Plated steel

Abstract

The plated steel material to be adopted has a plating layer disposed on the surface of a base steel material, the plating layer containing, by mass%, 5.0 to 40.0% Al, 0.5 to 15.0% Mg, 5.0 to 40.0% Fe, with the balance being Zn and impurities, and in a cross section perpendicular to the surface of the plated steel material, when a cross section of the plated steel material of a predetermined length in a direction parallel to the surface is taken as the observation region, the length L of the boundary line between the plating layer and the base steel material satisfies the following formula (1), and the plating layer includes a first region having an Fe concentration of less than 5.0 mass% and a second region having an Fe concentration of 5.0 mass% or more, and the first region contains an Al-containing phase in an area ratio of 5% or more. (L-L0) / L0×100≧2.0(%) …(1) L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

Description

[Technical Field]

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

[0002] For example, steel structures are used in the civil engineering and infrastructure fields. Steel structures are exposed to severely corrosive environments, such as coastal areas and areas where de-icing salt is used. Therefore, stainless steel materials are used to prevent corrosion and maintain steel structures over the long term.

[0003] On the other hand, stainless steel materials use high-cost alloy elements such as Cr and Ni. Therefore, the installation of steel structures using stainless steel materials is costly. Therefore, pre-plated products (e.g., Zn-Al-Mg plated steel materials) have come to be used as a substitute for stainless steel materials.

[0004] However, in the case of large steel structures or pipe-shaped steel structures, the plating layer may disappear due to welding, and the plating layer may also disappear partially due to corrosion from the cut end surface, etc. Furthermore, it is difficult to manufacture steel parts such as bolts and washers from sheet metal in the first place. For the reasons described above, large steel structures, pipe-shaped steel structures, and steel parts such as bolts and washers are generally manufactured by subjecting steel materials that have been processed into a predetermined shape to a post-plating process (so-called hot-dip plating process).

[0005] Hot dip Zn plating is widely used as a post-plating treatment, but recently Zn-Al-Mg plating has also come into use to improve corrosion resistance.

[0006] Patent Document 1 listed below describes a plated steel material having: a steel material; a surface plating layer disposed on the surface of the steel material and composed of a Zn-Al-Mg alloy layer having an Fe concentration of less than 3 mass%; an intermediate plating layer disposed between the steel material and the surface plating layer and composed of a Zn-Al-Mg alloy layer having an Fe concentration of 3 mass% or more and less than 30 mass% and having a layer thickness of 3 μm or more; and an interfacial alloy layer disposed between the steel material and the intermediate plating layer; wherein the total thickness of the surface plating layer and the intermediate plating layer is 8 μm or more and less than 300 μm; and the plating layer has an average chemical composition, in mass%, of more than 65.00% Zn, more than 6.5% but less than 22.5% Al, more than 3.0% but less than 12% Mg, and impurities; and the Mg concentration, in mass%, of the intermediate plating layer is more than 3.0%. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-4403 Summary of the Invention [Problem to be solved by the invention]

[0008] Recently, the use of hot-dip plated steel has been considered, not only in the civil engineering and infrastructure fields, but also as a material for automotive parts. When plated steel is used as a material for automotive parts, in addition to red rust resistance, improvements are required in the adhesion of the plating layer, corrosion resistance to the base steel, and sacrificial corrosion resistance.

[0009] The plated steel material described in Patent Document 1 has excellent red rust resistance, but there is no mention whatsoever of the adhesion of the plating layer, the corrosion resistance of the base steel, or the sacrificial corrosion resistance.

[0010] Therefore, an object of the present invention is to provide a plated steel material that has excellent red rust resistance, as well as excellent adhesion of the plating layer, corrosion resistance against the base steel, and sacrificial corrosion resistance. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention employs the following configuration. [1] A plated steel product comprising a base steel material and a plating layer disposed on the surface of the base steel material, The plating layer has a chemical composition of, by mass%, Al: 5.0 to 40.0%, Mg: 0.5 to 15.0% Fe: 5.0 to 40.0% Si: 0 to 2.0% Ca: 0 to 2.0% 、 under One or two selected from the group consisting of Group A and Group B 、 Contains The balance is Zn and impurities, In a cross section perpendicular to the surface of the plated steel material, a direction parallel to the surface to 100 μm When the cross section of the plated steel material is used as an observation area, the length L of the boundary line between the plated layer and the base steel material satisfies the following formula (1): the plating layer includes a first region that is disposed on the surface side of the plated steel material and has an Fe concentration of less than 5.0 mass%, and a second region that is disposed between the first region and the base steel material and has an Fe concentration of 5.0 mass% or more, The thickness of the first region is 5 to 100 μm, The thickness of the second region is 5 to 200 μm, The plated steel material contains, in the first region, an Al-containing phase containing Zn and 20 to 99 mass % of Al in an area ratio of 5% or more. [Group A] Ni: 0-1.0%. [Group B] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-2.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%, and one or more of the following, totaling 0-5%. (L-L0) / L0×100≧2.0(%) …(1) However, in formula (1), L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end. [2] The plated steel material according to [1], which satisfies the following formula (2): (L-L0) / L0×100≧4.0(%) …Formula (2) However, in formula (2), L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end. [3] The plated steel material according to [1], which satisfies the following formula (3): (L-L0) / L0×100≧6.0(%) …Formula (3) However, in formula (3), L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end. [4] The plated steel material according to any one of [1] to [3], wherein the thickness of the first region is 15 μm to 100 μm. [5] The plated steel material according to any one of [1] to [3], wherein the area ratio of the Al-containing phase in the first region is 15% or more. [6] The plated steel material according to any one of [1] to [3], wherein the first region contains an Mg-Zn phase containing Zn and 20 to 60 mass% of Mg, and the area ratio of the Mg-Zn phase in the first region is 15% or more. [7] The plated steel material according to any one of [1] to [3], wherein the first region contains a binary eutectic structure of an Al phase and an Mg-Zn phase, and the area ratio of the binary eutectic structure in the first region is 5% or more. [8] The plated steel material according to any one of [1] to [3], wherein the second region has a thickness of 15 μm to 200 μm. [9] The plated steel material according to any one of [1] to [3], wherein the second region contains an Mg-Zn phase containing Zn and 20 to 60 mass% of Mg, and the area ratio of the Mg-Zn phase in the second region is 15% or more.

[10] The plated steel material according to any one of [1] to [3], wherein the content of Mg relative to the total amount of Zn and Mg in the chemical composition of the plated layer (Mg / (Zn+Mg)(%)) is 5.0% or more.

[11] The plated steel material according to any one of [1] to [3], wherein the content of Mg relative to the total amount of Zn and Mg in the chemical composition of the plated layer (Mg / (Zn+Mg)(%)) is 6.5% or more.

[12] The plating layer contains Sn at a concentration of 0.02 to 2.0% by mass, The plated steel material according to any one of [1] to [3], wherein the plated layer contains an Mg2Sn phase. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a plated steel material that has excellent red rust resistance, as well as excellent adhesion of the plating layer, corrosion resistance of the base steel, and sacrificial corrosion resistance. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional schematic view showing a plated steel material according to an embodiment of the present invention; [Figure 2] FIG. 1 is a cross-sectional schematic view showing a plated steel material according to an embodiment of the present invention, illustrating an observation area. [Figure 3] FIG. 2 is a cross-sectional view showing a plated steel material according to an embodiment of the present invention, illustrating a method for determining the ranges of a first region and a second region. [Figure 4]FIG. 2 is a cross-sectional view showing a plated steel material according to an embodiment of the present invention, illustrating a method for determining the ranges of a first region and a second region. [Figure 5] 5 is a cross-sectional schematic view showing a plated steel material according to an embodiment of the present invention, and is an enlarged view of an area M in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have conducted investigations in order to provide a plated steel material that is excellent in red rust resistance, as well as in adhesion of the plating layer, corrosion resistance of the base steel, and sacrificial corrosion resistance.

[0015] The plated steel material described in Patent Document 1 may have an interfacial alloy layer with a thickness of 1 μm to 5 μm. In the plated steel material described in Patent Document 1, if the interfacial alloy layer is formed too thick, the adhesion and workability of the plated layer will be significantly reduced, so the thickness of the interfacial alloy layer is limited to 5 μm or less. However, the present inventors have discovered that a layer containing a large amount of Fe, such as an interfacial alloy layer, can improve the corrosion protection of the base steel by its barrier effect. Therefore, the present inventors have succeeded in improving the corrosion protection of the base steel without reducing the adhesion of the plated layer, and further increasing the red rust resistance and sacrificial corrosion protection, by forming a thick layer containing a large amount of Fe between the Mg-Al-Zn alloy layer and the base steel and controlling the morphology of the interface between the layer containing a large amount of Fe and the base steel.

[0016] More specifically, they discovered that by imparting strain to the surface of the base steel before forming a coating layer on the base steel by hot-dip plating and by controlling the cooling conditions after removal from the coating bath to control the morphology of the interface between the base steel and the coating layer, they could obtain plated steel with excellent red rust resistance, coating layer adhesion, substrate corrosion protection, and sacrificial corrosion protection. They also discovered that by precipitating an Al-containing phase on the surface of the coating layer and keeping the Fe concentration low, they could further improve red rust resistance and substrate corrosion protection.

[0017] Hereinafter, a plated steel material according to an embodiment of the present invention will be described.

[0018] The plated steel material of this embodiment is a plated steel material comprising a base steel material and a plating layer disposed on the surface of the base steel material, the plating layer having a chemical composition, in mass %, of Al: 5.0 to 40.0%, Mg: 0.5 to 15.0%, Fe: 5.0 to 40.0%, Si: 0 to 2.0%, and Ca: 0 to 2.0%, and further containing one or two elements selected from the group consisting of Group A and Group B below, with the balance being Zn and impurities, and when a cross section of the plated steel material of a predetermined length in a direction parallel to the surface is observed in a cross section perpendicular to the surface of the plated steel material, The plated steel material has a first region that is disposed on the surface side of the plated steel material and has an Fe concentration of less than 5.0 mass%, and a second region that is disposed between the first region and the base steel material and has an Fe concentration of 5.0 mass% or more, the first region having a thickness of 5 to 100 μm and the second region having a thickness of 5 to 200 μm, and the first region contains an Al-containing phase that contains Zn and 20 to 99 mass% Al in an area ratio of 5% or more. [Group A] Ni: 0-1.0%. [Group B] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-2.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%, and one or more of the following, totaling 0-5%. (L-L0) / L0×100≧2.0(%) …(1) In the formula (1), L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

[0019] Furthermore, it is preferable that the plated steel material of this embodiment satisfies the following formula (2). (L-L0) / L0×100 ≧ 4.0(%) …Formula (2) Furthermore, it is preferable that the plated steel material of this embodiment satisfies the following formula (3). (L-L0) / L0×100 ≧ 6.0(%) …Formula (3) In the formulas (2) and (3), L0 is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

[0020] The thickness of the first region is preferably 15 μm to 100 μm. The area ratio of the Al-containing phase contained in the first region is preferably 15% or more. Preferably, the first region contains an Mg—Zn phase containing Zn and 20 to 60 mass % of Mg, and the area ratio of the Mg—Zn phase in the first region is 15% or more. Preferably, the first region contains a binary eutectic structure of an Al phase and an Mg—Zn phase, and the area ratio of the binary eutectic structure in the first region is 5% or more.

[0021] The thickness of the second region is preferably 15 μm to 200 μm. Preferably, the second region contains an Mg—Zn phase containing Zn and 20 to 60 mass % of Mg, and the area ratio of the Mg—Zn phase in the second region is 15% or more.

[0022] Furthermore, in the chemical composition of the plating layer, the content of Mg relative to the total amount of Zn and Mg (Mg / (Zn+Mg)(%)) is preferably 5.0% or more. Furthermore, in the chemical composition of the plating layer, the content of Mg relative to the total amount of Zn and Mg (Mg / (Zn+Mg)(%)) is preferably 6.5% or more.

[0023] It is also preferable that the plating layer contains Sn at a concentration of 0.02 to 2.0% by mass, and that the plating layer contains an Mg2Sn phase.

[0024] In the following description, the "%" designation for the content of each element in the chemical composition means "mass %." The content of an element in the chemical composition may be expressed as an element concentration (for example, Zn concentration, Mg concentration, etc.). "Adhesion of the plating layer" refers to the property of the plating layer that makes it difficult to peel off. "Red rust resistance" refers to the property of suppressing the occurrence of red rust in a plating layer when the plating layer corrodes. "Base steel corrosion resistance" refers to the property of the plating layer itself to be resistant to corrosion. "Sacrificial corrosion protection" refers to the property of inhibiting corrosion of the base steel at exposed parts of the base steel (for example, the cut end surface of plated steel, areas where the plating layer breaks during processing, and areas where the base steel is exposed due to peeling of the plating layer).

[0025] As shown in FIG. 1 , the plated steel material 1 according to this embodiment includes a base steel material 11. The shape of the base steel material 11 is not particularly limited. Examples of the form of the base steel material 11 include steel plates, angle bars with L-shaped cross sections, and expanded metal. The base steel material 11 may also be formed into a base steel material such as a steel pipe, civil engineering and construction materials (fences, corrugated pipes, drainage ditch covers, sand-flying prevention plates, bolts, wire mesh, guardrails, water-stopping walls, etc.), home appliance components (such as the housing of an outdoor unit of an air conditioner), or automobile parts (such as suspension components). The base steel material 11 may also be a formed product obtained by forming a steel plate into a predetermined shape. The base steel material 11 may also be formed into the shape of, for example, an automobile part by welding together two or more formed products obtained by forming a steel plate into a predetermined shape. The forming process may be any of various plastic processing techniques, such as pressing, roll forming, and bending.

[0026] There are no particular limitations on the material of the base steel material 11. The base steel material 11 can be various steel materials 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). The base steel material 11 may also be a hot-rolled steel sheet, hot-rolled steel strip, cold-rolled steel sheet, or cold-rolled steel strip described in JIS G 3302:2010. There are also no particular limitations on the method for manufacturing the steel sheet (hot rolling method, pickling method, cold rolling method, etc.) and the specific manufacturing conditions thereof.

[0027] Furthermore, the base steel material 11 serving as the plating base sheet may be a pre-plated steel material in which a pre-plating is formed on the surface of the base steel material 11. An example of a pre-plated steel material is a Ni pre-plated steel material in which a Ni plating is formed on the surface of the base steel material 11. The pre-plated steel material is obtained, for example, by electrolytic treatment or displacement plating. Electrolytic treatment is performed by immersing the base steel material 11 in a sulfate bath or chloride bath containing metal ions of various pre-plating components. Displacement plating is performed by immersing the base steel material in an aqueous solution containing metal ions of various pre-plating components and having the pH adjusted with sulfuric acid, to cause displacement deposition of the metal.

[0028] The plated steel material 1 according to this embodiment has a plating layer 12 disposed on the surface of a base steel material 11. As described below, the plating layer 12 includes a first region 12A having an Fe concentration of less than 5.0 mass % and a second region 12B having an Fe concentration of 5.0 mass % or more. The plating layer 12 including the first region 12A and the second region 12B has a chemical composition that includes Zn and other alloying elements and may further include impurities. Alternatively, the plating layer 12 may contain Zn and other alloying elements, with the remainder being impurities.

[0029] The chemical composition of the plating layer will be described in detail below. Note that elements whose lower limit of concentration is 0% are not essential for solving the problems of the plated steel material according to this embodiment, but are optional elements that are allowed to be contained in the plating layer for the purpose of improving characteristics, etc.

[0030] <Al:5.0~40.0%> Al contributes to improving red rust resistance, base steel corrosion resistance, and sacrificial corrosion resistance. Therefore, the Al concentration is set to 5.0% or more. The Al concentration may be set to 10.0% or more, 15.0% or more, or 20.0% or more. On the other hand, if the Al concentration is excessive, the Mg concentration and Zn concentration will relatively decrease, which may result in deterioration of sacrificial corrosion resistance in particular. Furthermore, the appearance of the coating layer may be significantly deteriorated. Therefore, the Al concentration is set to 40.0% or less. The Al concentration may also be set to 35.0% or less, or 30.0% or less.

[0031] <Mg: 0.5 to 15.0%> Mg is an essential element to ensure subway corrosion resistance and sacrificial corrosion resistance. It is also necessary to precipitate the MgZn2 phase. Therefore, the Mg concentration should be 0.5% or more. The Mg concentration may be 2.0% or more, 3.0% or more, or 4.0% or more. On the other hand, if the Mg concentration is excessive, the workability, especially the powdering property, deteriorates, and furthermore, the subway corrosion resistance may deteriorate. Also, the appearance of the plating layer may be significantly reduced. Therefore, the Mg concentration should be 15.0% or less. The Mg concentration may be 10.0% or less or 8.0% or less.

[0032] <Mg / (Zn + Mg): 5.0% or more or 6.5% or more> The content ratio of Mg to the total amount of Zn and Mg in the chemical composition of the plating layer (Mg / (Zn + Mg)(%)) may be 5.0% or more or 6.5% or more. Thereby, the sacrificial corrosion resistance can be further enhanced. Mg and Zn in (Mg / (Zn + Mg)) are the Mg concentration and Zn concentration in the plating layer, respectively.

[0033] <Fe: 5.0% to 40.0%> A certain amount of Fe is contained in the first region and the second region of the plating layer of this embodiment. Most of the Fe is contained in the plating layer by diffusing from the mother steel material which is the plating substrate into the plating layer. It has been confirmed that there is no adverse effect on the performance even if it is contained in the plating layer until the Fe concentration reaches 40.0% or less. Since most of the Fe exists as an Al-Fe alloy phase in the second region in many cases, the Fe concentration tends to increase as the thickness of the second region increases. When the Fe concentration is less than 5.0%, the subway corrosion resistance may deteriorate in the later stage of corrosion of the plating layer. Therefore, the Fe concentration is in the range of 5.0 to 40.0%. The Fe concentration may be 10.0% or more, 15.0% or more, or 20.0% or more. Also, the Fe concentration may be 30.0% or less or 28.0% or less. <​​​​Si is an optional element and may be 0%. However, the inclusion of Si can form phases such as Mg2Si, Al-Ca-Si-Zn, and Mg-Al-Si-Zn in the coating layer, improving the corrosion resistance of the coating layer. Therefore, the Si concentration may be greater than 0%, 0.1% or more, or 0.2% or more. On the other hand, excessive Si concentration may degrade the base steel corrosion resistance and sacrificial corrosion resistance. Therefore, the Si concentration is set to 2.0% or less. The Si concentration may also be set to 0.8% or less or 0.6% or less.

[0035] <Ca:0%~2.0%> Ca is an optional element and may be 0%. However, the inclusion of Ca can form Al-Ca-Zn phases, Al-Ca-Si-Zn phases, Ca-Zn phases, and other phases in the coating layer, improving the corrosion resistance of the coating layer. Ca is also an element that can adjust the optimal amount of Mg elution to provide corrosion protection to the steel substrate. Therefore, the Ca concentration may be 0.05% or more, or 0.1% or more. On the other hand, excessive Ca concentration can deteriorate the steel substrate's corrosion protection and workability. Therefore, the Ca concentration is set to 2.0% or less. The Ca concentration may also be set to 1.0% or less.

[0036] Furthermore, the plating layer of this embodiment may contain one or two types selected from the group consisting of Group A and Group B below.

[0037] [Group A] Ni: 0-1.0% [Group B] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-2.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%, and one or more of the following, totaling 0-5%.

[0038] <Ni:0~1.0%> The concentration of Ni in Group A may be 0%. 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, the corrosion protection of the base steel may deteriorate. Therefore, the Ni concentration is set to 1.0% or less. The Ni concentration may also be 0.8% or less, 0.6% or less, 0.5% or less, 0.1% or less, or 0.01% or less.

[0039] The plating layer according to this embodiment may contain one or more of the elements in Group B in a total amount of 0 to 5%. If the total content of the elements in Group B exceeds 5%, the corrosion resistance or sacrificial corrosion resistance of the base steel may decrease. The elements in Group B will be described below.

[0040] <Sb、Pb:それぞれ0~0.5%> The concentrations of Sb and Pb may be 0%. Sb and Pb contribute to improving sacrificial corrosion protection. Therefore, the concentrations of Sb and Pb may be 0.001% or more, 0.005% or more, or 0.01% or more. On the other hand, excessive concentrations of Sb and Pb may deteriorate the corrosion protection of the base steel. Therefore, the concentrations of Sb and Pb should be 0.5% or less. The concentrations of Sb and Pb may also be 0.3% or less, 0.1% or less, or 0.05% or less.

[0041] <Cu、Ti、Cr、Nb、Zr、Mn、Mo、AgおよびLi:それぞれ0~1.0%> The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li may each be 0%. These elements contribute to improving sacrificial corrosion protection. Therefore, the concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li may each be 0.005% or more, or 0.01% or more. On the other hand, excessive concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li may degrade the corrosion protection of the base steel. Therefore, the concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li each should be 1.0% or less. The concentrations of Cu, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li each may be 0.5% or less, 0.1% or less, or 0.05% or less.

[0042] <Sn:0~2.0%> The Sn concentration may be 0%. Sn is an element that forms an intermetallic compound with Mg and improves the sacrificial corrosion protection of the coating layer. Therefore, the Sn concentration may be 0.01% or more, 0.02% or more, or 0.05% or more. However, if the Sn concentration is excessive, the corrosion protection of the base steel may deteriorate. Therefore, the Sn concentration is set to 2.0% or less. The Sn concentration may also be 1.5% or less, 1.0% or less, 0.5% or less, or 0.2% or less. In order to contain the Mg2Sn phase, the Sn content is preferably 0.02 to 2.0%.

[0043] <La、Ce、B、Y、PおよびSr:それぞれ0~0.5%> The concentrations of La, Ce, B, Y, P, and Sr may each be 0%. La, Ce, B, Y, P, and Sr contribute to improving sacrificial corrosion protection. Therefore, the concentrations of La, Ce, B, Y, P, and Sr may each be 0.005% or more, or 0.01% or more. On the other hand, excessive concentrations of La, Ce, B, Y, P, and Sr may degrade the corrosion protection of the base steel. Therefore, the concentrations of La, Ce, B, Y, P, and Sr each are 0.5% or less. The concentrations of La, Ce, B, Y, P, and Sr each may be 0.2% or less, 0.1% or less, 0.05% or less, or 0.02% or less.

[0044] <Co、Bi、In、V、W:それぞれ0~0.5%> The concentrations of Co, Bi, In, V, and W may each be 0%. Co, Bi, In, V, and W contribute to improving sacrificial corrosion protection. Therefore, the concentrations of Co, Bi, In, V, and W may each be 0.001% or more, 0.002% or more, or 0.004% or more. On the other hand, excessive concentrations of Co, Bi, In, V, and W may degrade the corrosion protection of the base steel. Therefore, the concentrations of Co, Bi, In, V, and W are each set to 0.5% or less. The concentrations of Co, Bi, In, V, and W may each be set to 0.1% or less, 0.05% or less, 0.02% or less, or 0.01% or less.

[0045] <Remainder: Zn and impurities> The remainder of the components of the coating layer according to this embodiment is Zn and impurities. Zn is an element that provides the coating layer with anti-corrosion properties for the base steel and sacrificial anti-corrosion properties. The Zn concentration is not particularly limited, but may be 15.0% or more, 30.0% or more, or 50.0% or more. Impurities refer to components contained in raw materials or components mixed in during the manufacturing process. For example, trace amounts of components other than Fe may be mixed into the coating layer as impurities due to mutual atomic diffusion between the base steel and the coating bath.

[0046] The chemical composition of the plating layer is measured by the following method. First, an acid containing an inhibitor that suppresses corrosion of the base steel is used to immerse the base steel for 20 minutes at room temperature to obtain an acid solution that removes and dissolves the plating layer. Next, the obtained acid solution is quantitatively analyzed by ICP atomic emission spectroscopy. This allows the chemical composition of the plating layer to be obtained. For example, a 10% hydrochloric acid solution containing 0.06 mass% of an inhibitor (Ivit 710K, manufactured by Asahi Chemical Industry Co., Ltd.) can be used as the acid containing the inhibitor. Note that the chemical composition measured by the above-mentioned method is the chemical composition of the entire plating layer.

[0047] Next, the plating layer of this embodiment will be described in more detail. In the plated steel material of this embodiment, the interface between the plating layer and the base steel material has an uneven surface. The uneven surface at the interface between the plating layer and the base steel material significantly improves the adhesion of the plating layer.

[0048] Whether the interface between the plating layer and the base steel is an uneven surface to the extent that the adhesion of the plating layer is improved can be confirmed by checking whether the length L of the boundary line 13 between the plating layer 12 and the base steel 11 satisfies the following formula (1), when a predetermined length, for example, 100 μm, of the cross section of the plated steel in a direction parallel to the surface 1a of the plated steel is set as the observation region in a cross section perpendicular to the surface of the plated steel, as shown in FIG. 2. Note that in FIG. 2, a cross section of the plated steel that is more than 100 μm long in a direction parallel to the surface 1a of the plated steel is observed, but the length of the cross section is not limited to 100 μm and can be any length (predetermined length). Specifically, in a cross section perpendicular to the surface 1a of the plated steel, a cross section of the plated steel that is 100 μm long in a direction parallel to the surface 1a is set as the observation region. Then, the linear distance L0 between one end 13a and the other end 13b of the boundary line 13 in the observation area and the length L of the boundary line 13 between the one end 13a and the other end 13b are determined, and the value of ((L-L0) / L0×100) is calculated. As shown in formula (1), when (L-L0) / L0×100 is 2.0% or more, the adhesion of the plating layer is improved. The plated steel material of this embodiment may satisfy the following formula (2) or formula (3) instead of the following formula (1). There is no particular upper limit required for (L-L0) / L0×100, but if it is too large, the surface smoothness of the plating layer will decrease. Therefore, it is preferably 40.0% or less, or alternatively 10.0% or less, or 9.0% or less.

[0049] (L-L0) / L0×100≧2.0(%) …(1) (L-L0) / L0×100≧4.0(%) …(2) (L-L0) / L0×100≧6.0(%) …(3)

[0050] The observation area is a cross section of the plated steel material of a predetermined length in a direction parallel to the surface 1a of the plated steel material when observed at a magnification of 1000x or more using an SEM (JEOL "JSM-7000F", accelerating voltage: 15 kV). When the predetermined length is 100 μm, the resolution of the observation area is 2560 pixels or more horizontally and 1920 pixels or more vertically.

[0051] Furthermore, as shown in FIG. 2, when the surface 1a of the plated steel material is not flat in a microscopic region (a region of about 100 μm) of the observation area, it is difficult to observe the surface 1a in a wider region of the plated steel material (for example, a region of several mm 2 The direction parallel to the surface in the above-mentioned region (for example, the direction in which the surface of a flat plate extends when placed on it) can be taken as the direction in which the surface 1a extends. Based on this direction, the "cross section perpendicular to the surface 1a" and the "direction parallel to the surface 1a" will be specified.

[0052] Furthermore, as shown in FIG. 2, one end 13a and the other end 13b of the boundary line 13 are the intersections of the boundary line 13 and the straight line that divides the observation area. L0 is the length of the straight line connecting the one end 13a and the other end 13b. L is the length of the boundary line 13 from the one end 13a to the other end 13b. The length L of the boundary line 13 can be measured, for example, using ImageJ, a public domain image processing software. An image observed with an SEM at a magnification of 1000x or more is used as image data with the above resolution or higher. The length of the boundary line 13 is measured for this image data using the measurement function of ImageJ.

[0053] Next, the structure of the plating layer will be described. The proportion of phases and structures contained in the plating layer of this embodiment affects the red rust resistance, base metal corrosion resistance, and sacrificial corrosion resistance of the plated steel material. Even plating layers with the same component composition can have different properties due to the phases or structures contained in the metal structure depending on the manufacturing method. The metal structure of the plating layer can be easily confirmed by mirror-finishing a cross section perpendicular to the surface of the plated steel material and analyzing the cross section with an electron probe microanalyzer equipped with scanning electron microscope functions (SEM-EPMA, EPMA measuring device: JEOL JXA-8230, acceleration voltage: 15 kV, current: 0.05 μA, irradiation time: 50 ms). The thickness of the plating layer of this embodiment is approximately 10 to 300 μm. With the SEM, the magnification is set to 200 to 5000 times, and the field of view is 36,000 μm. 2In this embodiment, since the SEM field of view for the plating layer may be a local field of view, 25 fields of view are selected from the above cross section to obtain average information on the plating layer. That is, a total of 25 × 36000 μm 2 The metallographic structure in the field of view is observed to determine the area ratio of the phase or structure that constitutes the metallographic structure of the plating layer. If necessary, measurements may be taken on multiple cross sections. It is preferable that the cross sections be near the center of the flat surface of the object to be measured (sample).

[0054] To confirm each phase, elemental analysis using EPMA was performed to confirm the phase composition through point analysis, and phases with equivalent components were identified through elemental mapping. Point analysis involved analyzing the elements Al, Zn, Mg, Fe, and Si at 250 pixel x 250 pixel grid points in the EPMA analysis results. The electron beam diameter was 1 μm or less. Phases with equivalent components could be identified by identifying phases with approximately the same composition through elemental mapping. That is, to confirm each phase, point analysis was performed in SEM-EPMA analysis for regions other than the lamellar structure (Al / MgZn2 binary eutectic structure), and phases with approximately the same components were identified through elemental mapping. The area of ​​each phase was measured using the image analysis software "Image J (Ver. 1.54f)." The percentage of the total area of ​​each phase relative to the total area of ​​the observation field was defined as the area ratio (%) of each phase.

[0055] The area ratio (area rate) of each phase in the observed field of view corresponds to the volume rate of the phase in the first region or the second region.

[0056] As already described, the coating layer of this embodiment includes a first region having an Fe concentration of less than 5.0 mass % and a second region having an Fe concentration of 5.0 mass % or more. The phases and structures contained in either or both of the first and second regions will be described below.

[0057] Al-containing phase The Al-containing phase of this embodiment is a phase containing Zn and 20 to 99 mass% Al. The Zn content in the Al-containing phase may be 1 to 80 mass%. The Al-containing phase may also contain a total of 5 mass% or less of other elements. Here, the other elements include Mg, Si, etc. The Al-containing phase may be in the form of a solid solution of Zn in Al, or may be an aggregate of a fine Zn phase with a grain size of less than 1 μm and a fine Al phase with a grain size of less than 1 μm. The Al-containing phase can be clearly distinguished from other phases and structures by identifying the phase containing Zn and 20 to 99 mass% Al by elemental mapping using an EPMA. Note that in this embodiment, Al contained in the [Al / MgZn2 binary eutectic structure] is not included in the Al-containing phase.

[0058] The Al-containing phase is contained mainly in the first region. A plating layer containing a large amount of the Al-containing phase in the first region has excellent red rust resistance.

[0059] Mg-Zn phase The Mg-Zn phase is a phase containing Zn and 20 to 60 mass% of Mg. The Zn content in the Mg-Zn phase may be 40 to 80 mass%. The Mg-Zn phase may also contain other elements in a total amount of 5 mass% or less. The other elements here include Mg, Si, etc. Specific examples of the Mg-Zn phase include MgZn2 phase and Mg2Zn 11 The Mg-Zn phase can be clearly distinguished from Al-containing phases, [Al / MgZn2 binary eutectic structure], etc. by identifying the phase containing Zn and 20 to 60 mass% Mg by elemental mapping with EPMA.

[0060] The Mg-Zn phase is contained in the first region. The Mg-Zn phase may also be contained in the second region. The inclusion of the Mg-Zn phase in the coating layer improves red rust resistance and corrosion resistance of the base steel, and further improves sacrificial corrosion resistance.

[0061] [Al / MgZn2 binary eutectic structure] The [Al / MgZn2 binary eutectic structure] is a eutectic structure consisting of an Al phase and an MgZn2 phase. The [Al / MgZn2 binary eutectic structure], which exhibits a lamellar structure consisting of an Al phase and an MgZn2 phase, is clearly distinguishable in SEM backscattered electron images from the Al-containing phase, Mg-Zn phase, and Fe-Al phase contained as the main phase of the coating layer. Note that identification of structures other than the [Al / MgZn2 binary eutectic structure], such as the above-mentioned Al phase and Mg-Zn phase, can be performed by excluding the [Al / MgZn2 binary eutectic structure], which exhibits a lamellar structure.

[0062] The [Al / MgZn2 binary eutectic structure] may be contained in the first region. The presence of a certain amount of the [Al / MgZn2 binary eutectic structure] can improve sacrificial corrosion protection.

[0063] Fe-Al alloy phase The Fe-Al alloy phase is a phase containing Al and 20 to 60 mass% of Fe. The Al content in the Fe-Al alloy phase may be 40 to 80 mass%. The Fe-Al alloy phase may also contain a total of 5 mass% or less of other elements. Here, the other elements include Si. The Fe-Al alloy phase is a phase mainly composed of Al5Fe. The Fe-Al alloy phase may also contain AlFe, Al3Fe, Al5Fe2, etc. in addition to Al5Fe. Furthermore, when the coating layer contains Si, the Fe-Al alloy phase may become an Fe-Al-Si compound phase. The identified Fe-Al-Si compound phase is the AlFeSi phase, and isomers such as α-, β-, q1-, and q2-AlFeSi phases exist.

[0064] The Fe-Al alloy phase is mainly included in Region 2. The Fe-Al alloy phase has a certain degree of corrosion resistance against Fe, and because the Fe-Al alloy phase is an intermetallic compound phase, it has high insulating properties and is resistant to corrosion.

[0065] The plating layer may contain other intermetallic compounds as the balance, such as Mg2Si phase, Mg2Sn phase, Zn phase, Al-Ca-Zn phase, Al-Ca-Si-Zn phase, Ca-Zn phase, and Mg-Al-Si-Zn phase.

[0066] Mg2Si phase When the plating layer contains Si, the Si may precipitate as an Mg2Si phase. The Mg2Si phase has excellent corrosion resistance. The presence of Mg2Si can be measured using SEM / EPMA, which will be described later. A phase that satisfies the following conditions can be determined to be an Mg2Si phase: 50 to 70 at% Mg and 30 to 50 at% Si.

[0067] Mg2Sn phase The presence of the Mg2Sn phase in the coating layer further improves the red rust resistance and base steel corrosion protection of the coated steel material. Because the Mg2Sn phase is present in small amounts, its presence can be confirmed by X-ray diffraction measurement. For the Mg2Sn phase to be present, the Sn content in the chemical composition of the coating layer is preferably 0.02 to 2.0%. The presence of the Mg2Sn phase is determined by X-ray diffraction measurement using Cu-Kα radiation at an X-ray output of 50 kV and 300 mA, with a measurement range of 2θ = 10 to 30° and a scan step of 0.02°. The presence of the Mg2Sn phase is determined when a diffraction peak is detected at 23.4±0.3°.

[0068] Zn phase The Zn phase contains more than 80 mass% Zn, and may contain less than 20 mass% Al, and may contain other elements such as Si and Mg in total of 5 mass% or less. The Zn phase may be contained in the first region. The inclusion of the Zn phase improves sacrificial corrosion protection. The Zn phase appears white in a backscattered electron image of an SEM, and can therefore be clearly distinguished from other phases and structures.

[0069] Al-Ca-Zn phase, Al-Ca-Si-Zn phase, Ca-Zn phase, Mg-Al-Si-Zn phase When Ca or Si is present in the plating bath, these intermetallic compound phases may precipitate in the plating layer. These intermetallic compound phases have even better corrosion resistance than the aforementioned Mg2Si phase. The presence of these intermetallic compound phases can be confirmed by X-ray diffraction measurement in addition to SEM and EPMA measurements. The X-ray diffraction conditions can be the same as for the Mg2Sn phase.

[0070] As already described, the plating layer of this embodiment includes a first region having an Fe concentration of less than 5.0 mass % and a second region having an Fe concentration of 5.0 mass % or more. The boundary between the first region and the second region is determined as follows.

[0071] First, a cross section perpendicular to the surface of the plated steel is exposed. The exposed cross section is then mirror-finished. The Fe concentration is measured by point analysis using an electron probe microanalyzer (EPMA). The results of the EPMA analysis used to identify each phase of the plated layer can be used.

[0072] First, as shown in FIG. 3, in the first stage of measurement, multiple linear analysis lines are set in the cross section of the plating layer 12, parallel to the direction perpendicular to the thickness direction of the plating layer 12. Ten analysis lines are set at equal intervals in the thickness direction of the plating layer. Note that if the thickness of the plating layer is greater than 100 μm, the analysis lines are spaced 10 μm apart. Ten measurement points are set on the analysis lines at 10 μm intervals in the direction perpendicular to the thickness direction. If the length of the analysis line is less than 90 μm and it is not possible to set 10 measurement points at 10 μm intervals, the intervals may be narrowed or the number of measurement points may be reduced. In FIG. 3, the dashed lines represent the analysis lines, and the black dots on the analysis lines represent the measurement points. Note that the analysis lines are set to maximize the number of analysis lines in the cross section of the plating layer 12. If the thickness of the plating layer 12 is 10 μm or less, the first stage of measurement is omitted and the second stage of measurement described below is performed.

[0073] At each measurement point, the Fe concentration (mass%) in the plating layer is measured by point analysis. The electron beam output during point analysis is 15 kV, 4 × 10-7 The spot diameter at the tip of the electron beam is 0.2 μm. For each analysis line, the average Fe concentration at 10 measurement points is calculated, and this average is used as the Fe concentration for that analysis line. Analysis line A, which has an Fe concentration less than 5.0% but is closest to 5.0%, and analysis line B, which has an Fe concentration greater than 5.0% but is closest to 5.0% are then identified.

[0074] Next, in the second stage of measurement, the Fe concentration is analyzed in the region between analysis line A and analysis line B on the cross section of the plating layer 12, as shown in Figures 4 and 5. Figure 4 is a diagram showing analysis lines A and B among the multiple analysis lines. Figure 5 is an enlarged view of region M between analysis line A and analysis line B in Figure 4.

[0075] In the second-stage measurement, as shown in Figures 4 and 5, multiple analysis lines are set at 1 μm intervals in the thickness direction of the plating layer in the region between analysis line A and analysis line B. Ten measurement points are set at 10 μm intervals on the analysis lines. Figures 4 and 5 show only some of the analysis lines set between analysis line A and analysis line B as an example. Then, the Fe concentration (mass %) is measured at each measurement point by point analysis. The electron beam output and spot diameter at the tip of the electron beam during point analysis are the same as in the first-stage measurement.

[0076] For each analysis line, the Fe concentration at 10 measurement points is averaged, and this average is designated as the Fe concentration for that analysis line. The analysis line with the Fe concentration closest to 5.0% is then identified as the "analysis line F with an Fe concentration of 5.0%" (e.g., analysis line F in Figure 5). Using the "analysis line F with an Fe concentration of 5.0% by mass" as the boundary, the region closer to the surface 1a of the plated steel material (the analysis line A side) than the analysis line F is designated as the first region 12A, and the region closer to the base steel material 11 than the analysis line F (the analysis line B side) is designated as the second region 12B.

[0077] 4 and 5, the first region 12A is the region between the surface 1a of the plated steel material and the analysis line F where the Fe concentration is 5.0 mass%, and the second region 12B is the region between the analysis line F where the Fe concentration is 5.0 mass% and the interface 13 between the plated layer 12 and the base steel material 11. The first region 12A and the second region 12B are formed in layers throughout the plated layer 12. The first region 12A is located closer to the surface 1a of the plated steel material 1 than the second region 12B in the plated layer 12. The second region 12B is located closer to the base steel material 11 than the first region 12A in the plated layer 12, adjacent to the base steel material 11.

[0078] <First area> The first region is located on the surface side of the plated steel material and is a region containing less than 5.0 mass% Fe. The upper surface of the first region constitutes the surface of the plated steel material. The presence of the first region improves the red rust resistance, base steel corrosion resistance, and sacrificial corrosion resistance of the plated steel material, and particularly improves red rust resistance in the early stages of corrosion.

[0079] The first region contains an Al-containing phase at an area ratio of 5% or more. The area ratio of the Al-containing phase may be 10% or more, 15% or more, or 20% or more. Preferably, it is 15% or more. The more the Al-containing phase, the more Al phase is contained in the first region. The surface of the Al phase contained in the coating layer is passivated. The presence of a large amount of such Al phase slows the corrosion rate of the first region in the early stages of corrosion, allowing the first region to remain for a long period of time. Furthermore, since the Fe concentration in the first region is low, at less than 5.0 mass%, almost no red rust occurs during corrosion. The presence of such a first region on the surface side of the coating layer significantly improves the red rust resistance of the plated steel material. The upper limit of the area ratio of the Al-containing phase in the first region may be, for example, 60% or less.

[0080] The first region may contain an Mg-Zn phase in an area ratio of 15% or more. The Mg-Zn phase has superior sacrificial corrosion protection properties compared to Al-containing phases. Therefore, from the viewpoint of sacrificial corrosion protection, it is preferable that the first region contains as much Mg-Zn phase as possible. This improves the sacrificial corrosion protection properties of the plated steel material. There is no particular need to limit the upper limit of the Mg-Zn phase in the first region, but for example, 90% or less is preferable.

[0081] The first region may contain an [Al / MgZn2 binary eutectic structure] in an area ratio of 5% or more. The inclusion of the [Al / MgZn2 binary eutectic structure] in the first region further enhances the sacrificial corrosion protection of the plated steel material. There is no particular need to limit the upper limit of the [Al / MgZn2 binary eutectic structure] in the first region, but for example, 80% or less is preferable, and it may be 20% or less.

[0082] The first region may contain, as the balance, an Mg2Si phase, an Mg2Sn phase, a Zn phase, an Al-Ca-Zn phase, an Al-Ca-Si-Zn phase, a Ca-Zn phase, an Mg-Al-Si-Zn phase, etc. Furthermore, the first region may contain an Fe-Al alloy phase at an area ratio of 3% or less.

[0083] The thickness of the first region is 5 to 100 μm. If the thickness of the first region is less than 5 μm, red rust resistance will decrease. On the other hand, since it may be difficult to make the thickness of the first region greater than 100 μm in manufacturing, the upper limit is set to 100 μm or less. The thickness of the first region may be 70 μm or less, 50 μm or less, or 40 μm or less. The thickness of the first region is the average thickness. The average thickness is the arithmetic mean value of the distance in the thickness direction of the plating layer from the surface of the plating layer to the analysis line F, which indicates an Fe concentration of 5.0%, measured at 10 points spaced 10 μm or more apart in the image obtained by the SEM observation described above.

[0084] <Second area> The second region is located between the first region and the base steel and contains 5.0% or more by mass of Fe. Because the second region contains 5.0% or more by mass of Fe, it contains a large amount of Fe-Al phase. Of the phases or structures contained in the second region, the Fe-Al alloy phase occupies the largest area ratio. The second region may also contain an Mg-Zn phase in an amount roughly equal to that of the Fe-Al alloy layer. The presence of the second region containing 5.0% or more by mass of Fe in the coating layer improves the base steel corrosion protection of the coating layer. The reason for this improved base steel corrosion protection is presumably because the second region contains 5.0% or more by mass of Fe, resulting in a large amount of Fe-Al alloy phase, which functions as a barrier layer for the base steel.

[0085] Furthermore, as described above, the second region may contain an Mg-Zn phase in addition to the Fe-Al phase. The area ratio of the Mg-Zn phase in the second region may be 15% or more. This further improves sacrificial corrosion protection. The Mg-Zn phase has higher sacrificial corrosion protection than the Fe-Al phase. Therefore, from the viewpoint of sacrificial corrosion protection, it is preferable that the second region contains more Mg-Zn phase. There is no particular need to limit the upper limit of the MgZn2 phase in the second region, but for example, 50 % or less is preferable.

[0086] The second region may contain, as the balance, an Al-containing phase, an Mg2Si phase, an Mg2Sn phase, a Zn phase, an Al-Ca-Zn phase, an Al-Ca-Si-Zn phase, a Ca-Zn phase, an Mg-Al-Si-Zn phase, etc. The area ratio of these balance phases is preferably 10% or less in total.

[0087] The thickness of the second region is set to 5 to 200 μm. By setting the thickness of the second region to 5 μm or more, the corrosion resistance of the base steel is significantly improved. A thickness of 20 μm or more is more preferable. On the other hand, since it may be difficult to make the thickness of the second region exceed 200 μm in manufacturing, the upper limit is set to 200 μm or less. The thickness of the second region may be set to 70 μm or less, 50 μm or less, or 40 μm or less. Furthermore, the thickness of the second region may be set to 10 μm or more, 20 μm or more, or 30 μm or more. The thickness of the second region is defined as the average thickness. The average thickness is determined by measuring the distance in the thickness direction of the coating layer from the analysis line F, where the Fe concentration is 5.0%, to the boundary line between the coating layer and the base steel at 10 points spaced 10 μm or more apart in the image obtained by the SEM observation described above, and taking the arithmetic mean value of the measured values.

[0088] The thickness of the plating layer is the total thickness of the first region and the second region, that is, the thickness of the plating layer is preferably 10 μm to 300 μm.

[0089] In addition, in the plated steel material of this embodiment, it is preferable that the base steel material and the second region are in direct contact with each other, i.e., it is preferable that no interfacial alloy layer separate from the second region exists between the base steel material and the second region.

[0090] Next, a method for manufacturing a plated steel material according to this embodiment will be described. The method for producing plated steel material of this embodiment includes a blasting step of shot-blasting the surface of a base steel material, a flux application step of applying flux to the base steel material after the blasting step, a plating step of immersing the base steel material after the flux application step in a plating bath and then pulling it out, and a cooling step of cooling the plating layer deposited by the plating step. The plating method in the plating step is a so-called hot-dip plating method.

[0091] In the blasting process, shot blasting is performed on the surface of the base steel material, which causes strain on the surface of the base steel material. The conditions for the shot blasting are described below. Shot material can be of various shapes and materials, but steel shot material conforming to JIS Z 0311:2004 is preferred, with spherical shot being particularly preferred. The median particle size of the shot material should be in the range of 40 to 450 μm. The hardness should be Hv390 to 510. Specifically, for example, steel shot (TSH-30) manufactured by WINOA IKK JAPAN Co., Ltd. can be used.

[0092] In the blasting process, shots are collided with the surface of the base steel by centrifugal force or air pressure, in accordance with the General Rules for Blasting Treatment Methods for Surface Conditioning (JIS Z 0310:2016). The shot amount is 5 to 400 kg / m. 2 The range of the shot amount is 10 kg / m 2 More than 15kg / m 2 The shot amount is 100 kg / m or more. 2 Less than 50kg / m 2 The following is also acceptable.

[0093] The blasting process imparts strain to the surface of the base steel. When the strained base steel is then hot-dip plated, the reaction between the base steel and the Al in the plating bath becomes more active when the base steel is immersed in the plating bath, resulting in the formation of a relatively large amount of Fe-Al alloy phase. Furthermore, the impartation of strain creates a distribution in the reaction rate between the base steel and Al, which tends to make the interface between the plating layer and the base steel uneven, resulting in a plated steel that satisfies the relationship in formula (1) above. This improves the adhesion of the plating layer.

[0094] Next, in the flux application process, the base steel is immersed in a flux solution at 80°C for 30 seconds, then pulled out and dried in an air atmosphere at 150°C. The flux is based on ZnCl2, and contains NaCl, KCl, NaF, SnCl2, and SnCl 4、A solution containing various salts such as BiCl3, surfactants, etc., dissolved therein and acidified with hydrochloric acid as necessary is used. By applying the flux to the base steel before plating, oxides on the surface of the base steel are removed, stabilizing the plating reaction. An example of the flux is a flux dissolved in water to a concentration of 0-100 g / L NaCl, 0-100 g / L KCl, 0-20 g / L SnCl2, and 100-300 g / L ZnCl2.

[0095] Next, in the plating process, the base steel material after application of flux is immersed in a plating bath and then removed. The composition of the plating bath may be substantially the same as the chemical composition of the plating layer. Alternatively, the composition of the plating bath may be appropriately adjusted so that it falls within the range of the chemical composition of the plating layer of this embodiment. Specifically, it is preferable to increase the amount of Mg, Al, and other alloying elements other than Zn by approximately 1.01 to 1.20 times the target value of the chemical composition of the plating layer so that it falls within the range of the chemical composition of the plating layer of this embodiment.

[0096] The immersion time in the coating bath is preferably in the range of 5 to 300 seconds, for example. This promotes the growth of the second region. If the immersion time is less than 5 seconds, the second region of the coating layer is not sufficiently formed, and the interface between the coating layer and the base steel is unlikely to become uneven, resulting in a decrease in the corrosion protection of the base steel and a decrease in the adhesion of the coating layer. On the other hand, if the immersion time exceeds 300 seconds, the second region grows excessively, making the coating layer itself more susceptible to cracking.

[0097] The temperature of the coating bath is preferably in the range of 400°C to 680°C, and may be 460 to 670°C. If the bath temperature is too high, the growth of the Fe-Al alloy phase will be accelerated, resulting in excessive formation of the Fe-Al alloy phase, which may result in the formation of another interfacial alloy layer between the second region and the base steel material, and will also result in severe wear on the coating equipment. If the bath temperature is too low, coating defects such as non-coating and adhesion of foreign matter will be more likely to occur.

[0098] After being pulled out of the plating bath, the coating weight is adjusted as necessary by wiping with N2 gas or by adjusting the speed at which the base steel is pulled out of the plating bath.

[0099] Next, in the cooling step, the coating layer is cooled (controlled cooling). In the cooling step, the temperature of the coating layer is cooled from the bath temperature to the controlled cooling stop temperature at an average cooling rate of 5.0°C / sec or more, more preferably 10.0°C / sec or more. The upper limit of the average cooling rate is not particularly limited, but it can be, for example, 15.0°C / sec. The controlled cooling stop temperature is preferably 330°C or less. Cooling is performed, for example, by spraying a cooling gas. When cooling by spraying a cooling gas, multiple cooling gas spray nozzles can be arranged along the transport path of the base steel material, and the cooling gas can be sprayed from the nozzles. The type of cooling gas may be air, nitrogen (N2), argon, etc., and nitrogen (N2) gas is preferred.

[0100] Cooling suppresses the alloying reaction between Fe and Al in the surface layer of the coating layer, forming a first region with an Fe concentration of less than 5.0 mass%. Furthermore, by setting the average cooling rate to 5.0°C / s or more, precipitation of the Al-containing phase occurs preferentially, increasing the area ratio of the Al-containing phase in the first region. Furthermore, cooling from the bath temperature to the controlled cooling stop temperature at an average cooling rate of 5.0°C / s or more promotes precipitation of the Al-containing phase followed by the Mg-Zn phase. Furthermore, the eutectic reaction between the Al phase and the MgZn2 phase progresses, promoting the formation of a binary eutectic structure of the Al phase and the MgZn2 phase (an Al / MgZn2 binary eutectic structure).

[0101] In the cooling step, the controlled cooling stop temperature is preferably set to 330° C. or lower. If cooling is stopped at a temperature higher than 330° C. at an average cooling rate of 5.0° C. / sec or higher, alloying of the coating layer and the base steel material may progress, and the content of the Al-containing phase in the first region may fall outside the range of the present invention.

[0102] On the base steel side of the coating layer, the reaction between the Fe diffused from the base steel and the Al in the coating bath progresses, forming a second region with an Fe concentration of 5.0% or more. The second region contains a large amount of Fe-Al alloy phase, and Mg-Zn phase may also be formed.

[0103] In this manner, the plated steel material of this embodiment can be manufactured.

[0104] Furthermore, the plated steel material of this embodiment may be formed by a plating film formation method such as vapor deposition plating, thermal spraying, or cold spraying, and the same effects as when formed by hot-dip plating can be obtained. [Example]

[0105] The effects of the present invention will be specifically described below with reference to examples. As the base steel material, base steel materials (SS400 as defined in JIS G 3101) having the following shapes A, B, and C were used.

[0106] A: Steel plate 200mm long x 100mm wide x 3.2mm thick. B: An angle bar (length 200 mm, short side length 50 mm, plate thickness 3.2 mm) with an L-shaped cross section, made by bending the steel plate A above so that the bending angle is 90° at the center of the plate width. C: Expanded metal (JIS G 3351:1987 XS-62 (plate thickness 3.2 mm)). In the case of expanded metal, the "surface of the plated steel material" refers to the surface that is perpendicular to the thickness direction of the plate in its overall shape with multiple through holes.

[0107] In the case of the above-mentioned materials B and C, it was difficult to observe and measure the cross-sectional structure and evaluate the plating adhesion. Therefore, in the test examples where the base steel was material B or material C, plated steel was separately produced by changing the base steel to material A, and observations, measurements, and evaluations were made on the plated steel using material A as the base steel.

[0108] The above base steel was subjected to a blasting process. In the blasting process, steel shot (TSH-30) manufactured by WINOA IKK JAPAN Co., Ltd. was used as the shot material, and the shot material was bombarded onto the surface of the base steel by air pressure in accordance with the General Rules for Blasting Treatment Methods for Surface Preparation (JIS Z 0310:2016). The amount of shot material projected was as shown in Tables 2A and 2B. The projection conditions were a discharge pressure of 0.5 MPa, a distance from the nozzle to the sample (base steel) of 800 mm, and a projection angle of 90°.

[0109] Next, the base steel material after the blasting process was subjected to a flux application process, in which it was immersed in an aqueous flux solution (ZnCl2 / NaCl / SnCl2 = 220g / 20g / 10g / L) at 80°C for 30 seconds, then removed and thoroughly dried in a drying oven at 150°C.

[0110] Next, the steel material after the flux application step was immersed in a plating bath and then pulled out. The plating bath temperature and immersion time were as shown in Tables 2A and 2B.

[0111] Next, in the cooling process, compressed air was blown onto the base steel material removed from the coating bath as a cooling gas, and the base steel material was cooled while controlling the cooling rate from the coating bath temperature to the controlled cooling stop temperature. The cooling rate and controlled cooling stop temperature were as shown in Tables 2A and 2B. The base steel material was allowed to cool in the temperature range below the controlled cooling stop temperature. In this way, a coated steel material was produced.

[0112] The composition of the plating layer was measured by quantitatively analyzing the elements dissolved in a hydrochloric acid solution by the above-mentioned method using ICP atomic emission spectrometry for a sample cut to 30 mm x 30 mm.

[0113] Whether or not the boundary between the coating layer and the base steel material is an uneven surface that satisfies formula (1) was confirmed as follows.

[0114] First, a small sample measuring 20 mm x 15 mm x 3.2 mm was taken from the plated steel, embedded in resin, and then polished to a mirror finish to expose a cross section perpendicular to the plated steel surface. This test piece was observed using a field emission scanning electron microscope (SEM) (JEOL "JSM-7000F", accelerating voltage: 15 kV) to obtain image data. The observation area was a 100 μm long cross section of the plated steel parallel to the surface of the plated steel when observed with the SEM at a magnification of 1000 times or more. The image resolution was 2560 pixels or more horizontally and 1920 pixels or more vertically.

[0115] L0 and L were determined for the image data using the method described above. The coating layer and the base steel were distinguished based on the Fe concentration of 90% determined by the EPMA analysis described above, and the portion with an Fe concentration of 90% or more was defined as the base steel. The relationship between L0 and L was then evaluated to see if it satisfied formula (1). The calculation results (values) for the left side of formula (1) are shown in Tables 3A and 3B.

[0116] The boundary between the first and second regions of the plating layer was determined as follows. A small sample measuring 20 mm x 15 mm x 3.2 mm was taken from the plated steel, embedded in resin, and then polished to a mirror finish to expose a cross section perpendicular to the plated steel surface. The Fe concentration was measured by point analysis while observing this test piece with an electron probe microanalyzer equipped with scanning electron microscope functions (SEM-EPMA, EPMA measurement device: JEOL JXA-8230, accelerating voltage: 15 kV, current: 0.05 μA, irradiation time: 50 ms).

[0117] First, in the first stage of measurement, as shown in Figure 3, linear analysis lines parallel to the direction perpendicular to the thickness direction of the plating layer were set on the cross section of the exposed plating layer. Ten analysis lines were set at equal intervals along the thickness direction of the plating layer. Ten measurement points were set on the analysis lines at 10 μm intervals in the direction perpendicular to the thickness direction of the plating layer. In Figure 3, the dashed dotted line is the analysis line, and the black dots on the analysis lines are the measurement points.

[0118] The Fe concentration (mass%) in the plating layer was measured by point analysis at the measurement points of each analysis line. The measurement conditions for the point analysis were as described above. For each analysis line, the average value of the Fe concentrations at 10 measurement points was calculated, and this average value was used as the Fe concentration for that analysis line. Analysis line A, which had an Fe concentration less than 5.0% and closest to 5.0%, and analysis line B, which had an Fe concentration greater than 5.0% and closest to 5.0%, were identified.

[0119] Next, in the second stage of measurement, the analysis line closest to an Fe concentration of 5.0% was identified using the method described above. The analysis line with an Fe concentration of 5.0% by mass was used as the boundary line, and the region closer to the surface of the plated steel than that analysis line was designated as the first region, and the region closer to the base steel than that analysis line was designated as the second region.

[0120] Next, the area ratios of the phases and structures in the first and second regions were determined as follows. The samples used to determine the first and second regions were used as they were, and a cross section in the thickness direction of the coating layer perpendicular to the surface of the base steel was observed. The magnification of the SEM observation was 200 to 5000 times, and the area ratios of the phases and structures in the first and second regions were determined as follows. 2 The cross section of the plating layer in the area was checked. Since the SEM field of view for the plating layer may observe a local field of view, 25 fields of view were selected from any cross section to obtain average information on the plating layer. In other words, a total of 36,000 × 25 μm 2 The metal structure in each field of view was observed to determine the area ratio of the phase or structure that constitutes the metal structure of the plating layer.

[0121] First, a eutectic structure consisting of an Al phase and an MgZn2 phase, which exhibited a lamellar structure, was designated the "Al / MgZn2 binary eutectic structure." In the region other than the "Al / MgZn2 binary eutectic structure," a phase containing Zn and 20 to 99 mass% Al was designated the Al-containing phase. Furthermore, a phase containing Zn and 20 to 60 mass% Mg was designated the Mg-Zn phase. Furthermore, a phase containing Al and 20 to 60 mass% Fe was designated the Fe-Al alloy phase. The area fractions of these phases and structures were then calculated. In the second region, phases other than the Mg-Zn phase were Fe-Al phases, except for the remaining phase of 10% or less.

[0122] The presence or absence of the Mg2Sn phase was confirmed using the method described above. When a diffraction peak was detected at 23.4±0.3°, it was determined that the Mg2Sn phase was present. The results are shown in Tables 3A and 3B.

[0123] The coating adhesion was evaluated as follows. The coated steel was subjected to a chipping test. Using a gravelometer, 400 g of crushed stone No. 6 (JIS A500, particle size 5-13 mm) was struck against the test piece at room temperature from a distance of 50 cm with an air pressure of 400 kPa. The projection angle was 90° relative to the surface of the base steel. The test piece was then subjected to ultrasonic cleaning (room temperature, pure water, 10 minutes), and the weight per unit area (g / m) of the test piece before ultrasonic cleaning was measured. 2 ) and the weight per unit area of ​​the test piece after ultrasonic cleaning (g / m 2 The plating adhesion was evaluated from the difference (weight loss) between the measured value and the test piece. The evaluation criteria were as follows, with AAA, AA, and A being considered acceptable.

[0124] AAA: Weight loss is 10g / m 2 less than AA: Weight loss 10g / m 2 More than 60g / m 2 less than A: Weight loss is 60g / m 2 More than 120g / m 2 less than B: Weight loss is 120g / m 2 End

[0125] Red rust resistance was evaluated as follows. Plated steel materials were subjected to an accelerated corrosion test specified in JASO-CCT-M609. The number of cycles required for red rust to appear was then measured. The evaluation criteria were as follows, with AAA, AA, and A being considered pass.

[0126] AAA: Red rust occurs after 1,200 cycles or more AA: Red rust occurs between 900 and 1200 cycles A: Red rust occurs between 540 and 900 cycles B: Red rust occurs less than 540 times

[0127] The corrosion protection of the base steel was evaluated as follows. Plated steel was cut into samples measuring 150 mm in length and 70 mm in width and subjected to the accelerated corrosion test specified in JASO-CCT-M609. The corrosion depth (μm) of the samples after 1,560 cycles was measured and evaluated. For the measurement, a 30 mm cross section was taken from a position halfway along the length of the sample (75 mm) and at the center of the width and observed. For the observation, the sample was embedded in resin and mirror-polished, and the field of view was photographed using an optical microscope at 40x magnification. The maximum corrosion depth (μm) was measured at 30 mm across the cross section. The evaluation criteria were as follows, with AAA, AA, and A being considered pass.

[0128] AAA: Less than 50 μm AA: 50 μm or more and less than 200 μm A: 200 μm or more and less than 800 μm B:800μm or more

[0129] Sacrificial corrosion protection was evaluated as follows. The plated steel was cut perpendicular to the surface of the plated steel using a fine cutter to expose the cut edge. That is, the cross section of the plating layer and the cross section of the base steel were exposed at the cut edge. The cut edge was subjected to a neutral salt spray test as specified in JIS Z2371:2015, and the time (h) until red rust appeared at the cut edge was measured. The evaluation criteria were as follows, with AAA, AA, and A being considered pass.

[0130] AAA: 2400h 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

[0131] As shown in Tables 1A to 4B, the chemical composition of the coating layer, the thickness of the first region, the area ratio of the Al-containing phase in the first region, and the thickness of the second region were within the ranges of the present invention in Examples 1 to 32. As a result, the coating layer had excellent adhesion, red rust resistance, corrosion resistance to the base steel, and sacrificial corrosion resistance.

[0132] The first region in Examples 1 to 32 contained one or more of the following phases as the balance: Mg2Si phase, Mg2Sn phase, Zn phase, Al-Ca-Zn phase, Al-Ca-Si-Zn phase, Ca-Zn phase, and Mg-Al-Si-Zn phase. Furthermore, the first region in some Examples contained an Fe-Al alloy phase at an area ratio of 3% or less. The second region in Examples 1 to 32 contained an Fe-Al alloy phase as the balance. Furthermore, the second region sometimes contained one or more of the following phases as the balance: Mg2Si phase, Mg2Sn phase, Zn phase, Al-Ca-Zn phase, Al-Ca-Si-Zn phase, Ca-Zn phase, and Mg-Al-Si-Zn phase.

[0133] On the other hand, as shown in Tables 1A to 4B, in Comparative Examples 33 to 43, any one of the chemical composition of the coating layer, the thickness of the first region, the area ratio of the Al-containing phase in the first region, and the thickness of the second region was outside the range of the present invention, resulting in inferior coating layer adhesion, red rust resistance, corrosion resistance of the base steel, and sacrificial corrosion resistance.

[0134] In Comparative Example 33, the amount of Al in the coating layer was insufficient, which resulted in an insufficient area ratio of the Al-containing phase in the first region, resulting in poor red rust resistance and corrosion resistance to the base steel. In Comparative Example 34, the amount of Al in the plating layer was excessive, which resulted in poor flux reaction and significant deterioration in the appearance of the plating layer.

[0135] In Comparative Example 35, the amount of Mg in the plating layer was insufficient and the amount of Fe was excessive, which resulted in poor red rust resistance and sacrificial corrosion protection. In Comparative Example 36, the amount of Mg in the plating layer was excessive, which resulted in poor flux reaction and a significant deterioration in appearance.

[0136] In Comparative Example 37, the coating layer had an excessive amount of Si and an insufficient amount of Fe, which resulted in an insufficient thickness of the second region and inferior corrosion resistance of the base steel. In Comparative Example 38, the amount of Ca in the plating layer was excessive, and the amount of Fe was insufficient. Furthermore, the flux reaction was poor, and the appearance was significantly deteriorated.

[0137] In Comparative Example 39, the amount of shots projected in the blasting step was insufficient, which meant that formula (1) was not satisfied, resulting in poor adhesion of the plating layer.

[0138] In Comparative Example 40, the cooling rate in the cooling step was insufficient, which resulted in the area ratio of the Al-containing phase in the first region being outside the range of the present invention, resulting in poor red rust resistance.

[0139] In Comparative Example 41, the immersion time in the plating bath was insufficient, which resulted in an insufficient thickness of the second region and inferior corrosion resistance of the base steel.

[0140] Shot blasting was not performed in Comparative Example 42. As a result, sufficient strain could not be introduced into the base steel material before plating, and as a result, formula (1) was not satisfied, resulting in poor adhesion of the plating layer.

[0141] In Comparative Example 43, cooling at an average cooling rate of 5.0°C / s or more was completed at 360°C, and slow cooling was performed at a cooling rate of less than 5.0°C / s from 360°C. As a result, the area ratio of the Al-containing phase in the first region fell outside the range of the present invention, and the red rust resistance was inferior.

[0142] [Table 1A]

[0143] [Table 1B]

[0144] [Table 2A]

[0145] [Table 2B]

[0146] [Table 3A]

[0147] [Table 3B]

[0148] [Table 4A]

[0149] [Table 4B] [Industrial Applicability]

[0150] The plated steel material of the present invention has excellent red rust resistance, as well as excellent adhesion of the plating layer, corrosion resistance of the base steel, and sacrificial corrosion resistance. This has the potential to be applied in the civil engineering and infrastructure fields, as well as in automotive parts. [Explanation of symbols]

[0151] 1...plated steel material, 1a...surface, 11...base steel material, 12...plated layer, 12A...first region, 12B...second region, 13...boundary line (interface).

Claims

1. A plated steel product comprising a base steel material and a plating layer disposed on a surface of the base steel material, The plating layer has a chemical composition, expressed in mass%, Al: 5.0-40.0%, Mg: 0.5-15.0%, Fe: 5.0 to 40.0%, Si: 0-2.0%, Ca: 0-2.0%, One or two selected from the group consisting of Group A and Group B below: Contains The balance is Zn and impurities, In a cross section perpendicular to the surface of the plated steel material, when a cross section of the plated steel material of 100 μm in a direction parallel to the surface is taken as an observation area, the length L of the boundary line between the plated layer and the base steel material satisfies the following formula (1): the plating layer includes a first region that is disposed on the surface side of the plated steel material and has an Fe concentration of less than 5.0 mass %, and a second region that is disposed between the first region and the base steel material and has an Fe concentration of 5.0 mass % or more, The thickness of the first region is 5 to 100 μm, The thickness of the second region is 5 to 200 μm, The first region contains an Al-containing phase containing Zn and 20 to 99 mass % of Al in an area ratio of 5% or more. [Group A] Ni: 0 to 1.0%. [Group B] Sb: 0-0.5%, Pb: 0-0.5%, Cu: 0-1.0%, Sn: 0-2.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Zr: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Li: 0-1.0%, La: 0-0.5%, Ce: 0-0.5%, B: 0-0.5%, Y: 0-0.5%, P: 0-0.5%, Sr: 0-0.5%, Co: 0-0.5%, Bi: 0-0.5%, In: 0-0.5%, V: 0-0.5%, W: 0-0.5%. One or more of these is 0-5% in total. L-L ０ ) / L ０ ×100≧2.0(%) …(1) However, L in formula (1) ０ is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

2. The plated steel material according to claim 1, which satisfies the following formula (2): (L-L ０ ) / L ０ × 100 ≧ 4.0 (%) …Formula (2) However, L in formula (2) ０ is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

3. The plated steel material according to claim 1, which satisfies the following formula (3): (L-L ０ ) / L ０ × 100 ≧ 6.0 (%) …Formula (3) However, L in formula (3) ０ is the linear distance between one end and the other end of the boundary line in the observation area, and L is the length of the boundary line between the one end and the other end.

4. The plated steel material according to any one of claims 1 to 3, wherein the thickness of the first region is 15 µm to 100 µm.

5. The plated steel material according to any one of claims 1 to 3, wherein the area ratio of the Al-containing phase in the first region is 15% or more.

6. 4. The plated steel material according to claim 1, wherein the first region contains an Mg—Zn phase containing Zn and 20 to 60 mass% of Mg, and an area ratio of the Mg—Zn phase in the first region is 15% or more.

7. The plated steel material according to any one of claims 1 to 3, wherein the first region contains a binary eutectic structure of an Al phase and an Mg-Zn phase, and an area ratio of the binary eutectic structure in the first region is 5% or more.

8. The plated steel material according to any one of claims 1 to 3, wherein the second region has a thickness of 15 µm to 200 µm.

9. 4. The plated steel material according to claim 1, wherein the second region contains an Mg—Zn phase containing Zn and 20 to 60 mass% of Mg, and an area ratio of the Mg—Zn phase in the second region is 15% or more.

10. The plated steel material according to any one of claims 1 to 3, wherein in a chemical composition of the plating layer, a content of Mg relative to a total amount of Zn and Mg (Mg / (Zn+Mg) (%)) is 5.0% or more.

11. The plated steel material according to any one of claims 1 to 3, wherein in a chemical composition of the plating layer, a content of Mg relative to a total amount of Zn and Mg (Mg / (Zn+Mg) (%)) is 6.5% or more.

12. The plating layer contains Sn at a concentration of 0.02 to 2.0% by mass, The plating layer is Mg ２ The plated steel material according to any one of claims 1 to 3, which contains an Sn phase.

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