Plated steel material

Abstract

The present invention adopts a plated steel material provided with a plating layer formed on at least part of a surface of a base steel material, wherein: at least part of a surface of the plating layer has a site where a plurality of cracks is observed; the plurality of cracks extends in substantially the same direction as one another; and in the site, when a cross-section that is perpendicular to the direction in which the plurality of cracks extends and perpendicular to a surface of the plated steel material and that has a length of 200 μm in the direction parallel to the surface is taken as an observation region, the number ratio of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer is 80% or more based on all cracks observed in the observation region, the number ratio of distances Lc satisfying formula (1) is 80% or more based on all distances Lc observed in the observation region, and the average value of widths Wc of the cracks at a thickness position T / 2 away from the surface of the plating layer is 10 μm or less in the observation region, wherein a distance between adjacent cracks is denoted as Lc, and the thickness of the plating layer is denoted as T.　(1): 0.3T ≤ Lc ≤ 1.6T

Description

Plated steel

[0001] The present invention relates to a plated steel material.

[0002] Zn-Al-Mg-plated steel sheets having a Zn-Al-Mg-based plating layer containing Zn, Al, and Mg are used in the fields of building materials and civil engineering due to their excellent corrosion resistance, particularly sacrificial corrosion protection. When using Zn-Al-Mg-plated steel sheets in these fields, the Zn-Al-Mg-plated steel sheets may be processed into various shapes to produce plated steel products with bent portions. However, the Zn-Al-Mg-plated layer may have lower corrosion resistance in bent portions than a typical Zn-plated layer.

[0003] Patent Document 1 describes a plated steel material that includes a steel material and a plating layer that includes a Zn—Al—Mg alloy layer disposed on the surface of the steel material, wherein the Zn—Al—Mg alloy layer has a Zn phase and the Zn phase contains an Mg—Sn intermetallic compound phase, and the plating layer contains, in mass%, more than 65.0% Zn, more than 5.0% but less than 25.0% Al, more than 3.0% but less than 12.5% ​​Mg, and 0.1% to 20.0% Sn, and has a chemical composition that satisfies the following formulas 1 to 5, but does not consider the corrosion resistance of a bent portion: Formula 1: Bi + In < Sn Formula 2: Y + La + Ce ≦ Ca Formula 3: Si < Sn Formula 4: 0 ≦ Cr + Ti + Ni + Co + V + Nb + Cu + Mn < 0.25 Formula 5: 0 ≦ Sr + Sb + Pb + B < 0.5 In Formulas 1 to 5, the element symbols indicate the content of each element in mass %.

[0004] Patent Document 2 describes a hot-dip plated steel material comprising a steel material and a hot-dip plated layer disposed on the surface of the steel material, the hot-dip plated layer having a chemical composition, in mass %, of Al: 10.0 to 30.0%, Mg: 3.0 to 15.0%, Fe: 0.01 to 15.0%, and the balance: Zn and impurities, and the diffraction intensity obtained from an X-ray diffraction measurement of the hot-dip plated layer satisfies the relationships of the following formulas (1a) and (2a), but does not examine the corrosion resistance of bent portions: 0.3≦I(002) ＭｇＺｎ２ / {I(100) ＭｇＺｎ２ +I(101) ＭｇＺｎ２}≦3.0...(1a) 5.0<I(111) α / I (200) α ≦40.0 ... (2a) However, I(002) in formula (1a) ＭｇＺｎ２ is MgZn ２ is the diffraction intensity of the (002) plane of the phase, and I(100) ＭｇＺｎ２ is MgZn ２ is the diffraction intensity of the (100) plane of the phase, and I(101) ＭｇＺｎ２ is MgZn ２ In equation (2a), I(111)α is the diffraction intensity of (111) of the α phase, and I(200)α is the diffraction intensity of (200) of the α phase.

[0005] Patent Document 3 discloses a steel sheet having a steel plate and a plating layer formed on at least a part of the surface of the steel plate, the plating layer having a chemical composition, in mass %, of Al: 6.00 to 35.00%, Mg: 2.00 to 12.00%, Ca: 0.005 to 2.00%, and the balance: Zn and impurities, and the plating layer has a cross section in the thickness direction of the steel sheet having a composition of MgZn ２ The area ratio of the MgZn phase is 15 to 60%. ２ The document describes a hot-dip Zn-plated steel sheet containing a Ca-based intermetallic compound having a circle-equivalent diameter of 0.10 μm or less, but does not examine the corrosion resistance of the bent portion.

[0006] International Publication No. WO 2018 / 139619 International Publication No. WO 2023 / 182398 International Publication No. WO 2022 / 080004

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated steel material that has excellent sacrificial corrosion resistance and corrosion resistance in bent portions.

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A plated steel material comprising a base steel material and a plating layer formed on at least a part of a surface of the base steel material, wherein the chemical composition of the plating layer is, in mass%, Al: 1.0 to 30.0%, Mg: 1.0 to 10.0%, Fe: 0 to 2.0%, Si: 0 to 2.0%, Ni: 0 to 1.00%, Ca: 0 to 1.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Sn: 0 to 1.00%, Cu: 0 to 1.00%, Ti: 0 to 1.00%, Cr: 0 to 1.00%, Nb: 0 to 1.00%, Zr: 0 to 1.00%, Mn: 0 to 1.00%, Mo: 0 to 1.00%, Ag: 0 to 1.00%, Li: 0 to 1.00%, Bi: 0 to 1.00%, V: 0 to 1.00%, Co: 0 to 1.00%, In: 0 to 1.00%, La: 0 to 0.50%, Ce: 0 to 0.50%, B: 0 to 0.50%, Y: 0 to 0.50%, P: 0 to 0.50%, Sr: 0 to 0.50%, balance: 50.0 to 98.0% Zn and impurities, and the total of Sb, Pb, Cu, Sn, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, In, La, Ce, B, Y, P, and Sr is 0 to 5.00%, and at least a portion of the surface of the plating layer has a portion where a plurality of cracks are observed, a plated steel material in which, in the region of the observation, a cross section of the plated steel material having a length of 200 μm, which is perpendicular to the direction in which the cracks extend and perpendicular to the surface of the plated steel material and parallel to the surface, accounts for 80% or more of the number of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer; a distance between adjacent cracks, Lc, which is T, and a thickness of the plating layer, which satisfies the following formula (1):0.3T≦Lc≦1.6T ... (1) [2] The plated steel material according to [1], wherein, of all the cracks observed in the observation region of the portion, the proportion of cracks inclined at an angle of 40° to 50° with respect to the thickness direction of the plating layer is 70% or more. [3] The plated steel material according to [1] or [2], wherein the Al and Mg contents in the chemical composition of the plating layer are Al: 10.0 to 30.0 mass% and Mg: 4.0 to 10.0 mass%, respectively, and the proportion of the number of spacings Lc that satisfy the following formula (2) of all the spacings Lc observed in the observation region is 80% or more: 0.5T≦Lc≦1.4T ... (2) [4] The plated steel material according to [1] or [2], wherein the Al and Mg contents in the chemical composition of the plating layer are Al: 15.0 to 30.0 mass% and Mg: 5.0 to 8.0 mass%, respectively, and the proportion of the number of spacings Lc that satisfy the following formula (3) among all spacings Lc observed in the observation area is 80% or more. 0.5T≦Lc≦1.2T ... (3) [5] The plated steel material according to any one of [1] to [4], wherein the average value of the width Wc of the cracks at a thickness position T / 2 away from the surface of the plating layer in the observation area is 3 μm or less. [6] The plated steel material according to any one of [1] to [5], wherein the site is present on the inner side of a bent portion of a bent portion of the base steel material. [7] The plated steel material according to any one of [1] to [6], wherein the portion is present in a bent-back portion of the base steel material.

[0009] According to the present invention, a plated steel material having excellent sacrificial corrosion resistance and corrosion resistance of processed portions can be provided.

[0010] FIG. 2A is a schematic cross-sectional view showing a plated steel material according to an embodiment of the present invention. FIG. 2B is a schematic cross-sectional view illustrating a bent portion of a plated steel material according to an embodiment of the present invention. FIG. 2C is an enlarged cross-sectional view of the bent portion in FIG. 2A. FIG. 2D is a schematic cross-sectional view illustrating a bent-back portion of a plated steel material according to an embodiment of the present invention. FIG. 2E is a schematic plan view showing the surface of a plating layer of a plated steel material according to an embodiment of the present invention, illustrating a crack. FIG. 2F is a schematic cross-sectional view of a plating layer of a plated steel material according to an embodiment of the present invention. FIG. 2G is a schematic cross-sectional view of a plated steel material according to an embodiment of the present invention.

[0011] When a plated steel sheet having a Zn-Al-Mg-based plating layer is bent or otherwise processed into various shapes, cracks may occur in the plating layer at the bent or unbent portions. Cracks are likely to occur when compressive stress is applied to the plating layer during bending. The inventors have found that, in particular, irregular cracks in the plating layer degrade corrosion resistance, while regular cracks in the plating layer relieve compressive stress and prevent corrosion resistance degradation in the bent portion. Here, regular cracks refer to cracks that propagate in the depth direction of the plating layer, are inclined relative to the thickness direction of the plating layer, and are spaced approximately the same apart. Based on these findings, the inventors have successfully generated regular cracks in the plating layer at the bent portion by controlling the cooling conditions during the plating layer manufacturing process, thereby suppressing deterioration of corrosion resistance in the bent portion. Based on these findings, the inventors have completed the present invention.

[0012] A plated steel material according to an embodiment of the present invention is a plated steel material comprising a base steel material and a plating layer formed on at least a portion of the surface of the base steel material, and the plating layer has a chemical composition, in mass %, of Al: 1.0 to 30.0%, Mg: 1.0 to 10.0%, Fe: 0 to 2.0%, Si: 0 to 2.0%, Ni: 0 to 1.00%, Ca: 0 to 1.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Sn: 0 to 1.00%, Cu: 0 to 1.00%, Ti: 0 to 1.00%, and ... and the plating layer has a chemical composition, in mass %, of Al: 1.0 to 30.0%, Mg: 1.0 to 10.0%, Fe: 0 to 2.0%, Si: 0 to 2.0%, Ni: 0 to 1.00%, Ca: 0 to 1.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Sn: 0 to 1.00%, Cu: 0 to 1.00%, Ti: 0 to 1.00%, and Mg: 0 to 10.00%, and the plating layer has a chemical composition, in mass %, of Al: 1.0 to 30.0%, Mg: 1.0 to 10.0%, Fe : 0-1.00%, Cr: 0-1.00%, Nb: 0-1.00%, Zr: 0-1.00%, Mn: 0-1.00%, Mo: 0-1.00%, Ag: 0-1.00%, Li: 0-1.00%, Bi: 0-1.00%, V: 0-1.00%, Co: 0-1.00%, In: 0-1.00%, La: 0-0.50%, Ce: 0-0.50%, B: 0-0.50%, Y: 0-0.50%, P: 0-0.50%, Sr: 0-0.50%, balance: The plating layer has a surface having a region where a plurality of cracks are observed, and the cracks extend in substantially the same direction in the region, and the cracks are perpendicular to the direction in which the cracks extend in the region, and the cracks are 200 μm long in a cross section perpendicular to the surface of the plated steel material and parallel to the surface. When the cross section of a plated steel material is used as an observation area, of all cracks observed within the observation area, the proportion of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer is 80% or more, and when the distance between adjacent cracks is Lc and the thickness of the plating layer is T, of all distances Lc observed within the observation area, the proportion of distances Lc that satisfy the following formula (1) is 80% or more, and the average value of the width Wc of the cracks at a thickness position T / 2 away from the surface of the plating layer within the observation area is 10 μm or less. 0.3T≦Lc≦1.6T ... (1)

[0013] In a plated steel material according to an embodiment of the present invention, it is preferable that, of all cracks observed in the observation region of the portion, the proportion of cracks inclined at an angle of 40° to 50° with respect to the thickness direction of the plating layer is 70% or more. In a plated steel material according to an embodiment of the present invention, it is preferable that the chemical composition of the plating layer contains Al and Mg such that Al: 10.0 to 30.0 mass% and Mg: 4.0 to 10.0 mass%, respectively, and that, of all gaps Lc observed in the observation region, the proportion of the number of gaps Lc that satisfy the following formula (2) is 80% or more: 0.5T≦Lc≦1.4T (2) In a plated steel material according to an embodiment of the present invention, it is preferable that the chemical composition of the plating layer contains Al and Mg such that Al: 15.0 to 30.0 mass% and Mg: 5.0 to 8.0 mass%, respectively, and that, of all gaps Lc observed in the observation region, the proportion of the number of gaps Lc that satisfy the following formula (3) is 80% or more. 0.5T≦Lc≦1.2T (3) In addition, in the plated steel material according to an embodiment of the present invention, it is preferable that the average value of the width Wc of cracks at a thickness position T / 2 away from the surface of the plating layer within the observation region is 3 μm or less. It is also preferable that the site is located on the inside of the bent portion of the bent portion of the base steel material. It is also preferable that the site is located on the unbent portion of the base steel material.

[0014] The plated steel material of this embodiment is manufactured by subjecting a plated steel sheet, which serves as a raw material, to forming processes such as press working, roll forming, and bending. Therefore, the plated steel material has at least one bent portion. The plated steel material may also have a bent-back portion. The bent-back portion is formed by bending the plated steel sheet, which serves as a raw material, to form a bent portion, and then performing a bent-back process.

[0015] FIG. 1 shows a schematic cross-sectional view of a plated steel material 1. As shown in FIG. 1, the plated steel material 1 according to this embodiment includes a base steel material 11 and a plating layer 12 formed on at least a portion of the surface of the base steel material 11. The base steel material 11 is formed into various shapes by forming a steel plate. The shape of the base steel material 11 constituting the plated steel material 1 is not particularly limited. The base steel material 11 may be used, for example, as a steel pipe, a civil engineering and construction material (such as a fence, a corrugated pipe, a drainage ditch cover, a sand-flying prevention plate, a bolt, a wire mesh, a guardrail, a water cut-off wall, etc.), a home appliance component (such as a housing for an outdoor unit of an air conditioner), or an automotive component (such as an undercarriage component, an exterior component, an interior component, a structural component, etc.).

[0016] The material of the base steel material 11 is not particularly limited. The base steel material 11 may be made of various steels, such as general steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steels containing strengthening elements such as Ni and Cr). Similar to the base steel sheets (so-called base steel sheets) of various hot-dip galvanized steel sheets and steel strips described in JIS G 3302:2010, the base steel material 11 may be a hot-rolled steel sheet, a hot-rolled steel strip, a cold-rolled steel sheet, a cold-rolled steel strip, or the like. The chemical composition of the steel sheet that is the raw material for the base steel material 11, the manufacturing method (hot rolling method, pickling method, cold rolling method, etc.), and the specific manufacturing conditions thereof are also not particularly limited.

[0017] The plated steel material 1 according to this embodiment has a plating layer 12 disposed on at least a portion of the surface of a base steel material 11. The plating layer 12 is preferably a plating film produced by a so-called hot-dip galvanizing process. In the plated steel material 1 according to this embodiment, it is sufficient that the plating layer 12 is formed on at least a portion of the surface of the base steel material 11.

[0018] The plating layer 12 is mainly composed of a Zn-Al-Mg alloy layer due to its chemical composition, which will be described later. The plating layer 12 may include an Fe-Al-based interfacial alloy layer, mainly composed of Fe and Al, between the base steel 11 and the Zn-Al-Mg alloy layer. In other words, the plating layer 12 may have a single-layer structure of a Zn-Al-Mg alloy layer, or a multilayer structure including a Zn-Al-Mg alloy layer and an Fe-Al-based interfacial alloy layer.

[0019] In the following description, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. However, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," it means a range that does not include these numerical values ​​as the lower or upper limit. Next, the chemical composition of the plating layer 12 will be described below, and the "%" representation of the content of each element in the chemical composition means "mass %." The content of an element in the chemical composition may be expressed as element concentration (e.g., Zn concentration, Mg concentration, etc.).

[0020] "Corrosion resistance of processed portions" refers to the property of suppressing the occurrence of red rust in the bent portions 24 or bent-back portions 22A of the plated steel material 1. "Sacrificial corrosion protection" refers to the property of suppressing corrosion of the base steel material 11 at bare portions of the base steel material 11 (for example, the cut end surface of the plated steel material 1, cracks in the plated layer 12 during processing, and areas where the base steel material 11 is exposed due to peeling of the plated layer 12). "Base steel corrosion protection" refers to the property of the plated layer 12 itself being resistant to corrosion. "Wear resistance" refers to the property of the plated layer 12 being resistant to wear.

[0021] The plating layer 12 according to this embodiment contains Zn and other alloying elements. The plating layer 12 may also contain Zn, other alloying elements, and the remainder being impurities. Furthermore, the plating layer 12 may consist of Zn, other alloying elements, and the remainder being impurities. The chemical composition of the plating layer 12 will be described in detail below. Elements described as having a lower limit of 0% concentration are optional elements that are not essential for solving the problem but are allowed to be included in the plating layer 12 for purposes such as improving characteristics.

[0022] <Al: 1.0 to 30.0%> Al contributes to improving planar corrosion resistance and workability. Therefore, the Al concentration is set to 1.0% or more. On the other hand, if Al is excessive, the Mg concentration and Zn concentration are relatively reduced, resulting in deterioration of sacrificial corrosion protection. Therefore, the Al concentration is set to 30.0% or less. The Al concentration may be 5.0% or more, 10.0% or more, or 12.0% or more, or may be 28.0% or less, 25.0% or less, or 20.0% or less.

[0023] <Mg: 1.0 to 10.0%> Mg is an essential element for ensuring plane corrosion resistance. ２ Mg is also necessary for the crystallization of the Sn phase. Therefore, the Mg concentration is set to 1.0% or more. On the other hand, if the Mg concentration is excessive, the plating layer 12 becomes hard, the proportion of cracks 101 with an inclination angle of 35 to 55° decreases, the corrosion resistance of the processed part decreases, and further, the flat corrosion resistance may deteriorate. Therefore, the Mg concentration is set to 10.0% or less. The Mg concentration may be 3.0% or more or 5.0% or more, or 8.0% or less or 7.0% or less.

[0024] The plated steel material 1 of this embodiment may also have an Al and Mg content of 10.0 to 30.0 mass% Al and 4.0 to 10.0 mass% Mg. This results in a percentage of cracks 101 with an inclination angle of 40 to 50° of 70% or more. Furthermore, by limiting the Al and Mg contents to 10.0 to 30.0 mass% Al and 4.0 to 10.0 mass% Mg and by optimizing the manufacturing conditions, the percentage of the number of gaps Lc satisfying the above formula (2) is 80% or more. This further improves the corrosion resistance and sacrificial corrosion protection of the processed portion. Furthermore, by limiting the Al and Mg contents to 15.0 to 30.0 mass% Al and 5.0 to 8.0 mass% Mg and by optimizing the manufacturing conditions, the percentage of the number of gaps Lc satisfying the above formula (3) is 80% or more. This further improves the corrosion resistance and sacrificial corrosion protection of the processed portion.

[0025] The elements explained below are all optional elements except for Zn, and therefore the lower limit is set to 0%.

[0026] <Fe: 0 to 2.0%> The Fe concentration may be 0%, but since Fe may be mixed into the plating layer 12 from the steel, the plating layer 12 may contain 0.01% or more. It has been confirmed that an Fe concentration of 2.0% or less does not adversely affect the performance of the plating layer 12. The Fe concentration may be, for example, 0.01% or more, 0.1% or more, or 0.3% or more, or 1.0% or less, 0.8% or less, or 0.7% or less.

[0027] <Si: 0% to 2.0%> The Si concentration may be 0%. On the other hand, Si contributes to improving flat surface corrosion resistance. Therefore, the Si concentration may be greater than 0%, 0.01% or more, 0.1% or more, or 0.2% or more. On the other hand, if the Si concentration is excessive, flat surface corrosion resistance deteriorates. Therefore, the Si concentration is set to 2.0% or less. The Si concentration may also be set to 1.0% or less, 0.8% or less, or 0.5% or less.

[0028] <Ni: 0 to 1.00%> The Ni concentration may be 0%. On the other hand, Ni contributes to improving sacrificial corrosion protection. Therefore, the Ni concentration may be 0.001% or more. On the other hand, if the Ni concentration is excessive, planar corrosion resistance deteriorates. Therefore, the Ni concentration is set to 1.00% or less. The Ni concentration may also be 0.80% or less, 0.60% or less, or 0.50% or less.

[0029] <Ca: 0 to 1.00%> The Ca concentration may be 0%. On the other hand, Ca is an element that can adjust the amount of Mg elution that is optimal for imparting flat surface corrosion resistance. Therefore, the Ca concentration may be 0.01% or more, or 0.05% or more. On the other hand, if the Ca concentration is excessive, flat surface corrosion resistance and workability deteriorate. Therefore, the Ca concentration is set to 1.00% or less. The Ca concentration may also be set to 0.50% or less, 0.30% or less, or 0.20% or less.

[0030] <Sb, Pb: 0 to 0.50% each> The concentrations of Sb and Pb may be 0%. On the other hand, Sb and Pb contribute to improving sacrificial corrosion protection. Therefore, the concentrations of Sb and Pb may be 0.001% or more, 0.003% or more, or 0.005% or more. On the other hand, excessive concentrations of Sb and Pb deteriorate plane corrosion resistance. Therefore, the concentrations of Sb and Pb are set to 0.50% or less. The concentrations of Sb and Pb may also be set to 0.40% or less.

[0031] <Sn: 0 to 1.00%> The Sn concentration may be 0%. On the other hand, Sn is an element that forms an intermetallic compound with Mg and improves the planar corrosion resistance of the plating layer 12. Therefore, the Sn concentration may be 0.01% or more, or 0.05% or more. However, if the Sn concentration is excessive, the planar corrosion resistance will deteriorate. Therefore, the Sn concentration is set to 1.00% or less. The Sn concentration may also be 0.80% or less, 0.60% or less, 0.50% or less, or 0.20% or less.

[0032] <Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li: 0 to 1.00% each> The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li may each be 0%. On the other hand, these elements contribute to improving sacrificial corrosion protection. Therefore, the concentrations of these elements may each be 0.001% or more. On the other hand, excessive concentrations of these elements deteriorate planar corrosion resistance. Therefore, the concentrations of these elements are each set to 1.00% or less. The concentrations of these elements may each be set to 0.90% or less, 0.80% or less, 0.50% or less, 0.30% or less, or 0.20% or less.

[0033] <Bi, V, Co, In: 0 to 1.00% each> The concentrations of Bi, V, Co, and In may each be 0%. On the other hand, each of these elements contributes to improving sacrificial corrosion protection. Therefore, the concentrations of these elements may each be 0.001% or more or 0.01% or more. On the other hand, excessive concentrations of these elements deteriorate planar corrosion resistance. Therefore, the concentrations of Bi, V, Co, and In are each set to 1.00% or less. The concentrations of these elements may also be set to 0.90% or less, 0.50% or less, and 0.30% or less, respectively.

[0034] <La, Ce: 0 to 0.50% each> The concentrations of La and Ce may be 0%. On the other hand, La and Ce contribute to improving sacrificial corrosion protection. Therefore, the concentrations of these elements may each be 0.001% or more. On the other hand, excessive concentrations of La and Ce deteriorate planar corrosion resistance. Therefore, the concentrations of these elements are each set to 0.50% or less. The concentrations of these elements may also be set to 0.30% or less, 0.20% or less, or 0.10% or less, respectively.

[0035] <P: 0 to 0.50%> The P concentration may be 0%. On the other hand, P contributes to improving sacrificial corrosion protection. Therefore, the P concentration may be 0.001% or more, 0.005% or more, or 0.01% or more. On the other hand, if the P concentration is excessive, planar corrosion resistance deteriorates. Therefore, the P concentration is set to 0.50% or less. The P concentration may also be set to 0.30% or less.

[0036] <B, Y, and Sr: 0 to 0.50% each> The concentrations of B, Y, and Sr may each be 0%. On the other hand, B, Y, and Sr contribute to improving sacrificial corrosion protection. Therefore, the concentrations of these elements may each be 0.001% or more, 0.005% or more, or 0.01% or more. On the other hand, excessive concentrations of B, Y, and Sr deteriorate planar corrosion resistance. Therefore, the concentrations of these elements are each set to 0.50% or less. The concentrations of these elements may also be set to 0.40% or less, or 0.30% or less, respectively.

[0037] <Total of Sb, Pb, Cu, Sn, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, In, La, Ce, B, Y, P, Sr: 0 to 5.00%> The total of these elements is set to 0 to 5.00%. If the total exceeds 5.00%, flat surface corrosion resistance or sacrificial corrosion protection may decrease.

[0038] <Balance: Zn and Impurities> The balance of the chemical composition of the plating layer 12 according to this embodiment is 50.0 to 98.0% Zn and impurities. Zn is an element that provides the plating layer 12 with planar corrosion resistance and sacrificial corrosion protection, and therefore must be present in an amount of 50.0% or more. Zn may be 60.0% or more, 65.0% or more, 70.0% or more, 80.0% or more, or 90.0% or more. Zn is set to 98.0% or less. Impurities are elements that are primarily introduced from raw materials during the manufacturing process. The total concentration of impurities is typically 0.5% or less, but may also be 0.4% or less, 0.3% or less, 0.2% or less, or 0.1% or less. For various reasons, such as reducing raw material costs, raw materials containing relatively high amounts of elements other than those listed above, including Zn, may be used. Therefore, in this embodiment, these elements (elements other than the above-mentioned elements, including Zn) are all regarded as impurity elements, regardless of whether they are mixed in or intentionally added.

[0039] Furthermore, the plating layer 12 of the plated steel material 1 according to this embodiment may contain elements other than the above-mentioned alloying elements, Zn, and impurities.

[0040] The chemical composition of the plating layer 12 is measured by the following method. First, an acid containing an inhibitor that inhibits corrosion of the base steel 11 is used to remove and dissolve the plating layer 12 to obtain an acid solution. Next, the obtained acid solution is subjected to ICP analysis. This allows the chemical composition of the plating layer 12 to be obtained. For example, Hibilon (A-6), a pickling corrosion inhibitor, can be used as the inhibitor. Specifically, a 10% hydrochloric acid aqueous solution containing a 1% concentration of Hibilon (A-6) can be used as the acid containing the inhibitor.

[0041] Next, the plating layer 12 of the plated steel material 1 of this embodiment will be described. At least a portion of the surface of the plating layer 12 of this embodiment has a region where multiple cracks 101 are observed. The region where multiple cracks 101 are observed is preferably located on the inner bend side 24A of the bent portion 24. Alternatively, the region where multiple cracks are observed may be located in the unbent portion 22A of the plated steel material 1.

[0042] Here, "multiple cracks are observed" means that the appearance of the cracks 101 can be recognized when the surface of the plating layer 12 is observed with the naked eye, a magnifying glass, an optical microscope, or an electron microscope. Furthermore, the "area where multiple cracks are observed" may be any area on the surface of the plating layer 12 where multiple cracks 101 are adjacent to each other, and the size and shape of the area are not particularly limited.

[0043] In this embodiment, the bent portion 24 refers to a portion where the radius R of the bent inner side 24A is 10 times or less (i.e., R≦10t) the sheet thickness t of the plated steel material 1. The bending angle of the bent portion 24 is not particularly limited and may be, for example, 10° or more, 30° or more, 45° or more, 60° or more, 90° or more, or 120° or more, and is not limited to these exemplary angles.

[0044] Furthermore, in this embodiment, the bent-back portion 22A refers to the portion that has undergone a bending process after undergoing a bending process in which the bending radius R is 10 times or less the plate thickness t of the plated steel material (i.e., R≦10t).

[0045] In the present embodiment, even if there is a region in which a plurality of cracks 101 are observed in at least a part of the plating layer 12, it is not necessary for the plurality of cracks 101 to be observed and for the requirements described below to be satisfied (specifically, requirement 1: the proportion of the number of cracks 101 inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer 12 is 80% or more, requirement 2: the proportion of the number of cracks with intervals Lc satisfying formula (1) is 80% or more, and requirement 3: the average value of the widths Wc of the cracks 101 at thickness positions T / 2 away from the surface of the plating layer 12 is 10 μm or less). It is sufficient that a plurality of cracks 101 are observed in at least a part of the plating layer 12, and when measured according to the measurement method described below, there is a region in which a plurality of cracks 101 are observed that satisfies the requirements described below.

[0046] A plurality of cracks 101 are observed on the inner bend side 24A of the bent portion 24 with a bend radius R≦10t, and when measured according to the measurement method described below, there is a region where a plurality of cracks 101 that satisfy the requirements described below are observed. Similarly, a plurality of cracks 101 are observed on one side (the surface that was the inner bend side 24A at the time of the initial bending) of the unbent portion 22A that has been unbent after bending to a bend radius R≦10t, and when measured according to the measurement method described below, there is a region where a plurality of cracks 101 that satisfy the requirements described below are observed.

[0047] Furthermore, even if the radius R of the inner side of the bend 24A is less than 10 times the sheet thickness t of the plated steel sheet 1, there may be a portion on the inner side of the bend 24A where multiple cracks 101 are observed and where the multiple cracks 101 satisfy the requirements described below. Similarly, regardless of the bend radius R, there may be a portion on one or both sides of the unbent portion 22A that has been bent and then unbent, where multiple cracks 101 are observed and where the multiple cracks 101 satisfy the requirements described below when measured according to the measurement method described below.

[0048] 2A has a hat-shaped cross section and includes a flat portion 21, a vertical wall portion 22, and a flange portion 23, and a bent portion 24 is provided between the flat portion 21 and the vertical wall portion 22. A portion on the surface of the bent inner side 24A of the bent portion 24 has a portion where multiple cracks 101 are observed.

[0049] 2B is an enlarged cross-sectional view of the bent portion 24 of the hat-shaped plated steel material 1 shown in FIG. 2A. As shown in FIG. 2B, a plurality of cracks 101 have occurred in the plating layer 12 on the inner side 24A of the bend. The extension direction of these cracks 101 is substantially along the extension direction of the bent portion 24 (the direction perpendicular to the paper surface of FIGS. 2A and 2B). In other words, the extension direction of these cracks 101 is substantially the same direction as the extension direction of the bent portion 24.

[0050] 3 has a hat-shaped cross section and includes a flat portion 21, a vertical wall portion 22, and a flange portion 23. A bent-back portion 22A is provided in the widthwise center of the vertical wall portion 22. The bent-back portion 22A is formed by bending back the bent portion. A portion of the bent-back portion 22A that was on the inner side of the bent portion has a surface where multiple cracks 101 are observed.

[0051] Fig. 4 is a partially enlarged view of the surface of the plating layer 12, showing a region where multiple cracks 101 are observed. As shown in Fig. 4, the multiple cracks 101 extend in substantially the same direction and are aligned in a direction perpendicular to the extension direction of the cracks 101. The extension direction of the cracks 101 is substantially the same as the extension direction of the bent portion 24. The cracks 101 may be linear, or may have an irregular shape as shown in Fig. 4.

[0052] Next, the morphology of the cracks 101 in the cross section of the plating layer 12 will be described. Fig. 5 shows a cross section perpendicular to the direction in which the multiple cracks 101 extend and perpendicular to the surface of the plated steel material 1. Fig. 5 is a cross section of the plating layer 12 in an observation area K. The observation area K is a 200 µm long cross section of the plated steel material 1 that is approximately perpendicular to the direction in which the multiple cracks 101 extend and parallel to the surface of the plated steel material 1. Multiple cracks 101 are observed in the plating layer 12 in the observation area K. The number of observation areas K in the plating layer 12 is five.

[0053] The procedure for preparing the observation area K is as follows. A specimen for observation (e.g., a size of 100 mm x 50 mm x plate thickness) is cut out so that the plating layer 12 is not damaged by machining during cross-sectional observation, and this is embedded in resin to create a test piece. After embedding in resin, the test piece is cut and polished to a mirror finish to expose the cross section of the plating layer and base steel material. When cutting, the cut is made in a direction perpendicular to the surface of the plated steel material 1 (plating layer 12). The cross section of this test piece is observed with a scanning electron microscope (SEM), and after setting the observation area K, cracks in the cross section of the plating layer are observed.

[0054] 5 shows a state in which the tips of all cracks 101 within the observation region K have reached the interface between the base steel material 11 and the plating layer 12, but the present invention is not limited to this, and as shown in Fig. 2B, there may be cracks 101 whose tips have not reached the interface between the base steel material 11 and the plating layer 12. As shown in Fig. 2B, cracks 101 whose tips have not reached the interface between the base steel material 11 and the plating layer 12 are also included as objects to be measured.

[0055] In this embodiment, in the region where the plurality of cracks 101 are observed, the direction in which the plurality of cracks 101 extend in the depth direction of the plating layer 12 is inclined with respect to the thickness direction of the plating layer 12, and the interval Lc between adjacent cracks 101 is substantially constant. The presence of the cracks 101 at such regular intervals improves the corrosion resistance of the processed portion, i.e., the inner bent portion 24A and the unbent portion 22A of the bent portion 24.

[0056] In this embodiment, with regard to the direction of the cracks 101 extending in the depth direction of the plating layer 12, the number ratio of the cracks 101 inclined at an angle θ of 35° to 55° with respect to the thickness direction of the plating layer 12 is 80% or more among all the cracks 101 observed in the five observation regions K. The presence of 80% or more of the cracks 101 with an inclination angle θ in the range of 35° to 55° in the observation region K makes it possible to relieve the compressive stress applied to the plating layer 12 during bending, suppressing the occurrence of irregular cracks 101 and improving the corrosion resistance of the inner bend side 24A and the unbent portion 22A of the bent portion 24. The number ratio of the cracks 101 with an angle θ of 35° to 55° may be 85% or more, 90% or more, 95% or more, or 98% or more.

[0057] Preferably, the proportion of cracks 101 having an inclination angle θ in the range of 40° to 50° may be 70% or more. The proportion of cracks 101 having an angle θ of 40° to 50° may be 80% or more, 85% or more, 90% or more, 95% or more, or 98% or more.

[0058] The cross-sectional shape of the crack 101 is not particularly limited, and may be approximately V-shaped as shown in Figure 5, or may be a crack with an irregular cross-sectional shape, such as crack 101A depicted at the right end of Figure 5.

[0059] As shown in FIGS. 5 and 6, the inclination angle θ of the crack 101 is determined by the width W of the opening of the crack 101 on the surface of the plating layer 12. １ The center position of the opening (width W １ the widthwise center position of the crack 101 on the base steel material 11 side) and the opening width W ２ The center position (opening width W ２ a slanted imaginary line L connecting the １ When the virtual line L １ The angle θ between the direction W and the thickness direction of the plating layer 12 is defined as the inclination angle of the crack 101. １／２ , W ２／２ is the width of the opening W １ , W ２ If the tip of the crack 101 does not reach the interface between the base steel material 11 and the plating layer 12, the position of the tip and the width W of the opening of the crack on the surface of the plating layer 12 are １ The center position of the opening (width W １ The line connecting the two (the center position in the width direction) is the inclined imaginary line L １ This can be done as follows.

[0060] Next, the spacing Lc between the cracks 101 will be described. When the spacing Lc between adjacent cracks 101 is Lc and the thickness of the plating layer 12 is T, the proportion of the spacing Lc that satisfies the following formula (1) among all the spacings Lc observed in the five observation regions K must be 80% or more. If Lc is less than 0.3T, the spacing Lc between the cracks 101 is too narrow, making the cracks 101 more likely to be irregularly spaced, and reducing the corrosion resistance of the processed portion. If Lc exceeds 1.6T, the spacing Lc between the cracks 101 is too wide, making the cracks 101 more likely to be irregularly spaced. Furthermore, if the proportion of the spacing Lc that satisfies the following formula (1) is less than 80%, the occurrence of irregularly spaced cracks 101 cannot be sufficiently suppressed, and the corrosion resistance of the processed portion may be reduced.

[0061] To further improve the corrosion resistance of the processed portion, it is preferable that the proportion of the number of spacings Lc satisfying the following formula (2) among all spacings Lc observed in the five observation regions K be 80% or more, and it is even more preferable that the proportion of the number of spacings Lc satisfying the following formula (3) be 80% or more. To achieve a proportion of the number of spacings Lc satisfying the following formula (2) or (3) be 80% or more, as described above, it is preferable to set the Al content and Mg content of the plating layer 12 to a more preferable range and to limit the manufacturing conditions to a suitable range. This further improves the corrosion resistance and sacrificial corrosion protection of the processed portion. The proportion of the number of spacings Lc satisfying the following formula (1) may be 85% or more, 90% or more, or 95% or more. Similarly, the proportion of the number of spacings Lc satisfying the following formula (2) may be 85% or more, 90% or more, or 95% or more, and the proportion of the number of spacings Lc satisfying the following formula (3) may be 85% or more, 90% or more, or 95% or more.

[0062] 0.3T≦Lc≦1.6T…(1) 0.5T≦Lc≦1.4T…(2) 0.5T≦Lc≦1.2T…(3)

[0063] As shown in FIGS. 5 and 6, the interval Lc between the cracks 101 is determined by the width W of the opening of each crack 101 on the surface of the plated steel material 1 (i.e., the surface of the plating layer 12) in the five observation areas K. １ The center position of the opening (width W of the opening when observing the cross section) １ The ratio of the number of cracks 101 satisfying each of the formulas (1) to (3) is the ratio obtained by taking the number of intervals between all cracks 101 observed in the five observation regions K as the denominator and the number of intervals that satisfy the respective formula (i.e., formula (1), formula (2), or formula (3)). For example, in FIG. 5, a total of four cracks 101 are observed. A total of three intervals Lc between cracks are observed.

[0064] Next, within the five observation regions K, the average value of the crack width Wc at a thickness position T / 2 away from the surface of the plating layer 12 (hereinafter referred to as the T / 2 position) must be 10 μm or less. If the width Wc of the crack 101 exceeds 10 μm, the corrosion resistance of the processed portion will decrease, which is undesirable. The width Wc of the crack 101 may be 5 μm or less, or may be 3 μm or less. There is no particular need to limit the lower limit of the width Wc of the crack 101, and it may be around 0 μm, that is, it may be a width that allows signs of cracking of the plating layer 12 to be observed in the observation region K.

[0065] Next, Mg is added to the plating layer 12. ２ When the Sn phase is contained, the corrosion resistance of the base steel of the plated steel material 1 is further improved. Therefore, the plating layer 12 contains Mg ２ It is preferable that the Sn phase is contained. ２ Since the Sn phase is present in a small amount, its presence can be confirmed by X-ray diffraction measurement. ２ In order to contain the Sn phase, the chemical composition of the plating layer 12 preferably contains Sn: 0.02 to 1.0%.

[0066] X-ray diffraction measurement is performed by the θ-2θ method. The X-ray diffraction device used is Rigaku Corporation's RINT1500 or a device with performance equivalent to or better than the RINT1500. Kα rays from a Cu tube are used as the X-ray source. The X-ray output conditions are a voltage of 40 kV and a current of 150 mA. The measurement range is 2θ = 10 to 30° in 0.02° steps. When a diffraction peak is detected at 23.4±0.3°, Mg ２ It is determined that a Sn phase is present.

[0067] The thickness of the plating layer 12 may be, for example, within a range of 5 to 100 μm. By making the thickness of the plating layer 12 5 μm or more, the planar corrosion resistance and sacrificial corrosion protection of the plated steel material 1 can be further improved. On the other hand, by making the thickness 100 μm or less, regular cracks 101 are more likely to occur, improving the corrosion resistance of the processed portion. The thickness of the plating layer 12 may be 10 μm or more, 25 μm or more, or 30 μm or more. The thickness of the plating layer 12 may also be 70 μm or less, 60 μm or less, or 50 μm or less.

[0068] Next, a method for manufacturing the plated steel material 1 according to this embodiment will be described, but the method for manufacturing the plated steel material 1 according to this embodiment is not particularly limited. For example, the plated steel material 1 according to this embodiment can be obtained according to the manufacturing conditions described below.

[0069] As described above, the plated steel material 1 of this embodiment is manufactured by subjecting a plated steel sheet, which serves as a raw material, to forming processes such as press working, roll forming, and bending. Plated steel sheets are manufactured by forming a plating layer on the surface of a steel sheet by hot-dip galvanizing and controlling the cooling conditions after the steel sheet is pulled out of the plating bath. The plated steel material 1 of this embodiment is then manufactured by subjecting this plated steel sheet to forming processing. When the plated steel sheet is formed, compressive stress is applied to the plating layer 12 on the inner bend side 24A of the bent portion 24, causing regular cracks 101 to occur. Similarly, regular cracks 101 also occur when bending is performed to form the bent-back portion 22A. In this way, the plated layer 12 of this embodiment is obtained.

[0070] Therefore, in the following description, first, a method for manufacturing a plated steel sheet that is the raw material for the plated steel product 1 will be described.

[0071] In the method for producing a plated steel sheet, a steel sheet is annealed in a reducing atmosphere, the annealed steel sheet is immersed in a hot-dip galvanizing bath, and the steel sheet is pulled out of the hot-dip galvanizing bath to form a plated layer 12 on the surface of the steel sheet. Next, the temperature of the plated layer 12 is increased from the bath temperature to 390°C by a speed of 30,000 to 40,000 (L / min / m ２ The material is then cooled to a temperature range of 390 to 20°C at an average cooling rate of 20 to 40°C / sec while blowing cooling gas at a flux of 1000 rpm. After cooling is complete, the material is reheated at a soaking temperature of 70 to 230°C for a soaking time of 10 to 2000 seconds.

[0072] Annealing of the steel sheet to be used as the base sheet for plating is carried out in a reducing atmosphere. The reducing atmosphere and annealing conditions are not particularly limited. By this annealing, oxides present on the surface of the steel sheet are removed as much as possible.

[0073] The steel sheet immediately after annealing is then immersed in a hot dip coating bath. Before immersing the steel sheet in the coating bath, the steel sheet immediately after annealing may be cooled with a cooling gas such as nitrogen until the temperature of the steel sheet reaches about (coating bath temperature + 20)°C.

[0074] The chemical composition of the plating bath may be adjusted as appropriate to obtain the above-described chemical composition of the plating layer 12. The temperature of the plating bath is not particularly limited, and any temperature at which hot-dip plating can be performed may be appropriately selected. For example, the plating bath temperature may be set to a value approximately 20°C or more higher than the melting point of the plating bath.

[0075] Next, the steel sheet is pulled up from the hot-dip galvanizing bath. The thickness of the plating layer 12 can be controlled by controlling the pulling speed of the steel sheet. If necessary, the steel sheet to which the plating layer 12 is attached may be wiped to control the thickness of the plating layer 12. The thickness of the plating layer 12 is not particularly limited and can be, for example, within the above-mentioned range.

[0076] Next, the plating layer 12 is cooled. First, the plating layer 12 is cooled from the bath temperature to 390°C at an average cooling rate of 15 to 19°C / sec. The cooling is performed, for example, by spraying cooling gas, and the flux of the cooling gas at this time is set to 30,000 to 40,000 (L / min / m ２ When cooling is performed by spraying cooling gas, a plurality of nozzles for spraying the cooling gas may be arranged along the steel plate transport path, and the cooling gas may be sprayed from the nozzles.

[0077] When the temperature of the coating layer 12 reaches from the bath temperature to 390°C, a cooling gas is blown at a predetermined flux to supercool the surface of the coating layer 12 and to vibrate it. This promotes nucleation of phases and structures that form relatively hard regions on the surface of the coating layer 12. The cooling gas flux is then set to 30,000 to 40,000 (L / min / m ２ ) range, cracks 101 are more likely to occur regularly in the subsequent forming process, and the corrosion resistance of the processed portion is improved.

[0078] Furthermore, if the average cooling rate at which the temperature of the plating layer 12 is reduced from the bath temperature to 390°C is 15°C / s or more, the phases and structures constituting the relatively hard regions on the surface of the plating layer 12 are sufficiently formed, relatively soft regions are not excessively precipitated, and cracks 101 tend to occur regularly during subsequent forming. On the other hand, if the average cooling rate is 19°C / s or less, the phases and structures constituting the relatively hard regions on the surface of the plating layer 12 are sufficiently formed, and cracks 101 tend to occur regularly during subsequent forming. If the average cooling rate exceeds 19°C / s, the entire plating layer is supercooled, and the phases and structures constituting the hard regions crystallize not only on the surface of the plating layer but also inside it, making it difficult to localize the hard regions on the surface of the plating layer.

[0079] Next, the steel sheet is cooled to a temperature range of 390 to 20°C at an average cooling rate of 20 to 40°C / second while being sprayed with cooling gas. In this case, multiple spray nozzles for cooling gas are also arranged along the steel sheet transport path, but the flux of cooling gas during cooling in the range of 390 to 20°C is not particularly limited. After cooling is complete, the steel sheet is reheated at a soaking temperature of 70 to 230°C for a soaking time of 10 to 2000 seconds.

[0080] If the cooling end temperature exceeds 20°C, the aging effect on the phases and structures constituting the relatively hard regions will be insufficient, resulting in excessive precipitation of relatively soft regions, making it difficult for cracks 101 to occur regularly. Therefore, it is necessary to continue cooling at an average rate of 20°C / sec or more until the temperature reaches 20°C.

[0081] By setting the average cooling rate in the range of 390 to 20°C to 20°C to 20°C, the formation of phases and structures constituting the relatively hard regions is sufficient, and relatively soft regions are not excessively precipitated, making it easier for cracks 101 to occur regularly during subsequent forming. Furthermore, by setting the average cooling rate to 40°C / sec or less, the formation of phases and structures constituting the relatively hard regions is sufficient, making it easier for cracks 101 to occur regularly during subsequent forming. If the average cooling rate exceeds 40°C / sec, excessive vacancies that act as a driving force for aging precipitation are introduced, making it more difficult to control the strengthening state due to aging precipitation in the subsequent heat treatment process (reheating). For this reason, the average cooling rate in the range of 390 to 20°C is set to 40°C / sec or less.

[0082] The plated layer 12 is cooled to a temperature range of 390 to 20°C at an average cooling rate of 20 to 40°C / second, and then reheated. Reheating promotes the formation of relatively soft regions within the plated layer 12 and allows the distribution of the soft regions within the plated layer 12 to be controlled to a preferred state, which makes it easier for cracks 101 to occur regularly during subsequent forming. Reheating after cooling is performed under the conditions of a soaking temperature of 70 to 230°C and a soaking time of 10 to 2000 seconds, as described above. More preferably, the soaking temperature is 120 to 180°C and a soaking time of 120 to 2000 seconds.

[0083] In the cooling range from the bath temperature to 390°C and from 390°C to 20°C, the type of cooling gas to be sprayed is not particularly limited, and may be a non-oxidizing gas such as nitrogen, an inert gas such as argon, or air, or a mixed gas of these.

[0084] When controlling the flux of cooling gas, the diameter of the gas nozzle from which the cooling gas is ejected is, for example, in the range of 1 to 50 mm. The angle between the tip of the gas nozzle and the steel plate is, for example, in the range of 70 to 110°, more preferably 90° (right angle). The distance between the tip of the gas nozzle and the steel plate is in the range of 30 to 1000 mm.

[0085] Next, the manufactured plated steel sheet is subjected to forming. The forming conditions do not need to be particularly limited, and press working, roll forming, bending, etc. can be applied. The forming preferably includes bending of at least 10T or more. 10T bending refers to bending in which the bending radius R of the inner bend 24A of the bent portion 24 is 10 times or less the thickness t of the plated steel sheet (R≦10t). The forming may also include rebending. Rebending refers to bending under conditions in which the bending radius R is 10t or less, followed by rebending.

[0086] The plated steel material 1 of this embodiment is manufactured by performing forming processing. The plated steel material 1 includes a region in which multiple cracks 101 are observed in at least a portion of the plating layer 12. The multiple cracks 101 extend in approximately the same direction. Within the observation region K, the percentage of cracks 101 inclined at an angle of 35° to 55° is 80% or more, the percentage of the number of cracks whose spacing Lc satisfies the above formula (1) is 80% or more, and the average width Wc of the cracks 101 at the T / 2 position is 10 μm or less.

[0087] Furthermore, in order for the plated steel material 1 to satisfy the above formula (2), it is preferable to set the Al and Mg contents in the chemical composition of the plating layer 12 to Al: 10.0 to 30.0 mass % and Mg: 4.0 to 10.0 mass %, respectively, and then perform reheating under suitable conditions, i.e., a soaking temperature of 120 to 180°C and a soaking time of 120 to 2000 seconds.

[0088] Furthermore, in order for the plated steel material 1 to satisfy the above formula (3), it is preferable that the Al and Mg contents in the chemical composition of the plating layer 12 are set to Al: 15.0 to 30.0 mass% and Mg: 5.0 to 8.0 mass%, respectively, and that the average cooling rate in the range of 390 to 20°C is set to 30°C / second or more, and that reheating is performed under conditions of a soaking temperature of 120 to 180°C and a soaking time of 120 to 2000 seconds.

[0089] Furthermore, in order to make the average width Wc of the cracks 101 3 μm or less, it is preferable to set the average cooling rate in the range of 390 to 20°C to 35°C / second or more, and to set the reheating conditions to a soaking temperature of 120 to 180°C and a soaking time of 120 to 2000 seconds.

[0090] Examples of the present invention will be described below. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0091] The base steel sheet used for plating was a cold-rolled steel sheet with a thickness of 1.0 mm (steel type A in Tables 1-1 and 1-2) or a hot-rolled steel sheet with a thickness of 3.2 mm (steel type B in Tables 1-1 and 1-2). The chemical composition of the base steel sheet was 0.05% C-0.1% Si-0.2% Mn. The base steel sheet was annealed. The annealing conditions were N with the oxygen concentration controlled to 20 ppm or less. ２ -4% H ２ The conditions were a soaking temperature of 600°C and a soaking time of 2 minutes in a nitrogen atmosphere. ２ The temperature during immersion in the plating bath was adjusted to (plating bath temperature + 20)°C by air cooling with gas, and then the steel was immersed in various hot dip plating baths and pulled up at a pulling speed of 20 to 200 mm / sec. ２ The coating weight was controlled by wiping gas. After the base steel sheet was pulled out of the coating bath, it was cooled under the conditions shown in Tables 2-1 and 2-2.

[0092] In the cooling range of the bath temperature to 390°C and the cooling range of 390 to 20°C, the cooling gas was N ２ During cooling in the bath temperature range of 390°C, the gas flux was controlled as shown in Tables 2-1 and 2-2. The diameter of the gas nozzle from which the cooling gas was ejected was 6 mm, the angle between the tip of the gas nozzle and the steel plate was a right angle, and the distance between the tip of the gas nozzle and the steel plate was 35 mm.

[0093] Furthermore, the plated steel sheets after cooling were reheated under the conditions shown in Tables 2-1 and 2-2. In this way, plated steel sheets were produced.

[0094] The obtained plated steel sheets were subjected to press working using a punch and a die to produce plated steel materials Nos. 1 to 43 each having a hat-shaped cross section as shown in FIG. 2A.

[0095] The press working was adjusted so that the bending radius R of the bent portion between the flat portion and the vertical wall portion was three times the thickness t of the plated steel sheet (3T bend) or ten times the thickness t (10T bend). In addition, for some plated steel materials, the cross-sectional shape was formed into a hat shape by press working, and then the bent portion between the flat portion and the vertical wall portion was bent back to form the bent-back portion. The processing columns in Tables 2-1 and 2-2 are denoted as follows:

[0096] A: Bent section (bending radius R = plate thickness (mm) x 3 (3T bend)) B: Bent section (bending radius R = plate thickness (mm) x 10 (10T bend)) C: Unbent section (bent at a bending radius R = 5 mm and then unbent)

[0097] The chemical compositions of the plating layers were as shown in Tables 1-1 and 1-2. Furthermore, the corrosion resistance and sacrificial corrosion protection of the processed parts of the plated steel materials were evaluated, and the results are shown in Tables 5-1 and 5-2.

[0098] The evaluation method will be described below.

[0099] The chemical composition of the plating layer was measured by immersing a sample cut to a size of 30 mm x 30 mm in a 10% HCl aqueous solution containing 1% inhibitor (Hibilon (A-6)) to pickle and remove the plating layer, and then performing ICP analysis of the elements eluted into the aqueous solution. The results are shown in Table 1.

[0100] In addition, Mg in the plating layer ２ The presence of the Sn phase was confirmed by X-ray diffraction measurement. The X-ray diffraction measurement was performed by the θ-2θ method. The X-ray diffraction device used was RINT1500 manufactured by Rigaku Corporation. Kα rays from a Cu tube were used as the X-ray source. The X-ray output conditions were a voltage of 40 kV and a current of 150 mA. The measurement range was 2θ = 10 to 30° in 0.02° steps. When a diffraction peak was detected at 23.4±0.3°, it was determined that the Sn phase was Mg. ２It was determined that the Sn phase was present. ２ The presence or absence of Sn phase is indicated.

[0101] Next, the occurrence of cracks in the plated steel material was confirmed. Test specimens were prepared by cutting out the bent or unbent portions from the manufactured plated steel material. The test specimens were 100 mm long and 50 mm wide. After embedding the test specimens in resin, they were polished to a mirror finish to expose the cross-sections of the plating layer and base steel. The occurrence of cracks in the cross-sections of the plating layer of these test specimens was observed using a scanning electron microscope (SEM). The results are shown in Tables 3-1 to 4-2.

[0102] The cracks were confirmed by the following method. When observing the cross section of the plating layer with a scanning electron microscope (SEM), the observation area was a 200 μm long area in a direction parallel to the surface, perpendicular to the direction in which the cracks extended and perpendicular to the surface of the plated steel material. The number of observation areas K was five.

[0103] Then, among all cracks observed in the five observation regions, the percentage of cracks inclined at an angle θ of 35° to 55° with respect to the thickness direction of the plating layer was calculated. Similarly, the percentage of cracks with an inclination angle θ in the range of 40° to 50° was calculated.

[0104] There are no particular restrictions on the cross-sectional shape of the crack to be measured. For example, as shown in Figure 5, cracks that are approximately V-shaped, as well as cracks with irregular cross-sectional shapes, such as crack 101A depicted on the right side of Figure 5, can be measured.

[0105] The inclination angle θ of the crack 101 is, for example, as shown in FIGS. 5 and 6, the width W of the opening of the crack on the surface of the plating layer. １ The center position of the opening (width W １ The width of the crack on the base steel side is W ２ The center position of the opening (width W ２ a slanted imaginary line L connecting the １ When the virtual line L １ and the thickness direction of the plating layer was defined as the inclination angle of the crack 101.

[0106] As shown in Figures 5 and 6, the crack spacing Lc was calculated by dividing the width W of the openings of adjacent cracks on the surface of the plating layer in the five observation areas. １ The ratio of the number of cracks satisfying each of the above formulas (1) to (3) was determined as the ratio of the number of cracks to the number of intervals between cracks observed within the five observation regions K.

[0107] Next, the crack width Wc was determined as the crack width Wc at the T / 2 position as shown in Fig. 5. The average value of all the crack widths Wc observed in the five observation regions K was calculated.

[0108] <Corrosion Resistance of Processed Part> The corrosion resistance of processed parts was evaluated as follows. A bent or unbent part was cut out from the manufactured plated steel material to prepare a test specimen. The test specimen had a length of 100 mm and a width of 50 mm. The longitudinal direction of the test specimen was aligned with the bending axis direction of the bent part or the bending axis direction of the unbent part. An accelerated corrosion test specified in 8.1 Neutral Salt Spray Cycle Test Method of JIS H8502:1999 was conducted on a portion of the bent or unbent part of the test specimen where multiple cracks were observed. The number of cycles until red rust appeared in the bent or unbent part was then measured. The evaluation criteria were as follows, with AAA, AA, and A being considered pass.

[0109] AAA: Red rust occurs in 360 or more cycles. AA: Red rust occurs in 240 or more cycles but less than 360 cycles. A: Red rust occurs in 120 or more cycles but less than 240 cycles. B: Red rust occurs in less than 120 cycles.

[0110] <Sacrificial corrosion protection> Sacrificial corrosion protection was evaluated as follows. Before forming, a plated steel sheet was cut perpendicular to the surface of the plated steel sheet using a fine cutter to expose the cut edge. The cross section of the plating layer and the cross section of the base steel were exposed at the cut edge. A neutral salt spray test according to JIS Z2371:2015 was performed on this cut edge, and the time (h) until red rust appeared at the cut edge was measured. The evaluation criteria were as follows, with B being considered a failure and AAA, AA, and A being considered passes.

[0111] AAA: 2400 hours or more AA: 1500 hours or more but less than 2400 hours A: 720 hours or more but less than 1500 hours B: Less than 720 hours

[0112] As shown in Tables 1-1 to 5-1, inventive examples Nos. 1 to 28, multiple cracks were observed in the bent or unbent portions. The multiple cracks extended in approximately the same direction, with each crack extending along the longitudinal direction of the bent portion or the longitudinal direction of the unbent portion, and the cracks were aligned perpendicular to the direction of crack propagation. Furthermore, the chemical composition of the plating layer and the crack specifications were within the scope of the present invention. This resulted in excellent corrosion resistance and sacrificial corrosion protection in the processed portion of the plating layer.

[0113] In Nos. 1, 2, 4, 6, 8 to 24, and 26 to 28, the percentage of cracks inclined at an angle of 40° to 50° relative to the thickness direction of the plating layer was 80% or more, and the corrosion resistance and sacrificial corrosion protection of the processed part were good.

[0114] In addition, in Examples 2, 6, 10, 11, 18, and 28, the percentage of crack spacing Lc satisfying formula (2) was 80% or more. Furthermore, in Examples 1, 8, 9, 12 to 17, 19 to 24, 26, and 27, the percentage of crack spacing Lc satisfying formula (2) was 80% or more, and the percentage of crack spacing Lc satisfying formula (3) was 80% or more. All of these Examples had particularly good corrosion resistance and sacrificial corrosion protection in the processed portion.

[0115] On the other hand, in Comparative Example No. 29, the Mg concentration in the plating layer was insufficient. Furthermore, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, and the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%. This resulted in poor corrosion resistance and sacrificial corrosion protection in the processed area.

[0116] In No. 30, the Mg concentration in the plating layer was excessive. Furthermore, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0117] In Nos. 31 and 39, the reheating temperature was low. This made it difficult for cracks to occur regularly during forming, and as a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and further, the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0118] In No. 32, the Al concentration in the plating layer was insufficient. Furthermore, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. Multiple cracks were concentrated in almost one location and were not regular. This resulted in poor corrosion resistance in the processed area.

[0119] In No. 33, the Al concentration in the plating layer was excessive. Furthermore, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0120] In No. 34, the average cooling rate in the range of 390 to 20°C was insufficient. As a result, cracks were less likely to occur regularly during forming. As a result, the percentage of cracks inclined at an angle of 35 to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0121] In No. 35, the cooling time from 390°C was set to 45°C. This made it difficult for cracks to occur regularly during forming, and as a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and further, the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0122] In No. 36, the average cooling rate in the bath temperature range of 390°C was insufficient. This made it difficult for cracks to occur regularly during forming. As a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0123] In No. 37, the cooling gas flux was excessive in the bath temperature range of 390°C or less. This made it difficult for cracks to form regularly during forming. As a result, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0124] In No. 38, the reheating time was 2010 seconds. This made it difficult for cracks to occur regularly during forming, and as a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and further, the crack width Wc exceeded 10 μm. This resulted in inferior corrosion resistance in the processed area.

[0125] No. 40 had a high reheating temperature. This made it difficult for cracks to occur regularly during forming, and as a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0126] In No. 41, the average cooling rate in the bath temperature range of 390°C or less was excessive. This made it difficult for cracks to occur regularly during forming. As a result, the percentage of cracks inclined at an angle of 35° to 55° relative to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and the crack width Wc exceeded 10 μm. This resulted in poor corrosion resistance in the processed area.

[0127] In No. 42, the reheating time was 0 seconds. This made it difficult for cracks to occur regularly during forming, and as a result, the percentage of cracks inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and further, the crack width Wc exceeded 10 μm. This resulted in inferior corrosion resistance in the processed area.

[0128] In No. 43, the average cooling rate in the range of 390 to 20°C was excessive. This made it difficult for cracks to occur regularly during forming. As a result, the percentage of cracks inclined at an angle of 35 to 55° with respect to the thickness direction of the plating layer was less than 80%, the percentage of cracks with a spacing Lc satisfying formula (1) was less than 80%, and further, the crack width Wc exceeded 10 μm. This resulted in inferior corrosion resistance in the processed area.

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[0139] INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that it can provide a plated steel material that is excellent in sacrificial corrosion resistance and corrosion resistance of processed portions.

[0140] 1...plated steel material, 11...base steel material, 12...plated layer, 22A...bent back portion, 24...bent portion, 24A...inside of bent portion, 101...crack.

Claims

1. A plated steel material comprising a base steel material and a plated layer formed on at least a portion of the surface of the base steel material, wherein the chemical composition of the plated layer is, in mass %, Al: 1.0 to 30.0%, Mg: 1.0 to 10.0%, Fe: 0 to 2.0%, Si: 0 to 2.0%, Ni: 0 to 1.00%, Ca: 0 to 1.00%, Sb: 0 to 0.50%, Pb: 0 to 0.50%, Sn: 0 to 1.00%, Cu: 0 to 1.00%, Ti: 0 to 1.00%, Cr: 0 to 1.00%, Nb: 0 to 1.00%, Zr: 0 to 1.00%, Mn: 0 to 1.00%, Mo: 0 to 1.00%, Ag: 0 to 1.00%, Li: 0 to 1.00%, Bi: 0 to 1.00%, V: 0 to 1.00%, Co: 0 to 1.00%, In: 0 to 1.00%, La: 0 to 0.50%, Ce: 0 to 0.50%, B: 0 to 0.50%, Y: 0 to 0.50%, P: 0 to 0.50%, Sr: 0 to 0.50%, balance: 50.0 to 98.0% Zn and impurities, and the total of Sb, Pb, Cu, Sn, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, Bi, V, Co, In, La, Ce, B, Y, P, and Sr is 0 to 5.00%, and at least a portion of the surface of the plating layer has a portion where a plurality of cracks are observed, A plated steel material in which, in the region, the cracks extend in approximately the same direction, and when an observation region is a cross section of the plated steel material that is perpendicular to the direction in which the cracks extend and perpendicular to the surface of the plated steel material and has a length of 200 μm in a direction parallel to the surface, the proportion of cracks that are inclined at an angle of 35° to 55° with respect to the thickness direction of the plating layer is 80% or more of all the cracks observed in the observation region, and when the distance between adjacent cracks is Lc and the thickness of the plating layer is T, the proportion of the number of distances Lc that satisfy the following formula (1) is 80% or more of all the distances Lc observed in the observation region, and the average value of the width Wc of the cracks at a thickness position T / 2 away from the surface of the plating layer in the observation region is 10 μm or less. 0.3T≦Lc≦1.6T ... (1) 2. The plated steel material according to claim 1, wherein, of all the cracks observed within the observation area of ​​the portion, the number of cracks inclined at an angle of 40° to 50° relative to the thickness direction of the plating layer is 70% or more.

3. The plated steel product according to claim 1 or 2, wherein the Al and Mg contents of the chemical composition of the plated layer are Al: 10.0 to 30.0 mass % and Mg: 4.0 to 10.0 mass %, respectively, and the proportion of the number of intervals Lc that satisfy the following formula (2) among all intervals Lc observed within the observation area is 80% or more: 0.5T≦Lc≦1.4T ... (2) 4. The plated steel product according to claim 1 or 2, wherein the Al and Mg contents of the chemical composition of the plated layer are Al: 15.0 to 30.0 mass % and Mg: 5.0 to 8.0 mass %, respectively, and the proportion of the number of intervals Lc that satisfy the following formula (3) among all intervals Lc observed within the observation area is 80% or more: 0.5T≦Lc≦1.2T ... (3) 5. A plated steel material according to any one of claims 1 to 4, wherein the average width Wc of the cracks at a thickness position T / 2 away from the surface of the plating layer within the observation area is 3 μm or less.

6. The plated steel material according to any one of claims 1 to 5, wherein the portion is present on the inner side of the bent portion of the base steel material.

7. The plated steel material according to any one of claims 1 to 6, wherein the portion is present in a bent-back portion of the base steel material.

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