US20240263288A1 - Cold rolled steel sheet and method for producing same - Google Patents

Cold rolled steel sheet and method for producing same Download PDF

Info

Publication number
US20240263288A1
US20240263288A1 US18/566,434 US202218566434A US2024263288A1 US 20240263288 A1 US20240263288 A1 US 20240263288A1 US 202218566434 A US202218566434 A US 202218566434A US 2024263288 A1 US2024263288 A1 US 2024263288A1
Authority
US
United States
Prior art keywords
steel sheet
rolling
rolled steel
less
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
US18/566,434
Other languages
English (en)
Inventor
Takafumi Yokoyama
Satoshi Hirose
Hiroyuki Tsuruoka
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: HIROSE, SATOSHI, TSURUOKA, HIROYUKI, YOKOYAMA, TAKAFUMI
Publication of US20240263288A1 publication Critical patent/US20240263288A1/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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • 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
    • 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
    • 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
    • C21D8/0221—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 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 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
    • C21D8/0221—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 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 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
    • C21D8/0247—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 characterised by the heat treatment
    • C21D8/0263—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 characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties 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
    • C21D8/0247—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 characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/002—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
    • C22C38/08—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
    • C22C38/22—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
    • C22C38/28—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
    • C22C38/32—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
    • C22C38/38—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—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
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • 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
    • C21D2211/005—Ferrite
    • 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
    • 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
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

  • the present disclosure relates to a cold rolled steel sheet and a method for producing the same.
  • “Hydrogen embrittlement cracking” is the phenomenon where a steel member to which high stress is being applied in the usage situation suddenly fractures due to the hydrogen penetrating the steel from the environment. This phenomenon is also called “delayed fracture” from the form of occurrence of the fracture. In general, it is known that hydrogen embrittlement cracking of steel sheet occurs more easier the more the tensile strength of the steel sheet rises. It is believed that this is because the stress remaining at the steel sheet after a part is shaped increases the higher the tensile strength of the steel sheet. The sensitivity to hydrogen embrittlement cracking (delayed fracture) is referred to as the “hydrogen embrittlement resistance”.
  • PTL 1 discloses an ultrahigh strength cold rolled steel sheet having a tensile strength of 1300 MPa or more and excellent in hydrogen embrittlement resistance, wherein the ultrahigh strength cold rolled steel sheet has a predetermined chemical composition, and values of amount of dissolved B solB (mass %) in the steel and prior austenite grain size D ⁇ ( ⁇ m) satisfying the relationship of formula (1): solB-D ⁇ 0.0010, and further has a steel microstructure comprising, by area ratio, polygonal ferrite in 10% or less, bainite in 30% or less, retained austenite in 6% or less, and tempered martensite in 60% or more, wherein a number density of Fe carbides in the tempered martensite is 1 ⁇ 10 6 /mm 2 or more, an average dislocation density of the steel as a whole is 1.0 ⁇ 10 15 /m 2 or more and 2.0 ⁇ 10 16 /m 2 or less, and an effective crystal grain size is 7.0 ⁇ m or less.
  • PTL 2 discloses a cold-rolled steel sheet comprising a predetermined chemical composition, and a microstructure in which tempered martensite and bainite are contained in a total area ratio of 95% or more and 100% or less with respect to a whole volume of the microstructure, a number of inclusion groups having a total length in a rolling direction of more than 120 ⁇ m is at most 0.8/mm 2 , the inclusion groups being formed by one or more inclusion particles, the one or more inclusion particles having a major axis length of 0.3 ⁇ m or more and extending and/or distributed in a dot-sequence manner along the rolling direction, and in the case of an inclusion group being formed by two or more inclusion particles, the two or more inclusion particles are spaced apart from one another by 30 ⁇ m or less, a number of carbides mainly composed of Fe that have an aspect ratio of 2.5 or less and a major axis length of 0.20 ⁇ m or more and 2 ⁇ m or less is at most 3500/mm 2 , a number of carbides that
  • PTL 3 discloses an ultra-high-strength steel sheet excellent in resistance to delayed fracture at a cut end thereof, having a predetermined chemical composition, and a structure comprising, by area ratio based on a whole structure, martensite: 90% or more, and residual austenite: 0.5% or more, the ultra-high-strength steel sheet has 2% or more by area ratio of a region where a local Mn concentration is at least 1.1 times a Mn content in a whole steel sheet, and the ultra-high-strength steel sheet has a tensile strength of 1470 MPa or more.
  • the inventors intensively tackled the improvement of the hydrogen embrittlement resistance of sheared parts and as a result obtained the following pointer. They discovered that the better the shape of the steel sheet, i.e., the flatter the steel sheet, the better the hydrogen embrittlement resistance of sheared parts. This is believed to be because if shearing steel sheet which is not flat, an angle would be given between the punch and steel sheet at the time of shearing and the damage to the sheared parts would become greater.
  • PTL 4 discloses an ultrahigh strength cold rolled steel sheet having a predetermined chemical composition, a metallographic structure of solely martensite, a tensile strength of 980 MPa or more, and a flatness of the steel sheet of 10 mm or less and a method for producing the same.
  • PTL 5 discloses a method for producing a high strength cold rolled steel sheet excellent in shape of the steel sheet, having a predetermined chemical composition and a metallographic microstructure containing tempered martensite in 65 area % or more, wherein the method comprises an annealing step of heating a steel material satisfying the above chemical composition in an austenite single phase region for 15 to 600 seconds to anneal it, a primary cooling step, after annealing, of gradually cooling it down to a primary cooling stop temperature at a 650 to 800° C.
  • the arts disclosed in the above PTLs 4 and 5 did not improve the shape of the steel sheet with the intent of improving the hydrogen embrittlement resistance of sheared parts, and therefore were insufficient in improving the hydrogen embrittlement resistance of sheared parts.
  • the “maximum warping height” is used as an indicator for evaluating the quality of the steel sheet shape, but it was learned that even if the “maximum warping height” were in the range of the above patent literature, the hydrogen embrittlement resistance of sheared parts was not necessarily excellent.
  • the present invention has as its object the provision of a cold rolled steel sheet having high tensile strength and total elongation while being improved in hydrogen embrittlement resistance.
  • the inventors discovered that to improve the hydrogen embrittlement resistance of sheared parts, it is necessary to improve not the “maximum warping height” of a steel sheet, but the amount of “curvature” expressing the degree of curving of a curved surface. Further, the inventors studied the method for producing the steel sheet necessary for improving the curvature of the steel sheet and as a result obtained the following findings:
  • the present invention was realized based on the above findings. Specifically, it is as follows:
  • a cold rolled steel sheet having a chemical composition comprising, by mass %,
  • (A) a hot rolling step comprising rough rolling and finish rolling a slab having a chemical composition according to the above (1) or (2), wherein the hot rolling step satisfies the conditions of the following (A1) to (A3):
  • (B) a cold rolling step comprising cold rolling the obtained hot rolled steel sheet using a tandem mill consisting of N number (N ⁇ 3) of rolling stands, wherein a cumulative cold rolling reduction is 30% or more, and the cold rolling step satisfies the following formulas (2) and (3):
  • (C) a heat treatment step comprising heat treating the obtained cold rolled steel sheet, wherein the heat treatment step satisfies the conditions of the following (C1) to (C3):
  • FIG. 1 is a schematic view of shearing relating to a hydrogen embrittlement test.
  • the C content is an element essential for securing the steel sheet strength.
  • the C content is 0.16% or more.
  • the C content may also be 0.18% or more, 0.20% or more, or 0.22% or more.
  • the C content is 0.40% or less.
  • the C content may also be 0.37% or less, 0.33% or less, or 0.30% or less.
  • Si is an element suppressing the formation of iron carbides and contributing to improvement of strength and shapeability. To sufficiently obtain these effects, the Si content is 0.05% or more. The Si content may also be 0.10% or more, 0.20% or more, or 0.40% or more. On the other hand, excessive addition sometimes causes the toughness or weldability and further the hydrogen embrittlement resistance to drop. Therefore, the Si content is 2.00% or less. The Si content may also be 1.60% or less, 1.30% or less, or 1.00% or less.
  • Mn manganese
  • Mn content is a powerful austenite stabilizing element and an element effective for making a steel sheet high strength.
  • the Mn content is 0.50% or more.
  • the Mn content may also be 0.80% or more, 1.00% or more, or 1.30% or more.
  • the Mn content is 4.0% or less.
  • the Mn content may also be 3.0% or less, 2.5% or less, or 2.0% or less.
  • P phosphorus
  • the P content is limited to 0.050% or less.
  • the P content is preferably 0.045% or less, 0.035% or less, or 0.020% or less.
  • the P content may be 0% as well, but to excessively reduce the P content, the dephosphorization cost rises, therefore from the viewpoint of economy, the lower limit is preferably 0.001%.
  • S sulfur
  • S is an element contained as an impurity. It forms MnS in steel to cause the toughness and hole expandability to deteriorate. Therefore, the S content is limited to 0.0100% or less as a range where deterioration of the toughness or hole expandability is not remarkable.
  • the S content is preferably 0.0050% or less, 0.0040% or less, or 0.0030% or less.
  • the S content may also be 0%, but to excessively reduce the S content, the desulfurization cost rises, therefore from the viewpoint of economy, the lower limit is preferably 0.0001%.
  • A1 (aluminum) is added in at least 0.001% for deoxidation of the steel.
  • the A1 content may be 0.005% or more, 0.01% or more, or 0.02% or more.
  • the A1 content has 1.00% as its upper limit.
  • the A1 content may also be 0.80% or less, 0.60% or less, or 0.30% or less.
  • N nitrogen
  • the N content is an element contained as an impurity. If its content is large, coarse nitrides are formed inside the steel and sometimes the bendability or hole expandability is made to deteriorate. Therefore, the N content is limited to 0.0100% or less.
  • the N content is preferably 0.0080% or less, 0.0060% or less, or 0.0050% or less.
  • the N content may also be 0%, but to excessively reduce the N content, the denitridation cost rises, therefore from the viewpoint of economy, the lower limit is preferably 0.0001%.
  • O oxygen
  • the O content is an element contained as an impurity. If the content is large, coarse oxides are formed in the steel and sometimes the bendability and hole expandability are made to deteriorate. Therefore, the O content is limited to 0.0100% or less.
  • the O content is preferably 0.0080% or less, 0.0060% or less, or 0.0050% or less.
  • the O content may also be 0%, but from the viewpoint of the production costs, the lower limit is preferably 0.0001%.
  • the basic chemical composition of the cold rolled steel sheet according to an embodiment of the present invention and the slab used for its production is as explained above. Furthermore, the cold rolled steel sheet and slab may contain the following optional elements in accordance with need. The lower limit of content in the case of not including optional element is 0%.
  • the contents are Cr: 0 to 2.00%, Mo: 0 to 1.00%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, B: 0 to 0.0100%, Co: 0 to 1.00%, W: 0 to 1.00%, Sn: 0 to 1.00%, Sb: 0 to 1.00%, Nb: 0 to 0.100%, Ti: 0 to 0.200%, and V: 0 to 0.50%.
  • the elements may also be 0.001% or more, 0.005% or more, or 0.010% or more.
  • the B content may be 0.0001% or more or 0.0005% or more.
  • Ca (calcium), Mg (magnesium), Ce (cerium), Zr (zirconium), La (lanthanum), Hf (hafnium), and a REM (rare earth element) other than Ce and La are elements contributing to the fine dispersion of steel inclusions while Bi (bismuth) is an element lightening the microsegregation of Mn, Si, and other substitution type alloy elements in the steel. These contribute to the improvement of the workability of the steel sheets, therefore one or more of these elements may be added in accordance with need. However, excessive addition triggers deterioration of the ductility. Therefore, the content is 0.0100% as an upper limit. Further, the elements may be contained in 0.0001% or more, 0.0005% or more, or 0.0010% or more.
  • the balance other than the above constituents is consisting of Fe and impurities.
  • “Impurities” are constituents, etc., entering due to various factors in the production process, such as the ore, scraps, and other such raw materials, when industrially producing a cold rolled steel sheet.
  • the steel microstructure in a range of 1 ⁇ 8 thickness to 3 ⁇ 8 thickness centered on 1 ⁇ 4 thickness from the surface of the cold rolled steel sheet comprises, by area %, martensite: 90.0 to 99.5%, ferrite: 0 to 5%, retained austenite: 0.5 to 7.0%, and balance: bainite and a ratio of tempered martensite to the total martensite is 80 to 100%.
  • the desired tensile strength can be obtained.
  • the area ratio of the martensite is 90.0 to 99.5% and the ratio of the tempered martensite to the total martensite is 80 to 100%.
  • the lower limit of the area ratio of the martensite is preferably 93.0% or more, more preferably 95.0% or more.
  • the upper limit of the area ratio of the martensite may also be 99.0% or less or 98.0% or less.
  • the lower limit of the ratio of the tempered martensite to the total martensite is preferably 85% or more, more preferably 90% or more.
  • the upper limit of the ratio of the tempered martensite to the total martensite may be 98% or less or 95% or less.
  • the area ratio of ferrite is 0 to 5%.
  • the upper limit of the area ratio of ferrite is preferably 4% or less, more preferably 2% or less, ideally 0%.
  • the area ratio of retained austenite is 0.5 to 7.0%.
  • the lower limit of the area ratio of retained austenite is preferably 1.0% or more and may also be 2.0% or more.
  • the upper limit of the area ratio of the retained austenite is preferably 6.0% or less and may also be 5.0% or less or 4.0% or less.
  • the steel microstructure may also contain a balance microstructure in addition to the martensite, ferrite, and retained austenite.
  • a balance microstructure for example, bainite can be illustrated.
  • the area ratio of the balance microstructure 0 to 9.5% is illustrated.
  • the area ratios of the structures other than the retained austenite are evaluated by the SEM-EBSD method (electron beam backscatter diffraction method) and examination of an SEM secondary electron image.
  • SEM-EBSD method electron beam backscatter diffraction method
  • a sample is taken using as the examined surface the cross-section of sheet thickness parallel to the rolling direction of the steel sheet.
  • the examined surface is machine polished to finish it to a mirror surface, then is electrolytically polished.
  • an area of a total of 3000 ⁇ m 2 or more is analyzed for crystal structure and orientation by the SEM-EBSD method.
  • crystal grains where neither substructures nor iron-based carbides are recognized and where the crystal structure is BCC are judged to be ferrite.
  • crystal grains where substructures are recognized and where iron-based carbides precipitate in single variants or crystal grains where iron-based carbides are not recognized are judged to be bainite.
  • crystal grains where cementite precipitates in a lamella form are judged to be pearlite.
  • pearlite is not included.
  • the balance is judged to be martensite and retained austenite. By subtracting from the area ratio of the balance the area ratio of retained austenite explained later, the area ratio of the martensite is found.
  • crystal grains where substructures are recognized and where two or more iron-based carbides precipitate in multiple variants are judged to be tempered martensite.
  • the area ratio of the retained austenite is calculated by measurement using X-rays. That is, the part of the steel sheet from the surface down to a depth 1 ⁇ 4 position in the sheet thickness direction is removed by mechanical polishing and chemical polishing. Further, after polishing, the sample is examined using MoKal rays as the characteristic X-rays.
  • the structural fraction of the retained austenite is calculated from the integrated intensity ratios of the diffraction peaks of ( 200 ), ( 211 ) of the bcc phase and ( 200 ), ( 220 ), ( 311 ) of the fcc phase. This is deemed the area ratio of the retained austenite.
  • the shape of the steel sheet having such a high flatness is prescribed using the maximum value of curvature 1/R corresponding to the reciprocal of the curvature radius R (mm). More specifically, the maximum value of curvature 1/R in the present invention is defined by the following formula (1) using two main curvatures ⁇ 1 , ⁇ 2 on the curved surface. In an embodiment according to the present invention, the maximum value of curvature 1/R is controlled to 0.010 or less.
  • the “curvature” in the present invention is the larger value of the absolute values of the main curvatures ⁇ 1, ⁇ 2 on a curved surface.
  • the main curvatures ⁇ 1, ⁇ 2 are measured using a general shape measuring instrument and are evaluated from 3D geometric data with measurement noise suppressed.
  • a typical shape measuring instrument an ATOS 3D scanner made by GOM can be used for measurement.
  • the “total width” means the length of the steel sheet in a direction vertical to the longitudinal direction of the cold rolled steel sheet (cold rolled coil).
  • the cold rolled steel sheet according to the present invention has a maximum value of the distribution of curvature measured in this way of 0.010 or less. For example, if the cold rolled steel sheet becomes warped or wavy and the maximum value of the distribution of curvature exceeds 0.010, an angle is given between a punch and the cold rolled steel sheet at the time of shearing and the damage to the sheared parts is believed to become greater. As a result, the hydrogen embrittlement resistance of the sheared parts deteriorates.
  • the maximum value of curvature 1/R may, for example, be 0.008 or less, 0.006 or less, 0.004 or less, or 0.002 or less.
  • the lower limit value is not particularly limited, but the maximum value of curvature 1/R may also be, for example, 0.0005 or more, 0.0006 or more, 0.0007 or more, 0.0008 or more, 0.0009 or more, or 0.001 or more. According to an embodiment of the present invention, as explained above, despite being a 1470 MPa or more high strength, an extremely high flatness can be achieved. As specifically shown in the examples, even in the case of more than 1800 MPa extremely high tensile strength, it is possible to realize a flatness of the maximum value of curvature 1/R of 0.001.
  • the measurement of the distribution of curvature is not limited to any specific conditions such as the timing of measurement, etc.
  • it may be performed on cold rolled steel sheet treated for flattening using a leveler, etc., after production or may be performed on cold rolled steel sheet right after production when no specific mechanical flattening treatment is performed.
  • a leveler etc.
  • it is extremely difficult to control the maximum value of curvature 1/R explained above to 0.010 or less.
  • a slab having a predetermined chemical composition is used, as explained in detail later, to produce the cold rolled steel sheet while suitably controlling the conditions of the hot rolling step, cold rolling step, and heat treatment step to thereby enable achievement of such a high flatness.
  • the cold rolled steel sheet has a plated layer, since the plated layer does not particularly affect measurement of the distribution of curvature, the plated layer is not peeled off: the distribution of the curvature is measured for the cold rolled steel sheet provided with the plated layer.
  • tensile strength is preferably 1490 MPa or more, more preferably 1500 MPa or more.
  • the upper limit is not particularly limited, but, for example, the tensile strength may be 2000 MPa or less, 1900 MPa or less, or 1800 MPa or less.
  • the cold rolled steel sheet it is possible to achieve a high total elongation (El) and more specifically possible to achieve a 6.0% or more total elongation.
  • the total elongation is preferably 7.0% or more, more preferably 8.0% or more.
  • the upper limit is not particularly limited, but, for example, the total elongation may be 20.0% or less or 15.0% or less.
  • the tensile strength and total elongation of the cold rolled steel sheet are measured by taking a JIS No. 5 tensile test piece from a direction perpendicular to the rolling direction of the steel sheet at room temperature (25° C.) in the atmosphere and performing a tensile test prescribed in JIS Z 2241: 2011.
  • the cold rolled steel sheet it is possible to achieve a high hole expandability, more specifically it is possible to achieve a 20% or more hole expansion rate ( ⁇ ).
  • the hole expansion rate is preferably 25% or more, more preferably 30% or more.
  • the upper limit is not particularly limited, but for example the hole expansion rate may also be 80.0% or less or 70.0% or less.
  • the hole expansion rate ( ⁇ ) is measured by the “JFS T 1001: 1996 Hole Expansion Test Method” of the standard of the Japan Iron and Steel Federation.
  • the cold rolled steel sheet according to an embodiment of the present invention is characterized by not cracking in a hydrogen embrittlement test conducted by the following method.
  • the shearing operation is performed by the method shown in FIG. 1 .
  • a T (thickness) ⁇ 50 W (width) ⁇ 50 L (length) (unit: mm) sample is taken from steel sheet so as to include a location giving the maximum value of curvature 1/R.
  • the shear angle is 1 degree, and the clearance CL is 0.15 ⁇ T.
  • the sheet restraining pressure is at least 1 ton or more.
  • the sample is cut by shearing, then the product side (sheet restrainer side) steel sheet is heat treated at 170° C. for 10 minutes.
  • the cold rolled steel sheet according to an embodiment of the present invention has, for example, a 0.5 to 3.0 mm sheet thickness. While not particularly limited, the sheet thickness may also be 0.6 mm or more, 0.8 mm or more, or 1.0 mm or more. Similarly, the sheet thickness may be 2.8 mm or less, 2.6 mm or less, or 2.3 mm or less.
  • the cold rolled steel sheet according to an embodiment of the present invention has, for example, a 500 mm or more sheet width. While not particularly limited, the sheet width may also be 700 mm or more, 800 mm or more, or 900 mm or more. The upper limit of the sheet width is not particularly limited, but the sheet width may be 2000 mm or less, 1800 mm or less, 1600 mm or less, 1400 mm or less, 1300 mm or less, 1200 mm or less, or 1100 mm or less.
  • the cold rolled steel sheet according to an embodiment of the present invention may have a plated layer on both surfaces or one surface, preferably on both surfaces.
  • a plated layer an electrogalvanized layer, hot dip galvanized layer, or hot dip galvannealed layer may be typically illustrated.
  • These galvanized layers may have any compositions known to persons skilled in the art.
  • Zn, Al, Mg, and other additive elements may be included.
  • the amount of deposition of the plated layer is not particularly limited and may be a general amount of deposition.
  • a slab having the same chemical composition as the chemical composition explained in relation to the cold rolled steel sheet is heated before hot rolling, then is rough rolled and finish rolled.
  • the heating temperature of the slab has to be 1150° C. or more so as to sufficiently melt the borides, carbides, etc., 1200° C. or more is preferred.
  • the steel slab used is preferably cast by the continuous casting method from the viewpoint of the production ability, but it may also be produced by ingot casting and thin slab casting.
  • the heated slab is rough rolled before the finish rolling.
  • the rough rolling conditions are not particularly limited, but the operation is preferably performed at 1050° C. to give a total rolling reduction of 60% or more. If the total rolling reduction is less than 60%, the recrystallization during the hot rolling becomes insufficient, therefore sometimes this leads to an uneven microstructure of the hot rolled steel sheet.
  • the total rolling reduction may, for example, be 90% or less.
  • the steel sheet finished being rough rolled is heated to reheat the width edge parts so that the temperature (Te) of the width edge parts is 10 to 150° C. higher than a temperature (Tc) of the width center part.
  • Te temperature of the width edge parts
  • Tc temperature of the width center part
  • a shape defect called a “center wave” where the width center part is stretched more than the width edge parts results.
  • the curvature becomes worse at the final product.
  • a shape defect called an “edge wave” where the edge parts are stretched from the center part results.
  • the edges are heated so that the temperature of the width edge parts is 10 to 150° C. higher than the temperature of the width center part. Preferably, they become higher by 20 to 100° C., more preferably 40 to 90° C.
  • the width edge parts can be heated (reheated) by any suitable means known to persons skilled in the art. While not particularly limited, for example, the heating can be performed using an edge heater.
  • finish rolling is performed.
  • the conditions for this are not particularly limited, but this is desirably performed in a range satisfying the conditions of a finish rolling entry side temperature of 950 to 1050° C., a finish rolling exit side temperature of 850 to 1000° C., and a total rolling reduction of 70 to 95%. If the finish rolling entry side temperature falls below 950° C., the finish rolling exit side temperature falls below 850° C., or the total rolling reduction exceeds 95%, the hot rolled steel sheet develops texture, therefore anisotropy sometimes appears at the final product sheet.
  • finish rolling entry side temperature exceeds 1050° C.
  • finish rolling exit side temperature exceeds 1000° C.
  • total rolling reduction falls below 70%
  • the steel sheet after the finish rolling, can be coiled up at a 450 to 650° C. coiling temperature so as to improve the shape of the steel sheet after cold rolling. If the coiling temperature falls under 450° C., the hot rolled steel sheet becomes high strength, therefore the shape of the steel sheet after cold rolling deteriorates. On the other hand, if the coiling temperature exceeds 650° C., the cementite coarsens and undissolved cementite remains, therefore sometimes the workability is impaired.
  • pickling is performed to remove the scale in accordance with need.
  • the pickling method may be based on an ordinary method. Further, to correct the shape of the hot rolled coil and improve the pickling ability, before the pickling, skin pass rolling or shot blasting or other pretreatment may be performed.
  • a cold rolling step comprising cold rolling the obtained hot rolled steel sheet using a tandem mill consisting of N number (N ⁇ 3) of rolling stands is performed, a cumulative cold rolling reduction is 30% or more, and the cold rolling step satisfies the following formulas (2) and (3):
  • the forward tension and the backward tension at the rolling stands in a tandem mill are generally measured parameters.
  • the forward tension and the backward tension at the rolling stands in a tandem mill are generally measured parameters.
  • ⁇ 0 is the flow stress of the steel sheet before passing the first stand, i.e., the yield strength of the hot rolled steel sheet.
  • ⁇ 0 is obtained by obtaining a JIS No. 5 tensile test piece along the rolling direction from the width center part of the hot rolled steel sheet and performing a tensile test based on JIS Z 2241: 2011.
  • Formula (2) means that if applying a large rolling reduction in the state with a large difference between the forward tension/flow stress and the backward tension/flow stress, the value becomes larger. To reduce formula (2), it is necessary to reduce the difference between the forward tension/flow stress and the backward tension/flow stress.
  • the left side of formula (2) becomes 3.0 or more, the shape of the steel sheet after cold rolling remarkably worsens and the curvature at the final product no longer satisfies formula (1).
  • the lower limit is not particularly prescribed, but, for example, the left side of formula (2) may be 0.1 or more or 0.2 or more.
  • Formula (2) is one preferable indicator for balancing well the tension and yield strength of the hot rolled steel sheet before and after the rolling stands so as to realize stable cold rolling free of slip and other rolling problems. Therefore, to realize such stable cold rolling, it is also possible to utilize another control method instead of the control method according to formula (2).
  • the cumulative cold rolling reduction being 30% or more is important in obtaining a good steel sheet shape with a high flatness. If the cumulative cold rolling reduction is less than 30%, the shape of the steel sheet after cold rolling is not sufficiently improved and as a result the curvature in the final product no longer satisfies formula (1).
  • the cumulative cold rolling reduction may also be 40% or more or 50% or more.
  • the upper limit is not particularly prescribed, but excessive rolling reduction causes the rolling load to become excessive and the load of the cold rolling mill increases, therefore, for example, the cumulative cold rolling reduction may be 75% or less or 70% or less.
  • the obtained cold rolled steel sheet is supplied to a predetermined heat treatment in the heat treatment step.
  • the steel sheet is heated at Ac3° C. or more for 10 seconds or more. If the heating temperature is less than Ac3° C. or the holding time is less than 10 seconds, austenite transformation does not sufficiently proceed, therefore the desired steel microstructure comprised mainly of martensite is not obtained and sufficient strength is not obtained. On the other hand, if the heating temperature is more than 950° C. or the holding time is more than 500 seconds, the crystal grain size coarsens and an increase of the fuel costs and damage to the facilities is invited.
  • Ac3 (° C.) is calculated by the following formula. The mass % of the elements are entered for the symbols of elements in the following formula. For elements which are not contained, 0 mass % is entered.
  • the steel sheet After heating, the steel sheet is cooled down to a range of 110 to 250° C. If T1 is below 110° C., the retained austenite falls below 0.5% by area ratio and the total elongation falls. On the other hand, if more than 250° C., the ratio of tempered martensite to the martensite becomes smaller than 80% and as a result the hydrogen embrittlement resistance falls.
  • the cooling stop temperature may be 120° C. or more and/or may be 220° C. or less.
  • the “average cooling rate” in the present invention is a rate including the later explained natural cooling.
  • the T1 to 300° C. average cooling rate (average cooling rate 2) 1.0 to 20° C./s and using a gas (for example, nitrogen gas) as a cooling medium for cooling relatively moderately, it is possible to suppress an increase in temperature spread inside steel sheet, therefore it becomes possible to decrease the curvature of the steel sheet. If the average cooling rate over that range is less than 1.0° C./s, the martensite fraction becomes lower and the desired tensile strength can no longer be obtained. On the other hand, if more than 20° C./s, the temperature spread inside the steel sheet increases and the steel sheet becomes worse in curvature. Further, for the cooling medium, from the viewpoint of reliably suppressing an increase in temperature spread inside the steel sheet, it is necessary to use a gas.
  • a gas for example, nitrogen gas
  • Ms (° C.) is calculated by the following formula.
  • the mass % of the elements are entered for the symbols of elements in the following formula. For elements which are not contained, 0 mass % is entered.
  • the tension applied to the cold rolled steel sheet has to be limited to 6 to 20 MPa.
  • the tension By controlling the tension to such a range, it is possible to improve the flatness of the cold rolled steel sheet and possible to decrease the curvature of the finally obtained cold rolled steel sheet.
  • the tension if the tension is outside the above range, the curvature of the cold rolled steel sheet becomes worse.
  • This tension may also be 8 MPa or more. Similarly, this tension may also be 16 MPa or less.
  • the steel sheet After cooling down to the cooling stop temperature T1, the steel sheet is held at 200 to 300° C. for 100 to 1000 seconds. Due to this, it is possible to place carbon at the nontransformed austenite to obtain retained austenite. If the temperature is less than 200° C. or the holding time is less than 100 seconds, the desired amount of retained austenite is not obtained. On the other hand, if the temperature is more than 300° C. or the holding time is more than 1000 seconds, the desired steel microstructure is not obtained and as a result the desired tensile strength and total elongation are not obtained.
  • the cold rolled steel sheet obtained by the method for producing the cold rolled steel sheet according to an embodiment of the present invention may be post-treated by a plating step for forming a plated layer on one surface or both surfaces of the cold rolled steel sheet, etc.
  • the plating step or other post step can be performed by an ordinary method.
  • a JIS No. 5 tensile test piece was taken from a direction perpendicular to the rolling direction of the steel sheet at room temperature (25° C.) in the atmosphere.
  • a tensile test was conducted based on JIS Z 2241: 2011 to measure the tensile strength (TS) and total elongation (El). Further, a test was conducted by the “JFS T 1001: 1996 Hole Expansion Test Method” of the standard of the Japan Iron and Steel Federation to measure the hole expansion rate ( ⁇ ).
  • the maximum value of curvature 1/R was determined in the following way: First, a just produced cold rolled steel sheet not subjected to any specific mechanical flattening treatment was measured using an ATOS 3D scanner made by GOM for points of a total width ⁇ 300 mm length area to thereby obtain the distribution of curvature in the cold rolled steel sheets. Next, the larger of the absolute values of the main curvatures ⁇ 1, ⁇ 2 in the distribution of curvature measured in this way was determined as the maximum value of curvature 1/R.
  • the hydrogen embrittlement resistance was evaluated by a hydrogen embrittlement test utilizing the shear operation shown in FIG. 1 . Specifically, first, a T (thickness) ⁇ 50 W (width) ⁇ 50 L (length) (unit: mm) sample was taken from steel sheet so as to include a location giving the maximum value of curvature 1/R. The shear angle was 1 degree, the clearance CL was 0.15 ⁇ T, and the sheet restraining pressure was 1 ton or more. The sample was cut by shearing, then the product side (sheet restrainer side) steel sheet was heat treated at 170° C. for 10 minutes.
  • Comparative Example 2 in the cold rolling step, the formula (2) was not satisfied, therefore the maximum value of curvature 1/R became higher and the hydrogen embrittlement resistance fell.
  • Comparative Example 4 in the hot rolling step, the difference in temperature of the width edge parts and the temperature of the width center part of the steel sheet after rough rolling was not suitable, therefore the maximum value of curvature 1/R became higher and the hydrogen embrittlement resistance fell.
  • Comparative Example 4 in the cold rolling step, the cumulative cold rolling reduction was low, therefore the maximum value of curvature 1/R became higher and the hydrogen embrittlement resistance fell.
  • Comparative Example 5 in the heat treatment step, the cooling stop temperature T1 was low, therefore retained austenite was not sufficiently formed and the El fell.
  • Comparative Example 45 the Si content was low, therefore retained austenite was not sufficiently formed and the El fell.
  • Comparative Example 46 the Mn content was low, therefore martensite was not sufficiently formed and the TS fell.
  • Comparative Example 47 the C content was low, therefore the TS fell.
  • Comparative Examples 48 to 50 the C, Mn, or Si content was high, therefore the hydrogen embrittlement resistance fell.
  • the steel had the predetermined chemical composition and microstructure and, further, the maximum value of curvature 1/R was controlled to 0.010 or less, therefore cold rolled steel sheet having a high tensile strength and total elongation while being improved in hydrogen embrittlement resistance could be obtained.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
US18/566,434 2021-09-09 2022-08-24 Cold rolled steel sheet and method for producing same Pending US20240263288A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2021-146956 2021-09-09
JP2021146956 2021-09-09
PCT/JP2022/031939 WO2023037878A1 (ja) 2021-09-09 2022-08-24 冷延鋼板およびその製造方法

Publications (1)

Publication Number Publication Date
US20240263288A1 true US20240263288A1 (en) 2024-08-08

Family

ID=85506635

Family Applications (1)

Application Number Title Priority Date Filing Date
US18/566,434 Pending US20240263288A1 (en) 2021-09-09 2022-08-24 Cold rolled steel sheet and method for producing same

Country Status (7)

Country Link
US (1) US20240263288A1 (https=)
EP (1) EP4400614A4 (https=)
JP (1) JPWO2023037878A1 (https=)
KR (1) KR20240032929A (https=)
CN (1) CN117616144A (https=)
MX (1) MX2024000959A (https=)
WO (1) WO2023037878A1 (https=)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN118726854A (zh) * 2024-06-27 2024-10-01 武汉钢铁有限公司 一种厚规格的冷轧高强钢及生产方法
CN119640153B (zh) * 2024-12-13 2025-08-26 燕山大学 一种高强高韧抗氧化热成形钢及其力学冶金制备方法

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4640872A (en) * 1983-05-14 1987-02-03 Kawasaki Steel Corporation Corrosion-resistant steel strip having Zn-Fe-P alloy electroplated thereon

Family Cites Families (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4947176B2 (ja) 2010-03-24 2012-06-06 Ｊｆｅスチール株式会社 超高強度冷延鋼板の製造方法
JP5482513B2 (ja) * 2010-06-30 2014-05-07 新日鐵住金株式会社 冷延鋼板およびその製造方法
JP6047037B2 (ja) * 2012-03-29 2016-12-21 株式会社神戸製鋼所 鋼板形状に優れた高強度冷延鋼板の製造方法
WO2015151427A1 (ja) * 2014-03-31 2015-10-08 Ｊｆｅスチール株式会社 高降伏比高強度冷延鋼板およびその製造方法
JP6295893B2 (ja) 2014-08-29 2018-03-20 新日鐵住金株式会社 耐水素脆化特性に優れた超高強度冷延鋼板およびその製造方法
JP2016153524A (ja) 2015-02-13 2016-08-25 株式会社神戸製鋼所 切断端部での耐遅れ破壊特性に優れた超高強度鋼板
KR101987570B1 (ko) 2015-03-25 2019-06-10 제이에프이 스틸 가부시키가이샤 냉연 강판 및 그 제조 방법
KR101767780B1 (ko) * 2015-12-23 2017-08-24 주식회사 포스코 고항복비형 고강도 냉연강판 및 그 제조방법
KR102387095B1 (ko) * 2017-12-26 2022-04-14 제이에프이 스틸 가부시키가이샤 고강도 냉연 강판 및 그의 제조 방법
CN112955575B (zh) * 2018-10-31 2022-07-08 杰富意钢铁株式会社 高强度构件、高强度构件的制造方法和高强度构件用钢板的制造方法
US11905570B2 (en) * 2019-02-06 2024-02-20 Nippon Steel Corporation Hot dip galvanized steel sheet and method for producing same
US12338505B2 (en) * 2019-08-30 2025-06-24 Jfe Steel Corporation Steel sheet, member, and methods for producing the same

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4640872A (en) * 1983-05-14 1987-02-03 Kawasaki Steel Corporation Corrosion-resistant steel strip having Zn-Fe-P alloy electroplated thereon

Also Published As

Publication number Publication date
CN117616144A (zh) 2024-02-27
WO2023037878A1 (ja) 2023-03-16
KR20240032929A (ko) 2024-03-12
MX2024000959A (es) 2024-02-09
JPWO2023037878A1 (https=) 2023-03-16
EP4400614A4 (en) 2024-12-11
EP4400614A1 (en) 2024-07-17

Similar Documents

Publication Publication Date Title
US20240182997A1 (en) Hot dip galvanized steel sheet and method for producing same
EP3650569B1 (en) Hot-rolled steel sheet and method for manufacturing same
EP2258886B1 (en) High-strength hot-dip galvanized steel sheet with excellent processability and process for producing the same
JP6777274B1 (ja) 溶融亜鉛めっき鋼板およびその製造方法
EP4026922B1 (en) Steel sheet
US11332804B2 (en) High-strength cold-rolled steel sheet, high-strength coated steel sheet, and method for producing the same
EP3495528A1 (en) Steel sheet and plated steel sheet
EP2695961B1 (en) High-strength steel sheet excellent in workability and manufacturing method thereof
EP3257959B1 (en) High-strength steel sheet and production method therefor
JPWO2018051402A1 (ja) 鋼板
US20180023161A1 (en) High-strength steel sheet and production method therefor
EP4186987A1 (en) Steel sheet and method for manufacturing same
US20240263288A1 (en) Cold rolled steel sheet and method for producing same
EP3276021A1 (en) High-strength steel sheet and production method therefor
US12559815B2 (en) High-strength steel sheet and method for producing same
JP7193044B1 (ja) 高強度鋼板およびその製造方法、ならびに、部材

Legal Events

Date Code Title Description
AS Assignment

Owner name: NIPPON STEEL CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:YOKOYAMA, TAKAFUMI;HIROSE, SATOSHI;TSURUOKA, HIROYUKI;REEL/FRAME:065759/0167

Effective date: 20230915

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

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

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

Free format text: NON FINAL ACTION COUNTED, NOT YET MAILED

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

Free format text: NON FINAL ACTION MAILED