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EP3658307B9 - Sheet metal component, produced by hot working a flat steel product, and method for the production thereof - Google Patents

Sheet metal component, produced by hot working a flat steel product, and method for the production thereof Download PDF

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Publication number
EP3658307B9
EP3658307B9 EP17754271.9A EP17754271A EP3658307B9 EP 3658307 B9 EP3658307 B9 EP 3658307B9 EP 17754271 A EP17754271 A EP 17754271A EP 3658307 B9 EP3658307 B9 EP 3658307B9
Authority
EP
European Patent Office
Prior art keywords
flat steel
steel product
steel
metal sheet
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.)
Active
Application number
EP17754271.9A
Other languages
German (de)
French (fr)
Other versions
EP3658307A1 (en
EP3658307B1 (en
EP3658307B8 (en
Inventor
Brigitte Hammer
Harald Hofmann
Thomas Heller
Sebastian STILLE
Georg Parma
Janko Banik
Jonas SCHWABE
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
ThyssenKrupp AG
Original Assignee
ThyssenKrupp Steel Europe AG
ThyssenKrupp AG
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Filing date
Publication date
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Application filed by ThyssenKrupp Steel Europe AG, ThyssenKrupp AG filed Critical ThyssenKrupp Steel Europe AG
Publication of EP3658307A1 publication Critical patent/EP3658307A1/en
Publication of EP3658307B1 publication Critical patent/EP3658307B1/en
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Publication of EP3658307B8 publication Critical patent/EP3658307B8/en
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Classifications

    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B21MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21DWORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02Stamping using rigid devices or tools
    • B21D22/022Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18Hardening; Quenching with or without subsequent tempering
    • C21D1/185Hardening; Quenching with or without subsequent tempering from an intercritical temperature
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D6/00Heat treatment of ferrous alloys
    • C21D6/005Heat treatment of ferrous alloys containing Mn
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/001Ferrous alloys, e.g. steel alloys containing N
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/005Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20Ferrous alloys, e.g. steel alloys containing chromium with copper
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C2/00Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C2/00Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224Two or more thermal pretreatments
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C2/00Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06Zinc or cadmium or alloys based thereon
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C2/00Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12Aluminium or alloys based thereon
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C2/00Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26After-treatment
    • C23C2/28Thermal after-treatment, e.g. treatment in oil bath
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/001Austenite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/008Martensite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling

Definitions

  • the invention relates to a sheet metal component produced by hot forming a flat steel product.
  • the invention relates to a method for producing a component according to the invention.
  • the flat steel products according to the invention are rolled products, such as steel strips, steel sheets or products made from them Blanks and blanks whose thickness is significantly less than their width and length.
  • these steels contain C: up to 0.5, Mn: from 4 to 12%, Si: up to 1.0%, Al: up to 3%, Cr: from 0.1 to 4%, Cu: up to 2.0%, Ni: up to 2.0%, N: up to 0.05%, P: up to 0.05%; S: up to 0.01%, and optionally one or more elements from the group "V, Nb, Ti", the sum of the contents of these elements not exceeding 0.5%.
  • the EP 2 383 353 A2 presented a process for the production of a coated or uncoated hot or cold strip.
  • a molten steel composed as described above is cast into a billet or strip, which is then subjected to a heat treatment to heat it up to a hot rolling start temperature of 1150 - 1000 °C to produce a starting product.
  • the respective starting product is then hot-rolled into a hot strip.
  • the finished hot strip is then wound into a coil.
  • This work step can optionally be followed by annealing of the hot strip, cold rolling of the annealed hot strip, annealing of the cold strip and coating of the surface of the hot or cold strip.
  • From the EP 2 778 247 A1 is a method of manufacturing a component by hot press forming a steel sheet after heating in Two-phase region, ie after heating to a temperature between the Ac1 and the Ac3 temperature of the respective steel alloy, is known.
  • the hot-rolled strip obtained is coiled, annealed and then cold-rolled.
  • the hot strip is then heated to a temperature between the Ac1 and Ac3 temperatures of the respective steel alloy and hot press formed.
  • the structure of the component obtained in this way consists of 5 - 50% by volume of retained austenite and the remainder of martensite, tempered martensite, bainite or ferrite.
  • a component is also known that is hot-formed from a steel sheet made of a steel which, in % by weight, contains 0.02 - 0.45% C, 3.50 - 9.0% Mn, at most 0.020% P , at most 0.020% S, the rest Fe and unavoidable impurities.
  • the steel can additionally contain 0.1 - 3.0% Ni, 0.2 - 3.0% Cr, 0.1 - 0.8% Mo, 0.3 - 2.3% Si, 0.5 - 2.0 % Cu, 0.0005 - 0.0050% B, 0.02 - 0.30% Nb, 0.002 - 0.250% N, 0.05 - 0.25% Ti, 0.02 - 0.25% V, 0.015 - 3.0% Al, 0.002 - 0.005% REM and 0.005 - 0.03% Ca included.
  • the manufacturing process envisaged for this includes the following steps: heating of the steel sheet, transfer of the steel sheet, pre-cooling of the steel sheet, forming of the part and cooling of the part.
  • the task was to create a sheet metal component which, compared to conventionally produced sheet metal components, enables energy savings through lower forming temperatures, allows increased residual elongation at high strengths and which has the highest possible potential for a cathodic protection against corrosion is maintained.
  • a sheet metal component that achieves this object has at least the features specified in claim 1 .
  • a sheet metal component according to the invention is accordingly produced by hot forming of a steel flat product consisting of (in % by weight) C: 0.02-0.5%, Si: 0.05-1%, Mn: 4-12%, Cr: 0 .1 - 4%, AI: up to 3.5%, N: up to 0.05%, P: up to 0.05%, S: up to 0.01%, in total > 0.04% up to 2% Cu and/or Ni, up to 0.5% in total of Ti, Nb or V, rare earths: up to 0.1% and the remainder consists of Fe and unavoidable impurities.
  • the content %C of C and the content %Cr of Cr in the steel of the steel flat product fulfill the following condition: (10x%C)+%Cr ⁇ 5.5% by weight.
  • the flat steel product according to the invention has a bending angle of more than 60°, determined according to VDA 238-100: 2010-12, after hot forming to form the sheet metal component.
  • the microstructure of the hot-formed sheet metal component according to the invention consists of 5-50% by volume of austenite and the remainder of martensite, tempered martensite or ferrite, it also being possible for the ferrite proportion to be “0”.
  • the average grain diameter of the grains of the structure is less than 5 ⁇ m, preferably less than 2 ⁇ m.
  • the flat steel product formed into the sheet metal component according to the invention consists of a steel which belongs to the class of so-called "middle manganese steels" which usually have Mn contents of 4-12% by weight, in particular 4-9% by weight.
  • Manganese "Mn” lowers the austenitization temperature and delays the transformation of ferrite, pearlite and bainite. This also allows the holding temperature in the furnace before hot forming to be reduced. The advantages obtained are further enhanced by holding and hot working in the two-phase region. During the subsequent cooling, a high proportion of austenite is retained. This leads to a very high residual elongation at break and a high possible bending angle up to the first cracks and thus higher energy absorption in the event of a crash.
  • the Mn content of a steel flat product processed according to the invention is set at 4-12 wt.
  • carbon “C” determines the strength of martensite on the one hand and others the amount and stability of the retained austenite. If the carbon content is too high, the weldability and toughness of the steel, e.g. B. negatively affected by the formation of Cr carbides. Therefore, the carbon content of Mn steels of the type selected according to the invention is at most 0.5% by weight, with lower C contents of less than 0.5% by weight, in particular of up to 0.3% by weight prove particularly favorable. However, if the carbon content is too low, the amount and stability of the retained austenite will be affected. The carbon content of a steel according to the invention is therefore at least 0.02% by weight.
  • Aluminum "AI” and silicon “Si” are strong ferrite formers. Both elements counteract the influence of the austenite formers C and Mn.
  • the main task of the elements Si and Al in the steel of a steel flat product hot-formed to form the sheet metal component according to the invention is to suppress carbide precipitation and thus promote the stability of the retained austenite.
  • Si and Al lead to solid solution hardening and reduce the specific weight of the steel.
  • the Si and Al content is too low, carbide precipitation may not be effectively suppressed.
  • the Si and Al contents are too high, processing is made more difficult both in the case of production using a continuous casting method and in the case of production using a strip casting method.
  • the invention therefore provides for the Si content to be limited to a maximum of 1% by weight, with the positive effects of the presence of Si already being able to be used effectively if the Si content of the steel of the flat steel product from which the inventive component is thermoformed is at least 0.05% by weight.
  • chromium “Cr” in amounts of 0.1-4% by weight specifically reduces the risk of stress corrosion cracking in a steel according to the invention.
  • Cr and Al hinder hydrogen-induced cracking.
  • Cr contributes to the increase in strength.
  • Cr also lowers the Ms temperature (martensite start temperature) and thus supports the stabilization of retained austenite.
  • the Cr content of the steel of a flat steel product hot-formed to form the component according to the invention is limited to a maximum of 4% by weight, because higher contents could produce Cr carbides which would adversely affect the ductility of the steel.
  • the invention stipulates that the carbon “C” content “%C” and the chromium “Cr” content “%Cr” of the steel of a component formed according to the invention must be taken into account Steel flat product must comply with the condition (10x%C) + %Cr ⁇ 5.5% by weight.
  • micro-alloying elements Ti, Nb and V can be present in the steel of the flat steel product from which the component according to the invention is formed in amounts totaling up to 0.5% by weight. These micro-alloying elements contribute to grain refinement and increased strength. However, contents of Ti, Nb and V above 0.5% by weight do not increase this effect, whereas the positive effects of Ti, Nb and V in the steel of the component according to the invention can be safely used if their in total is at least 0.05% by weight.
  • the austenitic structure can be additionally stabilized by adding nitrogen "N" in amounts of up to 0.05% by weight. If the N content is too high, processability during continuous casting is impaired and an brittle amount of nitrides is formed.
  • the content of phosphorus "P" in the steel of a component according to the invention is limited to a maximum of 0.05% by weight in order to reliably rule out negative influences from this element.
  • the sulfur "S" content of a steel according to the invention is limited to a maximum of 0.01% by weight.
  • Rare earths "REM” can contribute to grain refinement in the steel of the component according to the invention through the formation of oxides and improve the isotropy of the mechanical-technological properties via the texture.
  • the two rare earths cerium and lanthanum are chemically almost identical and therefore come in the Nature always communitized before. Due to their chemical similarity, they are very difficult and therefore difficult to separate. They have the same effect.
  • Rare earths can be freely substituted for use in steel. With contents above 0.1% by weight, however, there is, among other things, the risk of so-called "clogging" in industrial-scale casting of the steel, ie the clogging of the casting mold by locally solidifying melt.
  • the advantages of the presence of the REM can nevertheless be safely used in that the steel content of a component according to the invention is at least 0.0005% by weight.
  • the bending angle determined in accordance with VDA 238-100: 2010-12 is a measure of the folding behavior of the material in the event of a crash and is therefore an indicator of the ductility that a hot-formed component has.
  • Components according to the invention are characterized by a high bending angle of at least 60°, in particular at least 80° or more than 80°, such as at least 85°, after hot forming.
  • the uniform, very fine structure plays a supporting role here.
  • High austenite content such as that present when hot working occurs at temperatures in the two-phase mixing region (or lower) of the steel making up the flat steel product from which the component is formed, has beneficial effects.
  • Components according to the invention are distinguished by the fact that they have a structure which consists of at least 5% by volume of austenite, with the proportion of austenite in the structure being able to be up to 50% by volume.
  • the remaining structure of the component consists of strength-increasing proportions of martensite and tempered martensite. Ferrite may also be included.
  • the amount of other structural components that are technically unavoidable is so small that they are ineffective with regard to the properties of the component according to the invention.
  • the method according to the invention for producing a sheet metal component according to the preceding claims comprises the following work steps: a) Providing a flat steel product made from a steel which, in % by weight, consists of C: 0.02 - 0.5%, Si: 0.05 - 1%, Mn: 4-12%, Cr: 0.1 - 4%, Al: up to 3.5%, N: up to 0.05%, P: up to 0.05%, S: up to 0.01%, a total of 0.04% up to 2% Cu and/or Ni, a total of up to 0.5% Ti, Nb or V, SEM: up to 0.1% and the balance being Fe and unavoidable impurities, where the %C content of C and the %Cr content of Cr satisfies the following condition: 10 ⁇ %C + %Cr ⁇ 5 .5% , b) through heating the steel flat product to a heating temperature which is at least 200 °C and at most 800 °C; c) Hot forming of the flat steel product
  • the cooling rate at which the hot-formed component obtained is cooled is not subject to any restrictions.
  • EP 2 383 353 A2 The basic possibilities of producing steel flat products that are suitable for the purposes of the invention and are provided in step a) of the method of the invention are in EP 2 383 353 A2 described.
  • the diagram reproduced there and the associated sections [0031] to [0040] of EP 2 383 353 A2 are the different in methods available in practice for producing flat steel products which are suitable for producing components according to the invention.
  • Typical protective coatings present on components of the present invention are hot dip zinc-based protective coatings such as Zn (“Z”) coatings, zinc-iron coatings ("ZF”), Zinc-Magnesium-Aluminum Coatings ("ZM”), Zinc-Aluminum Coatings ("ZA”).
  • zinc-based protective coatings such as Zn (“Z") coatings, zinc-iron coatings (“ZF”), Zinc-Magnesium-Aluminum Coatings (“ZM”), Zinc-Aluminum Coatings (“ZA”).
  • aluminum-based protective coatings can be used, such as aluminum-zinc coatings ("AZ”), aluminum-silicon coatings ("AS”).
  • Electrolytically applied Zn-based protective coatings such as pure zinc “ZE” coatings or zinc-nickel (“ZN”) coatings can also be provided.
  • metallic anti-corrosion coatings which are known per se and are applied by deposition processes such as PVD, CVD or vapor spraying are also possible.
  • the invention shows a way in which resource-saving hot forming can be used to produce a component that has optimal mechanical properties after hot forming and, due to these properties and its other functional properties, can also meet high requirements in the event of a crash load on the component.
  • the high manganese content of flat steel products processed according to the invention enables lower hot forming temperatures than with conventional hot forming steels.
  • the invention thus makes it possible to save energy and costs.
  • the heating temperatures for hot forming should not be more than 60° C. above the Ac3 temperature of the respective steel of the steel flat product in order to obtain the desired positive properties.
  • the heating temperatures can be particularly low if the deformation is to take place in the two-phase region or at temperatures below that. In this case, the proportion of residual austenite in the resulting component is over 20% by volume and the elongation at break A80 is over 15%.
  • the hot forming according to the invention takes place here at heating temperatures that are typically above the Ac1 temperature and below the Ac3 temperature of the respective steel of the steel flat product, with heating temperatures that are at least 10 °C higher proving to be particularly favorable in the case of deformation in the two-phase region are lower than the Ac1 temperature and at least 50 °C lower than the Ac3 temperature of the respective steel of the steel flat product.
  • the heating temperature can be below the Ac1 temperature of the respective steel from which the flat steel product hot-formed according to the invention consists.
  • the proportion of austenite before hot forming is not important for anneals with heating temperatures above the Ac1 temperature, the desired proportion for forming below Ac1 must be set in a preceding annealing step.
  • the heating temperature during this additional annealing should be at least so high that the forming forces stand out positively from those of cold forming. Accordingly, in this case the heating temperature should be set in such a way that the forming forces during hot forming amount to a maximum of 85% of the forming forces at room temperature. This is at Heating temperatures of over 200 °C, in particular over 400 °C, secured.
  • the procedure according to the invention results in a structure which is characterized by optimized proportions of austenite and, as a result, has very good mechanical properties, in particular high residual elongation and high energy absorption in the event of a crash load.
  • the comparatively low heating temperatures in this range, at which the hot forming of the component according to the invention takes place, also prove to be particularly advantageous if the flat steel product processed according to the invention is to have cathodic corrosion protection.
  • the annealing times typically required for thorough heating in step b) are usually up to 60 minutes, with annealing times of up to 20 minutes, in particular up to 10 minutes, having proven to be particularly economical in practice.
  • Thorough heating can be carried out in conventional chamber furnaces or roller furnaces, in which the flat steel products to be hot-formed are brought to the heating temperature in a continuous flow or in batches. Since the properties of the flat steel product formed into the component are formed almost independently of the heating and cooling rate in compositions according to the invention, it can also prove advantageous if the heating is carried out by conductive or inductive heating, or also, for example, by means of solid-body contact or in a fluidized bed .
  • the alternative methods to conventional furnace heating mean that shorter annealing times can be achieved in comparison to pure radiation heating in a conventional furnace. At the same time, the alternative methods allow for more precisely controlled heating cycles since the course of the heating can follow precise specifications. Another advantage of using the alternative heating process is that it is possible to react quickly to production changes, which are typical for small batch production with different sheet metal thicknesses.
  • the hot forming (work step c)) of the steel flat product heated to the respective heating temperature to form the component according to the invention can be carried out in conventional hot forming tools available for this purpose in the prior art.
  • the hot forming takes place as soon as possible after the through heating (work step b)), so that the temperature at which the steel flat product enters the hot forming corresponds to the heating temperature with the exception of a technically insignificant difference.
  • stronger cooling is also permissible as long as the forming forces and springback are advantageous compared to cold forming.
  • the cooling of the component after the hot forming can also take place in a manner known per se in the hot forming tool.
  • the component can also be removed from the hot forming tool and cooled outside of the tool at a suitably short time interval. Since the cooling speed is not limited, it can even be less than 10K/s.
  • the invention has a particularly positive effect when producing components from flat steel products that are coated with a metallic protective layer to protect them from corrosion or other attacks.
  • each of the protective layers processed according to the invention and hot-formed into the component according to the invention typically have a surface-near boundary layer adjoining the steel substrate of the flat steel product prior to the hot-forming, which consists of metallic and/or oxidic iron and, if necessary, metallic and/or oxidic manganese and the other alloy components of the base material.
  • the parameters of the procedure according to the invention make it possible to maintain the cathodic protective effect of a layer containing Zn present on the flat steel product and to avoid critical cracks of more than 10 ⁇ m during hot forming.
  • the harmful consequences that would occur if the Zn layer were to melt are avoided. Due to the diffusion of Fe from the substrate into the layer, its melting point is raised sufficiently. However, in order to maintain cathodic protection against corrosion, the Fe content in the coating must be limited so that sufficient Zn-rich phases are retained after hot forming.
  • the Fe-Zn phases present in the coating were determined for the examples by X-ray diffractometry and are summarized in Table 3.
  • the comparison steel V which is conventionally used in hot forming, is typically annealed at 870 - 950 °C to set the target mechanical properties. This leads to the formation of a ⁇ / ⁇ 1 phase, which is comparatively temperature-stable, which limits the proportion of liquid Zn that forms and thus reduces the risk of liquid metal embrittlement occurring.
  • the high proportion of Fe contained in the ⁇ / ⁇ 1 phase severely limits the active corrosion protection of the layer.
  • the significantly higher Zn-rich ⁇ phase also remains due to the significantly lower oven temperature for setting the mechanical target properties, which leads to an improved corrosion protection potential.
  • the layer system Due to the layer structure caused by the alloying, the layer system is sufficiently temperature-stable so that no critical cracking of more than 10 ⁇ m depth occurs due to liquid Zn at hot forming temperatures according to the invention, at which crack propagation would be expected when the component is stressed.
  • components produced according to the invention have an optimized combination of high strength values, for which tensile strengths Rm of typically at least 1000 MPa stand, and optimized elongation properties, which are expressed in elongations at break A80 of regularly more than 10%.
  • the product Rm ⁇ A80 is accordingly also regularly in the range of 13,000-35,000 MPa%.
  • the tensile strengths Rm for components made from conventional steels for hot forming were produced at temperatures at which a fully austenitic structure is present, typically at least 1200 MPa, since they are fully martensitic after quenching.
  • these components only achieve significantly lower elongation at break values A80, so that the product Rm x A80 for these components is regularly only 6,000 - 11,000 MPa%.
  • Table 1 shows the Ac1 and Ac3 temperatures in °C determined for steels S1 - S3 and V in accordance with SEP 1680:1990-12.
  • the comparison melt V lies outside the specifications of the invention due to its low Mn content and the presence of B.
  • Sheet metal blanks were made from steels S1 - S3 and V.
  • the sheet metal blanks were each heated through in a conventional oven to a heating temperature Tew, then hot-formed in a conventional hot-forming tool to form a hat profile and then cooled in air.
  • the tensile strength Rm determined on the component obtained in each case, the yield point Rp0.2, the elongation at break A80, the product Rm ⁇ A80 and the bending angle are given in Table 2.
  • structural parameters of the component obtained are given there.
  • the austenite content of the respective component obtained and the estimated grain size as well as the crack depths at the most critical point of the hat profile are given there, as measured in the cross section under the light microscope.
  • the elongations at break A80 are more than 10% and the products Rm ⁇ A80 are more than 14,000 MPa%.
  • the examples have bending angles of more than 60°.
  • a particularly fine structure can be achieved by alloying micro-alloying elements and rare earth metals.
  • the austenite content was adjusted by annealing in the two-phase region prior to sheet metal cutting.

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Description

Die Erfindung betrifft ein Blechbauteil, hergestellt durch Warmumformen eines Stahlflachprodukts.The invention relates to a sheet metal component produced by hot forming a flat steel product.

Des Weiteren betrifft die Erfindung ein Verfahren zur Herstellung eines erfindungsgemäßen Bauteils.Furthermore, the invention relates to a method for producing a component according to the invention.

Wenn im vorliegenden Text Angaben zu Legierungsgehalten einzelner Elemente im erfindungsgemäßen Stahl gemacht werden, beziehen diese sich immer auf das Gewicht (Angabe in Gew.-%), sofern nichts anderes angegeben ist.If information is given in the present text on the alloy contents of individual elements in the steel according to the invention, these always relate to the weight (in percent by weight) unless otherwise stated.

Angaben zu den Bestandteilen des Gefüges eines Stahls, eines Stahlflachprodukts oder eines daraus geformten Bauteils beziehen sich hier dagegen immer auf das Volumen (Angabe in Vol.-%). Sofern erwähnt, sind die Anteile an Austenit dabei über XRD mit Fe-gefilterter Co-Kα-Strahlung gemessen worden. Das XRD - Messverfahren ist in folgender Quelle beschrieben: DIN EN 13925-Röntgendiffraktometrie von polykristallinen und amorphen Materialien Teil 1 und 2 aus 2003_7, Teil 3 aus 2005. Die weiteren Gefügebestandteile, sofern erwähnt, sind jeweils nach Nital-Ätzung lichtmikroskopisch identifiziert worden.Information on the components of the structure of a steel, a steel flat product or a component formed from it, on the other hand, always refers to the volume (in vol. %). If mentioned, the proportions of austenite were measured using XRD with Fe-filtered Co-Kα radiation. The XRD measuring method is described in the following source: DIN EN 13925 X-ray diffractometry of polycrystalline and amorphous materials Part 1 and 2 from 2003_7, Part 3 from 2005. The other structural components, if mentioned, have each been identified by light microscopy after Nital etching.

Bei den erfindungsgemäßen Stahlflachprodukten handelt es sich um Walzprodukte, wie Stahlbänder, Stahlbleche oder daraus gewonnene Zuschnitte und Platinen, deren Dicke wesentlich geringer ist als ihre Breite und Länge.The flat steel products according to the invention are rolled products, such as steel strips, steel sheets or products made from them Blanks and blanks whose thickness is significantly less than their width and length.

Die im vorliegenden Text erwähnten mechanischen Eigenschaften Zugfestigkeit Rm, Dehngrenze Rp0,2 und Bruchdehnung A80 sind gemäß der DIN EN ISO 6892-1 :2017-02 bestimmt worden.The mechanical properties mentioned in this text, namely tensile strength Rm, yield strength Rp0.2 and elongation at break A80, have been determined in accordance with DIN EN ISO 6892-1:2017-02.

Aus der EP 2 383 353 A2 sind Beispiele für höherfeste, Mn-haltige Stähle bekannt, die als beschichtetes oder unbeschichtetes Warm- oder Kaltband eine Bruchdehnung A80 von mindestens 4 % und eine Zugfestigkeit von 900 - 1500 MPa aufweisen. Diese Stähle enthalten neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) C: bis zu 0,5, Mn: von 4 bis 12 %, Si: bis zu 1,0 %, AI: bis zu 3 %, Cr: von 0,1 bis 4 %, Cu: bis zu 2,0 %, Ni: bis zu 2,0 %, N: bis zu 0,05 %, P: bis zu 0,05 %; S: bis zu 0,01%, sowie optional eines oder mehrere Elemente aus der Gruppe "V, Nb, Ti", wobei die Summe der Gehalte dieser Elemente höchstens gleich 0,5 % ist. Des Weiteren wird in der EP 2 383 353 A2 ein Verfahren zur Herstellung eines beschichteten oder unbeschichteten Warm- oder Kaltbands vorgestellt. Gemäß diesem Verfahren wird zur Erzeugung eines Ausgangsproduktes eine in der voranstehend angegebenen Weise zusammengesetzte Stahlschmelze zu einem Strang oder Band vergossen, das anschließend einer Wärmebehandlung unterzogen wird, um es auf eine Warmwalzstarttemperatur von 1150 - 1000 °C zu erwärmen. Im Anschluss daran wird das jeweilige Ausgangsprodukt zu einem Warmband warmgewalzt. Das fertige Warmband wird dann zu einem Coil gehaspelt. Diesem Arbeitsschritt können sich jeweils optional ein Glühen des Warmbands, ein Kaltwalzen des geglühten Warmbands, ein Glühen des Kaltbandes und ein Beschichten der Oberfläche des Warm- oder Kaltbands anschließen.From the EP 2 383 353 A2 Examples of high-strength, Mn-containing steels are known which, as coated or uncoated hot or cold strip, have an A80 elongation at break of at least 4% and a tensile strength of 900 - 1500 MPa. In addition to iron and unavoidable impurities (in % by weight), these steels contain C: up to 0.5, Mn: from 4 to 12%, Si: up to 1.0%, Al: up to 3%, Cr: from 0.1 to 4%, Cu: up to 2.0%, Ni: up to 2.0%, N: up to 0.05%, P: up to 0.05%; S: up to 0.01%, and optionally one or more elements from the group "V, Nb, Ti", the sum of the contents of these elements not exceeding 0.5%. Furthermore, in the EP 2 383 353 A2 presented a process for the production of a coated or uncoated hot or cold strip. According to this method, a molten steel composed as described above is cast into a billet or strip, which is then subjected to a heat treatment to heat it up to a hot rolling start temperature of 1150 - 1000 °C to produce a starting product. The respective starting product is then hot-rolled into a hot strip. The finished hot strip is then wound into a coil. This work step can optionally be followed by annealing of the hot strip, cold rolling of the annealed hot strip, annealing of the cold strip and coating of the surface of the hot or cold strip.

Aus der EP 2 778 247 A1 ist ein Verfahren zum Herstellen eines Bauteils durch Warmpressformen eines Stahlbleches nach einer Erwärmung im Zweiphasengebiet, das heißt nach einer Erwärmung auf eine Temperatur, die zwischen der Ac1- und der Ac3-Temperatur der jeweiligen Stahllegierung liegt, bekannt. Gemäß diesem Verfahren wird eine Bramme, die aus Eisen, unvermeidbaren Verunreinigungen und (in Gew.-%) C: 0,01 - 0,5 %, Si: bis zu 3,0 %, Mn: 3 - 15 %, P: 0,0001 - 0,1 %, S: 0,0001 -0,03 %, Al: bis zu 3 % und N: bis zu 0,03 % besteht, auf 1000 - 1400 °C erwärmt, warmgewalzt und anschließend in einem Temperaturbereich, der von der Ar3-Temperatur des Stahls bis 1000 °C reicht, fertig warmgewalzt. Das erhaltene warmgewalzte Band wird gehaspelt, geglüht und anschließend kaltgewalzt. Im Anschluss daran wird das Warmband auf eine Temperatur erwärmt, die zwischen der Ac1- und der Ac3-Temperatur der jeweiligen Stahllegierung liegt, und warmpressgeformt. Das Gefüge des so erhaltenen Bauteils besteht zu 5 - 50 Vol.-% aus Restaustenit und als Rest aus Martensit, angelassenem Martensit, Bainit oder Ferrit.From the EP 2 778 247 A1 is a method of manufacturing a component by hot press forming a steel sheet after heating in Two-phase region, ie after heating to a temperature between the Ac1 and the Ac3 temperature of the respective steel alloy, is known. According to this method, a slab consisting of iron, unavoidable impurities and (in % by weight) C: 0.01 - 0.5%, Si: up to 3.0%, Mn: 3 - 15%, P: 0.0001 - 0.1%, S: 0.0001 -0.03%, Al: up to 3% and N: up to 0.03%, heated to 1000 - 1400 °C, hot rolled and then in one Temperature range ranging from the Ar3 temperature of the steel to 1000°C, finished hot rolled. The hot-rolled strip obtained is coiled, annealed and then cold-rolled. The hot strip is then heated to a temperature between the Ac1 and Ac3 temperatures of the respective steel alloy and hot press formed. The structure of the component obtained in this way consists of 5 - 50% by volume of retained austenite and the remainder of martensite, tempered martensite, bainite or ferrite.

Aus der CN 102 127 675 B ist zudem ein Bauteil bekannt, dass aus einem Stahlblech aus einem Stahl warmgeformt ist, der, in Gew.-%, als Pflichtbestandteile 0,02 - 0,45 % C, 3,50 - 9,0 % Mn, höchstens 0,020 % P, höchstens 0,020 % S, Rest Fe und unvermeidbare Verunreinigungen enthält. Optional kann der Stahl zusätzlich 0,1 - 3,0 % Ni, 0,2 - 3,0 % Cr, 0,1 - 0,8 % Mo, 0,3 - 2.3 % Si, 0,5 - 2,0 % Cu, 0,0005 - 0,0050 % B, 0,02 - 0,30 % Nb, 0,002 - 0,250 % N, 0,05 - 0,25 % Ti, 0,02 - 0,25 % V, 0,015 - 3,0 % Al, 0,002 - 0,005 % REM und 0,005 - 0,03 % Ca enthalten. Das dazu vorgesehene Herstellungsverfahren umfasst die folgenden Schritte: Erwärmung des Stahlblechs, Transfer des Stahlblechs, Vorkühlung des Stahlblechs, Umformung des Teils und Abkühlung des Teils.From the CN 102 127 675 B a component is also known that is hot-formed from a steel sheet made of a steel which, in % by weight, contains 0.02 - 0.45% C, 3.50 - 9.0% Mn, at most 0.020% P , at most 0.020% S, the rest Fe and unavoidable impurities. Optionally, the steel can additionally contain 0.1 - 3.0% Ni, 0.2 - 3.0% Cr, 0.1 - 0.8% Mo, 0.3 - 2.3% Si, 0.5 - 2.0 % Cu, 0.0005 - 0.0050% B, 0.02 - 0.30% Nb, 0.002 - 0.250% N, 0.05 - 0.25% Ti, 0.02 - 0.25% V, 0.015 - 3.0% Al, 0.002 - 0.005% REM and 0.005 - 0.03% Ca included. The manufacturing process envisaged for this includes the following steps: heating of the steel sheet, transfer of the steel sheet, pre-cooling of the steel sheet, forming of the part and cooling of the part.

Eine weitere Möglichkeit höchstfeste Bauteile herzustellen, ist das Warmpresshärten konventioneller Warmumformstähle. Aus diesen Stählen bestehende Platinen werden für das Warmpressformen auf so hohe Temperaturen erwärmt, dass ihr Gefüge vollaustenitisch ist. Nach einem Abschrecken weisen die erhaltenen Bauteile dann ein martensitisches Gefüge auf, das allerdings ein relativ geringes Restverformungsvermögen besitzt. Problematisch ist dabei, dass wegen der hohen Austenitisierungstemperaturen ein kathodischer Schutz der Bleche durch eine metallische Korrosionsschutzbeschichtung nicht möglich ist.Another possibility to produce high-strength components is hot press hardening of conventional hot-forming steels. For hot press forming, blanks made of these steels are heated to such high temperatures that their structure is fully austenitic. After quenching, the components obtained then have a martensitic structure on, which, however, has a relatively low residual deformation capacity. The problem here is that because of the high austenitization temperatures, cathodic protection of the sheets by means of a metallic anti-corrosion coating is not possible.

Vor dem Hintergrund des voranstehend erläuterten Standes der Technik bestand die Aufgabe darin, ein Blechbauteil zu schaffen, welches im Vergleich zu konventionell hergestellten Blechbauteilen eine Energieeinsparung durch niedrigere Umformtemperaturen ermöglicht, eine erhöhte Restdehnung bei hohen Festigkeiten zulässt und bei denen ein möglichst hohes Potenzial für einen kathodischen Korrosionsschutz gewahrt ist.Against the background of the prior art explained above, the task was to create a sheet metal component which, compared to conventionally produced sheet metal components, enables energy savings through lower forming temperatures, allows increased residual elongation at high strengths and which has the highest possible potential for a cathodic protection against corrosion is maintained.

Darüber hinaus sollte ein Verfahren zur Herstellung eines solchen Blechbauteils angegeben werden.In addition, a method for producing such a sheet metal component should be specified.

Ein diese Aufgabe lösendes Blechbauteil weist erfindungsgemäß mindestens die in Anspruch 1 angegebenen Merkmale auf.According to the invention, a sheet metal component that achieves this object has at least the features specified in claim 1 .

Ein die voranstehend genannte Aufgabe erfindungsgemäß lösendes Verfahren ist in Anspruch 8 angegeben.A method that achieves the above-mentioned object according to the invention is specified in claim 8.

Vorteilhafte Ausgestaltungen der Erfindung sind in den abhängigen Ansprüchen angegeben und werden nachfolgend wie der allgemeine Erfindungsgedanke im Einzelnen erläutert.Advantageous refinements of the invention are specified in the dependent claims and are explained in detail below, along with the general idea of the invention.

Ein erfindungsgemäßes Blechbauteil ist demgemäß durch Warmumformen eines Stahlflachprodukts hergestellt, das aus (in Gew.-%) C: 0,02 - 0,5 %, Si: 0,05 - 1 %, Mn: 4 - 12 %, Cr: 0,1 - 4 %, AI: bis zu 3,5 %, N: bis zu 0,05 %, P: bis zu 0,05 %, S: bis zu 0,01 %, in Summe > 0,04 % bis 2 % Cu und/oder Ni, in Summe bis zu 0,5 % an Ti, Nb oder V, Seltene Erden: bis zu 0,1 % und als Rest aus Fe und unvermeidbaren Verunreinigungen besteht.A sheet metal component according to the invention is accordingly produced by hot forming of a steel flat product consisting of (in % by weight) C: 0.02-0.5%, Si: 0.05-1%, Mn: 4-12%, Cr: 0 .1 - 4%, AI: up to 3.5%, N: up to 0.05%, P: up to 0.05%, S: up to 0.01%, in total > 0.04% up to 2% Cu and/or Ni, up to 0.5% in total of Ti, Nb or V, rare earths: up to 0.1% and the remainder consists of Fe and unavoidable impurities.

Dabei erfüllen der Gehalt %C an C und der Gehalt %Cr an Cr des Stahls des Stahlflachprodukts folgende Bedingung: (10x%C)+%Cr < 5,5 Gew.-%.The content %C of C and the content %Cr of Cr in the steel of the steel flat product fulfill the following condition: (10x%C)+%Cr<5.5% by weight.

Gleichzeitig weist das erfindungsgemäße Stahlflachprodukt nach der Warmumformung zu dem Blechbauteil einen nach VDA 238-100: 2010-12 bestimmten Biegewinkel von mehr als 60° auf.At the same time, the flat steel product according to the invention has a bending angle of more than 60°, determined according to VDA 238-100: 2010-12, after hot forming to form the sheet metal component.

Das Gefüge des warmumgeformten erfindungsgemäßen Blechbauteils besteht zu 5 - 50 Vol.-% aus Austenit und als Rest aus Martensit, angelassenem Martensit oder Ferrit, wobei der Ferrit-Anteil auch "0" sein kann. Dabei liegen die mittleren Korndurchmesser der Körner des Gefüges unter 5 µm, vorzugsweise unter 2 µm.The microstructure of the hot-formed sheet metal component according to the invention consists of 5-50% by volume of austenite and the remainder of martensite, tempered martensite or ferrite, it also being possible for the ferrite proportion to be “0”. The average grain diameter of the grains of the structure is less than 5 μm, preferably less than 2 μm.

Das erfindungsgemäß zu dem Blechbauteil geformte Stahlflachprodukt besteht aus einem Stahl, der der Klasse der so genannten "Mittelmanganstähle" zuzuordnen ist, welche üblicherweise Mn-Gehalte von 4 - 12 Gew.-%, insbesondere 4 - 9 Gew.-%, aufweisen. Durch Mangan "Mn" wird die Austenitisierungstemperatur gesenkt und die Umwandlung von Ferrit, Perlit und Bainit verzögert. Damit kann auch die Haltetemperatur im Ofen vor der Warmumformung verringert werden. Die erhaltenen Vorteile werden durch Halten und Warmumformung im Zweiphasengebiet weiter verstärkt. Bei der anschließenden Abkühlung bleibt ein hoher Austenitanteil erhalten. Dieser führt zu einer sehr hohen Restbruchdehnung sowie einem hohen möglichen Biegewinkel bis zu ersten Rissen und damit einer höheren Energieaufnahme im Crashfall. Die Mn-Gehalte eines erfindungsgemäß verarbeiteten Stahlflachprodukts sind dabei mit 4 - 12 Gew.-% so eingestellt, dass die geforderten Mindestfestigkeiten eines erfindungsgemäßen Stahls sicher erreicht werden und gleichzeitig ein hoher Restaustenitanteil erhalten bleibt, der optimale Dehnungseigenschaften gewährleistet.The flat steel product formed into the sheet metal component according to the invention consists of a steel which belongs to the class of so-called "middle manganese steels" which usually have Mn contents of 4-12% by weight, in particular 4-9% by weight. Manganese "Mn" lowers the austenitization temperature and delays the transformation of ferrite, pearlite and bainite. This also allows the holding temperature in the furnace before hot forming to be reduced. The advantages obtained are further enhanced by holding and hot working in the two-phase region. During the subsequent cooling, a high proportion of austenite is retained. This leads to a very high residual elongation at break and a high possible bending angle up to the first cracks and thus higher energy absorption in the event of a crash. The Mn content of a steel flat product processed according to the invention is set at 4-12 wt.

Kohlenstoff "C" bestimmt beim Stahl eines erfindungsgemäß zu dem Bauteil geformten Stahlflachprodukts zum einen die Festigkeit von Martensit und zum anderen die Menge und die Stabilität des Restaustenits. Bei zu hohen Kohlenstoffgehalten wird die Schweißbarkeit und Zähigkeit des Stahls, z. B. durch Bildung von Cr-Karbiden, negativ beeinflusst. Deshalb beträgt der Kohlenstoffgehalt von Mn-Stählen der erfindungsgemäß ausgewählten Art höchstens 0,5 Gew.-%, wobei geringere C-Gehalte von weniger als 0,5 Gew.-%, insbesondere von bis zu 0,3 Gew.-%, sich als besonders günstig erweisen. Bei zu geringem Kohlenstoffgehalt wird jedoch die Menge und Stabilität des verbleibenden Restaustenits beeinträchtigt. Deshalb beträgt der C-Gehalt eines erfindungsgemäßen Stahls mindestens 0,02 Gew.-%.In the case of the steel of a flat steel product formed into the component according to the invention, carbon “C” determines the strength of martensite on the one hand and others the amount and stability of the retained austenite. If the carbon content is too high, the weldability and toughness of the steel, e.g. B. negatively affected by the formation of Cr carbides. Therefore, the carbon content of Mn steels of the type selected according to the invention is at most 0.5% by weight, with lower C contents of less than 0.5% by weight, in particular of up to 0.3% by weight prove particularly favorable. However, if the carbon content is too low, the amount and stability of the retained austenite will be affected. The carbon content of a steel according to the invention is therefore at least 0.02% by weight.

Aluminium "AI" und Silizium "Si" sind starke Ferritbildner. Beide Elemente wirken dem Einfluss der Austenitbildner C und Mn entgegen. Die wesentliche Aufgabe der Elemente Si und Al besteht im Stahl eines erfindungsgemäß zu dem Blechbauteil warmgeformten Stahlflachprodukts darin, die Karbidausscheidung zu unterdrücken und damit die Stabilität des Restaustenits zu fördern. Gleichzeitig führen Si und Al zu einer Mischkristallhärtung und reduzieren das spezifische Gewicht des Stahls. Bei zu geringem Si- und Al-Gehalt kann die Karbidausscheidung jedoch möglicherweise nicht effektiv unterdrückt werden. Bei zu hohen Gehalten an Si und Al wird dagegen die Verarbeitung sowohl bei einer Erzeugung über ein Strangguss- als auch bei einer Erzeugung über ein Bandgussverfahren erschwert. Deshalb sieht die Erfindung vor, den Si-Gehalt auf max. 1 Gew.-% zu beschränken, wobei die positiven Effekte der Anwesenheit von Si dann bereits effektiv genutzt werden können, wenn der Si-Gehalt des Stahls des Stahlflachprodukts, aus dem das erfindungsgemäße Bauteil warmgeformt ist, mindestens 0,05 Gew.-% beträgt.Aluminum "AI" and silicon "Si" are strong ferrite formers. Both elements counteract the influence of the austenite formers C and Mn. The main task of the elements Si and Al in the steel of a steel flat product hot-formed to form the sheet metal component according to the invention is to suppress carbide precipitation and thus promote the stability of the retained austenite. At the same time, Si and Al lead to solid solution hardening and reduce the specific weight of the steel. However, if the Si and Al content is too low, carbide precipitation may not be effectively suppressed. On the other hand, if the Si and Al contents are too high, processing is made more difficult both in the case of production using a continuous casting method and in the case of production using a strip casting method. The invention therefore provides for the Si content to be limited to a maximum of 1% by weight, with the positive effects of the presence of Si already being able to be used effectively if the Si content of the steel of the flat steel product from which the inventive component is thermoformed is at least 0.05% by weight.

Insbesondere höhere Al-Gehalte des Stahls des erfindungsgemäß für die Warmformung des erfindungsgemäßen Bauteils verwendeten Stahlflachprodukts verringern die Dichte des Stahls signifikant, führen jedoch zu erhöhten Ferrit-Anteilen im Gefüge und damit einhergehend zu einer Abnahme der Festigkeit. Bei zu hohen Al-Gehalten nimmt zudem die Schweißeignung ab, da sich beim Schweißvorgang stabile Schweißschlacke bildet und der elektrische Schweißwiderstand erhöht wird. Gleichzeitig wird die Ac3-Temperatur durch hohe Al-Gehalte so weit erhöht, dass eine niedrige Warmumformtemperatur, wie sie die Erfindung anstrebt, nicht mehr erzielbar ist.In particular, higher Al contents in the steel of the flat steel product used according to the invention for hot-forming the component according to the invention significantly reduce the density of the steel, but lead to increased ferrite proportions in the structure and, associated therewith, to a decrease in strength. If the Al content is too high, the suitability for welding also decreases, since stable welding slag forms during the welding process and the electrical welding resistance is increased. At the same time, the Ac3 temperature is increased by high Al contents to such an extent that a low hot forming temperature, as is the aim of the invention, can no longer be achieved.

Durch die Anwesenheit von Chrom "Cr" in Gehalten von 0,1 - 4 Gew.-% wird in einem erfindungsgemäßen Stahl die Gefahr der Entstehung von Spannungsrisskorrosion gezielt vermindert. Cr und Al behindern eine wasserstoffinduzierte Rissbildung. Zudem trägt Cr zur Festigkeitssteigerung bei. Des Weiteren senkt Cr auch die Ms-Temperatur (Martensitstarttemperatur) und unterstützt damit die Restaustenit-Stabilisierung. Ab einem Gehalt von 0,1 Gew.-% Cr, insbesondere aber ab Cr-Gehalten von mindestens 2,2 Gew.-%, sind diese positiven Effekte zu beobachten. Ab Cr-Gehalten von 2,2 Gew.-% wird im unbeschichteten Zustand zudem die Zunderbeständigkeit verbessert. Bei Stahlflachprodukten, die mit einer metallischen Korrosionsschutzbeschichtung versehen sind, kann eine positive Wirkung auf die Schicht ausgenutzt werden, wie beispielsweise die Wirkung als Diffusionssperre für das Eindiffundieren von Eisen in die Schutzbeschichtung. Der Cr-Gehalt des Stahls eines zu dem erfindungsgemäßen Bauteil warmgeformten Stahlflachprodukts ist auf max. 4 Gew.-% beschränkt, weil bei höheren Gehalten Cr-Karbide entstehen könnten, die die Duktilität des Stahls negativ beeinflussen würden.The presence of chromium “Cr” in amounts of 0.1-4% by weight specifically reduces the risk of stress corrosion cracking in a steel according to the invention. Cr and Al hinder hydrogen-induced cracking. In addition, Cr contributes to the increase in strength. Furthermore, Cr also lowers the Ms temperature (martensite start temperature) and thus supports the stabilization of retained austenite. These positive effects can be observed from a content of 0.1% by weight Cr, but in particular from Cr contents of at least 2.2% by weight. From a Cr content of 2.2% by weight, the resistance to scaling is also improved in the uncoated state. In the case of steel flat products that are provided with a metallic anti-corrosion coating, a positive effect on the layer can be exploited, such as the effect as a diffusion barrier for iron diffusing into the protective coating. The Cr content of the steel of a flat steel product hot-formed to form the component according to the invention is limited to a maximum of 4% by weight, because higher contents could produce Cr carbides which would adversely affect the ductility of the steel.

Ebenfalls im Hinblick auf die Vermeidung der Entstehung von höheren Cr-Karbidmengen schreibt die Erfindung vor, dass der Gehalt "%C" an Kohlenstoff "C" und der Gehalt "%Cr" an Chrom "Cr" des Stahls eines erfindungsgemäß zu dem Bauteil geformten Stahlflachprodukts die Bedingung (10x%C) + %Cr < 5,5 Gew.-% einhalten muss.Also with a view to avoiding the formation of higher amounts of Cr carbide, the invention stipulates that the carbon “C” content “%C” and the chromium “Cr” content “%Cr” of the steel of a component formed according to the invention must be taken into account Steel flat product must comply with the condition (10x%C) + %Cr < 5.5% by weight.

Durch Zugabe von Kupfer "Cu" oder Nickel "Ni" zum Stahl des erfindungsgemäß warmgeformten Stahlflachprodukts lässt sich der Widerstand gegen verschiedene Korrosionsmechanismen verbessern. Die positive Wirkung von Cu und Ni lässt sich dabei dadurch besonders sicher nutzen, dass diese Elemente in Gehalten zugegeben werden, in denen sie technisch wirksam werden. Dies ist zu erwarten, wenn im Stahl des erfindungsgemäßen Bauteils die Summe der Gehalte an Cu und Ni mindestens > 0,04 Gew.-% beträgt. Dagegen werden negative Auswirkungen, wie höhere Kosten und Heissrisssprödigkeit bei hohen Cu-Gehalten der einzelnen oder kombinierten Anwesenheit von Cu oder Ni in erfindungsgemäßen Stählen dadurch sicher vermieden, dass die Summe der Gehalte an Cu und Ni auf maximal 2 Gew.-% beschränkt ist.By adding copper "Cu" or nickel "Ni" to the steel of the hot worked steel flat product according to the present invention, resistance to various corrosion mechanisms can be improved. The positive effect of Cu and Ni can be used particularly safely by adding these elements in concentrations in which they become technically effective. This is to be expected if the sum of the contents of Cu and Ni in the steel of the component according to the invention is at least >0.04% by weight. On the other hand, negative effects such as higher costs and hot cracking brittleness with high Cu contents of the individual or combined presence of Cu or Ni in steels according to the invention are reliably avoided by limiting the sum of the Cu and Ni contents to a maximum of 2% by weight.

Die Mikrolegierungselemente Ti, Nb und V können im Stahl des Stahlflachprodukts, aus dem das erfindungsgemäße Bauteil geformt ist, in Gehalten von in Summe bis zu 0,5 Gew.-% anwesend sein. Diese Mikrolegierungselemente tragen zur Kornfeinung und Festigkeitssteigerung bei. In Summe oberhalb von 0,5 Gew.-% liegende Gehalte an Ti, Nb und V führen jedoch zu keiner Steigerung dieses Effekts, wogegen die positiven Wirkungen von Ti, Nb und V im Stahl des erfindungsgemäßen Bauteils sicher genutzt werden können, wenn ihr Gehalt in Summe mindestens 0,05 Gew.-% beträgt.The micro-alloying elements Ti, Nb and V can be present in the steel of the flat steel product from which the component according to the invention is formed in amounts totaling up to 0.5% by weight. These micro-alloying elements contribute to grain refinement and increased strength. However, contents of Ti, Nb and V above 0.5% by weight do not increase this effect, whereas the positive effects of Ti, Nb and V in the steel of the component according to the invention can be safely used if their in total is at least 0.05% by weight.

Durch die Zugabe von Stickstoff "N" in Gehalten von bis zu 0,05 Gew.-%, kann das austenitische Gefüge zusätzlich stabilisiert werden. Bei zu hohem N-Gehalt wird die Prozessierbarkeit beim Stranggiessen verschlechtert und eine versprödende Menge an Nitriden entsteht.The austenitic structure can be additionally stabilized by adding nitrogen "N" in amounts of up to 0.05% by weight. If the N content is too high, processability during continuous casting is impaired and an brittle amount of nitrides is formed.

Die Gehalte an Phosphor "P" des Stahls eines erfindungsgemäßen Bauteils sind auf maximal 0,05 Gew.-% beschränkt, um negative Einflüsse dieses Elements sicher auszuschließen.The content of phosphorus "P" in the steel of a component according to the invention is limited to a maximum of 0.05% by weight in order to reliably rule out negative influences from this element.

Aus demselben Grund ist der Gehalt an Schwefel "S" eines erfindungsgemäßen Stahls auf max. 0,01 Gew-% beschränkt.For the same reason, the sulfur "S" content of a steel according to the invention is limited to a maximum of 0.01% by weight.

Seltene Erden "REM" können im Stahl des erfindungsgemäßen Bauteils durch Bildung von Oxiden zur Kornfeinung beitragen und verbessern über die Textur die Isotropie der mechanisch-technologischen Eigenschaften. Die beiden Seltenen Erden Cer und Lanthan sind chemisch nahezu identisch und kommen daher in der Natur immer vergemeinschaftet vor. Durch ihre chemische Ähnlichkeit sind sie sehr schwer und daher aufwendig zu trennen. Dabei haben sie die gleiche Wirkung. Die Seltenen Erden kann man für die Nutzung im Stahl frei substituieren. Bei Gehalten über 0,1 Gew.-% ergibt sich allerdings unter anderem beim großtechnischen Vergießen des Stahls die Gefahr des so genannten "Cloggings", d.h. des Verstopfens der Gießkokille durch lokal erstarrende Schmelze. Die Vorteile der Anwesenheit der REM können dennoch dadurch sicher genutzt werden, dass der Gehalt des Stahls eines erfindungsgemäßen Bauteils mindestens 0,0005 Gew.-% beträgt.Rare earths "REM" can contribute to grain refinement in the steel of the component according to the invention through the formation of oxides and improve the isotropy of the mechanical-technological properties via the texture. The two rare earths cerium and lanthanum are chemically almost identical and therefore come in the Nature always communitized before. Due to their chemical similarity, they are very difficult and therefore difficult to separate. They have the same effect. Rare earths can be freely substituted for use in steel. With contents above 0.1% by weight, however, there is, among other things, the risk of so-called "clogging" in industrial-scale casting of the steel, ie the clogging of the casting mold by locally solidifying melt. The advantages of the presence of the REM can nevertheless be safely used in that the steel content of a component according to the invention is at least 0.0005% by weight.

Der gemäß VDA 238-100 : 2010-12 bestimmte Biegewinkel ist ein Maß für das Faltverhalten des Werkstoffs im Crashfall und somit ein Indikator für die Duktilität, die ein warmumgeformtes Bauteil besitzt. Erfindungsgemäße Bauteile zeichnen sich durch einen hohen Biegewinkel von mindestens 60°, insbesondere mindestens 80° oder mehr als 80°, wie beispielsweise mindestens 85°, nach der Warmumformung aus. Dabei spielt das gleichmäßige, sehr feine Gefüge eine fördernde Rolle. Ein hoher Austenitgehalt, wie er vorliegt, wenn die Warmumformung bei Temperaturen erfolgt, die im Zweiphasenmischgebiet des Stahls (oder tiefer) liegen, aus dem das Stahlflachprodukt besteht, aus welchem das Bauteil geformt ist, hat vorteilhafte Auswirkungen.The bending angle determined in accordance with VDA 238-100: 2010-12 is a measure of the folding behavior of the material in the event of a crash and is therefore an indicator of the ductility that a hot-formed component has. Components according to the invention are characterized by a high bending angle of at least 60°, in particular at least 80° or more than 80°, such as at least 85°, after hot forming. The uniform, very fine structure plays a supporting role here. High austenite content, such as that present when hot working occurs at temperatures in the two-phase mixing region (or lower) of the steel making up the flat steel product from which the component is formed, has beneficial effects.

Erfindungsgemäße Bauteile zeichnen sich dadurch aus, dass sie ein Gefüge aufweisen, welches zu mindestens 5 Vol.-% aus Austenit besteht, wobei der Austenit-Anteil des Gefüges bis zu 50 Vol.-% betragen kann. Das restliche Gefüge des Bauteils besteht aus festigkeitssteigernden Anteilen an Martensit und angelassenem Martensit. Außerdem kann Ferrit enthalten sein. Die Menge sonstiger technisch unvermeidbar vorhandener Gefügebestandteile, ist so gering, dass sie hinsichtlich der Eigenschaften des erfindungsgemäßen Bauteils unwirksam sind. Das erfindungsgemäße Verfahren zur Herstellung eines gemäß den voranstehenden Ansprüchen beschaffenen Blechbauteiis umfasst folgende Arbeitsschritte:
a) Bereitstellen eines Stahlflachprodukts aus einem Stahl, der in Gew.-% aus C: 0,02 - 0,5 %, Si: 0,05 - 1 %, Mn: 4 - 12 %, Cr: 0,1 - 4%, Al: bis zu 3,5 %, N: bis zu 0,05 %, P: bis zu 0,05 %, S: bis zu 0,01 %, in Summe 0,04 % bis zu 2 % Cu und/oder Ni, in Summe bis zu 0,5 % an Ti, Nb oder V, REM: bis zu 0,1 % und als Rest aus Fe und unvermeidbaren Verunreinigungen besteht, wobei der Gehalt %C an C und der Gehalt %Cr an Cr folgende Bedingung erfüllt: 10 × %C + %Cr < 5 ,5% ,

Figure imgb0001

b) Durcherwärmen des Stahlflachprodukts auf eine Erwärmungstemperatur, die mindestens 200 °C und höchstens 800 °C beträgt;
c) Warmumformen des auf die Erwärmungstemperatur erwärmten Stahlflachprodukts zu dem Bauteil.Components according to the invention are distinguished by the fact that they have a structure which consists of at least 5% by volume of austenite, with the proportion of austenite in the structure being able to be up to 50% by volume. The remaining structure of the component consists of strength-increasing proportions of martensite and tempered martensite. Ferrite may also be included. The amount of other structural components that are technically unavoidable is so small that they are ineffective with regard to the properties of the component according to the invention. The method according to the invention for producing a sheet metal component according to the preceding claims comprises the following work steps:
a) Providing a flat steel product made from a steel which, in % by weight, consists of C: 0.02 - 0.5%, Si: 0.05 - 1%, Mn: 4-12%, Cr: 0.1 - 4%, Al: up to 3.5%, N: up to 0.05%, P: up to 0.05%, S: up to 0.01%, a total of 0.04% up to 2% Cu and/or Ni, a total of up to 0.5% Ti, Nb or V, SEM: up to 0.1% and the balance being Fe and unavoidable impurities, where the %C content of C and the %Cr content of Cr satisfies the following condition: 10 × %C + %Cr < 5 .5% ,
Figure imgb0001

b) through heating the steel flat product to a heating temperature which is at least 200 °C and at most 800 °C;
c) Hot forming of the flat steel product, which has been heated to the heating temperature, to form the component.

Die Abkühlgeschwindigkeit, mit der das erhaltene warmumgeformte Bauteil abgekühlt wird, unterliegt dabei keinen Einschränkungen.The cooling rate at which the hot-formed component obtained is cooled is not subject to any restrictions.

Die grundsätzlichen Möglichkeiten der Erzeugung von Stahlflachprodukten, die für die erfindungsgemäßen Zwecke geeignet und im Arbeitsschritt a) des erfindungsgemäßen Verfahrens bereitgestellt werden, sind in der EP 2 383 353 A2 beschrieben. Im dort wiedergegebenen Diagramm und den zugehörigen Abschnitten [0031] bis [0040] der EP 2 383 353 A2 sind die verschiedenen in der Praxis zur Verfügung stehenden Wege zur Erzeugung von Stahlflachprodukten dargestellt, die zur Erzeugung von erfindungsgemäßen Bauteilen geeignet sind.The basic possibilities of producing steel flat products that are suitable for the purposes of the invention and are provided in step a) of the method of the invention are in EP 2 383 353 A2 described. In the diagram reproduced there and the associated sections [0031] to [0040] of EP 2 383 353 A2 are the different in methods available in practice for producing flat steel products which are suitable for producing components according to the invention.

Zusätzlich besteht die Möglichkeit, das gewalzte Band direkt, d.h. ohne vorherigen Glühschritt, dem Prozess der Warmumformung zuzuführen. Typische Schutzschichten, die auf erfindungsgemäßen Bauteilen vorhanden sind und mit denen die Stahlflachprodukte, aus denen erfindungsgemäße Bauteile geformt werden, belegt sein können, sind durch Schmelztauchbeschichten aufgetragene Schutzüberzüge auf Zinkbasis, wie z.B. Zn-Überzüge ("Z"), Zink-Eisen-Überzüge ("ZF"), Zink-Magnesium-Aluminium-Überzüge ("ZM"), Zink-Aluminium-Überzüge ("ZA"). Des Weiteren können Schutzüberzüge auf Aluminium-Basis zum Einsatz kommen, wie Aluminium-Zink-Überzüge ("AZ"), Aluminium-Silizium-Überzüge ("AS"). Ebenso können elektrolytisch aufgetragene Schutzüberzüge auf Zn-Basis, wie z.B. Reinzink "ZE" -Überzüge oder Zink-Nickel-Überzüge ("ZN") vorgesehen sein. Möglich sind aber auch an sich bekannte metallische Korrosionsschutzüberzüge, die durch abscheidende Verfahren, wie PVD, CVD oder Dampfspritzen, aufgebracht werden.There is also the option of feeding the rolled strip directly, i.e. without a previous annealing step, to the hot forming process. Typical protective coatings present on components of the present invention, and which may be coated on the flat steel products from which components of the present invention are formed, are hot dip zinc-based protective coatings such as Zn ("Z") coatings, zinc-iron coatings ("ZF"), Zinc-Magnesium-Aluminum Coatings ("ZM"), Zinc-Aluminum Coatings ("ZA"). Furthermore, aluminum-based protective coatings can be used, such as aluminum-zinc coatings ("AZ"), aluminum-silicon coatings ("AS"). Electrolytically applied Zn-based protective coatings such as pure zinc "ZE" coatings or zinc-nickel ("ZN") coatings can also be provided. However, metallic anti-corrosion coatings which are known per se and are applied by deposition processes such as PVD, CVD or vapor spraying are also possible.

Ausgehend hiervon zeigt die Erfindung einen Weg auf, wie durch ressourcenschonendes Warmformen ein Bauteil erzeugt werden kann, dass nach seiner Warmformgebung optimale mechanische Eigenschaften aufweist und aufgrund dieser Eigenschaften und seiner sonstigen Gebrauchseigenschaften auch hohen Anforderungen bei Crashbelastung des Bauteils gewachsen ist.Based on this, the invention shows a way in which resource-saving hot forming can be used to produce a component that has optimal mechanical properties after hot forming and, due to these properties and its other functional properties, can also meet high requirements in the event of a crash load on the component.

Der hohe Mangangehalt erfindungsgemäß verarbeiteter Stahlflachprodukte ermöglicht niedrigere Warmumformtemperaturen als bei üblichen Warmumformstählen. Damit erlaubt es die Erfindung, Energie und Kosten einzusparen.The high manganese content of flat steel products processed according to the invention enables lower hot forming temperatures than with conventional hot forming steels. The invention thus makes it possible to save energy and costs.

So sollten die Erwärmungstemperaturen zur Warmumformung nicht mehr als 60 °C oberhalb der Ac3-Temperatur des jeweiligen Stahls des Stahlflachprodukts liegen, um die gewünschten positiven Eigenschaften zu erhalten.For example, the heating temperatures for hot forming should not be more than 60° C. above the Ac3 temperature of the respective steel of the steel flat product in order to obtain the desired positive properties.

Besonders niedrig können die Erwärmungstemperaturen sein, wenn die Umformung im Zweiphasengebiet oder bei darunter liegenden Temperaturen erfolgen soll. In diesem Fall liegt der Restaustenitanteil im erhaltenen Bauteil über 20 Vol.-% und die Bruchdehnung A80 über 15 %. Die erfindungsgemäße Warmformgebung findet hier bei Erwärmungstemperaturen statt, die typischerweise oberhalb der Ac1-Temperatur und unterhalb der Ac3-Temperatur des jeweiligen Stahls des Stahlflachprodukts liegen, wobei sich im Fall einer Verformung im Zweiphasengebiet Erwärmungstemperaturen als besonders günstig erweisen, die um mindestens 10 °C höher sind als die Ac1-Temperatur und um mindestens 50 °C niedriger sind als die Ac3-Temperatur des jeweiligen Stahls des Stahlflachprodukts.The heating temperatures can be particularly low if the deformation is to take place in the two-phase region or at temperatures below that. In this case, the proportion of residual austenite in the resulting component is over 20% by volume and the elongation at break A80 is over 15%. The hot forming according to the invention takes place here at heating temperatures that are typically above the Ac1 temperature and below the Ac3 temperature of the respective steel of the steel flat product, with heating temperatures that are at least 10 °C higher proving to be particularly favorable in the case of deformation in the two-phase region are lower than the Ac1 temperature and at least 50 °C lower than the Ac3 temperature of the respective steel of the steel flat product.

Soll bei Temperaturen umgeformt werden, die unterhalb des Temperaturbereichs liegen, in denen ein zweiphasiges Gefüge im Stahlflachprodukt vorliegt, so kann dazu die Erwärmungstemperatur unterhalb der Ac1-Temperatur des jeweiligen Stahls liegen, aus dem das erfindungsgemäß warmumgeformte Stahlflachprodukt jeweils besteht.If forming is to take place at temperatures below the temperature range in which a two-phase structure is present in the flat steel product, the heating temperature can be below the Ac1 temperature of the respective steel from which the flat steel product hot-formed according to the invention consists.

Während bei Glühungen mit oberhalb der Ac1-Temperatur liegenden Erwärmungstemperaturen der Austenitanteil vor der Warmumformung nicht von Belang ist, muss der gewünschte Anteil bei Umformung unter Ac1 in einem vorangehenden Glühschritt eingestellt werden. Die Erwärmungstemperatur bei dieser zusätzlichen Glühung sollte dabei mindestens so hoch sein, dass die Umformkräfte sich von denen der Kaltumformung positiv abheben. Dementsprechend sollte die Erwärmungstemperatur in diesem Fall so eingestellt werden, dass die Umformkräfte der Warmumformung maximal 85 % der Umformkräfte bei Raumtemperatur betragen. Dies ist bei Erwärmungstemperaturen von über 200 °C, insbesondere von über 400 °C, gesichert.While the proportion of austenite before hot forming is not important for anneals with heating temperatures above the Ac1 temperature, the desired proportion for forming below Ac1 must be set in a preceding annealing step. The heating temperature during this additional annealing should be at least so high that the forming forces stand out positively from those of cold forming. Accordingly, in this case the heating temperature should be set in such a way that the forming forces during hot forming amount to a maximum of 85% of the forming forces at room temperature. This is at Heating temperatures of over 200 °C, in particular over 400 °C, secured.

Durch die erfindungsgemäße Vorgehensweise wird ein Gefüge erhalten, das durch optimierte Austenitanteile gekennzeichnet ist und in Folge dessen sehr gute mechanische Eigenschaften, insbesondere eine hohe Restdehnung und eine hohe Energieaufnahme im Crashlastfall, besitzt. Die in diesem Bereich liegenden, vergleichbar niedrigen Erwärmungstemperaturen, bei denen die Warmformgebung des erfindungsgemäßen Bauteils stattfindet, erweisen sich auch als besonders vorteilhaft, wenn das erfindungsgemäß verarbeitete Stahlflachprodukt einen kathodischen Korrosionsschutz haben soll.The procedure according to the invention results in a structure which is characterized by optimized proportions of austenite and, as a result, has very good mechanical properties, in particular high residual elongation and high energy absorption in the event of a crash load. The comparatively low heating temperatures in this range, at which the hot forming of the component according to the invention takes place, also prove to be particularly advantageous if the flat steel product processed according to the invention is to have cathodic corrosion protection.

Die Glühzeiten, die für die Durcherwärmung im Arbeitsschritt b) typischerweise benötigt werden, betragen üblicherweise bis zu 60 min, wobei sich in der Praxis Glühzeiten von bis 20 min, insbesondere bis zu 10 min, als besonders wirtschaftlich erwiesen haben. Die Durcherwärmung kann in konventionellen Kammeröfen oder Rollenöfen durchgeführt werden, in denen die warmzuverformenden Stahlflachprodukte im Durchlauf oder batchweise auf die Erwärmungstemperatur gebracht werden. Da bei erfindungsgemäßen Zusammensetzungen des zu dem Bauteil verformten Stahlflachprodukts die Eigenschaften nahezu unabhängig von Aufheiz- und Abkühlgeschwindigkeit gebildet werden, kann es sich jedoch auch als günstig erweisen, wenn die Erwärmung durch konduktive oder induktive Erwärmung vorgenommen wird, oder auch beispielsweise mittels Festkörperkontakt oder im Wirbelbett. Durch die zur konventionellen Ofenerwärmung alternativen Verfahren können im Vergleich zur reinen Strahlungserwärmung im konventionellen Ofen kürzere Glühzeiten erzielt werden. Gleichzeitig erlauben die alternativen Verfahren genauer gesteuerte Erwärmungszyklen, da bei ihnen der Verlauf der Erwärmung genauen Vorgaben folgen kann. Der weitere Vorteil des Einsatzes der alternativen Erwärmungsverfahren besteht darin, dass auf Produktionsänderungen, wie sie gerade typisch für kleine Stückzahlfertigungen mit unterschiedlichen Blechdicken sind, schnell reagiert werden kann.The annealing times typically required for thorough heating in step b) are usually up to 60 minutes, with annealing times of up to 20 minutes, in particular up to 10 minutes, having proven to be particularly economical in practice. Thorough heating can be carried out in conventional chamber furnaces or roller furnaces, in which the flat steel products to be hot-formed are brought to the heating temperature in a continuous flow or in batches. Since the properties of the flat steel product formed into the component are formed almost independently of the heating and cooling rate in compositions according to the invention, it can also prove advantageous if the heating is carried out by conductive or inductive heating, or also, for example, by means of solid-body contact or in a fluidized bed . The alternative methods to conventional furnace heating mean that shorter annealing times can be achieved in comparison to pure radiation heating in a conventional furnace. At the same time, the alternative methods allow for more precisely controlled heating cycles since the course of the heating can follow precise specifications. Another advantage of using the alternative heating process is that it is possible to react quickly to production changes, which are typical for small batch production with different sheet metal thicknesses.

Anpassungen der Erwärmungsparameter an die jeweils geänderten Anforderungen können entsprechend schnell vorgenommen werden
Die Warmformgebung (Arbeitsschritt c)) des auf die jeweilige Erwärmungstemperatur erwärmten Stahlflachprodukts zu dem erfindungsgemäßen Bauteil kann in hierzu im Stand der Technik verfügbaren, konventionellen Warmformgebungswerkzeugen vorgenommen werden. Dabei erfolgt die Warmformgebung in möglichst unmittelbarem Anschluss an die Durcherwärmung (Arbeitsschritt b)), so dass die Temperatur, mit der das Stahlflachprodukt in die Warmformgebung eintritt, bis auf einen technisch unwesentlichen Unterschied der Erwärmungstemperatur entspricht. Allerdings ist auch eine stärkere Abkühlung zulässig, solange die Umformkräfte und Rückfederung vorteilhaft gegenüber einem Kaltumformen sind.
Adaptations of the heating parameters to the changed requirements can be made accordingly quickly
The hot forming (work step c)) of the steel flat product heated to the respective heating temperature to form the component according to the invention can be carried out in conventional hot forming tools available for this purpose in the prior art. The hot forming takes place as soon as possible after the through heating (work step b)), so that the temperature at which the steel flat product enters the hot forming corresponds to the heating temperature with the exception of a technically insignificant difference. However, stronger cooling is also permissible as long as the forming forces and springback are advantageous compared to cold forming.

Die Abkühlung des Bauteils nach der Warmumformung kann in ebenso an sich bekannter Weise im Warmformgebungswerkzeug erfolgen. Alternativ kann das Bauteil nach der Warmformgebung jedoch auch in geeignet kurzem Zeitabstand aus dem Warmformgebungswerkzeug entnommen außerhalb des Werkzeugs abgekühlt werden. Da die Abkühlgeschwindigkeit nicht eingeschränkt ist, kann sie sogar auch kleiner 10K/s sein.The cooling of the component after the hot forming can also take place in a manner known per se in the hot forming tool. Alternatively, after the hot forming, the component can also be removed from the hot forming tool and cooled outside of the tool at a suitably short time interval. Since the cooling speed is not limited, it can even be less than 10K/s.

Wie schon erwähnt, wirkt sich die Erfindung besonders positiv bei der Erzeugung von Bauteilen aus Stahlflachprodukten aus, die mit einer metallischen Schutzschicht belegt sind, um sie vor Korrosion oder anderen Angriffen zu schützen.As already mentioned, the invention has a particularly positive effect when producing components from flat steel products that are coated with a metallic protective layer to protect them from corrosion or other attacks.

Hier zeigt sich, dass durch die vergleichbar niedrigen erforderlichen Erwärmungstemperaturen, bei denen die Warmformung des erfindungsgemäßen Bauteils durchgeführt werden kann, ein Auflegieren der Schutzbeschichtung durch Eindiffundieren von Legierungsbestandteilen aus dem Stahlsubstrat allenfalls vermindert stattfindet, so dass die Schutzbeschichtung auch nach der Warmformgebung des Bauteils ihre kathodische Schutzwirkung beibehält. Die auf dem jeweils erfindungsgemäß verarbeiteten, zu dem erfindungsgemäßen Bauteil warmverformten Stahlflachprodukt vorhandenen Schutzschichten weisen dabei typischerweise vor der Warmumformung eine oberflächennahe, an das Stahlsubstrat des Stahlflachprodukts angrenzende Grenzschicht auf, die aus metallischem und/oder oxidischem Eisen, sowie ggf. metallischem und/oder oxidischem Mangan und des weiteren Legierungsbestandteilen des Grundwerkstoffes besteht. Nach der Warmumformung zu dem Bauteil liegt aufgrund der erfindungsgemäß genutzten geringen Erwärmungstemperaturen, bei denen die erfindungsgemäße Warmformgebung stattfindet, ein gegenüber der konventionellen, höhere Umformtemperaturen vorsehenden Vorgehensweise verringerter Anteil spröder Phasen im Grenzschichtbereich vor, da es aufgrund der erfindungsgemäß abgesenkten Erwärmungstemperatur der Warmformgebung nur zu einer minimierten Durchlegierung der Schutzbeschichtung mit aus dem Stahlsubstrat stammenden Elementen kommt. Das Potential des kathodischen Korrosionsschutzes durch Zn-reiche Phasen bleibt damit erhalten.This shows that due to the comparably low required heating temperatures at which the component according to the invention can be hot-formed, alloying of the protective coating by diffusing alloying components from the steel substrate takes place at best to a reduced extent, so that the protective coating maintains its cathodic function even after the component has been hot-formed protective effect retained. the on The protective layers present on each of the protective layers processed according to the invention and hot-formed into the component according to the invention typically have a surface-near boundary layer adjoining the steel substrate of the flat steel product prior to the hot-forming, which consists of metallic and/or oxidic iron and, if necessary, metallic and/or oxidic manganese and the other alloy components of the base material. After the hot forming to form the component, due to the low heating temperatures used according to the invention, at which the hot forming according to the invention takes place, there is a reduced proportion of brittle phases in the boundary layer region compared to the conventional procedure, which provides for higher forming temperatures, since there is only one minimized alloying of the protective coating with elements originating from the steel substrate. The potential of cathodic corrosion protection through Zn-rich phases is thus retained.

Die Parameter der erfindungsgemäßen Vorgehensweise erlauben es, die kathodische Schutzwirkung einer auf dem Stahlflachprodukt vorhandenen Znhaltigen Schicht zu erhalten und kritische Risse bei der Warmumformung von mehr als 10 µm zu vermeiden.The parameters of the procedure according to the invention make it possible to maintain the cathodic protective effect of a layer containing Zn present on the flat steel product and to avoid critical cracks of more than 10 μm during hot forming.

Bei den beim erfindungsgemäßen Verfahren vogesehenen, vergleichsweise niedrigen Erwärmungs- bzw. Umformtemperaturen werden die schädlichen Konsequenzen vermieden, die bei einem Aufschmelzen der Zn-Schicht auftreten würden. Aufgrund der Diffusion von Fe aus dem Substrat in die Schicht wird deren Schmelzpunkt in ausreichendem Maße angehoben. Um jedoch einen kathodischen Korrosionsschutz zu wahren, ist eine Begrenzung des Fe-Anteils in der Beschichtung erforderlich, damit nach der Warmumformung noch ausreichend Zn-reiche Phasen erhalten bleiben. Die im Überzug vorliegenden Fe-Zn-Phasen wurden für die Beispiele per Röntgendiffraktometrie bestimmt und sind in Tabelle 3 zusammengefasst.With the comparatively low heating or forming temperatures provided for in the method according to the invention, the harmful consequences that would occur if the Zn layer were to melt are avoided. Due to the diffusion of Fe from the substrate into the layer, its melting point is raised sufficiently. However, in order to maintain cathodic protection against corrosion, the Fe content in the coating must be limited so that sufficient Zn-rich phases are retained after hot forming. The Fe-Zn phases present in the coating were determined for the examples by X-ray diffractometry and are summarized in Table 3.

Der konventionell in der Warmumformung eingesetzte Vergleichsstahl V wird zur Einstellung der mechanischen Zieleigenschaften typischerweise bei 870 - 950 °C geglüht. Dabei kommt es zur Ausbildung einer Γ/Γ1-Phase, welche vergleichsweise temperaturstabil ist, was den Anteil an entstehendem flüssigen Zn begrenzt und somit die Gefahr einer auftretenden Flüssigmetallversprödung eindämmt. Der in der Γ/Γ1-Phase enthaltene hohe Fe-Anteil schränkt jedoch den aktiven Korrosionsschutz der Schicht stark ein.The comparison steel V, which is conventionally used in hot forming, is typically annealed at 870 - 950 °C to set the target mechanical properties. This leads to the formation of a Γ/Γ 1 phase, which is comparatively temperature-stable, which limits the proportion of liquid Zn that forms and thus reduces the risk of liquid metal embrittlement occurring. However, the high proportion of Fe contained in the Γ/Γ 1 phase severely limits the active corrosion protection of the layer.

Bei den erfindungsgemäßen Proben Mittelmangan + Z bleibt aufgrund der deutlich niedrigeren Ofentemperatur zur Einstellung der mechanischen Zieleigenschaften zusätzlich die deutlich Zn-reichere δ-Phase bestehen, was zu einem verbesserten Korrosionsschutzpotenzial führt. Aufgrund des durchlegierungsbedingten Schichtaufbaus ist das Schichtsystem ausreichend temperaturstabil, so dass es bei erfindungsgemäßen Warmumformtemperaturen zu keiner kritischen Rissbildung über 10 µm Tiefe durch flüssiges Zn kommt, bei der ein Rissfortschritt bei Beanspruchung des Bauteils zu erwarten wäre.In the case of the middle manganese+Z samples according to the invention, the significantly higher Zn-rich δ phase also remains due to the significantly lower oven temperature for setting the mechanical target properties, which leads to an improved corrosion protection potential. Due to the layer structure caused by the alloying, the layer system is sufficiently temperature-stable so that no critical cracking of more than 10 μm depth occurs due to liquid Zn at hot forming temperatures according to the invention, at which crack propagation would be expected when the component is stressed.

Außerdem bildet sich an der freien Oberfläche des Schutzüberzugs in an sich bekannterWeise (s. EP 2 290 133 B1 ) eine manganhaltige Schicht in metallischer und/oder oxidischer Form an der freien Oberfläche des Bauteils aus, durch die die Wirksamkeit der Schutzbeschichtung weiter erhöht ist.In addition, in a manner known per se (see Fig. EP 2 290 133 B1 ) a manganese-containing layer in metallic and/or oxidic form on the free surface of the component, which further increases the effectiveness of the protective coating.

Erfindungsgemäß erzeugte Bauteile besitzen in Folge ihrer Verformung bei Temperaturen, die unterhalb einer Höchstgrenze liegen, welche der Ac3-Temperatur des jeweiligen Stahls + 60 °C entspricht, eine optimierte Kombination aus hohen Festigkeitswerten, für die Zugfestigkeiten Rm von typischerweise mindestens 1000 MPa stehen, und optimierten Dehnungseigenschaften, die sich in Bruchdehnungen A80 von regelmäßig mehr als 10 % ausdrücken. Das Produkt Rm x A80 liegt bei erfindungsgemäßen Bauteilen dementsprechend ebenso regelmäßig im Bereich von 13.000 - 35.000 MPa%. Dagegen liegen die Zugfestigkeiten Rm bei Bauteilen, die aus konventionellen Stählen für die Warmumformung hergestellt wurden, bei Temperaturen, bei denen ein vollaustenitisches Gefüge vorliegt, zwar typischerweise bei mindestens 1200 MPa, da sie nach Abschrecken vollmartensitisch sind. Jedoch erreichen diese Bauteile nur deutlich niedrigere Bruchdehnungswerte A80, so dass bei diesen Bauteilen das Produkt Rm x A80 regelmäßig nur 6.000 - 11.000 MPa% beträgt.As a result of their deformation at temperatures below a maximum limit, which corresponds to the Ac3 temperature of the respective steel + 60 °C, components produced according to the invention have an optimized combination of high strength values, for which tensile strengths Rm of typically at least 1000 MPa stand, and optimized elongation properties, which are expressed in elongations at break A80 of regularly more than 10%. In the case of components according to the invention, the product Rm×A80 is accordingly also regularly in the range of 13,000-35,000 MPa%. On the other hand, the tensile strengths Rm for components made from conventional steels for hot forming were produced at temperatures at which a fully austenitic structure is present, typically at least 1200 MPa, since they are fully martensitic after quenching. However, these components only achieve significantly lower elongation at break values A80, so that the product Rm x A80 for these components is regularly only 6,000 - 11,000 MPa%.

Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen näher erläutert.The invention is explained in more detail below using exemplary embodiments.

Es sind drei den Maßgaben der Erfindung entsprechende Schmelzen S1 - S3 und eine Vergleichsschmelze V erschmolzen worden, deren Zusammensetzungen jeweils in Gew.-% in Tabelle 1 angegeben sind. Zusätzlich sind in Tabelle 1 die zu den Stählen S1 - S3 und V gemäß SEP 1680:1990-12 ermittelten Ac1- und Ac3-Temperaturen in °C genannt.Three melts S1-S3 corresponding to the stipulations of the invention and one comparative melt V were melted, the compositions of which are each given in % by weight in Table 1. Table 1 also shows the Ac1 and Ac3 temperatures in °C determined for steels S1 - S3 and V in accordance with SEP 1680:1990-12.

Die Vergleichsschmelze V liegt aufgrund ihres zu geringen Mn-Gehalts und der Anwesenheit von B außerhalb der Vorgaben der Erfindung.The comparison melt V lies outside the specifications of the invention due to its low Mn content and the presence of B.

Aus den Stählen S1 - S3 und V sind Blechzuschnitte hergestellt worden.Sheet metal blanks were made from steels S1 - S3 and V.

In Beispiel 1, 4, 11 und 8 wurden Blechproben untersucht, die aus Warmbändern geschnitten worden sind, die aus einem in konventioneller Weise erzeugten Vorprodukt auf eine Dicke "d" warmgewalzt (Zustand "WW") und anschließend unter einer Haube (Zustand "HG") oder in einem Durchlaufofen (Zustand "DO") geglüht worden sind. Bei den Beispielen 2 und 5 wurden die Blechproben aus Bändern geschnitten, die aus Warmbändern erzeugt worden sind, welche zusätzlich auf eine Dicke "d" kaltgewalzt worden sind (Zustand "KW"). Vor dem Blechzuschnitt sind einige der kaltgewalzten Bänder zum Teil, wie bei den Beispielen 3, 6,12, haubengeglüht (Zustand "HG") oder, wie bei den Beispielen 7, 9, 10, 13 - 16, in einem Durchlaufofen (Zustand "DO") geglüht worden. Einige der Blechzuschnitte sind zudem mit einer reinen Zink-Schicht elektrolytisch ("ZE") oder feuerbeschichtet ("Z"), mit einer Zink-Eisen-Schicht ("ZF") oder mit einer Aluminium-Silizium-Schicht ("AS") beschichtet worden.In Examples 1, 4, 11 and 8, sheet metal samples were examined which had been cut from hot strip, which had been hot-rolled to a thickness "d" from a pre-product produced in a conventional manner (condition "WW") and then under a hood (condition "HG ") or have been annealed in a continuous furnace ("DO" condition). In Examples 2 and 5, the sheet samples were cut from strip produced from hot strip which had been additionally cold rolled to a thickness "d"("KW" condition). Before the sheet metal is cut, some of the cold-rolled strips are bell annealed (state "HG"), as in examples 3, 6,12, or in a continuous furnace (state "DO") has been annealed. Some of the Sheet metal blanks have also been coated with a pure zinc layer electrolytically ("ZE") or hot-dip coated ("Z"), with a zinc-iron layer ("ZF") or with an aluminum-silicon layer ("AS") .

Die Blechzuschnitte sind jeweils in einem konventionellen Ofen auf eine Erwärmungstemperatur Tew durcherwärmt, dann in einem konventionellen Warmformwerkzeug zu einem Hutprofil warmumgeformt und anschließend an Luft abgekühlt worden.The sheet metal blanks were each heated through in a conventional oven to a heating temperature Tew, then hot-formed in a conventional hot-forming tool to form a hat profile and then cooled in air.

Die am jeweils erhaltenen Bauteil ermittelte Zugfestigkeit Rm, die Dehngrenze Rp0,2, die Bruchdehnung A80, das Produkt Rm x A80 und der Biegewinkel sind in Tabelle 2 angegeben. Darüber hinaus sind dort, soweit diese Merkmale bestimmt worden sind, Gefügekenngrößen des jeweils erhaltenen Bauteils angegeben.The tensile strength Rm determined on the component obtained in each case, the yield point Rp0.2, the elongation at break A80, the product Rm×A80 and the bending angle are given in Table 2. In addition, where these features have been determined, structural parameters of the component obtained are given there.

Darüber hinaus sind dort, soweit diese Merkmale bestimmt worden sind, die Austenitanteile des jeweils erhaltenen Bauteils und die abgeschätzte Korngröße sowie die Risstiefen an der kritischsten Stelle des Hutprofils angegeben, wie sie im Querschliff unter dem Lichtmikroskop gemessen wurden.In addition, as far as these characteristics have been determined, the austenite content of the respective component obtained and the estimated grain size as well as the crack depths at the most critical point of the hat profile are given there, as measured in the cross section under the light microscope.

Es zeigt sich, dass bei den erfindungsgemäßen Beispielen die Bruchdehnungen A80 über 10 % liegen und die Produkte Rm x A80 mehr als 14.000 MPa% betragen. Gleichzeitig weisen die Beispiele Biegewinkel von über 60° auf.It is found that in the examples according to the invention the elongations at break A80 are more than 10% and the products Rm×A80 are more than 14,000 MPa%. At the same time, the examples have bending angles of more than 60°.

Bei den Beispielen 1 - 3 wurde beim Erwärmen eine überwiegend austenitische Struktur eingestellt, die beim Abkühlen weitgehend in Martensit umwandelt, was zu den hohen Festigkeiten führt.In Examples 1 - 3, a predominantly austenitic structure was set during heating, which largely transforms into martensite on cooling, which leads to the high strengths.

Bei den Beispielen 4 - 13 wurde der Austenitanteil durch Wärmen im Zweiphasengebiet so optimiert, dass besonders hohe Produkte Rm x A80 und hohe Biegewinkel erhalten wurden.In Examples 4 - 13, the proportion of austenite was optimized by heating in the two-phase region in such a way that particularly high products Rm x A80 and high bending angles were obtained.

Ein besonders feines Gefüge kann durch Zulegieren von Mikrolegierungselementen und Seltenen Erdmetallen erzielt werden.A particularly fine structure can be achieved by alloying micro-alloying elements and rare earth metals.

In den Beispielen 14 - 16 wurde der Austenitgehalt durch die dem Blechzuschnitt vorangegangen Glühungen im Zweiphasengebiet eingestellt.In Examples 14 - 16, the austenite content was adjusted by annealing in the two-phase region prior to sheet metal cutting.

Beim Warmumformen unterhalb von Ac1 wird im Wesentlichen nur noch der Martensit angelassen. Letzteres Verfahren hat neben guten mechanischen Eigenschaften insbesondere Vorteile in Bezug auf die Beschichtung. Da die Temperaturen unter der Schmelztemperatur des Überzugs liegen, können Risse im Substrat durch eindringendes Zink bei der Warmumformung weitgehend vermieden werden.In the case of hot forming below Ac1, essentially only the martensite is tempered. In addition to good mechanical properties, the latter method has particular advantages with regard to the coating. Since the temperatures are below the melting point of the coating, cracks in the substrate caused by penetrating zinc during hot forming can be largely avoided.

Aber auch bei Erwärmungstemperaturen im Zweiphasengebiet (Beispiele 8 - 10) ist der Überzug so beschaffen, dass Risse in einem akzeptierbaren Rahmen von höchstens 10 µm bleiben. Tabelle 1 Stahl C Si Mn Al Cr Cu + Ni N Ti + Nb + V REM B Ac1 [°C] Ac3 [°C] Erfindungsgemäß? S1 0,09 0,15 6,5 0,03 0,45 0,15 0,009 0,08 0,004 - 570 735 JA S2 0,12 0,09 7,2 0,02 1,6 0,31 0,006 - 0,007 - 580 720 JA S3 0,08 0,18 5,3 0,03 2,3 0,13 0,004 0,15 - - 620 750 JA V 0,24 0,2 1,2 0,04 0,2 0,04 0,003 0,04 - 0,0024 705 800 NEIN Gehaltsangaben in Gew.-%, Rest Fe und unvermeidbare Verunreinigungen
nicht erfindungsgemäße Gehalte sind unterstrichen
Tabelle 2 Versuch Stahl Zustand*) Schutzschicht d Tew Rp0,2 Rm A80 RmxA80 Biege-winkel Risstiefe Gefüge [mm] [°C] [MPa] [MPa] [%] [MPax%] [°] [µm] Austenit Korngröße [Vol.-%] [µm] 1 S1 WW+HG keine 3 700 570 1245 14,1 17555 62 - 15 <5 2 S1 KW keine 1,5 700 551 1245 11,6 14442 91 - 30 <2 3 S1 KW+HG keine 1,5 750 855 1485 10,1 14999 66 - 10 <2 4 S1 WW+HG keine 3 650 550 1060 25,8 27348 95 - 40 <5 5 S1 KW keine 1,5 650 906 1020 22 22440 146 - 30 <2 6 S3 KW+HG ZE 1,5 650 503 1117 19,8 22117 104 25 <2 7 S1 KW+DO keine 1,5 650 905 1082 19,6 21207 110 - 35 <2 8 S2 WW+DO Z 2 650 610 1010 18,5 18685 - 9 40 <4 9 S2 KW+DO Z 1,4 630 605 1060 22,5 23850 125 8 30 <3 10 S3 KW+DO Z 1,5 660 636 1144 18,7 21393 - 10 25 <3 11 S3 WW+HG keine 3,3 650 440 1130 16,5 18645 - - - - 12 S1 KW+HG ZE 1,6 640 650 1030 18,5 19055 - - - - 13 S2 KW+DO ZF 1,5 635 540 1010 25,5 25755 - - - - 14 S3 KW+DO Z 1,4 500 875 1059 19,7 20862 - 3 - - 15 S3 KW+DO Z 1,6 400 892 1070 20,2 21614 106 1 30 <3 16 S3 KW+DO Z 1,5 300 880 1074 21,2 22769 - 0 17 V KW+DO keine 1,5 925 1010 1527 5,9 9009 68 - - - 18 V KW+DO AS 1,5 925 1050 1535 5,6 8596 39 - - - "-" = Nicht bestimmt
*) "WW"= warmgewalzt, "KW" = kaltgewalzt, "HG" = haubengeglüht, "DO" = durchlaufofengeglüht

Figure imgb0002
But even at heating temperatures in the two-phase range (Examples 8-10), the coating is such that cracks remain within an acceptable range of at most 10 μm. <b>Table 1</b> steel C si Mn Al Cr Cu + Ni N Ti + Nb + V SEM B Ac1 [°C] Ac3 [°C] According to the invention? S1 0.09 0.15 6.5 0.03 0.45 0.15 0.009 0.08 0.004 - 570 735 YES S2 0.12 0.09 7.2 0.02 1.6 0.31 0.006 - 0.007 - 580 720 YES S3 0.08 0.18 5.3 0.03 2.3 0.13 0.004 0.15 - - 620 750 YES V 0.24 0.2 1.2 0.04 0.2 0.04 0.003 0.04 - 0.0024 705 800 NO Contents in % by weight, remainder Fe and unavoidable impurities
contents not according to the invention are underlined
attempt steel Status*) protective layer i.e Tev Rp0.2 rm A80 RmxA80 bending angle crack depth structure [mm] [°C] [MPa] [MPa] [%] [MPax%] [°] [µm] austenite grain size [% by volume] [µm] 1 S1 WW+HG none 3 700 570 1245 14.1 17555 62 - 15 <5 2 S1 week none 1.5 700 551 1245 11.6 14442 91 - 30 <2 3 S1 KW+HG none 1.5 750 855 1485 10.1 14999 66 - 10 <2 4 S1 WW+HG none 3 650 550 1060 25.8 27348 95 - 40 <5 5 S1 week none 1.5 650 906 1020 22 22440 146 - 30 <2 6 S3 KW+HG ZE 1.5 650 503 1117 19.8 22117 104 25 <2 7 S1 CW+THU none 1.5 650 905 1082 19.6 21207 110 - 35 <2 8th S2 WW+TH Z 2 650 610 1010 18.5 18685 - 9 40 <4 9 S2 CW+THU Z 1.4 630 605 1060 22.5 23850 125 8th 30 <3 10 S3 CW+THU Z 1.5 660 636 1144 18.7 21393 - 10 25 <3 11 S3 WW+HG none 3.3 650 440 1130 16.5 18645 - - - - 12 S1 KW+HG ZE 1.6 640 650 1030 18.5 19055 - - - - 13 S2 CW+THU IF 1.5 635 540 1010 25.5 25755 - - - - 14 S3 CW+THU Z 1.4 500 875 1059 19.7 20862 - 3 - - 15 S3 CW+THU Z 1.6 400 892 1070 20.2 21614 106 1 30 <3 16 S3 CW+THU Z 1.5 300 880 1074 21.2 22769 - 0 17 V CW+THU none 1.5 925 1010 1527 5.9 9009 68 - - - 18 V CW+THU AS 1.5 925 1050 1535 5.6 8596 39 - - - "-" = Not determined
*) "WW"= hot rolled, "KW" = cold rolled, "HG" = batch annealed, "DO" = continuous furnace annealed
Figure imgb0002

Claims (13)

  1. Metal sheet component, manufactured by hot forming a flat steel product which consists of in % by weight C: 0,02 - 0.5%, Si: 0.05 - 1%, Mn: 4 - 12 %, Cr: 0.1 - 4 %, Al: N: P: S: up to 3.5%, up to 0.05%, up to 0.05%, up to 0.01%, Cu, Ni: in total up to 2%, wherein the content of Cu and Ni is > 0,04%, Ti, Nb, V: in total up to 0.5%, Rare earth metals: up to 0.1%, and Fe as a remainder and unavoidable impurities ,
    wherein the content %C of C and the content %Cr of Cr meet the following condition: 10 × %C + %Cr < 5 .5% ,
    Figure imgb0005
    wherein the flat steel product after the hot forming into the metal sheet component has a bending angle determined according to VDA 238-100: 2010-12 of more than 60°
    and
    wherein the structure of the hot-formed metal sheet component consists of 5 - 50 % by volume austenite and as the remainder of martensite, tempered martensite or ferrite, wherein the ferrite proportion can also be "0" and wherein the average grain diameter of the grains of the structure is less than 5 µm.
  2. Metal sheet component according to claim 1, characterised in that its C content is up to 0.3% by weight.
  3. Metal sheet component according to any one of the preceding claims, characterised in that its Cr content is at least 2.2% by weight.
  4. Metal sheet component according to any one of the preceding claims, characterised in that the average grain diameter is below 2 µm.
  5. Metal sheet component according to any one of the preceding claims, characterised in that the bending angle is more than 80°.
  6. Metal sheet component according to any one of the preceding claims, characterised in that after hot forming the tensile strength Rm of the flat steel product is at least 1000 MPa, its elongation at break A80 is more than 10% and the product Rm*A80 formed of its tensile strength Rm and its elongation at break A80 is more than 13000 MPa%.
  7. Metal sheet component according to any one of the preceding claims, characterised in that it is provided with a metallic protective coating.
  8. Method for manufacturing a metal sheet component provided according to any one of the preceding claims, comprising the following work steps:
    a) Providing a flat steel product made of a steel, which in % - by weight consists of C: 0,02 - 0.5%, Si: 0.05 - 1%, Mn: 4 - 12%, Cr: 0.1 - 4%, Al: up to 3.5%, N: up to 0.05%, P: up to 0.05%, S: up to 0.01%, in total more than 0,04% and up to 2% Cu and/or Ni, in total up to 0.5 % of Ti, Nb or V, REM: up to 0.1%,
    and Fe as a remainder and unavoidable impurities, wherein the content %C of C and the content %Cr of Cr meet the following condition: 10 × %C + %Cr < 5 .5%
    Figure imgb0006
    b) Heating up the flat steel product to a heating temperature which is at least 200°C and at most equal to the Ac3 temperature +60°C of the steel, of which the flat steel product consists in each case;
    c) Hot forming the flat steel product heated to the heating temperature into the component.
  9. Method according to claim 8, characterised in that the heating temperature is at most 800°C.
  10. Method according to claim 8, characterised in that the heating temperature is above the Ac1 temperature and below the Ac3 temperature of the steel, of which the flat steel product consists in each case.
  11. Method according to claim 8, characterised in that the heating temperature is below the Ac1 temperature of the steel, of which the flat steel product consists in each case.
  12. Method according to any one of claims 8 to 11, characterised in that the flat steel product provided in work step a) has a metallic corrosion protection layer.
  13. Method according to any one of claims 8 to 11, characterised in that the heating-up in work step b) is carried out by means of a conductively or inductively acting heating method.
EP17754271.9A 2017-07-25 2017-07-25 Sheet metal component, produced by hot working a flat steel product, and method for the production thereof Active EP3658307B9 (en)

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MX2022010321A (en) * 2020-05-13 2022-09-19 Nippon Steel Corp Hot stamped molded body.
CN113913700B (en) * 2021-10-26 2023-01-24 江苏沙钢集团有限公司 1700 MPa-grade hot forming steel and production method thereof

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ES2384135T3 (en) 2009-08-25 2012-06-29 Thyssenkrupp Steel Europe Ag Procedure for manufacturing a steel component provided with a corrosion protection metallic coating and steel component
EP2383353B1 (en) 2010-04-30 2019-11-06 ThyssenKrupp Steel Europe AG High tensile steel containing Mn, steel surface product made from such steel and method for producing same
CN102127675B (en) * 2011-02-21 2012-11-14 钢铁研究总院 Production method of steel plate warm formed parts with high efficiency, low energy consumption and high quality
EP2524970A1 (en) * 2011-05-18 2012-11-21 ThyssenKrupp Steel Europe AG Extremely stable steel flat product and method for its production
KR101382981B1 (en) * 2011-11-07 2014-04-09 주식회사 포스코 Steel sheet for warm press forming, warm press formed parts and method for manufacturing thereof
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RU2659549C2 (en) 2014-01-06 2018-07-02 Ниппон Стил Энд Сумитомо Метал Корпорейшн Hot-formed member and process for its manufacturing
CN106232852B (en) * 2014-04-15 2018-12-11 蒂森克虏伯钢铁欧洲股份公司 The manufacturing method and flat cold-rolled bar product of flat cold-rolled bar product with high-yield strength
PL3170912T3 (en) * 2014-07-18 2019-09-30 Nippon Steel & Sumitomo Metal Corporation Steel product and manufacturing method of the same
EP3187601B1 (en) * 2014-08-07 2019-01-09 JFE Steel Corporation High-strength steel sheet and method for manufacturing same
CN104846274B (en) 2015-02-16 2017-07-28 重庆哈工易成形钢铁科技有限公司 Hot press-formed use steel plate, hot press-formed technique and hot press-formed component
US20160312323A1 (en) 2015-04-22 2016-10-27 Colorado School Of Mines Ductile Ultra High Strength Medium Manganese Steel Produced Through Continuous Annealing and Hot Stamping
KR101677398B1 (en) * 2015-11-30 2016-11-18 주식회사 포스코 Steels for hot forming and method of manufacturion component using thereof
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CN110944765A (en) 2020-03-31
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US20210087662A1 (en) 2021-03-25
WO2019020169A1 (en) 2019-01-31
CN110944765B (en) 2022-02-25
EP3658307B8 (en) 2021-11-03

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