Plated steel sheet

Abstract

Provided is a plated steel sheet with which it is possible to improve the appearance design of hairlines when viewed from a close range. In this plated steel sheet, in a surface roughness profile of a measurement range having a length of 5000 [mu] m in a direction perpendicular to a hairline extension direction of the surface, the measurement range is divided by minute regions n having a length pitch of 50 [mu] m, and in each minute region n, a peak count RPc having a dead zone width of 360 nm is obtained. The total number of first control units in which the absolute difference between the peak counts RPc of adjacent minute regions n is 6 or more is defined as N, and the total number of second control units in which the absolute difference between the peak counts RPc of minute regions m and m + 1 is less than 6 and the absolute difference between the peak counts RPc of minute regions m and m + 2 is 6 or more is defined as M. The total number J of the control units in formula (1) is greater than 7, where K is the total number of the third control units in which the absolute difference between the peak counts RPc of the minute regions k and k + 1 is 6 or greater, and the absolute difference between the peak counts RPc of the minute regions k + 1 and k + 2 is 6 or greater. J = N + M-K (1).

Description

Technical Field

[0001] The present disclosure relates to a plated steel sheet, and more specifically, to a plated steel sheet having a plating layer with graining formed on the surface. Background Art

[0002] Corrosion resistance and design properties are sometimes required for articles such as electrical equipment, building materials, and automobiles. As a material suitable for such applications, plated steel sheets having graining as a type of texture formed on the surface of the plating layer have been proposed.

[0003] For example, in Japanese Unexamined Patent Application Publication No. 2010-509495 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2006-124824 (Patent Document 2), in a plated steel sheet having a hot-dip galvanized layer, hairline cracks are formed on the surface of the hot-dip galvanized layer to improve the design of the plated steel sheet.

[0004] In addition, in Japanese Patent Application Laid-Open No. 2017-136645 (Patent Document 3) and Japanese National Publication No. 2013-536901 (Patent Document 4), in a plated steel sheet having an electroplated zinc layer, hairline lines are formed on the surface of the electroplated zinc layer to improve the design properties of the plated steel sheet.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application No. 2010-509495

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2006-124824

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-136645

[0010] Patent Document 4: Japanese Patent Application No. 2013-536901 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] In the above-mentioned patent document, the design properties of the plated steel sheet are improved by adjusting the surface roughness of the plating layer where hairline lines are formed.

[0013] Furthermore, the required visibility of hairline patterns varies depending on the intended use. For example, in the case of plated steel sheets for electrical equipment, hairline patterns must be visually detectable when viewed from a close distance of less than 1 meter. In this specification, the ability to visually detect hairline patterns is referred to as having a high degree of design appeal.

[0014] An object of the present disclosure is to provide a plated steel sheet capable of improving the design of hairline texture when observed from a close distance.

[0015] Solutions for solving problems

[0016] The coated steel sheet disclosed in the present invention comprises a base steel sheet and a coating. The coating is formed on the base steel sheet, and has hairline grooves formed on the surface. On the surface of the coating, the surface roughness profile is measured within a measurement range of 5000 μm in length in a direction perpendicular to the extension direction of the hairline grooves using a laser microscope, and the surface roughness profile of the measurement range is obtained. The measurement range is divided into 100 micro-areas n (n is an integer from 1 to 100) arranged at intervals of 50 μm in length from the end of the measurement range, and for each micro-area n, the peak count RPc is obtained with a dead zone width (insensitive width) of 360 nm. Within the measurement range, the total number of the first control parts in which the absolute difference in the peak count RPc of adjacent micro-areas n is 6 or more is set to N. The total number of second comparison sections, where the absolute difference between the peak count RPc of micro region m (m is an integer from 1 to 98) and the peak count RPc of micro region m+1 is less than 6, and the absolute difference between the peak count RPc of micro region m and the peak count RPc of micro region m+2 is 6 or greater, is set to M. The total number of third comparison sections, where the absolute difference between the peak count RPc of micro region k (k is an integer from 1 to 98) and the peak count RPc of micro region k+1 is 6 or greater, and the absolute difference between the peak count RPc of micro region k+1 and the peak count RPc of micro region k+2 is 6 or greater, is set to K. In this case, the total number J of comparison sections defined by equation (1) is greater than 7.

[0017] J=N+MK (1)

[0018] Effects of the Invention

[0019] The plated steel sheet of the present disclosure can improve the design properties of the hairline texture when observed from a close distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a photographic image showing an example of cracks formed on the surface of the zinc-based plating layer of a plated steel sheet.

[0021] Figure 2 This is an SEM image of the surface of the plating layer where hairline cracks are formed.

[0022] Figure 3A This is a schematic diagram showing an example of the surface roughness of the plating layer in a cross section perpendicular to the extending direction of the hairline.

[0023] Figure 3B Is to express Figure 3ASchematic diagram of an example of different surface roughness of the plating layer in a cross section perpendicular to the direction in which the hairline extends.

[0024] Figure 4 It is a cross-sectional view of a plated steel sheet according to this embodiment.

[0025] Figure 5 Observed from above the coating Figure 4 Top view of the coated steel sheet shown.

[0026] Figure 6 This is a diagram showing an example of a surface roughness profile measured by a laser microscope.

[0027] Figure 7 This is a schematic diagram for explaining a method for measuring the peak count RPc in one micro region n (n is an integer from 1 to 100).

[0028] Figure 8 This is a diagram showing an example of the peak count RPc in the measurement range.

[0029] Figure 9 Is to express Figure 8 A diagram showing an example of peak counts RPc in different measurement ranges. DETAILED DESCRIPTION

[0030] The present inventors have studied methods for improving the design quality of the hairline texture when viewed from a close distance in the case of a plated steel sheet with hairline texture. In this specification, "close distance" refers to a distance of less than 1 meter from the hairline textured steel sheet. Furthermore, "high design quality" means that the hairline texture is visually recognizable.

[0031] In conventional plated steel sheets with hairline formation, the surface roughness (e.g., arithmetic mean roughness Ra) of the coating layer with hairline formation is adjusted. When hairline formation occurs on the surface of the coating layer of the plated steel sheet, a plurality of grinding marks extending in one direction are formed on the surface of the coating layer using a grinding belt or the like. In conventional plated steel sheets, the depth of the grinding marks is increased to improve the visibility of the hairline formation and enhance the wear resistance. Figure 1 Shown is the visibility of hairline cracks on the plated surface.

[0032] The above technical concept is based on the premise that the contrast of hairline lines is correlated with the depth of grinding marks (the height difference between the unevenness formed on the surface). In this case, it is believed that the contrast in the macroscopic region of the hairline lines, which can be visually identified, is correlated with the contrast of the unevenness in the microscopic region of the surface where the hairline lines can be visually identified. Therefore, the present inventors confirmed the contrast of the unevenness in the microscopic region of the surface of the plating layer where the hairline lines can be visually identified using the following method.

[0033] Specifically, a scanning electron microscope was used to observe a micro region on the surface of the plating layer where the cracks were formed. Figure 2 This is an SEM image of a microscopic region of the surface of the plating layer where hairline cracks are formed (secondary electron image: viewing area: 750 μm×750 μm). Figure 2 In the microscopic area of ​​the surface where hairline is visually recognized, grinding marks (concave and convex parts) extending in one direction are formed, and the comparison based on the depth of the grinding marks (the height difference between the concave and convex parts) is confirmed. However, it is found that the macroscopic comparison of hairline that can be visually recognized is different from that of the Figure 2 The contrast of the concavities and convexities in the microscopic region shown is not necessarily relevant. In other words, the depth of the grinding marks (concavities and convexities) on the surface of the plating layer of the plated steel sheet is not necessarily relevant to the design quality of the hairline when the plated steel sheet is observed from a close distance.

[0034] Based on the above new findings, the present inventors studied a method other than deepening the grinding marks to increase the average height difference of the surface irregularities in order to improve the design of the hairline texture when observed at a close distance.

[0035] As a result of their research, the present inventors discovered that the visibility of hairline lines is significantly correlated with the distribution of grinding marks (the density difference between the asperities) compared to the depth of the grinding marks (the average height difference between the asperities). Specifically, when "visible asperities" are defined as those with a height difference that is visually discernible as a contrast, and when the area perpendicular to the direction of the hairline is divided into a plurality of micro-regions, the greater the density difference between the visible asperities between adjacent micro-regions, the higher the visibility of the contrast at the boundary between adjacent micro-regions. As a result, the visibility of the hairline lines increases. The smaller the density difference between the visible asperities between adjacent micro-regions, the lower the visibility of the boundary between adjacent micro-regions. As a result, the visibility of the hairline lines decreases. In the following description, the boundary between adjacent micro-regions, that is, the boundary with a large density difference between the visible asperities between adjacent micro-regions, is referred to as a "contrast area." The more contrast areas there are, the higher the visibility of the hairline lines. In other words, by adjusting the density distribution of visible asperities, the visibility of the hairline lines can be improved.

[0036] Figure 3A This is a schematic diagram showing the surface roughness of the plating layer in a cross section perpendicular to the direction in which the hairline extends. Figure 3A , it is assumed that the surface of the coating is divided into a plurality of micro-regions 1 to 8 of a predetermined length L in a direction perpendicular to the extension direction of the hairline. Each micro-region 1 to 8 has the same length. In each micro-region 1 to 8, the density (number / L) of bumps and depressions with a predetermined height difference or more, i.e., bumps and depressions that can be visually recognized (visible bumps and depressions) is calculated. Figure 3AIn the example, the visible concavo-convex density in micro region 1 is set to 10 / L, the visible concavo-convex density in micro region 2 is set to 2 / L, and the visible concavo-convex density in micro region 3 is set to 1 / L. Figure 3A In the example, the boundary where the difference in visible unevenness density between adjacent micro-regions is 6 or more per L can be visually recognized. Therefore, this boundary is identified as the “control area”. Figure 3A The visible unevenness density difference at the boundary between micro regions 1 and 2, the visible unevenness density difference at the boundary between micro regions 3 and 4, and the visible unevenness density difference at the boundary between micro regions 7 and 8 are all 6 or more per L. Therefore, these boundaries correspond to the control areas.

[0037] The present inventors have also found that when observing the hairline from a close distance, if the interval between adjacent contrast portions is too narrow, the hairline cannot be seen as visible unevenness, and the design quality of the hairline is reduced. Figure 3B In the case of , the visible uneven density difference at the boundary between micro area 1 and micro area 2, the visible uneven density difference at the boundary between micro area 2 and micro area 3, the visible uneven density difference at the boundary between micro area 3 and micro area 4, and the visible uneven density difference at the boundary between micro area 7 and micro area 8 are each 6 or more / L. Therefore, these boundaries correspond to the control area. Figure 3B In the case of visually identifying hairlines from a close distance, finer hairlines can be visually identified compared to the case of visually identifying hairlines from a long distance. However, even at a close distance, if the contrast portions exist continuously, it is difficult to distinguish adjacent continuous contrast portions. Therefore, when observing hairlines from a close distance, since multiple contrast portions are close in the area of ​​micro area 1 to micro area 4, these contrast portions are identified as one contrast portion. On the other hand, on the surface of the plating layer, Figure 3A In the case of the hairline, the plurality of contrasting portions are arranged with gaps between each other and are not arranged continuously. Therefore, when the hairline is observed from a close distance, each contrasting portion can be visually identified, and the designability of the hairline is improved.

[0038] Based on the above findings, the present inventors further investigated methods for improving the design properties of hairline textures when observed from a close distance. As a result, they discovered that the design properties of hairline textures when observed from a close distance are improved if the surface roughness profile of a zinc-based plated layer, measured using a laser microscope over a 5000 μm length in a direction perpendicular to the direction in which the hairline textures extend, satisfies the following requirements.

[0039] Specifically, within the surface roughness profile of the measurement range, the measurement range is divided into 100 microregions n (n is an integer from 1 to 100) arranged at 50 μm intervals from the end of the measurement range. For each microregion n, the peak count RPc is calculated to achieve a dead zone width of 360 nm. Within the measurement range, the total number of first comparison sections in which the absolute difference in peak counts RPc between adjacent microregions n is 6 or greater is N. The total number of second comparison sections in which the absolute difference in peak counts RPc between microregion m (m is an integer from 1 to 98) and the peak count RPc of microregion m+1 is less than 6, and the absolute difference in peak counts RPc between microregion m and the peak count RPc of microregion m+2 is 6 or greater is M. The total number of third comparison sections in which the absolute difference in peak counts RPc between microregion k (k is an integer from 1 to 98) and the peak count RPc of microregion k+1 is 6 or greater, and the absolute difference in peak counts RPc between microregion k+1 and the peak count RPc of microregion k+2 is 6 or greater is K. In this case, the total number J of control parts defined by formula (1) is greater than 7.

[0040] J=N+MK(1)

[0041] The gist of the plated steel sheet of the present embodiment, which was completed based on the above findings, is as follows.

[0042] [1] A coated steel sheet comprising: a base steel sheet; and a coating layer formed on the base steel sheet and having hairline grooves formed on the surface, wherein a surface roughness profile of the coating layer is measured using a laser microscope within a measurement range of 5000 μm in a direction perpendicular to the extension direction of the hairline grooves, and the surface roughness profile of the measurement range is obtained, the measurement range is divided into 100 micro-areas n (n is an integer of 1 to 100) arranged at intervals of 50 μm in length from the end of the measurement range, and for each micro-area n, a peak count RPc is obtained with a dead zone width of 360 nm, and within the measurement range, the first micro-area n having an absolute difference of 6 or more in the peak count RPc of the adjacent micro-areas n is selected. The total number of comparison sections is set to N, the total number of second comparison sections in which the absolute difference between the peak count RPc of the micro area m (m is an integer from 1 to 98) and the peak count RPc of the micro area m+1 is less than 6, and the absolute difference between the peak count RPc of the micro area m and the peak count RPc of the micro area m+2 is 6 or more is set to M, and the total number of third comparison sections in which the absolute difference between the peak count RPc of the micro area k (k is an integer from 1 to 98) and the peak count RPc of the micro area k+1 is 6 or more, and the absolute difference between the peak count RPc of the micro area k+1 and the peak count RPc of the micro area k+2 is 6 or more is set to K. At this time, the total number J of comparison sections defined by formula (1) is greater than 7.

[0043] J=N+MK (1)

[0044] [2] The plated steel sheet according to [1], wherein the exposure rate of the base steel sheet when the plated layer is viewed from above is less than 5.0%.

[0045] [3] The plated steel sheet according to [1] or [2], wherein the plating layer is a zinc-based plating layer.

[0046] Hereinafter, the plated steel sheet of the present embodiment will be described with reference to the accompanying drawings. The same or corresponding components in each drawing are denoted by the same reference numerals, and the same description will not be repeated.

[0047] [Regarding plated steel sheets 1]

[0048] Figure 4 : is a cross-sectional view of the plated steel sheet 1 of this embodiment. Figure 4 In FIG, the rolling direction of the plated steel sheet 1 is defined as RD. The plate thickness direction of the plated steel sheet 1 is defined as TD. The plate width direction perpendicular to the rolling direction RD and the plate thickness direction TD of the plated steel sheet 1 is defined as WD.

[0049] Reference Figure 4 The plated steel sheet 1 includes a base steel sheet 100 and a plated layer 10. The plated layer 10 is formed on the surface of the base steel sheet 100. Figure 4 In the embodiment, the plating layer 10 is formed only on one surface of the base steel plate 100 . However, the plated steel plate 1 may have the plating layer 10 formed on both surfaces of the base steel plate 100 .

[0050] The plated steel sheet 1 may further include a resin layer (not shown). If the plated steel sheet 1 includes a resin layer, the resin layer is formed on the surface of the coating 10. Furthermore, the plated steel sheet 1 may also include a chemical conversion film (not shown). The chemical conversion film is formed on the surface of the coating 10. The plated steel sheet 1 may also include a chemical conversion film formed on the coating 10 and a resin layer formed on the chemical conversion film.

[0051] Figure 5 The coating 10 is viewed from above. Figure 4 The top view of the plated steel sheet 1 is shown. Figure 5 , hairline HL is formed on the surface of the coating layer 10 of the plated steel sheet 1. The hairline HL is composed of a plurality of fine irregularities extending along the rolling direction RD. The fine irregularities are, for example, grinding marks. The following describes the base steel sheet 100 and the coating layer 10.

[0052] [About base steel plate 100]

[0053] The base steel plate 100 can be a known steel plate used for plated steel sheets (e.g., electrogalvanized steel sheet, electrogalvanized alloy steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, etc.) depending on the mechanical properties (e.g., tensile strength, workability, etc.) required for the plated steel sheet 1 to be produced. For example, the base steel plate 100 can be a steel plate for electrical equipment or a steel plate for building materials. The base steel plate 100 can be either a hot-rolled steel plate or a cold-rolled steel plate.

[0054] The chemical composition of the base steel plate includes, for example, by mass % C: 0.01-0.25%, Si: 0.001-1.200%, Mn: 0.01-2.50%, P: 0.001-0.200%, S: 0.001-0.050%, sol.Al: 0.015-0.060%, and the balance Fe and impurities.

[0055] [About Plating 10]

[0056] The coating 10 is formed on the surface of the base steel plate 100. The type of coating 10 is not particularly limited. Examples of the coating 10 include Ni-based coatings, Cu-based coatings, zinc-based coatings, Au-based coatings, Sn-based coatings, Al-based coatings, and alloy coatings containing two or more of Ni, Cu, Zn, Au, Sn, and Al. The X-based coating (X is one of Ni, Cu, Zn, Au, Sn, and Al) refers to a coating mainly composed of X. Mainly composed of X means that the content of X as the main component element in the coating is at least 50.0%. For example, a zinc-based coating refers to a coating having a Zn content of 50.0% or more.

[0057] From the viewpoint of the aesthetic appearance of the formed hairline HL, the plating layer 10 is preferably a Ni-based plating layer, a Cu-based plating layer, an Au-based plating layer, a Sn-based plating layer, an Al-based plating layer, or an alloy plating layer containing two or more of Ni, Cu, Au, Sn, and Al, which have excellent durability.

[0058] On the other hand, considering the damage to the plating layer 10 caused by the formation of hairline HL on the surface of the plating layer 10, the plating layer 10 preferably has a composition that provides excellent corrosion resistance even when hairline HL is formed. Therefore, from the perspective of achieving both aesthetics and corrosion resistance, the preferred plating layer 10 is a zinc-based plating layer that has a sacrificial corrosion protection function and excellent corrosion resistance.

[0059] When the coating 10 is a zinc-based coating, as described above, this means that the Zn content in the coating is at least 50.0%. The chemical composition of the zinc-based coating, for example, contains 50.0% or more Zn by mass, and contains 0 to 50.0% of one or more selected from the group consisting of Al, Mg, Si, Ni, Fe, Co, Cr, Ca, Y, La, Ce, Sn, Bi, In, Ti, V, Nb, Cu, Mn, Sr, Sb, Pb, and B as arbitrary elements. Furthermore, it may further contain 0 to 5.0% of C as an arbitrary element. The chemical composition of the zinc-based coating may not contain Al, Mg, Si, Ni, Fe, Co, Cr, Ca, Y, La, Ce, Sn, Bi, In, Ti, V, Nb, Cu, Mn, Sr, Sb, Pb, B, and C.

[0060] The preferred lower limit of the Zn content in the zinc-based coating is 80.0%, more preferably 85.0%. In other words, the zinc-based coating comprises Zn or a Zn alloy, with the remainder being impurities. The zinc-based coating is a layer comprising zinc plating or a zinc alloy plating. Furthermore, the zinc-based coating may be an electroplated zinc-based coating or a hot-dip galvanized coating. Furthermore, as mentioned above, the chemical composition of the zinc-based coating is well known.

[0061] [Method for measuring the chemical composition of the plating layer 10]

[0062] The chemical composition of the coating 10, which is composed of an X-based coating, can be measured using the following method. A sample is collected, including a cross section parallel to the thickness direction TD of the plated steel sheet 1 and containing the coating 10. The cross section parallel to the thickness direction TD is referred to as the observation surface. On the observation surface of the sample, line analysis using EPMA (Electron Probe Micro Analyzer) is performed along the thickness direction TD from the surface of the plated steel sheet 1 to determine the content (mass %) of each element along the line to be measured. In the line analysis, the region (range) containing 50.0% or more of X as the main component element is defined as the X-based coating. Line analysis is performed at any ten locations on the observation surface of the sample to determine the content (mass %) of each element within the range (line) of the X-based coating 10 determined by the line analysis. The arithmetic mean of the content of each element within the range of the X-based coating 10, obtained from the line analysis at the ten locations, is determined. The chemical composition of the X-based coating 10 is determined based on the arithmetic mean of the content of each element determined.

[0063] [Regarding the Thickness of the Plating Layer 10]

[0064] The thickness of the plating layer 10 is not particularly limited, and any known thickness may be sufficient. When the plating layer 10 is a zinc-based plating layer, the thickness of the plating layer 10 is, for example, 0.5 to 25.0 μm.

[0065] [Method for measuring the thickness of the plating layer 10]

[0066] The thickness of the coating 10 can be determined by the following method. Collect a sample including a cross section parallel to the plate thickness direction TD of the plated steel plate 1 and including the coating 10. The cross section parallel to the plate thickness direction is called an observation surface. The observation surface of the sample is mirror-polished. Using a scanning electron microscope, the mirror-polished observation surface is observed at a magnification (500 to 3000 times) that allows the entire length (thickness) of the plate thickness direction TD of the coating 10 to be observed, and a reflected electron image is generated. In the reflected electron image, the base steel plate 100 and the coating 10 can be easily distinguished by comparison. Therefore, the coating 10 is determined based on the comparison. The length (thickness) of the determined coating 10 in the plate thickness direction TD is measured at any 10 locations. The arithmetic mean of the thicknesses measured at the 10 locations is defined as the thickness (μm) of the coating 10.

[0067] [About hairline HL]

[0068] like Figure 5 As shown in FIG. 1 , hairline HL is formed on the surface of the plating layer 10. Figure 5 In the embodiment, the extension direction of the hairline HL is the rolling direction RD. However, it is also possible that the hairline HL does not extend along the rolling direction RD but extends along other directions. The hairlines HL are arranged in a direction perpendicular to the extension direction of the hairline HL. Figure 5 In the , the hairline HL is arranged along the width direction WD. Figure 2 As described above, in a minute region of the surface of the plating layer 10 where the hairline HL is formed, recesses and projections extending in one direction are formed.

[0069] [Regarding the control portion in the micro area]

[0070] As described above, the visibility of the hairline HL is related to the density of contrasting portions, which serve as boundaries where the density difference between visible concave and convex surfaces between adjacent microscopic regions is significant, when the multiple concave and convex portions formed perpendicular to the direction of extension of the hairline HL on the surface of the plating layer 10 are divided into multiple microscopic regions. Furthermore, the spacing between adjacent contrasting portions also affects the design quality of the hairline HL when viewed from a close distance. The following describes a method for determining contrasting portions.

[0071] [Method for determining the control part]

[0072] The control part was defined as follows.

[0073] like Figure 5 As shown, an arbitrary range of 5000 μm in length perpendicular to the extending direction of the hairline HL on the surface of the plated layer 10 is defined as the measurement range MR. The surface roughness profile of the measurement range MR is measured using a laser microscope. The laser microscope satisfies the following conditions.

[0074] Use a confocal laser microscope.

[0075] The wavelength of the light source should be 410 nm or less.

[0076] · Reduce the height display resolution to less than 1nm.

[0077] The width accuracy shall be within ±5% of the measured value.

[0078] When observing a length of 5000 μm in one field of view, the accuracy of the measured value in the height direction can be guaranteed.

[0079] An example of a laser microscope that meets the above conditions is the shape analysis laser microscope VK-X250 manufactured by KEYENCE Corporation. Furthermore, if the accuracy of the measured value in the height direction (Z-axis direction) cannot be guaranteed when observing a 5000 μm length in one field of view, a plurality of continuous images observed at a magnification that can guarantee the accuracy of the measured value in the Z-axis direction can be connected together to form a single profile for measurement. An example of the obtained profile is shown in FIG. Figure 6 middle.

[0080] If a resin layer and / or chemical conversion film is formed on the surface of the plating layer 10, the resin layer and chemical conversion film are removed using a stripping agent such as a solvent or a remover that does not corrode the plating layer 10. After the resin layer and chemical conversion film are removed, the surface roughness profile of the measurement range MR of the plating layer 10 is measured. An example of the stripping agent is Neoever S-701, manufactured by Sancai Chemical Industry Co., Ltd.

[0081] A laser microscope measures the surface shape optically. Light can pass through the resin layer formed on the coating 10. Therefore, even if a resin layer is formed on the coating 10, the surface shape of the coating 10 can be measured using a laser microscope. However, the laser light emitted from the laser microscope may be refracted or scattered by the resin layer. In this case, the accuracy of the roughness profile may be reduced. Therefore, if a resin layer is formed on the coating 10, the resin layer should be removed before measuring the surface roughness profile of the coating 10.

[0082] Using the surface roughness profile obtained within the measurement range MR, the peak count RPc is calculated using the following method, referring to JIS B0601:2013. In the surface roughness profile, the measurement range MR is divided into 100 microregions n (n is an integer from 1 to 100) arranged at 50 μm intervals from the end P of the measurement range MR. The peak count RPc is then calculated for each of the 100 microregions n.

[0083] The peak count RPc is obtained by the following method. Figure 7 This is a schematic diagram for explaining a method for measuring the peak count RPc in a micro area n. Figure 7 As shown in FIG, the measured cross-sectional curve is processed with a cutoff wavelength λ = 0.08 mm to obtain a surface roughness profile C1. A dead zone DB with a width of 360 nm is set with the average line X of the obtained surface roughness profile C1 as the center. In the surface roughness profile C1, the peaks from the point protruding downward from the dead zone DB to the point protruding upward from the dead zone DB and then protruding downward from the dead zone DB again are counted as one peak. Figure 7 In the example, the peak count is 6. Furthermore, the dead zone DB is set to 360 nm because 360 ​​nm is the minimum wavelength of visible light. In other words, the bumps and grooves counted as peak counts RPc are visually discernible. Bumps and grooves with a height difference greater than the dead zone DB are defined as "visible bumps and grooves." The peak count RPc for each microregion n is calculated using the above method. The peak count for microregion n refers to the density of visible bumps and grooves within microregion n.

[0084] Based on the obtained peak counts RPc for each micro region, comparison areas are identified as boundaries where the visible concavity and convexity of adjacent micro regions n have a predetermined density difference. Specifically, the total number of first comparison areas N, the total number of second comparison areas M, and the total number of third comparison areas K are determined using the following method.

[0085] (1) Within the measurement range MR, the absolute difference in peak counts RPc between adjacent micro regions n represents the difference in density of visible concavity and convexity between adjacent micro regions n and n+1. Therefore, the region where the absolute difference in peak counts RPc between adjacent micro regions n is 6 or greater is defined as a "first comparison portion." The first comparison portion is an area that can be visually recognized from a close distance. The total number of first comparison portions within the measurement range MR is N.

[0086] (2) Within the measurement range MR, the area where the absolute difference between the peak count RPc of micro region m (m is an integer from 1 to 98) and the peak count RPc of micro region m+1 is less than 6, and the absolute difference between the peak count RPc of micro region m and the peak count RPc of micro region m+2 is 6 or greater is defined as a "second comparison portion." The second comparison portion is an area that can be visually recognized from a close distance, similar to the first comparison portion. The total number of second comparison portions within the measurement range MR is denoted as M.

[0087] (3) A region where the absolute difference between the peak count RPc of micro region k (k is an integer from 1 to 98) and the peak count RPc of micro region k+1 is 6 or greater, and where the absolute difference between the peak count RPc of micro region k+1 and the peak count RPc of micro region k+2 is 6 or greater, is defined as a "third comparison portion." A third comparison portion is a region where two comparison portions are continuously adjacent and visually recognized as a single comparison portion. The total number of third comparison portions in the measurement range MR is K.

[0088] The total number of control sections J in the measurement range MR is defined by equation (1) using the total number N of the first control sections, the total number M of the second control sections, and the total number K of the third control sections determined by the above method.

[0089] J=N+MK(1)

[0090] The total number of contrast portions J refers to the density of the boundaries of the microscopic region (contrast portions) visible within the measurement range MR, and refers to the density of the visually recognizable hairlines HL. When the total number of contrast portions J is greater than 7, the density of contrast portions visible from a close distance is sufficiently high. Therefore, the design quality of the hairlines is enhanced when observed from a close distance.

[0091] Figure 8 This is an example of the peak count RPc in the measurement range MR. Figure 8 In the measurement range MR, the first control part (in Figure 8 The total number N of the second control part (marked as N in Figure 8 The total number M of the third control part (marked as M in Figure 8 The total number K of the control parts (denoted as K in FIG) is 1. Therefore, the total number J of the control parts in the measurement range MR is 17. Figure 8 In the case of , the design of the hairline when observed from a close distance becomes higher.

[0092] Figure 9 is with Figure 8 An example of a different peak count RPc in the measurement range MR. Figure 9 In the measurement range MR, the first control part (in Figure 9 The total number N of the second control part (marked as N in Figure 9 The total number M of the third control part (marked as M in Figure 9 The total number K of the control parts (denoted as K in FIG) is 1. Therefore, the total number J of the control parts in the measurement range MR is 7. Figure 9 In the case of , the designability of the hairline when observed from a close distance is low.

[0093] As described above, in the plated steel sheet 1 of this embodiment, the total number J of contrast portions derived from the peak counts RPc in the microscopic regions partitioned at 50 μm intervals within the measurement range MR is greater than 7. In this case, the density of contrast portions on the surface of the coating 10 is sufficiently high. Consequently, the design quality of the hairline texture when observed from a close distance is enhanced.

[0094] The lower limit of the total number J is preferably 10, more preferably 14.

[0095] [Preferred Exposure Ratio of the Base Steel Sheet 100 When the Plated Steel Sheet 1 is Seen from Above]

[0096] The exposure rate of the base steel sheet 100 when the coating layer 10 of the plated steel sheet 1 is viewed from above is preferably less than 5.0%. The exposure rate of the base steel sheet 100 is more preferably 0%. In this case, sufficient corrosion resistance (long-term corrosion resistance) can be obtained in the plated steel sheet 1.

[0097] In the plated steel sheet 1 of this embodiment, unlike conventional plated steel sheets, the visibility and design of the hairline HL are enhanced by increasing the average height difference (such as the depth of grinding marks) of the surface irregularities of the coating 10. Instead, the density of the contrasting portions is increased to enhance the design of the hairline HL when viewed from a close distance. Therefore, unlike conventional steel sheets with hairline formations, the plated steel sheet 1 of this embodiment does not need to be ground more than necessary to enhance the design of the hairline HL. As a result, the exposure rate of the base steel sheet 100 can be easily reduced in the plated steel sheet 1. In particular, when the coating 10 of the plated steel sheet 1 is an electroplated layer, the electroplated layer can be formed with a relatively thin thickness of 1.5 to 6.0 μm. Even in such cases, the exposure rate of the base steel sheet 100 can be reduced to less than 5.0% in the plated steel sheet 1 of this embodiment. As a result, it is possible to ensure long-term corrosion resistance and improve the visibility of the hairline HL when observed from a close distance.

[0098] [Measurement method of exposure rate]

[0099] The exposure rate of the base steel plate 100 in the plated steel plate 1 is determined by the following method. First, according to the above-mentioned [method for determining the chemical composition of the coating 10], the chemical composition of the coating is determined, and the main component element X of the coating is determined. In the obtained chemical composition, the element that is 50.0% or more in mass % is set as the main component element X. Next, using the plated steel plate 1 after collecting the sample of the [method for determining the chemical composition of the coating 10], the plated steel plate 1 is observed from above the coating 10 (the plated steel plate 1 is observed from above), and 5 arbitrary rectangular areas of 1 mm × 1 mm are selected. EPMA analysis (surface analysis) is performed on the selected rectangular areas. By image analysis, in each rectangular area, an area where the main component element X of the coating is not detected (an area where the coating is not detected) is determined. In this embodiment, an area where the detection intensity of the main component element X of the coating is less than 1 / 16 of the detection intensity when the standard sample (pure metal sample) is measured is identified as an area where the main component element of the coating is not detected. The ratio (%) of the total area of ​​the regions where the main component element of the plating is not detected to the total area of ​​the five rectangular regions is defined as the exposure rate (%) of the base steel plate 100 .

[0100] [Other aspects of the plated steel sheet 1 according to this embodiment]

[0101] The plated steel sheet 1 of this embodiment is not limited to the above-described embodiment. As described above, in the plated steel sheet 1 of this embodiment, one or more resin layers may be formed on the surface of the coating 10. Furthermore, in the plated steel sheet 1 of this embodiment, a chemical conversion film may be formed on the surface of the coating 10. Furthermore, in the plated steel sheet 1 of this embodiment, a chemical conversion film may be formed on the surface of the coating 10, and a resin layer may be formed on the chemical conversion film.

[0102] [Method for Manufacturing Plated Steel Sheet 1]

[0103] An example of a method for manufacturing the plated steel sheet 1 of this embodiment will be described below. The plated steel sheet 1 may be manufactured by a method other than the method described below. However, the method described below is a preferred example of a method for manufacturing the plated steel sheet 1 of this embodiment.

[0104] An example of a method for producing the plated steel sheet 1 includes the following steps.

[0105] (Process 1) Base Steel Plate Preparation Process

[0106] (Step 2) Plating layer forming step

[0107] (Process 3) Hairline Formation Process

[0108] Hereinafter, each step will be described.

[0109] [(Process 1) Base Steel Plate Preparation Process]

[0110] In the base steel plate preparing step, the base steel plate 100 is prepared. As described above, the base steel plate 100 may be a hot-rolled steel plate or a cold-rolled steel plate.

[0111] [(Step 2) Plating Layer Forming Step]

[0112] In the coating forming step, the coating 10 is formed on the surface of the base steel plate 100 by electroplating or hot-dip coating. The coating 10 can be formed by electroplating or hot-dip coating. When the coating 10 is a zinc-based coating, for example, the following electrogalvanizing or hot-dip galvanizing method can be implemented.

[0113] [Electrogalvanizing method]

[0114] When the zinc coating 10 is formed by the electrogalvanizing method, the electrogalvanizing method can be implemented by a known method. In this specification, the electrogalvanizing method also includes the electrogalvanizing method. It is sufficient to use a known plating solution as the plating solution used in the electrogalvanizing method. The electrogalvanizing solution is, for example, a sulfuric acid bath, a chloride bath, a zincate bath, a cyanide bath, a pyrophosphoric acid bath, a boric acid bath, a citric acid bath, other complex baths and combinations thereof. The electrogalvanizing method, for example, contains more than one single ion or complex ion selected from the group consisting of Fe, Ni, Co, Cr and C in addition to containing Zn ions. In addition, organic additives can also be appropriately added to the plating solution in order to obtain the desired effects such as the leveling effect and / or the hardness increase.

[0115] [Hot-dip galvanizing method]

[0116] When the zinc coating 10 is formed by hot-dip galvanizing, the hot-dip galvanizing method can be carried out by a known method. A known coating bath is sufficient for the hot-dip galvanizing method. For example, a hot-dip galvanizing bath containing Al, with the remainder being Zn and impurities can be used. An example of an impurity is Fe. Alternatively, the hot-dip galvanizing bath may contain, in addition to Zn, Al, and Fe, one or more elements selected from the group consisting of Mg, Si, Ca, Y, La, Ce, Sn, Bi, In, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Sr, Sb, Pb, and B.

[0117] [(Step 3) Hairline Forming Step]

[0118] In the grain forming step, grain processing is performed on the surface of the plating layer 10 to form grains HL on the surface of the plating layer 10 .

[0119] The grinding device for graining processing includes a conveyor roller, a pair of contact rollers, and an endless grinding belt. The pair of contact rollers holds the endless grinding belt. As the pair of contact rollers rotate, the endless grinding belt moves between the pair of contact rollers. A base steel plate 100 having a coating 10 on its surface is conveyed between the conveyor rollers and the endless grinding belt. The endless grinding belt is pressed against the surface of the coating 10. As the pair of contact rollers rotate, the endless grinding belt grinds the surface of the coating 10 of the base steel plate 100. As a result, grains HL are formed on the surface of the coating 10. The grinding device may also include a grinding brush instead of the grinding belt.

[0120] During the grinding process, the speed at which the plated steel sheet 1 passes through the grinding apparatus, the rotational speed of the touch roller, and the pressing force of the touch roller against the plated steel sheet 1 can be adjusted as appropriate. By adjusting the rotational speed of the touch roller and the pressing force of the touch roller against the plated layer 10, the amount of plated layer 10 removed during the grinding process can be adjusted. If the grinding apparatus includes a grinding brush, the amount of plated layer 10 removed can be adjusted by, for example, adjusting the rotational speed of the grinding brush and / or the pressing force of the grinding brush against the plated layer 10.

[0121] Preferably, the abrasive grain size and / or abrasive grain density are distributed differently in the width direction of the grinding belt or grinding brush. Here, the width direction of the grinding belt or grinding brush corresponds to the plate width direction of the base steel plate 100.

[0122] The abrasive grain size and density of conventional grinding belts and brushes used for hairline processing are uniform across the width. Furthermore, to improve the visibility of the hairline, the abrasive grain size is typically increased. In contrast, in the manufacturing method of this embodiment, the abrasive grain size and / or density are distributed differently across the width of the grinding belt or brush. This allows for adjustment of the density of visible unevenness in each microregion n perpendicular to the direction of extension of the hairline HL, and thus the density of the contrasting portion. Furthermore, the distribution of the abrasive grain size and density across the width of the grinding belt or brush can be adjusted appropriately based on the desired appearance.

[0123] When a grinding brush is used in graining processing, the annular grinding brush includes a central axis portion and a plurality of bristle materials extending radially along the central axis portion. The bristle materials are arranged along the axial direction of the grinding brush. A plurality of bristle materials having different abrasive density are arranged along the axial direction. Graining processing is performed using such a grinding brush. By changing the abrasive density of the bristle material in the axial direction of the grinding brush, the density of the grinding marks (concavities and convexities) formed on the surface of the coating by the grinding brush can be changed. The abrasive density of the bristle material of the grinding brush is adjusted so that the total number J of the contrast portions defined by formula (1) on the surface of the coating is greater than 7.

[0124] When using an abrasive tape for graining, the abrasive density is varied across the width of the tape. This allows the density of the grinding marks (concavities and convexities) formed on the surface of the coating layer by the abrasive tape to be varied. The abrasive density of the abrasive tape is adjusted so that the total number of contrast areas J defined by equation (1) on the surface of the coating layer is greater than 7.

[0125] Example

[0126] The following examples further illustrate the effects of one aspect of the present invention. The conditions in the following examples are examples of conditions adopted to confirm the feasibility and effects of the plated steel sheet of this embodiment.

[0127] The plated steel sheets of the test numbers shown in Table 1 were prepared. The base steel sheet of each plated steel sheet was the SPCC specified in JIS G 3141 (2017), and the thickness was 0.6 mm. For each base steel sheet, a coating forming process was performed in such a manner as to obtain various coating thicknesses. Specifically, an electrogalvanizing treatment was performed to form an electrogalvanized layer as a coating. In addition, the thickness of the coating was 0.5 to 25.0 μm. The thickness of the coating was measured according to the above-mentioned [method for measuring the thickness of the coating 10].

[0128] [Table 1]

[0129] Table 1

[0130]

[0131] The surface of the plated layer on the base steel sheet of each test number was subjected to a texture formation process. In this process, multiple abrasive tapes with varying abrasive grain density distributions across their widths were prepared to form textures. Through the above manufacturing process, textured plated steel sheets were produced.

[0132] The plated steel sheet with hairline cracks was subjected to a chemical conversion treatment to form a chemical conversion film on the plated layer. Specifically, the following silane coupling agent A and silane coupling agent B were prepared.

[0133] Silane coupling agent A: 3-aminopropyltrimethoxysilane

[0134] Silane coupling agent B: 3-glycidoxypropyltrimethoxysilane

[0135] Silane coupling agent A and silane coupling agent B were added to water adjusted to pH 4, with a solid content mass ratio (silane coupling agent A / silane coupling agent B) of 1.0. The mixture was then stirred for a predetermined time to produce an organosilicon compound. The produced organosilicon compound was further added with phosphoric acid as a phosphate compound to produce a treatment liquid.

[0136] The treatment liquid is picked up by a roller and transferred to the plated layer. At this time, the adhesion amount of the chemical conversion film after sintering and drying is 0.3g / m 2 The treatment liquid is transferred to the coating in a manner.

[0137] The steel sheet, to which the treatment liquid had been transferred onto the coating, was then sintered and dried. Specifically, the steel sheet, to which the treatment liquid had been transferred onto the coating, was placed in a furnace maintained at 180°C and held there until its final temperature reached 130°C. After reaching 130°C, the steel sheet was removed from the furnace and air-cooled to room temperature. The above process formed a chemical conversion coating on the coating.

[0138] A resin layer was formed on the steel sheet with the chemical conversion coating. A polyurethane resin (trade name: HUX-232, manufactured by ADEKA Co., Ltd.) was used as the binder resin for the resin coating. Polyethylene resin particles (trade name: CHEMIPEARL, manufactured by Mitsui Chemicals, Inc.) were used as the resin particles. The binder resin and resin particles were dispersed in water to prepare a coating.

[0139] The prepared coating was scooped up with a roller and transferred to the steel plate. The amount of treatment liquid applied was adjusted so that the average thickness of the resin coating after sintering and drying was 5 μm. The steel plate to which the treatment liquid had been transferred was placed in a furnace maintained at 250°C. The steel plate remained in the furnace until its final temperature reached 180°C. After reaching 180°C, the steel plate was removed from the furnace and air-cooled to room temperature. The above steps formed a resin layer.

[0140] [Evaluation test]

[0141] The following evaluation tests were performed on the plated steel sheets of each test number.

[0142] (Test 1) Total J measurement test of control part

[0143] (Test 2) Grinding Mark Depth Measurement

[0144] (Test 3) Base Steel Plate Exposure Ratio Measurement Test

[0145] (Test 4) Hairline design evaluation test at close distance

[0146] (Test 5) Corrosion resistance evaluation test

[0147] Hereinafter, Tests 1 to 5 will be described.

[0148] [(Test 1) Total J measurement test of control part]

[0149] For the plated steel sheets of each test number, the total number N of the first control section, the total number M of the second control section, and the total number K of the third control section were determined according to the method described in the [Method for Determining Control Sections] above, and the total number J of control sections was also determined. A VK-X250 shape analysis laser microscope manufactured by KEYENCE Corporation was used as a laser microscope. Furthermore, the resin layer and chemical conversion coating were removed using a stripping agent. Neorev S-701 manufactured by Sancai Chemical Industry Co., Ltd. was used as a stripping agent. The obtained N, M, K, and J are shown in Table 1.

[0150] [(Test 2) Grinding Mark Depth Measurement]

[0151] For the plated steel sheets of each test number, the difference between the maximum height and the minimum height of the surface roughness profile C1 obtained by the [Control Portion Determination Method] described above was defined as the grinding mark depth (μm). The grinding mark depth (μm) of the plated steel sheets of each test number is shown in Table 1.

[0152] [(Test 3) Base Steel Plate Exposure Ratio Measurement Test]

[0153] For the plated steel sheets of each test number, the exposure ratio of the base steel sheet was measured according to the method described in [Exposure Ratio Measurement Method] above. The main component element of the plating was Zn. The measured exposure ratios (%) are shown in Table 1.

[0154] [(Test 4) Hairline Design Evaluation Test at Close Distance]

[0155] The design properties of the plated steel sheets with each test number were evaluated for hairline patterns at close range using the following method. First, the plated steel sheets with each test number were set indoors at a 60° angle relative to the horizontal. The plates were positioned with the coating facing the ceiling. Next, an observer visually observed the plated steel sheets from a location 50 cm away from the plated steel sheets on the indoor floor, facing the plated steel sheets. The observer's line of sight was at the same height as the plated steel sheets. A total of 10 observers performed visual observations, conducting a sensory evaluation to determine whether the design properties were excellent. Specifically, if hairline patterns could be clearly identified during visual observation, the design properties were judged to be excellent. Scores were assigned based on the number of people who judged the design properties to be excellent, with scores of B or higher being considered acceptable. The evaluation results (A to C) are shown in the "Design" column of the "Evaluation Results" section of Table 1.

[0156] 8 or more people judge the design to be excellent: A

[0157] 5 or more but less than 8 people judge the design to be excellent: score B

[0158] Less than 5 people judged the design to be excellent: score C

[0159] [(Test 5) Corrosion resistance evaluation test]

[0160] For the plated steel sheets of each test number, the corrosion resistance (long-term corrosion resistance) was evaluated by the following method. A test piece of 75 mm × 100 mm × plate thickness was collected from the plated steel sheets of each test number. The surface of 75 mm × 100 mm in the test piece was set as the measurement surface. The end face and back face of the test piece were sealed with tape to protect them. Afterwards, a salt spray test of 5% NaCl maintained at 35°C was carried out in accordance with JIS Z 2371 (2015). The test was carried out for 240 hours, and the rust rate after the test was calculated. Specifically, the rusted area was visually calculated on the measurement surface after the test. The rust rate (%) as the area ratio of rust was calculated based on the rusted area and the area of ​​the measurement surface. If the rust rate is less than 5%, it is evaluated as qualified (indicated by "E (Excellent)" in the "Corrosion Resistance" column of the "Evaluation Results" column in Table 1). On the other hand, when the rust rate was 5% or more, it was evaluated as unacceptable (indicated by the evaluation "B (Bad)" in the "Corrosion Resistance" column of the "Evaluation Results" column in Table 1).

[0161] [Evaluation results]

[0162] The evaluation results are shown in Table 1. In the plated steel sheets with test numbers 1 to 10, the total number of control portions J was greater than 7. Therefore, the plated steel sheets with these test numbers exhibited excellent design properties. In test numbers 1 to 7, the exposure rate was less than 5.0%. Therefore, the plated steel sheets with these test numbers exhibited excellent design properties as well as excellent corrosion resistance.

[0163] On the other hand, in the plated steel sheets of test numbers 11 to 13, the total number J of the control portions was 7 or less. Therefore, excellent design properties were not obtained.

[0164] As described above, it is understood that by setting the total number J of the control portions to be greater than 7, it is possible to obtain excellent design properties even when the grinding mark depth is relatively shallow.

[0165] The embodiments of the present disclosure have been described above. However, the above embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above embodiments, and the above embodiments may be appropriately modified within the scope of the present disclosure.

[0166] Description of Reference Numerals

[0167] 1. Coated steel plate; 10. Coating; HL, hairline.

Claims

1. A plated steel sheet comprising: parent steel plate; and A coating is formed on the base steel plate and has hairline texture on the surface. On the surface of the coating, The surface roughness profile is measured using a laser microscope within a measurement range of 5000 μm in a direction perpendicular to the extending direction of the hairline, and the surface roughness profile within the measurement range is obtained. The measurement range is divided into 100 micro-regions n arranged at 50 μm intervals from the end of the measurement range, where n is an integer from 1 to 100. For each micro-region n, the peak count RPc is calculated with a dead zone width of 360 nm. Within the measurement range, The total number of first comparison portions in which the absolute difference in peak counts RPc between adjacent micro regions n is 6 or greater is defined as N. The total number of second comparison parts, in which the absolute difference between the peak count RPc of the micro region m and the peak count RPc of the micro region m+1 is less than 6 and the absolute difference between the peak count RPc of the micro region m and the peak count RPc of the micro region m+2 is 6 or more, is set to M, where m is an integer from 1 to 98. The total number of third comparison sections, in which the absolute difference between the peak count RPc of the micro area k and the peak count RPc of the micro area k+1 is greater than 6, and the absolute difference between the peak count RPc of the micro area k+1 and the peak count RPc of the micro area k+2 is greater than 6, is set to K, where k is an integer from 1 to 98. In this case, the total number J of comparison sections defined by formula (1) is greater than 7. J=N+MK(1).

2. The plated steel sheet according to claim 1, wherein The exposure rate of the base steel plate when the coating layer is viewed from above is less than 5.0%.

3. The plated steel sheet according to claim 1 or claim 2, wherein: The coating is a zinc coating.

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