Surface-treated member and composite structure

Abstract

[Problem] To provide a surface-treated member using a zinc-based plated steel material that can exhibit excellent corrosion resistance even in concrete. [Solution] In this surface-treated member, an exposed region having a steel base exposed section is present in at least a portion of a zinc-based plating layer, and when a cross-section obtained by cutting the exposed region in the thickness direction of the steel material is observed by a microscope, the length of the steel base exposed section present in the width direction is within the range of 1-100 [mu] m. The number of exposed portions of the steel base body per unit length is within the range of 3-20 / mm, and the total length of the exposed portions of the steel base body per unit length in the width direction is 600 [mu] m / mm or less. In addition, the sum of the surface areas in a plan view is 0.7% or more of the surface area of the steel material in a plan view in each region of a cross-section in which the sum of the lengths in the width direction for providing the exposed steel base part per unit length is 600 [mu] m / mm or less from above.

Description

Technical Field

[0001] This invention relates to surface-treated components and composite structures. Background Technology

[0002] Zinc-plated steel, with various zinc-based coatings applied as surface treatment layers to the surface of the base steel, is a widely used raw material in construction, automotive, and other fields to improve the corrosion resistance of structural components. After being processed into various shapes, the zinc-plated steel raw material is joined together as needed using fasteners such as screws and / or bolts, rivets, and / or various welding methods to form a surface-treated component with the desired shape.

[0003] It is believed that surface-treated components, as described above, are exposed to various corrosive environments depending on their intended use. Therefore, various studies have been conducted previously regarding the corrosion resistance of surface-treated steel as raw material.

[0004] For example, Patent Document 1 proposes a surface-treated steel with a coating containing zinc or a zinc-based alloy and a specified amount of Mg or In, designed to achieve excellent corrosion resistance in various corrosive environments, including alkaline, seawater, tap water, high-temperature humid, soil, and atmospheric environments. Patent Document 1 utilizes the excellent sacrificial corrosion protection properties of zinc to study corrosion resistance under various corrosive environments.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 11-158657 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] It is presumed that when surface-treated components are installed in desired locations, at least a portion of them are usually embedded in concrete. If the exposed portion of the surface-treated component is exposed to the atmosphere, corrosion can be easily assessed visually. However, for the portion embedded in concrete, unlike in the atmosphere, corrosion is difficult to assess visually, and maintenance of corroded portions is also challenging. Therefore, surface-treated components used in concrete require high corrosion resistance.

[0010] The inventors conducted a study on the corrosion status of zinc-plated steel in concrete. The results showed that even when surface-treated components are manufactured using the surface-treated steel disclosed in Patent Document 1 as the raw material, there is room for improvement in their corrosion resistance in concrete.

[0011] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a surface-treated component using zinc-plated steel that exhibits excellent corrosion resistance even in concrete, and a composite structure formed by combining the surface-treated component with concrete.

[0012] Solution for solving the problem

[0013] To address the aforementioned issues, the inventors conducted in-depth research and conceived of modifying the state of the zinc-based plating layer, which serves as a surface treatment layer, according to the corrosive environment exposed, such as in the atmosphere or concrete. Based on this concept, the inventors conducted further research and conceived of the surface treatment component and composite structure described below.

[0014] The main idea of ​​the present invention, which was completed based on this concept, is as follows.

[0015] (1) A surface-treated component comprising a steel having a base material and a zinc-based coating on the surface of the steel, wherein at least a portion of the zinc-based coating has an exposed area, the exposed area having a steel substrate exposed portion as a part of the surface of the steel exposed, wherein when a cross section of the exposed area is cut along the thickness direction of the steel according to the shape of the steel substrate exposed portion when viewed from above, and any 1.5 mm × 2.0 mm portion is observed under a microscope, the portion in the field of view in which the surface of the zinc-based coating exists for a length of 0.5 mm or more along the width direction orthogonal to the thickness direction of the steel is called a plating residue portion, and the area containing the steel substrate exposed portion located between two adjacent plating residue portions is called a plating residue portion. When region A is defined, the lengths of the exposed steel substrate portions in the width direction within region A are in the range of 1.0 to 100.0 μm, the number of exposed steel substrate portions per unit length in the width direction is in the range of 3.0 to 20.0 portions / mm, and the sum of the lengths of the exposed steel substrate portions per unit length in the width direction is 600.0 μm / mm or less. When the cross-section in the exposed region is observed under a microscope, when the region providing the cross-section where the sum of the lengths of the exposed steel substrate portions per unit length in the width direction is 600.0 μm / mm or less is defined as region B, the sum of the areas of each region B when viewed from above is 0.7% or more of the surface area of ​​the steel when viewed from above.

[0016] (2) The surface treatment component according to (1) is used by embedding at least a portion of the exposed area in concrete.

[0017] (3) According to the surface treatment component described in (1), wherein the exposed portion of the steel substrate is determined by performing a colorimetric test on the entire surface of the zinc-based coating to cause a colorimetric reaction in the exposed portion of the steel substrate, and when viewed from above the zinc-based coating, each of the determined exposed portions of the steel substrate has a short side size of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each of the above-mentioned exposed steel substrates. For each partition where the area ratio of the exposed steel substrate in the rectangular area is 3% or more, the cross section of the partition is observed.

[0018] (4) The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00% by mass, with the balance being Zn and impurities.

[0019] (5) The surface treatment component according to (4), wherein the zinc coating contains 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 by mass%.

[0020] (6) The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following 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 also containing one or more elements selected from the group consisting of the following element groups A, B, C, D, E and F, with the balance being Zn and impurities.

[0021] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%;

[0022] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%;

[0023] [Element Group C]: Selected from one or more elements in 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%.

[0024] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%;

[0025] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0026] [Element group F]: B: less than 0.50%.

[0027] (7) The surface-treated component according to (6) contains the above-mentioned element group A.

[0028] (8) The surface-treated component according to (6) contains the above-mentioned element group B.

[0029] (9) The surface-treated component according to (6) contains the above-mentioned element group C.

[0030] (10) The surface-treated component according to (6) contains the above-mentioned element group D.

[0031] (11) The surface-treated component according to (6) contains the above-mentioned element group E.

[0032] (12) The surface-treated component according to (6) contains the above-mentioned element group F.

[0033] (13) The surface treatment component according to (6), wherein the zinc coating contains at least 4.0% and less than 25.0% Al and 0.3% and less than 12.5% ​​Mg by mass.

[0034] (14) A composite structure comprising a surface-treated component and concrete, wherein the surface-treated component is composed of steel having a base material and a zinc-based coating on the surface of the steel, wherein at least a portion of the zinc-based coating has an exposed area, the exposed area having a steel substrate exposed portion as a portion exposing the surface of the steel, and at least a portion of the exposed area is in contact with concrete, wherein when a cross-section of the exposed area is cut along the thickness direction of the steel according to the shape of the exposed steel substrate when viewed from above, and a portion of any size 1.5 mm × 2.0 mm is observed under a microscope, in the field of view, a portion of the surface of the zinc-based coating having a length of 0.5 mm or more along the width direction orthogonal to the thickness direction of the steel is referred to as a coating residue portion, and ... is referred to as a coating residue portion, and a portion of the surface of the zinc-based coating having a length of 0.5 mm or more along the width direction is referred to as a coating residue portion, and a portion of the surface of the zinc-based coating having a length of 0.5 mm or more along the width direction is referred to as a coating residue portion, and a portion of the surface of the zinc-based coating having a length of 0.5 mm or more along the width direction is referred to as a coating residue portion When the region containing the exposed steel substrate between the aforementioned plating residue portions is defined as region A, in region A, the lengths of the exposed steel substrate in the width direction are respectively in the range of 1.0 to 100.0 μm, the number of exposed steel substrates per unit length in the width direction is in the range of 3.0 to 20.0 per mm, and the sum of the lengths of the exposed steel substrates per unit length in the width direction is 600.0 μm / mm or less. When the cross-section of the exposed region is observed under a microscope, when the region providing the cross-section where the sum of the lengths of the exposed steel substrates per unit length in the width direction is 600.0 μm / mm or less is defined as region B, the sum of the areas of each of the aforementioned regions B when viewed from above is more than 0.7% of the surface area of ​​the steel when viewed from above.

[0035] (15) The composite structure according to (14), wherein, in the exposed area in contact with the concrete, at least a portion of the interface between the zinc coating and the concrete or at least a portion of the interface between the steel and the concrete is provided with an Fe-Zn-Ca composite layer containing Fe, Zn and Ca.

[0036] (16) According to the composite structure described in (15), wherein the Fe-Zn-Ca composite layer is a layer having the following chemical composition: by mass%, it contains Fe: 1.0% or more and 20.0% or less, Zn: 10.0% or more and 40.0% or less, Ca: 5.0% or more and 15.0% or less, with the balance being H, C, O and impurities.

[0037] (17) According to the composite structure described in (16), wherein the chemical composition of the zinc-based coating further contains Al and Mg, and the chemical composition of the Fe-Zn-Ca composite layer further contains at least one of Al: 0% or more and 10.0% or less, and Mg: 0% or more and 10.0% or less to replace a portion of the balance of H, C, and O.

[0038] (18) According to the composite structure described in (14), the exposed portion of the steel substrate is determined by performing a colorimetric test on the entire surface of the zinc-based coating to cause a colorimetric reaction in the exposed portion of the steel substrate. When viewed from above the zinc-based coating, each of the determined exposed portions of the steel substrate has a short side size of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each of the above-mentioned exposed steel substrates. For each partition where the area ratio of the exposed steel substrate in the rectangular area is 3% or more, the cross section of the partition is observed.

[0039] (19) The composite structure according to any one of (14) to (18), wherein the zinc coating is a coating having the following chemical composition: containing Al: 0.10% or more and less than 40.00% by mass, Mg: 0.10% or more and less than 15.00%, with the balance being Zn and impurities.

[0040] (20) The composite structure according to (19), wherein the zinc coating contains 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 by mass%.

[0041] (21) The composite structure according to any one of (14) to (18), wherein the zinc coating is a coating having the following 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 also containing one or more elements selected from the group consisting of the following element groups A, B, C, D, E and F, with the balance being Zn and impurities.

[0042] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%;

[0043] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%;

[0044] [Element Group C]: Selected from one or more elements in 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%.

[0045] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%;

[0046] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0047] [Element group F]: B: less than 0.50%.

[0048] (22) The composite structure according to (21) contains the above-mentioned element group A.

[0049] (23) The composite structure according to (21) contains the above-mentioned element group B.

[0050] (24) The composite structure according to (21) contains the above-mentioned element group C.

[0051] (25) The composite structure according to (21) contains the above-mentioned element group D.

[0052] (26) The composite structure according to (21) contains the above-mentioned element group E.

[0053] (27) The composite structure according to (21) contains the above-mentioned element group F.

[0054] (28) The composite structure according to (21), wherein the zinc coating contains at least 4.0% and less than 25.0% Al and 0.3% and less than 12.5% ​​Mg by mass%.

[0055] The effects of the invention

[0056] As described above, according to the present invention, it is possible to provide a surface-treated component using zinc-plated steel that exhibits excellent corrosion resistance even in concrete, and a composite structure formed by combining the surface-treated component with concrete. Attached Figure Description

[0057] Figure 1 It is a schematic diagram used to illustrate a structure set on a concrete surface.

[0058] Figure 2 This is a schematic diagram illustrating the structure of the surface treatment component in an embodiment of the present invention.

[0059] Figure 3 This is a schematic diagram illustrating the structure of a surface treatment component in the same embodiment.

[0060] Figure 4 This is a schematic diagram illustrating the structure of a surface treatment component in the same embodiment.

[0061] Figure 5 This is an explanatory diagram illustrating the exposed steel substrate portion in a surface-treated component according to the same embodiment.

[0062] Figure 6 This is an explanatory diagram used to illustrate region A defined in a surface-treated component in the same embodiment.

[0063] Figure 7 This is an explanatory diagram illustrating the exposed steel substrate portion in a surface-treated component according to the same embodiment.

[0064] Figure 8 This is a schematic diagram illustrating the structure of a composite structure in the same embodiment.

[0065] Figure 9 This is a schematic diagram illustrating the structure of a composite structure in the same embodiment. Detailed Implementation

[0066] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in this specification and the accompanying drawings, constituent elements having substantially the same functional configuration are labeled with the same reference numerals, and repeated descriptions are omitted.

[0067] (Corrosion behavior in concrete)

[0068] Before describing the surface treatment components according to embodiments of the present invention, refer to Figure 1 The corrosion behavior in concrete discovered by the inventors will be described. Figure 1 It is a schematic diagram used to illustrate a structure set on a concrete surface.

[0069] like Figure 1 The diagram schematically illustrates various structures, such as pedestals supporting solar panels, road signs, guardrails, and traffic signals, mounted on a concrete surface serving as a base. In order to more stably mount the structures on the concrete surface, such as... Figure 1 As shown, most of them will include a part of the structure (e.g., near the lower end of the support column, etc.) in Figure 1 The part enclosed by the dotted line is embedded in the concrete.

[0070] From the perspective of factors such as production costs, various types of steel are generally used as raw materials for various structures. When a part of a structure using various types of steel as raw materials is embedded in concrete, there are concerns about corrosion of the steel used as raw materials because concrete is a highly alkaline environment.

[0071] It is known that when using various uncoated steels as structural blanks, the uncoated steel forms a passivation film on its surface in alkaline environments such as concrete, exhibiting high corrosion resistance. On the other hand, in environments such as the atmosphere, which are neutral but contain corrosive agents such as moisture, the exposed parts of the uncoated steel exhibit poor corrosion resistance.

[0072] Furthermore, even in parts present within concrete, chloride ions (Cl) are generated within the concrete. - In cases of chloride ion (Cl) penetration and / or the neutralization of concrete, the passivation film formed will disappear, reducing corrosion resistance. Furthermore, for steel exposed to the atmosphere, chloride ions (Cl...)... - Ions act as corrosion agents, thus the exposed parts of the steel are not sufficiently corrosion resistant.

[0073] Thus, when various uncoated steels are used as blanks for structures, there are concerns about their corrosion resistance (especially when exposed to chloride ions).

[0074] On the other hand, if zinc-plated steel, which has excellent corrosion resistance in the atmosphere as a neutral environment and also has excellent corrosion resistance even when chloride ions are attached in the atmosphere, is used as the blank material for the structure, then it can be said that a solution has been found for maintaining the corrosion resistance of the structure in the atmosphere.

[0075] Furthermore, it is known that when zinc-plated steel is embedded in concrete, a Ca-Zn reactive layer forms at the interface between the zinc plating and the concrete, improving corrosion resistance in alkaline concrete. Therefore, using zinc-plated steel as the raw material for structures embedded in concrete, from the viewpoint of maintaining the corrosion resistance of the structure in both concrete and the atmosphere, seems at first glance a viable solution. However, it is known that the protective effect of the Ca-Zn reactive layer, as described above, is lost when chloride ions penetrate the concrete. Therefore, even when using zinc-plated steel as the raw material for structures, there is still room for improvement from the viewpoint of corrosion resistance in concrete.

[0076] To clarify the corrosion behavior of zinc-plated steel in concrete, the inventors investigated the corrosion behavior of the Ca-Zn reaction layer in concrete. Specifically, in chloride-infiltrated concrete, the formation of the Ca-Zn reaction layer on the surface of the zinc plating was observed using a scanning electron microscope (SEM). The results showed that the Ca-Zn reaction layer exposed to chloride ions is porous.

[0077] Based on the above insights, the inventors have obtained the following insights: In order to improve the corrosion resistance of zinc-plated steel in concrete, it is important to change the Ca-Zn reaction layer formed in the zinc-plated coating in the concrete into a layer composed of products generated in a dense state.

[0078] In order to achieve a layer composed of products formed in a dense state in concrete, the inventors conducted further research and concluded that, unlike previous technical ideas, a portion of the zinc-based coating is intentionally provided to expose the surface of the steel (hereinafter referred to as "exposed steel substrate portion") in a specific proportion. Therefore, even in concrete, a composite layer composed of products in a dense state can be formed on the surface of the zinc-based coating.

[0079] In conventional techniques, zinc-based coatings are typically made dense to minimize exposure of the steel substrate, thus protecting the substrate by utilizing the sacrificial corrosion protection properties of zinc. However, the inventors have discovered that by intentionally creating portions of the zinc-based coating that expose the steel substrate, a dense composite layer can be formed starting from these exposed portions. This composite layer protects both the steel substrate and the surrounding zinc-based coating.

[0080] More specifically, by exposing the steel substrate within the concrete, both the zinc-based coating and the steel substrate are exposed to the various components constituting the concrete. Consequently, Zn ions dissolve from the zinc-based coating, and Fe ions dissolve from the steel substrate. In the atmosphere, the dissolved Zn and / or Fe ions are washed away by rain, etc., and rarely remain fixed in the exposed portion. On the other hand, in concrete, there is no such flow of water. Therefore, it is presumed that the dissolved Zn and / or Fe ions readily become fixed in the exposed steel substrate, forming a dense Fe-Zn-Ca composite oxide in the exposed portion.

[0081] Furthermore, the inventors' research results indicate that when the zinc-based coating is an alloy coating containing Mg and Al in addition to Zn, Mg and Al ions dissolve in concrete in addition to Zn ions. It is known that through this dissolution, a Fe-Zn-Al-Mg-Ca composite oxide is generated, further improving corrosion resistance.

[0082] Based on the insights described above, the inventors conducted further research and came up with the surface-treated components and composite structures of the present invention, as detailed below.

[0083] (Regarding surface-treated components)

[0084] The following is for reference Figures 2-4 The surface treatment components according to embodiments of the present invention will be described in detail. Figures 2-4 This is a schematic diagram illustrating the structure of the surface treatment component in this embodiment. Additionally, in Figures 2-4 For convenience, the coordinate axes shown in the figure are used for explanation.

[0085] As detailed below, the surface-treated component of this embodiment is constructed using surface-treated steel with a zinc-based coating as the blank. Here, the specific structure of the surface-treated component of this embodiment is not particularly limited. The specific structure of the surface-treated component of this embodiment can be, for example, box-shaped, or plate-shaped, such as the roof and / or walls of a building, using plate-shaped steel. Furthermore, the specific structure of the surface-treated component of this embodiment can be, for example, a molded body and / or joint using various types of steel, such as a solar panel mounting platform; a molded body and / or joint using various H-beams and / or prisms, such as the skeleton of a structure; or a molded body and / or joint using various steel pipes, such as various pillars, signs, signal lights, guardrails, etc.

[0086] Figure 2 This schematically illustrates a portion of the surface-treated component of this embodiment when viewed from above (Z-axis direction in the figure). Figure 2 As illustrated schematically, the surface treatment component 1 of this embodiment, as described below, uses a zinc-plated steel sheet on which a zinc-based coating 20 is provided on the surface of a steel sheet serving as the base material, as the blank, and on its surface (corresponding to...) Figure 2 At least a portion of the XY plane (the surface of the zinc coating 20) has an exposed area 203 of the steel substrate exposed portion 201, which has a portion of the surface of the steel exposed.

[0087] Here, in Figure 2 In the diagram, the exposed area 203 having the exposed steel substrate 201 is schematically represented as having a generally rectangular shape. However, in the surface treatment member 1 of this embodiment, the specific shape of the exposed steel substrate 201 and / or the exposed area 203 is not limited to [specific shape]. Figure 2 The shape shown.

[0088] Figure 3 Indicatively representing that Figure 2 The surface-treated component 1 shown is cut along the AA cutting line in the Z-axis direction. Figure 3 The cross-sectional view shown corresponds to the view obtained by cutting the portion of the surface treatment component 1 in this embodiment where there is no exposed steel substrate 201 along the thickness direction of the zinc-plated steel material that serves as the blank of the surface treatment component 1.

[0089] like Figure 3 As illustrated, the surface-treated component 1 of this embodiment, excluding the exposed steel substrate 201, is composed of surface-treated steel (i.e., zinc-plated steel) having a steel 10 as a base material and a zinc-based coating 20 on the surface of the steel 10.

[0090] The following is a detailed description of the steel 10 and the zinc coating 20.

[0091] <About Steel 10>

[0092] The steel 10 used as the base material for the surface-treated component 1 in this embodiment is not particularly limited, and various steels can be used depending on the mechanical strength (e.g., tensile strength) required for the surface-treated component 1. Examples of such steel 10 include various Al-killed steels, ultra-low carbon steels containing Ti, Nb, etc., high-strength steels that also contain strengthening elements such as P, Si, Mn, etc. in ultra-low carbon steel, and various steels containing other components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0093] Alternatively, a pre-plating layer can be applied before the zinc-based plating described later on the steel 10. Examples of metals that can be used in the pre-plating layer include Ni, Sn, or alloys combining these elements. Using pre-plated steel with these pre-plated coatings eliminates unplated areas (areas where the plating metal is rejected by oxide films, etc.). This is presumably because when the pre-plated steel is immersed in a hot-dip galvanizing bath, the metal elements in the bath react with the pre-plating layer to form Ni(Sn)-Al-Fe-Zn. The amount of pre-plated coating applied to each side is preferably 0.2~2.0 g / m². 2 Within the range. By setting the adhesion amount of the pre-coating to 0.2 g / m 2 The above demonstrates a reliable inhibition effect against uncoated areas based on pre-coating, as described above. Furthermore, by setting the pre-coating adhesion amount to 2.0 g / m²... 2 The following method can prevent the leaching of Fe from being suppressed by the pre-plating layer, making it difficult to form Fe-Zn composite oxides, and can achieve the unplating suppression effect mentioned above.

[0094] In addition, there is no particular limitation on the thickness of the steel 10; it can be set appropriately according to the mechanical strength required by the surface-treated component 1.

[0095] <Regarding Zinc-Based Coatings 20>

[0096] The zinc-based coating 20 is formed on both surfaces of the steel 10 as described above. This zinc-based coating 20 is not particularly limited as long as it contains at least zinc (Zn), and various known zinc-based coatings can be used.

[0097] Examples of zinc-based coatings include hot-dip galvanizing and / or alloyed hot-dip galvanizing, as well as zinc-nickel, zinc-iron, zinc-chromium, zinc-aluminum, zinc-titanium, zinc-magnesium, zinc-manganese, zinc-aluminum-magnesium, and zinc-aluminum-magnesium-silicon coatings. Furthermore, zinc-based coatings can also include those containing small amounts of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic, and / or those containing dispersed inorganic substances such as silicon dioxide, alumina, and titanium dioxide. The coating method is not particularly limited; various known coating methods such as electroplating, hot-dip galvanizing, vapor deposition, dispersion coating, and vacuum coating can be used.

[0098] Among the various zinc-based platings described above, the zinc-based plating layer 20 of this embodiment is more preferably a zinc-based plating layer having the chemical composition detailed below. As the zinc-based plating layer 20, by using a zinc-based plating layer having the chemical composition detailed below, various properties of the surface-treated component 1 of this embodiment, such as corrosion resistance, can be further improved. Hereinafter, a more preferred chemical composition of the zinc-based plating layer 20 described above will be explained in detail.

[0099] Chemical Composition of Zinc-Based Coating 20

[0100] According to a certain method, the zinc-based coating 20 of this embodiment has the following chemical composition: by mass%, it contains Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance is Zn and impurities.

[0101] Furthermore, in a certain chemical composition of the zinc-based coating 20 in this embodiment, the zinc-based coating 20 is more preferably a coating 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.

[0102] In addition, according to another method, the zinc-based coating 20 of this embodiment has the following chemical composition: by mass%, it contains Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and also 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, with the balance being Zn and impurities.

[0103] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%.

[0104] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%.

[0105] [Element Group C]: Selected from one or more elements in 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%.

[0106] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%.

[0107] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0108] [Element group F]: B: less than 0.50%

[0109] [Al: ≥0.10% by mass and <40.00% by mass]

[0110] In the preferred embodiment of the zinc-based coating 20, Al is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure). Therefore, to ensure the corrosion resistance of the coated steel, it is preferable to contain Al at a specified or higher content. If the Al content in the zinc-based coating 20 is less than 0.10% by mass, the aforementioned corrosion resistance may not be guaranteed. Therefore, in the zinc-based coating 20 of 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 keeping the Al content within the range described above, the corrosion resistance of the coated steel can be ensured.

[0111] On the other hand, when the Al content in the zinc-based coating 20 is 40.00% by mass or more, the excessive increase of the Al phase, which functions as a cathode, in a corrosive environment can easily lead to corrosion of the steel 10, potentially compromising the corrosion resistance of the coated steel. Therefore, in the zinc-based coating 20 of this embodiment, the Al content is preferably less than 40.00% by mass. The Al content is preferably 25.00% by mass or less, more preferably less than 25.00% by mass, and even more preferably 20.00% by mass or less.

[0112] [Mg: ≥0.10% by mass and <15.00% by mass]

[0113] In the preferred embodiment of the zinc-based coating 20, Mg is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure). Therefore, to ensure the corrosion resistance of the coated steel, it is preferable to contain Mg at a specified or higher content. If the Mg content in the zinc-based coating 20 is less than 0.10% by mass, the aforementioned corrosion resistance may not be guaranteed. Therefore, in the zinc-based coating 20 of 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 keeping the Mg content within the range described above, the corrosion resistance of the coated steel can be ensured.

[0114] On the other hand, when the Mg content in the zinc-based coating 20 is 15.00% by mass or more, anodic dissolution of the zinc-based coating can easily proceed under corrosive conditions, which may compromise the corrosion resistance of the coated steel. Therefore, in the zinc-based coating 20 of this embodiment, the Mg content is preferably less than 15.00% by mass. The Mg content is preferably less than 12.50% by mass, and more preferably less than 12.00% by mass. By keeping the Mg content within the range described above, corrosion resistance of the coated steel can be ensured.

[0115] In the zinc-based coating 20 of this embodiment, the balance of Al and Mg is Zn and impurities.

[0116] In the preferred embodiment of the zinc-based coating 20, Zn is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure) and is an important element for improving the corrosion resistance of the coated steel. Furthermore, the zinc-based coating 20 contains Al and Mg within the aforementioned range, and also contains Zn, thereby ensuring the required corrosion resistance of the coated steel.

[0117] Next, in a preferred embodiment of the zinc-based coating 20, the element groups A to F that may be present in the chemical composition of the zinc-based coating 20 will be described in detail.

[0118] It should be noted that in another embodiment of the zinc-based coating 20, when it contains at least one of the elements belonging to element group A to element group F, it is preferable that it contains at least one of the elements belonging to element group A to element group F within the following content range and with a total content of 60.00% by mass or less.

[0119] By setting the total content of elements belonging to element groups A to F to 60.00% by mass or less, the effects resulting from the addition of each element, as detailed below, can be enjoyed without any mutual impairment. 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.

[0120] ◇Element Group A

[0121] In another embodiment of the zinc-based coating 20, the element group A that may be contained in the zinc-based coating 20 will be described. At least one element in element group A shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0122] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%.

[0123] [Si: 0% by mass or more and 2.50% by mass or less]

[0124] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where Si is not present, and therefore its content is limited to 0% by mass. On the other hand, Si is an element that can suppress the excessive growth of Fe-Al metallographic structure formed at the interface between the zinc-based coating 20 and the steel 10, and further improve the adhesion between the zinc-based coating 20 and the steel 10. When the zinc-based coating 20 contains Si, in order to suppress the excessive growth of Fe-Al metallographic 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, when the Si content exceeds 2.50% by mass, excessive Si may form high-melting-point intermetallic compounds with Mg, which may hinder the formation of Al-Mg oxides that have the effect of suppressing Zn evaporation during welding.

[0125] Furthermore, if the Si content in the plating bath used to manufacture the zinc-based coating 20 is too high, the viscosity of the plating bath increases beyond what is necessary, potentially reducing the operability (hereinafter referred to as "plating operability") during the manufacture of the coated steel. Therefore, from the viewpoint of plating operability, the Si content in the plating bath is adjusted. The Si content in the zinc-based coating 20 is preferably 1.50% by mass or less, more preferably 1.00% by mass or less.

[0126] [Fe: ≥0% by mass and ≤5.00% by mass]

[0127] In the zinc-based coating 20, elements constituting the steel are sometimes mixed in from the steel 10, which serves as the base material. Particularly in hot-dip galvanizing, due to the interdiffusion of elements caused by the solid-liquid reaction between the steel 10 and the zinc-based coating 20, elements constituting the steel 10 easily mix into the zinc-based coating 20. Through this mixing, the zinc-based coating 20 typically contains a specified amount of Fe, usually 0.01% by mass or more. Promoting this interdiffusion improves the adhesion between the steel 10 and the zinc-based coating 20. From the viewpoint of improving the adhesion between the steel 10 and the zinc-based coating 20, the Fe content in the zinc-based coating 20 is preferably 0.20% by mass or more.

[0128] Furthermore, Fe can be intentionally added to the plating bath used in manufacturing the zinc-based coating 20 without impairing the effects of the present invention. However, if the Fe content in the plating bath is increased, a high-melting-point intermetallic compound of Fe and Al will form in the plating bath. In this case, the high-melting-point intermetallic compound adheres to the zinc-based coating 20 as dross, which tends to significantly reduce the appearance quality and is therefore undesirable. From this point of view, the Fe content in the plating bath is adjusted. The Fe content in the zinc-based coating 20 is preferably 5.00% by mass or less. The Fe content in the coating 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.

[0129] ◇Element Group B

[0130] In another embodiment of the zinc-based coating 20, the element group B that may be contained in the zinc-based coating 20 will be described. At least one element in element group B shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0131] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%.

[0132] [Sb: ≥0% by mass and ≤0.50% by mass]

[0133] [Pb: ≥0.50% by mass]

[0134] [Sr: 0% or more by mass and less than 0.50% by mass]

[0135] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where Sb, Pb, and Sr are not present, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, if the zinc-based coating 20 contains at least one of Sb, Pb, and Sr, zinc flowers will form on the surface of the zinc-based coating 20, thereby improving the metallic luster. Therefore, from the viewpoint of further improving the designability of the coated steel, it is preferable that the zinc-based coating 20 contains at least one of Sb, Pb, and Sr. This improvement in designability is manifested when the content of at least one of Sb, Pb, and Sr is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least one of Sb, Pb, and Sr, the content of each of these elements is preferably set independently to 0.05% by mass or more.

[0136] On the other hand, when a zinc-based coating 20 is formed in which the content of any one of Sb, Pb, and Sr exceeds 0.50% by mass, the amount of dross generated in the plating bath used to form the zinc-based coating 20 increases, which may prevent the production of coated steel with good coating properties. Therefore, the content of Sb, Pb, and Sr in the zinc-based coating 20 is preferably 0.50% by mass or less, each independently. The content of Sb, Pb, and Sr is preferably 0.20% by mass or less, each independently.

[0137] ◇Element Group C

[0138] In another embodiment of the zinc-based coating 20, the element group C that may be contained in the zinc-based coating 20 will be described. At least one element in element group C shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0139] [Element Group C]: Selected from one or more elements in 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%.

[0140] [Cu: ≥0.25% by mass]

[0141] [Ti: 0% by mass and less than 0.25% by mass]

[0142] [Cr: ≥0.25% by mass]

[0143] [Nb: ≥0.25% by mass]

[0144] [Ni: ≥0.25% by mass]

[0145] [Mn: ≥0% by mass and <0.25% by mass]

[0146] [Co: ≥0.25% by mass]

[0147] [V: 0% by mass and less than 0.25% by mass]

[0148] In another embodiment of the zinc-based coating 20, it is also possible to exclude Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, thus the lower limit of the content of these elements is 0% by mass. On the other hand, if the zinc-based coating 20 contains at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, these elements are introduced into the Fe-Al metallographic structure formed by welding when the coated steel is welded, which can further improve the corrosion resistance of the formed weld. This improvement in the corrosion resistance of the weld is evident when the content of at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based coating 20 is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, the content of each of these elements is preferably set to 0.05% by mass or more independently.

[0149] On the other hand, when a zinc-based coating 20 is formed in which the content of any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is 0.25% by mass or more, these elements form various intermetallic compounds in the plating bath used to form the zinc-based coating 20, leading to an increase in the viscosity of the plating bath, which may prevent the production of coated steel with good plating properties. Therefore, the content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based coating 20 is preferably each independently set to less than 0.25% by mass. The content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is preferably each independently set to 0.20% by mass or less.

[0150] ◇Element Group D

[0151] In another embodiment of the zinc-based coating 20, the element group D that may be contained in the zinc-based coating 20 will be described. At least one element in element group D shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0152] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%.

[0153] [Sn: 0% or more by mass and less than 20.00% by mass]

[0154] [Bi: 0% by mass and less than 5.00% by mass]

[0155] [In: 0% by mass and less than 2.00% by mass]

[0156] In another embodiment of the zinc-based coating 20, it is also possible to exclude Sn, Bi, and In, thus 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 coating 20, which can improve the weldability of the zinc-based coating 20. In addition, these intermetallic compounds have high melting points, so they do not evaporate after welding when welding coated steel, and remain as intermetallic compounds. By having these elements present, corrosion resistance and corrosion protection can be improved, as well as the corrosion resistance of the welded part during welding. This improvement in corrosion resistance is evident when the content of at least any one of Sn, Bi, and In in the zinc-based coating 20 is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least any one of Sn, Bi, and In, the content of each of these elements is preferably set to 0.05% by mass or more independently.

[0157] On the other hand, excessive Sn addition increases the amount of intermetallic compounds formed, which may reduce the corrosion resistance of the zinc-based coating 20 after welding. Furthermore, excessive Bi and In addition may make the zinc-based coating 20 brittle and prone to peeling, and may also reduce its corrosion resistance after welding. These phenomena become significant when the Sn content exceeds 20.00% by mass, when the Bi content is 5.00% by mass or more, or when the In content is 2.00% by mass or more. Therefore, the Sn content is preferably 20.00% by mass or less, the Bi content is preferably less than 5.00% by mass, and the In content is preferably less than 2.00% by mass. The Sn content is more preferably 10.00% by mass or less, the Bi content is more preferably 3.00% by mass or less, and the In content is more preferably 1.00% by mass or less.

[0158] ◇Element Group E

[0159] In another embodiment of the zinc-based coating 20, the element group E that may be contained in the zinc-based coating 20 will be described. At least one element in element group E shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0160] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0161] [Ca: ≥0% by mass and ≤3.00% by mass]

[0162] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where it does not contain Ca, and therefore the lower limit of its content is 0% by mass. On the other hand, if Ca is contained in the plating bath used to manufacture the zinc-based coating 20, it is possible to reduce the dross generated during the plating operation as the Mg concentration increases, thereby improving the plating operability.

[0163] Furthermore, if the zinc-based coating 20 contains Ca, it forms intermetallic compounds with Al and Zn. Moreover, if the zinc-based coating 20 contains Si along with Ca, Ca forms intermetallic compounds with Si. These intermetallic compounds have high melting points and stable structures, thus suppressing liquid metal embrittlement (LME) during welding of plated steel. When the zinc-based coating 20 contains Ca, setting the Ca content to 0.01% by mass or more demonstrates both improved coating operability and suppression of LME during welding. More preferably, the Ca content in the zinc-based coating 20 is 0.05% by mass or more.

[0164] On the other hand, if the Ca content in the zinc-based coating 20 exceeds 3.00% by mass, the corrosion resistance of the coated steel may decrease. From this point of view, the Ca content in the zinc-based coating 20 is preferably 3.00% by mass or less. The Ca content in the zinc-based coating 20 is preferably 2.00% by mass or less, and more preferably 1.00% by mass or less.

[0165] [La: 0% by mass and less than 0.50% by mass]

[0166] [Ce: 0% by mass and less than 0.50% by mass]

[0167] [Y: 0% or more by mass and less than 0.50% by mass]

[0168] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where La, Ce, and Y are not present, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit approximately the same effect as Ca. This is because the atomic radii of each element are close to the atomic radius of Ca, and if these elements are present in the zinc-based coating 20, they will displace Ca.

[0169] The improved plating operability and LME suppression during welding are achieved by independently setting the content of each of these elements to 0.01% by mass or more. Therefore, when at least one of La, Ce, and Y is contained, the content of each of these elements is preferably set to 0.01% by mass or more. The content of La, Ce, and Y in the zinc-based coating 20 is more preferably 0.05% by mass or more.

[0170] On the other hand, if the content of La, Ce, and Y in the plating bath used to manufacture the zinc-based coating 20 is too high, the viscosity of the plating bath increases beyond what is necessary, and the plating operability may decrease. Therefore, from the viewpoint of plating operability, the content of La, Ce, and Y in the plating bath is adjusted. The content of La, Ce, and Y is preferably each independently less than 0.50% by mass, less than 0.50% by mass, and less than 0.50% by mass. The content of La, Ce, and Y is preferably each independently less than 0.10% by mass.

[0171] ◇Element group F

[0172] In another embodiment of the zinc-based coating 20, the element group F that may be contained in the zinc-based coating 20 will be described. At least one element in the element group F shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0173] [Element group F]: B: less than 0.50%

[0174] [B: 0% by mass or more and less than 0.50% by mass]

[0175] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where no B is present, and therefore the lower limit of its content is 0% by mass. On the other hand, if the zinc-based coating 20 contains B, it has a further effect of suppressing LME. This is presumably because if the zinc-based coating 20 contains B, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. In addition, it is believed that by having B in the zinc-based coating 20, B diffuses from the zinc-based coating 20 to the steel 10, and through grain boundary strengthening, it has a further effect of suppressing LME of the steel 10. Furthermore, the various intermetallic compounds formed by B have extremely high melting points, so it is presumably also effective in suppressing Zn evaporation during welding. These improved effects are manifested by containing 0.05% by mass or more of B. Therefore, in the case where B is present, the content of B is preferably 0.05% by mass or more.

[0176] On the other hand, if the plating bath contains excessive amounts of B in order to include B in the zinc-based coating 20, it will cause a sharp increase in the plating melting point, reducing the plating operability and potentially making it impossible to produce coated steel with excellent plating properties. This reduction in plating operability becomes significant when the B content is 0.50% by mass or more, therefore the B content is preferably less than 0.50% by mass. The B content is more preferably 0.10% by mass or less.

[0177] Methods for measuring chemical composition

[0178] The chemical composition of the aforementioned zinc-based coating 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). It should be noted that ICP-AES is used for analysis of chemical composition down to 0.1% by mass, while ICP-MS is used for analysis of trace amounts of chemical composition less than 0.1% by mass. The coated steel is immersed in a 10% HCl aqueous solution containing an inhibitor for approximately 1 minute, and the zinc-based coating is peeled off to prepare a solution containing the dissolved zinc-based coating. Analysis of the obtained solution using ICP-AES or ICP-MS yields the overall average chemical composition of the zinc-based coating.

[0179] Regarding the adhesion amount of zinc-based coating 20

[0180] The zinc coating 20 described above is preferably applied at a rate of 10.0 g / m² per single side of the steel. 2 The above, more preferably 50.0 g / m 2 That's all. Furthermore, the adhesion amount of the zinc-based coating 20 is preferably 200.0 g / m² per single side of the steel. 2 Approximately, more preferably 150.0 g / m 2 Therefore, by ensuring that the amount of zinc-based plating 20 adheres within the range described above, the surface-treated component 1 of this embodiment can exhibit sufficient corrosion resistance.

[0181] It should be noted that, regarding the adhesion amount of the zinc-based coating 20, a 30mm × 30mm sample was cut from the surface treatment component 1, and its mass was measured beforehand. Adhesive tape was applied to one side of the sample to seal it, preventing the zinc-based coating on that side from dissolving in the next process. Then, the sample was immersed in a 10% HCl aqueous solution containing an inhibitor to pickle and peel off the zinc-based coating, and the mass of the sample after pickling was measured. Based on the change in sample mass before and after pickling, the adhesion amount of the zinc-based coating 20 on each single side can be determined.

[0182] Regarding the exposed steel substrate portion 201 and exposed area 203 in the zinc-based coating 20

[0183] Next, the exposed steel substrate portion 201 and the exposed area 203 having the exposed steel substrate portion 201, which exist in at least a portion of the zinc-based coating 20 of this embodiment, will be described in detail.

[0184] Figure 4 Indicatively representing that Figure 2 The surface-treated component 1 shown is cut along the BB cutting line in the Z-axis direction. Figure 4 The cross-sectional view shown corresponds to the view obtained by cutting the exposed area 203 of the exposed steel substrate 201 in the surface treatment member 1 of this embodiment along the thickness direction of the zinc-plated steel material that serves as the blank of the surface treatment member 1.

[0185] like Figure 4 As illustrated schematically, in the surface-treated member 1 of this embodiment, the portion having the exposed steel substrate 201 is composed of surface-treated steel (i.e., zinc-plated steel) having a steel 10 as a base material and a zinc-based coating 20 located on the surface of the steel 10. Furthermore, at least a portion of the zinc-based coating 20 has a portion that exposes the surface of the steel 10 (i.e., the steel substrate).

[0186] As briefly mentioned earlier, in this embodiment, the surface treatment member 1 intentionally includes a steel substrate exposed portion 201 in a specific proportion on a portion of the zinc-based coating 20. Therefore, when the portion of the surface treatment member 1 with the exposed steel substrate 201 is embedded in concrete, a dense composite layer, as described above, can be formed on the surface of the zinc-based coating 20 and / or the steel 10. Thus, the surface treatment member 1 of this embodiment exhibits excellent corrosion resistance even in concrete. In summary, the surface treatment member 1 of this embodiment is preferably used such that at least a portion of the exposed area 203 having the exposed steel substrate 201 is embedded in concrete. Furthermore, in the surface treatment member 1 of this embodiment, the exposed area 203 having the exposed steel substrate 201 is preferably provided at a predetermined embedding location in the concrete.

[0187] ◇Method for determining the location of the exposed steel substrate 201

[0188] The following section will first explain the method for determining the location of the exposed steel substrate 201 in the zinc-based coating 20.

[0189] In this embodiment, the exposed steel substrate portion 201 in the zinc-based coating 20 is a location where the steel substrate is exposed due to a deficiency in the zinc-based coating 20. Therefore, its location can be determined by performing various color development tests on the entire surface of the zinc-based coating 20 to cause a color development reaction in the exposed steel substrate portion.

[0190] Such colorimetric tests are not particularly limited, and various colorimetric tests can be applied. For example, the ferroxyl test specified in JISH 8626 (1995) is preferred, or the pinhole test disclosed in non-patent literature (Shozo Matsuda, Tadashi Tanaka, Keiichi Tanikawa, "A New Pinhole Test Method for Galvanized Steel Sheets", Metal Surface Technology, Vol. 23 (1972), pp. 142-146). In the above two colorimetric tests, after the reagent used for the colorimetric reaction is applied to the surface of the test object and a colorimetric reaction occurs, the surface of the test object is covered with test paper, and the area where the colorimetric reaction occurs is transferred to the test paper. Therefore, by using these colorimetric tests, the location of the exposed portion 201 of the steel substrate can be determined without depending on the shape of the surface-treated component 1.

[0191] Regarding the various reagents used in the colorimetric test, the test paper used for transferring the colorimetric site, and the steps of the colorimetric test, as long as they comply with the provisions in the literature that discloses each test method, they are acceptable.

[0192] ◇Regarding the state of the exposed steel substrate 201

[0193] Next, the state of the steel substrate exposed portion 201 in the zinc-based coating 20 of this embodiment will be described.

[0194] In the surface-treated component 1 of this embodiment, the presence state of the exposed steel substrate 201 in the zinc-based coating 20 is determined by observing the cross-section of the zinc-based coating 20. More specifically, it is determined from above (e.g., from...) Figure 2 The shape of the exposed steel substrate 201 when viewed from above (Z-axis direction) with the zinc-based coating 20 is determined by observing the cross-section obtained by cutting the exposed steel substrate 201 along the thickness direction of the steel 10 using a microscope. The microscope used is not particularly limited as long as it can achieve a magnification sufficient for cross-sectional observation. The microscope used for observation can be an optical microscope or an electron microscope such as a SEM.

[0195] In this embodiment, the cross-section obtained as described above is observed under a microscope to verify the existence of the cross-section of regions such as "Region A" and "Region B" as detailed below, thereby evaluating the existence of the exposed steel substrate 201.

[0196] The following is for reference Figures 5-8 The more specific steps will be explained. Figures 5-8 This is an explanatory diagram illustrating the exposed steel substrate 201 in the surface treatment component of this embodiment.

[0197] When confirming the presence of the exposed steel substrate 201, such as Figure 5 As shown in the upper left, firstly, a colorimetric test as described above is performed on the entire surface of the zinc-based coating 20 to determine the location of the exposed steel substrate 201. Then, as... Figure 5 As shown in the lower left, from above the zinc coating 20 ( Figure 2 Viewed from above along the Z-axis, each of the defined exposed steel substrate portions 201 is virtually divided. In this division, the shorter side b is 5 mm in size and its area (the area obtained by multiplying the longer side a by the shorter side b) is 1 cm². 2 The rectangular area is used as the unit for division.

[0198] Next, for each virtually divided region (a rectangular region), the area proportion occupied by the exposed steel substrate 201 in that region is calculated. For all regions, the proportion of the exposed steel substrate 201 in each region (area 1 cm²) is determined. 2 Does the area occupied by ) account for more than 3%?

[0199] Next, areas where the area ratio of all exposed steel substrate 201 is 3% or more (rectangular areas) are set as follows: Figure 5 The object area observed in the cross-section shown in the lower right corner. For example... Figure 5 As schematically shown in the lower right corner, the surface-treated component 1 corresponding to the area of ​​interest was cut at intervals of Δ = 50 μm. Microscopic observation was performed on all obtained cross-sections to verify the presence of the exposed steel substrate 201. It should be noted that regarding... Figure 5 The cutting direction shown in the lower right corner is used to obtain the cross-section. Refer to the following: Figure 8 Let me explain again.

[0200] Through microscopic observation as described above, it is possible to obtain, for example, information about each cross-section. Figure 6The observation field of view is shown schematically. Here, in the microscopic observation described above, an optical microscope (e.g., Nikon ECLIPSE LV150) is used, and a magnification of approximately 100x is selected. Furthermore, the size of the observation field is set to 1.5mm × 2.0mm.

[0201] Here, in the cross-section obtained as described above, when observing any 1.5mm × 2.0mm portion under a microscope, the portion in the field of view where the surface of the zinc-based coating 20 exists with a length of 0.5mm or more along the width direction orthogonal to the thickness direction of the steel 10 is called the "residual coating portion". Based on this, the area containing the exposed steel substrate portion 201 located between two adjacent residual coating portions is defined as "region A".

[0202] exist Figure 6 In the example shown, the width length of the leftmost zinc-based coating 20 block and the width length of the rightmost zinc-based coating 20 block are both set to 0.5 mm or more. In this case, the portion between the leftmost and rightmost zinc-based coating 20 blocks in the figure becomes... Figure 6 The portion corresponding to "Region A" in the illustrated field of view.

[0203] In the zinc-based coating 20 of this embodiment, the length in the width direction of the exposed steel substrate 201 in region A, as defined above, is in the range of 1.0 to 100.0 μm. Figure 6 In the example shown, there are 5 exposed steel substrates 201 in region A, but the lengths L1, L2, L3, L4 and L5 of each exposed steel substrate 201 in the width direction are in the range of 1.0~100.0μm.

[0204] When the length in the width direction of each exposed steel substrate portion 201 in region A is less than 1.0 μm, the surface exposure of the steel 10 is too low. As a result, when the exposed region 203 of the surface-treated component 1 is placed in concrete, a dense composite layer as described above cannot be formed, and the desired corrosion resistance cannot be achieved. By making the length in the width direction of each exposed steel substrate portion 201 in region A 1.0 μm or more, corrosion resistance in concrete can be achieved. The length in the width direction 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.

[0205] On the other hand, when the length in the width direction of each exposed steel substrate 201 in region A exceeds 100.0 μm, the surface of the steel 10 is excessively exposed. As a result, even if a dense composite layer as described above is locally formed in the exposed region 203 of the surface-treated member 1 in concrete, the desired corrosion resistance cannot be achieved. By making the length in the width direction of each exposed steel substrate 201 in region A 100.0 μm or less, corrosion resistance in concrete can be achieved. The length in the width direction of each exposed steel substrate 201 in region A is preferably 90.0 μm or less, more preferably 70.0 μm or less.

[0206] Furthermore, in the zinc-based coating 20 of this embodiment, in region A as defined above, the sum of the width-direction lengths of the exposed steel substrate 201 per unit length is 600.0 μm / mm or less. When the sum of the width-direction lengths of the exposed steel substrate 201 per unit length exceeds 600.0 μm / mm, the surface of the steel 10 is excessively exposed. As a result, even if a dense composite layer as described above is locally formed when the exposed area 203 of the surface-treated member 1 is placed in concrete, the desired corrosion resistance cannot be achieved. By ensuring that the sum of the width-direction lengths of the exposed steel substrate 201 per unit length is 600.0 μm / mm or less, Fe from the exposed steel substrate 201 and Zn from the zinc-based coating 20 are supplied at an appropriate supply rate, and a dense composite layer as described above is appropriately formed, the desired corrosion resistance can be achieved.

[0207] exist Figure 6 In the example shown, there are 5 exposed steel substrate portions 201 in region A, with width-direction lengths of L1, L2, L3, L4, and L5 for each portion, and width-direction length of region A is L0 [mm]. In this case, the sum of the width-direction lengths of each unit length of exposed steel substrate portion 201 is given by {(L1+L2+L3+L4+L5) / L0}.

[0208] The sum of the lengths in the width direction of the exposed steel substrate portion 201 per unit length is preferably 550.0 μm / mm or less, more preferably 500.0 μm / mm or less.

[0209] On the other hand, there is no particular specification for the lower limit of the sum of the lengths in the width direction of the exposed steel substrate 201 per unit length. However, if the sum of the lengths in the width direction of the exposed steel substrate 201 per unit length is less than 100.0 μm / mm, the degree of exposure of the surface of the steel 10 is too low. As a result, when the exposed area 203 of the surface-treated member 1 is placed in concrete, it may be impossible to form the dense composite layer as described above, and the desired corrosion resistance cannot be achieved. Therefore, the sum of the lengths in the width direction of the exposed steel substrate 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.

[0210] Furthermore, in the zinc-based coating 20 of this embodiment, the number of exposed steel substrate portions 201 per unit length in the width direction within region A as defined above is in the range of 3.0 to 20.0 portions / mm. When the number of exposed steel substrate portions 201 per unit length is less than 3.0 portions / mm, the surface exposure of the steel 10 is too low. As a result, when the exposed area 203 of the surface-treated member 1 is placed in concrete, a dense composite layer as described above cannot be formed, and the desired corrosion resistance cannot be achieved. By ensuring that the number of exposed steel substrate portions 201 per unit length in the width direction is 3.0 portions / mm or more, Fe from the exposed steel substrate portions 201 and Zn from the zinc-based coating 20 are appropriately supplied, and a dense composite layer as 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 per mm, and more preferably 10.0 or more per mm.

[0211] On the other hand, when the number of exposed steel substrate portions 201 per unit length in the width direction exceeds 20.0 per mm, the surface of the steel 10 is excessively exposed. As a result, even if a dense composite layer as described above is locally formed when the exposed area 203 of the surface-treated member 1 is placed in concrete, the desired corrosion resistance cannot be achieved. By reducing the number of exposed steel substrate portions 201 per unit length in the width direction to 20.0 per 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 per mm or less, and more preferably 15.0 per mm or less.

[0212] exist Figure 6In the example shown, there are 5 exposed steel substrate portions 201 in region A, and the length of region A in the width direction is L0 [mm]. In this case, the number of exposed steel substrate portions 201 per unit length is given by (5 / L0).

[0213] It should be noted that, in region A where the above conditions are met, the average length of the exposed steel substrate 201 is preferably in the range of 30.0 to 80.0 μm. By ensuring that the average length of the exposed steel substrate 201 is in the range of 30.0 to 80.0 μm, the surface-treated component of this embodiment can further improve corrosion resistance in concrete. More preferably, the average length of the exposed steel substrate 201 in region A is in the range of 50.0 to 70.0 μm.

[0214] Furthermore, in region A, which is sandwiched between two remaining plating portions as described above, the areas within the exposed steel substrate 201 where plating is retained in an island-like pattern 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 in 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, the Zn supply can be more appropriate, and a denser composite layer can be formed. The average length of the island-shaped plating portions in region A is more preferably 50.0 μm or more.

[0215] On the other hand, by making the average length of the island-shaped plating portion in region A 300.0 μm or less, the supply of Fe from the steel can be maintained at an appropriate level, and the supply of Zn can be made more appropriate, resulting in a denser composite layer. The average length of the island-shaped plating portion in region A is more preferably 200.0 μm or less.

[0216] For example in Figure 6 In the example shown, there are 4 island-shaped plating areas in region A, and the sum of the lengths of the island-shaped plating areas is given by {L0 - (L1 + L2 + L3 + L4 + L5)}. Therefore, Figure 6 The average length of the island-shaped plating in region A in the example shown is given by {L0-(L1+L2+L3+L4+L5)} / 4.

[0217] It should be noted that the various lengths in the field of view described above can be measured using the length measuring function of the microscope being used.

[0218] Furthermore, in the exposed area 203 of the zinc-based coating 20 in this embodiment, when observing the cross-section as described above under a microscope, the area where the sum of the lengths of the exposed steel substrate 201 per unit length in the width direction is 600.0 μm / mm or less is defined as "area B". That is, area B refers to the area where, as in... Figure 6For example, in region A as defined, the sum of the lengths in the width direction of the exposed steel substrate 201 per unit length is less than 600.0 μm / mm.

[0219] In the zinc-based coating 20 of this embodiment, the sum of the areas of each region B as defined above when viewed from above is 0.7% or more of the surface area of ​​the steel 10 when viewed from above. When the sum of the areas of regions B when viewed from above is less than 0.7%, the surface of the steel 10 is exposed too little. As a result, when the exposed area 203 of the surface-treated member 1 is placed in concrete, a dense composite layer as described above cannot be formed, and the desired corrosion resistance cannot be achieved. By ensuring that the sum of the areas of regions B when viewed from above is 0.7% or more, the desired corrosion resistance in concrete can be achieved. The sum of the areas of regions B when viewed from above is preferably 3.0% or more, and more preferably 5.0% or more.

[0220] On the other hand, the upper limit of the sum of the areas of region B when viewed from above can be 100.0%, but it is preferably substantially set to 40.0% or less. By making the sum of the areas of region B when viewed from above 40.0% or less, the corrosion resistance of the concrete can be further improved. The sum of the areas of region B when viewed from above is more preferably 30.0% or less, more preferably 20.0% or less, and even more preferably 15.0% or less.

[0221] Here, the sum of the areas of region B as described above when viewed from above can be determined as follows. That is, by observing... Figure 6 By illustrating such a cross-section, the cross-section of region B can be determined, and the sum of the lengths in the width direction of the exposed steel substrate 201 per unit length in region B can be determined. On the other hand, as... Figure 5 As explained, the cross-section for cross-sectional observation is obtained by cutting the surface-treated component 1 of interest at intervals of Δ = 50 μm. Therefore, the value obtained by multiplying the sum of the width-direction lengths of the exposed steel substrate 201 per unit length in region B obtained from the cross-sectional observation by the cross-sectional observation interval Δ = 50 μm can be regarded as the area of ​​region B when viewed from above, corresponding to the cross-section of interest. By performing this processing, the sum of the areas of region B when viewed from above can be calculated.

[0222] ◇Regarding the direction of the cutting line when observing the cross-section

[0223] Here, refer to Figure 7The direction of the cutting line when performing the cross-sectional observation as described above will be explained. In this embodiment, when determining the exposed steel substrate 201 in the surface-treated member 1, the surface-treated member 1 is cut along the thickness direction of the steel 10 in order to obtain the cross-section as described above. At this time, the direction of the cutting line is determined based on the shape and / or distribution of the exposed steel substrate 201 when viewed from above in relation to the zinc-based coating 20.

[0224] Figure 7 This diagram categorizes examples of the shape and / or distribution of the exposed steel substrate 201 when viewed macroscopically from above (Z-axis direction) the zinc-based coating 20. In the surface-treated component 1 of this embodiment, the shape and / or distribution of the exposed steel substrate 201 are broadly classified into... Figure 7 The previous section showed a set of directional cases, and Figure 7 The next section shows a set of cases with isotropic shapes, or cases where the shape and / or distribution are not directional.

[0225] exist Figure 7 In the group shown above, the exposed steel substrate 201 is roughly elliptical in shape and distributed in a manner that is roughly parallel to the direction of its respective major axis. Figure 7 The upper section, left end of the diagram), the exposed steel substrate 201 is roughly rectangular in shape and distributed in a manner where their respective long sides are roughly parallel. Figure 7 Like the diagrams at the top, center, and right, there exists a directional orientation. Figure 7 In the case of the upper section (the direction is up and down on the paper). In this case, in this embodiment, the direction orthogonal to the directional orientation is set as the direction of the cutting line.

[0226] in addition, Figure 7 The following section shows a distribution of exposed steel substrate 201 in a circular shape. Figure 7 The lower section, the left-hand diagram), shows the random distribution of the exposed square-shaped steel substrate 201. Figure 7 The lower section, the central diagram), shows the distribution of zinc-based coating 20 in an island-like pattern. Figure 7 As shown in the lower right figure, the exposed steel substrate 201 may have an isotropic shape or a shape and / or distribution that is not directional. In such cases, the direction of the cutting line is not particularly specified in this embodiment, and any direction may be used as the direction of the cutting line.

[0227] Above, refer to Figures 2-7 The surface treatment component 1 of this embodiment is described in detail.

[0228] It should be noted that the above description describes the case where the surface treatment component 1 of this embodiment is disposed in concrete, but the surface treatment component 1 of this embodiment can also be applied in environments other than concrete where Ca is present and alkalinity is exhibited.

[0229] (Regarding composite structures)

[0230] Next, refer to Figure 8 and Figure 9 The composite structure of the surface-treated component and concrete described in the above embodiment will be explained. Figure 8 and Figure 9 This is an explanatory diagram used to illustrate the composite structure of this embodiment.

[0231] like Figure 8 As illustrated, the composite structure 5 of this embodiment is a structure formed by combining the surface-treated component 1 of this embodiment described above with concrete. As described above, at least a portion of the surface of the zinc-based coating 20 of the surface-treated component 1 has an exposed area 203 with an exposed steel substrate 201. In the composite structure 5 of this embodiment, at least a portion of this exposed area 203 is in contact with concrete, thus forming a composite state between the surface-treated component 1 and concrete.

[0232] Here, the concrete of interest in the composite structure 5 of this embodiment includes not only various types of concrete, represented by "ready-mixed concrete" as specified in JIS A5308 (2019), but also similar materials such as steel slag hydrate solidified bodies, which contain a large amount of Ca and exhibit alkalinity.

[0233] Figure 9 Indicatively representing that Figure 8 The cross-section of the composite structure 5 shown is cut along the CC cutting line in the Z-axis direction. Figure 9 The cross-sectional view shown corresponds to the view obtained by cutting the exposed area 203 in contact with the concrete along the thickness direction of the zinc-plated steel blank used as the surface treatment member 1 in the composite structure 5 of this embodiment.

[0234] like Figure 9 As illustrated, in the composite structure 5 of this embodiment, the exposed area 203 that is in contact with the concrete is composed of surface-treated steel and concrete. The surface-treated steel has a steel 10, a zinc-based coating 20 on the surface of the steel 10, and an exposed steel substrate 201 that exists in a part of the zinc-based coating 20.

[0235] Furthermore, in the exposed area 203 in contact with concrete, preferably at least a Fe-Zn-Ca composite layer 50 containing Fe, Zn, and Ca is present at the interface between the zinc-based coating 20 and the concrete, or at least a portion of the interface between the steel 10 and the concrete. Additionally, as... Figure 9 As illustrated, the Fe-Zn-Ca composite layer 50 is preferably formed at both the interface between the zinc coating 20 and the concrete, and the interface between the steel 10 and the concrete.

[0236] Here, the steel 10 in the composite structure 5 of this embodiment has the same structure as the steel 10 in the surface treatment member 1 described above, and exhibits the same effect, so the description is omitted below.

[0237] Furthermore, regarding the zinc-based plating 20 in the composite structure 5 of this embodiment and the exposed steel substrate 201 present in the zinc-based plating 20, since they have the same structure as the zinc-based plating 20 and the exposed steel substrate 201 in the surface treatment member 1 described above, the description is omitted below.

[0238] It should be noted that in the interface portion of the zinc-based coating 20 in the composite structure 5 that is in contact with the concrete, due to the interdiffusion of components between the coating and the concrete, the chemical composition of the interface portion is considered to change relative to the chemical composition of the zinc-based coating 20 in the portion not in contact with the concrete. However, the average composition of the zinc-based coating 20 as a whole is the same as the chemical composition of the zinc-based coating 20 in the surface-treated component 1 described above.

[0239] The Fe-Zn-Ca composite layer 50 is a layer composed of reactants generated by the reaction of Fe from the steel 10, Zn from the zinc coating 20, and Ca from the concrete. Furthermore, the Fe-Zn-Ca composite compound generated through this reaction differs from the Ca-Zn composite compound in that it has a dense structure. Therefore, by having this Fe-Zn-Ca composite layer 50 present at at least a portion of the interface between the zinc coating 20 and the concrete, or at least a portion of the interface between the steel 10 and the concrete, the composite structure 5 of this embodiment exhibits excellent corrosion resistance in concrete.

[0240] The Fe-Zn-Ca composite layer 50 is preferably a layer having the following chemical composition: by mass%, it contains Fe: 1.0% or more and 20.0% or less, Zn: 10.0% or more and 40.0% or less, Ca: 5.0% or more and 15.0% or less, with the balance being H, C, O and impurities. The Fe-Zn-Ca composite layer 50 is composed of a Fe-Zn-Ca composite compound having the chemical composition described above, thereby the composite structure 5 of this embodiment exhibits superior corrosion resistance in concrete.

[0241] Furthermore, when the zinc-based coating 20 contains Al and Mg in its chemical composition, the Fe-Zn-Ca composite layer 50 preferably also contains at least one of Al: 0% or more and 10.0% or less, and Mg: 0% or more and 10.0% or less, to replace a portion of the balance of H, C, and O as described above. The Fe-Zn-Ca composite layer 50 is composed of a Fe-Zn-Ca composite compound having the chemical composition described above, thereby the composite structure 5 of this embodiment exhibits superior corrosion resistance in concrete.

[0242] Above, refer to Figure 8 and Figure 9 The composite structure 5 of this embodiment has been described.

[0243] (Regarding the manufacturing method of surface-treated components)

[0244] Hereinafter, an example of the manufacturing method of the surface treatment component 1 of this embodiment will be described.

[0245] <Manufacturing Method of Surface-Treated Steel as Raw Material>

[0246] The surface-treated steel used as the blank for the surface-treated component 1 in this embodiment is manufactured by forming a zinc-based coating on the surface of the steel 10 as described above, using the steel 10 as the base material.

[0247] In the formation of zinc-based coatings, in addition to hot-dip galvanizing, spraying, cold spraying, sputtering, vapor deposition, and electroplating can also be used. However, hot-dip galvanizing is the most cost-effective method.

[0248] Then, by performing the specific processing described below on the desired location (more specifically, the part where the exposed steel substrate is formed) of the obtained coated steel (steel 10 with a zinc-based coating), the exposed steel substrate is formed in the zinc-based coating. Thus, it is possible to manufacture a surface-treated steel blank as the surface-treated component 1 of this embodiment.

[0249] Hereinafter, an example of a method for manufacturing the surface-treated steel of this embodiment using hot-dip galvanizing will be described in detail.

[0250] In the manufacturing process of this surface-treated steel, firstly, a steel plate, which is used as a base material, is rolled to the desired thickness using the Sendzimir method, then coiled and placed on the hot-dip galvanizing production line.

[0251] In a hot-dip galvanizing production line, steel sheets are continuously passed through while being drawn from coils. At this time, the steel sheets are subjected to a reduction treatment at 800°C in an annealing device installed on the production line, for example, in an environment where oxidation is unlikely to occur (oxygen concentration below 20 ppm) and an atmosphere of N2-5% H2 gas. Afterward, the steel sheets are air-cooled with N2 gas to approximately +20°C the temperature of the subsequent plating bath, and then immersed in the plating bath.

[0252] Here, in the plating bath, a plating alloy having the chemical composition described above and in a molten state is prepared in advance. The bath temperature is set in advance above the melting point of the plating alloy (for example, around 460~660°C).

[0253] When preparing the material for the plating alloy, it is preferable to use a pure metal (purity of 99% or higher) as the alloying material. First, a specified amount of alloy metal is mixed in such a way that it becomes the composition of the coating as described above. The mixture is then completely melted in a high-frequency induction furnace and / or an electric arc furnace under vacuum or inactive gas purging conditions to form the alloy. Next, the alloy mixed with the specified composition (the composition of the coating described above) is dissolved in the atmosphere, and the resulting melt is used as the plating bath.

[0254] It should be noted that the above-described plating alloys are not restricted to using pure metals; existing Zn alloys, Mg alloys, and Al alloys can also be melted and used. In this case, as long as a specified composition alloy with few impurities is used, there will be no problem.

[0255] The steel sheet is immersed in the plating bath as described above, and then lifted at a specified speed. At this time, the amount of plating is controlled, for example, by using N2 wiping gas, to ensure that the formed zinc-based coating reaches the desired thickness. Here, except for the bath temperature, general plating operating conditions can be applied; no special equipment and / or conditions are required.

[0256] In addition, various heat treatments can be applied to the molten alloy coating on the steel plate as needed.

[0257] Then, the zinc-based coating is subjected to scratching or bending treatments at the desired locations on the manufactured surface-treated steel. As a result, the treated areas form exposed steel substrate portions 201.

[0258] For example, when forming the exposed steel substrate 201 through a scratching process, a blade with a tip width of 30 μm or less, a length of 50 μm or more, and sufficient hardness compared to the coated structure is used. The blade is pressed perpendicularly to the steel plate. Then, a certain amount of pressure is applied along the direction the blade penetrates the steel plate. By moving the blade linearly in this state, scratches are created on the surface of the zinc-based coating. The exposed steel substrate rate can be varied depending on the number of scratches per unit area. Furthermore, even without changing other manufacturing conditions, by using a blade with a wider tip as described above to create scratches, the shortest distance from any point of the exposed steel substrate to the zinc-based coating can be controlled to the desired condition by utilizing the blade deflection caused by pressure and the vibration of the blade caused by movement.

[0259] Here, as a method of applying pressure to the blade, consider adding a weight of 3 kg or 5 kg. This pressure is sufficient to scratch zinc-based coatings, but will hardly scratch steel. Furthermore, there is no particular limitation on the speed at which the blade moves. It should be noted that, in the case of the blade sliding against the steel, from the viewpoint of preventing the inability to form scratches, there are methods such as setting the blade movement speed to 50 cm / s or less.

[0260] Alternatively, for example, when the exposed steel substrate 201 is formed by bending, the winding method using a shaft or a die as specified in JIS Z2248 (2022) can be used. Here, the shaft is a cylinder with radius R, and the top end of at least one side of the die is not an acute angle but has a rounded corner with radius R (unit: mm).

[0261] The shaft or mold described above is positioned near the center of the desired coated steel. After fixing one side of the coated steel, the other side is wound around the shaft or mold to process the zinc coating. At this time, by controlling the plate thickness t (unit: mm) of the coated steel, the radius R (unit: mm) of the top of the shaft or mold, and the bending speed V (unit: cm / s), the steel substrate exposed portion 201 can be formed at the desired position of the zinc coating.

[0262] At this point, the processing is controlled such that the ratio t / R of the plate thickness t to the radius R of the top end of the shaft or mold satisfies the relationship 0.6 ≤ t / R ≤ 4.0. By setting such processing conditions, a large elongation is applied to the zinc-based coating, which can generate coating cracks and make the state of the exposed steel substrate 201 more ideal. In addition, the speed V of winding the coated steel on the shaft or mold is set to 1 cm / s or less. In this way, by reducing the processing speed to its limit, the generation of large local cracks can be suppressed, and the size of the exposed steel substrate 201 can be controlled.

[0263] The above provides a detailed description of an example of the manufacturing method for surface-treated steel according to this embodiment.

[0264] <Manufacturing Method of Surface-Treated Components>

[0265] Using the surface-treated steel obtained as described above as a blank, the surface-treated component of this embodiment is manufactured. Here, when obtaining the component for manufacturing the surface-treated component from the surface-treated steel, various forming processes, and / or joining processes based on fastening components such as bolts and / or rivets, and / or welding processes, etc., can be utilized. By appropriately combining these processes, it is possible to manufacture a surface-treated component with a desired shape from the surface-treated steel.

[0266] The above provides a brief description of an example of the manufacturing method of the surface-treated component according to this embodiment.

[0267] It should be noted that the above description describes the case where strain-imposing treatment is applied to the surface-treated steel to form the exposed steel substrate 201. However, strain-imposing treatment may not be performed during the manufacturing stage of the surface-treated steel, but may be performed as part of the processing when manufacturing the surface-treated component from the surface-treated steel. Alternatively, the processing itself when manufacturing the surface-treated component from the surface-treated steel may be used as the strain-imposing treatment for forming the exposed steel substrate 201.

[0268] (Regarding the manufacturing method of composite structures)

[0269] There are no particular limitations on the manufacturing method of the composite structure of this embodiment. For example, it is sufficient to embed at least a portion of the exposed area 203 of the surface-treated member 1 with the exposed steel substrate 201 in concrete and thereby bring the surface-treated member 1 into contact with the concrete.

[0270] Example

[0271] Hereinafter, the surface-treated components and composite structures of the present invention will be specifically described with reference to embodiments and comparative examples. It should be noted that the embodiments shown below are merely examples of the surface-treated components and composite structures of the present invention, and the surface-treated components and composite structures of the present invention are not limited to the examples described below.

[0272] In the test examples shown below, the base plates for plating shown in Table 1 (all manufactured by Nippon Steel Corporation) were cut into 100mm x 200mm pieces. Then, plating was performed using an intermittent hot-dip galvanizing test apparatus manufactured by our company, and multiple coated steel samples with the coating compositions shown in Table 2 were produced for each level. It should be noted that in Table 2 below, "%" refers to mass%.

[0273] [Table 1]

[0274]

[0275] [Table 2]

[0276]

[0277] The obtained coated steel is subjected to scratching or bending processes as described above on approximately the central part of the surface of the coating to form an exposed steel substrate, thus producing a surface-treated component.

[0278] In the scratching process, a cutting tool hard enough than the coating is used to create parallel, straight scratches. The desired exposed steel substrate is achieved by adjusting the maximum width of the cutting tool tip within a 50μm range and the spacing between the parallel scratches. It should be noted that the counterweight for applying pressure to the cutting tool is set to 5kg, and the cutting tool movement speed is set to 50cm / second. Through this scratching process, a surface treatment component is formed approximately in the central portion of its surface. Figure 7 The upper right figure shows the directional exposed steel substrate.

[0279] In addition, as a bending process, a bending process using the winding method according to JIS Z2248 (2022) was implemented. During the bending process, the thickness t (in mm) of the plated steel, the radius R (in mm) of the shaft or die, and the bending speed V (in cm / s) were controlled to obtain the desired steel substrate exposure rate. Through such a bending process, a shape is formed approximately in the central portion of the surface of each surface-treated component. Figure 7 The central diagram at the top shows the directional exposed steel substrate.

[0280] For the surface-treated components obtained through the two processing methods described above, the following measurements were taken according to the cross-sectional observation method previously described: the length of the exposed steel substrate width, the number of exposed steel substrates per unit length, the sum of the widths of exposed steel substrates per unit length in region A, and the area ratio of region B. Here, as a colorimetric test, the iron reagent test specified in JISH 8626 (1995) was performed. Furthermore, as an optical microscope, an ECLIPSELV150 manufactured by Nikon Corporation was used, with a magnification set to 200x.

[0281] The results for cases where scratching was performed are summarized in Tables 3-1 to 3-5 below, and the results for cases where bending was performed are summarized in Tables 4-1 to 4-5 below. It should be noted that in Tables 3-1 to 4-5 below, the "Coating Adhesion Amount" column indicates the coating adhesion amount per single side. Additionally, in Tables 3-1 to 4-5 below, the "Total Length of Exposed Steel Substrate per Unit Length" column indicates the maximum value among multiple values ​​obtained at each level.

[0282] The corrosion resistance of each surface-treated component was evaluated using the following test methods.

[0283] (Test method: Evaluation of corrosion resistance in concrete)

[0284] In the surface-treated component with adjusted steel substrate exposure as described above, corrosion resistance was evaluated by embedding it 100 mm along its long axis in concrete. Ordinary Portland cement with a water-cement ratio of 64.4% was used as the concrete. The coating thickness (distance from the zinc coating surface to the concrete surface) was set to 60 mm. After embedding, accelerated testing (JASO M609, 30 cycles) was conducted.

[0285] After the above-described experiments, the surface-treated component was removed from the concrete. A qualitative analysis of the constituent elements and chemical composition of the Fe-Zn-Ca composite layer at the interface between the surface-treated component and the concrete was performed using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) (Hitachi Advanced Technology Co., Ltd. SU6600 scanning electron microscope system). It should be noted that in Tables 3-1 to 4-5 below, the chemical composition of the Fe-Zn-Ca composite layer is expressed as % by mass, with the balance being H, C, O, and impurities.

[0286] The surface-treated components subjected to the above tests were pickled with hydrochloric acid to remove the zinc plating and corrosion products. Then, the corrosion condition of the steel was investigated using a shape measuring machine (KEYENCE, VR-5000). The evaluation criteria are as follows. Scores A, B, and C were set as acceptable. The results are summarized in Tables 3-1 to 4-5 below.

[0287] Rating A: No pits were formed in the steel.

[0288] B: The steel has formed pits with a depth of less than 10 μm.

[0289] C: The steel has formed pits with a depth of more than 10μm and less than 50μm.

[0290] D: The steel has formed pits with a depth of more than 50μm and less than 100μm.

[0291] E: The steel has formed pits with a depth of more than 100μm.

[0292] [Table 3-1]

[0293]

[0294] [Table 3-2]

[0295]

[0296] [Table 3-3]

[0297]

[0298] [Table 3-4]

[0299]

[0300] [Table 3-5]

[0301]

[0302] [Table 4-1]

[0303]

[0304] [Table 4-2]

[0305]

[0306] [Table 4-3]

[0307]

[0308] [Table 4-4]

[0309]

[0310] [Table 4-5]

[0311]

[0312] As can be seen from Tables 3-1 to 4-5 above, the surface-treated components corresponding to the embodiments of the present invention exhibit excellent corrosion resistance even in concrete. On the other hand, the surface-treated components corresponding to the comparative examples of the present invention cannot achieve sufficient corrosion resistance.

[0313] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to these examples. Various modifications and alterations will be readily apparent to anyone skilled in the art to which this invention pertains, within the scope of the technical concept set forth in the claims, and these are, of course, also understood to fall within the technical scope of this invention.

[0314] The embodiments disclosed herein are illustrative and not restrictive in all respects. The above embodiments can be omitted, substituted, or modified in various ways without departing from the appended claims, the technical scope and spirit of the invention as described below. For example, the constituent elements of the above embodiments can be arbitrarily combined without impairing their effects. Furthermore, based on such arbitrary combinations, the functions and effects of each constituent element involved in the combination can naturally be obtained, and according to the description herein, other functions and effects that can be understood by those skilled in the art can be obtained.

[0315] Furthermore, the effects described in this specification are merely illustrative or exemplary and not limiting. That is, the technology involved in this invention can achieve other effects, in addition to those described above, or in place of those described above, that are obvious to those skilled in the art based on the description herein.

[0316] It should be noted that the following configurations also fall within the technical scope of this invention. (1)

[0318] A surface-treated component is composed of surface-treated steel having steel as a base material and a zinc-based coating on the surface of the steel.

[0319] At least a portion of the zinc-based coating has exposed areas, and these exposed areas have exposed portions of the steel substrate that expose the surface of the steel.

[0320] When a section of the exposed area, obtained by cutting along the thickness direction of the steel material based on the shape of the exposed portion of the zinc-based coating when viewed from above, is examined under a microscope, any portion measuring 1.5 mm × 2.0 mm is examined.

[0321] In the aforementioned field of view, a portion of the surface of the zinc-based coating that has a length of 0.5 mm or more in the width direction orthogonal to the thickness direction of the steel is referred to as a plating residue portion. When region A is defined as the area containing the exposed steel substrate located between two adjacent plating residue portions, in region A, the width direction length of the exposed steel substrate portions is in the range of 1 to 100 μm, the number of exposed steel substrate portions per unit length in the width direction is in the range of 3 to 20 per mm, and the sum of the width direction lengths of the exposed steel substrate portions per unit length in the width direction is 600 μm or less.

[0322] When observing the cross section under a microscope in the exposed area, when the area of ​​the cross section in which the length of the exposed steel substrate per unit length in the width direction is 600 μm / mm or less is defined as region B, the sum of the areas of each of the above regions B when viewed from above is 0.7% or more of the surface area of ​​the steel when viewed from above. (2)

[0324] The surface treatment component according to (1) is used by embedding at least a portion of the exposed area in concrete. (3)

[0326] According to the surface treatment component described in (1) or (2), wherein,

[0327] The exposed portion of the steel substrate was determined by performing a colorimetric test on the entire surface of the zinc-based coating, causing a colorimetric reaction in the exposed portion of the steel substrate.

[0328] When viewed from above the zinc-based coating, each exposed portion of the aforementioned steel substrate has a shorter side of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each of the above-mentioned exposed steel substrates. For each partition where the area ratio of the exposed steel substrate in the rectangular area is 3% or more, the cross section of the partition is observed. (4)

[0330] The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%,

[0331] Al: ≥0.10% and <40.00%

[0332] Mg: ≥0.10% and <15.00%,

[0333] The balance consists of Zn and impurities. (5)

[0335] According to the surface-treated component described in (4), wherein the zinc-based coating contains, by mass%, %

[0336] Al: ≥0.10% and <40.00%

[0337] Mg: ≥0.10% and <15.00%

[0338] Zn: 60.00% or more of the coating. (6)

[0340] The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%,

[0341] Al: ≥0.10% and <40.00%

[0342] Mg: ≥0.10% and <15.00%,

[0343] It also contains one or more elements selected from the following groups: A, B, C, D, E, and F, with the balance being Zn and impurities.

[0344] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%;

[0345] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%;

[0346] [Element Group C]: Selected from one or more elements in 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%.

[0347] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%;

[0348] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0349] [Element group F]: B: less than 0.50%. (7)

[0351] The surface-treated component according to (6) contains the above-mentioned element group A. (8)

[0353] The surface-treated component according to (6) contains the above-mentioned element group B. (9)

[0355] The surface-treated component according to (6) contains the above-mentioned element group C. (10)

[0357] The surface-treated component according to (6) contains the above-mentioned element group D. (11)

[0359] The surface-treated component according to (6) contains the above-mentioned element group E. (12)

[0361] The surface-treated component according to (6) contains the above-mentioned element group F. (13)

[0363] The surface-treated component according to any one of (6) to (12), wherein the zinc-based coating contains at least [amount] by mass%.

[0364] Al: 4.0% or more but less than 25.0%

[0365] Mg: Coating with a content of 0.3% or more but less than 12.5%. (14)

[0367] A composite structure is a composite structure of a surface-treated component and concrete, wherein the surface-treated component is composed of surface-treated steel having steel as a base material and a zinc-based coating on the surface of the steel.

[0368] At least a portion of the zinc-based coating has an exposed area, which has an exposed portion of the steel substrate that exposes the surface of the steel, and at least a portion of the exposed area is in contact with concrete.

[0369] When a section of the exposed area, obtained by cutting along the thickness direction of the steel material based on the shape of the exposed portion of the zinc-based coating when viewed from above, is examined under a microscope, any portion measuring 1.5 mm × 2.0 mm is examined.

[0370] In the aforementioned field of view, a portion of the surface of the zinc-based coating that has a length of 0.5 mm or more in the width direction orthogonal to the thickness direction of the steel is referred to as a plating residue portion. When region A is defined as the area containing the exposed steel substrate located between two adjacent plating residue portions, in region A, the width direction length of the exposed steel substrate portions is in the range of 1.0 to 100.0 μm, the number of exposed steel substrate portions per unit length in the width direction is in the range of 3.0 to 20.0 portions / mm, and the sum of the width direction lengths of the exposed steel substrate portions per unit length in the width direction is 600.0 μm / mm or less.

[0371] When observing the cross section under a microscope in the exposed area, when the area of ​​the cross section in which the sum of the lengths of the exposed steel substrate per unit length in the width direction is 600.0 μm / mm or less is defined as region B, the sum of the areas of each of the above regions B when viewed from above is 0.7% or more of the surface area of ​​the steel when viewed from above. (15)

[0373] According to the composite structure described in (14), in the exposed area in contact with the concrete, at least a portion of the interface between the zinc coating and the concrete or at least a portion of the interface between the steel and the concrete contains an Fe-Zn-Ca composite layer containing Fe, Zn and Ca. (16)

[0375] According to the composite structure described in (15), the Fe-Zn-Ca composite layer is a layer having the following chemical composition: containing, by mass%,

[0376] Fe: 1.0% or more and 20.0% or less

[0377] Zn: 10.0% or more and 40.0% or less

[0378] Ca: 5.0% or higher and 15.0% or lower

[0379] The balance consists of H, C, O and impurities. (17)

[0381] According to the composite structure described in (16), wherein,

[0382] The chemical composition of the aforementioned zinc-based coatings also contains Al and Mg.

[0383] The chemical composition of the above Fe-Zn-Ca composite layer also contains

[0384] Al: Above 0% and below 10.0%

[0385] Mg: at least one of the following, between 0% and 10.0%, is used to replace a portion of the balance of H, C, and O. (18)

[0387] According to any one of (14) to (17) of the composite structure, wherein the exposed portion of the steel substrate is determined by performing a colorimetric test on the entire surface of the zinc-based coating to cause a colorimetric reaction in the exposed portion of the steel substrate, and when viewed from above the zinc-based coating, each of the determined exposed portions of the steel substrate has a short side size of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each of the above-mentioned exposed steel substrates. For each partition where the area ratio of the exposed steel substrate in the rectangular area is 3% or more, the cross section of the partition is observed. (19)

[0389] The composite structure according to any one of (14) to (18) wherein the zinc coating is a coating having the following chemical composition: containing Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00% by mass, with the balance being Zn and impurities. (20)

[0391] According to the composite structure described in (19), wherein the zinc coating contains, by mass%, a percentage of the total zinc content.

[0392] Al: ≥0.10% and <40.00%

[0393] Mg: ≥0.10% and <15.00%

[0394] Zn: 60.00% or more of the coating. (twenty one)

[0396] The composite structure according to any one of (14) to (18), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%,

[0397] Al: ≥0.10% and <40.00%

[0398] Mg: ≥0.10% and <15.00%,

[0399] It also contains one or more elements selected from the following groups: A, B, C, D, E, and F, with the balance being Zn and impurities.

[0400] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%;

[0401] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%;

[0402] [Element Group C]: Selected from one or more elements in 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%.

[0403] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%;

[0404] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0405] [Element group F]: B: less than 0.50%. (twenty two)

[0407] The composite structure described in (21) contains the aforementioned element group A. (twenty three)

[0409] The composite structure described in (21) contains the aforementioned element group B. (twenty four)

[0411] The composite structure described in (21) contains the aforementioned element group C. (25)

[0413] According to the composite structure described in (21), it contains the above-mentioned element group D. (26)

[0415] The composite structure described in (21) contains the aforementioned element group E. (27)

[0417] The composite structure described in (21) contains the aforementioned element group F. (28)

[0419] According to any one of (21) to (27), the composite structure wherein the zinc coating contains at least [amount] by mass%.

[0420] Al: 4.0% or more but less than 25.0%

[0421] Mg: Coating with a content of 0.3% or more but less than 12.5%.

[0422] Explanation of reference numerals in the attached figures

[0423] 1 Surface-treated components

[0424] 5. Composite Structure

[0425] 10. Steel

[0426] 20 Zinc-based coating

[0427] 50 Fe-Zn-Ca composite layer

[0428] 201 Exposed part of steel substrate

[0429] 203 Exposed Area

Claims

1. A surface-treated member composed of a surface-treated steel material having a steel material as a base material and a zinc-based plated layer on a surface of the steel material, an exposed region in which at least a part of the zinc-based plated layer is present is an exposed steel base exposed portion in which a portion of the surface of the steel material is exposed, when a cross section obtained by cutting the exposed region along a thickness direction of the steel material is observed under a microscope for an arbitrary 1.5 mm x 2.0 mm portion according to a shape of the exposed steel base exposed portion when the zinc-based plated layer is viewed from above, when a portion in which a surface of the zinc-based plated layer is present in a length of 0.5 mm or more in a width direction orthogonal to the thickness direction of the steel material is referred to as a plating residual portion and a region including the exposed steel base exposed portion between two adjacent plating residual portions is defined as a region A in the field of view, the length of the exposed steel base exposed portion in the width direction is in a range of 1.0 to 100.0 μm, the number of the exposed steel base exposed portions per unit length in the width direction is in a range of 3.0 to 20.0 pieces / mm, and a sum of the lengths of the exposed steel base exposed portions per unit length in the width direction is 600.0 μm / mm or less in the region A, when a region in which a sum of the lengths of the exposed steel base exposed portions per unit length in the width direction is 600.0 μm / mm or less is defined as a region B when the cross section is observed under the microscope in the exposed region, a sum of areas of each of the regions B when viewed from above is 0.7% or more with respect to a surface area of the steel material when viewed from above.

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 surface-treated member according to claim 1, wherein the exposed steel base exposed portion is determined by performing a color development test in which a portion of the zinc-based plated layer in which the steel base is exposed is subjected to a color development reaction, When viewed from above the zinc-based coating, each exposed portion of the steel substrate has a shorter side of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each exposed part of the steel substrate. For each partition where the exposed part of the steel substrate occupies more than 3% of the area in the rectangular area, the cross section of the partition is observed.

4. The surface treatment member according to any one of claims 1 to 3, wherein the zinc-based plated layer is a plated layer having a chemical composition containing, 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.

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

6. The surface treatment member according to any one of claims 1 to 3, wherein the zinc-based plated layer is a plated layer having a chemical composition containing, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further containing one or two or more 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, and the balance being Zn and impurities, element group A: one or both of Si: 2.50% or less and Fe: 5.00% or less. Element group B: one or two 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 two 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 two 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 two 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 treatment member according to claim 6, which contains the element group A.

8. The surface treatment member according to claim 6, which contains the element group B.

9. The surface treatment member according to claim 6, which contains the element group C.

10. The surface treatment member according to claim 6, which contains the element group D.

11. The surface treatment member according to claim 6, which contains the element group E.

12. The surface treatment member according to claim 6, which contains the element group F.

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

14. A composite structure which is a composite structure of a surface treatment member and concrete, the surface treatment member being composed of a surface treatment steel material having a steel material as a base material and a zinc-based plated layer on the surface of the steel material, there is an exposed region in at least a part of the zinc-based plated layer, the exposed region having a steel base exposed 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, when a cross section obtained by cutting the exposed region in the thickness direction of the steel material for the shape of the steel base exposed portion when the zinc-based plated layer is viewed from above is subjected to microscopic observation for an arbitrary 1.5 mm x 2.0 mm portion, In the field of view, a site where the surface of the zinc-based plating layer exists in a length of 0.5 mm or more in a width direction orthogonal to a thickness direction of the steel material is referred to as a plating residual portion, and a region including the steel substrate exposed portion between two adjacent plating residual portions is defined as region A, in the region A, the length of the steel substrate exposed portion in the width direction is in a range of 1.0 to 100.0 μm, the number of the steel substrate exposed portions per unit length in the width direction is in a range of 3.0 to 20.0 pieces / mm, and the sum of the length of the steel substrate exposed portion in the width direction per unit length in the width direction is 600.0 μm / mm or less, In the field of view, a site where the surface of the zinc-based plating layer exists in a length of 0.5 mm or more in a width direction orthogonal to a thickness direction of the steel material is referred to as a plating residual portion, and a region including the steel substrate exposed portion between two adjacent plating residual portions is defined as region A, in the region A, the length of the steel substrate exposed portion in the width direction is in a range of 1.0 to 100.0 μm, the number of the steel substrate exposed portions per unit length in the width direction is in a range of 3.0 to 20.0 pieces / mm, and the sum of the length of the steel substrate exposed portion in the width direction per unit length in the width direction is 600.0 μm / mm or less, 15. The composite structure of claim 14, wherein, In the exposed region, at least a part of the interface between the zinc-based plating layer and the concrete or at least a part of the interface between the steel material and the concrete has a Fe-Zn-Ca-based composite layer containing Fe, Zn, and Ca.

16. The composite structure of claim 15, wherein, The Fe-Zn-Ca-based composite layer is a layer having a chemical composition containing, in mass %, Fe: 1.0% or more and 20.0% or less, Zn: 10.0% or more and 40.0% or less, Ca: 5.0% or more and 15.0% or less, and the balance being H, C, O, and impurities.

17. The composite structure according to claim 16, wherein the chemical composition of the zinc-based plating layer further contains Al and Mg, 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, and Mg: 0% or more and 10.0% or less, instead of a part of the balance of H, C, and O.

18. The composite structure according to claim 14, wherein the steel substrate exposed portion is determined by performing a color development test that causes a color development reaction at a site where the steel substrate is exposed on the entire surface of the zinc-based plating layer, the zinc-based plating layer is a plating layer having a chemical composition containing, in mass %, When each of the steel base exposed portions is viewed from above the zinc-based plating layer, each of the steel base exposed portions is virtually divided as a unit into regions in a rectangular shape of 5 mm or more in size of a short side and 1 cm 2 in area, and for each of the regions in which the steel base exposed portion occupies 3% or more of the area of the region in the rectangular shape, the cross section of the region is observed.

19. The composite structure of any one of claims 14-18, wherein, 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. the zinc-based plating layer is a plating layer containing, in mass %, 20. The composite structure of claim 19, wherein, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, Zn: 60.00% or more. the zinc-based plating layer is a plating layer having a chemical composition containing, in mass %, 21. The composite structure of any one of claims 14-18, wherein, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, ​ Further contains one or two or more 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, with the balance being Zn and impurities, Element group A: one or two 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 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 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 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 two 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, which contains the element group A.

23. The composite structure according to claim 21, which contains the element group B.

24. The composite structure according to claim 21, which contains the element group C.

25. The composite structure according to claim 21, which contains the element group D.

26. The composite structure according to claim 21, which contains the element group E.

27. The composite structure according to claim 21, which contains the element group F.

28. The composite structure of claim 21, wherein, The zinc-based plating layer contains at least Al: 4.0% or more and less than 25.0%, Mg: 0.3% or more and less than 12.5% in mass%.

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