EP4139492A1 - Produit d'acier plat laminé à chaud et son procédé de fabrication - Google Patents

Produit d'acier plat laminé à chaud et son procédé de fabrication

Info

Publication number
EP4139492A1
EP4139492A1 EP20721198.8A EP20721198A EP4139492A1 EP 4139492 A1 EP4139492 A1 EP 4139492A1 EP 20721198 A EP20721198 A EP 20721198A EP 4139492 A1 EP4139492 A1 EP 4139492A1
Authority
EP
European Patent Office
Prior art keywords
hot
steel
flat steel
mass
steel product
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
EP20721198.8A
Other languages
German (de)
English (en)
Inventor
Nicholas WINZER
Ekaterina Bocharova
Roland Sebald
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.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
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 ThyssenKrupp Steel Europe AG filed Critical ThyssenKrupp Steel Europe AG
Publication of EP4139492A1 publication Critical patent/EP4139492A1/fr
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • 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
    • B21B1/46—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 metal immediately subsequent to continuous casting
    • B21B1/463—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 metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—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
    • C22C38/001—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
    • C22C38/02—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
    • C22C38/12—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
    • C22C38/22—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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
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    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • 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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—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
    • C23C2/04—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
    • 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
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    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C23C2/29—Cooling or quenching
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    • 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
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium

Definitions

  • the invention relates to a hot-rolled flat steel product which comprises a steel substrate and a zinc anti-corrosion layer applied thereon by hot-dip coating.
  • the invention also relates to a method for producing such a flat steel product.
  • flat steel products are understood to mean rolled products, the length and width of which are each significantly greater than their thickness. These include, in particular, steel strips and steel sheets.
  • impurities of a steel, zinc or other alloy are technically unavoidable steel components that get into the steel during production or cannot be completely removed from it, but whose contents are in any case so low that they have no influence on the properties of the steel.
  • the image analysis for quantitative structure determination is carried out optically by means of light microscopy (“LOM”) with 200 to 2,000 times and with a scanning electron microscope (“SEM”) with 2,000 to 20,000 times magnification.
  • LOM light microscopy
  • SEM scanning electron microscope
  • the distribution of manganese (Mn) in the structure of the steel substrate of a flat steel product according to the invention has been determined by wavelength-dispersive X-ray micro-range analysis (WDX) of the structure, which was published, for example, by Reimer L. (1998) in “Elemental Analysis and Imaging with X-Rays” in Scanning Electron Microscopy, Springer Series in Optica! Sciences, Vol. 45. Springer, Berlin, Heidelberg.
  • WDX wavelength-dispersive X-ray micro-range analysis
  • the strength and elongation properties mentioned here such as tensile strength Rm, yield point Rp0.2, uniform elongation Ag, elongation A50 and elongation A80 of flat steel products were determined in tensile tests according to DIN-EN 6892-1: 2017, unless otherwise noted.
  • Highly stressed passenger and truck components such as crash structures and chassis of automobile bodies, require a hot-dip galvanized steel sheet with a thickness of more than 1.5 mm and a tensile strength of more than 590 MPa.
  • Hot-rolled flat steel products which are made of complex phase steels (CP-W), the structure of which consists largely of bainite, are often used for the production of such components.
  • CP-W steels however, suffer from a relatively lower deformability, which prevents the design of geometrically complex components.
  • Dual-phase steels which consist of a combination of hard (e.g. martensite or bainite) and soft (e.g. ferrite) phases, are suitable for complex components due to their combination of high strength and good ductility.
  • DP-W hot-rolled dual-phase steels
  • the sheet must be heated to temperatures of more than 460 ° C (the zinc bath temperature). At these temperatures, however, the hard component of the structure, in particular martensite, is tempered, with the result that the DP characteristics are lost.
  • This procedure is similar to the manufacturing process of a DP-K steel with the exception of the cold rolling step.
  • a high-strength multiphase steel with minimum tensile strengths of 580 MPa is known from DE 102012013 113 A1.
  • the steel should preferably have a dual-phase structure and make it possible to produce cold-rolled or hot-rolled steel strips with improved forming properties, from which parts for lightweight vehicle construction in particular can be produced.
  • the known multiphase steel consists of, in mass%, 0.075% ⁇ C ⁇ 0.105%, 0.600% ⁇ Si ⁇ 0.800%, 1,000% ⁇ Mn ⁇ 2.250%, 0.280% ⁇ Cr ⁇ 0.480%, 0.010% ⁇ AI ⁇ 0.060%, ⁇ 0.020% P, ⁇ 0.0100% N, ⁇ 0.0150% S and the remainder of iron and impurities.
  • Another high-strength multiphase steel with a minimum tensile strength of 580 MPa is the steel known from DE 102012006017 A1.
  • the known steel consists of, in% by mass, 0.075% C 0.105%; 0.200% ⁇ Si ⁇ 0.300%, 1.000% ⁇ Mn ⁇ 2.000%, 0.280% ⁇ Cr ⁇ 0.480%, 0.010% ⁇ Al ⁇ 0.060%, up to 0.020% P, 0.005% ⁇ Nb ⁇ 0.025%, up to 0, 0 100% N, up to 0.0050% S and the remainder of iron and technically unavoidable impurities.
  • the steel known from DE 102013013067 A1 also belongs to the type of known multiphase steels explained above, which preferably have a dual-phase structure and are intended to be suitable for cold-rolled or hot-rolled steel strip with improved forming properties.
  • This known steel should have a maximum yield strength ratio of 73% and, in% by mass, 0.075% ⁇ C ⁇ 0.105%, 0.600% ⁇ Si ⁇ 0.800%, 1,000% ⁇ Mn ⁇ 1, 900%, 0.100% ⁇ Cr ⁇ 0.700%, 0.010% ⁇ AI ⁇ 0.060%, 0.0020% ⁇ N ⁇ 0.0120%, ⁇ 0.0030% S, 0.005% ⁇ Nb ⁇ 0.050%,
  • the invention should specify a method with which the production of flat steel products obtained according to the invention is operationally reliable.
  • the invention thus provides a hot-rolled flat steel product which comprises a steel substrate and a zinc (Zn) -based anti-corrosion layer applied thereon by hot-dip coating.
  • the steel of the steel substrate of a flat steel product according to the invention consists of, in% by mass,
  • the unavoidable impurities including less than 0.02% P, less than 0.005 S, less than 0.01% N and less than 0.005% Nb.
  • the steel substrate of a flat steel product according to the invention is at least 1.5 mm thick and has a structure that consists of, in area%, in total 50-90% ferrite and bainitic ferrite, 5-50% martensite, 2-15% residual austenite and up to 10% unavoidable other structural components due to the manufacturing process.
  • a flat steel product according to the invention has a yield point Rp0.2 of at least 290 MPa, a tensile strength Rm of at least 490 MPa and an elongation at break A80, which is determined according to the following formula (1):
  • A80 [%] B - Rm / 37 with 31 ⁇ B ⁇ 51.
  • a flat steel product according to the invention can be produced by going through at least the following work steps:
  • Hot rolling of the preliminary product into a hot-rolled steel strip the final temperature of the hot-rolling being at least 840-980 ° C and the thickness of the hot-rolled steel strip being 1.5-10 mm;
  • B.3 Cooling the hot-rolled steel strip at a cooling rate of 0.5-100 ° C / s to a bath inlet temperature BET, for which BT ⁇ BET ⁇ (BT + 20 ° C), where BT denotes the temperature of the molten zinc bath which is 450-480 ° C; B.4) Passing the hot-rolled steel strip cooled to the bath inlet temperature BET through the molten zinc bath, which consists of up to 5% by mass of Mg, up to 10% by mass of Al, the remainder Zn and unavoidable impurities;
  • a preheating temperature of at least 1150 ° C is required in step A.1 in order to completely homogenize the structure of the preliminary product.
  • the microstructure of the preliminary product would be passed on to the subsequently produced hot strip, so that the Mn segregations aimed at according to the invention could not be formed.
  • the alloying elements would remain bound in precipitates, so that their effects on the mechanical properties of a flat steel product according to the invention could not develop.
  • a final hot-rolling temperature of at least 840 ° C is required in order to be able to reliably roll the intermediate product alloyed according to the invention into a hot-rolled steel strip.
  • the rolling forces would be too high and the associated risk of damage to the rolls of the rolling stands used for hot rolling would increase disproportionately.
  • a hot rolling end temperature of at least 880 ° C can be provided.
  • the final hot rolling temperature should not exceed 980 ° C., since final hot rolling temperatures above this upper limit cannot be achieved in practice.
  • the steel strip hot-rolled according to the invention must be at least 1.5 mm thick so that the Mn segregations aimed at according to the invention can arise in the structure after hot rolling.
  • the hot-rolled steel strip would experience excessive deformations during hot-rolling, which in turn would result in an undesirable homogenization of the Mn distribution in the structure of the hot-rolled steel strip.
  • a steel belt with a thickness of more than 10 mm cannot be used for the intended purpose.
  • the maximum tape thickness is limited to 10 mm.
  • the coiling temperature at which the hot-rolled steel strip, which forms the steel substrate of the flat steel product according to the invention, is reeled is at least 510 ° C. in order to ensure that Mn segregation occurs during the cooling of the hot-rolled steel strip in the coil.
  • Higher reel temperatures can promote this process, so that reel temperatures of at least 530 ° C., in particular at least 550 ° C., are particularly advantageous. If the coiling temperatures are too low, an undesirably homogeneous Mn distribution would result, with which the mechanical properties aimed for according to the invention would not be achieved. Too high a coiling temperature would trigger the risk of pronounced grain boundary oxidation. To prevent this, the coiling temperature is limited to 640 ° C, preferably 620 ° C.
  • the hot-rolled steel strip can, if necessary, be pickled in a conventional manner in order to remove any scale present on the steel strip or to prepare the surface of the steel strip for the subsequent work steps.
  • the hot-rolled steel strip is first heated to an annealing temperature in a preheating stage at a rate of 0.5-100 ° C per second.
  • the heating rate must lie within this window in order to ensure sufficient transformation of the structure, in particular its complete recrystallization.
  • a Annealing temperature 750 - 950 ° C and a holding time of 10 - 1000 seconds required. If the annealing temperatures are too low or the holding times are too short, the structure would not completely recrystallize, with the result that there would not be enough austenite available during the subsequent cooling to form the desired martensite content of the structure.
  • An unrecrystallized steel substrate would also result in pronounced anisotropy of the mechanical properties of a flat steel product according to the invention.
  • the cooling from the annealing temperature to the zinc bath inlet temperature BET also takes place at a cooling rate of 0.5 to 100 ° C. per second.
  • the bath inlet temperature BET is at least the same and at most 20 ° C. higher than the melt bath temperature in order to prevent the melt bath temperature from changing significantly due to the introduction of the hot-rolled steel strip.
  • the hot-dip coating can be followed by a further heat treatment (“galvannealing") in which the hot-dip coated steel flat product is heated to up to 550 ° C in order to burn in the previously applied corrosion protection layer.
  • galvannealing a further heat treatment
  • the flat steel product obtained is cooled to room temperature at a cooling rate of 0.5-100 ° C./s.
  • the flat steel product produced in this way can optionally also be subjected to conventional skin pass rolling in order to optimize its dimensional accuracy and surface quality.
  • the skin-pass degree set is typically at least 0.3% and at most 2.0%, with skin-pass degrees of at least 0.5% having proven to be particularly practical.
  • a skin pass degree of less than 0.3% leads to a lower surface roughness of the corrosion protection layer, which would have a negative impact on the formability of the flat steel product.
  • the degree of skin pass is more than 2.0%, the yield strength Rp0.2 is increased and the elongation at break A80 is reduced, so that an elongation at break according to formula 1 could not be achieved.
  • a flat steel product which comprises a steel substrate alloyed according to the invention and exhibiting a structure according to the invention achieves high elongation at break values in the hot-rolled state which are comparable to the elongations at break A80 which conventional cold-rolled flat steel products of the type explained at the beginning have (“DP-K Steels "), which have similar strengths.
  • elongation at break values A80 can regularly be achieved for which parameter B in formula (1) is at least in the range 31-51, preferably 36-46.
  • the combination of high strength and high elongation at break results from the proportion of 2-15% retained austenite in the steel substrate of a flat steel product according to the invention, with retained austenite proportions of at least 5% by area regularly being present in the structure of the steel substrate of a flat steel product according to the invention and having a positive effect affect the mechanical properties of the flat steel product.
  • the retained austenite contents that can be determined in the flat steel product according to the invention are thus significantly higher than in a cold-rolled flat steel product with a comparable alloy.
  • the presence of larger residual austenite fractions in the structure is a consequence of the inheritance of Mn segregations, which are present in the hot-rolled steel substrate of a flat steel product according to the invention and are retained via the annealing treatment that the flat steel product undergoes for its hot-dip coating. It was thus possible to show that in the method according to the invention of producing a flat steel product according to the invention after coiling (sub-step A.6 of the method according to the invention) and before hot-dip coating (step B of the method according to the invention), the hot-rolled steel substrate is very has anisotropic and inhomogeneous structure with a high pearlite content, which is in line form.
  • Wavelength-dispersive X-ray micro-range analyzes (WDX) of the structure have shown that Mn segregates in the pearl cords and that the Mn segregations are very anisotropic and inhomogeneous distribution after reeling and before hot-dip coating.
  • the steel substrate of a flat steel product according to the invention undergoes annealing (substep B.2 of the method according to the invention) before entering the molten bath, during which it is kept at the annealing temperature for a period of time.
  • the annealing temperature and the annealing duration are coordinated with one another in such a way that there is no redistribution of the Mn segregations.
  • both the transformation temperature and the residual austenite content after cooling are more inhomogeneously distributed compared to hot-rolled flat steel products which, contrary to the provisions of the invention, have been coiled at lower temperatures .
  • the structural areas of the steel substrate in which there is a higher Mn concentration convert more easily and thus retain more austenite after cooling than the microstructural areas in which a lower Mn concentration is present. These convert at higher temperatures or not at all, which means that a higher proportion of the original ferrite is retained there.
  • the inhomogeneity of the Mn distribution in the steel substrate of a completely processed flat steel product according to the invention can be quantified by the total area of the structure of the steel substrate in which there is an Mn concentration (in% by mass) that is more than 15% higher than the mean value of the Mn concentrations in the entire structure of the steel flat product.
  • the sum of the surface fractions of the structure of the steel substrate of a steel flat product according to the invention which have an Mn concentration that is more than 15% higher than the mean value of the Mn concentration in the entire structure is expressed as “X “In a flat steel product according to the invention, X is at least 10%, in particular at least 12%, advantageously at least 15% of the total structure.
  • the area proportions forming the sum X can be evaluated using a WDX measurement, with the Mn concentration typically being over a measuring area of at least 200 x 200 ⁇ m with a step size of 0.5 ⁇ m is determined.
  • the steel of the steel substrate of a steel flat product according to the invention which is present as a hot-rolled steel strip in the course of production according to the invention, is composed as follows:
  • Carbon (C) is present in the steel substrate of a flat steel product according to the invention in contents of 0.04-0.23% by mass.
  • C is an essential element for the formation of martensite and austenite, which are required in order to achieve the strength properties required of a steel flat product according to the invention. So that this effect occurs to a sufficient extent, the steel according to the invention contains at least 0.04% by mass, the desired effect being achieved particularly reliably with C contents of at least 0.07% by mass. Too high a C content would have a negative effect on the welding behavior of the flat steel product.
  • the general rule here is that the weldability of a steel decreases with the level of its C content.
  • the C- Content limited to a maximum of 0.23% by mass, in particular a maximum of 0.20% by mass, with contents of at most 0.17% by mass being able to avoid the negative effects of the presence of C with particular certainty.
  • Si Silicon
  • Si is present in the steel substrate of a flat steel product according to the invention in contents of 0.04-0.54% by mass. Si is required to suppress the formation of pearlite in the structure during annealing, which would have a negative effect on the mechanical properties of the end product. A minimum Si content of 0.04% by mass is required for this. An excessively high Si content also prevents the formation of pearlite during coiling and the associated segregation of Mn in the structure of the steel substrate. Substantial segregation of Mn during coiling is required to achieve a high sum X and the desired mechanical properties. Too high a Si content would also impair the surface quality of a flat steel product according to the invention. For these reasons, the upper limit of the Si content is limited to 0.54 mass%.
  • Aluminum (Al) can optionally be added to the steel substrate of a flat steel product according to the invention in contents of 0.01-1.5% by mass in order to help suppress the formation of pearlite. Even if Al is used in the usual way to deoxidize the melt, the minimum Al content is 0.01% by mass. However, too high an Al content can have a negative effect on the castability of the steel and worsen the coating behavior during hot-dip coating. These negative influences of the presence of Al in the steel of the substrate of a flat steel product according to the invention can be avoided particularly reliably by limiting the Al content to a maximum of 1.0 mass%, in particular a maximum of 0.5 mass%.
  • Manganese (Mn) is present in the steel substrate of a flat steel product according to the invention in contents of 1.4-2.9% by mass. Mn is a mixed crystal element that contributes to the strength of the material. The presence of Mn in the steel of the substrate of a flat steel product according to the invention also stabilizes the austenite in the structure of the substrate.
  • a flat steel product according to the invention is an optimal combination of high tensile strength and high elongation at break as a result of the segregation of Mn in the bead strands of the steel substrate after coiling, which is also then remain intact when the flat steel product for the hot-dip coating has been annealed and has passed through the hot-dip bath.
  • Mn contents of at least 1.4% by mass are required, with regard to the reliability with which the positive influence of Mn on the properties of a flat steel product according to the invention sets, it is favorable if the Mn content is at least 1.5 mass%.
  • the upper limit of the Mn content of the steel substrate of a flat steel product according to the invention is limited to 2.9% by mass, preferably 2.5% by mass, the amount of Mn being added to the properties of a flat steel product according to the invention at Mn contents of up to 2.2 mass% can be used particularly effectively.
  • Chromium (Cr) and molybdenum (Mo) can be added to the steel of the steel substrate of a flat steel product according to the invention as optional elements for increasing strength.
  • Cr and / or Mo increases the formation of martensite compared to pearlite when the flat steel product is cooled from the intercritical area in a continuous coating system. If these effects are to be used, so are for this Contents of Cr and Mo required which total at least 0.02% by mass, in particular at least 0.05% by mass. If the Cr content is too high, however, the risk of pronounced grain boundary oxidation would be increased. Too high a Mo content should also be avoided for reasons of cost.
  • the upper limit of the total content of Cr and Mo is therefore set to 1.4% by mass, preferably 1.0% by mass.
  • Cr and Mo do not necessarily have to occur in combination, but can also be added to the steel alone in the contents of 0.02-1.4% by weight, in particular 0.05-1.0% by weight, specified according to the invention, to achieve the effects explained.
  • particularly beneficial effects result when Cr and Mo are present together in effective contents as long as the sum of these contents is within the limits according to the invention.
  • At least one of the elements titanium (Ti) and vanadium (V) is present as a mandatory component in the steel of the steel substrate of a flat steel product according to the invention in a content of 0.005-0.15% by mass, whereby it is also true here that an optimal effect of these elements occurs, when Ti and V are present together in effective contents.
  • Ti and V are micro-alloy elements that cause fine precipitates to form in steel. Such precipitates prevent the austenite grains from becoming coarser at temperatures which are higher than the Ar1 temperature of the steel, and in this way lead to a refinement of the structure.
  • a finer structure favors the segregation of Mn, which is aimed at according to the invention, during the reeling carried out in the course of the production of a flat steel product according to the invention, because the distance over which Mn diffuses is reduced by the presence of Ti and / or V.
  • Precipitations containing Ti and V also contribute to the strength of a flat steel product according to the invention through dispersion hardening.
  • Ti and V contents of at least 0.005 mass% in total is required. At contents above 0.15% by mass, the presence of Ti and / or V im results. With regard to the properties aimed for according to the invention, there is no longer any particular increase. Rather, Ti and V can be used particularly effectively when the sum of their contents does not exceed 0.1% by mass.
  • the content of niobium (Nb) is limited to less than 0.005% by mass, so that, if niobium is present at all, it is one of the impurities that are technically ineffective. Higher Nb contents would lead to the formation of fine Nb precipitates, which would make them susceptible to cracking during continuous casting or during slab cooling or reheating. Therefore, the Nb content is preferably limited to less than 0.003 mass%, in particular less than 0.002 mass%.
  • Boron (B) can also optionally be added to the steel of the steel substrate of a flat steel product according to the invention in contents of 0.0005-0.005% by mass in order to prevent the formation of ferrite during the cooling from the intercritical range during the production of the flat steel product.
  • B promotes the formation of bainite, which increases strength.
  • a minimum content of 0.0005 mass% B is required for this.
  • too high a B content can lead to undesirable embrittlement. Therefore, according to the invention, the upper limit of the ' B content, if B is added, is set to at most 0.005% by mass, in particular 0.002% by mass.
  • Phosphorus (P) is one of the undesirable but technically generally unavoidable impurities in the steel of the steel substrate of a flat steel product according to the invention and should therefore be as low as possible. P proves particularly unfavorable in terms of weldability. In order to safely avoid its unfavorable influence, the P content is according to the invention to less than 0.02 mass%, preferably less than 0.01 mass%, in particular less than 0.005 mass%.
  • S is also one of the undesirable but technically generally unavoidable impurities in the steel of the steel substrate of a flat steel product according to the invention and should therefore be as low as possible.
  • S leads to the formation of MnS or (Mn, Fe) S, which would have a negative effect on the elongation behavior of a flat steel product according to the invention.
  • the S content is limited according to the invention to less than 0.005% by mass, preferably less than 0.002% by mass.
  • N Nitrogen
  • N is also one of the undesirable, but technically generally unavoidable impurities in the steel of the steel substrate of a flat steel product according to the invention and should therefore be as low as possible.
  • N forms nitrides with aluminum or titanium. In the case of higher N contents, this would lead to coarse precipitations, which could be detrimental to the formability of the flat steel product.
  • the N content is therefore limited to less than 0.01% by mass, preferably less than 0.005% by mass.
  • the upper limit of the Ca content is limited to at most 0.005 mass%, preferably at most 0.002 mass%.
  • Copper (Cu), nickel (Ni), tin (Sn), arsenic (As), cobalt (Co), zircon (Zr), lanthanum (La) and / or cerium (Ce) are alloying elements that also contribute to the impurities of the Steel of the steel substrate of an inventive Flat steel product, the presence of which is undesirable per se.
  • the Cu content in the steel of the steel substrate of a flat steel product according to the invention is at most 0.2% by mass, the Ni content at at most 0.1% by mass, the Sn Content to a maximum of 0.05% by mass, the As content to a maximum of 0.02% by mass, the Co content to a maximum of 0.02% by mass, the Zr content to a maximum of 0.0002% by mass, the La content is limited to a maximum of 0.0002% by mass and the Ce content to a maximum of 0.0002% by mass.
  • Oxygen (O) is also an undesirable impurity, since the presence of larger amounts of O causes oxide deposits that have a negative effect both on the mechanical properties of the flat steel product and on the castability and rollability of the steel on its steel substrate.
  • the oxygen content is therefore limited to at most 0.005% by mass, preferably 0.002% by mass.
  • Hydrogen (H) is also one of the undesirable impurities in the steel of the steel substrate of a flat steel product according to the invention.
  • H is very mobile in interstitial spaces in steel and can lead to tears in the core when it cools down from hot rolling, especially in high-strength steels.
  • the content of H in the steel of the steel substrate of a flat steel product according to the invention is therefore to a maximum of 0.001% by mass, preferably a maximum of 0.0006% by mass, more preferably a maximum of 0.0004% by mass, most preferably a maximum of 0.0002% by mass, reduced.
  • the corrosion protection coating of a flat steel product according to the invention consists in its main part of zinc (Zn) and can otherwise be composed in a conventional manner. Accordingly, in addition to Zn and unavoidable impurities, the corrosion protection layer can contain up to 20% by mass Fe, up to 5% by mass
  • Mg Contain Mg and up to 10% by mass of Al.
  • at least 5% by mass of Fe, at least 1% by mass of Mg and / or at least 1% by mass of Al are provided in order to achieve optimal usage properties of the corrosion protection.
  • steels A - I were melted and cast into slabs, the composition of which is given in Table 1. Contents of an alloy element that are so low that they are “0” in the technical sense, that is, so low that they have no influence on the properties of the steel, are listed in Table 1 by the entry designated.
  • the slabs were thoroughly heated in a preheating furnace in which a preheating temperature VT prevailed.
  • the preheated slabs were then hot-rolled in a conventional manner into hot-rolled steel strips W1-W35, the hot-rolling having been terminated at a final rolling temperature ET.
  • the hot-rolled steel strips W1-W35 obtained in this way have, starting from a coiling temperature HT, been reeled into a coil in an equally conventional manner. For this purpose, if necessary, they have been cooled in a conventional manner to the reel temperature HT prior to reeling.
  • one of the combinations I-VIII given in Table 2 is required in the production of the hot-rolled steel strips W1-W35, which each consisted of one of the steels A-I of preheating furnace temperature VT, hot rolling end temperature ET and coiling temperature HT.
  • the preheating furnace temperatures VT, hot rolling end temperatures ET and coiling temperatures HT associated with each of the combinations I - VIII are given in Table 2.
  • Those preheating furnace temperatures VT, hot rolling end temperatures ET and coiling temperatures HT which in each case did not correspond to the requirements of the invention, are emphasized by underlining.
  • the hot-rolled steel strips W1 - W35 After cooling in the coiler, the hot-rolled steel strips W1 - W35 have been coated with a Zn-based corrosion protection layer by hot-dip coating. For this purpose, they were each subjected to one of six variants a - f of an annealing treatment and a melt application, in which they were heated in a preheating stage at a heating rate HR to an annealing temperature GT, at which they were then annealed for an annealing period of 40 s to 100 s have been held. The hot-rolled steel strips W1-W35 were then cooled at a cooling rate KR1 to a bath inlet temperature BET which was the same as the bath temperature of the melt bath through which the hot strips were passed after the respective annealing treatment a-f.
  • the molten bath consisted of at least 99% Zn by mass.
  • the now finished steel flat products emerging from the molten bath and produced on the basis of the hot-rolled steel strips W1 - W35 were then cooled to room temperature at a cooling rate KR2 Annealing treatment and the parameters associated with the melt application: heating rate HR, annealing temperature GT, cooling rate KR1, bath inlet temperature BET and cooling rate KR2 are shown in Table 3.
  • the slab was heated with a preheating temperature VT that was too low, so that the slab was not completely annealed. As a result, the alloying elements and the manufacturing process did not affect the mechanical properties.
  • the hot-rolled steel strip W3 contains too little Mn, so that Mn has not segregated to a sufficient extent in the pearl cords of the hot-rolled strip structure. This led to a lower residual austenite content and therefore to a relatively low elongation at break A80 of the flat steel product produced from the hot-rolled steel strip W3. As a result, parameter B was below 31 there.
  • the GT set was too low, so that the structure was not completely recrystallized. This resulted in a low austenite content in the structure of the steel substrate of the flat steel product obtained and therefore in a low elongation at break A80.

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Abstract

L'invention concerne un produit d'acier plat laminé à chaud d'une épaisseur inférieure à 1,5 mm qui présente des propriétés mécaniques optimisées et est particulièrement adapté pour l'application d'une couche de protection contre la corrosion à base de Zn par revêtement par immersion à chaud. À cet effet, le produit d'acier plat est constitué, en % en masse, de C : 0,04 à 0,23 %, Si : 0,04 à 0,54 %, Mn : 1,4 à 2,9 %, Ti + V, la somme de %Ti + %V des teneurs en Ti et V étant telle que 0,005 % < %Ti+%V < 0,15 %, et, dans chaque cas, éventuellement un ou plusieurs éléments du groupe AI, Cr, Mo, B" avec des teneurs qui sont, le cas échéant, comme suit : Ai : 0,01 à 1,5 %, somme de %Cr + %Mo des teneurs en Cr et M : 0,02 < %Mo+%Cr < 1,4 %, B : 0,0005 à 0,005 %, le reste étant constitué de fer et d'impuretés inévitables, parmi ces impuretés inévitables on trouve < 0,02 % P, < 0,005 % S, < 0,01 % N et < 0,005 % Nb. La structure du produit d'acier plat est constituée, en pourcentage en surface, de 50 à 90 % de ferrite et de ferrite de bainite, de 5 à 50 % de martensite, de 2 à 15 % d'austénite résiduelle et < 10 % d'autres éléments de structure. En même temps, le produit d'acier plat a un point d'élasticité Rp0,2 > 290 MPa, une résistance à la traction Rm > 490 MPa et un allongement à la rupture A80 qui est calculé selon la formule suivante (1) : A80 [%] = B - Rm / 37 avec 31 < B < 51. Sur au moins une surface du produit d'acier plat, un revêtement en Zn est appliqué par revêtement par immersion à chaud. L'invention concerne en outre un procédé de production d'un produit d'acier plat de ce type.
EP20721198.8A 2020-04-22 2020-04-22 Produit d'acier plat laminé à chaud et son procédé de fabrication Pending EP4139492A1 (fr)

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