Method for joining stainless steel and copper or copper alloy, and joined body of stainless steel and copper or copper alloy and method for producing same

Abstract

The present invention provides a simple method for joining stainless steel and copper or a copper alloy at low cost, the method being able to be carried out in the atmosphere. According to the present invention, Sn or an Sn alloy having an Sn content of 40% by mass or more is used as a joining metal. In the joining step, the copper or the copper alloy is heated by a heating device, and the stainless steel and the copper or the copper alloy are joined with each other by melting the joining metal while heating the stainless steel by means of heat transfer from the copper or the copper alloy. The highest temperature reached by the stainless steel is 350°C or less, and the residence time in the temperature range of 150°C or higher of the stainless steel is 5 seconds to 5 minutes inclusive.

Description

Method for joining stainless steel and copper or copper alloy, and joined body of stainless steel and copper or copper alloy and method for manufacturing the same

[0001] The present invention relates to a method for joining stainless steel and copper or a copper alloy, a joined body of stainless steel and copper or a copper alloy, and a method for producing the same.

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

[0003] In recent years, with the rise in copper prices, there has been a trend toward switching from copper and copper alloys to stainless steel as the material for heat exchangers made of copper and even copper alloys. However, it is difficult to switch all materials from copper and copper alloys to stainless steel, and some copper and copper alloy parts remain. In this case, products are manufactured by combining stainless steel parts with copper or copper alloy parts, which requires joining stainless steel and copper or copper alloy parts.

[0004] JP-T-2003-523830A JP-A-2005-349443A

[0005] Brazing is often used to join parts together in the manufacture of heat exchangers. The two main brazing methods used in the manufacturing process of heat exchangers are furnace brazing, in which components are heated in an atmospheric furnace to simultaneously join multiple parts, and torch brazing, in which the joint is heated with a torch in the atmosphere to join one part at a time. An appropriate brazing method is used depending on the part of the product and the assembly stage.

[0006] When brazing copper or copper alloys together, phosphorus copper brazing filler metal is generally used as the joining metal (brazing filler metal). However, when phosphorus copper brazing filler metal is used as the joining metal when brazing stainless steel to copper or copper alloy, an embrittlement layer is formed at the interface between the stainless steel and the joining metal. As a result, the joining metal peels off from the stainless steel, and a joint between stainless steel and copper or copper alloy cannot be obtained.

[0007] Therefore, silver brazing filler metal is commonly used when brazing stainless steel to copper or copper alloys. However, silver brazing filler metal is expensive. In addition, torch brazing, which is performed in the atmosphere, exposes the stainless steel to high temperatures due to heating by the torch. This results in the formation of a thick oxide film on the surface of the stainless steel, which inhibits the wetting and spreading of the brazing filler metal.

[0008] Furthermore, Patent Document 1 discloses "a method for joining copper or a copper alloy with an austenitic steel alloy, which comprises placing at least one intermediate layer between the joining surfaces of the objects to be joined, pressing the joining surfaces including the respective intermediate layers together, and heating at least the joining area to form a diffusion bond, characterized in that a first intermediate layer (3) is placed in contact with or against the joining surface of the steel object (2) to mainly prevent loss of nickel from the steel object (2), and at least one second intermediate layer (4) is placed in contact with or against the joining surface of the copper object (1) to activate the formation of the diffusion bond."

[0009] Patent Document 2 discloses "a method for joining stainless steel and an object to be joined to the stainless steel, comprising the steps of bringing a bonding agent consisting of solder and a bonding metal into contact between the stainless steel and the object to be joined, and performing a heat treatment while bringing the bonding agent into contact with the stainless steel and the object to be joined."

[0010] The technology described in Patent Document 1 provides an intermediate layer of nickel or the like between the joining surfaces of stainless steel and copper or copper alloy. The technology described in Patent Document 2 provides a joining metal, specifically, nickel foil or nickel particles, in addition to solder between the joining surfaces of stainless steel and copper or copper alloy. That is, both of the technologies described in Patent Documents 1 and 2 require the use of expensive nickel. Furthermore, the increase in manufacturing steps reduces productivity.

[0011] As described above, it cannot be said that a low-cost, simple method for joining stainless steel to copper or a copper alloy that can be carried out in the atmosphere has been developed, and therefore, there is a current demand for the development of such a method for joining stainless steel to copper or a copper alloy.

[0012] The present invention has been developed in view of the above-mentioned circumstances, and aims to provide a method for joining stainless steel and copper or a copper alloy that can be carried out in the atmosphere, at low cost, and easily. Another aim of the present invention is to provide a joined body of stainless steel and copper or a copper alloy, and a method for producing the same.

[0013] In order to achieve the above object, the inventors have conducted extensive research and have come to the conclusion that when joining stainless steel to copper or a copper alloy in the atmosphere, it is desirable to use Sn or an Sn alloy such as solder (hereinafter simply referred to as an Sn alloy) as the joining metal.

[0014] One of the factors that makes brazing stainless steel to copper or copper alloys difficult is the formation of an oxide film on the surface of the stainless steel. This oxide film reduces the wettability of the joining metals. Furthermore, during brazing, the joining is achieved by the slight diffusion of the constituent elements of the joining metals at the interface between the base materials. However, the oxide film prevents the diffusion of the constituent elements of the joining metals.

[0015] Therefore, when brazing stainless steel to copper or a copper alloy, it is necessary to prevent the formation of the oxide film. Here, the higher the temperature, the more likely the oxide film is to form. On the other hand, Sn alloys have a lower melting point than silver brazing and the like. They are also advantageous in terms of cost. Based on the above, the inventors have concluded that it is desirable to use Sn alloys as the joining metal when joining stainless steel to copper or a copper alloy in the atmosphere.

[0016] Based on the above considerations, the inventors used Sn alloy as the joining metal to join stainless steel and copper or copper alloy under various conditions in the atmosphere, and discovered the following: (1) In torch brazing, when the torch heats the vicinity of the joining target portion (the copper end in FIG. 1 or the stainless steel end in FIG. 2) of the overlapping joined materials, where stainless steel and copper or copper alloy are overlapped, the temperature of the stainless steel rises more quickly than that of the copper or copper alloy in the heated area. Furthermore, in copper or copper alloy, heat diffusion to unheated areas is more likely. That is, because copper or copper alloy has a higher thermal conductivity than stainless steel, the temperature of the stainless steel rises more quickly than that of the copper or copper alloy. (2) Therefore, even if the temperature of the stainless steel is raised above the melting point of the joining metal (Sn alloy), the temperature of the copper remains below the melting point of the joining metal. This results in the phenomenon of insufficient wetting and spreading of the joining metal. (3) On the other hand, when the joining target portion is heated so that the temperature of the copper or copper alloy is above the melting point of the joining metal, the stainless steel becomes even hotter. This causes a thick oxide film to form on the surface of the stainless steel, causing the joining metal to separate from the stainless steel, making it difficult to join stainless steel to copper or copper alloys.

[0017] Based on the above findings, the inventors conducted further research. As a result, the inventors discovered the following: Sn or an Sn alloy containing 40% or more by mass of Sn is used as the joining metal, and copper or a copper alloy of the materials to be joined is heated. The joining metal is melted while the stainless steel is heated by heat transfer from the copper or copper alloy. In addition, the maximum temperature reached by the stainless steel is set to 350°C or less, and the residence time of the stainless steel in a temperature range of 150°C or more is controlled to 5 seconds to 5 minutes. This allows the joining metal to be sufficiently wetted and spread, prevents the formation of a thick oxide film on the surface of the stainless steel, and joins the stainless steel and the copper or copper alloy.

[0018]

[0003] The inventors also attempted to join stainless steel and copper or copper alloys using a heating device with a heat generating element, such as a soldering iron, instead of torch brazing, to heat and melt the Sn alloy, which is the joining metal. However, depending on the joining conditions, particularly the type of copper or copper alloy used for the joined materials, the Sn alloy did not wet and spread sufficiently, and joining between stainless steel and copper or copper alloys was sometimes impossible. Furthermore, a thick oxide film was formed on the surface of the stainless steel, and joining between stainless steel and copper or copper alloys was sometimes impossible.

[0019] Therefore, the inventors conducted further experiments and studies and obtained the following findings. Specifically, it is important to appropriately control the heating position, particularly the contact position between the heating element of the heating device and the workpieces in the direction perpendicular to the joining (hereinafter simply referred to as the contact position), depending on the thermal conductivity of the copper or copper alloy used for the workpieces. Specifically, the contact position is determined by defining the overlapping edge, which is the starting point for pouring the joining metal onto the overlapping surfaces of the workpieces, as the reference position (0 mm), the stainless steel side as +, and the copper or copper alloy side as -. When the thermal conductivity of copper or copper alloy is 250 W / mK or higher, the contact position should be in the range of over 0 mm to +15 mm. When the thermal conductivity of copper or copper alloy is less than 250 W / mK, the contact position should be in the range of -15 mm to +15 mm. It is also important to limit the maximum temperature of the stainless steel to 250°C or lower and to control the residence time of the stainless steel in a temperature range of 100°C or higher to 5 seconds or more and 5 minutes or less. By simultaneously satisfying these conditions, the joining metals are sufficiently wetted and spread, and the formation of a thick oxide film on the surface of the stainless steel is prevented, thereby enabling the joining of stainless steel and copper or a copper alloy. The present invention was completed based on the above findings and further investigation.

[0020] That is, the gist of the present invention is as follows: 1. A method for joining stainless steel and copper or a copper alloy, comprising a joining step of joining overlapping materials to be joined, which are stainless steel and copper or a copper alloy, with a joining metal, wherein the joining metal is Sn or an Sn alloy having an Sn content of 40 mass % or more, and in the joining step, the copper is heated by a heating device, and the joining metal is melted while the stainless steel is heated by heat transfer from the copper or copper alloy, thereby joining the stainless steel and the copper or copper alloy, the maximum temperature reached by the stainless steel is 350°C or less, and the stainless steel is held in a temperature range of 150°C or more for 5 seconds to 5 minutes.

[0021] 2. The method for joining stainless steel and copper or a copper alloy according to 1 above, wherein the heating device is a torch.

[0022] 3. A joining process is included in which overlapping workpieces of stainless steel and copper or a copper alloy are joined with a joining metal, wherein the joining metal is Sn or an Sn alloy with an Sn content of 40% by mass or more, wherein in the joining process, a heating device having a heat generating part is used to bring the heat generating part into contact with the workpieces to melt the joining metal and join the stainless steel and the copper or copper alloy, wherein the contact position between the heat generating part and the workpieces in a direction perpendicular to the joining is set at the overlapping end portion where the joining metal starts to flow onto the overlapping surfaces of the workpieces as the reference position (0 mm), with the stainless steel side as + and the copper or copper alloy side as -, and when the thermal conductivity of the copper or copper alloy is 250 W / mK or more, the contact position is in the range of more than 0 mm to +15 mm, and when the thermal conductivity of the copper or copper alloy is less than 250 W / mK, the contact position is in the range of -15 mm to +15 mm, The method for joining stainless steel and copper or a copper alloy, wherein the stainless steel is held in a temperature range of 100°C or higher for 5 seconds or more and 5 minutes or less.

[0023] 4. The method for joining stainless steel and copper or a copper alloy according to 3 above, wherein the heating device is a soldering iron.

[0024] 5. A joined body of stainless steel and copper or a copper alloy, which is joined to stainless steel and copper or a copper alloy by the method for joining stainless steel and copper or a copper alloy as set forth in any one of 1 to 4 above.

[0025] 6. A method for producing a joined body of stainless steel and copper or a copper alloy, which joins stainless steel and copper or a copper alloy by the method for joining stainless steel and copper or a copper alloy as set forth in any one of 1 to 4 above.

[0026] According to the present invention, a low-cost, simple method for joining stainless steel to copper or a copper alloy can be obtained, which can be carried out in the atmosphere. Furthermore, the joined body obtained by the joining method of the present invention can be produced at a lower cost than when silver brazing is used, and is therefore extremely advantageous when applied to joining parts of stainless steel to copper or a copper alloy in various devices, such as gas water heaters and cold / hot water supply piping.

[0027] FIG. 1 is a schematic diagram showing an example of a positional relationship in a bonding method according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of a bonded body according to one embodiment of the present invention. FIG. 3 is a schematic diagram showing an example of a bonded body according to one embodiment of the present invention. FIG. 4 is an example of an optical microscope photograph of a cross section of a bonded portion in a bonded body (an example of a cross section of a bonded portion in Test No. 1-2 of Example 1). FIG. 5 is an example of an optical microscope photograph of a cross section of a bonded portion in a bonded body (an example of a cross section of a bonded portion in Test No. 3-2 of Example 3).

[0028] The present invention will be described based on the following embodiments. [1] Method for joining stainless steel and copper or copper alloy First, a method for joining stainless steel and copper or copper alloy (hereinafter simply referred to as a joining method) according to one embodiment of the present invention will be described.

[0029] A joining method according to a first embodiment includes a joining step of joining overlapping materials, which are stainless steel and copper or a copper alloy, with a joining metal, wherein the joining metal is Sn or an Sn alloy having an Sn content of 40 mass % or more, and in the joining step, the copper or copper alloy is heated by a heating device, and the joining metal is melted while the stainless steel is heated by heat transfer from the copper or copper alloy, thereby joining the stainless steel and the copper or copper alloy, the maximum temperature reached by the stainless steel is 350°C or less, and the stainless steel is held in a temperature range of 150°C or more for a period of 5 seconds to 5 minutes.

[0030] A joining method according to a second embodiment includes a joining step of joining overlapping workpieces of stainless steel and copper or a copper alloy with a joining metal, the joining metal being Sn or an Sn alloy having an Sn content of 40% by mass or more, the joining step using a heating device having a heat generating part to bring the heat generating part into contact with the workpieces to melt the joining metal and join the stainless steel and the copper or copper alloy, the contact position between the heat generating part and the workpieces in a direction perpendicular to the joining is determined by setting the overlapping end, which is the starting point for pouring the joining metal into the overlapping surfaces of the workpieces, as a reference position (0 mm), the stainless steel side as +, and the copper or copper alloy side as -, and when the thermal conductivity of the copper or copper alloy is 250 W / mK or more, the contact position is in the range of more than 0 mm to +15 mm, and when the thermal conductivity of the copper or copper alloy is less than 250 W / mK, the contact position is in the range of -15 mm to +15 mm, The residence time of the stainless steel in a temperature range of 100°C or higher is 5 seconds to 5 minutes.

[0031] Here, when the starting point of pouring the joining metal onto the overlapping surfaces of the workpieces (in the direction perpendicular to the joining) is the copper or copper alloy end (hereinafter also referred to as the copper end) as shown in Figure 1, the reference position is the copper end. When the starting point of pouring the joining metal onto the overlapping surfaces of the workpieces (in the direction perpendicular to the joining) is the stainless steel end as shown in Figure 2, the reference position is the stainless steel end.

[0032] In the joining method according to the second embodiment, when the reference position is the copper end, as shown in Fig. 1, the contact position is the surface of the workpiece on which copper or copper alloy is located (the top surface of the workpiece in Fig. 1, hereinafter also referred to as the copper-side surface of the workpiece). When the reference position is the stainless steel end, as shown in Fig. 2, the contact position is the surface of the workpiece on which stainless steel is located (the top surface of the workpiece in Fig. 2, hereinafter also referred to as the stainless steel-side surface of the workpiece).

[0033] 1 to 6, the X direction, Y direction, and Z direction are as follows: X direction: welding progress direction Y direction: welding perpendicular direction (direction perpendicular to the welding progress direction (X direction) and perpendicular to the thickness direction (Z direction) described below) Z direction: thickness direction of the materials to be welded (joined body) (hereinafter, also simply referred to as the thickness direction)

[0034] The bonding methods according to the first and second embodiments will be described in detail below. In the following description, if there is no particular specification as to whether the bonding method is according to the first embodiment or the second embodiment, the description applies to both the bonding methods according to the first and second embodiments.

[0035] (1) Stainless Steel This is stainless steel that will be the materials to be joined (the base material of the joined body after joining), and its shape is a plate (stainless steel plate) or a tube (stainless steel pipe). Note that the term "plate" here includes not only flat plates but also curved plates (curved plates). There are no particular restrictions on the thickness of the stainless steel (plate thickness or tube thickness), but from the viewpoint of heat transfer during joining, it is preferable that it be 0.1 mm or more. Furthermore, it is preferable that the thickness of the stainless steel be 2.0 mm or less. The thickness of the stainless steel is more preferably 0.2 mm or more, and even more preferably 0.3 mm or more. Furthermore, the thickness of the stainless steel is more preferably 1.0 mm or less.

[0036] When the stainless steel is in the form of a plate, the size of the plate is not particularly limited. For example, from the viewpoint of heat dissipation after joining, the size is preferably 10 mm square or more, and more preferably 30 mm square or more.

[0037] When the stainless steel base material has a tubular shape, the size (outer diameter and length) of the tube is not particularly limited. For example, from the viewpoint of heat dissipation after joining, the outer diameter of the tube is preferably at least four times the tube thickness (wall thickness). Furthermore, the outer diameter of the tube is preferably at least 5 mm. The outer diameter of the tube is preferably at most 500 mm. The length of the tube is preferably at least 10 mm, more preferably at least 30 mm.

[0038] The composition of the stainless steel is not particularly limited, and may be any of the common components for stainless steel. For example, an iron-based alloy containing 10.5 mass% or more of Cr and 50 mass% or more of Fe may be used. Examples include austenitic stainless steel plates, austenitic-ferritic stainless steel plates, ferritic stainless steel plates, martensitic stainless steel plates, and precipitation hardened stainless steel plates specified in JIS G 4305:2021, as well as processed products thereof. Also, stainless steel sanitary 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 processed products thereof, may be used. The stainless steel plates may include No. Steel sheets having various surface finishes can be used, including No. 2B finish (annealed, pickled, skin-pass finish), No. 2D finish (annealed, pickled finish), No. 4 finish (polished finish), No. 8 finish (mirror-polished finish), BA finish (bright annealed finish), HL (hairline) finish, dull finish, embossed finish, and blast finish.

[0039] (2) Copper or Copper Alloy Copper or copper alloy serves as the materials to be joined (the base material of the joined body after joining), and its shape is a plate (copper plate or copper alloy plate) or a tube (copper tube or copper alloy tube). Here, the term "plate" includes not only flat plates but also curved plates (curved plates). The thickness (plate thickness or tube thickness) of the copper or copper alloy is not particularly limited, but is preferably 0.1 mm or more from the viewpoint of heat transfer during joining. The thickness of the copper or copper alloy is more preferably 0.3 mm or more, and even more preferably 0.5 mm or more. The thickness of the copper or copper alloy is preferably 4.0 mm or less, more preferably 2.0 mm or less, and even more preferably 1.0 mm or less. In particular, in the joining method according to the second embodiment, the thickness of the copper or copper alloy is more preferably 2.0 mm or less, and even more preferably 1.0 mm or less from the viewpoint of suppressing the inhibition of temperature rise of the materials to be joined due to heat diffusion.

[0040] When the copper or copper alloy is in the form of a plate, the size of the plate is not particularly limited. For example, from the viewpoint of heat dissipation after joining, the size is preferably 10 mm square or more, and more preferably 30 mm square or more.

[0041] When the copper or copper alloy base material has a tubular shape, the size (outer diameter and length) of the tube is not particularly limited. For example, from the viewpoint of heat dissipation after joining, the outer diameter of the tube is preferably at least four times the tube thickness (wall thickness). Furthermore, the outer diameter of the tube is preferably at least 5 mm. The outer diameter of the tube is preferably at most 500 mm. The length of the tube is preferably at least 10 mm, more preferably at least 30 mm.

[0042] Note that copper or copper alloys as used herein include so-called pure copper consisting of Cu and unavoidable impurities, as well as copper alloys containing 50% by mass or more of Cu. Examples include various copper or copper alloy sheets and strips, as specified in JIS H 3100:2018, including oxygen-free copper, tough pitch copper, phosphorus-deoxidized copper, brass, free-cutting brass, and red brass, as well as processed products thereof. Furthermore, copper alloy sheets and strips, as specified in JIS H 3110:2018, including phosphorus bronze and nickel silver, as well as processed products thereof, can also be used. For example, the thermal conductivity of oxygen-free copper and tough pitch copper is 391 W / mK. The thermal conductivity of phosphorus-deoxidized copper is 339 to 381 W / mK. The thermal conductivity of brass and free-cutting brass is 117 to 121 W / mK. The thermal conductivity of red brass is 138 to 234 W / mK. The thermal conductivity of phosphor bronze is 58 to 201 W / mK. The thermal conductivity of nickel silver is 29 to 46 W / mK. In the case of plate-shaped copper or copper alloy plates with various surface finishes, such as HL (hairline) finish, matte finish, blast finish, and hammered finish, can be used. In the case of tubular copper or copper alloy seamless pipes and welded pipes specified in JIS H 3300:2018 and JIS H 3320:2006, as well as processed products thereof, can be used.

[0043] (3) Joining Metal: Sn or Sn Alloy with Sn Content of 40% by Mass or More In order to sufficiently melt the joining metal while suppressing excessive temperature rise of the stainless steel during joining, the joining metal is made of Sn or an Sn alloy with an Sn content of 40% by mass or more. Here, if the Sn content of the joining metal is less than 40% by mass, a large amount of heat is required to melt the joining metal. As a result, the joining metal does not melt sufficiently, and the stainless steel and copper or copper alloy are not joined. Therefore, the joining metal is made of Sn or an Sn alloy with an Sn content of 40% by mass or more. The Sn content of the joining metal is preferably 90% by mass or more. Furthermore, from the viewpoint of suppressing a decrease in brittleness in extremely cold regions, the Sn content of the joining metal is preferably 99.5% by mass or less, more preferably 97% by mass or less.

[0044] Examples of Sn alloys having an Sn content of 40% by mass or more include solder. In particular, solders having an Sn content of 40% by mass or more among the solders described in JIS Z 3282:2017 are preferably used. The joining metal may contain flux (so-called resin-cored solder may also be used).

[0045] The Sn alloys are exemplified below. (Sn—Ag-based alloy) Contains 4.5 to 5.5 mass% Ag, with the balance consisting of Sn and unavoidable impurities. (Sn—Cu-based alloy) Contains 2.0 to 4.0 mass% Cu, with the balance consisting of Sn and unavoidable impurities. (Sn—Sb-based alloy) Contains 4.0 to 6.0 mass% Sb, with the balance consisting of Sn and unavoidable impurities. (Sn—Ag—Cu-based alloy) Contains 0.5 to 4.5 mass% Ag and 0.2 to 1.0 mass% Cu, with the balance consisting of Sn and unavoidable impurities. (Sn—Pb-based alloy) Contains 3.0 to 60.0 mass% Pb, with the balance consisting of Sn and unavoidable impurities. (Sn—Ag—Bi—Cu-based alloy) Contains 2.0 to 3.0 mass% Ag, 0.5 to 1.5 mass% Bi, and 0.2 to 1.0 mass% Cu, with the balance consisting of Sn and unavoidable impurities. (Sn—In—Ag—Bi-based alloy) Contains 3.0 to 9.0 mass% In, 3.0 to 4.0 mass% Ag, and 0.2 to 1.0 mass% Bi, with the balance consisting of Sn and unavoidable impurities. (Sn—Zn-based alloy) Contains 8.0 to 10.0 mass% Zn, with the balance consisting of Sn and unavoidable impurities. (Sn—Zn—Bi-based alloy) Contains 7.0 to 9.0 mass% Zn, and 2.5 to 3.5 mass% Bi, with the balance consisting of Sn and unavoidable impurities. (Sn—Bi-based alloy) Contains 55.0 to 60.0 mass % of Bi, with the balance consisting of Sn and unavoidable impurities. (Sn—In-based alloy) Contains 50.0 to 55.0 mass % of In, with the balance consisting of Sn and unavoidable impurities.

[0046] Thus, the remainder of the joining metal other than Sn contains 60 mass% or less of metal elements such as Ag, Cu, Sb, Pb, Bi, In, and Zn (hereinafter also referred to as metal elements other than Sn). The content of metal elements other than Sn is preferably 10 mass% or less. However, the metal elements other than Sn do not include Ni. The content of metal elements other than Sn is preferably 0.5 mass% or more, more preferably 3.0 mass% or more. Suitable contents of each metal element other than Sn are, for example, Ag: 5.5 mass% or less, Cu: 4.0 mass% or less, Sb: 6.0 mass% or less, Pb: 60 mass% or less, Bi: 60 mass% or less, In: 55 mass% or less, and Zn: 10.0 mass% or less. More details are as described above.

[0047] Inevitable impurities contained in the bonding metal include elements such as Pb, Sb, Bi, Cd, Cu, Au, In, Ag, Al, As, Cd, Fe, Ni, Zn, Ge, P, and Ga, and a total of 2.0 mass% or less of these elements is acceptable. The inevitable impurities may be 0 mass%. Elements that are intentionally added to the bonding metal are not considered inevitable impurities.

[0048] The melting point of the joining metal is preferably 100 to 320° C. Here, the melting point T (° C.) of the joining metal is a temperature calculated from the solidus temperature Ts (° C.) and liquidus temperature Tl (° C.) of the joining metal by the following formula: T=(Ts+Tl) / 2

[0049] In particular, in the bonding method according to the first embodiment, the melting point of the bonding metal is preferably 100° C. or higher, more preferably 190° C. or higher. The melting point of the bonding metal is preferably 320° C. or lower, more preferably 300° C. or lower.

[0050] In the bonding method according to the second embodiment, the melting point of the bonding metal is preferably 100° C. or higher. The melting point of the bonding metal is preferably 320° C. or lower, more preferably 250° C. or lower, and even more preferably 240° C. or lower.

[0051] (4) Joining Step (4-1) First Embodiment In the joining step of the joining method according to the first embodiment, for example, while moving a heating device in the joining direction, overlapping joined materials, that is, stainless steel and copper or a copper alloy (hereinafter, in the description of the joining step of the joining method according to the first and second embodiments, copper and copper alloy will be collectively referred to as simply copper), are joined with a joining metal as shown in Fig. 1 or 2. Then, at this time, the copper of the joined materials is heated, and the stainless steel is heated by heat transfer from the copper, and the joining metal is melted to join the stainless steel and the copper.

[0052] Location Heated by Heating Device: Copper In the joining method according to the first embodiment, it is important to heat copper, one of the materials to be joined, with a heating device, and then heat the stainless steel by heat transfer from the copper, melting the joining metal and joining the stainless steel and copper. This ensures that the joining metal sufficiently wets and spreads, and prevents the formation of a thick oxide film on the surface of the stainless steel, thereby joining the stainless steel and copper. Therefore, the location heated by the heating device (hereinafter simply referred to as the heated location) is copper, one of the materials to be joined. Note that in the description of the heated location, copper and copper alloys will be collectively referred to simply as copper, even in the examples described below.

[0053] Here, the heated point being copper means the following: (Joining condition 1-a) As shown in Figure 1, when the part to be joined is near the copper end (the starting point for pouring the joining metal onto the overlapping surfaces of the materials to be joined is the copper end; in other words, the supply (installation) position of the joining metal is on the copper end side of the materials to be joined), and the heated area by the heating device (for example, in the case of a torch, the area that comes into contact with the gas flame; hereinafter simply referred to as the heated area) is the top surface of the copper (the surface of the copper opposite the side that overlaps with the stainless steel), "The heated point is copper" means that, in the direction perpendicular to the joining, the copper end is the reference position (0 mm), the stainless steel side is +, and the copper side is -, and the heated position is less than 0 mm, and stainless steel is not included in the heated area. (Joining condition 1-b) As shown in Figure 1, when the parts to be joined are near the copper end and the heated area by the heating device is the underside of the copper (the surface of the copper that overlaps with the stainless steel), "the heated area is copper" means that, in the direction perpendicular to the joining, the copper end is the reference position (0 mm), the stainless steel side is +, and the copper side is -, the heated position is less than -L (overlapping width) mm, and stainless steel is not included in the heated area. (Joining condition 2-a) As shown in Figure 2, when the parts to be joined are near the stainless steel end (the starting point for pouring the joining metal onto the overlapping surfaces of the joined materials is the stainless steel end; in other words, the supply (installation) position of the joining metal is on the stainless steel end side of the joined materials), and the heated area is the upper surface of the copper (the surface of the copper that overlaps with the stainless steel), "the heated area is copper" means that, in the direction perpendicular to the joining, the stainless steel end is the reference position (0 mm), the stainless steel side is +, and the copper side is -, the heated position is less than 0 mm, and stainless steel is not included in the heated area. (Joining condition 2-b) When the part to be joined is near the end of the stainless steel and the heated area is the underside of the copper (the surface of the copper opposite to the side overlapping with the stainless steel) as shown in Figure 2, "The heated area is copper" means that in the direction perpendicular to the joining, the end of the stainless steel is the reference position (0 mm), the stainless steel side is +, and the copper side is -, and the heated position is less than L (overlapping width) mm and the heated area does not include stainless steel. Note that the heated position here is the center position of the heated area in the direction perpendicular to the joining.

[0054] Furthermore, from the viewpoint of more reliably excluding the stainless steel from the heating region and sufficiently melting the joining metal while heating the stainless steel by heat transfer from the copper, it is preferable to set the heating position in the direction perpendicular to the joining according to the above joining conditions as follows: (Joining condition 1-a) With the copper-steel end as the reference position (0 mm), in the range of -(L+100) mm to -L mm on the upper surface of the copper (Joining condition 1-b) With the copper-steel end as the reference position (0 mm), in the range of -(L+100) mm to -(L+10) mm on the lower surface of the copper (Joining condition 2-a) With the stainless steel end as the reference position (0 mm), in the range of -100 mm to -10 mm on the upper surface of the copper (Joining condition 2-b) With the stainless steel end as the reference position (0 mm), in the range of -100 mm to 0 mm on the lower surface of the copper

[0055] Maximum temperature of stainless steel: 350°C or less In the joining method according to the first embodiment, it is important to suppress the formation of an oxide film on the surface of the stainless steel. In particular, when heating with a torch or the like, if the maximum temperature of the stainless steel during joining exceeds 350°C, an oxide film will rapidly form on the surface of the stainless steel, and the joining metal will detach from the stainless steel. Therefore, the maximum temperature of the stainless steel is set to 350°C or less. The maximum temperature of the stainless steel is preferably 300°C or less. There is no particular limit to the lower limit of the maximum temperature of the stainless steel. The maximum temperature of the stainless steel is, for example, preferably 200°C or more, more preferably 250°C or more.

[0056] Residence time of stainless steel in a temperature range of 150°C or higher (hereinafter also referred to as residence time of stainless steel at 150°C or higher): 5 seconds to 5 minutes. In the joining method according to the first embodiment, as described above, copper, one of the materials to be joined, is heated. Then, the stainless steel is heated by heat transfer from the copper, and the joining metal is melted and flows into the overlapping surfaces of the materials to be joined. During this process, excessive temperature rise of the stainless steel is prevented, and the formation of an oxide film on the surface of the stainless steel is suppressed. Here, if the residence time of the stainless steel at 150°C or higher is less than 5 seconds, the joining metal does not sufficiently flow into the overlapping surfaces of the materials to be joined, preventing the joining of the stainless steel and the copper. On the other hand, if the residence time of the stainless steel at 150°C or higher exceeds 5 minutes, a thick oxide film forms on the surface of the stainless steel, preventing the joining of the stainless steel and the copper. Therefore, the residence time of the stainless steel at 150°C or higher is set to 5 seconds to 5 minutes (300 seconds). The residence time of the stainless steel at 150°C or higher is preferably 15 seconds or longer. The residence time of the stainless steel at 150° C. or higher is preferably 3 minutes (180 seconds) or less, more preferably 1 minute (60 seconds) or less.

[0057] In measuring the temperature of the stainless steel to derive the maximum temperature reached by the stainless steel and the residence time at 150°C or higher, the entire surface of the stainless steel may be measured using, for example, a thermograph. Alternatively, depending on the heating area of ​​the heating device, the surface temperature of the stainless steel in the vicinity of the heating area may be measured using a thermocouple.

[0058] For example, in the case of the above (Joining Condition 1-a) and (Joining Condition 1-b), the copper end is set as the reference position (0 mm), and the surface temperature of the first surface of the stainless steel (the upper surface of the stainless steel in FIG. 1) is measured at a position of 0 mm (the copper end) to +20 mm in the direction perpendicular to the joint. Also, in the case of the above (Joining Condition 2-a) and (Joining Condition 2-b), the stainless steel end is set as the reference position (0 mm), and the surface temperature of the second surface of the stainless steel (the upper surface of the stainless steel in FIG. 2) is measured at a position of 0 mm (the stainless steel end) to +20 mm in the direction perpendicular to the joint.

[0059] Since the temperature of the stainless steel at the above positions is approximately the same during joining, the temperature measurement position can be determined from the above positions depending on the structure of the materials to be joined, etc. Here, the first surface of the stainless steel is the surface of the stainless steel on the side that overlaps with the copper (where the copper is arranged), and the second surface of the stainless steel is the surface of the stainless steel on the opposite side to the side that overlaps with the copper. In addition, the measurement interval for the temperature of the stainless steel in the joining direction is preferably, for example, 3 to 10 mm.

[0060] The maximum temperature of the stainless steel during joining and the residence time of the stainless steel at 150°C or higher can be controlled by adjusting, in addition to the heating position, for example, the joining speed (the movement speed of the heating device in the joining direction), the distance between the heating device and the materials to be joined, and the output of the heating device. For example, when a torch is used as the heating device, the maximum temperature of the stainless steel during joining and the residence time of the stainless steel at 150°C or higher can be controlled within the above ranges by adjusting the joining speed in the range of 30 to 200 mm / min, the distance between the heating device and the materials to be joined in the range of 50 to 150 mm, and the output of the heating device in the range of 2000 to 3000 kcal / hr depending on the type, size, and placement of the materials to be joined.

[0061] The heating device is not particularly limited as long as it can heat the stainless steel by heat transfer from the copper, melt the joining metal, and control the maximum temperature and residence time of the stainless steel during joining within the above-mentioned ranges. Among these, a torch (for example, a heating device specified in JIS Z 3001-1:2018), particularly a torch that uses a gas flame (torch burner), is preferred.

[0062] The size of the heating area is not particularly limited. To ensure that stainless steel is excluded from the heating area, the heating area is preferably within a 30 mm square. For example, a torch with a nozzle diameter of 10 to 20 mm may be used.

[0063] (4-2) Second Embodiment In the joining step of the joining method according to the second embodiment, for example, while moving a heating device in the joining direction, the heat-generating part of the heating device is brought into contact with the workpieces, which are made of overlapping stainless steel and copper as shown in Figure 1 or 2. This melts the joining metal, joining the stainless steel and copper. At this time, it is important to appropriately control the contact position depending on the thermal conductivity of the copper used in the workpieces.

[0064] Contact position when copper has a thermal conductivity of 250 W / mK or higher: greater than 0 mm to +15 mm. When copper has a thermal conductivity of 250 W / mK or higher, the contact position should be set to 0 mm or less. In other words, if the contact position is set to copper, much of the heat input from the heating element of the heating device is transferred to the copper, and the stainless steel is not sufficiently heated. As a result, the joining metal does not sufficiently flow into the overlapping surfaces of the joined materials, preventing the joining of the stainless steel and the copper. On the other hand, if the contact position is set to greater than +15 mm, the joining metal and the stainless steel near the overlapping surfaces of the joined materials are not sufficiently heated. As a result, the joining metal does not sufficiently flow into the overlapping surfaces of the joined materials, preventing the joining of the stainless steel and the copper. Therefore, when copper has a thermal conductivity of 250 W / mK or higher, the contact position should be set to a range of greater than 0 mm to +15 mm. The contact position is preferably greater than +1 mm. The contact position is more preferably less than +10 mm, and even more preferably less than +5 mm.

[0065] Contact position when copper has a thermal conductivity of less than 250 W / mK: -15 mm to +15 mm. When copper has a thermal conductivity of less than 250 W / mK, stainless steel can be sufficiently heated even if the contact position is copper. However, if the contact position is less than -15 mm, the stainless steel is not sufficiently heated. As a result, the joining metal does not sufficiently flow into the overlapping surfaces of the joined materials, preventing the joining of the stainless steel and copper. On the other hand, if the contact position is greater than +15 mm, the stainless steel near the overlapping surfaces of the joined materials is not sufficiently heated. As a result, the joining metal does not sufficiently flow into the overlapping surfaces of the joined materials, preventing the joining of the stainless steel and copper. Therefore, when copper has a thermal conductivity of less than 250 W / mK, the contact position should be in the range of -15 mm to +15 mm. The contact position is preferably -5 mm or greater. Furthermore, the contact position is more preferably +5 mm or less.

[0066] As mentioned above, the contact position is indicated by taking the overlapping end, which is the starting point for pouring the joining metal onto the overlapping surfaces of the workpieces, as the reference position (0 mm), the stainless steel side as +, and the copper side as -. Also, when the reference end is the copper end, the contact position is the copper side surface of the workpieces. Also, when the reference end is the stainless steel end, the contact position is the stainless steel side surface of the workpieces.

[0067] For example, as shown in Fig. 1, when the starting point of pouring the joining metal onto the overlapping surfaces of the workpieces is the copper end, in other words, when the joining metal is supplied (placed) on the copper end side of the workpieces, the reference position is the copper end of the workpieces. In this case, the contact position is the copper side surface of the workpieces (the upper surface of the workpieces in Fig. 1).

[0068] 2, when the starting point for pouring the joining metal onto the overlapping surfaces of the workpieces is the stainless steel end, in other words, when the joining metal is supplied (placed) on the stainless steel end side of the workpieces, the reference position is the stainless steel end. In this case, the contact position is the stainless steel side surface of the workpieces (the top surface of the workpieces in FIG. 2).

[0069] The contact position here refers to the center position in the direction perpendicular to the joining of the area where the heat generating part of the heating device and the workpieces come into contact.

[0070] In addition, since the joining metal can be melted by heat transfer from the materials to be joined, the heat generating part of the heating device may or may not come into contact with the joining metal. In addition, the heat generating part of the heating device may come into contact with the end face of the overlapping part of the materials to be joined on the reference position side.

[0071] Maximum temperature of stainless steel: 250°C or less In the joining method according to the second embodiment, it is important to suppress the formation of an oxide film on the surface of the stainless steel. In particular, in joining by the above heating method, if the maximum temperature of the stainless steel exceeds 250°C, an oxide film will rapidly form on the surface of the stainless steel, and the joining metal will detach from the stainless steel. Therefore, the maximum temperature of the stainless steel is set to 250°C or less. There is no particular limit on the lower limit of the maximum temperature of the stainless steel. The maximum temperature of the stainless steel is, for example, preferably 150°C or higher, more preferably 200°C or higher.

[0072] Residence time of stainless steel in a temperature range of 100°C or higher (hereinafter also referred to as residence time of stainless steel at 100°C or higher): 5 seconds to 5 minutes. In the joining method according to the second embodiment, as described above, a heating device having a heat generating part is used, and the heat generating part is brought into contact with the workpieces to heat them. This causes the joining metal to flow into the overlapping surfaces of the workpieces. During this process, excessive temperature rise of the stainless steel is prevented, suppressing the formation of an oxide film on the surface of the stainless steel. Here, if the residence time of the stainless steel at 100°C or higher is less than 5 seconds, the joining metal will not sufficiently flow into the overlapping surfaces of the workpieces, preventing the joining of the stainless steel and copper. On the other hand, if the residence time of the stainless steel at 100°C or higher exceeds 5 minutes, a thick oxide film will form on the surface of the stainless steel, preventing the joining of the stainless steel and copper. Therefore, the residence time of the stainless steel at 100°C or higher is set to 5 seconds to 5 minutes (300 seconds). The residence time of the stainless steel at 100°C or higher is preferably 15 seconds or longer. The residence time of the stainless steel at 100° C. or higher is preferably 3 minutes (180 seconds) or less, more preferably 1 minute (60 seconds) or less.

[0073] In measuring the temperature of the stainless steel to derive the maximum temperature reached by the stainless steel and the residence time of the stainless steel at 100°C or higher, the entire surface of the stainless steel may be measured using, for example, a thermograph. Also, depending on the heating area by the heating device (the contact area between the heat generating part of the heating device and the workpieces), the surface temperature of the stainless steel in the vicinity of the heating area may be measured using a thermocouple.

[0074] For example, in the case where the starting point of pouring the joining metal onto the overlapping surfaces of the joined materials is the copper end as shown in Figure 1, the copper end is set as the reference position (0 mm) and the surface temperature of the first surface of the stainless steel (the upper surface of the stainless steel in Figure 1) can be measured at a position 0 mm (copper end) to +20 mm in the direction perpendicular to the join. Also, in the case where the starting point of pouring the joining metal onto the overlapping surfaces of the joined materials is the stainless steel end as shown in Figure 2, the stainless steel end is set as the reference position (0 mm) and the surface temperature of the second surface of the stainless steel (the upper surface of the stainless steel in Figure 2) can be measured at a position 0 mm (stainless steel end) to +20 mm in the direction perpendicular to the join. In this case, the surface temperature of the end face of the stainless steel may also be measured.

[0075] Since the temperature of the stainless steel at the above positions is approximately the same during joining, the temperature measurement position can be determined from the above positions depending on the structure of the materials to be joined, etc. Here, the first surface of the stainless steel is the surface of the stainless steel on the side that overlaps with the copper (where the copper is arranged), and the second surface of the stainless steel is the surface of the stainless steel on the opposite side to the side that overlaps with the copper. In addition, the measurement interval for the temperature of the stainless steel in the joining direction is preferably, for example, 3 to 10 mm.

[0076] The maximum temperature of the stainless steel during joining and the residence time of the stainless steel at 100°C or higher can be controlled by adjusting, for example, the joining speed (the speed at which the heating device moves in the joining direction) and the output of the heating device, in addition to the contact area between the heat-generating part of the heating device and the materials to be joined. For example, when a soldering iron is used as the heating device, the maximum temperature of the stainless steel during joining and the residence time of the stainless steel at 100°C or higher can be controlled within the above ranges by adjusting the joining speed in the range of 30 to 200 mm / min and the output (heat amount) of the heating device in the range of 100 to 500 W depending on the type, size, and arrangement of the materials to be joined.

[0077] The heating device is not particularly limited as long as it has a heat-generating element as described above and can heat the materials to be joined by contacting the heat-generating element with the materials to be joined. An example of such a heating device is a soldering iron. The heat-generating element can be an electric type (mains-powered or battery-powered) or a gas type. The output (heat output) of the heating device is preferably 100 W or more. In other words, if the amount of heat generated is small, it takes a long time to heat the materials to be joined, which may lead to the formation of an oxide film on the stainless steel surface. Furthermore, the tip diameter of the heat-generating element (in the case of a soldering iron, the tip diameter of the iron tip) is preferably 1 to 5 mm. If the surface of the heat-generating element oxidizes due to its own heat generation, it is preferable to polish it with a metal file or the like to remove the oxide before starting joining.

[0078] Conditions other than those described above are not particularly limited in the joining methods according to the first and second embodiments, and may be in accordance with conventional methods.

[0079] For example, the joining metal may be applied or placed between the overlapping surfaces of the workpieces, or on the copper or stainless steel ends, before heating. Alternatively, the workpieces may be continuously supplied (by inserting a filler rod serving as the workpieces) during joining. It is particularly preferable to place the joining metal on the copper or stainless steel ends of the workpieces before heating.

[0080] The overlap width L (width in the direction perpendicular to the weld) between the stainless steel and copper is preferably, for example, 5 to 20 mm. The gap between the overlapping portions of the stainless steel and copper (the separation distance between the stainless steel and copper, hereinafter also simply referred to as the gap) is preferably, for example, 0.01 mm to 0.50 mm.

[0081] Furthermore, the maximum temperature that copper reaches during joining is preferably 500° C. or less, more preferably 350° C. or less, from the viewpoint of avoiding a decrease in the strength and corrosion resistance of copper, for example. Furthermore, the residence time of copper in a temperature range of 200° C. or more is preferably 5 minutes or less, more preferably 3 minutes or less, from the viewpoint of avoiding softening of copper.

[0082] Additionally, from the viewpoint of improving the wetting spread of the joining metals and improving workability, it is preferable to apply a flux to the joining target portions of the joined materials and their vicinity before the joining process. A typical flux for stainless steel is suitable as the flux. For example, it is preferable to use an aqueous solution containing 30 to 50 mass% zinc chloride, 1 to 10 mass% ammonium chloride, 1 to 10 mass% hydrogen chloride, and 30 to 70 mass% water, with the remainder consisting of unavoidable impurities. The flux may be applied to the joining target portions and their vicinity of both the stainless steel and copper joining materials, or to the joining target portions and their vicinity of either one of the joining targets. Furthermore, the flux may be applied only to the joining target portions or only to a portion of the joining target portions.

[0083] [2] Joined body of stainless steel and copper or copper alloy A joined body of stainless steel and copper or copper alloy according to one embodiment of the present invention (hereinafter also simply referred to as a joined body) has stainless steel, copper or copper alloy, and a joined portion between the stainless steel and copper or copper alloy, as shown in Figure 3 or Figure 4. The joined portion is located between the stainless steel and copper or copper alloy at the overlapping portion where the stainless steel and copper or copper alloy overlap each other. Such a joined body can be suitably obtained, for example, by the joining method described in [1] above.

[0084] The stainless steel and copper or copper alloy of the joined body are derived from the stainless steel and copper or copper alloy of the joined materials, as explained in [1] above.

[0085] The Sn content of the joint is preferably 40% by mass or more, more preferably 90% by mass or more. The Sn content of the joint is preferably 99.5% by mass or less, more preferably 97% by mass or less. The remainder may contain non-metallic particles such as oxides. Metal elements other than Sn and unavoidable impurities are the same as those in (3) Joining metal in [1] above, and therefore will not be described here.

[0086] The average thickness of the joint is preferably 0.50 mm or less, more preferably 0.20 mm or less, and is preferably 0.01 mm or more, more preferably 0.02 mm or more.

[0087] The average width of the joint (average length of the joint in the direction perpendicular to the joint) is preferably 1.0 mm or more, more preferably 2.0 mm or more, and even more preferably 5.0 mm or more.

[0088] When the starting point of pouring the joining metal onto the overlapping surfaces of the joined materials is the copper end side as shown in Fig. 1, a joined body is obtained in which the joining portion contacts the copper end as shown in Fig. 3. When the starting point of pouring the joining metal onto the overlapping surfaces of the joined materials is the stainless steel end side as shown in Fig. 2, a joined body is obtained in which the joining portion contacts the stainless steel end as shown in Fig. 4. The joining portion may contact both the copper end and the stainless steel end. The width of the joining portion may be equal to the overlap width L.

[0089] Here, the weld is defined, for example, as follows. First, a cross-sectional sample of the weld in the thickness direction (a sample having a cross section in a plane (YZ plane) perpendicular to the welding direction (X direction)) as shown in FIGS. 5 and 6 is prepared with a mirror-polished finish. Next, the cross-sectional sample is observed with an optical microscope or SEM at a magnification of 100x. Then, based on the difference in color tone (contrast) of each structure and the contrast of the interface observed in the obtained image, the interface between the weld and the stainless steel (base material) and the interface between the weld and the copper or copper alloy (base material) are determined, and the weld is defined. Then, based on the defined weld, the thickness and width of the weld in the cross-sectional sample are measured. This measurement is performed on four cross-sectional samples cut at random from the welded body, and the thickness and width of the weld in each cross-sectional sample are determined. Next, these average values ​​are calculated and used as the thickness and width of the weld in the welded body.

[0090] In the above cross-sectional sample, if the thickness of the joint is not uniform, for example, if there are portions that are not parallel to the interface between the joint and the stainless steel and the interface between the joint and the copper or copper alloy, the thickness of the joint in the cross section is calculated as follows: That is, in the joint defined as above, the thickness of the joint is measured at five equally spaced locations, including both ends. The average value of the thicknesses of the five measured locations is then taken as the thickness of the joint in the cross section.

[0091] The Sn content of the joint is measured at a position halfway through the thickness of the joint. For example, the Sn content of the joint can be measured as follows. First, a cross-sectional sample in the thickness direction (a sample with a cross section perpendicular to the X direction, which is the direction of joining (YZ plane)) is prepared as shown in Figures 5 and 6. The cross section is mirror-polished and then etched using an etching solution (5 mL of 38% by mass aqueous solution of iron (II) chloride - 15 mL of 36% by mass hydrochloric acid - 120 mL of distilled water). The obtained cross-sectional sample is then observed using an SEM at a magnification of 100x, and then subjected to SEM-EDS analysis. In this analysis, an EDS point scan is performed on the joint of the cross section to measure the Sn content (mass%). The EDS scan points were 10 randomly selected points at half the thickness of the joint (positions away from the interface between the copper or copper alloy and the joint metal on the stainless steel side by a distance equal to 2 times the thickness of the joint obtained from the above observation). The Sn content (mass%) measured at each point was then averaged to obtain the Sn content of the joint in the cross-sectional sample. This measurement was performed on four cross-sectional samples prepared by randomly sampling from the joint, and the average value of the Sn content of the joint in each cross-sectional sample was used to obtain the Sn content of the joint.

[0092] If the copper or stainless steel end faces are chamfered to facilitate the flow of the joining metal into the joining surfaces of the joined materials during joining, the thickness of the joint will be uneven. When chamfering is performed, it is preferable that the angle between the chamfered surface and the surface of the other joined material be 5 to 10 degrees. The length of the chamfered edge is preferably 1.0 to 3.0 mm in the direction perpendicular to the joining.

[0093] Furthermore, if the width of the joint is not uniform, for example, if it is different near the stainless steel and near the copper or copper alloy, that is, if the width of the joint varies depending on the position in the thickness direction, the minimum length of the joint in the direction perpendicular to the joint at the position in the thickness direction between the overlapping surfaces of the joined materials shall be the width of the joint.

[0094] A part of the joint may extend beyond the overlapping surfaces of the workpieces in the direction perpendicular to the joint. In this case, the thickness and width of the joint are measured excluding the part that extends beyond the overlapping surfaces of the workpieces.

[0095] Furthermore, the joints may be connected by caulking or by fitting, depending on the strength and airtightness required.

[0096] The joined body according to one embodiment of the present invention may be either plate-shaped (including not only flat plates but also curved plates (curved plates)) or tubular. In the case of a tubular shape, it is a joined body of a stainless steel pipe and a copper or copper alloy pipe. For example, the following combinations are possible. In these combinations, the stainless steel pipe may be joined by inserting a portion of the stainless steel pipe into the copper or copper alloy pipe, or by inserting a portion of the copper or copper alloy pipe into the stainless steel pipe. - A combination of a copper or copper alloy pipe and a stainless steel pipe, in which the outer diameter of the stainless steel pipe is approximately equal to the inner diameter of the copper or copper alloy pipe. - A combination of a copper or copper alloy pipe and a stainless steel pipe, the end of which has been expanded so that the diameter is approximately equal to the outer diameter of the stainless steel pipe. - A combination of a copper or copper alloy pipe and a stainless steel pipe, the end of which has been reduced so that the diameter is approximately equal to the inner diameter of the copper or copper alloy pipe,

[0097] Furthermore, a bonded body according to one embodiment of the present invention includes a bonded body having a plurality of bonded portions, at least one of which is the above-described bonded portion.

[0098] [3] Manufacturing Method of Joined Body of Stainless Steel and Copper or Copper Alloy Next, a manufacturing method of a joined body of stainless steel and copper or copper alloy (hereinafter also referred to as a manufacturing method of a joined body) according to one embodiment of the present invention will be described. The manufacturing method of a joined body according to one embodiment of the present invention includes a step of joining stainless steel and copper or copper alloy by the joining method described in [1] above. The manufacturing method of a joined body according to one embodiment of the present invention can suitably manufacture the joined body described in [2] above.

[0099] Example 1 A 1.0 mm thick stainless steel plate (SUS443J1 as defined in JIS G 4305:2021) and a 1.0 mm thick copper plate (phosphorus-deoxidized copper plate (C1220) as defined in JIS H 3100:2018) or copper alloy plate (C2680 as defined in JIS H 3100:2018) were each cut into 120 mm square pieces. Next, the copper plate or copper alloy plate was placed on the stainless steel plate so that the stainless steel plate and the copper plate or copper alloy plate overlapped with an overlap width L as defined in Table 1 (the arrangement shown in FIG. 1 ), to obtain a joined material. At this time, spacers were placed between the stainless steel plate and the copper plate or copper alloy plate at both ends of the overlapping portion of the joined materials in the welding direction so as to obtain the gaps as defined in Table 1, and the joined materials were then clamped with clips. Furthermore, flux (BS-45 manufactured by Taiyo Electric Industry Co., Ltd.) was applied in advance to the surfaces of the stainless steel at and near the overlapping surfaces of the workpieces.

[0100] Next, as shown in Figure 1, thermocouples were attached to the surface (first surface) of the stainless steel at intervals of 5 mm in the direction of welding, at positions 10 mm away from the copper end of the workpiece toward the stainless steel in the direction perpendicular to the welding (position +10 mm from the copper end, which is the reference position (0 mm)).

[0101] Next, a rod-shaped solder (Sn96.5Ag3Cu0.5 as specified in JIS Z 3282:2017) having a diameter of 2.0 was placed near the copper end of the workpiece.

[0102] Next, while moving the heating device in the joining direction, the workpiece was heated from the top surface of the copper or copper alloy plate to join the stainless steel plate and the copper or copper alloy plate, thereby obtaining a joined body of stainless steel and copper or copper alloy. The heating position was a position 20 mm away from the copper end (the reference position) on the copper side (position -20 mm). Note that for Tests No. 1-15 and No. 1-16 in Table 1, the workpiece was heated from the underside of the stainless steel, and the heating position was a position 20 mm away from the copper end (the reference position) on the stainless steel side (position +20 mm). Here, a torch using a gas flame, a so-called gas burner (RZ-820 manufactured by Shinfuji Burner Co., Ltd., heat amount: 2300 kcal / hour, nozzle diameter: φ16 mm), was used as the heating device. Note that under all conditions, joining was performed in an air atmosphere. Note that, for conditions not specified, the descriptions in the general description section above and common practices were followed. During joining, the temperature of the stainless steel was measured and recorded at 0.1 second intervals using the thermocouple and temperature logger, and the temperature history of the stainless steel was obtained from the output temperature log. From the obtained temperature history of the stainless steel, the following were derived: (I) the maximum temperature reached by the stainless steel, and (II) the residence time of the stainless steel at 150°C or higher. The results are also shown in Table 1.

[0103] Note that (I) and (II) were derived for each temperature measurement point where a thermocouple was installed. Table 1 lists only the maximum value of (I) and the minimum and maximum values ​​of (II) at each temperature measurement point. In the present invention example, (I) and (II) satisfied the above ranges at all temperature measurement points. This also applies to Example 2 described below.

[0104] Four cross-sectional samples were cut out from the bonded body thus obtained in the same manner as above, and the thickness and width of the bonded portion of each cross-sectional sample were measured. The feasibility of bonding was judged according to the following criteria. The results are also shown in Table 1. Acceptable: The width of the bonded portion of all four cross-sectional samples was 1.0 mm or more. Unacceptable: The width of the bonded portion of at least one cross-sectional sample was less than 1.0 mm.

[0105] Next, from the thickness and width of the joint of each cross-sectional sample measured above, (III) the average thickness of the joint, and (IV) the average width of the joint were calculated. Furthermore, (V) the Sn content (mass%) of the joint was measured in the same manner as above. The results are also shown in Table 1. For samples that were judged to be unjoinable, calculation and measurement of (III) to (V) were not performed. Furthermore, the fact that the average width of the joint is equal to the overlap width L means that the entire overlapping surface of the joined materials became the joint.

[0106] Here, the thickness and width of the joint were measured using a DSX510 optical microscope manufactured by Olympus Corporation (now Evident Co., Ltd.), and the Sn content (mass%) of the joint was measured using a Miniscope (registered trademark) TM3030plus scanning electron microscope (SEM) manufactured by Hitachi High-Tech Corporation and an AZtecOne energy dispersive X-ray spectrometer (EDS) manufactured by Oxford Instruments.

[0107]

[0108] As shown in Table 1, in all of the invention examples, a joined body of stainless steel and copper or copper alloy was obtained by a simple joining method in an atmospheric environment, while using a cost-effective Sn alloy as the joining metal.

[0109] On the other hand, in all of the comparative examples, the stainless steel and the copper alloy were not properly joined. That is, in the comparative example of Test No. 1-12, the maximum temperature reached by the stainless steel exceeded the appropriate range, so joining was not possible. In the comparative example of Test No. 1-13, the residence time of the stainless steel at 150°C or higher exceeded the appropriate range, so joining was not possible. In the comparative example of Test No. 1-14, the residence time of the stainless steel at 150°C or higher was less than the appropriate range, so joining was not possible. In the comparative example of Test No. 1-15, the heated part was stainless steel, so joining was not possible. In the comparative example of Test No. 1-16, the heated part was stainless steel, so the temperature of the stainless steel was excessively raised, so joining was not possible.

[0110] Example 2 A stainless steel pipe having the outer diameter and thickness (wall thickness) listed in Table 2, and a copper pipe (phosphorized deoxidized copper pipe (C1220T) specified in JIS H 3300:2018) or copper alloy pipe (brass pipe (C2700T) specified in JIS H 3100:2018) having the outer diameter and thickness (wall thickness) listed in Table 2 were cut to a length of 300 mm. The stainless steel pipe was inserted into the copper or copper alloy pipe (the arrangement shown in Figure 1), or the copper or copper alloy pipe was inserted into the stainless steel pipe (the arrangement shown in Figure 2), so that the overlap width L was 10 mm. These were used as the joined materials. The outer periphery of the end of the smaller-diameter pipe, which corresponds to the overlapping portion, was ground or polished in advance to adjust the gap between the stainless steel pipe and the copper or copper alloy pipe to 0.05 mm. The same flux as in Example 1 was applied in advance to the outer surface of the smaller-diameter pipe at and near the overlapping surface of the joined materials.

[0111] Next, for materials to be joined in which a stainless steel pipe was inserted into a copper or copper alloy pipe, thermocouples were attached to the outer surface (first surface) of the stainless steel pipe at positions 20 mm away from the copper end of the materials to be joined toward the stainless steel side in the direction perpendicular to the join (a position +20 mm from the copper end, which is the reference position (0 mm)), at 4 mm intervals in the direction of joining (circumferential direction). Also, for materials to be joined in which a copper or copper alloy pipe was inserted into a stainless steel pipe, thermocouples were attached to the outer surface (second surface) of the stainless steel pipe at positions 20 mm away from the stainless steel end of the materials to be joined toward the stainless steel side in the direction perpendicular to the join (a position +20 mm from the stainless steel end, which is the reference position (0 mm)), at 4 mm intervals in the direction of joining (circumferential direction).

[0112] Next, a φ1.0 bar-shaped solder (solder specified in JIS Z 3282:2017) shown in Table 2 was wound around the outer periphery of the small diameter pipe near the large diameter pipe end of the material to be joined.

[0113] Next, the materials to be joined were heated from the outside of the pipe while moving the heating device in the welding direction (circumferential direction), joining the stainless steel pipe and the copper or copper alloy pipe, and obtaining a joint of stainless steel and copper or copper alloy. The heating position was 20 mm away from the reference position (the stainless steel end or the copper end) on the copper side (position -20 mm). A gas burner, a torch that utilizes a gas flame, was used as the heating device. The gas burner used was the same as in Example 1 above. In all cases, the joining was performed in an air atmosphere. Conditions not specified were as described in the general description section above and in accordance with conventional methods. From the temperature history of the stainless steel obtained in the same manner as in Example 1, the following were calculated: (I) the maximum temperature reached by the stainless steel; and (II) the residence time of the stainless steel at 150°C or higher. The results are also shown in Table 2.

[0114] The resulting bonded bodies were judged for weldability in the same manner as in Example 1. Furthermore, the following were calculated and measured in the same manner as in Example 1: (III) average thickness of the bonded portions, (IV) average width of the bonded portions, and (V) Sn content (mass%) of the bonded portions. The results are also shown in Table 2.

[0115]

[0116] As shown in Table 2, in all of the invention examples, a joined body of stainless steel and copper or copper alloy was obtained by a simple joining method in an atmospheric environment, while using a cost-effective Sn alloy as the joining metal.

[0117] On the other hand, in the comparative example of Test No. 2-13, the Sn content of the joining metal was below the appropriate range, so the joining metal was not melted sufficiently and joining was not possible.

[0118] (Example 3) A 1.0 mm thick stainless steel plate (SUS443J1 as defined in JIS G 4305:2021) and a 1.0 mm thick copper plate (phosphorus deoxidized copper plate (C1220) as defined in JIS H 3100:2018, thermal conductivity: 339 W / mK) or copper alloy plate (brass plate (C2680) as defined in JIS H 3100:2018, thermal conductivity: 117 W / mK) were each cut into 120 mm squares. Next, a copper plate or copper alloy plate was placed on the stainless steel plate so that the stainless steel plate and the copper plate or copper alloy plate overlapped with the overlap width L shown in Table 3, to obtain a joined material. At this time, spacers were placed between the stainless steel plate and the copper or copper alloy plate at both ends of the overlapping portion of the workpieces in the direction of welding, and then the stainless steel plate and the copper or copper alloy plate were clamped with clips so as to obtain the gaps shown in Table 3. In addition, flux (BS-45 manufactured by Taiyo Electric Industry Co., Ltd.) was applied in advance to the surface of the stainless steel at the overlapping surfaces of the workpieces and in the vicinity thereof.

[0119] Next, as shown in Figure 1, thermocouples were attached to the surface (first surface) of the stainless steel at intervals of 5 mm in the direction of welding, at positions 10 mm away from the copper end of the workpiece toward the stainless steel in the direction perpendicular to the welding (position +10 mm from the copper end, which is the reference position (0 mm)).

[0120] Next, a rod-shaped solder (Sn96.5Ag3Cu0.5 as specified in JIS Z 3282:2017) having a diameter of 2.0 was placed near the copper end of the workpiece.

[0121] Next, the heating device was moved in the direction of welding while the heating element of the heating device was in contact with the workpieces at the contact positions shown in Table 3. This melted the welding metal, joining the stainless steel and copper or copper alloy to obtain a joint. A soldering iron (SS-152J (150W), a sheet metal soldering iron manufactured by Ishizaki Electric Mfg. Co., Ltd.) was used as the heating device. In all conditions, welding was performed in an air atmosphere. For conditions not specified, the description in the general section above and standard practices were followed. During welding, the temperature of the stainless steel was measured and recorded at 0.1-second intervals using the thermocouple and temperature logger, and the temperature history of the stainless steel was obtained from the output temperature log. From the obtained temperature history of the stainless steel, the following were derived: (I) the maximum temperature reached by the stainless steel; and (II) the residence time of the stainless steel at 100°C or higher. The results are also shown in Table 3.

[0122] Note that (I) and (II) were derived for each temperature measurement point where a thermocouple was installed. Table 3 lists only the maximum value of (I) and the minimum and maximum values ​​of (II) at each temperature measurement point. In the present invention example, (I) and (II) satisfied the above ranges at all temperature measurement points. The same applies to Example 4 described below.

[0123] The resulting bonded bodies were judged for weldability in the same manner as in Example 1. Furthermore, the following were calculated and measured in the same manner as in Example 1: (III) average thickness of the bonded portions, (IV) average width of the bonded portions, and (V) Sn content (mass%) of the bonded portions. The results are also shown in Table 3.

[0124]

[0125] As shown in Table 3, in all of the inventive examples, a joined body of stainless steel and copper or copper alloy was obtained by a simple joining method in an atmospheric environment while using a cost-effective Sn alloy as the joining metal. In addition, no discoloration (temper color) was observed on the surface of the stainless steel.

[0126] On the other hand, in all of the comparative examples, the stainless steel and copper or copper alloy were not properly joined. That is, in the comparative example of Test No. 3-12, the residence time of the stainless steel at 100°C or higher exceeded the appropriate range, so joining was not possible. In the comparative example of Test No. 3-13, the contact position was outside the appropriate range, the stainless steel did not reach 100°C or higher, and the residence time at 100°C or higher was shorter than the appropriate range, so joining was not possible. In the comparative example of Test No. 3-14, the contact position was outside the appropriate range, the stainless steel did not reach 100°C or higher, and the residence time at 100°C or higher was shorter than the appropriate range, so joining was not possible. In the comparative example of Test No. 3-15, the maximum temperature reached by the stainless steel exceeded the appropriate range, so joining was not possible. In the comparative example of Test No. 3-16, the residence time of the stainless steel at 100°C or higher was shorter than the appropriate range, so joining was not possible. In Comparative Example No. 3-17, the contact position was outside the appropriate range, the stainless steel did not reach 100°C or higher, and the residence time at 100°C or higher was shorter than the appropriate range, so welding was not possible. In Comparative Example No. 3-18, the contact position was outside the appropriate range, the stainless steel did not reach 100°C or higher, and the residence time at 100°C or higher was shorter than the appropriate range, so welding was not possible.

[0127] Example 4 A stainless steel pipe having the outer diameter and thickness (wall thickness) listed in Table 4, and a copper pipe (phosphorized deoxidized copper pipe (C1220T) specified in JIS H 3300:2018) or copper alloy pipe (brass pipe (C2700T) specified in JIS H 3100:2018) having the outer diameter and thickness (wall thickness) listed in Table 4 were cut to a length of 300 mm. The stainless steel pipe was inserted into the copper or copper alloy pipe (the arrangement shown in Figure 1), or the copper or copper alloy pipe was inserted into the stainless steel pipe (the arrangement shown in Figure 2) so that the overlap width L was 10 mm. These were used as the joined materials. The outer periphery of the end of the pipe on the smaller diameter side, which corresponds to the overlapping portion, was ground or polished in advance to adjust the gap between the stainless steel pipe and the copper or copper alloy pipe to 0.05 mm. The same flux as in Example 3 was applied in advance to the outer surface of the smaller diameter pipe at the overlapping surface of the joined materials and in the vicinity thereof.

[0128] Next, for materials to be joined in which a stainless steel pipe was inserted into a copper or copper alloy pipe, thermocouples were attached to the outer surface (first surface) of the stainless steel pipe at positions 15 mm away from the copper end of the materials to be joined toward the stainless steel side in the direction perpendicular to the join (a position +15 mm from the copper end, which is the reference position (0 mm)), at 4 mm intervals in the direction of joining (circumferential direction). Also, for materials to be joined in which a copper or copper alloy pipe was inserted into a stainless steel pipe, thermocouples were attached to the outer surface (second surface) of the stainless steel pipe at positions 15 mm away from the stainless steel end of the materials to be joined toward the stainless steel side in the direction perpendicular to the join (a position +15 mm from the stainless steel end, which is the reference position (0 mm)), at 4 mm intervals in the direction of joining (circumferential direction).

[0129] Next, a φ1.0 bar-shaped solder (solder specified in JIS Z 3282:2017) shown in Table 4 was wound around the outer periphery of the small diameter pipe near the large diameter pipe end of the joined material.

[0130] Next, the heating device was moved in the joining direction (circumferential direction) while the heat-generating part of the heating device was in contact with the materials to be joined. The contact position is as shown in Table 4. This melted the joining metal, joining the stainless steel and copper or copper alloy, and obtaining a joined body. Here, the same soldering iron as in Example 3 was used for the heating device. Note that, under all conditions, joining was performed in an air atmosphere. For conditions not specified, the descriptions in the general section above and conventional methods were used. Then, from the temperature history of the stainless steel obtained in the same manner as in Example 3, the following were derived: (I) the maximum temperature reached by the stainless steel; and (II) the residence time of the stainless steel at 100°C or higher. The results are also shown in Table 2.

[0131] The resulting bonded bodies were judged for weldability in the same manner as in Example 1. The following were also calculated and measured in the same manner as in Example 1: (III) average thickness of the bonded portions, (IV) average width of the bonded portions, and (V) Sn content (mass%) of the bonded portions. The results are also shown in Table 4.

[0132]

[0133] As shown in Table 4, in all of the inventive examples, a joined body of stainless steel and copper or copper alloy was obtained by a simple joining method in an atmospheric environment while using a cost-effective Sn alloy as the joining metal. In addition, no discoloration (temper color) was observed on the surface of the stainless steel.

[0134] On the other hand, in the comparative example of Test No. 4-13, the Sn content of the joining metal was below the appropriate range, so the joining metal was not melted sufficiently and joining was not possible.

[0135] The bonded article according to one embodiment of the present invention is suitable for application to a variety of products, including heat exchanger piping, hot water supply piping, water supply piping, gas hot water heater piping, air conditioner piping, housing equipment piping, electronic device parts, and household electrical appliances.

Claims

1. A method for joining stainless steel and copper or a copper alloy, comprising: a joining step of joining overlapping materials, which are stainless steel and copper or a copper alloy, with a joining metal, said joining metal being Sn or an Sn alloy having a Sn content of 40 mass% or more, said joining step comprising: heating said copper or copper alloy with a heating device, and melting said joining metal while heating said stainless steel by heat transfer from said copper or copper alloy, thereby joining said stainless steel and said copper or copper alloy, said stainless steel reaching a maximum temperature of 350°C or less, and said stainless steel remaining in a temperature range of 150°C or more for a period of 5 seconds to 5 minutes.

2. The method for joining stainless steel to copper or a copper alloy according to claim 1, wherein the heating device is a torch.

3. A joining process is provided in which overlapping joined materials, which are stainless steel and copper or copper alloy, are joined with a joining metal, the joining metal being Sn or an Sn alloy having an Sn content of 40 mass% or more, the joining process is provided in which a heating device having a heat generating part is used to bring the heat generating part into contact with the joined materials, thereby melting the joining metal and joining the stainless steel and the copper or copper alloy, the contact position in the direction perpendicular to the joining between the heat generating part and the joined materials is set to the overlapping end portion, which is the starting point for pouring the joining metal into the overlapping surfaces of the joined materials, as the reference position (0 mm), the stainless steel side is +, and the copper or copper alloy side is -, in the case where the thermal conductivity of the copper or copper alloy is 250 W / mK or more, the range is -15 mm to +15 mm, in the case where the thermal conductivity of the copper or copper alloy is less than 250 W / mK, the range is -15 mm to +15 mm, the maximum temperature reached by the stainless steel is 250°C or less, and The method for joining stainless steel and copper or a copper alloy, wherein the stainless steel is held in a temperature range of 100° C. or higher for 5 seconds or more and 5 minutes or less.

4. The method for joining stainless steel to copper or a copper alloy according to claim 3, wherein the heating device is a soldering iron.

5. A joined body of stainless steel and copper or a copper alloy, which is joined to stainless steel and copper or a copper alloy by the method for joining stainless steel and copper or a copper alloy according to any one of claims 1 to 4.

6. A method for producing a joined body of stainless steel and copper or a copper alloy, which comprises joining stainless steel and copper or a copper alloy by the method for joining stainless steel and copper or a copper alloy according to any one of claims 1 to 4.