Molten-plated steel material and method for producing molten-plated steel material

Abstract

A molten plated steel material having a steel material and a plating layer formed on the surface of the steel material and having a predetermined chemical composition, the plating layer having a thickness of 5 [mu] m or more, the plating layer having a first region and a second region, and satisfying the following formulae (1)-(6). RaA < = 10.0... (1), RaB < = 10.0... (2), 1.5 < = RaA-RaB... (3), 150 < = HVx < = 350... (4), 200 < = HVmax... (5), 0.80 < = HVbig / HVsml < = 1.50... (6).

Description

Technical Field

[0001] This disclosure relates to molten coated steel and a method for manufacturing molten coated steel.

[0002] This application claims priority based on Japanese Patent Application No. 2023-191984, filed in Japan on November 10, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Fused galvanized steel is widely used in the building materials, civil engineering, and automotive industries. This galvanized steel is then processed in various ways to manufacture steel structures. For example, in streets, there are many opportunities to directly see the metallic hues of galvanized steel used in guardrails, windbreaks, electrical panels, cable trays, and so on. Unlike ordinary galvanized steel, steel structures that form part of roads, railways, and streetscapes often require consideration of aesthetics. For example, anti-glare considerations for safety in road and railway infrastructure, black-based color schemes in recent urban spaces, and logos representing advertising and brand names all increase the demand for color and appearance design in galvanized steel. While painting is the most common method, the need for regular repairs due to deterioration and the cost proportional to the construction area become major bottlenecks. From a durability perspective, stainless steel and aluminum are sometimes used, but there are many instances where their use is difficult due to material costs and strength considerations.

[0004] As a means of solving these problems, there are techniques for marking the plated metal itself without coating when the molten-plated steel leaves the factory. For example, Patent Documents 1-3 show examples of molten-plated steel that impart an appearance design by controlling the internal constituent phases of the coating as a metal film and combining it with a resin-based coating. In these examples, the difference in the metal constituent phases in the coating is utilized to impart the appearance design. Therefore, in these examples, there are challenges in achieving clarity similar to that of characters, durability against corrosion of the coating, and large-area application of patterning.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-85089 Patent Document 2: Japanese Patent Application Publication No. 2021-172880 Patent Document 3: Japanese Patent Application Publication No. 2021-85085 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] This disclosure was made in view of the above circumstances, and its object is to provide a molten-coated steel and a method for manufacturing molten-coated steel, which can display text, designs, etc. on the coating, with excellent clarity and durability of text, designs, etc., and can realize large-area text, designs, etc.

[0008] means for solving problems

[0009] To address the aforementioned issues, this disclosure adopts the following structure.

[0010] [1] One aspect of the present disclosure is a melt-coated steel having a steel material and a coating formed on the surface of the steel material, wherein the average chemical composition of the coating, by mass%, comprises Al: more than 10.0% and less than 40.0%, Mg: more than 4.0% and less than 15.0%, Si: more than 0% and less than 1.00%, Sn: more than 0% and less than 0.7%, Bi: more than 0% and less than 0.3%, In: more than 0% and less than 0.3%, the total amount of Sn, Bi and In ΣX: more than 0% and less than 0.7%, Ca: more than 0% and less than 0.60%, Y: more than 0% and less than 0.30%, La : 0% or more and 0.30% or less, Ce: 0% or more and 0.30% or less, Sr: 0% or more and 0.30% or less, Li: 0% or more and 0.30% or less, the combined amount of Ca, Y, La, Ce, Sr and Li ΣYa: 0% or more and 0.60% or less, Cr: 0% or more and 1.00% or less, Ni: 0% or more and 1.0% or less, Mo: 0% or more and 0.25% or less, Cu: 0% or more and 1.0% or less, Ag: 0% or more and 0.25% or less, Sb: 0% or more and 0.25% or less, Pb: 0% or more and 0.25% or less, Cr, Ni, Mo, Cu, The combined amount of Ag, Sb, and Pb ΣYb: ≥0% and ≤1.0%; B: ≥0% and ≤0.50%; P: ≥0% and ≤0.50%; the combined amount of B and P ΣYc: ≥0% and ≤0.50%; Ti: ≥0% and ≤0.25%; Co: ≥0% and ≤0.25%; V: ≥0% and ≤0.25%; Nb: ≥0% and ≤0.25%; Mn: ≥0% and ≤0.25%; Zr: ≥0% and ≤0.25%; W: ≥0% and ≤0.25%; the combined amount of Ti, Co, V, Nb, Mn, Zr, and W ΣZ: ≥0%. The coating has a content of 0.25% or less, Fe: 0% or more and 5.0% or less, Zn: more than 42.0% and 85.0% or less, and a thickness of 5 μm or more. The coating has a first region and a second region, and one of the first region or the second region is configured in a predetermined shape. The arithmetic mean roughness Ra (μm) of the surface of the first region of the molten coated steel is set as Ra_A, and the arithmetic mean roughness Ra (μm) of the surface of the second region of the molten coated steel is set as Ra_B. The larger value of Ra_A or Ra_B is set as Ra_L, and the distance from the surface of the coating is (Ra_L+1).When the average value of Vickers hardness HV between a depth position of 0 μm and a depth position at half the thickness of the coating is set as HV_x, and the maximum value of Vickers hardness HV is set as HV_max, equations (1) to (5) below are satisfied. When the average value of Vickers hardness HV between a depth position of (Ra_L+1.0) μm from the surface of the coating and a depth position at half the thickness of the coating in the region of the first region or the second region where the arithmetic mean roughness Ra is larger is set as HV_big, and the average value of Vickers hardness HV between a depth position of (Ra_L+1.0) μm from the surface of the coating and a depth position at half the thickness of the coating in the region of the first region or the second region where the surface roughness Ra is smaller is set as HV_sml, equation (6) below is satisfied. Ra_A≤10.0…(1) Ra_B≤10.0…(2) 1.5≤|Ra_A-Ra_B|…(3) 150≤HV_x≤350…(4) 200≤HV_max…(5) 0.80≤HV_big / HV_sml≤1.50…(6)

[0011] [2] According to the molten coated steel described in [1], one of the first region or the second region may be configured in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern or a text, or a combination of two or more of them.

[0012] [3] According to the molten coated steel described in [1] or [2], one of the first region or the second region may be configured in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern or a combination of two or more of them.

[0013] [4] The molten coated steel according to any one of [1] to [3] may also be a steel plate, wherein the coating is provided on one side of the steel plate and on the back side of the one side, i.e., the other side. In either or both of the coating on one side or the coating on the other side, one of the first region or the second region is arranged in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern or a character, or a combination of two or more of them.

[0014] [5] The molten coated steel according to any one of [1] to [4] may also be a steel plate, wherein the coating is provided on one side of the steel plate and on the back side of the one side, i.e., the other side. In either or both of the coating on one side or the coating on the other side, one of the first region or the second region is arranged in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern or a character, or a combination of two or more of them.

[0015] [6] Another method for manufacturing molten coated steel according to this disclosure is the method for manufacturing molten coated steel according to any one of [1] to [3], wherein, on the surface of the coating formed on the surface of the steel by molten coating, ferrous or non-ferrous metal particles (shots) are collided by centrifugal force or air pressure to form one of the first region or the second region.

[0016] [7] Another aspect of the present disclosure is the method for manufacturing molten coated steel as described in [4] or [5], wherein, on the surface of the coating formed by molten coating on one side or the back side of the steel plate, i.e. the other side, one or both of the coatings on one side or the other side are subjected to centrifugal force or air pressure to cause iron or non-ferrous metal particles (shots) to collide with the molten coated steel, thereby forming one of the first region or the second region.

[0017] Invention Effects

[0018] According to the above-described method of this disclosure, a molten-coated steel material and a method for manufacturing molten-coated steel material can be provided, which can display text, designs, etc. on the coating, with excellent clarity and durability of the text, designs, etc., and can realize large-area display of text, designs, etc. Therefore, an inexpensive and aesthetically pleasing material can be provided, which can contribute to the development of industry. Attached Figure Description

[0019] Figure 1 This photograph shows an example of how shot peening imparts a unique appearance to a steel plate.

[0020] Figure 2 This is a schematic diagram of the cross-section of the molten coated steel disclosed herein. Detailed Implementation

[0021] The inventors have conducted in-depth research on methods for displaying text, designs, etc. on the surface (coating) of molten coated steel, improving the clarity and durability of text, designs, etc., and thereby enabling large-area display of text, designs, etc.

[0022] In order to display text, designs, and other visual effects in specific areas of a metal surface, it is considered that the areas representing text, designs, etc., should have different colors, gloss, reflectivity, etc., compared to the areas that become the background.

[0023] Among these factors, color difference is likely to be the most clearly defined aspect of appearance design. Generally, the surface of metallic materials, except for colors caused by oxide coatings on titanium and stainless steel, or anodized aluminum, has a roughly uniform hue. However, in metallic materials, alloys can vary the surface hue by altering the composition ratio of their chemical components. However, in molten-coated steel with a Zn-Al-Mg system coating where the chemical composition is consistently determined, it is difficult to partially change the chemical composition during coating manufacturing, thus making it difficult to intentionally create color differences in specific areas of the coating.

[0024] Furthermore, regarding gloss, there is a concern about the durability of the appearance design during long-term use of metallic materials. That is, as corrosion progresses with prolonged use, the gloss difference between the area displaying the design and the background area decreases, potentially making the design less noticeable. Additionally, gloss is also related to properties such as anti-glare, thus requiring careful control. Moreover, gloss, like color difference, is affected by the composition ratio of the alloy's chemical composition; however, for the same reasons mentioned above, it is difficult to intentionally alter the gloss in specific areas of a Zn-Al-Mg based coating.

[0025] On the other hand, reflectivity can be varied by controlling the surface roughness of the metallic material. Therefore, it is believed that even Zn-Al-Mg based coatings, where some chemical composition is difficult to control, can exhibit an appearance design by partially changing the reflectivity. Therefore, in this disclosure, an attempt was made to impart an appearance design to the coating by controlling the surface roughness of the coating surface.

[0026] As a means of altering the surface roughness of specific areas of a coating, this disclosure investigates the application of shot peening to the coated surface. However, in the steel industry, shot peening is used to remove rust, scale, and create uneven coating substrates by striking the steel surface with projected materials. However, common molten coatings, such as Zn and Al coatings, are relatively soft, and their thickness can be as thin as tens of micrometers. If such molten coatings are shot peened, they may deform and disappear within a short processing time, making it difficult to achieve the desired appearance. In contrast, the inventors conducted research and found that for sufficiently hard coatings, the appearance can be achieved by adjusting the shot peening time. However, it was also determined that excessively hard coatings result in low productivity due to long shot peening times, and the coating peels off as cracks form after shot peening. Therefore, the inventors conducted further research and found that a coating with a Vickers hardness in the range of 150 to 350 Hv is preferred as the application object, as it is moderately hard and moderately soft. Furthermore, it is preferable that a hard phase and a soft phase are mixed in the coating.

[0027] Regarding the durability of the appearance design, coatings with locally increased surface roughness through shot peening have a larger surface roughness and surface area compared to those without shot peening, resulting in a tendency for longer wetting time and increased susceptibility to corrosion. Therefore, when shot peening is applied to coated steel with a general Zn coating to achieve the desired appearance, white rust easily forms on the coating surface. Consequently, it becomes difficult to maintain the clarity of the appearance design after exposure to outdoor environments, for example, in Japan for more than a year. Furthermore, from the perspective of sacrificing corrosion resistance, coated steel with Al or Al-Zn coatings is mostly used on thinner steel sheets. However, if subjected to external force treatment such as shot peening, the steel will warp and deform, rendering it unusable as a steel structural material. Given this situation, for corrosion resistance, to maintain the clarity of the appearance design for a period equivalent to 10 years in outdoor environments in Japan, melt-coated steel with a Zn-Al-Mg system coating is appropriate.

[0028] Regarding the large-area application of shot peening, it can be handled by using fully automated shot peening and masking or local shot peening, whether in batches or continuously.

[0029] It has been clarified that shot peening has a superior effect in the process of giving appearance design due to the unique properties of Zn-Al-Mg based coatings. That is, by mixing hard and soft structures inside the coating, the development of internal cracks is suppressed. Therefore, the cracks generated by shot peening will not penetrate into the iron base, thus preventing coating peeling and reduced corrosion resistance.

[0030] The following describes the melt-coated steel according to the embodiments of this disclosure.

[0031] The molten-coated steel of this embodiment has steel and a coating formed on the surface of the steel. The average chemical composition of the coating, by mass%, includes Al: more than 10.0% and less than 40.0%, Mg: more than 4.0% and less than 15.0%, Si: more than 0% and less than 1.00%, Sn: more than 0% and less than 0.7%, Bi: more than 0% and less than 0.3%, In: more than 0% and less than 0.3%, the total amount of Sn, Bi and In ΣX: more than 0% and less than 0.7%, Ca: more than 0% and less than 0.60%, Y: more than 0% and less than 0.30%, La: more than 0% and less than 0.30%, Ce: more than 0% and less than 0.30%, and Sr: more than 0% and less than 0%. Below 30%, Li: 0% to 0.30%, combined amount of Ca, Y, La, Ce, Sr and Li ΣYa: 0% to 0.60%, Cr: 0% to 1.00%, Ni: 0% to 1.0%, Mo: 0% to 0.25%, Cu: 0% to 1.0%, Ag: 0% to 0.25%, Sb: 0% to 0.25%, Pb: 0% to 0.25%, combined amount of Cr, Ni, Mo, Cu, Ag, Sb and Pb ΣYb: 0% to 1.0%, B: 0% to 0.50%, P: 0% to 0.50%, combined amount of B and P The coating comprises the following components: ΣYc: 0% or more and 0.50% or less; Ti: 0% or more and 0.25% or less; Co: 0% or more and 0.25% or less; V: 0% or more and 0.25% or less; Nb: 0% or more and 0.25% or less; Mn: 0% or more and 0.25% or less; Zr: 0% or more and 0.25% or less; W: 0% or more and 0.25% or less; the combined component 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: more than 42.0% and less than 85.0%; the coating thickness is 5 μm or more; the coating has a first region and a second region, and one of the first region or the second region is configured as follows: Given a fixed shape, the arithmetic mean roughness Ra (μm) of the surface of the first region of the molten coated steel is set as Ra_A, the arithmetic mean roughness Ra (μm) of the surface of the second region of the molten coated steel is set as Ra_B, the larger of Ra_A or Ra_B is set as Ra_L, the average value of Vickers hardness HV between the depth position (Ra_L+1.0) μm from the surface of the coating and the depth position of 1 / 2 of the thickness of the coating is set as HV_x, and the maximum value of Vickers hardness HV is set as HV_max. Under the condition that equations (1) to (5) below are satisfied, the region with the larger arithmetic mean roughness Ra of the surface of the first region or the second region is located at a distance (Ra_L+1.0) μm from the surface of the coating.The average Vickers hardness HV between a depth position of 0 μm and a depth position at half the thickness of the coating is set as HV_big. When the average Vickers hardness HV between a depth position (Ra_L+1.0) μm from the coating surface and a depth position at half the thickness of the coating is set as HV_sml in the region with the smaller surface roughness Ra in either the first or second region, the following equation (6) is satisfied. Ra_A≤10.0…(1) Ra_B≤10.0…(2) 1.5≤|Ra_A-Ra_B|…(3) 150≤HV_x≤350…(4) 200≤HV_max…(5) 0.80≤HV_big / HV_sml≤1.50…(6)

[0032] Here, the coating thickness is calculated based on the coating adhesion amount. The coating adhesion amount is calculated by measuring the weight change when the coating is dissolved with acid. Any acid capable of dissolving the coating is acceptable; there are no particular restrictions, but an acid containing an inhibitor that suppresses corrosion of the iron-based (steel) material is preferred. By measuring the area and weight before and after dissolution, the coating adhesion amount (g / m²) can be obtained. 2 Coating adhesion amount (g / m) 2 The calculation of coating adhesion can be performed not only on steel plates but also on steel wires or bars. The coating adhesion amount can be calculated based on the surface area (diameter × π × length) of the steel wire or bar, according to the weight of the dissolved coating. This is achieved by dividing the coating adhesion amount by the coating specific gravity (g / m³). 3 ), and calculate the thickness of the coating.

[0033] In addition, by measuring the obtained acid solution using ICP luminescence spectrophotometry or ICP-MS, the chemical composition (average chemical composition) of the coating can be obtained as described later, and the coating specific gravity can be calculated based on the chemical composition value.

[0034] Furthermore, in the molten steel of this embodiment, it is preferable that one of the first region or the second region is arranged as the shape specified above, in a manner that is any one of the following shapes: a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern, or text, or a combination of two or more of these shapes. The shape of one of the first region or the second region may also be intentionally formed.

[0035] In the following explanation, the percentage (%) for the content of each element in the chemical composition refers to "mass %". Additionally, the numerical range indicated by "~" refers to the range including the values ​​before and after "~" as lower and upper limits. Furthermore, the numerical range marked "more than" or "less than" for values ​​before and after "~" refers to the range excluding those values ​​as lower or upper limits.

[0036] <Steel>

[0037] First, let's define steel. Steel primarily refers to steel plates, wires, or strips, with no particular restrictions on their dimensions. For example, steel plates are acceptable as long as they can be used in standard hot-dip galvanizing processes. Specifically, steel plates used in processes such as continuous hot-dip zinc galvanizing lines (CGLs), where the metal is immersed in molten metal and solidified, fall under this category. For example, hot-dip galvanized steel plates that meet JIS G 3323:2022 "Hot-dip zinc-aluminum-magnesium alloy coated steel sheets and strips," but are not limited to this. Regarding the dimensions of the steel plates, for example, plates with a thickness of 10 mm or less and a width of 2000 mm or less can be used, but the dimensions are not limited to these. Regarding the shape of the steel plates, this also includes striped steel plates with pre-defined embossed or recessed surfaces. As for steel wires or stripes, anything suitable for standard hot-dip galvanizing processes is acceptable.

[0038] There are no particular restrictions on the type of steel used. For example, ordinary steel, pre-plated steel with a thin coating of various metals, Al-killed steel, very low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steels containing corrosion-resistant strengthening elements such as Ni and Cr, etc.) can be used.

[0039] In addition, as a steel manufacturing process, common processes such as ironmaking and steelmaking in blast furnaces or electric furnaces, hot rolling, pickling, cold rolling, and heat treatment can be cited. However, the steel in this embodiment can undergo any process, and the processing conditions for each process are not limited.

[0040] <Coating>

[0041] Next, the coating will be described. The coating in this embodiment comprises a Zn-Al-Mg alloy layer. This was chosen because the hardness distribution of the coating is suitable for the desired appearance, and it exhibits high corrosion resistance, which is excellent from the viewpoint of durability of the appearance. Alternatively, the coating may also comprise an Al-Fe interface alloy layer.

[0042] The thickness of the coating is the sum of the thicknesses of the Zn-Al-Mg alloy layer and the Al-Fe layer. To achieve the desired appearance through shot peening and to impart surface roughness, the coating requires a specified thickness, specifically, 5 μm or more. On the other hand, for steel wire or steel rod, the maximum thickness of coatings formed by conventional melt-coating methods is mostly less than 100 μm. Therefore, the thickness of the coating on the melt-coated steel in this embodiment can, for example, be less than 100 μm.

[0043] The Zn-Al-Mg alloy layer is composed of Zn-Al-Mg alloys. Zn-Al-Mg alloys refer to ternary alloys whose main components are Zn, Al, and Mg, with any other elements included within these components. The main components refer to elements other than Fe that constitute the coating, with a total content of 95.0% or more.

[0044] The Al-Fe interfacial alloy layer is an interfacial alloy layer located between the steel and the Zn-Al-Mg alloy layer, and it is in contact with the surface of the steel.

[0045] That is, the coating can be a single-layer structure of Zn-Al-Mg alloy layer, or a stacked structure containing Zn-Al-Mg alloy layer and Al-Fe interface alloy layer. In the case of a stacked structure, the Zn-Al-Mg alloy layer can be set as the layer constituting the coating surface.

[0046] As described below, when using molten zinc-coated steel (in the form of steel sheet, steel wire, or steel wire) manufactured by CGL, or molten zinc alloy-coated steel manufactured by a batch molten zinc coating method, traces of the interfacial alloy layer of the coating material sometimes remain in the molten zinc-coated steel of this embodiment. Particularly when the coating material is a coated steel sheet, the flow rate relative to the plating bath during molten coating is higher, thus the Al-Fe interfacial alloy layer tends to become thinner. Furthermore, when using Ni-pre-coated steel, Sn-pre-coated steel, Cr-pre-coated steel, etc., as coating materials, these metals sometimes mix into the Al-Fe interfacial alloy layer.

[0047] The steel is bonded to the Zn-Al-Mg alloy layer through an Al-Fe interfacial alloy layer. The thickness of the Al-Fe interfacial alloy layer can be controlled to a certain extent by adjusting the plating bath temperature, immersion time, steel throughput speed, and wiping pressure during the manufacturing process of the molten steel.

[0048] An Al-Fe interfacial alloy layer is formed between the steel and the Zn-Al-Mg alloy layer, with the Al5Fe2 phase as the main phase. The Al-Fe interfacial alloy layer is formed during or after the steel passes through a molten plating bath through atomic diffusion between the iron matrix (steel) and the molten plating. When using a continuous molten plating method, an Al-Fe interfacial alloy layer is easily formed in coatings containing Al. In this embodiment, since the plating bath contains a certain concentration or higher of Al, the Al5Fe2 phase is formed most abundantly in the Al-Fe interfacial alloy layer. However, because atomic diffusion takes time, the Fe concentration in the Al-Fe interfacial alloy layer is uneven, sometimes with a higher Fe concentration near the iron matrix. Therefore, the Al-Fe interfacial alloy layer sometimes partially contains small amounts of AlFe phase, Al3Fe phase, Al5Fe2 phase, etc. Furthermore, since the plating bath also contains a certain concentration of Zn, the Al-Fe interfacial alloy layer sometimes also contains small amounts of Zn or Si, which easily accumulates at the interface.

[0049] Furthermore, in this embodiment, Si is sometimes contained in the coating. When Si is introduced into the Al-Fe interfacial alloy layer, an Al-Fe-Si intermetallic compound phase is formed. Among the identified intermetallic compound phases is the AlFeSi phase, and as isomers, α, β, q1, and q2-AlFeSi phases exist. Therefore, these AlFeSi phases are sometimes detected in the Al-Fe interfacial alloy layer. These Al-Fe interfacial alloy layers containing AlFeSi phases are also referred to as Al-Fe-Si alloy layers. This intermetallic compound is not dependent on the manufacturing method but is determined solely by the concentration of the coating components (the presence or absence of Si). Therefore, when the coating contains Si, an intermetallic compound phase containing Si is reliably formed.

[0050] The morphology of the Al-Fe interfacial alloy layer contributes little to corrosion resistance, which is the primary requirement for coating properties. However, it affects the adhesion and workability of the coating during the processing of molten-coated steel, specifically, the absence of cracking during processing. In particular, the morphology of the Al-Fe interfacial alloy layer can sometimes affect the powdering resistance, which indicates the degree of peeling during processing. Generally, a thinner Al-Fe interfacial alloy layer reduces the initiation points of cracking during processing, further improving powdering resistance. Therefore, for molten-coated steel that may be subjected to high processing requirements, a thinner Al-Fe interfacial alloy layer is preferable. Specifically, the thickness of the Al-Fe interfacial alloy layer is preferably 2.0 μm or less, but can be 1.0 μm or less, 0.7 μm or less, more preferably 0.5 μm or less, or 0.3 μm or less. Typically, the Al-Fe interfacial alloy layer is thinner than the Zn-Al-Mg alloy layer, usually less than 10% of the total coating thickness.

[0051] Furthermore, when the coating contains any element (Mg, Si, Cr, Ni, Co, Mn, V, Nb, Sn, Bi, In, B, La, Ca, Ce, Y), these elements sometimes mix into the Al-Fe interfacial alloy layer or exist as intermetallic compounds containing these elements. For example, Ni sometimes forms Al3Ni or Al-Ca-Si-Ni intermetallic compounds. Among these elements, those with high melting points tend to remain in the Al-Fe interfacial alloy layer in a layered manner. On the other hand, low-melting-point metals such as Sn are difficult to leave traces and are sometimes impossible to identify. Moreover, when using steel with a pre-plating layer containing Ni, Cr, etc., as the base material for plating, Ni, Cr, etc., sometimes remain in the interfacial alloy layer in a layered manner. These metals, as a metal layer formed through prior replacement and electroplating, i.e., a pure Ni, Cr layer, sometimes exist with a thickness of less than 1 μm.

[0052] <Chemical composition of the coating>

[0053] Next, the average chemical composition of the coating will be explained.

[0054] In the case of a single-layer structure where the coating is a Zn-Al-Mg alloy layer, the average chemical composition of the entire coating is the same as that of the Zn-Al-Mg alloy layer. Furthermore, when the coating is a stacked structure of an Al-Fe interface alloy layer and a Zn-Al-Mg alloy layer, the average chemical composition is the sum of the Al-Fe interface alloy layer and the Zn-Al-Mg alloy layer. In the coating of this embodiment, it is preferable that the thickness of the Al-Fe interface alloy layer is less than 10% of the overall coating thickness, and therefore the Fe content of the coating is mostly within 5.0%. Therefore, it is acceptable to consider the average chemical composition of the coating as approximately the composition of the Zn-Al-Mg alloy layer. Furthermore, traces of the original plating material are unlikely to be considered as residual chemical components of the coating. Therefore, the average chemical composition of the coating can be considered to be approximately the same as the composition of the plating bath used in manufacturing.

[0055] The chemical composition of the coating determines its hardness. In typical coating production lines, coatings typically reach the upper roller within 60 seconds of molten deposition. While the internal morphology of the coating is controlled through the solidification process, the chemical composition cannot be significantly altered. Therefore, regarding coating hardness, if the composition is identical, there will be no large deviations; hardness deviations converge within ±20%.

[0056] The molten steel in this embodiment is manufactured using a continuous molten steel coating method. Therefore, during manufacturing, Fe sometimes diffuses from the raw material to the coating layer. As described above, in this embodiment, the coating has a high Al content, sometimes forming an Al-Fe interfacial alloy layer, but the Al-Fe interfacial alloy layer is thin. As a result, the coating sometimes contains a maximum of 5.0% Fe.

[0057] The following describes the elements contained in the coating and their content (concentration).

[0058] A1: More than 10.0% and less than 40.0% Al, like Zn, is a major element constituting the coating. In Zn-Al-Mg coatings, the Al phase mainly forms in the coating. When the Al content is below 10.0%, the corrosion resistance of the coating is low, and the hardness of the coating deviates from the appropriate range, so it is not preferred. When the Al content is above 40.0%, the Zn content is relatively low, resulting in poor corrosion resistance, so it is also not preferred. 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.

[0059] Mg: ≥4.0% and ≤15.0% Mg, like Al and Zn, is a major element constituting the coating. Insufficient Mg results in poor corrosion resistance; therefore, the Mg content is set to exceed 4.0%. Preferably, the Mg content is 5.0% or more, or 6.0% or more. When the Mg content exceeds 15.0%, corrosion resistance deteriorates. Therefore, the Mg content is set to 15.0% or less. Preferably, the Mg content is less than 15.0%, 14.0% or less, 12.0% or less, 10.0% or less, 8.0% or less, 7.5% or less, or 7.0% or less.

[0060] Zn: Above 42.0% and below 85.0% The molten steel used in this embodiment is a highly versatile Zn-based coated steel, therefore the main phase element constituting the coating is Zn. If the Zn content is below 42.0%, the corrosion resistance is insufficient; if it exceeds 85.0%, the improved corrosion resistance from other elements such as Al and Mg cannot be achieved. Therefore, the Zn content is set to be above 42.0% but below 85.0%.

[0061] The coating may further contain the elements shown below. All elements described below are arbitrary, and new intermetallic compounds, substitutions for the main elements, etc., may be formed within the composition range described below. Containing more elements than the composition range significantly increases the hardness of the coating, making it difficult to impart roughness during shot peening. Furthermore, it significantly damages the surface properties of the coating; therefore, it is necessary to limit the content to an appropriate range.

[0062] Si: 0% or more and less than 1.00% Si may or may not be present in the coating, but when Si is present, intermetallic compounds form within the coating. The coating composition in this embodiment has a high melting point, thus the operating temperature during melt coating is around 500°C. At this operating temperature, when steel is immersed in the plating bath, Al, Zn, and Fe undergo active interdiffusion to form Fe-based intermetallic compounds, but Si inhibits this excessive reaction. Therefore, when Si is present, if it is 0.01% or more, the diffusion reaction of Fe is significantly suppressed, making it easy to control the formation of Fe-based intermetallic compounds in the coating. On the other hand, when the Si content is excessive, a large amount of intermetallic compounds consisting of Mg₂Si are formed by combining with Mg, potentially significantly increasing the hardness of the coating; therefore, 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.

[0063] Element group X Sn: 0% or more and 0.7% or less Bi: 0% or more and 0.3% or less In: 0% or more and 0.3% or less The total amount of Sn, Bi, and In, ΣX: above 0% and below 0.7%. Since the elements in element group X (Sn, Bi, In) can be included arbitrarily, their respective contents are set to 0% or more. When Sn is present, there is a tendency to form Mg2Sn and Mg9Sn5 in the coating. Bi also forms Mg3Bi2, and In forms Mg3In, etc. These elements are softer than the MgZn2 phase and have good workability; their inclusion can clearly demonstrate an improvement in workability. Furthermore, they exhibit very low electrochemical properties, thus sacrificing high corrosion resistance. Therefore, their inclusion can improve corrosion resistance. Each element has an upper limit on its content; if it is present in large quantities, the coating will harden excessively. Therefore, these elements are set below 0.7% in Sn and below 0.3% in Bi and In, and consequently, their total content ΣX also needs to be limited to below 0.7%.

[0064] Element group Ya Ca: 0% or more and 0.60% or less Y: Above 0% and below 0.30% La: 0% or more and 0.30% or less Ce: 0% or more and 0.30% or less Sr: 0% or more and 0.300% or less Li: 0% or more and 0.30% or less The combined amount of Ca, Y, La, Ce, Sr, and Li, ΣYa: ≥0% and ≤0.60% These elements, along with Si, control the reaction rate of the coating and also control Fe diffusion in the plating bath. Furthermore, the formation reaction of intermetallic compounds containing these elements between the iron-based matrix and the interfacial alloy layer ensures the adhesion between the iron-based matrix and the Al-Fe alloy layer. Ca sometimes forms Al₂CaSi₂ and Zn-Ca compounds. To achieve this effect, Ca content can be above 0.03%. However, excessive Ca leads to the formation of various scum in the plating bath, increasing plating defects, making the plating bath extremely viscous, reducing the amount of molten metal adhering to the steel when it is lifted from the bath, resulting in an extremely thin coating and poor corrosion resistance. Additionally, the coating hardness becomes excessively high. Therefore, the Ca content is set to 0.60% or less. The elements in element group Ya, excluding Ca, can achieve approximately the same effect as Ca, and therefore can be included as substitutes for Ca. However, they cannot be included in the same large quantities as Ca. That is, the content of each element in element group Ya, excluding Ca, is set to 0~0.30%, preferably 0.01~0.30%. In addition, the total amount ΣYa of element group Ya containing Ca is set to 0~0.60%.

[0065] element group Yb Cr: 0% or more and less than 1.00% Ni: 0% or more and 1.0% or less Mo: 0% or more and 0.25% or less Cu: 0% or more and 1.0% or less Ag: 0% or more and 0.25% or less Sb: 0% or more and 0.25% or less Pb: above 0% and below 0.25% The total amount of element group Yb of Cr, Ni, Mo, Cu, Ag, Sb and Pb, ΣYb: ≥0% and ≤1.0%. Since the elements in element group Yb can be included arbitrarily, their respective contents are set to 0% or more. The elements in element group Yb have similar properties to Zn and can be included in relatively large quantities. Cr and Mo form Mg-Al-Cr and Mg-Al-Mo compounds. When both element groups Yb and Ya are included, sometimes a portion of the Mg in the Mg-Al-Cr or Mg-Al-Mo compounds is replaced by Ya. Additionally, Ni forms Al-Ni compounds, etc. Cu, Ag, Sb, and Pb form Zn-Cu, Zn-Ag, Zn-Sb, and Zn-Sb compounds. When these elements are included within the above ranges, they have an effect on improved corrosion resistance. This effect is most noticeable when included at approximately 0.1%. However, when the total content of these elements is excessive, the hardness of the coating becomes excessively high. Therefore, the Cr content is set to 0~1.00%, preferably 0.01~1.00%, the Ni and Cu content is set to 0~1.0%, and the Mo, Ag, Sb, and Pb content is set to 0~0.25%. The total ΣYb content is set to 0% or more and 1.0% or less.

[0066] Element group Yc B: Above 0% and below 0.50% P: Above 0% and below 0.50% The combined amount of B and P, ΣYc: ≥0% and ≤0.50% Since the elements in element group Yc can be included arbitrarily, their respective contents are set to 0% or more. Elements in element group Yc readily form Al-B and Al-P compounds. Furthermore, when these elements are present within the aforementioned range, they improve corrosion resistance. This effect is observed when their total content is approximately 0.05%. On the other hand, a high content of these elements results in excessively high coating hardness. Therefore, the content of each element in element group Yc is set to 0-0.50%. The total content ΣYc is set to 0% or more and 0.50% or less.

[0067] Element group Z Ti: 0% or more and 0.25% or less Co: 0% or more and less than 0.25% V: Above 0% and below 0.25% Nb: 0% or more and 0.25% or less Mn: 0% or more and 0.25% or less Zr: 0% or more and 0.25% or less W: Above 0% and below 0.25% The summation ΣZ of element group Z of Ti, Co, V, Nb, Mn, Zr and W: above 0% and below 0.25% Since the elements in element group Z can be included arbitrarily, their respective contents are set to 0% or more. Although the elements in element group Z are elements that are difficult to include in the coating of this embodiment, they tend to combine with Al to form intermetallic compounds. When the elements in element group Z are included in the plating bath, corrosion resistance is improved. This effect is demonstrated by including them at a total content (concentration) of about 0.10%. On the other hand, when these elements are included in large quantities, the hardness of the coating becomes too high. Therefore, the content of each element in element group Z is set to 0 to 0.25%. The total content ΣZ is set to 0% or more and 0.25% or less.

[0068] Fe: 0% or more and 5.0% or less The molten steel in this embodiment is manufactured using a continuous molten steel coating method. Therefore, during manufacturing, Fe sometimes diffuses from the raw material to the coating layer. As described above, in this embodiment, the Al content of the coating is high, sometimes forming an Al-Fe interfacial alloy layer, but its thickness is thin. As a result, the coating sometimes contains a maximum of 5.0% Fe, but if the Fe content is limited to below 5.0%, it has no effect on the frequency of crack formation in the coating. Therefore, the Fe content is set to 0~5.0%. The Fe content can exceed 0%.

[0069] The balance other than those mentioned above can also be impurities. That is, it can also contain the elements mentioned above, and the balance includes impurities. Impurities refer to components contained in the raw materials or components mixed in during the manufacturing process, and are not intentionally present. For example, in the coating, due to the mutual atomic diffusion between the steel (iron-based) and the plating bath, components other than Fe are sometimes mixed in in trace amounts as impurities.

[0070] The average chemical composition of the coating can be determined using an acid solution prepared when measuring the thickness of the coating. Specifically, an acid solution is obtained by peeling and dissolving the coating with an acid containing an inhibitor that suppresses corrosion of the iron-based (steel) material. The chemical composition can then be determined by measuring the obtained acid solution using ICP-MS or ICP-luminescence spectrophotometry.

[0071] <Coating Structure>

[0072] The coating in this embodiment contains Zn, Al, MgZn2, and Mg2Zn. 11 MgZn, η-MgZn, Mg 32 (Zn, Al) 39The coating contains one or more of the following phases. The total volume fraction of these phases is mostly 90% or more. Furthermore, when viewed in cross-section along the thickness direction of the coating, the total area fraction of these phases is mostly 90% or more. In addition to containing one or more of these phases as individual phases, the coating also contains mixed structures composed of these phases. For example, a Zn-Al phase (Zn: 16.5~67%) containing fine Zn and fine Al phases, or a ternary eutectic structure containing Zn, Al, and MgZn2 phases.

[0073] These area fractions can be identified by obtaining EPMA images of Zn, Al, and MgZn2 phases in a horizontal cross-section, thus specifying the composition of the component. The method for determining area fractions is simple: by using image analysis software such as ImageJ to map the constituent regions of the target component, the area occupied by the major component and its constituent phase can be easily determined.

[0074] The main constituent phases in the coating determine its Vickers hardness. Harder phases are Mg-Zn compounds such as MgZn2, exhibiting a Vickers hardness of 200-400 Hv. On the other hand, softer phases are Zn, Al, and Zn-Al phases, exhibiting a Vickers hardness of 50-100 Hv. Regarding the ternary eutectic structure, the MgZn2 phase constitutes a relatively small proportion, thus exhibiting a Vickers hardness in the range of 100-200 Hv. Therefore, the hardness of the coating, particularly where the ternary eutectic structure is the main constituent phase, is less than 200 Hv. As in this embodiment, by ensuring that Al exceeds 10.0% and Mg exceeds 4.0%, the ternary eutectic structure can be prevented from becoming the main phase (50% or more), and the Vickers hardness of the coating can be controlled within the desired range. As the coating structure, it is preferable that the area fraction of the ternary eutectic structure comprising Zn, Al, and MgZn2 phases is less than 50%.

[0075] Other compounds are expressed as less than 10% by volume and area fraction. Therefore, it is possible to contain various elements in the coating without affecting the average hardness of the coating by more than 10%.

[0076] <First and Second Regions of the Coating>

[0077] In this embodiment, the surface layer (including the coating or a portion of the coating and steel) of the molten steel is formed with a first region and a second region. The first region is a region with a relatively small surface Ra (arithmetic mean roughness), and the second region is a region with a relatively large surface Ra.

[0078] One of the first or second regions is configured in a prescribed shape. More specifically, in the following description, a shape that is configured as any one of the following—a straight line, a curved line, a dot, a graphic, a number, a symbol, a pattern, or text, or a combination of two or more of these—is sometimes referred to as a patterned region, and the region other than the patterned region is sometimes referred to as a non-patterned region. For example, sometimes the first region is a patterned region and the second region is a non-patterned region. Conversely, sometimes the first region is a non-patterned region and the second region is a patterned region. The shape of a patterned region is permissible even if it is partially missing, such as a missing dot, as long as it can be identified as a whole. In addition, a non-patterned region can also be a shape that borders the boundary of a patterned region.

[0079] Thus, the patterned portion constituting either the first region or the second region and the non-patterned portion constituting the other region are areas formed on the surface of the molten steel. The first region and the second region are preferably formed in the same plane.

[0080] The boundary between the first and second regions can be determined with the naked eye. Alternatively, it can be determined using magnified images obtained from optical microscopes, magnifying glasses, etc. As described later, the arithmetic mean roughness Ra, which serves as the criterion for determining whether a region is the first or second, can be measured using a non-contact white interferometer microscope.

[0081] The patterned portion constituting either the first or second region can be formed to a size that allows the presence of the patterned portion to be discerned with the naked eye, under a magnifying glass, or under a microscope. Additionally, the non-patterned portion occupies most of the coating (the surface of the molten coating), and sometimes patterned portions are arranged within the non-patterned portion.

[0082] The patterned portion constituting either the first or second region is arranged in a predetermined shape within the non-patterned portion constituting the other of the first or second regions. Specifically, the patterned portion is arranged within the non-patterned portion in a shape that is any one or a combination of two or more of the following: straight lines, curves, dots, graphics, numbers, symbols, patterns, or text. By adjusting the shape of the patterned portion, a shape consisting of any one or a combination of two or more of the following—straight lines, curves, dots, graphics, numbers, symbols, patterns, or text—is displayed on the surface of the plating. For example, strings of text, strings of numbers, symbols, marks, line drawings, designs, or combinations thereof formed by the patterned portion are displayed on the surface of the plating. This shape is intentionally or artificially formed by the manufacturing method described later, and is not naturally formed.

[0083] In this embodiment, when the arithmetic mean roughness (sometimes simply referred to as surface roughness) Ra (μm) of the surface of the first region of the molten coated steel is set as Ra_A and the arithmetic mean roughness Ra (μm) of the surface of the second region of the molten coated steel is set as Ra_B, the following equations (1) to (3) need to be satisfied. Ra_A≤10.0…(1) Ra_B≤10.0…(2) 1.5≤|Ra_A-Ra_B|…(3)

[0084] As shown in equations (1) and (2), the arithmetic mean roughness (surface roughness) Ra (μm) of the first region, i.e., Ra_A, and the arithmetic mean roughness Ra (μm) of the second region, i.e., Ra_B, both need to be 10.0 μm or less. Surface roughness Ra refers to the arithmetic mean roughness Ra of the surface. By ensuring that the surface roughness Ra (μm) of the first and second regions is 10.0 μm or less, the specific surface area of ​​the coating becomes smaller, thereby slowing down the corrosion rate and suppressing changes in the appearance of the coating that accompany corrosion. Therefore, when forming a patterned portion consisting of the first or second region, the durability of the patterned portion can be ensured. In addition, the overall appearance of the coating also becomes better.

[0085] Furthermore, as shown in equation (3), the absolute value of the difference between the surface roughness Ra (μm) of the first region and the surface roughness Ra (μm) of the second region, i.e., |Ra_A-Ra_B|, needs to be 1.5 μm or more. By making |Ra_A-Ra_B| 1.5 μm or more, the difference in reflectivity between the first region and the second region increases, making it possible to distinguish the first region from the second region with the naked eye. When |Ra_A-Ra_B| is less than 1.5 μm, the difference in reflectivity between the first region and the second region is small, making it impossible to distinguish the first region from the second region with the naked eye. More preferably, |Ra_A-Ra_B| can be 2.0 μm or more.

[0086] Furthermore, when the larger of Ra_A or Ra_B is set as Ra_L, the average value of Vickers hardness HV between the depth position (Ra_L+1.0) μm from the surface of the coating (whether it is the surface of the first region or the surface of the second region) and the depth position of 1 / 2 the thickness of the coating is set as HV_x, and the maximum value of Vickers hardness HV is set as HV_max, the following equations (4) and (5) need to be satisfied. Setting the measurement range of Vickers hardness between the depth position (Ra_L+1.0) μm and the depth position of 1 / 2 the thickness of the coating is to prevent the measurement of Vickers hardness from being affected by surface roughness. The depth position (Ra_L+1.0) μm and the depth position of 1 / 2 the thickness of the coating are preferably located on the surface side of the coating. The reason for this is to avoid the influence of the Fe-Al interface alloy layer.

[0087] That is, HV_x represents the average Vickers hardness of the Zn-Al-Mg alloy layer in the coating, and HV_max represents the maximum Vickers hardness of the Zn-Al-Mg alloy layer.

[0088] Here, the reference surface (the surface of the coating) that serves as the reference surface at a depth position of Ra_L+1.0μm and a depth position of 1 / 2 the thickness of the coating is the distance from the average surface of the roughness in the measurement area (first region or second region). 150≤HV_x≤350…(4) 200≤HV_max…(5)

[0089] When the average Vickers hardness (HV_x) is less than 150 Hv, the deformation of the coating increases during shot peening, and the residual amount of the coating after shot peening is significantly low. Such a coating, due to the presence of iron in the base material, suffers from poor pattern clarity, increased corrosion, and cannot maintain the durability of the pattern. On the other hand, when the average Vickers hardness exceeds 350 Hv, the coating itself lacks flexibility, resulting in numerous cracks after shot peening and easy peeling. Therefore, the average Vickers hardness of the coating is in the range of 150 to 350 Hv. If the coating has the average chemical composition specified in this embodiment and has a Zn-Al-Mg alloy layer, the average Vickers hardness falls within this range. From the viewpoint of pattern clarity, a range of 200 to 300 Hv is preferred, and a range of 230 to 280 Hv is more preferred.

[0090] Furthermore, coatings with a maximum Vickers hardness (HV_max) of 200 Hv or higher indicate the presence of a certain amount of Mg-Zn compounds within the coating. These Mg-Zn compounds are moderately deformed during shot peening, preventing strain and process concentration in the surrounding soft phase. This suppresses crack formation. Through moderate deformation of the Mg-Zn compounds during shot peening, a fine microstructure is slowly formed with the surrounding soft phase. On the other hand, coatings with a maximum Vickers hardness of less than 200 Hv, as described above, contain a greater amount of ternary eutectic structure. Such coatings exhibit significant deformation after shot peening, resulting in poor pattern clarity and durability, and are therefore less desirable.

[0091] Furthermore, in this embodiment, the molten steel preferably satisfies the following equation (6) when the average value of the Vickers hardness HV between a depth position (Ra_L+1.0) μm from the coating surface and a depth position equal to half the coating thickness in the region with the larger surface roughness Ra in the first or second region is set as HV_big, and the average value of the Vickers hardness HV between a depth position (Ra_L+1.0) μm from the coating surface and a depth position equal to half the coating thickness in the region with the smaller surface roughness Ra in the first or second region is set as HV_sml. That is, HV_big / HV_sml is the ratio obtained by dividing the Vickers hardness of the region with the larger surface roughness Ra in the first or second region by the Vickers hardness of the region with the smaller surface roughness Ra, and this ratio is 0.80~1.50. 0.80≤HV_big / HV_sml≤1.50…(6)

[0092] If HV_big / HV_sml is greater than 0.80 and less than 1.50, the hardness difference between the first region and the second region becomes smaller. When an external force is applied to the coating, cracks are less likely to occur near the boundary between the first region and the second region, thus preventing the coating from becoming less corrosion resistant.

[0093] In a coating structure with a high proportion of harder phases, shot peening can soften the coating. Conversely, in a structure with a high proportion of softer phases, shot peening can harden the coating. When the hardness difference within the coating increases, cracks can be induced; therefore, the hardness ratio (HV_big / HV_sml) needs to be adjusted to the range described above. This can be achieved by changing the shot peening conditions or altering the coating composition. For example, increasing the shot peening time increases the difference between HV_big and HV_sml. The preferred range has a lower limit of 0.85 to 0.90 and an upper limit of 1.20 to 1.30.

[0094] The surface roughness Ra was measured using a non-contact white interferometric microscope.

[0095] First, evaluation test pieces are taken from the molten coated steel. These test pieces are taken from each of the first and second regions. The dimensions of the evaluation test pieces are determined by the surface area of ​​the coating to ensure a thickness of 10 mm. 2 The above area measurement method can be adopted.

[0096] For the test piece, the arithmetic mean roughness Ra of the surface was measured using a white interferometer microscope (manufactured by Bruker Corporation). In this embodiment, the surface height of a rectangular area with one side of 3.5 mm was obtained, and then the surface height information of each pixel with a size of 0.67 μm × 0.67 μm arranged in a grid pattern was obtained. The arithmetic mean roughness Ra within 3.5 mm × 3.5 mm can be calculated based on the height of each pixel. The calculation method of Ra is based on ISO 4287. If the observation range of the white interferometer microscope is aligned with the observation range of the optical microscope in advance, the average roughness corresponding to each region can be obtained. The measurement area of ​​the rectangular area with one side of 3.5 mm was selected to be a region close to the center of the first region or the second region. More specifically, all measurement points of the rectangular area with one side of 3.5 mm were selected to be positions separated from the boundary between the first region and the second region by more than 1 mm. The arithmetic mean roughness Ra (μm) of the first region was set as Ra_A, and the arithmetic mean roughness Ra (μm) of the second region was set as Ra_B.

[0097] Vickers hardness was measured using a micro Vickers hardness tester. In this embodiment, a sample for hardness testing was taken from any location on the molten steel coated with plating. A flat portion was selected when the steel exhibited unevenness during hardness testing. Before measuring the Vickers hardness, the sample was ground from the surface of the coating to a depth of (Ra - L + 1.0 μm) to achieve a mirror finish. The ground surface was a rectangular area with one side measuring 20 mm. Grinding was performed using sandpaper up to #2400 grit, followed by polishing with an alumina slurry to achieve a mirror finish. The grinding depth was determined by measuring the sample thickness using a micrometer or similar measuring device. Next, the Vickers hardness was measured.

[0098] Vickers hardness was determined using a micro Vickers hardness tester with a load set to 10 gf, according to JIS Z 2244. To avoid affecting adjacent Vickers indentations, a total of 25 measurement locations were selected from each region, and the Vickers hardness at each location was measured. The measurement locations were arranged in a grid pattern consisting of 5 points vertically and 5 points horizontally. The hardness measurement interval was 100 μm. Then, the average value of the Vickers hardness measured at the 25 locations was set as HV_x, and the maximum value was set as HV_max. The Vickers hardness measurement locations were determined by selecting the first and second regions based on observation using an optical microscope attached to the micro Vickers hardness tester, and the hardness of each region was measured.

[0099] In addition, the above measurements were performed in both the region with large surface roughness Ra and the region with small surface roughness Ra. The average value of Vickers hardness HV at a depth of 25 μm between the coating surface (Ra_L+1.0) μm and the coating thickness in the region with large surface roughness Ra was set as HV_big. The average value of Vickers hardness HV at a depth of 25 μm between the coating surface (Ra_L+1.0) μm and the coating thickness in the region with small surface roughness Ra was set as HV_sml.

[0100] <Evaluation of the durability of the design>

[0101] The coating is given an appearance design by intentionally forming a first region and a second region. The molten steel coated in this embodiment requires the durability of the appearance design. To evaluate the durability of the appearance design, the recognizability of the appearance design after corrosion is determined by visual inspection. White rust usually forms due to corrosion of the coating, but when the amount of white rust is large, forming raindrops or accumulating on the coated surface, the white rust affects the surface roughness of the first and second regions, making it difficult to recognize the appearance design.

[0102] Cyclic corrosion testing (CCT) is a test that demonstrates high relevance to exposure environments within Japan. Unlike salt spray testing (SST), which is a type of corrosion-promoting test, CCT involves repeated salt spraying, drying, and wetting processes, thus closely resembling atmospheric corrosion conditions and confirming a certain degree of relevance to exposure environments within Japan. Here, the JASO cycle (M609-91) is used as the CCT. These 30 cycles are equivalent to 10 years of typical corrosion in Japan. The durability of the appearance design is evaluated by assessing its recognizability before and after the CCT.

[0103] Specifically, the molten steel with the applied design is cut to an appropriate size, for example, 100×50mm, and the cut ends are coated with an epoxy resin coating to create an evaluation sample. Two types of evaluation samples are prepared. Evaluation sample (S1) is a sample with a 35×35mm rectangular patterned portion in the center and a non-patterned portion surrounding the patterned portion. Evaluation sample (S2) is a sample with a 35×35mm rectangular non-patterned portion in the center and a patterned portion surrounding the non-patterned portion. The patterned portion in each of evaluation samples (S1) and (S2) is an area formed by shot peening, while the non-patterned portion is an area that has not been shot peened. In this case, the non-patterned portion corresponds to the first region of this embodiment, and the patterned portion corresponds to the second region of this embodiment.

[0104] Five evaluation samples (S1) and (S2) were prepared, totaling 10 samples, for a corrosion test of 30 cycles of CCT (JASO cycle).

[0105] Before and after the test, the white rust area ratio of the evaluation surface was measured, and the white rust area ratio within a 35mm square was measured. The durability was evaluated in the following grades. S: The area of ​​white rust on the evaluation surface is less than 5%. A: The area of ​​white rust on the evaluation surface is 5% to less than 10%. B: The area of ​​white rust on the evaluation surface is 10% to less than 15%. C: The white rust area rate of the evaluation surface is above 15%.

[0106] Based on the above benchmark, evaluate samples (S1) and (S2). Combinations of (S1, S2) that are (S, S), (S, A), (A, S), (S, B), (B, S), (A, A), (A, B), or (B, A) are considered qualified, and all other combinations are considered unqualified.

[0107] In typical Zn-coated steel sheets, white rust easily forms in both shot-peened and un-shot-peened areas, making it difficult to obtain an S~B rating. Furthermore, in Al-coated steel sheets, while white rust formation is suppressed in un-shot-peened areas, it increases in shot-peened areas, making it difficult to obtain an S~B rating.

[0108] In contrast, compared with Zn-plated steel plates, Zn-Al-Mg coatings are less prone to white rust in both shot-peened and un-shot-peened areas.

[0109] As with the fused-coated steel of this embodiment, increasing the Mg and Al content of the coating can particularly improve corrosion resistance in the area after shot peening. Specifically, the Mg content is preferably more than 4.0% and less than 15.0%, and the Al content is preferably more than 10.0%. More preferably, the Mg content is 5.0% to 8.0%, and the Al content is 15.0% to 35.0%. Even more preferably, when the Mg content is 6.0% to 7.0% and the Al content is 19.0% to 30.0%, a fused-coated steel with excellent durability in appearance design can be obtained. Other arbitrary elements are almost irrelevant to corrosion prior to the JASO30 cycle, or are not substances that form distinct white rust; therefore, the durability index does not change significantly with the content of these elements.

[0110] In areas where shot peening is applied, the continuity of the coating structure is lost compared to unpeened areas. This loss of continuity leads to significant changes in the propagation of cracks in the coating. However, in areas where shot peening is applied, such as machined areas, corrosion resistance is improved.

[0111] Furthermore, when bending coated steel, cracks sometimes occur in the coating because the deformation of the base iron (the iron matrix) cannot be matched. However, the propagation direction of cracks near the interface between the base iron and the coating changes on the surface of the coated layer after shot peening. Therefore, the exposed portion of the base iron observed from the coating surface is significantly reduced in the bending section. As a result, the corrosion resistance of the processed section is improved in the areas with high surface roughness, i.e., the first or second region, where shot peening is applied.

[0112] When manufacturing coated steel with a coating having the chemical composition of this embodiment, cracks generated near the interface between the base iron and the coating typically propagate linearly from the interface to the coating surface. Therefore, when observing cracks generated in the interface alloy layer from the coating surface using an optical microscope or the like, an exposed area of ​​the base iron is confirmed in the machining section. On the other hand, when shot peening is applied (described later), the coating structure becomes finer and softer, and the continuity of the coating structure is lost, making it difficult for cracks generated in the interface alloy layer to propagate to the coating surface.

[0113] Therefore, the effect of shot peening is not only to improve the appearance design, but also to improve the corrosion resistance of the processed part, so that the shaped coated steel can obtain the preferred properties.

[0114] The steel used in the molten steel coating of this embodiment can also be a steel sheet. In this case, the coating may be provided on both one side (rolled surface) and the back side (rolled surface) of the steel sheet. In either or both of the coatings on one side or the coatings on the other side, one of the first or second regions may be arranged in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern, or text, or a combination of two or more of them, more preferably in a desired shape.

[0115] <Method for manufacturing molten-coated steel sheet according to this embodiment>

[0116] Next, the manufacturing method of the melt-coated steel according to this embodiment will be described.

[0117] Annealing of the steel used as the base material for plating is carried out in a reducing atmosphere. The reducing atmosphere and annealing conditions are not particularly limited. This annealing process removes as much of the oxides present on the steel surface as possible.

[0118] Next, the freshly annealed steel is immersed in a molten plating bath. The chemical composition of the plating bath can be adjusted appropriately to obtain the chemical composition of the coating described above. Furthermore, the temperature of the plating bath is not particularly limited; a suitable temperature for molten plating can be selected. For example, the plating bath temperature can be set to a value approximately 20°C higher than the melting point of the plating bath.

[0119] Next, the steel is lifted from the plating bath. The amount of coating can be controlled by adjusting the lifting speed of the steel sheet. Alternatively, the amount of coating can be controlled by wiping the coated steel sheet as needed. There are no particular limitations on the amount of coating; for example, it can be set within the range described above. When the steel is a steel sheet (or when the molten-coated steel is a molten-coated steel sheet), the coating is formed on both one side and the back side of that side, i.e., the other side.

[0120] Next, the coating is cooled. There are no particular restrictions on the cooling conditions; it can be done by blowing cooling gas or mist, or by natural cooling.

[0121] Next, the obtained coated steel is shot peened. Various shapes and materials can be considered for the shot peening material (medium), but spherical steel shot (Hv390~510), 0.5mm-SB-6 (JIS R 6001) is suitable. Using other materials may alter the roughness imparted to the Zn-Al-Mg coating, potentially introducing cracks into the coating, and is therefore not recommended. During shot peening, following the general rules for blasting methods for substrate conditioning (JIS Z 0310:2016), ferrous or non-ferrous metal particles (shot) are used to collide with the coating using centrifugal force or air pressure. This forms a first region and a second region on the surface of the coating. Furthermore, if the steel is a sheet and has a coating on both one and the other side, shot peening of either one or both sides of the coating is sufficient.

[0122] The surface roughness Ra of the first and second regions needs to satisfy the above (1) to (3). Therefore, when performing shot peening, the region where shot peening is performed is designated as the second region.

[0123] In forming the first and second regions, to obtain the desired pattern, it is preferable to mask the designated areas on the surface of the molten steel with a material of sufficient thickness, such as steel or wood. After the masking process, shot peening can be applied.

[0124] As an example of shot peening conditions, the projectile material is set to 0.5mm-SB-6 steel shot, the projectile rate is 3~7kg / min, the projectile speed is 50~70m / s, and the area is 1200cm². 2 Processing time: 60 seconds or more. If the processing time is too short, it will be difficult to form a clear pattern. Preferably, it is 150 seconds or more. The size of the area to be shot-peened depends on the dimensions of the design to be formed on the surface. A more suitable condition is 1200 cm² per area. 2 The processing time is in the range of 150 to 600 seconds. If the processing time is too long, the coating will deform significantly, sometimes the value of Hv_big / Hv_sml will increase or the coating will disappear, therefore this is not preferred. The above effects are amplified when the Mg content is high; therefore, in cases with high Mg content, a more preferred upper limit is 550 seconds, 500 seconds, or 450 seconds.

[0125] Figure 1 This illustrates an example of patterned areas formed through shot peening. Figure 1 The image shows an example of forming letters and heart-shaped markings on a coating with a pear-skin-like appearance through shot peening.

[0126] The molten steel in this embodiment can also have a film formed on the coating after shot peening (or roll forming). One or more films can be formed. Examples of films directly above the coating include chromate films, phosphate films, and chromate-free films. The chromate treatment, phosphate treatment, and chromate-free treatment for forming these films can be performed using known methods.

[0127] Chromate treatments include: electrolytic chromate treatment, which forms a chromate film through electrolysis; reactive chromate treatment, which forms a film by reacting with the raw material and then rinsing off excess treatment solution; and coating-type chromate treatment, which applies the treatment solution to the substrate and dries it without washing to form a film. Any treatment can be used. For aesthetic purposes, near-colorless and transparent materials are preferred.

[0128] Examples of electrolytic chromate treatments include those using chromic acid, silica sol, resins (phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene-butadiene latex, diisopropanolamine modified epoxy resin, etc.) and hard silica.

[0129] Chromate-free treatment is preferred as it does not impose a significant environmental burden. Types of chromate-free treatments include: electrolytic chromate-free treatment, which forms a chromate-free film through electrolysis; reactive chromate-free treatment, which forms a film by reacting with the raw materials and then rinsing off excess treatment solution; and coating-type chromate-free treatment, which involves applying the treatment solution to the substrate and drying it without washing to form a film. Any treatment method can be used.

[0130] Furthermore, one or more layers of organic resin film may be present on the film directly above the coating. The organic resin is not limited to a specific type; examples include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, or modified forms of these resins. Here, a modified form refers to a resin obtained by reacting reactive functional groups contained in the structure of these resins with other compounds (monomers, crosslinking agents, etc.) containing functional groups capable of reacting with those functional groups.

[0131] As such an organic resin, one or more organic resins (unmodified organic resins) can be used in combination, or at least one organic resin modified from another organic resin can be used in combination in the presence of at least one organic resin. Furthermore, the organic resin film can contain any coloring pigments or anti-rust pigments. Aqueous substances that are dissolved or dispersed in water can also be used.

[0132] Example

[0133] The following coated steel sheets are prepared for use as steel sheets for shot peening.

[0134] The clad steel sheet is manufactured by using a molten plating simulator made by Rhesca, which produces an alloy containing a specified amount of pure metals, etc., and then melts and performs molten plating.

[0135] The base plate used for plating is a 200mm×100mm×1.2mm thick cold-rolled steel sheet (equivalent to SPCC JIS G3141:2021) or a hot-rolled striped steel sheet (manufactured by Daifu Steel Co., Ltd.).

[0136] Before melt coating, the surface of the original plate is fully reduced by holding it at 800°C for 1 minute (dew point -40°C) under a 5% N2-H2 atmosphere. Then, it is immersed in a coating bath with a melting point of +30°C for 3 seconds and lifted off, and the coating thickness is adjusted by wiping with N2 gas. Immediately after wiping, it is cooled to room temperature at an average cooling rate of -10°C / second. The manufactured coated steel sheet is then subjected to surface finishing rolling with a reduction rate of less than 1% of the steel sheet thickness, resulting in a surface roughness Ra in the range of 0.8~1.5μm.

[0137] The shot peening conditions were set as follows: 0.5mm SB-6 steel shot, 5kg / min feed rate, 60m / s blasting speed, and 1200cm² area per shot. 2 The processing time is 50-720 seconds. The shot peening unit used is the SNT-1PE manufactured by Shinto Industrial. The scope of shot peening varies depending on the evaluation item.

[0138] After the designated area is masked with steel material, shot peening is performed to randomly generate 100 bold "0" to "9" numbers in Gothic font, 100pt in size.

[0139] The average chemical composition of the coating, the surface roughness (Ra_A, Ra_B) and Vickers hardness (Hv_x, Hv_max, Hv_big, Hv_sml) of the coating in a specified area are measured and evaluated as described in the embodiments.

[0140] (Evaluation of corrosion resistance of the machining section)

[0141] Before and after shot peening, coated steel sheets were cut to dimensions of 100×50×1.2mm. The cut ends were coated with epoxy resin to create test pieces with a 70×40mm evaluation surface in the center. For the coated steel sheet after shot peening, the area treated by shot peening was cut to serve as the evaluation surface. Then, using Eriksen machining, a process was performed to form a... An Erickson machining section with a diameter of 40 mm and a height of 5 mm was used. Then, a CCT test was performed, and the white rust area percentage was determined after 30 cycles according to JASOM 609-91. The corrosion resistance of the machining section was then evaluated according to the following evaluation criteria. S, A, and B were set as acceptable. S: The area of ​​white rust after shot peening is more than 20% lower than that before shot peening. A: The area of ​​white rust after shot peening is more than 10% lower and less than 20% lower than the area of ​​white rust before shot peening. B: The area of ​​white rust after shot peening is more than 5% lower and less than 10% lower than the area of ​​white rust before shot peening. C: The area of ​​white rust after shot peening is 0% to less than 5% lower than the area of ​​white rust before shot peening. Or, the area of ​​white rust after shot peening is greater than the area of ​​white rust before shot peening.

[0142] (Evaluation of clarity)

[0143] In the sharpness evaluation, a computer-generated character recognition function, including machine learning, was used. For the digits "0" to "9" formed by shot peening, a digital camera was used to photograph the area containing each digit from a 45-degree angle using a white LED light source, taken vertically. The photographs were saved as 1000 pixels × 1000 pixels. After cropping the digit areas, a 100-pixel × 100-pixel mosaic effect was applied, followed by binarization. One hundred binarized digit images extracted from the samples using the above method were prepared. Each digit image was classified into 0 to 9 by processing it with a convolutional neural network using the MNIST database, which serves as the set of digit images from 0 to 9. The formed digits were compared with the digits classified by the convolutional neural network; those that were the same were considered correct, and the correct answer rate for the 100 digit images was calculated. Then, the sharpness was evaluated according to the following evaluation criteria. A was designated as acceptable. A: The overall consistency rate of the numbers 1 to 10 is over 80%. B: The overall consistency rate of the numbers 1 to 10 is less than 80%.

[0144] <Evaluation of the durability of the design>

[0145] The shot-peened molten coated steel was cut into 100×50mm pieces, and the cut ends were coated with epoxy resin to create evaluation samples. Two types of evaluation samples were prepared. Evaluation sample (S1) consisted of a 35×35mm rectangular patterned area in the center surrounded by non-patterned areas. Evaluation sample (S2) consisted of a 35×35mm rectangular non-patterned area in the center surrounded by patterned areas. The patterned areas in both evaluation samples (S1) and (S2) were areas formed by shot peening, while the non-patterned areas were areas that were not shot-peened.

[0146] Five evaluation samples (S1) and (S2) were prepared, and a total of 10 samples were subjected to 30 cycles of CCT (JASO Cyclic Test (M609-91)). Before and after the test, the white rust area ratio of the evaluation surface was measured, and the white rust area ratio within a 35 mm square was measured. The durability was evaluated according to the following grading criteria. Evaluation samples (S1) and (S2) were evaluated according to the following evaluation criteria. Combinations of (S1, S2) such as (S, S), (S, A), (A, S), (S, B), (B, S), (A, A), (A, B), or (B, A) were set as acceptable. S: The area of ​​white rust on the evaluation surface is less than 5%. A: The area of ​​white rust on the evaluation surface is 5% to less than 10%. B: The area of ​​white rust on the evaluation surface is 10% to less than 15%. C: The white rust area rate of the evaluation surface is above 15%.

[0147] As shown in Tables 1-4, in Comparative Examples No. 1-4, the Al content in the chemical composition of the coating is less than 10.0% by mass, resulting in low coating hardness and a surface roughness exceeding 10.0 μm due to shot peening. Consequently, durability and corrosion resistance of the processed parts deteriorate.

[0148] In Comparative Examples No. 5-8, the Mg content in the chemical composition of the coating was less than 4.0% by mass, resulting in low coating hardness and a surface roughness exceeding 10.0 μm after shot peening. Consequently, durability and corrosion resistance of the processed parts deteriorated.

[0149] The plating composition of Example No. 9 is within the specified range, and the hardness of the coating is sufficient to ensure clarity and corrosion resistance of the processed parts even after shot peening.

[0150] In Comparative Example No. 10, the Mg content in the coating's chemical composition was less than 4.0%, resulting in low coating hardness and a surface roughness exceeding 10.0 μm after shot peening. Consequently, durability and corrosion resistance of the processed parts deteriorated.

[0151] The plating composition of Examples No. 11-28 and 30-32 is within the specified range, and the hardness of the plating layer is sufficient to ensure clarity, durability, and corrosion resistance of the processed parts.

[0152] In comparative examples No. 29 and 39, the shot peening treatment time was insufficient, and the surface roughness of the shot peened surface did not change sufficiently, resulting in poor clarity, durability, and corrosion resistance of the processed part.

[0153] Comparative Example No. 33 has a longer shot peening time. Therefore, HV_big / HV_sml deviates from the scope of the invention. As a result, durability is insufficient.

[0154] In Comparative Examples No. 34-37 and 41, the Mg content in the chemical composition of the coating does not meet the range of more than 4.0% and less than 15.0%. The Al content in No. 34-37 also deviates from the scope of the invention (more than 10.0% and less than 40.0%). Therefore, the hardness of the coating is not within the optimal range, and the surface roughness resulting from shot peening is either too small or too large (more than 10.0 μm). Consequently, clarity, durability, and corrosion resistance of the processed parts deteriorate.

[0155] Comparative Example No. 38 was not shot peened and no pattern was formed.

[0156] In Comparative Example No. 40, the shot peening process was too long, resulting in excessively high Ra_B and HV_big / HV_sml values. Consequently, durability and corrosion resistance of the machined area deteriorated.

[0157]

[0158]

[0159]

[0160]

[0161] Industrial availability According to this disclosure, a molten-coated steel material and a method for manufacturing molten-coated steel material can be provided, which can display text, designs, etc. on the coating with excellent clarity and durability, and can achieve large-area display of text, designs, etc. Therefore, an inexpensive and aesthetically pleasing material can be provided, which can contribute to the development of industry.

[0162] Explanation of reference numerals in the attached figures 1. Hot-dip galvanized steel 11. Steel 12 coatings 21 First District 22 The average surface of the first region 31 Second Region 32. Average surface of the second region L1 is the depth position (Ra_L+1.0μm) from the surface of the coating when the second region is set as the measurement region. L2 is the depth position at 1 / 2 the thickness of the coating when the second region is set as the measurement region.

Claims

1. A molten-coated steel material, comprising steel material and a coating formed on the surface of said steel material, The average chemical composition of the coating, expressed as a percentage by mass, includes A1: More than 10.0% and less than 40.0% Mg: ≥4.0% but ≤15.0% Si: 0% or more and less than 1.00% Sn: 0% or more and 0.7% or less Bi: 0% or more and less than 0.3% In: 0% or more and less than 0.3% The total amount of Sn, Bi, and In, ΣX: above 0% and below 0.7%, Ca: 0% or more and 0.60% or less Y: Above 0% and below 0.30% La: 0% or more and 0.30% or less Ce: 0% or more and 0.30% or less Sr: 0% or more and 0.30% or less Li: 0% or more and less than 0.30% The total amount of Ca, Y, La, Ce, Sr and Li, ΣYa: ≥0% and ≤0.60%, Cr: 0% or more and less than 1.00% Ni: 0% or more and less than 1.0% Mo: 0% or more and 0.25% or less Cu: 0% or more and 1.0% or less Ag: 0% or more and 0.25% or less Sb: 0% or more and 0.25% or less Pb: above 0% and below 0.25% The total amount of Cr, Ni, Mo, Cu, Ag, Sb and Pb, ΣYb: ≥0% and ≤1.0%. B: Above 0% and below 0.50% P: Above 0% and below 0.50% The combined amount of B and P, ΣYc: ≥0% and ≤0.50%, Ti: 0% or more and 0.25% or less Co: 0% or more and less than 0.25% V: Above 0% and below 0.25% Nb: 0% or more and 0.25% or less Mn: 0% or more and 0.25% or less Zr: 0% or more and 0.25% or less W: Above 0% and below 0.25% The total amount of Ti, Co, V, Nb, Mn, Zr, and W, ΣZ: above 0% and below 0.25%. Fe: 0% or more and 5.0% or less Zn: Above 42.0% and below 85.0%, The thickness of the coating is 5 μm or more. The coating has a first region and a second region. The first region or the second region is configured in a prescribed shape. Let the arithmetic mean surface roughness Ra (μm) of the first region of the molten steel be Ra_A. Let the arithmetic mean surface roughness Ra (μm) of the second region of the molten coated steel be Ra_B. Set the larger value of Ra_A or Ra_B as Ra_L. Let HV_x be the average value of the Vickers hardness HV between a depth position (Ra_L+1.0) μm from the surface of the coating and a depth position at half the thickness of the coating, and let HV_max be the maximum value of the Vickers hardness HV. Satisfying equations (1) to (5) below, The average value of the Vickers hardness HV between a depth position (Ra_L+1.0) μm from the surface of the coating and a depth position equal to half the thickness of the coating in the region where the arithmetic mean roughness Ra is larger in the first region or the second region is set as HV_big. When the average value of the Vickers hardness HV between a depth position (Ra_L+1.0) μm from the surface of the coating and a depth position equal to half the thickness of the coating in the region with the smaller surface roughness Ra in the first region or the second region is set as HV_sml, Satisfy the following equation (6): Ra_A≤10.0…(1) Ra_B≤10.0…(2) 1.5≤|Ra_A-Ra_B|…(3) 150≤HV_x≤350…(4) 200≤HV_max…(5) 0.80≤HV_big / HV_sml≤1.50…(6).

2. The molten steel according to claim 1, wherein, The first region or the second region is configured in a shape that is any one of the following: a straight line, a curved line, a dot, a graphic, a number, a symbol, a pattern, or a text, or a combination of two or more of them.

3. The molten steel according to claim 1, wherein, The first region or the second region is configured in a manner that is a shape that is any one of the following: a straight line, a curved line, a dot, a graphic, a number, a symbol, a pattern, or a word, or a combination of two or more of them.

4. The molten steel according to claim 1, wherein, The steel is steel plate. The coating is present on both one side of the steel plate and on the back side, i.e., the other side. In either or both of the coatings on one side or the coatings on the other side, one of the first region or the second region is configured in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern, or text, or a combination of two or more of them.

5. The molten steel according to claim 1, wherein, The steel is steel plate. The coating is present on both one side of the steel plate and on the back side, i.e., the other side. In either or both of the coatings on one side or the coatings on the other side, one of the first region or the second region is configured in a shape that is any one of a straight line, a curved line, a dot, a graphic, a number, a mark, a pattern, or text, or a combination of two or more of them.

6. A method for manufacturing molten-coated steel, comprising the method for manufacturing molten-coated steel according to any one of claims 1 to 3, wherein, On the surface of a coating formed on the surface of steel by a melt-coating method, ferrous or non-ferrous metal particles (shots) are collided using centrifugal force or air pressure to form one of the first region or the second region.

7. A method for manufacturing molten-coated steel, which is the method for manufacturing molten-coated steel according to claim 4 or 5, wherein, On the surface of a coating formed on one side or the back side of a steel plate by a melt-coating method, ferrous or non-ferrous metal particles (shots) are collided with the melt-coated steel by centrifugal force or air pressure, thereby forming one of the first region or the second region.

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