Hot-dip plated steel material and method for producing hot-dip plated steel material

Abstract

This hot-dip plated steel material includes a steel material and a plating layer disposed on the surface of the steel material. The plating layer has a prescribed chemical composition. The thickness of the plating layer is 5.0 μm or greater. A region A and a region B are provided on the surface of the plating layer. A black oxide layer containing a Zn oxide is formed in the region B at a thickness of 0.02 μm or greater. Formulas (1) to (3) are satisfied, where PA is the mass concentration ratio (O / Zn) of O and Zn in the region A on the surface of the plating layer, and PB is the mass concentration ratio (O / Zn) of O and Zn in the region B on the surface of the plating layer. Formula (1): 0 < PA < 0.80. Formula (2): 0.80 ≤ PB. Formula (3): 0.40 ≤ PB − PA.

Description

Hot-dip plated steel product and method for manufacturing hot-dip plated steel product

[0001] This disclosure relates to a hot-dip galvanized steel material and a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2023-191957, filed on November 10, 2023, the contents of which are incorporated herein by reference.

[0002] Hot-dip galvanized steel is widely used in the building, civil engineering, and automotive industries, where it is processed in various ways to produce steel structures. For example, metallic-colored hot-dip galvanized steel is often seen in urban areas, used in guardrails, windbreak fences, distribution panels, and cable racks. Unlike standard galvanized steel, steel structures that form part of roads, railways, and cityscapes often require consideration for aesthetic appeal. For example, there is a growing need to add color and design to hot-dip galvanized steel, such as anti-glare coatings for safety in road and railway infrastructure, or black-based colors and logos for advertising and brand names in modern urban spaces. While painting is the most commonly used method, significant drawbacks include the need for periodic repairs due to deterioration and the cost proportional to the area of ​​application. While stainless steel and aluminum are sometimes used for durability, they are often difficult to adopt due to material costs and strength considerations.

[0003] One way to solve these problems is to apply markings to the plated metal itself without painting when the hot-dip plated steel product is shipped. For example, Patent Documents 1 and 2 are examples of hot-dip plated steel sheets that are imparted with designs by controlling the internal constituent phases of the plating layer, which is a metal film, and combining it with a resin-based coating. These prior art examples utilize differences in the metal constituent phases in the design-imparting plating layer to create designs with excellent distinctiveness. However, these examples leave room for improvement in terms of achieving clarity like reading and permanence due to corrosion of the plating layer.

[0004] Japanese Patent No. 7107474 Japanese Patent Application Publication No. 2021-85084

[0005] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a hot-dip plated steel material having a plated layer imparted with a design that is excellent in clarity and permanence, and a method for manufacturing the same.

[0006] In order to solve the above problems and develop a plated steel product with a design that is highly distinct and durable, the present inventors discovered that a pattern of a desired shape can be formed on the surface of the plated layer by forming a specific highly corrosion-resistant plated layer on the surface of the steel product, forming an oxide layer with a specific element composition on the surface of the plated layer, and then partially irradiating the oxide layer with a laser.

[0007] [1] A hot-dip galvanized steel material according to one embodiment of the present disclosure has a steel material and a coating layer disposed on a surface of the steel material, and the coating layer has an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.00%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, a total amount ΣX of Sn, Bi, and In: 0% or more and not more than 0.7%, Ca: 0% or more and not more than 0.60%, Y : 0% or more, 0.30% or less, La: 0% or more, 0.30% or less, Ce: 0% or more, 0.30% or less, Sr: 0% or more, 0.30% or less, Li: 0% or more, 0.30% or less, total amount of Ca, Y, La, Ce, Sr, and Li ΣYa: 0% or more, 0.60% or less, Cr: 0% or more, 1.00% or less, Ni: 0% or more, 1.00% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.00% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb ΣYb: 0% or more, 1.00% or less, B : 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, total amount of B and P ΣYc: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more, 0.25% or less, V: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Mn: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less; ...5.0% or less; a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less; a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less; a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less; a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less; a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and Ａ and the mass concentration ratio of O to Zn (O / Zn) in the region B on the surface of the plating layer is P Ｂ When P is set as above, the following formulas (1) to (3) are satisfied. Ａ <0.80 ... (1) 0.80≦P Ｂ... (2) 0.40≦P Ｂ -P Ａ ...(3) [2] The hot-dip plated steel material according to [1] may satisfy the following formula (4): 0.50≦P Ｂ -P Ａ ...(4) [3] In the hot-dip galvanized steel material according to [1] or [2], the Mg mass concentration in the region B on the surface of the coating layer may be 3.2 mass% or more. [4] In the hot-dip galvanized steel material according to any of [1] to [3], the difference (ZB-ZA) between the surface height ZA of the region A and the surface height ZB of the region B may be 0.1 μm or more and less than 5.0 μm. [5] In the hot-dip galvanized steel material according to any of [1] to [4], the coating layer may include a region C adjacent to the region A, and the mass concentration ratio of O to Zn (O / Zn) in the region C may be P Ｃ In this case, the following formulas (5) and (6) may be satisfied: 0<P Ａ <P Ｃ <0.80...(5) P Ｃ <0.40+P Ａ... (6) [6] In the hot-dip galvanized steel material described in [5], the arithmetic mean roughness Ra in μm of the surface of the region C may satisfy the following formula (7): Ra<2.0... (7) [7] In the hot-dip galvanized steel material described in any of [1] to [6], the surface of the coating layer may be provided with a pattern portion including the region A, and the pattern portion may have an intentional shape. [8] In the hot-dip galvanized steel material described in any of [1] to [6], the surface of the coating layer may be provided with a pattern portion including the region A, and the pattern portion may have a shape of one or a combination of two or more of a straight line portion, a curved line portion, a dot portion, a figure, a number, a symbol, a design, or a letter. [9] In the hot-dip galvanized steel material according to any one of [1] to [6], a pattern portion including the region A is provided on the surface of the coating layer, and the pattern portion may have an intentional shape consisting of one or a combination of two or more of straight line portions, curved line portions, dots, figures, numbers, symbols, designs, or letters.

[10] In the hot-dip galvanized steel material according to [7], the pattern portion may include the region A, the region B, and the region C existing between the region A and the region B.

[11] In the hot-dip galvanized steel material according to [8], the pattern portion may include the region A, the region B, and the region C existing between the region A and the region B.

[12] In the hot-dip galvanized steel material according to [9], the pattern portion may include the region A, the region B, and the region C existing between the region A and the region B.

[13] In the hot-dip plated steel material according to any one of [1] to

[12] , a non-patterned portion consisting of the region B may be provided on the surface of the plated layer.

[14] A method for producing a hot-dip galvanized steel material according to another aspect of the present disclosure is the method for producing a hot-dip galvanized steel material according to [1], wherein the average chemical composition is, in mass%, Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.00%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, the total amount of Sn, Bi, and In ΣX: 0% or more and not more than 0.7%, Ca: 0% or more and not more than 0.60%, Y : 0% or more, 0.30% or less, La: 0% or more, 0.30% or less, Ce: 0% or more, 0.30% or less, Sr: 0% or more, 0.30% or less, Li: 0% or more, 0.30% or less, total amount of Ca, Y, La, Ce, Sr, and Li ΣYa: 0% or more, 0.60% or less, Cr: 0% or more, 1.00% or less, Ni: 0% or more, 1.00% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.00% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb ΣYb: 0% or more, 1.00% or less, B : 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, total amount of B and P ΣYc: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more, 0.25% or less, V: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Mn: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W the total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W being 0% or more and 0.25% or less, Fe being 0% or more and 5.0% or less, and Zn being 40.0% or more and 86.0% or less; a heating step of heating the plated steel material obtained by the hot-dip plating step under conditions of a relative humidity of 90% or more and 100°C or more to form a black oxide layer on the surface of the plated layer; and a laser treatment step of irradiating a part of the surface of the plated layer after the heating step with a laser to set the mass concentration ratio of O to Zn (O / Zn) on the surface of the irradiated part to less than 0.80.

[15] In the method for producing a hot-dip galvanized steel material described in

[14] , the irradiated portion may have a shape that is one of a straight line portion, a curved line portion, a dot portion, a figure, a number, a symbol, a pattern, or a letter, or a combination of two or more of these.

[0008] According to the above aspects of the present disclosure, it is possible to provide a hot-dip galvanized steel material having a coating layer with a design that is highly distinct and durable, and a method for manufacturing the same. The present disclosure can provide a material that is inexpensive and has excellent aesthetic appeal, thereby contributing to industrial development.

[0009] Fig. 1 is a schematic plan view showing an example of a pattern portion formed on the surface of a plating layer of a hot-dip plated steel material. Fig. 2 is an enlarged schematic plan view of region M in Fig. 1. Fig. 3 is a schematic cross-sectional view corresponding to line N-N in Fig. 2. Fig. 4 is an enlarged schematic plan view showing regions A and B.

[0010] The present inventors have conducted extensive research into means for forming letters, designs, etc. on the plating layer of hot-dip plated steel material and improving the clarity and permanence of the letters, designs, etc.

[0011] In order to express a design in a specific area of ​​a metal surface, it is possible to create differences in color tone, gloss, reflectivity, etc. between the area showing the letters, design, etc. and the background area.

[0012] Of these, color has the greatest potential to clarify a design. While the surface of metal materials generally has a uniform color tone, with the exception of, for example, the color developed by the oxide coating of titanium and stainless steel, or aluminum after anodizing, alloys among metal materials can change their surface color tone by varying the chemical composition ratio. However, with hot-dip galvanized steel products with a Zn-Al-Mg plating layer, whose chemical composition is uniform, it is generally difficult to change the chemical composition of the plating layer partially during manufacturing, making it generally difficult to intentionally change the color tone in a specific region of the plating layer.

[0013] Regarding gloss, there is a problem with the durability of the design over the long-term use of metal materials. That is, as corrosion of the metal surface progresses with long-term use, the difference in gloss between the area showing the design and the background area decreases, and the design may become less noticeable. Furthermore, gloss is related to properties such as anti-glare properties, so it must be carefully controlled. Furthermore, like color tone, gloss is affected by the composition ratio of the alloy's chemical components, but for the same reasons as above, it is difficult to intentionally change the gloss in specific areas of a Zn-Al-Mg plating layer.

[0014] Reflectivity can be varied by controlling the surface roughness of the metal material. Therefore, even with Zn-Al-Mg-based plating layers, where partial control of chemical composition is difficult, it is possible to create designs by partially varying the reflectivity. In this case, a large difference in surface roughness is required to ensure the clarity of the design. Mechanical processing is generally considered as a means of partially controlling the surface roughness of a plating layer. However, mechanical processing of a plating layer may cause cracks in the plating layer, which may reduce corrosion resistance.

[0015] The present inventors have investigated the possibility of expressing a design by differences in color tone, i.e., color difference. To express a design by patterning the surface of a plating layer, it is thought that the design can be expressed on the surface of the plating layer by, for example, making the pattern portion of the design a light color tone (e.g., white) and the background portion a dark color tone (e.g., black). However, because the surface of the plating layer has a metallic luster, even if a light-colored pattern portion is partially provided, it is not easy to increase the color difference from the background portion, and the design is not sufficiently clear. To solve this problem, it was thought that it would be necessary to change the color tone of the surface of the plating layer.

[0016] The present inventors attempted to form an oxygen-deficient oxide layer on the surface of a Zn—Al—Mg-based plating layer to give the entire plating layer a dark color tone (black), and then to partially irradiate the oxide layer with a laser to form a partially light-colored (e.g., white) region.

[0017] Generally, the surface of a Zn-Al-Mg based plating layer contains oxides such as ZnO, Al, and ２ O ３ Oxides such as MgO are produced, but these are usually white or colorless and transparent. However, the oxide layer produced by heat treatment in an atmosphere with a low oxygen concentration may be black because it contains oxygen-deficient oxides. When such an oxygen-deficient oxide layer is uniformly formed on the surface of the plating layer to a thickness of 0.02 μm or more, the surface of the plating layer becomes uniformly black. By irradiating this oxide layer with a laser, the oxide layer is removed, revealing the original metallic luster of the plating layer. The inventors have discovered that this results in a large color difference between the laser-irradiated area and the remaining area, allowing for the development of a design with excellent clarity.

[0018] The design formed by shaping the laser irradiation area into a desired shape is expressed by the color difference between the color tone of the oxide layer on the surface of the plating layer and the color tone of the underlying plating layer. Generally, in zinc-based plated steel materials (steel materials with a zinc-based plating layer), corrosion progresses in the plating layer over time. As corrosion of the plating layer progresses, white rust occurs. White rust occurs not only in the plating layer but also in the black oxide layer, discoloring both to gray, which causes the clarity of the design to be lost. To improve the durability of the design, it is necessary to reduce the amount of white rust occurring in the plating layer.

[0019] In addition, the oxide layer on the plating surface can be removed by mechanical means such as grinding or polishing. However, when the black oxide layer on the plating surface is removed by mechanical means, the removal area is relatively large, making it difficult to obtain a fine pattern shape. Furthermore, when the black oxide layer is removed by mechanical means, the underlying plating layer may be scraped off, reducing the thickness of the plating layer. Therefore, corrosion is more likely to progress in the area where the black oxide layer has been removed. For these reasons, it has been found that laser irradiation is a preferable method for removing the black oxide layer.

[0020] Furthermore, the chemical composition of the plating layer from which the oxide layer has been removed is preferably such that a strong natural oxide film is formed after the oxide layer has been removed, thereby minimizing the occurrence of white rust. Therefore, it has been found that it is preferable to use a Zn-Al-Mg-based plating containing high concentrations of both Al and Mg.

[0021] Hereinafter, a hot-dip plated steel material according to an embodiment of the present disclosure will be described.

[0022] A hot-dip plated steel material according to an embodiment of the present disclosure has a steel material and a plating layer disposed on a surface of the steel material, and the plating layer has an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.00%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, a total amount ΣX of Sn, Bi, and In: 0% or more and not more than 0.7%, Ca: 0% or more and not more than 0.60%, Y : 0% or more, 0.30% or less, La: 0% or more, 0.30% or less, Ce: 0% or more, 0.30% or less, Sr: 0% or more, 0.30% or less, Li: 0% or more, 0.30% or less, Total amount of Ca, Y, La, Ce, Sr, and Li ΣYa: 0% 0.60% or less, Cr: 0% or more, 1.00% or less, Ni: 0% or more, 1.00% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.00% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less. Pb: 0% or more, 0.25% or less, total amount of Cr, Ni, Mo, Cu, Ag, Sb and Pb, ΣYb: 0% or more, 1.00% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, total amount of B and P, ΣYc: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more, 0.25% or less, V: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Mn: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less; Fe: 0% or more and 5.0% or less; Zn: 40.0% or more and 86.0% or less; the plating layer has a thickness of 5.0 μm or more; a region A and a region B are provided on the surface of the plating layer; a black oxide layer containing Zn oxide is formed in a thickness of 0.02 μm or more in the region B; and the mass concentration ratio of O to Zn (O / Zn) in the region A on the surface of the plating layer is P Ａ The mass concentration ratio of O to Zn (O / Zn) in region B on the surface of the plating layer is P Ｂ When P is 0<P, the hot-dip plated steel material satisfies the following formulas (1) to (3): Ａ <0.80 ... (1) 0.80≦P Ｂ ... (2) 0.40≦PＢ -P Ａ …(3)

[0023] Furthermore, the hot-dip plated steel material of this embodiment preferably satisfies the following formula (4): 0.50≦P Ｂ -P Ａ …(4)

[0024] In addition, in the hot-dip plated steel material of this embodiment, the Mg mass concentration in region B on the surface of the plated layer is preferably 3.2 mass % or more.

[0025] In addition, in the hot-dip plated steel material of this embodiment, the difference (ZB-ZA) between the surface height ZA of region A and the surface height ZB of region B is preferably 0.1 μm or more and less than 5.0 μm.

[0026] In addition, the hot-dip plated steel material of this embodiment includes a region C adjacent to the region A in the coating layer, and the mass concentration ratio of O to Zn (O / Zn) in the region C is set to P Ｃ When P is set as above, it is preferable that the following formulas (5) and (6) are satisfied: 0<P Ａ <P Ｃ <0.80...(5) P Ｃ <0.40+P Ａ …(6)

[0027] Furthermore, in the hot-dip plated steel material of this embodiment, it is preferable that the arithmetic mean roughness Ra, which is an index of the surface flatness of the region C, satisfies the following formula (7): Ra<2.0 (7)

[0028] In addition, the hot-dip plated steel material of this embodiment preferably has a pattern portion including region A on the surface of the coating layer, and the pattern portion has an intentional shape. In addition, the hot-dip plated steel material of this embodiment preferably has a pattern portion including region A on the surface of the coating layer, and the pattern portion has a shape that is one of straight lines, curved lines, dots, figures, numbers, symbols, designs, or letters, or a combination of two or more of these. In addition, the hot-dip plated steel material of this embodiment preferably has a pattern portion including region A on the surface of the coating layer, and the pattern portion has an intentional shape that is one of straight lines, curved lines, dots, figures, numbers, symbols, designs, or letters, or a combination of two or more of these. Here, the intentional shape refers to a region having a size of 1.0 mm × 1.0 mm or more when viewed from a direction perpendicular to the surface of the coating layer. As will be described later, the pattern portion is formed by laser irradiation, and in this case, the size of the pattern portion is at least 1.0 mm × 1.0 mm or more. Furthermore, the pattern portion of the hot-dip plated steel material of this embodiment preferably includes region A, region B, and region C located between region A and region B. Furthermore, a non-pattern portion consisting of region B is preferably provided on the surface of the plating layer of the hot-dip plated steel material of this embodiment.

[0029] In the following description, the "%" used to indicate the content (concentration) of each element in the chemical composition means "mass %." Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. However, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit.

[0030] The steel material to be plated will now be described. The steel material is, for example, mainly a steel plate, a steel wire rod, or a steel wire, but there is no particular limitation on its size. For example, the steel plate may be any steel plate that can be applied to a conventional hot-dip galvanizing process. Specifically, this applies to steel plates that can be applied to processes in which the steel is immersed in molten metal and solidified, such as continuous hot-dip galvanizing lines (CGLs). The steel plate size may be, for example, a plate thickness of 10 mm or less and a plate width of 2000 mm or less, but the steel plate size is not limited to these. The steel plate shape also includes checkered steel plates, which have macroscopic surface irregularities pre-formed. The steel wire rod or steel wire may also be any steel plate that can be applied to a conventional hot-dip galvanizing process. Furthermore, components manufactured by processing steel plates, and shaped steel such as angle iron and L-angles, are also included in the steel material.

[0031] The steel material is not particularly limited, and examples of applicable steel materials include general steel, pre-plated steel thinly plated with various metals, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high alloy steels (steels containing elements that strengthen corrosion resistance, such as Ni and Cr).

[0032] Furthermore, the manufacturing process of steel material includes common processes such as pig iron and steel making processes using a blast furnace or an electric furnace, a hot rolling process, a pickling process, a cold rolling process, and a heat treatment process, but the steel material of this embodiment may have undergone any of these processes, and the processing conditions for each process are not limited.

[0033] Next, the plating layer will be described. The plating layer according to this embodiment includes a Zn—Al—Mg alloy layer and a black oxide layer formed on a portion of the surface of the Zn—Al—Mg alloy layer (such as a region B, which will be described later). The reason why the plating layer excluding the oxide layer includes the Zn—Al—Mg alloy layer is that Zn—Al—Mg alloys have high corrosion resistance and are excellent in terms of durability of the design. The plating layer may further include an Al—Fe interface alloy layer.

[0034] In this embodiment, the thickness of the plating layer is defined as the sum of the thicknesses of the Zn—Al—Mg alloy layer without an oxide layer and the Al—Fe layer. This is because a certain thickness is required for the plating layer formed by the plating process in order to form a black oxide layer on the surface of the plating layer and then irradiate it with a laser to create a design. It is also necessary to ensure a certain level of corrosion resistance even in areas where no oxide layer is present. For these reasons, the thickness of the plating layer must be at least 5.0 μm. Meanwhile, the thickness of the plating layer formed on steel sheets, steel wire rods, or steel wires by a conventional hot-dip plating method is affected by the withdrawal speed of the steel from the plating bath and the wiping conditions, and the maximum thickness is often 100.0 μm or less. Therefore, the thickness of the plating layer on the hot-dip plated steel material of this embodiment may be, for example, 100.0 μm or less.

[0035] The Zn-Al-Mg alloy layer is made of a Zn-Al-Mg alloy. The Zn-Al-Mg alloy refers to a ternary alloy whose main elements are Zn, Al, and Mg, and which further contains optional elements. The total amount of elements other than Fe that make up the plating layer is 95% or more.

[0036] The Al--Fe interfacial alloy layer is an interfacial alloy layer between the steel material and the Zn--Al--Mg alloy layer, and is in contact with the surface of the steel material.

[0037] The thickness of the Al-Fe interfacial alloy layer is preferably 2.0 μm or less, may be 1.0 μm or less, or may be 0.7 μm or less, more preferably 0.5 μm or less, or may be 0.3 μm or less. The Al-Fe interfacial alloy layer is usually thinner than the thickness of the Zn-Al-Mg alloy layer, and accounts for 10% or less of the entire plating layer.

[0038] The plating layer may be composed of a black oxide layer and a Zn—Al—Mg alloy layer, or may have a laminated structure including a black oxide layer, a Zn—Al—Mg alloy layer, and an Al—Fe interfacial alloy layer. In the case of a laminated structure, the Zn—Al—Mg alloy layer is preferably present closer to the surface of the plating layer than the Al—Fe interfacial alloy layer, and serves as a layer that constitutes the surface of the plating layer in regions where no oxide layer is present. In regions where an oxide layer is present, the oxide layer serves as a layer that constitutes the surface of the plating layer.

[0039] The thickness of the plating layer is calculated based on the plating weight. The weight change when the plating layer is dissolved with acid is measured. There are no particular restrictions on the type of acid, as long as it can dissolve the plating layer. It is preferable to use an acid containing an inhibitor that suppresses corrosion of the base steel (steel material). If the area and weight are measured before and after dissolution, the plating weight (g / m ２ ) can be obtained. ２ The calculation of the coating weight can be performed not only when the steel material is a steel plate but also when the steel material is a steel wire material or a steel wire, and it is possible to calculate the coating weight from the weight of the dissolved coating layer based on the surface area (diameter x π x length) of the steel wire material or the steel wire. ３ ) to determine the thickness of the plating layer. The plating specific gravity can be determined by measuring the chemical composition of the plating layer and calculating it from the results of the chemical composition measurement. As described below, the chemical composition of the plating layer is measured by dissolving the plating layer in acid, and measuring the content of each element in the solution using ICP atomic emission spectroscopy or ICP-MS.

[0040] Next, the average chemical composition of the plating layer will be described. When the plating layer is composed of an oxide layer and a Zn—Al—Mg alloy layer, the average chemical composition of the entire plating layer is the average chemical composition of the oxide layer and the Zn—Al—Mg alloy layer. When the plating layer has a laminated structure of an Al—Fe interface alloy layer, a Zn—Al—Mg alloy layer, and an oxide layer, the average chemical composition is the average chemical composition of the oxide layer, the Al—Fe interface alloy layer, and the Zn—Al—Mg alloy layer. However, in the plating layer defined in the present disclosure, the thickness of the Al—Fe interface alloy layer is preferably small, 10% or less of the total thickness of the plating layer, and therefore the Fe content of the plating layer is often within 5%. Furthermore, because the oxide layer is thin compared to the plating layer, its effect on the average chemical composition is almost negligible. Therefore, the average chemical composition of the plating layer can be considered to be roughly the composition of the Zn—Al—Mg alloy layer. Furthermore, traces of the original plating material are unlikely to remain as chemical components of the plating layer. Therefore, the average chemical composition of the plating layer can be considered to be approximately equivalent to the components of the plating bath used in its production.

[0041] The average chemical composition of the plating layer according to this embodiment must be in a composition range that enhances corrosion resistance and allows the formation of a black oxide layer on the surface of the plating layer. That is, it is necessary to include Al: more than 10.0% and 40.0% or less, Mg: more than 4.0% and 15.0% or less, Si: 0% or more and 1.00% or less, a total amount ΣX of Sn, Bi, and In: 0% or more and 0.7% or less, a total amount ΣYa of Ca, Y, La, Ce, Sr, and Li: 0% or more and 0.60% or less, a total amount ΣYb of Cr, Ni, Mo, Cu, Ag, Sb, and Pb: 0% or more and 1.00% or less, a total amount ΣYc of B and P: 0% or more and 0.50% or less, a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, and Zn: 40.0% or more and 86.0% or less.

[0042] As mentioned above, the role of Al and Mg is in the composition of the material, which affects the permanence of the design.Al and Mg are also essential elements for forming oxygen-deficient oxides, and if these elements are in short supply, the black color will be lighter and a white oxide called ZnO (zincite) will be more likely to form.

[0043] The other elements are optional and, within the composition ranges disclosed in this disclosure, form new intermetallic compounds or substitution products of the main elements. If the composition of these elements is outside the above composition ranges, it may be difficult to form black oxide in the plating layer, resulting in poor clarity or a significant decrease in durability. It has been confirmed that, within the composition ranges disclosed in this disclosure, there is no abnormality in the formation of the black oxide layer.

[0044] The content (concentration) of each element will be specifically described below.

[0045] Al: More than 10.0% and 40.0% or less Al, together with Zn, is an element that mainly constitutes the plating layer. In Zn-Al-Mg-based plating, it mainly forms the Al phase in the plating layer. If the Al content is 10.0% or less, the corrosion resistance of the plating layer decreases and the hardness of the plating layer falls outside the appropriate range, which is undesirable. If the Al content is more than 40.0%, the Zn content decreases relatively, which is undesirable, resulting in a decrease in sacrificial corrosion protection. The Al content is preferably 15.0% or more or 19.0% or more. Furthermore, the Al content is preferably 35.0% or less or 30.0% or less.

[0046] Mg: More than 4.0% and 15.0% or less Mg, together with Al and Zn, is an element that mainly constitutes the plating layer. If Mg is insufficient, the sacrificial corrosion protection of the plating layer decreases, so m is set to more than 4.0%. If the Mg content exceeds 15.0%, the corrosion resistance of the plating layer deteriorates. Therefore, the Mg content is set to 15.0% or less. The Mg content is preferably 5.0% or more or 6.0% or more. Furthermore, the Mg content is preferably 8.0% or less or 7.0% or less.

[0047] The elements described below are all elements that can be added arbitrarily.

[0048] Si: 0% or more, 1.00% or less. Si may or may not be contained in the coating layer. However, when Si is contained in the coating layer, it forms intermetallic compounds in the coating layer. The coating composition in this embodiment has a high melting point, and therefore, the operating temperature during hot-dip coating is approximately 500°C. At such operating temperatures, when a steel material is immersed in a coating bath, Al and Zn undergo active interdiffusion with Fe to form Fe-based intermetallic compounds. However, Si suppresses this excessive reaction. Therefore, when Si is contained, if it is 0.01% or more, the Fe diffusion reaction is significantly suppressed, making it easier to control the formation of Fe-based intermetallic compounds contained in the coating layer. On the other hand, if the Si content is excessive, the effect saturates, so the Si content is set to 1.00% or less. The Si content is preferably 0.05% or more or 0.25% or more. Furthermore, the Si content is preferably 0.75% or less.

[0049] Element Group X Sn: 0% or more, 0.7% or less Bi: 0% or more, 0.3% or less In: 0% or more, 0.3% or less Total amount ΣX of Sn, Bi, and In: 0% or more, 0.7% or less Each element of element group X (Sn, Bi, In) can be optionally contained, so the content of each is set to 0% or more. When these elements are contained, the sacrificial corrosion protection effect is enhanced. Each element has an upper limit of its content, and even if a large amount is contained, the effect saturates. Therefore, the upper limit of these elements is set to 0.7% or less for Sn, and 0.3% or less for Bi and In, and the total amount ΣX is also limited to 0.7% or less.

[0050] Element Group Ya Ca: 0% or more, 0.60% or less Y: 0% or more, 0.30% or less La: 0% or more, 0.30% or less Ce: 0% or more, 0.30% or less Sr: 0% or more, 0.30% or less Li: 0% or more, 0.30% or less Total Amount ΣYa of Ca, Y, La, Ce, Sr, and Li: 0% or more, 0.60% or less These elements, together with Si, control the reaction rate of the coating layer and can also control Fe diffusion in the coating bath. Furthermore, the formation reaction of intermetallic compounds containing these elements between the base steel (steel material) and the interface alloy layer can ensure adhesion between the base steel and the Al-Fe alloy layer. To achieve this effect, the Ca content should be 0.03% or more. Preferably, it is 0.10% or more. However, excessive Ca forms various floating dross in the coating bath, increasing coating defects, and extremely increasing the viscosity of the coating bath, reducing the amount of molten metal adhering to the steel material when it is pulled out of the coating bath, resulting in an extremely thin coating layer and poor corrosion resistance. Furthermore, the hardness of the coating layer becomes excessively high. Therefore, the upper limit of Ca is set to 0.60%.

[0051] Each element in the element group Ya other than Ca can be added as a substitute for Ca because it has effects similar to those of Ca. However, they cannot be added in amounts as large as Ca. That is, the content of each element in the element group Ya other than Ca is 0 to 0.30%, preferably 0.01 to 0.30%. The total amount ΣYa of the element group Ya including Ca is 0 to 0.60%.

[0052] Element group Yb Cr: 0% or more, 1.00% or less Ni: 0% or more, 1.00% or less Mo: 0% or more, 0.25% or less Cu: 0% or more, 1.00% or less Ag: 0% or more, 0.25% or less Sb: 0% or more, 0.25% or less Pb: 0% or more, 0.25% or less ΣYb of the total amount of element group Yb consisting of Cr, Ni, Mo, Cu, Ag, Sb, and Pb: 0% or more, 1.00% or less The elements in element group Yb can be optionally contained, so their respective contents are set to 0% or more. The elements in element group Yb have properties similar to Zn and can be contained in relatively large amounts. When these elements are contained within the above concentration ranges, they have the effect of improving corrosion resistance. This effect is apparent at a content of about 0.10%. However, if the total content of these elements becomes excessive, the effect saturates. Therefore, the Cr content is set to 0 to 1.00%, preferably 0.01 to 1.00%, the Ni and Cu contents are set to 0 to 1.00%, and the Mo, Ag, Sb, and Pb contents are set to 0 to 0.25%. The total amount ΣYb is set to 0% or more and 1.00% or less.

[0053] Element group Yc B: 0% or more, 0.50% or less P: 0% or more, 0.50% or less Total amount of B and P ΣYc: 0% or more, 0.50% or less The elements in the element group Yc can be contained arbitrarily, so the content of each is set to 0% or more. When these elements are contained within the above concentration ranges, they have the effect of improving corrosion resistance. This effect appears when their total content is about 0.05%. On the other hand, even if these elements are contained in large amounts, the effect saturates. Therefore, the content of each element in the element group Yc is set to 0 to 0.50%. The total amount ΣYc is set to 0% or more, 0.50% or less.

[0054] Element group Z Ti: 0% or more, 0.25% or less Co: 0% or more, 0.25% or less V: 0% or more, 0.25% or less Nb: 0% or more, 0.25% or less Mn: 0% or more, 0.25% or less Zr: 0% or more, 0.25% or less W: 0% or more, 0.25% or less Total amount ΣZ of element group Z of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more, 0.25% or less The elements included in element group Z are optional elements, so their respective contents are set to 0% or more. When elements of element group Z are included in the plating layer, corrosion resistance is improved. This effect is apparent when their total concentration is about 0.10%. However, even if these elements are included in large amounts, the effect saturates. Therefore, the content of each element in element group Z is set to 0-0.25%. The total amount ΣZ is set to 0% or more and 0.25% or less.

[0055] Fe: 0% or more, 5.0% or less The hot-dip plated steel material of this embodiment is produced by a hot-dip plating method, so Fe may diffuse from the base material to the plated layer during production. As described above, in this embodiment, the Al concentration of the plated layer is high, and an Al-Fe-based interfacial alloy layer may be formed, but its thickness is thin. As a result, the plated layer may contain up to 5.0% Fe, but as long as the Fe concentration is limited to 5.0% or less, there is no effect on the frequency of cracks in the plated layer, etc. Therefore, the Fe content is set to 0 to 5.0%. The Fe content may be greater than 0%.

[0056] Zn: 40.0% or more and 86.0% or less Since the hot-dip plated steel material of this embodiment is a highly versatile Zn-based plated steel material, the element constituting the main phase of the plated layer is Zn. If the Zn content is less than 40.0%, corrosion resistance will be insufficient, and if it exceeds 86.0%, the corrosion resistance-improving effect of other elements such as Al and Mg will not be obtained. Therefore, the Zn content is set to 40.0% or more and 86.0% or less.

[0057] The remainder other than the above may be impurities. That is, the above elements may be contained, and the remainder may consist of impurities. Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally added. For example, trace amounts of components other than Fe may be mixed into the plating layer as impurities due to mutual atomic diffusion between the steel material (base steel) and the plating bath.

[0058] The average chemical composition of the plating layer can be identified using the acid solution prepared when measuring the thickness of the plating layer. Specifically, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The resulting acid solution can then be analyzed using ICP atomic emission spectroscopy or ICP-MS to determine the chemical composition.

[0059] Next, regions A, B, and C on the surface of the plating layer will be described. The surface of the plating layer in this embodiment has at least regions A and B. Region A is a region where the black oxide layer on the surface of the plating layer has been removed, and region B is a region where the black oxide layer remains. Region A is formed by forming a black oxide layer on the surface of the plating layer and then partially removing the black oxide layer by laser irradiation. Region C is a region where the black oxide layer has not been completely removed despite being affected by the heat of the laser irradiation. Region C may be formed around region A. Region C is formed when the mass concentration ratio of O to Zn (O / Zn) is P Ｃ When the above equation is satisfied, the region A satisfies the formula (5) described below. Regions A and B can be easily distinguished by microscopic observation. For example, the surface of the plating layer can be observed at a magnification of 200 times using an optical microscope. Region C can also be visually recognized by microscopic observation, but the precise regions (the boundary between regions A and C, and the boundary between regions C and B) can be determined by measuring the mass concentration ratio on the plating surface as described below.

[0060] Furthermore, a patterned portion and a non-patterned portion are formed on the surface of the plating layer in this embodiment. The patterned portion is arranged on the surface of the plating layer so as to have a predetermined shape. More specifically, the patterned portion is one of straight lines, curved lines, dots, figures, numbers, symbols, patterns, and letters, or a combination of two or more of these. The non-patterned portion is an area other than the patterned portion. The shape of the patterned portion is acceptable even if it is partially missing, such as a missing dot, as long as it can be recognized as a whole. Furthermore, the non-patterned portion may have a shape that outlines the boundary of the patterned portion.

[0061] The patterned portion includes at least region A. The patterned portion may also include region B or region C. On the other hand, the non-patterned portion includes region B but does not include region A. In this way, when the patterned portion including region A and the non-patterned portion including region B are observed with the naked eye, a difference in brightness is observed between the two. Therefore, the boundary between the patterned portion and the non-patterned portion can be seen with the naked eye. The boundary between the patterned portion and the non-patterned portion may also be seen from a magnified image obtained with an optical microscope or a magnifying glass.

[0062] The pattern portion including region A is preferably formed to a size that allows the presence of the pattern portion to be discerned with the naked eye, under a magnifying glass, or under a microscope. The non-pattern portion constituting region B is an area that occupies the majority of the plating layer (surface of the hot-dip plating layer).

[0063] A patterned portion may be disposed within a non-patterned portion. In such cases, the patterned portion including region A is disposed in a predetermined shape within the non-patterned portion constituting region B. Specifically, the patterned portion within the non-patterned portion is formed as one or a combination of two or more of the following: straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters. By adjusting the shape of the patterned portion, a shape of one or a combination of two or more of the following: straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters appears on the surface of the plating layer. For example, the surface of the plating layer may appear as a character string, a number string, a symbol, a mark, a line drawing, a design, or a combination thereof, consisting of the patterned portion. This shape is intentionally or artificially formed by the manufacturing method described below, and is not formed naturally.

[0064] Region A is a region where the surface of the Zn—Al—Mg alloy layer constituting the plating layer is exposed. Therefore, region A has the matte appearance of the plating layer (Zn—Al—Mg alloy layer) itself. The matte appearance is achieved by the mixture of minute white regions and minute metallic luster regions. Region A is formed by forming a black oxide layer on the surface of the plating layer, and then irradiating the black oxide layer with a laser to partially remove the black oxide layer and expose the plating layer (Zn—Al—Mg alloy layer).

[0065] On the other hand, in region B, a black oxide layer having a thickness of 0.02 μm or more is formed on the surface of the Zn-Al-Mg alloy layer that mainly constitutes the plating layer. The black oxide layer contains at least Zn oxide. Part or all of the Zn oxide is oxygen-deficient Zn oxide. Therefore, the oxide layer exhibits a black color. Furthermore, this black oxide layer may contain oxides of one or both of Al and Mg in addition to Zn oxide. Furthermore, the black oxide layer may contain hydroxides of one or more of Zn, Al, and Mg. As described below, this oxide layer is formed by heating to 100° C. or higher in an atmosphere with a relative humidity of 90% or higher. As a result, oxygen-deficient Zn oxide is included.

[0066] The thickness of the black oxide layer is 0.02 μm or more. If the thickness of the oxide layer is less than 0.02 μm, the color tone of region B will be gray or the plated layer will have the inherent matte appearance, resulting in an appearance similar to that of the patterned portion including region A. For this reason, if the thickness of the oxide layer is less than 0.02 μm, it will be difficult to distinguish between the patterned portion and the non-patterned portion, reducing the visibility of the patterned portion, which is undesirable. There is no upper limit, but if the oxide layer is too thick, it will be difficult to remove and form a pattern, so the thickness of the black oxide layer is preferably 7.00 μm or less.

[0067] Region A is a region where the surface of the plating layer is exposed. Therefore, the amount of oxygen (O) is relatively small on the surface of region A. Therefore, the mass concentration ratio of O to Zn (O / Zn) in region A on the surface of the plating layer is defined as P Ａ In this case, P Ａ As shown in the following formula (1), P is in the range of more than 0 and less than 0.80. Ａ If the value is 0.80 or more, the color tone of the area A becomes close to the color tone of the area B, which is undesirable because it reduces the visibility of the pattern portion.

[0068] 0<P Ａ <0.80 ... (1)

[0069] In region A, as described above, a matte appearance is exhibited, but in order to enhance the clarity of the design, it is preferable for the metal color to be close to white. When the metal color is closer to white, the clarity of the design becomes more prominent. The metal color of the plating layer depends on the content of metal elements contained in the plating layer. In particular, when the Al concentration is high, the white color tends to become stronger, and furthermore, Al bonds with Zn to form an Al-Zn phase, thereby orienting the remaining Zn. In this state, P Ａ The smaller the value, the clearer the design. Ａ is more preferably 0.50 or less, and even more preferably 0.30 or less. In this case, the Al content in the average chemical composition of the plating layer is preferably 15.0 to 35.0 mass%, and more preferably 19 to 30 mass%.

[0070] On the other hand, in region B, a black oxide layer is present, and therefore the surface of region B contains a relatively large amount of oxygen (O). The mass concentration ratio of O to Zn (O / Zn) in region B on the surface of the plating layer is defined as P Ｂ In this case, P Ｂ As shown in the following formula (2), P is 0.80 or more, and preferably 0.90 or more. Ｂ If P is less than 0.80, the color tone of the region B becomes close to the color tone of the region A, and the visibility of the pattern portion decreases. Ｂ If P exceeds 1.40, the oxygen deficiency state is resolved, the oxide layer no longer exhibits black color, the color tone of region B becomes closer to the color tone of region A, and the visibility of the pattern portion may decrease. Ｂ is preferably 1.40 or less.

[0071] 0.80≦P Ｂ …(2)

[0072] P Ｂ In order to improve the durability of the design, it is advisable to include a certain amount of Mg in the plating layer. Preferably, the Mg content in the plating layer is 6.0 to 8.0 mass%. In order to further improve the durability of the design, it is preferable that the Mg mass concentration in region B is 3.2% or more. A concentration of 4.6% or more is more preferable as it further improves durability. To achieve this, the Mg content in the average chemical composition of the plating layer should be 6.0 to 7.0 mass%. In this case, MgZn is used as a constituent of the plating layer below the black oxide layer. ２ Although a certain amount of MgZn phase exists, ２ It is believed that the Mg phase improves the corrosion resistance of the surface of the plating layer after the black oxide layer is removed, thereby suppressing the occurrence of white rust and increasing the durability of the design. The Mg mass concentration in region B is determined by performing elemental analysis on the surface of region B using an energy dispersive elemental analyzer (EDS).

[0073] Furthermore, as shown in the following formula (3), P Ｂ and P in area A Ａ The difference between Ｂ -P Ａ ) must be 0.40 or more. Ｂ -PＡ When the ratio (P) is 0.40 or more, the amount of oxides present in region A is significantly less than the amount of oxides present in region B, and the difference in brightness between region A and region B becomes large, making it possible to distinguish the two with the naked eye. Ｂ -P Ａ If the ratio (P) is less than 0.40, it becomes impossible to distinguish between the area A and the area B with the naked eye. Ｂ -P Ａ ) is 0.50 or more, and more preferably 0.60 or more. By controlling the Al content and Mg content in the plating layer, the amount of Zn oxide formed can be controlled and removed when region A is formed, thereby making it possible to obtain an index that satisfies these requirements.

[0074] 0.40≦P Ｂ -P Ａ ... (3) 0.50≦P Ｂ -P Ａ …(4)

[0075] When a plating layer with a constant chemical composition is formed and an oxide layer of a constant thickness is also formed, the degree of blackness of the oxide layer depends on the chemical composition of the plating layer present underneath, and the color tone of the plating layer also depends on the chemical composition of the plating layer. In order to impart a design consisting of a pattern portion to the surface of the plating layer by forming a pattern portion including region A by laser irradiation, it is necessary to properly examine the Al content and Mg content of the plating layer, which are factors that determine the degree of blackness of the oxide layer in region B, as well as the range of the contents of other elements that can be added. In addition, after laser irradiation, the surface of the plating layer evaporates slightly, and a new surface that has reacted with the atmosphere (a new oxide film surface that has reacted with oxygen in the atmosphere) appears, so P Ａ , P Ｂ is a value specific to the metal composition.

[0076] Next, the region C will be described. The region C may be formed around the region A. The region C is formed when the mass concentration ratio of O to Zn (O / Zn) is P ＣWhen the black oxide layer is removed from the surface of the plating layer, the region A satisfies the following formula (5). As mentioned above, region A is formed by forming a black oxide layer on the surface of the plating layer and then partially removing the black oxide layer by laser irradiation. The region from which the black oxide layer has been removed is region A, and the region where the black oxide layer remains is region B. In this case, region C may be formed between region A and region B. Region C is a region where the black oxide layer has not been completely removed. Region C is thought to be a region that has been affected by heat during laser irradiation.

[0077] That is, P in area C Ｃ As shown in equation (5), Ａ Although the amount of oxygen is larger than that of P in region B, Ｂ The value is smaller than 0.80, which is the lower limit of the formula (6). In the present embodiment, it is preferable that region C satisfies formula (6). If the difference in oxygen content between region A and region C is less than 0.40, the difference in oxygen content between region C and the adjacent region A is reduced, and therefore it is possible to prevent the difference in corrosion resistance between region C and region A from widening. The presence of region C that satisfies formulas (5) and (6) reduces the difference in height between region A and region B, and it is possible to prevent a decrease in corrosion resistance in region A.

[0078] 0<P Ａ <P Ｃ <0.80...(5) P Ｃ <0.40+P Ａ …(6)

[0079] In addition, in this embodiment, the arithmetic mean roughness Ra in μm, which is an index of the flatness of the surface of region C, preferably satisfies Ra<2.0. In this embodiment, by forming the pattern portion by laser irradiation rather than mechanical grinding, Ra<2.0 can be achieved on the surface of region C. By having Ra of the surface of region C less than 2.0, local corrosion of the surface of region C can be prevented, and the design of the pattern portion can be maintained for a long period of time. On the other hand, when region A is formed by mechanically removing the black oxide layer, the Ra of region C usually exceeds 2.0.

[0080] Ra can be determined using a non-contact white light interference microscope. Specifically, for example, a white light interference microscope CONTOUR GT-I (manufactured by Bruker) is used to measure three arbitrary 150 × 150 mm visual fields including region C using vertical scanning low-coherence interferometry (CSI), and the Ra of region C in each visual field is calculated. The average value is defined as the Ra of region C in this embodiment.

[0081] The difference (ZB-ZA) between the surface height ZA of region A and the surface height ZB of region B is preferably 0.1 μm or more and less than 5.0 μm. In the plating layer according to this embodiment, the black oxide layer is formed and then removed by laser irradiation, so the surface height ZA of region A is lower than the surface height ZB of region B. If this difference (ZB-ZA) is too large, the thickness of the plating layer in region A may become thin, resulting in reduced corrosion resistance. Therefore, (ZB-ZA) is preferably less than 5.0 μm. (ZB-ZA) is more preferably less than 3.0 μm. On the other hand, if the surface height ZA of region A is close to the surface height ZB of region B, a large amount of the oxide layer may remain in region A, potentially reducing the clarity of the design. Therefore, (ZB-ZA) is preferably 0.1 μm or more. The measurement method for (ZB-ZA) is as follows. The region of the hot-dip plated steel material of interest where the pattern is formed is cut in the thickness direction of the hot-dip plated steel material (the direction perpendicular to the surface of the hot-dip plated steel material). This results in a cross-sectional sample of the Zn-Al-Mg-based plating layer and oxide layer. The obtained sample is then embedded in a room-temperature drying epoxy resin so that the cross-section in the thickness direction can be seen, and the cross-section is polished. Next, a field of view in which both region A and region B can be seen is selected from the cross-sectional sample, and observed using a scanning electron microscope (SEM, for example, JEOL JSM-7000F). The observation conditions may be, for example, an acceleration voltage of 15 kV, a probe current of 1.0 nA, a number of sweeps of 10, and an observation magnification of 5000x. The observed area is then imaged, and the ZB-ZA within the field of view is measured. More specifically, in measuring (ZB-ZA), first, a region where region A and region B can be observed within the same field of view is selected, and that region is observed at 1000x magnification using a scanning electron microscope. Next, the difference in height between the highest point on the surface of region B within the field of view and the lowest point on the surface of region A within the field of view is determined. Here, the "highest point" refers to the point on the plating surface that is furthest from the steel sheet surface toward the plating surface in region B within the field of view in the thickness direction of the plating, i.e., the direction perpendicular to the plating surface.Similarly, the "lowest point" refers to the point on the plating surface that is closest to the steel sheet surface in region A within the field of view in the thickness direction of the plating. Similar measurements are performed in 10 fields of view, and the average value of the height differences measured in each field of view is calculated. This average value is defined as the difference (ZB - ZA) between the surface height ZA of region A and the surface height ZB of region B in this embodiment.

[0082] The patterned portion includes region A, and the non-patterned portion includes region B. The patterned portion can be seen due to the difference in brightness between region A and region B. The patterned portion may also include region C in addition to region A, or may further include region B. When the patterned portion includes region A and region B, the difference in brightness between the patterned portion and the non-patterned portion becomes relatively small, but the inclusion of region A in the patterned portion makes it possible to see the patterned portion with the naked eye.

[0083] When the pattern portion includes regions A and B, the shape of the pattern portion can be exemplified by a shape in which a plurality of linear regions A are arranged substantially parallel to each other at intervals within the pattern portion, with regions B present between the linear regions A. Furthermore, when the pattern portion includes regions C, the regions C are disposed at the boundaries between the regions A and B. The width of each region A is preferably in the range of 10 to 250 μm, for example. Furthermore, the distance between the regions A, measured as the distance between the centers of the regions A in the width direction, is preferably in the range of 50 to 800 μm. When the regions A and B in the pattern portion have the above-described shapes, the pattern portion can be visually recognized with the naked eye.

[0084] An example of the patterned portion is shown in Figures 1 to 4. Figure 1 shows the Japanese hiragana character "me" appearing as a patterned portion on the surface of the plating layer. This hiragana character "me" is composed of area A, area B, and area C (not shown).

[0085] Fig. 2 shows an enlarged schematic plan view of region M surrounded by a dashed line in Fig. 1. Fig. 3 shows a schematic cross-sectional view taken along the line N-N in Fig. 2. As shown in Fig. 2, the pattern portion is configured by a plurality of regions A arranged substantially parallel to each other at predetermined intervals. For convenience, region C is omitted from Fig. 2. Therefore, in Fig. 2, the region other than region A is region B.

[0086] As shown in Fig. 3, the hot-dip plated steel material 1 of this embodiment has a steel material 2 and a coating layer 3 formed on the surface of the steel material. The coating layer 3 has a region A and a region B. In region A, the surface of the Zn-Al-Mg alloy layer 3A constituting the coating layer 3 is exposed. In region A, the outermost layer of the Zn-Al-Mg alloy layer 3A may be scraped off by laser irradiation. Meanwhile, in region B, a black oxide layer 4 is present on the Zn-Al-Mg alloy layer 3A in the coating layer 3.

[0087] 4 shows an enlarged plan view of region A. Region C is provided around region A. Region C is located at the boundary between region A and region B.

[0088] 2 to 4 include regions A, B, and C, but the pattern portion of this embodiment is not limited to this and may include regions A and B. Furthermore, the entire region of the pattern portion may be made up of region A, or the entire region of the pattern portion may be made up of region A and region C.

[0089] Next, P in areas A, B, and C Ａ and P Ｂ and P Ｃ The measurement method will be described. The measurement means is preferably an elemental analysis using an energy dispersive elemental analyzer (EDS) mounted on a scanning electron microscope. The measurement areas of region A and region B are 100 μm in each of region A and region B. ２ The measurement area of ​​area C is an area 3 μm away from the edge of area A identified in the SEM image, and an area of ​​10 μm×10 μm is analyzed by elemental analysis using EDS to determine P. Ａ , P ＢThe mass concentration is calculated in the same manner as above. In this embodiment, region A is a region where the Zn—Al—Mg alloy layer 3A is exposed. Therefore, the edge portion that is the boundary between region C, where the oxide layer 4 remains, and region A can be clearly distinguished in the SEM image. The measurement region is set to three arbitrarily separated locations, and the average value of the measured values ​​at the three locations is calculated. ZAF correction is used to calculate the mass concentration. The conditions are as follows: Acceleration voltage: 15 kV Beam diameter: 2 nm Measurement pitch: 0.1 nm Measurement start point: The position of the edge of region A in the observed image Measurement end point: The position 100 nm from the edge of region A in the observed image in a direction parallel to the plating layer surface By performing EDS analysis under the above conditions toward the surface of the plating layer, the mass concentrations of O and Zn are calculated in each of region A, region B, and region C, and from the results, the mass concentration ratio P Ａ = O / Zn, P Ｂ = O / Zn and P Ｃ = O / Zn.

[0090] Next, a method for measuring the thickness of the oxide layer will be described. The thickness of the oxide layer is measured by cutting the hot-dip plated steel to expose the cross section of the plating layer and mechanically polishing the cross section to a mirror finish. The measurement sample thus prepared is observed using a backscattered electron image with a scanning electron microscope, and the thickness of the black contrast layer present on the outermost surface of the plating layer is measured. Specifically, the region of the hot-dip plated steel of interest, where region B is formed, is cut in the thickness direction of the hot-dip plated steel (a direction perpendicular to the surface of the hot-dip plated steel) to obtain a cross-sectional sample of the oxide layer. The obtained sample is then embedded in a room-temperature drying epoxy resin so that the cross section in the thickness direction can be seen, and the cross section is polished. Next, an arbitrary location of the cross-sectional sample is observed using a scanning electron microscope (SEM, for example, JEOL JSM-7000F). The observation conditions may be, for example, an acceleration voltage of 15 kV, a probe current of 1.0 nA, 10 sweeps, and 5000x magnification. Images of the observed area are then taken, and the thickness of the oxide layer within the field of view is measured. Similarly, 10 fields of view randomly selected from within the sample are observed, and the oxide layer thicknesses measured in each field of view are averaged to obtain the average oxide layer thickness in this embodiment.

[0091] (Evaluation of Clarity) Next, a method for checking the clarity of a pattern portion will be described. Clarity is checked using a character recognition function of a computer that has been trained in character recognition and other machine learning. For example, a case will be described in which a laser irradiated portion of a predetermined shape is formed by irradiating a laser onto the surface of a plating layer on which a black oxide layer has been formed.

[0092] The laser-irradiated area is photographed from a vertical direction under the same conditions, including the specified distance and lighting distance and angle, and image analysis is used to apply mosaic processing to the pixels that make up the area encompassing the laser-irradiated area, resulting in a binarized judgment. Additionally, a black-and-white print of a pattern similar to the laser-irradiated area formed on the plating layer is made on paper as the printing medium. This is photographed under the same conditions as for the plated steel sheet, and image analysis is used to apply mosaic processing to the pixels that make up the area encompassing the pattern, resulting in a binarized judgment. When these two binarized judgment results are compared, the black-and-white match rate of the binarized judgment of the laser-irradiated area of ​​the plated steel sheet is measured against the pattern area on the paper, and the result is evaluated according to the following criteria: S, AA, A, and B are considered pass.

[0093] S: Black and white match rate is 98% or more and 100% or less. AA: Black and white match rate is 96% or more and less than 98%. A: Black and white match rate is 93% or more and less than 96%. B: Black and white match rate is 90% or more and less than 93%. C: Black and white match rate is less than 90%.

[0094] (Evaluation of Permanence) The permanence of a design is assessed based on the degree of deterioration in design clarity after corrosion. White rust is typically formed by corrosion of the plating layer. However, if the amount of white rust is large and it forms raindrops or accumulates on the plating surface, it becomes difficult to distinguish the design. Cyclic corrosion tests (CCT) are a test that provides a good correlation with domestic exposure environments. Unlike salt spray tests (SST), which are a type of accelerated corrosion test, CCT involves repeated salt spray, drying, and wetting cycles, which approximates corrosion conditions in an atmospheric environment and demonstrates a certain degree of correlation. The JASO cycle (M609-91) was used for the CCT, with 30 cycles equivalent to 10 years of general corrosive conditions in Japan. The clarity of the design was evaluated before and after the CCT according to the clarity evaluation method described above, and permanence was then assessed based on the change in clarity before and after the CCT.

[0095] After the design was applied, the plated steel sheet was cut into a size of 100 x 50 mm, and the cut edge was coated with an epoxy resin paint. A 70 x 40 mm evaluation surface was placed in the center of the steel sheet to prepare a test specimen. A laser-irradiated area of ​​any size, to which laser treatment was applied, was placed in the center of the evaluation surface. The area outside the laser-irradiated area was not laser-treated. Five such test specimens were prepared, and each was subjected to a 30-cycle corrosion test using the CCT (JASO cycle). The clarity of the test specimens before and after the CCT test was evaluated in the same manner as the clarity evaluation described above using a computer-based character recognition function that had been machine-learned to recognize characters and other features, and the black-and-white match rate was calculated. Furthermore, the difference between the black-and-white match rate of the test specimen before the CCT test and the black-and-white match rate of the test specimen after the CCT test was calculated. Evaluation was then performed according to the following evaluation criteria. S, A, and B were considered pass. S: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is less than 5 points. A: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 5 points or more but less than 10 points. B: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 10 points or more but less than 15 points. C: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 15 points or more.

[0096] Next, a method for producing the hot-dip plated steel material of this embodiment will be described. The hot-dip plated steel material of this embodiment is obtained by annealing a steel material to be plated, hot-dip plating it, cooling it, and then heating it again in an atmosphere of predetermined humidity and temperature, and then performing laser treatment. Each of these steps will be described below.

[0097] (Hot-dip coating process) The steel material to be plated is preferably annealed in a reducing atmosphere prior to immersion in the hot-dip coating bath. The reducing atmosphere and annealing conditions are not particularly limited, but this annealing preferably removes as much oxide as possible from the steel surface. The steel material immediately after annealing is then immersed in a hot-dip coating bath. The chemical composition of the coating bath may be appropriately adjusted so as to obtain the chemical composition of the coating layer described above. The temperature of the coating bath is also not particularly limited, and a temperature at which hot-dip coating can be performed may be appropriately selected. For example, the coating bath temperature may be set to a value approximately 20°C or more higher than the melting point of the coating bath.

[0098] Next, the steel material is pulled out of the coating bath. The coating weight of the coating layer can be controlled by controlling the pulling speed of the steel sheet. If necessary, the coating weight of the coating layer may be controlled by wiping the steel sheet to which the coating layer is attached. The coating weight of the coating layer is not particularly limited and can be, for example, within the above-mentioned range.

[0099] The plating layer is then cooled under any cooling conditions, including the application of a cooling gas or mist, or by allowing the plating layer to cool naturally.

[0100] (Heating Step) In the heating step, the plated steel material is heated (held) for 10 minutes or longer under conditions of a relative humidity of 90% RH or higher and an atmospheric temperature of 100°C or higher, thereby forming a black oxide layer on the surface of the plating layer to a thickness of 0.02 μm or higher, preferably 0.10 μm or higher. Forming a thickness of 0.02 μm or higher gives the plating layer a black appearance. Heating in an atmosphere with a relative humidity of 90% RH or higher forms an oxygen-deficient oxide layer with a relatively low oxygen content compared to heating in the air. Such an oxygen-deficient oxide layer has a black color.

[0101] The higher the atmospheric temperature, the faster the oxide layer forms, but once the oxide layer reaches a certain thickness (e.g., 5 μm), the degree of blackening and the growth of its thickness stop due to the rate-limiting effect of oxygen diffusion on the surface of the plating layer. Therefore, it is preferable to keep the atmospheric temperature in the heating step at 200° C. or less, because if it is raised too high, the white oxide and plating layer will begin to dissolve.

[0102] The treatment time is preferably in the range of 10 minutes to 80 hours. If the treatment time is less than 10 minutes, the black oxide layer cannot be formed sufficiently. If the treatment time exceeds 80 hours (4,800 minutes), the black oxide layer will be formed too thick, making it impossible to form a pattern in the subsequent laser irradiation step.

[0103] (Laser Treatment Step) In the laser treatment step, after forming a black oxide layer, a portion of the surface of the plating layer is irradiated with a laser to reduce the mass concentration ratio of O to Zn (O / Zn) at the irradiated portion to less than 0.80. The oxygen-deficient black oxide layer can be removed by mechanical means such as grinding or polishing, or by evaporation or decomposition. In this embodiment, however, the oxide layer on the surface of the plating layer is partially removed by laser irradiation. By irradiating a specific portion of the oxide layer on the surface of the plating layer with a laser beam while converging it, a localized high-temperature region is generated at the focus of the laser beam, making it possible to easily remove the oxide layer. The portion irradiated with the laser beam can be controlled so as to obtain the desired pattern.

[0104] The type of laser light is CO ２ The laser may be a gas laser such as a quartz laser or a solid-state laser such as a YAG laser, and there are no particular limitations on the laser output. The laser output must be set according to the thickness of the oxide. The laser irradiation conditions vary depending on the type of laser, but are typically an output of 1.5 to 20.0 W, a laser spot diameter of 0.01 to 0.20 mm, a laser scanning speed of 200 to 1000 mm / sec, and the number of repeated irradiations is not particularly limited, but may be, for example, 1 to 30 times. The atmosphere during laser irradiation is not particularly limited, and air may be used. If the laser output is too high or the laser scanning speed is too slow, the plating layer will melt. Therefore, it is desirable to irradiate the laser under conditions that do not melt the plating layer. Furthermore, if the oxide layer cannot be removed in a single scan, multiple scans may be performed.

[0105] In the hot-dip plated steel material of this embodiment, a coating may be formed on the plating layer after laser irradiation. One or more coatings may be formed. Examples of the type of coating directly on the plating layer include a chromate coating and a chromate-free coating. The chromate treatment and chromate-free treatment for forming these coatings can be performed by known methods.

[0106] Chromate treatments include electrolytic chromate treatments, which form a chromate film by electrolysis; reactive chromate treatments, which form a film by utilizing a reaction with the material and then wash away excess treatment solution; and paint-on chromate treatments, which apply a treatment solution to the substrate and then dry it without rinsing to form a film. Any of these treatments may be used. A nearly colorless and transparent finish is preferable to distinguish the design.

[0107] Examples of electrolytic chromate treatments include electrolytic chromate treatments using chromic acid, silica sol, resins (phosphoric acid, acrylic resins, vinyl ester resins, vinyl acetate acrylic emulsions, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resins, etc.), and hard silica.

[0108] Chromate-free treatments are particularly suitable because they do not place a burden on the environment. Chromate-free treatments include electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and paint-on chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0109] Furthermore, one or more organic resin coatings may be provided on the coating directly on the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. Here, the term "modified version" refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group.

[0110] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-corrosion pigment. Water-based organic resins prepared by dissolving or dispersing them in water may also be used.

[0111] The following plated steel sheets were prepared as steel sheets to be laser irradiated. For the plated steel sheets, alloys were prepared by mixing predetermined amounts of pure metals and the like using a hot-dip plating simulator manufactured by Rhesca, and the alloys were melted and hot-dip plated.

[0112] Cold-rolled steel sheets measuring 200 × 100 × 1.2 mm (corresponding to SPHC JIS G3141:2021) were used as the base sheets for plating. Some of the base sheets for plating (Nos. 3, 6, 14, 15, and 27) were hot-rolled steel sheets measuring 200 × 100 × 2.0 mm (corresponding to SPHC JIS G3193:2019).

[0113] Before plating, ２ -H ２ The steel sheet surface was held at 800°C for 1 minute in a 5% RH atmosphere (dew point -40°C) to be fully reduced, and then immersed in a plating bath (melting point of plating bath +30°C) for 3 seconds and pulled out. ２ Gas wiping was applied to adjust the thickness of the coating layer to 17 to 40 μm. Immediately after wiping, the coating was cooled to room temperature at an average cooling rate of 10°C / s. The produced coated steel sheets were skin-pass rolled under conditions where the reduction in thickness of the steel sheets was 1% or less, so that the surface roughness Ra was within the range of 0.8 to 1.5 μm.

[0114] The plated steel sheets were left at a relative humidity of 53 to 100% RH, an atmospheric temperature of 90 to 180°C, and atmospheric pressure for 5 to 6,000 minutes (100 hours) to form a black oxide layer on the plated surface. Except for Nos. 1 to 7, 9, 35, 36, and 42 to 45, a black oxide layer of 0.02 μm or more was formed.

[0115] Laser treatment is CO ２The steel sheets were irradiated with a carbon dioxide laser. As shown in Table 2, the heat input was 5.0 W, the spot size was 0.05 mm, the scanning speed was 600.0 mm / sec, and the number of scans was 2 to 30. The black oxide layer was removed by irradiating with the laser. The pattern portion consisted of multiple linear regions A arranged at intervals. The overall shape of the pattern portion was a shape representing the hiragana character "me" ("me"), as shown in Figure 1. The character size was 10 mm long x 10 mm wide. In this manner, plated steel sheets of the examples and comparative examples were manufactured. The area where the black oxide layer was removed by laser irradiation was designated region A, and the area where the laser was not irradiated was designated region B. Between region A and region B, region C was formed, where the black oxide layer had been partially removed due to the influence of laser irradiation.

[0116] The average chemical composition of the plating layer was identified as follows. The plating layer was dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material). The resulting acid solution was analyzed using ICP atomic emission spectroscopy or ICP-MS to determine the chemical composition of the plating layer. The results are shown in Tables 1A to 1C. In the tables, Σ represents the total amount of each element group.

[0117] To determine the thickness of the plating layer, the weight change when the plating layer was dissolved in acid was measured in order to measure the average chemical composition of the plating layer. The area of ​​the plating layer before dissolution and the weight change before and after dissolution were measured, and the plating coating weight (g / m ２ The plating density was calculated by the plating specific gravity (g / m ３ The plating specific gravity was calculated by measuring the chemical composition of the plating layer and then calculating the plating specific gravity from the measurement results of the chemical composition.

[0118] In addition, P in regions A, B, and C Ａ and P Ｂ and P Ｃ The measurement was performed using an energy dispersive elemental analyzer (EDS) mounted on a scanning electron microscope. The measurement areas of region A and region B were 100 μm ２The measurement area of ​​the area C was a 10 μm×10 μm area 20 μm away from the edge of the area A identified in the SEM image, and P was determined by elemental analysis using EDS. Ａ , P Ｂ The measurement area was set to three arbitrarily separated locations, and the average value of the measured values ​​at the three locations was calculated. ZAF correction was used to calculate the mass concentration. EDS analysis was performed toward the surface of the plating layer at an acceleration voltage of 15 kV to determine the mass concentrations of O and Zn in each of areas A, B, and C, and the mass concentration ratio P was calculated from the results. Ａ = O / Zn, P Ｂ = O / Zn and P Ｃ The arithmetic mean roughness Ra of the surface of region C was calculated in μm. The details of the method for calculating the arithmetic mean roughness Ra of the surface of region C are the same as those described above, and therefore will not be described here.

[0119] The Mg mass concentration in region B was determined by performing elemental analysis on the surface of region B using an energy dispersive elemental analyzer (EDS).

[0120] The difference between the surface height ZA of region A and the surface height ZB of region B (ZB-ZA) was determined by observing a cross section in which regions A and B could be simultaneously observed with a scanning electron microscope at 1000x magnification, and calculating the average value of the difference between the highest point on the surface of region B and the lowest point on the surface of region A. The details of the method for calculating ZB-ZA are the same as those described above, and therefore will not be described here.

[0121] Clarity was confirmed using a computerized character recognition function with machine learning for character recognition, etc. The pattern portion formed on the plated steel sheet was photographed from a vertical direction under the same conditions, including the specified distance and lighting distance and angle. Image analysis was performed, and pixels constituting a 10 mm x 10 mm area encompassing the character "め" were subjected to mosaic processing and binarized for evaluation. Additionally, a black-and-white pattern portion similar to that on the plated steel sheet was printed on paper as a printing medium, and photographed under the same photographing conditions as the pattern formed on the plated steel sheet. This was subjected to the same mosaic processing as above, and binarized for evaluation. When these two binarized evaluation results were compared, the black-and-white agreement rate of the binarized evaluation of the pattern portion on the plated steel sheet relative to the pattern portion on the paper was measured, and the results were evaluated according to the following criteria: S, AA, A, and B were considered acceptable.

[0122] S: Black and white match rate is 98% or more and 100% or less. AA: Black and white match rate is 96% or more and less than 98%. A: Black and white match rate is 93% or more and less than 96%. B: Black and white match rate is 90% or more and less than 93%. C: Black and white match rate is less than 90%.

[0123] Design permanence was assessed based on the degree of deterioration in design clarity after corrosion. White rust typically forms as a result of corrosion of the plating layer. However, if the amount of white rust is large and it forms raindrops or accumulates on the plating surface, it becomes difficult to distinguish the design. Cyclic corrosion tests (CCT) are a test that provides a good correlation with domestic exposure environments. Unlike salt spray tests (SST), which are a type of accelerated corrosion test, CCT involves repeated salt spray, drying, and wetting cycles, which approximates corrosion conditions in an atmospheric environment and demonstrates a certain degree of correlation. The JASO cycle (M609-91) was used for the CCT, with 30 cycles equivalent to 10 years of exposure to a general corrosive environment in Japan. The clarity of the design was assessed before and after CCT according to the clarity assessment method described above. Furthermore, permanence was assessed based on the degree of deterioration in design clarity before and after CCT.

[0124] After the design was applied, the plated steel sheet was cut into a size of 100 x 50 mm, the cut end faces were coated with an epoxy resin paint, and an evaluation surface of 70 x 40 mm was provided in the center of the steel sheet to prepare a test specimen.

[0125] In the center of the evaluation surface, a 10 mm x 10 mm hiragana character "me" was prepared, which had been laser-treated. The area outside the 10 mm square was a non-laser-treated area.

[0126] Five such test pieces were prepared, and each test piece was subjected to a corrosion test of 30 cycles of CCT (JASO cycle). Furthermore, five test pieces before the CCT test were prepared.

[0127] Before and after the test, clarity was evaluated in the same manner as the above-mentioned clarity evaluation using a computer-based character recognition function that had been machine-learned to recognize characters, etc., and the black-and-white match rate was calculated for each of the test pieces before and after the CCT test. The black-and-white match rate was taken as the average value of five test pieces. Furthermore, the difference between the black-and-white match rate for the test piece before the CCT test and the black-and-white match rate for the test piece after the CCT test was calculated. The results were evaluated according to the following evaluation criteria. S, A, and B were considered to be pass.

[0128] S: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is less than 5 points. A: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 5 points or more but less than 10 points. B: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 10 points or more but less than 15 points. C: Decrease in clarity (black and white agreement rate) of the evaluation surface before and after corrosion is 15 points or more.

[0129] As can be seen from Tables 1A to 3, in Examples 8, 10 to 33, 38 to 41, 47, and 48, a black oxide layer containing Zn oxide and having a thickness of 0.02 μm or more was formed, and as shown in Tables 1A to 3, the chemical composition of the plating layer, the thickness of the plating layer, and the relationship between regions A and B were all within the ranges of the present disclosure, and the clarity and permanence were good. However, in Example 48, the oxide layer was removed with sandpaper instead of laser treatment, resulting in the arithmetic mean roughness Ra of region C exceeding 2.0, and the clarity and permanence were both rated B.

[0130] On the other hand, as shown in Tables 1A to 3, in Comparative Examples 1 to 7, 9, 34 to 37, and 42 to 46, one or more of the chemical composition of the plating layer, the thickness of the plating layer, the thickness of the black oxide on the surface of the plating layer, and the relationship between Regions A and B were outside the range of the present disclosure, and the clarity or permanence was inferior.

[0131] In Comparative Examples 1 to 7, 9, and 34 to 37, the Al content, Mg content, or Si content of the plating layer was outside the range of the present disclosure. As a result, except for Comparative Example 34, the black oxide layer was not sufficiently formed, resulting in poor clarity or durability.

[0132] In Comparative Examples 42 to 46, the conditions of the heating step were outside the preferred range, so the P in region A Ａ or P in area B Ｂ However, this falls outside the scope of this disclosure and is less clear and durable.

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] According to the present disclosure, it is possible to provide a hot-dip galvanized steel product having a coating layer with a design that is highly distinct and durable, and a method for manufacturing the same. According to the present disclosure, it is possible to provide a material that is inexpensive and has excellent aesthetic appeal, which can contribute to the development of industry.

[0139] REFERENCE SIGNS LIST 1... hot-dip plated steel material 2... steel material 3... plated layer 3A... Zn-Al-Mg alloy layer 4... oxide layer

Claims

1. A steel material having a plating layer disposed on a surface of the steel material, the plating layer having an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.00%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, total amount ΣX of Sn, Bi and In: 0% or more and not more than 0.7%, Ca: 0% or more and not more than 0.60%, Y: 0% or more and not more than 0.30%, La: 0% or more and not more than 0.30%, Ce: 0% or more and not more than 0.30%, Sr: 0% or more and not more than 0.30%, Li: 0% or more and not more than 0.30%, Total amount of Ca, Y, La, Ce, Sr, and Li, ΣYa: 0% or more, 0.60% or less, Cr: 0% or more, 1.00% or less, Ni: 0% or more, 1.00% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.00% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb, ΣYb: 0% or more, 1.00% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, Total amount of B and P, ΣYc: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, the plating layer has a thickness of 5.0 μm or more, a surface of the plating layer is provided with an area A and an area B, and a black oxide layer containing Zn oxide is formed in the area B with a thickness of 0.02 μm or more, and a mass concentration ratio of O to Zn (O / Zn) in the area A on the surface of the plating layer is P Ａ The mass concentration ratio of O to Zn (O / Zn) in the region B on the surface of the plating layer is P Ｂ A hot-dip galvanized steel material that satisfies the following formulas (1) to (3) when 0<P Ａ <0.80 …(1) 0.80≦P Ｂ …(2) 0.40≦P Ｂ -P Ａ …(3) 2. The hot-dip plated steel material according to claim 1, which satisfies the following formula (4): 0.50≦P Ｂ -P Ａ …(4) 3. The hot-dip plated steel material according to claim 1, wherein the Mg mass concentration in the region B on the surface of the plated layer is 3.2 mass% or more.

4. The hot-dip galvanized steel material according to claim 1, wherein the difference (ZB-ZA) between the surface height ZA of the region A and the surface height ZB of the region B is 0.1 μm or more and less than 5.0 μm.

5. The plating layer includes an area C adjacent to the area A, and the mass concentration ratio of O to Zn (O / Zn) in the area C is P Ｃ The hot-dip plated steel material according to claim 1, wherein the following formulas (5) and (6) are satisfied when 0<P Ａ <P Ｃ <0.80...(5) P Ｃ <0.40+P Ａ …(6) 6. The hot-dip plated steel material according to claim 5, wherein the arithmetic mean roughness Ra in unit μm of the surface of the region C satisfies the following formula (7): Ra<2.0...(7) 7. The hot-dip plated steel material according to any one of claims 1 to 6, wherein a pattern portion including said region A is provided on the surface of said plating layer, and said pattern portion has an intentional shape.

8. The hot-dip plated steel material according to any one of claims 1 to 6, wherein a pattern portion including the region A is provided on the surface of the plating layer, and the pattern portion has a shape which is any one of straight line portions, curved line portions, dot portions, figures, numbers, symbols, designs and letters, or a combination of two or more of these.

9. The hot-dip galvanized steel material according to any one of claims 1 to 6, wherein a pattern portion including the region A is provided on the surface of the plating layer, and the pattern portion has an intentional shape comprising any one of straight line portions, curved line portions, dot portions, figures, numbers, symbols, designs and letters, or a combination of two or more of these.

10. The hot-dip plated steel material as described in claim 7, wherein the pattern portion includes the region A, the region B, and the region C located between the region A and the region B.

11. The hot-dip plated steel material according to claim 8, wherein the pattern portion includes the region A, the region B, and the region C located between the region A and the region B.

12. The hot-dip plated steel material according to claim 9, wherein the pattern portion includes the region A, the region B, and the region C located between the region A and the region B.

13. The hot-dip plated steel material according to any one of claims 1 to 6, wherein a non-patterned portion consisting of the region B is provided on the surface of the plating layer.

14. A method for producing hot-dip plated steel material according to claim 1, wherein the average chemical composition, in mass%, is: Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.00%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, total amount of Sn, Bi and In ΣX: 0% or more and not more than 0.7%, Ca: 0% or more and not more than 0.60%, Y: 0% or more and not more than 0.30%, La: 0% or more and not more than 0.30%, Ce: 0% or more and not more than 0.30%, Sr: 0% or more and not more than 0.30%, Li: 0% or more and not more than 0.30%, Total amount of Ca, Y, La, Ce, Sr, and Li, ΣYa: 0% or more, 0.60% or less, Cr: 0% or more, 1.00% or less, Ni: 0% or more, 1.00% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.00% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb, ΣYb: 0% or more, 1.00% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, Total amount of B and P, ΣYc: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, a hot-dip galvanizing process for forming a plating layer containing Co: 0% or more, 0.25% or less, V: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Mn: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W: 0% or more, 0.25% or less, total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more, 0.25% or less, Fe: 0% or more, 5.0% or less, Zn: 40.0% or more, 86.0% or less by a hot-dip galvanizing method; and a heating process for heating the plated steel material obtained by the hot-dip galvanizing process under conditions of a relative humidity of 90% or more and 100° C. or more to form a black oxide layer on a surface of the plating layer. a laser treatment step of irradiating a part of a surface of the plating layer after the heating step with a laser to set a mass concentration ratio of O to Zn (O / Zn) on the surface of the irradiated part to less than 0.

80.

15. A method for manufacturing hot-dip galvanized steel product as described in claim 14, wherein the irradiated portion has a shape that is one of a straight line portion, a curved portion, a dot portion, a figure, a number, a symbol, a pattern or a letter, or a combination of two or more of these.