WO2022185991A1 - 鋼板 - Google Patents
鋼板 Download PDFInfo
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- WO2022185991A1 WO2022185991A1 PCT/JP2022/007131 JP2022007131W WO2022185991A1 WO 2022185991 A1 WO2022185991 A1 WO 2022185991A1 JP 2022007131 W JP2022007131 W JP 2022007131W WO 2022185991 A1 WO2022185991 A1 WO 2022185991A1
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- Prior art keywords
- less
- rolling
- steel sheet
- content
- steel plate
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 87
- 239000010959 steel Substances 0.000 title claims abstract description 87
- 239000002344 surface layer Substances 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 239000000126 substance Substances 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 238000005096 rolling process Methods 0.000 claims description 68
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 7
- 229910052787 antimony Inorganic materials 0.000 claims description 4
- 229910052718 tin Inorganic materials 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 abstract 1
- 229910052757 nitrogen Inorganic materials 0.000 abstract 1
- 229910052698 phosphorus Inorganic materials 0.000 abstract 1
- 230000009467 reduction Effects 0.000 description 57
- 238000001816 cooling Methods 0.000 description 35
- 238000012360 testing method Methods 0.000 description 33
- 238000005452 bending Methods 0.000 description 27
- 230000000694 effects Effects 0.000 description 19
- 229910000859 α-Fe Inorganic materials 0.000 description 15
- 229910001566 austenite Inorganic materials 0.000 description 13
- 229910000734 martensite Inorganic materials 0.000 description 13
- 238000000034 method Methods 0.000 description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 12
- 239000013078 crystal Substances 0.000 description 11
- 238000005098 hot rolling Methods 0.000 description 11
- 230000006872 improvement Effects 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 8
- 229910001563 bainite Inorganic materials 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 150000002910 rare earth metals Chemical class 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 238000004804 winding Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 238000005266 casting Methods 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000001953 recrystallisation Methods 0.000 description 3
- 229910004283 SiO 4 Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910001567 cementite Inorganic materials 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 235000019362 perlite Nutrition 0.000 description 1
- 239000010451 perlite Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000000988 reflection electron microscopy Methods 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000010301 surface-oxidation reaction Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
- 229910052727 yttrium 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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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
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2201/00—Treatment for obtaining particular effects
- C21D2201/05—Grain orientation
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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 steel sheets.
- Patent Document 1 the average value of the X-ray random intensity ratio of the ⁇ 100 ⁇ ⁇ 011> to ⁇ 223 ⁇ ⁇ 110> orientation group of the plate surface at 1/2 plate thickness is 3.0 or more, and The average value of the X-ray random intensity ratios of the three crystal orientations ⁇ 554 ⁇ ⁇ 225>, ⁇ 111 ⁇ ⁇ 112>, and ⁇ 111 ⁇ ⁇ 110> is 3.5 or less, and r in the rolling direction A ferritic thin steel sheet is disclosed in which at least one of the r-value and the r-value in the direction perpendicular to the rolling direction is 0.7 or less.
- Patent Document 2 discloses a cold-rolled steel sheet having an X-ray random intensity ratio of (111)//ND of 3 or more and an X-ray random intensity ratio of (100)//ND of 1 or less.
- An object of the present invention is to solve the above problems and to provide a steel sheet having high tensile strength, low bending anisotropy, and excellent bendability.
- the present invention has been made to solve the above problems, and the gist thereof is the following steel plate.
- the chemical composition, instead of part of the Fe, is mass %, Containing 0.100% or less in total of one or more selected from Sn, Sb and Te,
- the inventors of the present invention conducted studies and experiments on methods for reducing the bending anisotropy of high-strength steel sheets with a tensile strength of 780 MPa or more, and found the following findings.
- the present inventors further investigated methods for suppressing the generation of shear bands in the surface layer of the steel sheet, and found that control of the texture in the surface layer of the steel sheet is extremely effective.
- conventionally only the texture inside the steel sheet has received attention, but the present inventors have found that the texture in the surface layer of the steel sheet has a great effect on the occurrence of cracks in the bending test.
- C 0.05-0.25% C is an element necessary for ensuring strength. If the C content is less than 0.05%, a tensile strength of 780 MPa or more cannot be obtained. On the other hand, if the C content exceeds 0.25%, the martensite is excessively hardened, degrading toughness and impairing weldability. Therefore, the C content should be 0.05 to 0.25%.
- the C content is preferably 0.07% or more or 0.09% or more, preferably 0.22% or less, 0.20% or less or 0.18% or less, and 0.15% or less It is more preferable to have
- Si 0.2-2.0%
- Si is an element that contributes to strength improvement.
- Si has the effect of forming Fe 2 SiO 4 having a low melting point on the surface of the steel sheet and acting to reduce the bending anisotropy of the texture of the surface layer developed by hot rolling.
- the Si content should be 0.2 to 2.0%.
- the Si content is preferably 0.3% or more or 0.5% or more and preferably 1.8% or less, 1.5% or less or 1.3% or less.
- Mn 1.2-3.0%
- Mn has the effect of stabilizing austenite, facilitating the formation of a low-temperature transformation phase, and contributing to ensuring strength.
- the Mn content should be 1.2 to 3.0%.
- the Mn content is preferably 1.5% or more or 1.7% or more and preferably 2.8% or less, 2.5% or less or 2.2% or less.
- P 0.030% or less P has the effect of increasing the strength, so it may be positively included. However, if it is contained excessively, embrittlement occurs due to grain boundary segregation.
- the P content is preferably 0.025% or less, more preferably 0.020% or less. There is no need to set a lower limit on the P content, and it may be 0%. However, excessive reduction causes an increase in manufacturing costs, so the P content is preferably 0.001% or more. In addition, in the steelmaking stage, about 0.010% of impurity level is usually mixed.
- S 0.050% or less S forms sulfide-based inclusions and lowers elongation, so the content is suppressed to 0.050% or less.
- the S content is preferably 0.0080% or less, more preferably 0.0030% or less. There is no need to set a lower limit on the S content, and it may be 0%. However, excessive reduction causes an increase in manufacturing costs, so the S content is preferably 0.0005% or more or 0.0010% or more.
- Al 0.01-0.55%
- Al is an element used for deoxidation.
- an excessive content makes stable continuous casting difficult. Therefore, the Al content is set to 0.01 to 0.55%.
- austenite at high temperatures becomes unstable, and it becomes necessary to excessively raise the finish rolling temperature in hot rolling. It is preferably 45% or less, 0.40% or less, 0.30% or less, or 0.20% or less.
- Al content means content of acid-soluble Al (sol.Al).
- the total content of Al and Si is preferably 1.0% or more.
- N 0.0100% or less
- N is an element that reduces elongation, so its content is made 0.0100% or less.
- the N content is preferably 0.0060% or less or 0.0040% or less. There is no need to set a lower limit on the N content, and it may be at the impurity level. Generally, about 0.0020% is mixed in at the steelmaking stage.
- Ti 0.010-0.250%
- Ti precipitates as a carbide in the structure of the hot-rolled sheet and contributes to strength improvement. Furthermore, it is an element that contributes to the improvement of toughness by suppressing coarsening of austenite crystal grains. Particularly in the present invention, finish rolling at a high temperature is essential in order to control the texture of the surface layer portion as described later. In order to suppress the coarsening of crystal grains caused by this, it is necessary to utilize the above effect. In addition, by improving the strength of ferrite, the difference in hardness from the hard second phase is reduced, contributing to the improvement of bendability. On the other hand, when it is contained excessively, coarse carbides or nitrides are formed during furnace heating before hot rolling, and elongation is lowered. Therefore, the Ti content should be 0.010 to 0.250%. The Ti content is preferably 0.030% or more or 0.050% or more, and preferably 0.200% or less or 0.150% or less.
- the steel sheet of the present invention in addition to the above elements, one selected from Cr, Ni, Cu, Nb, V, Zr, Mo, W, Sn, Sb, Te, Ca, Mg, REM and B
- the above elements may be contained.
- Ni 0.50% or less
- Cu 0.50% or less Cr
- Ni and Cu have the effect of increasing hardenability and effectively forming martensite and/or bainite. , may be included as necessary.
- the content of each of these elements is set to 0.50% or less.
- the content of any element is preferably 0.45% or less, 0.40% or less, or 0.35% or less.
- Nb 0.040% or less Nb precipitates as carbides or nitrides, suppresses recrystallization and coarsening of austenite, and has the effect of suppressing toughness deterioration of the weld zone. Therefore, it may be contained as necessary.
- an excessive Nb content excessively raises the recrystallization temperature of austenite, making it difficult to control the texture in the surface layer portion.
- the Nb content is preferably 0.035% or less or 0.030% or less. To obtain the above effects, the Nb content is preferably 0.010% or more, 0.015% or more, or 0.020% or more.
- V 0.15% or less
- Mo 0.15% or less
- W 0.15% or less
- the content of each of these elements should be 0.15% or less, preferably 0.12% or less.
- One or More Selected from Sn, Sb and Te 0.100% or Less in Total
- it may be contained as necessary. However, if they are contained excessively, they will segregate at grain boundaries and lower the toughness. In order to obtain the above effect, the total content of these elements is preferably 0.005% or more or 0.010% or more.
- Ca, Mg and REM total 0.0050% or less
- Ca, Mg and REM rare earth metal
- REM refers to 17 elements of Sc, Y and lanthanides.
- the REM content means the total content of these elements.
- REMs are industrially added in the form of misch metals.
- B 0.0050% or less B segregates at grain boundaries and strengthens the steel, thereby contributing to the improvement of the toughness of the steel sheet.
- the B content is preferably 0.0040% or less, more preferably 0.0020% or less.
- the content is preferably 0.0005% or more, 0.0007% or more, or 0.0010% or more.
- the balance is Fe and impurities.
- impurities refers to components that are mixed in with raw materials such as ores, scraps, etc., and various factors in the manufacturing process when steel is manufactured industrially. means something
- (B) Texture of steel sheet surface layer Random strength ratio: 8.0 or less ⁇ 110 ⁇ Minimum angle between the maximum strength orientation of the pole figure and the normal direction of the steel sheet rolled surface: 10 ° or less
- the steel sheet surface layer By controlling the texture in the part, the formation of shear bands, which is a precursor to cracking on the outer bending ridge, can be suppressed. Therefore, specifically, in the texture of the surface layer of the steel sheet, the random strength ratio is set to 8.0 or less, and the minimum angle formed by the maximum strength orientation of the ⁇ 110 ⁇ pole figure and the normal direction of the rolled surface of the steel sheet is set to 10° or less.
- the steel sheet surface portion means a region from the steel sheet surface to 200 ⁇ m in the depth direction.
- the random strength ratio of the texture in the surface layer of the steel sheet is preferably 7.0 or less, more preferably 5.0 or less.
- the minimum angle between the maximum strength direction of the ⁇ 110 ⁇ pole figure and the normal direction of the steel sheet rolling surface is preferably 7.5° or less.
- the random strength ratio of the texture in the surface layer of the steel sheet and the minimum angle between the maximum strength orientation of the ⁇ 110 ⁇ pole figure and the normal direction of the steel sheet rolled surface are measured by the following procedure. First, a cross-section parallel to the rolling direction and thickness direction of the steel sheet is revealed, and an area of 600 ⁇ m in the rolling direction and 200 ⁇ m from the surface in the thickness direction is separated by 0.5 ⁇ m by the electron beam backscatter diffraction (SEM-EBSD) method. to measure the crystal orientation.
- SEM-EBSD electron beam backscatter diffraction
- the sample symmetry is assumed to be a monoclinic system in which the cross section in the rolling direction-plate thickness direction is a mirror plane, and the ODF is obtained by the spherical harmonic expansion method with a half width of 5 degrees.
- the random intensity ratio of the crystal orientation is calculated at intervals of 5 degrees in the Euler space, and the largest random intensity ratio among them is obtained.
- the sample symmetry is set to a monoclinic system with the cross section in the rolling direction-plate thickness direction as a mirror plane, and the half width is 5 degrees.
- the ⁇ 110 ⁇ pole point The angle formed by the direction of maximum strength and the normal direction of the rolled surface, that is, the center point on the ⁇ 110 ⁇ pole figure is obtained.
- Test No. of Examples described later. 24 is a comparative example made by a method that deviates from suitable conditions.
- Test no. No. 24 steel plate was calculated assuming that the sample symmetry was a cubic system. Satisfied.
- the random intensity ratio is 8.2
- the angle formed by the center point on the ⁇ 110 ⁇ pole figure is 10 °, which is out of the scope of the present invention. This result also shows that the texture of the surface layer may not be correctly evaluated unless the method according to the present invention is used.
- the thickness of the steel plate according to the present invention is not particularly limited. It is preferably 0 mm, more preferably 1.2 to 3.2 mm.
- the metal structure at the center of the plate thickness of the steel plate should be 5 to 40% ferrite, 60 to 95% martensite in total, and It preferably contains bainite and the balance is less than 5%.
- the product of tensile strength and elongation at break is preferably 10000 MPa% or more.
- the product of tensile strength and elongation at break is more preferably 12000 MPa% or more, even more preferably 14000 MPa% or more.
- Ferrite is soft and contributes to the improvement of elongation. Therefore, in order to obtain excellent elongation while ensuring a tensile strength of 780 MPa or more, it is preferable to set the area ratio of ferrite to 5 to 40%.
- the area ratio of ferrite is more preferably 10% or more, more preferably 30% or less, and even more preferably 20% or less.
- the total area ratio of martensite and bainite is preferably 60 to 95%. Furthermore, if the above effects are to be obtained more reliably, the area ratio of martensite is preferably 15% or more or 20% or more. On the other hand, from the viewpoint of ensuring toughness in addition to the above effects, the area ratio of martensite is preferably 80% or less, more preferably 70% or less or 60% or less. In the present invention, martensite includes not only fresh martensite but also tempered martensite.
- the area ratio of the remainder other than ferrite, martensite and bainite is preferably less than 5%.
- Perlite, cementite and retained austenite can be mixed in as the residual structure. From the viewpoint of ensuring uniform elongation, the total area ratio of pearlite and cementite is preferably less than 5%.
- retained austenite is a structure that improves uniform elongation, its area ratio is preferably less than 5% from the viewpoint of ensuring hole expandability.
- a billet to be hot-rolled may be produced by a conventional method. That is, a slab obtained by continuous casting or casting/blooming, or a steel plate obtained by strip casting can be used.
- Hot rolling is performed on the billet. In order to control the texture in the steel sheet surface layer, it is important to adjust the hot rolling conditions. The conditions in the hot rolling process are described in detail below.
- Heating temperature 1050-1300°C
- the heating temperature before hot rolling is set to 1050° C. or higher in order to dissolve Ti in the steel.
- the heating temperature is preferably 1300° C. or lower.
- Effective rolling strain 0.20 to 0.80
- the austenite texture It is possible to suppress the excessive development of , and control the texture of the surface layer after ⁇ - ⁇ transformation. Effective rolling strain will be described below.
- the rolling stress is a value obtained by dividing the rolling load by the product of the projected contact length Ld between the rolls and the steel sheet and the width of the steel sheet.
- the contact projected length Ld is obtained by the following formula (1).
- the rolling strain is the absolute value of the true strain, that is, the effective rolling strain ⁇ eff is obtained by the following formula (2) or (3).
- Finish rolling temperature T SC °C or higher and 920 °C or higher and 1080 °C or lower
- T SC °C or higher and 920 °C or higher shown in the following formula (i)
- the texture in the surface layer of the steel sheet is controlled. It is particularly effective in reducing the minimum angle between the maximum strength direction of the ⁇ 110 ⁇ pole figure and the normal direction of the rolled surface of the steel sheet. The reason for this is not necessarily clear, but it is believed that at T SC °C or higher and 920 °C or higher, Fe 2 SiO 4 generated on the steel plate surface softens, thereby reducing the amount of shear deformation imparted to the steel plate surface.
- the “finish rolling temperature” means the temperature of the steel sheet after the final reduction.
- T SC 965+100 ⁇ ((5 ⁇ P+0.5 ⁇ Al)/Si) 2 ⁇ 170 ⁇ ((5 ⁇ P+0.5 ⁇ Al)/Si) (i)
- the element symbol in the formula represents the content (% by mass) of each element.
- the finish rolling temperature of hot rolling is set to 1080° C. or lower.
- Time between the final reduction and the previous reduction 0.50s or more If the time between the final reduction and the reduction immediately before the final reduction is less than 0.50s, the final reduction and the final There is a high possibility that the temperature difference between the rolling entry side and the roll immediately before the rolling will be less than 15°C. In this case, the strain accumulated in the reduction immediately before the final reduction is likely to be inherited to the final reduction, and the amount of shear deformation imparted to the steel sheet surface increases, and the maximum strength orientation of the ⁇ 110 ⁇ pole figure and the steel sheet rolling The minimum angle with the normal direction of the face increases. In addition, in some cases, the rolling stress at the final reduction may increase, causing rolling troubles.
- the time between the final reduction and the reduction immediately before the final reduction is 0 so that the rolling entry-side temperature of the final reduction is 15 ° C. or more lower than the rolling entry-side temperature of the reduction immediately before the final reduction. .50s or more.
- the time between the final reduction and the reduction immediately before the final reduction is preferably 0.75 s or more.
- the time is preferably 3.0 s or less, more preferably 2.0 s or less.
- Time from finish rolling to start of water cooling 0.50 s or more
- the texture of the surface layer after ⁇ - ⁇ transformation can be controlled. , and is particularly effective in reducing the random intensity ratio. If the time until the start of water cooling is less than 0.50 s, recrystallization of austenite is suppressed, and the austenite texture in the surface layer excessively developed by rolling is inherited by the ⁇ phase after transformation, which reduces bendability. . Therefore, the time from finish rolling to the start of water cooling is set to 0.50 s or longer, preferably 0.80 s or longer.
- the time from finish rolling to the start of water cooling is preferably 3.0 seconds or less, more preferably 1.5 seconds or less.
- Primary cooling rate 15°C/s or more
- the primary cooling rate is preferably 15° C./s or higher, more preferably 30° C./s or higher.
- the primary cooling rate is preferably less than 60° C./s.
- the primary cooling rate is the average cooling rate obtained by dividing the difference between the finish rolling temperature and the primary cooling stop temperature or 500 ° C., whichever is higher, by the time required to cool to the temperature. means
- the steel sheet may be cooled as it is to the coiling temperature described later, but cooling may be stopped in the range of 600 to 680° C. in order to obtain ferrite in the metal structure inside the steel sheet.
- the primary cooling stop temperature is preferably 630° C. or higher.
- a moderate amount of ferrite can be formed by setting the residence time to 2 to 15 seconds. More preferably, the residence time is 5-10 s.
- Secondary cooling rate 10° C./s or more When cooling is stopped at the above primary cooling temperature, secondary cooling is then performed. There are no particular restrictions on the secondary cooling rate. However, the secondary cooling rate is preferably 10° C./s or more. This makes it possible to reduce the structural fractions of pearlite and retained austenite to less than 5%. On the other hand, the secondary cooling rate is preferably 50° C./s or less from the viewpoint of suppressing flatness defects of the steel sheet and improving productivity.
- the secondary cooling rate means an average cooling rate obtained by dividing the difference between the primary cooling stop temperature and the winding temperature by the time required for cooling to that temperature.
- Winding temperature 100-500°C
- the coiling temperature is also not particularly limited, but from the viewpoint of ensuring strength by generating bainite and/or martensite, coiling at a temperature of 500° C. or less is preferable. On the other hand, if the coiling temperature is too low, the flatness of the steel sheet may be poor, which may hinder productivity. Therefore, the winding temperature is preferably 100 to 500°C, more preferably 150 to 450°C.
- ST0 is the entry-side temperature (° C.) in the reduction immediately before the final reduction
- ST1 is the entry-side temperature (° C.) in the final reduction
- FT is the finish rolling temperature (° C.).
- time between passes is the time between the final reduction and the reduction immediately before the final reduction
- time after rolling to the start of water cooling means the time after finish rolling until the start of water cooling.
- a cross-section parallel to the rolling direction and the thickness direction was cut out from the center of the plate thickness of the obtained steel plate, polished to a mirror surface, and then subjected to nital corrosion to reveal the metal structure, which was observed using an SEM. Furthermore, a cross section parallel to the rolling direction and thickness direction of the steel sheet was developed, and the crystal orientation was measured at intervals of 0.5 ⁇ m in a region of 600 ⁇ m in the rolling direction and 200 ⁇ m from the surface in the thickness direction by SEM-EBSD.
- the ODF is obtained by the spherical harmonic expansion method with the sample symmetry as the monoclinic system and the half width of 5 degrees, and the random intensity ratio of the crystal orientation at 5 degree intervals in the Euler space. was calculated, and the largest random intensity ratio among them was obtained.
- the sample symmetry is monoclinic, and the ⁇ 110 ⁇ pole figure is calculated by the spherical harmonic expansion method with the half width of 5 degrees. 110 ⁇ The angle formed by the center point on the pole figure was obtained.
- JIS No. 5 tensile test pieces specified in JIS Z 2241:2011 were taken so that the direction orthogonal to the rolling direction of the steel plate and the longitudinal direction of the test piece were aligned, and the tensile strength was measured according to the same standard.
- the thickness TS and breaking elongation EL were measured and their average values were obtained.
- the bending properties of steel sheets having a TS of 780 MPa or more and a TS ⁇ EL of 10000 MPa% or more were evaluated by the following bending test.
- a strip-shaped test piece was cut out from each steel plate, and after carefully removing burrs, it was subjected to a bending test. The test piece was cut so that the length in the direction along the bending ridge was 20 mm and the length in the direction perpendicular to the bending ridge was 45 mm, and the bending ridge was parallel and perpendicular to the rolling direction.
- Table 3 shows those results.
- the bendability when the bending ridge line of the test piece is parallel to the rolling direction is called L-direction bendability
- the bendability when the test piece is perpendicular to the rolling direction is called C-direction bendability.
- Test No. 21 the finish rolling temperature (FT) was low and the effective rolling strain was too high.
- Test no. In No. 22 the time from finish rolling to the start of water cooling was short, and the effective rolling strain was too high.
- Test No. 24 the time from finish rolling to the start of water cooling was too short. Test no. In 25, the finish rolling temperature (FT) was too low. Test no. In No. 26, the finish rolling temperature was low because the time between the final reduction and the reduction immediately before the final reduction was too long. Test no. In No. 27, the time between the final reduction and the reduction immediately before the final reduction was too short, so the temperature difference on the rolling entry side between the final reduction and the reduction immediately before the final reduction became small. Therefore, in these examples, the surface layer texture could not be controlled, resulting in poor bendability.
- FT finish rolling temperature
- Test No. 28 the Mn content is low. In No. 29, sufficient strength could not be obtained due to the low C content.
- Test no. In No. 32 since the Nb content was excessive, although the manufacturing conditions were appropriate, the surface layer texture could not be controlled, resulting in poor bendability.
- test No. 1 which satisfies all the provisions of the present invention. 1 to 20 had high strength, excellent elongation, excellent bendability, and no bending anisotropy.
- the steel sheet according to the present invention can be suitably used as a material for undercarriage parts of private cars, trucks, and the like.
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Abstract
Description
C:0.05~0.25%、
Si:0.2~2.0%、
Mn:1.2~3.0%、
P:0.030%以下、
S:0.050%以下、
Al:0.01~0.55%、
N:0.0100%以下、
Ti:0.010~0.250%、
残部:Feおよび不純物であり、
鋼板表層部における集合組織のランダム強度比が8.0以下であり、
前記集合組織の{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度が10°以下である、
鋼板。
Cr:0.50%以下、
Ni:0.50%以下、および、
Cu:0.50%以下、
から選択される1種以上を含有する、
上記(1)に記載の鋼板。
Nb:0.040%以下、
V:0.15%以下、
Zr:0.15%以下、
Mo:0.15%以下、および、
W:0.15%以下、
から選択される1種以上を含有する、
上記(1)または(2)に記載の鋼板。
Sn、SbおよびTeから選択される1種以上を、合計で0.100%以下、含有する、
上記(1)から(3)までのいずれかに記載の鋼板。
Ca、MgおよびREMから選択される1種以上を、合計で0.0050%以下、含有する、
上記(1)から(4)までのいずれかに記載の鋼板。
B:0.0050%以下、
を含有する、
上記(1)から(5)までのいずれかに記載の鋼板。
各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「%」は、「質量%」を意味する。
Cは、強度を確保するために必要な元素である。C含有量が0.05%未満では、780MPa以上の引張強さが得られない。一方、C含有量が0.25%を超えると、マルテンサイトが硬化しすぎて靭性が劣化するとともに溶接性を損なう。そのため、C含有量は0.05~0.25%とする。C含有量は0.07%以上または0.09%以上であるのが好ましく、0.22%以下、0.20%以下または0.18%以下であるのが好ましく、0.15%以下であるのがより好ましい。
Siは、強度向上に寄与する元素である。また、Siは、鋼板表面に融点の低いFe2SiO4を形成し、熱間圧延で発達する表層部の集合組織を曲げ異方性が小さくなるよう作用する効果を有する。一方、過剰に含有させると、熱間圧延時に表面酸化の問題が生じる。そのため、Si含有量は0.2~2.0%とする。Si含有量は0.3%以上または0.5%以上であるのが好ましく、1.8%以下、1.5%以下または1.3%以下であるのが好ましい。
Mnは、オーステナイトを安定化して低温変態相を形成させやすくし、強度確保に寄与する効果を有する。一方、過剰に含有させると、フェライトの体積率が低下し伸びが劣化する。そのため、Mn含有量は1.2~3.0%とする。Mn含有量は1.5%以上または1.7%以上であるのが好ましく、2.8%以下、2.5%以下または2.2%以下であるのが好ましい。
Pは、強度を増加させる効果を有するため、積極的に含有させてもよい。しかし、過剰に含有させると、粒界偏析による脆化が生じるため、含有させる場合には、その含有量を0.030%以下とする。P含有量は0.025%以下であるのが好ましく、0.020%以下であるのがより好ましい。P含有量に下限を設ける必要はなく、0%であってもよい。ただし、過剰な低減は製造コストの増加を招くため、P含有量は0.001%以上であるのが好ましい。なお、通常、製鋼段階において、不純物レベルとして0.010%程度混入してくる。
Sは、硫化物系介在物を形成し伸びを低下させるため、その含有量は0.050%以下に抑える。優れた伸びを確保したい場合には、S含有量は0.0080%以下であるのが好ましく、0.0030%以下であるのがより好ましい。S含有量に下限を設ける必要はなく、0%であってもよい。ただし、過剰な低減は製造コストの増加を招くため、S含有量は0.0005%以上または0.0010%以上であるのが好ましい。
Alは、脱酸のため用いられる元素である。しかし、過剰に含有させると、安定した連続鋳造を困難にする。そのため、Al含有量は0.01~0.55%とする。また、Al含有量が高い場合には、高温でのオーステナイトが不安定化し、熱間圧延における仕上圧延温度を過度に上昇させる必要が生じることから、その含有量を0.50%以下、0.45%以下、0.40%以下、0.30%以下、または0.20%以下とすることが好ましい。なお、本発明において、Al含有量は、酸可溶性Al(sol.Al)の含有量を意味する。残留オーステナイトを生成させて伸びを向上させる場合には、Alと前述のSiとの合計含有量を1.0%以上とすることが好ましい。
Nは、伸びを低下させる元素であるため、その含有量は0.0100%以下とする。N含有量は0.0060%以下または0.0040%以下であるのが好ましい。N含有量に下限を設ける必要はなく、不純物レベルであってもよい。通常、製鋼段階で0.0020%程度混入してくる。
Tiは、熱延板組織中に炭化物として析出し、強度向上に寄与する。さらにオーステナイトの結晶粒の粗大化を抑制することで、靭性の向上にも寄与する元素である。特に本発明においては、後述するように表層部の集合組織を制御するため、高温での仕上圧延が必須となる。それによる結晶粒の粗大化を抑制するためにも、上記の効果を活用する必要がある。加えて、フェライトの強度向上により硬質第二相との硬度差を低減し、曲げ性の向上にも寄与する。一方、過剰に含有させると、熱延前の炉加熱時に粗大な炭化物または窒化物を形成し、伸びを低下させる。そのため、Ti含有量は0.010~0.250%とする。Ti含有量は0.030%以上または0.050%以上であるのが好ましく、0.200%以下または0.150%以下であるのが好ましい。
Ni:0.50%以下
Cu:0.50%以下
Cr、NiおよびCuは、焼入れ性を高めて、マルテンサイトおよび/またはベイナイトを効果的に生成させる作用を有するため、必要に応じて含有させてもよい。しかし、過剰に含有させると、フェライトの生成が抑制されるため、それらの元素の含有量をそれぞれ0.50%以下とする。いずれの元素の含有量も0.45%以下、0.40%以下または0.35%以下であるのが好ましい。上記の効果を得たい場合は、上記の元素から選択される1種以上をそれぞれ0.10%以上、0.15%以上または0.20%以上含有させることが好ましい。
Nbは、炭化物または窒化物として析出し、オーステナイトの再結晶および粗大化を抑制し、溶接部の靭性劣化を抑制する効果を有する。そのため、必要に応じて含有させてもよい。しかし、過剰に含有させると、オーステナイトの再結晶温度を過度に上昇させ、表層部における集合組織の制御を困難にするため、Nb含有量は0.040%以下とする。Nb含有量は0.035%以下または0.030%以下であるのが好ましい。上記の効果を得たい場合は、Nb含有量を0.010%以上、0.015%以上または0.020%以上とすることが好ましい。
Zr:0.15%以下
Mo:0.15%以下
W:0.15%以下
V、Zr、MoおよびWは、熱延板組織中に炭化物として析出し、強度向上に寄与する元素である。加えて、フェライトの強度向上により硬質第二相との硬度差を低減し、曲げ性の向上にも寄与するため、必要に応じて含有させてもよい。しかし、過剰に含有させると、粗大な炭化物を形成して伸びを阻害するばかりか、合金コストの増加を招く。それらの元素の含有量をそれぞれ0.15%以下とし、好ましくは0.12%以下とする。上記の効果を得たい場合は、上記の元素から選択される1種以上をそれぞれ0.01%以上、0.03%以上または0.05%以上含有させることが好ましい。
Sn、SbおよびTeは、鋼の表面に偏析し、特に高Si添加鋼の内部酸化層の形成を抑制し、酸洗性の向上に寄与するため、必要に応じて含有させてもよい。しかし、過剰に含有させると、粒界に偏析し靭性を低下させるため、それらの含有量を合計で0.100%以下とし、好ましくは0.050%以下とする。上記の効果を得たい場合は、それらの含有量を合計で0.005%以上または0.010%以上含有させることが好ましい。
Ca、MgおよびREM(希土類金属)は、凝固中に析出する酸化物および窒化物を微細化して、鋳片の健全性を保つ作用を有するため、必要に応じて含有させてもよい。しかし、これらの元素はいずれも高価であるため、それらの含有量を合計で0.0050%以下とし、好ましくは0.0030%以下とする。上記の効果を得たい場合は、それらの含有量を合計で0.0005%以上または0.0010%以上含有させることが好ましい。
Bは、粒界に偏析し、強化することで鋼板の靭性向上に寄与するため、必要に応じて含有させてもよい。しかし、過剰に含有させると、鋳造時において鋼材表面に割れが発生し、生産性を阻害するため、その上限を0.0050%以下とする。B含有量は0.0040%以下であるのが好ましく、0.0020%以下であるのがより好ましい。上記の効果を得たい場合は、0.0005%以上、0.0007%以上または0.0010%以上含有させることが好ましい。
ランダム強度比:8.0以下
{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度:10°以下
上述のように、鋼板表層部における集合組織を制御することで、外側の曲げ稜線上で発生する割れの前駆現象であるせん断帯の形成を抑制することができる。そのため、具体的には、鋼板表層部の集合組織において、ランダム強度比を8.0以下とするとともに、{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度を10°以下とする。なお、本発明において、鋼板表層部とは、鋼板表面から深さ方向へ200μmまでの領域を意味する。
本発明に係る鋼板の厚さについて、特に制限はないが、自家用車およびトラック等の足回り部品の素材として用いる場合には、鋼板の厚さは、1.0~5.0mmであることが好ましく、1.2~3.2mmであることがより好ましい。
本発明においては、上述のように、表層部の集合組織を制御することによって曲げ性を改善することが可能である。そのため、鋼板の板厚中心部における金属組織については特に制限はない。
以下、本発明に係る鋼板の製造方法の一例について詳述する。本発明に係る鋼板は、例えば以下に示す工程を含む製造方法によって得ることができる。
熱間圧延に供する鋼片は常法で製造すればよい。すなわち、連続鋳造もしくは鋳造・分塊により得たスラブ、またはストリップキャスティングにより得た鋼板等を用いることができる。
鋼片に対して、熱間圧延を行う。鋼板表層部における集合組織を制御するためには、熱間圧延条件の調整が重要である。以下に熱間圧延工程における条件に付いて詳述する。
Tiを鋼中に固溶させるため、熱間圧延前の加熱温度は1050℃以上とする。一方、加熱炉の耐久性を鑑みて、加熱温度は1300℃以下とすることが好ましい。
最終圧下、または最終圧下および最終圧下の一つ前の圧下での圧延率を調整し、以下に定義する有効圧延ひずみを0.20~0.80の範囲内とすることで、オーステナイトの集合組織の過度な発達を抑制し、γ-α変態後の表層部の集合組織を制御することが可能となる。以下に、有効圧延ひずみについて説明する。
Ld=√(Rd(hin-hout)) ・・・(i)
Rd:ロール半径
hin:入側板厚
hout:出側板厚
(F1-F0)/F0≧0.18のとき
εeff=|ln(t0/tini)+ln(t1/t0)| ・・・(2)
(F1-F0)/F0<0.18のとき
εeff=|ln(t1/t0)| ・・・(3)
tini:最終圧下の一つ前の圧下における圧下前の板厚
t0:最終圧下の一つ前の圧下における圧下後の板厚
t1:最終圧下における圧下後の板厚
仕上圧延温度を、下記(i)式で示すTSC℃以上かつ920℃以上とすることで、鋼板表層部における集合組織を制御することができ、特に{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度の低減に効果を発揮する。この理由は必ずしも明らかではないが、TSC℃以上かつ920℃以上では、鋼板表面に生じるFe2SiO4が軟化し、それによって鋼板表面に付与されるせん断変形量が小さくなるためと考えられる。ここで、「仕上圧延温度」とは、最終圧下後の鋼板の温度を意味する。
TSC=965+100×((5×P+0.5×Al)/Si)2-170×((5×P+0.5×Al)/Si) ・・・(i)
ただし、式中の元素記号は、各元素の含有量(質量%)を表す。
最終圧下と最終圧下の一つ前の圧下との間の時間が0.50s未満であると、最終圧下と最終圧下の一つ前の圧下との圧延入側の温度差が15℃未満となる可能性が高くなる。この場合、最終圧下の一つ前の圧下でのひずみ累積が最終圧下まで引き継がれやすくなり、鋼板表面に付与されるせん断変形量が増大して、{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度が増大する。それに加えて、場合によっては、最終圧下での圧延応力の増大を招き圧延トラブルの原因となるおそれがある。そのため、最終圧下の圧延入側温度が最終圧下の一つ前の圧下の圧延入側温度より15℃以上低くなるように、最終圧下と最終圧下の一つ前の圧下との間の時間は0.50s以上とする。最終圧下と最終圧下の一つ前の圧下との間の時間は0.75s以上とすることが好ましい。一方、3.0sを超えるとライン速度の大幅な低下を招き、仕上圧延温度をTSC℃以上かつ920℃以上に維持できず、表層集合組織を適切に制御できなくなるおそれがある。このため、上記時間は3.0s以下とするのが好ましく、2.0s以下とするのがより好ましい。
仕上圧延後から水冷開始までの時間を0.50s以上とすることで、γ-α変態後の表層部の集合組織を制御することができ、特にランダム強度比の低減に効果を発揮する。水冷開始までの時間が0.50s未満であると、オーステナイトの再結晶が抑制され、圧延によって過度に発達した表層部のオーステナイトの集合組織が変態後のα相に引き継がれて曲げ性を低下させる。そのため、仕上圧延後、水冷開始までの時間を0.50s以上とし、好ましくは0.80s以上とする。一方、水冷開始までの時間が3.0sを超えると、オーステナイトの粒成長が顕著となり、フェライトの生成量が減少し伸びを損なうおそれがある。そのため、仕上圧延後から水冷開始までの時間は3.0s以下とするのが好ましく、1.5s以下とするのがより好ましい。
仕上圧延後の冷却速度については特に制限はない。しかし、一次冷却速度は、15℃/s以上とするのが好ましく、30℃/s以上とするのがより好ましい。これにより、パーライトの析出および析出物の粗大化を抑制し、強度を向上させることが可能となる。一方、マルテンサイトの過剰な生成を抑制し、フェライトを確保する観点からは、一次冷却速度は、60℃/s未満とすることが好ましい。なお、一次冷却速度とは、仕上圧延温度と、後述する一次冷却停止温度または500℃のいずれか高い方の温度との差を、当該温度まで冷却するのに要した時間で除した平均冷却速度を意味する。
仕上圧延後はそのまま後述する巻取温度まで冷却してもよいが、途中、鋼板内部の金属組織中にフェライトを得る目的で、600~680℃の範囲内で冷却を停止してもよい。より確実にその効果を得るためには、一次冷却停止温度は630℃以上とすることが好ましい。また、この効果を十分に得たい場合は、一次冷却停止温度の範囲内で2~15s滞留させることが好ましい。滞留時間を2~15sとすることで、適度な量のフェライトを形成することができる。滞留時間は5~10sとするのがより好ましい。
上記の一次冷却温度にて冷却を停止した場合には、その後、二次冷却を行う。二次冷却速度については特に制限はない。しかし、二次冷却速度は、10℃/s以上とするのが好ましい。これにより、パーライトおよび残留オーステナイトの組織分率を5%未満に低減することが可能となる。一方、鋼板の平坦不良を抑制して生産性を向上させる観点からは、二次冷却速度は、50℃/s以下とすることが好ましい。なお、二次冷却速度とは、一次冷却停止温度と巻取温度との差を、当該温度まで冷却するのに要した時間で除した平均冷却速度を意味する。
巻取温度:100~500℃
巻取温度についても特に制限はないが、ベイナイトおよび/またはマルテンサイトを生成させて強度を確保する観点からは、500℃以下の温度で巻取ることが好ましい。一方、巻取温度が低すぎると鋼板の平坦不良が生じて生産性を阻害するおそれがある。そのため、巻取温度は100~500℃とするのが好ましく、150~450℃とするのがより好ましい。
Claims (6)
- 化学組成が、質量%で、
C:0.05~0.25%、
Si:0.2~2.0%、
Mn:1.2~3.0%、
P:0.030%以下、
S:0.050%以下、
Al:0.01~0.55%、
N:0.0100%以下、
Ti:0.010~0.250%、
残部:Feおよび不純物であり、
鋼板表層部における集合組織のランダム強度比が8.0以下であり、
前記集合組織の{110}極点図の最大強度方位と鋼板圧延面の法線方向とがなす最小角度が10°以下である、
鋼板。 - 前記化学組成が、前記Feの一部に代えて、質量%で、
Cr:0.50%以下、
Ni:0.50%以下、および、
Cu:0.50%以下、
から選択される1種以上を含有する、
請求項1に記載の鋼板。 - 前記化学組成が、前記Feの一部に代えて、質量%で、
Nb:0.040%以下、
V:0.15%以下、
Zr:0.15%以下、
Mo:0.15%以下、および、
W:0.15%以下、
から選択される1種以上を含有する、
請求項1または請求項2に記載の鋼板。 - 前記化学組成が、前記Feの一部に代えて、質量%で、
Sn、SbおよびTeから選択される1種以上を、合計で0.100%以下、含有する、
請求項1から請求項3までのいずれかに記載の鋼板。 - 前記化学組成が、前記Feの一部に代えて、質量%で、
Ca、MgおよびREMから選択される1種以上を、合計で0.0050%以下、含有する、
請求項1から請求項4までのいずれかに記載の鋼板。 - 前記化学組成が、前記Feの一部に代えて、質量%で、
B:0.0050%以下、
を含有する、
請求項1から請求項5までのいずれかに記載の鋼板。
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001303175A (ja) | 2000-04-25 | 2001-10-31 | Nippon Steel Corp | 形状凍結性に優れたフェライト系薄鋼板及びその製造方法 |
WO2012141265A1 (ja) * | 2011-04-13 | 2012-10-18 | 新日本製鐵株式会社 | 局部変形能に優れた高強度熱延鋼板とその製造方法 |
JP2013104114A (ja) | 2011-11-15 | 2013-05-30 | Jfe Steel Corp | 曲げ加工性に優れた冷延鋼板およびその製造方法 |
JP2016050335A (ja) * | 2014-08-29 | 2016-04-11 | 新日鐵住金株式会社 | 熱延鋼板 |
JP2017206764A (ja) * | 2016-05-20 | 2017-11-24 | 新日鐵住金株式会社 | 穴拡げ性と溶接部疲労特性に優れた高強度熱延鋼板及びその製造方法 |
WO2020110843A1 (ja) * | 2018-11-28 | 2020-06-04 | 日本製鉄株式会社 | 熱延鋼板 |
WO2020110855A1 (ja) * | 2018-11-28 | 2020-06-04 | 日本製鉄株式会社 | 熱延鋼板 |
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Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001303175A (ja) | 2000-04-25 | 2001-10-31 | Nippon Steel Corp | 形状凍結性に優れたフェライト系薄鋼板及びその製造方法 |
WO2012141265A1 (ja) * | 2011-04-13 | 2012-10-18 | 新日本製鐵株式会社 | 局部変形能に優れた高強度熱延鋼板とその製造方法 |
JP2013104114A (ja) | 2011-11-15 | 2013-05-30 | Jfe Steel Corp | 曲げ加工性に優れた冷延鋼板およびその製造方法 |
JP2016050335A (ja) * | 2014-08-29 | 2016-04-11 | 新日鐵住金株式会社 | 熱延鋼板 |
JP2017206764A (ja) * | 2016-05-20 | 2017-11-24 | 新日鐵住金株式会社 | 穴拡げ性と溶接部疲労特性に優れた高強度熱延鋼板及びその製造方法 |
WO2020110843A1 (ja) * | 2018-11-28 | 2020-06-04 | 日本製鉄株式会社 | 熱延鋼板 |
WO2020110855A1 (ja) * | 2018-11-28 | 2020-06-04 | 日本製鉄株式会社 | 熱延鋼板 |
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