WO2013047739A1 - 機械切断特性に優れた高強度溶融亜鉛めっき鋼板、高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 - Google Patents
機械切断特性に優れた高強度溶融亜鉛めっき鋼板、高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 Download PDFInfo
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- WO2013047739A1 WO2013047739A1 PCT/JP2012/075061 JP2012075061W WO2013047739A1 WO 2013047739 A1 WO2013047739 A1 WO 2013047739A1 JP 2012075061 W JP2012075061 W JP 2012075061W WO 2013047739 A1 WO2013047739 A1 WO 2013047739A1
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- dip galvanized
- galvanized steel
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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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
- C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
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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
- C22C18/00—Alloys based on zinc
- C22C18/04—Alloys based on zinc with aluminium as the next major constituent
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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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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- 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
- 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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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0224—Two or more thermal pretreatments
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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
- C23C2/024—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
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
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- C—CHEMISTRY; METALLURGY
- 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
- C23C2/29—Cooling or quenching
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12785—Group IIB metal-base component
- Y10T428/12792—Zn-base component
- Y10T428/12799—Next to Fe-base component [e.g., galvanized]
Definitions
- the present invention relates to a high-strength hot-dip galvanized steel sheet, a high-strength galvannealed steel sheet excellent in mechanical cutting characteristics, and a method for producing them.
- the steel sheet described in Patent Document 1 the steel sheet structure is made of ferrite and martensite, and high elongation is ensured while having high strength. Furthermore, the steel sheet which consists of a ferrite, a retained austenite, and a bainite structure described in patent document 2 has obtained the further high ductility by utilizing the transformation induction plasticity of a retained austenite. Moreover, since the steel plates as described in Patent Documents 1 and 2 are excellent in collision energy absorption capability, they are used in many members as structural members for automobiles.
- the cutting process at the time of mechanical cutting and punching is the process of plastic deformation of the steel sheet, the contact position between the shear and punch and the steel sheet, the crack formation process at the contact position between the die and the steel sheet, and these cracks propagate and connect. It can be divided into three processes.
- the plastic deformation process and the crack propagation process as described above are classified as ductile fracture at room temperature or normal processing (strain) speed, so that the energy required for crack propagation increases as the steel sheet strength increases. As a result, an increase in the cutting load accompanying an increase in strength is inevitable.
- steel sheets described in Patent Documents 3 and 4 are known as steel sheets that have improved cutability and machinability during machining as described above.
- the steel sheets described in Patent Documents 3 and 4 add a predetermined amount of Pb, S, and Al to the steel, and disperse MnS-based sulfides and Al 2 O 3 , so that machinability at the time of cutting is achieved. Is an improvement.
- machinability is improved by dispersing inclusions having poor deformability such as MnS and Al 2 O 3 in steel and destroying these inclusions during cutting.
- Patent Documents 3 and 4 contain a large amount of inclusions (MnS-based sulfide, Al 2 O 3 ) throughout the steel, the steel sheet for automobiles represented by press molding and hole expansion processing. Therefore, there is a problem that it is difficult to apply to a member that performs press molding. In addition, there is a problem that the addition of Pb is not preferable from the viewpoint of environmental problems.
- Patent Document 5 discloses a steel sheet in which an oxide is dispersed only in the surface layer of the steel sheet. According to the technique described in Patent Document 5, while adding Si and Al to the steel sheet, high-temperature winding is performed during hot rolling, or additional processing is performed on the hot-rolled steel sheet, thereby the steel sheet surface layer. In other words, an oxide of Si or Mn is formed to improve workability such as mechanical cutting or punching.
- Patent Document 6 by mass, C: 0.07 to 0.25%, Si: 0.3 to 2.50%, Mn: 1.5 to 3.0%, Ti: 0.005 to 0.07%, B: 0.0001 to 0.01%, P: 0.001 to 0.03%, S: 0.0001 to 0.01%, Al: 0.60% or less, N: 0.00.
- the grain boundary of the steel sheet surface layer of 4 ⁇ m or less a high-strength cold-rolled steel sheet containing a Si-containing oxide with a distribution of 2 ⁇ 10 6 (pieces / mm 2 ) or more in either one or both of the crystal grains has been proposed.
- the high-strength cold-rolled steel sheet described in Patent Document 6 it is said that the maximum tensile strength of 900 MPa or more is ensured and the mechanical cutting characteristics are excellent.
- the high-strength cold-rolled steel sheet described in Patent Document 6 has a problem that the ductility is insufficient and it is difficult to form a member having a complicated shape.
- JP-A-57-143435 Japanese Patent Laid-Open No. 01-230715 JP 59-205453
- Japanese Patent Laid-Open No. 62-23970 Japanese Patent No. 3870891 JP 2011-111673 A
- the present invention has been made in view of the above-mentioned problems.
- a high-strength hot-dip galvanized steel sheet having high mechanical strength and high ductility can be obtained while ensuring high strength of a tensile maximum strength of 900 MPa or more, and high-strength alloying and melting.
- An object of the present invention is to provide a galvanized steel sheet and a production method thereof.
- the present inventors have intensively studied to solve the above problems. As a result, by optimizing the steel components, rolling conditions, annealing conditions after rolling, etc., while controlling the ratio of the retained austenite phase in the steel sheet structure to a predetermined level or more, the solute carbon contained in the retained austenite phase It has been found that the amount, average particle diameter, and average distance between particles can be limited to a predetermined range, and further, the thickness of the decarburized layer, the average particle diameter of the oxide, and the average density can be limited to a predetermined range.
- the gist of the present invention is as follows.
- the steel sheet structure contains at least a ferrite phase of 40 to 90% in volume fraction and a residual austenite phase of 3% or more, and the residual austenite phase is in the phase.
- the amount of solid solution carbon is 0.70 to 1.00%, and the average particle size is 2.0 ⁇ m or less, the average distance between particles is 0.1 to 5.0 ⁇ m, the thickness of the decarburized layer in the steel sheet surface layer part is 0.01 to 10.0 ⁇ m, and is included in the steel sheet surface layer part
- the oxide has an average particle size of 30 to 120 nm, an average density of 1.0 ⁇ 10 12 particles / m 2 or more, and a work hardening coefficient (n value) at the time of plastic deformation of 3 to 7%.
- Ti 0.001 to 0.150%
- Nb 0.001 to 0.100%
- V 0.001 to 0.300%
- the high-strength hot-dip galvanized steel sheet having excellent mechanical cutting characteristics as described in [1] above.
- Cr 0.01 to 2.00%
- Ni 0.01 to 2.00%
- Cu 0.01 to 2.00%
- Mo 0.01 to 2.
- One or more of 00%, B: 0.0001 to 0.0100%, W: 0.01 to 2.00% are contained, as described in [1] or [2] above High-strength hot-dip galvanized steel sheet with excellent mechanical cutting characteristics.
- the product After rapid cooling at a cooling rate of 10 ° C./s or more, the product is wound on a coil and slowly cooled to 400 ° C. over 1.0 hour, and after pickling following the hot rolling step, the total rolling reduction
- a cold rolling process in which cold rolling is performed to a content of 30 to 75%;
- the steel sheet after the process is heated to 750 ° C. or higher with an average heating rate between 600 and 750 ° C. being 20 ° C./s or less, and then an average cooling rate between 750 and 650 ° C. is 1.0 to 15.0 ° C. / S, and an average cooling rate from 650 ° C. is set to 3.0 ° C./s or more, and is kept at a temperature range of 300 to 470 ° C.
- An annealing process in which a bending process is performed at least once with a bending radius of 800 mm or less, and after the annealing process, a plating bath temperature: 450 to 470 ° C., a steel sheet temperature when entering the plating bath: 430 to 490 ° C., Effective amount of Al in the plating bath: A plating process in which a steel sheet is immersed in a galvanizing bath under conditions of 0.01 to 0.18% by mass to form a plating layer by hot dip galvanizing on the steel plate surface And a cooling step of cooling at an average cooling rate of 0.5 ° C./s or more to 150 ° C.
- the annealing step is performed in a unit volume in a mixed gas of air and fuel gas used for a preheating burner.
- Air ratio 0.7 to 1.2, which is a ratio of the volume of air contained in the mixed gas and the volume of air theoretically required to completely burn the fuel gas contained in the unit volume of mixed gas
- the oxide is generated on the surface layer of the steel sheet by passing the steel sheet while heating to a steel sheet temperature of 400 to 800 ° C., and then water vapor (H 2 O) and hydrogen (H 2 ) The oxide generated in the pre-tropics is reduced by heating to 750 ° C.
- the work hardening coefficient (n value) defined in the present invention is a characteristic value that serves as a guide for drawing workability (ductility), and approximates the relationship between stress ⁇ and strain ⁇ in the plastic region above the yield point. It means the index n at the time.
- the larger the n value the greater the elongation until the occurrence of local contraction, so that the ductility is improved.
- the smaller the n value the better the mechanical cutting characteristics.
- the steel composition, the steel sheet structure, the thickness of the decarburized layer in the steel sheet surface layer part, and the oxide The configuration that regulates the size and the like within the proper range is adopted. That is, when the retained austenite phase is contained in the steel sheet structure in a predetermined amount or more, the work hardening ability is enhanced, and the strength and ductility of the steel sheet can be improved, while the amount of solute carbon in the retained austenite phase is limited and the average particle size is increased.
- the mechanical cutting characteristics (punching workability) at the time of processing the steel sheet are improved. Furthermore, the adhesiveness of a plating layer improves by restrict
- the steel components are within an appropriate range, hot rolling and cold rolling, and annealing conditions after rolling are set.
- a method of limiting to a predetermined range is adopted.
- the thickness of the decarburized layer, the average particle diameter of the oxide, and the average density in the steel sheet surface layer portion can be limited to a predetermined range, the adhesion of the plating layer can be improved. Therefore, it is possible to produce a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet that can obtain excellent ductility and mechanical cutting characteristics while ensuring a maximum tensile strength of 900 MPa or more as described above. Become.
- the high strength hot dip galvanized steel sheet, the high strength alloyed hot dip galvanized steel sheet and the manufacturing method thereof, which are excellent in mechanical cutting characteristics of the present invention, and the production method thereof, particularly in the automobile field, are associated with safety associated with the enhancement of the strength of the vehicle body. It is possible to fully enjoy merits such as improvement of workability and workability at the time of member processing, and its social contribution is immeasurable.
- the high-strength hot-dip galvanized steel sheet, the high-strength alloyed hot-dip galvanized steel sheet, and their manufacturing methods that are excellent in mechanical cutting characteristics according to embodiments of the present invention will be described.
- the present embodiment will be described in detail in order to better understand the purpose of the high-strength hot-dip galvanized steel sheet, the high-strength galvannealed steel sheet, and the manufacturing method thereof excellent in mechanical cutting characteristics of the present invention. Therefore, the present invention is not limited unless otherwise specified.
- “%” represents “mass%” unless otherwise specified.
- High-strength hot-dip galvanized steel sheet The high-strength hot-dip galvanized steel sheet (hereinafter sometimes simply referred to as high-strength hot-dip galvanized steel sheet) having excellent mechanical cutting characteristics according to this embodiment is mass%, and C: 0.075 to 0.400%. Si: 0.01 to 2.00%, Mn: 0.80 to 3.50%, P: 0.0001 to 0.100%, S: 0.0001 to 0.0100%, Al: 0.001 to 2.00%, N: 0.0001 to 0.0100%, O: 0.0001 to 0.0100%, with the remainder having a plating layer on the surface of the steel plate made of iron and inevitable impurities .
- the high-strength hot-dip galvanized steel sheet according to this embodiment has a thickness of 0.6 to 5.0 mm. Further, the high-strength hot-dip galvanized steel sheet of this embodiment has a steel sheet structure having at least a volume fraction in the range from 1/8 thickness to 3/8 thickness centering on 1/4 of the sheet thickness from the surface of the steel sheet. 40% to 90% of ferrite phase and 3% or more of retained austenite phase. This retained austenite phase has a solid solution carbon content of 0.70 to 1.00% and an average particle size of 2 The average distance between particles is 0.1 to 5.0 ⁇ m.
- the thickness of the decarburized layer in the steel sheet surface layer part is 0.01 to 10.0 ⁇ m, and the average particle diameter of the oxide contained in the steel sheet surface layer part is 30 to 120 nm. And an average density of 1.0 ⁇ 10 12 pieces / m 2 or more.
- the high-strength hot-dip galvanized steel sheet according to this embodiment has an average work hardening coefficient (n value) of 0.080 or more at the time of plastic deformation of 3 to 7%.
- n value average work hardening coefficient
- the range from 1/8 thickness to 3/8 thickness centered on 1/4 of the plate thickness from the surface of the steel plate means 1/8 thickness centered on 1/4 of the plate thickness from the surface of the steel plate.
- the reason why the structure in this range is focused is that the structure in this range may be considered to represent the entire structure of the steel sheet excluding the decarburized layer in the steel sheet surface layer portion. That is, if the steel sheet structure is in the range of 1/8 thickness to 3/8 thickness, the entire steel sheet excluding the decarburized layer on the steel sheet surface layer portion can be determined to have the above structure.
- the inventors of the present invention have made extensive studies to achieve high mechanical cutting characteristics while ensuring excellent ductility in a high-strength hot-dip galvanized steel sheet having a maximum tensile strength of 900 MPa or more.
- the steel component is limited to an appropriate range, and the rolling condition and the annealing condition after rolling are set to an appropriate range described later, thereby controlling the ratio of the retained austenite phase in the steel sheet structure to a predetermined value or more.
- grains could be restrict
- the thickness of the high-strength hot-dip galvanized steel sheet of the present invention is 0.6 to 5.0 mm. If the plate thickness is less than 0.6 mm, it is difficult to keep the shape of the steel plate flat, which is not appropriate. Therefore, the plate thickness is preferably 0.6 mm or more. Moreover, when it exceeds 5.0 mm, the distortion accompanying bending will not enter, it will become difficult to make fine dispersion of bainite, and it will become difficult to produce
- the steel structure of the high-strength hot-dip galvanized steel sheet according to the present invention has a steel sheet structure of at least a volume fraction in the range of 1/8 thickness to 3/8 thickness centering on 1/4 of the plate thickness from the surface of the steel sheet. It contains 40 to 90% of ferrite phase and 3% or more of retained austenite phase.
- the residual austenite phase has a solid solution carbon content of 0.70 to 1.00%, an average particle size of 2.0 ⁇ m or less, and an average distance between particles of 0.1 to 5. 0 ⁇ m.
- the retained austenite phase is a structure that increases work hardening ability and improves strength and ductility.
- the volume fraction of the retained austenite phase is 3% or more.
- the volume fraction of the retained austenite phase is more preferably 5% or more, and further preferably 7% or more.
- the volume fraction of the retained austenite phase is preferably 30% or less.
- the volume fraction of the retained austenite phase is preferably 25% or less, and more preferably 20% or less.
- the volume fraction of retained austenite is calculated by performing an X-ray analysis with the plane parallel to the plate surface of the steel plate and 1/4 of the plate thickness from the surface of the steel plate as the observation surface, and calculating the area fraction. It can be regarded as the volume fraction of retained austenite at 1/8 to 3/8 thickness. As long as the observation surface is parallel to the plate surface of the steel plate, it may be set at an arbitrary position in the range of 1/8 thickness to 3/8 thickness centering on 1/4 of the plate thickness from the surface of the steel plate. Absent.
- the strength of martensite after transformation by processing is suppressed, and the amount of solute carbon in the residual austenite phase is limited so that it is easily transformed by mild processing.
- the steel sheet is easily broken against mechanical cutting.
- the amount of element dissolved in the retained austenite phase determines the stability of the retained austenite phase and changes the amount of strain necessary for the retained austenite phase to transform into hard martensite. For this reason, it is possible to control the work hardening behavior by controlling the amount of the solid solution element of the retained austenite phase, and to greatly improve the shape freezing property, ductility and tensile strength.
- the amount of dissolved carbon in the retained austenite phase is 1.00% or less.
- the amount of dissolved carbon in the retained austenite phase exceeds 1.00%, the retained austenite phase becomes excessively stable. Cutting such a steel plate is not preferable because the ductility of the surrounding ferrite structure is significantly deteriorated and then transformed into martensite, and the interface between ferrite and martensite is easily peeled off.
- the amount of solid solution carbon in the retained austenite phase is preferably 0.96% or less.
- the amount of dissolved carbon in the retained austenite phase is less than 0.70%, martensitic transformation starts in the process of cooling to room temperature after the annealing process, and the volume fraction of the retained austenite phase cannot be secured.
- the amount is 0.70% or more.
- the amount of solid solution carbon is preferably 0.75% or more, and more preferably 0.80% or more.
- the amount of solid solution carbon (C ⁇ ) in the retained austenite phase is determined by performing an X-ray diffraction test under the same conditions as the measurement of the area fraction of the retained austenite phase to obtain the lattice number a of the retained austenite phase. 1).
- Expression (1) is disclosed in the document “Scripta Metallurgica et Materialia, vol. 24, 1990, p509-514”.
- the method for measuring the amount of dissolved carbon is not limited to the above method.
- the concentration of various elements may be measured by performing direct observation using an EMA method or a three-dimensional atom probe (3D-AP).
- the retained austenite phase contained in the steel structure of the high-strength hot-dip galvanized steel sheet of the present invention has a solid solution carbon content of 0.70 to 1.00% and an average particle diameter of 2.0 ⁇ m or less.
- the average distance between the particles is 0.1 to 5.0 ⁇ m.
- the average particle diameter of a retained austenite phase is prescribed
- the average particle size of the retained austenite phase is more preferably 1.5 ⁇ m or less, and further preferably 1.2 ⁇ m or less.
- the lower limit of the average particle diameter of the retained austenite phase is not particularly defined, special equipment such as a rolling mill or a rapid heating device that applies a huge strain is required, and the cost increases significantly. It is preferable to do.
- the average distance between the particles of a retained austenite phase is prescribed
- the distance between the grains of the retained austenite phase is excessively narrow, cracks caused by martensite formed by transformation of one austenite grain or austenite grain are formed by transformation of adjacent austenite grains or austenite grains.
- the average distance between particles of the retained austenite phase needs to be 0.1 ⁇ m or more. Further, the average distance between particles of the retained austenite phase is more preferably 0.3 ⁇ m or more, and further preferably 0.5 ⁇ m or more.
- the crystal grains of the residual austenite phase are parallel to the rolling direction and perpendicular to the plate surface, and have a thickness of 1/8 to 3/8 from the surface of the steel plate, centering on 1/4 of the plate thickness.
- the range can be evaluated by performing a high-resolution crystal orientation analysis by an EBSD (Electron Bach-Scattering Diffraction) method using a Field Emission Scanning Electron Microscope (FE-SEM).
- the measurement step is set to 0.1 ⁇ m, and 10 or more points indicating the diffraction pattern of iron FCC are gathered, and a region where the difference in crystal orientation between each other is less than 10 ° is defined as residual austenite crystal grains.
- the average particle diameter can be measured by obtaining the area of each crystal grain in 30 to 300 randomly selected retained austenite crystal grains and obtaining the grain diameter as the equivalent circle diameter.
- the steel structure of the high-strength hot-dip galvanized steel sheet according to the present invention has a volume fraction other than the above-mentioned residual austenite phase, ferrite phase: 40 to 90%, bainitic ferrite phase and / or bainite phase: 50% or less
- the tempered martensite phase is preferably 50% or less and the fresh martensite phase is preferably 15% or less.
- the high-strength hot-dip galvanized steel sheet according to the present invention has such a steel sheet structure, and thus has a more excellent formability.
- the ferrite phase is a structure effective for improving ductility, and is preferably contained in the steel sheet structure in a volume fraction of 40 to 90%. If the volume fraction of the ferrite phase in the steel sheet structure is less than 40%, sufficient ductility may not be obtained.
- the volume fraction of the ferrite phase contained in the steel sheet structure is more preferably 45% or more, and further preferably 50% or more, from the viewpoint of ductility. On the other hand, since the ferrite phase is a soft structure, if the volume fraction exceeds 90%, sufficient strength may not be obtained.
- the volume fraction of the ferrite phase contained in the steel sheet structure is more preferably 85% or less, and further preferably 75% or less.
- the bainitic ferrite phase and / or bainite phase has a structure with an excellent balance between strength and ductility, and is preferably contained in the steel sheet structure in a volume fraction of 10 to 50%.
- the bainitic ferrite phase and / or bainite phase is a microstructure having an intermediate strength between the soft ferrite phase and the hard martensite phase, the tempered martensite phase and the retained austenite phase, and from the viewpoint of stretch flangeability More preferably, it is contained at 15% or more, and more preferably at least 20%.
- the volume fraction of the bainitic ferrite phase and / or the bainite phase exceeds 50%, the yield stress is excessively increased and the shape freezing property is deteriorated.
- the tempered martensite phase is a structure that greatly improves the tensile strength, and may be contained in the steel sheet structure in a volume fraction of 50% or less. From the viewpoint of tensile strength, the volume fraction of tempered martensite is preferably 10% or more. On the other hand, when the volume fraction of the tempered martensite contained in the steel sheet structure exceeds 50%, the yield stress is excessively increased and the shape freezing property is deteriorated, which is not preferable.
- the fresh martensite phase has the effect of greatly improving the tensile strength, but on the other hand, it becomes a starting point of fracture and greatly deteriorates the stretch flangeability. Therefore, the volume fraction in the steel sheet structure is limited to 15% or less. Is preferred. In order to enhance stretch flangeability, the volume fraction of the fresh martensite phase in the steel sheet structure is preferably 10% or less, and more preferably 5% or less.
- the steel sheet structure of the high-strength hot-dip galvanized steel sheet of the present invention may further include a structure other than the above, such as a pearlite phase and / or a coarse cementite phase.
- a structure other than the above such as a pearlite phase and / or a coarse cementite phase.
- the total volume fraction of the pearlite phase and / or coarse cementite phase contained in the steel sheet structure is preferably 10% or less, and more preferably 5% or less.
- volume fraction of each structure included in the steel sheet structure of the high-strength steel sheet of the present invention can be measured by, for example, the following method.
- the volume fraction of the ferrite phase, bainitic ferrite phase, bainite phase, tempered martensite phase and fresh martensite phase contained in the steel sheet structure of the high-strength hot-dip galvanized steel sheet of the present invention first, rolling the steel sheet A sample is taken with the cross section parallel to the direction and perpendicular to the plate surface as the observation surface. Then, the observation surface of this sample was polished and nital etched, and the range from 1/8 thickness to 3/8 thickness centered on 1/4 of the plate thickness from the surface of the steel plate was observed with a field emission scanning electron microscope. Then, the area fraction is measured and can be regarded as the volume fraction.
- composition the chemical component (composition) of the high-strength hot-dip galvanized steel sheet of the present invention will be described.
- % represents “mass%” unless otherwise specified.
- C: 0.075-0.400% C is contained to increase the strength of the high-strength steel plate.
- the C content is preferably 0.250% or less, and more preferably 0.220% or less.
- the C content is more preferably 0.085% or more, and further preferably 0.100% or more.
- Si: 0.01-2.00% Si is an element that suppresses the formation of iron-based carbides in the steel sheet and increases strength and formability. However, if the Si content exceeds 2.00%, the steel plate becomes brittle and ductility deteriorates, making cold rolling difficult. From the viewpoint of ductility, the Si content is preferably 1.80% or less, and more preferably 1.50% or less. On the other hand, when the Si content is less than 0.01%, it is difficult to sufficiently disperse the oxide in the decarburized layer. From this viewpoint, the lower limit value of Si is more preferably 0.20% or more, and further preferably 0.50% or more.
- Mn: 0.80 to 3.50% Mn is added to increase the strength of the steel sheet.
- Mn content exceeds 3.50%, a coarse Mn-concentrated portion is generated at the center of the steel plate thickness, and embrittlement is likely to occur, and troubles such as cracking of the cast slab are likely to occur.
- the Mn content needs to be 3.50% or less.
- the Mn content is more preferably 3.00% or less, and even more preferably 2.70% or less.
- the content of Mn is less than 0.80%, since a large amount of soft structure is formed during cooling after annealing, it becomes difficult to ensure a maximum tensile strength of 900 MPa or more.
- the content needs to be 0.80% or more.
- the Mn content is more preferably 1.00% or more, and further preferably 1.30% or more.
- P 0.0001 to 0.100%
- P tends to segregate in the central part of the plate thickness of the steel sheet, causing the weld to become brittle. If the P content exceeds 0.100%, the welded portion becomes significantly brittle, so the upper limit of the P content is 0.100%. Further, from the viewpoint of avoiding embrittlement of the welded portion, the upper limit of the P content is more preferably 0.030%. On the other hand, making the P content less than 0.0001% is accompanied by a significant increase in production cost, so 0.0001% is made the lower limit. Moreover, it is preferable that content of P from a viewpoint of reducing manufacturing cost more is 0.0010% or more.
- S 0.0001 to 0.0100% S adversely affects weldability and manufacturability during casting and hot rolling. For this reason, the upper limit of the S content is set to 0.0100% or less. Further, S is combined with Mn to form coarse MnS and lowers the ductility and stretch flangeability. Therefore, S is more preferably 0.0050% or less, and further preferably 0.0030% or less. On the other hand, making the S content less than 0.0001% is accompanied by a significant increase in manufacturing cost, so 0.0001% is made the lower limit. Further, the content of S from the viewpoint of further reducing the manufacturing cost is more preferably 0.0005% or more, and further preferably 0.0010% or more.
- Al: 0.001% to 2.00% Al suppresses the production of iron-based carbides and increases the strength and formability of the steel sheet. However, if the Al content exceeds 2.00%, the weldability deteriorates, so the upper limit of the Al content is 2.00%. From this point of view, the Al content is more preferably 1.50% or less, and further preferably 1.20% or less. On the other hand, the lower limit of the Al content is not particularly defined, but the effect of the present invention is exhibited. However, Al is an inevitable impurity present in a very small amount in the raw material, and its content is less than 0.001%. Is accompanied by a significant increase in manufacturing cost, so the Al content is 0.001%. Al is an element that is also effective as a deoxidizer, but in order to obtain a sufficient deoxidation effect, the Al content is more preferably 0.010% or more.
- N 0.0001 to 0.0100% N forms coarse nitrides and deteriorates ductility and stretch flangeability, so it is necessary to suppress the amount of addition. If the N content exceeds 0.0100%, the tendency becomes remarkable, so the upper limit of the N content is set to 0.0100%. From this point of view, the N content is more preferably 0.0070% or less, and further preferably 0.0050% or less. Moreover, since N causes the generation
- O forms an oxide and deteriorates ductility and stretch flangeability, so the content needs to be suppressed. If the O content exceeds 0.0100%, the stretch flangeability deteriorates significantly, so the upper limit of the O content is 0.0100%. Further, the O content is more preferably 0.0070% or less, and further preferably 0.0050% or less. Further, the lower limit of the O content is not particularly defined, and the effects of the present invention are exhibited. However, if the O content is less than 0.0001%, a significant increase in manufacturing cost is caused. 0.001% is the lower limit. Further, the content of O from the viewpoint of further reducing the manufacturing cost is more preferably 0.0003% or more, and further preferably 0.0005% or more.
- Cr: 0.01-2.00% Cr 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. If the Cr content exceeds 2.00%, the hot workability is impaired and the productivity is lowered. Therefore, the Cr content is preferably 2.00% or less. The lower limit of the Cr content is not particularly defined, and the effects of the present invention are exhibited. However, in order to sufficiently obtain a high strength by Cr, the content may be 0.01% or more. preferable.
- Ni 0.01-2.00%
- Ni 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. If the Ni content exceeds 2.00%, weldability is impaired, so the Ni content is preferably 2.00% or less.
- the lower limit of the content of Ni is not particularly defined, and the effect of the present invention is exhibited. However, in order to sufficiently obtain a high strength by Ni, the content may be 0.01% or more. preferable.
- Cu: 0.01-2.00% 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. If the Cu content exceeds 2.00%, weldability is impaired, so the content is preferably 2.00% or less. The lower limit of the Cu content is not particularly defined, and the effect of the present invention is exhibited. However, in order to sufficiently obtain the high strength by Cu, the content is preferably 0.01% or more. .
- Ti 0.001 to 0.150%
- Ti is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization.
- the Ti content is preferably 0.150% or less.
- the Ti content is more preferably 0.100% or less, and further preferably 0.070% or less.
- the lower limit of the Ti content is not particularly defined, and the effects of the present invention are exhibited.
- the Ti content should be 0.001% or more. Preferably, it is 0.005% or more.
- the Ti content is more preferably 0.010% or more, and further preferably 0.015% or more.
- Nb 0.001 to 0.100%
- Nb is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization.
- the Nb content is preferably 0.150% or less.
- the content of Nb is more preferably 0.100% or less, and further preferably 0.060% or less.
- the lower limit of the Nb content is not particularly defined, and the effects of the present invention are exhibited.
- the Nb content should be 0.001% or more. Preferably, it is 0.005% or more.
- the Nb content is more preferably 0.010% or more, and further preferably 0.015% or more.
- V 0.001 to 0.300%
- V is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization.
- the content is preferably 0.300% or less.
- the lower limit of the content of V is not particularly defined, and the effects of the present invention are exhibited.
- the content is preferably 0.001% or more. .
- Mo 0.01-2.00%
- 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. If the Mo content exceeds 2.00%, the hot workability is impaired and the productivity is lowered, so the Mo content is preferably 2.00% or less, and 1.00 More preferably, it is% or less. The lower limit of the Mo content is not particularly defined, and the effect of the present invention is exhibited. However, in order to sufficiently obtain the effect of increasing the strength by Mo, the content is 0.01% or more. Is preferred.
- W: 0.01-2.00% W is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and may be added in place of a part of C and / or Mn. If the W content exceeds 2.00%, hot workability is impaired and productivity is lowered, so the W content is preferably 2.00% or less, and 1.00 More preferably, it is% or less. The lower limit of the content of W is not particularly defined, and the effects of the present invention can be exhibited. However, in order to sufficiently obtain a high strength by W, the content is preferably 0.01% or more. .
- B 0.0001 to 0.0100%
- 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. If the B content exceeds 0.0100%, the hot workability is impaired and the productivity is lowered. Therefore, the B content is preferably 0.0100% or less. Further, from the viewpoint of productivity, the content of B is more preferably 0.0050% or less, and further preferably 0.0030% or less. The lower limit of the B content is not particularly defined, and the effects of the present invention are exhibited. However, in order to sufficiently obtain a high strength by B, the B content should be 0.0001% or more. preferable. In order to further increase the strength of the steel sheet, the B content is more preferably 0.0003% or more, and more preferably 0.0005% or more.
- Ca, Ce, Mg, Zr, La, and REM are effective elements for improving moldability, and one or more of them can be added. However, if the total content of one or more of Ca, Ce, Mg, Zr, La, and REM exceeds 0.5000%, the ductility may be adversely affected. The total is preferably 0.5000% or less, and more preferably 0.0100% or less. 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, but the effect of improving the formability of the steel sheet is exhibited. In order to obtain it sufficiently, the total content of each element is preferably 0.0001% or more.
- the total content of one or more of Ca, Ce, Mg, Zr, La, and REM is more preferably 0.0005% or more, and 0.0010% or more. More preferably it is.
- 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.
- the balance of the above elements may be Fe and inevitable impurities. It should be noted that any of the aforementioned Cr, Ni, Cu, Ti, Nb, V, Mo, W, and B may contain a trace amount less than the lower limit as an impurity. Also, 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 thickness of the decarburized layer in the steel sheet surface layer part is 0.01 to 10.0 ⁇ m, and the average particle diameter of the oxide contained in the steel sheet surface layer part is 30 to 120 nm.
- the average density is 1.0 ⁇ 10 12 pieces / m 2 or more.
- Decarburized layer In this invention, in order to improve the adhesiveness of the plating layer provided in the steel plate surface, a steel plate surface layer part is made into a decarburized layer with few hard structures. If the thickness of the decarburized layer is less than 0.01 ⁇ m, sufficient adhesion of the plating layer cannot be obtained, so the thickness of the decarburized layer is set to 0.01 ⁇ m or more. In order to further improve the adhesion of the plating layer, the thickness of the decarburized layer is more preferably 0.08 ⁇ m or more, and further preferably 0.15 ⁇ m or more. On the other hand, an excessively thick decarburized layer reduces the tensile strength and fatigue strength of the steel sheet.
- the thickness of the decarburized layer in the steel sheet surface layer portion is set to 10.0 ⁇ m or less. Further, from the viewpoint of fatigue strength, the thickness of the decarburized layer is more preferably 9.0 ⁇ m or less, and further preferably 8.0 ⁇ m or less.
- the decarburized layer described in the present invention is a region that is continuous from the outermost surface of the ground iron, and in this region, the region where the hard tissue fraction is less than or equal to half of the hard tissue fraction at 1 ⁇ 4 thickness. Shall be pointed to.
- the thickness of the decarburized layer is determined by finishing the cross section parallel to the rolling direction of the steel plate and perpendicular to the plate surface to a mirror surface and observing with FE-SEM. Measure and use the average value as the thickness of the decarburized layer.
- the hard structure described in the present invention refers to a structure composed of a phase harder than ferrite, that is, a structure composed mainly of phases such as bainite, bainitic ferrite, martensite and tempered martensite, and retained austenite. Shall. The fraction is based on the volume fraction.
- the oxide density is 1.0 ⁇ 10 12 pieces / m 2 or more. From the above viewpoint, the oxide density is more preferably 3.0 ⁇ 10 12 pieces / m 2 or more, and further preferably 5.0 ⁇ 10 12 pieces / m 2 or more.
- the oxide density is preferably limited to 1.0 ⁇ 10 16 pieces / m 2 or less.
- the oxide density is more preferably 5.0 ⁇ 10 15 pieces / m 2 or less, and 1.0 ⁇ 10 15 pieces / m 2. More preferably, it is as follows.
- the average particle diameter of the oxide is specified to be 30 nm or more in the present invention.
- the average particle diameter of the oxide is set to 500 nm or less.
- the average particle diameter of the oxide is more preferably 300 nm or less, further preferably 120 nm or less, and further preferably 100 nm or less. Further, in order to make the average particle size of the oxide less than 30 nm, it is necessary to strictly control the treatment atmosphere and temperature, and it is difficult in practical use.
- the oxide on the surface layer of the steel sheet as described above is observed with a FE-SEM by finishing a cross section parallel to the rolling direction of the steel sheet and having a mirror surface.
- the density of the oxide is obtained by observing the decarburized layer at 7 ⁇ m for 2 minutes and counting the number of oxides, or using the observation area required to count 1000 oxides.
- the oxide size is the average particle diameter obtained by averaging 100 to 1000 randomly selected equivalent circle diameters.
- a high-strength hot-dip galvanized steel sheet or a high-strength galvannealed steel sheet is formed by forming a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface of the steel sheet having the above structure. Is done.
- a high-strength hot-dip galvanized steel sheet having excellent corrosion resistance is obtained by forming a hot-dip galvanized layer on the surface of the steel sheet.
- an alloyed hot-dip galvanized layer on the surface of the steel plate a high-strength galvannealed steel plate having excellent corrosion resistance and excellent paint adhesion can be obtained.
- Machine cutting characteristics described in the present invention can be measured and evaluated by, for example, the method described below.
- the shear blades and the leading ends of the punches are worn and clearance is increased. For this reason, when the number of times of punching the steel sheet increases, the burrs on the shear cutting end face and the punching end face increase.
- a steel sheet having a thickness of 1.2 mm is formed by using a die having a hole diameter of 10.3 mm ⁇ , a punch material SKD11, a punch diameter of 10 mm ⁇ (clearance 12). .5%), a method of continuously punching and measuring the burr height every 50 times can be employed.
- the burr height increases because the punch tip wears and the clearance increases as the number of punches of the steel sheet increases.
- the punched hole is divided into four at 0 °, 90 °, 180 °, and 270 ° positions, and the test is completed when the burr height in any one direction exceeds 3.0 times the initial value.
- the number of punches at this time was defined as the limit number of punches.
- the maximum burr height in the range of 0 ° to 90 ° is h1
- the maximum burr height in the range of 90 ° to 180 ° is h2
- 180 ° to The maximum burr height in the range of 270 ° is h3
- the maximum burr height in the range of 270 ° to 360 ° is h4.
- the burr height when punched for the first time is h1 *, h2 *, h3 *, h4 *, and any one of h1 / h1 *, h2 / h2 *, h3 / h3 *, h4 / h4 *
- the number of punches when the above exceeds 3.0 is the limit number of punches.
- the test was performed so that the relative direction in the cold rolling direction of the punching punch, the die, and the steel plate was not changed, and the progress direction of the cold rolling was set to 0 ° in the rolling direction of the steel plate.
- a steel sheet having a number of punches exceeding 600 can be defined as a high-strength hot-dip galvanized steel sheet having excellent mechanical cutting characteristics. More preferably, the limit number of punching is 800 times, and more preferably 1000 times.
- the high-strength hot-dip galvanized steel sheet of this embodiment has an average work hardening coefficient (n value) of 0.080 or more at the time of plastic deformation of 3 to 7%.
- the work hardening coefficient (n value) defined in the present invention is a characteristic value that serves as a guide for drawing workability (ductility).
- the n value for improving ductility is specified to be 0.080 or more.
- the upper limit of the n value is not particularly defined, but in order to make the n value on average over 3-50% plastic deformation more than 0.250, the maximum tensile strength should be less than 900 MPa, or 0.40% Since it is necessary to add an excessive amount of C, it is not preferable.
- the n value is preferably 0.200 or less, and more preferably 0.180 or less from the viewpoint of tensile strength.
- the plastic deformation of 3 to 7% is a range of plastic working of a steel plate that is usually frequently used.
- the retained austenite phase when the retained austenite phase is contained by 3% or more in the steel sheet structure, the work hardening ability is enhanced, and the n value is 0.080 or more on average and has high ductility.
- the amount of dissolved carbon in the retained austenite phase is limited to 0.70 to 1.00%, the average particle diameter is 2.0 ⁇ m or less, and the average distance between particles is suppressed to 5.0 ⁇ m.
- mechanical cutting characteristics are improved. Thereby, it is possible to obtain both excellent ductility and mechanical cutting characteristics while ensuring high tensile strength.
- the maximum tensile strength is preferably 900 MPa or more as the steel plate strength. This is because, in a high-strength steel plate of 900 MPa or more, the strength at which tool deterioration during shear cutting or punching becomes significant. Moreover, even if it is a steel plate less than 900 MPa, although the effect of the mechanical cutting characteristic improvement which is the effect of this invention can be enjoyed, the effect is small in the steel plate with low tensile strength. For this reason, in this invention, it is preferable to apply to the high intensity
- the manufacturing method of the high-strength hot-dip galvanized steel sheet according to the present embodiment is such that the slab having the above-described chemical components is first or directly cooled and then heated to 1180 ° C. or higher, and a heat at a rolling completion temperature of 850 to 950 ° C. After the hot rolling, the steel sheet is rapidly cooled to 500 to 650 ° C. at an average cooling rate of 10 ° C./s or more, wound around a coil, and gradually cooled to 400 ° C.
- the pickling step is followed by a cold rolling step in which cold rolling is performed with a total rolling reduction of 30 to 75%.
- the steel sheet after the cold rolling process is heated to 750 ° C. or higher with an average heating rate between 600 and 750 ° C. being 20 ° C./s or less, and then an average cooling rate between 750 and 650 ° C. Is cooled to 1.0 to 15.0 ° C./s, the average cooling rate from 650 ° C. is set to 3.0 ° C./s or more, and is kept in the temperature range of 300 to 470 ° C. for 20 to 1000 seconds.
- An annealing process is provided in which a bending process is performed at least once with a bending radius of 800 mm or less while applying a tension of 5 to 100 MPa in the temperature range.
- the plating bath temperature 450 to 470 ° C.
- the steel plate temperature when entering the plating bath 430 to 490 ° C.
- the effective Al amount in the plating bath 0.01 to 0.18 mass
- the steel plate is dipped in a galvanizing bath under the condition of% to provide a plating step of forming a plating layer by performing hot dip galvanizing on the steel plate surface.
- the cooling process of cooling at an average cooling rate of 0.5 degrees C / s or more to 150 degrees C or less is provided after a plating process.
- the annealing step in the mixed gas of air and fuel gas used for the preheating burner, the volume of air contained in the unit volume of mixed gas and the fuel gas contained in the unit volume of mixed gas are completely changed.
- the air ratio is 0.7 to 1.2, which is the ratio of the theoretically required air volume for burning, the steel plate is passed while heating to a steel plate temperature of 400 to 800 ° C.
- a slab having the above chemical component (composition) is cast.
- a slab to be used for hot rolling for example, a continuous cast slab, a thin slab caster or the like can be used.
- the method for producing a high-strength steel sheet according to the present invention is compatible with a process such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.
- CC-DR continuous casting-direct rolling
- the heating temperature of the slab is set to 1180 ° C. or higher in order to relax the crystal orientation anisotropy caused by casting.
- the heating temperature of the slab is more preferably 1200 ° C. or higher.
- the upper limit of the heating temperature of this slab is not particularly defined, it is preferable to set the heating temperature to 1300 ° C. or lower because a large amount of energy needs to be input to heat the slab beyond 1300 ° C.
- the rolling completion temperature of hot rolling is set to 850 to 950 ° C. If the rolling completion temperature is less than 850 ° C., the rolling reaction force is excessively increased and the process load is increased. Therefore, in the present invention, this temperature is set to 850 ° C. or higher, and more preferably 870 ° C. or higher. On the other hand, when the rolling completion temperature exceeds 950 ° C., the microstructure in the hot-rolled steel sheet becomes coarse, and the microstructure after the cold rolling and annealing steps becomes coarse. It is 950 degrees C or less, and it is more preferable to set it as 930 degrees C or less.
- the average cooling rate when rapidly cooling to 500 to 600 ° C. is preferably 10 ° C./s or more. This is because the grain size of the hot-rolled steel sheet is made fine by proceeding transformation at a lower temperature, and the effective crystal grain size after cold rolling and annealing is made fine.
- the upper limit of the average cooling rate is not particularly defined, but if it exceeds 200 ° C./s, it is necessary to use a special refrigerant, which is not preferable in terms of cost.
- the steel sheet After the steel sheet is cooled rapidly, it is wound up as a hot rolled coil.
- this step by forming “pearlite” and / or “coarse cementite having a major axis exceeding 1 ⁇ m” in the steel sheet after hot rolling, a set of various transformation structures is formed in the annealing step after cold rolling described later. Tissue and morphology can be random.
- the cooling stop temperature of the rapid cooling after hot rolling is set to 500 ° C. or higher in the present invention.
- the cooling stop temperature is more preferably 530 ° C. or higher, and further preferably 550 ° C. or higher.
- the cooling stop temperature needs to be 650 ° C. or lower. From the above viewpoint, the cooling stop temperature is preferably 630 ° C. or lower. In the present invention, the steel sheet having the cooling stop temperature of 500 to 650 ° C. is wound as a hot rolled coil.
- the elapsed time which cools slowly from a rapid cooling stop to 400 degreeC shall be 1.0 hour or more.
- the elapsed time is more preferably 2.0 hours or more, and further preferably 3.0 hours or more.
- special equipment is required to stop the vehicle for more than 24.0 hours, which is not preferable in terms of cost, and is preferably set to 24.0 hours or less.
- pickling treatment is performed on the hot-rolled steel sheet manufactured under the above conditions.
- Pickling is important because it can remove oxides on the surface of the steel sheet, and thus improves the hot dip galvanizing property of the high-strength hot-dip galvanized steel sheet or high-strength galvannealed steel sheet.
- the pickling may be performed only once or may be performed in multiple steps.
- the steel plate after pickling is rolled so that the total rolling reduction is not less than 30% and not more than 75%.
- the rolling is preferably performed in a plurality of passes, and the number of rolling passes and the distribution of the rolling reduction to each pass are not questioned. If the rolling reduction of cold rolling is less than 30%, sufficient strain is not accumulated in the steel sheet, and in the subsequent annealing process, the recrystallized structure does not proceed sufficiently and the processed structure remains and the structure becomes coarse. In addition, the average distance between the particles of the retained austenite phase is increased, and the cutting property is deteriorated. In order to accumulate strain sufficiently, the total rolling reduction is more preferably 33% or more, and further preferably 36% or more.
- the total rolling reduction in cold rolling is set to 75% or less.
- the total rolling reduction is preferably 70% or less, and more preferably 65% or less.
- the steel sheet rolled under the above conditions is subjected to an annealing process in an annealing process under the following conditions, followed by a hot dip galvanizing process in the plating process.
- an annealing process in an annealing process under the following conditions, followed by a hot dip galvanizing process in the plating process.
- the pre-tropical atmosphere may be any of an oxidizing atmosphere, a non-oxidizing atmosphere, and a direct reducing atmosphere.
- the annealing process set as the above condition is performed in the mixed gas of air and fuel gas used for the preheating burner in a unit volume mixed gas.
- Condition of air ratio 0.7 to 1.2, which is the ratio of the volume of air contained and the volume of air theoretically required to completely burn the fuel gas contained in the unit volume of mixed gas
- P (H 2 O) / H 2 O and H 2 P (H 2 ) By heating to 750 ° C.
- the plating step after the annealing step is as follows: plating bath temperature: 450 to 470 ° C., steel plate temperature when entering the plating bath: 430 to 490 ° C., effective amount of Al in the plating bath: 0.01 to 0.18 mass%
- the hot dip galvanizing can be performed under the condition that the steel sheet is immersed in the galvanizing bath.
- the heating rate in the annealing process affects the recrystallization behavior in the steel sheet.
- the heating rate at 600 to 750 ° C. is important.
- the average heating rate is more preferably 15 ° C./s or less, and further preferably 12 ° C./s or less.
- the minimum in particular of an average heating rate is not defined, since productivity will fall remarkably when an average heating rate is less than 0.5 degree-C / s, it is preferable to set it as 0.5 degree-C / s or more.
- the temperature of the steel sheet when passing through the pre-tropical zone is 400 to 800 ° C.
- the air ratio ⁇ [the mixed gas of air and fuel gas used in the preheating burner, The ratio of the volume of air theoretically required to completely burn the fuel gas contained in the mixed gas of the volume] [volume of air contained in the unit volume of mixed gas (m 3 )] / [unit volume of By preheating under the condition that the volume of air (m 3 )] ⁇ theoretically necessary for complete combustion of the fuel gas contained in the mixed gas is 0.7 to 1.2, the surface layer of the steel sheet is reduced to 0.
- An Fe oxide film of 0.01 to 20 ⁇ m is formed.
- the oxide film serves as an oxygen supply source for generating an oxide of Si and / or Mn in the reduction zone, when the air ratio is too small as less than 0.7, a predetermined oxide is used. Cannot be obtained.
- the steel sheet temperature when passing through the pre-tropical zone is less than 400 ° C., a sufficient oxide film cannot be formed.
- the oxide film grows excessively. It becomes difficult to keep the thickness within a predetermined range.
- the maximum heating temperature in the annealing process is low, coarse cementite remains undissolved and ductility deteriorates remarkably.
- the maximum heating temperature is 750 ° C. or higher, and more preferably 760 ° C. or higher.
- the upper limit of the heating temperature is not particularly defined, but heating exceeding 1000 ° C significantly deteriorates the surface quality and deteriorates the wettability of the plating, so the maximum heating temperature may be 1000 ° C or less. Preferably, it is 950 degrees C or less.
- the maximum heating temperature (750 ° C. or higher) in the annealing process is preferably reached in the reduction zone.
- the Fe oxide film formed in the oxidation zone is reduced to form a decarburized layer, and Si and / or Mn oxide is appropriately dispersed. 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 is formed only on the outermost surface layer, and Si and / or Mn oxide is moderately contained inside the decarburized layer. It becomes difficult to disperse.
- P (H 2 O) / P (H 2 ) exceeds 2.00, decarburization proceeds excessively, and the thickness of the decarburized layer may not be controlled within a predetermined range.
- P (H 2 O) / P (H 2 ) is more preferably in the range of 0.001 to 1.50, and further preferably in the range of 0.002 to 1.20.
- the average cooling rate from the maximum heating temperature described above is important for sufficiently generating ferrite. Therefore, in the present invention, the average cooling rate up to 750 to 650 ° C., which is the temperature range where ferrite is generated, is set to 1.0 to 15.0 ° C./s. When the average cooling rate from the maximum heating temperature exceeds 15.0 ° C./s, a sufficient amount of ferrite may not be obtained, and ductility deteriorates. On the other hand, if the average cooling rate is less than 1.0 ° C./s, a sufficient amount of hard structure cannot be obtained due to excessive generation of ferrite or generation of pearlite, and the strength deteriorates.
- the average cooling rate from the steel plate temperature of 650 ° C. until the cooling is stopped to enter the plating bath is preferably 3.0 ° C./s or more. This is to obtain a hard structure having a more random crystal orientation by further lowering the transformation temperature to the hard structure.
- the average cooling rate is more preferably 5.0 ° C./s or more.
- the upper limit of the average cooling rate is not particularly defined, a special cooling facility is required to obtain an average cooling rate exceeding 200 ° C./s.
- the composition of the plating bath is mainly composed of zinc, and the effective Al amount, which is a value obtained by subtracting the total Fe amount from the total Al amount in the bath, is preferably 0.01 to 0.20% by mass, More preferably, the content is 0.18% by mass.
- the amount of effective Al in the bath is more preferably 0.07 to 0.12% by mass in order to control the progress of alloying of the plating layer.
- the effective amount of Al in the bath may be in the range of 0.18 to 0.20 mass%.
- the plating bath temperature is preferably 450 ° C. to 470 ° C. When the plating bath temperature is less than 450 ° C., the viscosity of the plating bath is excessively increased, and it becomes difficult to control the thickness of the plating layer, and the appearance of the steel sheet is impaired.
- the plating bath temperature is preferably 470 ° C. or less.
- the temperature of the steel sheet entering the plating bath is preferably 430 ° C. to 490 ° C. If the steel sheet temperature when the steel sheet enters the plating bath is lower than 430 ° C., it is necessary to apply a large amount of heat to the plating bath in order to stabilize the plating bath temperature to 450 ° C. or higher, which is not practical.
- the steel sheet in order to sufficiently obtain retained austenite, the steel sheet is retained in the range of 300 to 470 ° C. before and / or after being immersed in the plating bath, and the bainite transformation is advanced.
- the dwell time in the range of 300 to 470 ° C. is 20 to 1000 seconds, including the time for dipping in the plating bath. If the retention time is less than 20 seconds, the bainite transformation does not proceed sufficiently, and the concentration of carbon to the retained austenite becomes insufficient.
- the retention time is more preferably 35 seconds or more, and further preferably 50 seconds or more.
- the retention time exceeds 1000 seconds, carbon is excessively concentrated in the retained austenite, or generation of cementite starts and predetermined characteristics cannot be obtained.
- the retention time is preferably 600 seconds or less, and more preferably 450 seconds or less.
- nucleation of bainite and / or bainitic ferrite is promoted and austenite of the parent phase is finely divided by nucleation from various parts of the steel sheet. It is valid. For this reason, bending deformation is performed between 300 and 470 ° C. with tensile stress applied to the steel sheet, and nucleation of a large number of bainite and / or bainitic ferrite is promoted.
- the stress at this time is 3 to 100 MPa with the rolling direction as the tensile axis. If the applied stress is less than 3 MPa, the effect of promoting nucleation is not recognized, so this is the lower limit.
- the load stress is more preferably 5 MPa or more, and further preferably 7 MPa or more.
- the load stress is set to 100 MPa or less.
- the load stress is more preferably 70 MPa or less, and further preferably 50 MPa or less.
- the bending radius is preferably set to 650 mm or less.
- the lower limit of the bending radius is not particularly set.
- the bending radius is preferably 50 mm or more, and more preferably 100 mm or more. .
- the number of bending processes is set to 1 or more, and more preferably, 2 or more times since nucleation is promoted as the degree of processing increases.
- the upper limit of the number of times of processing is not particularly defined, it is difficult to perform bending processing of 20 times or more within the retention time in the temperature range, and the number of processing times is preferably 20 times or less.
- an alloying treatment of the plated layer on the steel sheet surface may be further performed at a temperature of 470 to 620 ° C.
- a Zn—Fe alloy formed by alloying the hot dip galvanized layer is formed on the surface, and a high-strength galvannealed steel sheet excellent in rust prevention is obtained.
- the alloying treatment temperature is set to 470 ° C. or higher because alloying does not proceed sufficiently if it is less than 470 ° C. Further, when the alloying treatment temperature exceeds 620 ° C., coarse cementite is generated and the strength is remarkably lowered. Therefore, in the present invention, the temperature is set to 620 ° C. or less.
- the alloying treatment temperature is more preferably 480 to 600 ° C., and further preferably 490 to 580 ° C.
- the alloying treatment time is not particularly limited, but it is necessary to take 2 seconds or more in order to sufficiently advance alloying, and it is preferably 5 seconds or more. On the other hand, if the alloying treatment time exceeds 200 seconds, the plating layer may be over-alloyed and the characteristics may be deteriorated. Therefore, the treatment time is 200 seconds or less, preferably 100 seconds or less.
- the alloying treatment is preferably performed immediately after immersion in the plating bath. However, after the immersion, the steel plate temperature may be allowed to cool to 150 ° C. or lower and then reheated to the alloying treatment temperature.
- the average cooling rate when cooling to 150 ° C. or lower after the plating treatment is less than 0.5 ° C./s, coarse cementite is produced, and there is a concern that strength and / or ductility deteriorates.
- the said average cooling rate shall be 0.5 degree-C / s or more, and it is more preferable to set it as 1.0 degree-C / s or more.
- the upper limit of the average cooling rate is not particularly defined, but a special cooling facility is required to obtain an average cooling rate exceeding 200 ° C./s. More preferably, it is s or less.
- the timing of performing the above-described bainite transformation treatment may be before or after the alloying treatment.
- reheating treatment may be performed for the purpose of tempering martensite during or after cooling.
- the heating temperature at the time of reheating is preferably 200 ° C. or higher because tempering does not proceed sufficiently if it is lower than 200 ° C.
- strength will deteriorate remarkably when heating temperature exceeds 620 degreeC, it is preferable to set it as 620 degrees C or less, and it is more preferable to set it as 550 degrees C or less.
- the high strength hot dip galvanized steel sheet or the high strength alloyed hot dip galvanized steel sheet cooled to room temperature is subjected to cold rolling with a rolling reduction of 3.00% or less for shape correction. It doesn't matter.
- the manufacturing method of this invention is not limited to the example mentioned above.
- Such a film made of phosphorus oxide and / or composite oxide containing phosphorus can function as a lubricant when processing the steel sheet, and protects the plating layer formed on the surface of the base steel sheet. Can do.
- the high-strength hot-dip galvanized steel sheet and high-strength galvannealed steel sheet with excellent mechanical cutting characteristics according to the present invention, as described above, in the steel component, steel sheet structure, steel sheet surface layer portion A configuration in which the thickness of the decarburized layer and the size of the oxide are defined within an appropriate range is adopted. That is, when the retained austenite phase is contained in the steel sheet structure in a predetermined amount or more, the work hardening ability is enhanced, and the strength and ductility of the steel sheet can be improved, while the amount of solute carbon in the retained austenite phase is limited and the average particle size is increased.
- the mechanical cutting characteristics (punching workability) at the time of processing the steel sheet are improved. Furthermore, the adhesiveness of a plating layer improves by restrict
- the steel components are within an appropriate range, hot rolling and cold rolling, and annealing conditions after rolling.
- the method of restricting to a predetermined range is adopted.
- the thickness of the decarburized layer, the average particle diameter of the oxide, and the average density in the steel sheet surface layer portion can be limited to a predetermined range, the adhesion of the plating layer can be improved. Therefore, it is possible to produce a high-strength hot-dip galvanized steel sheet and a high-strength galvannealed steel sheet that can obtain excellent ductility and mechanical cutting characteristics while ensuring a maximum tensile strength of 900 MPa or more as described above. Become.
- the high strength hot dip galvanized steel sheet, the high strength alloyed hot dip galvanized steel sheet and the manufacturing method thereof, which are excellent in mechanical cutting characteristics of the present invention, and the production method thereof, particularly in the automobile field, are associated with safety associated with the enhancement of the strength of the vehicle body. It is possible to fully enjoy merits such as improvement of workability and workability at the time of member processing, and its social contribution is immeasurable.
- Step structure First, the structure of the steel sheet of each experimental example was observed using a scanning electron microscope (SEM), and the structure fraction of the steel sheet and the average distance and average particle diameter of the residual austenite phase were measured. 9-13.
- SEM scanning electron microscope
- the identification of ferrite, martensite, pearlite, cementite, bainite, austenite and the remaining structure, the observation of the existing position and the measurement of the area ratio are carried out using the Nital reagent and the reagent disclosed in JP-A-59-219473.
- the steel sheet in the rolling direction cross section or the cross section in the rolling direction perpendicular direction was corroded, and the 1/4 thickness position of the plate thickness was observed at 1000 to 10,000 times.
- the amount of solid solution carbon in the retained austenite phase was determined by performing an X-ray diffraction test under the same conditions as the measurement of the area fraction of the retained austenite phase described above to obtain the lattice number a of the retained austenite phase. ).
- Decarburized layer thickness, average oxide density and average particle size in steel sheet surface layer The thickness of the decarburized layer in the surface layer of the steel sheet is measured by measuring the thickness of the decarburized layer at three or more locations in one steel sheet by finishing the section of the plate thickness parallel to the rolling direction of each steel sheet to a mirror surface and observing it using FE-SEM The average value was taken as the thickness of the decarburized layer.
- the oxide in the surface layer portion of the steel plate first, as in the above, the plate thickness cross section parallel to the rolling direction is finished to a mirror surface and observed using FE-SEM, and then the decarburized layer is observed for 7 ⁇ m for 2 minutes. By counting the number of oxides, the oxide density was measured, and the results are shown in Tables 9 to 13 below. Regarding the size of this oxide, the average equivalent particle diameter was obtained by averaging the equivalent circle diameters of 100 to 1000 randomly selected oxide particles.
- plating peeling test JIS, which evaluates plating adhesion at the time of processing where compressive stress is applied to the steel sheet for the steel sheet produced by the above procedure.
- Metal material bending test method described in Z2248, a plating peeling test was performed. Specifically, as disclosed in the document “Hot-dip galvanized steel sheet manual, p53-55”, after performing a 60 ° V-shaped bending test using each steel plate, a tape was applied to the inside of the bent portion. Then, the tape was peeled off. Then, the plating adhesion was evaluated from the peeling state of the plating layer peeled off with the tape, and the results are shown in Tables 9 to 13 below.
- the nominal stress at the point where the nominal strain 3% is 7% is read from the test result of the tensile strength, and the nominal stress and the nominal strain are converted into the true stress and the true strain, respectively. It calculated
- required according to following Formula ⁇ n log ((sigma) 7% / (sigma) 4% ) / log ((epsilon) 7% / (epsilon) 4% )].
- the steel sheet having a uniform elongation of less than 7% was determined according to the above formula from the two points of the nominal strain of 3% and the point of maximum tensile stress.
- High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet are the volume fraction of the ferrite phase and residual austenite phase in the steel sheet structure, the amount of solute carbon in the residual austenite phase, the average particle diameter, and the average distance between particles, All of the thickness of the decarburized layer in the surface layer portion of the steel sheet, the average particle diameter and average density of the oxide, and the work hardening coefficient (n value) were within the range specified in claim 1 of the present invention.
- These steel sheets of the present invention are excellent in appearance characteristics and peeling characteristics of the plating surface, are excellent in yield stress, tensile strength, total elongation, and n-value tensile characteristics, and all have a limit punching number of 650 times. As described above, it can be seen that the machine cutting characteristics are excellent. Therefore, from these evaluation results, the high-strength hot-dip galvanized steel sheet and high-strength galvannealed steel sheet according to the present invention have excellent ductility and mechanical cutting characteristics at the same time while ensuring a maximum tensile strength of 900 MPa or more. It became clear that they would have both.
- the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet of the comparative example do not satisfy any of the steel components and production conditions specified in the present invention, and the steel sheet characteristics specified in the present invention Either is not satisfied.
- the comparative example as described below, any item of each tensile property, or any item of the steel sheet appearance and plating peeling property cannot satisfy the target property. became.
- the retention time at 300 to 470 ° C. in the annealing process greatly exceeded the specified range of the present invention, and the amount of solute carbon in the retained austenite phase greatly exceeded the specified range of the present invention. Since it exceeds the limit, the limit punching number is as low as 400 times, which indicates that the mechanical cutting characteristics are inferior.
- the hot dip galvanized steel sheet of Experimental Example 12 is an atmosphere in which the partial pressure ratio ⁇ P (H 2 O) / P (H 2 ) ⁇ of water vapor and hydrogen in the reduction zone in the annealing process is zero and almost no water vapor is contained.
- a decarburized layer is not generated in the steel plate surface layer portion.
- the average particle diameter of the oxide is large, the density of the oxide is low. Since the thickness of the decarburized layer, the average particle diameter of the oxide, and the density of the oxide all deviate from the specified range of the present invention, the limit punching number is extremely low, 300 times, and the mechanical cutting characteristics are inferior. I understand that.
- the maximum heating temperature of the slab in the hot rolling process is lower than the specified range of the present invention, and as a result, the n value is 0.076, which is lower than the specified range of the present invention. This shows that the ductility is inferior.
- the average cooling rate in the hot rolling process is lower than the specified range of the present invention, and both the average particle diameter of the retained austenite phase and the average distance between the particles are specified by the present invention. It is out of range. For this reason, the limit punching frequency is as low as 600 times, which indicates that the mechanical cutting characteristics are inferior.
- the cooling stop temperature in the hot rolling process is below the specified range of the present invention, and both the average particle diameter of the retained austenite phase and the average distance between the particles are defined by the present invention. It is out of range. For this reason, the limit number of times of punching is as low as 350 times, which indicates that the mechanical cutting characteristics are inferior.
- the alloyed hot-dip galvanized steel sheet of Experimental Example 48 is an example in which the peeling of the plating occurred in the plating peeling test because the treatment time when applying the alloying treatment to the plated layer after the plating process was extremely long. .
- the average cooling rate at 750 to 650 ° C. in the annealing process is lower than the specified range of the present invention, and the volume fraction of the bainite phase and bainitic ferrite phase in the steel sheet structure is On the other hand, the martensite phase, the tempered martensite phase, the retained austenite phase and other phases are not formed. For this reason, it turns out that the yield stress and the tensile strength are low and the strength characteristics are inferior.
- the average cooling rate after the plating step is lower than the specified range of the present invention, so the volume fraction of the retained austenite phase in the steel sheet structure is lower than the specified range of the present invention.
- the volume fraction of other tissues is high.
- the average distance between the grains of the retained austenite phase exceeds the specified range of the present invention. For this reason, it turns out that a yield stress, tensile strength, and total elongation become low, and it turns out that it is inferior to an intensity
- the rolling completion temperature in the hot rolling process exceeds the specified range of the present invention, so that both the average particle diameter and the average inter-particle distance of the retained austenite phase are The specified range is exceeded.
- the limit punching frequency is as low as 250 times, which indicates that the mechanical cutting characteristics are inferior.
- the alloyed hot-dip galvanized steel sheet of Experimental Example 72 has a volume fraction of retained austenite phase in the steel sheet structure because the processing temperature when the alloying process is performed on the plated layer after the plating process exceeds the specified range of the present invention. Is below the specified range of the present invention, while the volume fraction of other tissues is high. Moreover, while the amount of solid solution carbon in a residual austenite phase is less than the prescription
- the retention time at 300 to 470 ° C. in the annealing process exceeds the specified range of the present invention, and the amount of solute carbon in the retained austenite phase falls within the specified range of the present invention. Since it is greatly exceeded, it can be seen that the limit punching number is as low as 350 times, and the mechanical cutting characteristics are inferior.
- the retention time at 300 to 470 ° C. in the annealing process is below the specified range of the present invention, and the volume fraction of the retained austenite phase is below the specified range of the present invention. Since the volume fraction of the martensite phase is high, the amount of dissolved carbon in the retained austenite phase is below the specified range of the present invention, and the average distance between particles exceeds the specified range of the present invention. Yes. For this reason, it turns out that an n value is as low as 0.060 and it is inferior to a machine cutting characteristic.
- the hot-dip galvanized steel sheets of Experimental Examples 121 to 123 are examples in which chemical components deviate from a predetermined range.
- Experimental Example 121 since the C amount is less than the lower limit specified in the present invention, a large amount of ferrite phase is generated in the steel sheet structure, resulting in low tensile strength and inferior strength characteristics. I understand that.
- Experimental Example 122 since the amount of C exceeds the upper limit defined in the present invention, a large amount of retained austenite phase is generated in the steel sheet structure, resulting in a low n value and poor ductility. Recognize.
- Experimental Example 123 since the amount of Mn is less than the lower limit specified in the present invention, a large amount of ferrite phase is generated in the steel sheet structure, resulting in low tensile strength and poor strength characteristics. Recognize.
- the alloyed hot-dip galvanized steel sheet of Experimental Example 124 is an example in which the tension in the temperature range of 300 to 470 ° C. exceeded the specified range of the present invention in the annealing process.
- the thickness of the steel sheet after the annealing process is reduced compared to the thickness of the steel sheet before the annealing process, and the experiment is stopped without obtaining a predetermined thickness accuracy.
- Experimental example 125 is an example in which the content of Si was large and the steel plate was broken in the cold rolling process, and the experiment was stopped.
- the alloyed hot-dip galvanized steel plate of Experimental Example 126 has a low Si content, and oxide generation at the surface layer portion of the steel sheet is not appropriate, and the oxide density deviates from the specified range of the present invention. For this reason, the limit punching number is as extremely low as 400 times, which indicates that the mechanical cutting characteristics are inferior.
- Experimental example 127 is an example in which the content of Mn is large and the slab breaks between the completion of casting and the hot rolling process, and the experiment is stopped.
- Experimental example 128 is an example in which the content of Al is large and the portions welded to the front and rear steel plates in the annealing process are broken and the experiment is stopped.
- the high-strength hot-dip galvanized steel sheet and the high-strength galvannealed steel sheet excellent in mechanical cutting characteristics of the present invention have excellent ductility while ensuring high strength of a tensile maximum strength of 900 MPa or more. It is clear that it has high machine cutting characteristics without deteriorating processing equipment and the like.
- the present invention for example, in the use of a member obtained by forming a steel sheet by press working or the like, excellent ductility and mechanical cutting characteristics can be obtained while ensuring a high tensile strength of 900 MPa or more. Strength and workability can be obtained simultaneously.
- the present invention for example, by applying the present invention to the field of automobile members, etc., it is possible to fully enjoy merits such as improved safety associated with increased strength of the vehicle body and improved workability during the manufacture of members. And its social contribution is immeasurable.
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Abstract
Description
即ち、本発明の要旨は以下のとおりである。
[2] さらに、質量%で、Ti:0.001~0.150%、Nb:0.001~0.100%、V:0.001~0.300%の1種または2種以上を含有することを特徴とする上記[1]に記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。
[3] さらに、質量%で、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1種または2種以上を含有することを特徴とする上記[1]または[2]に記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。
[4] さらに、質量%で、Ca、Ce、Mg、Zr、La、REMの1種または2種以上を合計で0.0001~0.0100%含有することを特徴とする上記[1]~[3]の何れかに記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。
[5] 上記[1]~[4]の何れかに記載の高強度溶融亜鉛めっき鋼板のめっき層が合金化されてなることを特徴とする機械切断特性に優れた高強度合金化溶融亜鉛めっき鋼板。
[7] 上記[6]に記載の方法で熱延工程、冷延工程、焼鈍工程、めっき工程までを行った後、さらに、前記めっき工程で形成されためっき層に470~620℃の温度で合金化処理を施すことを特徴とする機械切断特性に優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
本実施形態の機械切断特性に優れた高強度溶融亜鉛めっき鋼板(以下、単に高強度溶融亜鉛めっき鋼板と略称することがある)は、質量%で、C:0.075~0.400%、Si:0.01~2.00%、Mn:0.80~3.50%、P:0.0001~0.100%、S:0.0001~0.0100%、Al:0.001~2.00%、N:0.0001~0.0100%、O:0.0001~0.0100%を含有し、残部が鉄および不可避的不純物からなる鋼板の表面にめっき層を有してなる。また、本実施形態の高強度溶融亜鉛めっき鋼板は、板厚0.6~5.0mmである。また、本実施形態の高強度溶融亜鉛めっき鋼板は、鋼板の表面から板厚の1/4を中心とした1/8厚~3/8厚の範囲において、鋼板組織が、少なくとも体積分率で40~90%のフェライト相、および、3%以上の残留オーステナイト相を含み、この残留オーステナイト相は、相中における固溶炭素量が0.70~1.00%であり、平均粒子径が2.0μm以下であるとともに、粒子間の平均距離が0.1~5.0μmとされている。さらに、本実施形態の高強度溶融亜鉛めっき鋼板は、鋼板表層部における脱炭層の厚さが0.01~10.0μmであり、鋼板表層部に含まれる酸化物の平均粒子径が30~120nmであるとともに、その平均密度が1.0×1012個/m2以上とされている。そして、本実施形態の高強度溶融亜鉛めっき鋼板は、3~7%の塑性変形時における加工硬化係数(n値)が平均で0.080以上とされている。
ここで、鋼板の表面から板厚の1/4を中心とした1/8厚~3/8厚の範囲とは、鋼板の表面から板厚の1/4を中心とした1/8厚~鋼板の表面から板厚の1/4を中心とした3/8厚の範囲をいう。また、この範囲の組織に注目しているのは、この範囲の組織は鋼板表層部の脱炭層を除いた鋼板全体の組織を代表するものであると考えてよいからである。すなわち、1/8厚~3/8厚の範囲で上記のような鋼板組織であれば、鋼板表層部の脱炭層を除いた鋼板全体が上記のような組織であると判断できるからである。
本発明の高強度溶融亜鉛めっき鋼板の板厚は0.6~5.0mmである。板厚が0.6mm未満では鋼板の形状を平坦に保つことが困難であり、適当ではない。したがって、板厚は0.6mm以上であることが好ましい。また、5.0mmを超えると曲げ加工に伴うひずみが入らず、ベイナイトの微細分散化が困難となり、所定の鋼板組織を生成することが困難になる。したがって、板厚は5.00mm以下であることが好ましい。
本発明の高強度溶融亜鉛めっき鋼板の鋼板組織は、鋼板の表面から板厚の1/4を中心とした1/8厚~3/8厚の範囲において、鋼板組織が、少なくとも体積分率で40~90%のフェライト相、および、3%以上の残留オーステナイト相を含む。また、残留オーステナイト相は、相中における固溶炭素量が0.70~1.00%であり、平均粒子径が2.0μm以下であるとともに、粒子間の平均距離が0.1~5.0μmである。
残留オーステナイト相は加工硬化能を高め、強度および延性を向上させる組織であり、本発明においては、残留オーステナイト相の体積分率は3%以上とする。また、延性をさらに高めるためには、残留オーステナイト相の体積分率を5%以上とすることがより好ましく、7%以上とすることがさらに好ましい。一方、30%を超える残留オーステナイト相を得るには、CやMn等のオーステナイト安定化元素を多量に添加する必要があり、溶接性が著しく劣化してしまう。したがって、本発明では、残留オーステナイト相の体積分率を30%以下とすることが好ましい。また、溶接性の観点から、残留オーステナイト相の体積分率は25%以下であることが好ましく、20%以下であることがさらに好ましい。
なお、残留オーステナイトの体積分率は、鋼板の板面に平行かつ鋼板の表面から板厚の1/4の面を観察面としてX線解析を行い、面積分率を算出し、それを持って1/8厚~3/8厚における残留オーステナイトの体積分率とみなすことができる。なお、観察面は鋼板の板面に平行であれば、鋼板の表面から板厚の1/4を中心とした1/8厚~3/8厚の範囲の任意の位置に設定しても構わない。
本発明の高強度溶融亜鉛めっき鋼板の鋼板組織は、上述の残留オーステナイト相の他に、体積分率で、フェライト相:40~90%、ベイニティックフェライト相および/またはベイナイト相:50%以下、焼戻しマルテンサイト相:50%以下、フレッシュマルテンサイト相:15%以下を有することが好ましい。本発明の高強度溶融亜鉛めっき鋼板は、このような鋼板組織を有することにより、より優れた成形性を有する鋼板となる。
フェライト相は、延性の向上に有効な組織であり、鋼板組織中において体積分率で40~90%含まれていることが好ましい。鋼板組織中のフェライト相の体積分率が40%未満である場合、十分な延性が得られないおそれがある。また、鋼板組織中に含まれるフェライト相の体積分率は、延性の観点から45%以上含まれることがより好ましく、50%以上含まれることがさらに好ましい。一方、フェライト相は軟質な組織であるため、体積分率が90%を超えると十分な強度が得られない場合がある。また、鋼板の引張強度を十分に高めるには、鋼板組織中に含まれるフェライト相の体積分率を85%以下とすることがより好ましく、75%以下とすることがさらに好ましい。
ベイニティックフェライト相および/またはベイナイト相は、強度と延性のバランスに優れた組織であり、鋼板組織中に体積分率で10~50%含まれていることが好ましい。また、ベイニティックフェライト相および/またはベイナイト相は、軟質なフェライト相と硬質なマルテンサイト相、焼戻しマルテンサイト相および残留オーステナイト相の中間の強度を有するミクロ組織であり、伸びフランジ性の観点から15%以上含まれることがより好ましく、20%以上含まれることがさらに好ましい。一方、ベイニティックフェライト相および/またはベイナイト相の体積分率が50%を超えると、降伏応力が過度に高まり、形状凍結性が劣化するため好ましくない。
焼戻しマルテンサイト相は、引張強度を大きく向上させる組織であり、鋼板組織に体積分率で50%以下含まれていてもよい。引張強度の観点から、焼戻しマルテンサイトの体積分率は10%以上とすることが好ましい。一方、鋼板組織に含まれる焼戻しマルテンサイトの体積分率が50%を超えると、降伏応力が過度に高まり、形状凍結性が劣化するため好ましくない。
フレッシュマルテンサイト相は、引張強度を大きく向上させる効果があるが、一方で、破壊の起点となって伸びフランジ性を大きく劣化させるため、鋼板組織中における体積分率で15%以下に制限することが好ましい。また、伸びフランジ性を高めるには、鋼板組織中におけるフレッシュマルテンサイト相の体積分率を10%以下とすることがより好ましく、5%以下とすることがさらに好ましい。
本発明の高強度溶融亜鉛めっき鋼板の鋼板組織には、さらに、パーライト相および/または粗大なセメンタイト相等、上記以外の組織が含まれていてもよい。しかしながら、高強度鋼板の鋼板組織中にパーライト相および/または粗大なセメンタイト相が多くなると、延性が劣化するという問題が生じる。このことから、鋼板組織中に含まれるパーライト相および/または粗大なセメンタイト相の体積分率は、合計で10%以下であることが好ましく、5%以下であることがより好ましい。
本発明の高強度鋼板の鋼板組織に含まれる各組織の体積分率は、例えば、以下に示す方法によって測定できる。
次に、本発明の高強度溶融亜鉛めっき鋼板の化学成分(組成)について説明する。なお、以下の説明においては、特に指定の無い限り、「%」は「質量%」を表す。
Cは、高強度鋼板の強度を高めるために含有される。しかしながら、Cの含有量が0.400%を超えると溶接性が不十分となるので、0.400%以下であることが好ましい。また、溶接性の観点からは、Cの含有量は0.250%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0.075%未満だと、強度が低下し、900MPa以上の引張最大強度を確保することが困難となる。この観点から、鋼板の強度をより一層高めるためには、Cの含有量は0.085%以上であることがより好ましく、0.100%以上であることがさらに好ましい。
Siは、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の含有量が2.00%を超えると、鋼板が脆化して延性が劣化し、冷間圧延が困難となる。延性の観点から、Siの含有量は1.80%以下であることが好ましく、1.50%以下であることがより好ましい。一方、Siの含有量が0.01%未満では、脱炭層中に十分に酸化物を分散させることが困難となる。その観点からは、Siの下限値は0.20%以上であることがより好ましく、0.50%以上がさらに好ましい。
Mnは、鋼板の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、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い。また、Mnの含有量が3.50%を超えれば、溶接性も劣化する。したがってMnの含有量は、3.50%以下とする必要がある。また、溶接性の観点からは、Mnの含有量は3.00%以下であることがより好ましく、2.70%以下であることがさらに好ましい。一方、Mnの含有量が0.80%未満だと、焼鈍後の冷却中に軟質な組織が多量に形成されるため、900MPa以上の引張最大強度を確保することが難しくなることから、Mnの含有量は0.80%以上とする必要がある。また、強度をより高めるためには、Mnの含有量は1.00%以上であることがより好ましく、1.30%以上であることがさらに好ましい。
Pは、鋼板の板厚中央部に偏析する傾向があり、溶接部を脆化させる。Pの含有量が0.100%を超えると、溶接部が大幅に脆化するため、Pの含有量の上限は0.100%とする。また、溶接部の脆化を避ける観点では、Pの含有量の上限は0.030%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とから、0.0001%を下限とする。また、製造コストをより低減する観点でのPの含有量は0.0010%以上であることが好ましい。
Sは、溶接性ならびに鋳造時および熱延時の製造性に悪影響を及ぼす。このことから、Sの含有量の上限値を0.0100%以下とする。またSは、Mnと結びついて粗大なMnSを形成し、延性や伸びフランジ性を低下させるため、0.0050%以下とすることがより好ましく、0.0030%以下とすることがさらに好ましい。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ため、0.0001%を下限値とする。また、製造コストをより低減する観点でのSの含有量は、0.0005%以上であることがより好ましく、0.0010%以上であることがさらに好ましい。
Alは、鉄系炭化物の生成を抑えて鋼板の強度および成形性を高める。しかしながら、Alの含有量が2.00%を超えると、溶接性が悪化するため、Alの含有量の上限を2.00%とする。また、この観点から、Alの含有量は1.50%以下とすることがより好ましく、1.20%以下とすることがさらに好ましい。一方、Al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ためにAlの含有量は0.001%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量は0.010%以上とすることがより好ましい。
Nは、粗大な窒化物を形成し、延性および伸びフランジ性を劣化させることから、その添加量を抑える必要がある。Nの含有量が0.0100%を超えれば、その傾向が顕著となることから、Nの含有量の上限を0.0100%とする。また、この観点から、Nの含有量は、0.0070%以下とすることがより好ましく、0.0050%以下とすることがさらに好ましい。また、Nは、溶接時のブローホール発生の原因になることから、その含有量が少ない方が良い。N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とから、0.0001%以上とする。また、製造コストをより低減する観点でのNの含有量は、0.0005%以上であることがより好ましく、0.0010%以上であることがさらに好ましい。
Oは、酸化物を形成し、延性および伸びフランジ性を劣化させることから、含有量を抑える必要がある。Oの含有量が0.0100%を超えると、伸びフランジ性の劣化が顕著となることから、Oの含有量の上限を0.0100%とする。さらに、Oの含有量は0.0070%以下であることがより好ましく、0.0050%以下であることがさらに好ましい。また、O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ため、0.0001%を下限とする。また、製造コストをより低減する観点でのOの含有量は、0.0003%以上であることがより好ましく、0.0005%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/またはMnの一部に代えて添加してもよい。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とから、Crの含有量は2.00%以下であることが好ましい。なお、Cr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が、Crによる高強度化を十分に得るためには、その含有量が0.01%以上であることが好ましい。
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/またはMnの一部に代えて添加してもよい。Niの含有量が2.00%を超えると、溶接性が損なわれることから、Niの含有量は2.00%以下であることが好ましい。なお、Ni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が、Niによる高強度化を十分に得るためには、その含有量が0.01%以上であることが好ましい。
Cuは、微細な粒子として鋼中に存在することで強度を高める元素であり、Cおよび/またはMnの一部に代えて添加することができる。Cuの含有量が2.00%を超えると、溶接性が損なわれることから、その含有量は2.00%以下であることが好ましい。なお、Cu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が、Cuによる高強度化を十分に得るには、その含有量が0.01%以上であることが好ましい。
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り、鋼板の強度上昇に寄与する元素である。しかしながら、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0.100%以下であることがより好ましく、0.070%以下であることがさらに好ましい。なお、Ti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が、Tiによる強度上昇効果を十分に得るには、Tiの含有量は0.001%以上であることが好ましく、0.005%以上であることがさらに好ましい。また、鋼板の高強度化には、Tiの含有量は0.010%以上であることがより好ましく、0.015%以上であることがさらに好ましい。
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、鋼板の強度上昇に寄与する元素である。しかしながら、Nb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、Nb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、Nbの含有量は0.100%以下であることがより好ましく、0.060%以下であることがさらに好ましい。なお、Nb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が、Nb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く、0.005%以上であることがさらに好ましい。また、鋼板の高強度化には、Nbの含有量は0.010%以上であることがより好ましく、0.015%以上であることがさらに好ましい。
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、鋼板の強度上昇に寄与する元素である。しかしながら、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ため、その含有量が0.300%以下であることが好ましい。なお、V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が、Vによる強度上昇効果を十分に得るには、その含有量が0.001%以上であることが好ましい。
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/またはMnの一部に代えて添加してもよい。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とから、Moの含有量は2.00%以下であることが好ましく、1.00%以下であることがさらに好ましい。なお、Mo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が、Moによる高強度化の効果を十分に得るには、その含有量が0.01%以上であることが好ましい。
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/またはMnの一部に代えて添加してもよい。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とから、Wの含有量は2.00%以下であることが好ましく、1.00%以下であることがさらに好ましい。なお、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が、Wによる高強度化を十分に得るには、その含有量が0.01%以上であることが好ましい。
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/またはMnの一部に代えて添加してもよい。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生産性が低下することから、Bの含有量は0.0100%以下であることが好ましい。また、生産性の観点から、Bの含有量は0.0050%以下であることがより好ましく、0.0030%以下であることがさらに好ましい。なお、B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が、Bによる高強度化を十分に得るには、Bの含有量を0.0001%以上とすることが好ましい。また、鋼板をさらに高強度化するためには、Bの含有量が0.0003%以上であることがより好ましく、0.0005%以上であることがより好ましい。
本発明の高強度溶融亜鉛めっき鋼板においては、その他の元素として、Ca、Ce、Mg、Zr、La、REMの1種または2種以上を合計で0.0001~0.5000%、より好ましくは0.0001~0.0100%添加されていてもよい。これらの元素の添加理由は以下の通りである。
本発明の高強度溶融亜鉛めっき鋼板では、鋼板表層部における脱炭層の厚さが0.01~10.0μmであり、鋼板表層部に含まれる酸化物の平均粒子径が30~120nmであるとともに、その平均密度が1.0×1012個/m2以上とされている。
本発明では、鋼板表面に設けられるめっき層の密着性を高めるため、鋼板表層部を硬質組織の少ない脱炭層とする。この脱炭層の厚さが0.01μm未満では、めっき層の密着性を十分に得られないことから、脱炭層の厚さを0.01μm以上とする。また、めっき層の密着性をさらに向上させるには、脱炭層の厚さは0.08μm以上とすることがより好ましく、0.15μm以上であることがさらに好ましい。一方、過度に厚い脱炭層は、鋼板の引張強度や疲労強度を低下させる。この観点から、鋼板表層部における脱炭層の厚さは10.0μm以下とする。また、疲労強度の観点から、脱炭層の厚さは9.0μm以下であることがより好ましく、8.0μm以下であることがさらに好ましい。
脱炭層には、Siおよび/またはMnを含む酸化物を、結晶粒内および/または結晶粒界に分散させ、機械切断が容易に行えるよう切断性を高める。酸化物の密度が高いほど、切断性は改善されることから、本発明では、酸化物の密度を1.0×1012個/m2以上とする。また、酸化物の密度は、上記観点から、3.0×1012個/m2以上とすることがより好ましく、5.0×1012個/m2以上とすることがさらに好ましい。一方、酸化物の密度が1.0×1016個/m2を超えると酸化物間の距離が過度に近くなり、軽度の加工で鋼鈑表層部が破壊し、その上のめっき層を損なうことから、酸化物の密度は1.0×1016個/m2以下に制限することが好ましい。また、鋼板表層部における十分な成形性を確保するためには、酸化物の密度は5.0×1015個/m2以下とすることがより好ましく、1.0×1015個/m2以下とすることがさらに好ましい。
本発明においては、上記構成の鋼板の表面に、溶融亜鉛めっき層や、合金化した溶融亜鉛めっき層が形成されることにより、高強度溶融亜鉛めっき鋼板あるいは高強度合金化溶融亜鉛めっき鋼板として構成される。このように、鋼板の表面に溶融亜鉛めっき層が形成されることにより、優れた耐食性を有する高強度溶融亜鉛めっき鋼板が得られる。また、鋼板の表面に合金化した溶融亜鉛めっき層が形成されることにより、優れた耐食性を有し、塗料の密着性に優れた高強度合金化溶融亜鉛めっき鋼板が得られる。
本発明で説明する機械切断特性とは、例えば、以下に説明するような方法で測定し、評価することができる。
一般に、高強度鋼板に対し、シャー切断やポンチによる打ち抜き加工を多数行うと、シャー刃やポンチ先端が磨耗し、クリアランスが増加する。このため、鋼板の打ち抜き回数が増加すると、シャー切断端面や打ち抜き端面のバリが大きくなる。そこで、本発明に係る高強度溶融亜鉛めっき鋼板の機械切断特性を評価する方法としては、厚さ1.2mmの鋼板を、穴径10.3mmφのダイ、ポンチ材質SKD11、ポンチ径10mmφ(クリアランス12.5%)の条件にて、連続して打ち抜き加工を行い、50回毎にバリ高さを測定する方法を採用することができる。
本実施形態の高強度溶融亜鉛めっき鋼板は、3~7%の塑性変形時における加工硬化係数(n値)が平均で0.080以上とされている。
本発明においては、鋼板強度として引張最大強度が900MPa以上であることが好ましい。これは、900MPa以上の高強度鋼板において、シャー切断や打ち抜き加工の際の工具劣化が顕著になる強度だからである。また、900MPa未満の鋼板であっても、本発明の効果である機械切断特性改善の効果は享受できるものの、引張強度の低い鋼板では、その効果が小さい。このため、本発明では、上記効果と併せ、母材強度の確保の観点からも、900MPa以上の高強度溶融亜鉛めっき鋼板に適用することが好ましい。
次に、本発明の成形性に優れた高強度溶融亜鉛めっき鋼板の製造方法について説明する。
本実施形態の高強度溶融亜鉛めっき鋼板の製造方法は、まず、上記した化学成分を有するスラブを、直接または一旦冷却した後に1180℃以上に加熱し、850~950℃を圧延完了温度とする熱間圧延を施した後に、500~650℃まで平均冷却速度10℃/s以上で急冷した後、コイルに巻き取り、400℃まで1.0時間以上かけて徐冷する熱延工程と、この熱延工程に次いで酸洗した後、合計の圧下率を30~75%とする冷間圧延を行う冷延工程とを備える。また、本実施形態では、冷延工程後の鋼板を、600~750℃間の平均加熱速度を20℃/s以下として、750℃以上まで加熱し、次いで、750~650℃間の平均冷却速度を1.0~15.0℃/sとして冷却し、650℃からの平均冷却速度を3.0℃/s以上として冷却し、300~470℃の温度域において20~1000秒停留させながら、該温度域において5~100MPaの張力をかけつつ、曲げ半径を800mm以下とする曲げ加工を1回以上施す焼鈍工程を備える。さらに、本実施形態では、焼鈍工程の後、めっき浴温度:450~470℃、めっき浴進入時の鋼板温度:430~490℃、めっき浴中における有効Al量:0.01~0.18質量%の条件で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工程を備える。さらに、本実施形態では、めっき工程の後、150℃以下まで平均冷却速度0.5℃/s以上で冷却する冷却工程を備える。そして、本実施形態では、前記焼鈍工程として、予熱バーナーに用いる空気と燃料ガスの混合ガスにおいて、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る空気比:0.7~1.2とされた条件の予熱帯において、400~800℃の鋼板温度に加熱しながら通板させることで鋼板表層部に酸化物を生成させ、次いで、水蒸気(H2O)と水素(H2)との分圧比P(H2O)/P(H2):0.0001~2.0とされた還元帯において750℃以上まで加熱することにより、前記予熱帯において生成させた前記酸化物を還元した後に冷却を行う方法を採用している。
熱間圧延に供するスラブとしては、例えば、連続鋳造スラブや、薄スラブキャスター等で製造したものを用いることができる。また、本発明の高強度鋼板の製造方法は、鋳造後に直ちに熱間圧延を行う連続鋳造-直接圧延(CC-DR)のようなプロセスに適合する。
めっき浴温度は450℃~470℃とすることが好ましい。めっき浴温度が450℃未満では、めっき浴の粘度が過度に高まり、めっき層の厚さを制御することが困難となり、鋼板の外観を損なう。一方、めっき浴温度が470℃を超えると多量のヒュームが発生し、安全に製造することが困難となるため、めっき浴温度は470℃以下であることが好ましい。
また、めっき浴温度を安定させるため、めっき浴への鋼板の進入温度は430℃~490℃とすることが好ましい。鋼板がめっき浴に侵入する際の鋼板温度が430℃を下回ると、めっき浴温度を450℃以上に安定させるためにめっき浴に多量の熱量を与える必要が生じるため、実用上不適である。一方、鋼板がめっき浴に侵入する際の鋼板温度が490℃を上回ると、めっき浴温度を470℃以下に安定させるためにめっき浴から多量の熱量を抜熱する設備を導入する必要があり、製造コストの点で不適である。
これら、熱延工程から焼鈍工程にかけての歪付与と熱履歴および上記のベイナイト変態時の歪付与により、残留オーステナイト相中の固溶炭素量を0.70~1.00%にすることができ、加えて平均粒子径を2.0μm以下、粒子間の平均距離を0.1~5.0μmにすることができる。さらに、3~7%の塑性変形時に加工硬化係数を平均で0.080以上にすることができる。
なお、合金化処理はめっき浴への浸漬後、直ちに行うことが好ましいが、浸漬後に鋼板温度を150℃以下まで放冷してから、合金化処理温度まで再加熱しても構わない。
例えば、本発明においては、上述した方法により得られた高強度溶融亜鉛めっき鋼板のめっき層の表面に、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被膜を付与しても構わない。このような、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被膜は、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めっき層を保護することができる。
まず、製鋼工程において溶鋼の脱酸・脱硫と化学成分を制御することにより、下記表1に示す化学成分組成のスラブを得た。そして、鋳造後、直ちに下記表2~4に示す条件で、熱間圧延、冷却、巻取り、酸洗を施し、さらに、冷間圧延を施した。その後、得られた冷延鋼板を、下記表5~8に示す条件の連続焼鈍溶融亜鉛めっきラインを通板させて、実験例1~128の溶融亜鉛めっき鋼板を製造した。また、これら実験例1~128の内の一部においては、下記表5~8に示す条件で、めっき層の合金化処理を行うことにより、合金化溶融亜鉛めっき鋼板(GA)とした。それ以外の鋼板は合金化処理を行わないか、処理温度を470℃未満として、めっき層が合金化していない溶融亜鉛めっき鋼板(GI)とした。
上記方法によって製造した各実験例の鋼板について、以下のような評価試験を行い、結果を下記表9~13に示した。
まず、走査型電子顕微鏡(SEM)を用いて各実験例の鋼板の組織観察を行い、鋼板の組織分率、並びに、残留オーステナイト相の粒子間の平均距離および平均粒子径を測定し、下記表9~13に記載した。ここで、フェライト、マルテンサイト、パーライト、セメンタイト、ベイナイト、オーステナイト及び残部組織の同定や、存在位置の観察及び面積率の測定は、ナイタール試薬及び特開昭59-219473号公報に開示された試薬により、鋼板圧延方向断面又は圧延方向直角方向断面を腐食して、板厚の1/4厚み位置を1000~10000倍にて観察した。
鋼板表層部における脱炭層の厚さは、各鋼板の圧延方向に平行な板厚断面を鏡面に仕上げ、FE-SEMを用いて観察し、1つの鋼板において3箇所以上の脱炭層厚さを測定し、その平均値をもって脱炭層の厚さとした。
上記手順で製造した鋼板について、その外観の検査を行った。この際、鋼板表面の外観について、目視で不めっきの発生状況を目視判断し、結果を下記表9~13中に「○」、「×」で示した。なお、下記表9~13中に示す「×」は、直径0.5mm以上の不めっきが観察され、外観上の許容範囲を逸脱した鋼板であり、「○」は、それ以外の、実用上許容しうる外観を有する鋼板である。
上記手順で作製した鋼板について、鋼板に圧縮応力が加わる加工時におけるめっき密着性を評価する、JIS
Z 2248に記載の「金属材料曲げ試験方法」に従い、めっき剥離試験を行った。具体的には、文献「溶融亜鉛めっき鋼鈑マニュアル,p53-55」に開示されているように、各鋼板を用いて60°V字曲げ試験を行った後、曲げ部の内側にテープを貼り、そのテープを引き剥がした。そして、テープとともに剥離しためっき層の剥離状況からめっき密着性を評価し、結果を下記表9~13中に示した。なお、下記表9~13中に示す「有」は、剥離幅が7.0mm以上で実用上許容しえない鋼板であり、「-」は、それ以外の、実用上許容しうるめっき密着性を有する鋼板である。ここでは、テープにはニチバン製「セロテープ」(登録商標)を用いた。
各実験例の鋼板を、厚さが1.2mmとなるように、冷間圧延、焼鈍、めっきを行い、板厚1.2mmの鋼板を加工した後、穴径10.3mmφのダイ、ポンチ材質SKD11、ポンチ径10mmφ(クリアランス12.5%)の条件にて、連続して打ち抜き加工を行い、50回毎にバリ高さを測定した。この際、打ち抜き穴を、0°、90°、180°、270°の各位置で4分割し、何れか一方向のバリ高さが初期値の3.0倍を越えた時点で試験を終了し、この際の打ち抜き回数を限界の打ち抜き回数とした。なお、本実施例においては、製品鋼板の板厚を変えることなく種々の冷延率を得るために、熱延鋼板の厚みを種々変化させて製品鋼板を作製した。
各実験例の鋼板から、JIS
Z 2201に記載の5号試験片を加工して、JIS Z 2241に記載の試験方法に沿って、引張強度(MPa)及び全伸び(%)を測定し、また、JIS G 0202に記載の試験方法に沿って降伏強度(MPa)を測定した。
表9~13に示すように、本発明で規定する鋼成分を有するとともに本発明で規定する各製造条件によって製造された実施例(本発明例:表1~13の備考欄を参照)の高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板は、鋼板組織におけるフェライト相及び残留オーステナイト相の体積分率、残留オーステナイト相中の固溶炭素量と平均粒子径および粒子間の平均距離、鋼板表層部における脱炭層の厚さ、酸化物の平均粒子径及び平均密度、さらには加工硬化係数(n値)の何れもが、本発明の請求項1で規定する範囲であった。そして、これら本発明例の鋼板は、めっき表面の外観特性および剥離特性に優れ、また、降伏応力、引張強度、全伸び、n値の各引張特性に優れ、さらに、限界打ち抜き回数が全て650回以上であり、機械切断特性に優れていることがわかる。従って、これらの評価結果より、本発明例の高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板は、900MPa以上の引張最大強度を確保しながら、優れた延性と機械切断特性とを同時に兼ね備えることが明らかとなった。
Claims (7)
- 質量%で、
C :0.075~0.400%、
Si:0.01~2.00%、
Mn:0.80~3.50%、
P :0.0001~0.100%、
S :0.0001~0.0100%、
Al:0.001~2.00%、
N :0.0001~0.0100%、
O :0.0001~0.0100%
を含有し、残部が鉄および不可避的不純物からなる鋼板の表面にめっき層を有する板厚0.6~5.0mmの高強度溶融亜鉛めっき鋼板であって、
鋼板の表面から板厚の1/4を中心とした1/8厚~3/8厚の範囲において、鋼板組織が、少なくとも体積分率で40~90%のフェライト相、および、3%以上の残留オーステナイト相を含み、
前記残留オーステナイト相は、相中における固溶炭素量が0.70~1.00%であり、平均粒子径が2.0μm以下であるとともに、粒子間の平均距離が0.1~5.0μmであり、
鋼板表層部における脱炭層の厚さが0.01~10.0μmであり、前記鋼板表層部に含まれる酸化物の平均粒子径が30~120nmであるとともに、その平均密度が1.0×1012個/m2以上であり、
さらに、3~7%の塑性変形時における加工硬化係数(n値)が平均で0.080以上であることを特徴とする機械切断特性に優れた高強度溶融亜鉛めっき鋼板。 - さらに、質量%で、
Ti:0.001~0.150%、
Nb:0.001~0.100%、
V :0.001~0.300%の1種または2種以上を含有することを特徴とする請求項1に記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。 - さらに、質量%で、
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1種または2種以上を含有することを特徴とする請求項1に記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。 - さらに、質量%で、
Ca、Ce、Mg、Zr、La、REMの1種または2種以上を合計で0.0001~0.0100%含有することを特徴とする請求項1に記載の機械切断特性に優れた高強度溶融亜鉛めっき鋼板。 - 請求項1に記載の高強度溶融亜鉛めっき鋼板のめっき層が合金化されてなることを特徴とする機械切断特性に優れた高強度合金化溶融亜鉛めっき鋼板。
- 質量%で、
C :0.075~0.400%、
Si:0.01~2.00%、
Mn:0.80~3.50%、
P :0.0001~0.100%、
S :0.0001~0.0100%、
Al:0.001~2.00%、
N :0.0001~0.0100%、
O :0.0001~0.0100%
を含有し、残部が鉄および不可避的不純物の化学成分を有するスラブを、直接または一旦冷却した後に1180℃以上に加熱し、850~950℃を圧延完了温度とする熱間圧延を施した後に、500~650℃まで平均冷却速度10℃/s以上で急冷した後、コイルに巻き取り、400℃まで1.0時間以上かけて徐冷する熱延工程と、
前記熱延工程に次いで酸洗した後、合計の圧下率を30~75%とする冷間圧延を行う冷延工程と、
前記冷延工程後の鋼板を、600~750℃間の平均加熱速度を20℃/s以下として、750℃以上まで加熱し、次いで、750~650℃間の平均冷却速度を1.0~15.0℃/sとして冷却し、650℃からの平均冷却速度を3.0℃/s以上として冷却し、300~470℃の温度域において20~1000秒停留させながら、該温度域において5~100MPaの張力をかけつつ、曲げ半径を800mm以下とする曲げ加工を1回以上施す焼鈍工程と、
前記焼鈍工程の後、めっき浴温度:450~470℃、めっき浴進入時の鋼板温度:430~490℃、めっき浴中における有効Al量:0.01~0.18質量%の条件で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工程と、
前記めっき工程後に、150℃以下まで平均冷却速度0.5℃/s以上で冷却する冷却工程と、を備え、
前記焼鈍工程は、予熱バーナーに用いる空気と燃料ガスの混合ガスにおいて、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る空気比:0.7~1.2とされた条件の予熱帯において、400~800℃の鋼板温度に加熱しながら通板させることで鋼板表層部に酸化物を生成させ、次いで、水蒸気(H2O)と水素(H2)との分圧比P(H2O)/P(H2):0.0001~2.0とされた還元帯において750℃以上まで加熱することにより、前記予熱帯において生成させた前記酸化物を還元した後に冷却を行うことを特徴とする機械切断特性に優れた高強度溶融亜鉛めっき鋼板の製造方法。 - 請求項6に記載の方法で熱延工程、冷延工程、焼鈍工程、めっき工程までを行った後であって前記冷却工程の前、前記めっき工程で形成されためっき層に470~620℃の温度で合金化処理を施すことを特徴とする機械切断特性に優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
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US11268181B2 (en) | 2017-07-31 | 2022-03-08 | Nippon Steel Corporation | Hot-dip galvanized steel sheet |
US10953631B2 (en) | 2017-07-31 | 2021-03-23 | Nippon Steel Corporation | Hot-dip galvanized steel sheet |
JP6281671B1 (ja) * | 2017-07-31 | 2018-02-21 | 新日鐵住金株式会社 | 溶融亜鉛めっき鋼板 |
EP3663424A4 (en) * | 2017-07-31 | 2020-11-25 | Nippon Steel Corporation | HOT-GALVANIZED STEEL SHEET |
WO2019026106A1 (ja) * | 2017-07-31 | 2019-02-07 | 新日鐵住金株式会社 | 溶融亜鉛めっき鋼板 |
WO2019163513A1 (ja) * | 2018-02-21 | 2019-08-29 | 株式会社神戸製鋼所 | 高強度鋼板および高強度亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2019143199A (ja) * | 2018-02-21 | 2019-08-29 | 株式会社神戸製鋼所 | 高強度鋼板および高強度亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2021516292A (ja) * | 2018-03-13 | 2021-07-01 | エーケー スティール プロパティ−ズ、インク. | 準安定オーステナイト含有のコーティングされた鋼の上昇温度における圧下 |
JP7329304B2 (ja) | 2018-03-13 | 2023-08-18 | クリーブランド-クリフス スティール プロパティーズ、インク. | 準安定オーステナイト含有のコーティングされた鋼の上昇温度における圧下 |
TWI697563B (zh) * | 2019-09-26 | 2020-07-01 | 中國鋼鐵股份有限公司 | 鋼胚加熱爐及抑制鋼胚表面脫碳層之厚度增加的方法 |
WO2023153097A1 (ja) * | 2022-02-09 | 2023-08-17 | 日本製鉄株式会社 | 冷延鋼板およびその製造方法 |
WO2023153096A1 (ja) * | 2022-02-09 | 2023-08-17 | 日本製鉄株式会社 | 冷延鋼板 |
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MX357963B (es) | 2018-08-01 |
EP2762585B1 (en) | 2019-05-29 |
US9708679B2 (en) | 2017-07-18 |
TW201332673A (zh) | 2013-08-16 |
EP2762585A4 (en) | 2015-12-02 |
PL2762585T3 (pl) | 2020-01-31 |
EP2762585B8 (en) | 2019-07-31 |
CN103874776B (zh) | 2016-05-18 |
RU2566695C1 (ru) | 2015-10-27 |
JPWO2013047739A1 (ja) | 2015-03-26 |
ES2737678T3 (es) | 2020-01-15 |
CA2850332C (en) | 2016-06-21 |
TWI513524B (zh) | 2015-12-21 |
KR101594268B1 (ko) | 2016-02-15 |
KR20140050750A (ko) | 2014-04-29 |
US20140287263A1 (en) | 2014-09-25 |
MX2014003717A (es) | 2014-07-09 |
ZA201402355B (en) | 2015-01-28 |
BR112014007545B1 (pt) | 2019-05-14 |
JP5354135B2 (ja) | 2013-11-27 |
EP2762585A1 (en) | 2014-08-06 |
CA2850332A1 (en) | 2013-04-04 |
CN103874776A (zh) | 2014-06-18 |
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