EP2836614B1 - High-strength multi-phase steel, and method for producing a strip from said steel - Google Patents
High-strength multi-phase steel, and method for producing a strip from said steel Download PDFInfo
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- EP2836614B1 EP2836614B1 EP13717417.3A EP13717417A EP2836614B1 EP 2836614 B1 EP2836614 B1 EP 2836614B1 EP 13717417 A EP13717417 A EP 13717417A EP 2836614 B1 EP2836614 B1 EP 2836614B1
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- steel
- strip
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- 229910000831 Steel Inorganic materials 0.000 title claims description 144
- 239000010959 steel Substances 0.000 title claims description 144
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 238000000034 method Methods 0.000 claims description 69
- 238000000137 annealing Methods 0.000 claims description 58
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- 238000001816 cooling Methods 0.000 claims description 47
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- 230000009466 transformation Effects 0.000 claims description 12
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- 229910052804 chromium Inorganic materials 0.000 description 20
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- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 3
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical class [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
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- FFBHFFJDDLITSX-UHFFFAOYSA-N benzyl N-[2-hydroxy-4-(3-oxomorpholin-4-yl)phenyl]carbamate Chemical group OC1=C(NC(=O)OCC2=CC=CC=C2)C=CC(=C1)N1CCOCC1=O FFBHFFJDDLITSX-UHFFFAOYSA-N 0.000 description 2
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- 238000005482 strain hardening Methods 0.000 description 2
- CADICXFYUNYKGD-UHFFFAOYSA-N sulfanylidenemanganese Chemical compound [Mn]=S CADICXFYUNYKGD-UHFFFAOYSA-N 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
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- 229910000915 Free machining steel Inorganic materials 0.000 description 1
- 229910004283 SiO 4 Inorganic materials 0.000 description 1
- PGTXKIZLOWULDJ-UHFFFAOYSA-N [Mg].[Zn] Chemical compound [Mg].[Zn] PGTXKIZLOWULDJ-UHFFFAOYSA-N 0.000 description 1
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- JZQOJFLIJNRDHK-CMDGGOBGSA-N alpha-irone Chemical compound CC1CC=C(C)C(\C=C\C(C)=O)C1(C)C JZQOJFLIJNRDHK-CMDGGOBGSA-N 0.000 description 1
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- 150000001875 compounds Chemical class 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
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- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- AMWRITDGCCNYAT-UHFFFAOYSA-L manganese oxide Inorganic materials [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 description 1
- PPNAOCWZXJOHFK-UHFFFAOYSA-N manganese(2+);oxygen(2-) Chemical class [O-2].[Mn+2] PPNAOCWZXJOHFK-UHFFFAOYSA-N 0.000 description 1
- VCTOKJRTAUILIH-UHFFFAOYSA-N manganese(2+);sulfide Chemical class [S-2].[Mn+2] VCTOKJRTAUILIH-UHFFFAOYSA-N 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
- C21D8/0284—Application of a separating or insulating coating
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0224—Two or more thermal pretreatments
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
Definitions
- the invention relates to a high-strength multiphase steel according to the preamble of claim 1.
- the invention relates to a method for producing a hot or cold rolled strip of such a steel according to claim 6.
- the invention relates to steels with tensile strengths in the range of 580-900 MPa with low yield ratio of less than 67% for the production of components which have excellent formability and welding properties.
- the hotly contested automotive market is forcing manufacturers to constantly seek solutions to reduce fleet consumption while maintaining maximum comfort and occupant safety.
- the weight saving of all vehicle components plays a decisive role, on the other hand, but also a most favorable behavior of the individual components with high static and dynamic stress during operation as well as in the event of a crash.
- the suppliers of raw material suppliers are trying to meet this need by reducing the weight of the vehicles by providing high-strength and ultra-high-strength steels and reducing the sheet thickness, while at the same time improving forming and component behavior during production and operation.
- High-strength and higher-strength steels enable lighter vehicle components (eg cars, trucks), which consequently results in lower fuel consumption.
- the reduced CO 2 content reduces the environmental impact.
- These steels must therefore meet relatively high requirements in terms of their strength and ductility, energy absorption and in their processing, such as punching, hot and cold forming, welding and / or surface finishing (e.g., metallized, organically coated, painted).
- Newly developed steels must therefore meet the requirements for the required weight reduction, the increasing material requirements for yield strength, Tensile strength and elongation at break with good formability, as well as the component requirements for high toughness, edge crack resistance, energy absorption and strength on the work-hardening effect and the bake-hardening effect, but also improved joining suitability in the form of eg improved weldability.
- Improved edge tear resistance means increased hole widening and is known by synonyms such as High Hole Expansion (HHE) and Low Edge Crack (LEC).
- HHE High Hole Expansion
- LEC Low Edge Crack
- LCE Low Carbon Equivalent
- UP Under Peritectical
- dual-phase steels consist of a ferritic basic structure in which a martensitic second phase and possibly a further phase with bainite and retained austenite are incorporated.
- the bainite can be present in different forms.
- the steel grades determining processing characteristics of dual-phase steels such as a very low yield ratio and at the same time very high tensile strength, a strong work hardening and a good cold workability, are well known.
- Multiphase steels such as complex-phase steels, ferritic-bainitic steels, bainitic steels and martensitic steels, which are characterized by different microstructural compositions as described in EN 10346, are also used with increasing tendency.
- Complex-phase steels are steels which contain small amounts of martensite, retained austenite and / or pearlite in a ferritic / bainitic matrix, whereby extreme grain refinement is brought about by delayed recrystallization or by precipitation of micro-alloying elements.
- Ferritic-bainitic steels are steels that contain bainite or solidified bainite in a matrix of ferrite and / or solidified ferrite.
- the solidification of the matrix is effected by a high dislocation density, by grain refining and the excretion of micro-alloying elements.
- Bainitic steels are steels that are characterized by a very high yield strength and tensile strength at a sufficiently high elongation for cold forming processes. Due to the chemical composition a good weldability is given.
- the microstructure typically consists of bainite. Occasionally, small amounts of other phases, such as. As martensite and ferrite.
- Martensitic steels are steels that contain small amounts of ferrite and / or bainite in a matrix of martensite due to thermomechanical rolling.
- the steel grade is characterized by a very high yield strength and tensile strength at a sufficiently high elongation for cold forming processes. Within the group of multiphase steels, the martensitic steels have the highest tensile strength values.
- T Ailor R olled B lank lightweight technology allows a significant weight reduction by the load customized choice of thickness greater than the length of the component.
- TRB®s with multiphase structure are not without limitations, however, with currently known alloys and available continuous annealing equipment for widely varying tape thicknesses. for the heat treatment before cold rolling, possible. In areas of different tape thickness, i. in the presence of different Kaltabwalzgrade, due to a temperature gradient occurring in the common process windows no homogeneous multi-phase microstructure can be set in cold- as well as hot-rolled steel strips.
- the hot strip in typical thicknesses between 1.50 mm to 4.00 mm or cold strip, in typical thicknesses of 0.50 mm to 3.00 mm, heated in a continuous annealing furnace to a temperature such that during cooling the required microstructure established.
- a continuous annealing furnace heated in a continuous annealing furnace to a temperature such that during cooling the required microstructure established.
- a special heat treatment takes place, where e.g.
- comparatively soft components such as ferrite or bainitic ferrite
- the steel its low yield strength and its hard constituents, such as martensite or carbon-rich bainite its strength.
- the annealing treatment is usually carried out in a continuous annealing furnace upstream of the galvanizing bath.
- the required microstructure of the hot strip may also be adjusted in the continuous furnace during the annealing treatment, in order to achieve the required mechanical properties.
- a homogeneous temperature distribution is difficult to achieve, especially at different thicknesses in the transition region from one belt to another. This can result in alloy compositions with too small process windows in the continuous annealing, e.g. the thinner belt is either driven too slowly through the furnace and thereby the productivity is lowered, or that the thicker belt is driven too fast through the furnace and the necessary annealing temperatures and cooling gradients to achieve the desired structure is not achieved. The consequences are increased rejects with corresponding costs of misconduct.
- the decisive process parameter is thus the setting of the speed in the continuous annealing, since the phase transformation takes place depending on temperature and time.
- a method for producing a steel strip with different thickness over the strip length is z. B. in the DE 100 37 867 A1 described.
- the goal of achieving the resulting mechanical and technological properties in a narrow range over bandwidth and strip length by the controlled adjustment of the volume fractions of the structural phases has top priority and is therefore only possible through an enlarged process window.
- the known alloy concepts for multiphase steels are characterized by too narrow a process window and therefore unsuitable for solving the present problem, in particular in flexibly rolled strips.
- At present, only steels of a strength class with defined cross-sectional areas (strip thickness and strip width) can be represented with the known alloy concepts, so that altered alloy concepts are necessary for different strength classes and / or cross-sectional areas.
- the state of the art is that an increase in strength is achieved by the increase in the quantity of carbon and / or silicon and / or manganese and an increase in the strength via the microstructural adjustments and the solid solution hardening (mixed crystal hardening) with adapted temperature control.
- the hole expansion test according to ISO 11630 is used as one of several possible test methods.
- a low yield ratio (Re / Rm) is typical for a dual-phase steel and is used primarily for formability in drawing and deep drawing operations. This gives the designer information about the distance between onset of plastic deformation and failure of the material under quasistatic stress. Ask accordingly lower yield ratio ratios provide a greater safety margin for component failure.
- a higher yield ratio (Re / Rm), which is typical for complex phase steels, is also distinguished by resistance to edge cracks. This can be attributed to the smaller differences in the strengths of the individual structural components, which has a favorable effect on a homogeneous deformation in the area of the cutting edge.
- the analytical landscape for achieving multi-phase steels with minimum tensile strengths of 580 MPa has become very diverse and shows very large alloy areas in the strength-increasing elements carbon, silicon, manganese, phosphorus, aluminum and chromium and / or molybdenum, as well as in the addition of microalloys such Titanium and vanadium, as well as in the material-characterizing properties.
- the range of dimensions is broad and lies in the thickness range of about 0.50 to 4.00 mm. It can be found mainly bands up to about 1850mm application, but also slit strip dimensions caused by longitudinal parts of the bands. Sheets or sheets are made by cutting the strips.
- the invention is therefore based on the object, a new alloy concept for a high-strength multiphase steel with a minimum tensile strength of 580 MPa longitudinal and transverse to the rolling direction, preferably with dual-phase structure and a yield ratio of less than 67%, with the process window for the continuous annealing of hot or Cold bands can be extended so that in addition to bands with different cross sections and steel bands with over tape length and possibly bandwidth varying thickness, and thus the correspondingly varying degrees of cold rolling, can be produced with the most homogeneous mechanical and technological properties.
- a method for producing a strip made from this steel is to be specified.
- this object is achieved by a steel with the following contents in% by weight: C 0.075 to ⁇ 0.105 Si 0.200 to ⁇ 0.300 Mn 1,000 to ⁇ 2,000 Cr 0.280 to ⁇ 0.480 al 0.010 to ⁇ 0.060 P ⁇ 0.020 Nb ⁇ 0.005 to ⁇ 0.025 N ⁇ 0.0100 S ⁇ 0.0050
- the steel according to the invention offers the advantage of a significantly enlarged process window in comparison to the known steels. This results in an increased process reliability in the continuous annealing of cold and hot strip with dual-phase structure. Thus, homogenized mechanical-technological properties in the strip can be ensured for pass-annealed hot or cold strips even with different cross sections and otherwise identical process parameters.
- stress-optimized components can be produced by forming technology.
- the material produced can be produced both as a cold strip and as a hot strip via a hot-dip galvanizing line or a pure continuous annealing plant in the dressed and undressed and also in the heat-treated state (intermediate annealing).
- the steel strips produced with the alloy composition according to the invention are characterized in the production of a dual-phase steel by a much wider compared to the standard process window in terms of temperature and flow rate in the intercritical annealing between A c1 and A c3 or in a Austenitizing annealing over A c3 with final controlled cooling or annealing below the beginning of the two-phase region (eg A c1 - about 20 ° C) in comparison to the known alloy concepts of (see FIG. 9a . 9b . 9c ).
- Annealing temperatures of about 700 to 950 ° C have proved to be advantageous. Depending on the overall process, there are different approaches to realize the heat treatment.
- the strip is cooled starting from the annealing temperature at a cooling rate of 15 to 100 ° C / s to an intermediate temperature of 200 to 250 ° C.
- the cooling to room temperature is finally carried out at a cooling rate of 2 to 30 ° C / s.
- the cooling as described above is stopped before entering the molten bath and continued until after leaving the bath until reaching the intermediate temperature of 200 to 250 ° C. Depending on the molten bath temperature results in a holding temperature of about 420 to 470 ° C.
- the cooling to room temperature is again at a cooling rate of 2 to 30 ° C / s.
- the second variant of the temperature control in the hot dip finishing involves holding the temperature for about 1 to 20 seconds at the intermediate temperature of 200 to 250 ° C and then reheating to the temperature required for hot dipping refinement of about 420 to 470 ° C.
- the strip is cooled after refining again to 200 to 250 ° C.
- the cooling to room temperature is again at a cooling rate of 2 to 30 ° C / s.
- the basis for achieving a broad process window is the microalloying according to the invention exclusively with niobium, taking into account the above-mentioned. classical composition carbon / silicon / manganese / chromium, with a graded and defined manganese content to be displayed according to the strip thickness.
- niobium retards the recrystallization in the annealing treatment, thereby stabilizing the austinite grain size and achieving a broader process window in the final annealing treatment.
- Material characteristic is also that the addition of manganese with increasing weight percent of the ferrite is shifted to longer times and lower temperatures during cooling.
- the proportions of ferrite are more or less reduced by increased amounts of bainite.
- niobium enables the previously described process robustness.
- the manganese variation compensates for the cross-sectional influence in the time-temperature conversion behavior.
- the carbon equivalent can be reduced, thereby improving weldability and avoiding too much hardening during welding. In resistance spot welding, moreover, the electrode life can be significantly increased.
- the effect of the elements in the alloy according to the invention is described in more detail below.
- the multiphase steels are typically chemically designed to combine alloying elements with and without micro-alloying elements.
- Accompanying elements are unavoidable and are considered in the analysis concept with regard to their effect if necessary.
- Hydrogen (H) is the only element that can generate diffraction through the iron grid without creating lattice strains. As a result, the hydrogen in the iron grid is relatively mobile and can be absorbed relatively easily during production. Hydrogen can only be taken up in atomic (ionic) form in the iron lattice.
- Hydrogen has a strong embrittlement and preferably diffuses to energy-favorable sites (defects, grain boundaries, etc.). In this case, defects act as hydrogen traps and can significantly increase the residence time of the hydrogen in the material.
- a more uniform structure which in the steel according to the invention u.a. achieved by its microalloying reduces the susceptibility to hydrogen embrittlement.
- the hydrogen content in the steel should be as low as possible.
- Oxygen (O) In the molten state, the steel has a relatively high absorption capacity for gases, but at room temperature, oxygen is only soluble in very small quantities. Similar to hydrogen, oxygen can only diffuse into the material in atomic form. Due to the strong embrittling effect and the negative effects on the aging resistance, as much as possible is attempted during production to reduce the oxygen content.
- the oxygen content in the steel should be as low as possible.
- Nitrogen (N) is also a companion element of steelmaking. Steels with free nitrogen tend to have a strong aging effect. The nitrogen diffuses at low temperatures at dislocations and blocks them. It causes an increase in strength combined with a rapid loss of toughness. Nitrogen bonding in the form of nitrides is possible by alloying aluminum or titanium.
- the nitrogen content is limited to ⁇ 0.0100%, advantageously ⁇ 0.0090% or optimally ⁇ 0.0080% or amounts unavoidable in steel production.
- S Sulfur
- MnS manganese sulfide
- the manganese sulfides are often rolled in rows during the rolling process and act as nucleation sites for the transformation. This leads to a line-shaped structure, especially in the case of diffusion-controlled conversion, and can lead to impaired mechanical properties in the case of pronounced bristleness (for example, pronounced Martensitile instead of distributed martensite islands, anisotropic material behavior, reduced elongation at break).
- the sulfur content is limited to ⁇ 0.0050% or unavoidable amounts in steelmaking.
- Phosphorus (P) is a trace element from iron ore and is dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness by solid solution strengthening and improves hardenability.
- the phosphorus content is limited to ⁇ 0.020% or to unavoidable amounts in steelmaking.
- Alloying elements are usually added to the steel in order to specifically influence certain properties.
- an alloying element in different steels affect different characteristics. The effect generally depends strongly on the amount and the solution state in the material.
- Carbon (C) considered the most important alloying element in steel. Through its targeted introduction of up to 2.06% iron is only steel. Often the carbon content is drastically lowered during steelmaking. In the case of dual-phase steels for continuous hot-dip refinement, its maximum proportion is 0.23%; a minimum value is not specified.
- Carbon is also required to form carbides.
- a representative occurring almost in every steel is the cementite (Fe 3 C).
- significantly harder special carbides with other metals such as chromium, titanium, niobium, vanadium can form.
- the minimum C content is set to 0.075% and the maximum C content to 0.105%.
- silicon increases the strength and yield ratio of the ferrite with only a slight decrease Elongation at break.
- Another important effect is that silicon shifts the formation of ferrite to shorter times, thus allowing the formation of sufficient ferrite before quenching.
- the austenite is carbon enriched and stabilized.
- silicon stabilizes austenite markedly in the lower temperature range, especially in the area of bainite formation by preventing carbide formation.
- highly adherent scale may form at high silicon contents, which may affect further processing.
- silicon may diffuse to the surface during annealing and form film-like oxides alone or together with manganese. These oxides deteriorate the galvanizability by adversely affecting the galvanizing reaction (iron solution and inhibiting layer formation) when the steel strip is immersed in the molten zinc. This manifests itself in a poor zinc adhesion and unpigmented areas.
- a suitable kiln operation with adjusted moisture content in the annealing gas and / or by a low Si / Mn ratio and / or by the use of moderate amounts of silicon, however, a good galvanizability of the steel strip and a good zinc adhesion can be ensured.
- the minimum Si content is set at 0.200% and the maximum silicon content at 0.300%.
- Manganese (Mn) is added to almost all steels for desulfurization to convert the harmful sulfur into manganese sulfide. In addition, manganese increases the strength of the ferrite by solid solution strengthening and shifts the ⁇ / ⁇ conversion to lower temperatures.
- manganese tends to form oxides on the steel surface during annealing. Depending on the annealing parameters and the contents of other alloying elements (in particular silicon and aluminum), manganese oxides (eg MnO) and / or Mn mixed oxides (eg Mn 2 SiO 4 ) may occur. However, manganese is at one low Si / Mn or Al / Mn ratio to be considered as less critical, since forming more globular oxides instead of oxide films. However, high levels of manganese can negatively affect the appearance of the zinc layer and zinc adhesion.
- the manganese content is therefore set to 1,000 to 2,000% depending on the cross section (tape thickness at the same bandwidth).
- a manganese content 1.00-1.50 wt.%
- a manganese content of 1.50-2.00 wt.% Exposed.
- Chromium (Cr) On the one hand chromium in dissolved form can considerably increase the hardenability of steel even in small amounts. On the other hand, chromium causes particle hardening with appropriate temperature control in the form of chromium carbides. The associated increase in the number of seed sites with simultaneously reduced content of carbon leads to a reduction in the hardenability.
- chromium In dual phase steels, the addition of chromium mainly improves the hardenability. Chromium, when dissolved, shifts perlite and bainite transformation to longer times, while decreasing the martensite start temperature.
- Chromium is also a carbide former. If chromium is in carbide form, the austenitizing temperature must be high enough before curing to dissolve the chromium carbides. Otherwise, the increased germ count may lead to a deterioration of the hardenability.
- Chromium also tends to form oxides on the steel surface during the annealing process, which may degrade zinc-plating quality.
- the chromium content is therefore set to values of 0.280 to 0.480%.
- Molybdenum (Mo) The addition of molybdenum is similar to chromium to improve hardenability. The perlite and bainite transformation is pushed to longer times and the martensite start temperature is lowered.
- molybdenum considerably increases the tempering resistance, so that no loss of strength is to be expected in the zinc bath and, as a result of solid solution hardening, increases the strength of the ferrite.
- the content of molybdenum is limited to the unavoidable, steel-accompanying amounts.
- Copper (Cu): The addition of copper can increase the tensile strength and hardenability. In combination with nickel, chromium and phosphorus, copper can form a protective oxide layer on the surface, which can significantly reduce the corrosion rate.
- copper When combined with oxygen, copper can form harmful oxides at the grain boundaries, which can be detrimental to hot working processes in particular.
- the content of copper is therefore limited to quantities that are unavoidable in steel production.
- alloying elements such as nickel (Ni) or tin (Sn) are limited in their contents to unavoidable amounts in steelmaking.
- Microalloying elements are usually added only in very small amounts ( ⁇ 0.1%). They act in contrast to the alloying elements mainly by excretion formation but can also affect the properties in a dissolved state. Despite the small quantity additions, micro-alloying elements strongly influence the production conditions as well as the processing and final properties.
- micro-alloying elements carbide and nitride formers which are generally soluble in the iron lattice are used. Formation of carbonitrides is also possible because of the complete solubility of nitrides and carbides in one another. The tendency to form oxides and sulfides is usually most pronounced in the case of the micro-alloying elements, but as a rule it is purposefully prevented on account of other alloying elements.
- This property can be used positively by binding the generally harmful elements sulfur and oxygen.
- the setting may also have negative effects, if there are not enough micro-alloying elements for the formation of carbides available.
- Typical micro-alloying elements are aluminum, vanadium, titanium, niobium and boron. These elements can be dissolved in the iron lattice and form carbides and nitrides with carbon and nitrogen.
- Aluminum (Al) is usually added to the steel to bind the dissolved oxygen in the iron and nitrogen.
- the oxygen and nitrogen is thus converted into aluminum oxides and aluminum nitrides. These precipitations can cause a grain refining by increasing the germination sites and thus increase the toughness properties and strength values.
- Titanium nitrides have a lower formation enthalpy and are formed at higher temperatures.
- aluminum such as silicon shifts ferrite formation to shorter times, allowing the formation of sufficient ferrite in dual phase steel. It also suppresses carbide formation and thus leads to a delayed transformation of austenite. For this reason, aluminum is also used as an alloying element in retained austenitic steels to substitute part of the silicon with aluminum. The reason for this approach is that aluminum is somewhat less critical to the galvanizing reaction than silicon.
- the aluminum content is therefore limited to 0.010 to a maximum of 0.060%.
- Niobium (Nb) In addition to the above-described effect of widening the process window by delayed phase transformation in continuous annealing, niobium causes a high grain refining because it most effectively retards recrystallization of all the micro-alloying elements and also inhibits austenite grain growth.
- the strength-enhancing effect is qualitatively higher than that of titanium, as evidenced by the increased grain refining effect and the greater amount of strength-enhancing particles (bonding of the titanium to TiN at high temperatures).
- Niobium carbides form at temperatures below 1200 ° C. In the case of nitrogen bonding with titanium, niobium can be effective in forming small and effective ones Carbides in the lower temperature range (smaller carbide sizes) increase its strength-increasing effect.
- niobium Another effect of niobium is the retardation of the ⁇ / ⁇ conversion and the lowering of the martensite start temperature in the dissolved state. On the one hand this happens through the solute drag effect and on the other hand through the grain refining. This causes an increase in strength of the structure and thus a higher resistance to the increase in volume during martensite formation.
- the precipitation hardening can thus be effectively effective especially for steels with a low carbon content (greater supersaturation possible) and in hot forming processes (deformation-induced precipitation).
- the niobium content is therefore limited to values between 0.005 and 0.025%, wherein the contents are advantageously limited to ⁇ 0.005 to ⁇ 0.020% for cost reasons.
- vanadium content is limited to unavoidable steel accompanying amounts.
- the annealing temperatures for the dual-phase structure to be achieved are between about 700 and 950 ° C. for the steel according to the invention, thus achieving a recrystallized (single-phase region), partially austenitic (two-phase) or fully austenitic microstructure (austenite region) depending on the temperature range.
- the hot-dip coated material can be produced both as a hot strip and as a cold rolled hot strip or cold strip in the dressed (cold rolled) or undressed state and / or stretch bending or non-stretch bent state.
- Steel strips in the present case as hot strip, cold rolled hot strip or cold strip made of the alloy composition according to the invention are also characterized in the further processing by a high resistance to near-edge cracking.
- the hot strip according to the invention with Endwalztemperaturen in austenitic area above A c3 and reel temperatures above the bainite start temperature generated.
- FIG. 1 shows schematically the process chain for the production of the steel according to the invention. Shown are the different process routes relating to the invention. Up to position 5 (pickle) the process route is the same for all steels according to the invention, after which deviating process routes take place depending on the desired results.
- the pickled hot strip can be galvanized or cold rolled and galvanized. Or it can be annealed cold-rolled and galvanized.
- FIG. 2 shows results of a hole expansion test (relative values in comparison). Shown are the results of the hole widening tests for a steel according to the invention (variant 1, see FIG. 3 ) compared to the standard grades, the standard grade is Process 1 as reference. All materials have a sheet thickness of 2.50mm. The results apply to the test according to ISO 16630. It can be seen that the steels according to the invention achieve better expansion values for punched holes than the standard grades with the same processing.
- Process 1 here corresponds to annealing, for example, on a hot-dip galvanizing with a combined directly fired furnace and radiant tube furnace, as it is known in FIG. 9b is described.
- the process 2 corresponds for example to a process control in a continuous annealing plant, as in FIG.
- FIG. 3 shows the relevant alloying elements of the steel according to the invention over the standard grade, which exemplifies the state of the art.
- the comparative steel which corresponds to the state of the art
- the main difference lies in the carbon content, which lies in the super-architectural range, but also in the elements silicon, manganese and chromium.
- the standard grade is phosphorus-microalloyed.
- the steels of the invention are niobium-microalloyed and have a significantly increased manganese content.
- FIG. 4a shows the mechanical characteristics transverse and longitudinal to the rolling direction of the steel according to the invention, for example in its variant 1, 2 and 3, in comparison with the standard grade, which represents the prior art by way of example. All characteristic values achieved by annealing in the two-phase area correspond to the normative specification of an HCT600X.
- FIG. 4b Shows the mechanical characteristic values transverse to the rolling direction of the steel according to the invention, by way of example in its variants 1, 2 and 3, which was determined by a regression calculation. Shown are the mechanical characteristics depending on the band thickness related Mangangehaltvariationen (invention variants 1,2 and 3). All characteristic values correspond to the normative specification. The yield ratio is significantly below 67% for all variants.
- Figure 4c shows the mechanical characteristics transverse to the rolling direction and the chemical composition of the steel according to the invention, in its variant 1, with a material thickness of 0.77 mm and an annealing below the beginning of the two-phase region (eg A c1 - about 20 ° C) in comparison with the Standard quality, which exemplifies the state of the art. All characteristic values correspond to the normative specification of a HCT780X, ie the next higher strength class with reference to the HCT600X.
- FIG. 4d shows the mechanical characteristics transverse to the rolling direction and the chemical composition of the steel according to the invention (variant 1) with a material thickness of 2.50 mm and an annealing above A c3 . All characteristics correspond to the normative specification of a HDT580X.
- FIG. 5 shows schematically the time-temperature curve of the process steps hot rolling and continuous annealing of strips of the alloy composition according to the invention. Shown is the time- and temperature-dependent conversion for the hot rolling process as well as for a heat treatment after cold rolling, by way of example for variant 1.
- FIG. 6 Shows a schematic CCT diagram for the inventive steel, differentiated according to the variation 1, 2 and 3.
- the calculated CCT diagram with the corresponding chemical composition (varying only by levels of manganese) and the A c1 and A c3 temperature shown By setting appropriate temperature-time profiles during cooling, it is advantageously possible to set a broad spectrum of microstructural compositions in the steel material.
- Of particular interest here is the shift of ferrite nose, perlitnase and bainitic nose at later times in the staggered increase in manganese contents.
- the potential is made possible to set similar microstructural proportions over the entire thickness spectrum considered at a system speed that depends on the strip thickness.
- FIG. 7 shows the mechanical characteristics along the rolling direction with the same parameters of continuously annealed strips with varying degrees of rolling or different strip thickness in an exemplary consideration of variant 1. Shown are the characteristics of tensile strength, yield strength and elongation at break depending on selected degrees of reduction. Only the tensile strength increases with increasing Abwalzgrad. All values up to 30% reduction rate are in the range of the standard for a HCT600X. Higher degrees of finishing (greater than 75%) lead to a change in the steel grades towards HCT780X, with minimum strengths of 780 MPa.
- FIG. 8 shows an overview of the strength classes that can be set using the alloy concept according to the invention (variant 1).
- the alloy composition used corresponds to that in the FIG. 3 shown. Shown are the differently processed steel strips with their characteristics along the rolling direction and microstructural compositions. This clearly indicates the range of adjustable strength classes for hot and cold strip with the resulting microstructure constituents depending on the process steps carried out and the process parameters set.
- the Figures 9 show schematically the temperature-time courses in the annealing and cooling with three different variants and each different austenitization conditions according to the claims for registered method.
- the method 1 shows the annealing and cooling of the produced cold or hot rolled steel strip in a continuous annealing system.
- a temperature in the range of 700 to 950 ° C we heated the strip to a temperature in the range of 700 to 950 ° C.
- the annealed steel strip is then cooled from the annealing temperature at a cooling rate between 15 and 100 ° C / s to an intermediate temperature of approximately 200 to 250 ° C.
- a second intermediate temperature about 300 to 500 ° C
- the steel strip is cooled at a cooling rate between 2 and 30 ° C / s until it reaches room temperature in air or the cooling at a cooling rate between 15 and 100 ° C / s is maintained up to room temperature.
- the method 2 ( FIG. 9b ) shows the process according to method 1, but the cooling of the steel strip for the purpose of a hot dipping refinement is briefly interrupted when passing through the hot dipping vessel, then the cooling at a cooling rate between 15 and 100 ° C / s up to an intermediate temperature of 200 to 250 ° C. continue. Subsequently, the steel strip is cooled at a cooling rate between 2 and 30 ° C / s until it reaches room temperature in air.
- the method 3 ( FIG. 9c ) also shows the process according to method 1 in a hot dipping refinement, but the cooling of the steel strip is interrupted by a short break ( about 1 to 20 s) at an intermediate temperature in the range of 200 to 250 ° C and up to the temperature which refines to hot dipping necessary ( about 420 to 470 ° C) reheated. Subsequently, the steel strip is again cooled to an intermediate temperature of 200 to 250 ° C. At a cooling rate of 2 and 30 ° C / s, the final cooling of the steel strip takes place until air reaches the room temperature.
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Description
Die Erfindung betrifft einen hochfesten Mehrphasenstahl gemäß dem Oberbegriff des Anspruchs 1.The invention relates to a high-strength multiphase steel according to the preamble of
Des Weiteren betrifft die Erfindung ein Verfahren zur Herstellung eines warm- oder kaltgewaltzten Bandes aus einem solchen Stahl gemäß Patentanspruch 6.Furthermore, the invention relates to a method for producing a hot or cold rolled strip of such a steel according to
Insbesondere betrifft die Erfindung Stähle mit Zugfestigkeiten im Bereich von 580-900 MPa mit niedrigen Streckgrenzenverhältnissen von unter 67% zur Herstellung von Bauteilen, die eine hervorragende Umformbarkeit und Schweißeigenschaften aufweisen.In particular, the invention relates to steels with tensile strengths in the range of 580-900 MPa with low yield ratio of less than 67% for the production of components which have excellent formability and welding properties.
Der heiß umkämpfte Automobilmarkt zwingt die Hersteller ständig nach Lösungen zur Senkung des Flottenverbrauches unter Beibehaltung eines größtmöglichen Komforts und Insassenschutzes zu suchen. Dabei spielt einerseits die Gewichtsersparnis aller Fahrzeugkomponenten eine entscheidende Rolle andererseits aber auch ein möglichst günstiges Verhalten der einzelnen Bauteile bei hoher statischer und dynamischer Beanspruchung im Betrieb wie auch im Crashfall. Dieser Notwendigkeit versuchen die Vormaterial-Lieferanten dadurch Rechnung zu tragen, dass durch die Bereitstellung hochfester und höchstfester Stähle und die Reduzierung der Blechdicke das Gewicht der Fahrzeuge reduziert werden kann, bei gleichzeitig verbessertem Umform- und Bauteilverhalten bei der Fertigung und im Betrieb.The hotly contested automotive market is forcing manufacturers to constantly seek solutions to reduce fleet consumption while maintaining maximum comfort and occupant safety. On the one hand, the weight saving of all vehicle components plays a decisive role, on the other hand, but also a most favorable behavior of the individual components with high static and dynamic stress during operation as well as in the event of a crash. The suppliers of raw material suppliers are trying to meet this need by reducing the weight of the vehicles by providing high-strength and ultra-high-strength steels and reducing the sheet thickness, while at the same time improving forming and component behavior during production and operation.
Hochfeste und höherfeste Stähle ermöglichen leichtere Fahrzeugkomponenten (z.B. PKW, LKW), folgerichtig damit verbunden ist ein geringerer Kraftstoffverbrauch. Über den damit reduzierten CO2 Anteil wird die Umweltbelastung vermindert.High-strength and higher-strength steels enable lighter vehicle components (eg cars, trucks), which consequently results in lower fuel consumption. The reduced CO 2 content reduces the environmental impact.
Diese Stähle müssen daher vergleichsweise hohen Anforderungen hinsichtlich ihrer Festigkeit und Duktilität, Energieaufnahme und bei ihrer Verarbeitung, wie beispielsweise beim Stanzen, der Warm- und Kaltumformung, dem Schweißen und/oder der Oberflächenveredelung (z.B. metallisch veredelt, organisch beschichtet, lackieren) genügen.These steels must therefore meet relatively high requirements in terms of their strength and ductility, energy absorption and in their processing, such as punching, hot and cold forming, welding and / or surface finishing (e.g., metallized, organically coated, painted).
Neu entwickelte Stähle müssen sich somit den Anforderungen nach der geforderten Gewichtsreduzierung, den zunehmenden Materialanforderungen an Dehngrenze, Zugfestigkeit und Bruchdehnung bei guter Umformbarkeit stellen, wie auch den Bauteilanforderungen nach hoher Zähigkeit, Kantenrissunempfindlichkeit, Energieabsorption sowie Festigkeit über den Work-Hardening-Effekt und den Bake-Hardening-Effekt, aber auch verbesserter Fügeeignung in Form von z.B. verbesserte Schweißbarkeit.Newly developed steels must therefore meet the requirements for the required weight reduction, the increasing material requirements for yield strength, Tensile strength and elongation at break with good formability, as well as the component requirements for high toughness, edge crack resistance, energy absorption and strength on the work-hardening effect and the bake-hardening effect, but also improved joining suitability in the form of eg improved weldability.
Verbesserte Kantenrißunempfindlichkeit bedeutet erhöhte Lochaufweitung und ist durch Synonyme, wie High Hole Expansion (HHE) bzw. Low Edge Crack (LEC) bekannt.Improved edge tear resistance means increased hole widening and is known by synonyms such as High Hole Expansion (HHE) and Low Edge Crack (LEC).
Verbesserte Schweißbarkeit wird u.a. durch ein abgesenktes Kohlenstoffäquivalent erreicht. Dafür stehen Synonyme, wie Low Carbon Equivalent (LCE) bzw. Under Peritectical (UP).Improved weldability is u.a. achieved by a lowered carbon equivalent. For synonyms, such as Low Carbon Equivalent (LCE) or Under Peritectical (UP).
Im Fahrzeugbau finden daher zunehmend Dualphasenstähle Anwendung, die aus einem ferritischen Grundgefüge bestehen, in das eine martensitische Zweitphase und möglicherweise eine weitere Phase mit Bainit und Restaustenit eingelagert ist.In vehicle construction, therefore, dual-phase steels are increasingly being used, which consist of a ferritic basic structure in which a martensitic second phase and possibly a further phase with bainite and retained austenite are incorporated.
Der Bainit kann in unterschiedlichen Erscheinungsformen vorliegen.The bainite can be present in different forms.
Die die Stahlsorten bestimmenden Verarbeitungseigenschaften der Dualphasenstähle, wie ein sehr niedriges Streckgrenzenverhältnis bei gleichzeitig sehr hoher Zugfestigkeit, eine starke Kaltverfestigung und eine gute Kaltumformbarkeit, sind hinreichend bekannt.The steel grades determining processing characteristics of dual-phase steels, such as a very low yield ratio and at the same time very high tensile strength, a strong work hardening and a good cold workability, are well known.
Mit steigender Tendenz finden auch Mehrphasenstähle Anwendung, wie Complexphasenstähle, ferritisch-bainitische Stähle, bainitische Stähle sowie martensitische Stähle, die durch unterschiedliche Gefügezusammensetzungen charakterisiert sind wie in der EN 10346 beschrieben.Multiphase steels such as complex-phase steels, ferritic-bainitic steels, bainitic steels and martensitic steels, which are characterized by different microstructural compositions as described in EN 10346, are also used with increasing tendency.
Complexphasenstähle sind Stähle, die kleine Anteile von Martensit, Restaustenit und/oder Perlit in einem ferritisch/bainitischen Grundgefüge enthalten, wobei durch eine verzögerte Rekristallisation oder durch Ausscheidungen von Mikrolegierungselementen eine extreme Kornverfeinerung bewirkt wird. Complex-phase steels are steels which contain small amounts of martensite, retained austenite and / or pearlite in a ferritic / bainitic matrix, whereby extreme grain refinement is brought about by delayed recrystallization or by precipitation of micro-alloying elements.
Ferritisch-bainitische Stähle sind Stähle, die Bainit oder verfestigten Bainit in einer Matrix aus Ferrit und/oder verfestigten Ferrit enthalten. Ferritic-bainitic steels are steels that contain bainite or solidified bainite in a matrix of ferrite and / or solidified ferrite.
Die Verfestigung der Matrix wird durch eine hohe Versetzungsdichte, durch Kornfeinung und die Ausscheidung von Mikrolegierungselementen bewirkt.The solidification of the matrix is effected by a high dislocation density, by grain refining and the excretion of micro-alloying elements.
Bainitische Stähle sind Stähle, die sich durch eine sehr hohe Streckgrenze und Zugfestigkeit bei einer ausreichend hohen Dehnung für Kaltumformprozesse auszeichnen. Aufgrund der chemischen Zusammensetzung ist eine gute Schweißbarkeit gegeben. Das Gefüge besteht typischerweise aus Bainit. Vereinzelt können geringe Anteile anderer Phasen, wie z. B. Martensit und Ferrit, enthalten sein. Bainitic steels are steels that are characterized by a very high yield strength and tensile strength at a sufficiently high elongation for cold forming processes. Due to the chemical composition a good weldability is given. The microstructure typically consists of bainite. Occasionally, small amounts of other phases, such as. As martensite and ferrite.
Martensitische Stähle sind Stähle, die durch thermomechanisches Walzen kleine Anteile von Ferrit und/oder Bainit in einem Grundgefüge aus Martensit enthalten. Die Stahlsorte zeichnet sich durch eine sehr hohe Streckgrenze und Zugfestigkeit bei einer ausreichend hohen Dehnung für Kaltumformprozesse aus. Innerhalb der Gruppe der Mehrphasenstähle weisen die martensitischen Stähle die höchsten Zugfestigkeitswerte auf. Martensitic steels are steels that contain small amounts of ferrite and / or bainite in a matrix of martensite due to thermomechanical rolling. The steel grade is characterized by a very high yield strength and tensile strength at a sufficiently high elongation for cold forming processes. Within the group of multiphase steels, the martensitic steels have the highest tensile strength values.
Zum Einsatz kommen diese Stähle u. a. in Struktur-, Fahrwerks- und crashrelevanten Bauteilen, sowie als flexibel kaltgewalzte Bänder. Diese Tailor Rolled Blank Leichtbau-Technologie (TRB®) ermöglicht eine signifikante Gewichtsreduktion durch die belastungsangepasste Wahl der Blechdicke über die Bauteillänge.These steels are used, among other things, in structural, chassis and crash-relevant components, as well as flexibly cold-rolled strips. These T Ailor R olled B lank lightweight technology (TRB®) allows a significant weight reduction by the load customized choice of thickness greater than the length of the component.
Die Herstellung von TRB®s mit Mehrphasengefüge ist mit heute bekannten Legierungen und verfügbaren kontinuierlichen Glühanlagen für stark variierende Banddicken allerdings nicht ohne Einschränkungen, wie z.B. für die Wärmebehandlung vor dem Kaltwalzen, möglich. In Bereichen unterschiedlicher Banddicke, d.h. bei Vorliegen unterschiedlicher Kaltabwalzgrade, kann aufgrund eines bei den gängigen Prozessfenstern auftretenden Temperaturgefälles kein homogenes mehrphasiges Gefüge in kalt- wie auch warmgewalzten Stahlbändern eingestellt werden.The fabrication of TRB®s with multiphase structure is not without limitations, however, with currently known alloys and available continuous annealing equipment for widely varying tape thicknesses. for the heat treatment before cold rolling, possible. In areas of different tape thickness, i. in the presence of different Kaltabwalzgrade, due to a temperature gradient occurring in the common process windows no homogeneous multi-phase microstructure can be set in cold- as well as hot-rolled steel strips.
Üblicherweise werden kaltgewalzte hochfeste Stahlbänder aus wirtschaftlichen Gründen im Durchlaufglühverfahren rekristallisierend zu gut umformbarem Feinblech geglüht. Abhängig von der Legierungszusammensetzung und dem Bandquerschnitt werden die Prozessparameter, wie Durchlaufgeschwindigkeit, Glühtemperaturen und Abkühlgeschwindigkeit, entsprechend den geforderten mechanisch-technologischen Eigenschaften mit dem dafür notwendigen Gefüge eingestellt.Usually, cold-rolled high-strength steel strips are annealed by recrystallization in a continuous annealing process to give a readily deformable thin sheet for economic reasons. Depending on the alloy composition and the strip cross-section, the process parameters, such as throughput speed, annealing temperatures and cooling rate, are set according to the required mechanical and technological properties with the necessary structure.
Zur Einstellung des Dualphasengefüges wird das Warmband, in typischen Dicken zwischen 1,50mm bis 4,00mm oder Kaltband, in typischen Dicken von 0,50mm bis 3,00mm, im Durchlaufglühofen auf eine solche Temperatur aufgeheizt, dass sich während der Abkühlung die geforderte Gefügeausbildung einstellt. Gleiches gilt für die Einstellung eines Stahls mit Complexphasengefüge, martensitischem, ferritisch-bainitischem sowie rein bainitischem Gefüge.To set the dual-phase microstructure, the hot strip, in typical thicknesses between 1.50 mm to 4.00 mm or cold strip, in typical thicknesses of 0.50 mm to 3.00 mm, heated in a continuous annealing furnace to a temperature such that during cooling the required microstructure established. The same applies to the setting of a steel with Complex phase structure, martensitic, ferritic-bainitic and purely bainitic structure.
In der kontinuierlichen Glühanlage findet eine spezielle Wärmebehandlung statt, wo z.B. durch vergleichsweise weiche Bestandteile, wie Ferrit bzw. bainitischer Ferrit der Stahl seine geringe Streckgrenze und durch seine harten Bestandteile, wie Martensit bzw. kohlenstoffreicher Bainit seine Festigkeit erhält.In the continuous annealing plant, a special heat treatment takes place, where e.g. By comparatively soft components, such as ferrite or bainitic ferrite, the steel its low yield strength and its hard constituents, such as martensite or carbon-rich bainite its strength.
Wenn aufgrund hoher Korrosionsschutzanforderungen die Oberfläche des Warm- oder Kaltbandes schmelztauchverzinkt werden soll, erfolgt die Glühbehandlung üblicherweise in einem dem Verzinkungsbad vorgeschalteten Durchlaufglühofen.If, due to high corrosion protection requirements, the surface of the hot or cold strip is to be hot dip galvanized, the annealing treatment is usually carried out in a continuous annealing furnace upstream of the galvanizing bath.
Auch beim Warmband wird fallweise je nach Legierungskonzept das geforderte Gefüge erst bei der Glühbehandlung im Durchlaufofen eingestellt, um die geforderten mechanischen Eigenschaften zu realisieren.Depending on the alloy concept, the required microstructure of the hot strip may also be adjusted in the continuous furnace during the annealing treatment, in order to achieve the required mechanical properties.
Beim Durchlaufglühen von warm- oder kaltgewalzten Stahlbändern mit z.B. aus der
Bei dem aus der
Bei ausgeweiteten Prozessfenstern sind bei gleichen Prozessparametern die geforderten Bandeigenschaften auch bei größeren Querschnittsänderungen der zu glühenden Bänder möglich.With expanded process windows, the required strip properties are possible with the same process parameters, even with larger cross-sectional changes of the strips to be annealed.
Dies gilt neben flexibel gewalzten Bändern mit unterschiedlichen Banddicken über die Bandlänge vor allen Dingen auch bei Bändern mit unterschiedlicher Dicke und/oder unterschiedlicher Breite, die nacheinander geglüht werden müssen.This applies in addition to flexibly rolled strips with different strip thicknesses over the strip length above all, even with strips of different thickness and / or different width, which must be annealed successively.
Eine homogene Temperaturverteilung ist gerade bei unterschiedlichen Dicken im Übergangsbereich von einem Band zum anderen nur schwierig zu erreichen. Dies kann bei Legierungszusammensetzungen mit zu kleinen Prozessfenstern bei der Durchlaufglühung dazu führen, dass z.B. das dünnere Band entweder zu langsam durch den Ofen gefahren wird und dadurch die Produktivität gesenkt wird, oder dass das dickere Band zu schnell durch den Ofen gefahren wird und die notwendigen Glühtemperaturen und Kühlgradienten zur Erreichung des gewünschten Gefüges nicht erreicht wird. Die Folgen sind vermehrter Ausschuss mit entsprechenden Fehlleistungskosten.A homogeneous temperature distribution is difficult to achieve, especially at different thicknesses in the transition region from one belt to another. This can result in alloy compositions with too small process windows in the continuous annealing, e.g. the thinner belt is either driven too slowly through the furnace and thereby the productivity is lowered, or that the thicker belt is driven too fast through the furnace and the necessary annealing temperatures and cooling gradients to achieve the desired structure is not achieved. The consequences are increased rejects with corresponding costs of misconduct.
Der entscheidende Prozessparameter ist somit die Einstellung der Geschwindigkeit bei der Durchlaufglühung, da die Phasenumwandlung temperatur- und zeitabhängig abläuft. Je unempfindlicher der Stahl in Bezug auf die Gleichmäßigkeit der mechanischen Eigenschaften bei Änderungen im Temperatur- und Zeitverlauf bei der Durchlaufglühung ist, desto größer ist somit das Prozessfenster.The decisive process parameter is thus the setting of the speed in the continuous annealing, since the phase transformation takes place depending on temperature and time. The less sensitive the steel in terms of the uniformity of the mechanical properties with changes in the temperature and time course during the continuous annealing, the larger the process window.
Besonders gravierend wird das Problem eines sehr engen Prozessfensters bei der Glühbehandlung, wenn belastungsoptimierte Bauteile aus Warm- oder Kaltband hergestellt werden sollen, die über die Bandlänge und Bandbreite (z.B. durch flexibles Walzen) variierende Banddicken aufweisen.The problem of a very narrow process window in the annealing treatment becomes particularly serious when load-optimized components are to be produced from hot or cold strip which have varying strip thicknesses over the strip length and bandwidth (for example due to flexible rolling).
Ein Verfahren zur Herstellung eines Stahlbandes mit unterschiedlicher Dicke über die Bandlänge wird z. B. in der
Bei Anwendung der bekannten Legierungskonzepte für die Gruppe der Mehrphasenstähle ist es aufgrund des engen Prozessfensters schon beim Durchlaufglühen unterschiedlich dicker Bänder nur schwer möglich, über die gesamte Bandlänge des Bandes gleichmäßige mechanische Eigenschaften zu erreichen.When using the known alloy concepts for the group of multiphase steels, it is difficult to achieve uniform mechanical properties over the entire strip length of the strip due to the narrow process window already in the continuous annealing of different thickness tapes.
Bei flexibel gewalzten Kaltbändern aus Mehrphasenstählen bekannter Zusammensetzungen weisen, wegen des zu kleinen Prozessfensters, die Bereiche mit geringerer Banddicke aufgrund der Umwandlungsvorgänge bei der Abkühlung entweder zu hohe Festigkeiten durch zu große Martensitanteile auf oder die Bereiche mit größerer Banddicke erreichen zu geringe Festigkeiten durch zu geringe Martensitanteile. Homogene mechanisch-technologische Eigenschaften über die Bandlänge oder -breite sind mit den bekannten Legierungskonzepten beim Durchlaufglühen praktisch nicht zu erreichen.For flexibly rolled cold strips of multiphase steels of known compositions, because of the too small process window, the areas with lower strip thickness due to the transformation processes during cooling either too high strengths due to excessive martensite or on areas with larger strip thickness to low strengths due to low martensite , Homogeneous mechanical-technological properties over the strip length or width are virtually impossible to achieve with the known alloy concepts in continuous annealing.
Das Ziel, die resultierenden mechanisch-technologischen Eigenschaften in einem engen Bereich über Bandbreite und Bandlänge durch die gesteuerte Einstellung der Volumenanteile der Gefügephasen zu erreichen, hat oberste Priorität und ist deshalb nur durch ein vergrößertes Prozessfenster möglich. Die bekannten Legierungskonzepte für Mehrphasenstähle sind durch ein zu enges Prozessfenster charakterisiert und deshalb zur Lösung der vorliegenden Problematik, insbesondere bei flexibel gewalzten Bändern, ungeeignet. Mit den bekannten Legierungskonzepten sind derzeit nur Stähle einer Festigkeitsklasse mit definierten Querschnittsbereichen (Banddicke und Bandbreite) darstellbar, so dass für unterschiedliche Festigkeitsklassen und oder Querschnittsbereiche veränderte Legierungskonzepte notwendig sind.The goal of achieving the resulting mechanical and technological properties in a narrow range over bandwidth and strip length by the controlled adjustment of the volume fractions of the structural phases has top priority and is therefore only possible through an enlarged process window. The known alloy concepts for multiphase steels are characterized by too narrow a process window and therefore unsuitable for solving the present problem, in particular in flexibly rolled strips. At present, only steels of a strength class with defined cross-sectional areas (strip thickness and strip width) can be represented with the known alloy concepts, so that altered alloy concepts are necessary for different strength classes and / or cross-sectional areas.
Stand der Technik ist, dass eine Zunahme der Festigkeit durch das mengenmäßige Steigern von Kohlenstoff und/oder Silizium und/oder Mangan und eine Zunahme der Festigkeit über die Gefügeeinstellungen und die Mischkristallverfestigung (Mischkristallhärtung) bei angepasster Temperaturführung erreicht wird.The state of the art is that an increase in strength is achieved by the increase in the quantity of carbon and / or silicon and / or manganese and an increase in the strength via the microstructural adjustments and the solid solution hardening (mixed crystal hardening) with adapted temperature control.
Durch die Mengensteigerung der vorgenannten Elemente verschlechtern sich jedoch zunehmend die Materialverarbeitungseigenschaften, beispielsweise beim Schweißen, Umformen und Schmelztauchveredeln.Increasing the quantity of the aforementioned elements, however, causes the material processing properties to deteriorate, for example during welding, forming and hot dipping.
Bei der Stahlherstellung zeigt sich allerdings auch ein Trend zur Reduzierung des Kohlenstoff- und/oder Mangangehaltes, um eine verbesserte Kaltverarbeitbarkeit sowie bessere Gebrauchseigenschaften zu erreichen.However, in steelmaking, there is also a trend toward reducing carbon and / or manganese content to achieve improved cold workability and better performance.
Zur Beschreibung und Quantifizierung des Kantenrissverhaltens findet der Lochaufweitungstest nach ISO 11630 als eins von mehreren möglichen Prüfverfahren Anwendung.For the description and quantification of the edge cracking behavior, the hole expansion test according to ISO 11630 is used as one of several possible test methods.
Bei entsprechend optimierten Güten erwartet der Stahlanwender höhere Werte als beim Standardmaterial. Aber auch die Schweißeignung charakterisiert durch das Kohlenstoffäquivalent, rückt weiter in den Fokus.With suitably optimized grades, the steel user expects higher values than with the standard material. But also the weldability characterized by the carbon equivalent, moves further into focus.
Ein niedriges Streckgrenzenverhältnis (Re/Rm) ist typisch für einen Dualphasenstahl und dient vor allem der Umformbarkeit bei Streck- und Tiefziehvorgängen. Dieses gibt dem Konstrukteur Auskunft über den Abstand zwischen einsetzender plastischer Deformation und Versagen des Werkstoffes bei quasistatischer Beanspruchung. Dementsprechend stellen niedrigere Streckgrenzenverhältnisse einen größeren Sicherheitsabstand zum Bauteilversagen dar.A low yield ratio (Re / Rm) is typical for a dual-phase steel and is used primarily for formability in drawing and deep drawing operations. This gives the designer information about the distance between onset of plastic deformation and failure of the material under quasistatic stress. Ask accordingly lower yield ratio ratios provide a greater safety margin for component failure.
Ein höheres Streckgrenzenverhältnis (Re/Rm) wie es für Komplexphasenstähle typisch ist, zeichnet sich auch durch den Widerstand gegen Kantenrisse aus. Dies lässt sich auf die geringeren Unterschiede in den Festigkeiten der einzelnen Gefügebestandteile zurückführen, was sich günstig auf eine homogene Verformung im Bereich der Schnittkante auswirkt.A higher yield ratio (Re / Rm), which is typical for complex phase steels, is also distinguished by resistance to edge cracks. This can be attributed to the smaller differences in the strengths of the individual structural components, which has a favorable effect on a homogeneous deformation in the area of the cutting edge.
Die analytische Landschaft zur Erreichung von Mehrphasenstählen mit Mindestzugfestigkeiten von 580 MPa ist sehr vielfältig geworden und zeigt sehr große Legierungsbereiche bei den festigkeitssteigernden Elementen Kohlenstoff, Silizium, Mangan, Phosphor, Aluminium sowie Chrom und/oder Molybdän, wie auch in der Zugabe von Mikrolegierungen, wie Titan und Vanadium, sowie in den materialcharakterisierenden Eigenschaften.The analytical landscape for achieving multi-phase steels with minimum tensile strengths of 580 MPa has become very diverse and shows very large alloy areas in the strength-increasing elements carbon, silicon, manganese, phosphorus, aluminum and chromium and / or molybdenum, as well as in the addition of microalloys such Titanium and vanadium, as well as in the material-characterizing properties.
Das Abmessungsspektrum ist breit und liegt im Dickenbereich von etwa 0,50 bis 4,00mm. Es finden überwiegend Bänder bis etwa 1850mm Anwendung, aber auch Spaltbandabmessungen, die durch Längsteilen der Bänder entstehen. Bleche bzw. Tafeln werden durch Querteilen der Bänder gefertigt.The range of dimensions is broad and lies in the thickness range of about 0.50 to 4.00 mm. It can be found mainly bands up to about 1850mm application, but also slit strip dimensions caused by longitudinal parts of the bands. Sheets or sheets are made by cutting the strips.
Der Erfindung liegt daher die Aufgabe zugrunde, ein neues Legierungskonzept für einen hochfesten Mehrphasenstahl mit einer Mindestzugfestigkeit von 580 MPa längs und quer zur Walzrichtung, vorzugsweise mit Dualphasengefüge und einem Streckgrenzenverhältnis von weniger als 67%, mit dem das Prozessfenster für die Durchlaufglühung von Warm- oder Kaltbändern so erweitert werden kann, dass neben Bändern mit unterschiedlichen Querschnitten auch Stahlbänder mit über Bandlänge und ggf. Bandbreite variierender Dicke, und den damit entsprechend variierenden Kaltabwalzgraden, mit möglichst homogenen mechanisch-technologischen Eigenschaften erzeugt werden können. Außerdem soll ein Verfahren zur Herstellung eines aus diesem Stahl hergestellten Bandes angegeben werden.The invention is therefore based on the object, a new alloy concept for a high-strength multiphase steel with a minimum tensile strength of 580 MPa longitudinal and transverse to the rolling direction, preferably with dual-phase structure and a yield ratio of less than 67%, with the process window for the continuous annealing of hot or Cold bands can be extended so that in addition to bands with different cross sections and steel bands with over tape length and possibly bandwidth varying thickness, and thus the correspondingly varying degrees of cold rolling, can be produced with the most homogeneous mechanical and technological properties. In addition, a method for producing a strip made from this steel is to be specified.
Nach der Lehre der Erfindung wird diese Aufgabe gelöst durch einen Stahl mit folgenden Gehalten in Gewichts-%:
Rest Eisen, einschließlich erschmelzungsbedingter Verunreinigungen.Remaining iron, including contaminants due to melting.
Der erfindungsgemäße Stahl bietet den Vorteil eines deutlich vergrößerten Prozessfensters im Vergleich zu den bekannten Stählen. Daraus resultiert eine erhöhte Prozesssicherheit beim Durchlaufglühen von Kalt- und Warmband mit Dualphasengefüge. Somit können für durchlaufgeglühte Warm- oder Kaltbänder homogenere mechanisch-technologische Eigenschaften im Band auch bei unterschiedlichen Querschnitten und sonst gleichen Prozessparametern gewährleistet werden.The steel according to the invention offers the advantage of a significantly enlarged process window in comparison to the known steels. This results in an increased process reliability in the continuous annealing of cold and hot strip with dual-phase structure. Thus, homogenized mechanical-technological properties in the strip can be ensured for pass-annealed hot or cold strips even with different cross sections and otherwise identical process parameters.
Dies gilt für das Durchlaufglühen aufeinander folgender Bänder mit unterschiedlichen Bandquerschnitten wie auch für Bänder mit variierender Banddicke über Bandlänge bzw. Bandbreite. Z.B. ist damit eine Prozessierung in ausgewählten Dickenbereichen möglich (z.B., wie kleiner 1mm Banddicke, 1 bis 2mm Banddicke und 2 bis 4mm Banddicke).This applies to the continuous annealing of successive belts with different belt cross-sections as well as belts with varying belt thickness over belt length or belt width. For example, Thus, a processing in selected thickness ranges is possible (for example, such as smaller 1mm tape thickness, 1 to 2mm tape thickness and 2 to 4mm tape thickness).
Werden erfindungsgemäß im Durchlaufglühverfahren erzeugte höherfeste Warm- oder Kaltbänder aus Mehrphasenstahl mit variierenden Banddicken erzeugt, können aus diesem Material vorteilhaft belastungsoptimierte Bauteile umformtechnisch hergestellt werden.If higher-strength hot or cold strips produced from multiphase steel with varying strip thicknesses produced by the continuous annealing process according to the invention are advantageously produced from this material, stress-optimized components can be produced by forming technology.
Das erzeugte Material kann sowohl als Kalt- wie auch als Warmband über eine Feuerverzinkungslinie oder eine reine Durchlaufglühanlage erzeugt werden im dressierten und undressierten und auch im wärmebehandelten Zustand (Zwischenglühen).The material produced can be produced both as a cold strip and as a hot strip via a hot-dip galvanizing line or a pure continuous annealing plant in the dressed and undressed and also in the heat-treated state (intermediate annealing).
Gleichzeitig besteht die Option, durch gezielte Variierung der Prozessparameter die Gefügeanteile so einzustellen, dass Stähle in unterschiedlichen Festigkeitsklassen, wie HDT580X, HCT600X und HCT780X, z.B. nach EN 10346 herstellbar sind.At the same time, there is the option of adjusting the microstructural fractions by selective variation of the process parameters so that steels in different strength classes, such as HDT580X, HCT600X and HCT780X, e.g. can be produced according to
Die mit der erfindungsgemäßen Legierungszusammensetzung erzeugten Stahlbänder zeichnen sich bei der Fertigung eines Dualphasenstahles durch ein im Vergleich zum Standard deutlich breiteres Prozessfenster hinsichtlich Temperatur und Durchlaufgeschwindigkeit bei der interkritischen Glühung zwischen Ac1 und Ac3 bzw. bei einer austenitisierenden Glühung über Ac3 mit abschließender gesteuerter Abkühlung bzw. einer Glühung unterhalb des Beginn's des Zweiphasengebietes (z.B. Ac1 - zirka 20 °C) im Vergleich zu den bekannten Legierungskonzepten aus (siehe
Als vorteilhaft haben sich Glühtemperaturen von etwa 700 bis 950°C herausgestellt. Abhängig von dem Gesamtprozess gibt es unterschiedliche Ansätze zur Realisierung der Wärmebehandlung.Annealing temperatures of about 700 to 950 ° C have proved to be advantageous. Depending on the overall process, there are different approaches to realize the heat treatment.
Bei einer Durchlaufglühanlage ohne anschließende Schmelztauchveredelung wird das Band ausgehend von der Glühtemperatur mit einer Abkühlgeschwindigkeit von 15 bis 100°C/s auf eine Zwischentemperatur von 200 bis 250°C abgekühlt.In a continuous annealing plant without subsequent hot-dip finishing, the strip is cooled starting from the annealing temperature at a cooling rate of 15 to 100 ° C / s to an intermediate temperature of 200 to 250 ° C.
Erfindungsgemäß wird vorab mit einer Abkühlgeschwindigkeit von 15 bis 100°C/s auf eine vorherige Zwischentemperatur von 300 bis 500°C abgekühlt werden. Die Abkühlung bis zur Raumtemperatur erfolgt abschließend mit einer Abkühlgeschwindigkeit von 2 bis 30°C/s.According to the invention, it is previously cooled at a cooling rate of 15 to 100 ° C / s to a previous intermediate temperature of 300 to 500 ° C. The cooling to room temperature is finally carried out at a cooling rate of 2 to 30 ° C / s.
Bei einer Wärmebehandlung im Rahmen einer Schmelztauchveredelung gibt es zwei Möglichkeiten der Temperaturführung. Die Kühlung wie oben beschrieben wird vor dem Eintritt in das Schmelzbad angehalten und erst nach dem Austritt aus dem Bad bis zum Erreichen der Zwischentemperatur von 200 bis 250°C fortgesetzt. Abhängig von der Schmelzbadtemperatur ergibt sich dabei eine Haltetemperatur von zirka 420 bis 470°C. Die Abkühlung bis zur Raumtemperatur erfolgt wieder mit einer Abkühlgeschwindigkeit von 2 bis 30°C/s.In a heat treatment in the context of a hot dip refinement, there are two ways of temperature control. The cooling as described above is stopped before entering the molten bath and continued until after leaving the bath until reaching the intermediate temperature of 200 to 250 ° C. Depending on the molten bath temperature results in a holding temperature of about 420 to 470 ° C. The cooling to room temperature is again at a cooling rate of 2 to 30 ° C / s.
Die zweite Variante der Temperaturführung bei der Schmelztauchveredelung beinhaltet das Halten der Temperatur für zirka 1 bis 20s bei der Zwischentemperatur von 200 bis 250°C und ein anschließendes Wiedererwärmen auf die zur Schmelztauchveredelung benötigte Temperatur von zirka 420 bis 470°C. Das Band wird nach der Veredelung wieder auf 200 bis 250°C abgekühlt. Die Abkühlung auf Raumtemperatur erfolgt wieder mit einer Abkühlgeschwindigkeit von 2 bis 30°C/s.The second variant of the temperature control in the hot dip finishing involves holding the temperature for about 1 to 20 seconds at the intermediate temperature of 200 to 250 ° C and then reheating to the temperature required for hot dipping refinement of about 420 to 470 ° C. The strip is cooled after refining again to 200 to 250 ° C. The cooling to room temperature is again at a cooling rate of 2 to 30 ° C / s.
Bei klassischen Dualphasenstählen ist neben Mangan, Chrom und Silizium auch der Kohlenstoff für die Umwandlung von Austenit zu Martensit verantwortlich.In classical dual-phase steels, in addition to manganese, chromium and silicon, carbon is also responsible for the transformation of austenite to martensite.
Erst die erfindungsgemäße Kombination der in den angegebenen Grenzen zulegierten Elemente Kohlenstoff, Silizium, Mangan und Chrom sowie Niob sichert einerseits die geforderten mechanischen Eigenschaften von Mindestzugfestigkeiten von 580 MPa und Streckgrenzenverhältnisse von unterhalb 67% bei gleichzeitig deutlich verbreitertem Prozessfenster bei der Duchlaufglühung.It is only the combination according to the invention of the elements carbon, silicon, manganese and chromium and niobium alloyed within the specified limits that assures the one hand Required mechanical properties of minimum tensile strengths of 580 MPa and yield strength ratios of below 67% with a significantly widened process window during the Duchlaufglühung.
Die Grundlage für das Erreichen eines breiten Prozessfensters ist die erfindungsgemäße Mikrolegierung ausschließlich mit Niob, bei Berücksichtigung der o.g. klassischen Zusammensetzung Kohlenstoff/Silizium/Mangan/Chrom, bei einem nach der Banddicke darzustellenden, abgestuften und definierten Mangangehalt.The basis for achieving a broad process window is the microalloying according to the invention exclusively with niobium, taking into account the above-mentioned. classical composition carbon / silicon / manganese / chromium, with a graded and defined manganese content to be displayed according to the strip thickness.
Da mit zunehmendem Querschnitt bzw. Banddicke bei gleicher Breite die Geschwindigkeit in der Durchlaufglühanlage sich verringert, d.h. die damit vorhandene Zeit zur Umwandlung größer wird, muss zur Einstellung ähnlicher Gefügeanteile über den ausgewählten Dickenbereich (z.B. 0,5 bis 4,0mm) der Mangangehalt diese Aufgabe übernehmen und die Phasenumwandlungen entsprechend verschieben, wie in
Werkstoffcharakteristisch bewirkt die Zugabe von Niob eine Verzögerung der Rekristallisation bei der Glühbehandlung, dadurch wird die Austinitkorngröße stabilisiert und ein breiteres Prozessfenster bei der abschließenden Glühbehandlung erreicht.In terms of material properties, the addition of niobium retards the recrystallization in the annealing treatment, thereby stabilizing the austinite grain size and achieving a broader process window in the final annealing treatment.
Werkstoffcharakteristisch ist auch, dass durch die Zugabe von Mangan mit ansteigenden Gewichtsprozenten das Ferritgebiet zu längeren Zeiten und tieferen Temperaturen während der Abkühlung verschoben wird.Material characteristic is also that the addition of manganese with increasing weight percent of the ferrite is shifted to longer times and lower temperatures during cooling.
Die Anteile von Ferrit werden dabei durch erhöhte Anteile von Bainit je nach Prozessparameter mehr oder weniger stark reduziert.Depending on the process parameters, the proportions of ferrite are more or less reduced by increased amounts of bainite.
Bei Versuchen hat sich gezeigt, dass allein die Mikrolegierungselementzugabe von Niob in Gehalten von 0,005 bis 0,025% ausreichend ist, um ein breites Prozessfenster und den typischerweise hierfür geforderten Zugfestigkeiten von mindestens 580 MPa für Warmband und mindestens 600 MPa für kaltnachgewalztes Warmband und Kaltband zu erreichen ist.In experiments, it has been found that only the micro alloying element addition of niobium at levels of 0.005 to 0.025% is sufficient to achieve a broad process window and tensile strength of at least 580 MPa typically required for hot strip and at least 600 MPa for cold rolled hot strip and cold strip ,
Erst durch die abgestimmte Zugabe von Mangan in den angegebenen Gehalten, als Steuerungsgröße zur Kompensierung des Querschnitteinflusses, können gleichmäßige mechanischen Kennwerte und Gefügezusammensetzungen bei unterschiedlichen Banddicken ermöglicht werden.Only by the coordinated addition of manganese in the specified levels, as a control to compensate for the cross-sectional influence, uniform mechanical properties and microstructural compositions can be made possible at different tape thicknesses.
Durch die Mikrolegierung von Niob wird die zuvor beschriebene Prozessrobustheit ermöglicht.The microalloying of niobium enables the previously described process robustness.
Durch die Manganvariation wird der Querschnittseinfluss im Zeit-Temperatur-Umwandlungsverhalten kompensiert.The manganese variation compensates for the cross-sectional influence in the time-temperature conversion behavior.
Durch die Einstellung eines niedrigen Kohlenstoffgehaltes von ≤ 0,105% kann das Kohlenstoffäquivalent reduziert werden, wodurch die Schweißbarkeit verbessert und zu große Aufhärtungen beim Schweißen vermieden werden. Beim Widerstandspunktschweißen kann darüber hinaus die Elektrodenstandzeit deutlich erhöht werden.By setting a low carbon content of ≤ 0.105%, the carbon equivalent can be reduced, thereby improving weldability and avoiding too much hardening during welding. In resistance spot welding, moreover, the electrode life can be significantly increased.
Nachfolgend wird die Wirkung der Elemente in der erfindungsgemäßen Legierung näher beschrieben. Die Mehrphasenstähle sind typischerweise chemisch so aufgebaut, dass Legierungselemente mit und auch ohne Mikrolegierungselemente kombiniert werden. Begleitelemente sind unvermeidlich und werden im Analysenkonzept hinsichtlich ihrer Wirkung wenn notwendig berücksichtigt.The effect of the elements in the alloy according to the invention is described in more detail below. The multiphase steels are typically chemically designed to combine alloying elements with and without micro-alloying elements. Accompanying elements are unavoidable and are considered in the analysis concept with regard to their effect if necessary.
Begleitelemente sind Elemente, die bereits im Eisenerz vorhanden sind bzw. herstellungsbedingt in den Stahl gelangen. Aufgrund ihrer überwiegend negativen Einflüsse sind sie in der Regel unerwünscht. Es wird versucht, sie bis zu einem tolerierbaren Gehalt zu entfernen bzw. in unschädlichere Formen zu überführen. Accompanying elements are elements that are already present in the iron ore or, due to their production, enter the steel. Because of their predominantly negative influences, they are usually undesirable. An attempt is made to remove them to a tolerable level or to convert them into more harmless forms.
Wasserstoff (H); kann als einziges Element ohne Gitterverspannungen zu erzeugen durch das Eisengitter diffundieren. Dies führt dazu, dass der Wasserstoff im Eisengitter relativ beweglich ist und während der Fertigung verhältnismäßig leicht aufgenommen werden kann. Wasserstoff kann dabei nur in atomarer (ionischer) Form ins Eisengitter aufgenommen werden. Hydrogen (H); is the only element that can generate diffraction through the iron grid without creating lattice strains. As a result, the hydrogen in the iron grid is relatively mobile and can be absorbed relatively easily during production. Hydrogen can only be taken up in atomic (ionic) form in the iron lattice.
Wasserstoff wirkt stark versprödend und diffundiert bevorzugt zu energetisch günstigen Stellen (Fehlstellen, Korngrenzen etc.). Dabei fungieren Fehlstellen als Wasserstofffallen und können die Verweildauer des Wasserstoffes im Werkstoff erheblich erhöhen.Hydrogen has a strong embrittlement and preferably diffuses to energy-favorable sites (defects, grain boundaries, etc.). In this case, defects act as hydrogen traps and can significantly increase the residence time of the hydrogen in the material.
Durch eine Rekombination zu molekularem Wasserstoff können Kaltrisse entstehen. Dieses Verhalten tritt bei der Wasserstoffversprödung oder bei wasserstoffinduzierter Spannungsrisskorrosion auf. Auch beim verzögerten Riss, dem sogenannten Delayed-Fracture, der ohne äußere Spannungen auftritt, wird Wasserstoff oft als Grund genannt.By recombination to molecular hydrogen, cold cracks can arise. This behavior occurs in hydrogen embrittlement or in hydrogen-induced stress corrosion cracking. Even with the delayed crack, the so-called delayed-fracture, which occurs without external stresses, hydrogen is often mentioned as a reason.
Ein gleichmäßigeres Gefüge, was bei dem erfindungsgemäßen Stahl u.a. durch seine Mikrolegierung erzielt wird, vermindert die Anfälligkeit gegenüber einer Wasserstoffversprödung.A more uniform structure, which in the steel according to the invention u.a. achieved by its microalloying reduces the susceptibility to hydrogen embrittlement.
Daher sollte der Wasserstoffgehalt im Stahl so gering wie möglich sein.Therefore, the hydrogen content in the steel should be as low as possible.
Sauerstoff (O): Im schmelzflüssigen Zustand hat der Stahl eine verhältnismäßig große Aufnahmefähigkeit für Gase, bei Raumtemperatur ist Sauerstoff jedoch nur in sehr geringen Mengen löslich. Analog zum Wasserstoff kann Sauerstoff nur in atomarer Form in den Werkstoff diffundieren. Wegen der stark versprödenden Wirkung sowie der negativen Auswirkungen auf die Alterungsbeständigkeit wird während der Herstellung so weit wie möglich versucht, den Sauerstoffgehalt zu reduzieren. Oxygen (O) : In the molten state, the steel has a relatively high absorption capacity for gases, but at room temperature, oxygen is only soluble in very small quantities. Similar to hydrogen, oxygen can only diffuse into the material in atomic form. Due to the strong embrittling effect and the negative effects on the aging resistance, as much as possible is attempted during production to reduce the oxygen content.
Zur Verringerung des Sauerstoffs existieren zum Einen verfahrenstechnische Ansätze wie eine Vakuumbehandlung und zum Anderen analytische Ansätze. Durch Zugabe von bestimmten Legierungselementen kann der Sauerstoff in ungefährlichere Zustände überführt werden. So ist ein Abbinden des Sauerstoffes über Mangan, Silizium und/oder Aluminium in der Regel üblich. Die dadurch entstehenden Oxide können jedoch als Fehlstellen im Werkstoff negative Eigenschaften hervorrufen. Bei einer feinen Ausscheidung, speziell von Aluminiumoxiden, kann hingegen auch eine Kornfeinung erfolgen.For the reduction of oxygen exist on the one hand procedural approaches such as a vacuum treatment and on the other analytical approaches. By adding certain alloying elements, the oxygen can be converted to safer conditions. So a setting of the oxygen over manganese, silicon and / or aluminum is usually common. However, the resulting oxides can cause negative properties as defects in the material. With a fine excretion, especially of aluminum oxides, however, can also be done a grain refining.
Aus vorgenannten Gründen sollte deshalb der Sauerstoffgehalt im Stahl so gering wie möglich sein.For the above reasons, therefore, the oxygen content in the steel should be as low as possible.
Stickstoff (N): ist ebenfalls ein Begleitelement aus der Stahlherstellung. Stähle mit freiem Stickstoff neigen zu einem starken Alterungseffekt. Der Stickstoff diffundiert schon bei geringen Temperaturen an Versetzungen und blockiert diese. Er bewirkt damit einen Festigkeitsanstieg verbunden mit einem rapiden Zähigkeitsverlust. Ein Abbinden des Stickstoffes in Form von Nitriden ist durch Zulegieren von Aluminium oder Titan möglich. Nitrogen (N): is also a companion element of steelmaking. Steels with free nitrogen tend to have a strong aging effect. The nitrogen diffuses at low temperatures at dislocations and blocks them. It causes an increase in strength combined with a rapid loss of toughness. Nitrogen bonding in the form of nitrides is possible by alloying aluminum or titanium.
Aus vorgenannten Gründen ist der Stickstoffgehalt auf ≤ 0,0100%, vorteilhaft auf ≤ 0,0090% bzw. optimal auf ≤ 0,0080% bzw. auf bei der Stahlherstellung unvermeidbare Mengen begrenzt.For the abovementioned reasons, the nitrogen content is limited to ≦ 0.0100%, advantageously ≦ 0.0090% or optimally ≦ 0.0080% or amounts unavoidable in steel production.
Schwefel (S): ist wie Phosphor als Spurenelement im Eisenerz gebunden. Er ist im Stahl unerwünscht (Ausnahme Automatenstähle), da er zu starker Seigerung neigt und stark versprödend wirkt. Es wird deshalb versucht, möglichst geringe Mengen an Schwefel in der Schmelze zu erreichen (z. B. durch eine Tiefvakuumbehandlung). Des Weiteren wird der vorhandene Schwefel durch Zugabe von Mangan in die relativ ungefährliche Verbindung Mangansulfid (MnS) überführt. Sulfur (S): like phosphorus is bound as a trace element in iron ore. It is undesirable in steel (exception free cutting steels), because it tends to segregation strong and strong embrittling effect. It is therefore attempted to achieve the lowest possible amounts of sulfur in the melt (for example, by a deep vacuum treatment). Furthermore, the existing sulfur is converted by adding manganese into the relatively harmless compound manganese sulfide (MnS).
Die Mangansulfide werden während des Walzprozesses oft zeilenartig ausgewalzt und fungieren als Keimstellen für die Umwandlung. Dies führt vor allem bei diffusionsgesteuerter Umwandlung zu einem zeilig ausgeprägten Gefüge und kann bei stark ausgeprägter Zeiligkeit zu verschlechterten mechanischen Eigenschaften führen (z.B. ausgeprägte Martensitzeilen statt verteilte Martensitinseln, anisotropes Werkstoffverhalten, verminderte Bruchdehnung).The manganese sulfides are often rolled in rows during the rolling process and act as nucleation sites for the transformation. This leads to a line-shaped structure, especially in the case of diffusion-controlled conversion, and can lead to impaired mechanical properties in the case of pronounced bristleness (for example, pronounced Martensitile instead of distributed martensite islands, anisotropic material behavior, reduced elongation at break).
Aus vorgenannten Gründen ist der Schwefelgehalt auf ≤ 0,0050% bzw. auf bei der Stahlherstellung unvermeidbare Mengen begrenzt.For the above reasons, the sulfur content is limited to ≤ 0.0050% or unavoidable amounts in steelmaking.
Phosphor (P): ist ein Spurenelement aus dem Eisenerz und wird im Eisengitter als Substitutionsatom gelöst. Phosphor steigert durch Mischkristallverfestigung die Härte und verbessert die Härtbarkeit. Phosphorus (P): is a trace element from iron ore and is dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness by solid solution strengthening and improves hardenability.
Es wird allerdings in der Regel versucht, den Phosphorgehalt soweit wie möglich abzusenken, da er unter anderem durch seine geringe Diffusionsgeschwindigkeit stark zur Seigerung neigt und im hohen Maße die Zähigkeit vermindert. Durch die Anlagerung von Phosphor an den Korngrenzen treten Korngrenzenbrüche auf. Zudem setzt Phosphor die Übergangstemperatur von zähem zu sprödem Verhalten bis zu 300°C herauf. Während des Warmwalzens können oberflächennahe Phosphoroxide an den Korngrenzen zu Bruchaufreißungen führen.However, it is usually attempted to lower the phosphorus content as much as possible, since it is prone to segregation, inter alia due to its low diffusion rate, and to a great extent reduces its toughness. Due to the addition of phosphorus at the grain boundaries, grain boundary fractures occur. In addition, phosphorus increases the transition temperature from tough to brittle behavior up to 300 ° C. During hot rolling, near-surface phosphorus oxides at the grain boundaries can lead to breakage cracks.
In einigen Stählen wird er allerdings aufgrund der niedrigen Kosten und der hohen Festigkeitssteigerung in geringen Mengen (< 0,1%) als Mikrolegierungselement verwendet. Beispielsweise in höherfesten IF-Stählen (interstitial free) oder auch in einigen Legierungskonzepten für Dualphasenstählen.However, in some steels it is used as a micro-alloying element in small quantities (<0.1%) due to the low cost and high strength increase. For example, in higher-strength IF steels (interstitial free) or in some alloy concepts for dual-phase steels.
Aus vorgenannten Gründen ist der Phosphorgehalt auf ≤ 0,020% bzw. auf bei der Stahlherstellung unvermeidbare Mengen begrenzt.For the aforementioned reasons, the phosphorus content is limited to ≤ 0.020% or to unavoidable amounts in steelmaking.
Legierungselemente werden dem Stahl in der Regel zugegeben, um gezielt bestimmte Eigenschaften zu beeinflussen. Dabei kann ein Legierungselement in verschiedenen Stählen unterschiedliche Eigenschaften beeinflussen. Die Wirkung hängt im Allgemeinen stark von der Menge und dem Lösungszustand im Werkstoff ab. Alloying elements are usually added to the steel in order to specifically influence certain properties. In this case, an alloying element in different steels affect different characteristics. The effect generally depends strongly on the amount and the solution state in the material.
Die Zusammenhänge können demnach durchaus vielseitig und komplex sein. Im Folgenden soll auf die Wirkung der Legierungselemente näher eingegangen werden.The connections can therefore be quite varied and complex. In the following, the effect of the alloying elements will be discussed in greater detail.
Kohlenstoff (C): gilt als das wichtigste Legierungselement im Stahl. Durch seine gezielte Einbringung bis zu 2,06 % wird Eisen erst zum Stahl. Oft wird während der Stahlherstellung der Kohlenstoffanteil drastisch abgesenkt. Bei Dualphasenstählen für eine kontinuierliche Schmelztauchveredelung beträgt sein Anteil maximal 0,23%, ein Mindestwert ist nicht vorgegeben. Carbon (C): considered the most important alloying element in steel. Through its targeted introduction of up to 2.06% iron is only steel. Often the carbon content is drastically lowered during steelmaking. In the case of dual-phase steels for continuous hot-dip refinement, its maximum proportion is 0.23%; a minimum value is not specified.
Kohlenstoff wird aufgrund seines vergleichsweise kleinen Atomradius interstitiell im Eisengitter gelöst. Die Löslichkeit beträgt dabei im α-Eisen maximal 0,02% und im γ-Eisen maximal 2,06%. Kohlenstoff steigert in gelöster Form die Härtbarkeit von Stahl erheblich.Due to its comparatively small atomic radius, carbon is interstitially dissolved in the iron lattice. The solubility is 0.02% maximum in α-iron and 2.06% maximum in γ-iron. Carbon in dissolved form considerably increases the hardenability of steel.
Durch die unterschiedliche Löslichkeit werden ausgeprägte Diffusionsvorgänge bei der Phasenumwandlung notwendig, die zu sehr verschiedenen kinetischen Bedingungen führen können. Zudem erhöht Kohlenstoff die thermodynamische Stabilität des Austenits, was sich im Phasendiagramm in einer Erweiterung des Austenitgebiets zu niedrigeren Temperaturen zeigt. Mit steigendem zwangsgelösten Kohlenstoffgehalt im Martensit steigen die Gitterverzerrungen und damit verbunden die Festigkeit der diffusionslos entstandenen Phase.Due to the different solubility pronounced diffusion processes in the phase transformation are necessary, which can lead to very different kinetic conditions. In addition, carbon increases the thermodynamic stability of austenite, which is shown in the phase diagram in an extension of the austenite area to lower temperatures. As the constrained carbon content in martensite increases, the lattice distortions and, associated therewith, the strength of the diffusionless phase are increased.
Kohlenstoff ist zudem erforderlich um Carbide zu bilden. Ein nahezu in jedem Stahl vorkommender Vertreter ist der Zementit (Fe3C). Es können sich jedoch auch wesentlich härtere Sondercarbide mit anderen Metallen wie zum Beispiel Chrom, Titan, Niob, Vanadium bilden. Dabei ist nicht nur die Art sondern auch die Verteilung und Größe der Ausscheidungen von entscheidender Bedeutung für die resultierende Festigkeitssteigerung. Um einerseits eine ausreichende Festigkeit und andererseits eine gute Schweißbarkeit sicherzustellen, werden deshalb der minimale C-Gehalt auf 0,075% und der maximale C-Gehalt auf 0,105% festgelegt.Carbon is also required to form carbides. A representative occurring almost in every steel is the cementite (Fe 3 C). However, significantly harder special carbides with other metals such as chromium, titanium, niobium, vanadium can form. Not only the species but also the distribution and size of the precipitates is of crucial importance for the resulting increase in strength. Therefore, to ensure sufficient strength on the one hand and good weldability on the other hand, the minimum C content is set to 0.075% and the maximum C content to 0.105%.
Silizium (Si): bindet beim Vergießen Sauerstoff und vermindert somit Seigerungen sowie Verunreinigungen im Stahl. Zudem erhöht Silizium durch Mischkristallverfestigung die Festigkeit und das Streckgrenzenverhältnis des Ferrits bei nur geringfügig absinkender Bruchdehnung. Ein weiterer wichtiger Effekt ist, dass Silizium die Bildung von Ferrit zu kürzeren Zeiten verschiebt und somit die Entstehung von ausreichend Ferrit vor der Abschreckung ermöglicht. Durch die Ferritbildung wird derAustenit mit Kohlenstoff angereichert und stabilisiert. Bei höheren Gehalten stabilisiert Silizium im unteren Temperaturbereich speziell im Bereich der Bainitbildung durch Verhinderung von Carbidbildung den Austenit merklich. Silicon (Si): binds oxygen during casting, thus reducing segregation and impurities in the steel. In addition, by solid solution strengthening, silicon increases the strength and yield ratio of the ferrite with only a slight decrease Elongation at break. Another important effect is that silicon shifts the formation of ferrite to shorter times, thus allowing the formation of sufficient ferrite before quenching. By ferrite formation, the austenite is carbon enriched and stabilized. At higher levels, silicon stabilizes austenite markedly in the lower temperature range, especially in the area of bainite formation by preventing carbide formation.
Während des Warmwalzens kann sich bei hohen Siliziumgehalten stark haftender Zunder bilden, der die Weiterverarbeitung beeinträchtigen kann.During hot rolling, highly adherent scale may form at high silicon contents, which may affect further processing.
Beim kontinuierlichen Verzinken kann Silizium während des Glühens an die Oberfläche diffundieren und alleine oder zusammen mit Mangan filmartige Oxide bilden. Diese Oxide verschlechtern die Verzinkbarkeit durch Beeinträchtigung der Verzinkungsreaktion (Eisenlösung und Hemmschichtausbildung) beim Eintauchen des Stahlbandes in die Zinkschmelze. Dies äußert sich in einer schlechten Zinkhaftung und unverzinkten Bereichen. Durch eine geeignete Ofenfahrweise mit angepasstem Feuchtegehalt im Glühgas und/oder durch ein geringes Si/Mn-Verhältnis und/oder durch die Verwendung moderater Mengen an Silizium kann jedoch eine gute Verzinkbarkeit des Stahlbandes und eine gute Zinkhaftung sichergestellt werden.In continuous galvanizing, silicon may diffuse to the surface during annealing and form film-like oxides alone or together with manganese. These oxides deteriorate the galvanizability by adversely affecting the galvanizing reaction (iron solution and inhibiting layer formation) when the steel strip is immersed in the molten zinc. This manifests itself in a poor zinc adhesion and unpigmented areas. By a suitable kiln operation with adjusted moisture content in the annealing gas and / or by a low Si / Mn ratio and / or by the use of moderate amounts of silicon, however, a good galvanizability of the steel strip and a good zinc adhesion can be ensured.
Aus den vorgenannten Gründen werden der minimale Si-Gehalt auf 0,200% und der maximale Silizium-Gehalt auf 0,300% festgelegt.For the above reasons, the minimum Si content is set at 0.200% and the maximum silicon content at 0.300%.
Mangan (Mn): wird fast allen Stählen zur Entschwefelung zugegeben, um den schädlichen Schwefel in Mangansulfide zu überführen. Zudem erhöht Mangan durch Mischkristallverfestigung die Festigkeit des Ferrits und verschiebt die α-/γ-Umwandlung zu niedrigeren Temperaturen. Manganese (Mn): is added to almost all steels for desulfurization to convert the harmful sulfur into manganese sulfide. In addition, manganese increases the strength of the ferrite by solid solution strengthening and shifts the α / γ conversion to lower temperatures.
Ein Hauptgrund für das Zulegieren von Mangan in Dualphasenstählen ist die deutliche Verbesserung der Einhärtbarkeit. Aufgrund der Diffusionsbehinderung wird die Perlit- und Bainitumwandlung zu längeren Zeiten verschoben und die Martensitstarttemperatur gesenkt.One main reason for adding manganese into dual-phase steels is the significant improvement in hardenability. Due to the diffusion hindrance, the pearlite and bainite transformation is shifted to longer times and the martensite start temperature is lowered.
Mangan neigt wie Silizium zur Bildung von Oxiden auf der Stahloberfläche während der Glühbehandlung. In Abhängigkeit von den Glühparametern und den Gehalten an anderen Legierungselementen (insbesondere Silizium und Aluminium) können Manganoxide (z. B. MnO) und/oder Mn-Mischoxide (z.B. Mn2SiO4) auftreten. Allerdings ist Mangan bei einem geringen Si/Mn bzw. Al/Mn Verhältnis als weniger kritisch zu betrachten, da sich eher globulare Oxide statt Oxidfilme ausbilden. Dennoch können hohe Mangangehalte das Erscheinungsbild der Zinkschicht und die Zinkhaftung negativ beeinflussen.Like silicon, manganese tends to form oxides on the steel surface during annealing. Depending on the annealing parameters and the contents of other alloying elements (in particular silicon and aluminum), manganese oxides (eg MnO) and / or Mn mixed oxides (eg Mn 2 SiO 4 ) may occur. However, manganese is at one low Si / Mn or Al / Mn ratio to be considered as less critical, since forming more globular oxides instead of oxide films. However, high levels of manganese can negatively affect the appearance of the zinc layer and zinc adhesion.
Der Mangan-Gehalt wird deshalb abhängig vom Querschnitt (Banddicke bei gleicher Bandbreite) auf 1,000 bis 2,000% festgelegt. Als vorteilhaft hat sich für einen Banddickenbereich von 0,5-1,0mm ein Mangan-Gehalt von 1,00-1,50 Gew.%, für den Bereich 1,0-2,0mm 1,25-1,75 Gew.% und für den Bereich 2,0-4,0mm ein Mangan-Gehalt von 1,50-2,00 Gew.% herausgestellt.The manganese content is therefore set to 1,000 to 2,000% depending on the cross section (tape thickness at the same bandwidth). For a band thickness range of 0.5-1.0 mm, a manganese content of 1.00-1.50 wt.%, For the range 1.0-2.0 mm 1.25-1.75 wt. % and for the range 2.0-4.0mm a manganese content of 1.50-2.00 wt.% Exposed.
Chrom (Cr): So kann einerseits Chrom in gelöster Form schon in geringen Mengen die Härtbarkeit von Stahl erheblich steigern. Andererseits bewirkt Chrom bei entsprechender Temperaturführung in Form von Chromcarbiden eine Teilchenverfestigung. Die damit verbundene Erhöhung der Anzahl von Keimstellen bei gleichzeitig gesenktem Gehalt an Kohlenstoff führt zu einer Herabsetzung der Härtbarkeit. Chromium (Cr): On the one hand chromium in dissolved form can considerably increase the hardenability of steel even in small amounts. On the other hand, chromium causes particle hardening with appropriate temperature control in the form of chromium carbides. The associated increase in the number of seed sites with simultaneously reduced content of carbon leads to a reduction in the hardenability.
In Dualphasenstählen wird durch die Zugabe von Chrom hauptsächlich die Einhärtbarkeit verbessert. Chrom verschiebt im gelösten Zustand die Perlit- und Bainitumwandlung zu längeren Zeiten und senkt dabei gleichzeitig die Martensitstarttemperatur.In dual phase steels, the addition of chromium mainly improves the hardenability. Chromium, when dissolved, shifts perlite and bainite transformation to longer times, while decreasing the martensite start temperature.
Ein weiterer wichtiger Effekt ist, dass Chrom die Anlassbeständigkeit erheblich steigert, so dass es im Zinkbad zu fast keinen Festigkeitsverlusten kommt.Another important effect is that chromium increases the tempering resistance considerably, so that almost no loss of strength occurs in the zinc bath.
Chrom ist zudem ein Carbidbildner. Sollte Chrom in Carbidform vorliegen, muss die Austenitisierungstemperatur vor dem Härten hoch genug gewählt werden, um die Chromcarbide zu lösen. Ansonsten kann es durch die erhöhte Keimzahl zu einer Verschlechterung der Einhärtbarkeit kommen.Chromium is also a carbide former. If chromium is in carbide form, the austenitizing temperature must be high enough before curing to dissolve the chromium carbides. Otherwise, the increased germ count may lead to a deterioration of the hardenability.
Chrom neigt ebenfalls dazu während der Glühbehandlung Oxide auf der Stahloberfläche zu bilden, wodurch sich die Verzinkungsqualität verschlechtern kann.Chromium also tends to form oxides on the steel surface during the annealing process, which may degrade zinc-plating quality.
Der Chrom-Gehalt wird deshalb auf Werte von 0,280 bis 0,480% festgelegt.The chromium content is therefore set to values of 0.280 to 0.480%.
Molybdän (Mo): Die Zugabe von Molybdän erfolgt ähnlich wie bei Chrom zur Verbesserung der Härtbarkeit. Die Perlit- und Bainitumwandlung wird zu längeren Zeiten geschoben und die Martensitstarttemperatur gesenkt. Molybdenum (Mo): The addition of molybdenum is similar to chromium to improve hardenability. The perlite and bainite transformation is pushed to longer times and the martensite start temperature is lowered.
Molybdän erhöht zudem die Anlassbeständigkeit erheblich, so dass im Zinkbad keine Festigkeitsverluste zu erwarten sind und bewirkt durch Mischkristallverfestigung eine Festigkeitssteigerung des Ferrits.In addition, molybdenum considerably increases the tempering resistance, so that no loss of strength is to be expected in the zinc bath and, as a result of solid solution hardening, increases the strength of the ferrite.
Aus Kostengründen wird auf die Zugabe von Molybdän verzichtet.For cost reasons, the addition of molybdenum is omitted.
Der Gehalt an Molybdän wird bis auf die unvermeidbaren, stahlbegleitenden Mengen begrenzt.The content of molybdenum is limited to the unavoidable, steel-accompanying amounts.
Kupfer (Cu): Der Zusatz von Kupfer kann die Zugfestigkeit sowie die Einhärtbarkeit steigern. In Verbindung mit Nickel, Chrom und Phosphor kann Kupfer eine schützende Oxidschicht an der Oberfläche bilden, die die Korrosionsrate deutlich reduzieren kann. Copper (Cu): The addition of copper can increase the tensile strength and hardenability. In combination with nickel, chromium and phosphorus, copper can form a protective oxide layer on the surface, which can significantly reduce the corrosion rate.
In Verbindung mit Sauerstoff kann Kupfer an den Korngrenzen schädliche Oxide bilden, die besonders für Warmumformprozesse negative Auswirkungen hervorrufen können. Der Gehalt an Kupfer ist deshalb bis auf bei der Stahlherstellung unvermeidbare Mengen begrenzt.When combined with oxygen, copper can form harmful oxides at the grain boundaries, which can be detrimental to hot working processes in particular. The content of copper is therefore limited to quantities that are unavoidable in steel production.
Andere Legierungselemente wie z.B. Nickel (Ni) oder Zinn (Sn) sind in ihren Gehalten auf bei der Stahlherstellung unvermeidbare Mengen begrenzt.Other alloying elements such as nickel (Ni) or tin (Sn) are limited in their contents to unavoidable amounts in steelmaking.
Mikrolegierungselemente werden in der Regel nur in sehr geringen Mengen zugegeben (< 0,1%). Sie wirken im Gegensatz zu den Legierungselementen hauptsächlich durch Ausscheidungsbildung können aber auch in gelöstem Zustand die Eigenschaften beeinflussen. Trotz der geringen Mengenzugaben beeinflussen Mikrolegierungselemente die Herstellungsbedingungen sowie die Verarbeitungs- und Endeigenschaften stark. Microalloying elements are usually added only in very small amounts (<0.1%). They act in contrast to the alloying elements mainly by excretion formation but can also affect the properties in a dissolved state. Despite the small quantity additions, micro-alloying elements strongly influence the production conditions as well as the processing and final properties.
Als Mikrolegierungselemente kommen in der Regel im Eisengitter lösliche Carbid- und Nitridbildner zum Einsatz. Eine Bildung von Carbonitriden ist aufgrund der vollständigen Löslichkeit von Nitriden und Carbiden ineinander ebenfalls möglich. Die Neigung, Oxide und Sulfide zu bilden ist bei den Mikrolegierungselementen in der Regel am stärksten ausgeprägt wird aber aufgrund anderer Legierungselemente in der Regel gezielt verhindert.As micro-alloying elements, carbide and nitride formers which are generally soluble in the iron lattice are used. Formation of carbonitrides is also possible because of the complete solubility of nitrides and carbides in one another. The tendency to form oxides and sulfides is usually most pronounced in the case of the micro-alloying elements, but as a rule it is purposefully prevented on account of other alloying elements.
Diese Eigenschaft kann positiv genutzt werden, indem die im Allgemeinen schädlichen Elemente Schwefel und Sauerstoff abgebunden werden können. Die Abbindung kann aber auch negative Auswirkungen haben, wenn dadurch nicht mehr genügend Mikrolegierungselemente für die Bildung von Carbiden zur Verfügung stehen.This property can be used positively by binding the generally harmful elements sulfur and oxygen. The setting may also have negative effects, if there are not enough micro-alloying elements for the formation of carbides available.
Typische Mikrolegierungselemente sind Aluminium, Vanadium, Titan, Niob und Bor. Diese Elemente können im Eisengitter gelöst werden und bilden mit Kohlenstoff und Stickstoff Carbide und Nitride.Typical micro-alloying elements are aluminum, vanadium, titanium, niobium and boron. These elements can be dissolved in the iron lattice and form carbides and nitrides with carbon and nitrogen.
Aluminium (Al) wird in der Regel dem Stahl zulegiert, um den im Eisen gelösten Sauerstoff und Stickstoff zu binden. Der Sauerstoff und Stickstoff wird so in Aluminiumoxide und Aluminiumnitride überführt. Diese Ausscheidungen können über eine Erhöhung der Keimstellen eine Kornfeinung bewirken und so die Zähigkeitseigenschaften sowie Festigkeitswerte steigern. Aluminum (Al) is usually added to the steel to bind the dissolved oxygen in the iron and nitrogen. The oxygen and nitrogen is thus converted into aluminum oxides and aluminum nitrides. These precipitations can cause a grain refining by increasing the germination sites and thus increase the toughness properties and strength values.
Aluminiumnitrid wird nicht ausgeschieden, wenn Titan in ausreichenden Mengen vorhanden ist. Titannitride haben eine geringere Bildungsenthalpie und werden bei höheren Temperaturen gebildet.Aluminum nitride is not precipitated when titanium is present in sufficient quantities. Titanium nitrides have a lower formation enthalpy and are formed at higher temperatures.
In gelöstem Zustand verschiebt Aluminium wie Silizium die Ferritbildung zu kürzeren Zeiten und ermöglicht so die Bildung von ausreichend Ferrit im Dualphasenstahl. Es unterdrückt zudem die Carbidbildung und führt so zu einer verzögerten Umwandlung des Austenits. Aus diesem Grund wird Aluminium auch als Legierungselement in Restaustenitstählen verwendet, um einen Teil des Siliziums durch Aluminium zu substituieren. Der Grund für diese Vorgehensweise liegt darin, dass Aluminium etwas weniger kritisch für die Verzinkungsreaktion als Silizium ist.When dissolved, aluminum such as silicon shifts ferrite formation to shorter times, allowing the formation of sufficient ferrite in dual phase steel. It also suppresses carbide formation and thus leads to a delayed transformation of austenite. For this reason, aluminum is also used as an alloying element in retained austenitic steels to substitute part of the silicon with aluminum. The reason for this approach is that aluminum is somewhat less critical to the galvanizing reaction than silicon.
Der Aluminium-Gehalt wird deshalb auf 0,010 bis maximal 0,060% begrenzt.The aluminum content is therefore limited to 0.010 to a maximum of 0.060%.
Niob (Nb): Neben dem oben beschriebenen Effekt auf eine Verbreiterung des Prozessfensters durch eine verzögerte Phasenumwandlung bei der Durchlaufglühung, bewirkt Niob eine starke Kornfeinung, da es am effektivsten von allen Mikrolegierungselementen eine Verzögerung der Rekristallisation bewirkt und zudem das Austenitkornwachstum hemmt. Niobium (Nb) : In addition to the above-described effect of widening the process window by delayed phase transformation in continuous annealing, niobium causes a high grain refining because it most effectively retards recrystallization of all the micro-alloying elements and also inhibits austenite grain growth.
Die festigkeitssteigernde Wirkung ist qualitativ höher als die von Titan einzuschätzen, ersichtlich durch den erhöhten Kornfeinungseffekt und die größere Menge an festigkeitssteigernden Teilchen (Abbindung des Titans zu TiN bei hohen Temperaturen). Niobcarbide bilden sich bei Temperaturen unterhalb von 1200°C. Bei Stickstoffabbindung mit Titan kann Niob durch Bildung von kleinen und in Hinblick auf ihre Wirkung effektiven Carbiden im unteren Temperaturbereich (kleinere Carbidgrößen) seine festigkeitssteigernde Wirkung erhöhen.The strength-enhancing effect is qualitatively higher than that of titanium, as evidenced by the increased grain refining effect and the greater amount of strength-enhancing particles (bonding of the titanium to TiN at high temperatures). Niobium carbides form at temperatures below 1200 ° C. In the case of nitrogen bonding with titanium, niobium can be effective in forming small and effective ones Carbides in the lower temperature range (smaller carbide sizes) increase its strength-increasing effect.
Ein weiterer Effekt des Niobs ist die Verzögerung der α/γ-Umwandlung und das Absenken der Martensitstarttemperatur im gelösten Zustand. Zum Einen geschieht dies durch den Solute-Drag-Effekt und zum Anderen durch die Kornfeinung. Diese bewirkt eine Festigkeitssteigerung des Gefüges und somit auch einen höheren Widerstand gegen die Volumenvergrößerung bei der Martensitbildung.Another effect of niobium is the retardation of the α / γ conversion and the lowering of the martensite start temperature in the dissolved state. On the one hand this happens through the solute drag effect and on the other hand through the grain refining. This causes an increase in strength of the structure and thus a higher resistance to the increase in volume during martensite formation.
Prinzipiell ist das Zulegieren von Niob begrenzt bis zum Erreichen seiner Löslichkeitsgrenze. Diese begrenzt zwar die Menge an Ausscheidungen bewirkt aber beim Überschreiten vor allem eine frühe Ausscheidungsbildung mit recht groben Partikeln.In principle, the alloying of niobium is limited until it reaches its solubility limit. Although this limits the amount of excretions but causes above all an early excretion formation with very coarse particles.
Die Ausscheidungshärtung kann somit vor allem bei Stählen mit geringem KohlenstoffGehalt (größere Übersättigung möglich) und bei Warmumformprozessen (verformungsinduzierte Ausscheidung) effektiv wirksam werden.The precipitation hardening can thus be effectively effective especially for steels with a low carbon content (greater supersaturation possible) and in hot forming processes (deformation-induced precipitation).
Der Niob-Gehalt wird deshalb auf Werte zwischen 0,005 und 0,025% begrenzt, wobei die Gehalte vorteilhaft auf ≥ 0,005 bis ≤ 0,020% aus Kostengründen eingeschränkt sind.The niobium content is therefore limited to values between 0.005 and 0.025%, wherein the contents are advantageously limited to ≥ 0.005 to ≤ 0.020% for cost reasons.
Da bei dem vorliegenden Legierungskonzept eine Zugabe von Titan nicht notwendig ist, wird der Gehalt an Titan bis auf unvermeidbare, stahlbegleitende Mengen begrenzt.Since the addition of titanium is not necessary in the present alloy concept, the content of titanium is limited to unavoidable, steel-accompanying amounts.
Da bei dem vorliegenden Legierungskonzept eine Zugabe von Vanadium nicht notwendig ist, wird der Gehalt an Vanadium bis auf unvermeidbare, stahlbegleitende Mengen begrenzt.Since addition of vanadium is not necessary in the present alloy concept, the vanadium content is limited to unavoidable steel accompanying amounts.
Da bei dem vorliegenden Legierungskonzept eine Zugabe von Bor nicht notwendig ist, wird der Gehalt an Bor bis auf unvermeidbare, stahlbegleitende Mengen begrenzt.Since the addition of boron is not necessary in the present alloy concept, the content of boron is limited to unavoidable steel-accompanying amounts.
Bei mit dem erfindungsgemäßen Stahl durchgeführten Versuchen wurde herausgefunden, dass mit dem vorliegenden Legierungskonzept durch eine austenitisierende Glühung eines Warmbandes über Ac3 ein Dualphasenstahl mit einer Mindestzugfestigkeit von 580MPa erreicht werden kann.In tests carried out with the steel according to the invention, it was found that a dual-phase steel with a minimum tensile strength of 580 MPa can be achieved with the present alloy concept by austenitizing annealing of a hot strip via A c3 .
Mit einer interkritischen Glühung zwischen Ac1 und Ac3 bzw. einer austenitisierenden Glühung über Ac3 mit abschließender gesteuerter Abkühlung wurde ein Mehrphasenstahlband mit Dualphasengefüge in einer Dicke von 0,50 bis 4,00mm erzeugt, welches sich durch eine große Toleranz gegenüber Prozessschwankungen auszeichnete.With an intercritical annealing between A c1 and A c3 and an austenitizing annealing over A c3 with final controlled cooling, a multi-phase steel strip with dual-phase structure in a thickness of 0.50 to 4.00mm was produced, which was characterized by a large tolerance to process variations.
Damit liegt ein deutlich aufgeweitetes Prozessfenster für die erfindungsgemäße Legierungszusammensetzung im Vergleich zu bekannten Legierungskonzepten vor.This is a significantly expanded process window for the alloy composition according to the invention in comparison to known alloy concepts.
Die Glühtemperaturen für das zu erzielende Dualphasengefüge liegen für den erfindungsgemäßen Stahl zwischen zirka 700 und 950°C, damit wird so je nach Temperaturbereich ein rekristallisiertes (Einphasengebiet), teilaustenitisches (Zweiphasengebiet) bzw. ein vollaustenitisches Gefüge (Austenitgebiet) erreicht.The annealing temperatures for the dual-phase structure to be achieved are between about 700 and 950 ° C. for the steel according to the invention, thus achieving a recrystallized (single-phase region), partially austenitic (two-phase) or fully austenitic microstructure (austenite region) depending on the temperature range.
Die Versuche zeigen, dass die eingestellten Gefügeanteile nach der interkritischen Glühung zwischen Ac1 und Ac3 bzw. der austenitisierenden Glühung über Ac3 mit anschließender gesteuerter Abkühlung, auch nach einem weiteren Prozessschritt "Schmelztauchveredelung" bei Temperaturen zwischen 420 bis 470°C beispielsweise bei Z (Zink) und ZM (Zink-Magnesium) erhalten blieben.The experiments show that the set microstructural fractions after the intercritical annealing between A c1 and A c3 and austenitizing annealing via A c3 with subsequent controlled cooling, even after a further process step "Schmelztauchveredelung" at temperatures between 420 to 470 ° C, for example at Z (Zinc) and ZM (zinc-magnesium) were preserved.
Das schmelztauchveredelte Material kann sowohl als Warmband, als auch als kalt nachgewalztes Warmband bzw. Kaltband im dressierten (kaltnachgewalzten) bzw. undressierten Zustand und/oder streckbiegegerichteten bzw. nicht streckbiegerichteten Zustand gefertigt werden.The hot-dip coated material can be produced both as a hot strip and as a cold rolled hot strip or cold strip in the dressed (cold rolled) or undressed state and / or stretch bending or non-stretch bent state.
Stahlbänder, vorliegend als Warmband, kaltnachgewalztes Warmband bzw. Kaltband aus der erfindungsgemäßen Legierungszusammensetzung zeichnen sich außerdem bei der Weiterverarbeitung durch einen hohen Widerstand gegen kantennahe Rissbildung aus.Steel strips, in the present case as hot strip, cold rolled hot strip or cold strip made of the alloy composition according to the invention are also characterized in the further processing by a high resistance to near-edge cracking.
Die geringen Kennwertunterschiede des Stahlbandes, längs und quer zu seiner Walzrichtung, sind vorteilhaft beim späteren Materialeinsatz, der dadurch quer, längs und diagonal zur Walzrichtung erfolgen kann.The small differences in the characteristic of the steel strip, along and transverse to its rolling direction, are advantageous in the subsequent use of material, which can thereby be transverse, longitudinal and diagonal to the rolling direction.
Um die Kaltwalzbarkeit eines aus dem erfindungsgemäßen Stahl erzeugten Warmbandes zu gewährleisten, wird das Warmband erfindungsgemäß mit Endwalztemperaturen im austenitischen Gebiet oberhalb Ac3 und Haspeltemperaturen oberhalb der Bainitstarttemperatur erzeugt.In order to ensure the cold rollability of a hot strip produced from the steel according to the invention, the hot strip according to the invention with Endwalztemperaturen in austenitic area above A c3 and reel temperatures above the bainite start temperature generated.
Weitere Vorteile und Einzelheiten der Erfindung ergeben sich aus der nachfolgenden Beschreibung von in einer Zeichnung dargestellten Ausführungsbeispielen.Further advantages and details of the invention will become apparent from the following description of exemplary embodiments illustrated in a drawing.
Es zeigen:
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Figur 1 : schematisch die Prozesskette für die Herstellung des erfindungsgemäßen Stahles -
Figur 2 : Ergebnisse eines Lochaufweitungsversuches (Blechdicke 2,50mm) beispielhaft für den erfindungsgemäßen Stahl (Variante1) gegenüber dem Stand der Technik -
Figur 3 : Beispiele für analytische Unterschiede des erfindungsgemäßen Stahls gegenüber der Standardgüte, die den Stand der Technik beispielhaft darstellt -
Figur 4a : Beispiele für mechanische Kennwerte (quer und längs zur Walzrichtung) des erfindungsgemäßen Stahls im Vergleich zur Standardgüte, die den Stand der Technik in der Festigkeitsklasse HCT600X beispielhaft darstellt -
Figur 4b : Regressionsberechnungen für mechanische Kennwerte quer zur Walzrichtung des erfindungsgemäßen 1, 2 und 3Stahls Variante -
Figur 4c : Beispiel für mechanische Kennwerte (quer zur Walzrichtung) des erfindungsgemäßen Stahls (Variante 1) im Vergleich zur Standardgüte, die den Stand der Technik in der Festigkeitsklasse HCT780X für Banddicke < 1mm beispielhaft darstellt -
Figur 4d : Beispiel für mechanische Kennwerte (quer zur Walzrichtung) des erfindungsgemäßenStahls Variante 1 in der FestigkeitsklasseHDT580X für Banddicke 2,50mm -
Figur 5 : schematisch den Zeit-Temperaturverlauf der Prozessschritte Warmwalzen und Durchlaufglühen, beispielhaft für Erfindung Variante 1 -
Figur 6 : schematisches ZTU-Diagramm für den erfindungsgemäßen Stahl 1,2 und 3mit den Varianten -
Figur 7 : mechanische Kennwerte (längs zur Walzrichtung) bei Variation der Abwalzgrade (beispielhaft Variante 1) -
Figur 8 : Übersicht über die mit dem erfindungsgemäßen Legierungskonzept (beispielhaft für Variante 3) einstellbaren Festigkeitsklassen -
Figur 9a : Temperatur-Zeit-Kurve (schematisch, Verfahren 1) -
Figur 9b : Temperatur-Zeit-Kurve (schematisch, Verfahren 2) -
Figur 9c : Temperatur-Zeit-Kurve (schematisch, Verfahren 3)
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FIG. 1 : schematically the process chain for the production of the steel according to the invention -
FIG. 2 : Results of a hole widening test (sheet thickness 2.50 mm) by way of example for the steel according to the invention (variant 1) compared with the prior art -
FIG. 3 : Examples of analytical differences of the steel according to the invention over the standard grade, which exemplifies the state of the art -
FIG. 4a : Examples of mechanical characteristics (transverse and along the direction of rolling) of the steel according to the invention compared to the standard grade, which exemplifies the state of the art in the strength class HCT600X -
FIG. 4b : Regression calculations for mechanical characteristics transverse to the rolling direction of the 1, 2 and 3 according to the inventionsteel variant -
Figure 4c : Example of mechanical characteristics (transverse to rolling direction) of the steel according to the invention (variant 1) compared to the standard quality, which represents the state of the art in the strength class HCT780X for strip thickness <1 mm by way of example -
FIG. 4d : Example of mechanical characteristics (transverse to rolling direction) of the steel according to theinvention variation 1 in the strength class HDT580X for strip thickness 2.50mm -
FIG. 5 : Schematically the time-temperature curve of the process steps of hot rolling and continuous annealing, exemplary ofinvention variation 1 -
FIG. 6 : schematic ZTU diagram for the steel according to the invention with the 1, 2 and 3variants -
FIG. 7 : mechanical characteristics (lengthwise to rolling direction) with varying degrees of rolling (example variant 1) -
FIG. 8 : Overview of the strength classes which can be set with the alloy concept according to the invention (for example for variant 3) -
FIG. 9a : Temperature-time curve (schematic, method 1) -
FIG. 9b : Temperature-time curve (schematic, method 2) -
FIG. 9c : Temperature-time curve (schematic, method 3)
Besonderes Interesse liegt hierbei auf der Verschiebung der Ferritnase, Perlitnase und Bainitnase zu späteren Zeiten bei der gestaffelten Zunahme der Mangangehalte. Hierdurch wird das Potenzial ermöglicht, bei einer von der Banddicke abhängigen Anlagengeschwindigkeit, über das gesamte betrachtete Dickenspektrum ähnliche Gefügeanteile einzustellen.
Of particular interest here is the shift of ferrite nose, perlitnase and bainitic nose at later times in the staggered increase in manganese contents. As a result, the potential is made possible to set similar microstructural proportions over the entire thickness spectrum considered at a system speed that depends on the strip thickness.
Höhere Abwalzgrade (größer 75%) führen zum Stahlsortensprung in Richtung HCT780X, mit Mindestfestigkeiten von 780 MPa.
Higher degrees of finishing (greater than 75%) lead to a change in the steel grades towards HCT780X, with minimum strengths of 780 MPa.
Die
Das Verfahren 1 (
Das Verfahren 2 (
Das Verfahren 3 (
Claims (13)
- High-strength multiphase steel having minimum tensile strengths of 580 MPa for a cold-rolled or hot-rolled steel strip having improved forming properties, in particular for lightweight vehicle construction, consisting of the elements (contents in wt%):
C 0.075 to ≤ 0.105 Si 0.200 to ≤ 0.300 Mn 1.000 to ≤ 2.000 Cr 0.280 to ≤ 0.480 Al 0.010 to ≤ 0.060 P ≤ 0.020 Nb ≥ 0.005 to ≤ 0.025 N ≤ 0.0100 S ≤ 0.0050 the remainder being iron, including impurities resulting from the smelting process, with the provisothat the Mn content is ≥ 1.000 ≤ 1.500%for strip thicknesses of 0.50 - 1.00 mm,that the Mn content is ≥ 1.250 ≤ 1.750%for strip thicknesses of 1.00 - 2.00 mm, andthat the Mn content is ≥ 1.500 ≤ 2.000%for strip thicknesses of 2.00 - 4.00 mm. - Steel according to claim 1,
characterized
in that, in order to achieve a minimum tensile strength of 780 MPa, the Mn content is ≥ 1.500 ≤ 2.000% for strip thicknesses of 0.50 - 1.00 mm. - Steel according to claims 1-2,
characterized
in that the Nb content is ≤ 0.020%. - Steel according to one of claims 1-3,
characterized
in that the N content is ≤ 0.0090%. - Steel according to one of claims 1-3,
characterized
in that the N content is ≤ 0.0080%. - Method for producing a cold-rolled or hot-rolled steel strip from a steel produced according to one of claims 1 to 5, in which the required multiphase steel is produced during a continuous annealing,
characterized
in that the cold-rolled or hot-rolled steel strip is heated in the continuous annealing furnace to a temperature in the range from 700 to 950°C, and in that the annealed steel strip is then cooled from the annealing temperature at a cooling rate of between 15 and 100°C/s to a first intermediate temperature of 300 to 500°C and then at a cooling rate of between 15 and 100°C/s to a second intermediate temperature of 200 to 250°C, then the steel strip is cooled in air at a cooling rate of 2 to 30°C/s until room temperature is reached, or the cooling is maintained at a cooling rate of between 15 and 100°C/s from the first intermediate temperature to room temperature. - Method according to claim 6,
characterized
in that, in the case of a hot dip coating after the heating and subsequent cooling, the cooling is halted prior to entering the hot dip bath and, after the hot dip coating, the cooling is continued at a cooling rate of between 15 and 100°C/s to an intermediate temperature of 200 to 250°C, and then the steel strip is cooled in air at a cooling rate of 2 and 30°C/s until room temperature is reached. - Method according to claim 6,
characterized
in that, in the case of a hot dip coating after the heating and subsequent cooling to the intermediate temperature of 200 to 250°C, the temperature is held for 1 to 20 s prior to entering the hot dip bath and then the steel strip is reheated to the temperature of 420 to 470°C and, after the hot dip coating has taken place, a cooling takes place at a cooling rate of between 15 and 100°C/s to the intermediate temperature of 200 to 250°C and then cooling takes place in air at a cooling rate of 2 and 30°C/s until room temperature is reached. - Method according to one of claims 6 to 8,
characterized
in that, in order to achieve a minimum tensile strength of 780 MPa, a steel strip according to claim 2 is heat-treated below the transformation point Ac1. - Method according to one of claims 6 to 8,
characterized
in that, in order to achieve a minimum tensile strength of 780 MPa, a steel strip according to claim 2 with cold-rolling degrees greater than 75% is heat-treated between Ac1 and Ac3. - Method according to one of claims 6 to 8,
characterized
in that comparable microstructure conditions and mechanical characteristic values of the strips are set by adapting the system throughput speed to different strip thicknesses in the course of the heat treatment. - Method according to one of claims 6 to 11,
characterized
in that the steel strip is skin-passed after the heat treatment. - Method according to at least one of claims 6 to 12,
characterized
in that the steel strip is tension-levelled after the heat treatment.
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DE102012006017A DE102012006017A1 (en) | 2012-03-20 | 2012-03-20 | High strength multiphase steel and method of making a strip of this steel |
PCT/DE2013/000125 WO2013139319A1 (en) | 2012-03-20 | 2013-02-27 | High-strength multi-phase steel, and method for producing a strip from said steel |
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EP2836614A1 EP2836614A1 (en) | 2015-02-18 |
EP2836614B1 true EP2836614B1 (en) | 2019-09-11 |
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US (1) | US10519525B2 (en) |
EP (1) | EP2836614B1 (en) |
KR (1) | KR102048792B1 (en) |
DE (1) | DE102012006017A1 (en) |
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DE102014017275A1 (en) * | 2014-11-18 | 2016-05-19 | Salzgitter Flachstahl Gmbh | High strength air hardening multiphase steel with excellent processing properties and method of making a strip of this steel |
DE102014017273A1 (en) | 2014-11-18 | 2016-05-19 | Salzgitter Flachstahl Gmbh | High strength air hardening multiphase steel with excellent processing properties and method of making a strip of this steel |
DE102014017274A1 (en) | 2014-11-18 | 2016-05-19 | Salzgitter Flachstahl Gmbh | Highest strength air hardening multiphase steel with excellent processing properties and method of making a strip from this steel |
CN104551441A (en) * | 2014-11-27 | 2015-04-29 | 宝山钢铁股份有限公司 | Ultrahigh-strength gas protection welding wire containing V and manufacturing method thereof |
DE102015116186A1 (en) * | 2015-09-24 | 2017-03-30 | Thyssenkrupp Ag | Semi-finished product and method for producing a vehicle component, use of a semi-finished product and vehicle component |
DE102016100648B4 (en) * | 2015-12-23 | 2018-04-12 | Benteler Automobiltechnik Gmbh | A heat treatment furnace and method for heat treating a precoated sheet steel plate and method of making a motor vehicle component |
BR112018073110A2 (en) | 2016-08-08 | 2019-03-06 | Nippon Steel & Sumitomo Metal Corp | steel plate |
RU2691809C1 (en) * | 2018-05-25 | 2019-06-18 | Публичное акционерное общество "Северсталь" (ПАО "Северсталь") | Method for production of heavy-duty high-strength wear-resistant rolled stock (versions) |
RU2690076C1 (en) * | 2018-12-18 | 2019-05-30 | Публичное акционерное общество "Северсталь" | Rolled sheet and method of its production |
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DE102020110319A1 (en) | 2020-04-15 | 2021-10-21 | Salzgitter Flachstahl Gmbh | Process for the production of a steel strip with a multiphase structure and steel strip added |
US20230151468A1 (en) | 2020-04-22 | 2023-05-18 | Thyssenkrupp Steel Europe Ag | Hot-Rolled Flat Steel Product and Method for the Production Thereof |
CN111695271B (en) * | 2020-06-29 | 2023-07-25 | 武汉钢铁有限公司 | Tracking method of steel billet surface metal in plastic deformation |
CN113862580A (en) * | 2021-09-08 | 2021-12-31 | 唐山不锈钢有限责任公司 | Hot-rolled steel strip for 590 MPa-grade cold-rolled dual-phase steel and production method thereof |
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- 2012-03-20 DE DE102012006017A patent/DE102012006017A1/en not_active Withdrawn
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- 2013-02-27 EP EP13717417.3A patent/EP2836614B1/en active Active
- 2013-02-27 US US14/386,602 patent/US10519525B2/en active Active
- 2013-02-27 WO PCT/DE2013/000125 patent/WO2013139319A1/en active Application Filing
- 2013-02-27 RU RU2014142014A patent/RU2615957C2/en active
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DE102012006017A1 (en) | 2013-09-26 |
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EP2836614A1 (en) | 2015-02-18 |
US20150034215A1 (en) | 2015-02-05 |
KR20140138990A (en) | 2014-12-04 |
US10519525B2 (en) | 2019-12-31 |
WO2013139319A1 (en) | 2013-09-26 |
RU2615957C2 (en) | 2017-04-11 |
KR102048792B1 (en) | 2019-11-26 |
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