Copper and stainless steel joint and method for welding copper and stainless steel

Abstract

To provide a copper and stainless steel joined body improved more in joining strength and a copper and stainless steel welding method capable of manufacturing the joined body.SOLUTION: This joined body comprises: a first member made of copper; a second member made of stainless steel; and a joining part for joining the first and second members. In the joining part, copper is present along the crystal grain boundary of the steel, and particle copper is dispersed in the crystal grains of the steel. The welding method comprises a step of preparing the first member made of the copper, a step of preparing the second member made of the stainless steel, a step of butting together the first and second members, feeding a filler material made of copper or a copper alloy while forming an arc between the first member and an electrode, heating the first and second members and the filler material to melt, and forming a molten pond, and a step of coagulating the molten pond. In the melting step, the electrode is moved so that the heat gain of the first member can be larger than that of the second member.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a copper and stainless steel joint and a method for welding copper and stainless steel. [Background technology]

[0002] Conventionally, methods for welding copper materials and steel materials have been known, and this type of technology is disclosed in, for example, Patent Document 1.

[0003] Patent Document 1 discloses a method for joining copper and steel pipes by arc welding, with the ends of the pipes butted together. This method uses a welding wire with an iron content of 20% or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-87688 Summary of the Invention [Problem to be solved by the invention]

[0005] The joint of pipes disclosed in Patent Document 1 has a problem in that it is difficult to increase the joint strength between pipes made of copper and pipes made of steel, because copper and iron generally have properties that make them difficult to mix with each other.

[0006] An object of the present disclosure is to provide a joined body of copper and stainless steel with improved joining strength, and a method for welding copper and stainless steel that can produce such a joined body. [Means for solving the problem]

[0007] A copper and stainless steel joint according to the present disclosure includes a first member made of copper, a second member made of stainless steel, and a joint joining the first and second members. In the joint, copper is present along the grain boundaries of the steel, and granular copper is dispersed within the steel grains.

[0008] A method for welding copper and stainless steel according to the present disclosure includes a first preparation step of preparing a first member made of copper, a second preparation step of preparing a second member made of stainless steel, a melting step of butting the first member and the second member together and supplying a filler metal made of copper or a copper alloy while forming an arc between the first member and an electrode to heat and melt the first member, the second member, and the filler metal to form a molten pool, and a solidification step of solidifying the molten pool. In the melting step, the electrode is moved so that the heat input to the first member is greater than the heat input to the second member. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a joined body of copper and stainless steel with improved joining strength, and a copper and stainless steel welding method capable of producing such a joined body. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically showing the structure of a joined body of copper and stainless steel according to an embodiment. [Figure 2] FIG. 2 is a diagram schematically showing the structure of a joint of a joined body of copper and stainless steel according to the embodiment. [Figure 3] FIG. 3 is a flowchart showing the steps of a method for welding copper and stainless steel according to an embodiment. [Figure 4] FIG. 4 is a schematic diagram for explaining a method for welding copper and stainless steel according to an embodiment. [Figure 5] FIG. 5 is a photomicrograph of the joint of a copper and stainless steel joint. [Figure 6]FIG. 6 is a scanning electron microscopy (SEM) photograph of the joint of a copper and stainless steel joint. [Figure 7] FIG. 7 is a photograph showing the copper distribution in the joint of a copper and stainless steel joint, mapped by EDS (Energy Dispersive X-ray Spectroscopy). [Figure 8] Figure 8 shows a photograph of the iron distribution in the joint of a copper and stainless steel joint, mapped by EDS. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Outline of the embodiment] A copper and stainless steel joint according to the present disclosure includes a first member made of copper, a second member made of stainless steel, and a joint joining the first and second members. In the joint, copper is present along the grain boundaries of the steel, and granular copper is dispersed within the steel grains.

[0012] The present inventors have conducted extensive research into methods for improving the bonding strength of a bonded copper and stainless steel joint, and as a result, have newly discovered that the bonding strength can be dramatically improved by forming a structure in which copper is present along the grain boundaries of the steel and granular copper is dispersed within the steel grains in a bonded copper and stainless steel joint, and have arrived at the present invention based on this discovery.

[0013] The present disclosure is based on the above-mentioned viewpoint. That is, in the joint of the joined body of copper and stainless steel of the present disclosure, copper is present along the grain boundaries of the steel, and granular copper is dispersed within the steel grains. Therefore, the joined body of copper and stainless steel of the present disclosure can improve the joint strength compared to conventional joined bodies.

[0014] In the above-mentioned joined body of copper and stainless steel, the first member may be a first metal tube, and the second member may be a second metal tube. The longitudinal ends of the first metal tube and the longitudinal ends of the second metal tube may be joined via a joint.

[0015] A method for welding copper and stainless steel according to the present disclosure includes a first preparation step of preparing a first member made of copper, a second preparation step of preparing a second member made of stainless steel, a melting step of butting the first member and the second member together and supplying a filler metal made of copper or a copper alloy while forming an arc between the first member and an electrode to heat and melt the first member, the second member, and the filler metal to form a molten pool, and a solidification step of solidifying the molten pool. In the melting step, the electrode is moved so that the heat input to the first member is greater than the heat input to the second member.

[0016] The above welding method can form a structure in which copper is present along the grain boundaries of the steel and granular copper is dispersed within the steel grains at the joint between the first and second members, thereby enabling the production of a joint of copper and stainless steel with improved joint strength.

[0017] [Specific example of embodiment] Next, specific embodiments of the joined body of copper and stainless steel and the welding method of copper and stainless steel according to 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 their description will not be repeated.

[0018] (Copper and stainless steel joints) First, the configuration of a joined body 1 of copper and stainless steel (hereinafter also simply referred to as "joint body 1") according to an embodiment will be described with reference to Figs. 1 and 2. Fig. 1 is a cross-sectional view that schematically shows the configuration of the joined body 1. Fig. 2 is a diagram that schematically shows the structure of a joint 30 of the joined body 1. As shown in Fig. 1, the joined body 1 includes a first member 10 made of copper, a second member 20 made of stainless steel, and a joint 30 located between the first member 10 and the second member 20. The stainless steel that is the material of the second member 20 is preferably, but is not limited to, austenitic stainless steel, for example, but may also be ferritic stainless steel.

[0019] In this embodiment, the first member 10 is a first metal pipe (copper pipe), while the second member 20 is a second metal pipe (SUS (Steel Use Stainless) pipe). As shown in Fig. 1, an end 11 in the longitudinal direction of the first metal pipe (first member 10) and an end 21 in the longitudinal direction of the second metal pipe (second member 20) are joined via a joint 30.

[0020] 2, in the joint 30, copper 40 is present along the grain boundaries 31A of the steel, and granular copper 41 is dispersed within the steel grains 31. Copper 40 may be formed in a continuous network shape along the grain boundaries 31A of the steel, but is not limited to this, and may be interrupted midway along the grain boundaries 31A.

[0021] (Welding methods for copper and stainless steel) Next, a method for welding copper and stainless steel according to an embodiment will be described with reference to Figures 3 and 4. In this embodiment, a case in which a first member 10 and a second member 20 are joined by TIG (tungsten inert gas) welding will be described as an example.

[0022] First, a first preparation step is carried out (step S10 in FIG. 3). In this step S10, a first member 10 (copper pipe) made of copper is prepared.

[0023] Next, a second preparation step is carried out (step S20 in FIG. 3). In this step S20, a second member 20 (SUS pipe) made of stainless steel is prepared.

[0024] Next, a melting step is performed (step S30 in FIG. 3). In step S30, as shown in FIG. 4, a longitudinal end 11 of the first member 10 (copper pipe) and a longitudinal end 21 of the second member 20 (SUS pipe) are butted against each other, and a filler metal 60 made of copper or a copper alloy is supplied while an arc β is formed between the first member 10 and an electrode 52. The first member 10, the second member 20, and the filler metal 60 are heated and melted to form a molten pool. The filler metal 60 contains copper as a main component. Specifically, the filler metal 60 may contain 90% by mass or more of copper, or may contain 95% by mass or more of copper. Examples of materials that can be used for the filler metal 60 include pure Cu, a Cu-Fe alloy, a Cu-Si alloy, and a Cu-Sn alloy.

[0025] In the welding process S30, the electrode 52 is reciprocated in the lengthwise direction of the first member 10 and the second member 20 so that the heat input to the first member 10 is greater than the heat input to the second member 20. The electrode 52 is made of a high-melting-point metal material, such as tungsten, and is inserted into a hollow cylindrical nozzle 51. A shielding gas α can flow through the annular space between the outer circumferential surface of the electrode 52 and the inner circumferential surface of the nozzle 51. As shown in FIG. 4, the tip of the electrode 52 protrudes toward the first member 10 beyond the tip of the nozzle 51. The electrode 52 and the nozzle 51 constitute a welding torch 50.

[0026] In the welding step S30, with the end portion 11 of the first member 10 and the end portion 21 of the second member 20 butted against each other, the first member 10 and the second member 20 are rotated one revolution in the circumferential direction, and the welding torch 50 is moved back and forth between the first member 10 and the second member 20 so as to straddle the butted portion of both ends. At this time, the welding torch 50 waits on the first member 10 side for a first time before moving to the second member 20 side, and the welding torch 50 waits on the second member 20 side for a second time (a time shorter than the first time) before returning to the first member 10 side. This movement of the welding torch 50 continues while the first member 10 and the second member 20 make one revolution in the circumferential direction. As a result, a molten pool is formed in a portion including the end portion 11 of the first member 10 and a portion including the end portion 21 of the second member 20.

[0027] Next, a solidification step is carried out (step S40 in FIG. 3). In this step S40, the molten pool formed in step S30 above is solidified. This forms a joint 30 (FIG. 1), joining the first member 10 and the second member 20 to each other. The above steps S10 to S40 complete the copper and stainless steel welding method according to this embodiment.

[0028] As described above, in the joint 30 of the joined body 1 of copper and stainless steel according to this embodiment, copper 40 is present along the grain boundaries 31A of the steel, and granular copper 41 is dispersed within the steel crystal grains 31. Therefore, the joined body 1 can improve the joining strength between the first member 10 and the second member 20.

[0029] Figure 5 is a micrograph of a joint formed when copper and stainless steel are joined using the welding method of the above embodiment. As shown in Figure 5, copper 40 is present along the boundaries (grain boundaries) of steel crystal grains 31, and granular copper 41 is dispersed (scattered) within the crystal grains 31. Furthermore, when a tensile test was conducted on the joined body, no fracture was observed at the joint 30, confirming good joint strength. The welding conditions used to form the joint in the micrograph of Figure 5 are as follows: Argon (Ar) gas was flowed through the tubes of the first member 10 and the second member 20 as a back shield. Outer diameter of the first and second component tubes: 8mm Tube thickness of the first and second components: 1 mm Material of the first component: Copper Second component material: SUS304 Welding current (pulse welding method): 25A Filler shape: φ1.2mm Shielding gas: Ar (10 L / min)

[0030] Fig. 6 is an SEM photograph of a joint when copper and stainless steel are joined using the welding method of the above embodiment. Fig. 7 is an image of the joint when copper is mapped by EDS. Fig. 8 is an image of the joint when iron is mapped by EDS. As shown in Figs. 6 to 8, copper is present along the grain boundaries of the steel (the white linear areas in the photograph in Fig. 7), and granular copper is observed dispersed within the steel grains (the white dotted areas in the photograph in Fig. 7).

[0031] Here, other embodiments will be described.

[0032] In the above embodiment, the first member 10 and the second member 20 are welded by TIG welding as an example, but this is not limiting and MIG welding may also be used. In this case, the electrode also serves as a filler metal.

[0033] In the above embodiment, the first member 10 and the second member 20 are both metal pipes, but the present invention is not limited to this. For example, the first member and the second member may be metal plates.

[0034] The embodiments disclosed herein are illustrative in all respects and should not be construed as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0035] 1 Copper and stainless steel joint (joint), 10 first member, 11, 21 end, 20 second member, 30 joint, 31 crystal grain, 31A crystal grain boundary, 40, 41 copper, 50 welding torch, 51 nozzle, 52 electrode, 60 filler metal, α shielding gas, β arc.

Claims

1. a first member made of copper; a second member made of stainless steel; a joint portion that joins the first member and the second member, A joint of copper and stainless steel, wherein copper is present along the grain boundaries of the steel at the joint, and granular copper is dispersed within the steel grains.

2. the first member is a first metal tube, the second member is a second metal tube, 2. The copper and stainless steel joint according to claim 1, wherein the end of the first metal tube in the longitudinal direction and the end of the second metal tube in the longitudinal direction are joined via the joint.

3. a first preparation step of preparing a first member made of copper; a second preparation step of preparing a second member made of stainless steel; a melting step of butting the first member and the second member against each other, supplying a filler metal made of copper or a copper alloy while forming an arc between the first member and an electrode, heating and melting the first member, the second member, and the filler metal to form a molten pool; a solidification step of solidifying the molten pool, In the melting step, the electrode is moved so that the heat input amount of the first member is greater than the heat input amount of the second member; A method for welding copper and stainless steel, in which the solidification process solidifies the molten pool, and the first member and the second member are joined via a joint in which copper is present along the grain boundaries of the steel and granular copper is dispersed within the steel grains.

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