WO2015133061A1 - Cold-rolled steel sheet, method for producing same, high-strength hot-dipped galvanized steel sheet, and high-strength alloyed hot-dipped galvanized steel sheet - Google Patents
Cold-rolled steel sheet, method for producing same, high-strength hot-dipped galvanized steel sheet, and high-strength alloyed hot-dipped galvanized steel sheet Download PDFInfo
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- WO2015133061A1 WO2015133061A1 PCT/JP2015/000542 JP2015000542W WO2015133061A1 WO 2015133061 A1 WO2015133061 A1 WO 2015133061A1 JP 2015000542 W JP2015000542 W JP 2015000542W WO 2015133061 A1 WO2015133061 A1 WO 2015133061A1
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- steel sheet
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- cold
- rolled steel
- pickling
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 56
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims abstract description 32
- 239000008397 galvanized steel Substances 0.000 title claims abstract description 32
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 28
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 229910000831 Steel Inorganic materials 0.000 claims description 113
- 239000010959 steel Substances 0.000 claims description 113
- 238000005554 pickling Methods 0.000 claims description 65
- 239000002253 acid Substances 0.000 claims description 33
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 31
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 21
- 229910017604 nitric acid Inorganic materials 0.000 claims description 21
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 20
- 238000010438 heat treatment Methods 0.000 claims description 20
- 238000001816 cooling Methods 0.000 claims description 19
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 14
- 238000005246 galvanizing Methods 0.000 claims description 12
- 229910052748 manganese Inorganic materials 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 230000001590 oxidative effect Effects 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052718 tin Inorganic materials 0.000 claims description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 4
- 238000005275 alloying Methods 0.000 claims description 4
- 229910052787 antimony Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052739 hydrogen Inorganic materials 0.000 claims description 4
- 239000001257 hydrogen Substances 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims 1
- 238000007747 plating Methods 0.000 abstract description 38
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 21
- 238000000137 annealing Methods 0.000 description 16
- 230000000694 effects Effects 0.000 description 13
- 238000005728 strengthening Methods 0.000 description 9
- 239000002344 surface layer Substances 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 239000010410 layer Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 5
- 229920000298 Cellophane Polymers 0.000 description 4
- 150000007513 acids Chemical class 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 230000004580 weight loss Effects 0.000 description 4
- 239000011701 zinc Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 3
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 235000013980 iron oxide Nutrition 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 229910052725 zinc Inorganic materials 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 230000032683 aging Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- 235000006408 oxalic acid Nutrition 0.000 description 2
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000005238 degreasing Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- XPPKVPWEQAFLFU-UHFFFAOYSA-N diphosphoric acid Chemical compound OP(O)(=O)OP(O)(O)=O XPPKVPWEQAFLFU-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 229940005657 pyrophosphoric acid Drugs 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 238000004876 x-ray fluorescence Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/76—Adjusting the composition of the atmosphere
-
- 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
- C21D8/0236—Cold 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- 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
- C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
-
- 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
- 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
- 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
- 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
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
-
- 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
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/086—Iron or steel solutions containing HF
Definitions
- the present invention relates to a cold-rolled steel sheet, a manufacturing method thereof, a high-strength hot-dip galvanized steel sheet, and a high-strength galvannealed steel sheet.
- a solid solution strengthening element such as Si, Mn, or Cr may be included in the steel sheet.
- Cr increases the strength of the steel sheet with a smaller content than other elements. For this reason, Cr is effective in strengthening the material of the steel plate.
- the steel sheet When manufacturing a hot dip galvanized steel sheet, the steel sheet is heated and annealed at a temperature of about 600 to 900 ° C. in a non-oxidizing atmosphere or a reducing atmosphere, and then hot dip galvanized.
- easily oxidizable elements in steel are selectively oxidized in a generally used non-oxidizing atmosphere or reducing atmosphere, these elements are concentrated on the surface to form oxides during heat annealing. This oxide reduces wettability with molten zinc during the plating process and causes non-plating. That is, as the concentration of the easily oxidizable element in the steel increases, the wettability rapidly decreases and non-plating frequently occurs. Further, even when non-plating does not occur, if there is an oxide between the steel plate and the plating, the plating adhesion deteriorates.
- Patent Document 1 proposes a method for improving wettability with molten zinc. Specifically, in Patent Document 1, the steel sheet is heated in an oxidizing atmosphere in advance, and the oxidation of additive elements on the steel sheet surface is prevented by rapidly generating an Fe oxide film on the surface at an oxidation rate higher than a predetermined value. Then, a method of reducing annealing the Fe oxide film is described. However, in the technique described in Patent Document 1, when the amount of oxidation of the steel sheet is large, there arises a problem that iron oxide adheres to the in-furnace roll and the steel sheet is pressed.
- Patent Document 2 proposes a method of removing surface oxides by pickling the steel plate after annealing, then annealing the steel plate after pickling again, and performing hot dip galvanization.
- the technique described in Patent Document 2 cannot remove an acid-insoluble oxide, and thus does not improve the plating appearance of a steel sheet on which an acid-insoluble oxide is formed.
- a steel plate on which an acid-insoluble oxide is formed a steel plate containing Cr is known.
- Patent Document 3 proposes a method of improving the chemical conversion property of a cold-rolled steel sheet by removing the Cr oxide layer formed by annealing by performing hydrochloric acid pickling after annealing.
- the average value of the Cr concentration in the surface layer portion is 1.0% by mass or less, the Cr concentration in the surface layer is not sufficiently reduced, and the hot dip galvanizing has poor adhesion.
- the present invention relates to a cold-rolled steel sheet for producing a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet.
- the present invention provides a technique for improving the surface appearance and plating adhesion of a plated steel sheet.
- the Cr oxide can be removed together with the surface layer portion.
- the pickling reduction amount of the steel sheet can be appropriately controlled, it is possible to leave the low Cr concentration region immediately below the surface of the cold-rolled steel sheet and to remove the Cr oxide on the surface.
- a strong acid is used to dissolve and remove the surface layer of the steel sheet, iron-based oxides are slightly formed on the steel sheet surface. Since the amount of this iron-based oxide is small, it has been found that it has little effect on the plating appearance, but affects the plating adhesion of the hot-dip galvanized steel sheet.
- the present invention has been made based on the above knowledge and has the following features.
- a cold-rolled steel sheet used for production of a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet wherein C: 0.040% or more and 0.500% or less, Si: 1.00 % Or less, Mn: 2.00% or more and 3.80% or less, P: 0.010% or less, S: 0.010% or less, Al: 0.100% or less, N: 0.0100% or less, Cr: 0.3% or more and 1.00% or less, the balance is made of Fe and inevitable impurities, the Cr concentration within 0.5 ⁇ m in the thickness direction from the surface is 0.20% or less, and the Mn concentration is 1 Cold-rolled steel sheet characterized by being 8% or less.
- a heating step for holding the steel plate having the composition according to claims 1 to 3 for 20 to 600 seconds in a temperature range of 700 to 900 ° C, a cooling step for cooling the steel plate after the holding, and a steel plate after cooling A method for producing a cold-rolled steel sheet, comprising: pickling and removing the surface under conditions where the pickling loss is 4.0 to 20.0 g / m 2 in terms of Fe.
- the pickling solution used in the pickling step includes nitric acid and hydrochloric acid, the nitric acid concentration is more than 50 g / L and not more than 200 g / L, and the ratio of the hydrochloric acid concentration to the nitric acid concentration (HCl / HNO 3 ) is 0.
- the pickling solution used in the pickling step contains nitric acid and hydrofluoric acid, the nitric acid concentration is more than 50 g / L and not more than 200 g / L, and the hydrofluoric acid concentration relative to the nitric acid concentration (4) or (5), wherein the ratio (HF / HNO 3 ) is 0.01 to 1.00.
- Hot-dip galvanizing treatment is applied to the cold-rolled steel sheet according to any one of (1) to (3) above or the cold-rolled steel sheet produced by the production method according to any one of (4) to (7) above. High strength hot-dip galvanized steel sheet.
- the cold-rolled steel sheet of the present invention is excellent in surface appearance and plating adhesion while being a steel sheet containing Cr.
- Applying high-strength hot-dip galvanized steel sheets and high-strength alloyed hot-dip galvanized steel sheets manufactured using this cold-rolled steel sheet to automotive parts such as automotive structural members will improve fuel efficiency by reducing the weight of the vehicle body. Can do.
- FIG. 1 is a diagram showing an example of measurement of Cr and Mn concentrations.
- the cold-rolled steel sheet of the present invention is C: 0.040% or more and 0.500% or less, Si: 1.00% or less, Mn: 2.00% or more and 3.80% or less, P: 0.010 by mass%.
- C 0.040% or more and 0.500% or less
- C is an austenite generating element, which is an element that combines an annealed plate structure and contributes to improvement in strength and ductility.
- it is necessary to make content of C 0.04% or more.
- the C content exceeds 0.50%, the welded part and the heat-affected zone are markedly cured, and the mechanical properties of the welded part deteriorate. That is, when the C content exceeds 0.50%, spot weldability, arc weldability, and the like deteriorate. Since automobile parts are often joined to other parts by welding, automobile parts are required to have good weldability. Therefore, the C content is 0.50% or less.
- Si 1.00% or less Si is a ferrite-forming element and contributes to solid solution strengthening and work hardening ability of the ferrite of the annealed plate.
- the Si content is 1.00% or less.
- Mn 2.00% or more and 3.80% or less
- Mn is an austenite generating element and an element contributing to securing the strength of the annealed plate. In order to acquire this effect, it is necessary to make Mn content 2.00% or more. On the other hand, if the Mn content exceeds 3.80%, a large amount of oxide is formed on the steel sheet surface during annealing, and the plating appearance deteriorates. Therefore, the Mn content is 3.80% or less.
- Cr 0.3% or more and 1.00% or less Cr is an austenite generating element and an element contributing to securing the strength of the annealed plate. If the Cr content is less than 0.3%, it is difficult to ensure the strength of the cold-rolled steel sheet. On the other hand, if the Cr content exceeds 1.00%, the appearance of plating deteriorates because Cr oxide formed on the surface of the cold-rolled steel sheet cannot be removed even with the present invention. Therefore, the Cr content is 1.00% or less.
- P 0.010% or less
- P is an element effective for strengthening steel.
- the P content is preferably 0.001% or more.
- content of P shall be 0.010% or less.
- S 0.010% or less S becomes inclusions such as MnS, and deteriorates impact resistance or causes cracks along the metal flow of the welded portion. For this reason, the S content is preferably as low as possible. However, it is difficult to manufacture a cold-rolled steel sheet so as not to completely contain S from the viewpoint of manufacturing cost and the like. Then, when it contains S, content of S shall be 0.010% or less.
- Al 0.100% or less
- the Al content is 0.100% or less.
- it is 0.050% or less.
- N 0.0100% or less
- N is an element that greatly deteriorates the aging resistance of steel.
- the cold-rolled steel sheet of the present invention is further mass%, Mo: 0.01 to 0.50, Nb: 0.010% to 0.100%, B: 0.0003% to 0.0050. % Or less and Ti: at least one element selected from 0.010% or more and 0.100% or less may be contained.
- Mo 0.01% or more and 0.50% or less
- Mo is an austenite-generating element and contributes to securing the strength of the annealed plate. If the Mo content is less than 0.01%, it is difficult to obtain the effect of securing the strength. Moreover, since Mo is expensive, the increase in the content leads to an increase in cost. Therefore, when it contains Mo, content of Mo shall be 0.01% or more and 0.50% or less.
- Nb 0.010% or more and 0.100% or less
- Nb is an element that contributes to strength improvement by solid solution strengthening or precipitation strengthening. This effect can be obtained by setting the Nb content to 0.010% or more.
- the Nb content exceeds 0.100%, the ductility of the steel sheet is lowered. That is, the workability of the steel sheet is deteriorated. Therefore, when Nb is contained, Nb is made 0.010% or more and 0.100% or less.
- B 0.0001% or more and 0.0050% or less B is an element that enhances hardenability and contributes to improving the strength of the steel sheet. This effect can be obtained by setting the B content to 0.0001% or more. On the other hand, when B is contained excessively, the ductility of the steel sheet is lowered, and as a result, the workability of the steel sheet is deteriorated. Further, excessive inclusion of B causes an increase in cost. Therefore, when it contains B, content of B shall be 0.0001% or more and 0.0050% or less.
- Ti 0.010% or more and 0.100% or less
- Ti is an element that contributes to improving the strength of the steel sheet by forming fine carbide or fine nitride with C or N in the steel sheet.
- the Ti content needs to be 0.010% or more.
- this effect is saturated when the Ti content exceeds 0.100%. Therefore, when Ti is contained, the content of Ti is set to 0.010% or more and 0.100% or less.
- the cold-rolled steel sheet of the present invention is further, in mass%, Cu: 1.00% or less, V: 0.500% or less, Ni: 0.50% or less, Sb: 0.10% or less, Sn: It may contain at least one element selected from 0.01% or less, Ca: 0.0100% or less, and REM: 0.005% or less.
- Cu 1.00% or less
- V 0.500% or less
- Ni 0.50% or less
- Cu, V, and Ni are elements effective for strengthening steel. If it is in the range prescribed
- Sb 0.10% or less
- Sn 0.10% or less
- Sb and Sn have the effect of suppressing nitriding in the vicinity of the steel sheet surface layer. This effect is saturated when the content of these elements exceeds 0.10%. Therefore, when Sb is contained, the Sb content is 0.10% or less, and when Sn is contained, the Sn content is 0.10% or less.
- Ca 0.0100% or less
- REM 0.005% or less
- Ca improves the ductility of the steel sheet by shape control of sulfides such as MnS. The effect is saturated when the Ca content exceeds 0.0100%.
- REM controls the form of sulfide inclusions and contributes to the improvement of the workability of the steel sheet.
- the content of REM exceeds 0.005%, the amount of inclusions increases and the workability deteriorates. Therefore, when Ca is contained, the Ca content is 0.0100% or less, and when REM is contained, the REM content is 0.005% or less.
- the balance other than the above components is Fe and inevitable impurities.
- the cold-rolled steel sheet of the present invention having the above-described composition has a Cr concentration within 0.5 ⁇ m in the thickness direction from the steel sheet surface to 0.20% or less and a Mn concentration of 1.8% or less.
- % means “mass%”.
- the Cr concentration within 0.5 ⁇ m in the thickness direction from the steel plate surface exceeds 0.20%, the Cr oxide is easily formed on the steel plate surface, the plating appearance is deteriorated, and the plating adhesion is also lowered. For this reason, the Cr concentration within 0.5 ⁇ m in the thickness direction from the steel sheet surface is set to 0.20% or less.
- glow discharge emission analysis is used for the Cr concentration measurement just below the steel sheet surface.
- the Cr strength in the depth direction is measured from the steel plate surface by GDS, and the average value of the Cr strength within 0.5 ⁇ m from the steel plate surface is defined as the Cr concentration.
- the Cr intensity is measured at a depth exceeding 0.5 ⁇ m, and the average value of the intensity from the shallowest position in the region where the Cr intensity is constant to the depth of 0.5 ⁇ m is defined as the bulk Cr concentration. Since the element strength measured by GDS is proportional to the element concentration, the actual Cr concentration on the steel sheet surface is calculated from the ratio between the bulk Cr concentration calculated from GDS and the Cr concentration from the steel sheet surface to a depth of 0.5 ⁇ m. Can be calculated.
- Mn concentration within 0.5 ⁇ m from the steel sheet surface is 1.8% or less. Mn also forms an oxide on the steel sheet surface in the same manner as Cr and deteriorates the appearance of the plating surface. Similar to Cr, if there is a region with a low Mn concentration directly under the steel sheet surface, the formation of Mn oxide on the steel sheet surface during annealing is suppressed.
- Mn concentration within 0.5 ⁇ m in the thickness direction from the steel sheet surface exceeds 1.8%, Mn oxide is easily formed on the steel sheet surface when hot-dip galvanizing is performed on the cold-rolled steel sheet.
- the Mn oxide on the surface of the steel sheet deteriorates the plating appearance and lowers the plating adhesion. For this reason, the Mn concentration within 0.5 ⁇ m from the steel sheet surface is set to 1.8% or less.
- the concentration of Mn is also measured using GDS in the same manner as Cr.
- a steel sheet having the above component composition is used.
- the manufacturing process of this steel plate is not specified. After steel having the above composition is melted by a known method, it is made into a slab through slabs or continuous casting, hot rolled into a hot-rolled sheet, and then pickled to remove the oxidized scale on the surface. To do. Further, cold rolling is performed as necessary.
- the cold-rolled steel sheet of the present invention is manufactured through a heating process for heating the steel sheet, a cooling process for cooling the steel sheet after the heating process, and a pickling process for pickling the steel sheet after the cooling process.
- a heating process for heating the steel sheet for heating the steel sheet
- a cooling process for cooling the steel sheet after the heating process for cooling the steel sheet after the heating process
- a pickling process for pickling the steel sheet after the cooling process for pickling the steel sheet after the cooling process.
- Heating step is a temperature range of 700 to 900 ° C. in an atmosphere having a hydrogen concentration of 3.0 to 25.0 vol% and a dew point of ⁇ 40 to ⁇ 10 ° C. It is the process of holding.
- the steel sheet is heated under heating conditions that do not oxidize Fe.
- oxides of Cr and Mn are formed on the surface of the steel sheet, and a region having a low concentration of Cr and Mn is formed immediately below the surface of the steel sheet.
- the H 2 concentration in the atmosphere during heating needs to be sufficient to suppress the oxidation of Fe. Therefore, in the present invention, the hydrogen concentration is set to 3.0 vol% or more. In addition, if the H 2 concentration exceeds 25.0 vol%, the cost increases. Therefore, the H 2 concentration is set to 25.0 vol% or less. Components other than H 2 in the atmosphere are N 2 and unavoidable impurities.
- the dew point of the atmosphere during heating is less than ⁇ 40 ° C.
- the formation of Cr oxide and Mn oxide on the steel sheet surface is suppressed.
- the dew point exceeds ⁇ 10 ° C., damage to the heating furnace due to moisture becomes remarkable, and repair costs are increased. Therefore, the dew point is set to ⁇ 40 ° C. or higher and ⁇ 10 ° C. or lower.
- the steel sheet is heated at a predetermined temperature or temperature range of 700 ° C. or higher and 900 ° C. or lower.
- the holding time which is the time for holding the steel plate at the above temperature or temperature range.
- the holding time exceeds 600 seconds, the pickling efficiency decreases due to excessive Cr oxide formation, and the manufacturing efficiency decreases. Therefore, the holding time is 20 seconds or more and 600 seconds or less.
- Cooling process is a process of cooling the steel plate after this holding
- the cooling stop temperature is not particularly limited, but is generally 600 to 300 ° C. Cooling may be either water cooling or air cooling. Moreover, what is necessary is just to set cooling time, a cooling rate, etc. suitably.
- the pickling step is a step of pickling and removing the steel plate surface after the cooling step under the condition that the pickling loss is 4.0 to 20.0 g / m 2 in terms of Fe.
- the pickling weight loss is less than 4.0 g / m 2 in terms of Fe, Cr oxide remains on the steel sheet surface.
- the pickling weight loss exceeds 20.0 g / m 2 , the region where the Cr and Mn concentrations just below the surface are low is removed. Accordingly, the pickling weight loss is 4.0 g / m 2 or more and 20.0 g / m 2 or less in terms of Fe.
- nitric acid which is a strong oxidizing acid
- hydrochloric acid, hydrofluoric acid, sulfuric acid, or the like may be used as long as the above-described pickling weight loss can be satisfied, and the type of acid is not particularly limited. It is also effective to promote the dissolution of the steel sheet surface by adding a pickling accelerator to the acid or using an electrolytic treatment in combination.
- the pickling solution contains nitric acid and hydrochloric acid, the nitric acid concentration is more than 50 g / L and not more than 200 g / L, and the ratio of the hydrochloric acid concentration to the nitric acid concentration (HCl / HNO 3 ) is 0.01 to 1.00.
- the pickling solution contains nitric acid and hydrofluoric acid
- the nitric acid concentration is more than 50 g / L and not more than 200 g / L
- the ratio of the hydrofluoric acid concentration to the nitric acid concentration (HF / HNO 3 ) is 0.01 to It is preferably any one of 1.00.
- the re-pickling step is a step of re-pickling the steel sheet surface with a non-oxidizing acid different from the acid used in the pickling step after the pickling step.
- the re-pickling step is an optional step, and performing this step has an effect of improving plating adhesion.
- non-oxidizing acid examples include hydrochloric acid, dilute sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid, acetic acid, citric acid, hydrofluoric acid, oxalic acid, and acids obtained by mixing two or more of these.
- hydrochloric acid the hydrochloric acid concentration is preferably 0.1 to 50 g / L
- sulfuric acid the sulfuric acid concentration is preferably 0.1 to 150 g / L.
- the mixed acid it is preferable to use a mixed acid with a hydrochloric acid concentration of 0.1 to 20 g / L and a sulfuric acid concentration of 0.1 to 60 g / L.
- the temperature of the re-pickling solution be 20 to 70 ° C.
- the re-acid wash treatment time is preferably 1 to 30 seconds.
- the acid used in the re-pickling since the purpose of dissolving the iron oxides of the steel sheet surface, the acid used for the purpose of pickling step of dissolving each SiO 2 the steel base of sparingly soluble (the base steel) to the acid Different acid.
- the “different acid” does not mean only acids that cannot be used in the pickling process, but also includes acids that are not used in the actual pickling process among the acids that can be used in the pickling process.
- the cold-rolled steel sheet of the present invention obtained as described above is subjected to a treatment such as degreasing as necessary, followed by an annealing treatment and a hot dip galvanizing treatment.
- a treatment such as degreasing as necessary
- an annealing treatment and a hot dip galvanizing treatment are not particularly defined and may be a generally known process.
- temper rolling may be performed for shape correction after the alloying treatment.
- a steel having the composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in a converter and made into a slab by a continuous casting method.
- the obtained slab was heated to 1200 ° C., and then hot-rolled to a thickness of 1.6 to 4.5 mm and wound up.
- the obtained hot-rolled sheet was pickled and cold-rolled. Thereafter, heat treatment (heating process) is performed in a furnace capable of adjusting the atmosphere under the heat treatment conditions shown in Table 2 or Table 3.
- the steel sheet is cooled to 450 ° C., and subsequently pickling treatment shown in Tables 2 and 3 Pickling treatment was performed under the conditions, or pickling treatment and re- pickling treatment were performed under the conditions shown in Table 4 to obtain a cold-rolled steel sheet. Subsequently, annealing and hot dip galvanizing treatment were performed on a continuous hot dip galvanizing line to obtain a hot dip galvanized steel sheet. Moreover, after this plating process, a part was alloyed and the alloyed hot-dip galvanized steel plate was obtained.
- FIG. 1 shows an example of measurement.
- the plating adhesion of the galvannealed steel sheet was evaluated by evaluating the powdering resistance. Specifically, cellophane tape is applied to the alloyed hot-dip galvanized steel sheet, the tape surface is bent 90 degrees, bent back, and the cellophane with a width of 24 mm is parallel to the bent portion on the inner side (compressed side) of the processed portion. The tape was pressed and pulled away, and the amount of zinc adhering to the 40 mm long portion of the cellophane tape was measured as the Zn count by fluorescent X-rays.
- Tables 2 to 4 The results obtained for the above evaluations are shown in Tables 2 to 4. According to Tables 2 and 3, both the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet produced using the cold-rolled steel sheet of the present invention are excellent in surface appearance and plating adhesion. On the other hand, either the surface appearance or the plating adhesion is inferior in the comparative example. Moreover, according to Table 4, the invention example which performed re-pickling is more excellent in plating adhesiveness than the invention example which does not perform re-pickling.
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Abstract
Description
Cはオーステナイト生成元素であり、焼鈍板組織を複合化し、強度と延性の向上に寄与する元素である。上記効果を得るためには、Cの含有量を0.04%以上にする必要がある。C含有量が0.50%を超えると、溶接部および熱影響部の硬化が著しく、溶接部の機械的特性が劣化する。即ち、C含有量が0.50%を超えると、スポット溶接性、アーク溶接性等が低下する。自動車用部品は溶接により他の部品と接合される場合が多いため、自動車用部品は良好な溶接性を有することが求められる。したがって、Cの含有量は0.50%以下とする。 C: 0.040% or more and 0.500% or less C is an austenite generating element, which is an element that combines an annealed plate structure and contributes to improvement in strength and ductility. In order to acquire the said effect, it is necessary to make content of C 0.04% or more. When the C content exceeds 0.50%, the welded part and the heat-affected zone are markedly cured, and the mechanical properties of the welded part deteriorate. That is, when the C content exceeds 0.50%, spot weldability, arc weldability, and the like deteriorate. Since automobile parts are often joined to other parts by welding, automobile parts are required to have good weldability. Therefore, the C content is 0.50% or less.
Siはフェライト生成元素であり、焼鈍板のフェライトの固溶強化および加工硬化能の向上に寄与する。しかしながら、Siの含有量が過剰になると、焼鈍中に冷延鋼板表面に酸化物が形成し、冷延鋼板のめっき性が劣化する。したがって、Siの含有量は1.00%以下とする。 Si: 1.00% or less Si is a ferrite-forming element and contributes to solid solution strengthening and work hardening ability of the ferrite of the annealed plate. However, when the Si content is excessive, an oxide is formed on the surface of the cold-rolled steel sheet during annealing, and the plateability of the cold-rolled steel sheet is deteriorated. Therefore, the Si content is 1.00% or less.
Mnは、オーステナイト生成元素であり、焼鈍板の強度確保に寄与する元素である。この効果を得るためには、Mnの含有量を2.00%以上にすることが必要である。一方、Mnの含有量が3.80%を超えると、焼鈍中に鋼板表面で多量の酸化物が形成し、めっき外観が劣化する。したがって、Mnの含有量は3.80%以下とする。 Mn: 2.00% or more and 3.80% or less Mn is an austenite generating element and an element contributing to securing the strength of the annealed plate. In order to acquire this effect, it is necessary to make Mn content 2.00% or more. On the other hand, if the Mn content exceeds 3.80%, a large amount of oxide is formed on the steel sheet surface during annealing, and the plating appearance deteriorates. Therefore, the Mn content is 3.80% or less.
Crは、オーステナイト生成元素であり、焼鈍板の強度確保に寄与する元素である。Crの含有量が0.3%未満になると、冷延鋼板の強度を確保することが難しい。一方、Crの含有量が1.00%を超えると、本発明をもってしても冷延鋼板表面に形成したCr酸化物を除去しきれないため、めっき外観が劣化する。したがって、Crの含有量は1.00%以下とする。 Cr: 0.3% or more and 1.00% or less Cr is an austenite generating element and an element contributing to securing the strength of the annealed plate. If the Cr content is less than 0.3%, it is difficult to ensure the strength of the cold-rolled steel sheet. On the other hand, if the Cr content exceeds 1.00%, the appearance of plating deteriorates because Cr oxide formed on the surface of the cold-rolled steel sheet cannot be removed even with the present invention. Therefore, the Cr content is 1.00% or less.
Pは、鋼の強化に有効な元素である。この効果を得るためにはPの含有量は0.001%以上が好ましい。また、Pの含有量が0.010%を超えると、粒界偏析により脆化が起き、耐衝撃性が劣化する。したがって、Pを含有する場合、Pの含有量は0.010%以下とする。 P: 0.010% or less P is an element effective for strengthening steel. In order to obtain this effect, the P content is preferably 0.001% or more. On the other hand, when the P content exceeds 0.010%, embrittlement occurs due to grain boundary segregation, and impact resistance deteriorates. Therefore, when it contains P, content of P shall be 0.010% or less.
Sは、MnSなどの介在物となって、耐衝撃性を劣化させたり、溶接部のメタルフローに沿った割れの原因となったりする。このため、Sの含有量は極力低い方がよい。しかし、Sを完全に含まないように冷延鋼板を製造することは、製造コスト等の観点から困難である。そこで、Sを含有する場合、Sの含有量は0.010%以下とする。 S: 0.010% or less S becomes inclusions such as MnS, and deteriorates impact resistance or causes cracks along the metal flow of the welded portion. For this reason, the S content is preferably as low as possible. However, it is difficult to manufacture a cold-rolled steel sheet so as not to completely contain S from the viewpoint of manufacturing cost and the like. Then, when it contains S, content of S shall be 0.010% or less.
Alを過剰に含有すると、酸化物系介在物の増加による表面性状や成形性の劣化を招く。また、Alの過剰な含有は、製造コストを増加させる。そこで、Alを含有する場合、Alの含有量は0.100%以下とする。好ましくは0.050%以下である。 Al: 0.100% or less When Al is excessively contained, surface properties and moldability are deteriorated due to an increase in oxide inclusions. Moreover, the excessive content of Al increases the manufacturing cost. Therefore, when Al is contained, the Al content is 0.100% or less. Preferably it is 0.050% or less.
Nは、鋼の耐時効性を最も大きく劣化させる元素である。Nの含有量は少ないほど好ましい。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%以下とする。 N: 0.0100% or less N is an element that greatly deteriorates the aging resistance of steel. The smaller the N content, the better. When the content of N exceeds 0.0100%, deterioration of aging resistance becomes remarkable. Therefore, the N content is 0.0100% or less.
Moは、オーステナイト生成元素であり、焼鈍板の強度確保に寄与する。Moの含有量が0.01%未満では上記強度確保の効果を得ることが難しい。また、Moは高価であるため、その含有量の増加は、コストアップにつながる。したがって、Moを含有する場合、Moの含有量は、0.01%以上0.50%以下とする。 Mo: 0.01% or more and 0.50% or less Mo is an austenite-generating element and contributes to securing the strength of the annealed plate. If the Mo content is less than 0.01%, it is difficult to obtain the effect of securing the strength. Moreover, since Mo is expensive, the increase in the content leads to an increase in cost. Therefore, when it contains Mo, content of Mo shall be 0.01% or more and 0.50% or less.
Nbは固溶強化または析出強化により強度向上に寄与する元素である。この効果はNbの含有量を0.010%以上にすることで得られる。一方、Nbの含有量が0.100%を超えると鋼板の延性が低下する。即ち、鋼板の加工性が劣化する。したがって、Nbを含有する場合、Nbは0.010%以上0.100%以下とする。 Nb: 0.010% or more and 0.100% or less Nb is an element that contributes to strength improvement by solid solution strengthening or precipitation strengthening. This effect can be obtained by setting the Nb content to 0.010% or more. On the other hand, when the Nb content exceeds 0.100%, the ductility of the steel sheet is lowered. That is, the workability of the steel sheet is deteriorated. Therefore, when Nb is contained, Nb is made 0.010% or more and 0.100% or less.
Bは焼入れ性を高め、鋼板の強度向上に寄与する元素である。この効果はBの含有量を0.0001%以上にすることで得られる。一方、Bを過剰に含有すると、鋼板の延性が低下し、その結果、鋼板の加工性が劣化する。また、Bの過剰な含有は、コストアップの原因となる。したがって、Bを含有する場合、Bの含有量は0.0001%以上0.0050%以下とする。 B: 0.0001% or more and 0.0050% or less B is an element that enhances hardenability and contributes to improving the strength of the steel sheet. This effect can be obtained by setting the B content to 0.0001% or more. On the other hand, when B is contained excessively, the ductility of the steel sheet is lowered, and as a result, the workability of the steel sheet is deteriorated. Further, excessive inclusion of B causes an increase in cost. Therefore, when it contains B, content of B shall be 0.0001% or more and 0.0050% or less.
Tiは鋼板中でCまたはNと微細炭化物や微細窒化物を形成することにより、鋼板の強度向上に寄与する元素である。この効果を得るためにはTiの含有量を0.010%以上にすることが必要である。一方、Tiの含有量が0.100%を超えるとこの効果が飽和する。したがって、Tiを含有する場合、Tiの含有量は0.010%以上0.100%以下とする。 Ti: 0.010% or more and 0.100% or less Ti is an element that contributes to improving the strength of the steel sheet by forming fine carbide or fine nitride with C or N in the steel sheet. In order to obtain this effect, the Ti content needs to be 0.010% or more. On the other hand, this effect is saturated when the Ti content exceeds 0.100%. Therefore, when Ti is contained, the content of Ti is set to 0.010% or more and 0.100% or less.
Cu、V、Niは鋼の強化に有効な元素である。本発明で規定した範囲内であれば、鋼の強化のために、本発明の冷延鋼板はこれらの元素を含有できる。しかしながら、Cuの含有量が1.00%、Vの含有量が0.500%、Niの含有量が0.50%を超えると、著しい強度上昇により、鋼板の延性が低下する場合がある。また、これらの元素の過剰な含有は、コストアップの要因にもなる。したがって、これらの元素を含有する場合、その量をそれぞれCuは1.00%以下、Vは0.500%以下、Niは0.50%以下とする。 Cu: 1.00% or less, V: 0.500% or less, Ni: 0.50% or less Cu, V, and Ni are elements effective for strengthening steel. If it is in the range prescribed | regulated by this invention, the cold-rolled steel plate of this invention can contain these elements for reinforcement | strengthening of steel. However, if the Cu content is 1.00%, the V content is 0.500%, and the Ni content exceeds 0.50%, the ductility of the steel sheet may decrease due to a significant increase in strength. Further, excessive inclusion of these elements also causes an increase in cost. Therefore, when these elements are contained, the amounts of Cu are 1.00% or less, V is 0.500% or less, and Ni is 0.50% or less, respectively.
SbおよびSnは鋼板表層付近の窒化を抑制する作用がある。この効果はこれらの元素の含有量が0.10%を超えると飽和する。したがって、Sbを含有する場合、Sbの含有量は0.10%以下とし、Snを含有する場合、Snの含有量は0.10%以下とする。 Sb: 0.10% or less, Sn: 0.10% or less Sb and Sn have the effect of suppressing nitriding in the vicinity of the steel sheet surface layer. This effect is saturated when the content of these elements exceeds 0.10%. Therefore, when Sb is contained, the Sb content is 0.10% or less, and when Sn is contained, the Sn content is 0.10% or less.
Caは、MnSなど硫化物の形状制御によって、鋼板の延性を向上させる。その効果は、Caの含有量が0.0100%を超えると飽和する。また、REMは硫化物系介在物の形態を制御し、鋼板の加工性の向上に寄与する。しかし、REMの含有量が0.005%を超えると、介在物量が増加し、加工性が劣化する。したがって、Caを含有する場合、Caの含有量は0.0100%以下とし、REMを含有する場合、REMの含有量は0.005%以下とする。 Ca: 0.0100% or less, REM: 0.005% or less Ca improves the ductility of the steel sheet by shape control of sulfides such as MnS. The effect is saturated when the Ca content exceeds 0.0100%. Moreover, REM controls the form of sulfide inclusions and contributes to the improvement of the workability of the steel sheet. However, when the content of REM exceeds 0.005%, the amount of inclusions increases and the workability deteriorates. Therefore, when Ca is contained, the Ca content is 0.0100% or less, and when REM is contained, the REM content is 0.005% or less.
冷延鋼板の鋼板表面直下にCr濃度が低い領域が存在する場合、焼鈍時における鋼板表面でのCr酸化物形成が抑制される。その結果、表面外観に優れた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を得ることができる。一方、鋼板表面直下のCr濃度が高い場合、焼鈍時に鋼板表面でCr酸化物が形成され、不めっきを生じる。 Cr concentration within 0.5 μm in the thickness direction from the steel sheet surface is 0.20% or less. When there is a region with low Cr concentration directly under the steel sheet surface of the cold rolled steel sheet, formation of Cr oxide on the steel sheet surface during annealing is suppressed. Is done. As a result, a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet with excellent surface appearance can be obtained. On the other hand, when the Cr concentration directly under the steel sheet surface is high, Cr oxide is formed on the steel sheet surface during annealing, resulting in non-plating.
MnもCrと同様に鋼板表面に酸化物を形成し、めっき表面外観を劣化させる。Cr同様、鋼板表面直下にMn濃度が低い領域が存在すると、焼鈍時における鋼板表面でのMn酸化物形成が抑制される。 The Mn concentration within 0.5 μm from the steel sheet surface is 1.8% or less. Mn also forms an oxide on the steel sheet surface in the same manner as Cr and deteriorates the appearance of the plating surface. Similar to Cr, if there is a region with a low Mn concentration directly under the steel sheet surface, the formation of Mn oxide on the steel sheet surface during annealing is suppressed.
加熱工程とは、水素濃度が3.0~25.0vol%、露点が-40~-10℃の雰囲気の700~900℃の温度域で、上記成分組成を有する鋼板を20~600秒保持する工程である。 Heating step The heating step is a temperature range of 700 to 900 ° C. in an atmosphere having a hydrogen concentration of 3.0 to 25.0 vol% and a dew point of −40 to −10 ° C. It is the process of holding.
冷却工程とは、該保持後の鋼板を冷却する工程である。冷却停止温度は特に限定されないが、一般的には600~300℃である。冷却は水冷、空冷のいずれでもよい。また、冷却時間、冷却速度等は適宜設定すればよい。 Cooling process A cooling process is a process of cooling the steel plate after this holding | maintenance. The cooling stop temperature is not particularly limited, but is generally 600 to 300 ° C. Cooling may be either water cooling or air cooling. Moreover, what is necessary is just to set cooling time, a cooling rate, etc. suitably.
酸洗工程とは、冷却工程後の鋼板表面を、酸洗減量がFe換算で4.0~20.0g/m2となる条件で酸洗除去する工程である。 Pickling Step The pickling step is a step of pickling and removing the steel plate surface after the cooling step under the condition that the pickling loss is 4.0 to 20.0 g / m 2 in terms of Fe.
再酸洗工程とは、酸洗工程の後に、前記酸洗工程に用いる酸とは異なる非酸化性の酸で、鋼板表面を再酸洗する工程である。再酸洗工程は任意に行われる工程であり、本工程を行うことにはめっき密着性を向上させる効果がある。 Re-pickling step The re-pickling step is a step of re-pickling the steel sheet surface with a non-oxidizing acid different from the acid used in the pickling step after the pickling step. The re-pickling step is an optional step, and performing this step has an effect of improving plating adhesion.
不めっきやピンホールなどの外観不良の有無を目視にて判断し、外観不良がない場合には「良好(表中の○)」、外観不良がわずかにあるが概ね良好である場合には「概ね良好(表中の△)」、外観不良がある場合には「不良(表中の×)」と判定した。表面外観が良好および概ね良好を合格とした。 <Surface appearance>
Judging by visual inspection for appearance defects such as non-plating and pinholes, if there is no appearance defect, it is “Good (○ in the table)”. When there was an appearance defect in general “good (Δ)”, it was judged as “bad (× in the table)”. A surface appearance of good and almost good was regarded as acceptable.
合金化溶融亜鉛めっき鋼板のめっき密着性は、耐パウダリング性を評価することで評価した。具体的には、合金化溶融亜鉛めっき鋼板にセロハンテープを貼り、テープ面を90度曲げ、曲げ戻しをし、加工部の内側(圧縮加工側)に、曲げ加工部と平行に巾24mmのセロハンテープを押し当てて引き離し、セロハンテープの長さ40mmの部分に付着した亜鉛量を、蛍光X線によるZnカウント数として測定した。下記基準に照らしてランク1および2のものを「特に良好(表中の○)」、ランク3および4のものを「良好(表中の△)」、5以上のものを「不良(表中の×)」として評価した。ランク1~4のものを合格とした。
蛍光X線カウント数 ランク
0以上~2000未満 :1 (良)
2000以上~5000未満 :2
5000以上~8000未満 :3
8000以上~10000未満 :4
10000以上 :5 (劣)
合金化していない溶融亜鉛めっき鋼板については、ボールインパクト試験を行い、加工部をセロハンテープ剥離し、めっき層剥離の有無を目視判定することでめっき密着性を評価した。なお、ボールインパクト試験は、ボール質量1.8kg、落下高さ100cmで、インパクト部の直径を3/4インチと3/8インチで行った。
◎:3/4インチ、3/8インチで共にめっき層の剥離なし
○:3/4インチでめっき層の剥離なし、3/8インチでわずかにめっき層が剥離
×:3/4インチ、3/8インチで共にめっき層が剥離 <Plating adhesion>
The plating adhesion of the galvannealed steel sheet was evaluated by evaluating the powdering resistance. Specifically, cellophane tape is applied to the alloyed hot-dip galvanized steel sheet, the tape surface is bent 90 degrees, bent back, and the cellophane with a width of 24 mm is parallel to the bent portion on the inner side (compressed side) of the processed portion. The tape was pressed and pulled away, and the amount of zinc adhering to the 40 mm long portion of the cellophane tape was measured as the Zn count by fluorescent X-rays. Based on the criteria below, those with
X-ray fluorescence count Rank 0 or more and less than 2000: 1 (good)
2000 or more and less than 5000: 2
5000 or more and less than 8000: 3
8000 or more and less than 10,000: 4
10,000 or more: 5 (poor)
About the hot-dip galvanized steel sheet which is not alloyed, the ball impact test was performed, the processed part was peeled off with cellophane tape, and the plating adhesion was evaluated by visually judging the presence or absence of peeling of the plating layer. In the ball impact test, the ball mass was 1.8 kg, the drop height was 100 cm, and the diameter of the impact part was 3/4 inch and 3/8 inch.
A: No peeling of the plating layer at 3/4 inch and 3/8 inch. ○: No peeling of the plating layer at 3/4 inch. Slight peeling of the plating layer at 3/8 inch. X: 3/4 inch, 3 / 8 inches, both plating layers are peeled off
Claims (9)
- 高強度溶融亜鉛めっき鋼板及び高強度合金化溶融亜鉛めっき鋼板の製造に用いる冷延鋼板であって、
質量%でC:0.040%以上0.500%以下、Si:1.00%以下、Mn:2.00%以上3.80%以下、P:0.010%以下、S:0.010%以下、Al:0.100%以下、N:0.0100%以下、Cr:0.3%以上1.00%以下を含有し、残部がFeおよび不可避的不純物からなり、
表面から厚み方向に0.5μm以内におけるCr濃度が0.20%以下で、かつ、Mn濃度が1.8%以下であることを特徴とする冷延鋼板。 A cold-rolled steel sheet used for manufacturing high-strength hot-dip galvanized steel sheets and high-strength alloyed hot-dip galvanized steel sheets,
C: 0.040% to 0.500%, Si: 1.00% or less, Mn: 2.00% to 3.80%, P: 0.010% or less, S: 0.010 by mass% % Or less, Al: 0.100% or less, N: 0.0100% or less, Cr: 0.3% or more and 1.00% or less, with the balance consisting of Fe and inevitable impurities,
A cold-rolled steel sheet, characterized in that the Cr concentration within 0.5 μm in the thickness direction from the surface is 0.20% or less and the Mn concentration is 1.8% or less. - さらに、質量%で、Mo:0.01%以上0.50%以下、Nb:0.010%以上0.100%以下、B:0.0001%以上0.0050%以下及びTi:0.010%以上0.100%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に記載の冷延鋼板。 Further, in terms of mass%, Mo: 0.01% to 0.50%, Nb: 0.010% to 0.100%, B: 0.0001% to 0.0050% and Ti: 0.010 The cold-rolled steel sheet according to claim 1, comprising at least one element selected from% to 0.100%.
- さらに、質量%で、Cu:1.00%以下、V:0.500%以下、Ni:0.50%以下、Sb:0.10%以下、Sn:0.10%以下、Ca:0.0100%以下、REM:0.005%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に記載の冷延鋼板。 Further, in terms of mass%, Cu: 1.00% or less, V: 0.500% or less, Ni: 0.50% or less, Sb: 0.10% or less, Sn: 0.10% or less, Ca: 0.0. The cold-rolled steel sheet according to claim 1 or 2, comprising at least one element selected from 0100% or less and REM: 0.005% or less.
- 請求項1~3のいずれかに記載の冷延鋼板を製造する方法であって、
水素濃度が3.0~25.0vol%、露点が-40~-10℃の雰囲気の700~900℃の温度域で、請求項1~3に記載の成分組成を有する鋼板を20~600秒保持する加熱工程と、
該保持後の鋼板を冷却する冷却工程と、
該冷却後の鋼板表面を、酸洗減量がFe換算で4.0~20.0g/m2となる条件で酸洗除去する酸洗工程とを有することを特徴とする冷延鋼板の製造方法。 A method for producing the cold-rolled steel sheet according to any one of claims 1 to 3,
A steel plate having the composition according to claims 1 to 3 in a temperature range of 700 to 900 ° C in an atmosphere having a hydrogen concentration of 3.0 to 25.0 vol% and a dew point of -40 to -10 ° C for 20 to 600 seconds Holding heating process;
A cooling step for cooling the steel plate after the holding;
A method for producing a cold-rolled steel sheet, comprising: pickling and removing the surface of the steel sheet after cooling under conditions where the pickling loss is 4.0 to 20.0 g / m 2 in terms of Fe . - 前記酸洗工程で使用する酸は、硝酸、塩酸、弗酸及び硫酸から選ばれる少なくとも1種であることを特徴とする請求項4に記載の冷延鋼板の製造方法。 The method for producing a cold-rolled steel sheet according to claim 4, wherein the acid used in the pickling step is at least one selected from nitric acid, hydrochloric acid, hydrofluoric acid and sulfuric acid.
- 前記酸洗工程で使用する酸洗液は、硝酸及び塩酸を含み、硝酸濃度が50g/L超え200g/L以下であり、硝酸濃度に対する塩酸濃度の比(HCl/HNO3)が0.01~1.00であるか、
又は前記酸洗工程で使用する酸洗液は、硝酸及び弗酸を含み、硝酸濃度が50g/L超え200g/L以下であり、硝酸濃度に対する弗酸濃度の比(HF/HNO3)が0.01~1.00のいずれかであることを特徴とする請求項4又は5に記載の冷延鋼板の製造方法。 The pickling solution used in the pickling step contains nitric acid and hydrochloric acid, the nitric acid concentration is more than 50 g / L and not more than 200 g / L, and the ratio of the hydrochloric acid concentration to the nitric acid concentration (HCl / HNO 3 ) is 0.01 to 1.00 or
Alternatively, the pickling solution used in the pickling step contains nitric acid and hydrofluoric acid, the nitric acid concentration is more than 50 g / L and not more than 200 g / L, and the ratio of the hydrofluoric acid concentration to the nitric acid concentration (HF / HNO 3 ) is 0. The method for producing a cold-rolled steel sheet according to claim 4 or 5, wherein the method is any one of .01 to 1.00. - 前記酸洗工程の後に、前記酸洗工程に用いる酸とは異なる非酸化性の酸で、鋼板表面を再酸洗する再酸洗工程をさらに有することを特徴とする請求項6に記載の冷延鋼板の製造方法。 7. The cooling according to claim 6, further comprising a re-pickling step of re-pickling the steel sheet surface with a non-oxidizing acid different from the acid used in the pickling step after the pickling step. A method for producing rolled steel sheets.
- 請求項1~3のいずれかに記載の冷延鋼板又は請求項4~7のいずれかに記載の製造方法で製造した冷延鋼板に、溶融亜鉛めっき処理を施してなる高強度溶融亜鉛めっき鋼板。 A high-strength hot-dip galvanized steel sheet obtained by subjecting the cold-rolled steel sheet according to any one of claims 1 to 3 or the cold-rolled steel sheet produced by the manufacturing method according to any one of claims 4 to 7 to hot dip galvanizing treatment. .
- 請求項8に記載の高強度溶融亜鉛めっき鋼板に合金化処理を施してなる高強度合金化溶融亜鉛めっき鋼板。
A high-strength galvannealed steel sheet obtained by subjecting the high-strength galvanized steel sheet according to claim 8 to an alloying treatment.
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