Welded component and method for manufacturing welded component

Abstract

To provide a welded component where a member composed of copper and a member composed of a chromium-based stainless steel are joined to each other by welding, which improves strength of a welded part.SOLUTION: A welded component includes a first member composed of chromium-based stainless steel, a second member composed of copper, and a welded part for joining the first member and the second member. The welded part includes a first region containing an element contained in the chromium-based stainless steel constituting the first member as a main component, and a second region which is arranged so as to form an interface between the first region and the second region, and contains copper as a main component. In the second region, a plurality of first island regions containing the element contained in the chromium-based stainless steel constituting the first member as a main component exist while being separated from each other. In the first region, a plurality of second island regions containing copper as a main component exist while being separated from each other. The first region and the second region form a metal bond on the interface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to welded components and methods for manufacturing welded components. [Background technology]

[0002] Techniques for joining copper and steel members by welding have been known for some time, and it is also known that a copper-iron alloy can be used as a filler rod (filler material) for welding (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2016-087688 [Patent Document 2] Japanese Patent Publication No. 2020-076136 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, a copper member and a steel member can be joined by welding using conventional techniques. However, when a copper member and a chromium-based stainless steel member are joined by welding, there is a problem that the strength of the welded joint is insufficient.

[0005] Therefore, one of the objects of the present disclosure is to improve the strength of the welded portion in a welded component in which a member made of copper and a member made of chromium-based stainless steel are joined by welding. [Means for solving the problem]

[0006] A welded component according to the present disclosure includes a first member made of chromium-based stainless steel, a second member made of copper, and a weld joint joining the first member and the second member. The weld joint includes a first region whose main component is an element contained in the chromium-based stainless steel that constitutes the first member, and a second region whose main component is copper and is arranged to form an interface between the first region and the second region. Within the second region, a plurality of first island-shaped regions whose main component is an element contained in the chromium-based stainless steel that constitutes the first member are present and separated from one another. Within the first region, a plurality of second island-shaped regions whose main component is copper are present and separated from one another. The first region and the second region form a metallic bond at the interface.

[0007] A method for manufacturing a welded component according to the present disclosure includes the steps of: preparing a first member made of chromium-based stainless steel and a second member made of copper; forming an arc between an electrode and the first and second members, supplying a filler metal into the arc, and heating and melting the first and second members and the filler metal with the arc to form a molten pool; and solidifying the molten pool to form a weld that joins the first and second members. The filler metal contains 4.0% to 4.9% by mass of iron, with the remainder consisting of copper and unavoidable impurities. [Effects of the Invention]

[0008] According to the above-described welded part and manufacturing method for the welded part, in which a member made of copper and a member made of chromium-based stainless steel are joined by welding, the strength of the welded portion can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the structure of a welded part according to an embodiment. [Figure 2] FIG. 2 is a schematic enlarged view of part A in FIG. [Figure 3] FIG. 3 is a schematic enlarged view of part B in FIG. [Figure 4]FIG. 4 is a flowchart showing an outline of the method for manufacturing a welded component according to the embodiment. [Figure 5] FIG. 5 is a schematic front view for explaining the method for manufacturing the welded component according to the embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view for explaining the method for manufacturing the welded component according to the embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the structure of a welded part according to a modified example. [Figure 8] FIG. 8 is a schematic cross-sectional view for explaining a method for manufacturing a welded component according to a modified example. [Figure 9] FIG. 9 is a photograph showing the state of the test piece as a welded part after the tensile test. [Figure 10] FIG. 10 is a schematic cross-sectional view of the test piece used in the experiment. [Figure 11] FIG. 11 is an optical microscope photograph showing the metal structure of a portion corresponding to portion C in FIG. [Figure 12] FIG. 12 is an enlarged photograph showing the analysis results of the element distribution in the Z1 portion of FIG. [Figure 13] FIG. 13 is an enlarged photograph showing the analysis results of the element distribution in the Z2 portion of FIG. [Figure 14] FIG. 14 is an enlarged photograph showing the analysis results of element distribution in the Z3 portion of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Outline of the embodiment] The welded component of the present disclosure includes a first member made of chromium-based stainless steel, a second member made of copper, and a weld that joins the first member and the second member. The weld includes a first region whose main component is an element contained in the chromium-based stainless steel that constitutes the first member, and a second region whose main component is copper and that is disposed so as to form an interface between the first region and the second region. Within the second region, a plurality of first island-shaped regions whose main component is an element contained in the chromium-based stainless steel that constitutes the first member are present and separated from one another. Within the first region, a plurality of second island-shaped regions whose main component is copper are present and separated from one another. The first region and the second region form a metallic bond at the interface.

[0011] The present inventors have investigated ways to improve the strength of a welded joint in a welded component in which a copper member and a chromium-based stainless steel member are joined by welding, and have obtained the following findings.

[0012] When joining a member made of copper and a member made of chromium-based stainless steel by welding, it is difficult to form a weld in which copper and chromium-based stainless steel are uniformly mixed because copper and iron do not easily form a solid solution. Therefore, the weld has a first region whose main component is an element contained in the chromium-based stainless steel and a second region whose main component is copper, and an interface is formed between the first region and the second region.

[0013] In the welded component of the present disclosure, a plurality of first island regions, each composed primarily of an element contained in the chromium-based stainless steel, are present and separated from one another within the second region. A plurality of second island regions, each composed primarily of copper, are present and separated from one another within the first region. The first region and the second region form a metallic bond at the interface. As a result, the welded component of the present disclosure, in which a member made of copper and a member made of chromium-based stainless steel are joined by welding, can have an improved weld strength.

[0014] In the welded component, the chromium-based stainless steel may be a ferritic stainless steel. Ferritic stainless steel is suitable as the chromium-based stainless steel that constitutes the first member in the welded component of the present disclosure.

[0015] In the welded component, the ferritic stainless steel may be JIS standard SUS430 series stainless steel, which is suitable as the ferritic stainless steel constituting the first member in the welded component of the present disclosure.

[0016] In the above welded part, the first member and the second member may have a tubular shape. A longitudinal end of either the first member or the second member may include a joint portion into which an insertion portion, which is the longitudinal end of the other member, is inserted. The first member and the second member may be joined to each other by a weld at the end of the joint portion, with the insertion portion inserted into the joint portion. In welded parts in which members having tubular shapes are joined together, the strength of the weld may be an issue due to the influence of fluid flowing inside, the influence of vibration, and the like. The welded part of the present disclosure, which has improved strength at the weld, is suitable for application to such parts.

[0017] In the above welded component, the insert portion may be included in the first member, and the joint portion may be included in the second member. This structure is suitable as a joining structure between a first member made of chromium-based stainless steel and a second member made of copper.

[0018] The method for manufacturing a welded component of the present disclosure includes the steps of: preparing a first member made of chromium-based stainless steel and a second member made of copper; forming an arc between the first member, the second member, and an electrode, supplying a filler metal into the arc, heating the first member, the second member, and the filler metal with the arc to melt them and form a molten pool; and solidifying the molten pool to form a weld that joins the first member and the second member. The filler metal contains 4.0% to 4.9% by mass of iron, with the remainder consisting of copper and unavoidable impurities.

[0019] According to the inventors' investigations, by using a filler metal in arc welding containing 4.0 mass % to 4.9 mass % iron, with the remainder being copper and unavoidable impurities, it is easy to achieve a state in which a plurality of first island regions are present separately from one another in the second region, and a plurality of second island regions are present separately from one another in the first region, and the first region and the second region form a metallurgical bond. Therefore, the manufacturing method for a welded part of the present disclosure can improve the strength of the weld in a welded part in which a copper member and a chromium-based stainless steel member are joined by welding.

[0020] [Details of the embodiment] Next, an example of an embodiment of the welded component 10 of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated.

[0021] Fig. 1 is a schematic cross-sectional view showing the structure of a welded part 10 according to an embodiment. Fig. 2 is an enlarged view of part A in Fig. 1, and is a schematic view showing a welded part 3. Fig. 3 is an enlarged view of part B in Fig. 2, and is a schematic view showing the structure of the welded part 3. Referring to Fig. 1, the welded part 10 of this embodiment includes a first member 1 made of chromium-based stainless steel, a second member 2 made of copper, and a welded part 3 that joins the first member 1 and the second member 2 together.

[0022] The chromium-based stainless steel constituting the first member 1 is stainless steel containing chromium but not nickel, such as ferritic stainless steel. Examples of ferritic stainless steel include JIS standard SUS430 stainless steel (JIS G 4304:2012 and JIS G 4305:2012). Ferritic stainless steel includes JIS standard SUS430 stainless steel, as well as SUS405, SUS410L, SUS429, SUS434, SUS436L, SUS436J1L, SUS443J1, SUS444, SUS445J1, SUS445J2, SUS447J1, and SUSXM27. JIS standard SUS430 stainless steel includes JIS standard SUS430 and those with a symbol at the end of the standard. For example, SUS430, SUS430LX, SUS430J1L, and SUS430F fall under the category of "JIS standard SUS430 stainless steel." Furthermore, the chromium-based stainless steel constituting the first member 1 is not limited to ferritic stainless steel, but may be martensitic stainless steel. The second member 2 is made of pure copper, that is, copper with a purity of 99.9% by mass or more.

[0023] Here, in the present disclosure, "nickel-free" includes those that can be considered to be nickel-free, and is not "nickel-free" in the strict sense. For example, in a stainless steel containing chromium, if the nickel content is 1 mass% or less, it falls into the category of chromium-based stainless steel.

[0024] The first member 1 comprises a first main body portion 11 and a joint portion 12. The joint portion 12 is a portion into which the longitudinal end portion of the second member 2 is inserted. In this embodiment, the portion of the second member 2 that is inserted into the joint portion 12 is referred to as the "insertion portion 22." The joint portion 12 extends from the longitudinal end portion of the first main body portion 11 along the central axis. The joint portion 12 is included in the longitudinal end portion of the first member 1.

[0025] In the first member 1, the first main body portion 11 includes an outer peripheral surface 111 and an inner peripheral surface 112. The outer peripheral surface 111 has a cylindrical surface shape. The inner peripheral surface 112 has a cylindrical surface shape that shares a central axis with the outer peripheral surface 111. The outer peripheral surface 111 and the inner peripheral surface 112 are concentrically arranged when viewed along the central axis. The first member 1 has a flow path (hereinafter, sometimes referred to as a first flow path 13) that is formed by being surrounded by the inner peripheral surface 112. The first member 1 has a tubular shape. The first member 1 is a pipe made of chromium-based stainless steel.

[0026] The joint portion 12 includes an outer peripheral surface (hereinafter referred to as the "joint outer peripheral surface 121") and an inner peripheral surface (hereinafter referred to as the "joint inner peripheral surface 122"). The joint outer peripheral surface 121 has a cylindrical surface shape. The diameter of the joint outer peripheral surface 121 is longer than the diameter of the outer peripheral surface 111. The outer peripheral surface 111 and the joint outer peripheral surface 121 are connected via an outer connecting surface 123. The outer connecting surface 123 is inclined relative to the outer peripheral surface 111 and the joint outer peripheral surface 121 so as to extend radially outward in the central axial direction from the outer peripheral surface 111 to the joint outer peripheral surface 121. The joint inner peripheral surface 122 has a cylindrical surface shape that shares a common central axis with the joint outer peripheral surface 121. The diameter of the joint inner peripheral surface 122 (the inner diameter of the joint portion 12) is longer than the diameter of the inner peripheral surface 112. The diameter of the joint inner circumferential surface 122 (the inner diameter of the joint portion 12) is equal to the outer diameter of the second member 2. In this disclosure, "equal" includes a range in which the objects being compared are substantially the same. For example, pipes with the same nominal diameter have equal diameters.

[0027] The second member 2 includes a second main body portion 21 and an insertion portion 22. The insertion portion 22 protrudes from a longitudinal end of the second main body portion 21 along the central axis. The inner diameter of the second main body portion 21 and the inner diameter of the insertion portion 22 are the same length. In this embodiment, the second main body portion 21 and the insertion portion 22 are formed integrally without any seams. The inner diameter of the insertion portion 22 may be shorter or longer than the inner diameter of the second main body portion 21.

[0028] In the second member 2, the second main body portion 21 and the insertion portion 22 include an outer peripheral surface 211 and an inner peripheral surface 212. The diameter of the outer peripheral surface 211 is the same as the diameter of the outer peripheral surface 111 of the first member 1, and the second member 2 has a cylindrical shape with a common central axis with the outer peripheral surface 211. The diameter of the inner peripheral surface 212 is the same as the diameter of the inner peripheral surface 112 of the first member 1, and the second member 2 has a cylindrical shape with a common central axis with the inner peripheral surface 212. The inner peripheral surface 212 has a common central axis with the outer peripheral surface 111. The second member 2 has a flow path (hereinafter, sometimes referred to as a second flow path 23) formed by being surrounded by the inner peripheral surface 212. The second member 2 has a tubular shape. The second member 2 is a pipe made of copper. When the insertion portion 22 is inserted into the joint portion 12, the first flow path 13 and the second flow path 23 communicate with each other to form a single flow path.

[0029] By making the diameter of the inner circumferential surface 112 of the first member 1 (the inner diameter of the first member 1) and the diameter of the inner circumferential surface 212 of the second member 2 (the inner diameter of the second member 2) the same length, pressure loss is unlikely to occur in the fluid flowing through the flow path. The outer diameter of the first main body portion 11 of the first member 1 and the outer diameter of the second member 2 may be different lengths.

[0030] The first member 1 and the second member 2 are joined to each other by the welded portion 3 at the tip of the joint portion 12 when the insertion portion 22 is inserted into the joint portion 12. Referring to FIG. 2 , the welded portion 3 includes a first region 31 and a second region 32. An interface 33 is formed between the first region 31 and the second region 32. That is, the second region 32 is disposed so as to form the interface 33 with the first region 31. The first region 31 is a region mainly composed of elements contained in the chromium-based stainless steel constituting the first member 1. The second region 32 is a region mainly composed of copper. The first region 31 is located closer to the first member 1 than the interface 33 in the longitudinal direction (direction along the central axis) of the welded part 10. The second region 32 is located closer to the second member 2 than the interface 33 in the longitudinal direction (direction along the central axis) of the welded part 10. The interface 33 crosses the welded portion 3 within the thickness of the welded portion 3. The interface 33 may be an uneven surface, a curved surface, or a flat surface.

[0031] Referring to FIG. 3 , a plurality of first island regions 321, each composed primarily of an element contained in the chromium-based stainless steel constituting the first member 1, are present and separated from one another within the second region 32. The plurality of first island regions 321 exist within the thickness of the second region 32, and some of the plurality of first island regions 321 appear on the surface of the second region 32. A plurality of second island regions 311, each composed primarily of copper, are present and separated from one another within the first region 31. The plurality of second island regions 311 exist within the thickness of the first region 31, and some of the plurality of second island regions 311 appear on the surface of the first region 31. The first region 31 and the second region 32 form a metallic bond at the interface 33. Here, a state in which a metallic bond is formed at the interface 33 means a state in which the lattice of metal atoms constituting the first region 31 and the lattice of metal atoms constituting the second region 32 are continuous at the interface 33.

[0032] In the welded component 10 of this embodiment, the second region 32 contains a plurality of first island regions 321 containing elements contained in the chromium-based stainless steel that constitutes the first member 1 as its main component. The first region 31 contains a plurality of second island regions 311 containing copper as its main component. As described above, the first region 31 and the second region 32 form a metallic bond at the interface 33. As a result, the welded component 10 of this embodiment has improved strength of the welded portion 3.

[0033] Next, an example of a method for manufacturing the welded part 10 of this embodiment will be described. Fig. 4 is a flowchart outlining the method for manufacturing the welded part 10. Figs. 5 and 6 are schematic views for explaining the method for manufacturing the welded part 10.

[0034] Referring to FIG. 4, in the manufacturing method of the welded component 10 of this embodiment, a material preparation step is first performed as step S10. In step S10, a first member 1 made of chromium-based stainless steel and a second member 2 made of copper are prepared as materials. Referring to FIG. 5, the first member 1 has a first body portion 11 and a joint portion 12. The second member 2 has a second body portion 21 and an insertion portion 22. The first body portion 11 and the second body portion 21 have, for example, hollow cylindrical shapes with the same inner and outer diameters. In step S10, the first member 1 and the second member 2 are arranged such that the insertion portion 22 is inserted into the joint portion 12.

[0035] Next, a molten pool formation step is carried out as step S20. In this step S20, referring to Fig. 6, an arc 6 is formed between the end portion (tip portion of joint portion 12) of first member 1 prepared in step S10, a portion of second member 2 adjacent to insertion portion 22 (second body portion 21), and electrode 42. A filler rod 5 is supplied into arc 6 as a filler material, and joint portion 12, second body portion 21, and filler rod 5 are heated and melted by arc 6, thereby forming a molten pool 7. The molten pool 7 is formed in the inside corner formed by the end portion of joint portion 12 and second body portion 21.

[0036] The electrode 42 is made of a high-melting-point metal material such as tungsten (W). The outer peripheral surface of the electrode 42, excluding the tip, is surrounded by a hollow cylindrical nozzle 41, and the tip of the electrode 42 is exposed to the outside through the nozzle 41. The nozzle 41 and the electrode 42 constitute the welding torch 4. A shielding gas is discharged from the annular space between the outer peripheral surface of the electrode 42 and the inner peripheral surface of the nozzle 41 along arrow A toward the outer peripheral surface of the joint portion 12 (joint outer peripheral surface 121) and the outer peripheral surface 211 of the second body portion 21. An inert gas such as argon (Ar) can be used as the shielding gas. A mixed gas of Ar and helium (He) can also be used as the shielding gas.

[0037] Shielding gas is discharged along arrow A, insulating the arc 6 from the outside air. The filler rod 5 is heated by the arc 6 and melts, forming droplets 51 that reach the molten pool 7. The molten pool 7 is composed of the molten first component 1, the molten second component 2, and the molten filler rod 5. The filler rod 5 contains 4.0% to 4.9% by mass of iron, with the remainder consisting of copper and unavoidable impurities.

[0038] Next, a solidification step is performed as step S30. In step S30, the molten pool 7 formed in step S20 is solidified to form a weld 3 joining the first member 1 and the second member 2. Specifically, the first member 1 and the second member 2, on which the molten pool 7 was formed in step S20, are rotated circumferentially by a predetermined angle, for example, approximately 5 to 10 degrees. As a result, the arc 6 forms a new molten pool 7 in an area adjacent to the previously formed molten pool 7, and the previously formed molten pool 7 solidifies to form the weld 3 (bead) (see FIG. 1 ). This procedure is repeated until the weld 3 is formed around the entire circumference of the first member 1 and the second member 2, thereby completing the method for manufacturing the welded component 10 of this embodiment and obtaining the welded component 10 of this embodiment.

[0039] In step S20 of the manufacturing method for welded component 10 according to the present embodiment, a filler rod 5 (filler metal) is used, which contains 4.0% by mass or more and 4.9% by mass or less of iron, with the remainder consisting of copper and unavoidable impurities. This facilitates the formation of a metallurgical bond between first region 31 and second region 32, with multiple first island regions 321 present within second region 32 and multiple second island regions 311 present within first region 31. As a result, the manufacturing method for welded component 10 according to the present embodiment can improve the strength of weld 3. Preferably, filler rod 5 contains 4.0% by mass or more and 4.8% by mass or less of iron, with the remainder consisting of copper and unavoidable impurities. Because the melting point of iron is higher than that of copper, solid phase iron and liquid phase copper coexist in the temperature range above the melting point of copper and below the melting point of iron. By reducing the iron content to 4.8 mass % or less, iron segregation is suppressed, which contributes to improving the strength of the welded portion 3.

[0040] The diameter of the filler rod 5 is preferably 1.2 mm or less, and more preferably 0.9 mm or less. By using such a filler rod 5, it becomes easier to achieve a state in which a plurality of first island regions 321 exist within the second region 32 and a plurality of second island regions 311 exist within the first region 31, and the first region 31 and the second region 32 form a metallic bond.

[0041] [Modification of welding parts] In the above embodiment, the first member 1 and the second member 2 are joined by the welded portion 3 with the insertion portion 22 inserted into the joint portion 12. However, as shown in FIG. 7 , the first member 1 and the second member 2 may be joined by butt welding. FIG. 7 is a schematic cross-sectional view showing the structure of a welded part 10 according to a modified example. FIG. 8 is a schematic cross-sectional view showing the welded part 10 according to the modified example in a state before welding. Referring to FIG. 7 , the diameter of the inner circumferential surface 112 of the first member 1 is the same as the diameter of the inner circumferential surface 212 of the second member 2. The diameter of the outer circumferential surface 111 of the first member 1 is the same as the diameter of the outer circumferential surface 211 of the second member 2.

[0042] Referring to FIG. 8 , among the end faces of the first member 1 in the central axis direction, the end face facing the second member 2 (hereinafter referred to as the “first end face 14”) includes a tapered surface. Among the end faces of the second member 2 in the central axis direction, the end face facing the first member 1 (hereinafter referred to as the “second end face 24”) includes a tapered surface. The tapered surfaces of the first end face 14 and the second end face 24 are inclined with respect to an imaginary plane perpendicular to the central axes of the first member 1 and the second member 2 so that the distance between them increases radially outward. The angle of the tapered surface with respect to the imaginary plane (hereinafter referred to as the bevel angle θ) is preferably 10 degrees or more and 45 degrees or less, more preferably 15 degrees or more and 30 degrees or less. This configuration facilitates the formation of a first region and a second region via an interface 33 in the weld.

[0043] Each of the first end face 14 and the second end face 24 may have a root face. The root face is a plane perpendicular to the central axis of the first member 1 and the second member 2 at the end faces 14, 24. In this embodiment, the root face is a surface other than the tapered surface at the end faces 14, 24. When the first member 1 and the second member 2 are arranged so that their central axes coincide and in a position where they can be welded, the root faces face each other with a predetermined distance (root spacing W). The root spacing W is preferably 0.01 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.4 mm or less. This configuration makes it easy to form the first region 31 and the second region 32 via the interface 33 in the weld.

[0044] The welded portion 3 joins the first member 1 and the second member 2. As in the above embodiment, an inert gas such as argon can be used as the shielding gas. In the molten pool formation process, a back shielding gas is flowed through the first flow path 13 and the second flow path 23. As in the shielding gas, an inert gas such as argon or a mixed gas of argon and helium can be used as the back shielding gas. As described in the manufacturing method of the above embodiment, the welded portion 3 is formed by solidifying the molten pool 7 formed between the first member 1 and the second member 2 in the solidification process. The welded portion 3 is formed around the entire circumference of the first member 1 and the second member 2, thereby obtaining a welded part 10.

[0045] [Other variations] In the above embodiment, the first member 1 and the second member 2 are both pipes, but in the present disclosure, the first member 1 and the second member 2 do not have to be pipes. For example, the first member 1 may be a welded pipe joint made of chromium-based stainless steel, and the second member 2 may be a pipe made of copper. Furthermore, the first member 1 and the second member 2 may be members having a shape other than a cylindrical shape (for example, a flat plate shape, a block shape, etc.).

[0046] Although the first member 1 according to the above embodiment is formed only from chromium-based stainless steel, the first member 1 may contain impurities. The second member 2 may also contain impurities.

[0047] In the above embodiment, the first member 1 has the joint portion 12 and the second member 2 has the insertion portion 22, but the first member 1 may have the insertion portion 22 and the second member 2 may have the joint portion 12. [Example]

[0048] Welded component 10 according to the present disclosure was fabricated, and an experiment was conducted to confirm the effects of welded component 10 according to the present disclosure and to confirm the metal structure of welded portion 3. The procedure of the experiment is as follows. However, welded component 10 according to the present disclosure is not limited to the following examples.

[0049] A test piece was produced as the welded part 10, in which a flat chromium-based stainless steel plate and copper were joined, by the manufacturing method for the welded part 10 described in the above embodiment. A flat ferritic stainless steel plate was used as the chromium-based stainless steel constituting the first member 1. JIS standard SUS430 was used as the ferritic stainless steel. Ar gas was used as the shielding gas. The flow rate of the shielding gas was 15 L / min. The diameter of the electrode 42 was 2.4 mm, and the inner diameter of the nozzle 41 was 6 mm. The material constituting the electrode 42 was tungsten (W) with 2 mass % cerium (Ce) added.

[0050] A DC welding power source was used, and pulse welding was used to control the current. The pulse control frequency was 400 Hz. The base current / pulse peak current was 12 A / 60 A. Referring to FIG. 10 , a copper plate was placed as the second member 2 on a ferritic stainless steel plate as the first member 1, and welding was then performed between the tip of the second member 2 and the main surface of the first member 1.

[0051] The composition of the filler rod 5 was 4.5 mass% iron and 95.5 mass% copper (4.5 mass% iron, with the remainder consisting of copper and unavoidable impurities), and three test pieces were prepared under the same conditions. The obtained test pieces were subjected to (1) confirmation of workability and (2) tensile tests as follows.

[0052] (1) Checking workability Welding was performed according to the procedure described in the above embodiment, and it was confirmed whether or not a good weld was achieved. If a good weld was achieved visually, it was judged as "pass," and if a large number of voids were generated or if a good weld was not achieved visually, it was judged as "fail."

[0053] (2) Tensile test A tensile test was conducted in which the welded part 10 was pulled in the longitudinal direction and fractured. The test was conducted with the test piece at room temperature. If the fracture occurred at a location other than the welded part 3, the test piece was judged as "passed," and if the fracture occurred at the welded part 3, the test piece was judged as "failed."

[0054] Next, the results of the experiments related to (1) and (2) above will be described. All three welded components 10 were judged to pass the workability test and also to pass the tensile test.

[0055] FIG. 9 is a photograph showing the state of the welded part 10 after the tensile test. As is clear from FIG. 9, the test piece fractured in a region other than the welded portion 3, specifically, in the second member 2. In the tensile test, the maximum stress until fracture was equivalent to the tensile strength of copper O material (annealed material). As described above, in all test pieces, no cracks occurred in the welded portion 3 in the tensile test, and fracture occurred in the second member 2, confirming that the tensile strength of the welded portion 3 is greater than the tensile strength of the second member 2.

[0056] Next, the state of the metal structure of the weld 3 of the prepared test specimen was confirmed. Figures 11, 12, 13, and 14 are optical microscope photographs showing the metal structure of the weld 3. Figure 11 is an optical microscope photograph of a portion corresponding to portion C in Figure 10. Figure 12 is a photograph of Zone 1 (portion Z1) of the first region 31 in Figure 11, enlarged 1000 times. Figure 13 is a photograph of Zone 2 (portion Z2) of the first region 31 in Figure 11, enlarged 1000 times. Figure 14 is a photograph of Zone 3 (portion Z3) of the second region 32 in Figure 11, enlarged 1000 times. Table 1 shows the results of analyzing the distribution of elements in the weld 3 using EDS (Energy Dispersive X-ray Spectroscopy).

[0057] [Table 1] 11, in first region 31 mainly composed of elements contained in chromium-based stainless steel, the element distribution was analyzed at two locations: a location (zone 1) close to interface 33 with second region 32, and a location (zone 2) far from interface 33. In second region 32 mainly composed of elements contained in copper, the element distribution in Zone 3 was analyzed. 11 to 14 and Table 1, the welded portion 3 includes a first region 31 containing elements (Fe, Cu, Ni, and Cr) contained in SUS430 constituting the first member 1 as its main component, and a second region 32 containing Cu as its main component, with an interface 33 as the boundary between them. Second region 32 contains a plurality of first island regions 321 (Fe phase in Table 1) containing elements contained in SUS430 as its main component, and first region 31 contains a plurality of second island regions 311 (Cu phase in Table 1) containing copper as its main component. The trace amount of Ni contained in the Fe phase is thought to be due to the Ni being measured as an impurity contained in chromium-based stainless steel.

[0058] As described above, the welded portion 3 includes a first region 31 and a second region 32. Within the second region 32, there are a plurality of first island regions 321 primarily composed of elements contained in SUS430. Within the first region 31, there are a plurality of second island regions 311 primarily composed of copper. Furthermore, in the tensile test, no cracks occurred in the welded portion 30 of any of the test specimens. From the above, it can be determined that the first region 31 and the second region 32 form a metallic bond at the interface 33. In other words, it was confirmed that the strength of the welded portion 3 was improved in the three test specimens as the welded component 10 that satisfied the requirements for the welded component 10 of the present disclosure.

[0059] The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as limiting in any respect. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0060] 10 welding part, 1 first member, 11 first body portion, 111 outer peripheral surface, 112 inner peripheral surface, 12 joint portion, 121 joint outer peripheral surface, 122 joint inner peripheral surface, 123 outer connecting surface, 13 first flow path, 14 first end surface, 2 second member, 21 second body portion, 22 insertion portion, 211 outer peripheral surface, 212 inner peripheral surface, 23 second flow path, 24 second end surface, 3 weld portion, 31 first region, 311 second island region, 32 second region, 321 first island region, 33 interface, 4 welding torch, 41 nozzle, 42 electrode, 5 filler rod, 51 droplet, 6 arc, 7 molten pool, W root spacing, θ bevel angle.

Claims

1. a first member made of chromium-based stainless steel; a second member made of copper; a welded portion that joins the first member and the second member, The welded portion is a first region containing, as a main component, an element contained in the chromium-based stainless steel constituting the first member; a second region that is arranged to form an interface with the first region and that is primarily composed of copper; a plurality of first island regions, each of which is separated from the other and whose main component is an element contained in the chromium-based stainless steel constituting the first member, are present in the second region; a plurality of second island regions each containing copper as a main component are present and separated from one another within the first region; The first region and the second region form a metallurgical bond at the interface.

2. The welded component of claim 1 , wherein the chromium-based stainless steel is a ferritic stainless steel.

3. 3. The welded part according to claim 2, wherein the ferritic stainless steel is JIS standard SUS430 stainless steel.

4. the first member and the second member have a tubular configuration; a longitudinal end portion of one of the first member and the second member includes a joint portion into which an insertion portion, which is an end portion of the other of the first member and the second member, is inserted; 4. The welded part according to claim 1, wherein the first member and the second member are joined to each other by the weld portion at a tip end of the joint portion with the insertion portion inserted into the joint portion.

5. the insert is included in the first member; The welded component according to claim 4 , wherein the joint portion is included in the second member.

6. providing a first member made of chromium-based stainless steel and a second member made of copper; supplying a filler metal into an arc while forming an arc between the first member and the second member and an electrode, and heating and melting the first member, the second member, and the filler metal by the arc to form a molten pool; and solidifying the molten pool to form a weld that joins the first member and the second member, The method for manufacturing a welded part, wherein the filler metal contains 4.5 mass % to 4.9 mass % iron, with the remainder consisting of copper and unavoidable impurities.

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