Method for coating steel materials and method for manufacturing steel products

Abstract

To provide a method for coating steel materials and a method for manufacturing steel products that can efficiently form a coating layer on the surface of steel materials that fully exhibits effects such as corrosion resistance and has a good appearance. [Solution] A method for covering the surface of a steel material with a thin metal sheet, comprising: a preparation step of laminating the thin metal sheet onto the surface of the steel material via a brazing material having a lower melting point than the thin metal sheet; a temporary welding step of irradiating the laminated material with laser light from the thin metal sheet side to partially melt the brazing material at multiple locations and temporarily fixing the steel material and the thin metal sheet by brazing; and a final welding step of irradiating the temporarily welded laminated material with laser light from the thin metal sheet side to completely melt the brazing material and fix the steel material and the thin metal sheet by brazing.

Description

【Technical Field】 【0001】 The present invention relates to a coating method for covering the surface of a steel material with a thin metal plate material and a method for manufacturing a steel product. 【Background Art】 【0002】 In recent years, in the global trend towards carbon neutrality, there is a demand for the active spread of biomass power generation and waste incineration power generation. The fuel sources used in these power generations are organic substances derived from plants and chemicals and contain chlorine and sulfur, which promotes the corrosion of the water pipes (boiler tubes) used in combustion boilers and leads to a reduction in their lifespan. As a result, it causes an increase in operating costs and hinders the spread of these power generation plants. Therefore, overlay welding of a metal having corrosion resistance on the surface of the water pipe has been carried out (for example, see Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2017-77603 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 However, when overlay welding is performed, the components of the water pipe may dissolve into the coating layer formed on the surface of the water pipe, diluting the components of the coating layer, and there is a risk that the corrosion resistance effect of the coating layer will decrease. In addition, the coating layer formed by overlay welding has a wavy shape, which causes deterioration in appearance. Furthermore, it takes time to form the coating layer. 【0005】 An object of the present invention is to provide a coating method for a steel material and a method for manufacturing a steel product that can efficiently form a coating layer on the surface of the steel material that sufficiently exhibits effects such as corrosion resistance and has good appearance. 【Means for Solving the Problems】 【0006】 The inventors of the present invention conducted various studies on methods for coating steel materials with metal materials and found that the above problem can be solved by laminating a thin metal sheet material onto the surface of the steel material via a brazing material with a lower melting point than the thin metal sheet material, partially melting the brazing material at multiple locations with a laser beam to temporarily fix it, and then completely melting the brazing material to braze and fix the steel material and the thin metal sheet material, thus completing the present invention. 【0007】 The gist of this invention is as follows: [1] A method for covering a steel material by covering the surface of the steel material with a thin metal sheet, A preparatory step of laminating the thin metal sheet material onto the surface of the steel material via a brazing material having a lower melting point than the thin metal sheet material, A temporary fixing welding process is performed in which a laser beam is irradiated from the metal sheet side of the laminated material to partially melt the brazing material at multiple locations, thereby brazing and temporarily fixing the steel material and the metal sheet material. The main welding process involves irradiating the laminated material that has been temporarily welded with a laser beam from the metal sheet material side to completely melt the brazing material, thereby brazing and fixing the steel material and the metal sheet material together. A method for coating steel materials, characterized by comprising the following: 【0008】 [2] The method for coating steel material according to [1] above, characterized in that the thickness of the thin metal sheet material is 0.1 to 3 mm. 【0009】 [3] The method for coating steel materials according to [1] or [2] above, characterized in that the melting point of the brazing material is 500 to 1300°C. 【0010】 [4] A method for coating steel materials according to any one of [1] to [3] above, characterized in that the brazing material is an alloy mainly composed of Ni. 【0011】 [5] A method for coating a steel material according to any one of [1] to [4] above, characterized in that the steel material is a tubular member, and the outer surface of the tubular member is covered with the thin metal sheet material. 【0012】 [6] A method for manufacturing steel products, characterized by manufacturing steel products using the method for coating steel materials described in any of [1] to [5] above. [Effects of the Invention] 【0013】 According to the present invention, a coating layer that exhibits sufficient effects such as corrosion resistance and has a good appearance can be efficiently formed on the surface of a steel material. [Brief explanation of the drawing] 【0014】 [Figure 1] (a) is a perspective view of a steel product manufactured using the steel coating method according to an embodiment of the present invention, and (b) is a perspective view of another steel product manufactured using the same steel coating method. [Figure 2] (a) is an explanatory diagram of the preparation process for the steel coating method according to the embodiment, (b) is an explanatory diagram of the temporary welding process for the steel coating method, and (c) is an explanatory diagram of the main welding process for the steel coating method. [Figure 3] This is an optical microscope image of a steel product manufactured using the steel coating method according to the same embodiment. [Figure 4] This is an optical microscope image of a steel product manufactured using the steel coating method described in the comparative example. [Modes for carrying out the invention] 【0015】 The present invention relates to a method for coating steel materials, comprising: a preparation step of laminating the thin metal sheet material onto the surface of the steel material via a brazing material having a lower melting point than the thin metal sheet material; a temporary welding step of irradiating the laminated material with laser light from the thin metal sheet material side to partially melt the brazing material at multiple locations and temporarily fixing the steel material and the thin metal sheet material by brazing; and a final welding step of irradiating the temporarily welded laminated material with laser light from the thin metal sheet material side to completely melt the brazing material and permanently fixing the steel material and the thin metal sheet material by brazing. 【0016】 The laser welding used in the method for coating a steel material of the present invention is a welding method that utilizes the energy of laser light. For example, compared with other welding methods such as TIG welding, it is a welding method with less heat input. As a method of laser welding, as long as the brazing material can be melted by irradiating laser light from the side of the metal thin plate material of the laminated material, it is not particularly limited. For example, in the temporary fixing welding process, scanner welding is preferable, and in the main welding process, laser heat treatment is preferable. This scanner welding is a method of performing welding by using a plurality of deflection mirrors to control the irradiation position of the laser light at high speed and with high precision, thereby enabling high-speed and high-quality welding. In laser heat treatment, it is desirable to have an optical system that can heat the metal surface with a uniform energy density over a wide area. 【0017】 The steel material products manufactured using the method for coating a steel material of the present invention are not particularly limited as long as the surface of the steel material is covered with a metal thin plate material. For example, finished products, semi-finished products (intermediate products), materials, etc. can be mentioned. Specifically, for example, it is preferably a product in which build-up welding, spraying, cladding, etc. have been conventionally performed on the surface of the steel material, and tubular members such as water pipes and evaporation pipes used in boilers (see Fig. 1(b)), plate-like members such as various panels, etc. can be mentioned (see Fig. 1(a)). 【0018】 The material of the steel material used in the method for coating a steel material of the present invention can be appropriately selected according to the use environment and use purpose of the steel material, etc., and is not particularly limited. For example, carbon steel and alloy steel (special steel) can be mentioned. Here, as carbon steel, those mainly composed of iron and carbon, for example, general structural rolled steel materials (SS materials), carbon steel materials for mechanical structures (SC materials), etc. can be mentioned. As alloy steel, in addition to iron and carbon, specific elements such as nickel, chromium, molybdenum, etc. are added to improve properties such as corrosion resistance and wear resistance. For example, alloy steel for mechanical structures such as chromium steel materials, nickel chromium steel materials, nickel chromium molybdenum steel materials, chromium molybdenum steel materials, manganese molybdenum steel materials, etc., and high-tensile steel (high-tensile steel), etc. can be mentioned. 【0019】 As the thin metal plate material used in the method for coating a steel material of the present invention, it can be appropriately selected according to the usage environment, usage purpose, etc. of the steel material, and is not particularly limited. For example, steel materials, stainless steel materials, copper materials, brass materials, nickel materials, Ni-based superalloy materials (such as Inconel (registered trademark)), titanium materials, aluminum materials, magnesium materials, cemented carbide materials (WC-Co), etc. can be mentioned. The thickness of this thin metal plate material is not particularly limited as long as the effect of the coating layer formed on the surface of the steel material can be obtained. For example, it is preferably 0.1 to 3 mm, more preferably 0.3 to 2.5 mm, even more preferably 0.5 to 2 mm, and particularly preferably 0.7 to 1.5 mm. 【0020】 The brazing material used in the method for coating a steel material of the present invention is preferably, for example, a foil-shaped (thin plate material) or paste-shaped member disposed between the steel material and the thin metal plate material. Its thickness (the interval between the surface of the steel material and the thin metal plate material: gap) is thinner than the thin metal plate material. For example, it is preferably 1 to 50 μm, more preferably 10 to 45 μm, and even more preferably 20 to 40 μm. 【0021】 The material of the brazing material is not particularly limited and can be appropriately selected according to the material of the thin metal plate material, etc. For example, a silver brazing material (Ag-based brazing material) which is an alloy mainly composed of Ag, a nickel brazing material (Ni-based brazing material) which is an alloy mainly composed of Ni, a copper brazing material (Cu-based brazing material), a brass brazing material (Cu-Zn-based brazing material), an aluminum brazing material (Al-based brazing material), etc. can be mentioned. As the components of these brazing materials, specifically, for example, the silver brazing material is Ag-Cu-Zn (possibly containing Sn, Ni, Mn, etc. further), the nickel brazing material is Ni-Cr-B-Si-Fe (possibly containing P further), the copper brazing material is pure Cu, Cu-Mn, Cu-Ni, etc., the brass brazing material is Cu-Zn (brass), and the aluminum brazing material is Al-Si. 【0022】 Here, suitable brazing materials for the thin metal sheets of each material described above include, specifically, for example: 1) in the case of steel, silver brazing material, nickel brazing material, copper brazing material, and brass brazing material; 2) in the case of stainless steel, silver brazing material and nickel brazing material; 3) in the case of copper, silver brazing material, copper brazing material, and brass brazing material; 4) in the case of brass, silver brazing material and brass brazing material; 5) in the case of nickel, silver brazing material and nickel brazing material; 6) in the case of Ni-based superalloy material, nickel brazing material; 7) in the case of titanium, silver brazing material; 8) in the case of aluminum, aluminum brazing material; 9) in the case of magnesium, silver brazing material; and 10) in the case of cemented carbide material, silver brazing material. 【0023】 The brazing material is not particularly limited as long as it has a lower melting point than the thin metal sheet material covering the surface of the steel material. Its melting point is preferably, for example, 500 to 1300°C, more preferably 900 to 1300°C, even more preferably 900 to 1200°C, and particularly preferably 900 to 1100°C. This allows for brazing while suppressing the melting of steel and thin metal sheets, thus enabling the thin metal sheet to be fixed to the surface of the steel while preventing components of the steel from dissolving into the thin metal sheet. 【0024】 According to the steel coating method of the present invention, a brazing material is placed between the steel material and the thin metal sheet, and a laser beam with a low heat input is used to partially melt the brazing material and perform tack welding. This suppresses the leaching of steel components into the thin metal sheet and also suppresses warping of the thin metal sheet that may occur due to heat effects during the subsequent main welding. Furthermore, even in the main welding, which welds the entire surface, a laser beam with a low heat input is used, thus suppressing the leaching of steel components into the thin metal sheet. Therefore, the effects of corrosion resistance and other properties of the coating layer formed on the surface of the steel material can be fully demonstrated, and a coating layer with a better appearance can be efficiently formed on the surface of the steel material compared to other welding methods such as arc welding and TIG welding. 【0025】 The present invention provides a method for coating steel materials, comprising a preparation step, a tack welding step, and a main welding step. However, other steps may be included before, after, or between each step. Specifically, for example, between the preparation step and the tack welding step, an oxygen-free atmosphere placement step may be included, in which the steel material, on which thin metal sheets are laminated via brazing material on the surface, is placed in a vacuum atmosphere or an inert atmosphere. This reduces the effects of oxidation and enables more stable coating. 【0026】 The following describes each step of the present invention. 【0027】 (preparation process) The preparation process involves laminating thin metal sheets onto the surface of the steel material, with a brazing material having a lower melting point than the thin metal sheets in between (see Figure 2(a)). In other words, it is a process of placing brazing material on the surface of the steel material and then placing thin metal sheets on top to form a laminate. 【0028】 It is preferable to adjust the shape of the thin metal sheet material by bending or cutting so that it conforms to (contacts) the surface shape of the steel material to be covered. Specifically, for example, if the surface shape of the steel material is curved, it is preferable to bend the thin metal sheet material to match the surface shape, and if it is flat, it is preferable to flatten the thin metal sheet material to match the surface shape, so that they are as close to each other as possible. If the brazing material is a foil-like thin sheet material, it is preferable to adjust its shape to match the area to be covered (thin metal sheet material), and if it is a paste, it is preferable to apply it evenly (without unevenness) to the surface of the steel material. 【0029】 Furthermore, in the tack welding and main welding processes described later, it is desirable to position and fix the thin metal sheet (and even the brazing material) so that its relative position to the surface of the steel material does not shift. Specifically, for example, one can cite an example of a method in which the laminated steel material and thin metal sheet (and even the brazing material) are positioned and fixed together using clamping devices such as vises, and by welding around them. Note that the positioning and fixing only needs to prevent the relative positions of the steel material and thin metal sheet (and even the brazing material), so it is preferable to remove the members used for positioning after the tack welding process or after the main welding process. 【0030】 (Temporary welding process) The tack welding process involves irradiating the laminated material with laser light from the metal sheet side to partially melt the brazing material at multiple points, thereby brazing the steel material and the metal sheet material together for temporary fastening (see Figure 2(b)). 【0031】 In this temporary welding process, as long as it can prevent warping of the thin metal sheet material in the main welding process described later, and especially prevent separation of the thin metal sheet material from the steel surface in the central region excluding the peripheral area when viewed from above, the process is not particularly limited. For example, this could involve spot melting the brazing material at equal or random intervals across the entire surface of the thin metal sheet material, or spot welding or continuous welding the edges of the thin metal sheet material. It is particularly preferable to partially melt more of the brazing material in areas where the thin metal sheet material is prone to separating from the steel surface material. In the tack welding process, methods such as scanner welding, welding using a processing device with a laser welding machine attached to a robot, or a handheld laser welding machine can be used. However, in order to partially melt the brazing material and suppress warping of the thin metal sheet in the subsequent main welding process, it is preferable to perform scanner welding, which allows for accurate welding to the precise location mentioned above. 【0032】 (Main welding process) This welding process involves irradiating the tack-welded laminated material with laser light from the metal sheet side to completely melt the brazing material, thereby brazing and fixing the steel material and the metal sheet material together (see Figure 2(c)). 【0033】 In this welding process, the method is not particularly limited as long as the thin metal sheet material is fixed to the surface of the steel material, that is, in a state where the thin metal sheet material does not peel off from the surface of the steel material. For example, it is preferable to continuously irradiate the thin metal sheet material with laser light to completely melt the brazing material over the entire surface. In this welding process, since the brazing material is completely melted by irradiating it with laser light, warping of the thin metal sheet material is likely to occur. Therefore, it is preferable to melt the brazing material with a lower-power laser beam than that used for tack welding. In this case, it is preferable to repeatedly irradiate the area irradiated with laser light multiple times. Furthermore, it is preferable to implement feedback control so that the surface of the thin metal sheet material can be heated to a constant temperature. 【0034】 From the above, steel products can be obtained, but if necessary, surface treatments such as polishing can be applied to the surface of the thin metal sheet material that has been coated with the steel material. [Examples] 【0035】 The following are examples of the present invention, but the technical scope of the present invention is not limited thereto. Here, we will describe a steel product in which a thin metal sheet is coated on the surface of a flat steel material, as shown in Figure 1(a), but the same applies to a steel product in which a thin metal sheet is coated on the surface of a cylindrical steel material, as shown in Figure 1(b). 【0036】 (preparation process) As shown in Figure 2(a), a thin metal sheet was laminated onto the surface of a steel material, with a brazing sheet having a lower melting point than the thin metal sheet in between. For the steel material, we used SS400 with a thickness of 6 to 10 mm. For the thin metal sheets, we used SUS304 with thicknesses of 1 mm and 2 mm, and Inconel® 625 with a thickness of 1 mm. As waxed sheet materials, BNi2 (Cr: 7 mass%, B: 3.2 mass%, Si: 4.5 mass%, Fe: 3 mass%, remainder Ni) and BNi9 (Cr: 15 mass%, B: 3.5 mass%, remainder Ni) were used. Furthermore, the broad surface of the brazed sheet material is approximately the same size as the metal sheet material used to cover the surface of the steel material. 【0037】 (Temporary welding process) As shown in Figure 2(b), a laser beam was irradiated from the metal sheet side of the laminated material to partially melt the brazed metal sheet at multiple locations, and the steel material and metal sheet were brazed together to temporarily fix them in place. Laser welding was performed at multiple points on the surface of the thin metal sheet at a predetermined pitch to prevent warping and separation from the steel surface during the main welding process described later. When SUS304 was used as the thin metal sheet, scanner welding was also performed. The laser welding conditions were set to an output of approximately 1 to 1.5 kW and an irradiation time of approximately 50 to 100 mm / s. 【0038】 (Main welding process) As shown in Figure 2(c), a laser beam was irradiated from the metal sheet side of the tack-welded laminated material to completely melt the brazed metal sheet, thereby brazing and fixing the steel material and the metal sheet together. Laser welding was performed continuously on the entire surface of the thin metal sheet. Furthermore, the laser welding was repeated multiple times on the same location. For laser welding, the power output was reduced compared to tack welding, to approximately 0.7-1.2 kW, and the welding speed was set to approximately 5-20 mm / s. This resulted in the steel product shown in Figure 1(a). 【0039】 (Test results) 1) When the thin metal sheet material is SUS304 We were able to bond thin metal sheets to the surface of steel materials. We confirmed that by placing a brazing sheet between the steel surface and the thin metal sheet and using laser light, it is possible to suppress the leaching of steel components into the thin metal sheet and form a coating layer with a good appearance on the steel surface. 【0040】 2) When the thin metal sheet material is Inconel® 625 As shown in Figure 3, the metal sheet material was successfully bonded to the steel surface while suppressing the melting of the brazed sheet material and the leakage of steel components into the metal sheet material. Figure 3 is an optical microscope image of the welding process in which feedback control was applied to heat the surface of the thin metal sheet to 1300°C, the welding speed was set to approximately 5 mm / s, and laser welding was repeated three times on the same location. Furthermore, ultrasonic testing (UT) was also performed, confirming that the thin metal sheet material was completely fixed to the surface of the steel material. 【0041】 Here, we will explain a comparative example in which only the main welding process was performed without the tack welding process, referring to Figure 4. Figure 4 is an optical microscope image of the main welding process in which feedback control was used to heat the surface of the thin metal sheet to 1200°C, the welding speed was set to about 10 mm / s, and laser welding was repeated five times on the same location. As shown in Figure 4, in the comparative example where the main welding process was performed without a tack welding process, when laser welding was performed in the main welding process, warping occurred in the thin metal sheet material, creating a gap between the steel material and the thin metal sheet material, making it impossible to fix the steel material and the thin metal sheet material together. 【0042】 As described above, it has been confirmed that by using the steel coating method of the present invention, a coating layer that exhibits sufficient effects such as corrosion resistance and has a good appearance can be efficiently formed on the surface of the steel material. 【0043】 Although the present invention has been described above with reference to embodiments, the present invention is not limited in any way to the configurations described in the embodiments described above, and includes other embodiments and modifications that can be considered within the scope of the matters described in the claims. For example, the scope of the present invention also includes cases where some or all of the above embodiments and modifications are combined to constitute the steel coating method and steel product manufacturing method of the present invention. [Industrial applicability] 【0044】 This invention is industrially useful because it can efficiently form a coating layer on the surface of a steel material that exhibits sufficient effects such as corrosion resistance and has a good appearance.

Claims

[Claim 1] A method for covering a steel material by covering the surface of the steel material with a thin metal sheet, A preparatory step of laminating the thin metal sheet material onto the surface of the steel material via a brazing material having a lower melting point than the thin metal sheet material, A temporary fixing welding process is performed in which a laser beam is irradiated from the metal sheet side of the laminated material to partially melt the brazing material at multiple locations, thereby brazing and temporarily fixing the steel material and the metal sheet material. The main welding process involves irradiating the laminated material that has been temporarily welded with a laser beam from the metal sheet material side to completely melt the brazing material, thereby brazing and fixing the steel material and the metal sheet material together. A method for coating steel materials, characterized by comprising the following: [Claim 2] The method for coating steel materials according to claim 1, characterized in that the thickness of the thin metal sheet material is 0.1 to 3 mm. [Claim 3] The method for coating steel materials according to claim 1, characterized in that the melting point of the brazing material is 500 to 1300°C. [Claim 4] The method for coating steel materials according to claim 1, characterized in that the brazing material is an alloy mainly composed of Ni. [Claim 5] The method for coating a steel material according to claim 1, characterized in that the steel material is a tubular member, and the outer surface of the tubular member is covered with the thin metal sheet material. [Claim 6] A method for manufacturing a steel product, characterized by manufacturing a steel product using a method for coating steel according to any one of claims 1 to 5.

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