Surface-treated member

Abstract

[Problem] The present invention provides a surface-treated member which uses a steel material as a starting material and is capable of exhibiting excellent corrosion resistance even in soil at a depth of about several cm from the soil surface. [Solution] A surface-treated member according to the present invention comprises: a steel material that serves as a base material; and a protective layer that is positioned on the surface of the steel material. The protective layer has a Zn concentration of not less than 5.00 mass% but less than 30.00 mass%, an Si concentration of not less than 5.00 mass% but less than 25.00 mass%, and contains SiO2 and a Zn / Al-based carbonate type layered double hydroxide.

Description

Surface treatment materials

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

[0002] Steel materials are widely used as materials for various structures. The steel materials as materials are processed into various shapes and then joined together as necessary using fastening members such as screws, bolts, and caulking, or by joining processes using various welding methods, to form members having desired shapes (for example, various steel structures).

[0003] It is believed that the above-mentioned steel members (steel members) are exposed to various environments depending on the applications of the steel members, which may result in staining or corrosion on the surface. Therefore, various studies have been conducted on techniques for improving the stain resistance and corrosion resistance of steel members.

[0004] For example, Patent Document 1 below discloses a technology for improving the antifouling properties (particularly resistance to fouling by algae) of coated steel materials by providing a coating layer on the surface of various steel sheets that contains a pyrithione compound, at least one of a silicate compound and its cured product, and hydrotalcites, but does not contain a resin paint.

[0005] Furthermore, Patent Document 2 listed below discloses a water-wash-less repair method as a repair method for improving the corrosion resistance of a steel structure, which includes a surface preparation step of performing a treatment on the surface of a corroded steel structure so that the exposed surface area ratio of the surface of the corroded steel structure is 30% or more to obtain a surface that has been prepared; a corrosion inhibition step of applying a corrosion inhibitor containing hydrocalumite and / or hydrotalcite to the surface; a polishing / grinding step of grinding or polishing the surface to which the corrosion inhibitor has been applied; a paint application step of applying a zinc powder-containing paint to the surface after the polishing / grinding treatment; and a painting step of further painting the surface after the zinc powder-containing paint has been applied.

[0006] JP 2017-109417 A JP 2017-213557 A

[0007] Here, when various steel members made of steel are installed in desired locations, it is assumed that at least a portion of the members is often buried in soil. For steel members that are exposed to the atmosphere, it is easy to visually inspect the corrosion status of the exposed portion. However, for parts buried in soil, unlike those in the atmosphere, it is difficult to visually inspect the corrosion status, and maintenance of corroded portions is also difficult. Therefore, high corrosion resistance is required for steel members used in soil.

[0008] The present inventors have studied the corrosion state of steel members in soil. As a result, as will be described later, they have found that the corrosion behavior of steel members in soil at a depth of 1 m or more from the soil surface is significantly different from the corrosion behavior of steel members in soil at a depth of about several centimeters from the soil surface. Furthermore, they have found that even if steel members are manufactured using the techniques disclosed in Patent Documents 1 and 2 above in soil at a depth of about several centimeters from the soil surface, there is room for improvement in the corrosion resistance of the steel members.

[0009] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a surface-treated member made of steel that can exhibit excellent corrosion resistance even in soil several centimeters deep from the soil surface.

[0010] In order to solve the above problems, the present inventors have conducted extensive research and have found that, in order to suppress corrosion of steel members in soil at a depth of about several centimeters from the soil surface, it is necessary to add SiO ２ On the other hand, the main component of the protective layer is SiO ２ Since steel is a hard material, there was concern that microscopic defects would occur in the protective layer when the steel material provided with the protective layer was processed into a desired shape. If microscopic defects exist in the protective layer, corrosion factors (especially chloride ions (Cl)) can penetrate through the defects. － ) may reach the steel surface, leading to localized corrosion.

[0011] Based on the above findings, the present inventors have ２ and a zinc-containing compound containing zinc element and having sacrificial corrosion protection ability. Furthermore, the inventors have come up with the idea of ​​using a specific content of Zn / Al-based carbonate layered double hydroxide (i.e., Zn / Al-based hydrotalcites), which is a compound capable of trapping corrosion factors such as anions, as the zinc-containing compound. The gist of the present invention, which was completed based on these findings, is as follows.

[0012] (1) A steel sheet comprising a steel material as a substrate and a protective layer located on the surface of the steel material, wherein the protective layer has a Zn concentration of 1.00 mass% or more and less than 30.00 mass%, a Si concentration of 1.00 mass% or more and less than 25.00 mass%, and a SiO ２ and a Zn / Al-based carbonate layered double hydroxide. (2) The surface-treated member according to (1), wherein the thickness of the protective layer is 0.1 μm or more and 50.0 μm or less. (3) The surface-treated member according to (1) or (2), wherein, in a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the peak intensity of the peak attributed to the Zn / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less. (4) The surface-treated member according to (1) or (2), wherein the protective layer has a Mg concentration of 0.10 mass% or more and 5.00 mass% or less and further contains a Mg / Al-based carbonate layered double hydroxide. (5) The surface-treated member according to (4), wherein, in a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the peak intensity of the peak attributed to the Mg / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less. (6) In a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the peak intensity of the peak attributed to the SiO ２(7) The surface-treated member according to (1) or (2), wherein, when the distribution of the Si concentration in the thickness direction of the protective layer is examined, the Si concentration at half the thickness on the surface side of the protective layer is 1.3 times or more of the Si concentration at half the thickness on the steel side of the protective layer. (8) The protective layer is formed of the SiO ２ SiO having a particle size of 0.1 to 1.0 μm ２ (9) The surface-treated member according to (1) or (2), further comprising a second protective layer located on the protective layer, the second protective layer comprising SiO particles having a particle size of 1.0 to 30.0 μm. ２ The surface-treated member according to (1) or (2), containing particles. (10) The surface-treated member according to (9), wherein the thickness of the second protective layer is 1 μm or more and 100 μm or less. (11) The surface-treated member according to (1) or (2), further comprising a zinc-based plating layer between the steel material and the protective layer. (12) The surface-treated member according to (11), wherein the zinc-based plating layer has an Al concentration of 0.10 mass% or more and less than 40.00 mass% and a Zn concentration of 60.00 mass% or more. (13) The surface-treated member according to (12), wherein the zinc-based plating layer has a Mg concentration of 0.10 mass% or more and less than 15.00 mass%. (14) The surface-treated member according to (11), wherein the thickness of the zinc-based plating layer is 1 μm or more and 200 μm or less.

[0013] As described above, according to the present invention, it is possible to provide a surface-treated member made of steel that can exhibit excellent corrosion resistance even in soil several centimeters deep from the soil surface.

[0014] FIG. 1 is a schematic diagram for explaining a structure installed on the soil surface. FIG. 2 is a schematic diagram for explaining the structure of a surface treatment member according to an embodiment of the present invention. FIG. 3 is a schematic diagram for explaining an example of the structure of a surface treatment member according to the same embodiment. FIG. 4 is a schematic diagram for explaining an example of the structure of a surface treatment member according to the same embodiment. FIG. 5 is a schematic diagram for explaining another example of the structure of a surface treatment member according to the same embodiment. FIG. 6 is a schematic diagram for explaining a protective layer that the surface treatment member according to the same embodiment has.

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0016] (Corrosion behavior in soil several centimeters deep from the soil surface) Before describing the surface treated member according to an embodiment of the present invention, the corrosion behavior discovered by the present inventors in soil several centimeters deep from the soil surface will be described with reference to Fig. 1. Fig. 1 is a schematic diagram for explaining a structure installed on the soil surface. In the following, "soil several centimeters deep from the soil surface" may be referred to as "surface layer of soil" for convenience.

[0017] As shown schematically in Figure 1, various structures are installed on the soil surface, including, for example, stands on which photovoltaic panels are mounted, road signs, guardrails, traffic lights, etc. In this case, in order to install the structures more stably on the soil surface, as shown in Figure 1, a portion of the structure (for example, the portion surrounded by a dashed line in Figure 1, such as near the lower end of the support) is often buried in the soil.

[0018] Here, various structures are often made of various steel materials, for example, from the viewpoint of production costs, etc. Here, when a part of a structure made of various steel materials is buried in the soil, there is a concern that the steel materials may corrode.

[0019] Soil has two effects on steel corrosion: moisture retention, a corrosion factor, and oxygen diffusion inhibition, another corrosion factor. Moisture retention increases the corrosion rate, while oxygen diffusion inhibition decreases the corrosion rate. In soil, a moist environment (i.e., moisture) is maintained for a longer period of time after rainfall than in the atmosphere. Meanwhile, soil inhibits the penetration and diffusion of oxygen from the atmosphere, slowing the corrosion rate. The actual corrosion rate in soil is determined by the interaction of the two trade-off effects described above. Generally, the inhibition of oxygen diffusion is greater than the influence of moisture retention, so the corrosion rate in soil is slower than in the atmosphere.

[0020] On the other hand, the situation is quite different in soil several centimeters below the soil surface (surface layer of soil). Even in the surface layer of soil, moisture is less likely to evaporate from the soil, so steel remains in contact with moisture for longer periods of time than in the atmosphere. On the other hand, in the surface layer of soil, the distance from the atmosphere is short, and oxygen is supplied from the atmosphere quickly, so the effect of soil on inhibiting oxygen diffusion is small. Therefore, combined with the effect of moisture retention, it is believed that the corrosion inhibition effect of soil is almost nonexistent in the surface layer of soil. Thus, the surface layer of soil that the inventors focused on is an extremely severe corrosion environment compared to soil at depths of 1 m or more below the soil surface. Therefore, it can be said that extremely high corrosion resistance is required for steel installed in the surface layer of soil.

[0021] In order to achieve such extremely high corrosion resistance, the inventors have investigated the effect of adding SiO ２ On the other hand, the main component of the protective layer is SiO ２ Since steel is a hard material, there was concern that microscopic defects would occur in the protective layer when the steel material provided with the protective layer was processed into a desired shape. If microscopic defects exist in the protective layer, corrosion factors (especially chloride ions (Cl)) can penetrate through the defects. －) may reach the steel surface, leading to localized corrosion.

[0022] Based on the above findings, the present inventors have ２ and a zinc-containing compound containing zinc element having sacrificial corrosion protection ability. ２ By further containing a zinc-containing compound having sacrificial corrosion protection ability, the protective layer having high barrier properties containing the above compound further contains a zinc-containing compound having sacrificial corrosion protection ability, and thus, even if a corrosion factor reaches the protective layer, further improvement in corrosion resistance is realized.

[0023] The present inventors have also come up with the idea of ​​using a specific content of a Zn / Al carbonate layered double hydroxide (i.e., a Zn / Al hydrotalcite), which is a compound capable of trapping corrosion factors such as anions, as the zinc-containing compound. As can be inferred from the term "layered," a carbonate layered double hydroxide is a compound having a layered structure in which plate-like structures are stacked at predetermined intervals, and Cl is present between the layers. － This allows the carbonate layered double hydroxide to trap anions, including zinc ions. This not only provides the sacrificial corrosion protection provided by zinc, but also allows the carbonate layered double hydroxide itself to trap anions, which are corrosion factors. As a result, even if corrosion factors do reach the protective layer, it is possible to further prevent the corrosion factors from reaching the steel material, thereby achieving further improvements in corrosion resistance.

[0024] This makes it possible to improve the corrosion resistance of the steel material even when the surface-treated member made of steel is placed in the surface layer of the soil.

[0025] Based on the findings described above, the present inventors have conducted further studies and have come up with the idea of ​​a surface-treated member according to an embodiment of the present invention, as described in detail below.

[0026] (Regarding the Surface-Treated Member) The surface-treated member according to an embodiment of the present invention will be described in detail below with reference to Figures 2 to 4B. Figures 2 to 4B are schematic diagrams for explaining the structure of the surface-treated member according to this embodiment. For convenience, the explanation will be given using the coordinate axes shown in Figures 2 to 4B.

[0027] As described in detail below, the surface-treated member according to this embodiment is constructed using various steel materials as its raw material. Here, the specific structure of the surface-treated member according to this embodiment is not particularly limited. The specific structure of the surface-treated member according to this embodiment may be, for example, a box-like structure, or a plate-like structure using plate-like steel materials, such as the roof or wall of a building. Furthermore, the specific structure of the surface-treated member according to this embodiment may be, for example, a formed body or a joined body using various shaped steels, such as a solar panel mounting frame, a formed body or a joined body using various H-shaped steels or square columns, such as the framework of a structure, or a formed body or a joined body using various steel pipes, such as various supports, signs, traffic lights, guardrails, etc. Such a surface-treated member is used, for example, by burying at least a portion of the surface-treated member in soil.

[0028] 2 is a schematic diagram showing a part of the surface-treated member 1 according to this embodiment as viewed from above (Z-axis direction in the drawing) its surface. As shown in FIG. 2, the surface-treated member 1 according to this embodiment is made from a surface-treated steel material 10 having a steel material 11 as a substrate and a protective layer 13 containing a specific component provided on the surface of the steel material 11, as will be described later.

[0029] 3A to 4B are schematic cross-sectional views of the surface-treated member 1 shown in Fig. 2 cut in the Z-axis direction along the cutting line A-A. The cross-sectional views shown in Fig. 3A to 4B correspond to the surface-treated member 1 according to this embodiment cut in the thickness direction of the surface-treated steel material 10 that is the raw material for the surface-treated member 1.

[0030] As shown schematically in Fig. 3A, the surface-treated member 1 according to this embodiment is configured as a surface-treated steel material 10 having a steel material 11 as a substrate and protective layers 13 located on the front and back surfaces of the steel material 11. Furthermore, as shown schematically in Fig. 3B, the surface-treated steel material 10 may further have a zinc-based plating layer 15 between the steel material 11 and the protective layer 13.

[0031] First, the steel material 11, the protective layer 13, and the zinc-based plating layer 15 will be described below.

[0032] <Regarding the Steel Material 11> The steel material 11 used as the substrate of the surface-treated steel material 10 according to this embodiment is not particularly limited, and various steel materials can be used depending on the mechanical strength (e.g., tensile strength) required of the surface-treated member 1. Examples of such steel materials 11 include various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., high-strength steel in which ultra-low carbon steel further contains strengthening elements such as P, Si, and Mn, and various steel materials containing various other elements (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0033] Furthermore, as shown in FIG. 3B , a zinc-based plating layer 15 (described later) may be located on the surface of the steel material 11. However, a pre-plating layer may be provided on the surface of the steel material 11 before the zinc-based plating for forming the zinc-based plating layer 15 is performed. Metals that can be used for the pre-plating layer include Ni, Sn, and alloys combining these elements. Using pre-plated steel material that has been pre-plated with such a plating can eliminate bare spots (areas where the plated metal is repelled by an oxide film, etc.). This is presumably because, when the pre-plated steel material is immersed in a hot-dip plating bath, the metal elements in the hot-dip plating bath react with the pre-plating layer, forming Ni(Sn)-Al-Fe-Zn. The coating weight of the pre-plating layer per side is 0.2 to 2.0 g / m. ２ It is preferable that the coating weight of the pre-plating layer is within the range of 0.2 g / m. ２By setting the coating weight of the pre-plating layer at 2.0 g / m or more, it is possible to reliably achieve the effect of suppressing unplated areas by the pre-plating. ２ By setting the thickness as follows, it is possible to achieve the above-described effect of suppressing unplated areas while preventing the pre-plated layer from suppressing the elution of Fe, which makes it difficult to generate Fe-Zn-based composite oxides.

[0034] The thickness of the steel material 11 is not particularly limited, and may be set appropriately depending on the mechanical strength required of the surface-treated member 1, etc.

[0035] <Regarding the protective layer 13> The protective layer 13 is a layer located on the surface of the steel material 11 (Fig. 3A) or on the surface of the zinc-based plating layer 15 (Fig. 3B), and has a Zn concentration of 5 mass% or more and less than 30 mass%, a Si concentration of 5 mass% or more and less than 25 mass%, and a SiO ２ and a Zn / Al-based carbonate layered double hydroxide. The surface treated member 1 according to this embodiment has the protective layer 13 as described above, and therefore exhibits excellent corrosion resistance even when at least a portion of the surface treated member 1 is placed in the surface layer of soil.

[0036] The detailed structure of the protective layer 13 will be described later.

[0037] <Regarding the zinc-based plating layer 15> As shown in Fig. 3B, a zinc-based plating layer 15 may be located between the steel material 11 and the protective layer 13. The zinc-based plating layer 15 is not particularly limited as long as it contains at least zinc (Zn), and various known zinc-based platings can be applied.

[0038] Examples of such zinc-based plating include zinc plating, such as hot-dip galvanizing and galvannealed hot-dip galvanizing, zinc-nickel plating, zinc-iron plating, zinc-chromium plating, zinc-aluminum plating, zinc-titanium plating, zinc-magnesium plating, zinc-manganese plating, zinc-aluminum-magnesium plating, and zinc-aluminum-magnesium-silicon plating. Furthermore, zinc-based plating may contain small amounts of different metal elements or impurities, such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic, or may have inorganic substances, such as silica, alumina, and titania, dispersed therein. The plating method is not particularly limited, and various known plating methods, such as electroplating, hot-dip plating, vapor deposition plating, dispersion plating, and vacuum plating, may be used.

[0039] Among the various zinc-based platings described above, the zinc-based plating layer 15 according to this embodiment is preferably a zinc-based plating layer having, for example, the chemical composition described in detail below. By using a zinc-based plating layer 15 having the chemical composition described in detail below, it is possible to further improve the corrosion resistance and other properties of the surface-treated member 1 according to this embodiment. First, the more preferable chemical composition of the zinc-based plating layer 15 described above will be described in detail below.

[0040] <Regarding the Chemical Composition of the Zinc-Based Plating Layer 15> According to one aspect, the chemical composition of the zinc-based plating layer 15 according to this embodiment contains, in mass %, 0.10% or more and less than 40.00% Al, with the balance being 60.00% or more Zn and impurities.

[0041] In addition, in the chemical composition of a certain aspect of the zinc-based plating layer 15 according to the present embodiment, the chemical composition of the zinc-based plating layer 15 more preferably further contains Mg: 0.10% or more and less than 15.00% in place of a part of the remaining Zn.

[0042] According to another aspect, the chemical composition of the zinc-based plating layer 15 according to this embodiment contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being Zn and impurities.

[0043] [Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 2.00% or less, Bi: less than 0.50%, and In: less than 2.00%. [Element group E]: one or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element group F]: B: less than 0.50%.

[0044] [Al: 0.10% by mass or more and less than 40.00% by mass] In a preferred embodiment of the zinc-based plating layer 15 according to this embodiment, Al is an element necessary for constituting the main metal structure (Zn-Al-based metal structure). Therefore, Al is preferably contained at a predetermined content or more to ensure corrosion resistance as a plated steel material. If the Al content in the zinc-based plating layer 15 is less than 0.10% by mass, the above-described corrosion resistance may not be ensured. Therefore, in the zinc-based plating layer 15 according to this embodiment, the Al content is preferably 0.10% by mass or more. The Al content is preferably 3.00% by mass or more, more preferably 4.00% by mass or more, and even more preferably 6.00% by mass or more. By ensuring the Al content within the above range, it is possible to ensure corrosion resistance as a plated steel material.

[0045] On the other hand, if the Al content in the zinc-based plating layer 15 is 40.00 mass% or more, the Al phase that functions as a cathode when placed in a corrosive environment will increase excessively, facilitating corrosion of the steel material 11, and there is a possibility that the corrosion resistance of the plated steel material will not be ensured. Therefore, in the zinc-based plating layer 15 according to this embodiment, the Al content is preferably less than 40.00 mass%. The Al content is preferably 25.00 mass% or less, more preferably less than 25.00 mass%, and even more preferably 20.00 mass% or less.

[0046] In the zinc-based plating layer 15 according to this embodiment, the balance of the Al is Zn and impurities. In a preferred embodiment of the zinc-based plating layer 15 according to this embodiment, Zn is an element necessary for constituting the main metal structure (Zn-Al-based metal structure) and is an important element for improving the corrosion resistance of the plated steel material. Furthermore, when the zinc-based plating layer 15 contains the Al within the above range and further contains Zn, it is possible to ensure the corrosion resistance required of the plated steel material.

[0047] [Mg: 0.10% by mass or more and less than 15.00% by mass] In a more preferred embodiment of the zinc-based plating layer 15 according to this embodiment, Mg is an important element for constituting the main metal structure (Zn—Al—Mg-based metal structure). Therefore, in order to ensure the corrosion resistance of the plated steel material, it is more preferable that Mg be contained in a content equal to or greater than a predetermined amount. If the Mg content in the zinc-based plating layer 15 is less than 0.10% by mass, the corrosion resistance described above may not be ensured. Therefore, in the zinc-based plating layer 15 according to this embodiment, the Mg content is preferably 0.10% by mass or more. The Mg content is preferably 0.30% by mass or more, and more preferably 3.00% by mass or more. By ensuring the Mg content within the above range, the corrosion resistance of the plated steel material can be ensured.

[0048] On the other hand, if the Mg content in the zinc-based plating layer 15 is 15.00 mass% or more, anodic dissolution of the zinc-based plating layer is likely to proceed when placed in a corrosive environment, which may result in the corrosion resistance of the plated steel material not being ensured. Therefore, in the zinc-based plating layer 15 according to this embodiment, the Mg content is preferably less than 15.00 mass%. The Mg content is preferably less than 12.50 mass%, and more preferably 12.00 mass% or less. By ensuring that the Mg content falls within the above range, it is possible to ensure the corrosion resistance of the plated steel material.

[0049] Next, in a preferred embodiment of the zinc-based plating layer 15 according to this embodiment, element groups A to F that may be contained in the chemical composition of the zinc-based plating layer 15 will be described in detail.

[0050] In addition, when the zinc-based plating layer 15 according to another aspect of the present embodiment contains at least one of the elements belonging to the following element groups A to F, it is preferable that the at least one of the elements belonging to the following element groups A to F be contained within the following content ranges, and that the total content be 60.00 mass% or less.

[0051] By setting the total content of elements belonging to element groups A to F to 60.00% by mass or less, it becomes possible to enjoy the effects exerted by the addition of each element, as described in detail below, without impairing each other. The total content of elements belonging to element groups A to F is preferably 50.00% by mass or less, and more preferably 40.00% by mass or less.

[0052] Element Group A In another aspect of the zinc-based plating layer 15 according to this embodiment, element group A that may be contained in the zinc-based plating layer 15 will be described. At least one element in element group A shown below is an element that may be contained in the zinc-based plating layer 15 in place of a portion of the remaining Zn. [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less, and Fe: 5.00% or less

[0053] [Si: 0 to 2.50 mass%] In another embodiment of the zinc-based plating layer 15 according to the present embodiment, a case where Si is not contained is also conceivable, and therefore the lower limit of the Si content is 0 mass%. Meanwhile, Si is an element that can suppress the excessive growth of an Fe-Al-based metallic structure formed at the interface between the zinc-based plating layer 15 and the steel material 11, thereby further improving the adhesion between the zinc-based plating layer 15 and the steel material 11. When Si is contained in the zinc-based plating layer 15, the Si content is preferably 0.05 mass% or more, more preferably 0.20 mass% or more, in order to suppress the excessive growth of an Fe-Al-based metallic structure. Meanwhile, if the Si content exceeds 2.50 mass%, there is a possibility that high-melting-point intermetallic compounds are formed with Mg in excess, inhibiting the formation of Al-Mg oxides, which have the effect of suppressing Zn evaporation during welding.

[0054] Furthermore, if the Si content in the plating bath for producing the zinc-based plating layer 15 is too high, the viscosity of the plating bath increases more than necessary, which may result in a decrease in operability during the production of plated steel materials (hereinafter referred to as "plating operability"). Therefore, the Si content in the plating bath is adjusted from the viewpoint of plating operability. The Si content in the zinc-based plating layer 15 is preferably 1.50 mass% or less, and more preferably 1.00 mass% or less.

[0055] [Fe: 0 to 5.00 mass %] Elements constituting the steel material 11, which is the substrate, may be mixed into the zinc-based plating layer 15. In particular, in the hot-dip galvanizing method, elements constituting the steel material 11 are easily mixed into the zinc-based plating layer 15 due to interdiffusion of elements caused by a solid-liquid reaction between the steel material 11 and the zinc-based plating layer 15. Due to the incorporation of such elements, the zinc-based plating layer 15 often contains a predetermined amount of Fe, and the content is often 0.01 mass % or more. If the interdiffusion is promoted, the adhesion between the steel material 11 and the zinc-based plating layer 15 is improved. From the viewpoint of improving the adhesion between the steel material 11 and the zinc-based plating layer 15, the Fe content in the zinc-based plating layer 15 is preferably 0.20 mass % or more.

[0056] Furthermore, Fe may be intentionally added to the plating bath used to produce the zinc-based plating layer 15, provided that the effects of the present invention are not impaired. However, if the Fe content in the plating bath is increased, high-melting-point intermetallic compounds of Fe and Al are formed in the plating bath. In this case, such high-melting-point intermetallic compounds tend to adhere to the zinc-based plating layer 15 as dross, significantly degrading the appearance quality, which is undesirable. From this perspective, the Fe content in the plating bath is adjusted. The Fe content in the zinc-based plating layer 15 is preferably 5.00% by mass or less. The Fe content in the zinc-based plating layer 15 is more preferably 3.00% by mass or less, even more preferably 2.00% by mass or less, 1.00% by mass or less, or 0.50% by mass or less.

[0057] Element Group B In another aspect of the zinc-based plating layer 15 according to this embodiment, element group B that may be contained in the zinc-based plating layer 15 will be described. At least one element in element group B shown below is an element that may be contained in the zinc-based plating layer 15 in place of a portion of the remaining Zn. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%

[0058] [Sb: 0 to 0.50 mass%] [Pb: 0 to 0.50 mass%] [Sr: 0 to 0.50 mass%] In another embodiment of the zinc-based plating layer 15 according to the present embodiment, it is possible that Sb, Pb, and Sr are not contained, and therefore the lower limit of the content of these elements is 0 mass%. On the other hand, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 15, spangles are formed on the surface of the zinc-based plating layer 13, thereby improving metallic luster. Therefore, from the viewpoint of further improving the design of the plated steel material, it is preferable that at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 15. Such an effect of improving design is realized when the content of at least one of Sb, Pb, and Sr is 0.05 mass% or more. Therefore, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 15, the content of each of these elements is preferably set independently to 0.05 mass % or more.

[0059] On the other hand, when a zinc-based coating layer 15 is formed in which any one of the Sb, Pb, and Sr contents exceeds 0.50 mass%, the amount of dross generated in the coating bath used to form the zinc-based coating layer 15 increases, and it may be impossible to produce a plated steel material with good coating properties. Therefore, the contents of Sb, Pb, and Sr in the zinc-based coating layer 15 are preferably each independently 0.50 mass% or less. The contents of Sb, Pb, and Sr are each independently preferably 0.20 mass% or less.

[0060] Element Group C In another aspect of the zinc-based plating layer 15 according to this embodiment, element group C that may be contained in the zinc-based plating layer 15 will be described. At least one element in element group C shown below is an element that may be contained in the zinc-based plating layer 15 in place of a portion of the remaining Zn. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%

[0061] [Cu: 0% by mass or more and less than 0.25% by mass] [Ti: 0% by mass or more and less than 0.25% by mass] [Cr: 0% by mass or more and less than 0.25% by mass] [Nb: 0% by mass or more and less than 0.25% by mass] [Ni: 0% by mass or more and less than 0.25% by mass] [Mn: 0% by mass or more and less than 0.25% by mass] [Co: 0% by mass or more and less than 0.25% by mass] [V: 0% by mass or more and less than 0.25% by mass] In another aspect of the zinc-based plating layer 15 according to this embodiment, it is possible that Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are not contained, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the zinc-based plating layer 15, these elements are incorporated into the Fe-Al-based metal structure produced by welding when such plated steel is welded, thereby further improving the corrosion resistance of the welded joint. This effect of improving the corrosion resistance of the welded joint is achieved when the content of at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 13 is 0.05 mass% or more. Therefore, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the zinc-based plating layer 15, the content of each of these elements is preferably independently 0.05 mass% or more.

[0062] On the other hand, when forming a zinc-based plating layer 15 in which any of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is present in an amount of 0.25 mass% or more, these elements may form various intermetallic compounds in the plating bath used to form the zinc-based plating layer 15, resulting in an increase in the viscosity of the plating bath and making it impossible to produce a plated steel material with good plating properties. Therefore, the contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 15 are preferably each independently less than 0.25 mass%. The contents of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are each independently preferably 0.20 mass% or less.

[0063] Element Group D In another aspect of the zinc-based plating layer 15 according to this embodiment, element group D that may be contained in the zinc-based plating layer 13 will be described. At least one element in element group D shown below is an element that may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%

[0064] [Sn: 0% by mass or more to 2.00% by mass] [Bi: 0% by mass or more to less than 0.50% by mass] [In: 0% by mass or more to less than 2.00% by mass] In another embodiment of the zinc-based plating layer 15 according to the present embodiment, Sn, Bi, and In may not be contained. Therefore, the lower limit of the content of these elements is 0% by mass. On the other hand, Sn, Bi, and In form intermetallic compounds with Mg in the zinc-based plating layer 15, thereby improving the weldability of the zinc-based plating layer 13. Furthermore, since these intermetallic compounds all have high melting points, they do not evaporate after welding when plated steel materials are welded, and remain as intermetallic compounds. The presence of these elements improves corrosion resistance and corrosion prevention, and also improves the corrosion resistance of welds during welding. The effect of improving corrosion resistance is achieved when the content of at least one of Sn, Bi, and In in the zinc-based plating layer 15 is 0.05% by mass or more. Therefore, when at least one of Sn, Bi, and In is contained in the zinc-based plating layer 15, the content of each of these elements is preferably set independently to 0.05 mass % or more.

[0065] On the other hand, excessive Sn addition increases the amount of intermetallic compounds formed, which may reduce the corrosion resistance of the zinc-based plating layer 15 after welding. Furthermore, excessive Bi and In addition may make the zinc-based plating layer 15 brittle and prone to peeling, and may also reduce the corrosion resistance of the zinc-based plating layer 15 after welding. These phenomena become more pronounced when the Sn content exceeds 2.00 mass%, when the Bi content is 0.50 mass% or more, or when the In content is 2.00 mass% or more. Therefore, the Sn content is preferably 2.00 mass% or less, the Bi content is preferably less than 0.50 mass%, and the In content is preferably less than 2.00 mass%. The Sn content is more preferably 1.00 mass% or less, the Bi content is more preferably 0.30 mass% or less, and the In content is more preferably 1.00 mass% or less.

[0066] Element Group E In another aspect of the zinc-based plating layer 15 according to this embodiment, element group E that may be contained in the zinc-based plating layer 15 will be described. At least one element in element group E shown below is an element that may be contained in the zinc-based plating layer 15 in place of a portion of the remaining Zn. [Element Group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less

[0067] [Ca: 0 to 3.00 mass%] In another aspect of the zinc-based plating layer 15 according to the present embodiment, it is possible that no Ca is contained, and therefore the lower limit of the Ca content is 0 mass%. On the other hand, when Ca is contained in the plating bath for producing the zinc-based plating layer 15, it is possible to reduce dross that is generated with an increase in the Mg concentration during plating operations, and it is possible to improve plating operability.

[0068] Furthermore, when Ca is contained in the zinc-based plating layer 15, it forms an intermetallic compound with Al and Zn. Furthermore, when Si is contained together with Ca in the zinc-based plating layer 15, Ca forms an intermetallic compound with Si. These intermetallic compounds have a high melting point and a stable structure, making it possible to suppress liquid metal embrittlement (LME) when plated steel is welded. When Ca is contained in the zinc-based plating layer 15, the effect of improving plating operability and the effect of suppressing LME during welding are achieved by setting the Ca content to 0.01% by mass or more. The Ca content in the zinc-based plating layer 15 is more preferably 0.05% by mass or more.

[0069] On the other hand, if the Ca content in the zinc-based plating layer 15 exceeds 3.00 mass%, the corrosion resistance of the plated steel material may be reduced. From this viewpoint, the Ca content in the zinc-based plating layer 15 is preferably 3.00 mass% or less. The Ca content in the zinc-based plating layer 15 is preferably 2.00 mass% or less, and more preferably 1.00 mass% or less.

[0070] [La: 0% by mass or more and less than 0.50% by mass] [Ce: 0% by mass or more and less than 0.50% by mass] [Y: 0% by mass or more and less than 0.50% by mass] In another aspect of the zinc-based plating layer 15 according to this embodiment, it is possible that La, Ce, and Y are not contained, so the lower limits of the contents of these elements are 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit effects almost equivalent to those of Ca. This is because the atomic radius of each element is close to the atomic radius of Ca, and when these elements are contained in the zinc-based plating layer 15, they substitute for Ca positions.

[0071] The effect of improving plating operability and the effect of suppressing LME during welding are realized by making the contents of these elements independently 0.01% by mass or more. Therefore, when at least one of La, Ce, and Y is contained, the contents of these elements independently are preferably 0.01% by mass or more. The contents of La, Ce, and Y in the zinc-based plating layer 15 are each independently more preferably 0.05% by mass or more.

[0072] On the other hand, if the La, Ce, and Y contents in the plating bath for producing the zinc-based plating layer 15 are too high, the viscosity of the plating bath may increase more than necessary, potentially reducing plating operability. Therefore, the La, Ce, and Y contents in the plating bath are adjusted from the perspective of plating operability. The La, Ce, and Y contents are preferably each independently less than 0.50 mass%, less than 0.50 mass%, and 0.50 mass% or less. The La, Ce, and Y contents are each independently preferably 0.10 mass% or less.

[0073] Element Group F In another aspect of the zinc-based plating layer 15 according to this embodiment, element group F that may be contained in the zinc-based plating layer 15 will be described. The elements in element group F shown below are elements that may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group F]: B: less than 0.50%

[0074] [B: 0% by mass or more and less than 0.50% by mass] In another embodiment of the zinc-based plating layer 15 according to the present embodiment, a case where B is not contained is also conceivable, and therefore the lower limit of the B content is 0% by mass. On the other hand, when B is contained in the zinc-based plating layer 15, it has the effect of further suppressing LME. This is presumably because, when B is contained in the zinc-based plating layer 15, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. Furthermore, the presence of B in the zinc-based plating layer 13 is presumably effective in diffusing from the zinc-based plating layer 15 to the steel material 11 and further suppressing LME of the steel material 11 through grain boundary strengthening. Furthermore, because the various intermetallic compounds formed with B have extremely high melting points, it is presumed that they also act to suppress Zn evaporation during welding. These improving effects are achieved by including 0.05% by mass or more of B. Therefore, when B is included, the B content is preferably 0.05% by mass or more.

[0075] On the other hand, if an excessive amount of B is added to the plating bath in order to incorporate B into the zinc-based plating layer 15, a rapid rise in the plating melting point may occur, resulting in a deterioration in plating operability and the possibility of not being able to produce a plated steel material with excellent plating properties. Such a deterioration in plating operability becomes significant when the B content is 0.50 mass% or more, so the B content is preferably less than 0.50 mass%. The B content is more preferably 0.10 mass% or less.

[0076] [Method for Measuring Chemical Composition] The chemical composition of the zinc-based plating layer 15 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). ICP-AES is used to analyze chemical compositions down to 0.1% by mass, and ICP-MS is used to analyze trace amounts of chemical compositions less than 0.1% by mass. The plated steel material is immersed in a 10% aqueous HCl solution containing an inhibitor for about 1 minute to remove the zinc-based plating layer, and a solution in which the zinc-based plating layer is dissolved is prepared. The resulting solution can be analyzed by ICP-AES or ICP-MS to obtain the overall average chemical composition of the zinc-based plating layer.

[0077] <<Thickness of the zinc-based plating layer 15>> The thickness of the zinc-based plating layer 15 (thickness d ｐ ) is, for example, preferably 1 μm or more, and more preferably 3 μm or more. The thickness of the zinc-based plating layer 15 is, for example, preferably 200 μm or less, and more preferably 50 μm or less. When the thickness of the zinc-based plating layer 15 is within the above range, the surface-treated member 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0078] The thickness of the zinc-based plating layer 15 can be measured by direct observation of the cross section. Specifically, a cross-sectional sample including the zinc-based plating layer 15 is obtained by cutting the surface-treated member 1 of interest at an arbitrary position in the thickness direction of the surface-treated member 1. The obtained cross-sectional sample is then embedded in a room-temperature drying epoxy resin so that the cross section can be observed, and the embedded surface is mechanically polished and then observed with an SEM. In such SEM observation, a person skilled in the art can easily distinguish the steel material 11, the zinc-based plating layer 15, and the protective layer 13 from their appearance. The thickness of the zinc-based plating layer 15 is measured at any five locations, and the average value of the thicknesses obtained at the five locations is taken as the thickness of the zinc-based plating layer 15.

[0079] 4A and 4B are schematic diagrams showing another example of the structure of the surface-treated member 1 according to this embodiment. As shown in FIGS. 4A and 4B, the surface-treated member 1 according to this embodiment may further include a second protective layer 17 on the protective layer 13.

[0080] The detailed configuration of the second protective layer 17 will be described later.

[0081] <Detailed Structure of Protective Layer 13> Next, the detailed structure of the protective layer 13 of the surface treated member 1 according to this embodiment will be described. As mentioned above, the protective layer 13 according to this embodiment has a Zn concentration of 1 mass % or more and less than 30 mass %, a Si concentration of 1 mass % or more and less than 25 mass %, and SiO ２ and a Zn / Al-based carbonate layered double hydroxide.

[0082] <SiO ２ As mentioned above, the protective layer 13 according to this embodiment is made of SiO ２ By containing SiO ２ This allows the surface treated member 1 according to this embodiment to have excellent barrier properties due to the above.

[0083] Such SiO ２ is not particularly limited, and various known SiO ２It is possible to use such SiO ２ Examples of suitable silica include silica sand, colloidal silica, fumed silica, water-dispersed silica, precipitated silica, and silica gel.

[0084] Here, the protective layer 13 of the surface-treated member 1 is made of SiO ２ Whether or not the protective layer 13 contains SiO is determined by measuring the surface of the protective layer 13 by X-ray diffraction (XRD). ２ The determination can be made depending on whether or not a peak attributed to

[0085] Here, SiO ２ An example of the peak attributed to the above is a peak observed at 2θ=26.65±0.50. Here, the XRD measurement may be carried out, for example, by the following method.

[0086] Method for Measuring the XRD Pattern of the Protective Layer 13 First, a sample is cut out from the surface-treated member 1 having the protective layer 13. The dimensions of this sample, as viewed from a direction perpendicular to the surface of the surface-treated member 1, are, for example, 20 mm x 20 mm. Next, the XRD pattern of the sample is measured using an X-ray diffraction device (for example, RINT-TTR III manufactured by Rigaku Corporation). Examples of XRD pattern measurement conditions are listed below.

[0087] XRD pattern measurement conditions: X-ray output: 50 kV, 300 mA X-ray tube: Cu Measurement range: start angle 5°, end angle 100° Scan speed: 2 deg / min Step width: 0.01 deg Scan axis: 2 Theta / Theta Soller slit: 5° Divergence slit: 1 / 2° Divergence vertical limiting slit: 10 mm Scattering slit: open (fully open) Receiving slit: open (fully open) Goniometer radius: 285 mm Detector: one-dimensional detector D / tex Ultra-HE, monochromator installed in front of the detector

[0088] The data of the measurement results obtained under the above measurement conditions was subjected to background subtraction using an application (e.g., PDXL2 manufactured by Rigaku Corporation) installed in the X-ray diffraction apparatus, and the SiO ２ The peaks assigned to

[0089] In addition, in the protective layer 13 according to this embodiment, the SiO ２ The peak intensity of the peak attributed to is preferably 500 cps or more and 100,000 cps or less. When the peak intensity is within the above range, the protective layer 13 contains a sufficient amount of SiO to exhibit a barrier effect against corrosion factors. ２ It can be determined that the material contains SiO. ２ The peak intensity of the peak attributed to is more preferably 1000 cps or more.

[0090] The protective layer 13 according to this embodiment is made of the above-mentioned SiO ２ SiO having a particle size of 0.10 to 1.00 μm ２ It is preferable that the material contains SiO particles. ２ The average particle size of the particles is preferably 0.10 to 1.00 μm. ２ The particles are particles containing the element Si and the element O, in which the sum of the mass % of Si and the mass % of O is 95 mass % or more, and (mol number of Si / sum of mol number of Si and mol number of O) is 0.25 or more and 0.50 or less. ２ By including the particles, the density of the protective layer 13 can be improved, and as a result, the barrier properties of the protective layer 13 can be further improved. ２ The average particle size of the particles is preferably 0.50 μm or less.

[0091] Total SiO ２ SiO particles having the above particle size (0.10 to 1.00 μm) ２ The ratio of the particles is determined by the ratio of the SiO ２It is preferable that the ratio of the total number of particles is 70 to 100%. ２ By including the particles in the above content, it is possible to further improve the density of the protective layer 13, and therefore the barrier properties of the protective layer 13. ２ The ratio of the particles is determined by the ratio of the SiO ２ It is more preferably 80% or more of the total number of particles.

[0092] Here, the above-mentioned SiO ２ Particle size and SiO ２ SiO having the above particle size (0.10 to 1.00 μm) as a proportion of the total particles ２ The proportion of SiO particles can be measured by direct observation of the cross section. ２ The particle size of the particles is determined by the SiO ２ It is defined as the particle size.

[0093] SiO ２ Specifically, the method for measuring the particle size is as follows. First, an arbitrary position of the surface-treated member 1 of interest is cut in the thickness direction of the surface-treated member 1 (i.e., in a direction perpendicular to the surface of the surface-treated member 1) to obtain a cross-sectional sample of the protective layer 13. The obtained cross-sectional sample is then embedded in a room-temperature drying epoxy resin so that the cross-section can be observed, and the embedded surface is mechanically polished and then observed with an SEM. In this embodiment, particles with a measured particle size of 0.05 μm or more are considered to be "SiO ２ Particles measuring less than 0.05 μm in size are defined as SiO ２ In this embodiment, only the edges of the particles are observed, or the particles themselves are too fine and have little effect on the barrier effect of the protective layer 13. ２ are not treated as "particles."

[0094] The size of the field of view during SEM observation is 200 μm × 300 μm. In any five fields of view, all SiO particles with a particle size of 0.05 μm or more present in the field of view are counted. ２The particle size and number of particles are measured. ２ The number of particles is calculated. ２ "Number of particles" / "SiO with particle size of 0.05 μm or more ２ The number of particles can be calculated.

[0095] In addition, all SiO particles present in the field of view with a particle size of 0.05 μm or more ２ The average particle size of the SiO particles (sum of particle sizes of all particles / total number of particles) was calculated. ２ The average particle size of the particles can be calculated.

[0096] In addition, a person skilled in the art would understand that in the above cross-sectional observation, SiO ２ Furthermore, even if the surface-treated member has already been buried in soil, the above-mentioned cross-sectional observation can be carried out by taking a measurement sample from the buried surface-treated member.

[0097] <Zn / Al-based carbonate layered double hydroxide> As mentioned above, the protective layer 13 according to this embodiment contains a Zn / Al-based carbonate layered double hydroxide, which traps anions, which act as corrosion factors, that have entered the protective layer 13. This makes it possible to improve the corrosion resistance of the surface-treated member 1 according to this embodiment.

[0098] Zn / Al-based layered double hydroxides (hydrotalcites) are compounds having the general formula shown in (1) below. [Zn １－Ｘ Al Ｘ (OH) ２ ] Ｘ＋ [A ｎ－ Ｘ／ｎ ・mH ２ O] Ｘ－ ...(1)

[0099] Here, in the above general formula (1), A ｎ－ Ha, OH － , F － , Cl － ,Br － , NO ２－ , CO３ ２－ , S.O. ４ ２－ , Fe(CN) ３ ３－ , C.H. ３ COO － , oxalate ion, salicylate ion, or other n-valent anion. X is a value greater than 0 and not greater than 0.33. Among these Zn / Al-based layered double hydroxides, A ｎ－ As a result, carbonate ions (CO ３ ２－ ) is a Zn / Al-based carbonate layered double hydroxide.

[0100] Among the above-mentioned Zn / Al carbonate layered double hydroxides, zinc aluminum hydroxide carbonate hydrate (Zn ６ Al ２ (OH) １６ CO ３ ・4H ２ It is more preferable to use .O.

[0101] <Mg / Al-based carbonate layered double hydroxide> The protective layer 13 according to this embodiment is made of the above-mentioned SiO ２ In addition to the Zn / Al-based carbonate layered double hydroxide, it is preferable that the protective layer 13 further contains an Mg / Al-based carbonate layered double hydroxide. Like the Zn / Al-based carbonate layered double hydroxide, the Mg / Al-based carbonate layered double hydroxide is a compound with a layered structure and can trap anions between its layers. The interlayer length of the Mg / Al-based carbonate layered double hydroxide is different from that of the Zn / Al-based carbonate layered double hydroxide, and therefore the Mg / Al-based carbonate layered double hydroxide can trap different types of corrosion factors than the Zn / Al-based carbonate layered double hydroxide. Therefore, when the protective layer 13 according to this embodiment further contains an Mg / Al-based carbonate layered double hydroxide in addition to the Zn / Al-based carbonate layered double hydroxide, the corrosion resistance of the surface-treated member 1 can be further improved.

[0102] Zn / Al-based layered double hydroxides (hydrotalcites) are compounds having the general formula (2) below: [Mg １－Ｘ Al Ｘ (OH)２ ] Ｘ＋ [A ｎ－ Ｘ／ｎ ・mH ２ O] Ｘ－ ...(1)

[0103] Here, in the above general formula (1), A ｎ－ Ha, OH － , F － , Cl － ,Br － , NO ２－ , CO ３ ２－ , S.O. ４ ２－ , Fe(CN) ３ ３－ , C.H. ３ COO － , oxalate ion, salicylate ion, or other n-valent anion. X is a value greater than 0 and not greater than 0.33. Among these Mg / Al-based layered double hydroxides, A ｎ－ As a result, carbonate ions (CO ３ ２－ ) is a Mg / Al-based carbonate layered double hydroxide.

[0104] Among the above Mg / Al carbonate layered double hydroxides, magnesium aluminum hydroxide carbonate hydrate (Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ It is more preferable to use .O.

[0105] <<Method for Identifying Carbonate Layered Double Hydroxide>> Whether or not the protective layer 13 of the surface-treated member 1 contains the above-mentioned Zn / Al-based carbonate layered double hydroxide or Mg / Al-based carbonate layered double hydroxide can be determined by measuring the surface of the protective layer 13 by XRD and determining whether or not a peak attributed to the Zn / Al-based carbonate layered double hydroxide or the Mg / Al-based carbonate layered double hydroxide is present in the obtained measurement results.

[0106] Here, an example of a peak attributed to the Zn / Al-based carbonate layered double hydroxide is a peak observed at 2θ = 11.64 ± 0.50. Furthermore, an example of a peak attributed to the Mg / Al-based carbonate layered double hydroxide is a peak observed at 2θ = 11.71 ± 0.50. Here, the XRD measurement conditions are the same as those described above, and therefore detailed explanations are omitted below.

[0107] Furthermore, in the protective layer 13 according to this embodiment, the peak intensity of the peak attributed to the Zn / Al-based carbonate layered double hydroxide, measured as described above, is preferably 1,000 cps or more and 150,000 cps or less. When the peak intensity is within the above range, it can be determined that the protective layer 13 contains a Zn / Al-based carbonate layered double hydroxide to an extent that it can sufficiently trap anions, which are corrosion factors. The peak intensity of the peak attributed to the Zn / Al-based carbonate layered double hydroxide is more preferably 5,000 cps or more.

[0108] Furthermore, when the protective layer 13 according to this embodiment contains an Mg / Al-based carbonate layered double hydroxide, the peak intensity of the peak attributed to the Mg / Al-based carbonate layered double hydroxide measured as described above is preferably 1,000 cps or more and 150,000 cps or less. When the peak intensity is within the above range, it can be determined that the protective layer 13 contains an Mg / Al-based carbonate layered double hydroxide to an extent that it can sufficiently trap anions, which are a corrosion factor. The peak intensity of the peak attributed to the Mg / Al-based carbonate layered double hydroxide is more preferably 5,000 cps or more.

[0109] <Other Components> In addition to the components described above, the protective layer 13 according to this embodiment may contain various Si-containing compounds, Zn-containing compounds, Al-containing compounds, Mg-containing compounds, and the like.

[0110] ◇Si-Containing Compound Examples of the Si-containing compound that can be contained in the protective layer 13 according to this embodiment include various silicate-based compounds and their cured products. Examples of such silicate-based compounds include 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldiethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3- Methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropyltrimethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropyltriethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropylmethyldiethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropylmethyldiethoxysilane, 3-anilinopropyltrimethoxysilane, 3-anilinopropylmethyldimethoxysilane, 3-anilinopropyltriethoxysilane, 3-anilinopropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldimethoxysilyl)propyl]ammonium chloride,Examples include octadecyldimethyl[3-(triethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldiethoxysilyl)propyl]ammonium chloride, 3-chloropropylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane.

[0111] Zn-containing compound Examples of Zn-containing compounds that can be contained in the protective layer 13 according to this embodiment include ZnO and Zn(OH). ２ , Zn ５ (OH) ８ Cl ２ ・H ２ O, Zn ５ (CO ３ ) ２ (OH) ６ , Zn ２ Al(OH) ６ Cl 1.8H ２ O and the like can be mentioned.

[0112] Al-containing compounds that can be contained in the protective layer 13 according to this embodiment include, for example, Al ２ O ３ , Al(OH) ３ The following can be mentioned:

[0113] Mg-containing compound Examples of the Mg-containing compound that can be contained in the protective layer 13 according to this embodiment include MgZn. ２ The following can be mentioned:

[0114] Organic Resin The protective layer 13 according to this embodiment may contain various organic resins as film-forming components. When the protective layer 13 according to this embodiment further contains an organic resin, the corrosion resistance of the protective layer 13 can be further improved.

[0115] Examples of such organic resins include known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenolic resin, acrylic resin, polyolefin resin, and fluororesin. Furthermore, modified versions of these resins and other film-forming resin components crosslinked with crosslinking agents include butylated melamine resin, methylated melamine resin, butylmethyl-mixed melamine resin, urea resin, isocyanate resin, and mixtures of these resins. Electron beam-curable resins and ultraviolet-curable resins may also be used as organic resins. To further enhance adhesion to the steel material 11 and the zinc-based plating layer 15, it is preferable to use at least one resin (such as polyester resin, urethane resin, epoxy resin, or acrylic resin) having a forced moiety or polar functional group in the molecular chain. These organic resins may be used alone or in combination.

[0116] Other Components The protective layer 13 according to this embodiment may contain, in addition to the various components described above, a zirconium compound, a fluoride, a vanadium compound, tannin, tannic acid, or the like.

[0117] Furthermore, the protective layer 13 according to this embodiment may further contain various rust-preventive pigments in addition to the various components described above. Examples of such rust-preventive pigments that can be used include calcium ion-exchanged silica (also commonly known as calcium silicate), magnesium oxide, calcium molybdate, aluminum molybdate, and barium molybdate.

[0118] Furthermore, the protective layer 13 according to this embodiment may further contain, as necessary, an extender pigment such as precipitated barium sulfate or clay, or a color pigment such as titanium oxide. Furthermore, in addition to the above-mentioned rust-preventive pigment, extender pigment, and color pigment, the protective layer 13 according to this embodiment may further contain, as necessary, additives such as a colorant, a viscosity adjuster, a leveling agent, an antifoaming agent, and an ultraviolet absorber.

[0119] Regarding the element concentrations of the protective layer 13, the protective layer 13 according to this embodiment containing the components described above has a Zn concentration of 5.00 mass% or more and less than 30.00 mass% and a Si concentration of 5.00 mass% or more and less than 25.00 mass%. Furthermore, the protective layer 13 according to this embodiment preferably has an Al concentration of 0.01 mass% or more and 10.00 mass% or less.

[0120] [Zn: 1.00% by mass or more and less than 30.00% by mass] If the Zn concentration is less than 1.00% by mass, the content of the Zn / Al-based carbonate layered double hydroxide in the protective layer 13 according to this embodiment is insufficient, and sufficient corrosion resistance cannot be obtained. When the Zn concentration is 1.00% by mass or more, the surface-treated member 1 can exhibit sufficient corrosion resistance even when placed in the surface layer of soil. In the protective layer 13 according to this embodiment, the Zn concentration is preferably 10.00% by mass or more, and more preferably 15.00% by mass or more.

[0121] On the other hand, when the Zn concentration is 30.00 mass % or more, the content of the Zn / Al-based carbonate layered double hydroxide in the protective layer 13 according to this embodiment is too high, and SiO ２ When the Zn concentration is less than 30.00 mass%, the content of SiO ２ The surface treated member 1 can exhibit sufficient corrosion resistance even when placed in the surface layer of soil while ensuring the Zn content. In the protective layer 13 according to this embodiment, the Zn concentration is preferably 25.00 mass% or less, and more preferably 20.00 mass% or less.

[0122] [Si: 1.00 mass % or more and less than 25.00 mass %] When the Si concentration is less than 1.00 mass %, the protective layer 13 according to this embodiment contains SiO ２ The Si content is insufficient, and sufficient corrosion resistance cannot be obtained. When the Si concentration is 1.00 mass% or more, the surface treated member 1 can exhibit sufficient corrosion resistance even when placed in the surface layer of soil. In the protective layer 13 according to this embodiment, the Si concentration is preferably 10.00 mass% or more, and more preferably 15.00 mass% or more.

[0123] On the other hand, when the Si concentration is 25.00 mass % or more, in the protective layer 13 according to this embodiment, SiO ２ If the Si content is too high, the Zn / Al-based carbonate layered double hydroxide content will be insufficient. By making the Si concentration less than 25.00 mass%, the surface treated member 1 can exhibit sufficient corrosion resistance even when placed in the surface layer of soil while ensuring the Zn / Al-based carbonate layered double hydroxide content. In the protective layer 13 according to this embodiment, the Si concentration is preferably 20.00 mass% or less, and more preferably 15.00 mass% or less.

[0124] [Mg: 0.10% by mass or more and 5.00% by mass or less] When the protective layer 13 according to this embodiment contains a Mg-containing compound such as an Mg / Al-based carbonate layered double hydroxide, the Mg concentration in the protective layer 13 is preferably 0.10% by mass or more and 5.00% by mass or less.

[0125] When the Mg concentration in the protective layer 13 is 0.10% by mass or more, the protective layer 13 according to this embodiment contains an Mg / Al-based carbonate layered double hydroxide that is sufficient to trap anions, which are a corrosion factor, and exhibits superior corrosion resistance. The Mg concentration in the protective layer 13 is more preferably 0.50% by mass or more, and even more preferably 1.00% by mass or more.

[0126] On the other hand, by making the Mg concentration in the protective layer 13 5.00% by mass or less, the protective layer 13 according to this embodiment is prevented from having an insufficient content of the Zn / Al-based carbonate layered double hydroxide, and the Zn / Al-based and Mg / Al-based carbonate layered double hydroxides are each able to trap various corrosion factors in a well-balanced manner, thereby exhibiting better corrosion resistance. The Mg concentration in the protective layer 13 is more preferably 4.00% by mass or less, and even more preferably 3.00% by mass or less.

[0127] The Zn concentration, Si concentration, and Mg concentration can be measured as follows. First, an arbitrary position on the surface-treated member 1 of interest is cut in the thickness direction of the surface-treated member 1 (i.e., in a direction perpendicular to the surface of the surface-treated member 1) to obtain a cross-sectional sample of the protective layer 13. A section from an arbitrary position on the surface of the protective layer 13 in the cross-sectional sample is analyzed along the thickness direction of the protective layer 13 (e.g., the Z-axis direction in FIG. 3A ) to the interface with the zinc-based plating layer 15 or the interface with the steel material 11 using an energy dispersive X-ray spectroscopy (EDS) analyzer installed in a scanning electron microscope (SEM, for example, a JEOL JSM-7000F), and the obtained analysis results are mapped. Here, the elements of interest in the above analysis are Zn, Si, Al, Mg, and C. The observation conditions for SEM-EDS in this case may be, for example, an acceleration voltage of 15 kV, a probe current of 4.91 nA, a number of sweeps of 10, and an observation magnification of 500 times.

[0128] Those skilled in the art can easily determine the range corresponding to the protective layer 13 from an SEM image. However, in this embodiment, in the depth profile of each element obtained as described above, the portion where the Zn concentration and Si concentration fall within the above range is treated as the region of the protective layer 13. Then, the average concentrations of Zn, Si, and Mg elements in the region of the protective layer 13 are calculated from the obtained depth profiles of the Zn, Si, and Mg elements.

[0129] The above-described measurements are carried out in the same manner at any five locations on the obtained cross-sectional sample, and the average values ​​of the obtained average concentrations of each of the multiple elements over the number of measurement locations can be treated as the Zn, Si, and Mg concentrations in the protective layer 13.

[0130] <<Distribution of Si Elements in Protective Layer 13>> Next, the distribution of Si elements in the thickness direction of the protective layer 13 according to this embodiment will be specifically described with reference to Fig. 5. Fig. 5 is an explanatory diagram for describing the distribution of Si elements in the protective layer 13 according to this embodiment.

[0131] As schematically shown in Fig. 5 , a region extending from the surface side of the protective layer 13 (the positive Z-axis direction side in Fig. 5 ) toward the steel material 11 side to the center of the thickness of the protective layer 13 will be referred to as "region a" for convenience. Similarly, a position extending from the center of the thickness of the protective layer 13 toward the steel material 11 side to the interface with the steel material 11 (in the case where a zinc-based plating layer 15 is present, the interface with the zinc-based plating layer 15) will be referred to as "region b" for convenience.

[0132] In the same manner as in the above-described Si concentration measurement method, a depth profile of the Si element in the region a and a depth profile of the region b are measured, and the Si concentrations in the region a and the region b are calculated in the same manner as described above. The Si concentration in the region a thus obtained is expressed as [Si] ａ and the Si concentration in region b is expressed as [Si] ｂ It will be written as follows.

[0133] At this time, the protective layer 13 according to this embodiment has a Si concentration at half the thickness on the surface side of the protective layer 13 (i.e., [Si] ａ ) is the Si concentration at 1 / 2 thickness of the protective layer 13 on the steel material 11 side (i.e., [Si] ｂ ) is 1.3 times or more (i.e., [Si] ａ ≧1.3×[Si] ｂ It is preferable that the following relationship holds:

[0134] [Si] ａ ≧1.3×[Si] ｂ When the relationship above holds, it means that the Si element in the protective layer 13 is unevenly distributed in the region a rather than in the region b. It is thought that corrosion factors penetrate from the region on the surface side of the protective layer 13 (i.e., the region a) toward the steel material 11. Therefore, by unevenly distributing the Si element on the region a side, it is possible to more effectively prevent the penetration of corrosion factors, and it is possible to further improve the corrosion resistance of the protective layer 13.

[0135] Si concentration in region a [Si] ａ is the Si concentration in region b [Si] ｂ It is more preferably 1.4 times or more, and even more preferably 1.5 times or more.ａ / [Si] ｂ ) is preferably as large as possible, and although there is no upper limit to this, the upper limit is practically about 2.0 times.

[0136] <<Thickness of Protective Layer 13>> The thickness of the protective layer 13 according to this embodiment having the above-described configuration (thickness d1 in FIGS. 3A to 4B ) is preferably 0.1 μm or more and 50.0 μm or less. When the thickness d1 of the protective layer 13 is 0.1 μm or more, the surface-treated member 1 according to this embodiment exhibits superior corrosion resistance. The thickness d1 of the protective layer 13 is more preferably 1.0 μm or more.

[0137] On the other hand, when the thickness d1 of the protective layer 13 is 50.0 μm or less, the surface-treated member 1 exhibits superior corrosion resistance while ensuring the adhesion of the protective layer 13. The thickness d1 of the protective layer 13 is more preferably 30.0 μm or less.

[0138] The thickness of the protective layer 13 can be measured by direct observation of the cross section. Specifically, the surface-treated member 1 of interest is cut at any position in the thickness direction of the surface-treated member 1 to obtain a cross-sectional sample including the protective layer 13. The obtained cross-sectional sample is then embedded in a room-temperature drying epoxy resin so that the cross section can be observed, and the embedded surface is mechanically polished and then observed with an SEM. In such SEM observation, a person skilled in the art can easily distinguish the steel material 11, the zinc-based plating layer 15, and the protective layer 13 from their appearance. The thickness of the protective layer 13 can be measured at any five positions, and the average value of the thicknesses obtained at the five points can be taken as the thickness of the protective layer 13.

[0139] The detailed configuration of the protective layer 13 according to this embodiment has been described above.

[0140] <Detailed Configuration of Second Protective Layer 17> As schematically shown in FIGS. 4A and 4B , in the surface-treated member 1 according to this embodiment, it is preferable that a second protective layer 17 is further positioned on the protective layer 13.

[0141] As shown in FIGS. 4A and 4B, the second protective layer 17 is made of SiO ２The SiO particles 19 are contained. ２ The particles 19 have an average particle size of 1.00 to 30.00 μm. ２ When the average particle size of the particles 19 is 1.00 to 30.00 μm, the second protective layer 17 becomes a layer having barrier properties, and the corrosion resistance of the surface-treated member 1 is further improved. ２ The average particle size of the particles 19 is more preferably 10.00 μm or more. ２ The average particle size of the particles 19 is more preferably 15.00 μm or less.

[0142] In addition, the SiO ２ The average particle size of the particles 19 is ２ It can be measured in the same manner as the average particle size of the particles.

[0143] In the second protective layer 17 according to this embodiment, SiO ２ The proportion of particles 19 (SiO 2 having a particle size of 1.00 to 30.00 μm) ２ "Number of particles" / "SiO with particle size of 0.05 μm or more ２ The "number of particles" is preferably 10 to 80%. ２ When the ratio of the particles 19 is 10% or more, it is possible to further improve the corrosion resistance of the surface-treated member 1. SiO having a particle size of 1.00 to 30.00 μm ２ The proportion of the particles 19 is more preferably 30% or more.

[0144] On the other hand, SiO having a particle size of 1.00 to 30.00 μm ２ When the proportion of the particles 19 is 80% or less, it is possible to further improve the corrosion resistance of the surface-treated member 1 while maintaining the adhesion of the second protective layer 19. ２ The proportion of the particles 19 is more preferably 70% or less.

[0145] Here, the SiO in the second protective layer 17 ２ The particle size and number of particles are determined by the SiO ２ It can be measured in the same manner as the method for measuring the content of .

[0146] The second protective layer 17 according to this embodiment is made of SiO ２ In addition to the particles 19, various compounds containing elements such as Zn, Al, Mg, and C (for example, oxides and carbonate compounds containing at least one of these elements) may be contained.

[0147] The thickness of the second protective layer 19 according to this embodiment (thickness d2 in FIGS. 4A and 4B ) is preferably 1.0 μm or more and 100.0 μm or less. When the thickness d2 of the second protective layer 19 is 1.0 μm or more, the surface-treated member 1 according to this embodiment exhibits superior corrosion resistance. The thickness d2 of the second protective layer 19 is more preferably 10.0 μm or more.

[0148] On the other hand, when the thickness d2 of the second protective layer 19 is 100.0 μm or less, the surface-treated member 1 exhibits superior corrosion resistance while ensuring the adhesion of the second protective layer 19. The thickness d2 of the second protective layer 19 is more preferably 50.0 μm or less.

[0149] The thickness d2 of the second protective layer 19 can be measured in the same manner as the thickness d1 of the protective layer 13 described above.

[0150] Here, a person skilled in the art can easily distinguish from an SEM image the area corresponding to the protective layer 13 and the area corresponding to the second protective layer 19. However, in the depth profile of each element by SEM-EDS described above, the area containing particles located further above (on the side opposite to the steel material 11) the area determined as the area of ​​the protective layer 13 is treated as the area of ​​the second protective layer 17.

[0151] The detailed configuration of the second protective layer 19 according to this embodiment has been described above.

[0152] (Regarding the Manufacturing Method of the Surface-Treated Member) Hereinafter, an example of a manufacturing method of the surface-treated member 1 according to this embodiment will be described.

[0153] <Method for manufacturing the surface-treated steel material 10 as the raw material> The surface-treated steel material 10 as the raw material for the surface-treated member 1 according to this embodiment is manufactured by using the above-described steel material 11 as a base material, forming a zinc-based plating layer 15 on the surface of the steel material 11, applying a treatment agent for forming a protective layer to the surface of the zinc-based plating layer 15, and further storing the surface after the application of the treatment agent in a specific atmosphere for a predetermined period of time.

[0154] <<Method of Forming Zinc-Based Plating Layer 15>> In addition to hot-dip plating, other methods such as thermal spraying, cold spraying, sputtering, vapor deposition, and electroplating can be used to form the zinc-based plating layer 15. However, hot-dip plating is most preferable in terms of cost.

[0155] An example of a manufacturing method for obtaining the zinc-based plating layer 15 according to the present embodiment using a hot-dip galvanizing method will be described in detail below. In the manufacturing process for the zinc-based plating layer 15, first, a steel sheet as an example of a steel material 11 used as a substrate is rolled by a Sendzimir method to a desired thickness, and then the steel sheet is wound into a coil and placed in a hot-dip galvanizing line.

[0156] In the hot dip plating line, the steel sheet is continuously fed from the coil and passed through the line. At this time, the steel sheet is annealed by an annealing facility installed on the line in an environment where oxidation is unlikely to occur, for example, an oxygen concentration of 20 ppm or less, and N ２ -5% H ２ After heating and reducing at 800°C in a gas atmosphere, the temperature was increased by approximately 20°C to the subsequent plating bath temperature. ２ The plate is cooled with gas and then immersed in a plating bath.

[0157] Here, a molten plating alloy having the above-described chemical components is prepared in the plating bath, and the temperature of the plating bath is set to be equal to or higher than the melting point of the plating alloy (for example, about 460 to 660°C).

[0158] When preparing a plating alloy material, it is preferable to use pure metals (purity of 99% or higher) as the alloying materials. First, predetermined amounts of alloying metals are mixed to obtain the above-described plating layer composition, and the alloy is completely melted in a high-frequency induction furnace, arc furnace, or the like under vacuum or inert gas purging conditions to obtain an alloy. Next, the alloy mixed with the predetermined components (the above-described plating layer composition) is melted in the atmosphere, and the resulting molten material is used as a plating bath.

[0159] In addition, there is no particular restriction on using pure metals for the production of the plating alloys described above, and existing Zn alloys, Mg alloys, and Al alloys may be melted and used. In this case, there is no problem as long as an alloy of a predetermined composition with few impurities is used.

[0160] After immersing the steel sheet in the plating bath, it is pulled up at a predetermined speed. At this time, the steel sheet is pulled up at a predetermined speed so that the zinc-based plating layer to be formed has a desired thickness. ２ The plating weight is controlled by wiping gas. Here, general plating operating conditions can be applied except for the bath temperature, and no special equipment or conditions are required.

[0161] Furthermore, the molten plating alloy located on the steel sheet may be subjected to various heat treatments as required.

[0162] <<Method for forming protective layer 13 and second protective layer 17>> The protective layer 13 and second protective layer 17 in the surface-treated steel material 10 according to this embodiment are formed by applying a treatment agent for forming a protective layer to the surface of the zinc-based plating layer 15 formed as described above, and then storing the surface after the treatment agent has been applied in a specific atmosphere for a predetermined period of time.

[0163] Preparation of a treatment agent for forming a protective layer The treatment agent for forming a protective layer is prepared by mixing the components to be contained in the protective layer (more specifically, SiO ２ The layered double hydroxide is prepared by mixing various kinds of carbonate-type layered double hydroxides, such as Zn / Al-based and Mg / Al-based components.

[0164] Here, SiO contained in the treatment agent ２ The components include various SiO２ In this case, SiO ２ SiO having a plurality of types of average particle diameters ２ A mixture of particles (hereinafter simply referred to as "SiO ２ It is more preferable to use a mixture of the above.

[0165] For example, SiO ２ As a mixture, SiO having an average particle size of 0.1 to 1.0 μm ２ By using the particles, a treatment agent for forming the protective layer 13 can be obtained. Here, SiO ２ The particle content is SiO ２ It is preferable that the content of the additive is, for example, 50 to 75% by mass based on the total mass of the mixture.

[0166] Similarly, SiO ２ As a mixture, SiO having an average particle size of 1.0 to 30.0 μm ２ By using the particles, a treatment agent for forming the second protective layer 17 can be obtained. Here, SiO particles having an average particle size of 1.0 to 30.0 μm can be used. ２ The particle content is SiO ２ It is preferable that the content is, for example, 10 to 20% by mass based on the total mass of the mixture.

[0167] Here, the amount of water in each treatment agent (i.e., the water content of the treatment agent) is determined by the following formula: ２ It is preferable to set the volume ratio of water to the pores of the mixture to be 50% or more and 80% or less. ２ The pores in the mixture are formed by the SiO ２ The specific gravity "A" of SiO before adding water ２ It is possible to determine this in advance based on the void ratio {1-(B / A)} obtained from the bulk specific gravity "B" of the mixture.

[0168] Furthermore, the pH of the water used as a solvent for each treatment agent is preferably within the range of 4 to 9. This allows the reactivity of the treatment agent to be more favorable. This allows plating components (particularly components such as Zn) to be easily eluted from the zinc-based plating layer 15. As a result, in the storage step described below, the components of the already formed zinc-based plating layer 15 react appropriately with the components of the treatment agent for forming the protective layer and the treatment agent for forming the second protective layer, thereby forming the protective layer 13 and the second protective layer 17 according to this embodiment.

[0169] Application of Treatment Agent The treatment agent for forming the protective layer prepared as described above may be applied to the surface of the zinc-based plating layer 15 to a thickness of 0.5 mm to 3.0 mm. The application of the treatment agent described above can be carried out by a commonly known application method, such as roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, or brush coating.

[0170] Storage of steel material coated with treatment agent The steel material coated with the treatment agent as described above (steel material 11 having zinc-based plating layer 15) is stored in an atmosphere at a temperature of 10 to 40°C and a relative humidity of 80% or higher. This allows the components of the already formed zinc-based plating layer 15 to react appropriately with the components of the treatment agent for forming the protective layer, forming the protective layer 13 according to this embodiment.

[0171] Here, the storage time of the above-described steel material is preferably 240 hours or more. This makes it possible to form the protective layer 13 of the surface-treated steel material 10 according to this embodiment. On the other hand, the upper limit of the storage time of the steel material is not particularly specified, but is practically about 1,440 hours. In particular, by setting the storage time of the steel material to 360 hours or more and 720 hours or less, it becomes possible to form the protective layer 13 having a more preferable thickness.

[0172] Furthermore, when a second protective layer 17 is formed as an upper layer on the protective layer 13 formed as described above, a portion of the protective layer 13 formed as described above may be removed as necessary, and then a treatment agent for forming the second protective layer may be applied to the protective layer 13, and the protective layer may be stored in the same manner as described above.

[0173] Here, the application conditions and storage conditions for the treatment agent for forming the second protective layer are the same as those for forming the protective layer, and therefore detailed explanations will be omitted below.

[0174] Note that the zinc-based plating layer 15 formed on the surface of the steel material 11 may react with all the components of the treatment agent during this storage step, and may disappear from the surface of the steel material 11. Furthermore, depending on the storage time, the zinc-based plating layer 15 may remain between the steel material 11 and the formed protective layer 13.

[0175] Furthermore, in the treatment agent for forming the protective layer, the pH of the water used as the solvent is set to 4 to 5, which makes it easier to dissolve the plating components, and the temperature during the storage process is set to 30 to 40°C, which makes it possible to further concentrate element Si on the surface side of the protective layer 13.

[0176] By going through the steps described above, it is possible to manufacture the surface-treated steel material 10 that serves as the raw material for the surface-treated member 1 according to this embodiment. An example of the method for manufacturing the surface-treated steel material 10 according to this embodiment has been specifically described above.

[0177] <Method for manufacturing surface-treated member> The surface-treated steel material 10 obtained as described above is used as a raw material to manufacture the surface-treated member 1 according to this embodiment. Here, in order to obtain components for manufacturing the surface-treated member 1 from the surface-treated steel material 10, various shaping processes can be used, such as various molding processes, joining processes using fastening members such as bolts and caulking, and welding processes. By appropriately combining these processes, the surface-treated member 1 having the desired shape can be manufactured from the surface-treated steel material 10.

[0178] An example of the method for manufacturing the surface treated member 1 according to this embodiment has been briefly described above.

[0179] The surface-treated member according to the present invention will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the surface-treated member according to the present invention, and the surface-treated member according to the present invention is not limited to the examples below.

[0180] <Preparation of Plated Steel Material> In the test examples shown below, cold-rolled steel sheets and Ni-plated cold-rolled steel sheets (both manufactured by Nippon Steel Corporation) shown in Table 1 below were prepared as base steel sheets for plating and cut into pieces measuring 60 mm x 60 mm. Plating was performed using an in-house manufactured batch-type hot-dip galvanizing test apparatus, and multiple plated steel materials having the coating layer compositions shown in Table 2 below were produced for each level. The coating thickness per side for each level is shown in Table 4 below.

[0181]

[0182]

[0183] <Preparation of Treatment Agent for Forming Protective Layer> Commercially available SiO ２ Using silica powder (Silica Flower series manufactured by Masuoka Ceramic Materials Co., Ltd.), a treatment agent for forming a protective layer containing the components shown at each level in Tables 4-1 to 4-6 was prepared. In preparing the treatment agent for forming the protective layer, a pH adjuster shown in Table 3 was used as needed.

[0184]

[0185] The prepared treatment agent was applied to the surface of the plated steel material, and the steel was stored under the conditions shown in Tables 4-1 to 4-6 below to form a protective layer and a second protective layer. ２ After removing the coating, the steel was air-dried to obtain a surface-treated steel material. A plurality of such surface-treated steel materials were prepared for each level. For each surface-treated steel material thus obtained, various measurements were carried out on the protective layer, second protective layer, and plating layer in accordance with the above-described methods. The results are summarized in Tables 5-1 to 5-6 below.

[0186]

[0187]

[0188]

[0189]

[0190]

[0191]

[0192]

[0193]

[0194]

[0195]

[0196]

[0197]

[0198] Furthermore, the corrosion resistance in soil of each of the surface-treated steel materials thus obtained was evaluated according to the following method.

[0199] <Corrosion resistance evaluation method> The surface-treated steel materials obtained at each level were buried in soil simulating the surface layer of soil to evaluate corrosion resistance. Silica sand (Flattery 40H manufactured by Yamakawa Sangyo Co., Ltd.) with an average particle size of 200 μm was used as the soil. The cover thickness of each surface-treated steel material was 50 mm. After burying each surface-treated steel material in this manner, 0.3 mass % NaCl and 0.1 mass % Na were added to the soil. ２ SO ４ Deionized water containing 1,000 mg of methyl cellulose was dropped onto the sample to adjust the moisture content to 100%. Then, the following drying and wetting processes were repeated. Samples were prepared by repeating the process 20 times, 40 times, and 100 times, and evaluated. Drying process: Stored at 30°C for 7 days. Wetting process: Deionized water was dropped onto the sample to adjust the moisture content to 100%.

[0200] After the above test, the surface-treated steel material was pickled with hydrochloric acid to remove the second protective layer, the protective layer, the plating layer underneath the protective layer, and corrosion products from the steel material. The mass of the steel material was then measured and compared with the mass of the test material (before plating) to determine corrosion weight loss. The evaluation criteria were as follows, with ratings of "A," "B," and "C" being considered acceptable. The results are summarized in Tables 6-1 to 6-6 below. <Evaluation criteria> Rating A: Corrosion weight loss of 1 g / m ２B: Corrosion weight loss of 1 g / m ２ Super 5g / m ２ C: Corrosion weight loss is 5g / m ２ Super 15g / m ２ D: Corrosion weight loss of 15 g / m ２ , 200 g / m ２ E: Corrosion weight loss is 200g / m ２ super

[0201]

[0202]

[0203]

[0204]

[0205]

[0206]

[0207] As is clear from Tables 4-1 to 6-6 above, the examples of the present invention exhibit excellent corrosion resistance, while the comparative examples of the present invention exhibit insufficient corrosion resistance.

[0208] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0209] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0210] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0211] The following configuration also falls within the technical scope of the present invention: (1) A steel substrate, and a protective layer located on the surface of the steel substrate, wherein the protective layer has a Zn concentration of 1.00 mass% or more and less than 30.00 mass%, a Si concentration of 1.00 mass% or more and less than 25.00 mass%, and a SiO ２and a Zn / Al-based carbonate layered double hydroxide. (2) The surface-treated member according to (1), wherein the thickness of the protective layer is 0.1 μm or more and 50.0 μm or less. (3) The surface-treated member according to (1) or (2), wherein, in a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the peak intensity of the peak attributed to the Zn / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less. (4) The surface-treated member according to any one of (1) to (3), wherein the protective layer has a Mg concentration of 0.10 mass% or more and 5.00 mass% or less and further contains a Mg / Al-based carbonate layered double hydroxide. (5) The surface-treated member according to (4), wherein, in a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the peak intensity of the peak attributed to the Mg / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less. (6) In a measurement result obtained by measuring the surface of the protective layer by X-ray diffraction (XRD), the SiO ２ (7) The surface-treated member according to any one of (1) to (6), wherein, when the distribution of the Si concentration in the thickness direction of the protective layer is examined, the Si concentration at half the thickness on the surface side of the protective layer is 1.3 times or more of the Si concentration at half the thickness on the steel side of the protective layer. (8) The protective layer is formed of the SiO ２ SiO having a particle size of 0.1 to 1.0 μm ２ (9) The surface-treated member according to any one of (1) to (7), further comprising a second protective layer located on the protective layer, the second protective layer comprising SiO particles having a particle size of 1.0 to 30.0 μm. ２The surface-treated member according to any one of (1) to (8), containing particles. (10) The surface-treated member according to (9), wherein the thickness of the second protective layer is 1 μm or more and 100 μm or less. (11) The surface-treated member according to any one of (1) to (10), further comprising a zinc-based plating layer between the steel material and the protective layer. (12) The surface-treated member according to (11), wherein the zinc-based plating layer has an Al concentration of 0.10 mass% or more and less than 40.00 mass% and a Zn concentration of 60.00 mass% or more. (13) The surface-treated member according to (11) or (12), wherein the zinc-based plating layer has a Mg concentration of 0.10 mass% or more and less than 15.00 mass%. (14) The surface-treated member according to any one of (11) to (13), wherein the thickness of the zinc-based plating layer is 1 μm or more and 200 μm or less.

[0212] REFERENCE SIGNS LIST 1 Surface-treated member 10 Surface-treated steel material 11 Steel material 13 Protective layer 15 Zinc-based plating layer 17 Second protective layer 19 SiO ２ particle

Claims

1. A steel substrate, comprising: a steel material; and a protective layer located on the surface of the steel material, wherein the protective layer has a Zn concentration of 1.00 mass% or more and less than 30.00 mass%, a Si concentration of 1.00 mass% or more and less than 25.00 mass%, and a SiO ２ and a Zn / Al-based carbonate layered double hydroxide.

2. The surface-treated member according to claim 1, wherein the thickness of the protective layer is 0.1 μm or more and 50.0 μm or less.

3. A surface-treated member according to claim 1 or 2, wherein the surface of the protective layer is measured by X-ray diffraction (XRD), and the peak intensity of the peak attributed to the Zn / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less.

4. The surface-treated member according to claim 1 or 2, wherein the protective layer has a Mg concentration of 0.10 mass % or more and 5.00 mass % or less, and further contains an Mg / Al-based carbonate layered double hydroxide.

5. The surface-treated member according to claim 4, wherein the surface of the protective layer is measured by X-ray diffraction (XRD), and the peak intensity of the peak attributed to the Mg / Al-based carbonate layered double hydroxide is 1,000 cps or more and 150,000 cps or less.

6. The surface of the protective layer is measured by X-ray diffraction (XRD), and the SiO ２ The surface-treated member according to claim 1 or 2, wherein the peak intensity of the peak attributed to is 500 cps or more and 100,000 cps or less.

7. A surface-treated member according to claim 1 or 2, wherein, when the distribution of Si concentration in the thickness direction of the protective layer is examined, the Si concentration at half the thickness on the surface side of the protective layer is 1.3 times or more the Si concentration at half the thickness on the steel side of the protective layer.

8. The protective layer is made of the SiO ２ SiO having a particle size of 0.1 to 1.0 μm ２ The surface-treated member according to claim 1 or 2, which contains particles.

9. The method further comprises a second protective layer located on the protective layer, the second protective layer being made of SiO having a particle size of 1.0 to 30.0 μm. ２ The surface-treated member according to claim 1 or 2, which contains particles.

10. The surface-treated member according to claim 9, wherein the thickness of the second protective layer is 1 μm or more and 100 μm or less.

11. The surface-treated member according to claim 1 or 2, further comprising a zinc-based plating layer between the steel material and the protective layer.

12. The surface-treated member according to claim 11, wherein the zinc-based plating layer has an Al concentration of 0.10 mass % or more and less than 40.00 mass %, and a Zn concentration of 60.00 mass % or more.

13. The surface-treated member according to claim 12, wherein the zinc-based plating layer has a magnesium concentration of 0.10 mass % or more and less than 15.00 mass %.

14. The surface-treated member according to claim 11, wherein the thickness of the zinc-based plating layer is 1 μm or more and 200 μm or less.

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