A welding method suitable for copper tungsten and steel

Abstract

The application discloses a welding method suitable for copper-tungsten and steel, and the method comprises the following steps: S1, raw material preparation, taking copper-tungsten alloy parts and steel parts; S2, cleaning and assembling, assembling the copper-tungsten alloy parts, silver soldering pieces and the steel parts to obtain workpieces; S3, vacuum brazing, placing the workpieces in a vacuum brazing furnace for welding, and then cooling and taking out of the furnace; the application can realize copper and steel connection by copper transition on the copper-tungsten alloy and steel welding surface position, solve the welding defects of traditional brazing process by adopting the vacuum silver brazing process, improve the bonding strength between the matrix, and ensure the quality consistency and stability of the welding products, so that mass production can be realized and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of vacuum brazing technology, and more specifically to a welding method applicable to copper-tungsten and steel. Background Technology

[0002] Traditional brazing of copper-tungsten alloys and steel is called hard brazing. The solder has poor wettability with the base materials, such as steel and copper-tungsten alloys, resulting in unreliable welds. Large, visible holes may appear at the joint after welding, leading to a low brazing rate. During the finished product processing, the copper-tungsten alloy and steel are prone to detachment.

[0003] Currently, the welding method between copper-tungsten and steel irregular parts is mostly brazing. However, the quality of brazing cannot be guaranteed. Usually, in order to improve the bonding strength between the two, the design drawings are changed to a stepped shape to increase the welding area. This design increases the amount of silver solder used, increases the welding cost, and requires higher technical skills from the operators. Porosity in the weld is difficult to avoid after welding, which seriously affects the welding quality and product delivery. Summary of the Invention

[0004] To address the above problems, the present invention provides a welding method applicable to copper-tungsten and steel.

[0005] The technical solution of this invention is: a welding method suitable for copper-tungsten and steel, comprising the following steps:

[0006] S1. Raw material preparation:

[0007] Take the copper-tungsten alloy parts and steel parts that need to be welded, wherein the welding surface of the copper-tungsten alloy parts is coated with a copper metal layer with a thickness of 0.5mm;

[0008] S2. Cleaning and assembly:

[0009] The copper metal layer surface of the copper-tungsten alloy part and the welding surface of the steel part are cleaned with a cleaning solution. A silver solder sheet is placed on the welding surface. The copper-tungsten alloy part, the silver solder sheet and the steel part are assembled to obtain the workpiece. The melting point of the silver solder sheet is lower than that of the steel part.

[0010] S3, Vacuum Brazing:

[0011] The workpiece is placed in a vacuum brazing furnace, and a vacuum of 10°C is applied. -3 ~10 -2 Pa, heat at a rate of 5-7℃ / min to 790-800℃; then hold at that temperature for 15-20 minutes to complete the welding, and then cool and remove from the furnace to obtain the welded part.

[0012] Note: The copper-tungsten alloy and steel welding surfaces are connected by copper, which enhances the welding composite effect between copper and steel. Vacuum silver brazing process solves the defects of traditional brazing process, such as many holes, low brazing rate, and detachment between copper-tungsten alloy and steel. It improves the bonding strength between the base materials, and the brazing rate can reach over 99%. The welded appearance is good, the processing is simple, the time consumption is short, and mass production can be achieved.

[0013] Furthermore, in step S2, the silver solder sheet is made of Cu-Ag50 solder material with a melting point temperature of 779-790℃.

[0014] Note: When the melting point of silver solder is lower than that of steel, it melts first during vacuum brazing and exerts its strong bonding effect between the copper-tungsten alloy and the steel, thus completing the welding process. Conversely, when the melting point of silver solder is higher, the melting time is slower, making it difficult to exert its bonding effect and reducing the welding effect.

[0015] Further, in step S1, the method for attaching a 0.5mm thick copper metal layer to the welding surface of the copper-tungsten alloy part is as follows:

[0016] If the copper-tungsten alloy is prepared by melt infiltration and a copper metal layer is attached to the surface of the copper-tungsten alloy with a thickness greater than 0.5 mm, the surface of the copper metal layer is ground to a thickness of 0.5 mm and a surface roughness Ra of 1.2 to 1.5 to complete the adhesion; otherwise, a copper metal layer is covered on the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer is 0.5 mm.

[0017] Note: The above judgment method can be used to determine the adhesion of copper layer in specific cases of copper-tungsten alloys. Copper-tungsten alloys obtained by melt infiltration have copper layer adhesion and the copper layer fills the pores of tungsten. The two are very firmly combined, which increases the strength of the weld. In other methods, the copper layer is used to connect with steel, which can enhance the welding composite effect between copper-tungsten and steel.

[0018] Further, in step S1, the method for covering the copper metal layer is as follows: take a copper metal layer with a thickness of 0 to 0.5 mm, grind the copper-tungsten alloy part and the covering surface of the copper metal layer to a roughness Ra of 1.2 to 1.5, and then extrude it for 1 to 2 minutes under a pressure of 120 to 150 MPa to cover the copper-tungsten alloy part with the copper metal layer.

[0019] Note: The above method provides a way to cover copper-tungsten alloy parts with a copper metal layer, so as to pre-composite the two and improve the connection effect, thereby improving the subsequent welding effect.

[0020] Further, in step S1, the method for covering the copper metal layer is as follows: take copper powder with a particle size of 1 to 5 μm, and under a set extrusion pressure, extrude the copper powder onto the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer formed after extrusion is 0.5 mm.

[0021] Note: The above method for covering the copper metal layer is more preferred, as it strengthens the connection between the copper metal layer and the copper-tungsten alloy part, and the coverage of the copper metal layer is more uniform, making the formed surface easier to weld, increasing the flatness of the contact welding surface, and thus improving the welding effect.

[0022] Furthermore, the set extrusion pressure is 50-200 MPa.

[0023] Note: The pressure set above provides the best squeezing effect. Exceeding this range will result in loose coverage or reduced surface adhesion to the steel.

[0024] Further, the extrusion composite method is as follows: at room temperature, the covering surface of the copper-tungsten alloy part is first ground to a roughness Ra of 0.8 to 1.1, and then copper powder is sprayed onto the covering surface of the copper-tungsten alloy part in multiple applications, with each application having a thickness of 0.1 to 0.2 mm. Then, through multiple extrusions, the copper powder is extruded after each application until the thickness of the copper metal layer formed after extrusion is 0.5 mm.

[0025] The method of multiple extrusions is as follows: the first extrusion pressure is 50-80 MPa and the extrusion time is 14s; the second extrusion pressure is 81-120 MPa and the extrusion time is 12s; in subsequent extrusion processes, the extrusion pressure is 30 MPa greater than the previous pressure, and the extrusion time is kept constant at 10s.

[0026] Note: The above-mentioned multiple extrusion composite method can further improve the composite effect of copper-tungsten alloy parts and copper. By differentiating the pressure and time in the multiple extrusion, the filling density of copper powder can be increased, the bonding force between each layer can be enhanced, and the bonding effect can be easily exerted in the subsequent vacuum brazing process, while reducing the generation of voids.

[0027] Furthermore, during the multiple extrusion processes, the extrusion pressure increases at a rate of 0.5 to 1 MPa per second, while the temperature decreases at a rate of 5 °C per second, until the extrusion is completed.

[0028] Note: The relative changes in pressure and temperature described above can enhance the combined effect.

[0029] Furthermore, in step S2, when the copper-tungsten alloy parts and steel parts are welded with concave and convex surfaces, a placement groove is opened at the upper part of the side welding surface of the two parts, and the silver solder sheet is placed in the placement groove; at the same time, the silver solder sheet is placed in the bottom welding surface of the two parts, and then assembly is performed.

[0030] Note: The above-mentioned placement groove is designed to ensure that the molten silver during welding is filled and bonded through capillary flow, thereby enhancing the welding effect.

[0031] Further, in step S2, the gap at the joint position between the copper-tungsten alloy part and the steel part is 0.01 to 1 mm; the area of ​​the silver solder sheet placed at the joint position between the copper-tungsten alloy part and the bottom surface of the steel part is smaller than the area of ​​the bottom welding surface of the two parts, and the edge of the silver solder sheet is 0.5 to 1 mm away from the edge of the welding surface.

[0032] Note: The above specific numerical limits result in a better welding composite effect and a stronger weld.

[0033] Furthermore, in step S3, when the temperature is raised to 450-500°C, a welding pressure of 30 MPa is applied to the copper-tungsten alloy part and the steel part. As the temperature rises, the welding pressure gradually decreases, and the rate of decrease is: for every 10-15°C increase in temperature, the welding pressure decreases by 1 MPa until the pressure drops to zero.

[0034] Furthermore,

[0035] Note: Applying the above welding pressure can form a diffusion composite surface at the beginning of welding, enhancing the connection between workpieces. As the temperature rises, the welding pressure should be reduced accordingly to avoid squeezing out the silver solder and thus reducing the welding effect.

[0036] Further, in step S2, the cleaning solution is obtained by mixing alcohol ether phosphate and methyl dimethoxysilane in a mass ratio of 5:2 to 3.

[0037] Note: Alcohol ether phosphate has strong surface activity and dissolving ability, which can effectively remove grease, dirt and other surface contaminants; methyldimethoxysilane itself does not have a cleaning effect, but is used to improve the adhesion of materials. However, the mixture of methyldimethoxysilane and alcohol ether phosphate can improve the cleaning effect of alcohol ether phosphate and the surface treatment effect of metal, making it easier for the next step of processing.

[0038] The beneficial effects of this invention are:

[0039] This invention enables a copper transition at the welding surface between copper-tungsten alloy and steel, connecting the copper and steel. It employs vacuum silver brazing to overcome welding defects inherent in traditional brazing processes, improving the bond strength between the substrates, ensuring weld quality, achieving a brazing rate of over 99%, and producing a good post-weld appearance. Furthermore, this welding method guarantees consistent and stable weld quality, ensures bonding strength, reduces the technical requirements for operators, enables mass production, and improves production efficiency. Attached Figure Description

[0040] Figure 1 This is a cross-sectional view of the welding in Embodiment 1 of the present invention;

[0041] Figure 2 This is a cross-sectional view of the welding in Comparative Example 1 of the present invention. Detailed Implementation

[0042] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0043] Example 1:

[0044] A welding method applicable to copper-tungsten and steel includes the following steps:

[0045] S1. Raw material preparation:

[0046] The copper-tungsten alloy parts are prepared by powder metallurgy and have no copper layer attached to their surface. The welding of the copper-tungsten alloy parts and steel parts is a concave-convex welding surface. The copper-tungsten alloy parts and steel parts to be welded are taken, and the welding surface of the copper-tungsten alloy parts is covered with a copper metal layer with a thickness of 0.5 mm. The method of covering the copper metal layer is as follows: take a copper metal layer with a thickness of 0.5 mm, grind the copper-tungsten alloy parts and the covering surface of the copper metal layer to a roughness Ra of 1.4, and then extrude it under a pressure of 130 MPa for 1.5 min to cover the copper-tungsten alloy parts with the copper metal layer.

[0047] S2. Cleaning and assembly:

[0048] The copper metal layer surface of the copper-tungsten alloy part and the welding surface of the steel part are cleaned with a cleaning solution, which is an alcohol ether phosphate ester. Silver solder sheets are placed on the welding surfaces, and the copper-tungsten alloy part, silver solder sheets and steel parts are assembled to obtain the workpiece. A placement groove is opened above the side welding surfaces of the two parts, and the silver solder sheets are placed in the placement groove. At the same time, silver solder sheets are placed on the bottom welding surfaces of the two parts, and then assembled. The gap at the joint position of the copper-tungsten alloy part and the steel part on the side is 0.05mm. The area of ​​the silver solder sheet placed at the joint position of the bottom surface of the copper-tungsten alloy part and the steel part is smaller than the area of ​​the bottom welding surface of the two parts, and the edge of the silver solder sheet is 0.6mm away from the edge of the welding surface.

[0049] The silver solder sheet selected has a melting point lower than that of the steel part, and the thickness of the silver solder sheet is 5mm; the silver solder sheet is made of Cu-Ag50 solder material with a melting point temperature of 785℃.

[0050] S3, Vacuum Brazing:

[0051] The workpiece is placed in a vacuum brazing furnace, and a vacuum of 10°C is applied. -3Pa, heated at a rate of 6℃ / min to 795℃; then held at that temperature for 18min to complete the welding, followed by cooling and removal from the furnace to obtain the welded part.

[0052] Example 2

[0053] The difference between this embodiment and embodiment 1 is that the temperature parameters in the vacuum brazing are different. S3, Vacuum brazing: The workpiece is placed in a vacuum brazing furnace, and a vacuum is drawn to 10°C. -3 Pa, heat at a rate of 7℃ / min to 790℃; then hold at that temperature for 15 minutes to complete the welding, and then cool and remove from the furnace.

[0054] Example 3

[0055] The difference between this embodiment and embodiment 1 is that the temperature parameters in the vacuum brazing are different. S3, Vacuum brazing: The workpiece is placed in a vacuum brazing furnace, and a vacuum is drawn to 10°C. -2 Pa, heat at a rate of 5℃ / min to 800℃; then hold at that temperature for 20 minutes to complete the welding, and then cool and remove from the furnace.

[0056] Example 4

[0057] The difference between this embodiment and embodiment 1 is that the grinding and extrusion parameters are different in the copper metal layer covering. The copper-tungsten alloy part and the copper metal layer covering surface are ground to a roughness Ra of 1.5, and then extruded for 1 minute under a pressure of 150 MPa to cover the copper-tungsten alloy part with the copper metal layer.

[0058] Example 5

[0059] The difference between this embodiment and Embodiment 1 is that the grinding and extrusion parameters are different in the copper metal layer covering. The copper-tungsten alloy part and the copper metal layer covering surface are ground to a roughness Ra of 1.2, and then extruded for 2 minutes under a pressure of 120 MPa to cover the copper-tungsten alloy part with the copper metal layer.

[0060] Example 6

[0061] The difference between this embodiment and embodiment 1 is that the grinding and extrusion parameters are different in the copper metal layer covering. The copper-tungsten alloy part and the copper metal layer covering surface are ground to a roughness Ra of 1.5, and then extruded for 1 minute under a pressure of 120 MPa to cover the copper-tungsten alloy part.

[0062] Example 7

[0063] The difference between this embodiment and Embodiment 1 is that the method for covering the copper metal layer is as follows: copper powder with a particle size of 1-5 μm is taken and extruded onto the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer formed after extrusion is 0.5 mm. The extrusion bonding method is as follows: at room temperature, the covering surface of the copper-tungsten alloy part is first ground to a roughness Ra of 0.9, and then copper powder is uniformly sprayed onto the covering surface of the copper-tungsten alloy part. The thickness of each spray is 0.15 mm. Through the extrusion process, the copper powder is extruded after each spray until the thickness of the copper metal layer formed after extrusion is 0.5 mm. The method of multiple extrusions is as follows: the first extrusion pressure is 60 MPa and the extrusion time is 14 s, the second extrusion pressure is 100 MPa and the extrusion time is 12 s. In the subsequent extrusion process, the extrusion pressure is 30 MPa greater than the previous pressure, and the extrusion time is kept constant at 10 s.

[0064] Example 8

[0065] The difference between this embodiment and Embodiment 7 is that the extrusion composite method is as follows: at room temperature, the covering surface of the copper-tungsten alloy part is first ground to a roughness Ra of 1.1, and then copper powder is uniformly sprayed onto the covering surface of the copper-tungsten alloy part. The thickness of each spray is 0.2 mm. Through the extrusion process, the copper powder is extruded after each spray until the thickness of the copper metal layer formed after extrusion is 0.5 mm. The method of multiple extrusions is as follows: the first extrusion pressure is 80 MPa and the extrusion time is 14 s, the second extrusion pressure is 81 MPa and the extrusion time is 12 s. In the subsequent extrusion process, the extrusion pressure is 30 MPa greater than the previous pressure, and the extrusion time is kept constant at 10 s.

[0066] Example 9

[0067] The difference between this embodiment and Embodiment 1 is that the extrusion composite method is as follows: at room temperature, the covering surface of the copper-tungsten alloy part is first ground to a roughness Ra of 0.8, and then copper powder is uniformly sprayed onto the covering surface of the copper-tungsten alloy part. The thickness of each spray is 0.1 mm. Through the extrusion process, the copper powder is extruded after each spray until the thickness of the copper metal layer formed after extrusion is 0.5 mm. The method of multiple extrusions is as follows: the first extrusion pressure is 50 MPa and the extrusion time is 14 s, the second extrusion pressure is 120 MPa and the extrusion time is 12 s. In the subsequent extrusion process, the extrusion pressure is 30 MPa greater than the previous pressure, and the extrusion time is kept constant at 10 s.

[0068] Example 10

[0069] The difference between this embodiment and embodiment 7 is that, during the multiple extrusion processes, the extrusion pressure increases at a rate of 0.8 MPa per second, while the temperature decreases at a rate of 5 °C per second until the extrusion is completed.

[0070] Example 11

[0071] The difference between this embodiment and embodiment 10 is that, during the multiple extrusion processes, the extrusion pressure increases at a rate of 1 MPa per second, while the temperature decreases at a rate of 5 °C per second, until the extrusion is completed.

[0072] Example 12

[0073] The difference between this embodiment and embodiment 10 is that, during the multiple extrusion processes, the extrusion pressure increases at a rate of 0.5 MPa per second, while the temperature decreases at a rate of 5 °C per second, until the extrusion is completed.

[0074] Example 13

[0075] The difference between this embodiment and embodiment 10 is that, in step S2, the gap at the joint position between the copper-tungsten alloy part and the steel part is 0.01mm; the area of ​​the silver solder sheet placed at the joint position between the copper-tungsten alloy part and the bottom surface of the steel part is smaller than the area of ​​the bottom welding surface of the two parts, and the edge of the silver solder sheet is 1mm away from the edge of the welding surface.

[0076] Example 14

[0077] The difference between this embodiment and embodiment 10 is that, in step S2, the gap at the joint position between the copper-tungsten alloy part and the steel part is 1mm; the area of ​​the silver solder sheet placed at the joint position between the copper-tungsten alloy part and the bottom surface of the steel part is smaller than the area of ​​the bottom welding surface of the two parts, and the edge of the silver solder sheet is 0.5mm away from the edge of the welding surface.

[0078] Example 15

[0079] The difference between this embodiment and embodiment 10 is that in step S3, when the temperature is raised to 480°C, a welding pressure of 30 MPa is applied to the copper-tungsten alloy part and the steel part. As the temperature rises, the welding pressure gradually decreases. The rate of decrease is: for every 13°C increase in temperature, the welding pressure decreases by 1 MPa until the decrease is completed and the application is stopped.

[0080] Example 16

[0081] The difference between this embodiment and embodiment 15 is that in step S3, when the temperature is raised to 450°C, a welding pressure of 30 MPa is applied to the copper-tungsten alloy part and the steel part. As the temperature rises, the welding pressure gradually decreases, and the rate of decrease is: for every 10°C increase in temperature, the welding pressure decreases by 1 MPa until the reduction is completed and the application is stopped.

[0082] Example 17

[0083] The difference between this embodiment and embodiment 15 is that in step S3, when the temperature is raised to 500°C, a welding pressure of 30 MPa is applied to the copper-tungsten alloy part and the steel part. As the temperature rises, the welding pressure gradually decreases. The rate of decrease is: for every 15°C increase in temperature, the welding pressure decreases by 1 MPa until the decrease is completed and the application is stopped.

[0084] Example 18

[0085] The difference between this embodiment and Embodiment 1 is that in step S2, the cleaning solution is obtained by mixing alcohol ether phosphate and methyl dimethoxysilane in a mass ratio of 5:2.

[0086] Example 19

[0087] The difference between this embodiment and Embodiment 1 is that in step S2, the cleaning solution is obtained by mixing alcohol ether phosphate and methyl dimethoxysilane in a mass ratio of 5:3.

[0088] Example 20

[0089] The difference between this embodiment and Embodiment 1 is that in step S1, the copper-tungsten alloy is prepared by melt infiltration, and a copper metal layer with a thickness of 0.8 mm is attached to the surface of the copper-tungsten alloy. The surface of the copper metal layer is then polished to a thickness of 0.5 mm and a surface roughness Ra of 1.4, thus completing the attachment.

[0090] Example 21

[0091] The difference between this embodiment and Embodiment 1 is that in step S1, the copper-tungsten alloy is prepared by melt infiltration, and a copper metal layer with a thickness of 0.1 mm is attached to the surface of the copper-tungsten alloy. The copper metal layer is then covered on the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer is 0.5 mm. The copper-tungsten alloy part and the surface covered by the copper metal layer are polished to a roughness Ra of 1.4. Then, the part is extruded for 1.5 min under a pressure of 130 MPa to cover the copper-tungsten alloy part with the copper metal layer.

[0092] Experimental Example

[0093] Comparative Example 1: Take the same workpiece as in Example 1 and weld it using a hard brazing process;

[0094] Comparative Example 2: The difference from Example 1 is that the silver solder used in step S2 has a melting point of 810°C;

[0095] Comparative Example 3: Unlike Example 1, no placement groove was provided; instead, silver solder sheets were placed directly on the bottom welding surfaces of both components before assembly.

[0096] First, observe and compare the welding effect of the welded products obtained in Example 1 and Comparative Example 1.

[0097] Each as Figure 1 , Figure 2 ,from Figure 1 As can be seen, the welding quality of Example 1 is good, with no holes, and its contact surface is relatively flat and the connection is relatively firm. Figure 2 As can be seen, the silver solder cannot fully fill the welding surface, there are large pores, the welding effect is poor, and the subsequent welding may result in poor bond strength.

[0098] II. The brazing rates (‰) obtained in Examples 1-19 were obtained through implementation;

[0099] Examples 1, 7, 10, 15, and 18, and Comparative Examples 1 to 3 were compared, as shown in Table 1.

[0100] Table 1. Experimental results of welding rate under different treatments.

[0101]

[0102]

[0103] As can be seen from Table 1, by comparing Example 1 with Comparative Example 1, it can be concluded that the copper transition welding method of Example 1 can significantly improve the brazing rate, indicating that the welding method of Example 1 can avoid the problems of poor wettability, unreliable welding and low brazing rate that occur in the traditional copper-tungsten and steel brazing, and improve the welding effect.

[0104] Comparing Example 1 and Comparative Example 2, it can be concluded that using the silver solder sheet set in Example 1 is beneficial to improving the welding rate, indicating that an excessively high melting point of the silver solder sheet will affect the welding effect.

[0105] Comparing Example 1 and Comparative Example 3, it can be seen that the workpiece assembly method of Example 1 can ensure that the molten silver during welding is filled and bonded through capillary flow in the uneven welding surface.

[0106] Comparing Example 1 and Example 7, it can be found that the method of covering the copper metal layer used in Example 7 is more able to give full play to the transition effect of the copper layer and improve the brazing rate.

[0107] Comparing Example 7 and Example 10, it can be found that the change in the extrusion pressure setting in Example 10 can effectively improve the brazing rate by making the copper layer more flat and firmly in contact with the two welding surfaces.

[0108] Comparing Example 10 and Example 15, it can be found that by adjusting the temperature and pressure settings of vacuum welding, the welding effect can be further improved.

[0109] Comparing Example 1 and Example 18, it can be seen that the cleaning solution promotes the composite and welding processes and enhances the surface adhesion of the welded contact.

[0110] Comparing Example 1 and Example 20, it can be seen that the copper layer prepared by the melt infiltration method and then polished improves the brazing rate.

Claims

1. A welding method suitable for copper-tungsten and steel, characterized in that, Includes the following steps: S1. Raw material preparation: Take the copper-tungsten alloy parts and steel parts that need to be welded, wherein the welding surface of the copper-tungsten alloy parts is coated with a copper metal layer with a thickness of 0.5mm; S2. Cleaning and assembly: The copper metal layer surface of the copper-tungsten alloy part and the welding surface of the steel part are cleaned with a cleaning solution. A silver solder sheet is placed on the welding surface. The copper-tungsten alloy part, the silver solder sheet and the steel part are assembled to obtain the workpiece. The melting point of the silver solder sheet is lower than that of the steel part. S3, Vacuum Brazing: The workpiece is placed in a vacuum brazing furnace, and a vacuum of 10°C is applied. -3 ~10 -2 Pa, heat at a rate of 5~7℃ / min to 790~800℃; then hold at that temperature for 15~20min to complete the welding, then cool and remove from the furnace to obtain the welded part; In step S2, the silver solder sheet is made of Cu-Ag50 solder material with a melting point temperature of 779~790℃; In step S1, the method for attaching a 0.5mm thick copper metal layer to the welding surface of the copper-tungsten alloy part is as follows: If the copper-tungsten alloy is prepared by melt infiltration and a copper metal layer is attached to the surface of the copper-tungsten alloy with a thickness greater than 0.5 mm, the surface of the copper metal layer is polished until its thickness is 0.5 mm and the surface roughness Ra is 1.2~1.5, thus completing the adhesion; otherwise, a copper metal layer is covered on the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer is 0.5 mm. In step S1, the method of covering the copper metal layer is as follows: take a copper metal layer with a thickness of 0~0.5mm, grind the copper-tungsten alloy part and the covering surface of the copper metal layer to a roughness Ra of 1.2~1.5, and then extrude it for 1~2 minutes under a pressure of 120~150MPa to cover the copper metal layer onto the copper-tungsten alloy part; Alternatively, the method for covering the copper metal layer is as follows: take copper powder with a particle size of 1~5μm, and under a set extrusion pressure, extrude the copper powder onto the welding surface of the copper-tungsten alloy part until the thickness of the copper metal layer formed after extrusion is 0.5mm; the set extrusion pressure is 50~200MPa; The extrusion composite method is as follows: at room temperature, the surface of the copper-tungsten alloy part is first ground to a roughness Ra of 0.8~1.

1. Then, copper powder is sprayed onto the surface of the copper-tungsten alloy part in multiple layers, with each layer being 0.1~0.2mm thick. After each layer is sprayed, the copper powder is extruded until the thickness of the copper metal layer formed after extrusion is 0.5mm. The method of multiple extrusions is as follows: the first extrusion pressure is 50~80MPa and the extrusion time is 14s; the second extrusion pressure is 81~120MPa and the extrusion time is 12s; in the subsequent extrusion process, the extrusion pressure is 30MPa greater than the previous pressure, and the extrusion time is kept constant at 10s. In step S2, when the copper-tungsten alloy parts and steel parts are welded with concave and convex surfaces, a placement groove is opened at the upper part of the side welding surface of the two parts, and the silver solder sheet is placed in the placement groove; at the same time, the silver solder sheet is placed in the bottom welding surface of the two parts, and then the assembly is performed. In step S2, the gap between the copper-tungsten alloy part and the side of the steel part is 0.01~1mm; the area of ​​the silver solder sheet placed at the joint position between the copper-tungsten alloy part and the bottom surface of the steel part is smaller than the area of ​​the bottom welding surface of the two parts, and the edge of the silver solder sheet is 0.5~1mm away from the edge of the welding surface.

2. The welding method applicable to copper-tungsten and steel as described in claim 1, characterized in that, During the multiple extrusion processes, the extrusion pressure increases at a rate of 0.5~1MPa per second, while the temperature decreases at a rate of 5℃ / s until the extrusion is completed.

3. The welding method applicable to copper-tungsten and steel as described in claim 1, characterized in that, In step S3, when the temperature is raised to 450~500℃, a welding pressure of 30MPa is applied to the copper-tungsten alloy part and the steel part. As the temperature rises, the welding pressure gradually decreases. The rate of decrease is: for every 10~15℃ increase in temperature, the welding pressure decreases by 1MPa until the pressure drops to zero.

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