Surface-treated member and composite structure

Abstract

[Problem] To provide a surface-treated member using a zinc-based plated steel material capable of exhibiting excellent corrosion resistance even in concrete. [Solution] In a surface-treated member of the present invention, an exposed region, which has steel base exposed parts, exists in at least a portion of a zinc-based plating layer. When a cross-section obtained by cutting the exposed region in the thickness direction of a steel material is observed with a microscope, the lengths in the width direction of the existing steel base exposed parts are in the range of 1-100 μm, the number of existing steel base exposed parts per unit length is in the range of 3-20 pieces / mm, and the total length in the width direction of the steel base exposed parts per unit length is 600 μm / mm or less. Further, the total area of the regions that, in plan view from above, respectively have cross-sections, in which the total of the lengths in the width direction of the steel base exposed parts per unit length are 600 μm / mm or less, is 0.7% or more with respect to the surface area of the steel material in plan view.

Description

Surface treated components and composite structures

[0001] The present invention relates to a surface-treated member and a composite structure.

[0002] Zinc-plated steel materials, in which various zinc-based plating layers are provided as surface treatment layers on the surface of a steel material serving as a base material, are widely used materials from the viewpoint of improving the corrosion resistance of structural members in the fields of construction, automobiles, etc. The zinc-plated steel materials as materials are processed into various shapes and then joined together as necessary using fastening members such as screws, bolts, and caulking, or by joining processes using various welding methods, etc., to form surface-treated members having desired shapes.

[0003] The surface-treated members described above are likely to be exposed to various corrosive environments depending on the applications of the surface-treated members, and therefore, various studies have been conducted on the corrosion resistance of the surface-treated steel materials that are the raw materials for the surface-treated members.

[0004] For example, Patent Document 1 below proposes a surface-treated steel provided with a coating containing zinc or a zinc-based alloy and a predetermined amount of at least one of Mg and In, with the aim of achieving excellent corrosion resistance in various corrosive environments such as alkaline corrosive environments, seawater corrosive environments, tap water corrosive environments, high-temperature wet corrosive environments, soil corrosive environments, atmospheric corrosive environments, etc. Patent Document 1 examines corrosion resistance in various corrosive environments by utilizing the excellent sacrificial anticorrosion effect of zinc.

[0005] Japanese Patent Application Publication No. 11-158657

[0006] When installing a surface-treated member in a desired location, it is assumed that at least a portion of the member is often buried in concrete. If the portion of the surface-treated member is exposed to the atmosphere, it is easy to inspect the corrosion condition by visually inspecting the exposed portion. However, for the portion buried in concrete, unlike the portion in the atmosphere, it is difficult to inspect the corrosion condition visually, and maintenance of the corroded portion is also difficult. Therefore, high corrosion resistance is required for the surface-treated member used in concrete.

[0007] The present inventors have studied the corrosion state of zinc-based plated steel materials in concrete, and as a result have found that even if a surface-treated member is manufactured using the surface-treated steel as disclosed in the above-mentioned Patent Document 1 as a material, there is room for improvement in the corrosion resistance of the surface-treated member in concrete.

[0008] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a surface-treated member using a zinc-based plated steel material that can exhibit excellent corrosion resistance even in concrete, and a composite structure in which such a surface-treated member is combined with concrete.

[0009] To solve the above problems, the present inventors conducted extensive research and came up with the idea of ​​changing the state of a zinc-based plating layer provided as a surface treatment layer depending on the corrosive environment to which the material will be exposed, i.e., the atmosphere or concrete. Based on this idea, the present inventors conducted further research and came up with the surface-treated member and composite structure described below. The gist of the present invention, which was completed based on this idea, is as follows:

[0010] (1) A surface-treated member made of a surface-treated steel material having a base steel material and a zinc-based plating layer located on the surface of the steel material, wherein at least a part of the zinc-based plating layer has an exposed region having an exposed steel base portion, which is a portion where the surface of the steel material is exposed, and when a cross section obtained by cutting the exposed region in the thickness direction of the steel material according to the shape of the exposed steel base portion when the zinc-based plating layer is viewed in plan from above is observed under a microscope, a portion in the field of view where the surface of the zinc-based plating layer exists for a length of 0.5 mm or more along the width direction, which is a direction perpendicular to the thickness direction of the steel material, is referred to as a remaining plating portion, and a region including the exposed steel base portion located between two adjacent remaining plating portions is referred to as a region. (2) A surface-treated member according to (1), wherein, in region A, the widthwise lengths of the exposed steel substrate portions present are each within a range of 1.0 to 100.0 μm, the number of the exposed steel substrate portions present per unit length in the widthwise direction is within a range of 3.0 to 20.0 / mm, and the sum of the widthwise lengths of the exposed steel substrate portions per unit length in the widthwise direction is 600.0 μm / mm or less, and when a cross section of the exposed region is observed under a microscope, a region giving a cross section in which the sum of the widthwise lengths of the exposed steel substrate portions per unit length in the widthwise direction is 600.0 μm / mm or less is defined as region B, and the sum of the areas of the regions B when viewed from above in a plan view is 0.7% or more of the surface area of ​​the steel material when viewed in a plan view. (3) The exposed steel substrate portions are identified by conducting a color reaction test on the entire surface of the zinc-based plating layer, in which a color reaction occurs at the site where the steel substrate is exposed. When each of the identified exposed steel substrate portions is viewed in plan from above the zinc-based plating layer, the exposed steel substrate portions are each sized to have a short side of 5 mm or more and an area of ​​1 cm or less. ２(1) The surface-treated member according to (1), wherein the surface is virtually divided into rectangular regions each having an area ratio of 3% or more of the rectangular region where the exposed steel substrate portion occupies, and the cross section of each of the regions is observed. (4) The surface-treated member according to any one of (1) to (3), wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, 0.10% or more and less than 40.00% Al, 0.10% or more and less than 15.00% Mg, and the balance consisting of Zn and impurities. (5) The surface-treated member according to (4), wherein the zinc-based plating layer is a plating layer containing, by mass%, 0.10% or more and less than 40.00% Al, 0.10% or more and less than 15.00% Mg, and 60.00% or more Zn. (6) The surface-treated member according to any one of (1) to (3), wherein the zinc-based plating layer contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (7) The surface-treated member according to (6), which contains element group A. (8) The surface-treated member according to (6), which contains element group B. (9) The surface-treated member according to (6), which contains element group C. (10) The surface-treated member according to (6), which contains element group D.(11) The surface-treated member according to (6), which contains the element group E. (12) The surface-treated member according to (6), which contains the element group F. (13) The surface-treated member according to (6), in which the zinc-based plating layer is a plating layer containing, in mass%, at least 4.0% or more and less than 25.0% Al and 0.3% or more and less than 12.5% ​​Mg. (14) A composite structure of concrete and a surface-treated member made of a steel material as a base material and a surface-treated steel material having a zinc-based plating layer located on the surface of the steel material, wherein at least a part of the zinc-based plating layer has an exposed region having an exposed steel base portion, which is a portion where the surface of the steel material is exposed, and at least a part of the exposed region is in contact with concrete, and when a section of 1.5 mm x 2.0 mm in size is observed under a microscope on a cross section obtained by cutting the exposed region in the thickness direction of the steel material according to the shape of the exposed steel base portion when the zinc-based plating layer is viewed in plan from above, a portion in the field of view where the surface of the zinc-based plating layer exists for a length of 0.5 mm or more along the width direction, which is a direction perpendicular to the thickness direction of the steel material, is referred to as a residual plating portion, and two adjacent residual plating portions are referred to as a residual plating portion. a composite structure in which, when a region including the exposed steel base portions located between adjacent ones of the adjacent steel base portions is defined as region A, the widthwise lengths of the exposed steel base portions present in region A are each within a range of 1.0 to 100.0 μm, the number of the exposed steel base portions present per unit length in the widthwise direction is within a range of 3.0 to 20.0 portions / mm, and the sum of the widthwise lengths of the exposed steel base portions per unit length in the widthwise direction is 600.0 μm / mm or less; when a region B is defined as a region that, when the cross section of the exposed region is observed under a microscope, gives a cross section in which the sum of the widthwise lengths of the exposed steel base portions per unit length in the widthwise direction is 600.0 μm / mm or less, the sum of the areas of the regions B when viewed in plan from above is 0.7% or more of the surface area of ​​the steel material when viewed in plan.(15) The composite structure according to (14), wherein an Fe-Zn-Ca-based composite layer containing Fe, Zn, and Ca is present in at least a part of the interface between the zinc-based plating layer and the concrete or the interface between the steel material and the concrete in the exposed region in contact with the concrete. (16) The composite structure according to (15), wherein the Fe-Zn-Ca-based composite layer contains, by mass%, 1.0% to 20.0% Fe, 10.0% to 40.0% Zn, and 5.0% to 15.0% Ca, with the remainder being a layer having a chemical composition consisting of H, C, O, and impurities. (17) The composite structure according to (16), wherein the zinc-based plating layer further contains Al and Mg as a chemical composition, and the chemical composition of the Fe-Zn-Ca-based composite layer further contains at least one of Al: 0% to 10.0% and Mg: 0% to 10.0% in place of a portion of the remaining H, C, and O. (18) The exposed steel substrate portions are identified by conducting a coloration test over the entire surface of the zinc-based plating layer, in which a coloration reaction occurs in the areas where the steel substrate is exposed, and when each of the identified exposed steel substrate portions is viewed in plan from above the zinc-based plating layer, the size of the short side of each exposed steel substrate is 5 mm or more and the area of ​​each exposed steel substrate is 1 cm. ２(19) The composite structure according to any one of (14) to (18), wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, 0.10% or more and less than 40.00% Al, 0.10% or more and less than 15.00% Mg, and the balance consisting of Zn and impurities. (20) The composite structure according to (19), wherein the zinc-based plating layer is a plating layer containing, by mass%, 0.10% or more and less than 40.00% Al, 0.10% or more and less than 15.00% Mg, and 60.00% or more Zn. (21) The composite structure according to any one of (14) to (18), wherein the zinc-based plating layer contains, in mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the remainder being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (22) The composite structure according to (21), which contains the element group A. (23) The composite structure according to (21), which contains the element group B. (24) The composite structure according to (21), which contains the element group C.(25) The composite structure according to (21), which contains the element group D. (26) The composite structure according to (21), which contains the element group E. (27) The composite structure according to (21), which contains the element group F. (28) The composite structure according to (21), wherein the zinc-based plating layer is a plating layer containing, in mass %, at least 4.0% or more and less than 25.0% Al and 0.3% or more and less than 12.5% ​​Mg.

[0011] As described above, according to the present invention, it is possible to provide a surface-treated member using a zinc-based plated steel material that can exhibit excellent corrosion resistance even in concrete, and a composite structure in which such a surface-treated member is combined with concrete.

[0012] FIG. 1 is a schematic diagram for explaining a structure installed on a concrete surface. FIG. 2 is a schematic diagram for explaining the structure of a surface treated member according to an embodiment of the present invention. FIG. 3 is a schematic diagram for explaining the structure of a surface treated member according to the same embodiment. FIG. 4 is a schematic diagram for explaining the structure of a surface treated member according to the same embodiment. FIG. 5 is an explanatory diagram for explaining an exposed steel base portion in the surface treated member according to the same embodiment. FIG. 6 is an explanatory diagram for explaining an area A defined in the surface treated member according to the same embodiment. FIG. 7 is an explanatory diagram for explaining an exposed steel base portion in the surface treated member according to the same embodiment. FIG. 8 is a schematic diagram for explaining the structure of a composite structure according to the same embodiment. FIG. 9 is a schematic diagram for explaining the structure of a composite structure according to the same embodiment.

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0014] (Corrosion Behavior in Concrete) Prior to describing the surface treated member according to an embodiment of the present invention, the corrosion behavior in concrete discovered by the present inventors will be described with reference to Fig. 1. Fig. 1 is a schematic diagram for explaining a structure installed on a concrete surface.

[0015] As shown schematically in Fig. 1, various structures, including mounts on which photovoltaic panels are mounted, road signs, guardrails, traffic lights, etc., are installed on concrete surfaces as foundations. In this case, in order to install the structures on the concrete surfaces more stably, as shown in Fig. 1, a portion of the structure (for example, the portion surrounded by a dashed line in Fig. 1, such as near the bottom end of a support) is often buried in the concrete.

[0016] Here, various structures often use various steel materials as their raw materials, for example, from the viewpoint of production costs, etc. Here, when a part of a structure made of various steel materials is buried in concrete, there is a concern that the steel materials may corrode due to the strong alkaline environment in concrete.

[0017] When unplated steel materials are used as structural materials, it is known that the unplated steel materials form a passive film on their surfaces and exhibit high corrosion resistance in alkaline environments such as those in concrete. On the other hand, unplated steel materials have poor corrosion resistance in exposed areas in neutral environments such as the atmosphere, where corrosion factors such as moisture are present.

[0018] In addition, even if the part is present in concrete, chloride ions (Cl － When chloride ions (Cl ions) penetrate the steel or when concrete becomes neutralized, the passive film formed disappears, resulting in a decrease in corrosion resistance. － Since these ions act as corrosion factors, the corrosion resistance of exposed steel material is insufficient.

[0019] Thus, when using steel material that has not been plated with various platings as the material for a structure, there is room for consideration from the viewpoint of corrosion resistance (particularly from the viewpoint of corrosion resistance when exposed to chloride ions).

[0020] On the other hand, if zinc-based plated steel, which has excellent corrosion resistance in the atmosphere, a neutral environment, and which also has excellent corrosion resistance even when chloride ions adhere to the steel in the atmosphere, is used as the material for the structure, it can be said that a solution to the problem of maintaining the corrosion resistance of the structure in the atmosphere is within reach.

[0021] Furthermore, it is known that when zinc-plated steel is embedded in concrete, a Ca-Zn reaction layer is formed at the interface between the zinc-plated steel and the concrete, improving corrosion resistance in alkaline concrete. Therefore, using zinc-plated steel as a material for a structure partially embedded in concrete may at first glance appear to offer a solution in terms of maintaining the corrosion resistance of the structure in concrete and the atmosphere. However, it is known that the protective properties of the Ca-Zn reaction layer are lost when chloride ions penetrate into the concrete. Therefore, even when zinc-plated steel is used as a material for a structure, there is still room for improvement in terms of the corrosion resistance of the structure in concrete.

[0022] The present inventors investigated the corrosion behavior of a Ca-Zn reaction layer in concrete in order to study the corrosion behavior of zinc-based plated steel in concrete. Specifically, they observed the state of the Ca-Zn reaction layer formed on the surface of a zinc-based plating layer in concrete into which chloride ions had penetrated, using a scanning electron microscope (SEM) or the like. As a result, they found that the Ca-Zn reaction layer exposed to chloride ions was in a porous state.

[0023] From the above findings, the present inventors have come to the conclusion that, in order to improve the corrosion resistance of zinc-based plated steel materials in concrete, it is important to change the Ca-Zn-based reaction layer formed on the zinc-based plating layer in concrete into a layer composed of products formed in a dense state.

[0024] As a result of further investigations by the present inventors to realize a layer composed of products formed in a dense state in concrete, they came up with the idea of ​​intentionally providing a part of the zinc-based plating layer where the surface of the steel material is exposed (hereinafter referred to as "exposed steel substrate part") at a specific abundance ratio, which is different from the conventional technical idea. This makes it possible to form a composite layer composed of products formed in a dense state on the surface of the zinc-based plating layer even in concrete.

[0025] In the conventional technical concept, a zinc-based plating layer is formed in a dense state so as to minimize the exposure of the steel substrate, and the steel substrate is protected by utilizing the sacrificial corrosion protection effect of zinc. However, the present inventors have discovered that by intentionally providing portions in the zinc-based plating layer that expose the steel substrate, it is possible to form a dense composite layer starting from such exposed portions. This composite layer protects the steel substrate and the zinc-based plating layer in its vicinity.

[0026] More specifically, since the exposed steel substrate is located in concrete, both the zinc-based plating layer and the steel substrate are exposed to the various components that make up the concrete. This causes Zn ions to elute from the zinc-based plating layer and Fe ions to elute from the steel substrate. In the atmosphere, the eluted Zn and Fe ions are washed away by rain and other factors and rarely adhere to the exposed portions. On the other hand, in concrete, there is no water flow as described above. Therefore, it is presumed that the eluted Zn and Fe ions are likely to adhere to the exposed steel substrate, and that dense Fe-Zn-Ca composite oxides are formed in the exposed steel substrate.

[0027] Furthermore, as a result of investigations by the present inventors, it has been found that when the zinc-based plating layer is an alloy plating layer containing Mg and Al in addition to Zn, Mg ions and Al ions are eluted in addition to Zn ions in concrete. It has also been found that such elution produces Fe-Zn-Al-Mg-Ca composite oxides, which further improves corrosion resistance.

[0028] Based on the findings described above, the present inventors have conducted further studies and have come up with the surface-treated member and composite structure according to the embodiments of the present invention, as described in detail below.

[0029] (Regarding the Surface-Treated Member) The surface-treated member according to an embodiment of the present invention will be described in detail below with reference to Figures 2 to 4. Figures 2 to 4 are schematic diagrams for explaining the structure of the surface-treated member according to this embodiment. For convenience, the explanation will be given using the coordinate axes shown in Figures 2 to 4.

[0030] As described in detail below, the surface-treated member according to this embodiment is constructed using a surface-treated steel material having a zinc-based plating layer as its raw material. Here, the specific structure of the surface-treated member according to this embodiment is not particularly limited. The specific structure of the surface-treated member according to this embodiment may be, for example, a box-like structure, or a plate-like structure using plate-shaped steel material, such as the roof or wall of a building. Furthermore, the specific structure of the surface-treated member according to this embodiment may be, for example, a formed body or a joined body using various shaped steel, such as a solar panel mounting frame, a formed body or a joined body using various H-shaped steel or square columns, such as the framework of a structure, or a formed body or a joined body using various steel pipes, such as various supports, signs, traffic lights, guardrails, etc.

[0031] Fig. 2 is a schematic diagram showing a part of the surface-treated member according to the present embodiment, as viewed from above (in the Z-axis direction in the drawing). As shown in Fig. 2, the surface-treated member 1 according to the present embodiment is made of a zinc-based plated steel sheet, which is a base steel sheet and has a zinc-based plating layer 20 formed on the surface thereof, as will be described later. At least a part of the surface (corresponding to the XY plane in Fig. 2, the surface of the zinc-based plating layer 20) has an exposed region 203 having an exposed steel base portion 201, which is a portion where the surface of the steel is exposed.

[0032] 2, the entire exposed region 203 having the exposed steel base portion 201 is shown schematically as a substantially rectangular shape. However, in the surface-treated member 1 according to this embodiment, the specific shapes of the exposed steel base portion 201 and the exposed region 203 are not limited to the shapes shown in FIG.

[0033] Fig. 3 shows a schematic cross section of the surface-treated member 1 shown in Fig. 2 cut in the Z-axis direction along the cutting line A-A. The cross section shown in Fig. 3 corresponds to a section of the surface-treated member 1 according to this embodiment, in which a portion where the exposed steel base portion 201 does not exist, is cut in the thickness direction of the zinc-based plated steel material that is the raw material for the surface-treated member 1.

[0034] As shown schematically in FIG. 3 , the portion of the surface-treated member 1 according to this embodiment other than the exposed steel base portion 201 is made of a surface-treated steel material (i.e., a zinc-based plated steel material) having a steel material 10 as a base material and a zinc-based plating layer 20 located on the surface of the steel material 10.

[0035] First, the steel material 10 and the zinc-based plating layer 20 will be described in detail below.

[0036] <Regarding the Steel Material 10> The steel material 10 used as the base material of the surface-treated member 1 according to this embodiment is not particularly limited, and various steel materials can be used depending on the mechanical strength (e.g., tensile strength) required of the surface-treated member 1. Examples of such steel materials 10 include various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., high-strength steel in which ultra-low carbon steel further contains strengthening elements such as P, Si, and Mn, and various steel materials containing various other elements (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0037] Furthermore, a pre-plated layer may be provided on the steel material 10 before zinc-based plating as described below is performed. Metals that can be used for the pre-plated layer include Ni, Sn, and alloys combining these elements. Using pre-plated steel material that has been pre-plated with these platings in advance can eliminate bare spots (areas where the plated metal is repelled by an oxide film or the like). This is presumably because, when the pre-plated steel material is immersed in a hot-dip plating bath, the metal elements in the hot-dip plating bath react with the pre-plated layer to form Ni(Sn)-Al-Fe-Zn. The coating weight of the pre-plated layer per side is 0.2 to 2.0 g / m ２ It is preferable that the coating weight of the pre-plating layer is within the range of 0.2 g / m. ２ By setting the coating weight of the pre-plating layer at 2.0 g / m or more, it is possible to reliably achieve the effect of suppressing unplated areas by the pre-plating. ２ By setting the thickness as follows, it is possible to achieve the above-described effect of suppressing unplated areas while preventing the pre-plating layer from suppressing the elution of Fe, which makes it difficult to generate Fe-Zn-based composite oxides.

[0038] Furthermore, the thickness of the steel material 10 is not particularly limited, and may be set appropriately depending on the mechanical strength required of the surface-treated member 1, etc.

[0039] <Regarding the zinc-based plating layer 20> The zinc-based plating layer 20 is formed over the entire surfaces of both surfaces of the above-described steel material 10. The zinc-based plating layer 20 is not particularly limited as long as it contains at least zinc (Zn), and various known zinc-based platings can be applied.

[0040] Examples of such zinc-based plating include zinc plating, such as hot-dip galvanizing and galvannealed hot-dip galvanizing, zinc-nickel plating, zinc-iron plating, zinc-chromium plating, zinc-aluminum plating, zinc-titanium plating, zinc-magnesium plating, zinc-manganese plating, zinc-aluminum-magnesium plating, and zinc-aluminum-magnesium-silicon plating. Furthermore, zinc-based plating may contain small amounts of different metal elements or impurities, such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic, or may have inorganic substances, such as silica, alumina, and titania, dispersed therein. The plating method is not particularly limited, and various known plating methods, such as electroplating, hot-dip plating, vapor deposition plating, dispersion plating, and vacuum plating, may be used.

[0041] Among the various zinc-based platings described above, the zinc-based plating layer 20 according to this embodiment is preferably a zinc-based plating layer having, for example, the chemical composition described in detail below. By using a zinc-based plating layer 20 having the chemical composition described in detail below, it is possible to further improve the corrosion resistance and other properties of the surface-treated member 1 according to this embodiment. First, the more preferable chemical composition of the zinc-based plating layer 20 described above will be described in detail below.

[0042] <Regarding the Chemical Composition of the Zinc-Based Plating Layer 20> According to one aspect, the chemical composition of the zinc-based plating layer 20 according to this embodiment contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance being Zn and impurities.

[0043] In addition, in the chemical composition of a certain aspect of the zinc-based plating layer 20 according to the present embodiment, the zinc-based plating layer 20 is more preferably a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

[0044] According to another aspect, the chemical composition of the zinc-based plating layer 20 according to this embodiment contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being Zn and impurities.

[0045] [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: one or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element group F]: B: less than 0.50%.

[0046] [Al: 0.10% by mass or more and less than 40.00% by mass] In a preferred embodiment of the zinc-based plating layer 20 according to this embodiment, Al is an element necessary for constituting the main metal structure (Zn-Al-Mg metal structure). Therefore, Al is preferably contained at a predetermined content or more to ensure corrosion resistance as a plated steel material. If the Al content in the zinc-based plating layer 20 is less than 0.10% by mass, the above-described corrosion resistance may not be ensured. Therefore, in the zinc-based plating layer 20 according to this embodiment, the Al content is preferably 0.10% by mass or more. The Al content is preferably 3.00% by mass or more, more preferably 4.00% by mass or more, and even more preferably 6.00% by mass or more. By ensuring the Al content within the above range, corrosion resistance as a plated steel material can be ensured.

[0047] On the other hand, if the Al content in the zinc-based plating layer 20 is 40.00 mass% or more, the Al phase that functions as a cathode when placed in a corrosive environment will increase excessively, facilitating corrosion of the steel material 10, and there is a possibility that the corrosion resistance of the plated steel material will not be ensured. Therefore, in the zinc-based plating layer 20 according to this embodiment, the Al content is preferably less than 40.00 mass%. The Al content is preferably 25.00 mass% or less, more preferably less than 25.00 mass%, and even more preferably 20.00 mass% or less.

[0048] [Mg: 0.10% by mass or more and less than 15.00% by mass] In a preferred embodiment of the zinc-based plating layer 20 according to this embodiment, Mg is an element necessary for constituting the main metal structure (Zn—Al—Mg-based metal structure). Therefore, Mg is preferably contained in a predetermined amount or more to ensure corrosion resistance as a plated steel material. If the Mg content in the zinc-based plating layer 20 is less than 0.10% by mass, the above-described corrosion resistance may not be ensured. Therefore, in the zinc-based plating layer 20 according to this embodiment, the Mg content is preferably 0.10% by mass or more. The Mg content is preferably 0.30% by mass or more, and more preferably 3.00% by mass or more. By ensuring the Mg content within the above range, it is possible to ensure corrosion resistance as a plated steel material.

[0049] On the other hand, if the Mg content in the zinc-based plating layer 20 is 15.00 mass% or more, anodic dissolution of the zinc-based plating layer is likely to proceed when placed in a corrosive environment, which may result in the corrosion resistance of the plated steel material not being ensured. Therefore, in the zinc-based plating layer 20 according to this embodiment, the Mg content is preferably less than 15.00 mass%. The Mg content is preferably less than 12.50 mass%, and more preferably 12.00 mass% or less. By ensuring that the Mg content falls within the above range, it is possible to ensure the corrosion resistance of the plated steel material.

[0050] In the zinc-based plating layer 20 according to this embodiment, the balance of the Al and Mg is Zn and impurities. In a preferred embodiment of the zinc-based plating layer 20 according to this embodiment, Zn is an element necessary for constituting the main metal structure (Zn-Al-Mg metal structure) and is an important element for improving the corrosion resistance of the plated steel material. Furthermore, when the zinc-based plating layer 20 contains the Al and Mg within the above ranges and further contains Zn, it is possible to ensure the corrosion resistance required of the plated steel material.

[0051] Next, in a preferred embodiment of the zinc-based plating layer 20 according to another aspect of this embodiment, element groups A to F that may be contained in the chemical composition of the zinc-based plating layer 20 will be described in detail.

[0052] In addition, when the zinc-based plating layer 20 according to another aspect of the present embodiment contains at least one of the elements belonging to the following element groups A to F, it is preferable that the at least one of the elements belonging to the following element groups A to F be contained within the following content ranges and in a total content of 60.00 mass% or less.

[0053] By setting the total content of elements belonging to element groups A to F to 60.00% by mass or less, it becomes possible to enjoy the effects exerted by the addition of each element, as described in detail below, without impairing each other. The total content of elements belonging to element groups A to F is preferably 50.00% by mass or less, and more preferably 40.00% by mass or less.

[0054] Element Group A In another aspect of the zinc-based plating layer 20 according to this embodiment, element group A that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group A shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less, and Fe: 5.00% or less

[0055] [Si: 0% by mass or more and 2.50% by mass or less] In another embodiment of the zinc-based plating layer 20 according to the present embodiment, a case where Si is not contained is also conceivable, and therefore the lower limit of the Si content is 0% by mass. On the other hand, Si is an element that can suppress the excessive growth of an Fe-Al-based metallic structure formed at the interface between the zinc-based plating layer 20 and the steel material 10, and further improve the adhesion between the zinc-based plating layer 20 and the steel material 10. When Si is contained in the zinc-based plating layer 20, in order to suppress the excessive growth of an Fe-Al-based metallic structure, the Si content is preferably 0.05% by mass or more, and more preferably 0.20% by mass or more. On the other hand, if the Si content exceeds 2.50% by mass, there is a possibility that high-melting-point intermetallic compounds are formed with Mg in excess, inhibiting the formation of Al-Mg oxides, which have the effect of suppressing Zn evaporation during welding.

[0056] Furthermore, if the Si content in the plating bath for producing the zinc-based plating layer 20 is too high, the viscosity of the plating bath increases more than necessary, which may result in a decrease in operability during the production of plated steel materials (hereinafter referred to as "plating operability"). Therefore, the Si content in the plating bath is adjusted from the viewpoint of plating operability. The Si content in the zinc-based plating layer 20 is preferably 1.50 mass% or less, and more preferably 1.00 mass% or less.

[0057] [Fe: 0% by mass or more and 5.00% by mass or less] Elements constituting the steel material 10, which is the base material, may be mixed into the zinc-based plating layer 20. In particular, in the hot-dip galvanizing method, elements constituting the steel material 10 are likely to be mixed into the zinc-based plating layer 20 due to interdiffusion of elements caused by a solid-liquid reaction between the steel material 10 and the zinc-based plating layer 20. Due to the incorporation of such elements, the zinc-based plating layer 20 often contains a predetermined amount of Fe, and the content thereof is often 0.01% by mass or more. If the interdiffusion is promoted, the adhesion between the steel material 10 and the zinc-based plating layer 20 is improved. From the viewpoint of improving the adhesion between the steel material 10 and the zinc-based plating layer 20, the Fe content in the zinc-based plating layer 20 is preferably 0.20% by mass or more.

[0058] Furthermore, Fe may be intentionally added to the plating bath used to produce the zinc-based plating layer 20, provided that the effects of the present invention are not impaired. However, if the Fe content in the plating bath is increased, high-melting-point intermetallic compounds of Fe and Al are formed in the plating bath. In this case, such high-melting-point intermetallic compounds tend to adhere to the zinc-based plating layer 20 as dross, significantly degrading the appearance quality, which is undesirable. From this perspective, the Fe content in the plating bath is adjusted. The Fe content in the zinc-based plating layer 20 is preferably 5.00% by mass or less. The Fe content in the plating layer 20 is more preferably 3.00% by mass or less, and even more preferably 2.00% by mass or less, 1.00% by mass or less, or 0.50% by mass or less.

[0059] ◇Element Group B In another aspect of the zinc-based plating layer 20 according to this embodiment, element group B that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group B shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%

[0060] [Sb: 0% by mass or more and 0.50% by mass or less] [Pb: 0% by mass or more and 0.50% by mass or less] [Sr: 0% by mass or more and 0.50% by mass or less] In another embodiment of the zinc-based plating layer 20 according to this embodiment, it is possible that Sb, Pb, and Sr are not contained. Therefore, the lower limit of the content of these elements is 0% by mass. On the other hand, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 20, spangles are formed on the surface of the zinc-based plating layer 20, thereby improving metallic luster. Therefore, from the viewpoint of further improving the design of the plated steel material, it is preferable that at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 20. Such an effect of improving the design is exhibited when the content of at least one of Sb, Pb, and Sr is 0.05% by mass or more. Therefore, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 20, the content of each of these elements is preferably set independently to 0.05 mass% or more.

[0061] On the other hand, when forming a zinc-based coating layer 20 in which any one of the Sb, Pb, and Sr contents exceeds 0.50 mass%, the amount of dross generated in the coating bath used to form the zinc-based coating layer 20 increases, and there is a possibility that a plated steel material with good coating properties cannot be produced. Therefore, the contents of Sb, Pb, and Sr in the zinc-based coating layer 20 are each preferably independently 0.50 mass% or less. The contents of Sb, Pb, and Sr are each preferably independently 0.20 mass% or less.

[0062] Element Group C In another aspect of the zinc-based plating layer 20 according to this embodiment, element group C that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group C shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%

[0063] [Cu: 0% by mass or more and less than 0.25% by mass] [Ti: 0% by mass or more and less than 0.25% by mass] [Cr: 0% by mass or more and less than 0.25% by mass] [Nb: 0% by mass or more and less than 0.25% by mass] [Ni: 0% by mass or more and less than 0.25% by mass] [Mn: 0% by mass or more and less than 0.25% by mass] [Co: 0% by mass or more and less than 0.25% by mass] [V: 0% by mass or more and less than 0.25% by mass] In another aspect of the zinc-based plating layer 20 according to this embodiment, it is possible that Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are not contained, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the zinc-based plating layer 20, these elements are incorporated into the Fe-Al-based metal structure produced by welding when such plated steel is welded, thereby further improving the corrosion resistance of the welded joint. This effect of improving the corrosion resistance of the welded joint is realized when the content of at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 20 is 0.05 mass% or more. Therefore, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the zinc-based plating layer 20, the content of each of these elements is preferably independently 0.05 mass% or more.

[0064] On the other hand, when forming a zinc-based plating layer 20 in which any of the elements Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is 0.25% by mass or more, these elements may form various intermetallic compounds in the plating bath used to form the zinc-based plating layer 20, resulting in an increase in the viscosity of the plating bath and making it impossible to produce a plated steel material with good plating properties. Therefore, the contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 20 are preferably each independently less than 0.25% by mass. The contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are each independently preferably 0.20% by mass or less.

[0065] Element Group D In another aspect of the zinc-based plating layer 20 according to this embodiment, element group D that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group D shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%

[0066] [Sn: 0% by mass or more and 20.00% by mass or less] [Bi: 0% by mass or more and less than 5.00% by mass] [In: 0% by mass or more and less than 2.00% by mass] In another embodiment of the zinc-based plating layer 20 according to the present embodiment, Sn, Bi, and In may not be contained. Therefore, the lower limit of the content of these elements is 0% by mass. On the other hand, Sn, Bi, and In form intermetallic compounds with Mg in the zinc-based plating layer 20, thereby improving the weldability of the zinc-based plating layer 20. Furthermore, since these intermetallic compounds all have high melting points, when plated steel materials are welded, they do not evaporate after welding and remain as intermetallic compounds. The presence of these elements can improve corrosion resistance and corrosion prevention, and can also improve the corrosion resistance of welds during welding. The effect of improving corrosion resistance is achieved when the content of at least one of Sn, Bi, and In in the zinc-based plating layer 20 is 0.05% by mass or more. Therefore, when at least one of Sn, Bi, and In is contained in the zinc-based plating layer 20, the content of each of these elements is preferably set independently to 0.05 mass% or more.

[0067] On the other hand, excessive Sn addition increases the amount of intermetallic compounds formed, which may reduce the corrosion resistance of the zinc-based plating layer 20 after welding. Furthermore, excessive Bi and In addition may make the zinc-based plating layer 20 brittle and prone to peeling, and may also reduce the corrosion resistance of the zinc-based plating layer 20 after welding. These phenomena become more pronounced when the Sn content exceeds 20.00 mass%, when the Bi content is 5.00 mass% or more, or when the In content is 2.00 mass% or more. Therefore, the Sn content is preferably 20.00 mass% or less, the Bi content is preferably less than 5.00 mass%, and the In content is preferably less than 2.00 mass%. The Sn content is more preferably 10.00 mass% or less, the Bi content is more preferably 3.00 mass% or less, and the In content is more preferably 1.00 mass% or less.

[0068] Element Group E In another aspect of the zinc-based plating layer 20 according to this embodiment, element group E that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group E shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less

[0069] [Ca: 0% by mass or more and 3.00% by mass or less] In another aspect of the zinc-based plating layer 20 according to the present embodiment, it is possible that no Ca is contained, and therefore the lower limit of the Ca content is 0% by mass. On the other hand, when Ca is contained in the plating bath for producing the zinc-based plating layer 20, dross generated with an increase in the Mg concentration during plating operations can be reduced, and plating operability can be improved.

[0070] Furthermore, when Ca is contained in the zinc-based plating layer 20, it forms an intermetallic compound with Al and Zn. Furthermore, when Si is contained together with Ca in the zinc-based plating layer 20, Ca forms an intermetallic compound with Si. These intermetallic compounds have a high melting point and a stable structure, making it possible to suppress liquid metal embrittlement (LME) when plated steel is welded. When Ca is contained in the zinc-based plating layer 20, the effect of improving plating operability and the effect of suppressing LME during welding are achieved by setting the Ca content to 0.01% by mass or more. The Ca content in the zinc-based plating layer 20 is more preferably 0.05% by mass or more.

[0071] On the other hand, if the Ca content in the zinc-based plating layer 20 exceeds 3.00 mass%, the corrosion resistance of the plated steel material may be reduced. From this viewpoint, the Ca content in the zinc-based plating layer 20 is preferably 3.00 mass% or less. The Ca content in the zinc-based plating layer 20 is preferably 2.00 mass% or less, and more preferably 1.00 mass% or less.

[0072] [La: 0% by mass or more and less than 0.50% by mass] [Ce: 0% by mass or more and less than 0.50% by mass] [Y: 0% by mass or more and less than 0.50% by mass] In another aspect of the zinc-based plating layer 20 according to this embodiment, it is possible that La, Ce, and Y are not contained, so the lower limits of the contents of these elements are 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit effects almost equivalent to those of Ca. This is because the atomic radius of each element is close to the atomic radius of Ca, and when these elements are contained in the zinc-based plating layer 20, they substitute for Ca positions.

[0073] The effect of improving plating operability and the effect of suppressing LME during welding are realized by making the contents of these elements independently 0.01% by mass or more. Therefore, when at least one of La, Ce, and Y is contained, the contents of these elements independently are preferably 0.01% by mass or more. The contents of La, Ce, and Y in the zinc-based plating layer 20 are each independently more preferably 0.05% by mass or more.

[0074] On the other hand, if the La, Ce, and Y contents in the plating bath for producing the zinc-based plating layer 20 are too high, the viscosity of the plating bath may increase more than necessary, potentially reducing plating operability. Therefore, the La, Ce, and Y contents in the plating bath are adjusted from the perspective of plating operability. The La, Ce, and Y contents are preferably each independently less than 0.50 mass%, less than 0.50 mass%, and 0.50 mass% or less. The La, Ce, and Y contents are each independently preferably 0.10 mass% or less.

[0075] Element Group F In another aspect of the zinc-based plating layer 20 according to this embodiment, element group F that may be contained in the zinc-based plating layer 20 will be described. At least one element in element group F shown below is an element that may be contained in the zinc-based plating layer 20 in place of a portion of the remaining Zn. [Element Group F]: B: Less than 0.50%

[0076] [B: 0% by mass or more and less than 0.50% by mass] In another embodiment of the zinc-based plating layer 20 according to the present embodiment, a case where B is not contained is also conceivable, and therefore the lower limit of the B content is 0% by mass. On the other hand, when B is contained in the zinc-based plating layer 20, it has the effect of further suppressing LME. This is presumably because, when B is contained in the zinc-based plating layer 20, B combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. Furthermore, the presence of B in the zinc-based plating layer 20 is presumably effective in further suppressing LME of the steel material 10 through grain boundary strengthening. Furthermore, because the various intermetallic compounds formed with B have extremely high melting points, it is presumed that they also act to suppress Zn evaporation during welding. These improving effects are achieved by including 0.05% by mass or more of B. Therefore, when B is included, the B content is preferably 0.05% by mass or more.

[0077] On the other hand, if an excessive amount of B is added to the plating bath in order to incorporate B into the zinc-based plating layer 20, a rapid rise in the plating melting point may occur, resulting in a deterioration in plating operability and the possibility of not being able to produce a plated steel material with excellent plating properties. Such a deterioration in plating operability becomes significant when the B content is 0.50 mass% or more, so the B content is preferably less than 0.50 mass%. The B content is more preferably 0.10 mass% or less.

[0078] [Method for Measuring Chemical Composition] The chemical composition of the zinc-based plating layer 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). ICP-AES is used to analyze chemical compositions down to 0.1 mass%, and ICP-MS is used to analyze trace amounts of chemical compositions less than 0.1 mass%. The plated steel material is immersed in a 10% HCl aqueous solution containing an inhibitor for about 1 minute to peel off the zinc-based plating layer, and a solution in which the zinc-based plating layer is dissolved is prepared. The resulting solution can be analyzed by ICP-AES or ICP-MS to obtain the overall average chemical composition of the zinc-based plating layer.

[0079] <Regarding the coating weight of the zinc-based plating layer 20> The coating weight of the zinc-based plating layer 20 as described above is, for example, 10.0 g / m per one side of the steel material. ２ It is preferable that the content is 50.0 g / m or more. ２ The coating weight of the zinc-based plating layer 20 is, for example, 200.0 g / m per one side of the steel material. ２ It is preferable that the density is about 150.0 g / m ２ When the coating weight of the zinc-based plating layer 20 falls within the above range, the surface-treated member 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0080] The deposition weight of the zinc-based plating layer 20 is determined by cutting a sample measuring 30 mm x 30 mm from the surface-treated member 1 and measuring its mass in advance. A tape seal is attached to one side of the sample to prevent the zinc-based plating layer on that side from dissolving in the next process. The sample is then immersed in a 10% HCl aqueous solution containing an inhibitor to peel off the zinc-based plating layer by pickling, and the mass of the sample after pickling is measured. The deposition weight of the zinc-based plating layer 20 per side can be determined from the change in mass of the sample before and after pickling.

[0081] <Regarding the exposed steel base portion 201 and exposed region 203 in the zinc-based plating layer 20> Next, the exposed steel base portion 201 present in at least a part of the zinc-based plating layer 20 according to this embodiment and the exposed region 203 having such exposed steel base portion 201 will be described in detail.

[0082] Fig. 4 is a schematic cross-section of the surface-treated member 1 shown in Fig. 2 taken in the Z-axis direction along the B-B cutting line. The cross-section shown in Fig. 4 corresponds to a cross-section of the exposed region 203, where the exposed steel substrate portion 201 is present, of the surface-treated member 1 according to this embodiment, taken in the thickness direction of the zinc-based plated steel material that is the raw material for the surface-treated member 1.

[0083] As shown schematically in Fig. 4, in the surface-treated member 1 according to this embodiment, the portion where the exposed steel base portion 201 exists is made of a surface-treated steel material (i.e., a zinc-based plated steel material) having a steel material 10 as a base material and a zinc-based plating layer 20 located on the surface of the steel material 10. Furthermore, at least a portion of the zinc-based plating layer 20 has a portion where the surface of the steel material 10 (i.e., the steel base) is exposed.

[0084] As briefly mentioned above, the surface-treated member 1 according to this embodiment intentionally includes an exposed steel substrate portion 201 at a specific abundance ratio in a portion of the zinc-based plating layer 20. As a result, when a portion of the surface-treated member 1 according to this embodiment, including the exposed steel substrate portion 201, is embedded in concrete, a dense composite layer can be formed on the surface of the zinc-based plating layer 20 and the steel material 10, as described above. This allows the surface-treated member 1 according to this embodiment to exhibit excellent corrosion resistance even in concrete. For these reasons, the surface-treated member 1 according to this embodiment is preferably used so that at least a portion of the exposed region 203 including the exposed steel substrate portion 201 is embedded in concrete. Furthermore, the exposed region 203 including the exposed steel substrate portion 201 is preferably provided in a location of the surface-treated member 1 according to this embodiment that is intended to be embedded in concrete.

[0085] Method for identifying the location of the exposed steel substrate portion 201 Below, we will first explain a method for identifying the location of the exposed steel substrate portion 201 in the zinc-based plating layer 20. The exposed steel substrate portion 201 in the zinc-based plating layer 20 according to this embodiment is a portion where the zinc-based plating layer 20 is missing and the steel substrate is exposed. Therefore, the location can be identified by performing various color tests that cause a color reaction in the portion where the steel substrate is exposed over the entire surface of the zinc-based plating layer 20.

[0086] Such a color test is not particularly limited, and various color tests can be applied. However, it is preferable to use, for example, the ferroxyl test specified in JIS H8626 (1995) or the pinhole test disclosed in a non-patent document (Shozo Matsuda, Tadashi Tanaka, Keiichi Tanigawa, "New Pinhole Test Method for Galvanized Steel Sheets," Metal Surface Technology, Vol. 23 (1972), pp. 142-146). In the above two types of color tests, a reagent for a color reaction is applied to the surface of a test specimen to cause a color reaction, and then the surface of the test specimen is covered with a test paper, and the area where the color reaction occurred is transferred to the test paper. Therefore, by using these color tests, the area where the exposed steel substrate portion 201 exists can be identified regardless of the shape of the surface-treated member 1.

[0087] Here, the various reagents used in the coloration test, the test papers used for transferring the colored areas, and the procedures for the coloration test may be in accordance with those specified in the literature disclosing the respective test methods.

[0088] Regarding the state of the exposed steel substrate portion 201: Next, the state of the exposed steel substrate portion 201 in the zinc-based plating layer 20 according to this embodiment will be described. In the surface-treated member 1 according to this embodiment, the state of the exposed steel substrate portion 201 in the zinc-based plating layer 20 is identified by observing a cross section of the zinc-based plating layer 20. More specifically, the state is identified by observing a cross section obtained by cutting the exposed steel substrate portion 201 in the thickness direction of the steel material 10 according to the shape of the exposed steel substrate portion 201 when the zinc-based plating layer 20 is viewed in plan from above (e.g., from the Z-axis direction in FIG. 2 ). The microscope used in this case is not particularly limited as long as it can achieve a magnification that allows cross-sectional observation. The microscope used for observation may be an optical microscope or an electron microscope such as a SEM.

[0089] In this embodiment, the cross section obtained as described above is observed under a microscope, and the state of existence of the cross section that gives the regions "Region A" and "Region B" as described in detail below is verified to evaluate the state of existence of the exposed steel substrate portion 201.

[0090] A more specific procedure will be described below with reference to Figures 5 to 8. Figures 5 to 8 are explanatory diagrams for explaining the exposed steel base portion 201 in the surface treated member according to this embodiment.

[0091] When checking the state of the exposed steel substrate portions 201, as shown in the upper left of Fig. 5, first, the coloration test as described above is performed on the entire surface of the zinc-based plating layer 20 to identify the locations of the exposed steel substrate portions 201. Then, as shown in the lower left of Fig. 5, each of the identified exposed steel substrate portions 201 is viewed in plan from above the zinc-based plating layer 20 (the Z-axis direction in Fig. 2), and each exposed steel substrate portion 201 is virtually partitioned. When partitioning, a virtual section with a short side b of 5 mm and an area (area obtained by multiplying the long side a by the short side b) is created. ２ The partitioning is performed using rectangular regions as units.

[0092] Next, for each of the virtually partitioned regions (rectangular regions), the area ratio of the exposed steel substrate 201 to the region is calculated. ２ It is determined whether the area ratio of the exposed steel substrate portion 201 to the total area (area) of the steel substrate 201 is 3% or more for all regions.

[0093] Next, all of the regions (rectangular regions) where the area ratio of the exposed steel substrate portion 201 was 3% or more were designated as target regions for cross-sectional observation, as shown in the lower right of Figure 5. As schematically shown in the lower right of Figure 5, the surface-treated member 1 corresponding to the region of interest was cut at intervals of △ = 50 μm. All of the obtained cross sections were observed under a microscope to verify the state of the exposed steel substrate portion 201. The cutting direction for obtaining the cross sections shown in the lower right of Figure 5 will be explained again below with reference to Figure 8.

[0094] By the above-described microscopic observation, an observation field such as that shown in FIG. 6 can be obtained for each cross section. For the above-described microscopic observation, an optical microscope (e.g., ECLIPSE LV150 manufactured by Nikon Corporation) is used, and a magnification of approximately 100x is selected. The size of the observation field is 1.5 mm x 2.0 mm.

[0095] Here, when an arbitrary portion of 1.5 mm × 2.0 mm in size in the cross section obtained as described above is observed with a microscope, a portion in the observation field where the surface of the zinc-based plating layer 20 exists for a length of 0.5 mm or more along the width direction, which is a direction perpendicular to the thickness direction of the steel material 10, is referred to as a "remaining plating portion." In addition, a region including an exposed steel base portion 201 located between two adjacent remaining plating portions is defined as "region A."

[0096] In the example shown in Fig. 6, it is assumed that the widthwise length of the chunk of zinc-based plating layer 20 located at the leftmost position in the figure and the widthwise length of the chunk of zinc-based plating layer 20 located at the rightmost position in the figure are 0.5 mm or more. In this case, the portion located between the chunks of zinc-based plating layer 20 located at the leftmost position and the rightmost position in the figure corresponds to "area A" in the observation field of view as exemplified in Fig. 6.

[0097] In the zinc-based plating layer 20 according to this embodiment, the widthwise lengths of the exposed steel substrate portions 201 present in the region A defined above are each within the range of 1.0 to 100.0 μm. In the example shown in Fig. 6, there are five exposed steel substrate portions 201 present in the region A, and the widthwise lengths L1, L2, L3, L4, and L5 of the exposed steel substrate portions 201 are each within the range of 1.0 to 100.0 μm.

[0098] If the width direction length of each exposed steel substrate portion 201 in region A is less than 1.0 μm, the degree of exposure of the surface of the steel material 10 will be too low, and as a result, when the exposed region 203 of such surface-treated member 1 is placed in concrete, the dense composite layer described above will not be formed, and the desired corrosion resistance will not be achieved. By ensuring that the width direction length of each exposed steel substrate portion 201 in region A is 1.0 μm or more, it is possible to achieve corrosion resistance in concrete. The width direction length of each exposed steel substrate portion 201 in region A is preferably 3.0 μm or more, and more preferably 5.0 μm or more.

[0099] On the other hand, if the width direction length of each exposed steel substrate portion 201 in region A exceeds 100.0 μm, the degree of surface exposure of the steel material 10 is too high, and as a result, when the exposed region 203 of such surface-treated member 1 is placed in concrete, the desired corrosion resistance cannot be achieved even if a dense composite layer as described above is partially formed. By making the width direction length of each exposed steel substrate portion 201 in region A 100.0 μm or less, it becomes possible to achieve corrosion resistance in concrete. The width direction length of each exposed steel substrate portion 201 in region A is preferably 90.0 μm or less, and more preferably 70.0 μm or less.

[0100] Furthermore, in the zinc-based plating layer 20 according to this embodiment, in the region A defined as above, the sum of the widthwise lengths of the exposed steel substrate portions 201 per unit length in the width direction is 600.0 μm / mm or less. If the sum of the widthwise lengths of the exposed steel substrate portions 201 per unit length exceeds 600.0 μm / mm, the degree of exposure of the surface of the steel material 10 is too high. As a result, when the exposed region 203 of such a surface-treated member 1 is placed in concrete, the desired corrosion resistance cannot be achieved even if a dense composite layer as described above is partially formed. By setting the sum of the widthwise lengths of the exposed steel substrate portions 201 per unit length to 600.0 μm / mm or less, the Fe derived from the exposed steel substrate portions 201 and the Zn derived from the zinc-based plating layer 20 are supplied at an appropriate supply speed, and the dense composite layer as described above is appropriately formed, thereby achieving the desired corrosion resistance.

[0101] 6, there are five exposed steel substrate portions 201 in region A, and the widthwise lengths of the respective exposed steel substrate portions 201 are L1, L2, L3, L4, and L5, and the widthwise length of region A is L0 [mm]. In this case, the total widthwise length of the exposed steel substrate portions 201 per unit length is given by {(L1 + L2 + L3 + L4 + L5) / L0}.

[0102] The total widthwise length of the exposed steel substrate portion 201 per unit length is preferably 550.0 μm / mm or less, and more preferably 500.0 μm / mm or less.

[0103] On the other hand, the lower limit of the total widthwise length of the exposed steel substrate portions 201 per unit length is not particularly specified. However, if the total widthwise length of the exposed steel substrate portions 201 per unit length is less than 100.0 μm / mm, the degree of exposure of the surface of the steel material 10 will be too low, and when the exposed region 203 of such a surface-treated member 1 is placed in concrete, the dense composite layer described above will not be formed, and the desired corrosion resistance may not be achieved. Therefore, the total widthwise length of the exposed steel substrate portions 201 per unit length is preferably 100.0 μm / mm or more, more preferably 150.0 μm / mm or more, and even more preferably 200.0 μm / mm or more.

[0104] Furthermore, in the zinc-based plating layer 20 according to this embodiment, in the region A defined as above, the number of exposed steel substrate portions 201 per unit length in the width direction is within a range of 3.0 to 20.0 portions / mm. If the number of exposed steel substrate portions 201 per unit length is less than 3.0 portions / mm, the degree of surface exposure of the steel material 10 is too low. As a result, when the exposed region 203 of such a surface-treated member 1 is placed in concrete, the dense composite layer described above is not formed, and the desired corrosion resistance cannot be achieved. If the number of exposed steel substrate portions 201 per unit length in the width direction is 3.0 portions / mm or more, the Fe derived from the exposed steel substrate portions 201 and the Zn derived from the zinc-based plating layer 20 are appropriately supplied, and the dense composite layer described above is appropriately formed, thereby achieving the desired corrosion resistance. The number of exposed steel substrate portions 201 per unit length in the width direction is preferably 5.0 or more / mm, and more preferably 10.0 or more / mm.

[0105] On the other hand, if the number of exposed steel substrate portions 201 per unit length in the width direction exceeds 20.0 / mm, the degree of surface exposure of the steel material 10 is too high, and as a result, when the exposed region 203 of such surface-treated member 1 is placed in concrete, the desired corrosion resistance cannot be achieved even if a dense composite layer as described above is partially formed. By keeping the number of exposed steel substrate portions 201 per unit length in the width direction at 20.0 / mm or less, the desired corrosion resistance can be achieved. The number of exposed steel substrate portions 201 per unit length in the width direction is preferably 18.0 / mm or less, and more preferably 15.0 / mm or less.

[0106] 6, there are five exposed steel base portions 201 in region A, and the length in the width direction of region A is L0 [mm]. In this case, the number of exposed steel base portions 201 present per unit length is given by (5 / L0).

[0107] In region A where the above conditions are satisfied, the average length of the exposed steel substrate portions 201 is preferably within the range of 30.0 to 80.0 μm. By ensuring that the average length of the exposed steel substrate portions 201 is within the range of 30.0 to 80.0 μm, the surface-treated member according to this embodiment can further improve its corrosion resistance in concrete. The average length of the exposed steel substrate portions 201 in region A is more preferably within the range of 50.0 to 70.0 μm.

[0108] In addition, in region A sandwiched between the two remaining plating portions as described above, the portions where the plating remains in island shapes within the exposed steel substrate portion 201 are referred to as "island-shaped plating portions." In this case, the average length of the island-shaped plating portions in region A is preferably within the range of 10.0 μm or more and 300.0 μm or less. By making the average length of the island-shaped plating portions 10.0 μm or more, it is possible to more appropriately adjust the amount of Zn supplied, and it is possible to form a denser composite layer. The average length of the island-shaped plating portions in region A is more preferably 50.0 μm or more.

[0109] On the other hand, by making the average length of the island-shaped plating portions in region A 300.0 μm or less, it becomes possible to make the amount of Zn supplied from the steel material more appropriate while maintaining an appropriate amount of Fe supplied, and it becomes possible to form a denser composite layer. The average length of the island-shaped plating portions in region A is more preferably 200.0 μm or less.

[0110] For example, in the example shown in Figure 6, there are four island-shaped plating portions in region A, and the total length of the island-shaped plating portions is given by {L0 - (L1 + L2 + L3 + L4 + L5)}. Therefore, in the example shown in Figure 6, the average length of the island-shaped plating portions in region A is given by {L0 - (L1 + L2 + L3 + L4 + L5)} / 4.

[0111] The various lengths in the observation field as described above can be measured using a length measurement function or the like implemented in the microscope used.

[0112] Furthermore, in the exposed region 203 of the zinc-based plating layer 20 according to this embodiment, when the cross section as described above is observed under a microscope, a region that gives a cross section in which the total widthwise length of the exposed steel base portion 201 per unit length in the width direction is 600.0 μm / mm or less is defined as "region B." In other words, region B refers to a region in region A defined as shown in Figure 6 in which the total widthwise length of the exposed steel base portion 201 per unit length is 600.0 μm / mm or less.

[0113] In the zinc-based plating layer 20 according to this embodiment, the total area of ​​each of the regions B defined above, when viewed from above in a plan view, is 0.7% or more of the surface area of ​​the steel material 10 when viewed from above. If the total area of ​​the regions B when viewed from above in a plan view is less than 0.7%, the degree of exposure of the surface of the steel material 10 is too low. As a result, when the exposed region 203 of such a surface-treated member 1 is placed in concrete, a dense composite layer as described above is not formed, and the desired corrosion resistance cannot be achieved. When the total area of ​​the regions B when viewed from above in a plan view is 0.7% or more, the desired corrosion resistance in concrete can be achieved. The total area of ​​the regions B when viewed from above in a plan view is preferably 3.0% or more, and more preferably 5.0% or more.

[0114] On the other hand, the upper limit of the total area of ​​region B when viewed from above may be 100.0%, but is preferably set to 40.0% or less. By setting the total area of ​​region B when viewed from above to 40.0% or less, it is possible to further improve corrosion resistance in concrete. The total area of ​​region B when viewed from above is more preferably 30.0% or less, even more preferably 20.0% or less, and even more preferably 15.0% or less.

[0115] The total area of ​​region B when viewed from above can be determined as follows. That is, by observing a cross section such as that shown in FIG. 6, the cross section that provides region B can be identified, and the total widthwise length of the exposed steel base portion 201 per unit length in region B can be determined. As described with reference to FIG. 5, the cross section used for cross-sectional observation is obtained by cutting the surface-treated member 1 of interest at intervals of Δ = 50 μm. Therefore, the value obtained by multiplying the total widthwise length of the exposed steel base portion 201 per unit length in region B obtained by cross-sectional observation by the cross-sectional observation interval Δ = 50 μm can be considered to be the area of ​​region B when viewed from above, corresponding to the cross section of interest. By performing this process, the total area of ​​region B when viewed from above can be determined.

[0116] Regarding the direction of the cutting line when observing the cross section, the direction of the cutting line when observing the cross section as described above will now be described with reference to Fig. 7. In the surface-treated member 1 according to this embodiment, when identifying the exposed steel base portion 201, the surface-treated member 1 is cut in the thickness direction of the steel material 10 to obtain the cross section as described above. In this case, the direction of the cutting line is determined depending on the shape and distribution of the exposed steel base portion 201 when the zinc-based plating layer 20 is viewed in plan from above.

[0117] 7 shows a classification of examples of the shape and distribution of the exposed steel substrate portions 201 when viewed macroscopically in a plan view from above (in the Z-axis direction) the zinc-based plating layer 20. In the surface-treated member 1 according to this embodiment, the shape and distribution of the exposed steel substrate portions 201 are roughly classified into those with directional characteristics, as shown in the group in the upper part of Fig. 7, and those with an isotropic shape or those with no directional shape or distribution, as shown in the group in the lower part of Fig. 7.

[0118] In the group shown in the upper part of Fig. 7, there is a directional orientation (the vertical direction on the paper in the case of the upper part of Fig. 7), such as in the group where the exposed steel substrate portions 201 are approximately elliptical in shape and are distributed so that the long axis directions of the ellipses are approximately parallel (the leftmost drawing in the upper part of Fig. 7), and in the group where the exposed steel substrate portions 201 are approximately rectangular in shape and are distributed so that the long side directions of the ellipses are approximately parallel (the center and rightmost drawings in the upper part of Fig. 7). In such cases, in this embodiment, the direction perpendicular to the directional orientation is taken as the direction of the cutting line.

[0119] Furthermore, the group shown in the lower part of Fig. 7 includes groups in which the exposed steel base portions 201 have an isotropic shape or no directionality in the shape or distribution, such as a group in which circular exposed steel base portions 201 are distributed (the leftmost diagram in the lower part of Fig. 7), a group in which square exposed steel base portions 201 are randomly distributed (the center diagram in the lower part of Fig. 7), and a group in which the zinc-based plating layer 20 is distributed in an island-like manner (the rightmost diagram in the lower part of Fig. 7). In such cases, in this embodiment, the direction of the cutting line is not particularly specified, and any direction may be used as the direction of the cutting line.

[0120] The surface treated member 1 according to this embodiment has been described in detail above with reference to FIGS.

[0121] Although the above description has been given of the case where the surface-treated member 1 according to the present embodiment is provided in concrete, the surface-treated member 1 according to the present embodiment can also be applied to environments other than concrete that contain Ca and exhibit alkaline properties.

[0122] (Composite Structure) Next, a composite structure of the surface treated member according to the present embodiment as described above and concrete will be described with reference to Fig. 8 and Fig. 9. Fig. 8 and Fig. 9 are explanatory diagrams for describing the composite structure according to the present embodiment.

[0123] 8 , the composite structure 5 according to this embodiment is a structure in which the surface-treated member 1 according to this embodiment as described above is combined with concrete. As previously described, at least a portion of the surface of the zinc-based plating layer 20 of the surface-treated member 1 has an exposed region 203 having an exposed steel substrate 201. In the composite structure 5 according to this embodiment, at least a portion of the exposed region 203 is in contact with the concrete, and the surface-treated member 1 and the concrete are combined together.

[0124] Here, the concrete of interest in the composite structure 5 according to this embodiment includes not only various types of concrete such as "ready-mixed concrete" as defined in JIS A5308 (2019), but also concrete-like substances that contain a lot of Ca and are alkaline, such as hydrated iron and steel slag solidified bodies.

[0125] Fig. 9 is a schematic cross-sectional view of the composite structure 5 shown in Fig. 8 cut in the Z-axis direction along the C-C cutting line. The cross-sectional view shown in Fig. 9 corresponds to a cross-section of the exposed region 203 in contact with concrete in the composite structure 5 according to this embodiment cut in the thickness direction of the zinc-based plated steel material that is the raw material for the surface-treated member 1.

[0126] As shown schematically in FIG. 9 , in the composite structure 5 according to this embodiment, the portion where the exposed region 203 is in contact with the concrete is made up of a steel material 10, a surface-treated steel material having a zinc-based plating layer 20 located on the surface of the steel material 10, and an exposed steel base portion 201 present in part of the zinc-based plating layer 20, and concrete.

[0127] In addition, in the exposed region 203 in contact with the concrete, an Fe-Zn-Ca-based composite layer 50 containing Fe, Zn, and Ca is preferably present in at least a part of the interface between the zinc-based plating layer 20 and the concrete or the interface between the steel material 10 and the concrete. Furthermore, as illustrated in Fig. 9, the Fe-Zn-Ca-based composite layer 50 is preferably formed in both the interface between the zinc-based plating layer 20 and the concrete and the interface between the steel material 10 and the concrete.

[0128] Here, the steel material 10 in the composite structure 5 according to this embodiment has the same configuration as the steel material 10 in the surface-treated member 1 previously described and exhibits the same effects, so further description will be omitted below.

[0129] Furthermore, the zinc-based plating layer 20 in the composite structure 5 according to this embodiment and the exposed steel base portion 201 present in the zinc-based plating layer 20 have the same configuration as the zinc-based plating layer 20 and the exposed steel base portion 201 in the surface-treated member 1 described above, and therefore will not be described below.

[0130] In the composite structure 5, interdiffusion of components may occur between the interface of the zinc-based plating layer 20 and the concrete, and therefore the chemical composition of the interface may be different from the chemical composition of the zinc-based plating layer 20 in the portion not in contact with the concrete. However, the average composition of the zinc-based plating layer 20 as a whole is the same as the chemical composition of the zinc-based plating layer 20 in the surface-treated member 1 described above.

[0131] The Fe-Zn-Ca composite layer 50 is a layer composed of a reaction product produced by the mutual reaction of Fe derived from the steel material 10, Zn derived from the zinc-based plating layer 20, and Ca derived from the concrete. The Fe-Zn-Ca composite compound produced by such a reaction has a dense structure, unlike Ca-Zn composite compounds. Therefore, the presence of the Fe-Zn-Ca composite layer 50 at least partially at the interface between the zinc-based plating layer 20 and the concrete or at the interface between the steel material 10 and the concrete allows the composite structure 5 according to this embodiment to exhibit excellent corrosion resistance in concrete.

[0132] Such an Fe-Zn-Ca-based composite layer 50 preferably has a chemical composition containing, by mass %, Fe: 1.0% to 20.0%, Zn: 10.0% to 40.0%, and Ca: 5.0% to 15.0%, with the remainder consisting of H, C, O, and impurities. Since the Fe-Zn-Ca-based composite layer 50 is composed of an Fe-Zn-Ca-based composite compound having the above-mentioned chemical composition, the composite structure 5 according to this embodiment exhibits superior corrosion resistance in concrete.

[0133] Furthermore, when the zinc-based plating layer 20 further contains Al and Mg in its chemical composition, it is preferable that the chemical composition of the Fe-Zn-Ca-based composite layer 50 further contains at least one of Al: 0% to 10.0% and Mg: 0% to 10.0% in place of a portion of the remaining H, C, and O. When the Fe-Zn-Ca-based composite layer 50 is composed of an Fe-Zn-Ca-based composite compound having the above-mentioned chemical composition, the composite structure 5 according to this embodiment exhibits superior corrosion resistance in concrete.

[0134] The composite structure 5 according to this embodiment has been described above with reference to FIGS.

[0135] (Regarding the Manufacturing Method of the Surface-Treated Member) Hereinafter, an example of a manufacturing method of the surface-treated member 1 according to this embodiment will be described.

[0136] <Method for manufacturing surface-treated steel material as a base material> The surface-treated steel material as a base material for the surface-treated member 1 according to this embodiment is manufactured by using the above-described steel material 10 as a base material and forming a zinc-based plating layer on the surface of the steel material 10.

[0137] Here, the zinc-based plating layer can be formed by hot-dip plating, thermal spraying, cold spraying, sputtering, vapor deposition, electroplating, etc. However, hot-dip plating is most preferable in terms of cost.

[0138] Thereafter, a specific processing treatment as described below is performed on the obtained plated steel material (steel material 10 having a zinc-based plating layer) at a desired position (more specifically, a portion where an exposed steel base portion is to be formed) to form an exposed steel base portion in the zinc-based plating layer. This allows the production of a surface-treated steel material that is the raw material for the surface-treated member 1 according to this embodiment.

[0139]

[0033] In the following, an example of a manufacturing method for obtaining a surface-treated steel material according to the present embodiment using a hot-dip galvanizing method will be described in detail. In the manufacturing process of such a surface-treated steel material, first, a steel sheet as an example of a steel material 10 used as a base material is rolled by the Sendzimir method to a desired thickness, and then wound into a coil and placed in a hot-dip galvanizing line.

[0140] In the hot dip plating line, the steel sheet is continuously fed from the coil and passed through the line. At this time, the steel sheet is annealed by an annealing facility installed on the line in an environment where oxidation is unlikely to occur, for example, an oxygen concentration of 20 ppm or less, and N ２ -5% H ２ After heating and reducing at 800°C in a gas atmosphere, the temperature was increased by approximately 20°C to the subsequent plating bath temperature. ２ The plate is cooled with gas and then immersed in a plating bath.

[0141] Here, a molten plating alloy having the above-mentioned chemical components is prepared in the plating bath, and the temperature of the plating bath is set to be equal to or higher than the melting point of the plating alloy (for example, about 460 to 660°C).

[0142] When preparing a plating alloy material, it is preferable to use pure metals (purity of 99% or higher) as the alloying materials. First, predetermined amounts of alloying metals are mixed to obtain the above-described plating layer composition, and the alloy is completely melted in a high-frequency induction furnace, arc furnace, or the like under vacuum or inert gas purging conditions to obtain an alloy. Next, the alloy mixed with the predetermined components (the above-described plating layer composition) is melted in the atmosphere, and the resulting molten material is used as a plating bath.

[0143] In addition, there is no particular restriction on using pure metals for the production of the plating alloys described above, and existing Zn alloys, Mg alloys, and Al alloys may be melted and used. In this case, there is no problem as long as an alloy of a predetermined composition with few impurities is used.

[0144] After immersing the steel sheet in the plating bath, it is pulled up at a predetermined speed. At this time, the steel sheet is pulled up at a predetermined speed so that the zinc-based plating layer to be formed has a desired thickness. ２ The plating weight is controlled by wiping gas. Here, general plating operating conditions can be applied except for the bath temperature, and no special equipment or conditions are required.

[0145] Furthermore, the molten plating alloy located on the steel sheet may be subjected to various heat treatments as required.

[0146] Thereafter, the zinc-based plating layer is subjected to a processing treatment such as scratching or bending at a desired position on the manufactured surface-treated steel material, thereby forming an exposed steel base portion 201 at the processed portion.

[0147] For example, when forming the exposed steel substrate portion 201 by a scratching process, a blade having a length of 50 μm or more and a portion with a tip width of 30 μm or less and sufficiently hard compared to the coating structure is used, and the blade is pressed perpendicularly against the steel sheet. A constant pressure is then applied along the direction in which the blade penetrates the steel sheet. Scratches can be generated on the surface of the zinc-based coating layer by moving the blade linearly under this condition. The steel substrate exposure rate can be changed by varying the number of scratches per unit area. Furthermore, even if other manufacturing conditions are not changed, by using a blade with a wide tip width as described above to generate scratches, it is possible to control the shortest distance from any point in the exposed steel substrate portion to the zinc-based coating layer as desired by utilizing the blade deflection caused by pressure and the blade vibration caused by moving the blade.

[0148] Here, one possible method for applying pressure to the blade is to place a weight of 3 kg or 5 kg on the blade. This pressure is sufficient to scratch the zinc-based plating layer, but is a pressure that barely scratches the steel material. The speed at which the blade is moved is not particularly limited. If the blade and the steel material slip, one method is to set the blade movement speed to 50 cm / sec or less, from the perspective of preventing the blade from being unable to scratch the steel material.

[0149] Furthermore, for example, when forming the exposed steel base portion 201 by bending processing, a winding method using a shaft or a mold as defined in JIS Z2248 (2022) may be used. Here, the shaft is cylindrical with a radius R, and the mold has at least one tip that is not acute but has a rounded shape with a radius R (unit: mm).

[0150] The shaft or mold described above is placed near the center of the desired plated steel material, and one side of the plated steel material is fixed while the other side is wrapped around the shaft or mold to process the zinc-based plating layer. At this time, by controlling the thickness t (unit: mm) of the plated steel material, the radius R (unit: mm) of the tip of the shaft or mold, and the bending speed V (unit: cm / s), it is possible to form an exposed steel base portion 201 at the desired position of the zinc-based plating layer.

[0151] In this case, the ratio t / R, which is the ratio of the sheet thickness t to the radius R of the tip of the shaft or mold, is controlled to satisfy the relationship 0.6≦t / R≦4.0. By setting these processing conditions, a large elongation is applied to the zinc-based coating layer, which causes coating cracks, making it possible to make the state of the exposed steel substrate portion 201 more preferable. In addition, the speed V at which the plated steel material is wound around the shaft or mold is set to 1 cm / s or less. By reducing the processing speed to the minimum in this way, it is possible to suppress the occurrence of large localized cracks and control the size of the exposed steel substrate portion 201.

[0152] An example of the method for manufacturing a surface-treated steel material according to this embodiment has been specifically described above.

[0153] <Method for manufacturing surface-treated member> The surface-treated steel material obtained as described above is used as a raw material to manufacture the surface-treated member according to this embodiment. Here, in order to obtain components for manufacturing the surface-treated member from the surface-treated steel material, various shaping processes can be used, such as various forming processes, joining processes using fastening members such as bolts and caulking, and welding processes. By appropriately combining these processes, a surface-treated member having a desired shape can be manufactured from the surface-treated steel material.

[0154] An example of the method for manufacturing the surface treated member according to this embodiment has been briefly described above.

[0155] In the above description, a case has been described in which a strain-imparting treatment is performed on a surface-treated steel material to form the exposed steel base portion 201, but the strain-imparting treatment may not be performed at the stage of manufacturing the surface-treated steel material, but may be performed as part of the processing performed when manufacturing a surface-treated member from the surface-treated steel material. Furthermore, the processing performed when manufacturing a surface-treated member from the surface-treated steel material may itself be used as a strain-imparting treatment for forming the exposed steel base portion 201.

[0156] (Method for Manufacturing Composite Structure) The method for manufacturing the composite structure according to this embodiment is not particularly limited. For example, the surface-treated member 1 manufactured as described above may be brought into contact with concrete such that at least a portion of the exposed region 203 having the exposed steel base portion 201 is embedded in the concrete.

[0157] The surface-treated member and composite structure according to the present invention will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the surface-treated member and composite structure according to the present invention, and the surface-treated member and composite structure according to the present invention are not limited to the following examples.

[0158] In the test examples shown below, the base sheets for plating shown in Table 1 below (all manufactured by Nippon Steel Corporation) were used, and the base sheets for plating were cut into pieces measuring 100 mm x 200 mm. Then, plating was performed using a batch-type hot-dip plating test apparatus manufactured by our company, and multiple plated steel materials having the plating layer compositions shown in Table 2 below were produced for each level. In Table 2 below, "%" in the table means mass %.

[0159]

[0160]

[0161] Each of the obtained plated steel materials was subjected to the above-described scratching or bending process at approximately the center of the surface of the plating layer to form an exposed steel base portion, thereby obtaining a surface-treated member.

[0162] The scratching process was performed by using a blade that was significantly harder than the plating layer to form parallel, linear scratches. The maximum width of the 50 μm range at the tip of the scratching blade and the spacing between parallel scratches were adjusted to obtain the desired exposed steel base. The weight used to pressurize the blade during the scratching process was 5 kg, and the blade movement speed was 50 cm / sec. This scratching process resulted in exposed steel base with a directional distribution, as shown in the upper right diagram in the upper row of Figure 7, near the center of the surface of each surface-treated member.

[0163] The bending was performed using the winding method of JIS Z2248 (2022). The plated steel sheet thickness t (unit: mm), the shaft or die radius R (unit: mm), and the bending speed V (unit: cm / s) were controlled to obtain a desired steel base exposure rate. This bending process resulted in the formation of a steel base exposure portion with a directional distribution at approximately the center of the surface of each surface-treated member, as shown in the center diagram in the upper part of Figure 7.

[0164] For the surface-treated members obtained by the above two types of processing, the width of the exposed steel substrate portion, the number of exposed steel substrate portions per unit length, the total width of the exposed steel substrate portions per unit length in region A, and the area ratio of region B were measured according to the cross-sectional observation method described above. Here, the coloration test was the ferroxyl test specified in JIS H8626 (1995). Furthermore, an ECLIPSE LV150 optical microscope manufactured by Nikon Corporation was used at a magnification of 200x.

[0165] The results for the scratched specimens are summarized in Tables 3-1 to 3-5 below, and the results for the bent specimens are summarized in Tables 4-1 to 4-5 below. In Tables 3-1 to 4-5 below, the column for "coating weight" indicates the coating weight per side. In Tables 3-1 to 4-5 below, the column for "total length of exposed steel substrate per unit length" indicates the maximum value among multiple values ​​obtained for each level.

[0166] The corrosion resistance of each of the surface-treated members obtained was evaluated by the following test method.

[0167] (Test method: Evaluation of corrosion resistance in concrete) Of the surface-treated members obtained as described above, with the exposed steel substrate adjusted, a length of 100 mm in the longitudinal direction was embedded in concrete to evaluate corrosion resistance. The concrete used was ordinary Portland cement, prepared with a water-cement ratio of 64.4%. The cover thickness (distance from the surface of the zinc-based plating layer to the concrete surface) was 60 mm. After embedding, an accelerated test (JASO M609, 30 cycles) was performed.

[0168] After the above tests, the surface-treated members were extracted from the concrete, and a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) (a scanning electron microscope system SU6600 manufactured by Hitachi High-Technologies Corporation) were used to carry out qualitative analysis to identify the constituent elements and chemical composition of the Fe-Zn-Ca-based composite layer located at the interface between the surface-treated member and the concrete. In Tables 3-1 to 4-5 below, the units of the chemical composition of the Fe-Zn-Ca-based composite layer are mass%, with the remainder being H, C, O, and impurities.

[0169] After the above tests, the surface-treated members were pickled with hydrochloric acid to remove the zinc-based plating layer and corrosion products. The corrosion state of the steel material was then investigated using a shape measuring instrument (Keyence, VR-5000). The evaluation criteria were as follows. Grades A, B, and C were considered to be pass. The results are summarized in Tables 3-1 to 4-5 below. Grade A: No pits were formed on the steel material. B: Pits with a depth of less than 10 μm were formed on the steel material. C: Pits with a depth of 10 μm or more and less than 50 μm were formed on the steel material. D: Pits with a depth of 50 μm or more and less than 100 μm were formed on the steel material. E: Pits with a depth of 100 μm or more were formed on the steel material.

[0170]

[0171]

[0172]

[0173]

[0174]

[0175]

[0176]

[0177]

[0178]

[0179]

[0180] As is clear from Tables 3-1 to 4-5 above, the surface-treated members corresponding to the examples of the present invention exhibited excellent corrosion resistance even in concrete, whereas the surface-treated members corresponding to the comparative examples of the present invention were unable to obtain sufficient corrosion resistance.

[0181] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0182] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0183] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0184] The following configurations also fall within the technical scope of the present invention: (1) A surface-treated member made of a surface-treated steel material having a base steel material and a zinc-based plating layer located on the surface of the steel material, wherein at least a part of the zinc-based plating layer has an exposed region having an exposed steel base portion where the surface of the steel material is exposed, and when the exposed region is cut in the thickness direction of the steel material according to the shape of the exposed steel base portion when the zinc-based plating layer is viewed in plan from above, and a portion of 1.5 mm x 2.0 mm of the cross section obtained by cutting the exposed region in the thickness direction of the steel material is observed under a microscope, In the above-mentioned field of view, a portion of the surface of the zinc-based plating layer existing for a length of 0.5 mm or more along the width direction that is a direction perpendicular to the thickness direction of the steel material is referred to as a remaining plating portion, and a region including the exposed steel base portion located between two adjacent remaining plating portions is defined as region A, wherein in region A, the lengths of the exposed steel base portions existing in the width direction are each within a range of 1 to 100 μm, the number of the exposed steel base portions existing per unit length in the width direction is within a range of 3 to 20 / mm, and the total length of the exposed steel base portions in the width direction per unit length in the width direction is 600 μm / mm or less, (2) A surface-treated member according to (1), which is used by embedding at least a part of the exposed region in concrete. (3) The exposed steel substrate portions are identified by carrying out a color reaction test over the entire surface of the zinc-based plating layer, in which a color reaction occurs in the part where the steel substrate is exposed, and each of the identified exposed steel substrate portions is determined to have a short side of 5 mm or more and an area of ​​1 cm or more when viewed in plan from above the zinc-based plating layer. ２(4) The surface-treated member according to any one of (1) to (3), wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance consisting of Zn and impurities. (5) The surface-treated member according to (4), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more. (6) The surface-treated member according to any one of (1) to (3), wherein the zinc-based plating layer contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (7) The surface-treated member according to (6), which contains the element group A. (8) The surface-treated member according to (6), which contains the element group B. (9) The surface-treated member according to (6), which contains the element group C.(10) The surface-treated member according to (6), which contains the element group D. (11) The surface-treated member according to (6), which contains the element group E. (12) The surface-treated member according to (6), which contains the element group F. (13) The surface-treated member according to any one of (6) to (12), wherein the zinc-based plating layer is a plating layer containing at least, in mass %, Al: 4.0% or more but less than 25.0% and Mg: 0.3% or more but less than 12.5%. (14) A composite structure of a surface-treated member made of a steel material as a base material and a surface-treated steel material having a zinc-based plating layer located on the surface of the steel material, and concrete, wherein at least a part of the zinc-based plating layer has an exposed region having an exposed steel base portion which is a portion where the surface of the steel material is exposed, and at least a part of the exposed region is in contact with concrete, and when a cross section obtained by cutting the exposed region in the thickness direction of the steel material according to the shape of the exposed steel base portion when the zinc-based plating layer is viewed in plan from above is observed under a microscope, In the above-mentioned field of view, a portion of the surface of the zinc-based plating layer existing for a length of 0.5 mm or more along the width direction that is a direction perpendicular to the thickness direction of the steel material is referred to as a remaining plating portion, and a region including the exposed steel base portion located between two adjacent remaining plating portions is defined as region A, wherein in region A, the lengths of the exposed steel base portions existing in the width direction are each within a range of 1.0 to 100.0 μm, the number of the exposed steel base portions existing per unit length in the width direction is within a range of 3.0 to 20.0 pcs / mm, and the total length of the exposed steel base portions in the width direction per unit length in the width direction is 600.0 μm / mm or less, A composite structure in which, when the cross section of the exposed region is observed under a microscope, the region that gives a cross section in which the sum of the widthwise lengths of the exposed steel base portions per unit length in the widthwise direction is 600.0 μm / mm or less is defined as region B, and the sum of the areas of each of the regions B when viewed in a planar view from above is 0.7% or more of the surface area of ​​the steel material when viewed in a planar view.(15) The composite structure according to (14), wherein an Fe-Zn-Ca-based composite layer containing Fe, Zn, and Ca is present in at least a part of the interface between the zinc-based plating layer and the concrete or the interface between the steel material and the concrete in the exposed region in contact with the concrete. (16) The composite structure according to (15), wherein the Fe-Zn-Ca-based composite layer contains, in mass %, Fe: 1.0% to 20.0%, Zn: 10.0% to 40.0%, and Ca: 5.0% to 15.0%, with the remainder being a layer having a chemical composition consisting of H, C, O, and impurities. (17) The composite structure according to (16), wherein the zinc-based plating layer further contains Al and Mg in its chemical composition, and the chemical composition of the Fe-Zn-Ca-based composite layer further contains at least one of Al: 0% or more and 10.0% or less Mg: 0% or more and 10.0% or less in place of a part of the remaining H, C, and O. (18) The exposed steel substrate portions are identified by conducting a coloration test, over the entire surface of the zinc-based plating layer, in which a coloration reaction occurs in the parts where the steel substrate is exposed, and wherein, when each of the identified exposed steel substrate portions is viewed in plan from above the zinc-based plating layer, the size of the short side of each exposed steel substrate portion is 5 mm or more and the area of ​​each exposed steel substrate portion is 1 cm. ２(19) The composite structure according to any one of (14) to (18), wherein the composite structure is virtually divided into rectangular regions each having an area ratio of 3% or more of the rectangular region to the exposed steel substrate, and the cross section of each of the regions is observed for each of the regions having an area ratio of 3% or more of the exposed steel substrate to the rectangular region. (19) The composite structure according to any one of (14) to (18), wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the balance consisting of Zn and impurities. (20) The composite structure according to (19), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more. (21) The composite structure according to any one of (14) to (18), wherein the zinc-based plating layer contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: one or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (22) The composite structure according to (21), which contains the element group A. (23) The composite structure according to (21), which contains the element group B.(24) The composite structure according to (21), which contains the element group C. (25) The composite structure according to (21), which contains the element group D. (26) The composite structure according to (21), which contains the element group E. (27) The composite structure according to (21), which contains the element group F. (28) The composite structure according to any one of (21) to (27), wherein the zinc-based plating layer is a plating layer containing at least, in mass %, Al: 4.0% or more and less than 25.0% and Mg: 0.3% or more and less than 12.5%.

[0185] REFERENCE SIGNS LIST 1 Surface-treated member 5 Composite structure 10 Steel material 20 Zinc-based plating layer 50 Fe—Zn—Ca-based composite layer 201 Exposed steel base 203 Exposed region

Claims

1. A surface-treated member made of a surface-treated steel material having a base steel material and a zinc-based plating layer located on the surface of the steel material, wherein at least a portion of the zinc-based plating layer has an exposed region having an exposed steel base portion which is a portion where the surface of the steel material is exposed, and when a cross section obtained by cutting the exposed region in the thickness direction of the steel material according to the shape of the exposed steel base portion when the zinc-based plating layer is viewed in a plan view from above is observed under a microscope at an arbitrary portion of 1.5 mm x 2.0 mm in size, In the above-mentioned field of view, a portion of the surface of the zinc-based plating layer that exists over a length of 0.5 mm or more along the width direction that is a direction perpendicular to the thickness direction of the steel material is referred to as a remaining plating portion, and a region including the exposed steel base portion located between two adjacent remaining plating portions is defined as region A, the lengths of the exposed steel base portions that exist in region A in the width direction are each within a range of 1.0 to 100.0 μm, the number of the exposed steel base portions present per unit length in the width direction is within a range of 3.0 to 20.0 pcs / mm, and the total length of the exposed steel base portions in the width direction per unit length in the width direction is 600.0 μm / mm or less, A surface-treated member, wherein, when the cross section of the exposed region is observed under a microscope, a region that gives a cross section in which the sum of the widthwise lengths of the exposed steel base portions per unit length in the widthwise direction is 600.0 μm / mm or less is defined as region B, and the sum of the areas of each of the regions B when viewed in plan from above is 0.7% or more of the surface area of ​​the steel material when viewed in plan.

2. The surface treated member according to claim 1, which is used by embedding at least a part of the exposed region in concrete.

3. The exposed steel base is identified by conducting a color test that causes a color reaction at the site where the steel base is exposed over the entire surface of the zinc-based plating layer, and when each of the identified exposed steel base parts is viewed in plan from above the zinc-based plating layer, the size of the short side of each exposed steel base is 5 mm or more and the area is 1 cm or less. ２ 2. The surface-treated member according to claim 1, wherein a rectangular region is virtually divided into units, and the cross section of each of the sections is observed for each section in which the area ratio of the exposed steel base portion to the rectangular region is 3% or more.

4. The surface-treated member according to any one of claims 1 to 3, wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the balance being Zn and impurities.

5. The surface-treated member according to claim 4, wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

6. The surface treated member according to any one of claims 1 to 3, wherein the zinc-based plating layer contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the remainder being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or more selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less [Element group B]: One or more selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50% [Element group C]: One or more selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25% [Element group D]: One or more selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00% [Element group E]: one or more selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% 7. The surface treated member according to claim 6, containing said element group A.

8. The surface treated member according to claim 6, which contains said element group B.

9. The surface treated member according to claim 6, containing said element group C.

10. The surface-treated member according to claim 6, containing said element group D.

11. The surface-treated member according to claim 6, containing said element group E.

12. The surface-treated member according to claim 6, containing the element group F.

13. The surface-treated member according to claim 6, wherein the zinc-based plating layer is a plating layer containing, by mass%, at least: Al: 4.0% or more and less than 25.0% Mg: 0.3% or more and less than 12.5%.

14. A composite structure of a base steel material, a surface-treated member made of a surface-treated steel material having a zinc-based plating layer located on the surface of the steel material, and concrete, wherein at least a part of the zinc-based plating layer has an exposed area having an exposed steel base part which is a part where the surface of the steel material is exposed, and at least a part of the exposed area is in contact with concrete, and when a cross section obtained by cutting the exposed area in the thickness direction of the steel material according to the shape of the exposed steel base part when the zinc-based plating layer is viewed in a plan view from above is observed under a microscope, In the above-mentioned field of view, a portion of the surface of the zinc-based plating layer that exists over a length of 0.5 mm or more along the width direction that is a direction perpendicular to the thickness direction of the steel material is referred to as a remaining plating portion, and a region including the exposed steel base portion located between two adjacent remaining plating portions is defined as region A, the lengths of the exposed steel base portions that exist in region A in the width direction are each within a range of 1.0 to 100.0 μm, the number of the exposed steel base portions present per unit length in the width direction is within a range of 3.0 to 20.0 pcs / mm, and the total length of the exposed steel base portions in the width direction per unit length in the width direction is 600.0 μm / mm or less, A composite structure, wherein when the cross section of the exposed region is observed under a microscope, a region that gives a cross section in which the sum of the widthwise lengths of the exposed steel base portions per unit length in the widthwise direction is 600.0 μm / mm or less is defined as region B, and the sum of the areas of each of the regions B when viewed in a planar view from above is 0.7% or more of the surface area of ​​the steel material when viewed in a planar view.

15. The composite structure according to claim 14, wherein in the exposed region in contact with the concrete, an Fe-Zn-Ca-based composite layer containing Fe, Zn, and Ca is present in at least a portion of the interface between the zinc-based plating layer and the concrete or the interface between the steel material and the concrete.

16. The composite structure according to claim 15, wherein the Fe-Zn-Ca based composite layer is a layer having a chemical composition containing, in mass%, Fe: 1.0% to 20.0%, Zn: 10.0% to 40.0%, Ca: 5.0% to 15.0%, with the remainder consisting of H, C, O and impurities.

17. The composite structure according to claim 16, wherein the zinc-based plating layer further contains Al and Mg as a chemical composition, and the Fe-Zn-Ca-based composite layer further contains at least one of the following in place of a portion of the remaining H, C, and O: Al: 0% or more and 10.0% or less Mg: 0% or more and 10.0% or less.

18. The exposed steel base is identified by conducting a color test that produces a color reaction at the site where the steel base is exposed over the entire surface of the zinc-based plating layer, and each of the identified exposed steel base is identified as having a short side of 5 mm or more and an area of ​​1 cm or less when viewed from above the zinc-based plating layer. ２ The composite structure according to claim 14, wherein a rectangular region is virtually divided into units, and the cross section of each of the sections in which the area ratio of the exposed steel base portion to the rectangular region is 3% or more is observed.

19. A composite structure according to any one of claims 14 to 18, wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being Zn and impurities.

20. The composite structure according to claim 19, wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

21. A composite structure according to any one of claims 14 to 18, wherein the zinc-based plating layer contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element group A, element group B, element group C, element group D, element group E, and element group F below, with the remainder being a plating layer having a chemical composition consisting of Zn and impurities. [Element group A]: One or more selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less [Element group B]: One or more selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50% [Element group C]: One or more selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25% [Element group D]: One or more selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00% [Element group E]: one or more selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% 22. The composite structure according to claim 21, containing said element group A.

23. The composite structure according to claim 21, containing said element group B.

24. The composite structure according to claim 21, containing said element group C.

25. The composite structure according to claim 21, containing said element group D.

26. The composite structure of claim 21, containing element group E.

27. The composite structure according to claim 21, containing said element group F.

28. The composite structure according to claim 21, wherein the zinc-based plating layer is a plating layer containing, by mass%, at least: Al: 4.0% or more and less than 25.0% Mg: 0.3% or more and less than 12.5%.