US20210301364A1 - Producing a hardened steel product - Google Patents

Producing a hardened steel product Download PDF

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Publication number
US20210301364A1
US20210301364A1 US17/262,237 US201917262237A US2021301364A1 US 20210301364 A1 US20210301364 A1 US 20210301364A1 US 201917262237 A US201917262237 A US 201917262237A US 2021301364 A1 US2021301364 A1 US 2021301364A1
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thickness
steel substrate
precoating
coating
steel
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Stefan Pohl
Elisabeth Danger
Thorsten Labudde
Jürgen Butzkamm
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Muhr und Bender KG
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Muhr und Bender KG
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C23C2/29—Cooling or quenching

Definitions

  • metallic components can be coated for corrosion protection and formed into parts by hot forming.
  • aluminum-silicon coated high-strength and ultra-high-strength quenched and tempered steels in particular manganese-boron containing quenched and tempered steels such as 22MnB5 or 34MnB5, are used for safety-relevant vehicle body components.
  • a method for producing a hot stamped coated steel section comprising the steps of: precoating a steel strip with aluminum or aluminum alloy by melt dipping, wherein the thickness of the precoating is 20 to 33 micrometers on each side, cutting the precoated steel strip into a steel blank, heating the steel blank in a furnace, transferring the heated blank to a die, hot stamping the steel blank in the die, and cooling the steel blank.
  • a process for producing flexibly rolled strip material with a cathodic corrosion protection coating is known.
  • the coating of the strip material is carried out at elevated strip temperature in a zinc pot (hot dipped galvanized steel).
  • the zinc coating is rolled with the same ratio as the actual strip thickness, wherein a final coating thickness after flexible rolling of greater than or equal to 7.5 micrometers is aimed for.
  • a process for producing a sheet metal component is known from WO 2008/113426 A2, wherein a hot strip or cold strip is hot-dip coated or electrolytically coated and then subjected to a flexible rolling process.
  • a hot strip or cold strip is hot-dip coated or electrolytically coated and then subjected to a flexible rolling process.
  • different sheet thicknesses of the flexibly rolled steel strip are produced by different rolling pressures.
  • the coating is formed to different thicknesses during the coating process, wherein the coating thickness is formed greater with increasing expected rolling pressure.
  • WO 2006 097 237 A1 a process and an installation for hot-dip coating of hot-rolled steel strip is known.
  • the steel strip passes through a pickling station, a rinsing station, a drying station, a heating furnace and then a melting bath.
  • the finished thickness and the thickness tolerance of the hot-dip coated steel strip are achieved by a controlled thickness reduction in a rolling stand in the process line by monitoring the finish thickness at the outlet of the rolling stand by a thickness gauge and feeding back deviations from the target thickness as an actuating signal to the adjustment of the rolling stand.
  • a process for hot forming a steel component is known.
  • the steel component is provided with a corrosion-resistant scale protection layer and, prior to hot forming, a surface oxidation is carried out in which a corrosion-resistant oxidation layer is formed on the scale protection layer.
  • the present disclosure encompasses a process for producing coated hardened steel products, in particular for use as a structural component of a motor vehicle.
  • the method for producing a coated and hardened component, in particular as a structural component for a motor vehicle, has good corrosion protection resistance in areas with different thicknesses.
  • a method for producing a hardened steel product comprises: providing a steel substrate with a base material of hardenable steel; coating the steel substrate with a precoating comprising aluminum to produce a pre-coated steel substrate, the coating of the pre-coated steel substrate having a thickness (d 1 ) of at least 34 micrometers ( ⁇ m); flexible rolling the precoated steel substrate such that successive portions of the precoated steel substrate are rolled out differently to produce a varying thickness along the length of the precoated steel substrate, wherein after the flexible rolling the precoating has in thinner first portions a reduced first thickness (d 2 a ) of less than 33 micrometers and in thicker second portions a reduced second thickness (d 2 b ) which is thicker than the reduced first thickness (d 2 a ); working a blank out of the flexibly rolled strip material; heating the blank such that the base material of the blank is at least partially austenitized, wherein diffusion processes take place between the base material and the precoating through the heating; hot forming the heated blank, where
  • the substrate has a sufficiently thick coating even after flexible rolling. It has been found that during heating for subsequent hot forming the coating grows due to the diffusion processes, so that the final thickness of the coating after hot forming is greater than the respective coating thickness after flexible rolling and before heating for hot forming. Because the precoating has a thickness of at least 34 micrometers, the coating is sufficiently thick to achieve good corrosion protection even in the thinner first portions, despite the reduction in thickness that occurs during flexible rolling, due to the subsequent heating for hot forming. In the thicker portions of the finished component, which usually have to withstand higher loads, the coating is also correspondingly thicker so that these portions are particularly well protected. Overall, this results in a load-optimized and/or weight-reduced component with excellent coating protection in all thickness regions.
  • the steel substrate can, for example, be a hardenable and/or heat-treatable steel material, in particular a material containing manganese. It can contain other microalloying elements In addition to manganese.
  • the steel material may, for example, contain the following proportions of alloying elements, in percent by weight respectively:
  • Al with a maximum of 0.1%
  • the substrate may contain, respectively in percent by weight, in particular at least one of:
  • the mass fraction of the optional alloying elements can also be lower, for example molybdenum can also be included with at most 0.8%, 0.5% or 0.25%.
  • the mass fraction of the optional alloying elements in total amounts to maximum 1.55%, in particular maximum 1.0%, in particular maximum 0.8%.
  • the alloying element niobium advantageously produces a fine-grained structure of a component hot-formed from the alloy. In particular in combination with molybdenum, which can inhibit grain growth, a particularly fine-grained structure is obtained, which in turn has a favorable effect on the strength of the component made therefrom.
  • Examples of usable boron-manganese-containing steel materials are 17MnB5, 20MnB5, 20MnB8, 22MnB5, 26MnB5 or 34MnB5.
  • the starting material may have a tensile strength of at least 450 MPa, for example.
  • a formed part made from the coated steel substrate may have a final tensile strength of, for example, at least 1100 MPa, in particular at least 1500 MPa. It is also possible for certain portions of the formed part to be configured, where necessary, to a lower tensile strength of less than 1100 MPa and higher ductility in return.
  • the steel substrate may have an initial thickness of, for example, between 1.0 and 4.0 mm.
  • the coating contains at least 85 weight percent aluminum, which includes the possibility of using a pure aluminum coating (100 weight percent Al), as well as the use of an alloy containing as main alloying component aluminum with at least 85 weight percent and optionally further alloying components, for example silicon with for example between 5 and 15 weight percent and/or iron with up to 5 weight percent and/or one or more other alloying elements in smaller proportions.
  • the proportion of the other alloying elements for example at least one of the group of Mn, Cr, Ti, B, P, S, Cu, Ni, Nb, Mo, V, may together be, for example, up to 1.5 weight percent.
  • the terms aluminum coating or aluminum-based coating are also used, and are intended to include the mentioned possibilities of other alloy compositions.
  • the aluminum coating can be applied to the steel substrate, for example, by hot-dip coating in a molten bath containing at least 85 percent by weight of aluminum and, as the case may be, other alloying components, or by other conventional coating processes.
  • An exemplary composition of the molten bath or the applied coating may contain up to 3 weight percent iron, 9 to 12 weight percent silicon, optionally one or more further alloying elements with a total of up to 1.5 weight percent, and remainder aluminum. It is understood that unavoidable impurities may also be present.
  • the precoating is applied to the steel substrate with a thickness (d 1 ) of at least 36 micrometers, in particular at least 40 micrometers.
  • the steel substrate precoated in this way forms the basis for a hardened component with varying thicknesses to be produced therefrom.
  • the coating of the steel substrate may be applied, for example, by means of hot-dip coating, wherein the steel substrate is immersed in a pool of molten coating material. It is to be understood that other known coating processes may be used as well.
  • the precoated steel substrate is flexibly rolled after the precoating, wherein it is to be understood that further steps, such as heating, winding on or unwinding from the coil, straightening, cleaning or the like can be interposed.
  • the steel substrate is heated in the coating device after application of the precoating in order to achieve pre-diffusion between the precoating and the steel substrate.
  • Heating for pre-diffusion is carried out at temperatures below the melting temperature of the coating material, for example in a temperature window between 0.5 and 0.9 times the melting temperature of the coating material. Due to the pre-diffusion, a thicker interdiffusion zone is already formed between the base material of the steel substrate and the coating material during the coating process. This makes it possible to carry out heating more quickly in the course of hot forming, which has an overall favorable effect on the cycle times in hot forming.
  • strip material with substantially uniform sheet thickness is rolled out into strip material with varying sheet thickness along its length by changing the rolling gap during the process.
  • the portions of varying thickness produced by flexible rolling extend transversely to the longitudinal direction and rolling direction of the strip material, respectively.
  • the strip material can be easily wound again into a coil and fed for further processing elsewhere, or it can be processed further directly, for example by cutting the strip material to length to form individual sheet elements.
  • Flexible rolling can be carried out with rolling degrees of at least 1% and/or a maximum of 60% starting from the initial thickness (d 1 ) of the precoated steel substrate, in particular with rolling degrees between 3% and 55%. Flexible rolling also reduces the thickness of the precoating along with the steel substrate.
  • the precoating can comprise in thinner first portions in particular a reduced first thickness (d 2 a ) of less than 20 micrometers.
  • the flexible rolling is carried out such that after the flexible rolling the precoating comprises in thicker second portions a reduced second thickness (d 2 b ) of more than 33 micrometers, in particular of more than 36 micrometers. It is understood that between thinnest portions and thickest portions of the strip material, depending on the desired component geometry, there may be any other thickness regions or transition regions in between.
  • blanks are produced from the flexibly rolled strip material. This process step is also referred to as separating.
  • the separation can be carried out by mechanical cutting or by laser cutting.
  • the term blanks is intended to encompass both rectangular metal sheets that have been cut out of the strip material and shaped cuts.
  • Shape cuts are sheet metal elements cut out of the strip material, the outer contour of which is already adapted to the shape of the end product.
  • the sheet blanks are hot formed, wherein further process steps may be interposed, as required.
  • the blank is heated to austenitizing temperature at least in a partial region; then placed into a hot forming tool and formed in the hot forming tool and rapidly cooled so that a hardened formed part is produced. Heating is performed in a suitable heating device, such as a continuous furnace.
  • Heating to austenitizing temperature means a temperature range at which at least partial austenitizing takes place and/or is present, i.e. a microstructure in the two-phase region ferrite and austenite.
  • the blank is heated to a temperature above Ac1, i.e., the temperature at which the formation of austenite begins.
  • the blank may be heated to a temperature above 880° C. and/or up to 960° C.
  • the blank is heated at a heating rate greater than 12 K/sec for austenitizing at least until a temperature of 700° C. is reached. Rapid heating reduces the manufacturing time.
  • the blank is formed and rapidly cooled. Rapid cooling of the formed part in the forming tool produces a hardened, at least partially martensitic microstructure in the part. This process of hot forming and rapid cooling in a forming tool is also known as press hardening.
  • the precoating and the underlying steel substrate form the coating, which increases compared to the thickness of the precoating due to diffusion processes.
  • the first final thickness (d 3 a ) in the thinner first portions of the finished component is preferably formed with more than 15 micrometers, in particular more than 20 micrometers, and less than 50 micrometers, in particular less than 40 micrometers.
  • the coating may have in the thicker second portions a second final thickness (d 3 b ) of less than 60 micrometers, in particular less than 50 micrometers, and/or more than 30 micrometers, in particular more than 35 micrometers, after the hot forming.
  • the coating in the thinner regions grows more than in the thicker regions during hot forming.
  • the coating is formed with a final thickness ratio (d 3 a /d 3 b ) of the first final thickness (d 3 a ) to the second final thickness (d 3 b ) that is greater than an intermediate thickness ratio (d 2 a /d 2 b ) of the reduced first thickness (d 2 a ) to the reduced second thickness (d 2 b ).
  • the different coating thicknesses overall converge in an advantageous manner, so that good overall corrosion protection is achieved in all portions of the component.
  • hot forming can be carried out as an indirect process comprising the sub-steps of cold preforming, subsequent heating of the cold preformed component to austenitizing temperature, and subsequent hot forming to produce the final contour of the product.
  • hot forming can also be carried out as a direct process, characterized by heating the component directly to austenitizing temperature and then hot forming it to the desired final contour in one step. No prior (cold) preforming takes place in this case.
  • the coating prior to forming in the forming tool, can be produced such that a metal oxide layer is formed on the surface.
  • a metal oxide layer is corrosion-resistant and inert, so that tool wear during forming is reduced.
  • the layer thicknesses specified in the present disclosure for the condition after hot forming refer to the total coating thickness, i.e. including the oxide layer.
  • FIG. 1 schematically shows an example process for producing a coated, hardened formed part
  • FIG. 2A shows a section of the coated steel substrate after precoating in an enlarged schematic view
  • FIG. 2B shows a section of the coated steel substrate after flexible rolling in enlarged schematic view
  • FIG. 2C shows a section of the coated and flexibly rolled steel substrate after hot forming in enlarged schematic view.
  • FIGS. 1 and 2A to 2C are described together below.
  • FIG. 1 shows a process for producing a hardened product from a coated steel substrate 2 .
  • the steel substrate in strip form is also referred to as a steel strip or generally as strip material.
  • the steel substrate is also referred to as a blank.
  • the steel substrate 2 may include a hardenable steel flat product which may contain, for example, the following proportions of alloying elements, each in percent by weight:
  • Al with a maximum of 0.1%
  • This alloy composition includes, for example, steel materials containing boron-manganese, such as 17MnB5, 20MnB5, 20MnB8, 22MnB5, 26MnB5 and 34MnB5.
  • the steel material may have an initial yield strength of, for example, 150 to 1100 MPa and/or a tensile strength of at least 450 MPa.
  • the optional further alloying elements may be selected from the group:
  • the steel substrate 2 which in the initial state may be wound to a coil 3 , is provided with a precoating 4 .
  • the precoating 4 contains aluminum with at least 85 percent by weight and silicon with up to 15 percent by weight. It is understood that other alloying elements may be included at the expense of the silicon content, for example iron and/or other alloying elements totaling up to 5 weight percent.
  • the precoating 4 may be applied to the steel substrate 2 by generally known methods. A possibility is the application by a hot-dip process.
  • the steel substrate 2 passes through a molten bath 5 of liquid coating material 4 in a coating device 6 , which adheres to the surface of the substrate 2 , so that a pre-coated steel substrate is produced.
  • the melt of the coating material may contain, for example, 8 to 15% by weight of silicon, 2 to 4% by weight of iron, optionally one or more further alloying elements, such as, for example, at least one from the group of Mn, Cr, Ti, B, P, S, Cu, Ni, Nb, Mo, V, of together up to 1.5% by weight, and as the remainder aluminum, as well as unavoidable impurities.
  • the precoating 4 is applied to the steel substrate 2 with a thickness d 1 of at least 36 micrometers, in particular at least 40 micrometers.
  • the coating thickness d 1 can have a maximum thickness of 60 micrometers, in particular up to 50 micrometers.
  • FIG. 2A schematically shows a section of the steel substrate 2 with precoating 4 , the combination of steel substrate with precoating being marked with reference sign 2 ′.
  • the coated steel substrate 2 ′ is flexibly rolled (S 2 ).
  • the coated steel strip 2 ′ which before flexible rolling has a substantially constant sheet thickness D 1 along its length, is rolled by rolls 7 , 8 such that it acquires a varying sheet thickness D 2 a , D 2 b , D 2 c along the rolling direction.
  • the coated and flexibly rolled steel substrate is marked with reference 12 .
  • Flexible rolling is carried out in accordance with the desired target thickness profile of a blank to be cut from the strip material 12 and/or a component to be produced therefrom. Flexible rolling can be carried out with rolling degrees of at least 1% and/or at most 60% starting from the initial thickness D 1 of the precoated steel substrate 2 ′, in particular with rolling degrees between 3% and 55%.
  • FIG. 2B shows a section of the precoated steel substrate 12 after flexible rolling.
  • the flexibly rolled strip material 12 after rolling has more strongly rolled-out first regions a with a first thickness D 2 a and less strongly rolled-out second regions b with a second thickness D 2 b as well as transition regions c with variable thickness D 2 c lying therebetween.
  • the thickness of both the substrate 2 and the precoating 4 is reduced.
  • both the thickness of the substrate 2 and the thickness of the precoating 4 applied thereto decrease.
  • the precoating 4 After flexible rolling, the precoating 4 has a reduced first thickness d 2 a of, in particular, less than 20 micrometers in the thinner first portions a, and a reduced second thickness d 2 b of, in particular, more than 33 micrometers, preferably more than 36 micrometers, in thicker second portions b.
  • the strip material 12 can be rewound to a coil 3 so that it can be transported to a subsequent processing station.
  • the steel strip 12 can be straightened in a subsequent process step, which takes place in a strip straightening device.
  • the process step of straightening is optional and can also be omitted.
  • the coated and flexibly rolled steel strip 12 is separated in method step S 3 .
  • Individual sheet blanks 22 are worked out of the steel strip 12 , for example by a punching and/or cutting device 10 . Depending on the shape of the sheet blanks 22 to be produced, these can be punched out of the strip material 12 as a shaped cut, with an edge which is not used further being discarded as scrap, or the strip material 12 can simply be cut to length into sections.
  • the blanks 22 are hot-formed in a subsequent step S 4 , which can also be referred to as press hardening.
  • the blanks 22 are heated to a temperature that is usually above the AC1 and/or AC3 temperature of the material, for example between 750° C. to 1000° C. Heating may be accomplished by suitable methods, such as by inductive heating, conductive heating, roller hearth furnace heating, hot plate contact heating, infrared, or other known methods.
  • the blank 22 is then placed in a hot forming tool 11 and formed therein and cooled and/or quenched so rapidly that at least a partial martensitic hardness structure is formed in the formed part so produced.
  • hot forming can be carried out as a direct process.
  • the blank 22 is heated directly to austenitizing temperature and then hot formed to the desired final contour in one step. No prior (cold) preforming takes place here.
  • hot forming can also be carried out as an indirect process comprising the sub-steps of cold preforming, subsequent heating of the cold preformed component to austenitizing temperature and subsequent hot forming to produce the final contour of the formed part.
  • the holding time for austenitizing the coated blank 22 depends on the selected temperature and can range from 4 to 10 minutes.
  • the coating 4 of the hot-formed product 32 has a final coating thickness d 3 a of more than 15 micrometers, in particular more than 20 micrometers.
  • the coating 4 may have after heating and/or hot forming a second final thickness d 3 b , in particular of more than 30 micrometers, preferably more than 35 micrometers.
  • the final thickness d 3 a of the coating 4 in the thin portions a is less than 50 micrometers, in particular less than 40 micrometers, and in the thicker portions b is less than 60 micrometers, in particular less than 50 micrometers.
  • surface oxidation of the coated and flexibly rolled substrate 2 can be carried out before hot forming (S 4 ).
  • an oxidation layer is formed on the coating 4 .
  • the blank in the course of hot forming, the blank can be heated at a heating rate of more than 12 K/sec at least until a temperature of 700° C. is reached.

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US17/262,237 2018-07-25 2019-07-10 Producing a hardened steel product Abandoned US20210301364A1 (en)

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DE102018118015.2A DE102018118015A1 (de) 2018-07-25 2018-07-25 Verfahren zur Herstellung eines gehärteten Stahlprodukts
DE102018118015.2 2018-07-25
PCT/EP2019/068581 WO2020020644A1 (fr) 2018-07-25 2019-07-10 Procédé pour la fabrication d'un produit en acier durci

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DE102020120580A1 (de) 2020-08-04 2022-02-10 Muhr Und Bender Kg Verfahren zum herstellen von beschichtetem stahlband, und verfahren zum herstellen eines gehärteten stahlprodukts
EP3964602A1 (fr) * 2020-09-02 2022-03-09 ThyssenKrupp Steel Europe AG Procédé de fabrication d'un composant en tôle par formage à chaud d'un produit en acier plat pourvu d'un revêtement de protection contre la corrosion

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WO2020020644A1 (fr) 2020-01-30
CN112567054A (zh) 2021-03-26
EP3827103A1 (fr) 2021-06-02

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