The Study Of Process And Properties Of YG8/42CrMo Joint Produced By Vacuum Composite Welding

The characteristics and major welding problems such as low joint strength, large residualstress, low anti-abrasive corrosion ability and short service life in industrial applications ofhardalloy were summarized in this paper. Some welding methods that may be used onhardalloy, including flame brazing, laser brazing, induction brazing, vacuum brazing,microwave brazing, electron beam brazing, diffusion welding and so on were reviewed, andthe forwarding problems were also pointed out.A new type of composite welding for YG8/42CrMo was developed by combining theadvantages that lower welding temperature, higher joint strength of diffusion and lowerresidual stress, and perfect chemical and metallurgical bond of vacuum brazing using avacuum furnace. The effect of welding processing parameters such as coating thickness,brazing and diffusion parameters on microstructure and mechanical properties such as theshare strength and the minimum microhardness of the joint area were studied in this paper.And the cross-section morphology, fracture characteristic, microstructure, chemicalcomponents, elements diffusion, microhardness, share strength, wettability and coatingbinding ability were studied by metalloscope, X-ray diffraction (XRD), scanning electronmicroscope (SEM) with energy dispersive spectrometer (EDS), microhardness tester and theuniversal mechanical testing machine, grid-based method and so on. The defects both inmacro and micro formed in the joint were also studied.The study shows that, the best joint was obtained when the thickness of pure Ni layer is60μm, the brazing temperature maintain at1045℃for15min, the diffusion temperaturemaintain at750℃for40min under the pressure of8MPa. The obtained joint is smooth andgood, without obvious deformation and defects such gas holes, inclusions and cracks. Theshear strength is364MPa, the minimum microhardness of the joint is HV187. The shearing fracture of the joints usually occurs within the hardalloy, which shows thatthe Ni layer cannot eliminate the joint stress exhaustively. And the fracture mechanism isductile and brittle type judged by fracture morphology. The composite welding method willimprove the joint properties of boring or cutting tools greatly.