Hot-dip plated steel sheet

Abstract

The hot-dip plated steel sheet has a hot-dip plated layer formed on the surface of the steel sheet, the hot-dip plated layer containing Al: 4 to 22 mass%, Mg: 1.0 to 10 mass%, and the remainder including Zn and impurities, a pattern portion and a non-pattern portion are formed in the hot-dip plated layer, an element concentration region containing an element M and an interface alloy layer containing Fe and Al exist at the interface between the steel sheet and the hot-dip plated layer at the pattern portion, the average concentration of the element M contained in the hot-dip plated layer and the element concentration region existing in the pattern portion is 0.0010 to 2 mass%, and in the element concentration region, the element M is concentrated by 2 times or more, or the element M is unevenly present, with respect to the hot-dip plated layer existing in the pattern portion.

Description

Technical Field

[0001] This invention relates to hot-dip galvanized steel sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2022-094362 filed on June 10, 2022, the contents of which are incorporated herein by reference. Background Technology

[0003] Compared with hot-dip galvanized steel sheets, Zn-Al-Mg series hot-dip galvanized steel sheets, which have high corrosion resistance, are widely used in various manufacturing industries such as building materials, home appliances, and automobiles, and their usage has been increasing in recent years.

[0004] However, in order to make text, designs, etc. appear on the surface of the hot-dip galvanized steel sheet, sometimes printing or coating processes are carried out on the hot-dip galvanized layer to make text, designs, etc. appear on the surface of the hot-dip galvanized layer.

[0005] However, if printing or coating processes are applied to the hot-dip galvanized coating, the cost and time required for adding text or designs increase. Furthermore, when text or designs are displayed on the surface of the coating through printing or coating, not only does the metallic luster, which is highly valued by consumers, disappear, but the durability is also poor due to the deterioration of the coating itself and its adhesion over time, potentially causing the text or designs to fade away. Additionally, while using printing ink to display text or designs on the surface of the coating can reduce cost and time, there are concerns that the ink may reduce the corrosion resistance of the hot-dip galvanized coating. Moreover, while grinding the hot-dip galvanized coating to display patterns and designs provides excellent durability, the significantly reduced thickness of the coating at the ground area inevitably leads to decreased corrosion resistance, raising concerns about reduced plating properties.

[0006] As shown in the patent documents below, various technologies have been developed for Zn-Al-Mg based hot-dip galvanized steel sheets, but technologies to improve their durability while making text, designs, etc. visible on the surface of the coating are unknown.

[0007] Regarding Zn-Al-Mg based hot-dip galvanized steel sheets, there are prior techniques aimed at making the pear-skin-like coating appearance seen on Zn-Al-Mg based hot-dip galvanized steel sheets more attractive.

[0008] For example, Patent Document 1 describes a Zn-Al-Mg based hot-dip galvanized steel sheet with a pear-skin-like appearance characterized by fine texture and a smooth, glossy surface. Specifically, it has a desirable pear-skin-like appearance with a high number of white portions per unit area and a large proportion of glossy areas. Furthermore, Patent Document 1 describes a less desirable pear-skin appearance where irregular white portions are mixed with rounded glossy portions and dispersed across the surface.

[0009] Furthermore, Patent Document 2 describes a Zn-Al-Mg coated steel sheet, in which the appearance of the coating is improved by making the portion in the thickness direction section where there are no Al crystals between the interface between the coating and the base metal and the coated surface layer account for 10% to 50% of the width direction length of the section.

[0010] Furthermore, Patent Document 3 describes a hot-dip galvanized steel sheet with excellent formability, wherein the average roughness Ra of the centerline of the coated steel sheet surface is 0.5 to 1.5 μm, the PPI (the number of peaks larger than 1.27 μm per inch (2.54 cm)) is 150 to 300, and the Pc (the number of peaks larger than 0.5 μm per cm) is Pc≥PPI / 2.54+10.

[0011] In addition, Patent Document 4 describes a high corrosion-resistant hot-dip galvanized steel sheet, which improves the overall gloss and appearance uniformity of the coating by refining the ternary eutectic structure of Al / MgZn2 / Zn.

[0012] However, a technique to improve the durability of a coating without reducing its corrosion resistance while allowing text or other features to appear on the surface of the coating was previously unknown.

[0013] Existing technical documents

[0014] Patent documents

[0015] Patent Document 1: Japanese Patent No. 5043234

[0016] Patent Document 2: Japanese Patent No. 5141899

[0017] Patent Document 3: Japanese Patent No. 3600804

[0018] Patent Document 4: International Publication No. 2013 / 002358 Summary of the Invention

[0019] The problem that the invention aims to solve

[0020] The present invention was made in view of the above circumstances, and the objective is to provide a hot-dip galvanized steel sheet that can display text, designs, etc. on the surface of the hot-dip galvanized layer, and that has excellent durability and corrosion resistance, and further, has excellent adhesion of the hot-dip galvanized layer at the parts where text and designs are displayed.

[0021] Methods for solving problems

[0022] To address the aforementioned issues, the present invention employs the following configuration.

[0023] [1] A hot-dip galvanized steel sheet comprising a steel sheet and a hot-dip galvanized coating formed on the surface of the steel sheet.

[0024] The above-mentioned hot-dip coating contains, on average, 4-22% Al, 1.0-10% Mg, with the remainder consisting of Zn and impurities.

[0025] The aforementioned hot-dip coating has patterned and non-patterned portions.

[0026] At the interface between the steel plate and the hot-dip galvanized layer in the aforementioned patterned area, there exists: an elemental concentration region containing one or more elements M selected from Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, Ni, Ti, Zr, Mo, W, REM, Hf, and C; and an interface alloy layer containing Fe and Al.

[0027] The average concentration of element M contained in the hot-dip galvanized layer of the above-mentioned patterned area and the above-mentioned element concentration region is 0.0010 to 2% by mass.

[0028] In the aforementioned element concentration region, relative to the hot-dip coating present in the aforementioned patterned portion, the aforementioned element M is concentrated at more than twice the amount, or the aforementioned element M exists unevenly.

[0029] [2] According to the hot-dip galvanized steel sheet described in [1], it has an interface alloy layer containing Fe and Al at the interface between the steel sheet and the hot-dip galvanized layer in the non-patterned portion.

[0030] [3] According to the hot-dip galvanized steel sheet described in [1] or [2], wherein the concentration of element M at the interface of the patterned portion is more than 1.5 times the concentration of element M at the interface of the non-patterned portion.

[0031] [4] The hot-dip galvanized steel sheet according to any one of [1] to [3] is characterized in that the patterned portion is arranged in a shape that is any one of straight lines, curves, dots, graphics, numbers, symbols or text, or a combination of two or more of them.

[0032] [5] The hot-dip galvanized steel sheet according to any one of [1] to [4] is characterized in that the hot-dip galvanized layer further contains Si: 0.0001 to 2% by mass on an average basis.

[0033] [6] The hot-dip galvanized steel sheet according to [5] further contains Si in the interface alloy layer formed on the above-mentioned patterned portion.

[0034] [7] The hot-dip galvanized steel sheet according to [5] or [6] further contains Si in the interface alloy layer formed in the above-mentioned non-patterned portion.

[0035] [8] The hot-dip galvanized steel sheet according to any one of [1] to [7] is characterized in that, except for the above-mentioned element concentration region, the hot-dip galvanized layer further contains, on average, 0.0001 to 1% by mass of any one or two or more of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C.

[0036] [9] A hot-dip galvanized steel sheet according to any one of [1] to [8], characterized in that the amount of the hot-dip galvanized coating on both sides of the steel sheet is 30 to 600 g / m². 2 .

[0037] Invention Effects

[0038] According to the present invention, a hot-dip galvanized steel sheet is provided that can display text, designs, etc. on the surface of the hot-dip galvanized layer, and that the text, designs, etc., have excellent durability and corrosion resistance, and that the hot-dip galvanized layer has excellent adhesion at the parts where the text, designs, etc. are displayed. Attached Figure Description

[0039] Figure 1 This is a cross-sectional schematic diagram illustrating the patterned and non-patterned portions of a hot-dip galvanized steel sheet according to an embodiment of the present invention. Detailed Implementation

[0040] The hot-dip galvanized steel sheet according to embodiments of the present invention will be described.

[0041] The hot-dip galvanized steel sheet of this embodiment includes a steel sheet and a hot-dip galvanized layer formed on the surface of the steel sheet.

[0042] The hot-dip coating contains, on average, 4–22% Al and 1.0–10% Mg, with the remainder being Zn and impurities.

[0043] In the hot-dip coating, patterned and non-patterned areas are formed.

[0044] The interface between the steel plate and the hot-dip galvanized layer in the patterned section has an element concentration area and an interface alloy layer.

[0045] An interface alloy layer is provided at the interface between the steel plate in the non-patterned part and the hot-dip galvanized layer.

[0046] The pattern section is arranged in a way that forms one or more of the following shapes: straight lines, curves, dots, graphics, numbers, symbols, or text.

[0047] The pattern section is the part that is intentionally formed.

[0048] There are no particular restrictions on the material of the steel sheet that serves as the base for the hot-dip coating. Although details will be described below, there are no particular restrictions on the material used, such as general steel, Al-killed steel, and some high-alloy steels. There are also no particular restrictions on the shape. By applying the hot-dip coating method described later to the steel sheet, the hot-dip coating of this embodiment can be formed.

[0049] Next, the chemical composition of the hot-dip coating will be explained.

[0050] The hot-dip coating contains, on an average basis, 4-22% by mass of Al and 1.0-10% by mass of Mg, with the remainder being Zn and impurities. More preferably, it contains, on an average basis, 4-22% by mass of Al and 1.0-10% by mass of Mg, with the remainder being Zn and impurities. Furthermore, the hot-dip coating may also contain, on an average basis, 0.0001-2% by mass of Si. Moreover, the hot-dip coating may also contain, on an average basis, any one or more of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C, totaling 0.0001-1% by mass.

[0051] The Al content ranges from 4% to 22% by mass on an average composition basis. It is preferable to include Al to ensure corrosion resistance. If the Al content in the hot-dip coating is 4% by mass or more, the effect of improving corrosion resistance is further enhanced. If the Al content exceeds 22% by mass, the effect of improving corrosion resistance becomes saturated. From the viewpoint of corrosion resistance, the lower limit is preferably 5% by mass, more preferably 6% by mass. The upper limit is preferably 18% by mass, more preferably 16% by mass.

[0052] The Mg content, based on the average composition, ranges from 1.0% to 10% by mass. Mg is preferably included to improve corrosion resistance. If the Mg content in the hot-dip galvanized coating is 1.0% by mass or more, the effect of improving corrosion resistance is further enhanced. However, if Mg exceeds 10% by mass, slag formation in the plating bath becomes significant, making it difficult to stably manufacture hot-dip galvanized steel sheets; therefore, the Mg content is set to 10% by mass or less. From the viewpoint of balancing corrosion resistance and slag formation, the lower limit of the Mg content is preferably 1.5% by mass, more preferably 2.0% by mass. The upper limit is preferably 6.0% by mass, more preferably 5.0% by mass.

[0053] The hot-dip coating may contain 0.0001 to 2% by mass of Si on an average basis. Si is an effective element for improving the adhesion of the hot-dip coating. In order to exhibit the effect of improving adhesion by containing more than 0.0001% by mass of Si in the hot-dip coating, it is preferable to contain more than 0.0001% by mass of Si. On the other hand, even if the Si content exceeds 2% by mass, the effect of improving coating adhesion is saturated, so even when Si is contained in the hot-dip coating, the Si content is set to 2% by mass or less. From the viewpoint of coating adhesion, the lower limit of the Si content in the hot-dip coating may be set to 0.0010% by mass or 0.0100% by mass. The upper limit may be set to 1.0% by mass or 0.8% by mass.

[0054] The hot-dip coating may also contain one or more of the following elements in total, ranging from 0.0001 to 1% by mass, on an average basis: Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C. The presence of these elements further improves the corrosion resistance of the hot-dip coating. REM refers to one or more rare earth elements with atomic numbers 57 to 71 in the periodic table. These elements may be included in the hot-dip coating by adding them to the hot-dip bath or by diffusion from solidification nuclei; however, in this embodiment, it is sufficient that the total amount of the aforementioned elements in the coating, excluding the element concentration region, is in the range of 0.0001 to 1% by mass.

[0055] The remaining chemical composition of the hot-dip galvanized coating consists of zinc and impurities. Among the impurities are substances that, besides zinc, are inevitably contained in the base metal, and substances that are contained through the dissolution of the steel in the plating bath.

[0056] It should be noted that the average composition of the hot-dip coating can be determined by the following method. First, it can be determined by removing the surface coating with a non-corrosive coating stripper (e.g., NEOREVER SP-751 manufactured by Sansai Chemical Co., Ltd.), dissolving the hot-dip coating in hydrochloric acid with an inhibitor (e.g., HIBIRON manufactured by SUGIMURA Chemical Industrial Co., Ltd.), and then subjecting the resulting solution to inductively coupled plasma (ICP) luminescence spectrophotometry analysis. Furthermore, if there is no surface coating, the surface coating removal process can be omitted.

[0057] Next, the microstructure of the hot-dip coating will be described. The microstructure of the hot-dip coating in this embodiment can also have, for example, the following structure. As a result, the surface of the hot-dip coating has a pear-skin-like appearance, resulting in excellent aesthetics. It should be noted that any coating with the above-described chemical composition can be obtained, therefore, the microstructure of the hot-dip coating is not necessarily limited in this invention.

[0058] The hot-dip coating containing Al, Mg, and Zn includes both an Al phase and a ternary eutectic structure of Al / Zn / MgZn2. Specifically, it has a morphology in which the Al phase is included in the matrix of the ternary eutectic structure of Al / Zn / MgZn2. Furthermore, the MgZn2 phase and the Zn phase may also be included in the matrix of the ternary eutectic structure of Al / Zn / MgZn2. In addition, when Si is included, the Mg2Si phase may also be included in the matrix of the ternary eutectic structure of Al / Zn / MgZn2.

[0059] [Ternary eutectic structure of Al / Zn / MgZn2]

[0060] [The ternary eutectic structure of Al / Zn / MgZn2] refers to the ternary eutectic structure of Al phase, Zn phase and intermetallic compound MgZn2 phase. The Al phase forming this ternary eutectic structure is, for example, equivalent to the "Al″ phase" at high temperature in the equilibrium state diagram of the Al-Zn-Mg ternary system (which is an Al solid solution of Zn, containing a small amount of Mg).

[0061] The Al″ phase at high temperature typically separates into fine Al and fine Zn phases at room temperature. The Zn phase in this ternary eutectic structure is a Zn solid solution containing a small amount of Al and, depending on the situation, a small amount of Mg. The MgZn2 phase in this ternary eutectic structure is an intermetallic compound phase present in the Zn-Mg binary equilibrium diagram, approximately 84% by mass of Zn.

[0062] Based on the phase diagram, it is believed that no other added elements are dissolved in each phase, or if so, the amount is extremely small. However, since the amount cannot be clearly distinguished through ordinary analysis, the ternary eutectic structure containing these three phases is referred to in this specification as [a ternary eutectic structure of Al / Zn / MgZn2].

[0063] [Al phase]

[0064] The Al phase refers to a phase with clearly defined boundaries and an island-like appearance within the matrix of an Al / Zn / MgZn2 ternary eutectic structure. For example, it corresponds to the "Al″ phase" at high temperature in the equilibrium diagram of the Al-Zn-Mg ternary system (an Al solid solution of Zn containing a small amount of Mg). Regarding this high-temperature Al″ phase, the amount of dissolved Zn and Mg varies depending on the Al and Mg concentrations in the plating bath. At room temperature, the high-temperature Al″ phase typically separates into fine Al and fine Zn phases, but the island-like shape observed at room temperature is believed to originate from the shape of the high-temperature Al″ phase.

[0065] Based on the phase diagram, it is believed that no other added elements are dissolved in this phase, or if so, the amount is extremely small. However, it is not possible to clearly distinguish them through ordinary analysis. Therefore, the phase derived from the Al″ phase at this high temperature and whose shape is derived from the Al″ phase is referred to as the [Al phase] in this specification.

[0066] The Al phase can be clearly distinguished from the Al phase that forms a ternary eutectic structure of Al / Zn / MgZn2 under a microscope.

[0067] [Zn phase]

[0068] The Zn phase refers to a phase with clearly defined boundaries and an island-like appearance within the ternary eutectic structure of Al / Zn / MgZn2. It may actually contain small amounts of dissolved Al and Mg. Based on the phase diagram, it is believed that no other additive elements are dissolved in this phase, or if so, the amount is extremely small.

[0069] The Zn phase can be clearly distinguished from the Zn phase that forms a ternary eutectic structure of Al / Zn / MgZn2 under a microscope. In the hot-dip coating of this embodiment, the Zn phase may be present depending on the manufacturing conditions, but no effect on corrosion resistance caused by the Zn phase has been observed. Therefore, even if the hot-dip coating contains the Zn phase, there is no particular problem.

[0070] [MgZn2 phase]

[0071] The MgZn2 phase refers to a phase with clearly defined boundaries and an island-like appearance within a ternary eutectic structure of Al / Zn / MgZn2. It may actually contain a small amount of dissolved Al. Based on the phase diagram, it is believed that no other additive elements are dissolved in this phase, or if so, the amount is extremely small.

[0072] The MgZn2 phase can be clearly distinguished from the MgZn2 phase that forms a ternary eutectic structure of Al / Zn / MgZn2 under a microscope. In the hot-dip coating of this embodiment, the MgZn2 phase may not be present depending on the manufacturing conditions, but it is present in the hot-dip coating under most manufacturing conditions.

[0073] [Mg2Si phase]

[0074] The Mg₂Si phase refers to a phase with clearly defined boundaries and an island-like appearance in the solidification structure of Si-added coatings. Based on the phase diagram, it is believed that the Mg₂Si phase contains no dissolved Zn, Al, or other additive elements, or if dissolved, in extremely small amounts. The Mg₂Si phase can be clearly distinguished from other phases under a microscope in hot-dip galvanized coatings.

[0075] The hot-dip coating of this embodiment is formed by immersing a steel sheet in a plating bath, then removing it and allowing the molten metal adhering to the surface of the steel sheet to solidify. At this time, the [Al phase] forms first, and then, as the temperature of the molten metal decreases, a [ternary eutectic structure of Al / Zn / MgZn2] is formed. Depending on the chemical composition of the hot-dip coating (i.e., the chemical composition of the plating bath), a [Mg2Si phase], a [MgZn2 phase], or a [Zn phase] may also form in the [Al / Zn / MgZn2 ternary eutectic structure] matrix.

[0076] Next, the patterned and non-patterned portions of the hot-dip coating will be explained.

[0077] In this embodiment, the surface of the hot-dip galvanized layer has patterned and non-patterned portions arranged in a predetermined shape. From the viewpoint of ensuring the aesthetics of the patterned portions, they are preferably arranged in a predetermined shape. Furthermore, from the viewpoint of ensuring the visual recognizability of the patterned portions, a larger size of the patterned portions is preferred. For example, the patterned portions preferably have an artificial shape. The patterned portions are preferably arranged in an intentional shape. The patterned portions are preferably arranged in a shape that is one of straight lines, curves, dots, graphics, numbers, symbols, or text, or a combination of two or more of these. For example, on the surface of the hot-dip galvanized layer, a series of text, numbers, symbols, marks, line drawings, designs, or combinations thereof formed by the patterned portions are displayed. The straight and curved portions in the patterned portions are preferably each 1 mm or longer. It can be said that the patterned portions are intentionally formed by displaying these shapes. The straight and curved portions in the patterned portions preferably have a width that is visually recognizable as described later, and each have a length of 1 mm or longer. The dots in the pattern area preferably have an equivalent circle diameter of 1 mm or more but less than 10 mm, and multiple dots are more preferably arranged in a regular pattern. Furthermore, when the pattern area is a graphic, number, symbol, or text, it is preferable that these shapes can be visually identified as described later. It can be said that such dimensions and shapes are intentionally formed. The non-pattern area refers to the area outside the pattern area. Furthermore, even if the shape of the pattern area is partially missing, such as a missing dot, it is permissible as long as it is identifiable as a whole. Furthermore, the non-pattern area can also be a shape where the boundaries of the pattern area are trimmed.

[0078] When a shape consisting of any one or more of straight lines, curves, dots, graphics, numbers, symbols, or text, or a combination thereof, is arranged on the surface of a hot-dip galvanized coating, these areas can be designated as patterned areas, and the remaining areas as non-patterned areas. This shape is intentionally or artificially formed through the manufacturing method described later, and is not naturally formed. Anyone skilled in the art who is familiar with the appearance of a typical hot-dip galvanized coating can easily distinguish between patterned and non-patterned areas with artificially shaped features.

[0079] The patterned area should ideally be formed in a manner that allows for assessment of its extent using the naked eye, or by visual inspection with a magnifying glass or microscope. Furthermore, the non-patterned area occupies the majority of the hot-dip galvanized layer (the surface of the hot-dip galvanized layer), and the patterned area is arranged in a prescribed shape within the non-patterned area. Specifically, the patterned area is arranged within the non-patterned area in a shape that is one or a combination of two or more of the following: straight lines, curves, graphics, dots, figures, numbers, symbols, or text. By intentionally adjusting the shape of the patterned area, one or a combination of two or more of the following shapes is displayed on the surface of the hot-dip galvanized layer: straight lines, curves, graphics, dots, figures, numbers, symbols, or text. For example, a series of text, numbers, symbols, marks, line drawings, designs, or combinations thereof formed by the patterned area may be displayed on the surface of the hot-dip galvanized layer. This shape is intentionally or artificially formed by the manufacturing method described later, and is not naturally formed. Anyone skilled in the art who is familiar with the appearance of typical hot-dip coatings can easily distinguish between patterned and non-patterned areas with artificial shapes. In particular, areas that can contain at least a square with one side of 1 mm (this size can be less than or greater than 1 mm) and have artificial shapes can be easily identified as patterned areas.

[0080] It should be noted that, from the viewpoint of improving the visual recognizability of the patterned portion, the area occupied by the patterned portion on the surface of the hot-dip galvanized layer is preferably significantly smaller than that of the non-patterned portion. For example, the area occupied by the patterned portion on the surface of the hot-dip galvanized layer is preferably 30% or less, 25% or less, 20% or less, or 15% or less.

[0081] Patterned areas are regions with a high metallic luster on their surface. Conversely, unpatterned areas are regions with a low metallic luster, appearing white or gray, exhibiting a pear-skin-like appearance similar to that seen on Zn-Al-Mg based hot-dip galvanized steel sheets. Therefore, patterned and unpatterned areas can be distinguished by the naked eye.

[0082] Furthermore, patterned and unpatterned areas can also be identified under a microscope. Specifically, the shape formed by the patterned areas only needs to be identifiable at a field of view of 50x or less. At a field of view of 50x or less, patterned and unpatterned areas can be identified by the difference in their surface conditions.

[0083] The patterned portion and the non-patterned portion are preferably distinguishable at a magnification of 20 times or less, more preferably 10 times or less, and even more preferably 5 times or less.

[0084] The patterned and non-patterned portions may further satisfy any of the following (a), (b), and (c).

[0085] (a) The patterned area is the region where the exposure ratio of the Al phase in the surface of the hot-dip galvanized coating is less than 30% of the area, and the non-patterned area is the region where the exposure ratio of the Al phase in the surface of the hot-dip galvanized coating is more than 30% of the area.

[0086] (b) The patterned area is the region with an arithmetic mean surface roughness Sa of less than 1.0 μm, and the unpatterned area is the region with an arithmetic mean surface roughness Sa of more than 1.0 μm.

[0087] (c) The relationship between the reflected light from the patterned portion in the normal direction and the reflected light from the non-patterned portion in the normal direction and the incident light in the range where the incident angle is 0° or more and less than 90° relative to the normal direction of the steel plate surface satisfies the following equations (1) and (2).

[0088] |I PH -I BH | / |I PM -I BM |<1.0 (1)

[0089] |I PL -I BL | / |I PM -I BM |<1.0 (2)

[0090] In equations (1) to (2), I PH I is the reflection intensity of the patterned portion in the normal direction relative to incident light with an angle of incidence greater than 0° and less than 35°. BH I is the reflection intensity of the unpatterned portion in the normal direction relative to incident light with an angle of incidence greater than 0° and less than 35°. PM I is the reflection intensity of the patterned portion in the normal direction relative to incident light with an incident angle of 35° to 80°. BM I is the reflection intensity of the unpatterned portion in the normal direction relative to incident light with an incident angle of 35° to 80°. PL I is the reflection intensity of the patterned portion in the normal direction relative to incident light with an angle of incidence exceeding 80° but less than 90°. BL The intensity of reflection of the unpatterned portion in the normal direction relative to incident light with an incident angle greater than 80° and less than 90°.

[0091] In the hot-dip galvanized coating, at least the [Al phase] and the [Al / Zn / MgZn2 ternary eutectic structure] are present. However, in the patterned area, the [Al phase] is unevenly distributed on the steel plate side in the thickness direction of the hot-dip galvanized coating. On the other hand, on the surface side in the thickness direction, the [Al phase] is relatively scarce, and other structures or phases besides the [Al phase] are more abundant. Therefore, in the patterned area, the exposed proportion of the [Al phase] at the surface of the hot-dip galvanized coating is less than 30% by area.

[0092] Furthermore, a relatively large amount of [Al / Zn / MgZn2 ternary eutectic structure] exists on the surface of the patterned area. However, since the [Al / Zn / MgZn2 ternary eutectic structure] forms a relatively flat surface during the solidification of the hot-dip coating, the arithmetic mean surface roughness Sa of the patterned area is in the range of 1.0 μm or less.

[0093] Thus, it is speculated that in the patterned area, since the exposure ratio of the [Al phase] is less than 30% of the area, or the arithmetic mean surface roughness Sa is relatively small and less than 1.0 μm, a metallic luster is exhibited.

[0094] On the other hand, in the hot-dip galvanized coating, at least the [Al phase] and the [Al / Zn / MgZn2 ternary eutectic structure] are present. However, in the non-patterned areas, the [Al phase] is not unevenly distributed on the steel plate side in the thickness direction of the hot-dip galvanized coating, but rather widely distributed throughout the entire thickness direction. Therefore, in the non-patterned areas, the exposed proportion of the [Al phase] at the surface of the hot-dip galvanized coating exceeds 30% of the area.

[0095] Furthermore, this results in a larger exposed area of ​​the [Al phase] in the unpatterned region compared to the first region. The [Al phase] is a phase that forms in the early stages of the solidification of the hot-dip coating and crystallizes in a dendritic form. Since the [Al phase], which crystallizes in a dendritic form, is more abundant on the surface of the hot-dip coating, the arithmetic mean surface roughness Sa of the unpatterned region exceeds 1.0 μm.

[0096] Thus, it is speculated that in the unpatterned area, since the exposed proportion of the [Al phase] exceeds 30% of the area, or the arithmetic mean surface roughness Sa is relatively large and exceeds 1.0 μm, the light incident on the unpatterned area undergoes diffuse reflection and appears white to gray.

[0097] The exposure ratio of the [Al phase] was determined using the following method. First, the surface of the hot-dip coating was photographed using a 100x scanning electron microscope, and the elemental distribution was analyzed using an energy-dispersive X-ray elemental analyzer (EDS) attached to the scanning electron microscope. For example, five 1mm images of the patterned area were prepared. 2 Images of the field of view, 5 images of the non-patterned area taken at 1mm. 2Images of the field of view. For each image, commercially available image analysis software was used to determine the area of ​​the [Al phase] exposed to the surface of the hot-dip galvanized coating. The [Al phase] can be determined by observing the Al-concentrated region in surface analysis and the morphology of the [Al phase] obtained using reflectance electron imaging. The [Al phase] mostly exists in a dendritic form. In both the patterned and unpatterned areas, the average exposed area of ​​the [Al phase] in five images was calculated. Then, by dividing the average exposed area of ​​the [Al phase] by the total area of ​​the observation field of view, the average exposed area ratio (%) of the [Al phase] in the observation field of view was calculated for both the patterned and unpatterned areas. The average exposed area ratio (%) of the [Al phase] obtained in this way was taken as the exposure ratio of the [Al phase]. It should be noted that, for example, the field of view of the image can also be set to be less than 1 mm. 2 Evaluation is conducted using a smaller field of view. (For sizes smaller than 1mm) 2 In the case of a given field of view, as long as the total area is 5mm... 2 That's all.

[0098] The arithmetic mean surface roughness Sa is measured using the following method. Using a 3D laser microscope (manufactured by KEYENCE Co., Ltd.), with a 20x standard lens installed, the height Z is measured at intervals of 50 μm. The number of measurement points is preferably set to 100 points (10 points vertically × 10 points horizontally). With 100 measurement points and the resulting height Z100 points defined as heights Z1 to Z100, Sa is calculated using the following formula. Zave is set as the average of the height Z100 points. Sa = 1 / 100 × Σ[x = 1 → 100](|height Zx - Zave|)

[0099] The Al phase formed during the solidification of a hot-dip galvanized coating typically crystallizes along the entire thickness of the coating. However, if a nucleus is pre-placed on the steel plate surface, a large amount of Al phase crystallizes from these nuclei during the solidification of the molten metal adhering to the steel plate surface. The resulting Al phase forms closer to the steel plate. Furthermore, in areas with nuclei, the Al phase forms at a relatively high density, preventing it from becoming coarse and maintaining a fine-grained structure. Consequently, the Al phase does not grow to the surface of the hot-dip galvanized coating in areas with nuclei, resulting in a smaller exposed proportion of the Al phase.

[0100] In this way, areas on the steel plate surface where solidification nuclei exist become the patterned portions of the hot-dip galvanized coating, while areas where solidification nuclei do not exist become the non-patterned portions of the hot-dip galvanized coating. Furthermore, since the patterned portions are formed using the mechanism described above, there is an elemental concentration region originating from the solidification nuclei at the interface between the base steel plate of the patterned portions and the hot-dip galvanized coating. More specifically, there is an elemental concentration region at the interface between the steel plate of the patterned portions and the hot-dip galvanized coating containing one or more of the element M selected from Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, Ni, C, Ti, Zr, Mo, W, REM, Hf, and C.

[0101] In the element-concentrated region, element M is concentrated at more than twice the amount present in the hot-dip coating of the patterned area, or in a region where element M is not uniformly present. Here, the term "non-uniformly present element M" means that element M originating from solidification nuclei is present in the element-concentrated region, but element M is not detected in the patterned area outside the element-concentrated region.

[0102] During the hot-dip galvanizing process, it is possible that a portion of the solidification nucleus diffuses into the hot-dip galvanized coating. In cases where this diffusion occurs, element M, which constitutes the solidification nucleus, is also incorporated into the hot-dip galvanized coating. In this situation, the concentration of element M in the element-concentrated region becomes more than twice that of element M contained in the hot-dip galvanized coating.

[0103] On the other hand, in the hot-dip coating formation process, it is also possible that the solidification nuclei do not diffuse into the hot-dip coating at all. In this case, the element M constituting the solidification nuclei is no longer included in the hot-dip coating, but is only included in the element concentration region. That is, the element concentration region becomes a region where element M exists unevenly with respect to the hot-dip coating of the patterned area.

[0104] The concentration of element M in the element-concentrated region is set to be more than twice that of element M in the hot-dip coating. If the concentration of element M in the element-concentrated region is less than twice that of the hot-dip coating in the patterned area, it will not function as a solidification nucleus and will be difficult to form the patterned area.

[0105] The average concentration of element M in the hot-dip galvanized layer and element concentration region of the patterned area is 0.0010 to 2% by mass. When the average concentration is below 0.0010% by mass, it does not function as a solidification nucleus, making it difficult to form the patterned area. On the other hand, if the average concentration exceeds 2% by mass, although the patterned area has sufficient shape performance, the excessive presence of solidification nuclei may reduce the adhesion between the hot-dip galvanized layer and the steel sheet at the patterned area, leading to peeling of the hot-dip galvanized layer at the patterned area. Therefore, the average concentration of element M in the hot-dip galvanized layer and element concentration region of the patterned area is preferably in the range of 0.0010 to 2% by mass. The preferred lower limit is 0.1% by mass, and the preferred upper limit is 1.00% by mass.

[0106] On the other hand, since the non-patterned portion is a region without solidification nuclei, element M is essentially absent (i.e., below the detection limit) or present in extremely small amounts at the interface between the steel plate and the hot-dip galvanized layer in the non-patterned portion. Therefore, the concentration of element M at the interface of the patterned portion, i.e., the concentration of element M in the element-concentrated region, is at least 1.5 times that at the interface of the non-patterned portion. Preferably, it is 2 times or more, more preferably 4 times or more. Furthermore, at the interface between the steel plate and the hot-dip galvanized layer in the non-patterned portion, when element M is below the detection limit, the ratio of the concentration of element M becomes impossible to calculate.

[0107] To confirm the presence and concentration ratio of the aforementioned elements at the interface between the steel sheet and the hot-dip galvanized coating in both patterned and non-patterned areas, this can be achieved by exposing a cross-section of the hot-dip galvanized steel sheet along its thickness direction and performing surface analysis of the elemental distribution at the interface between the hot-dip galvanized coating and the steel sheet using an electron beam probe microanalysis (EPMA). Furthermore, the presence of the interface alloy layer, described later, can be confirmed using the same method. The thickness of the interface alloy layer can be confirmed by observing the reflected electron image using a scanning electron microscope (SEM).

[0108] As described above, before immersing the steel sheet in the hot-dip galvanizing bath, solidification nuclei are arranged on the surface of the steel sheet in shapes that are either straight lines, curves, graphics, numbers, symbols, or text, or combinations of two or more of them, thereby forming patterned portions with these shapes in the hot-dip galvanizing layer.

[0109] Next, the interface alloy layer will be explained. In the hot-dip galvanized steel sheet of this embodiment, an interface alloy layer exists between the hot-dip galvanized layer and the steel sheet. The interface alloy layer exists in both the patterned area and the non-patterned area. At the interface between the hot-dip galvanized layer and the steel sheet at the patterned area, there is an element concentration region and the interface alloy layer. In the hot-dip galvanized steel sheet of this embodiment, by forming an interface alloy layer also in the patterned area where the element concentration region exists, the adhesion of the hot-dip galvanized layer at the patterned area becomes equal to the adhesion of the hot-dip galvanized layer at the non-patterned area. As a result, there is no risk of peeling off the patterned area of ​​the hot-dip galvanized layer, and the corrosion resistance of the hot-dip galvanized steel sheet is improved throughout the entire surface of the hot-dip galvanized layer.

[0110] The interface alloy layer contains at least Fe and Al. Furthermore, when the hot-dip galvanized layer contains Si, the interface alloy layer contains at least Fe, Si, and Al.

[0111] An interfacial alloy layer is a layer formed on the surface of the base steel sheet (specifically, between the base steel sheet and the hot-dip galvanized layer), with the Al5Fe2 phase as the main phase in terms of microstructure. Generally, the interfacial alloy layer is formed through atomic diffusion between the base metal (steel sheet) and the plating bath. When using hot-dip galvanizing as the manufacturing method, an interfacial alloy layer containing both Fe and Al is easily formed in Al-containing hot-dip galvanized layers. Since the plating bath contains a certain concentration or higher of Al, the Al5Fe2 phase is formed most abundantly. However, atomic diffusion takes time, and there are also regions with higher Fe concentrations near the base metal. Therefore, the interfacial alloy layer may also contain small amounts of AlFe phase, Al3Fe phase, etc. Furthermore, since the plating bath also contains a certain concentration of Zn, the Al-Fe alloy phase also contains small amounts of Zn.

[0112] When the hot-dip galvanized layer contains Si, Si is easily absorbed into the interfacial alloy layer, potentially dissolving in the Al-Fe alloy phase or forming an Al-Fe-Si intermetallic compound phase. Examples of Al-Fe-Si intermetallic compound phases include α, β, q1, and q2 phases. Therefore, these Al-Fe-Si intermetallic compound phases may be detected in the interfacial alloy layer.

[0113] In this embodiment, since no solidification nuclei are provided on the surface of the steel plate in the non-patterned area, atomic diffusion between the base metal (base steel plate) and the plating bath easily occurs in the non-patterned area, facilitating the formation of an interface alloy layer. On the other hand, since solidification nuclei are provided on the surface of the steel plate in the patterned area, atomic diffusion between the base metal (base steel plate) and the plating bath does not occur in the patterned area, resulting in no interface alloy layer forming at all, or even if it does form, its thickness is extremely thin and undetectable. Therefore, in this embodiment, especially in order to promote the growth of the interface alloy layer in the patterned area, a reheating treatment is required after the hot-dip plating process.

[0114] The thickness of the interface alloy layer is preferably set in the range of 10 to 500 nm in both the patterned and unpatterned portions, and more preferably in the range of 10 to 100 nm. This further improves the adhesion between the patterned and unpatterned portions.

[0115] Figure 1 The diagram shows cross-sectional schematics of patterned portion 1 and unpatterned portion 2. In unpatterned portion 2, an interface alloy layer 5 exists between steel plate 3 and coating 4. In patterned portion 1, an interface alloy layer 5 and a concentration region 6 exist between steel plate 3 and coating 4. It is believed that in patterned portion 1, the elemental concentration region 6 in the interface alloy layer 5 exists independently without solid solution. However, due to their fine structures, they are difficult to distinguish even by cross-sectional analysis such as EPMA. In the elemental distribution map of the cross section obtained using EPMA, the elemental distribution image appears as if the interface alloy layer 5 and the concentration region 6 exist in the same location.

[0116] The hot-dip galvanized steel sheet of this embodiment may also have a chemical conversion treatment film layer or a coating layer on the surface of the hot-dip galvanized layer. Here, the type of chemical conversion treatment film layer or coating layer is not particularly limited, and known chemical conversion treatment film layers or coating layers can be used.

[0117] As an example of a chemical conversion treated coating, a chemical conversion treated coating containing phthalocyanine pigment coated with at least one of a resin and a surfactant can be illustrated. By coloring the coating surface with phthalocyanine pigment, a hot-dip immersion coating with such a chemical conversion treated coating can be given preferred pattern design characteristics, and the visual recognizability of the patterned areas is further improved. Furthermore, the corrosion resistance, weather resistance, and other properties of the chemical conversion treated coating can be improved.

[0118] Next, the manufacturing method of the Zn-Al-Mg hot-dip galvanized steel sheet of this embodiment will be described.

[0119] First, hot-rolled steel sheets are manufactured and annealed as needed. After pickling, they are cold-rolled to produce cold-rolled sheets. The cold-rolled sheets are then degreased, washed, and annealed (cold-rolled sheet annealing). The annealed cold-rolled sheets are then immersed in a hot-dip galvanizing bath to form a hot-dip coating.

[0120] Here, during the period from cold rolling to immersion in the hot-dip galvanizing bath, solidification nuclei are attached to the surface of the steel sheet to form a patterned portion in the shape of any one of straight lines, curves, graphics, numbers, symbols, and text, or a combination of two or more of them. The attachment of solidification nuclei is carried out at any stage between cold rolling and annealing of the cold-rolled sheet, between annealing of the cold-rolled sheet and immersion in the hot-dip galvanizing bath, or just before the final annealing of the cold-rolled sheet. The solidification nuclei can be attached in a solution-dispersed state or by vapor deposition.

[0121] As a component that forms a nucleus (hereinafter sometimes referred to as a nucleus-forming component), any component that forms a nucleus during the solidification process of the coating is acceptable and is not particularly limited. Examples of nucleus-forming components include any one or more of Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, Ni, Ti, Zr, Mo, W, REM, Hf, and C, or compounds containing any one or more of the above elements. One or more of the above components may also be used in combination. An example of a method for attaching nuclei to the surface of a steel sheet is the following: in addition to containing the nucleus-forming component itself, the alloy foil, resin, surfactant, ink, oil, etc., contains the nucleus-forming component and attaches it to the surface of the steel sheet. These nucleus-forming components can be solids themselves, or dissolved or dispersed in water or organic solvents. Alternatively, they can be included as pigments or dyes in inks.

[0122] Methods for attaching solidification nuclei to the surface of a steel plate include, for example, transferring, coating, or blowing a material containing solidification nuclei onto the surface of the steel plate. Examples of common printing methods include foil transfer using hot stamping or cold printing, printing using various printing plates (gravure printing, flexographic printing, offset printing, screen printing, etc.), inkjet printing, and thermal transfer using ink ribbons.

[0123] As an example of a transfer method using alloy foil, the following method can be described: an alloy foil containing nucleation-forming components is bonded to the surface of a steel plate, and a heated silicon roller is pressed onto the alloy foil to transfer it to the surface of the steel plate.

[0124] As an example of a printing method using a printing plate, the following method can be described: ink or surfactant containing components that act as nucleation sites is adhered to a rubber roller or rubber mold on which a printing pattern is formed on the peripheral surface, and the rubber roller or rubber mold is pressed against the surface of a steel plate to transfer the ink or surfactant. If this method is used, for steel plates that are continuously processed, the nucleation site-forming components can be efficiently adhered to the surface of the steel plate.

[0125] The amount of solidified nuclei attached is preferably, for example, 50 mg / m³. 2 ~5000mg / m 2 Within the range. When the adhesion concentration is below 50 mg / m³. 2 In such cases, the first region may become so small that it is not visible to the naked eye, which is therefore undesirable. On the other hand, when the adhesion concentration exceeds 5000 mg / m²... 2 In such cases, the adhesion of the hot-dip coating may decrease, therefore it is not preferred.

[0126] Next, the steel plate with the patterned portion formed on its surface is immersed in a hot-dip galvanizing bath. Preferably, the hot-dip galvanizing bath contains Al: 4–22% by mass, Mg: 1.0–10% by mass, with Zn and impurities as the remainder. Furthermore, the hot-dip galvanizing bath may also contain Si: 0.0001–2.0% by mass. Moreover, the hot-dip galvanizing bath may also contain any one or more of Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C, totaling 0.0001–1% by mass.

[0127] It should be noted that the composition of the hot-dip coating can be determined by the following method. It can be determined as follows: First, the surface coating is removed with a non-corrosive coating stripper (e.g., NEOREVER SP-751 manufactured by Sansai Chemical Co., Ltd.). Then, the hot-dip coating is dissolved in hydrochloric acid containing an inhibitor (e.g., HIBIRON manufactured by SUGIMURA Chemical Industrial Co., Ltd.). The resulting solution is then subjected to inductively coupled plasma (ICP) luminescence spectrophotometry analysis.

[0128] The preferred temperature of the hot-dip plating bath is in the range of 400–500°C. This is because if the temperature of the hot-dip plating bath is within this range, the desired hot-dip coating can be formed.

[0129] Furthermore, the adhesion amount of the hot-dip galvanized coating can be adjusted simply by wiping the steel sheet after it has been removed from the hot-dip galvanizing bath with gas. The preferred adhesion amount is 30–600 g / m², calculated as the total adhesion amount on both sides of the steel sheet. 2 Adjust the range accordingly. When the adhesion amount is below 30g / m²2 In cases where the corrosion resistance of Zn-Al-Mg based hot-dip galvanized steel sheet decreases, it is not preferred. When the coating thickness exceeds 600 g / m²... 2 In such cases, molten metal drips onto the steel plate, making it impossible to smooth the surface of the hot-dip galvanized coating, which is therefore undesirable.

[0130] After adjusting the adhesion amount of the hot-dip coating, a reheating treatment is performed, followed by cooling of the steel sheet. The reheating treatment is performed under conditions where the interface alloy layer in the patterned area is 10 nm or more, and the interface alloy layer in the non-patterned area is 500 nm or less. While the specific reheating conditions vary depending on the coating composition, it is preferable to hold the plate at a temperature range of (Tw+15)°C to (Tw+50)°C for 1 to 10 seconds relative to the surface temperature Tw of the molten coating immediately after wiping. The cooling conditions after the reheating treatment are preferably set at a cooling rate of 3°C / second or higher but lower than 30°C / second, preferably 3 to 25°C / second, until the temperature reaches 300 to 340°C. It should be noted that if the reheating temperature is too low or the reheating time is too short, an interface alloy layer of sufficient thickness cannot be formed in the patterned area, and the adhesion of the hot-dip coating in the patterned area will not improve. Furthermore, if the reheating temperature is too high or the reheating time is too long, the diffusion of Fe into the hot-dip coating in the pattern section becomes excessive, resulting in alloying of the hot-dip coating and making it difficult to realize the pattern design brought about by the pattern section.

[0131] Cooling of the molten metal adhering to the steel plate begins after the steel plate is removed from the hot-dip galvanizing bath. Although it varies depending on the composition of the hot-dip galvanizing bath, for example, the [Al phase] begins to crystallize from around 430°C. Then, [MgZn2] begins to crystallize from around 370°C, and a [ternary eutectic structure of Al / Zn / MgZn2] crystallizes from around 340°C, completing solidification.

[0132] At this point, in the areas where solidification nuclei adhere to the steel plate surface, the Al phase begins to crystallize, using these nuclei as nuclei. The Al phase crystallizes extensively near the interface between the steel plate and the molten metal. Because the Al phase forms at a relatively high density through solidification nuclei, it does not become coarse but remains in a fine state. Therefore, the Al phase does not grow to the surface side of the hot-dip galvanized layer, and the exposed proportion of the Al phase becomes relatively small. It is speculated that, through this operation, the areas on the steel plate surface where solidification nuclei exist become the patterned areas of the hot-dip galvanized layer.

[0133] On the other hand, in areas on the steel plate surface where no solidification nuclei are attached, the Al phase crystallizes along the entire thickness of the molten metal. That is, because the Al phase has a relatively low crystal density, its crystallization is not hindered. Consequently, the Al phase coarsens. Therefore, the Al phase grows to the surface side of the hot-dip galvanized layer, resulting in a higher proportion of the Al phase exposed at the surface of the hot-dip galvanized layer.

[0134] It is speculated that through this mechanism, the areas on the steel plate surface where there are no solidification nuclei become the non-patterned parts of the hot-dip galvanized coating.

[0135] When a chemical conversion treatment layer is formed on the surface of a hot-dip galvanized steel sheet, a chemical conversion treatment is performed on the sheet after the hot-dip galvanized layer is formed. There are no particular limitations on the type of chemical conversion treatment; any known chemical conversion treatment can be used.

[0136] Furthermore, when a coating layer is formed on the surface of a hot-dip galvanized layer or a chemical conversion treatment layer, the hot-dip galvanized steel sheet after the formation of the hot-dip galvanized layer or the chemical conversion treatment layer is then coated. There are no particular limitations on the type of coating treatment; any known coating treatment may be used.

[0137] As an example of chemical conversion treatment, a chemical conversion treatment using a chemical conversion agent containing phthalocyanine pigment coated with at least one of a resin and a surfactant can be illustrated. Specifically, the chemical conversion agent can be an aqueous coating agent containing polyurethane resin particles having at least one of silanol and alkoxysilyl groups, ethylene-unsaturated carboxylic acid copolymer resin particles, silica particles, an organotitanium compound, and the aforementioned phthalocyanine pigment. The phthalocyanine pigment content is 0.01 to 10 parts by mass relative to 100 parts by mass of the total polyurethane resin particles and ethylene-unsaturated carboxylic acid copolymer resin particles, and the primary particle size of the phthalocyanine pigment is 0.01 to 1.0 μm. The hot-dip coating subjected to such chemical conversion treatment, by being colored with phthalocyanine pigment, can impart a preferred pattern design to the coating surface, thereby improving the corrosion resistance, weather resistance, etc., of the formed chemical conversion film.

[0138] According to this embodiment, a hot-dip galvanized steel sheet can be provided that has excellent corrosion resistance, high durability in displaying text and design patterns, and excellent adhesion of the hot-dip galvanized coating on the patterned areas.

[0139] In particular, in this embodiment, by attaching solidification nuclei to the surface of the steel sheet in an arbitrary pattern, the extent of the patterned portion can be intentionally determined, and the patterned portion can be arranged in a shape that is one of straight lines, curves, graphics, numbers, symbols, and text, or a combination of two or more of them. Therefore, various pattern designs can be implemented on the surface of the hot-dip galvanized layer without painting or grinding, improving the recognizability and designability of the steel sheet. Furthermore, by forming an interface alloy layer together with the element concentration region at the patterned portion, the adhesion of the hot-dip galvanized layer at the patterned portion can be improved to the same degree as the adhesion of the hot-dip galvanized layer at the non-patterned portion.

[0140] Furthermore, according to this embodiment, various patterns, trademarks, and other identification marks can be displayed on the surface of the hot-dip galvanized layer without printing or painting, thereby improving the recognizability and design appeal of the steel sheet. In addition, the pattern section can also provide the hot-dip galvanized steel sheet with information required for process management or inventory management, as well as any information requested by the customer. This further contributes to improving the productivity of hot-dip galvanized steel sheets.

[0141] Example

[0142] The embodiments of the present invention will be described next.

[0143] (No. 1~71)

[0144] First, the cold-rolled steel sheet is degreased and washed with water. Ink containing the nucleation-forming components shown in Table 1 is applied to a rubber plate with a checkerboard pattern spaced 50 mm apart. Here, the checkerboard pattern is formed in lines with a line width of 10 mm. By pressing the rubber plate onto the washed steel sheet, the ink containing the nucleation-forming components is applied to the steel sheet surface in a checkerboard pattern with 50 mm intervals. Next, the steel sheet is cold-rolled and annealed. The annealed steel sheet is immersed in a hot-dip galvanizing bath at 400–500°C to form a hot-dip galvanized coating on the steel sheet surface. Then, the amount of coating is controlled using a wiping nozzle, followed by reheating and further cooling. Regarding the reheating treatment, the wiped steel sheet is heated to the reheating temperatures recorded in Tables 2A and 2B, held at these temperatures, and cooled to a range of 300–340°C at the average cooling rates recorded in Tables 2A and 2B. As a result, Zn-Al-Mg hot-dip galvanized steel sheets No. 1 to 71 shown in Tables 3A to 4B were manufactured.

[0145] (No. 72)

[0146] After controlling the coating adhesion amount using a wiping nozzle, the material was cooled without reheating. Otherwise, the same procedure as described above was followed to manufacture Zn-Al-Mg hot-dip galvanized steel sheets. The results are shown as No. 72 in Tables 3B and 4B.

[0147] (No. 73)

[0148] Except for the absence of ink transfer using a rubber plate, Zn-Al-Mg based hot-dip galvanized steel sheets were manufactured using the same procedures as described above. Subsequently, a checkerboard pattern with 50mm intervals was printed onto the surface of the hot-dip galvanized layer using inkjet printing. The results are shown as No. 73 in Tables 3B and 4B.

[0149] (No. 74)

[0150] Except for the absence of ink transfer using a rubber plate, Zn-Al-Mg based hot-dip galvanized steel sheets were manufactured using the same procedures as described above. The surface of the hot-dip galvanized layer was then ground to form a checkerboard pattern with 50mm intervals. The results are shown as No. 74 in Tables 3B and 4B.

[0151] Evaluation method for the exposure ratio of [Al phase]

[0152] The surface of the hot-dip coating was photographed using a 100x scanning electron microscope, and the elemental distribution was determined using an energy-dispersive X-ray diffraction (EDS) apparatus attached to the scanning electron microscope. Five 1mm images of the patterned area were prepared. 2 Images of the field of view, 5 images of the non-patterned area taken at 1mm. 2 Images of the field of view. For each image, the area of ​​the [Al phase] exposed to the surface of the hot-dip galvanized coating was determined using commercially available image analysis software. The [Al phase] was determined by observing the morphology of the [Al phase] in the Al-concentrated region from surface analysis and using reflectance electron imaging. In both the patterned and unpatterned regions, the average exposed area of ​​the [Al phase] in five images was calculated. Then, by dividing the average exposed area of ​​the [Al phase] by the total area of ​​the field of view, the average exposed area ratio (%) of the [Al phase] in the field of view was calculated for both the patterned and unpatterned regions. The average exposed area ratio (%) of the [Al phase] obtained in this way was taken as the exposure ratio of the [Al phase].

[0153] [Method for determining the arithmetic mean surface roughness Sa]

[0154] An imaginary grid of lines is drawn at 0.5 mm intervals on the surface of the hot-dip galvanized layer. The arithmetic mean surface roughness Sa is measured in each of the multiple regions divided by the imaginary grid. Regions with an arithmetic mean surface roughness Sa of 1 μm or more are designated as unpatterned areas, while regions with an arithmetic mean surface roughness Sa of less than 1 μm are designated as patterned areas. The arithmetic mean surface roughness Sa is measured using a 3D laser microscope (manufactured by KEYENCE Co., Ltd.). In this embodiment, a 20x standard lens is used, and the height Z within each of the multiple regions divided by the imaginary grid is measured at 50 μm intervals. When the measurement is performed on the grid, 100 measurement points are obtained within each region. These 100 height points Z are then set as heights Z1 to Z2. 100 When Z is in Z, use the following formula to calculate Sa. ave Set to the average of height Z100 points.

[0155] Sa=1 / 100×Σ[x=1→100](|heightZ) x -Z ave |)

[0156] It should be noted that the location for measuring the arithmetic mean surface roughness Sa is set to a different location than the location for measuring the exposure ratio of the Al phase. This setting applies equally to both patterned and unpatterned areas.

[0157] [Element Concentration Regions and Interface Alloy Layers]

[0158] The cross-section along the thickness direction of the hot-dip galvanized steel sheet is exposed. The interface between the hot-dip galvanized layer and the steel sheet is analyzed using an electron beam probe microanalysis (EPMA) system to determine the elemental distribution, identify the elemental concentration regions and the interfacial alloy layer, and simultaneously determine the concentration and concentration factor of element M. The thickness of the interfacial alloy layer is determined using a scanning electron microscope (SEM) with reflected electron images.

[0159] [Pattern Design]

[0160] For the test panels of the embodiments and comparative examples, the ability to visually recognize the checkerboard pattern was evaluated based on the following criteria. The evaluation was conducted on test panels immediately after manufacture and after 6 months of outdoor exposure. Both the initial state and the extended state were designated as acceptable (A or B). A condition was deemed unacceptable (C) if at least one of the initial state or the extended state was acceptable.

[0161] A: The checkerboard pattern can be visually identified from 5 meters in front.

[0162] B: The checkerboard pattern is not visually discernible from 5m in front, but it is highly visually discernible from 2m in front.

[0163] C: The checkerboard pattern is not visually discernible from 2m in front.

[0164] [Corrosion Resistance]

[0165] For test plates cut into 150×70mm sections, a corrosion acceleration test (CCT) of 30 cycles was performed according to JASO-M609. Afterwards, corrosion resistance was evaluated based on the rust condition as follows. A or B was designated as acceptable.

[0166] A: It hasn't rusted and maintains its beautiful pattern design.

[0167] B: The design of the pattern is slightly damaged due to rust.

[0168] C: Due to rust, the appearance quality is significantly reduced.

[0169] [Plating Adhesion]

[0170] For test plates cut into 150×70mm sections, the portion with the checkerboard pattern is subjected to a 2T bend. The coating adhesion is evaluated based on the following criteria. Set A or B as acceptable.

[0171] A: The coating does not detach even when the tape is peeled off. B: The coating detaches if the tape is peeled off, but it does not detach if the tape is not peeled off. C: The coating detaches even without peeling the tape.

[0172] As shown in Tables 2A to 4B, the manufacturing conditions of No. 1 to 61 meet the preferred conditions, the average composition of the hot-dip coating meets the scope of the invention, and the hot-dip coating has patterned and non-patterned portions. At the interface between the base steel sheet and the hot-dip coating at the patterned portion, there is an element-concentrated region containing element M and an interface alloy layer containing Fe and Al. The average concentration of element M contained in the hot-dip coating and the element-concentrated region is 0.0010 to 2% by mass. In the element-concentrated region, element M is more than twice as concentrated as the hot-dip coating present in the patterned portion, or element M exists unevenly. Therefore, No. 1 to 61 are excellent in terms of pattern design, corrosion resistance, and coating adhesion. Furthermore, the interface alloy layer between the patterned and non-patterned portions of No. 1 to 61 contains Fe and Al. In addition, when the coating contains Si, the interface alloy layer between the patterned and non-patterned portions contains Fe, Al, and Si.

[0173] The hot-dip coating No. 62 has an insufficient Al content in its average composition. Therefore, the corrosion resistance of the hot-dip coating is inadequate.

[0174] The Al content in the average composition of the hot-dip coating No. 63 becomes excessive. Therefore, the corrosion resistance of the hot-dip coating becomes insufficient.

[0175] The hot-dip coating No. 64 has an insufficient Mg content in its average composition. Therefore, the corrosion resistance of the hot-dip coating is inadequate.

[0176] The Mg content in the average composition of the hot-dip coating No. 65 becomes excessive. As a result, slag is generated in the plating bath, and the corrosion resistance of the hot-dip coating becomes insufficient.

[0177] No. 66 Because the residence time in the reheat treatment exceeds the preferred upper limit, diffusion of the M element, which is added as a solidification nucleus, occurs inside the coating, and the homogenization of the coating progresses. As a result, the pattern designability is reduced.

[0178] No. 67 Because the heating temperature during the reheating process is lower than the preferred lower limit, no interface alloy layer is formed in the patterned area, resulting in reduced adhesion.

[0179] No. 68 Because the residence time in the reheat treatment is lower than the preferred lower limit, no interface alloy layer is formed in the patterned area, resulting in reduced adhesion.

[0180] No. 69 Because the heating time in the reheating process exceeds the preferred upper limit, diffusion of the M element, which is added as a solidification nucleus, occurs inside the coating, reducing the adhesion.

[0181] No. 70 Because the average cooling rate during reheating is below the preferred lower limit, diffusion of the M element, which is added as a solidification nucleus, occurs inside the coating, leading to homogenization of the coating. As a result, the pattern designability is reduced.

[0182] No. 71 Because the average cooling rate during reheating exceeds the preferred upper limit, the coating surface becomes roughened due to the blowing of cooling gas during cooling, reducing the pattern designability.

[0183] Because No. 72 was not reheated, no interface alloy layer was formed in the patterned area, resulting in reduced adhesion.

[0184] No. 73 Because the pattern is formed by printing, the design quality of the pattern decreases over time.

[0185] No. 74 Because the pattern is formed by grinding, the coating thickness at the pattern area is reduced, resulting in decreased corrosion resistance.

[0186] [Table 1]

[0187]

[0188] [Table 2A]

[0189]

[0190] [Table 2B]

[0191]

[0192] The underlined portion indicates that the manufacturing conditions are outside the preferred range.

[0193] [Table 3A]

[0194]

[0195] [Table 3B]

[0196]

[0197] The underlined portion indicates that it is outside the scope of this invention.

[0198] [Table 4A]

[0199]

[0200] (*1) The average concentration of element M contained in the hot-dip galvanized layer of the patterned area and the element concentration area.

[0201] (*2) The concentration ratio of element M relative to the hot-dip coating of the patterned area.

[0202] (*3) The concentration ratio of element group M at the interface of the patterned part to element group M at the interface of the non-patterned part.

[0203] [Table 4B]

[0204]

[0205] The underlined portion indicates that it is outside the scope of this invention.

[0206] (*1) The average concentration of element M contained in the hot-dip galvanized layer of the patterned area and the element concentration area.

[0207] (*2) The concentration ratio of element M relative to the hot-dip coating of the patterned area.

[0208] (*3) The concentration ratio of element group M at the interface of the patterned part to element group M at the interface of the non-patterned part.

[0209] Furthermore, a chemical conversion coating was formed on the surface of the hot-dip galvanized steel sheets No. 57 to 59 to confirm the pattern design. The chemical conversion coating was formed by chemical conversion treatment using a chemical conversion agent containing phthalocyanine pigment. As the chemical conversion agent, the following aqueous coating agent was used: polyurethane resin particles containing silanol groups and alkoxysilyl groups, ethylene-unsaturated carboxylic acid copolymer resin particles, silica particles, organotitanium compounds, and Cu phthalocyanine. The content of Cu phthalocyanine pigment was 0.01 to 10 parts by mass relative to 100 parts by mass of the total polyurethane resin particles and ethylene-unsaturated carboxylic acid copolymer resin particles, and the primary particle size of Cu phthalocyanine was 0.01 to 1.0 μm.

[0210] The pattern designability of hot-dip galvanized steel sheets No. 57 to 59 with chemical conversion coating was evaluated. The results showed that the evaluation was A for both the hot-dip galvanized steel sheets immediately after manufacturing and those that had been exposed to the outdoors for 6 months. The pattern designability was further improved by setting a chemical conversion coating containing phthalocyanine Cu.

[0211] Explanation of symbols

[0212] 1 Patterned area, 2 Non-patterned area, 3 Steel plate, 4 Hot-dip galvanized layer, 5 Interface alloy layer, 6 Element concentration area.

Claims

1. A hot-dip galvanized steel sheet, comprising a steel sheet and a hot-dip galvanized coating formed on the surface of said steel sheet. The hot-dip coating contains, on average, 4-22% Al and 1.0-10% Mg, with the remainder consisting of Zn and impurities. The hot-dip coating has patterned and non-patterned portions. At the interface between the steel plate and the hot-dip galvanized layer in the patterned area, there exists: an elemental concentration region containing one or more elements M selected from Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, Ni, Ti, Zr, Mo, W, REM, Hf, and C; and an interface alloy layer containing Fe and Al, wherein the interface alloy layer is mainly composed of Al5Fe2 phase. The average concentration of element M contained in the hot-dip galvanized layer of the patterned portion and the element concentration region is 0.0010–2% by mass. In the element concentration region, the element M is concentrated at more than twice the amount of the hot-dip coating present in the patterned portion, or the element M exists unevenly.

2. The hot-dip galvanized steel sheet according to claim 1, wherein the steel sheet in the non-patterned portion has an interface alloy layer comprising Fe and Al at the interface between the steel sheet and the hot-dip galvanized layer.

3. The hot-dip galvanized steel sheet according to claim 1 or claim 2, wherein, The concentration of element M at the interface of the patterned portion is more than 1.5 times the concentration of element M at the interface of the non-patterned portion.

4. The hot-dip galvanized steel sheet according to claim 1, characterized in that, The patterned portion is configured in a shape that is any one of straight lines, curves, dots, graphics, numbers, symbols, or text, or a combination of two or more of them.

5. The hot-dip galvanized steel sheet according to claim 1, characterized in that, The hot-dip coating further contains Si: 0.0001–2% by mass on an average basis.

6. The hot-dip galvanized steel sheet according to claim 5, wherein the interface alloy layer formed in the patterned portion further contains Si.

7. The hot-dip galvanized steel sheet according to claim 5, wherein the interface alloy layer formed in the non-patterned portion further contains Si.

8. The hot-dip galvanized steel sheet according to any one of claims 1, 2, 4, 5, 6, and 7, characterized in that, The hot-dip coating, excluding the element concentration region, further contains, on an average basis, 0.0001 to 1% by mass of any one or more of the following: Ni, Ti, Zr, Sr, Fe, Sb, Pb, Sn, Ca, Co, Mn, P, B, Bi, Cr, Sc, Y, REM, Hf, and C.

9. The hot-dip galvanized steel sheet according to claim 1, characterized in that, The adhesion amount of the hot-dip galvanized coating on both sides of the steel plate is 30-600 g / m². 2 .

10. The hot-dip galvanized steel sheet according to claim 1, characterized in that, The thickness of the alloy layer in the non-patterned portion is 10nm to 45nm, and the thickness of the alloy layer in the patterned portion is 10nm to 45nm.

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