CA3183159A1 - Heat treated cold rolled steel sheet and a method of manufacturing thereof - Google Patents
Heat treated cold rolled steel sheet and a method of manufacturing thereofInfo
- Publication number
- CA3183159A1 CA3183159A1 CA3183159A CA3183159A CA3183159A1 CA 3183159 A1 CA3183159 A1 CA 3183159A1 CA 3183159 A CA3183159 A CA 3183159A CA 3183159 A CA3183159 A CA 3183159A CA 3183159 A1 CA3183159 A1 CA 3183159A1
- Authority
- CA
- Canada
- Prior art keywords
- steel sheet
- rolled steel
- cold rolled
- anyone
- heat treated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 39
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 87
- 239000010959 steel Substances 0.000 claims abstract description 87
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 29
- 239000000203 mixture Substances 0.000 claims abstract description 19
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 19
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 15
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 14
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 8
- 230000001955 cumulated effect Effects 0.000 claims abstract description 5
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 229910052742 iron Inorganic materials 0.000 claims abstract description 4
- 238000012545 processing Methods 0.000 claims abstract description 4
- 238000001816 cooling Methods 0.000 claims description 26
- 238000000034 method Methods 0.000 claims description 23
- 238000010438 heat treatment Methods 0.000 claims description 18
- 238000000137 annealing Methods 0.000 claims description 13
- 239000011572 manganese Substances 0.000 claims description 13
- 229910052799 carbon Inorganic materials 0.000 claims description 12
- 229910052782 aluminium Inorganic materials 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 11
- 238000005096 rolling process Methods 0.000 claims description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 9
- 229910052710 silicon Inorganic materials 0.000 claims description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 8
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 8
- 239000011651 chromium Substances 0.000 claims description 8
- 238000005496 tempering Methods 0.000 claims description 8
- 238000005098 hot rolling Methods 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 7
- 230000008569 process Effects 0.000 claims description 7
- 239000010703 silicon Substances 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 4
- 229910052791 calcium Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 238000003303 reheating Methods 0.000 claims description 4
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 238000005097 cold rolling Methods 0.000 claims description 2
- 239000011265 semifinished product Substances 0.000 claims 2
- 239000010936 titanium Substances 0.000 description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 239000010955 niobium Substances 0.000 description 8
- 230000000694 effects Effects 0.000 description 7
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 6
- 230000001627 detrimental effect Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 230000002411 adverse Effects 0.000 description 4
- 238000009749 continuous casting Methods 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 230000001186 cumulative effect Effects 0.000 description 4
- 239000011574 phosphorus Substances 0.000 description 4
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 3
- 229910001335 Galvanized steel Inorganic materials 0.000 description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 3
- 239000011575 calcium Substances 0.000 description 3
- 239000008397 galvanized steel Substances 0.000 description 3
- 239000011733 molybdenum Substances 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 238000007711 solidification Methods 0.000 description 3
- 230000008023 solidification Effects 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 239000011593 sulfur Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000012827 research and development Methods 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- -1 Aluminum Nitrides Chemical class 0.000 description 1
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 241001484259 Lacuna Species 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000005864 Sulphur Substances 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 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
- C22C38/18—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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
- B21C47/02—Winding-up or coiling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- 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
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
- 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
- C21D8/0268—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment between cold rolling steps
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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
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- 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
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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
- C22C38/54—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
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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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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- Heat Treatment Of Steel (AREA)
Abstract
A heat treated cold rolled steel sheet comprising of the following elements,0.1% ? C ? 0.2 %; 1.2 % ? Mn ? 2.2 %; 0.05% ? Si ? 0.6 %; 0.001% ? Al ? 0.1 %; 0.01% ? Cr ? 0.5 %;0% ? S ? 0.09%; 0% ? P ? 0.09%; 0% ? N ? 0.09%; 0% ? Mo ? 0.5%; 0% ? Ti ? 0.1%; 0% ? Nb ? 0.1%; 0% ? V? 0.1%; 0% ? Ni ? 1%; 0% ? Cu ? 1%; 0% ? Ca ? 0.005%; 0% ? B ? 0.05%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel comprising, by area percentage, 60% to 85% of tempered martensite, a cumulated amount of ferrite and bainite of 15 % to 38%, an optional amount of residual austenite of 0% to 5% and an optional amount of fresh martensite of 0 to 5%.
Description
HEAT TREATED COLD ROLLED STEEL SHEET AND A METHOD OF
MANUFACTURING THEREOF
The present invention relates to cold rolled steel sheet with high strength and high formability.
Automotive parts are required to satisfy two inconsistent necessities, viz.
ease of forming and strength but in recent years a third requirement of improvement in fuel consumption is also bestowed upon automobiles in view of global environment concerns. Thus, now automotive parts must be made of material having high formability in order that to fit in the criteria of ease of fit in the intricate automobile assembly and at same time have to improve strength for vehicle crashworthiness and durability while reducing weight of vehicle to improve fuel efficiency.
Therefore, intense Research and development endeavors are put in to reduce the amount of material utilized in car by increasing the strength of material.
Conversely, an increase in strength of steel sheets decreases formability, and thus development of materials having both high strength and high formability is necessitated.
Earlier research and developments in the field of high strength and high formability steel sheets have resulted in several methods for producing high zo strength and high formability steel sheets, some of which are enumerated herein for conclusive appreciation of the present invention:
EP3187608 is high-strength hot-dip galvanized steel sheet having a tensile strength (TS) of 1,300 MPa or more and excellent in ductility and in-plane uniformity of material properties is provided, and a method for manufacturing the steel sheet is also provided. The high-strength hot-dip galvanized steel sheet has a specific composition including C, Si, Mn, etc. In this chemical composition, the content of Ti [Ti] and the content of N [N] satisfy [Ti] > 4[N]. The high-strength hot-dip galvanized steel sheet has a microstructure including martensite at an area fraction of 60% or more and 90% or less, polygonal ferrite at an area fraction of more than
MANUFACTURING THEREOF
The present invention relates to cold rolled steel sheet with high strength and high formability.
Automotive parts are required to satisfy two inconsistent necessities, viz.
ease of forming and strength but in recent years a third requirement of improvement in fuel consumption is also bestowed upon automobiles in view of global environment concerns. Thus, now automotive parts must be made of material having high formability in order that to fit in the criteria of ease of fit in the intricate automobile assembly and at same time have to improve strength for vehicle crashworthiness and durability while reducing weight of vehicle to improve fuel efficiency.
Therefore, intense Research and development endeavors are put in to reduce the amount of material utilized in car by increasing the strength of material.
Conversely, an increase in strength of steel sheets decreases formability, and thus development of materials having both high strength and high formability is necessitated.
Earlier research and developments in the field of high strength and high formability steel sheets have resulted in several methods for producing high zo strength and high formability steel sheets, some of which are enumerated herein for conclusive appreciation of the present invention:
EP3187608 is high-strength hot-dip galvanized steel sheet having a tensile strength (TS) of 1,300 MPa or more and excellent in ductility and in-plane uniformity of material properties is provided, and a method for manufacturing the steel sheet is also provided. The high-strength hot-dip galvanized steel sheet has a specific composition including C, Si, Mn, etc. In this chemical composition, the content of Ti [Ti] and the content of N [N] satisfy [Ti] > 4[N]. The high-strength hot-dip galvanized steel sheet has a microstructure including martensite at an area fraction of 60% or more and 90% or less, polygonal ferrite at an area fraction of more than
2 5% and 40% or less, and retained austenite at an area fraction of less than 3%
(including 0%). The average hardness of the martensite is 450 or more and 600 or less in terms of Vickers hardness, and the average crystal grain diameter of the martensite is 10 pm or less. The standard deviation of the crystal grain diameters of the martensite is 4.0 pm or less. EP3187608 is able to provide the tensile strength above 980MPa but does not have an elongation of 8% or more.
EP3473741 is a steel sheet having a tensile strength of 950 MPa or more and good toughness and a method for manufacturing the same. The steel sheet has a specific composition and a metallographic structure containing: a ferrite area fraction of 30% or less (including 0%), a tempered martensite area fraction of 70%
or more (including 100%), and a retained austenite area fraction of 4.5% or less (including 0%), wherein the average aspect ratio of an iron based carbide, precipitated in tempered martensite grains, having a grain size in the largest 10%
is 3.5 or more. But the steel of EP3473741 is not able to provide the ultimate tensile strength of 950 or more in both rolling as well as the transversal direction.
The known prior art related to the manufacture of high strength and high formability steel sheets is inflicted by one or the other lacuna: hence there lies a need for a cold rolled steel sheet having high strength and high formability and a method of manufacturing the same.
The purpose of the present invention is to solve these problems by making available cold-rolled steel sheets that simultaneously have:
- an ultimate tensile strength from 980 MPa to 1150MPa in both transversal direction as well as rolling direction and preferably from 980 MPa to 1150MPa in both transversal direction as well as rolling direction.
In a preferred embodiment, the total elongation of the steel sheet is greater than or equal to 8%, In a preferred embodiment, a yield strength from 700 MPa to 850MPa in both transversal direction as well as rolling direction and preferably from 720 MPa to 850MPa in both transversal direction as well as rolling direction.
(including 0%). The average hardness of the martensite is 450 or more and 600 or less in terms of Vickers hardness, and the average crystal grain diameter of the martensite is 10 pm or less. The standard deviation of the crystal grain diameters of the martensite is 4.0 pm or less. EP3187608 is able to provide the tensile strength above 980MPa but does not have an elongation of 8% or more.
EP3473741 is a steel sheet having a tensile strength of 950 MPa or more and good toughness and a method for manufacturing the same. The steel sheet has a specific composition and a metallographic structure containing: a ferrite area fraction of 30% or less (including 0%), a tempered martensite area fraction of 70%
or more (including 100%), and a retained austenite area fraction of 4.5% or less (including 0%), wherein the average aspect ratio of an iron based carbide, precipitated in tempered martensite grains, having a grain size in the largest 10%
is 3.5 or more. But the steel of EP3473741 is not able to provide the ultimate tensile strength of 950 or more in both rolling as well as the transversal direction.
The known prior art related to the manufacture of high strength and high formability steel sheets is inflicted by one or the other lacuna: hence there lies a need for a cold rolled steel sheet having high strength and high formability and a method of manufacturing the same.
The purpose of the present invention is to solve these problems by making available cold-rolled steel sheets that simultaneously have:
- an ultimate tensile strength from 980 MPa to 1150MPa in both transversal direction as well as rolling direction and preferably from 980 MPa to 1150MPa in both transversal direction as well as rolling direction.
In a preferred embodiment, the total elongation of the steel sheet is greater than or equal to 8%, In a preferred embodiment, a yield strength from 700 MPa to 850MPa in both transversal direction as well as rolling direction and preferably from 720 MPa to 850MPa in both transversal direction as well as rolling direction.
3 Preferably, such steel can also have a good suitability for forming, in particular for rolling with good weldability and coat ability.
Another object of the present invention is also to make available a method for the manufacturing of these sheets that is compatible with conventional industrial applications while being robust towards manufacturing parameters shifts.
Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention.
Carbon is present in the steel from 0.1% to 0.2%. Carbon is an element necessary for increasing the strength of a steel sheet by producing a low-temperature transformation phase such as martensite. A content less than 0.1% would not allow the formation of martensite there by tempered martensite, thereby decreasing strength as well as ductility. On the other hand, at a carbon content exceeding 0.2%, a weld zone and a heat-affected zone are significantly hardened, and thus the mechanical properties of the weld zone are impaired. The preferred limit for Carbon is from 0.12 to 0.19% and more preferably is from 0.13 to 0.17%.
Manganese content of the steel of present invention is from 1.2% to 2.2%.
Manganese is an element that imparts strength. An amount of at least about 1.2%
by weight of manganese has been found in order to provide the strength and zo hardenability of the steel sheet. Thus, a higher percentage of Manganese such as 1.3% to 2.1% is preferred. But when manganese is more than 2.2%, this produces adverse effects such as slowing down the transformation of austenite to ferrite during the slow cooling after annealing, leading to a reduction of ductility.
Moreover, a manganese content above 2.2% would also reduce the weldability of the present steel. Hence the preferred limit for the steel of present invention is from 1.3% to 2.1% and more preferably from 1.6% to 2.0%.
Silicon is an essential element for the steel of present invention, Silicon is present from 0.05% to 0.6%. Silicon is added to the steel of present invention to impart strength by solid solution strengthening. Silicon plays a part in the formation of the microstructure by preventing the precipitation of carbides and by promoting the
Another object of the present invention is also to make available a method for the manufacturing of these sheets that is compatible with conventional industrial applications while being robust towards manufacturing parameters shifts.
Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention.
Carbon is present in the steel from 0.1% to 0.2%. Carbon is an element necessary for increasing the strength of a steel sheet by producing a low-temperature transformation phase such as martensite. A content less than 0.1% would not allow the formation of martensite there by tempered martensite, thereby decreasing strength as well as ductility. On the other hand, at a carbon content exceeding 0.2%, a weld zone and a heat-affected zone are significantly hardened, and thus the mechanical properties of the weld zone are impaired. The preferred limit for Carbon is from 0.12 to 0.19% and more preferably is from 0.13 to 0.17%.
Manganese content of the steel of present invention is from 1.2% to 2.2%.
Manganese is an element that imparts strength. An amount of at least about 1.2%
by weight of manganese has been found in order to provide the strength and zo hardenability of the steel sheet. Thus, a higher percentage of Manganese such as 1.3% to 2.1% is preferred. But when manganese is more than 2.2%, this produces adverse effects such as slowing down the transformation of austenite to ferrite during the slow cooling after annealing, leading to a reduction of ductility.
Moreover, a manganese content above 2.2% would also reduce the weldability of the present steel. Hence the preferred limit for the steel of present invention is from 1.3% to 2.1% and more preferably from 1.6% to 2.0%.
Silicon is an essential element for the steel of present invention, Silicon is present from 0.05% to 0.6%. Silicon is added to the steel of present invention to impart strength by solid solution strengthening. Silicon plays a part in the formation of the microstructure by preventing the precipitation of carbides and by promoting the
4 formation of martensite. But whenever the silicon content is more than 0.6%, surface properties and weldability of steel is deteriorated, therefore the Silicon content is preferred from 0.1% to 0.5% and more preferably 0.1% to 0.4%.
Aluminum content of the present invention is from 0.001% to 0.1%.
Aluminum is added to de-oxidise the steel of present invention. Aluminum is an alphageneous element. This can increase the formability and ductility of steel. In order to obtain such an effect, Aluminum content is required at 0.001% or more.
However, when the Aluminum content exceeds 0.1%, Ac3 point increases beyond acceptable, austenite single phase is very difficult to achieve industrially hence hot rolling in complete austenite region cannot be performed. Therefore, Aluminum content must not be more than 0.1% .The preferable limit for the presence of Aluminum is from 0.001% to 0.09% and more preferably 0.001% to 0.06%.
Chromium content of the steel of present invention is from 0.01% to 0.5%.
Chromium is an essential element that provide strength and hardening to the steel, but when used above 0.5 % impairs surface finish of the steel. The preferred limit for Chromium is from 0.1% to 0.4% and more preferably 0.1% to 0.3%.
Phosphorus content of the steel of present invention is limited to 0.09%.
zo Phosphorus is an element which hardens in solid solution and also interferes with formation of carbides. Therefore a small amount of phosphorus, of at least 0.002%
can be advantageous, but phosphorus has adverse effects also, such as a reduction of the spot weldability and the hot ductility, particularly due to its tendency to segregation at the grain boundaries or co-segregation with manganese. For these reasons, its content is preferably limited a maximum of 0.09%.
Sulfur is not an essential element but may be contained as an impurity in steel up to 0.09%. The sulfur content is preferred as low as possible, but between 0.001% and 0.03% is preferred from the viewpoint of manufacturing cost.
Further if higher sulfur is present in steel it combines to form sulfide especially with Mn and Ti and reduces their beneficial impact on the present invention.
Nitrogen is limited to 0.09% in order to avoid ageing of material. Nitrogen can form nitrides or carbonitrides together with carbon, that can impart strength to the steel of present invention by precipitation strengthening with Vanadium and Niobium but whenever the presence of nitrogen is more than 0.09% it can form high amount of Aluminum Nitrides which are detrimental for the present invention hence the preferable limit for the nitrogen is between 0.001% and 0.01%.
Aluminum content of the present invention is from 0.001% to 0.1%.
Aluminum is added to de-oxidise the steel of present invention. Aluminum is an alphageneous element. This can increase the formability and ductility of steel. In order to obtain such an effect, Aluminum content is required at 0.001% or more.
However, when the Aluminum content exceeds 0.1%, Ac3 point increases beyond acceptable, austenite single phase is very difficult to achieve industrially hence hot rolling in complete austenite region cannot be performed. Therefore, Aluminum content must not be more than 0.1% .The preferable limit for the presence of Aluminum is from 0.001% to 0.09% and more preferably 0.001% to 0.06%.
Chromium content of the steel of present invention is from 0.01% to 0.5%.
Chromium is an essential element that provide strength and hardening to the steel, but when used above 0.5 % impairs surface finish of the steel. The preferred limit for Chromium is from 0.1% to 0.4% and more preferably 0.1% to 0.3%.
Phosphorus content of the steel of present invention is limited to 0.09%.
zo Phosphorus is an element which hardens in solid solution and also interferes with formation of carbides. Therefore a small amount of phosphorus, of at least 0.002%
can be advantageous, but phosphorus has adverse effects also, such as a reduction of the spot weldability and the hot ductility, particularly due to its tendency to segregation at the grain boundaries or co-segregation with manganese. For these reasons, its content is preferably limited a maximum of 0.09%.
Sulfur is not an essential element but may be contained as an impurity in steel up to 0.09%. The sulfur content is preferred as low as possible, but between 0.001% and 0.03% is preferred from the viewpoint of manufacturing cost.
Further if higher sulfur is present in steel it combines to form sulfide especially with Mn and Ti and reduces their beneficial impact on the present invention.
Nitrogen is limited to 0.09% in order to avoid ageing of material. Nitrogen can form nitrides or carbonitrides together with carbon, that can impart strength to the steel of present invention by precipitation strengthening with Vanadium and Niobium but whenever the presence of nitrogen is more than 0.09% it can form high amount of Aluminum Nitrides which are detrimental for the present invention hence the preferable limit for the nitrogen is between 0.001% and 0.01%.
5 .. Molybdenum is an optional element that constitutes from 0% to 0.5% of the Steel of present invention; Molybdenum increases the hardenabty of the steel of present invention and influences the transformation of austenite to Ferrite and Bainite during cooling after annealing. However, the addition of Molybdenum excessively increases the cost of the addition of alloy elements, so that for economic reasons its content is limited to 0.5%.
Niobium is an optional element that can be added to the steel up to 0.1%, preferably between 0.0010 and 0.1%. It is suitable for forming carbonitrides to impart strength to the steel according to the invention by precipitation hardening.
Because niobium delays the recrystallization during the heating, the microstructure formed at the end of the holding temperature and as a consequence after the complete annealing is finer, this leads to the hardening of the product. But, when the niobium content is above 0.1% the amount of carbo-nitrides is not favorable for the present invention as large amount of carbo-nitrides tend to reduce the ductility of the steel.
Titanium is an optional element which may be added to the steel of the present invention up to 0.1%, preferably between 0.001% and 0.1%. As niobium, it is involved in carbo-nitrides so plays a role in hardening. But it is also involved to form TiN appearing during solidification of the cast product. The amount of Ti is so limited to 0.1% to avoid coarse TiN detrimental for hole expansion. In case the titanium content is below 0.001% it does not impart any effect on the steel of present invention.
Vanadium is an optional element which may be added to the steel of the present invention up to 0.1%, preferably from 0.001% to 0.01%. As niobium, it is involved in carbo-nitrides so plays a role in hardening. But it is also involved to form VN appearing during solidification of the cast product. The amount of V is so limited
Niobium is an optional element that can be added to the steel up to 0.1%, preferably between 0.0010 and 0.1%. It is suitable for forming carbonitrides to impart strength to the steel according to the invention by precipitation hardening.
Because niobium delays the recrystallization during the heating, the microstructure formed at the end of the holding temperature and as a consequence after the complete annealing is finer, this leads to the hardening of the product. But, when the niobium content is above 0.1% the amount of carbo-nitrides is not favorable for the present invention as large amount of carbo-nitrides tend to reduce the ductility of the steel.
Titanium is an optional element which may be added to the steel of the present invention up to 0.1%, preferably between 0.001% and 0.1%. As niobium, it is involved in carbo-nitrides so plays a role in hardening. But it is also involved to form TiN appearing during solidification of the cast product. The amount of Ti is so limited to 0.1% to avoid coarse TiN detrimental for hole expansion. In case the titanium content is below 0.001% it does not impart any effect on the steel of present invention.
Vanadium is an optional element which may be added to the steel of the present invention up to 0.1%, preferably from 0.001% to 0.01%. As niobium, it is involved in carbo-nitrides so plays a role in hardening. But it is also involved to form VN appearing during solidification of the cast product. The amount of V is so limited
6 to 0.1% to avoid coarse VN detrimental for hole expansion. In case the vanadium content is below 0.001% it does not impart any effect on the steel of present invention.
Nickel may be added as an optional element in an amount of 0% to 10/ to increase .. the strength of the steel and to improve its toughness. A minimum of 0.01%
is required to produce such effects. However, when its content is above 1%, Nickel causes ductility deterioration.
Copper may be added as an optional element in an amount of 0% to 1% to increase the strength of the steel and to improve its corrosion resistance. A minimum of 1.0 0.01% is required to produce such effects. However, when its content is above 1%.
copper causes hot ductility deterioration during hot rolling.
Calcium is an optional element which may be added to the steel of present invention up to 0.005%, preferably from 0.001% to 0.005%. Calcium is added to steel of present invention as an optional element especially during the inclusion .. treatment. Calcium contributes towards the refining of the steel by arresting the detrimental sulphur content in globularizing it.
Other elements such as cerium, boron, magnesium or zirconium can be added individually or in combination in the following proportions: Ce < 0.1%, B <
0.05%, Mg < 0.05% and Zr < 0.05%. Up to the maximum content levels indicated, zo these elements make it possible to refine the grain during solidification.
The remainder of the composition of the steel consists of iron and inevitable impurities resulting from processing.
The microstructure of the steel sheet according to the invention comprises 60% to 85% of tempered martensite, 0% to 5% of residual austenite, 0% to 5% of fresh martensite and cumulative amount of ferrite and bainite of 15% to 38% in area fractions, Tempered Martensite constitutes the matrix phase for the steel of present invention
Nickel may be added as an optional element in an amount of 0% to 10/ to increase .. the strength of the steel and to improve its toughness. A minimum of 0.01%
is required to produce such effects. However, when its content is above 1%, Nickel causes ductility deterioration.
Copper may be added as an optional element in an amount of 0% to 1% to increase the strength of the steel and to improve its corrosion resistance. A minimum of 1.0 0.01% is required to produce such effects. However, when its content is above 1%.
copper causes hot ductility deterioration during hot rolling.
Calcium is an optional element which may be added to the steel of present invention up to 0.005%, preferably from 0.001% to 0.005%. Calcium is added to steel of present invention as an optional element especially during the inclusion .. treatment. Calcium contributes towards the refining of the steel by arresting the detrimental sulphur content in globularizing it.
Other elements such as cerium, boron, magnesium or zirconium can be added individually or in combination in the following proportions: Ce < 0.1%, B <
0.05%, Mg < 0.05% and Zr < 0.05%. Up to the maximum content levels indicated, zo these elements make it possible to refine the grain during solidification.
The remainder of the composition of the steel consists of iron and inevitable impurities resulting from processing.
The microstructure of the steel sheet according to the invention comprises 60% to 85% of tempered martensite, 0% to 5% of residual austenite, 0% to 5% of fresh martensite and cumulative amount of ferrite and bainite of 15% to 38% in area fractions, Tempered Martensite constitutes the matrix phase for the steel of present invention
7 Tempered Martensite constitutes from 60% to 85% of the microstructure by area fraction. Tempered martensite is formed from the martensite which forms during the second step of cooling after annealing and particularly when the temperature drops below Ms temperature and more particularly from Ms-10 C to 15 C.Such martensite is then tempered during the holding at a tempering temperature Temper from 150 C to 300 C. The martensite of the present invention imparts ductility and strength to such steel. Preferably, the content of martensite is from 62% to 80%
and more preferably from 62% to 75%.
Fresh martensite is an optional microconstituent which is limited in the steel at an amount of from 0% to 5%, preferably from 0 to 2% and even better equal to 0%. Fresh martensite may form during the final cooling after tempering.
The cumulated amount of ferrite and bainite represents from 15% to 38% of the microstructure. The cumulated amounts of bainite and ferrite is greater than 15%
is mandatory to ensure a balance between strength and elongation in which is presence of Bainite impart tensile strength of 980 MPa and Ferrite ensure the elongation. Bainite forms during the reheating before tempering. Bainite can impart strength to the steel but when present in a too big amount, it may adversely impact the yield strength of the steel. Ferrite imparts elongation as well as formability to the steel of the present invention. To ensure an elongation of 8% and preferably zo 9% or more it is preferred to have 10% of Ferrite. Ferrite is formed during the first step of cooling after annealing. But when the cumulative presence of bainite and ferrite are present above 38% the mechanical properties may get impacted adversely specifically the tensile strength and yield strength in transverse direction.
Hence the preferred limit for the cumulative presence ferrite and bainite is kept 25 from 20% to 37% and more preferably from 25% to 36%.
Residual Austenite is an optional microstructure that can be present from 0%
to 5% in the steel. The presence of Residual austenite till 5% is not detrimental to the mechanical properties. Up to 5% Residual austenite imparts ductility and elongation to the steel. It is preferred residual austenite between 0% and 3%
and 30 more preferably from 0% to 2%.
and more preferably from 62% to 75%.
Fresh martensite is an optional microconstituent which is limited in the steel at an amount of from 0% to 5%, preferably from 0 to 2% and even better equal to 0%. Fresh martensite may form during the final cooling after tempering.
The cumulated amount of ferrite and bainite represents from 15% to 38% of the microstructure. The cumulated amounts of bainite and ferrite is greater than 15%
is mandatory to ensure a balance between strength and elongation in which is presence of Bainite impart tensile strength of 980 MPa and Ferrite ensure the elongation. Bainite forms during the reheating before tempering. Bainite can impart strength to the steel but when present in a too big amount, it may adversely impact the yield strength of the steel. Ferrite imparts elongation as well as formability to the steel of the present invention. To ensure an elongation of 8% and preferably zo 9% or more it is preferred to have 10% of Ferrite. Ferrite is formed during the first step of cooling after annealing. But when the cumulative presence of bainite and ferrite are present above 38% the mechanical properties may get impacted adversely specifically the tensile strength and yield strength in transverse direction.
Hence the preferred limit for the cumulative presence ferrite and bainite is kept 25 from 20% to 37% and more preferably from 25% to 36%.
Residual Austenite is an optional microstructure that can be present from 0%
to 5% in the steel. The presence of Residual austenite till 5% is not detrimental to the mechanical properties. Up to 5% Residual austenite imparts ductility and elongation to the steel. It is preferred residual austenite between 0% and 3%
and 30 more preferably from 0% to 2%.
8 In addition to the above-mentioned microstructure, the microstructure of the cold rolled steel sheet is free from microstructural components such as pearlite and cementite.
The steel according to the invention can be manufactured by any suitable methods.
It is however preferable to use the method according to the invention that will be detailed, as a non-limitative example.
Such preferred method consists in providing a semi-finished casting of steel with a chemical composition of the prime steel according to the invention. The casting can be done either into ingots or continuously in form of thin slabs or thin strips, i.e. with a thickness ranging from approximately 220mm for slabs up to several tens of millimeters for thin strip.
For example, a slab having the chemical composition according to the invention is manufactured by continuous casting wherein the slab optionally underwent a direct soft reduction during the continuous casting process to avoid central segregation and to ensure a ratio of local Carbon to nominal Carbon kept below 1.10. The slab provided by continuous casting process can be used directly at a high temperature after the continuous casting or may be first cooled to room temperature and then reheated for hot rolling.
zo The temperature of the slab, which is subjected to hot rolling, must be at least 1000 C and must be below 1280 C. In case the temperature of the slab is lower than 1000 C, excessive load is imposed on a rolling mill and, further, the temperature of the steel may decrease to a Ferrite transformation temperature during finishing rolling, whereby the steel will be rolled in a state in which transformed Ferrite contained in the structure. Therefore, the temperature of the slab must be high enough so that hot rolling should be completed in the temperature range of Ac3 to Ac3+100 C. Reheating at temperatures above 1280 C must be avoided because they are industrially expensive.
The steel according to the invention can be manufactured by any suitable methods.
It is however preferable to use the method according to the invention that will be detailed, as a non-limitative example.
Such preferred method consists in providing a semi-finished casting of steel with a chemical composition of the prime steel according to the invention. The casting can be done either into ingots or continuously in form of thin slabs or thin strips, i.e. with a thickness ranging from approximately 220mm for slabs up to several tens of millimeters for thin strip.
For example, a slab having the chemical composition according to the invention is manufactured by continuous casting wherein the slab optionally underwent a direct soft reduction during the continuous casting process to avoid central segregation and to ensure a ratio of local Carbon to nominal Carbon kept below 1.10. The slab provided by continuous casting process can be used directly at a high temperature after the continuous casting or may be first cooled to room temperature and then reheated for hot rolling.
zo The temperature of the slab, which is subjected to hot rolling, must be at least 1000 C and must be below 1280 C. In case the temperature of the slab is lower than 1000 C, excessive load is imposed on a rolling mill and, further, the temperature of the steel may decrease to a Ferrite transformation temperature during finishing rolling, whereby the steel will be rolled in a state in which transformed Ferrite contained in the structure. Therefore, the temperature of the slab must be high enough so that hot rolling should be completed in the temperature range of Ac3 to Ac3+100 C. Reheating at temperatures above 1280 C must be avoided because they are industrially expensive.
9 The sheet obtained in this manner is then cooled at a cooling rate of at least 20 C/s to the coiling temperature which must be below 650 C. Preferably, the cooling rate will be less than or equal to 200 C/s.
The hot rolled steel sheet is then coiled at a coiling temperature below 650 C
to avoid ovalization and preferably from 475 C to 625 C to avoid scale formation, with an even prefererred range for such coiling temperature from 500 C to 625 C.
The coiled hot rolled steel sheet is then cooled down to room temperature before subjecting it to optional hot band annealing.
The hot rolled steel sheet may be subjected to an optional scale removal step to remove the scale formed during the hot rolling before optional hot band annealing.
The hot rolled sheet may then be subjected to an optional hot band annealing.
In a preferred embodiment, such hot band annealing is performed at temperatures from 400 C to 750 C, preferably for at least 12 hours and not more than 96 hours, the temperature preferably remaining below 750 C to avoid transforming partially the hot-rolled microstructure and, therefore, possibly losing the microstructure homogeneity. Thereafter, an optional scale removal step of this hot rolled steel sheet may be performed through, for example, pickling of such sheet.
This hot rolled steel sheet is then subjected to cold rolling to obtain a cold rolled steel sheet with a thickness reduction from 35 to 90%.
zo Thereafter the cold rolled steel sheet is being heat treated which will impart the steel of present invention with requisite mechanical properties and microstructure.
The cold rolled steel sheet is then heated in a two steps heating process wherein the first step of heating starts from room temperature, the cold rolled steel sheet being heated, at a heating rate HR1 of at least 10 C/s, to a temperature HT1 which is in a range from 550 C to 750 C. In a preferred embodiment, the heating rate HR1 for such first step of heating is at least 12 C/s and more preferably at least 15 C/s. The preferred HT1 temperature for such first step is from 575 C to 725 C
and more preferably from 575 C to 700 C.
In the second step of heating, the cold rolled steel sheet is heated from HT1 to an annealing temperature Tsoak which is from Ac3 to Ac3 + 100 C, preferably from Ac3 +10 C to Ac3 + 100 C, at a heating rate HR2 which is from 1 C/s to 15 C/s.
In a preferred embodiment, the heating rate HR2 for the second step of heating is 5 from 1 C/s to 8 C/s and more from 1 C/s to 4 C/s, wherein Ac3 for the steel sheet is calculated by using the following formula:
Ac3 = 910 ¨ 203[C]"(1/2) ¨ 15.2 [Ni] + 44.7[Si] + 104[V] + 31.5[Mo] + 13.1[W]
¨ 30[Mn] ¨ 11[Cr] ¨ 20[Cu] + 700[P] + 400[A/] + 120[As]
+ 400 [Ti]
The hot rolled steel sheet is then coiled at a coiling temperature below 650 C
to avoid ovalization and preferably from 475 C to 625 C to avoid scale formation, with an even prefererred range for such coiling temperature from 500 C to 625 C.
The coiled hot rolled steel sheet is then cooled down to room temperature before subjecting it to optional hot band annealing.
The hot rolled steel sheet may be subjected to an optional scale removal step to remove the scale formed during the hot rolling before optional hot band annealing.
The hot rolled sheet may then be subjected to an optional hot band annealing.
In a preferred embodiment, such hot band annealing is performed at temperatures from 400 C to 750 C, preferably for at least 12 hours and not more than 96 hours, the temperature preferably remaining below 750 C to avoid transforming partially the hot-rolled microstructure and, therefore, possibly losing the microstructure homogeneity. Thereafter, an optional scale removal step of this hot rolled steel sheet may be performed through, for example, pickling of such sheet.
This hot rolled steel sheet is then subjected to cold rolling to obtain a cold rolled steel sheet with a thickness reduction from 35 to 90%.
zo Thereafter the cold rolled steel sheet is being heat treated which will impart the steel of present invention with requisite mechanical properties and microstructure.
The cold rolled steel sheet is then heated in a two steps heating process wherein the first step of heating starts from room temperature, the cold rolled steel sheet being heated, at a heating rate HR1 of at least 10 C/s, to a temperature HT1 which is in a range from 550 C to 750 C. In a preferred embodiment, the heating rate HR1 for such first step of heating is at least 12 C/s and more preferably at least 15 C/s. The preferred HT1 temperature for such first step is from 575 C to 725 C
and more preferably from 575 C to 700 C.
In the second step of heating, the cold rolled steel sheet is heated from HT1 to an annealing temperature Tsoak which is from Ac3 to Ac3 + 100 C, preferably from Ac3 +10 C to Ac3 + 100 C, at a heating rate HR2 which is from 1 C/s to 15 C/s.
In a preferred embodiment, the heating rate HR2 for the second step of heating is 5 from 1 C/s to 8 C/s and more from 1 C/s to 4 C/s, wherein Ac3 for the steel sheet is calculated by using the following formula:
Ac3 = 910 ¨ 203[C]"(1/2) ¨ 15.2 [Ni] + 44.7[Si] + 104[V] + 31.5[Mo] + 13.1[W]
¨ 30[Mn] ¨ 11[Cr] ¨ 20[Cu] + 700[P] + 400[A/] + 120[As]
+ 400 [Ti]
10 wherein the elements contents are expressed in weight percentage of the cold rolled steel sheet.
The cold rolled steel sheet is held at Tsoak during 10 seconds to 500 seconds to ensure a complete recrystallization and full transformation to austenite of the strongly work hardened initial structure.
The cold rolled steel sheet is then cooled in a two steps cooling process wherein the first step of cooling starts from Tsoak, the cold rolled steel sheet being cooled down, at a cooling rate CR1 between 1 C/s and 15 C/s, to a temperature Ti which is in a range from 630 C to 685 C. In a preferred embodiment, the cooling rate CR1 for such first step of cooling is from 1 C/s to 10 C/s and more preferably from zo 1 C/s to 4 C/s. The preferred Ti temperature for such first step is from 640 C to 685 C and more preferably from 650 C to 685 C.
In the second step of cooling, the cold rolled steel sheet is cooled down from Ti to a temperature T2 which is from Ms-10 C to 15 C, at a cooling rate CR2 of at least 100 C/s. In a preferred embodiment, the cooling rate CR2 for the second step of cooling is at least 200 C/s and more preferably at least 300 C/s. The preferred T2 temperature for such second step is from Ms-20 C to 20 C and more preferably from Ms-50 C to 20 C.
Ms for the steel sheet is calculated by using the following formula:
The cold rolled steel sheet is held at Tsoak during 10 seconds to 500 seconds to ensure a complete recrystallization and full transformation to austenite of the strongly work hardened initial structure.
The cold rolled steel sheet is then cooled in a two steps cooling process wherein the first step of cooling starts from Tsoak, the cold rolled steel sheet being cooled down, at a cooling rate CR1 between 1 C/s and 15 C/s, to a temperature Ti which is in a range from 630 C to 685 C. In a preferred embodiment, the cooling rate CR1 for such first step of cooling is from 1 C/s to 10 C/s and more preferably from zo 1 C/s to 4 C/s. The preferred Ti temperature for such first step is from 640 C to 685 C and more preferably from 650 C to 685 C.
In the second step of cooling, the cold rolled steel sheet is cooled down from Ti to a temperature T2 which is from Ms-10 C to 15 C, at a cooling rate CR2 of at least 100 C/s. In a preferred embodiment, the cooling rate CR2 for the second step of cooling is at least 200 C/s and more preferably at least 300 C/s. The preferred T2 temperature for such second step is from Ms-20 C to 20 C and more preferably from Ms-50 C to 20 C.
Ms for the steel sheet is calculated by using the following formula:
11 Ms = 545 ¨ 601.2 * (1 ¨ EXP(-0.868[C])) ¨ 34.4[Mn] ¨ 13.7[Si] ¨ 9.2 [Cr]
¨ 17 .3[Ni] ¨ 15.4[Mo] + 10.8[V] + 4.7[Co] ¨ 1.4[Al] ¨ 16.3[Cu]
¨ 361[Nb] ¨ 2.44 [Ti] ¨ 3448[B]
Thereafter the cold rolled steel sheet is reheated to a tempering temperature Ttemper between 150 C and 300 C with a heating rate of at least 5 C/s and preferably of at least 10 C/s and more preferably 12 C/s or more during 100 s to 600 s. The preferred temperature range for tempering is from 175 C to 280 C
and the preferred duration for holding at Ttemper is from 200 s to 500 s.
According to the present invention the tempering temperature is selected such that the difference between Ti and Ttemper is from 415 C to 455 C. AT is determined as follows:
AT = (Ti ¨ Ttemper) When AT is less than 415 C then the cumulative amount of bainite and ferrite exceeds 38% which is detrimental for the mechanical properties specifically the tensile strength in transversal direction. When AT is greater than 455 C then the amount of tempered martensite is too high, thereby the steel of present invention in rolling direction exceeds 1150 MPa. The preferred AT is between 420 C and zo 440 C
Then, the cold rolled steel sheet is cooled down to room temperature to obtain a heat treated cold rolled steel sheet.
The heat treated cold rolled steel sheet of the present invention may optionally be coated with zinc or zinc alloys, or with aluminum or aluminum alloys to improve its corrosion resistance.
The heat treated cold rolled steel sheet can also be coated by any of the known industrial processes such as Electro-galvanization, JVD, PVD, etc,.
Then an optional post batch annealing may be done at a temperature between 150 C and 300 C during 30 minutes to 120 hours.
¨ 17 .3[Ni] ¨ 15.4[Mo] + 10.8[V] + 4.7[Co] ¨ 1.4[Al] ¨ 16.3[Cu]
¨ 361[Nb] ¨ 2.44 [Ti] ¨ 3448[B]
Thereafter the cold rolled steel sheet is reheated to a tempering temperature Ttemper between 150 C and 300 C with a heating rate of at least 5 C/s and preferably of at least 10 C/s and more preferably 12 C/s or more during 100 s to 600 s. The preferred temperature range for tempering is from 175 C to 280 C
and the preferred duration for holding at Ttemper is from 200 s to 500 s.
According to the present invention the tempering temperature is selected such that the difference between Ti and Ttemper is from 415 C to 455 C. AT is determined as follows:
AT = (Ti ¨ Ttemper) When AT is less than 415 C then the cumulative amount of bainite and ferrite exceeds 38% which is detrimental for the mechanical properties specifically the tensile strength in transversal direction. When AT is greater than 455 C then the amount of tempered martensite is too high, thereby the steel of present invention in rolling direction exceeds 1150 MPa. The preferred AT is between 420 C and zo 440 C
Then, the cold rolled steel sheet is cooled down to room temperature to obtain a heat treated cold rolled steel sheet.
The heat treated cold rolled steel sheet of the present invention may optionally be coated with zinc or zinc alloys, or with aluminum or aluminum alloys to improve its corrosion resistance.
The heat treated cold rolled steel sheet can also be coated by any of the known industrial processes such as Electro-galvanization, JVD, PVD, etc,.
Then an optional post batch annealing may be done at a temperature between 150 C and 300 C during 30 minutes to 120 hours.
12 EXAMPLES
The following tests and examples presented herein are non-restricting in nature and must be considered for purposes of illustration only, and will display the .. advantageous features of the present invention and expound the significance of the parameters chosen by inventors after extensive experiments and further establish the properties that can be achieved by the steel according to the invention.
Samples of the steel sheets according to the invention and to some comparative grades were prepared with the compositions gathered in table 1 and the processing parameters gathered in table 2. The corresponding microstructures of those steel sheets were gathered in table 3 and the properties in table 4.
Table 1 depicts the steels with the compositions expressed in percentages by weight.
Table 1 : composition of the trials Steel C Mn Si Al Cr P 5 N Mo Ti Nb V Ni B
1 0.15 1.90 0.19 0.04 0.18 0.0031 0.001 0.0034 0.002 0.02 0..001 0.06 0.015 0.001 2 0.15 1.90 0.18 0.04 0.18 0.0031 0.001 0.004 0.0021 0.02 0.001 0.06 0.015 0.001 3 0.15 1.89 0.21 0.03 0.19 0.0025 0.0013 0.005 0.0031 0.025 0.001 0.03 0.02 0.001 4 0.15 1.88 0.20 0.03 0.18 0.0018 0.0012 0.0045 0.0022 0.025 0.001 0.02 0.015 0.001 5 0.15 1.91 0.20 0.03 0.19 0.0016 0.0025 0.004 0.0035 0.025 0.001 0.02 0.017 0.001 6 0.15 1.87 0.21 0.027 0.18 0.0018 0.0023 0.004 0.0043 0.025 0..001 0.02 0.015 0.001 7 0.14 1.87 0.21 0.027 0.18 0.0018 0.0023 0.004 0.0043 0.025 0..001 0.02 0.015 0.001 8 0.15 1.88 0.20 0.025 0.20 0.0023 0.0021 0.004 0.0043 0.025 0..001 0.03 0.015 0.001
The following tests and examples presented herein are non-restricting in nature and must be considered for purposes of illustration only, and will display the .. advantageous features of the present invention and expound the significance of the parameters chosen by inventors after extensive experiments and further establish the properties that can be achieved by the steel according to the invention.
Samples of the steel sheets according to the invention and to some comparative grades were prepared with the compositions gathered in table 1 and the processing parameters gathered in table 2. The corresponding microstructures of those steel sheets were gathered in table 3 and the properties in table 4.
Table 1 depicts the steels with the compositions expressed in percentages by weight.
Table 1 : composition of the trials Steel C Mn Si Al Cr P 5 N Mo Ti Nb V Ni B
1 0.15 1.90 0.19 0.04 0.18 0.0031 0.001 0.0034 0.002 0.02 0..001 0.06 0.015 0.001 2 0.15 1.90 0.18 0.04 0.18 0.0031 0.001 0.004 0.0021 0.02 0.001 0.06 0.015 0.001 3 0.15 1.89 0.21 0.03 0.19 0.0025 0.0013 0.005 0.0031 0.025 0.001 0.03 0.02 0.001 4 0.15 1.88 0.20 0.03 0.18 0.0018 0.0012 0.0045 0.0022 0.025 0.001 0.02 0.015 0.001 5 0.15 1.91 0.20 0.03 0.19 0.0016 0.0025 0.004 0.0035 0.025 0.001 0.02 0.017 0.001 6 0.15 1.87 0.21 0.027 0.18 0.0018 0.0023 0.004 0.0043 0.025 0..001 0.02 0.015 0.001 7 0.14 1.87 0.21 0.027 0.18 0.0018 0.0023 0.004 0.0043 0.025 0..001 0.02 0.015 0.001 8 0.15 1.88 0.20 0.025 0.20 0.0023 0.0021 0.004 0.0043 0.025 0..001 0.03 0.015 0.001
13 Table 2 gathers the annealing process parameters implemented on steels of Table 1.
Table 2 : process parameters of the trials All the examples and counter examples are reheated to a temperature of 1200 C and then hot rolled wherein the hot rolled finishing temperature is 890 C
thereafter the hot rolled steel strip is cooled at a rate of 80 C/s and coiled at 530 C
and cold rolled reduction for all examples and counter examples is 50%.
Table 2a Trial Steel HRI HTI HR2 T soak Soaking Ti ( C) Sample ( C/s) ( C) ( C/s) ( C) time (s) ( C/s) II 1 17 640 1.8 850 154 680 1.5 12 2 15 620 1.8 849 164 680 1.4 13 3 15 600 1.9 850 164 664 1.5
Table 2 : process parameters of the trials All the examples and counter examples are reheated to a temperature of 1200 C and then hot rolled wherein the hot rolled finishing temperature is 890 C
thereafter the hot rolled steel strip is cooled at a rate of 80 C/s and coiled at 530 C
and cold rolled reduction for all examples and counter examples is 50%.
Table 2a Trial Steel HRI HTI HR2 T soak Soaking Ti ( C) Sample ( C/s) ( C) ( C/s) ( C) time (s) ( C/s) II 1 17 640 1.8 850 154 680 1.5 12 2 15 620 1.8 849 164 680 1.4 13 3 15 600 1.9 850 164 664 1.5
14 4 20 600 2.7 850 117 660 2.1 RI 5 15 530 3.1 865 137 690 1.7 R2 6 15 560 2.3 855 154 667 1.6s R3 7 15 600 2.3 855 154 665 1.6 R4 8 12 560 2.2 850 189 670 1.2 underlined values: not according to the invention lo Table 2b Heating T2 CR2 rate to Ttemper Tempering A T Ms Trial Ac3 ( C) ( C) ( C/s) Ttemper ( C) time (s) ( C) ( C) ( C/s) underlined values: not according to the invention.
Table 3 gathers the results of test conducted in accordance of standards on different microscopes such as Scanning Electron Microscope for determining microstructural composition of both the inventive steel and reference trials.
Table 3 : microstructures of the trials Steel Martensite Ferrite + Residual Fresh Sample (tempered) Bainite Austenite martensite underlined values: not according to the invention.
Table 4 gathers the mechanical properties of both the inventive steel and reference steel. The tensile strength, yield strength and total elongation test are conducted in accordance with NF EN ISO 6892 standards, Table 4 : mechanical properties of the trials Tensile Tensile Yield Yield Total Strength (MPa) Strength Strength Strength Elongation Trials TD (MPa) RD (MPa) TD (MPa) RD (0/0) 11 1069 1064 798 807 8.0 12 1072 1064 789 797 9.4 13 1044 1035 719 744 9.4 14 1076 1076 737 767 9.8 R1 1177 1159 887 895 8.7 R2 960 958 653 670 11.5 R3 959 954 652 662 10.4 R4 971 966 658 732 9.1 underlined values: not according to the invention.
The examples show that the steel sheets according to the invention are the 5 only one to show all the targeted properties thanks to their specific composition and microstructures.
Table 3 gathers the results of test conducted in accordance of standards on different microscopes such as Scanning Electron Microscope for determining microstructural composition of both the inventive steel and reference trials.
Table 3 : microstructures of the trials Steel Martensite Ferrite + Residual Fresh Sample (tempered) Bainite Austenite martensite underlined values: not according to the invention.
Table 4 gathers the mechanical properties of both the inventive steel and reference steel. The tensile strength, yield strength and total elongation test are conducted in accordance with NF EN ISO 6892 standards, Table 4 : mechanical properties of the trials Tensile Tensile Yield Yield Total Strength (MPa) Strength Strength Strength Elongation Trials TD (MPa) RD (MPa) TD (MPa) RD (0/0) 11 1069 1064 798 807 8.0 12 1072 1064 789 797 9.4 13 1044 1035 719 744 9.4 14 1076 1076 737 767 9.8 R1 1177 1159 887 895 8.7 R2 960 958 653 670 11.5 R3 959 954 652 662 10.4 R4 971 966 658 732 9.1 underlined values: not according to the invention.
The examples show that the steel sheets according to the invention are the 5 only one to show all the targeted properties thanks to their specific composition and microstructures.
Claims (18)
1. A heat treated cold rolled steel sheet comprising of the following elements, expressed in percentage by weight:
0.1% C 0.2 %;
1.2 % Mn 2.2 %;
0.05% Si 0.6 %;
0.001% Al 0.1 %;
0.01% Cr 0.5 %;
0% S 0.09%;
0% P 0.09%;
0% N 0.09%;
and can contain one or more of the following optional elements 0% Mo 0.5%;
0% Ti 0.1%;
0% Nb 0.1%;
0% V 0.1%;
0% Ni 1%;
0% Cu 1%;
0% Ca 0.005%;
0% B 0.05%;
the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel comprising, by area percentage, 60% to 85% of tempered martensite, a cumulated amount of ferrite and bainite of 15 %
to 38%, an optional amount of residual austenite of 0% to 5% and an optional amount of fresh martensite of 0 to 5%.
0.1% C 0.2 %;
1.2 % Mn 2.2 %;
0.05% Si 0.6 %;
0.001% Al 0.1 %;
0.01% Cr 0.5 %;
0% S 0.09%;
0% P 0.09%;
0% N 0.09%;
and can contain one or more of the following optional elements 0% Mo 0.5%;
0% Ti 0.1%;
0% Nb 0.1%;
0% V 0.1%;
0% Ni 1%;
0% Cu 1%;
0% Ca 0.005%;
0% B 0.05%;
the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel comprising, by area percentage, 60% to 85% of tempered martensite, a cumulated amount of ferrite and bainite of 15 %
to 38%, an optional amount of residual austenite of 0% to 5% and an optional amount of fresh martensite of 0 to 5%.
2. The heat treated cold rolled steel sheet according to claim 1, wherein the composition includes 0.12% to 0.19% of carbon.
3. The heat treated cold rolled steel sheet according to claim 1 or 2, wherein the composition includes 0.1% to 0.5% of Silicon.
4. The heat treated cold rolled steel sheet according to anyone of claims 1 to claim 3, wherein the composition includes 0.001 % to 0.09% of Aluminum.
5. The heat treated cold rolled steel sheet according to anyone of claims 1 to 4, wherein the composition includes 1.3% to 2.1% of Manganese.
6. The heat treated cold rolled steel sheet according to anyone of claims 1 to 5, wherein the composition includes 0.1% to 0.4% of Chromium.
7. The heat treated cold rolled steel sheet according to anyone of claims 1 to 6, wherein, the amount of tempered martensite is between 62% and 80%.
8. The heat treated cold rolled steel sheet according to anyone of claims 1 to 7, wherein the cumulated amount of ferrite and bainite is between 20% and 37%.
9. The heat treated cold rolled steel sheet according to anyone of claims 1 to 8, wherein said sheet has an ultimate tensile strength of 980 MPa to 1150MPa in transversal direction, and an ultimate tensile strength of 980 MPa to 1150 MPa in rolling direction.
10. A method of production of heat treated cold rolled steel sheet comprising the following successive steps:
- providing a steel composition according to anyone of claims 1 to 6;
- reheating said semi-finished product to a temperature between 1000 C and 1280 C;
- rolling the said semi-finished product in the austenitic range wherein the hot rolling finishing temperature is from Ac3 to Ac3 + 100 C to obtain a hot rolled steel sheet;
- cooling the sheet at a cooling rate of at least 20 C/s to a coiling temperature which is below 650 C; and coiling the said hot rolled sheet;
- cooling the said hot rolled sheet to room temperature;
- optionally performing scale removal process on said hot rolled steel sheet;
- optionally performing annealing on hot rolled steel sheet;
- optionally performing scale removal process on said hot rolled steel sheet;
- cold rolling the said hot rolled steel sheet with a reduction rate between 35 and 90% to obtain a cold rolled steel sheet;
- then heating the said cold rolled steel sheet in a two steps heating wherein:
o the first step of heating the cold rolled steel sheet starts from room temperature to a temperature HT1 from 550 C to 750 C, with a heating rate HR1 of at least 10 C/s;
o the second step of heating starts from HT1 to a temperature Tsoak from Ac3 to Ac3+100 C, with a heating rate HR2 from 1 C/s to 15 C/s, where it is held during 10 to 500 seconds - then cooling the said cold rolled steel sheet in a two steps cooling wherein:
o the first step of cooling the cold rolled steel sheet starts from Tsoak down to a temperature T1 from 630 C to 685 C, with a cooling rate CR1 from 1 C/s to 15 C/s;
o the second step of cooling starts from T1 down to a temperature T2 from Ms-10 C to 15 C, with a cooling rate CR2 of at least 100 C/s, - then reheating the said cold rolled steel sheet at a rate of at least 5 C/s to a tempering temperature Ttemper between 150 C and 300 C where it is held during 100 to 600 seconds wherein AT = (T1 ¨ Ttemper) must be from 415 C
to 455 C;
- then cooling to room temperature with a cooling rate of at least 1 C/s to obtain a heat treated cold rolled steel sheet.
- providing a steel composition according to anyone of claims 1 to 6;
- reheating said semi-finished product to a temperature between 1000 C and 1280 C;
- rolling the said semi-finished product in the austenitic range wherein the hot rolling finishing temperature is from Ac3 to Ac3 + 100 C to obtain a hot rolled steel sheet;
- cooling the sheet at a cooling rate of at least 20 C/s to a coiling temperature which is below 650 C; and coiling the said hot rolled sheet;
- cooling the said hot rolled sheet to room temperature;
- optionally performing scale removal process on said hot rolled steel sheet;
- optionally performing annealing on hot rolled steel sheet;
- optionally performing scale removal process on said hot rolled steel sheet;
- cold rolling the said hot rolled steel sheet with a reduction rate between 35 and 90% to obtain a cold rolled steel sheet;
- then heating the said cold rolled steel sheet in a two steps heating wherein:
o the first step of heating the cold rolled steel sheet starts from room temperature to a temperature HT1 from 550 C to 750 C, with a heating rate HR1 of at least 10 C/s;
o the second step of heating starts from HT1 to a temperature Tsoak from Ac3 to Ac3+100 C, with a heating rate HR2 from 1 C/s to 15 C/s, where it is held during 10 to 500 seconds - then cooling the said cold rolled steel sheet in a two steps cooling wherein:
o the first step of cooling the cold rolled steel sheet starts from Tsoak down to a temperature T1 from 630 C to 685 C, with a cooling rate CR1 from 1 C/s to 15 C/s;
o the second step of cooling starts from T1 down to a temperature T2 from Ms-10 C to 15 C, with a cooling rate CR2 of at least 100 C/s, - then reheating the said cold rolled steel sheet at a rate of at least 5 C/s to a tempering temperature Ttemper between 150 C and 300 C where it is held during 100 to 600 seconds wherein AT = (T1 ¨ Ttemper) must be from 415 C
to 455 C;
- then cooling to room temperature with a cooling rate of at least 1 C/s to obtain a heat treated cold rolled steel sheet.
11. A method according to claim 10, wherein said coiling temperature is from 475 C to 625 C.
12. A method according to claim 10 or 11, wherein Tsoak is from Ac3+10 C to Ac3+100 C.
13. A method according to anyone of claims 10 to 12, wherein CR1 is from 1 C/s to 10 C/s.
14. A method according to anyone of claim 10 to 13, wherein T1 is from 640 C
to 685 C
to 685 C
15. A method according to anyone of claims 10 to 14, wherein CR2 is at least 200 C/s.
16. A method according to anyone of claims 10 to 15, wherein T2 is from Ms-20 C to 20 C.
17. A method according to anyone of claims 10 to 16, wherein Ttemper is from 175 C to
18. Use of a steel sheet obtainable according to anyone of claims 1 to 9 or a steel sheet manufactured according to the method of anyone of claims 10 to 17, for manufacturing a structural part of a vehicle.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/IB2020/056787 WO2022018481A1 (en) | 2020-07-20 | 2020-07-20 | Heat treated cold rolled steel sheet and a method of manufacturing thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA3183159A1 true CA3183159A1 (en) | 2022-10-27 |
Family
ID=71786996
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA3183159A Pending CA3183159A1 (en) | 2020-07-20 | 2020-07-20 | Heat treated cold rolled steel sheet and a method of manufacturing thereof |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US20230287531A1 (en) |
| EP (1) | EP4182488A1 (en) |
| JP (1) | JP2023534180A (en) |
| KR (1) | KR20230016218A (en) |
| CN (1) | CN115698365B (en) |
| BR (1) | BR112022023896A2 (en) |
| CA (1) | CA3183159A1 (en) |
| MX (1) | MX2023000811A (en) |
| WO (1) | WO2022018481A1 (en) |
| ZA (1) | ZA202212175B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20240057522A (en) * | 2022-10-24 | 2024-05-03 | 주식회사 포스코 | Steel sheet having excellent bendability and manufacturing method thereof |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0941079A (en) * | 1995-05-19 | 1997-02-10 | Kobe Steel Ltd | Ultra-high strength steel sheet excellent in delayed fracture resistance and its production |
| CN101960038B (en) * | 2008-03-07 | 2013-01-23 | 株式会社神户制钢所 | Cold-rolled steel sheets |
| JP5329979B2 (en) * | 2009-01-05 | 2013-10-30 | 株式会社神戸製鋼所 | High-strength cold-rolled steel sheet with an excellent balance between elongation and stretch flangeability |
| JP5136609B2 (en) * | 2010-07-29 | 2013-02-06 | Ｊｆｅスチール株式会社 | High-strength hot-dip galvanized steel sheet excellent in formability and impact resistance and method for producing the same |
| JP5126399B2 (en) * | 2010-09-06 | 2013-01-23 | Ｊｆｅスチール株式会社 | High-strength cold-rolled steel sheet with excellent stretch flangeability and manufacturing method thereof |
| CN103459647B (en) * | 2011-03-28 | 2015-09-02 | 新日铁住金株式会社 | Hot-rolled steel sheet and manufacture method thereof |
| TWI468534B (en) * | 2012-02-08 | 2015-01-11 | Nippon Steel & Sumitomo Metal Corp | High-strength cold rolled steel sheet and manufacturing method thereof |
| JP6048382B2 (en) * | 2013-12-09 | 2016-12-21 | Ｊｆｅスチール株式会社 | High-strength cold-rolled steel sheet and manufacturing method thereof |
| WO2015088523A1 (en) * | 2013-12-11 | 2015-06-18 | ArcelorMittal Investigación y Desarrollo, S.L. | Cold rolled and annealed steel sheet |
| JP2015200012A (en) * | 2014-03-31 | 2015-11-12 | 株式会社神戸製鋼所 | High-strength cold-rolled steel sheet, high-strength galvanized steel sheet, and high-strength alloy galvanized steel sheet having excellent ductility, stretch-flangeability, and weldability |
| JP5967318B1 (en) | 2014-08-28 | 2016-08-10 | Ｊｆｅスチール株式会社 | High-strength hot-dip galvanized steel sheet and manufacturing method thereof |
| US20180037969A1 (en) * | 2015-03-18 | 2018-02-08 | Jfe Steel Corporation | High-strength cold-rolled steel sheet and method of producing the same |
| KR101736620B1 (en) * | 2015-12-15 | 2017-05-17 | 주식회사 포스코 | Ultra-high strength steel sheet having excellent phosphatability and hole expansibility, and method for manufacturing the same |
| JP6354919B1 (en) | 2016-08-30 | 2018-07-11 | Ｊｆｅスチール株式会社 | Thin steel plate and manufacturing method thereof |
| CN110475892B (en) * | 2017-04-05 | 2022-01-14 | 杰富意钢铁株式会社 | High-strength cold-rolled steel sheet and method for producing same |
-
2020
- 2020-07-20 US US18/015,487 patent/US20230287531A1/en active Pending
- 2020-07-20 MX MX2023000811A patent/MX2023000811A/en unknown
- 2020-07-20 JP JP2023501095A patent/JP2023534180A/en active Pending
- 2020-07-20 WO PCT/IB2020/056787 patent/WO2022018481A1/en unknown
- 2020-07-20 KR KR1020227045459A patent/KR20230016218A/en unknown
- 2020-07-20 BR BR112022023896A patent/BR112022023896A2/en unknown
- 2020-07-20 CA CA3183159A patent/CA3183159A1/en active Pending
- 2020-07-20 EP EP20746281.3A patent/EP4182488A1/en active Pending
- 2020-07-20 CN CN202080101746.5A patent/CN115698365B/en active Active
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2022
- 2022-11-08 ZA ZA2022/12175A patent/ZA202212175B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| KR20230016218A (en) | 2023-02-01 |
| BR112022023896A2 (en) | 2023-01-31 |
| CN115698365B (en) | 2024-03-26 |
| ZA202212175B (en) | 2023-06-28 |
| JP2023534180A (en) | 2023-08-08 |
| US20230287531A1 (en) | 2023-09-14 |
| EP4182488A1 (en) | 2023-05-24 |
| MX2023000811A (en) | 2023-02-27 |
| CN115698365A (en) | 2023-02-03 |
| WO2022018481A1 (en) | 2022-01-27 |
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