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Selection of welding materials for high temperature brazing furnace
The vacuum brazing furnace is to apply flux to the welding part of the cleaning and deconditioning workpiece and put flux (powder, granulated, flake) on the other part to be welded (the welding surface is also coated with flux). After positioning and fixing the two parts, the welding is completed by heating them up to the melting temperature of the solder. It is the use of furnace temperature to lift the temperature of the workpiece, the melting temperature is lower than the workpiece solder melting, so that the workpiece welding.
High temperature brazing furnace
Among them, the choice of solder is very important, then, how to choose the welding material of vacuum brazing? In fact, as long as you carefully understand the properties of brazing solder you will know how to choose:
Brazing tool steels and cemented carbide are usually made of pure copper, copper, zinc and silver.
Pure copper has good wettability to all kinds of hard alloys, but it needs to be brazed in the reducing atmosphere of hydrogen to get the best effect. At the same time, due to the high brazing temperature, the stress in the joint is great, which leads to the increase of crack tendency. The joint brazed with pure copper has a shear strength of about 150MPa and a high plasticity, but it is not suitable for high-temperature work.
Copper and zinc solder is the most commonly used solder for brazing tool steel and cemented carbide. In order to improve the wettability and strength of the solder, Mn, Ni, Fe and other alloy elements are often added in the solder. For example, W (Mn)4% is added to B-CU58zNMn, which makes the shear strength of carbide brazing joint reach 300 ~ 320MPa at room temperature. It can maintain 220 ~ 240MPa at 320℃. By adding a small amount of Co on the basis of B-CU58zNMn, the shear strength of brazing joint can reach 350MPa, and it has high impact toughness and fatigue strength, which significantly improves the service life of cutting tools and rock drilling tools.
The low melting point of silver brazing alloy and the low thermal stress of brazing joint are beneficial to reduce the cracking tendency of hard alloy brazing. In order to improve the wettability of the solder and increase the strength and working temperature of the joint, Mn, Ni and other alloy elements are often added to the solder. For example, B-AG50CUzNCDNI brazing alloy has excellent wettability and brazing joint has good comprehensive performance.
In addition to the above three types of solder, Mn base and Ni base alloy, such as B-MN50NICucrCO and B-NI75Crsib, can be used for the hard alloy working above 500℃ and the joint strength requirement is high. For the brazing of high-speed steel, the brazing temperature and quenching temperature should be matched by a special filler metal. This filler metal is divided into two types, one is ferro manganese, which is mainly composed of ferro manganese and borax. The brazing joint’s shear strength is generally around 100MPa, but the joint is prone to crack. Another type of special copper alloy containing Ni, Fe, Mn and Si, with which the brazed joint is not easy to crack, and its shear strength can be increased to 300MPa.