WO2022207913A1 - Steel strip made of a high-strength multiphase steel and process for producing such a steel strip - Google Patents
Steel strip made of a high-strength multiphase steel and process for producing such a steel strip Download PDFInfo
- Publication number
- WO2022207913A1 WO2022207913A1 PCT/EP2022/058767 EP2022058767W WO2022207913A1 WO 2022207913 A1 WO2022207913 A1 WO 2022207913A1 EP 2022058767 W EP2022058767 W EP 2022058767W WO 2022207913 A1 WO2022207913 A1 WO 2022207913A1
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- Prior art keywords
- steel
- steel strip
- weight
- strength
- cev
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 164
- 239000010959 steel Substances 0.000 title claims abstract description 164
- 238000000034 method Methods 0.000 title claims abstract description 18
- 230000008569 process Effects 0.000 title abstract description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 34
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 34
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 32
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 31
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 24
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 21
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 21
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 20
- 229910052742 iron Inorganic materials 0.000 claims abstract description 18
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 238000010438 heat treatment Methods 0.000 claims description 33
- 238000004519 manufacturing process Methods 0.000 claims description 23
- 238000001816 cooling Methods 0.000 claims description 19
- 229910052751 metal Inorganic materials 0.000 claims description 10
- 239000002184 metal Substances 0.000 claims description 10
- 229910001562 pearlite Inorganic materials 0.000 claims description 9
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 230000000717 retained effect Effects 0.000 claims description 3
- 239000003973 paint Substances 0.000 claims description 2
- 239000000470 constituent Substances 0.000 abstract description 2
- 238000002844 melting Methods 0.000 abstract 1
- 230000008018 melting Effects 0.000 abstract 1
- 235000019362 perlite Nutrition 0.000 abstract 1
- 239000010451 perlite Substances 0.000 abstract 1
- 238000000137 annealing Methods 0.000 description 46
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 30
- 238000005275 alloying Methods 0.000 description 30
- 230000000694 effects Effects 0.000 description 23
- 230000015572 biosynthetic process Effects 0.000 description 22
- 239000011572 manganese Substances 0.000 description 22
- 239000011651 chromium Substances 0.000 description 21
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 20
- 230000009466 transformation Effects 0.000 description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 17
- 239000000463 material Substances 0.000 description 17
- 229910052760 oxygen Inorganic materials 0.000 description 17
- 239000001301 oxygen Substances 0.000 description 17
- 239000010936 titanium Substances 0.000 description 17
- 229910052757 nitrogen Inorganic materials 0.000 description 15
- 239000010949 copper Substances 0.000 description 13
- 229910052719 titanium Inorganic materials 0.000 description 13
- 238000011282 treatment Methods 0.000 description 13
- 229910052804 chromium Inorganic materials 0.000 description 12
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 11
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 11
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 11
- 229910052796 boron Inorganic materials 0.000 description 11
- 229910052739 hydrogen Inorganic materials 0.000 description 11
- 239000001257 hydrogen Substances 0.000 description 11
- 238000001556 precipitation Methods 0.000 description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 10
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 10
- 239000010955 niobium Substances 0.000 description 10
- 229910052698 phosphorus Inorganic materials 0.000 description 10
- 239000011574 phosphorus Substances 0.000 description 10
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 9
- 229910052748 manganese Inorganic materials 0.000 description 9
- 239000000203 mixture Substances 0.000 description 9
- 239000010703 silicon Substances 0.000 description 9
- 239000011575 calcium Substances 0.000 description 8
- 150000001247 metal acetylides Chemical class 0.000 description 8
- 229910052758 niobium Inorganic materials 0.000 description 8
- 150000004767 nitrides Chemical class 0.000 description 8
- 238000005496 tempering Methods 0.000 description 8
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 7
- -1 aluminum nitrides Chemical class 0.000 description 7
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 7
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 6
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 6
- 229910052802 copper Inorganic materials 0.000 description 6
- 229910052759 nickel Inorganic materials 0.000 description 6
- 230000009467 reduction Effects 0.000 description 6
- 229910052717 sulfur Inorganic materials 0.000 description 6
- 239000011593 sulfur Substances 0.000 description 6
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 5
- 238000007792 addition Methods 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 229910052791 calcium Inorganic materials 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 238000001953 recrystallisation Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 229910052720 vanadium Inorganic materials 0.000 description 5
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 5
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 230000003111 delayed effect Effects 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 4
- 230000007246 mechanism Effects 0.000 description 4
- 229910052750 molybdenum Inorganic materials 0.000 description 4
- 239000011733 molybdenum Substances 0.000 description 4
- 230000002829 reductive effect Effects 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 238000013459 approach Methods 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 238000005246 galvanizing Methods 0.000 description 3
- 238000004881 precipitation hardening Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- 150000004763 sulfides Chemical class 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical class [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- 239000011362 coarse particle Substances 0.000 description 2
- 238000005097 cold rolling Methods 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000006477 desulfuration reaction Methods 0.000 description 2
- 230000023556 desulfurization Effects 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
- VCTOKJRTAUILIH-UHFFFAOYSA-N manganese(2+);sulfide Chemical class [S-2].[Mn+2] VCTOKJRTAUILIH-UHFFFAOYSA-N 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 239000011573 trace mineral Substances 0.000 description 2
- 235000013619 trace mineral Nutrition 0.000 description 2
- 238000009489 vacuum treatment Methods 0.000 description 2
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910000915 Free machining steel Inorganic materials 0.000 description 1
- 238000003723 Smelting Methods 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 230000003679 aging effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 244000052616 bacterial pathogen Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- VDZMENNHPJNJPP-UHFFFAOYSA-N boranylidyneniobium Chemical compound [Nb]#B VDZMENNHPJNJPP-UHFFFAOYSA-N 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 210000003850 cellular structure Anatomy 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000006355 external stress Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- AMWRITDGCCNYAT-UHFFFAOYSA-L manganese oxide Inorganic materials [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 description 1
- 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 1
- PPNAOCWZXJOHFK-UHFFFAOYSA-N manganese(2+);oxygen(2-) Chemical class [O-2].[Mn+2] PPNAOCWZXJOHFK-UHFFFAOYSA-N 0.000 description 1
- 230000010534 mechanism of action Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- ZLANVVMKMCTKMT-UHFFFAOYSA-N methanidylidynevanadium(1+) Chemical class [V+]#[C-] ZLANVVMKMCTKMT-UHFFFAOYSA-N 0.000 description 1
- 238000010327 methods by industry Methods 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 229910001392 phosphorus oxide Inorganic materials 0.000 description 1
- LFGREXWGYUGZLY-UHFFFAOYSA-N phosphoryl Chemical class [P]=O LFGREXWGYUGZLY-UHFFFAOYSA-N 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- CADICXFYUNYKGD-UHFFFAOYSA-N sulfanylidenemanganese Chemical compound [Mn]=S CADICXFYUNYKGD-UHFFFAOYSA-N 0.000 description 1
- 238000000844 transformation Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/84—Controlled slow cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/663—Bell-type furnaces
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
-
- 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
- C21D9/0043—Muffle furnaces; Retort furnaces
Definitions
- Steel strip made from a high-strength multi-phase steel and method for producing such a steel strip
- the invention relates to a steel strip made from a high-strength multi-phase steel which has a tensile strength of at least 780 MPa in the longitudinal direction.
- the invention also relates to a method for producing a steel strip from a high-strength multi-phase steel which has a tensile strength of at least 780 MPa.
- multi-phase steels Due to their multi-phase structure, multi-phase steels have an excellent combination of strength, formability and ductility.
- phase fractions of more than 30% by volume of martensite and/or bainite are an essential microstructural component in order to achieve high tensile strengths (e.g. > 600 MPa).
- strength classes up to over 980 MPa are also possible, depending on the chemical composition.
- the proportion of hard phase components (martensite or bainite, possibly also tempered) must be higher in order to achieve greater strength.
- Steel strip is understood below to mean a hot-rolled or cold-rolled and annealed steel strip.
- Typical thicknesses of a hot-rolled steel strip also referred to as hot strip, are between 1.8 mm and 18 mm.
- Cold-rolled, annealed steel strips are referred to as cold strip or thin sheet and usually have thicknesses in the range from 0.5 mm to 2.5 mm, with the strip thickness also being able to be adjusted in different flexible ways by specific processing, even within a cold strip or thin sheet.
- strip sheets are also used on an industrial scale as coiled strips in furnaces such as e.g. B.
- batch annealing plants heat treated "as a whole".
- Batch annealing of low alloy strip is done either as a recovery anneal or as a recrystallization/soft anneal.
- recovery annealing a strip sheet that is usually cold-worked is annealed at temperatures below 700 °C in order to achieve high tensile strength with a simultaneously high yield point and low ductility in the steel strip produced by the annealing.
- a recovery-annealed steel usually has a pronounced yield point, moderate ductility and a high yield point/tensile strength ratio > 0.8, which can be critical for the further processing of the steel strip.
- the material-related mechanism of recovery which is the cause of the technological parameters after batch annealing, is very much dependent on the annealing temperature, the annealing time and the previous cold deformation (e.g. degree of cold rolling) of the strip.
- the strip is annealed at temperatures around the Ai transformation temperature for several hours to days.
- the tensile strength after the annealing treatment described above is below 600 MPa and is significantly lower compared to the strength before the annealing treatment.
- the ductility increases significantly with a recrystallization anneal compared to the unannealed and cold-rolled material.
- the hotly contested automotive market is forcing manufacturers to constantly find solutions to reduce fleet fuel consumption and CO2 emissions while maintaining the greatest possible comfort and occupant protection.
- the weight saving of all vehicle components plays a decisive role, but on the other hand, the best possible behavior of the individual components under high static and dynamic loads during operation and in the event of a crash also plays a role.
- the steel manufacturers contribute to the solution of this task by providing high-strength steels.
- high-strength steels with a lower sheet thickness the weight of the vehicle components can be reduced with the same and possibly even improved component behavior.
- Multiphase steels are known, for example, from the published patent applications DE 102017 131 247 A1, DE 102017 130237 A1 and DE 102015 111 177 A1.
- the material properties disclosed there result from a high phase proportion of bainite and/or martensite, which require sufficiently rapid cooling conditions. Large-scale processing of such multi-phase steels takes place with continuous annealing systems.
- a first aspect of the invention relates to a steel strip made of a high-strength multi-phase steel which has a tensile strength of at least 780 MPa in the longitudinal direction, the multi-phase steel consisting of the following elements in % by weight:
- V 0.001 to ⁇ 0.30
- Remainder iron including the usual steel-related ones caused by smelting consists of impurities and has a carbon equivalent CEV which is greater than 0.49 and less than 0.9, the carbon equivalent CEV changing according to the formula
- CEV C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5 from the contents of the corresponding elements in % by weight (i.e. the mass fractions of these elements) and where the ratio from the carbon equivalent CEV and the sum of the contents of Si and Al in % by weight is less than 2.3 (CEV/ (Si+Al)
- the multi-phase steel having a microstructure in which the sum of the volume fractions of the microstructure components martensite, tempered martensite, retained austenite, upper bainite and/or lower bainite is at least 30% by volume, and the remaining microstructure consists of ferrite and pearlite .
- a steel strip of this type can be produced from a rolled strip of steel of the appropriate composition by heat treatment of this strip – in particular rolled up into a coil – “as a whole” using the method for producing a steel strip described below. Said heat treatment is also referred to as "annealing" and can be carried out, for example, by the batch-type annealing system mentioned at the beginning.
- the invention makes it possible to provide a steel strip which has a high tensile strength> 780 MPa, in particular with a good ductility Aso> 5% and a low yield strength ratio R p o , 2 / Rm ⁇ 0.8, and in which these technological Post heat treatment characteristics are not significantly affected by microstructure or by cold working prior to heat treatment.
- the ratio of yield point to tensile strength R p o , 2/Rm is below 0.8 and the elongation at break Aso >5%.
- the content in % by weight of the element C is between 0.09 and 0.2 and/or the content in % by weight of the element Mo is less than 0.4.
- the content in % by weight of the element Mn is between 1.8 and 2.5 and/or that the content in % by weight of the sum of the elements Si + Al is between 0.25 and 1 is
- the carbon equivalent CEV is less than 0.7.
- Such a steel can be processed particularly well.
- the proportion by volume of the common structural components martensite, tempered martensite, residual austenite, upper bainite and/or lower bainite in the structure of the multiphase steel is at least 50% by volume, particularly preferably at least 70% by volume , and the remaining structure consists of ferrite and pearlite.
- the steel strip has a constant thickness, whereby the term "constant thickness” is to be understood in the sense of the usual standard tolerance (e.g. according to EN 10051).
- the steel strip has a thickness that is purposefully different in the longitudinal extent.
- the ratio between the maximum thickness and the minimum thickness is in particular between 1.16 and 3. For nominal strip thicknesses of 2.0 mm or more, this ratio lies outside the usual standard tolerance.
- Such a steel strip with a thickness that is purposefully different in the longitudinal extension is, in particular, a flexibly rolled steel strip for so-called “tailor rolled blanks”.
- the flexibly rolled steel strip is flexibly rolled as sheet metal before heat treatment, with the rollers producing different sheet thicknesses by moving them up and down.
- the advantage is the homogeneous transition between different thicknesses.
- the steel strip has a thickness of between 4 mm and 18 mm, which is not readily possible in industrial production in continuous annealing furnaces.
- a second aspect of the invention relates to a method for producing a steel strip from a high-strength multiphase steel, in particular a steel strip mentioned above, which has a tensile strength of at least 780 MPa in the longitudinal direction, a rolled steel strip consisting of the elements in % by weight:
- V 0.001 to ⁇ 0.30
- Formula CEV C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5 from the contents of the corresponding elements in
- the process z. B. be implemented with a batch-type annealing system.
- this is only possible with low-alloy steels using the production method according to the invention, since the method includes specific phase transformations during the heat treatment.
- the necessary annealing temperatures can vary depending on the chemical composition of the steel strip.
- the corresponding product is a hot-rolled and/or cold-rolled steel strip with a multi-phase structure and the associated characteristic technological properties of the aforementioned multi-phase steels.
- phase components bainite and/or martensite which are characteristic of multi-phase steels, are formed from austenitic phase components when cooling a steel from temperatures above the Ai temperature. To ensure that the austenite does not transform into the phases ferrite and/or pearlite, the material must be sufficiently hardened in accordance with the technically possible cooling rate.
- the hardenability of a steel depends on the chemical composition and can be approximately described by the following carbon equivalent CEV:
- a low annealing temperature should preferably be selected in order to locally enrich the alloying elements in the austenite and thus achieve better through-hardenability locally in the austenite.
- the CEV is limited to 0.49 to a maximum of 0.9, preferably to 0.75, preferably to a maximum of 0.7.
- the proportion of alloying elements and thus the CEV should be kept low.
- the average cooling rate should be between 1 K/h and 300 K/h in the critical temperature range of 750 °C to 200 °C.
- the strength-enhancing microstructure components of multi-phase steels are formed from the austenitic phase components during cooling at temperatures below 570 °C.
- the local high strengths of the martensite and bainite phases are reduced by so-called tempering or self-tempering.
- This material-scientific mechanism leads in particular to the precipitation of forcibly dissolved carbon to form carbides and the reduction of transformation-related stresses to a reduction in strength of the hard phases bainite and martensite and thus also to a reduction in strength of the annealed steel strip.
- This starting mechanism is thermally activated.
- the elements Si and Al in particular are helpful in delaying the kinetics of carbide formation and thus in stabilizing the hard phases. Lowering the transformation temperatures of bainite and martensite also leads to fewer tempering effects with the same process control.
- the elements described in the CEV also bring about a reduction in the transformation temperatures of bainite and in particular martensite, which is positive for the invention.
- high proportions of Cr or Mn can also lead to the formation of additional carbides during the annealing treatment, which can also lead to a lower maximum strength.
- the A r 3 temperature depends on the chemical composition and can be estimated using the following formula
- the sheet metal strip is heated from 100° C. to a temperature of 750°C, and in which the strip sheet remains in the temperature range from 750°C to Ar3 + 70°C for at least 1 h, the numerical value of the temperature Ar3 being calculated using the above formula from the contents of the corresponding elements in % by weight is calculated.
- the sheet steel strip preferably reaches a maximum temperature of at least 780° C. and at most 900° C., preferably at least 790° C. and at most 850° C., during the heat treatment.
- heating of at least 1 hour is preferably provided. Longer holding times are beneficial for more homogeneous heating, but are not recommended due to the associated grain growth, which in turn causes a drop in strength.
- the steel strip is provided with a surface coating in the form of a metallic coating, organic coating or paint finish.
- the strip sheet provided for the heat treatment has in particular a constant thickness, the term “constant thickness” being to be understood in the sense of the usual standard tolerance (eg according to EN 10051).
- the points for the Heat treatment provided strip sheet with advantage in the longitudinal extent specifically different thicknesses, the ratio between maximum thickness and minimum thickness is in particular between 1.16 and 3. For nominal strip thicknesses of 2.0 mm or more, this ratio lies outside the usual standard tolerance.
- Such a sheet metal strip with a thickness that is purposefully different in the longitudinal extension is, in particular, a flexibly rolled sheet metal strip for so-called “tailor rolled blanks”.
- the flexibly rolled strip is rolled again before heat treatment, with the rolls producing different sheet thicknesses by moving them up and down.
- the advantage is the homogeneous transition between different thicknesses.
- the resulting steel strip is then a flexibly rolled steel strip made from a high-strength multi-phase steel.
- the effect of the elements in the steel strip according to the invention with a multi-phase structure is described in more detail below.
- the multi-phase steels are typically chemically structured in such a way that alloying elements are combined with and without micro-alloying elements.
- Accompanying elements are unavoidable and, if necessary, are taken into account in the analysis concept with regard to their effect.
- Tramp elements are elements that are already present in the iron ore or that get into the steel as a result of the production process. Due to their predominantly negative influences, they are generally undesirable. Attempts are being made to remove them to a tolerable level or to convert them into less harmful forms.
- Hydrogen (H) is the only element that can diffuse through the iron lattice without creating lattice strains. As a result, the hydrogen in the iron lattice is relatively mobile and relatively easy to absorb during manufacture. Hydrogen can only be absorbed into the iron lattice in atomic (ionic) form. Hydrogen has a strong embrittling effect and preferentially diffuses to energetically favorable points (vacancies, grain boundaries, etc.). Defects act as hydrogen traps and can significantly increase the residence time of the hydrogen in the material. Cold cracks can occur as a result of recombination to form molecular hydrogen. This behavior occurs in hydrogen embrittlement or hydrogen-induced stress corrosion cracking.
- Oxygen (O) In the molten state, steel has a relatively high absorption capacity for gases, but oxygen is only soluble in very small amounts at room temperature. Analogous to hydrogen, oxygen can only diffuse into the material in atomic form. Due to the strong embrittling effect and the negative effects on the aging resistance, attempts are made during production to reduce the oxygen content as much as possible. To reduce the oxygen there are, on the one hand, process engineering approaches such as vacuum treatment and, on the other hand, analytical approaches. By adding certain alloying elements, the oxygen can be converted into less dangerous states.
- Binding of the oxygen via manganese, silicon and/or aluminum is usually common.
- the resulting oxides can cause negative properties as defects in the material.
- grain refinement can also occur.
- the oxygen content in the steel should be as low as possible.
- Nitrogen (N) is also a by-element from steel production. Steels with free nitrogen tend to have a strong aging effect. Even at low temperatures, the nitrogen diffuses at dislocations and blocks them. It thus causes an increase in strength combined with a rapid loss of toughness. Binding of the nitrogen in the form of nitrides is possible by alloying, for example, aluminum or titanium. For the reasons mentioned above, the nitrogen content is limited to ⁇ 0.016% by weight or to the amounts unavoidable in steel production.
- sulfur (S) is bound as a trace element in iron ore. It is undesirable in steel (with the exception of free-cutting steels) because it tends to segregate and is very brittle. Attempts are therefore made to achieve the lowest possible amounts of sulfur in the melt (e.g. by means of deep vacuum treatment). Furthermore, the sulfur present is converted into the relatively harmless compound manganese sulfide (MnS) by adding manganese.
- MnS manganese sulfide
- the manganese sulphides are often rolled out in rows during the rolling process and act as nuclei for the transformation. In the case of diffusion-controlled transformation in particular, this leads to a cellular structure and, in the case of pronounced cellularity, can lead to deteriorated mechanical properties (e.g. pronounced martensite lines instead of distributed martensite islands, anisotropic material behavior, reduced elongation at break).
- the sulfur content is ⁇ 0.01% by weight or at the steel production limited to unavoidable quantities.
- Phosphorus (P) is a trace element from iron ore and is dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness through solid solution strengthening and improves hardenability. However, attempts are generally made to reduce the phosphorus content as much as possible, since its low diffusion rate, among other things, has a strong tendency to segregate and greatly reduces toughness. Grain boundary fractures occur as a result of the accumulation of phosphorus at the grain boundaries. In addition, phosphorus increases the transition temperature from tough to brittle behavior by up to 300 °C. During hot rolling, near-surface phosphorus oxides at the grain boundaries can lead to cracking. By alloying small amounts of boron, the negative effects of phosphorus can be partially compensated.
- boron increases grain boundary cohesion and decreases phosphorus segregation at grain boundaries.
- P is used in small amounts ( ⁇ 0.1%) as a micro-alloying element due to the low cost and the high increase in strength, for example in higher-strength IF steels (interstitial free).
- the phosphorus content is limited to ⁇ 0.050% or to the amounts unavoidable in steel production.
- Alloying elements are usually added to the steel in order to specifically influence certain properties.
- An alloying element can influence different properties in different steels.
- the connections are varied and complex. The effect of the alloying elements will be discussed in more detail below.
- Carbon (C) is considered the most important alloying element in steel. Iron only becomes steel through its targeted introduction of up to 2.06%. The carbon content is often drastically reduced during steel production. In the multi-phase steel according to the invention, its proportion is 0.08% by weight to 0.23% by weight. Due to its comparatively small atomic radius, carbon is dissolved interstitially in the iron lattice. The solubility is a maximum of 0.02% in a-iron and a maximum of 2.06% in g-iron. In dissolved form, carbon increases the hardenability of steel considerably. Due to the different solubility, pronounced diffusion processes are necessary during the phase transformation, which can lead to very different kinetic conditions.
- Aluminum (AI) is usually alloyed with steel to bind the oxygen and nitrogen dissolved in the iron. The oxygen and nitrogen are thus converted into aluminum oxides and aluminum nitrides. These precipitations can cause grain refinement by increasing the nucleation sites and thus increase the toughness and strength values.
- Aluminum nitride is not precipitated when titanium is present in sufficient quantity. Titanium nitrides have a lower enthalpy of formation and are formed at higher temperatures. In the dissolved state, aluminum, like silicon, shifts ferrite formation to shorter times, thus allowing sufficient ferrite to form. It also suppresses carbide formation and thus leads to delayed austenite transformation. For this reason, Al is also used as an alloying element in retained austenitic steels in order to replace some of the silicon with aluminum. The reason for this approach is that Al is slightly less critical to the galvanizing reaction than Si.
- Silicon (Si) binds oxygen during casting and thus reduces segregation and contamination in the steel.
- silicon increases the strength of the ferrite through solid solution strengthening with only a slightly decreasing elongation at break.
- Another important effect is that silicon shifts the formation of ferrite to shorter times, thus allowing sufficient ferrite to form before quenching in continuously annealed material.
- the formation of ferrite enriches and stabilizes the austenite with carbon. At higher levels, silicon stabilizes the austenite noticeably in the lower temperature range, especially in the area of bainite formation by preventing carbide formation. During hot rolling with high silicon contents, highly adhering scale can form, which can impair further processing.
- a total content of Al and Si is set at 0.25 to 2% by weight, preferably up to a maximum of 1% by weight.
- Manganese (Mn) is added to almost all steels for desulfurization in order to convert the harmful sulfur into manganese sulfides.
- manganese increases the strength of the ferrite through solid solution strengthening and shifts the transformation to lower temperatures.
- a main reason for alloying manganese is the significant improvement in hardenability. Due to the hindrance to diffusion, the pearlite and bainitic transformation is shifted to longer times and the martensite start temperature is lowered. Like silicon, manganese tends to form oxides on the steel surface during annealing.
- manganese oxides eg MnO
- Mn mixed oxides eg Mn 2 Si0 4
- Mn content is therefore set at 1.5% to 3.5% by weight, preferably 1.8 to 2.5% by weight.
- Chromium (Cr) The addition of chromium mainly improves hardenability. In the dissolved state, chromium shifts the pearlite and bainitic transformation to longer times and at the same time lowers the martensite start temperature. Another important effect is that chromium significantly increases tempering resistance. Chromium is also a carbide former. If chromium is present in carbide form, the austenitizing temperature before hardening must be high enough to dissolve the chromium carbides. Otherwise the hardenability can deteriorate due to the increased number of germs. Chrome also tends to during the annealing treatment to form oxides on the steel surface, which can degrade the galvanizing quality. The optional Cr content is therefore set at values of 0.05 to 1.0% by weight.
- Molybdenum (Mo): The addition of molybdenum is similar to chromium to improve hardenability. The pearlite and bainitic transformation is pushed to longer times and the martensite start temperature is lowered. Molybdenum also increases the tempering resistance considerably and increases the strength of the ferrite through solid solution strengthening.
- the Mo content is added depending on the dimensions, the system configuration and the microstructure. For cost reasons, the optional Mo content is set at 0.05 to 1.0% by weight, preferably up to a maximum of 0.4% by weight.
- Copper (Cu): The addition of copper can increase tensile strength and hardenability. In combination with nickel, chromium and phosphorus, copper can form a protective oxide layer on the surface, which can significantly reduce the rate of corrosion. In combination with oxygen, copper can form harmful oxides at the grain boundaries, which can have negative effects, especially for hot forming processes. The maximum copper content is therefore limited to 0.2% by weight.
- Calcium is used in the manufacture of high-strength steels for deoxidation, desulfurization and to control the size and shape of oxides and sulfides. In the case of high-strength steels in particular, this results in improved ductility and toughness. In addition, steels with additions of calcium are less prone to hot cracking, e.g. during hot rolling. For the above reasons and because of the very low solubility of calcium in steel - if required - the calcium content is therefore limited to 0.0005 to 0.0060% by weight.
- Micro-alloying elements are usually only added in very small amounts ( ⁇ 0.1%). Typical micro-alloying elements are aluminum, vanadium, titanium, and niobium Boron. In contrast to the alloying elements, they mainly act through the formation of precipitates, but they can also influence the properties in the dissolved state. Despite the small amounts added, micro-alloying elements strongly influence the manufacturing conditions as well as the processing and final properties. Carbide and nitride formers that are soluble in the iron lattice are generally used as microalloying elements. A formation of carbonitrides is also possible due to the complete solubility of nitrides and carbides in each other.
- the tendency to form oxides and sulfides is usually most pronounced with the micro-alloying elements, but is usually specifically prevented due to other alloying elements. This property can be used positively in that the elements sulfur and oxygen, which are generally harmful, can be bound. However, setting can also have negative effects if there are no longer enough micro-alloying elements available for the formation of carbides.
- Titanium (Ti) forms very stable nitrides (TiN) and sulfides (T1S2) even at high temperatures. Depending on the nitrogen content, some of these only dissolve in the melt. If the precipitates produced in this way are not removed with the slag, they form coarse particles in the material due to the high temperature at which they form, which are generally not conducive to the mechanical properties.
- the binding of free nitrogen and oxygen has a positive effect on toughness.
- titanium protects other dissolved micro-alloying elements, such as niobium, from being bound by nitrogen. These can then optimally develop their effect.
- Nitrides which only form at lower temperatures due to the drop in oxygen and nitrogen content, can also effectively impede austenite grain growth.
- Unset titanium forms titanium carbides at temperatures above 1150 °C and can thus cause grain refinement (inhibition of austenite grain growth, grain refinement through delayed recrystallization and/or increase in the number of nuclei during ⁇ /Y transformation) and precipitation hardening.
- the optional Ti content therefore has values of 0.005 to 0.150% by weight.
- Niobium (Nb) causes strong grain refinement, as it is the most effective of all micro-alloying elements in delaying recrystallization and also inhibiting austenite grain growth.
- the strength-increasing effect is qualitatively higher than that of titanium, evident from the increased grain refinement effect and the larger quantity of strength-increasing particles (bonding of the titanium to form coarse TiN at high temperatures).
- Niobium carbides form at temperatures below 1200 °C. When nitrogen is bonded with titanium, niobium can increase its strength-increasing effect through the formation of small carbides that are effective in terms of their effect in the lower temperature range (smaller carbide sizes).
- niobium Another effect of the niobium is the delay in the ⁇ /Y transformation and the lowering of the martensite start temperature in the dissolved state. On the one hand, this is due to the solute drag effect and, on the other hand, to grain refinement. This causes an increase in the strength of the structure and thus also a higher resistance to the increase in volume during martensite formation.
- the alloying of niobium is limited until its solubility limit is reached. Although this limits the amount of precipitation, if it is exceeded it primarily causes early formation of precipitation with very coarse particles. Precipitation hardening can thus be effective primarily in steels with a low carbon content (higher oversaturation possible) and in hot forming processes (deformation-induced precipitation). The Nb content is therefore limited to values of 0.005 to 0.150% by weight.
- Vanadium (V) Carbide and nitride formation of vanadium only begins at temperatures around 1000 °C or after the a/g transformation, i.e. much later than with titanium and niobium. Due to the small number of precipitations present in austenite, vanadium has hardly any grain-refining effect. The austenite grain growth is also not inhibited by the late precipitation of the vanadium carbides. Thus, the strength-increasing effect is based almost entirely on precipitation hardening. An advantage of vanadium is its high solubility in austenite and the large volume fraction of fine precipitates caused by the low precipitation temperature. The optional V content is therefore limited to values of 0.001 to 0.300% by weight.
- B Boron
- An increase in hardness on the surface is not achieved (except for boriding with the formation of FeB and Fe2B in the edge zone of a workpiece).
- boron in very small amounts leads to a significant improvement in hardenability.
- boron The mechanism of action of boron can be described in such a way that boron atoms accumulate at the grain boundaries with suitable temperature control and, by reducing the grain boundary energy, make the formation of viable ferrite nuclei significantly more difficult.
- care must be taken to ensure that boron is predominantly atomically distributed in the grain boundary and is not present in the form of precipitates due to excessively high temperatures.
- the effectiveness of boron decreases with increasing grain size and increasing carbon content (> 0.8%).
- an amount exceeding 60 ppm causes a decrease in hardenability since boron carbides act as nuclei on the grain boundaries.
- boron diffuses extremely well and has a very high affinity for oxygen, which can lead to a reduction in the boron content in areas close to the surface (up to 0.5 mm).
- annealing at over 1000 °C is not recommended. This is also recommended, since boron can lead to strong coarse grain formation at annealing temperatures of over 1000 °C.
- the B content is limited to values of 0.0005 to 0.0050% by weight.
- the invention also relates to the use of an above-mentioned steel strip to produce a motor vehicle component.
- FIG. 1 shows a graphical representation of the temperature profile over time of a rolled steel strip and a plant that heat-treats this strip during a heat treatment according to a preferred embodiment of the invention in a temperature-time diagram
- the annealing treatments according to the invention can be multi-stage or additional annealing treatments can be provided in relation to the overall process.
- An example time-temperature cycle showing the characteristic Temperature ranges for holding times, cooling rates and heating rates are shown in FIG.
- a rolled strip of steel of the appropriate composition is brought into a compact form, in particular rolled up into a coil, which makes it possible to place the strip as a whole in an apparatus for heat treatment.
- the sheet metal strip is heated to a temperature T > 750° C. within about 3 hours.
- the sheet metal strip is then kept at a temperature above 750° C. for about 8 hours by means of the apparatus.
- T max ⁇ Ar3 +70 K The strip sheet is then cooled. During this cooling, the temperature range from 750 °C to 200 °C is covered in a period of about 14 hours.
- the sheet steel made of steel with a suitable steel concept i.e. a suitable composition
- the desired microstructure results and the steel strip made of high-strength multiphase steel is produced.
- Cooling down to a certain temperature is preferably carried out in the heat treatment apparatus. This is, for example, a batch-type annealing system.
- the example shown is in a preferred cooling range of 20 K/h to 80 K/h.
- Table 1 shows examples of material concepts, more precisely steel concepts, and their chemical composition in % by weight. Steel concepts according to the invention are marked accordingly. In addition to the steel concepts according to the invention, which are used in the form of a hot-rolled or cold-rolled sheet metal strip as the input material for manufacturing a product according to the invention, steel concepts that are not according to the invention are also given as a comparison.
- Steel A is not according to the invention, since the sum of hardenability-increasing alloying elements described by the CEV is below the required value of 0.49 is.
- steel A After a heat treatment with the process parameters according to the invention, steel A has formed a microstructure consisting of ferrite and pearlite and no portions of bainite and/or martensite. The associated stress-strain curve can be seen in FIG.
- the heat treated steel A from has a tensile strength of 540 MPa and an undesirably high yield point.
- Steel B from Table 2 is also not according to the invention, although steel B with a CEV value of 2.34 has sufficient through-hardenability. However, the ratio of CEV/(Si+Al) > 2.34 and thus the content of Si and Al is not sufficient in relation to the use of through-hardenability-increasing elements. This can also be seen from the achievable tensile strength of a maximum of 762 MPa.
- Steels C and D are exemplary material concepts that are suitable for an annealing treatment according to the invention and the production of steel strips designed according to the invention. After a heat treatment with the process parameters according to the invention, the steels C and D have a martensite and/or bainite content of more than 30%. Due to the microstructure adjusted in this way, the steels also have the material properties characteristic of multiphase steels , such as a yield point-tensile strength ratio (R p o .2/Rm) between 0.45 and 0.6, a high tensile strength R m above 780 MPa and a high elongation at break So> 8%.
- R p o .2/Rm yield point-tensile strength ratio
Abstract
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EP22722412.8A EP4314356A1 (en) | 2021-04-01 | 2022-04-01 | Steel strip made of a high-strength multiphase steel and process for producing such a steel strip |
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PCT/EP2022/058767 WO2022207913A1 (en) | 2021-04-01 | 2022-04-01 | Steel strip made of a high-strength multiphase steel and process for producing such a steel strip |
Country Status (5)
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EP (1) | EP4314356A1 (en) |
KR (1) | KR20230164098A (en) |
CN (1) | CN117222754A (en) |
DE (1) | DE102021108448A1 (en) |
WO (1) | WO2022207913A1 (en) |
Citations (9)
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JP2003313636A (en) * | 2002-04-25 | 2003-11-06 | Jfe Steel Kk | Hot-dipped steel sheet with high ductility and high strength, and manufacturing method therefor |
EP2202327A1 (en) * | 2007-10-25 | 2010-06-30 | JFE Steel Corporation | High-strength hot-dip zinc plated steel sheet excellent in workability and process for manufacturing the same |
EP2824210A1 (en) * | 2012-03-07 | 2015-01-14 | JFE Steel Corporation | High-strength cold-rolled steel sheet and process for manufacturing same |
DE102015111177A1 (en) | 2015-07-10 | 2017-01-12 | Salzgitter Flachstahl Gmbh | High strength multi-phase steel and method of making a cold rolled steel strip therefrom |
EP3394307A1 (en) * | 2015-12-21 | 2018-10-31 | voestalpine Stahl GmbH | High strength galvannealed steel sheet and method of producing such steel sheet |
EP3394297A1 (en) * | 2015-12-21 | 2018-10-31 | Arcelormittal | Method for producing a high strength coated steel sheet having improved ductility and formability, and obtained coated steel sheet |
DE102017130237A1 (en) | 2017-12-15 | 2019-06-19 | Salzgitter Flachstahl Gmbh | High strength hot rolled flat steel product with high edge crack resistance and high bake hardening potential, a process for producing such a flat steel product |
DE102017131247A1 (en) | 2017-12-22 | 2019-06-27 | Voestalpine Stahl Gmbh | Method for producing metallic components with adapted component properties |
SE542818C2 (en) * | 2019-01-22 | 2020-07-14 | Voestalpine Stahl Gmbh | A high strength high ductility complex phase cold rolled steel strip or sheet |
Family Cites Families (2)
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TWI290177B (en) | 2001-08-24 | 2007-11-21 | Nippon Steel Corp | A steel sheet excellent in workability and method for producing the same |
DE102007019196A1 (en) | 2007-04-20 | 2008-10-23 | Muhr Und Bender Kg | Rolling process to make a flexible ribbon with a cathode anti-corrosion coating on hot dipped or electro-galvanized steel |
-
2021
- 2021-04-01 DE DE102021108448.2A patent/DE102021108448A1/en active Pending
-
2022
- 2022-04-01 CN CN202280026258.1A patent/CN117222754A/en active Pending
- 2022-04-01 KR KR1020237036344A patent/KR20230164098A/en unknown
- 2022-04-01 EP EP22722412.8A patent/EP4314356A1/en active Pending
- 2022-04-01 WO PCT/EP2022/058767 patent/WO2022207913A1/en active Application Filing
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2003313636A (en) * | 2002-04-25 | 2003-11-06 | Jfe Steel Kk | Hot-dipped steel sheet with high ductility and high strength, and manufacturing method therefor |
EP2202327A1 (en) * | 2007-10-25 | 2010-06-30 | JFE Steel Corporation | High-strength hot-dip zinc plated steel sheet excellent in workability and process for manufacturing the same |
EP2824210A1 (en) * | 2012-03-07 | 2015-01-14 | JFE Steel Corporation | High-strength cold-rolled steel sheet and process for manufacturing same |
DE102015111177A1 (en) | 2015-07-10 | 2017-01-12 | Salzgitter Flachstahl Gmbh | High strength multi-phase steel and method of making a cold rolled steel strip therefrom |
EP3394307A1 (en) * | 2015-12-21 | 2018-10-31 | voestalpine Stahl GmbH | High strength galvannealed steel sheet and method of producing such steel sheet |
EP3394297A1 (en) * | 2015-12-21 | 2018-10-31 | Arcelormittal | Method for producing a high strength coated steel sheet having improved ductility and formability, and obtained coated steel sheet |
DE102017130237A1 (en) | 2017-12-15 | 2019-06-19 | Salzgitter Flachstahl Gmbh | High strength hot rolled flat steel product with high edge crack resistance and high bake hardening potential, a process for producing such a flat steel product |
DE102017131247A1 (en) | 2017-12-22 | 2019-06-27 | Voestalpine Stahl Gmbh | Method for producing metallic components with adapted component properties |
SE542818C2 (en) * | 2019-01-22 | 2020-07-14 | Voestalpine Stahl Gmbh | A high strength high ductility complex phase cold rolled steel strip or sheet |
Also Published As
Publication number | Publication date |
---|---|
EP4314356A1 (en) | 2024-02-07 |
DE102021108448A1 (en) | 2022-10-06 |
KR20230164098A (en) | 2023-12-01 |
CN117222754A (en) | 2023-12-12 |
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