WO2020170542A1 - Tôle d'acier galvanisée par immersion à chaud à haute résistance et procédé de fabrication de ladite tôle - Google Patents

Tôle d'acier galvanisée par immersion à chaud à haute résistance et procédé de fabrication de ladite tôle Download PDF

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WO2020170542A1
WO2020170542A1 PCT/JP2019/046447 JP2019046447W WO2020170542A1 WO 2020170542 A1 WO2020170542 A1 WO 2020170542A1 JP 2019046447 W JP2019046447 W JP 2019046447W WO 2020170542 A1 WO2020170542 A1 WO 2020170542A1
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steel sheet
hot
strength
cold
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PCT/JP2019/046447
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Japanese (ja)
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秀和 南
友輔 奥村
聡 前田
横田　毅
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Ｊｆｅスチール株式会社
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Priority to MX2021009947A priority Critical patent/MX2021009947A/es
Priority to JP2020518833A priority patent/JP6777267B1/ja
Publication of WO2020170542A1 publication Critical patent/WO2020170542A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc

Definitions

  • the present invention relates to a high-strength galvanized steel sheet and a method for manufacturing the same.
  • Exceptional formability is required for high-strength steel sheets used for automobile reinforcement parts and frame structure parts.
  • a part such as a crash box has a punched end face and a bent portion
  • a steel plate having high punchability, stretch flangeability, and bendability is suitable from the viewpoint of formability.
  • high-strength steel sheets used for automobile reinforcement parts and frame structure parts are required to be able to manufacture parts with high dimensional accuracy.
  • it is important to control the yield ratio (YR yield strength YS/tensile strength TS) of the steel plate within a certain range.
  • Yield strength YS/tensile strength TS yield ratio of the steel plate
  • Patent Document 1 the steel sheet structure is mainly composed of ferrite and bainite, the number density of non-metallic inclusions of more than 5 ⁇ m contained in the steel sheet is 15 pieces/mm 2 or less, and the tensile strength is 540 MPa or more.
  • a high-strength steel sheet having excellent stretch-flangeability and a manufacturing method thereof are disclosed.
  • the area ratio of the martensite phase in the entire structure is 30% or more, containing the ferrite phase and the martensite phase, and (area occupied by the martensite phase)/(area occupied by the ferrite phase)
  • a high-strength cold-rolled steel sheet, a high-strength hot-dip galvanized steel sheet excellent in hole expandability and bendability, which is more than 0.45 and less than 1.5 and has an average grain size of a martensite phase of 2 ⁇ m or more, and a manufacturing method thereof. Is disclosed.
  • Patent Document 3 20% or more of ferrite is contained as a main phase, 5 to 80% or less of martensite and bainite in total is contained as a second phase, and the residual austenite volume ratio is 10%.
  • Patent Document 1 bendability and plating property are not taken into consideration.
  • Patent Document 2 YR and platability, which are indicators of dimensional accuracy during molding, are not considered.
  • Patent Document 3 YR and stretch flangeability are not taken into consideration. As described above, there is no steel sheet that comprehensively satisfies the strength, punchability, stretch flangeability, bendability, and plating property and is capable of manufacturing parts with high dimensional accuracy.
  • the present invention has been made in view of such circumstances, and is excellent in punching property, stretch flangeability, bendability and plating property, and is capable of manufacturing parts with high dimensional accuracy. It is an object to provide a high-strength galvanized steel sheet and a method for manufacturing the same.
  • YR is 45% or more and 75% or less in TS:780 MPa class, TS:980 MPa. It means 50% or more and 80% or less in the class, and 60% or more and 90% or less in the TS:1180 MPa class.
  • excellent stretch flangeability means that the value of the hole expansion ratio ( ⁇ ), which is an index of stretch flangeability, is 20% or more.
  • excellent bendability means that a bending test was performed by a V-block method with a bending angle of 90°, and a ridgeline portion of a bending apex was observed with a microscope of 40 times, and a crack having a crack length of 200 ⁇ m or more was recognized.
  • a value (R/t) obtained by dividing the disappearing minimum bending radius (R) by the plate thickness (t) is 3.0 or less in TS: 780 MPa class and 980 MPa class, and 4.0 or less in TS: 1180 MPa class. Means that.
  • excellent in plating property means that the surfaces of the manufactured hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet are visually observed and that the surface of the steel sheet has no non-plating defect.
  • a high-strength steel sheet having excellent dimensional accuracy during forming is obtained by forming a structure mainly composed of ferrite and bainite, which are soft phases, and dispersing hardened martensite and tempered martensite, which are hard phases, in the structure. Can be realized.
  • the present invention was made based on the above findings. That is, the gist of the present invention is as follows.
  • a high-strength hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer formed on the surface of the base steel sheet, and having a tensile strength of 780 MPa or more,
  • the base material steel plate In mass %, C: 0.050% or more and 0.200% or less, Si: 0.10% or more and 0.90% or less, Mn: 2.00% or more and 3.50% or less, P: 0.001% or more and 0.100% or less, S: 0.0200% or less, Al: 1.000% or less, N: 0.0100% or less, Ca: 0.0200% or less and Cr: 0.300% or less, And having a composition of [%Mn]/[%Si] satisfying the relationship of 2.9 or more and 11.7 or less, and the balance being Fe and inevitable impurities,
  • One or two selected from the group consisting of bainite and ferrite has a total area ratio of 5% or more and 85% or less, The area ratio of tempered
  • the above-mentioned component composition further comprises mass %, Ti: 0.001% or more and 0.100% or less, Nb: 0.001% or more and 0.100% or less, V: 0.001% or more and 0.100% or less, B: 0.0001% or more and 0.0100% or less, Mo: 0.005% or more and 2.000% or less, Cu: 0.01% or more and 1.00% or less, Ni: 0.01% or more and 0.50% or less, Sb: 0.001% or more and 0.200% or less, Sn: 0.001% or more and 0.200% or less, Ta: 0.001% or more and 0.100% or less, Mg: 0.0001% or more and 0.0200% or less, Zn: 0.001% or more and 0.020% or less, Co: 0.001% or more and 0.020% or less, Zr: 0.001% or more and 0.020% or less, and REM: 0.0001% or more and at least one selected from the group consisting of 0.0200% or less, and the above [1]
  • a steel slab having the composition as described in [1] or [3] above is hot-rolled to form a hot-rolled sheet, Then, pickling the hot rolled sheet, Then, the hot-rolled sheet is cold-rolled at a rolling reduction of 30% or more to obtain a cold-rolled sheet, Then, the cold-rolled sheet, an annealing furnace, and having a hot dip galvanizing equipment located downstream of the annealing furnace, the hot dip galvanizing equipment, a hot dip galvanizing bath, the steel strip out of the annealing furnace Supplying to a continuous hot-dip galvanizing apparatus, which is connected and comprises a snout whose tip is immersed in the hot-dip galvanizing bath, First, in the annealing furnace, the cold rolled sheet is heated to a maximum ultimate temperature of 750° C.
  • the dew point of the atmosphere in the region where the cold-rolled sheet reaches the maximum attainable temperature is ⁇ 40° C. or lower, and the first hydrogen concentration of the atmosphere is 5% by volume or more and 10% by volume or less, and the cold rolling is performed. Hold the plate at the highest temperature above for 5s to 100s, Then, the cold-rolled sheet is cooled from the highest temperature to 600° C.
  • the cold-rolled sheet is moved from the inside of the annealing furnace to the hot-dip galvanizing bath through the snout with a residence time of 15 s or more before entering the hot-dip galvanizing bath. Is further cooled under the condition that the hydrogen concentration of the atmosphere of the compartment containing the roll passing immediately before entering the snout is 50% or more and 95% or less of the first hydrogen concentration,
  • a method for producing a high-strength hot-dip galvanized steel sheet in which the cold-rolled sheet is immersed in the hot-dip galvanizing bath, subjected to hot-dip galvanizing treatment, and then cooled to 50°C or lower.
  • FIG. 1 shows an outline of a cross section of a high-strength hot-dip galvanized steel sheet 1 according to an embodiment.
  • the high-strength hot-dip galvanized steel sheet 1 has a hot-dip galvanized layer 3 or an alloyed hot-dip galvanized layer on the surface of a base steel sheet 2.
  • % representing the content of the constituent elements of the base steel sheet means “mass %” unless otherwise specified.
  • C 0.050% or more and 0.200% or less C is effective for generating a desired amount of quenched martensite or tempered martensite, setting TS to 780 MPa or more, and obtaining excellent dimensional accuracy during molding. It is an element. If the C content is less than 0.050%, the area ratio of quenched martensite decreases and the area ratio of ferrite or bainite increases, making it difficult to set TS to 780 MPa or more. In addition, the dimensional accuracy during molding is reduced. On the other hand, when the content of C exceeds 0.200%, the carbon concentration in the hardened martensite and the tempered martensite increases, and the hardness of the hardened martensite and the tempered martensite increases.
  • the content of C is set to 0.050% or more and 0.200% or less.
  • the content of C is preferably 0.060% or more, and more preferably 0.065% or more.
  • the content of C is preferably 0.150% or less, more preferably 0.110% or less.
  • Si 0.10% or more and 0.90% or less
  • the base material steel sheet is heated at the maximum ultimate temperature and held at the maximum ultimate temperature in the annealing furnace described later. Concentration of Si and Mn on the surface layer is suppressed, and good plating properties can be realized. If the Si content is less than 0.10%, the amount of Mn enriched on the surface of the steel sheet increases during the above heating and holding at the highest temperature, and Mn oxide that causes non-plating defects is generated on the surface of the steel sheet. Therefore, it becomes difficult to achieve good plating properties.
  • the Si content exceeds 0.90%, the amount of Si enriched on the surface of the steel sheet increases during the above heating and holding at the maximum reached temperature, and Si oxidation that causes non-plating defects on the surface of the steel sheet. It is difficult to achieve good plating property because the product is generated. If the Si content exceeds 0.90%, the volume ratio of retained austenite increases. Since the generated retained austenite has a high hydrogen concentration, voids are generated inside the martensite when it is subjected to martensite transformation by being processed during punching and bending test. Therefore, the total void number density after punching increases, and the punchability and stretch-flangeability deteriorate.
  • the Si content is set to 0.10% or more and 0.90% or less.
  • the Si content is preferably 0.20% or more, more preferably 0.30% or more. Further, the Si content is preferably 0.85% or less, and more preferably 0.80% or less.
  • Mn 2.00% or more and 3.50% or less Mn is effective for generating a desired amount of quenched martensite or tempered martensite, setting TS to 780 MPa or more, and obtaining excellent dimensional accuracy during molding. It is an element. If the Mn content is less than 2.00%, the area ratio of quenched martensite decreases, the area ratio of ferrite or bainite increases, and it becomes difficult to set TS to 780 MPa or more. In addition, the dimensional accuracy during molding is also reduced. Furthermore, it becomes difficult to achieve good plating properties.
  • the Mn content is set to 2.00% or more and 3.50% or less.
  • the Mn content is preferably 2.20% or more, more preferably 2.30% or more.
  • the Mn content is preferably 3.30% or less, more preferably 3.00% or less.
  • P 0.001% or more and 0.100% or less
  • P is an element that has the effect of solid solution strengthening and increases the strength of the base steel sheet. In order to obtain such effects, the P content is set to 0.001% or more. On the other hand, if the P content exceeds 0.100%, P segregates in the old austenite grain boundaries and embrittles the grain boundaries, resulting in poor punchability and stretch flangeability. Therefore, the content of P is set to 0.001% or more and 0.100% or less.
  • the content of P is preferably 0.002% or more, more preferably 0.003% or more.
  • the content of P is preferably 0.050% or less, more preferably 0.030% or less.
  • S 0.0200% or less S exists as a sulfide in steel, and if the content exceeds 0.0200%, the ultimate deformability of the base steel sheet is reduced, so that punchability, stretch flangeability, And bendability is reduced. Therefore, the S content is 0.0200% or less.
  • the lower limit of the S content is not particularly specified, it is preferable that the S content is 0.0001% or more due to restrictions in production technology.
  • the S content is more preferably 0.0040% or less.
  • Al 1.000% or less Al suppresses carbide formation during annealing and increases the volume ratio of retained austenite. Since the generated retained austenite has a high hydrogen concentration, voids are generated inside the martensite when it undergoes martensite transformation by being processed during punching and bending test. Therefore, punching property and stretch flangeability are deteriorated. Moreover, since the voids become the starting points of cracks, bendability also decreases. Therefore, the Al content is set to 1.000% or less.
  • the lower limit of the Al content is not particularly specified, but the Al content is preferably 0.010% or more in order to sufficiently obtain the effect as the deoxidizer.
  • the Al content is preferably 0.100% or less, more preferably 0.070% or less. Further, the Al content is more preferably 0.020% or more.
  • N 0.0100% or less N exists as a nitride in the steel, and if the content exceeds 0.0100%, the ultimate deformability of the base steel sheet is reduced, so punchability, stretch flangeability, And bendability is reduced. Therefore, the content of N is set to 0.0100% or less. Although the lower limit of the N content is not particularly specified, it is preferable that the N content is 0.0005% or more due to the limitation in production technology. The N content is preferably 0.0050% or less.
  • Cr 0.300% or less
  • Cr is an element that enhances the hardenability, forms a desired amount of hardened martensite or tempered martensite, and sets TS to 780 MPa or more and obtains excellent dimensional accuracy during molding. It is an effective element for.
  • the content of Cr exceeds 0.300%, the area ratio of quenched martensite and tempered martensite increases, the area ratio of ferrite and bainite decreases, and the dimensional accuracy during molding deteriorates. Therefore, the content of Cr is set to 0.300% or less.
  • the lower limit of the Cr content may be 0.000%, but from the viewpoint of enhancing hardenability, the Cr content is preferably 0.010% or more. Therefore, the content of Cr is set to 0.300% or less.
  • the Cr content is preferably 0.010% or more.
  • the Cr content is preferably 0.100% or less.
  • Ca 0.0200% or less Ca exists as an inclusion in the base steel sheet.
  • the content of Ca exceeds 0.0200%, when the base steel sheet contains diffusible hydrogen, the inclusions serve as the starting points of cracks during the bending test, so that the bendability deteriorates. Therefore, the content of Ca is set to 0.0200% or less.
  • the lower limit of the Ca content may be 0.0000%, it is preferable that the Ca content is 0.0001% or more because of the limitation in the production technology. Further, the Ca content is preferably 0.0020% or less.
  • [%Mn]/[%Si] is 2.9 or more and 11.7 or less
  • [%Mn]/[%Si] By setting [%Mn]/[%Si] to 2.9 or more and 11.7 or less, both Si enrichment and Mn enrichment on the surface of the base material steel plate are suppressed, and the surface layer of the base material steel plate described later is suppressed.
  • the ratio of the Si enrichment amount to the Mn enrichment amount can be set within a desired range, and good plating properties can be realized.
  • [%Mn]/[%Si] is less than 2.9, the amount of Si enriched on the surface of the base steel sheet increases during the heating and holding at the highest temperature, which causes a non-plating defect on the surface of the steel sheet.
  • [%Mn]/[%Si] exceeds 11.7, the amount of Mn enriched on the surface of the base steel sheet during heating and holding at the highest temperature reached increases, and the content of Mn on the surface of the base steel sheet is reduced. Since Mn oxide, which causes plating defects, is generated, it becomes difficult to achieve good plating properties.
  • [%Mn]/[%Si] is preferably 3.1 or more, and more preferably 3.3 or more.
  • [%Mn]/[%Si] is preferably 11.0 or less, more preferably 10.0 or less.
  • the high-strength steel sheet of the present invention is, in addition to the above-mentioned component composition, further, in mass %, Ti: 0.001% or more and 0.100% or less, Nb: 0.001% or more and 0.100% or less, V: 0.001% or more and 0.100% or less, B: 0.0001% or more and 0.0100% or less, Mo: 0.005% or more and 2.000% or less, Cu: 0.01% or more and 1.00% or less, Ni: 0.01% to 0.50%, Sb: 0.001% to 0.200%, Sn: 0.001% to 0.200%, Ta: 0.001% to 0.100%
  • Mg 0.0001% to 0.0200%
  • Zn 0.001% to 0.020%
  • Co 0.001% to 0.020%
  • Zr 0.001% to 0.0.
  • Ti, Nb and V increase TS by forming fine carbides, nitrides or carbonitrides during hot rolling or annealing.
  • the content of at least one of Ti, Nb and V is set to 0.001% or more.
  • the content of at least one of Ti, Nb, and V exceeds 0.100%, large amounts of coarse precipitates and inclusions are formed, and when diffusible hydrogen is contained in the steel sheet, Since the precipitates and inclusions become the starting points of cracks during the bending test, bendability decreases. Therefore, when at least one of Ti, Nb and V is added, the content of each is 0.001% or more and 0.100% or less.
  • their content is preferably 0.005% or more.
  • at least one of Ti, Nb and V is added, their contents are preferably 0.060% or less.
  • B is an element that can improve hardenability by segregating to austenite grain boundaries.
  • B By adding B to the steel, it is possible to suppress the generation of ferrite and grain growth during annealing and cooling. In order to obtain such effects, the B content is set to 0.0001% or more.
  • the content of B exceeds 0.0100%, cracking occurs inside the steel sheet during hot rolling, which lowers the ultimate deformability of the steel sheet, resulting in poor punchability, stretch flangeability, and bendability. To do. Therefore, when B is added, its content is set to 0.0001% or more and 0.0100% or less.
  • When B is added its content is preferably 0.0002% or more.
  • B When B is added, its content is preferably 0.0050% or less.
  • Mo is an element that enhances the hardenability, and is an element that is effective for further increasing the TS and further improving the dimensional accuracy during molding by setting the area ratio of the hardened martensite and the tempered martensite within a more suitable range. Is. In order to obtain such effects, the Mo content is set to 0.005% or more. On the other hand, when the Mo content exceeds 2.000%, the area ratio of quenched martensite and tempered martensite increases, it becomes difficult to set TS to 780 MPa, and the dimensional accuracy at the time of molding deteriorates. Furthermore, when coarse precipitates and inclusions increase and the diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions become the starting points of cracks in the bending test, and the bendability decreases. Therefore, when Mo is added, its content is 0.005% or more and 2.000% or less. When Mo is added, its content is preferably 0.020% or more. When Mo is added, its content is preferably 0.500% or less.
  • Cu is an element that enhances the hardenability, and is an element that is effective for further increasing TS by increasing the area ratio of the hardened martensite and the tempered martensite within a more preferable range and further improving the dimensional accuracy during molding. Is. In order to obtain such effects, the content of Cu is set to 0.01% or more. On the other hand, if the Cu content exceeds 1.00%, the area ratio of quenched martensite and tempered martensite increases, TS becomes 780 MPa or more, and it becomes difficult to obtain excellent dimensional accuracy during molding. In addition, when coarse precipitates and inclusions increase and the diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions become the starting points of cracks during the bending test, and the bendability decreases. Therefore, when Cu is added, its content is set to 0.01% or more and 1.00% or less. When Cu is added, its content is preferably 0.02% or more. When Cu is added, its content is preferably 0.20% or less.
  • Ni is an element that enhances the hardenability, and is an element that is effective for further increasing the TS and further improving the dimensional accuracy during molding by setting the area ratio of the hardened martensite and the tempered martensite within a more suitable range. Is. In order to obtain such effects, the Ni content is set to 0.01% or more. On the other hand, if the Ni content exceeds 0.50%, the area ratio of quenched martensite and tempered martensite increases, and TS and dimensional accuracy during molding deteriorate. In addition, when coarse precipitates and inclusions increase and the diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions become the starting points of cracks during the bending test, and the bendability decreases. Therefore, when Ni is added, its content is set to 0.01% or more and 0.50% or less. When Ni is added, its content is preferably 0.02% or more. When Ni is added, the content is preferably 0.20% or less.
  • ⁇ Sb and Sn are effective elements for suppressing the oxidation of the surface of the base steel sheet during annealing and obtaining better plating properties.
  • the contents of one or two of Sb and Sn are each set to 0.001% or more.
  • the content of one or two of Sb and Sn exceeds 0.200%, coarse precipitates and inclusions increase, and when the base steel sheet contains diffusible hydrogen, the precipitation Since the objects and inclusions become the starting points of cracks during the bending test, the bendability decreases. Therefore, when 1 type or 2 types of Sb and Sn are added, the content shall be 0.001% or more and 0.200% or less, respectively.
  • their contents are preferably 0.005% or more.
  • one or two kinds of Sb and Sn are added, their contents are preferably 0.050% or less.
  • Ta increases TS by forming fine carbides, nitrides or carbonitrides during hot rolling or annealing.
  • Ta partially dissolves in Nb carbides and Nb carbonitrides to form complex precipitates such as (Nb,Ta)(C,N), which significantly suppresses coarsening of the precipitates. Then, stabilizing the precipitation strengthening is considered to have the effect of improving the strength of the base steel sheet.
  • the content of Ta is set to 0.001% or more.
  • the Ta content exceeds 0.100%, a large amount of coarse precipitates and inclusions are generated, and when diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions crack during the bending test.
  • Ta when Ta is added, its content is 0.001% or more and 0.100% or less.
  • the content of each is preferably 0.005% or more.
  • the content of each of them is preferably 0.020% or less.
  • Mg is an element that is effective for making the shapes of inclusions such as sulfides and oxides spherical, improving the ultimate deformability of the steel sheet, and improving stretch flangeability.
  • the content of Mg is set to 0.0001% or more.
  • the content of Mg exceeds 0.0200%, a large amount of coarse precipitates and inclusions are produced, and when diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions crack during the bending test. As a result, the bendability is lowered. Therefore, when adding Mg, the content is set to 0.0001% or more and 0.0200% or less.
  • the content of each is preferably 0.0005% or more.
  • their content is preferably 0.0050% or less.
  • Zn, Co and Zr are all effective elements for making the shape of inclusions spherical, improving the ultimate deformability of the steel sheet, and improving stretch flangeability.
  • the content of one kind or two or more kinds of Zn, Co and Zr is made 0.001% or more.
  • the content of one or more of Zn, Co and Zr exceeds 0.020%, a large amount of coarse precipitates and inclusions are formed, and diffusible hydrogen is contained in the steel sheet.
  • bendability decreases.
  • the content of one or more of Zn, Co and Zr is 0.0001% or more and 0.020% or less.
  • their content is preferably 0.002% or more.
  • at least one of Zn, Co and Zr is added, their contents are preferably 0.010% or less.
  • REM is an element that is effective for making the shape of inclusions spherical, improving the ultimate deformability of the steel sheet, and improving stretch flangeability.
  • the content of REM is set to 0.0001% or more.
  • REM exceeds 0.0200%, a large amount of coarse precipitates and inclusions are generated, and when diffusible hydrogen is contained in the steel sheet, the precipitates and inclusions crack during the bending test. As a result, the bendability is lowered. Therefore, when REM is added, its content is set to 0.0001% or more and 0.0200% or less.
  • REMs are added, their contents are preferably 0.0010% or more.
  • REM is added, their content is preferably 0.0100% or less.
  • the balance other than the above components is Fe and inevitable impurities.
  • the content of the above optional components is less than the lower limit value, the effect of the present invention is not impaired. Therefore, when these optional elements are included below the lower limit values, they are treated as unavoidable impurities.
  • One or two selected from the group consisting of bainite and ferrite has a total area ratio of 5% or more and 85% or less.
  • Ferrite and bainite which are soft phases, have low solid solubility in hydrogen, and thus are mainly composed of these phases.
  • the amount of diffusible hydrogen in the base steel sheet can be reduced.
  • YR can be controlled in a desired range by including ferrite and bainite. As a result, excellent punchability, stretch flangeability, bendability, and dimensional accuracy can be obtained.
  • the total area ratio of one or two of ferrite and bainite is set to 5% or more.
  • the total area ratio of one or two types of ferrite and bainite exceeds 85%, it becomes difficult to set TS to 780 MPa or more. Therefore, the total area ratio of one or two of ferrite and bainite is set to 5% or more and 85% or less.
  • the total area ratio of one or two of ferrite and bainite is preferably 80% or less, more preferably 70% or less.
  • Bainite is a structure composed of bainitic ferrite and a very small amount of carbide, and the area ratio of bainite can also be defined as the area ratio of bainitic ferrite.
  • Area ratio of tempered martensite 65% or less
  • tempered martensite having a hardness intermediate between that of ferrite and bainite, and tempered martensite By including tempered martensite having a hardness intermediate between that of ferrite and bainite, and tempered martensite, dimensional accuracy at the time of molding is further improved, and more excellent stretch flangeability. Can be obtained.
  • the area ratio of tempered martensite exceeds 65%, YS increases, YR cannot be controlled in a desired range, and dimensional accuracy during molding deteriorates.
  • the lower limit of the area ratio of tempered martensite is not particularly specified, in order to further improve the dimensional accuracy at the time of molding and to obtain more excellent stretch flangeability, the area ratio of tempered martensite is 3% or more. It is preferable that the content is 5% or more, and more preferably 5% or more.
  • the area ratio of tempered martensite is preferably 60% or less, more preferably 55% or less.
  • Area ratio of hardened martensite 5% or more and 40% or less
  • TS can be 780 MPa or more.
  • the area ratio of quenched martensite is set to 5% or more.
  • quenched martensite has a high hydrogen concentration because it is generated from austenite having a high solid solubility of hydrogen. Therefore, when the area ratio of the hardened martensite exceeds 40%, voids are generated inside the hardened martensite at the time of punching, so that the punchability and stretch-flangeability deteriorate.
  • the area ratio of quenched martensite is set to 5% or more and 40% or less.
  • the area ratio of quenched martensite is preferably 6% or more, more preferably 7% or more.
  • the area ratio of quenched martensite is preferably 35% or less, more preferably 30% or less.
  • the measuring method of each area ratio of ferrite and bainite, tempered martensite, and quenched martensite is as follows.
  • the sample is cut out so that the cross section (L cross section) parallel to the rolling direction of the steel sheet becomes the observation surface, and then the observation surface is polished with diamond paste.
  • finish polishing is performed on the observation surface using alumina.
  • 1 vol. % Corrod the observation surface with Nital about 1/4 position of the thickness of the steel plate (a position corresponding to 1/4 of the thickness in the depth direction from the steel plate surface), using a scanning electron microscope (SEM; Scanning Electron Microscope), 3 fields of view at a magnification of 3000 times To do.
  • the obtained tissue image is analyzed using Adobe Photoshop of Adobe Systems.
  • ferrite and bainite have a gray structure (base structure)
  • tempered martensite has a structure in which fine white carbide is precipitated on a gray base
  • quenched martensite has a white structure. Therefore, it is possible to identify each tissue and measure the area ratio.
  • volume ratio of retained austenite 5.0% or less
  • the volume ratio of retained austenite exceeds 5.0%, the retained austenite has a high hydrogen concentration, and therefore, the austenite is processed by punching or bending test to produce martensite.
  • the site is transformed, voids are generated inside the martensite. Therefore, the total void number density after punching increases, and the punchability and stretch-flangeability deteriorate.
  • the volume ratio of retained austenite is 5.0% or less.
  • the lower limit of the volume ratio of retained austenite is not particularly specified, it is preferably 0.2% or more, and more preferably 0.4% or more in order to further improve the dimensional accuracy during molding.
  • the volume ratio of retained austenite is preferably 4.0% or less, more preferably 3.5% or less.
  • the method for measuring the volume ratio of retained austenite is as follows. After mechanically grinding the steel plate in the plate thickness direction (depth direction) to 1/4 of the plate thickness, chemical polishing with oxalic acid was performed to obtain an observation surface. The observation surface was observed by the X-ray diffraction method. As the incident X-ray, a Co K ⁇ radiation source was used, and the retained austenite (200), (220), (311) planes of the respective diffraction intensities of the ferrite (200), (211), and (220) planes were measured. The volume ratio of retained austenite was calculated from the diffraction intensity ratio.
  • the steel structure in addition to the above-mentioned ferrite, bainite (bainitic ferrite), tempered martensite, quenched martensite, and retained austenite, pearlite, cementite and other carbides, and other structures, the effect of the present invention. You may contain in the range which does not spoil.
  • the area ratio of other structures is preferably 3% or less.
  • the types and area ratios of other tissues (remainder tissues) may be determined by, for example, SEM observation.
  • Ratio of Si enrichment amount to Mn enrichment amount of base material steel plate surface layer 0.7 or more and 1.3 or less
  • the ratio of the Si enrichment amount to the Mn enrichment amount of the base material steel sheet surface layer is represented by the following formula.
  • (Ratio of Si enrichment amount to Mn enrichment amount of base material steel plate surface layer) (ISi Surface /ISi Bulk )/(IMn Surface /IMn Bulk )
  • the ISi Surface , the ISi Bulk , the IMn Surface and the IMn Bulk are Si strengths in a region of a depth of 0.6 ⁇ m from the surface of the steel plate, which are measured by glow discharge emission spectroscopy (GDS; Glow Discharge Spectroscopy), respectively.
  • GDS glow discharge emission spectroscopy
  • the Si strength in the region where the depth from the steel plate surface is 6.0 ⁇ m, the Mn strength in the region where the depth from the steel plate surface is 0.6 ⁇ m, and the Mn strength in the region where the depth from the steel plate surface is 6.0 ⁇ m is there.
  • the hot dip galvanized layer or the alloyed hot dip galvanized layer on the surface of the steel sheet is removed as described later.
  • the amount of Si concentration and the amount of Mn concentration to the outermost surface layer of the base material steel sheet affect the plating property, the outermost surface layer of the base material steel sheet is incorporated into the hot dip galvanized layer or the alloyed hot dip galvanized layer.
  • the Si enrichment amount and the Mn enrichment amount in the outermost surface layer of the base steel sheet by GDS analysis.
  • the concentration of Si or Mn in the outermost layer of the base steel sheet the amount of Si or Mn decreases in the region where the depth from the steel sheet surface is 6.0 ⁇ m.
  • the concentration of Si or Mn in the outermost layer of the base steel sheet was evaluated based on the Si and Mn strengths in the region where the depth from the steel sheet surface was 6.0 ⁇ m. ..
  • the amount of Mn enriched in the surface layer of the base material steel plate is controlled by adding Si and Mn in the steel plate in the above-described ratio in combination and controlling the dew point and hydrogen concentration of the atmosphere in which the cold-rolled plate reaches the highest temperature as described below. It is possible to control the ratio of the amount of Si enriched with respect to 0.7 to 1.3 or less, and it is possible to realize good plating properties.
  • the ratio of the amount of Si concentration to the amount of Mn concentration of the base material steel sheet surface is less than 0.7, the Si strength is low in the region where the depth from the steel sheet surface is 0.6 ⁇ m, and a Si deficient layer is formed.
  • the ratio of the Si enrichment amount to the Mn enrichment amount of the base material steel sheet surface layer is set to 0.7 or more and 1.3 or less.
  • the ratio of the Si enrichment amount to the Mn enrichment amount of the base material steel sheet surface layer is preferably 0.8 or more, and more preferably 0.9 or more. Further, the ratio of the Si enrichment amount to the Mn enrichment amount of the base material steel sheet surface layer is preferably 1.2 or less, more preferably 1.1 or less.
  • the calculation method of the Si enrichment amount and the Mn enrichment amount of the base material steel sheet surface layer is as follows. First, the hot-dip galvanized layer or the alloyed hot-dip galvanized layer of the high-strength galvanized steel sheet is removed by a router to obtain a test piece. The measurement sample is analyzed in the depth direction from the surface of the steel sheet by GDS.
  • the GDS apparatus is System 3580 manufactured by Rigaku Denki Kogyo Co., Ltd., and the measurement conditions are as follows.
  • ⁇ Measurement mode DC mode ⁇ Electrode size: ⁇ 4 [mm] ⁇ Ar gas flow rate: 250 [cc/min] ⁇ Current: 20 [mA]
  • a sample is cut out from a high-strength galvanized steel sheet, analyzed by changing the sputtering time, and the sputter rate is calculated from the sputter trace depth of the sample.
  • the Mn intensity IMn Surface at the sputtering time at which the sputtering distance is 0.6 ⁇ m and the Mn strength IMn Bulk at the sputtering time at which the sputtering distance is 6.0 ⁇ m are obtained, and the IMn Surface /IMn Bulk is calculated.
  • Amount of diffusible hydrogen in the base steel sheet 0.80 mass ppm or less
  • the present inventors have conducted intensive studies in order to realize a high-strength steel sheet excellent in punching property and stretch-flangeability, and as a result, the amount of diffusible hydrogen in the base steel sheet is punchable, stretch-flangeability, and bending. It was found to be related to sex. As a result of further study, it was found that by reducing the amount of diffusible hydrogen in the base steel sheet to 0.80 mass ppm or less, excellent punchability, stretch flangeability, and bendability can be obtained, and the present invention has been achieved. It came to completion.
  • the lower limit of the amount of diffusible hydrogen in the base material steel sheet is not particularly specified, but it is preferable that the amount of diffusible hydrogen in the base material steel sheet is 0.01 mass ppm or more because of the limitation in production technology.
  • the amount of diffusible hydrogen in the base steel sheet is more preferably 0.05 mass ppm or more.
  • the amount of diffusible hydrogen in the base steel sheet is preferably 0.50 mass ppm or less, more preferably 0.40 mass ppm or less, and further preferably 0.35 mass ppm or less.
  • the base material steel plate for measuring the amount of diffusible hydrogen is not limited to the base material steel plate of the high-strength hot-dip galvanized steel sheet after the plating treatment and before processing, such as punching, stretch flange forming, and bending after the plating treatment. It may be a base material steel plate of a processed steel plate, or may be a base material portion of a product manufactured by welding a processed steel plate.
  • the method for measuring the amount of diffusible hydrogen in the base steel sheet is as follows.
  • a test piece having a length of 30 mm and a width of 5 mm is taken from the high-strength galvanized steel sheet, and the hot-dip galvanized layer or the alloyed hot-dip galvanized layer is alkali-removed.
  • the amount of hydrogen released from the test piece is measured by the thermal desorption analysis method. Specifically, after continuously heating from room temperature to 300° C. at a heating rate of 200° C./h, it was cooled to room temperature, and the cumulative amount of hydrogen released from the test piece was measured from room temperature to 210° C. The amount of diffusible hydrogen in the material steel sheet.
  • the composition of the hot-dip galvanized layer is not particularly limited and may be a general one.
  • the plating layer contains Fe: 20 mass% or less, Al: 0.001 mass% or more and 1.0 mass% or less, and further contains Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr. , Co, Ca, Cu, Li, Ti, Be, Bi, and REM, and one or more selected from the group consisting of 0 mass% to 3.5 mass% in total, the balance Zn and unavoidable It has a composition consisting of specific impurities.
  • the Fe content in the plating layer is less than 7% by mass in one example, and in the case of an alloyed hot dip galvanized layer, the Fe content in the plating layer is one example.
  • the amount is 7% by mass or more and 15% by mass or less, more preferably 8% by mass or more and 13% by mass or less.
  • the coating amount is not particularly limited, but it is preferable that the coating amount per one surface of the base steel sheet is 20 to 80 g/m 2 .
  • the hot-dip galvanized layer preferably has cracks. Since the hot-dip galvanized layer has cracks, the amount of diffusible hydrogen in the base steel sheet can be reduced to a more preferable range. As a result, punchability, stretch flangeability, and bendability can be improved.
  • the hot-dip galvanized layer had cracks was determined as follows.
  • the hot-dip galvanized layer formed on the surface of the base steel sheet was observed at a magnification of 1500 times using SEM, and two views were observed on each of the front and back surfaces of the base steel sheet, for a total of four views, and 10 ⁇ m or more.
  • one or more cracks having a length of 1 exist in any of the above four visual fields, it was determined to have cracks.
  • the high-strength hot-dip galvanized steel sheet including the base steel sheet and the hot-dip galvanized layer described above has a tensile strength (TS) of 780 MPa or more.
  • TS tensile strength
  • JIS Z2241 JIS No. 5 test pieces are taken from the high-strength hot-dip galvanized steel sheet so that the longitudinal direction is perpendicular to the rolling direction of the steel sheet. Using the test piece, a tensile test is performed under the condition that the crosshead displacement velocity Vc is 1.67 ⁇ 10 ⁇ 1 mm/s, and TS is measured.
  • the plate thickness of the high-strength galvanized steel sheet according to the present invention is not particularly limited, but is usually 0.3 mm or more and 2.8 mm or less.
  • a method for manufacturing the high strength galvanized steel sheet of the present invention will be described.
  • a steel slab having the above-described composition is manufactured.
  • a steel material is melted into a molten steel having the above composition.
  • the melting method is not particularly limited, and any known melting method such as converter melting or electric furnace melting is suitable.
  • the obtained molten steel is solidified to produce a steel slab (slab).
  • the method for producing a steel slab from molten steel is not particularly limited, and a continuous casting method, an ingot making method, a thin slab casting method, or the like can be used.
  • the steel slab is preferably manufactured by a continuous casting method.
  • the manufactured steel slab is subjected to hot rolling including rough rolling and finish rolling to obtain a hot rolled sheet.
  • the steel slab produced as described above is once cooled to room temperature, then slab heated and then rolled.
  • the slab heating temperature is preferably 1100° C. or higher from the viewpoint of melting carbides and reducing rolling load. Further, in order to prevent an increase in scale loss, it is preferable that the slab heating temperature is 1300°C or lower.
  • the slab heating temperature is based on the temperature of the slab surface during heating.
  • hot rolling may be performed by applying an energy-saving process.
  • As an energy saving process without cooling the manufactured steel slab to room temperature, it is directly charged into a heating furnace as a hot piece and hot-rolled directly, or after slightly heating the manufactured steel slab.
  • Direct rolling which involves immediate rolling, may be mentioned.
  • the steel slab is roughly rolled under normal conditions to form a sheet bar.
  • the sheet bar is subjected to finish rolling to obtain a hot rolled sheet.
  • the finish rolling temperature is for reducing the rolling load, and when the reduction ratio in the unrecrystallized state of austenite is high, an abnormal structure elongated in the rolling direction develops, and the workability of the annealed sheet decreases, The Ar 3 transformation point or higher is preferable.
  • the hot rolled sheet is wound and collected.
  • the winding temperature is preferably 300°C or higher and 700°C or lower from the viewpoint of the formability of the annealed plate.
  • rough rolling plates may be joined together during hot rolling and continuous finish rolling may be performed.
  • the rough rolled plate (sheet bar) may be temporarily wound before the finish rolling.
  • part or all of the finish rolling may be lubrication rolling. Performing the lubrication rolling is also effective from the viewpoint of uniformizing the shape of the steel sheet and uniformizing the material.
  • the coefficient of friction during lubrication rolling is preferably in the range of 0.10 or more and 0.25 or less.
  • the hot rolled sheet is pickled. Oxidation on the surface of the steel sheet can be removed by pickling, and thus good plating quality in the high-strength hot-dip galvanized steel sheet of the final product can be ensured.
  • pickling may be performed only once or may be performed in multiple times.
  • the pickled hot rolled sheet is cold rolled at a reduction rate of 30% or more to obtain a cold rolled sheet.
  • the cold rolling may be performed without heat treatment, or the cold rolling may be performed after the heat treatment.
  • Cold rolling reduction 30% or more
  • the total area ratio of one or two selected from the group consisting of ferrite and bainite is 85% or less
  • TS can be 780 MPa or more.
  • the upper limit of the reduction ratio of cold rolling is not particularly specified, but it is preferably 80% or less, and more preferably 70% or less in order to further improve the dimensional accuracy during forming.
  • the reduction rate of cold rolling is preferably 35% or more, more preferably 40% or more.
  • the number of rolling passes and the rolling reduction of each pass are not particularly limited as long as the cumulative rolling reduction is 30% or more.
  • the cold-rolled sheet obtained as described above is supplied to a continuous hot-dip galvanizing apparatus and annealed.
  • the continuous hot-dip galvanizing apparatus has an annealing furnace and a hot-dip galvanizing equipment located downstream of the annealing furnace, and the hot-dip galvanizing equipment is connected to the hot-dip galvanizing bath and the steel strip exit side of the annealing furnace. , And a snout whose tip is immersed in a hot dip galvanizing bath.
  • a general continuous hot-dip galvanizing line configured to continuously perform a series of treatments including heating, cooling, hot-dip galvanizing, and alloying treatment of hot-dip galvanizing.
  • the cold-rolled sheet supplied to the continuous hot-dip galvanizing apparatus is annealed while being first conveyed in an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order.
  • the specific annealing conditions are as follows.
  • the number of times of annealing is not particularly limited, but preferably once (single annealing method).
  • the cold-rolled sheet is supplied to an annealing furnace and heated to a maximum attainable temperature of 750°C to 900°C at an average heating rate of 10°C/s or less in a temperature range of 200°C to 650°C.
  • Average heating rate in the temperature range of 200° C. or higher and 650° C. or lower 10° C./s or lower Structures mainly composed of ferrite and bainite that are soft phases by reducing the average heating rate in the temperature range of 200° C. or higher and 650° C. or lower It is possible to form a structure in which hardened martensite and tempered martensite, which are hard phases, are dispersed, and to obtain excellent dimensional accuracy during molding.
  • the average heating rate in the temperature range of 200° C. or higher and 650° C. or higher exceeds 10° C./s, the area ratio of quenched martensite increases, and punchability and stretch flangeability deteriorate. In addition, bendability also decreases.
  • the average heating rate in the temperature range of 200°C to 650°C is 10°C/s or less.
  • the lower limit of the average heating rate in the temperature range of 200° C. or higher and 650° C. or lower is not specified, but it is 2° C./s or higher in order to increase TS and dimensional accuracy during molding. It is more preferably 4° C./s or more.
  • the average heating rate in the temperature range of 200° C. or higher and 650° C. or lower is preferably 9° C./s or less, more preferably 8° C./s or less.
  • Maximum ultimate temperature 750° C. or higher and 900° C. or lower If the maximum ultimate temperature is less than 750° C., the austenite generation rate during heating in the two-phase region of ferrite and austenite becomes insufficient, so the area ratio of ferrite and bainite is It becomes difficult to increase TS to 780 MPa, and the dimensional accuracy at the time of molding deteriorates. On the other hand, when the maximum temperature reached exceeds 900° C., heating occurs in the austenite single-phase region, so the area ratio of ferrite and bainite, which are soft phases after annealing, decreases, and the area ratio of tempered martensite increases. However, it becomes difficult to obtain excellent dimensional accuracy during molding.
  • the maximum attainable temperature is 750°C or higher and 900°C or lower.
  • the highest temperature reached is preferably 770°C or higher, more preferably 780°C or higher. Further, the highest temperature reached is preferably 880°C or lower, and more preferably 860°C or lower.
  • the maximum temperature is based on the surface temperature of the base steel sheet.
  • the annealing furnace is composed of a heating zone, a soaking zone and a cooling zone in order from the inlet side. Since the steel plate is heated in the soaking zone from the heating zone and is cooled in the cooling zone after that, it is assumed that the region where the cold-rolled sheet reaches the maximum temperature is the soaking zone side before the start of cooling. You can
  • Hold time at maximum temperature of cold-rolled sheet 5 s or more and 100 s or less If the hold time at maximum temperature is less than 5 s, the austenite formation rate becomes insufficient during heating in the two-phase region of ferrite and austenite. Therefore, the area ratio of ferrite or bainite increases, making it difficult to set TS to 780 MPa, and the dimensional accuracy at the time of molding decreases. On the other hand, when the holding time at the highest temperature exceeds 100 s, the austenite generation rate becomes excessive, so that the area ratio of ferrite or bainite, which is a soft phase, decreases, and the area ratio of tempered martensite increases. However, the dimensional accuracy during molding is reduced.
  • the holding time at the maximum reached temperature is set to 5 s or more and 100 s or less.
  • the holding time at the highest reached temperature is preferably 10 s or more, more preferably 15 s or more.
  • the holding time at the highest temperature is preferably 80 s or less, more preferably 60 s or less.
  • Dew point of the atmosphere in the region where the cold-rolled sheet reaches the highest temperature is an extremely important invention constituent element in the present invention.
  • the Si concentration and Mn concentration in the surface layer of the base steel sheet can be reduced, and good plating properties can be obtained. Can be realized.
  • the lower limit of the dew point in the region where the highest temperature is reached is not specified, it is preferable that the dew point of the atmosphere in the region where the cold-rolled sheet reaches the highest temperature is ⁇ 60° C. or higher because of the limitation in production technology. More preferably, the temperature is ⁇ 55° C. or higher.
  • the dew point of the atmosphere in the region where the cold-rolled sheet reaches the maximum temperature is preferably ⁇ 42° C. or lower, more preferably ⁇ 45° C. or lower.
  • First hydrogen concentration in the atmosphere of the region where the cold-rolled sheet reaches the highest temperature 5% by volume or more and 10% by volume or less
  • the hydrogen concentration (first hydrogen concentration) of the atmosphere in the region where the cold-rolled sheet reaches the highest temperature is less than 5% by volume
  • the Si concentration and the Mn concentration in the surface layer of the steel sheet increase, and the steel sheet surface is not plated. Since Si oxides and Mn oxides that cause defects are generated, it becomes difficult to achieve good plating properties.
  • the first hydrogen concentration is set to 5% by volume or more and 10% by volume or less.
  • the first hydrogen concentration is preferably 6% by volume or more.
  • the first hydrogen concentration is preferably 9% by volume or less.
  • nitrogen is preferable as the balance other than hydrogen in the atmosphere of the region where the cold-rolled sheet reaches the highest temperature.
  • the cold-rolled sheet held under the above-mentioned conditions at the maximum ultimate temperature is cooled from the maximum ultimate temperature to 600°C in the annealing furnace at an average cooling rate of 5°C/s or more.
  • Average cooling rate from the highest temperature to 600°C 5°C/s or more
  • the area ratio of ferrite and bainite can be controlled within a desired range. It is possible to obtain TS of 780 MPa or more and obtain excellent dimensional accuracy during molding.
  • the average cooling rate from the highest temperature to 600°C is set to 5°C/s or more.
  • the upper limit of the average cooling rate from the highest temperature to 600°C is not specified, but in order to further improve the dimensional accuracy during molding and to improve stretch flangeability and bendability, the maximum
  • the upper limit of the average cooling rate from the ultimate temperature to 600°C is preferably 40°C/s or less, more preferably 30°C/s or less.
  • the average cooling rate from the highest temperature to 600°C is preferably 7°C/s or more, more preferably 10°C/s or more.
  • the cold-rolled sheet cooled to 600°C as described above is passed through the steel strip exit side of the cooling zone, and moved to the hot-dip galvanizing bath via the snout whose tip is immersed in the hot-dip galvanizing bath. While further cooling. At this time, the residence time until the cold-rolled sheet cooled to 600° C. enters the hot-dip galvanizing bath is set to 15 s or more.
  • a roll for changing the traveling direction of the cold-rolled sheet to enter the snout is provided, and the cold-rolled sheet passes through the roll. Intrudes into the snout.
  • the hydrogen concentration of the atmosphere of the section for accommodating the roll in the cooling zone is 50% or more and 95% or less of the above-mentioned first hydrogen concentration.
  • the balance of the atmosphere in the compartment containing the roll in the cooling zone other than hydrogen is preferably nitrogen.
  • Residence time until cold-rolled sheet cooled to 600° C. or lower penetrates into hot-dip galvanizing bath 15 s or more
  • the upper limit of the residence time until the cold-rolled sheet cooled to 600° C. or less penetrates into the hot-dip galvanizing bath is not particularly specified, but from the viewpoint of ensuring the area ratio of hard martensite and tempered martensite that are hard phases. , 700 s or less, and more preferably 500 s or less. Further, the residence time until the cold-rolled sheet cooled to 600° C. or lower penetrates into the hot dip galvanizing bath is preferably 20 s or more, more preferably 25 s or more.
  • Hydrogen concentration in the atmosphere of the compartment containing the roll passing immediately before the cold-rolled sheet penetrates into the snout 50% or more and 95% or less of the above-mentioned first hydrogen concentration is an extremely important invention constituent element in the present invention.
  • the cold rolled sheet passes through the roll by setting the hydrogen concentration of the atmosphere of the compartment containing the roll passing immediately before the cold rolled sheet enters the snout to be 95% or less of the first hydrogen concentration described above.
  • the amount of diffusible hydrogen in the steel sheet is reduced, excellent punchability, stretch flangeability, and bendability can be obtained.
  • the hydrogen concentration of the compartment containing the roll that passes immediately before the cold-rolled sheet penetrates into the snout is set to 50% or more and 95% or less of the first hydrogen concentration described above.
  • the hydrogen concentration of the compartment containing the roll passing immediately before the cold-rolled sheet penetrates into the snout is preferably 60% or more, more preferably 70% or more of the first hydrogen concentration described above.
  • the hydrogen concentration of the compartment accommodating the roll passing immediately before the cold-rolled sheet penetrates into the snout is preferably 93% or less, and more preferably 90% or less of the first hydrogen concentration described above.
  • the cold-rolled sheet led to the hot-dip galvanizing bath through the snout is dipped in the hot-dip galvanizing bath to perform hot-dip galvanizing treatment.
  • the bath temperature of the hot dip galvanizing bath is 440° C. or more and 500° C. or less in one example.
  • the hot-dip galvanizing bath it is preferable to use one having a composition in which the Al content is 0.10 mass% or more and 0.23 mass% or less and the balance is Zn and inevitable impurities.
  • a galvanizing alloying treatment may be further performed to form an alloyed hot dip galvanizing layer.
  • the alloying treatment is preferably performed in a temperature range of 460° C. or higher and 600° C. or lower. If the alloying temperature is less than 460° C., the Zn—Fe alloying rate becomes excessively slow, and alloying becomes extremely difficult. On the other hand, if the alloying temperature exceeds 600° C., untransformed austenite may transform into pearlite, and TS and El may decrease.
  • the alloying treatment is preferably performed in a temperature range of 470° C. or higher and 560° C. or lower, and more preferably 470° C. or higher and 530° C. or lower.
  • the coating weight of the hot-dip galvanized steel sheet (GI) and the alloyed hot-dip galvanized steel sheet (GA) is preferably 20 to 80 g/m 2 per side (double-sided plating).
  • the amount of plating applied can be adjusted by performing gas wiping or the like after hot dip galvanizing.
  • the average cooling rate up to 50° C. after the galvanizing treatment or the galvanizing alloying treatment is performed is 5° C./s or more.
  • the average cooling rate up to 50° C. after the galvanizing treatment or the galvanizing alloying treatment is performed is 40° C./s or less because of the limitation in production technology.
  • the average cooling rate up to 50° C. after the galvanizing treatment or the galvanizing alloying treatment is more preferably 7° C./s or more.
  • the average cooling rate up to 50°C after the galvanizing treatment or the galvanizing alloying treatment is more preferably 30°C/s or less.
  • the cooling rate below 50°C is not particularly limited, and it can be cooled to a predetermined temperature by any method.
  • a cooling method gas jet cooling, mist cooling, water cooling, air cooling, or the like can be applied. Note that, normally, high-strength hot-dip galvanized steel sheets are traded after being cooled to room temperature.
  • the high-strength hot-dip galvanized steel sheet that has been subjected to hot dip galvanizing treatment or further alloying hot dip galvanizing treatment is cooled to 50° C. or lower, and then the elongation ratio of 0.05% or more and 1.00% or less May be rolled in.
  • a crack can be introduced into the galvanized layer by setting the elongation percentage of rolling performed after cooling to 50° C. or less to 0.05% or more. By introducing cracks in the galvanized layer, it is possible to reduce the amount of diffusible hydrogen in the steel sheet, and as a result, it is possible to further improve punchability and stretch flangeability. On the other hand, when the elongation percentage of rolling after cooling to 50° C.
  • the elongation percentage of rolling after cooling to 50° C. or lower is preferably 1.00% or less, and more preferably 0.70% or less. Further, the elongation percentage of rolling after cooling to 50° C. or lower is more preferably 0.10% or higher.
  • the rolling after cooling to 50° C. or less may be performed (online) on a device continuous with the above-mentioned continuous hot dip galvanizing device, or on a device discontinuous with the above continuous hot dip galvanizing device ( You can do that (offline).
  • the target elongation rate may be achieved by one rolling, or a plurality of times may be performed and a total elongation rate of 0.05% or more and 1.00% or less may be achieved.
  • the rolling described here generally refers to temper rolling, but as long as an elongation rate equivalent to that of temper rolling can be imparted, rolling by a method such as processing by a leveler may be used.
  • heat may be kept in the temperature range of room temperature to 300°C.
  • the amount of diffusible hydrogen in the steel sheet can be further reduced.
  • the total void number density can be reduced and ⁇ can be 20% or more. it can.
  • R/t can be set to a desired value or less.
  • the heat retention time is usually about 3 to 7 days, but the heat retention may be up to about 6 months.
  • a steel material having the composition shown in Table 1 with the balance being Fe and inevitable impurities was melted in a converter and made into a steel slab by the continuous casting method.
  • the obtained steel slab was heated to 1250° C. and roughly rolled.
  • finish rolling was performed at a finish rolling temperature of 900°C, and winding was performed at a winding temperature of 450°C to obtain a hot rolled sheet.
  • the hot-rolled sheet was pickled and then cold-rolled.
  • the cold rolling reduction ratio was as shown in Table 2.
  • the plate thickness after cold rolling was 1.2 mm.
  • the cold-rolled sheet after rolling was annealed under the conditions shown in Table 2. Then, the annealed cold rolled sheet was subjected to hot dip galvanizing treatment, cooled to 50° C. or lower, and then rolled under the conditions shown in Table 2 to obtain a high strength hot dip galvanized steel sheet (GI). For some high-strength hot-dip galvanized steel sheets, after the hot-dip galvanizing treatment, further alloying treatment, cooling to 50°C or lower, and rolling under the conditions shown in Table 2 A steel plate (GA) was obtained.
  • GI hot dip galvanized steel sheet
  • a hot dip galvanizing bath in the case of producing GI, a hot dip galvanizing bath containing Al: 0.20 mass% and the balance Zn and unavoidable impurities was used. Further, in the case of producing GA, a hot dip galvanizing bath containing Al: 0.14 mass% and the balance Zn and unavoidable impurities was used. The bath temperature was 470°C. Coating weight, when manufacturing a GI is a 45 ⁇ 72g / m 2 (two-sided plating) degree per side, In the production of the GA is set to the extent per side 45 g / m 2 (two-sided plating). The alloying treatment for producing GA was performed at about 550°C.
  • the composition of the GI plating layer contained Fe: 0.1 to 1.0% by mass and Al: 0.2 to 1.0% by mass, with the balance being Fe and inevitable impurities.
  • the composition of the plating layer of GA contained Fe: 7 to 15% by mass, Al: 0.1 to 1.0% by mass, and the balance Fe and unavoidable impurities.
  • the tensile test was performed according to JIS Z 2241. From the obtained steel sheet, JIS No. 5 test pieces were sampled so that the longitudinal direction was perpendicular to the rolling direction of the steel sheet. Using the test piece, a tensile test was conducted under the condition that the crosshead displacement velocity Vc was 1.67 ⁇ 10 -1 mm/s, and YS, TS and El were measured. In the present invention, TS: 780 MPa or more was judged to be acceptable.
  • YR which is an index of dimensional accuracy at the time of molding, is 45% or more and 75% or less in TS: 780 MPa class, 50% or more and 80% or less in TS: 980 MPa class, and 60% or more 90% in TS: 1180 MPa class. In the following cases, it was judged that the dimensional accuracy during molding was good. Note that YR was calculated based on the above formula (1).
  • the punchability was evaluated by the number of voids after punching.
  • a 100 mm ⁇ 100 mm sample was sheared from the obtained steel plate.
  • a hole having a diameter of 10 mm was punched out in the sample with a clearance of 12.5%.
  • an observation sample of 15 mmL ⁇ 10 mmW was cut out so that the plate thickness cross section (L cross section) parallel to the rolling direction of the steel plate became the observation surface and included the punched end face.
  • the observation surface is polished with diamond paste, and then 1 vol. % Corroded with Nital.
  • the images were taken continuously at a magnification of 3000 times using an SEM up to a region 300 ⁇ m away from the punched end face, and the total number of voids generated in the region 150 ⁇ m away from the punched end face was counted from the obtained tissue image.
  • the total number density of voids was evaluated. Further, all the voids, the voids generated inside the quenched martensite and tempered martensite, and the voids generated at the interface of the soft phase and the hard phase, the total void number density after punching, after punching, The ratio of the void number densities generated inside the quenched martensite and the tempered martensite was calculated.
  • the total void number density after punching is 2000/mm 2 or less, and the ratio of the void number density generated inside the quenched martensite and the tempered martensite after punching to the total void number density after punching is 0.85 or less. It was judged that the punchability was good.
  • the stretch flangeability was evaluated by a hole expanding test.
  • the hole expanding test was performed according to JIS Z 2256. A 100 mm ⁇ 100 mm sample was sheared from the obtained steel plate. A hole having a diameter of 10 mm was punched in the sample with a clearance of 12.5%. A die having an inner diameter of 75 mm was used to press a conical punch having an apex angle of 60° into the hole while suppressing the wrinkle holding force of 9 ton (88.26 kN) around the hole, and the hole diameter at the crack generation limit was measured.
  • the limit hole expansion ratio: ⁇ (%) was obtained from the following formula, and the hole expandability was evaluated from the value of the limit hole expansion ratio.
  • the bending test was performed according to JIS Z 2248.
  • a strip-shaped test piece having a width of 30 mm and a length of 100 mm was sampled from the obtained steel sheet such that the direction parallel to the rolling direction of the steel sheet was the axial direction of the bending test.
  • a bending test was performed by the V-block method with a bending angle of 90° under the condition that the pressing load was 100 kN and the pressing holding time was 5 seconds.
  • a 90° V bending test was performed, and the ridge line portion of the bending apex was observed with a microscope (RH-2000: manufactured by Hylox Corporation) at a magnification of 40 times, and cracks having a crack length of 200 ⁇ m or more were recognized.
  • the bending radius when it was no longer possible was defined as the minimum bending radius (R).
  • R The bending radius when it was no longer possible was defined as the minimum bending radius (R).
  • R/t A value obtained by dividing R by the plate thickness (t) (R/t) is 3.0 or less in TS: 780 MPa class and TS: 980 MPa class, and 4.0 or less in TS: 1180 MPa class. was judged to be good.
  • the platability is evaluated by visually observing the presence or absence of non-plating defects on the front surface and the back surface of the obtained hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet, and there is no non-plating defect. The case was judged to be excellent in plating property.
  • the quantity was measured.
  • the presence or absence of cracks in the hot-dip galvanized layer or the alloyed hot-dip galvanized layer was determined.
  • the remaining structure was also confirmed by structure observation. The results are shown in Table 3.
  • TS was 780 MPa or more, and dimensional accuracy (YR) at the time of molding, punchability, stretch flangeability ( ⁇ ), bendability (R/t), and plating property Both were excellent.
  • YR dimensional accuracy
  • ⁇ stretch flangeability
  • R/t bendability
  • plating property plating property

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Abstract

La présente invention concerne : une tôle d'acier galvanisée par immersion à chaud à haute résistance ayant des propriétés de poinçonnage, des propriétés de bordage par étirage, des propriétés de flexion et des propriétés de placage exceptionnelles, la tôle d'acier permettant de fabriquer des composants avec une précision dimensionnelle élevée, et la tôle d'acier ayant en outre une résistance à la traction de 780 MPa ou plus ; et un procédé de fabrication de la tôle d'acier galvanisée par immersion à chaud à haute résistance. Dans la tôle d'acier galvanisée par immersion à chaud à haute résistance selon l'invention : une tôle d'acier de matériau parent a une composition de composant contenant C, Si, Mn, P, S, Al, N, Ca et Cr, la composition de composant satisfaisant une relation telle que le rapport [% de Mn]/[% de Si] est de 2,9 à 11,7 inclus, et le reste étant du Fe et des impuretés inévitables ; la tôle d'acier de matériau parent a une composition d'acier contenant un ou deux éléments choisis dans le groupe constitué de la baïnite et la ferrite, ainsi que de la martensite revenue, de la martensite trempée et de l'austénite résiduelle ; la quantité de concentration de Si par rapport à la quantité de concentration de Mn dans une couche de surface de la tôle de matériau parent est de 0,7 à 1,3 inclus ; et la quantité d'hydrogène diffusible dans la tôle d'acier de matériau parent est de 0,80 ppm en masse ou moins.
PCT/JP2019/046447 2019-02-22 2019-11-27 Tôle d'acier galvanisée par immersion à chaud à haute résistance et procédé de fabrication de ladite tôle WO2020170542A1 (fr)

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MX2021009947A MX2021009947A (es) 2019-02-22 2019-11-27 Lamina de acero galvanizado por inmersion en caliente de alta resistencia y metodo para producir la misma.
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WO2022136684A1 (fr) * 2020-12-23 2022-06-30 Voestalpine Stahl Gmbh Feuillard ou acier laminé à froid influencé par la température de bobinage
WO2022136689A1 (fr) * 2020-12-23 2022-06-30 Voestalpine Stahl Gmbh Bande ou tôle d'acier revêtu de zinc ou d'alliage de zinc présentant une adhérence au zinc améliorée
WO2023181390A1 (fr) * 2022-03-25 2023-09-28 Ｊｆｅスチール株式会社 Procédé de fabrication de tôle d'acier recuite après galvanisation par immersion à chaud
JP7364119B1 (ja) * 2022-12-01 2023-10-18 Ｊｆｅスチール株式会社 溶融亜鉛めっき鋼板、溶融亜鉛めっき鋼板を用いてなる部材、部材からなる自動車の骨格構造部品用又は自動車の補強部品、ならびに溶融亜鉛めっき鋼板及び部材の製造方法
WO2023218731A1 (fr) * 2022-05-11 2023-11-16 Ｊｆｅスチール株式会社 Feuille d'acier, élément et procédé de production associé
WO2023218730A1 (fr) * 2022-05-11 2023-11-16 Ｊｆｅスチール株式会社 Tôle d'acier, élément, et procédés de fabrication de ceux-ci

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Publication number Priority date Publication date Assignee Title
WO2022136684A1 (fr) * 2020-12-23 2022-06-30 Voestalpine Stahl Gmbh Feuillard ou acier laminé à froid influencé par la température de bobinage
WO2022136689A1 (fr) * 2020-12-23 2022-06-30 Voestalpine Stahl Gmbh Bande ou tôle d'acier revêtu de zinc ou d'alliage de zinc présentant une adhérence au zinc améliorée
WO2023181390A1 (fr) * 2022-03-25 2023-09-28 Ｊｆｅスチール株式会社 Procédé de fabrication de tôle d'acier recuite après galvanisation par immersion à chaud
JP7480928B2 (ja) 2022-03-25 2024-05-10 Ｊｆｅスチール株式会社 合金化溶融亜鉛めっき鋼板の製造方法
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