WO2013069210A1 - High-tensile-strength hot-rolled plated steel sheet and method for producing same - Google Patents

High-tensile-strength hot-rolled plated steel sheet and method for producing same Download PDF

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Publication number
WO2013069210A1
WO2013069210A1 PCT/JP2012/006647 JP2012006647W WO2013069210A1 WO 2013069210 A1 WO2013069210 A1 WO 2013069210A1 JP 2012006647 W JP2012006647 W JP 2012006647W WO 2013069210 A1 WO2013069210 A1 WO 2013069210A1
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Prior art keywords
less
hot
steel sheet
rolled
tensile
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PCT/JP2012/006647
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French (fr)
Japanese (ja)
Inventor
珠子 有賀
船川　義正
康信 内田
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Ｊｆｅスチール株式会社
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Priority to JP2013542814A priority Critical patent/JP5594438B2/en
Publication of WO2013069210A1 publication Critical patent/WO2013069210A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface treatment
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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

Definitions

  • the present invention relates to a high-tensile hot-rolled plated steel sheet suitable for transportation equipment such as automobile parts and structural materials, and a method for producing the same (high-strength-galvanized hot-rolled steel sheet and method manufacturing for the same.
  • Patent Document 1 discloses that by weight, C: 0.03-0.25%, Si: 2.0% or less, Mn: 2.0% or less, P: 0.1% or less, S: 0.007% or less, Al: 0.07% or less, and Cr : A composition containing 1.0% or less, a composite structure composed of ferrite and the second phase, and by specifying the hardness, volume ratio, and particle size of the second phase, the tensile strength (TS) is 490 N / mm A technique for improving fatigue properties and stretch flangeability of high-strength hot-rolled steel sheets exceeding 2 (490 MPa) has been proposed.
  • the second phase is one or more of pearlite, bainite, martensite, and retained austenite.
  • Patent Document 2 wt%, C: 0.01 to 0.10%, Si: 1.5% or less, Mn: more than 1.0% to 2.5%, P: 0.15% or less, S: 0.008% or less, Al: 0.01 to
  • the chemical composition contains 0.08%, one or two of Ti and Nb: 0.10 to 0.60%, the ferrite content is 95% or more in area ratio, and the average crystal grain size of ferrite is 2.0 to 10.0 ⁇ m
  • the strength of the steel sheet is improved and fine ferrite grains are obtained by setting the Mn content to more than 1.0% to 2.5%.
  • Patent Document 3 in mass%, C: 0.01 to 0.1%, S ⁇ 0.03%, N ⁇ 0.005%, Ti: 0.05 to 0.5%, Si: 0.01 to 2%, Mn: 0.05 to 2% , P ⁇ 0.1%, Al: 0.005 to 1.0%, and a composition containing Ti in a range that satisfies Ti-48 / 12C-48 / 14N-48 / 32S ⁇ 0%, and the particle size in steel is 5nm or more by the minimum interval average size at 10 1 ⁇ 10 3 nm of precipitates containing the Ti or less 10 1 nm ultra 10 4 nm, burring workability high-strength hot-rolled steel sheet tensile strength is at least 640MPa Technologies for improving (Burring formability) and fatigue properties have been proposed.
  • the tensile strength is 590 MPa or more and It is difficult to stably supply a high tension (hot rolled) plated steel sheet having excellent workability (stretch flangeability, bending workability).
  • the present invention advantageously solves the above-described problems of the prior art, is suitable as a material for automobile parts, has a tensile strength of 590 MPa or more, and has excellent stretch flangeability and excellent bending workability.
  • An object is to provide a high-tensile hot-rolled plated steel sheet excellent in workability and a method for producing the same.
  • the present inventors diligently studied various factors affecting the increase in strength and workability of hot-rolled plated steel sheets, particularly stretch flangeability and bending workability. As a result, the following findings were obtained. 1) When the steel sheet structure is a ferrite single-phase structure with a low dislocation density and excellent workability, and when fine carbide is dispersed and precipitated to strengthen the precipitation, the stretch flangeability and bending workability of the hot-rolled plated steel sheet are maintained. Strength is improved.
  • Carbide containing Ti is effective as fine carbide contributing to precipitation strengthening.
  • any of the above precipitation forms of carbide is effective for increasing the strength of the hot-rolled steel sheet.
  • a hot-rolled sheet in which the carbides are dispersed and precipitated mainly in a row is obtained.
  • the above coiling temperature is set to a temperature lower than the optimum temperature for precipitation of carbide containing Ti, and a hot rolled sheet suppressing precipitation of carbide containing Ti is formed.
  • B ⁇ 0.0003-0.00025Mn (2) (Mn, B: content of each element (mass%))
  • Mn, B content of each element (mass%)
  • the steel material is subjected to hot rolling consisting of rough rolling and finish rolling. After finishing rolling, the steel material is cooled, wound and formed into a hot rolled sheet, and then subjected to continuous annealing treatment and plating treatment on the hot rolled sheet.
  • the steel material in mass%, C: 0.010% or more and 0.050% or less, Si: 0.2% or less, Mn: 0.10% to 0.80%, P: 0.025% or less, S: 0.01% or less, N: 0.01% or less, Al: 0.1% or less, Ti: 0.05% or more and 0.10% or less containing C, S, N, and Ti so that the following formula (1) is satisfied, with the balance being Fe and inevitable impurities,
  • the finish rolling temperature of the finish rolling is 880 ° C.
  • the average cooling rate of the cooling is 10 ° C./s or more
  • the winding temperature is 400 ° C. or more and less than 550 ° C.
  • the annealing temperature of the continuous annealing treatment is 550 ° C.
  • excellent workability that can be applied satisfactorily as a material for an undercarriage component or the like that is suitable as a material for automobile parts, has a tensile strength of 590 MPa or more, and has a complicated cross-sectional shape at the time of pressing ( A high-tensile hot-rolled plated steel sheet having stretch flangeability and bending workability) can be produced industrially stably, and has a remarkable industrial effect.
  • the hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention is a fine matrix in which the ferrite phase is 95% or more in terms of the area ratio with respect to the entire structure, and the matrix contains Ti and the average particle diameter is less than 10 nm. It has a structure in which carbides are dispersed and precipitated.
  • the fine carbide is preferably a carbide in which the ratio of the number Ps of precipitates in a row and the number Pr of random precipitates satisfies Pr / Ps ⁇ 0.8.
  • the volume ratio of the fine carbide to the whole structure is preferably 0.0005 or more.
  • Ferrite phase 95% or more in area ratio with respect to the entire structure
  • formation of a ferrite phase is essential to ensure the workability (stretch flangeability, bending workability) of the hot-rolled plated steel sheet.
  • it is effective to make the structure of the hot-rolled steel sheet used as the substrate of the hot-rolled plated steel sheet into a ferrite phase having excellent ductility with a low dislocation density.
  • the structure of the hot-rolled steel sheet is a ferrite single-phase structure, but even if it is not a complete ferrite single-phase structure, it is substantially a ferrite single-phase structure, that is, If the area ratio with respect to the entire structure is 95% or more of the ferrite phase, the above effects are sufficiently exhibited. Therefore, the area ratio of the ferrite phase to the entire structure is 95% or more.
  • the phases other than the ferrite phase include cementite, pearlite, bainite phase, martensite phase, retained austenite phase, etc., and the total of these may be about 5% or less in terms of the area ratio relative to the entire structure. Is acceptable.
  • Fine carbide containing Ti Ti is a strong carbide constituent element, and carbide containing Ti tends to be a fine carbide having an extremely small average particle diameter. Therefore, in the present invention to increase the strength of the hot-rolled plated steel sheet by dispersing and precipitating fine carbides in the hot-rolled steel sheet as a substrate of the hot-rolled plated steel sheet, the fine carbides that cause dispersed precipitation in the hot-rolled steel sheet As a fine carbide containing Ti.
  • Average particle diameter of fine carbide less than 10nm
  • desired strength tensile strength: 590MPa or more
  • the average particle size is extremely important.
  • the average particle size of the fine carbide containing Ti is set to less than 10 nm.
  • the fine carbide acts as a resistance to dislocation movement that occurs when the steel sheet is deformed, thereby strengthening the hot-rolled plated steel sheet.
  • the thickness is less than 10 nm, the above action becomes more remarkable. Therefore, the average particle diameter of the fine carbide containing Ti is set to less than 10 nm. More preferably, it is 5 nm or less.
  • Ratio between the number Ps of fine carbides deposited in a row and the number Pr of fine carbides randomly deposited Pr / Ps ⁇ 0.8
  • carbides containing fine Ti fine carbides
  • coarse carbides fine carbides
  • the interface between the fine carbide and the matrix becomes a crack generation part during bending, but if the fine carbide is dispersed and precipitated in a row, cracks generated at the interface between the fine carbide and the matrix are likely to propagate. is there.
  • the ratio Pr / Ps between the number Ps of fine carbides precipitated in a row and the number Pr of fine carbides randomly precipitated is preferably 0.8 or more.
  • the hot-rolled plated steel sheet strength In order to stably obtain the hot-rolled plated steel sheet strength, it is effective to control the amount of fine carbide dispersed and precipitated in the hot-rolled steel sheet as a substrate of the hot-rolled plated steel sheet. It is preferable to disperse and precipitate fine carbides containing Ti and having an average particle diameter of less than 10 nm so that the volume ratio with respect to the entire hot-rolled steel sheet structure is 0.0005 or more. However, if the volume ratio exceeds 0.003, the strength becomes too high and the stretch flangeability may be deteriorated. Therefore, the volume ratio is preferably 0.0005 or more and 0.003 or less.
  • C 0.010% or more and 0.050% or less
  • C is an essential element for forming fine carbides and strengthening steel. If the C content is less than 0.010%, sufficient fine carbide cannot be secured, and a tensile strength of 590 MPa or more cannot be obtained. On the other hand, when the C content exceeds 0.050%, pearlite is easily formed in the steel sheet, and stretch flangeability is impaired. Therefore, the C content is 0.010% or more and 0.050% or less. Preferably they are 0.020% or more and 0.035% or less.
  • Si 0.2% or less Si is a solid solution strengthening element and is an element effective for increasing the strength of steel.
  • the Si content is 0.2% or less.
  • it is 0.05% or less.
  • it is preferably 0.005% or more for strengthening the solid solution.
  • Mn 0.10% to 0.80%
  • Mn is a solid solution strengthening element and is an element effective for increasing the strength of steel. In order to obtain such an effect, it is desirable to contain 0.10% or more, but if the Mn content exceeds 0.80%, segregation is likely to occur, and a phase other than the ferrite phase, that is, a hard phase is formed, and the elongation is increased. Flangeability decreases. Therefore, the Mn content is 0.10% or more and 0.80% or less. Preferably it is 0.10% or more and 0.5% or less. More preferably, it is 0.10% or more and 0.45% or less.
  • P 0.025% or less
  • P is a solid solution strengthening element and is an element effective for increasing the strength of steel.
  • the P content is 0.025% or less.
  • it is 0.02% or less. Further, it is preferably 0.005% or more for strengthening the solid solution.
  • S 0.01% or less S is an element that lowers hot workability (hot rollability), increases the hot cracking susceptibility of slabs, and is present as MnS in steel and stretch flangeability of hot rolled steel sheets. Deteriorate. Therefore, in the present invention, it is preferable to reduce S as much as possible, and set it to 0.01% or less. Preferably it is 0.005% or less.
  • N 0.01% or less N is a harmful element in the present invention and is preferably reduced as much as possible.
  • the N content is 0.01% or less.
  • it is 0.006% or less.
  • Al 0.1% or less
  • Al is an element that acts as a deoxidizer. In order to acquire such an effect, it is desirable to contain 0.001% or more, but inclusion exceeding 0.1% lowers workability (stretch flangeability and bending workability). For this reason, Al content shall be 0.1% or less.
  • Ti 0.05% or more and 0.10% or less Ti is one of the most important elements in the present invention.
  • Ti is an element that contributes to increasing the strength of a steel sheet while maintaining excellent stretch flangeability and bending workability by forming carbides. In order to acquire such an effect, it is desirable to contain 0.05% or more. However, if the Ti content exceeds 0.10%, the stretch flangeability tends to decrease, so the Ti content is 0.10% or less. Preferably they are 0.05% or more and 0.095% or less.
  • the hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention contains C, S, N, and Ti in the above-described range and satisfying the expression (1).
  • Ti * Ti- (N / 14 x 48 + S / 32 x 48) (C, S, N, Ti: content of each element (mass%))
  • the above formula (1) is a requirement to be satisfied in order to bring the fine carbide containing Ti into the above-described desired precipitation state, and is an extremely important index in the present invention.
  • fine carbides containing Ti are dispersed and precipitated in the hot-rolled steel sheet serving as the substrate.
  • the carbide containing Ti has a strong tendency to become a fine carbide having an extremely small average particle diameter, the carbide tends to be coarsened when Ti combined with C becomes C or more in atomic ratio. And it becomes difficult to ensure desired steel plate strength (tensile strength: 590 MPa or more) with the coarsening of carbides. Therefore, in the present invention, it is necessary to increase the atomic percent of C (C / 12) contained in the steel material more than the atomic percent of Ti (Ti * / 48) that can contribute to carbide formation.
  • a predetermined amount of Ti is added to the steel material, and fine carbides containing Ti are dispersed and precipitated in the hot-rolled steel sheet as a substrate.
  • the carbide inside is melted and deposited mainly in the steps after the winding after the hot rolling (winding step and continuous annealing step).
  • Ti * Ti ⁇ (N / N) for the purpose of increasing the atomic percent of C (C / 12) to the atomic percent of Ti (Ti * / 48) that can contribute to carbide formation. 14 ⁇ 48 + S / 32 ⁇ 48), and each element of C, S, N, and Ti is contained so as to satisfy Ti * / 48 ⁇ C / 12.
  • Ti * / 48 is C / 12 or more, fine carbides containing Ti are easily coarsened.
  • the carbide containing Ti heats the steel material to the austenite region before hot rolling, dissolves the carbide in the steel material, and disperses and precipitates in the subsequent hot rolling process.
  • the transformation temperature from the transformation from austenite to ferrite is adjusted to a temperature suitable for precipitation of carbide containing Ti, winding at that temperature, fine carbide containing Ti is aligned at the same time as austenite ⁇ ferrite transformation. It precipitates in the shape (phase interface precipitation).
  • carbides containing Ti are precipitated at a high temperature range.
  • the carbides precipitated at such a high temperature range are easily coarsened, a desired fine carbide ( (Average particle diameter less than 10 nm) cannot be obtained. Therefore, in the present invention, it is preferable to lower the temperature at which the steel material is transformed from austenite to ferrite to a temperature sufficient to precipitate fine carbides.
  • B 0.0035% or less may be further contained so as to satisfy the following formula (2). It can. B ⁇ 0.0003-0.00025Mn (2) (Mn, B: content of each element (mass%))
  • B 0.0035% or less
  • B is an element that lowers the austenite ⁇ ferrite transformation temperature of steel.
  • the refinement of carbides containing Ti is reduced. Can be achieved.
  • the B content is preferably 0.0003% or more.
  • the above effect is saturated even if the content exceeds 0.0035%. Therefore, the B content is preferably 0.0035% or less. More preferably, it is 0.0003% or more and 0.0020% or less.
  • B ⁇ 0.0003-0.00025Mn (2) (Mn, B: content of each element (mass%))
  • Mn, B content of each element (mass%)
  • the present inventors studied a means for finely dispersing (including an average particle diameter of less than 10 nm) a carbide containing Ti in a matrix having an area ratio of 95% or more with respect to the entire structure of the ferrite phase.
  • the austenite of the steel ⁇ It was found that the ferrite transformation temperature can be adjusted to the target range.
  • the value on the right side 0.0003-0.00025Mn
  • the value on the right side is assumed to be zero.
  • the content of Mn which is a solid solution strengthening element
  • a desired steel plate strength (tensile strength: 590 MPa or more) can be ensured without using the effect of B described above. it can.
  • the Mn content is 0.35% or less, it may be difficult to secure a desired steel sheet strength without using the above-described effect of B. Therefore, when the Mn content is 0.35% or less, it is preferable to contain B for the purpose of making the carbide containing Ti finer.
  • any one of Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, Ta You may contain 1% or less of seeds or more in total. Preferably it is 0.1% or less, More preferably, it is 0.03% or less. Components other than the above are Fe and inevitable impurities.
  • the high-tensile hot-rolled plated steel sheet of the present invention has a plating film on the surface of the above-described hot-rolled steel sheet.
  • the hot rolled steel sheet has improved corrosion resistance, high strength, excellent workability, and high tensile hot rolling suitable for materials exposed to severe corrosive environments, such as automobile undercarriage parts.
  • a plated steel sheet is obtained.
  • the kind of said plating film is not specifically limited, For example, a hot dip galvanization film, an alloyed hot dip galvanization film, etc. are used suitably.
  • the manufacturing method of the high-tensile hot-rolled plated steel sheet of this invention is demonstrated.
  • the steel material having the above composition is subjected to hot rolling consisting of rough rolling and finish rolling, and after finishing rolling, the steel material is cooled, wound, and hot rolled, and then continuously annealed on the hot rolled plate.
  • a hot-rolled plated steel sheet is obtained by sequentially performing the treatment and the plating treatment.
  • the finish rolling temperature of the finish rolling is 880 ° C. or more
  • the average cooling rate of the cooling is 10 ° C./s or more
  • the winding temperature of the winding is 400 ° C. or more and less than 550 ° C.
  • the continuous annealing treatment The annealing temperature of is 550 ° C. or higher and 750 ° C. or lower.
  • the melting method of the steel material is not particularly limited, and a known melting method such as a converter or an electric furnace can be employed. Moreover, after melting, it is preferable to use a slab (steel material) by a continuous casting method because of problems such as segregation, but a slab can also be formed by a known casting method such as ingot-bundling rolling or thin slab continuous casting. good. In addition, when hot-rolling the slab after casting, the slab may be rolled after being reheated in a heating furnace, and when the temperature is maintained at a predetermined temperature or higher, direct rolling without heating the slab You may do it.
  • the steel material obtained as described above is subjected to heating, rough rolling, and finish rolling.
  • the heating temperature of the steel material is preferably 1150 ° C. or higher.
  • the heating temperature of the steel material is excessively high, the surface is excessively oxidized and TiO 2 is generated and Ti is consumed. Is preferably 1300 ° C. or lower.
  • the step of heating the steel material before rough rolling is It can be omitted.
  • the rough rolling conditions are not particularly limited.
  • Finishing rolling temperature 880 ° C. or more Optimization of the finishing rolling temperature is important for maintaining the stretch flangeability and bending workability of the hot-rolled plated steel sheet and reducing the rolling load of finishing rolling.
  • the finish rolling temperature is 880 ° C. or higher.
  • it is 900 degreeC or more. If the finish rolling temperature is excessively high, wrinkles due to the secondary scale on the surface of the hot rolled sheet are likely to occur, and therefore the finish rolling temperature is desirably 1000 ° C. or lower.
  • the austenite ⁇ ferrite transformation temperature (ferrite transformation region in the CCT diagram) of the steel material is adjusted to a temperature range suitable for precipitation of carbide containing Ti.
  • the carbide containing Ti has a temperature range in which precipitation is particularly easy among the temperature ranges suitable for precipitation, and the temperature range is approximately 600 to 650 ° C. In this temperature range of 600 to 650 ° C, the driving force for carbide formation (change in free energy in which carbide is generated from solute Ti and solute C in steel) is large, and the diffusion rate of atoms becomes large.
  • the contained carbide is most easily precipitated. Therefore, forced cooling is performed after hot rolling is completed, and forced cooling is stopped in the temperature range (approx. 600 to 650 ° C) most suitable for precipitation of Ti-containing carbides, so that austenite ⁇ ferrite transformation occurs during winding. If so, almost the entire amount of Ti in the steel precipitates as fine carbides with the austenite ⁇ ferrite transformation during winding.
  • the carbides of Ti that precipitate at the same time as the austenite ⁇ ferrite transformation (phase interface precipitation) are dispersed and precipitated in a row, which contributes to improving the strength of the steel sheet but adversely affects the workability (bending properties) of the steel sheet. May affect. Therefore, in the present invention, the average cooling rate after completion of hot rolling is increased and the winding temperature is within the transformation temperature range from austenite to ferrite (within the ferrite transformation region in the CCT diagram) and includes Ti.
  • the temperature By regulating the temperature to a temperature lower than the most suitable temperature range (about 600 to 650 ° C) for the precipitation of fine carbides, the interfacial precipitation that is dispersed and precipitated in a row at the same time as the austenite ⁇ ferrite transformation is suppressed. And, by carrying out the random dispersion and precipitation of fine carbides containing Ti during the subsequent annealing process before the plating process, which is the next process, workability (particularly bending workability) is ensured while increasing the strength of the hot-rolled plated steel sheet. .
  • the average cooling rate 10 ° C / s or more
  • the austenite ⁇ ferrite transformation temperature becomes high, and carbide containing Ti is contained.
  • the average cooling rate is 10 ° C./s or more.
  • it is 30 ° C./s or more.
  • it is preferably less than 200 ° C./s.
  • Winding temperature 400 ° C. or more and less than 550 ° C. Optimization of the winding temperature is achieved by changing the structure of the hot-rolled steel sheet as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention to a desired structure throughout the entire width direction of the hot-rolled steel sheet, That is, a matrix in which the ferrite phase has an area ratio of 95% or more with respect to the entire structure, and a structure in which fine carbides containing Ti and having an average particle diameter of less than 10 nm are dispersed and precipitated, and the number Ps of fine carbides precipitated in a row It is extremely important for increasing the ratio Pr / Ps of the number Pr of the fine carbides randomly precipitated with respect to.
  • the most suitable temperature range (about 600 to 650 ° C) for precipitation of carbide containing Ti.
  • the austenite ⁇ ferrite transformation at the time of winding almost all the Ti in the steel precipitates as fine carbides, and the hot-rolled sheet in which fine carbides are dispersed and precipitated in a certain direction in a row turn into.
  • carbide containing Ti is actively precipitated in the cooling and winding process after hot rolling, the precipitation form of carbide contained in the finally obtained hot-rolled plated steel sheet is mainly lined precipitation and bending. There is concern about deterioration of workability.
  • the steel material is heated to the austenite region before hot rolling to dissolve carbides in the steel material, and precipitation of carbides containing Ti is suppressed in the subsequent winding process to obtain a hot rolled sheet. Then, by subjecting this hot-rolled sheet to a predetermined continuous annealing treatment, fine carbides having a desired average particle diameter (Ti-containing carbides) are precipitated, and the number of fine carbides randomly precipitated among the fine carbides ( Pr) is increased to increase the ratio Pr / Ps.
  • Ti-containing carbides fine carbides having a desired average particle diameter
  • Pr fine carbides randomly precipitated among the fine carbides
  • the precipitation form becomes a line shape
  • the precipitation form becomes random. Therefore, in the present invention, the columnar precipitation is suppressed by setting the coiling temperature lower, and the random precipitation during the subsequent continuous annealing treatment is promoted.
  • the coiling temperature is 400 ° C. or higher and lower than 550 ° C.
  • the coiling temperature is 400 ° C. or higher and lower than 550 ° C.
  • it is 450 degreeC or more and less than 550 degreeC.
  • Ti added to the steel material partially precipitates as carbide during winding, the matrix is substantially a ferrite single phase, and a part of Ti remains as a solid solution in the matrix.
  • a hot rolled sheet is obtained.
  • the thus obtained hot-rolled sheet is subjected to continuous annealing treatment at a predetermined annealing temperature, thereby precipitating fine carbide (a carbide containing Ti) in a desired precipitation form.
  • the temperature rising conditions at the time of heating a hot-rolled sheet to an annealing temperature are not specifically limited.
  • Annealing temperature of continuous annealing treatment When the annealing temperature is 550 ° C. or higher and 750 ° C. or lower exceeds 750 ° C., carbides containing Ti are coarsened and the strength is lowered. Therefore, the annealing temperature is set to 750 ° C. or lower. Preferably it is 700 degrees C or less. On the other hand, when the annealing temperature is less than 550 ° C., the amount of fine carbides containing Ti is insufficient, and the desired steel plate strength cannot be obtained. Therefore, the annealing temperature is set to 550 ° C. or higher. Preferably it is 600 degreeC or more.
  • the holding time (annealing time) at the annealing temperature is preferably 60 s or more and 600 s or less from the viewpoint of promoting the precipitation of fine carbides containing Ti and preventing the coarsening thereof. More preferably, it is 60 seconds or more and 300 seconds or less.
  • the hot-rolled sheet after the continuous annealing treatment is subjected to a plating treatment.
  • the kind of the plating treatment is not particularly limited, and a conventionally known plating treatment can be applied.
  • the hot dip galvanizing treatment is particularly suitable, for example, annealing at the above annealing temperature in a continuous annealing plating line, dipping in a 480 ° C zinc plating bath (0.1% Al-Zn, etc.) It is possible to form a hot dip galvanized film of m 2 (attachment amount per side).
  • the alloying process can be performed at 520 ° C. following the hot dip galvanizing process.
  • a matrix having an area ratio of 95% or more with respect to the entire structure of the ferrite phase and a fine particle having an average particle diameter of less than 10 nm including Ti is obtained. It is possible to obtain a hot-rolled sheet having a structure in which carbides are dispersed and precipitated, and having a high ratio of fine carbides randomly precipitated among the fine carbides.
  • the hot-rolled sheet has excellent workability that has a tensile strength of 590 MPa or more and has both excellent stretch flangeability and bending workability.
  • the hot-rolled sheet after the continuous annealing treatment to plating treatment or further alloying treatment, and forming a plating film (for example, hot-dip galvanized film or alloyed hot-dip galvanized film) on the surface thereof
  • a plating film for example, hot-dip galvanized film or alloyed hot-dip galvanized film
  • Molten steel having the composition shown in Table 1 was melted and continuously cast by a generally known technique to obtain a slab (steel material) having a thickness of 250 mm. These slabs are heated to 1250 ° C., then roughly rolled and subjected to finish rolling at the finish rolling temperature shown in Table 2, and after finish rolling, the temperature range from the finish rolling temperature to the winding temperature is shown in Table 2. It cooled at the average cooling temperature, wound up at the winding temperature shown in Table 2, and was set as the hot rolled sheet. The obtained hot-rolled sheet was pickled to remove the surface scale, and then subjected to continuous annealing treatment at the annealing temperatures shown in Table 2.
  • the hot-rolled sheet after the continuous annealing treatment is immersed in a hot dip galvanizing bath (plating bath composition: 0.1% Al-Zn, bath temperature: 480 ° C.), and the adhesion amount is 45 g / m 2 (the adhesion amount per side). )
  • a hot dip galvanized steel sheet hot rolled galvanized steel sheet.
  • some hot-dip galvanized steel sheets hot rolling numbers b1, d1, h, i, j, k, and l in Table 2 were alloyed at 520 ° C. to obtain alloyed hot-dip galvanized steel sheets. .
  • Test specimens were collected from the hot-rolled galvanized steel sheets (hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets) obtained as described above, and subjected to microstructure observation, precipitate observation, tensile test, hole expansion test, bending test, and ferrite phase. Area ratio, average particle size and volume ratio of fine carbide containing Ti, and precipitation form, tensile strength, hole expansion rate (stretch flangeability), and critical bending radius (bending workability) of the fine carbide were determined. . The test method was as follows.
  • the particle size of fine carbide containing Ti was determined by image processing based on the observation results of 30 visual fields at 260,000 times, and the particle size was obtained by circular approximation. The calculated particle diameters of each particle were arithmetically averaged to obtain an average particle diameter.
  • the volume ratio of fine carbide containing Ti is the weight of Ti carbide based on the extraction residue analysis of the residue collected by electrolysis of the ground iron using 10% acetylacetone-1% tetramethylammonium chloride-methanol solution (AA solution). The volume was determined by dividing this by the density of Ti carbide (TiC), and this volume was divided by the volume of the dissolved iron.
  • Dispersion precipitation form TEM photograph with a magnification of 260,000 was taken for each test piece, 20 counts of the number Ps of fine carbides observed in a row and the number Pr of those observed randomly, Pr / Ps Asked. In the observation, those in which fine carbides were not observed in a line even when the test piece was tilted to 30 ° were regarded as randomly precipitated fine carbides.
  • Each of the examples of the present invention is a hot rolled galvanized steel sheet that has both high strength of tensile strength TS: 590 MPa or more, stretch flangeability of hole expansion ratio ⁇ : 100% or more, and bending workability of critical bending radius of 0.9 or less. It has become.
  • a predetermined high strength cannot be ensured, or the hole expansion rate ⁇ or the limit bending radius cannot be ensured.

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Abstract

Provided are: a high-tensile-strength hot-rolled plated steel sheet provided with both strength and workability (stretch flangeability and bending workability); and a method for producing same. The plated steel sheet has a plating film on at least one surface of a hot-rolled steel sheet that is the substrate, wherein the high-tensile-strength hot-rolled plated steel sheet having a tensile strength of at least 590 MPa and superior workability results by causing the hot-rolled steel sheet to have: a composition containing, by mass%, 0.010%-0.050% inclusive of C, no greater than 0.2% of Si, 0.10-0.80% inclusive of Mn, no greater than 0.025% of P, no greater than 0.01% of S, no greater than 0.01% of N, no greater than 0.1% of Al, and 0.05-0.10% inclusive of Ti in a manner so that C, S, N, and Ti satisfy Ti*/48 < C/12 (where Ti* = Ti - (N/14×48 + S/32×48), and C, S, N, and Ti represent the amount contained (mass%) of the respective elements), the remainder comprising Fe and unavoidable impurities; a matrix such that there is at least 95% by area ratio of ferrite phase with respect to the structure as a whole; and a structure such that minute carbides containing Ti and having an average grain size of less than 10 nm are dispersed/precipitated.

Description

高張力熱延めっき鋼板およびその製造方法High tensile hot rolled galvanized steel sheet and method for producing the same
　本発明は、自動車用部品等の輸送機材、構造材の素材に好適な高張力熱延めっき鋼板およびその製造方法(high strength galvanized hot rolled steel sheet and method for producing the same)に関する。 The present invention relates to a high-tensile hot-rolled plated steel sheet suitable for transportation equipment such as automobile parts and structural materials, and a method for producing the same (high-strength-galvanized hot-rolled steel sheet and method manufacturing for the same.
地球環境保全の観点からCO2排出量を削減すべく、自動車車体の強度を維持しつつその軽量化を図り、自動車の燃費を改善することが、自動車業界においては常に重要な課題とされている。自動車車体の強度を維持しつつ車体の軽量化を図るうえでは、自動車部品用素材となる鋼板の高強度化により、鋼板を薄肉化することが有効である。特に、自動車の足回り部品用鋼板の高強度薄肉化は、自動車車体の大幅な軽量化につながるため、自動車の燃費向上に極めて有効な手段である。そのため、これらの部品用の素材に対する高強度化の要望は非常に強い。 In order to reduce CO 2 emissions from the viewpoint of global environmental conservation, maintaining the strength of the car body while reducing its weight and improving the fuel efficiency of the car has always been an important issue in the automobile industry. . In order to reduce the weight of the vehicle body while maintaining the strength of the automobile body, it is effective to reduce the thickness of the steel sheet by increasing the strength of the steel sheet used as a material for automobile parts. In particular, reducing the strength and thickness of steel plates for undercarriage parts of automobiles is a very effective means for improving the fuel efficiency of automobiles because it leads to significant weight reduction of automobile bodies. For this reason, there is a strong demand for increasing the strength of materials for these parts.
また、自動車部品、特に足回り部品は、腐食環境に晒されることが多いため、自動車部品用鋼板は所望の耐食性を有することも必須となる。そのため、自動車部品用鋼板としては、耐食性に優れた高張力（熱延）めっき鋼板が広く用いられている。
一方、鋼板を素材とする自動車部品の多くは、プレス加工やバーリング加工等によって成形されるため、自動車部品用鋼板には優れた伸び、伸びフランジ性(stretch-flange formability)等の加工性を有することが要求される。例えば、足回り部品は複雑な形状を有することから、足回り部品用素材としての鋼板には、強度および耐食性とともに加工性が重要視され、伸びフランジ性および曲げ加工性等の加工性に優れた高張力（熱延）めっき鋼板が求められている。 In addition, since automobile parts, particularly undercarriage parts are often exposed to corrosive environments, it is essential that the steel sheet for automobile parts has a desired corrosion resistance. Therefore, as a steel sheet for automobile parts, a high tension (hot rolled) plated steel sheet having excellent corrosion resistance is widely used.
On the other hand, many automotive parts made of steel sheets are formed by pressing, burring, etc., and therefore, steel sheets for automobile parts have excellent workability such as elongation and stretch-flange formability. Is required. For example, because the undercarriage parts have a complicated shape, the steel sheet as the material for the undercarriage parts is emphasized in workability as well as strength and corrosion resistance, and has excellent workability such as stretch flangeability and bending workability. There is a need for high tension (hot rolled) plated steel sheets.
しかしながら、一般的に鉄鋼材料は高強度化に伴い加工性が低下する。高張力（熱延）めっき鋼板の加工性は通常の軟鋼板よりもはるかに劣っている。そのため、高張力（熱延）めっき鋼板を足回り部品等に適用するうえでは、強度と加工性を兼ね備えた高張力（熱延）鋼板（めっき鋼板の基材となる鋼板）の開発が必須となり、現在までに多くの研究が為され、様々な技術が提案されている。 However, in general, the workability of steel materials decreases with increasing strength. The workability of a high-tensile (hot rolled) plated steel sheet is much inferior to that of a normal mild steel sheet. Therefore, in order to apply high-tensile (hot-rolled) plated steel sheets to undercarriage parts, etc., it is essential to develop high-tensile (hot-rolled) steel sheets (steel sheets used as the base material for plated steel sheets) that have both strength and workability. A lot of research has been done so far, and various techniques have been proposed.
　例えば、特許文献１には、重量％で、C：0.03～0.25％、Si：2.0％以下、Mn：2.0％以下、P：0.1％以下、S：0.007％以下、Al：0.07％以下及びCr：1.0％以下を含有する組成とし、フェライトと第２相からなる複合組織とし、第２相の硬さ、体積率、および粒径を規定することにより、引張強さ(TS)が490N/mm2(490MPa)を超える高強度熱延鋼板の疲労特性(Fatigue property)と伸びフランジ性を向上させる技術が提案されている。前記第２相は、パーライト、ベイナイト、マルテンサイト、残留オーステナイト(retained austenite)の１種以上である。 For example, Patent Document 1 discloses that by weight, C: 0.03-0.25%, Si: 2.0% or less, Mn: 2.0% or less, P: 0.1% or less, S: 0.007% or less, Al: 0.07% or less, and Cr : A composition containing 1.0% or less, a composite structure composed of ferrite and the second phase, and by specifying the hardness, volume ratio, and particle size of the second phase, the tensile strength (TS) is 490 N / mm A technique for improving fatigue properties and stretch flangeability of high-strength hot-rolled steel sheets exceeding 2 (490 MPa) has been proposed. The second phase is one or more of pearlite, bainite, martensite, and retained austenite.
　しかしながら、特許文献１で提案された技術では、鋼板にプレス加工等を施して所望の部品形状に成形する際、軟質のフェライトと硬質の第２相との界面が、加工時の割れ発生起点となり易く、加工性が安定しないという問題を有する。また、特許文献１で提案された技術では、鋼板の引張強さを590MPa級に高めた場合、加工性、特に伸びフランジ性が低下するという問題も見られる。 However, in the technique proposed in Patent Document 1, when a steel sheet is pressed to form a desired part shape, the interface between the soft ferrite and the hard second phase is the starting point for cracking during processing. It has the problem that it is easy and processability is not stable. In the technique proposed in Patent Document 1, when the tensile strength of the steel sheet is increased to a 590 MPa class, there is a problem that workability, particularly stretch flangeability is deteriorated.
　また、特許文献２には、wt％で、C：0.01～0.10％、Si：1.5％以下、Mn：1.0％超～2.5％、P：0.15％以下、S：0.008％以下、Al：0.01～0.08％、Ti，Nbの１種又は２種の合計：0.10～0.60％を含む化学成分とし、フェライト量が面積率で95％以上であり、かつフェライトの平均結晶粒径が2.0～10.0μm であり、マルテンサイトおよび残留オーステナイトを含まない組織とすることにより、引張強さが490MPa以上である高強度熱延鋼板の疲労強度、特に伸びフランジ性を向上させる技術が提案されている。そして、特許文献２で提案された技術では、Mn含有量を1.0％超～2.5％とすることにより、鋼板強度が向上するとともに微細フェライト粒が得られるとされている。 In Patent Document 2, wt%, C: 0.01 to 0.10%, Si: 1.5% or less, Mn: more than 1.0% to 2.5%, P: 0.15% or less, S: 0.008% or less, Al: 0.01 to The chemical composition contains 0.08%, one or two of Ti and Nb: 0.10 to 0.60%, the ferrite content is 95% or more in area ratio, and the average crystal grain size of ferrite is 2.0 to 10.0μm There has been proposed a technique for improving the fatigue strength, particularly the stretch flangeability of a high-strength hot-rolled steel sheet having a tensile strength of 490 MPa or more by making the structure free from martensite and retained austenite. In the technique proposed in Patent Document 2, the strength of the steel sheet is improved and fine ferrite grains are obtained by setting the Mn content to more than 1.0% to 2.5%.
しかしながら、特許文献２で提案された技術では、鋼板のMn含有量が高いため、鋼板の板厚中央部にMnが偏析し、鋼板のプレス成形の際、加工時に割れを誘発するので、優れた伸びフランジ性を安定的に得ることができないという問題がある。また、特許文献２で提案された技術では、Tiを所定含有量としてTi炭化物を形成することにより、伸びフランジ性に悪影響を及ぼす固溶Cの低減化を図っているが、Cに対して過剰のTiを含有させると、Ti炭化物が粗大化し易くなり、所望の強度を安定的に得られないという問題が見られる。 However, in the technique proposed in Patent Document 2, since the Mn content of the steel sheet is high, Mn segregates in the central part of the thickness of the steel sheet, and when the steel sheet is press-formed, cracks are induced during processing. There is a problem that stretch flangeability cannot be obtained stably. In the technique proposed in Patent Document 2, Ti carbide is formed with Ti as a predetermined content to reduce solid solution C that adversely affects stretch flangeability. When Ti is contained, Ti carbide tends to be coarsened, and there is a problem that a desired strength cannot be stably obtained.
また、特許文献３には、質量％にて、C：0.01～0.1％、S≦0.03％、N≦0.005％、Ti：0.05～0.5％、Si：0.01～2％、Mn：0.05～2％、P≦0.1％、Al：0.005～1.0％を含み、さらにTi－48/12C－48/14N－48/32S≧0％を満たす範囲でTiを含有する組成とし、鋼中の粒子で5nm以上のTiを含む析出物の平均サイズを101～103nmで最小間隔を101 nm超104 nm以下とすることにより、引張強さが640MPa以上である高強度熱延鋼板のバーリング加工性(Burring formability)と疲労特性を向上させる技術が提案されている。 In Patent Document 3, in mass%, C: 0.01 to 0.1%, S ≦ 0.03%, N ≦ 0.005%, Ti: 0.05 to 0.5%, Si: 0.01 to 2%, Mn: 0.05 to 2% , P ≤ 0.1%, Al: 0.005 to 1.0%, and a composition containing Ti in a range that satisfies Ti-48 / 12C-48 / 14N-48 / 32S ≥ 0%, and the particle size in steel is 5nm or more by the minimum interval average size at 10 1 ~ 10 3 nm of precipitates containing the Ti or less 10 1 nm ultra 10 4 nm, burring workability high-strength hot-rolled steel sheet tensile strength is at least 640MPa Technologies for improving (Burring formability) and fatigue properties have been proposed.
しかしながら、特許文献３で提案された技術では、鋼板に含まれる析出物のサイズの分布が大きく、所望の強度を安定的に確保することができないという問題が見られる。また、特許文献３で提案された技術では、鋼板の伸びフランジ性が不十分である。 However, with the technique proposed in Patent Document 3, there is a problem that the distribution of the size of precipitates contained in the steel sheet is large and the desired strength cannot be secured stably. Moreover, with the technique proposed by patent document 3, the stretch flangeability of a steel plate is inadequate.
特開平４－３２９８４８号公報JP-A-4-329848 特開２０００－３２８１８６号公報JP 2000-328186 A 特開２００２－１６１３４０号公報JP 2002-161340 A
大量生産される自動車部品に対しては、その素材を安定的に供給すべく熱延鋼板を工業的に大量生産する必要があるが、上記した従来技術では、引張強さが590MPa以上であり且つ優れた加工性（伸びフランジ性、曲げ加工性）を有する高張力（熱延）めっき鋼板を、安定的に供給することが困難である。本発明は、上記した従来技術が抱える問題を有利に解決し、自動車部品用の素材として好適な、引張強さが590MPa以上であり且つ優れた伸びフランジ性と優れた曲げ加工性を兼備する、加工性に優れた高張力熱延めっき鋼板およびその製造方法を提供することを目的とする。 For automobile parts that are mass-produced, it is necessary to industrially mass-produce hot-rolled steel sheets in order to stably supply the materials. However, in the above-mentioned conventional technology, the tensile strength is 590 MPa or more and It is difficult to stably supply a high tension (hot rolled) plated steel sheet having excellent workability (stretch flangeability, bending workability). The present invention advantageously solves the above-described problems of the prior art, is suitable as a material for automobile parts, has a tensile strength of 590 MPa or more, and has excellent stretch flangeability and excellent bending workability. An object is to provide a high-tensile hot-rolled plated steel sheet excellent in workability and a method for producing the same.
　上記課題を解決すべく、本発明者らは、熱延めっき鋼板の高強度化と加工性、特に伸びフランジ性と曲げ加工性に及ぼす各種要因について鋭意検討した。その結果、以下のような知見を得た。
１）鋼板組織を転位密度が低い加工性に優れたフェライト単相組織とし、更に、微細炭化物を分散析出させて析出強化すると、熱延めっき鋼板の伸びフランジ性および曲げ加工性を維持したまま、強度が向上すること。
２）加工性に優れ且つ引張強さ：590MPa以上の高強度を有する熱延めっき鋼板を得るためには、析出強化に有効な平均粒子径が10nm未満である微細炭化物を分散析出させる必要があること。 In order to solve the above-mentioned problems, the present inventors diligently studied various factors affecting the increase in strength and workability of hot-rolled plated steel sheets, particularly stretch flangeability and bending workability. As a result, the following findings were obtained.
1) When the steel sheet structure is a ferrite single-phase structure with a low dislocation density and excellent workability, and when fine carbide is dispersed and precipitated to strengthen the precipitation, the stretch flangeability and bending workability of the hot-rolled plated steel sheet are maintained. Strength is improved.
2) In order to obtain hot rolled galvanized steel sheets having excellent workability and high tensile strength: 590 MPa or more, it is necessary to disperse and precipitate fine carbides having an average particle diameter of less than 10 nm effective for precipitation strengthening. thing.
３）析出強化に寄与する微細炭化物としては、Tiを含む炭化物が有効であること。
４）Tiを含む炭化物には、一方向に列状に分散析出するものと、ランダムに分散析出するものが存在するが、熱延めっき鋼板の高強度化を図りつつ加工性、特に曲げ加工性を確保するうえでは、ランダムに分散析出するTiを含む炭化物の比率を高めることが有効であること。一方、熱延めっき鋼板の高強度化には、上記何れの析出形態の炭化物も有効であること。 3) Carbide containing Ti is effective as fine carbide contributing to precipitation strengthening.
4) There are carbides containing Ti that are dispersed and precipitated in a line in one direction and those that are randomly dispersed and precipitated, but workability, especially bending workability, while increasing the strength of hot-rolled steel sheets. It is effective to increase the proportion of carbides containing Ti that is randomly dispersed and precipitated. On the other hand, any of the above precipitation forms of carbide is effective for increasing the strength of the hot-rolled steel sheet.
５）Tiを含む炭化物を平均粒子径：10nm未満とし、更に分散析出させた該炭化物の粗大化を抑制するためには、鋼中のC含有量に対するTi*含有量を制御する必要があること。（但し、Ti*＝Ti－(N/14×48＋S/32×48) であり、C、S、N、Tiは各元素の含有量（質量％）である。）
６）所定の組成を有する鋼素材を熱間圧延したのち、冷却して巻き取り熱延めっき鋼板の基材となる熱延板を製造するに際し、Tiを含む炭化物の析出に最適な温度で巻き取ると、上記炭化物が主として列状に分散析出した熱延板が得られること。
７）上記巻取り温度を、Tiを含む炭化物の析出に最適な温度よりも低い温度に設定して、Tiを含む炭化物の析出を抑制した熱延板とし、係る熱延板に、所定の焼鈍温度で連続焼鈍処理を施して該連続焼鈍処理時にTiを含む炭化物をランダムに析出させることにより、ランダムに分散析出した炭化物を多く含む熱延鋼板（熱延めっき鋼板の基板であって、焼鈍後めっき前の基板）が得られること。 5) To make the carbide containing Ti have an average particle size of less than 10 nm and further suppress the coarsening of the dispersed and precipitated carbide, it is necessary to control the Ti * content relative to the C content in the steel. . (However, Ti * = Ti− (N / 14 × 48 + S / 32 × 48) where C, S, N, and Ti are the contents (mass%) of each element.)
6) After hot-rolling a steel material having a predetermined composition, it is cooled and wound at a temperature optimum for precipitation of carbides containing Ti when manufacturing a hot-rolled sheet to be a base material of a rolled hot-rolled plated steel sheet. As a result, a hot-rolled sheet in which the carbides are dispersed and precipitated mainly in a row is obtained.
7) The above coiling temperature is set to a temperature lower than the optimum temperature for precipitation of carbide containing Ti, and a hot rolled sheet suppressing precipitation of carbide containing Ti is formed. By performing continuous annealing treatment at a temperature and precipitating carbides containing Ti at random during the continuous annealing treatment, a hot-rolled steel sheet containing a large amount of randomly dispersed carbides (a substrate of a hot-rolled steel sheet, after annealing) Substrate before plating) is obtained.
　本発明は上記の知見に基づき完成されたものであり、その要旨は次のとおりである。
［１］　基板である熱延鋼板の少なくとも一方の表面にめっき皮膜を有するめっき鋼板であって、前記熱延鋼板が、質量％で、
C ：0.010％以上0.050％以下、     Si：0.2％以下、
Mn：0.10％以上0.80％以下、       P ：0.025％以下、
S ：0.01％以下、　　　　　　　    N ：0.01％以下、
Al：0.1％以下、                 Ti：0.05％以上0.10％以下
を、C、S、N、およびTiが下記(1)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成と、フェライト相の組織全体に対する面積率が95％以上であるマトリックスと、Tiを含み平均粒子径が10nm未満である微細炭化物が分散析出した組織を有し、引張強さが590MPa以上である、高張力熱延めっき鋼板。
　　　　　　　　　　　Ti*/48 ＜ C/12　 ・・・ (1)
　　　　　　　　ここで、Ti*＝Ti－(N/14×48＋S/32×48)
　　　　　　　（C、S、N、Ti：各元素の含有量（質量％）） The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] A plated steel sheet having a plating film on at least one surface of a hot-rolled steel sheet as a substrate, wherein the hot-rolled steel sheet is in mass%.
C: 0.010% or more and 0.050% or less, Si: 0.2% or less,
Mn: 0.10% to 0.80%, P: 0.025% or less,
S: 0.01% or less, N: 0.01% or less,
Al: 0.1% or less, Ti: 0.05% or more and 0.10% or less, containing C, S, N, and Ti so that the following formula (1) is satisfied, with the balance being Fe and inevitable impurities, High tensile strength with a matrix with an area ratio of 95% or more with respect to the entire structure of the ferrite phase and a structure in which fine carbides containing Ti and an average particle diameter of less than 10 nm are dispersed and precipitated, and a tensile strength of 590 MPa or more Hot-rolled steel sheet.
Ti * / 48 <C / 12 (1)
Where Ti * = Ti- (N / 14 x 48 + S / 32 x 48)
(C, S, N, Ti: content of each element (mass%))
［２］　前記［１］において、前記組成に加えてさらに、質量％でB ：0.0035％以下を、下記(2)式を満足するように含有する、高張力熱延めっき鋼板。
　　　　　　　　　　B ≧ 0.0003－0.00025Mn ・・・ (2)
　　　　　　　　　（Mn、B：各元素の含有量（質量％））
［３］前記Bが、0.0003％以上、0.0020％以下である、［２］に記載の高張力熱延めっき鋼板。 [2] A high-tensile hot-rolled plated steel sheet according to the above [1], further containing B: 0.0035% or less by mass% so as to satisfy the following formula (2) in addition to the above composition.
B ≧ 0.0003-0.00025Mn (2)
(Mn, B: content of each element (mass%))
[3] The high-tensile hot-rolled plated steel sheet according to [2], wherein B is 0.0003% or more and 0.0020% or less.
［４］　前記［１］または［２］において、前記微細炭化物が、列状に析出したものの個数Psとランダムに析出したものの個数Prとの比率が下記(3)式を満足する、高張力熱延めっき鋼板。
　　　　　　　　　　　　Pr/Ps ≧　0.8 ・・・ (2)
　　　　　　（Pr：ランダムに析出している微細炭化物の個数）
　　　　　　　（Ps：列状に析出している微細炭化物の個数） [4] In the above [1] or [2], the ratio of the number Ps of fine carbides precipitated in a row to the number Pr of random precipitates satisfies the following formula (3): Plated steel sheet.
Pr / Ps ≥ 0.8 (2)
(Pr: number of fine carbides that are randomly deposited)
(Ps: number of fine carbides deposited in a row)
［５］　前記［１］または[２]において、前記微細炭化物の組織全体に対する体積比が0.0005以上である、高張力熱延めっき鋼板。
［６］前記体積比が、0.0005以上、0.003以下である［５］に記載の高張力熱延めっき鋼板。 [5] The high-tensile hot-rolled plated steel sheet according to [1] or [2], wherein a volume ratio of the fine carbide to the entire structure is 0.0005 or more.
[6] The high-tensile hot-rolled plated steel sheet according to [5], wherein the volume ratio is 0.0005 or more and 0.003 or less.
［７］　前記［１］または[２]において、前記組成に加えてさらに、質量％で、Cu、Sn、Ni、Ca、Mg、Co、As、Cr、W、Nb、Mo、V、Pb、Taのいずれか１種以上を合計で1％以下含有する、高張力熱延めっき鋼板。 [7] In the above [1] or [2], in addition to the above composition, Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, High-tensile hot-rolled plated steel sheet containing at least 1% of any one of Ta in total.
［８］　鋼素材に、粗圧延と仕上げ圧延からなる熱間圧延を施し、仕上げ圧延終了後、冷却し、巻き取り、熱延板としたのち、該熱延板に連続焼鈍処理およびめっき処理を順次施して熱延めっき鋼板とする、高張力熱延めっき鋼板の製造方法において、
前記鋼素材を、質量％で、
C ：0.010％以上0.050％以下、     Si：0.2％以下、
Mn：0.10％以上0.80％以下、       P ：0.025％以下、
S ：0.01％以下、　　　　　　　    N ：0.01％以下、
Al：0.1％以下、                 Ti：0.05％以上0.10％以下
を、C、S、N、およびTiが下記(1)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成とし、
前記仕上げ圧延の仕上げ圧延温度を880℃以上とし、前記冷却の平均冷却速度を10℃/s以上とし、前記巻取り温度を400℃以上550℃未満とし、前記連続焼鈍処理の焼鈍温度を550℃以上750℃以下とする、引張強さが590MPa以上である高張力熱延めっき鋼板の製造方法。
　　　　　　　　　　　Ti*/48 ＜ C/12　 ・・・ (1)
　　　　　　　　ここで、Ti*＝Ti－(N/14×48＋S/32×48)
　　　　　　　（C、S、N、Ti：各元素の含有量（質量％）） [8] The steel material is subjected to hot rolling consisting of rough rolling and finish rolling. After finishing rolling, the steel material is cooled, wound and formed into a hot rolled sheet, and then subjected to continuous annealing treatment and plating treatment on the hot rolled sheet. In the manufacturing method of high-tensile hot-rolled plated steel sheet, which is sequentially applied to make a hot-rolled plated steel sheet,
The steel material in mass%,
C: 0.010% or more and 0.050% or less, Si: 0.2% or less,
Mn: 0.10% to 0.80%, P: 0.025% or less,
S: 0.01% or less, N: 0.01% or less,
Al: 0.1% or less, Ti: 0.05% or more and 0.10% or less containing C, S, N, and Ti so that the following formula (1) is satisfied, with the balance being Fe and inevitable impurities,
The finish rolling temperature of the finish rolling is 880 ° C. or more, the average cooling rate of the cooling is 10 ° C./s or more, the winding temperature is 400 ° C. or more and less than 550 ° C., and the annealing temperature of the continuous annealing treatment is 550 ° C. A method for producing a high-tensile hot-rolled plated steel sheet having a tensile strength of 590 MPa or more and a temperature of 750 ° C. or less.
Ti * / 48 <C / 12 (1)
Where Ti * = Ti- (N / 14 x 48 + S / 32 x 48)
(C, S, N, Ti: content of each element (mass%))
［９］　前記［８］において、前記組成に加えてさらに、質量％でB ：0.0035％以下を、下記(2)式を満足するように含有する、高張力熱延めっき鋼板の製造方法。
　　　　　　　　　　B ≧ 0.0003－0.00025Mn ・・・ (2)
（Mn、B：各元素の含有量（質量％））
［１０］前記Bが、0.0003％以上、0.0020％以下である、［９］に記載の高張力熱延めっき鋼板の製造方法。 [9] The method for producing a high-tensile hot-rolled steel sheet according to [8], further including B: 0.0035% or less by mass% in addition to the composition so as to satisfy the following expression (2).
B ≧ 0.0003-0.00025Mn (2)
(Mn, B: content of each element (mass%))
[10] The method for producing a high-tensile hot-rolled plated steel sheet according to [9], wherein B is 0.0003% or more and 0.0020% or less.
［１１］　前記［８］または［９］において、前記組成に加えてさらに、質量％で、Cu、Sn、Ni、Ca、Mg、Co、As、Cr、W、Nb、Mo、V、Pb、Taのいずれか１種以上を合計で1％以下含有する、高張力熱延めっき鋼板の製造方法。 [11] In the above [8] or [9], in addition to the above composition, in mass%, Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, A method for producing a high-tensile hot-rolled steel sheet containing at least 1% of any one of Ta in total.
　本発明によれば、自動車部品用の素材として好適な、引張強さが590MPa以上で、かつ、プレス時の断面形状が複雑な足回り部品等の素材として十分に適用可能な優れた加工性（伸びフランジ性、曲げ加工性）を有する高張力熱延めっき鋼板を、工業的に安定して生産することが可能となり、産業上格段の効果を奏する。 According to the present invention, excellent workability that can be applied satisfactorily as a material for an undercarriage component or the like that is suitable as a material for automobile parts, has a tensile strength of 590 MPa or more, and has a complicated cross-sectional shape at the time of pressing ( A high-tensile hot-rolled plated steel sheet having stretch flangeability and bending workability) can be produced industrially stably, and has a remarkable industrial effect.
　以下、本発明について詳細に説明する。
　まず、本発明の高張力熱延めっき鋼板の基板となる熱延鋼板の組織および炭化物の限定理由について説明する。
　本発明の高張力熱延めっき鋼板の基板となる熱延鋼板は、フェライト相が組織全体に対する面積率で95％以上であるマトリックスと、該マトリックスにTiを含み平均粒子径が10nm未満である微細炭化物が分散析出した組織を有する。前記微細炭化物は、列状に析出したものの個数Psとランダムに析出したものの個数Prとの比率がPr/Ps ≧0.8を満足する炭化物とすることが好ましい。また、前記微細炭化物の組織全体に対する体積比を0.0005以上とすることが好ましい。 Hereinafter, the present invention will be described in detail.
First, the structure of the hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention and the reasons for limiting the carbide will be described.
The hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention is a fine matrix in which the ferrite phase is 95% or more in terms of the area ratio with respect to the entire structure, and the matrix contains Ti and the average particle diameter is less than 10 nm. It has a structure in which carbides are dispersed and precipitated. The fine carbide is preferably a carbide in which the ratio of the number Ps of precipitates in a row and the number Pr of random precipitates satisfies Pr / Ps ≧ 0.8. The volume ratio of the fine carbide to the whole structure is preferably 0.0005 or more.
　フェライト相：組織全体に対する面積率で95％以上
　本発明においては、熱延めっき鋼板の加工性（伸びフランジ性、曲げ加工性）を確保するうえでフェライト相の形成が必須となる。熱延めっき鋼板の加工性の向上には、熱延めっき鋼板の基板となる熱延鋼板の組織を、転位密度の低い延性に優れたフェライト相とすることが有効である。特に、伸びフランジ性の向上には、上記熱延鋼板の組織をフェライト単相組織とすることが好ましいが、完全なフェライト単相組織でない場合であっても、実質的にフェライト単相組織、すなわち、組織全体に対する面積率で95％以上がフェライト相であれば、上記の効果を十分に発揮する。したがって、フェライト相の組織全体に対する面積率は95％以上とする。 Ferrite phase: 95% or more in area ratio with respect to the entire structure In the present invention, formation of a ferrite phase is essential to ensure the workability (stretch flangeability, bending workability) of the hot-rolled plated steel sheet. In order to improve the workability of the hot-rolled plated steel sheet, it is effective to make the structure of the hot-rolled steel sheet used as the substrate of the hot-rolled plated steel sheet into a ferrite phase having excellent ductility with a low dislocation density. In particular, in order to improve stretch flangeability, it is preferable that the structure of the hot-rolled steel sheet is a ferrite single-phase structure, but even if it is not a complete ferrite single-phase structure, it is substantially a ferrite single-phase structure, that is, If the area ratio with respect to the entire structure is 95% or more of the ferrite phase, the above effects are sufficiently exhibited. Therefore, the area ratio of the ferrite phase to the entire structure is 95% or more.
なお、上記熱延鋼板において、フェライト相以外の相としては、セメンタイト、パーライト、ベイナイト相、マルテンサイト相、残留オーステナイト相等が挙げられ、これらの合計は組織全体に対する面積率で5％程度以下であれば許容される。 In the above hot-rolled steel sheet, the phases other than the ferrite phase include cementite, pearlite, bainite phase, martensite phase, retained austenite phase, etc., and the total of these may be about 5% or less in terms of the area ratio relative to the entire structure. Is acceptable.
Tiを含む微細炭化物
　Tiは強力な炭化物構成元素であり、Tiを含む炭化物は、その平均粒子径が極めて小さい微細炭化物となる傾向が強い。そのため、熱延めっき鋼板の基板となる熱延鋼板中に微細炭化物を分散析出させることにより熱延めっき鋼板の高強度化を図る本発明においては、上記熱延鋼板中に分散析出をさせる微細炭化物として、Tiを含む微細炭化物とする。 Fine carbide containing Ti Ti is a strong carbide constituent element, and carbide containing Ti tends to be a fine carbide having an extremely small average particle diameter. Therefore, in the present invention to increase the strength of the hot-rolled plated steel sheet by dispersing and precipitating fine carbides in the hot-rolled steel sheet as a substrate of the hot-rolled plated steel sheet, the fine carbides that cause dispersed precipitation in the hot-rolled steel sheet As a fine carbide containing Ti.
微細炭化物の平均粒子径：10nm未満
熱延めっき鋼板に所望の強度（引張強さ：590MPa以上）を付与するうえでは、熱延めっき鋼板の基板となる熱延鋼板中に分散析出させる微細炭化物の平均粒子径が極めて重要であり、本発明においてはTi を含む微細炭化物の平均粒子径を10nm未満とする。マトリックス中に微細炭化物が析出すると、その微細炭化物が、鋼板に変形が加わった際に生じる転位の移動に対する抵抗として作用することにより熱延めっき鋼板が強化されるが、微細炭化物の平均粒子径を10nm未満とすると、上記の作用がより一層顕著となる。したがって、Ti を含む微細炭化物の平均粒子径は10nm未満とする。より好ましくは5nm以下である。 Average particle diameter of fine carbide: less than 10nm For imparting desired strength (tensile strength: 590MPa or more) to hot rolled galvanized steel sheet, The average particle size is extremely important. In the present invention, the average particle size of the fine carbide containing Ti is set to less than 10 nm. When fine carbide precipitates in the matrix, the fine carbide acts as a resistance to dislocation movement that occurs when the steel sheet is deformed, thereby strengthening the hot-rolled plated steel sheet. When the thickness is less than 10 nm, the above action becomes more remarkable. Therefore, the average particle diameter of the fine carbide containing Ti is set to less than 10 nm. More preferably, it is 5 nm or less.
列状に析出した微細炭化物の個数Psとランダムに析出した微細炭化物の個数Prとの比率：Pr/Ps≧0.8
Tiを含む炭化物（微細炭化物）には、ある一定の方向に列状に分散析出するものと、ランダムに分散析出するものが存在するが、列状に分散析出した微細炭化物は、熱延鋼板の曲げ加工性に悪影響を及ぼす。微細炭化物とマトリックスとの界面は曲げ加工時の亀裂発生部となるが、微細炭化物が列状に分散析出していると、微細炭化物とマトリックスとの界面で発生した亀裂が伝搬し易くなるためである。 Ratio between the number Ps of fine carbides deposited in a row and the number Pr of fine carbides randomly deposited: Pr / Ps ≧ 0.8
There are carbides containing fine Ti (fine carbides) that are dispersed and precipitated in a row in a certain direction, and those that are randomly dispersed and precipitated. It adversely affects bending workability. The interface between the fine carbide and the matrix becomes a crack generation part during bending, but if the fine carbide is dispersed and precipitated in a row, cracks generated at the interface between the fine carbide and the matrix are likely to propagate. is there.
以上の理由により、本発明では、最終的に得られる熱延めっき鋼板において、ランダムに析出する微細炭化物の比率を高め、熱延めっき鋼板の曲げ加工性の劣化を抑制することが好ましい。列状に析出した微細炭化物の個数Psとランダムに析出した微細炭化物の個数Prとの比率Pr/Psは、0.8以上とすることが好ましい。 For the above reasons, in the present invention, in the finally obtained hot-rolled steel sheet, it is preferable to increase the proportion of fine carbides that precipitate at random and suppress the deterioration of the bending workability of the hot-rolled steel sheet. The ratio Pr / Ps between the number Ps of fine carbides precipitated in a row and the number Pr of fine carbides randomly precipitated is preferably 0.8 or more.
熱延めっき鋼板強度を安定して得るためには、熱延めっき鋼板の基板となる熱延鋼板中に分散析出させる微細炭化物の分散析出量を制御することが有効であり、本発明においては、Tiを含み平均粒子径が10nm未満である微細炭化物の、上記熱延鋼板組織全体に対する体積比が0.0005以上となるように分散析出させることが好ましい。但し、上記体積比が0.003超になると、強度が高くなり過ぎ、伸びフランジ性が低下するおそれがあるため、上記体積比は0.0005以上0.003以下とすることが好ましい。 In order to stably obtain the hot-rolled plated steel sheet strength, it is effective to control the amount of fine carbide dispersed and precipitated in the hot-rolled steel sheet as a substrate of the hot-rolled plated steel sheet. It is preferable to disperse and precipitate fine carbides containing Ti and having an average particle diameter of less than 10 nm so that the volume ratio with respect to the entire hot-rolled steel sheet structure is 0.0005 or more. However, if the volume ratio exceeds 0.003, the strength becomes too high and the stretch flangeability may be deteriorated. Therefore, the volume ratio is preferably 0.0005 or more and 0.003 or less.
　次に、本発明の高張力熱延めっき鋼板の基板となる熱延鋼板の成分組成の限定理由について説明する。なお、以下の成分組成を表す％は、特に断らない限り質量％を意味するものとする。
　C ：0.010％以上0.050％以下、
　Cは、微細炭化物を形成し、鋼を強化するうえで必須の元素である。C含有量が0.010％未満であると、微細炭化物を十分に確保することができず、590MPa以上の引張強さが得られなくなる。一方、C含有量が0.050％を超えると、鋼板中にパーライトが形成され易くなり、伸びフランジ性を損なう。したがって、C含有量は0.010％以上0.050％以下とする。好ましくは0.020％以上0.035％以下である。 Next, the reason for limitation of the component composition of the hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention will be described. In addition,% showing the following component composition shall mean the mass% unless there is particular notice.
C: 0.010% or more and 0.050% or less,
C is an essential element for forming fine carbides and strengthening steel. If the C content is less than 0.010%, sufficient fine carbide cannot be secured, and a tensile strength of 590 MPa or more cannot be obtained. On the other hand, when the C content exceeds 0.050%, pearlite is easily formed in the steel sheet, and stretch flangeability is impaired. Therefore, the C content is 0.010% or more and 0.050% or less. Preferably they are 0.020% or more and 0.035% or less.
Si：0.2％以下
Siは、固溶強化元素であり、鋼の高強度化に有効な元素である。しかしながら、Si含有量が0.2％を超えると、フェライト相からのC析出が促進され、粒界に粗大なFe炭化物が析出し易くなり、伸びフランジ性が低下する。また、過剰なSiは、めっき性に悪影響を及ぼす。したがって、Si含有量は0.2％以下とする。好ましくは0.05％以下である。また、固溶強化のために0.005％以上であるのが好ましい。 Si: 0.2% or less
Si is a solid solution strengthening element and is an element effective for increasing the strength of steel. However, when the Si content exceeds 0.2%, C precipitation from the ferrite phase is promoted, coarse Fe carbides are likely to precipitate at the grain boundaries, and stretch flangeability is deteriorated. In addition, excessive Si adversely affects the plating properties. Therefore, the Si content is 0.2% or less. Preferably it is 0.05% or less. Further, it is preferably 0.005% or more for strengthening the solid solution.
Mn：0.10％以上0.80％以下
Mnは、固溶強化元素であり、鋼の高強度化に有効な元素である。このような効果を得るためには0.10％以上含有することが望ましいが、Mn含有量が0.80％を超えると偏析が生じ易くなり、且つ、フェライト相以外の相、すなわち硬質相が形成され、伸びフランジ性が低下する。したがって、Mn含有量は0.10％以上0.80％以下とする。好ましくは0.10％以上0.5％以下である。より好ましくは0.10％以上0.45％以下である。 Mn: 0.10% to 0.80%
Mn is a solid solution strengthening element and is an element effective for increasing the strength of steel. In order to obtain such an effect, it is desirable to contain 0.10% or more, but if the Mn content exceeds 0.80%, segregation is likely to occur, and a phase other than the ferrite phase, that is, a hard phase is formed, and the elongation is increased. Flangeability decreases. Therefore, the Mn content is 0.10% or more and 0.80% or less. Preferably it is 0.10% or more and 0.5% or less. More preferably, it is 0.10% or more and 0.45% or less.
P ：0.025％以下
Pは、固溶強化元素であり、鋼の高強度化に有効な元素であるが、P含有量が0.025％を超えると偏析が顕著になり、伸びフランジ性が低下する。したがって、P含有量は0.025％以下とする。好ましくは0.02％以下である。また、固溶強化のために0.005％以上であるのが好ましい。 P: 0.025% or less
P is a solid solution strengthening element and is an element effective for increasing the strength of steel. However, when the P content exceeds 0.025%, segregation becomes significant and stretch flangeability deteriorates. Therefore, the P content is 0.025% or less. Preferably it is 0.02% or less. Further, it is preferably 0.005% or more for strengthening the solid solution.
S ：0.01％以下
　Sは、熱間加工性（熱間圧延性）を低下させる元素であり、スラブの熱間割れ感受性を高めるほか、鋼中にMnSとして存在して熱延鋼板の伸びフランジ性を劣化させる。そのため、本発明ではSを極力低減することが好ましく、0.01％以下とする。好ましくは0.005％以下である。 S: 0.01% or less S is an element that lowers hot workability (hot rollability), increases the hot cracking susceptibility of slabs, and is present as MnS in steel and stretch flangeability of hot rolled steel sheets. Deteriorate. Therefore, in the present invention, it is preferable to reduce S as much as possible, and set it to 0.01% or less. Preferably it is 0.005% or less.
N ：0.01％以下
　Nは、本発明においては有害な元素であり、極力低減することが好ましい。特にN含有量が0.01％を超えると、鋼中に粗大な窒化物が生成することに起因して、伸びフランジ性が低下する。したがって、N含有量は0.01％以下とする。好ましくは0.006％以下である。 N: 0.01% or less N is a harmful element in the present invention and is preferably reduced as much as possible. In particular, when the N content exceeds 0.01%, the stretch flangeability deteriorates due to the formation of coarse nitrides in the steel. Therefore, the N content is 0.01% or less. Preferably it is 0.006% or less.
Al：0.1％以下
　Alは、脱酸剤として作用する元素である。このような効果を得るためには0.001％以上含有することが望ましいが、0.1％を超える含有は、加工性（伸びフランジ性および曲げ加工性）を低下させる。このため、Al含有量は0.1％以下とする。 Al: 0.1% or less Al is an element that acts as a deoxidizer. In order to acquire such an effect, it is desirable to contain 0.001% or more, but inclusion exceeding 0.1% lowers workability (stretch flangeability and bending workability). For this reason, Al content shall be 0.1% or less.
Ti：0.05％以上0.10％以下
Tiは、本発明において最も重要な元素の一つである。Tiは、炭化物を形成することにより、優れた伸びフランジ性および曲げ加工性を維持しつつ、鋼板の高強度化に寄与する元素である。このような効果を得るためには0.05％以上含有することが望ましい。但し、Ti含有量が0.10％を超えると、伸びフランジ性が低下する傾向にあることから、Ti含有量は0.10％以下とする。好ましくは0.05％以上0.095％以下である。 Ti: 0.05% or more and 0.10% or less
Ti is one of the most important elements in the present invention. Ti is an element that contributes to increasing the strength of a steel sheet while maintaining excellent stretch flangeability and bending workability by forming carbides. In order to acquire such an effect, it is desirable to contain 0.05% or more. However, if the Ti content exceeds 0.10%, the stretch flangeability tends to decrease, so the Ti content is 0.10% or less. Preferably they are 0.05% or more and 0.095% or less.
本発明の高張力熱延めっき鋼板の基板となる熱延鋼板は、C、S、N、Tiを、上記した範囲で且つ(1)式を満足するように含有する。
Ti*/48 ＜ C/12　 ・・・ (1)
ここで、Ti*＝Ti－(N/14×48＋S/32×48)
（C、S、N、Ti：各元素の含有量（質量％））
上記(1)式は、Tiを含む微細炭化物を、上記した所望の析出状態とするために満足すべき要件であり、本発明において極めて重要な指標である。 The hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention contains C, S, N, and Ti in the above-described range and satisfying the expression (1).
Ti * / 48 <C / 12 (1)
Where Ti * = Ti- (N / 14 x 48 + S / 32 x 48)
(C, S, N, Ti: content of each element (mass%))
The above formula (1) is a requirement to be satisfied in order to bring the fine carbide containing Ti into the above-described desired precipitation state, and is an extremely important index in the present invention.
先述のとおり、本発明においては基板となる熱延鋼板中にTiを含む微細炭化物を分散析出させる。ここで、Tiを含む炭化物は、その平均粒子径が極めて小さい微細炭化物となる傾向が強いものの、Cと結合するTiが原子比でC以上になると、炭化物が粗大化し易くなる。そして、炭化物の粗大化に伴って、所望の鋼板強度（引張強さ：590MPa以上）を確保することが困難となる。そのため、本発明では、鋼素材に含まれるCの原子％（C/12）を、炭化物生成に寄与できるTiの原子％（Ti*/48）よりも多くする必要がある。 As described above, in the present invention, fine carbides containing Ti are dispersed and precipitated in the hot-rolled steel sheet serving as the substrate. Here, although the carbide containing Ti has a strong tendency to become a fine carbide having an extremely small average particle diameter, the carbide tends to be coarsened when Ti combined with C becomes C or more in atomic ratio. And it becomes difficult to ensure desired steel plate strength (tensile strength: 590 MPa or more) with the coarsening of carbides. Therefore, in the present invention, it is necessary to increase the atomic percent of C (C / 12) contained in the steel material more than the atomic percent of Ti (Ti * / 48) that can contribute to carbide formation.
また、本発明においては、鋼素材に所定量のTiを添加し、基板となる熱延鋼板中にTiを含む微細炭化物を分散析出させるが、この微細炭化物は、熱延前の加熱で鋼素材中の炭化物を溶解し、主に熱間圧延後の巻取り以降の工程（巻取り工程および連続焼鈍工程）で析出させる。しかしながら、鋼素材に添加したTiの全量が炭化物生成に寄与するわけではなく、鋼素材に添加したTiの一部は窒化物や硫化物の形成に消費される。巻取り温度よりも高温域では、Tiが炭化物よりも窒化物や硫化物を形成し易く、熱延鋼板の製造時、巻取り工程の前にTiが窒化物や硫化物を形成するためである。よって、鋼素材に添加したTiのうち炭化物生成に寄与できるTi（Ti*）は、「Ti*＝Ti－(N/14×48＋S/32×48)」で表すことができる。 In the present invention, a predetermined amount of Ti is added to the steel material, and fine carbides containing Ti are dispersed and precipitated in the hot-rolled steel sheet as a substrate. The carbide inside is melted and deposited mainly in the steps after the winding after the hot rolling (winding step and continuous annealing step). However, the total amount of Ti added to the steel material does not contribute to carbide formation, and a part of Ti added to the steel material is consumed for the formation of nitrides and sulfides. This is because Ti forms nitrides and sulfides more easily than carbides at temperatures higher than the coiling temperature, and Ti forms nitrides and sulfides prior to the winding process when manufacturing hot-rolled steel sheets. . Therefore, Ti (Ti * ) that can contribute to carbide generation among Ti added to the steel material can be represented by “Ti * = Ti− (N / 14 × 48 + S / 32 × 48)”.
以上の理由により、本発明では、Cの原子％（C/12）を、炭化物生成に寄与できるTiの原子％（Ti*/48）よりも多くする目的で、Ti*＝Ti－(N/14×48＋S/32×48)とし、Ti*/48 ＜ C/12 を満足するようにC、S、N、Tiの各元素を含有することとする。
　Ti*/48がC/12以上となると、Tiを含む微細炭化物が粗大化し易くなる。 For the above reasons, in the present invention, Ti * = Ti− (N / N) for the purpose of increasing the atomic percent of C (C / 12) to the atomic percent of Ti (Ti * / 48) that can contribute to carbide formation. 14 × 48 + S / 32 × 48), and each element of C, S, N, and Ti is contained so as to satisfy Ti * / 48 <C / 12.
When Ti * / 48 is C / 12 or more, fine carbides containing Ti are easily coarsened.
また、Tiを含む炭化物は、熱延前に鋼素材をオーステナイト域まで加熱して鋼素材中の炭化物を溶解し、その後の熱延工程において分散析出させる。この時、オーステナイトからフェライトへの変態への変態温度を、Tiを含む炭化物の析出に適した温度に調整し、その温度で巻き取ると、オーステナイト→フェライト変態と同時に、Tiを含む微細炭化物が列状に析出（相界面析出）する。
ここで、鋼素材がオーステナイトからフェライトに高温で変態すると、高温域でTiを含む炭化物が析出することになるが、このように高温域で析出した炭化物は粗大化し易いため、所望の微細炭化物（平均粒子径10nm未満）を得ることができない。したがって、本発明では、鋼素材がオーステナイトからフェライトに変態する温度を、微細な炭化物が析出するに十分な温度まで低下させることが好ましい。 Moreover, the carbide containing Ti heats the steel material to the austenite region before hot rolling, dissolves the carbide in the steel material, and disperses and precipitates in the subsequent hot rolling process. At this time, when the transformation temperature from the transformation from austenite to ferrite is adjusted to a temperature suitable for precipitation of carbide containing Ti, winding at that temperature, fine carbide containing Ti is aligned at the same time as austenite → ferrite transformation. It precipitates in the shape (phase interface precipitation).
Here, when the steel material is transformed from austenite to ferrite at a high temperature, carbides containing Ti are precipitated at a high temperature range. Since the carbides precipitated at such a high temperature range are easily coarsened, a desired fine carbide ( (Average particle diameter less than 10 nm) cannot be obtained. Therefore, in the present invention, it is preferable to lower the temperature at which the steel material is transformed from austenite to ferrite to a temperature sufficient to precipitate fine carbides.
　そこで、本発明においては、オーステナイト→フェライト変態の温度を、低温化する目的で、上記した組成に加えてさらにB ：0.0035％以下を、次の(2)式を満足するように含有することができる。
B ≧ 0.0003－0.00025Mn ・・・ (2)
（Mn、B：各元素の含有量（質量％）） Therefore, in the present invention, for the purpose of lowering the temperature of the austenite → ferrite transformation, in addition to the above-described composition, B: 0.0035% or less may be further contained so as to satisfy the following formula (2). it can.
B ≧ 0.0003-0.00025Mn (2)
(Mn, B: content of each element (mass%))
　B ：0.0035％以下
　Bは、鋼のオーステナイト→フェライト変態温度を低下させる元素であり、本発明では、Bを添加して鋼のオーステナイト→フェライト変態温度を下げることによって、Tiを含む炭化物の微細化を図ることができる。このような効果を得るためには、B含有量を0.0003％以上とすることが好ましい。一方、0.0035％を超えて含有しても上記の効果が飽和する。したがって、B含有量は0.0035％以下とすることが好ましい。より好ましくは0.0003％以上0.0020％以下である。 B: 0.0035% or less B is an element that lowers the austenite → ferrite transformation temperature of steel. In the present invention, by adding B to lower the austenite → ferrite transformation temperature of steel, the refinement of carbides containing Ti is reduced. Can be achieved. In order to obtain such an effect, the B content is preferably 0.0003% or more. On the other hand, the above effect is saturated even if the content exceeds 0.0035%. Therefore, the B content is preferably 0.0035% or less. More preferably, it is 0.0003% or more and 0.0020% or less.
　B ≧ 0.0003－0.00025Mn ・・・ (2)
（Mn、B：各元素の含有量（質量％））
　本発明において、Bを含有する場合には、鋼中のB含有量とMn含有量との比率を適正範囲に制御することも重要である。本発明者らは、フェライト相の組織全体に対する面積率が95％以上であるマトリックス中に、Tiを含む炭化物を微細（平均粒子径が10nm未満）に分散析出させる手段について検討した。その結果、熱間圧延終了後の冷却過程におけるオーステナイト→フェライト変態温度（CCT図におけるフェライト変態域）を、Tiを含む微細炭化物の析出に適した温度範囲に調整することが、Tiを含む炭化物を平均粒子径：10nm未満にまで微細化する極めて有効な手段であることを新たに知見した。 B ≧ 0.0003-0.00025Mn (2)
(Mn, B: content of each element (mass%))
In the present invention, when B is contained, it is also important to control the ratio of the B content and the Mn content in the steel within an appropriate range. The present inventors studied a means for finely dispersing (including an average particle diameter of less than 10 nm) a carbide containing Ti in a matrix having an area ratio of 95% or more with respect to the entire structure of the ferrite phase. As a result, adjusting the austenite → ferrite transformation temperature (ferrite transformation region in the CCT diagram) in the cooling process after hot rolling to a temperature range suitable for the precipitation of fine carbides containing Ti Average particle size: It was newly discovered that this is an extremely effective means of miniaturization to less than 10 nm.
また、本発明者らは更に検討を進めた結果、本発明の鋼組成においては、鋼素材のB含有量とMn含有量とが所望の関係を満たすように制御することにより、鋼のオーステナイト→フェライト変態温度を目的とする範囲に調整できることを知見した。ここで、上式において、右辺（0.0003－0.00025Mn）の値がゼロ以下となる場合には、右辺の値をゼロと見なすものとする。 Further, as a result of further investigations by the present inventors, in the steel composition of the present invention, by controlling the B content and Mn content of the steel material to satisfy a desired relationship, the austenite of the steel → It was found that the ferrite transformation temperature can be adjusted to the target range. Here, in the above equation, when the value on the right side (0.0003-0.00025Mn) is less than or equal to zero, the value on the right side is assumed to be zero.
なお、本発明において、固溶強化元素であるMnの含有量が0.35％超であれば、上記したBの効果を用いることなく所望の鋼板強度（引張強さ：590MPa以上）を確保することができる。しかしながら、Mnの含有量が0.35％以下では、上記したBの効果を利用せずに所望の鋼板強度を確保することが困難な場合がある。そこで、Mnの含有量が0.35％以下の場合には、Tiを含む炭化物をより微細化させる目的でBを含有することが好ましい。 In the present invention, if the content of Mn, which is a solid solution strengthening element, exceeds 0.35%, a desired steel plate strength (tensile strength: 590 MPa or more) can be ensured without using the effect of B described above. it can. However, if the Mn content is 0.35% or less, it may be difficult to secure a desired steel sheet strength without using the above-described effect of B. Therefore, when the Mn content is 0.35% or less, it is preferable to contain B for the purpose of making the carbide containing Ti finer.
　本発明の高張力熱延めっき鋼板の基板となる熱延鋼板においては、Cu、Sn、Ni、Ca、Mg、Co、As、Cr、W、Nb、Mo、V、Pb、Taのいずれか１種以上を合計で1％以下含有してもよい。好ましくは0.1％以下、より好ましくは0.03％以下である。また、上記以外の成分は、Feおよび不可避的不純物である。 In the hot-rolled steel sheet used as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention, any one of Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, Ta You may contain 1% or less of seeds or more in total. Preferably it is 0.1% or less, More preferably, it is 0.03% or less. Components other than the above are Fe and inevitable impurities.
　本発明の高張力熱延めっき鋼板は、上記した熱延鋼板の表面に、めっき皮膜を具えたものである。めっき皮膜を具備することにより、熱延鋼板の耐食性が向上し、高強度であるとともに加工性に優れ、厳しい腐食環境に晒される部品、例えば自動車の足回り部品の素材に好適な高張力熱延めっき鋼板が得られる。上記めっき皮膜の種類は特に限定されず、例えば溶融亜鉛めっき皮膜や合金化溶融亜鉛めっき皮膜等が好適に用いられる。 The high-tensile hot-rolled plated steel sheet of the present invention has a plating film on the surface of the above-described hot-rolled steel sheet. By providing a plating film, the hot rolled steel sheet has improved corrosion resistance, high strength, excellent workability, and high tensile hot rolling suitable for materials exposed to severe corrosive environments, such as automobile undercarriage parts. A plated steel sheet is obtained. The kind of said plating film is not specifically limited, For example, a hot dip galvanization film, an alloyed hot dip galvanization film, etc. are used suitably.
　次に、本発明の高張力熱延めっき鋼板の製造方法について説明する。
本発明は、上記した組成の鋼素材に、粗圧延と仕上げ圧延からなる熱間圧延を施し、仕上げ圧延終了後、冷却し、巻き取り、熱延板としたのち、該熱延板に連続焼鈍処理およびめっき処理を順次施して熱延めっき鋼板とする。この際、前記仕上げ圧延の仕上げ圧延温度を880℃以上とし、前記冷却の平均冷却速度を10℃/s以上とし、前記巻き取りの巻取り温度を400℃以上550℃未満とし、前記連続焼鈍処理の焼鈍温度を550℃以上750℃以下とすることを特徴とする。 Next, the manufacturing method of the high-tensile hot-rolled plated steel sheet of this invention is demonstrated.
In the present invention, the steel material having the above composition is subjected to hot rolling consisting of rough rolling and finish rolling, and after finishing rolling, the steel material is cooled, wound, and hot rolled, and then continuously annealed on the hot rolled plate. A hot-rolled plated steel sheet is obtained by sequentially performing the treatment and the plating treatment. At this time, the finish rolling temperature of the finish rolling is 880 ° C. or more, the average cooling rate of the cooling is 10 ° C./s or more, the winding temperature of the winding is 400 ° C. or more and less than 550 ° C., and the continuous annealing treatment The annealing temperature of is 550 ° C. or higher and 750 ° C. or lower.
　本発明において、鋼素材の溶製方法は特に限定されず、転炉、電気炉等、公知の溶製方法を採用することができる。また、溶製後、偏析等の問題から連続鋳造法によりスラブ（鋼素材）とするのが好ましいが、造塊－分塊圧延法、薄スラブ連鋳法等、公知の鋳造方法でスラブとしても良い。なお、鋳造後にスラブを熱間圧延するにあたり、加熱炉でスラブを再加熱した後に圧延しても良いし、所定温度以上の温度を保持している場合には、スラブを加熱することなく直送圧延しても良い。 In the present invention, the melting method of the steel material is not particularly limited, and a known melting method such as a converter or an electric furnace can be employed. Moreover, after melting, it is preferable to use a slab (steel material) by a continuous casting method because of problems such as segregation, but a slab can also be formed by a known casting method such as ingot-bundling rolling or thin slab continuous casting. good. In addition, when hot-rolling the slab after casting, the slab may be rolled after being reheated in a heating furnace, and when the temperature is maintained at a predetermined temperature or higher, direct rolling without heating the slab You may do it.
　上記の如く得られた鋼素材に、加熱、粗圧延および仕上げ圧延を施すが、本発明においては、粗圧延前に鋼素材中の炭化物を溶解しておく必要がある。炭化物形成元素であるTiを含有する本発明において、鋼素材の加熱温度は1150℃以上とすることが好ましい。但し、鋼素材の加熱温度が過剰に高くなると、表面が過剰に酸化されTiO2が生じてTiが消費され、鋼板にした場合に表面近傍の硬さの低下が生じ易くなるため、上記加熱温度は1300℃以下とすることが好ましい。また、先述のとおり、粗圧延前の鋼素材が、所定温度以上の温度を保持しており、鋼素材中の炭化物が溶解している場合には、粗圧延前の鋼素材を加熱する工程は省略可能である。なお、粗圧延条件については特に限定する必要はない。 The steel material obtained as described above is subjected to heating, rough rolling, and finish rolling. In the present invention, it is necessary to dissolve carbides in the steel material before rough rolling. In the present invention containing Ti which is a carbide forming element, the heating temperature of the steel material is preferably 1150 ° C. or higher. However, if the heating temperature of the steel material is excessively high, the surface is excessively oxidized and TiO 2 is generated and Ti is consumed. Is preferably 1300 ° C. or lower. In addition, as described above, when the steel material before rough rolling maintains a temperature equal to or higher than a predetermined temperature, and the carbide in the steel material is dissolved, the step of heating the steel material before rough rolling is It can be omitted. The rough rolling conditions are not particularly limited.
仕上げ圧延温度：880℃以上
　仕上げ圧延温度の適正化は、熱延めっき鋼板の伸びフランジ性および曲げ加工性の維持、並びに、仕上げ圧延の圧延荷重の低減化を図るうえで重要となる。仕上げ圧延温度が880℃未満であると、熱延板表層の結晶粒が粗大粒となり、加工性（伸びフランジ性、曲げ加工性）が損なわれる。したがって、仕上げ圧延温度は880℃以上とする。好ましくは900℃以上である。なお、仕上げ圧延温度が過剰に高くなると、熱延板表面の二次スケールによる疵が発生し易くなるため、仕上げ圧延温度は1000℃以下とすることが望ましい。 Finishing rolling temperature: 880 ° C. or more Optimization of the finishing rolling temperature is important for maintaining the stretch flangeability and bending workability of the hot-rolled plated steel sheet and reducing the rolling load of finishing rolling. When the finish rolling temperature is less than 880 ° C., the crystal grains of the hot-rolled sheet surface layer become coarse grains, and workability (stretch flangeability, bending workability) is impaired. Accordingly, the finish rolling temperature is 880 ° C. or higher. Preferably it is 900 degreeC or more. If the finish rolling temperature is excessively high, wrinkles due to the secondary scale on the surface of the hot rolled sheet are likely to occur, and therefore the finish rolling temperature is desirably 1000 ° C. or lower.
平均冷却速度および巻取り温度
平均冷却速度および巻取り温度の適正化は、本発明において極めて重要である。先述のとおり本発明では、鋼素材の組成を規定することで、鋼素材のオーステナイト→フェライト変態温度（CCT図におけるフェライト変態域）を、Tiを含む炭化物の析出に適した温度範囲に調整している。ここで、Tiを含む炭化物には、析出に適した温度範囲のなかでも特に析出し易い温度域が存在し、その温度域は概ね600～650℃である。この600～650℃の温度域では、炭化物生成の駆動力（鋼中の固溶Tiと固溶Cから炭化物が生成する自由エネルギー変化）が大きく、かつ原子の拡散速度が大きくなるため、Tiを含む炭化物が最も析出し易くなる。したがって、熱間圧延終了後に強制冷却し、Tiを含む炭化物の析出に最も適した温度域（約600～650℃）で強制冷却を停止して巻き取り、巻き取り時にオーステナイト→フェライト変態が生じるようにすれば、巻き取り時のオーステナイト→フェライト変態に伴い鋼中のTiのほぼ全量が微細炭化物として析出する。 Average cooling rate and winding temperature Optimization of the average cooling rate and winding temperature is extremely important in the present invention. As described above, in the present invention, by defining the composition of the steel material, the austenite → ferrite transformation temperature (ferrite transformation region in the CCT diagram) of the steel material is adjusted to a temperature range suitable for precipitation of carbide containing Ti. Yes. Here, the carbide containing Ti has a temperature range in which precipitation is particularly easy among the temperature ranges suitable for precipitation, and the temperature range is approximately 600 to 650 ° C. In this temperature range of 600 to 650 ° C, the driving force for carbide formation (change in free energy in which carbide is generated from solute Ti and solute C in steel) is large, and the diffusion rate of atoms becomes large. The contained carbide is most easily precipitated. Therefore, forced cooling is performed after hot rolling is completed, and forced cooling is stopped in the temperature range (approx. 600 to 650 ° C) most suitable for precipitation of Ti-containing carbides, so that austenite → ferrite transformation occurs during winding. If so, almost the entire amount of Ti in the steel precipitates as fine carbides with the austenite → ferrite transformation during winding.
しかし、Tiの炭化物のうち、オーステナイト→フェライト変態と同時に析出（相界面析出）する炭化物は、列状に分散析出するため、鋼板強度向上には寄与するものの鋼板の加工性（曲げ特性）に悪影響を及ぼす場合がある。そこで本発明においては、熱間圧延終了後の平均冷却速度を大きくするとともに巻取り温度を、オーステナイトからフェライトへの変態温度の範囲内（CCT図におけるフェライト変態域の範囲内）で且つTiを含む微細炭化物の析出に最も適した温度域（約600～650℃）よりも低い温度に規定することによって、オーステナイト→フェライト変態と同時に列状に分散析出する相界面析出を抑制する。そして、次工程であるめっき処理前の連続焼鈍処理時にTiを含む微細炭化物をランダムに分散析出させることで、熱延めっき鋼板の高強度化を図りつつ加工性（特に曲げ加工性）を確保する。 However, among the carbides of Ti, the carbides that precipitate at the same time as the austenite → ferrite transformation (phase interface precipitation) are dispersed and precipitated in a row, which contributes to improving the strength of the steel sheet but adversely affects the workability (bending properties) of the steel sheet. May affect. Therefore, in the present invention, the average cooling rate after completion of hot rolling is increased and the winding temperature is within the transformation temperature range from austenite to ferrite (within the ferrite transformation region in the CCT diagram) and includes Ti. By regulating the temperature to a temperature lower than the most suitable temperature range (about 600 to 650 ° C) for the precipitation of fine carbides, the interfacial precipitation that is dispersed and precipitated in a row at the same time as the austenite → ferrite transformation is suppressed. And, by carrying out the random dispersion and precipitation of fine carbides containing Ti during the subsequent annealing process before the plating process, which is the next process, workability (particularly bending workability) is ensured while increasing the strength of the hot-rolled plated steel sheet. .
　平均冷却速度：10℃/s以上
仕上げ圧延終了後、仕上げ圧延温度から巻取り温度までの平均冷却速度が10℃/s未満であると、オーステナイト→フェライト変態温度が高くなり、Tiを含む炭化物が熱延板中に列状、かつ粗大に析出してしまう。したがって、上記平均冷却速度は10℃/s以上とする。好ましくは30℃/s以上である。また、フェライト組織を得るために、200℃/s未満であるのが好ましい。 Average cooling rate: 10 ° C / s or more After finishing rolling, if the average cooling rate from the finish rolling temperature to the coiling temperature is less than 10 ° C / s, the austenite → ferrite transformation temperature becomes high, and carbide containing Ti is contained. In the hot-rolled sheet, it is deposited in a row and coarsely. Therefore, the average cooling rate is 10 ° C./s or more. Preferably it is 30 ° C./s or more. Further, in order to obtain a ferrite structure, it is preferably less than 200 ° C./s.
巻取り温度：400℃以上550℃未満
　巻取り温度の適正化は、本発明の高張力熱延めっき鋼板の基板となる熱延鋼板の組織を、熱延鋼板の幅方向全域にわたり所望の組織、すなわち、フェライト相が組織全体に対する面積率で95％以上であるマトリックスと、Tiを含み平均粒子径が10nm未満である微細炭化物が分散析出した組織とし、且つ列状に析出した微細炭化物の個数Psに対するランダムに析出した微細炭化物の個数Prの比率Pr/Psを高めるうえで、極めて重要である。 Winding temperature: 400 ° C. or more and less than 550 ° C. Optimization of the winding temperature is achieved by changing the structure of the hot-rolled steel sheet as the substrate of the high-tensile hot-rolled plated steel sheet of the present invention to a desired structure throughout the entire width direction of the hot-rolled steel sheet, That is, a matrix in which the ferrite phase has an area ratio of 95% or more with respect to the entire structure, and a structure in which fine carbides containing Ti and having an average particle diameter of less than 10 nm are dispersed and precipitated, and the number Ps of fine carbides precipitated in a row It is extremely important for increasing the ratio Pr / Ps of the number Pr of the fine carbides randomly precipitated with respect to.
先述のとおり、本発明の組成を有する鋼素材を熱間圧延したのち、冷却して巻き取り熱延板とするに際し、Tiを含む炭化物の析出に最も適した温度域（約600～650℃）で巻き取ると、巻き取り時のオーステナイト→フェライト変態に伴い鋼中のTiのほぼ全量が微細炭化物として析出してしまい、主として微細炭化物がある一定の方向に列状に分散析出した熱延板となってしまう。このように熱間圧延後の冷却・巻き取り過程においてTiを含む炭化物を積極的に析出させると、最終的に得られる熱延めっき鋼板に含まれる炭化物の析出形態は主として列状析出となり、曲げ加工性の劣化が懸念される。 As described above, when the steel material having the composition of the present invention is hot-rolled and then cooled to form a rolled hot-rolled sheet, the most suitable temperature range (about 600 to 650 ° C) for precipitation of carbide containing Ti. When rolled in, the austenite → ferrite transformation at the time of winding almost all the Ti in the steel precipitates as fine carbides, and the hot-rolled sheet in which fine carbides are dispersed and precipitated in a certain direction in a row turn into. In this way, when carbide containing Ti is actively precipitated in the cooling and winding process after hot rolling, the precipitation form of carbide contained in the finally obtained hot-rolled plated steel sheet is mainly lined precipitation and bending. There is concern about deterioration of workability.
そこで本発明では、熱延前に鋼素材をオーステナイト域まで加熱して鋼素材中の炭化物を溶解し、その後の巻取り工程においてTiを含む炭化物の析出を抑制して熱延板とする。そして、この熱延板に所定の連続焼鈍処理を施すことにより、所望の平均粒子径を有する微細炭化物（Ti含む炭化物）を析出させるとともに、該微細炭化物のうちランダムに析出した微細炭化物の個数（Pr）を増加させ、前記比率Pr/Psを高める。先述のとおり、Tiを含む炭化物は、オーステナイト→フェライト変態と同時に析出すると析出形態が列状になり、変態完了後の焼鈍処理時に析出すると析出形態がランダムとなる。そこで、本発明では、巻取り温度を低めに設定することにより列状析出を抑制し、続く連続焼鈍処理時のランダム析出を促進することとした。 Therefore, in the present invention, the steel material is heated to the austenite region before hot rolling to dissolve carbides in the steel material, and precipitation of carbides containing Ti is suppressed in the subsequent winding process to obtain a hot rolled sheet. Then, by subjecting this hot-rolled sheet to a predetermined continuous annealing treatment, fine carbides having a desired average particle diameter (Ti-containing carbides) are precipitated, and the number of fine carbides randomly precipitated among the fine carbides ( Pr) is increased to increase the ratio Pr / Ps. As described above, when carbide containing Ti precipitates simultaneously with the austenite → ferrite transformation, the precipitation form becomes a line shape, and when precipitated during the annealing treatment after the transformation is completed, the precipitation form becomes random. Therefore, in the present invention, the columnar precipitation is suppressed by setting the coiling temperature lower, and the random precipitation during the subsequent continuous annealing treatment is promoted.
　巻取り温度が400℃未満であると、マトリックスが実質的にフェライト単相組織とならず、所望の加工性を得ることができない。一方、巻取り温度が550℃以上になると、微細炭化物（Tiを含む炭化物）が巻き取り時に大量に列状析出してしまう。そして、この巻き取り時に析出する微細炭化物の主たる析出形態は、一方向に列状に分散析出した列状析出となるため、高張力熱延めっき鋼板の曲げ加工性を確保することが困難となる。したがって、巻取り温度は400℃以上550℃未満とする。好ましくは450℃以上550℃未満である。 When the winding temperature is less than 400 ° C., the matrix does not substantially have a ferrite single-phase structure, and desired workability cannot be obtained. On the other hand, when the coiling temperature is 550 ° C. or higher, fine carbides (carbides containing Ti) are deposited in a large amount at the time of winding. And since the main precipitation form of the fine carbide which precipitates at the time of winding is a row-like precipitation dispersed and precipitated in a row in one direction, it becomes difficult to ensure the bending workability of the high-tensile hot-rolled plated steel sheet. . Therefore, the coiling temperature is 400 ° C. or higher and lower than 550 ° C. Preferably it is 450 degreeC or more and less than 550 degreeC.
　以上の工程を経ることにより、巻き取り時には鋼素材に添加したTiが部分的に炭化物として析出し、マトリックスが実質的にフェライト単相であり且つTiの一部がマトリックス中に固溶分として残存した熱延板が得られる。このようにして得られた熱延板に、所定の焼鈍温度で連続焼鈍処理を施すことにより、所望の析出形態の微細炭化物（Tiを含む炭化物）を析出させる。なお、熱延板に連続焼鈍処理を施すに際しては、事前に酸洗処理を施して表面スケールを除去することが好ましい。また、熱延板を焼鈍温度まで加熱する際の昇温条件は特に限定されない。 Through the above steps, Ti added to the steel material partially precipitates as carbide during winding, the matrix is substantially a ferrite single phase, and a part of Ti remains as a solid solution in the matrix. A hot rolled sheet is obtained. The thus obtained hot-rolled sheet is subjected to continuous annealing treatment at a predetermined annealing temperature, thereby precipitating fine carbide (a carbide containing Ti) in a desired precipitation form. In addition, when performing a continuous annealing process to a hot-rolled sheet, it is preferable to perform a pickling process beforehand and to remove a surface scale. Moreover, the temperature rising conditions at the time of heating a hot-rolled sheet to an annealing temperature are not specifically limited.
連続焼鈍処理の焼鈍温度：550℃以上750℃以下
焼鈍温度が750℃を超えると、Tiを含む炭化物が粗大化して強度が低下する。したがって、焼鈍温度は750℃以下とする。好ましくは700℃以下である。一方、焼鈍温度が550℃未満になると、Tiを含む微細炭化物の析出量が不足し、所望の鋼板強度が得られなくなるため、焼鈍温度は550℃以上とする。好ましくは600℃以上である。
また、上記焼鈍温度での保持時間（焼鈍時間）は、60s以上600s以下とすることが、Tiを含む微細炭化物の析出を促進するとともにその粗大化を防止する観点から好ましい。より好ましくは60s以上300s以下である。 Annealing temperature of continuous annealing treatment: When the annealing temperature is 550 ° C. or higher and 750 ° C. or lower exceeds 750 ° C., carbides containing Ti are coarsened and the strength is lowered. Therefore, the annealing temperature is set to 750 ° C. or lower. Preferably it is 700 degrees C or less. On the other hand, when the annealing temperature is less than 550 ° C., the amount of fine carbides containing Ti is insufficient, and the desired steel plate strength cannot be obtained. Therefore, the annealing temperature is set to 550 ° C. or higher. Preferably it is 600 degreeC or more.
The holding time (annealing time) at the annealing temperature is preferably 60 s or more and 600 s or less from the viewpoint of promoting the precipitation of fine carbides containing Ti and preventing the coarsening thereof. More preferably, it is 60 seconds or more and 300 seconds or less.
連続焼鈍処理後の熱延板は、めっき処理に供される。めっき処理の種類は特に限定されず、従前公知のめっき処理が適用可能である。中でも特に、溶融亜鉛めっき処理が好適であり、例えば連続焼鈍めっきラインにおいて前記の焼鈍温度で焼鈍し、480℃の亜鉛めっき浴（0.1％Al-Zn等）中に浸漬して、付着量45g/m2（片面あたりの付着量）の溶融亜鉛めっき皮膜を形成することができる。 The hot-rolled sheet after the continuous annealing treatment is subjected to a plating treatment. The kind of the plating treatment is not particularly limited, and a conventionally known plating treatment can be applied. Among them, the hot dip galvanizing treatment is particularly suitable, for example, annealing at the above annealing temperature in a continuous annealing plating line, dipping in a 480 ° C zinc plating bath (0.1% Al-Zn, etc.) It is possible to form a hot dip galvanized film of m 2 (attachment amount per side).
また、めっき処理に続き合金化処理を施すことの可能であり、例えば上記溶融亜鉛めっき処理に続き、520℃で合金化処理を行うことができる。 Further, it is possible to perform an alloying process following the plating process. For example, the alloying process can be performed at 520 ° C. following the hot dip galvanizing process.
　以上のように、本発明の方法によると、上記連続焼鈍処理を施すことにより、フェライト相の組織全体に対する面積率が95％以上であるマトリックスと、Tiを含み平均粒子径が10nm未満である微細炭化物が分散析出した組織を有し、且つ、前記微細炭化物のうちランダムに析出した微細炭化物の比率が高い熱延板を得ることができる。そして、係る熱延板は、引張強さが590MPa以上であり且つ優れた伸びフランジ性と曲げ加工性とを兼備した優れた加工性を示す。 As described above, according to the method of the present invention, by performing the above-described continuous annealing treatment, a matrix having an area ratio of 95% or more with respect to the entire structure of the ferrite phase and a fine particle having an average particle diameter of less than 10 nm including Ti. It is possible to obtain a hot-rolled sheet having a structure in which carbides are dispersed and precipitated, and having a high ratio of fine carbides randomly precipitated among the fine carbides. The hot-rolled sheet has excellent workability that has a tensile strength of 590 MPa or more and has both excellent stretch flangeability and bending workability.
また、連続焼鈍処理後の上記熱延板に対してめっき処理、或いは更に合金化処理を施し、その表面にめっき皮膜（例えば溶融亜鉛めっき皮膜、或いは合金化溶融亜鉛めっき皮膜）を形成することにより、高強度であり且つ優れた加工性を有し、しかも耐食性にも優れた高張力熱延めっき鋼板が得られる。 In addition, by subjecting the hot-rolled sheet after the continuous annealing treatment to plating treatment or further alloying treatment, and forming a plating film (for example, hot-dip galvanized film or alloyed hot-dip galvanized film) on the surface thereof Thus, a high-tensile hot-rolled plated steel sheet having high strength, excellent workability, and excellent corrosion resistance can be obtained.
　表１に示す組成の溶鋼を通常公知の手法により溶製、連続鋳造して肉厚250mmのスラブ（鋼素材）とした。これらのスラブを、1250℃に加熱後、粗圧延し、表２に示す仕上げ圧延温度とする仕上げ圧延を施し、仕上げ圧延終了後、仕上げ圧延温度から巻取り温度までの温度域を表２に示す平均冷却温度で冷却し、表２に示す巻取り温度で巻き取り、熱延板とした。得られた熱延板を酸洗して表面スケールを除去したのち、表２に示す焼鈍温度で連続焼鈍処理を施した。次いで、連続焼鈍処理後の熱延板を、溶融亜鉛めっき浴（めっき浴の組成：0.1％Al-Zn、浴温：480℃）に浸漬し、付着量45g/m2（片面あたりの付着量）の溶融亜鉛めっき皮膜を両面に形成して溶融亜鉛めっき鋼板（熱延めっき鋼板）とした。また、一部の溶融亜鉛めっき鋼板（表２の熱延番号b1,d1,h,i,j,k,l）については、520℃で合金化処理を施し、合金化溶融亜鉛めっき鋼板とした。 Molten steel having the composition shown in Table 1 was melted and continuously cast by a generally known technique to obtain a slab (steel material) having a thickness of 250 mm. These slabs are heated to 1250 ° C., then roughly rolled and subjected to finish rolling at the finish rolling temperature shown in Table 2, and after finish rolling, the temperature range from the finish rolling temperature to the winding temperature is shown in Table 2. It cooled at the average cooling temperature, wound up at the winding temperature shown in Table 2, and was set as the hot rolled sheet. The obtained hot-rolled sheet was pickled to remove the surface scale, and then subjected to continuous annealing treatment at the annealing temperatures shown in Table 2. Next, the hot-rolled sheet after the continuous annealing treatment is immersed in a hot dip galvanizing bath (plating bath composition: 0.1% Al-Zn, bath temperature: 480 ° C.), and the adhesion amount is 45 g / m 2 (the adhesion amount per side). ) Was formed on both sides to obtain a hot dip galvanized steel sheet (hot rolled galvanized steel sheet). Also, some hot-dip galvanized steel sheets (hot rolling numbers b1, d1, h, i, j, k, and l in Table 2) were alloyed at 520 ° C. to obtain alloyed hot-dip galvanized steel sheets. .
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　上記により得られた熱延めっき鋼板（溶融亜鉛めっき鋼板および合金化溶融亜鉛めっき鋼板）から試験片を採取し、組織観察および析出物観察、引張試験、穴拡げ試験、曲げ試験を行い、フェライト相の面積率、Tiを含む微細炭化物の平均粒子径および体積比、並びに、該微細炭化物の析出形態、引張強さ、穴拡げ率（伸びフランジ性）、限界曲げ半径（曲げ加工性）を求めた。試験方法は次のとおりとした。 Test specimens were collected from the hot-rolled galvanized steel sheets (hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets) obtained as described above, and subjected to microstructure observation, precipitate observation, tensile test, hole expansion test, bending test, and ferrite phase. Area ratio, average particle size and volume ratio of fine carbide containing Ti, and precipitation form, tensile strength, hole expansion rate (stretch flangeability), and critical bending radius (bending workability) of the fine carbide were determined. . The test method was as follows.
（i）組織観察
　得られた熱延めっき鋼板から試験片を採取し、試験片の圧延方向断面を機械的に研磨し、ナイタールで腐食した後、板厚中心の位置を走査型電子顕微鏡（SEM）で倍率：3000倍にて撮影した組織写真（SEM写真）を用い、画像解析装置によりフェライト相、フェライト相以外の組織の種類、および、それらの面積率を求めた。
　また、熱延めっき鋼板（板厚中心の位置）から作製した薄膜を透過型電子顕微鏡（TEM）によって倍率：260000倍で観察し、Tiを含む微細炭化物の粒子径、体積比、および分散析出形態を求めた。
Tiを含む微細炭化物の粒子径は、260000倍での30視野の観察結果をもとに、画像処理で個々の粒子の面積を求め、円近似で粒子径を求めた。求めた各粒子の粒子径を算術平均し、平均粒子径とした。
Tiを含む微細炭化物の体積比は、10％アセチルアセトン－1％塩化テトラメチルアンモニウム－メタノール溶液（AA溶液）を用いて地鉄を電解し、ろ過捕集した残渣の抽出残渣分析によりTi炭化物の重量を求め、これをTi炭化物（TiC）の密度で割ることによって体積を求め、この体積を溶解した地鉄の体積で除することによって求めた。
分散析出形態は、倍率260000倍のTEM写真を、試験片毎に20枚撮影し、微細炭化物が列状に観察されるものの個数Psとランダムに観察されるものの個数Prを数え、Pr/Psを求めた。観察に当たっては、試験片を30°まで傾けても微細炭化物が列状に観察されないものを、ランダムに析出した微細炭化物とした。 (I) Microstructure observation A specimen was taken from the obtained hot-rolled plated steel sheet, and the cross section in the rolling direction of the specimen was mechanically polished and corroded with nital. ) Magnification: Using a structure photograph (SEM photograph) taken at a magnification of 3000 times, the type of the structure other than the ferrite phase and the ferrite phase and the area ratio thereof were determined by an image analyzer.
In addition, a thin film produced from hot-rolled plated steel sheet (position at the center of the plate thickness) was observed with a transmission electron microscope (TEM) at a magnification of 260,000, and the particle size, volume ratio, and dispersion precipitation form of fine carbides containing Ti Asked.
The particle size of fine carbide containing Ti was determined by image processing based on the observation results of 30 visual fields at 260,000 times, and the particle size was obtained by circular approximation. The calculated particle diameters of each particle were arithmetically averaged to obtain an average particle diameter.
The volume ratio of fine carbide containing Ti is the weight of Ti carbide based on the extraction residue analysis of the residue collected by electrolysis of the ground iron using 10% acetylacetone-1% tetramethylammonium chloride-methanol solution (AA solution). The volume was determined by dividing this by the density of Ti carbide (TiC), and this volume was divided by the volume of the dissolved iron.
Dispersion precipitation form, TEM photograph with a magnification of 260,000 was taken for each test piece, 20 counts of the number Ps of fine carbides observed in a row and the number Pr of those observed randomly, Pr / Ps Asked. In the observation, those in which fine carbides were not observed in a line even when the test piece was tilted to 30 ° were regarded as randomly precipitated fine carbides.
（ii）引張試験
　得られた熱延めっき鋼板から、圧延方向に対して直角方向を引張方向とするJIS　5号引張試験片（JIS Z 2201）を採取し、JIS Z 2241の規定に準拠した引張試験を行い、引張強さ(TS)を測定した。 (Ii) Tensile test JIS No. 5 tensile test piece (JIS Z 2201) with the direction perpendicular to the rolling direction as the tensile direction was taken from the obtained hot-rolled plated steel sheet and pulled according to the provisions of JIS Z 2241 A test was conducted and the tensile strength (TS) was measured.
（iii）穴拡げ試験
　得られた熱延めっき鋼板から、試験片（大きさ：130mm×130mm）を採取し、該試験片に、ポンチにより初期直径d0：10mmφの穴を打ち抜き加工で形成した。これら試験片を用いて、穴拡げ試験を実施した。すなわち、該穴に頂角：60°の円錐ポンチを挿入し、該穴を押し広げ、亀裂が熱延めっき鋼板（試験片）の板厚を貫通したときの穴の径dを測定し、次式で穴拡げ率λ(％)を算出した。
　　　　　　　　　穴拡げ率λ(％)＝{(d－d0)/d0}×100 (Iii) Hole expansion test A test piece (size: 130 mm x 130 mm) was collected from the obtained hot-rolled plated steel sheet, and a hole having an initial diameter d 0 of 10 mmφ was formed by punching the test piece. . Using these test pieces, a hole expansion test was performed. That is, a conical punch having an apex angle of 60 ° is inserted into the hole, the hole is expanded, and the diameter d of the hole when the crack penetrates the thickness of the hot-rolled plated steel sheet (test piece) is measured. The hole expansion rate λ (%) was calculated by the equation.
Hole expansion rate λ (%) = {(d−d 0 ) / d 0 } × 100
（iv）限界曲げ試験
　得られた熱延めっき鋼板から、圧延方向に対して直角方向を長手方向とした、幅50mm、長さ100mmの試験片を採取し、JIS Z 2248(2006)の規定に準拠して頂角90°のＶ曲げ試験（Ｖブロック法）を行い、割れの生じない最小の曲げ半径R(mm)と板厚t(mm)の比R/tを限界曲げ半径として測定した。
　得られた結果を表３に示す。 (Iv) Limit bending test A specimen with a width of 50 mm and a length of 100 mm, with the direction perpendicular to the rolling direction as the longitudinal direction, was taken from the obtained hot-rolled plated steel sheet and specified in JIS Z 2248 (2006). A V-bend test (V-block method) with an apex angle of 90 ° was performed, and the ratio R / t of the minimum bending radius R (mm) and thickness t (mm) without cracks was measured as the critical bending radius. .
The obtained results are shown in Table 3.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　本発明例は何れも、引張強さTS：590MPa以上の高強度と、穴拡げ率λ：100％以上の伸びフランジ性、および限界曲げ半径0.9以下の曲げ加工性を兼備した熱延めっき鋼板となっている。一方、本発明の範囲を外れる比較例は、所定の高強度が確保できていないか、穴拡げ率λ或いは限界曲げ半径が確保できていない。 Each of the examples of the present invention is a hot rolled galvanized steel sheet that has both high strength of tensile strength TS: 590 MPa or more, stretch flangeability of hole expansion ratio λ: 100% or more, and bending workability of critical bending radius of 0.9 or less. It has become. On the other hand, in a comparative example outside the scope of the present invention, a predetermined high strength cannot be ensured, or the hole expansion rate λ or the limit bending radius cannot be ensured.

Claims (11)

  1. 基板である熱延鋼板の少なくとも一方の表面にめっき皮膜を有するめっき鋼板であって、前記熱延鋼板が、質量％で、
    C ：0.010％以上0.050％以下、     Si：0.2％以下、
    Mn：0.10％以上0.80％以下、       P ：0.025％以下、
    S ：0.01％以下、　　　　　　　    N ：0.01％以下、
    Al：0.1％以下、                 Ti：0.05％以上0.10％以下
    を、C、S、N、およびTiが下記(1)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成と、フェライト相の組織全体に対する面積率が95％以上であるマトリックスと、Tiを含み平均粒子径が10nm未満である微細炭化物が分散析出した組織を有し、引張強さが590MPa以上である、高張力熱延めっき鋼板。
    　　　　　　　　　　　Ti*/48 ＜ C/12　 ・・・ (1)
    　　　　　　　　ここで、Ti*＝Ti－(N/14×48＋S/32×48)
    　　　　　　　（C、S、N、Ti：各元素の含有量（質量％））     A plated steel sheet having a plating film on at least one surface of a hot-rolled steel sheet as a substrate, wherein the hot-rolled steel sheet is in mass%,
    C: 0.010% or more and 0.050% or less, Si: 0.2% or less,
    Mn: 0.10% to 0.80%, P: 0.025% or less,
    S: 0.01% or less, N: 0.01% or less,
    Al: 0.1% or less, Ti: 0.05% or more and 0.10% or less, containing C, S, N, and Ti so that the following formula (1) is satisfied, with the balance being Fe and inevitable impurities, High tensile strength with a matrix with an area ratio of 95% or more with respect to the entire structure of the ferrite phase and a structure in which fine carbides containing Ti and an average particle diameter of less than 10 nm are dispersed and precipitated, and a tensile strength of 590 MPa or more Hot-rolled steel sheet.
    Ti * / 48 <C / 12 (1)
    Where Ti * = Ti- (N / 14 x 48 + S / 32 x 48)
    (C, S, N, Ti: content of each element (mass%))
  2. 前記組成に加えてさらに、質量％でB ：0.0035％以下を、下記(2)式を満足するように含有する、請求項１に記載の高張力熱延めっき鋼板。
    　　　　　　　　　　B ≧ 0.0003－0.00025Mn ・・・ (2)
    （Mn、B：各元素の含有量（質量％））     The high-tensile hot-rolled plated steel sheet according to claim 1, further containing, in addition to the composition, B: 0.0035% or less by mass% so as to satisfy the following formula (2).
    B ≧ 0.0003-0.00025Mn (2)
    (Mn, B: content of each element (mass%))
  3. 前記Bが、0.0003％以上、0.0020％以下である、請求項２に記載の高張力熱延めっき鋼板。 The high-tensile hot-rolled plated steel sheet according to claim 2, wherein B is 0.0003% or more and 0.0020% or less.
  4. 　前記微細炭化物が、列状に析出したものの個数Psとランダムに析出したものの個数Prとの比率が下記(3)式を満足する、請求項１または２に記載の高張力熱延めっき鋼板。
    　　　　　　　　　　　　Pr/Ps ≧　0.8 ・・・ (2)
    　　　　　　（Pr：ランダムに析出している微細炭化物の個数）
    　　　　　　　（Ps：列状に析出している微細炭化物の個数）     The high-tensile-strength hot-rolled plated steel sheet according to claim 1 or 2, wherein a ratio between the number Ps of fine carbides precipitated in a row and the number Pr of random fine particles satisfies the following expression (3).
    Pr / Ps ≥ 0.8 (2)
    (Pr: number of fine carbides that are randomly deposited)
    (Ps: number of fine carbides deposited in a row)
  5. 　前記微細炭化物の組織全体に対する体積比が0.0005以上である、請求項１または２に記載の高張力熱延めっき鋼板。 The high-tensile hot-rolled plated steel sheet according to claim 1 or 2, wherein a volume ratio of the fine carbide to the whole structure is 0.0005 or more.
  6. 前記体積比が、0.0005以上、0.003以下である、請求項５に記載の高張力熱延めっき鋼板。 The high-tensile hot-rolled plated steel sheet according to claim 5, wherein the volume ratio is 0.0005 or more and 0.003 or less.
  7. 前記組成に加えてさらに、質量％で、Cu、Sn、Ni、Ca、Mg、Co、As、Cr、W、Nb、Mo、V、Pb、Taのいずれか１種以上を合計で1％以下含有する、請求項１または２に記載の高張力熱延めっき鋼板。
          In addition to the above composition, in addition to mass, one or more of Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, and Ta total 1% or less in total. The high-tensile hot-rolled plated steel sheet according to claim 1 or 2, which is contained.
  8. 鋼素材に、粗圧延と仕上げ圧延からなる熱間圧延を施し、仕上げ圧延終了後、冷却し、巻き取り、熱延板としたのち、該熱延板に連続焼鈍処理およびめっき処理を順次施して熱延めっき鋼板とする、高張力熱延めっき鋼板の製造方法において、
    前記鋼素材を、質量％で、
    C ：0.010％以上0.050％以下、     Si：0.2％以下、
    Mn：0.10％以上0.80％以下、       P ：0.025％以下、
    S ：0.01％以下、　　　　　　　    N ：0.01％以下、
    Al：0.1％以下、                 Ti：0.05％以上0.10％以下
    を、C、S、N、およびTiが下記(1)式を満足するように含有し、残部がFeおよび不可避的不純物からなる組成とし、
    前記仕上げ圧延の仕上げ圧延温度を880℃以上とし、前記冷却の平均冷却速度を10℃/s以上とし、前記巻取り温度を400℃以上550℃未満とし、前記連続焼鈍処理の焼鈍温度を550℃以上750℃以下とする、引張強さが590MPa以上である、高張力熱延めっき鋼板の製造方法。
    　　　　　　　　　　　Ti*/48 ＜ C/12　 ・・・ (1)
    　　　　　　　　ここで、Ti*＝Ti－(N/14×48＋S/32×48)
    　　　　　　　（C、S、N、Ti：各元素の含有量（質量％））     The steel material is subjected to hot rolling consisting of rough rolling and finish rolling. After finishing rolling, the steel material is cooled, wound, hot rolled, and then subjected to continuous annealing and plating sequentially. In the manufacturing method of the high-tensile hot-rolled plated steel sheet,
    The steel material in mass%,
    C: 0.010% or more and 0.050% or less, Si: 0.2% or less,
    Mn: 0.10% to 0.80%, P: 0.025% or less,
    S: 0.01% or less, N: 0.01% or less,
    Al: 0.1% or less, Ti: 0.05% or more and 0.10% or less containing C, S, N, and Ti so that the following formula (1) is satisfied, with the balance being Fe and inevitable impurities,
    The finish rolling temperature of the finish rolling is 880 ° C. or more, the average cooling rate of the cooling is 10 ° C./s or more, the winding temperature is 400 ° C. or more and less than 550 ° C., and the annealing temperature of the continuous annealing treatment is 550 ° C. A method for producing a high-tensile hot-rolled plated steel sheet having a tensile strength of 590 MPa or more and a temperature of 750 ° C. or less.
    Ti * / 48 <C / 12 (1)
    Where Ti * = Ti- (N / 14 x 48 + S / 32 x 48)
    (C, S, N, Ti: content of each element (mass%))
  9. 前記組成に加えてさらに、質量％でB ：0.0035％以下を、下記(2)式を満足するように含有する、請求項８に記載の高張力熱延めっき鋼板の製造方法。
    　　　　　　　　　　B ≧ 0.0003－0.00025Mn・・・ (2)
    　　　　　　　　　（Mn、B：各元素の含有量（質量％））     The method for producing a high-tensile hot-rolled plated steel sheet according to claim 8, further comprising, in addition to the composition, B: 0.0035% or less by mass% so as to satisfy the following formula (2).
    B ≧ 0.0003-0.00025Mn ... (2)
    (Mn, B: content of each element (mass%))
  10. 前記Bが、0.0003％以上、0.0020％以下である、請求項９に記載の高張力熱延めっき鋼板の製造方法。 The method for producing a high-tensile hot-rolled plated steel sheet according to claim 9, wherein B is 0.0003% or more and 0.0020% or less.
  11. 前記組成に加えてさらに、質量％で、Cu、Sn、Ni、Ca、Mg、Co、As、Cr、W、Nb、Mo、V、Pb、Taのいずれか１種以上を合計で1％以下含有する、請求項６または７に記載の高張力熱延めっき鋼板の製造方法。
          In addition to the above composition, in addition to mass, one or more of Cu, Sn, Ni, Ca, Mg, Co, As, Cr, W, Nb, Mo, V, Pb, and Ta total 1% or less in total. The manufacturing method of the high-tensile-strength hot-rolled plated steel plate according to claim 6 or 7.
PCT/JP2012/006647 2011-11-08 2012-10-17 High-tensile-strength hot-rolled plated steel sheet and method for producing same WO2013069210A1 (en)

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WO2015118864A1 (en) * 2014-02-05 2015-08-13 Ｊｆｅスチール株式会社 High-strength hot-rolled steel sheet and production method therefor
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