Vacuum Brazing Process of Cemented Carbide

【Summary Description】 Vacuum Brazing Process of Cemented Carbide 1. Selection of Cemented Carbide Solder Cemented carbide and steel brazing filler metal according to the melting point and brazing temperature is divided into high temperature brazing filler metal, normal temperature brazing filler metal and low temperature brazing filler metal three categories. Brazing temperature above 1000 ℃ solder is called high temperature solder, such as copper and 106 solder, etc. The brazing temperature of medium temperature solder is between 850 and 1000 ℃, such as H62, H68 brass solder, etc. Low temperature solder refers to the brazing temperature between 650 and 850 ℃, such as B- Ag-1 and L-Ag-49 and other silver-containing solder. The main requirements for hard alloy brazing filler metals are as follows: 1) The brazing filler metal should have good wetting ability to brazed carbide and steel substrate to ensure that the brazing filler metal has good fluidity and permeability. 2) One of the characteristics of cemented carbide is that it has high red hardness, so it is necessary to ensure that the brazing weld has sufficient strength at room temperature and high temperature. 3) The melting point of the brazing filler metal should be as low as possible to reduce the brazing stress and prevent cracks, but the melting point of the brazing filler metal should be higher than the working temperature of the weld by 300 ℃ to ensure that the tool can work normally during high-speed cutting. 4) The solder should not contain elements with low evaporation point, so as not to affect the quality of the joint or harm to human health due to the evaporation of the elements in the solder during brazing heating. Cemented carbide brazing commonly used brazing material grades and uses a brief description of the following: 1) The brazing temperature of the copper solder is high and the weld strength is low, and it is mostly used for vacuum brazing. Pure copper brazing filler metal is a single-phase organization, relatively easy to control the brazing temperature, all kinds of cemented carbide has good wetting ability, good plasticity, the price is the cheapest. The shear stress of copper brazing weld is about 150MPa, which can be used below 400 ℃. 2) The brazing temperature of H68 brass is much lower than that of copper, but it is not used frequently because of the low weld strength. 3) The melting point and brazing temperature of H62 brass are relatively low, and the weld has a certain room temperature strength, which is a more commonly used cemented carbide brazing filler metal. It is generally used for brazing carbide tools used under medium and small load conditions. 4) the need for high temperature strength of the weld or welding surface is small, should use 105 brazing filler metal. 5)L-Ag-49 low temperature silver solder is widely used in foreign countries, because of its low melting point (690~710 ℃), good wettability to cemented carbide, convenient brazing and low stress. When necessary, copper sheets can be used as compensation gaskets, which can almost completely eliminate brazing stress and avoid brazing cracks. It can be used to braze some cracked carbide or some carbide tools with large brazing surfaces. As the workpiece brazed with L-Ag-49 silver solder with the use of temperature increases, the weld strength decreases rapidly, so the workpiece with L-Ag-49 solder working temperature should be limited to 200 ℃ or less. The flux used in conjunction with L-Ag-49 silver solder contains more fluoride and chloride, which requires higher cleaning work after welding, otherwise it will cause corrosion on the surface of the workpiece due to unclean cleaning. 6)B-Ag-1 brazing filler metal is a kind of ultra-low temperature silver brazing filler metal, the melting point is about 600~610 ℃, which can further reduce the residual stress of hard alloy joint, and can also be used as compensation gasket to braze some easily cracked workpieces. Due to the ultra-low melting point of B- Ag-1 silver solder and good wettability to tungsten carbide, it is also suitable for brazing some diamond tools such as diamond saw blades. However, B- Ag-1 silver solder has high price and low high temperature strength, it is only suitable for use at temperatures below 150°C. The cadmium content in the solder is 24%, and it is easy to evaporate when the brazing temperature is high, which is harmful to human health. In addition to the brazing temperature must be controlled during brazing, an exhaust device should be installed at the brazing operation. After brazing, the workpiece should also be cleaned to avoid corrosion of the workpiece.

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