Surface-treated steel material and surface-treated member

Abstract

[Problem] To provide a surface-treated steel material and a surface-treated member that exhibit excellent corrosion resistance even in soil having a depth of approximately several cm from the soil surface and containing chloride ions. [Solution] A surface-treated steel material according to the present invention comprises: a steel material that serves as a base material; a zinc plating layer that is positioned on a surface of the steel material and contains Mg, Al, and Zn; and a chemical conversion coating layer that is positioned on the surface of the zinc plating layer. The zinc plating layer is a plating layer having a chemical composition that contains, in mass%, at least 0.10% and less than 40.00% of Al and at least 0.10% and less than 15.00% of Mg, with the remainder containing impurities and at least 60.00% of Zn. The chemical conversion coating layer contains P, and the average value of the P concentration in a surface-side region of the chemical conversion coating layer is 1.1-1.5 times the average value of the P concentration in a plating-side region. The average value of the Mg concentration in a Mg-rich region is 1.2-2.0 times the average value of the Mg concentration in the zinc plating layer excluding the Mg-rich region.

Description

Surface-treated steel materials and surface-treated components

[0001] This invention relates to surface-treated steel materials and surface-treated members.

[0002] Zinc-plated steel, which has various zinc-based plating layers applied as a surface treatment layer to the surface of a base steel material, is a material widely used in fields such as construction and automobiles from the viewpoint of improving the corrosion resistance of structural members. After being processed into various shapes, zinc-plated steel as a material is joined together as needed using fastening members such as screws, bolts, and rivets, or various welding methods, to become a surface-treated member with the desired shape.

[0003] The surface-treated components described above are expected to be exposed to various corrosive environments depending on their intended use. Therefore, various studies have been conducted regarding the corrosion resistance of the surface-treated steel material.

[0004] For example, Patent Document 1 discloses a surface-treated steel sheet having a surface-treated film with a thickness of 0.02 to 5 μm, formed by applying a surface treatment composition containing a water-dispersible resin and / or a water-soluble resin, which is a reaction product of an epoxy group-containing resin and an active hydrogen-containing compound, a silane coupling agent, and phosphoric acid and / or a hexafluorometallic acid to the surface of a zinc-plated steel sheet or an aluminum-plated steel sheet, and then drying it.

[0005] Furthermore, Patent Document 2 discloses a surface-treated steel sheet in which the surface of a zinc-plated steel sheet is coated with a Cr-free film, and the surface of the zinc-plated film has a compound layer containing the elements P, Zn, and O, as well as one or more elements selected from Mn, Mg, and Al, with a silica-enriched layer on top of that, and an organic resin layer on top of that.

[0006] Furthermore, Patent Document 3 discloses a hot-dip galvanized steel sheet having a conversion coating mainly composed of one or more hydroxides, oxides, oxygen acids, oxygen salts, and fluorides of valve metal, provided on a Mg-containing zinc alloy plating layer via an interfacial reaction layer containing one or more selected from magnesium fluoride, magnesium phosphate, and a composite compound of magnesium and valve metal oxyacids.

[0007] Japanese Patent Publication No. 2003-105554, Japanese Patent Publication No. 2005-42190, Japanese Patent Publication No. 2007-23309

[0008] When installing surface-treated components at desired locations, it is presumed that at least a portion of them will often be buried in the soil. For parts of the surface-treated component exposed to the atmosphere, it is easy to visually inspect the corrosion status of the exposed portion. However, unlike in the atmosphere, visual inspection of corrosion status is difficult for parts buried in the soil, and maintenance of corroded areas is also challenging. Therefore, surface-treated components used in soil require high corrosion resistance. In particular, soils containing chloride ions, which can act as corrosive factors, require even higher corrosion resistance.

[0009] The inventors of the present invention were investigating the corrosion behavior of zinc-plated steel materials in soil containing chloride ions, and as will be described later, they found that the corrosion behavior of zinc-plated steel materials in soil at a depth of 1 m or more from the soil surface differs significantly from the corrosion behavior of zinc-plated steel materials in soil at a depth of several centimeters from the soil surface. Furthermore, they found that in soil containing chloride ions at a depth of several centimeters from the soil surface, even if surface-treated members are manufactured using surface-treated steel sheets as disclosed in the above-mentioned Patent Documents 1 to 3 as the material, there is room for further improvement in their corrosion resistance.

[0010] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a surface-treated steel material using zinc-plated steel that can exhibit excellent corrosion resistance even in soil containing chloride ions at a depth of several centimeters from the soil surface, and a surface-treated member using such surface-treated steel material.

[0011] To solve the above problems, the inventors diligently studied and conceived of providing a chemical conversion coating layer on the surface of a zinc-based plating layer used as a material for surface treatment members, in which P and Mg are in a specific distribution state. Based on this idea, further studies were conducted and resulted in the surface treatment member described below. The gist of the present invention, completed based on this idea, is as follows.

[0012] (1) The material comprises a base material steel, a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer has a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities, and the chemical conversion coating layer contains P, and the thickness of the chemical conversion coating layer is denoted as t, and the surface side region is defined as a range starting from the surface of the chemical conversion coating layer and ending at a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer. (1) The surface-treated steel material wherein, when the plated side region is defined as the range starting at a position 5t / 10 in the thickness direction from the surface of the chemical conversion treated film layer and ending at the interface between the chemical conversion treated film layer and the zinc-based plating layer, the average value of the P concentration in the surface side region is 1.10 to 1.50 times the average value of the P concentration in the plating side region, and when the Mg-enriched region is defined as the range starting at a position 8t / 10 in the thickness direction from the surface of the chemical conversion treated film layer and ending at a position 12t / 10 in the thickness direction from the surface of the chemical conversion treated film layer toward the zinc-based plating layer, the average value of the Mg concentration in the Mg-enriched region is 1.20 to 2.00 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region. (3) The surface-treated steel material according to (1) or (2), wherein the P concentration in the chemical conversion coating layer is 0.1% by mass or more and less than 3.0% by mass. (4) The surface-treated steel material according to (1) or (2), wherein the chemical conversion coating layer further contains V, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, and the range starting from the surface of the chemical conversion coating layer and ending at a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer is defined as the surface-side region, and the range starting from a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer and ending at the interface between the chemical conversion coating layer and the zinc-based plating layer is defined as the plating-side region, the average value of the V concentration in the surface-side region is 1.10 to 1.50 times the average value of the V concentration in the plating-side region.(5) The surface-treated steel material according to (4), wherein the V concentration in the chemical conversion coating layer is 0.1% by mass or more and less than 2.0% by mass. (6) The surface-treated steel material according to (4), wherein in the narrow spectrum of V2p obtained by analyzing the plated side region of the chemical conversion coating layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of the peak having a maximum value at 515.90 ± 0.25 eV to the integrated intensity of the peak having a maximum value at 517.20 ± 0.25 eV is 0.20 to 0.50. (7) The surface-treated steel material according to (1) or (2), wherein the chemical conversion coating layer further contains Mo, the Mo concentration in the chemical conversion coating layer is 0.1% by mass or more and 2.5% by mass or less, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, the range starting from the surface of the chemical conversion coating layer and ending at a position 2t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer is defined as the surface region, the range starting from a position 8t / 10 in the thickness direction from the surface of the chemical conversion coating layer and ending at the interface between the chemical conversion coating layer and the zinc-based plating layer is defined as the interface region, and the range located between the surface region and the interface region is defined as the intermediate region, the average value of the Mo concentration in the surface region is 1.10 to 1.50 times the average value of the Mo concentration in the intermediate region. (8) The surface-treated steel material according to (7), wherein the Mo concentration in the chemical conversion coating layer is 0.1% by mass or more and less than 2.0% by mass. (9) The surface-treated steel material according to (1) or (2), wherein the thickness t of the chemical conversion coating layer is 0.1 to 30.0 μm. (10) The surface-treated steel material according to (2), wherein the organic resin is at least one of a urethane resin, an acrylic resin, an epoxy resin, or an olefin resin. (11) The amount of zinc-based plating layer is 30 to 500 g / m per side. ２The surface-treated steel material according to (1) or (2). (12) The zinc-based plating layer contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element groups A to F below, with the remainder being 60.00% or more of Zn and impurities, the surface-treated steel material according to (1) or (2). [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element group F]: B: less than 0.50%. (13) The surface-treated steel material according to (12), containing element group A. (14) The surface-treated steel material according to (12), containing element group B. (15) The surface-treated steel material according to (12), containing element group C. (16) The surface-treated steel material according to (12), containing element group D. (17) The surface-treated steel material according to (12), containing element group E. (18) The surface-treated steel material according to (12), containing element group F. (19) The surface-treated steel material according to (1) or (12), wherein the zinc-based plating layer has a chemical composition in mass%, containing Al: 4.00% or more and less than 25.00%, Mg: 0.30% or more and less than 12.50%, with the remainder being 60.00% or more of Zn and impurities.(20) A surface treatment member having a laminated structure in at least a part of the member, comprising a base material steel, a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer is a plating layer having a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities, and the chemical conversion coating layer contains P, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, and starting from the surface of the chemical conversion coating layer, toward the zinc-based plating layer, a position of 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer A surface treatment member wherein, when the range ending at the position is defined as the surface side region, and the range starting at a position 5t / 10 in the thickness direction from the surface of the chemical conversion treatment film layer and ending at the interface between the chemical conversion treatment film layer and the zinc-based plating layer is defined as the plating side region, the average value of the P concentration in the surface side region is 1.1 to 1.5 times the average value of the P concentration in the plating side region, and when the range starting at a position 8t / 10 in the thickness direction from the surface of the chemical conversion treatment film layer and ending at a position 12t / 10 in the thickness direction from the surface of the chemical conversion treatment film layer toward the zinc-based plating layer is defined as the Mg-enriched region, the average value of the Mg concentration in the Mg-enriched region is 1.2 to 2.0 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region. (21) The surface treatment member according to (20), wherein at least a part of the portion having the laminated structure is buried in the soil. (22) The surface treatment member according to (21), wherein the soil is soil having a chloride ion concentration of 3 to 1000 mmol per 1 kg of soil.

[0013] As described above, the present invention makes it possible to provide surface-treated steel materials and surface-treated members that exhibit excellent corrosion resistance even in soil containing chloride ions at a depth of several centimeters from the soil surface.

[0014] This is a schematic diagram illustrating a structure installed on a soil surface. This is a schematic diagram illustrating the structure of a surface-treated steel material according to an embodiment of the present invention. This is a schematic diagram illustrating the structure of a surface-treated steel material according to the same embodiment. This is a schematic diagram illustrating the chemical conversion coating layer of the surface-treated steel material according to the same embodiment.

[0015] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0016] (Corrosion behavior in soil containing chloride ions at a depth of several centimeters from the soil surface) Before describing the surface treatment member according to an embodiment of the present invention, the inventors will describe the corrosion behavior in soil containing chloride ions at a depth of several centimeters from the soil surface, as discovered by the inventors, with reference to Figure 1. Figure 1 is a schematic diagram for illustrating a structure installed on the soil surface. In the following, "soil at a depth of several centimeters from the soil surface" may be conveniently referred to as the "soil surface layer."

[0017] As schematically shown in Figure 1, various structures, such as mounting frames for solar power generation panels, road signs, guardrails, and traffic lights, are installed on the soil surface. In order to install these structures more stably on the soil surface, a portion of the structure (for example, the area near the lower end of a support column, as enclosed by a dashed line in Figure 1) is often buried in the soil.

[0018] In this context, various structures often utilize different types of steel as materials, for example, from the perspective of production costs. When a portion of a structure made from these different types of steel is buried in the soil, there is a concern about the corrosion of the steel material.

[0019] The effects of soil on steel corrosion can be broadly categorized into two types: retention of moisture, a corrosive factor, and inhibition of oxygen diffusion, another corrosive factor. Moisture retention increases the corrosion rate, while inhibition of oxygen diffusion decreases it. Compared to the atmosphere, soil retains a humid environment (i.e., moisture) for longer periods after rainfall. On the other hand, soil inhibits the penetration and diffusion of oxygen from the atmosphere, thus reducing the corrosion rate. In actual soil, the corrosion rate is determined by the interaction of these two trade-off effects. Generally, the effect of oxygen diffusion inhibition is greater than the effect of moisture retention, so the corrosion rate in soil is lower than in the atmosphere.

[0020] On the other hand, the situation is quite different in soil containing chloride ions at a depth of only a few centimeters from the surface (the topsoil layer). Even in the topsoil layer, moisture does not evaporate easily due to the soil. Therefore, steel materials remain in contact with moisture containing chloride ions for a longer period of time compared to the atmosphere. On the other hand, in the topsoil layer, due to the close distance from the atmosphere, oxygen is supplied quickly from the atmosphere, so the effect of the soil suppressing oxygen diffusion is small. Therefore, combined with the effect of retaining moisture containing chloride ions, it is thought that there is almost no corrosion suppression effect from the soil in the topsoil layer. Thus, the topsoil layer containing chloride ions, which the inventors focused on, can be said to be an extremely harsh corrosion environment compared to soil at a depth of 1 meter or more from the surface.

[0021] The inventors investigated the corrosion behavior of zinc-plated steel materials in the surface layer of soil containing chloride ions, and found the following: The zinc-plated layer of zinc-plated steel materials exhibits high corrosion resistance in the atmosphere by covering the surface of the plating layer with zinc-based corrosion products. However, it was found that the corrosion protection function by such zinc-based corrosion products is low in the surface layer of soil.

[0022] When zinc-based corrosion products formed on the zinc-based plating layer in the surface layer of soil were observed using a scanning electron microscope (SEM), it was found that the zinc-based corrosion products formed in the surface layer of soil were in a more porous state compared to zinc-based corrosion products formed in the atmosphere. This was thought to be because corrosion progresses much more rapidly in the surface layer of soil compared to in the atmosphere.

[0023] Based on the above findings, the inventors conducted further investigations and found that in order to improve the corrosion resistance of zinc-plated steel materials in the surface layer of soil, it is important to provide a chemical conversion treatment film layer containing at least phosphorus element P on the surface of the zinc-plated layer, and to ensure that magnesium Mg and P derived from the zinc-plated layer are in a specific distribution state.

[0024] More specifically, the inventors have found that it is important to react P contained in the chemical conversion agent for forming the chemical conversion coating layer with a component derived from the zinc-based plating layer to form a chemical conversion coating layer containing the reaction product of P and the plating layer component, and to achieve a state in which Mg is concentrated in the vicinity of the interface between the chemical conversion coating layer and the zinc-based plating layer.

[0025] The reaction product between P and the plating layer components (more specifically, a P-Mg composite oxide, which is a reaction product between P and Mg, one of the plating layer components) is generated, resulting in a specific distribution state of element P within the formed chemical conversion coating layer. This reaction product (P-Mg composite oxide) exhibits a barrier effect that suppresses the penetration of chloride ions, which are a corrosive factor. This barrier effect makes it possible to suppress corrosion of the plating layer located beneath the chemical conversion coating layer.

[0026] Furthermore, the concentration of Mg near the interface between the chemical conversion coating layer and the zinc-based plating layer promotes a reaction in which chloride ions penetrate beyond the barrier effect described above, causing a reaction between the chloride ions and the components of the zinc-based plating layer (i.e., a portion of the plating layer corrodes) to form dense corrosion products. The formation of dense corrosion products prevents the zinc-based plating layer from continuing to corrode, thus maintaining corrosion resistance. Through the above mechanism, it becomes possible to improve the corrosion resistance of surface-treated steel materials and surface-treated components even in soil containing chloride ions (especially the surface layer of soil containing chloride ions).

[0027] Furthermore, as a result of investigations by the present inventors, it was found that the corrosion resistance of surface-treated steel materials and surface-treated components is further improved when the chemical conversion coating layer further contains at least one of the elements vanadium V or molybdenum Mo, and these elements exist in a specific distribution state.

[0028] Based on the findings described above, the inventors conducted further studies and arrived at the surface-treated steel material and surface-treated member according to the embodiment of the present invention, which will be described in detail below.

[0029] (Regarding surface-treated steel materials) Below, with reference to Figures 2 and 3, surface-treated steel materials according to embodiments of the present invention will be described in detail. Figures 2 and 3 are schematic diagrams for illustrating the structure of surface-treated steel materials according to this embodiment. Furthermore, for convenience, the coordinate axes shown in Figures 2 and 3 will be used in the explanation.

[0030] The surface-treated steel material according to this embodiment is a steel material having a zinc-based plating layer and a chemical conversion coating layer, as detailed below, and is used as a material for surface-treated members.

[0031] Figure 2 schematically shows a part of the surface-treated steel material 1 according to this embodiment, viewed from above (in the Z-axis direction in the figure) from above its surface. As schematically shown in Figure 2, the surface-treated steel material 1 according to this embodiment has a zinc-based plating layer 13 and a chemical conversion coating layer 15 sequentially provided on the surface of the base material steel material 11, as will be described later.

[0032] Figure 3 schematically shows a cross-section of the surface-treated steel material 1 shown in Figure 2 when it is cut in the Z-axis direction along the A-A cutting line. The cross-sectional view shown in Figure 3 corresponds to the surface-treated steel material 1 according to this embodiment, cut in the thickness direction of the surface-treated steel material 10 which is the base material for the surface-treated steel material 1.

[0033] As schematically shown in Figure 3, the surface-treated steel material 1 according to this embodiment comprises a base material steel material 11, a zinc-based plating layer 13 located on the front and back surfaces of the steel material 11, and a chemical conversion treatment layer 15 located on the surface of the zinc-based plating layer 13.

[0034] Below, we will first describe in detail the steel material 11, the zinc-based plating layer 13, and the chemical conversion treatment layer 15.

[0035] <Regarding the steel material 11> The steel material 11 used as the base material of the surface-treated steel material 1 according to this embodiment is not particularly limited, and various types of steel materials can be used depending on the mechanical strength (e.g., tensile strength) required for the surface-treated steel material 1. Examples of such steel materials 11 include various types of Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., high-strength steel further containing reinforcing elements such as P, Si, Mn in ultra-low carbon steel, and various other steel materials containing various components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0036] Furthermore, a pre-plating layer may be applied to the steel material 11 before performing zinc-based plating as described later. Suitable metals for the pre-plating layer include Ni, Sn, or alloys combining these elements. Using a pre-plated steel sheet with these platings applied beforehand eliminates areas of non-plating (areas where the plating metal is repelled by an oxide film, etc.). This is presumed to be because, when the pre-plated steel sheet is immersed in the 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 applied per side is 0.2 to 2.0 g / m². ２It is preferable that the amount of pre-plating layer is 0.2 g / m². ２ By doing so, it becomes possible to reliably achieve the pre-plating effect of suppressing non-plating by the pre-plating described above. Also, the amount of pre-plating layer to adhere is 2.0 g / m ２ By doing the following, it becomes possible to achieve the above-mentioned non-plating suppression effect while preventing the dissolution of Fe by the pre-plating layer from being suppressed and thus making it difficult for Fe-Zn-based composite oxides to be formed.

[0037] Furthermore, the thickness of the steel material 11 is not particularly limited and can be set appropriately according to the mechanical strength and other requirements for the surface-treated steel material 1.

[0038] <About the zinc-based plating layer 13> The zinc-based plating layer 13 is formed over the entire surface of both the front and back surfaces of the steel material 11 as described above. This zinc-based plating layer 13 is a ternary plating layer containing aluminum (Al) and magnesium (Mg). Examples of such zinc-based plating include zinc-aluminum-magnesium plating and zinc-aluminum-magnesium-silicon plating. In addition, as zinc-based plating, the above plating may contain a small amount of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, etc., or may contain dispersed inorganic materials such as silica, alumina, titania. The plating method is not particularly limited, and various known plating methods such as electroplating, hot-dip plating, vapor deposition, dispersion plating, and vacuum plating may be used.

[0039] Among the various zinc-based platings described above, the zinc-based plating layer 13 according to this embodiment is, for example, a zinc-based plating layer having the chemical composition detailed below. By using a zinc-based plating layer 13 having the chemical composition detailed below, it is possible to improve various properties of the surface-treated steel material 1 according to this embodiment, including its corrosion resistance. Below, we will first describe in detail the chemical composition of the zinc-based plating layer 13 as described above.

[0040] ≪Chemical composition of zinc-based plating layer 13≫ According to one embodiment, the chemical composition of the zinc-based plating layer 13 is, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities.

[0041] Furthermore, according to another embodiment, the chemical composition of the zinc-based plating layer 13 in this embodiment contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element group A, element group B, element group C, element group D, element group E, and element group F, with the remainder being a chemical composition consisting of 60.00% or more Zn and impurities.

[0042] [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element Group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element Group F]: B: less than 0.50%

[0043] [Al: 0.10% by mass or more and less than 40.00% by mass] Al is an element necessary to constitute the main metal structure (Zn-Al-Mg metal structure) in the zinc-based plating layer 13 according to this embodiment, and is included in a predetermined amount or more in order to ensure corrosion resistance as a plated steel material. If the Al content in the zinc-based plating layer 13 is less than 0.10% by mass, it may not be possible to ensure the above-mentioned corrosion resistance. For this reason, in the zinc-based plating layer 13 according to this embodiment, the Al content is 0.10% by mass or more. The Al content is preferably 3.00% by mass or more, more preferably 4.00% by mass or more, and even more preferably 6.00% by mass or more. By having an Al content within the above range, it is possible to ensure corrosion resistance as a plated steel material.

[0044] On the other hand, if the Al content in the zinc-based plating layer 13 is 40.00% by mass or more, the Al phase that functions as a cathode when placed in a corrosive environment increases excessively, making the corrosion of the steel material 11 more likely to progress, and thus the corrosion resistance of the plated steel material cannot be guaranteed. For this reason, in the zinc-based plating layer 13 according to this embodiment, the Al content is less than 40.00% by mass. The Al content is preferably 25.00% by mass or less, more preferably less than 25.00% by mass, and even more preferably 20.00% by mass or less.

[0045] [Mg: 0.10% by mass or more, less than 15.00% by mass] Mg is an element necessary to constitute the main metal structure (Zn-Al-Mg metal structure) in the zinc-based plating layer 13 according to this embodiment, and is included in a predetermined amount or more in order to ensure corrosion resistance as a plated steel material. If the Mg content in the zinc-based plating layer 13 is less than 0.10% by mass, the above-mentioned corrosion resistance cannot be guaranteed. Therefore, in the zinc-based plating layer 13 according to this embodiment, the Mg content is 0.10% by mass or more. Preferably, the Mg content is 0.30% by mass or more, and more preferably 3.00% by mass or more. By having an Mg content within the above range, it is possible to ensure corrosion resistance as a plated steel material.

[0046] On the other hand, if the Mg content in the zinc-based plating layer 13 is 15.00% by mass or more, the anode dissolution of the zinc-based plating layer is more likely to progress when placed in a corrosive environment, making it impossible to guarantee corrosion resistance as a plated steel material. Therefore, in the zinc-based plating layer 13 according to this embodiment, the Mg content is less than 15.00% by mass. Preferably, the Mg content is less than 12.50% by mass, and more preferably 12.00% by mass or less. By keeping the Mg content within the above range, it becomes possible to guarantee corrosion resistance as a plated steel material.

[0047] In the zinc-based plating layer 13 according to this embodiment, the remainder of the Al and Mg consists of 60.00% by mass or more of Zn and impurities. Zn is an element necessary for constituting the main metal structure (Zn-Al-Mg metal structure) in the zinc-based plating layer 13 according to this embodiment, and is an important element for improving the corrosion resistance of the plated steel material. Furthermore, by containing Al and Mg within the above ranges, and also containing 60.00% by mass or more of Zn, the corrosion resistance required for plated steel materials can be ensured.

[0048] Next, in a zinc-based plating layer 13 according to another embodiment of this embodiment, the element groups A to F that the chemical composition of such zinc-based plating layer 13 may have will be described in detail.

[0049] In addition, in the zinc-based plating layer 13 according to another embodiment of this embodiment, if at least one of the elements belonging to element groups A to F below is included, it is preferable that at least one of the elements belonging to element groups A to F below is included within the following content range, and the total content is 60.00% by mass or less.

[0050] By keeping the total content of elements belonging to element groups A to F to 60.00% by mass or less, it becomes possible to enjoy the effects exhibited by the addition of each element, as detailed below, without impairing each other. The total content of elements belonging to element groups A to F is preferably 50.00% by mass or less, and more preferably 40.00% by mass or less.

[0051] ◇Element Group A In another embodiment of the zinc-based plating layer 13 according to this embodiment, element group A that the zinc-based plating layer 13 may contain will be described. At least one of the elements of element group A shown below may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less

[0052] [Si: 0 to 2.50 mass%] In the zinc-based plating layer 13 according to this embodiment, it is possible that Si may not be included, so the lower limit of its content is 0 mass%. On the other hand, Si is an element that can suppress the excessive growth of the Fe-Al metal structure formed at the interface between the zinc-based plating layer 13 and the steel material 11, and further improve the adhesion between the zinc-based plating layer 13 and the steel material 11. When Si is included in the zinc-based plating layer 13, the Si content is preferably 0.05 mass% or more, and more preferably 0.20 mass% or more, in order to suppress the excessive growth of the Fe-Al metal structure. On the other hand, if the Si content exceeds 2.50 mass%, it may excessively form high-melting-point intermetallic compounds with Mg, which may inhibit the formation of Al-Mg oxides that have a Zn evaporation suppression effect during welding.

[0053] Furthermore, if the Si content in the plating bath for producing the zinc-based plating layer 13 is too high, the viscosity of the plating bath may increase excessively, potentially reducing the operability during the production of plated steel materials (hereinafter referred to as "plating operability"). Therefore, the Si content in the plating bath is adjusted from the viewpoint of plating operability. The Si content in the zinc-based plating layer 13 is preferably 1.50% by mass or less, and more preferably 1.00% by mass or less.

[0054] [Fe: 0-5.00 mass%] Elements constituting the steel material 11 may be mixed into the zinc-based plating layer 13. In particular, in the hot-dip galvanizing method, elements constituting the steel material 11 are easily mixed into the zinc-based plating layer 13 due to interdiffusion of elements caused by solid-liquid reactions between the steel material 11 and the zinc-based plating layer 13. Due to such elemental mixing, the zinc-based plating layer 13 often contains a predetermined amount of Fe, and its content is often 0.01 mass% or more. If the above interdiffusion is promoted, the adhesion between the steel material 11 and the zinc-based plating layer 13 is improved. From the viewpoint of improving the adhesion between the steel material 11 and the zinc-based plating layer 13, it is preferable that the Fe content in the zinc-based plating layer 13 be 0.20 mass% or more.

[0055] Furthermore, within a range that does not impair the effects of the present invention, Fe may be intentionally added to the plating bath used when manufacturing the zinc-based plating layer 13. However, if the Fe content in the plating bath increases, high-melting-point intermetallic compounds of Fe and Al will form in the plating bath. In this case, such high-melting-point intermetallic compounds tend to adhere to the zinc-based plating layer 13 as dross, significantly degrading the appearance quality, which is undesirable. From this viewpoint, the Fe content in the plating bath is adjusted. The Fe content in the zinc-based plating layer 13 is preferably 5.00% by mass or less. The Fe content in the zinc-based plating layer 13 is more preferably 3.00% by mass or less, and even more preferably 2.00% by mass or less, 1.00% by mass or less, or 0.50% by mass or less.

[0056] ◇Element Group B In the zinc-based plating layer 13 according to this embodiment, element group B which may be contained in the zinc-based plating layer 13 will be described below. At least one of the elements of element group B shown below may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%

[0057] [Sb: 0 to 0.50 mass%] [Pb: 0 to 0.50 mass%] [Sr: 0 to 0.50 mass%] In the zinc-based plating layer 13 according to this embodiment, it is possible that Sb, Pb, and Sr may not be contained, so the lower limit of the content of these elements is 0 mass%. On the other hand, if at least one of Sb, Pb, and Sr is contained in the zinc-based plating layer 13, spangles will be formed on the surface of the zinc-based plating layer 13, making it possible to improve the metallic luster. For this reason, from the viewpoint of further improving the design of the plated steel material, it is preferable that at least one of Sb, Pb, and Sr be contained in the zinc-based plating layer 13. This design improvement effect is manifested when the content of at least one of Sb, Pb, and Sr is 0.05 mass% or more. Therefore, when at least one of Sb, Pb, and Sr is included in the zinc-based plating layer 13, it is preferable that the content of each of these elements be 0.05% by mass or more, independently.

[0058] On the other hand, when forming a zinc-based plating layer 13 in which the content of any of Sb, Pb, or Sr exceeds 0.50% by mass, the amount of dross generated in the plating bath used to form the zinc-based plating layer 13 increases, and it may not be possible to produce plated steel with good plating properties. For this reason, it is preferable that the content of Sb, Pb, and Sr in the zinc-based plating layer 13 is 0.50% by mass or less, independently of each other. Preferably, the content of Sb, Pb, and Sr is 0.20% by mass or less, independently of each other.

[0059] ◇Element Group C In the zinc-based plating layer 13 according to this embodiment, the element group C that the zinc-based plating layer 13 may contain will be described below. At least one of the elements in element group C shown below may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

[0060] [Cu: 0% by mass or more and less than 0.25% by mass] [Ti: 0% by mass or more and less than 0.25% by mass] [Cr: 0% by mass or more and less than 0.25% by mass] [Nb: 0% by mass or more and less than 0.25% by mass] [Ni: 0% by mass or more and less than 0.25% by mass] [Mn: 0% by mass or more and less than 0.25% by mass] [Co: 0% by mass or more and less than 0.25% by mass] [V: 0% by mass or more and less than 0.25% by mass] In the zinc-based plating layer 13 according to this embodiment, it is also possible that it does not contain Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, so the lower limit of the content of these elements is 0% by mass. On the other hand, if at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, or V is contained in the zinc-based plating layer 13, when such plated steel is welded, these elements are incorporated into the Fe-Al-based metal structure generated by welding, making it possible to further improve the corrosion resistance of the welded area that may be formed during processing. This effect of improving the corrosion resistance of the welded area is achieved when the content of at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, or V in the zinc-based plating layer 13 is 0.05% by mass or more. Therefore, when at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, or V is contained in the zinc-based plating layer 13, it is preferable that the content of each of these elements be independently 0.05% by mass or more.

[0061] On the other hand, when forming a zinc-based plating layer 13 such that any of the elements Cu, Ti, Cr, Nb, Ni, Mn, Co, and V are present in an amount of 0.25% by mass or more, these elements may form various intermetallic compounds in the plating bath used to form the zinc-based plating layer 13, leading to an increase in the viscosity of the plating bath and potentially making it impossible to produce plated steel with good plating properties. Therefore, it is preferable that the content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based plating layer 13 be independently less than 0.25% by mass. Preferably, the content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is independently 0.20% by mass or less.

[0062] ◇Element Group D In another embodiment of the zinc-based plating layer 13 according to this embodiment, element group D that the zinc-based plating layer 13 may contain will be described. At least one of the elements of element group D shown below may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%.

[0063] [Sn: 0% by mass or more and 20.00% by mass or less] [Bi: 0% by mass or more and less than 5.00% by mass] [In: 0% by mass or more and less than 2.00% by mass] In the zinc-based plating layer 13 according to this embodiment, it is possible that Sn, Bi, and In may not be contained, 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, making it possible to improve the weldability of the zinc-based plating layer 13. Furthermore, since these intermetallic compounds all have high melting points, when the plated steel material is welded, they remain as intermetallic compounds after welding without evaporating. The presence of these elements makes it possible to improve corrosion resistance and corrosion protection, and also to improve the corrosion resistance of the welded part during welding. This effect of improving corrosion resistance is manifested when the content of at least one of Sn, Bi, and In in the zinc-based plating layer 13 is 0.05% by mass or more. Therefore, when at least one of Sn, Bi, and In is included in the zinc-based plating layer 13, it is preferable that the content of each of these elements be 0.05% by mass or more, independently.

[0064] On the other hand, excessive Sn addition may increase the amount of intermetallic compounds formed, potentially reducing the corrosion resistance of the zinc-based plating layer 13 after welding. Furthermore, excessive Bi and In addition may make the zinc-based plating layer 13 brittle and prone to peeling, as well as reduce its corrosion resistance after welding. These phenomena become particularly noticeable when the Sn content exceeds 20.00 mass%, the Bi content is 5.00 mass% or more, and the In content is 2.00 mass% or more. Therefore, it is preferable that the Sn content be 20.00 mass% or less, the Bi content be less than 5.00 mass%, and the In content be less than 2.00 mass%. More preferably, the Sn content is 10.00 mass% or less, the Bi content is 3.00 mass% or less, and the In content is 1.00 mass% or less.

[0065] ◇Element Group E In the zinc-based plating layer 13 according to this embodiment, the element group E that the zinc-based plating layer 13 may contain will be described below. At least one of the elements in the element group E shown below may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less.

[0066] [Ca: 0 to 3.00 mass%] In the zinc-based plating layer 13 according to this embodiment, it is possible that Ca may not be contained, so the lower limit of its content is 0 mass%. On the other hand, if Ca is contained in the plating bath for producing the zinc-based plating layer 13, it is possible to reduce the dross generated as the Mg concentration increases during plating operations, thereby improving plating operability.

[0067] Furthermore, when Ca is included in the zinc-based plating layer 13, it forms intermetallic compounds with Al and Zn. Moreover, when Si is included in the zinc-based plating layer 13 along with Ca, Ca forms intermetallic compounds with Si. These intermetallic compounds have high melting points and stable structures, making it possible to suppress liquid metal embrittlement cracking (LME) when the plated steel is welded. When Ca is included in the zinc-based plating layer 13, this LME suppression effect during welding is achieved by setting the Ca content to 0.01% by mass or more. More preferably, the Ca content in the zinc-based plating layer 13 is 0.05% by mass or more.

[0068] On the other hand, if the Ca content in the zinc-based plating layer 13 exceeds 3.00% by mass, the corrosion resistance of the plated steel may decrease. From this viewpoint, it is preferable that the Ca content in the zinc-based plating layer 13 be 3.00% by mass or less. Preferably, the Ca content in the zinc-based plating layer 13 is 2.00% by mass or less, and more preferably 1.00% by mass or less.

[0069] [La: 0% by mass or more and less than 0.50% by mass] [Ce: 0% by mass or more and less than 0.50% by mass] [Y: 0% by mass or more and 0.50% by mass or less] In the zinc-based plating layer 13 according to this embodiment, it is possible that La, Ce, and Y are not contained, so the lower limit of the content of these elements is 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit almost the same effect as Ca. This is because the atomic radius of each element is close to the atomic radius of Ca, and when these elements are contained in the zinc-based plating layer 13, they are substituted for Ca.

[0070] The effects of improving plating operability and suppressing LME during welding are achieved by setting the content of each of these elements to 0.01% by mass or more, independently. Therefore, when at least one of La, Ce, and Y is included, it is preferable that the content of each of these elements be 0.01% by mass or more, independently. The content of La, Ce, and Y in the zinc-based plating layer 13 is more preferably 0.05% by mass or more, independently.

[0071] On the other hand, if the La, Ce, and Y content in the plating bath for producing the zinc-based plating layer 13 is too high, the viscosity of the plating bath may increase excessively, potentially reducing the operability of the plating process. Therefore, from the viewpoint of operability, it is preferable that the La, Ce, and Y content in the plating bath be adjusted so that the La, Ce, and Y content is less than 0.50% by mass, less than 0.50% by mass, and 0.50% by mass or less, respectively. Preferably, the La, Ce, and Y content is 0.10% by mass or less, respectively.

[0072] ◇Element Group F In another embodiment of the zinc-based plating layer 13 according to this embodiment, the element group F that the zinc-based plating layer 13 may contain will be described. The elements of element group F shown below are elements that may be contained in the zinc-based plating layer 13 in place of a portion of the remaining Zn. [Element Group F]: B: Less than 0.50%

[0073] [B: 0% by mass or more and less than 0.50% by mass] In the zinc-based plating layer 13 according to this embodiment, it is possible that B may not be contained, so the lower limit of its content is 0% by mass. On the other hand, when B is contained in the zinc-based plating layer 13, it has the effect of further suppressing LME. This is presumed to be because when B is contained in the zinc-based plating layer 13, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. Furthermore, it is thought that the presence of B in the zinc-based plating layer 13 causes B to diffuse from the zinc-based plating layer 13 to the steel material 11, and that this has the effect of further suppressing LME of the steel material 11 through grain boundary strengthening. Moreover, it is presumed that the various intermetallic compounds formed with respect to B have extremely high melting points and therefore also act to suppress Zn evaporation during welding. These improvement effects are achieved by containing 0.05% by mass or more of B. For this reason, when B is included, it is preferable that the content of B is 0.05% by mass or more.

[0074] On the other hand, if an excessive amount of B is included in the plating bath in order to include B in the zinc-based plating layer 13, it can cause a rapid increase in the plating melting point, leading to a decrease in plating operability and potentially making it impossible to produce plated steel with excellent plating properties. This decrease in plating operability becomes particularly noticeable when the B content is 0.50% by mass or more, so it is preferable that the B content be less than 0.50% by mass. More preferably, the B content is 0.10% by mass or less.

[0075] [Method for measuring chemical composition] The chemical composition of the zinc-based plating layer 13 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer) or ICP-MS (Inductively Coupled Plasma Mass Spectrometer). When analyzing chemical composition down to 0.1 mass%, ICP-AES should be used, and when analyzing trace amounts of chemical composition less than 0.1 mass%, ICP-MS should be used. The plated steel material is immersed in a 10% HCl aqueous solution with an inhibitor added for about 1 minute to remove the zinc-based plating layer, and a solution is prepared by dissolving this zinc-based plating layer. The resulting solution can be analyzed by ICP-AES or ICP-MS to obtain the overall average chemical composition of the zinc-based plating layer.

[0076] Regarding the amount of zinc-based plating layer 13 applied: As described above, the amount of zinc-based plating layer 13 applied is, for example, 30.0 to 500.0 g / m² per side of the steel material. ２ It is preferable that the concentration be around 50.0 to 300.0 g / m². ２ It is more preferable that the amount of zinc-based plating layer 13 is within the above range. By having the amount of zinc-based plating layer 13 adhered within the above range, the surface-treated steel material 1 according to this embodiment can exhibit sufficient corrosion resistance.

[0077] The amount of zinc-based plating layer 13 attached is determined by cutting a 30 mm x 30 mm sample from the surface-treated steel material 1 and measuring the mass of the sample. Then, a protective tape, such as a tape-like seal, is applied to one side of the sample to prevent the zinc-based plating layer 13 on that side from dissolving in the next step. The protective tape should adhere closely to the surface of the surface-treated steel material 1 and not allow the HCl solution described later to penetrate. After that, the sample is immersed in a 10% HCl aqueous solution with an inhibitor added, and the zinc-based plating layer 13 on the side without the protective tape is pickled and removed, and the mass of the sample after pickling is measured. From the change in mass of the sample before and after pickling, it is possible to determine the amount of zinc-based plating layer 13 attached to each side. In this embodiment, the amount of chemical conversion coating layer 15 having the thickness described in detail below is 1 g / m². ２ On the other hand, it is difficult to remove only the chemical conversion coating layer 15 by physical or chemical means. Therefore, when measuring the amount of zinc-based plating layer 13 attached, it is not necessary to remove the chemical conversion coating layer 15 from the sample. Furthermore, when determining the amount of zinc-based plating layer 13 attached to a surface-treated member that has already been manufactured using surface-treated steel material 1, if there are welds on the surface-treated member, a sample should be cut from an area at least 5 cm away from the welds on the surface-treated member and used for the above measurement.

[0078] <About the chemical conversion coating layer 15> The chemical conversion coating layer 15 according to this embodiment is formed over the entire surface of the zinc-based plating layer 13 as described above. Here, the chemical conversion coating layer 15 according to this embodiment contains at least the element phosphorus P. In other words, the chemical conversion coating layer 15 according to this embodiment contains a compound containing the element phosphorus P. At least a part of this compound containing the element phosphorus P is the "reaction product of P and the plating layer component (P-Mg complex oxide)" as described above.

[0079] <<Regarding the thickness t of the chemical conversion coating layer 15>> The chemical conversion coating layer 15 according to this embodiment has a predetermined thickness t (unit: μm). Below, the distribution state of various elements in the surface-treated steel material according to this embodiment will be described. In this embodiment, the thickness t of the chemical conversion coating layer 15 serves as an indicator when referring to the distribution position of various elements.

[0080] The thickness of the chemical conversion treatment coating layer 15 according to this embodiment (thickness t in Figure 3) is preferably in the range of 0.1 to 30.0 μm.

[0081] By making the thickness of the chemical conversion coating layer 15 0.1 μm or more, the surface-treated steel material 1 according to this embodiment can achieve even better corrosion resistance. The thickness of the chemical conversion coating layer 15 is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more.

[0082] On the other hand, by making the thickness of the chemical conversion coating layer 15 10.0 μm or less, the surface-treated steel material 1 according to this embodiment can achieve better corrosion resistance while ensuring adhesion between the zinc-based plating layer 13 and the chemical conversion coating layer 15. The thickness of the chemical conversion coating layer 15 is more preferably 5.0 μm or less, and even more preferably 3.0 μm or less.

[0083] <Regarding the distribution state of elements P and Mg in the chemical conversion coating layer 15> In the surface-treated steel material 1 according to this embodiment, the distribution state of elements P and Mg in the chemical conversion coating layer 15 is determined by utilizing the thickness t of the chemical conversion coating layer 15 and the measurement results of the depth profiles for elements P and Mg.

[0084] Figure 4 is a schematic diagram illustrating the chemical conversion coating layer 15 of the surface-treated steel material 1 according to this embodiment. In this embodiment, as schematically shown in Figure 4, the surface of the chemical conversion coating layer 15 is taken as the origin, and the direction toward the zinc-based plating layer 13, which is perpendicular to the surface of the chemical conversion coating layer 15, is treated as the coordinate axis representing the thickness direction. In this embodiment, the thickness t of the chemical conversion coating layer 15 is virtually divided into 10 equal parts along this coordinate axis, and the size corresponding to (0.1 × t) is treated as the unit quantity when focusing on the distribution state of each element.

[0085] In this case, the region that is 0 or more and 1.0 t (= {10 / 10} × t) or less becomes the region corresponding to the chemical conversion coating layer 15, and the region that is more than 1.0 t becomes the region corresponding to the zinc-based plating layer 13.

[0086] Hereinafter, when referring to the distribution state of the element P, as shown in FIG. 4, the region corresponding to the chemical conversion coating layer 15 is virtually divided into a region from 0 to 0.5 t (= {5 / 10} × t) and a region from 0.5 t to 1.0 t. Then, the region from 0 to 0.5 t (= {5 / 10} × t) (region R in FIG. 4 Ａ ) is referred to as the "surface side region" of the chemical conversion coating layer 15, and the region from 0.5 t to 1.0 t (region R in FIG. 4 Ｂ ) is referred to as the "plating side region" of the chemical conversion coating layer 15.

[0087] Further, when referring to the distribution state of the element Mg, as shown in FIG. 4, the region from 0.8 t (= {8 / 10} × t) to 1.2 t (= {12 / 10} × t) (region R in FIG. 4 Ｃ ) is referred to as the "Mg enrichment region". Also, the region of the zinc-based plating layer 11 excluding such Mg enrichment region R Ｃ is denoted as region R Ｄ .

[0088] In the surface-treated steel material 1 according to the present embodiment, the average value of the P concentration in the surface side region (region R in FIG. 4 Ａ ) is 1.10 to 1.50 times the average value of the P concentration in the plating side region (region R in FIG. 4 Ｂ ), and the element P is distributed such that, and the average value of the Mg concentration in the Mg enrichment region (region R in FIG. 4 Ｃ ) is 1.20 to 2.00 times the average value of the Mg concentration in the region of the zinc-based plating layer 11 excluding the Mg enrichment region R Ｃ (region R in FIG. 4 Ｄ ), and the element Mg is distributed.

[0089] With the concentration distribution described above achieved, it can be determined that the surface-treated steel material 1 according to this embodiment has the presence of reaction products between P and the plating layer components (more specifically, P-Mg composite oxides, which are reaction products between P and Mg, one of the plating layer components), and that the concentration of Mg in the region on the steel material side 1 is higher than that of the reaction products, as mentioned earlier. As a result, the surface-treated steel material 1 can achieve sufficient corrosion resistance in soil containing chloride ions.

[0090] ◇Regarding the distribution state of element P, the above surface-side region (region R in Figure 4) Ａ The average value of the P concentration in the plated region (region R in Figure 4) Ｂ If the P concentration in the above-mentioned surface region (region R in Figure 4) is less than 1.10 times the average value, the formation of reaction products between P and the plating layer components will be insufficient, and sufficient corrosion resistance cannot be achieved in soil containing chloride ions. Ａ The average value of the P concentration in the plated region (region R in Figure 4) is Ｂ The P concentration is preferably 1.15 times or more, and more preferably 1.20 times or more, compared to the average value of the P concentration. By achieving such a distribution of P concentration, sufficient P-Mg composite oxides are generated, making it possible to further improve the corrosion resistance of the surface-treated steel material 1.

[0091] On the other hand, the surface-side region (region R in Figure 4) Ａ The average value of the P concentration in the plated region (region R in Figure 4) Ｂ If the P concentration in the above region (region R in Figure 4) is more than 1.50 times the average value, excessive reaction products between P and the plating layer components are generated, resulting in the chemical conversion coating layer 15 becoming prone to peeling. Therefore, when the surface-treated steel material 1 is processed into a desired shape to become a surface-treated member, peeling of the chemical conversion coating layer 15 in the processed area becomes significant, making it impossible to achieve sufficient corrosion resistance in the processed area. Ａ The average value of the P concentration in the plated region (region R in Figure 4) is Ｂ The P concentration is preferably 1.45 times or less, and more preferably 1.40 times or less, compared to the average value of the P concentration.

[0092] ◇Regarding the distribution state of element Mg, also the above-mentioned Mg-enriched region (region R in Figure 4) Ｃ The average value of the Mg concentration in the Mg-enriched region R Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ If the Mg concentration in the above-mentioned region RC is less than 1.20 times the average value, it means that the Mg concentration is insufficient in the region near the interface between the chemical conversion coating layer 15 and the zinc-based plating layer 13. In this case, when corrosion factors such as chloride ions reach this region RC, the formation of dense corrosion products will be insufficient, and sufficient corrosion resistance cannot be achieved as a zinc-plated steel material. The above-mentioned Mg-enriched region (region R in Figure 4) Ｃ The average value of the Mg concentration in the Mg-enriched region R is Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ The average Mg concentration of the sample is preferably 1.25 times or more, and more preferably 1.30 times or more.

[0093] On the other hand, the above-mentioned Mg-enriched region (region R in Figure 4) Ｃ The average value of the Mg concentration in the Mg-enriched region R Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ If the Mg concentration in the above-mentioned region (region R in Figure 4) is more than 2.00 times the average value, the Mg concentration becomes excessively pronounced, resulting in the chemical conversion coating layer 15 becoming prone to peeling. Therefore, when the surface-treated steel material 1 is processed into a desired shape to form a surface-treated member, the peeling of the chemical conversion coating layer 15 in the processed area becomes significant, making it impossible to achieve sufficient corrosion resistance in the processed area. Ｃ The average value of the Mg concentration in the Mg-enriched region R is Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ The average value of the Mg concentration is preferably 1.95 times or less, and more preferably 1.90 times or less.

[0094] ◇Method for determining the average values ​​of P and Mg concentrations in each region Here, the average values ​​of elemental concentrations in each region as described above are first determined by an ICP (Inductively Coupled Plasma) mass spectrometry (ICP-MS) or an energy-dispersive X-ray analyzer installed in a transmission electron microscope (TEM, for example, JEOL Ltd.'s JEM-2100). A detector (EDX, for example, EX-24201M1G2T manufactured by JEOL Ltd.) is used to determine the average value of the P concentration in the chemical conversion coating layer 15 as a whole, and the average value of the Mg concentration in the chemical conversion coating layer 15 and the zinc-based plating layer 13 as a whole. Then, the obtained overall concentration can be distributed to each region using the integrated intensity of the depth profile of each element obtained by RF-Glow Discharge Optical Emission Spectrometry (RF-GD-OES), thereby allowing for specific determination.

[0095] More specifically, ICP-MS shall be used for measurements of the zinc-based plating layer 13, and ICP-MS or TEM shall be used for measurements of the chemical conversion treatment layer 15.

[0096] First, a sample (size: 50 mm x 50 mm) for ICP mass spectrometry is taken from the surface-treated steel material of interest. If welds or machined parts exist on the surface-treated steel material, the sample should be taken from a location at least 20 mm away from these parts. The obtained sample is then immersed in a 10% HCl aqueous solution with an inhibitor added for about 1 minute to remove the zinc-based plating layer, and a solution is prepared by dissolving this zinc-based plating layer. The obtained solution is analyzed by ICP-MS to obtain the overall average chemical composition of the zinc-based plating layer 13 and the chemical conversion coating layer 15.

[0097] Furthermore, a sample of the chemical conversion coating layer 15 is obtained by cutting the surface-treated steel material of interest at an arbitrary position. In such cases, if there are welded or processed parts on the surface-treated steel material, the sample shall be taken from a location at least 20 mm away from the welded or processed parts.

[0098] Then, the cumulative intensity corresponding to each region is determined using the measurement results of the depth profile of each element. In measuring the depth profile, first, the sample is cut to the required measurement size (e.g., 50 mm x 50 mm). After that, the obtained sample for measurement is measured under the following measurement conditions, focusing on at least the elements P, Mg, V, Mo, Zn, Al, Fe, C, and O. The measurement can be performed using a glow discharge surface analyzer (e.g., GDS850A manufactured by LECO Corporation). The measurement conditions should be, for example, as follows, and should be carried out until the iron spectral intensity derived from the underlying steel saturates. In addition, in such measurements, depth profiles may be measured for all elements that can be of interest. Output: 15W Voltage: 1000V Gas type: Ar gas (Ar concentration 99.9999% or higher) Gas pressure: 6 Torr (Note: 1 Torr is approximately 133.32 Pa) Anode diameter: 4 mm Anode material: Cu Measurement area: 4 mmφ Measurement conditions: High frequency Measurement pitch: 0.05 seconds Data analysis software: LICO GDS Quantitative Depth Profile (manufactured by LICO Corporation)

[0099] By performing measurements as described above, it becomes possible to understand the distribution of various elements along the thickness direction (Z-axis direction in Figure 3), starting from the surface of the chemical conversion coating layer 15 and extending to the vicinity of the interface between the zinc-based plating layer 13 and the steel material 11. Based on the measurement results of the obtained depth profile, the depth position (or sputtering time) of the surface-treated steel material 1 is plotted on the horizontal axis, and the luminescence intensity calculated based on the obtained measurement results is plotted on the vertical axis, thereby visualizing the depth profile of various elements in GD-OES.

[0100] In this embodiment, in the depth profile obtained as described above, the "position of the interface between the chemical conversion coating layer 15 and the zinc-based plating layer 13" and the "position of the interface between the zinc-based plating layer 13 and the steel material 11" are defined as follows.

[0101] First, the relative intensities of P and Fe in the depth direction are examined in the obtained depth profiles, and their respective maximum values ​​are identified. Next, regions where the relative intensities of both P and Fe are 1 / 10 or less of the maximum intensity are identified, and the maximum relative intensity of Zn in these regions is calculated.

[0102] When checking the relative intensity of Zn in the depth direction from the outermost surface of the chemical conversion coating layer 15, the location where the relative intensity of Zn first reaches 70% of the "maximum value of the relative intensity of Zn in the region where the relative intensity of P and the relative intensity of Fe are both 1 / 10 or less of the maximum intensity" is defined as the interface between the chemical conversion coating layer 15 and the zinc-based plating layer 13.

[0103] Furthermore, the interface between the zinc-based plating layer 13 and the steel material 11 is defined as the position located on the surface side of the chemical conversion coating layer 15, which is further from the position where the relative intensity of Fe is at its maximum value, and where, when the relative intensity of Zn is checked from the position where the relative intensity of Fe is at its maximum value toward the surface, the Zn concentration for the first time exceeds 70% of "the maximum value of the relative intensity of Zn in the region where the relative intensity of both P and Fe are 1 / 10 or less of their maximum intensity".

[0104] ◇Method for measuring the thickness t of the chemical conversion coating layer 15 When measuring the thickness t of the chemical conversion coating layer 15 from the state of the surface-treated steel material 1 that has already been manufactured, the thickness t can be measured from the depth profiles for various elements in RF-GD-OES. More specifically, for a sample measured with RF-GD-OES, the depth of the depression formed at the measurement site and the time required until the position of the interface between the chemical conversion coating layer 15 and the zinc-based plating layer 13 can be observed should be entered into the data analysis software attached to the device. The depth of the depression formed at the measurement site can be measured by using a roughness meter (for example, SURFCOM TOUCH 50 manufactured by Tokyo Seimitsu Co., Ltd.) and comparing the average height of the measurement site with the average height of the area other than the measurement site. This allows the thickness t of the chemical conversion coating layer 15 to be measured.

[0105] For example, when focusing on the average concentration of element P in each region, the cumulative intensity of element P in the region corresponding to 0 to 0.5t and the cumulative intensity of element P in the region corresponding to 0.5t to 1.0t can be identified using the measurement results of the depth profile of element P. Then, the average value of the overall P concentration of the chemical conversion treated film layer 15 obtained as described above can be distributed using the cumulative intensity in each region. In this way, the surface region (region R in Figure 4) can be identified. Ａ The average value of the P concentration in the plated region (region R in Figure 4) and the plated region. Ｂ The average value of the P concentration and can be identified.

[0106] Furthermore, for example, when focusing on the average concentration of element Mg in each region, the measurement results of the depth profile of element Mg can be used to determine the cumulative intensity of element Mg within the region corresponding to 0.8t to 1.2t, and the Mg-enriched region R. Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ The cumulative intensity of element Mg corresponding to ) is identified, and so on. Then, the average value of the overall Mg concentration of the chemical conversion coating layer 15 and the zinc-based plating layer 13 obtained as described above can be distributed using the cumulative intensity in each region. In this way, the Mg-enriched region (region R in Figure 4) is identified. ＣThe average value of the Mg concentration and the Mg-enriched region R Ｃ Region of the zinc-based plating layer 11 excluding the region R in Figure 4 Ｄ The average value of the Mg concentration in ) and can be identified.

[0107] ≪Regarding the P concentration in the chemical conversion coating layer 15≫ In the chemical conversion coating layer 15 according to this embodiment, the overall P concentration is preferably 0.10% by mass or more and less than 3.00% by mass. By having a P concentration of 0.10% by mass or more, the chemical conversion coating layer 15 according to this embodiment can ensure a sufficient amount of P element to achieve excellent corrosion resistance regardless of whether it is present in the soil or not, and the surface-treated steel material 1 according to this embodiment will exhibit even better corrosion resistance. The P concentration of the chemical conversion coating layer 15 is more preferably 1.00% by mass or more, and even more preferably 2.00% by mass or more.

[0108] On the other hand, in the chemical conversion coating layer 15 according to this embodiment, by having a P concentration of less than 3.00% by mass, it is possible to ensure a sufficient amount of P element to achieve excellent corrosion resistance regardless of whether it is present in the soil, while preventing a decrease in adhesion to the processed part. As a result, the surface-treated steel material 1 according to this embodiment exhibits even better corrosion resistance. The P concentration of the chemical conversion coating layer 15 is more preferably 2.70% by mass or less, and even more preferably 2.30% by mass or less.

[0109] Furthermore, the overall P concentration in the chemical conversion treatment coating layer 15 according to this embodiment can be measured by ICP mass spectrometry, as described above.

[0110] <Regarding the content and distribution state of element V in the chemical conversion coating layer 15> In this embodiment, it is more preferable that the chemical conversion coating layer 15 further contains element V (i.e., further contains a compound containing element V), and that such element V is in a specific distribution state.

[0111] With respect to element V, the distribution state of element V in the chemical conversion coating layer 15 is determined by utilizing the thickness t of the chemical conversion coating layer 15 identified as described above, and the measurement results of the depth profile for element V.

[0112] In the following discussion of the distribution state of element V, as shown in Figure 4, the region corresponding to the chemical conversion coating layer 15 is hypothetically divided into two regions: one from 0 to 0.5t (= {5 / 10} × t) and another from 0.5t to 1.0t. Then, the region from 0 to 0.5t (= {5 / 10} × t) (region R in Figure 4) Ａ The area ) is referred to as the "surface side region" of the chemical conversion coating layer 15, and the region from 0.5t to 1.0t (region R in Figure 4) Ｂ This region will be referred to as the "plating-side region" of the chemical conversion coating layer 15.

[0113] In the chemical conversion coating layer 15 according to this embodiment, the surface region (region R in Figure 4) Ａ The average value of the V concentration in the plated region (region R in Figure 4) Ｂ It is preferable that the V concentration is 1.1 to 1.5 times the average value of the V concentration.

[0114] The above surface-side region (region R in Figure 4) Ａ The average value of the V concentration in the plated region (region R in Figure 4) Ｂ By making the V concentration in the above-mentioned surface region (region R in Figure 4) 1.10 times or more than the average value, V is included as one of the constituent elements of the "reaction product between P and plating layer components" explained earlier (more specifically, a P-Mg-V composite oxide is formed), thereby making it possible to achieve a further improvement in corrosion resistance in soil containing chloride ions. Ａ The average value of the V concentration in the plated region (region R in Figure 4) is Ｂ It is more preferable that the V concentration is 1.15 times or more than the average value of the V concentration, and even more preferable that it is 1.20 times or more.

[0115] On the other hand, the surface-side region (region R in Figure 4) Ａ The average value of the V concentration in the plated region (region R in Figure 4) Ｂ By making the V concentration in the above-mentioned surface region (region R in Figure 4) 1.50 times or less of the average value, it becomes possible to prevent a decrease in the corrosion resistance of the processed part while further improving corrosion resistance. ＡThe average value of the V concentration in the plated region (region R in Figure 4) is Ｂ The V concentration of the product is preferably 1.45 times or less, and more preferably 1.40 times or less, compared to the average value of the V concentration.

[0116] Here, the average value of the V concentration in each region, as described above, can be determined by first identifying the average value of the V concentration of the entire chemical conversion coating layer 15 using ICP-MS, and then distributing the overall concentration to each region using the integrated intensity of the depth profile of element V obtained by GD-OES as described above.

[0117] Furthermore, among the compounds containing element V as described above, it is even more preferable for further improvement of corrosion resistance if compounds containing pentavalent V are present in a predetermined amount or more. The presence of such pentavalent V is beneficial in the plated region (region R in Figure 4) of the chemical conversion treatment film layer 15. Ｂ This can be confirmed by analyzing it using X-ray photoelectron spectroscopy (XPS) and focusing on the V2p spectrum.

[0118] More specifically, the chemical conversion coating layer 15 according to this embodiment is located in the plating-side region R. Ｂ In the V2p narrow spectrum obtained by analyzing by XPS, if the ratio of the integrated intensity of the peak with a maximum value at 515.90 ± 0.25 eV to the integrated intensity of the peak with a maximum value at 517.20 ± 0.25 eV is between 0.20 and 0.50, it can be determined that pentavalent V is present in the desired state.

[0119] When the cumulative strength ratio is 0.20 or higher, the surface-treated steel material 1 exhibits superior corrosion resistance in soil in the chemical conversion treatment coating layer 15 according to this embodiment. The cumulative strength ratio is more preferably 0.25 or higher, and even more preferably 0.30 or higher.

[0120] On the other hand, when the ratio of cumulative strength is 0.50 or less, the surface-treated steel material 1 exhibits better corrosion resistance in soil. The ratio of cumulative strength is more preferably 0.45 or less, and even more preferably 0.40 or less.

[0121] Here, the ratio of the cumulative intensity as described above can be determined as follows. First, each of three arbitrary locations on the surface of the surface-treated member 1 of interest is measured using an X-ray photoelectron spectrometer (for example, Quantum 2000 from ULVAC-PHIE). An 800 μm × 300 μm area of ​​the surface of the surface-treated steel material (surface of the chemical conversion coating layer 15) that has not undergone pretreatment such as cleaning or sputtering is analyzed under the following conditions, for example. The obtained V2p spectrum is separated into a peak with a maximum value at 517.20 ± 0.25 eV and a peak with a maximum value at 515.90 ± 0.25 eV, and the cumulative intensity of these peaks is determined, and the cumulative intensity ratio is calculated based on this cumulative intensity.

[0122] However, the narrow spectrum obtained through analysis may have its peak positions shifted left or right depending on the measuring instrument and conditions. Therefore, first, the obtained spectrum is corrected so that the peak position (the position with the maximum value) of the C1s spectrum is 284.8 eV. Then, the V2p spectrum is separated into a peak with a maximum value at 517.20 ± 0.25 eV and a peak with a maximum value at 515.90 ± 0.25 eV.

[0123] For measurement, the V2p spectrum will be measured in the 510.00–520.00 eV range. Of this range, the peak separation region will be based on 514.00–518.5 eV, and extended from this range depending on the spectrum. Furthermore, for measurement, the full width at half maximum (FWHM) of the peak with a maximum value at 517.20 ± 0.25 eV will be assumed to be 517.20 ± 0.20 eV, and the FWHM of the peak with a maximum value at 515.90 ± 0.25 eV will be assumed to be 515.90 ± 0.20 eV. Since no sample pretreatment is performed during analysis, care must be taken in handling the sample to prevent oil, dirt, etc. from adhering to it as much as possible.

[0124] The XPS measurement conditions are as follows: (Measurement conditions) X-ray source: monoAlKα (1486.6 eV) X-ray output: 15 kV 25 W X-ray diameter: 100 μmφ Analysis room vacuum (before sample introduction): 2.2 × 10⁻⁶ －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 (ULVAC-PHI)

[0125] <<Regarding the V concentration in the chemical conversion coating layer 15>> In the chemical conversion coating layer 15 according to this embodiment, the overall V concentration is preferably 0.10% by mass or more and less than 2.00% by mass. By having a V concentration of 0.10% by mass or more, the chemical conversion coating layer 15 according to this embodiment can ensure a sufficient amount of element V to generate the P-Mg-V composite oxide described above, and the surface-treated steel material 1 according to this embodiment will exhibit better corrosion resistance. The V concentration of the chemical conversion coating layer 15 is more preferably 0.11% by mass or more, and even more preferably 0.12% by mass or more.

[0126] On the other hand, in the chemical conversion coating layer 15 according to this embodiment, by having a V concentration of less than 2.0 mass%, it is possible to ensure a sufficient amount of element V to achieve excellent corrosion resistance regardless of whether it is present in the soil, while preventing a decrease in adhesion to the processed part. As a result, the surface-treated steel material 1 according to this embodiment exhibits even better corrosion resistance. The V concentration of the chemical conversion coating layer 15 is more preferably 0.19 mass% or less, and even more preferably 0.18 mass% or less.

[0127] Furthermore, the overall V concentration in the chemical conversion treated film layer 15 according to this embodiment can be measured by TEM-EDX as described above.

[0128] <Regarding the content and distribution state of element Mo in the chemical conversion treated coating layer 15> In this embodiment, it is more preferable that the chemical conversion treated coating layer 15 further contains element Mo (i.e., further contains a compound containing element Mo), and that such element Mo is in a specific distribution state.

[0129] With regard to element Mo, the distribution state of element Mo in the chemical conversion coating layer 15 is determined by utilizing the thickness t of the chemical conversion coating layer 15 identified as described above, and the measurement results of the depth profile for element Mo.

[0130] In the following discussion of the distribution state of element Mo, as shown in Figure 4, the region corresponding to the chemical conversion coating layer 15 is hypothetically divided into three regions: a region from 0 to 0.2t (= {2 / 10} × t), a region from 0.2t to 0.8t (= {8 / 10} × t), and a region from 0.8t to 1.0t. Then, the region from 0 to 0.2t (region R in Figure 4) Ｅ The area ) is referred to as the "surface region" of the chemical conversion coating layer 15, and the region from 0.2t to 0.8t (region R in Figure 4) Ｆ The region between 0.8t and 1.0t (region R in Figure 4) is referred to as the "intermediate region" of the chemical conversion coating layer 15. Ｇ This area will be referred to as the "interface region" of the chemical conversion coating layer 15.

[0131] In the chemical conversion treated coating layer 15 according to this embodiment, the surface region (region R in Figure 4) Ｅ The average value of the Mo concentration in the intermediate region (region R in Figure 4) Ｆ It is preferable that the V concentration is 1.1 to 1.5 times the average value of the V concentration.

[0132] The above surface region (region R in Figure 4) Ｅ The average value of the Mo concentration in the intermediate region (region R in Figure 4) Ｆ By increasing the Mo concentration to 1.10 times or more the average value of the Mo concentration in the above-mentioned surface region (region R in Figure 4), soluble Mo becomes concentrated in the surface layer of the chemical conversion treatment coating 15, making it possible to further improve the corrosion resistance of the processed area. Ｅ The average Mo concentration in the intermediate region (region R in Figure 4) is Ｆ It is more preferable that the Mo concentration is 1.15 times or more, and even more preferable that it is 1.20 times or more, compared to the average value of the Mo concentration.

[0133] On the other hand, the surface region (region R in Figure 4) Ｅ The average value of the Mo concentration in the intermediate region (region R in Figure 4)Ｆ By making the average Mo concentration in the above-mentioned surface region (region R in Figure 4) 1.50 times or less, it becomes possible to prevent appearance defects in condensation environments caused by excessive soluble components while further improving corrosion resistance. Ｅ The average Mo concentration in the intermediate region (region R in Figure 4) is Ｆ The average Mo concentration of the sample is preferably 1.45 times or less, and more preferably 1.40 times or less.

[0134] Here, the average Mo concentration in each region, as described above, can be determined by first identifying the average Mo concentration of the entire chemical conversion coating layer 15 using TEM-EDX, and then distributing the overall concentration to each region using the integrated intensity of the elemental Mo depth profile obtained by GD-OES as described above.

[0135] ≪Regarding the Mo concentration in the chemical conversion coating layer 15≫ In the chemical conversion coating layer 15 according to this embodiment, the overall Mo concentration is preferably 0.1% by mass or more and less than 2.0% by mass. By having a Mo concentration of 0.1% by mass or more, the chemical conversion coating layer 15 according to this embodiment can ensure a sufficient amount of Mo element for the concentration of Mo in the surface region as described above, and the surface-treated steel material 1 according to this embodiment will exhibit better corrosion resistance. The Mo concentration of the chemical conversion coating layer 15 is more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more.

[0136] On the other hand, in the chemical conversion coating layer 15 according to this embodiment, by having a Mo concentration of less than 2.0% by mass, it is possible to ensure a sufficient amount of Mo element to achieve excellent corrosion resistance regardless of whether it is present in the soil, while preventing poor appearance in condensation environments due to an excessive amount of soluble components. As a result, the surface-treated steel material 1 according to this embodiment exhibits even better corrosion resistance. The Mo concentration of the chemical conversion coating layer 15 is more preferably 1.9% by mass or less, and even more preferably 1.8% by mass or less.

[0137] Furthermore, the overall Mo concentration in the chemical conversion treated film layer 15 according to this embodiment can be measured by TEM-EDX as described above.

[0138] The elements present in the chemical conversion coating layer 15 according to this embodiment and their distribution state have been described in detail above. The distribution state of each element as described above is largely due to the affinity between each element and the plating components of the zinc-based plating layer 13. Furthermore, when the chemical conversion coating layer 15 contains an organic resin as a component, the affinity between each element and the organic resin also contributes significantly. The distribution state of each element as described above is achieved by manufacturing the surface-treated steel material under the manufacturing conditions detailed below.

[0139] ≪Specific Examples of Compounds Containing Element P≫ In the chemical conversion treatment coating layer 15 according to this embodiment, various phosphoric acids and their salts can be used as compounds containing element P as described above. Examples of phosphoric acids and their salts include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, subphosphoric acid, phosphorous acid, hypophosphoric acid, triphosphoric acid, tetraphosphoric acid and their salts, ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate, phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) and their salts, organic phosphoric acids such as phytic acid and their salts. In addition to ammonium salts, examples of phosphoric acid salts other than ammonium salts include metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, etc. Phosphoric acids and their salts may be used alone or in combination of two or more.

[0140] ≪Specific examples of compounds containing element V≫ In the chemical conversion coating layer 15 according to this embodiment, a compound containing element V as described above is, for example, vanadium pentoxide V ２ O ５ Metavanadate HVO ３ ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl ３ Vanadium V trioxide２ O ３ , vanadium dioxide VO ２ , vanadium oxysulfate VOSO ４ , vanadium oxyacetylacetonate VO(OC(=CH ２ )CH ２ COCH ３ )) ２ Vanadium acetylacetonate V (OC (=CH ２ )CH ２ COCH ３ )) ３ Vanadium trichloride (VCl) ３ Various compounds such as lymphanodomlybdic acid can be used.

[0141] Here, when using the various vanadium compounds described above, it is possible to control the ratio of the integrated intensities in the XPS spectrum to a desired state by adjusting the blending ratio of compounds containing pentavalent V.

[0142] ≪Specific Examples of Compounds Containing Element Mo≫ In the chemical conversion coating layer 15 according to this embodiment, various molybdenum compounds can be used as compounds containing element Mo as described above. Among these, it is more preferable to use a soluble molybdenum oxyacid with oxidizing properties as the compound containing element Mo. Examples of such soluble molybdenum oxyacids with oxidizing properties include hexavalent molybdenum oxyacids such as molybdic acid, ammonium molybdate, and alkali metal molybdate salts.

[0143] <<Regarding other components in the chemical conversion coating layer 15>> In addition to the compounds containing element P, the compounds containing element V, and the compounds containing element Mo mentioned above, the chemical conversion coating layer 15 according to this embodiment may also contain one or more selected from the group consisting of, for example, silane coupling agents, valve metals, and organic resins. By further including such components, the chemical conversion coating layer 15 according to this embodiment can improve film formation after application of the chemical conversion solution, the barrier properties (density) of the film against corrosive factors such as moisture and corrosive ions, and the adhesion of the film to the plated surface, thereby contributing to raising the corrosion resistance of the film.

[0144] [Silane Coupling Agents] 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- Tacryloxypropylmethyldiethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropyltrimethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropyltriethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropylmethyldiethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyl Triethoxysilane, 3-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropylmethyldiethoxysilane, 3-anilinopropyltrimethoxysilane, 3-anilinopropylmethyldimethoxysilane, 3-anilinopropyltriethoxysilane, 3- Anilinopropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(triethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldiethoxysilyl)propyl]ammonium chloride,Examples include 3-chloropropylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane.

[0145] [Valve Metal] Valve metal is a metal whose oxide exhibits high insulation resistance. Examples of valve metals include Zr, Hf, V, Mo, Nb, Ta, and W. However, it is important to note that the behavior of Ti with respect to corrosive factors is often different from that of the elements Mo and V, which are the focus of this embodiment. Therefore, when further valve metal is included in the chemical conversion coating layer 15 according to this embodiment, it is preferable not to use element Ti as the valve metal. The chemical conversion coating layer 15 according to this embodiment may contain one or more of these valve metals. The type of valve metal compound used is not particularly limited as long as it is soluble in water. Examples of such valve metal compounds include ammonium salts, sodium salts, potassium salts, oxides, hydrogenates, oxygenates, hydroxides, phosphates, nitrates, sulfates, organic acidates, etc. of the above metals. Among these compounds, it is particularly preferable to use oxides, oxygenates, and phosphates of the above metals.

[0146] [Organic Resins] As organic resins, known organic resins such as ester resins, urethane resins, epoxy resins, phenolic resins, acrylic resins, olefin resins, and fluororesins can be used. It is also possible to use film-forming resin components such as modified resins of these resins, which are crosslinked with butylated melamine resins, methylated melamine resins, butylmethyl mixed melamine resins, urea resins, isocyanate resins, or crosslinking agent components of mixed systems of these resins. Furthermore, electron beam curable resins and ultraviolet curable resins may be used as organic resins. To further improve adhesion to the plating layer, it is preferable to use at least one resin (ester resins, urethane resins, epoxy resins, acrylic resins, etc.) that has forced sites or polar functional groups in its molecular chain.

[0147] Among the various organic resins described above, it is more preferable to use urethane resins, acrylic resins, epoxy resins, or olefin resins. In particular, it is even more preferable to use a water-soluble or water-dispersible urethane resin obtained by the reaction of an organic polyisocyanate compound and a polyol compound, especially a self-emulsifying urethane resin, as the organic resin.

[0148] Examples of organic polyisocyanate compounds include aliphatic diisocyanates such as phenylenediisocyanate, tolylenediisocyanate, diphenylmethanediisocyanate, and naphthalenediisocyanate, and alicyclic diisocyanates such as cyclohexanediisocyanate, isophoronediisocyanate, norbornanediisocyanate, xylylenediisocyanate, and tetramethylxylylenediisocyanate.

[0149] Polyol compounds include polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, and polyolefin polyols such as polybutadiene.

[0150] The above-mentioned organic resins may be used individually or in combination of two or more types.

[0151] Here, the total amount of silane coupling agent, valve metal, and organic resin in the solid content of the chemical conversion treatment solution is preferably in the range of 30 to 80% by mass. If the total amount is less than 30% by mass, there will be insufficient film-forming components, making it difficult to uniformly coat the chemical conversion treatment film layer with the steel material. On the other hand, if the total amount is more than 80%, it will be difficult to sufficiently include the components containing P, V, Mo and other components as described above, making it difficult to achieve both corrosion resistance of the flat parts of the chemical conversion treatment film layer, corrosion resistance of the processed parts, adhesion between the chemical conversion treatment film layer and the steel material, and resistance to blackening.

[0152] [Other components] In addition to the various components described above, the chemical conversion treated film layer 15 according to this embodiment may also contain silica, fluoride, tannin, or tannic acid.

[0153] Furthermore, the chemical conversion treatment coating layer 15 according to this embodiment may further contain various rust-preventive pigments in addition to the various components described above. As such rust-preventive pigments, any of the following can be used, for example: calcium ion exchange silica (sometimes commonly called calcium silicate), magnesium oxide, calcium molybdate, aluminum molybdate, barium molybdate, water-dispersible silica, fumed silica, etc.

[0154] Furthermore, the chemical conversion treatment film layer 15 according to this embodiment may further contain, if necessary, extender pigments such as precipitated barium sulfate and clay, and coloring pigments such as titanium dioxide. In addition, the chemical conversion treatment film layer 15 according to this embodiment may contain, if necessary, additives such as colorants, viscosity modifiers, leveling agents, defoamers, and ultraviolet absorbers, in addition to the rust-preventive pigments, extender pigments, and coloring pigments described above.

[0155] The surface-treated steel material 1 according to this embodiment has been described in detail above with reference to Figures 2 to 4.

[0156] (Regarding the surface-treated member) Next, with reference to Figure 5, the surface-treated member according to this embodiment will be described. The surface-treated member according to this embodiment is a member that is processed into a desired shape using the surface-treated steel material 1 according to this embodiment as described above as one of the materials.

[0157] Herein, the specific structure of the surface treatment member according to this embodiment is not particularly limited. The specific structure of the surface treatment member according to this embodiment may be, for example, a box shape, or a plate shape made of plate-shaped steel material, such as the roof or wall of a building. Furthermore, the specific structure of the surface treatment member according to this embodiment may be, for example, a molded or joined body made of various types of shaped steel, such as a solar power generation panel frame, or a molded or joined body made of various types of H-shaped steel or rectangular columns, such as the framework of a structure, or a molded or joined body made of various types of steel pipes, such as various pillars, signs, traffic lights, guardrails, etc.

[0158] Such a surface-treated member uses a surface-treated steel material 1, which is composed of a laminated structure having a steel material 11, a zinc-based plating layer 13, and a chemical conversion coating layer 15, as described above, as at least a part of the member. Furthermore, such a surface-treated member is used by burying at least a part of the portion having the laminated structure described above in the soil.

[0159] Here, the surface-treated steel material 1 used as the material for the surface-treated member according to this embodiment exhibits excellent corrosion resistance even in soil containing chloride ions, as described above. Therefore, by using this surface-treated steel material 1 as the material for the part that will be located in the soil, excellent corrosion resistance can be achieved even in soil with a high chloride ion concentration, such as soil with a chloride ion concentration of about 3 to 1000 mmol per kg of soil.

[0160] (Regarding the manufacturing method of surface-treated steel material) Below, an example of a manufacturing method for the surface-treated steel material 1 according to this embodiment will be described.

[0161] The surface-treated steel material 1 used as the material for the surface-treated member according to this embodiment is manufactured by using the steel material 11 described above as the base material and forming a zinc-based plating layer 13 and a chemical conversion coating layer 15 on the surface of the steel material 11.

[0162] <Method for forming the zinc-based plating layer 13> In addition to the hot-dip galvanizing method, the following methods can be applied to form the zinc-based plating layer 13: thermal spraying, cold spraying, sputtering, vapor deposition, electroplating, etc. However, the hot-dip galvanizing method is the most preferable in terms of cost.

[0163] In the following, an example of a manufacturing method for obtaining the zinc-based plating layer 13 according to this embodiment using a hot-dip galvanizing method will be described in detail. In the manufacturing process of such a zinc-based plating layer 13, first, a steel sheet, as an example of the steel material 11 to be used as the base material, is rolled to a desired thickness by the Zenzimir method, then wound into a coil, and placed on the hot-dip galvanizing line.

[0164] In the molten plating line, the steel sheet is continuously passed through while being drawn out from the coil. At this time, by the annealing equipment provided on the line, the steel sheet is, for example, in an environment where oxidation hardly occurs with an oxygen concentration of 20 ppm or less, N ２ - 5% H ２ After heat reduction treatment at 800 °C in a gas atmosphere, it is air-cooled with N ２ gas to a temperature around the plating bath temperature of the subsequent stage + 20 °C and then immersed in the plating bath.

[0165] Here, in the plating bath, a molten plating alloy having the above-described chemical components is prepared. The bath temperature of the plating bath is set to be not lower than the melting point of the plating alloy (for example, about 460 to 660 °C).

[0166] When producing the material of the plating alloy, it is preferable to prepare it by mixing a predetermined amount of alloy metals so as to have the composition of the plating layer as described above and completely melting it using a high-frequency induction furnace or an arc furnace in a vacuum or an inert gas-substituted state to form an alloy. Further, the alloy mixed with the predetermined components (the composition of the plating layer) is melted in the atmosphere, and the obtained melt is used as the plating bath.

[0167] Note that there are no particular restrictions on using pure metals in the production of the plating alloy as described above, and existing Zn alloys, Mg alloys, and Al alloys may be melted and used. At this time, there is no problem as long as a predetermined composition alloy with few impurities is used.

[0168] After immersing the steel sheet in the plating bath as described above, it is pulled up at a predetermined speed. At this time, for example, N ２ The amount of plating adhesion is controlled by wiping gas so that the formed zinc-based plating layer has a desired thickness. Here, for conditions other than the bath temperature, general plating operation conditions may be applied, and no special equipment or conditions are required.

[0169] In addition, various heat treatments may be performed on the molten plating alloy located on the steel sheet as needed.

[0170] <Method for forming the chemical conversion coating layer 15> The chemical conversion coating layer 15 according to this embodiment can be formed by applying a chemical conversion agent containing the components constituting the chemical conversion coating layer 15 as described above to the surface of the zinc-based plating layer 13 formed as described above, and then baking and hardening the steel material after the chemical conversion agent has been applied to reach a predetermined temperature (PMT). Here, the concentrations of P, V, and Mo in the solid content of the chemical conversion agent are approximately the concentrations of P, V, and Mo in the formed chemical conversion coating layer 15.

[0171] <<Preheating of Zinc-Plated Steel Materials>> When applying the above-mentioned chemical conversion agent to the surface of the zinc-plated layer 13, it is important to preheat the manufactured zinc-plated steel material so that the plate temperature at the time of application of the chemical conversion agent is 40.0°C or higher. This promotes the reaction between the components of the zinc-plated layer 13 and the components of the chemical conversion agent. There is no specific upper limit for the preheating temperature of zinc-plated steel materials, but in practice, it is around 60.0°C.

[0172] <<Reaction Atmosphere and Reaction Time between Chemical Conversion Agent and Zinc-Plated Steel Material>> Furthermore, in order to allow sufficient reaction between the components contained in the chemical conversion agent and the plating components in the zinc-plated layer, it is important to maintain the zinc-plated steel material, which has been kept at the above-mentioned plate temperature, and the chemical conversion agent in an atmosphere where the temperature (room temperature) is 40.0°C or lower and the relative humidity is 80.0% or higher, for at least 5.0 seconds. However, if the reaction time exceeds 10.0 seconds, the concentration of elements P, V, and Mo will become excessive, so care must be taken.

[0173] Here, there is no specific lower limit for the temperature of the reaction atmosphere (room temperature), but in practice, it is around 10.0°C. Similarly, there is no specific upper limit for the relative humidity, and it may be 100.0%. Furthermore, regarding the upper limit for the reaction time between the zinc-plated steel and the chemical conversion agent, it is preferable to set it to, for example, 10.0 seconds or less to prevent excessive reaction between the chemical conversion agent and the zinc-plated steel, which could affect the distribution of each element.

[0174] <<Reaction conditions when the chemical conversion agent contains V>> Furthermore, in order to achieve the distribution state of element V as explained above, the chemical conversion agent containing V should be applied within 180.00 seconds after the plating solidifies of the zinc-plated steel material in order to further promote the reaction between the surface of the zinc-plated layer and the chemical conversion agent containing V. This is because if the time after solidification exceeds 180.00 seconds, an excessive surface oxide layer may grow on the surface of the plating layer, and a reaction with the chemical conversion agent may not occur.

[0175] Furthermore, in order to further promote the reaction with the chemical treatment agent containing V, the preheating temperature of the zinc-plated steel material should be higher than the above 40.0°C, to 50.0°C or higher. The reaction atmosphere and reaction time should be the same as described above.

[0176] <<Method for preparing a chemical treatment agent containing V>> Furthermore, in order to achieve the distribution state of element V as described above, care must be taken in the preparation of the chemical treatment agent. More specifically, a compound containing the desired element V is dissolved in water with a pH of 10.00 to 12.00 containing amines, and then applied to the zinc-based plating layer 12 within 24.00 hours after the preparation of the chemical treatment agent. Here, the pH of the chemical treatment agent containing element V and amines can be adjusted using ammonia water.

[0177] Examples of amines to be incorporated into the chemical treatment agent include aliphatic amines such as dimethylamine, trimethylamine, diethylamine, and triethylamine; alicyclic amines such as cyclohexylamine and hexamethylenediamine; and alkanolamines such as triethanolamine, isopropanolamine, and diethylethanolamine. Furthermore, it is preferable to determine the amount of amines incorporated into the chemical treatment agent such that the molar ratio to V contained in the chemical treatment film layer is 0.10 to 5.00.

[0178] <Conditions for applying the chemical conversion agent containing V> Furthermore, in order to further promote the reaction between the surface of the zinc-based plating layer and the chemical conversion agent containing V, the chemical conversion agent containing V should be applied within 180.00 seconds after the solidification of the zinc-based plated steel. This is because if the time after solidification exceeds 180.00 seconds, an excessive surface oxide layer may grow on the surface of the plating layer, and a reaction with the chemical conversion agent may not occur.

[0179] ≪Method for preparing a chemical treatment agent containing Mo≫ Furthermore, in order to achieve the distribution state of elemental Mo as previously described, it is important to have the Mo ions in a complexed state in the chemical treatment agent so that the compound containing elemental Mo does not react easily with the compound containing elemental P and the plating component (Mg). More specifically, it is important to dissolve the compound containing elemental Mo in water with a pH of 9 to 11 that contains ammonia. As a result, the compound containing Mo dissolves sufficiently in the water containing ammonia, and it becomes possible to reliably complex the Mo ions. In this case, in order to make the complexation of Mo ions more certain, it is more preferable that the ammonia ion concentration in the water containing ammonia is 1.50 times or more the molar concentration of Mo.

[0180] Furthermore, when the chemical treatment agent contains both element V and element Mo, the chemical treatment agent should be prepared and applied in such a way that it satisfies all of the above conditions regarding V and Mo.

[0181] Here, the application of the chemical treatment agent described above can be carried out by generally known application methods, such as roll coating, curtain flow coating, air spray, airless spray, immersion, bar coating, or brush application.

[0182] By following the process described above, the surface-treated steel material 1, which will be the material for the surface-treated member according to this embodiment, can be manufactured. An example of a method for manufacturing the surface-treated steel material 1 according to this embodiment has been specifically described above.

[0183] <Method for Manufacturing Surface-Treated Members> Using the surface-treated steel material 1 obtained as described above as a material, a surface-treated member according to this embodiment is manufactured. Here, in order to obtain parts for manufacturing the surface-treated member from the surface-treated steel material 1, various shaping processes such as various forming processes, fastening members such as bolts and rivets, and joining processes such as welding can be used. By appropriately combining these processes, a surface-treated member having a desired shape can be manufactured from the surface-treated steel material 1.

[0184] The above briefly describes an example of a method for manufacturing a surface-treated member according to this embodiment.

[0185] The surface-treated steel materials and surface-treated members according to the present invention will be described in detail below with reference to examples and comparative examples. Note that the following examples are merely examples of the surface-treated steel materials and surface-treated members according to the present invention, and the surface-treated steel materials and surface-treated members according to the present invention are not limited to the examples below.

[0186] <Preparation of plated steel> In the test examples shown below, the plating base plate shown in Table 1 was used, and the plating base plate was cut to a size of 100 mm x 200 mm. Then, plating was performed using a batch-type hot-dip galvanizing test apparatus manufactured in-house, and multiple plated steel materials having the plating layer composition shown in Table 2 were produced for each level.

[0187]

[0188]

[0189] <Preparation of Chemical Conversion Agents> Chemical conversion agents for forming a chemical conversion coating layer were prepared using commercially available compounds as shown in Tables 3 to 9 below. Table 3 shows the compounds used as organic resins, Table 4 shows the phosphorus compounds used, Table 5 shows the vanadium compounds used, and Table 6 shows the molybdenum compounds used. In addition, Table 7 shows the silane coupling agents used, Table 8 shows the valve metals used, and Table 9 shows the vanadium reducing agents used. Note that all compounds shown in Tables 4 to 9 are general reagents.

[0190]

[0191]

[0192]

[0193]

[0194]

[0195]

[0196]

[0197] Using the various compounds described above, chemical treatment agents with the formulations shown in Tables 10-1 to 10-8 below were prepared.

[0198] <Formation of the chemical conversion treatment layer> The chemical conversion treatment agent prepared as described above was applied to the surface of the plated steel material described earlier using a bar coater to form a chemical conversion treatment layer. The conditions for forming the chemical conversion treatment layer are shown in Tables 11-1 to 11-8 below. In this way, multiple surface-treated steel materials for each level were prepared as test materials, as shown in Tables 12-1 to 12-8 below.

[0199]

[0200]

[0201]

[0202]

[0203]

[0204]

[0205]

[0206]

[0207]

[0208]

[0209]

[0210]

[0211]

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218]

[0219]

[0220]

[0221]

[0222]

[0223] For each surface-treated steel material obtained, various measurements concerning the zinc-based plating layer and the chemical conversion coating layer were performed in accordance with the method described above. The results obtained are summarized in Tables 12-1 to 12-8 above.

[0224] Furthermore, each surface-treated steel material obtained was evaluated in terms of soil corrosion resistance, coating adhesion, processed area corrosion resistance, and appearance under condensation. The evaluation methods and criteria for each aspect are as follows.

[0225] <Soil corrosion resistance> Each of the obtained surface-treated steel materials at each level was buried in soil simulating the surface layer of the soil to evaluate its corrosion resistance. As the soil, a mixture of silica sand with an average particle size of 200 μm (Flattery 40H manufactured by Yamakawa Sangyo Co., Ltd.) at a mass ratio of 60% and silica sand with an average particle size of 5 μm (CFP-M50 of Migaoka Ceramics Raw Materials Co., Ltd.) at a mass ratio of 40% was used. The covering thickness of each surface-treated steel material was 100 mm. After burying each surface-treated steel material in such a form, an ion-exchanged water containing 0.1 mmol% of NaCl and 0.2 mmol% of Na ２ SO ４ was dripped, and the water content was adjusted to 50%. Then, the container containing the native soil and the surface-treated steel material was stored in a thermo-hygrostat set at 40 °C and 95%. The storage times were 120 hours, 240 hours, and 480 hours.

[0226] After the above test was carried out, the surface-treated steel material was pickled with hydrochloric acid to remove the chemical conversion coating layer, the zinc-based plating layer, and the corrosion products of the steel material. Then, the mass of the steel material was measured, and the corrosion loss was measured by comparing the mass with the mass of the plating base plate (before plating). The evaluation criteria are as follows, and the scores "5", "4", and "3" were regarded as passing. The obtained results are summarized in Tables 13-1 to 13-8 below. <Evaluation criteria> Score 5: Corrosion loss is 10 g / m ２ or less 4: Corrosion loss is more than 10 g / m ２ and 50 g / m ２ or less 3: Corrosion loss is more than 50 g / m ２ and 100 g / m ２ or less 2: Corrosion loss is 100 g / m ２ , 200 g / m ２ or less 1: Corrosion loss is more than 200 g / m ２ exceeded

[0227] <Coating Adhesion> Flat test specimens were prepared and subjected to adhesion bending in accordance with JIS Z 2248:2006. A cellophane tape peel test was then performed on the adhesion-bent portion. Subsequently, the peeled portion of the cellophane tape was observed using a scanning electron microscope to evaluate the remaining coating. The evaluation criteria were as follows, and a score of "2" was considered to indicate excellent coating adhesion. The results obtained are summarized in Tables 13-1 to 13-8 below. <Evaluation Criteria> Score 2: No coating peeling observed 1: Coating peeling observed

[0228] <Corrosion Resistance of Machined Parts> Flat test pieces (50 mm x 50 mm) were prepared from the obtained surface-treated steel material, and after performing the Erichsen test (7 mm extrusion), a salt spray test in accordance with JIS Z 2371:2015 was performed for 140 hours, and the occurrence of white rust was observed. The evaluation criteria were as follows, and a score of "4" or "3" was judged to indicate excellent corrosion resistance of the machined part. The obtained results are summarized in Tables 13-1 to 13-8 below. <Evaluation Criteria> Score 4: Rust occurrence is less than 5% of the machined area 3: Rust occurrence is 5% or more but less than 15% of the machined area 2: Rust occurrence is 15% or more but less than 30% of the machined area 1: Rust occurrence is 30% or more of the machined area

[0229] <Appearance under Condensation> A test plate (300 mm x 300 mm) was prepared from the obtained surface-treated steel material, and 5 ml of deionized water was dropped onto the surface of the test plate. The surface-treated steel material was then stored for 24 hours in a constant temperature and humidity chamber at 40°C and 90% humidity. The evaluation criteria were as follows, and a score of "2" was judged to indicate excellent appearance under condensation. The results obtained are summarized in Tables 13-1 to 13-8 below. Score 2: No appearance abnormalities 1: Water contact marks appear below the deionized water droplet

[0230]

[0231]

[0232]

[0233]

[0234]

[0235]

[0236]

[0237]

[0238] As is clear from Tables 13-1 to 13-8 above, the surface-treated steel materials corresponding to the embodiments of the present invention showed excellent corrosion resistance even in soil, while the surface-treated steel materials corresponding to the comparative examples of the present invention could not obtain sufficient corrosion resistance.

[0239] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0240] The embodiments disclosed herein are illustrative and not restrictive in all respects. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the appended claims, the technical scope of the invention as described later, and the spirit thereof. For example, the constituent elements of the embodiments described above can be combined in any way without impairing their effects. Furthermore, such any combination will naturally yield the effects and benefits of each constituent element in the combination, as well as other effects and benefits that will be obvious to those skilled in the art from the description herein.

[0241] Furthermore, the effects described herein are merely descriptive or illustrative, and not limiting. In other words, the technology according to the present invention may produce other effects that will be apparent to those skilled in the art from the description herein, in addition to or instead of the effects described above.

[0242] Furthermore, the following configuration also falls within the technical scope of the present invention: (1) A base material consisting of a steel material, a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel material, and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer has a chemical composition in mass%, containing Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities, the chemical conversion coating layer contains P, and the thickness of the chemical conversion coating layer is t, A surface-treated steel material in which, starting from the surface of the chemical conversion-treated film layer and extending toward the zinc-based plating layer, the range extending 5t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer to the zinc-based plating layer is defined as the surface-side region, and starting from 5t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer and extending toward the interface between the chemical conversion-treated film layer and the zinc-based plating layer is defined as the plating-side region, the average value of the P concentration in the surface-side region is 1.10 to 1.50 times the average value of the P concentration in the plating-side region, and, starting from 8t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer and extending toward the zinc-based plating layer, the range extending 12t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer to the zinc-based plating layer is defined as the Mg-enriched region, the average value of the Mg concentration in the Mg-enriched region is 1.20 to 2.00 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region. (2) The surface-treated steel material according to (1), wherein the chemical conversion coating layer further contains an organic resin. (3) The surface-treated steel material according to (1) or (2), wherein the P concentration in the chemical conversion coating layer is 0.10% by mass or more and less than 3.00% by mass.(4) The surface-treated steel material according to any one of (1) to (3), wherein the chemical conversion coating layer further contains V, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, and the range from the surface of the chemical conversion coating layer as the starting point toward the zinc-based plating layer, ending at a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer, is defined as the surface-side region, and the range from the position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer as the starting point toward the zinc-based plating layer, ending at the interface between the chemical conversion coating layer and the zinc-based plating layer, is defined as the plating-side region, wherein the average value of the V concentration in the surface-side region is 1.10 to 1.50 times the average value of the V concentration in the plating-side region. (5) The surface-treated steel material according to (4), wherein the V concentration in the chemical conversion coating layer is 0.10% by mass or more and less than 2.00% by mass. (6) The surface-treated steel material according to (4) or (5), wherein, in the V2p narrow spectrum obtained by analyzing the plated side region of the chemical conversion treatment film layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of the peak having a maximum value at 515.90 ± 0.25 eV to the integrated intensity of the peak having a maximum value at 517.20 ± 0.25 eV is 0.20 to 0.50. (7) The surface-treated steel material according to any one of (1) to (6), wherein the chemical conversion coating layer further contains Mo, the Mo concentration in the chemical conversion coating layer is 0.1% by mass or more and 2.5% by mass or less, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, the surface region is defined as a range starting from the surface of the chemical conversion coating layer and ending at a position 2t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer, the interface region is defined as a range starting from a position 8t / 10 in the thickness direction from the surface of the chemical conversion coating layer and ending at the interface between the chemical conversion coating layer and the zinc-based plating layer, and the range located between the surface region and the interface region is defined as an intermediate region, the average value of the Mo concentration in the surface region is 1.10 to 1.50 times the average value of the Mo concentration in the intermediate region. (8) The surface-treated steel material according to (7), wherein the Mo concentration in the chemical conversion treatment coating layer is 0.10% by mass or more and less than 2.00% by mass.(9) The surface-treated steel material according to any one of (1) to (8), wherein the thickness t of the chemical conversion coating layer is 0.1 to 30.0 μm. (10) The surface-treated steel material according to any one of (2) to (9), wherein the organic resin is at least one of a urethane resin, an acrylic resin, an epoxy resin, or an olefin resin. (11) The amount of zinc plating layer deposited is 30 to 500 g / m per side. ２The surface-treated steel material according to any one of (1) to (10). (12) The zinc-based plating layer contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element group A to element group F, with the remainder being 60.00% or more of Zn and impurities, the surface-treated steel material according to any one of (1) to (11). [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element group F]: B: less than 0.50%. (13) The surface-treated steel material according to (12), containing element group A. (14) The surface-treated steel material according to (12), containing element group B. (15) The surface-treated steel material according to (12), containing element group C. (16) The surface-treated steel material according to (12), containing element group D. (17) The surface-treated steel material according to (12), containing element group E. (18) The surface-treated steel material according to (12), containing element group F. (19) The surface-treated steel material according to (1) or (12), wherein the zinc-based plating layer has a chemical composition in mass%, containing Al: 4.00% or more and less than 25.00%, Mg: 0.30% or more and less than 12.50%, with the remainder being 60.00% or more of Zn and impurities.(20) A surface treatment member having a laminated structure in at least a part of the member comprising: a base material steel; a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel; and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer is a plating layer having a chemical composition by mass %, containing Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities; the chemical conversion coating layer contains P; and the thickness of the chemical conversion coating layer is t. A surface-treated member wherein, when the surface of the chemical conversion-treated film layer is defined as the starting point and the range extending toward the zinc-based plating layer is defined as the surface-side region, and the range extending toward the zinc-based plating layer is defined as the plating-side region, when the starting point is the 5t / 10 position in the thickness direction from the surface of the chemical conversion-treated film layer and the range extending toward the interface between the chemical conversion-treated film layer and the zinc-based plating layer is defined as the plating-side region, the average value of the P concentration in the surface-side region is 1.10 to 1.50 times the average value of the P concentration in the plating-side region, and when the range extending toward the zinc-based plating layer is defined as the Mg-enriched region, when the starting point is the 8t / 10 position in the thickness direction from the surface of the chemical conversion-treated film layer and the range extending toward the zinc-based plating layer is defined as the Mg-enriched region, the average value of the Mg concentration in the Mg-enriched region is 1.20 to 2.00 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region. (21) The surface treatment member according to (20), wherein at least a portion of the part having the layered structure is buried in soil. (22) The surface treatment member according to (21), wherein the soil is soil having a chloride ion concentration of 3 to 1000 mmol per 1 kg of soil.

[0243] 1 Surface-treated steel material 11 Steel material 13 Zinc-based plating layer 15 Chemical conversion coating layer

Claims

1. A base material comprising: a steel material; a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel material; and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer has a chemical composition in mass%, containing Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities; the chemical conversion coating layer contains P; and the thickness of the chemical conversion coating layer is t. A surface-treated steel material in which, starting from the surface of the chemical conversion-treated film layer and extending toward the zinc-based plating layer, the range extending 5t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer to the zinc-based plating layer is defined as the surface-side region, and starting from 5t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer and extending toward the interface between the chemical conversion-treated film layer and the zinc-based plating layer is defined as the plating-side region, the average value of the P concentration in the surface-side region is 1.10 to 1.50 times the average value of the P concentration in the plating-side region, and, starting from 8t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer and extending toward the zinc-based plating layer, the range extending 12t / 10 in the thickness direction from the surface of the chemical conversion-treated film layer to the zinc-based plating layer is defined as the Mg-enriched region, the average value of the Mg concentration in the Mg-enriched region is 1.20 to 2.00 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region.

2. The surface-treated steel material according to claim 1, wherein the chemical conversion coating layer further contains an organic resin.

3. The surface-treated steel material according to claim 1 or 2, wherein the P concentration in the chemical conversion treatment coating layer is 0.10% by mass or more and less than 3.00% by mass.

4. The surface-treated steel material according to claim 1 or 2, wherein the chemical conversion coating layer further contains V, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, and the surface-side region is defined as a range starting from the surface of the chemical conversion coating layer and ending at a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer, and the plating-side region is defined as a range starting from a position 5t / 10 in the thickness direction from the surface of the chemical conversion coating layer and ending at the interface between the chemical conversion coating layer and the zinc-based plating layer, the average value of the V concentration in the surface-side region is 1.10 to 1.50 times the average value of the V concentration in the plating-side region.

5. The surface-treated steel material according to claim 4, wherein the concentration of V in the chemical conversion treatment coating layer is 0.10% by mass or more and less than 2.00% by mass.

6. The surface-treated steel material according to claim 4, wherein, in the V2p narrow spectrum obtained by analyzing the plated side region of the chemical conversion treatment film layer by X-ray photoelectron spectroscopy (XPS), the ratio of the integrated intensity of the peak having a maximum value at 515.90 ± 0.25 eV to the integrated intensity of the peak having a maximum value at 517.20 ± 0.25 eV is 0.20 to 0.

50.

7. The surface-treated steel material according to claim 1 or 2, wherein the chemical conversion coating layer further contains Mo, the Mo concentration in the chemical conversion coating layer is 0.10% by mass or more and 2.50% by mass or less, and in the chemical conversion coating layer, the thickness of the chemical conversion coating layer is t, the surface region is defined as a range starting from the surface of the chemical conversion coating layer and ending at a position 2t / 10 in the thickness direction from the surface of the chemical conversion coating layer toward the zinc-based plating layer, the interface region is defined as a range starting from a position 8t / 10 in the thickness direction from the surface of the chemical conversion coating layer and ending at the interface between the chemical conversion coating layer and the zinc-based plating layer, and the range located between the surface region and the interface region is defined as an intermediate region, the average value of the Mo concentration in the surface region is 1.10 to 1.50 times the average value of the Mo concentration in the intermediate region.

8. The surface-treated steel material according to claim 7, wherein the Mo concentration in the chemical conversion treatment coating layer is 0.10% by mass or more and less than 2.00% by mass.

9. The surface-treated steel material according to claim 1 or 2, wherein the thickness t of the chemical conversion treatment film layer is 0.1 to 30.0 μm.

10. The surface-treated steel material according to claim 2, wherein the organic resin is at least one of a urethane resin, an acrylic resin, an epoxy resin, or an olefin resin.

11. The amount of zinc-based plating layer to adhere is 30 to 500 g / m² per side. ２ The surface-treated steel material according to claim 1 or 2.

12. The surface-treated steel material according to claim 1 or 2, wherein the zinc-based plating layer contains, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further contains one or more elements selected from the group consisting of element groups A to F below, with the remainder being 60.00% or more of Zn and impurities. [Element Group A]: One or two elements selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less. [Element Group B]: One or more elements selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%. [Element Group C]: One or more elements selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%. [Element Group D]: One or more elements selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%. [Element Group E]: One or more elements selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less. [Element Group F]: B: less than 0.50% 13. The surface-treated steel material according to claim 12, comprising the element group A.

14. The surface-treated steel material according to claim 12, comprising the element group B.

15. The surface-treated steel material according to claim 12, comprising the element group C.

16. The surface-treated steel material according to claim 12, comprising the element group D.

17. The surface-treated steel material according to claim 12, comprising the element group E.

18. The surface-treated steel material according to claim 12, comprising the element group F.

19. The surface-treated steel material according to 1 or 12, wherein the zinc-based plating layer has a chemical composition in mass%, containing Al: 4.00% or more and less than 25.00%, Mg: 0.30% or more and less than 12.50%, with the remainder being 60.00% or more of Zn and impurities.

20. A surface treatment member having a laminated structure in at least a part of the member comprising: a base material steel; a zinc-based plating layer containing Mg, Al, and Zn located on the surface of the steel; and a chemical conversion coating layer located on the surface of the zinc-based plating layer, wherein the zinc-based plating layer has a chemical composition containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, with the remainder being 60.00% or more of Zn and impurities; the chemical conversion coating layer contains P; and the thickness of the chemical conversion coating layer is t. A surface-treated member wherein, when the surface of the chemical conversion-treated film layer is defined as the starting point and the range extending toward the zinc-based plating layer is defined as the surface-side region, and the range extending toward the zinc-based plating layer is defined as the plating-side region, when the starting point is the 5t / 10 position in the thickness direction from the surface of the chemical conversion-treated film layer and the range extending toward the interface between the chemical conversion-treated film layer and the zinc-based plating layer is defined as the plating-side region, the average value of the P concentration in the surface-side region is 1.10 to 1.50 times the average value of the P concentration in the plating-side region, and when the range extending toward the zinc-based plating layer is defined as the Mg-enriched region, when the starting point is the 8t / 10 position in the thickness direction from the surface of the chemical conversion-treated film layer and the range extending toward the zinc-based plating layer is defined as the Mg-enriched region, the average value of the Mg concentration in the Mg-enriched region is 1.20 to 2.00 times the average value of the Mg concentration in the zinc-based plating layer excluding the Mg-enriched region.

21. The surface treatment member according to claim 20, wherein at least a portion of the layered structure is buried in the soil.

22. The surface treatment member according to claim 21, wherein the soil is soil having a chloride ion concentration of 3 to 1000 mmol per 1 kg of soil.

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