Plated steel material

Abstract

This plated steel material comprises a plating layer formed on at least a part of the surface of a base steel sheet. In a cross-section of the plating layer taken perpendicular to the surface of the plated steel material, if fifty second-measurement-lines are drawn in a 45° direction relative to the direction parallel to the surface of the plated steel material, the plated steel material satisfies formulae (1) and (2), and further, the number of second-measurement-lines satisfying formula (3) is 40 or more.　Formula (1): 0≤ΣLs / L≤0.95; Formula (2): 0.05≤Ave(Σds / d)≤0.90; Formula (3): 0.05≤Σds / d≤0.90.

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. When using Zn-Al-Mg-plated steel sheets in these fields, the Zn-Al-Mg-plated steel sheets may be processed into various shapes. However, because the Zn-Al-Mg-based plating layer has a higher hardness than a typical Zn plating layer, there is a concern that powdering may occur during processing. On the other hand, attempts to improve powdering resistance may result in poor abrasion resistance. Therefore, Zn-Al-Mg-plated steel sheets are required to have excellent corrosion resistance as well as excellent abrasion resistance and powdering resistance.

[0003] For example, Patent Document 1 describes a plated steel material that includes a steel material and a plating layer including a Zn—Al—Mg alloy layer disposed on the surface of the steel material, in which the Zn—Al—Mg alloy layer has a Zn phase and an Mg—Sn intermetallic compound phase is contained in the Zn 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: 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] An object of the present invention is to provide a plated steel material that is excellent in corrosion resistance, wear resistance, and powdering resistance.

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A plated steel material comprising a base steel sheet and a plating layer formed on at least a portion of a surface of the base steel sheet, 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: 0.00 to 1.00%, V: 0.00 to 1.00%, Co: 0.00 to 1.00%, In: 0.00 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%, A plated steel material in which, when a first measurement line is drawn in a direction parallel to the surface of the plated steel material at a depth of 1.0 μm from the surface of the plated steel material in a cross section of the plating layer perpendicular to the surface of the plated steel material, the following formula (1) is satisfied; and when 50 second measurement lines are drawn at a 45° angle to a direction parallel to the surface of the plated steel material in the cross section excluding the region from the surface of the plated steel material to 1.0 μm and the region from the base steel sheet to 1.0 μm, the following formula (2) is satisfied; and further, the proportion of second measurement lines that satisfy the following formula (3) is 80% or more: 0≦ΣLs / L≦0.95 ... (1) 0.05≦Ave(Σds / d)≦0.90 ... (2) 0.05≦Σds / d≦0.90 ... (3) where L, ΣLs, d, Σds, and Ave(Σds / d) in the above formulas (1) to (3) are as follows.L: length of the first measurement line, ΣLs: total length Ls of portions of the first measurement line where the nanoindentation hardness is less than 1.8 GPa, d: total length of each second measurement line, Σds: total length ds of portions of the plating layer of each second measurement line where the nanoindentation hardness is less than 1.8 GPa, Ave(Σds / d): average value of Σds / d. [2] The plated steel material according to [1], wherein the chemical composition of the plating layer contains Al: 10.0 to 30.0 mass% and Mg: 4.0 to 10.0 mass%, respectively, and the proportion of second measurement lines that satisfy the following formula (4) is 80% or more. 0.10≦Σds / d≦0.70 ... (4) [3] The plated steel material according to [1], wherein the Al and Mg contents in the chemical composition of the plating layer are Al: 15.0 to 30.0 mass%, Mg: 5.0 to 8.0 mass%, respectively, and the proportion of second measurement lines satisfying the following formula (5) is 70% or more. 0.10≦Σds / d≦0.40 ... (5) [4] The plated steel material according to any one of [1] to [3], which satisfies the following formula (6) instead of the formula (1): 0≦ΣLs / L≦0.60 ... (6) [5] The plated steel material according to any one of [1] to [3], which satisfies the following formula (7) instead of the formula (1): 0≦ΣLs / L≦0.20 (7) [6] The plated steel material according to any one of [1] to [5], wherein the plating layer has a portion having a nanoindentation hardness of 2.5 GPa or more.

[0009] According to the present invention, a plated steel material having excellent corrosion resistance, wear resistance, and powdering resistance can be provided.

[0010] Fig. 1 is a cross-sectional schematic diagram showing a plated steel material according to an embodiment of the present invention. Fig. 2 is a schematic diagram for explaining formula (1) in a plated steel material according to an embodiment of the present invention. Fig. 3 is a schematic diagram for explaining formula (2) in a plated steel material according to an embodiment of the present invention.

[0011] When a plated steel material having a Zn-Al-Mg-based plating layer is subjected to bending or other processes, powdering of the plating layer may occur at the bent portion. Powdering of the plating layer is likely to occur when compressive stress is applied to the plating layer during bending. The inventors have found that powdering is particularly pronounced when irregular cracks occur in the plating layer, while regular cracks in the plating layer alleviate the compressive stress and suppress powdering. Further investigation by the inventors has also found that the locations where cracks occur in the plating layer when compressive stress is applied are affected by the distribution of hardness within the plating layer. 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.

[0012] As a result of further investigation, it was found that by controlling the cooling conditions in the manufacturing process of the plating layer, low-hardness regions having a relatively low hardness compared to the surrounding area are mixed into the Zn-Al-Mg plating layer, and that these low-hardness regions are dispersed and distributed along a 45° angle with respect to the surface of the plating layer, thereby successfully suppressing powdering. However, it was found that if many low-hardness regions exist near the surface of the plating layer, the wear resistance of the plating layer decreases, so it is necessary to minimize the presence of low-hardness regions on the surface of the plating layer. Based on these findings, the present inventors have completed the present invention.

[0013] A plated steel material according to an embodiment of the present invention is a plated steel material comprising a base steel sheet and a plating layer formed on at least a portion of the surface of the base steel sheet, 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%, and Nb: 0 to 1.00%. %, Zr: 0-1.00%, Mn: 0-1.00%, Mo: 0-1.00%, Ag: 0-1.00%, Li: 0-1.00%, Bi: 0.00-1.00%, V: 0.00-1.0 0%, Co: 0.00-1.00%, In: 0.00-1.00%, La: 0-0.50%, Ce: 0-0.50%, B: 0-0.50%, Y: 0-0.50%, P: 0-0.50 %, Sr: 0 to 0.50%, and the 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 when a first measurement line is drawn in a direction parallel to the surface at a depth of 1.0 μm from the surface of the plated steel material in a cross section of the plating layer perpendicular to the surface of the plated steel material, the following formula (1) is satisfied; and when 50 second measurement lines are drawn in a direction at a 45° angle to a direction parallel to the surface of the plated steel material in the cross section excluding a region from the surface of the plated steel material to 1.0 μm and a region from the base steel sheet to 1.0 μm, the following formula (2) is satisfied; and further, the proportion of second measurement lines that satisfy the following formula (3) is 80% or more. 0≦ΣLs / L≦0.95 (1) 0.05≦Ave(Σds / d)≦0.90 (2) 0.05≦Σds / d≦0.90 (3) Here, L, ΣLs, d, Σds, and Ave(Σds / d) in the above formulas (1) to (3) are defined as follows: L: length of the first measurement line, ΣLs: sum of lengths Ls of portions in the first measurement line where the nanoindentation hardness is less than 1.8 GPa, d: total length of each second measurement line, Σds: sum of lengths ds of portions in the plating layer in each second measurement line where the nanoindentation hardness is less than 1.8 GPa, Ave(Σds / d): average value of Σds / d.

[0014] In a plated steel material according to an embodiment of the present invention, the Al and Mg contents are preferably 10.0 to 30.0 mass% Al and 4.0 to 10.0 mass% Mg, respectively, and the proportion of the second measurement lines that satisfy the following formula (4) is preferably 80% or more: 0.10≦Σds / d≦0.70 ... (4) In a plated steel material according to an embodiment of the present invention, the Al and Mg contents in the chemical composition of the plating layer are preferably 15.0 to 30.0 mass% Al and 5.0 to 8.0 mass% Mg, respectively, and the proportion of the second measurement lines that satisfy the following formula (5) is preferably 70% or more: 0.10≦Σds / d≦0.40 ... (5) In a plated steel material according to an embodiment of the present invention, the Al and Mg contents in the chemical composition of the plating layer are preferably 15.0 to 30.0 mass% Al and 5.0 to 8.0 mass% Mg, respectively, and the proportion of the second measurement lines that satisfy the following formula (6) is preferably 0.10≦Σds / d≦0.40 ... (5) 0≦ΣLs / L≦0.60 (6) Furthermore, the plated steel material according to an embodiment of the present invention preferably satisfies the following formula (7) instead of the above formula (1): 0≦ΣLs / L≦0.20 (7) Furthermore, the plated steel material according to an embodiment of the present invention preferably has a portion in the plating layer where the nanoindentation hardness is 2.5 GPa or more.

[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 has a base steel sheet 11. There are no particular limitations on the shape of the base steel sheet 11. The base steel sheet 11 may also be a base steel sheet 11 to be formed into, for example, steel pipes, civil engineering and construction materials (fences, corrugated pipes, drainage ditch covers, sand-flying prevention plates, bolts, wire mesh, guardrails, water-stop walls, etc.), home appliance components (casings for air conditioner outdoor units, etc.), automotive components (suspension components, exterior components, interior components, structural components, etc.), etc. The forming process may be any of various plastic processing techniques, such as pressing, roll forming, and bending.

[0016] The material of the base steel sheet 11 is not particularly limited. The base steel sheet 11 can be various steel sheets, 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 sheet 11 may be a hot-rolled steel sheet, hot-rolled steel strip, cold-rolled steel sheet, or cold-rolled steel strip. The chemical composition, manufacturing method (hot rolling, pickling, cold rolling, etc.), and specific manufacturing conditions of the base steel sheet 11 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 sheet 11. In Fig. 1, the plating layer 12 is formed on one side of the base steel sheet 11, but the plating layer 12 may be formed on both sides of the base steel sheet 11. The plating layer 12 is preferably a plating film produced by a so-called hot-dip galvanizing process.

[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. Furthermore, the plating layer 12 of the plated steel material 1 according to this embodiment may include an Fe-Al-based interfacial alloy layer, mainly composed of Fe and Al, between the base steel sheet 11 and the Zn-Al-Mg alloy layer. That is, 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 "%" indication 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 or concentration (e.g., Zn concentration, Mg concentration, etc.).

[0020] In this specification, the "corrosion resistance" of the plating layer 12 mainly refers to "sacrificial corrosion protection." "Sacrificial corrosion protection" refers to the property of inhibiting corrosion of the base steel sheet 11 at exposed portions of the base steel sheet 11 (for example, cut end surfaces of plated steel, cracked portions of the plating layer during processing, and portions where the base steel sheet 11 is exposed due to peeling of the plating layer 12). The plating layer 12 of this embodiment also has excellent "base steel corrosion protection." "Base steel corrosion protection" refers to the property of the plating layer 12 itself that makes it resistant to corrosion. "Wear resistance" refers to the property of the plating layer 12 that makes it resistant to wear. "Powdering resistance" refers to the property of the plating layer 12 that makes it resistant to powdering.

[0021] The plating layer 12 according to this embodiment contains Zn and other alloying elements. The chemical composition of the plating layer 12 will be described in detail below. Note that elements described as having a lower limit concentration of 0% are optional elements that are not essential for solving the problems of the plated steel material 1 according to this embodiment, but are allowed to be included in the plating layer 12 for the purpose of improving characteristics, etc.

[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 to crystallize the Sn phase. Therefore, the Mg concentration is set to 1.0% or more. On the other hand, if the Mg concentration is excessive, powdering properties may deteriorate and furthermore, 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 elements explained below are all optional elements except for Zn, and therefore the lower limit is set to 0%.

[0025] <Fe: 0 to 2.0%> The Fe concentration may be 0%, but because Fe may be mixed into the plating layer 12 from the base steel sheet 11, 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.

[0026] <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.

[0027] <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 set to 0.80% or less or 0.60% or less.

[0028] <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.

[0029] <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.

[0030] <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, 0.20% or less, or 0.10% or less.

[0031] <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.

[0032] <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 each be set to 0.90% or less. Furthermore, the concentrations of these elements may each be set to 0.10% or more or 0.30% or more.

[0033] <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.

[0034] <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.

[0035] <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.

[0036] <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.

[0037] <Remainder: Zn and Impurities> The remainder 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 edge corrosion resistance, so it 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 considered to be impurity elements, regardless of whether they are mixed in or intentionally added.

[0038] Furthermore, the plating layer of the plated steel material according to this embodiment may contain elements other than the above-mentioned alloying elements, Zn, and impurities.

[0039] 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 sheet 11 is used to peel 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.

[0040] Next, the plating layer 12 of the plated steel material 1 of this embodiment will be described. In the following description, the portion where the nanoindentation hardness is less than 1.8 GPa may be referred to as the "low hardness region." Also, the portion where the nanoindentation hardness is 2.5 GPa or more may be referred to as the "high hardness region."

[0041] The plating layer 12 of this embodiment has a portion (low hardness region) where the nanoindentation hardness is less than 1.8 GPa in a cross section of the plating layer 12 perpendicular to the surface of the plated steel material 1. The plating layer 12 of this embodiment may also have a portion (high hardness region) where the nanoindentation hardness is 2.5 GPa or more in a cross section of the plating layer 12. Regions other than the low hardness region and the high hardness region, i.e., regions where the nanoindentation hardness is 1.8 GPa or more and less than 2.5 GPa, are almost nonexistent, or even if present, their area ratio is 30 area % or less in the cross section of the plating layer 12.

[0042] The presence of a low hardness region having a nanoindentation hardness of less than 1.8 GPa in a distribution state described below can improve the powdering resistance of the plating layer 12. Furthermore, the presence of a high hardness region having a nanoindentation hardness of 2.5 GPa or more can improve the wear resistance of the plating layer 12.

[0043] Next, the distribution state of the low hardness regions in the plating layer 12 will be described. The plated steel material 1 of this embodiment satisfies the following formula (1) in a cross section of the plating layer 12 perpendicular to the surface of the plated steel material 1. By satisfying the following formula (1), the wear resistance of the plating layer 12 is significantly improved. If ΣLs / L exceeds 0.95, the low hardness regions become excessively exposed on the surface of the plating layer 12, and the wear resistance of the surface of the plating layer 12 decreases. The smaller ΣLs / L is, the more preferable, and instead of the following formula (1), the following formula (6) or formula (7) may be satisfied. Furthermore, ΣLs / L may be 0.85 or less, 0.80 or less, 0.70 or less, 0.40 or less, or 0.30 or less.

[0044] 0≦ΣLs / L≦0.95 (1) 0≦ΣLs / L≦0.60 (6) 0≦ΣLs / L≦0.20 (7)

[0045] Here, L and ΣLs in the above formulas (1), (6), and (7) are as follows: L: total length of the first measurement line, ΣLs: total length Ls of the portions of the first measurement line where the nanoindentation hardness is less than 1.8 GPa.

[0046] Whether or not the above formula (1) is satisfied is determined as follows. First, a small sample piece measuring, for example, 20 mm x 15 mm x 1 mm x 10 mm is taken from the plated steel material 1, embedded in resin, and then polished to a mirror finish to expose a cross section perpendicular to the surface of the plated steel material 1. This sample is placed on the observation stage of a nanoindenter, and the cross section of the plating layer 12 is observed under a microscope. Microscopic observation may be performed using an optical microscope or a scanning probe microscope. The nanoindentation hardness of the plating layer 12 is measured using the nanoindenter on the cross section of the plating layer 12 perpendicular to the surface of the plated steel material 1 (plating layer 12). However, because the nanoindentation hardness measurement value of the plating layer 12 near the surface is affected by factors such as the hardness of the resin, the first measurement line is positioned 1.0 μm deep from the surface of the plating layer 12 (with the center of the indentation within a range of 1.0 ± 0.2 μm).

[0047] The nanoindentation hardness is measured in accordance with JIS Z2255:2003 using a Bruker Triboindenter TI980 as the measuring device. The measurement conditions are: test temperature: room temperature, test force: 500 μN (HTL 0.5), load time: 5 seconds, hold time: 2 seconds, and unload time: 5 seconds.

[0048] FIG. 2 shows a schematic diagram of the plating layer 12. In FIG. 2, reference numeral 11 denotes the base steel sheet 11, reference numeral 12 denotes the plating layer 12, reference numeral 12a denotes the surface of the plating layer 12 (i.e., the interface between the plating layer 12 and the resin), and reference numeral 13 denotes the interface between the base steel sheet 11 and the plating layer 12, which is also the surface of the base steel sheet 11. Furthermore, low-hardness regions 14 are dispersed within the plating layer 12. Regions other than the low-hardness regions 14 are regions with a nanoindentation hardness of 1.8 GPa or more. Reference numeral M1 denotes a first measurement line drawn in a direction parallel to the surface 12a at a depth of 1.0 μm from the surface 12a of the plated steel material 1. The first measurement line is located 1.0 μm away from the surface 12a toward the plating layer 12.

[0049] The length Ls of the first measurement line M1 across the low hardness region 14 is measured, that is, the length Ls of the portion of the first measurement line M1 where the nanoindentation hardness is less than 1.8 GPa. If there are multiple low hardness regions 14 in the first measurement line M1, the lengths Ls of all of the low hardness regions 14 are measured. In other words, the lengths Ls of the portions of the first measurement line M1 where the nanoindentation hardness is less than 1.8 GPa are measured. Then, the sum ΣLs of Ls is calculated. The total length L of the first measurement line M1 is 200 μm. For measurement convenience, if necessary, the first measurement line M1 may not be a single line, but multiple first measurement lines may be used. However, in this case, the total length L of the multiple first measurement lines M1 (total length) is 200 μm, and the length of each first measurement line is 40 μm or more.

[0050] Next, in the plated steel material 1 of this embodiment, when 50 second measurement lines extending in a direction at 45° to a direction parallel to the surface 12a of the plating layer 12 are drawn in a cross section of the plating layer 12 perpendicular to the surface of the plated steel material 1, excluding the region from the surface of the plated steel material 1 up to 1.0 μm and the region from the base steel sheet 11 up to 1.0 μm, the following formula (2) is satisfied, and the proportion (number ratio) of second measurement lines that satisfy the following formula (3) is 80% or more.

[0051] 0.05≦Ave(Σds / d)≦0.90…(2) 0.05≦Σds / d≦0.90…(3)

[0052] Here, d, Σds, and Ave(Σds / d) in the above formulas (2) and (3) are as follows: d: total length of each second measurement line; Σds: total length ds of portions in each second measurement line where the nanoindentation hardness in the plating layer is less than 1.8 GPa; Ave(Σds / d): average value of Σds / d.

[0053] If Ave(Σds / d) is less than 0.05, the powdering resistance is reduced due to the small number of low-hardness regions, which is undesirable. Also, the higher Ave(Σds / d) is, the better the powdering resistance is, but in consideration of the chemical composition of the plating layer 12, it is difficult for Ave(Σds / d) to exceed 0.90, so the upper limit is set to 0.90 or less.

[0054] The percentage of second measurement lines satisfying formula (3) of 80% or more means that, when Σds / d is measured for each of 50 second measurement lines, the number of second measurement lines for which Σds / d is in the range of 0.05 to 0.90 is 40 or more. This means that there is little variation in Σds / d, i.e., low hardness regions are evenly distributed without uneven distribution. If the number of second measurement lines satisfying formula (3) is less than 80%, cracks are less likely to occur regularly when compressive stress is applied to the plating layer 12, which is undesirable because it reduces powdering resistance. The percentage of second measurement lines satisfying formula (3) may be 84% or more, 88% or more, 92% or more, or 96% or more, or even 100%.

[0055] The measurements of the above equations (2) and (3) are carried out on the sample used for the first measurement line M1. As with the first measurement line M1, the measurement range excludes the region from the surface of the plating layer 12 to a depth of 1 μm, which is affected by the hardness of the resin, as well as the region from the interface 13 between the base steel sheet 11 and the plating layer 12 to a depth of 1 μm, which is affected by the hardness of the base steel sheet 11. The nanoindentation hardness measurement device and measurement conditions are the same as for the first measurement line described above.

[0056] Figure 3 shows a schematic diagram of the observation area. In Figure 3, reference numeral 11 denotes the base steel sheet 11, reference numeral 12 denotes the plating layer 12, reference numeral 12a denotes the surface of the plating layer 12 (i.e., the interface between the plating layer 12 and the resin), and reference numeral 13 denotes the interface between the base steel sheet 11 and the plating layer 12, which is the surface of the base steel sheet 11. Furthermore, low hardness regions 14 are dispersed within the plating layer 12. Regions other than the low hardness regions 14 are regions with a nanoindentation hardness of 1.8 GPa or more.

[0057] 3, symbol M2 denotes a second measurement line inclined at 45° with respect to the surface 12a of the plating layer 12. Symbol m1 is a line drawn to demarcate the region from the surface 13a of the plated steel material 1 to 1.0 μm, and symbol m2 is a line drawn to demarcate the region from the interface between the base steel sheet 11 and the plating layer 12 to 1.0 μm toward the surface 13a.

[0058] As shown in Fig. 3, ten second measurement lines M2 are drawn on the plating layer 12, each at an angle of 45° to a direction parallel to the surface of the plating layer 12. The direction of the 45° angle may be arbitrary, and may be, for example, an angle of 135°, but all second measurement lines M2 are inclined in the same direction as shown in Fig. 3. The intervals between the second measurement lines M2 in the direction parallel to the surface 12a of the plating layer 12 are equal intervals of 15 µm.

[0059] Furthermore, one end of the second measurement line M2 is located 1 μm away from the contour line of the surface 12 a of the coating layer 12, and the other end of the second measurement line M2 is located 1 μm away from the contour line of the interface 13 (the surface of the base steel sheet 11) between the coating layer 12 and the base steel sheet 11. The distance between one end and the other end of the second measurement line M2 is the length d of each second measurement line M2. Note that in Figures 3 and 4 , one end of the second measurement line M2 is on line m1, and the other end of the second measurement line M2 is on line m2. That is, one end of the second measurement line M2 is located 1 μm away from the contour line of the surface 12 a, and the other end of the second measurement line M2 is located 1 μm away from the contour line of the interface 13.

[0060] The process of drawing ten such second measurement lines M2 is repeated five times at intervals of 500 μm in a direction parallel to the surface 12 a of the plating layer 12, thereby drawing fifty second measurement lines M2. All of the fifty second measurement lines M2 are in the same direction at an angle of 45°.

[0061] Next, the length ds of each second measurement line M2 across the low hardness region is measured. Figure 4 shows one of the ten second measurement lines M2 shown in Figure 3 and the low hardness region 14 across which that second measurement line M2 crosses. As shown in Figure 4, the second measurement line M2 may cross multiple low hardness regions 14. In such cases, the length ds is measured for each low hardness region 14. Σds / d is then calculated for each second measurement line M2. Σds is the sum of the lengths ds of the low hardness regions 14 across which the second measurement line M2 crosses. In other words, Σds is the sum of the lengths ds of the portions of each second measurement line M2 in the plating layer 12 where the nanoindentation hardness is less than 1.8 GPa. Furthermore, the average value of Σds / d for the 50 second measurement lines M2 is calculated, and this is designated as Ave(Σds / d).

[0062] Furthermore, it is confirmed whether the Σds / d for each second measurement line M2 satisfies formula (3). Then, out of the total number N (N=50) of second measurement lines M2, the number N' of second measurement lines M2 that satisfy formula (3) is determined. That is, 50 second measurement lines M2 are drawn, the average Σds / d value of the 50 second measurement lines M2 is 0.05 to 0.90, and the proportion (number ratio) of the 50 second measurement lines M2 that satisfy formula (3) below is 80% or more (i.e., 40 or more).

[0063] Furthermore, in the plating layer 12 of this embodiment, when the Al and Mg contents in the chemical composition of the plating layer 12 are 10.0 to 30.0 mass% Al and 4.0 to 10.0 mass% Mg, respectively, the proportion (number ratio) of second measurement lines M2 satisfying the following formula (4) is preferably 80% or more of the total (i.e., 40 or more). This proportion may be 84% or more, 88% or more, 92% or more, or 96% or more. This can further improve powdering resistance.

[0064] Furthermore, when the Al and Mg contents of the plating layer 12 in its chemical composition are 15.0 to 30.0 mass% Al and 5.0 to 8.0 mass% Mg, respectively, the proportion (number ratio) of second measurement lines M2 satisfying the following formula (5) is preferably 70% or more (i.e., 35 or more) of the total. This proportion may be 76% or more, 80% or more, 84% or more, or 88% or more. This further improves powdering resistance.

[0065] 0.10≦Σds / d≦0.70 (4) 0.10≦Σds / d≦0.40 (5)

[0066] The presence or absence of a portion (high hardness region) where the nanoindentation hardness is 2.5 GPa or more can be determined by measuring the nanoindentation hardness along the first measurement line M1 and the second measurement line M2. Specifically, when measuring the nanoindentation hardness along the first measurement line M1 and the second measurement line M2, if there is even one portion where the nanoindentation hardness is 2.5 GPa or more, it is determined that a high hardness region exists, and if there is no portion where the nanoindentation hardness is 2.5 GPa or more, it is determined that a high hardness region does not exist.

[0067] In addition, the plating layer 12 contains Mg 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 1.00%.

[0068] 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.

[0069] The coating weight of the plating layer 12 per side is, for example, 15 to 300 g / m ２ The amount of adhesion per side should be within the range of 20 g / m ２ By setting the coating weight per surface to 300 g / m or more, the flat corrosion resistance and sacrificial corrosion protection of the plated steel material 1 can be further improved. ２ By setting the coating weight of the plating layer 12 to 20 g / m or less, the powdering resistance of the plated steel material 1 can be improved. ２ or more than 30 g / m ２ The coating weight of the plating layer per side is 250 g / m ２ Below, 100g / m ２ Below, 60g / m ２ or less than 50 g / m ２ The following is also acceptable.

[0070] 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.

[0071] In the method for producing the plated steel material 1 of this embodiment, the base steel sheet 11 is annealed in a reducing atmosphere, the annealed base steel sheet 11 is immersed in a hot-dip galvanizing bath, and the base steel sheet 11 is pulled out of the hot-dip galvanizing bath, thereby forming a coating layer 12 on the surface of the base steel sheet 11. Next, the temperature of the coating layer 12 is increased from the bath temperature to 390°C by a speed of 30,000 to 40,000 (L / min / m ２The 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 base steel sheet 11, which will be 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 base steel sheet 11 are removed as much as possible.

[0073] Next, the base steel sheet 11 immediately after annealing is immersed in a hot-dip galvanizing bath. Before immersing the base steel sheet 11 in the galvanizing bath, the base steel sheet 11 immediately after annealing may be cooled with a cooling gas such as nitrogen until the temperature of the base steel sheet 11 reaches about (galvanizing 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 base steel sheet 11 is pulled up from the hot-dip coating bath. The deposition weight of the coating layer 12 can be controlled by controlling the pulling speed of the base steel sheet 11. If necessary, the deposition weight of the coating layer 12 may be controlled by wiping the base steel sheet 11 to which the coating layer 12 is attached. The deposition weight of the coating 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), the steel plate is vibrated during transportation. When cooling is performed by spraying cooling gas, a plurality of spray nozzles for the cooling gas may be arranged along the steel plate transport path, and the cooling gas may be sprayed from the nozzles. More preferably, the flux of the cooling gas is set to 35,000 to 40,000 (L / min / m ２ ) range.

[0077] When the temperature of the plating layer 12 reaches from the bath temperature to 390°C, a cooling gas is blown at a predetermined flux to supercool and vibrate the surface of the plating layer 12. This promotes nucleation of phases and structures that constitute high hardness regions on the surface of the plating layer 12, making it difficult for low hardness regions to form.

[0078] Furthermore, if the average cooling rate at which the temperature of the plating layer 12 is cooled from the bath temperature to 390°C is 15°C / sec or more, high-hardness regions are sufficiently formed on the surface of the plating layer 12, low-hardness regions are not excessively precipitated, and wear resistance is improved. On the other hand, if the average cooling rate exceeds 19°C / sec, the cooling rate becomes excessive, and not only the surface 12a of the plating layer 12 but the entire plating layer 12 is supercooled, making it difficult to nucleate high-hardness regions on the surface 12a of the plating layer 12. Therefore, the average cooling rate is set to 19°C / sec or less.

[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 high hardness region will be insufficient, resulting in excessive precipitation of the low hardness region. 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 to 20°C to 20°C to 30°C / s or more, the formation of high hardness regions is sufficient and low hardness regions are not excessively formed. On the other hand, if the average cooling rate exceeds 40°C / s, excessive vacancies that act as the driving force for aging precipitation are introduced, making it difficult to control the strengthening state due to aging precipitation in the subsequent heat treatment step (reheating). For this reason, the average cooling rate in the range of 390 to 20°C is preferably 40°C / s or less.

[0082] Reheating is performed after cooling in the range of 390 to 20°C at an average cooling rate of 20°C / second or more. Reheating promotes the formation of low hardness regions within the plating layer 12 and also makes it possible to control the distribution of the low hardness regions in the plating layer 12 to a preferred state. As described above, reheating after cooling is performed under conditions of a soaking temperature of 70 to 230°C and a soaking time of 10 to 2000 seconds. More preferably, reheating is performed under conditions of a soaking temperature of 120 to 180°C and a soaking time of 120 to 2000 seconds.

[0083] In the cooling range from the bath temperature to 3900°C and the cooling range 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] Furthermore, in order for the plated steel material 1 to satisfy the above formula (4), it is preferable that the Al and Mg contents in the chemical composition of the plating layer 12 are set to Al: 10.0 to 30.0 mass% and Mg: 4.0 to 10.0 mass%, respectively, and that the average cooling rate in the range of 390 to 20°C is set to 30°C / s or more.

[0086] Furthermore, in order for the plated steel material 1 to satisfy the above formula (5), 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 / s or more.

[0087] Furthermore, in order for the plated steel material 1 to satisfy the above formula (6), the temperature range of the plated layer 12 from the bath temperature to 390°C is set to 35,000 (L / min / m ２ ) It is advisable to perform cooling by spraying cooling gas at a flux of at least 1000 kJ / min.

[0088] Furthermore, in order for the plated steel material 1 to satisfy the above formula (7), the contents of Al and Mg 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 the range in which the temperature of the plating layer 12 is increased from the bath temperature to 390°C is set to 35,000 (L / min / m ２ ) It is advisable to perform cooling by spraying cooling gas at a flux of at least 1000 kJ / min.

[0089] 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.

[0090] 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. This 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. ２The 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.

[0091] 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.

[0092] Furthermore, the plated steel sheets after cooling were reheated under the conditions shown in Tables 2-1 and 2-2. In this manner, plated steel materials Nos. 1 to 41 were produced.

[0093] The chemical compositions of the plating layers were as shown in Tables 1-1 and 1-2. The distribution of low-hardness regions in the plating layers was also evaluated, with the results shown in Tables 3-1 and 3-2. Furthermore, the abrasion resistance, powdering resistance, and sacrificial corrosion protection of the plated steel materials were evaluated, with the results shown in Tables 4-1 and 4-2.

[0094] The chemical composition of the plating layer was measured by immersing a sample cut to a size of 30 mm × 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.

[0095] 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. ２ It was determined that the Sn phase was present. ２ The presence or absence of Sn phase is indicated.

[0096] The distribution of low-hardness regions in the plating layer was evaluated as follows. First, a small sample measuring 20 mm × 15 mm was taken from the plated steel material, embedded in resin, and polished to a mirror finish to expose the cross section of the plating layer and base steel sheet. For this test piece, a first measurement line (L = 200 μm) was drawn directly below the surface of the plating layer, and ten second measurement lines were drawn at a 45° angle parallel to the surface of the plating layer for each of five measurement regions, and nanoindentation hardness was measured using the method described above. Regions with a nanoindentation hardness of less than 1.8 GPa were defined as low-hardness regions, and regions with a nanoindentation hardness of 2.5 GPa or greater were defined as high-hardness regions. However, the region of the plating layer from the surface to a depth of 1.0 μm and the region from the interface between the base steel sheet and the plating layer to a depth of 1.0 μm were excluded from the measurement range.

[0097] The nanoindentation hardness was measured using a Bruker Triboindenter TI980 as a measuring device under the following measurement conditions: test temperature: room temperature, test load: 500 μN, load time: 5 seconds, hold time: 0 seconds, and unload time: 5 seconds.

[0098] Next, the length Ls of each low hardness region on the first measurement line and the length ds of each low hardness region on the second measurement line were measured by the above-mentioned method, and ΣLs / L and the average Σds / d (i.e., Ave(Σds / d)) were calculated by the above-mentioned method.

[0099] Further, it was confirmed whether the Σds / d for each second measurement line satisfied formula (3). Then, out of the total number of second measurement lines N (N = 50), the number N' of second measurement lines satisfying formula (3) was calculated. N' / N x 100 (%) was then calculated. The results are shown in the "Percentage (%) where Σds / d satisfies 0.05 to 0.9" column in Tables 3-1 and 3-2. Similarly, the "Percentage (%) where Σds / d satisfies 0.1 to 0.7" and "Percentage (%) where Σds / d satisfies 0.1 to 0.4" were calculated and shown in Tables 3-1 and 3-2. When N' / N x 100 (%) was 80% or more, it was evaluated that the number of second measurement lines satisfying formula (3) was 40 or more.

[0100] Furthermore, the presence or absence of a high hardness region was confirmed. Regarding the presence or absence of a high hardness region, if there was a portion in the 200 μm first measurement line and the 50 second measurement lines where the nanoindentation hardness was 2.5 GPa or more, the high hardness region was judged to be "present," and if there was no portion in the 200 μm first measurement line and the 50 second measurement lines where the nanoindentation hardness was 2.5 GPa or more, the high hardness region was judged to be "absent."

[0101] <Wear Resistance> Wear resistance was evaluated by the weight loss before and after the wear test. A HEiDOn friction and wear tester (Type: HHS2000S) manufactured by Shinto Chemical Co., Ltd. was used. The measurement conditions were a sample size of 100 x 50 mm, which was fixed to the test table with a magnet. The object to be worn was emery paper #80. The wear conditions were a load of 500 gf and 200 reciprocations. The weight change before and after the wear test was then determined. The evaluation criteria were as follows, with B being a failure and AAA, AA, and A being passes.

[0102] AAA: Weight loss is 5g / m ２ AA: Weight loss is less than 5 g / m ２ Above, 10g / m ２ A: Weight loss is less than 10 g / m ２ Above, 20g / m ２ B: Weight loss is less than 20 g / m ２ That's all.

[0103] <Powdering Resistance> Powdering resistance was evaluated based on the occurrence of powdering. Plated steel materials were cut into pieces measuring 40 mm (C) × 100 mm (L) × thickness (t), and these were bent 90° at 5R (bending radius 5 times the thickness of the plated steel material) with the C direction as the bending axis direction using a V-bending tester manufactured by Electrical Discharge Precision Machining Research Institute. After that, cellophane tape was used to peel off the processed part, and the powdering resistance was evaluated based on the average value of five peeled widths of the plating layer that occurred. The evaluation criteria were as follows, with B being a failure and AAA, AA, and A being passes.

[0104] AAA: No peeling occurred at all. AA: Average peel width was 0.5 mm or more and less than 1.0 mm. A: Average peel width was 1.0 mm or more and less than 2.0 mm. B: Average peel width was 2.0 mm or more.

[0105] <Sacrificial corrosion protection> Sacrificial corrosion protection was evaluated as follows. A plated steel material was cut perpendicular to the surface of the plated steel material using a fine cutter to expose the cut edge. The cross section of the plating layer and the cross section of the base steel sheet 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.

[0106] AAA: 2400 hours or more. AA: 1500 hours or more, less than 2400 hours. A: 720 hours or more, less than 1500 hours. B: Less than 720 hours.

[0107] As shown in Tables 1-1 to 4-2, the chemical compositions of the plating layers and the distribution of the low hardness regions of the example Nos. 1 to 28 were within the ranges of the present invention, resulting in excellent abrasion resistance, powdering resistance, and sacrificial corrosion protection of the plating layers.

[0108] Among the examples, Nos. 13, 17, 21, and 24 had Al and Mg contents of 10.0 to 30.0% by mass and 4.0 to 10.0% by mass, respectively, and the average cooling rate in the range of 390 to 20°C was 30°C / sec or more. Therefore, the proportion of second measurement lines satisfying 0.10≦Σds / d≦0.70 was 80% or more, and the wear resistance and powdering resistance were improved.

[0109] In addition, among the examples, Nos. 5 to 12, 14 to 16, 19, 20, 22, 23, and 25 to 40 had Al and Mg contents of 15.0 to 30.0% by mass and 5.0 to 8.0% by mass, respectively, and the average cooling rate in the range of 390 to 20°C was 30°C / sec or more. Therefore, the proportion of second measurement lines satisfying 0.10≦Σds / d≦0.40 was 70% or more, and the wear resistance and powdering resistance were improved.

[0110] Furthermore, among the examples, Nos. 5, 7 to 9, and 13 were measured in a range from the bath temperature to 390°C, with a flow rate of 35,000 (L / min / m ２) or more, the condition 0≦ΣLs / L≦0.60 was satisfied, and the wear resistance was improved.

[0111] Furthermore, among the examples, Nos. 10 to 12, 24 to 25, 27, and 28 are examples in which the Al and Mg contents in the chemical composition of the plating layer are set to Al: 15.0 to 30.0 mass% and Mg: 5.0 to 8.0 mass%, respectively, and the range in which the temperature of the plating layer is increased from the bath temperature to 390°C is set to 35,000 (L / min / m ２ ) or more, the condition 0≦ΣLs / L≦0.20 was satisfied, and the wear resistance was improved.

[0112] On the other hand, in the comparative example No. 29, the Al concentration in the plating layer was insufficient, and the formulas (1) and (2) were not satisfied, resulting in inferior wear resistance.

[0113] In No. 30, the Al concentration in the plating layer was excessive. In addition, the proportion of the number of second measurement lines satisfying formula (3) was less than 80% of the total. This resulted in poor powdering resistance.

[0114] In No. 31, the Mg concentration in the plating layer was insufficient, and formula (1) was not satisfied. As a result, the wear resistance and sacrificial corrosion protection were both poor.

[0115] In No. 32, the Mg concentration in the plating layer was excessive. In addition, the ratio of the number of second measurement lines satisfying the following formula (3) was less than 80% of the total. This resulted in poor powdering resistance.

[0116] In No. 33, the average cooling rate in the bath temperature range of 390°C was excessive, and formula (1) was not satisfied. This resulted in poor wear resistance.

[0117] In No. 34, the cooling gas flux was insufficient in the bath temperature range of up to 390° C., and formula (1) was not satisfied. This resulted in poor wear resistance.

[0118] In No. 35, the average cooling rate in the range of 390 to 20°C was excessive, and formula (1) was not satisfied. This resulted in poor wear resistance.

[0119] No. 36 had a low reheating temperature and did not satisfy formula (1), resulting in poor wear resistance.

[0120] No. 37 had a high reheating temperature and did not satisfy formula (1), resulting in poor wear resistance.

[0121] In No. 38, the reheating temperature was low. Furthermore, formula (2) was not satisfied. Furthermore, the ratio of the number of second measurement lines satisfying formula (3) below was less than 80% of the total. This resulted in poor powdering resistance.

[0122] In No. 39, the reheating time was 0 seconds, and formula (1) was not satisfied. As a result, the wear resistance was poor.

[0123] No. 40 had a reheating time of 2010 seconds, and did not satisfy formula (1). This resulted in poor wear resistance.

[0124] In No. 41, the cooling time from 390° C. was set to 44° C., which did not satisfy formula (1). This resulted in poor wear resistance.

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[0133] INDUSTRIAL APPLICABILITY The present invention can provide a plated steel material that is excellent in corrosion resistance, wear resistance, and powdering resistance, and therefore has industrial applicability.

[0134] 1...plated steel material, 11...base steel sheet, 12...plated layer, M1...first measurement line, M2...second measurement line.

Claims

1. A plated steel product comprising a base steel sheet and a plating layer formed on at least a portion of the surface of the base steel sheet, 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: 0.00 to 1.00%, V: 0.00 to 1.00%, Co: 0.00 to 1.00%, In: 0.00 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%, A plated steel material in which, when a first measurement line is drawn in a direction parallel to the surface at a depth of 1.0 μm from the surface of the plated steel material in a cross section of the plating layer perpendicular to the surface of the plated steel material, the following formula (1) is satisfied; and when 50 second measurement lines are drawn at a 45° angle to a direction parallel to the surface of the plated steel material in the cross section excluding the region from the surface of the plated steel material to 1.0 μm and the region from the base steel sheet to 1.0 μm, the following formula (2) is satisfied; and further, the proportion of second measurement lines that satisfy the following formula (3) is 80% or more: 0≦ΣLs / L≦0.95 ... (1) 0.05≦Ave(Σds / d)≦0.90 ... (2) 0.05≦Σds / d≦0.90 ... (3) where L, ΣLs, d, Σds, and Ave(Σds / d) in the above formulas (1) to (3) are as follows.L: length of the first measurement line, ΣLs: sum of lengths Ls of portions in the first measurement line where the nanoindentation hardness is less than 1.8 GPa, d: total length of each second measurement line, Σds: sum of lengths ds of portions in the plating layer in each second measurement line where the nanoindentation hardness is less than 1.8 GPa, Ave(Σds / d): average value of Σds / d.

2. The plated steel product according to claim 1, 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 second measurement lines satisfying the following formula (4) is 80% or more: 0.10≦Σds / d≦0.70 ... (4) 3. The plated steel product according to claim 1, wherein the Al and Mg contents in 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 second measurement lines satisfying the following formula (5) is 70% or more: 0.10≦Σds / d≦0.40 ... (5) 4. The plated steel material according to any one of claims 1 to 3, which satisfies the following formula (6) instead of the formula (1): 0≦ΣLs / L≦0.60 (6) 5. The plated steel material according to any one of claims 1 to 3, which satisfies the following formula (7) instead of the formula (1): 0≦ΣLs / L≦0.20 (7) 6. The plated steel material according to any one of claims 1 to 5, wherein the plated layer has a portion having a nanoindentation hardness of 2.5 GPa or more.

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