Surface-treated components and composite structures

Abstract

[Problem] Excellent corrosion resistance is achieved even in soil at a depth of several centimeters from the soil surface. [Solution] The surface-treated component of the present invention is constructed of surface-treated steel, which comprises: steel as a base material, a zinc-based plating layer on the surface of the aforementioned steel, and a chemical conversion treatment layer on the surface of the aforementioned zinc-based plating layer; the aforementioned chemical conversion treatment layer contains: a compound containing phosphorus element P; after the aforementioned chemical conversion treatment layer, in a 1 m² volume of the aforementioned surface-treated steel, is immersed in ion-exchanged water at a temperature of 35~45°C for 60 minutes, the amount of P dissolved from the aforementioned chemical conversion treatment layer into the aforementioned ion-exchanged water is 5~50 mg / m².

Description

Technical Field

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

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

[0003] It is foreseeable that surface-treated components, as described above, will be exposed to various corrosive environments depending on their intended use. Therefore, the corrosion resistance of surface-treated steel as a material has been the subject of numerous reviews.

[0004] For example, Patent Document 1 discloses a polyolefin-coated heavy-duty corrosion-resistant steel, which consists of layers sequentially deposited on a base steel or a chromate-coated steel having a chromate layer on its surface: an epoxy primer layer, a maleic anhydride-modified polyolefin layer, and a polyolefin layer; and an epoxy primer layer is formed using a phenolic hardener and epoxy resin with an oxygen permeability within a specific range. Patent Document 1 states that this polyolefin-coated heavy-duty corrosion-resistant steel can be used even in extremely harsh corrosive environments such as soil, rivers, and oceans.

[0005] Furthermore, Patent Document 2 discloses a coated steel material in which a phosphate chemical conversion treatment film and a coating film are sequentially formed on the surface of steel having a zinc-based plating layer; the phosphate chemical conversion treatment film contains at least one element, such as nickel, magnesium, or calcium, in addition to zinc and manganese; the coating film contains phosphate-based anti-rust pigments and sulfates of alkaline earth metals. Patent Document 2 states that the coated steel material can be used by partially embedding it in concrete or the ground.

[0006] [Previous Technical Documents] [Patent Literature] [Patent Document 1] Japanese Patent Application Publication No. 2005-132105 [Patent Document 2] Japanese Patent Application Publication No. 2007-262561 Summary of the Invention

[0007] Invention Summary The problem that the invention aims to solve As emphasized in Patent Documents 1 and 2 above, when a surface-treated component is installed at a desired location, it can be assumed that at least a portion of it will be buried in the soil. If any part of the surface-treated component is exposed to the atmosphere, the corrosion status can be easily investigated by visual inspection of that exposed portion. However, the portion buried in the soil is different from that in the atmosphere; it is difficult to inspect the corrosion status by visual inspection, and the corroded portion is also difficult to maintain. Therefore, surface-treated components used in soil require high corrosion resistance.

[0008] The inventors in this case examined the corrosion of zinc-plated steel in soil. The results, as described below, indicate that the corrosion behavior of zinc-plated steel in soil at a depth of 1 meter or more from the soil surface is significantly different from that in soil at a depth of only a few centimeters from the soil surface. Furthermore, the soil corrosion environment described in Patent Document 2 primarily corresponds to the corrosion behavior in soil at a depth of 1 meter or more from the soil surface. Additionally, it was observed that even when using the surface-treated steel disclosed in Patent Documents 1 and 2 as a material to manufacture surface-treated components in soil at a depth of only a few centimeters from the soil surface, there is still room for improvement in its corrosion resistance.

[0009] Therefore, the present invention was made in view of the above-mentioned problems. The object of the present invention is to provide a surface-treated component using zinc-plated steel and a composite structure using the surface-treated component, which can exhibit excellent corrosion resistance even in soil at a depth of about a few centimeters from the soil surface.

[0010] The means to solve the problem To address the aforementioned issues, the inventors of this invention conducted intensive research and arrived at the concept of altering the state of the chemical conversion treatment layer applied to the surface of surface-treated steel with a zinc-based plating layer, depending on the corrosive environment it is exposed to (e.g., in the atmosphere or soil). Based on this concept, the inventors of this invention conducted further research and conceived of a surface-treated component as described below. The key points of the present invention based on this concept are as follows.

[0011] (1) A surface-treated component is made of surface-treated steel, which has: steel as a base material, a zinc-based plating layer on the surface of the steel, and a chemical conversion treatment layer on the surface of the zinc-based plating layer; the chemical conversion treatment layer contains: a compound containing phosphorus element P; after the chemical conversion treatment layer, in a 1 m2 size of the surface-treated steel, is immersed in ion-exchange water at a temperature of 35~45°C for 60 minutes, the amount of P dissolved from the chemical conversion treatment layer into the ion-exchange water is 5~50 mg / m2. (2) The surface-treated component as described in (1) is used in such a way that at least a portion of the aforementioned surface-treated steel is buried in the soil. (3) The surface-treated component as described in (1), wherein the ratio of the cumulative intensity of the peak with a maximum value at 133.90±0.25eV to the cumulative intensity of the narrow spectrum of P2p obtained by X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aforementioned chemical conversion treated layer is 0.20 to 0.50. (4) The surface-treated component as described in (1), wherein when energy dispersive X-ray spectroscopy (EDS) is performed on the chemical conversion treatment layer from its surface to its 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 by mass in the depth profile of the obtained P concentration. (5) The surface-treated component as described in (1), wherein the P concentration of the aforementioned chemical conversion treatment layer is 0.1 to 15.0 by mass when converted to P. (6) The surface treatment component as described in (1), wherein the thickness of the aforementioned chemical conversion treatment layer is 30~5000 nm. (7) The surface treatment component as described in (1), wherein the aforementioned chemical conversion treatment layer contains one or more of the following selected from the group consisting of silane coupling agents, valve metals and organic resins. (8) The surface treatment component described in any one of (1) to (7), wherein the aforementioned zinc plating layer is a plating layer having the following chemical composition, which, in mass % contains: Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the remainder is composed of Zn and impurities. (9) The surface-treated component as described in (8), wherein the aforementioned zinc-based plating layer contains the following plating layer: Al: 0.10% or more and less than 40.00% by mass%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more. (10) The surface-treated component as described in any one of (1) to (7), wherein the aforementioned zinc-based plating layer is a plating layer having the following chemical composition, which, in mass % contains: 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 remainder consisting of Zn and impurities; [Element Group A]: Selected from one or two elements in the group consisting of Si: 2.50% or less and Fe: 5.00% or less; [Element Group B]: Selected from one or more elements in the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%; [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%; [Element Group D]: Selected from one or more elements in the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%; [Element Group E]: Selected from one or more elements in the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%; [Element group F]:B: less than 0.50%. (11) The surface-treated component as described in (10) contains the aforementioned element group A. (12) The surface treatment component described in (10) contains the aforementioned element group B. (13) The surface-treated component as described in (10) contains the aforementioned element group C. (14) The surface-treated component as described in (10) contains the aforementioned element group D. (15) The surface-treated component as described in (10) contains the aforementioned element group E. (16) The surface-treated component as described in (10) contains the aforementioned element group F. (17) The surface-treated component as described in (10), wherein the aforementioned zinc-based plating layer contains at least the following plating layer: Al: 4.0% or more and less than 25.0% by mass, Mg: 0.3% or more and less than 12.5%. (18) A composite structure is a composite structure of a surface-treated component and soil; the surface-treated component is made of surface-treated steel, the surface-treated steel having: steel as a base material, a zinc-based plating layer on the surface of the steel, and a chemical conversion treatment layer on the surface of the zinc-based plating layer; at least a portion of the interface between the surface-treated component and the soil, between the chemical conversion treatment layer and the soil, is a P-Zn composite layer containing Zn and P. (19) The composite structure described in (18) wherein the aforementioned P-Zn composite layer is a layer having the following chemical composition, which, in mass %, contains: Zn: 1.0% or more and 10.0% or less, P: 0.5% or more and 5.0% or less, and the remainder consists of H, C, O, Si and impurities. (20) The composite structure described in (19) further contains Al and Mg as chemical components; the aforementioned P-Zn composite layer further contains at least one of the following to replace a portion of the remaining H, C, O, and Si: Al: 0% or more and 10.0% by mass or less, Mg: 0% or more and 10.0% by mass or less.

[0012] Invention Effects As explained above, according to the present invention, the surface-treated components using zinc-plated steel and the composite structures using the surface-treated components can achieve excellent corrosion resistance even in soil at a depth of about a few centimeters from the soil surface. Simple Explanation of the Diagram

[0013] Figure 1 is a schematic diagram illustrating a structure placed on the soil surface. Figure 2 is a schematic diagram illustrating the structure of the surface treatment component according to an embodiment of the present invention. Figure 3 is a schematic diagram illustrating the structure of the surface treatment component in this embodiment. Figure 4 is an explanatory diagram illustrating the composite structure of the surface treatment component and soil in this embodiment. Figure 5 is an explanatory diagram illustrating the composite structure of the surface treatment component and soil in this embodiment. Implementation

[0014] Embodiments of the present invention Forms used to implement inventions The present invention will now be described in detail with reference to the accompanying drawings, taking into account suitable embodiments thereof. Furthermore, in this specification and drawings, constituent elements having substantially the same functional configuration are given the same reference numerals to avoid redundant descriptions.

[0015] (Corrosion behavior in soil at a depth of approximately several centimeters from the soil surface) Before describing the surface treatment component according to an embodiment of the present invention, the corrosion behavior in soil at a depth of about a few centimeters from the soil surface, as discovered by the inventors of this case, will be described with reference to FIG1. ​​FIG1 is a schematic diagram illustrating a structure installed on the soil surface. For convenience, the "soil at a depth of about a few centimeters from the soil surface" will sometimes be referred to as the "soil surface portion".

[0016] As illustrated in Figure 1, various structures are placed on the soil surface, such as pedestals supporting solar panels, road signs, guardrails, and signal generators. In order to make the structures more stable on the soil surface, as shown in Figure 1, a part of the structure (e.g., the area near the lower end of the support column, enclosed by the dashed circle in Figure 1) is often buried in the soil.

[0017] In this context, for example, based on production costs, various types of steel are often used as the material for structures. When a portion of a structure made of steel is buried in the soil, the steel itself may corrode.

[0018] The effects of soil on steel corrosion can be categorized into two main aspects: the retention of moisture (a corrosion factor) and the inhibition of oxygen diffusion (another corrosion factor). Moisture retention tends to increase the corrosion rate, while the inhibition of oxygen diffusion tends to decrease it. Compared to the atmosphere, soil maintains a relatively moist environment (i.e., moisture) for extended periods, such as after rainfall. On the other hand, soil inhibits the penetration and diffusion of oxygen from the atmosphere, thus reducing the corrosion rate. In terms of actual corrosion rates in soil, as described above, these two effects interact in a trade-off relationship, resulting in a stable corrosion rate at a certain level. Generally, the effect of inhibiting oxygen diffusion is greater than that of moisture retention; therefore, compared to the atmosphere, soil exhibits a slower corrosion rate.

[0019] On the other hand, the situation is quite different in the soil layer (the top layer of soil) at a depth of about a few centimeters from the surface. Even in the top layer, moisture is difficult to evaporate due to the soil, so the steel remains in contact with moisture for a longer period of time compared to the atmosphere. Furthermore, the top layer of soil is sometimes closer to the atmosphere, and oxygen is quickly supplied from the atmosphere, so the effect of the soil inhibiting oxygen diffusion is relatively small. Therefore, it can be considered that, in conjunction with the effect of moisture retention, the corrosion-inhibiting effect of the soil is almost impossible to obtain in the top layer of soil. Thus, compared to soil layers with a depth of more than 1 meter from the surface, the top layer of soil, which the inventors of this invention focused on, can be described as an extremely harsh corrosive environment.

[0020] In order to examine the corrosion behavior of steel in the surface layer of soil, the inventors of this case examined the corrosion behavior of zinc-plated steel in the surface layer of soil and obtained the following insights. In other words, the zinc coating of zinc-plated steel exhibits high corrosion resistance because zinc-based corrosion products can coat the surface of the coating in the atmosphere. However, it should be noted that the corrosion protection provided by these zinc-based corrosion products is poor in the surface layer of soil.

[0021] The inventors in this case used a scanning electron microscope (SEM) to observe zinc corrosion products formed on zinc-based coatings in the surface layer of soil. The results clarified that, compared to zinc corrosion products formed in the atmosphere, the zinc corrosion products formed in the soil surface layer are porous. This can be attributed to the fact that corrosion progresses more rapidly in the soil surface layer compared to in the atmosphere.

[0022] Based on the above insights, the inventors of this case have the insight that, in order to improve the corrosion resistance of zinc-plated steel in the surface layer of soil, it is important to make the layer composed of corrosion products formed on the surface of the zinc-plated layer in the surface layer of soil become dense.

[0023] To achieve a dense corrosion product layer in the surface layer of soil, the inventors conducted further investigations. They discovered that, to improve the corrosion resistance of zinc-plated steel in the surface layer of soil, it is effective to include phosphorus (P) in the zinc-plated corrosion products during their formation. Furthermore, the inventors conceived of using a P-containing chemical conversion treatment layer on the surface of the zinc-plated layer as a source of P.

[0024] This chemical conversion treatment layer exhibits adequate corrosion resistance in the atmosphere, and together with the zinc-based plating layer, it helps to improve the corrosion resistance of the surface-treated components. In the atmosphere, phosphorus (P) dissolved from the chemical conversion treatment layer (presumably in P ion form) is washed away by rain and other factors, and rarely adheres to the surface of the chemical conversion treatment layer. On the other hand, it can be inferred that in soil, there is no water flow as described above, so the dissolved P would adhere to the interface between the chemical conversion treatment layer and the soil.

[0025] In this way, during the formation of zinc-based corrosion products, phosphorus (P) is dissolved from the chemically converted layer in a specific amount, thereby forming a dense P-Zn composite oxide at the interface between the chemically converted layer and the soil. This P-Zn composite oxide-containing corrosion product forms at the interface between the chemically converted layer and the soil, thereby enhancing the corrosion resistance of surface-treated components in the soil through the corrosion product layer, the chemically converted layer, and the zinc plating layer.

[0026] Furthermore, according to the results of the review by the inventors of this case, if the zinc-based coating is an alloy coating containing not only Zn but also Mg and Al, then in the soil, in addition to the dissolution of Zn ions, Mg ions and Al ions will be dissolved, thereby generating P-Zn-Al-Mg composite oxides, which will further enhance the corrosion resistance.

[0027] Based on the insights described above, the inventors of this case conducted further reviews and came up with the surface treatment component of the present invention as detailed below.

[0028] (Regarding surface-treated components) Hereinafter, a detailed description of the surface treatment component according to an embodiment of the present invention will be provided with reference to FIGS. 2 and 3. FIGS. 2 and 3 are schematic diagrams illustrating the structure of the surface treatment component according to this embodiment. Furthermore, in FIGS. 2 and 3, for convenience, the description will be conducted using the coordinate axes shown in the figures.

[0029] As detailed below, the surface-treated component of this embodiment is constructed from surface-treated steel, which has a zinc-based plating layer and a chemical conversion treatment layer. The specific structure of the surface-treated component of this embodiment is not particularly limited. For example, the surface-treated component of this embodiment can be a box-shaped object, or a plate-shaped object using sheet steel, such as a roof or wall of a building. Furthermore, the specific structure of the surface-treated component of this embodiment can be a shaped or joined body using various types of steel, such as a solar panel frame, or a shaped or joined body using various H-beams or corner posts, such as a structural frame, or a shaped or joined body using various steel pipes, such as various pillars, signs, signal devices, or guardrails. This surface-treated component is used, for example, by burying at least a portion of the surface-treated steel in the soil.

[0030] Figure 2 schematically shows a portion of the surface-treated component 1 of this embodiment as viewed from above its surface (in the Z-axis direction of the figure). As shown in Figure 2, the surface-treated component 1 of this embodiment, as described below, is made of surface-treated steel 10, which has a zinc-based plating layer 13 and a chemical conversion treatment layer 15 on the surface of the steel 11 used as the base material.

[0031] Figure 3 schematically shows a cross-section of the surface-treated component 1 shown in Figure 2 when it is cut along the AA cutting line in the Z-axis direction. The cross-sectional view shown in Figure 3 corresponds to the surface-treated component 1 of this embodiment being cut in the thickness direction of the surface-treated steel 10 of the material of the surface-treated component 1.

[0032] As shown schematically in Figure 3, the surface treatment component 1 of this embodiment is made of surface-treated steel 10, which has: steel 11 as the base material, zinc-based plating layer 13 on the front and back of the steel 11, and chemical conversion treatment layer 15 on the surface of zinc-based plating layer 13.

[0033] The following section will first describe in detail the steel 11, the zinc-based plating layer 13, and the chemical conversion treatment layer 15.

[0034] <About Steel 11> The steel 11 used as the base material for the surface-treated component 1 in this embodiment is not particularly limited, and various types of steel can be used depending on the required mechanical strength (e.g., tensile strength) of the surface-treated component 1. Examples of such steel 11 include: various aluminum-deoxidized steels, ultra-low carbon steels containing Ti, Nb, etc., high-strength steels that further contain strengthening elements such as P, Si, Mn, etc., and various steels containing other components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0035] Alternatively, a pre-plating layer can be applied to the steel 11 before the zinc plating process described later. Metals suitable for the pre-plating layer include Ni, Sn, or alloys combining these elements. Using pre-plated steel with these pre-plated materials eliminates unplated areas (areas where the plating metal is rejected by oxide films, etc.). This is presumably because when the pre-plated steel is immersed in a molten plating bath, the metal elements in the molten plating bath react with the pre-plating layer to form Ni(Sn)-Al-Fe-Zn. The amount of pre-plating layer adhering to each side should preferably be in the range of 0.2~2.0 g / m². Setting the amount of pre-plating layer to 0.2 g / m² or more ensures that the anti-unplating effect achieved by the pre-plating is effectively demonstrated. Furthermore, the adhesion amount of the pre-plated coating is set to less than 2.0 g / m2, which can prevent the pre-plated coating from inhibiting Fe dissolution and making it difficult for Fe-Zn composite oxides to be formed, while achieving the above-mentioned effect of inhibiting unplated coating.

[0036] Furthermore, the thickness of the steel 11 is not particularly limited, and can be appropriately set according to the mechanical strength required by the surface-treated component 1.

[0037] <Regarding Zinc-Based Coatings 13> The zinc-based coating 13 is formed on both sides of the steel 11 as described above. The zinc-based coating 13 is not particularly limited as long as it contains at least zinc (Zn), and various known zinc-based coatings can be used.

[0038] Examples of zinc-based plating include: zinc plating represented by molten zinc plating or alloyed molten zinc plating; 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 can be obtained by including small amounts of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic in the above-mentioned platings; or by dispersing inorganic substances such as silicon dioxide, aluminum oxide, and titanium oxide in the above-mentioned platings. The plating method is not particularly limited; various well-known plating methods such as electroplating, molten plating, vapor deposition, dispersion plating, and vacuum plating can be used.

[0039] Among the various zinc-based platings described above, the zinc-based plating layer 13 of this embodiment is preferably a zinc-based plating layer having a chemical composition as detailed below. By using a material having a chemical composition as detailed below as the zinc-based plating layer 13, the surface-treated component 1 of this embodiment can further improve its various properties, primarily corrosion resistance. Hereinafter, the preferred chemical composition of the zinc-based plating layer 13 as described above will be described in detail.

[0040] Regarding the chemical composition of zinc-based plating layer 13 The chemical composition of the zinc-based plating layer 13 in this embodiment, according to a certain sample, is as follows: it contains Al: 0.10% or more and less than 40.00% by mass, Mg: 0.10% or more and less than 15.00%, and the remainder consists of Zn and impurities.

[0041] Furthermore, in the chemical composition of a certain sample of the zinc-based plating layer 13 in this embodiment, the zinc-based plating layer 13 is preferably a plating layer containing the following: by mass % Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, Zn: 60.00% or more.

[0042] Furthermore, the chemical composition of the zinc-based plating layer 13 in this embodiment, according to other embodiments, has the following chemical composition: containing Al: 0.10% or more and less than 40.00% by mass, Mg: 0.10% or more and less than 15.00%, 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, with the remainder consisting of Zn and impurities.

[0043] [Element Group A]: Selected from one or two elements in the group consisting of Si: 2.50% or less and Fe: 5.00% or less; [Element Group B]: Selected from one or more elements in the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%; [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%; [Element Group D]: Selected from one or more elements in the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%; [Element Group E]: Selected from one or more elements in the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%; [Element group F]:B: less than 0.50%.

[0044] [Al: ≥0.10% by mass and <40.00% by mass] Al is an essential element for forming the main metallic structure (Zn-Al-Mg metallic structure) in the suitable state of the zinc-based coating 13 of this embodiment. Therefore, in order to ensure the corrosion resistance of the coated steel, it is advisable to contain Al at a predetermined or higher content. When the Al content in the zinc-based coating 13 is less than 0.10% by mass, the corrosion resistance described above may not be guaranteed. Therefore, in the zinc-based coating 13 of this embodiment, the Al content is preferably 0.10% by mass or more. The Al content is preferably 3.00% by mass or more, more preferably 4.00% by mass or more, and more preferably 6.00% by mass or more. With the Al content in the range described above, the corrosion resistance of the coated steel can be guaranteed.

[0045] On the other hand, if the Al content in the zinc-based coating 13 reaches 40.00% by mass or more, the Al phase, which functions as a cathode in a corrosive environment, will increase excessively, making it easier for the steel 11 to corrode, and thus the corrosion resistance of the coated steel may not be guaranteed. Therefore, in the zinc-based coating 13 of this embodiment, the Al content is preferably less than 40.00% by mass. The Al content is preferably less than 25.00% by mass, more preferably less than 25.00% by mass, and even more preferably less than 20.00% by mass.

[0046] [Mg: ≥0.10% by mass and <15.00% by mass] Mg is an essential element for constituting the main metallic structure (Zn-Al-Mg metallic structure) in the suitable state of the zinc-based coating 13 of this embodiment. Therefore, in order to ensure the corrosion resistance of the coated steel, it is advisable to contain Mg at a predetermined or higher content. When the Mg content in the zinc-based coating 13 is less than 0.10% by mass, the corrosion resistance described above may not be guaranteed. Therefore, in the zinc-based coating 13 of this embodiment, the Mg content is preferably 0.10% by mass or more. The Mg content is preferably 0.30% by mass or more, and more preferably 3.00% by mass or more. With the Mg content within the above range, the corrosion resistance of the coated steel can be guaranteed.

[0047] On the other hand, if the Mg content in the zinc-based coating 13 reaches 15.00% by mass or more, anodic dissolution of the zinc-based coating will easily occur in a corrosive environment, thus potentially compromising the corrosion resistance of the coated steel. Therefore, in the zinc-based coating 13 of this embodiment, the Mg content is preferably less than 15.00% by mass. The Mg content is preferably less than 12.50% by mass, and more preferably less than 12.00% by mass. With the Mg content within the aforementioned range, the corrosion resistance of the coated steel can be guaranteed.

[0048] In the zinc-based plating layer 13 of this embodiment, the remaining portion of Al and Mg is Zn and impurities. Zn is an essential element for forming the main metallic structure (Zn-Al-Mg metallic structure) in the suitable sample of the zinc-based coating 13 of this embodiment, and is also an important element for improving the corrosion resistance of the coated steel. Furthermore, the zinc-based coating 13 contains Al and Mg within the above-mentioned range and further contains Zn, thereby ensuring the required corrosion resistance of the coated steel.

[0049] Next, in suitable counterparts of other zinc-based plating layers 13 of this embodiment, the element groups A to F that may be present in the chemical composition of the zinc-based plating layer 13 will be described in detail.

[0050] In addition, in other zinc-based plating layers 13 of this embodiment, if they contain at least one of the elements belonging to element groups A to F, they should preferably contain at least one of the elements belonging to element groups A to F within the following content range and with a total content of 60.00% by mass or less.

[0051] The total content of elements belonging to element groups A through F should be set to 60.00% by mass or less. This allows one to enjoy the effects of adding each element, as detailed below, without compromising their mutual effects. The total content of elements belonging to element groups A through F should preferably be 50.00% by mass or less, and more preferably 40.00% by mass or less.

[0052] ◇Element Group A In other embodiments of the zinc-based plating layer 13 of this embodiment, the element group A that may be contained in the zinc-based plating layer 13 will be described. At least any element in element group A shown below is an element that can replace a portion of the remaining Zn and is contained in the zinc-based plating layer 13. [Element Group A]: Selected from one or two elements in the group consisting of Si: 2.50% or less and Fe: 5.00% or less.

[0053] [Si: 0~2.50% by mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing Si is also considered, therefore the lower limit of its content is 0% by mass. On the other hand, Si inhibits the excessive growth of Fe-Al metal structure at the interface between the zinc-based plating layer 13 and the steel 11, thereby improving the adhesion between the zinc-based plating layer 13 and the steel 11. When the zinc-based plating layer 13 contains Si, in order to inhibit the excessive growth of Fe-Al metal structure, the Si content should preferably be 0.05% by mass or more, and more preferably 0.20% by mass or more. On the other hand, when the Si content is greater than 2.50% by mass, it will excessively form high-melting-point intermetallic compounds with Mg, which may hinder the formation of Al-Mg oxides that have the effect of inhibiting Zn evaporation during welding.

[0054] Furthermore, if the Si content in the plating bath used to manufacture the zinc-based coating 13 is too high, the viscosity of the plating bath will increase to a necessary level, and the workability (hereinafter referred to as "plating workability") when manufacturing the plated steel may decrease. Therefore, the Si content in the plating bath can be adjusted from the viewpoint of plating workability. The Si content in the zinc-based coating 13 should preferably be 1.50% by mass or less, and more preferably 1.00% by mass or less.

[0055] [Fe: 0~5.00% by mass] In the zinc-based plating layer 13, elements constituting the steel may sometimes be mixed in from the base material, i.e., the steel 11. In particular, during the melt plating process, the solid-liquid reaction between the steel 11 and the zinc-based plating layer 13 leads to interdiffusion of elements, thus easily causing elements constituting the steel 11 to mix into the zinc-based plating layer 13. Due to this mixing, the zinc-based plating layer 13 will typically contain a predetermined amount of Fe, usually exceeding 0.01% by mass. Promoting this interdiffusion enhances the adhesion between the steel 11 and the zinc-based plating layer 13. From the viewpoint of improving the adhesion between the steel 11 and the zinc-based plating layer 13, the Fe content in the zinc-based plating layer 13 should preferably be 0.20% by mass or more.

[0056] Furthermore, without compromising the effectiveness of the present invention, Fe can be intentionally added to the plating bath used in manufacturing the zinc-based plating layer 13. However, if the Fe content in the plating bath increases, a high-melting-point intermetallic compound of Fe and Al will form in the plating bath. In this case, the high-melting-point intermetallic compound will adhere to the zinc-based plating layer 13 as scum, which tends to significantly reduce the appearance quality, and is therefore undesirable. The Fe content in the plating bath can be adjusted from this point of view. 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, and 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 other embodiments of the zinc-based plating layer 13, the element group B that may be contained in the zinc-based plating layer 13 will be described. At least any element in element group B shown below is an element that can replace a portion of the remaining Zn and is contained in the zinc-based plating layer 13. [Element Group B]: Selected from one or more elements in the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%.

[0058] [Sb: 0~0.50% by mass] [Pb: 0~0.50% by mass] [Sr: 0~0.50% of mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing Sb, Pb, and Sr is also considered, therefore the lower limit of the content of these elements is 0% by mass. On the other hand, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 13, zinc flowers will form on the surface of the zinc-based plating layer 13, thereby enhancing the metallic luster. Therefore, from the viewpoint of further improving the designability of the coated steel, at least one of Sb, Pb, and Sr should preferably be contained in the zinc-based plating layer 13. This effect of improving designability will be exhibited when the content of at least one of Sb, Pb, and Sr is 0.05% by mass or more. Therefore, when at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 13, the content of each of these elements should preferably be set independently to 0.05% by mass or more.

[0059] On the other hand, when the content of any one of Sb, Pb, and Sr is greater than 0.50% by mass, the amount of dross generated in the plating bath used to form the zinc-based coating 13 will increase, which may prevent the production of coated steel with good plating properties. Therefore, the content of Sb, Pb, and Sr in the zinc-based coating 13 should preferably be individually 0.50% by mass or less. The content of Sb, Pb, and Sr should preferably be individually 0.20% by mass or less.

[0060] ◇Group C In other embodiments of the zinc-based plating layer 13 of this embodiment, the element group C that may be contained in the zinc-based plating layer 13 will be described. At least any element in element group C shown below is an element that can replace a portion of the remaining Zn and is contained in the zinc-based plating layer 13. [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

[0061] [Cu: 0% by mass and less than 0.25% by mass] [Ti: 0% by mass and less than 0.25% by mass] [Cr: ≥0.25% by mass] [Nb: ≥0.25% by mass] [Ni: 0% by mass and less than 0.25% by mass] [Mn: ≥0.25% by mass] [Co: 0% by mass and less than 0.25% by mass] [V: 0% by mass and less than 0.25% by mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is also considered, therefore the lower limit of the content of these elements is 0% by mass. On the other hand, if at least any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is contained in the zinc-based plating layer 13, these elements will be incorporated into the Fe-Al metal structure generated by the welding when the plated steel is welded, thereby further improving the corrosion resistance of the welded portion. This effect of improving the corrosion resistance of the welded portion will be exhibited when the content of at least any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 13 is 0.05% by mass or more. Therefore, when the zinc-based plating layer 13 contains at least any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, the content of each of these elements should preferably be set independently to 0.05% by mass or more.

[0062] On the other hand, when a zinc-based plating layer 13 containing any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, or V at a content of 0.25% by mass or more is formed, these elements may form various intermetallic compounds in the plating bath used to form the zinc-based plating layer 13, leading to increased viscosity of the plating bath and potentially preventing the production of plating steel with good plating properties. Therefore, the content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 13 should preferably be individually set to less than 0.25% by mass. The content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V should preferably be individually set to less than 0.20% by mass.

[0063] ◇Element Group D In other embodiments of the zinc-based plating layer 13, the element group D that may be contained in the zinc-based plating layer 13 will be described. At least any element in element group D shown below is an element that can replace a portion of the remaining Zn and is contained in the zinc-based plating layer 13. [Element Group D]: Selected from one or more elements in the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%.

[0064] [Sn: 0% mass or more, 20.00% mass] [Bi: 0% by mass or more and less than 5.00% by mass] [In: 0% by mass and less than 2.00% by mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing Sn, Bi, and In is also considered, so 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, which can improve the weldability of the zinc-based plating layer 13. Furthermore, these intermetallic compounds have high melting points, so they will not evaporate after welding when plating steel, but will exist in the form of intermetallic compounds. By having these elements present, corrosion resistance and corrosion protection can be improved, as well as the corrosion resistance of the welded part during welding. This effect of improving corrosion resistance will be exhibited 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 the zinc-based plating layer 13 contains at least one of Sn, Bi, and In, the content of each of these elements should preferably be set to 0.05% by mass or more independently.

[0065] On the other hand, adding excessive Sn will increase the amount of intermetallic compounds formed, which may reduce the corrosion resistance of the zinc-based plating layer 13 after welding. Furthermore, adding excessive Bi or In may not only make the zinc-based plating layer 13 embrittled and easier to peel off, but may also reduce its corrosion resistance after welding. These phenomena become significant when the Sn content is greater than 20.00% by mass, the Bi content is 5.00% by mass or more, or the In content is 2.00% by mass or more. Therefore, the Sn content should preferably be 20.00% by mass or less, the Bi content should preferably be less than 5.00% by mass, and the In content should preferably be less than 2.00% by mass. The Sn content should preferably be 10.00% by mass or less, the Bi content should preferably be 3.00% by mass or less, and the In content should preferably be 1.00% by mass or less.

[0066] ◇Element Group E In other embodiments of the zinc-based plating layer 13, the element group E that may be contained in the zinc-based plating layer 13 will be described. At least any element in element group E shown below is an element that can replace a portion of the remaining Zn and is contained in the zinc-based plating layer 13. [Element Group E]: Selected from one or more elements in the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0067] [Ca: 0~3.00% by mass] In other forms of the zinc-based plating layer 13 in this embodiment, the possibility of not containing Ca is also considered, so the lower limit of its content is 0% by mass. On the other hand, if the plating bath used to manufacture the zinc-based plating layer 13 contains Ca, the dross generated during the plating operation can be reduced as the Mg concentration increases, and the plating workability can be improved.

[0068] Furthermore, if Ca is present in the zinc-based plating layer 13, it will form intermetallic compounds with Al and Zn. Even more significantly, if the zinc-based plating layer 13 contains both Ca and Si, Ca will form intermetallic compounds with Si. These intermetallic compounds have high melting points and stable structures, thus suppressing liquid metal embrittlement (LME) during the welding of the plated steel. When the zinc-based plating layer 13 contains Ca, the aforementioned effects of improving plating workability and suppressing LME during welding can be achieved by setting the Ca content to 0.01% by mass or more. The Ca content in the zinc-based plating layer 13 is preferably 0.05% by mass or more.

[0069] On the other hand, when the Ca content in the zinc-based coating 13 is greater than 3.00% by mass, the corrosion resistance of the coated steel may decrease. From this perspective, the Ca content in the zinc-based coating 13 should preferably be 3.00% by mass or less. The Ca content in the zinc-based coating 13 should preferably be 2.00% by mass or less, and more preferably 1.00% by mass or less.

[0070] [La: 0% by mass and less than 0.50% by mass] [Ce: 0% by mass and less than 0.50% by mass] [Y: 0% or more by mass, less than 0.50% by mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing La, Ce, and Y is also considered, therefore the lower limit of the content of these elements is 0% by mass. On the other hand, elements such as La, Ce, and Y exhibit almost the same effect as Ca. This is because the atomic radii of each element are close to the atomic radius of Ca, and when these elements are contained in the zinc-based plating layer 13, they will substitute at the Ca positions.

[0071] The improved plating workability and the suppression of LME during welding can be achieved by individually setting the content of each element to 0.01% by mass or more. Therefore, if at least one of La, Ce, and Y is present, the content of each element should preferably be individually set to 0.01% by mass or more. The content of La, Ce, and Y in the zinc-based plating layer 13 should preferably be individually set to 0.05% by mass or more.

[0072] On the other hand, in the plating bath used to manufacture the zinc-based plating layer 13, if the contents of La, Ce, and Y are too high, the viscosity of the plating bath will increase to a necessary level, and the plating workability may decrease. Therefore, the contents of La, Ce, and Y in the plating bath can be adjusted from the viewpoint of plating workability. The contents of La, Ce, and Y should each be individually less than 0.50% by mass, less than 0.50% by mass, or less than 0.50% by mass. The contents of La, Ce, and Y should each be individually less than 0.10% by mass.

[0073] ◇Element Group F In other embodiments of the zinc-based plating layer 13, the 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 can replace a portion of the remaining Zn and are contained in the zinc-based plating layer 13. [Element group F]:B: Less than 0.50%

[0074] [B: 0% by mass and less than 0.50% by mass] In other embodiments of the zinc-based plating layer 13, the possibility of not containing B is also considered, therefore its content is limited to 0% by mass. On the other hand, if B is present in the zinc-based plating layer 13, it has a more effective effect in suppressing LME (light metal evaporation). This is presumably because when B is present in the zinc-based plating layer 13, it will combine with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. It can also be assumed that, through the presence of B in the zinc-based plating layer 13, B will diffuse from the zinc-based plating layer 13 towards the steel 11, and through grain boundary strengthening, it has a more effective effect in suppressing LME in the steel 11. Furthermore, it can be presumed that the various intermetallic compounds formed with B have extremely high melting points, and therefore also have the effect of suppressing Zn evaporation during welding. These improved effects can be exhibited by having B content of 0.05% by mass or more. Therefore, when B is present, the B content should preferably be 0.05% by mass or more.

[0075] On the other hand, if the plating bath contains excessive amounts of B in order to include B in the zinc-based coating 13, it will cause a sharp increase in the plating melting point, reducing the plating workability and potentially preventing the production of coated steel with excellent plating properties. This reduction in plating workability becomes significant when the B content reaches 0.50% by mass or higher; therefore, the B content should preferably be less than 0.50% by mass. The B content is more preferably below 0.10% by mass.

[0076] Methods for measuring chemical composition The chemical composition of the aforementioned 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). Furthermore, ICP-AES is used for chemical composition analysis up to 0.1% by mass, while ICP-MS is used for trace chemical composition analysis of less than 0.1% by mass. The plated steel is immersed in a 10% HCl aqueous solution with added inhibitor for approximately 1 minute, and the zinc-based plating layer is partially peeled off to prepare a solution in which the zinc-based plating layer has been dissolved. The obtained solution is analyzed using ICP-AES or ICP-MS to obtain the chemical composition on an overall average basis for the zinc-based plating layer.

[0077] Regarding the adhesion amount of zinc-based coating 13 As described above, the adhesion amount of the zinc-based coating 13 should preferably be, for example, 10.0 g / m² or more per single side of the steel, and more preferably 50.0 g / m² or more. Furthermore, the adhesion amount of the zinc-based coating 13 should preferably be, for example, less than 200.0 g / m² per single side of the steel, and more preferably less than 150.0 g / m². When the adhesion amount of the zinc-based coating 13 is within the range described above, the surface-treated component 1 of this embodiment can exhibit sufficient corrosion resistance.

[0078] Furthermore, regarding the adhesion amount of the zinc plating layer 13, the sample is first cut into 30mm × 30mm dimensions from the surface treatment component 1, and the mass of the sample is measured. Then, a waterproof protective tape is applied to one side of the sample to prevent the zinc plating layer 13 on that side from dissolving in subsequent steps. Based on this, the sample is immersed in a 10% HCl aqueous solution with added inhibitor, and the zinc plating layer 13 on the side without the protective tape is acid-washed and peeled off. The mass of the sample after acid washing is measured. The change in sample mass before and after acid washing determines the adhesion amount of the zinc plating layer 13 on each side. In this embodiment, the chemical conversion treatment layer 15, having a thickness as detailed below, has an adhesion amount of approximately 1 g / m²; on the other hand, it is difficult to remove the chemical conversion treatment layer 15 solely through physical or chemical methods. Therefore, when measuring the adhesion amount of the zinc plating layer 13, the chemical conversion treatment layer 15 may not need to be removed from the sample.

[0079] <Regarding Chemical Conversion Treatment Layer 15> The chemical conversion treatment layer 15 of this embodiment is formed on the entire surface of the zinc-based plating layer 13 as described above. Here, the chemical conversion treatment layer 15 of this embodiment contains at least a phosphorus-containing compound. At least a portion of this phosphorus-containing compound serves as the source of phosphorus (P) during the formation of the P-Zn composite oxide as previously described.

[0080] Regarding the amount of P leached from chemically converted layer 15 Regarding the chemical conversion treatment layer 15 of this embodiment, after immersing a portion of the surface-treated steel 10 corresponding to a size of 1 m² in ion-exchange water at a temperature of 35-45°C for 60 minutes, the amount of phosphorus (P) leached from the chemical conversion treatment layer 15 into the ion-exchange water will be 5-50 mg / m² per side. Here, the water temperature of 35-45°C is an assumed natural environment temperature. Furthermore, regarding the form of phosphorus (P) leached from the chemical conversion treatment layer 15, although the details are unclear, it can be inferred that it is leached in the form of phosphate ions.

[0081] When the P leaching amount is less than 5 mg / m², the amount of P leached from the chemical conversion treatment layer 15 is too small, and the corrosion product layer composed of the P-Zn composite oxide as described above cannot be sufficiently formed, thus failing to improve the corrosion resistance of the surface-treated component 1. When the P leaching amount reaches 5 mg / m² or more, a corrosion product layer composed of the P-Zn composite oxide can be formed, and this corrosion product layer can improve the corrosion resistance of the surface-treated component 1. The aforementioned P leaching amount is preferably 10 mg / m² or more, and more preferably 15 mg / m² or more.

[0082] On the other hand, in the surface-treated component 1 of this embodiment, it is important to consider not only the corrosion resistance of the surface-treated component 1 located in the soil, but also, importantly, the corrosion resistance of the portion of the surface-treated component 1 not located in the soil (e.g., the portion located in the atmosphere). When the P leaching amount is greater than 50 mg / m², the amount of P leached from the chemical conversion treatment layer 15 becomes excessive, resulting in the inability to guarantee the corrosion resistance of the surface-treated component 1 not only in the soil, but also in the portion not located in the soil. A P leaching amount of 50 mg / m² or less ensures the corrosion resistance of the portion not located in the soil while simultaneously improving the corrosion resistance of the portion located in the soil. The P leaching amount is preferably 45 mg / m² or less.

[0083] Here, when determining the amount of phosphorus (P) dissolved, ion-exchanged water of grade A1 or higher as specified in JIS K0557:1998 is prepared and preheated to a temperature of 35-45°C. Furthermore, a sample with a top-view dimension of 40mm × 40mm is cut from the surface-treated component 1 and placed in a container with a diameter of 150mm, a volume of 3000mL, and a lid. Then, 2000ml of the aforementioned ion-exchanged water at a temperature of 35-45°C is poured in, and the mixture is left to stand for 60 minutes while maintaining the temperature within the 35-45°C range. Afterward, the ion-exchanged water is taken from the container, and the amount of dissolved P is determined using ICP-MS. For example, an Agilent Technologies Agilent 8800 model can be used for the ICP-MS.

[0084] ≪Cumulative Intensity of Peaks in X-ray Photoelectron Spectroscopy Results≫ As previously stated, in the surface-treated component 1 of this embodiment, the corrosion products containing P-Zn composite oxides on the surface of the surface-treated component 1 disposed in the soil have the effect of improving the corrosion resistance in the soil. The properties of the P-Zn composite oxides affect the effect of improving corrosion resistance. Based on this viewpoint, after repeated and focused research, it was found that when the surface of the chemical conversion treatment layer 15 of this embodiment was analyzed by X-ray photoelectron spectroscopy (XPS), in the narrow spectrum of P2p, if the ratio of the cumulative intensity of the peak with a maximum value at 132.80±0.25eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25eV is in the range of 0.20 to 0.50, the corrosion resistance of the surface-treated component 1 in the soil is even better than in the case where this intensity ratio is not met. The reason is unclear, but it is speculated that it is due to the change in the form of dissolved P ions, which in turn changes the form of P-Zn composite oxides and improves their barrier properties.

[0085] The cumulative strength ratio is 0.20 or higher, thereby enabling the surface-treated component 1 to exhibit superior corrosion resistance in soil within the chemical conversion treatment layer 15 of this embodiment. The cumulative strength ratio is preferably 0.25 or higher, and more preferably 0.30 or higher.

[0086] On the other hand, when the ratio of the aforementioned cumulative strength is 0.50 or less, the surface-treated component 1 will exhibit superior corrosion resistance in soil. The ratio of the aforementioned cumulative strength is preferably 0.45 or less, and more preferably 0.40 or less.

[0087] Here, the ratio of cumulative intensity as described above can be identified in the following manner. First, three arbitrary locations on the surface of the surface-treated component 1 under consideration were measured using an X-ray photoelectron spectrometer (e.g., a Quantum2000 model manufactured by ULVAC-PHI). Additionally, if a portion of the surface-treated component 1 had a welded area, the area from the end of the welded area to 5 cm was excluded from measurement. An 800 μm × 300 μm region on the surface of the surface-treated steel (the surface of the chemical conversion treatment layer 15) before pretreatment such as cleaning or sputtering was analyzed, for example, under the following conditions: The obtained P2p spectrum was separated into two peaks: one with a maximum value at 133.90 ± 0.25 eV and the other with a maximum value at 132.80 ± 0.25 eV. The cumulative intensity of these peaks was then calculated, and the cumulative intensity ratio was calculated based on these cumulative intensities.

[0088] However, the narrow spectra obtained from the analysis may sometimes have their peak positions shifted to the left or right due to the measuring equipment and conditions. Therefore, firstly, position correction was performed on the obtained spectra using the peak position (the position with the maximum value) of the C1s spectrum as 284.8 eV. Then, the P2p spectrum was separated into two peaks with maximum values: one at 133.90 ± 0.25 eV and the other at 132.80 ± 0.25 eV.

[0089] During the measurement, the P2p spectrum is measured in the region of 130.00–135.00 eV. The region for peak separation is essentially defined as 130.00–135.00 eV, and extended beyond this range according to the spectrum. Furthermore, the half-width at half-maximum (WWHM) of the peak with a maximum value at 133.90 ± 0.25 eV is assumed to be 1.35 ± 0.20 eV, and the WWHM 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, careful sample handling is essential to minimize the adhesion of oil, dirt, etc.

[0090] In addition, the measurement conditions for XPS are as follows. (Measurement conditions) X-ray source: monoAlKα (1486.6 eV) X-ray output: 15kV 25W X-ray diameter: 100μmφ Vacuum level in the analytical chamber (before sample placement): 2.2 × 10⁻⁹ torr (Note: 1 torr is approximately 133.32 Pa.) Detection angle: 45° Neutralization: electron neutralization, ion neutralization Data analysis software: MultiPak V.8.0 (Made by ULVAC-PHI)

[0091] ≪On Depth Profiling in Energy Dispersive X-ray Spectroscopy≫ Furthermore, in the chemical conversion treatment layer 15 of this embodiment, after performing energy dispersive X-ray spectroscopy (EDS) line analysis on the chemical conversion treatment layer 15 from its surface to its interface with the zinc-based plating layer 13, the average P concentration on the surface side of the chemical conversion treatment layer 15 in the obtained depth profile of P concentration is preferably 1 to 20% by mass. Here, the surface side of the chemical conversion treatment layer 15 refers to the range from half the thickness of the chemical conversion treatment layer 15 to its surface.

[0092] The average P concentration on the surface side of the chemical conversion treatment layer 15 is 1% by mass or more, thereby ensuring a sufficient amount of P element dissolved from the chemical conversion treatment layer 15, and the surface-treated component 1 of this embodiment will exhibit superior corrosion resistance. The average P concentration on the surface side is preferably 2% by mass or more, and more preferably 3% by mass or more.

[0093] On the other hand, the average P concentration on the surface side of the chemical conversion treatment layer 15 is 5% by mass or less. This allows for the suppression of excessive P leaching while ensuring sufficient P leaching from the chemical conversion treatment layer 15, resulting in superior corrosion resistance for the surface-treated component 1 of this embodiment. The average P concentration on the surface side is preferably 15% by mass or less, and more preferably 10% by mass or less.

[0094] Here, the average concentration of P in the depth profile described above can be determined in the following manner. First, a cross-sectional sample of the chemical conversion treatment layer 15 is obtained by cutting at any position on the surface-treated component 1 along its thickness direction (perpendicular to the surface of the surface-treated component 1). From any position on the surface of the chemical conversion treatment layer 15 in this cross-sectional sample, along the thickness direction of the chemical conversion treatment layer 15 (perpendicular to the surface of the chemical conversion treatment layer 15, for example, the Z-axis direction in Figure 3), analysis is performed using an EDS analysis device installed in a scanning electron microscope (SEM; for example, JEOL JSM-7000F, etc.), up to the interface with the zinc-based plating layer 13. The obtained analytical results are then mapped. Here, the elements considered in the above analysis are at least P, Zn, Al, Mg, Si, Ti, Zr, C, and O; however, mapping analysis can also be performed for all elements. Among the elements examined here, Zn, Al, and Mg are elements derived from zinc-based plating layers, while Si, Ti, Zr, C, and O are components derived from chemically converted plating layers. The SEM-EDS observation conditions are set as follows: accelerating voltage: 15 kV, irradiation current: 4.9147 nA, number of scans: 10, and magnification: 500x.

[0095] Regarding the area corresponding to the chemical conversion treatment layer 15, those skilled in the art can easily identify it from SEM images. In this embodiment, in the depth profiles of each element obtained by the above method, the area corresponding to a P concentration of 0.01% or higher is treated as the region of the chemical conversion treatment layer 15. This allows the thickness of the chemical conversion treatment layer 15 within the obtained depth profile to be identified. The area corresponding to half the thickness thus obtained is treated as the half-thickness area of ​​the chemical conversion treatment layer 15.

[0096] Subsequently, the average concentration of P element is calculated from the depth profile obtained, from the position of 1 / 2 thickness as described above to the surface of the chemical conversion layer 15 (the opposite side of the interface between the zinc plating layer 13 and the chemical conversion layer 15).

[0097] The same measurements were performed on any 5 sites of the obtained cross-sectional sample. The average concentration of P obtained from the number of measurement sites was taken as the average concentration of P on the surface side of the chemical conversion treatment layer 15.

[0098] Regarding the P concentration in chemical conversion treatment layer 15 In the chemical conversion treatment layer 15 of this embodiment, the P concentration, calculated as P, is preferably 0.1 to 15.0% by mass. With a P concentration of 0.1% by mass or more, the chemical conversion treatment layer 15 of this embodiment ensures a sufficient amount of P element to achieve excellent corrosion resistance, regardless of its presence in the soil. The surface-treated component 1 of this embodiment will then exhibit even better corrosion resistance. The P concentration of the chemical conversion treatment layer 15 is preferably 1.0% by mass or more, and more preferably 2.0% by mass or more.

[0099] Here, the above-mentioned P concentration can be determined in the following manner. First, a cross-sectional sample of the chemical conversion treatment layer 15 is obtained by cutting at any position along the thickness direction of the surface treatment component 1. From any position on the surface of the chemical conversion treatment layer 15 in this cross-sectional sample, along the thickness direction of the chemical conversion treatment layer 15 (perpendicular to the surface of the chemical conversion treatment layer 15, for example, the Z-axis direction in Figure 3), analysis is performed using an EDS analysis device installed in a scanning electron microscope (SEM, such as the JEOL JSM-7000F). The analysis continues until the interface with the zinc-based plating layer 13 is reached, and the obtained analytical results are then plotted. Here, the element considered in the above analysis is defined as P. The SEM-EDS observation conditions are, for example, accelerating voltage: 15 kV, irradiation current: 4.9147 nA, number of scans: 10, and magnification: 500x.

[0100] Regarding the area corresponding to the chemical conversion treatment layer 15, those skilled in the art can easily identify it from SEM images. However, in this embodiment, the area corresponding to the chemical conversion treatment layer 15 is identified based on the measurement results of the P concentration in the range from the surface of the chemical conversion treatment layer 15 to the surface of the zinc-based plating layer 13. More specifically, in the depth profiles of each element obtained by the above method, the portion corresponding to a P concentration of 0.01% or higher is treated as the area of ​​the chemical conversion treatment layer 15. Then, the average P concentration in the area of ​​the chemical conversion treatment layer 15 is calculated from the obtained P element depth profiles.

[0101] The same measurements were performed at any 5 locations of the obtained profile sample. The average concentration of the P element obtained was the average value of the number of measurement locations and was treated as the "P concentration converted to P in the chemical transformation treatment layer 15".

[0102] ≪Specific Examples of Compounds Containing Phosphorus (P)≫ In the chemical conversion treatment layer 15 of this embodiment, various phosphates and their salts can be used as compounds containing phosphorus element P as described above. Examples of phosphoric acid and its salts include: orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, hypophosphorous acid, phosphorous acid, hypophosphorous acid, tripolyphosphoric acid, tetrapolyphosphoric acid, and other phosphoric acid salts; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; phosphonic acids such as aminotris(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid); and organic phosphoric acids such as phytic acid and their salts. In addition, salts other than ammonium salts of phosphoric acid include: metal salts containing Na, Mg, Al, K, Ca, Mn, Ni, Zn, and Fe. Phosphoric acid and its salts can be used alone or in combination of two or more.

[0103] Furthermore, in the chemical conversion treatment layer 15 of this embodiment, among the various compounds mentioned above, it is more appropriate to use a compound that can also function as a so-called anti-rust pigment.

[0104] Regarding other components in chemical conversion treatment layer 15 In addition to the phosphorus-containing compound as described above, the chemical conversion treatment layer 15 of this embodiment also contains one or more components selected from the group consisting of silane coupling agents, valve metals, and organic resins as film-forming elements. By further including these components, the film-forming properties of the chemical conversion treatment layer 15 after coating with the chemical conversion treatment solution, the barrier properties (density) of the film against corrosive agents such as moisture or corrosive ions, and the adhesion of the film to the plated surface are improved, thereby contributing to enhancing the corrosion resistance of the film.

[0105] [Silane coupling agent] Examples of silane coupling agents include: 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldiethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldiethoxysilane. Oxysilanes, 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-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, methyl Trimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropylmethyldiethoxysilane, 3-anilinepropyltrimethoxysilane, 3-anilinepropylmethyldimethoxysilane, 3-anilinepropyltriethoxysilane, 3-anilinepropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane Silane, 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, 3-chloropropylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, etc.

[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 treatment layer 15 of this embodiment may also contain one or more of these valve metals. Furthermore, the type of valve metal compound used is not particularly limited if it is soluble in water. Such valve metal compounds include, for example, ammonium salts, sodium salts, potassium salts, oxides, hydroates, oxyacid salts, hydroxides, phosphates, nitrates, sulfates, and organic acid salts of the aforementioned metals. Among these compounds, oxides, oxyacid salts, and phosphates of the aforementioned metals are particularly preferred.

[0107] [Organic resin] Organic resins such as polyester resins, polyurethane resins, epoxy resins, phenolic resins, acrylic resins, polyolefin resins, and fluororesins can be used. Alternatively, resins obtained by crosslinking film-forming resin components such as modified resins of these resins with butylated melamine resins, methylated melamine resins, butylmethyl mixed melamine resins, urea resins, isocyanate resins, or mixtures of these resins using a crosslinking agent. Furthermore, electron wire curing resins and UV curing resins can also be used. To further improve the adhesion of the plating layer, it is advisable to use at least one of the following: resins with forced sites or polar functional groups in their molecular chains (polyester resins, polyurethane resins, epoxy resins, acrylic resins, etc.). These organic resins can be used alone or in combination of two or more.

[0108] Here, in the solid components of the chemical conversion treatment solution, the total content of silane coupling agent, valve metal, and organic resin is, for example, in the range of 30% to 80% by mass. When the total content is less than 30% by mass, the film-forming components are insufficient, making it difficult to uniformly coat the steel with the chemical conversion treatment layer. On the other hand, when the total content is greater than 80%, it is not sufficient to contain phosphorus or other components, making it difficult to simultaneously achieve the desired corrosion resistance in the flat areas, corrosion resistance in the processed areas, adhesion between the chemical conversion treatment layer and the steel, and resistance to blackening.

[0109] [Other ingredients] In addition to the various components mentioned above, the chemical conversion treatment layer 15 of this embodiment may also contain zirconium compounds, silicon dioxide, fluorides, vanadium compounds, tannins, or tannic acid.

[0110] Furthermore, in addition to the various components mentioned above, the chemical conversion treatment layer 15 of this embodiment may also contain various anti-rust pigments. These anti-rust pigments can be made of any material, such as calcium ion-exchange silica (sometimes also known as calcium silicate), magnesium oxide, calcium molybdate, aluminum molybdate, barium molybdate, water-dispersible silica, fumed silica, etc.

[0111] Furthermore, the chemical conversion treatment layer 15 of this embodiment may also contain filler pigments such as precipitated barium sulfate and clay, or coloring pigments such as titanium dioxide, as needed. In addition, besides containing the rust-preventive pigments, filler pigments, and coloring pigments mentioned above, the chemical conversion treatment layer 15 of this embodiment may also contain additives such as colorants, viscosity modifiers, leveling agents, defoamers, and ultraviolet absorbers, as needed.

[0112] Regarding the thickness of the chemical conversion treatment layer 15 The thickness of the chemical conversion treatment layer 15 as described above (thickness d in Figure 3) should preferably be in the range of 30~5000 nm.

[0113] The thickness of the chemical conversion treatment layer 15 is 30 nm or more, thereby enabling the surface-treated component 1 of this embodiment to achieve superior corrosion resistance. The thickness of the chemical conversion treatment layer 15 is preferably 100 nm or more, and more preferably 200 nm or more.

[0114] On the other hand, the thickness of the chemical conversion treatment layer 15 is 5000 nm or less. Therefore, the surface treatment component 1 of this embodiment can ensure the adhesion between the zinc-based plating layer 13 and the chemical conversion treatment layer 15 while achieving superior corrosion resistance. The thickness of the chemical conversion treatment layer 15 is preferably 3000 nm or less, and more preferably 2000 nm or less.

[0115] Here, the thickness of the aforementioned chemical conversion layer 15 can be measured by direct observation of its cross-section. Specifically, the plated steel sheet 1 is embedded in room-temperature drying epoxy resin in a manner that allows observation of its cross-section. After mechanical grinding of the embedded surface, it is observed using SEM. In this SEM observation, those skilled in the art can easily distinguish the chemical conversion layer 15 from the zinc-based plating layer 13 by appearance. The thickness of the chemical conversion layer 15 is measured at any five locations, and the average thickness of the five points is defined as the thickness of the chemical conversion layer 15.

[0116] The surface treatment component 1 of this embodiment has been described in detail above.

[0117] (Regarding composite structures) Next, referring to Figures 4 and 5, the composite structure 5 of the surface treatment component 1 and soil as described above will be explained. Figures 4 and 5 are explanatory diagrams used to explain the composite structure of this embodiment.

[0118] As illustrated in Figure 4, the composite structure 5 of this embodiment is a structure obtained by combining the surface-treated component 1 of this embodiment with soil, as described above. As previously explained, a chemical conversion treatment layer 15 is formed on the surface of the surface-treated steel 10 constituting the surface-treated component 1. In the composite structure 5 of this embodiment, at least a portion of the chemical conversion treatment layer 15 is in contact with the soil, thus presenting a state of composite formation of the surface-treated component 1 and soil.

[0119] Figure 5 is a schematic illustration: a cross-section of the composite structure 5 shown in Figure 4 after being cut along the AA cutting line in the X-axis direction. The cross-sectional view shown in Figure 5 corresponds to the following: the part of the composite structure 5 in this embodiment that is in contact with the soil is obtained by cutting the surface-treated component 1, i.e., the surface-treated steel 10, in the thickness direction.

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

[0121] Here, the steel 11 in the composite structure 5 of this embodiment has the same structure as the steel 11 in the previously described surface-treated component 1 and will exhibit the same effect, so the description is omitted below.

[0122] Furthermore, regarding the zinc plating layer 13 and the chemical conversion treatment layer 15 in the composite structure 5 of this embodiment, since they have the same structure as the zinc plating layer 13 and the chemical conversion treatment layer 15 in the previously described surface treatment member 1, the following description is omitted.

[0123] Furthermore, at the interface portion of the composite structure 5 that is in contact with the soil, since component interdiffusion may occur between the interface and the soil, it can be assumed that the chemical composition of the interface portion of the chemical conversion treatment layer 15 will change from the chemical composition of the chemical conversion treatment layer 15 in the portion not in contact with the soil. However, it can be inferred that the average composition of the chemical conversion treatment layer 15 as a whole will be the same as the chemical composition of the chemical conversion treatment layer 15 in the surface treatment component 1 previously described.

[0124] As an example of a P-Zn composite layer containing Zn and P, the oxide layer 21 is a layer composed of P-Zn composite oxides formed by the reaction of P from the chemical conversion treatment layer 15 and Zn from the zinc-based plating layer 13. It can be inferred that even in soil, the P-containing compounds in the chemical conversion treatment layer 15 are dissolved from the chemical conversion treatment layer 15 in the form of phosphate ions. The P-Zn composite compound formed by this reaction is a substance with a dense structure. Therefore, at least a portion of the interface between the chemical conversion treatment layer 15 and the soil contains the oxide layer 21 composed of this P-Zn composite oxide, thereby enabling the composite structure 5 of this embodiment to exhibit excellent corrosion resistance in soil.

[0125] This oxide layer 21 is preferably a layer having the following chemical composition, which, by mass percent, contains: Zn: 1.0% or more and 10.0% or less, P: 0.5% or more and 5.0% or less, with the remainder consisting of H, C, O, Si, and impurities. The oxide layer 21 is composed of a P-Zn-based composite compound having the chemical composition described above, thereby enabling the composite structure 5 of this embodiment to exhibit superior corrosion resistance in soil.

[0126] Furthermore, when the zinc-based plating layer 13 further contains Al and Mg as chemical components, the chemical composition of the oxide layer 21 should preferably contain at least one of the following to replace the remaining H, C, O, and Si portions as described above: Al: 0% or more and 10.0% by mass or less; Mg: 0% or more and 10.0% by mass or less. The oxide layer 21 is composed of a P-Zn-Al-Mg composite compound having the chemical composition described above, thereby enabling the composite structure 5 of this embodiment to exhibit superior corrosion resistance in soil.

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

[0128] The above description of the composite structure 5 of this embodiment has been completed with reference to Figures 4 and 5.

[0129] (Regarding the manufacturing method of surface-treated components) The following describes one example of a manufacturing method for the surface-treated component 1 of this embodiment.

[0130] <Manufacturing Method of Surface-Treated Steel 10 as Material> The surface-treated steel 10 of the surface-treated component 1 of this embodiment can be manufactured by using the steel 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 11.

[0131] Method for forming zinc-based coating 13 In this regard, the zinc-based coating 13 can be formed not only by melt plating, but also by spraying, cold spraying, sputtering, vapor deposition, electroplating, etc. However, in terms of cost, melt plating is the best.

[0132] The following describes in detail one example of the manufacturing method, which uses a melt-plating method to obtain the zinc-based plating layer 13 of this embodiment. In the manufacturing steps of the zinc-based coating 13, firstly, taking a steel plate as an example of steel material 11 used as the base material, the steel plate is rolled to the desired thickness using the Sendzimir process, then rolled into a coil and placed on the melt coating production line.

[0133] In the molten plating production line, steel sheets are continuously passed through the coil while being uncoiled. At this time, the steel sheets are heated and reduced at 800°C in an annealing device installed on the production line, for example, in an environment where the oxygen concentration is below 20ppm and oxidation is difficult, using a N2-5%H2 gas environment. After that, the steel sheets are cooled with N2 gas until the temperature of the subsequent plating bath is about +20°C, and then immersed in the plating bath.

[0134] Here, a plating alloy with the chemical composition described above and in a molten state is prepared in advance in the plating bath. The temperature of the plating bath should be set above the melting point of the plating alloy (for example, around 460~660°C).

[0135] When preparing the plating alloy material, it is advisable to use pure metal (purity of 99% or higher) as the alloying material. First, a predetermined amount of alloy metal is mixed to form the composition of the plating layer as described above. Then, under vacuum or with an inactive gas substituted, the mixture is completely melted using a high-frequency induction furnace or electric arc furnace to form the alloy. Further, this alloy, mixed with the predetermined components (the composition of the plating layer described above), is melted in the atmosphere to obtain a molten material, which is then used as the plating bath.

[0136] Furthermore, the plating alloys described above are not particularly limited to using pure metals in their fabrication; existing Zn alloys, Mg alloys, and Al alloys can also be melted and used. In this case, as long as a predetermined alloy composition with low impurities is used, there is no problem.

[0137] The steel sheet is immersed in the plating bath as described above, and then lifted out at a predetermined speed. At this time, the amount of plating is controlled by, for example, using N2 wiping gas, to achieve the desired thickness of the zinc-based plating layer. Regarding conditions other than the bath temperature, any conditions suitable for general plating operations are acceptable; no special equipment or conditions are required.

[0138] Furthermore, various heat treatments can be applied to the molten alloy plating on the steel plate as needed.

[0139] Method for forming chemical conversion treatment layer 15 The chemical conversion treatment layer 15 of this embodiment can be formed by coating a chemical conversion agent onto the surface of the zinc-based plating layer 13 as described above, wherein the chemical conversion agent contains the components constituting the chemical conversion treatment layer 15 as described above, and then sintering and hardening it at a predetermined temperature to form the layer. In this way, after immersing a portion of the chemical conversion treatment layer corresponding to 1m² of the surface-treated steel in ion-exchange water at a temperature of 35-45°C for 60 minutes, the amount of P dissolved from the chemical conversion treatment layer into the ion-exchange water can be set within a desired range.

[0140] Furthermore, by forming the chemical conversion treatment layer 15 through the heating steps detailed below, the chemical conversion treatment layer 15 formed thereby satisfies the relationship of cumulative peak intensity in XPS as explained above, and can control the amount of P dissolved from the chemical conversion treatment layer into the ion-exchanged water to a better range. The following section provides a detailed explanation of the conditions for this heating direction.

[0141] <Heating Method> In the heating step of heating the chemical conversion agent applied to the zinc-based plating layer, the heating method for the chemical conversion agent is to heat the chemical conversion agent from the steel side. By heating the chemical conversion agent from the steel side, the ratio of the cumulative intensity of the peak with a maximum value at 132.80±0.25 eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV in the narrow P2p spectrum obtained by XPS analysis of the outermost surface of the chemical conversion layer 15 can be set to 0.20 or higher.

[0142] Specific heating methods include, for example, induction heating (IH). When IH is used to heat steel coated with a chemical conversion agent (i.e., steel with a zinc-based coating), the steel is heated directly. Therefore, the chemical conversion agent is heated through heat conduction from the steel, thus the chemical conversion agent is heated from the steel side.

[0143] By heating the chemical conversion agent from the steel side, the ratio of the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV in the narrow spectrum of P2p obtained by XPS analysis of the outermost surface of the chemical conversion layer 15 can be set to 0.20 or higher. The mechanism is not yet clear. However, the inventors of this case speculate that it is due to the following reasons.

[0144] Phosphorus (P) exists in the chemical conversion agent as a water-soluble anion. When the chemical conversion agent is heated, causing the water used as a solvent to evaporate, P or positively charged metal ions in the chemical conversion agent will undergo a precipitation reaction. At this time, the anionic P reacts with the positively charged metal ions to form an insoluble compound.

[0145] It can be assumed that the evaporation of water as a solvent increases the concentration, leading to the following phenomena: the precipitation reaction of P in the chemical conversion agent with positively charged metal ions, or the formation of insoluble compounds accompanying this precipitation reaction. When the chemical conversion agent is heated from the steel side, the formation of insoluble compounds preferentially occurs near the steel. That is, when the chemical conversion agent is heated from the steel side, metal ions near the steel are preferentially consumed. Subsequently, P that does not form insoluble compounds with positively charged metal ions precipitates as soluble P on the surface of the chemical conversion layer. As a result, in the narrow spectrum of P2p obtained by XPS analysis of the outermost surface of the chemical conversion layer 15, the ratio of the cumulative intensity of the peak with a maximum value at 132.80±0.25 eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV can be set to 0.20 or higher.

[0146] <Maximum temperature reached by the steel during the heating process> In the heating step described above, the steel coated with the chemical conversion agent is heated and dried until it becomes sticky. The maximum temperature reached by the steel in this heating step should preferably be above 50°C and below 100°C, more preferably above 50°C and below 80°C, and even more preferably above 50°C and below 70°C. If the maximum temperature is below 50°C, the solvent of the chemical conversion agent will not completely evaporate, which is undesirable. On the other hand, if the maximum temperature is above 100°C, in the narrow spectrum of P2p obtained by XPS analysis of the outermost surface of the chemical conversion layer 15, the ratio of the cumulative intensity of the peak with a maximum value at 133.90±0.25eV to the cumulative intensity of the peak with a maximum value at 132.80±0.25eV will be less than 0.20. While the reason is unclear, it can be inferred that this is because the heat input causes a change in the chemical bonding state of P.

[0147] Relative humidity inside the heating furnace In the heating steps described above, the relative humidity inside the heating furnace should be set to 85% or higher and 98% or lower. Heating under this relative humidity environment allows the ratio of the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV in the narrow P2p spectrum obtained by XPS analysis of the outermost surface of the chemical conversion treatment layer 15 to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV to be set to 0.20 or higher and 0.50 or lower.

[0148] When the relative humidity is less than 85%, the ratio of the cumulative intensity with a peak value of 133.90±0.25 eV to the cumulative intensity with a peak value of 132.80±0.25 eV cannot be set to 0.20 or higher. While the reason is unclear, it can be presumed to be due to the following: When the relative humidity is less than 85%, even if the chemical conversion agent is heated from the steel side, solvent evaporation will still occur in the outermost layer of the chemical conversion agent. At this time, the phosphorus (P) in the chemical conversion agent will form insoluble compounds with positively charged metal ions. As a result, the ratio of the cumulative intensity as described above cannot be set to 0.20 or higher.

[0149] On the other hand, when the relative humidity is greater than 98%, the ratio of the cumulative intensity at the peak with a maximum value of 133.90 ± 0.25 eV to the cumulative intensity at the peak with a maximum value of 132.80 ± 0.25 eV cannot be set below 0.50. While the reason is unclear, it can be presumed to be due to the following: When the relative humidity is greater than 98%, solvent evaporation is suppressed. As a result, even after heating the chemical conversion treatment agent, water, as a solvent, remains in the film. Influenced by this water, P becomes more likely to exist in the form of soluble compounds, thus the ratio of cumulative intensity cannot be set below 0.50.

[0150] <Heating rate of steel during the heating process> In the heating step described above, the heating rate of the steel should preferably be set to 1°C / second or higher and 15°C / second or lower. By using a heating rate of 15°C / second or lower, and employing a method that heats the chemical conversion agent from the steel side, the phosphorus (P) concentration of the chemical conversion agent can be set to 0.1-15% by mass. This allows for an average P concentration of 1-20% by mass on the surface side of the chemically converted layer. Furthermore, a heating rate of 1°C / second or lower results in poor productivity.

[0151] Furthermore, by heating the chemical conversion agent from the steel side to achieve a P concentration of 0.1-15% by mass and a heating rate of less than 15°C / second, the average P concentration on the surface of the chemical conversion layer can be 1-20% by mass. The mechanism of this method is not yet clear. However, the inventors of this invention speculate that it is due to the following reasons.

[0152] If the chemical conversion agent is heated from the steel side, the solvent on the steel side will easily evaporate during the formation of the chemical conversion layer, and the phosphorus (P) concentration near the steel will increase. Therefore, due to this concentration difference, P will migrate to the surface side where the concentration is lower. Furthermore, a heating rate of 15°C / second or less requires more time for the chemical conversion layer to form as the solvent evaporates compared to a rate greater than 15°C / second. Therefore, it can be assumed that during the formation of the chemical conversion layer, the time for P to migrate in the solvent increases, the amount of P migrating towards the surface of the chemical conversion layer increases, and P becomes more easily concentrated on the surface side. Therefore, by setting the P concentration of the chemical conversion agent to 0.1~15% by mass, the average P concentration on the surface side of the chemical conversion layer can be set to 1~20% by mass.

[0153] <Cooling steps after heating> The cooling step after heating is determined to be a method other than water cooling. Specific cooling methods include air cooling. If water cooling is used, the water-soluble P contained in the chemical conversion treatment layer 15 will dissolve into the cooling water, resulting in insufficient P dissolution.

[0154] <Cooling rate after heating> The cooling rate after heating should preferably be 3°C / second or higher and 50°C / second or lower, more preferably 15°C / second or higher and 40°C / second or lower, and even more preferably 20°C / second or higher and 40°C / second or lower. If the cooling rate is 3°C / second or lower, the ratio of the cumulative intensity of the peak with a maximum value at 132.80±0.25 eV to the cumulative intensity of the peak with a maximum value at 133.90±0.25 eV in the narrow spectrum of P2p obtained by XPS analysis of the outermost surface of the chemical conversion treatment layer 15 cannot be set to 0.20 or higher. Although the reason is unclear, it can be speculated that the chemical conversion treatment agent is still heated during the cooling step, and the chemical bonding state of P will change. On the other hand, a cooling rate greater than 50°C / second is uneconomical and therefore undesirable.

[0155] Here, the coating of the chemical conversion treatment agent mentioned above can be carried out by commonly known coating methods, such as: roller coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, brush coating, etc.

[0156] By following the steps described above, the surface-treated steel 10, which serves as the material for the surface-treated component 1 of this embodiment, can be manufactured. This concludes the detailed explanation of one example of the manufacturing method for the surface-treated steel 10 of this embodiment.

[0157] <Manufacturing Method of Surface-Treated Components> The surface-treated steel 10 obtained in the above manner is used as the material to manufacture the surface-treated component 1 of this embodiment. Here, when obtaining the parts for manufacturing the surface-treated component 1 from the surface-treated steel 10, various shape processing methods can be used, such as various forming processing methods or joining processes performed by fastening components such as bolts, riveting, or welding. By appropriately combining these processes, a surface-treated component 1 with the desired shape can be manufactured from the surface-treated steel 10.

[0158] The above briefly describes one example of the manufacturing method of the surface-treated component 1 in this embodiment. [Example]

[0159] Hereinafter, the surface treatment component of the present invention will be specifically described with reference to embodiments and comparative examples. Furthermore, the embodiments shown below are merely one example of the surface treatment component of the present invention, and the surface treatment component of the present invention is not limited to the examples described below.

[0160] <Preparation for Plated Steel> In the test examples shown below, the plating master sheets shown in Table 1 were used and cut to a size of 100mm × 200mm. Then, plating was performed using our batch melt plating test apparatus, and several plated steel samples with the plating layers shown in Table 2 were produced according to various criteria.

[0161] [Table 1]

[0162] [Table 2]

[0163] Preparation of Chemical Conversion Treatment Agents Prepare chemical conversion agents for forming the chemical conversion treatment layer using commercially available compounds as shown in Tables 3 to 7 below. Table 3 lists the compounds used as phosphorus-containing compounds, Table 4 lists the silane coupling agents used, and Table 5 lists the valve metals used. These compounds are all general reagents. Table 6 lists the organic resins used, and Table 7 lists the other compounds used. Additionally, in Table 7, compounds other than silica sols are general reagents.

[0164] [Table 3]

[0165] [Table 4]

[0166] [Table 5]

[0167] [Table 6]

[0168] [Table 7]

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

[0170] <Formation of the Chemical Conversion Treatment Layer> Using a bar coater, the chemical conversion agent prepared as described above is applied to the surface of the previously described plated steel to form a chemical conversion layer. The conditions for forming the chemical conversion layer are listed in Tables 8 to 11-8 below. In this manner, several surface-treated steel samples are produced as test materials according to various criteria.

[0171] [Table 8]

[0172] [Table 9]

[0173] For each surface-treated steel obtained, the concentrations of various phosphorus (P) and the XPS intensity ratio in the chemical conversion treatment layer were measured, and the thickness of the chemical conversion treatment layer was also measured. Furthermore, according to the previously described method, a dissolution test was performed to measure the amount of P dissolved in ion-exchanged water. The results are summarized and listed in Tables 11-1 to 11-8 below.

[0174] Furthermore, the corrosion resistance in soil was evaluated for each of the obtained surface-treated steels using the following two test methods. Simultaneously, the formation of an oxide layer, an example of a P-Zn composite layer, was confirmed by burying the steels in the soil. Moreover, for each of the obtained surface-treated steels…

[0175] (Test Method 1: Evaluation of corrosion resistance in general soil) The surface-treated steel obtained by the above method was buried in soil, and its corrosion resistance was evaluated. The soil used was silica sand with an average particle size of 300 μm. The cover thickness (distance from the surface of the chemical conversion treatment layer to the soil surface) was set to 20 mm. After burial, to simulate ordinary soil, ion-exchange water with 0.03% by mass of NaCl was dripped into the soil, and the moisture content was adjusted to 100%. Here, the NaCl added to the ion-exchange water is to simulate the electrolyte present in the soil. Then, the following drying and wetting steps were repeated 50 times. Drying steps: Store at 30℃ for 7 days. Wetting step: Add ion-exchange water droplets to adjust the moisture content to 100%.

[0176] For the surface-treated steel after the above-described tests, the method described earlier was used to confirm whether an oxide layer formed between the chemical conversion treatment layer and the soil. Furthermore, the surface treatment agent after the tests was pickled with hydrochloric acid to remove the plating layer, chemical conversion treatment layer, and corrosion products. Subsequently, the corrosion status of the steel was investigated using a shape measuring machine (Keyence VR-5000). The evaluation criteria are as follows. Scores A, B, and C were considered acceptable. The results are summarized and listed in Tables 12-1 to 12-8 below. score A: No pits were formed on the steel. B: For steel, pits with a depth of less than 10μm are formed. C: For steel, pits with a depth of more than 10μm and less than 50μm are formed. D: For steel, pits with a depth of more than 50μm and less than 100μm are formed. E: For steel, pits with a depth of more than 100μm are formed.

[0177] (Experimental Method 2: Evaluation of corrosion resistance in acidic soil) The surface-treated steel obtained by the above method was buried in soil, and its corrosion resistance was evaluated. The soil used was silica sand with an average particle size of 100 μm. The cover thickness was set at 50 mm. After burial, to simulate acidic soil, the soil was dripped with the following HCl aqueous solution and adjusted to achieve a moisture content of 100%; the HCl aqueous solution was prepared by adding HCl to water during ion exchange and adjusting it to pH 4. Then, the following drying and wetting steps were repeated 50 times. Drying steps: Store at 30℃ for 7 days. Wetting step: Add ion-exchange water droplets to adjust the moisture content to 100%.

[0178] For the surface-treated steel after the above-described tests, the method described earlier was used to confirm whether an oxide layer formed between the chemical conversion treatment layer and the soil. Furthermore, the surface treatment agent after the tests was pickled with hydrochloric acid to remove the plating layer and corrosion products. Subsequently, the corrosion status of the steel was investigated using a shape measuring machine (Keyence, VR-5000). The evaluation criteria are as follows. Scores A, B, and C were considered acceptable. The results are summarized and listed in Tables 12-1 to 12-8 below. score A: No pits were formed on the steel. B: For steel, pits with a depth of less than 10μm are formed. C: For steel, pits with a depth of more than 10μm and less than 50μm are formed. D: For steel, pits with a depth of more than 50μm and less than 100μm are formed. E: For steel, pits with a depth of more than 100μm are formed.

[0179] (Test Method 3: Evaluation of corrosion resistance in the atmosphere) The surface-treated steel obtained by the above method was cut into 50×100mm dimensions. The back side of the test surface and the cut end were protected with seal tape (Nitto Denko Co., Ltd., No. 31C, electrical insulation polyester adhesive tape). Then, a composite cyclic corrosion test as specified in JIS G 0594:2019 was performed. This test consisted of a cyclic corrosion test comprising 1 hour of salt spray, 4 hours of drying, and 3 hours of humid environment. This test was performed for 120 hours (15 cycles).

[0180] The corrosion status of the surface-treated steel after the above-described tests was visually observed, and the area percentage of white rust was investigated. The evaluation criteria are as follows. Scores A, B, and C were considered acceptable. The results are summarized and listed in Tables 12-1 to 12-8 below. score A: The area where white rust forms is less than 5%. B: The area where white rust forms is greater than 5% but less than 10%. C: The area of ​​white rust formation is greater than 10% and less than 20%. D: The area of ​​white rust formation is greater than 20% and less than 50%. E: The area where white rust forms is greater than 50%.

[0181] [Table 10-1]

[0182] [Table 10-2]

[0183] [Table 10-3]

[0184] [Table 10-4]

[0185] [Table 10-5]

[0186] [Table 10-6]

[0187] [Table 10-7]

[0188] [Table 10-8]

[0189] [Table 11-1]

[0190] [Table 11-2]

[0191] [Table 11-3]

[0192] [Table 11-4]

[0193] [Table 11-5]

[0194] [Table 11-6]

[0195] [Table 11-7]

[0196] [Table 11-8]

[0197] [Table 12-1]

[0198] [Table 12-2]

[0199] [Table 12-3]

[0200] [Table 12-4]

[0201] [Table 12-5]

[0202] [Table 12-6]

[0203] [Table 12-7]

[0204] [Table 12-8]

[0205] As can be seen from Tables 10-1 to 12-8 above, the surface-treated components conforming to the embodiments of the present invention still exhibit excellent corrosion resistance even in soil. On the other hand, the surface-treated components conforming to the comparative examples of the present invention cannot obtain sufficient corrosion resistance.

[0206] The present invention has been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the examples described. Those skilled in the art to which this invention pertains will be able to conceive of various modifications or alterations within the scope of the technical concept described in the claims, and will understand that such modifications or alterations should also fall within the technical scope of this invention.

[0207] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. These embodiments may also be omitted, substituted, and modified in various forms without departing from the scope of the appended patent application, falling within the technical scope and spirit of the present invention as described below. For example, the constituent elements of the above embodiments can be arbitrarily combined without impairing their effects. Furthermore, such arbitrary combinations not only obtain the functions and effects of each constituent element related to the combination, but also obtain other functions and effects that are readily apparent to those skilled in the art from the description herein.

[0208] Furthermore, the effects described in this specification are merely illustrative or exemplary and not limiting. That is, the technology of this invention can not only achieve the above-mentioned effects, but may also achieve other effects that are obvious to those skilled in the art from the description in this specification, in lieu of the above-mentioned effects.

[0209] Furthermore, the following configurations also fall within the technical scope of this invention. (1) A surface-treated component, constructed of surface-treated steel, wherein the surface-treated steel has: Steel as the base material, The zinc plating layer on the surface of the aforementioned steel, and A chemical conversion treatment layer located on the surface of the aforementioned zinc-based plating layer; The aforementioned chemical conversion treatment layer contains: compounds containing phosphorus element P; When the aforementioned chemical conversion treatment layer, corresponding to a 1m² area of ​​the aforementioned surface-treated steel, is immersed in ion-exchange water at a temperature of 35-45°C for 60 minutes, the amount of P dissolved from the aforementioned chemical conversion treatment layer into the aforementioned ion-exchange water is 5-50 mg / m². (2) The surface-treated component as described in (1) is used in such a way that at least a portion of the aforementioned surface-treated steel is buried in the soil. (3) The surface-treated component as described in (1) or (2), wherein, The narrow spectrum of P2p obtained by X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aforementioned chemically converted layer... The ratio of the cumulative intensity with a peak at 132.80±0.25eV to the cumulative intensity with a peak at 133.90±0.25eV is 0.20 to 0.50. (4) The surface-treated component described in any one of (1) to (3), wherein, When performing energy-dispersive X-ray spectroscopy (EDS) line analysis on the aforementioned chemical conversion treated layer from its surface to its interface with the aforementioned zinc-based plating layer, the obtained depth profile regarding P concentration... The average P concentration on the surface side of the aforementioned chemical conversion treatment layer is 1~20 by mass. (5) The surface treatment component described in any one of (1) to (4), wherein the P concentration of the aforementioned chemical conversion treatment layer is 0.1 to 15.0 by mass when converted to P. (6) The surface treatment component described in any one of (1) to (5), wherein the thickness of the aforementioned chemical conversion treatment layer is 30 to 5000 nm. (7) The surface treatment component described in any one of (1) to (6), wherein the aforementioned chemical conversion treatment layer contains one or more of the group consisting of silane coupling agents, valve metals and organic resins. (8) The surface-treated component as described in any one of (1) to (7), wherein the aforementioned zinc-based plating layer is a plating layer having the following chemical composition, which, in mass percent, contains: Al: ≥0.10% and <40.00% Mg: ≥0.10% and <15.00%, The remaining part consists of Zn and impurities. (9) The surface-treated component as described in (8), wherein the aforementioned zinc-based plating layer comprises the following plating layer: In terms of mass%, Al: ≥0.10% and <40.00% Mg: ≥0.10% and <15.00% Zn: 60.00% or more. (10) The surface-treated component described in any one of (1) to (7), wherein the aforementioned zinc-based plating layer is a plating layer having the following chemical composition, which, in mass % contains: Al: ≥0.10% and <40.00% Mg: ≥0.10% and <15.00%, It 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 remainder consisting of Zn and impurities; [Element Group A]: Selected from one or two elements in the group consisting of Si: 2.50% or less and Fe: 5.00% or less; [Element Group B]: Selected from one or more elements in the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%; [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%; [Element Group D]: Selected from one or more elements in the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%; [Element Group E]: Selected from one or more elements in the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%; [Element group F]:B: less than 0.50%. (11) The surface-treated component as described in (10) contains the aforementioned element group A. (12) The surface treatment component described in (10) contains the aforementioned element group B. (13) The surface-treated component as described in (10) contains the aforementioned element group C. (14) The surface-treated component as described in (10) contains the aforementioned element group D. (15) The surface-treated component as described in (10) contains the aforementioned element group E. (16) The surface-treated component as described in (10) contains the aforementioned element group F. (17) The surface-treated component as described in (10), wherein the aforementioned zinc-based plating layer comprises at least the following plating layers: In terms of mass%, Al: 4.0% or more but less than 25.0% Mg: ≥0.3% and <12.5%. (18) A composite structure is a composite structure of a surface-treated component and soil; the surface-treated component is made of surface-treated steel, the surface-treated steel having: steel as a base material, a zinc-based plating layer on the surface of the aforementioned steel, and a chemical conversion treatment layer on the surface of the aforementioned zinc-based plating layer; At least a portion of the interface between the aforementioned surface-treated component and the aforementioned soil, between the aforementioned chemically converted treatment layer and the aforementioned soil, exists a P-Zn composite layer containing Zn and P. (19) The composite structure as described in (18), wherein the aforementioned P-Zn composite layer is a layer having the following chemical composition, which, in mass percent, contains: Zn: 1.0% or more and 10.0% or less P: Above 0.5% and below 5.0%, The remaining part consists of H, C, O, Si and impurities. (20) The composite structure described in (19) further contains Al and Mg as chemical components; The aforementioned P-Zn composite layer, based on its chemical composition, further contains at least one of the following to replace a portion of the remaining H, C, O, and Si: Al: 0% or more and less than 10.0% by mass Mg: ≥0% and ≤10.0% by mass.

[0210] 1: Surface-treated components 5: Composite structure 10: Surface-treated steel 11: Steel 13: Zinc-based coating 15: Chemical conversion treatment layer 21: Oxide layer AA: Cut line d: thickness

Claims

1. A surface-treated component, comprising surface-treated steel having: a steel base material, a zinc-based plating layer on the surface of the steel, and a chemical conversion treatment layer on the surface of the zinc-based plating layer; the chemical conversion treatment layer containing a compound containing phosphorus (P); after immersing the chemical conversion treatment layer in ion-exchange water at a temperature of 35-45°C for 60 minutes in a 1 m² volume of the surface-treated steel, the amount of P dissolved from the chemical conversion treatment layer into the ion-exchange water is 5-50 mg / m².

2. The surface-treated component as claimed in claim 1, which is used in such a way that at least a portion of the aforementioned surface-treated steel is buried in the soil.

3. The surface-treated component as requested in item 1, wherein, In the narrow spectrum of P2p obtained by X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aforementioned chemically converted layer, the ratio of the cumulative intensity of the peak with a maximum value at 133.90±0.25eV to the cumulative intensity of the peak with a maximum value at 132.80±0.25eV is 0.20~0.

50.

4. The surface-treated component as requested in item 1, wherein, When energy dispersive X-ray spectroscopy (EDS) was performed on the aforementioned chemical conversion treatment layer from its surface to its interface with the aforementioned zinc-based plating layer, the average P concentration on the surface side of the aforementioned chemical conversion treatment layer was 1 to 20 by mass in the obtained depth profile of P concentration.

5. The surface-treated component as requested in item 1, wherein, The P concentration of the aforementioned chemical conversion treatment layer is 0.1 to 15.0 by mass.

6. The surface-treated component as requested in item 1, wherein, The thickness of the aforementioned chemical conversion treatment layer is 30~5000 nm.

7. The surface-treated component as requested in item 1, wherein, The aforementioned chemical conversion treatment layer contains one or more of the following: silane coupling agents, valve metals, and organic resins.

8. A surface-treated component as described in any one of requests 1 to 7, wherein, The aforementioned zinc-based plating layer is a plating layer having the following chemical composition, which, in mass percent, contains: Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder consisting of Zn and impurities.

9. The surface-treated component as described in claim 8, wherein the aforementioned zinc-based plating layer contains the following components: Al: 0.10% or more and less than 40.00% by mass, Mg: 0.10% or more and less than 15.00%, Zn: 60.00% or more.

10. A surface-treated component as described in any one of claims 1 to 7, wherein, The aforementioned zinc-based plating layer is a plating layer having the following chemical composition, which, in mass % contains: 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 remainder consisting of Zn and impurities; [Element group A]: selected from one or two elements selected from the group consisting of Si: less than 2.50% and Fe: less than 5.00%; [Element group B]: selected from 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%. [Element Group C]: Selected from one or more of the following groups: 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]: Selected from one or more of the following groups: Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%; [Element Group E]: Selected from one or more of the following groups: Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%; [Element Group F]: B: less than 0.50%.

11. The surface-treated component of claim 10, which contains the aforementioned element group A.

12. The surface-treated component of claim 10 contains the aforementioned element group B.

13. The surface-treated component of claim 10, which contains the aforementioned element group C.

14. The surface-treated component of claim 10 contains the aforementioned element group D.

15. The surface-treated component of claim 10, which contains the aforementioned element group E.

16. The surface-treated component of claim 10 contains the aforementioned element group F.

17. The surface-treated component as claimed in claim 10, wherein, The aforementioned zinc-based coating contains at least the following components: Al: 4.0% or more and less than 25.0% by mass, and Mg: 0.3% or more and less than 12.5%.

18. A composite structure comprising a surface-treated component and soil; the surface-treated component being constructed of surface-treated steel having: a steel base material, a zinc-based plating layer on the surface of the steel, and a chemical conversion treatment layer on the surface of the zinc-based plating layer; at least a portion of the interface between the surface-treated component and the soil, between the chemical conversion treatment layer and the soil, contains a P-Zn composite layer containing Zn and P.

19. A composite structure as described in claim 18, wherein, The aforementioned P-Zn composite layer is a layer having the following chemical composition, which, in mass percent, contains: Zn: 1.0% or more and 10.0% or less, P: 0.5% or more and 5.0% or less, with the remainder consisting of H, C, O, Si and impurities.

20. A composite structure as described in claim 19, wherein, The aforementioned zinc-based coating further contains Al and Mg as chemical components; the aforementioned P-Zn composite layer further contains at least one of the following to replace a portion of the remaining H, C, O, and Si: Al: 0% or more and 10.0% by mass, Mg: 0% or more and 10.0% by mass.

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