103] Al is a deoxidizer, and when considering recent general refinement (including secondary refinement), it is preferable that the Al content, which is included in the steel, is 0.001% or more. In addition, Al stabilizes ferrite during annealing, and suppresses cementite precipitation during bainitic transformation (during retention within a predetermined temperature range). In this way, Al increases the concentration of C in austenite, and contributes to the safety of retained austenite. When the Al content is increasing, the effect still increases. However, when Al is excessively added to steel, the surface qualities, ability to paint, weldability, and the like deteriorate. In this way, the upper limit of the Al content is set at 2.0%. In the event that an effect of obtaining stable retained austenite is sufficiently exhibited by Al, it is preferable that the Al content is 0.01% or more, and more preferably 0.02% or more. In addition, in the case of additional safety of surface qualities, paintability, weldability, and the like, it is preferable that the Al content is 1.8% or less, and more preferably 1.5% or less.
O: 0.01% or less [00104] O (oxygen) is an impurity, and when the O content exceeds 0.01%, ductility deteriorates. In this way, the upper limit of the O content is set at 0.01%. Furthermore, since O is inevitably contained in steel, it is not particularly necessary to limit the lower limit of the O content, and the lower limit is 0%. Furthermore, when considering recent general refinement (including refinement
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29/71 secondary), the lower limit of the O content can be 0.0005%.
Si + Al: 1.0% to 4.5% [00105] These elements are deoxidizing as described above, and it is preferable that the sum of the Si content and the Al content is 1.0% or more. In addition, both Si and Al stabilize ferrite during annealing and suppress cementite precipitation during bainitic transformation (during retention within a predetermined temperature range). In this way, these elements increase the concentration of C in austenite, and contribute to the safety of retained austenite. However, when these elements are excessively added to steel, the surface qualities, paintability, weldability, and the like deteriorate, and thus the sum of the Si content and the Al content is set at 4.5% or less. In the case of still increasing surface qualities, paintability, weldability, and the like, it is preferable that the sum is 4.0% or less, more preferably 3.5% or less, and even more preferably 3.0% or less.
[00106] The chemical elements described above are basic components (basic elements) of steel in the modality, and the chemical composition in which the basic elements are controlled (included or limited), and in which the balance including Fe and unavoidable impurities is a composition basic modality. However, in the modality, in addition, for the basic components (instead of a part of Fe of the equilibrium), the following chemical elements (selective elements) can still be included in the steel when necessary. In addition, even when the selective elements are inevitably included (for example, in an amount less than the lower limits of the quantities of the respective selective elements) in steel, the effect in the modality does not deteriorate.
[00107] That is, the cold-rolled steel sheet for modalida
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30/71 can include one or more types among Ti, Nb, B, Mg, REM, Ca, Mo, Cr, V, W, Ni, Cu, Co, Sn, Zr, and As as a selective element to improve local formability, for example, by controlling inclusions or refining the precipitate.
[00108] Ti, Nb, B, Cu, and W improve the quality of the material through a mechanism such as carbon and nitrogen fixation, precipitation resistance, microstructure control, and refinement resistance. In this way, one or more types between Ti, Nb, B, Cu, and W can be added to the steel when necessary. In this case, with respect to the lower limits of the levels of the respective chemical elements, the Ti content is preferably 0.001% or more, the Nb content is preferably 0.005% or more, the B content is preferably 0.0001% or more, the Cu content is preferably 0.001% or more, and the W content is preferably 0.001% or more. However, even when these chemical elements are excessively added to steel, a notable effect is not obtained, and conversely, weldability and fabricability deteriorate. Thus, with respect to the upper limits of the levels of the respective chemical elements, the Ti content is limited to 0.2% or less, the Nb content is limited to 0.2% or less, the B content is limited to 0.005% or less, the Cu content is limited to 2.0% or less, and the W content is limited to 1.0% or less. In addition, in view of the reduction in alloy cost, it is not necessary to intentionally add these chemical elements to the steel, and all lower limits of the Ti content, the Nb content, the B content, the Cu content, and the W content is 0%.
[00109] Mg, REM (Rare Earth Metal), and Ca are important selective elements to improve the local deformability of the steel plate by controlling the inclusions in a harmless way. In this way, one or more types between Mg, REM, and Ca can be added to the steel when necessary. In this case, all lower limits of the
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The amounts of the respective chemical elements are preferably 0.0001%. On the other hand, when these chemical elements are excessively added to steel, cleanliness deteriorates. Thus, with respect to the upper limits of the amounts of the respective chemical elements, the Mg content is limited to 0.01% or less, the REM content is limited to 0.1% or less, and the Ca content is limited to 0.01% or less. In addition, in consideration of the reduction in the cost of alloy, it is not necessary to intentionally add these chemical elements to the steel, and all lower limits of the Mg content, the REM content, and the Ca content are 0%.
[00110] Mo and Cr have an effect of increasing the mechanical strength or an effect of improving the quality of a material, and thus one or both of Mo and Cr can be added to the steel when necessary. In this case, with respect to the lower limits of the amounts of the respective chemical elements, the Mo content is preferably 0.001% or more, and the Cr content is preferably 0.001% or more. However, when these chemical elements are excessively added to steel, reverse weldability deteriorates. Thus, with respect to the upper limits of the quantities of the respective chemical elements, the Mo content is limited to 1.0%, and the Cr content is limited to 2.0%. In addition, in view of the reduction in alloy cost, it is not necessary to intentionally add these chemical elements to the steel, and all lower limits of Mo content and Cr content are 0%.
[00111] V is effective for precipitation resistance, and a generation of deterioration of orifice expandability, which is caused by precipitation resistance, is small, and thus V is an effective selective element for a case where good expansion of high strength orifice are required. In this way, V can be added to the steel when necessary. In this case, it is preferable that the
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32/71
V is 0.001% or more. However, when V is excessively added to the steel, weldability deteriorates, so the V content is limited to 1.0% or less. In addition, in view of the reduction in alloy cost, it is not necessary to intentionally add V to the steel, and the lower limit of the V content is 0%.
[00112] Ni, Co, Sn, Zr, and As are selective elements that increase strength, and thus one or more types between Ni, Co, Sn, Zr, and As can be added to steel when necessary. In this case, as the effective levels (lower limits of quantities) of the respective chemical elements, the Ni content is preferably 0.001% or more, the Co content is preferably 0.0001% or more, the Sn content is preferably 0, 0001% or more, the Zr content is 0.0001% or more, and the As content is preferably 0.0001% or more. However, when these chemical elements are excessively added to steel, formability is lost. Thus, with respect to the upper limits of the quantities of the respective chemical elements, the Ni content is limited to 2.0% or less, the Co content is limited to 1.0% or less, the Sn content is limited to 0.2% or less, the Zr content is limited to 0.2% or less, and the As content is limited to 0.5% or less. In addition, in view of the reduction in alloy cost, it is not necessary to intentionally add these chemical elements to the steel, and all the lower limits of the Ni content, the Co content, the Sn content, the Zr content, and the As content is 0%.
[00113] As described above, the cold rolled steel sheet related to the modality has a chemical composition including the basic elements described above, the balance consisting of Fe and unavoidable impurities, or a chemical composition including the basic elements described above and at least a selected type of the selective elements described above, the balance consisting of Fe and unavoidable impurities.
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33/71 [00114] In the modality, a hot dip galvanizing treatment or a bonding treatment after galvanizing can be carried out on a surface of the cold rolled steel sheet described above, and thus the cold rolled steel sheet it may have a hot dip galvanized bed or an annealed galvanized layer on a bed surface.
[00115] Furthermore, in the modality, the cold rolled steel sheet (including hot dip galvanized steel sheet and an annealed galvanized steel sheet) can be subjected to various types of surface treatments (electro coating, coating by hot dip, deposition coating, a chrome treatment, a non-chrome treatment, a lamination treatment, a treatment using various types of salts, and the like), and so the cold rolled steel sheet can have a metal film (a coating or the like) or an organic film (a laminated film or the like) on a surface thereof.
[00116] In addition, in the modality, the plate thickness of the cold-rolled steel plate is not particularly limited, but, for example, the plate thickness can be from 0.5 mm to 2.5 mm, or from 0 , 5 mm less than 2.0 mm. In addition, the strength of the cold-rolled steel sheet is also not particularly limited, and, for example, the strength limit can be from 440 MPa to 1,500 MPa.
[00117] Next, a method of producing cold rolled steel sheet related to a modality of the present invention will be described.
[00118] In order to achieve excellent orifice expansion and excellent elongation, it is important to form a texture (undeveloped texture) that has a pole density of less anisotropy. In this way, details of production conditions that the cold rolled steel sheet, which is produced, satisfy the conditions described in
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34/71 points above the respective pole densities will be described below. [00119] A production method prior to hot rolling is not particularly limited. For example, various types of secondary refining can be carried out subsequently to melt and refine using a blast furnace, an electric furnace, a converter, or the like to melt steel that satisfies the chemical composition described above, thus steel (molten steel) ) It can be obtained. Then, to obtain an ingot or a steel plate, for example, steel can be melted by casting methods such as a common continuous casting method, an ingot method, and a thin plate casting method. In the case of continuous casting, the steel can be hot rolled after cooling the steel once to a low temperature (for example, room temperature), and reheating the steel. Alternatively, the steel (molten plate) immediately after being melted can be continuously hot rolled. In addition, as a raw material for steel (molten steel), fragment can be used. [00120] In addition, in hot rolling to be described later, after the draft rolling, a finished rolling can be performed continuously after joining a sheet bar. On that occasion, a rough bar can be wound at once on a coil, and can be stored in a lid having a heat retention function when needed, and the joint can be made after cooling the coil again.
[00121] To obtain a high-strength steel sheet that is excellent in local deformability, it is preferable to satisfy the following conditions.
[00122] First, in order to increase the local deformability, an austenite grain size after the draft lamination, that is, before finishing the lamination is important. That is, it is preferable that the austenite grain size before finishing the lamination is small.
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35/71 queno. In addition, it has been proven that when an average austenite grain size before finishing lamination is 200 μπι or less, this is effective in ensuring sufficient local deformability. In addition, in a case where rC and r30 are effectively controlled in a range of 0.70 or more and 1.10 or less, respectively, the average austenite grain size before finishing lamination can be 200 μΐη or any less.
[00123] As shown in FIGURE 5, to obtain an average austenite grain size of 200 μΐη or less before finishing rolling, steel can be rolled one or more times (one or more steps) with a reduction ratio of lamination of 40% or more by draft lamination (a first hot lamination) within a temperature range of 1,000 ° C to 1,200 ° C (preferably 1,150 ° C or lower).
[00124] When the lamination reduction ratio and the number of lamination reduction times, a fine austenite grain can be obtained. For example, in sketch lamination, it is preferable to control the average grain size of austenite to 100 μΐη or less. To perform grain size control, it is preferable that a lamination in which a lamination reduction ratio of one pass is 40% or more can be performed two or more times (two or more passes). However, with regard to draft lamination, when the proportion of reduction of one-step lamination is limited to 70% or less, or the number of times the reduction of lamination (the number of passes) is limited to 10 times or less, a consideration of a decrease in temperature or excessive generation of scales is capable of being reduced. In this way, the proportion of lamination reduction of a pass in sketch lamination can be 70% or less, and the number of times of lamination reduction (the number of passes) can be 10 times or less.
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36/71 [00125] As described above, when the austenite grain size before the finishing lamination is made small, the recrystallization of austenite in the subsequent finishing lamination is promoted, and thus the reduction of the austenite grain size is effective to improve the expandability of the orifice. In addition, the reduction in austenite grain size before finishing lamination is also effective from the perspective of rC and r30 control.
[00126] The effect is considered because an austenite grain contour after the thick lamination (that is, before the finishing lamination) works as one of the recrystallization cores during the finishing lamination.
[00127] In order to confirm the austenite grain size after coarse lamination, it is preferable to quickly cool the steel (steel plate) before entering the finishing lamination at a rate of cooling rate as high as possible. For example, the steel sheet is cooled at an average cooling rate of 10 ° C / s or more. In addition, a cross section of a sheet piece collected from the steel sheet obtained after cooling is engraved to outline the austenite grain in a microstructure that emerges forward, and then the measurement using an optical microscope is performed. At that time, with respect to the 20 viewing fields or more at a magnification of 50 times or more, the size of the austenite grain is measured by image analysis or an interception method, and the respective austenite grain sizes are average for obtain an average austenite grain size.
[00128] Furthermore, as a condition for controlling the average pole density of the {100} <011> to {223} <110> orientation group and the crystal density of the {332} <113> crystal orientation in the central portion of the plate thickness within a range of 5/8 to 3/8 of the plate thickness range to be within the density ranges
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37/71 of the pole described above, the lamination is controlled in the finishing lamination (a second hot lamination) after the thick lamination with a temperature T1 (° C), which can be determined as shown in Expression 11 below by a composition (mass%) of steel, defined as a reference.
T1 = 850 + 10 x ([C] + [N]) x [Mn] + 350 x [Nb] + 250 x [Ti] + 40 x [B] + x [Cr] + 100 x [Mo] + 100 χ [V] ... (Expression 11) [00129] Furthermore, in Expression 11, [C], [N], [Mn], [Nb], [Ti], [B], [Cr], [ Mo], and [V] represent mass percentages of C, N, Mn, Nb, Ti, B, Cr, Mo, and V in steel, respectively. In addition, the calculation is performed while defining the quantities of chemical elements (chemical components) not contained in Expression 11a 0%. Therefore, in the basic composition that contains only the basic components described above, Expression 12 below can be used instead of Expression 11.
T1 = 850 + 10 x ([C] + [N]) x [Mn] ... (Expression 12) [00130] In addition, when steel includes selective elements, a temperature calculated by Expression 11 is required instead of temperature calculated by Expression 12 to be defined as T1 (° C).
[00131] In finishing lamination, the temperature T1 (° C) that can be obtained by Expression 11 or Expression 12 is defined as a reference, a large proportion of lamination reduction is fixed in a temperature range of T1 + 30 ° C to T1 + 200 ° C (preferably, a temperature range of T1 + 50 ° C to T1 + 100 ° C), and the lamination reduction ratio is limited to a small range (including 0%) in a range of temperature that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C. When finishing lamination is carried out in addition to coarse lamination, the local deformability of a final product can be raised.
[00132] This is when the large proportion of blade reduction
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38/71 tion is set in a temperature range of T1 + 30 ° C to T1 + 200 ° C, and the lamination reduction ratio is limited to a temperature range that is equal to or greater than Ar3 ° C and less than T1 + 30 ° C, the average pole density of the orientation group from {100} <011> to {223} <110> and the pole density of the crystal orientation {332} <113> in the central portion of the thickness of the plate are sufficiently controlled. Consequently, the expandability of the orifice of the final product is dramatically improved.
[00133] The temperature T1 itself is empirically obtained. The present inventors have empirically discovered the fact to follow through experiments. That is, the temperature range in which recrystallization in an austenite range for each steel is promoted can be determined with the temperature T1 defined as a reference. In order to obtain more excellent orifice expandability, it is important to accumulate a large amount of tension by reducing lamination, and thus a proportion of accumulative lamination reduction within a temperature range of T1 + 30 ° C to T1 + 200 ° C is 50% or more. In addition, from the perspective of promoting recrystallization by the accumulation of tension, it is preferable that the proportion of accumulative lamination reduction is 70% or more. In addition, when the upper limit of the cumulative lamination reduction ratio is limited, the lamination temperature can still be set sufficiently, and thus a lamination can still be suppressed. Consequently, the proportion of cumulative lamination reduction can be 90% or less.
[00134] In addition, in order to increase the elongation and local ductility of a final product due to the increase in the homogeneity of the steel (original hot-rolled sheet), the finishing lamination is controlled to include a large bearing reduction pass having a lamination reduction ratio of 30% or
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39/71 more in a temperature range from T1 + 30 ° C to T1 + 200 ° C to the limit. In this way, in the finishing lamination, in a temperature range of T1 + 30 ° C to T1 + 200 ° C, at least once a reduction of lamination having a proportion of reduction of lamination of 30% or more. Particularly, when considering cooling control, to be described later, the proportion of lamination reduction in the final passage in the temperature range is 30% or more. That is, it is preferable that the final pass is the large lamination reduction pass. In a case where even greater workability is required, the lamination reduction ratios of two final passages in a temperature range from T1 + 30 ° C to T1 + 200 ° C can be adjusted to 30% or more, respectively. In a case of more homogeneity of increase of a hot rolled sheet, the proportion of lamination reduction of the large lamination reduction pass (one pass) can be 40% or more. In addition, in the case of obtaining another excellent shape of a steel sheet, the lamination reduction ratio of the large lamination reduction pass (one pass) can be 70% or less.
[00135] Furthermore, as a condition in which the rL and r60 described above satisfy rL> 0.70, and r60 <1.10, in addition to an appropriate control of a waiting time to be described later, in the range of temperature from T1 + 30 ° C to T1 + 200 ° C, an increase in the temperature of a steel sheet between the respective passages during the reduction of the rolling is preferably suppressed at 18 ° C or less.
[00136] In addition, in the temperature range from T1 + 30 ° C to T1 + 200 ° C, when the temperature rise of a steel sheet between the respective lamination passages is suppressed, uniform recrystallized austenite can be obtained.
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40/71 [00137] In addition, uniform recrystallization is promoted by the release of accumulated tension. Consequently, after the lamination reduction in a temperature range from T1 + 30 ° C to T1 + 200 ° C is completed, an amount of processing in a temperature range that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C (preferably T1 ° C for less than T1 + 30 ° C) is suppressed to be as small as possible. Consequently, the proportion of cumulative lamination reduction in a temperature range that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C is limited to 30% or less. In case of fixing the excellent shape of the sheet in this temperature range, the proportion of accumulative lamination reduction of 10% or more is preferable. However, in a case where a high value is adjusted in the orifice expandability, it is preferable that the cumulative lamination reduction ratio is 10% or less, and more preferably 0%. That is, in a temperature range that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C, it is not necessary to perform lamination reduction, and even when lamination reduction is performed, the proportion of Cumulative lamination is adjusted to 30% or less.
[00138] Furthermore, when the proportion of lamination reduction in a temperature range that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C is large, the recrystallized austenite grain is extended, and thus the expandability the hole deteriorates.
[00139] That is, with regard to production conditions related to the realization, when austenite is uniformly and finely recrystallized in the finishing lamination, the texture of a product is controlled. Consequently, the expandability of the orifice can be improved.
[00140] When the lamination is carried out in a temperature range lower than Ar3 ° C, or the proportion of reduction of ac lamination
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41/71 mulative in a temperature range that is greater than or equal to Ar3 ° C and less than T1 + 30 ° C is very large, the texture of the austenite develops. As a result, a steel sheet that can finally be obtained does not satisfy at least one condition where the average pole density of the orientation group from {100} <011> to {223} <110> in the central portion of the thickness of the plate is 1.0 to 6.5, and a condition in which the pole density of the crystal orientation {332} <113> in the central portion of the plate thickness is 1.0 to 5.0. On the other hand, in finishing lamination, when lamination is carried out in a temperature range greater than T1 + 200 ° C, or the proportion of accumulative lamination reduction is very small, coarse grains or mixed grains can be included in the microstructure , or the microstructure may consist of mixed grains. In addition, in this case, a fraction of coarse grain or an average volume diameter increases.
[00141] Here, the lamination reduction ratio can be obtained by the current results or calculation in the measurement of a lamination load or sheet thickness, and the like. In addition, a rolling temperature (for example, each of the above temperature ranges) can be obtained by the current measurement using a thermometer between stands, by calculating through a calculation simulation taking into account the processing heat generation due to the speed of the line, a lamination reduction ratio, or similar, or performing both (current measurement and calculation). In addition, in the above description, the ratio of lamination reduction in one pass represents a percentage of an amount of lamination reduction in one pass to a thickness of the input plate before passing through the lamination support (a difference between the thickness of the input plate before passing through the laminating support and a thickness of the output plate after passing the support
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42/71 lamination). When a thickness of the input plate before the first lamination pass in each of the temperature ranges is defined as a reference, the cumulative lamination reduction ratio represents a proportion of the cumulative lamination reduction amount for the reference (a difference between the thickness of the entry plate before the first pass in the lamination in each of the temperature ranges and the thickness of the exit plate after the final passage in the lamination in each of the temperature ranges). In addition, the Ar3 temperature is obtained by Expression 13 below.
Ar ₃ = 879.4 - 516.1 x [C] - 65.7 x [Mn] + 38.0 x [Si] + 274.7 x [P] ...
(Expression 13) [00142] Regarding the hot lamination (finishing lamination) that is carried out as described above, the hot lamination is finished at a temperature higher than Ar3 ° C. When hot rolling is finished at a temperature less than Ar ₃ (° C), the steel is rolled in a two-phase region (two-phase region) including austenite and ferrite, and thus the integration of the crystal orientation into the group orientation from {100} <011> to {223} <110> becomes strong. As a result, the orifice expandability significantly deteriorates. Here, when the finishing temperature of the finishing lamination lamination is T1 ° C or more, an amount of stress in a temperature range of T1 ° C or less can be reduced, and thus anisotropy can also be reduced. Consequently, the finishing temperature of the finishing lamination can be T1 ° C or more.
[00143] In addition, the cooling (first cooling) after a large pass of reduction of the final lamination (reduction of lamination in a lamination support) of the lamination in a temperature range of T1 + 30 ° C to T1 + 200 ° C has a big effect on the size
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43/71 of the austenite grain, and the size of the austenite grain has a strong effect on an equiaxial grain fraction and a coarse grain fraction of a microstructure after cold rolling and annealing.
[00144] The steel is cooled after a lamination support corresponding to the final passage among the large lamination reduction passages in such a way that a waiting time t (second), which is done before a first start of cooling after carrying out the final pass among the large lamination reduction passages (as described above, the large lamination reduction passages represent lamination reduction (pass) having a lamination reduction ratio of 30% or more in the temperature range of T1 + 30 ° C to T1 + 200 ° C) in hot rolling is carried out, satisfies Expression 14 (the first cooling). Here, t1 in Expression 14 can be obtained from Expression 15 below. In Expression 15, Tf represents a temperature (° C) of a steel sheet at the time of the final passage in the large lamination reduction passages, and P1 represents a lamination reduction ratio (%) in the final passage among the large ones lamination reduction passages. Here, when considering operability (for example, format correction or controllability of the second cooling), the first cooling can be carried out between the lamination supports.
[00145] When the waiting time t exceeds the value on the right side (t1 x 2.5) of Expression 14, recrystallization is almost completed, on the other hand, a grain is significantly cultivated, and thus a grain size increases. Therefore, the r value (for example, rC and r30) and elongation significantly decrease. Consequently, when the start of cooling is controlled in such a way that the waiting time t meets Expression 14 below, a grain size is appropriately controlled. Therefore, the control of the beginning of the coldPetition 870180072452, of 17/08/2018, p. 46/86
44/71 ment has an effect on fixing sufficient elongation.
t <2.5 x t1 ... (Expression 14) t1 = 0.001 x ((Tf-T1) x P1 / 100) ² - 0.109 x ((Tf-T1) x P1 / 100) + 3.1 .. .
(Expression 15) [00146] When the waiting time t is also limited to be less than t1 seconds (Expression 16 below), grain growth can be largely suppressed. In this case, an average volume diameter of a final product is also decreased, so the limitation is effective in controlling the average volume diameter to be 15 μΐιι or less. As a result, even when the recrystallization does not progress sufficiently, the elongation of the steel sheet can also be increased at the same time, and the fatigue properties can be improved.
t <t1 ... (Expression 16) [00147] On the other hand, when the waiting time t is also limited within a range of t1 seconds to 2.5 x t1 seconds (Expression 17 below), the diameter average volume increases compared to a case where the waiting time t is less than t1 seconds. However, recrystallization progresses sufficiently, so the crystal orientation becomes random. Consequently, the elongation of the steel sheet can be sufficiently improved at the same time, and isotropy can be greatly improved.
t1 <t <2.5 x t1 ... (Expression 17) [00148] In addition, the first cooling described above can be carried out between the lamination supports or after the final support. That is, after performing the first cooling, lamination having a low proportion of lamination reduction (for example, 30% or less (or less than 30%)) can be carried out in a temperature range of Ar3 ° C or more ( for example, from Ar3 (° C) to T1 + 30 (or Tf) (° C)).
[00149] It is preferable that a variation of the cooling temperature
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45/71 which is a difference between a temperature of the steel plate (temperature of the steel) at the time of the start of the cooling and a temperature of the steel plate (temperature of the steel) at the time of the end of the cooling in the first cooling is 40 ° C to 140 ° C. In addition, it is preferable that the temperature of the steel plate T2 at the end of cooling the first cooling is T1 + 100 ° C or less. When the variation of the cooling temperature is 40 ° C or more, the growth of the recrystallized austenite grain can also be suppressed. And so, the strength and the stretch can be increased. When the variation in the cooling temperature is 140 ° C or less, the recrystallization can also be progressed sufficiently, and thus the pole density can also be improved. Consequently, the expandability of the orifice can also be increased.
[00150] Furthermore, when the variation of the cooling temperature is limited to 140 ° C or less, the temperature of the steel plate can be controlled in a relatively easy way, and the variant selection (avoiding the variant limitation) can be controlled in a relatively effective way, and so the development of a texture can also be suppressed. Consequently, in this case, the isotropy can also be high, and thus the dependence on workability orientation can also be increased. In addition, when the temperature of the steel plate T2 at the end of the cooling of the first cooling is T1 + 100 ° C or less, another sufficient cooling effect can be obtained. Due to the cooling effect, the growth of the grain can be suppressed, and thus an increase in the size of the grain can also be suppressed.
[00151] In addition, it is preferable that an average cooling rate in the first cooling is 50 ° C / s or more. When the average cooling rate in the first cooling is 50 ° C / s or more, the
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46/71 cement of the recrystallized austenite grain can also be suppressed. On the other hand, it is not necessary to define the upper limit of the average cooling rate particularly, but the average cooling rate can be 200 ° C / s or less from the perspective of a plate shape.
[00152] Furthermore, other cooling conditions in a range from the end of the first cooling to the start of the winding (a second cooling) are not particularly limited, and according to the purpose, the microstructure can be flexibly controlled within a range of the microstructure described above by adjusting a cooling pattern. In addition, for example, in case the austenite grain size retention is relatively fine, cooling (this cooling is included in the second cooling) can be carried out after passing through the final rolling support of a rolling mill. finishing. In this way, the second cooling is carried out subsequent to the first cooling. The second cooling can be started within 10 seconds after the first cooling is completed. In this way, when the second cooling is started within 10 seconds after completing the first cooling, a grain can also become fine.
[00153] In addition, the steel is cooled to a temperature of 650 ° C or less (this cooling is included in the second cooling), and then the steel (original hot-rolled sheet) is wound over a temperature range of 650 ° C or less. When the steel is wound before reaching a temperature of 650 ° C or less, the anisotropy of a steel sheet after cold rolling increases, and thus the orifice expandability significantly decreases. The lower limit of a winding temperature is not particularly limited, but the lower limit can be 350 ° C or more in order to suppress a cold rolling load by suppressing the generation of martensite.
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47/71 [00154] The original hot-rolled sheet that is produced as described above is cooled and subjected to pickling, and then cold rolling is carried out in a reduction ratio of rolling (a reduction ratio of cold rolling) ) from 30% to 90%. When the proportion of lamination reduction is less than 30%, it is difficult for recrystallization to occur in the subsequent annealing process, and thus a texture control (pole density control) by the recrystallized ferrite to be described later becomes difficult . In addition, in this case, the equiaxial grain fraction decreases, and thus a grain after annealing becomes coarse. In addition, when the lamination reduction ratio exceeds 90%, a texture is developed during annealing, and thus anisotropy of a crystal orientation becomes strong. Therefore, the reduction ratio of cold rolling mill is set from 30% to 90%. To control a grain to be also fine by improving the fraction of equiaxial grain, it is preferable that the reduction ratio of cold rolling lamination is 40% or more. In addition, to also reduce the anisotropy of a crystal orientation, it is preferable that the reduction ratio of cold lamination lamination is 80% or less, more preferably 70% or less, and even more preferably 60% or any less.
[00155] In the case where a strong texture is developed in cold rolled steel (steel plate), even when subsequent annealing is carried out, the texture has a tendency to be carried out in a microstructure after annealing. As a result, the ductility and expandability of the orifice may deteriorate. Therefore, in the case of cold rolling, in addition, for a texture control of a hot-rolled steel sheet, it is necessary to weaken the texture, which is developed by cold rolling, due to the control of the annealing conditions. . The annealing effect
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48/71 is displayed by performing heating in two stages which is satisfying Expressions 19 and 20. The detailed reason why the texture and mechanical properties of the steel plate can be adequately controlled by heating in two stages is not clear. However, a texture weakening effect is considered to have a relationship with the recovery of the displacement introduced during cold rolling and recrystallization. That is, when a heating rate within a temperature range of 650 ° C to Aci ° C is high, ferrite is not recrystallized, and worked non-recrystallized ferrite remains during the reverse transformation. In addition, when a steel including 0.01% C content,% by mass, is annealed in a two-phase region including ferrite and austenite, austenite that is formed blocks the growth of recrystallized ferrite, and non-crystallized ferrite has a tendency to remain after annealing. Non-recrystallized ferrite has a strong texture, and thus has a negative influence on local deformability. In addition, non-crystallized ferrite contains a lot of displacement, and thus largely deteriorates ductility. Therefore, it is preferable that a heating rate within a temperature range of 650 ° C to Aci ° C is low. However, since the driving force of the recrystallization is an accumulation of tension by the lamination, in the case where a heating rate at 650 ° C is low, the displacement introduced by the cold lamination is recovered, and thus the recrystallization does not occur. As a result, the texture that is developed during cold rolling remains intact, and thus the local deformability deteriorates. Particularly, in the case where a heating rate within a temperature range at room temperature (for example, 25 ° C) at 650 ° C is low, a displacement density, which is included in the microstructure at the beginning of recrystallization, decreases. As a result, it takes a long time for recrystallization, and therefore it is necessary to be affordable at the
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49/71 heating within the temperature range of 650 ° C to Aci ° C (it is necessary to have a long steel retention time in a temperature region in which recrystallization occurs). Consequently, the two-stage heating, which is satisfying Expressions 19 and 20, is carried out during annealing. That is, an average heating rate HR1 (° C / s) in a temperature range (previous step) at room temperature (for example, 25 ° C) at 650 ° C is 0.3 ° C / s or more, and an average heating rate HR2 (° C / s) over a temperature range (later stage) of more than 650 ° C to Aci ° C is 0.5 x HR1 (° C / s) or less. Here, the upper limit of the average heating rate HR1 in the previous step and the upper limit of the average heating rate HR2 in the later step are not particularly limited, and, for example, HR1 can be 200 ° C / s or less, and HR2 it can be 0.15 ° C / s or more. In addition, two-stage heating can be carried out using continuous annealing equipment, continuous hot-dip galvanizing equipment and continuous galvanizing equipment.
[00156] However, the texture, which is developed on the original hot-rolled sheet, is carried even after cold rolling and annealing. Therefore, in the case where the texture of the original hot-rolled sheet is not adequately controlled, even when the heating conditions during annealing are controlled to the conditions described above, the local deformability of a steel sheet deteriorates. Consequently, as preconditions before cold rolling and annealing, when hot rolling is controlled by the conditions described above to make the texture of an original hot rolled sheet random, and then the heating conditions during annealing are controlled for the conditions described above, excellent ductility and excellent expandability of the orifice can be sufficiently improved.
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50/71 [00157] In addition, the steel that is heated is retained within a temperature range of Aci ° C to 900 ° C which is obtained by heating two stages for 1 second to 300 seconds. At a temperature less than Aci ° C or for a time shorter than 1 second, the reverse transformation of a low temperature phase such as ferrite to austenite does not progress sufficiently, so a second phase cannot be achieved in a cooling process subsequent, and sufficient strength cannot be obtained. In addition, in this case, the low temperature phase such as ferrite and the texture after cold rolling remain intact, and thus the local deformability deteriorates. On the other hand, at a temperature greater than 900 ° C or for a time longer than 300 seconds, a grain becomes thicker by retention, and the r or elongation value decreases.
[00158] Here, Aci, the average heating rate HR1 in the previous step, and the average heating rate HR2 in the later step can be obtained by Expression 18, Expression 19, and Expression 20, respectively.
Aci = 723 - 10.7 x [Mn] - 16.9 x [Ni] + 29.1 x [Si] + 16.9 x [Cr] + 290 x [As] + 6.38 x [W]. .. (Expression 18)
HR1> 0.3 ... (Expression 19)
HR2 <0.5 x HR1 ... (Expression 20) [00159] The steel is then cooled to a temperature range of 580 ° C to 780 ° C at an average cooling rate of 1 ° C / s to 20 ° C / s (a third cooling, cooling in the first stage). When the average cooling rate is less than 1 ° C / s or the temperature at the end of cooling is 780 ° C or more, a required fraction of ferrite is not obtained, and the elongation decreases. On the other hand, when the average cooling rate is 20 ° C / s or more, or the cooling end temperature is less than 580 ° C, pearlite must be generated, and thus the orifice expandability decreases.
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51/71 [00160] The steel is then cooled to a temperature range of 350 ° C to 500 ° C at an average cooling rate of 5 ° C / s to 200 ° C / s (a fourth cooling, cooling on the second stage). As a method, after cooling, the steel is retained intact within a temperature range of 350 ° C to 500 ° C for a time of 0 seconds to 1,000 seconds. In addition, as another method, after the cooling described above, the steel is further cooled as it is to 350 ° C or less (a fifth cooling), and then the steel is reheated to a temperature range of 350 ° C to 500 ° C, and the steel is retained within a temperature range of 350 ° C to 500 ° C for a time of 10 seconds to 1,000 seconds. When the steel is retained for a shorter time than 0 seconds or in a temperature range that is less than 350 ° C or greater than 500 ° C, the bainitic transformation does not progress sufficiently, and thus good orifice expansion cannot be achieved . Among these conditions, when the steel is retained for a shorter time than 0 seconds or in a temperature range below 350 ° C, a large amount of martensite must be generated, and thus not only the expansion of the orifice but also the elongation deteriorates. In addition, when the steel is retained in a temperature range greater than 500 ° C, a large amount of pearlite must be generated, and thus the orifice expandability also decreases. In addition, when the average cooling rate in the fourth cooling is set to 5 ° C / s or more, pearlite generation can also be suppressed. In addition, it is not necessary to particularly limit the upper limit of the average cooling rate in the fourth cooling, but the upper limit can be 200 ° C / s to increase the accuracy of the temperature control.
[00161] Here, io can be obtained by Expression 21 below. [Mathematical Expression 2]
-425) ^J +1.18
... (Expression 21) t _0A = 10 ^{OOOO2 (T} Petition 870180072452, of 08/17/2018, page 54/86
52/71 [00162] Here, Toa represents a holding temperature in a temperature range of 350 ° C to 500 ° C.
[00163] In addition, with respect to the cold-rolled steel sheet that is obtained, the lamination of skin passage can be carried out as needed. According to the skin passage lamination, a tension of the stretcher that occurs during machining can be prevented, and a shape of a steel plate can be corrected.
[00164] In addition, with respect to the cold rolled steel sheet that is produced as above, a galvanizing treatment described above or a galvanizing treatment can be carried out as necessary to form a hot dip galvanized layer or an annealed layer after galvanizing on a cold rolled steel sheet surface. In this case, before forming a coating layer, an atmosphere in an oven can be controlled in such a way that a logarithm (log (pH2o / pH2)) of a ratio of a partial water vapor pressure PH20 to a hydrogen pressure partial pH2 satisfies from -3.0 to 0.0, and annealing (for example, heating under predetermined conditions described above or retention within a predetermined temperature range) can be performed. According to annealing, the generation of an uncoated portion, which has a tendency to occur on a steel plate, which is including the Si content, can be suppressed, or the alloy can be promoted. Consequently, a coating quality can also be high.
[00165] In addition, various types of surface treatment as described above can be applied to obtainable cold-rolled steel sheet.
[00166] By reference, figures 9 and 10 show a flow chart illustrating the outline of a method of production of cold rolled steel sheet related to the modality.
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Examples [00167] A technical content of the present invention will be described with reference to the examples of the present invention.
[00168] The results of the examination performed using Plate No. A to Y and Plate No. a to g having a chemical composition shown in Tables 1 to 3 (the balance includes Fe and inevitable impurities) will be described.
[00169] The steel was melted and melted. Then, the steel was heated to a temperature range of 900 ° C to 1,300 ° C as it was, or the steel was heated to a temperature range of 900 ° C to 1,300 ° C after reheating the steel which was cooled once to room temperature. Then, hot rolling was performed while controlling a steel plate temperature in production conditions shown in Tables 4 and 7. After the hot rolling was finished at a temperature higher than Ar3, the steel was cooled. Then, the steel was wound to obtain an original hot-rolled sheet having a thickness of 2 mm to 5 mm. Then, the steel (original hot-rolled plate) was subjected to pickling, and was cold rolled to a thickness of 1.2 mm to 2.3 mm. Then, in order to anneal, the steel was heated and retained. Then, the steel sheet that was obtained was cooled in two steps, and was retained. Then, with respect to the steel plate, the skin passing lamination was performed at 0.5% of a reduction ratio of lamination to obtain a cold rolled steel plate. Here, the cold rolled steel sheet was produced in such a way that the production conditions after the hot rolling met the production conditions in Tables 8 to 11. In addition, in relation to Production No. A1, in addition to the uncoated cold-rolled steel (original cold-rolled sheet), a hot-dip galvanized steel sheet and a steel sheet annealed after galvanizing were also produced by the formation of a galvanic layer
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54/71 hot-dipped and annealed layer after galvanizing on a steel sheet surface. In addition, in Production No. 02, the reduction in lamination having a proportion of lamination reduction of 30% or more was not performed in the temperature range of T1 + 30 ° C to T1 + 200 ° C, and thus it was impossible to calculate t1. Therefore, in Production No. 02, a lamination reduction ratio of one final pass in the temperature range from T1 + 30 ° C to T1 + 200 ° C was used as P1.
[00170] The chemical components of each steel are shown in Tables 1 to 3, and each production condition is shown in Tables 4 to 7, and Tables 8 to 11. In addition, a microstructure and mechanical properties of a steel plate that was obtained are shown in Tables 12 to 15. In addition, in Tables 12 to 15, F, B, retained γ, Μ, P, and tM represents the proportion of areas of ferrite, bainite, retained austenite, martensite, pearlite, and tempered martensite respectively.
[00171] In addition, with respect to the results that were obtained, a relationship between the TS resistance and orifice expansion λ is shown in figure 6, and a relationship between the TS resistance and the EL elongation is shown in figure 7.
[00172] In addition, the tensile strength TS, the elongation (total elongation) EL, the r values in the respective directions (rL, rC, r30, and r60: according to J IS Z 2254 (2008) (ISO10113 (2006 ))) were determined by the stress test according to JIS Z 2241. In addition, orifice expandability λ was determined by an orifice expansion test according to Japan Iron and Steel Federation Standard JFS T1001. In addition, other conditions in the measurement of the r-values were the same as the conditions of the realization.
[00173] Furthermore, with respect to the central portion of the plate thickness, within a region of 5/8 to 3/8 of a cross section of the
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55/71 sheet thickness, which is parallel to a lamination direction in a 1/4 position in a sheet width direction, a pole density was measured in a step of 0.5 gm using the EBSD described above.
[00174] As shown in figures 6 and 7, it is able to be understood that a steel plate, in which a chemical composition and a microstructure (particularly, pole densities and the respective crystal orientations) of the steel plate are adequately controlled, it has excellent orifice expandability and ductility. In addition, in a hot-dip galvanized steel sheet and a steel sheet annealed after galvanizing that were obtained in Production No. A1, the microstructure and mechanical properties of the respective coated steel sheet were the same as the microstructure and properties mechanics of original cold-rolled sheets (Tables 12 to 15) corresponding to the Production of Numbers.
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56/71 [Table 1]
STEELN " CHEMICAL COMPONENT / ¾ IN MASS G Si Mn P s N Al O Si + Al THE 0.168 1.40 2.05 0.001 0.007 0.0026 0.032 0.0032 1.43 R 0.191 1.33 2.25 0.001 0.005 0.0032 0.035 0.0023 1.36 G 0.255 0.97 1.55 0.002 0.007 0.0033 0.038 0.0026 1.01 D 0.380 2.46 3.80 0.001 0.005 0.0033 0.710 0.0021 3.17 AND 0.280 0.75 1.35 0.002 0.005 0.0055 0.310 0.0029 1.06 F 0.144 1.05 3.20 0.012 0.003 0.0032 0.040 0.0038 1.09 G 0.266 0.90 1.54 0.001 0.002 0.0025 0.101 0.0029 1.00 H 0.111 0.57 2.20 0.001 0.029 0.0019 0.690 0.0023 1.26 I 0.211 1.87 1.88 0.001 0.003 0.003 0.030 0.003 1.90 J 0.263 1.70 1.46 0.001 0.003 0.0034 0.850 0.0031 2.55 K 0.303 1.00 2.52 0.001 0.002 0.0024 0.021 0.0031 1.02 L 0.360 2.03 1.78 0.001 0.003 0.0032 0.018 0.0028 2.05 M 0.177 0.62 1.40 0.001 0.003 0.0033 1,700 0.0034 2.32 N 0.140 1.29 2.82 0.001 0.003 0.0033 0.035 0.0022 1.33 0 0.281 1.38 2.20 0.001 0.003 0.0022 0.035 0.0035 1.41 P 0.361 1.11 2.77 0.001 0.003 0.0033 0.032 0.0036 1.14 Q 0.185 1.35 1.82 0.001 0.005 0.0032 0.025 0.0031 1.37 R 0.108 1.60 2.40 0.001 0.002 0.0022 0.033 0.0011 1.63 s 0.171 1.00 2.05 0.001 0.005 0.0029 0.025 0.0031 1.03 T 0.296 1.27 2.44 0.001 0.003 0.0032 0.030 0.0035 1.30 u 0.101 1.01 1.40 0.001 0.002 0.0033 0.003 0.0024 1.01 V 0.320 1.17 2.20 0.001 0.003 0.0021 0.028 0.0036 1.20 w 0.282 0.98 2.26 0.003 0.015 0.0027 0.033 0.0019 1.01 X 0.060 1.31 1.02 0.001 0.015 0.0041 0.018 0.0022 1.33 Y 0.151 1.60 0.88 0.002 0.007 0.0029 0.011 0.0031 1.61 The 0.610 1.05 2.20 0.001 0.003 0.0021 0.035 0.0012 1.09 B 0.177 1.00 4.50 0.020 0.003 0.0041 0.034 0.0015 1.03 ç 0.178 1.27 2.00 0.001 0.003 0.0042 0.033 0.0034 1.30 d 0.165 0.99 2.40 0.001 0.003 0.0035 0.035 0.0026 1.03 and 0.201 1.01 1.00 0.001 0.067 0.0035 0.036 0.0022 1.05 f 0.164 1.10 2.20 0.001 0.003 0.0023 0.033 0.0036 1.13 g 0.290 0.97 1.90 0.001 0.003 0.0044 0.032 0.0035 1.00
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57/71 [Table 2]
STEELN CHEMICAL COMPONENT / MASS% You Nb B Mg REM Here Mo Cr V w Ni Ass Co Sn Zr At THE 0.02 0.02 B Ç - 0.04 D 0.020.0020 - 0.0035 AND - 0.02 F 0.03 0.07 - - 0.0044 - - 0.1 - - - - - - - - G - 0.02 H 0.15 0.03 - - 0.0005 0.0009 - - - 0.05 - - - - - - 1 J K 0.03 L - - 0.0002 - - - - - - - - - - - - - M - - - - - 0.0022 - - 0.15 - - - - - - - N 0 0.05 - - - - - - - 0.20 - - - - - - 0.01 P 0.04 - - 0.006 - - 0.022 - 0.05 - - - - - - - Q - - 0.0002 - - - - - - - - - 0.4 - - - R 0.05 0.01 - 0.004 0.004 - - 0.8 - - - - - - - - s - - - - - - - - - - - - - 0.11 - - T 0.03 - 0.0002 - - - - - - - 1.4 - - - - - u 0.10 - - - - - 0.01 - - - - 1.1 - - - - V - - - 0.004 0.0050.18 - w - - - - - - 0.88 - - - - - - - - - X Y - - - - - - - 1.96 - - - - - - - - The B ç ÇL25 d - O and f - - - 0Ό2 - - - - U o - - - - - - - AND - - - - oj 5
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58/71 [Table 3]
STEEL N ^D T1Zc Ar3/ ° c Agí / ° c Comments THE 865 712 742 Example B 054 684 737 Example G 868 683 735 Example D 869 528 754 Example AND 862 675 730 Example F 886 638 721 Example G 060 675 733 Example H 900 699 716 Example 1 854 718 757 Example J 854 713 757 Example K 865 596 725 Example L 856 654 763 Example M 868 720 726 Example N 854 671 730 Example 0 889 642 743 Example P 877 553 726 Example Q 853 716 743 Example R 877 727 757 Example s 854 695 730 Example T 865 615 710 Example u 877 774 737 Example V 857 615 734 Example w 944 623 727 Example X 851 831 750 Example Y 871 805 793 Example The 863 460 730 Comparative Example B 858 536 704 Comparative Example ç 916 705 739 Comparative Example d 942 674 726 Comparative Example and 852 749 742 Comparative Example f 964 692 731 Comparative Example g 856 642 731 Comparative Example
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59/71 [Table 4]
Production n ° OÇO o < Lamination from 1,000 ° C to 1,200 ^to C Lamination from T1 + 30 ° C to T1 + 200 ° C Number of lamination reduction times of 40% or more í - Lamination reduction ratio of each lamination reduction of 40% or more /% ΦΌIrtD) JSE E O * ãο (Λ -, € 3CÍE rc H Proportion of accumulative lamination reduction /% the ω cs α c n and the EΠ Z Φ Number of lamination reduction times of 30% or more / - Temperature rise between the respective passages! ° C TO 1 THE 2 45/45 80 64 2 2 10 A2 THE 2 45/45 85 69 3 2 5 A3 THE 2 40/40 80 58 2 2 10 A4 THE 2 40/40 80 58 2 2 12 A5 THE 2 40/40 80 51 2 2 15 B1 B 2 45/45 85 66 3 2 10 B2 B 2 45/45 80 64 2 2 15 B3 B 2 40/40 80 51 2 2 13 B4 B 2 40/40 80 51 2 2 13 B5 B 2 40/40 80 64 2 2 13 C1 Ç 2 40/40 80 64 2 2 18 C2 Ç 0 - 250 64 2 2 15 D1 D 1 40 120 50 2 1 9 D2 D 1 50 130 35 1 1 10 E1 AND 2 45/45 90 67 2 2 5 E2 AND 2 45/45 80 64 2 2 8 F1 F 2 45/45 75 62 2 2 13 F2 F 1 50 110 69 3 2 13 F3 F 2 45/45 80 69 3 2 13 G1 G 3 40/40/40 80 71 3 2 8 H1 H 2 45/45 80 71 3 2 10 11 I 2 45/45 75 74 3 2 5 12 I 2 45/45 75 58 2 2 12 13 I 1 50 120 64 2 2 9 14 I 2 45/45 75 64 2 2 5 15 I 2 45/45 75 58 2 2 5 16 I 2 45/45 75 61 2 2 5 17 I 2 45/45 75 61 2 2 5 18 I 2 45/45 75 64 2 2 5 19 I 2 45/45 75 61 2 2 5
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60/71 [Table 5]
Production n ° Lamination reduction ratio before a passage of the final passage of the large lamination reduction passage/%Time spent before the start of the second cooling after completion of the first cooling / C Time spent before the start of the second cooling after completion of the first cooling! s Proportion of accumulative lamination reduction at a temperature equal to or greater than Ar3 ° C and less thanT1 + 30 ° C/% Ϊ- °l · - τ- « X (D iD hi1 TO 1 35 45 100 1.5 0 984 0.13 0.33 0.28 2.13 A2 35 40 80 1.5 10 934 0.87 2.18 1.15 1.32 A3 35 35 60 1.0 0 912 1.59 3.97 1.60 1.01 A4 35 35 60 1.0 0 900 1.93 4.81 2.00 1.04 A5 30 30 65 0.5 0 892 2.29 5.73 2.15 0.94 BI 30 40 120 2.0 0 982 0.14 0.35 0.29 2.02 B2 40 40 80 1.5 0 922 0.88 2.21 1.15 1.30 B3 30 30 60 1.0 5 889 2.08 5.19 1.02 0.49 B4 30 30 60 1.5 0 899 1.82 4.55 0.07 0.04 B5 40 40 60 1.5 0 899 1.47 3.68 0.07 0.05 C1 40 40 100 0.5 0 966 0.37 0.92 0.37 1.01 C2 40 40 30 1.5 0 936 0.88 2.20 1.15 1.31 D1 29 30 100 1.5 0 963 0.83 2.07 0.49 0.59 D2 - 35 100 1.0 0 963 0.60 1.50 0.70 1.16 E1 40 45 30 2.5 40 909 1.22 3.04 1.47 1.21 E2 40 40 80 1.0 0 929 0.88 2.20 1.15 1.31 F1 30 45 120 1.5 15 944 0.95 2.37 1.04 1.09 F2 35 40 120 1.5 0 954 0.88 2.21 6.00 6.78 F3 35 40 100 2.0 0 954 0.88 2.21 2.01 2.27 G1 40 40 100 1.0 0 958 0.36 0.91 0.37 1.01 H1 40 40 100 2.0 20 959 1.10 2.75 1.21 1.10 11 40 45 100 1.0 0 952 0.24 0.60 0.49 2.04 12 30 40 80 1.5 0 922 0.88 2.20 1.15 1.31 13 40 40 100 1.0 0 911 1.14 2.84 2.00 1.76 14 40 40 100 1.0 0 933 0.49 1.22 0.97 1.98 15 40 30 100 1.0 0 920 0.75 1.86 1.20 1.61 16 40 35 100 1.0 0 980 0.13 0.34 0.29 2.16 17 40 35 100 1.0 0 951 0.25 0.62 0.33 1.33 18 40 40 100 1.0 0 890 1.60 3.99 1.50 0.94 19 40 35 100 1.0 0 920 0.75 1.86 1.41 1.89
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61/71 [Table 6]
Production n ° Steel No. Lamination from 1,000 ³ C to 1,200 ° C Lamination from T1 + 3D ° C to T1 + 2DD ° C Number of lamination reduction times of 40% or more / - Lamination reduction ratio of each lamination reduction of 40% or more /% u0ilEo c p * 3 3.0 «-Π5ANDH 4>U CCO --3 3£S “t O £L £C cl E2 roCL sH CO 01 c N '= 41 E> COE = g _u re «re c re H = C α> E ~> re zi ® _ω θ γ -D _C A 2 O oi ci CO <L> £ □ 73 2 · ° Z φ »cscl E gThe Φits re o,SixQj £ ΪANDΦ+ J J1 J 3 40/40/40 85 85 2 2 12 J2 J 2 45/45 75 58 2 2 15 Kl K 3 40/40/40 50 68 2 2 14 K2 K 3 40/40/40 50 71 3 2 15 L1 L 2 45/45 80 67 3 1 13 L2 L 2 45/45 80 66 3 2 18 M1 M 1 50 150 55 2 1 10 M2 M 1 50 150 52 2 1 10 NI N 2 45/45 75 58 2 1 5 N2 N 1 50 130 54 3 2 15 N3 N 2 45/45 70 72 3 2 25 01 0 2 45/45 80 52 2 1 10 02 0 1 40 120 25 1 0 15 PI P 2 45/45 75 64 2 2 10 Q1 Q 2 45/45 80 69 3 2 12 R1 R 2 45/45 75 71 3 2 12 S1 s 2 45/45 80 69 3 2 13 S2 s 2 45/45 75 64 2 2 8 T1 T 2 40/40 80 67 2 2 9 T2 T 2 45/45 85 64 2 2 6 UI u 2 45/45 75 67 2 2 5 V1 V 2 45/45 85 71 3 2 12 W1 w 1 50 130 50 1 1 13 X1 X 2 40/50 80 54 2 2 15 X2 X 2 45/50 75 63 2 2 16 Y1 Y 2 45/40 70 51 2 2 13 Y2 Y 2 40/40 85 64 2 2 16 to 1 The 2 45/45 75 76 3 2 16 b1 B 1 50 120 67 2 2 15 d ç 2 45/45 75 67 2 2 18 dl d 2 45/45 75 64 2 2 18 e1 and 2 45/45 80 51 2 1 15 f1 f 2 45/45 80 61 3 2 12 2 45/45 75 51 2 1 10
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62/71 [Table 7]
Production n ° Lamination reduction ratio before a passage of the final passage of the large lamination reduction passageΦ * ff Φ 'Φ 2 £ 2, E © * OEO' Ϊ È. «Ε φ 2 ® £ EU c ^Ό te *« w ο Έ oo ^w H s_ tf w K „- <U ®-σ υ σ 'Ε E Φ 3 C £ L σι O p ^Ό α« 1- Time spent before the start of the second cooling after completion of the first cooling/ s Proportion of accumulative lamination reduction at a temperature equal to or greater than Ar3 ° C and less than T1 + 30 ° C/% 1- 'r- (Λ+ J —l. 2.5 x t 1/ s M-ι (Λ J1 30 50 50 1.0 0 962 0.13 0.33 0.30 2.34 J2 30 40 60 1.5 0 922 0.88 2.20 1.46 1.66 Kl 35 50 100 1.5 0 961 0.17 0.43 0.42 2.44 K2 35 45 100 1.5 0 923 0.93 2.32 0.98 1.06 LI 25 45 120 1.0 0 953 0.25 0.62 0.37 1.49 L2 30 40 100 1.0 0 923 0.90 2.24 0.66 0.74 M1 25 40 120 1.5 10 966 0.36 0.89 0.49 1.38 M2 20 40 80 1.0 0 966 0.36 0.89 0.25 0.70 NI 30 40 80 1.0 0 952 0.37 0.92 0.49 1.34 N2 30 30 70 1.5 25 930 1.14 2.84 2.01 1.77 N3 40 40 90 2.5 10 899 1.46 3.66 1.33 0.91 01 20 40 100 1.0 0 985 0.38 0.96 0.37 0.97 02 - 25 100 1.5 10 955 1.57 3.91 1.15 0.74 PI 45 35 20 1.0 0 973 0.58 1.44 0.49 0.85 Q1 35 40 100 1.0 0 952 0.36 0.91 0.37 1.02 R1 40 40 100 1.0 0 985 0.26 0.64 0.39 1.52 S1 35 40 80 1.0 0 992 0.13 0.33 0.28 2.16 S2 40 40 80 1.5 0 922 0.87 2.18 0.81 0.93 T1 45 40 100 1.0 15 961 0.39 0.96 0.37 0.96 T2 40 40 100 1.5 0 931 0.91 2.28 0.98 1.07 U1 45 40 80 1.0 10 976 0.36 0.89 0.49 1.38 V1 40 40 80 1.5 0 953 0.39 0.96 0.49 1.27 W1 - 50 80 2.0 10 1051 0.13 0.33 0.32 2.44 X1 30 30 50 2.0 5 961 0.59 1.47 0.31 0.53 X2 30 40 120 1.5 10 890 1.63 4.08 2.00 1.23 Y1 30 30 80 2.0 25 920 1.71 4.28 2.10 1.23 Y2 40 40 40 1.5 10 883 2.60 6.50 0.26 0.10 to 1 45 45 100 1.0 0 960 0.25 0.64 0.37 1.45 b1 40 45 100 1.0 0 954 0.26 0.65 0.49 1.88 cl 40 45 100 1.5 0 994 0.51 1.26 0.79 1.56 dl 40 40 100 2.0 0 999 1.12 2.79 1.21 1.08 e1 25 35 100 1.0 0 951 0.53 1.31 0.49 0.93 f1 30 30 100 2.0 0 1012 1.75 4.37 1.21 0.69 and! 25 35 100 1.5 0 953 0.55 1.37 0.49 0.89
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63/71 [Table 8]
Production n ° Winding temperaturel ° C Cold rolling reduction ratio /% T- ^W Qí O I t. healthyI t.Annealing temperaturerc Retention time during annealing1 sec TO 1 500 45 2.0 0.9 742 790 60 A2 500 45 1.5 0.7 742 660 60 A3 550 55 2.0 0.8 742 830 60 A4 500 65 2.5 1.2 742 820 50 A5 550 58 0.9742 800 90 B1 500 45 2.5 1.0 737 850 30 B2 500 45 2.7 1.1 737 850 90 B3 400 35 1.3 0.5 737 800 50 B4 450 45 1.1 0.5 737 830 100 B5 500 92 2.2 1.0 737 850 100 C1 600 50 2.5 1.0 735 800 30 C2 600 50 3.0 1.2 735 800 30 D1 600 40 2.1 1.0 754 820 40 D2 600 40 2.1 0.8 754 820 40 E1 600 50 1.8 0.6 730 750 40 E2 600 50 1.6 0.7 730 750 40 F1 500 40 2.3 1.1 721 830 90 F2 500 40 1.5 0.6 721 830 90 F3 680 40 2.1 1.0 721 820 60 G1 600 55 2.0 1.0 733 760 30 H1 500 45 2.0 0.8 716 850 90 11 600 50 1.5 0.7 757 780 30 12 600 50 1.7 0.8 757 780 90 13 600 55 0.2 0.4 757 780 30 14 600 45 2.5 1.2 757 950 30 15 600 50 1.4 0.5 757 820 400 16 600 53 1.5 0.6 757 800 0.5 17 600 58 1.3 0.6 757 850 40 18 600 60 1.4 0.7 757 850 10 19 600 50 0.8 0.4 757 780 60
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64/71 [Table 9]
Production n ° Third cooling Cooling room Fifth cooling g °Retention time/ s Average cooling rate / ° C / s Cooling end temperature / ° C Average cooling rate / ° C / s Cooling end temperature / ° C Average cooling rate rc / s Cooling end temperature / ° C TO 1 3 650 10 360 - - 360 106 350 A2 2 610 10 350 - - 350 202 250 A3 2 700 30 380 - - 380 38 19 A4 2.5 650 30 330 - - 330 966 250 A5 10 650 12 400 - - 400 20 200 B1 5 740 20 350 - - 350 202 350 B2 3 650 60 350 - - 350 202 350 B3 1.5 750 60 - 60 200 400 20 150 B4 2 680 110 - 80 150 350 202 250 B5 2 650 50 430 - - 430 15 200 C1 3 730 70 430 - - 430 15 350 C2 3 730 60 430 - - 430 15 350 D1 2 750 50 370 - - 370 61 400 D2 1.5 780 10 370 - - 370 61 400 E1 2 700 60 430 - - 430 15 350 E2 6 580 10 430 - - 430 15 300 F1 1.5 730 60 380 - - 380 38 250 F2 2 700 50 380 - - 380 38 250 F3 3 650 40 440 - - 440 17 100 G1 7 600 10 410 - - 410 17 100 H1 2 710 70 400 - - 400 20 375 11 4 700 50 480 - - 480 61 150 12 2 650 10 560 - - 560 - 350 13 4 650 50 420 - - 420 15 100 14 2 650 50 400 - - 400 20 250 15 2 700 50 430 - - 430 15 200 16 3 680 50 420 - - 420 15 150 17 0.5 780 50 380 - - 380 38 100 18 1 810 50 420 - - 420 15 30 19 2 700 2 450 - - 450 20 100
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65/71 [Table 10]
Production n ° Winding temperature/ ° C 0 »σOOOU __ztC - ϊ ε oQ.OCL T- ^ω Oí Õ IL, SgT the °<L. Annealing temperature/ ° C Retention time during annealing / sec J1 600 50 1.5 0.6 757 780 30 J2 600 50 1.3 0.6 757 780 90 K1 550 40 1.9 0.9 725 855 30 K2 600 45 1.8 0.6 725 800 90 L1 600 45 2.0 1.0 763 800 30 L2 600 45 2.3 1.0 763 800 30 M1 500 50 2.1 1.0 726 040 60 M2 500 2Ü 1.6 0.7 726 840 60 N1 550 40 1.1 0.5 730 870 100 N2 500 50 1.5 0.7 730 800 20 N3 550 50 1.2 0.5 730 790 60 01 600 40 1.2 0.6 743 000 30 02 600 40 1.2 0.5 743 000 30 P1 600 40 1.3 0.4 726 300 40 Q1 600 50 1.5 0.5 743 810 40 IR 500 40 1.7 0.8 757 830 90 SI 550 55 1.0 0.4 730 780 60 S2 550 45 0.6 0.2 730 780 60 YOU 500 50 3.0 1.4 710 900 200 T2 500 50 2.5 1.2 710 870 20 U1 500 45 2.1 1.0 737 850 30 SAW 600 50 2.0 1.0 734 860 40 W1 550 40 1.8 0.8 727 300 40 XI 500 80 1.6 0.7 750 780 50 X2 500 60 1.6 0.7 750 020 50 Y1 450 60 2.0 1.0 793 850 60 Y2 550 60 1.4 0.6 793 830 60 al 600 45 1.3 0.5 730 820 30 bl 600 45 1.0 0.4 704 820 30 c1 600 45 1.3 0.6 739 020 30 d1 600 45 1.2 0.4 726 020 30 e1 600 50 1.3 0.5 742 820 30 f1 600 40 1.1 0.5 731 820 30 Hey 600 55 1.6 0.7 731 820 30
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66/71 [Table 11]
Production n “ Third cooling Cooling room Fifth coolingJ-F Retention time1 sec Kings cooling rate Cooling end temperature/ ° C Kings cooling rate Rc cooling end temperature Kings cooling rate Cooling end temperature/ ° C J1 2 730 10 490 - - 490 106 200 J2 1 710 40 490 - - 490 106 250 K1 4 760 10 350 - - 350 202 350 K2 2.5 630 10 480 - - 480 61 300 L1 4 710 10 480 - - 480 61 300 L2 4 710 40 480 - - 480 61 400 M1 2.5 720 60 380 - - 380 38 250 M2 3 710 50 380 - - 380 38 300 N1 2 720 70 405 - - 405 18 250 N2 23 570 20 400 - - 400 20 50 N3 3 680 40 390 - - 390 27 150 01 4 710 50 350 - - 350 202 250 02 4 710 60 350 - - 350 202 15Q P1 2 740 15 300 - - 3PQ - 350 Q1 4 700 60 430 - - 430 15 350 IR 2 690 50 430 - - 430 15 350 S1 2 680 10 400 - - 400 20 400 S2 2.5 670 40 400 - - 400 20 400 YOU 1 750 50 430 - - 430 15 400 T2 15 670 30 430 - - 430 15 400 U1 6 710 70 430 - - 430 15 400 SAW 6 690 60 400 - - 400 20 400 W1 4 680 60 430 - - 430 15 400 X1 3.5 650 20 - 20 300 380 38 200 X2 3 700 40 380 - - 380 38 150 Y1 5 600 20 410 - - 410 17 150 Y2 4 650 40 - 40 250 420 15 40 to 1 5 710 60 430 - - 430 15 350 bl 4 730 50 430 - - 430 15 350 d 6 690 50 430 - - 430 15 350 d1 4 700 40 430 - - 430 15 350 el 5 700 40 430 - - 430 15 350 f1 5 710 50 430 - - 430 15 350 gl 4 720 30 430 - - 430 15 350
Petition 870180072452, of 17/08/2018, p. 69/86
67/71 [Table 12]
Production n ° Ξ Ί CMQ - u. B/% γ Residual/%O. s t-M /% HVb / - ò-e _l O TO 1 2.6 2.5 31 48 11 4 6 0 309 1.1 0.83 0.84 A2 6.6 3.0 81 9 3 5 2 0 238 0.6 0.80 0.81 A3 2.3 1.9 36 3 4 53 4 0 249 0.7 0.88 0.89 A4 2.9 2.3 35 4 3 55 3 0 255 0.6 0.91 0.98 A5 6.9 5.2 59 19 4 10 8 0 255 0.6 1.19 1.13 B1 2.1 2.6 25 45 13 7 10 0 311 1.2 0.84 0.85 B2 2.2 3.0 22 46 12 10 10 0 278 1.1 0.79 0.81 B3 1.5 2.4 30 11 15 2 2 40 244 1.3 0.91 0.89 B4 1.9 2.7 17 10 10 3 3 57 271 1.3 1.01 0.99 B5 6.7 5.9 32 48 12 7 1 0 258 1.3 1.21 1.19 Cl 3.0 2.5 37 42 16 0 5 0 250 1.3 0.78 0.80 C2 6.6 3.5 30 41 5 19 3 2 244 1.6 0.40 0.40 D1 3.1 3.8 22 51 6 17 4 0 291 1.1 0.83 0.84 D2 aa aa 20 65 3 1 10 1 303 0.7 0.84 0.85 El 6.7 7.1 29 55 12 0 4 0 240 1.4 0.73 0.75 E2 3.6 2.5 60 13 17 5 5 0 261 1.7 0.79 0.81 F1 3.2 4.0 20 55 9 6 10 0 249 1.3 0.72 0.75 F2 1.1 1.2 24 57 10 9 0 0 244 0.8 1.17 1.11 F3 6.6 4.6 33 48 10 9 0 0 261 0.8 0.93 0.89 G1 3.4 2.0 49 33 16 2 0 0 263 1.3 0.78 0.80 H1 3.1 3.6 25 43 11 11 10 0 221 1.3 0.72 0.76 11 3.5 2.8 30 33 17 16 4 0 211 1.6 0.74 0.77 12 3.2 2.5 36 12 1 29 22 0 144 0.8 0.78 0.80 13 6.8 5.1 42 33 12 13 0 0 241 1.2 1.22 1.19 14 2.6 2.1 5 79 12 4 0 0 250 1.6 1.19 1.11 15 3.0 2.5 30 33 17 16 4 0 238 1.6 1.12 1.11 16 2.2 1.8 87 4 3 4 2 0 244 1.6 0.91 0.88 17 2.8 2.6 4 81 11 1 3 0 271 1.6 0.87 0.87 18 2.4 2.3 3 85 9 3 0 0 243 1.6 0.92 0.91 19 3.5 2.8 41 11 1 16 31 0 251 1.6 0.93 0.90
Petition 870180072452, of 17/08/2018, p. 70/86
68/71 [Table 13]
Production n ° r30/ - r60/ - Proportion of coarse grain area /% Average volume diameter / um Equiaxial grain fraction/% CD EL /% í* 5* £ Comments TO 1 0.85 0.88 2.5 3.3 29 785 24 72 19000 56888 Example A2 0.90 0.92 10.5 11.2 73 320 34 91 10880 29234 Comparative Example A3 0.83 0.81 9.2 10.0 60 1115 9 24 10035 27119 Comparative Example A4 0.85 0.84 8.9 6.9 65 1199 8 22 9592 26077 Comparative Example A5 0.69 0.71 9.8 8.1 41 591 27 41 15957 24231 Comparative Example B1 0.86 0.89 2.6 Ó.4 29 788 24 78 19000 61512 Example B2 0.90 0.92 10.5 11.2 73 778 24 75 19000 58459 Example B3 0.85 0.86 9.3 10.0 66 1091 21 53 2291 1 57823 Example B4 0.91 0.88 0.6 3.1 19 1233 17 49 20961 60417 Example B5 0.85 0.79 0.6 2.8 7 955 16 19 15280 18145 Comparative Example C1 0.91 0.93 3.4 4.1 34 598 28 92 17000 55089 Example G2 1.26 1.15 10.5 11.2 73 598 22 48 13412 28919 Comparative Example D1 0.99 0.99 4.5 5.2 40 1216 14 30 17000 36221 Example D2 0.95 0.96 6.4 7.1 50 1211 8 6 9732 7268 Comparative Example E1 1.01 1.01 13.4 14.0 89 585 29 38 17000 22321 Comparative Example E2 0.90 0.92 10.5 11.2 73 588 29 90 17000 53121 Example F1 0.97 0.98 9.4 10.1 67 1198 14 40 17000 47420 Example F2 0.89 0.91 41.0 16.1 91 1100 15 27 16500 29714 Comparative Example F3 0.66 0.69 13.0 5.8 79 1001 13 15 13013 15015 Comparative Example G1 0.91 0.93 3.4 4.1 34 594 29 90 17000 53627 Example H1 0.97 0.98 11.0 11.7 76 844 20 62 17000 52621 Example 11 0.94 0.95 4.5 5.2 40 593 37 90 22000 53484 Example 12 0.90 0.92 10.5 11.2 73 583 38 29 22000 16912 Comparative Example 13 0.99 0.91 4.5 7.4 40 709 18 31 12762 21979 Comparative Example 14 0.94 0.95 38.0 16.4 31 889 14 22 12446 19558 Comparative Example 15 0.90 0.92 30.3 15.3 33 711 19 23 13509 16353 Comparative Example 16 0.81 0.81 10.1 7.3 55 288 36 71 10368 20448 Comparative Example 17 0.83 0.88 8.1 6.3 56 1081 11 34 11891 36754 Comparative Example 18 0.83 0.84 2.1 4.1 63 1121 9 39 10089 43719 Comparative Example 19 0.83 0.88 7.3 7.4 73 661 13 31 8593 20491 Comparative Example
Petition 870180072452, of 17/08/2018, p. 71/86
69/71 [Table 14]
Production n ° Q Ί <NQ - '-S LLγ Residual/% M/% Q. c ’ t-M/% HVb/ - Hi _ |L. O ¹ L. J1 2.9 2.2 34 29 14 19 4 0 188 1.5 0.82 0.83 J2 3.2 2.5 34 41 5 15 5 0 200 1.0 0.78 0.80 K1 2.7 3.8 24 51 9 11 5 0 290 1.0 0.76 0.79 K2 3.5 3.5 35 40 10 12 3 0 212 1.3 0.73 0.76 L1 3.0 3.0 30 47 11 4 8 0 180 1.6 0.78 0.80 L2 3.4 3.4 32 39 14 6 9 0 192 1.5 0.74 0.77 M1 2.9 2.8 26 38 22 4 10 0 267 1.5 0.89 0.89 M2 6.9 5.3 26 42 16 7 9 0 240 1.4 0.93 0.92 N1 2.6 3.8 11 68 18 1 2 0 229 1.8 0.74 0.77 N2 2.2 1.9 37 24 4 6 29 0 260 0.8 0.88 0.87 N3 3.1 2.9 41 34 11 6 8 0 266 1.1 1.09 1.05 01 3.0 3.5 30 48 9 9 4 0 325 1.3 0.78 0.80 02 ÊJ. 5J5 44 4 7 43 2 0 340 1.1 0.58 0.58 P1 3.3 3.8 11 6 1 11 7 64 330 0.5 0.74 0.77 Q1 2.9 2.5 31 46 17 2 4 0 266 1.6 0.78 0.80 R1 2.8 3.6 27 40 9 16 8 0 239 1.2 0.76 0.79 S1 2.8 2.6 33 33 21 4 9 0 236 2.1 0.83 0.84 S2 3.7 3.5 40 39 17 0 4 0 250 1.6 0.72 0.76 T1 2.3 2.5 7 73 13 1 6 0 251 1.5 0.78 0.80 T2 2.8 3.0 10 62 21 0 7 0 240 1.9 0.73 0.76 U1 2.8 3.3 21 63 12 2 2 0 244 1.3 0.74 0.77 V1 2.7 2.8 15 59 15 4 7 0 231 1.6 0.76 0.79 W1 3.6 3.2 23 51 5 20 1 0 262 1.0 0.79 0.81 X1 4.0 4.0 41 21 15 0 4 19 253 1.3 0.88 0.85 X2 2.1 2.3 25 55 14 2 4 0 249 1.1 0.89 0.91 Y1 1.8 1.4 35 41 9 10 5 0 253 1.1 0.87 0.87 Y2 5.1 4.5 37 10 13 3 2 35 241 1.2 0.97 0.99 to 1 2.8 3.0 22 51 5 21 1 0 249 0.7 0.77 0.79 b1 4.0 3.9 22 42 12 23 1 0 244 0.7 0.53 0.64 d 8.3 9.5 30 51 9 4 6 0 261 1.3 0.42 0.56 d1 8.4 9.6 27 48 8 8 9 0 283 1.1 0.41 0.55 e1 3.1 2.8 30 41 7 21 1 0 240 1.2 0.75 0.78 f1 6.6 8.1 27 41 6 22 4 0 261 1.1 0.42 0.56 ê1 3.1 2.3 24 48 13 7 8 0 250 1.5 0.74 0.77
Petition 870180072452, of 17/08/2018, p. 72/86
70/71 [Table 15]
Production n ° o, ÍO. The r <X> Proportion of coarse grain area /% Oεξ poE h> ZL□ □The 3,73 ra Yes o * - *íkí σ The CDANDL_ fú £ 1LU - λ/% -i - £ Comments J1 D.B8 0.91 2.8 3.5 30 608 36 92 22000 55638 Example 42 0.90 0.92 13.2 13.9 88 603 36 91 22000 54683 Example Kl 0.95 0.96 4.5 5.2 40 1194 16 29 19000 35112 Example K2 0.99 0.99 8.9 9.6 64 1194 16 28 19000 33412 Example L1 0.91 0.93 3.4 4.1 34 795 28 68 22000 54439 Example L2 0.95 0.96 6.0 6.7 48 785 28 67 22000 52920 Example Ml 1.00 1.00 4.5 5.2 40 592 29 94 17000 55626 Example M2 0.95 0.97 17.1 13.4 17 592 22 49 13032 29027 EsemploComparaüvo NI 092 0.94 4.5 5.2 40 974 17 51 17000 49242 Example N2 0.81 0.79 5.9 7.4 41 901 14 33 12614 29335 EsempioComparaüvo N3 0.79 0.81 15.0 13.0 51 011 19 39 15409 31629 Example 01 0.89 0.91 3.4 1.1 34 874 19 59 17000 51554 Example 02 1JB 1.31 10.5 11.2 73 984 I4 13 13998 12389 And without peep Comparative · PI 0.94 0.95 4.5 5.2 40 1483 6 33 8899 49554 And without comparative peep qi 0.91 0.93 3.4 4.1 34 600 32 93 19000 55527 Example IR 0.92 0.93 3.5 4.3 35 1110 15 43 17000 47316 Example SI 0.86 0.89 2.6 3.3 29 594 32 94 19000 56102 Example Ξ2 0.96 0.96 7.4 8.1 55 590 32 89 19000 52836 Example YOU 0.92 0.94 3.4 4.1 34 1004 19 49 19000 49585 Example T2 0.98 0.98 8.9 9.6 64 989 19 47 19000 46071 Example 111 0.94 0.95 4.5 5.2 40 665 26 86 17000 57158 Example SAW 0.94 0.95 4.5 5.2 40 756 22 76 17000 57346 Example W1 1.05 1.04 14.7 11.6 96 1459 12 32 17000 46227 Example XI 0.71 0.70 2.8 16 31 901 27 53 24327 47753 Example X2 0.85 0.83 18.2 12.2 95 1021 24 57 24504 58197 Example Yl 0.83 0.84 16.9 13.4 91 1051 24 58 25224 60958 Example Y2 0.85 0.81 3.0 3.5 38 1190 18 34 21420 40460 Example to 1 0.96 0.97 4.0 11.2 38 893 14 13 12537 11496 And without comparative peep bl U7 1.23 5.3 10.0 29 1091 5 14 5455 15099 And without comparative peep cl 1.20 1.22 8.5 7.1 33 893 15 29 13429 25708 Comparative Esempio dl1.21 12.9 10.1 49 1058 8 23 8539 24749 Comparative Esempio e1 0.91 0.93 5.4 11.7 39 722 14 25 10108 17849 And without comparative peep fl 1.13 1.29 13.5 3.5 80 1079 13 9 13763 9192 Comparative Esempio0.90 0.92 5.1 9.6 43 688 20 25 13768 17210 And without peep Comparative ·
[00178] Previously, preferred examples of the present invention have been described, but the present invention is not limited to the examples. Addition, omission, substitution and other configuration changes can be made within a range without departing from the essence of the present invention. The present invention is not limited
Petition 870180072452, of 17/08/2018, p. 73/86
71/71 by the description described above, and is limited only by the appended claims.
Industrial Applicability [00179] Regarding TRIP steel, a cold rolled high strength steel plate that is excellent in ductility and orifice expansion, and a method of producing it are provided.
Petition 870180072452, of 17/08/2018, p. 74/86
1/8

权利要求:
Claims (13)
[1]
1. Cold rolled steel sheet, characterized by the fact that it comprises a chemical composition of the steel sheet consisting of,% by mass,
C: 0.02% to 0.4%;
Si: 0.001% to 2.5%;
Mn: 0.001% to 4.0%;
Al: 0.001% to 2.0%;
P: limited to 0.15% or less;
S: limited to 0.03% or less;
N: limited to 0.01% or less;
O: limited to 0.01% or less;
optionally one or more selected from the group consisting of
Ti: 0.001% to 0.2%;
Nb: 0.005% to 0.2%;
B: 0.0001% to 0.005%;
Mg: 0.0001% to 0.01%;
REM: 0.0001% to 0.1%;
Ca: 0.0001% to 0.01%;
Mo: 0.001% to 1.0%;
Cr: 0.001% to 2.0%;
V: 0.001% to 1.0%;
W: 0.001% to 1.0%;
Ni: 0.001% to 2.0%;
Cu: 0.001% to 2.0%;
Co: 0.0001% to 1.0%;
Sn: 0.0001% to 0.2%;
Zr: 0.0001% to 0.2%; and
As: 0.0001% to 0.5%; and
Petition 870180072452, of 17/08/2018, p. 75/86
[2]
2/8 the equilibrium consisting of Fe and unavoidable impurities, where a sum of the Si content and the Al content is 1.0% to 4.5% in the chemical composition of the steel sheet, an average pole density of one orientation group from {100} <011> to {223} <110>, which is a pole density expressed by an arithmetic mean of pole densities of the respective crystal orientations {100} <011>, {116} <110 >, {114} <110>, {112} <110>, and {223} <110>, is 1.0 to 6.5, and a pole density of a {332} <113> crystal orientation is 1.0 to 5.0 in a central portion of the plate thickness within a range of 5/8 to 3/8 of a plate thickness, a microstructure of the steel plate includes grains, the microstructure of the steel plate consists of , by an area ratio, 5% to 80% ferrite, 5% to 80% bainite, and 2% to 30% retained austenite, in the microstructure, martensite is limited to 20% or less, pearlite is limited to 10 % or less, and tempered martensite is limited to 60% or less, where rC, which is a Lankford value in one the direction orthogonal to a rolling direction is 0.70 to 1.10, and r30, which is a Lankford value in one direction forming an angle of 30 ° with the rolling direction, is 0.70 to 1 , 10, rL, which is the Lankford value in the rolling direction, is 0.70 to 1.10, and r60, which is a Lankford value in one direction forming an angle of 60 ° with the rolling direction, is 0.70 to 1.10, and where a Vickers hardness of bainite is 180 HV or more, and an average concentration of C in the retained austenite is 0.9% or more.
2. Cold-rolled steel sheet according to claim 1, characterized by the fact that the average grain volume diameter is 2 μιη to 15 μιη.
[3]
3. Cold rolled steel sheet according to claim
Petition 870180072452, of 17/08/2018, p. 76/86
3/8 cation 1, characterized by the fact that the average pole density of the orientation group from {100} <011> to {223} <110> is 1.0 to 5.0, and the density of the crystal orientation {332} <113> is 1.0 to 4.0.
[4]
4. Cold rolled steel sheet according to claim 1, characterized by the fact that among the grains, a proportion of grain area that exceeds 35 pm in an equivalent circle diameter is limited to 10% or less.
[5]
5. Cold rolled steel sheet, according to claim 1, characterized by the fact that among the grains, a proportion of grains, in which a value obtained by dividing a length of a grain in the rolling direction by the length of a grain in a sheet thickness direction is 3.0 or less, it is 50% to 100%.
[6]
6. Cold rolled steel sheet according to claim 1, characterized by the fact that a hot dip galvanized layer or an annealed layer after galvanizing is provided on a surface of the steel sheet.
[7]
7. Production method of cold rolled steel sheet, the production method characterized by the fact that it comprises:
a first hot rolling process to perform a hot rolling with respect to a steel, in order to adjust an average austenite grain size of the steel by 200 pm or less, wherein the first hot rolling process includes at least a lamination reduction pass with a lamination reduction ratio of 40% or more over a temperature range of 1,000 ° Ca 1,200 ° C, and the chemical composition of the steel consisting of,% by mass,
C: 0.02% to 0.4%;
Si: 0.001% to 2.5%;
Petition 870180072452, of 17/08/2018, p. 77/86
4/8
Μη: 0.001% to 4.0%;
Al: 0.001% to 2.0%;
P: limited to 0.15% or less;
S: limited to 0.03% or less;
N: limited to 0.01% or less;
O: limited to 0.01% or less;
optionally one or more selected from the group consisting of
Ti: 0.001% to 0.2%,
Nb: 0.005% to 0.2%,
B: 0.0001% to 0.005%,
Mg: 0.0001% to 0.01%,
REM: 0.0001% to 0.1%,
Ca: 0.0001% to 0.01%,
Mo: 0.001% to 1.0%
Cr: 0.001% to 2.0%,
V: 0.001% to 1.0%,
W: 0.001% to 1.0%,
Ni: 0.001% to 2.0%,
Cu: 0.001% to 2.0%,
Co: 0.0001% to 1.0%,
Sn: 0.0001% to 0.2%,
Zr: 0.0001% to 0.2%, and
As: 0.0001% to 0.5%, and the balance consisting of Fe and unavoidable impurities, and in which a sum of Si and Al content is 1.0% to 4.5%;
a second hot rolling process to perform a hot rolling with respect to steel, wherein the hot rolling process includes, wherein the second hot rolling is
Petition 870180072452, of 17/08/2018, p. 78/86
5/8 a finishing lamination, a large lamination reduction pass with a lamination reduction ratio of 30% or more in a temperature range from T1 + 30 ° C to T1 + 200 ° C when a temperature calculated by Expression 1 below is set to T1 ° C, a cumulative lamination reduction ratio in the temperature range from T1 + 30 ° C to T1 + 200 ° C is 50% to 90%, where a final pass is the large pass of lamination reduction, an optional cumulative lamination reduction ratio after performing the first cooling in a temperature range where it is greater than or equal to Ar3 ° C calculated by Expression 4 below and less than T1 + 30 ° C is limited to 30% or less, and a rolling finish temperature is Ar3 ° C calculated by Expression 4 below or more;
a first cooling process to perform a cooling with respect to the steel, so that a waiting time t second, which is adjusted as a moment from the conclusion of the final passage between the passages of great reduction of rolling to an beginning of cooling, satisfies Expression 2 below, where an average cooling rate in the first cooling is 50 "C / s to 200" C / s, a variation of the cooling temperature, which is a difference between a steel temperature at the moment from the beginning of the cooling and a temperature of the steel at the time of the end of the cooling, is 40 ° C to 140 ° C, in the first cooling, and the temperature of the steel at the time of the end of the cooling is T1 + 100 ° C or less;
a second cooling process to perform a cooling with respect to the steel, in which the second cooling is started within 10 seconds after the steel is passed through a final rolling support and after the end of the first cooling;
a winding process to perform a winding
Petition 870180072452, of 17/08/2018, p. 79/86
6/8 with respect to steel in a temperature range of 350Ό to 650 ° C;
a pickling process to carry out a pickling with respect to steel;
a cold rolling process to perform cold rolling with respect to steel in a rolling reduction ratio of 30% to 90%;
a two-stage heating process to perform a two-stage heating with respect to steel, in which an average heating rate HR1 in a temperature range from ambient temperature to 650 ° C is 0.3 ° C / s ΣΟΟΌ / β, and an average heating rate HR2 over a temperature range from more than 650 ° C to Aci ° C, when Aci is calculated by Expression 5 below, is 0.5 x HR1 or less, in the unit ° C / s;
a retention process to carry out the retention with respect to the steel within a temperature range of Aci ° C to 900 ° C for 1 second to 300 seconds;
a cooling process to perform cooling with respect to steel up to a temperature range of 580 ° C to 780 ° C at an average cooling rate of 1 ° C / s to 20 ° C / s;
a cooling process to perform cooling with respect to steel to a temperature Toa, which is within a temperature range of 350 ° C to 500 ° C, at an average cooling rate of 5 ° C / s to 200 ° C / s; and a retention process to carry out a retention with respect to the steel in order to obtain a steel plate, in which the steel is retained within the temperature range of 350 ° C to 500 ° C for a time of toA seconds or more, which is calculated by Expression 6 below, the
1000 seconds or less, or a cooling and retention process to perform a cooling and retention with respect to steel in order to obtain a plate
Petition 870180072452, of 17/08/2018, p. 80/86
7/8 steel, where the steel is further cooled to a temperature of 350 ° C or less, then the steel is reheated to a temperature range of 350 ° C to 500 ° C, and the steel is retained within the range of temperature from 350 ° C to 500 ° C for a time of 10 seconds or more, which is calculated by Expression 6 below, at 1000 seconds or less, where,
T1 = 850 + 10 x ([C] + [N]) x [Mn] ... (Expression 1) where [C], [N], and [Mn] represent mass percentages of the C, content of N, and of the content of Mn in steel, respectively, where the temperature calculated by Expression 7 below in place of the temperature calculated by Expression 1 is adjusted as T1 ° C,
T1 = 850 + 10 x ([C] + [N]) x [Mn] + 350 x [Nb] + 250 x [Ti] +
40 x [B] + 10 x [Cr] + 100 x [Mo] + 100 x [V] ... (Expression 7) where, [C], [N], [Mn], [Nb], [ Ti], [B], [Cr], [Mo], and [V] represent mass percentages of C, N, Mn, Nb, Ti, B, Cr, Mo, and V, respectively, t <2.5 x t1 ... (Expression 2) here, t1 is expressed by Expression 3 below, t1 = 0.001 x ((Tf - T1) x P1 / 100) ² - 0.109 x ((Tf - T1) x P1 / 100) + 3.1 ... (Expression 3) here, Tf represents a temperature in Celsius of the steel at the time of completion of the final pass, and P1 represents a percentage of the rolling reduction ratio during the final pass,
Ar ₃ = 879.4 - 516.1 x [C] - 65.7 x [Mn] + 38.0 x [Si] + 274.7 x [P] ... (Expression 4)
Aci = 723 - 10.7 x [Mn] - 16.9 x [Ni] + 29.1 x [Si] + 16.9 x
Petition 870180072452, of 17/08/2018, p. 81/86
[8]
8/8 [Cr] + 290 x [ T ] + 6.38 x [W] ... (Expression 5) [Mathematical Expression 1] * ΟΑ |. Θ0 (Χ> 02 _{(Τ ΟΑ} -425) ^+1.18
... (Expression 6).
8. Method of producing a cold-rolled steel sheet according to claim 7, characterized by the fact that the waiting time t second satisfies Expression 8 below using t1
0 <t <t1 ... (Expression 8).
[9]
9. Method of producing a cold-rolled steel sheet, according to claim 7, characterized by the fact that the waiting time t second satisfies Expression 9 below using t1 t1 <t <2.5 x t1. .. (Expression 9).
[10]
10. Method of producing a cold rolled steel sheet according to claim 7, characterized by the fact that the first hot rolling includes a passage that has a rolling reduction ratio of 40% or more at least two or more times, in order to control an average grain size of steel from the steel to be 100 μιη or less.
[11]
11. Method of producing a cold-rolled steel sheet, according to claim 7, characterized by the fact that an increase in the temperature of the steel between the respective passages in the temperature range from T1 + 30 ° C to T1 + 200 ° C is set to 18 ° C or less in the second hot rolling.
[12]
12. Method of producing a cold-rolled steel sheet, according to claim 7, characterized by the fact that the first cooling is carried out between the rolling supports.
[13]
13. Method of producing a cold-rolled steel sheet according to claim 7, characterized by the fact that a hot-dip galvanized layer or an annealed layer after galvanizing is formed on a surface of the steel sheet.
Petition 870180072452, of 17/08/2018, p. 82/86
1/6
TS X EL (MPa%) TS x λ (MPa%)
D1 (-)

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法律状态:
2018-05-22| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|

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2018-09-25| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2018-11-06| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/03/2012, 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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JP2011070725|2011-03-28|

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JP2011/070725|2011-03-28|

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PCT/JP2012/058199|WO2012133563A1|2011-03-28|2012-03-28|Cold rolled steel sheet and production method therefor|

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