Surface-treated steel material and method for producing surface-treated steel material

Abstract

This surface-treated steel material is provided with a plating layer that is disposed on the surface of a steel material, and the average chemical composition of the plating layer contains, in mass%, more than 10.0% but not more than 40.0% of Al and more than 4.0% but not more than 15.0% of Mg, with the balance being made up of 40% or more of Zn and impurities. A zinc phosphate crystal layer that contains Zn3(PO4)2∙4H2O is superposed on the surface of the plating layer. The zinc phosphate crystal layer contains Mg at a concentration of 1.5% or more and Al at a concentration of 1.0% or more, and a first region that has a C concentration of 2.5% or more is provided in a part of the surface of the zinc phosphate crystal layer.

Description

Surface-treated steel material and method for manufacturing the surface-treated steel material

[0001] The present invention relates to a surface-treated steel material and a method for manufacturing the surface-treated steel material. This application claims priority to Japanese Patent Application No. 2024-014239, filed February 1, 2024, the contents of which are incorporated herein by reference.

[0002] Hot-dip galvanized steel sheets are widely used in the fields of building materials, civil engineering, and automobiles. In these fields, hot-dip galvanized steel sheets are subjected to various processes to be made into steel structures. For example, in cities, we often see steel structures used for guardrails, windbreak fences, distribution boards, cable racks, etc., which are manufactured by forming metallic-colored hot-dip galvanized steel sheets.

[0003] Steel structures that form part of roads, railways, and cityscapes often require consideration for the landscape. For example, road and railway infrastructure requires anti-glare properties for safety reasons, while modern urban spaces require a color tone based on black. Furthermore, there is a growing need to impart color tones and designs to hot-dip galvanized steel sheets in order to display logos and other advertising and brand names.

[0004] To meet these demands, it is conceivable to paint hot-dip galvanized steel sheets, but major obstacles include the need for periodic repairs as the paint deteriorates and the rising cost of painting in proportion to the area of ​​application.Stainless steel and aluminum are sometimes used from the perspective of durability, but in some cases it is difficult to adopt stainless steel or aluminum from the perspective of material cost and strength.

[0005] As a means for solving these problems, there is a technique for marking the metal or alloy itself that constitutes the plating layer without painting when hot-dip plated steel products are shipped.

[0006] For example, Patent Documents 1 and 2 are examples of hot-dip plated steel sheets to which designs are imparted by controlling the internal constituent phases of the plating layer, which is a metal coating.

[0007] Furthermore, in consideration of urban landscapes, zinc-plated steel materials that have undergone phosphate treatment, which specifies Munsell values ​​and other parameters, have recently come into use. Phosphating involves forming a coating of phosphate on the surface of the plating layer, which blackens the surface of the plating layer and enhances anti-glare properties, resulting in metal materials with a subdued appearance. However, because phosphate treatment uniformly blackens the metal surface, it is difficult to change the color tone locally. Furthermore, the coating formed by phosphate treatment has a short lifespan, and color changes may occur over time after the coating disappears.

[0008] Japanese Patent No. 7107474 Japanese Patent Application Publication No. 2021-85084

[0009] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a surface-treated steel material that can clearly and permanently express designs such as letters and designs on the surface, and a method for manufacturing the same.

[0010] In order to solve the above problems, the present invention employs the following configuration: [1] A steel material and a plating layer disposed on a surface of the steel material, wherein the plating layer has an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% to 1.0%, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, total amount ΣX of Sn, Bi, and In: 0% to 0.7%, Ca: 0% to 0.6%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%, Sr: 0% to 0.3%, Li: 0% to 0.3%. Total amount of Ca, Y, La, Ce, Sr, and Li, ΣYa: 0% or more, 0.6% or less, Cr: 0% or more, 3.0% or less, Ni: 0% or more, 1.0% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.0% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb, ΣYb: 0% or more, 3.0% or less, B: 0% or more, 0.5% or less, P: 0% or more, 0.5% or less, Total amount of B and P, ΣYc: 0% or more, 0.5% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more and 0.25% or less, V: 0% or more and 0.25% or less, Nb: 0% or more and 0.25% or less, Mn: 0% or more and 0.25% or less, Zr: 0% or more and 0.25% or less, W: 0% or more and 0.25% or less, total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, balance: 40% or more of Zn and impurities, and Zn is deposited on the surface of the plating layer. ３ (P.O. ４ ) ２ ・4H ２[2] A surface-treated steel material according to [1], wherein a zinc phosphate crystal layer containing O is laminated on the surface of the zinc phosphate crystal layer, the zinc phosphate crystal layer containing Mg at a concentration of 1.5% or more and Al at a concentration of 1.0% or more, and a first region having a C concentration of 2.5% or more is provided on a part of the surface of the zinc phosphate crystal layer. [2] A surface-treated steel material according to [1], wherein the surface of the zinc phosphate crystal layer is provided with the first region having a C concentration of 2.5% or more and a second region having a C concentration of 0.1% or less. [3] A surface-treated steel material according to [1], wherein a coating amount of the zinc phosphate crystal layer on the surface of the plating layer is 1.0 g / m ２ [4] The Munsell value N of the second region ２ [5] The surface-treated steel material according to [2], wherein the Munsell value N of the first region is 3.5 or less. １ and the Munsell value N of the second region ２ The difference between (N １ -N ２ [6] A surface-treated steel material according to [2], wherein the surface of the steel material is provided with a zinc phosphate crystal layer on its surface, and the surface of the steel material is provided with a laser irradiation step of irradiating the surface of the steel material with a laser, the steel material being provided with a plating layer on its surface, and the zinc phosphate crystal layer being provided on the plating layer, and the zinc phosphate crystal layer is provided with Zn ３ (P.O. ４ ) ２ ・4H ２1. A method for producing a surface-treated steel material, comprising: a zinc phosphate crystal layer containing 0, Mg at a concentration of 1.5% or more, and Al at a concentration of 1.0% or more; and the laser irradiation step is a step of irradiating a surface of the zinc phosphate crystal layer with a laser in the atmosphere. [7] A method for manufacturing a plated steel material, the method comprising: a film formation step of forming a zinc phosphate crystal layer on a surface of a plated steel material comprising a steel material and a plating layer disposed on a surface of the steel material; and a laser irradiation step of irradiating a part of the surface of the zinc phosphate crystal layer with a laser, wherein the average chemical composition of the plating layer is, in mass%, Al: more than 10.0% and 40.0% or less, Mg: more than 4.0% and 15.0% or less, Si: 0% or more and 1.0% or less, Sn: 0% or more and 0.7% or less, Bi: 0% or more and 0.3% or less, In: 0% or more and 0.3% or less, total amount ΣX of Sn, Bi and In: 0% or more and 0.7% or less, Ca: 0% or more and 0.6% or less, Y: 0% or more and 0.3% or less, La: 0% or more and 0.3% or less, Ce: 0% or more and 0.3% or less, Sr: 0% or more, 0.3% or less, Li: 0% or more, 0.3% or less, Total amount of Ca, Y, La, Ce, Sr, and Li ΣYa: 0% or more, 0.6% or less, Cr: 0% or more, 3.0% or less, Ni: 0% or more, 1.0% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.0% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb ΣYb: 0% or more, 3.0% or less, B: 0% or more, 0.5% or less, P: 0% or more, 0.5% or less, the total amount ΣYc of B and P: 0% or more and 0.5% or less, Ti: 0% or more and 0.25% or less, Co: 0% or more and 0.25% or less, V: 0% or more and 0.25% or less, Nb: 0% or more and 0.25% or less, Mn: 0% or more and 0.25% or less, Zr: 0% or more and 0.25% or less, W: 0% or more and 0.25% or less, the total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, the balance: 40% or more of Zn and impurities, and the film forming step comprises depositing a zinc phosphate solution of pH 5.0 or less on the surface of the plating layer to form a film of Zn. ３ (P.O. ４ )２ ・4H ２ a step of forming a zinc phosphate crystal layer containing O and also containing 1.5% or more of Mg and 1.0% or more of Al, and the laser irradiation step is a step of irradiating a surface of the zinc phosphate crystal layer with a laser in the atmosphere.

[0011] The present invention provides a surface-treated steel material and a method for manufacturing the same that can clearly and permanently express designs such as letters and designs on the surface, thereby enabling the provision of inexpensive materials with excellent aesthetic appeal and contributing to industrial development.

[0012] Fig. 1 is a cross-sectional schematic diagram showing a surface-treated steel material according to an embodiment of the present invention. Fig. 2 is an electron microscope photograph showing the surface of a zinc phosphate crystal layer before laser irradiation. Fig. 3 is an electron microscope photograph showing the surface of a zinc phosphate crystal layer after laser irradiation. Fig. 4 is a photograph showing a state in which a first region has been formed on the surface of the zinc phosphate crystal layer.

[0013] The present inventors have conducted extensive research into means for imparting anti-glare properties to hot-dip plated steel materials and for imparting designs that are excellent in clarity and permanence.

[0014] To impart a design to a specific area on a metal surface, the design may be expressed by differences in color, gloss, reflectivity, etc. Among these, designs expressed on metal surfaces by utilizing differences in color may have the greatest potential for clarity. However, the surface of metal materials is almost uniform in color tone, except for the color developed by the oxide film on titanium and stainless steel, and aluminum after anodizing. Therefore, with materials such as hot-dip galvanized steel sheets, where the metal composition is uniformly determined, it is difficult to change the metal composition locally, making it difficult to create color differences.

[0015] Designs created on metal surfaces using differences in gloss have a disadvantage in terms of durability. Because gloss tends to decrease with metal corrosion, the gloss difference may become smaller over time, making the design unclear. Furthermore, it is difficult to partially change the gloss level on hot-dip galvanized steel sheets, for which the metal composition is uniform.

[0016] Regarding reflectance, for example, by changing the surface roughness of a metal material, the reflectance can be controlled within a certain range, so that designs can be imparted by utilizing the difference in reflectance without having to partially change the metal component composition, and anti-glare properties can also be ensured. However, since the surface of a metal material generally has a metallic luster, it is not possible to change the color tone itself.

[0017] On the other hand, phosphate treatment can impart a black color to various metal surfaces by precipitating phosphate as a crystalline phase on the surface, thereby changing the color tone. In public works projects, etc., there are cases where the delivery of galvanized steel sheets with specified Munsell values ​​is required for aesthetic reasons.

[0018] The present inventors have investigated means for imparting designs to phosphate-treated zinc-based plating layers. The Munsell value N of phosphate-treated zinc-plated steel sheets is often approximately 4.0 to 5.0. One possible means for imparting designs to such zinc-plated steel sheets is to display letters or numbers by printing or engraving. However, it is difficult to maintain the permanence of printed designs, and engraving can cause scratches on the plating layer and the phosphate-treated layer, which can result in a decrease in corrosion resistance. Furthermore, the Munsell value N of the phosphate-treated layer is relatively high, at 4.0 to 5.0, which may result in insufficient anti-glare properties.

[0019] Therefore, the present inventors discovered that, in order to lower the Munsell value N of the plating layer after phosphate treatment, specifically to make the Munsell value N 3.5 or less, the zinc phosphate layer can be made to contain small amounts of Mg and Al when it is formed, thereby lowering the Munsell value N and improving the antiglare properties.

[0020] Furthermore, in order to impart a design to the surface of the zinc phosphate crystal layer, the zinc phosphate layer with a lower Munsell value N was irradiated with a laser in the atmosphere, and the color tone of the zinc phosphate layer at the laser irradiated portion was successfully changed from the color tone of the original zinc phosphate layer. This change in color tone of the zinc phosphate crystal layer is presumed to be due to the fact that when a part of the zinc phosphate layer is heated to a high temperature by laser irradiation, the zinc phosphate reacts with carbon dioxide in the atmosphere to form a carbonate compound in part, and the presence of this carbonate compound whitens part of the zinc phosphate layer.

[0021] It was also found that in the zinc phosphate layer, the corrosion rate slows in the area where a carbonate compound is formed by laser irradiation, and the durability of the laser-irradiated area is increased.

[0022] By shaping the laser irradiation area into any shape, it is now possible to make symbols, letters, numbers, patterns, etc. appear.

[0023] Hereinafter, a surface-treated steel material according to an embodiment of the present invention will be described.

[0024] The surface-treated steel material of this embodiment includes a steel material and a plating layer disposed on the surface of the steel material, and the plating layer has an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% or more and not more than 1.0%, Sn: 0% or more and not more than 0.7%, Bi: 0% or more and not more than 0.3%, In: 0% or more and not more than 0.3%, and a total amount ΣX of Sn, Bi, and In: 0% or more and not more than 0.7%. or less, Ca: 0% or more, 0.6% or less, Y: 0% or more, 0.3% or less, La: 0% or more, 0.3% or less, Ce: 0% or more, 0.3% or less, Sr: 0% or more, 0.3% or less, Li: 0% or more, 0.3% or less, total amount of Ca, Y, La, Ce, Sr and Li ΣYa: 0% or more, 0.6% or less, Cr: 0% or more, 3.0% or less, Ni: 0% or more, 1.0% or less, Mo: 0% or more, 0.25% or less, C u: 0% or more, 1.0% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, total amount of Cr, Ni, Mo, Cu, Ag, Sb and Pb ΣYb: 0% or more, 3.0% or less, B: 0% or more, 0.5% or less, P: 0% or more, 0.5% or less, total amount of B and P ΣYc: 0% or more, 0.5% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more and 0.25% or less, V: 0% or more and 0.25% or less, Nb: 0% or more and 0.25% or less, Mn: 0% or more and 0.25% or less, Zr: 0% or more and 0.25% or less, W: 0% or more and 0.25% or less, total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, balance: 40% or more of Zn and impurities, and ３ (P.O. ４ ) ２ ・4H ２The surface-treated steel material has a zinc phosphate crystal layer containing O laminated thereon, the zinc phosphate crystal layer containing Mg at a concentration of 1.5 mass% or more and Al at a concentration of 1.0 mass% or more, and a first region having a C concentration of 2.5 mass% or more provided on a part of the surface of the zinc phosphate crystal layer. Furthermore, the surface-treated steel material of this embodiment preferably has the first region having a C concentration of 2.5 mass% or more and a second region having a C concentration of 0.1 mass% or less provided on the surface of the zinc phosphate crystal layer. Furthermore, the surface-treated steel material of this embodiment has a coating weight of the zinc phosphate crystal layer on the surface of the plating layer of 1.0 g / m ２ Furthermore, the surface-treated steel material of this embodiment has a Munsell value N ２ In addition, the surface-treated steel material of this embodiment has a Munsell value N １ and the Munsell value N of the second region ２ The difference between (N １ -N ２ ) is preferably 0.5 or more.

[0025] In the following description, the "%" used to indicate the content of each element in the chemical composition means "mass %." Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit.

[0026] As shown in FIG. 1 , the surface-treated steel material 1 of this embodiment is composed of a steel material 11, a plating layer 12 disposed on the surface of the steel material 11, and a zinc phosphate crystal layer 13 laminated on the plating layer 12.

[0027] The steel material 11 is, for example, mainly a steel plate, but its size is not particularly limited. The steel material 11 may be any material that can be applied to a normal hot-dip galvanizing process. Specifically, this applies to steel plates that can be applied in processes such as continuous hot-dip galvanizing lines (CGLs) where the steel is immersed in molten metal and solidified. The size of the steel material 11 may be, for example, a plate thickness of 10 mm or less and a plate width of 2000 mm or less, but the size of the steel material 11 is not limited to this. The steel plate shape also includes checkered steel plates that have macroscopic surface irregularities previously provided.

[0028] There are no particular limitations on the material of the steel material 11. For example, the steel material 11 can be general steel, pre-plated steel thinly plated with various metals, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high alloy steels (steels containing elements that strengthen corrosion resistance, such as Ni and Cr).

[0029] Furthermore, the manufacturing process for the steel material 11 includes common processes such as pig iron and steel making processes using a blast furnace or electric furnace, hot rolling processes, pickling processes, cold rolling processes, and heat treatment processes, but the steel material of this embodiment may have undergone any of these processes, and the processing conditions for each process are not limited.

[0030] Next, the plating layer 12 will be described. The plating layer 12 according to this embodiment includes a Zn—Al—Mg alloy layer. The reason for using such a plating layer is that when the plating layer 12 is phosphate treated, a dark black zinc phosphate layer having a Munsell value of N=3.5 or less is formed.

[0031] The Zn—Al—Mg alloy layer is made of a Zn—Al—Mg alloy. The Zn—Al—Mg alloy refers to a ternary alloy whose main elements are Zn, Al, and Mg, and which is allowed to contain optional elements. The main elements refer to elements other than Fe that constitute the plating layer 12, and refer to elements that account for a total of 95% or more of the total.

[0032] The Al—Fe-based interfacial alloy layer is an interfacial alloy layer between the steel material 11 and the Zn—Al—Mg-based alloy layer, and is in contact with the surface of the steel material 11 .

[0033] That is, the plating layer 12 may have a single-layer structure of a Zn—Al—Mg alloy layer, or a laminated structure including a Zn—Al—Mg alloy layer and an Al—Fe interfacial alloy layer. In the case of a laminated structure, the Zn—Al—Mg alloy layer is preferably a layer that constitutes the surface of the plating layer 12.

[0034] The overall thickness of the plating layer 12 is affected by the plating conditions, and therefore there are no particular limitations on the upper and lower limits of the overall thickness of the plating layer 12. That is, in a typical hot-dip plating method, the overall thickness of the plating layer 12 is affected by the viscosity and specific gravity of the plating bath. It is also affected by the withdrawal speed of the steel material 11 from the plating bath and the wiping conditions. Since the maximum thickness of the plating layer 12 formed on a steel wire material or steel wire by a typical hot-dip plating method is often 100 μm or less, the plating thickness of the hot-dip plated steel material of this embodiment may be, for example, 100 μm or less.

[0035] In the Zn-Al-Mg alloy layer, a very small amount of the plating layer 12 dissolves during phosphate treatment, and the metal ions of the dissolved plating layer 12 react with phosphoric acid, so from the viewpoint of ensuring corrosion resistance, it is preferable that the plating layer 12 have a certain thickness or more. Therefore, the thickness of the plating layer 12 is preferably 5 μm or more.

[0036] Next, the average chemical composition of the plating layer 12 will be described. When the plating layer 12 has a single-layer structure of a Zn—Al—Mg alloy layer, the average chemical composition of the entire plating layer 12 is the average chemical composition of the Zn—Al—Mg alloy layer. When the plating layer 12 has a laminate structure of an Al—Fe interface alloy layer and a Zn—Al—Mg alloy layer, the average chemical composition is the combined average chemical composition of the Al—Fe interface alloy layer and the Zn—Al—Mg alloy layer. In the plating layer 12 defined in the present invention, the thickness of the Al—Fe interface alloy layer is preferably small, 10% or less of the overall thickness of the plating layer 12, and therefore the Fe concentration of the plating layer 12 is often within 5%. Therefore, the average chemical composition of the plating layer 12 can be safely considered to be roughly the composition of the Zn—Al—Mg alloy layer. Furthermore, traces of the original plating sheet are unlikely to remain as chemical components of the plating layer 12. Therefore, the average chemical composition of the plating layer 12 can be considered to be approximately equivalent to the components of the plating bath used in its production.

[0037] The chemical composition of the plating layer 12 determines the hardness of the plating layer 12. That is, the plating layer 12 produced on a normal plating production line is often completed in a short time (up to 60 seconds or less) from hot dip plating to reaching the top roll, and is ultimately phosphate treated, so there is no need to impose any particular conditions on the solidification state of these metal layers.

[0038] The average chemical composition of the plating layer 12 is, in mass%, Al: more than 10.0% and 40.0% or less, Mg: more than 4.0% and 15.0% or less, Si: 0% or more and 1.0% or less, a total amount ΣX of Sn, Bi, and In: 0.03% or more and 0.7% or less, a total amount ΣYa of Ca, Y, La, Ce, Sr, and Li: 0% or more and 0.6% or less, a total amount ΣYb of Cr, Ni, Mo, Cu, Ag, Sb, and Pb: 0% or more and 3.0% or less, a total amount ΣYc of B and P: 0% or more and 0.5% or less, a total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, and the balance including 40% or more of Zn and impurities. That is, Zn, Al, and Mg are the main elements in the plating layer 12, and the total of these elements accounts for 95% or more.

[0039] The content of each element will be explained below.

[0040] Al: More than 10.0% and 40.0% or less. Al is the main constituent element of the plating layer 12 and contributes to improving flat surface corrosion resistance and sacrificial corrosion protection. Furthermore, to reduce the Munsell value of the zinc phosphate crystal layer 13, it is necessary to dissolve a portion of the plating layer 12 during phosphate treatment to incorporate Al into the zinc phosphate crystal layer 13. If the Al concentration in the plating layer 12 is low, it may be impossible to incorporate Al into the zinc phosphate crystal layer 13. Therefore, the Al concentration is set to be more than 10.0%. The Al concentration may be set to 11.0% or more, 12.0% or more, or 15.0% or more. On the other hand, if the Al concentration is excessive, the Mg concentration and Zn concentration will be relatively reduced, resulting in deterioration of sacrificial corrosion protection. Therefore, the Al concentration is set to be 40.0% or less. The Al concentration may be set to 35.0% or less, 30.0% or less, or 25.0% or less. In particular, in order to incorporate Al and Mg into the zinc phosphate crystal layer 13, the Al concentration is preferably 15.0% or more and 35.0% or less, and more preferably 19.0% or more and 30.0% or less.

[0041] Mg: More than 4.0% and 15.0% or Less Like Zn, Mg is an element that mainly constitutes the plating layer 12. Mg contributes to improving flat surface corrosion resistance and sacrificial corrosion protection. Furthermore, to reduce the Munsell value of the zinc phosphate crystal layer 13, it is necessary to dissolve a portion of the plating layer 12 during phosphate treatment to incorporate Mg into the zinc phosphate crystal layer 13. If the Mg concentration in the plating layer 12 is low, it may be impossible to incorporate Mg into the zinc phosphate crystal layer 13. Therefore, the Mg concentration is set to more than 4.0%. The Mg concentration may be set to 4.5% or more, 5.0% or more, or 6.0% or more. On the other hand, excessive Mg concentration may deteriorate workability, particularly powdering resistance, and further deteriorate flat surface corrosion resistance. Therefore, the Mg concentration is set to 15.0% or less. The Mg concentration may also be set to 12.0% or less, 10.0% or less, or 8.0% or less. In particular, in order to include Al and Mg in the zinc phosphate crystal layer 13, the Mg concentration is preferably 5.0% or more and 8.0% or less, and more preferably 6.0% or more and 7.0% or less.

[0042] Si: 0% or more, 1.0% or less. The Si concentration may be 0%, but when Si is contained in the coating layer 12, it forms intermetallic compounds in the coating layer 12. The coating composition in this embodiment has a high melting point, and therefore, the operating temperature during hot-dip coating is approximately 500°C. At such operating temperatures, when a steel material is immersed in a coating bath, Al and Zn undergo active interdiffusion with Fe to form Fe-based intermetallic compounds, but Si suppresses this excessive reaction. Therefore, when Si is contained, if it is 0.01% or more, the Fe diffusion reaction is significantly suppressed, making it easier to control the formation of Fe-based intermetallic compounds contained in the coating layer 12. On the other hand, if the Si content is excessive, the effect saturates, so the Si content is set to 1.0% or less. The Si content is preferably 0.05% or more or 0.25% or more. Furthermore, the Si content is preferably 0.75% or less.

[0043] Element Group X Sn: 0% or more, 0.7% or less Bi: 0% or more, 0.3% or less In: 0% or more, 0.3% or less Total amount ΣX of Sn, Bi, and In: 0% or more, 0.7% or less Each element of element group X (Sn, Bi, In) can be optionally contained, and therefore the content of each is set to 0% or more. However, when each element of element group X is contained in the plating layer 12, it improves the sacrificial corrosion protection effect of the plating layer 12. Furthermore, each element of element group X has the effect of promoting the dissolution of Mg during phosphate treatment and reducing the Munsell value of the zinc phosphate crystal layer 13. Therefore, each element of element group X (Sn, Bi, In) is preferably set to 0.03% or more or 0.05% or more. On the other hand, excessive content of each element of element group X deteriorates planar corrosion resistance. Therefore, Sn is set to 0.7% or less, and Bi and In are each set to 0.3% or less. For the same reason, the total amount ΣX of these elements is set to 0% or more and 0.7% or less, and preferably 0.003% or more.

[0044] Note that optional added elements other than element X may form intermetallic compounds that are more noble than Zn in the plating layer 12, and therefore are not involved in the growth of zinc phosphate crystals.

[0045] Element Group Ya Ca: 0% or more, 0.6% or less Y: 0% or more, 0.3% or less La: 0% or more, 0.3% or less Ce: 0% or more, 0.3% or less Sr: 0% or more, 0.3% or less Li: 0% or more, 0.3% or less Total amount ΣYa of Ca, Y, La, Ce, Sr, and Li: 0% or more, 0.6% or less Each element in the element group Ya is an optional element, and its content may be 0% or less. Ca, one of the elements in the element group Ya, is an element that can adjust the optimal amount of Mg elution to impart planar corrosion resistance. When Ca is contained, it may be 0.01% or more or 0.02% or more. On the other hand, excessive Ca concentration deteriorates planar corrosion resistance. Furthermore, various floating dross is formed in the coating bath, increasing coating defects and significantly deteriorating the appearance of the coating layer 12. Therefore, the Ca concentration is set to 0.6% or less. The Ca concentration may be 0.5% or less or 0.3% or less.

[0046] The elements of the element group Ya other than Ca (Y, La, Ce, Sr, and Li) can be added as a substitute for Ca because they have effects similar to those of Ca. When these elements are added, they may each be 0.01% or more or 0.02% or more. Furthermore, the content of each of these elements Y, La, Ce, Sr, and Li is 0.3% or less. If the content of each element exceeds 0.3%, the plane corrosion resistance decreases. Preferably, it is 0.2% or less or 0.1% or less.

[0047] The total amount ΣYa of the element group Ya is set to the range of 0 to 0.6% in order to improve the plane corrosion resistance.

[0048] Element group Yb Cr: 0% or more, 3.0% or less Ni: 0% or more, 1.0% or less Mo: 0% or more, 0.25% or less Cu: 0% or more, 1.0% or less Ag: 0% or more, 0.25% or less Sb: 0% or more, 0.25% or less Pb: 0% or more, 0.25% or less Total amount ΣYb of Cr, Ni, Mo, Cu, Ag, Sb, and Pb: 0% or more, 3.0% or less Each element of the element group Yb (Cr, Ni, Mo, Cu, Ag, Sb, and Pb) is an optional added element, so their respective contents may be 0%. On the other hand, each element of the element group Yb has properties similar to Zn and can be contained in a relatively large amount. When these elements are contained within the above concentration ranges, corrosion resistance is improved. Therefore, when these elements are contained, the content may be 0.01% or more, or 0.02% or more. On the other hand, if the concentration of each element in the element group Yb is excessive, the effect saturates. Therefore, the content of each element in the element group Yb is set to 3.0% or less for Cr, 1.0% or less for Ni and Cu, and 0.25% or less for Mo, Ag, Sb, and Pb.

[0049] The total amount ΣYb of the element group Yb is set to the range of 0 to 3.0% in order to improve the sacrificial corrosion resistance.

[0050] Element group Yc B: 0% or more, 0.5% or less P: 0% or more, 0.5% or less Total amount of B and P ΣYc: 0% or more, 0.5% or less Since each element (B, P) of the element group Yc is an optional added element, the content of each may be 0%. On the other hand, each element of the element group Yc contributes to improving the corrosion resistance of the flat portion. Therefore, the concentration of each element of the element group Yc may be 0.01% or more or 0.02% or more. On the other hand, if the concentration of each element of the element group Yc is excessive, the effect will saturate. Therefore, the concentration of each element of the element group Yc is set to 0.5% or less. The concentration of each element of the element group Yc may be 0.4% or less or 0.3% or less.

[0051] The total amount ΣYc of the element group Yc is set to the range of 0 to 0.5% in order to improve the corrosion resistance of the flat surface portion.

[0052] Element Group Z Ti: 0% or more, 0.25% or less Co: 0% or more, 0.25% or less V: 0% or more, 0.25% or less Nb: 0% or more, 0.25% or less Mn: 0% or more, 0.25% or less Zr: 0% or more, 0.25% or less W: 0% or more, 0.25% or less Total amount ΣZ of Ti, Co, V, Nb, Mn, Zr, and W: 0% or more, 0.25% or less Each element of element group Z (Ti, Co, V, Nb, Mn, Zr, and W) is an optional element, so their respective contents may be 0% or less. On the other hand, each element of element group Z contributes to improving flat corrosion resistance. Therefore, the concentration of each element of element group Z may be 0.01% or more or 0.02% or more. On the other hand, if the concentration of each element of element group Z is excessive, the effect saturates. Therefore, the concentration of each element in element group Z is set to 0.25% or less. The concentration of each element in element group Z may also be set to 0.20% or less, or 0.10% or less, respectively.

[0053] The total amount ΣZ of the element group Z is set to the range of 0 to 0.25% in order to improve the corrosion resistance of the flat surface portion.

[0054] Fe: 0% or more, 5.0% or less The Fe concentration may be 0%. However, because the plating layer 12 of the surface-treated steel material of this embodiment is produced by a hot-dip galvanizing method, Fe may diffuse from the steel material to the plating layer 12 during production. Therefore, the plating layer 12 may contain 0.01% or more Fe. The Fe concentration may be, for example, 0.05% or more, 0.1% or more, 0.5% or more, or 1.0% or more. On the other hand, it has been confirmed that an Fe concentration of 5.0% or less does not adversely affect the performance of the plating layer 12. The Fe concentration may be, for example, 2.0% or less.

[0055] Balance: Zn and impurities The balance preferably contains Zn. In the plating layer 12 according to this embodiment, Zn is the element contained in the largest amount. Zn is an element that provides flat surface corrosion resistance and sacrificial corrosion protection to the plating layer 12, so the Zn concentration needs to be 40% or more.

[0056] Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally included. For example, trace amounts of components other than Fe may be mixed into the plating layer 12 as impurities due to mutual atomic diffusion between the steel material (base steel) and the plating bath. Furthermore, since metals with 3N purity are typically used to manufacture plating alloys, the total concentration of impurities may be approximately 0.03% or less.

[0057] To identify the average chemical composition of the plating layer 12, the plating layer 12 is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) (for example, an acid solution prepared by adding 0.01% propargyl alcohol to a 5% aqueous hydrochloric acid solution). The chemical composition can then be determined by measuring the resulting acid solution using ICP atomic emission spectroscopy or ICP-MS. There are no particular restrictions on the type of acid, as long as it can dissolve the plating layer 12. Before stripping and dissolving the plating layer 12, the surface-treated steel material 1 is immersed in a 20% aqueous solution of chromium (VI) oxide to remove the zinc phosphate crystal layer 13.

[0058] Next, the zinc phosphate crystal layer 13 formed on the surface of the plating layer 12 will be described. The zinc phosphate crystal layer 13 is formed by phosphate treatment of the plating layer 12. By performing phosphate treatment on the plating layer 12 containing 40 mass % or more of Zn using a treatment solution containing zinc phosphate, crystalline zinc phosphate tetrahydrate called hopite (Zn ３ (P.O. ４ ) ２ ・4H ２ O) is formed. ３ (P.O. ４ ) ２ ・4H ２ The O content is 95% by mass or more, preferably 98% by mass or more.

[0059] The zinc phosphate crystal layer 13 also contains Mg at a concentration of 1.5 mass % or more and Al at a concentration of 1.0 mass % or more. The Mg and Al contained in the zinc phosphate crystal layer 13 originate from the plating layer 12. That is, during the phosphate treatment, the pH of the phosphate treatment solution is adjusted to slightly dissolve the surface of the plating layer 12, promoting the elution of Al and Mg, and the eluted Al ions and Mg ions are captured in the zinc phosphate crystal layer 13.

[0060] By containing Mg at a concentration of 1.5% by mass or more and Al at a concentration of 1.0% by mass or more in the zinc phosphate crystal layer 13, the zinc phosphate crystal layer 13 appears black, thereby reducing the intensity of reflected light and improving anti-glare properties. Specifically, the Munsell value N of the zinc phosphate crystal layer 13 becomes 3.5 or less. Furthermore, the color tone difference with the laser-irradiated area increases, making the design clearer. When the zinc phosphate crystal layer 13 does not contain Mg and Al, the Munsell value N is approximately 4.0. However, when the zinc phosphate crystal layer 13 contains Mg and Al, the Munsell value N becomes 3.5 or less, and the zinc phosphate crystal layer 13 becomes increasingly black. When the Mg concentration in the zinc phosphate crystal layer 13 is less than 1.5% by mass or the Al concentration is less than 1.0% by mass, the Munsell value of the zinc phosphate crystal layer 13 cannot be sufficiently reduced. The reason why the Munsell value decreases when a small amount of Mg and Al is contained in the zinc phosphate crystal layer 13 is unknown, but it is presumed that this is due to a change in the crystal structure of the zinc phosphate crystals or the formation of an oxygen-deficient oxide film on the surface of the plating layer 12.

[0061] The amount of zinc phosphate crystal layer 13 deposited on the surface of the plating layer 12 is 1.0 g / m ２ It is preferable that the content is 1.5 g / m or more, and more preferably 1.5 g / m ２ The coating weight of the zinc phosphate crystal layer 13 is preferably 1.0 g / m or more. ２ If the amount is 10.0 g / m or more, sufficient antiglare properties can be ensured. ２ The following is good:

[0062] The Mg concentration and Al concentration in the zinc phosphate crystal layer 13 are measured as follows. A scanning electron microscope equipped with an energy dispersive elemental analyzer is used as the measuring device. The surface of the zinc phosphate crystal layer 13 is observed with the scanning electron microscope. The conditions for the scanning electron microscope are an electron gun acceleration voltage of 15 kV, an observation magnification of 1000 to 3000 times, and an observation region of 40 × 30 μm. Ten observation regions are arbitrarily selected. Quantitative elemental analysis is performed on each observation region with the energy dispersive elemental analyzer. The deposition weight of the zinc phosphate crystal layer 13 is 1.0 g / m ２ It has been confirmed that if the deposition amount is equal to or greater than this, characteristic X-rays from the underlying plating layer 12 will not be detected when the acceleration voltage of the electron gun is set to 15 kV. The elements targeted for quantitative analysis are C, O, Mg, Al, Si, P, Mn, Ni, and Zn. When the total amount of the target elements is taken as 100 mass%, the Mg content (mass%) and Al content (mass%) are determined for each observation region, and the average values ​​are taken as the Mg concentration and Al concentration in the zinc phosphate crystal layer 13.

[0063] In addition, the zinc phosphate crystal layer 13 contains zinc phosphate tetrahydrate (Zn ３ (P.O. ４ ) ２ ・4H ２ Whether or not ZnO is contained is confirmed by X-ray diffraction measurement. X-ray diffraction measurement is performed over a range of 0 to 180 degrees using a Cu X-ray tube, an X-ray output of 40 kV, 100 mA, and a scan speed of 5 degrees / min, to obtain the X-ray diffraction results. ３ (P.O. ４ ) ２ ・4H ２ The presence of O diffraction peaks is confirmed.

[0064] The amount of zinc phosphate crystal layer 13 attached can be measured by immersing the surface-treated steel material in a 20% aqueous solution of chromium (VI) oxide at room temperature (e.g., 25°C) to dissolve the zinc phosphate crystal layer 13. The amount of attachment can then be measured from the change in weight before and after immersion in the 20% aqueous solution of chromium (VI) oxide.

[0065] Next, the first and second regions formed on the surface of the zinc phosphate crystal layer 13 will be described. In the surface-treated steel material of this embodiment, a first region having a C (carbon) concentration of 2.5 mass % or more is provided on a portion of the surface of the zinc phosphate crystal layer 13. Furthermore, a second region having a C concentration of 0.1 mass % or less is provided on the surface of the zinc phosphate crystal layer 13. The first region is a region on the surface of the zinc phosphate crystal layer 13 that is irradiated with laser light, and the second region is a region that is not irradiated with laser light. Compared to the second region, which has a relatively black appearance, the first region has a white appearance, so the shape of the first region can be visually recognized when the surface of the zinc phosphate layer is visually inspected.

[0066] Furthermore, the region to be irradiated with the laser light can be formed into any pattern by adjusting the laser scanning conditions, and specifically, the first region can be formed into a pattern such as letters, numbers, figures, or patterns. Therefore, by providing the first region on the surface of the zinc phosphate crystal layer 13, it becomes possible to create a design consisting of patterns such as letters, numbers, figures, or patterns. Note that visual inspection includes not only observation with the naked eye, but also visual inspection of a magnified image using a magnifying glass or microscope.

[0067] The reason why the carbon concentration of the first region is 2.5 mass % or more will be explained below. The zinc phosphate crystal layer 13 before laser irradiation has a Munsell value N of 3.5 or less. When a laser beam is irradiated onto the zinc phosphate crystal layer 13 having such a relatively low Munsell value N, the amount of heat absorbed increases, resulting in a partial temperature rise in the laser irradiated area. The laser beam is CO ２ Examples include laser light for metal processing, such as a laser or a YAG laser.

[0068] When the zinc phosphate crystal layer 13 is irradiated with laser light, the heat input by the laser light causes the hopite (zinc phosphate tetrahydrate (Zn ３ (P.O. ４ ) ２ ・4H ２O)) and the crystals are dehydrated to form amorphous structures, forming new discolored areas. Furthermore, when irradiated with laser light, zinc phosphate reacts with atmospheric CO ２ The zinc phosphate crystal layer 13 reacts with the metal oxide to generate carbonates (carbonate compounds) of Mg or Zn. As a result, the C content of the zinc phosphate crystal layer 13, which was 0.1% or less before the laser light irradiation, increases to 2.5% by mass or more after the laser light irradiation. In particular, the increased C content causes the laser-irradiated area to assume a white color, and the Munsell value N increases. The formed carbonates (carbonate compounds) also have the effect of suppressing the progression of corrosion, thereby suppressing the deterioration of the first region over time.

[0069] Fig. 2 is an SEM photograph of the zinc phosphate crystal layer 13 before laser light irradiation, and Fig. 3 is an SEM photograph of the zinc phosphate crystal layer 13 after laser light irradiation. Black spot-like holes formed by laser irradiation can be observed in Fig. 3. It is presumed that the black spot-like holes were formed by evaporation of the water of crystallization of the hopite due to the heat input from the laser light.

[0070] 4 shows an example of the first region in which the characters "22 / 07" are displayed. In FIG. 4, reference numeral 21 denotes the second region, and reference numeral 22 denotes the first region.

[0071] The effects of increasing the carbon concentration in the first region, whitening due to an increase in the Munsell value, and decreasing the corrosion rate increase with an increase in the number of times the first region is irradiated with laser light. In particular, the carbon concentration of the zinc phosphate layer before laser light irradiation is 0.1% by mass or less, a concentration equivalent to an impurity, whereas the carbon concentration in the first region irradiated with laser light increases to 2.5% by mass or more, with the carbon concentration increasing with each irradiation. If the carbon concentration is less than 2.5% by mass, the Munsell value N does not increase sufficiently compared to the second region, whitening of the first region does not progress, and the difference in appearance from the second region is not clearly apparent, making it difficult to visually distinguish the first region. The C concentration in the first region is more preferably 3.0% by mass or more, and even more preferably 3.5% by mass or more. The upper limit of the carbon concentration does not need to be particularly limited, but since repeated laser light irradiation does not exceed 5.0% by mass, the upper limit may be set to 5.0% by mass or less. The carbon concentration is correlated with the Mg concentration in the zinc phosphate crystal layer 13, and the increase in carbon concentration may be influenced by the formation behavior of Mg carbonate.

[0072] The carbon concentrations in the first and second regions are measured in the same manner as the Al and Mg concentrations in the zinc phosphate crystal layer 13. Specifically, the surfaces of the first and second regions of the zinc phosphate crystal layer 13 are observed using a scanning electron microscope. The scanning electron microscope conditions are an electron gun acceleration voltage of 15 kV, an observation magnification of 1000 to 3000 times, and an observation region of 40 × 30 μm. Ten observation regions are arbitrarily selected. In each observation region, five measurement locations are arbitrarily selected for the first and second regions, and quantitative elemental analysis is performed at the selected locations using an energy dispersive elemental analyzer. The elements targeted for quantitative analysis are C, O, Mg, Al, Si, P, Mn, Ni, and Zn. The carbon content (mass%) is calculated for each measurement location, assuming the total amount of the target elements to be 100 mass%, and the average value is used as the carbon content in the first and second regions.

[0073] Munsell value N of the first region １ is the Munsell value N of the second region ２It is preferable that the Munsell value N of the first region is 0.5 or more larger than that of the first region. １ and the Munsell value N of the second region ２ The difference between (N １ -N ２ The Munsell value N of the second region is preferably 0.5 or more. ２ is preferably 3.5 or less. １ -N ２ When the Munsell value N of the second region is 0.5 or more, the appearance of the first region and the appearance of the second region become different, and the shape of the first region can be visually confirmed. ２ However, when the value is 3.5 or less, the brightness of the appearance of the zinc phosphate crystal layer 13 decreases and the layer 13 becomes blacker, making it easier to identify the first region.

[0074] The Munsell value is determined by determining the degree of blackness of the first and second regions using a spectrophotometer or a color difference meter. As an example, a spectrophotometer (CM-26dG manufactured by Konica Minolta) is used to measure the Munsell value N under geometric condition c in accordance with JIS Z 8722:2009. Here, N means achromatic color.

[0075] The first regions are preferably arranged to have a predetermined shape when the zinc phosphate crystal layer 13 is viewed in plan. Specifically, the first regions are preferably arranged to have a shape consisting of one or more of a straight line, a curved line, a dot, a figure, a number, a symbol, a pattern, or a letter. For example, the surface of the zinc phosphate crystal layer 13 may be formed with a character string, a number string, a symbol, a mark, a diagram, a design, or a combination thereof, consisting of the first regions. The shape of the first regions is intentionally or artificially formed by a manufacturing method described below, and is not naturally formed.

[0076] The second region may be a region other than the first region. The second region may have a shape that borders the boundary with the first region. The second region may occupy most of the surface of the zinc phosphate crystal layer 13, or the first region may be disposed within the second region.

[0077] The boundary between the first and second regions can be seen with the naked eye. It may also be seen from a magnified image using an optical microscope or a magnifying glass. That is, the first region should be formed to a size that allows the presence of the first region to be discerned with the naked eye, under a magnifying glass, or under a microscope. For example, the first region may be distinguishable in a field of view with a magnification of 50 times or less. In a field of view of 50 times or less, the first region and the second region can be distinguished by their difference in appearance. The first region and the second region can be distinguished preferably at a magnification of 20 times or less, more preferably at a magnification of 10 times or less, and even more preferably at a magnification of 5 times or less.

[0078] Next, a manufacturing method of the surface-treated steel material of this embodiment will be described. The manufacturing method of the surface-treated steel material of this embodiment includes a laser irradiation step of irradiating a laser beam in the atmosphere onto the surface of a material to be treated, the surface of which is provided with a zinc phosphate crystal layer 13. The material to be treated, which is the target of laser light irradiation, includes a steel material, a plating layer 12 provided on the surface of the steel material, and the zinc phosphate crystal layer 13 provided on the surface of the plating layer 12. The zinc phosphate crystal layer 13 is composed of Zn ３ (P.O. ４ ) ２ ・4H ２ It contains O, as well as Mg at a concentration of 1.5 mass % or more and Al at a concentration of 1.0 mass % or more.

[0079] First, a method for manufacturing the treated material will be described. The treated material is manufactured by manufacturing a plated steel material comprising a steel material and a plating layer 12 disposed on the surface of the steel material, and then forming a zinc phosphate crystal layer 13 on the surface of the plating layer 12 of the plated steel material.

[0080] The plated steel material is preferably produced by a continuous hot-dip galvanizing method, although it may also be produced by a batch-type hot-dip galvanizing method if necessary due to size restrictions of the steel material.

[0081] Specifically, the steel material is annealed in a reducing atmosphere, and the temperature of the annealed steel material is adjusted to about (the plating bath temperature ±30)°C, and then the steel material is immersed in a hot-dip plating bath and pulled out of the hot-dip plating bath, thereby forming a plating layer 12 on the surface of the steel material. For example, the reducing atmosphere is a nitrogen atmosphere containing 5% by volume of hydrogen, and the steel material is heated and held at a temperature of around 800°C for about 1 minute to sufficiently reduce the surface of the steel material. When the steel material is immersed in the plating bath, N ２ Gas cooling is used to prevent fluctuations in the plating bath temperature during the manufacturing process.

[0082] Next, the steel material with a sufficiently reduced surface is immersed in a reduced state in a coating bath. The chemical composition of the coating bath may be adjusted appropriately so as to obtain the chemical composition of the coating layer 12 described above. The temperature of the coating bath is also not particularly limited, and any temperature at which hot-dip coating can be performed may be selected appropriately. For example, the coating bath temperature may be set to a value approximately 20°C or more higher than the melting point of the coating bath. The immersion time of the steel material in the coating bath may be, for example, in the range of 1 to 5 seconds.

[0083] After immersion in the coating bath, the thickness of the coating layer 12 is adjusted by wiping immediately. After wiping is completed, the coating layer 12 is cooled. There are no particular restrictions on the cooling conditions. In this manner, a coated steel material is produced. The produced coated steel sheet is preferably skin-pass rolled to achieve a steel sheet thickness reduction of 1% or less so that the surface roughness of the coated steel sheet falls within the range of Ra 0.8 to 1.5 μm. If the surface roughness of the coated steel sheet is within the range of Ra 0.8 to 1.5 μm, the load on the roll during temper rolling (zinc wrapping) and press formability are not impaired, and the formation of carbonate crystals by laser irradiation is promoted. Note that Ra refers to the arithmetic mean roughness, and was measured in accordance with JIS B 0601:2013.

[0084] Next, the plated steel is subjected to a phosphate treatment as a film formation process. In the phosphate treatment, the surface of the plating layer 12 is degreased and then rinsed with water. Next, if necessary, the surface of the plating layer 12 is subjected to a surface conditioning treatment. Next, the plated steel is immersed in a phosphate treatment solution, or the phosphate treatment solution is applied or sprayed onto the surface of the plating layer 12, thereby adhering the phosphate treatment solution to the surface of the plating layer 12. Thereafter, the phosphate treatment solution is removed from the surface of the plating layer 12 by rinsing with water or the like.

[0085] The specific procedure for the degreasing treatment is not particularly limited. For example, a degreasing bath prepared by adding an alkaline degreasing agent (trade name: Fine Cleaner (FD-E6408)) manufactured by Nihon Parkerizing Co., Ltd. to water is used, the temperature of the degreasing bath is adjusted to a range of 55 to 65°C, and the plated steel material is immersed in the degreasing bath for about 5 to 15 minutes.

[0086] The water rinse after the degreasing treatment may be carried out by immersing the plated steel material in a water bath filled with water, or by spraying water onto the plated steel material.

[0087] After rinsing with water, a surface conditioning treatment may be performed to increase the surface reactivity of the plating layer 12. The surface conditioning treatment is performed by immersing the plated steel material in a conditioning bath containing a surface conditioner immediately before treatment with a phosphate treatment solution, or by applying or spraying the conditioning bath onto the plating layer 12. As the surface conditioner, for example, a surface treatment agent (product name: Preparen X) manufactured by Nihon Parkerizing Co., Ltd. can be used. The temperature of the conditioning bath is set to room temperature (e.g., 10°C) to 40°C, and the immersion time, if any, is set to about 30 to 60 seconds.

[0088] The phosphate treatment is performed by immersing the plated steel in a bath of the phosphate treatment solution, or by applying or spraying the phosphate treatment solution onto the plating layer 12. The phosphate treatment solution is an aqueous solution containing zinc phosphate (zinc phosphate solution) adjusted to a pH of 5.0 or less. The pH of the phosphate treatment solution is preferably 3.0 to 4.0. A low pH increases the time required for zinc phosphate treatment, so a pH of 3.0 or higher is preferable. Making the phosphate treatment solution acidic promotes dissolution of the plating layer 12 and promotes the elution of Al and Mg from the plating layer 12. The phosphate treatment solution may contain other additives as long as they do not inhibit the phosphate treatment. Examples of phosphate treatment solutions that can be used include the phosphate treatment solution manufactured by Nippon Parkerizing Co., Ltd. (product name: Palbond (PB-SX35)). The temperature of the phosphate treatment solution is set to 33 to 37°C, and the immersion time is set to about 1.5 to 2.0 minutes.

[0089] After the phosphate treatment, the material is washed with warm water at 70°C or higher and then dried, thereby obtaining a treated material having a zinc phosphate crystal layer 13 containing Mg at a concentration of 1.5% by mass or higher and Al at a concentration of 1.0% by mass or higher.

[0090] Next, a laser irradiation process is performed on the material to be treated. In the laser irradiation process, a portion of the surface of the zinc phosphate crystal layer 13 of the material to be treated is irradiated with a laser in the atmosphere, thereby increasing the carbon concentration at the irradiated portion to 2.5% or more. By irradiating a specific portion of the zinc phosphate crystal layer 13 with a laser beam while converging it, a high-temperature portion is generated locally at the focus of the laser beam. As a result, Mg or Zn contained in the zinc phosphate reacts with carbon dioxide in the atmosphere to form a carbonate of Mg or Zn, thereby increasing the carbon concentration to 2.5% or more. In this way, a first region is formed. The portion irradiated with the laser beam may be controlled so as to obtain a first region of the desired shape.

[0091] The laser irradiation conditions are not particularly limited as long as the carbon concentration in the first region is 2.5% or more. ２The irradiation conditions vary depending on the type of laser, but are preferably an output of 0.3 to 20 W, a laser beam spot diameter of 5 to 300 μm, preferably 5 to 10 μm, and an output per unit area at the irradiated site of 2500 W / μm. ２ Less than 2500W / μm ２ If the laser beam scanning speed exceeds this value, the zinc phosphate layer may be lost. The laser beam scanning speed is 1 to 1000 mm / sec. When irradiating adjacent locations with laser beam multiple times, the irradiation interval is 100 μm or less on the surface of the zinc phosphate crystal layer 13. The number of repeated irradiations is not particularly limited, but may be, for example, 1 to 30 times. The atmosphere during laser irradiation is preferably air. Air contains a trace amount of carbon dioxide, and by irradiating the laser in the presence of carbon dioxide, carbonates of Mg or Zn are formed. If the output power of the laser beam per unit area is too high or the scanning speed of the laser beam is too slow, the zinc phosphate crystal layer 13 will be dissolved, so it is desirable to irradiate the laser beam under conditions that do not melt the zinc phosphate crystal layer 13.

[0092] In this embodiment, the surface of the plating layer 12 is phosphate-treated using a phosphate treatment solution adjusted to a pH of 5.0 or less, whereby a portion of the plating layer 12 dissolves in the phosphate treatment solution containing phosphoric acid, and the dissolved constituent elements of the plating layer 12 undergo a chemical reaction with the phosphoric acid, resulting in the precipitation of phosphate (zinc phosphate) on the plating layer 12. It is presumed that the Al and Mg constituent elements of the plating layer 12 are incorporated into the zinc phosphate during this process. The zinc phosphate crystal layer 13 containing Al and Mg exhibits an appearance close to black and has a Munsell value N of 3.5 or less.

[0093] Furthermore, by irradiating the surface of the zinc phosphate crystal layer 13 with a laser, carbonate is formed in the irradiated area, resulting in the formation of a first region having a higher Munsell value N than the surrounding area. In this manner, the surface-treated steel material of this embodiment is manufactured.

[0094] Furthermore, one or more organic resin coating layers may be formed on the zinc phosphate crystal layer 13. The organic resin is not limited to a specific type, and examples thereof include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified versions of these resins. Here, the modified version refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group in its structure that can react with the functional group.

[0095] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-rust pigment. Water-based organic resins obtained by dissolving or dispersing them in water may also be used.

[0096] Examples of the present invention will be described below. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0097] The following plated steel sheets were prepared as plated steel materials to which zinc phosphate treatment was applied. For the plated steel sheets, alloys were prepared by mixing predetermined amounts of pure metals and the like to have the chemical compositions shown in Tables 2A, 2B, 3, and 4 using a hot-dip galvanizing simulator manufactured by Rhesca Co., Ltd., and the alloys were melted and hot-dip plated.

[0098] The base sheet for plating was 200 × 100 × 1.2 mm (cold-rolled steel sheet SPCC JIS G3141). A hot-rolled checkered steel sheet was used for some of the substrates for plating.

[0099] Before plating, ２ -H ２ (N ２ : 95% by volume, H ２The steel sheet surface was kept in a 5% by volume atmosphere at 800°C for 1 minute (dew point -40°C) to be fully reduced, and then immersed in a plating bath at a bath temperature of +30°C for 3 seconds and pulled out. ２ Gas wiping was applied to the plated material to a thickness of 25 μm. Immediately after wiping, the plated material was cooled to room temperature at an average cooling rate of 10° C. / sec.

[0100] The produced plated steel sheets were skin-pass rolled at a steel sheet thickness reduction rate of 1% or less so that the surface roughness of the plated steel sheets would fall within the range of Ra 0.8 to 1.5 μm. The arithmetic mean roughness Ra of the plated steel sheets after skin-pass rolling was measured in accordance with JIS B 0601:2013. The obtained results are shown in Table 1.

[0101] Next, a phosphate treatment was carried out. First, the surface of the plating layer was degreased. For the degreasing treatment, a degreasing bath containing an alkaline degreaser (product name: Fine Cleaner (FD-E6408)) manufactured by Nihon Parkerizing Co., Ltd. added to water was used, and the temperature of the degreasing bath was set to a range of 55 to 65°C, and the plated steel sheet was immersed in the degreasing bath for approximately 5 to 15 minutes.

[0102] Next, as a water rinse after the degreasing treatment, the plated steel sheet was immersed in a water bath filled with water to perform water rinse.

[0103] After rinsing with water, the surface of the plating layer was subjected to a surface conditioning treatment. The surface conditioning treatment was performed by immersing the plated steel sheet in an adjusting bath containing a surface conditioner. The surface conditioner used was a surface treatment agent (product name: Preparen X) manufactured by Nihon Parkerizing Co., Ltd. The temperature of the adjusting bath was set to room temperature (e.g., 10°C) to 40°C, and the immersion time was set to 30 to 60 seconds.

[0104] Next, the plated steel material was immersed in a bath of phosphate treatment solution to form a zinc phosphate crystal layer. The phosphate treatment solution used was a phosphate treatment solution (product name: Palbond (PB-SX35)) manufactured by Nihon Parkerizing Co., Ltd., and the pH of the phosphate treatment solution was adjusted to a range of 3.0 to 4.0. The temperature of the phosphate treatment solution was 33 to 37°C, and the immersion time was 1.5 to 2.0 minutes.

[0105] After the phosphate treatment, the material was washed with warm water at the temperature conditions shown in Table 1 and then dried with warm air at 100°C using a hot air blower. In this way, the treated material was produced. In Comparative Example 38, the material was washed at 20°C (less than 70°C).

[0106] Next, a laser irradiation step was performed in the atmosphere to form a first region. The shape of the first region was a rectangle of 35 mm length x 35 mm width. The laser irradiation conditions were CO ２ A laser was used, with an output of 10 W, a spot diameter of 5 μm, and an output per unit area at the irradiated site of 2500 W / μm ２ The scanning speed was set to 1 mm / sec. The laser irradiation path was a single linear path along the vertical direction of the first region, and multiple such linear paths were formed so as to be aligned in parallel in the horizontal direction. The horizontal irradiation interval was set to 20 μm. The number of reciprocating laser irradiations per linear path was set to 25. In this manner, surface-treated steel materials Nos. 1 to 38 were manufactured.

[0107] The average chemical compositions of the plating layers were as shown in Tables 2A to 4. Among the manufacturing conditions, the pH of the phosphate treatment solution was as shown in Table 5. In addition, the Munsell values ​​N of the first and second regions of the zinc phosphate crystal layer were measured, and the results are shown in Table 35. The measured Munsell value differences of the surface-treated steel materials after manufacturing are shown in Table 6.

[0108] To identify the average chemical composition of the plating layer, the surface-treated steel material was immersed in a 20% aqueous solution of chromium (VI) oxide at room temperature (for example, 25°C) to dissolve the zinc phosphate crystal layer, and then the plating layer was stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) (an acid solution prepared by adding 0.01% propargyl alcohol to a 5% aqueous hydrochloric acid solution), to obtain an acid solution, and the chemical composition was determined by measuring the obtained acid solution using ICP atomic emission spectroscopy and ICP-MS.

[0109] The Mg concentration and Al concentration in the zinc phosphate crystal layer were measured as follows. A scanning electron microscope equipped with an energy dispersive elemental analyzer was used as the measurement device. The surface of the zinc phosphate crystal layer was observed using the scanning electron microscope. The conditions for the scanning electron microscope were an electron gun acceleration voltage of 15 kV, an observation magnification of 1000 to 3000 times, and an observation area of ​​40 × 30 μm. Ten observation areas were arbitrarily selected. Quantitative elemental analysis was performed on each observation area using the energy dispersive elemental analyzer. The elements targeted for quantitative analysis were C, O, Mg, Al, Si, P, Mn, Ni, and Zn. The Mg content (mass%) and Al content (mass%) were determined for each observation area, assuming the total amount of the target elements to be 100 mass%, and the average values ​​were used as the Mg concentration and Al concentration in the zinc phosphate crystal layer.

[0110] The carbon concentrations of the first and second regions were measured in the same manner as described above. Five measurement points were selected from the ten observation regions for each of the first and second regions, and quantitative analysis of elements was performed at the selected points using an energy dispersive elemental analyzer to determine the average carbon concentration.

[0111] In addition, zinc phosphate tetrahydrate (Zn ３ (P.O. ４ ) ２ ・4H ２ Whether or not ZnO is contained was confirmed by X-ray diffraction measurement. X-ray diffraction measurement was performed over a range of 0 to 180 degrees using a Cu X-ray tube, an X-ray output of 40 kV, 100 mA, and a scan speed of 5 degrees / min, to obtain the X-ray diffraction results. ３ (P.O. ４ ) ２ ・4H ２ The presence of O diffraction peaks was confirmed.

[0112] The amount of zinc phosphate crystal layer deposited was measured by immersing the surface-treated steel material in a 20% aqueous solution of chromium (VI) oxide at 25° C. to dissolve the zinc phosphate crystal layer. The amount of deposition was then determined from the change in weight before and after immersion in the 20% aqueous solution of chromium (VI) oxide.

[0113] To evaluate the permanence of the design imparted to the plating layer, a corrosion test was conducted and visual inspection was conducted to determine whether the design was recognizable after corrosion. The cyclic corrosion test (CCT) was used as a test that provides a good correlation with the exposure environment in Japan. Unlike the salt spray test (SST), which is a type of accelerated corrosion test, this test involves repeated salt spray, drying, and wetting processes, which is closer to the corrosion conditions in an atmospheric environment and a certain degree of correlation has been observed. Specifically, the JASO cycle (M609-91) was used, with the 30th cycle corresponding to 10 years in a general corrosive environment in Japan, and the degree of design recognition before and after the CCT was evaluated.

[0114] More specifically, the surface-treated steel material after the design was applied was cut into a size of 100 mm x 50 mm to prepare a test piece, and the cut end surface was coated with an epoxy-based resin paint to create an evaluation surface of 70 mm x 40 mm in size in the center of the steel plate.

[0115] A rectangular first region measuring 35 mm x 35 mm was placed in the center of the evaluation surface. Outside the first region was a second region.

[0116] A total of 10 test pieces were prepared and subjected to a corrosion test of 30 cycles of CCT (JASO cycle).

[0117] After the test, the Munsell values ​​of the first and second regions of each test piece were measured, the average value of the 10 test pieces was calculated, and the difference in the Munsell values ​​(average values) was calculated. The evaluation criteria were as follows, with "S", "AA", "A", and "B" being considered pass and "C" being fail. The Munsell values ​​after the test and the following evaluations are shown in Table 6 as durability evaluations.

[0118] S: The difference in Munsell values ​​is 2.0 or more. AA: The difference in Munsell values ​​is 1.5 or more and less than 2.0. A: The difference in Munsell values ​​is 1.0 or more and less than 1.5. B: The difference in Munsell values ​​is 0.5 or more and less than 1.0. C: The difference in Munsell values ​​is less than 0.5.

[0119] The Munsell value N was measured using a spectrophotometer (CM-26dG manufactured by Konica Minolta) in accordance with JIS Z 8722:2009 under geometrical condition c, where N means achromatic color.

[0120] As shown in Tables 2A to 5, Nos. 9, 11 to 33 satisfied the ranges of the present invention for the average chemical composition of the plating layer, the Al concentration and Mg concentration of the zinc phosphate crystal layer, and the carbon concentration of the first region. This resulted in excellent durability of the design. In addition, the Munsell value N ２ In addition, the zinc phosphate crystal layer contained zinc phosphate tetrahydrate (Zn ３ (P.O. ４ ) ２ ・4H ２ O) was contained.

[0121] Nos. 1 to 8, 10, and 35 to 37 had an insufficient amount of Mg in the coating layer, and Nos. 1 to 4 had an insufficient amount of Al in the coating layer. Therefore, Nos. 1 to 8, 10, and 35 to 37 had zinc phosphate tetrahydrate (Zn ３ (P.O. ４ ) ２ ・4H ２ In No. 38, the zinc phosphate crystal layer contained 0.0 Mg, but the Mg concentration was less than 1.5% by mass, and the Al concentration was less than 1.0% by mass, which prevented carbonation during laser irradiation and resulted in a carbon concentration in the first region that did not satisfy the range of the present invention.

[0122] In addition, No. 34 had an excessive amount of Mg in the plating layer, which resulted in a decrease in the corrosion resistance of the plating layer and poor durability of the design.

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] The surface-treated steel material and the manufacturing method thereof disclosed herein are capable of clearly and permanently expressing designs such as letters and designs, and therefore have high industrial applicability.

[0131] 1... surface-treated steel material, 11... steel material, 12... plating layer, 13... zinc phosphate crystal layer

Claims

1. A steel material comprising a steel material and a plating layer disposed on a surface of the steel material, wherein the plating layer has an average chemical composition, in mass%, of Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% to 1.0%, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, total amount of Sn, Bi, and In ΣX: 0% to 0.7%, Ca: 0% to 0.6%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%, Sr: 0% to 0.3%, Li: 0% to 0.3%, Total amount of Ca, Y, La, Ce, Sr, and Li, ΣYa: 0% or more, 0.6% or less, Cr: 0% or more, 3.0% or less, Ni: 0% or more, 1.0% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.0% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb, ΣYb: 0% or more, 3.0% or less, B: 0% or more, 0.5% or less, P: 0% or more, 0.5% or less, Total amount of B and P, ΣYc: 0% or more, 0.5% or less, Ti: 0% or more, 0.25% or less, Co: 0% or more and 0.25% or less, V: 0% or more and 0.25% or less, Nb: 0% or more and 0.25% or less, Mn: 0% or more and 0.25% or less, Zr: 0% or more and 0.25% or less, W: 0% or more and 0.25% or less, total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, balance: 40% or more of Zn and impurities, and Zn is deposited on the surface of the plating layer. ３ (P.O. ４ ) ２ ・4H ２ A surface-treated steel material comprising a zinc phosphate crystal layer containing O laminated thereon, the zinc phosphate crystal layer containing Mg at a concentration of 1.5 mass% or more and Al at a concentration of 1.0 mass% or more, and a first region having a C concentration of 2.5 mass% or more provided on a part of the surface of the zinc phosphate crystal layer.

2. The surface-treated steel material according to claim 1, wherein the surface of the zinc phosphate crystal layer is provided with the first region having a C concentration of 2.5% or more and the second region having a C concentration of 0.1% or less.

3. The coating weight of the zinc phosphate crystal layer on the surface of the plating layer is 1.0 g / m ２ The surface-treated steel material according to claim 1 .

4. Munsell value N of the second region ２ The surface-treated steel material according to claim 2, wherein the value of the surface roughness is 3.5 or less.

5. Munsell value N of the first region １ and the Munsell value N of the second region ２ The difference between (N １ -N ２ 3. The surface-treated steel material according to claim 2, wherein the value of σ is 0.5 or more.

6. A method for manufacturing a processed material, comprising: a laser irradiation step of irradiating a surface of a processed material having a zinc phosphate crystal layer disposed on the surface thereof with a laser; the processed material comprising: a steel material; a plating layer disposed on the surface of the steel material; and the zinc phosphate crystal layer disposed on the surface of the plating layer; and the zinc phosphate crystal layer is made of Zn ３ (P.O. ４ ) ２ ・4H ２ 1. A method for producing a surface-treated steel material, comprising: a zinc phosphate crystal layer containing 0, Mg at a concentration of 1.5% or more, and Al at a concentration of 1.0% or more; and the laser irradiation step is a step of irradiating a surface of the zinc phosphate crystal layer with a laser in the atmosphere.

7. A method for manufacturing a plated steel material, the method comprising: a film formation step of forming a zinc phosphate crystal layer on the surface of a plated steel material comprising a steel material and a plating layer disposed on the surface of the steel material; and a laser irradiation step of irradiating a part of the surface of the zinc phosphate crystal layer with a laser, wherein the average chemical composition of the plating layer is, in mass %, Al: more than 10.0% and not more than 40.0%, Mg: more than 4.0% and not more than 15.0%, Si: 0% to 1.0%, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, total amount of Sn, Bi and In ΣX: 0% to 0.7%, Ca: 0% to 0.6%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%. Sr: 0% or more, 0.3% or less, Li: 0% or more, 0.3% or less, Total amount of Ca, Y, La, Ce, Sr, and Li ΣYa: 0% or more, 0.6% or less, Cr: 0% or more, 3.0% or less, Ni: 0% or more, 1.0% or less, Mo: 0% or more, 0.25% or less, Cu: 0% or more, 1.0% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, Total amount of Cr, Ni, Mo, Cu, Ag, Sb, and Pb ΣYb: 0% or more, 3.0% or less, B: 0% or more, 0.5% or less, P: 0% or more, 0.5% or less, the total amount ΣYc of B and P: 0% or more and 0.5% or less, Ti: 0% or more and 0.25% or less, Co: 0% or more and 0.25% or less, V: 0% or more and 0.25% or less, Nb: 0% or more and 0.25% or less, Mn: 0% or more and 0.25% or less, Zr: 0% or more and 0.25% or less, W: 0% or more and 0.25% or less, the total amount ΣZ of Ti, Co, V, Nb, Mn, Zr and W: 0% or more and 0.25% or less, Fe: 0% or more and 5.0% or less, the balance: 40% or more of Zn and impurities, and the film forming step comprises depositing a zinc phosphate solution of pH 5.0 or less on the surface of the plating layer to form a film of Zn. ３ (P.O. ４ ) ２ ・4H ２ a step of forming a zinc phosphate crystal layer containing O and also containing 1.5% or more of Mg and 1.0% or more of Al, and the laser irradiation step is a step of irradiating a surface of the zinc phosphate crystal layer with a laser in the atmosphere.

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