HIGH-STRENGTH, HIGH-DUCTILITY ELECTROLYTIC ZINC-COATED STEEL SHEET AND METHOD FOR ITS PRODUCTION

Abstract

A high-strength, high-ductility electrolytic zinc-coated steel sheet with excellent bending capacity and a method for its production are provided. The high-strength, high-ductility electrolytic zinc-coated steel sheet comprises an electrolytic zinc coating on the surface of a base steel sheet. The base steel sheet has a predetermined component composition and a steel microstructure in which the total area percentage of one or two of either martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more throughout the steel microstructure.the percentage of total area of ​​one or two of the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet, and the total perimeter of individual carbide particles having an average particle size of 50 nm or less in the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less present in the region is 50 µm / mm2 or more, in which the amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less.

Description

HIGH-STRENGTH, HIGH-DUCTILITY ELECTROLYTIC ZINC-COATED STEEL SHEET AND METHOD FOR ITS PRODUCTION FIELD OF INVENTION The present invention relates to a high-strength, high-ductility electrolytic zinc-coated steel sheet and a method for its production. More specifically, the present invention relates to a high-strength, high-ductility electrolytic zinc-coated steel sheet used, for example, for automotive components, and a method for its production, and in particular, to a high-strength, high-ductility electrolytic zinc-coated steel sheet with excellent bending capacity and a method for its production. BACKGROUND OF THE INVENTION In recent years, active efforts have been made to reduce the weight of vehicle bodies. The thickness of the steel sheets used for vehicle bodies has been reduced by increasing the strength of the steel sheets. In particular, there have been advances in the use of high-strength steel sheets with a tensile strength (TS) of 1,320 to 1,470 MPa for vehicle frame components, such as center pillar reinforcements (R / F), bumpers, and impact frame members (hereafter also referred to as “components”). Furthermore, from the perspective of further reducing the weight of car bodies, studies have been conducted on the use of steel sheets with a TS of 1,800 MPa (1.8 GPa) or higher. Additionally, from a workability standpoint, there is a growing demand for steel sheets with bending capabilities. With increased strength in steel sheets, hydrogen embrittlement can occur. In recent years, it has been suggested that plating hinders the release of hydrogen that has entered a steel sheet during its production process, and there is a risk of decreased ductility, particularly local ductility. It has also been suggested that the accumulation of hydrogen in steel around coarse carbides in a surface layer promotes post-working cracking. For example, Patent Document 1 provides a high-strength steel sheet having a chemical composition containing C: 0.12% to 0.3%, Si: 0.5% or less, Mn: less than 1.5%, P: 0.02% or less, S: 0.01% or less, Al: 0.15% or less, and N: 0.01% or less, the remainder being Fe and incidental impurities. The steel sheet has a microstructure of only tempered martensite and a breaking strength of 1.0 to 1.8 GPa. Patent Document 2 provides a high-strength steel sheet composed of a steel having a chemical composition containing C: 0.17% to 0.73%, Si: 3.0% or less, Mn: 0.5% to 3.0%, P: 0.1% or less, S: 0.07% or less, Al: 3.0% or less, and N: 0.010% or less, the remainder being Fe and incidental impurities. The steel sheet has a good balance between strength and ductility and a tensile strength of 980 MPa to 1.8 GPa, wherein the increased strength of the steel sheet is obtained by the use of a martensitic microstructure. The retained austenite necessary to provide the TRIP effect is stably provided by the use of a superior bainite transformation, and the martensite is partially transformed into tempered martensite. QfrMrnn / Lznz / e / YiAi List of Appointments Patent Documents PTL 1: Publication of Unexamined Japanese Patent Application No. 2011-246746 PTL 2: Publication of Unexamined Japanese Patent Application No. 2010-90475 BRIEF DESCRIPTION OF THE INVENTION Technical Problem In the technique disclosed in the Patent Document, although the microstructure of only tempered martensite results in excellent strength, inclusions and carbides that promote crack growth cannot be reduced; thus, the steel sheet is not considered to be excellent in bending capacity. In the technique disclosed in Patent Document 2, although there is no description of the bending capacity, austenite having an fcc structure has a greater amount of dissolved hydrogen than martensite and bainite having a body-centered cubic (bcc) or body-centered tetragonal (bct) structure; thus, the steel specified in Patent Document 2, which contains a large amount of austenite, apparently contains a large amount of diffusible hydrogen and is not considered to be excellent in bending capacity. The present invention relates to a high-strength, high-ductility electrolytic zinc-coated steel sheet that has excellent bending capacity and a method for producing the steel sheet. In the present invention, the term “high strength and high ductility” refers to a tensile strength (TS) of 1,320 MPa or more, an elongation (El) of 7.0% or more, and TS x El = 12,000 or more. The term “excellent bending capability” indicates that the limit bending radius / thickness (R / t) is 4.0 or less in a predetermined bending test. In a steel sheet coated with electrolytic zinc, a surface of a base steel sheet refers to the interface between the base steel sheet and an electrolytic zinc coating. A region that extends from a surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet is also referred to as a “surface layer portion”. Solution to the Problem The present invention provides a high-strength, high-ductility electrolytic zinc-coated steel sheet containing a predetermined amount of fine carbides in a portion of the surface layer to reduce the amount of diffusible hydrogen in the steel and thus give it excellent bending ability, and a method for producing the steel sheet. Specifically, a high-strength, high-ductility electrolytic zinc-coated steel sheet according to the present invention includes an electrolytic zinc-based coating layer on a surface of a base steel sheet and has a steel microstructure in which the total area percentage of one or two of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more throughout the steel microstructure, the total area percentage of one or two of martensite QfrMrnn / Lznz / e / YiAi containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet, and the total perimeter of individual carbide particles having an average particle size of 50 nm or less in the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less present in the region is 50 pm / mm2 or more, and the amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less, the tensile strength (TS) is 1,320 MPa or more, the elongation (El) is 7.0% or more, TS xEI is 12,000 or more, and R / t is 4.0 or less. The inventors have conducted in-depth studies to solve the aforementioned problems and have found that the amount of diffusible hydrogen in the steel must be reduced to 0.20 ppm by mass or less to achieve excellent bending capacity. To reduce the amount of diffusible hydrogen in the steel, fine carbides that serve as hydrogen trapping sites must be increased in a portion of the steel's surface layer. To this end, decarburization must be avoided. It has also been found that decarburization is suppressed by adjusting the composition of the steel components and shortening the residence time between the completion of the rolling finish and coiling. This successfully produces an electrolytic zinc-coated steel sheet with excellent bending capacity. A microstructure containing primarily martensite and bainite results in high ductility and high strength.The summary of the present invention is described below. [1] A high-strength, high-ductility electrolytic zinc-coated steel sheet includes an electrolytic zinc-based coating on a surface of a base steel sheet, wherein the base steel sheet has a composition of components containing, on a mass percentage basis, C: 0.12% or more and 0.40% or less, If: 0.001% or more and 2.0% or less, Mn: 1.7% or more and 5.0% or less, P: 0.050% or less, S: 0.0050% or less, To: 0.010% or more and 0.20% or less, N: 0.010% or less, and Sb: 0.002% or more and 0.10% or less, the remainder being Fe and incidental impurities; and a steel microstructure in which the total area percentage of one or two of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more throughout the steel microstructure, the total area percentage of one or two of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet, and the total particle perimeter of QfrMrnn / Lznz / e / YiAi individual carbides having an average particle size of 50 nm or less in martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less present in the region is 50 pm / mm2 or more, in which the amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less. [2] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in [1], the component composition additionally contains, on a mass percentage basis: B: 0.0002% or more and less than 0.0035%. [3] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in [1] or [2], the component composition additionally contains, on a mass percentage basis, one or two selected from: Nb: 0.002% or more and 0.08% or less, and Ti: 0.002% or more and 0.12% or less. [4] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in any of [1] to [3], the component composition additionally contains, on a mass percentage basis, one or two selected from: Cu: 0.005% or more and 1% or less, and Ni: 0.01% or more and 1% or less. [5] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in any of [1] to [4], the component composition additionally contains, on a mass percentage basis, one or two or more selected from: Cr: 0.01% or more and 1.0% or less, Mo: 0.01% or more and less than 0.3%, V: 0.003% or more and 0.5% or less, Zr: 0.005% or more and 0.2% or less, and W: 0.005% or more and 0.2% or less. [6] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in any of [1] to [5], the component composition additionally contains, on a mass percentage basis, one or two or more selected from: Ca: 0.0002% or more and 0.0030% or less, Ce: 0.0002% or more and 0.0030% or less, The: 0.0002% or more and 0.0030% or less, and Mg: 0.0002% or more and 0.0030% or less. [7] In the high-strength, high-ductility electrolytic zinc-coated steel sheet described in any of [1] to [6], the component composition additionally contains, on a mass percentage basis: Sn: 0.002% or more and 0.1% or less. [8] A method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet includes: a hot rolling stage for hot rolling a block of steel having the component composition described in any of [1] to [7] at a heating temperature QfrMrnn / Lznz / e / YiAi block of 1,200°C or higher and a hot rolling finish temperature of 840°C or higher, carry out cooling to a primary cooling stop temperature of 700°C or lower at an average cooling rate of 40°C / s greater in a temperature range from the hot rolling finish temperature to 700°C, carry out cooling at an average cooling rate of 2°C / s greater in a temperature range from the primary cooling stop temperature to 650°C, carry out cooling to a coiling temperature of 630°C or lower, and carry out coiling; an annealing step for heating a steel sheet after the hot rolling step to an annealing temperature equal to or greater than AC3 or carrying out heating to an annealing temperature equal to or greater than AC3 and carrying out temperature holding, carrying out cooling to a cooling stop temperature of 350°C or less at an average cooling rate of 3°C / s greater in a temperature range from the annealing temperature to 550°C, and carrying out holding at a holding temperature in a temperature range of 100°C to 200°C for 20 to 1,500 seconds; and a coating treatment step for cooling the steel sheet after the annealing step to room temperature and subjecting the steel sheet to electrolytic zinc-based coating for an electrodeposition time of 300 seconds or less. [9] The method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet described in [8] further includes, after the hot rolling stage, a cold rolling stage to cold roll the steel sheet between the hot rolling stage and the annealing stage.

[10] The method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet described in [8] or [9] further includes an annealing step to retain the steel sheet after the coating treatment step at a temperature range of 250°C or lower for a holding time t that satisfies formula (1) below: (T + 273)(logt + 4) < 2,700 (1) where in formula (1), T is a holding temperature (°C) in the tempering stage, and t is the holding time (s) in the tempering stage. Advantageous Effects of the Invention The present invention provides a high-strength, high-ductility electrolytic zinc-coated steel sheet that has excellent bending capacity by adjusting the component composition and production method to suppress decarburization in the surface layer portion, increase the amount of fine carbides in the surface layer portion, and reduce the amount of diffusible hydrogen in the steel. The use of the high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention for automotive structural members can achieve both increased strength and improved flexural strength of automotive steel sheets. In other words, according to the present invention, the performance of automotive bodies is improved. QfrMrnn / Lznz / e / YiAi DETAILED DESCRIPTION OF THE INVENTION Description of Modalities The inventors have conducted various studies in order to solve the above problems and have found that a high-strength, high-ductility electrolytic zinc-coated steel sheet with excellent bending capacity is obtained. The steel sheet has a predetermined component composition and a steel microstructure in which the percentage of the total area of ​​one or two of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more throughout the microstructure of the steel sheet.The percentage of total area of ​​one or two of the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet, and the total perimeter (total perimeter) of individual carbide particles having an average particle size of 50 nm or less in the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less present in the region is 50 pm / mm² or more, and the amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less. These results have led to the completion of the present invention. The embodiments of the present invention are described below. The present invention is not limited to the embodiments described below. A high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention includes an electrolytic zinc-based coating layer on a surface of a steel sheet that serves as a base (base steel sheet). First, the component composition of the base steel sheet (hereinafter also referred to simply as a “steel sheet”) of the present invention will be described. In the description of the component composition, the content of each component is expressed in units of “%” indicating “% by mass”. C: 0.12% or More and 0.40% or Less Carbon (C) is a hardenable element incorporated to achieve a predetermined percentage of martensite and / or bainite area and to increase the strength of the martensite and bainite layers, thus ensuring a tensile strength (TS) greater than 1,320 MPa. Finely dispersed carbides trap hydrogen in the steel, reducing the amount of diffusible hydrogen and thereby improving bending ability. When the carbon content is less than 0.12%, fine carbides cannot be ensured in the surface layer portion of the steel, resulting in poor bending ability. Therefore, the carbon content is 0.12% or higher. To achieve a higher TS, such as TS greater than 1,470 MPa, the carbon content is preferably greater than 0.16%, and more preferably 0.18% or higher. When the C content is more than 0.40%, the carbides in martensite and bainite thicken.The presence of coarse carbides in the surface layer portion causes them to act as the initiation points for bending cracks, thereby impairing the flexural strength. Therefore, the carbon content is 0.40% or less. The carbon content is preferably... QfrMrnn / Lznz / e / YiAi 0.30% or less, more preferably 0.25% or less. Yes: 0.001% or More and 2.0% or Less Silicon (Si) is an element that contributes to hardening through solid solution hardening. When a steel sheet is held at a temperature of 200°C or higher, Si suppresses the excessive formation of coarse carbides, contributing to improved bending capacity. Si also reduces manganese (Mn) segregation in the central portion of the sheet along the thickness direction, contributing to the suppression of MnS formation. Additionally, Si helps suppress decarburization and deburring caused by oxidation of the surface layer portion of the steel sheet during continuous annealing. To adequately provide the effects described above, the Si content is 0.001% or more. The Si content is preferably 0.003% or more, and more preferably 0.005% or more.An excessively high silicon content results in the extension of segregation in the thickness direction, readily forming coarse MnS in the thickness direction, thereby impairing flexural strength. Additionally, carbide formation is suppressed; thus, the absence of fine carbides increases the amount of diffusible hydrogen in the surface layer of the steel, further impairing flexural strength. Therefore, the silicon content is 2.0% or less. The silicon content is preferably 1.5% or less, and more preferably 1.2% or less. Mn: 1.7% or More and 5.0% or Less Manganese (Mn) is incorporated to improve the hardenability of steel and to obtain a predetermined percentage of martensite and / or bainite. A manganese content of less than 1.7% results in ferrite formation in the surface layer portion of the steel sheet, decreasing its strength. Additionally, the absence of fine carbides in the surface layer portion increases the amount of diffusible hydrogen in the steel's surface layer, impairing its bending capacity. Therefore, the manganese content must be 1.7% or higher. The manganese content is preferably 2.4% or higher, and more preferably 2.8% or higher. An excessively high manganese content can result in an increase in coarse carbides in the surface layer portion, significantly impairing bending capacity. Therefore, the manganese content is 5.0% or lower. The manganese content is preferably 4%.8% or less, more preferably 4.4% or less. P: 0.050% or Less Phosphorus (P) is an element that hardens steel. High P content promotes cracking. Thus, even with a small amount of diffusible hydrogen in the steel, its bending capacity deteriorates significantly. Therefore, the P content is 0.050% or less. Preferably, it is 0.030% or less, and more preferably 0.010% or less. The lower limit for P content is not particularly restricted. Currently, the industrially feasible lower limit is approximately 0.003%. S: 0.0050% or Less Sulfur (S) significantly and negatively affects flexural strength through the formation of inclusions such as MnS, TiS, and Ti(C,S). To reduce the detrimental effect of these inclusions, the S content must be 0.0050% or less. The S content is preferably 0.0020% or less, more preferably 0.0010% or less, and even more preferably 0.0005% or less. The lower limit for the S content is not particularly restricted. Currently, the industrially feasible lower limit is approximately 0.0002%. To: 0.010% or More and 0.20% or Less Aluminum is added to sufficiently deoxidize the steel and reduce coarse inclusions. This effect is achieved at 0.010% or more. The aluminum content is preferably 0.015% or more. At aluminum contents above 0.20%, carbides containing mainly iron, such as cementite, formed during coiling after hot rolling, do not readily dissolve during annealing. This results in the formation of coarse inclusions and carbides that impair bending capacity. Therefore, the aluminum content is 0.20% or less. The aluminum content is preferably 0.17% or less, and more preferably 0.15% or less. N: 0.010% or Less Nitrogen (N) is an element that forms coarse nitride and carbonitride inclusions, such as TIN, (Nb,Ti), (C,N), and AlN, in steel, and impairs its bending strength through the formation of these inclusions. To prevent this impairment, the N content must be 0.010% or less. The N content is preferably 0.007% or less, and more preferably 0.005% or less. The lower limit for the N content is not particularly restricted. Currently, the industrially feasible lower limit is approximately 0.0006%. Sb: 0.002% or more and 0.10% or less Sb suppresses oxidation and nitriding of the surface layer portion of the steel sheet, thereby suppressing decarburization caused by oxidation and nitriding in that portion. Suppression of decarburization suppresses ferrite formation in the surface layer portion, thus contributing to increased strength. Additionally, fine carbides can be provided in the surface layer portion of the steel to reduce the amount of diffusible hydrogen. From this perspective, Sb must be present in an amount of 0.002% or more. The Sb content is preferably 0.004% or more, and more preferably 0.007% or more. When Sb is present in an amount greater than 0.002%, the Sb content is considered high.At 10%, Sb segregates at the grain boundaries of the previous γ to promote cracking, thereby impairing flexural strength. Therefore, the Sb content is 0.10% or less. The Sb content is preferably 0.08% or less, more preferably 0.06% or less. The steel sheet of the present invention has a composition of components comprising the above-mentioned components, the remainder being Fe (iron) and incidental impurities. The steel sheet of the present invention preferably has the composition of components comprising the above-mentioned components and the remainder being Fe and incidental impurities. The steel sheet of the present invention may additionally contain the following components as optional components. In the case where the optional components are contained in quantities less than the lower limits, the components are considered to be contained as incidental impurities. B: 0.0002% or More and Less Than 0.0035% Boron is an element that improves the hardenability of steel, and has the advantage that martensite and bainite form with predetermined area percentages even in the case of a QfrMrnn / Lznz / e / YiAi low Mn content. To provide the effects of B, B is preferably contained in an amount of 0.0002% or more. The B content is more preferably 0.0005% or more, and even more preferably 0.0007% or more. From the point of view of immobilizing N, B is preferably added in combination with 0.002% or more of Ti. A B content of 0.0035% or more results in a decrease in the rate of cementite dissolution during annealing, leaving carbides containing mainly Fe, such as undissolved cementite. This leads to the formation of inclusions and coarse carbides, thereby impairing the bending capacity. Consequently, the B content is preferably less than 0.0035%. The content of B is more preferably 0.0030% or less, even more preferably 0.0025% or less. One or two selected from among Nb: 0.002% or more and 0.08% or less and Ti: 0.002% or more and 0.12% or less Nitrogen (Nb) and titanium (Ti) contribute to increased strength through a reduction in grain size. The fine Nib and Ti carbides formed serve as hydrogen trapping sites to reduce the amount of diffusible hydrogen in the steel, thereby improving bending capacity. From this perspective, each of Nib and Ti is preferably contained in an amount of 0.002% or more. The Nib and Ti content is more preferably 0.003% or more, and even more preferably 0.005% or more. When large amounts of Nb and Ti are contained, the coarse Nb-based precipitates that remain undissolved, such as NbN, Nb(C,N), and (Nb,Ti)(C,N), and the coarse Ti-based precipitates, such as TiN, Ti(C,N), Ti(C,S), and TiS, increase during block heating in the hot rolling stage to impair bending ability.Therefore, Nb is preferably contained in an amount of 0.08% or less. The Nb content is more preferably 0.06% or less, and even more preferably 0.04% or less. Ti is preferably contained in an amount of 0.12% or less. The Ti content is more preferably 0.10% or less, and even more preferably 0.08% or less. One or two selected from among Cu: 0.005% or more and 1% or less and Ni: 0.01% or more and 1% or less Copper (Cu) and nickel (Ni) are effective in improving corrosion resistance in automotive environments and in suppressing hydrogen ingress into steel sheets by allowing corrosion products to coat the steel sheet surfaces. From this perspective, Cu is preferably contained at 0.005% or more, and Ni at 0.01% or more. Regarding improving flexural strength, Cu and Ni are preferably contained at 0.05% or more, or even more preferably 0.08% or more. However, excessively high amounts of Cu and Ni lead to surface defects that impair coating and chemical conversion treatment capabilities. Therefore, the Cu and Ni contents are preferably 1% or less.Each of the Cu content and Ni content is more preferably 0.8% or less, even more preferably 0.6% or less. One or Two or More Selected from among Cr: 0.01% or More and 1.0% or Less, Mo: 0.01% or More and Less Than 0.3%, V: 0.003% or More and 0.5% or Less, Zr: 0.005% or More and 0.2% or Less, and W: αίτΜτηη / Lznz / e / YiAi 0.005% or more and 0.2% or less Cr, Mo, and V can be incorporated to improve the hardenability of steel. To achieve this effect, the Cr and Mo content is preferably 0.01% or more. The Cr and Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. V is preferably 0.003% or more. The V content is more preferably 0.005% or more, and even more preferably 0.007% or more. However, excessively large amounts of any of the Cr, Mo, and V lead to carbide thickening, which impairs the bending capacity. Therefore, the Cr content is preferably 1.0% or less. The Cr content is more preferably 0.4% or less, and even more preferably 0.2% or less. The Mo content is preferably less than 0.3%. The Mo content is more preferably 0.2% or less, even more preferably 0.1% or less. The V content is preferably 0.5% or less. The V content is more preferably 0.4% or less, even more preferably 0.3% or less. Zr and W contribute to increased strength through a reduction in the previous γ grain size. From this perspective, the content of both Zr and W is preferably 0.005% or more. More preferably, the content of both Zr and W is 0.006% or more, and even more preferably 0.007% or more. However, when large amounts of Zr and W are present, the coarse precipitates that remain undissolved increase during block heating in the hot rolling stage, impairing bending capacity. Therefore, the content of both Zr and W is preferably 0.2% or less. More preferably, the content of both Zr and W is 0.15% or less, and even more preferably 0.1% or less. One or Two or More Selected from among Ca: 0.0002% or More and 0.0030% or Less, Ce: 0.0002% or More and 0.0030% or Less, La: 0.0002% or More and 0.0030% or Less, and Mg: 0.0002% or More and 0.0030% or Less Calcium (Ca), Ce, and La immobilize sulfur (S) in the form of sulfides, serve as hydrogen trapping sites in steel, and reduce the amount of diffusible hydrogen in the steel, thus contributing to improved bending strength. For this reason, the content of each of Ca, Ce, and La is preferably 0.0002% or more. More preferably, 0.0003% or more, and even more preferably 0.0005% or more. The addition of large amounts of Ca, Ce, and La thickens the sulfides, impairing bending strength. Therefore, the content of each of Ca, Ce, and La is preferably 0.0030% or less. More preferably, 0.0020% or less, and even more preferably 0.0010% or less. Magnesium (Mg) immobilizes oxygen (O) in the form of MgO, serves as a hydrogen trapping site in steel, and reduces the amount of diffusible hydrogen in the steel, thus contributing to improved bending strength. Therefore, the Mg content is preferably 0.0002% or more. More preferably, 0.0003% or more, and even more preferably, 0.0005% or more. Adding a large amount of Mg increases the MgO content, impairing bending strength. Therefore, the Mg content is preferably 0.0030% or less. More preferably, 0.0020% or less, and even more preferably, 0.0010% or less. Sn: 0.002% or more and 0.1% or less Tin (Sn) suppresses oxidation and nitriding of the surface layer portion of the steel sheet, thereby suppressing decarburization caused by oxidation and nitriding in this area. Suppression of decarburization suppresses ferrite formation in the surface layer portion, thus contributing to increased strength. Additionally, fine carbides can be provided in the surface layer portion of the steel to reduce the amount of diffusible hydrogen. From this perspective, Sn is preferably contained in an amount of 0.002% or more. The sulfur content is more preferably 0.003% or more, and even more preferably 0.004% or more. When Sn is contained in an amount greater than 0.002%, the sulfur content is considered high.At 1%, Sn segregates at the grain boundaries of the previous γ to promote cracking, thereby impairing flexural strength. Therefore, Sn is contained in an amount of 0.1% or less. The Sn content is more preferably 0.08% or less, and even more preferably 0.06% or less. Diffusible Hydrogen Content in Steel of 0.20 ppm by Mass or Less The amount of diffusible hydrogen in the present invention refers to the cumulative amount of hydrogen released from an initial heating temperature (25°C) up to 200°C when heating is carried out at a temperature increase rate of 200°C / h using a thermal desorption spectroscopy system immediately after the removal of the coating from the electrolytic zinc-coated steel sheet. When the amount of diffusible hydrogen in the steel exceeds 0.20 ppm by mass, cracking is promoted during bending, impairing the bending capacity. Therefore, the amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less. The amount of diffusible hydrogen in the steel is preferably 0.17 ppm by mass or less, and more preferably 0.13 ppm by mass or less. The lower limit of the amount of diffusible hydrogen in the steel is not particularly restricted and may be 0 ppm by mass.The diffusible hydrogen content in steel is determined using a measurement method described in the Examples. In the present invention, the diffusible hydrogen content in the steel must be 0.20 ppm by mass or less before forming or welding the steel sheet. Regarding a product (member) after forming or welding the steel sheet, if a sample is cut from the product in a common use environment and the diffusible hydrogen content in the steel is measured and found to be 0.20 ppm by mass or less, the diffusible hydrogen content in the steel may be considered to be 0.20 ppm by mass or less even before forming or welding. The microstructure of the steel sheet of the present invention will be described below. Percentage of Total Area of ​​One or Two of between Martensite Containing Carbide Having Average Particle Size of 50 nm or Less and Bainite Containing Carbide Having Average Particle Size of 50 nm or Less Is 90% or More To achieve high tensile strength (TS > 1,320 MPa), the total area percentage of one or two of the following is required: martensite containing a carbide with an average particle size of 50 nm or less, and bainite containing a carbide with an average particle size of 50 nm or less, must be 90% or more of the total steel microstructure. Below this value, ferrite increases, impairing strength. The total area percentage of martensite and bainite can be 100% of the total steel microstructure. The area percentage of one of the martensite and bainite can fall within the range described above, and the total area percentage of both can also fall within the range described above. Martensite is defined as the total of freshly quenched martensite and tempered martensite.In the present invention, martensite refers to a hard microstructure formed from austenite at a low temperature (martensitic transformation temperature or lower). Tempered martensite refers to a microstructure that has been tempered during reheating. Bainite refers to a hard microstructure in which fine carbides are dispersed in acicular or plate-like ferrite and which forms from austenite at a relatively low temperature (martensitic transformation temperature or higher). Residual microstructures other than martensite or bainite include, for example, ferrite, pearlite, and retained austenite. When the total amount of such microstructure is 10% or less by area, the residual microstructure is permissible. The area percentage of the residual microstructure may be 0%. In the present invention, ferrite refers to a microstructure formed by the transformation of austenite at a relatively high temperature and consisting of grains with a bcc lattice. Pearlite refers to a layered microstructure composed of layers of ferrite and cementite. Retained austenite refers to austenite that does not transform into martensite when the martensitic transformation temperature is equal to or lower than room temperature. In the present invention, the area percentage of each phase in the steel microstructure is determined by a method described in the Examples. Percentage of Total Area of ​​One or Two of between Martensite Containing Carbide Having Average Particle Size of 50 nm or Less and Bainite Containing Carbide Having Average Particle Size of 50 nm or Less in Region Extending from Base Steel Sheet Surface to Depth of 1 / 8 of Base Steel Sheet Thickness Is 80% or More Bend cracking occurs from a surface layer in a ridge-line portion formed by bending a plated steel sheet; thus, the microstructure of the surface layer portion of the steel sheet is significantly important. In the present invention, the use of fine carbides in the surface layer portion as a hydrogen trapping site reduces the amount of diffusible hydrogen in the vicinity of the steel's surface layer, thereby improving bending capacity.Therefore, in the case where the total area percentage of one or both of the martensite containing a carbide with an average particle size of 50 nm or less and the bainite containing a carbide with an average particle size of 50 nm or less in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of the base steel sheet thickness is 80% or more, the desired bending capacity can be ensured. The area percentage is preferably 82% or more, more preferably 85% or more. The upper limit of the area percentage is not particularly restricted and can be 100%. In the region described above, one of the martensite and the bainite can be within the above range, and the total area percentage of both can be within the above range. Total perimeter of individual carbide particles having an average particle size of 50 nm or less in carbide-containing martensite having an average particle size of 50 nm or less and carbide-containing bainite having an average particle size of 50 nm or less present in the region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet is 50 pm / mm2 or more The amount of diffusible hydrogen in the surface layer portion of the steel is reduced by an increase in the surface area of ​​fine carbide particles present in the vicinity of the surface layer. Thus, the increase in the surface area of ​​fine carbide particles is significant. In the present invention, fine carbide particle perimeters are used as an index of the surface area of ​​fine carbide particles. The total perimeter of carbide particles having an average particle size of 50 nm or less in martensite containing a carbide having an average particle size of 50 nm or less and in bainite containing a carbide having an average particle size of 50 nm or less, present in a region extending from a surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet, is 50 pm / mm² or more (50 pm or more per 1 mm²).The overall perimeter of the carbide particles is preferably 55 pm / mm² or more, more preferably 60 pm / mm² or more. In the present invention, the overall perimeter of the carbide particles is determined by a method described in the Examples. The high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention includes an electrolytic zinc coating on a steel sheet surface that serves as a base (base steel sheet). The type of zinc coating is not particularly limited and may be, for example, a zinc coating (pure Zn) or a zinc alloy coating (e.g., Zn-Ni, Zn-Fe, Zn-Mn, Zn-Cr, or Zn-Co). The coating weight of the electrolytic zinc coating is preferably 25 g / m² or more per surface area to improve corrosion resistance. The coating weight of the electrolytic zinc coating is preferably 50 g / m² or less per surface area to avoid impairing flexural strength.The high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention may include the electrolytic zinc coating on one surface of the base steel sheet or may include the electrolytic zinc coating on each surface of the base steel sheet. The high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention preferably includes the electrolytic zinc coating on each surface of the base steel sheet when used for automobiles. The high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention has a tensile strength of 1,320 MPa or more. The tensile strength is preferably 1,400 MPa or more, more preferably 1,470 MPa or more, and even more preferably 1,600 MPa or more. The upper limit of the tensile strength is preferably, but not necessarily, 2,200 MPa or less, from the standpoint of easily achieving a balance with other characteristics. The high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention has an elongation (El) of 7.0% or more. The elongation is preferably QfrMrnn / Lznz / e / YiAi of 7.2% or more, more preferably 7.5% or more. Additionally, TS (MPa) x El (%) is 12,000 or more. TS xEI is preferably 13,000 or more, more preferably 13,500 or more. Each of the tensile strength (TS) and elongation (El) is measured by a method described in the Examples. The limit bending radius / thickness (R / t) of the high-strength, high-ductility electrolytic zinc-coated steel sheet of the present invention is 4.0 or less in a predetermined bending test (bend test described in the Examples). R / t is preferably 3.8 or less, more preferably 3.6 or less. A method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet in accordance with an embodiment of the present invention will be described below. The method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet according to one embodiment of the present invention includes at least one hot rolling step, one annealing step, and one coating treatment step. Additionally, a cold rolling step may be included between the hot rolling step and the annealing step. A tempering step may be included after the coating treatment step. These steps are described below. A temperature described below refers to the surface temperature of a block, a steel sheet, or the like. (Hot Rolling Stage) Block Heating Temperature A steel block with the component composition described above is subjected to hot rolling. Using a block heating temperature of 1200°C or higher promotes sulfide dissolution and reduces manganese segregation, thereby decreasing the amount of coarse inclusions described above and improving bending capacity. For this reason, the block heating temperature is 1200°C or higher. More preferably, the block heating temperature is 1230°C or higher, and even more preferably 1250°C or higher. For example, the heating rate during block heating can be 5 to 15°C / min, and the holding time at the block temperature can be 30 to 100 minutes. Hot Rolling Finishing Temperature The hot-rolling finish temperature must be 840°C or higher. At a hot-rolling finish temperature below 840°C, time is required to reduce the temperature. This can lead to the formation of inclusions that impair bending ability and deteriorate the internal quality of the steel sheet. Additionally, decarburization of a surface layer decreases the percentage of bainite and martensite areas containing carbides in the surface layer portion of the steel, reducing the number of fine carbides that act as hydrogen-trapping sites near the surface layer. This makes it difficult to ensure the desired bending ability. Therefore, the hot-rolling finish temperature must be 840°C or higher. The hot-rolling finish temperature is preferably 860°C or higher.The upper limit of the hot rolling finishing temperature is preferably, but not necessarily, 950°C or lower due to a problem that lies in cooling to a coiling temperature, which is described below. The hot rolling finishing temperature is more preferably 920°C or lower. After the completion of hot rolling, cooling is carried out to a primary cooling stop temperature of 700°C or lower at an average cooling rate of 40°C / s over a temperature range from the hot rolling finish temperature to 700°C. A slow cooling rate results in the formation of inclusions. An increase in the size of these inclusions impairs bending ability. Decarburization of the surface layer decreases the percentage of martensite and bainite carbide-containing areas in the surface layer portion of the steel, thus reducing the number of fine carbides that serve as hydrogen trapping sites near the surface layer, making it difficult to ensure the desired bending ability.Therefore, after the completion of hot rolling, the average cooling rate is 40°C / s higher from the hot rolling finish temperature to 700°C. The average cooling rate is preferably 50°C / s higher. The upper limit of the average cooling rate is preferably, but not necessarily, approximately 250°C / s. The primary cooling stop temperature is 700°C or lower. At a primary cooling stop temperature above 700°C, carbides readily form up to 700°C. The fouling of carbides impairs bending ability. The lower limit of the primary cooling stop temperature is not particularly restricted. At a primary cooling stop temperature of 650°C or lower, the effect of rapid cooling on suppressing carbide formation is diminished.In this way, the primary cooling stop temperature is preferably above 650°C. After that, cooling is carried out at an average cooling rate of 2°C / s greater over a temperature range from the primary cooling stop temperature to 650°C, and then further cooling is performed to a roll temperature of 630°C or lower. A slow cooling rate to 650°C results in the formation of inclusions. An increase in the size of the inclusions impairs the bending capacity. Decarburization of the surface layer decreases the percentage of martensite and bainite area containing carbides in the surface layer portion of the steel, thus reducing the fine carbides that serve as hydrogen trapping sites near the surface layer, making it difficult to ensure the desired bending capacity.Therefore, as described above, after cooling to a primary cooling stop temperature of 700°C or lower is carried out at an average cooling rate of 40°C / s greater in the temperature range up to 700°C, the average cooling rate is 2°C / s greater in the temperature range from the primary cooling stop temperature to 650°C. The average cooling rate is preferably 3°C / s greater, more preferably 5°C / s. The average cooling rate from 650°C to the winding temperature is preferably, but not necessarily, 0.1°C / s greater and 100°C / s less. The rolling temperature is 630°C or lower. A rolling temperature above 630°C can result in decarburization on the surface of the base steel, leading to a difference in microstructure between the interior and surface of the steel sheet, which QfrMrnn / Lznz / e / YiAi causes a lack of uniformity in the alloy concentration. Additionally, decarburization in the surface layer decreases the percentage of martensite and bainite carbide-containing areas in the surface layer portion of the steel, reducing the fine carbides that serve as hydrogen trapping sites near the surface layer. This makes it difficult to ensure the desired bending capacity. Consequently, the rolling temperature is 630°C or lower. The rolling temperature is preferably 600°C or lower. The lower limit of the rolling temperature is not particularly restricted. To avoid a decrease in cold rolling capacity when cold rolling is carried out, the rolling temperature is preferably 500°C or higher. Cold Rolling Stage After the hot rolling stage, a cold rolling stage may be carried out. In the case where the cold rolling stage is carried out, the steel sheet (hot-rolled steel sheet) wound in the hot rolling stage is pickled and then cold-rolled to produce a cold-rolled steel sheet. The pickling conditions are not particularly limited. The reduction by rolling is not particularly limited. At a reduction by rolling of less than 20%, the surfaces may have poor flatness, leading to a non-uniform microstructure. Thus, the reduction by rolling is preferably 20% or more. The cold rolling stage may be omitted as long as the microstructure and mechanical properties satisfy the requirements of the present invention. (Annealing Stage) Steel sheet that has undergone hot rolling or cold rolling following hot rolling is heated to an annealing temperature equal to or higher than AC3. An annealing temperature lower than AC3 results in ferrite formation in the microstructure, preventing the desired strength from being achieved. Therefore, the annealing temperature is AC3 or higher. The annealing temperature is preferably AC3 + 10°C or higher, and more preferably AC3 + 20°C or higher. The upper limit of the annealing temperature is not particularly restricted. To suppress austenite thickening and thus prevent impairment of bending capacity, the annealing temperature is preferably 900°C or lower. The atmosphere during annealing is not particularly restricted.From the point of view of avoiding decarburization in the surface layer portion, the dew point is preferably -50°C or higher and -5°C or lower. The AC3 point (°C) used here is calculated from the following formula. In the formula, each (% element symbol) refers to the amount of the corresponding element contained (% by mass). Point Ac3 = 910- 203(%C)1 / 2+ 45(%S¡) - 30(%Mn) - 20(%Cu) - 15(%N¡) + 11 (%Cr) + 32(%Mo) + 104(%V) + 400(%Ti) + 460(%AI) After heating to an annealing temperature equal to or greater than AC3, cooling is carried out to a stop-cooling temperature of 350°C or lower at an average cooling rate of 3°C / s greater over a temperature range from the annealing temperature to 550°C, and holding is carried out at a holding temperature within a temperature range of 100°C to 200°C for 20 to 1,500 seconds.When QfrMrnn / Lznz / e / YiAi is heated to an annealing temperature equal to or higher than point AC3, temperature holding at the annealing temperature may be carried out. The temperature holding time here is preferably, but not necessarily, 10 seconds or more and 300 seconds or less, more preferably 15 seconds or more and 250 seconds or less. An average cooling rate of less than 3°C / s in the temperature range from the annealing temperature to 550°C leads to excessive ferrite formation, hindering the achievement of the desired strength. Additionally, ferrite formation in the surface layer portion makes it difficult to increase the carbide-containing fractions of martensite and bainite near the surface layer, thereby impairing the bending capacity.Therefore, the average cooling rate in the temperature range from the annealing temperature to 550°C is 3°C / s higher, preferably 5°C / s higher, more preferably 10°C / s higher. The quench stop temperature is 350°C or lower. A quench stop temperature above 350°C results in the formation of bainite, which contains coarse carbides, decreasing the amount of fine carbides in the surface layer portion of the steel, thereby impairing its bending capacity. The average cooling rate is defined by (the cooling start temperature - the cooling stop temperature) / the cooling time from the cooling start temperature to the cooling stop temperature, unless otherwise specified. Next, a holding temperature is applied in the range of 100°C to 200°C for 20 to 1,500 seconds. The carbides distributed within the bainite are formed during the holding temperature range after quenching and serve as hydrogen trapping sites, preventing deterioration of flexural strength. When the holding temperature is below 100°C or the holding time is less than 20 seconds, bainite does not form, and freshly quenched martensite, which does not contain carbides, develops. This reduces the amount of fine carbides in the surface layer of the steel, thus failing to provide the aforementioned effect.When the holding temperature exceeds 200°C or the holding time exceeds 1,500 seconds, decarburization occurs, and coarse carbides form in the bainite, thereby impairing flexural strength. The holding temperature is preferably 120°C or higher. The holding temperature is preferably 180°C or lower. The holding time is preferably 50 seconds or more. The holding time is preferably 1,000 seconds or less. After the annealing stage, cooling to room temperature is carried out. The cooling rate at this point is not particularly limited. Up to 50°C, the average cooling rate is preferably 1°C / s greater. The term “room temperature” indicates, for example, from 10°C to 30°C. (Coating Treatment Stage) After cooling to room temperature, the steel sheet undergoes electrolytic zinc plating. The type of electrolytic zinc plating can be, but is not limited to, any of the following: pure zinc, zinc-nitrogen, zinc-Fe, zinc-manganese, zinc-chromium, zinc-cobalt, and others. To suppress hydrogen ingress into the steel and achieve a diffusible hydrogen content of 0.20 ppm by mass or less in electroplated zinc-coated steel sheets, the electrodeposition time is critical. Electrodeposition times exceeding 300 seconds result in prolonged immersion of the steel in acid, leading to a diffusible hydrogen content exceeding 0.20 ppm by mass, which impairs its flexural strength. Therefore, the electrodeposition time should be 300 seconds or less. Ideally, it should be 280 seconds or less, and more preferably 250 seconds or less. The steel sheet, after the coating treatment stage (electrolytic zinc-coated steel sheet), can be subjected to the tempering stage. The amount of diffusible hydrogen in the steel can be reduced through the tempering stage to further increase its bending capacity. The tempering stage is preferably a holding stage for the steel sheet after the coating treatment stage at a temperature range of 250°C lower for a holding time t that satisfies formula (1) below: (T + 273)(log t + 4) < 2,700 (1) where in formula (1), T is the holding temperature (°C) in the tempering stage, and t is the holding time (seconds) in the tempering stage. In the production method according to the modality described above, the high-strength, high-ductility electrolytic zinc-based coated steel sheet that has excellent bending capacity can be produced by controlling the production condition of the base steel sheet before the coating treatment stage and the coating treatment conditions in order to form fine carbides in the surface layer portion of the steel and use the fine carbides as hydrogen trapping sites to reduce the amount of diffusible hydrogen in the steel. Hot-rolled steel sheet, after the hot rolling stage, can undergo heat treatment to soften its microstructure. After the coating treatment stage, tempering can be carried out to adjust its shape. EXAMPLES The present invention will be specifically described below with reference to the Examples. 1. Production of Steel Sheet for Evaluation Cast steels having the component compositions provided in Table 1, the remainder being Fe and incidental impurities, were produced using a vacuum melting furnace. Each steel was block-rolled into a steel block 27 mm thick. The resulting steel block was hot-rolled into hot-rolled steel sheet 4.0 mm thick (hot-rolling stage). For the samples to be cold-rolled, the hot-rolled steel sheets were ground to a thickness of 3.2 mm and then cold-rolled to the rolling reductions provided in Tables 2-1 to 2-4 into cold-rolled steel sheets 1.4 mm thick (cold-rolling stage). In Table 2-1, samples for which numerical values ​​of the reduction by rolling in cold rolling are not described were not subjected to cold rolling.Hot-rolled steel sheets and cold-rolled steel sheets produced as described above were subjected to heat treatment (annealing stage) and coating (coating treatment stage) under the conditions provided in Tables 2-1 to 2-4 to produce electro-zinc-coated steel sheets. Blanks in Table 1, which presents the component composition, indicate that components are not intentionally added. These blanks also include the case where components are not contained (0% by mass) and the case where components are incidentally contained. Some samples underwent the tempering stage. In Tables 2-1 to 2-4, the tempering condition cells that are blank indicate that no tempering stage was performed. In the coating treatment stage, for the pure Zn coating, an electrodeposition solution was prepared by adding 440 g / L of zinc sulfate heptahydrate to deionized water and adjusting the pH to 2.0 with sulfuric acid. For the Zn-Ni coating, an electrodeposition solution was prepared by adding 150 g / L of zinc sulfate heptahydrate and 350 g / L of nickel sulfate hexahydrate to deionized water and adjusting the pH to 1.3 with sulfuric acid. For the Zn-Fe coating, an electrodeposition solution was prepared by adding 50 g / L of zinc sulfate heptahydrate and 350 g / L of iron sulfate to deionized water and adjusting the pH to 2.0 with sulfuric acid. Inductively coupled plasma (ICP) analysis of the coatings revealed that the alloy compositions of the coatings will be 100% Zn, Zn-13% Ni, and Zn-46% Fe.The coating weight of each electrolytic zinc-based coating ranged from 25 to 50 g / m² per surface. Specifically, the 100% zinc coating had a coating weight of 33 g / m² per surface. The zinc-13% nickel coating had a coating weight of 27 g / m² per surface. The zinc-46% iron coating also had a coating weight of 27 g / m² per surface. These electrolytic zinc-based coatings were applied to both surfaces of the steel sheets. QfrMrnn / Lznz / e / YiAi w 01 N 01 O 01 Table 1 Steel grade Component composition (%by mass) Point Acs C Si Mn PS Al N Sb B Nb Ti Cu Ni Cr Mo V Zr W Ca Ce La Mg Sn A 0.008 0.0003 0068 0.0048 0.01 820 C 013 1.0 3.0 0.008 0.0005 0.080 0.0021 0.02 829 D 0.27 1.2 2.9 0.018 0.020 0.020 0.0043 0.01 781 E 0.35 1.2 3.0 0.010 0.0010 0077 0.0043 0.01 789 F 0.24 0.002 3.5 0.010 0.0010 0.040 G 0.22 1.7 3.4 0.007 0.0004 0036 0.0014 0.01 806 H 022 0.9 1.8 0.007 0.0010 0.078 0.0034 0.02 837 0.21 0.20.80 0.0007 0096 0.0046 0.03 822 J 0.23 0.9 4.9 0.025 0.0002 0092 0.0028 0.01 748 K 019 1.0 3.5 0.009 0.009 0.009 0.036 0.0028 0.005 773 L 022 0.9 3.7 0.016 0.0004 0.039 0.0028 0.003 763 M 0.23 0.8 3.4 0.005 0.0004 0050 0.0015 0.077 N7070. 3.5 0.006 0.0010 0066 0.0053 0.09 776 0 023 1.1 3.6 0.038 0.0006 0051 0.0040 0.01 778 P 019 0.1 2.09 0.02 0.060. 0.0027 0.01 0O020 767 Q 0.24 0.8 3.1 0.009 0.0002 0.063 0.0051 0.05 0.0200 780 R 0.20 01 31 0.007 0.004 0.004 .038 0.0051 0.01 0.017 755 S 025 01 2.8 0.006 0.0003 0.040 0.0037 0.01 0.0015 0.0150 0.015 753. The underlined values ​​are outside the scope of the present invention. a ω ω μ μ ο σι ο σι ο σ> σι Continuation of Table 1 Steel grade Component composition (%by mass) Point Acs C Si Mn P s Al N Sb B Nb Ti Cu Ni Cr Mo V Zr W Ca Ce La Mg Sn T 3.5 0.009 0.0003 0.096 0.0060 0.01 0.15 0.04 762 V 0.20 0.6 34 0.025 0.0010 0.096 0.0020 0.01.290 4.1 w 0.008 0.0010 0.068 0.0020 0.02 0.2 731 X 0.22 04 4.0 0.009 0.0001 0.057 0.0043 0.01 0.17 0.10 736 40 0.009 0.0009 0.042 0.0029 0.03 0.012 0.01 0.0008 0.0009 0.0006 0.0004 776 z 0.20 1.0 34 0.0009 0.004 0.004 0 0.004 778 AA 0.18 0.8 34 0.045 0.0010 0.034 0.0033 0.04 0.0015 0.0150 0.01 0.01 778 AB 0.60. 0.01 0.003 0.0027 0.01 764 AC 042 1.1 3.2 0.019 0.0002 0.035 0.0021 0.01 748 AD 008 1.0 3.0 0.006 0.0002 8035 40.0077 0.21 24 3.1 0.008 0.0010 0.023 0.0028 0.01 843 AF 0.22 1.1 15 0.026 0.0006 0.069 0.0024 0.01 0.2 851 0.0007 0.059 0.0010 0.01 787 AH 0.19 0.8 3.2 0.018 0.0080 0.069 0.0058 0.01 795 Al 0.22 1.1 2.8 0.007 0.0004 0.250 0.0028 0.01 895 AJ 025 0.8 3.3 0.006 0.0003 0.064 0.0150 0.01 775 AK 0.21 0.6 3.3 0.018 0.0008 0.071 0.0017 0.001 778 AL 0.18 0.01 3.1 0.009 0.0005 0.076 0.0015 015 767. The underlined values ​​are outside the scope of the present invention. > Β h Ch Table 2-1 No. Steel Grade Hot Rolled Cold Rolled Annealed Roughing Heating Temperature Hot Roll Finishing Temperature Average Cooling Rate to 700°C'1 Average Cooling Rate to 650°C'2 Rolling Temperature Reduction by Rolling Temperature Dew Point °C °C °S °C °C % °C °C 1 A 1250 880 232 31 550 56 820 15 2 1250 880 245 33 550 56 825 15 3 1250 880 225 32 550 56 830 15 4 1250 880 246 34 550 56 830 15 5 1250 880 248 50 550 56 840 15 6 1250 880 247 18 550 56 840 15 7 1250 880 239 13 550 56 860 15 8 1250 880 251 1 550 56 830 15 9 B 1250 880 235 33 550 56 887 15 10 1240 880 237 35 550 56 902 15 11 1210 880 241 37 550 56 896 15 12 1180 880 242 34 550 56 890 15 13 C 1250 900 239 38 550 56 863 15 14 1250 880 242 35 550 56 904 15 15 1250 850 250 36 550 56 894 •5 16 1250 820 247 34 550 56 862 15 17 D 1250 880 250 32 550 56 822 15 18 1250 880 100 31 550 56 830 15 19 1250 880 40 38 550 56 834 6 20 1250880 20 34 550 56 848 15 21 E 1250 880 228 30 550 56 817 15 22 1250 880 229 35 580 56 833 15 23 1250 880 231 37 620 56 849 15 24 1250 880 234 34 650 56 840 15 25 F 1250 880 227 35 550 804 15 26 1250 880 229 33 550 812 15 27 1250 880 230 32 550 830 15 28 1250 880 231 36 550 785 15 29 G 1250 880 230 35 550 56 846 15 30 1250 880 234 38 550 56 835 15 31 1250 880 238 37 550 56 830 15 32 1250 880 237 34 550 56 800 15 *1 Average cooling rate from hot rolling finish temperature to 700°C. *2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. *3 Average cooling rate in the temperature range from annealing temperature to 550°C. The underlined poets are outside the scope of the present invention. Üi EITHER Ül O01 W Ü1 Continuation of Table 2-1 No. Annealing Coating Tempering Condition Average Cooling Rate³ Cooling Stop Temperature Holding Temperature Holding Time Coating Type Plating Time Holding Temperature Holding Time °C / s °C °C ss °C s 1 28 150 150 150 Zn 120 Example 2 26 150 150 150 Zd 180 250 10 Example 3 27 150 150 150 Zd 260 80 3600 Example 4 30 150 170 150 Zd 320 Comparative Example 5 25 150 170 150 Zd 230 Example 6 34 150 170 150 Zd 230 Example 7 25 150 170 150 Zd 230 Example 8 27 150 170 150 Zd 240 Comparative Example 9 30 150 170 150 Zd 230 Example 10 24 150 170 150 Zd 230 Example 11 25 150 170 150 Zd 250 Example 12 29 150 170 150 Zd 230 Comparative Example 13 35 150 170 150 Zd 260 Example 14 28 150 170 150 Zd 230 Example 15 27 150 170 150 Zd 230 Example 16 26 150 170 150 Zd 230 Comparative Example 17 30 150 170 150 Zd 240 200 30 Example 18 25 150 170 150 Zd 230 150 180 Example 19 28 150 170 150 Zd 250 Example 20 30 150 170 150 Zd 230Comparative Example 21 26 150 170 150 Zd 260 Example 22 37 150 170 150 Zd 230 Example 23 30 150 170 150 Zd 230 Example 24 26 150 170 150 Zd 230 Comparative Example 25 25 150 170 150 Zd 260 Example 26 28 150 170 150 Zd 230 Example 27 30 150 170 150 Zd 250 Example 28 34 150 170 150 Zd 240 Example 29 28 150 170 150 Zd 230 Example 30 27 150 170 150 Zd 260 Example 31 30 150 170 150 Zd 230 Example 32 26 150 170 150 Zd 250 Comparative example *1 Average cooling rate from hot rolling finish temperature to 700°C. *2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. *3 Average cooling rate in the temperature range from the annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. Taba 2-2 ω (Λ σι No. Grade of Steel Hot Rolling Cold Rolling Annealing Roughing Heating Temperature Hot Rolling Finishing Temperature Average Cooling Rate to 700°C Average Cooling Rate to 650°C Rolling Temperature Reduction by Rolling Annealing Temperature Dew Point °C °C / s °C(s C % °C °C 33 H 1250 880 241 31 550 56 865 15 34 1250 880 235 32 550 56 870 15 35 1250 880 236 33 550 56 880 19 36 1250 880 238 35 550 56 870 15 37 I 1250 880 244 36 550 56 850 15 38 1250 880 241 38 550 56 860 15 39 1250 880 237 39 550 56 854 15 40 1250 880 229 34 550 56 880 15 41 J 1250 880 235 35 550 56 790 15 42 1250 880 234 31 550 56 780 15 43 1250 880 228 30 550 56 820 15 44 1250 880 229 32 550 56 819 15 45K 1250 880 230 35 550 56 809 15 46 1250 880 247 37 550 56 816 15 47 1250 880 246 36 550 56 804 15 48 1250 880 241 34 550 56 820 15 49 L 1250 880 300 33 550 56 793 15 50 1250 880 220 32 550 56 801 15 51 1250 880 150 35 550 56 8217 52 1250 880 15 38 550 56 810 15 53 M 1250 880 247 30 550 56 801 15 54 1250 880 242 21 550 56 795 15 55 1250 880 245 14 550 56 823 15 56 1250 880 239 1 550 56 818 15 57 N 1250 880 234 34 550 56 806 15 58 1250 880 235 35 550 56 815 15 59 1250 880 237 36 550 56 831 15 60 1250 880 236 32 550 56 824 15 '1 Average cooling rate from hot rolling stop temperature to 700°C. '2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. '3 Average cooling rate during the temperature gap from the annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. > B h C hcc 4 4 C ω ω μ ιη ο σι > B h C h Continuation of Table 2-2 No. Annealing Coating Tempering Condition Average Cooling Rate*3 Cooling Stop Temperature Holding Temperature Holding Time Coating Type Plating Time Holding Temperature Holding Time °C / s °C °C ss °C s 33 30 150 170 150 Zn 230 Example 34 18 150 170 150 Zn 230 Example 35 6 150 170 150 Zn 260 Example 36 2 150 170 150 Zn 230 Comparative Example 37 28 370 170 150 Zn 240 Comparative Example 38 27 340 170 150 Zn 230 Example 39 26 320 170 150 Zn 230 Example 40 30 120 170 150 Zn 250 Example 41 25 150 170 1750 Zn 230 Comparative Example 42 35 150 170 800 Zn 260 Example 43 29 150 170 100 Zn 230 Example 44 30 150 170 8 Zn 230 Comparative Example 45 27 150 90 150 Zn 200 Comparative Example 46 28 150 150 150 Zn 180 Example 47 27 150 170 150 Zn 160 Example 48 30 150 220 150 Zn 120 Comparative Example 49 26 150 170 150 Zn 230 Example 50 35 150 170 150 Zn 230 Example 51 29 150 170 150 Zn 230 Example 52 27 150 170 150 Zn 240Comparative example 53 28 150 170 150 Zn 230 Example 54 29 150 170 150 Zn 230 Example 55 30 150 170 150 Zn 250 Example 56 38 150 170 150 Zn 230 Comparative example 57 27 150 170 150 Zn-Ni 400 Comparative example 58 29 150 170 150 Zn-Ni 1 Comparative example 59 28 150 170 150 Zn-Ni 240 Example 60 28 150 170 150 Zn-Ni 130 Example *1 Average cooling rate from hot rolling stop temperature to 700°C. *2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. *3 Average cooling rate in the temperature range from annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. DC 4 C σι σι ο01 Taba 2-3 No. Grade of Steel Hot Rolling Cold Rolling Annealing Roughing Heating Temperature Hot Rolling Finishing Temperature Average Cooling Rate to 700°C Average Cooling Rate to 650°C Rolling Temperature Reduction by Rolling Annealing Temperature Dew Point °C °C / s °C / s °C % °C 61 0 1250 880 180 31 550 56 811 15 62 1250 880 120 30 550 56 807 27 63 1250 880 60 37 550 56 830 15 64 1250 880 35 35 550 56 806 15 65 P 1250 880 237 38 550 56 793 15 66 1250 880 235 34 550 56 807 15 67 1250 880 233 35 550 56 820 15 68 1250 880 238 31 550 56 814 7 69 Q 1250 880 241 32 550 56 802 30 70 1250 880 240 35 550 56 811 15 71 1250 880 241 33 550 56 834 15 72 1250 880 240 34 550 56 822 35 73 R 1250 880 246 36 550 56 789 15 74 1250 880 238 31 550 56 781 15 75 1250 880 237 32 550 56 805 15 76 1250 880 237 34 550 56 810 6 77 S 1250 880 235 37 550 56 787 15 78 1250 880 239 38 550 56 798 15 79 1250 880 242 35 550 56 81015 80 1250 880 243 39 550 56 794 15 81 T 1250 880 400 35 550 56 808 15 82 1250 880 140 34 550 56 819 15 83 1250 880 30 32 550 56 824 15 85 u 1250 880 1148 36 550 56 798 15 86 1250 880 500 32 550 56 789 15 87 1250 880 170 31 550 56 808 26 88 1250 880 35 30 550 56 804 15 89 V 1250 880 110 35 550 56 816 15 90 1250 880 70 37 550 56 827 15 91 1250 880 30 38 550 56 830 15 92 1250 880 1187 36 550 56 824 15 '1 Average cooling rate from the hot rolling finish temperature to 700°C. '2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. '3 Average cooling rate in the temperature range from the annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. Id 0) > B h C hcc 4 C ο ω μ μ -ι σι ο ω ο σι σι Continuation of Table 2-3 No. Annealing Coating Tempering Condition Average Cooling Rate*3 Cooling Stop Temperature Holding Temperature Holding Time Coating Type Plating Time Holding Temperature Holding Time °C / s CC ss °C s 61 29 150 170 150 Zn-Ni 230 Example 62 30 150 170 150 Zn-Ni 230 Example 63 29 150 170 150 Zn-Ni 260 Example 64 27 150 170 150 Zn-Ni 240 Comparative Example 65 28 150 150 80 Zn-Ni 230 Example 66 36 150 150 1840 Zn-Ni 230 Comparative Example 67 27 150 150 8 Zn-Ni 260 Comparative Example 68 30 150 150 600 Zn-Ni 230 Example 69 29 150 150 300 Zn-Ni 250 Example 70 28 150 150 1630 Zn-Ni 230 Comparative Example 71 29 150 150 7 Zn-Ni 230 Comparative Example 72 37 150 150 60 Zn-Ni 240 Example 73 30 150 150 1720 Zn-Ni 230 Comparative Example 74 29 150 150 6 Zn-Ni 230 Comparative Example 75 28 150 150 1200 Zn-Ni 260 Example 76 26 150 150 900 Zn-Ni 250 Example 77 28 150 150 1750 Zn-Fe 230 Comparative example 78 27 150 150 500Zn-Fe 230 Example 79 30 150 230 200 Zn-Fe 230 Comparative Example 80 29 150 80 400 Zn-Fe 240 Comparative Example 81 33 150 150 150 Zn-Fe 230 Example 82 27 150 150 150 Zn-Fe 230 Example 83 28 150 150 150 Zn-Fe 260 Comparative Example 85 30 150 150 150 Zn-Fe 230 100 120 Example 86 28 150 150 150 Zn-Fe 250 Example 87 29 150 150 150 Zn-Fe 230 Example 88 27 150 150 150 Zn-Fe 230 Comparative Example 89 28 150 150 150 Zn-Fe 260 Example 90 26 150 150 150 Zn-Fe 230 Example 91 29 150 150 150 Zn-Fe 240 Comparative Example 92 30 150 150 150 Zn-Fe 230 Example *1 Average cooling rate from hot rolling finish temperature to 70°C. *2 Average cooling rate from 700°C (primary cooling stop temperature) to 650°C. *3 Average cooling rate in the temperature range from annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. Tab ω ω M ro -> j Oí 0 Ü1 0 Ü1 0 a 2-4 üi C h C No. Steel Grade Hot Rolling Cold Rolling Annealing c 4 4 4 CM 00 Rough Heating Temperature Hot Rolling Finishing Temperature Average Cooling Rate to 701TC'' Average Cooling Rate to 65ÍC'2 Rolling Temperature Reduction by Rolling Annealing Temperature Dew Point “C °C “C / s °C / s °C % °C °c 93 W 1250 880 130 35 550 56 760 15 94 1250 880 60 38 550 56 779 15 95 1250 880 15 35 550 56 790 15 96 1250 880 120 34 550 56 783 15 97 X 1250 880 238 1124 550 56 776 15 98 1250 880 237 160 550 56 798 15 99 1250 880 234 1 550 56 805 15 100 1250 880 241 48 550 56 788 15 101 Y 1250 880 246 71 550 56 808 15 102 1250 880 242 1 550 56 804 15 103 1250 880 236 34 550 56 806 27 104 1250 880 235 41 550 56 813 5 105 z 1250 880 233 75 550 56 804 15 106 1250 880 232 90 550 56 814 15 107 1250 880 228 840 550 56 823 15 108 1250 880 229 1 550 56 805 15 109 AA 1250 880 22734 550 56 808 •5 110 1250 880 230 32 550 56 812 15 111 1250 880 229 31 550 56 825 15 112 1250 880 225 30 550 56 806 15 113 AB 1250 880 234 35 550 56 790 15 114 1250 880 236 38 550 56 793 15 115 1250 880 228 37 550 56 809 30 116 1250 880 229 35 550 56 795 15 117 AC 1250 880 230 36 550 56 783 15 118 AD 1250 880 240 35 550 56 874 15 119 AE 1250 880 231 34 550 56 882 15 120 AF 1250 880 242 36 550 56 884 15 121 AG 1250 880 250 33 550 56 820 15 122 AH 1250 880 237 32 550 56 830 15 123 A! 1250 880 240 35 550 56 929 15 124 AJ 1250 880 245 35 550 56 802 15 125 AK 1250 880 237 36 550 56 816 15 126 AL 1250 880 239 30 550 56 807 15 '1 Average cooling rate from the hot rolling finish temperature to 70°C. *2 Average slow cooling rate from 700°C (primary cooling stop temperature) to 650°C. '3 Average cooling rate in the temperature range from the annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. ω ω μ μ I heard O Ü1 O -1 -1 σι ο Continuation of Table 2-4 No. Annealing Coating Tempering Condition Average Cooling Rate'3 Cooling Stop Temperature Holding Temperature Holding Time Coating Type Plating Time Holding Temperature Holding Time 'C / s °C °C ss °C s 93 28 150 150 150 Zn-Fe 250 150 20 Example 94 32 150 150 150 Zn-Fe 230 150 150 Example 95 29 150 150 150 Zn-Fe 230 Comparative Example 96 28 150 150 150 Zn-Fe 230 Example 97 29 150 150 150 Zn-Ni 230 Example 98 27 150 150 150 Zn-Ni 250 Example 99 28 150 150 150 Zn-Ni 230 Comparative Example 190 28 150 150 150 Zn-Ni 230 Example 101 30 150 150 150 Zn-Ni 240 Example 102 29 150 150 150 Zn-Ni 230 Comparative Example 103 27 150 150 150 Zn-Ni 260 Example 104 26 150 150 150 Zn-Ni 230 Example 105 34 150 150 150 Zn-Ni 250 Example 106 27 150 150 150 Zn-Ni 230 Example 107 30 150 150 150 Zn-Ni 230 Example 108 28 150 150 150 Zn-Ni 260 Comparative Example 109 29 150 150 150 Zn-Ni 230 Example 110 31 270 120 150 Zn-Ni 240 Example111 27 320 120 150 Zn-Ni 230 Example 112 27 370 200 150 Zn-Ni 250 Comparative Example 113 30 150 200 150 Zn-Ni 230 Example 114 29 360 200 150 Zn-Ni 260 Comparative Example 115 28 300 200 150 Zn-Ni 230 Example 116 33 150 200 150 Zn-Ni 230 Example 117 29 150 150 150 Zn-Ni 240 Comparative Example 118 27 150 150 150 Zn-Ni 230 Comparative Example 119 30 150 150 150 Zn-Ni 230 Comparative Example 120 28 150 150 150 Zn-Ni 230 Comparative Example 121 29 150 150 150 Zn-Ni 230 Comparative Example 122 30 150 150 150 Zn-Ni 230 Comparative Example 123 28 150 150 150 Zn-Ni 230 Comparative Example 124 27 150 150 150 Zn-Ni 230 Comparative Example 125 26 150 150 150 Zn-Ni 230 Comparative Example 126 30 150 150 150 Zn-Ni 230 Comparative Example Ί Average cooling rate from hot rolling finish temperature to 7C0'C. *2 Average cooling rate from 700cC (primary cooling stop temperature) to 650'C. *3 Average cooling rate in the temperature range from annealing temperature to 550°C. The underlined values ​​are outside the scope of the present invention. > B h C hcc 4 4 C 2. Evaluation Method With respect to the electrolytic zinc-coated steel sheets produced under various manufacturing conditions, the microstructure fractions were examined using steel microstructure analysis. Tensile characteristics, such as tensile strength, were evaluated by performing a tensile test. Flexural strength was assessed by a bending test. The evaluation methods are described below. (Percentage of Total Area of ​​One or Two of between Martensite Containing Carbide Having Average Particle Size of 50 nm or Less and Bainite Containing Carbide Having Average Particle Size of 50 nm or Less) A specimen was taken from a portion of each of the electro-zinc-coated steel sheets in the rolling direction and in a direction perpendicular to the rolling direction. An L-shaped cross-section extending in the thickness direction and parallel to the rolling direction was mirror-polished, chemically etched with Nital to reveal the microstructures, and observed using a scanning electron microscope. The percentage area of ​​each martensite and bainite was examined using a dot-counting method in which a 16 × 15 dot grid at 4.8 µm intervals was placed on a region measuring 82 µm × 57 µm in actual length of a 1,500x SEM image, and the dots in each phase were counted.The area percentage of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less throughout the microstructure was defined as the average value of their area percentages from SEM images obtained by continuous observation of the entire cross-section in the thickness direction at a magnification of x1,500.The area percentage of martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less in a region extending from a base steel sheet surface to a depth of 1 / 8 of the base steel sheet thickness was defined as the average value of their area percentages from SEM images obtained by continuous observation of the region extending from the base steel sheet surface to a depth of 1 / 8 of the base steel sheet thickness at a magnification of *1,500. Martensite and bainite appear as white microstructures in which blocks and bundles are revealed within the grain boundaries of pre-austenite and fine carbides precipitate therein.One problem can arise in revealing the carbides within the blocks, depending on the crystallographic orientation of a block grain and the degree of chemical etching. In such cases, sufficient chemical etching must be performed and verified. The average particle size of the carbides in martensite and bainite was calculated using a method described below. (Average Particle Size of Carbide in Martensite and Bainite) A test specimen was taken from a portion of each of the steel sheets coated with electrolytic zinc in the rolling direction and in a direction perpendicular to the rolling direction. An L-shaped cross-section extending in the thickness direction and in a direction parallel to the rolling direction was mirror polished and chemically etched with QfrMrnn / Lznz / e / YiAi Nital was used to reveal the microstructures, and the sample was observed using a scanning electron microscope. The number of carbides in pre-austenite grains containing martensite and bainite was calculated from a SEM image obtained by continuous observation of the region extending from the surface of the base steel sheet to a depth of 1 / 8 of the base steel sheet thickness at 5,000x magnification. The total carbide area in a grain was calculated by binarizing the microstructure. The area of ​​a carbide particle was calculated from the number and total carbide area. The average particle size of the carbides in the region extending from the surface of the base steel sheet to a depth of 1 / 8 of the base steel sheet thickness was calculated.One method for measuring the average particle size of carbides throughout the microstructure is as follows: A point located at a depth of 1 / 4 of the thickness of the base steel sheet was observed using a scanning electron microscope. The average particle size of carbides throughout the microstructure was then measured in the same way as the method for calculating the average particle size of carbides in the region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet. Here, the microstructure located at a depth of 1 / 4 of the thickness of the base steel sheet is considered to be the average microstructure of the entire microstructure. (Total Perimeter of Carbide Particles Having an Average Particle Size of 50 nm or Less) The total perimeter of individual carbide particles having an average particle size of 50 nm or less in martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less present in the region extending from the surface of the base steel sheet to a depth of 1 / 8 of the thickness of the base steel sheet was determined as follows: With respect to individual carbide particles having an average particle size of 50 nm or less in martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less present in the region,The perimeters of individual carbide particles were calculated by multiplying the average particle size of the individual carbide particles by the circular constant π. The average of the resulting perimeters was determined. The total perimeter was determined by multiplying the average by the number of carbide particles with an average particle size of 50 nm or less. The average particle size of individual carbide particles is defined as the average value of the long and short axis lengths of the carbide particle images when the microstructure was binarized as described above. (Tensile Test) JIS No. 5 test specimens having a gauge length of 50 mm, a gauge width of 25 mm, and a thickness of 1.4 mm were taken from the electrolytic zinc-coated steel sheets in the rolling direction and subjected to a tensile test at a crosshead speed of 10 mm / min to measure breaking stress (TS) and elongation (El). (Bending Test) Bend specimens, 25 mm wide and 100 mm long, were taken from electrolytic zinc-coated steel sheets such that the rolling direction was the bending direction. The specimens were tested (n = 3) using a press bending method in accordance with JIS Z 2248 at a pressing speed of 100 mm / s and at various bend radii. A bend radius at which no crack formed in three specimens was defined as the limit bend radius. The evaluation was based on the ratio of the limit bend radius to the thickness of the steel sheet. The presence or absence of a crack was verified by observing the outer sides of the bent portions using a magnifying glass with 30x magnification.In cases where no cracks formed along a 25 mm width of each specimen, or where a maximum of five microcracks formed with a length of 0.2 pm or less along a 25 mm width of each specimen, the specimen was considered crack-free. The evaluation criterion for flexural strength was as follows: limit bending radius / thickness (R / t) < 4.0. (Hydrogen Analysis Method) A strip-shaped plate with a long axis length of 30 mm and a short axis length of 5 mm was taken from the central portion of each of the electrolytic zinc-coated steel sheets in the width direction. The coating on the strip surfaces was completely removed using a hand-held grinder. Hydrogen analysis was performed using a thermal desorption spectroscopy system at a temperature increase rate of 200°C / h. Note that the hydrogen analysis was carried out immediately after the strip-shaped plate was taken and the coating was subsequently removed. The cumulative amount of hydrogen released from an initial heating temperature of 25°C to 200°C was measured and used as the amount of diffusible hydrogen in the QfrMrnn / Lznz / e / YiAi steel. 3. Evaluation Result Tables 3-1 to 3-4 present the evaluation results. αίτΜτηη / Lznz / e / viAi Table 3-1 No. Steel Grade Steel Microstructure Mechanical Properties TM + B'1 TM + B'2 in surface layer portion Total perimeter of fine carbide 3 Amount of diffusible hydrogen in steel TS TS x R / t % % μm / mm2 ppm by mass MPa % MPa-% 1 A 97 87 67 0.03 1840 7.8 14352 3.1 Example 2 96 88 61 0.07 1830 7.7 14091 3.6 Example 3 97 88 64 0.06 1840 7.7 14168 3.3 Example 4 95 90 63 0.29 1810 7.6 13756 4.2 Comparative Example 5 97 87 67 0.17 1820 7.8 14196 3.5 Example 6 97 92 66 0.16 1830 7.7 14091 3.2 Example 7 98 80 55 0.13 1840 7.7 14168 3.4 Example 8 96 77 48 0.18 1820 7.8 14196 4.1 Comparative Example 9 B 93 88 60 0.19 1570 8.7 13659 3.5 Example 10 92 83 66 0.16 1560 8.7 13572 3.6 Example 11 93 84 55 0.20 1570 8.7 13659 3.3 Example 12 94 89 43 0.15 1580 8.7 13746 4.5 Comparative Example 13 C 93 87 61 0.16 1580 8.6 13588 3.6 Example 14 93 85 64 0.09 1580 8.6 13588 3.2 Example 15 92 87 51 0.10 1570 8.7 13659 3.8 Example 16 93 78 45 0.07 1580 8.7 13746 4.7 Comparative Example 17 D 97 91 64 0.02 1830 7.8 14274 3.6 Example 18 98 93 69 0.05 1840 7.7 14168 3.5 Example 19 98 81 52 0.08 1840 7.7 14168 3.8 Example 20 96 77 47 0.13 1820 7.8 14196 4.4 Comparative Example 21 E 99 91 56 0.11 2020 7.4 14948 3.4 Example 22 99 93 55 0.18 2010 7.4 14874 3.7 Example 23 98 81 64 0.17 2000 7.4 14800 3.7 Example 24 99 77 58 0.10 2030 7.3 14819 4.5 Comparative Example 25 F 97 89 52 0.18 1950 7.5 14625 3.4 Example 26 97 91 51 0.17 1950 7.5 14625 3.2 Example 27 98 89 53 0.18 1960 7.5 14700 3.3 Example 28 98 90 51 0.10 1960 7.4 14504 3.5 Example 29 G 96 86 68 0.18 1880 7.6 14288 3.2 Example 30 94 87 65 0.06 1860 7.7 14322 3.4 Example 31 91 84 67 0.10 1820 7.8 14196 3.6 Example 32 88 74 65 0.32 1740 7.9 13746 4.5 Comparative example. * 1 The percentage of total area of ​​martensite (TM) containing a carbide having an average particle size of 50 nm or less and bainite (B) containing a carbide having an average particle size of 50 nm or less throughout the microstructure. * 2 The percentage of total area of ​​TM that contains a carbide having an average particle size of 50 nm or less and B that contains a carbide having an average particle size of 50 nm or less in a region extending from a surface to a depth of 1 / 8 of the sheet thickness (surface layer portion). * 3 The total perimeter of carbide particles having an average particle size of 50 nm or less in TM containing a carbide having an average particle size of 50 nm or less and B containing a carbide having an average particle size of 50 nm or less present in the surface layer portion. The underlined values ​​are outside the scope of the present invention. Table 3-2 αίτΜτηη / Lznz / e / YiAi No. Steel Grade Steel Microstructure Mechanical Properties TM+ B'1 TM + B'2 in surface layer portion Total perimeter of fine carbide '3 Amount of diffusible hydrogen in steel TS The TSxEI R / t % % pm / mm2 ppm by mass MPa % MPa-% 33 H 92 84 70 0.13 1400 9.4 13160 3.3 Example 34 91 84 68 0.13 1410 9.4 13254 3.4 Example 35 90 83 60 0.18 1360 9.6 13056 3.0 Example 36 84 79 61 0.24 1290 9.8 12642 4.2 Comparative Example 37 I 92 76 48 0.15 1590 8.6 13674 4.8 Comparative Example 38 92 81 51 0.05 1580 8.7 13746 3.2 Example 39 93 84 60 0.14 1600 8.6 13760 3.5 Example 40 92 85 53 0.11 1580 8.7 13746 3.7 Example 41 J 99 75 45 0.16 2150 7.1 15265 4.1 Comparative Example 42 97 96 69 0.16 2160 7.1 15336 3.2 Example 43 97 96 58 0.09 2160 7.1 15336 3.3 Example 44 98 96 45 0.05 2140 7.1 15194 4.3 Comparative example 45 K 97 82 42 0.16 1850 7.7 14245 4.2 Comparative example 46 98 82 54 0.20 1860 7.7 14322 3.8 Example 47 97 83 66 0.09 1850 7.7 14245 3.3 Example 48 96 78 42 0.14 1830 7.8 14274 4.4 Comparative Example 49 L 99 84 56 0.10 1960 7.5 14700 3.5 Example 50 99 82 64 0.11 1960 7.5 14700 3.6 Example 51 98 81 60 0.06 1980 7.4 14652 3.8 Example 52 98 68 41 0.19 1970 7.5 14775 4.1 Comparative Example 53 M 98 93 62 0.09 1900 7.6 14440 3.1 Example 54 97 89 57 0.16 1890 7.6 14364 3.7 Example 55 99 82 54 0.17 1910 7.6 14516 3.4 Example 56 98 78 46 0.15 1900 7.6 14440 4.4 Comparative example 57 N 99 93 64 0.21 1910 7.4 14134 4.2 Comparative example 58 98 91 65 0.22 1880 7.5 14100 4.3 Comparative example 59 99 91 60 0.09 1890 7.6 14364 3.2 Example 60 99 92 68 0.06 1900 7.8 14820 3.0 Example. * 1 The percentage of total area of ​​martensite (TM) containing a carbide having an average particle size of 50 nm or less and bainite (B) containing a carbide having an average particle size of 50 nm or less throughout the microstructure. * 2 The percentage of total area of ​​TM that contains a carbide having an average particle size of 50 nm or less and B that contains a carbide having an average particle size of 50 nm or less in a region extending from a surface to a depth of 1 / 8 of the sheet thickness (surface layer portion). * 3 The total perimeter of carbide particles having an average particle size of 50 nm or less in TM containing a carbide having an average particle size of 50 nm or less and B containing a carbide having an average particle size of 50 nm or less present in the surface layer portion. The underlined values ​​are outside the scope of the present invention. ω σι Μ σι μ ο σι σι Table 3-3 No. Grade of Steel Microstructure of Steel Mechanical Properties TH+B'' TMW Portion of Surface Layer Total Perimeter Carbide'3 Amount of Diffusible Hydrogen in Steel TS The TSxEI R / t % % pmmm2 ppminmass MPa % MPa% ¢1 0 98 95 66 0.17 1960 7.5 14700 3.7 Example 62 99 91 61 0.11 1950 7.5 14625 3.0 Example 63 99 82 53 0.15 1940 7.5 14550 3.6 Example 64 99 78 45 0.09 1950 7.5 14625 42 Comparative Example 65 P 92 82 60 0.03 1670 8.3 13861 3.7 Example 66 94 11 45 0.09 1690 8.4 14196 42 Comparative example 67 92 82 42 0.02 1670 8.3 13861 42 Comparative example 68 93 87 64 0.18 1680 8.2 13776 3.8 Example 69 Q 96 86 66 0.06 1830 7.8 14274 3.0 Example 70 95 78 43 0.07 1820 7.8 14196 43 Comparative example 71 97 91 49 0.06 1840 7.7 14168 43 Comparative example 72 97 88 67 0.06 1830 7.8 14274 3.0 Example 73 R 94 11 49 0.08 1750 8.0 14000 46 Comparative example 74 95 85 45 0.04 1760 8.0 14080 45 Comparative example 75 92 86 69 0.12 1710 8.2 14022 3.6 Example 76 93 84 60 0.04 1730 8.1 14013 3.9 Example 77 S 93 11 47 0.09 1760 8.0 14080 43 Comparative Example 78 93 85 57 0.07 1750 8.0 14000 3.6 Example 79 94 79 48 0.18 1760 8.0 14080 £1 Comparative Example 80 92 86 46 0.06 1730 8.1 14013 42 Comparative Example 81 T 94 89 62 0.05 1800 7.8 14040 3.3 Example 82 95 90 61 0.06 1810 7.8 14118 3.2 Example 83 93 11 48 0.01 1790 7.8 13962 £1 Comparative Example 85 u 96 91 63 0.16 1890 7.6 14364 3.3 Example 86 98 91 55 0.10 1920 7.6 14592 3.2 Example 87 96 89 67 0.15 1900 7.6 14440 3.0 Example 88 97 77 45 0.15 1900 7.6 14440 44 Comparative Example 89 V 96 89 69 0.03 1840 7.7 14168 3.5 Example 90 95 81 53 0.16 1830 7.7 14091 3.2 Example 91 95 ζθ 48 0.02 1830 7.7 14091 43 Comparative example 92 96 90 55 0.04 1840 7.7 14168 3.7 Example. *1 The percentage of total area of ​​martensite (TM) containing a carbide having an average particle size of 50 nm or less and bainite (B) containing a carbide having an average particle size of 50 nm or less throughout the microstructure. *2 The percentage of total area of ​​TM containing a carbide having an average particle size of 50 nm or less and B containing a carbide having an average particle size of 50 nm or less in a region extending from a surface to a depth of 1 / 8 of the sheet thickness (surface layer portion), '3 The total perimeter of carbide particles having an average particle size of 50 nm or less in TM containing a carbide having an average particle size of 50 nm or less and B containing a carbide having an average particle size of 50 nm or less present in the surface layer portion. The underlined values ​​are outside the scope of the present invention. oh He / She > B h C hcc 4 4 C o o m o s i o s i M -i o si o si Table 3-4 No. Steel Grade Steel Microstructure Mechanical Properties TM+B'1 TM+B'2 in surface layer portion Total perimeter of fine Carbide'3 Diffusible Hydrogen Content in Steel TS The TSxEI Rt % % pm / mm2 ppm by mass MPa % MP3·% 93 W 99 91 59 0.14 2130 7.1 15123 3.4 Example 94 99 82 53 0.12 2110 7.2 15192 3.5 Example 95 99 78 45 0.10 2090 7.2 15048 44 Comparative Example 96 99 96 65 0.03 2140 7.1 15194 3.5 Example 97 X 99 95 70 0.08 2060 7.3 15038 3.4 Example 98 99 90 70 0.02 2040 7.3 14892 3.4 Example 99 99 78 45 0.18 2050 7.3 14965 42 Comparative Example 100 99 91 61 0.03 2040 7.3 14892 3.6 Example 101 and 99 92 66 0.16 1930 7.5 14475 3.5 Example 102 99 77 43 0.06 1940 7.5 14550 43 Comparative Example 103 99 89 68 0.16 1930 7.5 14475 3.0 Example 104 98 93 68 0.10 1920 7.6 14592 3.8 Example 105 z 97 91 59 0.02 1840 7.7 14168 3.4 Example 106 96 88 55 0.13 1820 7.8 14196 3.5 Example 107 97 91 65 0.07 1830 7.7 14091 3.6 Example 108 95 76 46 0.11 1800 7.8 14040 44 Comparative Example 109 AA 94 86 67 0.20 1800 7.8 14040 3.9 Example 110 96 88 57 0.14 1820 7.8 14196 3.6 Example 111 96 89 56 0.08 1820 7.8 14196 3.6 Example 112 95 77 49 0.16 1810 7.8 14118 42 Comparative Example 113 AB 97 89 61 0.15 1820 7.8 14196 3.6 Example 114 96 91 45 0.15 1810 7.8 14118 43 Comparative Example 115 95 86 61 0.03 1800 7.8 14040 3.0 Example 116 95 85 64 0.10 1800 7.8 14040 3.3 Example 117 AC 98 96 65 0.12 2230 65 14495 3.4 Comparative Example 118 AD 83 74 67 0.24 1480 9.0 13320 44 Comparative Example 119 AE 94 89 41 122 1770 7.9 13983 42 Comparative Example 120 AF 93 78 45 0.05 1310 9.8 12838 44 Comparative Example 121 AG 94 79 60 0.20 1770 7.9 13983 47 Comparative example 122 AH 93 78 67 0.03 1760 8.0 14080 44 Comparative example 123 Al 93 87 44 0.10 1700 8.2 13940 44 Comparative example 124 AJ 96 89 47 0.18 1910 7.6 14516 44 Comparative example 125 AK 98 92 48 0.16 1830 7.9 14457 11 Comparative example 126 AL 94 79 66 0.03 1700 8.2 13940 11 Comparative example. *1 The percentage of total area of ​​martensite (TM) containing a carbide having an average particle size of 50 nm or less and bainite (B) containing a carbide having an average particle size of 50 nm or less throughout the microstructure > B h C hcc 4 4 C *2 The percentage of total area of ​​TM that contains a carbide having an average particle size of 50 nm or less and B that contains a carbide having an average particle size of 50 nm or less in a region extending from a surface to a depth of 1(8 of the sheet thickness (surface layer portion). *3 The total perimeter of carbide particles having an average particle size of 50 nm or less in TM containing a carbide having an average particle size of 50 nm or less and B containing a carbide having an average particle size of 50 nm or less present in the surface layer portion. The underlined values ​​are outside the scope of the present invention. In the examples, a steel sheet that satisfies TS > 1,320 MPa, El > 7.0%, TS x El > 12,000, and R / t < 4.0 was deemed acceptable and is presented as an “Example” in Tables 3-1 to 3-4. A steel sheet that does not satisfy at least one of TS > 1,320 MPa, El > 7.0%, TS x El > 12,000, and R / t < 4.0 was deemed unacceptable and is presented as a “Comparative Example” in Tables 3-1 to 3-4. The underlines in Tables 1 to 3-4 indicate that the requirements, production conditions, and properties of the present invention are not met.

Claims

I. A high-strength, high-ductility electrolytic zinc-coated steel sheet characterized in that it comprises an electrolytic zinc-based coating on a surface of a base steel sheet, wherein the base steel sheet has a component composition containing, on a mass percentage basis, C: 0.12% or more and 0.40% or less, Si: 0.001% or more and 2.0% or less, Mn: 1.7% or more and 5.0% or less, P: 0.050% or less, S: 0.0050% or less, Al: 0.010% or more and 0.20% or less, N: 0.010% or less, and Sb: 0.002% or more and 0.10% or less, the remainder being Fe and incidental impurities; and a steel microstructure in which a total area percentage of one or two of either martensite containing a carbide having an average particle size of 50 nm or less and bainite containing a carbide having an average particle size of 50 nm or less is 90% or more throughout the steel microstructure,a total area percentage of one or two of the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less is 80% or more in a region extending from the surface of the base steel sheet to a depth of 1 / 8 of a thickness of the base steel sheet, and a total perimeter of individual carbide particles having an average particle size of 50 nm or less in the martensite containing a carbide having an average particle size of 50 nm or less and the bainite containing a carbide having an average particle size of 50 nm or less present in the region is 50 pm / mm2 or more, wherein an amount of diffusible hydrogen in the steel is 0.20 ppm by mass or less.

2. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to claim 1, further characterized in that the component composition additionally contains, on a mass percentage basis: B: 0.0002% or more and less than 0.0035%.

3. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to claim 1 or 2, further characterized in that the component composition additionally contains, on a mass percentage basis, one or two selected from: Nb: 0.002% or more and 0.08% or less, and Ti: 0.002% or more and 0.12% or less.

4. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to any of claims 1 to 3, further characterized in that the component composition additionally contains, on a mass percentage basis, one or two selected from: QfrMrnn / Lznz / e / YiAi Cu: 0.005% or more and 1% or less, and Ni: 0.01% or more and 1% or less.

5. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to any of claims 1 to 4, further characterized in that the component composition additionally contains, on a mass percentage basis, one or two or more selected from: Cr: 0.01% or more and 1.0% or less, Mo: 0.01% or more and less than 0.3%, V: 0.003% or more and 0.5% or less, Zr: 0.005% or more and 0.2% or less, and W: 0.005% or more and 0.2% or less.

6. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to any of claims 1 to 5, further characterized in that the component composition additionally contains, on a mass percentage basis, one or two or more selected from: Ca: 0.0002% or more and 0.0030% or less, Ce: 0.0002% or more and 0.0030% or less, La: 0.0002% or more and 0.0030% or less, and Mg: 0.0002% or more and 0.0030% or less.

7. The high-strength, high-ductility electrolytic zinc-coated steel sheet according to any of claims 1 to 6, further characterized in that the component composition additionally contains, on a mass percentage basis: Sn: 0.002% or more and 0.1% or less.

8. A method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet, characterized in that it comprises: a hot rolling step for hot rolling a steel block having the component composition described in any one of claims 1 to 7 to a block heating temperature of 1,200°C or higher and a hot-roll finish temperature of 840°C or higher, carrying out cooling to a primary cooling stop temperature of 700°C or lower at an average cooling rate of 40°C / s greater in a temperature range from the hot-roll finish temperature to 700°C, carrying out cooling at an average cooling rate of 2°C / s greater in a temperature range from the primary cooling stop temperature to 650°C, carrying out cooling to a coiling temperature of 630°C or lower,and carry out coiling; an annealing step of heating a steel sheet after the hot rolling step to an annealing temperature equal to or greater than point ACs or carrying out heating to an annealing temperature equal to or greater than point AC3 and carrying out temperature holding, carrying out cooling to a cooling stop temperature of 350°C or less at an average cooling rate of 3°C / s greater in a temperature range from the annealing temperature to 550°C, and carrying out holding at a holding temperature in a temperature range of 100°C to 200°C for 20 to 1,500 seconds; and a coating treatment step of cooling the steel sheet after the annealing step to room temperature and subjecting the steel sheet to electrolytic zinc-based coating for an electrodeposition time of 300 seconds or less.

9. The method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet according to claim 8, further characterized in that it additionally comprises, after the hot rolling stage, a cold rolling stage for cold rolling the steel sheet between the hot rolling stage and the annealing stage.

10. The method for producing a high-strength, high-ductility electrolytic zinc-coated steel sheet according to claim 8 or 9, further comprising an tempering step for retaining the steel sheet after the coating treatment step at a temperature range of 250°C or lower for a retention time t satisfying formula (1) below: (T + 273)(log t + 4) < 2,700 (1) where in formula (1), T is a retention temperature (°C) in the tempering step, and t is the retention time (s) in the tempering step.