WO2011122030A1 - 加工性に優れた高張力溶融亜鉛めっき鋼板およびその製造方法 - Google Patents
加工性に優れた高張力溶融亜鉛めっき鋼板およびその製造方法 Download PDFInfo
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- WO2011122030A1 WO2011122030A1 PCT/JP2011/001930 JP2011001930W WO2011122030A1 WO 2011122030 A1 WO2011122030 A1 WO 2011122030A1 JP 2011001930 W JP2011001930 W JP 2011001930W WO 2011122030 A1 WO2011122030 A1 WO 2011122030A1
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- Prior art keywords
- less
- hot
- steel sheet
- dip galvanized
- galvanized steel
- Prior art date
Links
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims abstract description 110
- 239000008397 galvanized steel Substances 0.000 title claims abstract description 110
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 25
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 115
- 239000010959 steel Substances 0.000 claims abstract description 115
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 64
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 61
- 239000006104 solid solution Substances 0.000 claims abstract description 44
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 37
- 239000002245 particle Substances 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims abstract description 23
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 20
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 18
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 18
- 239000012535 impurity Substances 0.000 claims abstract description 11
- 239000011159 matrix material Substances 0.000 claims abstract description 7
- 238000005096 rolling process Methods 0.000 claims description 46
- 239000000463 material Substances 0.000 claims description 43
- 238000000137 annealing Methods 0.000 claims description 35
- 238000001816 cooling Methods 0.000 claims description 23
- 238000005246 galvanizing Methods 0.000 claims description 20
- 238000005098 hot rolling Methods 0.000 claims description 16
- 238000004804 winding Methods 0.000 claims description 16
- 229910052758 niobium Inorganic materials 0.000 claims description 11
- 229910052750 molybdenum Inorganic materials 0.000 claims description 10
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 abstract description 5
- 238000000576 coating method Methods 0.000 abstract description 5
- 229910052748 manganese Inorganic materials 0.000 abstract description 4
- 150000001247 metal acetylides Chemical class 0.000 description 49
- 238000000034 method Methods 0.000 description 33
- 238000001556 precipitation Methods 0.000 description 33
- 238000012360 testing method Methods 0.000 description 20
- 238000005452 bending Methods 0.000 description 17
- 239000010408 film Substances 0.000 description 16
- 239000002244 precipitate Substances 0.000 description 15
- 230000000694 effects Effects 0.000 description 14
- 239000010410 layer Substances 0.000 description 14
- 229910004688 Ti-V Inorganic materials 0.000 description 11
- 229910010968 Ti—V Inorganic materials 0.000 description 11
- 238000010438 heat treatment Methods 0.000 description 10
- 238000005728 strengthening Methods 0.000 description 10
- 238000009864 tensile test Methods 0.000 description 10
- 230000008569 process Effects 0.000 description 9
- 239000000758 substrate Substances 0.000 description 9
- 239000002131 composite material Substances 0.000 description 8
- 238000005275 alloying Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 230000007797 corrosion Effects 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 5
- 230000007423 decrease Effects 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 239000013078 crystal Substances 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000005457 optimization Methods 0.000 description 3
- 238000007747 plating Methods 0.000 description 3
- 229910052725 zinc Inorganic materials 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- -1 Ti and Nb Chemical class 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- YLRAQZINGDSCCK-UHFFFAOYSA-M methanol;tetramethylazanium;chloride Chemical compound [Cl-].OC.C[N+](C)(C)C YLRAQZINGDSCCK-UHFFFAOYSA-M 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- 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
-
- 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
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
-
- 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
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
-
- 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
-
- 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
-
- 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
- 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
-
- 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
-
- 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
-
- 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
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
-
- 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
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0224—Two or more thermal pretreatments
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
-
- 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
Definitions
- the present invention relates to a high-tensile hot-dip galvanized steel sheet having a high tensile strength (TS): 980 MPa or more, which is suitable for materials such as automobile parts, and excellent workability, and a method for producing the same.
- TS tensile strength
- Patent Document 1 discloses a carbide containing Ti and Mo having a substantially single-phase ferrite structure and an average particle diameter of less than 10 nm.
- Patent Document 1 A technique related to a high-tensile steel sheet excellent in workability having a tensile strength of 590 MPa or more, characterized by being dispersed and precipitated, has been proposed.
- the technique proposed in Patent Document 1 has a problem of incurring high manufacturing costs because expensive Mo is used.
- a technique relating to a high-strength hot-rolled steel sheet having a steel structure containing 70% by volume or more of ferrite having an average particle diameter of 5 ⁇ m or less and a hardness of 250 Hv or more, having a strength of 880 MPa or more and a yield ratio of 0.80 or more has been proposed.
- Patent Document 3 contains, by mass, C: 0.0002 to 0.25%, Si: 0.003 to 3.0%, Mn: 0.003 to 3.0%, and Al: 0.002 to 2.0%, with the balance being Fe and inevitable impurities.
- P has a composition of 0.15% or less, S is 0.05% or less, and N is 0.01% or less.
- 70% or more of the metal structure is the ferrite phase, and its average crystal
- the grain size is 20 ⁇ m or less, the aspect ratio is 3 or less, 70% or more of the ferrite grain boundaries are composed of large angle grain boundaries, and the maximum diameter is 30 ⁇ m or less and the minimum diameter is 5 nm among the ferrite phases formed at the large angle grain boundaries.
- the area ratio of the precipitate is 2% or less of the metal structure, and the average crystal grain size of the second phase having the largest area ratio among the remaining phases excluding the ferrite phase and the precipitate is 20 ⁇ m or less.
- Patent Document 3 describes that the metal structure is made a ferrite single-phase structure by reducing the C content very much and the content of Mn, which is an austenite stabilizing element.
- Patent Document 4 includes mass%, C: 0.02% to 0.20%, Si: 0.3% or less, Mn: 0.5% to 2.5%, P: 0.06% or less, S: 0.01% or less, Al: 0.1% or less, Ti: 0.05% or more and 0.25% or less, V: 0.05% or more and 0.25% or less, with the remaining component composition consisting of Fe and inevitable impurities, and substantially a ferrite single-phase structure, the ferrite In the single-phase structure, Ti contained in precipitates having a size of less than 20 nm is 200 massppm or more and 1750 massVppm or less, V is 150 mass ppm or more and 1750 mass ppm or less, and the solid solution V is 200 mass ppm or more and less than 1750mass ppm A technique relating to a high-strength steel sheet excellent in stretch flange characteristics after processing and corrosion resistance after painting, characterized by having a certain structure has been proposed.
- the strength of the steel sheet is increased by refining precipitates contained in the steel sheet (less than 20 nm in size). Moreover, in the technique described in Patent Document 4, a precipitate containing Ti-V is used as a precipitate that can maintain the precipitate contained in the steel sheet as fine as possible, and further, the amount of solute V contained in the steel sheet is desired. By making it into this range, the stretch flange characteristics after processing are improved. According to the technique described in Patent Document 4, it is said that a high-strength hot-rolled steel sheet having excellent stretch flangeability after processing and corrosion resistance after coating and having a tensile strength of 780 MPa or more is obtained. The obtained hot-rolled steel sheet is also suitable as a substrate for a hot-dip galvanized steel sheet on which a hot-dip galvanized film or an alloyed hot-dip galvanized film is formed.
- a hot-rolled steel sheet having excellent workability (elongation and stretch flangeability) and strength up to about 780 MPa class can be produced.
- the size of the precipitate is set to less than 20 nm.
- precipitation strengthening is further refined, and the precipitate having a particle diameter of less than about 10 nm is used.
- the precipitation strengthening ability tends to be unstable only by defining the size of less than 20 nm. For this reason, the technique proposed in Patent Document 4 has a problem that it is difficult to reliably ensure a strength of 980 MPa or higher while maintaining excellent workability.
- the present invention advantageously solves the above-mentioned problems of the prior art, and is suitable for automobile parts, for tensile parts (TS): 980 MPa or more, and for suspension parts with a complicated cross-sectional shape during pressing, etc.
- TS tensile parts
- the present inventors have made high-strength and workability (elongation, stretch-flangeability or further bending characteristics) of a hot-dip galvanized steel sheet, and a hot-rolled steel sheet as a hot-dip galvanized steel sheet substrate.
- Hot research was conducted on hot dip galvanizing properties and various factors affecting productivity in the industrial mass production of hot dip galvanized steel sheets.
- the following findings were obtained. 1)
- the steel sheet structure is a ferrite single-phase structure with low dislocation density and excellent workability, and fine carbides are dispersed and precipitated and strengthened by precipitation, the elongation of the hot dip galvanized steel sheet is not reduced so much and the strength is improved.
- the deterioration of the characteristics of the end of the hot rolled steel sheet in the width direction seen in the prior art is that the end of the width direction becomes supercooled during cooling after hot rolling, and Ti-V fine carbide is sufficiently dispersed and precipitated. Not due to not. 9)
- the coiling temperature of the hot-rolled sheet By setting the coiling temperature of the hot-rolled sheet to be lower than the coiling temperature suitable for the precipitation of Ti-V type fine carbide, the internal oxide layer of the hot-rolled sheet is suppressed and the hot dip galvanizing property is improved. To do.
- the bending properties should be improved by making the total of solid solution Ti and solid solution V in the steel more than a predetermined amount. Moreover, the total of solid solution Ti and solid solution V in steel can be controlled more than predetermined amount by controlling the cooling rate after the finish rolling in hot rolling.
- the present invention has been completed based on the above findings, and the gist thereof is as follows.
- the processing further comprises one or two of Cr: 1% or less and B: 0.003% or less by mass%. High-tensile hot-dip galvanized steel sheet with excellent properties.
- the processing further comprises 0.01% or less of one or two of Nb and Mo in total by mass%. High-tensile hot-dip galvanized steel sheet with excellent properties.
- Hot rolling consisting of rough rolling and finish rolling is performed on the steel material, and after finishing rolling, cooling, winding, hot-rolled sheet is made, and the hot-rolled sheet is continuously annealed, hot-dip galvanized or
- the steel material in mass%, C: 0.07% or more and 0.13% or less, Si: 0.3% or less, Mn: 0.5% to 2.0%, P: 0.025% or less, S: 0.005% or less, N: 0.0060% or less, Al: 0.06% or less, Ti: 0.10% or more and 0.14% or less, V: Contains 0.15% or more and 0.30% or less, and contains C, Ti, V, S and N so as to satisfy the following formulas (1) and (2), with the balance being Fe and inevitable impurities
- the finish rolling finish temperature of the finish rolling is 880 ° C.
- the winding temperature of the winding is 480 ° C. or higher and lower than 580 ° C.
- the annealing temperature of the continuous annealing treatment is 750 ° C. or lower.
- the composition further comprises one or two of Cr: 1% or less and B: 0.003% or less by mass%.
- a method for producing a tension hot-dip galvanized steel sheet in any one of (5) to (7), in addition to the above composition, the composition further includes one or two of Nb and Mo in a mass% of 0.01% or less in total. A method for producing a tension hot-dip galvanized steel sheet.
- excellent workability (elongation, elongation flange) suitable for automobile steel sheets and the like, which can be applied as a material for undercarriage parts having a tensile strength (TS) of 980 MPa or more and a complicated sectional shape, etc.
- TS tensile strength
- High-tensile hot-dip galvanized steel sheet having excellent surface quality and good surface quality can be industrially stably produced, and has a remarkable industrial effect.
- the ferrite phase has a matrix area ratio of 97% or more with respect to the entire structure, and fine carbides containing Ti and V and having an average particle diameter of less than 10 nm are dispersed and precipitated. It is a steel plate formed by forming a hot-dip galvanized film or an alloyed hot-dip galvanized film on the surface of a hot-rolled steel sheet having a structure of 0.007 or more in volume ratio with respect to the entire structure.
- Ferrite phase 97% or more in area ratio with respect to the entire structure
- formation of a ferrite phase is essential to ensure the workability (elongation and stretch flangeability) of the hot-dip galvanized steel sheet.
- it is effective to make the structure of the hot dip galvanized steel sheet a ferrite phase having a low dislocation density and excellent ductility.
- the structure of the hot-dip galvanized steel sheet is a ferrite single phase, but even if it is not a complete ferrite single phase, it is substantially a ferrite single phase, that is, the entire structure. If the ferrite phase is 97% or more in terms of the area ratio relative to the above, the above effect is sufficiently exhibited. Therefore, the area ratio of the ferrite phase to the entire structure is 97% or more.
- examples of the structure other than the ferrite phase include cementite, pearlite phase, bainite phase, martensite phase, residual austenite phase, and the like. If it is less than about, it is acceptable.
- Fine carbides containing Ti and V Carbides containing Ti and V tend to be fine carbides having an extremely small average particle size. Therefore, in the present invention for increasing the strength of a hot dip galvanized steel sheet by dispersing and precipitating fine carbide in the hot dip galvanized steel sheet, the fine carbide containing Ti and V is used as the fine carbide to be dispersed and precipitated.
- the present invention is characterized by using a carbide containing V together with Ti. Since Ti has a strong tendency to form carbides, when it does not contain V, Ti carbides are likely to coarsen, and the contribution to increasing the strength of the steel sheet is reduced. Therefore, in order to give the steel sheet a desired strength (tensile strength: 980 MPa or more), it is necessary to add more Ti to form Ti carbide.
- the hot-dip galvanized steel sheet of the present invention when manufacturing a hot-rolled steel sheet as a substrate of the hot-dip galvanized steel sheet of the present invention, it is necessary to dissolve carbides in the steel material before hot rolling.
- the desired strength tensile strength: 980 MPa or more
- the previous slab heating temperature must be as high as 1300 ° C.
- Such a slab heating temperature is a temperature exceeding a general slab heating temperature before hot rolling, which requires special equipment, and is difficult to manufacture with current production equipment.
- a composite carbide containing V together with Ti is used as the carbide to be dispersed and precipitated.
- V is effective in suppressing the coarsening of the carbide because the tendency of carbide formation is lower than that of Ti.
- the combination of Ti and V is an extremely effective combination for lowering the dissolution temperature of carbides, by using a composite carbide containing V together with Ti, the dissolution temperature of carbides is higher than the dissolution temperature of Ti single carbides. Is also significantly reduced.
- the fine carbide containing Ti and V does not include a single carbide in the structure, but refers to a composite carbide in which both Ti and V are contained in one fine carbide.
- Average particle diameter of fine carbide less than 10 nm
- the average particle diameter of fine carbide is extremely important for imparting the desired strength (tensile strength: 980 MPa or more) to hot-dip galvanized steel sheets.
- the average particle size of the fine carbide contained is set to less than 10 nm.
- the fine carbide acts as a resistance to dislocation movement that occurs when the steel sheet is deformed, thereby strengthening the hot-dip galvanized steel sheet.
- the thickness is less than 10 nm, the above action becomes more remarkable. Therefore, the average particle diameter of the fine carbide containing Ti and V is less than 10 nm. More preferably, it is 5 nm or less.
- volume ratio of fine carbide to the entire structure 0.007 or more
- the desired strength tensile strength: 980 MPa or more
- the dispersion and precipitation state of fine carbide containing Ti and V is extremely important.
- fine carbides containing Ti and V and having an average particle diameter of less than 10 nm are dispersed and precipitated so that the structure fraction of the whole structure is 0.007 or more in volume ratio.
- the desired hot-dip galvanized steel sheet strength tensile strength: 980 MPa or more
- the tissue fraction is set to 0.007 or more. Preferably, it is 0.008 or more.
- the precipitation form of fine carbides containing Ti and V in addition to the row precipitation that is the main precipitation form, even if fine carbides that are randomly precipitated are mixed, the characteristics are affected.
- the form of precipitation is not limited, and various precipitation forms are collectively referred to as dispersion precipitation.
- C 0.07% or more and 0.13% or less C is an element essential for forming fine carbides and strengthening the hot dip galvanized steel sheet. If the C content is less than 0.07%, fine carbide having a desired structure fraction cannot be secured, and a tensile strength of 980 MPa or more cannot be obtained. On the other hand, if the C content exceeds 0.13%, problems such as spot welding become difficult. Therefore, the C content is 0.07% or more and 0.13% or less. Preferably, it is 0.08% or more and 0.12% or less.
- the Si content is 0.3% or less.
- the Si content is 0.3% or less.
- it is 0.15% or less, desirably 0.05% or less.
- Mn 0.5% or more and 2.0% or less
- Mn is a solid solution strengthening element and is an element effective for increasing the strength. From the viewpoint of strengthening the hot dip galvanized steel sheet, the Mn content is preferably 0.5% or more. However, when the Mn content exceeds 2.0%, segregation becomes significant, and a phase other than the ferrite phase, that is, a hard phase. Is formed, and stretch flangeability is reduced. Therefore, the Mn content is 0.5% or more and 2.0% or less. Preferably they are 1.0% or more and 2.0% or less.
- the P content is 0.025% or less.
- the P content is 0.025% or less.
- it is 0.02% or less.
- S 0.005% or less
- S is an element that decreases the hot workability (hot rollability), and increases the hot cracking susceptibility of the slab. Degradation of stretch flangeability). Therefore, in the present invention, it is preferable to reduce S as much as possible, and set it to 0.005% or less. Preferably it is 0.003% or less.
- N 0.0060% or less
- N is a harmful element in the present invention and is preferably reduced as much as possible.
- the N content exceeds 0.0060%, the stretch flangeability deteriorates due to the formation of coarse nitrides in the steel. Therefore, the N content is 0.0060% or less.
- Al 0.06% or less
- Al is an element that acts as a deoxidizer. In order to acquire such an effect, it is desirable to contain 0.001% or more, but inclusion exceeding 0.06% reduces elongation and stretch flangeability. For this reason, Al content shall be 0.06% or less.
- Ti 0.10% or more and 0.14% or less Ti is one of the important elements in the present invention.
- Ti is an element that contributes to increasing the strength of a steel sheet while ensuring excellent elongation and stretch flangeability by forming a composite carbide with V. If the Ti content is less than 0.10%, the desired hot-dip galvanized steel sheet strength (tensile strength: 980 MPa or more) cannot be ensured. On the other hand, if the Ti content exceeds 0.14%, the stretch flangeability tends to decrease. Further, when manufacturing a hot-rolled steel sheet as a hot-dip galvanized steel sheet substrate, there is a high possibility that carbides will not dissolve unless the slab heating temperature before hot rolling is set to a high temperature of 1300 ° C.
- Ti content shall be 0.10% or more and 0.14% or less.
- V 0.15% or more and 0.30% or less
- V is one of the important elements in the present invention.
- V is an element that strengthens the hot-dip galvanized steel sheet while ensuring excellent elongation and stretch flangeability by forming composite carbide with Ti. If the V content is less than 0.15%, the desired steel plate strength (tensile strength: 980 MPa or more) cannot be ensured. On the other hand, when the V content exceeds 0.30%, center segregation becomes prominent, leading to a decrease in elongation and toughness. Therefore, the V content is 0.15% or more and 0.30% or less.
- the hot dip galvanized steel sheet of the present invention contains C, N, S, Ti, and V so as to satisfy the above formulas (1) and (2).
- Ti ⁇ 0.10+ (N / 14 ⁇ 48 + S / 32 ⁇ 48) (1) 0.8 ⁇ (Ti / 48 + V / 51) / (C / 12) ⁇ 1.2 ⁇ ⁇ ⁇ (2) (C, Ti, V, S, N: content of each element (mass%))
- the above formulas (1) and (2) are requirements that must be satisfied in order to bring the fine carbide containing Ti and V into the above-described desired precipitation state, and are extremely important indices in the present invention.
- fine carbides containing Ti and V are dispersed and precipitated in the hot-dip galvanized steel sheet.
- This fine carbide dissolves the carbides in the steel material by heating before hot rolling, and thereafter Precipitated during hot rolling, cooling after hot rolling, winding and continuous annealing. Further, the fine carbide is formed by first Ti being precipitated as a nucleus and V being precipitated in a composite manner.
- the fine carbide the size of which is less than the average particle diameter of less than 10 nm, so that the volume ratio with respect to the entire structure of the finally obtained hot-dip galvanized steel sheet is 0.007 or more.
- the Ti, N and S contents are controlled so as to satisfy the formula (1) Ti ⁇ ⁇ 0.10+ (N / 14 ⁇ 48 + S / 32 ⁇ 48). This ensures a sufficient amount of Ti as a nucleus for precipitation of fine carbides, and allows the fine carbides to be stably precipitated with an average particle size of less than 10 nm. It can be dispersed and precipitated so that the proportion of the whole is 0.007 or more by volume.
- the Ti, N, and S contents in the steel that is the material of the hot dip galvanized steel sheet are controlled so as to satisfy the formula (1) Ti ⁇ 0.10+ (N / 14 ⁇ 48 + S / 32 ⁇ 48). .
- the content of Ti, V, and C in the steel that is the material of the hot dip galvanized steel sheet satisfies the following formula (2): 0.8 ⁇ (Ti / 48 + V / 51) / (C / 12) ⁇ 1.2 To control.
- Solid solution V 0.04% or more and 0.1% or less Solid solution V effectively works to improve stretch flangeability of hot-dip galvanized steel sheet.
- the content of solute V is less than 0.04%, the above effect will not be fully manifested, and it can be used as a material for undercarriage parts with complex cross-sectional shapes. Applicable stretch flangeability cannot be ensured.
- the content of solute V exceeds 0.1%, the above effect is saturated, and fine carbides containing Ti and V necessary to ensure the desired steel sheet strength (tensile strength: 980 MPa or more) Not enough.
- the solid solution V amount is 0.04% or more and 0.1% or less.
- they are 0.04% or more and 0.07% or less. More preferably, it is 0.04% or more and 0.06% or less.
- Solid solution Ti 0.05% or less
- the present invention contains the desired solid solution V for the purpose of ensuring stretch flangeability of the hot dip galvanized steel sheet, but such effect is recognized in the solid solution Ti.
- solute Ti means that the amount of Ti that effectively acts as a nucleus for precipitation is substantially reduced. Therefore, in order to ensure the desired steel plate strength (tensile strength: 980 MPa or more), the solid solution Ti is made 0.05% or less. Preferably it is 0.03% or less, More preferably, it is 0.02% or less.
- Total of solid solution V and solid solution Ti 0.07% or more
- the grain boundary is strengthened and the bending characteristics are improved.
- the total amount of solid solution V (0.04% or more and 0.1% or less) and solid solution Ti (0.05% or less) is 0.15% or less.
- the total amount of the solid solution V and the solid solution Ti is preferably set to 0.10% or less.
- the above is the basic composition in the present invention.
- one or two of Cr: 1% or less and B: 0.003% or less can be further contained. Both Cr and B are elements having an action of increasing the strength of steel, and can be selected and contained as necessary.
- Cr 1% or less Cr is an element that effectively acts in strengthening the ferrite phase in a solid solution state. In order to acquire such an effect, it is desirable to contain 0.05% or more, but even if it contains exceeding 1%, the effect is saturated and it is not economical. Therefore, the Cr content is preferably 1% or less.
- B 0.003% or less
- B is an element effective in lowering the Ar 3 transformation point of steel, and may be used to adjust the area ratio of the entire structure of the ferrite phase during the cooling process in hot rolling. .
- the B content is preferably 0.003% or less.
- B content shall be 0.0005% or more.
- Nb and Mo are combined with Ti and V to form a composite carbide and contribute to obtaining a desired strength. Therefore, Nb and Mo can be contained as necessary. In order to obtain such effects, it is preferable to contain Nb and Mo in a total amount of 0.005% or more. However, since the elongation tends to deteriorate if contained excessively, it is preferable that one or two of Nb and Mo be 0.01% or less in total amount.
- components other than the above are Fe and inevitable impurities.
- Inevitable impurities include O, Cu, Sn, Ni, Ca, Co, As and the like. These are allowed to contain 0.1% or less, but preferably 0.03% or less.
- the steel material is subjected to hot rolling consisting of rough rolling and finish rolling. After finishing rolling, the steel material is cooled, wound, and formed into a hot-rolled sheet.
- the hot-rolled sheet is continuously annealed, hot-dip galvanized or further alloyed.
- the treatment is sequentially performed to obtain a hot dip galvanized steel sheet.
- the finish rolling finish temperature of finish rolling is set to 880 ° C. or higher
- the winding temperature is set to 480 ° C. or higher and lower than 580 ° C.
- the annealing temperature in the continuous annealing treatment is set to 750 ° C. or lower.
- the average cooling rate of the cooling after hot rolling is preferably 20 ° C./s or more.
- the melting method of the steel material is not particularly limited, and a known melting method such as a converter or an electric furnace can be employed. Moreover, after melting, it is preferable to use a slab (steel material) by a continuous casting method because of problems such as segregation, but a slab can also be formed by a known casting method such as ingot-bundling rolling or thin slab continuous casting. good. In addition, when hot-rolling the slab after casting, it may be rolled after reheating the slab in a heating furnace, and when the temperature is maintained at a predetermined temperature or higher, direct-rolling without heating the slab You may do it.
- the steel material obtained as described above is subjected to rough rolling and finish rolling.
- the heating temperature of the steel material is preferably 1150 ° C. or higher and 1280 ° C. or lower.
- the step of heating the steel material before rough rolling can be omitted. It is.
- the rough rolling conditions are not particularly limited.
- Finishing rolling end temperature 880 ° C. or more Optimization of the finishing rolling end temperature is important for securing elongation and stretch flangeability of the hot-rolled steel sheet and reducing the rolling load of finish rolling.
- the finish rolling finish temperature is less than 880 ° C.
- the crystal grains of the hot rolled steel sheet surface layer become coarse grains, and the elongation and stretch flangeability are impaired.
- the finish rolling finish temperature is set to 880 ° C. or higher.
- the finish rolling finish temperature is 900 degreeC or more. If the finish rolling finish temperature is excessively high, the crystal grains become coarse and adversely affect the desired strength of the steel sheet (tensile strength: 980 MPa or more), so the finish rolling finish temperature may be 1000 ° C. or less. desirable.
- Winding temperature 480 ° C or more and less than 580 ° C Optimization of the winding temperature suppresses the internal oxide layer of the hot-rolled steel sheet (hot-rolled sheet) that will be the substrate of the hot-dip galvanized steel sheet, and finally obtains the melt
- the desired structure of the structure of the galvanized steel sheet in the entire width direction of the steel sheet that is, a matrix in which the ferrite phase is 97% or more in terms of the area ratio with respect to the entire structure, and fine carbides containing Ti and V and having an average particle diameter of less than 10 nm It is extremely important for dispersing and precipitating to obtain a structure having a volume ratio of 0.007 or more with respect to the entire structure of the fine carbide.
- the coiling temperature is set to 480 ° C. or more and less than 580 ° C.
- the coiling temperature is the coiling temperature measured at the center in the width direction of the rolled material, or the coiling temperature at the center in the width direction of the rolled material calculated by simulation or the like.
- the cooling to coiling temperature shall be cooling of an average cooling rate: 20 degrees C / s or more.
- the average cooling rate from the temperature of 880 ° C. or higher to the coiling temperature is less than 20 ° C./s after the finish rolling is finished, the Ar 3 transformation point tends to be high, and carbides containing Ti and V are likely to be coarsened. For this reason, the solid solution V and solid solution Ti in steel effective in improving bendability are easily consumed.
- the total of the solid solution V and the solid solution Ti is 0.07% or more.
- the average cooling rate is preferably 20 ° C./s or more. More preferably, it is 30 ° C./s or more.
- the upper limit value of the average cooling rate is not particularly defined, but from the viewpoint of preventing uneven cooling, the average cooling rate is preferably 60 ° C./s or less.
- the hot-rolled sheet obtained as described above is sequentially subjected to continuous annealing, hot-dip galvanizing or further alloying to obtain a hot-dip galvanized steel sheet. This is the optimization of the annealing temperature.
- a hot dip galvanizing process, or a further alloying process it is preferable to perform by a continuous hot dip galvanizing line (CGL) from a viewpoint of production efficiency.
- Annealing temperature 750 ° C. or less
- the coiling temperature of the hot-rolled sheet is lowered. It is set. That is, in the present invention, the coiling temperature of the hot-rolled sheet is set to a temperature lower than the coiling temperature suitable for the precipitation of fine carbides containing Ti and V. Precipitation of fine carbides containing Ti and V is insufficient at the direction end.
- the annealing temperature in the continuous annealing process is optimized, and the precipitation of fine carbides including Ti and V is promoted during the continuous annealing process.
- the annealing temperature is set. It is appropriate that the temperature is 750 ° C or lower. Even if this annealing temperature is raised to over 750 ° C., the effect is saturated, so there is no need to raise it further.
- an annealing temperature shall be 700 degrees C or less. Further, when the annealing temperature is less than 600 ° C., precipitation of the fine carbides tends to be insufficient, so the annealing temperature is preferably 600 ° C. or higher.
- conditions other than the annealing temperature are not particularly limited, but it is preferable to hold the annealing temperature at 120 to 300 s.
- the hot dip galvanizing treatment condition and the alloying treatment condition are not particularly limited, and the hot dip galvanized film or the alloyed hot dip galvanized film can be formed under generally known conditions.
- hot dip galvanizing with excellent workability (elongation and stretch flangeability) that can be used as a material for undercarriage parts with a tensile strength (TS) of 980 MPa or more and a complicated cross-sectional shape.
- TS tensile strength
- Ti Ti ⁇ 0.10 + (N / 14 ⁇ 48 + S / 32 ⁇ 48)
- N and S content in the steel that is the material of the hot dip galvanized steel sheet.
- C, Ti, V in the steel that is the material of the hot dip galvanized steel sheet satisfies the predetermined relationship (0.8 ⁇ (Ti / 48 + V / 51) / (C / 12) ⁇ 1.2)
- the composition is controlled so that fine carbides having an average particle size of less than 10 nm are sufficiently dispersed and precipitated.
- the winding temperature of the hot-rolled sheet is set to a temperature lower than the winding temperature suitable for the precipitation of fine carbides containing Ti and V. Precipitation of fine carbides including Ti and V is insufficient.
- fine carbides containing Ti and V are precipitated in the continuous annealing process before the hot dip galvanizing process. Yes. Therefore, when manufacturing a hot-rolled sheet to be a hot-dip galvanized steel sheet substrate, even if overcooling occurs in the width direction end in the cooling and winding after finishing rolling, the end in the width direction is subjected to continuous annealing treatment.
- the solid solution Ti can be 0.07% or more in the total amount. Thereby, it becomes a hot-dip galvanized steel sheet having good bending characteristics.
- a hot-rolled sheet serving as a substrate for a hot-dip galvanized steel sheet suppresses the formation of an internal oxide layer, so that a hot-dip galvanized steel sheet having excellent surface quality is obtained.
- Example 1 Molten steel having the composition shown in Table 1 was melted and continuously cast by a generally known technique to obtain a slab (steel material) having a thickness of 250 mm. These slabs are heated to 1250 ° C, then roughly rolled, and subjected to finish rolling at the finish rolling end temperature shown in Table 2, wound at the winding temperature shown in Table 2, and a hot rolled sheet having a thickness of 2.3 mm. It was. Various hot-rolled sheets obtained as described above were subjected to continuous annealing treatment at the annealing temperature and annealing temperature under the conditions shown in Table 2 in a continuous hot-dip galvanizing line, and then hot-dip zinc at 550 ° C.
- a hot dip galvanized steel sheet was manufactured by dip galvanizing and applying a hot dip galvanizing treatment to form a hot dip galvanized film on the surface.
- the coating amount was 50 g / m 2 .
- Some hot-rolled sheets were subjected to alloying treatment under the conditions shown in Table 2 after the hot dip galvanizing treatment.
- Samples were collected from the hot-dip galvanized steel sheet obtained as described above, and subjected to structure observation, tensile test, and hole expansion test.
- the ferrite phase area ratio, the average particle diameter and volume ratio of fine carbides containing Ti and V, The dissolved V content, the solid solution Ti content, the presence or absence of the internal oxide layer, the tensile strength, the total elongation, and the hole expansion rate (stretch flangeability) were determined.
- the test method was as follows.
- test piece was taken from the obtained hot-dip galvanized steel sheet (part of the hot-rolled steel sheet other than the hot-dip galvanized film in the hot-dip galvanized steel sheet) (plate width direction central part), and the test piece was rolled. After mechanically polishing the directional cross section and corroding with nital, using a structure photograph (SEM photograph) taken at a magnification of 3000x with a scanning electron microscope (SEM), using an image analyzer, other than ferrite phase and ferrite phase The types of tissues and their area ratios were determined.
- the thin film produced from the hot dip galvanized steel sheet (part of the hot galvanized steel sheet other than the hot dip galvanized film in the hot dip galvanized steel sheet) (plate width direction central part) was observed with a transmission electron microscope (TEM), Ti The particle size and volume ratio of fine carbides containing V and V were determined.
- the vicinity of the surface layer was observed with a scanning electron microscope (SEM) at a magnification of 5000 times to determine the presence or absence of the internal oxide layer.
- SEM scanning electron microscope
- All examples of the present invention have high tensile strength TS: 980 MPa or more, total elongation El: 15% or more, and excellent workability of hole expansion ratio ⁇ : 40% or more, and the internal oxide layer is suppressed.
- This is a hot-dip galvanized steel sheet.
- it is confirmed that a predetermined high strength is not ensured, or whether the desired total elongation El and the hole expansion ratio ⁇ are not ensured, or a large amount of internal oxide layers are confirmed. .
- JIS IV No. 5 tensile test specimens were collected in the same manner as above from the vicinity of the edge in the plate width direction (edge portion) in addition to the center portion in the plate width direction described above. Then, a tensile test was performed. Table 4 shows the results of comparing the plate width direction central portion and the plate width direction end portion vicinity (edge portion) with respect to the tensile strength (TS) measured by the tensile test.
- the tensile strength TS equivalent to the center part in the plate width direction is obtained even in the vicinity (edge part) in the plate width direction, and the properties are excellent also in the end part in the plate width direction. I understand.
- Example 2 Molten steel having the composition shown in Table 5 is melted and continuously cast into a slab (steel material) having a thickness of 250 mm by a generally known method. These slabs are heated to 1250 ° C. and roughly rolled, and shown in Table 6. Finish rolling is performed at the finish rolling end temperature, cooled at the average cooling rate shown in Table 6 (average cooling rate from the finish rolling end temperature to the winding temperature), wound at the winding temperature shown in Table 6, and sheet thickness : 2.3 mm hot-rolled steel sheet.
- the various hot-rolled sheets obtained as described above were subjected to continuous annealing treatment at the annealing temperature and annealing temperature under the conditions shown in Table 6 in a continuous hot dip galvanizing line, and then melted at 550 ° C.
- a hot dip galvanized steel sheet was manufactured by dipping in zinc and performing hot dip galvanizing treatment to form a hot dip galvanized film on the surface. The coating amount was 50 g / m 2 . Further, some hot-rolled sheets were subjected to an alloying treatment under the conditions shown in Table 6 after the hot dip galvanizing treatment.
- Samples are taken from the hot-dip galvanized steel sheet (center in the plate width direction) obtained as described above, and subjected to structure observation, tensile test, and hole expansion test, and the ferrite phase area ratio, average of fine carbides containing Ti and V
- the particle diameter and volume ratio, solute V content, solute Ti content, presence or absence of internal oxide layer, tensile strength, total elongation, and hole expansion ratio (stretch flangeability) were determined.
- the test method was the same as in Example 1. Moreover, the bending test piece was extract
- All examples of the present invention have high tensile strength TS: 980 MPa or more, total elongation El: 15% or more, and excellent workability of hole expansion ratio ⁇ : 40% or more, and the internal oxide layer is suppressed.
- This is a hot-dip galvanized steel sheet.
- the tensile strength TS high strength of 980 MPa or more, total elongation El: 15% or more, and the hole expansion ratio ⁇ : 40% or more
- it also has excellent bending characteristics such as the critical bending radius R / t: 0.7 or less, and it is a hot-dip galvanized steel sheet with excellent workability.
- the tensile strength TS equivalent to the center part in the plate width direction is obtained even in the vicinity (edge part) in the plate width direction, and the properties are excellent also in the end part in the plate width direction. I understand.
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Abstract
Description
優れた加工性を確保しつつ鋼板の高強度化を図る技術としては、例えば、特許文献1には、実質的にフェライト単相組織であり、平均粒子径10nm未満のTiおよびMoを含む炭化物が分散析出していることを特徴とする、引張強さが590MPa以上の加工性に優れた高張力鋼板に関する技術が提案されている。しかしながら、特許文献1で提案された技術では、高価なMoを利用するため、製造コスト高を招くという問題を有していた。
また、特許文献3には、質量%で、C:0.0002~0.25%、Si:0.003~3.0%、Mn:0.003~3.0%及びAl:0.002~2.0%を含有し、残部はFe及び不可避的不純物からなり、不可避的不純物中のPは0.15%以下、Sは0.05%以下、Nは0.01%以下である成分組成を有し、面積割合で金属組織の70%以上がフェライト相で、その平均結晶粒径が20μm以下、アスペクト比が3以下であり、フェライト粒界の70%以上が大角粒界からなり、大角粒界で形成されたフェライト相のうち、最大径が30μm以下、最小径が5nm以上である析出物の面積割合が金属組織の2%以下であり、フェライト相と析出物とを除く残部相のなかで面積割合が最大である第二相の平均結晶粒径が20μm以下であり、最も近い第二相間にフェライト相の大角粒界が存在することを特徴とする熱延鋼板に関する技術が提案されている。また、特許文献3には、C含有量を非常に少なくし、かつオーステナイト安定化元素であるMnの含有量を少なくすることで、金属組織をフェライト単相組織とすることが記載されている。
1)鋼板組織を転位密度が低い加工性に優れたフェライト単相組織とし、更に、微細炭化物を分散析出させて析出強化すると、溶融亜鉛めっき鋼板の伸びはさほど落ちず、強度が向上すること。
3)析出強化に寄与する微細炭化物としては、強度確保等の観点からは、Ti-Vを含む炭化物が有効であること。
6)溶融亜鉛めっき鋼板に所定量以上の固溶Tiが多量に存在すると、引張強さが目標に達しないこと。
7)溶融亜鉛めっき鋼板組織のマトリックスを実質的にフェライト単相とし、上記の如く10nm未満であるTi-V系微細炭化物を所望の体積率で分散析出させるためには、熱延板の巻取り温度および溶融亜鉛めっき処理前に行う連続焼鈍処理の焼鈍温度を所望の温度範囲に制御することが重要であること。
9)熱延板の巻取り温度を、Ti-V系微細炭化物の析出に適した巻取り温度よりも低く設定することにより、熱延板の内部酸化層が抑制され、溶融亜鉛めっき性が向上すること。
11)連続焼鈍処理時に析出するTi-V系微細炭化物は、フェライト相内に分散析出した析出形態を有すること。
13)上記に加えて更に、鋼中の固溶Tiと固溶Vの合計を所定量以上とすることで、曲げ特性が向上すること。また、熱間圧延における仕上げ圧延後の冷却速度を制御することで、鋼中の固溶Tiと固溶Vの合計を所定量以上に制御できること。
(1) 質量%で、
C :0.07%以上0.13%以下、 Si:0.3%以下、
Mn:0.5%以上2.0%以下、 P :0.025%以下、
S :0.005%以下、 N :0.0060%以下、
Al:0.06%以下、 Ti:0.10%以上0.14%以下、
V :0.15%以上0.30%以下
を、C、Ti、V、SおよびNが下記(1)式および(2)式を満足するように含有し、且つ、固溶V:0.04%以上0.1%以下、固溶Ti:0.05%以下であり、残部がFeおよび不可避的不純物からなる組成と、フェライト相の組織全体に対する面積率が97%以上であるマトリックスと、TiおよびVを含み平均粒子径が10nm未満である微細炭化物が分散析出し、該微細炭化物の組織全体に対する体積率が0.007以上である組織とを有する熱延鋼板の表面に溶融亜鉛めっき皮膜または合金化溶融亜鉛めっき皮膜を有することを特徴とする、引張強さが980MPa以上である加工性に優れた高張力溶融亜鉛めっき鋼板。
Ti ≧ 0.10+(N/14×48+S/32×48) ・・・ (1)
0.8 ≦ (Ti/48+V/51)/(C/12)≦ 1.2 ・・・ (2)
(C、Ti、V、S、N:各元素の含有量(質量%))
(2) (1)において、前記固溶Vと前記固溶Tiとの合計が質量%で0.07%以上であることを特徴とする、加工性に優れた高張力溶融亜鉛めっき鋼板。
(3) (1)または(2)において、前記組成に加えてさらに、質量%でCr:1%以下、B:0.003%以下のうちの1種または2種を含むことを特徴とする、加工性に優れた高張力溶融亜鉛めっき鋼板。
(4) (1)ないし(3)のいずれかにおいて、前記組成に加えてさらに、質量%でNb、Moのうちの1種または2種を合計で0.01%以下含むことを特徴とする、加工性に優れた高張力溶融亜鉛めっき鋼板。
前記鋼素材を、質量%で、
C :0.07%以上0.13%以下、 Si:0.3%以下、
Mn:0.5%以上2.0%以下、 P :0.025%以下、
S :0.005%以下、 N :0.0060%以下、
Al:0.06%以下、 Ti:0.10%以上0.14%以下、
V :0.15%以上0.30%以下
を含み、かつ、C、Ti、V、SおよびNを下記(1)式および(2)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成とし、前記仕上げ圧延の仕上げ圧延終了温度を880℃以上とし、前記巻き取りの巻取り温度を480℃以上580℃未満とし、前記連続焼鈍処理の焼鈍温度を750℃以下とすることを特徴とする、加工性に優れた高張力溶融亜鉛めっき鋼板の製造方法。
Ti ≧ 0.10+(N/14×48+S/32×48) ・・・ (1)
0.8 ≦ (Ti/48+V/51)/(C/12)≦ 1.2 ・・・ (2)
(C、Ti、V、S、N:各元素の含有量(質量%))
(6) (5)において、前記冷却の平均冷却速度が20℃/s以上であることを特徴とする、高張力溶融亜鉛めっき鋼板の製造方法。
(7) (5)または(6)において、前記組成に加えてさらに、質量%でCr:1%以下、B:0.003%以下のうちの1種または2種を含むことを特徴とする、高張力溶融亜鉛めっき鋼板の製造方法。
(8) (5)ないし(7)のいずれかにおいて、前記組成に加えてさらに、質量%でNb、Moのうちの1種または2種を合計で0.01%以下含むことを特徴とする、高張力溶融亜鉛めっき鋼板の製造方法。
まず、本発明鋼板の組織の限定理由について説明する。
本発明の溶融亜鉛めっき鋼板は、フェライト相が組織全体に対する面積率で97%以上であるマトリックスと、TiおよびVを含み平均粒子径が10nm未満である微細炭化物が分散析出し、該微細炭化物の組織全体に対する体積率で0.007以上である組織を有する熱延鋼板の表面に、溶融亜鉛めっき皮膜または合金化溶融亜鉛めっき皮膜を形成してなる鋼板である。
本発明においては、溶融亜鉛めっき鋼板の加工性(伸びおよび伸びフランジ性)を確保する上でフェライト相の形成が必須となる。溶融亜鉛めっき鋼板の伸びおよび伸びフランジ性の向上には、溶融亜鉛めっき鋼板の組織を、転位密度の低い延性に優れたフェライト相とすることが有効である。特に、伸びフランジ性の向上には、溶融亜鉛めっき鋼板の組織をフェライト単相とすることが好ましいが、完全なフェライト単相でない場合であっても、実質的にフェライト単相、すなわち、組織全体に対する面積率で97%以上がフェライト相であれば、上記の効果を十分に発揮する。したがって、フェライト相の組織全体に対する面積率は97%以上とする。
Ti、Vを含む微細炭化物
TiおよびVを含む炭化物は、その平均粒子径が極めて小さい微細炭化物となる傾向が強い。そのため、溶融亜鉛めっき鋼板中に微細炭化物を分散析出させることにより溶融亜鉛めっき鋼板の高強度化を図る本発明においては、分散析出させる微細炭化物として、TiおよびVを含む微細炭化物とする。
Tiは炭化物形成傾向が強いため、Vを含まない場合はTi炭化物が粗大化し易く、鋼板の高強度化への寄与度が低くなる。それゆえ、鋼板に所望の強度(引張強さ:980MPa以上)を付与するために、より多くのTiを添加してTi炭化物を形成することが必要となる。その一方で、Tiを過剰に添加すると、加工性(伸びおよび伸びフランジ性)の低下が懸念され、断面形状が複雑な足回り部品等の素材としても適用可能な優れた加工性が得られなくなる。
微細炭化物の平均粒子径:10nm未満
溶融亜鉛めっき鋼板に所望の強度(引張強さ:980MPa以上)を付与する上では微細炭化物の平均粒子径が極めて重要であり、本発明においてはTiおよびVを含む微細炭化物の平均粒子径を10nm未満とする。マトリックス中に微細炭化物が析出すると、その微細炭化物が、鋼板に変形が加わった際に生じる転位の移動に対する抵抗として作用することにより溶融亜鉛めっき鋼板が強化されるが、微細炭化物の平均粒子径を10nm未満とすると、上記の作用がより一層顕著となる。したがって、TiおよびVを含む微細炭化物の平均粒子径は10nm未満とする。より好ましくは5nm以下である。
溶融亜鉛めっき鋼板に所望の強度(引張強さ:980MPa以上)を付与する上ではTiおよびVを含む微細炭化物の分散析出状態も極めて重要であり、本発明においては、TiおよびVを含み平均粒子径が10nm未満である微細炭化物の、組織全体に対する組織分率が体積率で0.007以上となるように分散析出させる。この組織分率が0.007未満である場合には、たとえTiおよびVを含む微細炭化物の平均粒子径が10nm未満であっても、所望の溶融亜鉛めっき鋼板強度(引張強さ:980MPa以上)を確実に確保することが困難となる。したがって、上記組織分率は0.007以上とする。好ましくは、0.008以上である。
次に、本発明溶融亜鉛めっき鋼板の成分組成の限定理由について説明する。なお、以下の成分組成を表す%は、特に断らない限り質量%を意味するものとする。
Cは、微細炭化物を形成し、溶融亜鉛めっき鋼板を強化する上で必須の元素である。C含有量が0.07%未満であると所望の組織分率の微細炭化物を確保することができず、980MPa以上の引張強さが得られなくなる。一方、C含有量が0.13%を超えると、スポット溶接が困難になる等の支障をきたす。したがって、C含有量は0.07%以上0.13%以下とする。好ましくは、0.08%以上0.12%以下である。
Si含有量が0.3%を超えると、フェライト相からのC析出が促進され、粒界に粗大なFe炭化物が析出し易くなり、伸びフランジ性が低下する。また、Si含有量が0.3%を超えると圧延負荷が増大し、圧延材の形状が不良となる。したがって、Si含有量は0.3%以下とする。好ましくは0.15%以下であり、望ましくは0.05%以下である。
Mnは、固溶強化元素であり、高強度化に有効な元素である。溶融亜鉛めっき鋼板を強化する観点からはMn含有量を0.5%以上とすることが好ましいが、Mn含有量が2.0%を超えると偏析が顕著になり、且つ、フェライト相以外の相、すなわち硬質相が形成され、伸びフランジ性が低下する。したがって、Mn含有量は0.5%以上2.0%以下とする。好ましくは1.0%以上2.0%以下である。
P含有量が0.025%を超えると、偏析が顕著になり伸びフランジ性が低下する。したがって、P含有量は0.025%以下とする。好ましくは0.02%以下である。
Sは、熱間加工性(熱間圧延性)を低下させる元素であり、スラブの熱間割れ感受性を高めるほか、鋼中にMnSとして存在して熱延鋼板の加工性(伸びフランジ性)を劣化させる。そのため、本発明ではSを極力低減することが好ましく、0.005%以下とする。好ましくは0.003%以下である。
Nは、本発明においては有害な元素であり、極力低減することが好ましい。特にN含有量が0.0060%を超えると、鋼中に粗大な窒化物が生成することに起因して、伸びフランジ性が低下する。したがって、N含有量は0.0060%以下とする。
Alは、脱酸剤として作用する元素である。このような効果を得るためには0.001%以上含有することが望ましいが、0.06%を超える含有は、伸びおよび伸びフランジ性を低下させる。このため、Al含有量は0.06%以下とする。
Tiは、本発明において重要な元素のひとつである。Tiは、Vと複合炭化物を形成することにより、優れた伸びおよび伸びフランジ性を確保しつつ鋼板の高強度化に寄与する元素である。Ti含有量が0.10%未満では、所望の溶融亜鉛めっき鋼板強度(引張強さ:980MPa以上)を確保することができない。一方、Ti含有量が0.14%を超えると、伸びフランジ性が低下する傾向にある。また、溶融亜鉛めっき鋼板の基板となる熱延鋼板を製造するに際し、熱延前のスラブ加熱温度を1300℃以上という高温にしなければ炭化物が溶解しない可能性が高くなる。そのため、0.14%を超えてTiを含有させても析出する微細炭化物の組織分率は飽和し、含有量に見合った効果は得られない。したがって、Ti含有量は0.10%以上0.14%以下とする。
Vは、本発明において重要な元素のひとつである。上記したように、Vは、Tiと複合炭化物を形成することにより、優れた伸びおよび伸びフランジ性を確保しつつ溶融亜鉛めっき鋼板を強化する元素である。V含有量が0.15%未満では、所望の鋼板強度(引張強さ:980MPa以上)を確保することができない。一方、V含有量が0.30%を超えると、中心偏析が顕著になり、伸びや靭性の低下を招く。したがって、V含有量は0.15%以上0.30%以下とする。
Ti ≧ 0.10+(N/14×48+S/32×48) ・・・ (1)
0.8 ≦ (Ti/48+V/51)/(C/12) ≦ 1.2 ・・・ (2)
(C、Ti、V、S、N:各元素の含有量(質量%))
上記(1)式および(2)式は、TiおよびVを含む微細炭化物を、上記した所望の析出状態とするために満足すべき要件であり、本発明において極めて重要な指標である。
先述のとおり、本発明においては溶融亜鉛めっき鋼板中にTiおよびVを含む微細炭化物を分散析出させるが、この微細炭化物は、熱延前の加熱で、鋼素材中の炭化物を溶解し、その後の熱間圧延、熱間圧延後の冷却、巻取り、並びに連続焼鈍処理時に析出される。また、上記微細炭化物は、まずTiが核となって析出し、Vが複合的に析出することによって形成される。そのため、上記微細炭化物を、そのサイズを平均粒子径10nm未満として安定的に析出させ、最終的に得られる溶融亜鉛めっき鋼板の組織全体に対する体積率で0.007以上となるように分散析出させるためには、析出核となるTi量が十分に確保されている必要がある。
本発明においては、鋼中のTi、V含有量とC含有量との比率を適正範囲に制御することも重要である。というのは、鋼中のTi、V含有量に対してC含有量が多過ぎると、溶融亜鉛めっき鋼板にパーライト相の析出、炭化物の粗大化を招き、伸びおよび伸びフランジ性に悪影響を及ぼす。一方、鋼中のTi、V含有量に対してC含有量が少な過ぎると、所望の鋼板強度(引張強さ:980MPa以上)を確保するために必要なTiおよびVを含む微細炭化物が十分に得られない。したがって、本発明においては、溶融亜鉛めっき鋼板の素材となる鋼中のTi、V、C含有量を(2)式0.8 ≦ (Ti/48+V/51)/(C/12)≦ 1.2 を満足するように制御する。
固溶Vは、溶融亜鉛めっき鋼板の伸びフランジ性の向上に有効に作用する。溶融亜鉛めっき鋼板に含有されるVのうち、固溶Vの含有量が0.04%未満である場合には上記の効果が十分に発現せず、断面形状が複雑な足回り部品等の素材としても適用可能な伸びフランジ性を確保することができない。一方、固溶Vの含有量が0.1%を超えても上記の効果が飽和し、また所望の鋼板強度(引張強さ:980MPa以上)を確保するために必要なTiおよびVを含む微細炭化物が十分に得られなくなる。したがって、溶融亜鉛めっき鋼板に含有されるVのうち、固溶V量は0.04%以上0.1%以下とする。なお、好ましくは、0.04%以上0.07%以下である。より好ましくは、0.04%以上0.06%以下である。
上記のとおり、本発明においては溶融亜鉛めっき鋼板の伸びフランジ性を確保する目的で所望の固溶Vを含有するが、固溶Tiにはこのような効果は認められない上、固溶Tiが存在することは、すなわち、析出の核として有効に作用するTiが実質少なくなっていることを意味する。そのため、所望の鋼板強度(引張強さ:980MPa以上)を確保するために固溶Tiは0.05%以下とする。好ましくは0.03%以下、より好ましくは0.02%以下である。
フェライト相中に固溶したVとTiの合計量を所定の範囲とすることにより、粒界が強化されて曲げ特性が向上する。このため、上記した固溶V、固溶Tiの範囲内で且つ固溶Vと固溶Tiの合計量を0.07%以上に調整することが好ましい。固溶Vと固溶Tiの合計量が0.07%未満と少ないと、上記した所望の効果を得られない。一方、固溶Vと固溶Tiの合計量が過剰になると、TiおよびVを含む微細炭化物の析出が不十分となるおそれがある。このため、固溶V(0.04%以上0.1%以下)と固溶Ti(0.05%以下)の合計量は0.15%以下とする。含有するV、Tiの有効利用という観点からは、固溶Vと固溶Tiの合計量を0.10%以下とすることが好ましい。
Crは、固溶状態でフェライト相を強化する上で有効に作用する元素である。このような効果を得るためには0.05%以上含有することが望ましいが、1%を超えて含有させてもその効果は飽和し、経済的でない。したがって、Cr含有量は1%以下とすることが好ましい。
Bは、鋼のAr3変態点を低下させる上で有効な元素であり、熱間圧延における冷却過程でフェライト相の組織全体の面積率を調整するために活用してもよい。しかしながら、0.003%を超えて含有しても効果が飽和する。このため、B含有量は0.003%以下とすることが好ましい。なお、Bを活用する場合、上記効果を得るうえではB含有量を0.0005%以上とすることが好ましい。
鋼素材に、粗圧延と仕上げ圧延からなる熱間圧延を施し、仕上げ圧延終了後、冷却し、巻き取り、熱延板とし、該熱延板に連続焼鈍処理、溶融亜鉛めっき処理あるいは更に合金化処理を順次施し、溶融亜鉛めっき鋼板とする。この際、仕上げ圧延の仕上げ圧延終了温度を880℃以上とし、巻取り温度を480℃以上580℃未満とし、前記連続焼鈍処理の焼鈍温度を750℃以下とすることを特徴とする。また、熱間圧延後の冷却の平均冷却速度を20℃/s以上とすることが好ましい。
仕上げ圧延終了温度の適正化は、熱延鋼板の伸びおよび伸びフランジ性の確保、並びに、仕上げ圧延の圧延荷重の低減化を図る上で重要となる。仕上げ圧延終了温度が880℃未満であると、熱延鋼板表層の結晶粒が粗大粒となり、伸びおよび伸びフランジ性が損なわれる。また、未再結晶温度域で圧延が行われるため、圧延材に導入される歪の蓄積量が増大する。そして、歪の蓄積量が増大するにつれて圧延荷重が著しく増大し、熱延鋼板の薄物化が困難となる。したがって、仕上げ圧延終了温度は880℃以上とする。好ましくは900℃以上である。なお、仕上げ圧延終了温度が過剰に高くなると、結晶粒が粗大化して所望の鋼板強度(引張強さ:980MPa以上)の確保に悪影響を及ぼすため、仕上げ圧延終了温度は1000℃以下とすることが望ましい。
巻取り温度の適正化は、溶融亜鉛めっき鋼板の基板となる熱延鋼板(熱延板)の内部酸化層を抑制し、且つ、最終的に得られる溶融亜鉛めっき鋼板の組織を鋼板幅方向全域にわたり所望の組織、すなわち、フェライト相が組織全体に対する面積率で97%以上であるマトリックスと、TiおよびVを含み平均粒子径が10nm未満である微細炭化物が分散析出し、該微細炭化物の組織全体に対する体積率で0.007以上である組織とする上で、極めて重要である。
仕上げ圧延終了後、880℃以上の温度から巻取り温度までの平均冷却速度が20℃/s未満であると、Ar3変態点が高くなり易く、TiおよびVを含む炭化物が粗大化し易い。このため、曲げ性の向上に有効な鋼中の固溶Vおよび固溶Tiが消費され易い。上記したように、曲げ特性を良好とするためには、固溶Vと固溶Tiの合計を0.07%以上とすることが好ましいが、そのためには仕上げ圧延後880℃以上の温度から巻取り温度までの平均冷却速度を20℃/s以上とすることが好ましい。より好ましくは30℃/s以上である。なお、上記平均冷却速度の上限値は特に規定されないが、冷却むら防止という観点からは、上記平均冷却速度を60℃/s以下とすることが好ましい。
先述のとおり、本発明においては、溶融亜鉛めっき鋼板の基板となる熱延鋼板(熱延板)の内部酸化層を抑制すべく、熱延板の巻取り温度を低めに設定している。すなわち、本発明においては、熱延板の巻取り温度をTiおよびVを含む微細炭化物の析出に適した巻取り温度よりも低い温度に設定しているため、熱延板、特に熱延板幅方向端部においてTiおよびVを含む微細炭化物の析出が不十分となっている。
表1に示す組成の溶鋼を通常公知の手法により溶製、連続鋳造して肉厚250mmのスラブ(鋼素材)とした。これらのスラブを、1250℃に加熱後、粗圧延し、表2に示す仕上げ圧延終了温度とする仕上げ圧延を施し、表2に示す巻取り温度で巻取り、板厚:2.3mmの熱延板とした。
上記のようにして得られた各種熱延板に、連続溶融亜鉛めっきラインにて表2に示す条件の焼鈍温度・焼鈍温度での保持時間で連続焼鈍処理を施した後、550℃の溶融亜鉛に浸漬し、表面に溶融亜鉛めっき皮膜を形成する溶融亜鉛めっき処理を施すことにより、溶融亜鉛めっき鋼板を製造した。なお、めっき付着量は50g/m2とした。また、一部の熱延板については、溶融亜鉛めっき処理後、表2に示す条件で合金化処理を施した。
得られた溶融亜鉛めっき鋼板(溶融亜鉛めっき鋼板のうち、溶融亜鉛めっき皮膜以外の熱延鋼板の部分)(板幅方向中央部)から試験片を採取し、試験片の圧延方向断面を機械的に研磨し、ナイタールで腐食した後、走査型電子顕微鏡(SEM)で倍率:3000倍にて撮影した組織写真(SEM写真)を用い、画像解析装置によりフェライト相、フェライト相以外の組織の種類、および、それらの面積率を求めた。
得られた溶融亜鉛めっき鋼板から、圧延方向に対して直角方向を引張方向とするJIS 5号引張試験片(JIS Z 2201)を採取し、JIS Z 2241の規定に準拠した引張試験を行い、引張強さ(TS)、全伸び(El)を測定した。
得られた溶融亜鉛めっき鋼板から、試験片(大きさ:130mm×130mm)を採取し、該試験片に初期直径d0:10mmφの穴を打ち抜き加工で形成した。これら試験片を用いて、穴拡げ試験を実施した。すなわち、該穴に頂角:60°の円錐ポンチを挿入し、該穴を押し広げ、亀裂が鋼板(試験片)を貫通したときの穴の径dを測定し、次式で穴拡げ率λ(%)を算出した。
得られた結果を表3に示す。
表5に示す組成の溶鋼を通常公知の手法により溶製、連続鋳造して肉厚250mmのスラブ(鋼素材)とし、これらのスラブを、1250℃に加熱後、粗圧延し、表6に示す仕上げ圧延終了温度とする仕上げ圧延を施し、表6に示す平均冷却速度(仕上げ圧延終了温度から巻取り温度までの平均冷却速度)で冷却し、表6に示す巻取り温度で巻取り、板厚:2.3mmの熱延鋼板とした。
また、上記により得られた溶融亜鉛めっき鋼板から、曲げ試験片を採取し、曲げ試験を行った。試験条件は次のとおりとした
得られた溶融亜鉛めっき鋼板から、試験片の長手が圧延方向に対して直角になるように30mm×150mmの曲げ試験片を採取し、JIS Z 2248の規定に準拠したVブロック法(曲げ角:90°)で曲げ試験を実施した。試験は3本の試験片について行い、割れが発生しない最小の曲げ半径R(mm)を板厚t(mm)で除した値、R/tを、鋼板の限界曲げ半径として算出した。
得られた結果を表7に示す。
更に、固溶Vと固溶Tiの合計が0.07%以上である場合には、引張強さTS:980MPa以上の高強度と、全伸びEl:15%以上で穴拡げ率λ:40%以上という良好な加工性に加え、限界曲げ半径R/t:0.7以下という優れた曲げ特性を兼備し、加工性に優れた溶融亜鉛めっき鋼板となっている。
Claims (8)
- 質量%で、
C :0.07%以上0.13%以下、 Si:0.3%以下、
Mn:0.5%以上2.0%以下、 P :0.025%以下、
S :0.005%以下、 N :0.0060%以下、
Al:0.06%以下、 Ti:0.10%以上0.14%以下、
V :0.15%以上0.30%以下
を、C、Ti、V、SおよびNが下記(1)式および(2)式を満足するように含有し、且つ、固溶V:0.04%以上0.1%以下、固溶Ti:0.05%以下であり、残部がFeおよび不可避的不純物からなる組成と、フェライト相の組織全体に対する面積率が97%以上であるマトリックスと、TiおよびVを含み平均粒子径が10nm未満である微細炭化物が分散析出し、該微細炭化物の組織全体に対する体積率が0.007以上である組織とを有する熱延鋼板の表面に溶融亜鉛めっき皮膜または合金化溶融亜鉛めっき皮膜を有することを特徴とする、引張強さが980MPa以上である加工性に優れた高張力溶融亜鉛めっき鋼板。
記
Ti ≧ 0.10+(N/14×48+S/32×48) ・・・ (1)
0.8 ≦ (Ti/48+V/51)/(C/12)≦ 1.2 ・・・ (2)
(C、Ti、V、S、N:各元素の含有量(質量%)) - 前記固溶Vと前記固溶Tiとの合計が質量%で0.07%以上であることを特徴とする、請求項1に記載の加工性に優れた高張力溶融亜鉛めっき鋼板。
- 前記組成に加えてさらに、質量%でCr:1%以下、B:0.003%以下のうちの1種または2種を含むことを特徴とする、請求項1または2に記載の加工性に優れた高張力溶融亜鉛めっき鋼板。
- 前記組成に加えてさらに、質量%でNb、Moのうちの1種または2種を合計で0.01%以下含むことを特徴とする、請求項1ないし3のいずれか1項に記載の加工性に優れた高張力溶融亜鉛めっき鋼板。
- 鋼素材に、粗圧延と仕上げ圧延からなる熱間圧延を施し、仕上げ圧延終了後、冷却し、巻き取り、熱延板とし、該熱延板に連続焼鈍処理、溶融亜鉛めっき処理あるいは更に合金化処理を順次施し、溶融亜鉛めっき鋼板を製造するにあたり、
前記鋼素材を、質量%で、
C :0.07%以上0.13%以下、 Si:0.3%以下、
Mn:0.5%以上2.0%以下、 P :0.025%以下、
S :0.005%以下、 N :0.0060%以下、
Al:0.06%以下、 Ti:0.10%以上0.14%以下、
V :0.15%以上0.30%以下
を含み、かつ、C、Ti、V、SおよびNを下記(1)式および(2)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成とし、前記仕上げ圧延の仕上げ圧延終了温度を880℃以上とし、前記巻き取りの巻取り温度を480℃以上580℃未満とし、前記連続焼鈍処理の焼鈍温度を750℃以下とすることを特徴とする、加工性に優れた高張力溶融亜鉛めっき鋼板の製造方法。
記
Ti ≧ 0.10+(N/14×48+S/32×48) ・・・ (1)
0.8 ≦ (Ti/48+V/51)/(C/12)≦ 1.2 ・・・ (2)
(C、Ti、V、S、N:各元素の含有量(質量%)) - 前記冷却の平均冷却速度が20℃/s以上であることを特徴とする、請求項5に記載の高張力溶融亜鉛めっき鋼板の製造方法。
- 前記組成に加えてさらに、質量%でCr:1%以下、B:0.003%以下のうちの1種または2種を含むことを特徴とする、請求項5または6に記載の高張力溶融亜鉛めっき鋼板の製造方法。
- 前記組成に加えてさらに、質量%でNb、Moのうちの1種または2種を合計で0.01%以下含むことを特徴とする、請求項5ないし7のいずれか1項に記載の高張力溶融亜鉛めっき鋼板の製造方法。
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Also Published As
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US20130186523A1 (en) | 2013-07-25 |
CN102906295B (zh) | 2014-11-26 |
JP5041083B2 (ja) | 2012-10-03 |
JP2011225978A (ja) | 2011-11-10 |
EP2554705A4 (en) | 2017-12-06 |
TWI460307B (zh) | 2014-11-11 |
CN102906295A (zh) | 2013-01-30 |
KR101314979B1 (ko) | 2013-10-04 |
KR20120128721A (ko) | 2012-11-27 |
EP2554705B1 (en) | 2019-08-14 |
TW201144480A (en) | 2011-12-16 |
EP2554705A1 (en) | 2013-02-06 |
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