US20250108424A1 - Hot-stamping formed body - Google Patents

Hot-stamping formed body Download PDF

Info

Publication number
US20250108424A1
US20250108424A1 US18/834,189 US202318834189A US2025108424A1 US 20250108424 A1 US20250108424 A1 US 20250108424A1 US 202318834189 A US202318834189 A US 202318834189A US 2025108424 A1 US2025108424 A1 US 2025108424A1
Authority
US
United States
Prior art keywords
present
steel
hot
less
content
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
US18/834,189
Other languages
English (en)
Inventor
Shingo FUJINAKA
Jun Haga
Yuri Toda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: FUJINAKA, Shingo, HAGA, JUN, TODA, Yuri
Publication of US20250108424A1 publication Critical patent/US20250108424A1/en
Pending legal-status Critical Current

Links

Images

Classifications

    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • 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
    • 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
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • 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
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/06—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
    • C22C38/18—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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/18—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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/002—Bainite
    • 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 a hot-stamping formed body.
  • Hot stamping is attracting attention as a technique that achieves both the formability of a steel sheet into a vehicle member and strength of a vehicle member by performing hardening of the steel sheet in a die at the same time as press working.
  • Patent Document 1 discloses an electrolytic zinc-based plated steel sheet having a high yield ratio and excellent bendability, in which the critical hydrogen amount in the steel is 0.20 mass ppm or less.
  • Hydrogen embrittlement cracking is a phenomenon in which a steel member, to which high stress is applied in use, suddenly fractures due to hydrogen which is irrupted into the steel from an external environment. This phenomenon is also called delayed fracture due to the mode of the occurrence of fracture. It is generally known that hydrogen embrittlement cracking is more likely to occur in the steel sheet as tensile strength of the steel sheet increases. It is considered that this is because the higher tensile strength of the steel sheet, the greater residual stress in the steel sheet after a component is formed. This susceptibility to hydrogen embrittlement cracking (delayed fracture) is called hydrogen embrittlement resistance.
  • Patent Document 1 bendability is considered, but hydrogen embrittlement resistance are not considered.
  • the present invention has been made in view of the above-mentioned problem.
  • An object of the present invention is to provide a hot-stamping formed body having high strength and excellent hydrogen embrittlement resistance.
  • the gist of the present invention is as follows.
  • a hot-stamping formed body comprising, as a chemical composition, by mass %:
  • a surface layer region which is a region from a surface of the hot-stamping formed body to 1/25 depth of a sheet thickness from the surface
  • an area ratio of bainite is more than 10%
  • a maximum value of pole density of a texture is 4.0 or less
  • a deboronization index is 0.05 or more.
  • the hot-stamping formed body according to [1] may comprise, as the chemical composition, by mass %, one or more selected from the group consisting of:
  • FIG. 1 A figure explaining the method to obtain a deboronization index.
  • the present inventors found that in a surface layer region, by generating a desired amount of bainite, creating a texture with a desired crystal orientation, and achieving a desired deboronization index, hydrogen embrittlement resistance of the hot-stamping formed body can be improved.
  • the present inventors found that in order to obtain a hot-stamping formed body having the above features, it is particularly effective to perform annealing under a desired condition during manufacturing a steel sheet for hot stamping.
  • the hot-stamping formed body according to the present embodiment will be described in detail. First, the reason the chemical composition of the hot-stamping formed body according to the present embodiment is limited will be described.
  • a limited numerical range described using “to” described below includes a lower limit and an upper limit. Numerical values represented using “less than” or “more than” are not included in a numerical range. All percentages (%) related to the chemical composition mean mass %.
  • the hot-stamped formed body comprises, as a chemical composition, by mass %, C: more than 0.40% and 0.70% or less, Si: 0.010% to 3.000%, Mn: 0.10% or more and less than 0.60%, P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, 0: 0.0200% or less, Al: 0.0010% to 0.5000%, Nb: 0.0010% to 0.1000% c, Ti: 0.010% to 0.200%, Cr: 0.010% to 0.800%, Mo: 0.0010% to 1.0000%, B: 0.0005% to 0.0200%, and a remainder: Fe and impurities.
  • C more than 0.40% and 0.70% or less
  • Si 0.010% to 3.000%
  • Mn 0.10% or more and less
  • P 0.100% or less
  • S 0.0100% or less
  • N 0.0200% or less
  • 0: 0.0200% or less Al: 0.0010% to 0.500
  • C is an element that improves the strength of the hot-stamping formed body.
  • the C content is set to more than 0.40%.
  • the C content is preferably 0.42% or more or 0.44% or more.
  • the C content is set to 0.70% or less.
  • the C content is preferably 0.65% or less or 0.60% or less.
  • Si is an element that improves strength of the hot-stamping formed body by solid-solution strengthening.
  • the Si content is set to 0.010% or more.
  • the Si content is preferably 0.050% or more, 0.100% or more or 0.150% or more.
  • the Si content is set to 3.000% or less.
  • the Si content is preferably 2.000% or less, 1.000% or less or 0.600% or less.
  • Mn 0.10% or more and less than 0.60%
  • Mn is an element that increases strength of the hot-stamping formed body by increasing the hardenability of steel.
  • the Mn content is set to 0.10% or more.
  • the Mn content is preferably 0.20% or more or 0.25% or more.
  • the Mn content is 0.60% or more, a desired texture cannot be obtained. For this reason, the Mn content is set to less than 0.60%.
  • the Mn content is preferably 0.55% or less, 0.50% or less or 0.45% or less.
  • P is an impurity element, and decreases strength of the grain boundaries by segregating in the grain boundaries. This deteriorates hydrogen embrittlement resistance of the hot-stamping formed body.
  • the P content is set to 0.100% or less.
  • the P content is preferably 0.050% or less or 0.010% or less.
  • the lower limit of the P content is not particularly limited, but may be 0%. However, when the P content is reduced to less than 0.0001%, the dephosphorization cost increases significantly, which is not preferable economically. For this reason, the P content may be set to 0.0001% or more, 0.001% or more or 0.005% or more.
  • S is an impurity element, and forms inclusions in steel.
  • the inclusions trap a large amount of hydrogen and form a region with locally high hydrogen concentration, and thereby deteriorate hydrogen embrittlement resistance of the hot-stamping formed body.
  • the S content is set to 0.0100% or less.
  • the S content is preferably 0.0080% or less, 0.0050% or less or 0.0030% or less.
  • the lower limit of the S content is not particularly limited, but may be 0%. However, when the S content is reduced to less than 0.0001%, the desulfurization cost increases significantly, which is not preferable economically. For this reason, the S content may be set to 0.0001% or more, 0.0002% or more, 0.0003% or more or 0.0010% or more.
  • N is an impurity element, and forms nitrides in steel.
  • the nitrides trap a large amount of hydrogen and form a region with locally high hydrogen concentration, and thereby deteriorate hydrogen embrittlement resistance of the hot-stamping formed body.
  • the N content is set to 0.0200% or less.
  • the N content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less or 0.0040% or less.
  • the lower limit of the N content is not particularly limited, but may be 0%. However, when the N content is reduced to less than 0.0001%, the denitrification cost increases significantly, which is not preferable economically. For this reason, the N content may be set to 0.0001% or more or 0.0010% or more.
  • O forms coarse oxides when a large amount of O is comprised in steel.
  • the oxides trap a large amount of hydrogen and form a region with locally high hydrogen concentration, and thereby deteriorate hydrogen embrittlement resistance of the hot-stamping formed body.
  • the O content is set to 0.0200% or less.
  • the O content is preferably 0.0100% or less, 0.0070% or less or 0.0040% or less.
  • the O content may be 0%, in order to disperse many oxides during deoxidizing of molten steel, the O content may be set to 0.0005% or more or 0.0010% or more.
  • Al is an element having an effect of deoxidizing molten steel and achieving soundness of the steel.
  • the Al content is set to 0.0010% or more.
  • the Al content is preferably 0.0050% or more, 0.0100% or more or 0.0300% or more.
  • the Al content is set to 0.5000% or less.
  • the Al content is preferably 0.4000% or less, 0.3000% or less, or 0.2000% or less or 0.1000% or less.
  • Nb is an element that forms carbonitride in steel and improves strength of the hot-stamping formed body by precipitation strengthening.
  • the Nb content is set to 0.0010% or more.
  • the Nb content is preferably 0.0050% or more, 0.0090% v or more or 0.0150% or more.
  • the Nb content is set to 0.1000% or less.
  • the Nb content is preferably 0.0800% or less or 0.0600% or less.
  • Ti is an element that forms carbonitride in steel and improves strength of the hot-stamping formed body by precipitation strengthening.
  • the Ti content is set to 0.010% or more.
  • the Ti content is preferably 0.020% or more or 0.025% or more.
  • the Ti content is set to 0.200% or less.
  • the Ti content is preferably 0.150% or less, 0.090% or less, 0.080% or less, 0.070% or less, 0.060% or less or 0.050% or less.
  • Cr is an element that increases strength of the hot-stamping formed body by dissolving in prior austenite grains during heating before hot stamping.
  • the Cr content is set to 0.010% or more.
  • the Cr content is preferably 0.100% or more, 0.150% or more or 0.200% or more.
  • the Cr content is set to 0.800% or less.
  • the Cr content is preferably 0.700% or less, 0.500% or less or 0.400% or less.
  • Mo is an element that increases strength of the hot-stamping formed body by dissolving in prior austenite grains during heating before hot stamping.
  • Mo content is set to 0.0010% or more.
  • the Mo content is preferably 0.0100% or more, 0.0500% or more or 0.1000% or more.
  • the Mo content is set to 1.0000% or less.
  • the Mo content is preferably 0.8000% or less, 0.6000% or less or 0.4000% or less.
  • B is an element that improves the hardenability of steel.
  • the B content is set to 0.0005% or more.
  • the B content is preferably 0.0010% or more or 0.0015% or more.
  • the B content is set to 0.0200% or less.
  • the B content is preferably 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0040% or less or 0.0030% or less.
  • the remainder of the chemical composition of the hot-stamping formed body may be Fe and impurities.
  • Elements which are unavoidably mixed from a steel raw material or scrap and/or during the manufacture of steel and are allowed in a range where the properties of the hot-stamping formed body according to the present embodiment do not deteriorate are exemplary examples of the impurities.
  • the hot-stamping formed body may comprise the following elements as optional elements.
  • the content of the following optional elements obtained in a case where the following optional elements are not contained is 0%.
  • Co is an element that improves strength of the hot-stamping formed body by solid-solution strengthening. In order to reliably obtain the effect, it is preferable that the Co content be set to 0.01% or more. The Co content is more preferably set to 0.05% or more.
  • the Co content is set to 4.00% or less. If necessary, the upper limit of Co content may be set to 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • Ni has an effect of increasing strength of the hot-stamping formed body by dissolving in prior austenite grains during heating before hot stamping.
  • the Ni content is preferably set to 0.01% or more.
  • the Ni content is preferably set to 3.00% or less. If necessary, the upper limit of Ni content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • the Cu has an effect of increasing strength of the hot-stamping formed body by dissolving in prior austenite grains during heating before hot stamping.
  • the Cu content is preferably set to 0.01% or more.
  • the Cu content is more preferably set to 0.05% or more.
  • the Cu content is preferably set to 3.00% or less. If necessary, the upper limit of Cu content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • V 0% to 3.00%
  • V has an effect of forming carbonitride in steel and improves strength of the hot-stamping formed body by precipitation strengthening.
  • the V content is preferably set to 0.01% or more.
  • the V content is more preferably set to 0.05% or more.
  • V content when the V content is more than 3.00%, many coarse carbonitrides are generated in steel. The carbonitrides become sites with local increase in hydrogen concentration, and thereby hydrogen embrittlement resistance of the hot-stamping formed body deteriorates. For this reason, the V content is set to 3.00% or less. If necessary, the upper limit of V content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • the W has an effect of improving strength of the hot-stamping formed body.
  • the W content is preferably set to 0.01% or more.
  • the W content is preferably set to 0.05% or more.
  • the W content is preferably set to 3.00% or less. If necessary, the upper limit of W content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05% or 0.02%.
  • Ca is an element that suppresses generation of carbides that become starting points for fracture, and contributes to improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the Ca content is preferably set to 0.0001% or more.
  • the Ca content is set to 1.0000% or less. If necessary, the upper limit of Ca content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005% or 0.0002%.
  • Mg forms oxides and sulfides in molten steel, suppresses formation of a coarse MnS, disperses a lot of fine oxides, miniaturizes the microstructure. This contributes to improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the Mg content is preferably set to 0.0001% or more.
  • the Mg content is set to 1.0000% or less. If necessary, the upper limit of Mg content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005% or 0.0002%.
  • the REM suppresses generation of coarse oxides that become sites with local increase of hydrogen concentration. This contributes improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the REM content is preferably set to 0.0001% or more.
  • the REM content is set to 1.0000% or less. If necessary, the upper limit of REM content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005% or 0.0002%.
  • REM refers to a total of 17 elements that are composed of Sc, Y and lanthanoid, and the REM content refers to the total content of these elements.
  • the Sb suppresses generation of coarse oxides that become sites with local increase of hydrogen concentration. This contributes improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the Sb content is preferably set to 0.001% or more.
  • the Sb content is set to 1.000% or less. If necessary, the upper limit of Sb content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • the Sn suppresses generation of coarse oxides that become sites with local increase of hydrogen concentration. This contributes improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the Sn content is preferably set to 0.001% or more.
  • the Sn content is set to 1.000% or less. If necessary, the upper limit of Sn content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • the Zr suppresses generation of coarse oxides that become sites with local increase of hydrogen concentration. This contributes improvement of hydrogen embrittlement resistance of the hot-stamping formed body.
  • the Zr content is preferably set to 0.001% or more.
  • the Zr content is set to 1.000% or less. If necessary, the upper limit of Zr content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • the As content is preferably set to 0.001% or more.
  • the As content is set to 0.100% or less. If necessary, the upper limit of As content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005% or 0.002%.
  • the above-mentioned chemical composition of the hot-stamping formed body may be measured by a standard analysis method.
  • the chemical composition may be measured using inductively coupled plasma-atomic emission spectrometry (ICP-AES).
  • ICP-AES inductively coupled plasma-atomic emission spectrometry
  • C and S may be measured using a combustion-infrared absorption method
  • N may be measured using an inert gas fusion-thermal conductivity method
  • O may be measured using an inert gas fusion-nondispersive infrared absorption method.
  • the chemical composition is analyzed after the plating layer or the coating film is removed by mechanical grinding.
  • the area ratio of bainite is more than 10%
  • the maximum value of pole density of the texture is 4.0 or less
  • the deboronization index is 0.05 or more.
  • the surface layer region in the present embodiment refers to a region between the surface of the hot-stamping formed body and 1/25 depth of the sheet thickness (thickness of the hot-stamping formed body) from the surface.
  • the “surface” refers to the interface of the plating layer or the coating film and the base steel sheet, and for convenience, the plating layer or the coating film is excluded from the hot-stamping formed body.
  • the hot-stamping formed body has the plating layer or the coating film on the surface thereof, as described below, for convenience, a region where the Fe concentration is less than 90% by mass in GD-OES measurement, that is, the plating layer or the coating film is excluded from the hot-stamping formed body, the measuring point where the Fe concentration is 90% by mass (the interface of the base steel sheet and the plating layer) is regarded as the surface of the hot-stamping formed body.
  • the plating layer or the coating film is excluded from the hot-stamping formed body, when the thickness of the plating layer or the coating film is very small compared to the sheet thickness (thickness) of the hot-stamping formed body and can be ignored (however, when only the plating layer is formed, the thickness of the plating layer is often very small and can be ignored in most cases), when measuring the sheet thickness (thickness) of the hot-stamping formed body, the sheet thickness (thickness) of the hot-stamping formed body may be regarded as the sheet thickness (thickness) including the plating layer or the coating film.
  • bainite in the surface layer region By generating bainite in the surface layer region, dislocation density of the surface layer region can be decreased. As a result, irruption of hydrogen from the external environment can be suppressed, and hydrogen embrittlement resistance of the hot-stamping formed body can be improved. Furthermore, by generating bainite in the surface layer region, since excessive softening of the surface layer can be suppressed, hydrogen embrittlement resistance can be further improved while maintaining a load bearing of the member. When the area ratio of bainite in the surface layer region is 10% or less, hydrogen embrittlement resistance of the hot-stamping formed body deteriorates. For this reason, the area ratio of bainite is set to more than 10%, preferably 20% or more, 40% or more or 60% or more.
  • the upper limit of the area ratio of bainite is not particularly limited, but may be set to 100%, 90% or 80%.
  • martensite In the microstructure of the surface layer region, except for bainite, martensite of 0% to 90% (0% or more and 90% or less), ferrite and residual austenite of 0% to 65% (0% or more and 65% or less) may be included. Martensite in the present embodiment includes untempered martensite (fresh martensite) and tempered martensite.
  • the area ratio of the microstructure is calculated for the surface layer region (the region from the surface to 1/25 depth of the sheet thickness from the surface) by the following method.
  • a sample is cut out from an arbitrary position away from an end surface of the hot-stamping formed body by a distance of 50 mm or more (a position that avoids an end portion in a case where a sample cannot be collected at this position) so that a sheet thickness cross section parallel to the rolling direction can be observed.
  • the size of the sample depends on a measurement device, but is set to a size that can be observed by about 10 mm in the rolling direction.
  • the cross section of the sample After polishing the cross section of the sample using silicon carbide paper of #600 to #1500, the cross section is mirror-finished using liquid in which diamond powder having a grain size in the range of 1 ⁇ m to 6 ⁇ m is dispersed in a diluted solution of alcohol or the like or pure water.
  • the observation surface is finished by electrolytic polishing.
  • a region which has a length of 50 ⁇ m and is present between the surface of the hot-stamping formed body and 1/25 depth of the sheet thickness from the surface is measured at a measurement interval of 0.1 ⁇ m by an electron backscatter diffraction method, and thus, crystal orientation information is obtained.
  • An EBSD analyzer composed of a Schottky emission scanning electron microscope and an EBSD detector may be used for measurement, for example, an EBSD analyzer composed of JSM-7001F manufactured by JEOL Ltd. and DVC 5-type detector manufactured by TSL Solutions may be used for measurement.
  • the degree of vacuum in the EBSD analyzer may be set to 9.6 ⁇ 10 5 Pa or less, an accelerating voltage may be set to 15 kV, and an irradiation current level may be set to 13.
  • the region where “Grain Average Misorientation” is 0.5° or lower is extracted as ferrite.
  • the area ratio of ferrite is obtained.
  • the remaining region is extracted as martensite, and the area ratio thereof is calculated, thereby the area ratio of martensite is obtained.
  • the rolling direction of the hot-stamping formed body is determined by the following method.
  • a sample is cut out from an arbitrary position away from an end surface of the hot-stamping formed body by a distance of 50 mm or more so that a sheet thickness cross section parallel to a rolling direction can be observed.
  • observations with an optical microscope at 100, 200, 500, and 1000 magnifications are performed respectively.
  • an observation result with an appropriate magnification that the size of the inclusion can be measured is selected.
  • the observation area is width of 500 ⁇ m or more and full of the sheet thickness, and the areas with low brightness are determined to be inclusions. The observation may be performed at multiple fields when observing.
  • the cross-sectional observation of the plane parallel to the plane rotated in 5° increments is performed in the same way as the above method.
  • the average values of the lengths of the long axes of the plurality of inclusions in each cross section are calculated respectively.
  • the cross section in which the obtained average value of the length of the long axes of the inclusions is maximum is specified.
  • a direction parallel to the longitudinal direction of the inclusion in the cross section is determined as the rolling direction.
  • the maximum value of pole density of the texture in the surface layer region is more than 4.0, hydrogen embrittlement resistance of the hot-stamping formed body deteriorates.
  • the maximum value of pole density of the texture in the surface layer region is set to 4.0 or less, preferably 3.5 or less, 3.0 or less or 2.5 or less.
  • the lower limit of the pole density of the texture in the surface layer region is not particularly limited, but may be set to 1.0 or 1.2.
  • the texture in the surface layer region is obtained by the following method.
  • a sample is cut out from an arbitrary position away from an end surface of the hot-stamping formed body by a distance of 50 mm or more (a position that avoids an end portion in a case where the sample cannot be collected at this position) so that a sheet thickness cross section parallel to a rolling direction can be observed.
  • the size of the sample depends on a measurement device, but is set to a size that can be observed by about 10 mm in the rolling direction.
  • the cross section of the sample After polishing the cross section of the sample using silicon carbide paper of #600 to #1500, the cross section of the sample is mirror-finished using liquid in which diamond powder having a grain size in the range of 1 ⁇ m to 6 ⁇ m is dispersed in a diluted solution of alcohol or the like or pure water.
  • the observation surface is finished by electrolytic polishing.
  • a region which has a length of 1000 ⁇ m and is present between the surface and 1/25 depth of the sheet thickness from the surface is measured at a measurement interval of 5.0 ⁇ m by an electron backscatter diffraction method, and thus, crystal orientation information is obtained.
  • An EBSD analyzer composed of a Schottky emission scanning electron microscope and an EBSD detector may be used for measurement, for example, an EBSD analyzer composed of JSM-7001F manufactured by JEOL Ltd. and DVC 5-type detector manufactured by TSL Solutions may be used for measurement.
  • the degree of vacuum in the EBSD analyzer may be set to 9.6 ⁇ 10 5 Pa or less, an accelerating voltage may be set to 15 kV, and an irradiation current level may be set to 13.
  • the deboronization index is an index that quantitatively represents the amount of decrease of the B concentration in the surface layer region. By decreasing the B concentration in the surface layer region, deformability of prior austenite grain is improved by reducing strength of prior austenite before transformation, and the generation of grains having random orientation is facilitated in the surface layer region.
  • the deboronization index in the surface layer region is less than 0.05, grains having a desired texture cannot be obtained in the surface layer region. For this reason, the deboronization index is set to 0.05 or more, preferably 0.20 or more, 0.30 or more or 0.35 or more.
  • the upper limit of the deboronization index is not particularly limited, but may be set to 1.00, 0.80 or 0.60.
  • the deboronization index in the surface layer region is obtained by the following method.
  • An element concentration distribution in the sheet thickness direction in the hot-stamping formed body is measured using glow discharge optical emission spectrometry (GD-OES: Manufactured by Horiba, Ltd., Marcus type high-frequency glow discharge optical emission spectrometer, GD-PROFILER-HR).
  • the measurement conditions are an analysis diameter of 4 mm ⁇ , a sputtering rate of 4 ⁇ m/min, an argon pressure of 600 Pa, an RF output of 35 W, and a measurement interval of 0.02 ⁇ m or less. All elements that are comprised in the hot-stamping formed body are measured.
  • the “surface” refers to the interface of the plating layer and the base steel sheet.
  • GD-OES measurement is performed after removing a part or all of the plating layer or the coating film by mechanical polishing or chemical polishing such that measurement to 200 ⁇ m depth from the surface of the base steel sheet (the interface of the plating layer and the base steel sheet) can be performed.
  • a measuring point where the Fe concentration becomes 90 mass % is regarded as the surface of the hot-stamping formed body.
  • the hot-stamping formed body may be referred to as a base steel sheet.
  • B concentrations from the surface of the hot-stamping formed body to at least 100 ⁇ m depth from the surface are measured.
  • the measurement in the depth direction of the B concentration is finished at the position of 100 ⁇ m depth from the surface.
  • the measurement of the B concentration in the depth direction is continued. Then, each time a new B concentration measurement value is obtained in the depth direction, the average value of the B concentration in the region between the deepest part and 20 ⁇ m from the deepest part to the surface side is calculated.
  • the absolute value of the difference between the average value of the B concentration in the region between the deepest part and 20 ⁇ m from the deepest part to the surface side and the maximum value of the measured value of the B concentration in the region between the deepest part and 20 ⁇ m from the deepest part to the surface side is 0.0006 mass % or less
  • the absolute value of the difference between the average value of the B concentration in the region between the deepest part and 20 ⁇ m from the deepest part to the surface side and the minimum value of the measured value of the B concentration in the region between the deepest part and 20 ⁇ m from the deepest part to the surface side is 0.0006 mass % or less
  • the measurement of the B concentration in the depth direction is finished at the position of 150 ⁇ m depth from the surface.
  • the measurement of the B concentration in the depth direction is finished when the measurement of the B concentration at the position of 200 ⁇ m depth from the surface is completed. Then, at the time when the measurement of the B concentration in the depth direction is finished, the average value of the B concentration in the region between the deepest part (the deepest position where the B concentration used for calculating the deboronization index was obtained) and the position of 20 ⁇ m from the deepest part to the surface side is used for the below calculation of the deboronization index (hereinafter, the average value of the B concentration in the region will be referred to as the average B concentration at the deepest part of 20 ⁇ m).
  • the shallowest depth position that satisfies the ending condition for the B concentration measurement in the depth direction is searched for, and in a case where the depth position is found, the deboronization index may be calculated without using the measurement results of the B concentration at the position deeper than the shallowest depth position.
  • the B concentration may be measured from the surface to 200 ⁇ m depth from the surface, in this case, in a case where a shallowest depth position that satisfies the ending condition for B concentration measurement in the depth direction exists in a region of 100 ⁇ m or more depth from the surface, the measurement is regarded as ending at the depth position, and the deboronization index is calculated.
  • the amount of decrease in the B concentration per unit depth (the value obtained by subtracting the B concentration at each measurement point from the average B concentration at the deepest part of 20 ⁇ m) is calculated, the integrated value of the product of the unit depth and the amount of decrease in the B concentration is calculated and determined as the area of the B-depletion region (area of region A in FIG. 1 ).
  • the value obtained by subtracting the B concentration at each measurement point from the average B concentration at the deepest part of 20 ⁇ m is negative, it is integrated as 0 (due to the B removal phenomenon near the surface, the B concentration at each measurement point is in most cases lower than the average B concentration at the deepest part of 20 ⁇ m, and the integrated value becomes positive).
  • the product of the average B concentration at the deepest part of 20 ⁇ m and the length of 200 ⁇ m is calculated as a reference area (area of rectangular region B in FIG. 1 ).
  • the value obtained by dividing a B-depletion area (area of region A) by the reference area (area of region B) is defined as the deboronization index (area of region A/area of region B).
  • the reference area (area of region B) is calculated by assuming that the length by which the average B concentration at the deepest part of 20 ⁇ m is multiplied is 200 ⁇ m.
  • the microstructure of a region other than the surface layer region is not particularly limited as long as a desired strength and hydrogen embrittlement resistance can be obtained, for example, in area %, the microstructure may consist of martensite and bainite of 90% to 100% (90% or more and 100% or less) in total, and ferrite and residual austenite of 0% to 10% (0% or more and 10% or less) in total.
  • the microstructure of a region other than the surface layer region is measured by the following method. Note that the microstructure in the region other than the surface layer region is measured from 1 ⁇ 8 depth of the sheet thickness from the surface to 3 ⁇ 8 depth of the sheet thickness from the surface. The reason is that the microstructure in this region shows a typical microstructure of the hot-stamping formed body.
  • a sample is cut out from an arbitrary position away from an end surface of the hot-stamping formed body by a distance of 50 mm or more (a position that avoids an end portion in a case where the sample cannot be collected at this position) so that a sheet thickness cross section parallel to the rolling direction can be observed.
  • the size of the sample depends on a measurement device, but is set to a size that can be observed by about 10 mm in the rolling direction.
  • the cross section of the sample After polishing the cross section of the sample using silicon carbide paper of #600 to #1500, the cross section is mirror-finished using liquid in which diamond powder having a grain size in the range of 1 ⁇ m to 6 ⁇ m is dispersed in a diluted solution of alcohol or the like or pure water.
  • the observation surface is finished by electrolytic polishing.
  • a region which has a length of 50 ⁇ m and is present between 1 ⁇ 8 depth of the sheet thickness from the surface and 3 ⁇ 8 depth of the sheet thickness from the surface is measured at a measurement interval of 0.1 ⁇ m by an electron backscatter diffraction method, and thus, crystal orientation information is obtained.
  • An EBSD analyzer composed of a Schottky emission scanning electron microscope and an EBSD detector may be used for measurement, for example, an EBSD analyzer composed of JSM-7001F manufactured by JEOLLtd. and DVC 5-type detector manufactured by TSL Solutions may be used for measurement.
  • the degree of vacuum in the EBSD analyzer may be set to 9.6 ⁇ 10 Pa or less, an accelerating voltage may be set to 15 kV, and an irradiation current level may be set to 13.
  • the area ratio of the remaining region (the region where “Grain Average Misorientation” is more than 0.5°) is calculated, and this area ratio is determined as the total area ratio of martensite and bainite.
  • the hot-stamping formed body may have a plating layer on the surface.
  • the plating layer By having the plating layer on the surface, corrosion resistance can be improved after hot stamping.
  • the plating layer include an aluminum plating layer, aluminum-galvanized layer, aluminum-silicon plating layer, hot-dip galvanized layer, electrogalvanized layer, galvannealed layer, zinc-nickel plating layer, aluminum-magnesium-zinc-based plating layer.
  • the steel sheet for hot stamping has the above-described chemical composition.
  • the microstructure of the steel sheet for hot stamping is not particularly limited as long as a desired strength and hydrogen embrittlement resistance are obtained after hot stamping, for example, in area %, the microstructure may consist of ferrite: 5% to 90%, bainite and martensite: 0% to 100%, pearlite: 10% to 95%, and residual austenite: 0% to 5%.
  • iron carbides, alloy carbides, intermetallic compounds, and inclusions may be included,
  • the steel sheet for hot stamping may have a plating layer on the surface.
  • the plating layer By having the plating layer on the surface, corrosion resistance can be improved after hot stamping.
  • the plating layer include an aluminum plating layer, aluminum-galvanized layer, aluminum-silicon plating layer, hot-dip galvanized layer, electrogalvanized layer, galvannealed layer, zinc-nickel plating layer, aluminum-magnesium-zinc-based plating layer.
  • a manufacturing method to obtain the steel sheet for hot stamping for obtaining the hot-stamping formed body according to the present embodiment will be described.
  • it is particularly effective to control the annealing condition in the manufacturing method of the steel sheet for hot stamping.
  • the casting method of molten steel the conditions of heating before hot rolling, rough rolling, finish rolling, coiling, and cold rolling are not particularly limited, and may be standard conditions.
  • a softening heat treatment may be performed on the coil after coiling.
  • the softening heat treatment method is not particularly limited, and standard conditions may be adopted.
  • annealing After cold rolling, it is preferable to perform annealing to heat for 15 seconds or more in an oxidizing atmosphere. Generally, it is preferable to perform annealing in a reducing atmosphere in order to suppress formation of scale.
  • formation of scale on the steel sheet surface is promoted by performing annealing in the oxidizing atmosphere.
  • the scale formed on the steel sheet surface becomes an oxidation source, and C and B in the surface layer region are oxidized. Since oxidized C and B leave the surface layer of the steel sheet, the amounts of C and B are reduced in the surface layer region.
  • the strength of the prior austenite grains decreases and they become easily deformed, and grains having random orientation are likely to be generated. Thereby, grains having a desired texture can be generated in the surface layer region.
  • the heating temperature during annealing may be set to a temperature range of 730° C. to 900° C., and by staying in this heating temperature range for 15 seconds or more, formation of scale can be promoted while suppressing peeling of scale.
  • the time for annealing is preferably 100 seconds or more, more preferably 200 seconds or more, and even more preferably 300 seconds or more.
  • annealing for more than 3600 seconds is not preferable since the prior austenite grain sizes become coarser, the grain boundary diffusion rate of B decreases, removal of B does not proceed, and the deboronization index cannot be 0.05 or more. For this reason, the annealing time is preferably 3600 seconds or less.
  • the annealing step may be performed again in an oxidizing atmosphere or a non-oxidizing atmosphere unless a treatment for removing oxide scale (for example, pickling) is performed.
  • the oxidizing atmosphere may be any heating atmosphere that generates oxide scale on the surface layer of the steel sheet, and may be a standard condition.
  • a gas combustion atmosphere it is preferable to create an atmosphere in which the mixture ratio of air and fuel (air-fuel ratio) is controlled to 1.00 or more, and more preferably controlled to 1.10 or more. It is preferable to generate an oxide scale of 15 ⁇ m or more on the steel sheet surface by annealing in the oxidizing atmosphere.
  • oxide scale on the steel sheet surface remain in subsequent processes. That is, it is preferable to perform hot stamping, which will be described later, with the oxide scale remaining. Oxide scale is removed by shot blasting after hot stamping.
  • oxide scale remains at the interface between the base steel sheet and the plating layer.
  • the oxide scale disappears after hot stamping due to an alloying reaction during heating before hot stamping.
  • a hot-stamping formed body according to the present embodiment is obtained by hot stamping the steel sheet for hot stamping manufactured by the above-described method.
  • the hot stamping conditions are not particularly limited. However, for example, it is preferable to heat the steel sheet for hot stamping to a temperature range of 800° C. to 1000° C. and hold in this temperature range for 60 to 1200 seconds.
  • the heating temperature is lower than 800° C., austenitization becomes insufficient, and hydrogen embrittlement resistance may deteriorate or a desired strength may not be obtained in the hot-stamping formed body.
  • the heating temperature is higher than 1000° C., the grains of prior austenite grow excessively, and hydrogen embrittlement resistance may deteriorate or a desired strength may not be obtained in the hot-stamping formed body.
  • the holding time is shorter than 60 seconds, austenitization becomes insufficient, and hydrogen embrittlement resistance may deteriorate or a desired strength may not be obtained in the hot-stamping formed body.
  • the holding time is longer than 1200 seconds, grains of prior austenite grow excessively, and hydrogen embrittlement resistance may deteriorate or a desired strength may not be obtained in the hot-stamping formed body.
  • a heating atmosphere is not particularly limited, and may be standard conditions, for example, such as the atmosphere, a gas combustion atmosphere with a controlled ratio of air and fuel, or a nitrogen atmosphere, and the dew point of these gases may be controlled.
  • hot stamping After holding in the temperature range, hot stamping is performed. After hot stamping, cooling may be performed to a temperature range of 250° C. or lower at an average cooling rate of 20° C./s or faster.
  • heating methods before hot stamping include heating using an electric furnace and gas furnace, flame heating, electrical heating, high-frequency heating, and induction heating.
  • the hot-stamping formed body according to the present embodiment is obtained.
  • a tempering treatment at 130° C. to 600° C. may be performed for softening after hot stamping, or a baking hardening treatment after painting may be performed.
  • a portion of the hot-stamping formed body may be tempered by laser irradiation or the like to provide a partially softened region.
  • the obtained steel sheets for hot stamping were heated to a temperature range shown in Tables 3A to 3C in a furnace continuously supplied with nitrogen gas (hot stamp heating), held in the temperature range, subjected to hot stamping, and then cooled to 250° C. or lower at an average cooling rate of 20° C./s or faster.
  • hot stamp heating nitrogen gas
  • the hot-stamping formed bodies shown in Tables 4A to 4 C were obtained.
  • the underlines in the tables indicate that it is outside the scope of the present invention, falls outside the preferable manufacturing conditions, or the characteristic value is not preferable.
  • the microstructure of the surface layer region of the hot-stamping formed bodies according to the present invention examples included, in area %, martensite of 90% or more, and ferrite and residual austenite of 65% or less in total.
  • the microstructure in the region other than the surface layer region of the hot-stamping formed body according to the present invention examples consisted of, in area %, martensite and bainite of 90% or more in total, and ferrite and residual austenite of 10% or less in total.
  • Measurements of the microstructure, deboronization index, and pole density of the texture of the hot-stamping formed body were performed by the above-described methods.
  • the mechanical properties of the hot-stamping formed body were evaluated by the following methods.
  • the tensile (maximum) strength TS of the hot-stamping formed body was obtained, in accordance with JIS Z 2241:2011, by preparing a No. 5 test piece from an arbitrary position of the hot-stamping formed body and conducting a tensile test.
  • the crosshead speed was set to 1 mm/min.
  • the tensile strength TS was 2200 MPa or more, it was determined as having high strength and successful, and when the tensile strength TS was less than 2200 MPa, it was determined as not having high strength and not successful.
  • Hydrogen embrittlement resistance of the hot-stamping formed body was evaluated by the following method.
  • a test piece with a length of 68 mm and a width of 6 mm was taken from an arbitrary position of the hot-stamping formed body, and the edges of the test piece were polished using silicon carbide paper of #200 to #1500, and then mirror finishing was performed using a liquid in which diamond powder with a particle size of 1 ⁇ m to 6 ⁇ m was dispersed in a diluent such as alcohol and pure water. Furthermore, the corners of the test piece were chamfered using silicon carbide paper of #200 to #1500.
  • a stress of 800 MPa or more was applied to the test piece, the test piece was immersed in a liter of hydrochloric acid adjusted to pH 4 at room temperature for 48 hours, and the presence or absence of cracks was determined.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
  • Road Signs Or Road Markings (AREA)
  • Heat Treatment Of Articles (AREA)
US18/834,189 2022-04-14 2023-03-02 Hot-stamping formed body Pending US20250108424A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2022067023 2022-04-14
JP2022-067023 2022-04-14
PCT/JP2023/007780 WO2023199635A1 (ja) 2022-04-14 2023-03-02 ホットスタンプ成形体

Publications (1)

Publication Number Publication Date
US20250108424A1 true US20250108424A1 (en) 2025-04-03

Family

ID=88329336

Family Applications (1)

Application Number Title Priority Date Filing Date
US18/834,189 Pending US20250108424A1 (en) 2022-04-14 2023-03-02 Hot-stamping formed body

Country Status (7)

Country Link
US (1) US20250108424A1 (https=)
EP (1) EP4509240A4 (https=)
JP (1) JP7828012B2 (https=)
KR (1) KR102928025B1 (https=)
CN (1) CN118647743A (https=)
MX (1) MX2024009297A (https=)
WO (1) WO2023199635A1 (https=)

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11180837B2 (en) * 2018-03-29 2021-11-23 Nippos Steel Corporation Hot stamped article
US12043883B2 (en) 2018-10-18 2024-07-23 Jfe Steel Corporation High-yield-ratio high-strength electrogalvanized steel sheet and method for manufacturing the same
CN113597474B (zh) * 2019-03-20 2023-04-28 日本制铁株式会社 热冲压成形体
TW202039881A (zh) 2019-04-17 2020-11-01 日商日本製鐵股份有限公司 鋼板及其製造方法、以及成形體
EP4151758A4 (en) 2020-05-13 2023-10-18 Nippon Steel Corporation HOT STAMPED STEEL SHEET AND HOT STAMPED MOLDING
WO2021230149A1 (ja) 2020-05-13 2021-11-18 日本製鉄株式会社 ホットスタンプ成形体
JP7622982B2 (ja) 2020-10-19 2025-01-28 株式会社カレントダイナミックス 推進装置

Also Published As

Publication number Publication date
JPWO2023199635A1 (https=) 2023-10-19
WO2023199635A1 (ja) 2023-10-19
EP4509240A1 (en) 2025-02-19
KR20240132338A (ko) 2024-09-03
JP7828012B2 (ja) 2026-03-11
CN118647743A (zh) 2024-09-13
EP4509240A4 (en) 2025-10-15
KR102928025B1 (ko) 2026-02-19
MX2024009297A (es) 2024-08-06

Similar Documents

Publication Publication Date Title
KR20220129060A (ko) 핫 스탬프용 강판 및 핫 스탬프 성형체
CN115003841A (zh) 钢板、部件及它们的制造方法
WO2020203979A1 (ja) 被覆鋼部材、被覆鋼板およびそれらの製造方法
CN114945690B (zh) 钢板及其制造方法
CN117940597A (zh) 热轧钢板
JP7549277B2 (ja) ホットスタンプ用鋼板およびホットスタンプ成形体
KR20220091572A (ko) 핫 스탬프 성형체
CN115398035A (zh) 热压用钢板
KR20210151935A (ko) 핫 스탬프 성형체
CN114829651B (zh) 热压成形体
US20250108424A1 (en) Hot-stamping formed body
WO2023132344A1 (ja) 鋼板およびその製造方法
KR102928024B1 (ko) 핫 스탬프 성형체
WO2023032225A1 (ja) 熱延鋼板
JP7708344B1 (ja) 亜鉛めっき鋼板および部材、ならびに、それらの製造方法
US12358036B2 (en) Hot-stamping formed body
JP7063414B2 (ja) 鋼板
CN113874537B (zh) 热压用钢板
WO2025263579A1 (ja) 鋼部材及び鋼板
EP4534715A1 (en) Hot-stamp formed article
WO2023189183A1 (ja) ホットスタンプ成形体
WO2020241763A1 (ja) ホットスタンプ成形体

Legal Events

Date Code Title Description
AS Assignment

Owner name: NIPPON STEEL CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FUJINAKA, SHINGO;HAGA, JUN;TODA, YURI;REEL/FRAME:068145/0084

Effective date: 20240701

STPP Information on status: patent application and granting procedure in general

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION