Carbide and Steel Vacuum Brazing

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SIMUWU high temperature vacuum brazing furnace application: mainly used for vacuum brazing process of stainless steel, titanium alloy, cemented carbide, non-ferrous metal and other materials, also suitable for gas quenching, annealing and vacuum sintering of tool steel, die steel and other metal materials heat treatment process.

Main features of the equipment: The heating adopts multi-stage temperature control method, which can ensure good temperature uniformity in the temperature zone. Heating in a vacuum state can remove grease and oxide film on the surface of the workpiece, so the surface brightness of the part is high. No flux required, no post-solder cleaning required.

Optimal temperature control for brazing cemented carbide to steel is in direct conflict with the recommended procedures for quenching and tempering transformation hardening tool steels. A controlled low cooling rate is essential to adequately reduce the already high thermally induced residual stress. By slowly cooling from brazing temperature to room temperature, stress fillets that absorb and relieve thermally-induced relative motion of the joining partners through plastic deformation can relax. However, a sufficiently high cooling rate is essential to increase hardness, strength and stiffness and to avoid undesired mesophase mixtures in the steel, such as pearlite or bainite. In general, brazing carbide/transformation hardening tool steel joints are either free-cooled, cooled in a controlled manner, at a cooling rate between 3 and 15 °C/min, or the authors did not address the temperature-time curve for the cooling phase . The emphasis is generally on the properties of brazed joints, and the lack of consideration for ideal steel heat treatment and properties leaves room for further development in the manufacture of durable, wear-resistant carbide steel tools with balanced joint strength and sufficient mechanical steel properties.

1.Surface treatment before brazing

Before brazing, oxides, grease, dirt and paint on the surface of the workpiece must be carefully removed, because the molten solder cannot wet the surface of the uncleaned parts, nor can it fill the joint gap. Sometimes, in order to improve the brazability of the base metal and the corrosion resistance of the brazed joint, the parts must be pre-plated with a certain metal layer before brazing.

(1) To remove oil stains, oil stains can be removed with organic solvents

Commonly used organic solvents are alcohol, carbon tetrachloride, gasoline, trichloride, dichloroethane and trichloroethane. In small batch production, it can be immersed in organic solvent for cleaning. The most widely used in mass production is degreasing in the steam of organic solvents. In addition, cleaning in a hot alkaline solution can also give satisfactory results. For example, steel parts can be immersed in a 10% caustic soda solution at 70-80°C for degreasing, and copper and copper alloy parts can be cleaned in a solution of 50g trisodium phosphate, 50g sodium bicarbonate and 1L water, and the solution temperature is 60～80° C. Parts can also be degreased in detergent and then carefully washed with water. When the surface of the part can be completely wetted by water, it indicates that the surface grease has been removed. For small parts with complex shapes and a large number, ultrasonic cleaning can also be used in a special tank. Ultrasonic oil removal has high efficiency.

(2) Removal of oxides

Before brazing, the oxides on the surface of the parts can be carried out by mechanical methods, chemical etching methods and electrochemical etching methods. When cleaning mechanically, files, metal brushes, sandpaper, grinding wheels, sandblasting, etc. can be used to remove the oxide film on the surface. Among them, the file and sandpaper cleaning are used for single-piece production, and the grooves formed during cleaning are also conducive to the wetting and spreading of the solder. Grinding wheels, metal brushes, sandblasting and other methods are used in mass production. The surface of aluminum, aluminum alloy and titanium alloy should not be cleaned by mechanical method.

(3) Metal plating on the surface of the base metal

The main purpose of plating metal on the surface of the base metal is to improve the brazing properties of some materials, increase the wetting ability of the brazing filler metal to the base metal, and prevent the interaction between the base metal and the brazing filler metal from adversely affecting the quality of the joint, such as preventing the occurrence of Cracks, reducing the generation of brittle intermetallic compounds at the interface; as a brazing filler metal layer to simplify the assembly process and improve productivity.

2.Brazing case

Vacuum brazing of YT05 cemented carbide and 40 steel is often used in cutting tool welding. For example, carbide hobbing cutter is a kind of gear hobbing cutter that is widely used in gear production. It can not only process various gears, but also use scraping processing instead of grinding when processing hard-toothed gears. This gear hobbing cutter is welded by YT05 cemented carbide and 40Cr medium carbon quenched and tempered steel by vacuum brazing process.

(1)Gear hobbing cutter material

The material of the cutter body is 40Cr steel, and the material of the blade is YT05 carbide.

(2)Filling material

①The brazing material is made of pure copper BCu (Cu99.95%) with a thickness of 0.2mm, the melting temperature is 1083℃, and the brazing temperature is 1100~1150℃.

②The flux, the grade of flux is Y11, the main component is borax, and the melting temperature is 800~1150℃. Brazing flux QJ201 can also be used, the chemical composition is: boric acid 80%, borax 14.5%, calcium fluoride 5.5%; brazing temperature is about 850 ~ 1150 ℃.

3.Main points of brazing operation

①Cut the needle material according to the tooth shape and place it between the cutter body and the blade. The blade is fixed on the cutter body with a fixture, and the contact part between the fixture and the weldment should be coated with injection, and then put into the vacuum furnace.

②In the cold state, vacuum the furnace to 5×10-2Pa, then heat the furnace to 1000℃ at a speed of 450℃/h, and fill the furnace with high-purity argon gas to ensure that the pressure in the furnace is 2~3Pa , Stable for 30~40min, so that the temperature inside and outside the knife is uniform.

③Heat the furnace temperature to 1120 °C at a rate of 250 °C/h, keep the temperature for 15 minutes, and then cool the furnace temperature to below 900 °C with the pressure in the furnace; fill the furnace with high-purity argon again to raise the furnace pressure to 4×10Pa

④When the furnace temperature is cooled to below 400℃, increase the filling amount of argon gas to make the pressure in the furnace rise to 8×10Pa, and then start the fan to stir the argon gas. When the furnace temperature is cooled to below 65℃, the workpiece is released from the furnace.

⑤ After the hobbing cutter (including the fixture) is released, it is strictly forbidden to collide, and it should be cooled naturally in the air. At this time, the ambient temperature of the workshop should not be lower than zero.

⑥ After the cutter body and the blade are completely cooled and shrunk, slowly remove the fixture so that the fixture and the hobbing cutter are not damaged, and then clean the fully brazed hobbing cutter to complete the welding.

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