Influence Of Cryogenic Treatment Process On Residual Stress And Impact Toughness Of Brazed Joint

The pick is the core component of the rock-breaking and coal-removing technology in the fully mechanized coal mining equipment.It is brazed with cemented carbide and alloy steel and installed on the roadheader and shearer as part of the tooth head.During the working process,the picks are in direct contact with the coal rock,and are subject to severe impact,pressure,and combination of bending and twisting.Therefore,the shedding and failure of the hard alloy become a common failure form of the pick,resulting in a low life.Therefore,improving the impact toughness at the joint and reducing its residual stress is an important way to improve the service life of the pick.This project mainly uses YG8 cemented carbide and 42 CrMo alloy steel as test objects to study the influence of cryogenic treatment process on the residual stress and impact toughness of the brazed joint.The specific research content is as follows:(1)The experimental design was conducted with the cryogenic temperature and the number of cryogenic times as variables,and the residual stress of the brazed joint was numerically simulated by ANSYS finite element analysis software to analyze the effect of cryogenic temperature and number of cryogenic cycles on joint stress;(2)Through experiments,the residual stress,impact toughness and hardness of joints under different processing conditions are analyzed to verify the results of numerical analysis;(3)The microstructure,elemental energy spectrum analysis and microscopic mechanism analysis of the phase were performed by scanning electron microscope(SEM),energy dispersive spectroscopy(EDS)and X-ray scanning phase analysis(XRD).And the mechanism of the cryogenic process was analyzed from the microscopic point of view.Studies have shown that,under the same cryogenic treatment time,-160°Cis better than-80°C to relieve the internal stress of the joint part,which is mainly reflected in the reduction of stress in the joint,and the partial compressive stress of the base metal 42CrMo;By comparing the impact test results of joints that have not been cryogenic treatment and joints that have been treated for 24 hours at-80°C,the impact toughness of the joints after cryogenic treatment is increased by 31.48%;In terms of the microscopic mechanism,after the cryogenic treatment,the loss of Co in the reaction zone of the cemented carbide decreases,the brittle phase of the joint decreases,the diffusion of Cu and Zn increases,and the degree of alloying of the base metal and the solder increases.