WO2016072475A1 - 溶融亜鉛めっき鋼板 - Google Patents
溶融亜鉛めっき鋼板 Download PDFInfo
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- WO2016072475A1 WO2016072475A1 PCT/JP2015/081231 JP2015081231W WO2016072475A1 WO 2016072475 A1 WO2016072475 A1 WO 2016072475A1 JP 2015081231 W JP2015081231 W JP 2015081231W WO 2016072475 A1 WO2016072475 A1 WO 2016072475A1
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- steel sheet
- base steel
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- layer
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- 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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- 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
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—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
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—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
- C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
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- C23C2/0224—Two or more thermal pretreatments
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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- 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
- B32B2255/00—Coating on the layer surface
- B32B2255/06—Coating on the layer surface on metal layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B2311/00—Metals, their alloys or their compounds
- B32B2311/20—Zinc
Definitions
- the present invention relates to a hot dip galvanized steel sheet having excellent plating adhesion.
- Patent Document 4 a new annealing process and a pickling process are added before a general annealing process, the base-material steel plate surface is modified, plating A method for improving the adhesion has been proposed.
- the method described in Patent Document 4 has a problem in terms of cost because the number of steps is increased compared to a general method for producing a high-strength plated steel sheet.
- Patent Document 5 proposes a method of removing carbon from the surface layer portion of the base steel plate to improve the adhesion of plating.
- the strength of the region from which carbon is removed is significantly reduced.
- the method described in Patent Document 5 has a concern that the fatigue resistance, which strongly depends on the characteristics of the surface layer portion, is deteriorated and the fatigue strength is greatly reduced.
- Patent Documents 6 and 7 steel sheets are proposed in which the amounts of Mn, Al and Si in the plating layer are controlled within a suitable range to improve the plating adhesion.
- the steel sheets described in Patent Documents 6 and 7 it is necessary to control the amount of elements in the plating layer with high accuracy at the time of production, and there is a large operational load and there is a problem in cost.
- Patent Document 8 proposes a high-strength steel sheet in which the microstructure of the steel sheet is composed only of ferrite.
- the steel sheet described in Patent Document 8 cannot obtain a sufficiently high strength because the microstructure is only soft ferrite.
- alloyed hot-dip galvanized steel sheets that have been subjected to alloying after hot-dip galvanizing are widely used.
- the alloying process is a process in which the plating layer is heated to a temperature equal to or higher than the melting point of Zn, a large amount of Fe atoms are diffused from the base steel plate into the plating layer, and the plating layer is a Zn-Fe alloy-based layer.
- Patent Documents 9, 10, and 11 propose galvannealed steel sheets having excellent plating adhesion.
- Patent Document 12 describes a hot-dip galvanized steel sheet containing at least one selected from the group consisting of Si, Mn, and Al. Patent Document 12 describes that the plating bath intrusion temperature of the base steel sheet is controlled in the manufacturing process. Further, Patent Document 12 discloses a hot dip galvanized steel sheet that is excellent in plating adhesion and spot weldability, in which the area ratio of the cross section in the alloy layer formed at the interface between the base steel sheet and the plated layer is defined. Yes.
- Patent Document 12 states that when a steel sheet having Si and Mn oxide on the surface is intruded into a hot dip galvanizing bath, a large amount of unplated material that is not galvanized is generated. However, Patent Document 12 does not disclose a technique for reducing Si and Mn oxides before the start of plating. Moreover, in patent document 12, the plating bath penetration
- an object of the present invention is to provide a hot dip galvanized steel sheet having excellent strength, ductility, hole expansibility, and spot weldability.
- the inventors of the present invention have made extensive studies in order to obtain a hot-dip galvanized steel sheet having excellent plating adhesion. As a result, the present inventors have found that the ⁇ phase (FeZn 13 ) is generated in the plating layer, and the coarse oxide that is the starting point of the breakdown is taken into the plating layer, thereby suppressing plating peeling. Thereby, a hot-dip galvanized steel sheet having excellent plating adhesion can be obtained without subjecting the plating layer to alloying treatment.
- the present invention has been completed based on such findings, and the modes thereof are as follows.
- the hot dip galvanized layer has columnar crystals comprising a ⁇ phase on the surface of the steel sheet with an Fe content of more than 0% to 5% and an Al content of more than 0% to 1.0%.
- ⁇ crystal in which 20% or more of the total interface between the hot dip galvanized layer and the base steel sheet is coated with the ⁇ phase, and coarse oxides of ⁇ crystal grains are present in the hot dip galvanized layer.
- the interface formed between the grains and the base steel plate is 50% or less with respect to the total interface between the ⁇ phase and the base steel plate
- the base material steel plate is mass%, C: 0.040 to 0.400%, Si: 0.05-2.50%, Mn: 0.50 to 3.50%, P: 0.0001 to 0.1000%, S: 0.0001 to 0.0100%, Al: 0.001-1.500%, N: 0.0001 to 0.0100%, O: 0.0001 to 0.0100%, Si + 0.7Al ⁇ 0.30 (the element symbol in the formula represents the content (mass%) of the element), and the balance has a chemical component consisting of Fe and inevitable impurities, Having a refined layer in direct contact with the interface between the base steel sheet and the hot-dip galvanized layer, the refined layer has an average thickness of 0.1 to 5.0 ⁇ m, and the average ferrite phase in the refined layer
- the particle size is 0.1 to 3.0 ⁇ m
- the refined layer contains one or more oxides of Si and Mn
- the base material steel plate is in mass%, Cr: 0.01 to 2.00% Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Mo: 0.01 to 2.00% B: 0.0001 to 0.0100%, W: 0.01 to 2.00%
- the hot-dip galvanized steel sheet according to any one of (1) to (3) which contains one or more selected from among the above.
- the base steel plate is in mass%, and The hot-dip galvanized steel sheet according to any one of (1) to (4), which contains 0.0001 to 0.0100% of one or more of Ca, Ce, Mg, Zr, La, and REM in total.
- a hot-dip galvanized steel sheet excellent in strength, ductility, hole expansibility, spot weldability, and plating adhesion can be provided.
- a hot-dip galvanized steel sheet is a base steel sheet (hereinafter also simply referred to as a steel sheet) and a hot-dip galvanized layer (hereinafter also simply referred to as a plated layer) formed on at least one surface of the steel sheet. It consists of.
- the plating layer has an Fe content of more than 0% to 5% or less, an Al content of more than 0% to 1.0%, and includes columnar crystals composed of a ⁇ phase.
- the plating layer 20% or more of the entire interface between the plating layer and the base steel plate is covered with the ⁇ phase, and the ⁇ crystal grains and base material in which coarse oxide exists in the interface between the ⁇ phase and the base steel plate
- the ratio of the interface formed with the steel sheet is 50% or less.
- the hot dip galvanized layer has an Fe content of more than 0% to 5.0% and an Al content of more than 0% to 1.0%.
- the hot-dip galvanized layers are Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni , Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, REM may be contained or mixed therein.
- the hot-dip galvanized layer contains or mixes one or more of the above elements, the effects of the present invention are not impaired, and depending on the content, the corrosion resistance and workability may be reduced. In some cases, such as improvement.
- the hot dip galvanized layer includes columnar crystals composed of a ⁇ phase, and 20% or more of the entire interface between the plated layer and the base steel plate is covered with the ⁇ phase.
- the adhesion amount of the hot dip galvanized layer on one side of the base steel plate is preferably 10 g / m 2 or more and 100 g / m 2 or less.
- Fe content in hot-dip galvanized layer more than 0% to 5.0% or less
- the Fe content in the hot dip galvanized layer increases, the plating adhesion deteriorates, so the Fe content needs to be 5.0% or less.
- the Fe content in the plating layer is preferably 4.0% or less, and more preferably 3% or less.
- the lower limit of the Fe content in the plating layer is over 0%. If the Fe content is less than 0.5%, the ⁇ phase necessary for improving the adhesion may not be sufficiently obtained. For this reason, the Fe content in the plating layer is preferably 0.5% or more, and more preferably 1.0% or more.
- Al content in hot-dip galvanized layer more than 0% to 1.0% or less
- the Al content in the plating layer is preferably 0.8% or less, and more preferably 0.5% or less.
- the lower limit of the Al content in the plating layer is over 0%.
- the Al content in the plating layer is preferably 0.01% or more. From this viewpoint, the Al content in the plating layer is more preferably 0.05% or more.
- the hot-dip galvanized layers are Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni , Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, REM may be contained or mixed therein. Even if the hot-dip galvanized layer contains or mixes one or more of the above elements, the effects of the present invention are not impaired, and depending on the content, the corrosion resistance and workability are improved. It may be preferable.
- the hot dip galvanized layer of the present invention includes columnar crystals composed of a ⁇ phase (FeZn 13 ) that is an alloy of Fe and Zn.
- the ratio of the interface where the ⁇ phase is in contact with the base steel plate among all the interfaces between the plating layer and the base steel plate is 20% or more.
- a coarse oxide having a major axis of 0.2 ⁇ m or more containing Si and / or Mn that can act as a starting point of peeling is taken into the ⁇ phase from the surface of the base steel sheet.
- the ratio of the interface between the ⁇ phase and the base steel plate to the entire interface between the plating layer and the base steel plate is preferably 25% or more, and more preferably 30% or more.
- the upper limit of the ratio of the interface between the ⁇ phase and the base steel plate to all the interfaces between the plating layer and the base steel plate is not particularly defined and may be 100%.
- the major axis of the oxide containing Si and / or Mn is 0.2 ⁇ m or more, cracks starting from the oxide become prominent, and when the major axis is less than 0.2 ⁇ m, it becomes difficult to work as a starting point of cracks.
- the degree of stress concentration during deformation of the hot-dip galvanized steel sheet changes depending on the size of the oxide. Specifically, the larger the oxide (the longer the longer the axis), the easier the stress is concentrated during deformation, and the plating layer is more easily peeled off.
- the ratio of the interface between the ⁇ crystal grains (coarse oxide-containing ⁇ crystal grains) in which the coarse oxide exists in the crystals of ⁇ phase ( ⁇ crystal grains) and the base steel plate is expressed as ⁇ phase and base steel plate. And 50% or less for all the interfaces.
- the ratio of the interface between the coarse oxide-containing ⁇ crystal grains and the base steel plate is 50% or less, the coarse oxide containing Si and / or Mn existing without being taken into the ⁇ phase is sufficiently reduced.
- the ratio of the interface between the coarse oxide-containing ⁇ crystal grains and the base steel plate is preferably 35% or less with respect to all the interfaces between the ⁇ phase and the base steel plate. It is preferable that the amount of coarse oxide having a major axis of 0.2 ⁇ m or more is smaller at the interface between the ⁇ phase and the base steel plate. Of all the interfaces between the ⁇ phase and the base steel plate, the ratio of the interface formed by the coarse oxide-containing ⁇ crystal grains with the base steel plate is most preferably 0%.
- the hot dip galvanized layer may contain a ⁇ 1 phase (FeZn 7 ).
- a ⁇ 1 phase FeZn 7
- the ratio of the interface in which the ⁇ 1 phase is in contact with the base steel plate among all the interfaces between the plating layer and the base steel plate is preferably 20% or less.
- the ratio between the ⁇ phase and the base steel sheet occupies all the interfaces between the plating layer and the base steel sheet, and the interface between the ⁇ 1 phase and the base steel sheet occupies all the interfaces between the plating layer and the base steel sheet.
- the ratio can be obtained as follows. That is, a sample is taken from a hot-dip galvanized steel sheet, with a plate thickness section parallel to the rolling direction of the base steel sheet as an observation surface. The observation surface is mirror-polished, and using a field emission scanning electron microscope (FE-SEM), the total length L of the interface between the observed plating layer and the base steel plate is 200 ⁇ m or more. Observe until. When observing until the total length L of the interface becomes 200 ⁇ m or more, it may be observed in one plate thickness section until L becomes 200 ⁇ m or more, or in a plurality of plate thickness sections, L is 200 ⁇ m or more. You may observe until.
- the columnar crystal grains are the ⁇ phase or the ⁇ 1 phase, and the total length L1 of the interface between the ⁇ phase and the ⁇ 1 phase and the base steel plate is measured.
- high resolution crystal orientation analysis was performed by an EBSD (Electron Bach-Scattering Diffraction) method using FE-SEM, the ⁇ 1 phase was identified, and the ⁇ 1 phase and the base material The total length L2 of the steel plate interface is determined. (L1-L2) / L is regarded as the ratio of the interface between the ⁇ phase and the base steel sheet to the total interface between the plating layer and the base steel sheet.
- L2 / L is regarded as the ratio of the interface between the ⁇ 1 phase and the base material steel plate to all the interfaces between the plating layer and the base material steel plate.
- the separation of the ⁇ phase and the ⁇ 1 phase may be performed by a method other than the EBSD method.
- field element electron probe microanalyzer FE-EPMA: Field Emission Electron Probe MicroAnalyzer
- FE-EPMA Field Emission Electron Probe MicroAnalyzer
- the ratio of the interface between the ⁇ crystal grains (coarse oxide-containing ⁇ crystal grains) in which the coarse oxide exists in the crystals of ⁇ phase ( ⁇ crystal grains) and the base material steel plate is obtained as follows. That is, in the same field of view as when L was observed, the interface between the ⁇ phase and the base steel sheet was observed, and ⁇ crystal grains (coarse grains having a coarse oxide with a major axis of 0.2 ⁇ m or more at the interface between the ⁇ phase and the base steel sheet). Determine oxide-containing ⁇ crystal grains). The oxide present at the interface between the ⁇ phase of the plating layer and the base steel plate appears darker than the surroundings in the SEM reflected electron (BSE) image.
- BSE SEM reflected electron
- the observation surface of the sample may be mirror-polished and then the observation surface may be corroded with a corrosive liquid such as nital.
- the adhesion amount of the plating layer to one surface of the base steel sheet is 10 g / m 2 or more. From the viewpoint of corrosion resistance, the adhesion amount is more preferably 20 g / m 2 or more, 30 g / m 2 or more is more preferable.
- the adhesion amount of a plating layer shall be 100 g / m ⁇ 2 > or less.
- the adhesion amount is more preferably 93 g / m 2 or less, and further preferably 85 g / m 2 or less.
- the hot dip galvanized steel sheet according to the present invention includes the above-described plated layer, and the base steel sheet has a refined layer shown below.
- the refined layer is a region where the average particle size of the ferrite phase existing in the outermost layer is 1 ⁇ 2 or less of the average particle size of the ferrite phase in the lower layer.
- a boundary where the average particle diameter of the ferrite phase in the refined layer exceeds 1/2 of the average particle diameter of the ferrite phase in the lower layer is defined as a boundary between the refined layer and the lower layer.
- the refined layer is in direct contact with the interface between the base steel plate and the hot dip galvanized layer.
- the average thickness of the miniaturized layer is 0.1 to 5.0 ⁇ m.
- the average grain size of the ferrite phase in the refined layer is 0.1 to 3.0 ⁇ m.
- the miniaturized layer contains one or more oxides of Si and Mn, and the maximum diameter of the oxide is 0.01 to 0.4 ⁇ m.
- the average thickness of the miniaturized layer is 0.1 ⁇ m or more, and preferably 1.0 ⁇ m or more.
- miniaturization layer whose average thickness is 5.0 micrometers or less can be formed, suppressing the excessive alloying in a plating bath. Therefore, it is possible to prevent a decrease in plating adhesion due to an excessively large Fe content in the plating layer. For this reason, the average thickness of the miniaturized layer is 5.0 ⁇ m or less, and preferably 3.0 ⁇ m or less.
- the average particle diameter of the ferrite phase in the refined layer is 0.1 ⁇ m or more, and preferably 1.0 ⁇ m or more.
- the average particle diameter of the ferrite phase in the refined layer is 3.0 ⁇ m or less, and preferably 2.0 ⁇ m or less.
- One or more oxides of Si and Mn contained in the refined layer are selected from, for example, SiO 2 , Mn 2 SiO 4 , MnSiO 3 , Fe 2 SiO 4 , FeSiO 3 , and MnO. 1 type or 2 types or more are mentioned.
- the maximum diameter of one or more oxides of Si and Mn contained in the refined layer is 0.01 ⁇ m or more, the refined layer is formed and the generation of the ⁇ phase is sufficiently promoted.
- a plating layer can be formed.
- the maximum diameter of the oxide is preferably 0.05 ⁇ m or more.
- miniaturization layer whose maximum diameter of said oxide is 0.4 micrometer or less can be formed, suppressing the excessive alloying of a plating layer.
- the maximum diameter of the oxide is preferably 0.2 ⁇ m or less.
- the average thickness of the refined layer and the average grain size of the ferrite phase in the refined layer are measured by the following methods.
- a sample is taken from the hot-dip galvanized steel sheet, with the plate thickness section parallel to the rolling direction of the base steel sheet as the observation surface.
- An observation surface of the sample is processed by a CP (Cross section polisher) apparatus, and a backscattered electron image on a FE-SEM (Field Emission Scanning Electron Microscope) is observed at 5000 times and measured.
- CP Cross section polisher
- FE-SEM Field Emission Scanning Electron Microscope
- the maximum diameter of one or more oxides of Si and Mn contained in the refined layer is measured by the following method.
- a sample is taken from the hot-dip galvanized steel sheet, with the plate thickness section parallel to the rolling direction of the base steel sheet as the observation surface.
- a thin film sample is produced by processing the observation surface of the sample by FIB (Focused Ion Beam). Thereafter, the thin film sample is observed at 30000 times using FE-TEM (Field Emission Transmission Electron Microscope). Each thin film sample is observed in five visual fields, and the maximum value of the diameter of the oxide measured in the entire visual field is set as the maximum diameter of the oxide in the thin film sample.
- composition of the base steel plate constituting the hot dip galvanized steel plate according to this embodiment will be described below.
- [%] is [% by mass].
- C is an element added to increase the strength of the base steel sheet.
- the C content is set to 0.400% or less.
- the C content is preferably 0.300% or less, and more preferably 0.220% or less.
- the C content is set to 0.040% or more.
- the C content is preferably 0.055% or more, and more preferably 0.070% or more.
- Si 0.05-2.50%
- Si is an element that suppresses the formation of iron-based carbides in the base steel sheet and increases strength and formability.
- Si is also an element that embrittles a steel material, and when its content exceeds 2.50%, troubles such as cracking of a cast slab are likely to occur. Therefore, the Si content is set to 2.50% or less.
- Si forms an oxide on the surface of the base steel plate in the annealing process, and the adhesion of plating is remarkably impaired.
- the Si content is preferably 2.00% or less, and more preferably 1.60% or less.
- the Si content is less than 0.05%, a large amount of coarse iron-based carbide is generated in the plating step of the hot-dip galvanized steel sheet, and the strength and formability deteriorate.
- content of Si shall be 0.05% or more.
- the Si content is preferably 0.10% or more, and more preferably 0.25% or more.
- Mn 0.50 to 3.50%
- Mn is added to increase the strength by increasing the hardenability of the base steel sheet.
- the Mn content exceeds 3.50%, a coarse Mn-concentrated portion is generated in the central portion of the thickness of the base steel sheet, and embrittlement is likely to occur, and troubles such as cracking of the cast slab occur. It tends to happen. Therefore, the Mn content is 3.50% or less.
- the Mn content is preferably 3.00% or less, and more preferably 2.80% or less.
- the Mn content is 0.50% or more.
- the Mn content is preferably 0.80% or more, and more preferably 1.00% or more.
- P is an element that embrittles the steel material. If the P content exceeds 0.1000%, troubles such as cracking of the cast slab are likely to occur. For this reason, content of P shall be 0.1000% or less. Further, P is an element that embrittles the melted portion generated by spot welding, and in order to obtain sufficient weld joint strength, the P content is preferably 0.0400% or less, and 0.0200% or less. More preferably. On the other hand, making the P content less than 0.0001% is accompanied by a significant increase in production cost. For this reason, the P content is 0.0001% or more, preferably 0.0010% or more.
- S is an element that combines with Mn to form coarse MnS and lowers formability such as ductility, stretch flangeability and bendability. For this reason, content of S shall be 0.0100% or less. S is also an element that deteriorates spot weldability. For this reason, it is preferable to make S content into 0.0060% or less, and it is more preferable to set it as 0.0035% or less. On the other hand, making the S content less than 0.0001% is accompanied by a significant increase in production cost. For this reason, the S content is 0.0001% or more, preferably 0.0005% or more, and more preferably 0.0010% or more.
- Al 0.001-1.500%
- Al is an element that embrittles a steel material. If the Al content exceeds 1.500%, troubles such as cracking of the cast slab tend to occur, so the Al content is set to 1.500% or less. Moreover, since the spot weldability deteriorates as the Al content increases, the Al content is preferably 1.200% or less, and more preferably 1.000% or less. On the other hand, the effect of the present invention is exhibited even if the lower limit of the content of Al is not particularly defined, but Al is an inevitable impurity present in a minute amount in the raw material, and in order to make the content less than 0.001% This is accompanied by a significant increase in manufacturing costs. For this reason, Al content shall be 0.001% or more. Al is an element that is also effective as a deoxidizing material, but in order to obtain a sufficient deoxidation effect, the Al content is preferably 0.010% or more.
- N is an element that forms coarse nitrides and deteriorates formability such as ductility, stretch flangeability, and bendability, so it is preferable to suppress the amount of N added. If the N content exceeds 0.0100%, the moldability deteriorates significantly, so the upper limit of the N content is set to 0.0100%. Moreover, since excessive addition of N causes the generation
- the content is preferably suppressed. If the O content exceeds 0.0100%, the moldability deteriorates significantly, so the upper limit of the O content is 0.0100%. Further, the O content is preferably 0.0050% or less, and more preferably 0.0030% or less. Although the lower limit of the content of O is not particularly defined, the effect of the present invention is exhibited. However, when the content of O is less than 0.0001%, a significant increase in manufacturing cost is accompanied. For this reason, 0.0001% is made the lower limit.
- the O content is preferably 0.0003% or more, and more preferably 0.0005% or more.
- Si and Al are elements that suppress the formation of carbides accompanying the bainite transformation. In order to obtain retained austenite, it is preferable to add a certain amount or more of Si and / or Al. From this viewpoint, the addition amount of Si and the addition amount of Al must satisfy the following formula 2.
- the value of the left side (Si + 0.7Al) of the following formula 2 is preferably 0.45 or more, and more preferably 0.70 or more.
- Si and Al of Formula 2 are the addition amounts [mass%] of the respective elements.
- Ti was selected from 0.001 to 0.150%, Nb: 0.001 to 0.100%, and V: 0.001 to 0.300%. You may contain 1 type, or 2 or more types.
- Ti is an element contributing to an increase in strength of the base steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and strengthening dislocations by suppressing recrystallization.
- the Ti content is preferably 0.150% or less.
- the Ti content is more preferably 0.080% or less.
- the effect of the present invention is exhibited even if the lower limit of the Ti content is not particularly defined.
- the Ti content is preferably 0.001% or more.
- the Ti content is more preferably 0.010% or more.
- Nb is an element that contributes to increasing the strength of the base steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and strengthening dislocations by suppressing recrystallization.
- the Nb content exceeds 0.100%, carbonitride precipitation increases and the formability deteriorates, so the Nb content is more preferably 0.100% or less. From the viewpoint of moldability, the Nb content is more preferably 0.060% or less.
- the effect of the present invention is exhibited even if the lower limit of the Nb content is not particularly defined.
- the Nb content is preferably 0.001% or more.
- the Nb content is more preferably 0.005% or more.
- V is an element that contributes to increasing the strength of the base steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization.
- the V content is preferably 0.300% or less, and more preferably 0.200% or less.
- the effect of the present invention is exhibited even if the lower limit of the V content is not particularly defined.
- the V content is preferably 0.001% or more, and more preferably 0.010% or more.
- Cr 0.01 to 2.00%
- Ni 0.01 to 2.00%
- Cu 0.01 to 2.00%
- Mo One or more selected from 0.01 to 2.00%
- B 0.0001 to 0.0100%
- W 0.01 to 2.00%
- Cr 0.01-2.00%
- Cr is an element that suppresses phase transformation at high temperature and is effective for increasing the strength, and may be added instead of a part of C and / or Mn.
- the Cr content is preferably 2.00% or less, and more preferably 1.20% or less.
- the effect of the present invention is exhibited even if the lower limit of the Cr content is not particularly defined.
- the Cr content is preferably 0.01% or more, and more preferably 0.10% or more.
- Ni is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and may be added instead of a part of C and / or Mn. However, if the Ni content exceeds 2.00%, weldability is impaired. For this reason, the Ni content is preferably 2.00% or less, and more preferably 1.20% or less. On the other hand, the effect of the present invention is exhibited even if the lower limit of the Ni content is not particularly defined. In order to sufficiently obtain the effect of increasing the strength by adding Ni, the Ni content is preferably 0.01% or more, and more preferably 0.10% or more.
- Cu is an element that increases the strength by being present in the steel as fine particles, and can be added instead of a part of C and / or Mn.
- the Cu content is preferably 2.00% or less, and more preferably 1.20% or less.
- the effect of the present invention is exhibited even if the lower limit of the Cu content is not particularly defined.
- the Cu content is preferably 0.01% or more, and more preferably 0.10% or more.
- Mo is an element that suppresses phase transformation at high temperature and is effective for increasing the strength, and may be added instead of a part of C and / or Mn.
- the Mo content is preferably 2.00% or less, and more preferably 1.20% or less.
- the effect of the present invention is exhibited even if the lower limit of the Mo content is not particularly defined.
- the Mo content is preferably 0.01% or more, and more preferably 0.05% or more.
- B is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and may be added instead of a part of C and / or Mn.
- the B content is preferably 0.0100% or less.
- the B content is more preferably 0.0050% or less.
- the B content is preferably set to 0.0001% or more.
- the B content is more preferably 0.0005% or more.
- W is an element that suppresses phase transformation at high temperature and is effective for increasing the strength, and may be added instead of a part of C and / or Mn.
- the W content is preferably 2.00% or less, and more preferably 1.20% or less.
- the lower limit of the W content is not particularly defined, and the effects of the present invention are exhibited.
- the W content is preferably 0.01% or more, and more preferably 0.10% or more.
- REM is an abbreviation for Rare Earth Metal and refers to an element belonging to the lanthanoid series.
- REM and Ce are often added by misch metal, and may contain a lanthanoid series element in combination with La and Ce. Even if these lanthanoid series elements other than La and Ce are included as inevitable impurities, the effect of the present invention is exhibited. Even if the metal La or Ce is added, the effect of the present invention is exhibited.
- Ca, Ce, Mg, Zr, La, and REM are effective elements for improving moldability, and one or more can be added. However, if the total content of one or more of Ca, Ce, Mg, Zr, La, and REM exceeds 0.0100%, the ductility may be impaired. For this reason, the total content of each element is preferably 0.0100% or less, and more preferably 0.0070% or less. On the other hand, even if the lower limit of the content of one or more of Ca, Ce, Mg, Zr, La, and REM is not particularly defined, the effect of the present invention is exhibited. In order to sufficiently obtain the effect of improving the formability of the base steel sheet, the total content of these elements is preferably 0.0001% or more. From the viewpoint of moldability, the total content of one or more of Ca, Ce, Mg, Zr, La, and REM is more preferably 0.0010% or more.
- the balance of each element described above is Fe and inevitable impurities.
- Ti, Nb, V, Cr, Ni, Cu, Mo, B, and W are all allowed to contain trace amounts less than the respective lower limit values as impurities.
- Ca, Ce, Mg, Zr, La, and REM are allowed to contain a trace amount less than the lower limit of the total amount as impurities.
- the base steel sheet of the hot dip galvanized steel sheet according to the embodiment of the present invention includes a retained austenite phase.
- Residual austenite is a structure that greatly increases the strength-ductility balance.
- the volume fraction of retained austenite is set to 1% or more.
- the volume fraction of retained austenite is preferably 3% or more, and more preferably 5% or more.
- the volume fraction of retained austenite is preferably 25% or less. Residual austenite is transformed into hard martensite with deformation, and the martensite acts as a starting point of fracture, so that the stretch flangeability deteriorates. For this reason, the volume fraction of retained austenite is more preferably 20% or less.
- the base steel sheet of the hot dip galvanized steel sheet according to the embodiment of the present invention includes, in addition to retained austenite, granular ferrite, acicular ferrite, non-recrystallized ferrite, pearlite, bainite, bainitic ferrite, martensite, and tempered martensite. It may have a microstructure composed of one kind or two or more kinds of sites and coarse cementite.
- the base steel sheet can appropriately select the phase, the breakdown of the volume fraction of each structure, the structure size, and the arrangement.
- the volume fraction of each structure contained in the base steel sheet of the hot-dip galvanized steel sheet according to the embodiment of the present invention can be measured by, for example, the following method.
- the volume fraction of retained austenite contained in the base steel sheet structure of the hot dip galvanized steel sheet of this embodiment is evaluated by the X-ray diffraction method. In the range from 1/8 thickness to 3/8 thickness from the surface of the plate thickness, the surface parallel to the plate surface is finished as a mirror surface, and the area fraction of FCC iron is measured by X-ray diffraction method, and the volume of retained austenite Use fractions.
- the volume fraction of ferrite, bainitic ferrite, bainite, tempered martensite, fresh martensite, pearlite, and coarse cementite contained in the base steel sheet structure of the hot dip galvanized steel sheet of the present embodiment is calculated by the following method. .
- a sample is taken using a plate thickness cross section parallel to the rolling direction of the base steel plate as an observation surface.
- the specimen observation surface is polished and nital etched.
- a range of 1/8 to 3/8 thickness centered on 1/4 of the thickness of the observation surface is observed with a field emission scanning electron microscope (FE-SEM: Field Emission Scanning Electron Microscope). And take it as a volume fraction.
- FE-SEM Field Emission Scanning Electron Microscope
- the thickness of the base steel sheet is not particularly limited, but from the viewpoint of flatness of the hot dip galvanized steel sheet and controllability during cooling, the thickness of the base steel sheet is 0. A range of 6 mm or more and less than 5.0 mm is preferable.
- the method for producing a plated steel sheet according to the present embodiment includes an annealing process, a plating process, and a cooling process after plating, and between the annealing process and the plating process and / or in the cooling process after plating, retained austenite.
- a bainite transformation process described later is performed.
- the annealing step the base steel sheet is heated to 750 ° C. or higher at an average heating rate between 600 and 750 ° C. of 1.0 ° C./second or higher.
- the plating process is performed under the conditions that the plating bath temperature is 450 to 470 ° C., the steel plate temperature when entering the plating bath is 440 to 480 ° C., and the effective Al amount in the plating bath is 0.050 to 0.180 mass%. Is immersed in a galvanizing bath to subject the steel sheet surface to hot dip galvanizing to form a plating layer. In the cooling process after plating, the cooling process up to 350 ° C. satisfies the following formula (1), which will be described later, after the plating process.
- a base steel sheet is manufactured.
- the base steel sheet is manufactured by casting a slab to which an alloy element corresponding to characteristics is added, performing hot rolling, and performing cold rolling.
- each manufacturing process will be described in detail.
- a slab for hot rolling is cast.
- the chemical component (composition) of the slab is preferably the above-described component.
- a slab produced by a continuous casting slab, a thin slab caster or the like can be used as the slab used for hot rolling.
- the slab heating temperature is preferably set to 1080 ° C. or higher in order to suppress crystal orientation anisotropy caused by casting.
- the heating temperature of the slab is more preferably 1150 ° C. or higher.
- the upper limit of the heating temperature of the slab is not particularly defined. In order to heat a slab exceeding 1300 ° C., it is necessary to input a large amount of energy, which causes a significant increase in manufacturing cost. For this reason, the heating temperature of the slab is preferably 1300 ° C. or lower.
- the completion temperature of hot rolling shall be 850 degreeC or more, More preferably, it shall be 870 degreeC or more.
- the completion temperature of hot rolling in order to make the completion temperature of hot rolling higher than 980 ° C., an apparatus for heating the steel sheet is required in the process from the end of heating of the slab to the completion of hot rolling, which requires high cost.
- the completion temperature of hot rolling shall be 980 degrees C or less, and it is more preferable to set it as 960 degrees C or less.
- the hot rolled steel sheet after hot rolling is wound as a coil.
- the average cooling rate in the cooling process from hot rolling to winding is preferably 10 ° C./second or more. This is because the grain size of the hot-rolled steel sheet is made finer by proceeding transformation at a lower temperature, and the effective crystal grain size of the base steel sheet after cold rolling and annealing is made finer.
- the winding temperature of the hot-rolled steel sheet is preferably 350 ° C. or higher and 750 ° C. or lower. This is because pearlite and / or coarse cementite with a major axis of 1 ⁇ m or more is dispersed in the microstructure of the hot-rolled steel sheet to localize the strain introduced by cold rolling, and various crystal orientations in the annealing process This is for reverse transformation to austenite. This refines the effective crystal grains of the base steel plate after annealing. When the winding temperature is less than 350 ° C., pearlite and / or coarse cementite may not be generated, which is not preferable.
- the coiling temperature in order to reduce the strength of the hot-rolled steel sheet and facilitate cold rolling, it is more preferable to increase the coiling temperature to 450 ° C. or higher.
- the coiling temperature exceeds 750 ° C.
- pearlite and ferrite are each formed in a strip shape that is long in the rolling direction, and the effective crystal grains of the base steel sheet that are generated after cold rolling and annealing from the ferrite portion are elongated in the rolling direction. It tends to be coarse, which is not preferable.
- pickling of the hot-rolled steel sheet thus manufactured is performed.
- Pickling removes oxides on the surface of the hot-rolled steel sheet, and is therefore important for improving the plateability of the base steel sheet.
- Pickling may be performed once or may be performed in a plurality of times.
- Cold rolling process Next, the hot-rolled steel sheet after pickling is cold-rolled to obtain a cold-rolled steel sheet.
- the total reduction ratio exceeds 85%, the ductility of the steel sheet is lost, and the risk of the steel sheet breaking during cold rolling increases. For this reason, it is preferable that the total rolling reduction is 85% or less. From this viewpoint, the total rolling reduction is more preferably 75% or less, and further preferably 70% or less. There is no particular lower limit for the total rolling reduction in the cold rolling process. If the total rolling reduction is less than 0.05%, the shape of the base steel plate becomes inhomogeneous, the plating does not adhere uniformly, and the appearance is impaired.
- cold rolling is preferably performed in a plurality of passes, the number of cold rolling passes and the reduction rate distribution to each pass are not questioned.
- the total rolling reduction in the cold rolling step is preferably 10% or less, and more preferably 5.0% or less.
- the total rolling reduction is preferably 20% or more, and more preferably 30% or more.
- the cold-rolled steel sheet is annealed.
- the heating rate in the annealing step is related to the progress of decarburization in the steel sheet surface layer through the treatment time in the pre-tropical zone. If the heating rate in the annealing process is slow, the steel plate is exposed to an oxidizing atmosphere for a long time in the pre-tropical zone, and therefore decarburization in the steel sheet surface layer portion proceeds. Moreover, when a heating rate is too slow, the oxidation of a steel plate advances and a coarse oxide may produce
- the average heating rate during this period is 1.0 ° C./second or more.
- the average heating rate between 600 and 750 ° C. is preferably 1.5 ° C./second or more, and more preferably 2.0 ° C./second or more.
- the average heating rate at 600 to 750 ° C. is preferably 50 ° C./second or less in order to secure the treatment time in the pretropical zone and promote the formation of the ⁇ phase.
- the average heating rate is 50 ° C./second or less, a plating layer having a larger proportion of the interface between the ⁇ phase and the base steel plate among all the interfaces between the plating layer and the base steel plate can be obtained.
- the average heating rate is more preferably 10 ° C./second or less.
- Air ratio is the ratio of the volume of air contained in a unit volume of mixed gas and the volume of air that is theoretically required to completely burn the fuel gas contained in the unit volume of mixed gas, It is shown by the following formula.
- Air ratio [volume of air contained in unit volume of mixed gas (m 3 )] / [volume of air theoretically required for complete combustion of fuel gas contained in unit volume of mixed gas (m 3 ) ] ⁇
- the base steel sheet passing through the pre-tropical zone is preheated under the above conditions to form a 0.01 to 5.0 ⁇ m Fe oxide film on the surface layer of the base steel sheet.
- the Fe oxide film (oxide) generated on the surface layer portion of the steel sheet is reduced in the reduction zone and becomes a surface excellent in plating adhesion.
- the air ratio is preferably 1.2 or less, and more preferably 1, 1 or less.
- the air ratio is 0.7 or more, and preferably 0.8 or more.
- the steel plate temperature (preheating completion temperature) through which the pre-tropical plate is passed is 400 ° C. or higher, and preferably 600 ° C. or higher.
- the temperature of the steel plate through which the pre-tropical plate is passed exceeds 800 ° C., coarse Si and / or Mn-containing oxides that cannot be reduced in the next reduction zone are generated on the steel plate surface. Therefore, the temperature of the steel plate through which the pre-tropical zone is passed is set to 800 ° C. or less and preferably 750 ° C. or less.
- the maximum heating temperature in the annealing process is an important factor for controlling the fraction of the microstructure related to the formability of the steel sheet within a predetermined range. If the maximum heating temperature is low, coarse iron-based carbides remain undissolved in the steel and formability deteriorates. In order to sufficiently dissolve the iron-based carbide and improve the moldability, the maximum heating temperature is set to 750 ° C. or higher. In particular, in order to obtain retained austenite, the maximum heating temperature needs to be (Ac1 + 50) ° C. or higher. Although the upper limit of the maximum heating temperature is not particularly defined, it is preferably 950 ° C. or less, more preferably 900 ° C. or less, from the viewpoint of plating adhesion, in order to reduce the oxide on the base steel sheet surface.
- the Ac1 point of the steel plate is the starting point of the austenite reverse transformation. Specifically, the Ac1 point is obtained by cutting out a small piece from the steel sheet after hot rolling, heating it to 1200 ° C. at 10 ° C./second, and measuring the volume expansion therebetween.
- the maximum heating temperature (750 ° C. or higher) in the annealing process reaches in the reduction zone.
- the thin Fe oxide film on the surface of the steel sheet generated in the pre-tropical zone is reduced to improve the plating adhesion. Therefore, in the reduction zone atmosphere, the ratio of the water vapor partial pressure P (H 2 O) to the hydrogen partial pressure P (H 2 ), P (H 2 O) / P (H 2 ), is 0.0001 to 2.00.
- P (H 2 O) / P (H 2 ) is less than 0.0001, Si and / or Mn oxide, which is the starting point of plating peeling, is formed on the outermost surface layer.
- P (H 2 O) / P (H 2 ) exceeds 2.00, refinement of the steel sheet surface layer proceeds excessively, and alloying of the plating layer proceeds excessively, so that the plating adhesion deteriorates. . Further, when P (H 2 O) / P (H 2 ) exceeds 3.00, decarburization proceeds excessively, and the hard phase of the base steel sheet surface layer is significantly reduced. From the above viewpoint, P (H 2 O) / P (H 2 ) is preferably in the range of 0.002 to 1.50, and more preferably in the range of 0.005 to 1.20.
- the surface layer of the base material after annealing has an average thickness of 0.1 to 5.0 ⁇ m, an average particle diameter of the ferrite phase of 0.1 to 3.0 ⁇ m, and a maximum diameter of 0.00.
- a refined layer containing an oxide of Si and / or Mn having a thickness of 01 to 0.4 ⁇ m is formed.
- the average cooling rate from 750 ° C. to 700 ° C. is set to 1.0 ° C./second or more, and the average cooling rate from 700 ° C. to 500 ° C. is set to 5.0 ° C./second or more.
- the average cooling rate in the temperature range is preferably 100 ° C./second or less, and more preferably 70 ° C./second or less.
- the steel sheet is kept in a predetermined temperature range for a certain period of time as a martensitic transformation treatment after the steel sheet temperature reaches 500 ° C. and reaches the plating bath. It doesn't matter.
- the martensite transformation treatment temperature is more preferably the martensite transformation start temperature Ms point being the upper limit and the upper limit being (Ms point ⁇ 20 ° C.).
- the martensitic transformation treatment preferably has a lower limit of 50 ° C and more preferably a lower limit of 100 ° C.
- the martensitic transformation treatment time is preferably 1 second to 100 seconds, more preferably 10 seconds to 60 seconds.
- the martensite obtained by a martensitic transformation process changes into a tempered martensite by invading into a high temperature plating bath in a plating process.
- Ms point [° C.] 541-474C / (1-VF) -15Si-35Mn-17Cr-17Ni + 19Al
- VF represents the volume fraction of ferrite
- C, Si, Mn, Cr, Ni, and Al are addition amounts [mass%] of the respective elements. It is difficult to directly measure the volume fraction of ferrite during manufacture. For this reason, in determining the Ms point in the present invention, a small piece of cold-rolled steel sheet before cutting through the continuous annealing line is cut out, and annealing is performed with the same temperature history as when the small piece is passed through the continuous annealing line. Then, a change in the volume of the ferrite of the small piece is measured, and a numerical value calculated using the result is used as the volume fraction VF of the ferrite.
- the steel sheet may be retained in a temperature range of 250 ° C. to 500 ° C. for a certain period of time as a bainite transformation treatment.
- the bainite transformation treatment may be performed between the annealing step and the plating step, may be performed in the cooling step after plating, or may be performed at both time points.
- the sum of the retention time of the bainite transformation treatment performed between the annealing process and the plating process and in the post-plating cooling process needs to be 15 seconds or more and 500 seconds or less. When the sum of the retention times is 15 seconds or more, the bainite transformation proceeds sufficiently and sufficient retained austenite is obtained.
- the sum of the stop times is preferably 25 seconds or more.
- the sum of the retention times exceeds 500 seconds, pearlite and / or coarse cementite is generated. For this reason, the sum of stop time shall be 500 seconds or less, and preferably 300 seconds or less.
- the bainite transformation processing temperature When performing between an annealing process and a plating process, when the bainite transformation processing temperature exceeds 500 degreeC, the production
- the bainite transformation treatment temperature is preferably 300 ° C. or higher, more preferably 340 ° C. or higher.
- the martensite transformation process shall be performed before the bainite transformation process in the construction order.
- the plating bath is mainly composed of zinc and has a composition in which the effective Al amount, which is a value obtained by subtracting the total Fe amount from the total Al amount in the plating bath, is 0.050 to 0.180 mass%. If the effective Al amount in the plating bath is less than 0.050%, the penetration of Fe into the plating layer proceeds excessively and the plating adhesion is impaired, so it is necessary to make it 0.050% or more. From this viewpoint, the effective Al amount in the plating bath is preferably 0.065% or more, and more preferably 0.070% or more.
- the effective Al amount in the plating bath exceeds 0.180%, an Al-based oxide is generated at the boundary between the base steel plate and the plating layer, and the movement of Fe and Zn atoms at the boundary is inhibited, and ⁇ Phase formation is suppressed and plating adhesion is significantly impaired.
- the effective Al amount in the plating bath needs to be 0.180% or less, preferably 0.150% or less, and more preferably 0.135% or less.
- the plating baths are Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb,
- Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, and REM may be mixed, and depending on the content of each element, In some cases, the corrosion resistance and workability of the hot dip galvanized layer are improved.
- the temperature of the plating bath is 450 ° C to 470 ° C.
- the temperature of the plating bath is 450 ° C. or higher and preferably 455 ° C. or higher.
- the plating bath temperature is 470 ° C. or lower, and preferably 465 ° C. or lower.
- the temperature when the base steel plate enters the plating bath is set to 440 ° C. or higher and 480 ° C. or lower. In order to appropriately control the formation behavior of the ⁇ phase, it is more preferable to limit the temperature of the base steel sheet when entering the plating bath to 450 ° C. or higher and 470 ° C. or lower.
- the temperature of the plating bath is preferably stable at a temperature within the range of 450 to 470 ° C. If the temperature of the plating bath is unstable, the ⁇ phase in the plating layer becomes non-uniform, resulting in non-uniform appearance and adhesion of the plating layer.
- the steel plate temperature when entering the plating bath and the temperature of the plating bath are substantially matched. Specifically, from the limit of temperature controllability of the actual manufacturing equipment, the steel plate temperature when entering the plating bath is preferably within ⁇ 4 ° C of the plating bath temperature, and within ⁇ 2 ° C of the plating bath temperature. More preferred.
- T (t) [° C.] is a steel plate temperature
- t [second] is an elapsed time starting from the time when the steel plate comes out of the plating bath
- t 1 [second] The elapsed time from the time when the steel plate comes out of the plating bath until the steel plate temperature reaches 350 ° C.
- W * Al [mass%] is the effective amount of Al in the plating bath.
- ⁇ , ⁇ , and ⁇ are constant terms, which are 2.62 ⁇ 10 7 , 9.13 ⁇ 10 3 , and 1.0 ⁇ 10 ⁇ 1 , respectively.
- the above equation (1) is an equation related to the generation behavior of the ⁇ phase, and the larger the value of the above equation (1), the more the generation of the ⁇ phase in the plating layer proceeds.
- the value of the above formula (1) is decreased and the formation of the ⁇ phase is inhibited.
- said Formula (1) calculates in the range whose steel plate temperature is 350 degreeC or more.
- the value of the above formula (1) is less than 0.40, a sufficient ⁇ phase cannot be obtained in the plating layer, and the plating adhesion is impaired.
- the value of the above formula (1) is 0.40 or more, the generation of the ⁇ phase is sufficiently promoted, and the ⁇ phase and the base material steel plate among the entire interface between the hot dip galvanized layer and the base material steel plate.
- the proportion of the interface is 20% or more.
- the value of the above formula (1) is 0.40 or more, the ratio of the interface between the ⁇ crystal grain in which a coarse oxide is present and the base steel plate is present among the interface between the ⁇ phase and the base steel plate. 50% or less.
- the cooling process in order to obtain sufficient plating adhesion, it is necessary to control the cooling process so that the value of the above formula (1) is 0.40 or more. In order to further improve the plating adhesion, it is preferable to perform a cooling treatment so that the value of the above formula (1) is 0.50 or more, and more preferably 0.60 or more. On the other hand, when the value of the above formula (1) in the cooling treatment becomes excessively large, the alloying of the plating layer proceeds, the Fe content in the plating layer becomes excessively large, and the plating adhesion is impaired. From this viewpoint, it is necessary to control the cooling process so that the value of the formula (1) is 2.20 or less. In order to improve the plating adhesion, the cooling treatment is preferably controlled so that the value of the above formula (1) is 2.00 or less, and more preferably controlled to be 1.80 or less.
- the value of the above formula (1) is remarkably increased and the plating adhesion is deteriorated.
- the microstructure of the steel sheet is altered, and the predetermined retained austenite cannot be obtained and the strength is lowered.
- coarse carbides are generated and formability is deteriorated.
- the steel plate temperature after taking out from the plating bath must not exceed the higher one of the steel plate temperature before plating bath immersion and the plating bath temperature.
- the value of the above formula (1) is remarkably reduced.
- any cooling control mode may be adopted as long as the temperature control is such that the value of the above formula (1) is within the range of the present invention.
- a cooling mode in which cooling is performed rapidly after the isothermal holding process may be employed, or a cooling mode in which slow cooling is performed at a substantially constant speed may be employed.
- a bainite transformation treatment in which a retention is performed in a temperature range of 250 ° C. to 350 ° C. in order to obtain retained austenite after a sufficient amount of ⁇ phase is obtained in the plating layer by the cooling treatment satisfying the above formula (1). You may do.
- the bainite transformation temperature is less than 250 ° C., the bainite transformation does not proceed sufficiently and sufficient austenite cannot be obtained.
- the bainite transformation processing temperature shall be 250 degreeC or more.
- the bainite transformation treatment temperature is more preferably 300 ° C. or higher.
- the bainite transformation temperature exceeds 350 ° C., the diffusion of Fe atoms from the base steel plate to the plating layer proceeds excessively, and the plating adhesion deteriorates.
- the bainite transformation temperature is set to 350 ° C. or lower, preferably 340 ° C. or lower.
- the retained austenite in order to further stabilize the retained austenite, it may be reheated after cooling to 250 ° C. or lower.
- the treatment temperature and treatment time of the reheating treatment may be set as appropriate according to the target characteristics. However, if the reheating temperature is less than 250 ° C., a sufficient effect cannot be obtained. For this reason, the reheating treatment temperature is preferably 250 ° C. or higher, and more preferably 280 ° C. or higher. When the reheating temperature exceeds 350 ° C., the diffusion of Fe atoms from the base steel plate to the plating layer proceeds excessively, and the plating adhesion deteriorates. For this reason, the reheating treatment temperature is preferably 350 ° C. or lower, more preferably 340 ° C.
- the reheating treatment time exceeds 1000 seconds, the treatment effect is saturated, and therefore the treatment time is preferably 1000 seconds or less. Furthermore, in order to suppress the formation of pearlite and / or coarse cementite, the reheating treatment time is more preferably 500 seconds or less.
- the hot dip galvanized steel sheet according to the present embodiment can be manufactured by the manufacturing method described above, the present invention is not limited to the above embodiment.
- the cooling process after plating in which the cooling process up to 350 ° C. satisfies the above formula (1) is described as an example after the plating process has been described.
- the cooling process up to 350 ° C. may not satisfy the above formula (1).
- the plating bath immersion time needs to be 3 seconds or more, preferably 5 seconds or more, more preferably 7 seconds or more, and even more preferably 10 seconds or more. To do.
- the plating bath immersion time By setting the plating bath immersion time to 10 seconds or longer, the same hot-dip galvanized steel sheet as when the “cooling step after plating” in which the cooling process up to 350 ° C. satisfies the above formula (1) is performed is obtained.
- the proportion of the interface between the ⁇ phase and the base steel plate is 20% or more of the total interface between the hot-dip galvanized layer and the base steel plate, and the coarse oxide in the interface between the ⁇ phase and the base steel plate As a result, a plating layer in which the ratio of the interface formed between the ⁇ crystal grains and the base steel sheet is 50% or less is obtained.
- the hot dip galvanized steel sheet of this embodiment can be easily manufactured even in the production line of the hot dip galvanized steel sheet in which the above-described “post-plating cooling step” is difficult to execute.
- the plating bath immersion time can be appropriately determined according to the Al content in the plating bath and the like.
- the plating bath immersion time is preferably 20 seconds or less, and more preferably 15 seconds or less, in order to ensure good productivity.
- a film made of a composite oxide containing phosphorus oxide and / or phosphorus may be applied to the surface of the galvanized layer of the hot-dip galvanized steel sheet obtained by the above-described method. Absent. A film made of a complex oxide containing phosphorus oxide and / or phosphorus can function as a lubricant when processing a hot-dip galvanized steel sheet, and protects the galvanized layer formed on the surface of the base steel sheet Can do.
- the hot-dip galvanized steel sheet cooled to room temperature may be cold-rolled at a rolling reduction of 3.00% or less for shape correction.
- the manufacturing method of the hot dip galvanized steel sheet concerning embodiment of this invention mentioned above is applied to manufacture of the hot dip galvanized steel sheet whose board thickness of a base material steel plate is 0.6 mm or more and less than 5.0 mm. Is preferred. If the thickness of the base steel plate is less than 0.6 mm, it is difficult to keep the shape of the base steel plate flat, which may not be appropriate. In addition, when the thickness of the base steel plate is 5.0 mm or more, it may be difficult to control cooling in the annealing process and the plating process.
- the conditions in this example are one example of conditions used to confirm the feasibility and effects of the present invention.
- the present invention is not limited to this one condition example.
- the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
- Example 1 The slabs having the chemical components (compositions) shown in Tables 1 to 4 were cast and hot-rolled under the hot rolling process conditions (slab heating temperature, rolling completion temperature) shown in Tables 5 and 6, and the heat shown in Tables 5 and 6 was obtained. Cooling was performed under the rolling process conditions (average cooling rate from completion of hot rolling to winding, winding temperature) to obtain a hot rolled steel sheet. Thereafter, the hot-rolled steel sheet was pickled and cold-rolled under the cold-rolling process conditions (rolling rate) shown in Tables 5 and 6 to obtain a cold-rolled steel sheet.
- the hot rolling process conditions average cooling rate from completion of hot rolling to winding, winding temperature
- the heating process conditions in the annealing process shown in Tables 7 and 8 (the air ratio in the pretropical zone, the preheating completion temperature in the pretropical zone, the amount of H 2 O and H 2 in the reducing zone atmosphere) are shown Annealing was performed at a pressure ratio (P (H 2 O) / P (H 2 ), an average heating rate in a temperature range of 600 to 750 ° C., and a maximum heating temperature Tm). was in the range of 623-722 ° C.
- cooling conditions before plating shown in Tables 7 and 8 were performed.
- the bainite transformation treatment 1 conditions treatment temperature, treatment time
- martensite transformation treatment treatment temperature, treatment time
- a sample was collected from a plated steel plate using a plate thickness section parallel to the rolling direction of the base steel plate as an observation surface.
- the observation surface of the sample was subjected to a structure observation by a field emission scanning electron microscope (FE-SEM) and a high resolution crystal orientation analysis by an EBSD method.
- FE-SEM field emission scanning electron microscope
- the microstructure in the range of 8 thickness was observed to identify the constituent structure.
- F is granular ferrite
- WF is acicular ferrite
- NRF non-recrystallized ferrite
- P pearlite
- ⁇ coarse cementite
- BF bainitic ferrite
- B bainite
- M martensite
- ⁇ represents retained austenite.
- a small piece of 25 mm ⁇ 25 mm was taken as a test piece from the plated steel plate.
- the surface parallel to the plate surface is finished as a mirror surface, and the volume fraction of retained austenite ( ⁇ fraction) is measured by X-ray diffraction method. did.
- a sample was taken from the plated steel sheet, with the thickness cross section parallel to the rolling direction of the base steel sheet as an observation surface.
- the observation surface of the sample was observed with a field emission scanning electron microscope (FE-SEM), and the interface between the plating layer and the base steel plate was observed.
- FE-SEM field emission scanning electron microscope
- the amount of plating adhered was determined by melting the plating layer using hydrochloric acid containing an inhibitor and comparing the weight before and after melting.
- a DuPont impact test was performed on a plated steel sheet having a uniaxial tensile strain of 5%. Adhesive tape was applied to the plated steel sheet after the impact test, and then peeled off. The case where the plating did not peel off was judged as acceptable ( ⁇ ), and the case where the plating was peeled off was judged as unacceptable (x).
- the DuPont impact test was conducted by using a shooting mold having a radius of curvature at the tip of 1/2 inch and dropping a 3 kg weight from a height of 1 m.
- Spot weldability was evaluated by performing a continuous dot test. Under welding conditions in which the diameter of the molten part is 5.3 to 5.7 times the square root of the plate thickness, 1000 spot weldings are continuously performed, and the diameter of the molten part is set to the first point d 1 and the 1000th point d. In comparison with 1000 , the case where d 1000 / d 1 was 0.90 or more was regarded as acceptable ( ⁇ ), and the case where it was less than 0.90 was regarded as unacceptable (x).
- a test piece obtained by cutting a plated steel sheet into 150 ⁇ 70 mm was used.
- the test piece was subjected to a zinc phosphate dip-type chemical conversion treatment, followed by a cationic electrodeposition coating of 20 ⁇ m, an intermediate coating of 35 ⁇ m, and a top coating of 35 ⁇ m, and then the back and ends were sealed with an insulating tape.
- CCT having one cycle of SST 6 hr ⁇ dry 4 hr ⁇ wet 4 hr ⁇ freeze 4 hr was used.
- Evaluation of corrosion resistance after coating was performed by cross-cutting the coated surface to reach the base steel plate with a cutter and measuring the blister width after 60 cycles of CCT. The case where the swollen width was 3.0 mm or less was determined to be acceptable ( ⁇ ), and the case where the expansion width was greater than 3.0 mm was determined to be unacceptable (x).
- the chipping property was evaluated using a test piece obtained by cutting a plated steel sheet to 70 mm ⁇ 150 mm. First, each process of the degreasing
- Powdering property was evaluated using V bending (JIS Z 2248) in order to evaluate the workability of the plating layer.
- the plated steel plate was cut into 50 ⁇ 90 mm, and a molded body was formed with a 1R-90 ° V-shaped die press to obtain a test body. Tape peeling was carried out at the valley of each specimen. Specifically, a cellophane tape having a width of 24 mm was pressed against the bent portion of the test body and pulled away, and a portion of the cellophane tape having a length of 90 mm was visually determined.
- the evaluation criteria were as follows. The case where the peeling of the plating layer was less than 5% with respect to the processed part area was indicated as ( ⁇ ), and the case where the plating layer was peeled over 5% with respect to the processed part area was indicated as (x).
- Experimental Example 89 is an example in which the experiment was stopped because the Si content was large and the slab cracked during cooling in the casting process.
- Experimental Example 92 is an example in which the experiment was stopped because the P content was large and the slab was cracked during heating in the hot rolling process.
- Experimental Example 94 is an example in which the experiment was stopped because the Al content was large and the slab cracked during cooling in the casting process.
- Experimental Example 9 is an example in which the air ratio in the tropics in the annealing process is small, the occupancy ratio of the ⁇ phase is low, non-plating occurs in part of the steel sheet, and the appearance, plating adhesion, and corrosion resistance deteriorate.
- the air ratio in the tropics of the annealing process is large, and the decarburization on the steel sheet surface proceeds excessively, so the average thickness of the refined layer becomes thick, and TS 1.5 ⁇ El ⁇ ⁇ 0.5 is This is an example in which sufficient characteristics were not obtained.
- Experimental Example 3 is an example in which the value of Equation 1 in the plating process is too small, and the ⁇ phase is not sufficiently generated at the interface between the plating layer and the base steel sheet, and sufficient plating adhesion cannot be obtained.
- the value of Formula 1 in the plating process is excessive, Fe% in the plating layer is excessively increased, and sufficient plating adhesion cannot be obtained.
- Experimental Example C39 is an example in which the content of C is small, residual austenite is not generated, the volume fraction of the hard phase is small, and sufficient tensile strength cannot be obtained.
- Experimental Example C38 is an example in which the C content is large and spot weldability and formability are deteriorated.
- Experimental Example C40 the Mn content was small, a large amount of pearlite and coarse cementite were generated in the annealing process and the plating process, the residual austenite phase was not generated, and the tensile strength and formability of the steel sheet were not sufficiently obtained. It is an example.
- Experimental Example 91 is an example in which the experiment was stopped because the Mn content was large and the slab cracked during heating in the hot rolling process.
- Experimental Example C41 is an example in which the ductility and hole expansibility deteriorated because the S content was large and a large amount of coarse sulfide was generated.
- Experimental Example C42 is an example in which ductility and hole expansibility deteriorate due to the large N content and the generation of a large amount of coarse nitride.
- Experimental Example C43 is an example in which ductility and hole expansibility deteriorate due to the large O content and the generation of a large amount of coarse oxide.
- Experimental Example C34 is an example in which the balance between strength and formability deteriorated because the Si and Al contents did not satisfy Formula (2), a large amount of carbide was generated, and retained austenite was not obtained.
- Experimental Example C18 is an example in which the experiment was stopped because the hot rolling completion temperature was low and the shape of the steel sheet deteriorated significantly.
- Experimental example C22 is an example in which the experiment was stopped because the temperature taken up by the coil after hot rolling was low and the steel sheet broke in the cold rolling process.
- Experimental Example 6 is an example in which the hot-rolled steel sheet was not cold-rolled, the flatness of the plate was poor, the annealing process could not be performed, and the experiment was stopped.
- Experimental Example 35 is an example in which the experiment was stopped because the rolling reduction in cold rolling was excessively large and the steel sheet was broken.
- the maximum heating temperature in the annealing process is low, no retained austenite phase is generated, a large amount of coarse cementite is present in the steel sheet, TS 1.5 ⁇ El ⁇ ⁇ 0.5 is deteriorated, and sufficient This is an example in which characteristics were not obtained.
- the maximum heating temperature in the annealing process is lower than Ac1 + 50 ° C., no retained austenite phase is generated, a large amount of coarse cementite is present in the steel sheet, and TS 1.5 ⁇ El ⁇ ⁇ 0.5 deteriorates. This is an example in which sufficient characteristics were not obtained.
- Experimental Example C5 is an example in which the average cooling rate from 750 ° C. to 700 ° C. is small, a large amount of carbide is generated, and residual austenite cannot be obtained, so that the balance between strength and formability is deteriorated.
- Experimental Example C15 is an example in which the average cooling rate from 700 ° C. to 500 ° C. is small, a large amount of carbide is generated, and residual austenite cannot be obtained, so that the balance between strength and formability is deteriorated.
- Experimental Example C24 is an example in which the balance between strength and formability was deteriorated because bainite transformation treatment was not performed both before and after the plating treatment and no retained austenite was obtained.
- Experimental Example C25 is an example in which the balance between strength and formability deteriorated because the bainite transformation temperature before plating was high, a large amount of carbide was generated, and residual austenite was not obtained.
- Experimental Example C26 is an example in which the balance between strength and formability deteriorated because the bainite transformation temperature before plating treatment was low, the progress of bainite transformation was excessively suppressed, and residual austenite was not obtained.
- Experimental Example C9 is an example in which the balance between strength and formability deteriorated because the bainite transformation time before the plating treatment was short, the bainite transformation did not proceed sufficiently, and retained austenite was not obtained.
- Experimental Example C37 is an example in which the balance between strength and formability deteriorated because the bainite transformation treatment time before the plating treatment was long, a large amount of carbide was generated, and residual austenite was not obtained.
- Experimental Example C8 is an example in which the bainite transformation temperature after the plating treatment is high, the value of Formula (1) is excessively increased, and the amount of Fe in the plating layer is increased, so that the plating adhesion is deteriorated.
- Experimental Example C16 is an example in which the balance between strength and formability deteriorated because the bainite transformation temperature after plating was low, the progress of bainite transformation was excessively suppressed, and residual austenite was not obtained.
- Experimental Example C10 is an example in which the effective Al amount in the plating bath in the plating process is excessively small, the value of Formula 1 is excessive, Fe% in the plating layer is excessively increased, and sufficient plating adhesion cannot be obtained. It is.
- Experimental Example C17 the effective Al amount in the plating bath of the plating process is excessively large, the value of Equation 1 is excessively small, and the ⁇ phase is not sufficiently generated at the interface between the plating layer and the base steel sheet, and sufficient plating adhesion is achieved. This is an example in which no sex was obtained.
- the experimental examples other than the above are examples in which a hot-dip galvanized steel sheet having excellent strength, ductility, hole expansibility, spot weldability, and plating adhesion was obtained.
- Example 2 A test piece was collected from the plated steel sheet of Experimental Example 1 obtained in “Example 1”. Next, the test piece is polished by ion milling with a cross section of the base metal plate parallel to the rolling direction of the base steel plate as an observation surface, and reflected electrons are observed with a field emission scanning electron microscope (FE-SEM) under conditions of an acceleration voltage of 5 kV A (BSE) image was obtained. The result is shown in FIG. As shown in FIG. 2, the plated steel sheet of Experimental Example 1 was formed with a plated layer containing columnar crystals composed of the ⁇ phase. Moreover, the refined layer which contact
- Example 3 A cold-rolled steel plate was produced in the same manner as the plated steel plate of Experimental Example 1 obtained in “Example 1”, and an annealing process was performed in the same manner as the plated steel plate of Experimental Example 1 to obtain an annealed plate.
- the annealed plate was dipped in a galvanizing bath under the plating process conditions shown in Table 15 (effective amount of Al, plating bath temperature (bath temperature), steel plate entry temperature, dipping time) and plated. After the plating step, a cooling treatment was performed under the post-plating cooling step conditions (formula (1)) shown in Table 15. Further, cold rolling was performed under the conditions shown in Table 15 (rolling rate), and plated steel sheets of Experimental Examples 104 to 111 were obtained.
- Example 15 About the obtained plated steel plate, it carried out similarly to "Example 1," and observed the plating layer of the base material steel plate. The results are shown in Table 15. Further, the volume fraction ( ⁇ fraction) of retained austenite was measured in the same manner as in “Example 1” for the obtained plated steel sheet. The obtained plated steel sheet was determined in the same manner as in “Example 1” for the amount of adhesion of plating. The results are shown in Table 15. Further, the average thickness of the refined layer, the average particle diameter of the ferrite phase, and the maximum diameter of the oxide were determined in the same manner as in “Example 1” for the plated steel sheet. The results are shown in Table 15.
- Example 1 The obtained plated steel sheet was subjected to a tensile test, a hole expansion test, a bending test, an adhesion evaluation test, a spot welding test, and a corrosion test in the same manner as in “Example 1”. The results are shown in Table 15. The results of Experimental Example 1 are also shown in Table 15.
- Experimental Examples 105 to 111 which are examples of the present invention, had good plating adhesion, and were excellent in spot weldability and corrosion resistance.
- the ratio of the interface between the ⁇ phase and the base steel sheet ( ⁇ interface occupancy ratio) is 20 out of the total interface between the plating layer and the base steel sheet. Therefore, the plating adhesion and spot weldability were insufficient.
- the present invention is a technique effective for a hot dip galvanized steel sheet having excellent plating adhesion. And according to this invention, the hot dip galvanized steel plate excellent in the plating adhesiveness after shaping
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Abstract
Description
本願は、2014年11月05日に、日本に出願された特願2014-225398号に基づき優先権を主張し、その内容をここに援用する。
また、自動車用鋼板については、一般に屋外で使用されるため、優れた耐食性が要求されるのが通常である。
これらのような問題から、苛酷な曲げ加工などを施して使用される高強度鋼板としては、母材鋼板に対するめっき層の密着性が優れた溶融亜鉛めっき層を備えためっき鋼板が強く望まれている。
前記溶融亜鉛めっき層は、前記鋼板の表面に、Fe含有量が0%超~5%以下であり、Al含有量が0%超~1.0%以下であり、ζ相からなる柱状晶を含み、さらに、前記溶融亜鉛めっき層と母材鋼板との全界面のうち20%以上がζ相に被覆され、前記溶融亜鉛めっき層において、ζ結晶粒のうち粗大な酸化物が存在するζ結晶粒と母材鋼板との成す界面が、前記ζ相と母材鋼板との全界面に対して50%以下であり、
前記母材鋼板が、質量%で、
C :0.040~0.400%、
Si:0.05~2.50%、
Mn:0.50~3.50%、
P :0.0001~0.1000%、
S :0.0001~0.0100%、
Al:0.001~1.500%、
N :0.0001~0.0100%、
O :0.0001~0.0100%、
Si+0.7Al≧0.30(式中の元素記号は、その元素の含有量(質量%)を表す。)を満足し、残部がFeおよび不可避不純物からなる化学成分を有し、
前記母材鋼板と前記溶融亜鉛めっき層との界面に直接接する微細化層を有し、前記微細化層の平均厚さが0.1~5.0μm、前記微細化層内におけるフェライト相の平均粒径が0.1~3.0μmであり、前記微細化層中にSiおよびMnの1種または2種以上の酸化物を含有し、前記酸化物の最大径が0.01~0.4μmであり、
前記母材鋼板の表面から1/4厚を中心とした1/8厚~3/8厚の範囲において、体積分率で、残留オーステナイト相を1%以上有する溶融亜鉛めっき鋼板。
(2)前記溶融亜鉛めっき層について、前記母材鋼板の片面におけるめっき付着量が10g/m2以上、100g/m2以下である(1)に記載の溶融亜鉛めっき鋼板。
(3)前記母材鋼板が、質量%で、さらに、
Ti:0.001~0.150%、
Nb:0.001~0.100%、
V:0.001~0.300%、
のうちから選ばれた1種または2種以上を含有する(1)または(2)に記載の溶融亜鉛めっき鋼板。
(4)前記母材鋼板が、質量%で、さらに、
Cr:0.01~2.00%、
Ni:0.01~2.00%、
Cu:0.01~2.00%、
Mo:0.01~2.00%、
B:0.0001~0.0100%、
W:0.01~2.00%、
のうちから選ばれた1種または2種以上を含有する(1)~(3)のいずれかに記載の溶融亜鉛めっき鋼板。
(5)前記母材鋼板が、質量%で、さらに、
Ca、Ce、Mg、Zr、La、REMの1種または2種以上を合計で0.0001~0.0100%含有する(1)~(4)のいずれかに記載の溶融亜鉛めっき鋼板。
めっき層は、Fe含有量が0%超~5%以下であり、Al含有量が0%超~1.0%以下であり、ζ相からなる柱状晶を含む。めっき層は、めっき層と母材鋼板との全界面のうち20%以上がζ相に被覆され、ζ相と母材鋼板との界面のうち粗大な酸化物が存在するζ結晶粒と母材鋼板との成す界面の割合が50%以下である。
本発明の実施形態においては、溶融亜鉛めっき層は、Fe含有量が0%超~5.0%以下であり、Al含有量が0%超~1.0%以下である。さらに、溶融亜鉛めっき層はAg、B、Be、Bi、Ca、Cd、Co、Cr、Cs、Cu、Ge、Hf、I、K、La、Li、Mg、Mn、Mo、Na、Nb、Ni、Pb、Rb、Sb、Si、Sn、Sr、Ta、Ti、V、W、Zr、REMの1種または2種以上を含有、あるいは混入するものであってもよい。このように、溶融亜鉛めっき層が、上記の元素の1種または2種以上を含有、あるいは混入するものであっても、本発明の効果は損なわれず、その含有量によっては耐食性や加工性が改善される等好ましい場合もある。
また、本実施形態においては、溶融亜鉛めっき層はζ相からなる柱状晶を含み、めっき層と母材鋼板との全界面のうち20%以上がζ相に被覆されていることを特徴とする。
さらに、母材鋼板の片面における溶融亜鉛めっき層の付着量は10g/m2以上、100g/m2以下であることが好ましい。
溶融亜鉛めっき層におけるFe含有量が高まるとめっき密着性が劣化することから、Fe含有量を5.0%以下とする必要がある。めっき密着性を更に高めるため、めっき層中のFe含有量は4.0%以下とすることが好ましく、3%以下とすることが更に好ましい。めっき層中のFe含有量の下限は0%超とする。Fe含有量が0.5%未満では、密着性を改善するために必要なζ相が十分に得られないことがある。このため、めっき層中のFe含有量は0.5%以上とすることが好ましく、1.0%以上とすることが更に好ましい。
溶融亜鉛めっき層におけるAl含有量が高まるとめっき密着性が劣化することから、Al含有量を1.0%以下とする必要がある。めっき密着性を更に高めるため、めっき層中のAl含有量は0.8%以下とすることが好ましく、0.5%以下とすることが更に好ましい。めっき層中のAl含有量の下限は0%超とする。Al含有量を0.01%未満とするためには、めっき浴中のAl濃度を極端に下げる必要がある。めっき浴中のAl濃度を極端に下げると、めっき層の合金化が過度に進むことでめっき層中のFe含有量が増えてめっき密着性が劣化する。このことから、めっき層中のAl含有量は0.01%以上とすることが好ましい。この観点から、めっき層中のAl含有量は0.05%以上とすることがより好ましい。
図1に、本実施形態に係る溶融亜鉛めっき鋼板の断面の走査型電子顕微鏡(SEM)写真を示す。図1に示すとおり、本発明の溶融亜鉛めっき層は、FeとZnの合金であるζ相(FeZn13)からなる柱状晶を含む。特にめっき層と母材鋼板との全ての界面のうち、ζ相が母材鋼板と接している界面の割合が20%以上であることを特徴とする。これにより、剥離の起点として働きうるSiおよび/またはMnを含む長径0.2μm以上の粗大な酸化物が、母材鋼板表面からζ相内部に取り込まれる。これによって粗大な酸化物が破壊の起点として働きづらくなり、めっき層の密着性が向上する。この観点から、ζ相と母材鋼板の界面がめっき層と母材鋼板との全ての界面に対して占める割合は25%以上であることが好ましく、30%以上であることがより好ましい。なお、ζ相と母材鋼板の界面がめっき層と母材鋼板との全ての界面に占める割合の上限は特に定めず、100%であっても構わない。なお、Siおよび/またはMnを含む酸化物の長径が0.2μm以上であると、酸化物を起点とする割れが顕著となり、長径が0.2μm未満であると、割れの起点として働きにくくなる。これは、溶融亜鉛めっき鋼板の変形時における応力集中の度合いが、酸化物の大きさによって変化するためである。具体的には、酸化物が大きい(長径が長い)ほど、変形時に応力が集中しやすくなり、めっき層が剥離しやすくなる。
すなわち、溶融亜鉛めっき鋼板から、母材鋼板の圧延方向に平行な板厚断面を観察面として試料を採取する。観察面を鏡面研磨し、電界放射型走査型電子顕微鏡(FE-SEM:Field Emission Scanning Electron Microscope)を用いて、観察しためっき層と母材鋼板との界面の長さの合計Lが200μm以上となるまで観察する。界面の長さの合計Lが200μm以上となるまで観察するとは、1つの板厚断面内をLが200μm以上となるまで観察してもよいし、複数の板厚断面内をLが200μm以上となるまで観察してもよい。
(L1-L2)/Lをもってζ相と母材鋼板の界面がめっき層と母材鋼板との全ての界面に占める割合とみなす。
同様に、L2/Lをもってδ1相と母材鋼板の界面がめっき層と母材鋼板との全ての界面に占める割合とみなす。
なお、ζ相とδ1相との分離は、上記EBSD法以外の手法により行っても構わない。例えば、電界放射型電子プローブ微小分析器(FE-EPMA:Field Emission Electron Probe MicroAnalyser)により、めっき層中のZn元素マッピングを行い、Zn量の違いからζ相とδ1相の判別を行っても構わない。
溶融亜鉛めっき層の母材鋼板片面への付着量が少ないと十分な耐食性が得られないおそれがある。このことから、めっき層の母材鋼板片面への付着量は10g/m2以上とすることが好ましい。耐食性の観点から、付着量は20g/m2以上がより好ましく、30g/m2以上がさらに好ましい。一方、めっき層の付着量が多いと、スポット溶接を行った際の電極損耗が激しくなり、連続して溶接を行った際に溶融ナゲット径の減少や溶接継手強度の劣化が起こるおそれがある。このため、めっき層の付着量を100g/m2以下とすることが好ましい。連続溶接性の観点から、付着量は93g/m2以下であることがより好ましく、85g/m2以下であることがさらに好ましい。
微細化層とは、最表層に存在するフェライト相の平均粒径が、その下層におけるフェライト相の平均粒径の1/2以下となっている領域である。微細化層におけるフェライト相の平均粒径が、その下層におけるフェライト相の平均粒径の1/2超となる境界を、微細化層とその下層との境界と定義する。
微細化層中に含有するSiおよびMnの1種または2種以上の酸化物の最大径が0.01μm以上であると、微細化層を形成するとともに、ζ相の生成が十分に促進されためっき層を形成できる。上記の酸化物の最大径は、0.05μm以上であることが好ましい。また、上記の酸化物の最大径が0.4μm以下である微細化層は、めっき層の過度な合金化を抑制しながら形成できる。上記の酸化物の最大径は、0.2μm以下であることが好ましい。
Cは、母材鋼板の強度を高めるために添加される元素である。しかしながら、Cの含有量が0.400%を超えると、スポット溶接性が劣化し、好ましくないため、C含有量は0.400%以下とする。なお、スポット溶接性の観点から、Cの含有量は0.300%以下であることが好ましく、0.220%以下であることがより好ましい。一方、Cの含有量が0.040%未満であると、強度が低下し、十分な引張最大強度を確保することが困難となるため、C含有量は0.040%以上とする。なお、強度をより一層高めるためには、Cの含有量は0.055%以上であることが好ましく、0.070%以上であることがより好ましい。
Siは、母材鋼板における鉄系炭化物の生成を抑制し、強度と成形性を高める元素である。しかしながら、Siは鋼材を脆化させる元素でもあり、その含有量が2.50%を超えると、鋳造したスラブが割れるなどのトラブルが起こりやすくなる。このため、Siの含有量は2.50%以下とする。さらに、Siは焼鈍工程において母材鋼板の表面に酸化物を形成し、めっきの密着性を著しく損なう。この観点から、Siの含有量は2.00%以下であることが好ましく、1.60%以下であることがより好ましい。一方、Siの含有量が0.05%未満では、溶融亜鉛めっき鋼板のめっき工程において、粗大な鉄系炭化物が多量に生成され、強度および成形性が劣化する。このため、Siの含有量は0.05%以上とする。なお、鉄系炭化物の生成を抑制する観点から、Siの含有量は0.10%以上であることが好ましく、0.25%以上がより好ましい。
Mnは、母材鋼板の焼入れ性を高めることで強度を高めるために添加される。しかしながら、Mnの含有量が3.50%を超えると、母材鋼板の板厚中央部に粗大なMn濃化部が生じて、脆化が起こりやすくなり、鋳造したスラブが割れるなどのトラブルが起こりやすくなる。そのため、Mnの含有量は3.50%以下とする。また、Mnの含有量が増大するとスポット溶接性も劣化する。このことから、Mnの含有量は3.00%以下であることが好ましく、2.80%以下であることがより好ましい。一方、Mnの含有量が0.50%未満であると、焼鈍後の冷却中に軟質な組織が多量に形成されるため、充分に高い引張最大強度を確保することが難しくなる。したがって、Mnの含有量は0.50%以上とする。強度をより高めるためには、Mnの含有量は0.80%以上であることが好ましく、1.00%以上であることがより好ましい。
Pは、鋼材を脆化させる元素であり、さらにPの含有量が0.1000%を超えると、鋳造したスラブが割れるなどのトラブルが起こりやすくなる。このため、Pの含有量は0.1000%以下とする。また、Pはスポット溶接によって生じる溶融部を脆化させる元素でもあり、充分な溶接継手強度を得るためには、Pの含有量は0.0400%以下とすることが好ましく、0.0200%以下とすることがより好ましい。一方、Pの含有量を0.0001%未満とすることは、製造コストの大幅な増加を伴う。このことから、Pの含有量は、0.0001%以上とし、好ましくは0.0010%以上とする。
Sは、Mnと結びついて粗大なMnSを形成し、延性、伸びフランジ性および曲げ性といった成形性を低下させる元素である。このため、Sの含有量を0.0100%以下とする。またSは、スポット溶接性を劣化させる元素でもある。このため、S含有量は0.0060%以下とすることが好ましく、0.0035%以下とすることがより好ましい。一方、Sの含有量を0.0001%未満とすることは、製造コストの大幅な増加を伴う。このため、Sの含有量は、0.0001%以上とし、0.0005%以上とすることが好ましく、0.0010%以上とすることがより好ましい。
Alは、鋼材を脆化させる元素である。Alの含有量が1.500%を超えると、鋳造したスラブが割れるなどのトラブルが起こりやすくなるため、Alの含有量は1.500%以下とする。また、Alの含有量が増えるとスポット溶接性が悪化するため、Alの含有量は1.200%以下とすることが好ましく、1.000%以下とすることがより好ましい。一方、Alの含有量の下限は特に定めずとも本発明の効果は発揮されるが、Alは原料中に微量に存在する不可避不純物であり、その含有量を0.001%未満とするには製造コストの大幅な増加が伴う。このため、Al含有量は0.001%以上とする。またAlは、脱酸材としても有効な元素であるが、脱酸の効果を、より十分に得るためには、Alの含有量は0.010%以上とすることが好ましい。
Nは、粗大な窒化物を形成し、延性、伸びフランジ性および曲げ性といった成形性を劣化させる元素であることから、その添加量を抑えることが好ましい。Nの含有量が0.0100%を超えると、成形性の劣化が顕著となることから、N含有量の上限を0.0100%とする。またNの過剰な添加は、溶接時のブローホール発生の原因になることから、含有量は少ない方が良い。これらの観点から、N含有量は0.0070%以下であることが好ましく、0.0050%以下であることがより好ましい。一方、Nの含有量の下限は、特に定めなくても本発明の効果は発揮されるが、Nの含有量を0.0001%未満にすることは、製造コストの大幅な増加を招く。このことから、N含有量の下限は0.0001%以上とする。N含有量は0.0003%以上であることが好ましく、0.0005%以上であることがより好ましい。
Oは、酸化物を形成し、延性、伸びフランジ性および曲げ性といった成形性を劣化させることから、含有量を抑えることが好ましい。Oの含有量が0.0100%を超えると、成形性の劣化が顕著となることから、O含有量の上限を0.0100%とする。さらにOの含有量は0.0050%以下であることが好ましく、0.0030%以下であることがより好ましい。Oの含有量の下限は、特に定めなくても本発明の効果は発揮されるが、Oの含有量を0.0001%未満とすることは、製造コストの大幅な増加を伴う。このため、0.0001%を下限とする。O含有量は0.0003%以上であることが好ましく、0.0005%以上であることがより好ましい。
SiおよびAlはベイナイト変態に伴う炭化物の生成を抑制する元素である。残留オーステナイトを得るためには、Siおよび/またはAlを一定量以上添加することが好ましい。この観点からSiの添加量とAlの添加量は下記式2を満たす必要がある。下記式2の左辺(Si+0.7Al)の値は0.45以上であることが好ましく、0.70以上であることがより好ましい。
Si+0.7Al≧0.30・・・(式2)
但し、式2のSiおよびAlはそれぞれの元素の添加量[質量%]とする。
具体的には、上記化学成分に加え、Ti:0.001~0.150%、Nb:0.001~0.100%、V:0.001~0.300%、のうちから選ばれた1種または2種以上を含有してもよい。
Tiは、析出物強化、フェライト結晶粒の成長抑制による細粒強化、および再結晶の抑制を通じた転位強化によって、母材鋼板の強度上昇に寄与する元素である。しかし、Tiの含有量が0.150%を超えると、炭窒化物の析出が多くなって成形性が劣化するため、Tiの含有量は0.150%以下であることが好ましい。また、成形性の観点から、Tiの含有量は0.080%以下であることがより好ましい。一方、Tiの含有量の下限は、特に定めなくても本発明の効果は発揮される。Ti添加による強度上昇効果を十分に得るためには、Tiの含有量は0.001%以上であることが好ましい。母材鋼板のより一層の高強度化のためには、Tiの含有量は0.010%以上であることがより好ましい。
Nbは、析出物強化、フェライト結晶粒の成長抑制による細粒強化および再結晶の抑制を通じた転位強化により、母材鋼板の強度上昇に寄与する元素である。しかし、Nbの含有量が0.100%を超えると、炭窒化物の析出が多くなって成形性が劣化するため、Nbの含有量は0.100%以下であることがより好ましい。成形性の観点から、Nbの含有量は0.060%以下であることがより好ましい。一方、Nbの含有量の下限は、特に定めなくても本発明の効果は発揮される。Nb添加による強度上昇効果を十分に得るには、Nbの含有量は0.001%以上であることが好ましい。母材鋼板のより一層の高強度化のためには、Nbの含有量は0.005%以上であることがより好ましい。
Vは、析出物強化、フェライト結晶粒の成長抑制による細粒強化および再結晶の抑制を通じた転位強化により、母材鋼板の強度上昇に寄与する元素である。しかし、Vの含有量が0.300%を超えると、炭窒化物の析出が多くなって成形性が劣化する。このため、Vの含有量は0.300%以下であることが好ましく、0.200%以下であることがさらに好ましい。一方、Vの含有量の下限は、特に定めなくても本発明の効果は発揮される。Vの添加による強度上昇効果を十分に得るためには、Vの含有量は0.001%以上であることが好ましく、0.010%以上であることがさらに好ましい。
Crは、高温での相変態を抑制し、高強度化に有効な元素であり、Cおよび/又はMnの一部に代えて添加してもよい。しかし、Crの含有量が2.00%を超えると、熱間での加工性が損なわれて生産性が低下する。このことから、Crの含有量は2.00%以下とすることが好ましく、1.20%以下であることがさらに好ましい。一方、Crの含有量の下限は、特に定めなくても本発明の効果は発揮される。Cr添加による高強度化の効果を十分に得るためには、Crの含有量は0.01%以上であることが好ましく、0.10%以上であることがさらに好ましい。
Niは、高温での相変態を抑制し、高強度化に有効な元素であり、Cおよび/又はMnの一部に代えて添加してもよい。しかし、Niの含有量が2.00%を超えると、溶接性が損なわれる。このことから、Niの含有量は2.00%以下とすることが好ましく、1.20%以下であることがさらに好ましい。一方、Niの含有量の下限は、特に定めなくても本発明の効果は発揮される。Ni添加による高強度化の効果を十分に得るには、Niの含有量は0.01%以上であることが好ましく、0.10%以上であることがさらに好ましい。
Cuは、微細な粒子として鋼中に存在することにより強度を高める元素であり、Cおよび/又はMnの一部に替えて添加することができる。しかし、Cuの含有量が2.00%を超えると、溶接性が損なわれる。このことから、Cuの含有量は2.00%以下とすることが好ましく、1.20%以下であることがさらに好ましい。一方、Cuの含有量の下限は、特に定めなくても本発明の効果は発揮される。Cu添加による高強度化の効果を十分に得るには、Cuの含有量は0.01%以上であることが好ましく、0.10%以上であることがさらに好ましい。
Moは、高温での相変態を抑制し、高強度化に有効な元素であり、Cおよび/又はMnの一部に代えて添加してもよい。しかし、Moの含有量が2.00%を超えると、熱間での加工性が損なわれて生産性が低下する。このことから、Moの含有量は2.00%以下とすることが好ましく、1.20%以下であることがさらに好ましい。一方、Moの含有量の下限は、特に定めなくても本発明の効果は発揮される。Mo添加による高強度化の効果を十分に得るためには、Moの含有量は0.01%以上であることが好ましく、0.05%以上であることがさらに好ましい。
Bは、高温での相変態を抑制し、高強度化に有効な元素であり、Cおよび/又はMnの一部に代えて添加してもよい。しかし、Bの含有量が0.0100%を超えると、熱間での加工性が損なわれて生産性が低下することから、Bの含有量は0.0100%以下とすることが好ましい。生産性の観点からは、Bの含有量は0.0050%以下であることがより好ましい。一方、Bの含有量の下限は、特に定めなくても本発明の効果は発揮される。Bの添加による高強度化の効果を十分に得るには、Bの含有量を0.0001%以上とすることが好ましい。さらなる高強度化のためには、Bの含有量が0.0005%以上であることがより好ましい。
Wは、高温での相変態を抑制し、高強度化に有効な元素であり、Cおよび/又はMnの一部に代えて添加してもよい。しかし、Wの含有量が2.00%を超えると、熱間での加工性が損なわれて生産性が低下する。このことから、Wの含有量は2.00%以下が好ましく、1.20%以下であることがさらに好ましい。一方、Wの含有量の下限は、特に定めることなく本発明の効果は発揮される。Wによる高強度化を十分に得るためには、Wの含有量は0.01%以上であることが好ましく、0.10%以上であることがさらに好ましい。
なお、REMとは、Rare Earth Metalの略であり、ランタノイド系列に属する元素をさす。本発明の実施形態において、REMやCeはミッシュメタルにて添加されることが多く、LaやCeの他にランタノイド系列の元素を複合で含有する場合がある。不可避不純物として、これらLaやCe以外のランタノイド系列の元素を含んだとしても本発明の効果は発揮される。また、金属LaやCeを添加したとしても本発明の効果は発揮される。
次に、本発明の実施形態にかかる溶融亜鉛めっき鋼板の母材鋼板のミクロ組織について説明する。
「残留オーステナイト」
本発明の実施形態にかかる溶融亜鉛めっき鋼板の母材鋼板は、残留オーステナイト相を含む。残留オーステナイトは、強度-延性バランスを大きく高める組織である。母材鋼板の表面から1/4厚を中心とした1/8厚~3/8厚の範囲における残留オーステナイトの体積分率が1%未満では、強度―延性バランスを高める効果が小さい。このため、残留オーステナイトの体積分率を1%以上とする。強度―延性バランスを高めるため、残留オーステナイトの体積分率は3%以上とすることが好ましく、5%以上とすることが更に好ましい。一方、大量の残留オーステナイトを得るには、添加するC量を大幅に増やす必要があり、その結果、多量のCによって溶接性を著しく損なう懸念がある。このため、残留オーステナイトの体積分率を25%以下とすることが好ましい。また、残留オーステナイトは変形に伴って硬質なマルテンサイトに変態し、そのマルテンサイトが破壊の起点として働くことにより、伸びフランジ性が劣化する。このことから、残留オーステナイトの体積分率は20%以下とすることが更に好ましい。
次に、本発明の実施形態にかかる溶融亜鉛めっき鋼板を製造する方法について詳細に説明する。
焼鈍工程は、母材鋼板を、600~750℃間の平均加熱速度を1.0℃/秒以上として、750℃以上まで加熱する。めっき工程は、めっき浴温度を450~470℃、めっき浴進入時の鋼板温度を440~480℃、めっき浴中における有効Al量を0.050~0.180質量%とする条件で母材鋼板を亜鉛めっき浴に浸漬することにより、鋼板表面に溶融亜鉛めっきを施してめっき層を形成する。めっき後冷却工程は、めっき工程後に、350℃までの冷却過程が後述する下記式(1)を満たす。
母材鋼板は、特性に応じた合金元素を添加したスラブを鋳造し、熱間圧延を施し、冷間圧延を施すことで製造される。
以下、各製造工程について詳細に説明する。
まず、熱間圧延に供するスラブを鋳造する。スラブの化学成分(組成)は上述の成分であることが好ましい。熱間圧延に供するスラブは、連続鋳造スラブや薄スラブキャスターなどで製造したものを用いることができる。
熱延工程においては、鋳造に起因する結晶方位の異方性を抑制するため、スラブの加熱温度を1080℃以上とすることが好ましい。スラブの加熱温度は、より好ましくは、1150℃以上とする。一方、スラブの加熱温度の上限は、特に定めない。1300℃を超えてスラブを加熱するには、多量のエネルギーを投入する必要があり、製造コストの大幅な増加を招く。このことから、スラブの加熱温度は1300℃以下とすることが好ましい。
次に、酸洗後の熱延鋼板に冷間圧延を行って冷延鋼板を得る。
冷間圧延では、圧下率の合計が85%を超えると、鋼板の延性が失われ、冷間圧延中に鋼板が破断する危険性が高まる。このため、圧下率の合計を85%以下とすることが好ましい。この観点から、圧下率の合計は75%以下とすることがより好ましく、70%以下とすることが更に好ましい。冷間圧延工程における圧下率の合計の下限は特に定めない。圧下率の合計が0.05%未満では、母材鋼板の形状が不均質となり、めっきが均一に付着せず、外観が損なわれる。このため、0.05%以上とすることが好ましく、0.10%以上とすることが更に好ましい。なお、冷間圧延は複数のパスで行うことが好ましいが、冷間圧延のパス数や各パスへの圧下率の配分は問わない。
本発明の実施形態においては、冷延鋼板に焼鈍を施す。本発明の実施形態においては、予熱帯と還元帯とめっき帯とを有する連続焼鈍めっきラインを用いることが好ましい。そして、焼鈍工程を行いながら予熱帯と還元帯とを通過させ、めっき帯に到着するまでに焼鈍工程を終了し、めっき帯においてめっき工程を行うことが好ましい。
焼鈍工程における加熱速度は、予熱帯における処理時間を介して、鋼板表層部における脱炭の進行と関係する。焼鈍工程における加熱速度が遅いと、予熱帯での酸化雰囲気下に長時間さらされるため、鋼板表層部における脱炭が進行する。また、過度に加熱速度が遅いと、鋼板の酸化が進み、鋼板内部に粗大な酸化物が生成する場合がある。特に、600~750℃における加熱速度は重要であり、鋼板表層部の過度の脱炭および酸化を避けるため、この間の平均加熱速度を1.0℃/秒以上とする。鋼板表層部の脱炭を避けるため、600~750℃間の平均加熱速度は1.5℃/秒以上とすることが好ましく、2.0℃/秒以上とすることがより好ましい。600~750℃における平均加熱速度は、予熱帯における処理時間を確保して、ζ相の生成を促進するために、50℃/秒以下とすることが好ましい。平均加熱速度が50℃/秒以下であると、めっき層と母材鋼板との全界面のうち、ζ相と母材鋼板との界面の占める割合のより一層大きいめっき層が得られる。ζ相の生成を十分に促進するには、平均加熱速度が10℃/秒以下であることがより好ましい。
「空気比」とは、単位体積の混合ガスに含まれる空気の体積と、単位体積の混合ガスに含まれる燃料ガスを完全燃焼させるために理論上必要となる空気の体積との比であり、下記の式で示される。
空気比=[単位体積の混合ガスに含まれる空気の体積(m3)]/[単位体積の混合ガスに含まれる燃料ガスを完全燃焼させるために理論上必要となる空気の体積(m3)]}
本実施形態では、予熱帯を通過する母材鋼板に上記の条件で予熱を行うことで、母材鋼板の表層に0.01~5.0μmのFe酸化被膜を形成する。鋼板表層部に生成されたFe酸化被膜(酸化物)は、還元帯において還元され、めっき密着性に優れた表面となる。
また、予熱帯を通板させる鋼板温度が400℃未満だと、十分な酸化被膜を形成することができない。したがって、予熱帯を通板させる鋼板温度(予熱完了温度)は400℃以上とし、600℃以上とすることが好ましい。一方、予熱帯を通板させる鋼板温度が800℃を超える高温では、次の還元帯で還元できない、粗大なSiおよび/またはMnを含む酸化物が鋼板表面に生成する。したがって、予熱帯を通板させる鋼板温度は800℃以下とし750℃以下とすることが好ましい。
Ms点[℃]=541-474C/(1-VF)-15Si-35Mn-17Cr-17Ni+19Al
なお、製造中にフェライトの体積分率を直接測定することは困難である。このため、本発明においてMs点を決定するにあたっては、連続焼鈍ラインに通板させる前の冷延鋼板の小片を切り出し、その小片を連続焼鈍ラインに通板させた場合と同じ温度履歴で焼鈍して、小片のフェライトの体積の変化を測定し、その結果を用いて算出した数値をフェライトの体積分率VFとしている。
ベイナイト変態処理は、焼鈍工程とめっき工程との間に行ってもよいし、めっき後冷却工程において行ってもよいし、両方の時点で行ってもよい。
焼鈍工程とめっき工程との間と、めっき後冷却工程とにおいて行うベイナイト変態処理の停留時間の和は、15秒以上500秒以下とする必要がある。停留時間の和が15秒以上であると、ベイナイト変態が十分に進み、十分な残留オーステナイトが得られる。停留時間の和は25秒以上であることが好ましい。一方、停留時間の和が500秒を超えると、パーライトおよび/または粗大なセメンタイトが生成する。このため、停留時間の和を500秒以下とし、300秒以下とすることが好ましい。
なお、めっき前冷却工程後に、ベイナイト変態処理とマルテンサイト変態処理の両者を行う場合は、施工順についてはベイナイト変態処理前にマルテンサイト変態処理を行うこととする。
次に、このようにして得られた母材鋼板をめっき浴に浸漬する。
めっき浴は、亜鉛を主体とし、めっき浴中の全Al量から全Fe量を引いた値である有効Al量が0.050~0.180質量%である組成を有する。めっき浴中の有効Al量が0.050%を下回ると、めっき層中へのFeの侵入が過度に進み、めっき密着性が損なわれるため、0.050%以上とする必要がある。この観点から、めっき浴中の有効Al量は0.065%以上であることが好ましく、0.070%以上であることが更に好ましい。一方、めっき浴中の有効Al量が0.180%を超えると、母材鋼板とめっき層の境界にAl系の酸化物が生成し、同境界におけるFeおよびZn原子の移動が阻害され、ζ相の生成が抑制され、めっき密着性が著しく損なわれる。この観点から、めっき浴中の有効Al量は0.180%以下とする必要があり、0.150%以下とすることが好ましく、0.135%以下とすることが更に好ましい。
めっき浴工程後、室温に至るまでのめっき後冷却工程において、350℃までの冷却過程が下記式(1)を満たすように冷却処理を制御する。このことにより、めっき層中に適量のζ相が得られる。
なお、式(1)におけるT(t)[℃]は鋼板温度であり、t[秒]は鋼板がめっき浴から出た時点を起点とする経過時間であり、t1[秒]は鋼板がめっき浴から出た時点を起点として鋼板温度が350℃に至るまでの経過時間であり、W* Al[質量%]はめっき浴中の有効Al量である。また、ε、θおよびμは定数項であり、それぞれ、2.62×107、9.13×103、1.0×10-1である。
一方、一般的な溶融亜鉛めっき鋼板の製造方法に見られるように、めっき浴に浸漬した後に急冷を施すと、上記式(1)の値が著しく小さくなる。その結果、十分なζ相が得られず、めっき密着性が劣化する。上記式(1)の値を所定の範囲に留めるために、例えば、めっき浴から取り出した後に一定時間の等温保持処理を行い、その後に急冷しても構わない。
また、上記式(1)の値が所定の範囲に留まるならば、その他の任意の温度制御を行っても構わない。つまり、上記式(1)の値が本発明の範囲内となる温度制御であれば、いかなる冷却制御形態を採用してもよい。例えば、上記等温保持処理後に急冷する冷却形態でもよく、また略一定速の緩冷却を行う冷却形態でもよい。
また、再加熱処理時間が1000秒を超えると処理効果が飽和するため、処理時間は1000秒以下とすることが好ましい。さらに、パーライトおよび/または粗大なセメンタイトの生成を抑制するため、再加熱処理時間は500秒以下とすることがより好ましい。
リン酸化物および/またはリンを含む複合酸化物からなる皮膜は、溶融亜鉛めっき鋼板を加工する際に潤滑剤として機能させることができ、母材鋼板の表面に形成した亜鉛めっき層を保護することができる。
表1~4に示す化学成分(組成)を有するスラブを鋳造し、表5、6に示す熱延工程条件(スラブ加熱温度、圧延完了温度)で熱間圧延し、表5、6に示す熱延工程条件(熱延完了から巻取りまでの平均冷却速度、巻取温度)で冷却し、熱延鋼板を得た。
その後、熱延鋼板に酸洗を施して、表5、6に示す冷延工程条件(圧下率)の冷間圧延を施し、冷延鋼板を得た。
引き続き、表7、8に示すめっき前冷却工程条件(冷却速度1(750~700℃の温度域での平均冷却速度)、冷却速度2(700~500℃の温度域での平均冷却速度)、ベイナイト変態処理1条件(処理温度、処理時間)、マルテンサイト変態処理(処理温度、処理時間))で冷却処理を施した。なお、ベイナイト変態処理1、マルテンサイト変態処理を施さなかった鋼板については当該処理の条件欄は空欄とした。
めっき工程後、表9、10に示すめっき後冷却工程条件(式(1)、ベイナイト変態処理2条件(処理温度、処理時間)、再加熱処理条件(処理温度、処理時間))で冷却処理を施した。なお、ベイナイト変態処理2、再加熱処理を施さなかった鋼板については当該処理の条件欄は空欄とした。
さらに、表9、10に示す条件(圧下率)で冷間圧延を施し、実験例1~94、C1~C44のめっき鋼板を得た(ただし、一部の実験例においては、実験を中断したものもある)。
穴拡げ試験は、JIS Z 2256に記載の方法で行った。成形性のうち、延性(全伸び)Elおよび穴拡げ性λは、引張最大強度TSに伴って変化するが、下記式(3)を満たす場合に強度、延性および穴拡げ性を良好とする。
TS1.5×El×λ0.5 ≧ 2.5×106 ・・・式(3)
実験例C44は、予熱完了温度が高く、めっき前の鋼板表面にSiおよびMnを含む粗大な酸化物が多数生成したため、粗大な酸化物が存在するζ結晶粒と母材鋼板との成す界面が、ζ相と母材鋼板との全界面に対して50%を超えた例であり、めっき密着性が劣位である。
実験例43は、焼鈍工程の余熱帯における空気比が大きく、鋼板表面における脱炭が過度に進行したため、微細化層の平均厚さが厚くなり、TS1.5×El×λ0.5が低下し、十分な特性が得られなかった例である。
実験例26は、めっき工程における式1の値が過大であり、めっき層中のFe%が過度に高まり、十分なめっき密着性が得られなかった例である。
実験例C38は、Cの含有量が大きく、スポット溶接性および成形性が劣化した例である。
実験例91は、Mnの含有量が大きく、熱延工程において、スラブが加熱中に割れたため、実験を中断した例である。
実験例C22は、熱間圧延後にコイルに巻き取る温度が低く、冷間圧延工程において鋼板が破断したため、実験を中止した例である。
実験例6は、熱延鋼板に冷間圧延を施さなかった例であり、板の平坦度が悪く、焼鈍処理を行えず、実験を中止した例である。
実験例35は、冷間圧延における圧下率が過度に大きく、鋼板が破断したため、実験を中止した例である。
実験例C28は、焼鈍工程における最高加熱温度がAc1+50℃より低く、残留オーステナイト相が生成せず、粗大なセメンタイトが鋼板中に多数存在し、TS1.5×El×λ0.5が劣化し、十分な特性が得られなかった例である。
実験例40は、焼鈍工程の還元帯における水蒸気分圧P(H2O)と水素分圧P(H2)の比、P(H2O)/P(H2)が大きく、母材鋼板の表層の微細化層が過度に厚くなり、めっき層の合金化が過度に進行したため、めっき密着性、パウダリング性およびチッピング性が劣化した例である。
実験例C17は、めっき工程のめっき浴中における有効Al量が過度に大きく、式1の値が過小となり、めっき層と母材鋼板の界面にδ相が十分に生成せず、十分なめっき密着性が得られなかった例である。
「実施例1」で得た実験例1のめっき鋼板から試験片を採取した。次いで、試験片の母材鋼板の圧延方向に平行な板厚断面を観察面としてイオンミリング加工により研磨し、電界放射型走査型電子顕微鏡(FE-SEM)で、加速電圧5kVの条件で反射電子(BSE)像を得た。その結果を図2に示す。
図2に示すように、実験例1のめっき鋼板には、ζ相からなる柱状晶を含むめっき層が形成されていた。また、実験例1のめっき鋼板の母材鋼板には、めっき層との界面に直接接する微細化層が形成されていた。図2に示すように、実験例1のめっき鋼板の微細化層中には、酸化物(周囲と比較して暗く見える部分)が含まれていた。
「実施例1」で得た実験例1のめっき鋼板と同様にして冷延鋼板を製造し、実験例1のめっき鋼板と同様にして焼鈍工程を行い、焼鈍板を得た。焼鈍板を、表15に示すめっき工程条件(有効Al量、めっき浴温度(浴温)、鋼板の進入温度、浸漬時間)で亜鉛めっき浴に浸漬してめっきを施した。
めっき工程後、表15に示すめっき後冷却工程条件(式(1))で冷却処理を施した。さらに、表15に示す条件(圧下率)で冷間圧延を施し、実験例104~111のめっき鋼板を得た。
また、得られためっき鋼板について「実施例1」と同様にして、残留オーステナイトの体積分率(γ分率)を測定した。
また、得られためっき鋼板について「実施例1」と同様にして、めっきの付着量を求めた。その結果を表15に示す。
さらに、めっき鋼板について「実施例1」と同様にして、微細化層の平均厚さと、フェライト相の平均粒径と、酸化物の最大径とを求めた。その結果を表15に示す。
また、得られためっき鋼板について「実施例1」と同様にして、引張試験、穴拡げ試験、曲げ試験、密着性評価試験、スポット溶接試験、腐食試験を行った。その結果を表15に示す。
また、実験例1の結果についても、表15に併せて示す。
これに対し、表15に示すように、実験例104は、めっき層と母材鋼板との全界面のうち、ζ相と母材鋼板との界面の占める割合(ζ境界面占有率)が20%未満であるので、めっき密着性およびスポット溶接性が不十分であった。
Claims (5)
- 母材鋼板と前記母材鋼板の少なくとも一方の表面に形成された溶融亜鉛めっき層とからなり、
前記溶融亜鉛めっき層は、前記鋼板の表面に、Fe含有量が0%超~5%以下であり、Al含有量が0%超~1.0%以下であり、ζ相からなる柱状晶を含み、さらに、前記溶融亜鉛めっき層と母材鋼板との全界面のうち20%以上がζ相に被覆され、前記溶融亜鉛めっき層において、ζ結晶粒のうち粗大な酸化物が存在するζ結晶粒と母材鋼板との成す界面が、前記ζ相と母材鋼板との全界面に対して50%以下であり、
前記母材鋼板が、質量%で、
C :0.040~0.400%、
Si:0.05~2.50%、
Mn:0.50~3.50%、
P :0.0001~0.1000%、
S :0.0001~0.0100%、
Al:0.001~1.500%、
N :0.0001~0.0100%、
O :0.0001~0.0100%、
Si+0.7Al≧0.30(式中の元素記号は、その元素の含有量(質量%)を表す。)を満足し、残部がFeおよび不可避不純物からなる化学成分を有し、
前記母材鋼板と前記溶融亜鉛めっき層との界面に直接接する微細化層を有し、前記微細化層の平均厚さが0.1~5.0μm、前記微細化層内におけるフェライト相の平均粒径が0.1~3.0μmであり、前記微細化層中にSiおよびMnの1種または2種以上の酸化物を含有し、前記酸化物の最大径が0.01~0.4μmであり、
前記母材鋼板の表面から1/4厚を中心とした1/8厚~3/8厚の範囲において、体積分率で、残留オーステナイト相を1%以上有する溶融亜鉛めっき鋼板。 - 前記溶融亜鉛めっき層について、前記母材鋼板の片面におけるめっき付着量が10g/m2以上、100g/m2以下である請求項1に記載の溶融亜鉛めっき鋼板。
- 前記母材鋼板が、質量%で、さらに、
Ti:0.001~0.150%、
Nb:0.001~0.100%、
V:0.001~0.300%、
のうちから選ばれた1種または2種以上を含有する請求項1または請求項2に記載の溶融亜鉛めっき鋼板。 - 前記母材鋼板が、質量%で、さらに、
Cr:0.01~2.00%、
Ni:0.01~2.00%、
Cu:0.01~2.00%、
Mo:0.01~2.00%、
B:0.0001~0.0100%、
W:0.01~2.00%、
のうちから選ばれた1種または2種以上を含有する請求項1~3のいずれか一項に記載の溶融亜鉛めっき鋼板。 - 前記母材鋼板が、質量%で、さらに、
Ca、Ce、Mg、Zr、La、REMの1種または2種以上を合計で0.0001~0.0100%含有する請求項1~4のいずれか一項に記載の溶融亜鉛めっき鋼板。
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US10507629B2 (en) | 2014-11-05 | 2019-12-17 | Nippon Steel Corporation | Hot-dip galvanized steel sheet |
US10822683B2 (en) | 2014-11-05 | 2020-11-03 | Nippon Steel Corporation | Hot-dip galvanized steel sheet |
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