HOT PRINTED STEEL, COLD LAMINATED STEEL SHEET AND METHOD TO PRODUCE HOT STAMPED STEEL SHEET

专利摘要:
abstract patent of invention: "hot stamped steel, cold rolled steel sheet and method for producing hot stamped steel sheet". hot stamped steel according to the present invention has a predetermined chemical composition, satisfies (5 × [si] + [mn]) / [c]> 10 when [c] is the amount of ce,% by mass, [si] is the amount of si in% by mass, and [mn] is the amount of mn in% by mass, includes 40% to 95% of ferrite and 5% to 60% of martensite in fraction of area, and optionally also includes 10% or less of perlite in fraction of area. 5% or less of austenite retained in fraction of volume, and less than 40% of bainite in fraction of area. the fraction of total ferrite area and the fraction of martensite area is 60% or more, the hardness of the martensite measured with a nanoindenter satisfies h2 / h1 <1.10 and shm <20, and ts ×? what is the product of the tensile strength ts by the hole expansion ratio? is 50000 mpa ·% or more.
公开号:BR112015024777B1
申请号:R112015024777-6
申请日:2014-03-27
公开日:2020-05-12
发明作者:Yoshihiro Suwa；Toshiki Nonaka；Koichi Sato；Naruse Manabu；Iwasa Yasunori；Kobayashi Yoshifumi
申请人:Nippon Steel Corporation；
IPC主号:

专利说明:

DESCRIPTION REPORT OF THE INVENTION PATENT FOR HOT STAMPING STEEL, COLD LAMINATED STEEL SHEET AND METHOD FOR PRODUCING HOT STEEL STEEL SHEET.
Technical field of the invention [001] The present invention relates to a hot-stamped steel having excellent forming capacity (bore expansion capacity), excellent chemical conversion treatment property, and excellent coating adhesion after stamping a hot, a cold rolled steel sheet that is used as a material for hot stamped steel, and a method for producing hot stamped steel sheet.
[002] Priority is claimed over Japanese Patent Application No. 2013-076835, registered on April 2, 2013, the content of which is incorporated as a reference.
Relative technique [003] At the moment, a steel plate for a vehicle needs to be improved in terms of safety in the collision and have a reduced weight. In such a situation, hot stamping (also called hot pressing, hot stamping, rapid mold cooling, pressing cooling, etc.) is drawing attention as a method for achieving high strength. Hot stamping refers to a forming method in which a steel plate is heated to a high temperature of, for example, 700 ° C or more, and then hot forming in order to improve the forming capacity of the plate. steel, and quickly cooled by cooling after forming, thus obtaining the desired qualities for the material. As described above, the steel plate used for the structure of a vehicle chassis needs to have a high pressing work capacity and a high strength. A steel sheet that has a
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2/56 ferrite and martensite structure, a steel plate that has a ferrite and bainite structure, a steel plate containing austenite retained in the structure or the like is known as a steel plate that has both pressing and high strength work capacity. Among these steel sheets, a multi-stage steel sheet having martensite dispersed on a ferrite base has a low yield ratio and a high tensile strength, and in addition, it has excellent elongation characteristics. However, the multi-phase steel sheet has insufficient hole expansion capacity since stress is concentrated at the interface between ferrite and martensite, and the fracture is likely to start from the interface.
[004] For example, Patent Documents 1 to 3 describe the multi-stage steel sheet. In addition, Patent Documents 4 to 6 describe the relationship between the hardness and the forming ability of a steel sheet.
[005] However, even with these techniques of relative technique, it is difficult to obtain a steel sheet that meets the current requirements for a vehicle, such as additional weight reduction and more complicated shapes of a component. Various types of resistance can be improved both by adding elements such as Si and Mn and by changing the structure. However, when the amount of Si exceeds a constant amount as described below by adding Si, the elongation or bore expansion capacity of the steel can degrade. In addition, when the amount of Si or the amount of Mn increases, the chemical conversion treatment property or the adhesion of the coating after hot stamping can degrade, which is not preferable.
Prior art documents
Patent Documents [006] [Patent Document 1] - Japanese Patent Application
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Unexamined, First Publication No. H6-128688 [007] [Patent Document 2] - Japanese Patent Application
Unexamined, First Publication No. 2000-319756 [008] [Patent Document 3] - Japanese Patent Application
Unexamined, First Publication No. 2005-120436 [009] [Patent Document 4] - Japanese Patent Application
Unexamined, First Publication No. 2005-256141 [0010] [Patent Document 5] - Japanese Patent Application
Unexamined, First Publication No. 2001-355044 [0011] [Patent Document 6] - Japanese Patent Application
Unexamined, First Publication No. H11-189842
Description of the invention
Problems to be solved by the invention [0012] An objective of the present invention is to provide a cold rolled steel sheet capable of guaranteeing strength and having a more favorable hole expansion capacity, excellent chemical conversion treatment property and a excellent coating adhesion when produced from hot stamped steel, hot stamped steel, and a method for producing said hot stamped steel.
Means to solve the problem [0013] The present inventors carried out intense studies in relation to a cold-rolled steel sheet for hot stamping that would guarantee the strength after hot stamping (after rapid cooling in a hot stamping), had excellent forming capacity (bore expansion capacity), and had excellent chemical conversion treatment properties and excellent coating adhesion after hot stamping. As a result, it was found that when an adequate relationship is established between the amount of Si, the amount of Mn and the
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4/56 amount of C, the fraction of ferrite and the fraction of martensite in the steel plate are adjusted to predetermined fractions, and the hardness ratio (difference in hardness) of the martensite between the surface portion of a steel plate and the central portion of the plate thickness and the distribution of the martensite hardness in the central portion of the steel plate thickness are adjusted in specific ranges, it is possible to industrially produce a cold rolled steel plate for hot stamping capable of guaranteeing the forming capacity , that is, a characteristic of TS χ λ> 50000 MPa-% which is a value greater than ever in terms of TS χ λ which is the product of TS tensile strength by the bore expansion ratio λ. In addition, it was discovered that when this cold rolled steel sheet is used for hot stamping, a hot stamped steel is obtained that has excellent hole expansion capacity even after hot stamping. In addition, it has also been clarified that limiting the segregation of MnS in the central portion of the thickness of the cold rolled steel sheet for hot stamping is also effective in improving the hole expansion capacity of the hot stamped steel. In particular, it has been found that when the amount of Mn, which is the main element for improving the hardening capacity, is reduced and the fraction or hardness of the martensite decreases, the hole expansion capacity is maximized by limiting the segregation of MnS and the chemical conversion treatment and coating adhesion properties are excellent after hot stamping. In addition, it has also been found that, in cold rolling, adjusting the cold rolling reduction fraction for a total cold rolling reduction (cumulative rolling reduction) from the first laminating chair to the third laminating chair with base on the first lamination chair within a specific range is effective to control the hardness of the martensite. In addition, the inventors discovered a variety of
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5/56 aspects of the present invention as described below. In addition it has been found that the effects are not impaired even when a hot dip galvanized layer, an annealed and galvanized layer, an electro-galvanized layer and an aluminized layer are formed on the cold rolled steel sheet.
[0014] (1) That is, according to a first aspect of the present invention, a hot stamped steel includes, in% by weight, C: 0.030% to 0.150%, Si: 0.010% to 1,000%, Mn: 0 , 50% or more and less than 1.50%, P: 0.001% to 0.060%, S: 0.001% to 0.010%, N: 0.0005% to 0.0100%, Al: 0.010% to 0.050%, and optionally at least one element between B: 0.0005% to 0.0020%, Mo: 0.01% to 0.50%, Cr: 0.01% to 0.50%, V: 0.001% to 0.100%, Ti: 0.001% to 0.100%, Nb: 0.001% to 0.050%, Ni: 0.01% to 1.00%, Cu: 0.01% to 1.00%, Ca: 0.0005% to 0.0050 %, REM: 0.00050% to 0.0050%, a balance of Fe and impurities, in which, when [C] is the amount of C in mass%, [Si] is the amount of Si in mass% , and [Mn] is the amount of Mn in mass%, the expression A below is satisfied, the fraction of ferrite area is 40% to 95% and the fraction of martensite area is 5% to 60%, the the total fraction of the area of ferrite and the fraction of area of martensite is 60% or more, the hot stamped steel optionally also includes one or more between perlite, austeni retained, and a bainite, the fraction of area of the perlite is 10% or less, the volume fraction of the retained austenite is 5% or less, and the fraction of area of the bainite is less than 40%, the hardness of the martensite measured with a nanoindentator it satisfies the expression (B) and the expression (C) below, TS χ λ which is the product of the tensile strength TS by the bore expansion ratio is 50000 MPa-% or more, (5 χ [Si ] + [Mn]) / [C]> 10 (A),
H2 / H1 <1.10 (B), oHM <20 (C), and
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6/56 [0015] H1 is the average hardness of the martensite on a portion of the surface of the thickness of the hot-stamped steel sheet, the surface portion is an area having a width of 200 pm in the direction of thickness from the most external, H2 is the average hardness of the martensite in the central portion of the plate thickness, and σΗΜ is the variation of the average hardness of the martensite in the central portion of the thickness of the hot-stamped steel plate.
[0016] (2) In hot stamped steel as per item (1) above, the fraction of MnS area that exists in hot stamped steel and which has an equivalent circle diameter of 0.1 pm to 10 pm can be 0.01% or less, and the expression (D) below can be satisfied, n2 / n1 <1.5 (D), and [0017] n1 is the average numerical density per 10,000 pm2 of MnS having a circle diameter equivalent of 0.1 pm to 10 pm in a a portion of the thickness of the hot-stamped steel sheet, and n2 is the average numerical density per 10,000 pm2 of MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the thickness of the hot-stamped steel plate.
[0018] (3) In hot stamped steel according to item (1) or (2) above, a hot dip galvanized layer can be formed on its surface.
[0019] (4) In hot stamped steel as per item (3) above, the hot dip galvanized layer can be bonded.
[0020] (5) In the hot-stamped steel plate according to item (1) or (2) above, an electrogalvanized layer can be formed on its surface.
[0021] (6) In hot stamped steel according to item (1) or (2) above, an aluminized layer can be formed on its surface.
[0022] (7) In accordance with another aspect of the present invention, a method is provided for producing a hot stamped steel
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7/56 including casting a molten steel having a chemical composition as per item (1) above and obtaining a steel, heating the steel, hot rolling the steel with a hot rolling mill including a plurality of chairs, winding the steel after hot rolling, stripping the steel after winding, cold rolling the steel with a cold rolling mill including a plurality of chairs after stripping under a condition that meets the expression E then perform the annealing in which the steel it is annealed at 700 ° C to 850 ° C after cold rolling and is cooled, hardening the steel after annealing, and hot stamping in which the steel is heated to a temperature range of 700 ° C at 1000 ° C after hardening lamination, it is hot stamped within the temperature range, and is subsequently cooled to room temperature or more and 300 ° C or less,
1.5 x r1 / r + 1.2 x r2 / r + r3 / r> 1.00 (E), and [0023] ri (i = 1, 2, 3) is an individual reduction targeted in hot rolling in an i-th chair (i = 1, 2, 3) based on the first chair in the plurality of chairs in cold rolling in% units, r is the total reduction of cold rolling in the cold rolling unit in% .
[0024] (8) In the method for producing a hot stamped steel as per item (7) above, cold rolling can be performed under a condition that satisfies the expression (E ') below,
1.20> 1.5 x r1 / r + 1.2 x r2 / r + r3 / r> 1.00 (E '), and [0025] ri (i = 1, 2, 3) is the individual reduction of the desired cold rolling in the i-th chair (i = 1, 2, 3) based on the first chair in the plurality of chairs in cold rolling in units of%, er is the total reduction of cold rolling in cold rolling in% units. [0026] (9) In the method for producing hot stamped steel according to item (7) or (8) above,
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8/56 [0027] when CT is the winding temperature in winding in units of ° C. [C] is the amount of C in steel in mass%, [Mn] is the amount of Mn in steel in mass%, [Cr] is the amount of Cr in steel in mass%, and [Mo] is the amount of Mo in steel in% by mass, the following expression (F) can be satisfied.
560 - 474 χ [C] - 90 χ [Mn] - 20 χ [Cr] - 20 χ [Mo] <CT <830 - 270 χ [C] - 90 χ [Mn] - 70 χ [Cr] - 80 χ [Mo] (F).
[0028] (10) In the method for producing hot stamped steel according to any of items (7) to (9) above, when T is the heating temperature for heating in units of ° C, t is the time in the oven when heating in units of minutes, [Mn] is the amount of Mn in steel in mass%, and [S] is the amount of S in steel in mass%, the following expression (G) can be satisfied,
T χ ln (t) / (1.7 χ [Mn] + [S])> 1500 (G).
[0029] (11) The method for producing hot stamped steel according to any of items (7) to (10) above may also include galvanizing the steel between annealing and hardening lamination. [0030] (12) The method for producing hot stamped steel as per item (11) above may also include connecting the steel between galvanizing and hardening lamination.
[0031] (13) The method for producing a hot stamped steel according to any of items (7) to (10) may also include electrogalvanizing the steel after hardening lamination.
[0032] (14) The method for producing a hot stamped steel as per any of items (7) to (10) above may also include aluminizing the steel between annealing and hardening lamination.
[0033] (15) According to another aspect of the present invention, a cold rolled steel sheet includes, in mass%, C: 0.030% to 0.150%; Si: 0.010% to 1,000%; Mn: 0.50% or more and less than
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1.50%; P: 0.001% to 0.060%; S: 0.001% to 0.010%; N: 0.0005% to 0.0100%; Al: 0.010% to 0.050%, and optionally at least one element between B: 0.0005% to 0.0020%; Mo: 0.01% to 0.50%; Cr: 0.01% to 0.50%; V: 0.001% to 0.100%; Ti: 0.001% to 0.100%; Nb: 0.001% to 0.050%; Ni: 0.01% to 1.00%; Cu: 0.01% to 1.00%; Ca: 0.0005% to 0.0050%; REM: 0.0005% to 0.0050%, and a balance of Fe and the inevitable impurities, in which when [C] is the amount of C in mass%, [Si] is the amount of Si in mass% , and [Mn] is the amount of Mn in% by mass, the expression (A) below is satisfied, the fraction of area of ferrite is 40% to 95%, and the fraction of area of martensite is 5% to 60 %, the total ferrite area fraction and martensite area fraction is 60% or more, the cold rolled steel sheet optionally also includes one or more between perlite, retained austenite, and bainite, the area fraction of perlite is 10% or less, the volume fraction of the retained austenite is 5% or less, and the area fraction of the bainite is less than 40%, the hardness of the martensite measured with a nanoindentator satisfies the expression (H) and the expression (I) below, TS χ λ which is the product of the tensile strength TS by the bore expansion capacity ratio λ is 50000 MPa-% or more, (5 χ [Si] + [Mn]) / [C ]> 10 (A),
H20 / H10 <1.10 (H), σΗΜ0 <20 (I), and [0034] H10 is the average hardness of martensite on a surface portion of the plate thickness, the surface portion is an area having a width of 200 pm in the direction of thickness from the outermost layer, H20 is the average hardness of martensite in a central portion of the plate thickness, the central portion is an area having a width of 200 pm in the direction of thickness in the center of the thickness of the plate, and σΗΜ0 is the variation in the average hardness of the martensite in the central portion of the plate thickness.
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10/56 [0035] (16) In the cold-rolled steel sheet according to item (15) above, the fraction of MnS area that exists in the cold-rolled steel sheet and which has an equivalent circle diameter of 0, 1 pm to 10 pm can be 0.01% or less, the following expression (J) is satisfied, n20 / n10 <1.5 (J), and [0036] n10 is the average numerical density per 10,000 pm2 of the MnS having a equivalent circle diameter of 0.1 pm to 10 pm in the 1/4 part of the plate thickness, and n20 is the average numerical density per 10,000 pm2 of MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the plate thickness.
[0037] (17) In the cold-rolled steel plate according to item (15) or (16) above, a hot dip galvanized layer can be formed on its surface.
[0038] (18) In the cold-rolled steel sheet according to item (17) above, the hot-dip galvanized layer can be bonded.
[0039] (19) In the cold-rolled steel plate according to item (15) or (16) above, an electrogalvanized layer can be formed on its surface.
[0040] (20) In the cold-rolled steel plate according to item (15) or (16), an aluminized layer can be formed on its surface. Effects of the invention [0041] According to the aspect of the present invention described above, once a suitable relationship is established between the amount of C, the amount of Mn and the amount of Si, and the hardness of the martensite measured with a nanoindentator is adjusted to a suitable value in cold rolled steel sheet before hot stamping and in hot stamped steel after hot stamping, it is possible to obtain a more favorable hole expansion capacity in hot stamped steel and the property of conver treatment
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11/56 are chemical and the coating adherence is favorable even after hot stamping.
Brief description of the drawings [0042] FIGURE 1 is a graph showing the relationship between (5 x [Si] + [Mn]) / [C] and TS χ λ on a cold rolled steel plate for hot stamping before rapid cooling in hot stamping and hot stamped steel.
[0043] FIGURE 2A is a graph showing the basis of an expression (B) and a graph showing the relationship between H20 / H10 and σΗΜΟ on cold rolled steel plate for hot stamping before cooling in hot stamping and the relationship between H2 / H1 and σHM in hot stamped steel.
[0044] FIGURE 2B is a graph showing the basis of an expression (C) and is a graph showing the relationship between σHM0 and TS χ λ in cold rolled steel plate for hot stamping before rapid cooling in hot stamping and the relationship between σΗΜ and TS χ λ in hot stamped steel.
[0045] FIGURE 3 is a graph showing the relationship between n20 / n10 and TS χ λ on cold rolled steel plate for hot stamping before rapid cooling in hot stamping and the relationship between n2 / n1 and TS χ λ in hot stamped steel and showing the basis of an expression (D).
[0046] FIGURE 4 is a graph showing the relationship between 1.5 x r1 / r + 1.2 x r2 / r + r3 / r H20 / H10 on cold rolled steel plate for hot stamping before rapid cooling in hot stamping and the ratio between 1.5 x r1 / r + 1.2 x r2 / r + r3 / r H2 / H1 in hot stamped steel, and showing the basis of an expression (E).
[0047] FIGURE 5A is a graph showing the relationship between an expression (F) and the fraction of martensite.
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12/56 [0048] FIGURE 5B is a graph showing the relationship between the expression (F) and the fraction of perlite.
[0049] FIGURE 6 is a graph showing the relationship between T x ln (t) / (1.7 x [Mn] + [S]) and TS χ λ, and showing the underline of an expression (G).
[0050] FIGURE 7 is a perspective view of a hot stamped pack used in an example.
[0051] FIGURE 8 is a flow chart showing a method for producing hot stamped steel for which the cold rolled steel sheet for hot stamping is used according to an embodiment of the present invention.
Modalities of the invention [0052] As described above, it is important to establish an adequate relationship between the amount of Si, the amount of Mn and the amount of C and provide an adequate hardness to the martensite in a predetermined position on a hot-stamped steel (or a cold rolled steel plate) to improve the hole expansion capacity of hot stamped steel. So far, there have been no studies regarding the relationship between the hole expansion capacity or the martensite hardness in a hot stamped steel.
[0053] Here the reasons for limiting the chemical composition of a hot stamped steel according to a modality of the present invention (in some cases also referred to as hot stamped steel according to the present modality) and the steel used for its production will be described. Henceforth, “%” which is the unit of quantity for an individual component indicates “% by mass”.
[0054] C: 0.030% to 0.150% [0055] C is an important element to reinforce martensite and increase the strength of steel. When the amount of C is less than 0.030%, it is not possible to sufficiently increase the resistance of the
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13/56 steel. On the other hand, when the amount of C exceeds 0.150%, the degradation of the ductility (elongation) of the steel becomes significant. Therefore, the C amount range is adjusted to 0.030% to 0.150%. In a case where there is a demand for high hole expansion capacity, the amount of C is desirably adjusted to 0.100% or less.
[0056] Si: 0.010% to 1,000% [0057] Si is an important element to suppress the formation of harmful carbides and obtain a multi-phase structure including mainly a ferrite structure and the balance of martensite. However, in a case where the amount of Si exceeds 1,000%, the elongation or bore expansion capacity of the steel degrades, and the chemical conversion treatment property or the adhesion of the coating after hot stamping also degrades. Therefore, the amount of Si is adjusted to 1,000% or less. In addition, while Si is added for deoxidation, the effect of deoxidation is not sufficient when the amount of Si is less than 0.010%. Therefore, the amount of Si is adjusted to 0.010% or more.
[0058] Al: 0.010% to 0.050% [0059] Al is an important element as a deoxidizing agent.
To obtain the deoxidation effect, the amount of Al is adjusted to 0.010% or more. On the other hand, even when Al is added excessively, the effect described above is saturated, and consequently the steel becomes brittle. Therefore, the amount of Al is adjusted to be in a range of 0.010% to 0.050%.
[0060] Mn: 0.50% or more and less than 1.50% [0061] Mn is an important element to increase the steel's hardening capacity and reinforce the steel. However, when the amount of Mn is less than 0.50%, it is not possible to sufficiently increase the strength of the steel. On the other hand, Mn is selective oxidized
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14/56 on a surface similar to Si, and with this the chemical conversion treatment property or the adhesion of the coating after hot stamping degrades. As a result of the inventors' studies, it was found that when the amount of Mn is 1.50% or more, the adhesion of the coating degrades. Therefore, in the modality, the amount of Mn is adjusted to less than 1.5%. It is more preferable that the upper limit of the amount of Mn is 1.45%. Therefore, the amount of Mn is adjusted to be in a range of 0.50% to less than 1.50%. In a case where there is a demand for high elongation, the amount of Mn is desirably adjusted to 1.00% or less.
[0062] P: 0.001% to 0.060% [0063] In a case where the quantity is large, P secretes at the grain edge, and deteriorates the local ductility and the weldability of the steel. Therefore, the amount of P is adjusted to 0.060% or less. On the other hand, since an unnecessary decrease in the P content leads to an increase in the refining cost, the amount of P is desirably adjusted to 0.001% or more.
[0064] S: 0.001% to 0.010% [0065] S is an element that forms MnS and significantly deteriorates the local ductility or weldability of steel. Therefore, the upper limit on the amount of S is desirably set to 0.010%. In addition, to reduce refining costs, the lower limit on the amount of S is desirably adjusted to 0.001%. [0066] N: 0.0005% to 0.0100% [0067] N is an important element to precipitate AlN and the like and to refine the crystal grains. However, when the amount of N exceeds 0.0100%, a solute N (nitrogen solute) remains and the ductility of the steel is degraded. Therefore, the amount of N is adjusted to 0.0100% or less. Due to a refining cost problem
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15/56 no, the lower limit of the amount of N is desirably set to 0.0005%.
[0068] The hot stamped steel according to the modality has a basic composition including the elements described above. Fe and the inevitable impurities as a balance, but it can also contain any one or more elements selected from Nb, Ti, V, Mo, Cr, Ca, REM (rare earth metal), Cu, Ni and B as elements that have been used so far in quantities that are within the ranges described below to improve strength, to control the shape of a sulfide or an oxide, etc. Even when hot-stamped steel or cold-rolled sheet does not include Nb, Ti, V, Mo, Cr, Ca, REM, Cu, Ni, and B, various properties of hot-stamped steel or hot-rolled steel sheet cold can be improved sufficiently. Therefore, the lower limits of the amounts of Nb, Ti, V, Mo, Cr, Ca, REM, Cu, Ni, and B are 0%.
[0069] Nb, Ti and V are elements that precipitate fine carbonitrides and strengthen the steel. In addition, Mo and Cr are elements that increase the hardening capacity and strength of steel. To achieve these effects, steel desirably contains Nb: 0.001% or more, Ti: 0.001% or more, V: 0.001% or more, Mo: 0.01% or more and Cr: 0.01% or more. In the meantime, even when Nb: more than 0.050%, Ti: more than 0.100%, V: more than 0.100%, Mo: more than 0.50% or Cr: more than 0.50% are contained, the increase effect strength is saturated, and degradation of elongation or expansiveness of the hole can be caused.
[0070] Steel may also contain Ca in the range of 0.0005% at
0.0050%. Ca and rare earth metal (REM) control the form of sulfides or oxides and improve local ductility or bore expansion capacity. To achieve this effect using Ca, it is preferable to add 0.00-5% or more of Ca. However, since there is a concern that an excessive addition may deteriorate the workability,
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16/56 the upper limit for the amount of Ca is set to 0.0050%. For the same reason, also for rare earth metal (REM), it is preferable to set the lower limit of the quantity to 0.0005% and the upper limit of the quantity to 0.0050%.
[0071] Steel may also contain Cu: 0.01% to 1.00%, Ni: 0.01% to 1.00% and B: 0.0005% to 0.0020%. These elements can also improve hardening capacity and increase the strength of the steel. However, to obtain the effect, it is preferable to contain Cu: 0.01% or more, Ni: 0.01% or more and B: 0.0005% or more. In a case where the amounts are equal to or less than the values described above, the effect that reinforces the steel is small. On the other hand, when Cu: more than 1.00%, Ni: more than 1.00% and B: more than 0.0020% are added, the effect of increasing resistance is saturated, and there is a concern that the ductility can degrade.
[0072] In a case where the steel contains B, Mo, Cr, V, Ti, Nb, Ni,
Cu, Ca and REM, one or more elements are contained. The steel balance is made up of Fe and the inevitable impurities. Elements other than the elements described above (for example, Sn, As and the like) can also be contained as unavoidable impurities as long as the elements do not impair the characteristics. In addition, when B, Mo, Cr, V, Ti, Nb, Ni, Cu, Ca and REM are contained in quantities that are less than the lower limits described above, the elements are treated as unavoidable impurities.
[0073] In addition, in the hot stamped steel plate, according to the modality, as shown in FIGURE 1, when the amount of C (% by mass), the amount of Si (% by mass) and the amount of Mn ( Mass%) are represented by [C], [Si] and [Mn] respectively, it is important to satisfy the following expression (A):
(5 x [Si] + [Mn]) / [C]> 10 (A) [0074] To satisfy the condition of TS x λ> 50000 MPa-%, the
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17/56 above (A) is preferably satisfied. When the value of (5 χ [Si] + [Mn]) / [C] is 10 or less, it is not possible to obtain sufficient hole expansion capacity. This is because when the amount of C is large, the hardness of a hard phase becomes very high, the difference in hardness (hardness ratio) between the hard phase and the soft phase becomes large, and therefore the value of λ deteriorates, and when the amount of Si or the amount of Mn is small, TS becomes low. Regarding the value of (5 χ [Si] + [Mn]) / [C], since the value does not change even after hot stamping as described above, the expression is preferably satisfied when the steel sheet is rolled cold is produced.
[0075] Generally, it is martensite instead of ferrite that dominates the forming capacity (hole expansion capacity) in a double-phase steel (DP steel). As a result of the intense studies by the inventors regarding the hardness of the martensite, it was clarified that, when the difference in the hardness (the hardness ratio) of the martensite between the surface portion of the plate thickness, and the hardness distribution of the martensite in the portion central thickness of the plate are in a predetermined state in a phase before rapid cooling in the hot stamping, the state is almost maintained even after the hot stamping as shown in FIGURES 2A and 2B, and the forming ability such as elongation or the hole expansion capacity becomes favorable. This is considered to be because the distribution of the hardness of the martensite formed before rapid cooling in the hot stamping still has a significant effect even after the hot stamping, and connection elements concentrated in the central portion of the sheet thickness still maintain the state of being concentrated in the central portion of the plate thickness even after hot stamping. That is, on cold rolled steel sheet before cooling in hot stamping, in one case
Petition 870190097560, of 09/30/2019, p. 25/77
18/56 where the hardness ratio between the martensite in the surface portion of the plate thickness and the martensite in the central portion of the plate thickness is large, or the variation in the hardness of the martensite is large, the same trend is exhibited even after hot stamping. As shown in FIGURES 2A and 2B, the hardness ratio between the surface portion of the plate thickness and the central portion of the plate thickness on the cold rolled steel plate according to the mode before the rapid cooling in the hot stamping and the ratio of hardness between the surface portion of the plate thickness and the central portion of the plate thickness in hot stamped steel according to the modality are almost the same. In addition, similarly, the variation in the hardness of the martensite in the central portion of the plate thickness in the cold-rolled steel plate according to the modality before the rapid cooling in the hot stamping and the variation in the hardness of the martensite in the central portion of the plate thickness. in hot stamped steel according to the modality they are almost the same. Therefore, the forming capacity of cold rolled steel sheet according to the modality is similarly excellent to the forming capacity of hot stamped steel according to the modality.
[0076] In addition, in relation to the martensite hardness measured with a nanoindentator produced by Hysitron Corporation, the inventors found that the following expression (B) and expression (C) is advantageous for the hole expansion capacity of the hot stamped steel. Serving expression (H) and expression (I) is also advantageous in the same way. Here, “H1” is the average hardness of the martensite on the surface portion of the sheet thickness that is within an area that is 200 pm wide in the direction of thickness from the outermost layer of hot-pressed steel, “H2 ”Is the average hardness of the martensite in an area having a width
Petition 870190097560, of 09/30/2019, p. 26/77
19/56 ± 100 pm in the thickness direction from the central portion of the plate thickness to the central portion of the plate thickness in hot stamped steel, and “σΗΜ” is the variation in martensite hardness in an area having a width ± 100 Mm in the thickness direction from the central portion of the plate thickness in hot stamped steel. In addition, “H10” is the hardness of the martensite on the surface portion of the sheet thickness on the cold rolled steel sheet before rapid cooling in hot stamping, “H20” is the hardness of the martensite in the central portion of the sheet thickness , that is, in an area having a width of 200 μm in the direction of the thickness in the center of the thickness of the plate in the cold rolled steel plate before the rapid cooling in the hot stamping, and 'rtHM0 ”is the variation of the hardness of the martensite in the central portion of the plate thickness on the cold rolled steel plate before rapid cooling in the hot stamping. H1, H10, H2, H20, σHM and σHM0 are obtained from measurements of 300 points for each one. An area having a width of ± 100 μm in the direction of thickness from the central portion of the thickness of the sheet refers to an area having center in the center of the thickness of the sheet and having a width of 200 μm in the direction of the thickness.
H2 / H1 <1.10 (B) σHM <20 (C) H20 / H10 <1.10 (H) σHM0 <20 (I) [0077] In addition, here, the variation is a value obtained using the expression (K) below and indicating the distribution of martensite hardness.
σHM = (1 / n) χ Σ [n, i = 1] (xave - xi) 2 (K) [0078] xave is the average hardness value and xi is an i-th hardness.
[0079] An H2 / H1 value of 1.10 or more represents that it lasts
Petition 870190097560, of 09/30/2019, p. 27/77
20/56 za of the martensite in the central portion of the plate thickness is 1.10 or more times the hardness of the martensite in the surface portion of the plate thickness and, in this case, σΗΜ becomes 20 or more even after hot stamping as shown in FIGURE 2A. When the H2 / H1 value is 1.10 or more, the hardness of the central portion of the sheet thickness becomes very high, TS χ λ becomes less than 50,000 MPa-% as shown in FIGURE 2B, and a forming capacity enough cannot be achieved both before rapid cooling (ie before hot stamping) and after rapid cooling (ie after hot stamping). In addition, theoretically, there is a case where the lower limit of H2 / H1 becomes the same in the central portion of the plate thickness and in the surface portion of the plate thickness unless a special heat treatment is performed, however, in the current production process, when considering productivity, the lower limit is, for example, 1.005. What was described above in relation to the H2 / H1 value should also apply in a similar way to the H20 / H10 value.
[0080] In addition, the variation σΗΜ to be 20 or more even after hot stamping indicates that the dispersion of martensite hardness is large, and portions in which very high foot hardness exist locally. In this case, TS χ λ becomes less than 50,000 MPa-% as shown in FIGURE 2B, and a hole expansion capacity of hot stamped steel cannot be obtained. What was described above in relation to the value of σΗΜ should also apply in a similar way to the value of σΗΜ0.
[0081] In hot stamped steel according to the modality, the fraction of ferrite area is 40% to 95%. When the fraction of ferrite area is less than 40%, sufficient elongation or sufficient bore expansion capacity can be achieved. On the other hand, when the fraction of ferrite area exceeds 95%, the martensite becomes
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21/56 is insufficient, and sufficient strength cannot be obtained. Therefore, the fraction of ferrite area in hot-stamped steel is adjusted to 40% to 95%. In addition, hot stamped steel also includes martensite, the area fraction of martensite is 5% to 60%, and the total fraction of the area of ferrite and the fraction of area of martensite is 60% or more. All the main portions of hot stamped steel are occupied by ferrite and martensite, and in addition one or more between bainite and retained austenite can be included in hot stamped steel. However, when the retained austenite remains in the hot-stamped steel, the fragility of secondary work and the delayed fracture characteristic are liable to degrade. Therefore, it is preferable that the retained austenite is not substantially included; however, inevitably, 5% or less of austenite retained in a fraction of volume may be included. Since perlite is a hard and fragile structure, it is preferable not to include perlite in hot stamped steel; however, inevitably, up to 10% perlite in a fraction of an area may be included. In addition, the amount of bainite can be a maximum of 40% in fraction of area in relation to the region excluding ferrite and martensite. Here, ferrite, bainite and perlite were observed through the caustication Le pera. In both cases, a portion 1/4 of the thickness of the plate was observed at a magnification of 1000 times. The volume fraction of the retained austenite was measured with X-ray diffraction equipment after polishing the steel sheet up to the 1/4 part of the sheet thickness. The 1/4 portion of the plate thickness refers to a 1/4 portion of the steel plate thickness away from the surface of the steel plate in the direction of the thickness of the steel plate on the steel plate.
[0082] In the modality, the hardness of the martensite is specified by the hardness obtained using a nanoindentator under the following conditions:
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22/56 [0083] · Amplification to observe the indentation: x1000 [0084] · Visual field for observation: height of 90 pm and width of 120 pm [0085] · Shape of the Indentor: three-sided pyramid diamond inductor of the type Berkovich [0086] · Compression load: 500 pN (50 mgf) [0087] · Charge time for inductor compression: 10 seconds [0088] · Discharge time period for inductor compression: 10 seconds (the inductor is not is held in a maximum load position).
[0089] The relationship between the depth of compression and the load is obtained under the condition above, and the hardness is calculated from this relationship. The hardness can be calculated by a conventional method. The hardness is measured in 10 positions, the hardness of the martensite is obtained by the arithmetic mean of the 10 hardness values. The individual positions for measurement are not particularly limited as long as the positions are within the martensite grains. However, the distance between the measurement positions must be 5 pm or more.
[0090] Since a recess formed in a common Vickers hardness test is greater than the martensite, according to the Vickers hardness test, although the macroscopic hardness of the martensite and its peripheral structure (ferrite, etc.) can be obtained, it is not possible to obtain the hardness of the martensite itself. Since the forming capacity (bore expansion capacity) is significantly affected by the hardness of the martensite itself, it is difficult to sufficiently assess the forming capacity with Vickers hardness alone. On the contrary, in the modality, since the hardness distribution state is given based on the martensite hardness in the hot stamped steel measured with the nanoindentator, it is possible to obtain
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23/56 extremely favorable forming capacity.
[0091] In addition, in cold rolled steel plate before rapid cooling in hot stamping and hot stamped steel, as a result of observing MnS in a location 1/4 of the thickness of the plate and in the central portion of the plate thickness, it has been found that it is preferable that the fraction of MnS area having an equivalent circle diameter from 0.1 pm to 10 pm is 0.01% or less, and, as shown in FIGURE 3, the expression (D ) below (as well as the expression (J)) is satisfied to favorably and steadily satisfy the condition of TS χ λ> 50000 MPa-%. When MnS having an equivalent circle diameter of 0.1 pm or more exists during the hole expansion capability test, since stress is concentrated in its vicinity, the fracture is likely to occur. The reason for not counting MnS that has an equivalent circle diameter of less than 0.1 pm is that the effect on stress concentration is small. In addition, the reason for not counting MnS that has an equivalent circle diameter of more than 10 pm is that when MnS having the particle size described above is included in hot stamped steel or cold rolled steel sheet , the particle size is very large, and hot stamped steel or cold rolled steel sheet becomes unsuitable for the job. In addition, when the fraction of MnS area having an equivalent circle diameter from 0.1 pm to 10 pm exceeds 0.01%, since it is easy for the fractures generated to spread due to the stress concentration, the capacity hole expansion also deteriorates and there is a case where the condition of TS χ λ> 50000 MPa-% is not satisfied. Here, “n1” and “n10” are numerical densities of MnS that have an equivalent circle diameter of 0.1 pm to 10 pm in the 1/4 portion of the thickness of hot stamped steel and cold rolled steel sheet before rapid cooling in hot stamping, respectively
Petition 870190097560, of 09/30/2019, p. 31/77
24/56 and “n2” and “n20” are numerical densities of the MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the plate thickness in hot stamped steel and in rolled steel plate cold before rapid cooling in hot stamping, respectively.
n2 / n1 <1.5 (D) n20 / n10 <1.5 (J) [0092] These ratios are all identical for the steel plate before rapid cooling in the hot stamping, in the steel plate after the hot stamping, and in hot stamped steel.
[0093] When the fraction of area of the MnS having an equivalent circle diameter of 0.1 pm to 10 pm is greater than 0.01% after hot stamping, the hole expansion capacity is liable to degrade. The lower limit of the MnS area fraction is not particularly specified, however 0.0001% or more of MnS is present due to a measurement method described below, the amplification and visual field limitation, and the original amount of Mn or of S. In addition, the value of n2 / n1 (or n20 / n10) of 1.5 or more indicates that the numerical density of MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the The thickness of the hot-stamped steel plate (or cold-rolled steel plate before hot stamping) is 1.5 or more times the numerical density of the MnS having an equivalent circle diameter of 0.1 pm or more in the portion 1/4 of the thickness of the hot-stamped steel plate (or of the cold-rolled steel plate before hot stamping). In this case, the forming capacity is liable to degrade due to the segregation of MnS in the central portion of the thickness of the hot-stamped steel plate (or of the cold-rolled steel plate before hot stamping). In the modality, the equivalent circle diameter and the numerical density of the MnS having a circle diameter
Petition 870190097560, of 09/30/2019, p. 32/77
25/56 equivalent from 0.1 pm to 10 pm were measured with a field emission scanning electron microscope (Fe-SEM) produced by JEOL Ltd. In one measurement, the magnification was 1000 times, and the measurement area of the visual field was adjusted to 0.12 x 0.09 mm2 (= 10800 pm2 ~ 10000 pm2). Ten visual fields were observed in the portion at 1/4 of the plate thickness, and ten visual fields were observed in the central portion of the plate thickness. The fraction of the MnS area having an equivalent circle diameter from 0.1 pm to 10 pm was computed with particle analysis software. In the hot stamped steel plate according to the modality, the shape (shape Ed number) of the MnS formed before the hot stamping is the same before and after the hot stamping. FIGURE 3 is a view showing the relationship between n2 / n1 and TS χ λ after hot stamping and the relationship between n20 / n10 and TS χ λ before rapid cooling in hot stamping and, according to FIGURE 3, n20 / n10 of the cold rolled steel plate before rapid cooling in hot stamping and n2 / n1 of hot stamped steel are almost the same. This is because the shape of the MnS does not change at a typical hot stamping heating temperature.
[0094] When hot stamping is performed on cold rolled steel sheet having the modality described above, it is possible to obtain a hot stamped steel having a tensile strength of 400 MPa to 1000 MPa, and the ability to bore expansion is significantly improved on hot-stamped steel having a tensile strength of approximately 400 MPa to 800 MPa.
[0095] In addition, a hot-dip galvanized layer, an annealed and galvanized layer, an electrogalvanized layer or an aluminized layer can be formed on the surface in hot stamped steel depending on the modality. It is preferable to form the coating described above in terms of rust prevention. THE
Petition 870190097560, of 09/30/2019, p. 33/77
Formation of the coatings described above does not impair the effects of the present invention. The coatings described above can be carried out by a well known method.
[0096] A cold rolled steel sheet according to another embodiment of the present invention includes, in mass%, C: 0.030% to 0.150%; Si: 0.010% to 1,000%; Mn: 0.50% or more and less than 1.50%; P: 0.001% to 0.060%; S: 0.001% to 0.010%; N: 0.0005% to 0.0100%; Al: 0.010% to 0.050%, and optionally at least one between B: 0.0005% to 0.0020%; Mo: 0.01% to 0.50%; Cr: 0.01% to 0.50%; V: 0.001% to 0.100%; Ti: 0.001% to 0.100%; Nb: 0.001% to 0.050%; Ni: 0.01% to 1.00%; Cu: 0.01% to 1.00%; Ca: 0.0005% to 0.0050%; REM: 0.0005% to 0.0050%, and a balance of Fe and impurities, in which, when [C] is the amount of C in mass%, [Si] is the amount of Si in mass%, and [Mn] is the amount of Mn in% by mass, the expression (A) below is satisfied, the fraction of ferrite area is 40% to 95% and the fraction of martensite area is 5% to 60%, the total fraction of the ferrite area and the area fraction and the area fraction of the martensite is 60% or more, the cold rolled steel sheet optionally can also include one or more between perlite, retained austenite, and bainite, a fraction of perlite area is 10% or less, the volume fraction of retained austenite is 5% or less, and the fraction of PE bainite area less than 40%, the hardness of the martensite measured with a nanondenter satisfies the expression (H ) below and the expression (I) below, TS χ λ which is a product of the tensile strength TS by the expansion of bore ratio λ is 50000 MPa-% or more.
(5 χ [Si] + [Mn]) / [C]> 10 (A)
H20 / H10 <1.10 (H) oHMQ <20 (I) [0097] H10 is the average hardness of the martensite on a surface portion of the plate thickness, H20 is the average hardness of the martensite
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27/56 in a central portion of the plate thickness, the central portion is an area having a width of 200 pm in the direction of the thickness at the center of the plate thickness, and σΗΜΟ is the variation in the average hardness of the martensite in the central portion of the thickness the plate.
[0098] The hot-stamped steel sheet above is obtained by hot stamping of the cold-rolled steel sheet as described below. Even when the cold rolled steel sheet is hot stamped, the chemical composition of the cold rolled steel sheet does not change. In addition, as described above, when the hardness ratio of the martensite between the surface portion of the plate thickness, and the central portion of the plate thickness and the hardness distribution of the martensite in the central portion of the plate thickness are in the predetermined state above in a phase before rapid cooling in a phase before rapid cooling in hot stamping, the state is almost maintained even after hot stamping (see also FIGURE 2A and FIGURE 2B). In addition, when the state of ferrite, martensite, perlite, retained austenite, and bainite are in the predetermined state above in a phase before rapid cooling in hot stamping, the state is almost maintained even after hot stamping. . Consequently, the characteristics of the cold rolled steel sheet, depending on the modality, are substantially the same as the characteristics of the hot stamped steel above.
[0099] In cold rolled steel sheet according to the modality, the fraction of MnS area that exists in cold rolled steel sheet and which has an equivalent circle diameter of 0.1 Mm to 10 Mm can be 0.01 % or less, and the expression (J) below can be satisfied n20 / n10 <1.5 (J) [00100] n10 is the average numerical density per 10,000 μm2 of MnS that has an equivalent circle diameter of 0.1 μm to 10 μm in
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28/56 a portion 1/4 of the plate thickness, and n20 is the average numerical density per 10,000 pm2 of the MnS which has an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the plate thickness .
[00101] As described above, the ratio of n20 to n10 having the cold rolled steel sheet before hot stamping is almost maintained even after hot stamping the cold rolled steel sheet (see also FIGURE 3). In addition, the area fraction of MnS is almost the same before and after hot stamping. Consequently, characteristics having the cold rolled steel sheet according to the modality are substantially the same as the characteristics having the hot stamped steel above.
[00102] A hot dip galvanized layer can be formed on the surface of the cold rolled steel sheet according to the modality in a similar way to the hot stamped steel described above. In addition, the galvanized layer can be bonded to the cold-rolled steel plate depending on the mode. In addition, an electrogalvanized layer or an aluminized layer can be formed on the surface of the cold-rolled steel sheet depending on the modality.
[00103] Hereinafter, a method will be described for the production of cold rolled steel sheet (cold rolled steel sheet, galvanized cold rolled steel sheet, galvanized and annealed cold rolled steel sheet, an electrogalvanized cold rolled steel sheet and an aluminized cold rolled steel sheet) and a method for producing hot stamped steel for which the cold rolled steel sheet is used according to the modalities described here.
[00104] When producing cold rolled steel sheet and hot stamped steel for which cold rolled steel sheet is used according to the modalities, as a common condition, a steel
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29/56 cast in a converter is cast continuously, thus producing steel. In continuous casting, when the casting rate is fast, Ti precipitates and the like become very thin, and when the casting rate is slow, productivity deteriorates, and consequently the precipitates described above become stale and the number of grains (for example , ferrite, martensite, etc.) in the microstructure decrease, the grains become brittle in the microstructure, and so there is a case where other characteristics, such as a delayed fracture, cannot be controlled. Therefore, the casting rate is desirably 1.0 m / min to 2.5 m / min.
[00105] The steel after casting can be subjected to hot rolling in the state. Alternatively, in a case where the steel after cooling has been cooled to less than 1100 ° C, it is possible to reheat the steel after cooling to 1100 ° C to 1300 ° C in a tunnel oven or similar and subject the steel to lamination to hot. When the heating temperature is less than 1100 ° C, it is difficult to guarantee a finishing temperature in hot rolling, which causes the elongation to degrade. In addition, in the hot-stamped steel to which the cold-rolled steel plate is used, to which Ti and Nb are added, since the dissolution of the precipitates becomes insufficient during heating, this causes a decrease in strength. On the other hand, when the heating temperature is higher than 1300 ° C, the amount of scale formed increases, and there is a case in which it is not possible to make the surface property of hot stamped steel favorable.
[00106] In addition, to decrease the fraction of area of MnS having an equivalent circle diameter of 0.1 pm to 10 pm, when the amount of Mn and the amount of S in the steel are respectively represented by [Mn] and [ S] in% by mass, it is preferable that the temperature T (° C) of a heating oven before
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30/56 hot rolling, the time in the oven (t minutes), [Mn] and [S] satisfy the expression (G) as shown in FIGURE 6.
T χ ln (t) / (1.7 χ [Mn] + [S])> 1500 (G) [00107] When T χ ln (t) / (1.7 χ [Mn] + [S]) is equal to or less than 1500, the fraction of MnS area having an equivalent circle diameter from 0.1 pm to 10 pm becomes large, and there is the case that the difference between the numerical density of MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the 1/4 inch portion of the plate and the numerical density of the MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the plate thickness becomes large. The temperature of the heating furnace before the hot rolling takes place refers to the extraction temperature on the outlet side of the heating furnace, and the time in the furnace refers to the time elapsed from placing the steel in the heating furnace to the extraction heating steel. Since MnS does not change even after hot stamping as described above, it is preferable to satisfy expression (G) in a heating step before hot rolling.
[00108] Next, hot rolling is performed according to a conventional method. At this point, it is desirable to perform hot rolling on steel at the finishing temperature (hot rolling finish temperature) which is adjusted to be in a range from Ar3 to 970 ° C. When the finishing temperature is lower than the Ar3 temperature, the hot rolling includes a double phase rolling region (α + γ) (ferrite + martensite double phase rolling region), and there is a concern that the elongation may degrade. On the other hand, when the finishing temperature exceeds 970 ° C, the grain size of the austenite becomes brutish, and the ferrite fraction becomes small, so there is a concern that the elongation may degrade. The equipment for
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31/56 hot rolling can have a plurality of chairs.
[00109] Here the Ar3 temperature was estimated from an inflection point of a length of a specimen after the execution of the formastor test.
[00110] After hot rolling, the steel is cooled at an average cooling rate of 20 ° C / s to 500 ° C / s, and is wound at a predetermined winding temperature CT. In a case where the average cooling rate is less than 20 ° C / s, the perlite that causes the degradation of ductility is likely to be formed. On the other hand, the upper limit of the cooling rate is not particularly specified and is adjusted to approximately 500 ° C / s, in consideration of the equipment specification, but is not limited to this.
[00111] After winding the steel, pickling is carried out. At that time, to obtain a strip that satisfies the expression (C) described above as shown in FIGURE 4, cold rolling is performed under a condition in which the expression (E) below is satisfied. When the conditions for annealing, cooling, etc., described below are also satisfied after the rolling described above, TS χ λ> 50000 MPa-% is guaranteed on cold rolled steel plate before hot stamping and / or stamped steel the hot. From the point of view of productivity, cold rolling is desirably carried out with an in-line rolling mill in which a plurality of rolling mills are arranged linearly, and the steel sheet is rolled continuously in a single direction, thus obtaining a predetermined thickness.
1.5 χ r1 / r + 1.2 χ r2 / r + r3 / r> 1.00 (E) [00112] Here, “ri” is the individual reduction of the desired cold rolling (%) in an i- th chair (i = 1, 2, 3) from the first chair in cold rolling, and “r” is the total reduction desired in cold rolling (%) in cold rolling. The total reduction of cold rolling is a so-called cumulative reduction, and on the basis of sheet thickness
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32/56 at the entrance of the first chair, is a percentage of the cumulative reduction (difference between the thickness of the plate at the entrance before the first pass and the thickness of the plate at the exit after the final pass) in relation to the base described above.
[00113] When steel is cold rolled under the conditions in which the expression (E) is satisfied, it is possible to sufficiently divide the perlite in cold rolling even when a large amount of perlite exists before cold rolling. As a result, it is possible to eliminate the perlite or limit the fraction of the perlite area to a minimum through annealing performed after cold rolling, and therefore it is easy to obtain a structure in which expression (B) and expression (C ) (or expression (H) and expression (I)) are satisfied. On the other hand, in a case where the expression (E) is not satisfied, the reductions of cold rolling in the following chairs are not enough, the large perlite is liable to remain, and it is not possible to form the desired martensite in the next annealing . Therefore, it is not possible to obtain a structure in which expression (B) and expression (C) (or expression (H) and expression (I)) are satisfied. That is, in the case where the expression (E) is not satisfied, it is not possible to obtain a characteristic of H2 / H1 <1.10 (or H20 / H10 <1.10), and a characteristic of σΗΜ <20 (or σΗΜ0 <20). In addition, the inventors found that when the expression (E) is satisfied, a shape obtained from the martensite structure after annealing is kept in almost the same state even after hot stamping is performed, and therefore hot stamped steel as modality becomes advantageous in terms of elongation or the ability to expand the hole even after hot stamping. In a case where the hot stamped steel according to the modality is heated up to the two-stage region in the hot stamping, a hard phase including martensite before rapid cooling in the hot stamping becomes a structure.
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33/56 austenite tura, and the ferrite before rapid cooling remains as it was. The carbon (C) in austenite does not move to the peripheral ferrite. After that, when cooled, austenite turns into a hard phase including martensite. That is, when the expression (E) is satisfied, the expression (H) is satisfied before the hot stamping and the expression (B) is satisfied after the hot stamping, and so the hot stamped steel becomes excellent in terms of formability capacity.
[00114] r, r1, r2 and r3 are the desired reductions in cold rolling. Generally, cold rolling is performed while controlling the desired reduction in cold rolling and a real reduction in cold rolling becomes substantially the same value. It is not preferable to perform cold rolling in a state in which the actual reduction of cold rolling is unnecessarily made to be different from the desired reduction of cold rolling. However, in a case where there is a big difference between the reduction of the desired lamination and the reduction of the actual lamination, it is possible to consider that the modality is performed when the current lamination reductions satisfy the expression (E). In addition, the actual reduction in cold rolling is preferably within ± 10% of the desired reduction in cold rolling.
[00115] In addition, it is more preferable that the real cold rolling reductions satisfy the following expression.
1.20> 1.5 χ r1 / r + 1.2 χ r2 / r + r3 / r> 1.00 (E ') [00116] When “1.5 χ r1 / r + 1.2 χ r2 / r + r3 / r ”exceeds 1.20, a heavy load is applied to a cold rolling mill, productivity is degraded. The tensile strength of the steel sheet as described above is a range of 400 MPa to 1000 MPa, and is much higher than the tensile strength of typical cold-rolled steel sheets. It is necessary to apply a rolling load of 1800 t or more per chair in order to perform cold rolling under
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34/56 the conditions that “1.5 x r1 I r + 1.2 x r2 I r + r3 I r” exceeds 1.20 in the steel plate having such tensile strength. It is difficult to apply such a heavy laminating load in view of the rigidity of the chairs and / or the capacity of the laminating equipment. In addition, when such a heavy rolling load is applied, there is a concern that production efficiency will be degraded.
[00117] After cold rolling, the steel plate is recrystallized by annealing the steel. Annealing forms the desired martensite. In addition, in relation to the annealing temperature, it is preferable to perform annealing by heating the steel sheet to 700 ° C to 850 ° C, and to cool the steel sheet to room temperature or to a temperature at which a surface such as galvanizing is performed. When annealing is carried out in the range described above, it is possible to stably guarantee a fraction of the predetermined area of the ferrite and a fraction of the predetermined area of the martensite, to steadily adjust the total fraction of the ferrite area and the fraction of the area of the martensite to 60 % or more, and contribute to an improvement in TS χ λ. The retention time at 700 ° C to 850 ° C is preferably 1 second or longer as long as productivity is not impaired (e.g., 300 seconds) to safely obtain a predetermined structure. The rate of temperature increase is preferable in a range of 1 ° C / s up to an upper limit of the equipment's capacity. In a hardening lamination step, hardening lamination is performed with a conventional method. The ratio of elongation to hardening lamination is generally approximately 0.2% to 5%, and it is preferable within a range in which elongation at the yield point is avoided and the shape of the steel sheet can be corrected.
[00118] As an even more preferable condition of the modality, when the amount of C (% by mass), the amount of Mn (% in mass)
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35/56 mass), the amount of Cr (% by mass) and the amount of Mo (% by mass) of the steel are represented by [C], [Mn], [Cr] and [Mo], respectively, in relation to at winding temperature CT, it is preferable to satisfy the expression (F) below.
560 - 474 χ [C] - 90 χ [Mn] - 20 χ [Cr] - 20 χ [Mo] <CT <830 - 270 χ [C] - 90 χ [Mn] - 70 χ [Cr] - 80 χ [Mo] (F) [00119] As shown in FIGURE 5A, when the winding temperature CT is less than “560 - 474 χ [C] - 90 χ [Mn] - 20 χ [Cr] 20 χ [Mo]” , the martensite is excessively formed, the steel becomes very hard, and there is a case where the following cold rolling becomes very difficult. On the other hand, as shown in FIGURE 5B, when the CT winding temperature exceeds “830 - 270 χ [C] - 90 χ [Mn] 70 χ [Cr] - 80 χ [Mo]”, a combined structure of ferrite and perlite is liable to be formed and, in addition, the fraction of perlite in the central portion of the plate thickness is liable to increase. Therefore, the uniformity of the distribution of martensite formed at the next annealing degrades, and it becomes difficult to satisfy the expression (C) described above. In addition, there is the case where it becomes difficult to form enough martensite.
[00120] When the expression (F) is satisfied, the ferrite and the hard phase have an ideal distribution form before hot stamping as described above. In this case, when heating in the two-phase region is carried out in hot stamping, the form of distribution is maintained as described above. If it is possible to securely guarantee a microstructure having the characteristic described above by satisfying the expression (F), the microstructure is maintained even after hot stamping, and hot stamped steel becomes excellent in terms of forming capacity.
[00121] In addition, to improve the rust prevention capacity, it is also preferable to include a galvanizing step in the
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36/56 which the Galvanized layer is formed on the steel between the annealing step and the hardening lamination step, and to form the galvanized layer on the surface of the cold rolled steel sheet. In addition, it is also preferable that the method for production according to the modality includes a bonding step in which a bonding treatment is carried out after galvanizing the steel. In a case where the bonding treatment is carried out, a treatment in which a galvanized and annealed surface is brought into contact with a substance that oxidizes the galvanized and annealed surface such as water vapor, with what the thickening of a oxidized film can also run on the surface.
[00122] It is also preferable to include, for example, an electrogalvanizing step in which an electrogalvanized layer is formed on the steel after hardening lamination as well as the galvanizing step and the galvanizing and annealing step and to form an electrogalvanized layer on the surface of cold rolled steel sheet. In addition, it is also preferable to include, instead of the galvanizing step, an aluminizing step in which an aluminized layer is formed on the steel between the annealing step and the hardening step. Aluminization is generally hot-dip aluminization, which is preferable.
[00123] After a series of treatments described above, the steel is heated to a temperature in the range of 700 ° C to 1000 ° C, and is hot stamped in that temperature range. In the stamping step, hot stamping is desirably carried out, for example, under the following conditions. Initially, the steel sheet is heated to 700 ° C to 1000 ° C at a rate of temperature increase from 5 ° C / s to 500 ° C / s, and hot stamping (the hot stamping step) is performed after the retention time from 1 second to 120 seconds. To improve the conformability, the temperatu
Petition 870190097560, of 09/30/2019, p. 44/77
The heating temperature is preferably an Ac3 temperature or less. Subsequently, the steel sheet is cooled, for example, to room temperature at 300 ° C at a cooling rate of 10 ° C / s to 1000 ° C / s (rapid cooling in hot stamping). The Ac3 temperature was calculated from the inflection point of the specimen length after performing the formastor test and measuring the inflection point.
[00124] When the heating temperature in the hot stamping step is less than 700 ° C, rapid cooling is not sufficient, and consequently the resistance cannot be guaranteed, which is not preferable. When the heating temperature is greater than 1000 ° C, the steel sheet becomes very smooth, and in a case where the coating, particularly zinc coating, is formed on the surface of the steel sheet, there is a concern that zinc can be evaporated and burned, which is not preferable. Therefore, the heating temperature in the hot stamping is preferably 700 ° C to 1000 ° C. When the rate of temperature increase is less than 5 ° C / s, since it is difficult to control the heating in the hot stamping, and the productivity significantly degrades, it is preferable to perform the heating at a temperature increase rate of 5 ° C / s or more. On the other hand, the upper limit of the 500 ° C / s temperature rise rate depends on the current heating capacity, but is not necessarily limited to this. At a cooling rate of less than 10 ° C / s, since controlling the cooling rate after the hot stamping step is difficult, and productivity also degrades significantly, it is preferable to perform cooling at the cooling rate of 10 ° C / s or more. The upper limit of the 1000 ° C / s cooling rate depends on the current cooling capacity, but is not necessarily limited to this. The reason for adjusting the time until hot stamping after an increase in
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38/56 temperature for 1 second or more is the control capacity of the current process (the lower limit of the equipment's capacity), and the reason for adjusting the time until hot stamping after the temperature rise to 120 seconds or less is avoid evaporation of zinc or the like in a case where the galvanized or similar layer is formed on the surface of the steel sheet. The reason for adjusting the cooling temperature to room temperature at 300 ° C is to sufficiently guarantee the martensite and to guarantee the resistance of the hot stamped steel.
[00125] FIGURE 8 is a flow chart showing the method for producing the hot-stamped steel sheet according to the embodiment of the present invention. Each of the reference signals S1 to S13 in the drawing corresponds to an individual step described above.
[00126] In the hot stamped steel of the modality, the expression (B) and the expression (C) are satisfied even after the hot stamping is performed under the condition described above. In addition, consequently, it is possible to satisfy the condition of TS χ λ> 50000 MPa-% even after hot stamping is performed.
[00127] As described above, when the conditions described above are met, it is possible to produce hot stamped steel in which the distribution of hardness or structure is maintained even after hot stamping, and consequently strength is guaranteed and a capacity more favorable hole expansion can be obtained. Examples [00128] A steel having the composition described in Table 1-1 and Table 1-2 was cast continuously at a casting rate of 1.0 m / minute to 2.5 m / minute, the plate was heated in a heating furnace under the conditions shown in Table 5-1 and table 52 with a conventional method in the state or after cooling the plate once, and the hot rolling was carried out at a temperature of
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39/56 finishing from 910 ° C to 930 ° C, thus producing a hot rolled steel sheet. Thereafter, the hot rolled steel sheet was wound at a winding temperature CT described in Table 51 and Table 5-2. After that, pickling was carried out to remove the scale from the surface of the steel plate, and the thickness of the plate was made to be 1.2 mm to 1.4 mm through cold rolling. At that time, cold rolling was performed so that the value of the expression (E) became a value described in Table 5-1 and Table 5-2. After cold rolling, annealing was carried out in a continuous annealing furnace at an annealing temperature described in Table 2-1 and Table 2-2. In a part of the steel sheets, the galvanized layer was also formed in the middle of cooling after rinsing in the continuous annealing furnace, and then a bonding treatment was also carried out on part of the part of the steel sheets, thus forming a layer galvanized and annealed. In addition, an electrogalvanized layer or an aluminized layer was formed on another part of the steel sheets. In addition, hardening lamination was performed at an elongation ratio of 1% according to a conventional method. In this state, a sample was taken to assess the qualities of the material and the like before rapid cooling in the hot stamping, and a quality test of the material or similar was performed. Thereafter, to obtain a hot stamped steel having the shape shown in FIGURE 7, hot stamping was performed. In hot stamping, the temperature was increased at a temperature increase rate of 10 ° C / s to 100 ° C / s, the steel sheet was kept at a heating temperature of 800 ° C for 10 seconds, and was cooled at a cooling rate of 100 ° C / s to 200 ° C / s or less. A sample was cut from a location in FIGURE 7 on a hot stamped steel obtained, the material quality test and the like were performed, and the strength
Petition 870190097560, of 09/30/2019, p. 47/77
40/56 tensile strength (TS), elongation (El), bore expansion ratio (λ), etc., were obtained. The results are described in Table 2-1 through Table 5-2. The expansion ratios for hole λ in the tables were obtained from the expression (L) below.
λ (%) = {(d '- d) / d} x 100 (L) [00129] d': hole diameter when the fracture penetrates the thickness of the plate [00130] d: initial hole diameter [00131] In addition Furthermore, in relation to the type of coating in the Table
3-1 and in Table 3-2, CR represents an uncoated cold-rolled steel sheet, GI represents that the galvanized layer has been formed, GA represents that the galvanized and annealed layer has been formed, EG represents that the electro-galvanized layer is formed , and Al represents that the aluminized layer is formed.
[00132] In addition, the determination of G and B in the tables have the following meanings.
[00133] G: the expression of the target condition is satisfied.
[00134] B: the expression of the target condition is not satisfied [00135] The chemical conversion treatment property after hot stamping was evaluated as the surface property after hot stamping on a hot stamped steel produced from an uncoated cold-rolled steel sheet. The adhesion of the hot stamped steel coating was evaluated as a surface property after the hot stamping when zinc, aluminum, or the like was coated on a cold rolled steel plate from which a hot stamped steel was produced.
[00136] The chemical conversion treatment property was evaluated using the following procedure. Initially, a chemical conversion treatment was applied to each sample under a condition of
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41/56 that the bath temperature was 43 ° C and the time period for the chemical conversion treatment was 120 seconds using a commercial chemical conversion treatment agent (Palbond PBL3020 system produced by Nihon Parkerizing Co. Ltd. ). Second, the crystal uniformity of a conversion coating was assessed by an SEM on the surface of each sample to which the chemical conversion treatment is applied. The crystal uniformity of a conversion coating was classified by the following evaluation standards. Good (G) was given to a sample with no loss of masking on the crystals of the conversion coating, bad (B) was given to a sample with a loss of masking on an area of the crystals of the conversion coating, and very bad (VB) was given to a sample with a conspicuous loss of masking in the crystals of the conversion coating.
[00137] The adhesion of the coating was evaluated using the following procedure. Initially, a test plate specimen having a height of 100 mm, a width of 200 mm, and a thickness of 2 mm was taken from a coated cold-rolled steel plate. The adhesion of the coating was evaluated by applying a V-fold and performance test for the plate specimen. In the V-bend and performance test, the plate specimen above was folded using a template for the V-fold test (a 60 ° bend angle), and then the plate specimen after the V-fold was performed again by pressing work. A cellophane tape (“CELLOTAPETM CT405AP-24” produced by Nichiban Co. Ltd.) was attached to a portion (deformed portion) that was located inside a folded portion during V-folding in the performed plate specimen, and then the cellophane tape was removed by hand. Next, the width of the peeling coating layer that was stuck on the cellophane tape was measured.
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In the examples, good (G) was given to a plate specimen in which the width was 5 mm or less, bad (B) was given to a plate specimen in which the width was more than 5 mm and 10 mm or less, and very bad (VB) was given to a plate specimen in which the width was more than 10 mm.
Petition 870190097560, of 09/30/2019, p. 50/77 [Table 1-1]
Steel type reference symbolÇ Si Mn P s N Al Cr Mo V You Nb Ni Ass Here B REM Expression A THE Example 0.045 0.143 0.55 0.002 0.007 0.0033 0.031 0 0 0 0 0 0 0 0 0 0 28.1 B II 0.061 0.224 0.63 0.025 0.005 0.0054 0.025 0 0 0 0 0 0.5 0 0 0 0 28.7 Ç II 0.149 0.970 1.45 0.006 0.009 0.0055 0.035 0.22 0 0 0 0 0 0 0 0 0 42.3 D II 0.075 0.520 0.69 0.007 0.006 0.0025 0.020 0 0.25 0 0 0 0 0 0 0 0 43.9 AND II 0.082 0.072 0.51 0.006 0.009 0.0032 0.045 0.40 0 0 0 0 0 0 0 0 0 10.6 F II 0.098 0.212 1.15 0.007 0.009 0.0075 0.035 0 0 0 0 0 0 0.7 0.005 0 0 22.6 G II 0.102 0.372 0.82 0.013 0.008 0.0035 0.037 0 0 0 0 0 0 0 0 0 0 26.3 H II 0.085 0.473 0.53 0.056 0.001 0.0029 0.041 0.39 0.15 0 0 0 0 0 0.004 0 0 34.1 I II 0.095 0.720 0.72 0.008 0.002 0.0055 0.032 0 0 0.05 0 0 0 0 0 0 0 45.5 J II 0.071 0.777 0.82 0.006 0.008 0.0014 0.015 0 0.45 0 0 0 0 0 0 0 0 66.3 K II 0.091 0.165 1.21 0.006 0.009 0.0035 0.041 0 0 0 0 0 0 0 0 0 0 22.4 L II 0.102 0.632 1.11 0.015 0.007 0.0041 0.032 0 0.37 0 0.07 0 0 0 0 0 0 41.9 M II 0.105 0.301 1.22 0.012 0.009 0.0015 0.035 0 0 0 0 0 0 0 0 0 0 26.0 N II 0.105 0.253 1.44 0.008 0.005 0.0032 0.042 0 0.35 0 0 0 0 0 0 0.0019 0 25.8 O II 0.144 0.945 0.89 0.008 0.006 0.0043 0.035 0 0.21 0 0 0 0 0 0 0 0 39.0 P II 0.095 0.243 1.45 0.009 0.007 0.0025 0.039 0.49 0 0 0 0 0 0 0 0 0 28.1 Q II 0.115 0.342 1.03 0.015 0.004 0.0038 0.037 0 0.15 0 0 0.03 0 0 0 0.0011 0 23.8 R II 0.121 0.175 0.78 0.008 0.003 0.0038 0.036 0 0 0 0 0.03 0 0 0 0 0 13.7 s II 0.129 0.571 0.93 0.016 0.006 0.0024 0.039 0 0.19 0 0 0 0 0 0 0 0 29.3 T II 0.141 0.150 1.40 0.018 0.003 0.0029 0.031 0 0.21 0 0.03 0 0 0 0 0 0 15.2
99 / E17
Petition 870190097560, of 09/30/2019, p. 51/77
Steel type reference symbolÇ Si Mn P s N Al Cr Mo V You Nb Ni Ass Here B REM Expression A U II 0.129 0.105 1.35 0.018 0.007 0.0064 0.019 0 0.29 0 0 0 0 0 0 0.0009 0 14.5 W II 0.143 0.652 1.17 0.012 0.006 0.0019 0.038 0 0 0 0 0 0 0 0.003 0 0 31.0 X II 0.141 0.922 1.02 0.015 0.004 0.0066 0.026 0.25 0.16 0 0.07 0 0 0 0 0.0015 0.0025 39.9 Y II 0.131 0.155 1.47 0.008 0.006 0.0065 0.043 0.37 0 0 0 0 0 0 0 0.0013 0 17.1 Z II 0.149 0.105 1.32 0.009 0.003 0.0061 0.031 0 0.25 0.04 0 0 0 0 0 0 0 12.4
[Table 1-2]
Steel type reference symbolÇ Si Mn P s N Al Cr Mo V You Nb Ni Ass Here B REM Expression A AA Comparative example 0.079 0.205 0.89 0.012 0.006 0.0021 0.029 0 0 0 0 0 0 0 0 0 0 24.2 AB II 0.092 0.219 0.96 0.010 0.004 0.0029 0.041 0 0 0 0 0 0 0 0 0 0 22.3 B.C II 0.105 0.103 1.22 0.008 0.002 0.0041 0.039 0 0 0 0 0 0 0 0 0 0 16.5 AD II 0.076 0.355 0.98 0.013 0.005 0.0039 0.033 0 0 0 0 0 0 0 0 0 0 36.3 AE II 0.142 0.246 0.69 0.009 0.003 0.0030 0.031 0 0 0 0 0 0 0 0 0 0 13.5 AF II 0.129 0.363 1.28 0.007 0.003 0.0040 0.042 0 0 0 0 0 0 0 0 0 0 24.0 AG Comparative example 0.118 0.563 1.13 0.008 0.004 0.0039 0.041 0 0 0 0 0 0 0 0 0 0 33.4 AH II 0.027 0.323 1.49 0.006 0.002 0.0031 0.032 0 0 0 0 0 0 0 0 0 0.0050 115.0 THERE II 0.221 0.602 1.39 0.004 0.005 0.0013 0.040 0 0 0 0 0 0 0 0 0 0 19.0 AJ II 0.093 0.004 1.01 0.006 0.008 0.0039 0.036 0 0.23 0 0 0 0 0 0 0.0011 0 11.1
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Petition 870190097560, of 09/30/2019, p. 52/77
Steel type reference symbolÇ Si Mn P s N Al Cr Mo V You Nb Ni Ass Here B REM Expression A AK II 0.098 1,493 0.71 0.007 0.003 0.0041 0.036 0.38 0.33 0 0 0 0 0 0 0.0013 0 83.4 AL II 0.126 0.780 0.21 0.011 0.003 0.0035 0.032 0 0 0 0 0 0 0 0 O 0 32.6 AM II 0.136 0.040 2.75 0.008 0.003 0.0044 0.039 0 0 0 0 0 0 0 0 0 0 21.7 AN II 0.103 0.265 1.12 0.095 0.004 0.0025 0.042 0.36 0.12 0 0 0.03 0 0 0 0 0 23.7 TO II 0.072 0.223 1.41 0.002 0.025 0.0052 0.036 0 0 0 0 0 0.4 0 0 0 0 35.1 AP II 0.051 0.281 1.03 0.012 0.007 0.1630 0.032 0 0 0 0 0.04 0 0 0.003 0 0 47.7 AQ II 0.141 0.011 1.39 0.019 0.008 0.0045 0.003 0 0.23 0 0 0 0 0 0 0 0 10.2 AIR II 0.149 0.150 1.23 0.005 0.003 0.0035 0.065 0 0.37 0 0 0 0 0 0 0 0 13.3 AT II 0.133 0.030 1.10 0.012 0.004 0.0020 0.035 0 O 0 0 0 0 0 0 0.001 0 94 AT II 0.135 0.170 1.24 0.010 0.004 0.0023 0.035 0 O 0 0 0.02 0 0 0 0 0 15.5 AU II 0.139 0.331 1.43 0.013 0.002 0.0044 0.030 0 O 0 0 0.00 0 0 0 0 0 22.2 AV II 0.137 0.192 1.50 0.011 0.002 0.0041 0.033 0 O 0 0 0 0 0 0 0 0 18.0 A W II 0.136 0.040 2.75 0.008 0.003 0.0044 0.039 0 O 0 0 0 0 0 0 0 0 21.7 AX II 0.137 0.192 1.50 0.011 0.002 0.0041 0.033 0 O 0 0 0 0 0 0 0 0 18.0
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Petition 870190097560, of 09/30/2019, p. 53/77 [Table 2-1]
Symbol of Symbol of after the annealing and the lamination hardening and before gives stamping the hotArea fraction steel type reference test reference Annealing temperature (° C) TS(MPa) El (%) λ(%) TS x El TS x λ Ferrite area fraction(%) Fraction of martensite area(%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite (%) Bainite area fraction(%) Fraction of perlite area (%) perlite before cold rolling (%) THE 1 790 445 35.5 121 15798 53845 92 7 99 1 0 0 25 B 2 800 468 36.2 115 16942 53820 87 6 93 3 4 0 25 Ç 3 750 502 31.2 132 15662 66264 82 10 92 2 5 1 34 D 4 790 542 33.1 105 17940 56910 84 8 92 3 5 0 26 AND 5 795 542 34.8 98 18862 53116 78 7 85 4 11 0 42 F 6 790 585 26.5 86 15503 50310 78 6 84 2 7 7 62 G 7 745 552 27.2 92 15014 50784 65 8 73 4 15 8 72 H 8 792 622 29.1 87 18100 54114 88 6 94 3 3 0 35 I 9 782 598 28.3 93 16923 55614 82 9 91 4 5 0 42 J 10 771 565 29.2 105 16498 59325 75 9 84 3 7 6 29 K 11 811 635 27.1 79 17209 50165 78 10 88 2 6 4 34 L 12 752 672 30.6 89 20563 59808 87 7 94 0 5 1 15 M 13 782 612 31.4 82 19217 50184 56 27 83 2 6 9 8 N 14 821 631 29.6 87 18678 54897 58 27 85 5 4 6 42 O 15 769 629 28.7 89 18052 55981 78 13 91 4 3 2 33 P 16 781 692 27.1 77 18753 53284 71 24 95 2 2 1 25 Q 17 781 678 25.8 78 17492 52884 56 32 88 3 5 7 28 R 18 782 672 21.5 89 14448 59808 63 27 90 3 7 0 53 D 19 771 729 23.1 79 16840 57591 55 32 87 4 9 0 46 T 20 785 745 28.5 71 21233 52895 44 41 85 3 12 0 23 U 21 813 761 21.6 68 16438 51748 44 39 83 5 9 3 23 W 22 831 796 19.2 65 15283 51740 46 37 83 4 10 3 18 X 23 815 862 18.2 61 15688 52582 47 40 87 2 6 5 51 Y 24 802 911 19.2 59 17491 53749 45 38 83 2 15 0 43 Z 25 841 1021 13.5 55 13784 56155 43 41 84 4 12 0 15
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Petition 870190097560, of 09/30/2019, p. 54/77 [Table 2-2]
Steel type reference symbol Test reference symbol Annealing temperature (° C) after the annealing and the lamination hardening and before gives stamping the hot Fraction of perlite area before cold rolling (%) TS(MPa) El (%) λ(%) TS x El TS x λ Ferrite area fraction(%) Fraction of martensite area (%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite (%) Bainite area fraction (%) Fraction of perlite area (%) AA 26 804 582 27.2 76 15830 44232 62 8 70 2 13 15 25 AB 27 797 606 27.5 68 16665 41208 58 13 71 1 14 14 31 B.C 28 769 581 27.6 79 16036 45899 51 9 60 3 17 20 17 AD 29 756 611 21.3 66 13014 40326 31 15 46 1 29 24 42 AE 30 792 598 24.1 75 14412 44850 52 9 61 2 7 30 28 AF 31 742 643 27.2 71 17490 45653 59 21 80 2 8 11 41 AG 32 772 602 29.1 62 17518 37324 72 17 89 2 8 11 21 AH 33 761 372 40.8 117 15178 43524 96 0 96 1 3 0 3 THERE 34 789 1493 9.1 29 13586 43297 9 77 86 3 1 10 9 AJ 35 768 682 21.6 66 14731 45012 69 17 86 2 4 8 26 AK 36 802 602 30.3 59 18241 35518 76 20 96 2 2 0 7 AL 37 789 362 42.1 127 15240 45974 86 2 88 1 0 11 15 AM 38 766 832 15.7 42 13062 34944 35 42 77 3 13 7 14 AN 39 802 802 19.6 46 15719 36892 56 32 88 3 9 0 16 TO 40 816 598 24.1 38 14412 22724 69 19 88 4 5 3 16 AP 41 779 496 33.2 72 16467 35712 79 12 91 2 6 1 11 AQ 42 840 829 20.2 32 16746 26528 28 61 89 0 11 0 22
99 / ZIZ
Petition 870190097560, of 09/30/2019, p. 55/77
Steel type reference symbol Test reference symbol Annealing temperature (° C) after the annealing and the lamination hardening and before gives stamping the hot Fraction of perlite area before cold rolling (%) TS(MPa) El (%) λ(%) TS x El TS x λ Ferrite area fraction(%) Fraction of martensite area (%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite (%) Bainite area fraction (%) Fraction of perlite area (%) AIR 43 776 968 14.2 39 13746 37752 27 63 90 0 0 10 11 AT 45 778 912 16.2 45 14774 41040 46 32 78 0 18 4 13 AT 46 671 713 15.9 51 11337 36363 30 10 40 1 16 43 40 AU 47 889 1023 11.3 32 11560 32736 2 56 58 1 33 8 7 AV 48 832 956 18.1 55 17304 52580 44 39 83 2 13 2 45 A W 38 776 832 15.7 42 13062 34944 35 42 77 3 13 7 14 AX 48 832 956 18.1 55 17304 52580 44 39 83 2 13 2 45
48/56 [Table 3-1]
steel type reference symbol After hot stamping Type of coating *) TS(MPa) El(%) λ(%) TS x El TS x λ Ferrite area fraction (%) Fraction of martensite area (%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite(%) Bainite area fraction (%) Fraction of perlite area (%) THE 462 40.2 135 18572 62370 92 6 98 1 0 1 GA B 447 41.2 125 18416 55875 85 7 92 3 4 1 GI Ç 512 36.2 115 18534 58880 83 10 93 1 5 1 GA D 553 32.7 115 18083 63595 82 7 89 3 8 0 GA AND 589 32.9 99 19378 58311 81 6 87 1 12 0 CR F 589 32.1 87 18907 51243 82 7 89 2 4 5 GA
Petition 870190097560, of 09/30/2019, p. 56/77
steel type reference symbol After hot stamping Type of coating *) TS(MPa) El(%) λ(%) TS x El TS x λ Ferrite area fraction (%) Fraction of martensite area (%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite(%) Bainite area fraction (%) Fraction of perlite area (%) G 561 30.9 90 17335 50490 66 10 76 2 14 8 GI H 632 30.0 89 18960 56248 86 8 94 4 0 2 EG I 698 28.3 75 19753 52350 65 7 72 4 23 1 GA J 755 25.9 87 19555 65685 59 12 71 1 25 3 THERE K 721 24.5 72 17665 51912 52 22 74 1 19 6 GA L 752 24.2 78 18198 58656 53 23 76 2 21 1 CR M 789 20.9 69 16490 54441 57 35 92 2 6 0 CR N 768 19.8 72 15206 55296 59 27 86 5 4 5 GA O 802 21.2 65 17002 52130 41 35 76 4 11 9 GI P 835 18.8 75 15698 62625 45 23 68 1 31 0 EG Q 872 22.5 61 19620 53192 41 39 80 4 10 6 THERE R 852 21.5 69 18318 58788 47 31 78 4 13 5 CR s 912 20.1 56 18331 51072 56 32 88 4 2 6 CR T 965 18.5 62 17853 59830 41 41 82 3 12 3 GA U 989 17.0 55 16813 54395 49 37 86 1 13 0 GA W 1025 15.9 53 16298 54325 46 38 84 4 12 0 GA X 1049 17.2 49 18043 51401 46 37 83 3 11 3 GA Y 1102 14.5 51 15979 56202 43 40 83 1 16 0 GI Z 1189 13.1 55 15576 65395 45 48 93 2 5 0 GA
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Petition 870190097560, of 09/30/2019, p. 57/77 [Table 3-2]
steel type reference symbol After hot stamping Type of coating*) TS(MPa) El(%) λ(%) TSxEl TS x λ Ferrite area fraction (%) Fraction of martensite area (%) Fraction of ferrite + martensite area (%) Volume fraction of residual austenite(%) Bainite area fraction (%) Fraction of perlite area (%) AA 756 19.2 63 14515 47628 37 39 76 2 11 11 GA AB 821 18.3 57 15024 46797 39 42 81 1 6 12 CR B.C 891 17.6 51 15682 45441 32 41 73 2 10 15 GA AD 922 16.8 41 15490 37802 29 38 67 1 14 18 EG AE 1021 15.8 31 16132 31651 49 31 80 2 7 11 GI AF 1152 13.8 38 15898 43776 37 42 79 2 1 18 THERE AG 723 19.1 61 13809 44103 72 16 88 2 8 12 GI AH 412 42.1 109 17345 44908 97 0 97 0 3 0 EG THERE 1513 8.3 27 12558 40851 6 88 94 3 2 1 THERE AJ 821 16.9 52 13875 42692 57 25 82 2 13 3 GA AK 912 18.9 43 17237 39216 65 32 97 2 1 0 GA AL 398 41.2 113 16398 44974 86 2 88 0 1 11 GA AM 1023 14.2 43 14527 43989 45 43 88 3 8 1 GA AN 923 17.6 46 16245 42458 57 31 88 3 9 0 GI TO 736 19.2 41 14131 30176 63 26 89 4 7 0 CR AP 543 31.0 68 16833 36924 78 14 92 1 6 1 GA AQ 1128 14.3 34 16130 38352 29 63 92 0 6 2 GA AIR 1062 12.9 35 13700 37170 29 65 94 0 0 6 GA AT 1109 13.8 41 15304 45469 46 32 78 3 14 5 GA AT 1021 11.9 38 12150 38798 30 28 58 1 11 30 GI AU 1236 9.9 34 12236 42024 7 69 76 4 18 2 GI AV 1151 13.1 46 15078 52946 41 44 85 4 10 1 GI A W 1023 14.2 43 14527 43989 45 43 88 3 8 1 CR AX 1151 13.1 46 15078 52946 41 44 85 4 10 1 CR
50/56
Petition 870190097560, of 09/30/2019, p. 58/77 [Table 4-1]
steel type reference symbol Left side of expression (B) before hot stamping Determination Left side of expression (B) after hot stamping Determination Left side of expression (C) before hot stamping Determination Left side of expression (C) after hot stamping Determination MnS area fraction of 0.1 mm or more before hot stamping Fraction area0.1 mm or more MnS after hot stamping THE 1.01 G 1.02 G 13 G 15 G 0.004 0.004 B 1.04 G 1.02 G 17 G 16 G 0.006 0.005 Ç 1.05 G 1.07 G 5 G 3 G .0166. 0.014 D 1.08 G 1.07 G 17 G 15 G 0.006 0.006 AND 1.07 G 1.05 G 18 G 17 G 0.006 0.007 F 1.08 G 1.09 G 12 G 13 G 0.015 0.015 G 1.08 G 1.09 G 15 G 12 G 0.008 0.007 H 1.02 G 1.03 G 7 G 9 G 0.006 0.005 I 1.05 G 1.04 G 8 G 9 G 0.005 0.006 J 1.05 G 1.01 G 15 G 14 G 0.005 0.006 K 1.03 G 1.04 G 19 G 18 G 0.050 0.006 L 1.03 G 1.02 G 14 G 13 G 0.006 0.007 M 1.08 G 1.06 G 14 G 15 G 0.012 0.011 N 1.06 G 1.08 G 12 G 13 G 0.003 0.003 O 1.07 G 1.08 G 13 G 12 G 0.003 0.004 P 1.04 G 1.05 G 11 G 10 G 0.006 0.005 Q 1.04 G 1.06 G 12 G 12 G 0.005 0.006 R 1.02 G 1.04 G 15 G 15 G 0.006 0.007 s 1.06 G 1.05 G 16 G 18 G 0.008 0.008 T 1.09 G 1.08 G 10 G 15 G 0.003 0.004 U 1.07 G 1.06 G 6 G 5 G 0.014 0.013 W 1.09 G 1.08 G 7 G 9 G 0.006 0.007 X 1.06 G 1.08 G 17 G 16 G 0.006 0.006 Y 1.04 G 1.05 G 12 G 11 G 0.006 0.004 Z 1.06 G 1.05 G 10 G 9 G 0.006 0.007
51/56
Petition 870190097560, of 09/30/2019, p. 59/77 [Table 4-2]
steel type reference symbol Left side of expression (B) before hot stamping Determination Left side of expression (B) after hot stamping Determination Left side of expression (C) before hot stamping Determination Left side of expression (C) after hot stamping Determination Fraction area0.1 mm MnS ormore before hot stamping MnS area fraction of 0.1 mm or more after hot stamping AA 1.13 B 1.15 B 23 B 22 B 0.011 0.013 AB 1.15 B 1.16 B 22 B 21 B 0.008 0.007 B.C 1.13 B 1.15 B 21 B 20 B 0.050 0.006 AD 1.19 B 1.18 B 26 B 25 B 0.006 0.007 AE 1.13 B 1.13 B 22 B 21 B 0.009 0.009 AF 1.11 B 1.10 B 19 B 18 B 0.003 0.003 AG 1.16 B 1.17 B 25 B 24 B 0.003 0.003 AH - B - B - B - B 0.004 0.004 THERE 1.23 B 1.19 B 22 B 23 B 0.006 0.006 AJ 1.23 B 1.22 B 21 B 23 B 0.007 0.008 AK 1.19 B 1.18 B 23 B 22 B 0.007 0.006 ALBBBB 0.006 0.006 AM 1.41 B 1.39 B 31 B 30 B 0.006 0.007 AN 1.26 B 1.22 B 26 B 29 B 0.008 0.009 TO 1.29 B 1.31 B 28 B 33 B 0.005 0.004 AP 1.06 G 1.05 G 11 G 12 G 0.005 0.007 AQ 1.19 B 121 B 23 B 25 B 0.003 0.003 AIR 1.09 G 1.07 G 17 G 17 G 0.002 0.002
52/56
Petition 870190097560, of 09/30/2019, p. 60/77
steel type reference symbol Left side of expression (B) before hot stamping Determination Left side of expression (B) after hot stamping Determination Left side of expression (C) before hot stamping Determination Left side of expression (C) after hot stamping Determination Fraction area0.1 mm MnS ormore before hot stamping MnS area fraction of 0.1 mm or more after hot stamping AT 1.23 B 1.21 B 23 B 23 B 0.006 0.007 AT 1.28 B 1.26 B 27 B 28 B 0.005 0.006 AU 1.06 G 1.07 G 18 G 19 G 0.006 0.005 AV 1.06 G 1.07 G 18 G 19 G 0.006 0.005 A W 1.41 B 1.39 B 31 B 30 B 0.006 0.007 AX 1.06 G 1.07 G 18 G 19 G 0.006 0.005
- the hardness was not measured because the fraction of the martensite area is significantly small.
[Table 5-1]
53/56
steel type reference symbol before stamping the hot after The stamping the hot Surface property after hot stamping Left side of expression (E) Determination Left side of expression (F) CT Right side of expression(F) Determination Heating oven temperature Heating oven time (minutes) Left side of expression (G) Determination n1 n2 left side of expression(D) Determination n1 n2 left side of expression(D) Determination THE 10 12 1.2 G 8 11 1.4 G O 1.32 G 489 580 768 G 1180 65 5229 G B 6 7 1.2 G 6 5 0.8 G O 1.13 VG 474 650 757 G 1250 72 4968 G Ç 3 5 1Z B 3 5 1Z B O 1.23 G 354 510 644 G 1154 68 1968 G D 7 6 0.9 G 6 6 1.0 G O 1.29 G 457 580 728 G 1260 72 4570 G AND 2 2 1.0 G 2 2 1.0 G O 1.51 G 467 615 734 G 1215 116 6593 G F 2 2 1.0 G 2 2 1.0 G O 1.23 G 410 721 700 B 1322 135 3302 G
Petition 870190097560, of 09/30/2019, p. 61/77
steel type reference symbol before stamping the hot after The stamping the hot Surface property after hot stamping Left side of expression (E) Determination Left side of expression (F) CT Right side of expression(F) Determination Heating oven temperature Heating oven time (minutes) Left side of expression (G) Determination n1 n2 left side of expression(D) Determination n1 n2 left side of expression(D) Determination G 1 1 1.0 G 1 1 1.0 G O 1.43 G 438 741 729 B 1173 123 4026 G H 5 6 1.2 G 5 5 1.0 G O 1.10 VG 461 585 720 G 1205 95 6084 G I 3 4 1.3 G 4 4 1.0 G O 1.38 G 450 542 740 G 1180 87 4331 G J 4 4 1.0 G 4 5 1.3 G O 1.34 G 444 562 701 G 1221 89 3909 G K 5 7 1.2 G 7 9 1.3 G O 1.22 G 408 715 697 B 1202 95 2649 G L 6 7 1.4 G 5 6 1.2 G O 1.42 G 404 482 673 G 1212 165 3267 G M 11 20 12 B 11 19 12 B O 1.24 G 400 463 692 G 1105 25 1708 G N 5 6 1.2 G 8 7 1.2 G O 1.33 G 374 502 644 G 1295 195 2784 G O 3 3 1.0 G 3 3 1.0 G O 1.36 G 407 631 694 G 1240 135 4004 G P 5 6 1.2 G 5 5 1.0 G O 1.52 G 375 527 640 G 1298 201 2785 G Q 8 9 1.1 G 7 8 1.1 G O 1.61 G 410 526 694 G 1192 120 3252 G R 16 18 1.1 G 15 18 1.2 G O 1.40 G 432 543 727 G 1250 179 4879 G s 11 12 1.1 G 10 12 1.2 G O 1.28 G 411 554 696 G 1232 122 3729 G T 6 7 1.2 G 6 6 1.0 G O 1.20 VG 363 523 649 G 1232 162 2630 G U 7 15 2.1 B 7 14 20 B O 1.41 G 372 621 650 G 1113 20 1448 B W 16 20 1.3 G 15 19 1.3 G O 1.07 VG 387 521 686 G 1260 125 3049 G X 22 26 1.2 G 22 22 1.0 G O 1.26 G 393 682 670 B 1180 141 3360 G Y 22 29 1.3 G 21 28 1.3 G O 1.24 G 358 482 638 G 1280 162 2600 G Z 27 32 1.2 G 26 32 1.2 G O 1.55 G 366 451 651 G 1260 181 2915 G
54/56
Petition 870190097560, of 09/30/2019, p. 62/77 [Table 5-2]
steel type reference symbol before hot stamping after The hot stamping Surface property after hot stamping Left side of expression (E) Determination Left side of expression (F) CT Right side of expression(F) Determination Heating oven temperature Heating oven time (minutes) Left side of expression (G) Determination n1 n2 left side of expression (D) Determination n1 n2 left side of expression (D) Determination AA 12 13 1.1 G 12 14 1.2 G O 0.86 B 442 582 729 G 1210 128 3865 G AB 10 12 1.2 G 10 13 1.3 G O 0.81 B 430 535 719 G 1236 116 3591 G B.C 15 18 1.2 G 16 19 1.2 G O 0.59 B 400 426 692 G 1210 125 2814 G AD 6 8 1.3 G 6 7 1.2 G O 0.64 B 436 623 721 G 1210 145 3604 G AE 12 16 1.3 G 12 15 1.3 G O 0.72 B 431 611 730 G 1152 152 4921 G AF 18 22 1.2 G 17 22 1.3 G O 0.98 B 384 396 680 G 1198 86 2449 G AG 6 7 1.2 G 5 7 1.4 G O 0.77 B 402 557 696 G 1209 147 3134 G AH 4 5 1.3 G 4 4 1.0 G O 1.18 VG 413 462 689 G 1209 135 2339 G THERE 12 15 1.3 G 12 14 1.2 G O 1.16 VG 325 476 643 G 1260 165 2717 G AJ 17 21 1.2 G 15 21 1.4 G O 1.26 G 430 543 696 G 1230 98 3269 G AK 12 14 1.2 G 12 13 1.1 G O 1.25 G 435 558 687 G 1211 156 5054 G AL 2 2 1.0 G 2 2 1.0 G O 1.16 VG 481 721 777 G 1180 161 16656 G AM 16 22 1.4 G 15 21 1.4 G X 1.26 G 248 539 546 G 1291 332 1602 G AN 10 12 1.2 G 10 11 1.1 G O 1.19 VG 401 560 667 G 1219 135 3134 G TO 11 12 1.1 G 10 11 1.1 G O 1.08 VG 396 523 673 G 1266 173 2694 G AP 7 9 1.3 G 7 8 1.1 G O 1.17 VG 443 551 724 G 1230 125 3378 G AQ 13 14 11.0 G 14 16 1.1 G O 1.08 VG 363 402 648 G 1250 140 2605 G AIR 21 26 1.2 G 22 25 1.1 G O 1.36 G 371 432 649 G 1241 192 3115 G AT 18 19 1.1 G 18 18 1.0 G O 1.16 VG 398 630 695 G 1263 191 3540 G AT 15 17 1.1 G 16 18 1.0 G O 1.17 VG 384 669 682 G 1203 203 3026 G AU 17 19 1.1 G 16 18 1.1 G O 1.39 G 385 456 664 G 1248 192 2697 G AV 17 19 1.1 G 16 18 1.1 G Δ 1.42 G 360 456 658 G 1248 192 2571 G A W 16 22 1.4 G 15 21 1.4 G X 1.25 G 248 539 546 G 1291 332 1602 G AX 17 19 1.1 G 16 18 1.1 G Δ 1.43 G 360 456 658 G 1248 192 2571 G
55/56
Petition 870190097560, of 09/30/2019, p. 63/77
[00138] Based on the examples and comparative examples described above, it is found that as long as the conditions of the present invention are met, it is possible to obtain a cold rolled steel sheet, a galvanized cold rolled steel sheet, a electrogalvanized cold rolled steel sheet, or an aluminized cold rolled steel sheet, all of which satisfy TS χ λ> 50000 MPa-% even after hot stamping, and a hot stamped steel produced from the steel sheet obtained cold rolled. Industrial applicability [00139] Since the cold rolled steel sheet and hot stamped steel that are obtained in the present invention can satisfy TS χ λ> 50000 MPa-% after hot stamping, cold rolled steel sheet and hot-stamped steel have a high pressing workability and high strength, and meet the current requirements for a vehicle such as additional weight reduction and a more complicated component shape.
Brief description of reference symbols
S1: CASTING STEP
S2: INGING STEP
S3: HEATING STEP
S4: HOT LAMINATION STEP
S5: COILING STAGE
S6: STRAINING STEP
S7: COLD LAMINATION STEP
S8: RECOVERY STEP
S9: STEEL LAMINATION STEP
S10: GALVANIZATION STEP
S11: CONNECTION STEP
S12: ALUMINIZATION STEP
S13: ELECTROGALVANIZATION STEP

权利要求:
Claims (20)
[1]
1. Hot stamped steel, characterized by the fact that it comprises, in mass%,
C: 0.030% to 0.150%;
Si: 0.010% to 1,000%;
Mn: 0.50% or more and less than 1.50%;
P: 0.001% to 0.060%;
S: 0.001% to 0.010%;
N: 0.0005% to 0.0100%;
Al: 0.010% to 0.050%, and optionally at least one among
B: 0.0005% to 0.0020%;
Mo: 0.01% to 0.50%;
Cr: 0.01% to 0.50%;
V: 0.001% to 0.100%;
Ti: 0.001% to 0.100%;
Nb: 0.001% to 0.050%;
Ni: 0.01% to 1.00%;
Cu: 0.01% to 1.00%;
Ca: 0.0005% to 0.0050%;
REM: 0.0005% to 0.0050%, and a balance of Fe and impurities, where when [C] is the amount of C in mass%, [Si] is the amount of Si in mass%, and [ Mn] is the amount of Mn and mass%, the expression (A) below is satisfied, the fraction of ferrite area is 40% to 95% and the fraction of martensite area is 5% to 60%, the total of the ferrite area fraction and the martensite area fraction is 60% or more, the hot stamped steel optionally also includes
Petition 870190097560, of 09/30/2019, p. 65/77
[2]
2/8 one or more between perlite, retained austenite, and bainite, the area fraction of the perlite is 10% or less, the volume fraction of the retained austenite is 5% or less, and the area fraction of the bainite is less than 40%, the martensite hardness measured with a nanoindentator satisfies the expression (B) below and the expression (C) below,
TS χ λ which is the product of the tensile strength TS by the bore expansion ratio λ is 50000 MPa-% or more, (5 χ [Si] + [Mn]) / [C]> 10 (A),
H2 / H1 <1.10 (B), σΗΜ <20 (C), and
H1 and the average hardness of the martensite on a portion of the surface of the thickness of the hot-stamped steel plate, the surface portion is an area having a width of 200 pm in the direction of thickness from the outermost layer, H2 is the hardness average of martensite in a central portion of the plate thickness, of hot stamped steel, the central portion is an area having a width of 200 pm in the direction of the thickness at the center of the plate thickness, and σΗΜ is the variation of the average hardness of the martensite in the central portion of the thickness of the hot-stamped steel plate.
2. Hot stamped steel according to claim 1, characterized by the fact that the fraction of MnS area that exists in hot stamped steel and having an equivalent circle diameter from 0.1 pm to 10 pm is 0.01 % or less, the expression (D) below is satisfied n2 / n1 <1.5 (D), and n1 is the average numerical density per 10,000 pm2 of MnS having an equivalent circle diameter of 0.1 pm to 10 pm in a portion 1/4 of the thickness of the hot-stamped steel plate, and n2 is the average numerical density per 10,000 pm2 of the MnS having a dia
Petition 870190097560, of 09/30/2019, p. 66/77
[3]
3/8 meter of equivalent circle from 0.1 pm to 10 pm in the central portion of the hot stamped steel plate thickness.
Hot-stamped steel according to claim 1 or 2, characterized by the fact that the hot-dip galvanized layer is formed on its surface.
[4]
4. Hot stamped steel according to claim
3, characterized by the fact that the hot dip galvanized layer is bonded.
[5]
5. Hot stamped steel according to claim 1 or 2, characterized by the fact that an electrogalvanized layer is formed on its surface.
[6]
6. Hot stamped steel according to claim 1 or 2, characterized by the fact that an aluminized layer is formed on its surface.
[7]
7. Method for the production of hot-stamped steel, characterized by the fact that it comprises:
ingot a molten steel having a chemical composition as defined in claim 1, and obtaining a steel;
heat the steel;
hot rolling steel with a hot rolling mill including a plurality of chairs;
winding steel after hot rolling;
stripping the steel after winding;
cold rolling steel with a cold rolling mill including a plurality of chairs after pickling under a condition that satisfies the expression (E) below;
annealing in which the steel is annealed at 700 ° C to 850 ° C after cold rolling and is cooled;
perform hardening lamination on steel after annealing;
Petition 870190097560, of 09/30/2019, p. 67/77
4/8 hot stamping in which the steel is heated to a temperature range of 700 ° C to 1000 ° C after hardening lamination is hot stamped within the temperature range, and is subsequently cooled to room temperature or more and 300 ° C or less,
1.5 χ r1 / r + 1.2 χ r2 / r + r3 / r> 1.00 (E), and ri (i = 1, 2, 3) is the individual reduction of the desired cold rolling in an i ^the chair (i = 1,2,3) based on the first chair of the plurality of chairs in cold rolling in units of%, er is the total reduction in cold rolling in units of%.
[8]
8. Method for producing hot stamped steel according to claim 7, characterized by the fact that cold rolling is carried out under a condition that satisfies the expression (E ') below,
1.20> 1.5 χ r1 / r + 1.2 χ r2 / r + r3 / r> 1.00 (E '), and ri (i = 1, 2, 3) is the individual reduction of cold rolling desired in i -th chair (i = 1, 2, 3) based on the first chair of the plurality of chairs in cold rolling in% units, er is the total reduction of cold rolling in% units.
[9]
9. Method for the production of hot-stamped steel according to claim 7 or 8, characterized by the fact that when CT is the winding temperature in the winding in ° C units, [C] is the amount of C in the steel in% by mass, [Mn] is the amount of Mn in steel in% by mass, [Cr] is the amount of Cr in steel in% by mass, and [Mo] is the amount of Mo in steel in% by mass , the expression (F) below is satisfied.
560 - 474 χ [C] - 90 χ [Mn] - 20 χ [Cr] - 20 χ [Mo] <CT <
830 - 270 χ [C] - 90 χ [Mn] - 70 χ [Cr] - 80 χ [Mo] (F)
[10]
Method for the production of hot stamped steel according to any one of claims 7 to 9, characterized by
Petition 870190097560, of 09/30/2019, p. 68/77
5/8 fact that when T is the heating temperature for heating in units of ° C, t is the time in the oven for heating in units of minutes, [Mn] is the amount of Mn in steel in mass%, and [S] is the amount of S in steel in% by mass, the expression (G) below is satisfied,
T χ ln (t) / (1.7 χ [Mn] + [S])> 1500 (G).
[11]
11. Method for producing hot stamped steel according to any one of claims 7 to 10, characterized by the fact that it also comprises:
galvanize the steel between annealing and hardening lamination.
[12]
12. Method for the production of hot stamped steel according to claim 11, characterized by the fact that it also comprises:
connect the steel between galvanizing and hardening lamination.
[13]
13. Method for producing hot stamped steel according to any one of claims 7 to 10, characterized by the fact that it also comprises:
electrogalvanize steel after hardening lamination.
[14]
14. Method for producing hot stamped steel according to any one of claims 7 to 10, characterized by the fact that it also comprises:
aluminize the steel between annealing and hardening lamination.
[15]
15. Cold rolled steel sheet, characterized by the fact that it comprises, in mass%:
C: 0.030% to 0.150%;
Si: 0.010% to 1,000%;
Petition 870190097560, of 09/30/2019, p. 69/77
6/8
Mn: 0.50% more and less than 1.50%;
P: 0.001% to 0.060%;
S: 0.001% to 0.010%;
N: 0.0005% to 0.0100%;
Al: 0.010% to 0.050%, and optionally at least one element between
B: 0.0005% to 0.0020%;
Mo: 0.01% to 0.50%;
Cr: 0.01% to 0.50%;
V: 0.001% to 0.100%;
Ti: 0.001% to 0.100%;
Nb: 0.001% to 0.050%;
Ni: 0.01% to 1.00%;
Cu: 0.01% to 1.00%;
Ca: 0.0005% to 0.0050%;
REM: 0.0005% to 0.0050%, and a balance of Fe and the inevitable impurities, where when [C] is the amount of C in mass%, [Si] is the amount of Si in mass%, and [Mn] is the amount of Mn in mass%, the expression (A) below is satisfied, the fraction of ferrite area is 40% to 95% and the fraction of martensite area is 5% to 60%, the total area fraction of the ferrite and the area fraction of the martensite is 60% or more, the cold rolled steel sheet optionally also includes one or more between perlite, retained austenite, and bainite, the perlite area fraction is 10 % or less, the volume fraction of the retained austenite is 5% or less, and the area fraction of the bainite is less than 40%, the martensite hardness n = measured with a nanoindentator satisfies the expression (H) below and the expression (I) below,
Petition 870190097560, of 09/30/2019, p. 70/77
7/8
TS χ λ which is the product of the tensile strength TS by the bore expansion ratio λ is 50000 MPa-% or more, (5 χ [Si] + [Mn]) / [C]> 10 (A),
H20 / H10 <1.10 (H), σΗΜ0 <20 (I), and
H10 is the average hardness of the martensite on a surface portion of the sheet thickness, the surface portion is an area having a width of 200 pm in the direction of thickness from the outermost layer, H20 is the average hardness of the martensite on a central portion of the plate thickness, the central portion is an area having a width of 200 pm in the direction of the thickness at the center of the plate thickness, and σΗΜ0 is the variation in the average hardness of the martensite in the central portion of the plate thickness.
[16]
16. Cold rolled steel sheet according to claim 15, characterized by the fact that the fraction of MnS area that exists in the cold rolled steel sheet and having an equivalent circle diameter from 0.1 pm to 10 pm is 0.01% or less, the following expression (J) is satisfied, n20 / n10 <1.5 (J), and n10 is the average numerical density per 10,000 pm2 of MnS having an equivalent circle diameter of 0, 1 pm to 10 pm in a portion 1/4 of the plate thickness, and n20 is the average numerical density per 10,000 pm2 of the MnS having an equivalent circle diameter of 0.1 pm to 10 pm in the central portion of the plate thickness .
[17]
17. Cold-rolled steel sheet according to claim 15 or 16, characterized by the fact that the hot-dip galvanized layer is formed on its surface.
[18]
18. Cold-rolled steel sheet according to claim 17, characterized by the fact that the galvanized layer by
Petition 870190097560, of 09/30/2019, p. 71/77
8/8 hot immersion is switched on.
[19]
19. Cold rolled steel sheet according to claim 15 or 16, characterized by the fact that an electrogalvanized layer is formed on its surface.
[20]
20. Cold-rolled steel sheet according to claim 15 or 16, characterized by the fact that an aluminized layer is formed on its surface.

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法律状态:
2018-11-13| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2019-07-02| B07A| Application suspended after technical examination (opinion) [chapter 7.1 patent gazette]|

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2019-09-10| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

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2020-03-24| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2020-05-12| 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 27/03/2014, OBSERVADAS AS CONDICOES LEGAIS. |

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2022-01-18| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 8A ANUIDADE. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2013076835|2013-04-02|

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JP2013-076835|2013-04-02|

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PCT/JP2014/058950|WO2014162984A1|2013-04-02|2014-03-27|Hot-stamp-molded article, cold-rolled steel sheet, and method for manufacturing hot-stamp-molded article|

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