Surface treated member

Abstract

[Problem] To provide a surface-treated member which exhibits excellent corrosion resistance even in soil having a depth of about several cm from the soil surface. [Solution] The surface-treated member of the present invention comprises a surface-treated steel material having a steel material as a base material and a zinc-based plating layer, and is characterized in that: a steel substrate exposed part is present in at least a portion of the zinc-based plating layer; when a cross section obtained by cutting the exposed part of the steel substrate in the thickness direction of the steel material in accordance with the shape of the exposed part of the steel substrate when the zinc plating layer is viewed from above in a plan view, there are at least one cross section having a steel substrate exposure rate within the range of 1.0-40.0%, and in the cross section having a steel substrate exposure rate within the range of 1.0-40.0%, the steel substrate has a thickness of 1.0-40.0%. The shortest distance from an arbitrary point on the surface of the exposed steel material to the zinc-based plating layer is more than 0 [mu] m and 50.0 [mu] m or less, and the total area of a region providing a cross-section in which the steel base exposure rate is more than 40.0% is 5.0% or less of the total area of the steel base exposed portion.

Description

Technical Field

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

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

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

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

[0005] Existing technical documents

[0006] Patent documents

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

[0008] The problem the invention aims to solve

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

[0010] The inventors conducted a study on the corrosion of zinc-plated steel in soil. The results showed that, as described below, the corrosion behavior of zinc-plated steel in soil at a depth of 1 meter or more from the soil surface differed significantly from that in soil at a depth of only a few centimeters. Therefore, the soil corrosion environment described in Patent Document 1 primarily corresponds to the corrosion behavior in soil at a depth of 1 meter or more from the soil surface. Based on this, it was found that even when using the surface-treated steel disclosed in Patent Document 1 as a raw material to manufacture surface-treated components in soil at a depth of only a few centimeters from the soil surface, there is room for improvement in its corrosion resistance.

[0011] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a surface-treated component using zinc-plated steel, which exhibits excellent corrosion resistance even in soil at a depth of several centimeters from the soil surface.

[0012] Solution for solving the problem

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

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

[0015] (1) A surface-treated steel member comprising a steel material having a base material and a zinc-based coating on the surface of the steel material, wherein at least a portion of the zinc-based coating has a portion exposing the surface of the steel material, i.e., a steel substrate exposed portion, and when observing a cross section obtained by cutting the steel substrate exposed portion along the thickness direction of the steel material according to the shape of the steel substrate exposed portion when viewed from above using a microscope, there is at least one cross section in which the proportion of the portion exposing the surface of the steel material in the cross section, i.e., the steel substrate exposure rate, is in the range of 1.0 to 40.0%, and in the cross section in the range of 1.0 to 40.0%, the shortest distance from any point on the surface of the exposed steel material to the zinc-based coating is greater than 0 μm and less than 50.0 μm, and for each region providing the cross section with a steel substrate exposure rate of more than 40.0%, the sum of the areas of the region when viewed from above is less than 5.0% of the total area of ​​the steel substrate exposed portion.

[0016] (2) The surface treatment component according to (1) is used by burying at least a portion of the exposed portion of the steel substrate in the soil.

[0017] (3) According to the surface treatment component described in (2), the exposed steel substrate portion is determined by performing a color development test on the entire surface of the zinc-based coating to cause a color development reaction in the exposed steel substrate portion. When viewed from above the zinc-based coating, each of the determined exposed steel substrate portions has a short side size of 5 mm or more and an area of ​​1 cm². 2 The rectangular area is used as a unit to virtually divide each of the above-mentioned exposed steel substrates. For each partition where the area of ​​the exposed steel substrate occupies more than 3% of the rectangular area, the cross section of the partition is observed, and the steel substrate exposure rate is measured. The total area of ​​the partitions with the steel substrate exposure rate in the range of 1.0 to 40.0% accounts for more than 5.0% of the area of ​​the part buried in the soil.

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

[0019] (5) The surface treatment component according to (4), wherein the zinc coating contains Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more by mass%.

[0020] (6) The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and also containing one or more elements selected from the group consisting of the following element groups A, B, C, D, E and F, with the balance being Zn and impurities.

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

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

[0023] [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

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

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

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

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

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

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

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

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

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

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

[0034] (14) The surface-treated component according to any one of (1) to (3), wherein the upper limit of the measured value of the exposed steel substrate is denoted as A [%], and the average adhesion amount of the zinc coating on each side is denoted as B [g / m]. 2 When ], both of the following equations (1) and (2) are satisfied.

[0035] A≤0.8×10 -1 ×B+28.0…Equation (1)

[0036] A≤40.0…Equation (2)

[0037] (15) The surface-treated component according to any one of (1) to (3), wherein the amount of the zinc-based coating is an average of 50.0 to 150.0 g / m² per surface. 2 .

[0038] (16) The surface-treated component according to (14), wherein the amount of the zinc-based coating is an average of 50.0~150.0 g / m² per surface. 2 .

[0039] (17) The surface-treated component according to any one of (1) to (3), wherein at least one cross section has an exposure rate of 5.0% to 40.0% of the steel substrate.

[0040] The effects of the invention

[0041] As described above, according to the present invention, excellent corrosion resistance can be exhibited even in soil at a depth of several centimeters from the soil surface. Attached Figure Description

[0042] Figure 1 This is a schematic diagram used to illustrate a structure placed on the soil surface.

[0043] Figure 2 This is a schematic diagram illustrating the structure of the surface treatment component for an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram illustrating the structure of a surface treatment component in the same embodiment.

[0045] Figure 4 This is a schematic diagram illustrating the structure of a surface treatment component in the same embodiment.

[0046] Figure 5 This is an explanatory diagram illustrating the steel substrate exposure rate in a surface-treated component of the same embodiment.

[0047] Figure 6 This is an explanatory diagram illustrating the steel substrate exposure rate in a surface-treated component of the same embodiment.

[0048] Figure 7 This is an explanatory diagram illustrating the steel substrate exposure rate in a surface-treated component of the same embodiment.

[0049] Figure 8 This is an explanatory diagram illustrating a modified example of the steel substrate exposure rate in a surface-treated component of the same embodiment. Detailed Implementation

[0050] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in this specification and the accompanying drawings, constituent elements having substantially the same functional configuration are labeled with the same reference numerals, and repeated descriptions are omitted.

[0051] (Corrosion behavior in soil at a depth of several centimeters from the soil surface)

[0052] Before describing the surface treatment components according to embodiments of the present invention, refer to Figure 1 The corrosion behavior in soil at a depth of about several centimeters from the soil surface, as discovered by the inventors, will be described. Figure 1 This is a schematic diagram used to illustrate a structure placed on the soil surface. Additionally, for convenience, the term "soil at a depth of several centimeters from the soil surface" will sometimes be referred to as the "soil surface layer".

[0053] like Figure 1 The diagram schematically illustrates various structures, such as pedestals supporting solar panels, road signs, guardrails, and traffic signals, installed on the soil surface. In order to more stably position these structures on the soil surface, such as... Figure 1 As shown, most of them will include a part of the structure (e.g., near the lower end of the support column, etc.) in Figure 1 The part enclosed by the dotted line is buried in the soil.

[0054] From the perspective of factors such as production costs, various types of steel are generally used as raw materials for various structures. However, when a structure using various types of steel as raw materials is buried in the soil, there are concerns about the corrosion of the steel used as raw materials.

[0055] The effects of soil on steel corrosion can be summarized by two main factors: moisture retention as a corrosion factor and inhibition of oxygen diffusion as another corrosion factor. Moisture retention increases the corrosion rate, while inhibition of oxygen diffusion decreases it. In soil, the environment remains moist for a longer period, such as after rainfall, compared to the atmosphere. On the other hand, due to the soil, the penetration and diffusion of oxygen from the atmosphere is inhibited, thus reducing the corrosion rate. For the actual corrosion rate in soil, these two factors, in a trade-off relationship, interact, resulting in a corrosion rate that remains relatively constant. Generally, the effect of inhibition of oxygen diffusion is greater than that of moisture retention; therefore, in soil, the corrosion rate is suppressed compared to the atmosphere.

[0056] On the other hand, the situation is quite different in the soil at a depth of several centimeters below the surface (the topsoil). Even in the topsoil, the soil makes it difficult for moisture to evaporate, thus keeping the steel in contact with moisture for a longer period compared to the atmosphere. Furthermore, the topsoil is closer to the atmosphere, allowing for earlier supply of oxygen, thus reducing the effect of oxygen diffusion inhibition caused by the soil. Therefore, combined with the effect of moisture retention, it can be considered that the corrosion inhibition effect from the soil is almost negligible in the topsoil. Thus, the topsoil, which the inventors focused on, represents an extremely harsh corrosive environment compared to soil at a depth of 1 meter or more below the surface.

[0057] In order to study the corrosion behavior of steel in the surface layer of soil, the inventors conducted a study on the corrosion behavior of zinc-plated steel in the surface layer of soil, and found the following results.

[0058] In other words, zinc-coated steel exhibits high corrosion resistance due to the zinc coating covering its surface with zinc corrosion products in the atmosphere. However, it has been determined that the corrosion protection function of these zinc corrosion products is low in the surface layer of soil.

[0059] The inventors observed zinc-based corrosion products formed on zinc-based coatings in the surface layer of soil using a scanning electron microscope (SEM). The results showed that the zinc-based corrosion products formed in the soil surface layer were porous compared to those formed in the atmosphere. This is attributed to the fact that corrosion occurs more rapidly in the soil surface layer compared to the atmosphere.

[0060] Based on the above insights, the inventors have obtained the following insights: In order to improve the corrosion resistance of zinc-plated steel in the surface layer of soil, it is important to change the corrosion products formed in the zinc-plated coating in the surface layer of soil into products formed in a dense state.

[0061] In order to achieve the formation of corrosion products in a dense state in the surface layer of soil, the inventors conducted further research and discovered that, unlike previous technical ideas, a portion of the zinc-based coating is intentionally provided to expose the surface of the steel (hereinafter referred to as "exposed steel substrate portion"). It was thus found that even in the surface layer of soil, a dense corrosion product can be formed on the surface of the zinc-based coating.

[0062] In conventional techniques, zinc-based coatings are made dense to minimize exposure of the steel substrate, thus protecting the substrate by utilizing the sacrificial corrosion protection properties of zinc. However, the inventors have discovered that by intentionally creating portions of the zinc-based coating that expose the steel substrate, corrosion products of a denser state than those in the atmosphere can be generated from these exposed portions. These corrosion products protect the steel substrate and the surrounding zinc-based coating.

[0063] Since the exposed steel substrate is located in the soil, both the zinc-based coating and the steel substrate are exposed to corrosive agents in the soil (i.e., moisture and oxygen). Consequently, Zn ions dissolve from the zinc-based coating, and Fe ions dissolve from the steel substrate. In the atmosphere, the dissolved Zn and / or Fe ions are washed away by rain, etc., and rarely remain fixed in the exposed portion. On the other hand, there is no water flow in the soil; therefore, it is presumed that the dissolved Zn and / or Fe ions readily become fixed in the exposed steel substrate, forming a dense Fe-Zn composite oxide as a corrosion product.

[0064] Furthermore, the inventors' research results indicate that when the zinc coating is an alloy coating containing Mg and Al in addition to Zn, Mg and Al ions dissolve in the soil in addition to Zn ions. It is known that through this dissolution, a Fe-Zn-Al-Mg composite oxide is generated, further improving corrosion resistance.

[0065] Based on the insights described above, the inventors conducted further research and came up with the surface treatment component of the present invention, which is described in detail below.

[0066] (Regarding surface-treated components)

[0067] The following is for reference Figures 2-4 The surface treatment components according to embodiments of the present invention will be described in detail. Figures 2-4 This is a schematic diagram illustrating the structure of the surface treatment component in this embodiment. Additionally, in Figures 2-4 For convenience, the coordinate axes shown in the figure are used for explanation.

[0068] As detailed below, the surface-treated component of this embodiment is constructed using surface-treated steel with a zinc-based coating as the blank. Here, the specific structure of the surface-treated component of this embodiment is not particularly limited. The specific structure of the surface-treated component of this embodiment can be, for example, box-shaped, or plate-shaped, such as the roof and / or walls of a building, using plate-shaped steel. Furthermore, the specific structure of the surface-treated component of this embodiment can be, for example, a molded body and / or joint using various types of steel, such as a solar panel mounting platform; a molded body and / or joint using various H-beams and / or prisms, such as the skeleton of a structure; or a molded body and / or joint using various steel pipes, such as various pillars, signs, signal lights, guardrails, etc.

[0069] Figure 2 This schematically illustrates a portion of the surface-treated component of this embodiment when viewed from above (Z-axis direction in the figure). For example... Figure 2 As illustrated schematically, the surface treatment component 1 of this embodiment, as described below, uses a zinc-plated steel sheet on which a zinc-based coating 20 is provided on the surface of a steel sheet serving as the base material, as the blank, and on its surface (corresponding to...) Figure 2 At least a portion of the XY plane (the surface of the zinc coating 20) is a part that exposes the surface of the steel, namely the exposed part of the steel substrate 201.

[0070] Here, in Figure 2 In the diagram, the exposed steel substrate 201 is schematically represented as having a generally rectangular shape. However, in the surface treatment component 1 of this embodiment, the specific shape of the exposed steel substrate 201 is not limited to this. Figure 2 The shape shown.

[0071] Figure 3 Indicatively representing that Figure 2 The surface-treated component 1 shown is cut along the AA cutting line in the Z-axis direction. Figure 3 The cross-sectional view shown corresponds to the view obtained by cutting the portion of the surface treatment component 1 in this embodiment where there is no exposed steel substrate 201 along the thickness direction of the zinc-plated steel material that serves as the blank of the surface treatment component 1.

[0072] like Figure 3 As illustrated, the surface-treated component 1 of this embodiment, excluding the exposed steel substrate 201, is composed of surface-treated steel (i.e., zinc-plated steel) having a steel 10 as a base material and a zinc-based coating 20 on the surface of the steel 10.

[0073] The following is a detailed description of the steel 10 and the zinc coating 20.

[0074] <About Steel 10>

[0075] The steel 10 used as the base material for the surface-treated component 1 in this embodiment is not particularly limited, and various steels can be used depending on the mechanical strength (e.g., tensile strength) required for the surface-treated component 1. Examples of such steel 10 include various Al-killed steels, ultra-low carbon steels containing Ti, Nb, etc., high-strength steels that also contain strengthening elements such as P, Si, Mn, etc. in ultra-low carbon steel, and various steels containing other components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.).

[0076] Alternatively, a pre-plating layer can be applied before the zinc-based plating described later on the steel 10. Examples of metals that can be used in the pre-plating layer include Ni, Sn, or alloys combining these elements. Using pre-plated steel with these pre-plated coatings eliminates unplated areas (areas where the plating metal is rejected by oxide films, etc.). This is presumably because when the pre-plated steel is immersed in a hot-dip galvanizing bath, the metal elements in the bath react with the pre-plating layer to form Ni(Sn)-Al-Fe-Zn. The average adhesion amount of the pre-plating layer on each side is preferably 0.2~2.0 g / m². 2 Within the range. By setting the adhesion amount of the pre-coating to 0.2 g / m 2 The above demonstrates a reliable inhibition effect against uncoated areas based on pre-coating, as described above. Furthermore, by setting the pre-coating adhesion amount to 2.0 g / m²... 2 The following method can prevent the leaching of Fe from being suppressed by the pre-plating layer, making it difficult to form Fe-Zn composite oxides, and can achieve the unplating suppression effect mentioned above.

[0077] In addition, there is no particular limitation on the thickness of the steel 10; it can be set appropriately according to the mechanical strength required by the surface-treated component 1.

[0078] <Regarding Zinc-Based Coatings 20>

[0079] The zinc-based coating 20 is formed on both surfaces of the steel 10 as described above. The zinc-based coating 20 is not particularly limited as long as it contains at least zinc (Zn), and various known zinc-based coatings can be used.

[0080] Examples of zinc-based coatings include hot-dip galvanizing and / or alloyed hot-dip galvanizing, as well as zinc-nickel, zinc-iron, zinc-chromium, zinc-aluminum, zinc-titanium, zinc-magnesium, zinc-manganese, zinc-aluminum-magnesium, and zinc-aluminum-magnesium-silicon coatings. Furthermore, zinc-based coatings can also include those containing small amounts of dissimilar metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic, and / or those containing dispersed inorganic substances such as silicon dioxide, alumina, and titanium dioxide. The coating method is not particularly limited; various known coating methods such as electroplating, hot-dip galvanizing, vapor deposition, dispersion coating, and vacuum coating can be used.

[0081] Among the various zinc-based platings described above, the zinc-based plating layer 20 of this embodiment is more preferably a zinc-based plating layer having the chemical composition detailed below. As the zinc-based plating layer 20, by using a zinc-based plating layer having the chemical composition detailed below, various properties of the surface-treated component 1 of this embodiment, such as corrosion resistance, can be further improved. Hereinafter, a more preferred chemical composition of the zinc-based plating layer 20 described above will be explained in detail.

[0082] Chemical Composition of Zinc-Based Coating 20

[0083] According to a certain method, the zinc-based coating 20 of this embodiment has the following chemical composition: by mass%, it contains Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance is Zn and impurities.

[0084] Furthermore, in a certain chemical composition of the zinc-based coating 20 in this embodiment, the zinc-based coating 20 is more preferably a coating containing, by mass %: Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and Zn: 60.00% or more.

[0085] In addition, according to another method, the zinc-based coating 20 of this embodiment has the following chemical composition: by mass%, it contains Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and also contains one or more elements selected from the group consisting of element group A, element group B, element group C, element group D, element group E and element group F, with the balance being Zn and impurities.

[0086] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%.

[0087] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%.

[0088] [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

[0089] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%.

[0090] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0091] [Element group F]: B: less than 0.50%

[0092] [Al: ≥0.10% by mass and <40.00% by mass]

[0093] In the preferred embodiment of the zinc-based coating 20, Al is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure). Therefore, to ensure the corrosion resistance of the coated steel, it is preferable to contain Al at a specified or higher content. If the Al content in the zinc-based coating 20 is less than 0.10% by mass, the aforementioned corrosion resistance may not be guaranteed. Therefore, in the zinc-based coating 20 of this embodiment, the Al content is preferably 0.10% by mass or more. The Al content is preferably 3.00% by mass or more, more preferably 4.00% by mass or more, and even more preferably 6.00% by mass or more. By keeping the Al content within the range described above, the corrosion resistance of the coated steel can be ensured.

[0094] On the other hand, when the Al content in the zinc-based coating 20 is 40.00% by mass or more, the excessive increase of the Al phase, which functions as a cathode, in a corrosive environment can easily lead to corrosion of the steel 10, potentially compromising the corrosion resistance of the coated steel. Therefore, in the zinc-based coating 20 of this embodiment, the Al content is preferably less than 40.00% by mass. The Al content is preferably 25.00% by mass or less, more preferably less than 25.00% by mass, and even more preferably 20.00% by mass or less.

[0095] [Mg: ≥0.10% by mass and <15.00% by mass]

[0096] In the preferred embodiment of the zinc-based coating 20, Mg is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure). Therefore, to ensure the corrosion resistance of the coated steel, it is preferable to contain Mg at a specified or higher content. If the Mg content in the zinc-based coating 20 is less than 0.10% by mass, the aforementioned corrosion resistance may not be guaranteed. Therefore, in the zinc-based coating 20 of this embodiment, the Mg content is preferably 0.10% by mass or more. The Mg content is preferably 0.30% by mass or more, and more preferably 3.00% by mass or more. By keeping the Mg content within the range described above, the corrosion resistance of the coated steel can be ensured.

[0097] On the other hand, when the Mg content in the zinc-based coating 20 is 15.00% by mass or more, anodic dissolution of the zinc-based coating can easily proceed under corrosive conditions, which may compromise the corrosion resistance of the coated steel. Therefore, in the zinc-based coating 20 of this embodiment, the Mg content is preferably less than 15.00% by mass. The Mg content is preferably less than 12.50% by mass, and more preferably less than 12.00% by mass. By keeping the Mg content within the range described above, corrosion resistance of the coated steel can be ensured.

[0098] In the zinc-based coating 20 of this embodiment, the balance of Al and Mg is Zn and impurities.

[0099] In the preferred embodiment of the zinc-based coating 20, Zn is an element required to form the main metallographic structure (Zn-Al-Mg metallographic structure) and is an important element for improving the corrosion resistance of the coated steel. Furthermore, the zinc-based coating 20 contains Al and Mg within the aforementioned range, and also contains Zn, thereby ensuring the required corrosion resistance of the coated steel.

[0100] Next, in a preferred embodiment of the zinc-based coating 20, the element groups A to F that may be present in the chemical composition of the zinc-based coating 20 will be described in detail.

[0101] It should be noted that in another embodiment of the zinc-based coating 20, when it contains at least one of the elements belonging to element group A to element group F, it is preferable that it contains at least one of the elements belonging to element group A to element group F within the following content range and with a total content of 60.00% by mass or less.

[0102] By setting the total content of elements belonging to element groups A to F to 60.00% by mass or less, the effects resulting from the addition of each element, as detailed below, can be enjoyed without any mutual impairment. The total content of elements belonging to element groups A to F is preferably 50.00% by mass or less, and more preferably 40.00% by mass or less.

[0103] ◇Element Group A

[0104] In another embodiment of the zinc-based coating 20, the element group A that may be contained in the zinc-based coating 20 will be described. At least one element in element group A shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0105] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%.

[0106] [Si: 0% by mass or more and 2.50% by mass or less]

[0107] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where Si is not present, and therefore its content is limited to 0% by mass. On the other hand, Si is an element that can suppress the excessive growth of Fe-Al metallographic structure formed at the interface between the zinc-based coating 20 and the steel 10, and further improve the adhesion between the zinc-based coating 20 and the steel 10. When the zinc-based coating 20 contains Si, in order to suppress the excessive growth of Fe-Al metallographic structure, the Si content is preferably 0.05% by mass or more, and more preferably 0.20% by mass or more. On the other hand, when the Si content exceeds 2.50% by mass, excessive Si may form high-melting-point intermetallic compounds with Mg, which may hinder the formation of Al-Mg oxides that have the effect of suppressing Zn evaporation during welding.

[0108] Furthermore, if the Si content in the plating bath used to manufacture the zinc-based coating 20 is too high, the viscosity of the plating bath increases beyond what is necessary, potentially reducing the operability (hereinafter referred to as "plating operability") during the manufacture of the coated steel. Therefore, from the viewpoint of plating operability, the Si content in the plating bath is adjusted. The Si content in the zinc-based coating 20 is preferably 1.50% by mass or less, more preferably 1.00% by mass or less.

[0109] [Fe: ≥0% by mass and ≤5.00% by mass]

[0110] In the zinc-based coating 20, elements constituting the steel are sometimes mixed in from the steel 10, which serves as the base material. Particularly in hot-dip galvanizing, due to the interdiffusion of elements caused by the solid-liquid reaction between the steel 10 and the zinc-based coating 20, elements constituting the steel 10 easily mix into the zinc-based coating 20. Through this mixing, the zinc-based coating 20 typically contains a specified amount of Fe, usually 0.01% by mass or more. Promoting this interdiffusion improves the adhesion between the steel 10 and the zinc-based coating 20. From the viewpoint of improving the adhesion between the steel 10 and the zinc-based coating 20, the Fe content in the zinc-based coating 20 is preferably 0.20% by mass or more.

[0111] Furthermore, Fe can be intentionally added to the plating bath used in manufacturing the zinc-based coating 20 without impairing the effects of the present invention. However, if the Fe content in the plating bath is increased, a high-melting-point intermetallic compound of Fe and Al will form in the plating bath. In this case, the high-melting-point intermetallic compound adheres to the zinc-based coating 20 as dross, which tends to significantly reduce the appearance quality and is therefore undesirable. From this point of view, the Fe content in the plating bath is adjusted. The Fe content in the zinc-based coating 20 is preferably 5.00% by mass or less. The Fe content in the coating 20 is more preferably 3.00% by mass or less, and even more preferably 2.00% by mass or less, 1.00% by mass or less, or 0.50% by mass or less.

[0112] ◇Element Group B

[0113] In another embodiment of the zinc-based coating 20, the element group B that may be contained in the zinc-based coating 20 will be described. At least one element in element group B shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0114] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%.

[0115] [Sb: ≥0% by mass and ≤0.50% by mass]

[0116] [Pb: ≥0.50% by mass]

[0117] [Sr: 0% or more by mass and less than 0.50% by mass]

[0118] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where Sb, Pb, and Sr are not present, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, if the zinc-based coating 20 contains at least one of Sb, Pb, and Sr, zinc flowers will form on the surface of the zinc-based coating 20, thereby improving the metallic luster. Therefore, from the viewpoint of further improving the designability of the coated steel, it is preferable that the zinc-based coating 20 contains at least one of Sb, Pb, and Sr. This improvement in designability is manifested when the content of at least one of Sb, Pb, and Sr is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least one of Sb, Pb, and Sr, the content of each of these elements is preferably set independently to 0.05% by mass or more.

[0119] On the other hand, when a zinc-based coating 20 is formed in which the content of any one of Sb, Pb, and Sr exceeds 0.50% by mass, the amount of dross generated in the plating bath used to form the zinc-based coating 20 increases, which may prevent the production of coated steel with good coating properties. Therefore, the content of Sb, Pb, and Sr in the zinc-based coating 20 is preferably 0.50% by mass or less, each independently. The content of Sb, Pb, and Sr is preferably 0.20% by mass or less, each independently.

[0120] ◇Element Group C

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

[0122] [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

[0123] [Cu: ≥0.25% by mass]

[0124] [Ti: 0% by mass and less than 0.25% by mass]

[0125] [Cr: ≥0.25% by mass]

[0126] [Nb: ≥0.25% by mass]

[0127] [Ni: ≥0.25% by mass]

[0128] [Mn: ≥0% by mass and <0.25% by mass]

[0129] [Co: ≥0.25% by mass]

[0130] [V: 0% by mass and less than 0.25% by mass]

[0131] In another embodiment of the zinc-based coating 20, it is also possible to exclude Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, thus the lower limit of the content of these elements is 0% by mass. On the other hand, if the zinc-based coating 20 contains at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, these elements are introduced into the Fe-Al metallographic structure formed by welding when the coated steel is welded, which can further improve the corrosion resistance of the formed weld. This improvement in the corrosion resistance of the weld is evident when the content of at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based coating 20 is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V, the content of each of these elements is preferably set to 0.05% by mass or more independently.

[0132] On the other hand, when a zinc-based coating 20 is formed in which the content of any one of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is 0.25% by mass or more, these elements form various intermetallic compounds in the plating bath used to form the zinc-based coating 20, leading to an increase in the viscosity of the plating bath, which may prevent the production of coated steel with good plating properties. Therefore, the content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V in the zinc-based coating 20 is preferably each independently set to less than 0.25% by mass. The content of Cu, Ti, Cr, Nb, Ni, Mn, Co, and V is preferably each independently set to 0.20% by mass or less.

[0133] ◇Element Group D

[0134] In another embodiment of the zinc-based coating 20, the element group D that may be contained in the zinc-based coating 20 will be described. At least one element in element group D shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0135] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%.

[0136] [Sn: 0% or more by mass and less than 20.00% by mass]

[0137] [Bi: 0% by mass and less than 5.00% by mass]

[0138] [In: 0% by mass and less than 2.00% by mass]

[0139] In another embodiment of the zinc-based coating 20, it is also possible to exclude Sn, Bi, and In, thus the lower limit of the content of these elements is 0% by mass. On the other hand, Sn, Bi, and In form intermetallic compounds with Mg in the zinc-based coating 20, which can improve the weldability of the zinc-based coating 20. In addition, these intermetallic compounds have high melting points, so they do not evaporate after welding when welding coated steel, and remain as intermetallic compounds. By having these elements present, corrosion resistance and corrosion protection can be improved, as well as the corrosion resistance of the welded part during welding. This improvement in corrosion resistance is evident when the content of at least any one of Sn, Bi, and In in the zinc-based coating 20 is 0.05% by mass or more. Therefore, when the zinc-based coating 20 contains at least any one of Sn, Bi, and In, the content of each of these elements is preferably set to 0.05% by mass or more independently.

[0140] On the other hand, excessive Sn addition increases the amount of intermetallic compounds formed, which may reduce the corrosion resistance of the zinc-based coating 20 after welding. Furthermore, excessive Bi and In addition may make the zinc-based coating 20 brittle and prone to peeling, and may also reduce its corrosion resistance after welding. These phenomena become significant when the Sn content exceeds 20.00% by mass, when the Bi content is 5.00% by mass or more, or when the In content is 2.00% by mass or more. Therefore, the Sn content is preferably 20.00% by mass or less, the Bi content is preferably less than 5.00% by mass, and the In content is preferably less than 2.00% by mass. The Sn content is more preferably 10.00% by mass or less, the Bi content is more preferably 3.00% by mass or less, and the In content is more preferably 1.00% by mass or less.

[0141] ◇Element Group E

[0142] In another embodiment of the zinc-based coating 20, the element group E that may be contained in the zinc-based coating 20 will be described. At least one element in element group E shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0143] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0144] [Ca: ≥0% by mass and ≤3.00% by mass]

[0145] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where it does not contain Ca, and therefore the lower limit of its content is 0% by mass. On the other hand, if Ca is contained in the plating bath used to manufacture the zinc-based coating 20, it is possible to reduce the dross generated during the plating operation as the Mg concentration increases, thereby improving the plating operability.

[0146] Furthermore, if the zinc-based coating 20 contains Ca, it forms intermetallic compounds with Al and Zn. Moreover, if the zinc-based coating 20 contains Si along with Ca, Ca forms intermetallic compounds with Si. These intermetallic compounds have high melting points and stable structures, thus suppressing liquid metal embrittlement (LME) during welding of plated steel. When the zinc-based coating 20 contains Ca, setting the Ca content to 0.01% by mass or more demonstrates both improved coating operability and suppression of LME during welding. More preferably, the Ca content in the zinc-based coating 20 is 0.05% by mass or more.

[0147] On the other hand, if the Ca content in the zinc-based coating 20 exceeds 3.00% by mass, the corrosion resistance of the coated steel may decrease. From this point of view, the Ca content in the zinc-based coating 20 is preferably 3.00% by mass or less. The Ca content in the zinc-based coating 20 is preferably 2.00% by mass or less, and more preferably 1.00% by mass or less.

[0148] [La: 0% by mass and less than 0.50% by mass]

[0149] [Ce: 0% by mass and less than 0.50% by mass]

[0150] [Y: 0% or more by mass and less than 0.50% by mass]

[0151] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where La, Ce, and Y are not present, and therefore the lower limit of the content of these elements is 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit approximately the same effect as Ca. This is because the atomic radii of each element are close to the atomic radius of Ca, and if these elements are present in the zinc-based coating 20, they will displace Ca.

[0152] The improved plating operability and LME suppression during welding are achieved by independently setting the content of each of these elements to 0.01% by mass or more. Therefore, when at least one of La, Ce, and Y is contained, the content of each of these elements is preferably set to 0.01% by mass or more. The content of La, Ce, and Y in the zinc-based coating 20 is more preferably 0.05% by mass or more.

[0153] On the other hand, if the content of La, Ce, and Y in the plating bath used to manufacture the zinc-based coating 20 is too high, the viscosity of the plating bath increases beyond what is necessary, and the plating operability may decrease. Therefore, from the viewpoint of plating operability, the content of La, Ce, and Y in the plating bath is adjusted. The content of La, Ce, and Y is preferably each independently less than 0.50% by mass, less than 0.50% by mass, and less than 0.50% by mass. The content of La, Ce, and Y is preferably each independently less than 0.10% by mass.

[0154] ◇Element group F

[0155] In another embodiment of the zinc-based coating 20, the element group F that may be contained in the zinc-based coating 20 will be described. At least one element in the element group F shown below is an element contained in the zinc-based coating 20 that can replace a portion of the balance Zn.

[0156] [Element group F]: B: less than 0.50%

[0157] [B: 0% by mass or more and less than 0.50% by mass]

[0158] In another embodiment of the zinc-based coating 20, it is also possible to consider a case where no B is present, and therefore the lower limit of its content is 0% by mass. On the other hand, if the zinc-based coating 20 contains B, it has a further effect of suppressing LME. This is presumably because if the zinc-based coating 20 contains B, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. In addition, it is believed that by having B in the zinc-based coating 20, B diffuses from the zinc-based coating 20 to the steel 10, and through grain boundary strengthening, it has a further effect of suppressing LME of the steel 10. Furthermore, the various intermetallic compounds formed by B have extremely high melting points, so it is presumably also effective in suppressing Zn evaporation during welding. These improved effects are manifested by containing 0.05% by mass or more of B. Therefore, in the case where B is present, the content of B is preferably 0.05% by mass or more.

[0159] On the other hand, if the plating bath contains excessive amounts of B in order to include B in the zinc-based coating 20, it will cause a sharp increase in the plating melting point, reducing the plating operability and potentially making it impossible to produce coated steel with excellent plating properties. This reduction in plating operability becomes significant when the B content is 0.50% by mass or more, therefore the B content is preferably less than 0.50% by mass. The B content is more preferably 0.10% by mass or less.

[0160] Methods for measuring chemical composition

[0161] The chemical composition of the aforementioned zinc-based coating 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). It should be noted that ICP-AES is used for analysis of chemical composition down to 0.1% by mass, while ICP-MS is used for analysis of trace amounts of chemical composition less than 0.1% by mass. The coated steel is immersed in a 10% HCl aqueous solution containing an inhibitor for approximately 1 minute, and the zinc-based coating is peeled off to prepare a solution containing the dissolved zinc-based coating. Analysis of the obtained solution using ICP-AES or ICP-MS yields the overall average chemical composition of the zinc-based coating.

[0162] Regarding the adhesion amount of zinc-based coating 20

[0163] The zinc coating 20 described above preferably has an average adhesion amount of 10.0 g / m² on each side of the steel. 2 The above, more preferably 50.0 g / m 2 That's all. Furthermore, the amount of zinc-based coating 20 applied is preferably 200.0 g / m² on average per side of the steel. 2 The preferred value is 150.0 g / m³. 2 Therefore, by ensuring that the amount of zinc-based plating 20 adheres within the range described above, the surface-treated component 1 of this embodiment can exhibit sufficient corrosion resistance.

[0164] It should be noted that, regarding the adhesion amount of the zinc-based coating 20, a 30mm × 30mm sample was cut from the surface treatment component 1, and its mass was measured beforehand. Adhesive tape was applied to one side of the sample to seal it, preventing the zinc-based coating on that side from dissolving in the next process. Then, the sample was immersed in a 10% HCl aqueous solution containing an inhibitor to pickle and peel off the zinc-based coating, and the mass of the sample after pickling was measured. Based on the change in sample mass before and after pickling, the average adhesion amount of the zinc-based coating 20 on each side can be determined.

[0165] Regarding the exposed steel substrate 201 in zinc-based coating 20

[0166] Next, the exposed steel substrate 201, which exists in at least a portion of the zinc-based coating 20 in this embodiment, will be described in detail.

[0167] Figure 4 Indicatively representing that Figure 2 The surface-treated component 1 shown is cut along the BB cutting line in the Z-axis direction. Figure 4 The cross-sectional view shown corresponds to the view obtained by cutting the portion of the surface treatment component 1 in this embodiment where the exposed steel substrate 201 exists along the thickness direction of the zinc-plated steel material that serves as the blank of the surface treatment component 1.

[0168] like Figure 4 As illustrated schematically, the portion of the surface-treated member 1 in this embodiment where the exposed steel substrate 201 exists is composed of surface-treated steel (i.e., zinc-plated steel) having a steel 10 as a base material and a zinc-based coating 20 located on the surface of the steel 10. Furthermore, at least a portion of the zinc-based coating 20 exposes the surface of the steel 10 (i.e., the steel substrate).

[0169] As briefly mentioned earlier, in this embodiment, the surface treatment component 1 intentionally includes a steel substrate exposed portion 201 in a specific proportion on a portion of the zinc-based coating 20. Therefore, when the portion of the surface treatment component 1 with the exposed steel substrate 201 is buried in soil, even in the surface layer, corrosion products of a dense state, as previously described, can form on the surface of the zinc-based coating 20. Thus, the surface treatment component 1 of this embodiment exhibits excellent corrosion resistance even in soil at a depth of approximately several centimeters from the soil surface.

[0170] ◇Method for determining the location of the exposed steel substrate 201

[0171] The following section will first explain the method for determining the location of the exposed steel substrate 201 in the zinc-based coating 20.

[0172] In this embodiment, the exposed steel substrate portion 201 in the zinc-based coating 20 is a location where the steel substrate is exposed due to a deficiency in the zinc-based coating 20. Therefore, its location can be determined by performing various color development tests on the entire surface of the zinc-based coating 20 to cause a color development reaction in the exposed steel substrate portion.

[0173] Such colorimetric tests are not particularly limited, and various colorimetric tests can be applied. For example, the ferroxyl test specified in JIS H 8626 (1995) is preferred, or the pinhole test disclosed in non-patent literature (Shozo Matsuda, Tadashi Tanaka, Keiichi Tanikawa, "A New Pinhole Test Method for Galvanized Steel Sheets", Metal Surface Technology, Vol. 23 (1972), pp. 142-146). In the above two colorimetric tests, after the reagent used for the colorimetric reaction is applied to the surface of the test object and a colorimetric reaction occurs, the surface of the test object is covered with test paper, and the area where the colorimetric reaction occurs is transferred to the test paper. Therefore, by using these colorimetric tests, the location of the exposed portion 201 of the steel substrate can be determined without depending on the shape of the surface-treated component 1.

[0174] Regarding the various reagents used in the colorimetric test, the test paper used for transferring the colorimetric site, and the steps of the colorimetric test, as long as they comply with the provisions in the literature that discloses each test method, they are acceptable.

[0175] ◇Regarding the state of the exposed steel substrate 201

[0176] Next, the state of the steel substrate exposed portion 201 in the zinc-based coating 20 of this embodiment will be described.

[0177] In the surface-treated component 1 of this embodiment, the presence state of the exposed steel substrate 201 in the zinc-based coating 20 is determined by observing the cross-section of the zinc-based coating 20. More specifically, it is determined from above (e.g., from...) Figure 2 The shape of the exposed steel substrate 201 when viewed from above (Z-axis direction) in relation to the zinc-based coating 20 is determined by observing the cross-section obtained by cutting the exposed steel substrate 201 along the thickness direction of the steel 10 using a microscope. The microscope used is not particularly limited as long as it provides sufficient magnification for cross-sectional observation. The microscope used for observation can be an optical microscope or an electron microscope such as a SEM.

[0178] The following is for reference Figures 5-7 The more specific steps will be explained. Figures 5-7 This is an explanatory diagram illustrating the steel substrate exposure rate in the surface-treated component of this embodiment.

[0179] When confirming the presence of the exposed steel substrate 201, such as Figure 5As shown in the upper left, firstly, a colorimetric test as described above is performed on the entire surface of the zinc-based coating 20 to determine the location of the exposed steel substrate 201. Then, as... Figure 5 As shown in the lower left, from above the zinc coating 20 ( Figure 2 Viewed from above along the Z-axis, each of the defined exposed steel substrate portions 201 is virtually divided. In this division, the shorter side b is 5 mm in size and its area (the area obtained by multiplying the longer side a by the shorter side b) is 1 cm². 2 The rectangular area is used as the unit for division.

[0180] Next, for each virtually divided region (a rectangular region), the area proportion occupied by the exposed steel substrate 201 in that region is calculated. For all regions, the proportion of the exposed steel substrate 201 in each region (area 1 cm²) is determined. 2 Does the area occupied by ) account for more than 3%?

[0181] Next, areas where the area ratio of all exposed steel substrate 201 is 3% or more (rectangular areas) are set as follows: Figure 5 The object area observed in the cross-section shown in the lower right corner. For example... Figure 5 As schematically shown in the lower right corner, the surface-treated component 1 corresponding to the area of ​​interest is cut at intervals of Δ = 50 μm. Microscopic observation is performed on all obtained cross-sections, and the steel substrate exposure rate, described later, is calculated. It should be noted that regarding... Figure 5 The cutting direction shown in the lower right corner is used to obtain the cross-section. Refer to the following: Figure 7 Let me explain again.

[0182] Through microscopic observation as described above, it is possible to obtain, for example, information about each cross-section. Figure 6 The observation field of view is shown schematically. Here, in the microscopic observation described above, an optical microscope (e.g., Nikon ECLIPSE LV150, etc.) is used, and a magnification of about 100x is selected.

[0183] exist Figure 6 Within the field of view shown, the exposed steel substrate 201 located at the far left and the exposed steel substrate 201 located at the far right are identified. Based on this, as... Figure 6 As shown, the length between the starting point and the ending point is measured as the reference length L0, with the starting point being 100 μm from the left end of the exposed steel substrate 201 located on the far left and the ending point being 100 μm from the right end of the exposed steel substrate 201 located on the far right and the ending point being 100 μm from the right end of the exposed steel substrate 201 located on the far right and the ending point being the right end of the view.

[0184] In addition, Figure 6Within the observation field shown, the length of each exposed steel substrate 201 is measured. The sum of the exposed steel substrate lengths is calculated as ΣLi (i is an integer parameter representing the number of exposed steel substrates 201 within the observation field). Figure 6 In the example shown, there are three exposed steel substrates 201 in the field of view, ΣLi=L1+L2+L3.

[0185] Thus, after measuring L0 and ΣLi, the value obtained by (ΣLi / L0)×100 (unit: %) is used as the steel matrix exposure rate of the section of interest.

[0186] In the exposed steel substrate portion 201 of the surface-treated component 1 of this embodiment, at least one cross-section exists with a steel substrate exposure rate ranging from 1.0% to 40.0%. Because the exposed steel substrate portion 201 exists in this manner, corrosion products of a denser state than those in the atmosphere can be generated from this exposed portion. These corrosion products protect the steel substrate and the surrounding zinc-based coating, ensuring the corrosion resistance of the surface-treated component 1 even when the exposed steel substrate portion 201 of the surface-treated component 1 of this embodiment is buried in soil.

[0187] The more sections with a steel substrate exposure rate in the range of 1.0% to 40.0%, the better, with no specific upper limit specified. Furthermore, it is more preferable that the steel substrate exposure rate in all obtained sections is in the range of 1.0% to 40.0%.

[0188] Furthermore, from the viewpoint of corrosion resistance as described above, in the surface-treated member 1 of this embodiment, it is more preferable that there is at least one cross-section with a steel substrate exposure rate in the range of 5.0% to 40.0%. The more cross-sections with a steel substrate exposure rate in the range of 5.0% to 40.0%, the better, and there is no particular upper limit. Furthermore, it is more preferable that the steel substrate exposure rate in all obtained cross-sections is in the range of 5.0% to 40.0%.

[0189] Furthermore, in the surface-treated component 1 of this embodiment, in the cross-section where the steel substrate exposure rate calculated as described above is in the range of 1.0 to 40.0%, the shortest distance from any point on the exposed surface of the steel 10 to the zinc-based coating 20 is greater than 0 μm and less than 50.0 μm. For example, in Figure 6In the example shown, considering point A on the exposed surface of the steel 10, the shortest distance to the zinc coating 20 corresponds to the length Ls in the figure. If this shortest distance exceeds 50.0 μm, it means the width of the exposed steel substrate 201 becomes excessive. In this case, when the exposed steel substrate 201 is buried in the soil, Zn cannot dissolve from the zinc coating 20 to the exposed steel substrate 201 in time, thus failing to ensure the corrosion resistance of the surface-treated component 1. Preferably, this shortest distance is greater than 0 μm and less than 40.0 μm, more preferably greater than 0 μm and less than 30.0 μm.

[0190] It should be noted that the various lengths in the field of view described above can be measured using the length measuring function of the microscope being used.

[0191] In the surface-treated member 1 of this embodiment, the total area of ​​the partitions with a steel substrate exposure rate in the range of 1.0% to 40.0% is preferably 5.0% or more of the area of ​​the portion buried in the soil. By making the total area of ​​the partitions 5.0% or more relative to the area of ​​the predetermined buried portion, the surface-treated member 1 of this embodiment exhibits superior corrosion resistance. More preferably, the total area of ​​the partitions with a steel substrate exposure rate in the range of 1.0% to 40.0% is 10.0% or more of the area of ​​the portion buried in the soil. It should be noted that the upper limit of the above ratio is not specifically defined and can be 100%.

[0192] Furthermore, when observing the cross-section of the exposed steel substrate 201 as described above, the total area of ​​the region providing a steel substrate exposure rate exceeding 40.0% (the total area when viewed from above) is less than 5% of the overall area of ​​the exposed steel substrate 201 of interest. If this total area ratio exceeds 5%, the zinc-based coating 20 peels excessively, the area exposing the steel substrate becomes too large, and the corrosion resistance of the surface-treated component 1 decreases. It should be noted that a smaller total area ratio is better, and 0% is most preferably preferred.

[0193] ◇Regarding the direction of the cutting line when calculating the steel matrix exposure rate

[0194] Here, refer to Figure 7 The direction of the cutting line when performing the cross-sectional observation as described above will be explained. In this embodiment, when determining the steel substrate exposure rate in the surface-treated member 1, the surface-treated member 1 is cut along the thickness direction of the steel 10 in order to obtain the cross-section as described above. At this time, the direction of the cutting line is determined based on the shape and / or distribution of the exposed steel substrate 201 when viewed from above in relation to the zinc-based coating 20.

[0195] Figure 7This diagram categorizes examples of the shape and / or distribution of the exposed steel substrate 201 when viewed macroscopically from above (Z-axis direction) the zinc-based coating 20. In the surface-treated component 1 of this embodiment, the shape and / or distribution of the exposed steel substrate 201 are broadly classified into... Figure 7 The previous section showed a set of directional cases, and Figure 7 The next section shows a set of cases with isotropic shapes, or cases where the shape and / or distribution are not directional.

[0196] exist Figure 7 In the group shown above, the exposed steel substrate 201 is roughly elliptical in shape and distributed in a manner that is roughly parallel to the direction of its respective major axis. Figure 7 The upper section (left end of the diagram) shows that the exposed steel substrate 201 is roughly rectangular in shape and distributed in a manner that is roughly parallel to each other along its long side. Figure 7 Like the diagrams at the top, center, and right, there exists a directional orientation. Figure 7 In the case of the upper section (the direction is up and down on the paper). In this case, in this embodiment, the direction orthogonal to the directional orientation is set as the direction of the cutting line.

[0197] in addition, Figure 7 The following section shows a distribution of exposed steel substrate 201 in a circular shape. Figure 7 (Lower section, left end of the figure), the random distribution of the exposed square-shaped steel substrate 201 ( Figure 7 The lower section, the central diagram), shows the distribution of zinc-based coating 20 in an island-like pattern. Figure 7 As shown in the lower right figure, the exposed steel substrate 201 may have an isotropic shape or a shape and / or distribution that is not directional. In such cases, the direction of the cutting line is not specifically defined in this embodiment, and any direction may be used as the direction of the cutting line.

[0198] ◇Relationship between steel substrate exposure rate and coating adhesion amount

[0199] The inventors, while manufacturing surface-treated components by varying the average coating thickness and steel substrate exposure rate of the zinc-based coating 20 on each side, buried the manufactured surface-treated components in soil to verify their corrosion resistance. Based on this, the horizontal axis is defined as the average coating thickness per side (unit: g / m²). 2On a coordinate plane where the vertical axis is defined as the upper limit of the measured value of the steel substrate exposure rate (unit: %), the distribution of the verification results of corrosion resistance is studied. The results show that the surface-treated component 1 of this embodiment exhibits superior corrosion resistance when both of the conditions shown in the following formulas (101) and (102) are met.

[0200] A≤0.8×10 -1 ×B+28.0…Equation (101)

[0201] A≤40.0…Equation (102)

[0202] Here, in equations (101) and (102) above, parameter A is the upper limit of the measured value of the steel substrate exposure rate (unit: %), and parameter B is the average adhesion amount per side of the zinc-based coating 20 (unit: g / m²). 2 The details of why equations (101) and (102) exhibit superior corrosion resistance when they are valid are not yet clear. However, the inventors speculate that the reason may be that the relationship between the extent of the exposed steel substrate and the amount of Zn leached from the zinc-based coating 20 that exactly matches that extent is appropriate.

[0203] In addition, the average adhesion amount of the zinc-based coating 20 on each side is 50.0~150.0 g / m². 2 Within the range, and both Equations (101) and (102) above are true, thereby the surface-treated component 1 of this embodiment exhibits even better corrosion resistance.

[0204] Above, refer to Figures 2-7 The surface treatment component 1 of this embodiment is described in detail.

[0205] The surface treatment member 1 of this embodiment, as described above, exhibits excellent corrosion resistance even in soil at a depth of several centimeters from the soil surface by changing the state of the zinc-based plating layer provided as the surface treatment layer according to the exposed corrosive environment. Here, there are no particular restrictions on the type of soil in which the surface treatment member 1 of this embodiment can be buried. However, it is presumed that the characteristics of the surface treatment member 1 of this embodiment will function more advantageously, for example, in soil that meets the following conditions.

[0206] For example, soils preferred for burial can include soils with a pH of around 3-12 where Fe leaching is easy, soils with a Cl ion concentration of 5 mg or more per 1 kg of soil, soils in saline-alkali areas, and soils where de-icing agents are frequently applied.

[0207] (A variation of the calculation method for steel substrate exposure rate)

[0208] In the above embodiments, a method for calculating the steel substrate exposure rate by microscopic observation of the cross-section of the zinc-based coating 20 was described. This method, by focusing on the cross-section, can determine the steel substrate exposure rate without depending on the shape of the surface-treated component 1 (e.g., whether it is a shape with more flat parts or more curved surfaces, etc.), and is therefore a preferred method.

[0209] The following is for reference Figure 8 A simplified explanation is provided of a method for calculating the steel substrate exposure rate by analyzing the surface of the zinc-based coating 20 using an EDX (Energy Dispersive X-ray Spectroscopy) analyzer installed on a SEM (e.g., JEOL JSM-7000F). This method differs from the previously described method of calculating the steel substrate exposure rate based on microscopic observation of a cross-section. The calculation method described below is particularly useful when the surface-treated component 1 has a shape consisting of gently curved flat sections or a planar shape, making it easy to view a portion of the zinc-based coating from above. In this case, the method described below can also be used instead of the previously described method of calculating the steel substrate exposure rate based on a cross-section.

[0210] Figure 8 This is an explanatory diagram illustrating a modified example of the steel substrate exposure rate in the surface-treated component of this embodiment. Here, a color development test is performed on the surface of the zinc-based plating 20, and the process continues until the exposed steel substrate 201 is virtually divided into rectangular units. Figure 5 Since they are the same, detailed explanations are omitted below.

[0211] In this modified example, the exposed steel substrate 201 in each virtually divided region is also included in the region (area 1 cm²). 2 Areas that account for more than 3% of the total area in the EDX analysis are considered as objects of the analysis.

[0212] In this modified example, the entire area to be analyzed is observed from the surface using SEM-EDX, and the distribution of elements Zn, Al, and Mg within this area is analyzed. The SEM-EDX observation conditions can be set, for example, to an accelerating voltage of 15 kV, an irradiation current of 0.005 nA, 10 scans, and a magnification of 500x. During this observation, mapping analysis can be performed on at least five elements: O, Zn, Al, Mg, and Fe, or on all elements.

[0213] Based on the obtained measurement results, a two-dimensional mapping was performed on the distribution of elements Zn, Al, and Mg. Within this distribution, areas where Zn content is below 1.0% by mass, Al content is below 1.0% by mass, and Mg content is below 0.5% by mass were designated as exposed areas of the steel matrix for further processing. Therefore, as... Figure 8 As schematically shown in the lower right figure, the specific shape and / or distribution of the exposed steel substrate within each zone can be determined. First, calculate the total area of ​​the exposed steel substrate thus obtained (in... Figure 8 In this example, the total area of ​​the exposed steel substrate in five locations is considered.

[0214] On the other hand, by connecting the outermost periphery of the determined exposed steel substrate, as shown in the figure... Figure 8 The bottom right figure shows the shape formed by connecting the outermost perimeter. The shape is determined by connecting points 100 μm further out from this outermost perimeter. The area of ​​this shape, formed by connecting points 100 μm further out from the outermost perimeter, is used as the reference area for calculating the steel substrate exposure rate.

[0215] Based on this, the value (in %) expressed as (total area of ​​exposed steel substrate / area used as the benchmark) × 100 can be used as the steel substrate exposure rate.

[0216] It should be noted that in this modified example, the result of connecting the outermost periphery is that its shape covers 1cm. 2 In the case of the entire region, the area of ​​the unit partition (1cm²) is considered. 2 This area serves as the reference area. Furthermore, the reference area reaches 0.3 cm². 2 The above partitions are used to calculate the steel substrate exposure rate.

[0217] The above provides a brief explanation of a variation of the calculation method for the steel substrate exposure rate.

[0218] (Regarding the manufacturing method of surface-treated components)

[0219] Hereinafter, an example of the manufacturing method of the surface treatment component 1 of this embodiment will be described.

[0220] <Manufacturing Method of Surface-Treated Steel as Raw Material>

[0221] The surface-treated steel used as the blank for the surface-treated component 1 in this embodiment is manufactured by forming a zinc-based coating on the surface of the steel 10 as described above, using the steel 10 as the base material.

[0222] In the formation of zinc-based coatings, in addition to hot-dip galvanizing, spraying, cold spraying, sputtering, vapor deposition, and electroplating can also be used. However, hot-dip galvanizing is the most cost-effective method.

[0223] Then, by performing the specific processing described below on the desired location (more specifically, the part where the exposed steel substrate is formed) of the obtained coated steel (steel 10 with a zinc-based coating), the exposed steel substrate is formed in the zinc-based coating. Thus, it is possible to manufacture a surface-treated steel blank as the surface-treated component 1 of this embodiment.

[0224] Hereinafter, an example of a manufacturing method for obtaining the surface-treated steel of this embodiment using hot-dip galvanizing will be described in detail.

[0225] In the manufacturing process of this surface-treated steel, firstly, a steel plate, which is used as a base material, is rolled to the desired thickness using the Sendzimir method, then coiled and placed on the hot-dip galvanizing production line.

[0226] In a hot-dip galvanizing production line, steel sheets are continuously passed through while being drawn from coils. At this time, the steel sheets are subjected to a reduction treatment at 800°C in an annealing device installed on the production line, for example, in an environment where oxidation is unlikely to occur (oxygen concentration below 20 ppm) and an atmosphere of N2-5% H2 gas. Afterward, the steel sheets are air-cooled with N2 gas to approximately +20°C the temperature of the subsequent plating bath, and then immersed in the plating bath.

[0227] Here, in the plating bath, a plating alloy having the chemical composition described above is prepared in advance in a molten state. The bath temperature is set in advance above the melting point of the plating alloy (for example, around 460~660°C).

[0228] When preparing the material for the plating alloy, it is preferable to use a pure metal (purity of 99% or higher) as the alloying material. First, a predetermined amount of alloy metal is mixed in such a way that it becomes the composition of the coating as described above. The mixture is then completely melted in a high-frequency induction furnace and / or an electric arc furnace under vacuum or inactive gas purging conditions to form the alloy. Next, the alloy mixed with the predetermined composition (the composition of the coating described above) is dissolved in the atmosphere, and the resulting melt is used as the plating bath.

[0229] It should be noted that the above-described plating alloys are not restricted to using pure metals; existing Zn alloys, Mg alloys, and Al alloys can also be melted and used. In this case, as long as a specified composition alloy with few impurities is used, there will be no problem.

[0230] The steel sheet is immersed in the plating bath as described above, and then lifted at a specified speed. At this time, the amount of plating is controlled, for example, by using N2 wiping gas, to ensure that the formed zinc-based coating reaches the desired thickness. Here, except for the bath temperature, general plating operating conditions can be applied; no special equipment and / or conditions are required.

[0231] In addition, various heat treatments can be applied to the molten alloy coating on the steel plate as needed.

[0232] Then, the zinc-based coating is subjected to scratching or bending treatments at the desired locations on the manufactured surface-treated steel. As a result, the treated areas form exposed steel substrate portions 201.

[0233] For example, when forming the exposed steel substrate 201 through a scratching process, a blade with a tip width of 30 μm or less, a length of 50 μm or more, and sufficient hardness compared to the coated structure is used. The blade is pressed perpendicularly to the steel plate. Then, a certain amount of pressure is applied along the direction the blade penetrates the steel plate. By moving the blade linearly in this state, scratches are created on the surface of the zinc-based coating. The exposed steel substrate rate can be varied depending on the number of scratches per unit area. Furthermore, even without changing other manufacturing conditions, by using a blade with a wider tip as described above to create scratches, the shortest distance from any point of the exposed steel substrate to the zinc-based coating can be controlled to the desired condition by utilizing the blade deflection caused by pressure and the vibration of the blade caused by movement.

[0234] Here, as a method of applying pressure to the blade, consider adding a weight of 3 kg or 5 kg. This pressure is sufficient to scratch zinc-based coatings, but will hardly scratch steel. Furthermore, there is no particular limitation on the speed at which the blade moves. It should be noted that, in the case of the blade sliding against the steel, from the viewpoint of preventing the inability to form scratches, there are methods such as setting the blade movement speed to 50 cm / s or less.

[0235] Alternatively, for example, when forming the exposed steel substrate 201 by bending, a hydraulic bending machine consisting of a die and a press can be used. Here, the die consists, for example, a punch with a apex of an isosceles right triangle and a die with a recess having the same shape as the apex of the punch. The apex of the punch is not an acute angle but has a rounded corner with a radius R (unit: mm).

[0236] A desired coated steel sheet is placed between a punch and a die as described above, and the two dies are pressed together using a stamping press, thereby processing the zinc coating. At this time, by controlling the thickness t (unit: mm) of the coated steel sheet, the radius R (unit: mm) of the top of the punch, and the pressing speed V (unit: cm / s) of the stamping press, the steel substrate can be exposed at the desired position of the zinc coating.

[0237] At this point, the processing is controlled such that the ratio t / R of the plate thickness t to the radius R of the top part of the punch satisfies the relationship 0.6 ≤ t / R ≤ 4.0. By setting such processing conditions, a large elongation is applied to the zinc-based coating, causing coating cracks, which allows the steel substrate exposure rate to be within the desired range. Furthermore, the pressing speed V of the press, from the contact between the punch and the zinc-based coating until processing is completed, is set to 1 cm / s or less. By reducing the processing speed to its limit, the generation of large local cracks can be suppressed, and the size of the exposed steel substrate 201 can be controlled.

[0238] The above provides a detailed description of an example of the manufacturing method for surface-treated steel according to this embodiment.

[0239] <Manufacturing Method of Surface-Treated Components>

[0240] Using the surface-treated steel obtained as described above as a blank, the surface-treated component of this embodiment is manufactured. Here, when obtaining the component for manufacturing the surface-treated component from the surface-treated steel, various forming processes, and / or joining processes based on fastening components such as bolts and / or rivets, and / or welding processes, etc., can be utilized. By appropriately combining these processes, it is possible to manufacture a surface-treated component with a desired shape from the surface-treated steel.

[0241] The above provides a brief description of an example of the manufacturing method of the surface-treated component according to this embodiment.

[0242] It should be noted that the above description describes the case where strain-imposing treatment is applied to the surface-treated steel to form the exposed steel substrate 201. However, strain-imposing treatment may not be performed during the manufacturing stage of the surface-treated steel, but may be performed as part of the processing when manufacturing the surface-treated component from the surface-treated steel. Alternatively, the processing itself when manufacturing the surface-treated component from the surface-treated steel may be used as the strain-imposing treatment for forming the exposed steel substrate 201.

[0243] Example

[0244] Hereinafter, the surface treatment component of the present invention will be specifically described with reference to embodiments and comparative examples. It should be noted that the embodiments shown below are merely examples of the surface treatment component of the present invention, and the surface treatment component of the present invention is not limited to the examples described below.

[0245] In the test examples shown below, the base plates for plating shown in Table 1 (all manufactured by Nippon Steel Corporation) were cut into 100mm × 200mm pieces. Then, plating was carried out using an intermittent hot-dip galvanizing test apparatus manufactured by our company, and multiple plating steels with the coating composition shown in Table 2 were produced for each level.

[0246] [Table 1]

[0247]

[0248] [Table 2]

[0249]

[0250] The obtained coated steel is subjected to scratching or bending processing as described above on approximately the central part of the surface of the coating to form an exposed steel substrate, thus producing a surface-treated component.

[0251] In the scratching process, a cutting tool hard enough than the coating is used to create parallel, straight scratches. The desired steel substrate exposure rate is achieved by adjusting the maximum width of the cutting tool tip within a 50μm range and the spacing between the parallel scratches. It should be noted that the counterweight for applying pressure to the cutting tool is set to 3kg, and the cutting tool movement speed is set to 50cm / second. Through this scratching process, a surface treatment layer is formed approximately in the central portion of the surface of each component. Figure 7 The upper right figure shows the directional exposed steel substrate.

[0252] In addition, bending was performed using a hydraulic bending machine. During bending, the thickness t (mm) of the coated steel sheet, the radius R (mm) of the die tip, and the pressing speed V (cm / s) of the press were controlled to obtain the desired steel substrate exposure rate. Through this bending process, a shape resembling... Figure 7 The central diagram at the top shows the directional exposed steel substrate.

[0253] For surface-treated components obtained through the two processing methods described above, the exposed steel substrate, the shortest distance to the zinc coating, the total area of ​​cross-sections with exposed steel substrate in the range of 1.0% to 40.0%, and the total area of ​​cross-sections with exposed steel substrate exceeding 40.0% were measured according to the cross-sectional observation method described earlier. Here, the iron reagent test specified in JIS H8626 (1995) was performed as a colorimetric test. Furthermore, an ECLIPSE LV150 manufactured by Nikon Corporation was used as an optical microscope, with a magnification set to 100x.

[0254] The results for cases where scratching was performed are summarized in Tables 3-1 to 3-3 below, and the results for cases where bending was performed are summarized in Tables 4-1 to 4-3 below. It should be noted that in Tables 3-1 to 4-3 below, the "Coating Adhesion Amount" column indicates the average coating adhesion amount per side, and the "Steel Substrate Exposure Rate" column indicates the upper limit of the obtained steel substrate exposure rate. Furthermore, in Tables 3-1 to 4-3 below, the "Longest Distance Among Shortest Distances" column essentially represents the value obtained by measuring the shortest distance from the center of the exposed steel substrate to the zinc-based coating at the widest point of the exposed steel substrate.

[0255] The corrosion resistance of each surface-treated component was evaluated using the following two test methods.

[0256] (Test Method 1: Evaluation of Corrosion Resistance in Ordinary Soil)

[0257] The surface-treated component with adjusted steel substrate exposure, obtained as described above, was buried in soil to evaluate corrosion resistance. Silica sand with an average particle size of 300 μm was used as the soil. The cover thickness (distance from the zinc coating surface to the soil surface) was set to 20 mm. After burial, to simulate ordinary soil, ion-exchanged water containing 0.03% NaCl was added dropwise to adjust the moisture content to 100%. Then, the drying and wetting processes described below were repeated 20 times.

[0258] Drying process: Store at 30℃ for 7 days.

[0259] Humidification process: Add ion-exchanged water dropwise to adjust the moisture content to 100%.

[0260] The surface-treated components subjected to the above tests were pickled with hydrochloric acid to remove the coating and corrosion products. Then, the corrosion condition of the steel was investigated using a shape measuring machine (KEYENCE, VR-5000). The evaluation criteria are as follows. Scores A, B, and C were set as acceptable. The results are summarized in Table 2 below.

[0261] Rating A: No pits were formed in the steel.

[0262] B: The steel has formed pits with a depth of less than 10 μm.

[0263] C: The steel has formed pits with a depth of more than 10μm and less than 50μm.

[0264] D: The steel has formed pits with a depth of more than 50μm and less than 100μm.

[0265] E: The steel has formed pits with a depth of more than 100μm.

[0266] (Test Method 2: Evaluation of Corrosion Resistance in Acidic Soils)

[0267] The surface-treated component with adjusted steel substrate exposure, obtained as described above, was buried in soil to evaluate corrosion resistance. Silica sand with an average particle size of 100 μm was used as the soil. The covering thickness was set to 50 mm. After burial, to simulate acidic soil, an HCl aqueous solution prepared by adding HCl to ion-exchange water to adjust the pH to 4 was dripped into the soil to adjust the moisture content to 100%. Then, the drying and wetting processes described below were repeated 20 times.

[0268] Drying process: Store at 30℃ for 7 days.

[0269] Humidification process: Add ion-exchanged water dropwise to adjust the moisture content to 100%.

[0270] The surface-treated components subjected to the above tests were pickled with hydrochloric acid to remove the coating and corrosion products. Then, the corrosion condition of the steel was investigated using a shape measuring machine (KEYENCE, VR-5000). The evaluation criteria are as follows. Scores A, B, and C were set as acceptable. The results are summarized in Table 2 below.

[0271] Rating A: No pits were formed in the steel.

[0272] B: The steel has formed pits with a depth of less than 10 μm.

[0273] C: The steel has formed pits with a depth of more than 10μm and less than 50μm.

[0274] D: The steel has formed pits with a depth of more than 50μm and less than 100μm.

[0275] E: The steel has formed pits with a depth of more than 100μm.

[0276] [Table 3-1]

[0277]

[0278] [Table 3-2]

[0279]

[0280] [Table 3-3]

[0281]

[0282] [Table 4-1]

[0283]

[0284] [Table 4-2]

[0285]

[0286] [Table 4-3]

[0287]

[0288] As can be seen from Tables 3-1 to 4-3 above, the surface-treated components corresponding to the embodiments of the present invention exhibit excellent corrosion resistance even in soil. On the other hand, the surface-treated components corresponding to the comparative examples of the present invention cannot achieve sufficient corrosion resistance.

[0289] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to these examples. Various modifications and alterations will be readily apparent to anyone skilled in the art to which this invention pertains, within the scope of the technical concept set forth in the claims, and these are, of course, also understood to fall within the technical scope of this invention.

[0290] The embodiments disclosed herein are illustrative and not restrictive in all respects. The above embodiments can be omitted, substituted, or modified in various ways without departing from the appended claims, the technical scope and spirit of the invention as described below. For example, the constituent elements of the above embodiments can be arbitrarily combined without impairing their effects. Furthermore, based on such arbitrary combinations, the functions and effects of each constituent element involved in the combination can naturally be obtained, and according to the description herein, other functions and effects that can be understood by those skilled in the art can be obtained.

[0291] Furthermore, the effects described in this specification are merely illustrative or exemplary and not limiting. That is, the technology involved in this invention can achieve other effects, in addition to those described above, or in place of those described above, that are obvious to those skilled in the art based on the description herein.

[0292] It should be noted that the following configurations also fall within the technical scope of this invention. (1)

[0294] A surface-treated component is composed of surface-treated steel having steel as a base material and a zinc-based coating on the surface of the steel.

[0295] At least a portion of the zinc-based coating has a portion that exposes the surface of the steel, i.e., an exposed steel substrate.

[0296] When observing a cross-section obtained by cutting the exposed steel substrate along the thickness direction of the steel material using a microscope based on the shape of the exposed steel substrate when viewed from above, at least one cross-section exists in which the proportion of the steel surface exposed within the cross-section, i.e., the steel substrate exposure rate, is in the range of 1.0% to 40.0%.

[0297] In the aforementioned cross-sections where the exposed steel substrate ratio is in the range of 1.0% to 40.0%, the shortest distance from any point on the exposed surface of the steel to the zinc coating exceeds 0 μm and is less than 50.0 μm.

[0298] For each region of a section providing a steel substrate exposure rate of more than 40.0%, the sum of the areas of the region when viewed from above is less than 5.0% of the total area of ​​the exposed steel substrate. (2)

[0300] The surface treatment component according to (1) is used by burying at least a portion of the exposed portion of the steel substrate in the soil. (3)

[0302] According to the surface treatment component described in (2), wherein,

[0303] The exposed portion of the steel substrate was determined by performing a colorimetric test on the entire surface of the zinc-based coating, causing a colorimetric reaction in the exposed portion of the steel substrate.

[0304] When viewed from above the zinc-based coating, each exposed portion of the aforementioned steel substrate has a shorter side of 5 mm or more and an area of ​​1 cm². 2 The aforementioned exposed steel substrate is virtually divided into rectangular regions as units. For each region where the exposed steel substrate occupies 3% or more of the area within the rectangular region, the cross-section of that region is observed, thereby determining the steel substrate exposure rate.

[0305] The total area of ​​the above-mentioned partitions of the cross-section where the exposed steel substrate rate is in the range of 1.0 to 40.0% accounts for more than 5.0% of the area of ​​the part buried in the soil. (4)

[0307] The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%,

[0308] Al: ≥0.10% and <40.00%

[0309] Mg: ≥0.10% and <15.00%,

[0310] The balance consists of Zn and impurities. (5)

[0312] According to the surface-treated component described in (4), wherein the zinc-based coating contains, by mass%, %

[0313] Al: ≥0.10% and <40.00%

[0314] Mg: ≥0.10% and <15.00%

[0315] Zn: 60.00% or more of the coating. (6)

[0317] The surface-treated component according to any one of (1) to (3), wherein the zinc-based coating is a coating having the following chemical composition: containing, by mass%,

[0318] Al: ≥0.10% and <40.00%

[0319] Mg: ≥0.10% and <15.00%,

[0320] It also contains one or more elements selected from the following groups: A, B, C, D, E, and F, with the balance being Zn and impurities.

[0321] [Element Group A]: Select one or two elements from the group consisting of Si: less than 2.50% and Fe: less than 5.00%;

[0322] [Element Group B]: Select one or more elements from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%;

[0323] [Element Group C]: Selected from one or more elements in the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%.

[0324] [Element Group D]: Select one or more elements from the group consisting of Sn: less than 20.00%, Bi: less than 5.00%, and In: less than 2.00%;

[0325] [Element Group E]: Select one or more elements from the group consisting of Ca: less than 3.00%, La: less than 0.50%, Ce: less than 0.50%, and Y: less than 0.50%.

[0326] [Element group F]: B: less than 0.50%. (7)

[0328] The surface-treated component according to (6) contains the above-mentioned element group A. (8)

[0330] The surface-treated component according to (6) contains the above-mentioned element group B. (9)

[0332] The surface-treated component according to (6) contains the above-mentioned element group C. (10)

[0334] The surface-treated component according to (6) contains the above-mentioned element group D. (11)

[0336] The surface-treated component according to (6) contains the above-mentioned element group E. (12)

[0338] The surface-treated component according to (6) contains the above-mentioned element group F. (13)

[0340] The surface-treated component according to any one of (6) to (12), wherein the zinc-based coating contains at least [amount] by mass%.

[0341] Al: 4.0% or more but less than 25.0%

[0342] Mg: Coating with a content of 0.3% or more but less than 12.5%. (14)

[0344] According to any one of (1) to (13), the upper limit of the measured value of the exposed steel substrate is denoted as A [%], and the average adhesion amount of the zinc coating on each side is denoted as B [g / m]. 2 When ], both of the following equations (1) and (2) are satisfied.

[0345] A≤0.8×10 -1 ×B+28.0…Equation (1)

[0346] A≤40.0…Equation (2) (15)

[0348] The surface-treated component according to any one of (1) to (14), wherein the amount of the zinc-based coating is an average of 50.0 to 150.0 g / m² per surface. 2 . (16)

[0350] The surface-treated component according to any one of (1) to (15) wherein at least one cross section has an exposure rate of 5.0% to 40.0% of the steel substrate.

[0351] Explanation of reference numerals in the attached figures

[0352] 1 Surface-treated components

[0353] 10. Steel

[0354] 20 Zinc-based coating

[0355] 201 Exposed part of steel substrate

Claims

1. A surface treatment member composed of a surface treatment steel material having a steel material as a base material and a zinc-based plated layer on a surface of the steel material, a steel base exposed portion in which a portion of the zinc-based plated layer is exposed to a surface of the steel material, when a cross section obtained by cutting the steel base exposed portion along a thickness direction of the steel material with respect to a shape of the steel base exposed portion when the zinc-based plated layer is viewed from above is observed with a microscope, there are at least one or more cross sections in which a proportion of a portion in which a surface of the steel material is exposed within the cross section, that is, a steel base exposure ratio, is within a range of 1.0 to 40.0%, and in the cross section in which the steel base exposure ratio is within the range of 1.0 to 40.0%, a shortest distance from an arbitrary point on the surface of the steel material that is exposed to the zinc-based plated layer is more than 0 μm and is 50.0 μm or less, with respect to each region that provides the cross section in which the steel base exposure ratio exceeds 40.0%, a sum of areas when the region is viewed from above is 5.0% or less with respect to a total area of the steel base exposed portion.

2. The surface treatment member according to claim 1, which is used by burying at least a portion of the steel base exposed portion in soil.

3. The surface treatment member according to claim 2, wherein the steel base exposed portion is determined by performing a color development test that causes a portion of the steel base to be exposed to develop a color on an entire surface of the zinc-based plated layer, In a case where each of the steel base exposed portions is virtually divided as a unit by a region in an oblong shape having a size of 5 mm or more in a short side and an area of 1 cm 2 2 or more, for each of the divided regions in which the steel base exposed portion occupies 3% or more of the area of the region in the oblong shape, the cross section of the divided region is observed, and thus the steel base exposure rate is measured, a proportion of a total area of the region that provides the cross section in which the steel base exposure ratio is within the range of 1.0 to 40.0% with respect to an area of the portion that is buried in the soil is 5.0% or more.

4. The surface treatment member according to any one of claims 1 to 3, wherein the zinc-based plated layer is a plated layer containing, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and the balance being Zn and impurities.

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

6. The surface treatment member according to any one of claims 1 to 3, wherein the zinc-based plated layer is a plated layer containing, in mass %, Al: 0.10% or more and less than 40.00%, Mg: 0.10% or more and less than 15.00%, and further containing one or two or more selected from the group consisting of Element Group A, Element Group B, Element Group C, Element Group D, Element Group E, and Element Group F, and the balance being Zn and impurities, Element Group A: one or both selected from the group consisting of Si: 2.50% or less and Fe: 5.00% or less; Element Group B: one or two or more selected from the group consisting of Sb: less than 0.50%, Pb: less than 0.50%, and Sr: less than 0.50%; Element Group C: one or two or more selected from the group consisting of Cu: less than 0.25%, Ti: less than 0.25%, Cr: less than 0.25%, Nb: less than 0.25%, Ni: less than 0.25%, Mn: less than 0.25%, Co: less than 0.25%, and V: less than 0.25%; Element group D: 1 or 2 or more selected from the group consisting of Sn: 20.00% or less, Bi: less than 5.00%, and In: less than 2.00%; Element group E: 1 or 2 or more selected from the group consisting of Ca: 3.00% or less, La: less than 0.50%, Ce: less than 0.50%, and Y: 0.50% or less; Element group F: B: less than 0.50%.

7. The surface treatment member according to claim 6, which contains the element group A.

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

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

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

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

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

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

14. The surface treatment member according to any one of claims 1 to 3, wherein The upper limit of the measured value of the steel substrate exposure ratio is denoted as A [%], and the average adhering amount of the zinc-based plating layer per face is denoted as B [g / m 2 ] when the following formula (1) and formula (2) are both satisfied, A < 0.8 x 10 -1 + 28.0 Equation (1), A < 40.0 … Equation (2).

15. The surface treatment member according to any one of claims 1 to 3, wherein The zinc-based plating layer has an average adhesion amount of 50.0 to 150.0 g / m 2 .

16. The surface treatment member of claim 14, wherein, The zinc-based plating layer has an average adhesion amount of 50.0 to 150.0 g / m 2 .

17. The surface treatment member according to any one of claims 1 to 3, wherein There is at least one or more cross sections in which the steel base exposure rate is in the range of 5.0 to 40.0%.

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