WO2013046697A1 - 熱延鋼板およびその製造方法 - Google Patents
熱延鋼板およびその製造方法 Download PDFInfo
- Publication number
- WO2013046697A1 WO2013046697A1 PCT/JP2012/006197 JP2012006197W WO2013046697A1 WO 2013046697 A1 WO2013046697 A1 WO 2013046697A1 JP 2012006197 W JP2012006197 W JP 2012006197W WO 2013046697 A1 WO2013046697 A1 WO 2013046697A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- hot
- steel sheet
- less
- rolled steel
- pearlite
- Prior art date
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 83
- 239000010959 steel Substances 0.000 title claims abstract description 83
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 229910001335 Galvanized steel Inorganic materials 0.000 claims abstract description 41
- 239000008397 galvanized steel Substances 0.000 claims abstract description 41
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 40
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 37
- 239000010960 cold rolled steel Substances 0.000 claims abstract description 32
- 239000013078 crystal Substances 0.000 claims abstract description 29
- 239000000203 mixture Substances 0.000 claims abstract description 10
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 239000000126 substance Substances 0.000 claims abstract description 5
- 239000002131 composite material Substances 0.000 claims abstract description 4
- 238000001816 cooling Methods 0.000 claims description 28
- 238000005098 hot rolling Methods 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 16
- 238000005096 rolling process Methods 0.000 claims description 16
- 238000004804 winding Methods 0.000 claims description 13
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 52
- 229910052742 iron Inorganic materials 0.000 abstract description 3
- 238000000137 annealing Methods 0.000 description 29
- 230000000694 effects Effects 0.000 description 28
- 239000010955 niobium Substances 0.000 description 20
- 230000007423 decrease Effects 0.000 description 12
- 238000005728 strengthening Methods 0.000 description 12
- 239000010949 copper Substances 0.000 description 11
- 239000010936 titanium Substances 0.000 description 11
- 230000001965 increasing effect Effects 0.000 description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 9
- 229910001566 austenite Inorganic materials 0.000 description 8
- 238000009749 continuous casting Methods 0.000 description 8
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 8
- 238000011282 treatment Methods 0.000 description 8
- 238000005275 alloying Methods 0.000 description 7
- 239000011651 chromium Substances 0.000 description 7
- 239000011572 manganese Substances 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 229910045601 alloy Inorganic materials 0.000 description 6
- 239000000956 alloy Substances 0.000 description 6
- 238000005097 cold rolling Methods 0.000 description 6
- 238000005246 galvanizing Methods 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 239000011701 zinc Substances 0.000 description 6
- 229910052725 zinc Inorganic materials 0.000 description 6
- 229910001567 cementite Inorganic materials 0.000 description 5
- 230000006872 improvement Effects 0.000 description 5
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 5
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 4
- 229910001563 bainite Inorganic materials 0.000 description 4
- 239000011575 calcium Substances 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 4
- 238000007747 plating Methods 0.000 description 4
- 229910052761 rare earth metal Inorganic materials 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- -1 MnS are formed Chemical class 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000005238 degreasing Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 229910052726 zirconium 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
- C22C38/001—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
- B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
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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
- 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
- C22C18/00—Alloys based on zinc
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C18/00—Alloys based on zinc
- C22C18/04—Alloys based on zinc with aluminium as the next major constituent
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
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- 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
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- 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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/004—Dispersions; Precipitations
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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
- C21D2211/009—Pearlite
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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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—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
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
Definitions
- the present invention relates to a hot-rolled steel sheet suitable for a member used, for example, in the field of the automobile industry, particularly for cold-rolled steel sheet or hot-dip galvanized steel sheet having excellent material uniformity and high yield ratio, and a method for producing the same.
- the shape freezing property is significantly reduced by increasing the strength and thinning of the steel sheet. Therefore, predict the shape change of the pressed parts after mold release in advance of press forming, and design the press die considering the amount of shape change. It is widely done.
- the tensile strength of the steel plate changes significantly, the deviation from the expected amount with these constants will increase, shape defects will occur, and it will be indispensable to rework the shape of each piece after press forming, for mass production. Reduces efficiency significantly. For this reason, it is requested
- Patent Document 1 discloses that a high-strength cold-rolled steel sheet that is precipitation strengthened by addition of Nb and Ti and has excellent stretch flange formability and impact absorption energy characteristics is disclosed.
- Patent Document 2 discloses a high-strength cold-rolled steel sheet in which the steel sheet structure includes recrystallized ferrite, non-recrystallized ferrite and pearlite, which is precipitation strengthened by addition of Nb and Ti.
- a high-strength cold-rolled steel sheet is greatly affected by the steel sheet structure and precipitation amount of the hot-rolled steel sheet, and is advantageous in increasing the strength of the hot-rolled steel sheet.
- a method for producing a hot-rolled steel sheet having high ductility and excellent material uniformity by adjusting the Ti content is disclosed, and Patent Document 4 further adjusts the Ti content. Discloses a hot-rolled steel sheet with improved material uniformity and hole expandability.
- Patent Documents 3 and 4 provide a method for producing a hot-rolled steel sheet that is excellent in high ductility or hole expandability, in order to produce a hot-rolled material and hot-dip galvanized material for producing a cold-rolled steel sheet. It is not considered as a hot rolled material. Therefore, the development of hot-rolled steel sheets for cold-rolled steel sheets and hot-rolled steel sheets for hot-dip galvanized steel sheets, which are excellent in material uniformity after annealing, becomes an issue.
- an object of the present invention is to solve the above-mentioned problems of the prior art, provide excellent material uniformity, and suitable for use in cold-rolled steel sheets or hot-dip galvanized steel sheets having a tensile strength of 590 MPa or more. It aims at providing about a steel plate and its manufacturing method.
- the present inventors have intensively studied to obtain a hot-rolled steel sheet for cold-rolled steel sheet or hot-dip galvanized steel sheet having excellent material uniformity and a high yield ratio, and found the following. That is, by cooling the steel slab after continuous casting to 600 ° C within 6 hours, the segregation in the slab is minimized and the crystal grains before hot rolling are refined, and then finished in the hot rolling process.
- the material variation of the hot-rolled steel sheet can be reduced and the subsequent annealing is performed. It was found that the strength of the later cold-rolled steel sheet and hot-dip galvanized steel sheet can be ensured and the material variation can be reduced.
- the structure is as follows.
- the chemical composition is mass%, C: 0.060 to 0.150%, Si: 0.15 to 0.70%, Mn: 1.00 to 1.90%, P: 0.10% or less, S: 0.010% or less, Al: 0.01 to 0.10% N: not more than 0.010% and Nb: 0.010-0.100%, the balance being Fe and inevitable impurities,
- the microstructure contains ferrite with an average crystal grain size of 18 ⁇ m or less in volume fraction of 75% or more, average crystal grain size: pearlite with a volume fraction of 2 ⁇ m or more in volume fraction of 5% or more, and the balance is a low-temperature composite phase
- a hot rolled steel sheet characterized in that the mean free path of pearlite is 5.0 ⁇ m or more.
- the mean free path of pearlite is a dispersed state of pearlite.
- the hot-rolled steel sheet is for a cold-rolled steel sheet or a hot-dip galvanized steel sheet.
- the hot dip galvanized steel sheet is a generic term for a steel sheet obtained by plating zinc on a steel sheet by a hot dip galvanizing method, whether or not an alloying treatment is performed. That is, the hot dip galvanized steel sheet in the present invention includes both a hot dip galvanized steel sheet that has not been subjected to an alloying treatment and an alloyed hot dip galvanized steel sheet that has been subjected to an alloying treatment.
- the molten steel having the composition described in any one of (1) to (4) above is continuously cast into a slab.
- the slab is cooled to 600 ° C. within 6 hours, and then reheated to Hot rolling start temperature: 1150 to 1270 ° C, finish rolling end temperature: 830 to 950 ° C, hot rolling, cooling the temperature range up to 650 ° C at an average cooling rate of 20 to 90 ° C / s, then A method for producing a hot-rolled steel sheet, wherein the winding is performed by cooling at an average cooling rate of 5 to 30 ° C / s to the winding temperature when winding in a temperature range of 470 to 640 ° C.
- a hot-rolled steel sheet that is a material for a cold-rolled steel sheet or a hot-dip galvanized steel sheet that has high workability and has a high yield ratio because of excellent material uniformity.
- cold-rolled steel sheet and hot-dip galvanized steel sheet are applied to automobile structural members, for example, to ensure collision safety in automobiles
- fuel consumption can be improved by reducing the weight of the vehicle body.
- Carbon (C) is an element effective for increasing the strength of the steel sheet, and particularly contributes to strengthening of the steel sheet by forming a carbide-forming element such as Nb and a fine alloy carbide or alloy carbonitride. Moreover, it is an element necessary for formation of pearlite in the steel sheet structure of the hot-rolled steel sheet in the present invention, and contributes to high strength. In order to obtain this effect, 0.060% or more must be added. On the other hand, if the C content is more than 0.150%, spot weldability deteriorates, so the upper limit of the C content is 0.150%. From the viewpoint of securing better weldability, the C content is preferably 0.120% or less.
- Si 0.15-0.70%
- Silicon (Si) is an element that contributes to the improvement of the strength-ductility balance after annealing because of its high work-hardening ability and relatively low decrease in ductility with increasing strength. Further, it is an element necessary for improving the material uniformity, which contributes to securing the desired crystal grain size and volume fraction of ferrite by promoting the ferrite transformation in the hot rolling stage. In order to obtain this effect, the Si content needs to be 0.15% or more. In order to further improve the material uniformity, the Si content is preferably 0.35% or more. On the other hand, if the Si content is more than 0.70%, the hot dip galvanizing deterioration after annealing becomes remarkable, so the Si content is 0.70% or less, more preferably 0.60% or less.
- Mn 1.00 to 1.90%
- Manganese (Mn) is an element that contributes to strengthening after annealing by forming solid solution strengthening and second phase.
- the Mn content needs to be 1.00% or more, preferably 1.20% or more.
- the Mn content is more than 1.90%, the ferrite transformation and pearlite transformation in the hot rolling stage are delayed, and it is difficult to secure the desired crystal grain size and area ratio of ferrite, and the material uniformity decreases. Due to concerns, its content is 1.90% or less, preferably 1.70% or less.
- Phosphorus (P) is an element contributing to high strength by solid solution strengthening.
- the content of P is preferably set to 0.005% or more.
- the P content is more than 0.10%, segregation to the grain boundary becomes remarkable, the grain boundary becomes brittle, weldability is lowered, and material uniformity is deteriorated.
- the value is 0.10%. Preferably, it is 0.05% or less.
- Al 0.01-0.10%
- Aluminum (Al) is an element necessary for deoxidation, and in order to obtain this effect, it is necessary to contain 0.01% or more, but even if contained over 0.10%, the effect is saturated, so 0.10 % Or less. Preferably, it is 0.05% or less.
- N 0.010% or less Nitrogen (N) forms a compound with Nb in the same manner as C, and becomes an alloy nitride or an alloy carbonitride, contributing to high strength.
- N Nitrogen
- the N content is set to 0.010% or less, preferably 0.005% or less.
- Niobium (Nb) forms compounds with C and N to form carbides and carbonitrides, and is also effective in refining crystal grains, in order to ensure the desired crystal grain size and volume fraction of ferrite and pearlite. It is an important element. Further, it is an element necessary for obtaining a high yield ratio by precipitation strengthening of carbonitride. In order to obtain this effect, the Nb content needs to be 0.010% or more. However, if the Nb content is more than 0.100%, the moldability deteriorates remarkably, so the upper limit of the Nb content is set to 0.100%. Preferably, it is 0.060% or less.
- Ti Less than 0.05% Titanium (Ti), like Nb, forms fine carbonitrides, has an effect on crystal grain refinement, and can contribute to increase in strength. However, if the Ti content is added to 0.05% or more, the formability is remarkably lowered. Therefore, the Ti content is less than 0.05%, preferably 0.035% or less. In addition, when exhibiting the strength increase effect after annealing, when containing Ti, it is preferable to contain 0.005% or more.
- V 0.10% or less Vanadium (V), like Nb, also forms fine carbonitrides, has an effect on crystal grain refinement, and can contribute to an increase in strength. Although it is an element that can be contained, even if the V content is more than 0.10%, the effect of increasing the strength exceeding 0.10% is small, and the alloy cost is also increased. For this reason, the V content is set to 0.10% or less. In addition, when exhibiting the strength increasing effect, when V is contained, it is preferable to contain 0.005% or more.
- Chromium (Cr) is an element that improves the hardenability during annealing and contributes to high strength by generating a second phase, and can be added as necessary.
- the Cr content is preferably set to 0.10% or more.
- the Cr content is 0.50% or less.
- Mo Molybdenum
- Mo is an element that improves the hardenability during annealing and contributes to increasing the strength by generating the second phase, and can be added as necessary.
- the Mo content is preferably 0.05% or more.
- the Mo content is 0.50% or less.
- Cu 0.50% or less Copper (Cu) is an element that contributes to strengthening by solid solution strengthening, improves hardenability during annealing, and also contributes to strengthening by generating a second phase. An element that can be added as needed. In order to exert this effect, the Cu content is preferably 0.05% or more. On the other hand, even if the Cu content is more than 0.50%, the improvement in the effect is not recognized, and surface defects caused by Cu are more likely to occur. Therefore, the Cu content is set to 0.50% or less.
- Ni 0.50% or less Nickel (Ni), like Cu, contributes to high strength by solid solution strengthening, and also improves the hardenability during annealing and increases the strength by generating a second phase.
- Ni nickel
- the Ni content is preferably 0.05% or more.
- the Ni content is 0.50% or less.
- B 0.0030% or less Boron (B) is an element that contributes to high strength by improving the hardenability during annealing and generating the second phase, and can be added as necessary. In order to exhibit this effect, it is preferable to make it contain 0.0005% or more. On the other hand, even if it contains more than 0.0030%, the effect is saturated, so the content is made 0.0030% or less.
- One or more types selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% Calcium (Ca) and rare earth elements (REM) spheroidize the shape of the sulfide and improve the negative effect of the sulfide on hole expansibility It is an element that contributes to this, and can be added as necessary. In order to exhibit these effects, it is preferable to contain 0.001% or more of each. On the other hand, even if the content exceeds 0.005%, the effect is saturated, so the content is made 0.005% or less respectively.
- the other balance of the chemical component is Fe and inevitable impurities.
- the inevitable impurities include, for example, Sb, Sn, Zn, Co, etc.
- the allowable ranges of these contents are Sb: 0.01% or less, Sn: 0.1% or less, Zn: 0.01% or less , Co: 0.1% or less.
- Ta, Mg and Zr are contained within the range of the normal steel composition, the effect is not lost.
- ferrite has an average crystal grain size of 18 ⁇ m or less and a volume fraction of 75% or more
- pearlite has an average crystal grain size of 2 ⁇ m or more and a volume fraction of 5% or more
- the balance consists of a low-temperature generation phase. It is a composite structure in which the mean free path of the pearlite is 5.0 ⁇ m or more.
- the volume fraction described here is the volume fraction with respect to the entire structure of the steel sheet, and so on.
- the volume fraction of ferrite in the hot-rolled sheet structure is less than 75%, there are many hard second phases, and the material uniformity deteriorates. Therefore, the volume fraction of ferrite is 75% or more.
- the upper limit of the volume fraction of ferrite is preferably 95% or less in order to ensure high strength after annealing (cold-rolled steel sheet or hot-dip galvanized steel sheet).
- the average grain size of ferrite exceeds 18 ⁇ m, it is difficult to ensure the desired strength after annealing (cold-rolled steel sheet or hot-dip galvanized steel sheet), so the average crystal grain size of ferrite is 18 ⁇ m or less.
- the lower limit of the average crystal grain size of ferrite is not particularly limited, but is preferably 5 ⁇ m or more in order to ensure good material uniformity after annealing.
- the pearlite volume fraction of the hot-rolled sheet structure is less than 5%, it is difficult to secure the desired strength after annealing (cold-rolled steel sheet or hot-dip galvanized steel sheet), so the pearlite volume fraction is 5% or more.
- the upper limit of the pearlite volume fraction is not particularly limited, but is preferably 15% or less from the viewpoint of obtaining good workability.
- the average crystal grain size of pearlite is less than 2 ⁇ m, it is difficult to ensure the desired strength after annealing (cold-rolled steel sheet or hot-dip galvanized steel sheet), so the average crystal grain size of pearlite is 2 ⁇ m or more.
- the upper limit of the average crystal grain size of pearlite is not particularly limited, but is preferably 15 ⁇ m or less in order to ensure good material uniformity after annealing (cold rolled steel sheet or hot dip galvanized steel sheet).
- the average free path of pearlite of the hot-rolled sheet structure is 5.0 ⁇ m or more. If the mean free path of pearlite is less than 5.0 ⁇ m, the ferrite-austenite during the two-phase annealing is not evenly distributed, so that the material uniformity after annealing (cold-rolled steel sheet or hot-dip galvanized steel sheet) decreases.
- the upper limit of the mean free process of pearlite is not specifically limited, 20 micrometers or less are preferable. The pearlite mean free path will be described later.
- the remaining structure other than ferrite and pearlite may be a mixed structure combining one or two or more low-temperature generation phases selected from martensite, bainite, retained austenite, spherical cementite, and the like. From the viewpoint of formability and material uniformity of the hot-dip galvanized steel sheet, the total volume fraction of the remaining structure other than ferrite and pearlite is preferably less than 10% in total.
- the hot-rolled steel sheet contains an Nb-based precipitate having an average particle size of 0.10 ⁇ m or less.
- the strain around the Nb-based precipitates can effectively act as a resistance to dislocation movement, contributing to strengthening of steel, and further annealing. This can contribute to a higher yield ratio later (cold-rolled steel sheet or hot-dip galvanized steel sheet).
- a cold-rolled steel sheet having excellent material uniformity and a high yield ratio according to the present invention, and a hot-rolled steel sheet used as a material for a hot-dip galvanized steel sheet are continuously cast from a molten steel having a component composition suitable for the above component composition range.
- a slab is prepared, and the slab is cooled to 600 ° C. within 6 hours, and then reheated, and hot-rolled at a hot rolling start temperature of 1150 to 1270 ° C. and finish rolling finish temperature of 830 to 950 ° C.
- the slab is first cast by a continuous casting method.
- the continuous casting machine is preferably a vertical bending die. This is because the vertical bending die is excellent in the balance between equipment cost and surface quality, and exhibits a remarkable effect of suppressing surface cracks.
- the slab is cooled to 600 ° C. within 6 hours. When cooling to 600 ° C for more than 6h (hours) after continuous casting, segregation such as Mn becomes noticeable and the crystal grains become coarse, so the average free path of pearlite after hot rolling decreases. , Material uniformity deteriorates.
- the steel slab after continuous casting is cooled to 600 ° C. within 6 hours, preferably cooled to 600 ° C. within 5 hours, more preferably 600 ° C. within 4 hours. Moreover, if it cools to 600 degreeC, after cooling to room temperature, it may be reheated and may be hot-rolled, or may be reheated as it is and may be hot-rolled.
- Finish rolling finish temperature 830-950 °C Hot rolling must be finished in the austenite single phase region in order to improve material uniformity by homogenizing the structure in the steel sheet and reducing material anisotropy, so the finish rolling finish temperature should be 830 ° C or higher. To do. On the other hand, when the finish rolling finish temperature exceeds 950 ° C., there is a concern that the hot-rolled structure becomes coarse and the material uniformity decreases. Therefore, the finish rolling finish temperature is set to 830 to 950 ° C.
- Cooling in the temperature range up to 650 ° C at an average cooling rate of 20 to 90 ° C / s When cooling at an average cooling rate of less than 20 ° C / s, the ferrite transformation proceeds excessively and the desired pearlite volume fraction is obtained. Therefore, the material uniformity of the annealed plate (cold-rolled steel plate or hot-dip galvanized steel plate) decreases. Further, when the average cooling rate exceeds 90 ° C./s, the ferrite transformation does not proceed sufficiently in the hot-rolled sheet structure, the desired ferrite crystal grain size and pearlite mean free path cannot be obtained, and the annealed sheet Material uniformity of (cold-rolled steel sheet or hot-dip galvanized steel sheet) decreases. Preferably, the average cooling rate is 30 to 70 ° C./s.
- the ferrite transformation proceeds excessively and the desired pearlite volume fraction is obtained.
- the material uniformity of the annealed plate (cold-rolled steel plate or hot-dip galvanized steel plate) decreases.
- the average cooling rate exceeds 30 ° C./s, the bainite transformation proceeds after winding, and the desired pearlite volume fraction and crystal grain size cannot be obtained.
- the material uniformity of the (steel plate) decreases.
- the average cooling rate is 10 to 25 ° C./s.
- the hot rolled sheet structure includes a martensite and bainite low-temperature formation phase (hard phase), resulting in an uneven hardness distribution in the hot rolled sheet, and an annealed sheet (cold rolled).
- the material uniformity of the steel sheet or hot-dip galvanized steel sheet is reduced.
- the coiling temperature exceeds 640 ° C.
- the crystal grain size of ferrite in the hot-rolled sheet structure becomes large, and it is difficult to ensure the desired strength of the annealed sheet (cold-rolled steel sheet or hot-dip galvanized steel sheet).
- the Nb carbonitride becomes coarse, and the material uniformity and yield ratio decrease. Therefore, the winding temperature is 470 to 640 ° C.
- the temperature is preferably 480 to 620 ° C.
- the hot-rolled steel sheet obtained through the above steps is pickled by a generally known method, and after performing pretreatment such as degreasing as necessary, it is subjected to a cold rolling step as necessary, and further annealed. It is used for the process or the hot dip galvanizing process.
- a cold rolling step as necessary, and further annealed. It is used for the process or the hot dip galvanizing process.
- the rolling reduction in cold rolling is preferably 30% or more.
- the annealing treatment is preferably held for 15 to 600 seconds in a temperature range of 750 to 900 ° C.
- the annealing temperature is less than 750 ° C or the holding time in the temperature range of 750 to 900 ° C is less than 15 s, an unrecrystallized structure may remain and the ductility may deteriorate, and the annealing temperature exceeds 900 ° C, or 750 This is because if the holding time in the temperature range of ⁇ 900 ° C. exceeds 600 s, the austenite grains grow remarkably, eventually forming a non-uniform structure, and the material stability may be lowered.
- the steel sheet may be heat-treated in any equipment as long as the heat history condition is satisfied.
- the alloying treatment is performed after the hot dip galvanization, the steel sheet of the present invention can be subjected to temper rolling after the alloying treatment to correct the shape.
- hot-rolled sheet is pickled and cold-rolled, and then annealed at 800 ° C., and if necessary, hot-dip galvanized or further galvanized alloyed, CR), hot dip galvanized steel sheet (GI), and galvannealed steel sheet (GA) were obtained.
- Some hot-rolled sheets are subjected to annealing, hot-dip galvanizing treatment, or further galvanizing alloying treatment after hot pickling and not cold rolling, hot-dip galvanized steel sheet (GI), alloyed hot-dip zinc A plated steel sheet (GA) was obtained.
- the hot dip galvanizing bath uses a zinc bath containing Al: 0.19% by mass for hot dip galvanized steel plate (GI), and uses a zinc bath containing Al: 0.14% by mass for alloyed hot dip galvanized steel plate (GA).
- the temperature was 460 ° C.
- the alloyed hot-dip galvanized steel sheet (GA) was alloyed at 550 ° C.
- the plating adhesion amount was 45 g / m 2 per side (double-sided plating), and the alloyed hot-dip galvanized steel sheet (GA) had an Fe concentration of 9 to 12% by mass in the plating layer.
- the volume fraction of ferrite and pearlite is 1/4 position of the plate thickness in the depth direction from the steel plate surface after corroding the plate thickness cross section (vertical cross section) parallel to the rolling direction of the steel plate and corroding with 3% nital.
- the average crystal grain size of ferrite and pearlite is obtained by calculating the area of each ferrite crystal grain or pearlite crystal grain using the above-mentioned Image-Pro, calculating the equivalent circle diameter, and averaging those values. It was.
- the mean free path of pearlite was calculated by the following formula on the assumption that the centroid of pearlite was obtained using the above-mentioned Image-Pro and was uniformly distributed without extreme bias.
- L M Mean free path
- d M Average crystal grain diameter
- ⁇ Circumferential ratio
- the remaining low-temperature generation phase can be discriminated by observation with a scanning electron microscope and a transmission electron microscope. That is, ferrite has a slightly black contrast, while martensite has a white contrast.
- Pearlite is a layered structure in which plate-like ferrite and cementite are alternately arranged, while bainite is a plate-like bainitic ferrite that has a higher dislocation density than polygonal ferrite. And a structure containing cementite.
- Spherical cementite is cementite having a spheroidized shape.
- an X-ray diffraction method (device: Integration of X-ray diffraction lines of ⁇ 200 ⁇ , ⁇ 211 ⁇ and ⁇ 220 ⁇ surfaces of iron ferrite and ⁇ 200 ⁇ , ⁇ 220 ⁇ and ⁇ 311 ⁇ surfaces of austenite by Rigaku RINT2200) The intensity was measured, and using these measured values, “X-ray diffraction handbook” (2000) Rigaku Corporation, p.
- the volume fraction of retained austenite is calculated from the formulas described in 26 and 62-64. If the volume fraction is 1% or more, it is determined that there is retained austenite. It was judged that there was nothing.
- the tensile test is performed in accordance with JIS Z2241 (2010) using JIS No. 5 test specimens sampled so that the tensile direction is parallel to the rolling direction.
- YS yield strength
- TS tensile
- YR was evaluated by the value of (YS / TS) ⁇ 100 (%). In the present invention, the case of YR ⁇ 70% of the annealed plate was determined as a high yield ratio.
- the material uniformity was evaluated as follows. Take the JIS No. 5 test piece from the center of the width of the hot-rolled sheet and the position 1/8 width from each width end (1/8 position of the full width) so that the tensile direction is parallel to the rolling direction. Tensile tests are performed in accordance with JIS Z2241 (2010), YS and TS are measured, and the value at the center of the width and the value at the width 1/8 position (Average value thereof) (the characteristic value at the center of the width ⁇ the absolute value of the characteristic value at the width 1/8 position) was calculated as ⁇ YS and ⁇ TS, respectively. In the present invention, the case of ⁇ YS ⁇ 40 MPa and ⁇ TS ⁇ 30 MPa was determined to be good from the viewpoint of material uniformity.
- the material variation is evaluated at two points, ie, the width center portion and the width 1/8 position, for example, from the center portion in the width direction of the hot-rolled plate and the hot-rolled plate width end (edge) to 1/4 of the plate width. Since the material near the edge is not evaluated for the difference in tensile strength from the position corresponding to (width 1/4 position), it is difficult to evaluate the material stability in the width direction. This is because the material stability of the annealed sheet can be appropriately evaluated by evaluating the difference in tensile strength between the / 8 position and the center of the width.
- the tensile direction is parallel to the rolling direction from the position of 1/8 width (1/8 position of full width) from the width center and both ends of the annealed sheet.
- JIS No. 5 test piece was collected, tensile test was conducted in accordance with JIS Z2241 (2010), YS and TS were measured, and the width center value and width 1/8 position (width 1/8 position) (The average value of the two at both ends) (the average value of the width-the absolute value of the characteristic value at the 1/8 width position) was calculated as ⁇ YS and ⁇ TS, respectively.
- YS and TS of the annealed plate were the average values at three locations, the center of the width and the 1/8 width position (1/8 position of the full width from each end).
- ⁇ YS ⁇ 40 MPa and ⁇ TS ⁇ 30 MPa was determined to be good from the viewpoint of material uniformity.
- Table 3 shows the results of the above investigations.
- the hot-rolled steel sheet according to the present invention has a TS of 590 MPa or more after subsequent annealing, a high yield ratio, and excellent material uniformity.
- a TS of 590 MPa or more after subsequent annealing has a high yield ratio, and excellent material uniformity.
- any one or more of strength, yield ratio, and material uniformity is inferior.
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Abstract
Description
(1)化学成分が、質量%で、C:0.060~0.150%、Si:0.15~0.70%、Mn:1.00~1.90%、P:0.10%以下、S:0.010%以下、Al:0.01~0.10%、N:0.010%以下およびNb:0.010~0.100%を含有し、残部がFeおよび不可避的不純物からなり、
ミクロ組織が、平均結晶粒径:18μm以下のフェライトを体積分率で75%以上、平均結晶粒径:2μm以上のパーライトを体積分率で5%以上含み、残部は低温生成相からなる複合組織であり、さらに、パーライトの平均自由行程が5.0μm以上であることを特徴とする熱延鋼板。
ここで、パーライトの平均自由行程とは、パーライトの分散状態である。
ここで、前記溶融亜鉛めっき鋼板は、合金化処理を施すか施さないかにかかわらず、溶融亜鉛めっき方法によって鋼板上に亜鉛をめっきした鋼板を総称する。すなわち、本発明における溶融亜鉛めっき鋼板とは、合金化処理を施していない溶融亜鉛めっき鋼板、合金化処理を施した合金化溶融亜鉛めっき鋼板の両方を含むものである。
本発明の熱延鋼板の各成分の含有量の限定理由を説明する。なお、以下において、鋼の化学成分に関する「%」表示は、特に断らない限り「質量%」を意味する。
炭素(C)は、鋼板の高強度化に有効な元素であり、特に、Nbのような炭化物形成元素と微細な合金炭化物、あるいは、合金炭窒化物を形成して鋼板の強化に寄与する。また、本発明における、熱延鋼板の鋼板組織におけるパーライトの形成に必要な元素であり、高強度化に寄与する。この効果を得るためには、0.060%以上の添加が必要である。一方、C含有量を0.150%よりも多く含有させると、スポット溶接性が低下することから、C含有量の上限は0.150%とする。なお、より良好な溶接性を確保する観点からは、C含有量を0.120%以下とすることが好ましい。
珪素(Si)は、高い加工硬化能をもつことから強度上昇に対して延性の低下が比較的少なく、焼鈍後の強度-延性バランスの向上にも寄与する元素である。また、熱延段階でのフェライト変態の促進により、所望のフェライトの結晶粒径および体積分率を確保するのに寄与する、材質均一性を向上させるために必要な元素である。この効果を得るためには、Si含有量を0.15%以上とすることが必要である。さらに材質均一性を高めるためには、Si含有量を0.35%以上とすることが好ましい。一方、Si含有量が0.70%よりも多いと、焼鈍後の溶融亜鉛めっき性の劣化が著しくなるため、Si含有量を0.70%以下とし、より好ましくは0.60%以下である。
マンガン(Mn)は、固溶強化および第2相を生成することで焼鈍後の高強度化に寄与する元素である。その効果を得るためにはMn含有量は1.00%以上とすることが必要であり、好ましくは1.20%以上である。一方、Mn含有量が1.90%よりも多いと、熱延段階でのフェライト変態とパーライト変態を遅延し、所望のフェライトの結晶粒径および面積率を確保することが難しく、材質均一性が低下する懸念があるため、その含有量は1.90%以下、好ましくは1.70%以下とする。
リン(P)は、固溶強化により高強度化に寄与する元素であり、この効果を得るためにはPの含有量は0.005%以上とすることが好ましい。また、P含有量が0.10%よりも多いと、粒界への偏析が著しくなって粒界を脆化させ、また溶接性が低下し、材質均一性が劣化するため、Pの含有量の上限値は0.10%とする。好ましくは、0.05%以下である。
硫黄(S)の含有量が多い場合には、MnSなどの硫化物が多く生成し、焼鈍後の伸びフランジ性に代表される局部伸びが低下するため、含有量の上限を0.010%とする。好ましくは、0.005%以下である。なお、S含有量の下限値については特に限定する必要は無いが、極低S化は製鋼コストの上昇をまねくため、0.0005%以上の範囲において低減すればよい。
アルミニウム(Al)は、脱酸に必要な元素であり、この効果を得るためには0.01%以上含有することが必要であるが、0.10%を超えて含有しても効果が飽和するため、0.10%以下とする。好ましくは、0.05%以下である。
窒素(N)は、Cと同様にNbと化合物を形成して、合金窒化物や合金炭窒化物となり、高強度化に寄与する。しかし、窒化物は比較的高温で生成しやすいため粗大になりやすく、炭化物に比べ強度への寄与が相対的に小さい。このため、焼鈍後の高強度化にはN含有量を低減して合金炭化物をより生成した方が有利である。このような観点から、Nの含有量は0.010%以下、好ましくは0.005%以下とする。
ニオブ(Nb)は、CやNと化合物を形成して炭化物や炭窒化物となり、さらには結晶粒微細化に効果があり、所望のフェライトおよびパーライトの結晶粒径および体積分率を確保するために重要な元素である。さらに、炭窒化物の析出強化により高降伏比を得るためにも必要な元素である。この効果を得るためには、Nb含有量を0.010%以上とすることが必要である。しかし、Nb含有量が0.100%よりも多いと、成形性の低下が著しくなるため、Nb含有量の上限値を0.100%とする。好ましくは、0.060%以下である。
Ti:0.05%未満
チタン(Ti)は、Nbと同様に、微細な炭窒化物を形成し、結晶粒微細化にも効果があり、強度上昇に寄与することができるため、必要に応じて含有することが出来る元素であるが、Ti含有量を0.05%以上添加すると、成形性が著しく低下するため、Ti含有量は0.05%未満とし、好ましくは0.035%以下である。なお、焼鈍後の強度上昇効果を発揮する上で、Tiを含有させる場合には、0.005%以上含有させることが好ましい。
バナジウム(V)もまた、Nbと同様に、微細な炭窒化物を形成し、結晶粒微細化にも効果があり、強度上昇に寄与することができるため、必要に応じて含有することが出来る元素であるが、V含有量を0.10%よりも多くしても、0.10%を超えた分の強度上昇効果は小さく、そのうえ、合金コストの増加も招いてしまう。このため、V含有量は0.10%以下とする。なお、強度上昇効果を発揮する上で、Vを含有させる場合には、0.005%以上含有させることが好ましい。
クロム(Cr)は、焼鈍時の焼入れ性を向上させ、第2相を生成することで高強度化に寄与する元素であり、必要に応じて添加することができる元素であるが、この効果を発揮させるためには、Cr含有量を0.10%以上とすることが好ましい。一方、Cr含有量を0.50%より多くしても、効果の向上は認められなくなるため、Cr含有量は0.50%以下とする。
モリブデン(Mo)は、焼鈍時の焼入れ性を向上させ、第2相を生成することで高強度化に寄与する元素であり、必要に応じて添加することができる元素であるが、この効果を発揮させるためには、Mo含有量を0.05%以上とすることが好ましい。一方、Mo含有量を0.50%より多くしても、効果の向上は認められなくなるため、Mo含有量は0.50%以下とする。
銅(Cu)は、固溶強化により高強度化に寄与し、また、焼鈍時の焼入れ性を向上させ、第2相を生成することでも高強度化に寄与する元素であり、必要に応じて添加することができる元素である。この効果を発揮させるためには、Cu含有量は0.05%以上とすることが好ましい。一方、Cu含有量が0.50%より多くしても、効果の向上は認められなくなり、さらに、Cuに起因する表面欠陥が発生しやすくなるため、Cu含有量は0.50%以下とする。
ニッケル(Ni)もまた、Cuと同様に、固溶強化により高強度化に寄与し、また、焼鈍時の焼入れ性を向上させ、第2相を生成することでも高強度化に寄与し、さらに、Cuとともに添加すると、Cu起因の表面欠陥を抑制する効果があるため、必要に応じて添加することができる元素である。この効果を発揮させるためには、Ni含有量を0.05%以上とすることが好ましい。一方、Ni含有量を0.50%より多くしても、効果の向上は認められなくなるため、Ni含有量は0.50%以下とする。
ボロン(B)は、焼鈍時の焼入れ性を向上させて第2相を生成することによって、高強度化に寄与する元素であり、必要に応じて添加することができる。この効果を発揮するためには、0.0005%以上含有させることが好ましい。一方、0.0030%超を含有させても効果が飽和するため、その含有量を0.0030%以下とする。
カルシウム(Ca)および希土類元素(REM)は、硫化物の形状を球状化し、穴広げ性への硫化物の悪影響を改善するのに寄与する元素であり、必要に応じて添加することができる。これらの効果を発揮するためには、それぞれ0.001%以上含有させることが好ましい。一方、0.005%超含有させても効果が飽和するため、その含有量をそれぞれ0.005%以下とする。
ここで、不可避的不純物としては、例えば、Sb、Sn、Zn、Co等が挙げられ、これらの含有量の許容範囲としては、Sb:0.01%以下、Sn:0.1%以下、Zn:0.01%以下、Co:0.1%以下である。また、本発明では、Ta、Mg、Zrを通常の鋼組成の範囲内で含有しても、その効果は失われない。
熱延板組織は、フェライトが平均結晶粒径18μm以下かつ体積分率75%以上であり、パーライトが平均結晶粒径2μm以上かつ体積分率5%以上であり、残部が低温生成相からなり、前記パーライトの平均自由行程が5.0μm以上である、複合組織である。ここで述べる体積分率は、鋼板の組織全体に対する体積分率であり、以下同様である。
なお、パーライトの平均自由行程については、後述する。
本発明の材質均一性に優れ、かつ高降伏比を有する冷延鋼板、溶融亜鉛めっき鋼板の素材となる熱延鋼板は、上記の成分組成範囲に適合した成分組成を有する溶鋼から連続鋳造にてスラブを作製し、該スラブを600℃まで6h以内に冷却し、その後、再加熱して、熱間圧延開始温度:1150~1270℃、仕上げ圧延の終了温度:830~950℃の条件で熱間圧延し、650℃までの温度域を平均冷却速度20~90℃/sで冷却し、その後、470~640℃の温度域にて巻取る際の該巻取り温度まで平均冷却速度5~30℃/sで冷却し巻取りを行うことによって製造できる。
本発明において、まずスラブは連続鋳造法により鋳造される。連続鋳造法は、本発明の課題からして前提となるものであり、しかも鋳型鋳造法と比較して生産能率が高いためである。連続鋳造機は垂直曲げ型が望ましい。これは、垂直曲げ型は設備コストと表面品質のバランスに優れ、かつ、表面亀裂の抑制効果が顕著に発揮されるためである。
この連続鋳造を経てスラブとした後は、600℃まで6h以内に冷却する。連続鋳造後、600℃まで6h(時間)を超えて冷却を行うと、Mn等の偏析が顕著となり、かつ結晶粒が粗大化するため、特に熱間圧延後のパーライトの平均自由行程が低下し、材質均一性が劣化する。このため、連続鋳造後の鋼スラブの冷却は600℃まで6h以内とし、好ましくは600℃まで5h以内まで冷却、さらに好ましくは600℃まで4h以内に冷却する。また、600℃まで冷却したならば、その後に、室温まで冷却した後に再加熱して熱間圧延を施しても良いし、そのまま温片のまま再加熱して熱間圧延を施しても良い。
・熱間圧延開始温度:1150~1270℃
熱間圧延開始温度は、1150℃よりも低くなると圧延負荷が増大し、生産性が低下するため好ましくなく、また、1270℃より高くしても加熱コストが増大するだけであるため、1150~1270℃とすることが好ましい。
熱間圧延は、鋼板内の組織均一化、材質の異方性低減により、材質均一性を向上させるため、オーステナイト単相域にて終了する必要があるので、仕上げ圧延終了温度は830℃以上にする。一方、仕上げ圧延終了温度が950℃超えでは、熱延組織が粗大になり、材質均一性が低下する懸念がある。このため、仕上げ圧延終了温度を830~950℃とする。
平均冷却速度が20℃/s未満での冷却では、フェライト変態が過剰に進行し、所望のパーライト体積分率が得られず、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の材質均一性が低下する。また、平均冷却速度が90℃/s超えでの冷却では、熱延板組織において、フェライト変態が十分に進行せず、所望のフェライト結晶粒径およびパーライトの平均自由行程を得られず、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の材質均一性が低下する。好ましくは平均冷却速度は30~70℃/sである。
平均冷却速度が5℃/s未満での冷却では、フェライト変態が過剰に進行し、所望のパーライト体積分率が得られず、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の材質均一性が低下する。また、平均冷却速度が30℃/s超での冷却では、巻取り後にベイナイト変態が進行し、所望のパーライト体積分率と結晶粒径が得られず、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の材質均一性が低下する。好ましくは平均冷却速度は10~25℃/sとする。
巻取り温度が470℃未満の場合、熱延板組織において、マルテンサイトやベイナイトの低温生成相(硬質相)を含む組織となり、熱延板で不均一な硬度分布が生じ、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の材質均一性が低下する。また、巻取り温度が640℃を超えた場合、熱延板組織のフェライトの結晶粒径が大きくなり、焼鈍板(冷延鋼板や溶融亜鉛めっき鋼板)の所望の強度確保が難しい。さらにNbの炭窒化物が粗大となり、材質均一性および降伏比が低下する。そのため、巻取り温度は470~640℃とする。好ましくは480~620℃である。
なお、一連の熱処理においては、熱履歴条件さえ満足されれば、鋼板はいかなる設備で熱処理を施されてもかまわない。加えて、溶融亜鉛めっき後に、合金化処理を施す場合は、合金化処理後に本発明の鋼板に調質圧延を施して形状矯正を行うことも可能である。
表1に示す成分組成を有し、残部がFeおよび不可避的不純物よりなる鋼を転炉にて溶製し、連続鋳造法にてスラブとし、表2に示す冷却時間にて600℃までの冷却を行った後、室温まで冷却した。その後、得られたスラブを再加熱後、表2に示す熱間圧延条件で2.3~4.5mmの各板厚まで熱間圧延を行い、表2に示す巻取り温度で巻き取った。
次いで、得られた熱延板を酸洗し、冷間圧延した後、800℃で焼鈍し、必要に応じて、溶融亜鉛めっき処理、またはさらに亜鉛めっきの合金化処理を施し、冷延鋼板(CR)、溶融亜鉛めっき鋼板(GI)、合金化溶融亜鉛めっき鋼板(GA)を得た。一部熱延板については、酸洗後、冷間圧延を施さないで、焼鈍、溶融亜鉛めっき処理、またはさらに亜鉛めっきの合金化処理を施し、溶融亜鉛めっき鋼板(GI)、合金化溶融亜鉛めっき鋼板(GA)を得た。溶融亜鉛めっき浴は溶融亜鉛めっき鋼板(GI)では、Al:0.19質量%含有亜鉛浴を使用し、合金化溶融亜鉛めっき鋼板(GA)では、Al:0.14質量%含有亜鉛浴を使用し、浴温は460℃とし、合金化溶融亜鉛めっき鋼板(GA)については、550℃で合金化処理を施した。めっき付着量は片面あたり45g/m2(両面めっき)とし、合金化溶融亜鉛めっき鋼板(GA)は、めっき層中のFe濃度を9~12質量%とした。
すなわち、フェライトとパーライトの体積分率は、鋼板の圧延方向に平行な板厚断面(垂直断面)を研磨後、3%ナイタールで腐食し、鋼板表面から深さ方向に板厚の1/4位置について、SEM(走査型電子顕微鏡)を用いて2000倍の倍率で10視野観察し、Media Cyberneticks社のImage-Proを用いて各相の面積率を10視野分算出し、それらの値を平均して求め、この面積率を体積分率とした。
また、フェライトとパーライトの平均結晶粒径は、上述のImage-Proを用いて、各々のフェライト結晶粒もしくはパーライト結晶粒の面積を求め、円相当直径を算出し、それらの値を平均して求めた。
パーライトの平均自由行程は、上述のImage-Proを用いて、パーライトの重心を求め、極端な偏りがなく均一に分散していることを前提に下記式により算出した。
記
LM:平均自由行程
dM:平均結晶粒径
π:円周率
f:面積率(=体積分率)
熱延板の幅中心部と、両幅端からそれぞれ1/8幅の位置(全幅の1/8位置)から、引張方向が圧延方向と平行となるように、JIS5号試験片を採取し、JIS Z2241(2010年)に準拠して引張試験を行ない、YSおよびTSを測定し、幅中心部の値と幅1/8位置の値(幅1/8位置は両端部あわせて2箇所あるが、その平均値)との差(幅中心部の特性値-幅1/8位置の特性値の絶対値)をそれぞれΔYSおよびΔTSとして算出した。なお、本発明では、ΔYS≦40MPa、ΔTS≦30MPaの場合を材質均一性の観点で良好と判定した。材質バラツキを、幅中心部と幅1/8位置の2点で評価するのは、例えば、熱延板の幅方向の中心部と熱延板幅端部(エッジ)から板幅の1/4に相当する位置(幅1/4位置)との引張強度の差では、エッジ付近の材質が評価されないため、十分な幅方向の材質安定性の評価が困難であるが、さらにエッジ寄りの幅1/8位置と幅中心部の引張強度の差で評価することで、焼鈍板の材質安定性の適切な評価が可能になるためである。
以上の各調査の結果を、表3に示す。
Claims (6)
- 化学成分が、質量%で、C:0.060~0.150%、Si:0.15~0.70%、Mn:1.00~1.90%、P:0.10%以下、S:0.010%以下、Al:0.01~0.10%、N:0.010%以下およびNb:0.010~0.100%を含有し、残部がFeおよび不可避的不純物からなり、
ミクロ組織が、平均結晶粒径:18μm以下のフェライトを体積分率で75%以上、平均結晶粒径:2μm以上のパーライトを体積分率で5%以上含み、残部は低温生成相からなる複合組織であり、さらに、パーライトの平均自由行程が5.0μm以上であることを特徴とする熱延鋼板。 - Fe成分の一部に代えて、さらに質量%で、Ti:0.05%未満を含有することを特徴とする請求項1に記載の熱延鋼板。
- Fe成分の一部に代えて、さらに質量%で、V:0.10%以下、Cr:0.50%以下、Mo:0.50%以下、Cu:0.50%以下、Ni:0.50%以下、B:0.0030%以下から選択される一種以上を含有することを特徴とする請求項1または2に記載の熱延鋼板。
- Fe成分の一部に代えて、さらに質量%で、Ca:0.001~0.005%およびREM:0.001~0.005%から選択される一種以上を含有することを特徴とする請求項1から3のいずれか1項に記載の熱延鋼板。
- 前記熱延鋼板が、冷延鋼板用または溶融亜鉛めっき鋼板用である請求項1から4のいずれか1項に記載の熱延鋼板。
- 請求項1から4のいずれか1項に記載の成分組成を有する溶鋼を連続鋳造してスラブとし、このスラブを600℃まで6h以内に冷却し、その後、再加熱して、熱間圧延開始温度:1150~1270℃、仕上げ圧延の終了温度:830~950℃の条件で熱間圧延し、650℃までの温度域を平均冷却速度20~90℃/sで冷却し、その後、470~640℃の温度域にて巻取る際の該巻取り温度まで平均冷却速度5~30℃/sで冷却し、前記巻取りを行うことを特徴とする熱延鋼板の製造方法。
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EP2762581B1 (en) | 2017-05-24 |
US20140246128A1 (en) | 2014-09-04 |
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