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    • 专利摘要:
    Patent Summary: "High strength cold rolled steel sheet and method for producing it". It is an object of the present invention to provide a high strength cold rolled steel plate having a tensile strength ts of 1180 mpa or greater, obtained by preparing the metallographic structure in a component system free of expensive bonding elements, thereby improving elongation. , the flanging capacity in the stretch, and the bending properties of the steel sheet. To achieve the objective, the steel plate of the present invention has a specific chemical composition, and a microstructure including ferrite phase: 40? 60 ', bainite phase: 10' 30?, tempered martensite phase: 20? 40 ', and retained austenite phase: 5' at 20? in volume fraction, and satisfying the condition that the temperate martensite phase ratio having a longer axis length? 5? M for a total volume fraction of the tempered martensite phase is 80? at 100?
    公开号:BR112014022007B1
    申请号:R112014022007-7
    申请日:2013-02-28
    公开日:2019-04-30
    发明作者:Hidetaka Kawabe Kawabe；Takeshi Yokota；Reiko Sugihara；Shigeyuki Aizawa；Kazuki Nakazato
    申请人:Jfe Steel Corporation；
    IPC主号:
    专利说明:

    Descriptive Report of the Invention Patent for RESISTANT COLD LAMINATED STEEL SHEET AND METHOD FOR PRODUCTION OF THE SAME.
    TECHNICAL FIELD [001] The present invention relates to a cold rolled steel sheet having excellent forming capacity, which can be used appropriately in automotive structure parts that need to be formed by pressing into complicated shapes, and refers to a method for producing it. In the present invention, the retained austenite phase is used as a metallographic structure, the martensite phase is softened by tempering and the size of the tempered martensite phase is controlled without intentionally adding expensive elements such as Nb, V, Cu, Ni, Cr, Mo , etc. in particular, thus obtaining a homogeneous and fine microstructure. The present invention aims to obtain a high-strength cold-rolled steel sheet having tensile strength (TS): 1180 MPa or more, as well as to improve the elongation (El) and the ability to flange in the stretch (typically evaluated in terms of hole expansion (l)), and even its folding properties.
    BACKGROUND TECHNIQUE [002] In recent years, to improve fuel efficiency by reducing car weight and improve crash safety, the application of steel plates having a tensile strength of 980 MPa or more for parts has been positively promoted of automobile structures. Recently, the application of even stronger steel plates has been studied.
    [003] High strength steel sheets with TS: 1180 MPa or more used to be commonly applied to elements subjected to general work, such as reinforcement of bumpers and door impact beams. The application of such steel sheets to structural parts
    Petition 870190003552, of 11/01/2019, p. 4/11
    2/33 car touring having various complicated shapes due to press forming has recently been studied to also ensure crash safety and improve fuel efficiency by reducing the weight of vehicle structures. Therefore, steel sheets having excellent forming capacity are highly in demand.
    [004] However, an increase in the strength of steel sheets is, in general, likely to be accompanied by a reduction in their forming capacity. Consequently, the prevention of fractures caused during forming by pressing was a major challenge in promoting the application of high-strength steel sheets. In addition, in cases where the strength of steel plates is increased to TS: 1180 MPa or more in particular, rare extremely expensive elements such as Nb, V, Cu, Ni, Cr, and Mo are often required to be added intentionally in addition to C and Mn to ensure sufficient strength.
    [005] Examples of conventional techniques in relation to high strength cold rolled steel sheet having excellent forming capacity include such techniques of obtaining a high strength cold rolled steel sheet having a martensite phase or a retained austenite phase as a constituent phase of steel composition through the restriction of steel components and microstructure and the optimization of hot rolling and annealing conditions for the production of steel sheets as described in PTL 1 (JP 2004-308002 A), PTL 2 (JP 2005-179703 A), PTL 3 (JP 2006-283130 A), PTL 4 (JP 2004-359974 A), PTL 5 (JP 2010-285657 A), PTL 6 (JP 2010-059452 A), and PTL 7 (JP 2004-068050 A).
    LIST OF QUOTES
    PATENT LITERATURE [006] PTL 1: JP 2004-308002 A
    Petition 870180039075, of 05/11/2018, p. 11/48
    3/33 [007] PTL 2: JP 2005-179703 A [008] PTL 3: JP 2006-283130 A [009] PTL 4: JP 2004-359974 A [0010] PTL 5: JP 2010-285657 A [0011] PTL 6: JP 2010-059452 A [0012] PTL 7: JP 2004-068050 A
    SUMMARY OF THE INVENTION (TECHNICAL PROBLEM) [0013] In PTL 1, expensive elements may not be necessary; however, the specific component system described by PLT 1 is a component system having a high C content of C> 0.3%, which would affect the spot welding ability. In addition, PLT 1 describes findings about achieving a high elongation (El) with a component system having a high C content; however, it does not describe any findings about balancing the stretch flanging capacity and bending properties in addition to El and the low C content of C <0.3%.
    [0014] In PTL 2, the steel plate has a disadvantage due to the fact that it requires Cu or Ni as a stabilizing element for austenite. PTL 2 describes findings about achieving a high level of El at the TS level: 780 MPa to 980 MPa through the use of retained austenite. However, for example, a high-strength steel with TS: 1180 MPa or more, having a high C content, cannot have sufficient flanging capacity in the stretch. In addition, PLT 2 does not describe findings about improved folding properties.
    [0015] In PTL 3, the tempered martensite phase has a high volume fraction, and it is difficult to achieve an excellent balance between TS and El on a high-strength steel plate having TS: 1180 MPa or more. In addition, PTL 3 does not write any findings about improved stretch flanging capacity and stripping properties 870180039075, 11/05/2018, pg. 12/48
    4/33 bramento.
    [0016] In PTL 4, it is necessary to add Mo or V, which are expensive elements.
    [0017] In PTL 5, the steel sheet contains a small amount of retained austenite, and a favorable elongation would not be guaranteed when a high resistance, in particular, TS: 1180 MPa or more is desired.
    [0018] In PTL 6, it is directed to obtain a cold rolled steel sheet that has good elongation and bending properties at a TS resistance level: 780 MPa or more. However, the volume fraction of the martensite phase in the steel plate is low; The specific level of TS described is low in the order of 1100 MPa; and the maximum elongation described is about 18%. Consequently, this technique would not be able to guarantee a good balance between TS and El to achieve high strength and TS: 1180 MPa or more.
    [0019] In PTL 7, the technique for obtaining good bending properties at a high TS resistance: 780 MPa or more is also described. However, the specific TS value described is low, in the order of 1100 MPa, and the maximum elongation value described is around 18%. Consequently, this technique would not be able to guarantee a good balance between TS and El to achieve a high TS resistance: 1180 MPa or more.
    [0020] The present invention is created in view of the above circumstances, and it is an objective of the present invention to provide a high-strength cold-rolled steel sheet having a TS tensile strength of 1180 MPa or more with elongation, flange capability in the stretching and bending properties improved by the preparation of the metallographic structure in a component system free of expensive connection elements such as Nb, V, Cu, Ni, Cr,
    Petition 870180039075, of 05/11/2018, p. 13/48
    5/33 or Mo. It is another object of the present invention to provide a method for producing the same advantageously.
    (SOLUTION TO THE PROBLEM) [0021] As a result of the studies investigated by the present inventors to solve the above problems, they found that, in terms of welding capacity and forming capacity, it is possible to produce a high strength steel plate having resistance tensile strength (TS): 1180 MPa or more while achieving improvements in elongation, the ability to stretch in flanging, and bending properties of steel without adding C or rare rare metals to steel by strict control of the metallographic structure, in particular, the volume fraction of the bainite phase generated in the low temperature transformation of austenite, the volume fraction of the tempered martensite phase, and the low volume of the retained austenite phase.
    [0022] The present invention is based on the findings mentioned above.
    [0023] Specifically, the main features of the present invention are as follows.
    [0024] 1. A high-strength cold-rolled steel sheet having a chemical composition containing, in weight%:
    [0025] C: 0.12% to 0.22%;
    [0026] Si: 0.8% to 1.8%;
    [0027] Mn: 2.2% to 3.2%;
    [0028] P: 0.020% or less;
    [0029] S: 0.0040% or less;
    [0030] Al: 0.005% to 0.08%;
    [0031] N: 0.008% or less;
    [0032] Ti: 0.001% to 0.040%;
    [0033] B: 0.0001% to 0.0020%; and [0034] the rest being Fe and incidental impurities,
    Petition 870180039075, of 05/11/2018, p. 14/48
    6/33 [0035] where the steel plate has a microstructure including the ferrite phase: 40% to 60%, the bainite phase: 10% to 30%, the tempered martensite phase: 20% to 40%, and the phase retained austenite: 5% to 20% in volume fraction, and satisfying the condition that the ratio of tempered martensite having a shaft length greater than 5 mm to the total volume of the fraction of the tempered martensite phase is 80% to 100%.
    [0036] 2. A method for producing a high-strength cold-rolled steel plate comprising subjecting a steel plate having the chemical composition according to Claim 1 to hot rolling, pickling, first annealing at a temperature in the range of 350 ° C to 650 ° C, cold rolling, second annealing at a temperature in the range of 820 ° C to 900 ° C, third annealing in a temperature range of 720 ° C to 800 ° C, cooling at a rate of cooling from 10 ° C / s to 80 ° C / s until cooling stop temperature: 300 ° C to 500 ° C, retention at the above cooling stop temperature for 100 s to 1000 s, and fourth annealing at a temperature in the range from 100 ° C to 300 ° C.
    (ADVANTAGEOUS EFFECT OF THE INVENTION) [0037] The present invention can provide a high-strength cold-rolled steel sheet having excellent elongation, stretch flanging ability, bending properties, and tensile strength of 1180 MPa or more, without addition of expensive connecting elements to the steel plate. The high-strength cold-rolled steel sheet obtained by the present invention is suitably used in particular for automotive frame parts that must be subjected to the required press forming.
    MODALITY DESCRIPTION [0038] The present invention will be described in detail below.
    [0039] The inventors have made several studies to improve the forming capacity of high-cold rolled steel sheets
    Petition 870180039075, of 05/11/2018, p. 15/48
    7/33 resistance and consequently found that the desired result can be advantageously achieved by strictly controlling the volume fractions of the ferrite phase, the bainite phase, the tempered martensite phase, and the retained austenite phase, and making the tempered martensite phase have a thin and homogeneous microstructure with a component system free of extremely expensive rat elements such as Nb, V, Cu, Ni, Cr, or Mo. Thus, the present invention has been completed.
    [0040] The reasons for limiting the chemical composition and microstructure of a cold rolled steel sheet of the present invention will be described in detail below.
    [0041] The preferred ranges of the contents of the components of the chemical composition of steel in the present invention and the reasons for specifying the contents of the components for the preferred ranges of contents will be described below. In addition, although the unit of the content of each element included in the steel plate is “% by mass”, it will be expressed simply by “%”, unless otherwise specified.
    [0042] C: 0.12% to 0.22% [0043] Carbon (C) contributes effectively to guarantee sufficient strength by controlling the microstructure using the reinforcement of the solid solution and a low temperature transformation phase. In addition, carbon is an essential element in ensuring a sufficient retained austenite phase. Carbon is also an element that has an influence on the volume fraction of the martensite phase and on the hardness of the martensite phase, and also on the flanging capacity in the drawing of steel. In this respect, a C content of less than 0.12% makes it difficult to obtain the necessary volume fraction of the martensite phase, while a C content exceeding 0.22% not only significantly deteriorates the spot welding capacity but also leads to to a
    Petition 870180039075, of 05/11/2018, p. 16/48
    8/33 excessive hardening of the martensite phase and an increase in the volume fraction of the martensite phase, accompanied by an excessive increase in TS. Thus, the forming capacity of the steel is deteriorated and its ability to flange in the drawing is particularly deteriorated. Consequently, the C content should be in the range of 0.12% to 0.22%, preferably in the range of 0.16% to 0.20%. [0044] Si: 0.8% to 1.8% [0045] Silicon (Si) is an important element to promote the concentration of carbon in the austenite phase to suppress the generation of carbides, thus stabilizing the retained austenite phase. The Si content is necessarily at least 0.8% to obtain the above effect. However, if the Si content added to the steel exceeds 1.8%, the steel sheet becomes brittle and susceptible to fractures. However, if the Si content added to the steel exceeds 1.8%, the steel sheet becomes brittle and susceptible to fractures. In addition, the forming capacity of steel also decreases. Consequently, the Si content in steel should be in the range of 0.8% to 1.8%, preferably in the range of 1.0% to 1.6%.
    [0046] Mn: 2.2% to 3.2% [0047] Manganese (Mn) is an element to improve the hardening capacity of steel, and helps to easily guarantee a temperature transformation phase that contributes to high strength of steel. The manganese content needs to be at least 2.2% to achieve the above effect. On the other hand, an Mn content exceeding 3.2% causes a strip structure due to its segregation, which disturbs the uniform conformation in the formation of the flange in the stretching and bending. Consequently, the Mn content in steel should be in the range of 2.2% to 3.2%, preferably in the range of 2.6% to 3.0%.
    [0048] P: 0.020% or less [0049] Phosphorus (P) not only adversely affects the spot welding ability, but also segregates at the grain edges
    Petition 870180039075, of 05/11/2018, p. 17/48
    9/33 to induce fractures at the grain edges, thus deteriorating the forming capacity. Consequently, a P content is preferably reduced as much as possible, although a P content of up to 0.020% is allowed. Reducing phosphorus to an excessively low level, however, decreases production efficiency in the steel production process and increases the cost of production. Consequently, the preferable lower limit of the phosphorus content in steel is about 0.001%.
    [0050] S: 0.0040% or less [0051] Sulfur (S) forms a sulfide inclusion such as MnS. The MnS is expanded by cold rolling to be the starting point of a fracture during deformation, so the local deformation capacity of the steel is reduced. Therefore, sulfur in steel is preferably reduced as much as possible, although an S content of up to 0.0040% is allowed. Reducing the sulfur content to an excessively low level, however, is industrially difficult and increases the cost of desulfurization in the steel production process. Consequently, the preferable lower limit of the S content is around 0.0001%. The preferable range of the S content is 0.0001% to 0.0030%.
    [0052] Al: 0.005% to 0.08% [0053] Aluminum (Al) is added mainly for the purpose of deoxygenation. In addition, Al is effective in producing the austenite phase retained by suppressing the production of carbides, and Al is also a useful element to improve the resistance-elongation balance. To achieve the above objectives, the Al content needs to be 0.005% or more. However, an Al content exceeding 0.08% deteriorates the forming capacity due to the increase in inclusions such as alumina. Consequently, the Al content should be in the range of 0.005% to 0.08%, preferably in the range of 0.02 to 0.06%.
    [0054] N: 0.008% or less
    Petition 870180039075, of 05/11/2018, p. 18/48
    10/33 [0055] Nitrogen (N) is an element that deteriorates the resistance to aging. When the N content exceeds 0.008%, the resistance to aging deteriorates significantly. In addition, when boron is added, N bound to B forms BN to consume B, which deteriorates the hardening capacity derived from solute B. This makes it difficult to guarantee a martensite phase having a predetermined volume fraction. In addition, N is present as an impurity element in the ferrite phase, and deteriorates ductility due to aging stress. Therefore, the N content is preferably less, although the N content up to 0.008% is allowed. Reducing the nitrogen content to an excessively low level, however, increases the cost of removing nitrogen in the steel production process. Consequently, the lower limit of the N content is preferably about 0.0001%. Therefore, the preferred range of N content is 0.001% to 0.006%.
    [0056] Ti: 0.001% to 0.040% [0057] Titanium (Ti) forms carbonitrides or sulfides in the steel and contributes effectively to the improvement of the strength of the steel. When boron is added, titanium fixes hydrogen as TiN to suppress the formation of BN. Thus, Ti is an element that is also effective in achieving the hardening capacity due to B. To achieve these effects, the Ti content needs to be 0.001% or more. However, a Ti content exceeding 0.040% excessively precipitates Ti in the ferrite phase, which results in degradation in elongation due to excessive reinforcement of precipitation. Consequently, the titanium content in steel should be in the range of 0.001% to 0.040%, preferably in the range of 0.010% to 0.030%.
    [0058] B: 0.0001% to 0.0020% [0059] Boron (B) contributes effectively to increase the steel's hardness capacity to guarantee the low temperature transformation phase such as martensite phase and retained austenite phase, and boron is
    Petition 870180039075, of 05/11/2018, p. 19/48
    11/33 a useful element to obtain an excellent balance of resistance and stretching. To achieve this effect, the B content must be 0.0001% or more. However, a B content exceeding 0.0020% saturates the above effect. Consequently, the boron content should be in the range of 0.0001% to 0.0020%.
    [0060] In a steel plate of the present invention, components other than the components mentioned above are iron (Fe) and incidental impurities. However, the present invention does not exclude the possibility that its chemical composition includes a component other than those described above unless the inclusion of the component adversely affects the effects of the present invention.
    [0061] In the following, the preferred bands in relation to the steel microstructure, which bands are critically important in the present invention, and the reasons for restricting the steel microstructure to such bands will be described hereinafter.
    [0062] Volume fraction of the ferrite phase: 40% to 60% [0063] The ferrite phase is soft and contributes to the improvement of ductility. The volume fraction of the ferrite phase must be 40% or more to obtain the desired elongation. When the volume fraction of the ferrite phase is less than 40%, the volume fraction of the hard tempered martensite phase increases to excessively increase the strength of the steel, so that the elongation and flanging in the steel stretch are deteriorated. On the other hand, a ferrite phase having a volume fraction exceeding 60% makes it difficult to guarantee resistance: 1180 MPa or more. Consequently, the volume fraction of ferrite phase is in the range of 40% to 60%, preferably in the range of 40% to 55%.
    [0064] Volume fraction of the bainite phase: 10% to 30% [0065] Promoting the transformation of bainite promotes the concentration of C in the austenite phase. To guarantee a given quantity
    Petition 870180039075, of 05/11/2018, p. 20/48
    12/33 of retained austenite phase that finally contributes to the elongation, the volume fraction of bainite phase needs to be 10% more. On the other hand, a bainite phase having a volume fraction that exceeds 30% excessively increases the steel's resistance to more than TS: 1180 MPa, which makes it difficult to guarantee sufficient steel elongation. Consequently, the volume fraction of the bainite phase is in the range of 10% to 30%, preferably in the range of 15% to 25%.
    [0066] Volume fraction of the tempered martensite phase: 20% to 40% [0067] The tempered martensite phase obtained by reheating the hard martensite phase contributes to increase the strength of the steel. To guarantee the resistance of TS: 1180 MPa or more, the volume fraction of the tempered martensite phase must be 20% or more. However, an excessively high volume fraction of the tempered martensite phase excessively increases the strength of the steel to reduce the elongation of the steel. Consequently, the volume fraction of the tempered martensite phase needs to be 40% or less. With such microstructures having a volume fraction of the tempered martensite phase in the range of 20% to 40%, a balanced material having good strength, elongation, flanging ability in the stretch, and bending properties can be obtained. The volume fraction of tempered martensite is preferably in the range of 25% to 35%.
    [0068] Fraction of volume retained in the austenite phase: 5% to 20% [0069] When the retained austenite phase is subjected to induced stress transformation, that is, transformation of a part of the austenite phase retained in the martensite phase due to the tension caused due to the deformation of the material, the deformed part is hardened, which prevents the concentration of stresses and improves the ductility of the steel. To obtain high ductility, the volume fraction of the retained austenite phase contained in the steel must be 5% or more. However, the retained austenite phase is
    Petition 870180039075, of 05/11/2018, p. 21/48
    13/33 lasts due to the high concentration of C; therefore, when the volume fraction of the austenite phase retained on a steel sheet is too high to exceed 20%, the steel sheet is locally hardened. This inhibits homogeneous deformation of the steel material during elongation and flange formation on the stretch, which makes it difficult to guarantee excellent elongation and excellent flanging capacity on the stretch. In particular, in terms of the stretch flanging capacity, less retained austenite is preferable. Consequently, the volume fraction of the retained austenite phase must be 5% to 20%, preferably in the range of 7% to 18%.
    [0070] Ratio of the tempered martensite phase having a longer axis length <5 mm for the total volume fraction of the tempered martensite phase: 80% to 100% [0071] The tempered martensite phase is harder than the ferrite phase as a base microstructure . In the case of the same fraction of total volume of the tempered martensite phase, a small ratio of tempered martensite phase having a larger axis of 5 mm or less leads to the location of the tempered martensite phase. This inhibits uniform deformation, and results in a disadvantageous stretch flanging capacity compared to the thin and homogeneous microstructure that presents a more uniform deformation. Consequently, a lower ratio of crude tempered martensite phase and a higher ratio of tempered martensite phase are preferred. Thus, the ratio of tempered martensite phase having an axis length greater than 5 mm for a fraction of the total volume of the tempered martensite phase should be in the range of 80% to 100%, preferably in the range of 85% to 100%.
    [0072] Note that the “major axis” here means the maximum diameter of the respective tempered martensite phase observed by observing the microstructure in a cross section of the steel sheet along the rolling direction.
    Petition 870180039075, of 05/11/2018, p. 22/48
    14/33 [0073] The following will describe a method for producing a high-strength cold-rolled steel sheet of the present invention.
    [0074] In the present invention, a hot-rolled steel sheet by hot rolling and subsequently pickling is subjected to annealing at a temperature in the range of 350 ° C to 650 ° C (first annealing), cold rolling, annealing at a temperature in the range of 820 ° C to 900 ° C (second annealing), annealing at a temperature in the range of 720 ° C to 800 ° C (third annealing), cooling at a cooling rate of 10 ° C / s to 80 ° C / s to a cooling stop temperature of 300 ° C to 50 ° C, retention in the above cooling stop temperature range for 100 s to 1000 s. and another annealing at a temperature in the range of 100 ° C to 300 ° C (fourth annealing). Thus, a high-strength cold-rolled steel sheet desired by the present invention can be obtained. The steel sheet can subsequently be subjected to skin pass lamination.
    [0075] The limited ranges of production conditions and the rationale for the limitation will be described in detail below.
    [0076] Annealing temperature (first): 350 ° C to 650 ° C [0077] In the present invention, the first annealing is carried out after hot rolling and pickling; annealing temperature on this occasion less than 350 ° C is insufficient to temper after hot rolling, which leads to the inhomogeneous microstructure in which ferrite, martensite and bainite are mixed. Such microstructure of hot-rolled steel sheet causes insufficiently homogeneous refining of the steel. Thus, the increased ratio of crude martensite in the final annealing material after the fourth annealing results in a non-homogeneous microstructure, so that the stretching flanging capacity of the final annealing material is impaired.
    Petition 870180039075, of 05/11/2018, p. 23/48
    15/33 [0078] On the other hand, a temperature of the first annealing exceeding 650 ° C results in a crude double phase structure having ferrite and martensite or ferrite and perlite is inhomogeneous and hardened, and consequently a non-homogeneous microstructure before cold rolling. Thus, the ratio of crude martensite in the final annealing material, and the flanging capacity in the stretching of the final annealing material is reduced as well in this case. Finally, to obtain a microstructure that is significantly homogeneous, the annealing temperature of the first annealing after this hot lamination needs to be in the range of 350 ° C to 65 ° C.
    [0079] Annealing temperature (second): 820 ° C to 900 ° C [0080] When the annealing temperature of the second annealing performed after cold rolling is less than 820 ° C, the concentration of C in the austenite phase is promoted excessively during annealing, thus excessively hardening the martensite phase. Thus, the steel sheet has a hard and non-homogeneous microstructure even after the final annealing, which reduces the flanging capacity in the stretch. On the other hand, when the steel sheet is heated to a high temperature range of the single austenite phase exceeding 900 ° C at the second annealing, the steel is homogeneous but the grain size of the austenite is excessively rough. Thus, the ratio of the raw martensite phase in the final annealing material is increased to reduce the flanging capacity in the stretching of the final annealing material. Consequently, the annealing temperature of the second annealing should be in the range of 820 ° C to 900 ° C.
    [0081] Conditions other than annealing temperature are not particularly restricted, and annealing can be carried out according to a conventional method. Conditions preferably include cooling rate: 10 ° C / s to 80 ° C / s to stop temperature
    Petition 870180039075, of 05/11/2018, p. 24/48
    16/33 of cooling, cooling stop temperature: 300 ° C to 500 ° C, holding time: 100 s to 1000 s in the cooling stop temperature range, for the following reasons. Specifically, when the average cooling rate after annealing is less than 10 ° C / s, the ferrite phase is excessively produced, which makes it difficult to guarantee the bainite phase and the martensite phase and makes the steel plate have a softened microstructure and non-homogeneous. This results in a final annealing material having a non-homogeneous microstructure; thus, the forming capacity such as elongation and flanging capacity in the drawing of the steel are liable to be deteriorated. On the other hand, when the average cooling rate after annealing exceeds 80 ° C / s, an excessive production of martensite excessively hardens the steel sheet, which results in an excessively hardened final annealing material. Thus, the forming capacity such as elongation and the flanging capacity in drawing the resulting steel is likely to be reduced.
    [0082] Cooling on annealing is preferably carried out by gas cooling; however, oven cooling, fog cooling, cylinder cooling, water cooling, and the like can also be used in combination. In addition, when the cooling stop temperature after annealing cooling is less than 300 ° C, the production of the retained austenite phase is suppressed, which leads to an excessive production of the martensite phase. This results in excessively high strength of the steel plate and difficulty in ensuring sufficient elongation of a material from the final annealing. On the other hand, at a stopping temperature of the cooling exceeding 500 ° C it suppresses the production of the retained austenite phase, which makes it difficult to obtain an excellent ductility of the material of the final annealing. Cooling stop temperature
    Petition 870180039075, of 05/11/2018, p. 25/48
    17/33 after cooling in the annealing process is preferably in the range of 300 ° C to 500 ° C so that the material of the final annealing having a ferrite phase as the main phase as well as a tempered martensite phase and a retained austenite phase have a controlled content ratio; the strength of TS steel: 1180 MPa or more is guaranteed: and a good balance between elongation and the ability to flange in the stretch can be achieved. A retention time of less than 100 s is insufficient to promote the concentration of C in the austenite phase, making it difficult to obtain the desired volume fraction of the austenite phase retained in the final annealing material. Thus, the elongation of the steel sheet is deteriorated. On the other hand, retention for more than 1000 s does not increase the amount of austenite retained, nor does it improve elongation. Instead, the stretch is likely to be saturated. Thus, the retention time is preferably in the range of 100 s to 1000 s.
    [0083] Annealing temperature (third): 720 ° C to 800 ° C [0084] When the annealing temperature of the third annealing is less than 720 ° C, the volume fraction of the ferrite phase is excessively high, which makes it difficult ensure sufficient strength of TS: 1180 MPa or more. On the other hand, in a case of annealing at more than 800 ° C in a region of double phase temperature, the volume fraction of the austenite phase during heating is increased, and the concentration of C in the austenite phase is reduced. Consequently, the resistance of the martensite phase to be finally obtained is reduced, which means that it is difficult to guarantee the resistance of TS: 1180 MPa or more. If the annealing is carried out at a higher annealing temperature in the temperature region of the austenite single phase, the resistance of TS: 1180 MPa can be guaranteed; however, the volume fraction of the ferrite phase is reduced while the volume fraction of the martensite phase is increased, which results in difficulties in ensuring
    Petition 870180039075, of 05/11/2018, p. 26/48
    18/33 a sufficient El. Consequently, the annealing temperature of the third annealing should be in the range of 720 ° C to 800 ° C.
    [0085] Cooling rate: 10 ° C / s to 80 ° C / s [0086] The cooling rate after the third annealing is important in terms of obtaining the desired volume fraction of a low temperature transformation phase. When the average cooling rate in the cooling process is less than 10 ° C / s, it is difficult to guarantee a sufficient bainite phase and a martensite phase. Consequently, an excessive amount of ferrite phase is produced, and the steel plate is softened. Thus, it is difficult to guarantee sufficient strength of the steel sheet. On the other hand, when the cooling rate after the third annealing exceeds 80 ° C / s, an excessive production of martensite excessively hardens the steel, which results in deterioration of the forming capacity such as elongation and stretching flanging capacity.
    [0087] This cooling is preferably carried out by gas cooling; however, oven cooling, fog cooling, cylinder cooling, water cooling, and the like can be used in combination.
    [0088] Cooling stop temperature: 300 ° C to 500 ° C [0089] When the cooling stop temperature of the cooling process after the third annealing is less than 300 ° C, the production of retained austenite is suppressed, the which leads to excessive production of martensite phase. This results in excessively high strength and difficulty in ensuring sufficient elongation of the steel. On the other hand, a cooling stop temperature exceeding 500 ° C suppresses the production of the retained austenite phase, which makes it difficult to obtain excellent ductility of the steel sheet. This cooling stop temperature must be in the range of 300 ° C to 500 ° C for the steel plate to have a ferrite phase as a phase
    Petition 870180039075, of 05/11/2018, p. 27/48
    19/33 main as well as martensite phase and retained austenite phase having a controlled content ratio; the strength of TS: 1180 MPa or more is guaranteed: and a good balance between elongation and stretching flanging capacity can be achieved.
    [0090] Retention time: 100 s to 1000 s [0091] The retention time at the cooling stop temperature described above less than 100 s is insufficient to promote the concentration of C in the austenite phase, making it difficult to obtain the fraction of desired volume of the austenite phase retained in the resulting steel plate. Thus, the elongation and the flanging capacity in the drawing of the steel sheet are deteriorated due to the excessive production of martensite phase leading to an excessively high resistance. On the other hand, the retention of more than 1000 s does not increase the volume fraction of the retained austenite phase, nor does it improve the elongation of the steel. On the contrary, the stretch is liable to be saturated. Therefore, the retention time should be in the range of 100 s to 1000 s. The cooling after retention need not be limited in particular, and the cooling can be carried out to the desired temperature by a given method.
    [0092] Annealing temperature (room): 100 ° C to 300 ° C [0093] When the temperature of the annealing room is less than 100 ° C, the martensite phase is not sufficiently softened by tempering, leading to an excessive hardening of the steel . Thus, the properties of flanging capacity in the drawing of steel are reduced. On the other hand, if the annealing temperature exceeds 300 ° C, the martensite phase is softened excessively to make it hard to guarantee TS: 1180 MPa or more. In addition, the retained austenite phase obtained after the third CAL (continuous annealing) is decomposed, so that the retained austenite phase can never have the desired volume fraction. Thus, it is difficult to obtain a steel cover that has
    Petition 870180039075, of 05/11/2018, p. 28/48
    20/33 excellent balance TS-El. Consequently, the annealing temperature of the fourth annealing should be in the range of 100 ° C to 300 ° C.
    [0094] Note that the first to fourth anneals can be performed by any annealing method as long as the above conditions are met, and the method can be either continuous annealing or box annealing.
    [0095] Other preferable production conditions are as follows. [0096] A plate can be produced by the method of continuous casting of thin plates or by conventional casting; however, the slab is preferably produced by the continuous casting method to reduce segregation.
    [0097] The heating temperature of the hot rolling mill is preferably 1100 ° C or more. In terms of reduced scaling and reduced fuel consumption, the upper limit of the heating temperature is preferably 1300 ° C.
    [0098] Hot rolling is preferably finished at 850 ° C or more thus avoiding the lamellar structure of the low temperature transformation phase such as ferrite and perlite. In addition, in terms of reducing scaling and making the structures thin and homogeneous by suppressing the hardening of the crystal grains, the upper limit of the hot rolling temperature is preferably 950 ° C.
    [0099] After hot rolling, cooling is carried out as appropriate until winding, and cooling conditions are not particularly limited.
    [00100] The winding temperature after hot rolling is preferably 450 ° C to 600 ° C in terms of cold rolling capacity and surface quality. The steel sheet that has been wound is subjected to pickling, annealing as described above (first), cold rolling process, and then annealing processes
    Petition 870180039075, of 05/11/2018, p. 29/48
    21/33 described above (second to fourth). Pickling after hot rolling can be carried out by a conventional method. In addition, cold rolling is preferably carried out at a rate of reduction of 20% or more in terms of suppressing the hardening of the grains during recrystallization in annealing processes or inhomogeneous microstructure production. Although the rate of reduction is allowed to be high, it is preferably 60% or less so as not to increase the lamination path.
    [00101] A cold-rolled steel sheet obtained as described above can be subjected to hardening lamination (skin pass lamination) to correct the shape and adjust the surface roughness. However, excessive skin pass lamination introduces tension in the steel plate and extends the crystal grains in the lamination direction. And then the ductility of the steel sheet can deteriorate. Consequently, the rate of reduction of the skin pass lamination is preferably 0.05% to 0.5%.
    EXAMPLES [00102] Steel samples having the respective chemical compositions shown in Table 1 were fused to obtain plates. Each plate was subjected to heating to 1220 ° C, hot rolling to a final delivery temperature of 880 ° C, and cooling at a rate of 50 ° C / s immediately after rolling, winding at 550 ° C, pickling with hydrochloric acid, processing the first annealing under the conditions shown in Table 2, and then cold rolling. Thus, the plates were finished as cold-rolled steel sheets having a thickness of 1.6 mm.
    [00103] Subsequently, the cold-rolled steel sheets thus obtained were subjected to the second to fourth annealing processes under the conditions shown in Table 2. The cooling after the second annealing was carried out under the preferred conditions 870180039075, 05/11 / 2018, p. 30/48
    22/33 channels described above: cooling rate: 10 ° C / s to 80 ° C / s until the cooling stop temperature, cooling stop temperature: 300 ° C to 500 ° C, and retention time in the cooling stop temperatures: in the range of 100 s to 1000 s. Material properties of each of the cold rolled steel sheet samples thus obtained were investigated by the material tests described below.
    [00104] The results obtained are shown in Table 3. Note that the values underlined in Tables 2 and 3 indicate that these values are outside the scope of the present invention. .
    (1) Structure of the steel sheet [00105] The structure of each of the cold rolled steel sheet samples was analyzed by observing the thickness of the sheet x position at 1/4 of the section of the cut steel sheet along the direction of laminating the steel plate sample by a scanning electron microscope (SEM). The observation was performed with N = 5 (i.e. with five observation fields). For the volume fraction of the ferrite phase in which no precipitate such as carbides was observed (polygonal ferrite phase), the area occupied by the ferrite phase present in a given 50 mm x 50 mm square area was determined by image analysis using a microphotograph of the sectional microstructure x 2000. As described above, the volume fraction of the ferrite phase was calculated.
    [00106] The volume fraction of the retained austenite phase was determined by the X-ray diffraction method using Mo K-alpha X-rays. Specifically, the volume fraction of the retained austenite phase was calculated based on the peak intensities of the plane (211) and plane (220) of the austenite phase and the plane (200) and plane (220) of the ferrite phase using a steel sheet specimen and analyzing, as a measuring surface, its surface in the vicinity of the 1/4 position
    Petition 870180039075, of 05/11/2018, p. 31/48
    23/33 depth in the direction of the plate thickness.
    [00107] For the volume fraction of the tempered martensite phase, the microstructure was observed with a scanning electron microscope (SEM) before and after the fourth annealing, the microstructure must have a relatively smooth surface in massive form before the quench was eventually annealed in the temper. When fine carbides were discovered to precipitate within a microstructure, the microstructure was defined as a tempered martensite phase. And the area ratio of the tempered martensite phase was measured and determined as the volume fraction of the tempered martensite phase. Each of the samples was observed using a sectional microphotography x 2000 d microstructure, and the area occupied by the tempered martensite phase in a given 50 mm x 50 mm square area was determined. Only when the temperature of the fourth final annealing was less than 100 ° C, the structure observed to have a massive smooth surface without carbides in the form of dots on the surface after the fourth final annealing was specified as a mixture of retained austenite phase and martensite phase. . The difference between the total volume fraction of the mixed phase and the volume fraction of the retained austenite determined by X-ray diffraction was determined as the volume fraction of the martensite phase that was not tempered.
    [00108] The ratio of the tempered martensite phase having an axis diameter greater than 5 mm or less was determined by calculating the ratio of the tempered martensite phase having an axis diameter greater than 5 mm. Specifically, the ratio of the area occupied by the tempered martensite phase having an axis diameter greater than 5 mm present in a given square area of 50 mm x 50 mm was determined by image analysis of the tempered martensite phase greater than 5 mm using a sectional microphotography x 2000 of the microstructure in the lamination direction. The area ratio thus obtained was subtracted from the
    Petition 870180039075, of 05/11/2018, p. 32/48
    24/33 total to obtain the volume fraction of the tempered martensite phase having an axis diameter greater than 5 mm or less. The “major axis” here refers to the maximum diameter of each tempered martensite phase.
    [00109] Initially, the ferrite phase and the low temperature transformation phase were differentiated, and the volume fraction of the ferrite phase was determined. Next, the volume fraction of the retained austenite phase was determined by X-ray diffraction, and the volume fraction of the tempered martensite phase was then discovered by observation in an SEM as described above. The final balance was considered as a Bainite phase. Thus, the volume fraction of each phase was determined.
    (2) Tensile properties [00110] A tensile test was performed according to JIS Z 2241 to evaluate the tensile properties of test samples No. 5 prepared according to JIS Z 2201 with its longitudinal (tensile) direction oriented to 90 ° rolling direction. For the evaluation criterion of the tensile properties, samples having TS x El> 20000 MPa-% (TS: tensile strength (MPa) and El: total elongation (%)) were evaluated as having good tensile properties.
    (3) Hole expansion ratio [00111] A test was performed based on Japan Iron and Steel Federation Standard JFS T 1001. A hole having an initial diameter of d0 = 10 mm was drilled in each sample. A tapered hole punch having a vertical angle of 60 ° was used to expand the hole until the fracture penetrates through the thickness of the plate. The diameter of the hole punch d after fracture penetration was measured to calculate the hole expansion ratio (%) = {(d - d0) / d0} x 100. Steel plates referenced with the same number of steel samples were tested three times to find the average value (l) of the bore expansion ratios. Note that for the stretch flange capacity criterion (TS
    Petition 870180039075, of 05/11/2018, p. 33/48
    25/33 x l), TS χ λ> 35000 MPa-% or more was rated as favorable.
    (4) Folding properties [00112] Samples were collected from a steel sheet having a sheet thickness of 1.6 mm in such a way that the groove of a folded portion of each sample is in parallel with the rolling direction. The samples were 40 mm x 100 mm in size (the longitudinal direction of each sample was perpendicular to the lamination direction). A V-fold (90 °) was carried out with a load underneath: 3 t at the bottom neutral using a metallic folding mold having a radius of curvature R = 1.0 mm, and if the tip of the fold is fractured or not determined by visual observation. Samples without fractures were evaluated as having favorable folding properties.
    Petition 870180039075, of 05/11/2018, p. 34/48 [TABLE 1]
    Steel sample Chemical composition (% by mass) Note Ç Si Mn P s Al N You B THE 0.180 1.45 2.80 0.004 0.0008 0.050 0.004 0.015 0.0005 Suitable steel B 0.140 1.65 3.15 0.008 0.0006 0.040 0.005 0.020 0.0015 Suitable steel Ç 0.210 1.25 2.40 0.012 0.0009 0.030 0.006 0.025 0.0010 Suitable steel D 0.160 1.00 3.05 0.015 0.0005 0.060 0.003 0.030 0.0015 Suitable steel AND 0.190 1.55 2.65 0.006 0.0007 0.050 0.004 0.010 0.0005 Suitable steel F 0.260 1.30 2.70 0.010 0.0008 0.040 0.004 0.020 0.0010 Comparative steel
    26/33 [TABLE 2]
    No. Steel sample Annealing temperature (first) (O) Annealing temperature (sec) (C) Annealing temperature (third) (C) Cooling rate(° C / s) Temp. cooling stop(° C) Retention time(s) Annealing temperature(fourth) (° C) Note 1 THE 600 855 760 20 380 180 200 Example of the Invention 2 B 550 845 770 25 400 200 210 Example of the Invention 3 Ç 500 835 780 30 420 220 180 Example of the Invention
    Petition 870180039075, of 05/11/2018, p. 35/48
    No. Steel sample Annealing temperature (first) (° C) Annealing temperature (sec) (° C) Annealing temperature(third) (° C) Cooling rate(° C / s) Temp. cooling stop(° C) Retention time(s) Annealing temperature (quarter) (° C) Note 4 D 640 840 740 15 360 150 220 Example of the Invention 5 AND 620 850 750 35 400 450 180 Example of the Invention 6 F 580 860 770 45 350 170 260 Comparative example 7 THE 150 870 790 55 375 190 140 Comparative example 8 THE 780 880 780 65 400 210 250 Comparative example 9 THE 550 740 770 75 425 230 150 Comparative example 10 THE 600 950 760 60 450 250 260 Comparative example 11 THE 650 855 700 50 350 300 160 Comparative example 12 THE 625 875 850 40 375 450 270 Comparative example 13 THE 575 890 780 5 400 550 170 Comparative example
    27/33
    Petition 870180039075, of 05/11/2018, p. 36/48
    No. Steel sample Annealing temperature (first) (° C) Annealing temperature (sec) (° C) Annealing temperature(third) (° C) Cooling rate(° C / s) Temp. cooling stop(° C) Retention time(s) Annealing temperature (quarter) (° C) Note 14 THE 550 870 770 100 425 400 280 Comparative example 15 THE 525 850 760 30 200 300 180 Comparative example 16 THE 400 830 750 20 550 200 265 Comparative example 17 THE 450 820 740 15 400 30 175 Comparative example 18 THE 525 860 760 35 360 200 80 Comparative example 19 THE 575 880 770 45 420 150 350 Comparative example
    28/33
    Petition 870180039075, of 05/11/2018, p. 37/48 [TABLE 3]
    No. Steel sample Microstructure Material properties Note Volume fraction of the ferrite phase (%) Volume fraction of the bainite phase (%) Volume fraction of the tempered martensite phase (%) Volume fraction of retained austenite phase (%) Tempered martensite phase ratio (diameter of the longest axis<5 pm) (%) YP(MPa) TS(MPa) El (%) λ (%) Fractures at the tip of the fold TS x El(MPaL%) TS x λ(MPaL%) 1 THE 42 15 34 9 86 875 1220 17.5 34 No 21350 41480 Example of the Invention 2 B 47 17 28 8 90 865 1200 17.5 31 No 21000 37200 Example of the Invention 3 Ç 49 15 27 9 87 860 1185 18.2 33 No 21567 39105 Example of the Invention 4 D 51 15 26 8 88 880 1180 18.5 32 No 21830 37760 Example of the Invention 5 AND 48 19 25 8 86 870 1190 18.1 31 No 21539 36890 Example of the Invention 6 F 31 15 48 6 83 1125 1350 13.8 22 Yes 18630 29700 Comparative example 7 THE 42 17 30 11 65 900 1280 15.5 18 Yes 19840 23040 Comparative example 8 THE 47 18 29 6 55 1105 1300 14.8 17 Yes 19240 22100 Comparative example 9 THE 35 12 45 8 89 1080 1330 14.2 19 Yes 18886 25270 Comparative example
    29/33
    Petition 870180039075, of 05/11/2018, p. 38/48
    No. Steel sample Microstructure Material properties Note Volume fraction of the ferrite phase (%) Volume fraction of the bainite phase (%) Volume fraction of the tempered martensite phase (%) Volume fraction of retained austenite phase (%) Tempered martensite phase ratio (diameter of the longest axis<5 pm) (%) YP(MPa) TS(MPa) El (%) λ (%) Fractures at the tip of the fold TS x El(MPaL%) TS x λ(MPaL%) 10 THE 45 16 33 6 60 990 1270 14.6 16 Yes 18542 20320 Comparative example 11 THE 78 11 7 4 100 720 1050 22.7 45 No 23835 47250 Comparative example 12 THE 32 24 39 5 82 1140 1290 14.4 26 Yes 18576 33540 Comparative example 13 THE 68 9 18 5 100 710 1080 23.1 48 No 24948 51840 Comparative example 14 THE 18 19 59 4 81 1165 1370 12.8 15 Yes 17536 20550 Comparative example 15 THE 32 16 48 4 82 990 1310 13.4 22 Yes 17554 28820 Comparative example 16 THE 56 18 22 4 93 860 1260 13.8 28 Yes 17388 35280 Comparative example 17 THE 34 8 55 3 85 1020 1340 11.9 16 Yes 15946 21440 Comparative example 18 THE 44 15 (* 33) 81210 1380 12.7 9 Yes 17526 12420 Comparative example
    30/33
    Petition 870180039075, of 05/11/2018, p. 39/48
    No. Steel sample Microstructure Material properties Note Volume fraction of the ferrite phase(%) Volume fraction of the bainite phase (%) Volume fraction of the tempered martensite phase (%) Volume fraction of retained austenite phase (%) Tempered martensite phase ratio (diameter of the longest axis<5 pm) (%) YP(MPa) TS(MPa) El(%) λ(%) Fractures at the tip of the fold TS x El(MPaL%) TS x λ(MPaL%) 19 THE 48 19 31 2 86 930 1020 19.3 52 Yes 19686 53040 Comparative example
    * Martensite that is not tempered once low temperature annealing has been carried out
    31/33
    Petition 870180039075, of 05/11/2018, p. 40/48
    32/33 [00113] Table 3 shows the following:
    [00114] In each sample of the examples of the invention Nos. 1 to 5, a cold-rolled steel sheet of high strength excellent in elongation, flanging ability in stretching, and bending properties was obtained. These cold rolled steel sheets met TS x El> 20000 MPa-% or more at TS> 1180 MPa and were bent in V at 90 ° at TS xl> 35000 MPa-% and R / t = 1.0 / 1, 6 = 0.625 without fractures.
    [00115] Meanwhile, sample no. 6 having a component outside the appropriate range specified by the present invention, no. 9 of low temperature in Second annealing, no. 14 of excessively high cooling rate, no. 15 of low temperature cooling stop, and the short retention time n ° 17 each had an excessively high volume fraction of tempered martensite phase, an excessively high tensile strength, and insufficient elongation and stretching flanging capacity.
    [00116] Sample No. 7 of low annealing temperature in the first annealing after hot rolling, No. 8 of high annealing temperature, and No. 10 of high annealing temperature in the second annealing had a high ratio of crude tempered martensite phase , leading to poor stretching flanging capacity.
    [00117] Sample no. 11 of low annealing temperature at the third annealing and no. 13 of slow cooling rate each had a high volume fraction of the ferrite phase, so that TS> 1180 MPa was not satisfied.
    [00118] Sample No. 12 of high annealing temperature in the third annealing had a low volume fraction of the ferrite phase and an excessively high resistance, resulting in insufficient elongation and stretching flanging capacity.
    Petition 870180039075, of 05/11/2018, p. 41/48
    33/33 [00119] The sample No. 16 of high temperature of cooling stop in the third annealing and the No. 19 of high temperature in the annealing of temper (fourth annealing) had low fraction of volume of retained austenite, resulting in insufficient ductility. In addition, the martensite phase of No. 19 was excessively softened, so that TS> 1180 MPa was not satisfied.
    [00120] The sample No. 18 of low temperature in the annealing of tempering (fourth annealing) had insufficient volume fraction of tempered martensite and excessively high resistance, resulting in insufficient flanging capacity.
    INDUSTRIAL APPLICABILITY [00121] According to the present invention, a high-strength cold-rolled steel sheet having tensile strength (TS): 1180 MPa or more and excellent forming capacity can be obtained at low cost by properly controlling the volume fractions of the ferrite phase, the tempered martensite phase, the retained austenite phase, and the bainite phase without intentionally adding expensive elements such as Nb, V, Cu, Ni, Cr, Mo, etc. to the steel plate.
    [00122] In addition, the high-strength cold-rolled steel sheet of the present invention is suitably used in particular for parts of automobile structures. Above all, it is advantageously used for applications such as architecture and home appliances that require accurate dimensional accuracy and good forming capacity.
    权利要求:
    Claims (2)
    [1]
    1. Resistant cold-rolled steel sheet, characterized by the fact that it has a chemical composition consisting of, in% by mass:
    C: 0.12% to 0.22%;
    Si: 0.8% to 1.8%;
    Mn: 2.2% to 3.2%;
    P: 0.020% or less;
    S: 0.0040% or less;
    Al: 0.005% to 0.08%;
    N: 0.008% or less;
    Ti: 0.001% to 0.040%;
    B: 0.0001% to 0.0020%; and the remainder being Fe and incidental impurities, in which the steel plate has a microstructure consisting of ferrite phase: 40% to 60%, bainite phase: 10% to 30%, tempered martensite phase: 20% to 40%, and retained austenite phase: 5% to 20% in volume fraction, and satisfying the condition that the ratio of the tempered martensite phase having an axis length greater than 5 mm to the total volume fraction of the tempered martensite phase is 80% to 100 %, and the steel sheet has a tensile strength of 1180 MPa or more, a TS x EL ratio> 20000 MPa ·% and a TS xl ratio> 35000 MPa-%.
    [2]
    2. Method for producing a cold-rolled resistant steel sheet as defined in claim 1, characterized in that it comprises subjecting a steel sheet having the chemical composition as defined in claim 1 to hot rolling at 1100 ° C or more up to 1300 ° C with finishing laminating temperature of 850 ° C or more up to 950 ° C, winding at a temperature
    Petition 870190003552, of 11/01/2019, p. 5/11
    2/2 winding from 450 ° C to 600 ° C, pickling, first annealing at a temperature in the range 350 ° C to 650 ° C, cold rolling, second annealing at a temperature in the range 820 ° C to 900 ° C, to the third annealing at a temperature in the range of 720 ° C to 800 ° C, to cooling at a cooling rate of 10 ° C / s to 80 ° C / s until the temperature of the cooling stop: 300 ° C to 500 ° C, retention to the above cooling stop range for 100 s to 1000 s, and the fourth annealing at a temperature in the range of 100 ° C to 300 ° C.
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    法律状态:
    2018-03-13| B06T| Formal requirements before examination [chapter 6.20 patent gazette]|
    2018-10-16| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application [chapter 6.1 patent gazette]|
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    2019-04-30| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/02/2013, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/02/2013, OBSERVADAS AS CONDICOES LEGAIS |
    2021-03-16| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 8A ANUIDADE. |
    2021-07-06| B24J| Lapse because of non-payment of annual fees (definitively: art 78 iv lpi, resolution 113/2013 art. 12)|Free format text: EM VIRTUDE DA EXTINCAO PUBLICADA NA RPI 2619 DE 16-03-2021 E CONSIDERANDO AUSENCIA DE MANIFESTACAO DENTRO DOS PRAZOS LEGAIS, INFORMO QUE CABE SER MANTIDA A EXTINCAO DA PATENTE E SEUS CERTIFICADOS, CONFORME O DISPOSTO NO ARTIGO 12, DA RESOLUCAO 113/2013. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2012050591A|JP5348268B2|2012-03-07|2012-03-07|High-strength cold-rolled steel sheet having excellent formability and method for producing the same|
    JP2012-050591|2012-03-07|
    PCT/JP2013/001217|WO2013132796A1|2012-03-07|2013-02-28|High-strength cold-rolled steel sheet and process for manufacturing same|
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