WO2019130713A1 - 高強度鋼板およびその製造方法 - Google Patents
高強度鋼板およびその製造方法 Download PDFInfo
- Publication number
- WO2019130713A1 WO2019130713A1 PCT/JP2018/037569 JP2018037569W WO2019130713A1 WO 2019130713 A1 WO2019130713 A1 WO 2019130713A1 JP 2018037569 W JP2018037569 W JP 2018037569W WO 2019130713 A1 WO2019130713 A1 WO 2019130713A1
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- WIPO (PCT)
- Prior art keywords
- less
- steel plate
- rolling
- high strength
- steel sheet
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 137
- 239000010959 steel Substances 0.000 title claims abstract description 137
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 27
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 47
- 239000001257 hydrogen Substances 0.000 claims abstract description 47
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 45
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 37
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 27
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 25
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 25
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 238000005096 rolling process Methods 0.000 claims description 55
- 238000001816 cooling Methods 0.000 claims description 37
- 238000000137 annealing Methods 0.000 claims description 32
- 238000000034 method Methods 0.000 claims description 28
- 230000000717 retained effect Effects 0.000 claims description 18
- 230000008569 process Effects 0.000 claims description 17
- 238000007747 plating Methods 0.000 claims description 15
- 230000032683 aging Effects 0.000 claims description 14
- 238000005097 cold rolling Methods 0.000 claims description 14
- 238000005098 hot rolling Methods 0.000 claims description 9
- 230000015572 biosynthetic process Effects 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- 238000005275 alloying Methods 0.000 claims description 5
- 239000013078 crystal Substances 0.000 claims description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 3
- 229910052725 zinc Inorganic materials 0.000 claims description 3
- 239000011701 zinc Substances 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 2
- 230000014759 maintenance of location Effects 0.000 claims 2
- 238000005452 bending Methods 0.000 description 26
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 16
- 239000010410 layer Substances 0.000 description 16
- 238000010438 heat treatment Methods 0.000 description 12
- 230000000694 effects Effects 0.000 description 11
- 238000012360 testing method Methods 0.000 description 10
- 239000002344 surface layer Substances 0.000 description 9
- 229910052742 iron Inorganic materials 0.000 description 7
- 229910001335 Galvanized steel Inorganic materials 0.000 description 6
- 239000008397 galvanized steel Substances 0.000 description 6
- 150000001247 metal acetylides Chemical class 0.000 description 6
- 229910052761 rare earth metal Inorganic materials 0.000 description 5
- 238000004804 winding Methods 0.000 description 5
- 229910052787 antimony Inorganic materials 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 238000009864 tensile test Methods 0.000 description 4
- 229910052718 tin Inorganic materials 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 3
- 229910052750 molybdenum Inorganic materials 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- 241000519995 Stachys sylvatica Species 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 238000007373 indentation Methods 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 235000019362 perlite Nutrition 0.000 description 2
- 239000010451 perlite Substances 0.000 description 2
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 241000872198 Serjania polyphylla Species 0.000 description 1
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000000845 anti-microbial effect Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 238000005246 galvanizing Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
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- 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
- 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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- 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
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- 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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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- 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
- C21D8/0273—Final recrystallisation annealing
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- 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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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- 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
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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
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- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
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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
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; 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
- 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
Definitions
- the present invention relates to a high-strength steel plate which is excellent in strength and processability and is suitable for automotive members, and a method of manufacturing the same.
- Patent Document 1 discloses a technique relating to a steel plate having excellent bendability by refining the average grain size of tempered martensite. Moreover, in patent document 2, the technique regarding the steel plate excellent in bendability is disclosed by controlling the quantity and form of an inclusion and a precipitate.
- the present invention has been made to solve the above-described problems, and an object thereof is to provide a high-strength steel sheet which is further excellent in achieving both strength and workability, and a method for producing the same.
- Patent Document 1 and Patent Document 2 focus only on the inclusions in the steel structure and the steel plate, and the study focusing on the trapped hydrogen trapped in the steel has not been conducted, but the present inventors have studied the above-mentioned trap Focusing on hydrogen, the present invention has been completed as follows.
- the present inventors optimize the steel sheet structure, introduce hydrogen into the steel sheet, trap it in oxide, and use it as trap hydrogen for bending. It has been found that the sex is significantly improved.
- the high strength means that the TS has a strength of 980 MPa or more, preferably 1180 MPa or more, and the excellent bendability has a ratio (R / t) of the minimum bending radius R to the thickness t where no microcracks are recognized. 1.5 or more in the range of less than 1180 MPa, 2.5 or less in the range of 1180 MPa to less than 1320 MPa, TS in the range of 1320 MPa to less than 1600 MPa, and TS in the range of 1600 MPa to less than 2100 MPa. Set to 0 or less.
- a micro crack is a crack with a crack length of 0.5 mm or more.
- the extension ferrite phase having an aspect ratio of 3 or more has an area ratio of 1% or less, the average crystal grain size of martensite in the region from the steel plate surface to 50 ⁇ m is 20 ⁇ m or less, and the short in the region from the steel plate surface to 50 ⁇ m Axis length is 0 8 ⁇ m following oxides 1.0 ⁇ 10 10 pieces / m 2 or more, coarse oxides minor axis length exceeds 1.0 ⁇ m in the region of the steel plate surface to 50 ⁇ m is 1.0 ⁇ 10 8 cells / m 2 or less
- the high-strength steel plate in which the amount of trapped hydrogen in the steel plate is 0.05 mass ppm or more.
- the slab having the component described in [1] or [2] is descaling treated at a pressure of 15 MPa or more after rough rolling, subjected to finish rolling at 800 to 950 ° C., and cooled after finish rolling to 550 ° C. or less And the hot rolled sheet obtained in the hot rolling step to 730 to 950 ° C., and a hydrogen concentration of 1.0 to 35.0% by volume and a dew point of -35 to 15 in this temperature range.
- the steel sheet after the annealing step and the annealing step held under the conditions of 10 to 1000 s in an atmosphere of ° C. is then cooled to 600 ° C.
- a slab having the component described in [1] or [2] is descaling treated at a pressure of 15 MPa or more after rough rolling, subjected to finish rolling at 800 to 950 ° C., and cooled after finish rolling at 550 ° C. or less
- a high strength steel plate excellent in bendability can be obtained, which is suitable as a material for automobile parts.
- C 0.05 to 0.40% C is an element effective to generate martensite, bainite or the like and raise TS. If the C content is less than 0.05%, such an effect can not be sufficiently obtained, and a TS of 980 MPa or more can not be obtained. Therefore, the C content is made 0.05% or more. Preferably, it is 0.07% or more, more preferably 0.09% or more, and further preferably 0.11% or more. On the other hand, when the C content exceeds 0.40%, the martensite hardens and the deterioration of bendability becomes remarkable. Therefore, the C content is 0.40% or less, preferably 0.37% or less, more preferably 0.35% or less, and still more preferably 0.32% or less.
- Si 0.10 to 3.0%
- Si is an element effective for solid solution strengthening of steel to raise TS.
- oxides containing Si are effective for trapping hydrogen.
- Si content is made into 0.10% or more.
- it is 0.20% or more, More preferably, it is 0.30% or more, More preferably, it is 0.40% or more.
- the Si content exceeds 3.0%, the steel is embrittled and the deterioration of bendability becomes remarkable. Therefore, the Si content is 3.0% or less.
- it is 2.5% or less, More preferably, it is 2.0% or less, More preferably, it is 1.8% or less.
- Mn 1.5 to 4.0% Mn is an element effective to generate martensite, bainite or the like and raise TS. If the Mn content is less than 1.5%, such effects can not be sufficiently obtained, and a TS of 980 MPa or more can not be obtained. Therefore, the Mn content is 1.5% or more. Preferably it is 1.8% or more, More preferably, it is 2.0% or more, More preferably, it is 2.2% or more. On the other hand, if the Mn content exceeds 4.0%, the steel becomes brittle and the bendability of the present invention can not be obtained. Therefore, the Mn content is 4.0% or less. It is preferably 3.8% or less, more preferably 3.6% or less, and still more preferably 3.4% or less.
- P 0. 100% or less (except 0%) It is desirable to reduce the amount of P as much as possible in order to embrittle the grain boundaries and to deteriorate the bendability, but in the present invention, it is acceptable up to 0.100%. Preferably it is 0.050% or less.
- the lower limit is not particularly defined, but if it is less than 0.001%, the production efficiency is lowered, so from the viewpoint of production efficiency, 0.001% or more is preferable.
- S 0.02% or less (excluding 0%) It is preferable to reduce the content of S as much as possible in order to increase inclusions and deteriorate the bendability, but in the present invention, the S content can be allowed up to 0.02%. Preferably it is 0.01% or less.
- the lower limit is not particularly specified, but if it is less than 0.0005%, the production efficiency is lowered, so from the viewpoint of production efficiency, 0.0005% or more is preferable.
- Al acts as a deoxidizer and is preferably added in the deoxidation step. Therefore, the Al content is made 0.010% or more. Preferably it is 0.015% or more. When a large amount of Al is contained, a large amount of soft ferrite phase is generated to cause a decrease in TS.
- the present invention allows up to 1.0%. Preferably, it is 0.50% or less.
- N 0.010% or less
- the lower limit is not particularly specified, but if it is less than 0.0005%, the production efficiency is lowered, so from the viewpoint of production efficiency, 0.0005% or more is preferable.
- the component composition of the present invention may contain the following elements as optional components.
- Cr 0.005 to 2.0%
- Ti 0.005 to 0.20%
- Nb 0.005 to 0.20%
- Mo 0.005 to 2.0%
- V 0.005 to 2.0%
- Ni 0.005 to 2.0%
- Cu 0.005 to 2.0%
- B 0.0001 to 0.0050%
- Ca 0.0001 to 0.0050%
- REM 0.0001 to 0.0050%
- Sn 0.01 to 0.50%
- Sb 0.0010 to 0.10% Cr
- Cu and Ni form martensite and bainite, and are effective elements for strengthening.
- it is preferable to set it as 0.005% or more, respectively. More preferably, it is 0.010% or more, further preferably 0.050% or more.
- the content of these elements is preferably 2.0% or less. More preferably, it is 1.5% or less, more preferably 1.0% or less.
- Ti, Nb, V, and Mo are elements effective for strengthening by forming carbides. In order to acquire such an effect, it is preferable to set it as 0.005% or more, respectively. More preferably, it is 0.010% or more. On the other hand, when each upper limit is exceeded, carbides are coarsened and solid solution carbon is also reduced, which causes the steel to be softened. Therefore, the Ti content is preferably 0.20% or less. More preferably, it is 0.10% or less, still more preferably 0.05% or less.
- Nb is preferably 0.20% or less. More preferably, it is 0.10% or less, still more preferably 0.05% or less.
- V is preferably 2.0% or less. More preferably, it is 1.0% or less, more preferably 0.5% or less. Moreover, it is preferable to make Mo into 2.0% or less. More preferably, it is 1.0% or less, more preferably 0.5% or less.
- B is an element that enhances the hardenability of the steel sheet, forms martensite and bainite, and is effective in increasing the strength. In order to acquire such an effect, it is preferable to set it as 0.0001% or more. More preferably, it is 0.0005% or more. On the other hand, when the B content exceeds 0.0050%, inclusions increase and the bendability is slightly deteriorated. Therefore, the B content is preferably 0.0050% or less. More preferably, it is 0.0030% or less.
- Ca and REM are elements effective for improving the bendability by controlling the form of inclusions. In order to acquire such an effect, it is preferable to set it as 0.0001% or more, respectively. More preferably, it is 0.0005% or more. When the content of Ca and REM exceeds 0.0050%, the amount of inclusions increases and the bendability is slightly deteriorated. Therefore, the content of each of Ca and REM is preferably set to 0.0050% or less. More preferably, it is 0.0030% or less.
- Sn and Sb are elements effective for suppressing the reduction in strength of the steel by suppressing decarburization, denitrification, deasphalting and the like. In order to acquire such an effect, it is preferable to make Sn 0.01% or more and Sb 0.0010% or more. When the contents of Sn and Sb exceed the respective upper limits, bendability is slightly deteriorated due to grain boundary embrittlement. Therefore, the Sn content is preferably 0.50% or less. More preferably, it is 0.10% or less. The Sb content is preferably 0.10% or less. More preferably, it is 0.05% or less.
- the balance is Fe and unavoidable impurities.
- the optional component When the above-mentioned optional component is contained below the above-mentioned lower limit, the optional component shall be contained as an unavoidable impurity.
- Zr, Mg, La, Ce, Bi, W, and Pb may be contained as an unavoidable impurity up to 0.002% in total.
- Total area ratio of lower bainite, martensite and retained austenite 40 to 100% If the total area ratio of lower bainite, martensite and retained austenite is less than 40%, a TS of 980 MPa or more can not be obtained. Therefore, the total area ratio described above is 40 to 100%, preferably 45 to 100%, more preferably 50 to 100%. Martensite includes both as-quenched martensite and tempered martensite. Also, lower bainite means bainite containing aligned carbides, and includes tempered bainite.
- the area ratio of martensite in the entire steel structure is preferably 30% or more. More preferably, it is 35% or more.
- the upper limit of the martensite area ratio is preferably 99% or less, more preferably 97% or less, and still more preferably 95% or less.
- Area ratio of retained austenite 15% or less Retained austenite transforms to martensite during bending to promote generation of cracks, and becomes significant when the area ratio to the entire structure exceeds 15%. Therefore, the area ratio of retained austenite is 15% or less, preferably 10% or less, more preferably 8% or less.
- the lower limit of the area ratio of retained austenite is not particularly limited, and may be 0%, preferably 1% or more, and more preferably 2% or more.
- Total area ratio of upper bainite and ferrite 0 to 60% If the total area ratio of upper bainite and ferrite exceeds 60%, a TS of 980 MPa or more can not be obtained. Therefore, the total area ratio of upper bainite and ferrite is set to 0 to 60%, preferably 0 to 50%, more preferably 0 to 45%. Particularly in high strength steels, the smaller one is preferable for bendability, the total area ratio is 10% or less in the range of 1320 MPa to less than 1600 MPa, and the total area ratio of 3% or less is preferable in the range of 1600 MPa to less than 2100 MPa. Also, upper bainite means bainite which does not contain aligned carbides.
- Area ratio of the expanded ferrite phase having an aspect ratio of 3 or more: 1% or less The expanded ferrite phase having a large aspect ratio promotes cracking at the time of bending and degrades bendability. In order to suppress such an effect, it is necessary to set the expansion ferrite phase having an aspect ratio of 3 or more at an area ratio of 1% or less with respect to the entire structure. Therefore, the area ratio of the extended ferrite phase having an aspect ratio of 3 or more is set to 1% or less.
- the steel structure of the present invention may contain other structures at a total area ratio of 5% or less.
- Other organizations include perlite and the like.
- Average grain size of martensite in the region from the surface of the steel plate to 50 ⁇ m 20 ⁇ m or less
- the main cause of micro cracks during bending is the region up to 50 ⁇ m from the surface of the steel plate (sometimes referred to as surface layer or surface layer)
- the average crystal grain size of martensite in the region up to 50 ⁇ m from the surface is set to 20 ⁇ m or less.
- the lower limit is not particularly limited, but is often 1 ⁇ m or more.
- the oxide dispersion on the surface of the steel sheet and the trapped hydrogen are extremely important, and by setting this to a predetermined range, excellent bendability can be obtained.
- this mechanism is not clear, when hydrogen is trapped in the oxide on the surface of the steel sheet, the interface between the oxide and the base iron separates at the time of bending to easily form fine voids, and macrocracks are caused by plastic relaxation. It is speculated that the occurrence of
- the bendability of the present invention when the oxide having a minor axis length of 0.8 ⁇ m or less in a region from the steel plate surface to 50 ⁇ m is less than 1.0 ⁇ 10 10 pieces / m 2 Can not be obtained.
- the oxide in the region up to 50 ⁇ m from the surface of the steel plate is 1.0 ⁇ 10 10 pieces / m 2 or more, preferably 100.0 ⁇ 10 10 pieces / m 2 or more, and the short axis length exceeds 1.0 ⁇ m
- the content is 1.0 ⁇ 10 8 particles / m 2 or less, more preferably 1.0 ⁇ 10 7 particles / m 2 or less.
- the oxides in the present invention are mainly Fe, Si, Mn, Al, Mg, Ti, etc., as a single substance or a complex oxide.
- the upper limit is not particularly limited, but it is often 500.0 ⁇ 10 10 / m 2 or less.
- An oxide having a minor axis length of more than 0.8 ⁇ m and less than 1.0 ⁇ m in a region up to 50 ⁇ m from the steel sheet surface does not greatly affect the effect of the present invention.
- the amount of trapped hydrogen in the steel sheet is 0.05 mass ppm or more, preferably 0.07 mass ppm or more.
- trapped hydrogen is hydrogen desorbed at 350 ° C. or higher when the temperature is increased at 200 ° C./hr. It is particularly preferable to set 0.05 ppm by weight or more of hydrogen desorbed at 350 to 600 ° C., and more preferably set 0.05 ppm by weight or more of hydrogen desorbed at 450 to 600 ° C.
- the upper limit is not particularly limited, but the trapped hydrogen in the steel sheet is often 1.00 mass ppm or less. Before bending, it is necessary to set the amount of trapped hydrogen in the steel plate to 0.05 mass ppm or more, but in the product after bending, the amount of trapped hydrogen in the steel plate in the non-bending portion is 0.05 mass ppm or more If it exists, it can be considered that the trapped hydrogen in the steel plate of the bending portion is 0.05 mass ppm or more.
- the area ratio of the structure means the ratio of the area of each structure to the observation area, and these area ratios cut out a sample from the steel plate after annealing and polish the plate thickness section parallel to the rolling direction After that, it is corroded with 3% nital, and the position of 300 ⁇ m in the vicinity of the steel sheet surface and in the thickness direction from the steel sheet surface is photographed for 3 fields of view at 1500 times magnification by SEM (scanning electron microscope).
- the area ratio of each tissue is determined using a company-made Image-Pro, and the average area ratio of the field of view is taken as the area ratio of each tissue.
- ferrite is black with no carbide inside
- upper bainite is gray or dark gray without internally oriented carbide
- retained austenite is white or light gray
- lower bainite is internally aligned Gray or dark gray containing carbide
- martensite is white or light gray or gray or dark gray containing carbide having plural orientations inside
- perlite is distinguished as black and white layered structure.
- carbides can be distinguished as white spots or lines.
- martensites having different characteristics are present depending on the state of tempering, but martensites different in the state of tempering are not particularly distinguished from each other and are all martensite.
- the area ratio of the extended ferrite phase having an aspect ratio of 3 or more can also be derived from the above image data.
- the area ratio of the retained austenite phase is fcc using the K ⁇ ray of Mo with an X-ray diffractometer on the surface polished 0.1 mm further by chemical polishing after grinding the steel plate after final production process to 1/4 position of plate thickness Measure integrated reflection intensity of (200) plane, (220) plane, (311) plane of iron (austenite phase), and (200 plane), (211) plane, (220) plane of bcc iron (ferrite phase)
- the volume ratio is determined from the intensity ratio of the integrated reflection intensity from each surface of fcc iron (austenite phase) to the integrated reflection intensity from each surface of bcc iron (ferrite phase), and the value of the volume ratio is taken as the value of area ratio .
- the area ratio of the retained austenite phase is determined by the above-mentioned X-ray diffraction method.
- the oxide of the surface layer of the steel plate corrodes the same sample with 0.05% nital, and the area from the surface layer of the steel plate to 50 ⁇ m is randomly photographed for 10 fields of view at a magnification of 5000 times with SEM.
- the obtained image data make Media Cybernetics
- the number of oxides having a minor axis length of 0.8 ⁇ m or less and the presence or absence of an oxide having a minor axis length of more than 0.8 ⁇ m can be investigated using Image-Pro. In the above image data, oxides can be distinguished as white spots or lines. Further, the average grain size of martensite in the surface layer of the steel sheet was also calculated from the image data of the above surface layer.
- the area of martensite was determined from image data, and the equivalent circle diameter determined from this area was used as the grain size of martensite, and the average grain size of martensite was calculated by number average.
- grain boundaries of martensite are grain boundaries with prior austenite grain boundaries or other structures, and do not include packet boundaries or block boundaries.
- the tensile strength (TS) is 980 MPa or more.
- the upper limit of TS is not particularly limited, but is preferably 2200 MPa or less from the viewpoint of harmony with other properties.
- the measuring method of TS is as described in the Example, JIS Z5 tensile test piece (JIS Z2201) is taken in a direction perpendicular to the rolling direction, and the strain rate is 10 -3 / s. This is a method of performing a tensile test according to the provisions of 2241 (1998).
- the present invention also has excellent bendability.
- the ratio (R / t) of the minimum bending radius R to the plate thickness t determined by the following method is TS in the range of 980 MPa or more and less than 1180 MPa, and TS is in the range of 1180 MPa or more and less than 1320 MPa In the range of 1320 MPa to less than 1600 MPa, and 3.5 or less in the range of 1600 MPa to less than 2100 MPa.
- the high strength steel plate of the present invention may have a film composed of one or more layers on the surface.
- a film an organic film, an inorganic film, an inorganic organic composite film, etc. can be illustrated.
- By having a film there are effects such as corrosion resistance, rust prevention, delayed fracture resistance, designability, lubricity, and antimicrobial properties.
- the high strength steel plate of the present invention may have a plating layer on the surface.
- a plating layer a hot-dip galvanization layer, an electrogalvanized layer, a hot-dip aluminum plating layer etc. can all be illustrated.
- the plating layer may be an alloyed hot-dip galvanized layer formed by performing an alloying treatment after hot-dip galvanizing.
- the method for manufacturing the high strength steel plate of the present invention heats the slab having the above-mentioned composition, roughing, descaling at a pressure of 15 MPa or more, and finish rolling at 800 to 950 ° C.
- Hot rolling process to obtain a hot rolled hot rolled sheet at 550 ° C. or less after cooling, and, if necessary, cold rolling process to obtain cold rolled sheet by cold rolling at a rolling reduction of 20% or more, 730 Annealing step of heating to ⁇ 950 ° C and holding for 10 to 1000 seconds in an atmosphere with a hydrogen concentration of 1.0 to 35.0% by volume and a dew point of -35 to 15 ° C in this temperature range, and then an average of 5 ° C / 600 ° C.
- Descaling pressure 15 MPa or more When the descaling pressure is less than 15 MPa, scale remains, and coarse oxide is easily generated on the surface of the steel sheet by oxygen supply from the scale during cooling after winding, and the bending property is deteriorated. . Therefore, the descaling pressure is 15 MPa or more. Although the upper limit is not particularly limited, it is preferably 75 MPa or less.
- Finish rolling temperature 800 to 950 ° C
- the finish rolling temperature is less than 800 ° C.
- ferrite is formed, extended ferrite is formed on the surface layer of the hot-rolled sheet, and remains even after annealing to form extended ferrite grains having an aspect ratio of 3 or more, and the bendability is degraded.
- the finish rolling temperature is set to 800 to 950.degree.
- the lower limit is preferably 830 ° C. or higher.
- the upper limit is preferably 920 ° C. or less.
- Winding temperature 550 ° C. or less
- the winding temperature is set to 550 ° C. or less, preferably 500 ° C. or less.
- the lower limit is not particularly defined, but is preferably 250 ° C. or more from the viewpoint of shape stability and the like.
- Cold rolling reduction 20% or more Cold rolling is not essential.
- the rolling reduction when cold rolling is performed, the rolling reduction must be 20% or more. If it is less than 20%, coarse extension ferrite is generated at the time of annealing to deteriorate the bendability. Therefore, when cold rolling is performed, the rolling reduction is set to 20% or more, preferably 30% or more.
- the upper limit is not particularly defined, but is preferably 90% or less from the viewpoint of shape stability and the like.
- Annealing temperature 730 to 950 ° C
- Annealing is performed on a hot-rolled steel plate when cold rolling is not performed, and is performed on a cold-rolled steel plate when cold rolling is performed.
- the annealing temperature is less than 730 ° C.
- the formation of austenite becomes insufficient. Since the austenite formed by annealing becomes martensite or bainite in the final structure due to bainite transformation or martensitic transformation, if the austenite formation becomes insufficient, a desired steel structure can not be obtained.
- the annealing temperature is set to 730 to 950.degree.
- the lower limit is preferably 750 ° C. or higher.
- the upper limit is preferably 930 ° C. or less.
- Annealing holding time 10 to 1000 s If the annealing holding time is less than 10 s, the formation of austenite is insufficient, and the desired steel structure or trapped hydrogen amount can not be obtained. On the other hand, if it exceeds 1000 s, coarse grains are generated and the microstructure of the present invention can not be obtained. Therefore, the annealing holding time is 10 to 1000 s.
- the lower limit is preferably 30 s or more.
- the upper limit is preferably 500 s or less.
- the annealing holding time is a residence time in the above-mentioned annealing temperature range, and does not necessarily have to be a constant holding, and includes heating and cooling in the range of 730 to 950.degree.
- Hydrogen concentration in the atmosphere at a temperature range of 730 to 950 ° C 1.0 to 35.0% by volume If the atmospheric hydrogen concentration in the temperature range of 730 to 950 ° C. is less than 1.0% by volume, the desired amount of trapped hydrogen can not be obtained. On the other hand, if it exceeds 35.0% by volume, the risk of steel plate breakage during operation increases due to hydrogen embrittlement. Therefore, the hydrogen concentration in the atmosphere in the temperature range of 730 to 950 ° C. is set to 1.0 to 35.0% by volume.
- the lower limit is preferably 4.0% by volume or more.
- the upper limit is preferably 32.0% by volume or less.
- the dew point in the temperature range of 730 to 950 ° C. is less than ⁇ 35 ° C.
- the internal oxidation becomes insufficient.
- the dew point in the temperature range of 730 to 950 ° C. is ⁇ 35 to 15 ° C.
- the lower limit is preferably ⁇ 30 ° C. or higher.
- the upper limit is preferably 5 ° C. or less.
- Average cooling rate from annealing temperature to 600 ° C . 5 ° C./s or more
- the average cooling rate from annealing temperature to 600 ° C. is less than 5 ° C./s, excessive polygonal ferrite is formed to obtain the microstructure of the present invention Absent. Therefore, the average cooling rate from the annealing temperature to 600 ° C. is 5 ° C./s or more, preferably 8 ° C./s or more.
- the upper limit is not particularly limited, but is preferably 1500 ° C./s or less.
- Cooling stop temperature more than Ms and 600 ° C. or less
- the cooling stop temperature is Ms or less
- tempered martensite is generated to cause a decrease in TS and a deterioration in bendability.
- the cooling stop temperature is set to more than Ms and not more than 600 ° C.
- the lower limit is preferably 440 ° C. or higher.
- the upper limit is preferably 560 ° C. or less.
- Residence time at Ms to 600 ° C 1000s or less
- the residence time at Ms to 600 ° C. is set to 1000 s or less, preferably 500 s or less, more preferably 200 s or less.
- the lower limit is preferably 5 s or more, more preferably 10 s or more. In addition, you may make it stay after heating to desired temperature after heating.
- Temperature range of Ms to 50 ° C 1.0 ° C / s or more
- the average cooling rate in the temperature range of Ms to 50 ° C. is set to 1.0 ° C./s or more.
- the upper limit is preferably 1500 ° C./s or less.
- the cooling stop temperature of the main cooling is room temperature. Room temperature means 15 to 25 ° C.
- Elongation rate of elongation rolling (tempered rolling): 0.05 to 1% If the elongation percentage of the elongation rolling is less than 0.05%, the desired amount of trapped hydrogen can not be obtained. On the other hand, if the elongation rate exceeds 1%, there is a risk that the oxide on the surface layer may be peeled off. Therefore, the elongation rate of elongation rolling is set to 0.05 to 1%.
- the lower limit is preferably 0.10% or more.
- the upper limit is preferably 0.7% or less, more preferably 0.5% or less.
- the slab is preferably produced by continuous casting to prevent macrosegregation, but it can also be produced by ingot casting or thin slab casting.
- the slab In order to hot-roll the slab, the slab may be cooled to room temperature and then re-heated to perform hot-rolling, or the slab may be charged into a heating furnace without cooling to room temperature and hot-rolled. You can also do Alternatively, an energy saving process in which hot rolling is performed immediately after slight heat retention can be applied.
- it is preferable to heat it to 1100 ° C. or more in order to melt carbides and prevent an increase in rolling load.
- it is preferable to set the heating temperature of the slab to 1300 ° C. or less.
- the slab temperature is the temperature of the slab surface.
- hot rolling a slab it is also possible to heat the rough bar after rough rolling.
- lubrication rolling in order to reduce the rolling load and to make the shape and material uniform, perform lubrication rolling with a coefficient of friction of 0.10 to 0.25 in all or part of the passes of finish rolling. Is preferred.
- the steel sheet after winding is subjected to annealing and hot dip galvanization after removing the scale by pickling or the like.
- Some hot rolled sheets may be cold rolled before annealing.
- coating process in any process after an annealing process.
- the film formation treatment include treatment performed under conditions such as roll coating, electrodeposition and immersion.
- the production method of the present invention is a method for producing a high strength steel plate having a plating layer on the surface
- the production method of the present invention further performs a plating treatment in the cooling step.
- the method of a plating process can employ
- an alloying process may be performed.
- a steel having the component composition shown in Table 1 (the balance being Fe and unavoidable impurities) was melted in a laboratory vacuum melting furnace, and rolled into a steel slab. After heating these steel slabs to 1200 ° C., they are roughly rolled and hot-rolled under the conditions shown in Table 2-1 to obtain hot-rolled sheets (HR). Subsequently, a part was cold rolled to 1.4 mm to make a cold rolled sheet (CR). The obtained hot rolled sheet and cold rolled sheet were subjected to annealing.
- Table 1 the balance being Fe and unavoidable impurities
- Annealing is performed in the laboratory under the conditions shown in Table 2-1 and Table 2-2 using heat treatment for some samples using a plating apparatus, cold rolled steel sheet (CR), hot-dip galvanized steel sheet (GI) and Alloyed galvanized steel sheets (GA) 1 to 34 were produced.
- the hot-dip galvanized steel sheet is immersed in a plating bath at 465 ° C. to form a plated layer with an adhesion amount of 35 to 45 g / m 2 , and the alloyed galvanized steel sheet is maintained at 500 to 600 ° C. for 1 to 60 s after formation of the plated layer. It manufactured by performing an alloying process. After plating treatment, it was cooled to room temperature at 8 ° C./s.
- ⁇ Tension test> Take a JIS No. 5 tensile test specimen (JIS Z 2201) in a direction perpendicular to the rolling direction from the annealed sheet, and conduct a tensile test in accordance with JIS Z 2241 (1998) with a strain rate of 10 -3 / s. I asked for TS. In the present invention, 980 MPa or more was taken as a pass.
- R / t is 1.5 or less in the range of 980 MPa or more and less than 1180 MPa, 2.5 or less in the range of 1180 MPa or more and less than 1320 MPa of TS, and 3.5 or less in the range of 1320 MPa or more and less than 1600 MPa
- TS was 5.0 or less in the range of 1600 MPa or more and less than 2100 MPa.
- the desired TS or the bendability is not obtained.
- the use of the high strength steel plate of the present invention for automobile parts application can greatly contribute to the improvement of the collision safety and the fuel consumption of a car.
Abstract
Description
(273+T)×(20+log10(t))≧6800 (1)
但し、Tは温度(℃)で200℃以下、tは時間(hr)である。
(273+T)×(20+log10(t))≧6800 (1)
但し、Tは温度(℃)で200℃以下、tは時間(hr)である。
Cは、マルテンサイトやベイナイト等を生成させてTSを上昇させるのに有効な元素である。C含有量が0.05%未満ではこのような効果が十分得られず、980MPa以上のTSが得られない。そこで、C含有量は0.05%以上とする。好ましくは0.07%以上、より好ましくは0.09%以上、さらに好ましくは0.11%以上である。一方、C含有量が0.40%を超えるとマルテンサイトが硬化して曲げ性の劣化が顕著になる。したがって、C含有量は0.40%以下とする、好ましくは0.37%以下、より好ましくは0.35%以下、さらに好ましくは0.32%以下とする。
Siは、鋼を固溶強化してTSを上昇させるのに有効な元素である。また、Siを含む酸化物は水素のトラップに有効である。Siを含む酸化物による上記効果を得るにはSi含有量を0.10%以上にする。好ましくは0.20%以上、より好ましくは0.30%以上、さらに好ましくは0.40%以上である。Si含有量が3.0%を超えると鋼が脆化して曲げ性の劣化が顕著になる。したがって、Si含有量は3.0%以下とする。好ましくは2.5%以下、より好ましくは2.0%以下、さらに好ましくは1.8%以下である。
Mnは、マルテンサイトやベイナイト等を生成させてTSを上昇させるのに有効な元素である。Mn含有量が1.5%未満ではこうした効果が十分得られず、980MPa以上のTSが得られない。そこで、Mn含有量は1.5%以上とする。好ましくは1.8%以上、より好ましくは2.0%以上、さらに好ましくは2.2%以上である。一方、Mn含有量が4.0%を超えると鋼が脆化して本発明の曲げ性が得られない。そこで、Mn含有量は4.0%以下とする。好ましくは3.8%以下、より好ましくは3.6%以下、さらに好ましくは3.4%以下とする。
Pは、粒界を脆化させて曲げ性を劣化させるため、その量は極力低減することが望ましいが、本発明では0.100%まで許容できる。好ましくは0.050%以下である。下限は特に規定しないが、0.001%未満では生産能率の低下を招くため、生産能率の観点からは0.001%以上が好ましい。
Sは、介在物を増加させて曲げ性を劣化させるため、その含有量は極力低減することが好ましいが、本発明ではS含有量を0.02%まで許容できる。好ましくは0.01%以下である。下限は特に規定しないが、0.0005%未満では生産能率の低下を招くため、生産能率の観点からは0.0005%以上が好ましい。
Alは、脱酸剤として作用し、脱酸工程で添加することが好ましい。そこで、Al含有量を0.010%以上とする。好ましくは0.015%以上である。Alを多量に含有すると軟質なフェライト相が多量に生成してTSの低下を招く。本発明では1.0%まで許容される。好ましくは0.50%以下とする。
Nが0.010%を超えると粗大窒化物を生じて曲げ性が劣化する。したがって、Nは0.010%以下とする。下限は特に規定しないが、0.0005%未満では生産能率の低下を招くため、生産能率の観点からは0.0005%以上が好ましい。
Cr、Cu、Niはマルテンサイトやベイナイトを生成させ、高強度化に有効な元素である。このような効果を得るにはそれぞれ0.005%以上とすることが好ましい。より好ましくは0.010%以上、さらに好ましくは0.050%以上である。一方、Cr、Cu、Niのそれぞれの含有量が2.0%を超えると、残留オーステナイトが多量に残存して曲げ性がやや劣化する。そこで、これらの元素の含有量は2.0%以下が好ましい。より好ましくは1.5%以下、さらに好ましくは1.0%以下である。
下部ベイナイト、マルテンサイトおよび残留オーステナイトの合計面積率が40%未満では980MPa以上のTSが得られない。したがって、上記の合計面積率は40~100%、好ましくは45~100%、より好ましくは50~100%とする。なお、マルテンサイトには焼き入れままマルテンサイトと焼き戻しマルテンサイトの両方を含む。また、下部ベイナイトとは方位の揃った炭化物を含むベイナイトを意味し、焼き戻しベイナイトを含むものとする。
残留オーステナイトは曲げ加工時にマルテンサイト変態して亀裂の発生を助長し、組織全体に対する面積率が15%を超えると顕著になる。したがって、残留オーステナイトの面積率は15%以下、好ましくは10%以下、より好ましくは8%以下とする。残留オーステナイトの面積率の下限は特に限定されず、0%でもよいが、1%以上が好ましく、より好ましくは2%以上である。
上部ベイナイトおよびフェライトの合計面積率が60%を超えると980MPa以上のTSが得られない。したがって、上部ベイナイトおよびフェライトの合計面積率は0~60%、好ましくは0~50%、より好ましくは0~45%とする。特に高強度鋼では少ない方が曲げ性に好ましく、TSが1320MPa以上1600MPa未満の範囲では合計面積率10%以下、TSが1600MPa以上2100MPa未満の範囲では合計面積率3%以下が好ましい。また、上部ベイナイトとは方位の揃った炭化物を含まないベイナイトを意味する。
アスペクト比が大きい伸展フェライト相は曲げ加工時の割れを助長し、曲げ性を劣化させる。このような効果を抑制するには、アスペクト比が3以上の伸展フェライト相を、組織全体に対して面積率で1%以下とする必要がある。したがって、アスペクト比が3以上の伸展フェライト相の面積率は1%以下とする。
本発明の鋼組織は、その他の組織を合計面積率で5%以下含有してもよい。その他の組織としてはパーライト等が挙げられる。
曲げ加工時に微小亀裂を生じるのは鋼板表面から50μmまでの領域(表層や鋼板表層という場合がある)が主体であり、鋼板表面から50μmまでの領域におけるマルテンサイトの平均結晶粒径を20μm以下とすることで曲げ加工時の微小亀裂が抑制され、本発明の曲げ性が得られる。したがって、鋼板表面から50μmまでの領域におけるマルテンサイトの平均結晶粒径は20μm以下とする。下限については特に限定されないが、1μm以上になることが多い。
鋼板表面から50μmまでの領域における短軸長が1.0μmを超える粗大酸化物が1.0×108個/m2以下
鋼板表面から50μmまでの領域における短軸長が0.8μm以下の酸化物が1.0×1010個/m2未満では本発明の曲げ性が得られない。一方、短軸長が1.0μmを超える酸化物が1.0×108個/m2を超えると曲げ性を劣化させる。したがって、鋼板表面から50μmまでの領域における酸化物は1.0×1010個/m2以上、好ましくは100.0×1010個/m2以上とし、短軸長が1.0μmを超える酸化物は1.0×108個/m2以下、より好ましくは1.0×107個/m2以下とする。なお、鋼板表面に皮膜を有する場合は地鉄と皮膜との界面を鋼板表面とする。また、本発明における酸化物は主にFe、Si、Mn、Al、Mg、Ti等の単体または複合酸化物である。上限については特に限定されないが500.0×1010個/m2以下になることが多い。なお、鋼板表面から50μmまでの領域における短軸長が0.8μm超1.0μm未満の酸化物は、本発明の効果に大きな影響を与えない。
鋼板内トラップ水素量が0.05質量ppm未満では本発明の曲げ性が得られない。したがって、鋼板内トラップ水素量は0.05質量ppm以上、好ましくは0.07質量ppm以上とする。なお、本発明においてトラップ水素とは、200℃/hrで昇温脱離させた際に、350℃以上で脱離する水素である。350~600℃で脱離する水素を0.05質量ppm以上とすることが特に好ましく、より好ましくは450~600℃で脱離する水素を0.05質量ppm以上とする。上限は特に限定されないが、鋼板内トラップ水素が、1.00質量ppm以下であることが多い。曲げ加工前に、鋼板内トラップ水素量を0.05質量ppm以上とすることが必要であるが、曲げ加工後の製品において、非曲げ加工部の鋼板内トラップ水素が0.05質量ppm以上であれば、曲げ加工部の鋼板内トラップ水素が0.05質量ppm以上であったとみなせる。
圧延方向に対して平行方向を曲げ試験軸方向とする、幅が30mm、長さが100mmの短冊形の試験片を採取し、曲げ試験を行う。ストローク速度が50mm/s、押込み荷重が10ton、押付け保持時間5秒、90°V曲げ試験を行い、曲げ頂点の稜線部を10倍の拡大鏡で観察し、亀裂長が0.5mm以上の亀裂が認められなくなる最小曲げ半径を求める。
本発明の高強度鋼板の製造方法は、上記の成分組成を有するスラブを加熱し、粗圧延後、15MPa以上の圧力でデスケーリング処理し、800~950℃で仕上げ圧延を施し、仕上げ圧延後冷却して550℃以下で巻取り熱延板を得る熱延工程と、必要に応じて行う、20%以上の圧下率で冷間圧延を施して冷延板を得る冷延工程と、730~950℃に加熱し、この温度域で水素濃度1.0~35.0体積%かつ露点-35~15℃の雰囲気中で10~1000s保持する焼鈍工程と、その後600℃まで平均5℃/s以上で冷却し、Ms超~600℃で冷却停止し、Ms超~600℃の温度域で1000s以下滞留させ、その後Ms~50℃の温度域を平均1.0℃/s以上で室温まで冷却する冷却工程と、その後0.05~1%の伸長率で圧延を施す伸長圧延工程と、以下の式を満たす条件で時効処理を施す時効処理工程とを有する。
(273+T)×(20+log10(t))≧6800、 T≦200
但し、Tは温度(℃)、tは時間(hr)である。
デスケーリング圧力が15MPa未満となると、スケールが残留し、巻取り後の冷却中にスケールからの酸素供給によって鋼板表層に粗大酸化物が生成しやすくなり、曲げ性を劣化させる。したがって、デスケーリング圧力は15MPa以上とする。上限は特に限定されないが75MPa以下が好ましい。
仕上げ圧延温度が800℃未満ではフェライトが生成して、伸展フェライトが熱延板の表層に生成し、焼鈍後も残留してアスペクト比3以上の伸展フェライト粒となり曲げ性が劣化する。また、950℃を超えると表層でのマルテンサイトの平均粒子径が大きくなり曲げ性が劣化する。したがって、仕上げ圧延温度は800~950℃とする。下限について好ましくは830℃以上である。上限について好ましくは920℃以下である。
巻取り温度が550℃を超えると鋼板表層に短軸長が0.8μmを超える酸化物が生成して、本発明の曲げ性が得られない。したがって、巻取り温度は550℃以下、好ましくは500℃以下とする。下限は特に規定しないが、形状安定性等の観点から250℃以上が好ましい。
冷間圧延は必須ではない。本発明では冷間圧延を施す場合は、圧下率を20%以上とする必要がある。20%未満では焼鈍時に粗大な伸展フェライトが生じて、曲げ性が劣化する。したがって、冷間圧延を施す場合はその圧下率を20%以上、好ましくは30%以上とする。上限は特に規定しないが、形状安定性等の観点からは90%以下が好ましい。
焼鈍は、冷間圧延を行わない場合は熱延鋼板に対して行い、冷間圧延を行う場合には冷延鋼板に対して行う。焼鈍温度が730℃未満ではオーステナイトの生成が不十分となる。焼鈍により生成したオーステナイトはベイナイト変態やマルテンサイト変態により最終組織におけるマルテンサイトあるいはベイナイトとなるため、オーステナイトの生成が不十分になると、所望の鋼組織が得られなくなる。一方、950℃を超えると粗粒を生じ、この場合も所望の鋼組織が得られない。したがって、焼鈍温度は730~950℃とする。下限について好ましくは750℃以上である。上限について好ましくは930℃以下である。
焼鈍保持時間が10s未満では、オーステナイトの生成が不十分となり、所望の鋼組織、またはトラップ水素量が得られない。一方、1000sを超えると粗粒が生じて本発明のミクロ組織が得られない。したがって、焼鈍保持時間は10~1000sとする。下限について好ましくは30s以上とする。上限について好ましくは500s以下とする。なお、本発明において焼鈍保持時間とは上記焼鈍温度域での滞留時間であり、必ずしも一定保持である必要はなく、730~950℃の範囲での加熱、冷却状態も含む。
730~950℃の温度域における雰囲気中水素濃度が1.0体積%未満では、所望のトラップ水素量が得られない。一方、35.0体積%を超えると、水素脆化により操業中の鋼板破断のリスクが大きくなる。したがって、730~950℃の温度域における雰囲気中の水素濃度は1.0~35.0体積%とする。下限について好ましくは4.0体積%以上である。上限について好ましくは32.0体積%以下とする。
730~950℃の温度域における露点が-35℃未満となると内部酸化が不十分となる。一方、15℃を超えると、ピックアップを生じて操業安定性を阻害する。したがって、730~950℃の温度域における露点は-35~15℃、下限について好ましくは-30℃以上である。上限について好ましくは5℃以下である。
焼鈍温度から600℃までの平均冷却速度が5℃/s未満ではポリゴナルフェライトが過剰に生成して本発明のミクロ組織が得られない。したがって、焼鈍温度から600℃までの平均冷却速度は5℃/s以上、好ましくは8℃/s以上とする。上限は特に限定されないが1500℃/s以下が好ましい。
冷却停止温度がMs以下では焼戻しマルテンサイトを生じて、TSの低下や曲げ性の劣化を招く。一方、600℃を超えるとポリゴナルフェライトが過剰に生成して、所望の鋼組織が得られない。したがって、冷却停止温度はMs超600℃以下とする。下限について好ましくは440℃以上である。上限について好ましくは560℃以下とする。
Ms~600℃での滞留時間が1000sを超えると、フェライト変態やベイナイト変態の進行が過剰になり、あるいはパーライトが過剰に生成して所望の鋼組織が得られないか、トラップ水素量が少なくなり曲げ性が劣化する。したがって、Ms~600℃での滞留時間は1000s以下、好ましくは500s以下、より好ましくは200s以下とする。下限について好ましくは5s以上、より好ましくは10s以上である。なお、加熱後に所望の温度まで加熱後に滞留させてもよい。
Ms~50℃の温度域の平均冷却速度が1.0℃/s未満となると水素が放散されて所望のトラップ水素量が得られなくなる。したがって、Ms~50℃の温度域の平均冷却速度は1.0℃/s以上とする。上限については1500℃/s以下が好ましい。本冷却の冷却停止温度は室温である。室温とは15~25℃を意味する。
伸長圧延の伸長率が0.05%未満では、所望のトラップ水素量が得られない。一方、伸長率が1%を超えると表層の酸化物が剥落する恐れがある。したがって、伸長圧延の伸長率は0.05~1%とする。下限について好ましくは0.10%以上である。上限について好ましくは0.7%以下、より好ましくは0.5%以下とする。
伸長圧延後の時効処理条件が上記を満たすことで、鋼中酸化物に水素がトラップされて、所望のトラップ水素量が得られる。上記条件を外れると、水素のトラップ状態が変化して本発明の曲げ性が得られない。したがって、伸長圧延後の時効処理は(273+T)×(20+log10(t))≧6800、T≦200を満たすものとする。但し、Tは温度(℃)、tは時間(hr)とする。
焼鈍板より圧延方向に対して直角方向にJIS5号引張試験片(JIS Z2201)を採取し、歪速度が10-3/sとするJIS Z 2241(1998)の規定に準拠した引張試験を行い、TSを求めた。なお、本発明では980MPa以上を合格とした。
焼鈍板より圧延方向に対して平行方向を曲げ試験軸方向とする、幅が30mm、長さが100mmの短冊形の試験片を採取し、曲げ試験を行った。ストローク速度が50mm/s、押込み荷重が10ton、押付け保持時間5秒、90°V曲げ試験を行い、曲げ頂点の稜線部を10倍の拡大鏡で観察し、亀裂長が0.5mm以上の亀裂が認められなくなる最小曲げ半径を求めた。最小曲げ半径Rの板厚tに対する比(R/t)を算出し、この比(R/t)によって曲げ性を評価した。
焼鈍板より長さが30mm、幅が5mmの試験片を採取し、めっき層をアルカリ除去後、トラップ水素量および水素の放出ピークの測定を行った。測定は昇温脱離分析法とし、昇温速度は200℃/hrとした。室温から800℃まで連続加熱後、室温まで冷却し、再度800℃まで昇温速度200℃/hrで加熱した。1回目と2回目の加熱の水素放出の差分を水素放出量とし、このうち350~600℃で検出された水素をトラップ水素とした。結果を表3に示した。
Claims (10)
- 質量%で、
C:0.05~0.40%、
Si:0.10~3.0%、
Mn:1.5~4.0%、
P:0.100%以下(0%は除く)、
S:0.02%以下(0%は除く)、
Al:0.010~1.0%、
N:0.010%以下を含み、残部がFeおよび不可避的不純物からなる成分組成と、
面積率で、下部ベイナイト、マルテンサイトおよび残留オーステナイトを合計で40~100%、残留オーステナイトを15%以下、上部ベイナイトおよびフェライトを合計で0~60%を含む鋼組織と、を有し、
前記鋼組織において、アスペクト比が3以上の伸展フェライト相が面積率で1%以下、鋼板表面から50μmまでの領域におけるマルテンサイトの平均結晶粒径が20μm以下、鋼板表面から50μmまでの領域における短軸長が0.8μm以下の酸化物が1.0×1010個/m2以上であり、鋼板表面から50μmまでの領域における短軸長が1.0μmを超える粗大酸化物が1.0×108個/m2以下であり、
鋼板内トラップ水素量が0.05質量ppm以上である高強度鋼板。 - さらに、質量%で、
Cr:0.005~2.0%、
Ti:0.005~0.20%、
Nb:0.005~0.20%、
Mo:0.005~2.0%、
V:0.005~2.0%、
Ni:0.005~2.0%、
Cu:0.005~2.0%、
B:0.0001~0.0050%、
Ca:0.0001~0.0050%、
REM:0.0001~0.0050%、
Sn:0.01~0.50%、
Sb:0.0010~0.10%から選ばれる1種以上を含む請求項1に記載の高強度鋼板。 - 表面に1以上の層から構成される皮膜を有する請求項1または2に記載の高強度鋼板。
- 表面に亜鉛めっき層を有する請求項1または2に記載の高強度鋼板。
- 表面に合金化溶融亜鉛めっき層を有する請求項1または2に記載の高強度鋼板。
- 請求項1または2に記載の成分を有するスラブを粗圧延後15MPa以上の圧力でデスケーリング処理し、800~950℃で仕上げ圧延を施し、仕上げ圧延後冷却して550℃以下で巻き取る熱延工程と、
前記熱延工程で得られた熱延板を、730~950℃に加熱し、この温度域で水素濃度1.0~35.0体積%かつ露点-35~15℃の雰囲気中で10~1000sの条件で保持する焼鈍工程と、
前記焼鈍工程後の鋼板を、その後600℃まで平均5℃/s以上で冷却し、Ms超600℃以下で冷却停止し、Ms超~600℃の温度域で1000s以下滞留させ、該滞留後Ms~50℃の温度域を平均冷却速度が1.0℃/s以上の条件で室温まで冷却する冷却工程と、
前記冷却工程後の鋼板を、0.05~1%の伸長率で圧延する伸長圧延工程と、
前記伸長圧延工程後の鋼板を、下記の式(1)を満たす条件で時効処理する時効処理工程と、を有する高強度鋼板の製造方法。
(273+T)×(20+log10(t))≧6800 (1)
但し、Tは温度(℃)で200℃以下、tは時間(hr)である。 - 請求項1または2に記載の成分を有するスラブを粗圧延後15MPa以上の圧力でデスケーリング処理し、800~950℃で仕上げ圧延を施し、仕上げ圧延後冷却して550℃以下で巻き取る熱延工程と、
前記熱延工程で得られた熱延板を、20%以上の圧下率で冷間圧延する冷延工程と、
前記冷延工程で得られた冷延板を、730~950℃に加熱し、この温度域で水素濃度1.0~35.0体積%かつ露点-35~15℃の雰囲気中で10~1000sの条件で保持する焼鈍工程と、
前記焼鈍工程後の鋼板を、その後600℃まで平均5℃/s以上で冷却し、Ms超600℃以下で冷却停止し、Ms超~600℃の温度域で1000s以下滞留させ、該滞留後Ms~50℃の温度域を平均冷却速度が1.0℃/s以上の条件で室温まで冷却する冷却工程と、
前記冷却工程後の鋼板を、0.05~1%の伸長率で圧延する伸長圧延工程と、
前記伸長圧延工程後の鋼板を、下記の式(1)を満たす条件で時効処理する時効処理工程と、を有する高強度鋼板の製造方法。
(273+T)×(20+log10(t))≧6800 (1)
但し、Tは温度(℃)で200℃以下、tは時間(hr)である。 - 前記焼鈍工程後のいずれかの工程中において皮膜付与処理を行う請求項6または7に記載の高強度鋼板の製造方法。
- 前記冷却工程において、亜鉛めっき処理を行う請求項6または7に記載の高強度鋼板の製造方法。
- 前記亜鉛めっき処理後にさらに合金化処理を行う請求項9に記載の高強度鋼板の製造方法。
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JP7482231B2 (ja) | 2019-12-31 | 2024-05-13 | 宝山鋼鉄股▲分▼有限公司 | 低炭素低コスト超高強度多相鋼板/鋼帯およびその製造方法 |
WO2022230401A1 (ja) * | 2021-04-27 | 2022-11-03 | 日本製鉄株式会社 | 鋼板及びめっき鋼板 |
WO2022230400A1 (ja) * | 2021-04-27 | 2022-11-03 | 日本製鉄株式会社 | 鋼板及びめっき鋼板 |
WO2022230399A1 (ja) * | 2021-04-27 | 2022-11-03 | 日本製鉄株式会社 | 鋼板及びめっき鋼板 |
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CN111527224B (zh) | 2021-11-05 |
CN111527224A (zh) | 2020-08-11 |
MX2020006763A (es) | 2020-08-24 |
EP3715493A4 (en) | 2020-11-25 |
JP6562180B1 (ja) | 2019-08-21 |
JPWO2019130713A1 (ja) | 2019-12-26 |
US20210062282A1 (en) | 2021-03-04 |
KR20200093002A (ko) | 2020-08-04 |
US11492677B2 (en) | 2022-11-08 |
KR102416655B1 (ko) | 2022-07-06 |
EP3715493A1 (en) | 2020-09-30 |
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