A manual high-precision flame brazing method for cemented carbide and stainless steel

Abstract

The present invention relates to a metal brazing technology, specifically to a method for ensuring high-precision manual flame brazing of cemented carbide and stainless steel. In the present invention, a hard metal sheet and stainless steel are welded into one by manual flame brazing. Among them, before pre-hanging solder on the surfaces to be welded of the cemented carbide and the lever, the cemented carbide sheet is subjected to vacuum high-temperature activation treatment with a vacuum degree of 1.33 Pa to 13.3 Pa, and the high-temperature treatment range is between the melting temperature of the solder and the phase transformation temperature of the base material. Then, pre-hang solder on the surfaces to be welded of the cemented carbide and stainless steel respectively, and apply a soldering flux on the welding surface of the stainless steel. Adjust and control the flame to be a neutral flame or a slightly outer flame as a reducing flame for manual welding, with a welding temperature of 800°C - 900°C, and stop heating the part when the cemented carbide sheet is dark red, complete the welding, and then carry out heat preservation and cooling out of the furnace. The method of the present invention can effectively ensure high-precision manual flame brazing of cemented carbide and stainless steel, reduce welding defects, and ensure welding quality through strict process control.

Description

Technical Field

[0001] The present invention relates to a metal brazing technology, specifically to a method for ensuring high-precision manual flame brazing of cemented carbide and stainless steel. Background Art

[0002] In the fuel regulating system of an aeroengine, the lever assembly is used for mechanical transmission, and a friction pair is formed between the lever transmission surface and the transmission part. Therefore, the form of welding cemented carbide and stainless steel body is adopted to realize the complementary advantages of materials and ensure its durability. During vacuum brazing, oxides on the surface of cemented carbide and elements prone to generating gas inside will volatilize to generate gas, resulting in the inability to meet the use requirements of parts after welding. Therefore, high-precision welding of the two materials cannot be achieved through equipment welding. The theoretical ideal state of welding is that there is no virtual welding or pores in the welded part. However, in the actual manual brazing process, welding defects are extremely difficult to avoid. Therefore, on the premise of meeting the use requirements of parts, it is necessary to ensure that the virtual welding (pores) of the welded joint surface is small enough.

[0003] The linear expansion coefficient of cemented carbide is 1 / 2 - 1 / 3 of that of steel, and there are certain differences in hardness and expansion coefficient between cemented carbide and stainless steel. The welding difficulty is great. When the filler metal is not selected reasonably or the pre-welding treatment is not good, it is easy to cause defects such as internal virtual welding, pores and cracks on the surface of cemented carbide, and the ideal state of brazing cannot be achieved. Summary of the Invention

[0004] The purpose of the present invention is to provide a brazing method that can effectively ensure high-precision manual flame brazing of cemented carbide and stainless steel, reduce welding defects, and ensure welding quality.

[0005] The technical solution of the present invention: A method for high-precision manual flame brazing of cemented carbide and stainless steel, which welds a hard metal sheet and stainless steel into one by manual flame brazing. Among them, before pre-hanging the filler metal on the surfaces to be welded of the cemented carbide and the lever, the cemented carbide sheet is subjected to vacuum high-temperature activation treatment, the vacuum degree is 1.33 Pa - 13.3 Pa, and the high-temperature treatment range is between the melting temperature of the filler metal and the phase transformation temperature of the base metal. Then, pre-hang the filler metal on the surfaces to be welded of the cemented carbide and the stainless steel respectively, and apply a flux on the welding surface of the stainless steel. Adjust and control the flame to a neutral flame or a reducing flame with a slightly outer flame for manual welding, the welding temperature is 800°C - 900°C, and stop heating the part when the cemented carbide sheet is dark red, complete the welding, and cool it out of the furnace after heat preservation.

[0006] The cemented carbide is YG6X, and the stainless steel material is 1Cr17Ni3.

[0007] The stainless steel is in a lever-shaped structure, and the thickness dimension consistency of the cemented carbide sheet is not greater than 0.02 mm.

[0008] The temperature range of the vacuum activation treatment is 950°C ± 10°C.

[0009] The solder is Bag50CdZnCu, and its thickness is not greater than 0.1 mm.

[0010] The soldering flux is Castolin 1802PF silver brazing flux (main components: potassium difluoride, potassium pentaborate tetrahydrate, potassium tetraborate, etc.). Compared with other ordinary soldering fluxes, this soldering flux can better remove the oxides on the surface of the base metal and the filler metal, ensure sufficient wetting ability at the brazing temperature, and thus guarantee the welding quality between the cemented carbide and the stainless steel.

[0011] The welding gas is composed of oxygen and acetylene gas in a theoretical proportion of (4.5 - 5):2. At this time, the flame is a neutral flame or a slightly excessive acetylene flame, which can effectively prevent excessive oxidation of the base metal and the filler metal, avoid problems such as non-sticking of the filler metal, false soldering, and porosity, which affect the welding quality, so that the brazing between the cemented carbide and the stainless steel can reach an ideal state.

[0012] The manual high-precision flame brazing method for the cemented carbide and the stainless steel is as follows:

[0013] Step 1: Before welding, check the pre-welding thickness dimensions of the cemented carbide sheet and the stainless steel respectively to ensure that the thickness dimension consistency of the parts to be welded is not greater than 0.02 mm;

[0014] Step 2: Grind the surface to be welded of the cemented carbide sheet to ensure a roughness Ra of 1.6, and ensure the spreading effect of the filler metal on the surface of the cemented carbide;

[0015] Step 3: Clean the surfaces of the cemented carbide sheet and the stainless steel to remove stains;

[0016] Step 4: Wet blast the surface of the cemented carbide sheet to remove the surface oxide film;

[0017] Step 5: Clean the cemented carbide sheet 1 and place it in a vacuum environment for vacuum high-temperature activation treatment. The vacuum degree of the vacuum furnace is 1.33 Pa - 13.3 Pa, heat it up to 950°C ± 10°C, and the holding time is at least 4 hours;

[0018] Step 6: Grind and clean the surface of the lever to be welded;

[0019] Step 7: Pre-hang the filler metal on the surfaces to be welded of the cemented carbide and the lever respectively. First, heat the cemented carbide sheet, observe the color of the cemented carbide sheet, add the soldering flux when it is preheated to a slightly dark red color, and at the same time fill the filler metal. Note that when filling the filler metal, it should be ensured that there is soldering flux on the surface of the cemented carbide sheet;

[0020] Step 8: Grind the surfaces with the filler metal hung respectively to ensure that the thickness of the filler metal is not greater than 0.1 mm;

[0021] Step 9: Apply Castolin 1802PF silver brazing flux (paste) on the surface of the lever to be welded. Control the amount of flux applied by the pressure of the tooling weight (about 80 g) and the height limit of the auxiliary support. Align the two welded parts; among them, the tooling is a transfer pointed pressing nail under the left end of the pressing block, with an auxiliary support at the right end. Ensure an appropriate solder thickness of about 0.2 - 0.5 mm by adjusting the height and generating a pressing force at the pressing nail. Controlling this thickness can ensure the degree of bubble removal, reduce welding defects, and ensure welding quality.

[0022] Step 10: Heat with a blowtorch to remove the moisture in the flux and ensure that the two parts do not slide relative to each other or fall off.

[0023] Step 11: Adjust the gas volume ratio of oxygen and acetylene according to the ratio (4.5 - 5):2. Control and observe the flame color to be light blue. When there is no obvious distinction between the inner and outer flames (at this time, it is a neutral flame or a slightly excessive acetylene flame), perform welding. The brazing temperature is 800℃ - 900℃. Press the two parts tightly with the tooling during welding and stop heating the parts when the cemented carbide sheet turns dark red to complete the welding. By controlling the above flame color, inner and outer flames, and temperature, the bubble removal efficiency can be effectively improved and the welding quality can be guaranteed.

[0024] Step 12: Keep the parts after welding warm. The furnace temperature is 200 ± 10℃ for 2 hours, and then cool them in the furnace.

[0025] After welding, it also includes the processes of wet sandblasting to remove the residual flux on the surface and removing the excess solder on the part surface.

[0026] Advantages of the present invention: The present invention relates to a process method for ensuring high-precision flame brazing of YG6X and 1Cr17Ni3, ensuring that the internal brazed joint allows for no more than 0.5 mm of lack of fusion or pores, and the sum of the lengths of lack of fusion or pores less than 0.5 mm does not exceed 1 / 5 of the perimeter of the brazed part, meeting the ultrasonic inspection requirements. Compared with the prior art, it has significant technological progress, specifically as follows:

[0027] 1. Using a silver-based filler metal, the thermal stress generated at the brazed joint is relatively small, and the cemented carbide sheet is not easily cracked. Moreover, this silver-based filler metal does not contain volatile elements, which can effectively avoid welding pores or lack of fusion caused by brazing volatilization.

[0028] 2. Perform vacuum activation treatment on the cemented carbide sheet to avoid the generation of gas in the cemented carbide sheet during welding and reduce the generation of lack of fusion and pores at the same time.

[0029] 3. Pre-hang solder on the surface to be welded in advance and use a method of grinding to control the solder thickness and remove bubbles in the solder, which can reduce the generation of welding pores and lack of fusion and avoid the risk of part repair and scrapping.

[0030] 4. Heating the soldering flux with a blowtorch after applying it can remove the excess moisture in the soldering flux and avoid the occurrence of false soldering and porosity caused by the evaporation of water vapor during welding heating.

[0031] 5. Determine the welding situation by the flame color and the color of the cemented carbide sheet to avoid excessive welding time and affecting the welding quality.

[0032] 6. Keep the workpiece warm after welding to avoid cracking of the cemented carbide sheet caused by the large difference in linear expansion coefficients between the two materials and too rapid cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the lever assembly structure;

[0034] Figure 2 Schematic diagram of hanging solder on the cemented carbide sheet;

[0035] Figure 3 Schematic diagram of hanging solder on the lever;

[0036] Figure 4 Schematic diagram of the tooling pressing during the welding of the lever assembly;

[0037] Figure 5 Yes Figure 4 Partial enlarged view,

[0038] In the figure, the serial number 1 is the cemented carbide sheet, 2 is the lever, 3 is the solder, 4 is the tooling, and 5 is the soldering flux. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] Embodiment 1

[0041] As Figures 1 to 5 shown, in this embodiment, the cemented carbide sheet is 1 and the stainless steel is the lever 2. When the manual high-precision flame brazing method of the cemented carbide and stainless steel of the present invention is specifically implemented, the process is as follows:

[0042] Step 1: Before welding, respectively inspect the pre-welding thickness dimensions of the cemented carbide sheet 1 and the lever 2 to ensure that the thickness dimension consistency of the parts to be welded is not greater than 0.02 mm, and record the actual dimension range to prepare for the subsequent solder allowance.

[0043] Step 2: Grind the surface to be welded of the cemented carbide sheet to ensure a roughness Ra of 1.6 to ensure the spreading effect of the filler metal on the surface of the cemented carbide.

[0044] Step 3: Clean the surfaces of the cemented carbide sheet 1 and the lever 2 with absolute alcohol to remove surface oil stains and dirt.

[0045] Step 4: Perform wet sandblasting on the surface of the cemented carbide sheet to remove the surface oxide film and ensure good wetting effect during solder hanging.

[0046] Step 5: Conduct vacuum activation treatment on the cemented carbide sheet. Clean the cemented carbide sheet 1 and place it in a vacuum environment. Keep it for a certain period of time at a temperature higher than the melting temperature of the filler metal and lower than the phase transformation temperature of the base material, forcing the volatile residual elements and surface oxides in the cemented carbide sheet 1 that are prone to generating gas to be released in advance. During brazing, the brazing temperature is lower than the activation temperature, and no more gas will be generated by the volatile elements, thus avoiding porosity defects. Considering the sintering temperature of YG6X material is 1540°C, the melting temperature of the filler metal (Bag50CdZnCu) is 630 - 800°C, the effective decomposition temperature of the brazing flux Castolin 1802PF silver brazing flux is 600 - 900°C, and the volatilization temperature of the main oxide WO2 is 800°C, set the activation treatment process parameters for the cemented carbide sheet 1: the vacuum degree of the vacuum furnace is 1.33 Pa - 13.3 Pa, heat up to 950°C ± 10°C, keep the temperature for 4 hours, and cool in the furnace. The control of the above specific vacuum degree and temperature range directly affects the activation treatment effect, thereby affecting the welding quality, which can effectively guarantee the welding quality between the cemented carbide and stainless steel, avoid defects, and reach an ideal state.

[0047] Step 6: Polish the surface of the lever to be welded with 800 - mesh sandpaper and clean it with absolute alcohol.

[0048] Step 7: Pre - hang the filler metal (Bag50CdZnCu) on the surfaces to be welded of the cemented carbide and the lever respectively. Pay attention to observing the color of the cemented carbide sheet. When it is pre - heated to a slightly dark red color, the filler metal should be filled, and it is necessary to ensure that there is brazing flux on the surface of the cemented carbide sheet at this time to ensure the effect of hanging the filler metal.

[0049] Step 8: Grind the surfaces with the filler metal hung respectively to ensure that the thickness of the filler metal is not greater than 0.1 mm, so as to better show the bubbles in the filler metal. At the same time, observe that there are no bubbles in the filler metal layer. If there are always bubbles, the filler metal needs to be re - hung.

[0050] Step 9: Apply Castolin 1802PF silver brazing flux on the surface of the lever to be welded. Pay attention to controlling the amount of brazing flux applied through the tooling pressure, and align the two welded parts.

[0051] Step 10: Heat with a blowtorch for 30 minutes to remove the moisture in the brazing flux and ensure that the two parts do not have relative sliding or falling off.

[0052] Step 11: Adjust the gas volume ratio of oxygen and acetylene so that the flame color is light blue. Use a neutral flame or a slightly reducing flame (outer flame) for welding. During welding, press the two parts tightly with a tooling, and stop heating the parts when the cemented carbide sheet turns dark red. After welding, through experiments, it is determined that heating the cemented carbide sheet 1 to dark red is the most suitable temperature (800°C - 900°C) for manual flame brazing of this part, which can significantly improve the welding qualification rate.

[0053] Step 12: Keep the welded parts warm. The furnace temperature is 200 ± 10°C and the time is 2 hours, then cool them in the furnace.

[0054] Step 13: Wet sandblast to remove the residual brazing flux on the surface.

[0055] Step 14: Remove the excess solder on the surface of the parts.

[0056] In addition, in addition to the above embodiments, the present invention can also be applied to manual flame brazing parts of cemented carbide and stainless steel such as bellows bushing assemblies, follower assemblies, and rod assemblies.

[0057] The above is only a specific embodiment of the present invention, which is described in detail. The parts not elaborated are conventional techniques. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A manual high-precision flame brazing method for cemented carbide and stainless steel, characterized in that The hard metal sheet and stainless steel are welded into one by manual flame brazing. Before pre-hanging the solder on the surfaces to be welded of the cemented carbide and the lever, the cemented carbide sheet is subjected to vacuum high-temperature activation treatment. The vacuum degree is 1.33 Pa to 13.3 Pa, and the high-temperature treatment range is between the melting temperature of the solder and the phase transformation temperature of the base material. Then, pre-hang the solder on the surfaces to be welded of the cemented carbide and stainless steel respectively, and apply a soldering flux on the stainless steel welding surface. Adjust and control the flame to be a neutral flame or a slightly reducing flame with a little outer flame for manual welding. The welding temperature is 800 °C - 900 °C, and when the cemented carbide sheet turns dark red, stop heating the parts, complete the welding, and then cool the furnace after heat preservation; The process is as follows: Step 1: Before welding, inspect the thickness dimensions of the cemented carbide sheet and stainless steel before welding respectively to ensure that the thickness dimension consistency of the parts to be welded is not greater than 0.02 mm; Step 2: Grind the surface to be welded of the cemented carbide sheet to ensure the roughness Ra1.6 to ensure the spreading effect of the solder on the surface of the cemented carbide; Step 3: Clean the surfaces of the cemented carbide sheet and stainless steel to remove stains; Step 4: Wet blast the surface of the cemented carbide sheet to remove the surface oxide film; Step 5: Clean the cemented carbide sheet and place it in a vacuum environment for vacuum high-temperature activation treatment. The vacuum degree of the vacuum furnace is 1.33 Pa to 13.3 Pa, heat up to 950 °C ± 10 °C, and the heat preservation time is at least 4 hours; Step 6: Grind and clean the surface of the lever part to be welded; Step 7: Pre-hang the solder on the surfaces to be welded of the cemented carbide and the lever respectively. First, heat the cemented carbide sheet, observe the color of the cemented carbide sheet, add the soldering flux when it is preheated to slightly dark red, and at the same time, fill the solder. Note that when filling the solder, ensure that there is soldering flux on the surface of the cemented carbide sheet; Step 8: Grind the surfaces with the pre-hung solder respectively to ensure that the solder thickness is not greater than 0.1 mm; Step 9: Apply the soldering flux on the surface to be welded of the lever, control the amount of soldering flux applied by the tooling pressure, and align the two welded parts; Step 10: Heat with a blowtorch to remove the moisture in the soldering flux so that the two parts do not slide or fall off relative to each other; Step 11: Adjust the gas volume ratio of oxygen and acetylene, the flame color is light blue, use a neutral flame or a slightly reducing flame for welding. The brazing temperature is 800 °C - 900 °C. When welding, press the two parts tightly with the tooling, and stop heating the parts when observing that the cemented carbide sheet turns dark red to complete the welding; Step 12: Keep the welded parts warm. The furnace temperature is 200 ± 10 °C for 2 hours, and cool with the furnace.

2. The manual high-precision flame brazing method for cemented carbide and stainless steel according to claim 1, characterized in that, The cemented carbide is YG6X, and the stainless steel is 1Cr17Ni3.

3. The manual high-precision flame brazing method for cemented carbide and stainless steel according to claim 1, characterized in that, The stainless steel is in a lever-like structure, and the thickness dimension consistency of the cemented carbide sheet is not greater than 0.02 mm.

4. The manual high-precision flame brazing method for cemented carbide and stainless steel according to claim 1, characterized in that, The temperature range of the vacuum high-temperature activation treatment is 950 °C ± 10 °C.

5. The method for manual high-precision flame brazing of cemented carbide and stainless steel according to claim 1, characterized in that, The solder is Bag50CdZnCu, and its thickness is not greater than 0.1 mm.

6. The method for manual high-precision flame brazing of cemented carbide and stainless steel according to claim 1, characterized in that, The soldering flux is Castolin 1802PF silver soldering flux.

7. The manual high-precision flame brazing method for cemented carbide and stainless steel according to claim 1, characterized in that, The welding gas is composed of oxygen and acetylene gas in a proportional ratio of (4.5 - 5):

2.

8. The method for manual high-precision flame brazing of cemented carbide and stainless steel according to claim 1, wherein After welding, it also includes the processes of wet sandblasting to remove the residual flux on the surface and removing the excess solder on the surface of the parts.

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