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EP4560039A1 - Tôle d'acier à haute résistance et son procédé de production, et élément et son procédé de production - Google Patents

Tôle d'acier à haute résistance et son procédé de production, et élément et son procédé de production Download PDF

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Publication number
EP4560039A1
EP4560039A1 EP23859902.1A EP23859902A EP4560039A1 EP 4560039 A1 EP4560039 A1 EP 4560039A1 EP 23859902 A EP23859902 A EP 23859902A EP 4560039 A1 EP4560039 A1 EP 4560039A1
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EP
European Patent Office
Prior art keywords
steel sheet
amount
rolled steel
steel
cold rolled
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
EP23859902.1A
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German (de)
English (en)
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EP4560039A4 (fr
Inventor
Lingling Yang
Yuki Toji
Yuji Tanaka
Yasuhiro Nagaoka
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.)
JFE Steel Corp
Original Assignee
JFE Steel Corp
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Filing date
Publication date
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Publication of EP4560039A1 publication Critical patent/EP4560039A1/fr
Publication of EP4560039A4 publication Critical patent/EP4560039A4/fr
Pending legal-status Critical Current

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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
    • 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
    • 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
    • C21D8/0273—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
    • C22C38/002—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
    • 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
    • C22C38/08—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
    • C22C38/34—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
    • C22C38/38—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
    • 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
    • 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
    • C21D2211/001—Austenite
    • 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 invention relates to a high strength steel sheet having a yield strength (YS) of not less than 800 MPa and a method of producing the same as well as a member and a method of producing the same.
  • Patent Literatures 1 to 3 each disclose a high strength steel sheet having a yield strength of not less than 800 MPa.
  • a high strength steel sheet having a yield strength of not less than 800 MPa usually improves processability due to a transformation induced plasticity (TRIP) effect of retained austenite.
  • TRIP transformation induced plasticity
  • retained austenite is transformed into martensite due to the TRIP effect during processing to enhance the strength and increase the strain dispersibility, thereby improving the ductility.
  • fracture resistance when such a steel sheet is formed into automotive parts, retained austenite is transformed into hard martensite, and this transformation sometimes degrades the fracture resistance at a collision (hereinafter, also simply referred to as "fracture resistance").
  • a steel sheet used as automotive parts is also required to be excellent in terms of proof stress at a collision (hereinafter, referred to as "collision proof stress").
  • the present invention aims at providing a high strength steel sheet having a yield strength of not less than 800 MPa and also having excellent collision proof stress and fracture resistance.
  • the present invention provides the following [1] to [10].
  • a high strength steel sheet having a yield strength of not less than 800 MPa and also having excellent collision proof stress and fracture resistance.
  • a high strength steel sheet of the present embodiment (hereinafter also referred to as the "present high strength steel sheet”) includes a steel sheet, and may further include a plating layer on a surface of the steel sheet as described later.
  • the steel sheet included in the present high strength steel sheet has chemical composition and microstructure which are to be described later, and satisfies an amount of diffusible hydrogen in steel to be described later.
  • high strength means having a yield strength (YS) of not less than 800 MPa.
  • the present high strength steel sheet has a yield strength of not less than 800 MPa and also has excellent collision proof stress and fracture resistance. Therefore, since the strength against a collision is sufficient, the steel sheet is preferably used as parts of transportation machines such as automobiles.
  • a general processing method such as press working can be used without limitation.
  • a general welding method such as spot welding or arc welding can be used without limitation.
  • the thickness of the steel sheet is not particularly limited and is, for example, not less than 0.5 mm and not more than 3.0 mm.
  • the amount of C is not less than 0.150%, preferably not less than 0.180%, and more preferably not less than 0.200%.
  • the amount of C is not more than 0.500%, preferably not more than 0.460%, and more preferably not more than 0.400%.
  • Si suppresses generation of carbides during a heat treatment and increases the yield strength.
  • an amount of Si is not less than 0.01%, preferably not less than 0.50%, and more preferably not less than 0.80%.
  • the amount of Si is not more than 3.00%, preferably not more than 2.60%, and more preferably not more than 2.40%.
  • Mn influences the area fraction of tempered martensite and bainite. From the viewpoint of obtaining a good collision proof stress and the yield strength of not less than 800 MPa, an amount of Mn is not less than 1.50%, preferably not less than 1.90%, and more preferably not less than 2.30%.
  • the amount of Mn is not more than 4.00%, preferably not more than 3.50%, and more preferably not more than 3.30%.
  • an amount of P is not more than 0.100%, preferably not more than 0.030%, and more preferably not more than 0.010%.
  • the amount of P is preferably 0.001%, more preferably 0.002%, and further preferably 0.003%.
  • an amount of S is not more than 0.0200%, preferably not more than 0.0100%, and more preferably not more than 0.0020%.
  • the lower limit of the amount of S is not particularly limited and is preferably 0.0001%, more preferably 0.0002%, and further preferably 0.0003% due to the production engineering restrictions.
  • Al acts as a deoxidizer.
  • an amount of Al is not more than 0.100%, preferably not more than 0.080%, and more preferably not more than 0.060%.
  • the lower limit of the amount of Al is not particularly limited and is, for example, 0.010% and preferably 0.020% because generation of carbides during the heat treatment is suppressed and generation of retained austenite is promoted.
  • N combines with Ti to form TiN.
  • an amount of N is not more than 0.0100%, preferably not more than 0.0080%, and more preferably not more than 0.0060%.
  • the lower limit of the amount of N is not particularly limited and is preferably 0.0001%, more preferably 0.0003%, and further preferably 0.0005% due to the production engineering restrictions.
  • an amount of O is not more than 0.0100%, preferably not more than 0.0050%, and more preferably not more than 0.0020%.
  • the present chemical composition may further include at least one element selected from the group consisting of elements described below, in percentage by mass.
  • B is preferably added because it is an element capable of improving the hardenability of the steel sheet by being segregated in an austenite grain boundary and increases the yield strength of the steel sheet.
  • an amount of B is preferably not more than 0.0100%, preferably not more than 0.0050%, more preferably not more than 0.0040%, and particularly preferably not more than 0.0030%.
  • the lower limit of the amount of B is not particularly limited and is, for example, 0.0005% and preferably 0.0010% from the viewpoint of obtaining the effect of addition of B.
  • Ti is preferably added because it forms fine carbides, nitrides or carbonitrides during hot rolling or a heat treatment to thereby increase the yield strength of the steel sheet.
  • the amount of Ti is preferably not more than 0.200%, more preferably not more than 0.100%, and further preferably not more than 0.050%.
  • the lower limit of the amount of Ti is not particularly limited and is, for example, 0.005%, and preferably 0.010% from the viewpoint of obtaining the effect of addition of Ti.
  • Nb, V and W are preferably added because each of them forms fine carbides, nitrides or carbonitrides during hot rolling or a heat treatment to thereby increase the yield strength of the steel sheet.
  • an amount of Nb is preferably not more than 0.200%, more preferably not more than 0.100%, and further preferably not more than 0.050%.
  • the lower limit thereof is not particularly limited and is, for example, 0.005% and is preferably 0.010% from the viewpoint of obtaining the effect of addition of Nb.
  • An amount of V is preferably not more than 0.200%, more preferably not more than 0.100%, and further preferably not more than 0.050%.
  • the lower limit thereof is not particularly limited and is, for example, 0.005% and preferably 0.010% from the viewpoint of obtaining the effect of addition of V.
  • An amount of W is preferably not more than 0.100%, more preferably not more than 0.080%, and further preferably not more than 0.050%.
  • the lower limit thereof is not particularly limited and is, for example, 0.010% and preferably 0.020% from the viewpoint of obtaining the effect of addition of W.
  • Mo and Cr are preferably added because they increase the hardenability of the steel sheet to thereby increase the yield strength of the steel sheet. Meanwhile, when an amount of each of these elements is excessively large, hard martensite is excessively generated, whereby the fracture resistance at a collision deteriorates.
  • an amount of Mo is preferably not more than 1.000%, more preferably not more than 0.800%, and further preferably not more than 0.500%.
  • the lower limit thereof is not particularly limited and is, for example, 0.010% and preferably 0.020% from the viewpoint of obtaining the effect of addition of Mo.
  • An amount of Cr is preferably not more than 1.000%, more preferably not more than 0.800%, and further preferably not more than 0.500%.
  • the lower limit thereof is not particularly limited and is, for example, 0.010% and preferably 0.020% from the viewpoint of obtaining the effect of addition of Cr.
  • Sb and Sn are preferably added because each of them suppresses decarburization of the surfaces of the steel sheet to thereby increase the yield strength of the steel sheet. Meanwhile, when an amount of each of these elements is excessively large, the steel is embrittled, whereby the fracture resistance at a collision deteriorates.
  • an amount of Sb is preferably not more than 0.200%, more preferably not more than 0.080%, and further preferably not more than 0.040%.
  • the lower limit thereof is not particularly limited and is, for example, 0.001% and preferably 0.002% from the viewpoint of obtaining the effect of addition of Sb.
  • An amount of Sn is preferably not more than 0.200%, more preferably not more than 0.080%, and further preferably not more than 0.040%.
  • the lower limit thereof is not particularly limited and is, for example, 0.001% and preferably 0.002% from the viewpoint of obtaining the effect of addition of Sn.
  • Zr and Te are preferably added because each of them spheroidizes the shapes of nitrides and sulfides to thereby improve the fracture resistance at a collision. Meanwhile, when an amount of each of these elements is excessively large, they increase coarse precipitates remaining in an undissolved state during steel slab heating, whereby the fracture resistance at a collision deteriorates.
  • an amount of Zr is preferably not more than 0.1000%, more preferably not more than 0.0800%, and further preferably not more than 0.0500%.
  • the lower limit thereof is not particularly limited and is, for example, 0.0050% and preferably 0.0100% from the viewpoint of obtaining the effect of addition of Zr.
  • An amount of Te is preferably not more than 0.100%, more preferably not more than 0.080%, and further preferably not more than 0.050%.
  • the lower limit thereof is not particularly limited and is, for example, 0.005% and preferably 0.010% from the viewpoint of obtaining the effect of addition of Te.
  • Cu is preferably added because it increases the hardenability of the steel sheet to thereby increase the yield strength of the steel sheet. Meanwhile, when an amount of Cu is excessively large, the fracture resistance at a collision deteriorates due to an increase of Cu inclusions.
  • an amount of Cu is preferably not more than 1.000%, more preferably not more than 0.800%, and further preferably not more than 0.500%.
  • the lower limit thereof is not particularly limited and is, for example, 0.010% and preferably 0.020% from the viewpoint of obtaining the effect of addition of Cu.
  • Ni is preferably added because it increases the hardenability of the steel sheet to thereby increase the yield strength of the steel sheet. Meanwhile, when an amount of Ni is excessively large, the fracture resistance at a collision deteriorates due to an increase of hard martensite.
  • an amount of Ni is preferably not more than 1.000%, more preferably not more than 0.800%, and further preferably not more than 0.500%.
  • the lower limit thereof is not particularly limited and is, for example, 0.010% and preferably 0.020% from the viewpoint of obtaining the effect of addition of Ni.
  • Ca, Mg and REM are preferably added because they spheroidize the shapes of precipitates such as sulfides and oxides to thereby increase the fracture resistance at a collision. Meanwhile, when an amount of each of these elements is excessively large, coarse sulfides become starting points of cracking at a collision, whereby the fracture resistance at a collision deteriorates.
  • an amount of Ca is preferably not more than 0.0100%, more preferably not more than 0.0050%, and further preferably not more than 0.0040%.
  • the lower limit thereof is not particularly limited and is, for example, 0.0005% and preferably 0.0010% from the viewpoint of obtaining the effect of addition of Ca.
  • An amount of Mg is preferably not more than 0.0100%, more preferably not more than 0.0050%, and further preferably not more than 0.0040%.
  • the lower limit thereof is not particularly limited and is, for example, 0.0005% and preferably 0.0010% from the viewpoint of obtaining the effect of addition of Mg.
  • An amount of REM is preferably not more than 0.0100%, more preferably not more than 0.0040%, and further preferably not more than 0.0030%.
  • the lower limit thereof is not particularly limited and is, for example, 0.0005% and preferably 0.0010% from the viewpoint of obtaining the effect of addition of REM.
  • Co, Ta, Hf and Bi are preferably added because they spheroidize the shapes of precipitates to thereby increase the fracture resistance at a collision. Meanwhile, when an amount of each of these elements is excessively large, coarse precipitates become starting points of cracking at a collision, and the fracture resistance at a collision deteriorates.
  • an amount of Co is preferably not more than 0.010%, more preferably not more than 0.008%, and further preferably not more than 0.007%.
  • the lower limit thereof is not particularly limited and is, for example, 0.001% and preferably 0.002% from the viewpoint of obtaining the effect of addition of Co.
  • An amount of Ta is preferably not more than 0.10%, more preferably not more than 0.08%, and further preferably not more than 0.07%.
  • the lower limit thereof is not particularly limited and is, for example, 0.01% and preferably 0.02% from the viewpoint of obtaining the effect of addition of Ta.
  • An amount of Hf is preferably not more than 0.10%, more preferably not more than 0.08%, and further preferably not more than 0.07%.
  • the lower limit thereof is not particularly limited and is, for example, 0.01% and preferably 0.02% from the viewpoint of obtaining the effect of addition of Hf.
  • An amount of Bi is preferably not more than 0.200%, more preferably not more than 0.100%, and further preferably not more than 0.080%.
  • the lower limit thereof is not particularly limited and is, for example, 0.001% and preferably 0.005% from the viewpoint of obtaining the effect of addition of REM.
  • the balance in the present chemical composition consists of Fe and inevitable impurities.
  • present microstructure a microstructure of the steel sheet included in the present high strength steel sheet.
  • the area fraction is an area fraction with respect to the entire microstructure.
  • the area fraction of each structure is determined by a method described in Examples below.
  • the total area fraction of tempered martensite and bainite is not less than 55%, preferably not less than 58%, and more preferably not less than 60%.
  • this total area fraction is not more than 95%, preferably not more than 92%, and more preferably not more than 88%.
  • the average grain size of retained austenite is not more than 5.0 ⁇ m, preferably not more than 4.0 ⁇ m, more preferably not more than 3.0 ⁇ m, further preferably not more than 2.0 ⁇ m, and particularly preferably not more than 1.0 ⁇ m.
  • a structure having a low carbon concentration has high toughness and high fracture resistance.
  • the structure having a low carbon concentration includes at least part of retained austenite.
  • the retained austenite having a low carbon concentration is liable to undergo martensitic transformation.
  • the retained austenite having a low carbon concentration undergoes martensitic transformation, so that strain at a collision is largely dispersed, and occurrence of cracks at a collision can be suppressed. In other words, the fracture resistance is improved.
  • the area fraction of a structure S 1 having a carbon concentration of more than 0.1 mass% and not more than 0.3 mass% is not less than 50.0%, preferably not less than 55.0%, and more preferably not less than 60.0%.
  • the upper limit of the area fraction of the structure S 1 is not particularly limited and is, for instance, 90.0% and preferably 95.0%.
  • the area fraction of the structure S 2 having a carbon concentration of not less than 0.5 mass% is not more than 10.0%, preferably not more than 8.0%, and more preferably not more than 7.0%.
  • the present microstructure may include a structure (remaining structure) other than tempered martensite, bainite and retained austenite.
  • Examples of the remaining structure include known structures such as fresh martensite; pearlite; ferrite; iron-based carbonitride; alloyed carbonitride; and inclusions such as MnS and Al 2 O 3 .
  • the area fraction of the remaining structure is preferably not more than 10%, more preferably not more than 8%, and further preferably not more than 5%. When the area fraction of the remaining structure falls within this range, the effect of the present invention would not be impaired.
  • the amount of diffusible hydrogen in steel is not more than 0.50 mass ppm, preferably not more than 0.30 mass ppm, and more preferably not more than 0.20 mass ppm.
  • the amount of diffusible hydrogen in steel is determined by a method described in Examples below.
  • the present high strength steel sheet may further have a plating layer on a surface of the steel sheet for the purpose of improving corrosion resistance and other properties.
  • Examples of the plating layer include a galvanizing layer, a galvannealing layer and an electrogalvanizing layer.
  • the plating layer is formed by a plating treatment described later.
  • present production method a method of producing a high strength steel sheet of the present embodiment.
  • present production method is a method of producing the present high strength steel sheet described above.
  • a temperature at which the steel slab, the steel sheet or the like is heated or cooled which is described below, means a surface temperature of the steel slab, the steel sheet or the like, unless otherwise specified.
  • a method of producing molten steel which becomes a steel slab (steel material) is not particularly limited, and known methods using a converter, an electric furnace or the like are applicable. It is preferable to obtain a steel slab from molten steel by a continuous casting method. Another method such as an ingot casting blooming method or thin slab continuous casting may be adopted to obtain a steel slab.
  • a steel slab having the present chemical composition described above is hot-rolled.
  • a hot rolled steel sheet is obtained.
  • the steel slab When the hot rolling is performed, the steel slab may be re-heated in a heating furnace and then rolled. When the steel slab maintains a temperature equal to or higher than a predetermined temperature, the steel slab may be directly rolled without being heated.
  • the steel slab is heated to dissolve carbides in the steel slab prior to rough rolling.
  • the temperature at the time of heating the steel slab is preferably not lower than 1100°C and more preferably not lower than 1150°C.
  • the steel slab heating temperature is preferably not higher than 1300°C and more preferably not higher than 1280°C.
  • a finish rolling end temperature is preferably 700 to 1100°C, and more preferably 800 to 1000°C.
  • the hot rolled steel sheet is subjected to cold rolling, whereby a cold rolled steel sheet is obtained.
  • a rolling rate of the cold rolling is preferably not less than 30% and more preferably not less than 35%.
  • the upper limit thereof is not particularly limited and is, for example, not more than 70% and preferably not more than 65%.
  • the cold rolled steel sheet obtained by the cold rolling is subjected to a heat treatment.
  • FIG. 1 is a flowchart diagram showing an example of the heat treatment.
  • the cold rolled steel sheet is heated at a heating temperature T1, cooled to a cooling stop temperature T2, then re-heated to a re-heating temperature T3, and re-cooled without being retained at the re-heating temperature T3.
  • the cold rolled steel sheet is cooled from the re-heating temperature T3 to at least (T3 - 30)°C.
  • the cold rolled steel sheet having undergone the heat treatment corresponds to the steel sheet included in the present high strength steel sheet described above.
  • Heating time t 1 10 s to 500 s>>
  • the cold rolled steel sheet is heated at the heating temperature T1.
  • the heating temperature T1 is too low or when a heating time t 1 (the time for retaining the cold rolled steel sheet at the heating temperature T1) is too short, the steel sheet is heated in a dual phase region of ferrite and austenite.
  • the final microstructure contains ferrite and the total area fraction of tempered martensite and bainite is reduced, it is difficult to ensure good collision proof stress and yield strength.
  • the heating temperature T1 is not lower than 750°C, preferably not lower than 800°C, and more preferably not lower than 850°C.
  • the heating time t 1 is preferably not less than 10 s, preferably not less than 50 s, and more preferably not less than 80 s.
  • the heating temperature T1 is not higher than 950°C, preferably not higher than 930°C, and more preferably not higher than 900°C.
  • the heating time t 1 is not more than 500 s, preferably not more than 300 s, and more preferably not more than 200 s.
  • the cold rolled steel sheet having been heated at the heating temperature T1 is cooled to the cooling stop temperature T2.
  • the cooling stop temperature T2 is not lower than 120°C, preferably not lower than 140°C, and more preferably not lower than 150°C.
  • the cooling stop temperature T2 is lower than 280°C, preferably not higher than 270°C, and more preferably not higher than 260°C.
  • the cold rolled steel sheet having been cooled to the cooling stop temperature T2 is re-heated to the re-heating temperature T3 and is re-cooled without being retained at the re-heating temperature T3.
  • the re-heating temperature T3 is not lower than 280°C, preferably not lower than 290°C, and more preferably not lower than 300°C.
  • the re-heating temperature T3 is not higher than 400°C, preferably not higher than 380°C, and more preferably not higher than 350°C.
  • the cold rolled steel sheet having been re-heated to the re-heating temperature T3 is re-cooled without being retained at the re-heating temperature T3.
  • the cold rolled steel sheet is cooled from the re-heating temperature T3 to at least (T3 - 30)°C.
  • the heat effect index P from the re-heating temperature T3 to (T3 - 30)°C for the cold rolled steel sheet is expressed by the following Formula (1).
  • P T 3 log 5 t + 12
  • t is the cooling time (unit: s) from the re-heating temperature T3 to (T3 - 30) °C.
  • the carbon concentration of each structure constituting the microstructure can be controlled by the heat effect index P.
  • the heat effect index P is not lower than 4000, preferably not lower than 4200, and more preferably not lower than 4400.
  • the heat effect index P is not more than 6000, preferably not more than 5800, and more preferably not more than 5500.
  • the re-cooled cold rolled steel sheet may be subjected to a plating treatment to form a plating layer on the surface thereof.
  • Examples of the plating layer include a galvanizing layer, a galvannealing layer and an electrogalvanizing layer.
  • galvanizing treatment galvannealing treatment, or electrogalvanizing treatment is preferred.
  • an apparatus configured to continuously perform the above-described heat treatment and galvanizing treatment may be used.
  • the steel sheet is immersed in a zinc bath having a bath temperature of 440°C to 500°C to be galvanized. Thereafter, it is preferable to adjust a coating weight of the plating layer by gas wiping or other methods.
  • a zinc bath having a chemical composition including the Al content of 0.10 to 0.23 mass% with a balance being Zn and inevitable impurities is preferred.
  • the alloying temperature is preferably 450°C to 600°C, more preferably 470°C to 550°C, and further preferably 470°C to 530°C.
  • an apparatus configured to be capable of successively performing the above-described heat treatment and electrogalvanizing treatment may be used.
  • the electrogalvanizing treatment is performed to thereby form an electrogalvanizing layer.
  • the types of electrogalvanizing layers are not particularly limited, and known electrogalvanizing layers are advantageously applicable.
  • the electrogalvanizing layer may be a zinc alloy plating layer obtained by adding, to Zn, one or more of such elements as Fe, Cr, Ni, Mn, Co, Sn, Pb and Mo in suitable amounts in accordance with the intended purpose.
  • the coating weight of the plating layer of the galvanized steel sheet (GI), the galvannealed steel sheet (GA), or the electrogalvanized steel sheet (EG) is preferably 20 to 80 g/m 2 per one side (double-sided plating).
  • the steel sheet having undergone the plating treatment is cooled to a temperature of, for example, not higher than 50°C.
  • the steel sheet having been cooled to a temperature of not higher than 50°C may be subjected to rolling at an elongation rate of 0.05% to 1.00%.
  • the elongation rate is preferably 0.08% to 0.70%.
  • the rolling may be performed in an apparatus that is continuous with an apparatus (plating apparatus) for performing the galvanizing treatment, or may be performed in an apparatus that is discontinuous with the plating device.
  • the desired elongation rate may be achieved by one rolling operation, or the desired elongation rate may be achieved by performing a plurality of rolling operations in total.
  • the rolling described here generally refers to temper rolling, but it may be rolling by processing using a leveler or the like as long as it is possible to impart an elongation rate equivalent to that achieved by temper rolling.
  • the retaining temperature such as the heating temperature or the re-heating temperature need not be constant as long as it is within the above-described temperature range.
  • a cooling rate may vary during cooling as long as it is within the above-described rate range.
  • the heat treatment may be performed in any equipment as long as the conditions such as the above-described temperature range are satisfied.
  • present member a member of the present embodiment (hereinafter also referred to as "present member”) is described.
  • the present member is a member formed by using the present high strength steel sheet described above as at least part of the member, and is, for example, a member formed into a target shape by processing (e.g., pressing) the present high strength steel sheet.
  • the present member is preferably a member for automotive parts.
  • the member for automotive parts may include a steel sheet other than the present high strength steel sheet as a material.
  • the present high strength steel sheet has a yield strength of not lower than 800 MPa and also has excellent collision proof stress and fracture resistance. Therefore, the present member is excellent in collision proof stress and fracture resistance and can contribute to reduction of the vehicle body weight, and thus is suitable for all members used in, among automotive parts, particularly skeletal structure parts or reinforcing parts of automobiles.
  • the present member is obtained by, for example, subjecting the present high strength steel sheet to at least one of a forming process and a joining process.
  • the forming process is not particularly limited, and examples thereof include press working.
  • the joining process is not particularly limited, and examples thereof include: general welding such as spot welding and arc welding; and crimping using rivets; and the like.
  • each steel slab was heated to 1250°C and rough rolled, and finish rolling was then performed at a finish rolling end temperature of 900°C.
  • the hot rolled steel sheet obtained was subjected to cold rolling at a rolling rate shown in Table 2 below, thereby obtaining a cold rolled steel sheet (thickness: 1.2 mm).
  • the cold rolled steel sheet obtained was subjected to the heat treatment under the conditions shown in Table 2 below.
  • both surfaces of the cold rolled steel sheet (CR) after the heat treatment were subjected to the plating treatment to obtain a galvanized steel sheet (GI), galvannealed steel sheet (GA), or electrogalvanized steel sheet (EG).
  • GI galvanized steel sheet
  • GA galvannealed steel sheet
  • EG electrogalvanized steel sheet
  • the bath temperature was 470°C for both GI and GA production.
  • the coating weight of the plating layer was 45 to 72 g/m 2 per one side when GI was produced, and 45 g/m 2 per one side when GA was produced.
  • the alloying temperature was 500°C.
  • the composition of the plating layer of GI was a composition including Fe: 0.1 to 1.0 mass% and Al: 0.2 to 1.0 mass% with the balance being Fe and inevitable impurities.
  • the composition of the plating layer of GA was a composition including Fe: 7 to 15 mass% and Al: 0.1 to 1.0 mass% with the balance being Fe and inevitable impurities.
  • an electrogalvanizing treatment was performed using an electrogalvanizing line such that the resulting plating layers had a coating weight of 30 g/m 2 per one side.
  • each of the cold rolled steel sheet (CR), the galvanized steel sheet (GI), the galvannealed steel sheet (GA), and the electrogalvanized steel sheet (EG) after the heat treatment is also simply referred to as "steel sheet.”
  • the obtained steel sheet was polished such that a cross section (L cross section) at a position of 1/4 of the sheet thickness and parallel to the rolling direction became an observation surface.
  • the observation surface was etched using 1 vol% Nital, and then enlarged and observed with a scanning electron microscope (SEM) at a magnification of 3,000X.
  • the observation surface was observed in 10 fields, and SEM images were obtained.
  • the obtained SEM images were analyzed to determine the total area fraction (unit: %) of tempered martensite and bainite.
  • the obtained steel sheet was subjected to buffing using a colloidal silica solution after grinding such that a cross section (L cross section) parallel to the rolling direction became an observation surface. Thereafter, 10 regions of 50 ⁇ m ⁇ 50 ⁇ m on the observation surface were measured by the EBSD method (electron beam accelerating voltage: 15 kV, step interval: 0.04 ⁇ m), and data for obtaining structure images was obtained.
  • the obtained data was processed using OIM Analysis software available from TSL Co. to obtain structure images. With the obtained structure images, the areas of the retained austenitic crystal grains were determined using Image-Pro available from Media Cybernetics Inc., and the circle equivalent diameters thereof were calculated. An average of these values was defined as the average grain size (unit: ⁇ m) of retained austenite.
  • the obtained steel sheet was polished using a diamond paste such that a cross section (L cross section) parallel to the rolling direction became an observation surface.
  • the observation surface was finished to a mirror surface by alumina polishing, and then cleaned using a plasma cleaner in order to eliminate contamination of hydrocarbons (carbon contamination, hereinafter referred to as "contamination") on the observation surface.
  • the cleaned observation surface was measured using an electron beam microanalyzer (FE-EPMA: Field Emission Electron Probe Micro Analyzer) equipped with a field emission electron gun to obtain data for obtaining elemental mapping images.
  • FE-EPMA Field Emission Electron Probe Micro Analyzer
  • the measurement conditions were an acceleration voltage of 7 kV and an electric current of 50 nA.
  • the steel sheet as a sample was heated and retained at 100°C and measured under conditions which do not allow contamination to be present.
  • the data after the measurement was converted to carbon concentration by a calibration method, and an elemental mapping image of carbon was obtained.
  • the measurement with the FE-EPMA was performed 30 times, and an elemental mapping image was obtained each time.
  • the ratio of a region (area fraction) where a carbon concentration was not less than 0.5 mass% was determined, and the average value of 30 measurements was defined as the area fraction (unit: %) of the structure S 2 .
  • a specimen having a length of 30 mm and a width of 5 mm was sampled from the obtained steel sheet.
  • the amount of diffusible hydrogen in steel was measured by the thermal desorption analytical method.
  • the heating rate was 200°C/hr.
  • the cumulative value of the amount of hydrogen detected in the temperature range from room temperature (25°C) to a temperature lower than 210°C was defined as the amount of diffusible hydrogen in steel (unit: mass ppm).
  • the steel sheet on which the plating layer had been formed was measured in the same manner after the plating layer was removed using a router (precision grinder).
  • the amount of diffusible hydrogen in steel is preferably not more than 0.50 mass ppm.
  • the obtained steel sheets were evaluated by the following methods. The results are shown in Table 3 below.
  • the strength can be determined to be high.
  • a member (hat member) having a hat-shaped cross section was produced, and a three-point bending test was performed to determine the maximum load (unit: kN).
  • a hat member 1 is described with reference to FIG. 2A .
  • FIG. 2A is a cross-sectional view showing the hat member 1.
  • the hat member 1 is joined to a flat plate 2 by spot welding (nugget diameter: 4.5 ⁇ t, spot-to-spot pitch: 35 mm).
  • the flat plate 2 is a cold-rolled steel sheet having no plating layer, and has a tensile strength (TS) of 590 MPa and a thickness t that is the same (1.2 mm) as that of the hat member 1.
  • TS tensile strength
  • FIG. 2B is a schematic view showing the hat member 1 subjected to the three-point bending test. Various dimensions are shown also in FIG. 2B .
  • the flat plate 2 joined to the hat member 1 is supported by a support member 3 which is a rigid body.
  • an impactor 4 which is a rigid body, is moved from above toward the hat member 1 at a velocity of 1 m/s. In this way, the three-point bending test is performed.
  • the three-point bending test was performed three times, and the average value of the maximum loads obtained in respective tests was defined as the maximum load of the steel sheet.
  • the collision proof stress can be rated as excellent.
  • test piece length of parallel portion: 40 mm, width of parallel portion: 20 mm
  • longitudinal direction tensile direction
  • a machined hole having a diameter of 8 mm was formed at a central position in the longitudinal direction of the parallel portion and at a center position in the width direction of the parallel portion in the test piece.
  • a tensile test with a constant tensile rate (2 mm/min) was performed 5 times in accordance with JIS Z 2241 using the specimen in which the machined hole was formed, and a fracture stroke was determined.
  • the steel sheets of Nos. 1 to 10, 15 to 17, 22, 25, 30, and 33 to 42 all had yield strengths of not less than 800 MPa and were excellent in collision proof stress and fracture resistance.

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EP23859902.1A 2022-08-29 2023-07-25 Tôle d'acier à haute résistance et son procédé de production, et élément et son procédé de production Pending EP4560039A4 (fr)

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JP6875915B2 (ja) 2016-05-30 2021-05-26 株式会社神戸製鋼所 高強度鋼板およびその製造方法
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CN108018484B (zh) * 2016-10-31 2020-01-31 宝山钢铁股份有限公司 抗拉强度1500MPa以上成形性优良的冷轧高强钢及其制造方法
WO2018115933A1 (fr) * 2016-12-21 2018-06-28 Arcelormittal Tôle d'acier laminée à froid à haute résistance présentant une formabilité élevée et son procédé de fabrication
EP3581670B1 (fr) * 2017-02-13 2021-04-07 JFE Steel Corporation Plaque d'acier à haute résistance et son procédé de fabrication
JP6631765B1 (ja) * 2018-05-01 2020-01-15 日本製鉄株式会社 亜鉛系めっき鋼板及びその製造方法
TW201945559A (zh) * 2018-05-01 2019-12-01 日商日本製鐵股份有限公司 鋅系鍍敷鋼板及其製造方法
JP7088140B2 (ja) * 2019-08-06 2022-06-21 Ｊｆｅスチール株式会社 高強度薄鋼板およびその製造方法
WO2022185804A1 (fr) * 2021-03-02 2022-09-09 Ｊｆｅスチール株式会社 Tôle d'acier, élément, procédé de production de ladite tôle d'acier et procédé de production dudit élément
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