WO2015015738A1 - 高強度高ヤング率鋼板およびその製造方法 - Google Patents
高強度高ヤング率鋼板およびその製造方法 Download PDFInfo
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- WO2015015738A1 WO2015015738A1 PCT/JP2014/003774 JP2014003774W WO2015015738A1 WO 2015015738 A1 WO2015015738 A1 WO 2015015738A1 JP 2014003774 W JP2014003774 W JP 2014003774W WO 2015015738 A1 WO2015015738 A1 WO 2015015738A1
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- Prior art keywords
- young
- steel sheet
- strength
- less
- modulus
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 133
- 239000010959 steel Substances 0.000 title claims abstract description 133
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 58
- 239000000835 fiber Substances 0.000 claims abstract description 42
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 35
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 21
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 18
- 239000013078 crystal Substances 0.000 claims abstract description 16
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 11
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 5
- 238000001816 cooling Methods 0.000 claims description 36
- 238000005097 cold rolling Methods 0.000 claims description 34
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 28
- 239000008397 galvanized steel Substances 0.000 claims description 28
- 230000009467 reduction Effects 0.000 claims description 18
- 238000005275 alloying Methods 0.000 claims description 17
- 239000010960 cold rolled steel Substances 0.000 claims description 17
- 238000007747 plating Methods 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 14
- 238000005246 galvanizing Methods 0.000 claims description 12
- 238000011282 treatment Methods 0.000 claims description 10
- 238000004804 winding Methods 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052787 antimony Inorganic materials 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052715 tantalum Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 238000005096 rolling process Methods 0.000 abstract description 57
- 239000006104 solid solution Substances 0.000 abstract description 5
- 238000000137 annealing Methods 0.000 description 44
- 238000000034 method Methods 0.000 description 35
- 238000010438 heat treatment Methods 0.000 description 29
- 230000000694 effects Effects 0.000 description 27
- 230000008569 process Effects 0.000 description 26
- 238000003303 reheating Methods 0.000 description 22
- 238000005098 hot rolling Methods 0.000 description 21
- 229910001566 austenite Inorganic materials 0.000 description 18
- 230000001965 increasing effect Effects 0.000 description 15
- 238000012360 testing method Methods 0.000 description 15
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 13
- 239000002244 precipitate Substances 0.000 description 13
- 229910045601 alloy Inorganic materials 0.000 description 8
- 239000000956 alloy Substances 0.000 description 8
- 230000009466 transformation Effects 0.000 description 8
- 238000001953 recrystallisation Methods 0.000 description 7
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 6
- 238000005259 measurement Methods 0.000 description 6
- 229910052725 zinc Inorganic materials 0.000 description 6
- 239000011701 zinc Substances 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 5
- 229910001563 bainite Inorganic materials 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 229910001562 pearlite Inorganic materials 0.000 description 4
- 230000000087 stabilizing effect Effects 0.000 description 4
- 229910052718 tin Inorganic materials 0.000 description 4
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 3
- 230000032683 aging Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000001771 impaired effect Effects 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 238000000465 moulding Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 239000013585 weight reducing agent Substances 0.000 description 3
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000001887 electron backscatter diffraction Methods 0.000 description 2
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- 230000001629 suppression Effects 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- -1 tempered martensite Chemical class 0.000 description 2
- 229910001208 Crucible steel Inorganic materials 0.000 description 1
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- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000009918 complex formation Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
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- 238000005336 cracking Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
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- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
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- 238000005482 strain hardening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
Classifications
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- 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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
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- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
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- C21D6/00—Heat treatment of ferrous alloys
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C—CHEMISTRY; METALLURGY
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
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- C22C—ALLOYS
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
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- C22C—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
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- 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
- 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, high-Young's modulus steel plate suitable for use mainly in structural parts of automobile bodies and a method for producing the same.
- the rigidity of the structural part is determined by the plate thickness and Young's modulus of the steel sheet if the cross-sectional shape is the same, it is effective to increase the Young's modulus of the steel sheet in order to achieve both weight reduction and rigidity of the structural part.
- the Young's modulus is largely governed by the texture of the steel sheet.
- the Young's modulus In the case of iron having a body-centered cubic lattice, the Young's modulus is high in the ⁇ 111> direction, which is the atomic dense direction, and conversely low in the ⁇ 100> direction where the atomic density is small. It has been known. It is known that the Young's modulus of normal iron having no anisotropy in crystal orientation is about 206 GPa. Also, by giving anisotropy to the crystal orientation and increasing the atomic density in a specific direction, the Young's modulus in that direction can be increased. However, when considering the rigidity of an automobile body, since a load is applied from various directions, a steel sheet having a high Young's modulus in each direction is required in addition to a specific direction.
- Patent Document 1 in mass%, C: 0.02 to 0.15%, Si: 0.3% or less, Mn: 1.0 to 3.5%, P: 0.05% or less, S: 0.01% or less, Al: 1.0% or less, N: 0.01% or less, and Ti: 0.1 to 1.0%, with the balance being Fe and A slab composed of inevitable impurities is hot-rolled, cold-rolled at a rolling reduction of 20 to 85%, and then recrystallized and annealed to have a ferrite single-phase microstructure, TS of 590 MPa or more, and rolling A high-strength steel sheet with excellent rigidity, characterized by having a Young's modulus in the 90 ° direction relative to the direction of 230 GPa or more and an average Young's modulus in the direction of 0 °, 45 °, and 90 ° relative to the rolling direction of 215 GPa or more. The manufacturing method of this is proposed.
- Patent Document 2 C: 0.02 to 0.15%, Si: 1.5% or less, Mn: 1.5 to 4.0%, P: 0.05% or less, S: A slab containing 0.01% or less, Al: 1.5% or less, N: 0.01% or less, and Nb: 0.02 to 0.40%, with the balance being Fe and inevitable impurities,
- recrystallization annealing has a mixed structure of ferrite and martensite, TS is 590 MPa or more, and the Young's modulus in the direction perpendicular to the rolling direction is A method for manufacturing a high-rigidity and high-strength steel sheet excellent in workability, characterized by being 225 GPa or more, has been proposed.
- Patent Document 1 in order to achieve a tensile strength of 780 MPa or more, for example, referring to the examples, addition of V: 0.4 mass% and W: 0.5 mass% is necessary. is there. Moreover, in order to further increase the strength, it is indispensable to use expensive elements such as Cr and Mo, and there is a problem that the alloy cost increases.
- the technique described in Patent Document 2 is effective for increasing the Young's modulus in only one direction of the steel sheet. However, it cannot be applied to the improvement of the rigidity of automobile structural parts that require steel plates having high Young's modulus in each direction.
- the present invention has a tensile strength of 780 MPa or more, a rolling direction and a Young's modulus in the direction of 45 ° with respect to the rolling direction of 205 GPa or more, and a Young's modulus in a direction perpendicular to the rolling direction of 220 GPa or more.
- An object of the present invention is to provide a high-strength, high-Young's modulus steel plate that has excellent deep drawability and a method for producing the same.
- the high-strength, high-Young's modulus steel sheet of the present invention is a so-called high-strength, high-Young's modulus cold-rolled steel sheet that is a cold-rolled steel sheet, a so-called high-strength, high-Young's modulus-plated steel sheet that has a plating film on its surface, So-called high strength high Young's modulus hot dip galvanized steel sheet, alloyed hot dip galvanized steel sheet having an alloyed hot dip galvanized film on its surface, so-called high strength high Young's modulus This includes alloyed hot-dip galvanized steel sheets.
- Nb and V added steel By using Nb and V added steel, and appropriately controlling the composition of the other alloy elements, by precipitating Nb and V as carbides while leaving solid solution C by winding at high temperature after hot rolling Then, by subsequent cold rolling, the texture of ⁇ -fiber and ⁇ -fiber can be developed. Furthermore, during annealing, by controlling the precipitates and the annealing temperature to develop an ⁇ -fiber and ⁇ -fiber texture, the Young's modulus in all directions is improved, and solute C is used to improve ferrite and martensite. The desired strength can be ensured by generating at least a certain ratio. Furthermore, it has been found that it is possible to produce a high-strength, high Young's modulus steel plate that also has good deep drawability.
- the present invention has been made on the basis of the above findings and has the following gist.
- a steel slab having the composition according to any one of [1] to [7] is heated to a temperature range of 1150 ° C. to 1300 ° C., and then heated to a temperature range of 850 ° C. to 1000 ° C.
- Hot rolled at a finishing temperature wound in a temperature range of 500 ° C. or higher and 800 ° C. or lower, and then cold-rolled sheet obtained through a process of cold rolling at a cold rolling reduction ratio of 40% or higher is 450 ° C. or higher and 800 ° C. or higher.
- a method for producing a high-strength, high-Young's modulus steel sheet characterized in that it is a cold-rolled steel sheet.
- a steel slab having the component composition according to any one of [1] to [7] is heated to a temperature range of 1150 ° C. to 1300 ° C., and then heated to a temperature range of 850 ° C. to 1000 ° C.
- Hot rolled at a finishing temperature wound in a temperature range of 500 ° C. or higher and 800 ° C. or lower, and then cold-rolled sheet obtained through a process of cold rolling at a cold rolling reduction ratio of 40% or higher is 450 ° C. or higher and 800 ° C. or higher.
- Heat to a temperature range of °C ° C. or less hold for 300 s or more in the temperature range, then heat to 750 ° C. or more and 950 ° C. or less, and then cool the temperature range of 550 ° C. to 700 ° C. at an average cooling rate of 3 ° C./s or more
- producing a hot galvanized steel sheet by hot dip galvanizing is produced by hot dip galvanizing.
- a steel slab having the composition according to any one of [1] to [7] is heated to a temperature range of 1150 ° C. to 1300 ° C., and then heated to a temperature range of 850 ° C. to 1000 ° C.
- Hot rolled at a finishing temperature wound in a temperature range of 500 ° C. or higher and 800 ° C. or lower, and then cold-rolled sheet obtained through a process of cold rolling at a cold rolling reduction ratio of 40% or higher is 450 ° C. or higher and 800 ° C. or higher.
- the tensile strength is 780 MPa or more
- the rolling direction and the Young's modulus in the direction of 45 ° with respect to the rolling direction are 205 GPa or more
- the Young's modulus in the direction perpendicular to the rolling direction is 220 GPa or more
- the average r value is 1.
- a high-strength, high Young's modulus steel sheet having a drawing ratio of 05 or more and a limit drawing ratio (LDR) of 2.03 or more is obtained.
- the high-strength and high Young's modulus steel sheet of the present invention and the manufacturing method thereof will be described in detail by dividing them into their component composition, microstructure and manufacturing method.
- C forms a precipitate (carbide) with Nb and V, thereby controlling grain growth during annealing, contributing to a higher Young's modulus, and using the strengthening of the structure by martensite. It is an indispensable element for adjusting the rate and hardness. If the C content is less than 0.060%, the ferrite grain size becomes coarse, and it becomes difficult to obtain martensite having a required area ratio, and the martensite is not cured, so that sufficient strength cannot be obtained. On the other hand, if the amount of C exceeds 0.150%, it is necessary to increase the amounts of Nb and V accordingly, and this will saturate the effect of carbides and increase the alloy cost. Therefore, the C content is 0.060% or more and 0.150% or less, preferably 0.080% or more and 0.130% or less.
- Si 0.50% or more and 2.20% or less
- Si is one of the important elements in the present invention.
- Si a ferrite stabilizing element, improves Young's modulus, average r value and LDR by promoting ferrite transformation in the cooling process during annealing, and stabilizes austenite by concentrating C in austenite. Since the generation of the low temperature transformation phase can be promoted, the strength of the steel can be increased as necessary. Further, Si dissolved in ferrite improves work hardening ability and increases the ductility of the ferrite itself. In order to obtain such an effect, the Si amount needs to be 0.50% or more.
- the Si content exceeds 2.20%, the weldability of the steel sheet is deteriorated, and the generation of firelite is promoted on the surface of the slab during heating before hot rolling. Helps generate surface defects. Furthermore, when used as a cold-rolled steel sheet, Si oxide generated on the surface deteriorates the chemical conversion processability. Further, when used as a hot dip galvanized steel sheet, Si oxide generated on the surface induces non-plating. Therefore, the Si content is 0.50% or more and 2.20% or less, preferably 0.80% or more and 2.10% or less.
- Mn contributes to increasing the strength by enhancing the hardenability and promoting the formation of a low-temperature transformation phase in the cooling process during annealing, and further contributes to increasing the strength as a solid solution strengthening element.
- the amount of Mn needs to be 1.00% or more.
- the amount of Mn exceeds 3.00%, the generation of ferrite necessary for improving Young's modulus, average r value and LDR is remarkably suppressed during the cooling process during annealing, and the low temperature transformation phase increases. Steel becomes extremely strong and workability deteriorates. Such a large amount of Mn also deteriorates the weldability of the steel sheet. Therefore, the Mn content is 1.00% or more and 3.00% or less, preferably 1.50% or more and 2.80% or less.
- P 0.100% or less
- P has an effect of strengthening solid solution, can be added according to a desired strength, and further promotes ferrite transformation, and is an element effective for complex organization. However, if the content exceeds 0.100%, spot weldability is deteriorated. In addition, when the alloying treatment of galvanizing is performed, the alloying speed is reduced and the plating property is impaired. Therefore, the P amount needs to be 0.100% or less.
- the amount of P is preferably 0.001% or more and 0.100% or less.
- S 0.0100% or less
- S is present as a sulfide and lowers local deformability. Therefore, the content is preferably reduced as much as possible. Therefore, the S content should be 0.0100% or less, preferably 0.0050% or less.
- S is preferably set to 0.0001% as the lower limit. Therefore, the S content is 0.0100% or less, preferably 0.0001% or more and 0.0100% or less, more preferably 0.0001% or more and 0.0050% or less.
- Al 0.010% or more and 2.500% or less
- the Al content is preferably 0.010% or more.
- Al which is a ferrite-forming element, promotes ferrite formation in the cooling process during annealing, stabilizes austenite by concentrating C in austenite, and promotes the formation of a low-temperature transformation phase. Accordingly, the strength of the steel can be increased.
- the Al content is more preferably 0.020% or more.
- the Al content is 0.010% or more and 2.500% or less, preferably 0.020% or more and 2.500% or less.
- N is an element that degrades the aging resistance of steel.
- the N content should be 0.0100% or less, preferably 0.0060% or less. Further, depending on production technology restrictions, an N content with a lower limit of about 0.0005% may be allowed.
- Nb is one of the important elements in the present invention. Nb forms fine precipitates at the time of hot rolling or annealing, generates ferrite having an orientation that is advantageous for improving Young's modulus, average r value, and LDR at the time of annealing, and the coarseness of recrystallized grains It contributes to the improvement of strength.
- the austenite phase generated by reverse transformation during annealing is refined, so that the microstructure after annealing is also refined and the strength is increased. In order to obtain such an effect, the Nb amount needs to be 0.001% or more.
- the Nb content exceeds 0.200%, the carbonitride cannot be completely dissolved at the time of normal slab reheating, and coarse carbonitrides remain, which increases the strength and suppresses recrystallization. The effect is not obtained.
- the Nb content is 0.001% or more and 0.200% or less, preferably 0.005% or more and 0.200% or less.
- V is one of the important elements in the present invention.
- V forms precipitates with C, generates ferrite with an orientation that is advantageous for improving Young's modulus, average r value, and LDR during annealing, suppresses the coarsening of recrystallized grains, Contributes effectively to improvement.
- the V amount needs to be 0.001% or more.
- the amount of V exceeds 0.200%, carbonitrides cannot be completely dissolved during normal slab reheating, and coarse carbonitrides remain, which increases strength and suppresses recrystallization. The effect is not obtained.
- the V amount is 0.001% or more and 0.200% or less, preferably 0.005% or more and 0.200% or less.
- C * showing the amount of solute C shall be 500 mass ppm or more and 1300 mass ppm or less like the said (1) Formula.
- C in the steel forms precipitates such as Nb, V, NbC, and VC.
- the amount of solute C in the steel can be determined by the above-mentioned C * in consideration of such precipitation.
- the high strength and high Young's modulus steel sheet of the present invention further includes Cr: 0.05% to 1.00%, Mo: 0.05% to 1.00%, Ni: 0 0.05% or more and 1.00% or less, and Cu: 0.05% or more and 1.00% or less, at least one element selected from B: 0.0003% or more and 0.0050% or less, Ca : At least one element selected from 0.0010% to 0.0050%, Mg: 0.0005% to 0.0100%, and REM: 0.0003% to 0.0050%, At least one element selected from Ta: 0.0010% or more and 0.1000% or less, Sn: 0.0020% or more and 0.2000% or less, and Sb: 0.0020% or more and 0.2000% or less.
- Alone, Rui is preferably contained in combination.
- Cr, Mo, Ni, and Cu not only serve as solid solution strengthening elements, but also stabilize austenite in the cooling process during annealing and facilitate complex formation.
- the Cr content, the Mo content, the Ni content, and the Cu content must each be 0.05% or more.
- the Cr content, the Mo content, the Ni content, and the Cu content each exceed 1.00%, the formability and spot weldability deteriorate. Therefore, when adding Cr, Mo, Ni, and Cu, the content is 0.05% or more and 1.00% or less, respectively.
- B suppresses the formation of pearlite and bainite from austenite, stabilizes the austenite and promotes the formation of martensite, and is therefore effective in securing strength. This effect is obtained when the B content is 0.0003% or more. On the other hand, even if B is added in excess of 0.0050%, the effect is saturated and the productivity during hot rolling is reduced. Therefore, when adding B, the content is made 0.0003% or more and 0.0050% or less.
- Ca, Mg, and REM are elements used for deoxidation, and are effective elements for spheroidizing the shape of the sulfide and improving the adverse effect of the sulfide on local ductility.
- the Ca content must be 0.0010% or more
- the Mg content must be 0.0005% or more
- the REM content must be 0.0003% or more.
- the Ca amount and the REM amount are each 0.0050%, and the Mg amount is more than 0.0100%, the inclusions and the like are increased to cause surface and internal defects.
- the Ca amount is 0.0010% or more and 0.0050% or less
- the Mg amount is 0.0005% or more and 0.0100% or less
- the REM amount is 0.0003% or more and 0. 0050% or less.
- Ta like Nb and V, generates alloy carbide and alloy carbonitride and contributes to high strength. In addition, it partially dissolves in Nb carbide and Nb carbonitride to produce a composite precipitate such as (Nb, Ta)-(C, N), thereby significantly suppressing the coarsening of the precipitate. It is thought that there is an effect of stabilizing the contribution to strength by strengthening. For this reason, it is preferable to contain Ta.
- the effect of stabilizing the precipitates described above can be obtained by setting the Ta content to 0.0010% or more. On the other hand, even if Ta is added excessively, the precipitate stabilizing effect is saturated and the alloy cost also increases. Therefore, when Ta is added, the content is within the range of 0.0010% to 0.1000%.
- C * showing the amount of solute C shall be 500 mass ppm or more and 1300 mass ppm or less like the said (2) formula.
- C in the steel forms precipitates with Nb, V and Ta.
- the amount of solute C in the steel can be determined by the above-mentioned C * in consideration of such precipitation.
- Sn and Sb are added as necessary from the viewpoint of suppressing decarburization in the region of several tens of ⁇ m of the steel sheet surface layer caused by nitriding and oxidation of the steel sheet surface.
- Sn and Sb can prevent a reduction in the amount of martensite produced on the steel sheet surface and improve fatigue characteristics and aging resistance.
- the Sn amount and the Sb amount must each be 0.0020% or more.
- the toughness is reduced. Therefore, when adding Sn and Sb, the content is within the range of 0.0020% or more and 0.2000% or less, respectively.
- the balance other than the components whose contents are shown above consists of Fe and inevitable impurities. In addition, if it is a range which does not impair the effect of this invention, it does not refuse inclusion of components other than the above.
- the content of oxygen (O) is preferably suppressed to 0.003% or less because non-metallic inclusions are generated and the steel plate quality is adversely affected.
- Ferrite has a texture development effect that is advantageous for improving Young's modulus, average r value, and LDR.
- the area ratio of ferrite needs to be 20% or more.
- the area ratio of ferrite is preferably 30% or more.
- the ferrite here includes bainitic ferrite, polygonal ferrite, and acicular ferrite that do not include precipitation of carbide.
- the area ratio of ferrite and martensite is 3 vol.
- ferrite has a gray structure (underground structure)
- martensite has a white structure.
- the average crystal grain size of ferrite is set to 20.0 ⁇ m or less. Further, although there is no particular limitation, since the ductility tends to decrease when the average crystal grain size of ferrite is less than 1 ⁇ m, the average crystal grain size of ferrite is preferably 1 ⁇ m or more.
- the average crystal grain size of ferrite is the crystal grain through which the line segment drawn on the image passes the value obtained by correcting the length of the line segment drawn on the image to the actual length using the above-mentioned Adobe Photoshop. Calculated by dividing by the number of.
- the total area ratio of ferrite and martensite is preferably 90% or more.
- carbides such as tempered martensite, bainite, tempered bainite, pearlite, cementite, and the like are included in an area ratio of 10% or less. The effect is not impaired.
- ⁇ -fiber is a fiber texture whose ⁇ 110> axis is parallel to the rolling direction
- ⁇ -fiber is a fiber texture whose ⁇ 111> axis is parallel to the normal direction of the rolling surface.
- the body-centered cubic metal is characterized in that ⁇ -fiber and ⁇ -fiber are strongly developed by rolling deformation, and a texture belonging to them is formed even by recrystallization.
- the inverse strength ratio of ⁇ -fiber to ⁇ -fiber in ferrite and martensite is obtained by polishing a plate thickness cross section (L cross section) parallel to the rolling direction of the steel plate, and then the position of the plate thickness 1/4 (from the steel plate surface).
- the crystal orientation was measured using the SEM-EBSD (Electron Back-Scatter Diffraction) method in the depth direction (position corresponding to 1/4 of the plate thickness), and the obtained data was used as AMETEK.
- SEM-EBSD Electromatter Diffraction
- a high strength and high Young's modulus steel sheet is obtained by controlling the steel having the above composition to the above microstructure.
- the high strength and high Young's modulus steel sheet of the present invention may be a cold rolled steel sheet, and has a plating film such as a hot dip galvanized film, an alloyed hot dip galvanized film, an electrogalvanized film, and an Al plated film on the surface. It may be a plated steel plate or a hot rolled steel plate.
- the high strength and high Young's modulus steel plate of the present invention having the above has the following characteristics.
- the Young's modulus in the rolling direction and 45 ° direction with respect to the rolling direction is 205 GPa or more, and Young's modulus in the direction perpendicular to the rolling direction is 220 GPa or more]
- the Young's modulus of the present invention is set to 205 GPa or more in the rolling direction and 45 ° direction with respect to the rolling direction, and 220 GPa or more in the direction perpendicular to the rolling direction. limit.
- the rolling direction and the 45 ° direction with respect to the rolling direction are 208 GPa or more, and the direction perpendicular to the rolling direction is 223 GPa or more. More preferably, the 45 ° direction with respect to the rolling direction and the rolling direction is 210 GPa or more, and the direction perpendicular to the rolling direction is 225 GPa or more.
- a high-strength steel sheet having a TS of 780 MPa or more is greatly deteriorated in press formability, particularly deep drawability, as compared with a mild steel sheet. Therefore, in order to correspond to members mainly of drawing molding such as inner and outer plate panels and undercarriages, the average r value of the present invention example is limited to 1.05 or more, preferably 1.07 or more, more preferably 1.10 or more. And
- LDR Limit drawing ratio
- a steel slab having the above composition obtained by a continuous casting method is heated to a temperature range of 1150 ° C. or higher and 1300 ° C. or lower (steel slab heating step), and then 850 ° C. or higher and 1000 ° C.
- hot rolling process hot rolling process
- winding in a temperature range of 500 ° C. or higher and 800 ° C. or lower
- cool at a cold rolling reduction of 40% or higher.
- the cold-rolled sheet obtained through the step of cold rolling is heated to a temperature range of 450 ° C. or higher and 800 ° C.
- heating step and held in the temperature range for 300 seconds or longer (holding after heating) Step), and then heated to 750 ° C. or higher and 950 ° C. or lower (reheating step), and then cooled to a temperature range of 300 ° C. or higher and 700 ° C. or lower at an average cooling rate of 3 ° C./s or higher (cooling step after reheating).
- the steel slab having the above composition is heated to a temperature range of 1150 ° C. to 1300 ° C. (heating process of the steel slab), and then finished in a temperature range of 850 ° C. to 1000 ° C.
- Step of hot rolling at a temperature hot rolling step
- winding in a temperature range of 500 ° C. to 800 ° C. winding step
- cold rolling step cold rolling at a cold rolling reduction of 40% or more
- the cold-rolled sheet obtained through the rolling step is heated to a temperature range of 450 ° C. or higher and 800 ° C. or lower (heating step), held in the temperature range for 300 seconds or longer (holding step after heating), and then 750 ° C.
- Hot dip galvanizing process a high-strength, high Young's modulus steel sheet that is a hot-dip galvanized steel sheet, that is, a high-strength, high Young's modulus hot-dip galvanized steel sheet is obtained.
- the alloying process of galvanization is performed in the temperature range of 470 degreeC or more and 600 degrees C or less (alloying process process).
- a high-strength, high Young's modulus steel sheet that is an alloyed hot-dip galvanized steel sheet, that is, a high-strength, high Young's modulus alloyed hot-dip galvanized steel sheet is obtained.
- each step will be described in detail.
- Step slab heating process The Nb and V-based precipitates present at the stage of heating the cast steel slab will remain as coarse precipitates in the steel sheet finally obtained as it is, and the strength, Young's modulus, average Does not contribute to r value and LDR. For this reason, when the steel slab is heated, it is necessary to redissolve the Nb and V-based precipitates precipitated during casting. The contribution to strength by this is recognized by heating at 1150 ° C. or higher. Moreover, in order to scale off defects such as bubbles and segregation in the surface layer of the slab and obtain a smooth steel plate surface with few cracks and irregularities, it is preferable to heat to 1150 ° C. or higher.
- the steel slab is heated to a temperature range of 1150 ° C. or higher and 1300 ° C. or lower. That is, the slab heating temperature is 1150 ° C. or higher and 1300 ° C. or lower.
- a hot rolling process consists of rough rolling and finish rolling, and the steel slab after a heating turns into a hot-rolled sheet through this rough rolling and finish rolling. If the finishing temperature of this hot rolling exceeds 1000 ° C., the amount of oxide (hot rolling scale) generated increases rapidly, and the interface between the base iron and the oxide becomes rough. Deteriorating the surface quality after the hot rolling process. On the other hand, when the finishing temperature of hot rolling is less than 850 ° C., the rolling load increases and the rolling load increases, and the austenite unrolled state in an unrecrystallized state increases to develop an abnormal texture. .
- the finishing temperature of hot rolling is 850 ° C. or higher and 1000 ° C. or lower, preferably 850 ° C. or higher and 950 ° C. or lower.
- the steel slab is made into a sheet bar by rough rolling under normal conditions.
- the heating temperature is lowered, it is preferable to heat the sheet bar using a bar heater or the like before finish rolling from the viewpoint of preventing troubles during hot rolling.
- Cold rolling is performed after the hot rolling step to accumulate ⁇ -fiber and ⁇ -fiber effective for improving Young's modulus, average r value, and LDR. That is, by developing ⁇ -fiber and ⁇ -fiber by cold rolling, even in the structure after the subsequent annealing process, the ferrite with ⁇ -fiber and ⁇ -fiber, especially ⁇ -fiber is increased, Young's modulus, average Increase r value and LDR. In order to obtain such an effect, the cold rolling reduction during cold rolling needs to be 40% or more. Furthermore, from the viewpoint of improving the Young's modulus, average r value, and LDR, the cold rolling reduction ratio is preferably 50% or more. On the other hand, when the cold rolling reduction ratio increases, the rolling load increases and manufacturing becomes difficult.
- the cold rolling reduction ratio is preferably 80% or less. Therefore, the cold rolling reduction ratio is 40% or more, preferably 40% or more and 80% or less, more preferably 50% or more and 80% or less. In addition, the effect of the present invention is exhibited without particularly defining the number of rolling passes and the cold rolling reduction ratio for each pass.
- annealing temperature When the annealing temperature at the time of heating is low, an unrecrystallized structure remains, it becomes difficult to accumulate in ⁇ -fiber, and the Young's modulus, average r value, and LDR in each direction decrease. For this reason, annealing temperature shall be 450 degreeC or more. Furthermore, from the viewpoint of improving the Young's modulus, average r value, and LDR, the annealing temperature is preferably set to 550 ° C. or higher. On the other hand, when the annealing temperature exceeds 800 ° C., the austenite grains become coarse, and it becomes difficult for the ferrite retransformed after annealing to accumulate in ⁇ -fiber and ⁇ -fiber, particularly ⁇ -fiber.
- the annealing temperature in the heating process is set to 450 ° C. or higher and 800 ° C. or lower. That is, in the heating step, heating is performed in a temperature range of 450 ° C. or higher and 800 ° C. or lower. Preferably it heats to the temperature range of 550 degreeC or more and 800 degrees C or less.
- Heating process after heating When the holding time in the above temperature range of 450 ° C. or higher and 800 ° C. or lower becomes less than 300 s, an unrecrystallized structure remains and it becomes difficult to accumulate in ⁇ -fiber, and Young's modulus in each direction, average r value, and LDR Decreases. For this reason, holding time shall be 300 s or more.
- holding time is 100,000 s or less. Accordingly, the holding time is 300 s or more, preferably 300 s or more and 100,000 s or less.
- the average cooling rate is 80 ° C./s or less. Preferably there is.
- the annealing temperature during reheating is less than 750 ° C.
- austenite generation is insufficient.
- the annealing temperature is set to 750 ° C. or higher.
- the annealing temperature at the time of annealing exceeds 950 degreeC, the crystal grain of austenite will coarsen and the tensile strength TS of the steel plate finally obtained tends to fall, Therefore It is preferable that it is 950 degreeC or less.
- the annealing temperature in the reheating step is set to 750 ° C. or more and 950 ° C. or less. That is, in the reheating step, heating is performed in a temperature range of 750 ° C. or higher and 950 ° C. or lower.
- the average cooling rate in the region is less than 3 ° C./s, untransformed austenite is transformed into pearlite, and the desired martensite area ratio cannot be secured, making it difficult to secure the desired strength. Therefore, when setting it as a cold-rolled steel plate, the average cooling rate in the temperature range of 300 degreeC or more and 700 degrees C or less shall be 3 degrees C / s or more. Moreover, when setting it as a hot dip galvanized steel plate, the average cooling rate in the temperature range of 550 degreeC or more and 700 degrees C or less shall be 3 degrees C / s or more.
- the above average cooling rate may be 80 ° C./s or less. preferable. Accordingly, the average cooling rate in the temperature range of 300 ° C. or more and 700 ° C. or less when the cold-rolled steel plate is used, and the temperature range of 550 ° C. or more and 700 ° C. or less when the hot-dip galvanized steel plate is used, is preferably 3 ° C./s or more. Is 3 ° C./s or more and 80 ° C./s or less.
- Hot dip galvanizing process When performing hot dip galvanization, it is preferable to apply in the temperature range of 420 degreeC or more and 550 degrees C or less, and it can carry out in the cooling process after annealing.
- a zinc bath containing 0.15 to 0.23% by mass of Al is used in GI (hot dip galvanized steel plate), and Al: 0.005 in GA (alloyed hot dip galvanized steel plate). It is preferable to use a zinc bath containing 12 to 0.20% by weight.
- the plating adhesion amount is preferably 20 to 70 g / m 2 (double-sided plating) per side, and GA is preferably subjected to the following alloying treatment so that the Fe concentration in the plating layer is 7 to 15% by mass. .
- the alloying treatment temperature during the alloying treatment is less than 470 ° C., there is a problem that alloying does not proceed. On the other hand, when the alloying temperature exceeds 600 ° C., the ferrite crystal grains are coarsened, and it is difficult to ensure a desired strength. Therefore, the alloying treatment temperature is set to 470 ° C. or more and 600 ° C. or less. That is, the alloying treatment of galvanization is performed in a temperature range of 470 ° C. or more and 600 ° C. or less.
- a reheating step is performed after a holding step after heating
- a holding step first annealing
- CAL continuous annealing line
- molten zinc is performed without performing a cooling step.
- a reheating step is performed in the plating line (CGL) to perform reheating (second annealing).
- the hot dip galvanizing is performed after the cooling step after the reheating described above in the cooling process after the reheating. Thereafter, an alloying treatment is appropriately performed.
- the elongation rate of skin pass rolling is preferably in the range of 0.1% to 1.5%. If it is less than 0.1%, the effect of shape correction is small and control is difficult, so this is the lower limit of the good range. Moreover, since productivity will fall remarkably when it exceeds 1.5%, this is made the upper limit of a favorable range.
- the skin pass rolling may be performed inline or offline. Further, a skin pass having a desired elongation rate may be performed at once, or may be performed in several steps.
- the average cooling rate after reheating (second annealing) in Table 2 is the average cooling rate in the temperature range of 300 to 700 ° C for CR, and the average cooling rate in the temperature range of 550 to 700 ° C for GI and GA. It's about speed.
- the hot dip galvanizing bath uses a zinc bath containing Al: 0.18% by mass in GI, uses a zinc bath containing Al: 0.15% by mass in GA, and the bath temperature is 470 ° C. did.
- the plating adhesion amount was 45 g / m 2 per side (double-sided plating), and GA had an Fe concentration of 9 to 12% by mass in the plating layer.
- the tensile test was performed using a JIS No. 5 test piece defined in JIS Z 2201 (1998), which was taken from a steel sheet subjected to temper rolling with an elongation of 0.5% so that the tensile direction was the rolling direction of the steel sheet.
- the tensile strength TS and the total elongation EL were measured according to JIS Z 2241 (1998).
- Young's modulus measurement is a test of 10 mm ⁇ 50 mm from three directions of the rolling direction (L direction) of the steel sheet, the 45 ° direction (D direction) with respect to the rolling direction of the steel sheet, and the direction perpendicular to the rolling direction of the steel sheet (C direction). A piece was cut out, and Young's modulus was measured using a lateral vibration type resonance frequency measuring device according to the American Society to Testing Materials standard (C1259).
- the average r-value measurement is performed according to JIS Z from three directions: a rolling direction of the steel plate (L direction), a 45 ° direction (D direction) with respect to the rolling direction of the steel plate, and a direction perpendicular to the rolling direction of the steel plate (C direction).
- L direction a rolling direction of the steel plate
- D direction a 45 ° direction
- C direction a direction perpendicular to the rolling direction of the steel plate
- the respective plastic strain ratios r L , r D , and r C are obtained in accordance with the provisions of JIS Z 2254, and the average r value is calculated by the following formula. did.
- Average r value (r L + 2r D + r C ) / 4
- the average r value is determined to be good when the average r value ⁇ 1.05.
- the deep drawing test was performed by a cylindrical drawing test, and the deep drawing property was evaluated by a limit drawing ratio (LDR).
- LDR limit drawing ratio
- a cylindrical punch having a diameter of 33 mm ⁇ was used for the test, and a die having a die diameter of 36.6 mm was used as the material having a plate thickness of 1.2 mm.
- the test was performed with a wrinkle holding force of 1.5 ton (14.71 kN). Since the sliding state of the surface changes depending on the plating state or the like, the test was performed under a high lubrication condition by placing a polyethylene sheet between the sample and the die so that the sliding state of the surface does not affect the test.
- the blank diameter was changed at a pitch of 1 mm, and the ratio (D / d) of blank diameter D to punch diameter d (D / d) that was not ruptured and squeezed out was defined as LDR.
- LDR the ratio of blank diameter D to punch diameter d
- the tensile strength TS is 780 MPa or more
- the Young's modulus in the 45 ° direction with respect to the rolling direction and the rolling direction is 205 GPa or more
- the Young's modulus in the direction perpendicular to the rolling direction has an excellent deep drawability of an average r value of 1.05 or more and a limit drawing ratio (LDR) of 2.03 or more, and desired mechanical properties. Obtained.
- LDR limit drawing ratio
- one or more of strength, Young's modulus in each direction, average r value, and LDR are inferior.
- the embodiment of the present invention has been described above.
- the present invention is not limited to the description that forms part of the disclosure of the present invention according to the present embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.
- the equipment for performing the heat treatment on the steel sheet is not particularly limited.
- the present invention can be applied to steel plates such as hot-rolled steel plates and electrogalvanized steel plates without plating to obtain high strength and high Young's modulus steel plates, and the same effect can be expected.
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Abstract
Description
500≦C*≦1300・・・(1)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。
500≦C*≦1300・・・(2)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V-(12.0/180.9)×Ta)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。
Cは、NbおよびVと析出物(炭化物)を形成することで、焼鈍時の粒成長を制御して、高ヤング率化に寄与するとともに、マルテンサイトによる組織強化を利用する際に、その面積率や硬度を調整するために不可欠な元素である。C量が0.060%未満では、フェライト粒径が粗大化し、また必要な面積率のマルテンサイトを得るのが困難になるとともに、マルテンサイトが硬化しないため、十分な強度が得られない。一方、C量が0.150%を超えると、それに応じてNbおよびVの添加量を多くする必要があり、そうすると、炭化物の効果が飽和するとともに、合金コストが増加する。したがって、C量は0.060%以上0.150%以下とし、好ましくは0.080%以上0.130%以下とする。
Siは、本発明において重要な元素の1つである。フェライト安定化元素であるSiは、焼鈍時の冷却過程においてフェライト変態を促進することでヤング率、平均r値およびLDRを向上させ、またオーステナイト中にCを濃化させることでオーステナイトを安定化させ、低温変態相の生成を促進することができるので、必要に応じて鋼の強度を高めることができる。さらに、フェライトに固溶したSiは、加工硬化能を向上させ、フェライト自身の延性を高める。こうした効果を得るためには、Si量は0.50%以上とする必要がある。一方、Si量が2.20%を超えると、鋼板の溶接性を劣化させ、また、熱間圧延前の加熱時にスラブ表面でファイヤライトの生成を促進し、いわゆる赤スケールと呼ばれる熱延鋼板の表面欠陥の発生を助長させる。さらに、冷延鋼板として使用される場合には、表面に生成するSi酸化物が化成処理性を劣化させる。また、溶融亜鉛めっき鋼板として使用される場合には、表面に生成するSi酸化物が不めっきを誘発する。したがって、Si量は0.50%以上2.20%以下とし、好ましくは0.80%以上2.10%以下とする。
Mnは、焼鈍時の冷却過程において、焼入れ性を高め、低温変態相の生成を促進することで高強度化に大きく寄与し、さらに固溶強化元素としても高強度化に寄与する。このような効果を得るためには、Mn量を1.00%以上とする必要がある。一方、Mn量が3.00%を超えると、焼鈍時の冷却過程でヤング率、平均r値およびLDRの向上に必要なフェライトの生成が著しく抑制され、また、低温変態相が増加することで鋼が極端に高強度化し、加工性が劣化する。また、このような多量のMnは鋼板の溶接性も劣化させる。したがって、Mn量は1.00%以上3.00%以下とし、好ましくは1.50%以上2.80%以下とする。
Pは、固溶強化の作用を有し、所望の強度に応じて添加でき、さらに、フェライト変態を促進するため複合組織化にも有効な元素である。しかしながら、0.100%を超えて含有すると、スポット溶接性の劣化を招く。そのうえ、亜鉛めっきの合金化処理を施す場合では、合金化速度を低下させ、めっき性を損なう。したがって、P量は0.100%以下とする必要がある。P量は、好ましくは0.001%以上0.100%以下とする。
Sは、熱間圧延時の熱間割れを引き起こす要因となる他、硫化物として存在して局部変形能を低下させるため、その含有量は極力低減するのが好ましい。したがって、Sの含有量は0.0100%以下とし、好ましくは0.0050%以下に抑えるのがよい。一方で、Sの含有量を0.0001%未満に抑えることとすると、製造コストが増加する。このため、Sは、0.0001%を下限値とすることが好ましい。したがって、S量は0.0100%以下とし、好ましくは0.0001%以上0.0100%以下、より好ましくは0.0001%以上0.0050%以下とする。
Alは鋼の脱酸元素として有用であるため、Al量は0.010%以上とすることが望ましい。さらに、フェライト生成元素であるAlは、焼鈍時の冷却過程においてフェライト生成を促進し、オーステナイト中にCを濃化させることでオーステナイトを安定化させ、低温変態相の生成を促進するので、必要に応じて鋼の強度を高めることができる。このような効果を得るためには、Al量は0.020%以上とすることがより望ましい。一方、2.500%を超えて含有されると、Ar3変態点を大きく上昇させ、オーステナイト単相域が消失し、オーステナイト域で熱間圧延を終了できなくなる。したがって、Al量は0.010%以上2.500%以下とし、好ましくは0.020%以上2.500%以下とする。
Nは、鋼の耐時効性を劣化させる元素である。特に、Nの含有量が0.0100%を超えると、耐時効性の劣化が顕著となる。したがって、Nの含有量は0.0100%以下とし、好ましくは0.0060%以下に抑えるのがよい。また、生産技術上の制約によっては、0.0005%程度を下限値とするNの含有量を許容してよい。
Nbは、本発明において重要な元素の1つである。Nbは、熱間圧延時あるいは焼鈍時に微細な析出物を形成して、焼鈍時にヤング率、平均r値およびLDRの向上に有利な方位の発達したフェライトを生成させ、また、再結晶粒の粗大化を抑制し、強度の向上に有効に寄与する。特にNbは添加量を適切な量とすることで、焼鈍時に逆変態で生成するオーステナイト相を微細化するため、焼鈍後のミクロ組織も微細化し、強度を上昇させる。このような効果を得るには、Nb量を0.001%以上とする必要がある。一方、Nb量が0.200%を超えると、通常のスラブ再加熱時において炭窒化物を全固溶させることができず、粗大な炭窒化物が残るため、高強度化や再結晶抑制の効果が得られない。また、連続鋳造されたスラブを、一旦冷却したのち再加熱を行う工程を経ることなく、そのまま熱間圧延する場合においても、Nb量が0.200%を超えた分の再結晶抑制効果の寄与分は小さく、合金コストの増加も招いてしまう。したがって、Nb量は0.001%以上0.200%以下とし、好ましくは0.005%以上0.200%以下とする。
Vは、本発明において重要な元素の1つである。Vは、Cと析出物を形成して、焼鈍時にヤング率、平均r値およびLDRの向上に有利な方位の発達したフェライトを生成させ、また、再結晶粒の粗大化を抑制し、強度の向上に有効に寄与する。このような作用を有するためには、V量を0.001%以上とする必要がある。一方、V量が0.200%を超えると、通常のスラブ再加熱時において炭窒化物を全固溶させることができず、粗大な炭窒化物が残るため、高強度化や再結晶抑制の効果が得られない。また、連続鋳造されたスラブを、一旦冷却したのち再加熱を行う工程を経ることなく、そのまま熱間圧延する場合においても、V量が0.200%を超えた分の再結晶抑制効果の寄与分は小さく、合金コストの増加も招いてしまう。したがって、V量は0.001%以上0.200%以下とし、好ましくは0.005%以上0.200%以下とする。
500≦C*≦1300・・・(1)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。
500≦C*≦1300・・・(2)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V-(12.0/180.9)×Ta)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。
本発明では、固溶C量を500質量ppm以上1300質量ppm以下の範囲に制御することで、冷間圧延および焼鈍時にヤング率、平均r値およびLDRの向上に有利な方位を発達させることができ、また強度を確保することができる。このため、固溶C量を表すC*を上記(2)式のように500質量ppm以上1300質量ppm以下とする。なお、上記したように、鋼中のCは、Nb、VおよびTaと析出物を形成する。このため、鋼中の固溶C量は、このような析出を考慮して、上記したC*にて求めることができる。
フェライトはヤング率、平均r値およびLDRの向上に有利な集合組織の発達効果を有する。こうした効果を得るには、フェライトの面積率は20%以上とする必要がある。より良好なヤング率、平均r値およびLDRを得るには、フェライトの面積率は30%以上とすることが好ましい。なお、ここでいうフェライトは、いわゆるフェライトに加えて、炭化物の析出を含まないベイニティックフェライト、ポリゴナルフェライト、アシキュラーフェライトを含む。
マルテンサイトを含有することにより、強度および強度-伸びバランスが向上する。マルテンサイトの面積率が5%未満では、必要な引張強度TS、具体的には780MPa以上の引張強度TSを確保することが困難である。したがって、マルテンサイトの面積率は5%以上とする必要がある。
フェライトの平均結晶粒径が20.0μmを超えると、高強度化が図れない。したがって、フェライトの結晶粒径を微細化し、強度の向上を図るために、フェライトの平均結晶粒径は20.0μm以下とする。また、特に限定する必要はないが、フェライトの平均結晶粒径が1μm未満では、延性が低下傾向にあるため、フェライトの平均結晶粒径は1μm以上であることが好ましい。
α-fiberとは<110>軸が圧延方向に平行な繊維集合組織であり、また、γ-fiberとは<111>軸が圧延面法線方向に平行な繊維集合組織である。体心立方金属では、圧延変形によりα-fiberおよびγ-fiberが強く発達し、再結晶でもそれらに属する集合組織が形成するという特徴がある。
フェライトおよびマルテンサイトでのγ-fiberを発達させることにより、各方向のヤング率、平均r値およびLDRを向上させることができることから、鋼板の1/4板厚におけるフェライトおよびマルテンサイトでのα-fiberに対するγ-fiberのインバース強度比を、1.00以上にする必要がある。ここで、フェライトおよびマルテンサイトでのα-fiberに対するγ-fiberのインバース強度比は、鋼板の圧延方向に平行な板厚断面(L断面)を研磨後、板厚1/4位置(鋼板表面から深さ方向で板厚の1/4に相当する位置)について、SEM-EBSD(Electron Back-Scatter Diffraction;電子線後方散乱回折)法を用いて結晶方位を測定し、得られたデータを、AMETEK EDAX社のOIM Analysisを用いて、各組織(フェライトおよびマルテンサイト)に分離し、各組織のα-fiberおよびγ-fiberのインバース強度比を求めることにより、算出した。
TS780MPa以上の高強度鋼板の適用により板厚を減少させる場合、構造部品の剛性が低下する。したがって、軽量化と構造部品の剛性を両立させるため、本発明のヤング率を、圧延方向、および圧延方向に対して45°方向は205GPa以上、かつ、圧延方向に対して直角方向は220GPa以上に限定する。好ましくは、圧延方向、および圧延方向に対して45°方向は208GPa以上、かつ、圧延方向に対して直角方向は223GPa以上である。より好ましくは、圧延方向、および圧延方向に対して45°方向は210GPa以上、かつ、圧延方向に対して直角方向は225GPa以上である。
TSが780MPa以上の高強度鋼板は、軟鋼板に比べてプレス成形性、特に深絞り性が大きく低下する。したがって、内外板パネルや足回りなどの絞り成形主体の部材に対応するため、本発明例の平均r値を1.05以上に限定し、好ましくは1.07以上、より好ましくは1.10以上とする。
TSが780MPa以上の高強度鋼板は、軟鋼板に比べてプレス成形性、特に深絞り性が大きく低下する。したがって、内外板パネルや足回りなどの絞り成形主体の部材に対応するため、本発明例の限界絞り比(LDR)を2.03以上に限定し、好ましくは2.06以上、より好ましくは2.09以上、さらに好ましくは2.12以上とする。
以下、各工程について詳細に説明する。
鋳造された鋼スラブを加熱する段階で存在しているNbおよびV系の析出物は、そのままでは最終的に得られる鋼板内に粗大な析出物として残存することになり、強度、ヤング率、平均r値およびLDRに寄与しない。このため、鋼スラブの加熱時には、鋳造時に析出したNbおよびV系析出物を再溶解させる必要がある。これによる強度への寄与は、1150℃以上の加熱で認められている。また、スラブ表層の気泡や偏析等の欠陥をスケールオフし、亀裂や凹凸の少ない平滑な鋼板表面を得るためにも、1150℃以上に加熱するのがよい。ただし、加熱温度が1300℃を超えるとオーステナイトの結晶粒の粗大化を引き起こす。その結果、最終組織が粗大化して強度および延性の低下を招く。したがって、鋼スラブは1150℃以上1300℃以下の温度域に加熱する。すなわち、スラブ加熱温度は1150℃以上1300℃以下とする。
熱間圧延工程は、粗圧延および仕上げ圧延からなり、加熱後の鋼スラブは、この粗圧延および仕上げ圧延を経て熱延板となる。この熱間圧延の仕上げ温度が1000℃を超えると、酸化物(熱延スケール)の生成量が急激に増加し、地鉄と酸化物との界面が荒れるため、後段の酸洗工程後や冷間圧延工程後の表面品質を劣化させる。一方で、熱間圧延の仕上げ温度が850℃未満になると、圧延荷重が増大して圧延負荷が大きくなる他、オーステナイトの未再結晶状態での圧下率が上昇して異常な集合組織が発達する。その結果、最終製品における面内異方性が顕著となって、材質の均一性が損なわれるだけでなくヤング率、平均r値およびLDRそのものの低下を招く。したがって、熱間圧延の仕上げ温度は850℃以上1000℃以下とし、好ましくは850℃以上950℃以下とする。
熱間圧延後の熱延板を巻き取る際の巻取温度が800℃を超えると、フェライト粒が粗大化し、冷間圧延での方位の集積が妨げられ、またNbやVの炭窒化物が粗大化し焼鈍時のフェライトの再結晶を抑制する効果や、オーステナイト粒の粗大化を抑制する効果が小さくなる。一方、巻取温度が500℃未満になると、フェライトの他に硬質なベイナイトやマルテンサイトが生成するようになる。この場合、冷間圧延での変形が不均一になる。その結果、焼鈍後の集合組織が発達せず、ヤング率、平均r値およびLDRが向上しない。したがって、巻取温度は、500℃以上800℃以下とする。すなわち、熱間圧延後は500℃以上800℃以下の温度域で巻き取る。
熱間圧延工程後に冷間圧延を行って、ヤング率、平均r値およびLDRの向上に有効なα-fiberおよびγ-fiberを集積させる。すなわち、冷間圧延によりα-fiberおよびγ-fiberを発達させることによって、その後の焼鈍工程後の組織でも、α-fiberおよびγ-fiber、特にγ-fiberを持つフェライトを増やし、ヤング率、平均r値およびLDRを高くする。このような効果を得るには、冷間圧延時の冷延圧下率を40%以上とする必要がある。さらに、ヤング率、平均r値およびLDRを向上させる観点からは、冷延圧下率を50%以上とすることが好ましい。一方で、冷延圧下率が大きくなると、圧延荷重が大きくなって製造が困難になるため、冷延圧下率を80%以下とすることが好ましい。したがって、冷延圧下率は40%以上とし、好ましくは40%以上80%以下、より好ましくは50%以上80%以下とする。なお、圧延パスの回数、各パス毎の冷延圧下率については特に規定することなく本発明の効果は発揮される。
加熱時の焼鈍温度が低い場合には、未再結晶組織が残存し、γ-fiberへの集積が難しくなり、各方向のヤング率、平均r値およびLDRが低下する。このため、焼鈍温度は450℃以上とする。さらに、ヤング率、平均r値およびLDRを向上させる観点からは、焼鈍温度を550℃以上とすることが好ましい。一方、焼鈍温度が800℃を超えると、オーステナイト粒が粗大化し、焼鈍後冷却時に再変態したフェライトがα-fiberおよびγ-fiber、特にγ-fiberに集積することが難しくなる。したがって、加熱工程での焼鈍温度は450℃以上800℃以下とする。すなわち、加熱工程では、450℃以上800℃以下の温度域に加熱する。好ましくは550℃以上800℃以下の温度域に加熱する。
[加熱後の保持工程]
上記した450℃以上800℃以下の温度域での保持時間が300s未満になると、未再結晶組織が残存し、γ-fiberへの集積が難しくなり、各方向のヤング率、平均r値およびLDRが低下する。このため、保持時間は300s以上とする。また、特に限定する必要はないものの、保持時間が100000sを超えると、再結晶フェライト粒径が粗大化するため、保持時間は100000s以下であることが好ましい。したがって、保持時間は300s以上とし、好ましくは300s以上100000s以下とする。加熱後の冷却工程を実施する場合には、室温まで冷却してもよく、また、過時効帯を通過させる処理を施してもよい。なお、特に限定する必要はないものの、室温または過時効帯までの平均冷却速度が80℃/sを超えると、鋼板形状が悪化する可能性があるため、平均冷却速度が80℃/s以下であることが好ましい。
再加熱時の焼鈍温度が750℃未満になると、オーステナイトの生成が不十分となる。その結果、再加熱工程での焼鈍後の冷却工程で十分な量のマルテンサイトが得られずに所望の強度を確保するのが困難となる。また、未再結晶組織が残存してしまい、延性を低下させる。したがって、焼鈍温度は750℃以上とする。また、焼鈍時の焼鈍温度が950℃を超えるとオーステナイトの結晶粒が粗大化し、最終的に得られる鋼板の引張強度TSが低下傾向にあるため、950℃以下であることが好ましい。したがって、再加熱工程での焼鈍温度は750℃以上950℃以下とする。すなわち、再加熱工程では、750℃以上950℃以下の温度域に加熱する。
上記した再加熱工程での焼鈍後の冷却時において、冷却速度が小さくなりすぎると、未変態オーステナイトがパーライトに変態し、所望のマルテンサイトの面積率を確保できずに、所望の強度を確保するのが困難となる。例えば、冷延鋼板とする場合は300℃以上700℃以下の温度域での平均冷却速度が3℃/s未満となると、また、溶融亜鉛めっき鋼板とする場合は550℃以上700℃以下の温度域での平均冷却速度が3℃/s未満となると、未変態オーステナイトがパーライトに変態し、所望のマルテンサイトの面積率を確保できずに、所望の強度を確保するのが困難となる。したがって、冷延鋼板とする場合は300℃以上700℃以下の温度域での平均冷却速度を3℃/s以上とする。また、溶融亜鉛めっき鋼板とする場合は550℃以上700℃以下の温度域での平均冷却速度を3℃/s以上とする。また、特に限定する必要はないものの、上記した平均冷却速度が80℃/sを超えると、鋼板形状が悪化する可能性があるため、上記した平均冷却速度は80℃/s以下であることが好ましい。したがって、冷延鋼板とする場合は300℃以上700℃以下の温度域の、溶融亜鉛めっき鋼板とする場合は550℃以上700℃以下の温度域の平均冷却速度は3℃/s以上とし、好ましくは3℃/s以上80℃/s以下とする。
溶融亜鉛めっきを施す場合は、420℃以上550℃以下の温度域で施すのが好ましく、焼鈍後の冷却工程の中で行うことができる。溶融亜鉛めっき浴は、GI(溶融亜鉛めっき鋼板)では、Al:0.15~0.23質量%を含有する亜鉛浴を使用し、GA(合金化溶融亜鉛めっき鋼板)では、Al:0.12~0.20質量%を含有する亜鉛浴を使用することが好ましい。また、めっき付着量は片面あたり20~70g/m2(両面めっき)が好ましく、GAは、下記の合金化処理を施すことによりめっき層中のFe濃度を7~15質量%とすることが好ましい。
合金化処理時の合金化処理温度が470℃未満になると、合金化が進行しないという問題が生じる。一方で、合金化処理温度が600℃を超える場合、フェライトの結晶粒の粗大化を引き起こし、所望の強度を確保するのが困難となる。したがって、合金化処理温度は470℃以上600℃以下とする。すなわち、亜鉛めっきの合金化処理は、470℃以上600℃以下の温度域で施す。
なお、溶融亜鉛めっき浴は、GIではAl:0.18質量%を含有する亜鉛浴を使用し、GAではAl:0.15質量%を含有する亜鉛浴を使用し、浴温は470℃とした。めっき付着量は片面あたり45g/m2(両面めっき)とし、GAは、めっき層中のFe濃度を9~12質量%とした。
引張試験は、伸長率0.5%の調質圧延を施した鋼板から、引張方向が鋼板の圧延方向となるように採取したJIS Z 2201(1998年)に規定のJIS5号試験片を用いてJIS Z 2241(1998年)に準拠して行い、引張強度TS、全伸びELを測定した。
ヤング率測定は鋼板の圧延方向(L方向)、鋼板の圧延方向に対して45°方向(D方向)、鋼板の圧延方向に対して直角方向(C方向)の3方向から10mm×50mmの試験片を切り出し、横振動型の共振周波数測定装置を用いて、American Society to Testing Materialsの基準(C1259)に従いヤング率を測定した。
平均r値測定は、鋼板の圧延方向(L方向)、鋼板の圧延方向に対して45°方向(D方向)、鋼板の圧延方向に対して直角方向(C方向)の3方向からそれぞれJIS Z 2201(1998年)に規定のJIS5号試験片を用いて、JIS Z 2254の規定に準拠してそれぞれの塑性歪比rL、rD、rCを求め、以下の式により平均r値を算出した。
平均r値=(rL+2rD+rC)/4
なお、本発明では、平均r値≧1.05の場合を平均r値が良好と判定した。
深絞り成形試験は、円筒絞り試験で行い、限界絞り比(LDR)により深絞り性を評価した。円筒深絞り試験条件は、試験には直径33mmφの円筒ポンチを用い、板厚1.2mm材は、ダイス径:36.6mmの金型を用いた。試験は、しわ押さえ力:1.5ton(14.71kN)で行った。めっき状態などにより表面の摺動状態が変わるため、表面の摺動状態が試験に影響しない様、サンプルとダイスの間にポリエチレンシートを置いて高潤滑条件で試験を行った。ブランク径を1mmピッチで変化させ、破断せず絞りぬけたブランク径Dとポンチ径dの比(D/d)をLDRとした。なお、本発明では、LDR≧2.03の場合を深絞り性が良好と判定した。
Claims (14)
- 質量%で、C:0.060%以上0.150%以下、Si:0.50%以上2.20%以下、Mn:1.00%以上3.00%以下、P:0.100%以下、S:0.0100%以下、Al:0.010%以上2.500%以下、N:0.0100%以下、Nb:0.001%以上0.200%以下、およびV:0.001%以上0.200%以下を含有し、C、NbおよびVの含有量が下記(1)式を満たし、残部がFeおよび不可避的不純物からなる成分組成を有し、フェライトの面積率が20%以上、マルテンサイトの面積率が5%以上であり、前記フェライトの平均結晶粒径が20.0μm以下、前記フェライトおよび前記マルテンサイトでのα-fiberに対するγ-fiberのインバース強度比が、それぞれ1.00以上であるミクロ組織を有することを特徴とする高強度高ヤング率鋼板;
500≦C*≦1300・・・(1)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。 - さらに、平均r値が1.05以上、かつ限界絞り比(LDR)が2.03以上であることを特徴とする請求項1に記載の高強度高ヤング率鋼板。
- さらに、質量%で、Cr:0.05%以上1.00%以下、Mo:0.05%以上1.00%以下、Ni:0.05%以上1.00%以下、およびCu:0.05%以上1.00%以下のうちから選ばれる少なくとも1種の元素を含有することを特徴とする請求項1または2に記載の高強度高ヤング率鋼板。
- さらに、質量%で、B:0.0003%以上0.0050%以下を含有することを特徴とする請求項1~3のいずれか1項に記載の高強度高ヤング率鋼板。
- さらに、質量%で、Ca:0.0010%以上0.0050%以下、Mg:0.0005%以上0.0100%以下、およびREM:0.0003%以上0.0050%以下のうちから選ばれる少なくとも1種の元素を含有することを特徴とする請求項1~4のいずれか1項に記載の高強度高ヤング率鋼板。
- さらに、質量%で、Ta:0.0010%以上0.1000%以下を含有し、C、Nb、VおよびTaの含有量が上記(1)式に代えて下記(2)式を満たすことを特徴とする請求項1~5のいずれか1項に記載の高強度高ヤング率鋼板;
500≦C*≦1300・・・(2)
ここで、C*=(C-(12.0/92.9)×Nb-(12.0/50.9)×V-(12.0/180.9)×Ta)×10000であり、式中の各元素記号は各元素の含有量(質量%)を表し、C*の単位は質量ppmである。 - さらに、質量%で、Sn:0.0020%以上0.2000%以下、およびSb:0.0020%以上0.2000%以下のうちから選ばれる少なくとも1種の元素を含有することを特徴とする請求項1~6のいずれか1項に記載の高強度高ヤング率鋼板。
- 前記高強度高ヤング率鋼板が、冷延鋼板であることを特徴とする請求項1~7のいずれか1項に記載の高強度高ヤング率鋼板。
- 前記高強度高ヤング率鋼板が、表面にめっき皮膜を有するめっき鋼板であることを特徴とする請求項1~7のいずれか1項に記載の高強度高ヤング率鋼板。
- 前記めっき皮膜が溶融亜鉛めっき皮膜であり、前記めっき鋼板が溶融亜鉛めっき鋼板であることを特徴とする請求項9に記載の高強度高ヤング率鋼板。
- 前記めっき皮膜が合金化溶融亜鉛めっき皮膜であり、前記めっき鋼板が合金化溶融亜鉛めっき鋼板であることを特徴とする請求項9に記載の高強度高ヤング率鋼板。
- 請求項1~7のいずれか1項に記載の成分組成を有する鋼スラブを1150℃以上1300℃以下の温度域に加熱し、次いで850℃以上1000℃以下の温度域の仕上げ温度で熱間圧延し、500℃以上800℃以下の温度域で巻き取った後、40%以上の冷延圧下率で冷間圧延する工程を経て得られた冷延板を450℃以上800℃以下の温度域に加熱し、当該温度域で300s以上保持し、次いで750℃以上950℃以下に加熱し、その後300℃以上700℃以下の温度域を平均冷却速度3℃/s以上で冷却して冷延鋼板とすることを特徴とする高強度高ヤング率鋼板の製造方法。
- 請求項1~7のいずれか1項に記載の成分組成を有する鋼スラブを1150℃以上1300℃以下の温度域に加熱し、次いで850℃以上1000℃以下の温度域の仕上げ温度で熱間圧延し、500℃以上800℃以下の温度域で巻き取った後、40%以上の冷延圧下率で冷間圧延する工程を経て得られた冷延板を450℃以上800℃以下の温度域に加熱し、当該温度域で300s以上保持し、次いで750℃以上950℃以下に加熱し、次いで550℃以上700℃以下の温度域を平均冷却速度3℃/s以上で冷却した後、溶融亜鉛めっきを施して溶融亜鉛めっき鋼板とすることを特徴とする高強度高ヤング率鋼板の製造方法。
- 請求項1~7のいずれか1項に記載の成分組成を有する鋼スラブを1150℃以上1300℃以下の温度域に加熱し、次いで850℃以上1000℃以下の温度域の仕上げ温度で熱間圧延し、500℃以上800℃以下の温度域で巻き取った後、40%以上の冷延圧下率で冷間圧延する工程を経て得られた冷延板を450℃以上800℃以下の温度域に加熱し、当該温度域で300s以上保持し、次いで750℃以上950℃以下に加熱し、次いで550℃以上700℃以下の温度域を平均冷却速度3℃/s以上で冷却した後、溶融亜鉛めっきを施し、その後470℃以上600℃以下の温度域で亜鉛めっきの合金化処理を施して合金化溶融亜鉛めっき鋼板とすることを特徴とする高強度高ヤング率鋼板の製造方法。
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JP2016141858A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2016141857A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2016141859A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
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EP2998415A1 (en) | 2016-03-23 |
EP2998415B1 (en) | 2017-09-06 |
KR20160014686A (ko) | 2016-02-11 |
US20160186299A1 (en) | 2016-06-30 |
CN105452509A (zh) | 2016-03-30 |
KR101753510B1 (ko) | 2017-07-04 |
EP2998415A4 (en) | 2016-07-13 |
US10385431B2 (en) | 2019-08-20 |
MX2016001272A (es) | 2016-05-24 |
JP5737485B1 (ja) | 2015-06-17 |
CN105452509B (zh) | 2017-06-30 |
JPWO2015015738A1 (ja) | 2017-03-02 |
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