EP3947754B1 - Method for producing a steel sheet with improved adhesion of metallic hot-dip coatings - Google Patents

Method for producing a steel sheet with improved adhesion of metallic hot-dip coatings Download PDF

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Publication number
EP3947754B1
EP3947754B1 EP20715830.4A EP20715830A EP3947754B1 EP 3947754 B1 EP3947754 B1 EP 3947754B1 EP 20715830 A EP20715830 A EP 20715830A EP 3947754 B1 EP3947754 B1 EP 3947754B1
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EP
European Patent Office
Prior art keywords
iron
steel strip
layer
oxygen
zinc
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.)
Active
Application number
EP20715830.4A
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German (de)
French (fr)
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EP3947754A1 (en
Inventor
Dr. Kai KÖHLER
Dr. Nils KÖPPER
Dr.-Ing. Friedrich LUTHER
Dr. Marc DEBEAUX
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.)
Salzgitter Flachstahl GmbH
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Salzgitter Flachstahl GmbH
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Publication of EP3947754A1 publication Critical patent/EP3947754A1/en
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    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
    • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • 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
    • 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
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • 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
    • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/026—Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection
    • 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
    • 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
    • C23C2/34—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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C23C28/025—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only with at least one zinc-based layer
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/028—Including graded layers in composition or in physical properties, e.g. density, porosity, grain size
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C25D5/50—After-treatment of electroplated surfaces by heat-treatment
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/06—Wires; Strips; Foils
    • C25D7/0614—Strips or foils
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
    • C25D17/10—Electrodes, e.g. composition, counter electrode
    • 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
    • C25D3/20—Electroplating: Baths therefor from solutions of iron

Definitions

  • the invention relates to a method for producing a cold- or hot-rolled steel strip with a metallic coating, the steel strip having iron as the main component and, in addition to carbon, an Mn content of 4.1 to 8.0% by weight and optionally one or more of the alloying elements Al , Si, Cr, B, Ti, V, Nb and/or Mo, wherein the surface of the uncoated steel strip is cleaned, a layer of pure iron with an average iron content of more than 96% by weight is applied to the cleaned surface an oxygen-containing, iron-based layer is applied to the layer of pure iron, which contains more than 5 percent by mass of oxygen, after which the steel strip is annealed with the oxygen-containing, iron-based layer and is reduction-treated in the course of the annealing treatment in a reducing furnace atmosphere, and then the treated and annealed in this way Steel strip is hot dip coated with the metallic coating. Furthermore, the invention relates to a steel strip with a metallic coating applied by hot dipping and the use of such a steel strip.
  • the cited publication discloses, among other things, a method in which, during annealing under oxidizing conditions, the steel strip is pre-oxidized in a first step, with which a specifically covering FeO layer is produced, which prevents selective external oxidation of the alloying elements. In a second step, this layer is then reduced back to metallic iron.
  • the patent specification DE 10 2013 105 378 B3 discloses a method for producing a flat steel product which, in addition to iron and unavoidable impurities, contains up to 35 Mn, up to 10 Al, up to 10 Si and up to 5 Cr by weight. After heating in a preheating furnace, in which the flat steel product is exposed to an oxidizing atmosphere, and recrystallizing annealing in the annealing furnace, in which an annealing atmosphere that has a reducing effect on FeO prevails, the flat steel product is coated in a hot-dip bath.
  • the disclosure document DE 10 2010 037 254 A1 discloses a method for hot-dip coating a flat steel product, the flat steel product being produced from a stainless steel which, in addition to iron and unavoidable impurities, contains in % by weight: 5 to 30 Cr, ⁇ 6 Mn, ⁇ 2 Si and ⁇ 0.2 Al.
  • the steel flat product is first heated under an oxidizing pre-oxidation atmosphere, held under a reducing holding atmosphere, and then passed through a molten bath.
  • the Disclosures U.S. 2016 010 23 79 A1 and U.S. 2013 030 49 82 A1 each disclose a method for producing a coated steel strip containing in weight %: 0.5 to 2 Si, 1 to 3 Mn, 0.01 to 0.8 Cr and 0.01 to 0.1 Al. After an oxidation treatment of the steel strip in an oxidative atmosphere, the steel strip is subjected to reduction annealing and then hot-dip coated.
  • a method for producing a coated steel sheet with reduced surface defects in which a coating of zinc or a zinc alloy is applied to at least one surface of a steel strip.
  • a layer of Fe is provided immediately below the coating of zinc or a zinc alloy, and a layer in which elements of the steel with an affinity for oxygen are concentrated is provided directly below the layer of Fe.
  • the low-carbon or very low-carbon steel strip to which the Fe plating is applied contains at least one component selected from the group of Si, Mn, P, Ti, Nb, Al, Ni, Cu, Mo, V, Cr and B in one Amount of at least 0.1% by weight for Si, Ti, Ni, Cu, Mo, Cr and V and at least 0.5% by weight for Mn, at least 0.05% by weight for P, Al and Nb and at least 0.001% by weight for B.
  • the layer of Fe has an application weight of 0.1 to 10 g/m 2 , an oxygen content of 0.1 to 10% by weight and a carbon content of 0.01% by weight. % to less than 10% by weight.
  • the aim here is to create a layer at the interface between the oxygen-containing Fe layer and the steel strip during annealing prior to hot-dip coating, in which the elements with an affinity for oxygen contained in the steel are concentrated. This is intended to prevent further diffusion of the oxygen-affinity elements contained in the steel in the direction of the Fe plating surface and to achieve good galvanizability.
  • EP 2 798 094 A1 discloses a method for producing a cold-rolled steel strip with an Mn content between 1 and 6% by weight and a C content of less than 0.3% by weight and with a metallic coating.
  • the steel strip is electroplated with a layer of pure iron, then the iron layer is oxidized to an iron oxide layer and then reduced at a temperature between 750 °C and 900 °C in an atmosphere with 1 to 20% by volume of hydrogen.
  • a zinc coating is then applied by hot dip coating.
  • U.S. 2004/0 121 162 A1 already described a cold- or hot-rolled steel strip with up to 0.5% by weight of C and with up to 15% by weight of Mn and with a coating.
  • the coating comprises an iron plating and a metallic zinc coating.
  • the disclosure discloses CN 109 477 191 A another cold or hot rolled coated steel strip with a coating.
  • the steel strip has 0.08 to 0.3% by weight of C, 3.1 to 8.0% by weight of Mn, 0.01 to 2.0% by weight of Si, 0.001 to 0.5% by weight of Al.
  • the coating consists of a layer based on elemental iron and a metallic coating applied to it by means of hot-dip coating.
  • the metallic coating is zinc, zinc-iron, zinc-aluminum or zinc-aluminum-magnesium.
  • EP 2 918 696 A1 is another steel strip composed of 0.05 to 0.50% by weight of C, 0.5 to 5.0% by weight of Mn, 0.2 to 3.0% by weight of Si and 0.001 to 1.0% by weight of Al described, which is hot-dip coated with a Zn-Fe alloy. At its interface with the Zn-Fe coating, the steel strip has a layer with at least 50% by volume ferrite and at least 90% unoxidized iron.
  • the object of the invention is therefore to specify a method for producing a cold- or hot-rolled steel strip with a metallic coating which, in addition to carbon, iron as the main component, has an Mn content of 4.1 to 8.0% by weight and optionally other oxygen-affine Contains elements such as Al, Si, Cr, B, which provides uniform and reproducible adhesion conditions for the coating on the steel strip surface, regardless of the current alloy composition of the steel strip.
  • the teaching of the invention includes a method for producing a cold- or hot-rolled steel strip with a metallic coating with improved adhesion, the steel strip has iron as the main component and, in addition to carbon, an Mn content of 4.1 to 8.0% by weight and optionally one or several of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo, whereby the surface of the uncoated steel strip is cleaned, a layer of pure iron with an average iron content of more than 96% by weight is applied to the cleaned surface % is applied, an oxygen-containing, iron-based layer is applied to the layer of pure iron, which contains more than 5% by mass of oxygen, after which the steel strip is annealed with the oxygen-containing, iron-based layer and is reduction-treated in the course of the annealing treatment in a reducing furnace atmosphere, and then the steel strip thus treated and annealed with the metallic coating is hot-dip coated, which is characterized in that a layer of pure iron is applied after cleaning and before the application of the oxygen-containing, iron
  • the teaching of the invention includes a steel strip, which, in addition to carbon, has iron as the main component, an Mn content of 4.1 to 8.0% by weight and optionally one or more of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo with a metallic coating applied to the surface of the steel strip by means of hot dipping, which is characterized in that a predominantly ferritic edge zone with more than 60% by volume ferrite is formed in the transition area between the metallic coating and the surface of the steel strip, which has a thickness from 0.15 to 1.1 ⁇ m and, viewed from the steel strip surface, consists of a pure iron layer with an average iron content of more than 96% by weight and on top of that an oxygen-containing, iron-based layer that has more than 5 Percentage by mass contains oxygen.
  • the teaching of the invention also includes the use of a steel strip according to the invention for the production of parts for motor vehicles.
  • the core of the invention consists in a combination of a pure iron coating applied to the steel strip surface with an oxygen-containing iron coating deposited over it with subsequent annealing and hot-dip finishing.
  • a layer with an average iron content of more than 96% by weight is understood as a pure iron layer.
  • the oxygen-containing, iron-based layer is understood to mean a layer with an iron content in % by weight of at least 50%, which contains more than 5% by weight of oxygen in the form of oxides and/or hydroxides.
  • the oxides and/or hydroxides can be present in the oxygen-containing, iron-based layer in the form of crystalline, amorphous or also as mixtures of crystalline, such as magnetite (Fe 3 O 4 ), and amorphous compounds.
  • magnetite Fe 3 O 4
  • amorphous compounds such as magnetite (Fe 3 O 4 )
  • the distribution of the amorphous and/or crystalline compounds is also not restricted.
  • the layer is thus characterized in that it contains oxygen-containing, reducible iron species.
  • the pure iron layer can preferably be deposited electrolytically or by deposition from the gas phase (e.g. by means of PVD, CVD).
  • sulphate or chloride electrolytes and combinations thereof are typically used, the pH of which is less than or equal to 5.5. At higher pH values, ferrous species precipitate as hydroxides. Iron with a purity in % by weight of greater than 99.5 is preferably used as the anode material. Electrolytic cells with separate anode and cathode compartments can also be used, which makes it possible to use oxygen-generating or insoluble anodes. To reduce the cell resistance, a conductive salt can optionally be added to the electrolyte. It is also possible to use other additives, such as surfactants to improve wetting and/or defoamers.
  • Electrolytic deposition takes place at current densities that result in a deposition thickness that is homogeneous over the length of the strip, regardless of the respective strip speed. Furthermore, the current density depends on the length of the anode in the direction of travel of the strip. Typical values are between 1 and 150 A/dm 2 per strip side. Below 1 A/dm 2 too long treatment lengths are required, which means that the process cannot be operated economically. At current densities above 150 A/dm 2 , homogeneous deposition is made significantly more difficult by burning or dendrite formation. The duration of the electrolytic deposition depends on the treatment length, the current density, the current yield and the desired layer coverage and is typically between 1 s and 30 s per side.
  • Example compositions of aqueous electrolytes and deposition conditions are shown in Table 1.
  • Table 1 electrolyte system composition conditions sulfate FeSO 4 .7H 2 O: 220 g/l pH 2.2; 35°C NaSO 4 : 90 g/l chloride FeCl 2 ⁇ 4H 2 O: 280 g/l pH 1.4; 48oC KCI: 210 g/l sulfate chloride FeSO 4 .7H 2 O: 400 g/l pH 1.6; 85oC FeCl 2 ⁇ 4H 2 O: 400 g/l CaCl 2 : 180 g/l sulfamate Fe(SO 3 NH 2 ) 2 : 220 g/l pH 3.2; 60°C NH 4 (SO 3 NH 2 ): 30 g/l fluoroborate Fe(BF 4 ) 2 : 240 g/l pH 2.1; 58oC NaCl: 8 g/l
  • the pure iron layer is deposited at an electrolyte temperature of 60 °C with a current density of 30 A/dm 2 using an iron anode with a purity in % by weight of greater than 99.5 in an aqueous sulfuric acid electrolyte with the following composition: 60 g/l iron(II), 20 g/l sodium, pH 1.8.
  • the preferred deposition of the oxygen-containing, iron-based layer takes place electrolytically from an electrolyte containing Fe(II) and/or Fe(III). Sulfate or chloride electrolytes and combinations thereof are typically used for this purpose, the pH of which is generally less than or equal to 5.5.
  • Electrolytic deposition takes place at current densities that result in a deposition thickness that is homogeneous over the length of the strip, regardless of the respective strip speed. Furthermore, the current density depends on the length of the anode in the direction of travel of the strip. Typical values are between 1 and 150 A/dm 2 per strip side. Below 1 A/dm 2 too long treatment lengths are required, which means that the process cannot be operated economically. At current densities above 150 A/dm 2 , homogeneous deposition is made significantly more difficult by burning or dendrite formation.
  • the deposition time depends on the length of treatment, the current density, the current yield and the desired layer coverage and is typically between 1 s and 30 s per side.
  • Example compositions of aqueous electrolytes and deposition conditions are shown in Table 2.
  • Table 2 complexing agent composition conditions citrate FeSO 4 .7H 2 O: 350 g/l pH 2.3; 45°C Fe 2 (SO 4 ) 3 : 10 g/l Na 2 SO 4 : 110 g/l Sodium citrate: 20 g/l triethanolamine Fe 2 (SO 4 ) 3 : 170 g/l pH 13; 80°C NaOH: 12 g/l C6 H15 NO3 : 15 g/l
  • a complexing agent for the iron ions is also required in the acidic electrolyte to produce oxygen-containing, iron-based layers.
  • This is typically a compound with one or more carbonyl functionalities, such as citric acid, acetic acid or else nitrilotriacetic acid (NTA) or ethanolamine.
  • Iron with a purity in % by weight of greater than 99.5 is preferably used as the anode material.
  • Electrolytic cells with separate anode and cathode compartments can also be used, which makes it possible to use oxygen-generating or insoluble anodes.
  • a conductive salt can optionally be added to the electrolyte. It is also possible to use other additives, such as surfactants to improve wetting and/or defoamers.
  • the oxygen-containing iron layer is deposited at 60° C. with a current density of 30 A/dm 2 using an iron anode with a purity in % by weight greater than 99.5 in an aqueous sulfuric acid electrolyte with the following composition: 60 g /l iron(II), 3 g/l iron(III), 25 g/l sodium, 11 g/l citrate, pH 1.8.
  • the surface of the steel strip is preferably activated by cleaning in a typically alkaline, aqueous medium and subsequent optional desmutting in an acidic, aqueous medium prior to deposition with the pure iron layer.
  • a sulfuric acid bath with an acid content of 20 to 70 g/l at temperatures of 30 to 70 °C is preferably used for desmutting.
  • the subsequent coating with the Oxygen-containing, iron-based layer on the previously deposited pure iron layer is preferably carried out wet on wet or after drying the steel strip surface.
  • the steel strip surface is preferably dried in order to prevent an undefined entry of water into the annealing furnace atmosphere.
  • a rinsing can optionally be used after each process step.
  • the layers can be deposited within one electrolytic cell or in a plurality of electrolytic cells arranged one after the other, the design of which is preferably horizontal or vertical.
  • the oxygen-containing, iron-based layer is deposited in particularly fine-crystalline form and leads to better adhesion of the hot-dip coating than if the oxygen-containing, iron-based layer is applied directly to the steel surface.
  • the nucleation conditions for the subsequent oxygen-containing, iron-based layer are significantly improved by the pre-coating with pure iron, whereby the nucleation rate increases and the crystallite size therefore decreases compared to a single-layer system.
  • the pure iron layer is formed with an average thickness of 0.05 to 0.5 ⁇ m and the oxygen-containing, iron-based layer is formed with an average thickness of 0.1 to 0.6 ⁇ m.
  • the pure iron layer has an average thickness of 0.1 to 0.4 ⁇ m and the oxygen-containing, iron-based layer has an average thickness of 0.2 to 0.5 ⁇ m.
  • the mean thickness of the oxygen-containing, iron-based layer is greater than the mean thickness of the pure iron layer.
  • the oxygen-containing, iron-based layer has an oxygen content of more than 5 to 40% by weight, advantageously of more than 10 to 30% by weight. In a particularly advantageous embodiment of the invention, this layer has an oxygen content of more than 12 to 25% by weight.
  • oxygen content is more than 5 to 40% by weight, advantageously of more than 10 to 30% by weight.
  • this layer has an oxygen content of more than 12 to 25% by weight.
  • the pure iron layer itself can be applied either electrolytically or by deposition from the gas phase, while the oxygen-containing, iron-based layer is advantageously deposited electrolytically.
  • a pure iron layer is a layer with an average iron content of more than 96% by weight.
  • the method according to the invention also includes an annealing treatment of the steel strip provided with a pure iron and an oxygen-containing, iron-based layer applied thereto in a continuous annealing furnace.
  • This furnace can be a combination of a furnace part with open combustion (DFF, Direct Fired Furnace / NOF, Non-Oxidizing Furnace) and a radiant tube furnace (RTF, Radiation Tube Furnace) arranged after it, or in an all radiant tube furnace (All Radiant Tube Furnace). take place.
  • DFF Direct Fired Furnace / NOF, Non-Oxidizing Furnace
  • RTF Radiation Tube Furnace
  • the steel strip is annealed at an annealing temperature of 550 °C to 880 °C and an average heating rate of 1 K/s to 100 K/s, as well as a holding time of the steel strip at the annealing temperature of between 30 s and 650 s.
  • a reducing annealing atmosphere consisting of 2% to 40% H 2 and 98 to 60% N 2 and a dew point between +15 °C and -70 °C is used in the radiant tube furnace, so that a surface consisting essentially of metallic iron is obtained .
  • the strip is then cooled to a temperature above the melt bath temperature of the coating and then coated with the metallic coating.
  • the strip can be cooled to a so-called overaging temperature between 200° C. and 600° C. and kept at this temperature for up to 500 s. If an overaging temperature below the melting bath temperature of the coating is chosen, for example to influence the structure and the resulting technological characteristics of the steel, the strip can be heated before it enters the melting bath, for example by inductive heating to a temperature above the melting bath temperature of between 400 °C and 750 °C so that the cold steel strip does not draw heat from the weld pool.
  • the use of the precoatings according to the invention makes an additional introduction of water vapor to increase the dew point, as is customary in the previously known processes, unnecessary. It has therefore been found to be sufficient for the annealing atmosphere in the furnace if the ratio of the partial pressures of water vapor and hydrogen during annealing in the radiant tube furnace is in the range 0.00077 > pH 2 O/pH 2 > 0.00021, advantageously between 0.00254 > pH 2 O/pH 2 > 0.00021.
  • An exemplary advantageous process sequence for the production of a steel strip according to the invention with improved adhesion of hot-dip galvanizing provides that first a hot-rolled steel strip (hot strip) is pickled, then cold-rolled and then galvanized in a hot-dip galvanizing line. Within the hot-dip galvanizing line, the strip goes through a pre-cleaning section, after pre-cleaning the strip goes through further strip activation (pickling/pickling) and then 6 electrolytic cells. An iron layer is deposited in the first 3 cells, and an oxygen-containing, iron-based layer in the next 3 cells. The coated strip then runs through rinsing and drying. The strip then enters the furnace section of the galvanizing line, where it is annealed and galvanized.
  • Aluminum-silicon AS, AISi
  • zinc Z
  • zinc-aluminum ZA, Galfan
  • zinc-aluminum-iron ZF, galvannealed
  • zinc-magnesium-aluminum ZM, ZAM
  • aluminium-zinc AZ, Galvalume
  • the metallic coating is based on zinc and the zinc coating contains 0.1 to 1% by weight Al or 0.1 to 6% by weight Al and 0.1 to 6% by weight Mg or 5 to 15% by weight Fe .
  • a steel strip according to the invention is further characterized in that a predominantly ferritic surface zone with more than 60% by volume ferrite is formed in the transition area between the metallic coating and the surface of the steel strip, which has a thickness of 0.15 to 1.1 ⁇ m and advantageously a thickness between 0 .3 and 0.9 ⁇ m.
  • the thickness of this edge zone results directly from the deposited pre-coatings, which, even after annealing and hot-dip coating, have a microstructure that differs from the steel substrate and thus has the desired positive effects.
  • Table 3 shows the results of galvanizing tests that were carried out on a hot-dip galvanizing simulator with test sheets made of medium manganese steel (6 percent by mass Mn and 2 percent by mass Si+Al).
  • the pre-coatings were deposited electrolytically with a current density of 75 A/dm 2 per side.
  • the tests were carried out at two different heat treatments (800°C for 200 seconds and 700°C for 120 seconds). Samples with complete zinc wetting and good adhesion could only be achieved by means of a pre-coating of pure iron and a pre-coating of an oxygen-containing, iron-based layer on top.
  • Coating adhesion is tested in two different test geometries to ensure adhesion in the different uses of the steels.
  • the coating adhesion in the forming process is tested using a ball impact test in accordance with SEP1931.
  • a hemispherical stamp is hit with high impact energy on a test panel.
  • the impact stress creates a dome-shaped impression in the test panel.
  • This process is carried out until there is a slight crack in the test panel, several times if necessary.
  • the surface is then checked visually for delamination and delamination of the zinc-based coating in the area of the calotte. The result is evaluated with grades from 1-4 (grades 1+2 passed, grades 3+4 failed).
  • the adhesion of the coating in the event of a crash is checked using an adhesive bead test.
  • a bead of adhesive in a defined geometry, preferably 10 mm wide and 5 mm high, of a 1-component epoxy resin structural adhesive is applied to the test panel.
  • the adhesive is then cured according to the data sheet and the sample is then quickly bent through 90° within a maximum of 2 s. During this process, the adhesive bead breaks under the strong tension and suddenly pulls on the already through the Bending stressed coating.
  • the samples are then assessed visually for zinc detachment.

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Description

Die Erfindung betrifft ein Verfahren zur Herstellung eines kalt- oder warmgewalzten Stahlbandes mit einem metallischen Überzug, das Stahlband Eisen als Hauptbestandteil und neben Kohlenstoff, einen Mn-Gehalt von 4,1 bis 8,0 Gewichts-% und optional eines oder mehrere der Legierungselemente Al, Si, Cr, B, Ti, V, Nb und/oder Mo aufweist, wobei die Oberfläche des unbeschichteten Stahlbandes gereinigt wird, auf die gereinigte Oberfläche eine Schicht aus Reineisen mit einem durchschnittlichen Eisengehalt von mehr als 96 Gewichts-% aufgebracht wird, auf die Schicht aus Reineisen eine sauerstoffhaltige, eisenbasierte Schicht aufgebracht wird, die mehr als 5 Massenprozent Sauerstoff enthält, danach das Stahlband mit der sauerstoffhaltigen, eisenbasierten Schicht glühbehandelt wird und im Zuge der Glühbehandlung in einer reduzierenden Ofenatmosphäre reduktionsbehandelt wird, und anschließend das so behandelte und glühbehandelte Stahlband mit dem metallischen Überzug schmelztauchbeschichtet wird. Des Weiteren betrifft die Erfindung ein Stahlband mit einem mittels Schmelztauchen aufgebrachten metallischen Überzug sowie die Verwendung eines solchen Stahlbandes.The invention relates to a method for producing a cold- or hot-rolled steel strip with a metallic coating, the steel strip having iron as the main component and, in addition to carbon, an Mn content of 4.1 to 8.0% by weight and optionally one or more of the alloying elements Al , Si, Cr, B, Ti, V, Nb and/or Mo, wherein the surface of the uncoated steel strip is cleaned, a layer of pure iron with an average iron content of more than 96% by weight is applied to the cleaned surface an oxygen-containing, iron-based layer is applied to the layer of pure iron, which contains more than 5 percent by mass of oxygen, after which the steel strip is annealed with the oxygen-containing, iron-based layer and is reduction-treated in the course of the annealing treatment in a reducing furnace atmosphere, and then the treated and annealed in this way Steel strip is hot dip coated with the metallic coating. Furthermore, the invention relates to a steel strip with a metallic coating applied by hot dipping and the use of such a steel strip.

Für die durch Schmelztauchen aufgebrachten Beschichtungen beziehungsweise Legierungsbeschichtungen sind unter anderem Aluminium-Silizium (AS/AlSi), Zink (Z), Zink-Aluminium (ZA), Zink-Eisen (ZF/ Galvannealed), Zink-Magnesium-Aluminium (ZM/ZAM) und Aluminium-Zink (AZ) bekannt. Diese Korrosionsschutzbeschichtungen werden üblicherweise in kontinuierlichen Durchlaufverfahren in einem Schmelzbad auf das Stahlband (Warm- oder Kaltband) aufgebracht.For the coatings or alloy coatings applied by hot dipping, aluminum-silicon (AS/AlSi), zinc (Z), zinc-aluminum (ZA), zinc-iron (ZF/Galvannealed), zinc-magnesium-aluminum (ZM/ZAM ) and aluminium-zinc (AZ). These anti-corrosion coatings are usually applied to the steel strip (hot or cold strip) in a continuous process in a molten bath.

Aus der Offenlegungsschrift WO 2013/007578 A2 ist bekannt, dass hochfeste Stähle mit höheren Gehalten an Elementen in Gewichts-% bis zu 35,0 % Mn, bis zu 10,0 % Al, bis zu 10,0 % Si, bis zu 5,0 % Cr im Zuge der dem schmelztauchbeschichten vorgeschalteten Glühung des Stahlbandes, selektiv passive, nicht benetzbare Oxide auf der Stahloberfläche bilden, wodurch die Haftung des Überzugs auf der Stahlbandoberfläche verschlechtert wird und dies gleichzeitig zur Ausbildung von unverzinkten Stellen führen kann. Diese Oxide bilden sich auf Grund der herrschenden Glühatmosphäre, die zwangsläufig immer geringe Spuren an H2O oder O2 enthält und oxidierend auf die genannten Elemente wirkt.From the disclosure document WO 2013/007578 A2 It is known that high-strength steels with higher element contents in % by weight up to 35.0% Mn, up to 10.0% Al, up to 10.0% Si, up to 5.0% Cr in the course of dem hot dip coating upstream annealing of the steel strip, selectively form passive, non-wettable oxides on the steel surface, which deteriorates the adhesion of the coating on the steel strip surface and at the same time can lead to the formation of non-galvanized areas. These oxides form due to the prevailing annealing atmosphere, which inevitably always contains small traces of H 2 O or O 2 and has an oxidizing effect on the elements mentioned.

Offenbart wird in der genannten Schrift unter anderem ein Verfahren, bei dem im Zuge einer Glühung unter oxidierenden Bedingungen in einem ersten Schritt eine Voroxidation des Stahlbandes stattfindet, mit der eine gezielt deckende FeO-Schicht erzeugt wird, die eine selektive externe Oxidation der Legierungselemente verhindert. In einem zweiten Schritt wird diese Schicht anschließend wieder zu metallischem Eisen reduziert.The cited publication discloses, among other things, a method in which, during annealing under oxidizing conditions, the steel strip is pre-oxidized in a first step, with which a specifically covering FeO layer is produced, which prevents selective external oxidation of the alloying elements. In a second step, this layer is then reduced back to metallic iron.

Die Patentschrift DE 10 2013 105 378 B3 offenbart ein Verfahren zur Herstellung eines Stahlflachprodukts, welches neben Eisen und unvermeidbaren Verunreinigungen in Gewichts-% bis zu 35 Mn, bis zu 10 Al, bis zu 10 Si und bis zu 5 Cr enthält. Nach einem Aufwärmen in einem Vorwärmofen, in welchem das Stahlflachprodukt einer oxidierenden Atmosphäre ausgesetzt wird und einem rekristallisierenden Glühen im Glühofen, in dem eine gegenüber FeO reduzierend wirkende Glühatmosphäre herrscht, wird das Stahlflachprodukt im Schmelztauchbad beschichtet.The patent specification DE 10 2013 105 378 B3 discloses a method for producing a flat steel product which, in addition to iron and unavoidable impurities, contains up to 35 Mn, up to 10 Al, up to 10 Si and up to 5 Cr by weight. After heating in a preheating furnace, in which the flat steel product is exposed to an oxidizing atmosphere, and recrystallizing annealing in the annealing furnace, in which an annealing atmosphere that has a reducing effect on FeO prevails, the flat steel product is coated in a hot-dip bath.

Die Offenlegungsschrift DE 10 2010 037 254 A1 offenbart ein Verfahren zum Schmelztauchbeschichten eines Stahlflachproduktes, wobei das Stahlflachprodukt aus einem nicht rostenden Stahl erzeugt ist, der neben Eisen und unvermeidbaren Verunreinigungen in Gewichts-% enthält: 5 bis 30 Cr, < 6 Mn, < 2 Si und < 0,2 Al. Das Stahlflachprodukt wird zunächst unter einer oxidierenden Voroxidationsatmosphäre erwärmt, unter einer reduzierenden Halteatmosphäre gehalten und sodann durch ein Schmelzbad geleitet.The disclosure document DE 10 2010 037 254 A1 discloses a method for hot-dip coating a flat steel product, the flat steel product being produced from a stainless steel which, in addition to iron and unavoidable impurities, contains in % by weight: 5 to 30 Cr, <6 Mn, <2 Si and <0.2 Al. The steel flat product is first heated under an oxidizing pre-oxidation atmosphere, held under a reducing holding atmosphere, and then passed through a molten bath.

Die Patentschrift US 5,447,802 beschreibt ein oberflächenbehandeltes Stahlband mit verminderten Beschichtungsfehlern und ein Verfahren zu dessen Herstellung, wobei der Basisstahl einen Gehalt an Mn von 4,0 Gew.-% nicht übersteigt. Auf die Stahlbandoberfläche wird eine oxidhaltige Eisenschicht aufgebracht, wodurch am Übergang von Stahlbandoberfläche zur oxidhaltigen Eisenschicht eine konzentrierte Schicht von Legierungselementen mit der Absicht geformt wird, dass diese Elemente nicht weiter in die oxidhaltige Eisenschicht vordringen.The patent specification U.S. 5,447,802 describes a surface treated steel strip with reduced coating defects and a method for the production thereof, wherein the base steel does not exceed a Mn content of 4.0% by weight. An oxide-containing iron layer is applied to the steel strip surface, which forms a concentrated layer of alloying elements at the transition from the steel strip surface to the oxide-containing iron layer with the intention that these elements do not penetrate further into the oxide-containing iron layer.

Die Offenlegungsschriften US 2016 010 23 79 A1 und US 2013 030 49 82 A1 offenbaren jeweils ein Verfahren zur Herstellung eines beschichteten Stahlbandes, das in Gewichts-% enthält: 0,5 bis 2 Si, 1 bis 3 Mn, 0,01 bis 0,8 Cr und 0,01 bis 0,1 Al. Nach einer Oxidationsbehandlung des Stahlbandes in oxidativer Atmosphäre wird das Stahlband reduzierend geglüht und anschließend schmelztauchbeschichtet.The Disclosures U.S. 2016 010 23 79 A1 and U.S. 2013 030 49 82 A1 each disclose a method for producing a coated steel strip containing in weight %: 0.5 to 2 Si, 1 to 3 Mn, 0.01 to 0.8 Cr and 0.01 to 0.1 Al. After an oxidation treatment of the steel strip in an oxidative atmosphere, the steel strip is subjected to reduction annealing and then hot-dip coated.

Aus der Patentschrift DE 693 12 003 T2 ist weiterhin ein Verfahren zur Herstellung eines beschichteten Stahlbleches mit reduzierten Oberflächenfehlern bekannt, bei welchem auf mindestens eine Oberfläche eines Stahlbandes eine Beschichtung aus Zink oder einer Zinklegierung aufgetragen ist. Zusätzlich sind unmittelbar unter der Beschichtung aus Zink oder einer Zinklegierung eine Schicht aus Fe und unmittelbar unter der Schicht aus Fe eine Schicht, in der sauerstoffaffine Elemente des Stahls konzentriert sind, vorgesehen. Das kohlenstoffarme oder sehr kohlenstoffarme Stahlband, auf das die Fe-Plattierung appliziert ist, enthält mindestens eine Komponente, ausgewählt aus der Gruppe Si, Mn, P, Ti, Nb, Al, Ni, Cu, Mo, V, Cr und B in einer Menge von mindestens 0,1 Gew.-% für Si, Ti, Ni, Cu, Mo, Cr und V und mindestens 0,5 Gew.-% für Mn, mindestens 0,05 Gew.-% für P, Al und Nb und mindestens 0,001 Gew.-% für B. Die Schicht aus Fe weist ein Auftraggewicht von 0,1 bis 10 g/m2, einen Sauerstoffgehalt von 0,1 bis 10 Gew.-% und einen Kohlenstoffgehalt von 0,01 Gew.-% bis weniger als 10 Gew.-% auf. Ziel soll hierbei sein, dass an der Grenzfläche zwischen der sauerstoffhaltigen Fe-Schicht und dem Stahlband während des Glühens vor der Schmelztauchbeschichtung eine Schicht entsteht, in der im Stahl enthaltenen sauerstoffaffinen Elemente konzentriert sind. Hierdurch soll die weitere Diffusion der im Stahl enthaltenen sauerstoffaffinen Elemente in Richtung auf die Fe-Plattieroberfläche verhindert werden und eine gute Verzinkbarkeit realisieren.From the patent DE 693 12 003 T2 a method for producing a coated steel sheet with reduced surface defects is also known, in which a coating of zinc or a zinc alloy is applied to at least one surface of a steel strip. In addition, a layer of Fe is provided immediately below the coating of zinc or a zinc alloy, and a layer in which elements of the steel with an affinity for oxygen are concentrated is provided directly below the layer of Fe. The low-carbon or very low-carbon steel strip to which the Fe plating is applied contains at least one component selected from the group of Si, Mn, P, Ti, Nb, Al, Ni, Cu, Mo, V, Cr and B in one Amount of at least 0.1% by weight for Si, Ti, Ni, Cu, Mo, Cr and V and at least 0.5% by weight for Mn, at least 0.05% by weight for P, Al and Nb and at least 0.001% by weight for B. The layer of Fe has an application weight of 0.1 to 10 g/m 2 , an oxygen content of 0.1 to 10% by weight and a carbon content of 0.01% by weight. % to less than 10% by weight. The aim here is to create a layer at the interface between the oxygen-containing Fe layer and the steel strip during annealing prior to hot-dip coating, in which the elements with an affinity for oxygen contained in the steel are concentrated. This is intended to prevent further diffusion of the oxygen-affinity elements contained in the steel in the direction of the Fe plating surface and to achieve good galvanizability.

Des Weiteren ist aus der Offenlegungsschrift US 2018 / 0 119 263 A1 und der parallelen Offenlegungsschrift EP 2 798 094 A1 ein Verfahren zur Herstellung eines kaltgewalzten Stahlbandes mit einem Mn-Gehalt zwischen 1 und 6 Gewichts-% und einem C-Gehalt kleiner 0,3 Gewichts-% und mit einem metallischen Überzug bekannt. Hierbei wird das Stahlband mit einer Schicht aus reinem Eisen elektroplattiert, dann die Eisenschicht zu einer Eisenoxidschicht oxidiert und anschließend bei einer Temperatur zwischen 750 °C und 900 °C in einer Atmosphäre mit 1 bis 20 Volumen-% Wasserstoff reduziert. Anschließend wird mittels Schmelztauchbeschichten ein Zink-Überzug aufgebracht.Furthermore, from the disclosure document U.S. 2018/0 119 263 A1 and the parallel disclosure EP 2 798 094 A1 discloses a method for producing a cold-rolled steel strip with an Mn content between 1 and 6% by weight and a C content of less than 0.3% by weight and with a metallic coating. Here, the steel strip is electroplated with a layer of pure iron, then the iron layer is oxidized to an iron oxide layer and then reduced at a temperature between 750 °C and 900 °C in an atmosphere with 1 to 20% by volume of hydrogen. A zinc coating is then applied by hot dip coating.

Auch ist in der Offenlegungsschrift US 2004 / 0 121 162 A1 bereits ein kalt- oder warmgewalztes Stahlband mit bis zu 0,5 Gewichts-% C und mit bis zu 15 Gewichts-% Mn und mit einer Beschichtung beschrieben. Die Beschichtung weist ausgehend von dem Stahlband eine Eisenplattierung und einen metallischen Zinküberzug auf.Also is in the disclosure document U.S. 2004/0 121 162 A1 already described a cold- or hot-rolled steel strip with up to 0.5% by weight of C and with up to 15% by weight of Mn and with a coating. Starting from the steel strip, the coating comprises an iron plating and a metallic zinc coating.

Ferner offenbart die Offenlegungsschrift CN 109 477 191 A ein weiteres kalt- oder warmgewalztes beschichtetes Stahlband mit einer Beschichtung. Das Stahlband weist 0,08 bis 0,3 Gewichts-% C, 3,1 bis 8,0 Gewichts-% Mn, 0,01 bis 2,0 Gewichts-% Si, 0,001 bis 0,5 Gewichts-% Al auf. Die Beschichtung besteht aus einer Schicht basierend auf elementarem Eisen sowie einem hierauf mittels Schmelztauchbeschichten aufgebrachten metallischen Überzug. Der metallische Überzug ist aus Zink, Zink-Eisen, Zink-Aluminium oder Zink-Aluminium-Magnesium.Furthermore, the disclosure discloses CN 109 477 191 A another cold or hot rolled coated steel strip with a coating. The steel strip has 0.08 to 0.3% by weight of C, 3.1 to 8.0% by weight of Mn, 0.01 to 2.0% by weight of Si, 0.001 to 0.5% by weight of Al. The coating consists of a layer based on elemental iron and a metallic coating applied to it by means of hot-dip coating. The metallic coating is zinc, zinc-iron, zinc-aluminum or zinc-aluminum-magnesium.

In der Offenlegungsschrift EP 2 918 696 A1 ist ein weiteres Stahlband aus 0,05 bis 0,50 Gewichts-% C, 0,5 bis 5,0 Gewichts-% Mn, 0,2 bis 3,0 Gewichts-% Si und 0,001 bis 1,0 Gewichts-% Al beschrieben, das mit einer Zn-Fe-Legierung schmelztauchbeschichtet ist. Das Stahlband weist an seiner Grenzfläche zu der Zn-Fe-Beschichtung eine Schicht mit mindestens 50 Volumen-% Ferrit und mindestens 90 % unoxidiertem Eisen auf.In the disclosure document EP 2 918 696 A1 is another steel strip composed of 0.05 to 0.50% by weight of C, 0.5 to 5.0% by weight of Mn, 0.2 to 3.0% by weight of Si and 0.001 to 1.0% by weight of Al described, which is hot-dip coated with a Zn-Fe alloy. At its interface with the Zn-Fe coating, the steel strip has a layer with at least 50% by volume ferrite and at least 90% unoxidized iron.

Außerdem zeigen die Offenlegungsschrift WO 2015/ 001 367 A1 und die parallele Offenlegungsschrift EP 3 017 073 A1 ein Stahlband mit einem Mn-Gehalt zwischen 3,5 und 10,0 Gewichts-% und einem C-Gehalt zwischen 0,1 und 0,5 Gewichts-%, auf dem eine Unterschicht aus reinem Ferrit mit einer Schichtdicke zwischen 10 und 50 µm, eine weitere Unterschicht aus Eisen und Oxiden mit einer Schichtdicke zwischen 1 und 8 µm und eine Deckschicht aus reinem Eisen mit einer Schichtdicke von 50 bis 300 nm angeordnet ist. Auf der Deckschicht erfolgt eine Schmelztauchbeschichtung mit AI, Zn oder Legierungen hiervon.Also show the disclosure document WO 2015/ 001 367 A1 and the parallel disclosure EP 3 017 073 A1 a steel strip with a Mn content between 3.5 and 10.0% by weight and a C content between 0.1 and 0.5% by weight, on which an underlayer of pure ferrite with a layer thickness between 10 and 50 µm , a further sub-layer of iron and oxides with a layer thickness between 1 and 8 μm and a top layer of pure iron with a layer thickness of 50 to 300 nm is arranged. Hot-dip coating with Al, Zn or alloys thereof takes place on the top layer.

Es hat sich allerdings gezeigt, dass bei Mn-Gehalten von über 4 bis 8,0 Gewichts-% im Stahl bei allen vorbekannten Lösungen zur Verbesserung der Benetzbarkeit der Stahloberfläche noch keine zufriedenstellende, reproduzierbare Haftung des Überzugs erzielt werden kann.However, it has been shown that with Mn contents of more than 4 to 8.0% by weight in the steel, no satisfactory, reproducible adhesion of the coating can be achieved with any of the previously known solutions for improving the wettability of the steel surface.

Ursächlich hierfür ist die Ausbildung eines massiven Saums von Oxiden der Legierungselemente an der Unterseite der (nach einer reduzierenden Glühung dann reduzierten) Eisenoxidschicht bzw. sauerstoffhaltigen Eisenschicht. Dieser Oxidsaum aus Oxiden der Legierungselemente stellt eine Schwachstelle des Systems in Bezug auf die Haftung dar. Das heißt, an der Grenzfläche der reduzierten Eisenoxidschicht bzw. sauerstoffhaltigen Eisenschicht zum Stahlsubstrat kann hier oftmals ein Haftungsversagen z. B. bei einem Umformprozess beobachtet werden.The reason for this is the formation of a massive seam of oxides of the alloying elements on the underside of the iron oxide layer (which is then reduced after reducing annealing) or the oxygen-containing iron layer. This oxide fringe of oxides from the alloying elements represents a weak point in the system with regard to adhesion. This means that adhesion failure can often occur here at the interface between the reduced iron oxide layer or the oxygen-containing iron layer and the steel substrate, e.g. B. be observed in a forming process.

Aufgabe der Erfindung ist es deshalb, ein Verfahren zur Herstellung eines kalt- oder warmgewalzten Stahlbandes mit einem metallischen Überzug anzugeben, das neben Kohlenstoff, Eisen als Hauptbestandteil, einen Mn-Gehalt von 4,1 bis 8,0 Gewichts-% und optional weitere sauerstoffaffine Elemente, wie zum Beispiel Al, Si, Cr, B, enthält, welches unabhängig von der aktuellen Legierungszusammensetzung des Stahlbandes, gleichmäßige und reproduzierbare Haftungsbedingungen für den Überzug auf der Stahlbandoberfläche liefert.The object of the invention is therefore to specify a method for producing a cold- or hot-rolled steel strip with a metallic coating which, in addition to carbon, iron as the main component, has an Mn content of 4.1 to 8.0% by weight and optionally other oxygen-affine Contains elements such as Al, Si, Cr, B, which provides uniform and reproducible adhesion conditions for the coating on the steel strip surface, regardless of the current alloy composition of the steel strip.

Die Lehre der Erfindung umfasst ein Verfahren zur Herstellung eines kalt- oder warmgewalzten Stahlbandes mit einem metallischen Überzug mit verbesserter Haftung, das Stahlband Eisen als Hauptbestandteil und neben Kohlenstoff, einen Mn-Gehalt von 4,1 bis 8,0 Gewichts-% und optional eines oder mehrere der Legierungselemente Al, Si, Cr, B, Ti, V, Nb und/oder Mo aufweist, wobei die Oberfläche des unbeschichteten Stahlbandes gereinigt wird, auf die gereinigte Oberfläche eine Schicht aus Reineisen mit einem durchschnittlichen Eisengehalt von mehr als 96 Gewichts-% aufgebracht wird, auf die Schicht aus Reineisen eine sauerstoffhaltige, eisenbasierte Schicht aufgebracht wird, die mehr als 5 Massen-% Sauerstoff enthält, danach das Stahlband mit der sauerstoffhaltigen, eisenbasierten Schicht glühbehandelt wird und im Zuge der Glühbehandlung in einer reduzierenden Ofenatmosphäre reduktionsbehandelt wird, und anschließend das so behandelte und glühbehandelte Stahlband mit dem metallischen Überzug schmelztauchbeschichtet wird, welches dadurch gekennzeichnet ist, dass nach dem Reinigen und vor dem Aufbringen der sauerstoffhaltigen, eisenbasierten Schicht eine Schicht aus Reineisen aufgebracht wird.The teaching of the invention includes a method for producing a cold- or hot-rolled steel strip with a metallic coating with improved adhesion, the steel strip has iron as the main component and, in addition to carbon, an Mn content of 4.1 to 8.0% by weight and optionally one or several of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo, whereby the surface of the uncoated steel strip is cleaned, a layer of pure iron with an average iron content of more than 96% by weight is applied to the cleaned surface % is applied, an oxygen-containing, iron-based layer is applied to the layer of pure iron, which contains more than 5% by mass of oxygen, after which the steel strip is annealed with the oxygen-containing, iron-based layer and is reduction-treated in the course of the annealing treatment in a reducing furnace atmosphere, and then the steel strip thus treated and annealed with the metallic coating is hot-dip coated, which is characterized in that a layer of pure iron is applied after cleaning and before the application of the oxygen-containing, iron-based layer.

Weiterhin umfasst die Lehre der Erfindung ein Stahlband, aufweisend neben Kohlenstoff, Eisen als Hauptbestandteil, einen Mn-Gehalt von 4,1 bis 8,0 Gewichts-% und optional weitere eines oder mehrere der Legierungselemente Al, Si, Cr, B, Ti, V, Nb und/oder Mo mit einem mittels Schmelztauchen auf die Stahlbandoberfläche aufgebrachten metallischen Überzug, welches dadurch gekennzeichnet ist, dass im Übergangsbereich zwischen metallischem Überzug und der Stahlbandoberfläche eine überwiegend ferritische Randzone mit mehr als 60 Volumen-% Ferrit ausgebildet ist, die eine Dicke von 0,15 bis 1,1 µm aufweist und von der Stahlbandoberfläche aus gesehen aus einer Reineisenschicht mit einem durchschnittlichen Eisengehalt von mehr als 96 Gewichts-% und darauf einer sauerstoffhaltigen, eisenbasierten Schicht besteht, die mehr als 5 Massenprozent Sauerstoff enthält.Furthermore, the teaching of the invention includes a steel strip, which, in addition to carbon, has iron as the main component, an Mn content of 4.1 to 8.0% by weight and optionally one or more of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo with a metallic coating applied to the surface of the steel strip by means of hot dipping, which is characterized in that a predominantly ferritic edge zone with more than 60% by volume ferrite is formed in the transition area between the metallic coating and the surface of the steel strip, which has a thickness from 0.15 to 1.1 µm and, viewed from the steel strip surface, consists of a pure iron layer with an average iron content of more than 96% by weight and on top of that an oxygen-containing, iron-based layer that has more than 5 Percentage by mass contains oxygen.

Auch umfasst die Lehre der Erfindung die Verwendung eines erfindungsgemäßen Stahlbandes zur Herstellung von Teilen für Kraftfahrzeuge.The teaching of the invention also includes the use of a steel strip according to the invention for the production of parts for motor vehicles.

Der Kern der Erfindung besteht in einer Kombination aus einer auf die Stahlbandoberfläche aufgebrachten Reineisenbeschichtung mit einer darüber abgeschiedenen sauerstoffhaltigen Eisenbeschichtung mit nachfolgender Glühung und Schmelztauchveredlung.The core of the invention consists in a combination of a pure iron coating applied to the steel strip surface with an oxygen-containing iron coating deposited over it with subsequent annealing and hot-dip finishing.

Als Reineisenschicht wird im Sinne der vorliegenden Erfindung eine Schicht mit einem durchschnittlichen Eisengehalt von mehr als 96 Gewichts-% verstanden.In the context of the present invention, a layer with an average iron content of more than 96% by weight is understood as a pure iron layer.

Unter der sauerstoffhaltigen, eisenbasierten Schicht wird eine Schicht mit einem Eisengehalt in Gewichts-% von mindestens 50 % verstanden, die Sauerstoff von mehr als 5 Gewichts-% in Form von Oxiden und/oder Hydroxiden enthält.The oxygen-containing, iron-based layer is understood to mean a layer with an iron content in % by weight of at least 50%, which contains more than 5% by weight of oxygen in the form of oxides and/or hydroxides.

Die Oxide und/oder Hydroxide können in der sauerstoffhaltigen, eisenbasierten Schicht sowohl in Form kristalliner, amorpher oder auch als Mischungen aus kristallinen, wie zum Beispiel Magnetit (Fe3O4), und amorphen Verbindungen vorliegen. Zusätzlich wird unter der sauerstoffhaltigen, eisenbasierten Schicht sowohl eine homogene stöchiometrische Eisenoxidschicht, z. B. eine Magnetitschicht (Fe3O4), als auch eine metallische Eisenschicht, die oxidische und/oder hydroxidische Einschlüsse (Dispersionsschicht) enthält, verstanden. Somit ist auch die Verteilung der amorphen und/oder kristallinen Verbindungen nicht eingeschränkt.The oxides and/or hydroxides can be present in the oxygen-containing, iron-based layer in the form of crystalline, amorphous or also as mixtures of crystalline, such as magnetite (Fe 3 O 4 ), and amorphous compounds. In addition, under the oxygen-containing, iron-based layer, both a homogeneous stoichiometric iron oxide layer, z. B. a magnetite layer (Fe 3 O 4 ), as well as a metallic iron layer containing oxidic and / or hydroxide inclusions (dispersion layer), understood. Thus, the distribution of the amorphous and/or crystalline compounds is also not restricted.

Die Schicht zeichnet sich somit dadurch aus, dass sie sauerstoffhaltige, reduzierbare Eisenspezies enthält.The layer is thus characterized in that it contains oxygen-containing, reducible iron species.

In Untersuchungen hat sich herausgestellt, dass ohne eine Vorbeschichtung aus Reineisen, während der Glühbehandlung vor der Schmelztauchbeschichtung eine massive Ausscheidung von Oxiden der Legierungselemente am Übergang vom Stahlsubstrat zur sauerstoffhaltigen, eisenbasierten Schicht stattfindet, die das Gesamtsystem schwächt und zu einem Haftungsversagen führen kann. Mit der Vorbeschichtung aus Reineisen scheiden sich die Oxide der Legierungselemente weniger lokal konzentriert aus und es findet kein Haftungsversagen mehr statt.Studies have shown that without a pre-coating of pure iron, massive precipitation of oxides of the alloying elements occurs at the transition from the steel substrate to the oxygen-containing, iron-based layer during the annealing treatment before the hot-dip coating, which weakens the entire system and can lead to adhesion failure. With the pre-coating of pure iron, the oxides of the alloying elements separate less locally concentrated and there is no longer any adhesion failure.

Die Abscheidung der Reineisenschicht kann bevorzugt elektrolytisch oder durch Abscheidung aus der Gasphase (z. B. mittels PVD, CVD) erfolgen.The pure iron layer can preferably be deposited electrolytically or by deposition from the gas phase (e.g. by means of PVD, CVD).

Bei der bevorzugten elektrolytischen Abscheidung der Reineisenschicht werden typischerweise sulfatische oder chloridische Elektrolyte sowie Kombinationen daraus eingesetzt, deren pH-Wert kleiner oder gleich 5,5 ist. Bei höheren pH-Werten fallen Eisen(II)-Spezies als Hydroxide aus. Als Anodenmaterial kommt vorzugweise Eisen mit einer Reinheit in Gewichts-% von größer 99,5 zum Einsatz. Auch können Elektrolysezellen mit getrennten Anoden- und Kathodenräumen zur Anwendung kommen, wodurch die Verwendung Sauerstoff erzeugendender bzw. unlöslicher Anoden ermöglicht wird. Zur Verringerung der Zellwiderstände kann optional ein Leitsalz dem Elektrolyten zugesetzt werden. Auch der Einsatz von weiteren Additiven, wie zum Beispiel Tensiden zur Verbesserung der Benetzung und oder Entschäumern ist möglich.In the preferred electrolytic deposition of the pure iron layer, sulphate or chloride electrolytes and combinations thereof are typically used, the pH of which is less than or equal to 5.5. At higher pH values, ferrous species precipitate as hydroxides. Iron with a purity in % by weight of greater than 99.5 is preferably used as the anode material. Electrolytic cells with separate anode and cathode compartments can also be used, which makes it possible to use oxygen-generating or insoluble anodes. To reduce the cell resistance, a conductive salt can optionally be added to the electrolyte. It is also possible to use other additives, such as surfactants to improve wetting and/or defoamers.

Die elektrolytische Abscheidung erfolgt bei Stromdichten, die unabhängig von der jeweiligen Bandgeschwindigkeit eine über die Bandlänge homogene Abscheidedicke ergeben. Weiterhin ist die Stromdichte von der Anodenbaulänge in Bandlaufrichtung abhängig. Typische Werte liegen zwischen 1 und 150 A/dm2 pro Bandseite. Unterhalb von 1 A/dm2 werden zu lange Behandlungslängen benötigt, wodurch der Prozess nicht wirtschaftlich betrieben werden kann. Bei Stromdichten oberhalb von 150 A/dm2 wird eine homogene Abscheidung durch Anbrennungen oder Dendritenbildung deutlich erschwert. Die Dauer der elektrolytischen Abscheidung ist abhängig von der Behandlungslänge, der Stromdichte, der Stromausbeute und der gewünschten Schichtauflage und liegt typischerweise zwischen 1 s und 30 s je Seite. Beispielhafte Zusammensetzungen wässriger Elektrolyte und Abscheidebedingungen sind in Tabelle 1 gezeigt. Tabelle 1: Elektrolytsystem Zusammensetzung Bedingungen Sulfat FeSO4·7H2O: 220 g/l pH 2,2; 35 °C NaSO4: 90 g/l Chlorid FeCl2·4H2O: 280 g/l pH 1,4; 48 °C KCI: 210 g/l Sulfat-Chlorid FeSO4·7H2O: 400 g/l pH 1,6; 85 °C FeCl2·4H2O: 400 g/l CaCl2: 180 g/l Sulfamat Fe(SO3NH2)2: 220 g/l pH 3,2; 60 °C NH4(SO3NH2): 30 g/l Fluoroborat Fe(BF4)2: 240 g/l pH 2,1; 58 °C NaCl: 8 g/l Electrolytic deposition takes place at current densities that result in a deposition thickness that is homogeneous over the length of the strip, regardless of the respective strip speed. Furthermore, the current density depends on the length of the anode in the direction of travel of the strip. Typical values are between 1 and 150 A/dm 2 per strip side. Below 1 A/dm 2 too long treatment lengths are required, which means that the process cannot be operated economically. At current densities above 150 A/dm 2 , homogeneous deposition is made significantly more difficult by burning or dendrite formation. The duration of the electrolytic deposition depends on the treatment length, the current density, the current yield and the desired layer coverage and is typically between 1 s and 30 s per side. Example compositions of aqueous electrolytes and deposition conditions are shown in Table 1. Table 1: electrolyte system composition conditions sulfate FeSO 4 .7H 2 O: 220 g/l pH 2.2; 35°C NaSO 4 : 90 g/l chloride FeCl 2 ·4H 2 O: 280 g/l pH 1.4; 48ºC KCI: 210 g/l sulfate chloride FeSO 4 .7H 2 O: 400 g/l pH 1.6; 85ºC FeCl 2 ·4H 2 O: 400 g/l CaCl 2 : 180 g/l sulfamate Fe(SO 3 NH 2 ) 2 : 220 g/l pH 3.2; 60℃ NH 4 (SO 3 NH 2 ): 30 g/l fluoroborate Fe(BF 4 ) 2 : 240 g/l pH 2.1; 58ºC NaCl: 8 g/l

In einer beispielhaften Ausführung erfolgt die Abscheidung der Reineisenschicht bei einer Elektrolyttemperatur von 60 °C mit einer Stromdichte von 30 A/dm2 unter Einsatz einer Eisenanode mit einer Reinheit in Gewichts-% von größer 99,5 in einem wässrigen schwefelsauren Elektrolyten folgender Zusammensetzung: 60 g/l Eisen(II), 20 g/l Natrium, pH 1,8.In an exemplary embodiment, the pure iron layer is deposited at an electrolyte temperature of 60 °C with a current density of 30 A/dm 2 using an iron anode with a purity in % by weight of greater than 99.5 in an aqueous sulfuric acid electrolyte with the following composition: 60 g/l iron(II), 20 g/l sodium, pH 1.8.

Die bevorzugte Abscheidung der sauerstoffhaltigen, eisenbasierten Schicht erfolgt elektrolytisch aus einem Fe(II)- und/oder Fe(III)-haltigen Elektrolyten. Hierzu werden typischerweise sulfatische oder chloridische Elektrolyte sowie Kombinationen daraus eingesetzt, deren pH-Wert in der Regel kleiner oder gleich 5,5 ist.The preferred deposition of the oxygen-containing, iron-based layer takes place electrolytically from an electrolyte containing Fe(II) and/or Fe(III). Sulfate or chloride electrolytes and combinations thereof are typically used for this purpose, the pH of which is generally less than or equal to 5.5.

Auch der Einsatz eines basischen Elektrolyten mit einem pH-Wert > 10 ist jedoch unter Einsatz eines geeigneten Komplexbildners wie z.B. Triethanolamin (TEA) möglich. Die elektrolytische Abscheidung erfolgt bei Stromdichten, die unabhängig von der jeweiligen Bandgeschwindigkeit eine über die Bandlänge homogene Abscheidedicke ergeben. Weiterhin ist die Stromdichte von der Anodenbaulänge in Bandlaufrichtung abhängig. Typische Werte liegen zwischen 1 und 150 A/dm2 pro Bandseite. Unterhalb von 1 A/dm2 werden zu lange Behandlungslängen benötigt, wodurch der Prozess nicht wirtschaftlich betrieben werden kann. Bei Stromdichten oberhalb von 150 A/dm2 wird eine homogene Abscheidung durch Anbrennungen oder Dendritenbildung deutlich erschwert. Die Abscheidezeit ist abhängig von der Behandlungslänge, der Stromdichte, der Stromausbeute und der gewünschten Schichtauflage und liegt typischerweise zwischen 1 s und 30 s je Seite. Beispielhafte Zusammensetzungen wässriger Elektrolyte und Abscheidebedingungen sind in Tabelle 2 gezeigt. Tabelle 2: Komplexbildner Zusammensetzung Bedingungen Citrat FeSO4·7H2O: 350 g/l pH 2,3; 45 °C Fe2(SO4)3: 10 g/l Na2SO4: 110 g/l Natriumcitrat: 20 g/l Triethanolamin Fe2(SO4)3: 170 g/l pH 13; 80 °C NaOH: 12 g/l C6H15NO3: 15 g/l However, the use of a basic electrolyte with a pH value >10 is also possible using a suitable complexing agent such as, for example, triethanolamine (TEA). Electrolytic deposition takes place at current densities that result in a deposition thickness that is homogeneous over the length of the strip, regardless of the respective strip speed. Furthermore, the current density depends on the length of the anode in the direction of travel of the strip. Typical values are between 1 and 150 A/dm 2 per strip side. Below 1 A/dm 2 too long treatment lengths are required, which means that the process cannot be operated economically. At current densities above 150 A/dm 2 , homogeneous deposition is made significantly more difficult by burning or dendrite formation. The deposition time depends on the length of treatment, the current density, the current yield and the desired layer coverage and is typically between 1 s and 30 s per side. Example compositions of aqueous electrolytes and deposition conditions are shown in Table 2. Table 2: complexing agent composition conditions citrate FeSO 4 .7H 2 O: 350 g/l pH 2.3; 45°C Fe 2 (SO 4 ) 3 : 10 g/l Na 2 SO 4 : 110 g/l Sodium citrate: 20 g/l triethanolamine Fe 2 (SO 4 ) 3 : 170 g/l pH 13; 80℃ NaOH: 12 g/l C6 H15 NO3 : 15 g/l

Zur Erzeugung sauerstoffhaltiger, eisenbasierter Schichten wird neben der genannten Fe(II)- und Fe(III)-lonen auch im sauren Elektrolyten ein Komplexbildner für die Eisenionen benötigt. Hierbei handelt es sich typischerweise um eine Verbindung mit einer oder mehreren Carbonylfunktionalitäten, wie Zitronensäure, Essigsäure oder auch Nitrilotriessigsäure (NTA) oder Ethanolamin.In addition to the Fe(II) and Fe(III) ions mentioned, a complexing agent for the iron ions is also required in the acidic electrolyte to produce oxygen-containing, iron-based layers. This is typically a compound with one or more carbonyl functionalities, such as citric acid, acetic acid or else nitrilotriacetic acid (NTA) or ethanolamine.

Als Anodenmaterial kommt vorzugsweise Eisen mit einer Reinheit in Gewichts-% von größer 99,5 zum Einsatz. Auch können Elektrolysezellen mit getrennten Anoden- und Kathodenräumen zur Anwendung kommen, wodurch die Verwendung Sauerstoff erzeugendender bzw. unlöslicher Anoden ermöglicht wird. Zur Verringerung der Zellwiderstände kann optional ein Leitsalz dem Elektrolyten zugesetzt werden. Auch der Einsatz von weiteren Additiven, wie zum Beispiel Tensiden zur Verbesserung der Benetzung und oder Entschäumern ist möglich.Iron with a purity in % by weight of greater than 99.5 is preferably used as the anode material. Electrolytic cells with separate anode and cathode compartments can also be used, which makes it possible to use oxygen-generating or insoluble anodes. To reduce the cell resistance, a conductive salt can optionally be added to the electrolyte. It is also possible to use other additives, such as surfactants to improve wetting and/or defoamers.

In einer beispielhaften Ausführung erfolgt die Abscheidung der sauerstoffhaltigen Eisenschicht bei 60 °C mit einer Stromdichte von 30 A/dm2 unter Einsatz einer Eisenanode mit einer Reinheit in Gewichts-% von größer 99,5 in einem wässrigen schwefelsauren Elektrolyten mit folgender Zusammensetzung: 60 g/l Eisen(II), 3 g/l Eisen(III), 25 g/l Natrium, 11 g/l Citrat, pH 1,8.In an exemplary embodiment, the oxygen-containing iron layer is deposited at 60° C. with a current density of 30 A/dm 2 using an iron anode with a purity in % by weight greater than 99.5 in an aqueous sulfuric acid electrolyte with the following composition: 60 g /l iron(II), 3 g/l iron(III), 25 g/l sodium, 11 g/l citrate, pH 1.8.

In einer bevorzugten, großtechnischen Umsetzung wird die Oberfläche des Stahlbandes vor der Abscheidung mit der Reineisenschicht vorzugsweise durch Reinigung in einem üblicherweise alkalischen, wässrigen Medium und einer anschließenden optionalen Dekapierung in einem sauren, wässrigen Medium aktiviert. Vorzugsweise kommt zur Dekapierung ein Schwefelsäurebad mit einem Säuregehalt von 20 bis 70 g/l bei Temperaturen von 30 bis 70 °C zur Anwendung. Die anschließende Beschichtung mit der sauerstoffhaltigen, eisenbasierten Schicht auf die zuvor abgeschiedene Reineisenschicht erfolgt vorzugsweise nass in nass oder nach Trocknung der Stahlbandoberfläche. Nach der Abscheidung der sauerstoffhaltigen, eisenbasierten Schicht wird die Stahlbandoberfläche vorzugsweise getrocknet, um einen undefinierten Eintrag von Wasser in die Glühofenatmosphäre zu unterbinden. Um Verunreinigungen auf der Stahlbandoberfläche und oder Verschleppungen zwischen den verschiedenen Prozessmedien zu verhindern, kann optional nach jedem Prozessschritt eine Spüle verwendet werden. Die Abscheidung der Schichten kann dabei innerhalb einer oder in mehreren nacheinander angeordneten Elektrolysezellen erfolgen, deren Bauform vorzugsweise horizontal oder vertikal ausgeführt ist.In a preferred, industrial-scale implementation, the surface of the steel strip is preferably activated by cleaning in a typically alkaline, aqueous medium and subsequent optional desmutting in an acidic, aqueous medium prior to deposition with the pure iron layer. A sulfuric acid bath with an acid content of 20 to 70 g/l at temperatures of 30 to 70 °C is preferably used for desmutting. The subsequent coating with the Oxygen-containing, iron-based layer on the previously deposited pure iron layer is preferably carried out wet on wet or after drying the steel strip surface. After the oxygen-containing, iron-based layer has been deposited, the steel strip surface is preferably dried in order to prevent an undefined entry of water into the annealing furnace atmosphere. In order to prevent contamination on the steel strip surface and/or carryover between the various process media, a rinsing can optionally be used after each process step. The layers can be deposited within one electrolytic cell or in a plurality of electrolytic cells arranged one after the other, the design of which is preferably horizontal or vertical.

Untersuchungen haben ergeben, dass infolge der Vorbeschichtung aus Reineisen die sauerstoffhaltige, eisenbasierte Schicht besonders feinkristallin abgeschieden wird und zu einer besseren Haftung des Schmelztauchüberzugs führt, als wenn die sauerstoffhaltige, eisenbasierte Schicht unmittelbar auf die Stahloberfläche aufgebracht wird. Offensichtlich werden durch die Vorbeschichtung mit Reineisen die Keimbildungsbedingungen für die nachfolgende sauerstoffhaltige, eisenbasierte Schicht signifikant verbessert, wodurch sich die Keimbildungsrate erhöht und die Kristallitgröße deshalb im Vergleich zu einem Einschichtsystem abnimmt.Studies have shown that as a result of the pre-coating of pure iron, the oxygen-containing, iron-based layer is deposited in particularly fine-crystalline form and leads to better adhesion of the hot-dip coating than if the oxygen-containing, iron-based layer is applied directly to the steel surface. Apparently, the nucleation conditions for the subsequent oxygen-containing, iron-based layer are significantly improved by the pre-coating with pure iron, whereby the nucleation rate increases and the crystallite size therefore decreases compared to a single-layer system.

In vorteilhaften Weiterbildungen der Erfindung ist vorgesehen, dass die Reineisenschicht mit einer mittleren Dicke von 0,05 bis 0,5 µm und die sauerstoffhaltige, eisenbasierte Schicht mit einer mittleren Dicke von 0,1 bis 0,6 µm ausgebildet wird.In advantageous developments of the invention, it is provided that the pure iron layer is formed with an average thickness of 0.05 to 0.5 μm and the oxygen-containing, iron-based layer is formed with an average thickness of 0.1 to 0.6 μm.

Als besonders vorteilhaft für verbesserte Haftungsbedingungen des Schmelztauchüberzugs hat sich herausgestellt, wenn die Reineisenschicht eine mittlere Dicke von 0,1 bis 0,4 µm und die sauerstoffhaltige, eisenbasierte Schicht eine mittlere Dicke von 0,2 bis 0,5 µm aufweist.It has been found to be particularly advantageous for improved adhesion conditions of the hot-dip coating if the pure iron layer has an average thickness of 0.1 to 0.4 μm and the oxygen-containing, iron-based layer has an average thickness of 0.2 to 0.5 μm.

Zudem ist es vorteilhaft für die Haftung des Schmelztauchüberzugs, wenn die mittlere Dicke der sauerstoffhaltigen, eisenbasierten Schicht größer ist als die mittlere Dicke der Reineisenschicht.In addition, it is advantageous for the adhesion of the hot-dip coating if the mean thickness of the oxygen-containing, iron-based layer is greater than the mean thickness of the pure iron layer.

Die sauerstoffhaltige, eisenbasierte Schicht weist in einer weiteren Ausgestaltung der Erfindung einen Anteil an Sauerstoff von mehr als 5 bis 40 Gewichts-% auf, vorteilhaft von mehr als 10 bis 30 Gewichts-%. In einer besonders vorteilhaften Ausgestaltung der Erfindung weist diese Schicht einen Sauerstoffgehalt von mehr als 12 bis 25 Gewichts-% auf. Bei Untersuchungen hat sich herausgestellt, dass, je mehr Sauerstoff in die Eisenschicht eingebaut wird, desto stärker kann die nachteilige externe Oxidation von Legierungselementen auf der Oberfläche unterdrückt werden, da dieser Sauerstoff bei der Glühung vor der Schmelztauchbeschichtung von den Legierungselementen zur internen Oxidation verwendet wird. Die Menge des in der sauerstoffhaltigen, eisenbasierten Schicht eingebauten Sauerstoffs hängt jedoch in einem wesentlichen Maße von den Abscheidebedingungen ab. Aufgrund von technischen und wirtschaftlichen Randbedingungen liegt der sinnvolle Maximalwert für den Sauerstoffgehalt bei 40 Gewichts-%.In a further embodiment of the invention, the oxygen-containing, iron-based layer has an oxygen content of more than 5 to 40% by weight, advantageously of more than 10 to 30% by weight. In a particularly advantageous embodiment of the invention, this layer has an oxygen content of more than 12 to 25% by weight. Studies have shown that the more oxygen is incorporated into the iron layer, the more the adverse external oxidation of alloying elements on the surface can be suppressed, since this oxygen is used by the alloying elements for internal oxidation during annealing before hot-dip coating. However, the amount of oxygen built into the oxygen-containing, iron-based layer depends to a large extent on the deposition conditions. Due to technical and economic boundary conditions, the sensible maximum value for the oxygen content is 40% by weight.

Die Reineisenschicht selbst kann erfindungsgemäß entweder elektrolytisch oder durch Abscheidung aus der Gasphase aufgebracht werden, während die sauerstoffhaltige, eisenbasierte Schicht vorteilhaft elektrolytisch abgeschieden wird. Als Reineisenschicht wird eine Schicht mit einem durchschnittlichen Eisengehalt von mehr als 96 Gewichts-% verstanden.According to the invention, the pure iron layer itself can be applied either electrolytically or by deposition from the gas phase, while the oxygen-containing, iron-based layer is advantageously deposited electrolytically. A pure iron layer is a layer with an average iron content of more than 96% by weight.

Das Stahlsubstrat für ein erfindungsgemäß hergestelltes Stahlband mit einem metallischen Schmelztauchüberzug kann folgende Zusammensetzung in Gewichts-% aufweisen:

  • C: 0,03 % bis 0,35 %,
  • Mn: 4,1 % bis 8,0 %,
  • Si: 0,008 % bis 2,5 %,
  • Al: 0,001 % bis 2,0 %,
  • optional
  • Cr: 0,01 % bis 0,7 %,
  • B: 0,001 % bis 0,08 %,
  • Ti: 0,005 % bis 0,3 %,
  • V: 0,005 % bis 0,3 %,
  • Nb: 0,005 % bis 0,2 %,
  • Mo: 0,005 % bis 0,7 %,
  • P ≤ 0,10 %,
  • S ≤ 0,010 %,
  • Rest Eisen und unvermeidbare Verunreinigungen.
The steel substrate for a steel strip produced according to the invention with a metallic hot-dip coating can have the following composition in % by weight:
  • C: 0.03% to 0.35%,
  • Mn: 4.1% to 8.0%,
  • Si: 0.008% to 2.5%,
  • Al: 0.001% to 2.0%,
  • optional
  • Cr: 0.01% to 0.7%,
  • B: 0.001% to 0.08%,
  • Ti: 0.005% to 0.3%,
  • V: 0.005% to 0.3%,
  • Nb: 0.005% to 0.2%,
  • Mo: 0.005% to 0.7%,
  • P ≤ 0.10%,
  • S ≤ 0.010%,
  • remainder iron and unavoidable impurities.

Das erfindungsgemäße Verfahren beinhaltet weiterhin eine Glühbehandlung des mit einer Reineisen und darauf aufgebrachten sauerstoffhaltigen, eisenbasierten Schicht versehenen Stahlbandes in einem Durchlaufglühofen. Dieser Ofen kann eine Kombination aus einem Ofenteil mit offener Verbrennung (DFF, Direct Fired Furnace / NOF, Non-Oxidizing Furnace) und einem danach angeordnetem Strahlrohrofen (RTF, Radiation Tube Furnace) sein oder aber in einem reinen Strahlrohrofen (All Radiant Tube Furnace) erfolgen. Das Stahlband wird bei einer Glühtemperatur von 550 °C bis 880 °C und einer mittleren Aufheizrate von 1 K/s bis 100 K/s, sowie einer Haltezeit des Stahlbandes auf Glühtemperatur zwischen 30 s und 650 s geglüht. Im Strahlrohrofen wird eine reduzierende Glühatmosphäre, bestehend aus 2 % bis 40 % H2 und 98 bis 60 % N2 und einem Taupunkt zwischen +15 °C und -70 °C verwendet, so dass eine im Wesentlichen aus metallischem Eisen bestehende Oberfläche erhalten wird. Anschließend wird das Band auf eine Temperatur oberhalb der Schmelzbadtemperatur des Überzugs abgekühlt und nachfolgend mit dem metallischen Überzug beschichtet. Optional kann nach der Glühbehandlung und vor der Beschichtung mit dem metallischen Überzug das Band auf eine so genannte Überalterungstemperatur zwischen 200 °C und 600 °C abgekühlt und bei dieser Temperatur für bis zu 500 s gehalten werden. Wird eine Überalterungstemperatur unterhalb der Schmelzbadtemperatur des Überzugs gewählt, um beispielsweise das Gefüge und die resultierenden technologischen Kennwerte des Stahls zu beeinflussen, so kann das Band vor dem Eintritt in das Schmelzbad beispielsweise durch eine induktive Erwärmung auf eine Temperatur oberhalb der Schmelzbadtemperatur zwischen 400 °C und 750 °C wiedererwärmt werden, um dem Schmelzbad nicht durch das kalte Stahlband Wärme zu entziehen.The method according to the invention also includes an annealing treatment of the steel strip provided with a pure iron and an oxygen-containing, iron-based layer applied thereto in a continuous annealing furnace. This furnace can be a combination of a furnace part with open combustion (DFF, Direct Fired Furnace / NOF, Non-Oxidizing Furnace) and a radiant tube furnace (RTF, Radiation Tube Furnace) arranged after it, or in an all radiant tube furnace (All Radiant Tube Furnace). take place. The steel strip is annealed at an annealing temperature of 550 °C to 880 °C and an average heating rate of 1 K/s to 100 K/s, as well as a holding time of the steel strip at the annealing temperature of between 30 s and 650 s. A reducing annealing atmosphere consisting of 2% to 40% H 2 and 98 to 60% N 2 and a dew point between +15 °C and -70 °C is used in the radiant tube furnace, so that a surface consisting essentially of metallic iron is obtained . The strip is then cooled to a temperature above the melt bath temperature of the coating and then coated with the metallic coating. Optionally, after the annealing treatment and before being coated with the metallic coating, the strip can be cooled to a so-called overaging temperature between 200° C. and 600° C. and kept at this temperature for up to 500 s. If an overaging temperature below the melting bath temperature of the coating is chosen, for example to influence the structure and the resulting technological characteristics of the steel, the strip can be heated before it enters the melting bath, for example by inductive heating to a temperature above the melting bath temperature of between 400 °C and 750 °C so that the cold steel strip does not draw heat from the weld pool.

Die Verwendung der erfindungsgemäßen Vorbeschichtungen macht eine zusätzliche Einleitung von Wasserdampf zur Erhöhung des Taupunktes, wie es bei den vorbekannten Verfahren üblich ist, unnötig. Für die Glühatmosphäre im Ofen hat es sich deshalb als ausreichend herausgestellt, wenn das Verhältnis der Partialdrücke von Wasserdampf und Wasserstoff bei der Glühung im Strahlrohrofen im Bereich 0,00077 > pH2O/pH2 > 0,00021, vorteilhaft zwischen 0,00254 > pH2O/pH2 > 0,00021, liegt.The use of the precoatings according to the invention makes an additional introduction of water vapor to increase the dew point, as is customary in the previously known processes, unnecessary. It has therefore been found to be sufficient for the annealing atmosphere in the furnace if the ratio of the partial pressures of water vapor and hydrogen during annealing in the radiant tube furnace is in the range 0.00077 > pH 2 O/pH 2 > 0.00021, advantageously between 0.00254 > pH 2 O/pH 2 > 0.00021.

Ein beispielhafter vorteilhafter Verfahrensablauf für die Herstellung eines erfindungsgemäßen Stahlbandes mit verbesserter Haftung einer Schmelztauchverzinkung sieht vor, dass zunächst ein warmgewalztes Stahlband (Warmband) gebeizt, danach kaltgewalzt und anschließend in einer Feuerverzinkungslinie verzinkt wird. Innerhalb der Feuerverzinkungslinie durchläuft das Band eine Vorreinigungssektion, nach der Vorreinigung durchläuft das Band weiter eine Bandaktivierung (Beize/Dekapierung) und nachfolgend 6 Elektrolysezellen. In den ersten 3 Zellen wird eine Eisenschicht abgeschieden, in den darauf folgenden 3 Zellen eine sauerstoffhaltige, eisenbasierte Schicht. Das beschichtete Band durchläuft anschließend Spüle und Trocknung. Anschließend läuft das Band in die Ofensektion der Verzinkungslinie ein, wird geglüht und verzinkt.An exemplary advantageous process sequence for the production of a steel strip according to the invention with improved adhesion of hot-dip galvanizing provides that first a hot-rolled steel strip (hot strip) is pickled, then cold-rolled and then galvanized in a hot-dip galvanizing line. Within the hot-dip galvanizing line, the strip goes through a pre-cleaning section, after pre-cleaning the strip goes through further strip activation (pickling/pickling) and then 6 electrolytic cells. An iron layer is deposited in the first 3 cells, and an oxygen-containing, iron-based layer in the next 3 cells. The coated strip then runs through rinsing and drying. The strip then enters the furnace section of the galvanizing line, where it is annealed and galvanized.

Als metallische Überzüge für das so geglühte Stahlband können beispielsweise Aluminium-Silizium (AS, AISi), Zink (Z), Zink-Aluminium (ZA, Galfan), Zink-Aluminium-Eisen (ZF, Galvannealed), Zink-Magnesium-Aluminium (ZM, ZAM) oder Aluminium-Zink (AZ, Galvalume) verwendet werden. In einer Ausgestaltung basiert der metallische Überzug auf Zink und der Zinküberzug enthält 0,1 bis 1 Gewichts-% Al oder 0,1 bis 6 Gewichts-% Al und 0,1 bis 6 Gewichts-% Mg oder 5 bis 15 Gewichts-% Fe.Aluminum-silicon (AS, AISi), zinc (Z), zinc-aluminum (ZA, Galfan), zinc-aluminum-iron (ZF, galvannealed), zinc-magnesium-aluminum ( ZM, ZAM) or aluminium-zinc (AZ, Galvalume) can be used. In one embodiment, the metallic coating is based on zinc and the zinc coating contains 0.1 to 1% by weight Al or 0.1 to 6% by weight Al and 0.1 to 6% by weight Mg or 5 to 15% by weight Fe .

Ein erfindungsgemäßes Stahlband ist weiterhin dadurch gekennzeichnet, dass im Übergangsbereich zwischen metallischem Überzug und der Stahlbandoberfläche eine überwiegend ferritische Randzone mit mehr als 60 Volumen-% Ferrit ausgebildet ist, die eine Dicke von 0,15 bis 1,1 µm und vorteilhaft eine Dicke zwischen 0,3 und 0,9 µm aufweist. Die Dicke dieser Randzone resultiert dabei unmittelbar aus den abgeschiedenen Vorbeschichtungen, die auch nach Glühung und Schmelztauchbeschichtung eine vom Stahlsubstrat abweichende Gefügeausprägung und damit die gewünschten positiven Effekte aufweist.A steel strip according to the invention is further characterized in that a predominantly ferritic surface zone with more than 60% by volume ferrite is formed in the transition area between the metallic coating and the surface of the steel strip, which has a thickness of 0.15 to 1.1 µm and advantageously a thickness between 0 .3 and 0.9 µm. The thickness of this edge zone results directly from the deposited pre-coatings, which, even after annealing and hot-dip coating, have a microstructure that differs from the steel substrate and thus has the desired positive effects.

In den Figuren 1 und 2 sind beispielhaft Untersuchungsergebnisse dargestellt.

  • Figur 1 zeigt eine rasterelektronenmikroskopische Aufnahme der Oberfläche eines erfindungsgemäßen Mittelmanganstahls vor und nach Abscheidung einer erfindungsgemäßen Vorbeschichtung aus Reineisen und sauerstoffhaltiger, eisenbasierter Schicht. Der Mittelmanganstahl weist 6 Massenprozent Mn sowie 2 Massenprozent Si+Al auf. Die Aufnahmen zeigen die Oberfläche vor und nach Abscheidung der erfindungsgemäßen Vorbeschichtung aus Reineisen und sauerstoffhaltiger, eisenbasierter Schicht.
  • Figur 2 zeigt die Ergebnisse von Tiefenprofilanalysen mittels GDOES (Glow Discharge Optical Emission Spectroscopy) an den in Figur 1 gezeigten Mittelmanganstahlproben nach einer Glühung bei 700 °C für 120 Sekunden in einer Stickstoffatmosphäre mit 5 % Wasserstoff (H2) und 95 % Stickstoffdioxid (N2) bei einem Ofentaupunkt von -50 °C. Die Proben mit der erfindungsgemäßen Vorbehandlung zeigen auf der Oberfläche signifikant geringere Gehalte an den für die Schmelztauchbeschichtung nachteiligen Elementen Sauerstoff, Mangan, Silizium und Aluminium.
In the figures 1 and 2 test results are shown as an example.
  • FIG. 1 shows a scanning electron micrograph of the surface of a medium-manganese steel according to the invention before and after the deposition of a pre-coating according to the invention made of pure iron and an oxygen-containing, iron-based layer. The medium manganese steel has 6% by mass of Mn and 2% by mass of Si+Al. The photographs show the surface before and after deposition of the precoating according to the invention made of pure iron and an oxygen-containing, iron-based layer.
  • Figure 2 shows the results of depth profile analyzes using GDOES (Glow Discharge Optical Emission Spectroscopy) on the medium manganese steel samples shown in Figure 1 after annealing at 700 °C for 120 seconds in a nitrogen atmosphere with 5% hydrogen (H 2 ) and 95% nitrogen dioxide (N 2 ) at an oven dew point of -50 °C. The samples with the pretreatment according to the invention show significantly lower contents of the elements oxygen, manganese, silicon and aluminum, which are disadvantageous for the hot-dip coating, on the surface.

Die nachfolgende Tabelle 3 zeigt die Ergebnisse aus Verzinkungsversuchen, die an einem Schmelztauchverzinkungssimulator mit Probeblechen aus Mittelmanganstahl (6 Massenprozent Mn sowie 2 Massenprozent Si+Al) durchgeführt wurden. Die Abscheidung der Vorbeschichtungen erfolgte elektrolytisch mit einer Stromdichte von 75 A/dm2 je Seite. Die Versuche wurden bei zwei verschiedenen Wärmebehandlungen durchgeführt (800 °C für 200 Sekunden und 700 °C für 120 Sekunden). Proben mit vollständiger Zinkbenetzung und guter Haftung konnten nur mittels einer Vorbeschichtung aus Reineisen und darüber angeordneter Vorbeschichtung aus einer sauerstoffhaltigen, eisenbasierten Schicht erzielt werden.Table 3 below shows the results of galvanizing tests that were carried out on a hot-dip galvanizing simulator with test sheets made of medium manganese steel (6 percent by mass Mn and 2 percent by mass Si+Al). The pre-coatings were deposited electrolytically with a current density of 75 A/dm 2 per side. The tests were carried out at two different heat treatments (800°C for 200 seconds and 700°C for 120 seconds). Samples with complete zinc wetting and good adhesion could only be achieved by means of a pre-coating of pure iron and a pre-coating of an oxygen-containing, iron-based layer on top.

Die Überzugshaftung wird in zwei verschiedenen Testgeometrien geprüft, um die Haftung in den verschiedenen Einsatzzwecken der Stähle sicherzustellen. Die Überzugshaftung im Umformprozess wird mittels Kugelschlagtest gemäß SEP1931 geprüft. Bei dieser Prüfung wird ein Halbkugelstempel unter hoher Schlagenergie auf ein Probeblech geschlagen. Durch die Schlagbeanspruchung entsteht in dem Probeblech ein kalottenförmiger Eindruck. Dieser Vorgang wird bis zu einem leichten Anriss des Probeblechs, falls notwendig mehrfach, durchgeführt. Anschließend wird die Oberfläche visuell auf Enthaftungen und Abblätterungen des zinkbasierten Überzugs im Bereich der Kalotte geprüft. Das Ergebnis wird mit Noten von 1-4 bewertet (Noten 1+2 bestanden, Noten 3+4 nicht bestanden).Coating adhesion is tested in two different test geometries to ensure adhesion in the different uses of the steels. The coating adhesion in the forming process is tested using a ball impact test in accordance with SEP1931. In this test, a hemispherical stamp is hit with high impact energy on a test panel. The impact stress creates a dome-shaped impression in the test panel. This process is carried out until there is a slight crack in the test panel, several times if necessary. The surface is then checked visually for delamination and delamination of the zinc-based coating in the area of the calotte. The result is evaluated with grades from 1-4 (grades 1+2 passed, grades 3+4 failed).

Die Überzugshaftung im Crashfall wird mittels eines Klebraupentests überprüft. Hierzu wird eine Klebstoffraupe in definierter Geometrie, vorzugsweise 10 mm breit und 5 mm hoch, eines 1K-Epoxidharz-Strukturklebstoffs auf das Probeblech aufgetragen. Anschließend wird der Klebstoff gemäß Datenblatt ausgehärtet und im Folgenden die Probe zügig innerhalb von maximal 2 s um 90° gebogen. Bei diesem Vorgang bricht die Klebraupe unter der starken Spannung und zieht schlagartig an dem bereits durch die Biegung beanspruchten Überzug.The adhesion of the coating in the event of a crash is checked using an adhesive bead test. For this purpose, a bead of adhesive in a defined geometry, preferably 10 mm wide and 5 mm high, of a 1-component epoxy resin structural adhesive is applied to the test panel. The adhesive is then cured according to the data sheet and the sample is then quickly bent through 90° within a maximum of 2 s. During this process, the adhesive bead breaks under the strong tension and suddenly pulls on the already through the Bending stressed coating.

Anschließend werden die Proben visuell nach Zinkablösungen beurteilt.

Figure imgb0001
The samples are then assessed visually for zinc detachment.
Figure imgb0001

Die Vorteile der Erfindung lassen sich wie folgt zusammenfassen:

  • reproduzierbare, gute Haftung des metallischen Überzugs auf dem Stahlsubstrat,
  • Verbesserung der Verzinkbarkeit von Stählen mit hohen Mangangehalten zwischen 4,1 und 8 Massenprozent,
  • Verbesserung der visuellen Oberflächenqualität des Schmelztauchüberzugs,
  • Stähle mit sehr hohen Legierungselementgehalten lassen sich bislang großtechnisch häufig nur elektrolytisch verzinken und neigen aufgrund des eingebrachten Wasserstoffs bei diesem Prozess zur Wasserstoffversprödung; diese Gefahr besteht bei der erfindungsgemäßen Schmelztauchbeschichtung nicht. Zwar kann bei der erfindungsgemäßen elektrolytischen Abscheidung an der Kathode auch Wasserstoff als Nebenprodukt gebildet werden, der zunächst auf der Oberfläche atomar adsorbiert vorliegt und im späteren Verlauf durch das Stahlsubstrat absorbiert werden kann. Jedoch sind während des sich anschließenden Glühprozesses die Bedingungen für eine Effusion des eingebrachten Wasserstoffs gegeben.
The advantages of the invention can be summarized as follows:
  • reproducible, good adhesion of the metallic coating on the steel substrate,
  • Improvement of the zincability of steels with high manganese contents between 4.1 and 8 percent by mass,
  • Improvement of the visual surface quality of the hot-dip coating,
  • Steels with very high alloying element contents can often only be electrolytically galvanized on an industrial scale and tend to hydrogen embrittlement due to the hydrogen introduced in this process; this risk does not exist with the hot-dip coating according to the invention. It is true that in the electrolytic deposition according to the invention the cathode, hydrogen is also formed as a by-product, which is initially atomically adsorbed on the surface and can later be absorbed by the steel substrate. However, during the subsequent annealing process, the conditions for effusion of the introduced hydrogen are given.

Claims (15)

  1. Method for producing a cold or hot rolled steel strip comprising a metal coating, the steel strip comprising iron as the main component and, in addition to carbon, an Mn content of 4.1 to 8.0 wt.% and optionally one or more of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo, wherein the surface of the uncoated steel strip is cleaned, a layer of pure iron having an average iron content of greater than 96 wt.% is applied to the cleaned surface, an oxygen-containing, iron-based layer containing greater than 5 mass percent of oxygen is applied to the layer of pure iron, the steel strip is then subjected to annealing treatment together with the oxygen-containing, iron-based layer and, during the annealing, is subjected to reduction treatment in a reducing furnace atmosphere, and finally the steel strip thus treated and annealed is subjected to hot dip coating with the metal coating.
  2. Method according to claim 1, characterised in that an average thickness of the pure iron layer is formed to be from 0.05 to 0.5 µm, preferably from 0.1 to 0.4 µm, and an average thickness of the oxygen-containing, iron-based layer is formed to be from 0.1 to 0.6 µm, preferably from 0.2 to 0.5 µm.
  3. Method according to at least one of claims 1 and 2, characterised in that the average thickness of the oxygen-containing, iron-based layer is greater than the average thickness of the pure iron layer.
  4. Method according to at least one of claims 1 to 3, characterised in that the oxygen-containing, iron-based layer having a proportion of oxygen of greater than 5 to 40 wt.%, preferably greater than 10 to 30 wt.%, particularly advantageously greater than 12 to 25 wt.%, is applied to the pure iron layer.
  5. Method according to at least one of claims 1 to 4, characterised in that the pure iron layer is deposited electrolytically or by deposition from the gas phase and the oxygen-containing, iron-based layer is deposited electrolytically.
  6. Method according to at least one of claims 1 to 5, characterised in that the steel strip has the following composition in wt.%:
    C: 0.03% to 0.35%,
    Mn: 4.1% to 8.0%,
    Si: 0.008% to 2.5%,
    Al: 0.001% to 2.0%,
    optionally
    Cr: 0.01% to 0.7%,
    B: 0.001% to 0.08%,
    Ti: 0.005% to 0.3%,
    V: 0.005% to 0.3%,
    Nb: 0.005% to 0.2%,
    Mo: 0.005% to 0.7%,
    P ≤ 0.10%,
    S ≤ 0.010%,
    and the remainder iron and unavoidable impurities.
  7. Method according to at least one of claims 1 to 6, characterised in that the annealing treatment is carried out in a radiant tube furnace as a continuous annealing furnace, at an annealing temperature of from 550°C to 880°C and an average heating rate of from 1 K/s to 100 K/s, with a reducing annealing atmosphere consisting of 2 to 40% H2 and 98 to 60% N2 and a dew point in the annealing furnace of between +15 and -70°C and a holding time of the steel strip at the annealing temperature of between 30 s and 650 s with optional subsequent cooling to a holding temperature of between 200°C and 600°C for up to 500 s with subsequent optional inductive heating to a temperature above the melt bath temperature of the metal coating at 400°C to 750°C and subsequently the hot dip coating of the steel strip with the metallic coating is carried out.
  8. Method according to at least one of claims 1 to 7, characterised in that the ratio of the partial pressures of water vapor and hydrogen during the annealing treatment in the radiant tube furnace is in the range 0.00077 > pH2O/pH2 > 0.00021, advantageously 0.00254 > pH2O/pH2 > 0.00021.
  9. Method according to at least one of claims 1 to 8, characterised in that aluminium-silicon (AS, AISi), zinc (Z), zinc-aluminium (ZA, Galfan), zinc-iron (ZF, Galvannealed), zinc-aluminium-magnesium (ZM, ZAM) or aluminium-zinc (AZ, Galvalume) are used as metal coatings.
  10. Steel strip, comprising, in addition to carbon, iron as the main component, an Mn content of 4.1 to 8.0 wt.% and optionally one or more of the alloying elements Al, Si, Cr, B, Ti, V, Nb and/or Mo together with a metal coating applied by means of hot dipping, characterised in that a predominantly ferritic edge zone having greater than 60 vol.% ferrite is formed in the transition region between the metal coating and the steel strip surface, the predominantly ferritic edge zone having a thickness of from 0.15 to 1.1 µm and, when viewed from the steel strip surface, consisting of a pure iron layer having an average iron content of greater than 96 wt.% and an oxygen-containing, iron-based layer thereon which contains greater than 5 mass percent of oxygen.
  11. Steel strip according to claim 10, characterised in that the predominantly ferritic edge zone has a thickness of between 0.3 and 0.9 µm.
  12. Steel strip according to at least one of claims 10 and 11, characterised by the following composition in wt.%:
    C: 0.03% to 0.35%,
    Mn: 4.1% to 8.0%,
    Si: 0.008% to 2.5%,
    Al: 0.001% to 2.0%,
    optionally
    Cr: 0.01% to 0.7%,
    B: 0.001% to 0.08%,
    Ti: 0.005% to 0.3%,
    V: 0.005% to 0.3%,
    Nb: 0.005% to 0.2%,
    Mo: 0.005% to 0.7%,
    P ≤ 0.10%,
    S ≤ 0.010%,
    and the remainder iron and unavoidable impurities.
  13. Steel strip according to at least one of claims 10 to 12, characterised by a metal coating made of aluminium-silicon (AS, AISi), zinc (Z), zinc-aluminium (ZA), zinc-aluminium-iron (ZF/Galvannealed), zinc-magnesium-aluminium (ZM, ZAM) or aluminium-zinc (AZ).
  14. Steel strip according to claim 13, characterised in that, with a metal coating based on zinc, the zinc coating contains
    0.1 to 1 wt.% Al or
    0.1 to 6 wt.% Al and 0.1 to 6 wt.% Mg or
    5 to 15 wt.% Fe.
  15. Use of a steel strip produced according to at least one of claims 1 to 9 or a steel strip according to at least one of claims 10 to 14 for producing parts for motor vehicles.
EP20715830.4A 2019-04-01 2020-03-27 Method for producing a steel sheet with improved adhesion of metallic hot-dip coatings Active EP3947754B1 (en)

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