Brazed joint and manufacturing method of the same

Abstract

To provide a brazed joint which can inhibit reduction of joint strength even when a brass which contains bismuth in place of lead and stainless steel are brazed with a brazing material, and to provide a manufacturing method of the brazed joint.SOLUTION: A brazed joint of stainless steel and a brass includes a layer structure in which the stainless steel, a first brazing material layer, a barrier layer, a second brazing material layer, and the brass are sequentially arranged in a laminar manner. The barrier layer blocks bismuth in the brass from being moved to the first brazing material layer by brazing the stainless steel and the brass to each other. The barrier layer is at least one of brass and phosphor bronze. A brazing material forming the first brazing material layer and the second brazing material layer is a liquid at a temperature ranging from 680 to 800°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brazed joint and a method for manufacturing the brazed joint, and more particularly to a brazed joint of stainless steel and brass and a method for manufacturing the brazed joint. [Background technology]

[0002] Conventionally, when joining dissimilar metals, such as stainless steel and brass, brazing has been performed (for example, Patent Document 1). Recently, the use of materials containing lead has become stricter from the viewpoint of environmental regulations, and there is a trend toward using bismuth (hereinafter sometimes referred to as "Bi") as a substitute for lead (hereinafter sometimes referred to as "Pb"). The same is true for brass, where lead has the effect of improving the machinability of brass, but bismuth is used instead of lead. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-276072 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when brass containing bismuth instead of lead is brazed to stainless steel using a brazing filler metal, the bonding strength between the stainless steel and the brazing filler metal may be reduced compared to when conventional lead-containing brass is brazed to stainless steel.

[0005] In view of the above problems, an object of the present invention is to provide a brazed joint and a method for manufacturing a brazed joint that can suppress a decrease in joint strength even when brass containing bismuth instead of lead and stainless steel are joined by brazing using a brazing filler metal. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the brazed joint of the present invention is a brazed joint of stainless steel and brass, and has a layer structure in which the stainless steel, a first brazing filler metal layer, a blocking layer, a second brazing filler metal layer, and the brass are arranged in layered form in this order, and the brass contains a Cu content of 57.4 to 64.0 mass%, a Pb content of 0.1 mass% or less, and a Bi content of 0.50 to 4.00 mass%, and the blocking layer is a layer that blocks Bi in the brass from migrating to the first brazing filler metal layer by brazing the stainless steel and the brass, and The blocking layer is at least one of brass having a Cu content of 59.0 to 71.5 mass% and a Pb content of 0.10 mass% or less, or phosphor bronze having an Sn content of 5.5 to 7.0 mass%, a P content of 0.03 to 0.35 mass%, a Pb content of 0.02 mass% or less, an Fe content of 0.10 mass% or less, a Zn content of 0.20 mass% or less, the balance being Cu, and the total of Cu, Sn, and P is 99.5 mass% or more, and the brazing filler metal constituting the first brazing filler metal layer and the second brazing filler metal layer is liquid at 680 to 800°C.

[0007] In the brazed joint of the present invention, the joining strength between the stainless steel and the brass is 100 N / mm 2 It may be more than that.

[0008] In the brazed joint of the present invention, the stainless steel may be any one of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and two-phase stainless steels thereof.

[0009] In the brazed joint of the present invention, the stainless steel may be SUS304, the first brazing filler metal layer and the second brazing filler metal layer may be layers of a brazing filler metal containing BAg-7, the barrier layer may be C2801, and the brass may be C6803.

[0010] In order to solve the above-mentioned problems, the method for producing a brazed joint of the present invention includes a first layer structure formation step of forming a first layer structure by arranging the stainless steel, a first brazing material, a barrier layer, a second brazing material, and the brass in layers, in that order; a first brazing step of heating the first layer structure so that the temperatures of the first brazing material and the second brazing material are 680 to 800°C to braze the stainless steel and the brass; and a first cooling step of cooling the first layer structure after the first brazing step to form a brazed joint having a layer structure of the stainless steel, a first brazing material layer, a barrier layer, a second brazing material layer, and the brass.

[0011] In the method for producing a brazed joint of the present invention, the first brazing filler metal and the second brazing filler metal may be brazing filler metals of the same composition.

[0012] In order to solve the above-mentioned problems, the method for producing a brazed joint of the present invention includes a second layer structure formation step of arranging the stainless steel, the barrier layer, and the brass in layers, and arranging a third brazing filler metal between the stainless steel and the barrier layer, between the barrier layer and the brass, or on a side of the barrier layer, to form a second layer structure; a second brazing step of heating the second layer structure so that the temperature of the third brazing filler metal is 680 to 800°C, thereby brazing the stainless steel and the brass; and a second cooling step of cooling the second layer structure after the second brazing step to form a brazed joint having a layer structure of the stainless steel, a first brazing filler metal layer, a barrier layer, a second brazing filler metal layer, and the brass. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a brazed joint and a method for manufacturing a brazed joint that can suppress a decrease in joint strength even when brass containing bismuth instead of lead and stainless steel are joined by brazing using a brazing filler metal. [Brief explanation of the drawings]

[0014] [Figure 1]These are SEM images of the cross section of a brazed joint between stainless steel and brass, where FIG. 1(A) is a brazed joint 200 of Conventional Example 1, which uses conventional lead-containing brass, FIG. 1(B) is a brazed joint 300 of Comparative Example 1, which uses bismuth-containing brass instead of lead, and FIG. 1(C) is a brazed joint 100 of Example 1, which uses bismuth-containing brass instead of lead and further has a barrier layer between the stainless steel and brass. [Figure 2] 2(A) and 2(B) are side views of a test piece used in a joining test and a jig used in the joining test, respectively. FIG. 2(A) shows the test piece before assembly of the jig and the test piece, FIG. 2(B) shows the test piece after assembly of the jig and the test piece, and FIG. 2(C) is an enlarged view of a portion of the circled joint portion of the brazed joint 200 shown in FIG. 2(A). [Figure 3] 3A and 3B are SEM images of a cross section of a brazed joint 100 taken with an SEM and an EDS element mapping image of bismuth in the cross section corresponding to the SEM image. Fig. 3A is an image of a cross section of a layer structure consisting of stainless steel 10, a first brazing filler metal layer 20, and a blocking layer 30, and Fig. 3B is an image of a cross section of a layer structure consisting of the blocking layer 30, a second brazing filler metal layer 40, and brass 50. [Figure 4] The figure shows an SEM image of a cross section of the layer structure of a brazed joint 300 consisting of stainless steel 10, a brazing material layer 80, and brass 50, taken with an SEM, and an image of bismuth element mapping by EDS on the cross section corresponding to the SEM image. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, one embodiment of the brazed joint and the method for manufacturing the brazed joint of the present invention will be described, although the present invention is not limited to the following example.

[0016] [Brazed joint] The brazed joint of the present invention is a brazed joint of stainless steel and brass, and has a layered structure in which stainless steel, a first brazing filler metal layer, a barrier layer, a second brazing filler metal layer, and brass are arranged in that order.

[0017] The brazed joint of the present invention is not particularly limited in shape as long as it has such a layer structure, and can be used for a variety of purposes as a part in which dissimilar metals, i.e., stainless steel and brass, are joined by brazing. Examples of parts include a brazed joint of a stainless steel cap and a brass joint in a pressure switch, a brazed joint of a stainless steel cap and a brass joint in a pressure sensor, a brazed joint of a stainless steel cap and a brass body in an electric valve, a brazed joint of a stainless steel tube and a brass body in an electromagnetic valve, a brazed joint of a stainless steel cap and a brass body in a regulating valve, and a brazed joint of a stainless steel cap and a brass body in an expansion valve.

[0018] 1A to 1C show SEM images of cross sections of brazed joints of stainless steel and brass, where Fig. 1C shows a brazed joint 100 of Example 1 in the examples described below, which is an example of the brazed joint of the present invention.

[0019] 1(C), the brazed joint 100 has a layered structure in which the stainless steel 10, the first brazing filler metal layer 20, the barrier layer 30, the second brazing filler metal layer 40, and the brass 50 are arranged in this order. That is, the stainless steel 10 and the brass 50 are joined by brazing, and in the present invention, the stainless steel 10 and the barrier layer 30 are brazed together, and the brass 50 and the barrier layer 30 are brazed together.

[0020] <Stainless Steel 10> The stainless steel 10 is not particularly limited, and examples thereof include stainless steels used for the above-mentioned parts. Specifically, austenitic stainless steel such as SUS304, ferritic stainless steel, martensitic stainless steel, and any of these two-phase stainless steels can be used.

[0021] <Brass 50> The brass 50 is not particularly limited, and examples thereof include brasses used for the above-mentioned components. Specifically, brasses having a Cu content of 57.4 to 64.0 mass%, a Pb content of 0.1 mass% or less, and a Bi content of 0.50 to 4.00 mass% can be used. More specifically, C6801B, C6802B, C6803B, C6804B, etc. can be used.

[0022] In the present invention, brass containing bismuth is used instead of lead, so it is ideal to contain as little Pb as possible, and the lower limit of the Pb content is 0% by mass, and in consideration of analytical accuracy, the lower limit is preferably below the detection limit of Pb. However, there are cases where Pb is unavoidably contained, or where a small amount is not a problem, so it is important that the Pb content does not exceed 0.1% by mass.

[0023] <Isolation layer 30> The barrier layer 30 is a layer that blocks Bi in the brass 50 from migrating to the first brazing material layer 20 when the stainless steel 10 and the brass 50 are brazed together.

[0024] In the case of a conventional brazed joint in which lead-containing brass and stainless steel 10 are brazed together, there is no problem with the joint strength. For example, the joint strength, which is the standard strength used for the above-mentioned parts, is 100 N / mm 2 It fully met the above criteria.

[0025] However, when brass 50 containing bismuth instead of lead is brazed to stainless steel 10, the bonding strength between the stainless steel and the brazing material decreases, and the bonding strength is 100 N / mm 2 In some cases, the bond strength was less than 1 / 2. When the cause of this decrease in bond strength was investigated, it was found that bismuth migrated from the brass 50 to the brazing filler metal layer, forming a brazing filler metal layer containing bismuth, and that the bismuth segregated at the stainless steel interface, resulting in a decrease in the bond strength between the brazing filler metal layer and the stainless steel 10. Therefore, in order to ensure sufficient bond strength, it is important that even if bismuth migrates from the brass 50 to the brazing filler metal layer, the bismuth does not reach the vicinity of the bond interface between the stainless steel 10 and the brazing filler metal layer.

[0026] Therefore, in the present invention, the blocking layer 30 is provided to prevent bismuth from reaching the vicinity of the joint interface with the stainless steel 10. Although bismuth migrates from the brass 50 to the second brazing filler metal layer 40 during brazing, the blocking layer 30 blocks the migration of bismuth, preventing the bismuth from migrating around the blocking layer 30 to the first brazing filler metal layer 20, thereby preventing a decrease in the joint strength between the stainless steel 10 and the first brazing filler metal layer 20. As a result, the stainless steel 10 and the brass 50 can be joined while maintaining sufficient strength.

[0027] It is important that the insulating layer 30, which fulfills this role, can withstand the heating temperature during brazing and does not contain excessive amounts of lead or bismuth. Even if the stainless steel 10, the first brazing filler metal layer 20, the second brazing filler metal layer 40, and the brass 50 have sufficient strength, if the strength of the insulating layer 30 is low, there is a risk of fracture at the insulating layer 30. Therefore, to prevent fracture at the insulating layer, the tensile strength of the insulating layer 30 itself is set to, for example, 400 N / mm 2 It is preferable that there is more than one.

[0028] Materials that satisfy these conditions and can be used as the insulating layer include the following brass and phosphor bronze, and at least one of these can be used alone or in combination.

[0029] (Brass for barrier layer 30) Brass having a Cu content of 59.0 to 71.5% by mass and a Pb content of 0.10% by mass or less can be used for the insulating layer 30. In the present invention, it is ideal for the insulating layer 30 to contain as little Pb and Bi as possible, with the lower limits for the Pb content and the Bi content being 0% by mass, and considering analytical accuracy, the lower limits are preferably below the detection limit for both Pb and Bi. However, there are cases where Pb and Bi are unavoidably contained, or where a small amount is not a problem. For example, it is important that the Pb content does not exceed 0.1% by mass.

[0030] As such brass, for example, C2680 and C2801 can be used.

[0031] (Phosphor bronze for barrier layer 30) The insulating layer 30 can be made of phosphor bronze containing 5.5 to 7.0 mass% Sn, 0.03 to 0.35 mass% P, 0.02 mass% or less Pb, 0.10 mass% or less Fe, 0.20 mass% or less Zn, and the remainder Cu, with the total of Cu, Sn, and P being 99.5 mass% or more. In the present invention, the insulating layer 30 should ideally contain as little Pb and Bi as possible, with the lower limits for the Pb and Bi contents being 0 mass%. Taking analytical accuracy into consideration, these lower limits are preferably below the detection limits for both Pb and Bi. However, there are cases where Pb and Bi are unavoidably contained, or where a small amount is not a problem. For example, it is important that the Pb content does not exceed 0.1 mass%, and the above phosphor bronze can be used without any problems.

[0032] As such phosphor bronze, for example, C5191 can be used.

[0033] (Shape and thickness of the blocking layer 30) A plate-like or thin film-like layer with a uniform thickness can be used as the blocking layer 30. When such a plate-like or thin film-like blocking layer 30 is used, its dimensions can be adjusted appropriately depending on the shape of the stainless steel 10 or brass 50. The thickness of the blocking layer 30 may be, for example, 0.4 to 1.2 mm.

[0034] <First brazing filler metal layer 20> The brazing filler metal constituting the first brazing filler metal layer 20 is liquid at 680 to 800° C. By using a brazing filler metal that is liquid at this temperature, the stainless steel 10 and the brass 50 can be joined together with the blocking layer 30 interposed therebetween.

[0035] The brazing filler metal that can be used for the first brazing filler metal layer 20 preferably does not contain Pb or Bi, and furthermore, in consideration of environmental regulations, it is preferable that it does not contain Cd. Examples of such brazing filler metals include BAg-4, BAg-5, BAg-6, BAg-7, BAg-7A, BAg-7B, BAg-8, BAg-8A, BAg-8B, BAg-20, and BAg-24. These brazing filler metals can be used alone or in combination.

[0036] For example, when SUS304 is used as the stainless steel 10, the first brazing filler metal layer 20 may be a layer of a brazing filler metal containing BAg-7.

[0037] <Second brazing filler layer 40> The brazing filler metal constituting the second brazing filler metal layer 40 is liquid at 680 to 800° C. By using a brazing filler metal that is liquid at this temperature, the stainless steel 10 and the brass 50 can be joined together with the blocking layer 30 interposed therebetween.

[0038] The brazing filler metal that can be used for the second brazing filler metal layer 40 preferably does not contain Pb or Bi, and furthermore, in consideration of environmental regulations, it is preferable that it does not contain Cd. Examples of such brazing filler metals include BAg-4, BAg-5, BAg-6, BAg-7, BAg-7A, BAg-7B, BAg-8, BAg-8A, BAg-8B, BAg-20, and BAg-24. These brazing filler metals can be used alone or in combination.

[0039] For example, when SUS304 is used as the stainless steel 10, the second brazing filler metal layer 40 may be a layer of a brazing filler metal containing BAg-7.

[0040] The second brazing filler metal layer 40 may be formed by brazing the stainless steel 10 and the brass 50 using the same brazing filler metal as the first brazing filler metal layer 20, or a different brazing filler metal may be used. However, bismuth migrates from the brass 50 to the second brazing filler metal layer 40 due to the heating for brazing. Therefore, the amount of bismuth is greater in the second brazing filler metal layer 40 than in the first brazing filler metal layer 20.

[0041] <Joining strength> The brazed joint of the present invention has a joint strength of 100 N / mm between stainless steel and brass. 2 It is preferable that the bonding strength is 100 N / mm or more. With such a bonding strength, it is suitable for the above-mentioned applications of the parts. 2 If the application does not require a bonding strength of 100 N / mm 2 It doesn't need to be more than that.

[0042] [Method of manufacturing brazed joint 1] Next, manufacturing method 1 will be described as an example of a method for manufacturing a brazed joint of the present invention. This manufacturing method is a method capable of manufacturing the brazed joint of the present invention described above, and includes a first layer structure forming step, a first brazing step, and a first cooling step. Hereinafter, the brazed joint 100 will be described as an example.

[0043] <First layer structure formation process> In this step, a first layer structure is formed by arranging, in order, stainless steel 10, first brazing filler metal, blocking layer 30, second brazing filler metal, and brass 50 in layers. The method for forming the first layer structure is not particularly limited, and the first layer structure may be formed by stacking, in order, the second brazing filler metal, blocking layer 30, first brazing filler metal, and stainless steel 10 on brass 50, or the first layer structure may be formed by stacking, in order, the first brazing filler metal, blocking layer 30, second brazing filler metal, and brass 50 on stainless steel 10.

[0044] The first layer structure may be formed manually or automatically using a device, and may be formed, for example, at 0°C to 50°C under atmospheric pressure of about 1 atmosphere. However, it is not preferable to perform this step at a temperature of 680°C or higher, as this would cause the brazing filler metal to melt.

[0045] The stainless steel 10, brazing filler metal, insulating layer 30, and brass 50 that can be used are as described above, and therefore further explanation will be omitted. The first brazing filler metal and the second brazing filler metal may be brazing filler metals of the same composition.

[0046] <First brazing process> In this step, the first layer structure is heated so that the temperatures of the first brazing filler metal and the second brazing filler metal reach 680 to 800° C., thereby brazing the stainless steel 10 and the brass 50 together.

[0047] Heating may be performed under atmospheric pressure of about 1 atmosphere or under a reducing gas atmosphere such as hydrogen or ammonia. Specifically, this step may be performed by placing the first layer structure in a heating device such as an oven, heating furnace, or reducing atmosphere furnace. The holding time for maintaining the temperature of the first brazing filler metal and the second brazing filler metal at 680 to 800°C may be set to, for example, 5 to 10 minutes. Brazing may also be performed by heating using a burner. The holding time for maintaining the temperature of the first brazing filler metal and the second brazing filler metal at 680 to 800°C may be set to, for example, several tens of seconds.

[0048] <First cooling process> In this step, the first layer structure after the first brazing step is cooled to form a brazed joint 100 having a layer structure of stainless steel 10, first brazing filler metal layer 20, barrier layer 30, second brazing filler metal layer 40, and brass 50. The liquid first brazing filler metal and second brazing filler metal solidify upon cooling to become the first brazing filler metal layer 20 and the second brazing filler metal layer 40, respectively, to form the brazed joint 100.

[0049] The method for cooling the first layer structure in this step is not particularly limited, and for example, the first layer structure that was placed in the heating device in the brazing step may be removed from the heating device and allowed to cool in an atmospheric pressure atmosphere of, for example, 0°C to 50°C and about 1 atmosphere.

[0050] [Method of manufacturing brazed joint 2] Next, manufacturing method 2 will be described as an example of a method for manufacturing a brazed joint of the present invention. This manufacturing method is a method capable of manufacturing the brazed joint of the present invention described above, and includes a second layer structure forming step, a second brazing step, and a second cooling step. Hereinafter, the brazed joint 100 will be described as an example.

[0051] <Second layer structure formation process> In this process, the stainless steel 10, the insulating layer 30, and the brass 50 are arranged in layers in this order, and a third brazing material is arranged between the stainless steel 10 and the insulating layer 30, between the insulating layer 30 and the brass 50, or on the side of the insulating layer 30 to form a second layer structure.

[0052] The method for forming the second layer structure is not particularly limited, and the second layer structure may be formed by stacking the insulating layer 30, the third brazing filler metal, and the stainless steel 10 in this order on the brass 50, or the second layer structure may be formed by stacking the third brazing filler metal, the insulating layer 30, and the brass 50 in this order on the stainless steel 10. Furthermore, the second layer structure may be formed by stacking the third brazing filler metal, the insulating layer 30, and the stainless steel 10 in this order on the brass 50, or the second layer structure may be formed by stacking the insulating layer 30, the third brazing filler metal, and the brass 50 in this order on the stainless steel 10.

[0053] When the third brazing material is arranged on the side of the blocking layer 30, for example, stainless steel 10, the blocking layer 30, and brass 50 are arranged in layers, and then a plate-shaped or ring-shaped third brazing material is arranged so as to contact the side of the blocking layer 30.

[0054] The second layer structure may be formed manually or automatically using a device, for example, by carrying out this step at 0°C to 50°C under atmospheric pressure of about 1 atmosphere. However, carrying out this step at a temperature of 680°C or higher is not preferable because the brazing filler metal will melt.

[0055] The stainless steel 10, brazing material, insulating layer 30, and brass 50 that can be used are as described above, and a description thereof will be omitted.

[0056] <Second brazing process> In this step, the second layer structure is heated so that the temperature of the third brazing filler metal becomes 680 to 800° C., and the stainless steel 10 and the brass 50 are brazed together.

[0057] Heating may be carried out under atmospheric pressure of about 1 atmosphere or under a reducing gas atmosphere such as hydrogen or ammonia. Specifically, this step may be carried out by placing the second layer structure in a heating device such as an oven, heating furnace, or reducing atmosphere furnace. The holding time for maintaining the temperature of the third brazing filler metal at 680 to 800°C may be set to, for example, 5 to 10 minutes. Brazing may also be performed by heating using a burner. The holding time for maintaining the temperature of the third brazing filler metal at 680 to 800°C may be set to, for example, several tens of seconds.

[0058] As explained in the second layer structure formation process, there are various ways to arrange the third brazing material, but the third brazing material melts in the second brazing process, and the third brazing material penetrates between the stainless steel 10 and the insulating layer 30, and between the insulating layer 30 and the brass 50 due to capillary action.

[0059] <Second cooling process> In this step, the second layer structure after the second brazing step is cooled to form a brazed joint 100 having a layer structure of stainless steel 10, first brazing filler metal layer 20, barrier layer 30, second brazing filler metal layer 40, and brass 50. The third brazing filler metal that has entered between the stainless steel 10 and the barrier layer 30, and between the barrier layer 30 and the brass 50, solidifies by cooling to become the first brazing filler metal layer 20 and the second brazing filler metal layer 40, respectively, to form the brazed joint 100.

[0060] The method for cooling the second layer structure in this process is not particularly limited, and for example, the second layer structure that was placed in the heating device during the brazing process may be removed from the heating device and allowed to cool in an atmospheric pressure atmosphere of, for example, 0°C to 50°C and approximately 1 atmosphere.

[0061] <Other processes> The methods 1 and 2 for manufacturing a brazed joint of the present invention may include other steps, such as a removal step for removing factors that inhibit brazing, such as dirt, deposits, and oxides, from the surfaces of the stainless steel 10, the blocking layer 30, and the brass 50 that come into contact with the brazing filler metal, and a step for applying flux to improve the wettability of the brazing filler metal. [Example]

[0062] The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples in any way.

[0063] [Preparation of test specimen] Example 1 A first layer structure was formed by stacking a 15 mm diameter, 0.15 mm thick disc-shaped second brazing filler metal (BAg-7), a 15 mm diameter, 0.6 mm thick disc-shaped barrier layer 30 (C2801), a 15 mm diameter, 0.15 mm thick disc-shaped first brazing filler metal (BAg-7), and a 21 mm diameter, 0.8 mm thick disc-shaped stainless steel 10 (SUS304) on a 15 mm diameter, 18 mm tall, approximately cylindrical brass 50 (C6803, Pb content 0.01 mass% or less, Bi content 0.5-4.0 mass%) in this order (first layer structure formation step).Then, this first layer structure was placed in a hydrogen atmosphere reduction furnace and maintained at a temperature range of 680°C to 720°C for 6 minutes (first brazing step). After the heating step, the first layer structure was cooled in the furnace, then removed from the reducing furnace, and allowed to cool at 25°C under atmospheric pressure to 25°C (first cooling step), producing a brazed joint 100, which was used as the test specimen of Example 1. A plurality of test specimens were prepared for use in a test to confirm the bonding strength and in SEM observation.

[0064] <Conventional Example 1> A layered structure was formed by stacking a 15 mm diameter, 18 mm tall, approximately cylindrical brass 60 (C3604, Pb content 1.8 to 3.7 mass%), a 15 mm diameter, 0.15 mm thick disc of brazing filler metal (BAg-7), and a 21 mm diameter, 0.8 mm thick disc of stainless steel 10 (SUS304) on top of the brass 60. This layered structure was then subjected to a first brazing step and a first cooling step in the same manner as in Example 1, producing a brazed joint 200 in which the brass 60 and the stainless steel 10 were brazed with a brazing filler metal layer 70. This was used as a test specimen for Conventional Example 1. A plurality of test specimens were prepared for use in a test to confirm the joining strength and for SEM observation.

[0065] Comparative Example 1 A layered structure was formed by stacking a roughly cylindrical brass 50 (C6803, Pb content 0.01 mass% or less, Bi content 0.5 to 4.0 mass%) with a diameter of 15 mm and a height of 18 mm, on top of which a disc-shaped brazing filler metal (BAg-7) with a diameter of 15 mm and a thickness of 0.15 mm and a disc-shaped stainless steel 10 (SUS304) with a diameter of 21 mm and a thickness of 0.8 mm were stacked in this order. This layered structure was then subjected to a first brazing step and a first cooling step in the same manner as in Example 1, to produce a brazed joint 300 in which the brass 50 and the stainless steel 10 were brazed with a brazing filler metal layer 80. This was used as a test specimen for Comparative Example 1. Multiple test specimens were prepared for use in a test to confirm the bonding strength and for SEM observation.

[0066] [Verifying joint strength] In order to confirm the bonding strength between brass and stainless steel, the tensile strength of the test specimen was measured using a tensile testing machine. Figure 2 shows a side view of the test specimen used in the bonding strength confirmation test and the jig used in the bonding strength confirmation test, with Figure 2(A) showing the state before the jig and test specimen were assembled, and Figure 2(B) showing the state after the jig and test specimen were assembled. Figure 2 shows a brazed joint 200, which is the test specimen of Conventional Example 1, as an example, and the bonding strength confirmation test was performed using an upper jig 400 and a lower jig 500.

[0067] The inner surface 510 of the lower jig 500 has a shape corresponding to the outer shape of the brazed joint 200, and the brass 60 side of the brazed joint 200 is inserted into the lower jig 500 so that the brass 60 protrudes from below the lower jig 500. Next, the upper jig 400 is inserted into the inner surface 510 of the lower jig 500. Here, the side surface 410 of the upper jig 400 is threaded to form a male thread, and the side surface 520 of the inner surface 510 of the lower jig 500 is threaded to form a female thread shape that corresponds to the shape of the male thread on the side surface 410. Then, the upper jig 400 is inserted into the inner surface 510 of the lower jig 500 while rotating, resulting in the state shown in assembly diagram 2(B), whereby the upper jig 400 and the lower jig 500 can be held in place even when pulled in the vertical direction.

[0068] After achieving the state shown in Figure 2(B), a tensile tester was used to grip and fix the brass 60 of the brazed joint 200 around the area marked with reference numeral 220 (gripping portion 220), and further grip the upper jig 400 around the area marked with reference numeral 420 (gripping portion 420) and pull the upper jig 400 vertically upward, thereby measuring the joint strength of the brazed joint 200.

[0069] The joint strength of the brazed joint 200, which is the test piece of Conventional Example 1, is 100 N / mm 2 As described above, the strength was sufficient for use in the above-mentioned parts.

[0070] The brazed joint 100, which was the specimen of Example 1, was also measured for joint strength in the same manner, and the joint strength was 100 N / mm 2 More than 100N / mm 2 The strength was well above this, and therefore the strength was sufficient for use in the above-mentioned parts.

[0071] Furthermore, when the joint strength of the brazed joint 300, which was the test piece of Comparative Example 1, was measured in the same manner, the joint strength was 100 N / mm 2 Less than 100N / mm 2 Since the strength was significantly lower than that of the above-mentioned components, it was not possible to demonstrate sufficient strength for use in the above-mentioned components.

[0072] [SEM observation and elemental mapping] The cross sections of the test specimens (brazed joints 100, 200, 300) of Example 1, Conventional Example 1, and Comparative Example 1 were photographed with a scanning electron microscope (SEM). These SEM images are shown in Fig. 1. As shown in Fig. 1(C), it was confirmed that the first brazing filler metal layer 20 and the second brazing filler metal layer 40 are separated by the blocking layer 30, and that the blocking layer 30 is disposed in a manner that can prevent the bismuth contained in the brass 50 from migrating to the first brazing filler metal layer 20.

[0073] Furthermore, elemental mapping of bismuth was performed by energy dispersive X-ray spectroscopy (EDS) on the cross sections of the specimens of Example 1, Conventional Example 1, and Comparative Example 1. Fig. 3 shows an image of the specimen of Example 1 (brazed joint 100), and Fig. 4 shows an image of the specimen of Comparative Example 1 (brazed joint 300).

[0074] The element mapping results confirmed that bismuth was scattered in the second brazing filler metal layer 40 of the specimen of Example 1 (FIG. 3(B)), but no bismuth was present in the first brazing filler metal layer 20 (FIG. 3(A)). Furthermore, the brazing filler metal layer 80 of the specimen of Comparative Example 1 contained more bismuth than the second brazing filler metal layer 40, and planar segregation of bismuth was confirmed near the interface between the brazing filler metal layer 80 and the stainless steel 10. Note that, since the brass 60 used in Conventional Example 1 did not contain bismuth, bismuth was not detected in the brazing filler metal layer 70.

[0075] [summary] From the above, it can be seen from the results of Comparative Example 1 that the bonding strength is reduced due to planar segregation of bismuth near the interface between the brazing filler metal layer 80 and the stainless steel 10. And from the results of Example 1, it can be seen that by using the blocking layer 30, even when brass 50 containing bismuth is used, the blocking layer 30 can block bismuth migrating from the brass 50, thereby preventing a reduction in bonding strength and providing sufficient bonding strength similar to Conventional Example 1.

[0076] As described above, the present invention provides a brazed joint and a method for manufacturing a brazed joint that can suppress a decrease in joint strength even when brass containing bismuth instead of lead and stainless steel are joined by brazing using a brazing filler metal, and is therefore industrially useful. [Explanation of symbols]

[0077] 10: Stainless steel 20: First brazing layer 30: Blocking layer 40: Second brazing layer 50: Brass 60: Brass 70: Brazing material layer 80: Brazing material layer 100: Brazed joint 200: Brazed joint 220: Grip 300: Brazed joint 400: Upper jig 410: Side 420: Grip 500: Lower jig 510:Inside 520: Side

Claims

1. A brazed joint of stainless steel and brass, a layer structure in which the stainless steel, a first brazing filler metal layer, a barrier layer, a second brazing filler metal layer, and the brass are arranged in this order, The brass has a Cu content of 57.4 to 64.0 mass%, a Pb content of 0.1 mass% or less, and a Bi content of 0.50 to 4.00 mass%, The barrier layer is a layer that blocks Bi in the brass from migrating to the first brazing filler metal layer when the stainless steel and the brass are brazed together, and the barrier layer is at least one of brass having a Cu content of 59.0 to 71.5 mass% and a Pb content of 0.10 mass% or less, or phosphor bronze having an Sn content of 5.5 to 7.0 mass%, a P content of 0.03 to 0.35 mass%, a Pb content of 0.02 mass% or less, an Fe content of 0.10 mass% or less, a Zn content of 0.20 mass% or less, the balance being Cu, and the total of Cu, Sn, and P being 99.5 mass% or more, A brazed joint, wherein the brazing filler metal constituting the first brazing filler metal layer and the second brazing filler metal layer is in a liquid state at 680 to 800°C.

2. The bonding strength between the stainless steel and the brass is 100 N / mm ２ The brazed joint according to claim 1 .

3. 2. The brazed joint according to claim 1, wherein the stainless steel is any one of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and two-phase stainless steels thereof.

4. The stainless steel is SUS304, the first brazing filler metal layer and the second brazing filler metal layer are layers of a brazing filler metal containing BAg-7, the barrier layer is C2801; The brazed joint of claim 1, wherein the brass is C6803.

5. A method for producing a brazed joint according to claim 1, a first layer structure forming step of forming a first layer structure by arranging the stainless steel, the first brazing filler metal, the barrier layer, the second brazing filler metal, and the brass in layers, in this order; a first brazing step of heating the first layer structure so that the temperatures of the first brazing filler metal and the second brazing filler metal are 680 to 800°C, and brazing the stainless steel and the brass together; a first cooling step of cooling the first layer structure after the first brazing step to form a brazed joint having a layer structure of the stainless steel, a first brazing material layer, a barrier layer, a second brazing material layer, and the brass; A method for producing a brazed joint, comprising:

6. The method for producing a brazed joint according to claim 5 , wherein the first brazing filler metal and the second brazing filler metal have the same composition.

7. A method for producing a brazed joint according to claim 1, a second layer structure forming step of forming a second layer structure by sequentially arranging the stainless steel, the barrier layer, and the brass in layers and disposing a third brazing filler metal between the stainless steel and the barrier layer, between the barrier layer and the brass, or on a side surface of the barrier layer; a second brazing step of heating the second layer structure so that the temperature of the third brazing filler metal is 680 to 800°C, and brazing the stainless steel and the brass together; a second cooling step of cooling the second layer structure after the second brazing step to form a brazed joint having a layer structure of the stainless steel, a first brazing material layer, a barrier layer, a second brazing material layer, and the brass; A method for producing a brazed joint, comprising:

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