Hot-dip galvanized steel sheet and its manufacturing method, as well as a component and its manufacturing method, and a frame structure component or reinforcing component of an automobile made from said component.

Abstract

The purpose of the present invention is to provide: a hot-dip galvanized steel sheet that has a high YR, has high stretch-flangeability and bendability immediately after production, and has improved trim edge quality; a production method for the hot-dip galvanized steel sheet; and a member.　A hot-dip galvanized steel sheet according to the present invention comprises a parent material steel sheet and a hot-dip galvanized layer that is at the surface of the parent material steel sheet. The parent material steel sheet has a prescribed component composition. At 1 / 4 of the sheet thickness thereof, the parent material steel sheet has a microstructure that has an area percentage of martensite of at least 30%, an area percentage of ferrite of no more than 70%, and a volume percentage of retained austenite of no more than 20.0%. The amount of hydrogen diffusible in a low-temperature range, which is the amount of hydrogen released from the parent material steel sheet when the parent material steel sheet is heated from room temperature to 50°C at 24 hours after the production of the hot-dip galvanized steel sheet, is no more than 0.015 mass ppm. The density of cracks that pass through the hot-dip galvanized layer is at least 30 / mm. The full width at half maximum of a δ1 phase of the hot-dip galvanized layer is at least 0.100.

Description

Technical Field

[0001] The present invention relates to a hot-dip galvanized steel sheet, a method for producing the same, a member and a method for producing the same, and a skeletal structure part or a reinforcing part of an automobile made of the member.

Background Art

[0002] In order to achieve both reduction of CO2 emissions by vehicle weight reduction and improvement of collision resistance performance by vehicle body weight reduction, the strength of steel sheets for automobiles has been increasing. In addition, new regulations have been introduced one after another. Therefore, for the purpose of increasing the vehicle body strength, the application cases of high-strength steel sheets for main structural parts and reinforcing parts (hereinafter also referred to as skeletal structure parts of automobiles, etc.) that form the skeleton of an automobile cabin are increasing. In particular, the application cases of high-strength steel sheets with a tensile strength (hereinafter also simply referred to as TS) of 980 MPa or more are increasing.

[0003] In addition, high-strength steel sheets used for skeletal structure parts of automobiles, etc. are required to have high part strength when formed into skeletal structure parts of automobiles, etc. Regarding the increase in part strength, for example, it is effective to increase the yield ratio of the steel sheet (= YS / TS×100, hereinafter also simply referred to as YR). Thereby, the impact absorption energy (hereinafter also simply referred to as impact absorption energy) at the time of an automobile collision increases.

[0004] Furthermore, among skeletal structure parts of automobiles, etc., for example, a crash box has a punched end face and a bent portion. Therefore, for such parts, from the viewpoint of formability, it is preferable to apply a steel sheet having high elongation flangeability and bendability. In addition, since the elongation flangeability and bendability are inspected immediately after production, it is necessary to guarantee the elongation flangeability and bendability immediately after production.

[0005] In addition, from the viewpoint of vehicle body rust prevention performance, a hot-dip galvanized steel sheet obtained by applying hot-dip galvanization may be applied to the steel sheet used as a material for skeletal structure parts of automobiles, etc.

[0006] As an example of technology relating to such hot-dip galvanized steel sheets, Patent Document 1 describes a high-strength hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer formed on the surface of the base steel sheet, having a tensile strength of 780 MPa or more, wherein the base steel sheet contains, by mass%, C: 0.050% to 0.200%, Si: 0.10% to 0.90%, Mn: 2.00% to 3.50%, P: 0.001% to 0.100%, S: 0.0200%, Al: 1.000%, N: 0.0100%, Ca: 0.0200%, and Cr: 0.300%, and satisfies the relationship [%Mn] / [%Si] of 2.9 to 11.7. A high-strength hot-dip galvanized steel sheet is disclosed, having a composition in which the remainder consists of Fe and unavoidable impurities, with one or two selected from the group consisting of bainite and ferrite accounting for a total area ratio of 5% to 85%, the area ratio of tempered martensite being 65% or less, the area ratio of quenched martensite being 5% to 40%, and the area ratio of retained austenite being 5.0% or less, the ratio of Si enrichment to Mn enrichment in the surface layer of the base steel sheet being 0.7 to 1.3, and the amount of diffusible hydrogen in the base steel sheet being 0.80 mass ppm or less. However, [%Mn] and [%Si] represent the Mn and Si content (mass%) in the steel, respectively. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6777267 [Overview of the project] [Problems that the invention aims to solve]

[0008] In a continuous annealing line, the edges of the coils are trimmed at the exit of the production line, so a stable trim edge is required. However, the hot-dip galvanized steel sheet described in Patent Document 1 does not take into consideration the quality of the trim edge. Furthermore, in the production of hot-dip galvanized steel sheets, immediately after production, that is, when the sheet is wound into a coil at the exit of the continuous annealing line, a large amount of diffusible hydrogen is contained in the steel sheet, and this amount of diffusible hydrogen decreases over time at room temperature. Therefore, from immediately after production until 24 hours have passed, the amount of diffusible hydrogen in the steel sheet is high, making it difficult to obtain high elongation flangeability and bendability, and a stable trim edge may not be obtained.

[0009] Therefore, from the perspective of increasing the application rate of hot-dip galvanized steel sheets, particularly for automotive structural components, there is a need for the development of hot-dip galvanized steel sheets that have a high YR (Yield Rate), excellent elongation flange properties and bendability immediately after manufacturing, and improved trim edge quality.

[0010] The present invention was developed in view of the above-mentioned circumstances, and aims to provide a hot-dip galvanized steel sheet that has a high YR, high elongation flangeability and high bendability immediately after manufacturing, and improved trim edge quality.

[0011] Furthermore, the present invention aims to provide a method for manufacturing the hot-dip galvanized steel sheet described above. Moreover, the present invention aims to provide a component made using the hot-dip galvanized steel sheet described above.

[0012] Here, "high YR" means that the YR is 55% or higher. YR is calculated using the following equation (1). YR = YS / TS × 100 ... (1) Furthermore, TS and YS will be measured in accordance with JIS Z 2241, respectively. "High elongation flange properties immediately after manufacturing" means that the hole expansion ratio (hereinafter simply referred to as λ), measured in accordance with JIS Z 2256, is 30% or more when measured 24 hours after manufacturing.

[0013] "High bendability immediately after manufacturing" means that the crack length at the edge of the bending apex of all samples after a bending test conducted in accordance with JIS Z 2248 (see the example below for details) is 200 μm or less when measured 24 hours after manufacturing. This is determined by performing a bending test using the V-block method with a bending angle of 90 degrees. Here, the bending test is performed on 5 samples at an R where the value R / t (bending radius (R) divided by plate thickness (t)) is approximately 4.5, i.e., 4.3 to 4.7. Next, the crack length at the edge of the bending apex of all 5 samples is evaluated, and if the crack length of all samples is 200 μm or less, it is determined that the material has high bendability immediately after manufacturing.

[0014] "High trim edge quality" means that no cracks are observed in the trim edges described in the examples below. [Means for solving the problem]

[0015] The inventors diligently conducted research to achieve the above objectives. As a result, they obtained the following findings. (1) The base steel sheet is given a predetermined composition and a steel structure containing a certain amount of martensite (quenched martensite, tempered martensite, and bainite). This results in a high YR (Yield Rate). (2) By setting the number density of cracks penetrating the plating layer to 30 cracks / mm or more, and the full width at half maximum of the δ1 phase of the plating layer to 0.100 degrees or more, the amount of low-temperature diffusible hydrogen in the base steel sheet after 24 hours from manufacturing can be reduced. This makes it possible to obtain high elongation flange properties and bendability, and to improve the quality of the trim edge.

[0016] This invention was completed based on the above findings and further investigations. Specifically, the gist of this invention is as follows: [1] A hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer on the surface of the base steel sheet, wherein the base steel sheet has a composition in mass% of C: 0.030% or more and 0.500% or less, Si: 0.01% or more and 2.50% or less, Mn: 0.10% or more and 5.00% or less, P: 0.100% or less, S: 0.0200% or less, Al: 0.100% or less, N: 0.0100% or less and O: 0.0100% or less, with the remainder being Fe and unavoidable impurities, and the area ratio of martensite at the 1 / 4 thickness position of the base steel sheet is 30% or more. A hot-dip galvanized steel sheet having a microstructure in which the area fraction of ferrite is 70% or less and the volume fraction of retained austenite is 20.0% or less, the amount of low-temperature diffusible hydrogen, which is the amount of hydrogen released from the base steel sheet when the base steel sheet is heated from room temperature to 50°C 24 hours after the manufacture of the hot-dip galvanized steel sheet, is 0.015 ppm by mass or less, the number density of cracks penetrating the hot-dip galvanized layer is 30 cracks / mm or more, and the full width at half maximum of the δ1 phase of the hot-dip galvanized layer is 0.100 degrees or more. [2] The hot-dip galvanized steel sheet according to [1], wherein the component composition further contains, by mass%, at least one element selected from Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less, Co: 0.010% or less, Ni: 1.00% or less, Cu: 1.00% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, REM: 0.0100% or less, Zr: 0.100% or less, Te: 0.100% or less, Hf: 0.10% or less, and Bi: 0.200% or less. [3] The hot-dip galvanized steel sheet according to [1] or [2], wherein the hot-dip galvanized layer is an alloyed hot-dip galvanized layer. A component made of a hot-dip galvanized steel sheet as described in any of [4][1] to [3]. A skeletal structure part or a reinforcing part of an automobile, which is composed of the members described in [5][4]. A method for manufacturing a hot-dip galvanized steel sheet, comprising: hot-rolling a steel slab having the component composition described in [6][1] or [2] to obtain a hot-rolled steel sheet, then pickling the hot-rolled steel sheet to obtain a pickled sheet, then cold-rolling the pickled sheet with a cumulative reduction ratio of 20% or more and 75% or less to obtain a cold-rolled steel sheet, then annealing the cold-rolled steel sheet under the condition that the annealing temperature is 780 °C or higher, then performing a hot-dip galvanizing treatment on the cold-rolled steel sheet to obtain a galvanized steel sheet, then cooling the galvanized steel sheet under the condition that the average cooling rate in the temperature range of 250 °C or higher and 400 °C or lower is 1.0 °C / s or more, and then performing a process of imparting a uniaxial tensile strain amount of 0.1% or more on the surface layer of the galvanized steel sheet. The method for manufacturing a hot-dip galvanized steel sheet according to [6], wherein during the cooling of the galvanized steel sheet, heat is retained for 5 s or more in the temperature range of 100 °C or higher and 450 °C or lower, then cooled, and then the above-mentioned process is performed. The method for manufacturing a hot-dip galvanized steel sheet according to [6], wherein during the cooling of the galvanized steel sheet, cooling is stopped at a cooling stop point of 25 Celsius degrees or lower, then reheated to the temperature range of (cooling stop temperature + 50 °C) or higher and 450 °C or lower, heat is retained for 5 s or more in this temperature range, then cooled, and then the above-mentioned process is performed. The method for manufacturing a hot-dip galvanized steel sheet according to [6], wherein during the cooling of the galvanized steel sheet, cooling is stopped at a cooling stop point of 25 Celsius degrees or lower, then the above-mentioned process is performed, then reheated to the temperature range of (cooling stop temperature + 50 °C) or higher and 450 °C or lower, heat is retained for 5 s or more in this temperature range, and then cooled. The method for manufacturing a hot-dip galvanized steel sheet according to any one of [6] to [9], wherein an alloying treatment is performed on the steel sheet after the hot-dip galvanizing treatment. The method for manufacturing a hot-dip galvanized steel sheet according to any one of [6] to

[10] , wherein when performing cold rolling, the sheet passing speed of the final pass is 50 mpm or more. The method for manufacturing a member, comprising a step of performing at least one of forming processing or joining processing on the hot-dip galvanized steel sheet according to any one of [1] to [3] to obtain a member.

Advantages of the Invention

[0017] According to the present invention, a hot-dip galvanized steel sheet having a high YR, high elongation flangeability and bendability, and improved quality of trim edges can be obtained. This high YR provides high part strength when applied to the skeletal structure parts of automobiles.

[0018] In particular, since the hot-dip galvanized steel sheet of the present invention is excellent in various characteristics, it can be applied to skeletal structure parts of automobiles of various sizes and shapes. Thereby, it is possible to improve the fuel efficiency by reducing the vehicle body weight, and the industrial utility value is extremely large.

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described. Note that the present invention is not limited to the following embodiments.

[0020] Regarding the base steel sheet: First, the component composition of the base steel sheet of the hot-dip galvanized steel sheet according to an embodiment of the present invention will be described. In the component composition, the unit is “mass%” in all cases, but hereinafter, unless otherwise specified, it is simply indicated as “%”.

[0021] [C: 0.030% or more and 0.500% or less] Carbon (C) is one of the important basic components of steel, and in particular in this disclosure, it is an important element that affects the area fraction of martensite and ferrite, the volume fraction of retained austenite, and the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing. If the C content is less than 0.030%, the area fraction of martensite decreases and the area fraction of ferrite increases, making it difficult to achieve the desired YR. On the other hand, if the C content exceeds 0.500%, the fraction of martensite increases, and furthermore, the fraction of quenched martensite within the martensite increases, so the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing increases. As a result, λ and bendability decrease, and the quality of the trim edge also deteriorates. Therefore, the C content should be between 0.030% and 0.500%. Preferably, the C content should be 0.080% or more. Preferably, the C content should be 0.400% or less. More preferably, the C content should be 0.110% or more. The content of C shall more preferably be 0.350% or less.

[0022] [Si:0.01% or more and 2.50% or less] Si is one of the important basic components of steel, and in particular, in this disclosure, it is an element that affects the volume fraction of retained austenite because it suppresses carbide formation during annealing and promotes the formation of retained austenite. Furthermore, Si forms an internal oxide layer on the surface of the steel sheet and induces cracks in the plating when strain is applied to the surface of the plated steel sheet, so it is an important element that affects the number density of cracks penetrating the plating layer. To obtain these effects, the Si content should be 0.01% or more. On the other hand, if the Si content exceeds 2.50%, the volume fraction of retained austenite increases, which increases the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing, so λ and bendability decrease, and further deteriorates the quality of the trim edge. Therefore, the Si content should be 0.01% or more and 2.50% or less. The Si content is preferably 0.20% or more. The Si content is preferably 2.00% or less. The Si content is more preferably 0.25% or more. The Si content is more preferably 1.50% or less.

[0023] [Mn: 0.10% or more and 5.00% or less] Mn is one of the important basic components of steel, and in particular in this disclosure, it is an important element that affects the area fraction of martensite and ferrite, and the volume fraction of retained austenite. Furthermore, Mn forms an internal oxide layer on the surface of the steel sheet and induces cracks in the plating when strain is applied to the plating layer of plated steel sheets, thus it is an important element that affects the number density of cracks penetrating the plating layer. To obtain these effects, the Mn content should be 0.10% or more. On the other hand, if the Mn content exceeds 5.00%, the fraction of martensite increases, and furthermore, the fraction of quenched martensite within the martensite increases, so the amount of low-temperature diffusible hydrogen in the base steel sheet after 24 hours from manufacture increases. As a result, λ and bendability decrease, and the quality of the trim edge also deteriorates. Therefore, the Mn content should be 0.10% or more and 5.00% or less. The Mn content should preferably be 1.00% or more. The Mn content should preferably be 4.00% or less. The Mn content is more preferably 2.00% or more. The Mn content is more preferably 3.50% or less.

[0024] [P:0.100% or less] When phosphorus (P) is in excess, it segregates at the prior austenite grain boundaries, embrittles the grain boundaries, and reduces the ultimate deformability of the steel sheet, thus decreasing λ and bendability. Therefore, the P content should be 0.100% or less. Although there is no specific lower limit for the P content, since P is a solid solution strengthening element and can increase the strength of the steel sheet, it is preferable to have a content of 0.001% or more. Therefore, the P content should be 0.100% or less. The P content should preferably be 0.001% or more. The P content should preferably be 0.070% or less.

[0025] [S:0.0200% or less] S exists as a sulfide and reduces the ultimate deformability of steel, thus decreasing λ and bendability. Therefore, the S content must be 0.0200% or less. Although there is no specific lower limit for the S content, due to production technology constraints, it is preferable that the S content be 0.0001% or more. Therefore, the S content should be 0.0200% or less. The S content should preferably be 0.0001% or more. The S content should preferably be 0.0050% or less.

[0026] [Al:0.100% or less] If Al is in excess, the A3 transformation point rises, and a large amount of ferrite is included in the microstructure, making it difficult to achieve the desired YR. Therefore, the Al content must be 0.100% or less. Although there is no specific lower limit for the Al content, it is preferable that the Al content be 0.001% or more, as this suppresses carbide formation during continuous annealing and promotes the formation of retained austenite. Therefore, the Al content should be 0.100% or less. The Al content is preferably 0.001% or more. The Al content is preferably 0.050% or less.

[0027] [N:0.0100% or less] N exists as a nitride and reduces the ultimate deformability of the steel sheet, thus decreasing λ and bendability. Therefore, the N content must be 0.0100% or less. Although there is no specific lower limit for the N content, due to production technology constraints, it is preferable that the N content be 0.0005% or more. Therefore, the N content should be 0.0100% or less. The N content should preferably be 0.0005% or more. The N content should preferably be 0.0050% or less.

[0028] [O:0.0100% or less] O exists as an oxide and reduces the ultimate deformability of the steel sheet, thus decreasing λ and bendability. Therefore, the O content must be 0.0100% or less. Although there is no specific lower limit for the O content, due to production technology constraints, it is preferable that the O content be 0.0001% or more. Therefore, the O content should be 0.0100% or less. The O content should preferably be 0.0001% or more. The O content should preferably be 0.0050% or less.

[0029] The base steel sheet of a hot-dip galvanized steel sheet according to one embodiment of the present invention has a component composition containing the above elements, with the remainder being Fe and unavoidable impurities. Preferably, the base steel sheet according to one embodiment of the present invention has a component composition containing the above elements, with the remainder being Fe and unavoidable impurities. Here, examples of unavoidable impurities include Zn, Pb, and As. These impurities are acceptable to be included if their total content is 0.100% or less.

[0030] The composition of the base steel sheet of the hot-dip galvanized steel sheet of this disclosure is, in addition to the essential components mentioned above, further comprising, in mass%, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less, Ni: 1.00% or less, Co: 0.010% or less, Cu: 1 It may contain at least one element selected from 0.00%, Sn: 0.200%, Sb: 0.200%, Ca: 0.0100%, Mg: 0.0100%, REM: 0.0100%, Zr: 0.100%, Te: 0.100%, Hf: 0.10%, and Bi: 0.200%, either alone or in combination.

[0031] [Ti:0.200% or less] Ti generates a large amount of coarse precipitates and inclusions, reducing the ultimate deformability of the steel sheet. Therefore, if the Ti content exceeds 0.200%, λ and bendability decrease. For this reason, the Ti content should be 0.200% or less. Although there is no specific lower limit for the Ti content, a Ti content of 0.001% or more forms fine carbides, nitrides, or carbonitrides during hot rolling or continuous annealing. This increases the strength of the steel sheet and allows the YR to be controlled within a desired range. For this reason, a Ti content of 0.001% or more is preferable. Therefore, when added, the Ti content should be 0.200% or less. The Ti content is preferably 0.001% or more. The Ti content is preferably 0.100% or less.

[0032] [Nb:0.200% or less] Nb generates a large amount of coarse precipitates and inclusions, reducing the ultimate deformability of the steel sheet. Therefore, if the Nb content exceeds 0.200%, λ and bendability decrease. For this reason, the Nb content should be 0.200% or less. Although there is no specific lower limit for the Nb content, setting the Nb content to 0.001% or more forms fine carbides, nitrides, or carbonitrides during hot rolling or continuous annealing. This increases the strength of the steel sheet and allows the YR to be controlled within a desired range. For this reason, it is preferable that the Nb content be 0.001% or more. Therefore, when added, the Nb content should be 0.200% or less. The Nb content is preferably 0.001% or more. The Nb content is preferably 0.100% or less.

[0033] [V:0.200% or less] V generates a large amount of coarse precipitates and inclusions, reducing the ultimate deformability of the steel sheet. Therefore, if the V content exceeds 0.200%, λ and bendability decrease. For this reason, the V content should be 0.200% or less. Although there is no specific lower limit for the V content, a V content of 0.001% or more forms fine carbides, nitrides, or carbonitrides during hot rolling or continuous annealing. This increases the strength of the steel sheet and allows the YR to be controlled within a desired range. For this reason, it is preferable that the V content be 0.001% or more. Therefore, when added, the V content should be 0.200% or less. The V content is preferably 0.001% or more. The V content is preferably 0.100% or less.

[0034] [Ta: 0.10% or less, W: 0.10% or less] If the content of Ta and W exceeds 0.10% each, a large amount of coarse precipitates and inclusions are generated, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the content of Ta and W should be 0.10% or less each. There is no specific lower limit for the content of Ta and W, but fine carbides, nitrides, or carbonitrides are formed during hot rolling or continuous annealing. This increases the strength of the steel sheet, so it is preferable that the content of Ta and W be 0.01% or more each. Therefore, when added, the content of Ta and W should be 0.10% or less each. The content of Ta and W is preferably 0.01% or more each. The content of Ta and W is preferably 0.08% or less each.

[0035] [B:0.0100% or less] If B is present in a concentration of 0.0100% or less, it does not cause cracks to form inside the steel sheet during casting or hot rolling, and does not reduce the ultimate deformability of the steel sheet, thus preventing a decrease in λ and bendability. Therefore, the B content should be 0.0100% or less. Although there is no specific lower limit for the B content, it is more preferable for the B content to be 0.0003% or more, as it is an element that segregates at the austenite grain boundaries during annealing and improves hardenability. Therefore, if B is present, its content should be 0.0100% or less. More preferably, the B content should be 0.0003% or more. Even more preferably, the B content should be 0.0080% or less.

[0036] [Cr: 1.00% or less, Mo: 1.00% or less, Ni: 1.00% or less] If the content of Cr, Mo, and Ni exceeds 1.00%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the content of Cr, Mo, and Ni should be 1.00% or less. Although there is no specific lower limit for the content of Cr, Mo, and Ni, since these are elements that improve hardenability, it is preferable that the content of Cr, Mo, and Ni be 0.01% or more. Therefore, when added, the content of Cr, Mo, and Ni should be 1.00% or less. The content of Cr, Mo, and Ni is preferably 0.01% or more. The content of Cr, Mo, and Ni is preferably 0.80% or less.

[0037] [Co:0.010% or less] If the Co content exceeds 0.010%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Co content should be 0.010% or less. Although there is no specific lower limit for the Co content, since Co is an element that improves hardenability, it is preferable that the Co content be 0.001% or more. Therefore, when added, the Co content should be 0.010% or less. The Co content is preferably 0.001% or more. The Co content is preferably 0.008% or less.

[0038] [Cu:1.00% or less] If the Cu content exceeds 1.00%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Cu content should be 1.00% or less. Although there is no specific lower limit for the Cu content, since Cu is an element that improves hardenability, it is preferable that the Cu content be 0.01% or more. Therefore, when added, the Cu content should be 1.00% or less. The Cu content is preferably 0.01% or more. The Cu content is preferably 0.80% or less.

[0039] [Sn:0.200% or less] If the Sn content exceeds 0.200%, cracks will form inside the steel sheet during casting or hot rolling, reducing the ultimate deformability of the steel sheet and thus decreasing λ and bendability. Therefore, the Sn content should be 0.200% or less. Although there is no specific lower limit for the Sn content, since Sn is an element that improves hardenability, it is preferable that the Sn content be 0.001% or more. Therefore, when added, the Sn content should be 0.200% or less. The Sn content is preferably 0.001% or more. The Sn content is preferably 0.100% or less.

[0040] [Sb:0.200% or less] If the Sb content exceeds 0.200%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Sb content should be 0.200% or less. Although there is no specific lower limit for the Sb content, since Sb is an element that controls the surface softening thickness and allows for strength adjustment, it is preferable that the Sb content be 0.001% or more. Therefore, when added, the Sb content should be 0.200% or less. The Sb content is preferably 0.001% or more. The Sb content is preferably 0.100% or less.

[0041] [Ca: 0.0100% or less, Mg: 0.0100% or less, REM: 0.0100% or less] If the content of Ca, Mg, and REM exceeds 0.0100% each, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the content of Ca, Mg, and REM should be 0.0100% or less each. Although there is no specific lower limit for the content of Ca, Mg, and REM, these elements spheroidize the shape of nitrides and sulfides and improve the ultimate deformability of the steel sheet, so it is preferable that the content of Ca, Mg, and REM be 0.0005% or more each. Therefore, when added, the content of Ca, Mg, and REM should be 0.0100% or less each. The content of Ca, Mg, and REM is preferably 0.0005% or more. The content of Ca, Mg, and REM is preferably 0.0050% or less. REM (Rare Earth Elements) refers to the collective term for 15 elements, from Sc, Y, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. The REM content referred to here is the total content of these elements.

[0042] [Zr: 0.100% or less, Te: 0.100% or less] If the Zr and Te content exceeds 0.100%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Zr and Te content should be 0.100% or less. Although there is no specific lower limit for the Zr and Te content, it is preferable that the Zr and Te content be 0.001% or more, as these elements spheroidize the shape of nitrides and sulfides and improve the ultimate deformability of the steel sheet. Therefore, when added, the Zr and Te content should be 0.100% or less. The Zr and Te content is preferably 0.001% or more, each. The Zr and Te content is preferably 0.080% or less, each.

[0043] [Hf:0.10% or less] If the Hf content exceeds 0.10%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Hf content should be 0.10% or less. Although there is no specific lower limit for the Hf content, it is preferable that the Hf content be 0.01% or more, as Hf is an element that spheroidizes the shape of nitrides and sulfides and improves the ultimate deformability of the steel sheet. Therefore, when added, the Hf content should be 0.10% or less. The Hf content is preferably 0.01% or more. The Hf content is preferably 0.08% or less.

[0044] [Bi:0.200% or less] If the Bi content exceeds 0.200%, the amount of coarse precipitates and inclusions increases, reducing the ultimate deformability of the steel sheet, and thus decreasing λ and bendability. Therefore, the Bi content should be 0.200% or less. Although there is no specific lower limit for the Bi content, since Bi is an element that reduces segregation, it is preferable that the Bi content be 0.001% or more. Therefore, when added, the Bi content should be 0.200% or less. The Bi content is preferably 0.001% or more. The Bi content is preferably 0.100% or less.

[0045] Furthermore, regarding the above-mentioned Ti, Nb, V, Ta, W, B, Cr, Mo, Ni, Co, Cu, Sn, Sb, Ca, Mg, REM, Zr, Te, Hf, and Bi, if their respective contents are below the preferred lower limit, the effects of the present invention will not be impaired. Therefore, these are to be included as unavoidable impurities.

[0046] Next, the microstructure of the base steel sheet of a hot-dip galvanized steel sheet according to one embodiment of the present invention will be described.

[0047] [Area ratio of martensite at the 1 / 4 thickness point of the base steel plate: 30% or more] The base steel sheet contains a certain amount of martensite in its microstructure. Specifically, by making the area ratio of martensite at the 1 / 4 thickness position of the base steel sheet 30% or more, it is possible to achieve the desired YR, high λ, and high bendability. Therefore, the area ratio of martensite at the 1 / 4 thickness position of the base steel sheet is set to 30% or more. The area ratio of martensite at the 1 / 4 thickness position of the base steel sheet is preferably 35% or more, more preferably 40% or more, and even more preferably 45% or more. There is no particular upper limit to the area ratio of martensite at the 1 / 4 thickness position of the base steel sheet. However, from the viewpoint of obtaining high YR, high λ, and high bendability, the area ratio of martensite at the 1 / 4 thickness position of the base steel sheet is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The martensite referred to here includes quenched martensite (fresh martensite), as well as tempered martensite and bainite.

[0048] [Ferrite area ratio at the 1 / 4 thickness point of the base steel plate: 70% or less] By reducing the ferrite area ratio at the 1 / 4 thickness position of the base steel sheet to 70% or less, the YR (Yield Rate) increases. Furthermore, λ (Latitude) increases, improving bendability. Therefore, the ferrite area ratio at the 1 / 4 thickness position of the base steel sheet should be 70% or less. Preferably, the ferrite area ratio at the 1 / 4 thickness position of the base steel sheet is 60% or less. However, the ferrite area ratio at the 1 / 4 thickness position of the base steel sheet may be 0%. However, from the viewpoint of reducing the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing and improving the quality of the trim edge, the ferrite area ratio at the 1 / 4 thickness position of the base steel sheet is preferably 1% or more, more preferably 2% or more. Note that ferrite as used here may sometimes be defined as bainitic ferrite.

[0049] Here, the method for measuring the area ratio of martensite (quenched martensite, tempered martensite, and bainite) and ferrite (bainite ferrite) at the 1 / 4 thickness position of the base steel sheet is as follows.

[0050] After cutting out a sample so that the cross-section (L-section) parallel to the rolling direction of the steel sheet becomes the observation surface, the observation surface is mirror-polished using diamond paste, and then etched with 3 vol.% nital to reveal the microstructure. Using a Scanning Electron Microscope (SEM) at an acceleration voltage of 15 kV, the observation position is set at 1 / 4 of the thickness of the base steel sheet, and three fields of view are observed at a magnification of 5000x with a field of view of 17 μm × 23 μm. The obtained microstructure images are processed using Adobe Photoshop from Adobe Systems as follows: Specifically, the area ratio of each constituent microstructure (ferrite (bainitic ferrite), martensite (tempered martensite, bainite, and quenched martensite)) is calculated for all three fields of view by dividing the area by the measured area, and these values ​​are averaged to obtain the area ratio of each microstructure. In the above microstructure images, ferrite (bainitic ferrite) is a flat microstructure that does not contain carbides and is located in the recesses. Furthermore, tempered martensite and bainite are structures with concave areas containing fine carbides, while quenched martensite is a structure with convex areas and fine irregularities within the structure, making them distinguishable from each other. However, since the combined area ratio of tempered martensite and bainite is calculated as the area ratio of martensite, they do not need to be distinguishable from each other.

[0051] [Volume fraction of retained austenite at the 1 / 4 thickness point of the base steel sheet: 20.0% or less] If the volume fraction of retained austenite in the microstructure of the base steel sheet is 20.0% or less, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced. Therefore, the volume fraction of retained austenite is set to 20.0% or less. Furthermore, if the volume fraction of retained austenite is 15.0% or less, the carbon concentration in the retained austenite increases, and stress-induced transformation of the retained austenite during tensile deformation is suppressed, thus enabling a high YR (Yield Rate). Therefore, the volume fraction of retained austenite is preferably 15.0% or less, more preferably 10.0% or less, and even more preferably 5.0% or less. Note that there is no particular lower limit to the volume fraction of retained austenite, and desired properties can be obtained even if it is 0%.

[0052] Here, the volume fraction of retained austenite at the 1 / 4 thickness position of the base steel plate is measured as follows.

[0053] After grinding, the base steel sheet is polished by a further 0.1 mm using chemical polishing so that the observation surface is located at a point 1 / 4 of the sheet thickness from the surface (corresponding to 1 / 4 of the sheet thickness in the depth direction from the surface of the base steel sheet). On this surface, the integrated reflectance intensities of the (200), (220), and (311) planes of fcc iron (austenite) and the (200), (211), and (220) planes of bcc iron are measured using an X-ray diffractometer with a Co Kα source. Next, the volume fraction of austenite is determined from the intensity ratio of the integrated reflectance intensities from each plane of fcc iron (austenite) to the integrated reflectance intensities from each plane of bcc iron, and this is taken as the volume fraction of retained austenite.

[0054] Furthermore, it is preferable that the area ratio of the remaining microstructure other than martensite, ferrite, and retained austenite at the 1 / 4 thickness position of the base steel sheet is 5% or less. Examples of the remaining microstructure include those known as other steel sheet microstructures, such as pearlite, cementite, and metastable carbides (epsilon (ε) carbide, eta (η) carbide, chi (χ) carbide, etc.). The identification of the remaining microstructure can be performed, for example, by observation using a scanning electron microscope (SEM).

[0055] Furthermore, the area ratio of the remaining tissue is calculated using the following formula. Note that the volume ratio of retained austenite is considered to be approximately equal to the area ratio, and this is defined in the following formula. [Percentage of remaining tissue (%)] = 100 - [Percentage of martensite (%)] - [Percentage of ferrite (%)] - [Percentage of retained austenite (%)] Furthermore, in a hot-dip galvanized steel sheet according to one embodiment of the present invention, it is essential to appropriately control the amount of hydrogen diffusible in the low-temperature range of the base steel sheet.

[0056] [Low-temperature diffusible hydrogen content of the base steel sheet 24 hours after manufacturing: 0.015 ppm by mass or less] The amount of hydrogen diffusible at low temperatures in the base steel sheet 24 hours after manufacturing is an extremely important requirement. In other words, the inventors diligently studied how to obtain a hot-dip galvanized steel sheet that has a high YR, high λ and bendability immediately after manufacturing, and improved trim edge quality. As a result, the amount of hydrogen diffusible at low temperatures in the base steel sheet 24 hours after manufacturing, that is, the amount of hydrogen released from the base steel sheet when the base steel sheet is heated from room temperature to 50°C 24 hours after manufacturing, affects the above characteristics. In particular, the inventors found that this amount of hydrogen greatly affects the quality of the trimmed edge at the exit of the manufacturing line in a continuous annealing line. In other words, the inventors found that the quality of the trim edge depends more on the amount of hydrogen released in the low temperature range, specifically from room temperature to 50°C, than on the amount of hydrogen released from the base steel sheet in the high temperature range when the base steel sheet is heated. Furthermore, in order to significantly improve the quality of the trim edge while maintaining high YR, high λ, and bendability, the following findings were obtained. Specifically, it was found that it is essential to reduce the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing, in particular to 0.015 mass ppm or less, and this led to the development of the present invention. Therefore, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing is set to 0.015 mass ppm or less. The lower the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing, the better, preferably 0.010 mass ppm or less, and more preferably 0.006 mass ppm or less. Note that the lower limit of the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing is not particularly limited and may be 0 mass ppm. However, due to production technology constraints, it is preferable that the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing is 0.001 mass ppm or more.

[0057] Here, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing is measured as follows.

[0058] Specifically, a large plate sample with a length of 500 mm is taken from the steel strip after production on the hot-dip galvanizing line. 24 hours after production, a test piece with a length of 30 mm and a width of 5 mm is taken from the center of the large plate sample by shearing. Immediately after taking the test piece, it is immersed in liquid nitrogen. Then, the hot-dip galvanizing layer of the test piece is removed by alkali while controlling the temperature of the treatment solution so that the surface temperature of the test piece is below room temperature. Next, the amount of hydrogen released from the test piece when it is heated is measured using a temperature rise desorption analysis method. Specifically, the test piece is heated from room temperature to a target temperature of 300°C and a heating rate of 200°C / hr, and then cooled to room temperature. At this time, the cumulative amount of hydrogen released from the test piece in the temperature range from room temperature to 50°C (hereinafter also referred to as the cumulative amount of released hydrogen) is measured. Then, the amount of hydrogen that can be diffused at low temperatures in the base steel sheet is calculated using the following formula. To determine whether the hot-dip galvanized layer of the test specimen has been completely removed, the test specimen is heated from room temperature, and if the amount of released hydrogen is confirmed to be zero by TDA analysis at 200-210°C, the plating layer is considered to have been completely removed. [Low-temperature diffusible hydrogen content of the base steel plate (mass ppm)] = [Cumulative hydrogen release (g)] ÷ [Mass of the test specimen (g)] × 10 6 Here, the point in time when 24 hours have elapsed since manufacturing means 24 hours ± 2 hours after the point in time when all processes in the hot-dip galvanizing line (annealing process to reheating process in Table 2) have been completed and the coil winding has been completed at the exit of the continuous annealing line.

[0059] Furthermore, room temperature within the range of 10 to 25°C does not particularly affect the measurement of the amount of diffusible hydrogen in the base steel sheet at low temperatures. However, if the room temperature falls outside the range of 10 to 25°C, 25°C should be used as the representative room temperature, and the cumulative amount of hydrogen released from the test specimen in the temperature range of 25°C to 50°C should be measured.

[0060] Furthermore, the amount of diffusible hydrogen at low temperatures can be measured in the same manner for hot-dip galvanized steel sheets (components) that have undergone cold working processes such as punching, stretching flange forming, and bending, as well as for components manufactured by further welding the hot-dip galvanized steel sheets (components) after such processing. Moreover, the amount of diffusible hydrogen at low temperatures in the base steel sheet portion of automotive frame structural components or reinforcing components made from such components can be measured in the same manner as described above.

[0061] Furthermore, the thickness of the base steel sheet of the hot-dip galvanized steel sheet according to one embodiment of the present invention is not particularly limited, but is usually between 0.3 mm and 2.8 mm.

[0062] Regarding the hot-dip galvanized layer: Next, the hot-dip galvanized layer of a hot-dip galvanized steel sheet according to one embodiment of the present invention will be described. The hot-dip galvanized layer referred to here includes an alloyed hot-dip galvanized layer obtained by applying an alloying treatment to the hot-dip galvanized layer. Furthermore, the hot-dip galvanized layer is provided on both surfaces of the base steel sheet.

[0063] The composition of the hot-dip galvanized layer is not particularly limited and can be any general composition. In one example, the hot-dip galvanized layer contains Fe: 20% by mass or less, and Al: 0.001% by mass or more and 1.0% by mass or less. Furthermore, it contains one or more elements selected from the group consisting of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM in a total amount of 0% by mass or more and 3.5% by mass or less. The remainder consists of Zn and unavoidable impurities. In the case of a non-alloyed hot-dip galvanized layer, in one example, the Fe content in the plating layer is less than 7% by mass. In the case of an alloyed hot-dip galvanized layer, in one example, the Fe content in the plating layer is 7% by mass or more and 15% by mass or less, more preferably 8% by mass or more and 13% by mass or less. However, the present invention is not limited to these.

[0064] Furthermore, while there are no particular limitations on the amount of plating deposited on one side, it is generally between 20 and 80 g / m². 2 It is preferable.

[0065] In addition, in a hot-dip galvanized steel sheet according to one embodiment of the present invention, it is essential to properly control the cracks in the hot-dip galvanized layer and the full width at half maximum of the δ1 phase.

[0066] [Crack density penetrating the hot-dip galvanized layer: 30 cracks / mm or more] This is an extremely important constituent element of the invention in this disclosure. By increasing the number density of cracks penetrating the plating layer, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced. As a result, the quality of the trim edge can be improved while maintaining high λ and bendability. In order to obtain this effect, the number density of cracks penetrating the plating layer must be 30 cracks / mm or more. There is no particular upper limit to the number density of cracks penetrating the plating layer, but it is preferable to be 100 cracks / mm or less because the plating quality will deteriorate. Therefore, the number density of cracks penetrating the plating layer should be 30 cracks / mm or more. Preferably, the number density of cracks penetrating the plating layer should be 40 cracks / mm or more. Preferably, the number density of cracks penetrating the plating layer should be 100 cracks / mm or less.

[0067] Here, the number density of cracks penetrating the plating layer is measured as follows.

[0068] After cutting out a sample of hot-dip galvanized steel sheet so that the cross-section (L-section) parallel to the rolling direction becomes the observation surface, the observation surface is mirror-polished using diamond paste. Using a scanning electron microscope (SEM) with an acceleration voltage of 15kV, the hot-dip galvanized layer is used as the observation position, and a field of view of 140μm in the rolling direction and 44μm in the thickness direction is used per sheet, with a 2mm area in the rolling direction being observed at a magnification of 2000x. In the above microstructure image, the number of cracks penetrating the hot-dip galvanized layer is measured, and the number density of cracks penetrating the plating layer is calculated by dividing this number by 2mm.

[0069] [Full width at half maximum of the δ1 phase in the hot-dip galvanized layer: 0.100 degrees or higher] This is an extremely important constituent element of the invention in this disclosure. By increasing the full width at half maximum of the δ1 phase of the plating layer, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced, and as a result, the quality of the trim edge can be improved while maintaining high λ and bendability. In order to obtain this effect, the full width at half maximum of the δ1 phase of the plating layer must be 0.100 degrees or more. There is no particular upper limit to the full width at half maximum of the δ1 phase of the plating layer, but it is preferable to be 0.150 degrees or less because the plating quality may deteriorate. Therefore, the full width at half maximum of the δ1 phase of the plating layer is set to 0.100 degrees or more. The full width at half maximum of the δ1 phase of the plating layer is preferably set to 0.110 degrees or more. The full width at half maximum of the δ1 phase of the plating layer is preferably set to 0.150 degrees or less.

[0070] Here, the full width at half maximum of the δ1 phase of the plating layer is measured as follows.

[0071] After cutting out a sample so that the surface of the hot-dip galvanized steel sheet would be the observation surface, the surface was measured using an X-ray diffractometer with a Cu tube, with a sampling angle step of 0.006° and a measurement time of 0.36 seconds per point. In addition, to subtract the full width at half maximum originating from the X-ray diffractometer and the radiation source itself, heat-treated Si and LaB6 were measured as strain-free standard samples with angle steps of 0.004° and 0.002°, respectively. From these results, the change in full width at half maximum was determined using the same method as described in "NL Okamoto, K. Tanaka, A. Yasuhara and H. Inui: Acta Cryst., B70(2014), 275."

[0072] The thickness of the hot-dip galvanized steel sheet according to one embodiment of the present invention is not particularly limited, but is usually between 0.3 mm and 2.8 mm.

[0073] Regarding the manufacturing method of hot-dip galvanized steel sheets: Next, a method for manufacturing a hot-dip galvanized steel sheet according to one embodiment of the present invention will be described.

[0074] First, a steel slab is manufactured by melting a steel material having the above-described component composition. In this disclosure, the method of melting the steel material is not particularly limited, and any known melting method, such as a converter or electric furnace, is suitable. Furthermore, while it is preferable to manufacture the steel slab (slab) by continuous casting to prevent macrosegregation, it is also possible to manufacture it by ingot casting or thin slab casting. In addition to the conventional method of cooling the steel slab to room temperature and then reheating it, energy-saving processes such as direct rolling, where the slab is charged into the heating furnace while still hot without cooling to room temperature, or where it is immediately rolled after a short period of heat retention, can also be applied without any problems.

[0075] Next, the manufactured steel slab is subjected to hot rolling consisting of rough rolling and finish rolling to produce a hot-rolled sheet. In one example, the steel slab manufactured as described above is cooled to room temperature, then heated, and then rolled. The slab heating temperature is preferably 1100°C or higher from the viewpoint of dissolving carbides and reducing rolling load. Furthermore, to prevent increased scale loss, the slab heating temperature is preferably 1300°C or lower. The slab heating temperature is based on the temperature of the slab surface during heating.

[0076] Next, the steel slab is roughly rolled into a sheet bar under normal conditions. If the slab heating temperature is kept low, it is preferable to heat the sheet bar using a bar heater or the like before finish rolling to prevent problems during rolling. Furthermore, the finish rolling temperature is preferably above the Ar3 transformation point. If the finish rolling temperature is lowered too much, it will lead to an increase in the rolling load and an increase in the reduction ratio in the unrecrystallized state of austenite. As a result, an abnormal structure elongated in the rolling direction will develop, and consequently, the workability of the steel sheet obtained after annealing may decrease. The Ar3 transformation point is determined by the following formula. Ar3(℃)=868-396×[%C]+24.6×[%Si]-68.1×[%Mn]-36.1×[%Ni]-20.7×[%Cu]-24.8×[%Cr] In the above formula, [% element symbol] represents the content (mass%) of the element in question in the above component composition, and should be set to 0 if the element is not present.

[0077] Furthermore, rough-rolled sheets may be joined together during hot rolling and continuously subjected to finish rolling. Alternatively, the rough-rolled sheets (sheet bars) may be wound up before finish rolling. Additionally, to reduce the rolling load during hot rolling, part or all of the finish rolling may be performed using lubricated rolling. Lubricated rolling is effective from the viewpoint of uniformizing the shape and material of the steel sheets. The coefficient of friction during lubricated rolling is preferably in the range of 0.10 to 0.25.

[0078] Next, the hot-rolled sheet is pickled. Pickling removes oxides from the surface of the steel sheet, which is important for ensuring good chemical conversion treatment properties and plating quality in the final high-strength steel sheet product. Pickling may be performed once or in multiple stages.

[0079] Next, the hot-rolled sheet after pickling, or the hot-rolled sheet (hot-rolled annealed sheet) that has been optionally heat-treated after pickling, is subjected to cold rolling to produce a cold-rolled steel sheet. Cold rolling is preferably performed by multi-pass rolling, such as tandem multi-stand rolling or reverse rolling, which requires two or more passes, as this allows for uniform and efficient introduction of strain and results in a uniform structure.

[0080] In this embodiment, a crucial constituent element of the invention is that the cumulative reduction rate is between 20% and 75%.

[0081] [Cumulative reduction ratio in cold rolling: 20% to 75%] By increasing the cumulative reduction ratio of cold rolling, the area ratio of martensite increases and the area ratio of ferrite decreases, thereby obtaining high YR, high λ, and high bendability. To obtain these effects, the cumulative reduction ratio of cold rolling should be 20% or more. On the other hand, if the cumulative reduction ratio of cold rolling exceeds 75%, the grain size of austenite generated during annealing becomes finer, and the amount of retained austenite in the annealed sheet increases. As a result, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing increases, so λ and bendability decrease, and the quality of the trim edge also deteriorates. Therefore, the cumulative reduction ratio of cold rolling should be 20% or more and 75% or less. The cumulative reduction ratio of cold rolling should preferably be 25% or more. The cumulative reduction ratio of cold rolling should preferably be 70% or less. The cumulative reduction ratio of cold rolling should more preferably be 27% or more. The cumulative reduction ratio of cold rolling should more preferably be 60% or less.

[0082] [Final pass speed in cold rolling: 50 mpm or higher (preferred conditions)] By increasing the sheet speed in the final pass of cold rolling, strain can be introduced into the surface layer of the base steel sheet, increasing the number density of cracks penetrating the plating layer. This is particularly effective when the steel sheet is further alloyed after hot-dip galvanizing. As a result, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced, and consequently, the quality of the trim edge can be improved while maintaining high λ and bendability. To obtain these effects, the sheet speed in the final pass of cold rolling should be 50 mpm or higher. There is no particular upper limit specified for the sheet speed in the final pass of cold rolling, but due to production technology constraints, it is preferable to keep it below 300 mpm. Therefore, the sheet speed in the final pass of cold rolling should be 50 mpm or higher. The sheet speed in the final pass of cold rolling should preferably be 70 mpm or higher. The sheet speed in the final pass of cold rolling should preferably be below 300 mpm.

[0083] The cold-rolled steel sheet obtained as described above is subjected to an annealing process. The annealing conditions are as follows:

[0084] [Heating temperature: 780℃ or higher] If the heating temperature (annealing temperature) is below 780°C, the annealing process will occur in the two-phase region of ferrite and austenite, resulting in the inclusion of a large amount of ferrite after annealing, making it difficult to achieve the desired YR. Although there is no particular upper limit to the heating temperature, as the heating temperature increases, the thickness of the softened surface layer after annealing increases, reducing TS, and the prior austenite grain size becomes coarser, reducing YR. Therefore, a temperature of 1000°C or lower is preferable. Accordingly, the heating temperature should be 780°C or higher. Preferably, it should be 820°C or higher. Preferably, the heating temperature should be 1000°C or lower. More preferably, the heating temperature should be 830°C or higher. More preferably, the heating temperature should be 980°C or lower. The heating temperature is measured based on the temperature of the steel sheet surface. Although there is no particular limit to the heat retention time at the above heating temperatures, it is preferably 10s to 600s.

[0085] After the annealing described above, the cold-rolled steel sheet is cooled before the hot-dip galvanizing treatment. The conditions for this cooling are not particularly limited and can be those of a standard practice. For example, the average cooling rate in the temperature range between the heating temperature and 500°C is not particularly limited, but from the viewpoint of controlling the area ratio of martensite and ferrite, it is preferable to set it to 5°C / s or more and 50°C / s or less.

[0086] [Plating process] Next, the cold-rolled steel sheet is plated to produce a plated steel sheet. Examples of plating treatments include hot-dip galvanizing. Alternatively, an alloying treatment may be performed after hot-dip galvanizing. Furthermore, annealing, cooling, and plating may be performed continuously on a single line (CGL (Continuous Galvanizing Line)). For example, after annealing, the cold-rolled steel sheet is cooled to a temperature of approximately 500°C. Then, the cold-rolled steel sheet is passed through the steel strip exit side of a cooling strip and moved into the hot-dip galvanizing bath via a snout whose tip is immersed in the hot-dip galvanizing bath, while being further cooled. The time from the end of cooling of the cold-rolled steel sheet to its entry into the hot-dip galvanizing bath is not particularly limited, but from the viewpoint of controlling the area ratio of martensite and ferrite, it is preferable to set it to 1 s to 300 s. Furthermore, a roll is provided immediately before the connection between the cooling zone and the snout to change the direction of travel of the cold-rolled steel sheet and allow it to enter the snout. The cold-rolled steel sheet passes through this roll before entering the snout. Next, the cold-rolled steel sheet, guided through the snout to the molten zinc plating bath, is immersed in the molten zinc plating bath and subjected to molten zinc plating to become a plated steel sheet.

[0087] In the hot-dip galvanizing process, for example, cold-rolled steel sheets are immersed in a hot-dip galvanizing bath at a temperature of 440°C to 500°C. It is also preferable to use a hot-dip galvanizing bath with a composition in which the Al content is 0.10% to 0.23% by mass, with the remainder being Zn and unavoidable impurities.

[0088] Furthermore, after the hot-dip galvanizing treatment described above, an alloying treatment may be performed in a temperature range of 460°C to 600°C. If the alloying treatment temperature is below 460°C, the Zn-Fe alloying rate becomes excessively slow, reducing productivity. On the other hand, if the alloying treatment temperature exceeds 600°C, the untransformed austenite transforms into pearlite, and the desired martensite area ratio may not be obtained. Therefore, the alloying treatment temperature is preferably between 460°C and 600°C. The alloying treatment temperature is preferably 470°C or higher. Also, the alloying treatment temperature is preferably 560°C or lower.

[0089] Furthermore, the amount of plating deposited is 20-80 g / m² per side. 2 (Double-sided plating) is preferred. The amount of plating can be adjusted by performing gas wiping or the like after the hot-dip galvanizing treatment.

[0090] [Optional cooling process] After the annealing process, the plated steel sheet is optionally cooled (cooling process). The average cooling rate in the range from below 500°C to above 400°C is not particularly limited, but it is preferably between 5°C / s and 30°C / s. In addition, in the temperature range between the heating temperature and above 400°C, the high-strength steel sheet may be cooled once and then the steel sheet temperature may be raised again.

[0091] [Average cooling rate in the temperature range of 250°C to 400°C: 1.0°C / s or higher (cooling process)] By increasing the average cooling rate in the temperature range of 250°C to 400°C, the area ratio of ferrite can be reduced and the area ratio of martensite can be increased. After the hot-dip galvanized layer solidifies, the base steel sheet undergoes martensitic transformation, which can increase the number density of cracks penetrating the plating layer. As a result, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced, and consequently, the quality of the trim edge can be improved while maintaining high λ and bendability. To obtain these effects, the average cooling rate in the temperature range of 250°C to 400°C should be 1.0°C / s or higher. Preferably, the average cooling rate in the temperature range of 250°C to 400°C should be 2.0°C / s or higher, more preferably 3.0°C / s or higher, and even more preferably 4.0°C / s or higher. While there is no specific upper limit for the average cooling rate in the temperature range of 250°C to 400°C, due to production technology constraints, it is preferably 100.0°C / s or less, and more preferably 80.0°C / s or less. If the cooling stop temperature exceeds 250°C, the average cooling rate shall be the value in the temperature range of 250°C to 400°C. The average cooling rate shall be measured based on the temperature of the steel plate surface.

[0092] Furthermore, cooling methods such as gas jet cooling, mist cooling, water cooling, and air cooling can be applied in the temperature range of 250°C to 400°C.

[0093] [Uniaxial tensile strain at the surface: 0.1% or more] By applying a process to the hot-dip galvanized steel sheet that has undergone the above annealing and cooling to increase the amount of uniaxial tensile strain in the surface layer to a certain level or higher, the crack number density penetrating the plating layer and the full width at half maximum of the δ1 phase of the plating layer can be increased. As a result, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing can be reduced, and consequently, the quality of the trim edge can be improved while maintaining high λ and bendability. In order to obtain these effects, the amount of uniaxial tensile strain in the surface layer must be 0.1% or higher. Preferably, the amount of uniaxial tensile strain in the surface layer is 0.5% or higher, more preferably 1.0% or higher. There is no particular upper limit specified for the amount of uniaxial tensile strain in the surface layer, but due to production technology constraints, it is preferable that the amount of uniaxial tensile strain in the surface layer be 10.0% or lower. More preferably, the amount of uniaxial tensile strain in the surface layer is 7.5% or lower.

[0094] Here, "surface layer" refers to the plating layer of a hot-dip galvanized steel sheet. The amount of uniaxial tensile strain in the surface layer is calculated by marking the surface of the hot-dip galvanized steel sheet in the direction of sheet passage after annealing and cooling, and measuring the displacement of the mark in the direction of sheet passage after strain is applied. The strain application methods described here include temper rolling, tension leveling, and repeated bending with rolls.

[0095] [Heat retention temperature during the cooling process: 100°C to 450°C (optimal conditions)] In the cooling process described above, it is preferable to maintain the heat retention temperature in the temperature range of 100°C to 450°C for 5 seconds or more. By staying within this range, the hot-dip galvanized steel sheet can be maintained and the area ratio of bainitic ferrite can be further reduced, thereby bringing the YR, λ, and bendability into a more favorable range. The heat retention temperature in the cooling process is more preferably 150°C or higher, and even more preferably 200°C or higher. Furthermore, the heat retention temperature in the cooling process is more preferably 400°C or lower, and even more preferably 350°C or lower. The temperature in the cooling process is based on the surface temperature of the steel sheet. After maintaining the heat at this temperature, the sheet is cooled, and a strain-inducing process is performed on the surface layer to achieve a uniaxial tensile strain of 0.1% or more. The cooling conditions after this heat retention are not particularly limited and can be followed according to conventional methods.

[0096] [Heat retention time during the cooling process: 5 seconds or more (optimal conditions)] By maintaining the heat retention temperature during the cooling process, YR, λ, and bendability can be brought within a more favorable range. To obtain this effect, the heat retention time at the heat retention temperature during the cooling process is preferably 5s or more, more preferably 10s or more, and even more preferably 15s or more. There is no particular upper limit specified for the heat retention time at the heat retention temperature during the cooling process, but in order to bring TS within a more favorable range, the heat retention time at the heat retention temperature during the cooling process is preferably 500s or less, and more preferably 250s or less.

[0097] [Cooling stop temperature: 250℃ or lower (preferred conditions)] In the cooling process described above, the cooling stop temperature is preferably 250°C or lower, and more preferably 200°C or lower. A cooling stop temperature of 250°C or lower prevents the formation of a large amount of retained austenite after annealing, thereby further improving YR, λ, and bendability. While there is no specific lower limit for the cooling stop temperature, it is preferable to set it above room temperature from a productivity standpoint. The cooling stop rate is measured based on the temperature of the steel sheet surface.

[0098] While there is no specific requirement for the average cooling rate up to the cooling stop temperature of 250°C or below, to further improve YR, the average cooling rate up to the cooling stop temperature of 250°C or below is preferably 1°C / s or more, and more preferably 2°C / s or more. On the other hand, due to production technology constraints, the average cooling rate up to the cooling stop temperature of 250°C or below is preferably 1000°C / s or less, and more preferably 150°C / s or less.

[0099] Furthermore, the cold-rolled steel sheet may be cooled from the cooling stop temperature to room temperature. The average cooling rate from the cooling stop temperature to room temperature is not particularly limited, and it can be cooled to room temperature by any method. Suitable cooling methods include gas jet cooling, mist cooling, water cooling, and air cooling.

[0100] As described above, the hot-dip galvanized steel sheet that has been annealed may be rolled after being cooled to the cooling stop temperature. The elongation rate of the rolling is preferably 0.05% or more, and more preferably 0.10% or more. By setting the elongation rate of the rolling performed after cooling to the cooling stop temperature to 0.05% or more, the YR can be controlled to a desired range. Furthermore, the elongation rate of the rolling is preferably 2.00% or less, and more preferably 1.00% or less. By setting the elongation rate of the rolling after cooling to the cooling stop temperature to 2.00% or less, the volume fraction of retained austenite can be set to a more suitable range, and the degree of damage to the shear end face in a corrosive environment can be set to a more suitable range.

[0101] The rolling after cooling to the aforementioned cooling stop temperature may be performed on equipment continuous with the continuous annealing equipment described above (online), or on equipment discontinuous with the continuous annealing equipment described above (offline). Furthermore, the desired elongation rate may be achieved in a single rolling pass, or multiple rolling passes may be performed to achieve a total elongation rate of 0.05% to 2.00%. Note that the rolling described here generally refers to temper rolling, but any processing method that can provide an elongation rate equivalent to temper rolling, such as repeated bending with a tension leveler or rolls, is also acceptable.

[0102] [Reheating process] [Reheating temperature: (cooling stop temperature + 50°C) or higher and 450°C or lower (preferred conditions)] After cooling to the aforementioned cooling stop temperature, or after further rolling following cooling to the aforementioned cooling stop temperature, the hot-dip galvanized steel sheet may be reheated (reheating step). Reheating the hot-dip galvanized steel sheet can bring the YR and bendability into a more favorable range. To obtain these effects, the reheating temperature is preferably (cooling stop temperature + 50°C) or higher, more preferably (cooling stop temperature + 100°C) or higher, and even more preferably (cooling stop temperature + 150°C) or higher. On the other hand, as the reheating temperature rises, tempering of the martensite progresses and the TS decreases, so the reheating temperature is preferably 450°C or lower, more preferably 400°C or lower, and even more preferably 380°C or lower. The above reheating temperature is based on the surface temperature of the steel sheet. After reheating and maintaining the heat at this temperature, it is cooled. This reheating may be performed after the aforementioned strain-inducing process in which the uniaxial tensile strain amount in the surface layer is 0.1% or more, or it may be performed before the strain-inducing process. The cooling conditions after reheating and heat retention are not particularly limited and should be followed according to standard procedures.

[0103] [Holding time at reheating temperature: 5 seconds or more (optimal conditions)] By maintaining the heat at the aforementioned reheating temperature, the YR and bendability can be brought within a more favorable range. To obtain this effect, the heat retention time at the reheating temperature is preferably 5 seconds or more, more preferably 10 seconds or more, and even more preferably 15 seconds or more. There is no particular upper limit specified for the heat retention time at the reheating temperature, but in order to bring the TS within a more favorable range, the heat retention time at the reheating temperature is preferably 500 seconds or less, and more preferably 250 seconds or less. The cooling rate from the aforementioned reheating temperature to room temperature is not particularly limited, and it can be cooled to room temperature by any method. Cooling methods that can be applied include gas jet cooling, mist cooling, water cooling, and air cooling.

[0104] Furthermore, when hot-dip galvanized steel sheets are traded, they are usually cooled to room temperature before being traded. Other manufacturing conditions besides those mentioned above can be met by conventional methods.

[0105] Regarding the components: Next, a component relating to one embodiment of the present invention will be described.

[0106] A component according to one embodiment of the present invention is a component made using the hot-dip galvanized steel sheet according to the above-described embodiment of the present invention. A component according to one embodiment of the present invention is, for example, a hot-dip galvanized steel sheet according to the above-described embodiment of the present invention that has been formed into a desired shape by cold pressing or the like. Therefore, even after being formed into a component, it retains the microstructure of the hot-dip galvanized steel sheet, the low-temperature diffusible hydrogen content, and the characteristics of the hot-dip galvanized layer. A component according to one embodiment of the present invention is preferably for use as a frame structure component of an automobile or as a reinforcing component of an automobile, and in one embodiment, these consist of the component of the present invention.

[0107] Herein, the hot-dip galvanized steel sheet according to the embodiment of the present invention described above is a hot-dip galvanized steel sheet that has a high YR, as well as elongation flangeability and bendability, and also has improved trim edge quality.Therefore, the member according to the embodiment of the present invention can contribute to the weight reduction of the vehicle body and can be suitably used in general for structural components of automobiles or for reinforcing components of automobiles. [Examples]

[0108] A steel slab (steel material) having the component composition shown in Table 1, with the remainder being Fe and unavoidable impurities, was melted in a converter, and steel slabs were obtained by continuous casting. The obtained steel slabs were heated to 1250°C and roughly rolled to obtain sheet bars. Next, the obtained sheet bars were finished rolled at a finishing rolling temperature of 900°C and wound at a winding temperature of 500°C. After cooling, hot-rolled steel sheets were obtained. After pickling the obtained hot-rolled steel sheets, cold rolling was performed under the conditions shown in Table 2 to obtain cold-rolled steel sheets with a thickness of 1.4 mm.

[0109] Next, the obtained cold-rolled steel sheet was annealed under the conditions shown in Table 2. Then, the cold-rolled steel sheet was subjected to the types of plating treatments shown in Table 2 to obtain plated steel sheets having hot-dip galvanized layers on both sides. In Table 2, GI indicates hot-dip galvanizing only (hot-dip galvanized steel sheet without alloying treatment), and GA indicates hot-dip galvanizing in addition to alloying treatment (alloyed hot-dip galvanized steel sheet).

[0110] [Table 1]

[0111] [Table 2]

[0112] For GI, a molten zinc plating bath containing 0.20% by mass of Al, with the remainder being Zn and unavoidable impurities, was used. Similarly, for GA, a molten zinc plating bath containing 0.14% by mass of Al, with the remainder being Zn and unavoidable impurities, was used. The plating bath temperature was 470°C in both cases. The plating deposition amount for GI was 45-72 g / m² per side. 2 (Double-sided plating) is recommended, and for GA, the rate is 45 g / m² per side. 2 The plating process was limited to (double-sided plating). In addition, for GA, the alloying treatment temperature was set to approximately 550°C.

[0113] Furthermore, the composition of the hot-dip galvanized layer of GI was Fe: 0.1-1.0 mass%, Al: 0.2-1.0 mass%, with the remainder being Zn and unavoidable impurities. The composition of the alloyed hot-dip galvanized layer of GA was Fe: 7-15 mass%, Al: 0.1-1.0 mass%, with the remainder being Zn and unavoidable impurities.

[0114] Next, the obtained hot-dip galvanized steel sheets were cooled and reheated under the conditions shown in Table 2. Conditions not explicitly stated were handled according to conventional methods.

[0115] The resulting steel sheets were subjected to microstructure identification at a position 1 / 4 of the base steel sheet thickness using the method described above. Furthermore, the amount of low-temperature diffusible hydrogen in the base steel sheet, the number density of cracks penetrating the plating layer, and the full width at half maximum of the δ1 phase of the plating layer were measured 24 hours after manufacturing. The results are shown in Table 3. The component composition of the base steel sheet of the obtained steel sheets was substantially the same as that of the steel slab stage, and all of the suitable steels were within the range of component composition according to the above embodiment, while all of the comparative steels were outside the range of component composition according to the above embodiment.

[0116] Furthermore, the obtained steel sheets were evaluated for their tensile properties, elongation flange properties immediately after manufacturing, bendability immediately after manufacturing, and trim edge quality according to the following test methods. The results are shown in Table 3. In the examples, "immediately after manufacturing" refers to 24 hours after manufacturing.

[0117] [Tensile test] Tensile tests were conducted in accordance with JIS Z 2241:2022. From the obtained steel plates, JIS No. 5 test specimens were taken perpendicular to the rolling direction of the steel plate, and the crosshead speed was 1.67 × 10⁻⁶. -1 Tensile tests were conducted under conditions of mm / s, and YS and TS were measured. In this invention, a yield ratio (YR) of 55% or higher was considered to indicate high component strength. YR was calculated using the calculation method described in formula (1) above.

[0118] [Hole widening test] The hole expansion test was conducted in accordance with JIS Z 2256. Steel plates 24 hours after manufacture were sheared to 100 mm x 100 mm, and then holes with a diameter of 10 mm were punched into the sheared plates with a clearance of 12.5%. Next, the steel plates were held down with a wrinkle-holding force of 9 tons (88.26 kN) using a die with an inner diameter of 75 mm, and in that state, a conical punch with a vertex angle of 60° was pressed into the holes to measure the hole diameter at the crack initiation limit. The limit hole expansion ratio λ (%) was then calculated using the following formula. Limit hole expansion rate: λ(%) = {(D f -D0) / D0} × 100 Here, D f λ is the hole diameter at the time of crack initiation (mm), and D0 is the initial hole diameter (mm). Furthermore, it was determined that the ductility flange performance immediately after manufacturing is excellent when the limit hole expansion ratio: λ is 30% or more.

[0119] [Bending test] The bending test was conducted in accordance with JIS Z 2248:2022. From the steel sheet 24 hours after manufacturing, a strip-shaped test piece with a width of 30 mm and a length of 100 mm was taken so that the direction parallel to the rolling direction of the steel sheet was the axial direction of the bending test. Subsequently, a 90° V bending test was performed under the conditions of a pressing load of 100 kN and a pressing holding time of 5 seconds. In this disclosure, the bending performance was evaluated by performing bending tests on 5 samples at R values ​​where the bending radius (R) divided by the plate thickness (t) was approximately 4.5, i.e., 4.3 to 4.7. Next, the length of the crack at the edge of the bending apex of all 5 samples was evaluated, and if the crack length was 200 μm or less, it was judged that the bending performance was excellent immediately after manufacturing. Here, the crack length was evaluated by measuring the edge of the bending apex using a digital microscope (RH-2000: manufactured by Hirox Co., Ltd.) at a magnification of 40 to 160 times.

[0120] [Trim Edge Quality] The trim edge quality was assessed by trimming the coil edge at the exit side of the CGL to an actual clearance of 15-20%, and then cutting the trimmed edge perpendicular to the observation surface, including the trimmed edge. The observation surface was then mirror-polished using diamond paste. Using a scanning electron microscope (SEM) at an acceleration voltage of 15kV, the trimmed edge was used as the observation position and observed at 30x magnification, ensuring that the entire trimmed edge was included. If no cracks were observed in the resulting image, the trimmed edge was judged to be of excellent quality. Here, a crack refers to a fissure with a length of 100μm or more.

[0121] Following the method described above, the area fractions of martensite and ferrite, the volume fraction of retained austenite, the amount of low-temperature diffusible hydrogen in the base steel sheet 24 hours after manufacturing, the crack number density penetrating the plating layer, and the full width at half maximum of the δ1 phase of the plating layer were determined. The remaining microstructure was observed using the method described below. After cutting out a sample so that the thickness cross section (L section) parallel to the rolling direction of the steel sheet became the observation surface, the observation surface was mirror-polished using diamond paste, and then etched with 3 vol.% nital to reveal the microstructure. Under conditions of an acceleration voltage of 15 kV, an SEM was used to observe the steel sheet at a position 1 / 4 of its thickness, at a magnification of 5000x, with a field of view of 17 μm × 23 μm, and three fields of view were observed. Carbides were identified as the remaining microstructure from the obtained microstructure images.

[0122] As shown in Table 3, the present invention example exhibits superior YR, λ, bendability, and trim edge quality. In contrast, the comparative example shows inferiority in one or more of the following: YR, λ, bendability, and trim edge quality.

[0123] [Table 3]

[0124] Although embodiments of the present invention have been described above, the present invention is not limited by the descriptions that constitute part of the disclosure of the present invention according to these embodiments. That is, other embodiments, examples, and operational techniques made by those skilled in the art based on these embodiments are all included in the scope of the present invention. For example, in the series of heat treatments in the manufacturing method described above, the equipment for heat-treating the steel plate is not particularly limited, as long as the thermal history conditions are satisfied. [Industrial applicability]

[0125] According to the present invention, a hot-dip galvanized steel sheet can be obtained that has excellent stretch flange properties, bendability, and trim edge quality, as well as high component strength.

[0126] In particular, the hot-dip galvanized steel sheet of the present invention has excellent trim edge quality, making it possible to apply it to various sizes and shapes of automotive frame structural components while achieving high component strength. This allows for improved fuel efficiency through vehicle weight reduction, and thus has significant industrial value.

Claims

1. A hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer on the surface of the base steel sheet, The aforementioned base steel plate is, by mass%, C: 0.030% or more and 0.500% or less, Si: 0.01% or more and 2.50% or less, Mn: 0.10% or more and 5.00% or less, P: 0.100% or less, S: 0.0200% or less, Al: 0.100% or less, N: 0.0100% or less and O: Contains 0.0100% or less, The component composition consists of Fe and unavoidable impurities as the remainder, At the position where the base steel plate thickness is 1 / 4, If the area ratio of martensite is 30% or more, The ferrite area ratio is 70% or less, and It has a microstructure in which the volume fraction of retained austenite is 20.0% or less, The amount of hydrogen released from the base steel sheet when the base steel sheet is heated from room temperature to 50°C 24 hours after the manufacture of the hot-dip galvanized steel sheet is 0.015 ppm by mass or less, and the amount of low-temperature diffusible hydrogen is 0.015 ppm by mass or less. In the aforementioned hot-dip galvanized layer, The number density of cracks penetrating the aforementioned hot-dip galvanized layer is 30 cracks / mm or more. A hot-dip galvanized steel sheet in which the full width at half maximum of the δ1 phase of the hot-dip galvanized layer is 0.100 degrees or more.

2. The aforementioned component composition is further expressed in mass%, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less Co: 0.010% or less, Ni: 1.00% or less, Cu: 1.00% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, REM: 0.0100% or less, Zr: 0.100% or less, Te: 0.100% or less, Hf: 0.10% or less, Bi: 0.200% or less, The hot-dip galvanized steel sheet according to claim 1, comprising at least one element selected from among the following.

3. The hot-dip galvanized steel sheet according to claim 1, wherein the hot-dip galvanized layer is an alloyed hot-dip galvanized layer.

4. The hot-dip galvanized steel sheet according to claim 2, wherein the hot-dip galvanized layer is an alloyed hot-dip galvanized layer.

5. A component made using a hot-dip galvanized steel sheet according to any one of claims 1 to 4.

6. A structural component for an automobile or a reinforcing component for an automobile, comprising the member described in claim 5.

7. A method for manufacturing a hot-dip galvanized steel sheet according to claim 1, wherein a steel slab having the above-mentioned component composition is used. Hot-rolled steel sheet is obtained by hot-rolling. Next, the hot-rolled steel sheet is pickled to make a pickled sheet. Next, the pickled plate is subjected to cold rolling with a cumulative reduction ratio of 20% to 75% and a final pass speed of 50 mpm or more to obtain a cold-rolled steel sheet. Next, the cold-rolled steel sheet is annealed under the condition of a heating temperature of 780°C or higher. Next, the cold-rolled steel sheet is subjected to a hot-dip galvanizing treatment to become a plated steel sheet. Next, the plated steel sheet is cooled under conditions where the average cooling rate in the temperature range of 250°C to 400°C is 1.0°C / s or more. A method for manufacturing a hot-dip galvanized steel sheet, further comprising the process of applying a treatment to the plated steel sheet to impart a uniaxial tensile strain of 0.1% or more to the surface layer.

8. A method for manufacturing a hot-dip galvanized steel sheet according to claim 2, wherein a steel slab having the above-mentioned component composition is used. Hot-rolled steel sheet is obtained by hot-rolling. Next, the hot-rolled steel sheet is pickled to make a pickled sheet. Next, the pickled plate is subjected to cold rolling with a cumulative reduction ratio of 20% to 75% and a final pass speed of 50 mpm or more to obtain a cold-rolled steel sheet. Next, the cold-rolled steel sheet is annealed under the condition of a heating temperature of 780°C or higher. Next, the cold-rolled steel sheet is subjected to a hot-dip galvanizing treatment to become a plated steel sheet. Next, the plated steel sheet is cooled under conditions where the average cooling rate in the temperature range of 250°C to 400°C is 1.0°C / s or more. A method for manufacturing a hot-dip galvanized steel sheet, further comprising the process of applying a treatment to the plated steel sheet to impart a uniaxial tensile strain of 0.1% or more to the surface layer.

9. A method for manufacturing a hot-dip galvanized steel sheet according to claim 7, wherein the plated steel sheet is kept at a temperature range of 100°C to 450°C for 5 seconds or more during cooling, then cooled, and then subjected to the processing described above.

10. A method for manufacturing a hot-dip galvanized steel sheet according to claim 8, wherein the plated steel sheet is kept heated at a temperature range of 100°C to 450°C for 5 seconds or more during cooling, then cooled, and then subjected to the processing described above.

11. A method for manufacturing a hot-dip galvanized steel sheet according to claim 7, wherein during the cooling of the plated steel sheet, the cooling is stopped at a cooling stop point of 250°C or lower, then the sheet is reheated to a temperature range of (cooling stop temperature + 50°C) to 450°C, the sheet is kept hot in this temperature range for 5 seconds or more, then cooled, and then the processing is carried out.

12. A method for manufacturing a hot-dip galvanized steel sheet according to claim 8, wherein during the cooling of the plated steel sheet, the cooling is stopped at a cooling stop point of 250°C or lower, then the sheet is reheated to a temperature range of (cooling stop temperature + 50°C) to 450°C, the sheet is kept hot in this temperature range for 5 seconds or more, then cooled, and then the processing is carried out.

13. A method for manufacturing a hot-dip galvanized steel sheet according to claim 7, wherein during the cooling of the plated steel sheet, the cooling is stopped at a cooling stop point of 250°C or lower, the processing is then performed, and then the sheet is reheated to a temperature range of (cooling stop temperature + 50°C) to 450°C, the heat is maintained in this temperature range for 5 seconds or more, and then it is cooled.

14. A method for manufacturing a hot-dip galvanized steel sheet according to claim 8, wherein during the cooling of the plated steel sheet, the cooling is stopped at a cooling stop point of 250°C or lower, the processing is then performed, and then the sheet is reheated to a temperature range of (cooling stop temperature + 50°C) to 450°C, the heat is maintained in this temperature range for 5 seconds or more, and then it is cooled.

15. A method for manufacturing a hot-dip galvanized steel sheet according to any one of claims 7 to 14, wherein the steel sheet after the hot-dip galvanizing treatment is subjected to an alloying treatment.

16. A method for manufacturing a component, comprising the step of forming or joining a hot-dip galvanized steel sheet according to any one of claims 1 to 4 to form a component.

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