Stainless steel and copper joined body, method for producing same, and method for joining stainless steel and copper

Abstract

Provided is a stainless steel and copper joined body having high reliability instead of silver brazing. A welded portion is formed at an overlapping portion where stainless steel and copper overlap each other, the welded portion is configured from a plurality of welding points that are connected in the welding direction on the copper-side surface of the joined body, the Cu / Fe ratio of the welded portion is 10.0 or more, MF and t satisfy the relationship of formula (1), and MF and B satisfy the relationship of formula (2). (1) MF > = 0.8 t, and (2) 0.10 MF < = B < = 1.25 MF.

Description

Technical Field

[0001] The present invention relates to a bonded body of stainless steel and copper, a manufacturing method thereof, and a bonding method of stainless steel and copper. Background Art

[0002] Stainless steel is a billet with excellent corrosion resistance and is widely used in various heat exchangers for automobiles, air conditioners, etc. in the form of steel plates or steel pipes. In addition, copper is a billet with excellent thermal conductivity and is widely used in various heat exchangers in the form of copper plates or copper pipes.

[0003] In recent years, with the soaring price of copper, it has been desired to change the billet from copper to stainless steel in copper heat exchangers. However, it is difficult to change all the billets from copper to stainless steel, and some copper parts remain. In this case, since stainless steel parts and copper parts need to be combined to manufacture a product, bonding of stainless steel and copper is required.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-523830

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-349443 Summary of the Invention

[0008] However, in the manufacture of heat exchangers, as a method of joining components to each other, brazing is generally used. Brazing is roughly classified into furnace brazing in which components are heated in an atmosphere furnace for multi-point simultaneous joining, and torch brazing in which a joining portion is heated with a welding torch in the atmosphere for single-point joining. Moreover, depending on the stage of product assembly, both methods can be used.

[0009] Among them, especially in torch brazing, the materials to be joined are exposed to high temperatures in the atmosphere. Therefore, when the material to be joined is stainless steel, it is easy to form a firm and dense oxide film on the surface of the stainless steel that hinders brazing. Therefore, when performing torch brazing of stainless steel parts and copper parts, brazing needs to be performed at a low temperature.

[0010] Based on the above situation, for bonding stainless steel and copper, silver brazing filler metal with a low melting point (melting point: about 600 to 700 °C) is generally used. However, silver brazing filler metal is expensive. In addition, appropriate torch brazing requires skilled operation. Furthermore, even at about 600 °C, an oxide film that hinders brazing may sometimes be formed on the surface of the stainless steel. Therefore, a flux needs to be used for bonding stainless steel and copper. However, due to the use of the flux, there is a concern that the corrosion resistance of stainless steel and copper may decrease. In addition, cleaning for removing the flux is time-consuming and laborious, resulting in a decrease in productivity.

[0011] Under such circumstances, it is required to develop a method for joining stainless steel and copper that replaces flame brazing using silver brazing filler metal (hereinafter also referred to as silver brazing).

[0012] As a method for joining stainless steel and copper that replaces silver brazing, for example, Patent Document 1 discloses "a method for joining copper or a copper alloy and an austenitic steel alloy, characterized in that at least one intermediate layer is disposed between the joining surfaces of the objects to be joined, the joining surfaces each containing the intermediate layer are pressed together, and at least the joining region is heated to form a diffusion bond. This method brings the joining surface of the first intermediate layer (3) into contact with, or disposes it on, the joining surface of the steel object (2), mainly preventing the loss of nickel from the steel object (2), and brings the joining surface of at least one second intermediate layer (4) into contact with, or disposes it on, the joining surface of the copper object (1) to activate the formation of the diffusion bond".

[0013] In addition, Patent Document 2 discloses "a joining method characterized by joining stainless steel and an object to be joined to the stainless steel, including: a step of causing a joining agent composed of a solder and a joining metal to be between the stainless steel and the object to be joined, and a step of performing a heat treatment while bringing the joining agent into contact with the stainless steel and the object to be joined".

[0014] Here, the technique described in Patent Document 1 provides an intermediate layer such as Ni between the joining surfaces of stainless steel and copper. In addition, the technique described in Patent Document 2 provides a solder and a joining metal between the joining surfaces of stainless steel and copper. However, products such as heat exchangers come into contact with liquids or produce condensation during use. Therefore, if a joined body of stainless steel and copper obtained by the techniques described in Patent Documents 1 and 2 is applied to such products, there is a strong concern about the occurrence of dissimilar metal contact corrosion caused by the potential difference between the intermediate layer and the solder and the joining metal and copper or stainless steel.

[0015] Therefore, for the joining of stainless steel and copper, a highly reliable joining method that replaces silver brazing has not been established, and there is a current expectation to develop such a joining method.

[0016] The present invention has been developed in view of the above situation, and its object is to provide a highly reliable method for joining stainless steel and copper that replaces silver brazing, and a joined body of stainless steel and copper and a manufacturing method thereof.

[0017] Then, in order to achieve the above object, the inventors of the present invention repeatedly conducted in-depth research and came to the conclusion that a highly reliable joining method that replaces silver brazing is preferably a welding method. However, in the past, it was considered difficult to weld stainless steel and copper. As one of the main reasons, cracks in the welded portion can be cited. The inventors of the present invention repeatedly studied the main cause of the cracks in the welded portion and obtained the following insights.

[0018] In the welding of stainless steel and copper, if the stainless steel and copper are melted and mixed, their liquid phase separates into two phases: a first liquid phase mainly composed of the stainless steel component and a second liquid phase mainly composed of the copper component. At this time, the more the melting amount of the stainless steel relative to the copper, the more the proportion of the first liquid phase increases.

[0019] The solidification structure formed by cooling the first liquid phase is brittle. In addition, during the cooling process after welding, internal stress is generated at the joint due to the difference in thermal shrinkage rates between the base material of the stainless steel and the base material of the copper. If the amount of the above-mentioned first liquid phase is large, the above-mentioned internal stress causes the solidification structure of the first liquid phase to be damaged. That is, it causes the generation of cracks in the welded part. This internal stress is particularly likely to concentrate at the starting end and the terminal end of the welding. Therefore, cracks in the welded part are particularly likely to be generated at the starting end and the terminal end of the welding. In addition, the generated cracks usually expand and penetrate the welded part.

[0020] Based on the above insights, the present inventors repeatedly conducted research and focused on the difference in melting points between stainless steel and copper. That is, the melting point of stainless steel is about 1400 - 1500 °C. On the other hand, the melting point of copper is about 1100 °C. Therefore, the present inventors studied the following method. That is, on the basis of making the joint form a lap joint, the electrode is arranged on the copper side of the overlapping part of the stainless steel and copper of the materials to be joined, and only the copper is actively melted. Then, by making the melted copper contact the surface of the stainless steel and solidifying it, the proportion of copper in the melted part is increased. That is, it was studied to suppress the generation amount of the first liquid phase mainly composed of the stainless steel component to prevent cracks in the welded part. Here, a lap joint means that the welded part (welding position) is located in the overlapping part where the stainless steel and copper overlap in the joined body (or the materials to be joined). It should be noted that the welded part being located in the overlapping part means that the entire welded part is located within the overlapping part. That is, as Figure 3 shown, in the direction perpendicular to the welding, taking the copper end of the overlapping part as the reference position (0), setting the copper side as + and the stainless steel side as -, the entire welded part is located within the range of 0 to +L. Here, L is the width (mm) of the overlapping part in the direction perpendicular to the welding. It is preferred that the welded part is located within the overlapping part and is separated from the copper end and the stainless steel end in the direction perpendicular to the welding.

[0021] However, even if one wants to melt only the copper under general welding conditions, there are cases where the heat of the melted copper conducts to the stainless steel and causes a large amount of the stainless steel to melt as well. Therefore, it can be seen that it is difficult to actively melt only the copper under general welding conditions.

[0022] Based on the above aspects, the present inventors studied a welding method that can precisely control the heat input conditions, especially TIG welding.

[0023] However, it is known that when only copper is actively melted, that is, when welding is performed while suppressing the melting of stainless steel, sufficient strength of the joint (hereinafter also referred to as joint strength) or airtightness may sometimes not be obtained. That is, if heat input is continuously performed as in general TIG welding, even if the melting of stainless steel is suppressed, the temperature of stainless steel will rise, and a firm oxide film will be formed on the surface of stainless steel. Moreover, it is known that the melted copper is repelled by this oxide film, and the copper cannot wet and spread on the surface of stainless steel, and sometimes sufficient joint strength or airtightness cannot be obtained.

[0024] Therefore, the present inventors further repeatedly studied a method of suppressing the formation of an oxide film on the surface of stainless steel during welding while only actively melting copper. As a result, the following insights were obtained.

[0025] That is, TIG welding is used as the welding method, and the electrode is disposed on the copper side of the materials to be joined. Moreover, it is effective to divide the heat input accompanying welding into multiple local and short-time heat inputs. In particular, it is effective to divide it into multiple heat inputs in such a way that the following conditions (a) to (e) are satisfied and the relationship of the following formula (4) is satisfied. Thereby, while only actively melting copper, the melting of stainless steel can be suppressed, and further, the temperature rise of stainless steel can be suppressed to suppress the formation of an oxide film on the surface of stainless steel during welding.

[0026] (a) Tilt angle α of the electrode: 0° to 45°

[0027] Here, the thickness direction of the materials to be joined is set as the reference angle (0°), and the angle formed by the direction in which the tip of the electrode faces and the thickness direction of the materials to be joined is set as the tilt angle of the electrode.

[0028] (b) Electrode height: greater than 0 mm and 3.0 mm or less

[0029] (c) Each heat input position in the direction perpendicular to welding: 0.5×0.03×I×d 0.5 / t 0.5 (mm) to L - 0.5×0.03×I×d 0.5 / t 0.5 (mm)

[0030] Here, I is the welding current (A), d is the welding time (s), t is the thickness of copper (mm), and L is the width of the overlapping portion where stainless steel and copper overlap each other. In addition, for each heat input position in the direction perpendicular to welding, the copper end of the overlapping portion is set as the reference position (0), the copper side is set as +, and the stainless steel side is set as -.

[0031] (d) Distance interval (mm) in the welding direction of each heat input point: 0.1×{D k－1 ×(1 - 0.2×t)} to Dk－1 ×(1 - 0.2×t)

[0032] Here, D k－1 is the diameter (mm) of the weld spot formed by the previous heat input on the copper-side surface of the material to be joined. t is the thickness (mm) of the copper.

[0033] (e) Time interval between each heat input: 100% or more of the welding time (s) of the previous heat input

[0034] t 1.5 / (1 - 0.2×t)÷0.03 ≤ I×d 0.5 ≤ t 1.5 / (1 - 0.2×t)÷0.03×6 ··· (4)

[0035] Here,

[0036] I: Welding current (A)

[0037] d: Welding time (s)

[0038] t: Thickness t (mm) of the copper.

[0039] In addition, the present inventors have also found that by dividing the heat input accompanying welding into the above-mentioned multiple local and short-time heat inputs, cracks in the welded portion can also be suppressed.

[0040] That is, cracks in the welded portion are caused by the internal stress at the joint due to the difference in thermal shrinkage rates between the stainless steel base material and the copper base material during the cooling process after welding. In particular, compared with joint shapes such as lap joints and lap corner joints, this internal stress (in other words, restraint stress) is likely to become larger. In this regard, the internal stress can be dispersed and reduced by dividing the heat input accompanying welding into multiple local and short-time heat inputs. In addition, excessive melting of the stainless steel can be suppressed by dividing the heat input accompanying welding into multiple local and short-time heat inputs. As a result, the penetration of the stainless steel into the molten portion can be suppressed, and further, the generation amount of the above-mentioned first liquid phase can be suppressed. Through the synergistic effect of these effects, cracks in the welded portion can be sufficiently suppressed.

[0041] It should be noted that even if the heat input accompanying welding is divided, if the heat input sites are too close to each other or the time interval between heat inputs is too short, the amount of heat input to the stainless steel is excessive. As a result, melting of the stainless steel sometimes occurs excessively, and cracks are generated in the welded portion. From the viewpoint of preventing such cracks in the welded portion and further suppressing the formation of the oxide film on the surface of the stainless steel during welding, in addition to the heat input amount itself, it is important to appropriately control the distance interval between the welding directions of the above-mentioned (d) each heat input point and the time interval between (e) each heat input.

[0042] In addition, the present inventors further repeatedly conducted research based on the above insights and found that by simultaneously satisfying the following points, a joined body of stainless steel and copper having sufficient joining strength and airtightness and without cracks in the welded portion can be obtained.

[0043] · The welded portion is located in the overlapping portion where the stainless steel and copper overlap each other, that is, a lap joint is formed. At the same time, the welded portion is composed of a plurality of welding points connected along the welding direction on the copper-side surface of the joined body.

[0044] · The Cu / Fe ratio of the welded portion is 10.0 or more.

[0045] · MF and t satisfy the relationship of the following formula (1). In addition, MF and B satisfy the relationship of the following formula (2).

[0046] MF ≥ 0.8t ··· (1)

[0047] 0.10MF ≤ B ≤ 1.25MF ··· (2)

[0048] Here,

[0049] MF: The distance (mm) between the welded portion and the molten boundary of copper in the direction perpendicular to the welding on the overlapping surface of the stainless steel and copper of the joined body

[0050] B: The average distance interval (mm) of the welding points on the copper-side surface of the joined body

[0051] t: The thickness (mm) of copper.

[0052] The present invention has been completed in view of the above insights and further research.

[0053] That is, the gist of the present invention is configured as follows.

[0054] 1. A joined body of stainless steel and copper, comprising stainless steel, copper, and a welded portion of the stainless steel and the copper,

[0055] The above-mentioned stainless steel and the above-mentioned copper are in plate or tubular form,

[0056] The above-mentioned welded portion is located in the overlapping portion where the above-mentioned stainless steel and the above-mentioned copper overlap each other, and the above-mentioned welded portion has a plurality of welding points connected along the welding direction on the copper-side surface of the joined body,

[0057] The Cu / Fe ratio of the above-mentioned welded portion is 10.0 or more,

[0058] MF and t satisfy the relationship of the following formula (1),

[0059] MF and B satisfy the relationship of the following formula (2).

[0060] MF ≥ 0.8t ··· (1)

[0061] 0.10 MF ≤ B ≤ 1.25 MF ···(2)

[0062] Here,

[0063] MF: The distance (mm) between the welded part in the welding right-angle direction and the melting boundary of copper on the overlapping surface of stainless steel and copper of the joined body

[0064] B: The average distance interval (mm) of the welding points on the copper side surface of the joined body

[0065] t: The thickness (mm) of copper.

[0066] 2. The joined body of stainless steel and copper according to item 1 above, wherein D max / D min Satisfies the relationship of the following formula (3).

[0067] D max / D min ≤ 1.4 ···(3)

[0068] Here,

[0069] D min : The minimum diameter (mm) of the welding points on the copper side surface of the joined body

[0070] D max : The maximum diameter (mm) of the welding points on the copper side surface of the joined body.

[0071] 3. A method for joining stainless steel and copper, which joins by welding the materials to be joined, and the materials to be joined are formed by overlapping stainless steel and copper,

[0072] The above welding is carried out by TIG welding,

[0073] In the above TIG welding,

[0074] The electrode is arranged on the copper side of the above materials to be joined, and multiple heat inputs are carried out under the conditions satisfying the following (a) to (e),

[0075] (a) The tilt angle α of the electrode: 0° to 45°

[0076] Here, the thickness direction of the material to be joined is set as the reference angle (0°), and the angle formed by the direction in which the front end of the electrode faces and the thickness direction of the material to be joined is set as the tilt angle of the electrode.

[0077] (b) The electrode height: greater than 0 mm and 3.0 mm or less

[0078] (c) Each heat input position in the welding right-angle direction: 0.5 × 0.03 × I × d0.5 / t 0.5 (mm) ~ L - 0.5×0.03×I×d 0.5 / t 0.5 (mm)

[0079] Here, I is the welding current (A), d is the welding time (s), t is the thickness of copper (mm), and L is the width of the overlapping part where stainless steel and copper overlap. In addition, for each heat input position in the welding right angle direction, the copper end of the overlapping part is set as the reference position (0), the copper side is set as +, and the stainless steel side is set as -.

[0080] (d) Distance interval (mm) in the welding direction of each heat input point: 0.1×{D k－1 ×(1 - 0.2×t)} ~ D k－1 ×(1 - 0.2×t)

[0081] Here, D k－1 is the diameter (mm) of the weld point formed by the previous heat input on the copper side surface of the material to be joined. t is the thickness of copper (mm).

[0082] (e) Time interval between each heat input: 100% or more of the welding time (s) of the previous heat input

[0083] Furthermore, in each heat input, the relationship of the following formula (4) is satisfied.

[0084] t 1.5 / (1 - 0.2×t)÷0.03 ≤ I×d 0.5 ≤ t 1.5 / (1 - 0.2×t)÷0.03×6 ··· (4)

[0085] Here,

[0086] I: Welding current (A)

[0087] d: Welding time (s)

[0088] t: Thickness t of copper (mm).

[0089] 4. According to the method for joining stainless steel and copper described in the above 3, wherein at least one of the following (f) to (h) is performed.

[0090] (f) In each heat input, make the welding current of the heat input not more than the welding current of the previous heat input.

[0091] (g) In each heat input, make the welding time of the heat input not more than the welding time of the previous heat input.

[0092] (h) Set a long time interval for heat input between some heat inputs.

[0093] Among them, the case where the welding current excluding each heat input, the welding time, and the time interval between heat inputs is constant is not included.

[0094] 5. A method for manufacturing a bonded body of stainless steel and copper, wherein the stainless steel and copper are bonded by the method for bonding stainless steel and copper described in 3 or 4 above.

[0095] According to the present invention, a method for bonding stainless steel and copper with high reliability in place of silver brazing (in other words, both sufficient bonding strength and sufficient airtightness can be obtained, and cracks in the welded portion are not generated), and a bonded body of stainless steel and copper can be obtained. In addition, the bonded body of stainless steel and copper of the present invention can be manufactured at a cost significantly lower than that of silver brazing, and is therefore extremely advantageous for the bonded portion of stainless steel and copper applied to various devices, such as heat exchangers. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 It is an example of a photomicrograph of a cross-section (Y-Z plane) perpendicular to the welding direction of the welded portion of the bonded body of stainless steel and copper according to one embodiment of the present invention.

[0097] Figure 2 It is an example of an external appearance photograph of the welded portion of the bonded body of stainless steel and copper according to one embodiment of the present invention, and is a photograph taken of the bonded body from the copper side in the thickness direction.

[0098] Figure 3 It is a schematic diagram showing an example of the spatial arrangement of the materials to be bonded in the method for bonding stainless steel and copper according to one embodiment of the present invention.

[0099] Figure 4 It is a schematic diagram showing an example of the spatial arrangement of the electrodes in the method for bonding stainless steel and copper according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0100] The present invention will be described based on the following embodiments.

[0101] [1] Bonded body of stainless steel and copper

[0102] The bonded body of stainless steel and copper according to one embodiment of the present invention includes stainless steel, copper, and a welded portion of the stainless steel and the copper.

[0103] The above-mentioned stainless steel and the above-mentioned copper are in the form of plates or tubes.

[0104] The above-mentioned welded portion is located in the overlapping portion where the above-mentioned stainless steel and the above-mentioned copper overlap each other, and the above-mentioned welded portion has a plurality of welding points connected along the welding direction on the copper-side surface of the bonded body.

[0105] The Cu / Fe ratio of the above-mentioned welded part is 10.0 or more,

[0106] MF and t satisfy the relationship of the above formula (1),

[0107] MF and B satisfy the relationship of the above formula (2).

[0108] It should be noted that Figures 1 to 4 the X direction, Y direction and Z direction are as follows respectively.

[0109] X direction: The welding direction (which can also be called the direction of the copper end edge in the overlapping surface of stainless steel and copper, and the long side direction of the welded part.).

[0110] Y direction: The direction perpendicular to the welding direction (the direction perpendicular to the welding direction and perpendicular to the thickness direction (Z direction) described later).

[0111] Z direction: The thickness direction of the joined body or the material to be joined (taking the overlapping surface of stainless steel and copper as the reference position (0), the copper side as +, and the stainless steel side as -). In addition, it can also be called the direction perpendicular to the overlapping surface of stainless steel and copper. Hereinafter, it is also simply referred to as the thickness direction.).

[0112] Here, Figure 1 is an example of an optical microscope photograph of a cross-section (Y - Z plane) perpendicular to the welding direction of the welded part of the joined body of stainless steel and copper according to an embodiment of the present invention.

[0113] Figure 2 is an example of an appearance photograph of the welded part of the joined body of stainless steel and copper according to an embodiment of the present invention, and is a photograph taken from the copper side in the thickness direction of the joined body.

[0114] Figure 3 is a schematic diagram showing an example of the spatial arrangement of the materials to be joined in the joining method of stainless steel and copper according to an embodiment of the present invention.

[0115] Figure 4 is a schematic diagram showing an example of the spatial arrangement of the electrodes in the joining method of stainless steel and copper according to an embodiment of the present invention.

[0116] (1) Stainless steel

[0117] The above-mentioned stainless steel is the stainless steel that serves as the base material, and its shape is plate-shaped (stainless steel plate) or tubular (stainless steel pipe). It should be noted that the so-called plate-shaped here includes not only flat plates but also curved plates (bent plates). The thickness of the stainless steel (plate thickness or pipe thickness) is not particularly limited, and from the perspective of bondability, it is preferably 0.1 mm or more. In addition, the thickness of the stainless steel is preferably 4.0 mm or less. The thickness of the stainless steel is more preferably 0.2 mm or more, and further preferably 0.3 mm or more. In addition, the thickness of the stainless steel is more preferably 2.0 mm or less, and further preferably 1.0 mm or less.

[0118] When the shape of the stainless steel serving as the base material is plate-shaped, the size of the plate is not particularly limited. For example, from the perspective of heat conduction and heat dissipation during welding, the length in the direction orthogonal to the welding direction is preferably 10 mm or more. More preferably, the length in the direction orthogonal to the welding direction is 30 mm or more.

[0119] When the shape of the stainless steel serving as the base material is tubular, the size of the tube (outer diameter and length) is not particularly limited. For example, from the perspective of heat conduction and heat dissipation during welding, the outer diameter of the tube is preferably 4 times or more of the tube thickness (wall thickness). The length of the tube is preferably 10 mm or more. More preferably, the length of the tube is 30 mm or more.

[0120] In addition, the component composition of the stainless steel is not particularly limited as long as it is a general component of stainless steel. For example, as long as it is an iron-based alloy containing 10.5 mass% or more of Cr and 50 mass% or more of Fe. As an example, austenitic stainless steel plates, austenitic-ferritic stainless steel plates, ferritic stainless steel plates, martensitic stainless steel plates, and precipitation hardening stainless steel plates specified in JIS G 4305:2021, as well as their processed products can be used. In addition, stainless steel sanitary water pipes, stainless steel pipes for general piping, stainless steel pipes for piping, and stainless steel pipes for boilers and heat exchangers specified in JIS G 3447:2015, JIS G 3448:2016, JIS G 3459:2021, JIS G 3463:2019, and JIS G 3468:2021, as well as their processed products can be used. It should be noted that stainless steel plates can be plates with various surface treatments represented by No. 2B treatment (annealing pickling and tempering treatment), No. 2D treatment (annealing pickling treatment), No. 4 treatment (grinding treatment), No. 8 treatment (mirror grinding treatment), BA treatment (bright annealing treatment), HL (hairline) treatment, matting treatment, embossing treatment, and sandblasting treatment.

[0121] (2) Copper

[0122] The copper described above is the copper that serves as the base material, and its shape is plate-like (copper plate) or tubular (copper tube). It should be noted that the so-called plate-like here includes not only flat plates but also curved plates (bent plates). The thickness of the copper (plate thickness or tube thickness) is not particularly limited, and from the viewpoint of bondability, it is preferably 0.1 mm or more. In addition, the thickness of the copper is preferably 4.0 mm or less. The thickness of the copper is more preferably 0.3 mm or more, and further preferably 0.5 mm or more. In addition, the thickness of the copper is more preferably 2.0 mm or less, and further preferably 1.0 mm or less.

[0123] When the shape of the copper serving as the base material is plate-like, the size of the plate is not particularly limited. For example, from the viewpoints of heat conduction and heat dissipation during welding, the length in the direction orthogonal to the welding direction is preferably 10 mm or more. More preferably, the length in the direction orthogonal to the welding direction is 30 mm or more.

[0124] When the shape of the copper serving as the base material is tubular, the size of the tube (outer diameter and length) is not particularly limited. For example, from the viewpoints of heat conduction and heat dissipation during welding, the outer diameter of the tube is preferably 4 times or more the tube thickness (wall thickness). The length of the tube is preferably 10 mm or more. More preferably, the length of the tube is 30 mm or more.

[0125] It should be noted that the so-called copper here not only refers to so-called pure copper composed of Cu and inevitable impurities but also includes copper alloys containing 50 mass% or more of Cu. As an example, various copper plates, bars, tubes represented by oxygen-free copper, refined copper, and phosphorus-deoxidized copper specified in JIS H 3100:2018, as well as their processed products, can be used. In addition, for example, seamless tubes and welded tubes of copper specified in JIS H 3300:2018 and JIS H 3320:2006, as well as their processed products, can be used. It should be noted that copper plates with various surface treatments represented by HL (hairline) treatment, pear surface treatment, sandblasting treatment, and hammering treatment can be used.

[0126] (3) Welded part

[0127] In the stainless steel and copper joint according to one embodiment of the invention, as Figure 1 shown, the stainless steel serving as the base material and the copper are joined through the welded part. In addition, the welded part is located in the overlapping part where the stainless steel and the copper overlap each other. That is, as described above, the entire welded part is located within the overlapping part. It is preferred that the welded part is located within the overlapping part and is separated from the copper end and the stainless steel end in the direction perpendicular to the welding. It should be noted that the welded part mentioned here does not include the so-called heat-affected zone.

[0128] The welded part is divided as follows, for example. That is, under a magnification of 100 times, SEM is used to observe the one produced according to the following procedure Figure 1Observation is carried out on cross-sectional specimens like that. Then, based on the shape of the cross-section confirmed in the reflected electron image, the contrast difference between each tissue, the contrast of the interface, the grain size, and the anisotropy (aspect ratio) of the grains, the interfaces between the welded part and the stainless steel (which becomes the base material) and between the welded part and the copper (which becomes the base material) (hereinafter also referred to as the fusion boundary) are determined, and the welded part is divided.

[0129] For example, the upper and lower surfaces of the cross-sections of copper (which becomes the base material) and stainless steel are parallel, and the grains are isotropic. In contrast, the upper and lower surfaces of the cross-section of the welded part are not parallel, and the grains are slender and highly anisotropic. Additionally, for example, there is a part where the contrast changes (hereinafter also referred to as the fusion line) at the interface between copper and the welded part. Furthermore, in most cases, the interface between the stainless steel and the welded part has a different contrast from the surroundings, or there is a fusion line as described above. Also, as Figure 2 shown, the welded part is composed of a plurality of welding points connected along the welding direction on the copper-side surface of the joined body. It should be noted that the number of welding points is not particularly limited as long as it is 2 or more, preferably 5 or more. In particular, it is more preferable that the number of welding points is 8 to 16 per 10 mm in the welding direction. Additionally, being connected along the welding direction means that as Figure 2 shown, on the surface of the welded part, a part of each welding point overlaps with the welding point adjacent in the welding direction.

[0130] Moreover, when observing the welded part from the copper side in the thickness direction, the entire welding bead is located between the copper end and the stainless steel end in the direction perpendicular to the welding. That is, here, the so-called welded part is different from the fillet welded part, and the copper end remains without melting.

[0131] It should be noted that whether the above-mentioned welded part is located in the overlapping part of the materials to be joined is determined as follows. First, the stainless steel end is confirmed by observing the joined body from the stainless steel-side surface of the joined body. In cases where it is difficult to confirm the stainless steel end from the stainless steel-side surface due to the structure of the joined body such as a tube, it can be confirmed by destructive inspections such as cutting the joined body to observe the cut surface or non-destructive inspections such as X-ray inspections. Next, the copper end is confirmed by observing the joined body from the copper-side surface of the joined body. Additionally, the stainless steel end is projected and transferred onto the copper-side surface of the joined body. Then, when the entire welded part (welding bead) confirmed by observing the joined body from the copper-side surface of the joined body is located between the copper end and the stainless steel end (the above-mentioned transferred part) in the direction perpendicular to the welding, it is determined that the welded part is located in the overlapping part.

[0132] Moreover, in the joined body of stainless steel and copper according to one embodiment of the present invention, it is particularly important to appropriately control the Cu / Fe ratio of the welded part, as well as the size and arrangement of the welding points constituting the welded part.

[0133] Cu / Fe ratio of the welded part: 10.0 or more

[0134] In the case of a so-called lap welding joint where the welded part is located in the overlapping part, compared with welded joints such as butt welding joints or lap fillet welding joints, the restraint stress is likely to increase. Here, the restraint stress refers to the internal stress at the joint generated by the difference in thermal shrinkage rates between the stainless steel base material and the copper base material during the cooling process after welding. In addition, this restraint stress is one of the factors leading to cracks in the welded part. In such a lap welding joint, in order to suppress cracks in the welded part, it is necessary to sufficiently increase the Cu / Fe ratio of the welded part. A high Cu / Fe ratio in the welded part means reducing the generation amount of the above-mentioned first liquid phase during welding. By reducing the generation amount of the first liquid phase, the generation of cracks in the welded part can be effectively suppressed.

[0135] Here, if the Cu / Fe ratio of the welded part is less than 10.0, the generation amount of the first liquid phase mainly composed of the stainless steel component is large, leading to the generation of cracks in the welded part. Therefore, the Cu / Fe ratio of the welded part is 10.0 or more. The Cu / Fe ratio of the welded part is preferably 20.0 or more. There is no particular limitation on the upper limit of the Cu / Fe ratio of the welded part. For example, the Cu / Fe ratio of the welded part is preferably 100.0 or less.

[0136] Here, the Cu / Fe ratio of the welded part is measured at the 1 / 2 position of the thickness of the copper. For example, the Cu / Fe ratio of the welded part is calculated as follows. First, a cross-sectional specimen in the thickness direction of the welded part as described Figure 1 (a specimen with a cross-section perpendicular to the X direction, which is the welding direction, being the YZ plane) is polished to a mirror finish. Next, the cross-sectional specimen is etched using picric acid hydrochloric acid (100 mL ethanol - 1 g picric acid - 5 mL hydrochloric acid). Next, the cross-sectional specimen is observed using SEM at a magnification of 100 times, and SEM-EDS analysis is performed. In this analysis, EDS point scanning is performed on the welded part of the cross-section, that is, the solidification structure part. The elements to be analyzed are two elements, Fe and Cu. Then, based on the mass ratios (mass %) of these two elements, the Cu / Fe ratio is measured by the following formula (5). The scanning points of EDS are 10 points randomly selected at the 1 / 2 position of the thickness of the copper (the 1 / 2t position with the overlapping surface of the stainless steel and the copper as the reference position (0)). Then, the Cu / Fe ratios measured at each point are averaged to obtain the Cu / Fe ratio of one cross-sectional specimen. This measurement is performed on 5 cross-sectional specimens randomly collected from the welded part, and the average value of the Cu / Fe ratios of the obtained cross-sectional specimens is used as the Cu / Fe ratio of the welded part.

[0137] Cu / Fe ratio = Cu / Fe ··· (5)

[0138] Here, Cu and Fe on the right side of the formula respectively refer to the mass ratios (mass %) of Cu and Fe obtained by EDS point scanning.

[0139] MF ≥ 0.8t ··· (1)

[0140] As Figure 1 shown, in the cross-section (Y-Z plane) perpendicular to the welding direction of the joined body, the welded part is arranged to be clamped by the molten boundary (fusion line) between copper and the welded part. Moreover, it is essential that the distance MF (mm) (hereinafter also simply referred to as the distance MF between the molten boundaries or MF) between the welded part in the welding right-angle direction of the overlapping surface of stainless steel and copper on the back side of copper and the molten boundary of copper satisfies the relationship of the above formula (1) according to the thickness t (mm) of copper (hereinafter also simply referred to as t).

[0141] Here, if MF is less than 0.8t, the heat input amount conducted to stainless steel during welding is insufficient, and the joining of stainless steel and copper is insufficient. As a result, sufficient joining strength cannot be obtained. Therefore, MF is 0.8t or more. MF is preferably 1.6t or more. The upper limit of MF is not particularly limited. From the viewpoint of preventing strain of copper, MF is preferably 6.0t or less, for example. In addition, MF is preferably 0.3 × L or less. Here, L is the width of the overlapping part where stainless steel and copper overlap each other in the joined body (the length in the welding right-angle direction). L is substantially the same as the width of the overlapping part where stainless steel and copper overlap each other in the material to be joined described later.

[0142] Here, MF is measured as follows.

[0143] The cross-sectional specimen made as described above is observed by SEM at a magnification of 100 times. Next, the molten boundary between the welded part and copper is determined and the welded part is divided according to the above-mentioned method. Then, the width in the welding right-angle direction of the welded part at the reference position (0) in the thickness direction of the overlapping surface of stainless steel and copper, that is, the distance between the two molten boundaries shown at the reference position (0) in the thickness direction, is measured as MF for one cross-sectional specimen. This measurement is performed using each cross-sectional specimen made by cutting the joined body to be the object into eight equal parts in the welding direction, and the average value of MF of each obtained cross-sectional specimen is taken as MF. Figure 1 Figure 1

[0144] 0.10MF ≤ B ≤ 1.25MF ··· (2)

[0145] If the average distance interval B (mm) of the welding points on the copper-side surface of the joined body (hereinafter also simply referred to as the average distance interval B of the welding points or B) is less than 0.10MF, the number of times of heat input to the same position becomes large, and the heat input amount to the same position is substantially excessive. As a result, the formation of the oxide film on the surface of stainless steel cannot be sufficiently suppressed, and sufficient joining strength cannot be obtained. In addition, sometimes the amount of generation of the first liquid phase mainly composed of the stainless steel component increases, resulting in the generation of cracks in the welded part.​​

[0146] On the other hand, if B is greater than 1.25 MF, even though the welding points are continuous on the surface of the welded part, the joint between the stainless steel and the copper is interrupted on the back surface of the copper at the overlapping surface of the stainless steel and the copper. Therefore, sufficient airtightness cannot be obtained.

[0147] Therefore, B is 0.10 MF to 1.25 MF. B is preferably 0.20 MF or more. B is preferably 1.00 MF or less.

[0148] Here, B is calculated by the following formula (6).

[0149] B = A / n ··· (6)

[0150] Here, A is the length in the welding direction of the welded part. n is the number of welding points. It should be noted that A can be measured using, for example, a vernier caliper.

[0151] According to the shape, for example, A can be obtained in the form of (D1 + D n ) / 2 + (B2 + B3 + ··· B n ). Here, D1 and D n are the diameters of the first and the nth welding points, respectively. In addition, B k is the shortest center-to-center distance (mm) between the kth welding point and the (k - 1)th welding point formed previously.

[0152] In addition, for example, in the case of a joint of a stainless steel pipe and a copper pipe (stainless steel and copper are tubular), when the welding points form one circle, that is, the initially welded welding point and the finally welded welding point are adjacent (overlapping), A becomes the entire circumferential length in the welding direction of the welded part. In this case, A can be obtained, for example, in the form of B1 + B2 + B3 + ··· B n . It should be noted that B1 is the shortest center-to-center distance (mm) between the first welding point and the nth welding point.

[0153] In addition, in the joint of stainless steel and copper according to an embodiment of the present invention, with the above configuration, cracks in the welded part and discontinuity of the joint at the overlapping surface of the stainless steel and the copper can be prevented. Therefore, good airtightness can be obtained, preferably airtightness of 0.2 MPa or more.

[0154] Here, for example, the airtightness is measured as follows.

[0155] · In the case of a joint of a stainless steel plate and a copper plate (stainless steel and copper are plate-shaped)

[0156] Cut out a test piece for airtightness evaluation from the center of the welded portion on the surface of the joined body (the surface on the side where the welded portion is arranged) so that the length in the welding direction becomes 20 mm. Next, apply pipe repair putty or the like (hereinafter also referred to as putty) to the end face in the welding direction of the overlapping portion of stainless steel and copper included in this test piece. Next, with the center of the welding direction of the copper end of this test piece as the center, draw a circle with a radius of 10 mm (diameter 20 mm) (hereinafter also referred to as the reference circle), and apply the putty in a donut shape on this reference circle. Next, vertically press the end of a copper pipe with an outer diameter of 20 mm and a wall thickness of 1 mm (the end face is formed in a plane perpendicular to the long side direction of the copper pipe) against the putty applied in a donut shape. Furthermore, as described later, in order to prevent air from leaking from the gap between the copper pipe and the joined body even when air is fed into the copper pipe, additional putty is applied to seal the gap between the copper pipe and the joined body. Next, connect a pressure regulator and a compressor to the other end of the copper pipe, and measure the airtightness in the same manner as in the case of the tubular body described later. It should be noted that when the joined body is small and it is impossible to draw the reference circle of the above dimensions on its surface, it is sufficient to install an auxiliary plate or the like on the joined body to seal one-sided end of the copper pipe.

[0157] · In the case of a joined body of a stainless steel pipe and a copper pipe (stainless steel and copper are tubular)

[0158] Seal one-sided end of the joined body with pipe repair putty or the like, and connect a pressure regulator and a compressor to the other end. Next, in an atmospheric environment, immerse the joined body in water with a depth of 20 cm, and set the inside of the joined body to a specified pressure (for example, 0.2 MPa) by feeding air into the inside of the joined body. It should be noted that when the depth of water is different according to the position of the welded portion due to reasons such as the welded portion not forming a flat surface, as long as the entire welded portion is immersed in water and its deepest point is 20 cm in water depth. If no bubbles come out from the joined body within 10 minutes after the inside of the joined body reaches the specified pressure, it is regarded that the airtightness of the joined body is above the specified pressure.

[0159] In addition, in the joined body of stainless steel and copper according to an embodiment of the present invention, the joining strength is preferably 60% or more, more preferably 80% or more of the lower strength (tensile strength) of stainless steel and copper that are the base materials.

[0160] In particular, by making the Cu / Fe ratio of the welded part 20.0 or more and making the MF 1.6 t or more, higher joint strength can be obtained. Specifically, joint strength of 80% or more of the lower strength of the stainless steel and copper that are the base materials can be obtained. Regarding the reason, the inventors considered as follows. That is, by making the Cu / Fe ratio of the welded part 20.0 or more, formation of the oxide film on the surface of the stainless steel can be more effectively suppressed, and the amount of generation of the first liquid phase mainly composed of the stainless steel component can be reduced. In addition, by making the MF 1.6 t or more, the area of the joint interface between the copper and the stainless steel increases. As a result, higher joint strength can be obtained.

[0161] Here, the joint strength is measured in accordance with JIS Z 2241:2011. Among them, the tensile test piece is collected from the joined body in such a manner that a joint part (welded part) exists in the parallel part of the test piece and the long side direction (tensile direction) of the test piece is the direction perpendicular to the welding. The maximum test force obtained by the tensile test is divided by the width of the parallel part of the test piece to calculate the maximum test force per unit width (unit length in the long side direction of the welded part). Then, the calculated maximum test force per unit width is used as the joint strength. It should be noted that a spacer is installed before the tensile test in the clamping parts (the clamping part of the stainless steel and the clamping part of the copper) of the tensile test piece collected from the joined body in such a manner that the tensile axis is parallel to the stainless steel and the copper. In addition, there is no overlapping part of the stainless steel and the copper in the clamping part.

[0162] In addition, for example, the strengths of the stainless steel and copper that are the base materials are measured as follows. Tensile test pieces are collected from the base material parts of the stainless steel and copper near the joint part of the joined body in such a manner that the long side direction of the test piece is the same as the long side direction (the direction perpendicular to the welding) of the test piece used in the measurement of the joint strength. Then, a tensile test is performed in the same manner as the measurement of the joint strength, and the maximum test force obtained by this tensile test is divided by the width of the parallel part of the test piece to calculate the maximum test force per unit width. Then, the calculated maximum test force per unit width is used as the strength of each of the stainless steel and the copper.

[0163] It should be noted that the shape of the above test piece can be arbitrarily determined according to the shape of the joined body as long as the width of the parallel part is 1 mm or more and the length of the parallel part is 5 mm or more.

[0164] The bonded body of stainless steel and copper according to an embodiment of the present invention may be plate-shaped (including curved plates (bent plates) in addition to flat plates) or tubular as long as a part of each base material overlaps and has the above-described welded portion. In the case of a tubular shape, it is a bonded body of a stainless steel pipe and a copper pipe. For example, in a combination where the outer diameter of the stainless steel pipe is approximately equal to the inner diameter of the copper pipe, a combination of a copper pipe whose end portion is expanded to be approximately equal to the outer diameter of the stainless steel pipe and a stainless steel pipe, and a combination of a stainless steel pipe and a copper pipe whose end portion is contracted to be approximately equal to the inner diameter of the copper pipe, etc., it may be a bonding method in which a part of the stainless steel pipe is inserted into the copper pipe. In addition, the bonded body according to an embodiment of the present invention includes a bonded body having a plurality of bonded portions and at least one of them being the above-described welded portion.

[0165] D max / D min ≤1.4

[0166] If the ratio of the maximum diameter D max (mm) to the minimum diameter D min (mm) of the welding points on the copper-side surface of the bonded body, that is, D max / D min (hereinafter also referred to as the bead width change rate) is 1.4 or less, an excellent appearance with little change in the bead width can be obtained. Therefore, D max / D min is preferably 1.4 or less. D max / D min is more preferably 1.2 or less. The lower limit of D max / D min is not particularly limited. For example, D max / D min only needs to be 1.0 or more.

[0167] It should be noted that D min and D max are the minimum value and the maximum value of the diameter D k (k = 1 to n) of the welding points, respectively.

[0168] Here, for example, the diameter D k of the welding points is calculated as follows. As Figure 2 shown, using a 10-fold magnifying glass, on the copper-side surface of the bonded body, from a direction perpendicular to the observation surface, in other words, observing the welding points of the welded portion of the bonded body from the copper side in the thickness direction. Then, measure the maximum length L k of each welding point in the welding perpendicular direction. Then, use this L k as the diameter D k of each welding point. It should be noted that the measurement of the maximum length of each welding point can be performed using a vernier caliper. It should be noted that asFigure 2 As shown, a part of the contour of the welding point will disappear due to the welding points formed later, so the above measurement method is adopted. It should be noted that k is a number representing each welding point (each number of heat inputs), and is an integer from 1 to n. n is the number of welding points (number of heat inputs).

[0169] [2] Joining method of stainless steel and copper

[0170] According to the joining method of stainless steel and copper according to an embodiment of the present invention, the materials to be joined are welded and joined. The materials to be joined are formed by overlapping stainless steel and copper.

[0171] The above welding is performed by TIG welding.

[0172] In the above TIG welding,

[0173] The electrode is disposed on the copper side of the material to be joined, and multiple heat inputs are performed under the conditions satisfying the following (a) to (e).

[0174] (a) Tilt angle α of the electrode: 0° to 45°

[0175] Here, the thickness direction of the material to be joined is set as the reference angle (0°), and the angle formed by the direction in which the front end of the electrode faces and the thickness direction of the material to be joined is set as the tilt angle of the electrode.

[0176] (b) Electrode height: greater than 0 mm and 3.0 mm or less

[0177] (c) Each heat input position in the welding right angle direction: 0.5×0.03×I×d 0.5 / t 0.5 (mm) to L - 0.5×0.03×I×d 0.5 / t 0.5 (mm)

[0178] Here, I is the welding current (A), d is the welding time (s), t is the thickness of copper (mm), and L is the width of the overlapping portion where stainless steel and copper overlap each other. In addition, for each heat input position in the welding right angle direction, the copper end of the overlapping portion is set as the reference position (0), the copper side is set as +, and the stainless steel side is set as -.

[0179] (d) Distance interval (mm) in the welding direction of each heat input point: 0.1×{D k－1 ×(1 - 0.2×t)} to D k－1 ×(1 - 0.2×t)

[0180] Here, D k－1 is the diameter (mm) of the welding point formed by the previous heat input on the copper side surface of the material to be joined. t is the thickness of copper (mm).

[0181] (e) Time interval between each heat input: 100% or more of the welding time (s) of the previous heat input

[0182] Furthermore, in each heat input, the relationship of the above formula (4) is satisfied.

[0183] Hereinafter, using Figure 3 a schematic diagram showing an example of the spatial arrangement of the materials to be joined and Figure 4 a schematic diagram showing an example of the spatial arrangement of the electrodes, the joining method of stainless steel and copper according to an embodiment of the present invention will be described.

[0184] In the joining method of stainless steel and copper according to an embodiment of the present invention, the materials to be joined Figure 3 formed by overlapping stainless steel and copper as described above are welded and joined. For example, in the case of a plate shape, it is preferable to overlap the copper plate on the upper side in the vertical direction of the stainless steel plate. In the case of a tubular shape, it is preferable to overlap with the stainless steel pipe on the inside and the copper pipe on the outside (for example, insert a part of the stainless steel pipe into the inside of the copper pipe). Although not particularly limited, the width of the overlapping portion of stainless steel and copper (width in the direction perpendicular to welding) is preferably 5 to 20 mm. Although not particularly limited, the gap thickness of the overlapping portion of stainless steel and copper is preferably 1 / 2 or less of the thickness of copper. It should be noted that the preferred thickness, shape, composition, etc. of stainless steel and copper are as described in [1].

[0185] Welding method: TIG welding

[0186] In the joining method of stainless steel and copper according to an embodiment of the present invention, in order to suppress the melting of stainless steel and only actively melt copper, it is necessary to precisely control the heat input conditions. Therefore, the welding method adopted in the lap welding is TIG welding.

[0187] Electrode arrangement: on the copper side of the materials to be joined

[0188] In the joining method of stainless steel and copper according to an embodiment of the present invention, in each heat input caused by TIG welding, stainless steel and copper are joined by melting copper and solidifying it on stainless steel. Therefore, in order to preferentially heat-input copper, as Figure 4 shown, the heat input point is set on the copper-side surface of the overlapping portion of the materials to be joined. That is, the electrode is arranged on the copper side of the materials to be joined.

[0189] In addition, in the method for joining stainless steel and copper according to an embodiment of the present invention, it is important to divide the heat input accompanying welding into multiple local and short-time heat inputs and satisfy the following conditions (a) to (e). It should be noted that the number of heat inputs is not particularly limited as long as it is 2 or more, and preferably 5 or more. In particular, it is more preferable that the number of heat inputs is 8 to 16 times per 10 mm in the welding direction.

[0190] (a) Tilt angle α of the electrode: 0° to 45°

[0191] From the viewpoint of forming a good welded part, the tilt angle α of the electrode (hereinafter also referred to as the electrode tilt angle α) is important. Here, as Figure 4 shown, the electrode tilt angle α is the tilt angle of the straight line connecting the tip of the electrode and the heat input point with respect to the thickness direction (the vertical direction of the overlapping surface of the materials to be joined). In addition, the electrode tilt angle α is based on the thickness direction as the reference angle (0°). It should be noted that the tilt direction of the electrode is not particularly limited.

[0192] As described above, in the method for joining stainless steel and copper according to an embodiment of the present invention, the copper throughout the entire thickness is locally melted and solidified on the stainless steel. Here, if the electrode tilt angle α is greater than 45°, the heat input area becomes wider and the temperature around the heat input part rises excessively. As a result, strain occurs around the joint due to thermal expansion and thermal contraction, causing defects in the shape of the joint and subsequent joining. Therefore, the electrode tilt angle α is 45° or less. The electrode tilt angle α is preferably 25° or less. The lower limit of the tilt angle α of the electrode is 0°. That is, the straight line connecting the electrode end and the heat input point is parallel to the thickness direction.

[0193] (b) Electrode height: greater than 0 mm and 3.0 mm or less

[0194] If the electrode height (that is, the distance between the tip of the electrode in the thickness direction and the materials to be joined) is 0 mm, no arc is generated and welding cannot be performed. In addition, if the electrode height exceeds 3.0 mm, the heat input area becomes wider and the heat input is dispersed. As a result, the melting amount of copper is insufficient and the joining is inadequate. Therefore, the electrode height is greater than 0 mm and 3.0 mm or less. In addition, if the electrode height is less than 0.5 mm, the tip of the electrode comes into contact with the molten copper during joining, and sometimes it solidifies and adheres to the electrode. In this case, an operation to remove the electrode from the solidified copper is required, resulting in a decrease in manufacturing efficiency. Therefore, the electrode height is preferably 0.5 mm or more. In addition, if the electrode height exceeds 2.0 mm, it is difficult to grasp the distance between the copper and the tip of the electrode, and it is difficult to control the electrode height. Therefore, the electrode height is preferably 2.0 mm or less.

[0195] (c) Positions of each heat input point in the welding right angle direction: 0.5 × 0.03 × I × d 0.5 / t 0.5 (mm) to L - 0.5 × 0.03 × I × d 0.5 / t 0.5 (mm)

[0196] If heat input is performed extremely close to the copper end in the overlapping portion of the materials to be joined, the copper end will melt, and the desired airtightness and joining strength cannot be obtained. On the other hand, if heat input is performed extremely close to the stainless steel end in the overlapping portion, there will be no stainless steel directly below the copper melting portion, and the desired joining strength cannot be obtained. Therefore, the positions of each heat input point in the welding right angle direction are 0.5 × 0.03 × I × d 0.5 / t 0.5 (mm) to L - 0.5 × 0.03 × I × d 0.5 / t 0.5 (mm).

[0197] Here, t is the thickness of copper (mm), I is the welding current (A), d is the welding time (s), and L is the width of the overlapping portion where stainless steel and copper overlap in the materials to be joined (the length of the overlapping surface of stainless steel and copper in the welding right angle direction of each heat input point). In addition, for each heat input position in the welding right angle direction, the copper end of the overlapping portion is set as the reference position (0), the copper side is set as +, and the stainless steel side is set as -.

[0198] In addition, L is not particularly limited. For example, it is preferably 5 to 30 mm.

[0199] (d) Distance interval (mm) in the welding direction of each heat input point: 0.1 × {D k－1 × (1 - 0.2 × t)} to D k－1 × (1 - 0.2 × t)

[0200] As described above, in the method for joining stainless steel and copper according to an embodiment of the present invention, it is important to divide the heat input accompanied by welding into multiple local and short-time heat inputs. In particular, the distance interval in the welding direction of each heat input point (hereinafter also referred to as the heat input point interval) is 0.1 × {D k－1 (hereinafter also referred to as the welding point diameter) in relation to the thickness t (mm) of copper as 0.1 × {D k－1 × (1 - 0.2 × t)} to D k－1 × (1 - 0.2 × t).

[0201] Here, if the heat input point interval is less than 0.1 × {D k－1×(1 - 0.2×t)}, the number of heat inputs to the same position increases, and substantially, the amount of heat input to the same position becomes excessive. As a result, the formation of the oxide film on the surface of the stainless steel cannot be sufficiently suppressed, and sufficient bonding strength cannot be obtained. In addition, the amount of the first liquid phase mainly composed of the stainless steel component increases, leading to the generation of cracks in the welded part. On the other hand, if the heat input point interval is greater than D k－1 ×(1 - 0.2×t), the bonding between the stainless steel and the copper is interrupted on the back surface of the overlapping surface of the stainless steel and the copper, and sufficient airtightness cannot be obtained. Therefore, the heat input point interval is 0.1×{D k－1 ×(1 - 0.2×t)} to D k－1 ×(1 - 0.2×t). The heat input point interval is preferably 0.2×{D k－1 ×(1 - 0.2×t)} or more. The heat input point interval is preferably 0.8×{D k－1 ×(1 - 0.2×t)} or less.

[0202] Here, the heat input point interval is the distance between the centers of adjacent heat input points. In addition, the diameter of each welding point can be calculated according to the above-mentioned method.

[0203] (e) The time interval (s) between each heat input: 100% or more of the welding time (s) of the previous heat input

[0204] As described above, in the method for bonding stainless steel and copper according to an embodiment of the present invention, it is important to cut the heat input accompanied by welding into multiple local and short-time heat inputs. In particular, the time interval between each heat input (hereinafter also referred to as the heat input time interval) is 100% or more of the welding time (hereinafter also referred to as the heat input time) of the previous heat input. Here, if the heat input time interval becomes too short, specifically, the heat input time interval is less than 100% of the heat input time, the amount of heat conducted to the periphery of the heat input part exceeds the amount of heat dissipated from the periphery of the heat input part, and the temperature of the periphery of the heat input part rises. As a result, the formation of the oxide film on the surface of the stainless steel cannot be sufficiently suppressed, and sufficient bonding strength cannot be obtained. In addition, the amount of the first liquid phase mainly composed of the stainless steel component increases, leading to the generation of cracks in the welded part. Furthermore, sometimes strains in the periphery of the joint due to thermal expansion and thermal contraction occur, causing defects in the shape of the joint and subsequent joints. Therefore, the heat input time interval is 100% or more of the heat input time. The heat input time interval is preferably 250% or more of the heat input time. In addition, the upper limit of the heat input time interval is not particularly limited. From the viewpoint of manufacturing efficiency, the heat input time interval is preferably 20000% or less of the heat input time.

[0205] The relationship between the welding current I (A), the welding time d (s), and the thickness t (mm) of copper in each heat input: t 1.5 / (1 - 0.2×t)÷0.03 ≤ I×d 0.5 ≤ t 1.5 / (1 - 0.2×t)÷0.03×6 ···(4)

[0206] If I×d 0.5 is less than the left - hand value of the above formula (4), the melting amount of copper is insufficient, MF is less than 0.8t, and the joining of stainless steel and copper becomes insufficient. On the other hand, if I×d 0.5 is greater than the right - hand value of the above formula (4), the Cu / Fe ratio of the welded part is less than 10.0. That is, a large amount of stainless steel melts into the weld metal. As a result, the amount of the first liquid phase mainly composed of the stainless - steel component increases, leading to the generation of cracks in the welded part. In addition, the formation of the oxide film on the surface of the stainless steel cannot be sufficiently suppressed, and sufficient joining strength cannot be obtained. Therefore, for each heat input, the welding current I (A), the welding time d (s), and the thickness t (mm) of copper should satisfy the relationship of the above formula (4). I×d 0.5 is preferably t 1.5 / (1 - 0.2×t)÷0.03×2 or more. In addition, I×d 0.5 is preferably t 1.5 / (1 - 0.2×t)÷0.03×5 or less. Especially to obtain higher joining strength, when the Cu / Fe ratio of the welded part is 20.0 or more and MF is 1.6t or more, it is preferable that the value of I×d 0.5 is in the range of t 1.5 / (1 - 0.2×t)÷0.03×2 to t 1.5 / (1 - 0.2×t)÷0.03×5.

[0207] It should be noted that if d is less than 0.05s, the arc may sometimes be unstable. In addition, if d is greater than 2.00s, heat is transferred to the periphery of the heat - input part and the temperature of the periphery is likely to rise. As a result, strain in the periphery of the joined part due to thermal expansion and thermal contraction may sometimes occur, causing defects in the shape of the joined part and subsequent joining. Therefore, d is preferably in the range of 0.05s to 2.00s.

[0208] I is selected from t and the above - mentioned d in such a way as to satisfy the above formula (4). For example, I can be selected from the range of 50A to 500A as long as it satisfies the above formula (4). It should be noted that from the viewpoint of preventing strain in the welded part, when there is a range of settable values for d and I, it is preferable to set d as low as possible and I as high as possible.

[0209] It should be noted that when using a pulse mode, uphill, downhill, and crater treatment in each heat input, the time obtained by combining the uphill time, welding time, downhill time, and crater - treatment time is substituted into d, and the time - average value of the welding current during this time is substituted into I to calculate I×d0.5 Value

[0210] In addition, each heat input can adopt a touch start mode or a high-frequency start mode. A thermoelectric arc can be used at the start of the heat input. However, the current and time consumed at the start of these heat inputs are not included in the welding current I (A) and welding time d (s) of each heat input.

[0211] The conditions other than those described above for TIG welding are not particularly limited. Just follow the conventional methods. For example, for the shielding gas and the backing gas, general inert gases can be used, and 100% Ar is preferred.

[0212] In addition, if the shielding gas flow rate is less than 1 L / min, the arc is likely to become unstable. On the other hand, if the shielding gas flow rate exceeds 30 L / min, the shielding gas forms a turbulent flow on the material to be joined. Since this turbulent flow entangles the atmosphere, the inert gas atmosphere around the heat input part is disturbed, and defects are likely to be generated in the welded part. Therefore, the shielding gas flow rate is preferably 1 to 30 L / min. The shielding gas flow rate is more preferably 25 L / min or less.

[0213] In addition, if the backing gas flow rate is less than 1 L / min, an oxide film is formed on the stainless steel surface on the back of the heat input part, and the corrosion resistance of the stainless steel is likely to decrease. On the other hand, if the backing gas flow rate exceeds 30 L / min, the backing gas forms a turbulent flow on the material to be joined. Since this turbulent flow entangles the atmosphere, an oxide film is formed on the stainless steel surface on the back of the heat input part, and the corrosion resistance of the stainless steel is likely to decrease. Therefore, the backing gas flow rate is preferably 1 to 30 L / min. The backing gas flow rate is more preferably 25 L / min or less.

[0214] If the preflow time is 0.05 seconds or more, the heat input starts in a state where a sufficient inert gas atmosphere is formed around the heat input part. Thereby, the arc is likely to be stable. Therefore, the preflow time is preferably 0.05 seconds or more. The preflow time is more preferably 0.15 seconds or more. The upper limit of the preflow time is not particularly limited. The preflow time is preferably 10 seconds or less, for example.

[0215] If the postflow time is 0.10 seconds or more, the generation of the oxide film directly above the welded part can be suppressed, and the appearance of the weld line is good. Therefore, the postflow time is preferably 0.10 seconds or more. The postflow time is more preferably 2.0 seconds or more. The upper limit of the postflow time is not particularly limited. The postflow time is preferably 10 seconds or less, for example.

[0216] In addition, by repeatedly performing thermal input multiple times, the temperature of the copper as the material to be joined is excessively increased. As a result, melting of the copper is easily promoted, and as welding progresses, the bead width, that is, the maximum length in the welding perpendicular direction of the welding points on the copper side surface of the material to be joined, sometimes gradually becomes wider. In this case, for example, it is preferable to cool the copper and stainless steel as the materials to be joined using a chill mold or a cooling pipe. Thereby, widening of the bead width can be suppressed, and a welded portion with excellent bead width stability can be obtained. Herein, "excellent bead width stability" means that the bead width change rate represented by D max / D min is 1.4 or less, and particularly 1.2 or less.

[0217] In addition, in addition to cooling the copper and stainless steel as the materials to be joined, for example, by performing at least one of the following (f) to (h), a welded portion with excellent bead width stability can also be appropriately obtained.

[0218] (f) In each thermal input, make the welding current of the thermal input less than or equal to the welding current of the previous thermal input.

[0219] (g) In each thermal input, make the welding time of the thermal input less than or equal to the welding time of the previous thermal input.

[0220] (h) Set a long time interval for thermal input between some thermal inputs.

[0221] Herein, the case where the welding current, welding time, and time interval during thermal input of each thermal input are constant is not included.

[0222] (f) In each thermal input, make the welding current of the thermal input less than or equal to the welding current of the previous thermal input.

[0223] As welding progresses, maintain or reduce the welding current of each thermal input. That is, in each thermal input, it is preferable to make the welding current of the thermal input less than or equal to the welding current of the previous thermal input. Herein, the case where the welding currents are the same in all thermal inputs is not included. In other words, it is preferable to make the welding current of the thermal input less than or equal to the welding current of the previous thermal input in all thermal inputs, and make the welding current of at least one thermal input in all thermal inputs less than the welding current of the previous thermal input. Thereby, the amount of thermal input is reduced according to the high temperature of the copper. That is, excessive melting of the copper is suppressed. As a result, widening of the bead width can be suppressed, and a welded portion with excellent bead width stability can be obtained.

[0224] (g) In each thermal input, make the welding time of the thermal input less than or equal to the welding time of the previous thermal input.

[0225] As welding progresses, maintain or reduce the welding time for each heat input. That is, in each heat input, it is preferable that the welding time of the heat input is less than or equal to the welding time of the previous heat input. This does not include the case where the welding times are the same for all heat inputs. In other words, it is preferable that in all heat inputs, the welding time of the heat input is less than or equal to the welding time of the previous heat input, and the welding time of at least one of the heat inputs in all heat inputs is less than the welding time of the previous heat input. Thereby, the heat input amount is reduced according to the high temperature of copper. That is, excessive melting of copper is suppressed. As a result, widening of the bead width can be suppressed, and a welded portion with excellent bead width stability can be obtained.

[0226] (h) Set a time interval of long-duration heat input between some heat inputs.

[0227] Set a time interval of long-duration heat input between some heat inputs. For example, it is preferable that whenever a specified number of heat inputs are performed, by setting a time interval of long-duration heat input, excessive high temperature of the material to be joined is suppressed. More specifically, for example, a heat input pattern that repeats "perform 3 heat inputs at 1-second intervals, and take 5 seconds (time interval of long-duration heat input) after the 3rd heat input" can be exemplified. Thereby, excessive high temperature of the material to be joined, particularly excessive melting of copper, is suppressed. As a result, widening of the bead width can be suppressed, and a welded portion with excellent bead width stability can be obtained.

[0228] Here, the time interval of long-duration heat input means a heat input time interval that is longer than the normal heat input time interval. In addition, the time interval of long-duration heat input is preferably 3.00 to 6.00 s. It should be noted that the normal heat input time interval can be exemplified as 0.8 to 2.0 s. In addition, the frequency of setting the time interval of long-duration heat input is preferably 1 time for every 2 to 4 heat input time intervals. The frequency of setting the time interval of long-duration heat input can be constant or not constant.

[0229] The protruding length of the welding electrode from the welding nozzle (hereinafter also referred to as the protruding length) is preferably -1 mm to 10 mm. Especially when performing manual welding and a part of the welding nozzle is abutted against the copper surface of the material to be joined and it is easy to control the position or angle of the welding gun, the protruding length is preferably -1 mm or more and less than 3 mm. In addition, in the case of performing manual welding in a general manner without the above-mentioned control, or in the case of performing automatic welding, in order to easily operate the welding gun, or in order to easily set the electrode height at which the electrode tip can be easily recognized, the protruding length is preferably 3 mm or more. In addition, in order to appropriately form an inert gas atmosphere, the protruding length is preferably 10 mm or less.

[0230] In addition, from the perspective of easy removal when the front end of the electrode is fixed to the molten pool, the front end angle of the welding electrode is preferably 45° or less. On the other hand, from the perspective of reducing the grinding frequency of the electrode and improving the manufacturing efficiency, the front end angle of the welding electrode is preferably 15° or more. From the perspective of easy aiming at the heat input position, the electrode diameter of the welding electrode is preferably 2.4 mm or less. On the other hand, from the perspective of ensuring the spot welding diameter, the electrode diameter of the welding electrode is preferably 1.2 mm or more. The type of the welding electrode can be arbitrarily selected. For example, it can be selected and used from general electrodes such as thorium tungsten electrode rods, cerium tungsten electrode rods, lanthanum, and pure tantalum.

[0231] It should be noted that the method for joining stainless steel and copper according to an embodiment of the present invention can be implemented, for example, by the arc spot welding mode of a TIG welding machine capable of precisely controlling the arc spot welding time. In addition, the method for joining stainless steel and copper according to an embodiment of the present invention can also be implemented in a TIG welding machine capable of widely and precisely adjusting the pulse width and pulse frequency by using a low-speed pulse welding mode on the basis of adjusting the pulse width. In addition, the method for joining stainless steel and copper according to an embodiment of the present invention can be implemented in various postures such as the downward posture, the standing posture, the horizontal posture, and the upward posture. Therefore, during the circumferential welding of the pipe, welding can also be performed without rotating the pipe.

[0232] [3] Method for manufacturing a joined body of stainless steel and copper

[0233] Next, a method for manufacturing a joined body of stainless steel and copper according to an embodiment of the present invention will be described.

[0234] The method for manufacturing a joined body of stainless steel and copper according to an embodiment of the present invention includes a step of joining stainless steel and copper by the above-described method for joining stainless steel and copper according to an embodiment of the present invention.

[0235] By the method for manufacturing a joined body of stainless steel and copper according to an embodiment of the present invention, a joined body of stainless steel and copper according to an embodiment of the present invention can be manufactured.

[0236] Examples

[0237] (Example 1)

[0238] A stainless steel plate (SUS443J1 specified in JIS G 4305:2021) with the thickness recorded in Table 1 and a phosphor-deoxidized copper plate (C1220 specified in JIS H 3100:2018) (hereinafter simply referred to as "copper plate") with the thickness recorded in Table 1 were cut into squares with a side length of 120 mm. Next, the copper plate was placed on the stainless steel plate with the ends in the welding direction aligned with the overlapping width L recorded in Table 1 to form a material to be joined. Next, the electrode was placed on the copper side of the overlapping part of the stainless steel and copper of the material to be joined, and welding was performed by TIG welding under the conditions recorded in Table 1 to obtain a joined body of the stainless steel plate and the copper plate. It should be noted that welding was performed using a TIG welding machine, DA-300P, manufactured by DAIHEN Corporation. The shielding gas and the backing gas were 100% Ar, and the shielding gas flow rate and the backing gas flow rate were 25 L / min respectively. The preflow was 0.5 s, and the postflow was 3.0 s. The conditions other than the above were in accordance with the conventional method. In addition, in Test Nos. 1-1 to 1-5 and 1-9 to 1-17, in order to suppress excessive high temperature of the material to be joined, welding was carried out while cooling the material to be joined using a cold mold. On the other hand, in Test Nos. 1-6 to 1-8 and 1-18, the material to be joined was not cooled using a cold mold or a cooling pipe. It should be noted that the values in Table 1 and Tables 2, 3, 4, and 5 described later are appropriately rounded by rounding to show the rounded values. In addition, the "appropriate range of the position of the heat input point" recorded in Table 1 and Table 2 represents the appropriate range of the "position of each heat input point in the direction perpendicular to the welding", with the copper end of the overlapping part represented as the reference position (0), the copper side represented as +, and the stainless steel side represented as -.

[0239] It should be noted that in each of Test Nos. 1-1 to 1-16, multiple heat inputs were carried out under the same conditions. In addition, in Test Nos. 1-17 and 1-18, under the conditions of a welding current of 180 A and 140 A, the arc length was 1.5 mm, and TIG welding was continuously carried out at a welding speed of 75 mm / min (without being divided into multiple heat inputs).

[0240] Using the joined body of the stainless steel plate and the copper plate obtained thereby, the following were measured according to the above-mentioned procedure:

[0241] (I) The position of the welded part (whether it is located in the overlapping part),

[0242] (II) The Cu / Fe ratio of the welded part,

[0243] (III) The distance MF between the melting boundaries,

[0244] (IV) The diameter of each welding point,

[0245] (V) The average distance interval B of the welding points.

[0246] The results are all entered in Table 1. It should be noted that, for (I), in the column of the position of the welded part, "the overlapping part" means that in the direction perpendicular to the welding, the whole welded part is located in the overlapping part. In addition, "outside the overlapping part" means that in the direction perpendicular to the welding, at least a part of the welded part is located outside the overlapping part. Furthermore, for (IV), the diameters of each welding point are only representatively recorded as the minimum diameter D min and the maximum diameter D max .

[0247] It should be noted that in the measurement of (II) the Cu / Fe ratio of the welded part and (III) the distance MF between the melting boundaries, a scanning electron microscope (SEM) Miniscope (registered trademark) TM3030plus manufactured by High-Tech Co., Ltd. of Japan and an energy dispersive X-ray spectroscopy device (EDS) AZtecOne manufactured by Oxford Instruments are used.

[0248] In addition, (VI) airtightness and (VII) joint strength are measured according to the above-mentioned procedures and evaluated according to the following criteria. The results are all entered in Table 1.

[0249] (VI) Airtightness

[0250] Qualified: 0.2 MPa or more

[0251] Unqualified: less than 0.2 MPa

[0252] (VII) Joint strength

[0253] Qualified (specially excellent, indicated as "excellent" in the table): The joint strength is 80% or more of the lower strength between stainless steel and copper

[0254] Qualified: The joint strength is 60% or more and less than 80% of the lower strength between stainless steel and copper

[0255] Unqualified: The joint strength is less than 60% of the lower strength between stainless steel and copper

[0256] It should be noted that in the evaluation of (VI) airtightness, Rectorseal manufactured by Rectorseal Corporation is used as putty.

[0257] [Table 1]

[0258]

[0259]

[0260] As shown in Table 1, desired airtightness and joint strength can be obtained in the inventive examples. That is, a joint body of stainless steel and copper having sufficient joint strength can be obtained without causing cracks in the welded portion or joint discontinuity. In particular, in Tests No. 1-1 to 1-3 and 1-6 to 1-8, particularly excellent joint strength can be obtained. It should be noted that, as described above, the above inventive examples were all subjected to multiple heat inputs under the same conditions. In addition, multiple heat inputs were separately carried out under different conditions. Specifically, based on the test conditions of these inventive examples, the heat input conditions for each heat input were changed. In this case, it was also confirmed that as long as the conditions of the above (a) to (e) and Equation (4) are satisfied, the desired Cu / Fe ratio of the welded portion, the distance MF between the melting boundaries, and the average distance interval B of the welding points can be obtained, and the desired airtightness and joint strength can be obtained.

[0261] On the other hand, in the comparative examples, at least one of the airtightness and the joint strength was insufficient.

[0262] That is, in the comparative example of Test No. 1-9, since the position of the heat input point did not satisfy the appropriate range, the heat input was performed at a position too close to the copper end portion, and at least a part of the welded portion was located outside the overlapping portion. In addition, a large amount of stainless steel melted into the welded portion, cracks were generated in the welded portion, and the desired airtightness was not obtained. In addition, the joint strength was also insufficient.

[0263] In the comparative example of Test No. 1-10, since the position of the heat input point exceeded the appropriate range, the heat input was performed at a position too close to the stainless steel end portion, and at least a part of the welded portion was located outside the overlapping portion. In addition, there was no stainless steel in a part directly below the molten portion of the copper, and the desired joint strength was not obtained.

[0264] In the comparative example of Test No. 1-11, since it was less than the lower limit value of Equation (4), the distance MF between the melting boundaries was less than the lower limit value of Equation (1), and the desired joint strength was not obtained.

[0265] In the comparative example of Test No. 1-12, since it exceeded the upper limit value of Equation (4), the heat input amount was excessive, and the Cu / Fe ratio of the welded portion did not satisfy the appropriate range. As a result, cracks were generated in the welded portion, and the desired airtightness was not obtained. In addition, the joint strength was also insufficient.

[0266] In the comparative example of Test No. 1-13, since the heat input distance interval was too large and the average distance interval B of the welding points exceeded the appropriate range, the joint between the stainless steel and the copper became discontinuous, and the desired airtightness was not obtained.

[0267] In the comparative examples of Test Nos. 1-14, since the distance interval of heat input was too small, the average distance interval B of the welding points did not satisfy the appropriate range, so the heat input amount was too large. As a result, the Cu / Fe ratio of the welded part did not satisfy the appropriate range, cracks occurred in the welded part, and the desired airtightness could not be obtained. In addition, the bonding strength was also insufficient.

[0268] In the comparative example of Test No. 1-15, since the electrode height exceeded the appropriate range, the melting of copper was insufficient, the distance MF between the melting boundaries was less than the lower limit value of formula (1), and the desired bonding strength could not be obtained.

[0269] In the comparative example of Test No. 1-16, since the heat input time interval did not satisfy the appropriate range, the Cu / Fe ratio of the welded part did not satisfy the appropriate range, cracks occurred in the welded part, and the desired airtightness could not be obtained. In addition, the bonding strength was also insufficient.

[0270] In the comparative examples of Test Nos. 1-17 and 1-18, since TIG welding was continuously performed under general conditions (without being divided into multiple heat inputs), the stainless steel was over-melted. As a result, the Cu / Fe ratio of the welded part did not satisfy the appropriate range, cracks occurred in the welded part, and the desired airtightness could not be obtained. In addition, the bonding strength was also insufficient.

[0271] (Example 2)

[0272] Cut stainless steel pipes (welded pipes made of SUS304, SUS316L, SUS443J1, SUS445J1, SUS430J1L, and SUS444 stainless steel plates specified in JIS G 4305:2021) and copper pipes (phosphorus-deoxidized copper pipes (C1220T) specified in JIS H 3300:2018) having the outer diameters and thicknesses (wall thicknesses) recorded in Table 2 to a length of 300 mm. Next, insert the stainless steel pipe into the copper pipe so as to have the overlapping width L recorded in Table 2 to form the materials to be joined. Next, arrange the electrodes on the copper side of the overlapping portion of the stainless steel and copper of the materials to be joined, and perform welding by TIG welding under the conditions recorded in Table 2 to obtain a joined body of the stainless steel pipe and the copper pipe. It should be noted that welding points are formed around the entire circumference (one round) of the overlapping portion so as to form a welded portion around the entire circumference. In addition, welding is performed using a TIG welding machine, YS-TIG200PACDC, manufactured by HAIGE Industry Co., Ltd. 100% Ar is used as the shielding gas and the backing gas, and the shielding gas flow rate and the backing gas flow rate are set to 25 L / min, respectively. The pre-flow is 0.5 s, and the post-flow is 3.0 s. Other conditions are in accordance with conventional methods. In addition, in Test Nos. 2-1 to 2-6 and 2-8 to 2-10, in order to suppress excessive high temperature of the materials to be joined, a cooling pipe connected to a cooler is wound around the materials to be joined, and welding is performed while cooling the materials to be joined. On the other hand, in Test No. 2-7, the materials to be joined were not cooled using a cold mold or a cooling pipe.

[0273] Using the joined body of the stainless steel plate and the copper plate thus obtained, measure according to the above-mentioned procedure:

[0274] (I) The position of the welded portion (whether it is located in the overlapping portion),

[0275] (II) The Cu / Fe ratio of the welded portion,

[0276] (III) The distance MF between the fusion boundaries,

[0277] (IV) The diameter of each welding point,

[0278] (V) The average distance interval B between the welding points.

[0279] Record the results in Table 2 together.

[0280] In addition, measure (VI) airtightness and (VII) joint strength according to the above-mentioned procedure, and evaluate according to the same criteria as in Example 1. Record the results in Table 2 together.

[0281] It should be noted that conditions other than those described above and those recorded in Table 2 are the same as in Example 1.

[0282] [Table 2]

[0283]

[0284]

[0285] As shown in Table 2, desired airtightness and bonding strength can be obtained in the inventive examples. That is, a bonded body of stainless steel and copper having sufficient bonding strength can be obtained without causing cracks in the welded portion or bonding discontinuity. In addition, particularly excellent bonding strength can be obtained in any of the inventive examples. It should be noted that, in the above-mentioned inventive examples, multiple heat inputs were performed under the same conditions. In addition, multiple heat inputs were separately performed under different conditions. Specifically, based on the test conditions of the above-mentioned inventive examples, the heat input conditions for each heat input were changed. In this case, it was also confirmed that as long as the conditions of (a) to (e) and formula (4) are satisfied, the desired Cu / Fe ratio of the welded portion, the distance MF between the melting boundaries, and the average distance interval B of the welding points can be obtained, and the desired airtightness and bonding strength can be obtained.

[0286] On the other hand, in the comparative examples, at least one of the airtightness and the bonding strength was insufficient.

[0287] That is, in the comparative examples of Test Nos. 2-8, since it is less than the lower limit value of formula (4), the distance MF between the melting boundaries is less than the lower limit value of formula (1), and the desired bonding strength cannot be obtained.

[0288] In the comparative example of Test No. 2-9, since it exceeds the upper limit value of formula (4), the heat input amount is excessive, and the Cu / Fe ratio of the welded portion does not satisfy the appropriate range. As a result, cracks are generated in the welded portion, and the desired airtightness cannot be obtained. In addition, the bonding strength is also insufficient.

[0289] In the comparative example of Test No. 2-10, since the heat input distance interval is too large and the average distance interval B of the welding points exceeds the appropriate range, the bonding of stainless steel and copper becomes discontinuous, and the desired airtightness cannot be obtained.

[0290] (Example 3)

[0291] A stainless steel plate (SUS443J1 specified in JIS G 4305:2021) with a cut-out length of 40 mm, width of 50 mm, and thickness of 1.5 mm, and a phosphor-deoxidized copper plate (C1220 specified in JIS H 3100:2018) with a length of 40 mm, width of 40 mm, and thickness of 0.5 mm (hereinafter simply referred to as "copper plate"). Next, the copper plate was placed on the stainless steel plate in such a way that the areas overlapped with a width of 20 mm, i.e., the overlapping width L = 20 mm, to form the material to be joined. Next, the electrode was placed on the copper side of the overlapping portion of the stainless steel and copper of the material to be joined, and welding was performed by TIG welding under the conditions described in Tables 3 and 4 to obtain a joined body of the stainless steel plate and the copper plate. In addition, (a) electrode tilt angle: 0°, (b) electrode height: 1.0 mm, (c) heat input point position: +10.0 mm. The position of the heat input point in (c) is within the range of 0.5×0.03×I×d 0.5 / t 0.5 (mm) to L - 0.5×0.03×I×d 0.5 / t 0.5 (mm). The number of heat inputs was 16 times each. The welding machine used was the TIG welding machine YS-TIG200PACDC manufactured by HAIGE Industry Co., Ltd. The shielding gas and the backing shielding gas were each used at a gas flow rate of 25 L / min with 100% Ar. The pre-flow was 0.3 s, and the post-flow was 2.0 s. The other conditions were in accordance with the conventional method. It should be noted that in Tests No. 3-3 and No. 3-4, a cold mold was used to cool the material to be joined. On the other hand, in Tests No. 3-1 and No. 3-2, the material to be joined was not cooled using a cold mold or a cooling pipe.

[0292] Here, Condition A in Table 4 is the condition where none of the above (f) to (h) are carried out, and the welding current, welding time, and time interval between heat inputs for each heat input are kept constant. In addition, Condition B in Table 4 is the condition where the above (f) and (h) are carried out.

[0293] Using the joined body of the stainless steel pipe and the copper pipe obtained in this way, the following were measured according to the above-mentioned procedures:

[0294] (I) The position of the welded part (whether it is located in the overlapping part),

[0295] (II) The Cu / Fe ratio of the welded part,

[0296] (III) The distance MF between the melting boundaries,

[0297] (IV) The diameter of each welded point,

[0298] (V) The average distance interval B of the welded points.

[0299] Record the results in Table 3 together.

[0300] In addition, measure the airtightness of (VI) and the joint strength of (VII) according to the above-mentioned procedures, and evaluate them based on the same criteria as in Example 1. Record the results in Table 3 together.

[0301] Furthermore, from the minimum diameter D min and the maximum diameter D max of the weld points on the copper-side surface of the joined body, calculate the change rate of the weld bead width (D min / D max ). Record the results in Table 3 together.

[0302] [Table 3]

[0303]

[0304] [Table 4]

[0305] Table 4

[0306]

[0307] Table 4 (continued)

[0308]

[0309] Table 4 (continued)

[0310]

[0311] As shown in Table 3, desired airtightness and joint strength can be obtained in the inventive examples. That is, a joined body of stainless steel and copper having sufficient joint strength can be obtained without cracks in the welded portion or discontinuous joints. In addition, excellent airtightness and particularly excellent joint strength can be obtained in any of the inventive examples. Furthermore, in Test No. 3-1 where the materials to be joined were not cooled, the change rate of the weld bead width was 1.5. In Test No. 3-2 where the materials to be joined were also not cooled, by performing the above (f) and (h), the widening of the weld bead width during welding was suppressed, and a joined body of stainless steel and copper with particularly excellent weld bead width stability could be obtained. It should be noted that in Test No. 3-3 where the materials to be joined were cooled, the widening of the weld bead width was suppressed compared to Test No. 3-1 where no cooling was performed. Furthermore, in Test No. 3-4 where the materials to be joined were cooled and the above (f) and (h) were performed, the widening of the weld bead width was minimized.

[0312] (Example 4)

[0313] Cut out a stainless steel pipe with an outer diameter of 10 mm, a thickness (wall thickness) of 0.5 mm, and a length of 500 mm (a welded pipe made of a stainless steel plate of SUS304 specified by JIS G 4305:2021), and a copper pipe with an outer diameter of 12 mm, a thickness (wall thickness) of 1.0 mm, and a length of 500 mm (phosphorus-deoxidized copper pipe (C1220T) specified by JIS H 3300:2018). Next, insert the stainless steel pipe into the copper pipe in an overlapping manner with a length of 10 mm, that is, with an overlapping width L = 10 mm, to make the materials to be joined. Next, place the electrode on the copper side of the overlapping part of the stainless steel and copper of the materials to be joined, and perform welding by TIG welding under the conditions described in Tables 4 and 5 to obtain a joined body of the stainless steel pipe and the copper pipe. It should be noted that welding points are formed around the entire circumference (one round) of the overlapping part so as to form a welded part around the entire circumference. In addition, (a) electrode tilt angle: 0°, (b) electrode height: 1.0 mm, (c) heat input point position: +5.0 mm. The (c) heat input point position is within the range of 0.5×0.03×I×d 0.5 / t 0.5 (mm) to L - 0.5×0.03×I×d 0.5 / t 0.5 (mm). The number of heat inputs is 13 times each. The welding machine used is a TIG welding machine manufactured by MATSUMOTO KIKAI CO., LTD., namely PIPE ACE. The shielding gas and the backing shielding gas are each used at a gas flow rate of 25 L / min with 100% Ar. The preflow is 5.0 s, and the postflow is 6.0 s. The conditions other than the above are in accordance with the conventional method. It should be noted that no cold mold or cooling pipe is used to cool the materials to be joined.

[0314] Here, Condition C in Table 4 is the condition where none of the above (f) to (h) are carried out and the welding current, welding time, and time interval of each heat input are constant. In addition, Condition D in Table 4 is the case where the above (g) is carried out, Condition E is the case where the above (f) is carried out, Condition F is the case where the above (h) is carried out, Condition G is the case where the above (f) and (g) are carried out, Condition H is the case where the above (g) and (h) are carried out, and Condition I is the case where the above (f), (g), and (h) are carried out.

[0315] Using the joined body of the stainless steel pipe and the copper pipe obtained thereby, measure according to the above-mentioned procedures:

[0316] (I) The position of the welded part (whether it is located in the overlapping part),

[0317] (II) The Cu / Fe ratio of the welded part,

[0318] (III) The distance MF between the melting boundaries,

[0319] (IV) The diameter of each welding point,

[0320] (V) Average distance interval B of the solder joints.

[0321] Record the results in Table 5 together.

[0322] In addition, measure (VI) airtightness and (VII) joint strength according to the above-mentioned procedures, and evaluate them based on the same criteria as in Example 1. Record the results in Table 5 together.

[0323] Furthermore, from the minimum diameter D of the solder joints on the copper side surface of the joined body min and the maximum diameter D max calculate the change rate of the bead width (D min / D max ). Record the results in Table 5 together.

[0324] [Table 5]

[0325]

[0326] As shown in Table 5, desired airtightness and joint strength can be obtained in the inventive examples. That is, a joined body of stainless steel and copper having sufficient joint strength can be obtained without cracks in the welded portion and discontinuous joints. In addition, excellent airtightness and particularly excellent joint strength can be obtained in any of the inventive examples. Furthermore, in Test Nos. 4-2 to 4-7, by performing at least one of the above (f) to (h), the widening of the bead width during welding is suppressed, and a joined body of stainless steel and copper with particularly excellent bead width stability can be obtained.

[0327] Industrial Applicability

[0328] The joined body of stainless steel and copper according to an embodiment of the present invention is suitable for application to various products represented by heat exchanger pipes, electronic device components, and household electrical appliance products.

Claims

1. A bonded body of stainless steel and copper, comprising stainless steel, copper, and a welded portion between the stainless steel and the copper, wherein the stainless steel and the copper are in the form of plates or tubes, the welded portion is located at an overlapping portion where the stainless steel and the copper overlap each other, and the welded portion has a plurality of welding points connected along the welding direction on the copper-side surface of the bonded body, the Cu / Fe ratio of the welded portion is 10.0 or more, MF and t satisfy the relationship of the following formula (1), MF and B satisfy the relationship of the following formula (2), MF ≥ 0.8t ··· (1) 0.10MF ≤ B ≤ 1.25MF ··· (2) where, MF is the distance between the welded portion in the welding right-angle direction and the melting boundary of the copper on the overlapping surface of the stainless steel and the copper of the bonded body, with the unit of mm, B is the average distance interval of the welding points on the copper-side surface of the bonded body, with the unit of mm, t is the thickness of the copper, with the unit of mm.

2. The bonded body of stainless steel and copper according to claim 1, wherein, D max / D min Satisfy the relationship of the following formula (3), D max / D min ≤1.4···(3) where, D min is the minimum diameter of the welding point on the copper side surface of the joined body, in mm D max The maximum diameter of the solder joint on the copper side surface of the bonded body, in mm.

3. A method for bonding stainless steel and copper, which performs welding on the materials to be bonded, and the materials to be bonded are formed by overlapping stainless steel and copper, the welding is performed by TIG welding, in the TIG welding, the electrode is disposed on the copper side of the materials to be bonded, and multiple heat inputs are performed under the conditions satisfying the following (a) to (e), (a) the inclination angle α of the electrode is 0° to 45°, Among them, taking the thickness direction of the materials to be bonded as the reference angle of 0°, and taking the angle formed by the direction towards the front end of the electrode and the thickness direction of the materials to be bonded as the inclination angle of the electrode, (b) the electrode height is greater than 0 mm and 3.0 mm or less, (c) The heat input positions in the right-angled direction of welding are 0.5 × 0.03 × I × d 0.5 / t 0.5 ~L - 0.5 × 0.03 × I × d 0.5 / t 0.5 , with the unit of mm, where, I is the welding current, with the unit of A, d is the welding time, with the unit of s, t is the thickness of the copper, with the unit of mm, L is the width of the overlapping portion where the stainless steel and the copper overlap each other. In addition, for each heat input position in the welding right-angle direction, taking the copper end of the overlapping portion as the reference position of 0, taking the copper side as +, and taking the stainless steel side as -, (d) The distance interval in the welding direction of each heat input point is 0.1×{D k－1 ×(1 - 0.2×t)}~D k－1 ×(1 - 0.2×t), and the unit of the distance interval is mm. Among them, D k－1 is the diameter of the welding point formed by the previous heat input on the copper side surface of the material to be joined, in mm, t is the thickness of the copper, in mm, (e) the time interval between each heat input is 100% or more of the welding time s of the previous heat input, furthermore, in each heat input, the relationship of the following formula (4) is satisfied, t 1.5 / (1 - 0.2×t)÷0.03 ≤ I×d 0.5 ≤ t 1.5 / (1 - 0.2×t)÷0.03×6···(4) where, I is the welding current, with the unit of A, d is the welding time, with the unit of s, t is the thickness t of the copper, with the unit of mm.

4. The method for joining stainless steel and copper according to claim 3, wherein, perform at least one of the following (f) to (h), (f) in each heat input, making the welding current of the heat input be less than or equal to the welding current of the previous heat input, (g) in each heat input, making the welding time of the heat input be less than or equal to the welding time of the previous heat input, (h) setting a long time interval for heat input between some of the heat inputs, where, the case where the welding current, welding time, and time interval between heat inputs of each heat input are constant is not included.

5. A method for manufacturing a bonded body of stainless steel and copper, which bonds stainless steel and copper by the method for bonding stainless steel and copper according to claim 3 or 4.

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