A brazing process for connecting hard alloy and steel dissimilar materials by using low-silver foil brazing filler metal and application thereof

Abstract

The application discloses a brazing process for realizing connection of hard alloy and steel dissimilar materials by using low-silver foil brazing filler metal and application thereof, realizes connection between the hard alloy and the steel, fully gives play to the advantages of the hard alloy and the steel, avoids precipitation of hard and brittle phases at a weld interface, solves the problem of excessive dissolution of base materials, and has the characteristics of high shear strength. The application provides a brazing process for realizing connection of hard alloy and steel dissimilar materials by using low-silver foil brazing filler metal, compared with other welding technologies, the brazing process has good welding effect, low production cost, safety and environmental protection. Meanwhile, the shear strength at a welding position is high, and the corrosion resistance is excellent, and the brazing process is especially suitable for welding of the hard alloy and the steel in a shield tunneling machine cutter.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and in particular relates to a brazing process for joining dissimilar materials such as cemented carbide and steel using low-silver foil with brazing filler metal, and its application. Background Technology

[0002] In the manufacturing of wide scrapers for tunnel boring machines (TBMs), cemented carbide cutting edges are the main wear-resistant components, constructed by welding a high-strength, high-toughness steel matrix together with cemented carbide. Welding is one of the key technologies in scraper manufacturing. Taking a commonly used 6-hole scraper as an example, 16 pieces of cemented carbide of four different sizes need to be simultaneously heated and welded onto the steel matrix. These cemented carbide blocks are distributed in different positions, including vertical, horizontal, and embedded welding, resulting in a very complex distribution of the overall temperature field during the cutting tool heating process and the residual stress field after welding. This complexity easily leads to problems such as incomplete alloy welding and spalling. Therefore, for TBM cutting tools requiring long service life and high reliability, the overall brazing technology places very high demands on it.

[0003] Due to the significant differences in physical properties between cemented carbide and steel, a hard and brittle Co3W3C(η) phase and high post-weld residual stress are easily generated at the cemented carbide interface during welding, which are the main factors affecting joint quality. Cemented carbide contains a large number of WC ceramic particles, and fusion welding methods such as laser welding, electron beam welding, and TIG welding can achieve the connection between cemented carbide and steel. However, the hard and brittle η phase easily aggregates at the cemented carbide interface, a problem that cannot be completely solved at present. Furthermore, diffusion welding requires relatively high welding temperatures, which can significantly impact the properties of cemented carbide.

[0004] Currently, tunnel boring machine (TBM) scrapers are primarily manufactured using brazing. Brazing operates at lower temperatures, has less impact on the properties of the base material, and produces relatively lower residual stress compared to other welding methods, making it widely used in the manufacture of cemented carbide tools. However, cemented carbide has poor brazing properties; at temperatures exceeding 900℃, the surface of WC cemented carbide is highly susceptible to oxidation. Induction brazing offers rapid heating, but precise control is difficult. Excessive power can lead to localized overheating of the workpiece and incomplete melting of the filler metal, resulting in cracks. Insufficient power results in prolonged heating times, which can cause oxidation of the cutter body and affect production efficiency. Furthermore, the significant difference in interfacial tension between the liquid filler metal and the cemented carbide and base metal leads to poor gap filling during brazing. The brazing process also faces challenges such as excessive residual stress and the formation of hard and brittle phases in the weld joint.

[0005] To address the problems of poor wetting and filling properties and precipitation of hard and brittle phases at the weld interface during the brazing of cemented carbide and steel, it is essential to propose a brazing filler metal and brazing process for brazing cemented carbide and steel. Summary of the Invention

[0006] To overcome the shortcomings and disadvantages of the prior art, the primary objective of this invention is to provide a brazing process for connecting dissimilar materials such as cemented carbide and steel using low-silver foil with brazing filler metal. This brazing process achieves the connection between cemented carbide and steel, fully utilizes the advantages of both cemented carbide and steel, avoids the precipitation of hard and brittle phases at the weld interface, solves the problem of excessive dissolution of the base material, and features high shear strength.

[0007] The second objective of this invention is to provide a brazing process for joining dissimilar materials, such as cemented carbide and steel, using low-silver foil with brazing filler metal, and its application in tunnel boring machine cutters.

[0008] The primary objective of this invention is achieved through the following technical solution:

[0009] A brazing process for joining dissimilar materials, cemented carbide and steel, using low-silver foil with solder, comprises the following steps:

[0010] Step 1: Cut the cemented carbide and steel plates, grind the welding surfaces of the two base materials (cemented carbide and steel plates) to remove the oxide film on the surface of the cemented carbide and steel plates, and grind the surface of the foil brazing filler metal.

[0011] Step 2: The polished cemented carbide, steel plate and foil brazing filler metal are placed in anhydrous ethanol for ultrasonic cleaning and then dried in a vacuum drying oven to obtain the cleaned cemented carbide, steel plate and foil brazing filler metal.

[0012] Step 3: Spread a layer of flux evenly on the welding surfaces of the cemented carbide and steel plate, and then perform pre-welding assembly. Place the foil brazing filler metal between the cemented carbide and the steel plate. After assembly, a structure of cemented carbide, flux, foil brazing filler metal, flux, and steel plate is formed, which is the assembled sample.

[0013] Step 4: Place the assembled sample in an alumina sintering boat and put it into a vacuum furnace. After evacuating the vacuum furnace, backfill it with inert gas to the target pressure value.

[0014] Step 5: After the inert gas pressure reaches the target pressure value, heat the vacuum furnace to 650℃ at a heating rate of 10℃ / min. To fully preheat the cemented carbide and steel samples, hold at 650℃ for 10 minutes. Then, heat from 650℃ to 790℃~870℃ at a heating rate of 10℃ / min, and hold at 790℃~870℃ for 0~15 minutes. After the holding period, cool with the furnace to room temperature to obtain the brazed cemented carbide and steel samples.

[0015] Preferably, the foil solder in step 1 is Ag. 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni1.5 (wt.%)

[0016] Preferably, the target air pressure value in step 1 is 0.95 atm.

[0017] Preferably, in step 1, 400#, 600#, and 800# metallographic sandpaper are used sequentially to polish the carbide and steel plate until the outer surface is bright, and 800# metallographic sandpaper is used to lightly polish the foil and remove the brazing filler metal to remove the oxide film.

[0018] Preferably, the foil solder used in step 1 is prepared according to the following steps:

[0019] (1) High-purity metal particles (content is 99.99%) are purified and impurities are removed. Silver particles, copper particles, zinc particles, manganese flakes, tin particles and nickel particles are prepared according to the mass ratio of 10.08:17.51:15.48:5.24:1.26:0.76 respectively.

[0020] (2) A master alloy silver-copper-manganese-nickel was obtained by high-frequency induction melting under argon protection. Zinc and tin elements were added to the master alloy and then melted to obtain the target brazing alloy.

[0021] (3) Cut the target brazing alloy obtained in step (2) into small pieces by electric spark cutting, and then polish the surface with 180 grit sandpaper to remove the oxide film; put the small pieces of brazing alloy into anhydrous ethanol for ultrasonic cleaning for 5 minutes and then blow dry. Take 10g and put it into a specially made flat-nozzle quartz tube with a bottom gap of 0.5 x 10 mm.

[0022] (4) The special quartz tube containing small pieces of brazing alloy is clamped and installed in the induction coil of the vacuum strip spinning machine, and the height of the quartz tube is adjusted so that the distance between the quartz tube nozzle and the cooling copper roller is 1mm.

[0023] (5) Close the furnace door and begin vacuuming until the vacuum level inside the furnace chamber is ≤1×10⁻⁶. -3 After Pa, 1 atm of high-purity argon gas is introduced and repeated three times. The gas filling valve is then adjusted so that the pressure difference between the external argon gas and the gas pressure inside the furnace chamber is 0.08 MPa, and the cooling copper roller speed is set to 30 m / s. The copper roller rotation switch is turned on, and after the copper roller speed reaches the specified speed and stabilizes, the heating switch is turned on, and the current of the induction coil is adjusted so that the brazing alloy inside the quartz tube melts.

[0024] (6) When the brazing alloy in the quartz tube melts to a yellowish-white color and the metal solution is in a state of constant fluctuation, turn on the spray switch and use the air pressure difference to spray the molten metal onto the surface of the high-speed rotating cooling copper roller; when no liquid is observed to flow out of the quartz tube, turn off the spray switch, heating switch and copper roller rotation switch in sequence, open the furnace door and take out the brazing foil strip, i.e., the foil strip brazing alloy.

[0025] Preferably, the ultrasonic cleaning in step 2 takes 5 minutes and is performed twice, and the vacuum degree of the vacuum drying oven is -0.085 MPa, with a drying time of 5 to 10 minutes.

[0026] Preferably, the flux used in step 3 is FB102, and the assembly diagram of the sample is shown below. Figure 2 As shown.

[0027] In the brazing process of connecting dissimilar materials such as cemented carbide and steel using low-silver foil and solder, the preparation step in step 5 involves heat treatment at 650°C to ensure that the solder is heated and melted uniformly. According to the DSC analysis of the solder, this temperature is not in the phase transition region and is about 40°C lower than the liquidus temperature of the solder. The heat treatment at 790°C to 870°C is to ensure that the solder undergoes a metallurgical reaction with the base materials on both sides to form an effective connection.

[0028] The second objective of this invention is achieved through the following technical solution:

[0029] Application of a low-silver foil brazing process for joining dissimilar materials, such as cemented carbide and steel, in tunnel boring machine cutters.

[0030] The inventive principle and beneficial effects of this invention are as follows:

[0031] This invention provides a brazing process for joining dissimilar materials, cemented carbide and steel, using a low-silver foil with brazing filler metal. Compared with other welding technologies, it offers better welding results, lower production costs, and is safer and more environmentally friendly. Furthermore, it exhibits high shear strength and excellent corrosion resistance at the weld site, making it particularly suitable for welding cemented carbide and steel in tunnel boring machine cutters. The foil with brazing filler metal (Ag)... 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 (wt.%) It possesses advantages such as high strength and toughness, good wettability, moderate melting point, high shear strength at the welding position, and excellent corrosion resistance of the weld. The sheet-like foil-shaped brazing filler metal allows for accurate relative positioning of the filler metal, simplifying the filling of the weld filler metal; during brazing, it is under gas protection throughout the process, and the selection of brazing heating curves takes into account the characteristics of cemented carbide and steel. While ensuring that the strength of the finished product and the hardness of the base material after welding meet the process requirements, the workpiece can be heated as a whole, which is suitable for mass production of finished products and has higher production efficiency. Attached Figure Description

[0032] Figure 1 A schematic diagram of brazing equipment and heating process;

[0033] Figure 2Schematic diagrams of brazing assembly method and (b) shearing method;

[0034] Figure 3 (a)~ Figure 3 (e) are microstructure images of the cross-section of the brazed seam in Examples 1-5, respectively;

[0035] Figure 4 (a)~ Figure 4 (d) are microstructure images of the cross-section of the brazed seam in Examples 6-9, respectively;

[0036] Figure 5 This is a cross-sectional element distribution diagram of the brazed seam in Example 8 of the brazing method;

[0037] Figure 6 The shear strength comparison diagrams for Examples 1 to 5 and Comparative Examples 1 to 4 at the brazing temperature are shown.

[0038] Figure 7 The shear strength comparison diagrams for Examples 6 to 9 and Comparative Examples 5 to 8 with the heat preservation time are shown. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto. All materials used in the examples of the present invention can be purchased commercially. In the specific embodiments, the cemented carbide refers to YG15 cemented carbide, and the steel plate refers to 42CrMo alloy.

[0040] Example 1

[0041] Step 1: Cut the cemented carbide and steel plates, grind the weld surfaces of the two base materials to remove the oxide film on the surfaces of the cemented carbide and steel, and then apply Ag... 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 (wt.%) Foil strip brazing material is used for surface polishing;

[0042] Step 2: Grind the cemented carbide, steel, and Ag. 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 (wt.%) The foil strips and brazing filler metals were ultrasonically cleaned in anhydrous ethanol for 5 min, and then dried in a vacuum drying oven to obtain cleaned cemented carbide, steel, and Ag. 20 Cu 35 Zn 31 Mn 10Sn 2.5 Ni 1.5 (wt.%) foil strip brazing filler metal;

[0043] Step 3: Evenly spread a layer of flux (FB102) on the welding surfaces of the cemented carbide and steel, then perform pre-welding assembly, and attach Ag... 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 (wt.%) The foil-strip brazing filler metal is placed between the cemented carbide and the steel, and after assembly, it forms a structure of cemented carbide, flux, foil-strip brazing filler metal, flux, and steel;

[0044] Step 4: Place the assembled sample in an alumina sintering boat and put it into a vacuum furnace. After evacuating the vacuum furnace, backfill it with inert gas to 0.95 atm.

[0045] Step 5: After the inert gas pressure reaches the target pressure value, heat the vacuum furnace to 650℃ at a heating rate of 10℃ / min, hold at 650℃ for 10min, then heat from 650℃ to 790℃ at a heating rate of 10℃ / min, and hold at 790℃ for 15min. After the holding period, cool the furnace to room temperature to obtain the brazed cemented carbide and steel samples.

[0046] The scanning electron microscope (SEM) image of the weld cross-section microstructure in this embodiment is shown below. Figure 3 As shown, the shear strength of the brazed cemented carbide and steel joint, tested using a universal testing machine, is 251.81 MPa.

[0047] Example 2

[0048] The difference between this embodiment and embodiment 1 is that in step 5, the temperature is increased from 650°C to 810°C at a heating rate of 10°C / min, and then held at 810°C for 15 minutes. Otherwise, it is the same as embodiment 1.

[0049] The scanning electron microscope (SEM) image of the weld cross-section microstructure in this embodiment is shown below. Figure 3 As shown, the shear strength of the brazed cemented carbide and steel joint was 255.25 MPa, as determined by a universal testing machine.

[0050] Example 3

[0051] The difference from Example 1 is that in step 5, the temperature is increased from 650°C to 830°C at a heating rate of 10°C / min, and then held at 830°C for 15 minutes. Otherwise, it is the same as Example 1.

[0052] Example 4

[0053] The difference from Example 1 is that in step 5, the temperature is increased from 650°C to 850°C at a heating rate of 10°C / min, and then held at 850°C for 15 minutes. The rest is the same as in Example 1.

[0054] Example 5

[0055] The difference from Example 1 is that in step 5, the temperature is increased from 650°C to 870°C at a rate of 10°C / min, and then held at 870°C for 15 minutes. The rest is the same as in Example 1.

[0056] The scanning electron microscope (SEM) images of the microstructure of the weld cross-sections in Examples 3-5 are shown below. Figure 3 As shown, the shear strengths of the brazed cemented carbide and steel joints, as tested by a universal testing machine, were 312.19 MPa, 304.48 MPa, and 274.13 MPa, respectively.

[0057] Comparative Examples 1-4: Unlike Examples 1-5, Comparative Examples 1-4 used brazing filler metal with Ag composition. 30 Cu 38 The specific welding temperature and corresponding holding time for Zn are shown in Table 1. Other aspects are the same as in Examples 2-5.

[0058] The shear strengths of the brazed cemented carbide and steel joints, as tested by a universal testing machine, were 201.4 MPa, 305.57 MPa, 316.68 MPa, and 289.57 MPa, respectively.

[0059] Example 6

[0060] The difference between this embodiment and embodiment 1 is that in step 5, the temperature is increased from 650°C to 830°C at a heating rate of 10°C / min, and no heat preservation is performed at 830°C. Otherwise, it is the same as embodiment 1.

[0061] The scanning electron microscope (SEM) image of the weld cross-section microstructure in this embodiment is shown below. Figure 4 As shown, the shear strength of the brazed joint between the cemented carbide and the steel was 167.39 MPa, as determined by a universal testing machine.

[0062] Examples 7-9: The difference between this example and Example 1 is that in step 5, the temperature is increased from 650°C to 830°C at a heating rate of 10°C / min, and then held at 830°C for 5 min, 10 min, and 15 min respectively. The rest is the same as in Example 1.

[0063] The scanning electron microscope (SEM) image of the weld cross-section microstructure in this embodiment is shown below. Figure 4As shown, the shear strengths of the brazed cemented carbide and steel joints, as tested by a universal testing machine, were 263.49 MPa, 322.91 MPa, and 312.19 MPa, respectively.

[0064] Comparative Examples 5-8: Unlike Examples 7-9, Comparative Examples 5-8 used brazing filler metal with Ag composition. 30 Cu 38 The specific welding temperature and corresponding holding time for Zn are shown in Table 2. Other aspects are the same as in Examples 6-9.

[0065] The shear strengths of the brazed cemented carbide and steel joints, as tested by a universal testing machine, were 305.57 MPa, 307.12 MPa, 238.51 MPa, and 187.88 MPa, respectively.

[0066] Table 1

[0067] Welding temperature T / ℃ Insulation time t / min <![CDATA[Shearing strength R τ / MPa]]> Example 1 790 15 251.81 Example 2 810 15 255.25 Example 3 830 15 MAX: 312.19 Example 4 850 15 304.48 Example 5 870 15 274.12 Comparative Example 1 790 15 201.40 Comparative Example 2 810 15 305.57 Comparative Example 3 830 15 MAX: 316.68 Comparative Example 4 850 15 289.57

[0068] Table 2

[0069] Welding temperature T / ℃ Insulation time t / min <![CDATA[Shearing strength R τ / MPa]]> Example 6 830 0 167.39 Example 7 830 5 263.49 Example 8 830 10 MAX: 322.91 Example 9 830 15 312.19 Comparative Example 5 830 0 187.88 Comparative Example 6 830 5 238.51 Comparative Example 7 830 10 MAX: 307.12 Comparative Example 8 830 15 305.57

[0070] like Figure 6 As shown in Examples 1 to 5 and Comparative Examples 1 to 4, the shear strength of the joint first increases and then decreases with increasing brazing temperature, reaching its maximum value of 312.19 MPa at a brazing temperature of 830°C. This was compared with commercial Ag... 30 The comparison of CuZn reveals Ag 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 With commercial Ag 30 The shear strength of CuZn brazed joints is similar.

[0071] like Figure 7 As shown in Examples 1 to 5 and Comparative Examples 1 to 4, the shear strength of the joint first increases and then decreases with the increase of brazing holding time, reaching a maximum of 322.91 MPa when the holding time is 10 min. This is compared with commercial Ag... 30 A comparison of CuZn reveals that, under the same processing conditions, the Ag content of this invention... 20 Cu 35 Zn 31 Mn 10 Sn 2.5 Ni 1.5 With commercial Ag 30CuZn brazed joints have similar shear strength and can be used to some extent as a substitute, which can greatly reduce material costs and promote their widespread adoption in the market.

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A brazing process for joining dissimilar materials, cemented carbide and steel, using low-silver foil with solder, characterized in that... It consists of the following steps: Step 1: Cut the cemented carbide and steel plates, grind the welding surfaces of the two base materials to remove the oxide film on the surface of the cemented carbide and steel plates, and grind the surface of the foil brazing filler metal. Step 2: The polished cemented carbide, steel plate and foil brazing filler metal are placed in anhydrous ethanol for ultrasonic cleaning and then dried in a vacuum drying oven to obtain the cleaned cemented carbide, steel plate and foil brazing filler metal. Step 3: Spread a layer of flux evenly on the welding surfaces of the cemented carbide and steel plate, and then perform pre-welding assembly. Place the foil brazing filler metal between the cemented carbide and the steel plate. After assembly, a structure of cemented carbide, flux, foil brazing filler metal, flux, and steel plate is formed, which is the assembled sample. Step 4: Place the assembled sample in an alumina sintering boat and put it into a vacuum furnace. After evacuating the vacuum furnace, backfill it with inert gas to the target pressure value. Step 5: After the inert gas pressure reaches the target pressure value, the vacuum furnace is heated to 650℃ at a heating rate of 10℃ / min. To fully preheat the cemented carbide and steel samples, the temperature is held at 650℃ for 10 minutes. Then, the temperature is increased from 650℃ to 790℃~870℃ at a heating rate of 10℃ / min, and held at 790℃~870℃ for 0~15 minutes. After the holding period, the temperature is cooled to room temperature with the furnace to obtain the brazed cemented carbide and steel samples. The foil solder mentioned in step 1 is 20Ag35Cu31Zn10Mn2.5Sn1.5Ni.

2. The brazing process for joining dissimilar materials, cemented carbide and steel, using low-silver foil with solder according to claim 1, is characterized in that... The target air pressure value in step 4 is 0.95 atm.

3. The brazing process for joining dissimilar materials, cemented carbide and steel, using low-silver foil with solder according to claim 1, is characterized in that... In step 1, use 400#, 600#, and 800# metallographic sandpaper to polish the carbide and steel plate until the outer surface is bright. Use 800# metallographic sandpaper to lightly polish the foil and remove the brazing filler metal to remove the oxide film.

4. The brazing process for joining dissimilar materials, cemented carbide and steel, using low-silver foil with solder according to claim 1, is characterized in that... The foil solder used in step 1 is prepared according to the following steps: (1) The high-purity metal particles were purified and impurities were removed. Silver particles, copper particles, zinc particles, manganese flakes, tin particles and nickel particles were prepared according to the mass ratio of 10.08:17.51:15.48:5.24:1.26:0.

76. (2) A master alloy silver-copper-manganese-nickel was obtained by high-frequency induction melting under argon protection. Zinc and tin elements were added in the form of the master alloy and then melted to obtain the target solder alloy. (3) Cut the target brazing alloy obtained in step (2) into small pieces by electrical discharge machining, and then polish the surface with 180 grit sandpaper to remove the oxide film; put the small pieces of brazing alloy into anhydrous ethanol for ultrasonic cleaning for 5 min and then blow dry, take 10 g and put it into a specially made flat-nozzle quartz tube with a gap of 0.5 * 10 mm at the bottom of the quartz tube. (4) The special quartz tube containing small pieces of brazing alloy is clamped and installed in the induction coil of the vacuum strip spinning machine, and the height of the quartz tube is adjusted so that the distance between the quartz tube nozzle and the cooling copper roller is 1 mm. (5) Close the furnace door and begin vacuuming until the vacuum level inside the furnace chamber is ≤1×10⁻⁶. -3 After Pa, 1 atm of high-purity argon gas is introduced and repeated three times. The gas filling valve is then adjusted so that the pressure difference between the external argon gas and the gas pressure inside the furnace cavity is 0.08 MPa, and the cooling copper roller speed is set to 30 m / s. Turn on the copper roller rotation switch. After the copper roller reaches the specified speed and stabilizes, turn on the heating switch and adjust the current of the induction coil to melt the brazing alloy inside the quartz tube. (6) When the brazing alloy in the quartz tube melts to a yellowish-white color and the metal solution is in a state of constant fluctuation, turn on the spray switch and use the air pressure difference to spray the molten metal onto the surface of the high-speed rotating cooling copper roller; when no liquid is observed to flow out of the quartz tube, turn off the spray switch, heating switch and copper roller rotation switch in sequence, open the furnace door and take out the brazing foil strip, i.e., the foil strip brazing alloy.

5. In the brazing process for connecting dissimilar materials such as cemented carbide and steel using low-silver foil with brazing filler metal as described in claim 1, the ultrasonic cleaning time in step 2 is 5 min, and the number of times is 2. The vacuum degree of the vacuum drying oven is -0.085 MPa.

6. In the brazing process for connecting dissimilar materials such as cemented carbide and steel using low-silver foil with solder according to claim 1, the flux used in step 3 is FB102.

7. The application of a brazing process for joining dissimilar materials, namely cemented carbide and steel, using low-silver foil with brazing filler metal according to any one of claims 1 to 6, in tunnel boring machine cutters.

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