Steel member, treatment liquid, steel member manufacturing method, and weld repair method

Abstract

To further improve corrosion resistance in the weld of a plated steel material by a simpler method.SOLUTION: A steel member including a bead part formed by welding includes: a plating layer provided in at least a part of the steel material and a coating film provided on the surfaces of the bead part, a plating disappearance part and at least a part of the plating layer. The coating film having a thickness of 10-100 μm includes: at least one kind of acid components A selected from a group of consisting of nitric acid and a nitric compound; a metal component B being metal or a metal compound including an element selected from a group consisting of Ca, Zn and Mn; an organic resin component C including an urethane resin; and Fe. The abundance ratio of the metal component B to the acid component A in the coating film is a molar ratio of 0.25-0.45, and at a position of 3 μm in the coating film thickness direction from an interface on the side of the bead part in the coating positioned on the bead part, the ratio of an element Fe to the total of elements P, N, Ca, Zn, Mn, C and Fe in the coating film is 5-20 atm%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steel member, a treatment liquid, a method for manufacturing a steel member, and a method for repairing a welded portion. [Background technology]

[0002] Conventionally, various steel materials, such as steel sheets and plated steel sheets in which the surface of the steel sheet is subjected to a Zn-based plating treatment, have been used in various applications, including exterior building materials. Among these steel materials, plated steel materials, for example, are sometimes welded during the forming process. Because the welded portion reaches high temperatures, the applied plating layer evaporates, exposing the steel material. As a result, the corrosion resistance of the plated steel material is insufficient in its current state, and therefore repairs are often performed by thermal spraying, painting, or the like.

[0003] There are various methods for welding steel materials, such as resistance welding, high-frequency induction welding, electron beam welding, plasma welding, gas welding, laser welding, etc. Among these, arc welding is often used for joining steel materials because the equipment required is simple.

[0004] When thermal spraying is used as a repair method for a weld formed by arc welding (arc weld), pure Zn or a Zn alloy is sprayed onto the weld to repair the welded steel material (see, for example, Patent Document 1 and Patent Document 2 below). When painting is used as a repair method for an arc weld, paint containing pure Zn is applied to the weld to repair the welded steel material (see, for example, Patent Document 3 below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 60-89559 [Patent Document 2] Japanese Patent Application Publication No. 8-127855 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-317492 Summary of the Invention [Problem to be solved by the invention]

[0006] Thermal spraying requires large equipment, and although it is sometimes used in steel pipe production lines where welding is performed continuously, it is difficult to use it for all welding, such as partial welding. Furthermore, these methods require grinding off the weld bead area as a pretreatment for thermal spraying.

[0007] Unlike thermal spraying, repair paints containing pure Zn do not require equipment and can be easily applied anywhere, making them a popular method for repairing welds. It is known that an oxide film forms on the exposed steel surface at welds. Arc welding, in particular, can reach high temperatures of 1,800–2,000°C, resulting in the formation of a thick oxide film. Such thick oxide films can result in poor paint adhesion, and the inherent corrosion protection of repair coatings may not be fully realized. Therefore, to ensure consistent corrosion resistance, it is necessary to remove the oxide film formed on the weld metal and bead area by grinding or other methods as a pretreatment before painting.

[0008] Therefore, the present invention has been made in consideration of the above circumstances, and aims to provide a treatment liquid that can further improve the corrosion resistance of welds in plated steel products in a simpler manner, a method for manufacturing a steel member and a method for repairing a weld using such a treatment liquid, and a steel member having further improved corrosion resistance in welds in plated steel products. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors conducted extensive research and came up with a treatment liquid having specific properties and consisting of specific components, and discovered that by using such a treatment liquid, it is possible to further improve the corrosion resistance of welds without removing the oxide film formed during welding. Furthermore, it was found that steel members repaired using such a treatment liquid have a specific element distribution in the coating formed on the weld bead, resulting in superior corrosion resistance. The gist of the present invention, which was completed based on these findings, is as follows.

[0010] (1) A steel member having a bead portion formed by welding, the steel member having a plating layer provided on at least a part of a base steel material, and a coating film provided on the surface of the bead portion, a plating loss portion adjacent to the bead portion where the plating layer has disappeared, and at least a part of the plating layer located around the plating loss portion, the coating film having a thickness of 10 to 100 μm and containing at least one acid component A selected from the group consisting of nitric acid and nitric acid compounds, and a group consisting of Ca, Zn, and Mn. a metal component B which is a metal or metal compound containing an element selected from the group consisting of: an organic resin component C which contains a urethane resin; and Fe, wherein the abundance ratio of the metal component B to the acid component A in the coating film (metal component B / acidic component A) is 0.25 to 0.45 in molar ratio, and the ratio of the element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film located on the bead portion, at a position 3 μm from the interface on the bead portion side in the coating film thickness direction, is 5 to 20 atm %. (2) The steel member according to (1), wherein the coating film further contains, as the acid component A, at least one selected from the group consisting of phosphoric acid and phosphoric acid compounds. (3) The steel member according to (1) or (2), wherein in the coating film located on the bead portion, at a position 3 μm from the interface on the surface side of the coating film in the coating film thickness direction, the ratio of the element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film is 5 atm% or less. (4) In the coating film located on the plating layer, the elements P, N, Ca, Zn, and Mn in the coating film at a position 3 μm from the interface on the plating layer side in the coating film thickness direction , C, Fe The steel member according to any one of (1) to (3), wherein the ratio of the element Zn to the total of the above is 5 to 25 atm %. (5) In the coating film located on the plating layer, the elements P, N, Ca, Zn, and Mn in the coating film at a position 3 μm from the interface on the surface side of the coating film in the coating film thickness direction , C, Fe The steel member according to any one of (1) to (4), wherein the ratio of the element Zn to the total of the above is 7 atm % or less. (6) The steel member according to any one of (1) to (5), wherein the coating film further contains a metal or a metal compound containing at least one of Mg and Sr, and the amount of the metal or metal compound containing at least one of Mg and Sr is in a molar ratio of 0.10 to 0.30 relative to the amount of the metal component B. (7) The steel member according to any one of (1) to (6), wherein the content of the organic resin component C in the coating film is 50 mass % or more. (8) The steel member according to any one of (1) to (7), wherein the concentration of the urethane resin in the organic resin component C in the coating film is 50 mass % or more. (9) The steel member according to any one of (1) to (8), wherein the metal component B in the coating film has a molar abundance ratio [Zn] / ([Ca]+[Mn]) of 0.20 to 0.35, calculated based on the amounts of Zn, Ca, and Mn present in the coating film. (10) The steel member according to any one of (1) to (9), wherein in the coating film, the ratio of the total amount of the acid component A and the metal component B to 1 g of the organic resin component C is 0.010 to 0.025 mol / g. (11) The steel member according to any one of (1) to (10), wherein the plating layer is a plating layer containing the following metal components and impurities: Zn: More than 65.0% by mass Al: more than 5.0 mass% and less than 25.0 mass% Mg: More than 2.0% by mass and less than 12.5% by mass Si: 0.1 mass% or more and 2.0 mass% or less (12) A treatment liquid for forming the coating film on the steel member according to any one of (1) to (11), comprising: nitrate ions as acid ions; at least one metal ion selected from the group consisting of Ca, Zn, and Mn; and a urethane resin, wherein the molar ratio of the metal ions to the acid ions is 0.25 to 0.45, and the pH is 1.0 to 3.0. (13) The treatment liquid according to (12), further containing phosphate ions as the acidic ions. (14) The treatment liquid according to (12) or (13), further comprising at least one metal ion selected from the group consisting of Mg and Sr. (15) A method for producing a steel member according to any one of (1) to (11), comprising: joining the steel material having the plating layer by welding; and then applying the treatment solution according to any one of (12) to (14) to a surface of the bead portion, a surface of the plating loss portion adjacent to the bead portion, and a surface of at least a part of the plating layer located around the plating loss portion, without removing an oxide film on the bead portion formed by the welding; and drying the treatment solution to form the coating film. (16) A method for repairing a weld in a steel member manufactured using a steel material having a plating layer, the method comprising: joining the steel material having the plating layer by welding; applying a treatment liquid according to any one of (12) to (14) to the weld without removing an oxide film formed on the weld by the welding; and drying the treatment liquid to form a coating film. [Effects of the Invention]

[0011] As described above, according to the present invention, it is possible to obtain a treatment liquid that can further improve the corrosion resistance of welds in plated steel products in a simpler manner, a method for manufacturing a steel member and a method for repairing a weld using such a treatment liquid, and a steel member having further improved corrosion resistance in welds in plated steel products. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram schematically illustrating an example of a steel member according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram schematically illustrating an example of a steel member according to the embodiment. [Figure 3] FIG. 2 is an explanatory diagram schematically illustrating an example of a steel member according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0014] (Regarding steel components) Hereinafter, a steel member according to an embodiment of the present invention will be described in detail with reference to Figs. 1 to 3. The steel member according to this embodiment is formed by joining a plurality of steel materials by welding, and the welded portion has a bead portion formed by welding. Note that the steel member according to the present invention can be manufactured by any welding method as long as it generates a bead, and the welding method is not particularly limited. In the following description, arc welding, which is often used when joining steel materials, will be taken as an example.

[0015] <Overall structure> Fig. 1 schematically illustrates a cross-sectional structure of a portion of a joined body in which plated steel sheets 10A and 10B (hereinafter, collectively referred to as "plated steel sheet 10"), which are an example of a plated steel material, are welded by arc welding as an example of a steel member 1. That is, Fig. 1 schematically illustrates only the structure on one side, and the structure on the other side is not illustrated. As shown in FIG. 1, a steel member 1 according to this embodiment includes plated steel sheets 10A and 10B, a bead portion 20 containing a weld metal as a main component, and a coating film 30.

[0016] The plated steel sheets 10A, 10B have base steel sheets 101A, 101B (hereinafter, sometimes collectively abbreviated as "base steel sheet 101") and plating layers 103A, 103B (hereinafter, sometimes collectively abbreviated as "plating layer 103") formed on the surfaces of the base steel sheets 101A, 101B.

[0017] The plating of the plating layers 103A, 103B of the plated steel sheets 10A, 10B has been partially lost due to heat generated by arc welding, resulting in plating loss portions 105A, 105B (hereinafter, sometimes collectively referred to as "plating loss portions 105"). As is clear from the formation process, these plating loss portions 105A, 105B are located adjacent to the bead portion 20.

[0018] Furthermore, the coating film 30 in this embodiment is provided so as to cover the surface of the bead portion 20, the surface of the plating loss portion 105, and at least a portion of the surface of the plating layer 103 located around the plating loss portion 105.

[0019] The plated steel sheet 10, the bead portion 20, and the coating film 30 will be described in more detail below.

[0020] In this embodiment, a plated steel sheet is used as an example of a plated steel material, but the plated steel material is not limited to this example. Various plated steel materials that may be arc-welded, such as various types of plated steel pipes and various types of plated steel sections, can also be used as plated steel materials.

[0021] <About Plated Steel Sheet 10> A plated steel sheet 10, which is an example of a base material of a steel member 1, has a base steel sheet 101 and a plated layer 103, as shown schematically in FIG.

[0022] [About Base Steel Plate 101] The base steel plate 101 is not particularly limited, and various types can be used depending on the mechanical strength (e.g., tensile strength) and other properties required of the steel member 1. Examples of such steel plates include various types of low-carbon steel, medium-carbon steel, high-carbon steel, and alloy steel. Furthermore, it is preferable that the base steel plate 101 be a deep-drawing steel plate such as a low-carbon Ti-added steel or a low-carbon Nb-added steel, from the viewpoint of improving the workability of the steel plate.

[0023] The thickness of the base steel plate 101 is not particularly limited either, and an appropriate thickness may be selected depending on the mechanical strength required of the steel member 1, etc.

[0024] [Regarding plating layer 103] A plating layer 103 is formed on the surface of the base steel sheet 101. Due to the presence of this plating layer 103, the plating layer 103 present around the bead portion 20 exhibits a sacrificial corrosion protection effect on the bead portion 20 and the plating loss portion 105 adjacent to the bead portion 20. This allows the base steel sheet 101 to exhibit higher corrosion resistance. Examples of plated steel sheets 10 having such a plating layer 103 include zinc-plated steel sheets, Zn-Al alloy-plated steel sheets, Zn-Al-Mg alloy-plated steel sheets, Zn-Al-Mg-Si alloy-plated steel sheets, and aluminum-plated steel sheets.

[0025] Among the various platings described above, the plating layer 103 is preferably a zinc-based plating having an average composition of 0 to 90 mass% Al, 0 to 10 mass% Mg, and the balance being Zn and impurities. Such plating layer 103 is more preferably a plating layer having an average composition of 4 to 22 mass% Al, 1 to 10 mass% Mg, and the balance being Zn and impurities, and even more preferably a plating layer having an average composition of more than 5.0 mass% but less than 25.0 mass% Al, and more than 2.0 mass% but less than 12.5 mass% Mg, and the balance being Zn and impurities.

[0026] The plating layer may contain, in its average composition, Si: 0.1% by mass or more and 2.0% by mass or less, and may also contain, in its average composition, 0.001 to 2% by mass in total of 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.

[0027] The coating weight of the plating layer 103 as described above is not particularly limited, but for example, it is 30 to 240 g / m per one side of the base steel sheet 101. 2By doing so, it is possible to provide a plating layer and thereby achieve sufficient corrosion resistance.

[0028] The plated steel sheet 10 according to this embodiment has been described in detail above.

[0029] <About the bead part 20> The bead portion 20 is formed by joining plated steel sheets 10, which are an example of plated steel materials, by arc welding, and is a portion made of weld metal. There are no particular limitations on the bead portion 20. In the process of forming the bead portion 20, part of the plating layer 103 of the adjacent plated steel sheet 10 disappears, and a plating loss portion 105 is formed.

[0030] <About Coating 30> In the steel member 1 according to this embodiment, a coating film 30 is provided on the surface of the bead portion 20, the surface of the plating loss portion 105, and at least a portion of the surface of the plating layer 103 located around the plating loss portion 105, so as to cover these areas.

[0031] [About thickness] The thickness (average thickness) of the coating film 30 is 10 to 100 μm. Here, the thickness of the coating film 30 refers to the average value of the distances from the surface of the bead portion 20, the surface of the plating loss portion 105, and the surface of the plating layer 103 to the surface of the coating film 30, as schematically shown in Fig. 1. Detailed measurement conditions and a method for calculating the average value will be described later.

[0032] If the thickness of the coating film 30 is less than 10 μm, the required improvement in corrosion resistance cannot be achieved. By making the thickness of the coating film 30 10 μm or more, a shielding effect from corrosion factors can be obtained, making it possible to significantly improve corrosion resistance. The thickness of the coating film 30 is preferably 20 μm or more. On the other hand, if the thickness of the coating film 30 exceeds 100 μm, the drying time required to dry and solidify the treatment liquid for forming the coating film 30 becomes long, and the appearance of the coating film 30 may be deteriorated, which is undesirable. By making the thickness of the coating film 30 100 μm or less, it is possible to prevent the drying time of the treatment liquid from being prolonged while maintaining a good appearance after application. The thickness of the coating film 30 is preferably 80 μm or less.

[0033] The thickness of the coating can be measured as follows. Specifically, a portion of the steel member 1 of interest is embedded in resin and mechanically polished to expose the cross section, which serves as the analysis surface. The resulting analysis surface is then observed using a scanning electron microscope to identify the surface of the bead portion 20, the surface of the plating loss portion 105, and the portion where the coating film 30 is formed on the plating layer 103. At any five locations within the coating film-forming portion, the positions of the interface between the surface of the bead portion 20, the surface of the plating loss portion 105, and the plating layer 103 and the coating film 30 are identified, and the thickness from the interface to the surface of the coating film 30 is measured from the cross-sectional image (thicknesses T1 to T5 in Figure 1). The area from both ends of the coating film cross section to 10% of the total width of the coating film cross section (the area marked "excluding measurement" in Figure 1) is excluded from the measurement. This measurement is performed at multiple cross-sectional locations (e.g., 10 locations), and the values measured at each measurement location are averaged across the number of measurement locations. The average value thus obtained is the coating film thickness (average thickness) T, as shown in Figure 1.

[0034] [Ingredients] As will be described in detail below, the coating film 30 contains components that can be broadly divided into four types: an acid component A, a metal component B, an organic resin component C, and Fe.

[0035] ≪Acid component A≫ The acid component A is at least one selected from the group consisting of nitric acid and nitric acid compounds. These acid components A are introduced to adjust the pH of the treatment liquid (which can also be considered a paint) used to form the coating film 30, and the coating film 30 formed by drying and solidifying the treatment liquid contains these acid components A. Since the treatment liquid contains acidic ions associated with these acid components, even if an acidic coating is present on or near the bead portion 20, it is possible to form the coating film 30 while dissolving the acidic coating. As a result, it is possible to more easily repair welds (and ultimately manufacture steel members).

[0036] Furthermore, the coating film 30 according to this embodiment preferably further contains at least one acid selected from the group consisting of phosphoric acid and phosphate compounds as the acid component A. In other words, the coating film 30 preferably contains at least one acid selected from the group consisting of nitric acid, nitric acid compounds, phosphoric acid, and phosphate compounds as the acid component A.

[0037] The phosphate ions contained in the treatment solution for forming the coating film 30 precipitate on the steel material as phosphoric acid or phosphoric acid compounds (more specifically, phosphate crystals) when dissolved and dried. These phosphate crystals are particularly effective in improving the corrosion resistance of the steel surface.

[0038] <Metal component B> The metal component B is a metal or a metal compound containing an element selected from the group consisting of Ca, Zn, and Mn. When the coating film 30 contains such a metal or metal compound, the corrosion resistance of the steel member 1 can be improved.

[0039] The acid component A and the metal component B react with each other, and are present in the coating film 30 mainly as a metal salt of the metal component B.

[0040] The metal salt of the acid component A and the metal component B dissolves when covered with water. The eluate reacts with the weld metal of the bead portion 20, the exposed steel in areas where no plating layer is present (e.g., the plating loss portion 105 or the end face of the steel member 1), the components of the plating layer 103, and / or metal ions derived from the plated steel sheet 10. As a result, salt formation and co-precipitation occur, forming a corrosion-resistant film at the reaction site, thereby imparting corrosion resistance.

[0041] To ensure that the above-described reaction occurs, the molar ratio of metal component B to acid component A (metal component B / acid component A) in the coating film 30 according to this embodiment is set to 0.25 to 0.45. The molar ratio of metal component B to acid component A (metal component B / acid component A) is preferably 0.25 to 0.40, and more preferably 0.25 to 0.35.

[0042] Furthermore, with regard to the metal component B, adjusting the amount of Zn present relative to Ca and Mn makes it possible to further improve corrosion resistance. Specifically, the ratio (molar ratio) of the amount of Zn present [Zn] to the total amount of Ca and Mn present ([Ca] + [Mn]) ([Zn] / ([Ca] + [Mn])) is preferably 0.20 or more and 0.45 or less. By setting this molar ratio to 0.20 or more, the effect of Zn in improving corrosion resistance becomes significant. The molar ratio is more preferably 0.25 or more. On the other hand, by setting this molar ratio to 0.45 or less, it becomes possible to more reliably prevent poor coating film formation. The molar ratio is more preferably 0.40 or less, and even more preferably 0.35 or less.

[0043] Furthermore, the coating film 30 according to this embodiment may further contain, in addition to the metal component B, a metal or metal compound containing at least one of Mg and Sr. In this case, the amount of the metal or metal compound containing at least one of Mg and Sr is preferably present at a molar ratio of 0.10 to 0.30 relative to the amount of the metal component B. By setting the molar ratio at 0.10 or greater, a eutectoid crystal with phosphate ions, Ca, Zn, and Mn is formed, further improving corrosion resistance. The molar ratio is more preferably 0.15 or greater, and even more preferably 0.20 or greater. On the other hand, by setting the molar ratio at 0.30 or less, a eutectoid crystal composition that enhances corrosion resistance is obtained. The molar ratio is more preferably 0.33 or less, and even more preferably 0.31 or less.

[0044] In addition, when considering the abundance ratio of metal component B to acid component A (metal component B / acid component A) described above, even if the coating film 30 contains a metal or metal compound containing at least one of the above-mentioned elements Mg or Sr, these metals or metal compounds will not be treated as being included in metal component B.

[0045] <Organic resin component C> The coating film 30 according to this embodiment contains a urethane resin as the organic resin component C. The urethane resin has good adhesion to the base steel sheet 101 of the plated steel sheet 10, the bead portion 20, the plating loss portion 105 adjacent to the bead portion 20, and the surface of the plating layer 103 around the bead portion 20, and can enhance the corrosion resistance of the steel material serving as the substrate for a long period of time.

[0046] In addition, the coating film 30 according to this embodiment may contain, as the organic resin component C, organic resins such as phenolic resin, polyester resin, acrylic resin, epoxy resin, polyolefin resin, and fluororesin in addition to the above-mentioned urethane resin.

[0047] In the coating film 30, the content of the organic resin component C is preferably 50% by mass or more relative to the total mass of the coating film 30. By making the content of organic resin component C 50% by mass or more, it becomes possible to more reliably retain the acid component A and metal component B as described above. The content of organic resin component C is more preferably 55% by mass or more. On the other hand, the content of organic resin component C is preferably 80% by mass or less relative to the total mass of the coating film 30. By making the content of organic resin component C 80% by mass or less, an appropriate balance of the shielding properties of the coating film and the corrosion prevention properties of the eluted components can be obtained, making it possible to further improve corrosion resistance. The content of organic resin component C is more preferably 65% by mass or less.

[0048] In the coating film 30, the concentration of the urethane resin in the organic resin component C is preferably 50% by mass or more relative to the total mass of the organic resin component C. By making the concentration of the urethane resin in the organic resin component C 50% by mass or more, it becomes possible to more reliably achieve the effect of maintaining corrosion resistance over a long period of time as described above. The concentration of the urethane resin in the organic resin component C is more preferably 50% by mass or more. On the other hand, the concentration of the urethane resin in the organic resin component C is not particularly limited and may be 100% by mass.

[0049] In the coating film 30 according to this embodiment, the ratio of the total amount (total molar amount) of the acid component A and the metal component B to 1 g of organic resin component C (total molar amount of acid component A and metal component B / 1 g of organic resin component C) is preferably 0.010 to 0.025 mol / g. If this ratio is less than 0.010 mol / g, the amount of acid component A and metal component B eluted from the coating film 30 in a corrosive environment may be reduced. As a result, the effect of improving corrosion resistance in the bead portion 20, the plating loss portion 105, and the surface of the plating layer 103 around the bead portion 20 may not be fully achieved. By setting this ratio to 0.010 mol / g or more, it is possible to more reliably maintain the amount of acid component A and metal component B eluted from the coating film 30 in a corrosive environment in an appropriate state, and it is possible to more reliably achieve the above-described effect of improving corrosion resistance. On the other hand, if this ratio is greater than 0.025 mol / g, the amount of components eluted from the coating film 30 in a corrosive environment will be too large, resulting in the coating film 30 becoming porous and potentially reducing the coating film's shielding properties. As a result, it may be difficult to achieve the corrosion resistance improvement effect. By setting this ratio to 0.025 mol / g or less, it is possible to more reliably maintain the appropriate amount of acidic component A and metal component B eluted from the coating film 30 in a corrosive environment, thereby more reliably achieving the corrosion resistance improvement effect described above. This ratio is more preferably 0.020 mol / g or less.

[0050] Fe The Fe contained in the coating film 30 was incorporated into the coating film 30 as a result of dissolution and diffusion of the oxide film on the bead portion 20, components of the weld metal forming the bead portion 20, components of the oxide film formed in the plating loss portion 105 adjacent to the bead portion 20, and components of the steel substrate during coating formation. Therefore, the Fe concentration in the coating film 30 near the bead portion 20 indicates the degree to which the oxide film on the bead portion 20 has been dissolved and removed, and serves as an index of the corrosion resistance of the coating film 30 ensured by the removal of the oxide film. By investigating the relationship between the Fe concentration in the coating film 30 near the bead portion 20 and the corrosion resistance of the coating film 30 formed on the bead portion 20, the Fe concentration in the coating film 30 required to ensure the corrosion resistance and adhesion of the coating film 30 was determined.

[0051] The bead portion 20 tends to have a thicker oxide film than ordinary steel, resulting in poor paint adhesion. The treatment solution for forming the coating film 30, as described in detail below, has a low pH, and is thought to become highly acidic as the pH is further lowered during the drying process. As shown below, the high Fe concentration in the coating film 30 near the bead portion 20 suggests that the treatment solution dissolves the oxide film on the bead portion 20 during the drying process and incorporates the oxide film into the coating film 30. Therefore, the coating film 30 is thought to contribute to excellent corrosion resistance of the bead portion 20 without compromising adhesion.

[0052] [Fe concentration in the coating thickness direction] Specifically, the atomic concentrations (atm %) of P, N, Ca, Zn, Mn, and C, which are the elements constituting the main components of the coating film 30, and the atomic concentration (atm %) of Fe were measured at predetermined positions in the thickness direction of the coating film 30, and an investigation was conducted into the atm % ratio and the performance of the coating film 30. As a result, the positions in the coating film 30 where the Fe concentration should be controlled and the concentration range were identified.

[0053] More specifically, as shown schematically in FIG. 2, attention is focused on a position (position A in FIG. 2) in the coating film 30 located on the bead portion 20, which is 3 μm from the interface on the bead portion 20 in the coating film thickness direction. Note that FIG. 2 is an enlarged schematic view of a portion of the coating film 30 located on the bead portion 20. In the coating film 30 according to this embodiment, at position A, the ratio of the element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film 30 is in the range of 5 to 20 atm%. Achieving this state allows an appropriate amount of the oxide film on the bead portion 20 to be dissolved and removed, thereby achieving the sufficient corrosion resistance required of the coating film 30. The ratio of the element Fe at position A is preferably in the range of 10 to 20 atm%.

[0054] As will be described later, the coating film according to the present invention exhibits excellent corrosion resistance even when it is formed after removing the oxide film present on the bead portion. Even after removing the oxide film, Fe elution from the bead portion occurs. Therefore, even when the coating film is formed after removing the oxide film, the corrosion resistance and other performance properties of the coating film can be achieved by setting the Fe concentration as described above.

[0055] Here, excessive dissolution of Fe during coating formation may adversely affect the performance of the coating film 30. As an indicator for confirming such excessive dissolution of Fe, we focus on the presence of element Fe at a position 3 μm in the coating film thickness direction from the interface on the surface side of the coating film 30 (position B in FIG. 2 ). If the ratio of element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film 30 at position B is within the range of 1 to 5 atm%, it can be determined that excessive dissolution of Fe during coating formation has not occurred and that the performance of the coating film 30 is maintained at the desired level. Therefore, for the coating film 30 on the bead portion 20, the ratio of element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating at position B is preferably 5 atm% or less. The ratio of element Fe at position B as described above is preferably 3 atm% or less. The lower limit of the ratio of element Fe at position B is not particularly limited, and the smaller the value, the better.

[0056] The ratio of element Fe at positions A and B is measured as follows. Specifically, a portion of the steel member 1 of interest is embedded in resin and mechanically polished to expose a cross section, which serves as the analysis surface. The resulting analysis surface is observed using a scanning electron microscope to identify the portion where the coating film 30 is formed on the bead portion 20. At any point in this specific portion, the position of the interface between the bead portion 20 and the coating film 30 is identified. Then, quantitative analysis of P, N, Ca, Zn, Mn, C, and Fe is performed using SEM-EDX at positions A (3 μm from the interface in the coating film thickness direction) and B (3 μm from the surface of the coating film 30 in the coating film thickness direction) as shown in FIG. 2 to determine the abundance (atm%) of each element and the ratio of element Fe. This measurement is performed at multiple cross-sectional locations (e.g., 10 locations), and the measured values obtained at each measurement location are averaged over the number of measurement locations. The average values thus obtained are the ratios of element Fe at positions A and B as shown in FIG. 2.

[0057] [Zn concentration in the coating thickness direction] In the coating film 30 formed on the plating layer 103, an increase in the metal element concentration is observed due to the dissolution and diffusion of the metal that is the main component of the plating layer. For example, if a zinc-based plating layer is provided as the plating layer 103, an increase in the concentration of element Zn is observed due to the dissolution and diffusion of Zn, the main component of the plating. In this case, if the plating layer 103 is a zinc-based plating layer, the Zn diffusing from the plating layer can further improve corrosion resistance. This point will be explained in detail below.

[0058] Zn is an element contained in metal component B and is a major component of the coating film 30. By appropriately controlling the increase in the concentration of element Zn, further improvements in corrosion resistance can be expected. In particular, the Zn concentration in the treatment solution for forming the coating film 30 has an upper limit due to the stability of the treatment solution. Therefore, dissolving Zn from the plating layer 103 has the advantage of achieving further improvements in corrosion resistance without impairing the stability of the treatment solution.

[0059] In order to consider the diffusion of Zn from the plating layer 103 as described above, in this embodiment, attention is focused on a position (position C in FIG. 3) in the coating film 20 located on the plating layer 103, which is 3 μm from the interface on the plating layer 103 side in the coating film thickness direction, as schematically shown in FIG. 3. Note that FIG. 3 is an enlarged schematic view of a portion of the coating film 30 located on the plating layer 103.

[0060] In the coating film 30 according to this embodiment, the ratio of the element Zn to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film 30 at position C is preferably within a range of 5 to 25 atm%. By realizing this state, enough Zn to achieve a further improvement in corrosion resistance is diffused from the plating layer 103, thereby achieving further improvement in corrosion resistance. The ratio of the element Zn at position C as described above is preferably within a range of 10 to 25 atm%.

[0061] Excessive dissolution of Zn from the plating layer 103 may cause unnecessary wear of the plating layer and potentially hinder the corrosion resistance improvement effect of the zinc-based plating around the welded portion. As an indicator for confirming such excessive Zn dissolution, attention is focused on the presence of elemental Zn at a position 3 μm in the thickness direction of the coating film 30 located on the plating layer 103 from the interface on the surface side of the coating film 30 (position D in FIG. 3 ). If the ratio of elemental Zn to the total of elements P, N, Ca, Zn, Mn, C, and Fe in the coating film 30 at position D is within the range of 2 to 7 atm%, it can be determined that excessive dissolution of Zn from the plating layer 103 has not occurred and that the performance of the coating film 30 is maintained at a desired level. Therefore, for the coating film 30 on the plating layer 103, the ratio of elemental Zn to the total of elements P, N, Ca, Zn, Mn, C, and Fe in the coating at position D is preferably 7 atm% or less. The lower limit of the ratio of element Zn at position D is not particularly specified, and the smaller the value, the better.

[0062] The ratio of element Zn at positions C and D is measured as follows. Specifically, a portion of the steel member 1 of interest is embedded in resin and mechanically polished to expose a cross section, which serves as the analysis surface. The obtained analysis surface is observed using a scanning electron microscope to identify the portion where the coating film 30 is formed on the plating layer 103. At any point in this specific portion, the position of the interface between the plating layer 103 and the coating film 30 is identified. Then, quantitative analysis of P, N, Ca, Zn, Mn, C, and Fe is performed using SEM-EDX at positions C (3 μm from the interface in the coating film thickness direction) and D (3 μm from the surface of the coating film 30 in the coating film thickness direction) as shown in FIG. 3 to determine the abundance (atm%) of each element and the ratio of element Zn. This measurement is performed at multiple cross-sectional locations (e.g., 10 locations), and the measured values obtained at each measurement location are averaged over the number of measurement locations. The average values thus obtained are the ratios of element Zn at positions C and D as shown in FIG. 3.

[0063] The steel member 1 according to this embodiment has been described in detail above with reference to FIGS.

[0064] (Regarding processing liquid) Next, the treatment liquid used to form the coating film 30 as described above will be described in detail below.

[0065] The treatment liquid according to this embodiment contains nitrate ions as acidic ions, at least one metal atom or metal ion selected from the group consisting of Ca, Zn, and Mn, and a urethane resin.

[0066] <Acidic ions> The treatment liquid according to this embodiment may further contain phosphate ions as acid ions. When the treatment liquid further contains phosphate ions, it becomes possible to further improve the corrosion resistance of the steel material to which the treatment liquid is applied. Note that the expression "phosphate ions" also includes phosphate compounds that dissociate in the treatment liquid to generate phosphate ions.

[0067] The phosphoric acid and phosphoric acid compound may be a normal phosphoric acid such as orthophosphoric acid or a complex phosphoric acid such as pyrophosphoric acid. In the phosphoric acid compound, examples of the cation that serves as a counter ion to the phosphate ion include a hydrogen ion, an alkali metal ion, an alkaline earth metal ion, an ammonium ion, a manganese ion, an aluminum ion, a titanium ion, a zirconium ion, a hafnium ion, and a zinc ion.

[0068] <Metal atoms and metal ions> The treatment liquid according to this embodiment contains at least one type of metal atom or metal ion selected from the group consisting of Ca, Zn, and Mn.

[0069] The metal atoms are added to the treatment solution in the form of, for example, phosphates, nitrates, sulfates, carbonates, acetates, oxalates, etc. The metal atoms are usually dissociated and ionized in the treatment solution, but some of them may remain in the form of salts in the treatment solution.

[0070] Here, by adjusting the content of Zn relative to Ca and Mn, it is possible to further improve the corrosion resistance of steel materials. Specifically, the ratio of the content of metal Zn or Zn ions to the total content of metal Ca, metal Mn, and their ions, {Zn / (Ca+Mn)}, is preferably set to a molar ratio of 0.25 or more to 0.45 or less. By setting this molar ratio to 0.25 or more, the effect of Zn in improving corrosion resistance can be made more pronounced. On the other hand, by setting this molar ratio to 0.45 or less, it is possible to more reliably prevent poor coating film formation. The molar ratio is more preferably 0.40 or less, and even more preferably 0.35 or less.

[0071] The molar ratio of the metal atoms or metal ions to the acidic ions is 0.25 to 0.45 (amount of metal ions / amount of acidic ions). It is believed that the metal atoms or metal ions co-precipitate with metal ions eluted from the steel material, thereby protecting the steel member and preventing corrosion. The presence of a large amount of such metal atoms or metal ions can further enhance the effect of improving corrosion resistance. From this perspective, the molar ratio of the metal atoms or metal ions to the acidic ions is set to 0.25 or more. Note that an excess of the metal atoms or metal ions tends to reduce the stability of the treatment solution, making it difficult to store and handle the treatment solution. From this perspective, the molar ratio of the metal atoms or metal ions to the acidic ions is set to 0.45 or less. The ratio of the metal atoms or metal ions to the acidic ions is preferably 0.40 or less, more preferably 0.35 or less.

[0072] Furthermore, the treatment liquid according to this embodiment may further contain at least one metal atom or ion selected from the group consisting of Mg and Sr, in addition to at least one metal atom or ion of Ca, Mn, and Zn. The at least one metal atom selected from the group consisting of Mg and Sr is also usually dissociated and ionized in the treatment liquid.

[0073] Here, the content of at least one metal atom or metal ion of Mg or Sr is preferably 0.10 to 0.30 in molar ratio to the content of at least one metal atom or metal ion selected from the group consisting of Ca, Zn, and Mn. By setting the molar ratio to 0.10 to 0.30, a eutectoid crystal of Ca, Zn, and Mn with phosphate ions is formed, making it possible to further improve corrosion resistance. The molar ratio is more preferably 0.15 to 0.30, and even more preferably 0.20 to 0.30.

[0074] The above-mentioned acidic ions such as nitrate ions and phosphate ions, metal atoms or ions of Ca, Zn, and Mn, and even metal atoms or ions of Mg and Sr react with the surface of the steel material to which the treatment solution has been applied and dried, or form salts or co-precipitate with metal ions derived from the plated steel material, thereby forming a corrosion-protective film and improving corrosion resistance. Furthermore, when the repair area where the treatment solution has been applied is covered with water due to rain or other reasons, acid component A and metal component B leach out of the coating film and act as inhibitors, improving the corrosion resistance of the steel member.

[0075] <Urethane resin> The urethane resin contained in the treatment liquid mainly constitutes the film structure of the coating film formed by applying and drying the treatment liquid. One type of urethane resin may be used, or multiple types may be used.

[0076] The treatment solution according to this embodiment preferably contains a nonionic urethane resin or a cationic urethane resin as the urethane resin. The nonionic urethane resin or cationic urethane resin more reliably shields the steel material, such as the bead portion, the plating loss portion adjacent to the bead portion, and the plating layer around the bead portion, from corrosion factors, improving corrosion resistance for a longer period of time. Furthermore, the nonionic urethane resin or cationic urethane resin has high miscibility with phosphate ions or metal ions, thereby further improving the storage stability and processability of the treatment solution.

[0077] From the viewpoints of ease of production of the coating film and safety, the cationic urethane resin is preferably a water-soluble or water-dispersible urethane resin, and more preferably a water-dispersible urethane resin.

[0078] Furthermore, the cationic urethane resin is preferably a urethane resin having a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group. The polyoxyalkylene group is likely to further increase the spreadability of the treatment liquid. Such a cationic urethane resin may be synthesized by reacting an organic polyisocyanate compound as described below with a polyol compound having the polyoxyalkylene group and a polyol compound not having the polyoxyalkylene group. Alternatively, such a cationic urethane resin may be synthesized by reacting a polyether alcohol with an isocyanurate, followed by reaction with a polyol compound.

[0079] The organic polyisocyanate compounds include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. Examples of aliphatic diisocyanates include tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, and trimethylhexamethylene diisocyanate. Examples of alicyclic diisocyanates include cyclohexane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate. Examples of aromatic diisocyanates include phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate.

[0080] The isocyanurate is preferably an isocyanurate trimer of the various diisocyanates mentioned above, and more preferably an isocyanurate trimer of an aliphatic diisocyanate.

[0081] The polyol compounds include polyolefin polyols, such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, and polybutadiene polyols.

[0082] Examples of the polyether alcohol include alkylene oxide adducts of alcohols having 1 to 18 carbon atoms and monoalkyl ethers of alkylene glycols having 1 to 18 carbon atoms.

[0083] <Organic resins other than urethane resins> Furthermore, the treatment liquid according to this embodiment may contain another organic resin in addition to the urethane resin. Examples of organic resins other than urethane resin include phenolic resin, polyester resin, acrylic resin, epoxy resin, polyolefin resin, and fluororesin. The content of the organic resin other than urethane resin is not particularly limited as long as it does not adversely affect the performance of the urethane resin. However, in order to effectively exhibit the performance of the urethane resin, the content of the organic resin other than urethane resin is preferably 50% or less by mass relative to the urethane resin.

[0084] <Organic resin content> The content of the organic resin in the treatment liquid is preferably 10% by mass or more relative to the total mass of the solids in the treatment liquid. Within this range, a sufficient amount of organic resin can be contained in the coating film to impart shielding properties to the coating film, thereby fully improving corrosion resistance. From this perspective, the content of the organic resin is more preferably 15% by mass or more, and even more preferably 20% by mass or more. There is no particular upper limit to the content of the organic resin. However, from the perspective of improving the coatability of the treatment liquid, the content of the organic resin is preferably 80% by mass or less. Preferably, the content of the nonionic urethane resin or cationic urethane resin is within the above range.

[0085] <Solvent> The solvent for the treatment liquid is preferably an aqueous medium from the viewpoint of explosion prevention during the production of a coating film. When preparing the treatment liquid, an aqueous emulsion or a water-soluble treatment solution of an organic resin can be suitably used to blend the organic resin. Such aqueous compositions have no flash point. Therefore, using an aqueous composition as a material for the treatment liquid is preferred, since it allows the production of a coating film even in drying equipment without explosion-proof equipment.

[0086] The aqueous medium is a liquid medium containing water as a main component, such as water or a mixture of water and a water-soluble organic solvent, etc. The content of such a solvent can be appropriately determined within the above-mentioned range of solid concentration that is suitable for application of the treatment liquid.

[0087] <Processing solution pH> In this embodiment, the pH of the treatment liquid is set within a range of 1.0 to 3.0. If the pH is less than 1, it becomes difficult to ensure the stability of the treatment liquid. By setting the pH to 1.0 or higher, it becomes possible to properly dissolve the oxide film on the bead portion while ensuring the stability of the treatment liquid. This eliminates the need for a search and removal process for the oxide film on the bead portion prior to the repair process, further improving the convenience of the repair process using the treatment liquid. The pH of the treatment liquid is preferably 1.5 or higher, and more preferably 2.0 or higher. On the other hand, if the pH of the treatment liquid exceeds 3, the oxide film on the bead portion will not be sufficiently dissolved, making it difficult to ensure the corrosion resistance of the bead portion. By setting the pH of the treatment liquid to 3.0 or lower, it becomes possible to properly dissolve the oxide film on the bead portion and ensure the corrosion resistance of the bead portion. The pH of the treatment liquid is preferably 2.5 or lower.

[0088] In such acidic treatment liquids, cationic urethane resins in particular are stable and do not easily cause gelation of the treatment liquid, which can further improve the storage stability and coatability of the treatment liquid.From this perspective, it is more preferable to use cationic urethane resins as the urethane resin.

[0089] <Other ingredients> In addition to the above components, the treatment liquid may further contain, for example, a valve metal compound, a rheology control agent, an etching agent, an inorganic compound, a lubricant, etc., within the scope of not impairing the effects of the present invention.

[0090] The valve metal compound imparts self-repairing properties to the coating film, contributing to further improvement of the corrosion resistance of the coating film. Examples of the valve metal include Ti, Zr, Hf, V, Nb, Ta, Mo, and W. The valve metal compound may be a salt of a valve metal, including an oxide, hydroxide, or fluoride of a valve metal. Note that the content of the metal atoms or metal ions described above does not include the content of these valve metals or their ions.

[0091] The rheology control agent prevents the settling of solids in the treatment liquid and contributes to improving the dispersibility of the solids. Examples of the rheology control agent include urethane, acrylic, polyolefin, amide, anionic surfactant, nonionic surfactant, polycarboxylic acid, cellulose, metolose, and urea.

[0092] The etching agent activates the surface of the steel material, contributing to improving the adhesion of the coating film to the steel material. Examples of the etching agent include fluorides. The inorganic compound further densifies the coating film, contributing to improving the water resistance of the coating film. Examples of inorganic compounds include oxides of V, W, Mn, Ni, B, Si, and Sn, as well as nitrates and phosphates of these elements. The lubricant enhances the lubricity of the coating film. Examples of the lubricant include inorganic lubricants such as molybdenum disulfide and talc.

[0093] The treatment liquid as described above is applied to the surface of the bead portion, the plating loss portion adjacent to the bead portion, the plating layer, etc. of the steel member and dried to form a coating film on these portions. In this case, the coating film may be formed by forming a film using the treatment liquid that does not contain the organic resin and then covering the film with the treatment liquid that contains the organic resin, or the coating film containing the acid ions and metal ions may be formed using the treatment liquid that contains the organic resin.

[0094] The treatment liquid according to this embodiment has been described in detail above.

[0095] (Methods for manufacturing steel components and repairing welded joints) In the method for producing a steel member according to this embodiment, steel materials having a plating layer as described above are joined by various welding methods, including arc welding, and then, without first removing the oxide film on the bead portion formed by welding, a treatment liquid as described above is applied to the surface of the bead portion, the surface of the plating loss portion adjacent to the bead portion, and the surface of the plating layer around the plating loss portion, and then dried. This forms a coating film as described above on the surface of the bead portion, the surface of the plating loss portion adjacent to the bead portion, and the surface of the plating layer around the plating loss portion. By undergoing the above-described steps, the steel member according to this embodiment can be produced.

[0096] The treatment liquid can be applied to the desired area by known application methods such as brushing or spraying. The applied treatment liquid can be dried at room temperature. However, from the viewpoint of productivity (continuous operation), the treatment liquid is preferably dried at 50°C or higher, more preferably at 100°C or higher. The drying temperature is preferably 300°C or lower to prevent thermal decomposition of the components in the treatment liquid.

[0097] As described above, the treatment liquid according to this embodiment is used for manufacturing steel members having a bead portion by arc welding or the like, but it can also be applied to repair welds on plated steel materials. Specifically, after joining steel materials having a plated layer by welding, the treatment liquid can be applied to the welds and surrounding damaged areas and sound plated areas without removing the oxide film formed on the joint, and then dried to form a coating. This allows the welds on the steel materials to be appropriately repaired.

[0098] The treatment liquid can be applied to the desired area by a known application method such as brushing or spraying. Drying can be carried out at room temperature, but from the viewpoint of productivity (continuous operation), it is preferably carried out at 50°C or higher, and more preferably at 100°C or higher. The drying temperature is preferably 300°C or lower to prevent thermal decomposition of the components in the treatment liquid.

[0099] The method for manufacturing a steel member and the method for repairing a weld according to this embodiment have been described above. [Example]

[0100] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0101] [Preparation of plated steel sheets] Plated steel sheets of various compositions were prepared by subjecting cold-rolled steel sheets (SPCC) to hot-dip Zn-19% by mass Al-6% by mass Mg-0.2% by mass Si alloy plating (hereinafter referred to as "steel sheet type A"), hot-dip Zn-6% by mass Al-3% by mass Mg alloy plating (hereinafter referred to as "steel sheet type B"), or hot-dip Zn plating (hereinafter referred to as "steel sheet type C"). The plated steel sheets had a thickness of 4.5 mm, and the coating weight on one side was 90 g / m 2 It was decided.

[0102] The plated steel sheet was cut into a width of 50 mm and a length of 100 mm, and the plated surface was arc-welded for 70 mm in the longitudinal direction using mild steel solid wire YM-28 and CO2 gas as the shielding gas during welding, with a current of 200 A.

[0103] [Preparation of processing solution] The materials shown in Table 1 below were blended to prepare a treatment liquid for forming a coating film.

[0104] The metal components Ca (Ca) was used as Ca nitrate, Zn (Zn) as Zn nitrate, Mn (Mn) as Mg nitrate, and Sr (Sr) as Sr nitrate were mixed in the treatment solution to achieve the desired concentrations. 2- 85% phosphoric acid was used as the 3- As the treatment agent, 69% nitric acid was used and mixed into the treatment solution to achieve a predetermined concentration.

[0105] As the organic resins, Hydran APX-601 manufactured by DIC Corporation was used as a nonionic urethane resin, Superflex 650 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used as a cationic urethane resin, and tannic acid manufactured by Fujifilm Wako Pure Chemical Industries was used as a polyphenol-based resin.

[0106] The pH of the treatment solution was adjusted to 2.0 by adding nitric acid, and the pH of the treatment solution was measured using a pH meter F-71 manufactured by Horiba.

[0107] Table 1 below shows the types and concentrations of the acid components, metal components and organic resins added to Treatment Solutions 1 to 38, the amount of metal / amount of acid ions, and the pH of each treatment solution.

[0108] [Table 1]

[0109] Treatment solutions 1 to 38 in Table 1 were applied by brush to the bead portions, plating loss areas, and plating layers around the bead portions of the above-mentioned plated steel sheets to a predetermined film thickness without removing the surface oxide film, and the sheets were dried at room temperature to prepare test specimens. Furthermore, zinc-rich paint (Roval, manufactured by Roval Corporation) was applied by brush to a film thickness of 50 μm to the bead portions of hot-dip Zn-19% Al-6% Mg-0.2% Si alloy-plated steel sheets, which were used as comparative materials.

[0110] The test specimens were coated with the above treatment solution, dried, embedded in resin, and mechanically polished to obtain cross-sections. The coating thickness was measured from the cross-sectional images. Quantitative analysis of P, N, Ca, Zn, Mn, C, and Fe was performed at a random location on the coating film (the center of the bead) 3 μm from the bead (position A in Figure 2) and 3 μm from the surface of the coating (position B in Figure 2). Quantitative analysis of P, N, Ca, Zn, Mn, C, and Fe was performed at a random location on the coating film (the center of the bead) 3 μm from the coating film (position C in Figure 3) and 3 μm from the surface of the coating (position D in Figure 3). For quantitative analysis, SEM-EDX (Hitachi High-Technologies Corporation SU6600 scanning electron microscope) was used to confirm the atomic percentages of each element. The analysis by SEM-EDX was carried out under the conditions of an acceleration voltage of 15 KV, an emission current of 90 μA, and a beam diameter of 20 nm.

[0111] [Corrosion resistance evaluation] Test pieces were cut to a width of 50mm and a length of 100mm, with 70mm of arc welding applied longitudinally to the plated surface. An accelerated corrosion test (CCT-JASO) was then carried out on the test pieces, and the CCT-JASO cycle (5 mass% salt spray (35°C, 2 hours) → dry (60°C, 4 hours) → wet (50°C, 95% RH or higher, 2 hours)) was measured at the point when the area ratio of red rust that had appeared in the bead and the area where the plating had disappeared exceeded 5%, to investigate the corrosion resistance of the test material. The evaluation criteria were as follows: Rating A: Red rust occurred on an area of over 5% for 150 cycles or more. Rating B: Red rust occurred on an area of over 5% for 150 cycles or more. Rating C: Red rust occurred on an area of over 5% for 90 cycles or more. Rating D: Red rust occurred on an area of over 5% for less than 90 cycles

[0112] Table 2 below shows the type of treatment solution used to form the coating, the type of coating, the atomic percentage ratio of the element Fe to the elements P, N, Ca, Zn, Mn, C, and Fe in the coating at a position 3 μm from the bead side in the coating thickness direction on the bead (position A in Figure 2) and a position 3 μm from the surface side of the coating (position B in Figure 2), the atomic percentage ratio of the element Zn to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating at a position 3 μm from the coating side in the coating thickness direction on the coating layer around the bead (position C in Figure 3) and a position 3 μm from the surface side of the coating (position D in Figure 3), and the corrosion resistance evaluation results for each steel.

[0113] In this experiment, a corrosion resistance rating of "C" or higher was deemed to have practical corrosion resistance and was therefore deemed to have passed the test.

[0114] [Table 2]

[0115] As is clear from Table 2 above, the examples corresponding to the examples of the present invention exhibit excellent corrosion resistance, while the examples corresponding to the comparative examples of the present invention exhibit poor corrosion resistance.

[0116] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Industrial Applicability]

[0117] The treatment liquid, which can further improve the corrosion resistance of welds in plated steel products and can easily repair welds anywhere, can further improve the corrosion resistance of plated steel products in which the base steel sheet is exposed by welding during forming, etc. For example, the steel member according to the present invention can be suitably used for steel members used in applications such as: 1) steel pipes, shaped steel, posts, beams, and transportation members for greenhouses or agricultural houses, 2) sound insulation walls, soundproof walls, sound absorption walls, snow protection walls, guardrails, balustrades, protective fences, and posts, and 3) railroad vehicle members, overhead line members, electrical equipment members, environmental safety members, structural members, and solar mounting stands. [Explanation of symbols]

[0118] 1 Steel parts 10. Plated steel sheet 20 Bead part (weld metal) 30 Paint film 101 Base material steel plate 103 plating layer 105 Plating loss area

Claims

1. A steel member having a bead portion formed by welding, The steel member is a plating layer provided on at least a part of a steel material serving as a base material; a coating film provided on the surface of the bead portion, a plating loss portion adjacent to the bead portion where the plating layer has disappeared, and at least a portion of the plating layer located around the plating loss portion; It has The coating film is The thickness is 10 to 100 μm, At least one acid component A selected from the group consisting of nitric acid and nitric acid compounds; a metal component B which is a metal or metal compound containing an element selected from the group consisting of Ca, Zn, and Mn; an organic resin component C containing a urethane resin; Fe and and In the coating film, the abundance ratio of the metal component B to the acid component A (metal component B / acidic component A) is 0.25 to 0.45 in terms of molar ratio, In the coating film located on the bead portion, a steel member, wherein a ratio of the element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film at a position 3 μm from the interface on the bead portion side in the coating film thickness direction is 5 to 20 atm %.

2. The steel member according to claim 1 , wherein the coating film further contains, as the acid component A, at least one selected from the group consisting of phosphoric acid and phosphoric acid compounds.

3. In the coating film located on the bead portion, 3. The steel member according to claim 1, wherein a ratio of the element Fe to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film at a position 3 μm from the interface on the surface layer side of the coating film in the coating film thickness direction is 5 atm % or less.

4. In the coating film located on the plating layer, 4. The steel member according to claim 1, wherein a ratio of the element Zn to a total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film at a position 3 μm from the interface on the plating layer side in a coating film thickness direction is 5 to 25 atm %.

5. In the coating film located on the plating layer, 5. The steel member according to claim 1, wherein a ratio of the element Zn to the total of the elements P, N, Ca, Zn, Mn, C, and Fe in the coating film at a position 3 μm from the interface on a surface layer side of the coating film in a coating film thickness direction is 7 atm % or less.

6. the coating film further contains a metal or a metal compound containing at least one element of Mg or Sr, The steel member according to any one of claims 1 to 5, wherein the amount of the metal or metal compound containing at least one element of Mg or Sr is 0.10 to 0.30 in terms of a molar ratio relative to the amount of the metal component B.

7. The steel member according to any one of claims 1 to 6, wherein the content of the organic resin component C in the coating film is 50 mass% or more.

8. The steel member according to any one of claims 1 to 7, wherein in the coating film, a concentration of the urethane resin in the organic resin component C is 50 mass% or more.

9. 9. The steel member according to claim 1, wherein the metal component B in the coating film has a molar abundance ratio [Zn] / ([Ca]+[Mn]) of 0.20 to 0.35, calculated based on the amounts of Zn, Ca, and Mn present in the coating film.

10. The steel member according to any one of claims 1 to 9, wherein in the coating film, a ratio of the total amount of the acid component A and the metal component B to 1 g of the organic resin component C is 0.010 to 0.025 mol / g.

11. The steel member according to any one of claims 1 to 10, wherein the plating layer is a plating layer comprising the following metal components and impurities: Zn: more than 65.0% by mass Al: more than 5.0 mass% and less than 25.0 mass% Mg: more than 2.0% by mass and less than 12.5% by mass Si: 0.1% by mass or more and 2.0% by mass or less

12. A treatment liquid for forming the coating film on a steel member according to any one of claims 1 to 11, Nitrate ions as acidic ions, at least one metal ion selected from the group consisting of Ca, Zn, and Mn; Urethane resin, Contains the molar ratio of the metal ions to the acidic ions is 0.25 to 0.45; The treatment solution has a pH of 1.0 to 3.

0.

13. The treatment liquid according to claim 12 , further comprising phosphate ions as the acidic ions.

14. The treatment liquid according to claim 12 or 13, further comprising at least one metal ion selected from the group consisting of Mg and Sr.

15. The method for manufacturing a steel member according to any one of claims 1 to 11, A method for producing a steel member, comprising: joining steel materials having a plating layer by welding; and then, without removing an oxide film on a bead portion formed by the welding, applying the treatment liquid according to any one of claims 12 to 14 to a surface of the bead portion, a surface of the plating loss portion adjacent to the bead portion, and a surface of at least a part of the plating layer located around the plating loss portion, and drying the treatment liquid to form the coating film.

16. A method for repairing a weld in a steel member manufactured using a steel material having a plating layer, comprising: A weld repair method comprising: joining steel materials having the plating layer by welding; applying the treatment liquid according to any one of claims 12 to 14 to the weld without removing an oxide film formed on the weld by the welding; and drying the treatment liquid to form a coating film.

Images