WO2023008003A1 - Tôle d'acier, élément, et procédés de fabrication de ceux-ci - Google Patents

Tôle d'acier, élément, et procédés de fabrication de ceux-ci Download PDF

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Publication number
WO2023008003A1
WO2023008003A1 PCT/JP2022/024964 JP2022024964W WO2023008003A1 WO 2023008003 A1 WO2023008003 A1 WO 2023008003A1 JP 2022024964 W JP2022024964 W JP 2022024964W WO 2023008003 A1 WO2023008003 A1 WO 2023008003A1
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steel sheet
temperature
content
delayed fracture
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PCT/JP2022/024964
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English (en)
Japanese (ja)
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大洋 浅川
真平 吉岡
真次郎 金子
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to EP22849078.5A priority Critical patent/EP4350016A1/fr
Priority to JP2022559509A priority patent/JP7226672B1/ja
Priority to KR1020247002167A priority patent/KR20240024947A/ko
Priority to CN202280050129.6A priority patent/CN117651786A/zh
Publication of WO2023008003A1 publication Critical patent/WO2023008003A1/fr

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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C23C2/29—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to steel sheets such as high-strength steel sheets for cold press forming that are used in automobiles and the like through cold press forming, members using the steel sheets, and manufacturing methods thereof.
  • steel sheets with a tensile strength TS of 1310 MPa class or higher have been increasingly applied to automobile frame parts for the purpose of weight reduction and collision safety of automobiles.
  • steel sheets with a tensile strength TS of 1470 MPa class or higher are being applied to bumpers, impact beam parts, and the like.
  • delayed fracture means that when a part is placed in a hydrogen penetration environment with high stress applied to the part, hydrogen penetrates into the steel plate that constitutes the part, reducing the interatomic bonding strength. It is a phenomenon in which microcracks are generated by causing local deformation and breakage occurs as the microcracks propagate.
  • Patent Document 1 discloses mass % C: 0.13% or more and 0.40% or less, Si: 1.5% or less, Mn: 1.8% or more and 4% or less, P: 0.02% or less, S: less than 0.0010%, sol.
  • the balance has a component composition consisting of Fe and unavoidable impurities, the area ratio of martensite and bainite to the entire structure is more than 90% and 100% or less, prior austenite grains
  • the average grain size is 6 to 15 ⁇ m, the inclusion group that satisfies specific conditions is reduced, the aspect ratio is 2.0 or less, and the major axis is 0.30 ⁇ m or more and 2 ⁇ m or less, mainly Fe A steel sheet with improved delayed fracture resistance, having a steel structure in which carbides as components are present at 4000/mm 2 or less, a thickness
  • a high-strength cold-rolled steel sheet having an average grain size of 5 ⁇ m or less and having excellent hydrogen embrittlement resistance and workability is disclosed.
  • the conventional technology is sufficient as a technology that secures a tensile strength TS of 1470 MPa or more and has excellent delayed fracture resistance.
  • the present invention has been made to solve such problems, and provides a steel sheet, a member, and a method for producing the same having a tensile strength of 1470 MPa or more (TS ⁇ 1470 MPa) and excellent delayed fracture resistance. intended to
  • excellent delayed fracture resistance means judging to have excellent delayed fracture resistance by the following evaluation.
  • a strip test piece of 100 mm in the direction perpendicular to the rolling direction and 30 mm in the rolling direction is taken from the 1/4 position of the coil width from the end of the obtained steel plate (coil) in the width direction.
  • the test piece is fixed with bolts while maintaining the shape of the test piece at the time of bending.
  • the shearing clearance was 13% and the rake angle was 1°.
  • Bending is performed with a tip bending radius of 10 mm and an angle inside the bending apex of 90 degrees (V bending).
  • the punch has a U-shaped punch whose tip radius is the same as the tip bending radius R (the tip R is semicircular and the thickness of the punch barrel is 2R), and the die has a corner radius of 30 mm.
  • the depth to which the punch pushes the steel plate is adjusted, and the steel plate is formed so that the bending angle of the tip (the angle inside the bending apex) is 90 degrees (V shape).
  • Sandwich the test piece with a hydraulic jack so that the distance between the flange ends of the straight piece when bending is the same as when bending (to cancel out the opening of the straight piece due to springback).
  • the bolt is passed through an elliptical hole (minor axis: 10 mm, major axis: 15 mm) previously provided 10 mm inward from the short side edge of the strip test piece and fixed.
  • (3) The resulting bolted test piece was immersed in a solution prepared by mixing 0.1% by mass of ammonium thiocyanate aqueous solution and McIlvaine buffer solution at a ratio of 1:1 and adjusting the pH to 8.0.
  • a delayed fracture resistance evaluation test is carried out. At this time, the temperature of the solution shall be 20° C., and the volume of the solution per 1 cm 3 of the surface area of the test piece shall be 20 ml.
  • the area ratio of martensite is 95% or more.
  • the average grain size (prior ⁇ grain size) of prior austenite grains is less than 11.2 ⁇ m.
  • the number density A of precipitates having an equivalent circle diameter of 500 nm or more satisfies the following conditions.
  • a (pieces/mm 2 ) ⁇ 8.5 ⁇ 10 5 ⁇ [B]
  • [B] represents the content of B (% by mass).
  • the present invention was completed through further studies based on the above findings, and the gist thereof is as follows. [1] % by mass, C: 0.15% or more and 0.45% or less, Si: 1.5% or less, Mn: more than 1.7%, P: 0.03% or less, S: less than 0.0040%, sol.
  • [B] represents the content of B (% by mass).
  • [2] The steel sheet according to Claim 1, wherein the chemical composition further contains one or two selected from Cu: 1.0% or less and Ni: 1.0% or less in mass%.
  • component composition in terms of mass %, Cr: 1.0% or less, Mo: less than 0.3%, V: 0.5% or less, Zr: 0.2% or less, and W: 0.2
  • the component composition of [1] to [4] further contains one or two selected from Sb: 0.1% or less and Sn: 0.1% or less in mass%.
  • a steel slab having the chemical composition according to any one of [1] to [5] is heated at a slab surface temperature from 1000 ° C. to a heating and holding temperature of 1250 ° C. or higher at an average heating rate of 10 ° C./min or less.
  • Hot finish rolling is performed under the conditions of a residence time of 20 seconds or more and 150 seconds or less at 900 to 1000 ° C. and a finish rolling temperature of 850 ° C. or more
  • Cooling is performed at an average cooling rate of 40 ° C./sec or more in the range from the finish rolling temperature to 650 ° C., After that, it is coiled at a coiling temperature of 650 ° C.
  • a cold-rolled steel sheet is obtained by cold-rolling the hot-rolled steel sheet at a rolling reduction of 40% or more,
  • the annealing temperature is 800 to 950° C.
  • the cold-rolled steel sheet is heated from 400° C. to the annealing temperature at an average heating rate of 1.0° C./second or more, Hold at the annealing temperature for 600 seconds or less, Cooling from the annealing temperature to 420 ° C. at a first average cooling rate of 2 ° C./sec or more, Cooling from 420 ° C. to a cooling stop temperature of 260 ° C.
  • steel plate manufacturing method The method for producing a steel sheet according to [8], wherein the surface of the steel sheet is plated after the continuous annealing.
  • a method for manufacturing a member comprising the step of subjecting the steel plate according to any one of [1] to [6] to at least one of forming and joining to form a member.
  • a high-strength steel plate, a member, and a method for manufacturing the same are provided, which are excellent in delayed fracture resistance.
  • the steel sheet of the present invention has, in mass %, C: 0.15% or more and 0.45% or less, Si: 1.5% or less, Mn: more than 1.7%, P: 0.03% or less, S: 0 less than .0040%, sol. Al: 0.20% or less, N: 0.005% or less, B: 0.0015% or more and 0.0100% or less, 0.005% or more and 0.080% or less in total of one or more of Nb and Ti containing, the balance being Fe and inevitable impurities, having a structure in which the area ratio of martensite to the entire structure is 95% or more and 100% or less, and prior austenite grains (hereinafter also referred to as prior ⁇ grains ) has an average grain size (prior ⁇ grain size) of less than 11.2 ⁇ m, and the number density A of precipitates having an equivalent circle diameter of 500 nm or more satisfies the following formula (1).
  • C 0.15% or more and 0.45% or less C is contained in order to improve the hardenability to obtain a martensite steel structure and to increase the strength of martensite.
  • the C content is made 0.15% or more.
  • the C content is preferably 0.20% or more, more preferably 0.27% or more, from the viewpoint of reducing the weight of automotive frame parts by increasing the tensile strength.
  • excessively added C causes deterioration of delayed fracture resistance due to formation of iron carbide and segregation to grain boundaries. From these points of view, the C content is limited to a range of 0.45% or less.
  • the C content is preferably 0.40% or less, more preferably 0.37% or less.
  • Si 1.5% or less Si is used as a strengthening element by solid solution strengthening, and from the viewpoint of suppressing the formation of film-like carbides when tempering in a temperature range of 200 ° C. or higher to improve delayed fracture resistance. contains.
  • Si is contained from the viewpoint of reducing Mn segregation in the central portion of the sheet thickness and suppressing the formation of MnS.
  • Si is contained in order to suppress decarburization and deboronation due to oxidation of the surface layer during annealing in a continuous annealing line (CAL).
  • the lower limit of the Si content is not specified, it is desirable to contain 0.02% or more of Si from the viewpoint of obtaining the above effects.
  • the Si content is preferably 0.10% or more, more preferably 0.20% or more.
  • the Si content should be 1.5% or less (including 0%).
  • the Si content is preferably 1.2% or less, more preferably 1.0% or less.
  • Mn more than 1.7% Mn is contained more than 1.7% in order to improve the hardenability of the steel and obtain the desired strength, and to keep the area ratio of martensite within a predetermined range. It preferably contains 1.8% or more.
  • Mn is an element that particularly promotes the formation and coarsening of MnS at the central portion of the plate thickness, and includes Al 2 O 3 , (Nb, Ti) (C, N), TiN, TiS, etc. precipitates in combination with other inclusion particles and promotes delayed fracture. Therefore, the Mn content is preferably 4.0% or less. More preferably, it is 3.0% or less.
  • P 0.03% or less
  • P is an element that strengthens steel, but when its content is high, it segregates at grain boundaries and lowers grain boundary strength, resulting in significant deterioration in delayed fracture resistance and spot weldability. Invite. From the above point of view, the P content should be 0.03% or less.
  • the P content is preferably 0.02% or less, more preferably 0.01% or less.
  • the lower limit of the P content is not specified, it is set to 0.002% as the lower limit currently industrially practicable.
  • S less than 0.0040% S forms coarse MnS and becomes a starting point for delayed fracture, thereby lowering the delayed fracture resistance. From the viewpoint of improving delayed fracture resistance, the S content should be at least less than 0.0040%.
  • the S content is preferably less than 0.0020%, more preferably 0.0010% or less, still more preferably 0.0007% or less.
  • the lower limit is not defined, it is set to 0.0002% as the lower limit currently industrially practicable.
  • sol. Al 0.20% or less Al is contained in order to sufficiently deoxidize and reduce inclusions in the steel. sol. Although the lower limit of Al is not specified, in order to stably deoxidize, sol. It is desirable to set the Al content to 0.005% or more. sol. The Al content is more preferably 0.01% or more, still more preferably 0.02% or more. On the other hand, sol. If the Al content exceeds 0.20%, the cementite generated during winding becomes less likely to form a solid solution during the annealing process, and the delayed fracture resistance deteriorates. Therefore, sol. Al content is 0.20% or less. sol. The Al content is preferably 0.10% or less, more preferably 0.05% or less.
  • N 0.005% or less N forms precipitates such as TiN, (Nb, Ti) (C, N) in the steel. , (Nb,Ti)C. These hinder adjustment to the steel structure required by the present invention, and adversely affect the delayed fracture resistance. In order to reduce such adverse effects, the N content is made 0.005% or less. The N content is preferably 0.0040% or less. Although the lower limit is not specified, it is set to 0.0006% as the lower limit currently industrially practicable.
  • B 0.0015% or more and 0.0100% or less B is an element that improves the hardenability of steel, and has the advantage of forming martensite with a predetermined area ratio even with a small Mn content.
  • B increases the cohesive force of the grain boundary by segregating at the grain boundary, and suppresses the segregation of P, which reduces the grain boundary strength, thereby improving the delayed fracture resistance.
  • the addition of excessive B increases Fe 23 (C, B) 6 and BN, and it becomes a starting point of delayed fracture, resulting in a decrease in the resistance to delayed fracture.
  • the B content is set to 0.0015% or more in order to obtain a sufficient grain boundary solid solution B amount.
  • the B content is preferably 0.0025% or more, more preferably 0.0040% or more.
  • the B content is set to 0.0100% or less.
  • the B content is preferably 0.0090% or less, more preferably 0.0080% or less.
  • Nb and Ti are contained in a total amount of 0.005% or more.
  • the total content of Nb and Ti is preferably 0.010% or more, more preferably 0.020% or more.
  • Nb and Ti do not completely dissolve in the slab reheating, and TiN, Ti(C,N), NbN, Nb(C, Precipitates having an equivalent circle diameter of 500 nm or more, such as N), (Nb, Ti), (C, N), increase and act as starting points for delayed fracture, rather degrading the delayed fracture resistance. Therefore, the upper limit of the total content of Nb and Ti is 0.080%.
  • the total content of Nb and Ti (Ti+Nb) is preferably 0.07% or less, more preferably 0.06% or less.
  • the chemical composition of the steel sheet in the present invention contains the above constituent elements as basic components, and the balance includes iron (Fe) and inevitable impurities.
  • the steel sheet of the present invention preferably has a chemical composition containing the above-described basic components, with the balance being iron (Fe) and unavoidable impurities.
  • one or more selected from the following (A) to (D) may be contained as the component composition.
  • Cu 1.0% or less
  • Cu improves corrosion resistance in the use environment of automobiles.
  • the inclusion of Cu has the effect of suppressing penetration of hydrogen into the steel sheet by coating the surface of the steel sheet with corrosion products.
  • Cu is an element that is mixed when scrap is used as a raw material, and by allowing Cu to be mixed, recycled materials can be used as raw materials, and manufacturing costs can be reduced.
  • the content of Cu is preferably 0.01% or more, and from the point of view of improving the delayed fracture resistance, the content of Cu is preferably 0.05% or more.
  • Cu content is more preferably 0.10% or more. However, if the Cu content is too high, surface defects may occur, so the Cu content is preferably 1.0% or less. From the above, when Cu is contained, the Cu content is set to 1.0% or less.
  • the Cu content is more preferably 0.50% or less, still more preferably 0.30% or less.
  • Ni 1.0% or less
  • Ni is also an element that acts to improve corrosion resistance.
  • Ni has the effect of reducing surface defects that tend to occur when Cu is contained. Therefore, from the above point of view, it is desirable to contain 0.01% or more of Ni.
  • the Ni content is more preferably 0.05% or more, still more preferably 0.10% or more.
  • the Ni content is set to 1.0% or less.
  • the Ni content is more preferably 0.50% or less, still more preferably 0.30% or less.
  • Cr 1.0% or less Cr can be added to obtain the effect of improving the hardenability of steel.
  • the Cr content is more preferably 0.05% or more, still more preferably 0.10% or more.
  • the Cr content exceeds 1.0%, the cementite dissolution rate during annealing is retarded, and undissolved cementite remains, thereby deteriorating the delayed fracture resistance of the sheared end face.
  • pitting corrosion resistance is also deteriorated.
  • it also degrades chemical convertibility. Therefore, when Cr is contained, the Cr content is set to 1.0% or less. Delayed fracture resistance, pitting corrosion resistance, and chemical conversion treatability all tend to start to deteriorate when the Cr content exceeds 0.2%. is more preferable.
  • Mo less than 0.3% Mo has the effect of improving the hardenability of steel, the effect of generating fine carbides containing Mo that serve as hydrogen trap sites, and the improvement of delayed fracture resistance by refining martensite. can be added for the purpose of obtaining the effect of If a large amount of Nb or Ti is added, these coarse precipitates are formed and the delayed fracture resistance deteriorates, but the solid solubility limit of Mo is larger than that of Nb and Ti. When added in combination with Nb and Ti, it forms fine precipitates in which these and Mo are combined, and has the effect of refining the structure.
  • Mo in addition to small amounts of Nb and Ti, it is possible to refine the structure without leaving coarse precipitates and disperse a large amount of fine carbides, thereby improving delayed fracture resistance. can be improved.
  • the Mo content is more preferably 0.03% or more, still more preferably 0.05% or more.
  • Mo content should be less than 0.3%.
  • the Mo content is preferably 0.2% or less.
  • V 0.5% or less
  • V has the effect of improving the hardenability of steel, the effect of forming fine carbides containing V that serve as hydrogen trap sites, and the improvement of delayed fracture resistance by refining martensite. It can be added for the purpose of obtaining an effect.
  • the V content is more preferably 0.03% or more, still more preferably 0.05% or more.
  • the V content should be 0.5% or less.
  • the V content is more preferably 0.3% or less, still more preferably 0.2% or less. Further, the V content is preferably 0.1% or less.
  • Zr 0.2% or less Zr contributes to high strength through refinement of prior ⁇ grains and the resulting refinement of the internal structure of martensite, and improves delayed fracture resistance.
  • the Zr content is desirably 0.005% or more.
  • the Zr content is more preferably 0.010% or more, still more preferably 0.015% or more.
  • the Zr content should be 0.2% or less.
  • the Zr content is more preferably 0.1% or less, still more preferably 0.04% or less.
  • W 0.2% or less W contributes to increasing the strength and improving the delayed fracture resistance through the formation of fine W-based carbides and carbonitrides that serve as hydrogen trap sites. From this point of view, it is desirable to contain W at 0.005% or more.
  • the W content is more preferably 0.010% or more, still more preferably 0.030% or more. However, if a large amount of W is contained, coarse precipitates that remain undissolved when the slab is heated in the hot rolling process increase, and the delayed fracture resistance of the sheared end faces deteriorates. Therefore, when W is contained, the W content should be 0.2% or less.
  • the W content is more preferably 0.1% or less.
  • Ca 0.0030% or less Ca fixes S as CaS and improves delayed fracture resistance. In order to obtain this effect, it is desirable to contain 0.0002% or more of Ca.
  • the Ca content is more preferably 0.0005% or more, still more preferably 0.0010% or more. However, since adding a large amount of Ca deteriorates the surface quality and bendability, the Ca content is preferably 0.0030% or less. As mentioned above, when containing Ca, Ca content shall be 0.0030% or less.
  • the Ca content is more preferably 0.0025% or less, still more preferably 0.0020% or less.
  • Ce 0.0030% or less Ce also fixes S and improves delayed fracture resistance. In order to obtain this effect, it is desirable to contain Ce at 0.0002% or more.
  • the Ce content is more preferably 0.0003% or more, and still more preferably 0.0005% or more.
  • the Ce content is preferably 0.0030% or less. From the above, when Ce is contained, the Ce content is set to 0.0030% or less.
  • the Ce content is more preferably 0.0020% or less, still more preferably 0.0015% or less.
  • La 0.0030% or less
  • La also fixes S and improves delayed fracture resistance.
  • the La content is more preferably 0.0005% or more, still more preferably 0.0010% or more.
  • the La content is preferably 0.0030% or less. From the above, when La is contained, the La content shall be 0.0030% or less.
  • the La content is more preferably 0.0020% or less, still more preferably 0.0015% or less.
  • REM 0.0030% or less REM also fixes S and improves delayed fracture resistance. In order to obtain this effect, it is desirable to contain 0.0002% or more of REM.
  • the REM content is more preferably 0.0003% or more, still more preferably 0.0005% or more.
  • the REM content is preferably 0.0030% or less. From the above, when REM is contained, the REM content is set to 0.0030% or less.
  • the REM content is more preferably 0.0020% or less, still more preferably 0.0015% or less.
  • REM includes scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.
  • Sc scandium
  • Y yttrium
  • La lanthanum
  • Lu lutetium
  • the REM concentration in the present invention is the total content of one or more elements selected from the above REMs.
  • Mg 0.0030% or less Mg fixes O as MgO and improves delayed fracture resistance. In order to obtain this effect, it is desirable to contain 0.0002% or more of Mg.
  • the Mg content is more preferably 0.0005% or more, still more preferably 0.0010% or more.
  • the Mg content is desirably 0.0030% or less. From the above, when Mg is contained, the Mg content should be 0.0030% or less.
  • the Mg content is more preferably 0.0020% or less, still more preferably 0.0015% or less.
  • Sb 0.1% or less Sb suppresses the oxidation and nitridation of the surface layer, thereby suppressing the reduction of C and B. Suppressing the reduction of C and B suppresses the formation of ferrite in the surface layer, contributing to higher strength and improved delayed fracture resistance.
  • the Sb content is desirably 0.002% or more.
  • the Sb content is more preferably 0.004% or more, still more preferably 0.006% or more.
  • the Sb content is preferably 0.1% or less. From the above, when Sb is contained, the Sb content is set to 0.1% or less.
  • the Sb content is more preferably 0.05% or less, still more preferably 0.02% or less.
  • Sn 0.1% or less Sn suppresses oxidation and nitridation of the surface layer, thereby suppressing a decrease in the content of C and B in the surface layer. Suppressing the reduction of C and B suppresses the formation of ferrite in the surface layer, contributing to higher strength and improved delayed fracture resistance. From this point of view, the Sn content is desirably 0.002% or more. The Sn content is preferably 0.003% or more. However, if the Sn content exceeds 0.1%, the castability deteriorates, and Sn segregates at prior ⁇ grain boundaries, resulting in deterioration of the delayed fracture resistance of sheared edges. Therefore, when Sn is contained, the Sn content is set to 0.1% or less. The Sn content is more preferably 0.05% or less, still more preferably 0.01% or less.
  • the arbitrary element When the content of the arbitrary element is less than the preferred lower limit, the arbitrary element is included as an unavoidable impurity.
  • the steel structure of the steel sheet of the present invention has the following structure.
  • (Configuration 1) The area ratio of martensite to the entire structure is 95% or more and 100% or less.
  • (Configuration 2) The average grain size of prior austenite grains is less than 11.2 ⁇ m.
  • (Structure 3) The number density A of precipitates having an equivalent circle diameter of 500 nm or more satisfies the following formula (1).
  • [B] represents the content of B (% by mass).
  • the area ratio of martensite to the entire structure is 95% or more and 100% or less.
  • the area ratio of martensite in the steel structure is set to 95% or more. More preferably 99% or more, still more preferably 100%.
  • the balance includes bainite, ferrite, and retained austenite (retained ⁇ ).
  • Other than these structures are trace amounts of carbides, sulfides, nitrides and oxides.
  • the residual tissue is 5% or less, preferably 1% or less.
  • martensite includes self-tempering during continuous cooling and martensite that is not tempered by staying at about 150° C. or higher for a certain period of time. Note that the area ratio of martensite may be 100% without including the remainder.
  • the average grain size of prior austenite grains is less than 11.2 ⁇ m.
  • the delayed fracture surface In steels with a martensite area ratio of 95% or more in the steel structure, the delayed fracture surface often exhibits intergranular fracture surface, and the initiation point of delayed fracture and the crack propagation path at the initial stage of delayed fracture are on the prior austenite grain boundary. Conceivable. Refinement of prior-austenite grains is effective for suppressing intergranular fracture, and refinement of prior-austenite grains significantly improves delayed fracture resistance.
  • the mechanism is thought to be that the area ratio of the prior austenite grain boundaries increases due to the refinement of the prior austenite grains, and the concentration of impurity elements such as P, which is a grain boundary embrittlement element, on the prior austenite grain boundaries decreases. Further, the refinement of the prior austenite grains also contributes to the improvement of the tensile strength. From the viewpoint of delayed fracture resistance and strength, the average grain size of prior austenite grains (prior ⁇ grain size) is less than 11.2 ⁇ m. This average particle size is preferably 10 ⁇ m or less, more preferably 7.0 ⁇ m or less, and still more preferably 5.0 ⁇ m or less.
  • the present inventors have found that by controlling the hot rolling conditions, the number density A of precipitates with an equivalent circle diameter of 500 nm or more is reduced, and by satisfying the following conditions, the delayed fracture resistance is improved by strengthening the grain boundaries of B and the origin of the precipitates It was found that it is possible to simultaneously suppress the destruction of the A (pieces/mm 2 ) ⁇ 8.5 ⁇ 10 5 ⁇ [B]
  • a (number/mm 2 ) ⁇ 5.0 ⁇ 10 5 ⁇ [B]
  • the area ratios of martensite, bainite, and ferrite are obtained by polishing the L section of the steel sheet (the section parallel to the rolling direction and perpendicular to the steel sheet surface (hereinafter also referred to as the vertical section parallel to the rolling direction)) with Nital. Corroded and observed at 1/4 thickness position from the surface of the steel plate with SEM at a magnification of 2000, 4 fields of view are observed, and the photographed structure photograph is image-analyzed and measured.
  • martensite and bainite refer to gray or white structures in SEM.
  • ferrite is a region exhibiting black contrast in SEM. Martensite and bainite contain trace amounts of carbides, nitrides, sulfides, and oxides, but since it is difficult to exclude them, the area ratio of the region including these is used as the area ratio.
  • bainite has the following characteristics. That is, it has an aspect ratio of 2.5 or more, exhibits a plate-like form, and is a slightly blacker structure than martensite.
  • the width of the plate is 0.3-1.7 ⁇ m.
  • the distribution density of carbides with a diameter of 10 to 200 nm inside the bainite is 0 to 3 pieces/ ⁇ m 2 .
  • the retained austenite (retained ⁇ ) is measured by chemically polishing the 200 ⁇ m surface layer of the steel plate with oxalic acid, and using the X-ray diffraction intensity method for the plate surface. It is calculated from the integrated intensities of (200) ⁇ , (211) ⁇ , (220) ⁇ , (200) ⁇ , (220) ⁇ , and (311) ⁇ diffraction plane peaks measured by Mo-K ⁇ rays.
  • the average grain size of prior austenite grains is measured by polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel sheet, and then applying a chemical solution that corrodes the prior ⁇ grain boundaries (such as a saturated picric acid aqueous solution or It was corroded by adding ferric chloride to this), and observed at 1/4 thickness position from the steel plate surface with an optical microscope at a magnification of 500 times. 15 lines are drawn in each direction at intervals of 10 ⁇ m or more in actual length, and the number of intersections between grain boundaries and lines is counted. Furthermore, the prior ⁇ grain size (average grain size of prior austenite grains) can be measured by multiplying the value obtained by dividing the total line length by the number of intersections by 1.13.
  • the number density A of precipitates with an equivalent circle diameter of 500 nm or more is obtained by polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel sheet, and then the area from the 1/5 position to the 4/5 position of the steel plate thickness, that is, from the steel plate surface.
  • an area of 2 mm 2 was continuously photographed with an SEM, and from the photographed SEM photographs, such precipitates It was obtained by counting the number of Also, the magnification for photographing is 2000 times.
  • each inclusion particle is magnified 10000 times, and the said precipitate is analyzed.
  • the precipitate having an equivalent circle diameter of 500 nm or more is a precipitate containing B such as Fe 23 (C, B) 6 , and an elemental analysis by energy dispersive X-ray spectroscopy (EDS) at an acceleration voltage of 3 kV The presence or absence of a B peak was examined, and when there was a B peak, it was evaluated that the above precipitates were present. If the slab is not sufficiently reheated, precipitates containing Nb and Ti also increase, and these precipitates also adversely affect the delayed fracture properties.
  • the equivalent circle diameter refers to the diameter of a perfect circle having an area of each precipitate calculated from the SEM photograph.
  • One of the characteristics of the present invention is that the delayed fracture resistance is good even if the tensile strength is 1470 MPa or more. Therefore, in the present invention, the tensile strength must be 1470 MPa or more. From the viewpoint of reducing the weight of automobile frame parts, it is preferably 1700 MPa or more.
  • the tensile strength of the steel sheet of the present invention may be 2100 MPa or less.
  • the tensile strength can be measured by cutting out a JIS No. 5 tensile test piece so that the direction perpendicular to the rolling direction is the longitudinal direction at the position of 1/4 of the coil width, and conducting a tensile test based on JIS Z2241.
  • the steel sheet of the present invention described above may be a steel sheet having a plating layer on its surface.
  • the plating layer may be Zn plating or plating of other metals. Further, it may be either a hot-dip plated layer or an electroplated layer.
  • a steel slab having the above chemical composition is heated at a slab surface temperature from 1000 ° C. to a heating and holding temperature of 1250 ° C. or higher at an average heating rate of 10 ° C./min or less, and this heating and holding After holding at the temperature for 30 minutes or more, hot finish rolling is performed under the conditions that the residence time at 900 to 1000°C is 20 seconds or more and 150 seconds or less, and the finish rolling temperature is 850°C or more, and the finish rolling temperature is 650°C.
  • Cooling is performed at an average cooling rate of 40 ° C./sec or more in the range of up to and then coiling at a coiling temperature of 650 ° C. or less to form a hot-rolled steel sheet, and the hot-rolled steel sheet is rolled at a reduction rate of 40% or more.
  • a cold-rolled steel sheet is obtained by cold rolling, the annealing temperature is set to 800 to 950 ° C., the cold-rolled steel plate is heated from 400 ° C. to the annealing temperature at an average heating rate of 1.0 ° C./sec or more, and the annealing is performed. The temperature is maintained for 600 seconds or less, cooled from the annealing temperature to 420 ° C.
  • the average heating rate is set at 10°C/min or less from 1000°C to the heating and holding temperature of 1250°C or higher, thereby promoting the dissolution of sulfides and the formation of inclusions. Reduction in size and number is achieved. Since Nb and Ti have high dissolution temperatures, the heating and holding temperature at the slab surface temperature is set to 1250° C. or higher, and the holding time is set to 30 minutes or longer to promote solid dissolution of Nb and Ti. reduction is achieved.
  • the heating and holding temperature is preferably 1300° C. or higher. More preferably, it is 1350° C. or higher.
  • the average heating rate is "(Temperature at the completion of slab heating (heating holding temperature) (°C) - Temperature at the start of slab heating (°C) (1000°C)) / Heating time from the start of heating to the completion of heating. (minutes)”.
  • the slab is held at 900-1000°C for 20 seconds or more and 150 seconds or less.
  • An increase in the residence time in the temperature range of 900 to 1000° C. produces and coarsens precipitates mainly composed of BN. Precipitates generated in these temperature ranges are difficult to form a solid solution by annealing heating, and reduce the amount of solid solution B after annealing. Therefore, if the residence time exceeds 150 seconds, it is not possible to obtain a solid solution B amount that is effective in suppressing delayed fracture. Therefore, the residence time is 150 seconds or less, preferably 120 seconds or less, and more preferably 100 seconds or less. On the other hand, if the residence time is less than 20 seconds, the tissue may become non-uniform. Therefore, the residence time is 20 seconds or longer, preferably 30 seconds or longer, and more preferably 40 seconds or longer.
  • the finish rolling temperature (FT) is set to 850°C or higher in order to suppress the precipitation of Nb, Ti, B, etc.
  • the finish rolling temperature is 930° C. or lower.
  • cooling after hot finish rolling is performed at an average cooling rate of 40°C/second or more in the range from the finish rolling temperature to 650°C.
  • the average cooling rate is less than 40° C./sec, the number of carbonitrides having an equivalent circle diameter of 1.0 ⁇ m or more increases due to the coarsening of Nb carbonitrides and Ti carbonitrides, and the desired delayed fracture resistance is obtained.
  • the average cooling rate is 250° C./s or less, more preferably 200° C./s or less.
  • the average cooling rate in the hot rolling process is "(temperature at the start of cooling (finish rolling temperature) (°C) - temperature at the completion of cooling (°C) (650°C)) / from the start of cooling to the completion of cooling. cooling time (seconds).
  • the winding temperature should be 650° C. or lower.
  • the winding temperature is 500°C or higher.
  • Cold rolling In cold rolling, if the rolling reduction (cold rolling rate) is 40% or more, recrystallization behavior and texture orientation in the subsequent continuous annealing can be stabilized. If it is less than 40%, some of the austenite grains during annealing may become coarse and the strength may decrease. Also, the cold rolling rate is preferably 80% or less.
  • the steel sheet is subjected to annealing and, if necessary, tempering and temper rolling in a continuous annealing line (CAL).
  • CAL continuous annealing line
  • Fe 23 (C, B) 6 is generated in the ferrite region during annealing heating and coarsens, in order to reduce Fe 23 (C, B) 6 and sufficiently obtain the effect of grain boundary strengthening by B, It is very important to increase the average heating rate above 400°C. Also, from the viewpoint of refining the prior ⁇ grain size to less than 11.2 ⁇ m, it is necessary to increase the heating rate. From the above point of view, the average heating rate at 400° C. or higher is 1.0° C./second or higher. Also, the average heating rate at 400° C.
  • the average heating rate is 10° C./sec or less.
  • the average heating rate is defined as "annealing temperature (° C.) ⁇ 400 (° C.) described later)/heating time (minutes) from 400° C. to the annealing temperature".
  • annealing temperature In order to sufficiently reduce precipitates such as Fe 23 (C, B) 6 remaining undissolved after annealing, annealing is performed at a high temperature for a long time. Specifically, the annealing temperature must be 800° C. or higher.
  • the annealing temperature exceeds 950°C, the prior ⁇ grain size becomes coarse and the desired structure cannot be obtained. Moreover, since BN may precipitate at grain boundaries and the delayed fracture resistance may deteriorate when annealing is performed at a temperature exceeding 900° C., the annealing temperature is preferably 900° C. or lower. Even if the soaking time (holding time) at the annealing temperature is prolonged, the prior ⁇ grain size becomes too coarse, so the soaking time is set to 600 seconds or less. Preferably, this soaking time is 10 seconds or longer.
  • the first average cooling rate is less than 2° C./second, a large amount of ferrite is formed, carbon is concentrated into ⁇ , martensite is hardened, and the delayed fracture resistance deteriorates.
  • the upper limit of the first average cooling rate is not particularly limited, it is preferably 100° C./sec.
  • the cold-rolled steel sheet is placed in the plating bath in the process of cooling from the annealing temperature to 420 ° C., more specifically, when cooling at the first average cooling rate in continuous annealing.
  • Plating treatment is preferably performed by immersion, and if necessary, alloying treatment can be performed by heating to 480° C. to 600° C. after immersion in the plating bath.
  • the cooling stop temperature from 420 ° C. to 260 ° C. or less is 10 ° C./sec. It is necessary to cool at the above second average cooling rate. In a structure in which a large amount of bainite is generated, the strength is lowered and the retained austenite is increased, so the delayed fracture resistance is deteriorated. Therefore, the second average cooling rate from 420° C. to the cooling stop temperature of 260° C. or less is set to 10° C./second or more.
  • the second average cooling rate is preferably 20° C./second or higher, more preferably 70° C./second or higher.
  • the upper limit of the second average cooling rate is not particularly limited, it is preferably 2000° C./sec.
  • the first average cooling rate is “(annealing temperature (° C.) ⁇ 420 (° C.))/(cooling time from annealing temperature to 420° C. (seconds))”.
  • the second average cooling rate is "(420 (° C.) ⁇ cooling stop temperature (° C.))/(cooling time from 420° C. to cooling stop temperature (seconds))”.
  • the cooling stop temperature exceeds 260°C, there is a problem that upper and lower bainite are generated, and retained austenite and fresh martensite increase. Therefore, the cooling stop temperature is set to 260° C. or lower.
  • the carbides distributed inside the martensite are carbides that are generated during holding in a low temperature range after quenching.
  • the continuous annealing is carried out at a holding temperature of 150 to 260° C. for 20 to 1500 seconds.
  • the steel sheet thus obtained can be subjected to skin-pass rolling from the viewpoint of stabilizing press formability, such as adjusting the surface roughness and flattening the plate shape.
  • the skin pass elongation rate is preferably 0.1% or more.
  • the skin pass elongation rate is preferably 0.6% or less.
  • dull rolls are used as the skin pass rolls, and it is preferable to adjust the roughness Ra of the steel sheet to 0.8 ⁇ m or more from the viewpoint of flattening the shape. Further, it is preferable to adjust the roughness Ra of the steel sheet to 1.8 ⁇ m or less.
  • the present steel sheet can be made into a plated steel sheet by subjecting it to hot-dip plating during cooling after soaking in annealing, or subjecting it to electroplating after continuous annealing.
  • Plating types include Zn-based plating (Zn-based, Zn--Ni-based, Zn--Fe-based, etc.) and Al plating.
  • hot-dip plating When hot-dip plating is applied, the steel sheet is immersed in the plating bath in the process of cooling from the annealing temperature to 420° C. at a first average cooling rate of 2° C./sec or more, and after immersion in the plating bath, it is heated to 480 to 600° C. An alloying treatment may be performed.
  • cooling is performed at the second average cooling rate described above, and a holding treatment at a holding temperature of 150 to 260° C. for 20 to 1500 seconds may be carried out.
  • heat treatment can be performed in a temperature range of 260° C. or lower in order to reduce the amount of hydrogen that has entered the steel.
  • the delayed fracture resistance of high-strength cold-rolled steel sheets is greatly improved, and the application of high-strength steel sheets contributes to the improvement of part strength and weight reduction.
  • the steel sheet of the present invention preferably has a thickness of 0.5 mm or more. Also, the plate thickness is preferably 2.0 mm or less.
  • the member of the present invention is obtained by subjecting the steel plate of the present invention to at least one of forming and joining. Further, the method for manufacturing a member of the present invention includes a step of subjecting the steel plate of the present invention to at least one of forming and joining to form a member.
  • the steel sheet of the present invention has a tensile strength of 1470 MPa or more and excellent delayed fracture resistance. Therefore, members obtained using the steel sheet of the present invention also have high strength and are superior in delayed fracture resistance to conventional high-strength members. Moreover, if the member of the present invention is used, the weight can be reduced. Therefore, the member of the present invention can be suitably used for, for example, vehicle body frame parts.
  • General processing methods such as press processing can be used without restrictions for molding.
  • general welding such as spot welding and arc welding, riveting, caulking, and the like can be used without limitation.
  • a slab having each component composition was heated at an average heating rate of 6° C./min up to the heating and holding temperature shown in Table 2 at the slab surface temperature, and held for the heating and holding time shown in Table 2. After that, the slab is retained for the residence time at 900 to 1000 ° C. shown in Table 2, and hot finish rolling is performed at a finish rolling temperature of 870 ° C.
  • the average cooling rate in the range from the finish rolling temperature to 650 ° C. is 50 ° C. / sec. After that, it was cooled and coiled at a coiling temperature of 550°C to obtain a hot-rolled steel sheet, and the hot-rolled steel sheet was cold-rolled at a reduction rate (cold rolling reduction rate) of 50% to obtain a cold-rolled steel sheet.
  • the cold-rolled steel sheet was heated from 400° C. to the annealing temperature shown in Table 2 at the average heating rate shown in Table 2, and soaked at the annealing temperature for the soaking time shown in Table 2. After that, it is cooled from the annealing temperature (first cooling start temperature) to 420 ° C. (second cooling start temperature) at the first average cooling rate shown in Table 2, and further from 420 ° C. (second cooling start temperature) to Table 2. is cooled at the second average cooling rate shown in Table 2 to the cooling stop temperature shown in Table 2, reheated as necessary, and then continuously annealed at the holding temperature shown in Table 2 for the holding time shown in Table 2. rice field.
  • the steel sheet in the continuous annealing, is immersed in a hot dip galvanizing bath at 480°C in the cooling process to 420°C at the first average cooling rate, then heated to 540°C and held for 15 seconds to alloy. It was processed and made into an alloyed hot-dip galvanized steel sheet. Thereafter, cooling at the second average cooling rate shown in Table 2 and holding treatment at the holding temperature and holding time shown in Table 2 were performed. Also, No. For 3, after continuous annealing, the obtained steel sheet was subjected to electroplating to obtain a steel sheet having a Zn plating layer formed thereon.
  • the metal structure of the obtained steel sheet was quantified by the method described above, and a tensile test and a delayed fracture resistance evaluation test were also performed.
  • the tissue measurement method was as follows.
  • the area ratios of martensite, bainite, and ferrite were determined by polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel sheet, corroding it with nital, and examining the 1/4 thickness position from the steel sheet surface with an SEM at a magnification of 2000 times. Visual field observation was performed, and the photographed tissue photograph was image-analyzed and measured.
  • martensite and bainite refer to gray or white structures in SEM.
  • bainite has the following characteristics.
  • the object has an aspect ratio of 2.5 or more, exhibits a plate-like form, and is a slightly blacker structure than martensite.
  • the width of the plate is 0.3-1.7 ⁇ m.
  • the distribution density of carbides with a diameter of 10 to 200 nm inside the bainite is 0 to 3 pieces/ ⁇ m 2 .
  • ferrite is a region exhibiting black contrast in SEM. Note that the interior of martensite and bainite contains trace amounts of carbides, nitrides, sulfides, and oxides, but since it is difficult to exclude these, the area ratio of the region including these was used as the area ratio.
  • the retained austenite (retained ⁇ ) was measured by chemically polishing a 200 ⁇ m surface layer of the steel plate with oxalic acid and using the X-ray diffraction intensity method for the plate surface. It was calculated from the integrated intensities of (200) ⁇ , (211) ⁇ , (220) ⁇ , (200) ⁇ , (220) ⁇ , and (311) ⁇ diffraction surface peaks measured by Mo-K ⁇ radiation.
  • the average grain size of prior austenite grains is measured by polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel sheet, and then applying a chemical solution that corrodes the prior ⁇ grain boundaries (such as a saturated picric acid aqueous solution or It was corroded by adding ferric chloride to this), and observed at 1/4 thickness position from the steel plate surface with an optical microscope at a magnification of 500 times. Fifteen lines in each direction were drawn at intervals of 10 ⁇ m or more in actual length, and the number of intersections between the grain boundaries and the lines was counted. The prior- ⁇ grain size was obtained by multiplying the value obtained by dividing the total line length by the number of intersections by 1.13.
  • the number density A of precipitates with an equivalent circle diameter of 500 nm or more is obtained by polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel sheet, and then the area from the 1/5 position to the 4/5 position of the steel plate thickness, that is, from the steel plate surface.
  • an area of 2 mm 2 was continuously photographed with an SEM, and from the photographed SEM photographs, such precipitates It was obtained by counting the number of Also, the magnification for photographing is 2000 times.
  • each inclusion particle is magnified 10000 times, and the said precipitate is analyzed.
  • the precipitate having an equivalent circle diameter of 500 nm or more is a precipitate containing B such as Fe 23 (C, B) 6 , and an elemental analysis by energy dispersive X-ray spectroscopy (EDS) at an acceleration voltage of 3 kV The presence or absence of a B peak was examined, and when there was a B peak, it was evaluated that the above precipitate was present.
  • B such as Fe 23 (C, B) 6
  • EDS energy dispersive X-ray spectroscopy
  • a JIS No. 5 tensile test piece was cut out so that the direction perpendicular to the rolling direction was the longitudinal direction at the position of 1/4 of the coil width, and a tensile test (based on JIS Z2241) was performed to evaluate YP, TS, and El.
  • Evaluation of delayed fracture resistance was performed as follows. A strip test piece of 100 mm in the direction perpendicular to the rolling direction and 30 mm in the rolling direction was taken from the 1/4 position of the coil width in the width direction of the obtained steel plate (coil). The end face of the long side with a length of 100 mm is cut out by shearing, and in the state of shearing (without machining to remove burrs), bending is performed so that the burrs are on the outer peripheral side of the bend. , the test piece was fixed with bolts while maintaining the shape of the test piece at the time of bending. The shearing clearance was 13% and the rake angle was 1°.
  • Bending was performed with a tip bending radius of 10 mm and an angle inside the bending apex of 90 degrees (V bending).
  • the punch has a U-shaped punch whose tip radius is the same as the tip bending radius R (the tip R is semicircular and the thickness of the punch barrel is 2R), and the die has a corner radius of 30 mm. was used.
  • the depth to which the punch pushes the steel plate was adjusted, and the steel plate was formed so that the bending angle of the tip (the angle inside the bending apex) was 90 degrees (V shape).
  • Sandwich the test piece with a hydraulic jack so that the distance between the flange ends of the straight piece when bending is the same as when bending (to cancel out the opening of the straight piece due to springback).
  • the bolt was passed through an elliptical hole (minor axis: 10 mm, major axis: 15 mm) previously provided 10 mm inward from the short side edge of the strip test piece and fixed.
  • the obtained test piece after bolting was mixed with 0.1% by mass of ammonium thiocyanate aqueous solution and McIlvaine buffer solution at a ratio of 1:1 and immersed in a solution adjusted to pH 8.0 for delayed fracture resistance.
  • a characterization test was performed. At this time, the temperature of the solution was set at 20° C., and the amount of the solution per 1 cm 3 of surface area of the test piece was set at 20 ml. After 24 hours had elapsed, the presence or absence of cracks at a visually recognizable level (1 mm or more in length) was confirmed, and those in which no cracks were observed were judged to have excellent delayed fracture resistance.
  • Table 3 shows the structure and properties of the obtained steel sheets.
  • the steel sheets within the scope of the present invention had high strength and excellent delayed fracture resistance.
  • No. In No. 13 (steel M), the C content was less than the lower limit of the specified value of the present invention, and the TS was insufficient.
  • No. In No. 14 (steel N), the C content exceeded the upper limit of the specified value of the present invention, and sufficient delayed fracture resistance was not obtained.
  • No. In No. 15 (steel O), the Mn content was less than the lower limit of the value specified in the present invention, and martensite was not sufficiently formed, and sufficient delayed fracture resistance was not obtained.
  • No. In No. 16 (Steel P), the P content exceeded the upper limit of the specified value of the present invention, and sufficient delayed fracture resistance was not obtained.
  • Step A the slab heating and holding time was less than the lower limit of the value specified in the present invention, the prior ⁇ grain size was large, and sufficient delayed fracture resistance was not obtained.
  • No. 26 the residence time at 900 to 1000° C. exceeded the upper limit of the specified value of the present invention, the number density A of precipitates was excessive, and sufficient delayed fracture resistance was not obtained.
  • No. 27 the average heating rate during annealing was less than the lower limit of the value specified in the present invention, the prior ⁇ grain size was large, and sufficient delayed fracture resistance was not obtained.
  • No. In No. 26 the residence time at 900 to 1000° C. exceeded the upper limit of the specified value of the present invention, the number density A of precipitates was excessive, and sufficient delayed fracture resistance was not obtained.
  • No. 27 the average heating rate during annealing was less than the lower limit of the value specified in the present invention, the prior ⁇ grain size was large, and sufficient delayed fracture resistance was not obtained.
  • Step A the soaking time during annealing exceeded the upper limit of the specified value of the present invention, the prior ⁇ grain size was large, and sufficient delayed fracture resistance was not obtained.
  • No. 29 (Steel A) the first average cooling rate during annealing was less than the lower limit of the specified value of the present invention, martensite was not sufficiently formed, and sufficient delayed fracture resistance was not obtained.
  • No. 30 (Steel A) the second average cooling rate during annealing was less than the lower limit of the specified value of the present invention, martensite was not sufficiently formed, and sufficient delayed fracture resistance was not obtained.
  • No. 31 the cooling stop temperature during annealing exceeded the upper limit of the value specified in the present invention, and martensite was not sufficiently formed, and sufficient delayed fracture resistance was not obtained.
  • the steel plate of the present invention example has high strength and excellent delayed fracture resistance in the members obtained by molding and the members obtained by joining processing using the steel plate of the example of the present invention. Therefore, it was found that the steel plate has high strength and excellent delayed fracture resistance like the steel plate of the example of the present invention.

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Abstract

L'invention fournit une tôle d'acier de solidité élevée et d'une excellente résistance à la rupture différée, et fournit également un procédé de fabrication de cette tôle d'acier.　Cette tôle d'acier comprend, en% en masse, ０,１５ à ０,４５％ de C, １,５％ ou moins de Si, plus de １,７％ de Mn, ０,０３％ ou moins de P, moins de ０,００４０％ de S, ０,２０％ ou moins de ｓｏｌ．Ａｌ, ０,００５％ ou moins de N, ０,００１５ à ０,０１００％ de B, et ０,００５ à ０,０８０％ au total de Nb et/ou Ti, le reste étant constitué de Fe et des impuretés inévitables. Le rapport surfacique d'une martensite pour l'ensemble de sa structure est compris entre ９５ et １００％. La taille de grains γ antérieur est inférieure à １１,2μｍ. La densité en nombre (A) de précipités de diamètre de cercle équivalent supérieur ou égal à ５００ｎｍ, satisfait la formule Ａ（nombre de précipités／ｍｍ２）≦　８,５×１０５×［Ｂ］.
PCT/JP2022/024964 2021-07-28 2022-06-22 Tôle d'acier, élément, et procédés de fabrication de ceux-ci WO2023008003A1 (fr)

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JP2022559509A JP7226672B1 (ja) 2021-07-28 2022-06-22 鋼板、部材およびそれらの製造方法
KR1020247002167A KR20240024947A (ko) 2021-07-28 2022-06-22 강판, 부재 및 그들의 제조 방법
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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4712882B2 (ja) 2008-07-11 2011-06-29 株式会社神戸製鋼所 耐水素脆化特性および加工性に優れた高強度冷延鋼板
WO2018062381A1 (fr) * 2016-09-28 2018-04-05 Ｊｆｅスチール株式会社 Tôle d'acier et son procédé de production
JP6354921B1 (ja) 2016-09-28 2018-07-11 Ｊｆｅスチール株式会社 鋼板およびその製造方法
WO2020129403A1 (fr) * 2018-12-21 2020-06-25 Ｊｆｅスチール株式会社 Tôle d'acier, élément et procédé de fabrication de ces derniers
WO2020184055A1 (fr) * 2019-03-12 2020-09-17 Ｊｆｅスチール株式会社 Élément de presse à chaud, procédé de production de tôle d'acier destinée à une presse à chaud, et procédé de production destiné à un élément de presse à chaud

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Publication number Priority date Publication date Assignee Title
JPS4712882Y1 (fr) 1968-08-13 1972-05-12
JPS60109606A (ja) 1983-11-16 1985-06-15 Toyooki Kogyo Co Ltd 分流弁
MX2021010128A (es) * 2019-02-21 2021-09-23 Jfe Steel Corp Miembro prensado en caliente, chapa de acero laminada en frio para prensado en caliente y metodo de fabricacion de los mismos.

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4712882B2 (ja) 2008-07-11 2011-06-29 株式会社神戸製鋼所 耐水素脆化特性および加工性に優れた高強度冷延鋼板
WO2018062381A1 (fr) * 2016-09-28 2018-04-05 Ｊｆｅスチール株式会社 Tôle d'acier et son procédé de production
JP6354921B1 (ja) 2016-09-28 2018-07-11 Ｊｆｅスチール株式会社 鋼板およびその製造方法
WO2020129403A1 (fr) * 2018-12-21 2020-06-25 Ｊｆｅスチール株式会社 Tôle d'acier, élément et procédé de fabrication de ces derniers
WO2020184055A1 (fr) * 2019-03-12 2020-09-17 Ｊｆｅスチール株式会社 Élément de presse à chaud, procédé de production de tôle d'acier destinée à une presse à chaud, et procédé de production destiné à un élément de presse à chaud

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