EP1929053B1 - Method for making a steel part of multiphase microstructure - Google Patents
Method for making a steel part of multiphase microstructure Download PDFInfo
- Publication number
- EP1929053B1 EP1929053B1 EP06808157A EP06808157A EP1929053B1 EP 1929053 B1 EP1929053 B1 EP 1929053B1 EP 06808157 A EP06808157 A EP 06808157A EP 06808157 A EP06808157 A EP 06808157A EP 1929053 B1 EP1929053 B1 EP 1929053B1
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- EP
- European Patent Office
- Prior art keywords
- steel
- blank
- microstructure
- ferrite
- process according
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 132
- 239000010959 steel Substances 0.000 title claims abstract description 132
- 238000000034 method Methods 0.000 title claims abstract description 24
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 52
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 50
- 238000001816 cooling Methods 0.000 claims abstract description 44
- 239000000203 mixture Substances 0.000 claims abstract description 32
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 27
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 27
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 26
- 238000010438 heat treatment Methods 0.000 claims abstract description 17
- 229910052742 iron Inorganic materials 0.000 claims abstract description 13
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 12
- 239000012535 impurity Substances 0.000 claims abstract description 12
- 238000004519 manufacturing process Methods 0.000 claims abstract description 11
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 11
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 11
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 10
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 9
- 229910052802 copper Inorganic materials 0.000 claims abstract description 8
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 7
- 238000005520 cutting process Methods 0.000 claims abstract description 4
- 229910000734 martensite Inorganic materials 0.000 claims description 36
- 229910001563 bainite Inorganic materials 0.000 claims description 22
- 229910052720 vanadium Inorganic materials 0.000 claims description 13
- 238000000576 coating method Methods 0.000 claims description 12
- 229910000794 TRIP steel Inorganic materials 0.000 claims description 10
- 239000011248 coating agent Substances 0.000 claims description 9
- 229910052758 niobium Inorganic materials 0.000 claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 5
- 239000002184 metal Substances 0.000 claims description 5
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 4
- 239000011701 zinc Substances 0.000 claims description 4
- 229910052725 zinc Inorganic materials 0.000 claims description 4
- 229910000838 Al alloy Inorganic materials 0.000 claims description 3
- 229910001297 Zn alloy Inorganic materials 0.000 claims description 2
- 238000003723 Smelting Methods 0.000 claims 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 abstract description 37
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 abstract description 26
- 229910052710 silicon Inorganic materials 0.000 abstract description 21
- 239000010703 silicon Substances 0.000 abstract description 21
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 18
- 229910052799 carbon Inorganic materials 0.000 abstract description 18
- 239000011572 manganese Substances 0.000 abstract description 17
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 abstract description 16
- 229910052748 manganese Inorganic materials 0.000 abstract description 13
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 abstract description 12
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 abstract description 12
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 abstract description 12
- 239000011651 chromium Substances 0.000 abstract description 11
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 abstract description 10
- 239000010936 titanium Substances 0.000 abstract description 10
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 abstract description 10
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 abstract description 9
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 abstract description 7
- 239000010949 copper Substances 0.000 abstract description 7
- 239000011733 molybdenum Substances 0.000 abstract description 7
- 239000011574 phosphorus Substances 0.000 abstract description 7
- 239000011593 sulfur Substances 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 description 16
- 238000007493 shaping process Methods 0.000 description 15
- 239000004411 aluminium Substances 0.000 description 12
- 239000010955 niobium Substances 0.000 description 10
- 230000009466 transformation Effects 0.000 description 9
- 229910001567 cementite Inorganic materials 0.000 description 8
- 230000000694 effects Effects 0.000 description 8
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 8
- 238000010521 absorption reaction Methods 0.000 description 6
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 238000005246 galvanizing Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 239000003381 stabilizer Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 240000008042 Zea mays Species 0.000 description 2
- 235000015115 caffè latte Nutrition 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
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- 239000006185 dispersion Substances 0.000 description 2
- 230000009977 dual effect Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 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 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 230000006641 stabilisation Effects 0.000 description 2
- KRQUFUKTQHISJB-YYADALCUSA-N 2-[(E)-N-[2-(4-chlorophenoxy)propoxy]-C-propylcarbonimidoyl]-3-hydroxy-5-(thian-3-yl)cyclohex-2-en-1-one Chemical compound CCC\C(=N/OCC(C)OC1=CC=C(Cl)C=C1)C1=C(O)CC(CC1=O)C1CCCSC1 KRQUFUKTQHISJB-YYADALCUSA-N 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 241001080024 Telles Species 0.000 description 1
- 229910000611 Zinc aluminium Inorganic materials 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- HXFVOUUOTHJFPX-UHFFFAOYSA-N alumane;zinc Chemical compound [AlH3].[Zn] HXFVOUUOTHJFPX-UHFFFAOYSA-N 0.000 description 1
- CSDREXVUYHZDNP-UHFFFAOYSA-N alumanylidynesilicon Chemical compound [Al].[Si] CSDREXVUYHZDNP-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000003416 augmentation Effects 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 230000000763 evoking effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 229910001338 liquidmetal Inorganic materials 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 150000003376 silicon Chemical class 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
Images
Classifications
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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
- C23C2/26—After-treatment
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/62—Quenching devices
- C21D1/673—Quenching devices for die quenching
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—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
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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
- C23C2/12—Aluminium or alloys based thereon
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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
- C23C2/26—After-treatment
- C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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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
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
Definitions
- the present invention relates to a method of manufacturing a multi-phased microstructure steel piece homogeneous in each of the zones of said part, and having high mechanical characteristics.
- TRIP steels the term meaning transformation induced plasticity
- dual phase steels which combine a very high mechanical strength with very high possibilities of deformation.
- TRIP steels have a microstructure composed of ferrite, residual austenite, and possibly bainite and martensite, which enables them to reach tensile strengths ranging from 600 to 1000 MPa.
- the dual-phase steels have a microstructure composed of ferrite and martensite, which enables them to reach tensile strengths ranging from 400 MPa to more than 1200 MPa.
- this type of parts it is cold forming, for example by stamping between tools, a blank cut in a cold rolled strip of dual phase steel or TRIP steel.
- the microstructure of the steel is no longer homogeneous in each of the areas of the room, and the behavior of the part in use is difficult to predict.
- the residual austenite is transformed into martensite under the effect of the deformation.
- the deformation is not homogeneous throughout the room, some areas of the room will still contain residual austenite not transformed into martensite and therefore having a significant residual ductility, while other areas of the room having undergone significant deformation will present a ferritic-martensitic structure optionally comprising ductile bainite.
- the object of the present invention is therefore to overcome the aforementioned drawbacks, and to propose a method of manufacturing a steel part comprising ferrite and having a homogeneous multi-phased microstructure in each of the zones of said part, and not exhibiting resilient return after forming a blank from a steel strip whose composition is typical of that of multi-phase microstructure steels.
- the area of the different phases is measured in a section made along a plane perpendicular to the plane of the strip (this plane may be parallel to to the rolling direction, or parallel to the direction transverse to the rolling).
- the different phases sought are revealed by a chemical attack adapted according to their nature.
- forming tool means any tool that makes it possible to obtain a part from a blank, such as for example a stamping tool. This excludes cold or hot rolling tools.
- the inventors have demonstrated that heating the blank to a holding temperature T1 between Ac1 and Ac3 gives, provided that the cooling rate is sufficient, a multi-phase microstructure comprising ferrite having mechanical properties. homogeneous regardless of the cooling rate of the blank between the tools.
- the homogeneity of the mechanical properties is defined in the sense of the invention by a dispersion of the tensile strength Rm in a range of cooling rates ranging from 10 to 100 ° C./s less than 25%.
- the invention has as its second object a steel part comprising ferrite and having a homogeneous multi-phased microstructure in each zone of said part, obtainable by said method.
- the third object of the invention is a motorized land vehicle comprising said part.
- the method according to the invention consists in shaping hot, in a certain temperature range, a blank previously cut in a steel strip whose composition is typical of that of multi-phase microstructure steels, but which initially does not does not necessarily have a multi-phased structure, to form a steel part that acquires a multi-phase microstructure during its cooling between the formatting tools.
- the inventors have furthermore demonstrated that, provided that the cooling rate is sufficient, a homogeneous multi-phased microstructure could be obtained whatever the rate of cooling of the blank between the tools.
- the advantage of this invention lies in the fact that it is not necessary to form the multi-phased microstructure at the stage of manufacture of the hot sheet, or of its coating, and that forming it at The stage of manufacture of the part, by hot forming, ensures a homogeneous final multi-phased microstructure in each of the zones of the part, which is advantageous in the case of a use for absorption parts. energy, because the microstructure is not altered as is the case when cold forming of dual-phase steel or TRIP steel parts.
- the inventors have indeed verified that the energy absorption capacity of a part, determined by the tensile strength multiplied by the elongation (Rm ⁇ A), is greater when the part has been obtained. according to the invention than when it was obtained by cold forming of a dual phase steel blank or TRIP steel. Indeed, cold forming consumes some of the energy absorption capacity.
- Another advantage of the invention lies in the fact that the hot shaping leads to a much higher shaping ability than cold.
- a variety of wider shapes can be accessed and new designs of parts can be envisaged while retaining steel compositions whose characteristics, such as weldability, are known.
- the part obtained has a multi-phase microstructure comprising ferrite at a proportion preferably greater than or equal to 25% by surface, and at least one of the following phases: martensite, bainite, residual austenite.
- a proportion of at least 25% ferrite surface area makes it possible to give the steel ductility sufficient for the formed parts to have a high energy absorption capacity.
- the remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
- this metal coating is chosen from zinc or zinc alloy coatings (zinc-aluminum for example), and if it is also desired to withstand good heat resistance, the coatings of aluminum or aluminum alloy (aluminum-silicon for example). These coatings are deposited in a conventional manner either by hot dipping in a bath of liquid metal, by electrodeposition, or under vacuum.
- the steel blank is heated to bring it to a holding temperature T1 greater than Ac1 but lower than Ac3, and is maintained at this temperature T1 for a holding time M that is adjusted so that steel, after heating the blank, comprises a proportion of austenite greater than or equal to 25% by surface.
- the heated blank is transferred into a forming tool to form a part, and cool it.
- the cooling of the workpiece within the shaping tool is performed with a cooling rate V sufficient to prevent all of the austenite from becoming ferrite, and so that the microstructure of the steel after cooling the piece is a multi-phase microstructure comprising ferrite, and which is homogeneous in each of the areas of the room.
- Homogeneous multi-phased microstructure in each of the zones of the part is understood to mean a microstructure having constancy in terms of proportion and morphology in each zone of the part, and in which the different phases are uniformly distributed.
- the shaping tools can be cooled, for example by fluid circulation.
- clamping force of the shaping tool must be sufficient to ensure intimate contact between the blank and the tool, and ensure efficient and homogeneous cooling of the room.
- Cold pre-deformation of the blank for example by profiling or cold stamping of the blank, before hot forming is advantageous insofar as it allows access to parts that may have a more complex geometry .
- the method according to the invention is used to manufacture a steel part having a multi-phase microstructure comprising either ferrite and martensite, either ferrite and bainite, or ferrite, martensite and bainite.
- the remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
- the blank is heated to a holding temperature T1 greater than Ac1 but less than Ac3, so as to to control the proportion of austenite formed during the heating of the blank, and not to exceed the preferential upper limit of 75% of austenite surface area.
- a proportion of austenite in the steel heated to a holding temperature T1 during a holding time M of between 25 and 75% by weight offers a good compromise in terms of the mechanical strength of the steel after shaping and regularity. mechanical characteristics of the steel thanks to the robustness of the process. Indeed, beyond 25% of austenite surface, sufficient hardening phases, such as for example martensite and / or bainite, are formed during the cooling of the steel so that the yield strength Re of the steel after shaping is sufficient.
- the holding time of the steel blank at the holding temperature T1 depends essentially on the thickness of the strip.
- the thickness of the strip is typically between 0.3 and 3 mm. Therefore, to form a proportion of austenite between 25 and 75% by surface, the holding time M is preferably between 10 and 1000 s. If the steel blank is maintained at a holding temperature T1 for a holding time M greater than 1000 s, the austenite grains increase and the elastic limit Re of the steel after forming will be limited. In addition, the hardenability of the steel is reduced and the surface of the steel oxidizes.
- the cooling rate V of the steel part in the forming tool depends on the deformation and the quality of the contact between the tool and the steel blank. However, the cooling rate V must be sufficiently high for the desired multi-phased microstructure to be obtained, and is preferably greater than 10 ° C./s. With a cooling rate V less than or equal to 10 ° C / s, it is likely to form carbides that will contribute to degrade the mechanical characteristics of the part.
- a multi-phase steel piece comprising more than 25% ferrite surface area is formed, the rest being martensite and / or bainite, the various phases being homogeneously distributed in each of the zones of the In a preferred embodiment of the invention, 25 to 75% ferrite surface area and 25 to 75% surface area of martensite and / or bainite are preferably formed.
- the method according to the invention is used to manufacture a TRIP steel part.
- TRIP steel a multiphase microstructure comprising ferrite, residual austenite, and possibly martensite and / or bainite.
- the remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
- the holding time of the steel blank at a holding temperature T1 greater than Ac1 but less than Ac3 essentially depends on the thickness of the strip.
- the thickness of the strip is typically between 0.3 and 3 mm. Therefore, to form a proportion of austenite greater than or equal to 25% by surface, the holding time M is preferably between 10 and 1000 s. If the steel blank is maintained at a holding temperature T1 for a holding time M greater than 1000 s, the austenite grains increase and the elastic limit Re of the steel after forming will be limited. In addition, the hardenability of the steel is reduced and the surface of the steel oxidizes. On the other hand, if the blank is held for a holding time M less than 10 s, the proportion of austenite formed will be insufficient, and sufficient residual austenite and bainite will not be formed during the cooling of the part between the tool.
- the cooling rate V of the steel part in the forming tool depends on the deformation and the quality of the contact between the tool and the steel blank. To obtain a steel part having a multi-phased microstructure TRIP, it is preferable that the cooling rate V is between 10 ° C./s and 200 ° C./s. In fact, below 10 ° C / s, ferrite and carbide will be essentially formed, and insufficient residual austenite and martensite, and above 200 ° C / s, essentially martensite will be formed. insufficient residual austenite.
- a multiphase steel part consisting, in% by surface, of ferrite at a proportion greater than or equal to 25%, of 3 to 30% of residual austenite, and possibly of martensite, is formed. / or bainite.
- the TRIP effect can advantageously be used to absorb energy in the event of high speed shocks. Indeed, during a significant deformation of a TRIP steel part, the residual austenite is gradually transformed into martensite by selecting the orientation of the martensite. This has the effect of reducing the residual stresses in the martensite, reducing the internal stresses in the part, and finally limiting the damage of the part, because the rupture thereof will take place for an elongation A more important than if it was not TRIP steel.
- the inventors have carried out tests both on steels presenting on the one hand a composition typical of that of mutli-phased microstructure steels comprising ferrite and martensite and / or bainite (point 1), and of on the other hand a composition typical of that of TRIP mutli-phased microstructure steels (point 2).
- Blanks 400 x 600 mm in size are cut from a steel strip whose composition, indicated in Table I, is that of a steel grade DP780 (Dual Phase 780).
- the strip has a thickness of 1.2 mm.
- the Ac1 temperature of this steel is 705 ° C and the Ac3 temperature is 815 ° C.
- the blanks are brought to a variable holding temperature T1, during a holding period of 5 minutes. Then, they are immediately transferred to a stamping tool in which they are both shaped and cooled with variable cooling rates V, keeping them in the tool for a period of 60 s.
- the stamped parts are similar to an Omega shape structure
- the purpose of this test is to show the interest of a hot shaping compared to a cold shaping, and to evaluate the elastic return.
- a piece of DP780 grade steel is manufactured by cold stamping a blank cut from a 1.2 mm thick steel strip, the composition of which is indicated in Table I, but which, unlike the strip used in point 1, already has before stamping a multi-phased microstructure comprising 70% ferrite surface, 15% martensite surface, and 15% bainite surface.
- FIG. 1 clearly shows that the part formed by cold stamping (marked in the figure by the letter G) has a strong springback, with respect to the piece A (see Table II) formed by hot stamping (marked by the letter AT).
- Blanks measuring 200 ⁇ 500 mm are cut from a steel strip whose composition, indicated in Table III, is that of a TRIP 800 grade steel.
- the strip has a thickness of 1.2 mm.
- the Ac1 temperature of this steel is 751 ° C and the Ac3 temperature is 875 ° C.
- the blanks are brought to a variable holding temperature T1, during a hold time of 5 minutes, and then immediately transferred to a stamping tool in which they are both shaped and cooled with a cooling rate V of 45 ° C / s, keeping them in the tool for 60 s.
- the stamped parts are similar to an Omega shape structure.
- Table III chemical composition of the steel according to the invention, expressed in% by weight, the balance being iron or impurities VS mn Yes al MB Cr P Ti Nb V 0.2 1.5 1.5 0.05 0,007 0.01 0,011 0.005 - - T1 (° C) Room Re (MPa) Rm (MPa) AT (%) Rm x A Microstructure (% surface area) * 760 H 541 1174 12.4 14558 35% F + 17% A + 48% M * 800 I 485 1171 12.8 14989 45% F + 11% A + 44% M * 840 J 454 1110 14.3 15873 45% F + 15% A + 38% M + 2% B * according to the invention
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Abstract
Description
La présente invention concerne un procédé de fabrication d'une pièce en acier de microstructure multi-phasée homogène dans chacune des zones de ladite pièce, et présentant de hautes caractéristiques mécaniques.The present invention relates to a method of manufacturing a multi-phased microstructure steel piece homogeneous in each of the zones of said part, and having high mechanical characteristics.
Afin de répondre aux exigences d'allègement des structures automobiles, il est connu d'utiliser soit les aciers TRIP (ce terme signifiant transformation induced plasticity), soit les aciers dual phase qui allient une très haute résistance mécanique à des possibilités très élevées de déformation. Les aciers TRIP ont une microstructure composée de ferrite, d'austénite résiduelle, et éventuellement de bainite et de martensite, qui leur permet d'atteindre des résistances à la traction allant de 600 à 1000 MPa. Les aciers dual-phase ont une microstructure composée de ferrite et de martensite, qui leur permet d'atteindre des résistances à la traction allant de 400 MPa à plus de 1200 MPa.In order to meet the requirements for lightening automotive structures, it is known to use either TRIP steels (the term meaning transformation induced plasticity) or dual phase steels which combine a very high mechanical strength with very high possibilities of deformation. . TRIP steels have a microstructure composed of ferrite, residual austenite, and possibly bainite and martensite, which enables them to reach tensile strengths ranging from 600 to 1000 MPa. The dual-phase steels have a microstructure composed of ferrite and martensite, which enables them to reach tensile strengths ranging from 400 MPa to more than 1200 MPa.
Ces types d'aciers sont largement utilisés pour la réalisation de pièces d'absorption d'énergie, comme par exemple des pièces de structure et de sécurité telles que les longerons, les traverses et les renforts.These types of steels are widely used for the realization of energy absorbing parts, such as structural and safety parts such as longitudinal members, sleepers and reinforcements.
Habituellement pour fabriquer ce type de pièces, on procède au formage à froid, par exemple par emboutissage entre outils, d'un flan découpé dans une bande laminée à froid en acier dual phase, ou en acier TRIP.Usually to manufacture this type of parts, it is cold forming, for example by stamping between tools, a blank cut in a cold rolled strip of dual phase steel or TRIP steel.
Procédés typiques par emboutissage sont divulgués dans
Cependant, le développement des pièces en acier dual phase ou en acier TRIP est limité du fait de la difficulté à maîtriser le retour élastique de la pièce mise en forme, retour élastique qui est d'autant plus important que la résistance à la traction Rm de l'acier est importante. En effet, pour pallier l'effet du retour élastique, les constructeurs automobiles sont obligés d'intégrer ce paramètre lors de la conception de nouvelles pièces, ce qui d'une part, nécessite de nombreux développements, et d'autre part, limite l'étendue des formes réalisables.However, the development of dual phase steel or TRIP steel parts is limited because of the difficulty in controlling the elastic return of the shaped part, elastic return which is even more important than the tensile strength Rm of steel is important. Indeed, to overcome the effect of springback, car manufacturers are obliged to integrate this parameter when designing new parts, which on the one hand, requires many developments, and on the other hand, limits extent of achievable forms.
En outre, en cas de déformation importante, la microstructure de l'acier n'est plus homogène dans chacune des zones de la pièce, et le comportement de la pièce en service est difficilement prévisible. Par exemple, lors de la mise en forme à froid d'une tôle en acier TRIP, l'austénite résiduelle se transforme en martensite sous l'effet de la déformation. La déformation n'étant pas homogène dans toute la pièce, certaines zones de la pièce comporteront encore de l'austénite résiduelle non transformée en martensite et présentant par conséquent une ductilité résiduelle importante, alors que d'autres zones de la pièce ayant subi une déformation importante présenteront une structure ferrito-martensitique comprenant éventuellement de la bainite peu ductile.In addition, in case of significant deformation, the microstructure of the steel is no longer homogeneous in each of the areas of the room, and the behavior of the part in use is difficult to predict. For example, during the cold forming of a TRIP steel sheet, the residual austenite is transformed into martensite under the effect of the deformation. The deformation is not homogeneous throughout the room, some areas of the room will still contain residual austenite not transformed into martensite and therefore having a significant residual ductility, while other areas of the room having undergone significant deformation will present a ferritic-martensitic structure optionally comprising ductile bainite.
Le but de la présente invention est donc remédier aux inconvénients précités, et de proposer un procédé de fabrication d'une pièce en acier comprenant de la ferrite et présentant une microstructure multi-phasée homogène dans chacune des zones de ladite pièce, et ne présentant pas de retour élastique après mise en forme d'un flan issu d'une bande en acier dont la composition est typique de celle des aciers de microstructure muti-phasée.The object of the present invention is therefore to overcome the aforementioned drawbacks, and to propose a method of manufacturing a steel part comprising ferrite and having a homogeneous multi-phased microstructure in each of the zones of said part, and not exhibiting resilient return after forming a blank from a steel strip whose composition is typical of that of multi-phase microstructure steels.
A cet effet, l'invention définie selon la revendication 1 a pour premier objet un procédé de fabrication d'une pièce en acier présentant une microstructure multi-phasée, ladite microstructure comprenant de la ferrite et étant homogène dans chacune des zones de ladite pièce, comprenant les étapes consistant à :
- découper un flan dans une bande en acier dont la composition est constituée en % en poids :
- 0,01 ≤ C ≤ 0,50 %
- 0,50 ≤ Mn ≤ 3,0 %
- 0,001 ≤ Si ≤ 3,0 %
- 0, 005 ≤ Al ≤ 3,0 %
- Mo ≤ 1,0 %
- Cr ≤ 1,5 %
- P ≤ 0,10%
- Ti≤0,15%
- V≤1,0%,
- Ni ≤ 2,0%
- Cu≤2,0%
- S≤0,05%
- Nb≤0,15%
- éventuellement pré-déformer à froid ledit flan,
- chauffer ledit flan jusqu'à atteindre une température de maintien T1 supérieure à Ac1 mais inférieure à Ac3, et le maintenir à cette température de maintien T1 pendant un temps de maintien M ajusté de manière à ce que l'acier après chauffage du flan comprenne une proportion d'austénite supérieure ou égale à 25 % surfacique,
- transférer ledit flan chauffé au sein d'un outillage de mise en forme de manière à former à chaud ladite pièce, et
- refroidir la pièce au sein de l'outillage avec une vitesse de refroidissement V telle que la microstructure de l'acier après refroidissement de la pièce soit une microstructure multi-phasée, ladite microstructure comprenant de la ferrite et étant homogène dans chacune des zones de ladite pièce.
- cutting a blank into a steel strip whose composition consists of% by weight:
- 0.01 ≤ C ≤ 0.50%
- 0.50 ≤ Mn ≤ 3.0%
- 0.001 ≤ If ≤ 3.0%
- 0, 005 ≤ Al ≤ 3.0%
- Mo ≤ 1.0%
- Cr ≤ 1.5%
- P ≤ 0.10%
- Ti≤0,15%
- V≤1,0%
- Ni ≤ 2.0%
- Cu≤2,0%
- S≤0,05%
- Nb≤0,15%
- optionally pre-deforming said blank,
- heating said blank until a holding temperature T1 higher than Ac1 but lower than Ac3, and maintain it at this holding temperature T1 for a hold time M adjusted so that the steel after heating the blank comprises a proportion of austenite greater than or equal to 25% by surface,
- transferring said heated blank into a shaping tool so as to heat said workpiece, and
- cooling the part within the tooling with a cooling rate V such that the microstructure of the steel after cooling of the part is a multi-phase microstructure, said microstructure comprising ferrite and being homogeneous in each of the zones of said room.
Pour déterminer les % surfaciques des différentes phases présentes dans une microstructure (phase ferritique, phase austénitique...), on mesure l'aire des différentes phases dans une coupe réalisée suivant un plan perpendiculaire au plan de la bande (ce plan pourra être parallèle à la direction de laminage, ou parallèle à la direction transverse au laminage). Les différentes phases recherchées sont révélées par une attaque chimique adaptée en fonction de leur nature.To determine the surface% of the various phases present in a microstructure (ferritic phase, austenitic phase, etc.), the area of the different phases is measured in a section made along a plane perpendicular to the plane of the strip (this plane may be parallel to to the rolling direction, or parallel to the direction transverse to the rolling). The different phases sought are revealed by a chemical attack adapted according to their nature.
Au sens de la présente invention, on entend par outil de mise en forme, tout outil qui permet d'obtenir une pièce à partir d'un flan, comme par exemple un outil d'emboutissage. Cela exclut donc les outils de laminage à froid, ou à chaud.For the purposes of the present invention, the term "forming tool" means any tool that makes it possible to obtain a part from a blank, such as for example a stamping tool. This excludes cold or hot rolling tools.
Les inventeurs ont mis en évidence qu'en chauffant le flan à une température de maintien T1 comprise entre Ac1 et Ac3, on obtient, sous réserve que la vitesse de refroidissement soit suffisante, une microstructure multi-phasée comprenant de la ferrite présentant des propriétés mécaniques homogènes quelle que soit la vitesse de refroidissement du flan entre les outils. L'homogénéité des propriété mécaniques est définie au sens de l'invention par une dispersion de la résistance à la traction Rm dans un domaine de vitesses de refroidissement variant de 10 à 100 °C/s inférieur à 25%. En effet, les inventeurs ont constaté, qu'en faisant subir au flan un traitement thermique dans le domaine intercritique, alors Rm (100°C/s) - Rm (10°C/s°) / Rm (100°C/s) < 0,25, Rm (100°C/s) étant la résistance à la traction de la pièce refroidie à 100°C/s, et Rm (10°C/s) étant la résistance à la traction de la pièce refroidie à 10°C/s.The inventors have demonstrated that heating the blank to a holding temperature T1 between Ac1 and Ac3 gives, provided that the cooling rate is sufficient, a multi-phase microstructure comprising ferrite having mechanical properties. homogeneous regardless of the cooling rate of the blank between the tools. The homogeneity of the mechanical properties is defined in the sense of the invention by a dispersion of the tensile strength Rm in a range of cooling rates ranging from 10 to 100 ° C./s less than 25%. Indeed, the inventors have found that by subjecting the blank to heat treatment in the intercritical range, then Rm (100 ° C / s) - Rm (10 ° C / sec) / Rm (100 ° C / sec) ) <0.25, Rm (100 ° C / s) being the tensile strength of the piece cooled to 100 ° C / s, and Rm (10 ° C / s) being the tensile strength of the cooled part at 10 ° C / s.
L'invention a pour deuxième objet une pièce en acier comprenant de la ferrite et présentant une microstructure multi-phasée homogène dans chacune des zones de ladite pièce, pouvant être obtenue par ledit procédé.The invention has as its second object a steel part comprising ferrite and having a homogeneous multi-phased microstructure in each zone of said part, obtainable by said method.
Enfin l'invention a pour troisième objet un véhicule terrestre à moteur comprenant ladite pièce.Finally, the third object of the invention is a motorized land vehicle comprising said part.
Les caractéristiques et avantages de la présente invention apparaîtront mieux au cours de la description qui va suivre, donnée à titre d'exemple non limitatif, en référence à la figure 1 annexée sur laquelle :
- la figure 1 est une photographie d'une pièce obtenue par mise en forme à froid (référence G) et d'une pièce obtenue par mise en forme à chaud (référence A).
- Figure 1 is a photograph of a part obtained by cold forming (reference G) and a part obtained by hot forming (reference A).
Le procédé selon l'invention consiste à mettre en forme à chaud, dans une certaine gamme de température, un flan préalablement découpé dans une bande en acier dont la composition est typique de celle des aciers de microstructure multi-phasée, mais qui au départ ne possède pas forcément une structure multi-phasée, pour former une pièce en acier qui acquière une microstructure multi-phasée lors de son refroidissement entre les outils de mise en forme. Les inventeurs ont par ailleurs mis en évidence que sous réserve que la vitesse de refroidissement soit suffisante, une microstructure multi-phasée homogène pouvait être obtenue quelque soit la vitesse de refroidissement du flan entre les outils.The method according to the invention consists in shaping hot, in a certain temperature range, a blank previously cut in a steel strip whose composition is typical of that of multi-phase microstructure steels, but which initially does not does not necessarily have a multi-phased structure, to form a steel part that acquires a multi-phase microstructure during its cooling between the formatting tools. The inventors have furthermore demonstrated that, provided that the cooling rate is sufficient, a homogeneous multi-phased microstructure could be obtained whatever the rate of cooling of the blank between the tools.
L'intérêt de cette invention réside dans le fait que l'on n'est pas tenu de former la microstructure multi-phasée au stade de la fabrication de la tôle à chaud, ou de son revêtement, et que le fait de la former au stade de la fabrication de la pièce, par mise en forme à chaud, permet de garantir une microstructure multi-phasée finale homogène dans chacune des zones de la pièce, ce qui est avantageux dans le cas d'une utilisation pour pièces d'absorption d'énergie, car la microstructure n'est pas altérée comme c'est le cas lors de la mise en forme à froid de pièces en acier dual-phase ou en acier TRIP.The advantage of this invention lies in the fact that it is not necessary to form the multi-phased microstructure at the stage of manufacture of the hot sheet, or of its coating, and that forming it at The stage of manufacture of the part, by hot forming, ensures a homogeneous final multi-phased microstructure in each of the zones of the part, which is advantageous in the case of a use for absorption parts. energy, because the microstructure is not altered as is the case when cold forming of dual-phase steel or TRIP steel parts.
Les inventeurs ont en effet vérifié que la capacité d'absorption d'énergie d'une pièce, déterminée par la résistance à la traction multipliée par l'allongement (Rm x A), est plus importante lorsque la pièce a été obtenue selon l'invention que lorsqu'elle a été obtenue par formage à froid d'un flan en acier dual phase ou en acier TRIP. En effet, le formage à froid consomme une partie de la capacité d'absorption d'énergie.The inventors have indeed verified that the energy absorption capacity of a part, determined by the tensile strength multiplied by the elongation (Rm × A), is greater when the part has been obtained. according to the invention than when it was obtained by cold forming of a dual phase steel blank or TRIP steel. Indeed, cold forming consumes some of the energy absorption capacity.
En outre, en procédant à une mise en forme à chaud, le retour élastique de la pièce devient négligeable, alors qu'il est très important dans le cadre d'une mise en forme à froid. Il est d'ailleurs d'autant plus important que la résistance à la traction Rm de l'acier augmente, ce qui constitue un frein à l'utilisation des aciers à très haute résistance.In addition, by carrying out a hot shaping, the elastic return of the part becomes negligible, while it is very important in the context of cold forming. It is also more important that the tensile strength Rm of steel increases, which is a brake on the use of very high strength steels.
Un autre avantage de l'invention réside dans le fait que la mise en forme à chaud conduit à une aptitude à la mise en forme nettement plus élevée qu'à froid. On peut ainsi accéder à une variété de formes plus larges et envisager de nouvelles conceptions de pièces tout en conservant des compositions d'acier dont les caractéristiques, comme par exemple la soudabilité, sont connues.Another advantage of the invention lies in the fact that the hot shaping leads to a much higher shaping ability than cold. Thus, a variety of wider shapes can be accessed and new designs of parts can be envisaged while retaining steel compositions whose characteristics, such as weldability, are known.
La pièce obtenue présente une microstructure multi-phasée comprenant de la ferrite à une proportion de préférence supérieure ou égale à 25 % surfacique, et au moins une des phases suivantes : martensite, bainite, austénite résiduelle. En effet, une proportion d'au moins 25 % surfacique de ferrite permet de conférer à l'acier une ductilité suffisante pour que les pièces formées présentent une capacité d'absorption d'énergie importante.The part obtained has a multi-phase microstructure comprising ferrite at a proportion preferably greater than or equal to 25% by surface, and at least one of the following phases: martensite, bainite, residual austenite. In fact, a proportion of at least 25% ferrite surface area makes it possible to give the steel ductility sufficient for the formed parts to have a high energy absorption capacity.
Le flan en acier destiné à être mis en forme, par exemple par emboutissage, est préalablement découpé soit dans une bande en acier laminée à chaud, soit dans une bande en acier laminée à froid, l'acier étant constitué des éléments suivants :
- du carbone à une teneur comprise entre 0,01 et 0,50 % en poids. Cet élément est essentiel à l'obtention de bonnes caractéristiques mécaniques, mais ne doit pas être présent en quantité trop importante pour ne pas léser la soudabilité. Pour favoriser la trempabilité, et obtenir une limite d'élasticité Re suffisante, la teneur en carbone doit être supérieure ou égale à 0,01 % en poids.
- du manganèse à une teneur comprise entre 0,50 et 3,0 % en poids. Le manganèse favorise la trempabilité, ce qui permet d'atteindre une limite d'élasticité Re élevée. Cependant, il faut éviter que l'acier ne comprenne trop de manganèse, pour éviter la ségrégation qui peut être mise en évidence dans les traitements thermiques qu'on évoquera ultérieurement dans la description. En outre, un excès de manganèse empêche le soudage par étincelage si la quantité de silicium est insuffisante, et détériore l'aptitude à la galvanisation de l'acier. Le manganèse joue également un rôle dans l'inter-diffusion du fer et de l'aluminium, en cas de revêtement de l'acier par de l'aluminium ou un alliage d'aluminium.
- du silicium à une teneur comprise entre 0,001 et 3,0 % en poids. Le silicium améliore la limite d'élasticité Re de l'acier. Cependant au-delà de 3,0 % en poids, la galvanisation au trempé à chaud de l'acier devient difficile, et l'aspect du revêtement de zinc n'est pas satisfaisant.
- de l'aluminium à une teneur comprise entre 0,005 et 3,0 % en poids. L'aluminium stabilise la ferrite. Sa teneur doit rester inférieure à 3,0 % en poids pour éviter de détériorer la soudabilité due à la présence d'oxyde d'aluminium dans la zone soudée. Cependant, un minimum d'aluminium est requis pour désoxyder l'acier.
- du molybdène à une teneur inférieure ou égale à 1,0 % en poids. Le molybdène favorise la formation de martensite et, augmente la résistance à la corrosion. Cependant, un excès de molybdène peut favoriser le phénomène de fissuration à froid dans les zones soudées, et réduire la ténacité de l'acier.
- du chrome à une teneur inférieure ou égale à 1,5 % en poids. La teneur en chrome doit être limitée pour éviter les problèmes d'aspect de surface en cas de galvanisation de l'acier.
- du phosphore à une teneur inférieure ou égale à 0,10 % en poids. Le phosphore est ajouté pour permettre de réduire la quantité de carbone et améliorer la soudabilité, tout en maintenant un niveau équivalent de limite d'élasticité Re de l'acier. Cependant, au-delà de 0,10 % en poids, il fragilise l'acier en raison de l'augmentation du risque de défauts de ségrégation, et la soudabilité est détériorée.
- du titane à une teneur inférieure ou égale à 0,20 % en poids. Le titane améliore la limite d'élasticité Re, cependant sa teneur doit être limitée à 0,20 % en poids pour éviter la dégradation de la ténacité.
- du vanadium à une teneur inférieure ou égale à 1,0 % en poids. Le vanadium améliore la limite d'élasticité Re par affinement du grain et favorise la soudabilité de l'acier. Cependant, au delà de 1,0 % en poids, la ténacité de l'acier est détériorée et des fissures risquent d'apparaître dans les zones soudées.
- à titre optionnel, du nickel à une teneur inférieure ou égale à 2,0 % en poids. Le nickel augmente la limite d'élasticité Re. On limite généralement sa teneur à 2,0 % en poids en raison de son coût élevé.
- à titre optionnel, du cuivre à une teneur inférieure ou égale à 2,0 % en poids. Le cuivre augmente la limite d'élasticité Re, cependant un excès de cuivre favorise l'apparition de fissures lors du laminage à chaud, et dégrade la formabilité à chaud de l'acier.
- à titre optionnel, du soufre à une teneur inférieure ou égale à 0,05 % en poids. Le soufre est un élément ségrégeant dont la teneur doit être limitée afin d'éviter les fissures lors du laminage à chaud.
- à titre optionnel, du niobium à une teneur inférieure ou égale à 0,15 % en poids. Le niobium favorise la précipitation de carbonitrure, ce qui augmente la limite d'élasticité Re. Cependant, au-delà de 0,15 % en poids, la soudabilité et la formabilité à chaud sont dégradées.
- carbon at a content of between 0.01 and 0.50% by weight. This element is essential to obtain good mechanical properties, but must not be present in too large a quantity not to damage the weldability. To promote quenchability, and obtain a sufficient elastic limit Re, the carbon content must be greater than or equal to 0.01% by weight.
- manganese at a content of between 0.50 and 3.0% by weight. Manganese promotes hardenability, which allows to achieve a yield strength Re high. However, it is necessary to avoid that the steel understands too much manganese, to avoid the segregation which can be highlighted in the heat treatments which will be evoked later in the description. In addition, an excess of manganese prevents spark welding if the amount of silicon is insufficient, and deteriorates the galvanizing ability of the steel. Manganese also plays a role in the inter-diffusion of iron and aluminum, when steel is coated with aluminum or an aluminum alloy.
- silicon at a content of between 0.001 and 3.0% by weight. Silicon improves the elasticity limit Re of steel. However, above 3.0% by weight, the hot dipping of the steel becomes difficult, and the appearance of the zinc coating is unsatisfactory.
- aluminum at a content of between 0.005 and 3.0% by weight. Aluminum stabilizes ferrite. Its content must remain below 3.0% by weight to avoid damaging the weldability due to the presence of aluminum oxide in the welded zone. However, a minimum of aluminum is required to deoxidize the steel.
- molybdenum at a content of not more than 1.0% by weight. Molybdenum promotes the formation of martensite and increases the resistance to corrosion. However, an excess of molybdenum can promote the phenomenon of cold cracking in welded areas, and reduce the toughness of the steel.
- chromium at a content less than or equal to 1.5% by weight. The chromium content must be limited to avoid surface appearance problems when galvanizing the steel.
- phosphorus at a content less than or equal to 0.10% by weight. Phosphorus is added to reduce the amount of carbon and improve weldability, while maintaining an equivalent level of steel yield strength Re. However, beyond 0.10% by weight, it weakens the steel because of the increased risk of segregation defects, and the weldability is deteriorated.
- titanium at a content less than or equal to 0.20% by weight. Titanium improves the yield strength Re, however its content must be limited to 0.20% by weight to avoid the degradation of toughness.
- vanadium at a content of less than or equal to 1.0% by weight. Vanadium improves the yield strength Re by grain refinement and promotes the weldability of steel. However, beyond 1.0% by weight, the toughness of the steel is deteriorated and cracks may appear in the welded areas.
- optionally, nickel at a content less than or equal to 2.0% by weight. Nickel increases the yield strength Re. Its content is generally limited to 2.0% by weight because of its high cost.
- optionally copper less than or equal to 2.0% by weight. Copper increases the yield strength Re, however an excess of copper promotes the appearance of cracks during hot rolling, and degrades the hot formability of the steel.
- optionally, sulfur at a content of less than or equal to 0.05% by weight. Sulfur is a segregating element whose content must be limited in order to avoid cracks during hot rolling.
- optionally, niobium at a content less than or equal to 0.15% by weight. Niobium promotes the precipitation of carbonitride, which increases the yield strength Re. However, beyond 0.15% by weight, the weldability and hot formability are degraded.
Le reste de la composition est constitué de fer et d'autres éléments que l'on s'attend habituellement à trouver en tant qu'impuretés résultant de l'élaboration de l'acier, dans des proportions qui n'influent pas sur les propriétés recherchées.The remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
Généralement, avant d'être découpées sous forme de flans, les bandes en acier sont protégées contre la corrosion par un revêtement métallique. Selon la destination finale de la pièce, ce revêtement métallique est choisi parmi les revêtements de zinc ou d'alliage de zinc (zinc-aluminium par exemple), et si l'on souhaite en plus une bonne tenue à la chaleur, les revêtements d'aluminium ou d'alliage d'aluminium (aluminium-silicium par exemple). Ces revêtements sont déposés d'une manière classique soit par trempé à chaud dans un bain de métal liquide, soit par électrodéposition, soit encore sous vide.Generally, before being cut into blanks, the steel strips are protected against corrosion by a metal coating. Depending on the final destination of the part, this metal coating is chosen from zinc or zinc alloy coatings (zinc-aluminum for example), and if it is also desired to withstand good heat resistance, the coatings of aluminum or aluminum alloy (aluminum-silicon for example). These coatings are deposited in a conventional manner either by hot dipping in a bath of liquid metal, by electrodeposition, or under vacuum.
Pour mettre en oeuvre le procédé de fabrication selon l'invention, on chauffe le flan d'acier pour le porter à une température de maintien T1 supérieure à Ac1 mais inférieure à Ac3, et on le maintient à cette température T1 pendant un temps de maintien M qu'on ajuste de manière à ce que l'acier, après chauffage du flan, comprenne une proportion d'austénite supérieure ou égale à 25 % surfacique.To implement the manufacturing method according to the invention, the steel blank is heated to bring it to a holding temperature T1 greater than Ac1 but lower than Ac3, and is maintained at this temperature T1 for a holding time M that is adjusted so that steel, after heating the blank, comprises a proportion of austenite greater than or equal to 25% by surface.
Immédiatement après cette opération de chauffage et de maintien en température du flan d'acier, on transfère le flan chauffé au sein d'un outillage de mise en forme pour former une pièce, et la refroidir. Le refroidissement de la pièce au sein de l'outil de mise en forme est réalisé avec une vitesse de refroidissement V suffisante pour éviter que la totalité de l'austénite ne se transforme en ferrite, et afin que la microstructure de l'acier après refroidissement de la pièce soit une microstructure multi-phasée comprenant de la ferrite, et qui soit homogène dans chacune des zones de la pièce.Immediately after this operation of heating and maintaining the temperature of the steel blank, the heated blank is transferred into a forming tool to form a part, and cool it. The cooling of the workpiece within the shaping tool is performed with a cooling rate V sufficient to prevent all of the austenite from becoming ferrite, and so that the microstructure of the steel after cooling the piece is a multi-phase microstructure comprising ferrite, and which is homogeneous in each of the areas of the room.
On entend par microstructure multi-phasée homogène dans chacune des zones de la pièce, une microstructure présentant une constance en termes de proportion et de morphologie dans chacune des zones de la pièce, et dans laquelle les différentes phases sont uniformément réparties.Homogeneous multi-phased microstructure in each of the zones of the part is understood to mean a microstructure having constancy in terms of proportion and morphology in each zone of the part, and in which the different phases are uniformly distributed.
Pour que les vitesses de refroidissement V soient suffisantes, les outils de mise en forme peuvent être refroidis, par exemple par circulation de fluide.In order for the cooling speeds V to be sufficient, the shaping tools can be cooled, for example by fluid circulation.
En outre, l'effort de serrage de l'outil de mise en forme doit être suffisant pour assurer un contact intime entre le flan et l'outil, et assurer un refroidissement efficace et homogène de la pièce.In addition, the clamping force of the shaping tool must be sufficient to ensure intimate contact between the blank and the tool, and ensure efficient and homogeneous cooling of the room.
De manière optionnelle, après avoir découpé le flan dans la bande d'acier, et avant de le chauffer, on peut éventuellement procéder à une pré-déformation à froid du flan.Optionally, after having cut the blank in the steel strip, and before heating it, it is possible to carry out a cold pre-deformation of the blank.
Une pré-déformation à froid du flan, en réalisant par exemple un profilage ou un léger emboutissage à froid du flan, avant mise en forme à chaud est avantageux dans la mesure où cela permet d'accéder à des pièces pouvant présenter une géométrie plus complexe.Cold pre-deformation of the blank, for example by profiling or cold stamping of the blank, before hot forming is advantageous insofar as it allows access to parts that may have a more complex geometry .
Par ailleurs, l'obtention de certaines géométries en une seule opération de mise en forme n'est possible que si l'on raboute entre eux deux flans. Une pré-déformation à froid peut ainsi permettre d'obtenir une pièce d'un seul tenant, c'est à dire une pièce obtenue par mise en forme d'un seul flan.Moreover, obtaining certain geometries in a single shaping operation is possible only if two blanks are folded between them. Cold pre-deformation can thus make it possible to obtain a part in one piece, that is to say a part obtained by forming a single blank.
Dans un premier mode de réalisation préféré de l'invention, on met en oeuvre le procédé selon l'invention pour fabriquer une pièce en acier présentant une microstructuré multi-phasée comprenant soit de la ferrite et de la martensite, soit de la ferrite et de la bainite, soit encore de la ferrite, de la martensite et de la bainite.In a first preferred embodiment of the invention, the method according to the invention is used to manufacture a steel part having a multi-phase microstructure comprising either ferrite and martensite, either ferrite and bainite, or ferrite, martensite and bainite.
Pour former cette microstructure, on adapte la composition de l'acier multi-phasé précédemment décrite, et en particulier la teneur en carbone, en silicium, en aluminium. Ainsi, l'acier comprend les éléments suivants :
- du carbone à une teneur de préférence comprise entre 0,01 et 0,25 % en poids, et plus préférentiellement comprise entre 0,08 et 0,15 %. La teneur en carbone est limitée à 0,25 % en poids pour limiter la formation de martensite et éviter ainsi la détérioration de la ductilité et de la formabilité.
- du manganèse à une teneur comprise de préférence entre 0,50 et 2,50 % en poids, et plus préférentiellement comprise entre 1,20 et 2,00 % en poids.
- du silicium à une teneur de préférence comprise entre 0,01 et 2,0 % en poids, et plus préférentiellement comprise entre 0,01 et 0,50 % en poids.
- de l'aluminium à une teneur de préférence comprise entre 0,005 et 1,5 % en poids, et plus préférentiellement comprise entre 0,005 et 1,0 % en poids. Il est préférable que la teneur en aluminium soit inférieure à 1,5 % en poids, de manière à éviter la dégradation de la soudabilité par étincelage due à la formation d'inclusions d'oxyde d'aluminium Al2O3.
- du molybdène à une teneur comprise de préférence entre 0,001 et 0,50 % en poids, et plus préférentiellement comprise entre 0,001 et 0,10 % en poids.
- du chrome à une teneur de préférence inférieure ou égale à 1,0 % en poids, et plus préférentiellement inférieure ou égale à 0,50 % en poids.
- du phosphore à une teneur de préférence inférieur ou égale à 0,10 % en poids.
- du titane à une teneur de préférence inférieure ou égale à 0,15 % en poids.
- du niobium à une teneur de préférence inférieure ou égale à 0,15 % en poids.
- du vanadium à une teneur de préférence inférieure ou égale à 0,25 % en poids.
- carbon at a content preferably between 0.01 and 0.25% by weight, and more preferably between 0.08 and 0.15%. The carbon content is limited to 0.25% by weight to limit the formation of martensite and thus avoid deterioration of ductility and formability.
- manganese at a content preferably between 0.50 and 2.50% by weight, and more preferably between 1.20 and 2.00% by weight.
- silicon at a content preferably between 0.01 and 2.0% by weight, and more preferably between 0.01 and 0.50% by weight.
- aluminum at a content preferably between 0.005 and 1.5% by weight, and more preferably between 0.005 and 1.0% by weight. It is preferable that the aluminum content is less than 1.5% by weight, so as to avoid the degradation of the spark weldability due to the formation of Al 2 O 3 aluminum oxide inclusions.
- molybdenum at a content preferably between 0.001 and 0.50% by weight, and more preferably between 0.001 and 0.10% by weight.
- chromium at a content preferably less than or equal to 1.0% by weight, and more preferably less than or equal to 0.50% by weight.
- phosphorus at a content preferably less than or equal to 0.10% by weight.
- titanium at a content preferably less than or equal to 0.15% by weight.
- niobium at a content preferably less than or equal to 0.15% by weight.
- vanadium at a content preferably less than or equal to 0.25% by weight.
Le reste de la composition est constitué de fer et d'autres éléments que l'on s'attend habituellement à trouver en tant qu'impuretés résultant de l'élaboration de l'acier, dans des proportions qui n'influent pas sur les propriétés recherchées.The remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
Pour former une pièce en acier multi-phasée comprenant de la ferrite, et de la martensite et/ou de la bainite selon l'invention, on chauffe le flan à une température de maintien T1 supérieure à Ac1 mais inférieure à Ac3, de manière à contrôler la proportion d'austénite formée lors du chauffage du flan, et ne pas dépasser la limite supérieure préférentielle de 75 % surfacique d'austénite.To form a multi-phase steel piece comprising ferrite, and martensite and / or bainite according to the invention, the blank is heated to a holding temperature T1 greater than Ac1 but less than Ac3, so as to to control the proportion of austenite formed during the heating of the blank, and not to exceed the preferential upper limit of 75% of austenite surface area.
Une proportion d'austénite dans l'acier chauffé à une température de maintien T1 pendant un temps de maintien M, comprise entre 25 et 75 % surfacique offre un bon compromis en termes de résistance mécanique de l'acier après mise en forme et de régularité des caractéristiques mécaniques de l'acier grâce à la robustesse du procédé. En effet, au-delà de 25 % surfacique d'austénite, on forme suffisamment de phases durcissantes, comme par exemple la martensite et/ou la bainite, lors du refroidissement de l'acier, pour que la limite d'élasticité Re de l'acier après mise en forme soit suffisante. En revanche, au-delà de 75 % surfacique d'austénite, on contrôle difficilement la proportion d'austénite dans l'acier, et l'on risque de former trop de phases durcissantes lors du refroidissement de l'acier et par conséquent, de former une pièce en acier présentant un allongement à la rupture A insuffisant, ce qui nuira à la capacité d'absorption de l'énergie de la pièce.A proportion of austenite in the steel heated to a holding temperature T1 during a holding time M of between 25 and 75% by weight offers a good compromise in terms of the mechanical strength of the steel after shaping and regularity. mechanical characteristics of the steel thanks to the robustness of the process. Indeed, beyond 25% of austenite surface, sufficient hardening phases, such as for example martensite and / or bainite, are formed during the cooling of the steel so that the yield strength Re of the steel after shaping is sufficient. On the other hand, above 75% of austenite surface, it is difficult to control the proportion of austenite in the steel, and one risks forming too many hardening phases during the cooling of the steel and consequently, of forming a steel part with insufficient elongation at break A, which will impair the energy absorption capacity of the part.
Le temps de maintien du flan d'acier à la température de maintien T1 dépend essentiellement de l'épaisseur de la bande. Dans le cadre de la présente invention, l'épaisseur de la bande est typiquement comprise entre 0,3 et 3 mm. Par conséquent, pour former une proportion d'austénite comprise entre 25 et 75 % surfacique, le temps de maintien M est de préférence compris entre 10 et 1000 s. Si on maintient le flan d'acier à une température de maintien T1 pendant un temps de maintien M supérieure à 1000 s, les grains d'austénite grossissent et la limite d'élasticité Re de l'acier après mise en forme sera limitée. En outre, la trempabilité de l'acier se réduit et la surface de l'acier s'oxyde. En revanche, si on maintient le flan pendant un temps de maintien M inférieur à 10 s, la proportion d'austénite formée sera insuffisante, et la proportion de martensite et/ou de bainite formée lors du refroidissement de la pièce entre outil, sera insuffisante pour que la limite d'élasticité Re de l'acier soit suffisante.The holding time of the steel blank at the holding temperature T1 depends essentially on the thickness of the strip. In the context of the present invention, the thickness of the strip is typically between 0.3 and 3 mm. Therefore, to form a proportion of austenite between 25 and 75% by surface, the holding time M is preferably between 10 and 1000 s. If the steel blank is maintained at a holding temperature T1 for a holding time M greater than 1000 s, the austenite grains increase and the elastic limit Re of the steel after forming will be limited. In addition, the hardenability of the steel is reduced and the surface of the steel oxidizes. On the other hand, if the blank is held for a holding time M less than 10 s, the proportion of austenite formed will be insufficient, and the proportion of martensite and / or bainite formed during the cooling of the part between tool, will be insufficient for the elastic limit Re of the steel is sufficient.
La vitesse de refroidissement V de la pièce en acier dans l'outil de mise en forme dépend de la déformation et de la qualité du contact entre l'outil et le flan d'acier. Cependant, la vitesse de refroidissement V doit être suffisamment élevée pour que la microstructure multi-phasée souhaitée soit obtenue, et est préférentiellement supérieure à 10 °C/s. Avec une vitesse de refroidissement V inférieure ou égale à 10°C/s, on risque de former des carbures qui vont contribuer à dégrader les caractéristiques mécaniques de la pièce.The cooling rate V of the steel part in the forming tool depends on the deformation and the quality of the contact between the tool and the steel blank. However, the cooling rate V must be sufficiently high for the desired multi-phased microstructure to be obtained, and is preferably greater than 10 ° C./s. With a cooling rate V less than or equal to 10 ° C / s, it is likely to form carbides that will contribute to degrade the mechanical characteristics of the part.
Dans ces conditions, après refroidissement, on forme une pièce en acier multi-phasée comprenant plus de 25 % surfacique de ferrite, le reste étant de la martensite et/ou de la bainite, les différentes phases étant homogènement réparties dans chacune des zones de la pièce.. Dans un mode de réalisation préféré de l'invention, on forme préférentiellement de 25 à 75 % surfacique de ferrite et 25 à 75 % surfacique de martensite et/ou de bainite,Under these conditions, after cooling, a multi-phase steel piece comprising more than 25% ferrite surface area is formed, the rest being martensite and / or bainite, the various phases being homogeneously distributed in each of the zones of the In a preferred embodiment of the invention, 25 to 75% ferrite surface area and 25 to 75% surface area of martensite and / or bainite are preferably formed.
Dans un deuxième mode de réalisation préféré de l'invention, on met en oeuvre le procédé selon l'invention pour fabriquer une pièce en acier TRIP. Dans le cadre de l'invention, on entend acier TRIP, une microstructure multiphasée comprenant de la ferrite, de l'austénite résiduelle, et éventuellement de la martensite et/ou de la bainite.In a second preferred embodiment of the invention, the method according to the invention is used to manufacture a TRIP steel part. In the context of the invention is meant TRIP steel, a multiphase microstructure comprising ferrite, residual austenite, and possibly martensite and / or bainite.
Pour former cette microstructure multi-phasée TRIP, on adapte la composition de l'acier multi-phasé précédemment décrite, et en particulier la teneur en carbone, en silicium, en aluminium. Ainsi, l'acier comprend les éléments suivants :
- du carbone à une teneur comprise de préférence entre 0,05 et 0,50 % en poids, et plus préférentiellement comprise entre 0,10 et 0,30 % en poids. Pour former de l'austénite résiduelle stabilisée, il est préférable que cet élément soit présent à une teneur supérieure ou égale à 0,05 % en poids. En effet, le carbone joue un rôle très important sur la formation de la microstructure et les propriétés mécaniques : selon l'invention, une transformation bainitique intervient à partir d'une structure austénitique formée à haute température, et des lattes de ferrite bainitique sont formées. Compte tenu de la solubilité très inférieure du carbone dans la ferrite par rapport à l'austénite, le carbone de l'austénite est rejeté entre les lattes. Grâce à certains éléments d'alliage de la composition d'acier selon l'invention, en particulier le silicium et le manganèse, la précipitation de carbures, notamment de cémentite, intervient très peu. Ainsi, l'austénite interlattes s'enrichit progressivement en carbone sans que la précipitation de carbures n'intervienne. Cet enrichissement est tel que l'austénite est stabilisée, c'est à dire que la transformation martensitique de cette austénite n'intervient pas lors du refroidissement jusqu'à la température ambiante.
- du manganèse à une teneur de préférence comprise entre 0,50 et 3,0 % en poids, et plus préférentiellement entre 0,60 et 2,0 % en poids. Le manganèse favorise la formation d'austénite, contribue à diminuer la température de début de transformation martensitique Ms et à stabiliser l'austénite. Cette addition de manganèse participe également à un durcissement efficace en solution solide et donc à l'obtention d'une limite d'élasticité Re élevée. Cependant, un excès de manganèse ne permettant pas de former suffisamment de ferrite lors du refroidissement, la concentration de carbone dans l'austénite résiduelle est insuffisante pour qu'elle soit stable. La teneur en manganèse est plus préférentiellement comprise entre 0,60 et 2,0 % en poids. De la sorte, les effets recherchés ci-dessus sont obtenus sans risque de formation d'une structure en bandes néfaste qui proviendrait d'une ségrégation éventuelle du manganèse lors de la solidification.
- du silicium à une teneur de préférence comprise entre 0,001 et 3,0 % en poids, et plus préférentiellement comprise entre 0,01 et 2,0 % en poids. Le silicium stabilise la ferrite et stabilise l'austénite résiduelle à température ambiante. Le silicium inhibe la précipitation de la cémentite lors du refroidissement à partir de l'austénite en retardant considérablement la croissance des carbures : ceci provient du fait que la solubilité du silicium dans la cémentite est très faible et que cet élément augmente l'activité du carbone dans l'austénite. De la sorte, un germe éventuel de cémentite se formant sera environné d'une zone austénitique riche en silicium qui aura été rejeté à l'interface précipité-matrice. Cette austénite enrichie en silicium est également plus riche en carbone et la croissance de la cémentite est ralentie en raison de la diffusion peu importante résultant du gradient réduit de carbone entre la cémentite et la zone austénitique avoisinante. Cette addition de silicium contribue donc à stabiliser une quantité suffisante d'austénite résiduelle pour obtenir un effet TRIP. De plus, cette addition de silicium permet d'augmenter la limite d'élasticité Re grâce à un durcissement en solution solide. Cependant, une addition excessive de silicium provoque la formation d'oxydes fortement adhérents, difficilement éliminables lors d'une opération de décapage, et l'apparition éventuelle de défauts de surface dus notamment à un manque de mouillabilité dans les opérations de galvanisation au trempé. Afin d'obtenir la stabilisation d'une quantité suffisante d'austénite tout en réduisant le risque de défauts de surface, la teneur en silicium est préférentiellement comprise entre 0,01 et 2,0 % en poids.
- de l'aluminium à une teneur de préférence comprise entre 0,005 et 3,0 % en poids. Comme le silicium, l'aluminium stabilise la ferrite et accroît la formation de ferrite lors du refroidissement du flan. Il est très peu soluble dans la cémentite et peut être utilisé à ce titre pour éviter la précipitation de la cémentite lors d'un maintien à une température de transformation bainitique et stabiliser l'austénite résiduelle.
- du molybdène à une teneur de préférence inférieure ou égale à 1,0 % en poids, et plus préférentiellement inférieure ou égale à 0,60 % en poids.
- du chrome à une teneur de préférence inférieure ou égale à 1,50 % en poids. La teneur en chrome est limitée pour éviter les problèmes d'aspect de surface en cas de galvanisation de l'acier.
- du nickel à une teneur de préférence inférieure ou égale à 2,0 % en poids.
- du cuivre à une teneur de préférence inférieure ou égale à 2,0 % en poids.
- du phosphore à une teneur de préférence inférieure ou égale à 0,10 % en poids. Le phosphore en combinaison avec le silicium augmente la stabilité de l'austénite résiduelle en supprimant la précipitation des carbures.
- du soufre à une teneur de préférence inférieure ou égale à 0,05 % en poids.
- du titane à une teneur de préférence inférieure ou égale à 0,20 % en poids.
- du vanadium à une teneur de préférence inférieure ou égale à 1,0 % en poids, et plus préférentiellement inférieure ou égale à 0,60 % en poids.
- carbon at a content preferably between 0.05 and 0.50% by weight, and more preferably between 0.10 and 0.30% by weight. To form stabilized residual austenite, it is preferable that this element is present at a content greater than or equal to 0.05% by weight. Indeed, the carbon plays a very important role on the formation of the microstructure and the mechanical properties: according to the invention, a bainitic transformation occurs from a high temperature austenitic structure, and bainitic ferrite slats are formed . Given the very solubility lower carbon in ferrite compared to austenite, the carbon of the austenite is rejected between the slats. Thanks to certain alloying elements of the steel composition according to the invention, in particular silicon and manganese, the precipitation of carbides, in particular of cementite, intervenes very little. Thus, the austenite interlatte is progressively enriched in carbon without the precipitation of carbides intervening. This enrichment is such that the austenite is stabilized, that is to say that the martensitic transformation of this austenite does not occur during cooling to room temperature.
- manganese at a content preferably between 0.50 and 3.0% by weight, and more preferably between 0.60 and 2.0% by weight. Manganese promotes the formation of austenite, helps to reduce the martensitic transformation start temperature Ms and to stabilize the austenite. This addition of manganese also contributes to an effective hardening in solid solution and thus to obtaining a yield strength Re high. However, since an excess of manganese does not make it possible to form enough ferrite during cooling, the carbon concentration in the residual austenite is insufficient for it to be stable. The manganese content is more preferably between 0.60 and 2.0% by weight. In this way, the effects sought above are obtained without risk of formation of a harmful band structure that would come from a possible segregation of manganese during solidification.
- silicon at a content preferably between 0.001 and 3.0% by weight, and more preferably between 0.01 and 2.0% by weight. Silicon stabilizes the ferrite and stabilizes the residual austenite at room temperature. Silicon inhibits the precipitation of cementite during cooling from austenite by considerably delaying the growth of carbides: this is due to the fact that the solubility of silicon in cementite is very low and that this element increases the activity of carbon in the austenite. In this way, an eventual germ of cementite forming will be surrounded by a zone austenitic silicon rich that will have been rejected at the precipitated-matrix interface. This silicon-enriched austenite is also richer in carbon and the growth of cementite is slowed down because of the small diffusion resulting from the reduced carbon gradient between the cementite and the surrounding austenitic zone. This addition of silicon thus contributes to stabilizing a sufficient amount of residual austenite to obtain a TRIP effect. In addition, this addition of silicon makes it possible to increase the yield strength Re by means of hardening in solid solution. However, an excessive addition of silicon causes the formation of strongly adherent oxides, which are difficult to eliminate during a stripping operation, and the possible appearance of surface defects due in particular to a lack of wettability in dip galvanizing operations. In order to obtain the stabilization of a sufficient amount of austenite while reducing the risk of surface defects, the silicon content is preferably between 0.01 and 2.0% by weight.
- aluminum at a content preferably between 0.005 and 3.0% by weight. Like silicon, aluminum stabilizes ferrite and increases the formation of ferrite during the cooling of the blank. It is very slightly soluble in cementite and can be used as such to prevent the precipitation of cementite during maintenance at bainitic transformation temperature and stabilize the residual austenite.
- molybdenum at a content preferably less than or equal to 1.0% by weight, and more preferably less than or equal to 0.60% by weight.
- chromium at a content preferably less than or equal to 1.50% by weight. The chromium content is limited to avoid surface appearance problems when galvanizing steel.
- nickel at a content preferably less than or equal to 2.0% by weight.
- copper at a content preferably less than or equal to 2.0% by weight.
- phosphorus at a content preferably less than or equal to 0.10% by weight. Phosphorus in combination with silicon increases the stability of residual austenite by suppressing the precipitation of carbides.
- sulfur at a content preferably less than or equal to 0.05% by weight.
- titanium at a content preferably less than or equal to 0.20% by weight.
- vanadium at a content preferably less than or equal to 1.0% by weight, and more preferably less than or equal to 0.60% by weight.
Le reste de la composition est constitué de fer et d'autres éléments que l'on s'attend habituellement à trouver en tant qu'impuretés résultant de l'élaboration de l'acier, dans des proportions qui n'influent pas sur les propriétés recherchées.The remainder of the composition is iron and other elements that are usually expected to be found as impurities resulting from steel making, in proportions that do not affect the properties of the steel. sought.
Le temps de maintien du flan d'acier à une température de maintien T1 supérieure à Ac1 mais inférieure à Ac3 dépend essentiellement de l'épaisseur de la bande. Dans le cadre de la présente invention, l'épaisseur de la bande est typiquement comprise entre 0,3 et 3 mm. Par conséquent, pour former une proportion d'austénite supérieure ou égale à 25 % surfacique, le temps de maintien M est de préférence compris entre 10 et 1000 s. Si on maintient le flan d'acier à une température de maintien T1 pendant un temps de maintien M supérieure à 1000 s, les grains d'austénites grossissent et la limite d'élasticité Re de l'acier après mise en forme sera limitée. En outre, la trempabilité de l'acier se réduit et la surface de l'acier s'oxyde. En revanche, si on maintient le flan pendant un temps de maintien M inférieur à 10 s, la proportion d'austénite formée sera insuffisante, et on ne formera pas suffisamment d'austénite résiduelle et de bainite lors du refroidissement de la pièce entre outil.The holding time of the steel blank at a holding temperature T1 greater than Ac1 but less than Ac3 essentially depends on the thickness of the strip. In the context of the present invention, the thickness of the strip is typically between 0.3 and 3 mm. Therefore, to form a proportion of austenite greater than or equal to 25% by surface, the holding time M is preferably between 10 and 1000 s. If the steel blank is maintained at a holding temperature T1 for a holding time M greater than 1000 s, the austenite grains increase and the elastic limit Re of the steel after forming will be limited. In addition, the hardenability of the steel is reduced and the surface of the steel oxidizes. On the other hand, if the blank is held for a holding time M less than 10 s, the proportion of austenite formed will be insufficient, and sufficient residual austenite and bainite will not be formed during the cooling of the part between the tool.
La vitesse de refroidissement V de la pièce en acier dans l'outil de mise en forme dépend de la déformation et de la qualité du contact entre l'outil et le flan d'acier. Pour obtenir une pièce en acier présentant une microstructure multi-phasée TRIP, il est préférable que la vitesse de refroidissement V soit comprise entre 10 °C/s et 200 °C/s. En effet, en deçà de 10 °C/s, on formera essentiellement de la ferrite et du carbure, et insuffisamment d'austénite résiduelle, et de martensite, et au delà de 200 °C/s, on formera essentiellement de la martensite et insuffisamment d'austénite résiduelle.The cooling rate V of the steel part in the forming tool depends on the deformation and the quality of the contact between the tool and the steel blank. To obtain a steel part having a multi-phased microstructure TRIP, it is preferable that the cooling rate V is between 10 ° C./s and 200 ° C./s. In fact, below 10 ° C / s, ferrite and carbide will be essentially formed, and insufficient residual austenite and martensite, and above 200 ° C / s, essentially martensite will be formed. insufficient residual austenite.
Il est indispensable de former une proportion d'austénite supérieure ou égale à 25 % surfacique lors du chauffage du flan, pour que lors du refroidissement de l'acier entre l'outil de mise en forme, il reste suffisamment d'austénite résiduelle et que l'effet TRIP recherché puisse être ainsi obtenu.It is essential to form a proportion of austenite greater than or equal to 25% by surface during heating of the blank, so that when cooling the steel between the forming tool, there is enough residual austenite and that the desired TRIP effect can thus be obtained.
Dans ces conditions, après refroidissement, on forme une pièce en acier multi-phasée constituée, en % surfacique, de ferrite à une proportion supérieure ou égale à 25 %, de 3 à 30 % d'austénite résiduelle, et éventuellement de la martensite et/ou de la bainite.Under these conditions, after cooling, a multiphase steel part consisting, in% by surface, of ferrite at a proportion greater than or equal to 25%, of 3 to 30% of residual austenite, and possibly of martensite, is formed. / or bainite.
L'effet TRIP peut avantageusement être mis à profit pour absorber l'énergie en cas de chocs à grande vitesse. En effet, lors d'une déformation importante d'une pièce en acier TRIP, l'austénite résiduelle se transforme progressivement en martensite en sélectionnant l'orientation de la martensite. Cela a pour effet de réduire les contraintes résiduelles dans la martensite, de réduire les contraintes internes dans la pièce, et finalement de limiter l'endommagement de la pièce, car la rupture de celle-ci interviendra pour un allongement A plus important que si elle n'était pas en acier TRIP.The TRIP effect can advantageously be used to absorb energy in the event of high speed shocks. Indeed, during a significant deformation of a TRIP steel part, the residual austenite is gradually transformed into martensite by selecting the orientation of the martensite. This has the effect of reducing the residual stresses in the martensite, reducing the internal stresses in the part, and finally limiting the damage of the part, because the rupture thereof will take place for an elongation A more important than if it was not TRIP steel.
L'invention va à présent être illustrée par des exemples donnés à titre indicatif, non limitatif, et en référence à la figure unique annexée qui est une photographie d'une pièce obtenue par mise en forme à froid (référence G) et d'une pièce obtenue par mise en forme à chaud (référence A).The invention will now be illustrated by examples given by way of nonlimiting indication and with reference to the single appended figure which is a photograph of a coin obtained by cold forming (reference G) and a part obtained by hot forming (reference A).
Les inventeurs ont réalisé des essais à la fois sur des aciers présentant d'une part une composition typique de celle des aciers de microstructure mutli-phasée comprenant de la ferrite et de la martensite et/ ou de la bainite (point 1), et d'autre part une composition typique de celle des aciers de microstructure mutli-phasée TRIP (point 2).The inventors have carried out tests both on steels presenting on the one hand a composition typical of that of mutli-phased microstructure steels comprising ferrite and martensite and / or bainite (point 1), and of on the other hand a composition typical of that of TRIP mutli-phased microstructure steels (point 2).
Des flans de dimension 400 x 600 mm sont découpés dans une bande en acier dont la composition, indiquée dans le tableau I, est celle d'un acier de nuance DP780 (Dual Phase 780). La bande présente une épaisseur de 1,2 mm. La température Ac1 de cet acier est de 705 °C et la température Ac3 est de 815 °C. Les flans sont portés à une température de maintien T1 variable, pendant une durée de maintien de 5 mn. Puis, ils sont immédiatement transférés dans un outil d'emboutissage dans lequel ils sont à la fois mis en forme et refroidis avec des vitesses de refroidissement V variables, en les maintenant dans l'outil pendant une durée de 60 s. Les pièces embouties s'apparentent à une structure de forme en OmégaBlanks 400 x 600 mm in size are cut from a steel strip whose composition, indicated in Table I, is that of a steel grade DP780 (Dual Phase 780). The strip has a thickness of 1.2 mm. The Ac1 temperature of this steel is 705 ° C and the Ac3 temperature is 815 ° C. The blanks are brought to a variable holding temperature T1, during a holding period of 5 minutes. Then, they are immediately transferred to a stamping tool in which they are both shaped and cooled with variable cooling rates V, keeping them in the tool for a period of 60 s. The stamped parts are similar to an Omega shape structure
Après refroidissement complet des pièces, on mesure leur limite d'élasticité Re, leur résistance à la traction Rm, et leur allongement à la rupture A, et on détermine la microstructure de l'acier. En ce qui concerne la microstructure, F représente la ferrite, M la martensite, et B la bainite. Les résultats sont présentés dans le tableau II.
Les résultats de cet essai montre bien que seul un chauffage de l'acier à une température comprise entre Ac1 et Ac3 permet d'obtenir une microstructure multi-phasée comprenant de la ferrite, quelque soit la vitesse de refroidissement de l'acier dans l'outil de mise en forme. En effet, lorsque l'acier est chauffé à une température supérieure à Ac3, il convient alors, de contrôler strictement la vitesse de refroidissement V lors de la mise en forme, pour obtenir un acier de microstructure multi-phasée comprenant plus de 25 % surfacique de ferrite, et de préférence entre 25 % et 75 % surfacique de ferrite.The results of this test show that only heating the steel at a temperature between Ac1 and Ac3 makes it possible to obtain a multi-phase microstructure comprising ferrite, whatever the speed of cooling of the steel in the shaping tool. Indeed, when the steel is heated to a temperature above Ac3, it is then necessary to strictly control the cooling rate V during shaping, to obtain a multi-phase microstructure steel comprising more than 25% per unit area. ferrite, and preferably between 25% and 75% ferrite surface.
Outre, une faible dispersion des caractéristiques mécaniques en fonction de la vitesse de refroidissement pour les pièces obtenues selon l'invention, leur capacité d'absorption d'énergie est supérieure à celle des pièces obtenues avec un chauffage à une température supérieure à Ac3.In addition, a low dispersion of the mechanical characteristics as a function of the cooling rate for the parts obtained according to the invention, their energy absorption capacity is greater than that of the parts obtained with heating at a temperature above Ac3.
Le but de cet essai est de montrer l'intérêt d'une mise en forme à chaud par rapport à une mise en forme à froid, et d'évaluer le retour élastique.The purpose of this test is to show the interest of a hot shaping compared to a cold shaping, and to evaluate the elastic return.
A cet effet, on fabrique une pièce en acier de nuance DP780 en emboutissant à froid un flan découpé dans une bande en acier, d'épaisseur 1,2 mm, dont la composition est indiquée dans le tableau I, mais qui contrairement à la bande utilisée dans le point 1, présente déjà avant emboutissage une microstructure multi-phasée comprenant 70 % surfacique de ferrite, 15 % surfacique de martensite, et 15 % surfacique de bainite. La figure 1 montre bien que la pièce formée par emboutissage à froid (repérée sur la figure par la lettre G) présente un fort retour élastique, par rapport à la pièce A (voir tableau II) formée par emboutissage à chaud (repérée par la lettre A).For this purpose, a piece of DP780 grade steel is manufactured by cold stamping a blank cut from a 1.2 mm thick steel strip, the composition of which is indicated in Table I, but which, unlike the strip used in point 1, already has before stamping a multi-phased microstructure comprising 70% ferrite surface, 15% martensite surface, and 15% bainite surface. FIG. 1 clearly shows that the part formed by cold stamping (marked in the figure by the letter G) has a strong springback, with respect to the piece A (see Table II) formed by hot stamping (marked by the letter AT).
Des flans de dimension 200 X 500 mm sont découpés dans une bande en acier dont la composition, indiquée dans le tableau III, est celle d'un acier de nuance TRIP 800. La bande présente une épaisseur de 1,2 mm. La température Ac1 de cet acier est de 751 °C et la température Ac3 est de 875°C. Les flans sont portés à une température de maintien T1 variable, pendant une durée de maintien de 5 mn, puis sont immédiatement transférés dans un outil d'emboutissage dans lequel ils sont à la fois mis en forme et refroidis avec une vitesse de refroidissement V de 45 °C/s, en les maintenant dans l'outil pendant une durée de 60 s. Les pièces embouties s'apparentent à une structure de forme en Oméga.Blanks measuring 200 × 500 mm are cut from a steel strip whose composition, indicated in Table III, is that of a TRIP 800 grade steel. The strip has a thickness of 1.2 mm. The Ac1 temperature of this steel is 751 ° C and the Ac3 temperature is 875 ° C. The blanks are brought to a variable holding temperature T1, during a hold time of 5 minutes, and then immediately transferred to a stamping tool in which they are both shaped and cooled with a cooling rate V of 45 ° C / s, keeping them in the tool for 60 s. The stamped parts are similar to an Omega shape structure.
Après refroidissement complet des pièces, on mesure leur limite d'élasticité Re, leur résistance à la traction Rm, et leur allongement à la rupture A, et on détermine la microstructure de l'acier. En ce qui concerne la microstructure, F représente la ferrite, A l'austénite résiduelle, M la martensite, et B la bainite. Les résultats sont présentés dans le tableau IV.
Les essais réalisés montrent bien que l'emboutissage des flans réalisés selon l'invention permet d'obtenir des pièces présentant des caractéristiques mécaniques très élevées, ainsi qu'une faible variation des caractéristiques mécaniques quelque soit la température de refroidissement.The tests carried out show that the stamping of the blanks made according to the invention makes it possible to obtain parts having very high mechanical characteristics, as well as a small variation of the mechanical characteristics whatever the cooling temperature.
Claims (17)
- Process for manufacturing a part made of steel having a multiphase microstructure, said microstructure comprising ferrite and being homogeneous in each of the regions of said part, which process comprises the steps consisting in:- cutting a blank from a strip of steel, the composition of which consists, in % by weight, of:0.01 ≤ C ≤ 0.5000.50 ≤ Mn ≤ 3.0%0.001 ≤ Si ≤ 3.0%0.005 ≤ Al ≤ 3.0%Mo ≤ 1.0%Cr ≤ 1.50P ≤ 0.10%Ti ≤ 0.20%V ≤ 1.0% andoptionally, one or more elements such as:Ni ≤ 2.0%Cu ≤ 2.0%S ≤ 0.05%Nb ≤ 0.15%,the balance of the composition being iron and impurities resulting from the smelting;- optionally, said blank undergoes prior cold deformation;- said blank is heated so as to reach a soak temperature Ts above Ac1 but below Ac3 and held at this soak temperature Ts for a soak time ts adjusted so that the steel, after the blank has been heated, has an austenite content equal to or greater than 25% by area;- said heated blank is transferred into a deep-drawing tool so as to hot-stamp said part; and- the part is cooled within the tool at a cooling rate V such that the microstructure of the steel, after the part has been cooled, is a multiphase microstructure, said microstructure comprising ferrite with a content equal to or greater than 25% by area and being homogeneous in each of the regions of said part.
- Process according to Claim 1, in which the composition of the steel comprises, in % by weight:0.01 ≤ C ≤ 0.2500.50 ≤ Mn ≤ 2.50%0.01 ≤ Si ≤ 2.0%0.005 ≤ Al ≤ 1.5%0.001 ≤ Mo ≤ 0.50%Cr ≤ 1.0%P ≤ 0.10%Ti ≤ 0.15%Nb ≤ 0.15%V ≤ 0.25%,the balance of the composition being iron and impurities resulting from the smelting; the blank is held at the soak temperature Ts for a soak time ts adjusted so that the steel, after heating, has an austenite content between 25 and 75% by area; and the microstructure of the steel, after the part has been cooled, is a multiphase microstructure comprising ferrite and either martensite, or bainite, or else both martensite and bainite.
- Process according to Claim 2, characterized futher that the steel comprises, in % by weight:0.08 ≤ C ≤ 0.15%1.20 ≤ Mn ≤ 2.00%0.01 ≤ Si ≤ 0.50%0.005 ≤ Al ≤ 1.0%0.001 ≤ Mo ≤ 0.10%Cr ≤ 0.50%P ≤ 0.10%Ti ≤ 0.15%Nb ≤ 0.15%V ≤ 0.25%,the balance of the composition being iron and impurities resulting from the smelting.
- Process according to either of Claims 2 and 3, characterized in that the soak time ts is between 10 and 1000 s.
- Process according to any one of Claims 2 to 4, characterized in that the cooling rate V is greater than 10°C/s.
- Process according to any one of Claims 2 to 5, characterized in that the multiphase structure of the steel, after said part has been cooled, comprises 25 to 75% ferrite by area and 25 to 75% martensite and/or bainite by area.
- Process according to Claim 1, in which the steel comprises, in % by weight:0.05 ≤ C ≤ 0.50%0.50 ≤ Mn ≤ 3.0%0.001 ≤ Si ≤ 3.0%0.005 ≤ Al ≤ 3.0%Mo ≤ 1.0%Cr ≤ 1.50%Ni ≤ 2.0%Cu ≤ 2.0%P ≤ 0.10%S ≤ 0.05%Ti ≤ 0.20%V ≤ 1.0%,the balance of the composition being iron and impurities resulting from the smelting; the microstructure of the steel, after the part has been cooled, is a TRIP multiphase microstructure comprising ferrite, residual austenite and optionally martensite and/or bainite.
- Process according to Claim 7, characterized futher that the steel comprises, in % by weight:0.10 ≤ C ≤ 0.30%0.60 ≤ Mn ≤ 2.0%0.01 ≤ Si ≤ 2.0%0.005 ≤ Al ≤ 3.0%Mo ≤ 0.60%Cr ≤ 1.50%Ni ≤ 0.20%Cu ≤ 0.20%P ≤ 0.10%S ≤ 0.05%Ti ≤ 0.20%V ≤ 0.60%,the balance of the composition being iron and impurities resulting from the smelting.
- Process according to either of Claims 7 and 8, characterized in that the soak time ts is between 10 and 1000 s.
- Process according to any one of Claims 7 to 9, characterized in that the cooling rate V is between 10 and 200°C/s.
- Process according to any one of Claims 7 to 10, characterized further in that, after the part has been cooled, the multiphase microstructure of the TRIP steel consists, in % by area, of ferrite with a content equal to or greater than 25%, of 3 to 30% residual austenite and optionally of martensite and/or bainite.
- Process according to any one of Claims 1 to 11, characterized in that the steel strip is coated beforehand with a metal coating, before being cut to form a blank.
- Process according to Claim 12, characterized in that the metal coating is a coating based on zinc or a zinc alloy.
- Process according to Claim 12, characterized in that the metal coating is a coating based on aluminum or an aluminum alloy.
- Hot-stamped part having a homogeneous multiphase microstructure in each of the regions of said part, said microstructure comprising ferrite with a content equal to or greater than 25% by area, which is obtained by the process according to any one of Claims 1 to 14.
- Use of the steel part according to Claim 15 for absorbing energy.
- Land motor vehicle that includes the steel part according to Claim 15.
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EP10010435A EP2287344A1 (en) | 2005-09-21 | 2006-09-18 | Method of manufacturing multi phase microstructured steel piece |
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US11459628B2 (en) | 2017-12-22 | 2022-10-04 | Voestalpine Stahl Gmbh | Method for producing metallic components having adapted component properties |
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ZA200802385B (en) | 2009-01-28 |
EP1767659A1 (en) | 2007-03-28 |
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KR20130017102A (en) | 2013-02-19 |
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UA96739C2 (en) | 2011-12-12 |
CA2623146A1 (en) | 2007-03-29 |
EP1929053A1 (en) | 2008-06-11 |
KR20080053312A (en) | 2008-06-12 |
WO2007034063A1 (en) | 2007-03-29 |
KR20110121657A (en) | 2011-11-07 |
KR20120099526A (en) | 2012-09-10 |
JP5386170B2 (en) | 2014-01-15 |
US8114227B2 (en) | 2012-02-14 |
ES2366133T3 (en) | 2011-10-17 |
EP2287344A1 (en) | 2011-02-23 |
JP2009508692A (en) | 2009-03-05 |
PL1929053T3 (en) | 2011-10-31 |
US20080308194A1 (en) | 2008-12-18 |
BRPI0616261A2 (en) | 2011-06-14 |
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