Overlay welding method

Abstract

An overlay welding method is provided that can suppress the reduction of the dilution rate of the repair weld formed in the repair welding of a weld layer made of a cobalt-based alloy. A method for overlay welding on a member comprising a steel member and an overlay weld formed on the steel member, wherein an arc is generated between a welding torch and an overlay weld, the surface of the overlay weld is melted by the arc to form a molten pool, and the welding material of the steel member and the welding material of the cobalt-based alloy formed on the steel member are simultaneously inserted into the molten pool.

Description

Technology Field

[0001] The present disclosure relates to an overlay welding method. Background Technology

[0002] As a method for performing surface hardening treatment on steel, there is a method of performing overlay welding using a hard material.

[0003] Patent Document 1 discloses a valve device having a bearing having a sliding surface with respect to a valve rod, wherein the bearing has a plasma powder overlay welding layer made of a heat-resistant cobalt alloy formed on the sliding surface with respect to the valve rod, and the welding layer comprises a first welding layer formed on the surface of the bearing with a dilution rate of 5 to 25% and a second welding layer formed on the first welding layer with a dilution rate of 50% or less of the dilution rate of the first welding layer.

[0004] Patent Document 2 discloses a method for forming a hardened overlay layer, characterized by filling a metal hollow pipe of a predetermined length with hard particles, closing both ends of the hollow pipe, placing the hollow pipe horizontally on a metal base material, bringing a welding torch close to the upper part of the hollow pipe to generate an arc between the electrode and the hollow pipe, melting the surface of the hollow pipe and the base material by the arc to form a molten pool, flowing the unmelted hard particles from inside the hollow pipe into the molten pool due to the melting of the hollow pipe, and moving the welding torch along the hollow pipe to form a hardened overlay layer on the surface of the base material that follows the movement trajectory of the welding torch. Prior art literature

[0005] International Publication No. 2008 / 111150 and Japanese Patent Publication No. 2018-1172 The problem to be solved

[0006] For the sliding and contact surfaces of major valve components such as steam turbines, wear resistance is improved by overlay welding with a harder material, such as a cobalt-based alloy (e.g., Stellite). To suppress cracks caused by age hardening in the overlay weld, it is necessary to manage the dilution rate (a parameter indicating the extent to which base material components are dissolved into the weld metal). Although dilution rate management is also applied to repair welding of the overlay weld, the overlay weld is a cobalt-based alloy, and the cobalt-based alloy melts while the base material does not. For this reason, during the repair of the overlay weld, there is no dilution with the base material, making it difficult to keep the dilution rate within the specified range. The overlay welding methods of Patent Documents 1 and 2 disclose a method of welding to the material to be welded (base material), and the base material melts directly. However, when repair welding a weld layer made of a cobalt-based alloy, the base material (steel) is not melted directly, so there was a possibility that the dilution rate of the repair weld would decrease and cracks in the repair weld could not be suppressed.

[0007] The present disclosure is made to solve the above problem and aims to provide an overlay welding method capable of suppressing a decrease in dilution rate by adding a deficient component (e.g., Fe) to the welding material in a repair weld formed in a repair weld of a welding layer made of a cobalt-based alloy. means of solving the problem

[0008] A method for overlay welding on a member having a steel material according to the present disclosure and an overlay weld portion formed on the steel material, wherein an arc is generated between a welding torch and the overlay weld portion, the surface of the overlay weld portion is melted by the arc to form a molten pool, and a welding material of the steel material and a welding material of the cobalt alloy formed on the cobalt alloy are simultaneously inserted into the molten pool. Effects of the invention

[0009] According to the overlay welding method of the present disclosure, the reduction in the dilution rate of the repair weld formed in the repair welding of a cobalt-based alloy can be suppressed. Brief explanation of the drawing

[0010] FIG. 1 is an enlarged perspective view of the vicinity of the removal area in the overlay welding method of the first embodiment. FIG. 2 is an enlarged cross-sectional view of the vicinity of the molten pool in the overlay welding method of the first embodiment. FIG. 3 is an enlarged cross-sectional view of the vicinity of the molten pool in the overlay welding method of the second embodiment. Figure 4 is an enlarged cross-sectional view of the vicinity of the removal area of ​​Comparative Example 1. Figure 5 is an enlarged cross-sectional view of the area near the removal region of Comparative Example 2. Figure 6 is an enlarged cross-sectional view of the area near the removal region of Comparative Example 3. Specific details for implementing the invention

[0011] <First Embodiment>

[0012] Hereinafter, the overlay welding method of the present disclosure will be described. FIG. 1 is an enlarged perspective view of the vicinity of the removal area in the overlay welding method of the first embodiment.

[0013] The overlay welding method of the present disclosure is a method of overlay welding on a member (10) having a steel material (11) and an overlay weld portion (12) made of a cobalt-based alloy formed on the steel material (11). An arc is generated between a welding torch (50) and the overlay weld portion (12), and the surface of the overlay weld portion (12) is melted by the arc to form a molten pool. The welding material (21) of the steel material (11) and the cobalt-based alloy welding material (22) made of a cobalt-based alloy are simultaneously inserted into the molten pool. Here, the dilution rate is a parameter indicating how much of the steel component is dissolved in the weld metal. Generally, if the total amount of the welded metal (weld metal) is A and the amount of steel dissolved in the weld metal is B, it refers to a value calculated as B / A × 100 (%). However, when applying the above formula, the weld metal must be cut. Since cutting the actual product is not possible, the dilution rate in this disclosure is a value obtained as a percentage of the ratio of at least one component (Y) (e.g., Fe value) of the weld metal to at least one component (X) (e.g., Fe value) of the steel, and is calculated as Y / X × 100 (%). In addition, the weld metal in this disclosure refers to the metal of a repair weld joint formed by melting and welding a metal-based welding material (21) and a cobalt-based alloy welding material (22). Below, the overlay welding method of the first embodiment will be described.

[0014] (Absence (10))

[0015] The member (10) comprises a steel material (11) and an overlay weld (12) made of a cobalt alloy formed on the steel material (11).

[0016] (Steel)

[0017] The steel material (11) can be 9Cr stainless steel, 12Cr stainless steel, etc. The chemical composition of 9Cr stainless steel is, for example, C: 0.06~0.12 mass%, Si: 0.2~0.5 mass%, Mn: 0.3~0.6 mass%, P: 0.02 mass% or less, S: 0.01 mass% or less, Ni: 0.4 mass% or less, Cr: 8.0~9.5 mass%, Mo: 0.85~1.05 mass%, remainder: Fe and impurities. The chemical composition of 12Cr-based stainless steel is, for example, C: 0.06~0.13 mass%, Si: 0.5 mass% or less, Mn: 0.6 mass% or less, P: 0.03 mass% or less, S: 0.04 mass% or less, Ni: 0.5 mass% or less, Cr: 12.0~13.5 mass%, Mo: 0.6 mass% or less, and remainder: Fe and impurities.

[0018] (Overlay weld)

[0019] The overlay weld (12) is made of a cobalt-based alloy. The overlay weld (12) is a portion of the molten metal that solidified during welding, and the overlay weld (12) does not contain a heat-affected zone (a portion where heat is introduced between the steel (11) and the overlay weld (12). Here, a cobalt-based alloy is an alloy containing 50 mass% or more of cobalt. The overlay weld (12) is a weld formed by performing overlay welding, for example, on a steel (11) using a cobalt-based alloy welding material (22) made of a cobalt-based alloy. It is preferable that the overlay weld (12) be harder than the steel (11).

[0020] (Molten pool formation area)

[0021] The planned area for forming the molten pool (molten pool forming area) is located on the overlay weld (12). The molten pool forming area is preferably an area where, for example, a portion of the overlay weld (12) is removed so that the steel (11) is not exposed. Specifically, the molten pool forming area is a removed area (15) after removing a defective portion of the overlay weld (12) with a cutter or the like.

[0022] (Gonggeum-gye welding materials)

[0023] The welding material (21) has a chemical composition that is the same or nearly equivalent to the chemical composition of the steel (11). If the steel (11) is 9Cr stainless steel, a welding material having a chemical composition that is the same or nearly equivalent to the chemical composition of the 9Cr stainless steel of the steel (11) is used.

[0024] The shape of the metal welding material (21) is not particularly limited and, for example, can be a rod shape or a wire shape. It is preferable that the metal welding material (21) be in a rod shape. When the metal welding material (21) is in a rod shape or a wire shape, the diameter (d1) of the metal welding material (21) is not particularly limited. The diameter (d1) of the metal welding material (21) can be appropriately selected according to the purpose.

[0025] (Cobalt alloy welding material (22))

[0026] The cobalt-based alloy welding material (22) is made of a cobalt-based alloy. A cobalt-based alloy refers to an alloy in which the cobalt content is 50 mass% or more relative to the total mass. Stellite®, Tribaloy®, etc. can be used as the cobalt-based alloy welding material (22). As for Stellite, Stellite 1 (Cr: 31 mass%, W: 13 mass%, C: 2.3 mass%, Si: 1.3 mass%, remainder: Co), Stellite 6 (Cr: 28.5 mass%, W: 4.5 mass%, C: 1.1 mass%, Si: 1.2 mass%, remainder: Co), Stellite 12 (Cr: 28.5 mass%, W: 7.7 mass%, C: 1.4 mass%, Si: 1.2 mass%, remainder: Co), Stellite 20 (Cr: 35 mass%, W: 18 mass%, C: 3.2 mass%, Si: 0.6 mass%, remainder: Co), Stellite 21 (Cr: 26 mass%, C: 0.22 mass%, Ni: 3 mass%, Mo: 5.8 mass%, Examples include Si: 1.2 mass%, remainder: Co), Stellite 32 (Cr: 26 mass%, W: 13 mass%, C: 1.95 mass%, Si: 1.2 mass%, remainder: Co), etc. It is preferable that the cobalt-based alloy welding material (22) be the same as the material (welding material) used to form the overlay weld (12).

[0027] The shape of the cobalt-based alloy welding material (22) is not particularly limited and is, for example, rod shape or wire shape. It is preferable for the cobalt-based alloy welding material (22) to be rod shape. When the cobalt-based alloy welding material (22) is rod shape or wire shape, the diameter (d2) of the cobalt-based alloy welding material (22) is not particularly limited. The diameter (d2) of the cobalt-based alloy welding material (22) can be appropriately selected according to the purpose.

[0028] It is preferable that the ratio (d2:d1) of the diameter (d2) of the cobalt-based alloy welding material (22) and the diameter (d1) of the supply-based welding material (21) be 70:30 to 60:40. More preferably, the ratio of the diameter (d2) of the cobalt-based alloy welding material (22) and the diameter (d1) of the supply-based welding material (21) is 65:35 to 60:40. By setting the ratio of the diameter (d2) of the cobalt-based alloy welding material (22) and the diameter (d1) of the supply-based welding material (21) to the above range, the decrease in the dilution rate of the repair weld can be further suppressed.

[0029] (Welding torch (50))

[0030] A welding torch (50) is equipped with a nozzle (52) with an open tip and an electrode (51) positioned on the central axis of the nozzle (52). Preferably, the welding torch (50) is a TIG (Tungsten Inert Gas) welding torch. In the case of TIG welding, the electrode (51) is a tungsten electrode. In the case of TIG welding, an inert gas (such as Ar) is supplied into the nozzle (52). While supplying the inert gas, an arc is generated between the welding torch (50) and the overlay weld (12), and the surface of the overlay weld (12) is melted by the arc to form a molten pool.

[0031] Next, the welding conditions are described. FIG. 2 is an enlarged cross-sectional view of the vicinity of the molten pool in the overlay welding method of the first embodiment. As shown in FIG. 2, an arc is generated between a welding torch (50) and an overlay weld (12), and the surface of the overlay weld (12) is melted by the generated arc to form a molten pool (13), and a cobalt alloy welding material (22) consisting of a steel (11) and a cobalt alloy welding material (22) is simultaneously inserted into the molten pool (13). As the molten pool (13) solidifies, a repair weld can be formed in the removal area (15) of the overlay weld (12).

[0032] (Preheating)

[0033] In the overlay welding method of the first embodiment, it is preferable to preheat the area near the planned welding area (e.g., removal area (15)) of the member (10) before performing overlay welding. The preheating temperature is, for example, 200°C to 300°C. By performing preheating, cracks in the repair weld area and the surrounding base material can be suppressed.

[0034] (Arc welding)

[0035] In the overlay welding method of the first embodiment, the welding method is not particularly limited as long as it is arc welding that generates an arc. Examples of arc welding include TIG welding and plasma welding. TIG welding is particularly preferred as the arc welding method.

[0036] (Welding current)

[0037] The welding current of the overlay welding method according to the first embodiment is not particularly limited as long as overlay welding can be performed. The welding current is, for example, 50 to 100 A.

[0038] (Inert gas)

[0039] In the overlay welding method according to the first embodiment, it is preferable to supply an inert gas (shielding gas). For example, the inert gas is Ar. The flow rate of the shielding gas is not particularly limited. For example, the flow rate of the shielding gas is 8 to 12 L / min.

[0040] (Method of inserting the metal-based welding material (21) and the cobalt-based alloy welding material (22) into the molten pool)

[0041] In the first embodiment, it is preferable to insert the fused metal welding material (21) into the molten pool (13) while it is in contact with the cobalt-based alloy welding material (22). By inserting the fused metal welding material (21) into the molten pool (13) while it is in contact with the cobalt-based alloy welding material (22), the reduction in the dilution rate of the repair weld can be further suppressed. The method of bringing the fused metal welding material (21) and the cobalt-based alloy welding material (22) into contact is not particularly limited. For example, the fused metal welding material (21) may be brought into contact with the cobalt-based alloy welding material (22) by fixing the fused metal welding material (21) and the cobalt-based alloy welding material (22) using a jig.

[0042] In the first embodiment, it is preferable to insert the metal-based welding material (21) and the cobalt-based alloy welding material (22) into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the metal-based welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material are nearly equal. By inserting the metal-based welding material (21) and the cobalt-based alloy welding material (22) into the molten pool (13) in this manner, the deviation in the dilution rate of the repair weld can be further suppressed.

[0043] The method of inserting the metal-based welding material (21) and the cobalt-based alloy welding material (22) into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the metal-based welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material is not particularly limited. The distance from the surface of the molten pool (13) to the center of the metal-based welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material may be the same. For example, the metal-based welding material (21) and the cobalt-based alloy welding material (22) can be inserted into the molten pool (13) approximately simultaneously in the following method. First, the metal-based welding material (21) and the cobalt-based alloy welding material (22) are fixed with a jig or the like so that the metal-based welding material (21) is in contact with the cobalt-based alloy welding material (22). Then, they are inserted into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the metal-based welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) are approximately the same along the thickness direction of the base material. The center of the metal-based welding material (21) is the center in a cross-section perpendicular to the length direction of the metal-based welding material (21). If the metal-based welding material (21) is in the shape of a rod or a wire, the center of the metal-based welding material (21) is the center of a circle. Likewise, the center of the cobalt-based alloy welding material (22) is the center in a cross-section perpendicular to the length direction of the cobalt-based alloy welding material (22). When the cobalt-based alloy welding material (22) is in the shape of a rod or a wire, the center of the cobalt-based alloy welding material (22) is the center of a circle.

[0044] After welding is finished (after the repair weld is formed), heating (post-heating) may be performed using a gas burner or the like. The heating temperature is, for example, 300°C to 400°C. After post-heating, it is preferable to cool the member (10) at a low speed by covering it with a glass cloth or the like.

[0045] It is advisable to check the dilution rate after welding is completed or after slow cooling following post-heating. The dilution rate can be determined by measuring the value of a specific element (e.g., Fe) in the repair weld using a fluorescent X-ray measuring device for Positive Material Identification (PMI) inspection. The dilution rate is set appropriately according to the application. For example, the dilution rate is 10% or more to 30% or less.

[0046] (Effective effects)

[0047] In the first embodiment described above, when overlay welding made of a cobalt-based alloy, components lacking in the repair weld formed in the repair welding can be added to the welding material to suppress the decrease in the dilution rate. Furthermore, in the overlay welding method of the first embodiment, the bonded metal welding material (21) is inserted into the molten pool (13) while in contact with the cobalt-based alloy welding material (22). Therefore, the decrease in the dilution rate of the repair weld can be further suppressed. In addition, in the overlay welding method of the first embodiment, the bonded metal welding material (21) and the cobalt-based alloy welding material (22) are inserted into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the bonded metal welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material are nearly equal. Therefore, the deviation in the dilution rate of the repair weld can be suppressed.

[0048] <Second Embodiment>

[0049] Hereinafter, the overlay welding method of the present disclosure is described. Hereinafter, details differing from the first embodiment are described, and detailed descriptions common to the overlay welding method of the first embodiment are omitted.

[0050] (Method of inserting the metal-based welding material (21) and the cobalt-based alloy welding material (22) into the molten pool)

[0051] In the overlay welding method of the second embodiment, the fused metal welding material (21) is inserted into the molten pool (13) while in contact with the cobalt-based alloy welding material (22). By inserting the fused metal welding material (21) into the molten pool (13) while in contact with the cobalt-based alloy welding material (22), the reduction in the dilution rate of the repair weld can be further suppressed. The method of bringing the fused metal welding material (21) into contact with the cobalt-based alloy welding material (22) is not particularly limited. For example, the fused metal welding material (21) may be brought into contact with the cobalt-based alloy welding material (22) by fixing the fused metal welding material (21) and the cobalt-based alloy welding material (22) using a jig.

[0052] One of the metal-based welding material (21) and the cobalt-based alloy welding material (22) is first inserted into the molten pool (13). Even if one of the metal-based welding material (21) and the cobalt-based alloy welding material (22) is first inserted into the molten pool (13), the reduction in the dilution rate of the repair weld can be suppressed.

[0053] The method of first inserting either the base metal welding material (21) or the cobalt-based alloy welding material (22) into the molten pool (13) is not particularly limited. For example, either the base metal welding material (21) or the cobalt-based alloy welding material (22) can be first inserted into the molten pool (13) in the following method. First, the base metal welding material (21) and the cobalt-based alloy welding material (22) are fixed with a jig or the like so that the base metal welding material (21) is in contact with the cobalt-based alloy welding material (22). Then, they are inserted into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the base metal welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) are different along the thickness direction of the base material.

[0054] (Effective effects)

[0055] In the second embodiment described above, when repair welding of an overlay weld (12) made of a cobalt-based alloy, components lacking in the repair weld formed during the repair welding can be added to the welding material to suppress the decrease in the dilution rate. Furthermore, in the overlay welding method of the second embodiment, the so-called welding material (21) is inserted into the molten pool (13) while in contact with the cobalt-based alloy welding material (22). Therefore, the decrease in the dilution rate of the repair weld can be further suppressed. In addition, in the overlay welding method of the second embodiment, either the so-called welding material (21) or the cobalt-based alloy welding material (22) is inserted into the molten pool (13) first. When inserted in this way, the amount of melting of either the so-called welding material (21) or the cobalt-based alloy welding material (22) increases, so the insertion method can be appropriately changed according to the shape of the weld part or the dilution rate. Even if one side is inserted into the molten pool (13) first, the overlay welding method according to the second embodiment can suppress the decrease in the dilution rate of the repair weld.

[0056] The overlay welding method of the present disclosure has been described above. According to the overlay welding method of the present disclosure, when repair welding of an overlay weld made of a cobalt-based alloy, the decrease in the dilution rate of the repair weld formed during the repair welding can be suppressed.

[0057] Furthermore, the technical scope of the present invention is not limited to the above embodiments, and various modifications are possible within the scope that does not depart from the spirit of the present invention. Additionally, it is appropriate to replace the components in the above embodiments with well-known components within the scope that does not depart from the spirit of the present invention.

[0058] Examples

[0059] Next, embodiments of the present invention will be described. The conditions in the embodiments are one example of conditions adopted to verify the feasibility and effects of the present invention, and the present invention is not limited to this one example of conditions. The present invention may adopt various conditions as long as the objectives of the present invention are achieved without departing from the gist of the present invention.

[0060] (Example 1)

[0061] The member (10) was prepared by forming an overlay weld (12) on a 9Cr-based stainless steel (9.0% Cr-1.0% Mo steel (ASTMA182MF91)) or 12Cr-based stainless steel of steel material (11). The composition of the steel material (11) is shown in Table 1. The overlay weld (12) of Example 1 was formed by plasma powder overlay welding using a powder of Co: 55 mass%, Cr: 25 mass%, and Ni: 3 mass%. Subsequent examples show results for 9Cr-based stainless steel.

[0062]

[0063] The metal-based welding material (21) was prepared having the same chemical composition as the steel (11). The cobalt-based alloy welding material (22) was prepared as a welding rod with Co: 55 mass%, Cr: 25 mass%, and Ni: 3 mass%, which was used to form the overlay weld (12). Both the cobalt-based alloy welding material (22) and the metal-based welding material (21) are in the form of rods, and the ratio of the diameter of the cobalt-based alloy welding material (22) to the diameter of the metal-based welding material (21) (diameter of the cobalt-based alloy welding material (22): diameter of the metal-based welding material (21)) was set to 60:40. In addition, the metal-based welding material (21) was fixed to the cobalt-based alloy welding material (22) with a jig. First, a portion of the overlay weld (12) on the surface of the member (10) was removed so that the steel (11) was not exposed, thereby forming a removal area (15). Next, the removal area (15) was heated to 200~300°C with a gas burner. The removal area (15) was confirmed to not expose the steel material (11) using a fluorescent X-ray measuring device for PMI inspection.

[0064] After heating, a welding torch (electrode: tungsten) (50) is brought close to the removal area (15), and an arc is generated between the welding torch (50) and the removal area (15) to melt the surface of the overlay weld (12) by the arc, thereby forming a molten pool (13).

[0065] After forming the molten pool (13), the fused metal welding material (21) and the cobalt-based alloy welding material (22) were simultaneously inserted into the molten pool (13). Specifically, as shown in FIG. 2, they were inserted into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the fused metal welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material were approximately the same. The welding current was set to 50 to 100 A, and Ar was used as the shielding gas at a rate of 8 to 12 L / min. A repair weld was formed by this welding.

[0066] (Example 2)

[0067] The member (10), the metal-based welding material (21), and the cobalt-based alloy welding material (22) were prepared to be the same as in Example 1. A portion of the overlay weld (12) on the surface of the member (10) was removed so that the steel (11) was not exposed, thereby forming a removal area (15). Subsequently, the removal area (15) was heated to 200 to 300°C using a gas burner. The removal area (15) was confirmed to not expose the steel (11) using a fluorescent X-ray measuring device for PMI inspection.

[0068] After heating, a welding torch (electrode: tungsten) (50) is brought close to the removal area (15), and an arc is generated between the welding torch (50) and the removal area (15) to melt the surface of the overlay weld (12) by the arc, thereby forming a molten pool (13).

[0069] After forming the molten pool (13), the fused metal welding material (21) and the cobalt-based alloy welding material (22) were simultaneously inserted into the molten pool (13). Specifically, as shown in FIG. 3, the fused metal welding material (21) was placed below the cobalt-based alloy welding material (22) so that the fused metal welding material (21) entered the molten pool (13) before the cobalt-based alloy welding material (22). The welding current was set to 50 to 100 A, and Ar was used as the shielding gas at a rate of 8 to 12 L / min. A repair weld was formed by this welding.

[0070] (Comparative Example 1)

[0071] The member (10) and the cobalt-based alloy welding material (22) were prepared to be the same as those in Example 1. As shown in FIG. 4, in Comparative Example 1, only the cobalt-based alloy welding material (22) was prepared. A portion of the overlay weld (12) on the surface of the member (10) was removed so that the steel (11) was not exposed, thereby forming a removal area (15). Subsequently, the removal area (15) was heated to 200 to 300°C using a gas burner. The removal area (15) was confirmed to not expose the steel (11) using a fluorescent X-ray measuring device for PMI inspection.

[0072] After heating, a welding torch (electrode: tungsten) (50) is brought close to the removal area (15), and an arc is generated between the welding torch (50) and the removal area (15) to melt the surface of the overlay weld (12) by the arc, thereby forming a molten pool (13).

[0073] After forming the molten pool (13), only the cobalt-based alloy welding material (22) was inserted into the molten pool (13) to form a repair weld. The welding current was set to 50 to 100 A, and Ar was used as the shielding gas at a rate of 8 to 12 L / min.

[0074] (Comparative Example 2)

[0075] The member (10) and the cobalt-based alloy welding material (22) were prepared to be the same as those in Example 1. As shown in FIG. 5, in Comparative Example 2, a portion of the overlay weld (12) on the surface of the member (10) was removed to expose the steel (11), thereby forming a removal area (15). Subsequently, the removal area (15) was heated to 200 to 300°C using a gas burner. The removal area (15) was confirmed to have the steel (11) exposed using a fluorescent X-ray measuring device for PMI inspection.

[0076] After heating, a welding torch (electrode: tungsten) (50) is brought close to the removal area (15), and an arc is generated between the welding torch (50) and the removal area (15) to melt the surface of the overlay weld (12) by the arc, thereby forming a molten pool (13).

[0077] After forming the molten pool (13), only the cobalt-based alloy welding material (22) was inserted into the molten pool (13) to form a repair weld. The welding current was set to 50 to 100 A, and Ar was used as the shielding gas at a rate of 8 to 12 L / min.

[0078] (Comparative Example 3)

[0079] The member (10) was prepared to be the same as in Example 1. As shown in FIG. 6, in Comparative Example 3, the cobalt-based alloy welding material (22) was replaced with a cobalt-based alloy welding material (22a). Specifically, the cobalt-based alloy welding material (22a) is a cobalt-based alloy welding material containing Fe to satisfy the dilution rate.

[0080] As in Example 1, a portion of the overlay weld (12) on the surface of the member (10) was removed so that the steel (11) was not exposed, thereby forming a removal area (15). Subsequently, the removal area (15) was heated to 200 to 300°C using a gas burner. It was confirmed that the steel (11) was not exposed in the removal area (15) using a fluorescent X-ray measuring device for PMI inspection.

[0081] After heating, a welding torch (50) (electrode: tungsten) is brought close to the removal area (15), and an arc is generated between the welding torch (50) and the removal area (15) to melt the surface of the overlay weld (12) by the arc, thereby forming a molten pool (13).

[0082] After forming the molten pool (13), only the cobalt-based alloy welding material (22) was inserted into the molten pool (13) to form a repair weld. The welding current was set to 50 to 100 A, and Ar was used as the shielding gas at a rate of 8 to 12 L / min.

[0083] (Surface dilution rate)

[0084] The surface dilution rate of the repair welds of Examples 1 and 2 and Comparative Examples 1 to 3 was measured. The measurement was performed by component analysis using a fluorescent X-ray device for PMI inspection. Specifically, the Fe content on the surface of the repair weld was measured using Olympus VANTA, and the surface dilution rate was evaluated based on the obtained iron (Fe) content value. The results obtained are shown in Table 2. A surface dilution rate within the range of 10–30% was classified as Good, and outside this range as Bad.

[0085] (Cross-sectional dilution rate)

[0086] The cross-sectional dilution rate of the repair welds of Examples 1 and 2 and Comparative Examples 1 to 3 was measured. The measurement was performed by component analysis using a fluorescent X-ray device for PMI inspection. The repair welds were cut using Olympus VANTA, and the cross-sectional dilution rate was evaluated by measuring the iron (Fe) content in the obtained cross-section. The results obtained are shown in Table 2. A cross-sectional dilution rate within the range of 10–30% was classified as Good, and outside this range as Bad.

[0087] (Cross-section observation)

[0088] The cross-sections of the repair welds of Examples 1 and 2 and Comparative Examples 1 to 3 were observed. The observation was performed using a scanning electron microscope. The results obtained are shown in Table 2. In the cross-sectional observation, "Good" was defined as having no welding defects (defects such as cracks), and "Bad" as having welding defects.

[0089]

[0090] As shown in Table 2, Examples 1 and 2, which satisfy the conditions of the overlay welding method of the present disclosure, passed the surface dilution rate, cross-sectional dilution rate, and cross-sectional observation. In addition, in the case of Example 1, the deviation in the dilution rate when welding was performed at 6 locations was within ±0.5%, while in the case of Example 2, the deviation in the dilution rate when welding was performed at 6 locations was within ±2.0%. Therefore, it was confirmed that the deviation in the dilution rate can be reduced by inserting into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the base metal welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) along the thickness direction of the base material are approximately the same. It was also confirmed that the same result is obtained even when the steel material (11) is 12Cr-based stainless steel.

[0091] In Comparative Example 1, the surface dilution rate fell below the lower limit of the surface dilution rate because welding was performed on the overlay weld (12) using a cobalt-based alloy welding material (22). In Comparative Example 2, welding was performed after removing the steel (11) until it was exposed, so the surface dilution rate was acceptable, but the surface dilution rate of the first layer exceeded the upper limit of the cross-sectional dilution rate. In Comparative Example 3, there were defective parts when observing the cross-section.

[0092] From the above results, it has been confirmed that by using the overlay welding method of the present disclosure, the reduction in the dilution rate of the repair weld formed in the repair welding of cobalt-based alloys can be suppressed.

[0093] <Appendix>

[0094] The overlay welding method described in the above embodiment can be understood as follows.

[0095] (1) An overlay welding method according to the first embodiment of the present disclosure is a method of overlay welding on a member (10) having a steel member (11) and an overlay weld portion (12) made of a cobalt-based alloy formed on the steel member (11), wherein an arc is generated between a welding torch (50) and the overlay weld portion (12), and the surface of the overlay weld portion (12) is melted by the arc to form a molten pool (13), and the cobalt-based alloy welding material (21) of the steel member (11) and the cobalt-based alloy welding material (22) made of a cobalt-based alloy are simultaneously inserted into the molten pool (13).

[0096] By doing so, the decrease in the dilution rate of the repair weld formed in the repair welding of cobalt-based alloys can be suppressed.

[0097] (2) The overlay welding method according to the second embodiment of the present disclosure is the overlay welding method of (1), wherein the shape of the metal-based welding material (21) is a rod shape or a wire shape and the shape of the cobalt-based alloy welding material (22) is a rod shape or a wire shape.

[0098] By doing this, the reduction in the dilution rate of the repair weld formed in the repair welding of the cobalt-based alloy can be further suppressed. In addition, since the amount of melting of either the welding material of the alloy (21) or the welding material of the cobalt-based alloy (22) increases, the insertion method can be appropriately changed according to the shape of the weld part or the dilution rate.

[0099] (3) The overlay welding according to the second embodiment of the present disclosure is an overlay welding method of (2), wherein the ratio of the diameter of the cobalt-based alloy welding material (22) to the diameter of the above-mentioned metal-based welding material (21) is 70:30 to 60:40.

[0100] By doing so, the reduction in the dilution rate of the repair weld formed in the repair welding of cobalt-based alloys can be further suppressed.

[0101] (4) The overlay welding method according to the fourth embodiment of the present disclosure is one of the overlay welding methods of (1) to (3), wherein a metal-based welding material (21) is inserted into the molten pool (13) while in contact with a cobalt-based alloy welding material (22).

[0102] By doing so, the reduction in the dilution rate of the repair weld formed in the repair welding of cobalt-based alloys can be further suppressed.

[0103] (5) The overlay welding method according to the fifth embodiment of the present disclosure is the overlay welding method of (4), wherein a metal-based welding material (21) and a cobalt-based alloy welding material (22) are inserted into the molten pool (13) such that the distance from the surface of the molten pool (13) to the center of the metal-based welding material (21) and the distance from the surface of the molten pool (13) to the center of the cobalt-based alloy welding material (22) are nearly equal along the thickness direction of the steel material (11).

[0104] By doing so, the deviation in the dilution rate of the repair weld formed in the repair welding of cobalt-based alloys can be suppressed.

[0105] (6) The overlay welding method according to the 6th embodiment of the present disclosure is an overlay welding method of any one of (1) to (5), and the molten pool (13) is to be formed in an area heated to 200°C to 300°C.

[0106] By doing this, cracks in the repair weld and surrounding base material can be suppressed.

[0107] (7) The overlay welding method according to the seventh embodiment of the present disclosure is the overlay welding method of (6), wherein the area is an area in which a portion of the overlay weld (12) is removed so that the steel (11) is not exposed.

[0108] By doing this, the defective part of the overlay weld (12) can be repaired while removed.

[0109] (8) The overlay welding method according to the eighth embodiment of the present disclosure is an overlay welding method of any one of (1) to (7), wherein the cobalt-based alloy welding material (22) is the same as the material used to form the overlay weld (12).

[0110] By doing this, the difference in composition between the repair weld and the overlay weld (12) can be reduced.

[0111] (9) The overlay welding method according to the ninth embodiment of the present disclosure is an overlay welding method of any one of (1) to (8), wherein the steel material (11) is 9Cr stainless steel or 12Cr stainless steel.

[0112] By doing this, the member (10) can obtain excellent room temperature and high temperature characteristics. Explanation of the symbols

[0113] 10 absence 11 steel 12 Overlay Welds 13 Molten Pool 15 removal area 21 Welding materials for the metalwork system 22 Cobalt-based alloy welding materials 50 welding torches 51 electrode 52 nozzles

Claims

Claim 1 A method for overlay welding on a member comprising a steel member and an overlay weld portion formed on the steel member, the method comprising generating an arc between a welding torch and the overlay weld portion, melting the surface of the overlay weld portion by the arc to form a molten pool, simultaneously inserting a welding material of the steel member and a welding material of the cobalt alloy formed on the cobalt alloy into the molten pool, wherein the shape of the welding material of the steel member is a rod shape or a wire shape and the shape of the cobalt alloy welding material is a rod shape or a wire shape, and the welding material of the steel member is inserted into the molten pool while in contact with the cobalt alloy welding material. Claim 2 An overlay welding method according to claim 1, wherein the ratio of the diameter of the cobalt-based alloy welding material to the diameter of the porcelain-based welding material is 70:30 to 60:

40. Claim 3 An overlay welding method according to claim 1, wherein the above-mentioned metal-based welding material and the above-mentioned cobalt-based alloy welding material are inserted into the molten pool such that the distance from the surface of the molten pool to the center of the metal-based welding material along the thickness direction of the steel material and the distance from the surface of the molten pool to the center of the cobalt-based alloy welding material are nearly identical. Claim 4 An overlay welding method according to claim 1, wherein the area where the molten pool is to be formed is heated to 200℃ to 300℃. Claim 5 In paragraph 4, an overlay welding method wherein the area is an area in which a portion of the overlay weld is removed so as not to expose the steel material. Claim 6 In claim 1, the overlay welding method in which the cobalt-based alloy welding material is the same as the material used to form the overlay weld. Claim 7 An overlay welding method according to claim 1, wherein the steel material is 9Cr-based stainless steel or 12Cr-based stainless steel. Claim 8 delete Claim 9 delete

Images