WO2024209641A1 - 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 - Google Patents

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 Download PDF

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Publication number
WO2024209641A1
WO2024209641A1 PCT/JP2023/014289 JP2023014289W WO2024209641A1 WO 2024209641 A1 WO2024209641 A1 WO 2024209641A1 JP 2023014289 W JP2023014289 W JP 2023014289W WO 2024209641 A1 WO2024209641 A1 WO 2024209641A1
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Prior art keywords
steel sheet
less
hot
dip galvanized
base steel
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Ceased
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PCT/JP2023/014289
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English (en)
French (fr)
Japanese (ja)
Inventor
秀和 南
由康 川崎
勇樹 田路
悠佑 和田
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JFE Steel Corp
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JFE Steel Corp
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Publication date
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Priority to JP2023572663A priority Critical patent/JP7711775B2/ja
Priority to KR1020257026735A priority patent/KR20250135253A/ko
Priority to PCT/JP2023/014289 priority patent/WO2024209641A1/ja
Priority to CN202380096205.1A priority patent/CN120917167A/zh
Priority to EP23932052.6A priority patent/EP4647519A4/en
Publication of WO2024209641A1 publication Critical patent/WO2024209641A1/ja
Priority to MX2025011830A priority patent/MX2025011830A/es
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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Definitions

  • the present invention relates to hot-dip galvanized steel sheets, members made of hot-dip galvanized steel sheets, automobile frame structural parts or automobile reinforcing parts made of the members, and methods for manufacturing hot-dip galvanized steel sheets and members.
  • High strength steel sheets used for automotive structural components and the like are required to have high stretch flangeability when formed into a desired shape. Furthermore, among the frame structural parts of an automobile, for example, crash boxes have bending parts, and therefore, from the viewpoint of formability, it is preferable to apply a steel sheet having high bendability to such parts.
  • Patent Document 1 describes 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, the high-strength hot-dip galvanized steel sheet having a tensile strength of 780 MPa or more, the base steel sheet containing, by mass%, C: 0.050% to 0.200%, Si: 0.10% to 0.90%, Mn: 2.00% to 3.50%, P: 0.001% to 0.100%, 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 the relationship [%Mn]/[%Si] is 2.9 to 11.7.
  • [%Mn] and [%Si] respectively indicate the Mn and Si contents (mass%) in the steel. " is described.
  • the hot-dip galvanized steel sheet described in Patent Document 1 does not take into consideration ultimate deformability and local ductility. Therefore, from the perspective of increasing the application ratio of high-strength steel sheets with a TS of 980 MPa or more to automotive frame structural parts, particularly hot-dip galvanized steel sheets, there is currently a demand for the development of hot-dip galvanized steel sheets with a TS of 980 MPa or more that have high ultimate deformability, high ductility, high stretch flangeability and bendability, and also high local ductility.
  • the present invention has been developed in view of the above-mentioned current situation, and has an object to provide a hot-dip galvanized steel sheet having a TS of 980 MPa or more, which has high ultimate deformability, high ductility, high stretch flangeability and bendability, and also has high local ductility. Another object of the present invention is to provide a method for producing the above hot-dip galvanized steel sheet. A further object of the present invention is to provide a member formed using the above-mentioned hot-dip galvanized steel sheet.
  • high ultimate deformability means that the ultimate deformability measured by the evaluation method described below is 0.10 or more.
  • high ductility means that the product (TS x El) of TS and total elongation (hereinafter also referred to as "El") measured in accordance with JIS Z 2241 is 10,000 MPa ⁇ % or more.
  • High stretch flangeability means that the hole expansion ratio (hereinafter also referred to as " ⁇ ") measured in accordance with JIS Z 2256 is 20% or more.
  • High bendability means that in a bending test conducted in accordance with JIS Z 2248 (for details, see the description of the Examples below), none of the five samples evaluated crack, or at least one of the five samples has microcracks of less than 200 ⁇ m.
  • high local ductility means that the product (TS x L.El) of TS and local elongation (hereinafter also referred to as "L.El") measured in accordance with JIS Z 2241 is 4500 MPa ⁇ % or more.
  • the base steel sheet has a predetermined chemical composition and a steel structure containing martensite (quenched martensite, tempered martensite, and bainite). This provides a TS of 980 MPa or more.
  • martensite quenched martensite, tempered martensite, and bainite.
  • a hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer on a surface of the base steel sheet,
  • the base steel plate is In mass percent, C: 0.030% or more and 0.500% or less, Si: 0.01% or more and 2.50% or less, Mn: 0.10% or more and 5.00% or less, P: 0.100% or less, S: 0.0200% or less, Al: 1.000% or less, A composition comprising N: 0.0100% or less and O: 0.0100% or less, with the balance being Fe and unavoidable impurities;
  • the area ratio of martensite is 30% or more,
  • the area ratio of ferrite is 70% or less,
  • the area ratio of retained austenite is 10% or less, Contains at least one of ferrite and retained austenite, In a region from the surface of the base steel plate to a depth of 10 ⁇ m, A steel structure in which the area ratio of martensite is 5% or
  • the composition further includes, in mass%, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less, Ni: 1.00% or less, Co: 0.010% or less, Cu: 1.00% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, REM: 0.0100% or less, Zr: 0.100% or less, Te: 0.100% or less,
  • the base steel plate has a surface soft layer which is a region having a Vickers hardness of 85% or less of the Vickers hardness at a 1/4 position of the plate thickness of the base steel plate and is within 200 ⁇ m from the surface of the base steel plate in the plate thickness direction;
  • the nano hardness was measured at 300 points or more in a 50 ⁇ m ⁇ 50 ⁇ m region of the sheet surface at a 1/4 position and a 1/2 position of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet.
  • the ratio of the number of measurements in which the nano hardness of the sheet surface at a 1/4 position of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet is 7.0 GPa or more to the total number of measurements is 0.10 or less,
  • the hot-rolled steel sheet is subjected to pickling
  • the hot-rolled steel sheet is Cumulative rolling reduction rate of 30% or more, cold rolling is performed under a unit tension of 10 kgf/mm2 or more between the final pass and the pass immediately before the final pass to obtain a cold-rolled steel sheet
  • the cold rolled steel sheet is The oxygen concentration in the temperature range of 250° C. to 700° C. is set to 0.5 vol.% to 5.0 vol.%, and the steel is heated to an annealing temperature T1 of 750° C.
  • Annealing is performed under conditions in which the dew point in the temperature range exceeding 700°C and not exceeding T1 is set to -30°C or higher, and the retention time in the temperature range is 10 s or more and 500 s or less,
  • the annealed cold rolled steel sheet is subjected to a hot dip galvanizing treatment to obtain a plated steel sheet, and then cooling the plated steel sheet to obtain a hot-dip galvanized steel sheet.
  • a method for producing a component comprising the step of subjecting the hot-dip galvanized steel sheet according to any one of [1] to [5] to at least one of forming and joining to form a component.
  • the present invention provides hot-dip galvanized steel sheets and components having high ultimate deformability, high ductility, high stretch flangeability and bendability, and high local ductility of 980 MPa or more, together with their manufacturing methods.
  • FIGS. 1A and 1B are schematic diagrams showing the preparation of samples for U-bending and close bending tests in the examples, in which Fig. 1A shows U-bending (primary bending) and Fig. 1B shows bending (secondary bending).
  • 2A and 2B are schematic diagrams showing the preparation of samples for V-bending and orthogonal VDA bending tests in the examples, in which Fig. 2A shows V-bending (primary bending) and Fig. 2B shows orthogonal VDA bending (secondary bending).
  • 3(a) is a front view of a test member
  • FIG. 3(b) is a front view of a test member
  • FIG. 3(c) is a schematic diagram showing an axial crush test.
  • Hot-dip galvanized steel sheet [1] Base steel sheet
  • the hot-dip galvanized steel sheet of the present invention comprises a base steel sheet and a hot-dip galvanized layer on the surface of the base steel sheet. First, the base steel sheet will be described.
  • [1-1-1] Component composition
  • the component composition of the base steel sheet will be described.
  • “%” representing the content of the component elements of the steel sheet means “mass%” unless otherwise specified.
  • a numerical range expressed using “to” means a range including the numerical values written before and after "to” as the lower and upper limits.
  • C 0.030% or more and 0.500% or less
  • C is one of the important basic components of steel, and in the present invention, it is an important element that affects the area ratio of martensite and ferrite.
  • the C content exceeds 0.500%, the area ratio of retained austenite increases, which makes it difficult to desorb hydrogen from the plated steel sheet. The separation is not promoted, the amount of diffusible hydrogen in the low temperature region of the base steel sheet increases, and it becomes difficult to achieve the desired local ductility.
  • the residual austenite transforms into martensite during punching, and the hole expansion The generation of voids increases, ⁇ decreases, and bendability may also decrease.
  • the C content is set to 0.030% or more and 0.500% or less.
  • the C content is preferably
  • the content is preferably 0.050% or more, more preferably 0.070% or more, and is preferably 0.400% or less, more preferably 0.300% or less.
  • Silicon is one of the important basic components of steel, and in the present invention, it is an important element that affects the area ratio of martensite and ferrite. If the silicon content is less than 0.01%, the surface layer The area ratio of ferrite is reduced, and the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m cannot be controlled within a desired range. As a result, high ultimate deformability and high local ductility are not obtained. On the other hand, if the Si content exceeds 2.50%, the formation of carbides during continuous annealing is suppressed and the residual Cr phase, which has a large hydrogen solid solubility, is formed.
  • the Si content is set to 0.01% or more and 2.0% or less. . 50% or less.
  • the Si content is preferably 0.05% or more, more preferably 0.10% or more, and is preferably 2.00% or less, more preferably 1.80% or less.
  • Mn 0.10% or more and 5.00% or less
  • Mn is one of the important basic components of steel, and in the present invention, it is an important element that affects the area ratio of martensite and ferrite.
  • the Mn content is set to 0.10% or more and 5.
  • the Mn content is preferably 0.80% or more, more preferably 1.00% or more, and is preferably 4.50% or less, more preferably 4.00% or less. do.
  • P is an element that segregates at prior austenite grain boundaries to embrittle the grain boundaries and reduce the ultimate deformability of the steel sheet, and may also reduce the local ductility and ⁇ . Therefore, the P content is set to 0.100%.
  • the lower limit of the P content is not particularly limited, but since P is a solid solution strengthening element and can increase the strength of the steel sheet, it is preferable that the P content be 0.001% or more. It is preferable that there is.
  • S exists as a sulfide and is an element that reduces the ultimate deformability of the steel sheet, and may reduce the local ductility and ⁇ . Therefore, the S content is set to 0.0200% or less, and preferably 0.0050%.
  • the lower limit of the S content is not particularly limited, but due to restrictions on production technology, it is preferably 0.0001% or more.
  • Al is an element that increases the A3 transformation point, and the amount of ferrite in the steel structure increases, which may make it difficult to achieve the desired TS. Therefore, the Al content is set to 1.000% or less, and preferably The lower limit of the Al content is not particularly limited, but it is preferably 0.001% or more because it suppresses the formation of carbides during continuous annealing and promotes the formation of retained austenite. preferable.
  • N 0.0100% or less
  • N exists as a nitride and is an element that reduces the ultimate deformability of the steel sheet, and may reduce the local ductility and ⁇ . Therefore, the N content is set to 0.0100% or less, and preferably 0.0050%. Although there is no particular lower limit for the N content, due to constraints on production technology, the N content is preferably 0.0001% or more.
  • O exists as an oxide and is an element that reduces the ultimate deformability of the steel sheet, and may reduce the local ductility and ⁇ . Therefore, the O content is set to 0.0100% or less, and preferably 0.0050% or less. Although there is no particular lower limit for the O content, the O content is preferably 0.0001% or more due to restrictions on production technology.
  • the base steel sheet of the present invention further contains, in mass%, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less, Ni: 1.00% or less, Co: 0.010% or less, Cu: 1.00% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, REM: 0.0100% or less, Zr: 0.020% or less, Te: 0.020% or less, At least one element selected from the group consisting of Hf: 0.10% or less and Bi: 0.200% or less may be contained. These elements may be contained alone or in combination of two or more kinds.
  • the Ti, Nb or V content is preferably 0.200% or less, and more preferably 0.100% or less.
  • the Ti, Nb or V content is preferably 0.001% or more.
  • the Ta or W content is preferably 0.10% or less, and more preferably 0.08% or less.
  • the Ta or W content is 0.01% or more.
  • the B content is preferably 0.0100% or less, and more preferably 0.0080% or less.
  • the B content is preferably 0.0003% or more.
  • the Cr, Mo or Ni content is preferably 1.00% or less, and more preferably 0.80% or less.
  • the Cr, Mo or Ni content is 0.01% or more.
  • the Co content is preferably 0.010% or less, and more preferably 0.008% or less, in order to avoid an increase in coarse precipitates and inclusions, a decrease in the ultimate deformability of the steel sheet, and ultimately a decrease in local ductility and ⁇ .
  • the Co content is 0.001% or more.
  • the Cu content is preferably 1.00% or less, and more preferably 0.80% or less. There is no particular lower limit for the Cu content, but since Cu is an element that improves hardenability, it is preferable that the Cu content be 0.01% or more.
  • the Sn content is preferably 0.200% or less, and more preferably 0.100% or less. There is no particular lower limit for the Sn content, but since Sn is an element that improves hardenability, the Sn content is preferably 0.001% or more.
  • the Sb content is preferably 0.200% or less, and more preferably 0.100% or less, in order to avoid an increase in coarse precipitates and inclusions, a decrease in the ultimate deformability of the steel plate, and ultimately a decrease in local ductility and ⁇ .
  • the Sb content is 0.001% or more.
  • the Ca, Mg or REM content is 0.0100% or less, and more preferably 0.0050% or less.
  • the Ca, Mg or REM content is 0.0005% or more.
  • the Zr or Te content is preferably 0.100% or less, and more preferably 0.080% or less.
  • the Zr or Te content is 0.001% or more.
  • the Hf content is preferably 0.10% or less, and more preferably 0.08% or less.
  • the Hf content is preferably 0.01% or more.
  • the Bi content is preferably 0.200% or less, and more preferably 0.100% or less, in order to avoid an increase in coarse precipitates and inclusions, a decrease in the ultimate deformability of the steel sheet, and ultimately a decrease in local ductility and ⁇ .
  • the Bi content is 0.001% or more.
  • the base steel plate of the present invention has a composition that contains essential components and, in some cases, optional components, with the balance being Fe and unavoidable impurities.
  • unavoidable impurities include Zn, Pb, As, Ge, Sr, and Cs. These unavoidable impurities are permitted to be contained in a total amount of 0.100% or less.
  • the area ratio of martensite at the 1/4 position of the thickness of the base steel plate is preferably 35% or more, more preferably 40% or more, and even more preferably 45% or more.
  • the area ratio of martensite at the 1/4 position of the thickness of the base steel plate is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.
  • the martensite referred to here includes quenched martensite (fresh martensite), as well as tempered martensite and bainite.
  • the area ratio of ferrite at the 1/4 position of the thickness of the base steel plate is set to 70% or less.
  • the area ratio of ferrite at the 1/4 position of the thickness of the base steel plate is preferably 65% or less, more preferably 60% or less, and even more preferably 55% or less.
  • the area ratio of ferrite at the 1/4 position of the thickness of the base steel plate is preferably 2% or more, more preferably 5% or more, and even more preferably 10% or more.
  • the ferrite referred to here includes bainitic ferrite as well as polygonal ferrite.
  • the method for measuring the area ratio of martensite (quenched martensite, tempered martensite, and bainite) at 1/4 of the plate thickness of the base steel plate and the area ratio of ferrite (polygonal ferrite and bainitic ferrite) at 1/4 of the plate thickness of the base steel plate is as follows.
  • a sample is cut out from the steel sheet so that the plate thickness cross section (L cross section) parallel to the rolling direction becomes the observation surface.
  • the observation surface of the sample is mirror-polished with diamond paste, then finish-polished with alumina, and further etched with 3 volume % nital to reveal the structure.
  • the sample is observed at a magnification of 3000 times using a scanning electron microscope (SEM) under conditions of an acceleration voltage of 10 kV, with the observation surface being a position at 1 ⁇ 4 of the sheet thickness of the steel sheet, to obtain SEM images of three fields of view (one field of view is 40 ⁇ m ⁇ 30 ⁇ m).
  • SEM scanning electron microscope
  • the area ratio of each structure (ferrite (polygonal ferrite and bainitic ferrite), martensite (quenched martensite, tempered martensite and bainite)) is calculated using Adobe Photoshop (manufactured by Adobe Systems). Specifically, the area ratio of each structure is determined by dividing the area of each structure by the measured area. The area ratio of each structure is calculated for three fields of view, and the average value of these is determined as the area ratio of each structure.
  • ferrite polygonal ferrite and bainitic ferrite
  • tempered martensite and bainite are structures containing fine carbides in the recesses
  • quenched martensite is a structure with fine irregularities inside the protrusions, and they are distinguishable from each other. Note that tempered martensite and bainite do not need to be distinguishable from each other, since the total area ratio is calculated as the area ratio of martensite.
  • the area ratio of the retained austenite at the 1/4 position of the sheet thickness of the base steel sheet is preferably as small as possible, preferably 7% or less, more preferably 5% or less. There is no particular limit to the lower limit of the area ratio of the retained austenite, and even if it is 0%, the desired characteristics can be obtained as long as the steel structure contains ferrite.
  • the method for measuring the area ratio of retained austenite at the 1/4 position of the plate thickness of the base steel plate is as follows.
  • the steel plate is ground so that the observation surface is located at 1/4 of the plate thickness from the surface (a position corresponding to 1/4 of the plate thickness in the depth direction from the surface of the steel plate), and is then further polished by 0.1 mm by chemical polishing to obtain a sample.
  • an X-ray diffractometer is used to measure the integrated reflection intensities of the (200), (220), and (311) planes of fcc iron (austenite), and the (200), (211), and (220) planes of bcc iron, using a Co K ⁇ radiation source.
  • the intensity ratio of the integrated reflection intensity from each surface of the fcc iron (austenite) to the integrated reflection intensity from each surface of the bcc iron is calculated.
  • the average value of the nine intensity ratios is taken as the volume fraction of the austenite from the retained austenite. This volume fraction of austenite is then regarded as being three-dimensionally uniform and is taken as the area fraction of the retained austenite at the 1/4 position of the plate thickness of the base steel plate.
  • the steel structure at the 1/4 position of the plate thickness of the base steel plate contains at least one of ferrite and retained austenite.
  • the total area ratio of ferrite and retained austenite is preferably 2% or more, more preferably 5% or more, and even more preferably 10% or more.
  • the steel structure at the 1/4 plate thickness position of the base steel plate may have a structure (remaining structure) other than martensite, ferrite, and retained austenite.
  • the remaining structure is a structure other than martensite, ferrite, and retained austenite, and may be a structure known as a structure of a steel sheet, such as pearlite, cementite, and carbides such as metastable carbides (epsilon ( ⁇ ) carbide, eta ( ⁇ ) carbide, chi ( ⁇ ) carbide, etc.).
  • the remaining structure may be identified, for example, by observation using a SEM.
  • the area ratio of the remaining structure at the 1/4 position of the sheet thickness of the steel sheet is preferably 5% or less, and may be 0%.
  • the area ratio of martensite in the surface layer of the base steel sheet is an extremely important configuration.
  • the area ratio of martensite in the surface layer of the base steel sheet in other words, by increasing the area ratio of phases with low hydrogen solid solubility such as ferrite, bainitic ferrite, and bainite in the surface layer of the base steel sheet, the desired bendability can be realized.
  • the area ratio of martensite in the region from the surface to a depth of 10 ⁇ m of the base steel sheet is set to 80% or less of the area ratio of martensite at the 1/4 position of the sheet thickness of the base steel sheet.
  • the area ratio of martensite in the region from the surface to a depth of 10 ⁇ m of the base steel sheet is preferably 75% or less of the area ratio of martensite at the 1/4 position of the sheet thickness of the base steel sheet, and more preferably 70% or less.
  • the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m is 5% or more, and preferably 10% or more.
  • the martensite referred to here includes quenched martensite (fresh martensite) as well as tempered martensite.
  • the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m is measured as follows. A sample is cut out so that the plate thickness cross section (L cross section) parallel to the rolling direction of the base steel plate becomes the observation surface. The observation surface of the sample is then polished. The observation surface of the sample is then etched with 3 volume % nital to reveal the structure. Next, the observation position is a region from the surface of the base steel plate to a depth of 10 ⁇ m, and three fields of view (40 ⁇ m ⁇ 10 ⁇ m, 10 ⁇ m corresponds to the depth) are observed with an SEM at a magnification of 3000 times.
  • the area of martensite is calculated for three fields of view using Adobe Photoshop from Adobe Systems. Next, the area of martensite calculated for each field of view is divided by the area of each field of view, and the arithmetic average value of these values is taken as the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m. In the above SEM image, the martensite exhibits a white structure.
  • the area ratio of structures other than martensite in the region from the surface of the base steel plate to a depth of 10 ⁇ m is preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, and is preferably 95% or less, more preferably 85% or less, even more preferably 70% or less.
  • the structure other than martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m is basically composed of ferrite (polygonal ferrite and bainitic ferrite).
  • the area ratio of ferrite in the region from the surface of the base steel plate to a depth of 10 ⁇ m is preferably 5% or more, more preferably 15% or more, even more preferably 30% or more, and is preferably 80% or less, more preferably 75% or less, and preferably 70% or less.
  • retained austenite may be contained as long as its area ratio is 5% or less, or may be 0%.
  • other structures known as structures of steel sheets such as bainite, pearlite, cementite, and carbides such as metastable carbides (epsilon ( ⁇ ) carbide, eta ( ⁇ ) carbide, chi ( ⁇ ) carbide, etc.), may be contained as long as its area ratio is 5% or less.
  • Identification of the structure can be performed, for example, by observation with a SEM (Scanning Electron Microscope).
  • [1-1-3] Amount of diffusible hydrogen in low temperature region of base steel sheet The amount of diffusible hydrogen in low temperature region of base steel sheet is an extremely important constituent element of the present invention. That is, the present inventors have conducted extensive research to obtain a hot-dip galvanized steel sheet having high ductility, high stretch flangeability and bendability, and high local ductility, and a TS of 980 MPa or more, and have found that the amount of diffusible hydrogen in low temperature region of base steel sheet, that is, the amount of hydrogen released from base steel sheet when the base steel sheet is heated from room temperature to 50°C, has a large effect on the above properties, particularly local ductility.
  • the local ductility is largely dependent on the amount of hydrogen released in the low temperature range, specifically, the temperature range from room temperature to 50°C (low temperature diffusible hydrogen amount), rather than the amount of hydrogen released from the base steel sheet in the high temperature range. If the amount exceeds 0.015 ppm by mass, it is difficult to obtain high local ductility while having high ductility, high stretch flangeability and bendability. Therefore, the low temperature diffusible hydrogen amount of the base steel sheet is set to 0.015 ppm by mass or less. The lower the low temperature diffusible hydrogen amount of the base steel sheet, the more preferable it is, and is preferably 0.010 ppm by mass or less, more preferably 0.006 ppm by mass or less, and may be 0 ppm.
  • the method for measuring the amount of diffusible hydrogen in low temperature region of the base steel sheet is as follows.
  • a test piece with a length of 30 mm and a width of 5 mm is taken from the center of the sample of the hot-dip galvanized steel sheet by shearing. After taking, the test piece is immediately immersed in liquid nitrogen.
  • the hot-dip galvanized layer of the test piece is alkali-removed while controlling the temperature of the treatment liquid so that the surface temperature of the test piece is 10°C or less.
  • the test piece is loaded into a thermal desorption analysis device, and after waiting for 5 minutes with Ar gas flowing, the temperature is increased.
  • the test piece is heated under the conditions of a temperature increase temperature of 300°C and a heating rate of 200°C/hr, and then cooled to room temperature.
  • the surface temperature of the test piece at the start of heating is 10°C or less.
  • the amount of low-temperature diffusible hydrogen in the base steel sheet can be measured in the same manner as above for hot-dip galvanized steel sheets that have been subjected to processes such as punching, stretch flange forming, and bending, and for products (components) manufactured by welding steel sheets that have been processed in the above manner.
  • the sheet thickness of the base steel sheet is not particularly limited and can be set according to the sheet thickness of the final hot-dip galvanized steel sheet.
  • the sheet thickness can be, for example, 0.3 mm or more and 3.0 mm or less.
  • the surface layer of the base steel sheet is preferably a soft layer (soft surface layer).
  • the soft surface layer contributes to suppressing the progression of bending cracks during press forming and vehicle body collision, and therefore the bending fracture resistance can be further improved.
  • the surface layer refers to a region corresponding to a thickness of 200 ⁇ m extending from the surface of the base steel sheet to 200 ⁇ m in the sheet thickness direction.
  • the soft layer refers to a region having a Vickers hardness of 85% or less of the Vickers hardness of a cross section (a surface parallel to the steel sheet surface) at 1/4 of the sheet thickness of the base steel sheet.
  • the soft layer includes a decarburized layer in the surface layer of the base steel sheet.
  • the surface soft layer refers to a soft layer included in the surface layer, and the entire surface layer may be a soft layer, or a part of the surface layer may be a soft layer.
  • the surface soft layer may be a region corresponding to a thickness of 200 ⁇ m or less from the surface of the base steel sheet in the sheet thickness direction. For example, if a region having a Vickers hardness of 85% or less on a cross section (plane parallel to the steel plate surface) at 1/4 of the plate thickness of the base steel plate is formed at a predetermined depth from the surface of the base steel plate in the plate thickness direction, when the predetermined depth is within 200 ⁇ m in the plate thickness direction, the region corresponding to the thickness from the surface to the predetermined depth in the plate thickness direction is the surface soft layer, and when the predetermined depth is more than 200 ⁇ m in the plate thickness direction, the region corresponding to a thickness of 200 ⁇ m from the surface of the base steel plate to a depth of 200 ⁇ m in the plate thickness direction is the surface soft layer.
  • the lower limit of the thickness of the soft surface layer is not particularly limited, but is preferably 8 ⁇ m or more, and more preferably more than 17 ⁇ m.
  • the Vickers hardness is measured based on JIS Z 2244-1 (2020) at a load of 10 gf.
  • the proportion of nanohardness of 7.0 GPa or more is 0.10 or less.
  • the proportion of nanohardness of 7.0 GPa or more is 0.10 or less, it means that the proportion of hard structures (martensite, etc.), inclusions, etc.
  • the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/4 of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet is 1.8 GPa or less, and further, the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/2 of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet is 2.2 GPa or less.
  • the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/4 of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet is 1.8 GPa or less
  • the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/2 of the sheet thickness direction depth of the soft surface layer from the surface of the base steel sheet is 2.2 GPa or less
  • a more preferred range for the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/4 of the way from the base steel sheet surface to the soft surface layer in the sheet thickness direction is 1.7 GPa or less.
  • a more preferred range for the standard deviation ⁇ of the nanohardness of the sheet surface at a position 1/2 of the way from the base steel sheet surface to the soft surface layer in the sheet thickness direction is 2.1 GPa or less.
  • the nano-hardness of the plate surface at the 1/4 and 1/2 positions in the plate thickness direction depth is a hardness measured by the following method.
  • the nano hardness is measured using a Berkovich-shaped diamond indenter under the following conditions: load: 500 ⁇ N, measurement area: 50 ⁇ m ⁇ 50 ⁇ m, and impact spacing: 2 ⁇ m.
  • the soft surface layer is mechanically polished to a position halfway down the thickness direction, buffed with diamond and alumina, and then polished with colloidal silica.Then, the nano-hardness is measured with a Berkovich diamond indenter under the following conditions: load: 500 ⁇ N, measurement area: 50 ⁇ m ⁇ 50 ⁇ m, and impact spacing: 2 ⁇ m.
  • the thickness of the surface soft layer can be measured by the following method. After smoothing the thickness cross section (L cross section) of the base steel plate parallel to the rolling direction by wet polishing, measurements were taken at 1 ⁇ m intervals using a Vickers hardness tester with a load of 10 gf from a position 1 ⁇ m in the thickness direction from the surface of the base steel plate to a position 100 ⁇ m in the thickness direction. After that, measurements were taken at 20 ⁇ m intervals up to the center of the thickness. The area where the hardness was reduced to 85% or less compared to the hardness at the 1/4 position in the thickness direction was defined as the soft layer (surface soft layer), and the thickness in the thickness direction of this area was taken as the thickness of the soft layer.
  • the base steel sheet preferably has a metal plating layer on one or both sides.
  • the metal plating layer contributes to suppressing the occurrence of bending cracks during press forming and vehicle collision, thereby further improving bending fracture resistance.
  • the metal plating layer is formed directly on the surface of the base steel sheet and contains more than 50 mass% in total of one or more elements selected from Al, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Rt, Au, Hg, Ti, Pb, and Bi, excluding zinc plating layers such as hot-dip galvanized layers, alloyed hot-dip galvanized layers, and electrogalvanized layers.
  • the first plating layer is preferably a metal electroplated layer, and the following description will be given taking a metal electroplated layer as an example.
  • the outermost metal electroplating layer helps to prevent bending cracks during press forming and vehicle collisions, further improving bending fracture resistance.
  • the metal type of the metal electroplating layer may be any of Al, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Rt, Au, Hg, Ti, Pb, and Bi, but Fe is more preferable.
  • the coating weight of the Fe-based electroplating layer is more than 0 g/ m2 , and preferably 2.0 g/ m2 or more .
  • the coating weight of the Fe-based electroplating layer per side is preferably 60 g/m2 or less.
  • the coating weight of the Fe-based electroplating layer is preferably 50 g/m2 or less, more preferably 40 g/ m2 or less, and even more preferably 30 g/m2 or less .
  • the adhesion weight of the Fe-based electroplating layer is measured as follows. A 10 x 15 mm sample is taken from the Fe-based electroplated steel sheet and embedded in resin to create a cross-section embedded sample. Three random locations on the cross section are observed using a scanning electron microscope (SEM) at an accelerating voltage of 15 kV and a magnification of 2,000 to 10,000 times depending on the thickness of the Fe-based plating layer, and the average thickness of the three fields of view is multiplied by the specific gravity of iron to convert it into the adhesion weight of the Fe-based plating layer per side.
  • SEM scanning electron microscope
  • the Fe-based electroplating layer in addition to pure Fe, alloy plating layers such as Fe-B alloy, Fe-C alloy, Fe-P alloy, Fe-N alloy, Fe-O alloy, Fe-Ni alloy, Fe-Mn alloy, Fe-Mo alloy, and Fe-W alloy can be used.
  • the composition of the Fe-based electroplating layer is not particularly limited, but it is preferable that the composition contains one or more elements selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co in a total amount of 10 mass% or less, with the remainder consisting of Fe and unavoidable impurities.
  • the C content is preferably 0.08 mass% or less.
  • the base steel sheet for hot-dip galvanizing may be a base steel sheet only or a base steel sheet with a metal plating layer, and preferably a base steel sheet with a metal plating layer formed on the surface of a base steel sheet having a soft surface layer.
  • the hot-dip galvanized layer in the hot-dip galvanized steel sheet will be described.
  • the hot-dip galvanized layer referred to here includes an alloyed hot-dip galvanized layer (a plating layer obtained by performing an alloying treatment on hot-dip galvanization).
  • the hot-dip galvanized layer can be provided on both surfaces of the base steel sheet.
  • the hot-dip galvanized layer may be formed directly on the surface of the base steel sheet, or, when the base steel sheet has a surface soft layer, a metal electroplating layer, or the like, it may be formed on those layers.
  • the hot-dip galvanized layer usually contains Zn (zinc) as the main component (Zn content is 50.0 mass% or more).
  • the composition is not particularly limited and may be a known composition.
  • the hot-dip galvanized layer is preferably composed of, for example, Zn, 20.0 mass% or less of Fe, and 0.001 mass% or more and 1.0 mass% or less of Al.
  • the hot-dip galvanized layer may optionally contain one or more elements selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM in a total amount of more than 0.0 mass% and 3.5 mass% or less.
  • the Fe content of the hot-dip galvanized layer is more preferably less than 7.0 mass%.
  • the remainder other than the above elements is unavoidable impurities.
  • the galvannealed layer is preferably composed of, for example, 20% by mass or less Fe and 0.001% by mass or more and 1.0% by mass or less Al.
  • the galvannealed layer may optionally contain one or more elements selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi and REM in a total amount of more than 0% by mass and 3.5% by mass or less.
  • the Fe content of the galvannealed layer is more preferably 7.0% by mass or more, and more preferably 8.0% by mass or more.
  • the Fe content of the galvannealed layer is more preferably 15.0% by mass or less, and more preferably 12.0% by mass or less.
  • the remainder other than the above elements is unavoidable impurities.
  • the coating weight of the hot-dip galvanized layer per one side is not particularly limited, and can be, for example, 20 g/m 2 or more and 80 g/m 2 or less.
  • the coating weight of the zinc plating layer is measured as follows.
  • a treatment solution is prepared by adding 0.6 g of a corrosion inhibitor for Fe (Ivit 700BK (registered trademark) manufactured by Asahi Chemical Industry Co., Ltd.) to 1 L of a 10 mass % aqueous hydrochloric acid solution.
  • a sample of a steel sheet having a zinc plating layer is then immersed in the treatment solution to dissolve the zinc plating layer.
  • the mass loss of the ampoule S before and after dissolution is then measured, and the value is divided by the surface area of the base steel sheet (the surface area of the part that was covered with plating) to calculate the coating weight (g/ m2 ).
  • the hot-dip galvanized layer preferably has cracks.
  • the presence or absence of cracks in the hot-dip galvanized layer is judged as follows: The surface (front and back) of the hot-dip galvanized layer of the hot-dip galvanized steel sheet is observed by SEM at a magnification of 3000 times, with two fields of view (one field: 30 ⁇ m ⁇ 40 ⁇ m) for each side, for a total of four fields of view. If one or more cracks penetrating the hot-dip galvanized coating are present in any of the four fields of view, it is judged that there are cracks. If no cracks penetrating the hot-dip galvanized coating are present in any of the four fields of view, it is judged that there are no cracks.
  • the thickness of the hot-dip galvanized steel sheet of the present invention is not particularly limited, but is usually 0.3 mm or more and 2.8 mm or less.
  • the TS of the hot-dip galvanized steel sheet of the present invention is 980 MPa or more.
  • the TS is measured in accordance with JIS Z 2241 as described in the examples below.
  • the hot-dip galvanized steel sheet of the present invention can have an ultimate deformability of 0.10 or more.
  • the local ductility and stretch flangeability of the hot-dip galvanized steel sheet are highly dependent on the ultimate deformability of the annealed sheet after cold rolling, and it is effective to set the ultimate deformability of the hot-dip galvanized steel sheet to 0.10 or more in terms of having high local ductility while having high ductility, high stretch flangeability and bendability.
  • the ultimate deformation capacity ( ⁇ l ) is calculated by the method described in "Mizunuma et al.: Report of the Institute of Physical and Chemical Research, 45-4 (1969), 79", and specifically, the ultimate deformation capacity ( ⁇ l ) is calculated using the following formula.
  • ⁇ w ln(W/W 0 )
  • ⁇ t ln(T/T 0 )
  • ⁇ l -( ⁇ w + ⁇ t )
  • W 0 initial sheet width
  • W fractured portion sheet width
  • T initial sheet thickness
  • T 0 fractured portion sheet thickness
  • the fractured portion sheet width and fractured portion sheet thickness are measured according to JIS Z 2241 and are as described in the examples described later.
  • the method for producing a hot-dip galvanized steel sheet of the present invention comprises the steps of:
  • the steel slab having the above composition is
  • the hot-rolled steel sheet is obtained by hot-rolling the steel sheet under the condition of a coiling temperature of 400° C. or more and 700° C. or less.
  • the hot-rolled steel sheet is subjected to pickling,
  • the hot-rolled steel sheet is Cumulative rolling reduction of 30% or more cold rolling is performed under a unit tension of 10 kgf/mm2 or more between the final pass and the pass immediately before the final pass to obtain a cold-rolled steel sheet;
  • the cold rolled steel sheet is The oxygen concentration in the temperature range of 250° C. to 700° C.
  • annealing temperature T1 of 750° C. to 950° C.
  • Annealing is performed under conditions in which the dew point in the temperature range exceeding 700°C and not exceeding T1 is set to -30°C or higher, and the retention time in the temperature range is 10 s or more and 500 s or less
  • the annealed cold rolled steel sheet is subjected to a hot dip galvanizing treatment to obtain a plated steel sheet
  • the plated steel sheet is cooled to obtain a hot-dip galvanized steel sheet.
  • all of the above temperatures are based on the surface temperature of the steel slab or steel plate.
  • the steel slab (slab) is hot rolled to produce a hot rolled steel sheet.
  • the method of producing the steel slab is not particularly limited, and any known method such as a converter or an electric furnace is suitable.
  • the steel slab is preferably produced by a continuous casting method to prevent macrosegregation, but it can also be produced by an ingot casting method or a thin slab casting method.
  • energy-saving processes such as direct rolling and direct rolling can also be applied without any problems.
  • Direct rolling is a process in which the hot slab is charged into the heating furnace without being cooled to room temperature.
  • Direct rolling is a process in which the slab is rolled immediately after being kept at room temperature for a short period of time.
  • the slab heating temperature is preferably 1100° C. or higher from the viewpoint of dissolving carbides and reducing the rolling load.
  • the slab heating temperature is preferably 1300° C. or lower in order to prevent an increase in scale loss.
  • the slab heating temperature is the temperature of the slab surface.
  • the slab is then hot rolled, which may consist of rough rolling and finish rolling.
  • the slab can be rough-rolled into a sheet bar.
  • the conditions for the rough rolling are not particularly limited and may be any known conditions.
  • the sheet bar can then be subjected to finish rolling.
  • the slab heating temperature is set to a low temperature, it is preferable to heat the sheet bar using a bar heater or the like before finish rolling in order to prevent problems during rolling.
  • the finish rolling temperature is preferably the Ar3 transformation point or higher.
  • the temperature is the Ar3 transformation point or higher, it is possible to avoid an increase in the rolling load and an increase in the reduction ratio in the non-recrystallized state of austenite, and thus it is possible to suppress the development of an abnormal structure elongated in the rolling direction, and to easily avoid a decrease in the workability of the steel sheet obtained after annealing.
  • the Ar3 transformation point is calculated by the following formula.
  • Ar 3 (°C) 868-396 ⁇ [%C]+24.6 ⁇ [%Si]-68.1 ⁇ [%Mn]-36.1 ⁇ [%Ni]-20.7 ⁇ [%Cu]-24.8 ⁇ [%Cr]
  • the symbol [% element symbol] represents the content (mass %) of the corresponding element in the above composition.
  • Finish rolling may be performed continuously by joining sheet bars together. Also, the sheet bars may be wound up once before finish rolling. Furthermore, in order to reduce the rolling load, part or all of the finish rolling may be performed as lubricated rolling. Performing lubricated rolling is also effective from the viewpoint of uniformity of the steel sheet shape and material quality.
  • the friction coefficient during lubricated rolling is preferably in the range of 0.10 to 0.25.
  • the area ratio of martensite in the region from the surface to a depth of 10 ⁇ m of the steel sheet is reduced, and the amount of diffusible hydrogen in the low temperature region of the base steel sheet is also reduced. As a result, high ultimate deformability, high local ductility, and elongation are obtained.
  • the coiling temperature is set to 400° C. or higher and 700° C. or lower.
  • the coiling temperature is preferably 430° C. or higher, more preferably 450° C. or higher, and is preferably 670° C. or lower, more preferably 650° C. or lower.
  • the cooling conditions after winding are not particularly limited, and known conditions can be used.
  • the cooling rate is preferably 0.001°C/s or more and 1°C/s or less
  • the cooling stop temperature is preferably 20°C or more and 200°C or less.
  • the hot-rolled sheet may be subjected to a heat treatment (hot-rolled sheet annealing).
  • the heat treatment conditions are not particularly limited, and the following conditions may be mentioned.
  • Heat treatment temperature 450° C. or higher and 650° C. or lower (preferred conditions)
  • the heat treatment temperature is preferably 450° C. or higher.
  • the heat treatment temperature is more preferably 460° C. or higher, even more preferably 470° C. or higher, and more preferably 600° C. or lower, even more preferably 550° C. or lower.
  • the residence time in the heat treatment temperature range is preferably 10 minutes or more, more preferably 100 minutes or more, and even more preferably 500 minutes or more.
  • the upper limit of the residence time in the heat treatment temperature range is not particularly limited, but from the viewpoint of controlling the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m within a more suitable range, it is preferably 3000 minutes or less, more preferably 2000 minutes or less.
  • the cumulative reduction ratio of cold rolling By increasing the cumulative reduction ratio of cold rolling, decarburization of the surface layer is promoted during annealing, and the area ratio of martensite in the region from the surface to a depth of 10 ⁇ m of the base steel sheet can be controlled within a desired range.
  • the cumulative reduction ratio of cold rolling is 30% or more.
  • the cumulative reduction ratio of cold rolling is preferably 35% or more, more preferably 40% or more.
  • the upper limit of the cumulative reduction ratio of cold rolling is not particularly limited, but due to constraints on production technology, it is preferably 90% or less, more preferably 85% or less.
  • the unit tension between the final pass of cold rolling and the pass immediately before the final pass is set to 10 kgf/mm 2 or more, preferably 15 kgf/mm 2 or more.
  • the upper limit of the unit tension between the final pass of cold rolling and the pass immediately before the final pass is not particularly limited, but due to production technology constraints, it is preferably 100 kgf/mm 2 or less, more preferably 50 kgf/mm 2 or less.
  • cold rolling conditions are not particularly limited, and known conditions can be used.
  • cold rolling can be performed by tandem multi-stand rolling or reverse rolling.
  • the number of rolling passes and the reduction rate of each pass are not particularly limited, and known conditions can be used.
  • the surface of the cold-rolled steel sheet obtained as described above may be subjected to a metal plating treatment to obtain a pre-annealed metal-plated steel sheet having a metal plating layer (pre-annealed metal plating layer) formed on at least one surface.
  • the pre-annealed metal-plated steel sheet is preferably a pre-annealed metal electroplated steel sheet having a pre-annealed metal electroplated layer.
  • the metal electroplating method is not particularly limited, but as described above, it is preferable to form a metal electroplating layer on the base steel sheet, and therefore it is preferable to perform a metal electroplating process.
  • a sulfuric acid bath, a hydrochloric acid bath, or a mixture of both can be used for an Fe-based electroplating bath.
  • the amount of adhesion of the metal electroplating layer before annealing can be adjusted by the current application time, etc.
  • the metal electroplated steel sheet before annealing means that the metal electroplating layer has not been subjected to an annealing process, and does not exclude hot-rolled steel sheet before metal electroplating, pickled sheet after hot rolling, or cold-rolled steel sheet that have been annealed in advance.
  • the metal species of the electroplating layer can be any of Al, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Rt, Au, Hg, Ti, Pb, and Bi, but since Fe is more preferable, the manufacturing method of Fe-based electroplating is described below.
  • the Fe ion content in the Fe-based electroplating bath before the start of energization is preferably 0.5 mol/L or more in terms of Fe 2+ . If the Fe ion content in the Fe-based electroplating bath is 0.5 mol/L or more in terms of Fe 2+ , a sufficient Fe deposition amount can be obtained. In addition, in order to obtain a sufficient Fe deposition amount, the Fe ion content in the Fe-based electroplating bath before the start of energization is preferably 2.0 mol/L or less.
  • the Fe-based electroplating bath may contain at least one element selected from the group consisting of B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V and Co in addition to Fe ions.
  • the total content of these elements in the Fe-based electroplating bath is preferably such that the total content of these elements in the Fe-based electroplating layer before annealing is 10 mass% or less.
  • the metal elements may be contained as metal ions, and the nonmetal elements may be contained as part of boric acid, phosphoric acid, nitric acid, organic acid, etc.
  • the iron sulfate plating solution may also contain a conductivity aid such as sodium sulfate or potassium sulfate, a chelating agent, or a pH buffer.
  • the temperature of the Fe-based electroplating solution is preferably 30° C. or higher from the viewpoint of constant temperature retention, and is preferably 85° C. or lower.
  • the pH of the Fe-based electroplating bath is not particularly limited, but is preferably 1.0 or higher from the viewpoint of preventing a decrease in current efficiency due to hydrogen generation, and is preferably 3.0 or lower from the viewpoint of the electrical conductivity of the Fe-based electroplating bath.
  • the current density is preferably 10 A/dm 2 or higher from the viewpoint of productivity, and is preferably 150 A/dm 2 or lower from the viewpoint of facilitating control of the deposition amount of the Fe-based electroplating layer.
  • the sheet passing speed is preferably 5 mpm or higher from the viewpoint of productivity, and is preferably 150 mpm or lower from the viewpoint of stably controlling the deposition amount.
  • a degreasing treatment and water washing for cleaning the surface of the cold-rolled steel sheet, and further, a pickling treatment and water washing for activating the surface of the cold-rolled steel sheet can be performed.
  • the Fe-based electroplating treatment is performed following these pretreatments.
  • the method of the degreasing treatment and water washing is not particularly limited, and a conventional method can be used.
  • various acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof can be used. Among them, sulfuric acid, hydrochloric acid, and mixtures thereof are preferred.
  • the concentration of the acid is not particularly limited, but is preferably 1% by mass or more and 20% by mass or less from the viewpoints of the ability to remove the oxide film and the prevention of roughness (surface defects) due to over-pickling.
  • the pickling treatment solution may also contain an antifoaming agent, a pickling promoter, a pickling inhibitor, and the like.
  • the oxygen concentration in the heating temperature region is set to 0.5 vol% or more.
  • the oxygen concentration in the heating temperature region is set to 0.5 vol% or more and 5.0 vol% or less.
  • the oxygen concentration in the heating temperature region is preferably 1.0 vol% or more, more preferably 1.5 vol% or more, and also preferably 4.5 vol% or less, more preferably 4.0 vol% or less.
  • the temperature of the heating temperature range is based on the surface temperature of the steel sheet. That is, when the surface temperature of the steel sheet is within the heating temperature range, the oxygen concentration may be adjusted to the above range.
  • the annealing temperature T1 is set to 750°C or more and 950°C or less.
  • the annealing temperature is preferably 770°C or more, more preferably 780°C or more.
  • the annealing temperature is preferably 900°C or less, more preferably 880°C or less.
  • the annealing temperature is the maximum temperature reached in the annealing process.
  • the heat retention time in the annealing temperature range (hereinafter also referred to as the annealing time) is not particularly limited, but it is preferably 10 seconds or more and 600 seconds or less from the viewpoint of controlling the area ratio of ferrite and martensite in the base steel sheet within a predetermined range.
  • the temperature during heat retention does not have to be always constant.
  • the residence time in the temperature range of more than 700 ° C. and not more than T1 is set to 10 s or more.
  • the residence time in the temperature range of more than 700 ° C. and not more than T1 exceeds 500 s, the area ratio of martensite in the region from the surface of the base steel sheet to a depth of 10 ⁇ m decreases, making it difficult to achieve the desired TS. Therefore, the residence time in the temperature range of more than 700 ° C. and not more than T1 is set to 10 s or more and not more than 500 s.
  • the residence time in the temperature range of more than 700 ° C. and not more than T1 is preferably 15 seconds or more, more preferably 20 seconds or more.
  • the residence time in the temperature range of more than 700 ° C. and not more than T1 is preferably 400 seconds or less, more preferably 300 seconds or less.
  • the temperature of the heating temperature region is based on the surface temperature of the steel sheet.
  • the dew point in the annealing temperature range is set to -30 ° C. or higher.
  • the upper limit of the dew point in the annealing temperature range is not particularly limited, but from the viewpoint of ensuring the desired TS, the dew point in the annealing temperature range is preferably 15 ° C. or lower, more preferably 5 ° C. or lower.
  • the temperature in the annealing temperature range is based on the surface temperature of the steel sheet. That is, when the surface temperature of the steel sheet is within the annealing temperature range, the dew point may be adjusted to fall within the above range.
  • the oxygen concentration in the annealing temperature range is not particularly limited, but it is preferably 2 ppm by volume or more and 30 ppm by volume or less from the viewpoint of controlling the area ratio of martensite in the region from the surface of the base steel plate to a depth of 10 ⁇ m within a predetermined range.
  • the temperature during heat retention does not have to be constant.
  • the cold-rolled steel sheet is cooled.
  • the conditions at this time are not particularly limited, and known conditions can be adopted.
  • the average cooling rate in the temperature range of T1 or less and 500°C or more is not particularly limited, but it is preferably 5°C/s or more and 50°C/s or less from the viewpoint of controlling the area ratio of ferrite and martensite of the base steel sheet within a predetermined range.
  • Hot-dip galvanizing process Next, the cold-rolled steel sheet is subjected to hot-dip galvanizing process. After the hot-dip galvanizing process, an alloying process may be performed.
  • the hot-dip galvanizing treatment can be performed in a temperature range of T1 or lower and 400° C. or higher.
  • the cold-rolled steel sheet may be once cooled to less than 400° C., and the steel sheet temperature may be raised again to 400° C. or higher before the hot-dip galvanizing treatment is performed.
  • Annealing, cooling and plating may be performed continuously in one line (CGL (Continuous Galvanizing Line)).
  • CGL Continuous Galvanizing Line
  • the cold-rolled steel sheet is cooled to a temperature range of about 500°C.
  • the cold-rolled steel sheet is passed through the steel strip outlet side of the cooling zone, and further cooled while being moved to the hot-dip galvanizing bath through a snout whose tip is immersed in the hot-dip galvanizing bath.
  • the time from the end of cooling of the cold-rolled steel sheet to its entry into the hot-dip galvanizing bath is not particularly limited, but is preferably 300 s or less from the viewpoint of controlling the area ratio of ferrite and martensite within a predetermined range.
  • a roll for changing the direction of travel of the cold-rolled steel sheet to enter the snout is provided immediately before the connection between the cooling zone and the snout, and the cold-rolled steel sheet enters the snout after passing through the roll.
  • the cold-rolled steel sheet is guided through the snout to the hot-dip galvanizing bath, where it is immersed in the bath and subjected to hot-dip galvanizing to produce a plated steel sheet.
  • the cold-rolled steel sheet is immersed in a hot-dip galvanizing bath at 440°C to 500°C. It is also preferable to use a hot-dip galvanizing bath with an Al content of 0.10% by mass to 0.23% by mass, with the remainder being Zn and unavoidable impurities.
  • an alloying treatment may be performed at a temperature range of 460°C or more and 600°C or less. If the alloying treatment temperature is less than 460°C, the Zn-Fe alloying rate becomes excessively slow, resulting in reduced productivity. On the other hand, if the alloying treatment temperature exceeds 600°C, untransformed austenite may transform into pearlite, resulting in reduced TS and El. Therefore, the alloying treatment temperature is preferably 460°C or more and 600°C or less. The alloying treatment temperature is preferably 470°C or more. Furthermore, the alloying treatment temperature is preferably 560°C or less.
  • the coating weight is preferably 20 to 80 g/m 2 per side (double-sided coating).
  • the galvannealed steel sheet (GA) is preferably subjected to the alloying treatment described below to set the Fe concentration in the coating layer to 7 to 15 mass %.
  • the coating weight can be adjusted by performing gas wiping or the like after the hot-dip galvanizing treatment.
  • Cooling Step After the hot-dip galvanizing treatment step, that is, the plated steel sheet which has been subjected to the hot-dip galvanizing treatment or the hot-dip galvanizing treatment and the alloying treatment, is cooled.
  • the cooling conditions are not particularly limited, and known conditions can be adopted.
  • the average cooling rate to the heat retention temperature or cooling stop temperature described below, and the cooling rate after heat retention or reheating described below are not particularly limited, but are preferably 2°C/s or more, more preferably 5°C/s or more, from the viewpoint of further improving TS.
  • the average cooling rate is preferably 50°C/s or less, more preferably 40°C/s or less, from the viewpoint of constraints on production technology.
  • the cooling method is not particularly limited, and gas jet cooling, mist cooling, water cooling, air cooling, etc. can be applied.
  • Heat retention temperature during cooling of plated steel sheet 100° C. or higher and 450° C. or lower (preferred conditions)]
  • the plated steel sheet may be kept at a temperature in the range of 100° C. or more and 450° C. or less for 5 seconds or more and then cooled.
  • the heat retention temperature during cooling of the plated steel sheet is preferably 100°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher.
  • the heat retention temperature during cooling of the plated steel sheet is preferably 450°C or lower, more preferably 400°C or lower, and even more preferably 350°C or lower.
  • the heat-keeping time during cooling of the plated steel sheet is preferably 5 seconds or more, more preferably 10 seconds or more, and further preferably 15 seconds or more.
  • the heat-keeping time during cooling of the plated steel sheet is preferably 300 seconds or less, and more preferably 100 seconds or less.
  • the cooling stop temperature during cooling of the plated steel sheet is preferably 300° C. or lower, more preferably 250° C. or lower, and further preferably 150° C. or lower.
  • the lower limit of the cooling stop temperature during cooling of the plated steel sheet is preferably 10° C. or higher, and more preferably 30° C. or higher.
  • the reheating temperature of the plated steel sheet is preferably (cooling stop temperature + 50°C) or higher, more preferably (cooling stop temperature + 80°C) or higher, and even more preferably (cooling stop temperature + 100°C) or higher. If the reheating temperature of the plated steel sheet exceeds 450°C, the area ratio of martensite decreases, and TS decreases. Therefore, the reheating temperature of the plated steel sheet is preferably 450°C or lower, more preferably 400°C or lower, and even more preferably 350°C or lower.
  • the retention time at the reheating temperature of the plated steel sheet is preferably 5 seconds or more, more preferably 10 seconds or more, and further preferably 15 seconds or more.
  • the retention time at the reheating temperature of the plated steel sheet is preferably 300 seconds or less, and more preferably 100 seconds or less.
  • the plated steel sheet is preferably rolled at an elongation rate of 0.05% or more and 1.00% or less.
  • an elongation rate of 0.05% or more By rolling at an elongation rate of 0.05% or more after cooling, cracks can be introduced into the hot-dip galvanized layer, and as a result, a further reduction in the amount of diffusible hydrogen in the low temperature region of the base steel sheet can be expected.
  • the elongation rate of the rolling is preferably 0.05% or more, and more preferably 0.10% or more.
  • the elongation rate of rolling is preferably 1.00% or less, more preferably 0.50% or less.
  • the rolling after cooling may be performed on an apparatus continuous with the continuous hot-dip galvanizing apparatus (online) or on an apparatus not continuous with the continuous hot-dip galvanizing apparatus (offline).
  • the target elongation may be achieved by a single rolling, or a total of 0.05% to 1.00% elongation may be achieved by multiple rolling.
  • the rolling after cooling generally refers to temper rolling, but may be a processing method such as repeated bending using a tension leveler or rolls, as long as it can impart an elongation rate equivalent to that of temper rolling.
  • the rolling treatment may be performed after the plated steel sheet is cooled to about room temperature, or the rolling treatment may be performed when cooling of the plated steel sheet is stopped, and then the plated steel sheet may be reheated.
  • hot-dip galvanized steel sheets When hot-dip galvanized steel sheets are traded, they are usually cooled to room temperature before being traded.
  • Manufacturing conditions other than those mentioned above are not particularly limited, and publicly known conditions can be used.
  • the member of the present invention is a member obtained by using the hot-dip galvanized steel sheet of the present invention described above.
  • the member can be produced, for example, by forming the hot-dip galvanized steel sheet of the present invention into a desired shape by press working or the like.
  • the hot-dip galvanized steel sheet of the present invention is a hot-dip galvanized steel sheet having high ductility, high stretch flangeability and bendability, and high local ductility, with a TS of 980 MPa or more. Therefore, by applying the hot-dip galvanized steel sheet of the present invention or a member made of the hot-dip galvanized steel sheet to, for example, an automobile frame structural part or an automobile reinforcing part, it is possible to improve fuel efficiency by reducing the weight of the vehicle body, and the industrial value of the steel sheet is extremely great.
  • a steel slab (steel material) having the composition shown in Table 1 and the balance consisting of Fe and unavoidable impurities was melted in a converter, and a steel slab was obtained by a continuous casting method.
  • the obtained steel slab was heated to 1250 ° C and roughly rolled to obtain a sheet bar.
  • the obtained sheet bar was then subjected to finish rolling at a finish rolling temperature of 900 ° C and coiled under the conditions shown in Table 2 to obtain a hot-rolled steel sheet.
  • the obtained hot-rolled steel sheet was pickled and then cold-rolled under the conditions shown in Table 2 to obtain a cold-rolled steel sheet having a sheet thickness of 1.4 mm.
  • hot-dip galvanized steel sheet in the category of coating treatment type means that only hot-dip galvanizing treatment was performed, and no alloying treatment was performed, while GA means that both hot-dip galvanizing treatment and alloying treatment were performed.
  • GI hot-dip galvanized steel sheet
  • GA a hot-dip galvanizing bath containing 0.20% by mass of Al with the balance being Zn and unavoidable impurities was used as the plating bath.
  • a hot-dip galvanizing bath containing 0.14% by mass of Al with the balance being Zn and unavoidable impurities was used.
  • the plating bath temperature was 470°C in both cases.
  • the coating weight was about 45 to 72 g/ m2 per side (double-sided plating) for GI, and about 45 g/ m2 per side (double-sided plating) for GA.
  • the alloying temperature for GA was about 550°C.
  • composition of the hot-dip galvanized layer of GI was Fe: 0.1-1.0 mass%, Al: 0.2-1.0 mass%, with the balance being Zn and unavoidable impurities, while the composition of the (alloyed) hot-dip galvanized layer of GA was Fe: 7-15 mass%, Al: 0.1-1.0 mass%, with the balance being Zn and unavoidable impurities.
  • the tensile test was carried out in accordance with JIS Z 2241. That is, a JIS No. 5 test piece was taken from the obtained hot-dip galvanized steel sheet so that the direction perpendicular to the rolling of the steel sheet (C direction) was the longitudinal direction. Next, a tensile test was carried out using the taken test piece under the condition of a crosshead speed of 1.67 ⁇ 10 ⁇ 1 mm/s, and YS, TS, El and L.El were measured. As for TS, a value of 980 MPa or more was determined to be acceptable. In addition, the product of TS and El (TS ⁇ El) was calculated from the measured TS and El, and TS ⁇ El was calculated.
  • a TS ⁇ El of 13000 MPa ⁇ % or more was determined to be acceptable. Furthermore, the product of TS and L.El (TS ⁇ L.El) was calculated from the measured TS and L.El, and TS ⁇ L.El was calculated. A TS ⁇ L.El of 4500 MPa ⁇ % or more was determined to be acceptable.
  • the hole expansion test was performed in accordance with JIS Z 2256. That is, the obtained hot-dip galvanized steel sheet was sheared to 100 mm x 100 mm, and then a hole with a diameter of 10 mm was punched in the sheared steel sheet with a clearance of 12.5%. Next, the steel sheet was held down with a blank holding force of 9 tons (88.26 kN) using a die with an inner diameter of 75 mm, and in this state, a conical punch with an apex angle of 60° was pressed into the hole to measure the hole diameter at the crack initiation limit. Then, the (limit) hole expansion ratio (%) was calculated by the following formula.
  • the bending test was performed in accordance with JIS Z 2248. From the obtained hot-dip galvanized steel sheet, a rectangular test piece with a width of 30 mm and a length of 100 mm was taken so that the axial direction of the bending test was parallel to the rolling direction (L direction) of the steel sheet. Then, a 90° V bending test was performed under the conditions of a pressing load of 100 kN and a pressing holding time of 5 seconds.
  • the bendability was evaluated by the pass rate of the bending test, and a bending test was performed on five samples at the maximum R (for example, when the plate thickness is 1.4 mm, the bending radius is 7.0 mm) at which the value R/t obtained by dividing the bending radius (R) by the plate thickness (t) is 5 or less. Then, the presence or absence of cracks at the ridgeline of the bending apex was evaluated, and when none of the five samples were cracked, the bendability was judged to be "excellent”. In addition, when microcracks of less than 200 ⁇ m occurred in one or more of the five samples, the bendability was judged to be "good".
  • a steel slab (steel material) having the composition shown in Table 1 and the balance consisting of Fe and unavoidable impurities was melted in a converter, and a steel slab was obtained by a continuous casting method.
  • the obtained steel slab was heated to 1250 ° C and roughly rolled to obtain a sheet bar.
  • the obtained sheet bar was then subjected to finish rolling at a finish rolling temperature of 900 ° C and coiled under the conditions shown in Table 4 to obtain a hot-rolled steel sheet.
  • the obtained hot-rolled steel sheet was pickled, and then cold-rolled under the conditions shown in Table 4 to obtain a cold-rolled steel sheet having a sheet thickness of 1.4 mm.
  • a metal electroplating process was performed on some of the cold-rolled steel sheets.
  • the column for metal electroplating (plating type) in Table 4 cases where "Yes (Fe)” is written are examples where Fe-based electroplating was performed, and cases where "(Ni)” is written are examples where Ni-based electroplating was performed.
  • the composition of the metal electroplating layer was Fe: 95 to 100 mass % for the Fe-based electroplating, and Ni: 95 to 100 mass % for the Ni-based electroplating, with the remainder being unavoidable impurities.
  • the cold-rolled steel sheets were subjected to the types of plating treatments (GI, GA) shown in Table 4 to obtain plated steel sheets having hot-dip galvanized layers on both sides.
  • the conditions for GI and GA were the same as above.
  • composition of the base steel plate of the obtained steel plate was substantially the same as the composition of the steel slab stage, and all of the suitable steels were within the range of composition according to the embodiment described above.
  • the hot-dip galvanized steel sheets obtained in this manner were measured for ultimate deformability, tensile properties, stretch flangeability, bendability, and amount of diffusible hydrogen in the bendable low-temperature region. The results are shown in Tables 5 and 6.
  • Method plating layer adhesion weight A sample of 10 mm ⁇ 15 mm was taken from the hot-dip galvanized steel sheet and embedded in resin to prepare a cross-section embedded sample. Three arbitrary points on the cross-section were observed using a scanning electron microscope (SEM) at an acceleration voltage of 15 kV and a magnification of 2000 to 10000 times depending on the thickness of the Fe-based plating layer, and the average thickness of the three fields of view was multiplied by the specific gravity of iron to convert it into the deposition amount of the Fe-based plating layer per side.
  • SEM scanning electron microscope
  • the nano-hardness of the soft surface layer of the base steel sheet of the obtained hot-dip galvanized steel sheet was measured. The results are shown in Table 5.
  • the 1/4 position of the soft surface layer is as follows: After the plating was peeled off from the obtained hot-dip galvanized steel sheet, mechanical polishing, buff polishing with diamond and alumina, and colloidal silica polishing were performed from the surface of the base steel sheet to a 1/4 position of the depth in the sheet thickness direction of the soft surface layer.
  • a Berkovich-shaped diamond indenter was used to Loading rate and unloading rate: 50 ⁇ N/s Maximum load: 500 ⁇ N Measurement area: 50 ⁇ m x 50 ⁇ m Data sampling pitch: 5 msec Dot spacing: 2 ⁇ m
  • the nano-hardness was measured at a total of 512 points under the above conditions.
  • the surface soft layer was mechanically polished to a position of 1/2 the depth in the plate thickness direction, buffed with diamond and alumina, and polished with colloidal silica.
  • a Tribo-950 manufactured by Hysitron a Berkovich-shaped diamond indenter, the nano hardness was measured at a total of 512 points under the same conditions as above.
  • the ground surface was placed on the inside of the bend (valley side) in the U-bend + close bending test, and the ground surface was placed on the outside of the bend (mountain side) in the V-bend + orthogonal VDA bending test during the V-bend test, and the ground surface was placed on the inside of the bend (valley side) during the subsequent VDA bending test.
  • the influence of sheet thickness is small in the U-bend + close bending test, V-bend + orthogonal VDA bending test, and axial crushing test of galvanized steel sheets with a sheet thickness of less than 1.2 mm, so the tests were conducted without grinding.
  • U-bend + close bending test The U-bend + close bending test was carried out as follows. From the obtained galvanized steel sheet, a test piece of 60 mm x 30 mm was taken by shearing and end face grinding. Here, the 60 mm side is parallel to the width (C) direction. A U-bending process (primary bending process) was performed in the width (C) direction with the rolling (L) direction as the axis at a curvature radius/sheet thickness of 4.2 to prepare a test piece. In the U-bending process (primary bending process), as shown in FIG. 1(a), a punch B1 was pressed into a steel sheet placed on a roll A1 to obtain a test piece T1. Next, as shown in FIG.
  • a contact bending process (secondary bending process) was performed in which the test piece T1 placed on a lower die A2 was crushed with an upper die B2.
  • D1 indicates the width (C) direction
  • D2 indicates the rolling (L) direction. Note that a spacer S described later was inserted between the test pieces.
  • the criteria for acceptance of the critical spacer thickness (ST) are as follows: When 980MPa ⁇ TS ⁇ 1180MPa, 4.5mm ⁇ ST When 1180MPa ⁇ TS ⁇ 1320MPa, 5.0mm ⁇ ST When 1320MPa ⁇ TS ⁇ 1470MPa, 5.5mm ⁇ ST When 1470MPa ⁇ TS, 6.0mm ⁇ ST
  • the criteria for failure of the critical spacer thickness (ST) are as follows: When 980MPa ⁇ TS ⁇ 1180MPa, 4.5mm ⁇ SF max When 1180MPa ⁇ TS ⁇ 1320MPa, 5.0mm ⁇ SF max When 1320MPa ⁇ TS ⁇ 1470MPa, 5.5mm ⁇ SF max When 1470MPa ⁇ TS, 6.0mm ⁇ SFmax
  • V-bend + orthogonal VDA bending test The V-bend + orthogonal VDA bend test is carried out as follows. From the obtained hot-dip galvanized steel sheet, a 60 mm x 65 mm test piece was taken by shearing and end face grinding. Here, the 60 mm side is parallel to the rolling (L) direction. The test piece was prepared by bending the steel sheet 90° (primary bending) in the rolling (L) direction with the width (C) direction as the axis at a curvature radius/sheet thickness of 4.2. In the 90° bending (primary bending), as shown in FIG. 2(a), a punch B3 was pressed into a steel sheet placed on a die A3 having a V groove to obtain a test piece T1.
  • a punch B4 was pressed into the test piece T1 placed on a support roll A4 so that the bending direction was perpendicular to the rolling direction to perform an orthogonal bending (secondary bending).
  • D1 indicates the width (C) direction
  • D2 indicates the rolling (L) direction.
  • V-bending conditions in the V-bending + orthogonal VDA bending test are as follows. Test method: Die support, punch pressing Molding load: 10 tons Test speed: 30 mm/min Holding time: 5 s Bending direction: Rolling (L) direction
  • VDA bending conditions in the V-bending + orthogonal VDA bending test are as follows. Test method: Roll support, punch pressing Roll diameter: ⁇ 30 mm Punch tip R: 0.4 mm Distance between rolls: (sheet thickness x 2) + 0.5 mm Stroke speed: 20 mm/min Test piece size: 60 mm x 60 mm Bending direction: perpendicular to rolling (C) direction
  • the stroke at maximum load is determined from the stroke-load curve obtained when the VDA bending is performed.
  • the average value of the stroke at maximum load when the V bending + orthogonal VDA bending test is performed three times is taken as SF max (mm).
  • SF max is an index for evaluating the fracture resistance property during a collision (the fracture resistance property of the bent ridgeline in an axial crushing test). The results are shown in Table 6.
  • the criteria for passing SF max are as follows: When 980MPa ⁇ TS ⁇ 1180MPa, 27.0mm ⁇ SF max When 1180MPa ⁇ TS ⁇ 1320MPa, 26.0mm ⁇ SF max When 1320MPa ⁇ TS ⁇ 1470MPa, 24.5mm ⁇ SF max When 1470MPa ⁇ TS, 24.0mm ⁇ SF max
  • the SF max failure criteria are as follows: When 980MPa ⁇ TS ⁇ 1180MPa, 27.0mm> SFmax When 1180MPa ⁇ TS ⁇ 1320MPa, 26.0mm> SFmax When 1320MPa ⁇ TS ⁇ 1470MPa, 24.5mm> SFmax When 1470MPa ⁇ TS, 24.0mm> SFmax
  • the axial crush test was carried out as follows. A test piece of 150 mm x 100 mm was taken from the obtained hot-dip galvanized steel sheet by shearing. Here, the 150 mm side was parallel to the rolling (L) direction. Using a die having a punch shoulder radius of 5.0 mm and a die shoulder radius of 5.0 mm, the test piece was formed (bended) to a depth of 40 mm to produce the hat-shaped member 10 shown in Figures 3(a) and 3(b). In addition, the steel plate used as the material for the hat-shaped member was separately cut to a size of 80 mm x 100 mm.
  • Figure 3(a) is a front view of the test member 30 prepared by spot welding the hat-shaped member 10 and the steel plate 20.
  • Figure 3(b) is a perspective view of the test member 30.
  • the position of the spot welded portion 40 was such that the end of the steel plate and the welded portion were spaced 10 mm apart, and the welded portions were spaced 20 mm apart.
  • the test member 30 was joined to the base plate 50 by TIG welding to prepare a sample for an axial crush test.
  • the present invention is not limited to the above-mentioned embodiment, which is a part of the disclosure of the present invention.
  • other embodiments, examples, and operational techniques made by those skilled in the art based on the above-mentioned embodiment are all included in the scope of the present invention.
  • the equipment for applying heat treatment to the steel plate is not particularly limited as long as the thermal history conditions are satisfied.
  • a hot-dip galvanized steel sheet having high ductility, high stretch flangeability and bendability, as well as high local ductility, and a TS of 980 MPa or more can be obtained.
  • the hot-dip galvanized steel sheet of the present invention has various excellent properties and can be applied to automotive structural components of various sizes and shapes. This makes it possible to improve fuel efficiency by reducing the weight of the vehicle body, and is of great industrial value.

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PCT/JP2023/014289 2023-04-06 2023-04-06 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 Ceased WO2024209641A1 (ja)

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JP2023572663A JP7711775B2 (ja) 2023-04-06 2023-04-06 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
KR1020257026735A KR20250135253A (ko) 2023-04-06 2023-04-06 용융 아연 도금 강판, 용융 아연 도금 강판을 사용하여 이루어지는 부재, 부재로 이루어지는 자동차의 골격 구조 부품 또는 자동차의 보강 부품, 그리고 용융 아연 도금 강판 및 부재의 제조 방법
PCT/JP2023/014289 WO2024209641A1 (ja) 2023-04-06 2023-04-06 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
CN202380096205.1A CN120917167A (zh) 2023-04-06 2023-04-06 热浸镀锌钢板、使用热浸镀锌钢板制成的部件、由部件构成的汽车的骨架结构构件或汽车的加强构件以及热浸镀锌钢板和部件的制造方法
EP23932052.6A EP4647519A4 (en) 2023-04-06 2023-04-06 HOT-DIP GALVANIZED STEEL SHEET, ELEMENT FORMED USING HOT-DIP GALVANIZED STEEL SHEET, AUTOMOBILE CHASSIS STRUCTURAL COMPONENT OR AUTOMOBILE REINFORCEMENT COMPONENT COMPRISING AN ELEMENT, AND METHOD FOR PRODUCING HOT-DIP GALVANIZED STEEL SHEET AND ELEMENT
MX2025011830A MX2025011830A (es) 2023-04-06 2025-10-02 Lamina de acero galvanizada por inmersion en caliente, miembro formado al usar lamina de acero galvanizada por inmersion en caliente, componente estructural del armazon de automoviles o componente de refuerzo de automoviles que comprende miembro, y metodo para producir lamina de acero galvanizada por inmersion en caliente y miembro

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Publication number Priority date Publication date Assignee Title
JPH083784A (ja) * 1994-06-17 1996-01-09 Sumitomo Metal Ind Ltd 電気めっき鋼板とその製造方法
WO2011065591A1 (ja) * 2009-11-30 2011-06-03 新日本製鐵株式会社 耐水素脆化特性に優れた引張最大強度９００ＭＰa以上の高強度鋼板及びその製造方法
WO2015002190A1 (ja) * 2013-07-01 2015-01-08 新日鐵住金株式会社 冷延鋼板、亜鉛めっき冷延鋼板及びそれらの製造方法
WO2020170542A1 (ja) 2019-02-22 2020-08-27 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板およびその製造方法
WO2022270053A1 (ja) * 2021-06-24 2022-12-29 Ｊｆｅスチール株式会社 溶融亜鉛めっき鋼板およびその製造方法、ならびに、部材

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US11530463B2 (en) * 2018-03-30 2022-12-20 Jfe Steel Corporation High-strength galvanized steel sheet, high strength member, and method for manufacturing the same
JP7235102B2 (ja) * 2019-04-11 2023-03-08 日本製鉄株式会社 鋼板及びその製造方法

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JPH083784A (ja) * 1994-06-17 1996-01-09 Sumitomo Metal Ind Ltd 電気めっき鋼板とその製造方法
WO2011065591A1 (ja) * 2009-11-30 2011-06-03 新日本製鐵株式会社 耐水素脆化特性に優れた引張最大強度９００ＭＰa以上の高強度鋼板及びその製造方法
WO2015002190A1 (ja) * 2013-07-01 2015-01-08 新日鐵住金株式会社 冷延鋼板、亜鉛めっき冷延鋼板及びそれらの製造方法
WO2020170542A1 (ja) 2019-02-22 2020-08-27 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板およびその製造方法
WO2022270053A1 (ja) * 2021-06-24 2022-12-29 Ｊｆｅスチール株式会社 溶融亜鉛めっき鋼板およびその製造方法、ならびに、部材

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See also references of EP4647519A1

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MX2025011830A (es) 2025-11-03

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