Surface-treated member and composite structure

Abstract

[Problem] To achieve excellent corrosion resistance even in soil at a depth of about several centimeters from the soil surface. [Solution] The surface-treated member according to the present invention is composed of a surface-treated steel material having a steel material serving as a base material, a zinc-based plating layer located on the surface of the steel material, and a chemical conversion treatment layer located on the surface of the zinc-based plating layer, wherein: the chemical conversion treatment layer contains a compound containing phosphorus P; and when the chemical conversion treatment layer having a size corresponding to 1 m2 of the surface-treated steel material is immersed in ion-exchanged water at a water temperature of 35-45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer into the ion-exchanged water is 5-50 mg / m2.

Description

Surface treated components and composite structures

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

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

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

[0004] For example, Patent Document 1 below discloses a polyolefin-coated heavy-duty corrosion-protected steel material in which an epoxy primer layer, a maleic anhydride-modified polyolefin layer, and a polyolefin layer are sequentially laminated onto a base steel material or a chromate-coated steel material in which a chromate layer is provided on the surface of the base steel material, and the epoxy primer layer is composed of a phenolic curing agent with an oxygen permeability within a specific range and an epoxy resin. Patent Document 1 also describes that such polyolefin-coated heavy-duty corrosion-protected steel material can be used even in extremely severe corrosive environments such as underground, in rivers, and in the ocean.

[0005] Furthermore, Patent Document 2 below discloses a coated steel material in which a phosphate chemical conversion coating containing at least one element selected from nickel, magnesium, and calcium in addition to zinc and manganese, and a paint coating containing a phosphate-based rust-preventive pigment and an alkaline earth metal sulfate are sequentially formed on the surface of a steel material having a zinc-based plating layer. Patent Document 2 states that such coated steel material can be used by partially burying it in concrete or the ground.

[0006] JP 2005-132105 A JP 2007-262561 A

[0007] As noted in Patent Documents 1 and 2, it is assumed that when a surface-treated member is installed in a desired location, at least a portion of the member is often buried in soil. For a portion of the surface-treated member exposed to the atmosphere, it is easy to visually inspect the corrosion state of the exposed portion. However, for a portion buried in soil, unlike in the atmosphere, it is difficult to visually inspect the corrosion state, and maintenance of the corroded portion is also difficult. Therefore, a surface-treated member used in soil is required to have high corrosion resistance.

[0008] The present inventors have studied the corrosion state of zinc-based plated steel materials in soil. As a result, as will be described later, they have found that the corrosion behavior of zinc-based plated steel materials in soil at a depth of 1 m or more from the soil surface is significantly different from the corrosion behavior of zinc-based plated steel materials in soil at a depth of only a few centimeters from the soil surface, and further that the soil corrosive environment focused on in Patent Document 2 mainly corresponds to the corrosion behavior in soil at a depth of 1 m or more from the soil surface. Furthermore, they have found that even if a surface-treated member is manufactured using the surface-treated steel disclosed in Patent Documents 1 and 2 as a material in such soil at a depth of only a few centimeters from the soil surface, there is room for improvement in the corrosion resistance of the surface-treated member.

[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 using a zinc-based plated steel material that can exhibit excellent corrosion resistance even in soil several centimeters deep from the soil surface, and a composite structure using such a surface-treated member.

[0010] To solve the above problems, the present inventors conducted extensive research and came up with the idea of ​​changing the state of the chemical conversion coating layer provided on the surface of a surface-treated steel material having a zinc-based plating layer, which is used as the base material for surface-treated members, depending on the corrosive environment to which the steel material is exposed (e.g., whether in the air or in soil). Further research based on this idea led the present inventors to come up with the surface-treated member described below. The gist of the present invention, which was completed based on this idea, is as follows:

[0011] (1) A surface-treated member made of a surface-treated steel material having a base steel material, a zinc-based plating layer on the surface of the steel material, and a chemical conversion coating layer on the surface of the zinc-based plating layer, wherein the chemical conversion coating layer contains a compound containing phosphorus element P, and the surface-treated steel material 1m ２ When the chemical conversion treatment layer in an amount corresponding to the size of the ion-exchanged water is immersed in ion-exchanged water at a temperature of 35 to 45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer into the ion-exchanged water is 5 to 50 mg / m ２(2) The surface-treated member according to (1), which is used by burying at least a portion of the surface-treated steel material in soil. (3) The surface-treated member according to (1), in which, in a narrow P2p spectrum obtained by analyzing the surface of the chemical conversion treatment layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of a peak having a maximum at 133.90±0.25 eV to the integrated intensity of a peak having a maximum at 132.80±0.25 eV is 0.20 to 0.50. (4) The surface-treated member according to (1), in which, in a depth profile of P concentration obtained by performing line analysis of the chemical conversion treatment layer by energy dispersive X-ray spectroscopy (EDS) from the surface to the interface with the zinc-based plating layer, the average P concentration on the surface side of the chemical conversion treatment layer is 1 to 20 mass%. (5) The surface-treated member according to (1), wherein the P concentration of the chemical conversion treatment layer is 0.1 to 15.0 mass % in terms of P. (6) The surface-treated member according to (1), wherein the thickness of the chemical conversion treatment layer is 30 to 5,000 nm. (7) The surface-treated member according to (1), wherein the chemical conversion treatment layer contains one or more elements selected from the group consisting of a silane coupling agent, a valve metal, and an organic resin. (8) The surface-treated member according to any one of (1) to (7), wherein the zinc-based plating layer has a chemical composition containing, by mass %, 0.10% or more but less than 40.00% Al, 0.10% or more but less than 15.00% Mg, and the balance consisting of Zn and impurities. (9) The surface-treated member according to (8), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more. (10) The surface-treated member according to any one of (1) to (7), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element group A, element group B, element group C, element group D, element group E, and element group F, with the balance being Zn and impurities.[Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (11) The surface-treated member according to (10), which contains element group A. (12) The surface-treated member according to (10), which contains element group B. (13) The surface-treated member according to (10), which contains element group C. (14) The surface-treated member according to (10), which contains element group D. (15) The surface-treated member according to (10), which contains element group E. (16) The surface-treated member according to (10), which contains element group F. (17) The surface-treated member according to (10), wherein the zinc-based plating layer is a plating layer containing, by mass%, at least 4.0% to less than 25.0% Al and 0.3% to less than 12.5% ​​Mg. (18) A composite structure including a surface-treated member made of a surface-treated steel material having a steel material as a base material, a zinc-based plating layer disposed on the surface of the steel material, and a chemical conversion coating layer disposed on the surface of the zinc-based plating layer, and soil, wherein a P-Zn-based composite layer containing Zn and P is present between the chemical conversion coating layer and the soil at at least a portion of the interface between the surface-treated member and the soil. (19) The composite structure according to (18), wherein the P-Zn-based composite layer is a layer having a chemical composition containing, by mass%, 1.0% to 10.0% Zn and 0.5% to 5.0% P, with the remainder consisting of H, C, O, Si, and impurities.(20) The composite structure according to (19), wherein the zinc-based plating layer further contains Al and Mg as a chemical composition, and the chemical composition of the P-Zn-based composite layer further contains at least one of Al: 0% or more and 10.0% or less by mass and Mg: 0% or more and 10.0% or less by mass, in place of a portion of the remaining H, C, O, and Si.

[0012] As described above, according to the present invention, it is possible to achieve excellent corrosion resistance in a surface-treated member using a zinc-based plated steel material and a composite structure using such a surface-treated member, even in soil at a depth of about several centimeters from the soil surface.

[0013] 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 the structure of a surface treatment member according to the same embodiment. Fig. 4 is an explanatory diagram for explaining a composite structure of the surface treatment member and soil according to the same embodiment. Fig. 5 is an explanatory diagram for explaining a composite structure of the surface treatment member and soil according to the same embodiment.

[0014] 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.

[0015] (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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] On the other hand, the situation is very different in soil several centimeters deep (surface soil portion). Even in the surface soil portion, moisture is less likely to evaporate from the soil, so the steel remains in contact with moisture for a longer period of time than in the atmosphere. On the other hand, in the surface soil portion, 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 thought that the corrosion inhibition effect of soil is almost impossible in the surface soil portion. Thus, the surface soil portion that the inventors focused on can be said to be an extremely severe corrosion environment compared to soil at a depth of 1 m or more from the soil surface.

[0020] The present inventors investigated the corrosion behavior of zinc-based plated steel materials in the surface layer of soil in order to study the corrosion behavior of steel materials in the surface layer of soil, and as a result, found the following: The zinc-based plating layer of zinc-based plated steel materials exhibits high corrosion resistance in the atmosphere by covering the surface of the plating layer with zinc-based corrosion products. However, it was found that the corrosion prevention function of such zinc-based corrosion products is low in the surface layer of soil.

[0021] The present inventors observed zinc-based corrosion products formed on a zinc-based plating layer in the soil surface layer using a scanning electron microscope (SEM) or the like. As a result, it was found that the zinc-based corrosion products formed in the soil surface layer were in a more porous state than the zinc-based corrosion products formed in the atmosphere. This was thought to be because corrosion progresses more rapidly in the soil surface layer than in the atmosphere.

[0022] From the above findings, the present inventors have come to the knowledge that, in order to improve the corrosion resistance of zinc-based plated steel material in the surface soil layer, it is important to change the layer made of corrosion products formed on the surface of the zinc-based plated layer in the surface soil layer to a dense state.

[0023] The present inventors conducted further studies to realize a dense corrosion product layer in the soil surface. As a result, they found that in order to improve the corrosion resistance of zinc-based plated steel in the soil surface, it is effective to make the zinc-based corrosion product contain phosphorus (P) when the zinc-based corrosion product is formed. Based on this, the present inventors came up with the idea of ​​providing a P-containing chemical conversion coating layer on the surface of the zinc-based plated layer as a supply source of P.

[0024] Such a chemical conversion coating layer exhibits appropriate corrosion resistance in the atmosphere and, together with the zinc-based plating layer, can contribute to improving the corrosion resistance of the surface-treated member. Here, in the atmosphere, the P element eluted from the chemical conversion coating layer (presumably eluted in the form of P ions) is washed away by rain or the like and is unlikely to adhere to the surface of the chemical conversion coating layer. On the other hand, in soil, since there is no water flow as described above, the eluted P element is presumed to adhere to the interface between the chemical conversion coating layer and the soil.

[0025] As a result, when zinc-based corrosion products are formed, a specific amount of P element is eluted from the chemical conversion coating layer, which allows a dense P-Zn-based composite oxide to be formed as a corrosion product at the interface between the chemical conversion coating layer and the soil. The formation of such corrosion products containing P-Zn-based composite oxides at the interface between the chemical conversion coating layer and the soil makes it possible to improve the corrosion resistance of the surface-treated member in soil by the corrosion product layer, the chemical conversion coating layer, and the zinc-based plating layer.

[0026] Furthermore, as a result of investigations by the present inventors, it has become clear that when the zinc-based plating layer is an alloy plating layer containing Mg and Al in addition to Zn, Mg ions and Al ions are eluted in the soil in addition to Zn ions, thereby generating P-Zn-Al-Mg composite oxides, thereby further improving corrosion resistance.

[0027] Based on the findings described above, the present inventors have conducted further studies and have come up with a surface-treated member according to an embodiment of the present invention, as described in detail below.

[0028] (Regarding the Surface-Treated Member) Hereinafter, a surface-treated member according to an embodiment of the present invention will be described in detail with reference to Fig. 2 and Fig. 3. Fig. 2 and Fig. 3 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 Fig. 2 and Fig. 3.

[0029] As described in detail below, the surface-treated member according to this embodiment is constructed using a surface-treated steel material having a zinc-based plating layer and a chemical conversion coating layer. The specific structure of the surface-treated member according to this embodiment is not particularly limited. The specific structure of the surface-treated member according to this embodiment may be, for example, a box-like structure, or a plate-like structure using plate-shaped steel material, such as the roof or wall of a building. The specific structure of the surface-treated member according to this embodiment may be, for example, a formed body or joint using various shaped steel, such as a solar panel mounting frame, a formed body or joint using various H-shaped steel or square columns, such as the framework of a structure, or a formed body or joint 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 steel material in soil.

[0030] Fig. 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 zinc-based plating layer 13 and a chemical conversion coating layer 15 provided on the surface of a steel material 11 serving as a base material, as will be described later.

[0031] Fig. 3 shows a schematic cross section of the surface-treated member 1 shown in Fig. 2 cut in the Z-axis direction along the cutting line A-A. The cross section shown in Fig. 3 corresponds to 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.

[0032] As shown schematically in FIG. 3 , the surface-treated member 1 according to this embodiment is composed of a surface-treated steel material 10 having a steel material 11 as a base material, zinc-based plating layers 13 formed on the front and back surfaces of the steel material 11, and a chemical conversion treatment layer 15 formed on the surface of the zinc-based plating layer 13.

[0033] In the following, the steel material 11, the zinc-based plating layer 13, and the chemical conversion treatment layer 15 will first be described in detail.

[0034] <Regarding the Steel Material 11> The steel material 11 used as the base material of the surface-treated member 1 according to this embodiment is not particularly limited, and various steel materials can be used depending on the mechanical strength (e.g., tensile strength) required of the surface-treated member 1. Examples of such steel materials 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.).

[0035] Furthermore, a pre-plated layer may be provided on the steel material 11 before zinc-based plating as described below. Metals that can be used for the pre-plated layer include Ni, Sn, and alloys combining these elements. Using pre-plated steel material that has been pre-plated with these platings in advance can eliminate bare spots (areas where the plated metal is repelled by an oxide film or the like). This is presumably because, when the pre-plated steel material is immersed in a hot-dip plating bath, the metal elements in the hot-dip plating bath react with the pre-plated layer to form Ni(Sn)-Al-Fe-Zn. The coating weight of the pre-plated layer per side is 0.2 to 2.0 g / m ２ It is preferable that the coating weight of the pre-plating layer is within the range of 0.2 g / m. ２ By setting the coating weight of the pre-plating layer at 2.0 g / m or more, it is possible to reliably achieve the effect of suppressing unplated areas by the pre-plating. ２By 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.

[0036] 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.

[0037] <Regarding the zinc-based plating layer 13> The zinc-based plating layer 13 is formed over the entire front and back surfaces of the above-described steel material 11. The zinc-based plating layer 13 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 13 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 13 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 13 described above will be described in detail below.

[0040] <Regarding the Chemical Composition of the Zinc-Based Plating Layer 13> According to one aspect, the chemical composition of the zinc-based plating layer 13 according to this embodiment contains, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance being Zn and impurities.

[0041] In addition, in the chemical composition of a certain aspect of the zinc-based plating layer 13 according to the present embodiment, the zinc-based plating layer 13 is more preferably a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

[0042] According to another aspect, the chemical composition of the zinc-based plating layer 13 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: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: one or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element group F]: B: less than 0.50%.

[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 13 according to this embodiment, Al is an element necessary for constituting the main metal structure (Zn—Al—Mg metal structure). Therefore, Al is preferably contained at a predetermined content or more to ensure corrosion resistance as a plated steel material. If the Al content in the zinc-based plating layer 13 is less than 0.10% by mass, the above-described corrosion resistance may not be ensured. Therefore, in the zinc-based plating layer 13 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 13 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 13 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] [Mg: 0.10% by mass or more and less than 15.00% by mass] In a preferred embodiment of the zinc-based plating layer 13 according to this embodiment, Mg is an element necessary for constituting the main metal structure (Zn—Al—Mg-based metal structure). Therefore, Mg is preferably contained in a predetermined amount or more to ensure corrosion resistance as a plated steel material. If the Mg content in the zinc-based plating layer 13 is less than 0.10% by mass, the above-described corrosion resistance may not be ensured. Therefore, in the zinc-based plating layer 13 according to this embodiment, the Mg content is preferably 0.10% by mass or more. The Mg content is preferably 0.30% by mass or more, and more preferably 3.00% by mass or more. By ensuring the Mg content within the above range, it is possible to ensure corrosion resistance as a plated steel material.

[0047] On the other hand, if the Mg content in the zinc-based plating layer 13 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 13 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.

[0048] In the zinc-based plating layer 13 according to this embodiment, the balance of the Al and Mg is Zn and impurities. In a preferred embodiment of the zinc-based plating layer 13 according to this embodiment, Zn is an element necessary for constituting the main metal structure (Zn-Al-Mg metal structure) and is an important element for improving the corrosion resistance of the plated steel material. Furthermore, when the zinc-based plating layer 13 contains the Al and Mg within the above ranges and further contains Zn, it becomes possible to ensure the corrosion resistance required of the plated steel material.

[0049] Next, in a preferred embodiment of the zinc-based plating layer 13 according to the present embodiment, element groups A to F that may be contained in the chemical composition of the zinc-based plating layer 13 will be described in detail.

[0050] In addition, when at least one of the elements belonging to the following element groups A to F is contained in the zinc-based plating layer 13 according to another aspect of the present embodiment, it is preferable that at least one of the elements belonging to the following element groups A to F is contained within the following content ranges and in a total content of 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 13 according to this embodiment, element group A that may be contained in the zinc-based plating layer 13 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 13 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 13 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 13 and the steel material 11, thereby further improving the adhesion between the zinc-based plating layer 13 and the steel material 11. When Si is contained in the zinc-based plating layer 13, 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 13 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 13 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 base material, may be mixed into the zinc-based plating layer 13. In particular, in the hot-dip galvanizing method, elements constituting the steel material 11 are easily mixed into the zinc-based plating layer 13 due to interdiffusion of elements caused by a solid-liquid reaction between the steel material 11 and the zinc-based plating layer 13. Due to the incorporation of such elements, the zinc-based plating layer 13 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 13 is improved. From the viewpoint of improving the adhesion between the steel material 11 and the zinc-based plating layer 13, the Fe content in the zinc-based plating layer 13 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 13, 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 13 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 13 is preferably 5.00% by mass or less. The Fe content in the zinc-based plating layer 13 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 13 according to this embodiment, the element group B that may be contained in the zinc-based plating layer 13 will be described. At least one element in the element group B 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 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 13 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 13, 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 13. Such an effect of improving the 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 13, 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 13 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 13 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 13 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 13 according to this embodiment, element group C that may be contained in the zinc-based plating layer 13 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 13 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 13 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 13, 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 13, 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 13 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 13, 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 13 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 13 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 20.00% by mass] [Bi: 0% by mass or more to less than 5.00% by mass] [In: 0% by mass or more to less than 2.00% by mass] In another embodiment of the zinc-based plating layer 13 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 13, thereby improving the weldability of the zinc-based plating layer 13. Furthermore, since these intermetallic compounds all have high melting points, when plated steel materials are welded, they do not evaporate after welding and remain as intermetallic compounds. The presence of these elements 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 13 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 13, 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 13 after welding. Furthermore, excessive Bi and In addition may make the zinc-based plating layer 13 brittle and prone to peeling, and may also reduce the corrosion resistance of the zinc-based plating layer 13 after welding. These phenomena become more pronounced when the Sn content exceeds 20.00 mass%, when the Bi content is 5.00 mass% or more, or when the In content is 2.00 mass% or more. Therefore, the Sn content is preferably 20.00 mass% or less, the Bi content is preferably less than 5.00 mass%, and the In content is preferably less than 2.00 mass%. The Sn content is more preferably 10.00 mass% or less, the Bi content is more preferably 3.00 mass% or less, and the In content is more preferably 1.00 mass% or less.

[0066] Element Group E In another aspect of the zinc-based plating layer 13 according to this embodiment, element group E that may be contained in the zinc-based plating layer 13 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 13 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 13 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 13, 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 13, it forms an intermetallic compound with Al and Zn. Furthermore, when Si is contained together with Ca in the zinc-based plating layer 13, 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 13, 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 13 is more preferably 0.05% by mass or more.

[0069] On the other hand, if the Ca content in the zinc-based plating layer 13 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 13 is preferably 3.00 mass% or less. The Ca content in the zinc-based plating layer 13 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 13 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 13, 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 13 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 13 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 13 according to this embodiment, element group F that may be contained in the zinc-based plating layer 13 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 13 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 13, it has the effect of further suppressing LME. This is presumably because, when B is contained in the zinc-based plating layer 13, B combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. Furthermore, the presence of B in the zinc-based plating layer 13 is presumably effective in diffusing from the zinc-based plating layer 13 to the steel material 11, thereby strengthening the grain boundaries and further suppressing LME of the steel material 11. 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 13, a rapid increase 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 Components] The chemical components of the zinc-based plating layer 13 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 components down to 0.1% by mass, and ICP-MS is used to analyze trace amounts of chemical components 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] <Regarding the deposition weight of the zinc-based plating layer 13> The deposition weight of the zinc-based plating layer 13 as described above is, for example, 10.0 g / m per one side of the steel material. ２ It is preferable that the content is 50.0 g / m or more. ２ The coating weight of the zinc-based plating layer 20 is, for example, 200.0 g / m per one side of the steel material. ２ Preferably, the total weight is 150.0 g / m or less. ２ When the coating weight of the zinc-based plating layer 13 falls within the above range, the surface-treated member 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0078] The deposition weight of the zinc-based plating layer 13 is determined by cutting a sample measuring 30 mm x 30 mm from the surface-treated member 1 and measuring the mass of the sample. Then, a moisture-impermeable protective tape is applied to one side of the sample to prevent the zinc-based plating layer 13 on that side from dissolving in the next process. The sample is then immersed in a 10% HCl aqueous solution containing an inhibitor, and the zinc-based plating layer 13 on the side not covered with the protective tape is peeled off by pickling, and the mass of the sample after pickling is measured. The deposition weight of the zinc-based plating layer 13 per side can be determined from the change in mass of the sample before and after pickling. In this embodiment, the deposition weight of the chemical conversion coating layer 15 having a thickness as described in detail below is 1 g / m. ２ However, it is difficult to remove only the chemical conversion coating layer 15 by physical or chemical methods. Therefore, when measuring the coating weight of the zinc-based plating layer 13, it is not necessary to remove the chemical conversion coating layer 15 from the sample.

[0079] <Regarding Chemical Conversion Layer 15> The chemical conversion layer 15 according to this embodiment is formed over the entire surface of the above-described zinc-based plating layer 13. Here, the chemical conversion layer 15 according to this embodiment contains at least a compound containing phosphorus element P. At least a portion of this compound containing phosphorus element P serves as a P supply source when the P—Zn-based composite oxide described above is produced.

[0080] <<Amount of P eluted from the chemical conversion coating layer 15>> The chemical conversion coating layer 15 according to this embodiment has a size of 1 m ２ When the chemical conversion treatment layer 15 corresponding to the surface-treated steel material 10 is immersed in ion-exchanged water at a temperature of 35 to 45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer 15 into the ion-exchanged water is 5 to 50 mg / m per side. ２ Here, the water temperature of 35 to 45°C is intended to be the temperature of water in a natural environment. Furthermore, although the form of the phosphorus element P eluted from the chemical conversion treatment layer 15 is not known in detail, it is presumed that it is eluted in the form of phosphate ions.

[0081] The amount of P dissolved is 5 mg / m ２If the amount of P eluted is less than 5 mg / m, the amount of P eluted from the chemical conversion coating layer 15 is too small to generate a sufficient corrosion product layer made of the P-Zn based composite oxide, and the corrosion resistance of the surface treated member 1 cannot be improved. ２ By achieving the above, it is possible to generate a corrosion product layer made of P—Zn-based composite oxides to an extent that the corrosion resistance of the surface-treated member 1 can be improved. The amount of P eluted is preferably 10 mg / m ２ More preferably, it is 15 mg / m or more. ２ That's all.

[0082] On the other hand, in the case of the surface-treated member 1 according to this embodiment, it is important to consider not only the corrosion resistance of the surface-treated member 1 disposed in the soil, but also the corrosion resistance of the surface-treated member 1 in the portion not present in the soil (for example, the portion present in the atmosphere). ２ If the amount of P eluted exceeds 50 mg / m, the amount of P eluted from the chemical conversion coating layer 15 becomes too large, and as a result, the corrosion resistance of the surface-treated member 1 cannot be ensured not only in the soil but also in the portion not present in the soil. ２ By satisfying the condition of 45 mg / m or less, it is possible to improve the corrosion resistance of the portion that is installed in the soil while ensuring the corrosion resistance of the portion that is not present in the soil. ２ The following is the result.

[0083] Here, when measuring the amount of P elution, ion-exchanged water of grade A1 or higher as specified in JIS K0557:1998 is prepared and preheated so that the water temperature is within the range of 35 to 45°C. Then, a sample measuring 40 mm x 40 mm in plan view is cut out from the surface-treated member 1 of interest, and the cut-out sample is placed in a lidded container with a diameter of 150 mm and a volume of 3000 mL. Then, 2000 ml of the ion-exchanged water at a temperature of 35 to 45°C is poured into the container, and the sample is left to stand for 60 minutes while the water temperature is maintained within the range of 35 to 45°C. The ion-exchanged water is then collected from the container, and the amount of eluted P is measured using ICP-MS. Here, an Agilent 8800 model manufactured by Agilent Technologies can be used as the ICP-MS.

[0084] <<Regarding the Integrated Intensity of Peaks in X-ray Photoelectron Spectroscopy Measurement Results>> As mentioned previously, in the surface-treated member 1 according to this embodiment, corrosion products containing P-Zn-based composite oxides on the surface of the surface-treated member 1 placed in soil have the effect of improving corrosion resistance in soil, and the performance of this P-Zn-based composite oxide affects the corrosion resistance improvement effect. As a result of extensive research from this perspective, it was found that in a narrow P2p spectrum obtained by analyzing the surface of the chemical conversion coating layer 15 according to this embodiment by X-ray photoelectron spectroscopy (XPS), when the ratio of the integrated intensity of the peak having a maximum value at 133.90±0.25 eV to the integrated intensity of the peak having a maximum value at 132.80±0.25 eV is within the range of 0.20 to 0.50, the corrosion resistance of the surface-treated member 1 in soil is further improved compared to when this intensity ratio is not satisfied. The reason for this is not clear, but it is speculated that this is due to a change in the form of the eluted P ions, which in turn changes the form of the P-Zn based composite oxide, improving the barrier properties.

[0085] When the integrated strength ratio is 0.20 or more, the surface treated member 1 exhibits superior corrosion resistance in soil in the chemical conversion treatment layer 15 according to this embodiment. The integrated strength ratio is more preferably 0.25 or more, and even more preferably 0.30 or more.

[0086] On the other hand, when the integrated strength ratio is 0.50 or less, the surface treated member 1 exhibits superior corrosion resistance in soil. The integrated strength ratio is more preferably 0.45 or less, and even more preferably 0.40 or less.

[0087] Here, the ratio of the integrated intensities as described above can be determined as follows. First, three arbitrary locations on the surface of the surface-treated member 1 of interest are measured using an X-ray photoelectron spectrometer (e.g., a Quantum 2000 model manufactured by ULVAC-PHI, Inc.). If a welded portion is present in a portion of the surface-treated member 1, the area extending up to 5 cm from the end of the weld is not measured. An 800 μm × 300 μm area on the surface of a surface-treated steel material (the surface of the chemical conversion coating layer 15) that has not undergone pretreatment such as cleaning or sputtering is analyzed under the following conditions, for example. The obtained P2p spectrum is separated into a peak having a maximum value at 133.90 ± 0.25 eV and a peak having a maximum value at 132.80 ± 0.25 eV, and the integrated intensities of these peaks are then determined. The integrated intensity ratio is calculated based on these integrated intensities.

[0088] However, the peak position of the narrow spectrum obtained by analysis may be shifted to the left or right depending on the measurement equipment and conditions. Therefore, the obtained spectrum is first corrected so that the peak position (the position having the maximum value) of the C1s spectrum is 284.8 eV, and then the P2p spectrum is separated into a peak having a maximum value at 133.90±0.25 eV and a peak having a maximum value at 132.80±0.25 eV.

[0089] During measurement, the P2p spectrum is measured in the 130.00 to 135.00 eV region. The peak separation region is based on 130.00 to 135.00 eV, and is extended from this range depending on the spectrum. Furthermore, during measurement, the half-width of the peak with a maximum value at 133.90 ± 0.25 eV is assumed to be 1.35 ± 0.20 eV, and the half-width of the peak with a maximum value at 132.80 ± 0.25 eV is assumed to be 1.15 ± 0.20 eV. Since no pretreatment is performed during analysis, care must be taken when handling samples to minimize the adhesion of oil and dirt.

[0090] The XPS measurement conditions were as follows: (Measurement conditions) X-ray source: monoAlKα (1486.6 eV) X-ray output: 15 kV 25 W X-ray diameter: 100 μmφ Degree of vacuum in analysis chamber (before sample introduction): 2.2×10 －９ torr (1 torr is approximately 133.32 Pa). Detection angle: 45°. Neutralization: electron neutralization, ion neutralization. Data analysis software: MultiPakV. 8.0 (manufactured by ULVAC-PHI, Inc.).

[0091] <<Regarding Depth Profiles in Energy Dispersive X-ray Spectroscopy>> Furthermore, in the chemical conversion treatment layer 15 according to this embodiment, the average concentration of P on the surface side of the chemical conversion treatment layer 15 is preferably 1 to 20 mass % in a depth profile relating to the P concentration obtained by performing line analysis of energy dispersive X-ray spectroscopy (EDS) on the chemical conversion treatment layer 15 from the surface to the interface with the zinc-based plating layer 13. Here, the surface side of the chemical conversion treatment layer 15 refers to the range from a position halfway through the thickness of the chemical conversion treatment layer 15 to the surface of the chemical conversion treatment layer 15.

[0092] By ensuring that the average P concentration on the surface side of the chemical conversion treatment layer 15 is 1 mass % or more, it is possible to ensure a sufficient amount of P element eluted from the chemical conversion treatment layer 15, and the surface treated member 1 according to this embodiment exhibits better corrosion resistance. The average P concentration on the surface side is more preferably 2 mass % or more, and even more preferably 3 mass % or more.

[0093] On the other hand, by setting the average P concentration on the surface side of the chemical conversion treatment layer 15 to 5 mass % or less, it is possible to suppress excessive P elution while ensuring a sufficient amount of P elution from the chemical conversion treatment layer 15, and the surface treated member 1 according to this embodiment exhibits better corrosion resistance. The average P concentration on the surface layer side is more preferably 15 mass % or less, and even more preferably 10 mass % or less.

[0094] The average P concentration in the depth profile described above may be measured as follows. First, a cross-sectional sample of the chemical conversion coating layer 15 is obtained by cutting the surface-treated member 1 at an arbitrary position in the thickness direction (perpendicular to the surface of the surface-treated member 1). The cross-sectional sample is analyzed from an arbitrary position on the surface of the chemical conversion coating layer 15 along the thickness direction (perpendicular to the surface of the chemical conversion coating layer 15; for example, the Z-axis direction in FIG. 3 ) of the chemical conversion coating layer 15 to the interface with the zinc-based plating layer 13 using an EDS analyzer attached to a scanning electron microscope (SEM, for example, JEOL JSM-7000F), and the obtained analysis results are mapped. The elements of interest in the analysis are at least P, Zn, Al, Mg, Si, Ti, Zr, C, and O, and mapping analysis may be performed for all elements. Among the elements of interest, Zn, Al, and Mg are elements derived from the zinc-based plating layer, and Si, Ti, Zr, C, and O are components derived from the chemical conversion treatment layer. The observation conditions for SEM-EDS in this case may be, for example, an acceleration voltage of 15 kV, a probe current of 4.9147 nA, a number of sweeps of 10, and an observation magnification of 500x.

[0095] Those skilled in the art can easily determine the area corresponding to the chemical conversion layer 15 from an SEM image. In this embodiment, in the depth profile of each element obtained as described above, the area corresponding to the range where the P concentration is 0.01% or more is treated as the area of ​​the chemical conversion layer 15. This makes it possible to identify the thickness of the chemical conversion layer 15 in the obtained depth profile. The position corresponding to half of the thickness obtained in this way is treated as the half-thickness position of the chemical conversion layer 15.

[0096] Then, from the obtained depth profile of the P element, the average concentration of the P element from the half-thickness position as described above to the surface of the chemical conversion treatment layer 15 (the surface on the opposite side from the interface between the zinc-based plating layer 13 and the chemical conversion treatment layer 15) is calculated.

[0097] The above-described measurements are carried out in the same manner at any five locations on the obtained cross-sectional sample, and the average value of the obtained average concentrations of the multiple P elements over the number of measurement locations can be treated as the "average P concentration on the surface side of the chemical conversion treatment layer 15."

[0098] <<Regarding the P Concentration of the Chemical Conversion Coating Layer 15>> In the chemical conversion coating layer 15 according to this embodiment, the P concentration, calculated as P, is preferably 0.1 to 15.0 mass%. By achieving a P concentration of 0.1 mass% or more, the chemical conversion coating layer 15 according to this embodiment can ensure a sufficient amount of P element to achieve excellent corrosion resistance regardless of whether it is present in the soil, and the surface-treated member 1 according to this embodiment exhibits even better corrosion resistance. The P concentration of the chemical conversion coating layer 15 is more preferably 1.0 mass% or more, and even more preferably 2.0 mass% or more.

[0099] The P concentration can be measured as follows. First, a cross-sectional sample of the chemical conversion coating 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 cross-sectional sample is analyzed from an arbitrary position on the surface of the chemical conversion coating layer 15 along the thickness direction of the chemical conversion coating layer 15 (a direction perpendicular to the surface of the chemical conversion coating layer 15; for example, the Z-axis direction in FIG. 3 ) to the interface with the zinc-based plating layer 13 using an EDS analyzer attached to a scanning electron microscope (SEM, for example, a JSM-7000F manufactured by JEOL). The analysis results are then mapped. The element of interest in this analysis is P. The SEM-EDS observation conditions may be, for example, an acceleration voltage of 15 kV, a probe current of 4.9147 nA, 10 sweeps, and a magnification of 500x.

[0100] A person skilled in the art would be able to easily determine the range corresponding to the chemical conversion layer 15 from an SEM image, but in this embodiment, the range corresponding to the chemical conversion layer 15 is determined based on the results of measuring the P concentration in the range from the surface of the chemical conversion layer 15 to the surface of the zinc-based plating layer 15. More specifically, in the depth profiles of each element obtained as described above, the portion corresponding to the range where the P concentration is 0.01% or more is treated as the region of the chemical conversion layer 15. Then, the average concentration of P in the region of the chemical conversion layer 15 is calculated from the obtained depth profile of P element.

[0101] The above-described measurements are carried out in the same manner at any five locations on the obtained cross-sectional sample, and the average value of the obtained average concentrations of the P element over the number of measurement locations can be treated as the "P concentration in terms of P in the chemical conversion treatment layer 15."

[0102] Specific Examples of Compounds Containing Phosphorus (P) In the chemical conversion coating layer 15 according to this embodiment, various phosphoric acids and salts thereof can be used as the compound containing phosphorus (P). Examples of phosphoric acids and salts thereof include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, triphosphoric acid, and tetraphosphoric acid, and salts thereof; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), and salts thereof; and organic phosphoric acids such as phytic acid and salts thereof. Examples of salts of phosphoric acid other than ammonium salts include metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, and the like. Phosphoric acids and salts thereof may be used alone, or two or more may be used in combination.

[0103] Furthermore, in the chemical conversion treatment layer 15 according to this embodiment, it is more preferable to use, among the various compounds described above, a compound that also functions as a so-called anti-rust pigment.

[0104] <<Regarding Other Components in Chemical Conversion Treatment Layer 15>> The chemical conversion treatment layer 15 according to this embodiment contains, in addition to the above-described compound containing phosphorus element P, one or more film-forming components selected from the group consisting of a silane coupling agent, a valve metal, and an organic resin. By further containing such components, the chemical conversion treatment layer 15 according to this embodiment has improved film-forming properties after application of the chemical conversion treatment solution, the barrier properties (density) of the film against corrosion factors such as moisture and corrosive ions, and the film adhesion to the plating surface, which can contribute to improving the corrosion resistance of the film.

[0105] [Silane Coupling Agent] Examples of the silane coupling agent 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-methacryloxypropyltriethoxysilane, Triacryloxypropylmethyldiethoxysilane, 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-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyl triethoxysilane, 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, octadecyldimethyl[3-(triethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldiethoxysilyl)propyl]ammonium chloride,Examples include 3-chloropropylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane.

[0106] [Valve Metal] A valve metal is a metal whose oxide exhibits high insulation resistance. Examples of valve metals include Ti, Zr, Hf, V, Mo, Nb, Ta, and W. The chemical conversion coating layer 15 according to this embodiment may contain one or more of these valve metals. The type of valve metal compound used is not particularly limited as long as it is soluble in water. Examples of such valve metal compounds include ammonium salts, sodium salts, potassium salts, oxides, hydrogen salts, oxygen acid salts, hydroxides, phosphates, nitrates, sulfates, and organic acid salts of the above metals. Among these compounds, it is particularly preferable to use oxides, oxygen acid salts, and phosphates of the above metals.

[0107] [Organic Resin] Examples of organic resins that can be used include known organic resins such as polyester resins, polyurethane resins, epoxy resins, phenolic resins, acrylic resins, polyolefin resins, and fluororesins. Modified versions of these resins and other film-forming resin components can also be used, such as butylated melamine resins, methylated melamine resins, butylmethyl-mixed melamine resins, urea resins, isocyanate resins, and mixtures of these resins crosslinked with a crosslinking agent component. Electron beam-curable resins and ultraviolet-curable resins can also be used as organic resins. To further enhance adhesion to the plating layer, it is preferable to use at least one resin (such as polyester resins, urethane resins, epoxy resins, and acrylic resins) that has a forced moiety or polar functional group in the molecular chain. These organic resins can be used alone or in combination.

[0108] Here, the total content of the silane coupling agent, valve metal, and organic resin relative to the solid content of the chemical conversion treatment solution is, for example, within the range of 30 to 80 mass%. If the total content is less than 30 mass%, the film-forming components will be insufficient, making it difficult to uniformly coat the steel material with the chemical conversion treatment layer. On the other hand, if the total content is more than 80%, it will be difficult to incorporate sufficient P and other components, making it difficult to achieve a balance between the corrosion resistance of the flat parts of the chemical conversion treatment layer, the corrosion resistance of the processed parts, the adhesion between the chemical conversion treatment layer and the steel material, and blackening resistance.

[0109] [Other Components] In addition to the various components described above, the chemical conversion treatment layer 15 according to this embodiment may contain zirconium compounds, silica, fluorides, vanadium compounds, tannin, tannic acid, or the like.

[0110] Furthermore, the chemical conversion coating layer 15 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, barium molybdate, water-dispersed silica, and fumed silica.

[0111] Furthermore, the chemical conversion coating layer 15 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 anti-rust pigment, extender pigment, and color pigment, the chemical conversion coating layer 15 according to this embodiment may further contain, as necessary, additives such as a colorant, a viscosity modifier, a leveling agent, an antifoaming agent, and an ultraviolet absorber.

[0112] <<Thickness of Chemical Conversion Treatment Layer 15>> The thickness of the chemical conversion treatment layer 15 described above (thickness d in FIG. 3) is preferably within a range of 30 to 5000 nm.

[0113] When the thickness of the chemical conversion treatment layer 15 is 30 nm or more, the surface treated member 1 according to this embodiment can achieve better corrosion resistance. The thickness of the chemical conversion treatment layer 15 is more preferably 100 nm or more, and even more preferably 200 nm or more.

[0114] On the other hand, by making the thickness of the chemical conversion treatment layer 15 5000 nm or less, the surface treated member 1 according to this embodiment can achieve better corrosion resistance while ensuring adhesion between the zinc-based plating layer 13 and the chemical conversion treatment layer 15. The thickness of the chemical conversion treatment layer 15 is more preferably 3000 nm or less, and even more preferably 2000 nm or less.

[0115] Here, the thickness of the chemical conversion treatment layer 15 can be measured by direct observation of the cross section. Specifically, the plated steel sheet 1 is 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 between the chemical conversion treatment layer 15 and the zinc-based plating layer 13 from their appearance. The thickness of the chemical conversion treatment layer 15 can be measured at any five points, and the average value of the thicknesses obtained at the five points can be taken as the thickness of the chemical conversion treatment layer 15.

[0116] The surface treated member 1 according to this embodiment has been described in detail above.

[0117] (Composite Structure) Next, a composite structure 5 made of the surface treated member 1 according to the present embodiment and soil as described above will be described with reference to Figures 4 and 5. Figures 4 and 5 are explanatory diagrams for explaining the composite structure according to the present embodiment.

[0118] As shown in Fig. 4, the composite structure 5 according to this embodiment is a structure in which the surface-treated member 1 according to this embodiment as described above is combined with soil. As previously explained, a chemical conversion layer 15 is formed on the surface of the surface-treated steel material 10 that constitutes the surface-treated member 1. In the composite structure 5 according to this embodiment, at least a portion of this chemical conversion layer 15 is in contact with the soil, and the surface-treated member 1 and the soil are combined together.

[0119] Fig. 5 is a schematic cross-sectional view of the composite structure 5 shown in Fig. 4 cut in the X-axis direction along the A-A cutting line. The cross-sectional view shown in Fig. 5 corresponds to a cut in the thickness direction of the surface-treated steel material 10 that is the raw material for the surface-treated member 1, at the portion of the composite structure 5 according to this embodiment that is in contact with the soil.

[0120] As shown schematically in Fig. 5, the portion of the composite structure 5 according to this embodiment that is in contact with the soil is composed of a steel material 11, a surface-treated steel material 10 having a zinc-based plating layer 13 located on the surface of the steel material 11 and a chemical conversion treatment layer 15, and the soil. Also, as shown schematically in Fig. 5, an oxide layer 21, which is an example of a P-Zn-based composite layer containing Zn and P, is formed at the interface between the chemical conversion treatment layer 15 and the soil.

[0121] Here, the steel material 11 in the composite structure 5 according to this embodiment has the same configuration as the steel material 11 in the surface-treated member 1 described above and exhibits the same effects, so further description will be omitted below.

[0122] Furthermore, the zinc-based plating layer 13 and the chemical conversion treatment layer 15 in the composite structure 5 according to this embodiment have the same configuration as the zinc-based plating layer 13 and the chemical conversion treatment layer 15 in the surface-treated member 1 described above, and therefore will not be described below.

[0123] In addition, since mutual diffusion of components may occur between the soil and the interface of the composite structure 5, it is possible that the chemical composition of the interface of the chemical treatment layer 15 changes from the chemical composition of the chemical treatment layer 15 in the portion not in contact with the soil. However, it is presumed that the average composition of the chemical treatment layer 15 as a whole is similar to the chemical composition of the chemical treatment layer 15 in the surface treated member 1 described above.

[0124] The oxide layer 21, which is an example of a P-Zn-based composite layer containing Zn and P, is a layer composed of a P-Zn-based composite oxide produced by the reaction between P derived from the chemical conversion treatment layer 15 and Zn derived from the zinc-based plating layer 13. It is presumed that, even in soil, compounds containing P contained in the chemical conversion treatment layer 15 are eluted from the chemical conversion treatment layer 15 in the form of phosphate ions. The P-Zn-based composite compound produced by such a reaction has a dense structure. Therefore, the presence of the oxide layer 21 composed of such a P-Zn-based composite oxide at at least a portion of the interface between the chemical conversion treatment layer 15 and the soil allows the composite structure 5 according to this embodiment to exhibit excellent corrosion resistance in soil.

[0125] Such oxide layer 21 preferably has a chemical composition containing, by mass %, Zn: 1.0% to 10.0%, P: 0.5% to 5.0%, and the remainder consisting of H, C, O, Si, and impurities. Since oxide layer 21 is made of a P-Zn-based composite compound having the above-mentioned chemical composition, composite structure 5 according to this embodiment exhibits superior corrosion resistance in soil.

[0126] Furthermore, when the zinc-based plating layer 13 further contains Al and Mg in its chemical composition, the chemical composition of the oxide layer 21 preferably further contains at least one of Al: 0% to 10.0% by mass and Mg: 0% to 10.0% by mass, in place of a portion of the remaining H, C, O, and Si. When the oxide layer 21 is composed of a P-Zn-Al-Mg-based composite compound having the above-mentioned chemical composition, the composite structure 5 according to this embodiment exhibits superior corrosion resistance in soil.

[0127] The chemical composition of the oxide layer 21 can be measured in the same manner as the chemical composition of the zinc-based plating layer 13 described above.

[0128] The composite structure 5 according to this embodiment has been described above with reference to FIGS.

[0129] (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.

[0130] <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 the base material and forming a zinc-based plating layer 13 and a chemical conversion treatment layer 15 on the surface of the steel material 11.

[0131] <<Method of Forming Zinc-Based Plating Layer 13>> 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 13. However, hot-dip plating is most preferable in terms of cost.

[0132] An example of a manufacturing method for obtaining the zinc-based coating layer 13 according to this embodiment using a hot-dip galvanizing method will be described in detail below. In the manufacturing process for the zinc-based coating layer 13, first, a steel sheet as an example of a steel material 11 used as a base material 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.

[0133] 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.

[0134] 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).

[0135] 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.

[0136] 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.

[0137] 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 coating weight is controlled by wiping gas. Here, with the exception of the bath temperature, general plating operating conditions may be applied, and no special equipment or conditions are required.

[0138] Furthermore, the molten plating alloy located on the steel sheet may be subjected to various heat treatments as required.

[0139] <<Method for forming chemical conversion layer 15>> The chemical conversion layer 15 according to this embodiment can be formed by applying a chemical conversion treatment agent containing the components constituting the chemical conversion layer 15 to the surface of the zinc-based plating layer 13 formed as described above, followed by baking at a predetermined temperature and hardening and drying. ２ When a chemical conversion treatment layer of an amount corresponding to the size of the ion-exchanged water is immersed in ion-exchanged water at a temperature of 35 to 45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer into the ion-exchanged water can be set within a desired range.

[0140] Furthermore, by forming the chemical conversion treatment layer 15 by the heating step described in detail below, the formed chemical conversion treatment layer 15 satisfies the relationship regarding the integrated peak intensity in XPS as described above, and the amount of P eluted from the chemical conversion treatment layer into ion-exchanged water can be set within a more preferable range. The various conditions for such heating directions will be described in detail below.

[0141] <Heating Method> In the heating step of heating the chemical conversion treatment agent applied to the zinc-based plating layer, a method is used that can heat the chemical conversion treatment agent from the steel material side. By heating the chemical conversion treatment agent from the steel material side, it is possible to make the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV in a narrow P2p spectrum obtained by analyzing the outermost surface of the chemical conversion treatment layer 15 by XPS 0.20 or more.

[0142] A specific heating method is, for example, an induction heating device (IH). When a steel material coated with a chemical conversion treatment agent (i.e., a steel material having a zinc-based plating layer formed thereon) is heated by IH, the IH can directly heat the steel material. Therefore, the chemical conversion treatment agent is heated by heat transfer from the steel material, and therefore the chemical conversion treatment agent is heated from the steel material side.

[0143] The mechanism by which the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV in the narrow P2p spectrum obtained by analyzing the outermost surface of the chemical conversion treatment layer 15 by XPS by heating the chemical conversion treatment agent from the steel side is able to be 0.20 or more is not clear. However, the present inventors speculate that this is due to the following reason.

[0144] In chemical conversion treatment agents, P exists as an anion soluble in water. When the chemical conversion treatment agent is heated and the water solvent evaporates, a precipitation reaction occurs between the P in the chemical conversion treatment agent and positively charged metal ions. During this reaction, the anion P reacts with the positively charged metal ions to form an insoluble compound.

[0145] The precipitation reaction between P in the chemical conversion treatment agent and positively charged metal ions, as well as the formation of insoluble compounds associated with this precipitation reaction, are thought to be triggered by an increase in concentration due to evaporation of the solvent water. When the chemical conversion treatment agent is heated from the steel side, the formation of insoluble compounds occurs preferentially near the steel. That is, by heating the chemical conversion treatment agent from the steel side, metal ions are preferentially consumed near the steel. Subsequently, P that does not form insoluble compounds with positively charged metal ions precipitates as soluble P on the surface of the chemical conversion treatment layer. As a result, in a narrow P2p spectrum obtained by analyzing the outermost surface of the chemical conversion treatment layer 15 using XPS, the ratio of the integrated intensity of the peak having a maximum value at 133.90±0.25 eV to the integrated intensity of the peak having a maximum value at 132.80±0.25 eV can be made 0.20 or greater.

[0146] <Maximum Temperature of Steel Material in Heating Process> In the heating process described above, the steel material coated with the chemical conversion treatment agent is heated, dried, and baked. The maximum temperature of the steel material in the heating process is preferably 50°C or higher and 100°C or lower, more preferably 50°C or higher and 80°C or lower, and even more preferably 50°C or higher and 70°C or lower. A maximum temperature lower than 50°C is not preferable because the solvent in the chemical conversion treatment agent does not completely volatilize. On the other hand, if the maximum temperature exceeds 100°C, the ratio of the integrated intensity of the peak having a maximum value at 133.90±0.25 eV to the integrated intensity of the peak having a maximum value at 132.80±0.25 eV in the narrow P2p spectrum obtained by analyzing the outermost surface of the chemical conversion treatment layer 15 using XPS is less than 0.20. The reason for this is unclear, but it is presumed to be due to changes in the chemical bonding state of P due to heat input.

[0147] <Relative Humidity in Heating Furnace> In the heating step described above, the relative humidity in the heating furnace is preferably 85% or more and 98% or less. By performing heating in an environment with such a relative humidity, in a narrow P2p spectrum obtained by analyzing the outermost surface of the chemical conversion treatment layer 15 by XPS, the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV can be set to 0.20 or more and 0.50 or less.

[0148] When the relative humidity is less than 85%, the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV cannot be 0.20 or more. The reason for this is unclear, but it is presumed to be due to the following reasons. When the relative humidity is less than 85%, even if a method is used that can heat the chemical conversion treatment agent from the steel side, solvent volatilization occurs in the outermost layer of the chemical conversion treatment agent. At this time, P in the chemical conversion treatment agent and positively charged metal ions form insoluble compounds. As a result, it becomes impossible to achieve the above-mentioned integrated intensity ratio of 0.20 or more.

[0149] On the other hand, when the relative humidity is greater than 98%, the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV cannot be set to 0.50 or less. The reason for this is not clear, but it is presumed to be due to the following reasons. When the relative humidity is greater than 98%, the evaporation of the solvent is suppressed. As a result, even after heating the chemical conversion treatment agent, water as the solvent remains in the coating. Due to the influence of this water, P is more likely to exist as a soluble compound, and as a result, the ratio of the integrated intensities cannot be set to 0.50 or less.

[0150] <Temperature increase rate of steel material in heating step> In the heating step described above, the temperature increase rate of the steel material in the heating step is preferably 1°C / sec or more and 15°C / sec or less. By using a method that can heat the chemical conversion treatment agent from the steel material side under conditions that result in a temperature increase rate of 15°C / sec or less and setting the P concentration of the chemical conversion treatment agent to 0.1 to 15 mass%, the average P concentration on the surface side of the chemical conversion treatment layer can be set to 1 to 20 mass%. Note that if the temperature increase rate is 1°C / sec or less, productivity will be poor.

[0151] The mechanism by which the average P concentration on the surface side of the chemical conversion treatment layer can be set to 1 to 20 mass % by heating the chemical conversion treatment agent from the steel side, setting the P concentration in the chemical conversion treatment agent to 0.1 to 15 mass %, and setting the temperature rise rate of the steel in the heating step to 15°C / second or less is not clear. However, the present inventors speculate that this is due to the following reason.

[0152] When a method for heating the chemical conversion treatment agent from the steel side is used, the solvent tends to volatilize on the steel side during the chemical conversion layer formation process, increasing the P concentration near the steel. Therefore, due to this concentration difference, P migrates to the surface side, where the concentration is lower. Furthermore, when the heating rate is 15°C / sec or less, it takes longer to form the chemical conversion layer due to the evaporation of the solvent compared to when the heating rate is greater than 15°C / sec. Therefore, it is thought that the time available for P to migrate in the solvent during the chemical conversion layer formation process is longer, increasing the amount of P that migrates to the surface side of the chemical conversion layer, making it easier for P to concentrate on the surface side. Therefore, by setting the P concentration of the chemical conversion treatment agent to 0.1 to 15 mass%, the average P concentration on the surface side of the chemical conversion layer can be set to 1 to 20 mass%.

[0153] <Cooling step after heating> The cooling step after heating is performed by a method other than water cooling. A specific cooling method is air cooling. If water cooling is performed, water-soluble P contained in the chemical conversion treatment layer 15 will dissolve into the cooling water, and a sufficient amount of P will not be dissolved.

[0154] <Cooling Rate After Heating> The cooling rate after heating is preferably 3°C / s or more and 50°C / s or less, more preferably 15°C / s or more and 40°C / s or less, and even more preferably 20°C / s or more and 40°C / s or less. If the cooling rate is 3°C / s or less, the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV in the narrow spectrum of P2p obtained by analyzing the outermost surface of the chemical conversion coating layer 15 by XPS cannot be 0.20 or more. The reason for this is unclear, but it is presumed that this is because the chemical conversion coating agent is also heated during the cooling process, causing a change in the chemical bonding state of P. On the other hand, a cooling rate of more than 50°C / s is uneconomical and therefore undesirable.

[0155] The chemical conversion treatment agent can be applied by a commonly known application method, such as roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, or brush coating.

[0156] 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.

[0157] <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.

[0158] An example of the method for manufacturing the surface treated member 1 according to this embodiment has been briefly described above.

[0159] 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.

[0160] <Preparation of Plated Steel Material> In the test examples shown below, the base sheets for plating shown in Table 1 below were used, and the base sheets for plating were cut into pieces measuring 100 mm x 200 mm. Then, plating was performed using a batch-type hot-dip plating test apparatus manufactured by our company, and multiple plated steel materials having the plating layer compositions shown in Table 2 below were produced for each level.

[0161]

[0162]

[0163] <Preparation of Chemical Conversion Treatment Agent> Chemical conversion treatment agents for forming a chemical conversion treatment layer were prepared using commercially available compounds as shown in Tables 3 to 7 below. Table 3 shows the compounds used as the phosphorus-containing compound, Table 4 shows the silane coupling agents used, and Table 5 shows the valve metals used. All of these compounds are general reagents. Table 6 shows the organic resins used, and Table 7 shows other compounds used. In Table 7, all compounds other than silica sol are general reagents.

[0164]

[0165]

[0166]

[0167]

[0168]

[0169] Using the various compounds described above, chemical conversion treatment agents having the formulations shown in Tables 10-1 to 10-8 below were prepared.

[0170] <Formation of Chemical Conversion Coating Layer> The chemical conversion coating agent prepared as described above was applied to the surface of the plated steel material described above using a bar coater to form a chemical conversion coating layer. The conditions for forming the chemical conversion coating layer are shown in Tables 8 to 11-8 below. In this manner, multiple surface-treated steel materials were produced as test materials for each level.

[0171]

[0172]

[0173] For each of the surface-treated steel materials obtained, the concentrations of various P elements in the chemical conversion coating layer and the XPS intensity ratios were measured, and the thickness of the chemical conversion coating layer was also measured. Furthermore, a leaching test was conducted to measure the amount of P eluted into ion-exchanged water, in accordance with the method described above. The results are summarized in Tables 11-1 to 11-8 below.

[0174] Furthermore, the corrosion resistance in soil of each of the obtained surface-treated steel materials was evaluated by the following two types of test methods, and it was confirmed whether or not an oxide layer, which is an example of a P-Zn based composite layer, was formed when the steel materials were buried in soil.

[0175] (Test method 1: Evaluation of corrosion resistance in general soil) The surface-treated steel material obtained as described above was buried in soil to evaluate its corrosion resistance. Silica sand with an average particle size of 300 μm was used as the soil. The cover thickness (distance from the surface of the chemical conversion coating layer to the soil surface) was 20 mm. After burial, to simulate general soil, ion-exchanged water containing 0.03 mass% NaCl was added dropwise to the soil, and the moisture content was adjusted to 100%. Here, the NaCl added to the ion-exchanged water simulates the electrolyte present in soil. Then, the following drying and wetting steps were repeated 50 times. Drying step: Stored at 30°C for 7 days Wetting step: Wetted with ion-exchanged water, and the moisture content was adjusted to 100%.

[0176] After the above test, the surface-treated steel materials were checked for the presence or absence of an oxide layer between the chemical conversion coating layer and the soil using the method described above. Furthermore, the surface treatment agent after the test was pickled with hydrochloric acid to remove the plating layer, the chemical conversion coating layer, and corrosion products. The corrosion state of the steel materials was then examined using a shape measuring instrument (Keyence VR-5000). The evaluation criteria are as follows. Grades A, B, and C were considered acceptable. The results are summarized in Tables 12-1 to 12-8 below. Grade A: No pits were formed on the steel material. Grade B: Pits with a depth of less than 10 μm were formed on the steel material. Grade C: Pits with a depth of 10 μm or more but less than 50 μm were formed on the steel material. Grade D: Pits with a depth of 50 μm or more but less than 100 μm were formed on the steel material. Grade E: Pits with a depth of 100 μm or more were formed on the steel material.

[0177] (Test method 2: Evaluation of corrosion resistance in acidic soil) The surface-treated steel material obtained as described above was buried in soil to evaluate its corrosion resistance. Silica sand with an average particle size of 100 μm was used as the soil. The cover thickness was 50 mm. After burial, in order to simulate acidic soil, an aqueous HCl solution prepared by adding HCl to ion-exchanged water to adjust the pH to 4 was dripped onto the soil, and the moisture content was adjusted to 100%. Thereafter, the following drying and wetting steps were repeated 50 times. Drying step: Stored at 30°C for 7 days Wetting step: Wetted with ion-exchanged water to adjust the moisture content to 100%

[0178] After the above test, the surface-treated steel materials were checked for the presence or absence of an oxide layer between the chemical conversion coating layer and the soil using the method described above. Furthermore, the surface treatment agent after the test was pickled with hydrochloric acid to remove the plating layer and corrosion products. The corrosion state of the steel materials was then examined using a shape measuring instrument (Keyence VR-5000). The evaluation criteria are as follows. Grades A, B, and C were considered acceptable. The results are summarized in Tables 12-1 to 12-8 below. Grade A: No pits were formed on the steel material. Grade B: Pits with a depth of less than 10 μm were formed on the steel material. Grade C: Pits with a depth of 10 μm or more but less than 50 μm were formed on the steel material. Grade D: Pits with a depth of 50 μm or more but less than 100 μm were formed on the steel material. Grade E: Pits with a depth of 100 μm or more were formed on the steel material.

[0179] (Test Method 3: Evaluation of Corrosion Resistance in Atmosphere) The surface-treated steel material obtained as described above was cut into pieces measuring 50 × 100 mm. The back surface of the test surface and the cut edge surfaces were protected with sealing tape (Nitto Denko Corporation, polyester-based adhesive tape for electrical insulation, No. 31C). A combined cyclic corrosion test according to JIS G 0594:2019 was then conducted. This test was a cyclic corrosion test consisting of 1 hour of salt spray, 4 hours of dryness, and 3 hours of humid environment. This test was conducted for 120 hours (15 cycles).

[0180] After the above test, the corrosion state of the surface-treated steel material was visually observed, and the area rate of white rust occurrence was investigated. The evaluation criteria were as follows. Grades A, B, and C were considered to be pass. The results are summarized in Tables 12-1 to 12-8 below. Grade A: White rust area rate of 5% or less B: White rust area rate of over 5% and up to 10% C: White rust area rate of over 10% and up to 20% D: White rust area rate of over 20% and up to 50% E: White rust area rate of over 50%

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[0205] As is clear from Tables 10-1 to 12-8 above, the surface-treated members corresponding to the examples of the present invention exhibited excellent corrosion resistance even in soil, whereas the surface-treated members corresponding to the comparative examples of the present invention were unable to obtain sufficient corrosion resistance.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] The following configurations also fall within the technical scope of the present invention: (1) A surface-treated member made of a surface-treated steel material having a base steel material, a zinc-based plating layer located on the surface of the steel material, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the chemical conversion coating layer contains a compound containing phosphorus (P), and the surface-treated steel material 1m ２When the chemical conversion treatment layer in an amount corresponding to the size of the ion-exchanged water is immersed in ion-exchanged water at a temperature of 35 to 45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer into the ion-exchanged water is 5 to 50 mg / m ２(2) The surface-treated member according to (1), which is used by burying at least a portion of the surface-treated steel material in soil. (3) The surface-treated member according to (1) or (2), in which, in a narrow P2p spectrum obtained by analyzing the surface of the chemical conversion treatment layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of a peak having a maximum at 133.90±0.25 eV to the integrated intensity of a peak having a maximum at 132.80±0.25 eV is 0.20 to 0.50. (4) The surface-treated member according to any one of (1) to (3), in which, in a depth profile of P concentration obtained by performing line analysis of the chemical conversion treatment layer by energy dispersive X-ray spectroscopy (EDS) from the surface to the interface with the zinc-based plating layer, the average concentration of P on the surface side of the chemical conversion treatment layer is 1 to 20 mass%. (5) The surface-treated member according to any one of (1) to (4), wherein the P concentration of the chemical conversion treatment layer is 0.1 to 15.0 mass % in terms of P. (6) The surface-treated member according to any one of (1) to (5), wherein the thickness of the chemical conversion treatment layer is 30 to 5,000 nm. (7) The surface-treated member according to any one of (1) to (6), wherein the chemical conversion treatment layer contains one or more selected from the group consisting of a silane coupling agent, a valve metal, and an organic resin. (8) The surface-treated member according to any one of (1) to (7), wherein the zinc-based plating layer has a chemical composition containing, in mass %, Al: 0.10% or more but less than 40.00%, Mg: 0.10% or more but less than 15.00%, and the balance consisting of Zn and impurities. (9) The surface-treated member according to (8), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more. (10) The surface-treated member according to any one of (1) to (7), wherein the zinc-based plating layer is a plating layer containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further containing one or more elements selected from the group consisting of element group A, element group B, element group C, element group D, element group E, and element group F below, with the balance being Zn and impurities.[Element group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element group B]: One or two or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element group C]: One or two or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element group D]: One or two or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less [Element group F]: B: less than 0.50% (11) The surface-treated member according to (10), which contains element group A. (12) The surface-treated member according to (10), which contains element group B. (13) The surface-treated member according to (10), which contains element group C. (14) The surface-treated member according to (10), which contains element group D. (15) The surface-treated member according to (10), which contains element group E. (16) The surface-treated member according to (10), which contains element group F. (17) The surface-treated member according to (10), wherein the zinc-based plating layer is a plating layer containing, by mass%, at least: Al: 4.0% or more but less than 25.0% and Mg: 0.3% or more but less than 12.5%. (18) A composite structure of soil and a surface-treated member made of a surface-treated steel material having a steel material as a base material, a zinc-based plating layer located on the surface of the steel material, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein a P-Zn-based composite layer containing Zn and P is present between the chemical conversion coating layer and the soil at at least a part of the interface between the surface-treated member and the soil. (19) The composite structure according to (18), wherein the P-Zn-based composite layer is a layer having a chemical composition containing, by mass%, Zn: 1.0% or more but less than 10.0% and P: 0.5% or more but less than 5.0%, with the remainder consisting of H, C, O, Si, and impurities.(20) The composite structure according to (19), wherein the zinc-based plating layer further contains Al and Mg as a chemical composition, and the chemical composition of the P-Zn-based composite layer further contains at least one of Al: 0% or more and 10.0% or less by mass and Mg: 0% or more and 10.0% or less by mass in place of a part of the remaining H, C, O, and Si.

[0210] REFERENCE SIGNS LIST 1 Surface-treated member 5 Composite structure 10 Surface-treated steel material 11 Steel material 13 Zinc-based plating layer 15 Chemical conversion coating layer 21 Oxide layer

Claims

1. A surface-treated member made of a surface-treated steel material having a base steel material, a zinc-based plating layer located on the surface of the steel material, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the chemical conversion coating layer contains a compound containing phosphorus element P, and the surface-treated steel material 1m ２ When the chemical conversion treatment layer in an amount corresponding to the size of the ion-exchanged water is immersed in ion-exchanged water at a temperature of 35 to 45°C for 60 minutes, the amount of P eluted from the chemical conversion treatment layer into the ion-exchanged water is 5 to 50 mg / m ２ A surface-treated component.

2. The surface-treated steel member according to claim 1, which is used by burying at least a part of the surface-treated steel member in soil.

3. The surface-treated member according to claim 1, wherein in a narrow P2p spectrum obtained by analyzing the surface of the chemical conversion coating layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of the peak having a maximum at 133.90±0.25 eV to the integrated intensity of the peak having a maximum at 132.80±0.25 eV is 0.20 to 0.

50.

4. The surface-treated member according to claim 1, wherein, in a depth profile of P concentration obtained by performing line analysis of the chemical conversion layer from the surface to the interface with the zinc-based plating layer by energy dispersive X-ray spectroscopy (EDS), the average P concentration on the surface side of the chemical conversion layer is 1 to 20 mass %.

5. The surface-treated member according to claim 1, wherein the P concentration of the chemical conversion treatment layer is 0.1 to 15.0 mass % in terms of P.

6. The surface-treated member according to claim 1, wherein the thickness of the chemical conversion coating layer is 30 to 5,000 nm.

7. The surface-treated member according to claim 1, wherein the chemical conversion coating layer contains one or more materials selected from the group consisting of a silane coupling agent, a valve metal, and an organic resin.

8. The surface-treated member according to any one of claims 1 to 7, wherein the zinc-based plating layer has a chemical composition containing, by mass%, Al: 0.10% or more but less than 40.00%, Mg: 0.10% or more but less than 15.00%, with the balance being Zn and impurities.

9. The surface-treated member according to claim 8, wherein the zinc-based plating layer is a plating layer containing, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

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

11. The surface-treated member according to claim 10, containing said element group A.

12. The surface-treated member according to claim 10, which contains the element group B.

13. The surface-treated member according to claim 10, containing said element group C.

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

15. The surface-treated member according to claim 10, which contains the element group E.

16. The surface-treated member according to claim 10, containing the element group F.

17. The surface-treated member according to claim 10, wherein the zinc-based plating layer is a plating layer containing at least, by mass%, Al: 4.0% or more but less than 25.0% Mg: 0.3% or more but less than 12.5%.

18. A composite structure comprising a surface-treated member made of surface-treated steel having a base steel material, a zinc-based plating layer on the surface of the steel material, and a chemical conversion coating layer on the surface of the zinc-based plating layer, and soil, wherein a P-Zn-based composite layer containing Zn and P exists between the chemical conversion coating layer and the soil at least in a portion of the interface between the surface-treated member and the soil.

19. The composite structure according to claim 18, wherein the P-Zn-based composite layer is a layer having a chemical composition containing, in mass %, Zn: 1.0% to 10.0%, P: 0.5% to 5.0%, with the remainder consisting of H, C, O, Si, and impurities.

20. A composite structure as set forth in claim 19, wherein the zinc-based plating layer further contains Al and Mg as a chemical composition, and the chemical composition of the P-Zn-based composite layer further contains at least one of Al: 0% or more and 10.0% or less by mass, and Mg: 0% or more and 10.0% or less by mass, in place of a portion of the remaining H, C, O, and Si.

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