WO2013069210A1 - Tôle en acier plaquée et laminée à chaud de force de traction élevée, et procédé de fabrication de celle-ci - Google Patents

Tôle en acier plaquée et laminée à chaud de force de traction élevée, et procédé de fabrication de celle-ci 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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English (en)
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/ja
Publication of WO2013069210A1 publication Critical patent/WO2013069210A1/fr

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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.

Abstract

L'invention fournit une tôle en acier plaquée et laminée à chaud de force de traction élevée, et un procédé de fabrication de celle-ci, laquelle tôle en acier combine des propriétés de résistance et d'usinabilité (aptitude à l'étirement des bords, et usinabilité au pliage). Plus précisément, l'invention concerne une tôle en acier plaquée possédant un film de placage sur au moins une surface d'une tôle en acier laminée à chaud constituant un substrat. Ladite tôle en acier laminée à chaud possède une composition comprenant, en % en masse, C : 0,010% au moins et 0,050% au plus, Si : 0,2% au plus, Mn : 0,10% au moins et 0,80% au plus, P : 0,025% au plus, S : 0,01% au moins, N : 0,01% au plus, Al : 0,1% au plus, et Ti :0,05% au moins et 0,10% au plus, de sorte que C, S, N et Ti satisfont Ti*/48<C/12 (ici, Ti*=Ti-(N/14×48+S/32×48), et C, S, N,Ti représentent respectivement la teneur des éléments (en % en masse)), le reste étant constitué de Fe et des impuretés inévitables. En outre, ladite tôle en acier laminée à chaud possède une matrice dans laquelle une phase de ferrite présente un taux surfacique de 95% au moins par rapport à l'ensemble d'une structure. Enfin, ladite tôle en acier laminée à chaud possède une structure dans laquelle un carbure microscopique contenant du Ti de diamètre de particule moyen de moins de 10nm, est dispersé et précipité. Par conséquent, la tôle en acier plaquée et laminée à chaud de force de traction élevée de l'invention, présente une force de traction de 590 MPa au moins, et est excellente en termes d'usinabilité.
PCT/JP2012/006647 2011-11-08 2012-10-17 Tôle en acier plaquée et laminée à chaud de force de traction élevée, et procédé de fabrication de celle-ci WO2013069210A1 (fr)

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CN104480397A (zh) * 2014-12-19 2015-04-01 山东钢铁股份有限公司 一种700MPa级热轧汽车结构用钢及其制备方法

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