EP4388140A1 - Acier ayant des propriétés de traitement améliorées pour travailler à des températures élevées - Google Patents

Acier ayant des propriétés de traitement améliorées pour travailler à des températures élevées

Info

Publication number
EP4388140A1
EP4388140A1 EP22764727.8A EP22764727A EP4388140A1 EP 4388140 A1 EP4388140 A1 EP 4388140A1 EP 22764727 A EP22764727 A EP 22764727A EP 4388140 A1 EP4388140 A1 EP 4388140A1
Authority
EP
European Patent Office
Prior art keywords
weight
sheet metal
temperature
metal part
content
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22764727.8A
Other languages
German (de)
English (en)
Inventor
Thomas Gerber
Janko Banik
Stefan Krebs
Bernd Linke
Cássia CASTRO MÜLLER
Tayfun DAGDEVIREN
Maria KÖYER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ThyssenKrupp Steel Europe AG filed Critical ThyssenKrupp Steel Europe AG
Publication of EP4388140A1 publication Critical patent/EP4388140A1/fr
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • 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
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0457—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface 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
    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • a "flat steel product” or a “sheet metal product” is mentioned below, this means rolled products such as steel strips or sheets, from which "sheet metal blanks” (also called blanks) are separated for the manufacture of body components, for example.
  • sheet metal blanks also called blanks
  • “Shaped sheet metal parts” or “sheet metal components” of the type according to the invention are made from sheet metal blanks of this type, the terms “shaped sheet metal part” and “sheet metal component” being used synonymously here.
  • a shaped sheet metal part and a method for producing such a shaped sheet metal part are also known from EP 2 553 133 B1.
  • the task was to further develop a flat steel product for hot forming in such a way that, in conjunction with an aluminum-based anti-corrosion coating, improved processing properties of the hot-formed sheet metal part can be achieved.
  • a method should be specified with which such shaped sheet metal parts can be produced in a practice-oriented manner.
  • the invention achieves this object by means of a flat steel product for hot forming, comprising a steel substrate made of steel which, in addition to iron and unavoidable impurities (in % by weight),
  • the steel substrate of the flat steel product according to the invention has an aluminum content of at least 0.06% by weight, preferably at least 0.07% by weight, in particular at least 0.08% by weight.
  • the aluminum content is preferably at least 0.10% by weight, particularly preferably at least 0.11% by weight, in particular at least 0.12% by weight, preferably at least 0.140% by weight, in particular at least 0.15% by weight %, preferably at least 0.16% by weight.
  • the maximum aluminum content is 1.0% by weight, in particular a maximum of 0.8% by weight.
  • the aluminum content is at least 0.07% by weight, in particular at least 0.08% by weight, preferably at least 0.10% by weight, particularly preferably at least 0.11% by weight. in particular at least 0.12% by weight, preferably at least 0.140% by weight, in particular at least 0.15% by weight, preferably at least 0.16% by weight.
  • the maximum aluminum content in this variant is at most 0.50% by weight, in particular at most 0.35% by weight, preferably at most 0.25% by weight, in particular at most 0.24% by weight.
  • the aluminum content is at least 0.50% by weight, preferably at least 0.60% by weight, preferably at least 0.70% by weight.
  • the maximum aluminum content is at most 1.0% by weight, in particular at most 0.9% by weight, preferably at most 0.80% by weight.
  • Aluminum (“AI") is known to be added as a deoxidizing agent during the production of steel. At least 0.01% by weight of Al is required to reliably bind the oxygen contained in the molten steel.
  • Al can also be used to bind undesired but production-related unavoidable N contents. Comparatively high aluminum contents have so far been avoided because the Ac3 temperature also shifts upwards with the aluminum content. This has a negative effect on austenitization, which is important for hot forming. However, it has been shown that increased aluminum contents surprisingly lead to positive effects in connection with an aluminum-based anti-corrosion coating.
  • iron diffuses from the steel substrate into the liquid anti-corrosion coating.
  • iron-aluminide compounds with a higher density are formed via a multi-stage phase transformation (Fe2Al5 ⁇ Fe2AI ⁇ FeAl ⁇ Fe3AI).
  • the formation of such dense phases is associated with higher aluminum consumption than in less dense phases.
  • This locally higher aluminum consumption leads to the formation of pores (voids) in the phase obtained.
  • These pores preferably form in the transition area between the steel substrate and the anti-corrosion coating, where the proportion of available aluminum is strongly influenced by the aluminum content of the steel substrate. In particular, there can be an accumulation of pores in the form of a band in the transition area.
  • the transmittable force at the connection point between two components is reduced after gluing or welding.
  • the Al content is too high, in particular if the Al content is more than 1.0% by weight, there is a risk of Al oxides forming on the surface of a product made from steel material alloyed according to the invention, which would impair the wetting behavior during hot-dip coating .
  • higher Al contents promote the formation of non-metallic Al-based inclusions, which, as coarse inclusions, have a negative impact on crash behavior.
  • the Al content is therefore preferably selected below the upper limits already mentioned.
  • the bending behavior of the sheet metal component is supported by the niobium content (“Nb”) according to the invention of at least 0.001% by weight.
  • the Nb content is preferably at least 0.005% by weight, in particular at least 0.010% by weight, preferably at least 0.015% by weight, particularly preferably at least 0.020% by weight, in particular at least 0.024% by weight, preferably at least 0.025% by weight %.
  • the specified Nb content leads to a distribution of niobium carbonitrides, particularly in the method described below for producing a flat steel product for hot forming with an anti-corrosion coating, which leads to a particularly fine hardened structure during subsequent hot forming.
  • the coated steel flat product is kept in a temperature range of 400°C and 300°C for a certain time. In this temperature range there is still a certain rate of diffusion of carbon ("C") in the steel substrate, while the thermodynamic solubility is very low. Thus, carbon diffuses to lattice defects and accumulates there.
  • Lattice defects are caused in particular by dissolved niobium atoms, which expand the atomic lattice due to their significantly higher atomic volume and thus enlarge the tetrahedron and octahedron gaps in the atomic lattice, so that the local solubility of C is increased. Consequently, there are clusters of carbon and niobium in the steel substrate, which are then formed in the subsequent austenitizing to very fine precipitates during the hot forming step and act as additional austenite nuclei. This results in a refined austenite structure with smaller austenite grains and thus also a refined hardened structure.
  • the refined ferritic structure in the interdiffusion layer supports the reduction of crack initiation tendencies under bending loads.
  • the higher Nb content has another advantage. Surprisingly, it has been shown that the higher Nb content in the steel substrate leads to a shift in the electrochemical potential in the final sheet metal part towards a more positive (i.e. nobler) potential.
  • the Nb content in the interdiffusion layer has proven to be a good indicator for the shift in the electrochemical potential.
  • the potential is about 100-150 mV higher than that of a comparative substrate with a lower Nb content.
  • the shaped sheet metal part made in this way therefore has a higher resistance to corrosion.
  • the Nb content is 0.2% by weight at maximum. Furthermore, the Nb content is preferably at most 0.20% by weight, in particular at most 0.15% by weight, preferably at most 0.10% by weight, in particular at most 0.05% by weight.
  • the Al/Nb ratio >2, in particular >3, is preferred.
  • the Al/Nb ratio is too high, AlN formation is no longer as advantageously fine, but rather increasingly coarser AlN particles occur, which reduces the grain refinement effect again. It has been shown that this effect occurs earlier with low manganese contents than with higher ones Manganese content, since the AC3 temperature decreases with increasing manganese content. It is therefore advantageous, optionally with low manganese contents of ⁇ 1.6% by weight, to have a ratio of Al/Nb
  • the Al/Nb ratio is preferably ⁇ 18.0, in particular ⁇ 16.0, preferably ⁇ 14.0, particularly preferably ⁇ 12.0, in particular ⁇ 10.0, preferably ⁇ 9.0, in particular ⁇ 8.0, preferably ⁇ 7.0.
  • the Al/Nb ratio is preferably ⁇ 28.0, in particular ⁇ 26.0, preferably ⁇ 24.0, particularly preferably ⁇ 22.0, preferably ⁇ 20.0, in particular ⁇ 18.0, in particular ⁇ 16.0, preferably ⁇ 14.0, particularly preferably ⁇ 12.0, in particular ⁇ 10.0, preferably ⁇ 9.0, in particular ⁇ 8.0, preferably ⁇ 7.0.
  • the Al/Nb ratio is preferably ⁇ 18.0, in particular ⁇ 16.0, preferably ⁇ 14.0, particularly preferably ⁇ 12.0, in particular ⁇ 10.0, preferably ⁇ 9.0, in particular ⁇ 8.0, preferably ⁇ 7.0.
  • Carbon is contained in the steel substrate of the steel flat product in amounts of 0.06 - 0.5% by weight.
  • C contents set in this way contribute to the hardenability of the steel by delaying the formation of ferrite and bainite and stabilizing the retained austenite in the structure.
  • a C content of at least 0.06% by weight is required in order to achieve adequate hardenability and the associated high strength.
  • the weldability can be adversely affected by high C contents.
  • the C content can be reduced to 0.5% by weight, preferably to a maximum of 0.5% by weight, in particular to a maximum of 0.45% by weight, preferably to 0.42% by weight. %, particularly preferably 0.40% by weight, preferably at most 0.38% by weight, in particular at most 0.35% by weight.
  • C contents of at least 0.10% by weight, preferably 0.11% by weight, in particular at least 0.13% by weight, preferably at least 0 .15% by weight can be provided. With these contents, tensile strengths of the sheet metal part of at least 1000 MPa, in particular at least 1100 MPa, can be reliably achieved after hot pressing, taking into account the further provisions of the invention.
  • the C content is at least 0.10% by weight, preferably 0.11% by weight, in particular at least 0.13% by weight, preferably at least 0.15% by weight.
  • the maximum C content is at most 0.30% by weight, in particular at most 0.25% by weight, preferably at most 0.25% by weight. With this maximum C content, the weldability can be significantly improved and a good ratio of force absorption and maximum bending angle in the bending test according to VDA238-100 in the press-hardened state can be achieved.
  • the C content is at least 0.25% by weight, preferably at least 0.30% by weight, in particular at least 0.32% by weight.
  • the maximum C content in this variant is at most 0.5% by weight, in particular at most 0.50% by weight, preferably at most 0.40% by weight, preferably at most 0.38% by weight, in particular at most 0.35% by weight.
  • the C content is at least 0.30% by weight, preferably at least 0.32% by weight, in particular at least 0.33% by weight, preferably at least 0.34% by weight at least 0.35% by weight, in particular at least 0.40% by weight, preferably at most 0.44% by weight.
  • the maximum C content is at most 0.5% by weight, in particular at most 0.50% by weight, preferably at most 0.48% by weight.
  • Silicon is used to further increase the hardenability of the steel flat product as well as the strength of the press hardened product via solid solution strengthening. Silicon also enables the use of ferro-silizio-manganese as an alloying agent, which has a beneficial effect on production costs. From an Si content of 0.05% by weight, this is already the case hardening effect on. From an Si content of at least 0.15% by weight, in particular at least 0.20% by weight, there is a significant increase in strength. Si contents above 0.6% by weight have an adverse effect on the coating behavior, particularly in the case of Al-based coatings. Si contents of at most 0.50% by weight, in particular at most 0.30% by weight, are preferably set in order to improve the surface quality of the coated flat steel product.
  • Manganese acts as a hardening element by greatly retarding the formation of ferrite and bainite. With manganese contents of less than 0.4% by weight, significant proportions of ferrite and bainite are formed during press hardening, even with very rapid cooling rates, which should be avoided. Mn contents of at least 0.5% by weight, in particular at least 0.7% by weight, preferably at least 0.8% by weight, in particular at least 0.9% by weight, preferably at least 1.00% by weight %, in particular at least 1.05% by weight, particularly preferably at least 1.10% by weight, are advantageous if a martensitic structure is to be ensured, in particular in areas of greater deformation.
  • Mn contents of more than 3.0% by weight have a disadvantageous effect on the processing properties, which is why the Mn content of flat steel products according to the invention is limited to at most 3.0% by weight, preferably at most 2.5% by weight. Above all, the weldability is severely restricted, which is why the Mn content is preferably limited to at most 1.6% by weight and in particular to 1.30% by weight, preferably to 1.20% by weight. Mn contents of less than or equal to 1.6% by weight are also preferred for economic reasons.
  • Titanium is a microalloying element that is alloyed to contribute to grain refinement, with at least 0.001% by weight Ti, particularly at least 0.004% by weight, preferably at least 0.010% by weight Ti, added for sufficient availability should be. Above 0.10% by weight Ti, the cold-rollability and recrystallizability deteriorate significantly, which is why larger Ti contents should be avoided. In order to improve cold-rollability, the Ti content may preferably be limited to 0.08% by weight, more preferably 0.038% by weight, more preferably 0.020% by weight, particularly 0.015% by weight. Titanium also has the effect of binding nitrogen and thus enabling boron to exert its strong ferrite-inhibiting effect.
  • the titanium content is more than 3.42 times the nitrogen content in order to achieve adequate binding of nitrogen.
  • Boron (“B”) is added to improve the hardenability of the flat steel product by allowing boron atoms or boron precipitates attached to the austenite grain boundaries to reduce the grain boundary energy, thereby suppressing nucleation of ferrite during press hardening.
  • B contents of at least 0.0005% by weight, preferably at least 0.0007% by weight, in particular at least 0.0010% by weight, in particular at least 0.0020% by weight. on.
  • the B content is limited to at most 0.01% by weight, preferably at most 0.0100% by weight, preferably at most 0.0050% by weight, in particular at most 0.0035% by weight, in particular at most 0.0030% by weight, preferably at most 0.0025% by weight.
  • Phosphorus (“P”) and sulfur (“S”) are elements that are introduced into steel as impurities from iron ore and cannot be completely eliminated in the large-scale steelworks process.
  • the P content and the S content should be kept as low as possible since the mechanical properties such as notched bar impact work deteriorate with increasing P or S content. From P contents of 0.03% by weight, the martensite also begins to become brittle, which is why the P content of a flat steel product according to the invention is limited to a maximum of 0.03% by weight, in particular a maximum of 0.02% by weight is.
  • the S content of a flat steel product according to the invention is limited to at most 0.02% by weight, preferably at most 0.0010% by weight, in particular at most 0.005% by weight.
  • N Nitrogen
  • the N content should be kept as low as possible and should not exceed 0.02% by weight.
  • nitrogen is harmful because it prevents the transformation-retarding effect of boron through the formation of boron nitrides, which is why the N content in this case is preferably at most 0.010% by weight, in particular at most 0.007% by weight. should be.
  • Sn tin
  • As arsenic
  • the total content of these “unavoidable impurities” is preferably at most 0.2% by weight, preferably at most 0.1% by weight.
  • the optional alloying elements Cr, Cu, Mo, Ni, V, Ca and W described below, for which a lower limit is given, can also occur in contents below the respective lower limit as unavoidable impurities in the steel substrate. In that case, they are also counted among the “unavoidable impurities”, the total content of which is limited to a maximum of 0.2% by weight, preferably a maximum of 0.1% by weight.
  • Chromium, copper, molybdenum, nickel, vanadium, calcium and tungsten can optionally be added to the steel of a flat steel product according to the invention, either individually or in combination with one another.
  • Chromium suppresses the formation of ferrite and pearlite during accelerated cooling of a flat steel product according to the invention and enables complete martensite formation even at lower cooling rates, thereby increasing hardenability.
  • the Cr content of the steel of the steel substrate is limited to at most 1.0% by weight, preferably at most 0.80% by weight, in particular at most 0.75% by weight, preferably at most 0.50% by weight. , In particular limited to a maximum of 0.30% by weight.
  • Vanadium can optionally be alloyed in amounts of 0.001 - 1.0% by weight.
  • the vanadium content is preferably at most 0.3% by weight. For cost reasons, a maximum of 0.2% by weight of vanadium is added.
  • Copper can optionally be alloyed in order to increase the hardenability with additions of at least 0.01% by weight, preferably at least 0.010% by weight, in particular at least 0.015% by weight.
  • copper improves the resistance to atmospheric corrosion of uncoated sheet metal or cut edges. If the Cu content is too high, the hot-rollability deteriorates significantly due to low-melting Cu phases on the surface, which is why the Cu content is limited to at most 0.2% by weight, preferably at most 0.1% by weight, in particular at most 0. 10 wt .-% is limited.
  • Molybdenum Molybdenum
  • Mo can be optionally added to improve process stability as it significantly slows down ferrite formation.
  • the Mo content is preferably at least 0.004% by weight, in particular at least 0.01% by weight. Due to the high costs associated with an alloy of molybdenum, the Mo content should be at most 0.3% by weight, in particular at most 0.10% by weight, preferably at most 0.08% by weight.
  • Nickel stabilizes the austenitic phase and can optionally be alloyed to reduce the Ac3 temperature and suppress ferrite and bainite formation. Nickel also has a positive effect on hot-rollability, especially when the steel contains copper. Copper degrades hot-rollability.
  • 0.01% by weight of nickel can be alloyed with the steel; the Ni content is preferably at least 0.015% by weight, in particular at least 0.020% by weight. For economic reasons, the nickel content should remain limited to a maximum of 0.5% by weight, in particular a maximum of 0.20% by weight. The Ni content is preferably at most 0.10% by weight.
  • a flat steel product according to the invention can optionally contain at least 0.0005% by weight Ca, in particular at least 0.0010% by weight, preferably at least 0.0020% by weight.
  • the maximum Ca content is 0.01% by weight, in particular a maximum of 0.007% by weight, preferably a maximum of 0.005% by weight. If the Ca content is too high, the probability increases that non-metallic inclusions involving calcium will form, which impair the degree of purity of the steel and also its toughness. For this reason, an upper limit of the Ca content of at most 0.005% by weight, preferably at most 0.003% by weight, in particular at most 0.002% by weight, preferably at most 0.001% by weight, should be observed.
  • Tungsten can optionally be added in amounts of 0.001 - 1.0% by weight to slow down the formation of ferrite.
  • W can optionally be added in amounts of 0.001 - 1.0% by weight to slow down the formation of ferrite.
  • a maximum of 1.0% by weight of tungsten is added.
  • the sum of the Mn content and the Cr content (“Mn+Cr”) is more than 0.7% by weight, in particular more than 0.8% by weight, preferably more than 1.1% by weight %. Below a minimum sum of both elements, their necessary conversion-inhibiting effect is lost. Irrespective of this, the sum of the Mn content and the Cr content is less than 3.5% by weight, preferably less than 2.5% by weight, in particular less than 2.0% by weight, particularly preferably less than 1.5% by weight.
  • the upper limit values of both elements are created by ensuring the coating performance and to ensure sufficient welding behavior.
  • the flat steel product preferably comprises an anti-corrosion coating in order to protect the steel substrate from oxidation and corrosion during hot forming and when the steel component produced is used.
  • the flat steel product preferably comprises an aluminum-based anti-corrosion coating.
  • the anti-corrosion coating can be applied to one side or both sides of the flat steel product.
  • the two opposite large surfaces of the flat steel product are referred to as the two sides of the flat steel product.
  • the narrow faces are called edges.
  • Such an anti-corrosion coating is preferably produced by hot-dip coating the steel flat product.
  • the flat steel product is passed through a liquid melt consisting of 0.1-15% by weight Si, preferably more than 1.0% by weight Si, optionally 2-4% by weight Fe, optionally up to 5% by weight % alkali or alkaline earth metals, preferably up to 1.0% by weight alkali or alkaline earth metals, and optionally up to 15% by weight Zn, preferably up to 10% by weight Zn and optional further components, the total content of which is limited to a maximum of 2.0% by weight, and the remainder is aluminum.
  • the Si content of the melt is 1.0-3.5% by weight or 5-15% by weight, preferably 7-12% by weight, in particular 8-10% by weight.
  • the optional content of alkali or alkaline earth metals in the melt comprises 0.1-1.0% by weight Mg, in particular 0.1-0.7% by weight Mg, preferably 0.1-0. 5% by weight Mg.
  • the optional content of alkali metals or alkaline earth metals in the melt can include in particular at least 0.0015% by weight Ca, in particular at least 0.01% by weight Ca.
  • the alloy layer rests on the steel substrate and is directly adjacent to it.
  • the alloy layer is essentially made up of aluminum and iron.
  • the remaining elements from the steel substrate or the melt composition do not enrich significantly in the alloy layer.
  • the alloy layer preferably consists of 35-60% by weight Fe, preferably a-iron, optional further components, the total content of which is limited to a maximum of 5.0% by weight, preferably 2.0%, and the remainder aluminum, with the Al content tends to increase towards the surface.
  • the optional further components include in particular the remaining components of the melt (ie silicon and optionally alkali metals or alkaline earth metals, in particular Mg or Ca) and the remaining components of the steel substrate in addition to iron.
  • the Al base layer lies on top of the alloy layer and is immediately adjacent to it.
  • the composition of the Al base layer preferably corresponds to the composition of the melt in the molten bath. That is, it consists of 0.1 - 15 wt.% Si, optionally 2 - 4 wt.% Fe, optionally up to 5.0 wt.% alkali or alkaline earth metals, preferably up to 1.0 wt. - % alkali metals or alkaline earth metals, optionally up to 15% by weight Zn, preferably up to 10% by weight Zn and optional other components, the total content of which is limited to a maximum of 2.0% by weight, and the remainder Aluminum.
  • the optional content of alkali or alkaline earth metals comprises 0.1-1.0% by weight Mg, in particular 0.1-0.7% by weight Mg, preferably 0.1-0 .5% by weight Mg.
  • the optional content of alkali or alkaline earth metals in the AI comprises in particular at least 0.0015% by weight of Ca, in particular at least 0.1% by weight of Ca.
  • the Si content in the alloy layer is lower than the Si content in the Al base layer.
  • the anti-corrosion coating preferably has a thickness of 5 to 60 ⁇ m, in particular 10 to 40 ⁇ m.
  • the coating weight of the anti-corrosion coating is in particular 30 - 360 ⁇ m for anti-corrosion coatings on both sides, or 15 - 180 ⁇ for the one-sided variant. m
  • the coating weight of the anti-corrosion coating is preferably 100-200% for m double-sided coatings, or 50-100% for one-sided coatings.
  • the m is particularly preferably
  • the thickness of the alloy layer is preferably less than 20 ⁇ m, particularly preferably less than 16 ⁇ m, in particular less than 12 ⁇ m, particularly preferably less than 10 ⁇ m, preferably less than 8 ⁇ m, in particular less than 5 ⁇ m.
  • the thickness of the Al base layer results from the difference in the thicknesses of the anti-corrosion coating and the alloy layer.
  • the thickness of the Al base layer is preferably at least 1 ⁇ m, even in the case of thin anti-corrosion coatings.
  • the flat steel product comprises an oxide layer arranged on the anti-corrosion coating.
  • the oxide layer lies in particular on the Al base layer and preferably forms the outer end of the anti-corrosion coating.
  • the oxide layer consists in particular of more than 80% by weight of oxides, with the majority of the oxides (ie more than 50% by weight of the oxides) being aluminum oxide.
  • hydroxides and/or magnesium oxide are present alone or as a mixture in the oxide layer in addition to aluminum oxide.
  • the remainder of the oxide layer not occupied by the oxides and optionally present hydroxides preferably consists of silicon, aluminum, iron and/or magnesium in metallic form.
  • zinc oxide components are also present in the oxide layer.
  • the oxide layer of the flat steel product preferably has a thickness that is greater than 50 nm. In particular, the thickness of the oxide layer is at most 500 nm.
  • the flat steel product includes a zinc-based anti-corrosion coating.
  • the anti-corrosion coating can be applied to one side or both sides of the flat steel product.
  • the two opposite large surfaces of the flat steel product are referred to as the two sides of the flat steel product.
  • the narrow faces are called edges.
  • Such a zinc-based anti-corrosive coating preferably comprises 0.2-6.0 wt% Al, 0.1-10.0 wt% Mg, optionally 0.1-40 wt% manganese or copper, optionally 0.1 - 10.0% by weight cerium, optionally at most 0.2% by weight other elements, unavoidable impurity and the balance zinc.
  • the Al content is at most 2.0% by weight, preferably at most 1.5% by weight.
  • the Mg content is in particular at most 3.0% by weight, preferably at most 1.0% by weight.
  • the anti-corrosion coating can be applied by hot dip coating or by physical vapor deposition or by electrolytic processes.
  • a further developed flat steel product preferably has a high uniform elongation Ag of at least 10.0%, in particular at least 11.0%, preferably at least 11.5%, in particular at least 12.0%.
  • the yield point of a specially designed flat steel product shows a continuous course or only a small extent.
  • continuous progression means that there is no pronounced yield point.
  • a continuous yield point can also be referred to as a yield point Rp0.2.
  • a low yield point is understood to mean a pronounced yield point in which the difference ARe between the upper yield point value ReH and the lower yield point value ReL is at most 45 MPa. The following applies:
  • a particularly good resistance to aging can be achieved with steel flat products, for which the difference ARe is at most 25 MPa.
  • a specially developed flat steel product has an elongation at break A80 of at least 15%, in particular at least 18%, preferably at least 19%, particularly preferably at least 20%.
  • the method according to the invention for the production of a flat steel product for hot forming with an anti-corrosion coating comprising the following work steps: a) Providing a slab or a thin slab made of steel which, in addition to iron and unavoidable impurities (in % by weight), consists of C: 0.06 - 0.5%,
  • Mn 0.4-3.0%
  • Al 0.06-1.0%
  • Nb 0.001-0.2%
  • Ti 0.001-0.10%
  • B 0.0005-0.01%
  • W 0.001 -1.00% passes; b) through heating of the slab or thin slab at a temperature (TI) of 1100 - 1400 °C; c) optional pre-rolling of the through-heated slab or thin slab into an intermediate product with an intermediate product temperature (T2) of 1000 - 1200 °C; d) hot-rolling into a hot-rolled steel flat product, the finish rolling temperature (T3) being 750 - 1000 °C; e) optional coiling of the hot-rolled steel flat product, the coiling temperature (T4) being at most 700 °C; f) optional descaling of the hot-rolled flat steel product; g) optional cold rolling of the steel flat product, the degree of cold rolling being at least 30%; h) annealing of the steel flat product at an annealing temperature (T5) of 650 - 900 °C; i) cooling the flat steel product to an immersion temperature (T6) which is 650-800° C., preferably 670-800° C.; j) coating the
  • step b) the semi-finished product is heated through at a temperature (TI) of 1100 - 1400 °C. If the semi-finished product has cooled down after casting, the semi-finished product is first reheated to 1100 - 1400 °C for thorough heating.
  • the through heating temperature should be at least 1100 °C to ensure good formability for the subsequent rolling process.
  • the heating temperature should not exceed 1400 °C in order to avoid molten phases in the semi-finished product.
  • the semi-finished product is pre-rolled into an intermediate product.
  • Thin slabs are usually not subjected to pre-rolling.
  • Thick slabs that are to be rolled into hot strip can be pre-rolled if necessary.
  • the temperature of the intermediate product (T2) at the end of rough rolling should be at least 1000°C so that the intermediate product contains enough heat for the subsequent finish rolling step.
  • high rolling temperatures can also promote grain growth during the rolling process, which adversely affects the mechanical properties of the flat steel product.
  • the temperature of the intermediate product should not exceed 1200 °C at the end of rough rolling.
  • step d) the slab or thin slab or, if step c) has been carried out, the intermediate product is rolled to form a hot-rolled flat steel product.
  • step c) the intermediate product is typically finish-rolled immediately after rough-rolling. Typically, finish rolling begins no later than 90 s after the end of rough rolling.
  • the slab, the thin slab or, if step c) has been carried out, the intermediate product are rolled at a finish rolling temperature (T3).
  • the final rolling temperature i.e. the temperature of the finished hot-rolled steel flat product at the end of the hot-rolling process, is 750 - 1000 °C.
  • the amount of free vanadium decreases because larger amounts of vanadium carbides are precipitated.
  • the vanadium carbides precipitated during finish rolling are very large. They typically have an average grain size of 30 nm or more and are no longer dissolved in subsequent annealing processes, such as those carried out before hot-dip coating.
  • the final rolling temperature is limited to a maximum of 1000 °C prevent coarsening of the austenite grains.
  • final rolling temperatures of no more than 1000 °C are process-technically relevant for setting coiling temperatures (T4) below 700 °C.
  • the hot rolling of the steel flat product can take place as continuous hot strip rolling or as reversing rolling.
  • step e) provides for an optional coiling of the hot-rolled flat steel product.
  • the hot strip is cooled to a coiling temperature (T4) within less than 50 s after hot rolling.
  • T4 a coiling temperature
  • the coiling temperature (T4) should not exceed 700 °C to avoid the formation of large vanadium carbides. In principle, there is no lower limit on the coiling temperature. However, coiling temperatures of at least 500 °C have proven to be favorable for cold-rollability.
  • the coiled hot strip is then cooled in air to room temperature in a conventional manner.
  • step f the hot-rolled flat steel product is optionally descaled in a conventional manner by pickling or by another suitable treatment.
  • the hot-rolled flat steel product that has been cleaned of scale can optionally be subjected to cold rolling before the annealing treatment in step g), in order, for example, to meet higher requirements for the thickness tolerances of the flat steel product.
  • the degree of cold rolling (KWG) should be at least 30% in order to introduce sufficient deformation energy into the steel flat product for rapid recrystallization.
  • the degree of cold rolling KWG is the quotient of the reduction in thickness during cold rolling AdKW divided by the hot strip thickness d:
  • the flat steel product before cold rolling is usually a hot strip with a hot strip thickness d.
  • the flat steel product after cold rolling is usually also referred to as cold strip.
  • the degree of cold rolling can assume very high values of over 90%. However, degrees of cold rolling of at most 80% have proven to be beneficial for avoiding strip cracks.
  • step h the flat steel product is subjected to an annealing treatment at annealing temperatures (T5) of 650 - 900 °C.
  • the flat steel product is first heated to the annealing temperature within 10 to 120 s and then held at the annealing temperature for 30 to 600 s.
  • the annealing temperature is at least 650°C, preferably at least 720°C. Annealing temperatures above 900°C are not desirable for economic reasons.
  • the flat steel product is cooled to an immersion temperature (T6) after annealing in order to prepare it for the subsequent coating treatment.
  • the immersion temperature is lower than the annealing temperature and is adjusted to the temperature of the melt pool.
  • the immersion temperature is 600-800°C, preferably at least 650°C, particularly preferably at least 670°C, particularly preferably at most 700°C.
  • the duration of the cooling of the annealed steel flat product from the annealing temperature T5 to the immersion temperature T6 is preferably 10-180 s.
  • the immersion temperature T6 differs from the temperature of the melt bath T7 by no more than 30K, in particular no more than 20K, preferably no more than IOK away.
  • the flat steel product is subjected to a coating treatment.
  • the coating treatment is preferably carried out by continuous hot dip coating.
  • the coating can be applied to only one side, to both sides or to all sides of the steel flat product.
  • the coating treatment preferably takes place as a hot-dip coating process, in particular as a continuous process.
  • the flat steel product usually comes into contact with the molten bath on all sides, so that it is coated on all sides.
  • the molten bath which contains the alloy to be applied to the flat steel product in liquid form, typically has a temperature (T7) of 660-800°C, preferably 680-740°C.
  • T7 temperature of 660-800°C, preferably 680-740°C.
  • Aluminum-based alloys have proven to be particularly suitable for coating age-resistant flat steel products with an anti-corrosion coating.
  • the molten bath contains up to 15% by weight Si, preferably more than 1.0%, optionally 2-4% by weight Fe, optionally up to 5% by weight alkali or alkaline earth metals, preferably up to 1.0% by weight of alkali metals or alkaline earth metals, and optionally up to 15% by weight of Zn, in particular up to 10% by weight of Zn and optional other components, the total content of which does not exceed 2.0% by weight. -% are limited, and the remainder aluminum.
  • the Si content of the melt is 1.0-3.5% by weight or 7-12% by weight, in particular 8-10% by weight.
  • the optional content of alkali or alkaline earth metals in the melt comprises 0.1-1.0% by weight Mg, in particular 0.1-0.7% by weight Mg, preferably 0.1-0. 5% by weight Mg.
  • the optional content of alkali metals or alkaline earth metals in the melt can include in particular at least 0.0015% by weight Ca, in particular at least 0.01% by weight Ca.
  • a first cooling time t mT in the temperature range between 600 °C and 450 °C is more than 5 s, preferably more than 10 s, in particular more than 14 s and a second cooling time t nT in the temperature range between 400 °C and 300 °C (low temperature range nT) more than 4s, preferably more than 8s, in particular more than 12s.
  • the first cooling time t mT can be implemented in the temperature range between 600° C. and 450° C. (average temperature range mT) by slow, continuous cooling or by holding at a temperature in this temperature range for a certain time. Even intermediate heating is possible. It is only important that the flat steel product remains in the temperature range between 600 °C and 450 °C for at least a cooling period t mT . In this temperature range, on the one hand, there is a significant rate of diffusion of iron in aluminum and, on the other hand, the diffusion of aluminum in steel is inhibited because the temperature is below half the melting point of steel. This allows diffusion of iron into the anti-corrosion coating without extensive diffusion of aluminum into the steel substrate.
  • the melting of the anti-corrosion coating is delayed during austenitizing before press hardening.
  • the thermal expansion coefficients of the anti-corrosion coating and the substrate are homogenized. This means that the transition area between the coefficient of thermal expansion of the substrate and the surface becomes wider, which reduces the thermal stresses during reheating.
  • diffusing aluminum into the steel substrate would have considerable disadvantages: Due to the very high affinity of aluminum for nitrogen, a high aluminum content can lead to nitrogen separating from fine precipitations, such as niobium carbonitrides or titanium carbonitrides, and coarse precipitations forming instead. such as aluminum nitrides, preferentially form on the grain boundaries. These would worsen the crash performance as well as reduce the bending angle.
  • the iron concentration in the transition boundary layer increases to such an extent that the activity of aluminum in the coating directly at the substrate boundary is further reduced. This then leads to an even further reduced aluminum absorption in the substrate during austenitization before press hardening, with the associated advantages described above.
  • the second cooling time t n in the temperature range between 400° C. and 300° C. can also be realized by slow, continuous cooling or by holding at a temperature in this temperature range for a certain time. Even intermediate heating is possible. It is only important that the flat steel product remains in the temperature range between 400 °C and 300 °C for at least a cooling period t nT .
  • transition carbides very fine iron carbides
  • the coated steel flat product can optionally be skin-passed with a skin-pass degree of up to 2% in order to improve the surface roughness of the steel flat product.
  • the invention further relates to a shaped sheet metal part formed from a flat steel product, comprising a steel substrate as explained above and an anti-corrosion coating.
  • the anti-corrosion coating has the advantage that it prevents scale formation during austenitization during hot forming. Furthermore, such an anti-corrosion coating protects the shaped sheet metal part against corrosion.
  • the shaped sheet metal part preferably comprises an aluminum-based anti-corrosion coating.
  • the anti-corrosion coating of the sheet metal part preferably comprises an alloy layer and an Al base layer.
  • the alloy layer is also often referred to as the interdiffusion layer.
  • the thickness of the anti-corrosion coating is preferably at least 10 ⁇ m, particularly preferably at least 20 ⁇ m, in particular at least 30 ⁇ m.
  • the thickness of the alloy layer is preferably less than 30 ⁇ m, particularly preferably less than 20 ⁇ m, in particular less than 16 ⁇ m, particularly preferably less than 12 ⁇ m.
  • the thickness of the Al base layer results from the difference in the thicknesses of the anti-corrosion coating and the alloy layer.
  • the alloy layer rests on the steel substrate and is directly adjacent to it.
  • the alloy layer of the shaped sheet metal part preferably consists of 35 - 90% by weight Fe, 0.1 - 10% by weight Si, optionally up to 0.5% by weight Mg and optional other components, the total content of which is at most 2 .0% by weight, and the remainder aluminum.
  • the proportions of Si and Mg are correspondingly lower than their respective proportions in the melt of the molten bath.
  • the alloy layer preferably has a ferritic structure.
  • the aluminum base layer of the shaped sheet metal part lies on the alloy layer of the steel component and is directly adjacent to it.
  • the Al base layer of the steel component preferably consists of 35-55% by weight Fe, 0.4-10% by weight Si, optionally up to 0.5% by weight Mg and optional other components, the total content of which is at most 2.0% by weight, and the remainder aluminum.
  • the Al base layer can have a homogeneous element distribution in which the local element contents vary by no more than 10%.
  • preferred variants of the Al base layer have low-silicon phases and high-silicon phases.
  • Low-silicon phases are areas whose average Si content is at least 20% less than the average Si content of the Al base layer.
  • Silicon-rich phases are areas whose average Si content is at least 20% more than the average Si content of the Al base layer.
  • the silicon-rich phases are arranged within the silicon-poor phase.
  • the silicon-rich phases form at least a 40% continuous layer bounded by silicon-poor regions.
  • the silicon-rich phases are arranged in islands in the silicon-poor phase.
  • island-shaped is understood to mean an arrangement in which discrete unconnected areas are surrounded by another material—that is, “islands” of a specific material are located in another material.
  • the steel component comprises an oxide layer arranged on the anti-corrosion coating.
  • the oxide layer lies in particular on the Al base layer and preferably forms the outer end of the anti-corrosion coating.
  • the oxide layer of the steel component consists in particular of more than 80% by weight of oxides, with the main proportion of the oxides (i.e. more than 50% by weight of the oxides) being aluminum oxide.
  • hydroxides and/or magnesium oxide are present alone or as a mixture in the oxide layer in addition to aluminum oxide.
  • the remainder of the oxide layer not occupied by the oxides and optionally present hydroxides preferably consists of silicon, aluminum, iron and/or magnesium in metallic form.
  • the oxide layer preferably has a thickness of at least 50 nm, in particular at least
  • the thickness is a maximum of 4 ⁇ m, in particular a maximum of 2 ⁇ m.
  • the shaped sheet metal part includes a zinc-based anti-corrosion coating.
  • Such a zinc-based anti-corrosion coating preferably comprises up to 80% by weight Fe, 0.2 - 6.0% by weight Al, 0.1 - 10.0% by weight Mg, optionally 0.1 - 40 % by weight of manganese or copper, optionally 0.1-10.0% by weight of cerium, optionally at most 0.2% by weight of other elements, unavoidable impurities and the remainder zinc.
  • the Al content is at most 2.0% by weight, preferably at most 1.5% by weight.
  • the Fe content which comes about as a result of indiffusion, is preferably more than 20% by weight, in particular more than 30% by weight.
  • the Fe content is in particular a maximum of 70% by weight, in particular a maximum of 60% by weight.
  • the Mg content is in particular at most 3.0% by weight, preferably at most 1.0% by weight.
  • the anti-corrosion coating can be applied by hot dip coating or by physical vapor deposition or by electrolytic processes.
  • the steel substrate of the shaped sheet metal part has a structure with at least partially more than 80% martensite and/or lower bainite, preferably at least partially more than 90% martensite and/or lower bainite, in particular at least partially more than 95%, particularly preferably at least sometimes more than 98%.
  • the steel substrate of the shaped sheet metal part has a structure with at least partially more than 80% martensite, preferably at least partially more than 90% martensite, in particular at least partially more than 95%, particularly preferably at least partially more than 98%.
  • “partially have” is to be understood as meaning that there are areas of the shaped sheet metal part that have the structure mentioned.
  • the shaped sheet metal part therefore has the above-mentioned structure in sections or in regions.
  • the steel substrate of the shaped sheet metal part has a structure with a ferrite content of more than 5%, preferably more than 10%, in particular more than 20%.
  • the ferrite content is preferably less than 85%, in particular less than 70%.
  • the martensite content is less than 80%, in particular less than 50%.
  • the microstructure can optionally contain bainite and/or pearlite. The exact ratio of the structural components depends on the level of the C content and the Mn content as well as on the cooling conditions during forming. The structure designed in this way has a higher ductility and therefore leads to improved forming behavior.
  • a corresponding shaped sheet metal part preferably has an elongation at break A80 in a range from 8% to 25%, preferably between 10% and 22%, in particular between 12% and 20%.
  • the former austenite grains of the martensite have an average grain diameter of less than 14 ⁇ m, in particular less than 12 ⁇ m, preferably less than 10 ⁇ m. Due to the fine structure, this is more homogeneous. There is an improvement in the mechanical properties, in particular a lower susceptibility to cracking and thus improved bending properties and a higher elongation at break.
  • the shaped sheet metal part at least partially has a yield point of at least 950 MPa, in particular at least 1100 MPa, in particular at least 1200 MPa, preferably at least 1300 MPa, preferably at least 1400 MPa, in particular at least 1500 MPa.
  • the shaped sheet metal part at least partially has a tensile strength of at least 1000 MPa, in particular at least 1100 MPa, preferably at least 1300 MPa, preferably at least 1400 MPa, in particular at least 1600 MPa, preferably at least 1700 MPa, in particular at least 1800 MPa.
  • the shaped sheet metal part at least partially has an elongation at break A80 of at least 3.5%, in particular at least 4%, in particular at least 4.5%, preferably at least 5%, particularly preferably at least 6%.
  • “partially have” is to be understood as meaning that there are areas of the sheet metal part that have the mechanical property mentioned.
  • the shaped sheet metal part therefore has the mechanical properties mentioned in sections or in regions. This is because different areas of the sheet metal part can receive different heat treatments. For example, individual areas can be cooled more quickly than others, as a result of which more martensite forms, for example, in the areas that have cooled more quickly. This is why different mechanical properties also appear in the different areas.
  • the shaped sheet metal part has fine precipitations in the structure, in particular in the form of niobium carbonitrides and/or titanium carbonitrides.
  • fine precipitations are all precipitations with a diameter of less than 30 nm.
  • the remaining exudates are referred to as coarse excretions.
  • the mean diameter of the fine precipitates is at most 11 nm, preferably at most 10 nm, in particular at most 8 nm, preferably at most 6 nm.
  • the shaped sheet metal part has largely fine precipitations in the structure.
  • largely fine precipitates are to be understood as meaning that more than 80%, preferably more than 90%, of all the precipitates are fine precipitates. This means that more than 80%, preferably more than 90%, of all precipitations have a diameter of less than 30 nm.
  • the fine precipitations require a particularly fine structure with small grain diameters. Due to the fine structure, this is more homogeneous. There is an improvement in the mechanical Properties, in particular a lower susceptibility to cracking and thus improved bending properties and a higher elongation at break. This also results in better toughness with more pronounced fracture necking behavior.
  • the real mechanical characteristics of the sheet metal part are determined by first cathodically coating the sheet metal part with dip paint or by subjecting it to an analogous heat treatment.
  • Cathodic dip coatings are usually carried out for corresponding components in the automotive industry.
  • cathodic dip painting the components are first coated in an aqueous solution. This coating is then burned in during a heat treatment.
  • the shaped sheet metal parts are heated to 170° C. and kept at this temperature for 20 minutes. The components are then cooled to room temperature in ambient air.
  • the shaped sheet metal part comprises a cathodic dip coating.
  • the electrochemical potential is preferably at least ⁇ 0.45 V, particularly preferably at least ⁇ 0.40 V, in particular at least ⁇ 0.39 V, particularly preferably at least ⁇ 0.38 V, in particular at least ⁇ 0.36 V, preferably at least ⁇ 0 34 V. Furthermore, the electrochemical potential is preferably at most -0.1 V, preferably at most -0.20 V, in particular -0.25 V, preferably at most -0.30 V.
  • a further developed variant of the shaped sheet metal part is characterized in that the anti-corrosion coating is an aluminum-based anti-corrosion coating and the shaped sheet metal part comprises an alloy layer and an Al base layer.
  • the area occupied by pores in the alloy layer is less than 250 ⁇ m 2 , preferably less than 200 ⁇ m 2 , in particular less than 180 ⁇ m 2 , particularly preferably less than 100 ⁇ m 2 , in particular less than 75 ⁇ m 2 .
  • Pores are cavities that could arise within the alloy layer for a variety of reasons.
  • One mechanism is the formation of higher density iron aluminide compounds via a multi-step phase transformation (Fe2Al5 ⁇ Fe2AI ⁇ FeAl ⁇ Fe3AI).
  • the formation of such dense phases is associated with higher aluminum consumption than in less dense phases.
  • This locally higher aluminum consumption leads to the formation of pores (voids) in the phase obtained.
  • These pores preferably form in the alloy layer in the transition area between the steel substrate and the anti-corrosion coating, where the proportion of available aluminum is strongly influenced by the aluminum content of the steel substrate.
  • the proportion of the area occupied by pores in the alloy layer with a diameter greater than or equal to 0.1 ⁇ m is less than 10%, in particular less than 5%, preferably less than 3%. Smaller pores have a much smaller impact on the reduction in mechanical integrity discussed. A particularly fine-pored alloy layer is therefore preferred.
  • the welding range is at least 0.9 kA, preferably at least 1.0 kA, particularly preferably at least 1.1 kA, in particular at least 1.2 kA.
  • the welding area is determined according to SEP 1220-2.
  • the welding range is a maximum of 1.6 kA, in particular a maximum of 1.4 kA. The areas mentioned enable particularly stable further processing of the shaped sheet metal parts.
  • the Nb content in the alloy layer is greater than 0.010% by weight, preferably greater than 0.015% by weight, in particular greater than 0.018% by weight.
  • the shaped sheet metal part according to the invention is preferably a component for a land vehicle, sea vehicle or aircraft. It is particularly preferably a Automobile part, in particular a body part.
  • the component is preferably a B-pillar, side member, A-pillar, rocker panel or cross member.
  • Mn 0.4-3.0%
  • Al 0.06-1.0%
  • Nb 0.001-0.2%
  • Ti 0.001-0.10%
  • B 0.0005-0.01%
  • W 0.001 -1.00% passes; a) heating of the sheet metal blank in such a way that the AC3 temperature of the blank is at least partially exceeded and the temperature T unit of the blank when it is placed in a forming tool provided for hot-press forming (step c)) at least partially a temperature above Ms+100°C, in particular above Ms+300°C, where Ms designates the martensite start temperature.
  • a blank is thus provided (step a)), which consists of steel suitably composed in accordance with the explanations above, which is then heated in a manner known per se such that the AC3 temperature of the blank is at least partially exceeded and the temperature T Einig of the blank when it is placed in a forming tool provided for hot-press forming (work step c)) is at least partially a temperature above Ms+100°C, in particular above Ms+300°C.
  • the temperature T eing of the blank during insertion at least partially exceeds 600°C.
  • the temperature T Ein ig of the blank during insertion is at least partially, in particular completely, in the range from 600° C. to 850° C.
  • partially exceeding a temperature means that at least 30%, in particular at least 60% of the volume of the blank, preferably the entire blank, exceeds a corresponding temperature.
  • a temperature in the interval 600° C. to 850° C. in the preferred variant explained above.
  • up to 70% of the volume of the blank when it is placed in the forming tool can consist of other structural components, such as tempered bainite, tempered martensite and/or non-recrystallized or partially recrystallized ferrite.
  • certain areas of the blank can be kept at a lower temperature level than others during heating.
  • the supply of heat can be directed only to specific sections of the blank, or the parts that are to be heated less can be shielded from the supply of heat.
  • no martensite or only significantly less martensite is formed in the course of forming in the tool, so that the structure there is significantly softer than in the other parts in which a martensitic structure is present.
  • a softer area can be specifically set in the formed sheet metal part in which, for example, there is optimal toughness for the respective application, while the other areas of the sheet metal part have maximized strength.
  • Maximum strength properties of the formed sheet metal part obtained can be made possible if the temperature at least partially reached in the sheet metal blank is between Ac3 and 1000° C., preferably between 850° C. and 950° C.
  • An optimally uniform distribution of properties can be achieved by completely heating the blank in step b).
  • the mean heating rate r O f en of the sheet metal blank during heating in step b) is at least 3 K/s, preferably at least 5 K/s, in particular at least 6 K/s, preferably at least 8 K/s, in particular at least 10 K/s, preferably at least 15 K/s.
  • the average heating rate of a furnace is to be understood as the average heating rate from 30 °C to 700 °C.
  • the normalized mean heating 0 norm is at least 5 Kmm/s, in particular at least 8 Kmm/s, preferably at least 10 Kmm/s.
  • the normalized mean heating is a maximum of 15 km/s, in particular a maximum of 14 km/s, preferably a maximum of 13 km/s.
  • the mean heating 0 is the product of the mean heating rate in Kelvin per second from 30° C. to 700° C. and the sheet thickness in millimeters.
  • ®norm 4 ⁇ the oven temperatures are to be entered in Kelvin.
  • the heating takes place in an oven with an oven temperature T O f en of at least Ac3+10° C., preferably at least 850° C., preferably at least 880° C., particularly preferably at least 900° C., in particular at least 920° C. and at most 1000°C, preferably at most 950°C, particularly preferably at most 930°C.
  • the dew point of the furnace atmosphere in the furnace is preferably at least ⁇ 20° C., preferably at least ⁇ 15° C., in particular at least ⁇ 5° C., particularly preferably at least 0° C. and at most +25° C., preferably at most +20° C., in particular at most +15°C.
  • the heating in step b) takes place in stages in areas with different temperatures.
  • the heating takes place in a roller hearth furnace with different heating zones.
  • heating takes place in a first heating zone at a temperature (so-called furnace inlet temperature) of at least 650.degree. C., preferably at least 680.degree. C., in particular at least 720.degree.
  • the maximum temperature in the first heating zone preferably 900 °C, in particular a maximum of 850 °C.
  • the maximum temperature of all heating zones in the furnace is preferably not more than 1200° C., in particular not more than 1000° C., preferably not more than 950° C., particularly preferably not more than 930° C.
  • the total time in the oven t oven which is made up of a heating time and a holding time, is preferably at least 2 minutes, in particular at least 3 minutes, preferably at least 4 minutes, in both variants (constant oven temperature, gradual heating). Furthermore, the total time in the oven in both variants is preferably a maximum of 20 minutes, in particular a maximum of 15 minutes, preferably a maximum of 12 minutes, in particular a maximum of 8 minutes. Longer total times in the furnace have the advantage that uniform austenitization of the sheet metal blank is ensured. On the other hand, holding above Ac3 for too long leads to grain coarsening, which has a negative effect on the mechanical properties.
  • the blank heated in this way is removed from the respective heating device, which can be, for example, a conventional heating furnace, an induction heating device that is also known per se, or a conventional device for keeping steel components warm, and transported into the forming tool so quickly that its temperature during Arrival in the tool is at least partially above Ms+100°C, in particular above Ms+300°C, preferably above 600°C, in particular above 650°C, particularly preferably above 700°C.
  • Ms denotes the martensite start temperature.
  • the temperature is at least partially above the ACI temperature.
  • the temperature is in particular a maximum of 900°C. Overall, these temperature ranges ensure good formability of the material.
  • the austenitized blank is transferred from the heating device used in each case to the forming tool within preferably a maximum of 20 s, in particular a maximum of 15 s. Such rapid transport is necessary to avoid excessive cooling before deformation.
  • the tool When the blank is inserted, the tool typically has a temperature between room temperature (RT) and 200.degree. C., preferably between 20.degree. C. and 180.degree. C., in particular between 50.degree. C. and 150.degree.
  • the tool can also have a temperature slightly below room temperature, for example if the is used cooling water is slightly colder (e.g. 15°C).
  • the tool thus has a temperature of between 10°C and 200°C in individual design variants when inserting the blank.
  • the tool can optionally be tempered at least in regions to a temperature T w of at least 200° C., in particular at least 300° C., in order to only partially harden the component.
  • the tool temperature T wz is preferably at most 600°C, in particular at most 550°C. It is only necessary to ensure that the tool temperature T wz is below the desired target temperature T target .
  • the residence time in the tool t wz is preferably at least 2s, in particular at least 3s, particularly preferably at least 5s.
  • the residence time in the tool is preferably a maximum of 25 s, in particular a maximum of 20 s, preferably a maximum of 10 s.
  • the target temperature T target of the sheet metal part is at least partially below 400° C., preferably below 300° C., in particular below 250° C., preferably below 200° C., particularly preferably below 180° C., in particular below 150° C.
  • the target temperature T target of the shaped sheet metal part is particularly preferably below Ms ⁇ 50° C., with Ms denoting the martensite start temperature.
  • the target temperature of the sheet metal part is preferably at least 20°C, particularly preferably at least 50°C.
  • the martensite start temperature of a steel within the specifications of the invention is according to the formula:
  • Ms [°C] (490.85 wt% - 302.6%C - 30.6%Mn - 16.6%Ni - 8.9%Cr + 2.4%Mo - 11.3%Cu + 8.58 %Co + 7.4 %W - 14.5 %Si) [°C/% by weight], where %C is the C content, %Mn is the Mn content, with %Mo the Mo content, with %Cr the Cr content, with %Ni the Ni content, with %Cu the Cu content, with %Co the Co content, with %W the W content and with %Si denotes the Si content of the respective steel in % by weight.
  • AC1[°C] (739 wt% - 22*%C - 7*%Mn + 2*%Si + 14*%Cr + 13*%Mo - 13*%Ni +20*%V )[° C/wt%]
  • AC3[°C] (902 wt% - 225*%C + 19*%Si - 11*%Mn - 5*%Cr + 13*%Mo - 20*%Ni +55*%V)[° C/% by weight], with %C being the C content, %Si being the Si content, %Mn being the Mn content, %Cr being the Cr content, and %Mo being the Mo content , the Ni content is denoted by %Ni and the vanadium content of the respective steel is denoted by +%V (Brandis H 1975 TEW-Techn. Ber. 1 8-10).
  • the blank is not only formed into the shaped sheet metal part, but is also quenched to the target temperature at the same time.
  • the cooling rate in the tool r W z to the target temperature is in particular at least 20 K/s, preferably at least 30 K/s, in particular at least 50 K/s, in a particular embodiment at least 100 K/s.
  • the sheet metal part After the sheet metal part has been removed in step e), the sheet metal part is cooled to a cooling temperature T A B of less than 100 °C within a cooling time t A ß of 0.5 to 600 s. This is usually done by air cooling.
  • FIG. 1a shows a schematic representation of a sample according to the invention with a low number of pores obtained from a micrograph.
  • FIG. 1b shows a schematic representation of a reference sample with an increased number of pores obtained from a micrograph.
  • FIG. 2a shows a schematic representation, obtained from a micrograph, of a sample according to the invention with a low number of pores after a corrosion test.
  • FIG. 2b shows a schematic representation, obtained from a micrograph, of a reference sample with an increased number of pores after a corrosion test.
  • FIG. 3 shows a grain representation of the reconstructed austenite.
  • the slabs were first pre-rolled into an intermediate product with a thickness of 40 mm, with the intermediate products, which can also be referred to as pre-strips in hot strip rolling, each having an intermediate product temperature T2 at the end of the pre-rolling phase.
  • the pre-strips were fed to finish-rolling immediately after rough-rolling, so that the intermediate product temperature T2 corresponds to the rolling start temperature for the finish-rolling phase.
  • the pre-strips were rolled out to hot strips with a final thickness of 3-7 mm and the respective final rolling temperatures T3 given in Table 2, cooled to the respective coiling temperature and wound up into coils at the respective coiling temperatures T4 and then cooled in still air.
  • the hot strips were descaled in a conventional manner by means of pickling before they were subjected to cold rolling with the cold rolling grades given in Table 2.
  • the cold-rolled flat steel products were heated in a continuous annealing furnace to an annealing temperature T5 and held at the annealing temperature for 100 s before they were cooled to their respective immersion temperature T6 at a cooling rate of 1 K/s.
  • the cold strips were passed through a molten coating bath at temperature T7 at their respective immersion temperature T6.
  • the composition of the coating bath is given in Table 3.
  • the coated tapes were blown off in a conventional manner, producing overlays with different layer thicknesses (see Table 3).
  • the strips were first cooled to 600 °C at an average cooling rate of 10 - 15 K/s.
  • the strips were cooled over the cooling times T mT and T nT given in Table 2. Between 450 °C and 400 °C and below 220 °C, the strips were cooled at a cooling rate of 5 - 15 K/s.
  • Table 4 summarizes which steel variant (see Table 1) was combined with which process variant (see Table 2) and which coating (see Table 3).
  • the thickness of the steel strips produced was between 1.4 mm and 1.7 mm in all tests. After cooling to room temperature, samples were taken transversely to the rolling direction from the cooled steel strips in accordance with DIN EN ISO 6892-1 sample form 2 (Annex B Tab. B1). The samples were subjected to a tensile test in accordance with DIN EN ISO 6892-1 sample form 2 (Annex B Tab. Bl). Table 4 gives the results of the tensile test.
  • the following material parameters were determined as part of the tensile test: the type of yield point, which is denoted by Re for a pronounced yield point and Rp for a continuous yield point, as well as the value for the yield point Rp0.2 in the case of a continuous yield point, and the values for in the case of a pronounced yield point the lower yield point ReL, the upper yield point ReH and the difference between the upper and lower yield point ARe, the tensile strength Rm, the uniform elongation Ag and the elongation at break A80. All specimens have a continuous yield point Rp or an only slightly pronounced yield point with a difference ARe between the upper and lower yield point of at most 45 MPa and a uniform elongation Ag of at least 11.5%. There is a pronounced yield point Re for samples 3 and 17 and a continuous yield point Rp for all other samples. Table 4 shows the lower yield point ReL and the upper yield point ReH for samples 3 and 17. The yield point Rp0.2 is specified for all other samples.
  • the blanks are then removed from the heating device and placed in a forming tool, which has the temperature T w z .
  • the transfer time t Tr ans made up of the removal from the heating device, transport to the tool and insertion into the tool was between 5 and 14 s.
  • the temperature T Einig of the blanks when they were inserted into the forming tool was above the respective temperature in all cases Martensite start temperature+100°C.
  • the blanks have been formed into the respective shaped sheet metal part in the forming tool, with the shaped sheet metal parts being cooled in the tool at a cooling rate r wz .
  • the dwell time in the tool is given by t wz designated.
  • Table 5 shows the parameters mentioned for the various variants, with "RT" abbreviating the room temperature.
  • Table 5 shows very different variants for the forming process.
  • Variant II almost completely forms a martensitic structure (see Table 8, Experiment 1)
  • the comparatively slow cooling of Variant X with the high mold temperature T w leads to a modified structure with high ferrite content, which is expressed in Form a higher elongation at break A80.
  • Table 6 lists the essential parameters for a further developed process variant.
  • the sheet metal blank was not heated in an oven with a constant oven temperature as in the experiments described above, but the sheet metal blanks were heated in stages in areas with different temperatures.
  • the tests were carried out in a roller hearth furnace with different heating zones. In principle, however, the process can also be implemented in several separate furnaces.
  • the blanks were first brought into an inlet area of the oven with an inlet temperature T inlet . From there the blanks were moved through a central area into an outlet area of the oven with an outlet temperature T Aus iauf .
  • Table 6 shows the inlet temperature T iniauf , the outlet temperature T out iiller and the maximum oven temperature T max through which the blanks pass. In most cases, the maximum furnace temperature was assumed in the outlet area. With variant AX, however, the maximum oven temperature was assumed to be in the central area. The rest of the process was identical to the process described above. The corresponding parameters are given in Table 6.
  • Table 7 summarizes the overall results for the sheet metal parts obtained.
  • the first columns indicate the sample number, the steel grade according to Table 1, the process variant according to Table 2, the coating according to Table 2 and the hot-forming variant according to Table 5 or Table 6.
  • the yield point, tensile strength and elongation at break A80 are given in the other columns. These values were determined according to DIN EN ISO 6892-1 specimen form 2 (Annex B Tab. Bl) on specimens perpendicular to the rolling direction.
  • the determined bending angle has been determined according to the VDA standard 238-100 with a bending axis transverse to the rolling direction.
  • the determined bending angle is calculated according to the formula specified in the standard from the stamp path (the determined bending angle (also referred to as maximum bending angle) is the bending angle at which the force in the bending test has its maximum). To the influence of To eliminate sheet thickness on the bending angle, the corrected bending angle was calculated from the determined bending angle according to the formula
  • Bending angle corrected bending angle determined ⁇ Sheet thickness where the sheet thickness in mm is to be entered in the formula. This applies to sheet thicknesses greater than 1.0 mm. For sheet thicknesses less than 1.0 mm, the corrected bending angle corresponds to the determined bending angle. Table 7 gives the measured maximum bending angle. To determine the corrected bending angle, these numerical values must therefore be multiplied by the square root of the sheet thickness, which is given in Table 4.
  • the mechanical characteristics in Table 7 were determined after a cathodic dip coating was applied to the formed sheet metal part. During this coating process, the shaped sheet metal parts were heated to 170° C. and held at this temperature for 20 minutes. The components are then cooled to room temperature in ambient air.
  • Table 8 gives the structural properties of the sheet metal part. The structural proportions are given in area %. All examples according to the invention have a martensite content of more than 90%.
  • Table 8 also shows the properties of the fine precipitations in the structure.
  • the precipitates are niobium carbonitrides and titanium carbonitrides, both of which contribute to grain refinement.
  • the excretions are determined with the help of electron-optical and X-ray images (TEM and EDX) using carbon extraction replicas (known in the technical literature as “carbon extraction replicas”). The carbon pull-out impressions were made on longitudinal sections (20x30mm). The resolution of the measurement la is between 10,000 and 200,000 times. Based on these recordings, the excretions can be divided into coarse and fine excretions. All precipitations with a diameter of less than 30 nm are referred to as fine precipitations. The remaining exudates are referred to as coarse excretions.
  • the proportion of fine waste in the total number of waste in the measuring field is determined by simply counting.
  • the average diameter of the fine waste is also calculated using computer-aided image analysis.
  • the proportion of fine precipitates is more than 90%.
  • the mean diameter of the fine precipitates is also less than 11 nm.
  • Table 8 also shows the grain diameter of the former austenite grains. For this purpose, the austenite grains would be reconstructed from EBSD measurements using the ARPGE software.
  • the software parameters were:
  • FIG. 3 shows a corresponding reconstruction of the austenite from test no. 1.
  • the mean diameter of the former austenite grains is 7.5 ⁇ m.
  • the average grain diameter of the former austenite grains is less than 14 ⁇ m.
  • the grain diameter of the former austenite grains was not determined in two tests. The entry in Table 8 is therefore "n.b.” (not determined).
  • Table 9 gives the application-related properties of the sheet metal part.
  • the area occupied by pores in the alloy layer is specified over a measuring length of 500 ⁇ m. In all examples according to the invention, this area is less than 250 ⁇ m 2 .
  • the Nb content in the alloy layer given in Table 9 is an average of the Nb content in this layer.
  • the Nb content in the alloy layer decreases slightly towards the surface and is approximately characterized by a linear decrease in the layer.
  • Table 9 also shows the proportion of the area occupied by pores with a diameter greater than or equal to 0.1 ⁇ m. In all examples according to the invention, this proportion is less than 10%.
  • the total area of the pores and the proportion of pores larger than 0.1 ⁇ m was determined using micrographs using computer-assisted image analysis.
  • FIG. 1a shows a micrograph of test 1 with a fine pore structure
  • FIG. are clear in FIG. 1b
  • the coarser pores can be seen as black spots in the alloy layer.
  • FIGS. 2a and 2b The effects of the coarser pores after a corrosion test are shown in FIGS. 2a and 2b.
  • FIGS. 2a and 2b show micrographs of the same tests, each after a corrosion test.
  • the samples were placed in a corrosive medium and subjected to a current to simulate prolonged electrochemical corrosion.
  • An aqueous 5% NaCl solution with a pH of 7 was used as the corrosive medium.
  • the current was ImA/cm 2 for a period of 6 hours. It can be clearly seen that in FIG. 2b the layer was almost completely detached, while in FIG. 2a the layer is still well connected to the substrate.
  • the examples according to the invention with finer pores thus withstand corrosion much better than the reference examples with the coarser pore structure.
  • Table 8 also shows the welding area according to SEP 1220-2.
  • the welding range is at least 0.9 and at most 1.6 kA.
  • Table 8 also shows the electrochemical potential.
  • the electrochemical potential is determined according to the DIN standard "DIN 50918 (2018.09) ("resting potential measurement on homogeneous mixed electrodes"). The specified absolute value is to be understood as a reference to the standard hydrogen electrode. An aqueous 5% NaCl solution with a pH value of 7, which represents typical corrosion conditions in the automotive sector, is used as the corrosive medium in the measurement. It can be clearly seen that all samples have an electrochemical potential that is greater than -0.50V.
  • Flat steel product for hot forming comprising a steel substrate made of steel which, in addition to iron and unavoidable impurities (in % by weight), consists of
  • Mn 0.4-3.0%
  • Al 0.06-1.0%
  • Nb 0.001-0.2%
  • Ti 0.001-0.10%
  • the alloy layer consists of 35-60% by weight Fe, optional further components, the total content of which is limited to a maximum of 5.0% by weight, and the remainder aluminum and/ or the Al base layer of 1.0-15 wt% Si, optionally 2-4 wt% Fe, optionally up to 5.0 wt% alkali or alkaline earth metals, optionally up to 10% Zn and optional other components, the total content of which is limited to a maximum of 2.0% by weight, and the remainder is aluminum.
  • Flat steel product according to one of sentences 1-6 characterized in that the flat steel product has a continuous yield point (Rp0.2) or a yield point with a difference (ARe) between the upper yield point value (ReH) and the lower yield point value (ReL) of at most 45 MPa and/or the flat steel product has a uniform elongation Ag of at least 10% and/or the flat steel product has an elongation at break A80 of at least 15%, preferably at least 20%.
  • a method for producing a flat steel product for hot forming with an anti-corrosion coating comprising the following work steps: a) providing a slab or a thin slab made of steel which, in addition to iron and unavoidable impurities (in % by weight), consists of C: 0.06 - 0.5%,
  • Mn 0.4-3.0%
  • Al 0.06-1.0%
  • Nb 0.001-0.2%
  • Ti 0.001-0.10%
  • B 0.0005-0.01%
  • W: 0.001 -1.0% passes b) through heating of the slab or thin slab at a temperature (TI) of 1100 - 1400 °C; c) optional pre-rolling of the through-heated slab or thin slab into an intermediate product with an intermediate product temperature (T2) of 1000 - 1200 °C; d) hot-rolling into a hot-rolled steel flat product, the finish rolling temperature (T3) being 750 - 1000 °C; e) optional coiling of the hot-rolled steel flat product, the coiling temperature (T4) being at most 700 °C; f) descaling the hot-rolled flat steel product; g) optional cold rolling of the flat steel product, the degree of cold rolling being at least 30%; h) annealing of the steel flat product at an annealing temperature (T5) of 650 - 900 °C; i) cooling the flat steel product to an immersion temperature (T6) which is 650-800° C., preferably 670-800° C.; j) coating the flat steel
  • Mn 0.4 - 3.0%
  • Al 0.06 - 1.0%
  • Nb 0.001 - 0.2%
  • Ti 0.001 - 0.10%
  • Sheet metal part according to one of sentences 11-12, characterized in that the steel substrate of the sheet metal part has a structure with at least partially more than 80% martensite and/or lower bainite, preferably more at least partially more than 90% martensite and/or lower bainite, and wherein the former austenite grains of the martensite preferably have an average grain diameter of less than 14 ⁇ m, in particular less than 12 ⁇ m, preferably less than 10 ⁇ m.
  • Sheet metal part according to one of clauses 11-13, characterized in that the sheet metal part at least partially has a yield point of at least 950 MPa, in particular at least 1100 MPa, preferably at least 1300 MPa, in particular at least 1500 MPa and/or the sheet metal part at least partially has a tensile strength of at least 1000 MPa, in particular at least 1100 MPa, preferably at least 1300 MPa, in particular at least 1800 MPa and/or the sheet metal part at least partially has an elongation at break A80 of at least 4%, preferably at least 5%, particularly preferably at least 6% and/or the shaped sheet metal part at least partially has a bending angle of at least 30°, in particular at least 40°, preferably at least 50°.
  • Sheet metal part according to one of sentences 11-15 characterized in that the electrochemical potential of the surface of the sheet metal part is at least -0.50 V in a corrosive medium.
  • Sheet metal part according to one of sentences 11-16 characterized in that the anti-corrosion coating is an aluminum-based anti-corrosion coating and comprises an alloy layer and an Al base layer, and in the cross-section of the alloy layer over a measuring length of 500 ⁇ m the surface occupied by pores in the Alloy layer is less than 250 pm 2 and in particular the proportion of the surface occupied by pores with a diameter greater than or equal to 0.1 pm is less than 10%.
  • the anti-corrosion coating is an aluminum-based anti-corrosion coating and comprises an alloy layer and an Al base layer, and in the cross-section of the alloy layer over a measuring length of 500 ⁇ m the surface occupied by pores in the Alloy layer is less than 250 pm 2 and in particular the proportion of the surface occupied by pores with a diameter greater than or equal to 0.1 pm is less than 10%.
  • Sheet metal part according to one of sentences 11-17 characterized in that the welding area is at least 0.9 kA.
  • Sheet metal part according to one of sentences 11-18 characterized in that the Nb content in the alloy layer is greater than 0.010% by weight, preferably greater than 0.015% by weight, in particular greater than 0.018% by weight.
  • a method for producing a shaped sheet metal part comprising the following
  • step c) Heating the sheet metal blank in such a way that the AC3 temperature of the blank is at least partially exceeded and the temperature T Einig of the blank when it is placed in a forming tool provided for hot-press forming (step c)) at least partially has a temperature above Ms+100°C where Ms denotes the martensite start temperature.

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Abstract

L'invention concerne un produit plat en acier pour le travail à chaud, une pièce en tôle d'acier usinée, un procédé de fabrication du produit plat en acier et un procédé de fabrication du produit en tôle d'acier usiné, le produit plat en acier et la pièce en tôle d'acier présentant des propriétés améliorées en particulier en association avec un revêtement anticorrosion à base d'aluminium.
EP22764727.8A 2021-08-19 2022-08-11 Acier ayant des propriétés de traitement améliorées pour travailler à des températures élevées Pending EP4388140A1 (fr)

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EP21192187 2021-08-19
PCT/EP2022/072555 WO2023020931A1 (fr) 2021-08-19 2022-08-11 Acier ayant des propriétés de traitement améliorées pour travailler à des températures élevées

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EP4388140A1 true EP4388140A1 (fr) 2024-06-26

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EP4174207A1 (fr) 2021-11-02 2023-05-03 ThyssenKrupp Steel Europe AG Produit plat en acier ayant des propriétés de traitement améliorées

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EP2374910A1 (fr) 2010-04-01 2011-10-12 ThyssenKrupp Steel Europe AG Acier, produit plat en acier, composant en acier et procédé de fabrication d'un composant en acier
CN102876969B (zh) * 2012-07-31 2015-03-04 宝山钢铁股份有限公司 一种超高强度高韧性耐磨钢板及其制造方法
WO2017006144A1 (fr) * 2015-07-09 2017-01-12 Arcelormittal Acier pour trempe à la presse et pièce trempée à la presse fabriquée à partir d'un tel acier
WO2019003449A1 (fr) * 2017-06-30 2019-01-03 Ｊｆｅスチール株式会社 Élément pressé à chaud et son procédé de fabrication, et tôle d'acier laminée à froid pour pressage à chaud
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CN108374127A (zh) * 2018-04-28 2018-08-07 育材堂（苏州）材料科技有限公司 热冲压成形用钢材、热冲压成形工艺及热冲压成形构件
WO2019223854A1 (fr) 2018-05-22 2019-11-28 Thyssenkrupp Steel Europe Ag Pièce façonnée en tôle composée d'acier et présentant une résistance élevée à la traction, et procédé de fabrication de ladite pièce
EP3976838A1 (fr) * 2019-05-29 2022-04-06 ThyssenKrupp Steel Europe AG Composant réalisé par formage d'un larget de tôle d'acier et procédé de réalisation correspondant

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