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WO2017150117A1 - Tôle en acier à haute résistance et son procédé de fabrication - Google Patents

Tôle en acier à haute résistance et son procédé de fabrication Download PDF

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Publication number
WO2017150117A1
WO2017150117A1 PCT/JP2017/004594 JP2017004594W WO2017150117A1 WO 2017150117 A1 WO2017150117 A1 WO 2017150117A1 JP 2017004594 W JP2017004594 W JP 2017004594W WO 2017150117 A1 WO2017150117 A1 WO 2017150117A1
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Prior art keywords
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steel sheet
residual
temperature
mass
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PCT/JP2017/004594
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English (en)
Japanese (ja)
Inventor
宗朗 池田
康二 粕谷
忠夫 村田
賢司 斉藤
俊夫 村上
裕一 二村
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Kobe Steel Ltd
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Kobe Steel Ltd
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Priority claimed from JP2016182966A external-priority patent/JP6749818B2/ja
Application filed by Kobe Steel Ltd filed Critical Kobe Steel Ltd
Priority to US16/080,571 priority Critical patent/US20190085426A1/en
Priority to MX2018010446A priority patent/MX2018010446A/es
Priority to EP17759588.1A priority patent/EP3412786B1/fr
Priority to CN201780013822.5A priority patent/CN108699653B/zh
Priority to KR1020187027683A priority patent/KR102174562B1/ko
Publication of WO2017150117A1 publication Critical patent/WO2017150117A1/fr
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to a high-strength steel plate and a manufacturing method thereof. Specifically, it has excellent workability at room temperature, and the tensile strength when processing at a temperature of 100 to 350 ° C. is much lower than the molding load when processing at room temperature is 980 MPa or more.
  • the present invention relates to a high-strength steel sheet and a manufacturing method thereof.
  • Steel sheets used for automobile structural parts and the like are required to have a high strength of 980 MPa or more in order to realize collision safety for passengers and fuel efficiency improvement.
  • a steel plate is usually formed into a part shape at room temperature, and this forming is subjected to press working. Therefore, the steel sheet is required to have good press workability (hereinafter sometimes simply referred to as workability).
  • a TRIP (Transformation Induced Plasticity) steel sheet is known as a steel sheet having both strength and workability (for example, Patent Document 1).
  • a TRIP steel sheet is a steel sheet containing metastable austenite (hereinafter sometimes referred to as residual austenite, sometimes referred to as residual ⁇ ), and transforms into martensite when the steel sheet deforms under stress. This has the effect of promoting the hardening of the deformed portion and preventing the concentration of strain, thereby improving the uniform deformability and exhibiting good elongation.
  • residual austenite hereinafter sometimes referred to as residual austenite, sometimes referred to as residual ⁇
  • the TRIP steel sheet may not be applied depending on the part shape. Therefore, it is desired to reduce the load on the press machine and reduce the molding load at the time of pressing. That is, it is recommended that the strength is low during press working and high strength when used after press working.
  • a method of press forming by heating the steel plate to, for example, about 100 ° C. to A 1 point is conceivable.
  • the deformation resistance is reduced by warming the steel plate, the forming load during press working can be reduced.
  • Patent Documents 2 and 3 are known as techniques for reducing the forming load during press working by warming and forming a steel plate.
  • Patent Document 2 describes a high-tensile steel sheet having a tensile strength of 450 MPa or more and excellent in warm formability and shape freezing property, which is suitable for a processing method in which heating is performed in a temperature range of 350 ° C. to A 1 point and press forming. Has been.
  • This high-tensile steel sheet satisfies a predetermined component composition, and the ratio of the tensile strength at 450 ° C. to the tensile strength at room temperature is 0.7 or less, and the crystal structure of the steel is that of the martensite phase.
  • the volume ratio is 10% or more and 80% or less, the average diameter of each dispersed martensite phase is 8 ⁇ m or less, and the volume ratio of the ferrite phase is the largest in the structure other than martensite.
  • the high-strength thin steel sheet described in Patent Document 2 has a small decrease in tensile strength at 150 ° C., and in order to obtain a sufficient effect of reducing the load at the time of forming, after all, it is in a temperature range of 350 ° C. to A 1 point. It is necessary to heat and press mold. However, when heated to such a high temperature, the surface state of the steel sheet is impaired by oxidation, and the energy for heating the steel sheet increases.
  • Patent Document 3 describes a high-strength steel sheet that sufficiently reduces strength when warm-formed at 150 to 250 ° C., but can ensure high strength of 980 MPa or more when used at room temperature after forming.
  • This high-strength steel sheet has an area ratio of 5 to 20% of retained austenite with respect to the entire structure, and the C concentration (C ⁇ R ) of the retained austenite is controlled to 0.5 to 1.0% by mass.
  • the present invention has been made paying attention to the above-mentioned circumstances, and the purpose thereof is excellent in workability at room temperature, in particular, elongation and hole expansibility, for a high-strength steel sheet having a tensile strength of 980 MPa or more.
  • Another object of the present invention is to provide a high-strength steel sheet having a reduced forming load when processed at a temperature of 100 to 350 ° C., and a method for producing the same.
  • One aspect of the present invention is, in mass%, C: 0.10 to 0.5%, Si: 1.0 to 3%, Mn: 1.5 to 3%, P: more than 0%, 0.1%
  • S more than 0%, 0.05% or less
  • Al 0.005 to 1%
  • N more than 0%, 0.01% or less
  • the metal structure of the steel sheet includes polygonal ferrite, bainite, tempered martensite, and retained austenite.
  • FIG. 1 is a diagram schematically showing a diffraction peak of residual ⁇ measured by an X-ray diffraction method.
  • FIG. 2 is a schematic diagram for explaining a form in which at least one selected from the group consisting of retained austenite and carbide is connected.
  • FIG. 3A is a schematic diagram for explaining a distribution state of bainite and tempered martensite.
  • FIG. 3B is a schematic diagram for explaining a distribution state of bainite and tempered martensite.
  • FIG. 4 is a schematic view showing an annealing pattern when manufacturing a high-strength steel sheet according to the present invention.
  • the metal structure of the high-strength steel sheet is a mixed structure containing polygonal ferrite, bainite, tempered martensite, and retained austenite.
  • the metal structure of the high-strength steel sheet is (A) When the metal structure is observed with a scanning electron microscope, Polygonal ferrite: 10 to 50 area%, Bainite: 10-50 area%, Tempered martensite: 10 to 80% by area satisfied, (B) When the metal structure is measured by the X-ray diffraction method, Residual austenite: 5.0% by volume or more, Residual austenite having a carbon concentration of 1.0% by mass or less: 3.5% by volume or more, It is important to satisfy the residual austenite having a carbon concentration of 0.8% by mass or less: 2.4% by volume or less.
  • Residual ⁇ is a structure necessary for improving uniform deformability and ensuring good elongation by the TRIP effect. Further, the residual ⁇ is a structure necessary for securing strength.
  • the volume ratio of residual ⁇ (hereinafter sometimes referred to as V ⁇ R ) is 5.0% or more, preferably 8%, with respect to the entire metal structure. Above, more preferably 10% or more.
  • V ⁇ R the volume fraction of residual ⁇ , relative to the entire metal structure, preferably 30% or less, more preferably 25% or less.
  • the residual ⁇ may be generated between laths, or an aggregate of lath-like structures, for example, blocks, packets, or old ⁇ grain boundaries on the MA mixed phase in which fresh martensite and residual ⁇ are combined. It may exist in a lump as a part.
  • MA is an abbreviation for Martensite-Authentite Constituent.
  • the volume ratio V ⁇ R of the residual ⁇ is a value measured by an X-ray diffraction method.
  • the high-strength steel sheet has a volume fraction of retained austenite having a carbon concentration of 1.0 mass% or less [hereinafter referred to as V ⁇ R (C), particularly when the metal structure is measured by an X-ray diffraction method. ⁇ 1.0%). ] Is a volume fraction of retained austenite having a carbon concentration of 0.8% by mass or less [hereinafter, V ⁇ R (C ⁇ 0.8%). ] Of 2.4% or less is important. That is, as described below, it is important to appropriately generate residual ⁇ having a carbon concentration of more than 0.8 mass% and 1.0 mass% or less.
  • the load during warming can be sufficiently reduced by setting the volume ratio of residual ⁇ having a carbon concentration of 1.0% by mass or less to a certain level or more.
  • ⁇ TS that is, tensile strength at room temperature (hereinafter sometimes referred to as room temperature TS), it is warm.
  • the value (room temperature TS ⁇ warm TS) obtained by subtracting the tensile strength (hereinafter sometimes referred to as “warm TS”) can be used. It can be said that the larger the ⁇ TS, the more the load during warming is sufficiently reduced.
  • ⁇ TS Decrease in deformation resistance due to high processing temperature; and (2) Residual ⁇ is unstable at room temperature and improves tensile strength TS, but is stable at warm temperature and does not improve tensile strength TS; A method of using can be considered.
  • V ⁇ R (C ⁇ 1.0%) is preferably 4.0% by volume or more, and more preferably 4.5% by volume or more.
  • the upper limit of V ⁇ R (C ⁇ 1.0%) is not particularly limited, and the maximum value of V ⁇ R (C ⁇ 1.0%) is equal to the volume ratio of residual ⁇ contained in the steel sheet.
  • V ⁇ R (C ⁇ 1.0%) is preferably 10% by volume or less, more preferably 8% by volume or less.
  • V ⁇ R (C ⁇ 0.8%) The volume fraction V ⁇ R (C ⁇ 0.8%) of residual ⁇ with a carbon concentration of 0.8% by mass or less was calculated.
  • the present inventors have found that the content may be 2.4% by volume or less with respect to the entire metal structure.
  • V ⁇ R (C ⁇ 0.8%) is preferably 2.3% by volume or less, more preferably 2.2% by volume or less, and still more preferably 2.1% by volume or less.
  • V ⁇ R (C ⁇ 0.8%) is preferably as small as possible, and most preferably 0% by volume.
  • V ⁇ R (C ⁇ 1.0%) to 3.5% by volume or more
  • ⁇ TS can be increased, and the molding load at warm temperature can be reduced more than the molding load at room temperature.
  • V ⁇ R (C ⁇ 0.8%) to 2.4% by volume or less, it is possible to increase the hole expansion ratio ⁇ when the hole expansion processing is performed at room temperature, and to improve the workability at room temperature. .
  • the present inventors confirmed that residual ⁇ having a carbon concentration exceeding 1.0 mass% is stable at both room temperature and warm, so that the influence on ⁇ TS and the hole expansion rate ⁇ at room temperature is small. ing.
  • the present invention focusing on the carbon concentration of individual residual ⁇ , not the average carbon concentration of residual ⁇ , the residual ⁇ having a carbon concentration of more than 0.8 mass% and 1.0 mass% or less is positive. It is greatly different from the conventional technology in that it is generated in the above. That is, even if the amount of residual ⁇ is the same and the average value of the carbon concentration of the residual ⁇ is the same, the amount of residual ⁇ generated and the carbon concentration of 1.0% by mass or less The present inventors have found that the characteristics obtained are greatly changed if the amount of ⁇ produced is different.
  • the volume fraction of residual ⁇ and the average carbon concentration of residual ⁇ are measured by X-ray diffraction after grinding to a thickness of 1 ⁇ 4 of the steel plate and then chemical polishing.
  • the measurement principle is ISIJ Int. Vol. 33, 1933, no. 7, p. 776 can be referred to.
  • an X-ray diffractometer (RINT-1500) manufactured by Rigaku Corporation was used as the X-ray diffractometer, and Co-K ⁇ rays were used as the X-ray.
  • the distribution of carbon concentration of residual ⁇ was determined as follows using three diffraction peaks of (200) ⁇ , (220) ⁇ , and (311) ⁇ measured with the above X-ray diffractometer.
  • FIG. 1 is a diagram schematically showing a diffraction peak of residual ⁇ measured by an X-ray diffraction method.
  • lattice constant a 0 seek (hkl), and their three lattice constants a 0 (hkl) and arithmetic mean of the determined lattice constants a 0.
  • a 0 (hkl) d (hkl) ⁇ (h 2 + k 2 + l 2 ) (2)
  • the following equation is obtained from the above equations (7) and (8):
  • V.gamma R is the total volume fraction of retained ⁇ to the entire metal structure.
  • Polygonal ferrite is softer than bainite and is a structure that acts to increase the elongation of the steel sheet and improve the workability at room temperature.
  • the area ratio of polygonal ferrite is 10% or more, preferably 20% or more, more preferably 25% or more with respect to the entire metal structure.
  • the area ratio of polygonal ferrite is 50% or less, preferably 45% or less, more preferably 40% or less, based on the entire metal structure. To do.
  • the area ratio of the polygonal ferrite can be measured with a scanning electron microscope.
  • Bainite generated by the bainite transformation is a structure that effectively acts to concentrate C into austenite and obtain residual ⁇ .
  • bainite has the intensity
  • the area ratio of bainite is 10% or more, preferably 15% or more, more preferably 20% or more with respect to the entire metal structure.
  • the amount of bainite produced becomes excessive, the strength decreases, so that the area ratio of bainite is 50% or less, preferably 40% or less, more preferably 30% or less with respect to the entire metal structure.
  • the bainite is a structure in which the average of the interval between at least one selected from the group consisting of residual ⁇ and carbide is 1 ⁇ m or more when observed with a scanning electron microscope after the section of the steel sheet is corroded with nital. In addition to bainitic ferrite with no carbide precipitation, it includes those with partial precipitation of carbide.
  • Tempered martensite is a structure that acts to increase both the strength and the hole expansion ratio ⁇ in a well-balanced manner.
  • the area ratio of tempered martensite is 10% or more, preferably 15% or more, more preferably 20% or more with respect to the entire metal structure.
  • the area ratio of tempered martensite is preferably 80% or less of the entire metal structure, preferably Is 70% or less, more preferably 60% or less.
  • the tempered martensite is an average of the interval between at least one selected from the group consisting of residual ⁇ and carbide when less than 1 ⁇ m is selected from the group consisting of residual ⁇ and carbide when the steel sheet is subjected to nital corrosion and then observed with a scanning electron microscope. Organization.
  • the average is the distance between the center positions of the adjacent residual ⁇ , the distance between the center positions of the adjacent carbides, or the residual ⁇ when the cross section of the steel sheet is subjected to Nital corrosion and observed with a scanning electron microscope. It is a value obtained by averaging the results of measuring the distance between the center positions of the carbides adjacent to the residual ⁇ .
  • the distance between the center positions means the distance between the center positions obtained by obtaining the center positions of each residual ⁇ or each carbide and measuring the most adjacent residual ⁇ , the carbides, or the residual ⁇ and the carbide.
  • the center position determines the major axis and minor axis of residual ⁇ or carbide, and is the position where the major axis and minor axis intersect.
  • FIG. 2 is a schematic diagram for explaining a form in which at least one selected from the group consisting of retained austenite and carbide is connected.
  • the distribution state of bainite and tempered martensite is not particularly limited, and both bainite and tempered martensite may be generated in the old austenite grains, and bainite and tempered martensite are generated for each old austenite grain. It may be.
  • FIGS. 3A and 3B The distribution state of bainite and tempered martensite is schematically shown in FIGS. 3A and 3B.
  • FIG. 3A shows a state in which both bainite 21 and tempered martensite 22 are mixed and formed in the prior austenite grains 23, and
  • FIG. 3B shows bainite 21 and tempered martensite 22 for each prior austenite grain 23. Shows how each is generated.
  • the black circle 24 shown in each figure shows the MA mixed phase.
  • 3A and 3B are schematic diagrams for explaining the distribution state of bainite and tempered martensite.
  • the metal structure of the high-strength steel sheet may be composed of polygonal ferrite, bainite, tempered martensite, and residual ⁇ .
  • other structures include MA mixed phase, pearlite.
  • remainder structures such as fresh martensite. Any remaining structure becomes a starting point of cracking and deteriorates the workability at room temperature, so it is preferable that the remaining structure be as small as possible.
  • the remaining structure is preferably 25 area% or less in total when the cross section of the steel plate is subjected to nital corrosion and then observed with a scanning electron microscope.
  • the area ratio of polygonal ferrite, bainite, and tempered martensite is measured with a scanning electron microscope, whereas the volume fraction of residual ⁇ is measured with an X-ray diffraction method, and the measurement method is different.
  • the total area ratio and volume ratio of these tissues may exceed 100%.
  • % in the component composition means mass%.
  • the high-strength steel plate has C: 0.10 to 0.5%, Si: 1.0 to 3%, Mn: 1.5 to 3%, P: more than 0%, 0.1% or less, S: 0 %, 0.05% or less, Al: 0.005 to 1%, and N: more than 0%, 0.01% or less.
  • the C is an element that increases the strength of the steel sheet, and is also an element that is necessary for stabilizing austenite and securing residual ⁇ . In order to exert such an effect, the C amount is 0.10% or more.
  • the amount of C is preferably 0.13% or more, more preferably 0.15% or more. However, if C is contained excessively, weldability deteriorates, so the C content is 0.5% or less.
  • the amount of C is preferably 0.30% or less, more preferably 0.25% or less.
  • Si is a solid solution strengthening element and is an element that contributes to increasing the strength of the steel sheet. Si is an important element for suppressing the precipitation of carbides and condensing and stabilizing C in austenite to secure residual ⁇ . In order to exert such effects, the Si amount is set to 1.0% or more. The Si amount is preferably 1.2% or more, more preferably 1.3% or more. However, if Si is excessively contained, reverse transformation of polygonal ferrite to austenite does not occur during annealing and soaking, and polygonal ferrite remains excessively, resulting in insufficient strength. Moreover, a scale is remarkably formed at the time of hot rolling, and a scale trace is attached to the steel sheet surface, which deteriorates the surface properties. For these reasons, the Si content is 3% or less. The amount of Si is preferably 2.5% or less, more preferably 2.0% or less.
  • Mn is an element that acts as a hardenability improving element, suppresses excessive formation of polygonal ferrite during cooling, and increases the strength of the steel sheet. Mn also contributes to stabilizing the residual ⁇ . In order to exhibit such an effect, the amount of Mn is 1.5% or more. The amount of Mn is preferably 1.8% or more, more preferably 2.0% or more. However, when Mn is contained excessively, the formation of bainite is remarkably suppressed, the desired amount of bainite cannot be secured, and the balance between strength and elongation is deteriorated. In addition, adverse effects such as slab cracking occur. Therefore, the Mn content is 3% or less. The amount of Mn is preferably 2.8% or less, more preferably 2.7% or less.
  • P is an inevitable impurity, and if contained excessively, it promotes grain boundary embrittlement due to grain boundary segregation and deteriorates workability at room temperature, so the P content is 0.1% or less.
  • the amount of P is preferably 0.08% or less, more preferably 0.05% or less.
  • the amount of P is preferably as small as possible, but is usually about 0.001%.
  • the S amount is 0.05% or less.
  • the amount of S is preferably 0.01% or less, more preferably 0.005% or less.
  • the amount of S is preferably as small as possible, but is usually about 0.0001%.
  • Al is an important element for securing the residual ⁇ by suppressing the precipitation of carbides.
  • Al is an element that also acts as a deoxidizer.
  • the Al amount is set to 0.005% or more.
  • the amount of Al is preferably 0.010% or more, more preferably 0.03% or more.
  • the Al content is set to 1% or less.
  • the amount of Al is preferably 0.8% or less, more preferably 0.5% or less.
  • N is an inevitable impurity, and if it is contained in excess, a large amount of nitride precipitates and becomes the starting point of cracking, and the workability at room temperature deteriorates, so the N amount is 0.01% or less.
  • the N amount is preferably 0.008% or less, more preferably 0.005% or less.
  • the amount of N is preferably as small as possible, but is usually about 0.001%.
  • the basic components of the high-strength steel plate are as described above, and the balance is iron and inevitable impurities.
  • As an inevitable impurity mixing of elements brought in depending on the situation of raw materials, materials, manufacturing facilities, etc. is allowed within a range that does not impair the effects of the present invention.
  • the high-strength steel plate may further contain at least one element belonging to the following (a) to (e) as another element. Further, the elements belonging to the following (a) to (e) may be contained alone, or a plurality of elements belonging to the following (a) to (e) may be contained in combination.
  • (A) Cr and Mo are elements that suppress the formation of excessive polygonal ferrite during cooling and prevent a decrease in strength.
  • the Cr content is preferably 0.02% or more, more preferably 0.1% or more, and further preferably 0.2% or more.
  • the amount of Mo is preferably 0.02% or more, more preferably 0.1% or more, and further preferably 0.2% or more.
  • the content is preferably 1% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.
  • the amount of Mo is preferably 1% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.
  • Cr and Mo may contain either one or both.
  • Ti, Nb, and V are all elements that act to refine the metal structure and improve the strength and toughness of the steel sheet.
  • the Ti content is preferably 0.01% or more, more preferably 0.015% or more, and further preferably 0.020% or more.
  • the Nb content is preferably 0.01% or more, more preferably 0.015% or more, and further preferably 0.020% or more.
  • the amount of V is preferably 0.01% or more, more preferably 0.015% or more, and further preferably 0.020% or more.
  • the effect is saturated even if Ti, Nb, and V are contained excessively.
  • carbides may precipitate at the grain boundaries and workability at room temperature may deteriorate.
  • the Ti content is preferably 0.15% or less, more preferably 0.12% or less, and still more preferably 0.10% or less.
  • the Nb content is preferably 0.15% or less, more preferably 0.12% or less, and still more preferably 0.10% or less.
  • the V amount is preferably 0.15% or less, more preferably 0.12% or less, and still more preferably 0.10% or less.
  • Ti, Nb, and V may contain any 1 type, and may contain 2 or more types chosen arbitrarily.
  • Cu and Ni are elements that act to improve the corrosion resistance of the steel sheet.
  • the amount of Cu is preferably 0.01% or more, more preferably 0.05% or more, and further preferably 0.10% or more.
  • the amount of Ni is preferably 0.01% or more, more preferably 0.05% or more, and further preferably 0.10% or more.
  • the effect is saturated even if Cu and Ni are contained excessively.
  • hot workability may deteriorate.
  • the Cu content is preferably 1% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.
  • the amount of Ni is preferably 1% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.
  • Cu and Ni may contain either one or both.
  • (D) B is an element that suppresses excessive formation of polygonal ferrite during cooling and prevents a decrease in strength.
  • the B content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.0010% or more.
  • the B content is preferably 0.005% or less, more preferably 0.004% or less, and still more preferably 0.003% or less.
  • Ca, Mg, and rare earth elements are all elements that have the effect of finely dispersing inclusions in the steel sheet.
  • the Ca content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.0010% or more.
  • the amount of Mg is preferably 0.0001% or more, more preferably 0.0005% or more, and still more preferably 0.0010% or more.
  • the amount of rare earth elements is preferably 0.0001% or more, more preferably 0.0005% or more, and still more preferably 0.0010% or more.
  • Ca, Mg, and rare earth elements are contained excessively, forgeability and hot workability may deteriorate.
  • the Ca content is preferably 0.01% or less, more preferably 0.005% or less, and still more preferably 0.003% or less.
  • the Mg content is preferably 0.01% or less, more preferably 0.005% or less, and still more preferably 0.003% or less.
  • the rare earth element content is preferably 0.01% or less, more preferably 0.005% or less, and still more preferably 0.003% or less.
  • Ca, Mg, and rare earth elements may contain any 1 type, and may contain 2 or more types chosen arbitrarily.
  • the rare earth element means a lanthanoid element (15 elements from La to Lu), Sc (scandium), and Y (yttrium).
  • the surface of the high-strength steel sheet has an electrogalvanized (EG) layer, a hot dip galvanized (GI) layer, or an alloyed hot dip galvanized (GA) layer. It may be. That is, the present invention includes high-strength electrogalvanized steel sheets, high-strength hot-dip galvanized steel sheets, and high-strength galvannealed steel sheets.
  • EG electrogalvanized
  • GI hot dip galvanized
  • GA alloyed hot dip galvanized
  • FIG. 4 is a schematic diagram showing an annealing pattern when manufacturing the high-strength steel sheet, where the horizontal axis represents time (seconds) and the vertical axis represents temperature (° C.).
  • a steel sheet satisfying the above component composition is heated to a T1 temperature range of 800 ° C. or more and Ac 3 points or less, and held in the T1 temperature range for 40 seconds or more and soaked (soaking step).
  • the steel plate may be a hot-rolled steel plate or a cold-rolled steel plate.
  • the soaking temperature in the T1 temperature region is hereinafter referred to as “T1”
  • the soaking time in the T1 temperature region is hereinafter referred to as “t1”.
  • the holding includes not only constant temperature holding but also a mode in which the temperature fluctuates within the T1 temperature range.
  • the soaking temperature T1 is set to 800 ° C. or higher.
  • the soaking temperature T1 is preferably 810 ° C. or higher, more preferably 820 ° C. or higher.
  • the soaking temperature T1 is set to Ac 3 points or less.
  • the soaking temperature T1 is preferably Ac 3 point ⁇ 10 ° C. or lower, more preferably Ac 3 point ⁇ 20 ° C. or lower.
  • the soaking time t1 in the T1 temperature range is set to 40 seconds or more.
  • the soaking time t1 is preferably 50 seconds or longer, more preferably 80 seconds or longer.
  • the upper limit of soaking time t1 is not specifically limited, If soaking time t1 is too long, productivity will worsen. Therefore, the soaking time t1 is preferably 500 seconds or less, and more preferably 450 seconds or less.
  • the temperature of Ac 3 point of the steel sheet is represented by the following formula (II) described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, published May 31, 1985, p.273). It can be calculated from In the following formula (II), [] indicates the content (% by mass) of each element, and the content of elements not included in the steel sheet may be calculated as 0% by mass.
  • First cooling step After the soaking, when the Ms point represented by the following formula (I) is 350 ° C. or higher, up to an arbitrary cooling stop temperature T2 satisfying 350 ° C. or lower and 100 ° C. or higher, or by the following formula (I) When the represented Ms point is lower than 350 ° C., it is cooled to an arbitrary cooling stop temperature T2 that satisfies the Ms point or lower and 100 ° C. or higher (first cooling step). In the first cooling step, cooling is performed from 700 ° C. to 300 ° C. or the higher one of the cooling stop temperatures T2 at an average cooling rate of 5 ° C./second or more.
  • the average cooling rate in the section By controlling the average cooling rate in the section from 700 ° C. to 300 ° C. or the higher one of the cooling stop temperatures T2 after soaking (hereinafter sometimes referred to as CR1), A predetermined amount of polygonal ferrite can be generated. That is, when the average cooling rate CR1 in the section is less than 5 ° C./second, polygonal ferrite is excessively generated and the strength is lowered. Therefore, the average cooling rate CR1 in the above section needs to be controlled to 5 ° C./second or more, preferably 10 ° C./second or more, more preferably 15 ° C./second or more.
  • the upper limit of the average cooling rate CR1 in the above section is not particularly limited, but if the average cooling rate CR1 becomes too large, temperature control becomes difficult. Therefore, the average cooling rate CR1 in the above section is preferably 80 ° C./second or less, more preferably 60 ° C./second or less.
  • the cooling stop temperature T2 is 100 to 350 ° C. However, when the Ms point calculated by the following formula (I) is less than 350 ° C., the cooling stop temperature T2 is set to 100 ° C. to Ms point.
  • cooling stop temperature T2 If the cooling stop temperature T2 is too low, tempered martensite is excessively generated and the amount of residual ⁇ is reduced, so that elongation is lowered and workability at room temperature cannot be improved.
  • the cooling stop temperature T2 if the cooling stop temperature T2 is too low, a large amount of residual ⁇ with a carbon concentration exceeding 1.0% by mass is generated, the amount of residual ⁇ with a carbon concentration of 1.0% by mass or less is relatively small, and ⁇ TS is The warm forming load cannot be sufficiently reduced compared with the forming load at room temperature.
  • the reason why a large amount of residual ⁇ with a carbon concentration exceeding 1.0% by mass is generated is that film-like residual ⁇ remains between the laths in the tempered martensite, and the carbon concentration of the residual ⁇ is high.
  • the cooling stop temperature T2 is set to 100 ° C. or higher.
  • the cooling stop temperature T2 is preferably 110 ° C. or higher, more preferably 120 ° C. or higher.
  • the cooling stop temperature T2 is set to 350 ° C. or lower.
  • the cooling stop temperature T2 is preferably 330 ° C.
  • the cooling stop temperature T2 is set to be equal to or lower than the Ms point.
  • the cooling stop temperature T2 is preferably Ms point ⁇ 20 ° C. or lower, more preferably Ms point ⁇ 50 ° C. or lower.
  • the temperature of the Ms point can be calculated from the following formula (I) in consideration of the polygonal ferrite fraction (Vf) in the formula described in the “Leslie Steel Material Science” (p. 231).
  • [] indicates the content (mass%) of each element, and the content of elements not included in the steel sheet may be calculated as 0 mass%.
  • Vf represents the polygonal ferrite fraction (area%), but since it is difficult to directly measure the polygonal ferrite fraction during production, the soaking is performed separately under the same conditions as the production conditions for the high-strength steel sheet.
  • the polygonal ferrite fraction in the sample obtained by cooling to room temperature at the same average cooling rate as the production conditions of the high-strength steel plate in the first cooling step may be Vf.
  • Ms point (° C.) 561 ⁇ 474 ⁇ [C] / (1 ⁇ Vf / 100) ⁇ 33 ⁇ [Mn] ⁇ 17 ⁇ [Ni] ⁇ 17 ⁇ [Cr] ⁇ 21 ⁇ [Mo] (I )
  • T3 temperature range After cooling to the above cooling stop temperature T2, it is reheated to a T3 temperature range of more than 350 ° C. and 540 ° C. or less, and held at the T3 temperature range for 50 seconds or longer (reheating step).
  • the reheating temperature in the T3 temperature range is hereinafter referred to as “T3”
  • the holding time in the T3 temperature range is hereinafter referred to as “t3”.
  • the holding includes not only constant temperature holding but also a mode in which the temperature fluctuates within the T3 temperature range.
  • the reheating temperature T3 is over 350 ° C.
  • the reheating temperature T3 is preferably 360 ° C. or higher, more preferably 370 ° C. or higher.
  • the bainite transformation does not proceed sufficiently, the amount of residual ⁇ decreases, and the elongation EL decreases.
  • the amount of residual ⁇ having a carbon concentration of 0.8% by mass or less increases, and the hole expansion rate ⁇ decreases.
  • the reheating temperature T3 is set to 540 ° C. or lower.
  • the reheating temperature T3 is preferably 520 ° C. or lower, more preferably 500 ° C. or lower.
  • the holding time t3 is set to 50 seconds or longer.
  • the holding time t3 is preferably 80 seconds or longer, more preferably 100 seconds or longer.
  • the upper limit of the holding time t3 is not particularly limited, but in consideration of productivity, for example, 20 minutes or less is preferable.
  • Cooling step After holding in the reheating step, cooling is performed at an average cooling rate of 10 ° C./second or more from the T3 temperature range to 300 ° C., and from 300 ° C. to 150 ° C., an average cooling rate of more than 0 ° C./second, 10 ° C. Cool in less than 1 second (second cooling step).
  • second cooling step After the above holding, when cooling from the T3 temperature range to 150 ° C., it is important to perform two-stage cooling with 300 ° C. as the boundary, and the high temperature side up to 300 ° C. can increase ⁇ TS by rapid cooling, The molding load during warming can be reduced. On the low temperature side from 300 ° C., the hole expansion ratio ⁇ can be increased by slow cooling, so that the workability at room temperature can be improved.
  • the average cooling rate up to 300 ° C. (hereinafter, sometimes referred to as CR2) is too small after reheating, the concentration of C into bainite transformed and untransformed austenite proceeds during cooling, and carbon While the amount of residual ⁇ exceeding 1.0% by mass increases, the amount of residual ⁇ having a carbon concentration of 1.0% by mass or less decreases. As a result, ⁇ TS decreases, and the molding load during warming cannot be reduced. Therefore, it is necessary to control the average cooling rate CR2 to 10 ° C./second or more, preferably 15 ° C./second or more, more preferably 20 ° C./second or more.
  • the upper limit of the average cooling rate CR2 is not particularly limited, but if the average cooling rate CR2 becomes too large, temperature control becomes difficult. Therefore, the average cooling rate CR2 is preferably 80 ° C./second or less, more preferably 60 ° C./second or less.
  • the average cooling rate CR3 in the above section needs to be controlled to less than 10 ° C./second, preferably 5 ° C./second or less, more preferably 2 ° C./second or less.
  • An electrogalvanized layer, a hot-dip galvanized layer, or an alloyed hot-dip galvanized layer may be formed on the surface of the high-strength steel plate.
  • the conditions for forming the electrogalvanized layer, hot dip galvanized layer, or alloyed hot dip galvanized layer are not particularly limited, and conventional electrogalvanized (EG) treatment, hot dip galvanized (GI) treatment, galvannealed alloyed zinc Plating (GA) treatment can be employed. Accordingly, an electrogalvanized steel sheet (hereinafter sometimes referred to as “EG steel sheet”), a hot dip galvanized steel sheet (hereinafter sometimes referred to as “GI steel sheet”), and an alloyed hot dip galvanized steel sheet (hereinafter referred to as “GA steel sheet”). Is sometimes obtained).
  • EG steel sheet electrogalvanized steel sheet
  • GI steel sheet hot dip galvanized steel sheet
  • GA steel sheet alloyed hot dip galvanized steel sheet
  • the steel sheet is energized while being immersed in a zinc solution at 55 ° C., for example, and electrogalvanizing is performed.
  • the above reheating process may serve as a hot dip galvanizing process. That is, after reheating to the T3 temperature range, the hot dip galvanization may be performed by immersing in a plating bath adjusted to the temperature of the T3 temperature range to serve as both hot dip galvanization and holding in the T3 temperature range. . At this time, the residence time in the T3 temperature region may satisfy the requirement for the holding time t3.
  • an alloying treatment may be subsequently performed in the T3 temperature range.
  • the residence time in the T3 temperature region may satisfy the requirement for the holding time t3.
  • the amount of galvanized adhesion is not particularly limited, and for example, it may be about 10 to 100 g / m 2 per side.
  • the plate thickness of the high-strength steel plate is not particularly limited, but may be a thin steel plate having a plate thickness of 3 mm or less, for example.
  • the tensile strength (TS) of the high-strength steel plate is 980 MPa or more, and preferably 1100 MPa or more.
  • the high-strength steel plate is excellent in workability at room temperature (TS ⁇ EL, ⁇ ).
  • the high-strength steel plate preferably has a TS ⁇ elongation (EL) of 16000 MPa ⁇ % or more, and more preferably 18000 MPa ⁇ % or more.
  • the high-strength steel sheet preferably has a hole expansion rate ⁇ of 20% or more, and more preferably 25% or more.
  • the high-strength steel sheet is excellent in workability at room temperature (TS ⁇ EL, ⁇ ), and the forming load during warming is sufficiently reduced.
  • the high-strength steel sheet preferably has a ⁇ TS of 150 MPa or more, and more preferably 180 MPa or more.
  • the above-mentioned high-strength steel sheet is suitably used as a material for structural parts of automobiles.
  • Structural parts of automobiles include, for example, front and rear side members and crashing parts such as crash boxes, pillars and other reinforcements (for example, bears, center pillar reinforcements, etc.), roof rail reinforcements, side sills , Body components such as floor members and kick sections, shock-absorbing parts such as bumper reinforcements and door impact beams, and seat parts.
  • One aspect of the present invention is, in mass%, C: 0.10 to 0.5%, Si: 1.0 to 3%, Mn: 1.5 to 3%, P: more than 0%, 0.1%
  • S more than 0%, 0.05% or less
  • Al 0.005 to 1%
  • N more than 0%, 0.01% or less
  • the metal structure of the steel sheet includes polygonal ferrite, bainite, tempered martensite, and retained austenite.
  • the elongation and hole expandability at room temperature are good, and the molding load when processing at a temperature of 100 to 350 ° C. is markedly reduced from the molding load when processing at room temperature.
  • a high-strength steel sheet having a tensile strength of 980 MPa or more can be provided.
  • the high-strength steel sheet further contains at least one element selected from the group consisting of Cr: more than 0%, 1% or less, and Mo: more than 0%, 1% or less as other elements, as other elements. Also good.
  • the high-strength steel plate as other elements, in mass%, Ti: more than 0%, 0.15% or less, Nb: more than 0%, 0.15% or less, and V: more than 0%, You may contain at least 1 sort (s) chosen from the group which consists of 0.15% or less.
  • the high-strength steel sheet further contains at least one element selected from the group consisting of Cu: more than 0%, less than 1%, and Ni: more than 0%, less than 1% as other elements. May be.
  • the high-strength steel sheet may further contain B: more than 0% and 0.005% or less in terms of mass% as other elements.
  • the high-strength steel sheet further includes, as other elements, mass%, Ca: more than 0%, 0.01% or less, Mg: more than 0%, 0.01% or less, and rare earth elements: more than 0%. , At least one selected from the group consisting of 0.01% or less.
  • the high-strength steel sheet includes a high-strength steel sheet having an electrogalvanized layer, a hot-dip galvanized layer, or an alloyed hot-dip galvanized layer on the surface.
  • a steel sheet satisfying the above component composition is heated to a T1 temperature range of 800 ° C. or higher and Ac 3 points or lower, and held in the T1 temperature range for 40 seconds or more to soak.
  • the Ms point represented by the following formula (I) is 350 ° C. or higher after the heating step and soaking, up to any cooling stop temperature T2 that satisfies 350 ° C. or lower and 100 ° C. or higher, or the following formula (I)
  • the cooling stop temperature T2 is less than the Ms point and is 100 ° C. or higher, and from 700 ° C. to 300 ° C.
  • Vf is the same average cooling rate as the production conditions for the high-strength steel plate in the first cooling step after separately performing the soaking step under the same conditions as the production conditions for the high-strength steel plate.
  • [] has shown content (mass%) of each element, and content of the element which is not contained in a steel plate is calculated as 0 mass%.
  • electrogalvanization may be performed after the second cooling step.
  • hot dip galvanization or alloyed hot dip galvanization may be performed in the reheating step.
  • the component composition and metal structure of the steel sheet are appropriately controlled, and in particular, the carbon concentration of residual ⁇ is strictly controlled, so that the elongation and hole expansibility at room temperature are good, It is possible to provide a high-strength steel sheet having a tensile strength of 980 MPa or more and a method for producing the same, in which a forming load when processing at a temperature of 100 to 350 ° C. is significantly reduced as compared with a forming load when processing at room temperature.
  • a steel material was manufactured by melting steel containing the components shown in Table 1 below, the balance being iron and inevitable impurities.
  • the obtained steel material was heated and held at 1250 ° C. for 30 minutes, then hot-rolled so that the reduction rate was about 90% and the finish rolling temperature was 920 ° C. From this temperature, the steel was wound at an average cooling rate of 30 ° C./second. It was cooled to a take-up temperature of 600 ° C. and wound up. After winding, it was cooled to room temperature to produce a hot-rolled steel plate having a thickness of 2.6 mm.
  • the obtained hot-rolled steel sheet was pickled to remove the surface scale, and then cold-rolled at a cold rolling rate of 46% to produce a cold-rolled steel sheet having a thickness of 1.4 mm.
  • the obtained cold-rolled steel sheet was continuously annealed to produce a test material. That is, the obtained cold-rolled steel sheet was heated to a soaking temperature T1 (° C.) shown in the following Table 2-1 or Table 2-2, and a soaking time t1 (shown in the following Table 2-1 or Table 2-2). Second) and soaking, and then cooled to the cooling stop temperature T2 (° C.) shown in Table 2-1 or Table 2-2 below.
  • the average cooling rate CR1 (° C./second) from 700 ° C. to 300 ° C. or higher of the cooling stop temperature T2 is shown in the following Table 2-1 or Table 2-2.
  • Tables 2-1 and 2-2 below also show the composition of the components shown in Table 1 below and the Ms point (° C.) calculated based on the above formula (I).
  • the reheating temperature T3 (° C.) to 300 ° C. is cooled at an average cooling rate CR2 (° C./second) shown in Table 2-1 or Table 2-2 below, and from 300 ° C. to 150 ° C., Cooling was performed at an average cooling rate CR3 (° C./second) shown in Table 2-1 or Table 2-2 below.
  • test materials obtained by continuous annealing were subjected to the following plating treatment to produce EG steel plates, GI steel plates, and GA steel plates.
  • Electrogalvanizing (EG) treatment After continuous annealing, it is cooled to room temperature, and then the specimen is immersed in a galvanizing bath at 55 ° C., subjected to electrogalvanizing treatment at a current density of 30 to 50 A / dm 2 , washed with water and dried to provide an EG steel sheet. Manufactured. The amount of electrogalvanized adhesion was 10 to 100 g / m 2 per side.
  • Table 2-1 The categories of the obtained specimens are shown in Table 2-1 or Table 2-2 below.
  • cold rolling indicates a cold rolled steel sheet
  • EG indicates an EG steel sheet
  • GI indicates a GI steel sheet
  • GA indicates a GA steel sheet.
  • Table 3-1 or Table 3-2 The measurement results are shown in Table 3-1 or Table 3-2 below.
  • F represents the area ratio of polygonal ferrite
  • B represents the area ratio of bainite
  • TM represents the area ratio of tempered martensite.
  • the balance is residual ⁇ , MA mixed phase in which fresh martensite and residual ⁇ are combined, pearlite, and fresh martensite.
  • the carbon concentration in the residual ⁇ is measured by the procedure described above, and the volume ratio of the residual ⁇ having a carbon concentration of 1.0 mass% or less [V ⁇ R (C ⁇ 1.0%)] with respect to the entire metal structure, and The volume fraction [V ⁇ R (C ⁇ 0.8%)] of residual ⁇ having a carbon concentration of 0.8% by mass or less was calculated.
  • TS was 980 MPa or more
  • TS ⁇ EL was 16000 MPa ⁇ % or more and ⁇ was 20% or more
  • ⁇ TS was 150 MPa or more
  • all of TS, TSxEL, (lambda), and (DELTA) TS satisfy a reference value was set as the pass.
  • the case where any of TS, TS ⁇ EL, ⁇ , or ⁇ TS did not satisfy the reference value was regarded as unacceptable.
  • Table 1 The following can be considered from Table 1, Table 2-1, Table 2-2, Table 3-1, and Table 3-2.
  • No. 1, 7, 8, 10, 13, 15, 17, 20, 22, 23, 26 to 31, 33, 37, 38, 40, and 42 are examples that satisfy the requirements defined in the present invention.
  • the TS measured at room temperature is 980 MPa or higher and has high strength. Further, TS ⁇ EL and ⁇ satisfy the acceptance criteria of the present invention, and the processability at room temperature is good. Furthermore, since ⁇ TS satisfied the acceptance criteria of the present invention, the molding load during warming could be reduced.
  • No. 2 to 6, 9, 11, 12, 14, 16, 18, 19, 21, 24, 25, 32, 34 to 36, 39, and 41 are examples that do not satisfy any of the requirements defined in the present invention.
  • at least one of the properties of strength, workability at room temperature, and reduction of warm forming load is deteriorated.
  • No. 2, 6, 12, and 41 are examples in which the average cooling rate CR3 from 300 ° C. to 150 ° C. after holding in the reheating step is too large, and a large amount of residual ⁇ having a carbon concentration of 0.8 mass% or less is generated. ⁇ was reduced and the processability at room temperature could not be improved.
  • No. 3, 5, and 39 the average cooling rate CR2 from the reheating temperature (the holding temperature in the reheating process) to 300 ° C. is too small, and the residual ⁇ amount with a carbon concentration of 1.0 mass% or less cannot be secured. In this example, ⁇ TS was small, and the molding load during warming could not be reduced.
  • No. 3 is an example simulating the above-mentioned Patent Document 1. As described in paragraph [0128] of the above-mentioned Patent Document 1, the average cooling rate to room temperature after holding was set to 5 ° C./second.
  • No. 4, 19, and 32 are examples in which the cooling stop temperature T2 after soaking is too high.
  • No. In 4, 19, and 32 since tempered martensite was not generated or the amount of generation was small, TS at room temperature was low, and strength could not be secured.
  • No. In 4, 19, and 32 since a large amount of residual ⁇ having a carbon concentration of 0.8 mass% or less was generated, ⁇ was small, and workability at room temperature could not be improved.
  • the retention time t3 was relatively long, and the amount of polygonal ferrite produced was relatively small, so it is considered that bainite was excessively produced. That is, the smaller the amount of polygonal ferrite produced, the less likely it is that C is concentrated in the surrounding austenite, so the bainite transformation is considered to occur faster.
  • No. No. 9 is an example in which polygonal ferrite was excessively generated because the average cooling rate CR1 in the section from 700 ° C. to 300 ° C. was too small after soaking. As a result, no. No. 9 could not secure the desired TS.
  • No. 11 is an example in which polygonal ferrite was hardly generated because the soaking temperature T1 was too high. As a result, no. No. 11, TS ⁇ EL was low, and the processability at room temperature could not be improved.
  • No. 14 is an example in which the cooling stop temperature T2 after soaking is too low.
  • No. 14 bainite was not generated, and tempered martensite was excessively generated, so that the amount of residual ⁇ generated could not be secured.
  • TS ⁇ EL was low, and the processability at room temperature could not be improved.
  • No. No. 14 could not secure the amount of residual ⁇ having a carbon concentration of 1.0% by mass or less, so ⁇ TS was small, and the molding load during warming could not be reduced.
  • No. No. 16 is an example in which polygonal ferrite is excessively generated because the soaking temperature T1 is too low. As a result, no. No. 16 could not secure the desired TS. No. No. 16, TS ⁇ EL decreased, and the processability at room temperature could not be improved. This is presumably because the work structure introduced during cold rolling remained.
  • No. 18 is an example in which the reheating temperature T3 is too high. No. In No. 18, bainite hardly formed and the amount of residual ⁇ could not be secured, so TS ⁇ EL was lowered and workability at room temperature could not be improved. No. In No. 18, since residual ⁇ having a carbon concentration of 0.8% by mass or less was excessively generated, ⁇ became small, and workability at room temperature could not be improved.
  • No. No. 21 is an example in which the amount of residual ⁇ having a carbon concentration of 1.0% by mass or less could not be secured because the reheating temperature T3 was too low. As a result, no. In No. 21, ⁇ TS was small, and the molding load during warming could not be reduced.
  • No. No. 24 is an example in which a desired residual ⁇ amount could not be ensured because the soaking time t1 was too short. As a result, no. In No. 24, TS ⁇ EL decreased, and the processability at room temperature could not be improved.
  • No. 25 is an example in which the holding time t3 is too short. No. 25, because the production amount of bainite and residual ⁇ could not be ensured, TS ⁇ EL decreased, and since the residual ⁇ with a carbon concentration of 0.8% by mass or less was excessively generated, ⁇ became small, at room temperature. It was not possible to improve the workability.
  • No. 34 to 36 are examples in which the component composition does not satisfy the requirements defined in the present invention.
  • No. 36 since the amount of Mn was too small, polygonal ferrite was excessively generated, TS was lowered, and the strength could not be secured. No. For 36, the amount of residual ⁇ produced could not be secured, so TS ⁇ EL decreased, and the processability at room temperature could not be improved. No. No. 36 was an example in which the amount of residual ⁇ with a carbon concentration of 1.0% by mass or less could not be ensured, ⁇ TS became small, and the molding load during warm could not be reduced.
  • the component composition and metal structure of the steel sheet are appropriately controlled, and in particular, the carbon concentration of residual ⁇ is strictly controlled, so that the elongation and hole expansibility at room temperature are good,
  • a high-strength steel sheet having a tensile strength of 980 MPa or more and a method for producing the same, in which a forming load when processing at a temperature of 100 to 350 ° C. is significantly reduced as compared with a forming load when processing at room temperature.

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Abstract

Dans un de ses aspects, la présente invention concerne une tôle en acier à haute résistance ayant une composition spécifique, la structure métallique de la tôle en acier comprenant de la ferrite polygonale, de la bainite, de la martensite revenue et de la martensite résiduelle. Observée au microscope électronique à balayage, la structure métallique satisfait aux proportions suivantes : 10 à 50 % en surface de ferrite polygonale, 10 à 50 % en surface de bainite et 10 à 80 % en surface de martensite revenue, par rapport à la structure métallique globale. Mesurée par diffractométrie aux rayons X, la structure métallique satisfait aux proportions suivantes : au moins 5 % en volume d'austénite résiduelle, au moins 3,5 % en volume d'austénite ayant une concentration en carbone de 1,0 % en masse ou moins, et 2,4 % en volume ou moins d'austénite résiduelle ayant une concentration en carbone de 0,8 % en masse ou moins, par rapport à la structure métallique.
PCT/JP2017/004594 2016-02-29 2017-02-08 Tôle en acier à haute résistance et son procédé de fabrication Ceased WO2017150117A1 (fr)

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US16/080,571 US20190085426A1 (en) 2016-02-29 2017-02-08 High strength steel sheet and manufacturing method therefor
MX2018010446A MX2018010446A (es) 2016-02-29 2017-02-08 Lamina de acero de alta resistencia y metodo de fabricacion de la misma.
EP17759588.1A EP3412786B1 (fr) 2016-02-29 2017-02-08 Tôle en acier à haute résistance et son procédé de fabrication
CN201780013822.5A CN108699653B (zh) 2016-02-29 2017-02-08 高强度钢板以及其制造方法
KR1020187027683A KR102174562B1 (ko) 2016-02-29 2017-02-08 고강도 강판 및 그의 제조 방법

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JP2020122213A (ja) * 2019-01-29 2020-08-13 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板およびその製造方法
JP2022510873A (ja) * 2018-12-18 2022-01-28 アルセロールミタル 冷間圧延熱処理鋼板及びその製造方法
JPWO2022102218A1 (fr) * 2020-11-11 2022-05-19
WO2022215389A1 (fr) * 2021-04-09 2022-10-13 Ｊｆｅスチール株式会社 Tôle d'acier laminée à froid à haute résistance et son procédé de fabrication
US20230046327A1 (en) * 2019-12-18 2023-02-16 Posco High strength steel sheet having superior workability and method for manufacturing same
JPWO2024057669A1 (fr) * 2022-09-15 2024-03-21
WO2024057670A1 (fr) * 2022-09-15 2024-03-21 Ｊｆｅスチール株式会社 Tôle d'acier, élément, et procédés de fabrication associés
WO2024090011A1 (fr) * 2022-10-26 2024-05-02 Ｊｆｅスチール株式会社 Feuille d'acier à haute résistance, élément et procédés de fabrication associés
CN120945294A (zh) * 2025-10-17 2025-11-14 鞍钢股份有限公司 一种1000MPa超高扩孔性能冷轧连退CH钢及其制备方法
JP7811551B2 (ja) 2020-11-11 2026-02-05 日本製鉄株式会社 鋼板およびその製造方法

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US20230046327A1 (en) * 2019-12-18 2023-02-16 Posco High strength steel sheet having superior workability and method for manufacturing same
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JP7811551B2 (ja) 2020-11-11 2026-02-05 日本製鉄株式会社 鋼板およびその製造方法
KR102884952B1 (ko) 2020-11-11 2025-11-13 닛폰세이테츠 가부시키가이샤 강판 및 그 제조 방법
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JP7276618B2 (ja) 2021-04-09 2023-05-18 Ｊｆｅスチール株式会社 高強度冷延鋼板およびその製造方法
JPWO2022215389A1 (fr) * 2021-04-09 2022-10-13
JPWO2024057669A1 (fr) * 2022-09-15 2024-03-21
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WO2024057670A1 (fr) * 2022-09-15 2024-03-21 Ｊｆｅスチール株式会社 Tôle d'acier, élément, et procédés de fabrication associés
JP7485240B1 (ja) * 2022-09-15 2024-05-16 Ｊｆｅスチール株式会社 鋼板、部材およびそれらの製造方法
JP7559978B2 (ja) 2022-09-15 2024-10-02 Ｊｆｅスチール株式会社 鋼板、部材およびそれらの製造方法
WO2024090011A1 (fr) * 2022-10-26 2024-05-02 Ｊｆｅスチール株式会社 Feuille d'acier à haute résistance, élément et procédés de fabrication associés
JP7522978B1 (ja) * 2022-10-26 2024-07-26 Ｊｆｅスチール株式会社 高強度鋼板、部材及びそれらの製造方法
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