WO2022180146A1 - Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d'un tel produit plat en acier - Google Patents

Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d'un tel produit plat en acier Download PDF

Info

Publication number
WO2022180146A1
WO2022180146A1 PCT/EP2022/054616 EP2022054616W WO2022180146A1 WO 2022180146 A1 WO2022180146 A1 WO 2022180146A1 EP 2022054616 W EP2022054616 W EP 2022054616W WO 2022180146 A1 WO2022180146 A1 WO 2022180146A1
Authority
WO
WIPO (PCT)
Prior art keywords
steel
flat
advantageously
thickness
ratio
Prior art date
Application number
PCT/EP2022/054616
Other languages
German (de)
English (en)
Inventor
Ingwer Denks
Djordje MIRKOVIC
Marco Witte
Original Assignee
Salzgitter Flachstahl Gmbh
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 Salzgitter Flachstahl Gmbh filed Critical Salzgitter Flachstahl Gmbh
Priority to MX2023007872A priority Critical patent/MX2023007872A/es
Priority to CN202280016717.8A priority patent/CN116888283A/zh
Priority to EP22708897.8A priority patent/EP4298255A1/fr
Priority to KR1020237028391A priority patent/KR20230148167A/ko
Priority to US18/547,444 priority patent/US20240141450A1/en
Publication of WO2022180146A1 publication Critical patent/WO2022180146A1/fr

Links

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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D6/02—Hardening by precipitation
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—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
    • C22C38/12—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—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
    • C22C38/54—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
    • C22C38/18—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
    • 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
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • 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
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
    • 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
    • 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
    • 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
    • C21D2211/009—Pearlite

Definitions

  • the invention relates to a high-strength, hot-rolled flat steel product with high local cold workability. Furthermore, the invention relates to a method for producing such a flat steel product.
  • cold formability is understood to mean formability at a temperature in the range from 10° C. to 700° C., preferably between 10° C. and 200° C., particularly preferably between 10 and 80° C. and particularly preferably at room temperature between 15 and 40° C .
  • the invention relates to a high-strength, micro-alloyed, predominantly bainitic hot strip with an optimized alloy composition and microstructure, which is used, for example, as a chassis component in the automotive industry.
  • the invention also relates to high-strength hot strip with tensile strengths of at least 760 MPa and at the same time high cold workability.
  • Parameters such as elongation at break, uniform elongation and hole expansion ratio are established parameters for describing cold formability.
  • the characteristic value hole expansion ratio was selected as a representative of the local formability and the characteristic value uniform elongation as a representative of the global cold formability.
  • the true sizes are given and not the technical (percentage) sizes, the determination of which is given in the description of the exemplary embodiments.
  • the invention particularly includes flat steel products made of steels with a multi-phase structure, which essentially contains, ie a proportion of more than 50% by volume, bainite and which have a yield point ratio of at least 0.8.
  • the flat steel product also has a high hole expansion capacity with a hole expansion ratio LA of at least 30%, a degree of cold workability FL of at least 0.12 and a local to global ratio Cold workability LFR in the range of at least 5 and at most 13.
  • bainitic steels are steels which are characterized by a comparatively high yield point and tensile strength with a sufficiently high elongation for cold forming processes. Good weldability is given due to the chemical composition.
  • the microstructure typically consists of bainite as the predominant component with portions of ferrite.
  • the microstructure may occasionally contain small amounts of other phases, such as martensite and retained austenite.
  • the weight of the vehicles can be reduced while at the same time improving the forming behavior of the steels used during production and operation.
  • High-strength steels must therefore meet comparatively high requirements in terms of their strength, ductility and energy absorption, without their processing, such as stamping, hot and cold forming, thermal hardening (e.g. air hardening, press hardening), welding and/or surface treatment, e.g. a metallic refinement, organic coating or painting, disadvantages occur compared to conventional steels.
  • thermal hardening e.g. air hardening, press hardening
  • welding and/or surface treatment e.g. a metallic refinement, organic coating or painting
  • Newly developed steels therefore have to meet the increasing material requirements for yield strength, tensile strength, hardening behavior and elongation at break with good processing properties such as formability and weldability, in addition to the required weight reduction through reduced sheet thicknesses.
  • a high-strength steel with a single- or multi-phase structure must therefore be used to ensure sufficient strength of the motor vehicle components and to meet the high forming and component requirements in terms of toughness, edge crack resistance, improved bending angle, bending radius and energy absorption.
  • Improved joint suitability in the form of better general weldability expressed by a larger usable welding area in resistance spot welding and improved failure behavior of the weld seam (fracture pattern) under mechanical stress, as well as sufficient resistance to delayed cracking due to hydrogen embrittlement, is also increasingly required.
  • the hole expansion capacity is a material property that describes the resistance of the material to crack initiation and crack propagation during forming operations in areas close to edges and previously sheared, such as when collaring.
  • the hole expansion test is normatively regulated in ISO 16630, for example. Accordingly, holes punched in sheet metal are widened by means of a dome.
  • the measured variable is the change in the hole diameter, based on the initial diameter, to the diameter at which the first crack through the sheet occurs at the edge of the hole.
  • Improved resistance to edge cracks means an increased formability of the sheet edges and is described by an increased hole expansion capacity. This fact is known under the synonyms “Low Edge Crack” (LEC) or under “High Hole Expansion” (HHE) as well as xpand®.
  • Patent specification EP 3516 085 B1 discloses a method for producing a high-strength hot-rolled steel strip with a tensile strength of at least 570 MPa, preferably at least 780 MPa, with which good cold-formability of the steel strip is to be achieved.
  • the procedure comprises the following steps:
  • the steel known from this consists of (in weight %): between 0.015 and 0.15 C; at most 0.5 Si; between 1.0 and 2.0 Mn; at most 0.06 P; at most 0.008S; at most 0.1 Al sol; at most 0.02N; between 0.02 and 0.45V; optionally one or more of: at least 0.05 and/or at most
  • the steel has a substantially single-phase ferritic microstructure containing a mixture of polygonal ferrite (PF) and acicular/bainitic ferrite (AF/BF) and wherein the total volume fraction of the sum of the ferrite constituents is at least 95% and wherein the ferrite constituents are mixed with fine Composite carbides and/or carbo-nitrides of V and optionally of Mo and/or Nb are precipitation strengthened.
  • PF polygonal ferrite
  • AF/BF acicular/bainitic ferrite
  • the steel has the following alloy composition in % by mass,
  • the present invention is based on the object of creating a high-strength, hot-rolled flat steel product and a method for producing such a flat steel product, and so, based on the steel, a To achieve a combination of high strength with high local cold formability and high cost-effectiveness.
  • a high-strength, hot-rolled flat steel product with high local cold formability having a tensile strength Rm of at least 760 MPa, a yield point ratio of at least 0.8 and a hole expansion ratio of at least 30%, advantageously at least 40%, particularly advantageously at least 50%, has an elongation at break of at least 10%, preferably at least 16%, a degree of cold workability of at least 0.12, advantageously at least 0.17 and a ratio of local to global cold workability of at least 5 and at most 13, and a structure consisting of more than 50% by volume Bainite, up to 10% by volume, advantageously up to 5% by volume, high-carbon microstructural components such as martensite, retained austenite, pearlite, retained austenite, remainder precipitation-hardened ferrite, with the following chemical composition of the steel (in percent by weight):
  • Ti up to 0.18 and/or Nb: up to 0.08 Mo: up to 0.35 with Ti+Nb more than 0.06% by weight, with a superstoichiometric proportion of carbon and nitrogen according to formula 1 below being present :
  • the hardness difference HV0.1 is a maximum of 20 HV 0.1, advantageously a maximum of 15 HV 0.1, even more advantageously a maximum of 10 HV 0.1 compared to the mean value over the entire thickness of the steel flat product, an excellent combination of Strength, elongation and forming properties.
  • the microstructure preferably consists of more than 50% by volume of bainite and the remainder of precipitation-strengthened ferrite.
  • the flat steel product is characterized by a combination of high strength and excellent cold formability.
  • the production of this flat steel product according to the invention based on the alloying elements C, Si, Mn, Nb and/or Ti is comparatively inexpensive.
  • the steel flat product according to the invention is specifically characterized by a high elongation at break A of at least 10%, a high hole expansion ratio (LA) of at least 30%, advantageously at least 40%, particularly advantageously at least 50%, a measure of cold workability (FL) of at least 0, 12, advantageously at least 0.17 and a ratio of local to global cold workability (LFR) of at least 5 and at most 13, while at the same time having a high tensile strength of at least 760 MPa.
  • LA hole expansion ratio
  • FL measure of cold workability
  • LFR local to global cold workability
  • the steel alloy has a advantageous further development of the invention optionally one or more elements of Cr, Ni, V or B with the following contents in % by weight: Cr: more than 0.1 up to 0.6, Ni: more than 0.1 up to 0 ,6, V: more than 0.01 up to 0.2 and B: more than 0.0005 up to 0.01, where there is a superstoichiometric proportion of carbon and nitrogen according to the following formula 2:
  • the steel is alloyed with Ca for inclusion control.
  • the inclusions of MnS and Al 2 O 3 which are unfavorable with regard to the final properties, are replaced by inclusions containing Ca that are less harmful, in particular with regard to the morphology.
  • the addition to the steel is a maximum of 0.01% by weight.
  • the flat steel product contains the following alloy composition in % by weight in order to achieve particularly favorable combinations of properties:
  • Ti at least 0.02, advantageously at least 0.04, more advantageously at least 0.06
  • Nb at least 0.01
  • Mo at least 0.05
  • Ti + Nb up to 0.2.
  • the microstructure consists mainly of bainite and, to a lesser extent, of ferrite.
  • the bainite is a mixture of constituents characterized by a main constituent of at least 50% by volume and minor constituents, the main constituent being bainitic ferrite formed by precipitations of (Ti, Nb, Mo)(C,N) or V( C,N) is hardened and the secondary components consist of carbon-rich components such as martensite, retained austenite, lower bainite and pearlite.
  • the structure advantageously consists of more than 75% by volume of bainite.
  • the structure may contain carbon-rich structural components.
  • microstructure contains a maximum of 10%, preferably a maximum of 5%, carbon-rich microstructure components (e.g. martensite, retained austenite, pearlite).
  • carbon-rich microstructure components e.g. martensite, retained austenite, pearlite
  • the grain elongation of all structural components in the rolling direction is characterized by the area-average aspect ratio of all microstructure components in the rolling direction of at most 2.0, and/or the mean value over the three areas close to the surface, 1/4 thickness and 1/2 thickness of the steel flat product is at most 2.0, advantageously 1.6.
  • the hot-rolled flat steel product according to the invention can be provided with a metallic or non-metallic coating.
  • the metallic coating can be applied to the flat steel product electrolytically or by hot dipping and is advantageously zinc-based.
  • Hot-rolled flat steel products according to the invention have thicknesses of 1.6 to 6.0 mm. However, thicknesses less than 1.6 mm or greater than 6.0 mm are also covered by the invention.
  • the flat steel product according to the invention advantageously has a tensile strength Rm of at least 760 MPa along the rolling direction, a yield point ratio of at least 0.8, an elongation at break A of at least 10%, preferably at least 16%, a hole expansion ratio of at least 30%, advantageously at least 40% or even at least 50%.
  • the degree of cold workability is at least 0.12, advantageously at least 0.17, with a ratio of local and global cold workability of at least 5 and at most 13.
  • Alloying elements are usually added to the steel in order to specifically influence certain properties.
  • An alloying element can influence different properties in different steels. The effect and interaction generally depends heavily on the amount, the presence of other alloying elements and the state of the solution in the material. The connections are varied and complex. The effect of the alloying elements in the alloy according to the invention will be discussed in more detail below.
  • Carbon C Needed for the formation of carbides, especially in connection with the so-called micro-alloying elements Nb, V and Ti, promotes the formation of martensite and bainite, stabilizes austenite and generally increases strength. Higher contents of C deteriorate the welding properties and lead to the deterioration of the elongation and toughness properties, which is why a maximum content of at most 0.08% by weight is specified. In order to achieve sufficient material strength, a minimum addition of 0.04% by weight is required.
  • Manganese Mn Stabilizes austenite, increases strength and toughness. Higher contents of > 2.0% by weight Mn increase the risk of central segregation, which significantly reduces ductility and thus product quality. Lower contents ⁇ 1.0% by weight do not allow the required strength and toughness to be achieved at the desired moderate analysis costs. Therefore, the content of Mn is specified to be 1.0 to 2.0% by weight.
  • Aluminum AI Used for deoxidation in the steelworks process. The amount of AI used depends on the process. Therefore, no minimum Al content is specified. An Al content of more than 0.06% by weight significantly impairs the casting behavior in continuous casting. This results in greater effort when casting. Therefore, the content of Al is set to 0.06% by weight at maximum Silicon Si: Is one of the elements that enable steel to be strengthened by solid solution strengthening in a cost-effective way. However, Si reduces the surface quality of the hot strip by promoting firmly adhering scale on the reheated slabs, which can only be removed with great effort or only insufficiently if the Si content is high. This is particularly disadvantageous during subsequent galvanizing. Therefore, the Si content is limited to a maximum of 0.6% by weight. For the effectiveness of Si, a lower limit of 0.1% by weight is to be regarded as reasonable.
  • Calcium Ca is added to the steel for inclusion control to prevent the formation of unfavorable inclusions of MnS and Al203 and to form, with these elements, less harmful Ca-containing inclusions in terms of morphology.
  • the addition to the steel is a maximum of 0.01% by weight.
  • Micro-alloying elements are usually only added in very small amounts ( ⁇ 0.2% by weight per element). In contrast to the alloying elements, they mainly act through the formation of precipitates, but can also influence the properties in the dissolved state. Despite the small amounts added, micro-alloying elements have a strong influence on the targeted manufacturing conditions as well as the processing and end properties of the product.
  • Typical micro-alloying elements are, for example, niobium and titanium. These elements can be dissolved in the iron lattice and form carbides, nitrides and carbonitrides with carbon and nitrogen. Since the micro-alloying elements are comparatively expensive, the alloyed proportion is kept as low as possible. On the other hand, the carbon that is over-stoichiometric and therefore not bound in precipitations of the micro-alloying elements in carbon-rich structural components contributes to the cost-effective and necessary increase in strength. Therefore, the over-stoichiometric proportion of carbon and nitrogen calculated according to formula 1: (C/12+N/14) / (Ti/48+Nb/93+Mo/96) is set to > 1.
  • Nb and Ti depends in particular on the process control during hot rolling and the subsequent cooling process. With the addition of micro-alloying elements, the aim is to achieve grain refinement in the course of the process and to produce precipitations in the nanometer size range. Hence an Nb+Ti content of more than 0.06% by weight is a prerequisite for achieving the desired strength and good elongation properties. A cumulative value of more than 0.2% by weight, on the other hand, no longer improves the properties of the steel, since contents above the specified cumulative value in the specified analysis and when using conventional furnaces can no longer be dissolved when the slabs are reheated and thus have no positive effect.
  • Niobium Nb The addition of niobium has a grain-refining effect, in particular due to the formation of carbides in the rolling process, which at the same time improves strength, toughness and elongation properties.
  • very fine Nb-containing precipitations can be formed after the phase transformation, which contribute significantly to the strength of the product. At contents of more than 0.08% by weight, saturation occurs, which is why a maximum content of less than or equal to 0.08% by weight. -% is provided. A minimum content of 0.01% by weight is provided for sufficient effectiveness.
  • Titanium Ti As a carbide former, it has a grain-refining effect, which improves strength, toughness and elongation properties at the same time. Contents of Ti of more than 0.18% by weight impair the ductility and the hole expansion capacity by the formation of very coarse, primary TiN precipitates, which is why a maximum content of 0.18% by weight is specified. A minimum content of 0.02, advantageously 0.04, even more advantageously 0.06% by weight is provided for sufficient effectiveness.
  • Molybdenum Mo Increases hardenability and reduces the critical cooling rate, thus promoting the formation of fine, bainitic structures. In addition, even the use of small amounts of Mo delays the coarsening of fine precipitates, which should be as fine as possible to increase the strength of micro-alloyed structures. A minimum content of 0.05% by weight is provided for sufficient effectiveness and is limited to a maximum of 0.35% by weight for cost reasons.
  • Phosphorus P Is a trace element from iron ore and is dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness through solid solution strengthening and improves hardenability. However, attempts are usually made to reduce the phosphorus content as much as possible, since it is, among other things, very susceptible to segregation and greatly reduced toughness. The accumulation of phosphorus at the grain boundaries can cause cracks to appear along the grain boundaries during hot rolling. In addition, phosphorus increases the transition temperature from tough to brittle behavior by up to 300 °C. However, the use of small amounts of P can also be used to increase the strength at low cost through targeted measures that are precisely controlled on the process side. For the above reasons, the phosphorus content is limited to a maximum of 0.06% by weight.
  • Sulfur S Like phosphorus, it is bound as a trace element in iron ore. It is generally undesirable in steel because it leads to undesirable inclusions of MnS, which degrades elongation and toughness properties. Attempts are therefore made to achieve the lowest possible amounts of sulfur in the melt and, if necessary, to convert the elongated inclusions into a more favorable geometric shape by means of a so-called Ca treatment. For the above reasons, the sulfur content is limited to a maximum of 0.01% by weight.
  • Nitrogen N Is also a secondary element from steel production. Steels with free nitrogen tend to have a strong aging effect. Even at low temperatures, the nitrogen diffuses at dislocations and blocks them. It thus causes an increase in strength combined with a rapid loss of toughness. Binding of the nitrogen in the form of nitrides is possible, for example, by alloying aluminum, niobium or titanium. As a result, however, the alloying elements mentioned are no longer available for the new formation of small precipitations, which are very efficient in terms of strength, in the later process. For the above reasons, the nitrogen content is limited to a maximum of 0.012% by weight.
  • Chromium Cr As an optional alloyed element, Cr improves strength and reduces corrosion rate and retards ferrite and pearlite formation.
  • the maximum content is set at a maximum of 0.6% by weight, since higher contents result in a deterioration in ductility. A content of more than 0.1% by weight is intended for sufficient effectiveness.
  • Nickel Ni The optional use of even small amounts of Ni promotes ductility while maintaining strength. Because of the comparatively high cost, the content of Ni is limited to at most 0.6% by weight. For a sufficient Effectiveness, a level of more than 0.1% by weight is contemplated.
  • Vanadium V With the present alloy concept, the addition of vanadium is not absolutely necessary. For cost reasons, the vanadium content is limited to a maximum of 0.2% by weight. If V is nevertheless intended to be added, the over-stoichiometric proportion of carbon and nitrogen is calculated using formula 2: (C/12+N/14) / (Ti/48+Nb/93+Mo/96+V/51) to > 1 fixed. A V content of more than 0.01% by weight is then also provided for sufficient effectiveness.
  • Boron B is an effective hardenability enhancing element that is effective in very small amounts.
  • the martensite start temperature remains unaffected.
  • boron must be in solid solution. Since it has a high affinity for nitrogen, the nitrogen must first be bound, preferably with the stoichiometrically required amount of titanium. Due to its low solubility in iron, the dissolved boron tends to accumulate at the austenite grain boundaries. There it partially forms Fe-B carbides, which are coherent and lower the grain boundary energy.
  • the boron content for the alloy concept according to the invention is limited to values of a maximum of 0.01% by weight. A content of more than 0.0005% by weight is intended for sufficient effectiveness.
  • a method according to the invention for producing a hot-rolled flat steel product with high local cold formability having a tensile strength Rm of at least 760 MPa, a yield point ratio of at least 0.8 and a hole expansion ratio of over 30%, advantageously at least 40%, particularly advantageously at least 50%, a measure the cold formability of at least 0.12, advantageously at least 0.17 and a ratio of local and global cold formability of at least 5 and at most 13, comprising the steps:
  • Mo up to 0.35 with Ti+Nb greater than 0.06 and with a superstoichiometric ratio of carbon and nitrogen according to Formula 1 below: 1.0 ⁇ (C/12+N/14)/(Ti/48+ Nb/93+Mo/96) with optional alloying of one or more elements of Cr, Ni, V, B or Ca, balance iron including unavoidable steel-accompanying elements
  • EWT ⁇ EWTmin 682 °C + 464 C + 6445 Nb - 644 x Nb0.5 + 732 V - 230 V0.5 + 890 Ti +363 AI - 36 Si (formula 3)
  • thermomechanical rolling is usually used to produce high-strength, micro-alloyed hot strip.
  • the finish rolling takes place in a low temperature range of less than EWTmin, in which the austenite no longer recrystallizes and as a result the accumulated dislocations lead to a high nucleus density at the beginning of the phase transformation and thus produce a fine hot strip structure.
  • a key goal of thermomechanical rolling is to increase strength and ductility by reducing the grain size of the hot strip structure.
  • the carbon in contrast to nitrogen, is not completely precipitated in the form of strength-increasing microalloy precipitates.
  • the carbon that is not precipitated in microalloy precipitates leads to the formation of carbon-rich structural components and different carbon-rich components of bainite. It is crucial for cold workability that the carbon-rich structural components and the carbon-rich components of the bainite are advantageously present in terms of size and distribution. Advantageously means that the size is small and the distribution is as uniform as possible.
  • the process paths are identical to The process paths.
  • the carbon is in the form of hard structural components such as carbides, pearlite or martensite.
  • the resulting product has high cold formability with a lower proportion of local cold formability. The strength is higher because a higher proportion of micro-alloying elements are precipitated.
  • An average coiling temperature of e.g. 550 ⁇ HT ⁇ 650 °C to produce a mixed structure consisting of high-temperature bainite (e.g. upper bainite and granular bainite) and ferrite with both high local cold workability and high strength due to a high proportion of precipitation has not been expedient up to now. Either only high cold formability was achieved or only high strength was achieved through a high proportion of precipitation.
  • the predominantly bainitic, micro-alloyed hot strip exhibits both high strength and high local cold formability when, in combination with the alloy composition and a super-stoichiometric ratio of 1.0 ⁇ (C/12+N /14) / (Ti/48+Nb/93+ Mo/96), the steel flat product is finish-rolled with a final rolling temperature of at least EWTmin according to formula 3 and then coiled and cooled in a temperature-time window that is characterized by a maximum coiling temperature HTmax according to formula 4 and characterized by 17000 ⁇ HP ⁇ 18800, where HP is calculated by Formula 5.
  • the hot-rolled steel flat product has a strength contribution to the tensile strength of at least 80 MPa or more due to precipitation formation when coiled and cooled in a temperature time window characterized by 17000 ⁇ HP ⁇ 18800 compared to a temperature time window , which is characterized by HP ⁇ 15990.
  • the strength contribution is necessary to cost-effectively achieve high tensile strength and high yield strength ratio.
  • HTmax is observed within the temperature-time window, the structure that is favorable for local formability and strength is formed.
  • the flat steel product according to the invention is characterized by compliance with the temperature-time window mentioned in that half of the precipitations of (Ti, Nb, Mo) (C,N) and / or V (C,N), the ferrite and the main component of bainitic Reinforce ferrite, have a diameter of less than 10 nm and/or the precipitates have an average spacing of less than 750 nm.
  • the flat steel product produced according to the invention has, in addition to a cost-effective alloy concept, high strength and, at the same time, high local cold workability.
  • the manufacturing method according to the invention is characterized by high process stability.
  • bainite In contrast to ferrite, bainite usually consists of different components. The different components of the bainite are formed from the austenitic phase with decreasing temperature during the production of the hot strip after the final rolling. Compared to ferrite, bainite forms at lower temperatures and bainite has a higher average dislocation density. Both the high strength and the high local cold formability can only be achieved with a predominantly bainitic structure. The reason is that the bainitic structure has a high density of dislocations and a small grain size.
  • hot strip can be achieved with either the property combination of comparatively low strength with comparatively high local cold workability or the property combination of comparatively high strength with comparatively low local cold workability.
  • the invention allows the property combination of high strength and high local cold workability to be achieved.
  • the degree of cold formability is described by the geometric mean of local and global formability:
  • Formability Level "FL” (true uniform elongation x true hole expansion ratio) 0.5
  • LFR Local Formability Ratio
  • test results presented in the appendix extend to exemplary embodiments with a tensile strength of at least 760 MPa.
  • a tensile strength of at least 760 MPa.
  • the following criteria are required for high local cold formability, especially for the area of application:
  • GOS Grain Orientation Spread
  • KAM Kernel Average Misorientation
  • the proportional specimen shape with the designation A for elongation at break was used.
  • the non-proportional specimen shape with an initial gauge length of 80 mm was used.
  • the mean value from at least 3 individual tests is always given.
  • EBSD electron backscatter images
  • KAM Kernel Average Misorientation
  • GKAM GKernel Average Misorientation
  • - Ferrite consists of polygonal and quasi-polygonal ferrite and the grains are delimited by grain boundaries with misorientation angles > 15°. There are no small-angle grain boundaries ⁇ 15° in the grain interior of the ferrite, the values of the grain orientation spread (GOS) are ⁇ 2° and the values of the grain kernel average misorientation (GKAM) are typically ⁇ 0.4°.
  • TEM images show a high density of (Ti, Nb, Mo)(C,N) precipitations in the interior of the grain.
  • (Fe.Mn)-carbides can be present in particular in the area of the grain interstices.
  • the granular bainite grains are delimited by grain boundaries of > 15°. Due to the displacive phase transformation of austenite into bainite, small-angle grain boundaries occur inside the grain, the GOS values are ⁇ 2° and the GKAM values are typically ⁇ 0.4°.
  • the GOS values are ⁇ 2° and the GKAM values are typically ⁇ 0.4°.
  • EBSD IPF Inverse Pole Figure
  • lancets of different orientation can typically be seen in the interior of the grain. Lancets that do not show a second phase in the EBSD Image Quality Map are referred to as "bainitic ferrite" in the following.
  • Interspersed between the grains of bainitic ferrite is a carbon-rich second phase in the form of martensite, MA phase, lower bainite, or pearlite. (Fe,Mn) carbides can be present in particular in the area of the interstices of the grain. The surface area of the second phase decreases with increasing coiling temperature and can be 0 -
  • the ratio of the X-axis intersections of the grain ellipses to the Y-axis intersections of the grain ellipses corresponds to the aspect ratio of the grains in the rolling direction to the sheet normal. This calculation method ensures that the stretching of grains whose long axis does not point exactly in the direction of rolling is only determined in the normal direction of rolling or sheet metal.
  • the HV0.1 hardness test was carried out on the microsection in points at different distances from the surfaces. No measurement is made at a distance from the surfaces and the center of 0.1 mm. In addition:
  • the hardness values are given as the average of 6 individual measurements.
  • 3 hardness indentations for the near-surface position are positioned between 0% and 10% and 90% and 100% distance from the surface based on the thickness of the sheet.
  • 3 hardness impressions each for the 1/4 position are positioned between 20% and 30% and 70% and 80% distance from the surface based on the thickness of the sheet.
  • 3 hardness impressions each for the 1/2 position are positioned between 40% and 50% and 50% and 60% distance from the surface based on the thickness of the sheet.
  • alloy compositions of two exemplary embodiments are summarized in Table 1. Alloys A and B are single casts, so all examples A1-A14 and B1-B20 have the same compositions. Table 1 also shows the calculated values for the hyper-stoichiometric ratio of carbon and nitrogen to micro-alloying elements (formula 2), i.e.
  • Table 1 shows the alloy compositions of two examples.
  • Tables 2 and 3 show the results from different exemplary embodiments. Also shown is an evaluation of the results with regard to achieving the required characteristic values with J (achieved) and N (not achieved). If the specifications according to the invention, according to the 2nd line in the tables, are not met, is marked with an underscore. The listed values are commercially rounded.
  • Table 2 lists the results for the mechanical characteristics with different process conditions. The underlined values are outside the required mechanical properties or outside the targeted process conditions.
  • EWT final rolling temperature
  • the cooling process T(t) is divided into n equal periods of time t, with the associated temperatures T , where n must be selected sufficiently large so that the result remains almost the same when divided into significantly more periods of time.
  • the strength contribution S P due to the formation of precipitates is determined in the following steps:
  • the material-related causes for the different local cold formability at high strength were analyzed using microstructure components and features in longitudinal sections.
  • the bainitic structure of the hot strip produced according to the invention consists of a main component of ⁇ 50% and secondary components, the main component being bainitic ferrite, which is strengthened by precipitations of (Ti, Nb, Mo)(C,N).
  • the minor components consist of higher carbon components such as martensite, MA phase, lower bainite, and pearlite. Since the main component has a higher formability than the secondary components, a minimum proportion of the main component of ⁇ 50% is advantageous.
  • Table 3 shows the results of the microstructure investigations for alloy A for different final rolling temperatures according to formula 3, different coiling temperatures according to formula 4 and HP values according to formula 5.
  • the structure of the hot strip samples is inhomogeneous and anisotropic across the strip thickness.
  • the inhomogeneity and the anisotropy can be described as follows for the two samples A2 and A6 with the HP values 17232 and 18380: a.
  • the samples consist of a ferritic-bainitic structure.
  • the ferrite content is 48% and 66%.
  • the deviation in the proportion of ferrite in the near-surface position and the %thickness position with respect to the 1/2thickness position is at most 59% and 17%.
  • the stretching of the structure is comparatively pronounced. This is especially true for item 14 thickness; here the aspect ratio is 2.9 and 2.5. i.e.
  • the hardness over thickness varies comparatively strongly.
  • the hardness on the surface in particular is lower and deviates by -24 HV0.1 and -26 HV0.1 from the mean value over the sample thickness.
  • the shear texture components vary relatively widely, being 0.92 and 0.96 in the near-surface position and 0.01 and 0.01 in the 14 thickness position.
  • An EWT of at least EWTmin according to formula 3 is necessary for complete recrystallization across the strip thickness in every thickness range.
  • the structure of the hot-rolled strip samples is comparatively homogeneous and isotropic across the strip thickness.
  • the homogeneity and the isotropy can be described as follows for the two samples with the HP values 18380 (sample A7) and 17232 (sample A9): a.
  • the samples consist of a predominantly bainitic structure.
  • the ferrite content is 22% and 49%.
  • the deviation in the proportion of ferrite in the near-surface position and the % thickness position with respect to the 1/2 thickness position is at most 7% and -2%.
  • the structural elongation is comparatively low. This is especially true for item 14 thickness; here the aspect ratio is 1.5 and 1.5. i.e. Hardness over thickness varies comparatively little.
  • the target-oriented structure was further characterized in the following point:
  • At least half of the precipitates of (Ti,Nb,Mo)(C,N) strengthening the main bainitic ferrite component are ⁇ 10 nm in diameter and/or the precipitates have an average spacing of less than 750 nm .
  • FIG. 1 shows a summary of the range of cold workability claimed according to the invention, which is limited by the data for FL and LFR.
  • FIG. 2 shows the positioning of the hardness indentations at a distance from the surfaces (0% and 100%): 0.1 mm and a distance from the center (50%): 0.1 mm, and the EBSD measuring fields at a distance from the surface (0%): 0.1mm Distance from center (50%): 0.1mm.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

Un objet de la présente invention est de fournir un produit plat en acier laminé à chaud à haute résistance et un procédé de production d'un tel produit plat en acier, et par conséquent d'obtenir, sur la base de l'acier, une combinaison de résistance élevée avec une aptitude au formage à froid locale élevée et une viabilité économique élevée. Cela est réalisé par un produit plat en acier laminé à chaud à haute résistance présentant une aptitude au formage à froid locale élevée, ayant une résistance à la traction Rm d'au moins 760 MPa, un rapport de limite d'élasticité d'au moins 0,8 et un rapport d'expansion de trou d'au moins 30 %, avantageusement au moins 40 %, de façon particulièrement avantageuse au moins 50 %, un allongement à la rupture d'au moins 10 %, de préférence au moins 16 %, une mesure de l'aptitude au formage à froid d'au moins 0,12, avantageusement au moins 0,17, et un rapport d'aptitude au formage à froid locale et globale d'au moins 5 et d'au plus 13, et une microstructure constituée de plus de 50 % en volume de bainite et jusqu'à 10 % en volume, avantageusement jusqu'à 5 % en volume, de constituants de microstructure riches en carbone tels que la martensite, l'austénite résiduelle, la perlite, la ferrite durcie par précipitation résiduelle, avec la composition chimique suivante de l'acier (en % en poids) : C : 0,04 à 0,08 ; Si : 0,1 à 0,6 ; Mn : 1,0 à 2,0 ; P : max 0,06 ; S : max 0,01 ; N : max 0 012 ; Al : jusqu'à 0,06 ; Ti : jusqu'à 0,18 et/ou Nb : jusqu'à 0,08 ; Mo : jusqu'à 0,35 ; avec Ti + Nb supérieur à 0,06, où il existe une proportion superstoechiométrique de carbone et d'azote selon la formule suivante : 1,0 < (C/12 + N/14) / (Ti/48 + Nb/93 + Mo/96), le reste étant du fer comprenant des éléments accompagnant l'acier inévitables.
PCT/EP2022/054616 2021-02-25 2022-02-24 Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d'un tel produit plat en acier WO2022180146A1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
MX2023007872A MX2023007872A (es) 2021-02-25 2022-02-24 Producto de acero plano laminado en caliente, de alta resistencia que tiene alta formabilidad en frio local y un metodo para producir tal producto de acero.
CN202280016717.8A CN116888283A (zh) 2021-02-25 2022-02-24 具有高局部冷成型性的高强度热轧扁钢产品及用于制造这种扁钢产品的方法
EP22708897.8A EP4298255A1 (fr) 2021-02-25 2022-02-24 Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d?un tel produit plat en acier
KR1020237028391A KR20230148167A (ko) 2021-02-25 2022-02-24 높은 국부 냉간 성형성을 갖는 고강도 열간 압연 평탄 강 제품 및 이러한 평탄 강 제품을 제조하는 방법
US18/547,444 US20240141450A1 (en) 2021-02-25 2022-02-24 High-strength hot-rolled flat steel product having high local cold formability and a method of producing such a flat steel product

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102021104584.3 2021-02-25
DE102021104584.3A DE102021104584A1 (de) 2021-02-25 2021-02-25 Hochfestes, warmgewalztes Stahlflachprodukt mit hoher lokaler Kaltumformbarkeit sowie ein Verfahren zur Herstellung eines solchen Stahlflachprodukts

Publications (1)

Publication Number Publication Date
WO2022180146A1 true WO2022180146A1 (fr) 2022-09-01

Family

ID=80683923

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2022/054616 WO2022180146A1 (fr) 2021-02-25 2022-02-24 Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d'un tel produit plat en acier

Country Status (7)

Country Link
US (1) US20240141450A1 (fr)
EP (1) EP4298255A1 (fr)
KR (1) KR20230148167A (fr)
CN (1) CN116888283A (fr)
DE (1) DE102021104584A1 (fr)
MX (1) MX2023007872A (fr)
WO (1) WO2022180146A1 (fr)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012002079A1 (de) 2012-01-30 2013-08-01 Salzgitter Flachstahl Gmbh Verfahren zur Herstellung eines kalt- oder warmgewalzten Stahlbandes aus einem höchstfesten Mehrphasenstahl
US9540719B2 (en) * 2011-03-24 2017-01-10 Arcelormittal Investigacion Y Desarrollo Sl Hot-rolled steel sheet and associated production method
US20170183753A1 (en) * 2014-07-11 2017-06-29 Arcelormittal Hot Rolled Steel Sheet and Associated Manufacturing Method
US20190309398A1 (en) * 2016-08-05 2019-10-10 Nippon Steel & Sumitomo Metal Corporation Steel sheet and plated steel sheet
EP3516085B1 (fr) 2016-09-22 2020-07-08 Tata Steel IJmuiden B.V. Procédé de production d'un acier haute résistance laminé à chaud avec une excellente formabilité de bord tombé et d'excellentes performances de fatigue d'arête
EP3492611B1 (fr) 2017-12-04 2020-10-28 SSAB Technology AB Acier laminé à chaud à haute résistance et procédé de fabrication d'acier laminé à chaud à haute résistance
US20200399727A1 (en) * 2017-12-15 2020-12-24 Salzgitter Flachstahl Gmbh High-strength, hot-rolled flat steel product with high edge cracking resistance and, at the same time, high bake-hardening potential, and method for producing such a flat steel product

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100942088B1 (ko) 2005-03-28 2010-02-12 가부시키가이샤 고베 세이코쇼 확공 가공성이 우수한 고강도 열연 강판 및 그의 제조방법
CA2759256C (fr) 2009-05-27 2013-11-19 Nippon Steel Corporation Tole d'acier a haute resistance, tole d'acier metallisee par immersion a chaud et tole d'acier immergee a chaud dans un alliage qui presente d'excellentes caracteristiques de fatigue, d'allongement et au choc et procede de fabrication pour lesdites toles d'acier
JP5724267B2 (ja) 2010-09-17 2015-05-27 Ｊｆｅスチール株式会社 打抜き加工性に優れた高強度熱延鋼板およびその製造方法
MX2015014436A (es) 2013-04-15 2016-02-03 Jfe Steel Corp Lamina de acero laminada en caliente de alta resistencia y metodo para la produccion de la misma.
WO2014171427A1 (fr) 2013-04-15 2014-10-23 新日鐵住金株式会社 Tôle d'acier laminée à chaud
KR20190142768A (ko) 2017-04-20 2019-12-27 타타 스틸 네덜란드 테크날러지 베.뷔. 우수한 연성 및 신장 플랜지성을 가진 고강도 강 시트

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9540719B2 (en) * 2011-03-24 2017-01-10 Arcelormittal Investigacion Y Desarrollo Sl Hot-rolled steel sheet and associated production method
DE102012002079A1 (de) 2012-01-30 2013-08-01 Salzgitter Flachstahl Gmbh Verfahren zur Herstellung eines kalt- oder warmgewalzten Stahlbandes aus einem höchstfesten Mehrphasenstahl
US20170183753A1 (en) * 2014-07-11 2017-06-29 Arcelormittal Hot Rolled Steel Sheet and Associated Manufacturing Method
US20190309398A1 (en) * 2016-08-05 2019-10-10 Nippon Steel & Sumitomo Metal Corporation Steel sheet and plated steel sheet
EP3516085B1 (fr) 2016-09-22 2020-07-08 Tata Steel IJmuiden B.V. Procédé de production d'un acier haute résistance laminé à chaud avec une excellente formabilité de bord tombé et d'excellentes performances de fatigue d'arête
EP3492611B1 (fr) 2017-12-04 2020-10-28 SSAB Technology AB Acier laminé à chaud à haute résistance et procédé de fabrication d'acier laminé à chaud à haute résistance
US20200399727A1 (en) * 2017-12-15 2020-12-24 Salzgitter Flachstahl Gmbh High-strength, hot-rolled flat steel product with high edge cracking resistance and, at the same time, high bake-hardening potential, and method for producing such a flat steel product

Also Published As

Publication number Publication date
US20240141450A1 (en) 2024-05-02
EP4298255A1 (fr) 2024-01-03
DE102021104584A1 (de) 2022-08-25
KR20230148167A (ko) 2023-10-24
CN116888283A (zh) 2023-10-13
MX2023007872A (es) 2023-08-29

Similar Documents

Publication Publication Date Title
DE60125253T2 (de) Hochfestes warmgewalztes Stahlblech mit ausgezeichneten Reckalterungseigenschaften
DE60311680T3 (de) Hochfestes Stahlblech mit guter Kragenziehbarkeit sowie hervorragender Erweichungsfestigkeit in einer Wärmeeinflußzone und Herstellungsverfahren dafür
EP3571324B1 (fr) Produit plat en acier laminé à chaud constitué d&#39;un acier à phase complexe ayant une structure essentiellement bainitique et procédé pour fabriquer un tel produit plat en acier
EP3027784B1 (fr) Acier multiphase à haute résistance, micro-allié et contenant du silicium, présentant une résistance minimale à la traction de 750 mpa et des propriétés améliorées et procédé de fabrication d&#39;une bande à partir de cet acier
EP3221484B1 (fr) Procédé de production d&#39;une bande en acier polyphasé, durcissant à l&#39;air, ayant une haute résistance et ayant d&#39;excellentes propriétés de mise en oeuvre
DE60300242T2 (de) Zugfestes warmgewalztes Stahlblech mit ausgezeichneter Bruchdehnung und Streckbördelverformfähigheit und dessen Herstellungsverfahren
EP3535431B1 (fr) Produit d&#39;acier à teneur en manganèse intermédiaire pour application à basse température et son procédé de fabrication
EP3221478B1 (fr) Bande à chaud ou à froid d&#39;un acier multiphasé à haute résistance durcissant à l&#39;air qui présente d&#39;excellentes propriétés de traitement et procédé de fabrication d&#39;une bande à chaud ou à froid à partir de cet acier multiphasé à haute résistance durcissant à l&#39;air
EP2366035A1 (fr) Feuillard d&#39;acier au manganèse à teneur accrue en phosphore et son procédé de fabrication
EP2905348B1 (fr) Produit en acier plat de haute résistance avec une structure bainitique-martensitique et procédé de fabrication d&#39;un tel produit acier plat
EP3221483B1 (fr) Acier multiphases autotrempant en profondeur à haute résistance mécanique avec excellent aptitude au faconnage et procédé de fabrication d&#39;une bande de cet acier
DE3401406A1 (de) Verfahren zur herstellung von stahlplatten mit hoher zugfestigkeit
EP3692178B1 (fr) Procede de fabrication d&#39;une bande d&#39;acier a partir d&#39;un acier multiphase a tres haute resistance
EP3974554A1 (fr) Produit plan en acier ayant une bonne résistance au vieillissement et son procédé de fabrication
EP3724359B1 (fr) Produit plat en acier laminé à chaud, à rigidité élevée, doté d&#39;une résistance à la fissuration de bords élevée ainsi que d&#39;une capacité de durcissement à la cuisson élevée et procédé de fabrication d&#39;un tel produit plat en acier
DE69724023T2 (de) Herstellungsverfahren eines dicken Stahlgegenstandes mit hoher Festigkeit und hoher Zähigkeit und hervorragender Schweissbarkeit und minimaler Variation der strukturellen und physikalischen Eigenschaften
DE112006003553B9 (de) Dicke Stahlplatte für eine Schweißkonstruktion mit ausgezeichneter Festigkeit und Zähigkeit in einem Zentralbereich der Dicke und geringen Eigenschaftsänderungen durch ihre Dicke und Produktionsverfahren dafür
DE60210767T2 (de) Hochzugfestes warmgewalztes stahlblech mit hervorragender masshaltigkeit und hervorragenden dauerfestigkeitseigenschaften nach dem formen
WO2020201352A1 (fr) Produit plat laminé à chaud en acier et son procédé de fabrication
EP4298255A1 (fr) Produit plat en acier laminé à chaud à haute résistance ayant une aptitude au formage à froid locale élevée et procédé de production d?un tel produit plat en acier
EP4136265A1 (fr) Procédé de fabrication d&#39;une bande d&#39;acier à structure multiphasée et bande d&#39;acier associée
WO2023025635A1 (fr) Produit plat en acier laminé à froid et son procédé de production
EP4301885A1 (fr) Produit plat en acier, son procédé de production, et utilisation d&#39;un tel produit plat en acier
DE102004025717B9 (de) Höherfester Multiphasenstahl mit verbesserten Eigenschaften

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22708897

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: MX/A/2023/007872

Country of ref document: MX

WWE Wipo information: entry into national phase

Ref document number: 18547444

Country of ref document: US

WWE Wipo information: entry into national phase

Ref document number: 202280016717.8

Country of ref document: CN

WWE Wipo information: entry into national phase

Ref document number: 2022708897

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: DE

ENP Entry into the national phase

Ref document number: 2022708897

Country of ref document: EP

Effective date: 20230925