Study On Brazing Process And Mechanism Of Cemented Carbide Cutting Tools In Ultra - Fine Pulverizer

The ultrafine mill can achieve the effect of crushing material through complex effects between materials and blades, gear, materials and materials. The hard alloy cutter of the ultrafine mill consists of a steel blade and hard alloy head. The ultrafine mill can not be used because of the failure of the hard alloy when the head crush materials unusable, this is often due to the low bonding strength between the head and the blade which will seriously affect the production efficiency and economic benefit of the enterprise The failure of the the hard alloy cutter of the ultrafine mill of a company was analyzed in the dissertation, the results indicated that the main reason of the the hard alloy cutter was caused by the problem of the unreasonable flame brazing process. The better process of vacuum brazing was used for the connection between hard alloy and steel aiming at the existing problems of the flame brazing. The effects of temperature, joint clearance and thickness of buffer layer Cu on properties of brazing joint was studied, and ansys software was applied to study the residual stress of brazing joint. The main research work and results were obtained in this paper were as follows:1. The hard alloy cutter of the ultrafine mill was analyzed in details by the actual working condition. The reasons for failure of the hard alloy cutter were analyzed by metallographic analysis, SEM, EDS analysis, and X-ray diffraction analysis. The main reasons for causing the hard alloy cutter failure were the defects which were produced in flame brazing joint such as lack of penetration, discontinuities. These defects changged chemical and phase change of jont which affected the wear resistance and impact toughness of ultrafine millcutter head, which led to premature failure of the hard alloy cutter.2. In this paper, the vacuum brazing of steel45and YG8was studied. Through shear strength test, SEM, EDS and so on, the effects of different temperature, joint clearance and thickness of Cu buffer layer on microstructure and properties of joint were studied respectively, research showed that:(1) The brazing joint was made of the middle area, steel side reaction area and hard alloy side reaction area. The Fe-Co-Ni based solid solution which were generated in two reaction areas could strengthen the metallurgical bonding of joint. In the middle area of the joint was the Cu-Mn based solid solution which had good plastic. (2) The brazing temperature was one of the most important process parameters in the vacuum brazing process. If the temperature was so low, the diffusion ability of the Fe and Co element was so weal and the brazing joint couldn’t form enough Fe-Co-Ni based solid solution, so the interface metallurgy combined of joint was poor. If the temperature was so high, too much of Fe-Co-Ni based solid solution were generated in two reaction areas, and increased the residual stress of joint which led to poor properties of the joint. The brazing temperature was1000℃, the shear strength was best which reached to289MPa.(3) The brazing clearance had great influence on the properties of joint. If the brazing clearance was so small, the brazing joint couldn’t release the residual stress, the brazing joint cracked near the hard alloy, the joint’s strength was generally low; If the brazing clearance was so big, the long-range diffusion of elements such as Fe、Co and Ni were difficult to cross the joint clearance to form enough Fe-Co-Ni based solid solution and the metallurgical bonding was so weak. When the brazing temperature was1000℃, the best joint clearance was0.18mm.(4) Cu buffer layer had good plasticity which was beneficial to alleviate the residual stress of the joint, but the Cu buffer layer hindered the diffusion of the Fe、Co and Ni elements, the reaction product of two areas was less, so the metallurgical bonding of the joint was weal. So adding Cu buffer layer to improve the strength of the joint was not obvious.3. The residual stress distribution of joint at the two different conditions was studied by ANSYS the finite element analysis software. The results showed that a large stress gradient existed in the joint at room temperature, and there was a maximum residual stress in the hard alloy near near the weld. This area was a dangerous area, the fracture would start from here under the action of external force. The heat treatment processes of reading arm were optimized by the failure analysis and ANSYS simulation. The normalizing process was adopted, the quenching medium and time The stress of joint had the same variation under the two different conditions. Residual stress gradually became with increasing brazing clearance and thickness of Cu buffer layer, and the residual stress was greatly reduced in the joint after adding Cu buffer layer. The simulation results proved that adding Cu buffer layer into joint could reduce residual stress successfully.