Research On Electron Beam Welding-brazing Of Wc-Co Cemented Carbide And Steel

In this paper, electron beam welding experiments of WC-Co cemented carbideand45steel with the thickness of30mm were carried out. The EBW weldability ofdissimilar material WC-Co/45steel was poor, results showed that cracking easilyoccurred in the WC-Co/45steel joints. Considering the analysis results of jointmicrostructure and joint stress field, filler metals were designed and prepared tocontrol the welding quality. Microstructures of the joints were examined by opticalmicroscopy (OM), scanning electron microscopy (SEM), energy spectrometer (EDS)and transmission electron microscopy (TEM). Combining with the numericalsimulation results, the joint forming mechanism, the cause of the joint crack and thecrack arrestment mechanism of the filler metal were studied. Moreover, themicrostructure transformation of the joints was also investigated.The forming process of WC-Co/45steel EBW joints and WC-Co/Ni-Fe/45steeljoints were basically similar. The welding pool, which was obtained through themelting of45steel or the filler metal and45steel, wetted and spreaded on thesurface of WC-Co and melting-brazing joints between WC-Co and45steel wereobtained. Moreover, a diffusion reaction layer or transitional zone formed at theWC-Co interface, and the effective bonding between the weld and WC-Co wasguaranteed.Macroscopic cracks easily occurred in electron beam welded WC-Co to45steel joints, and the two main influence factors were joint microstructure and jointresidual stress field. The joint microstructure analysis results showed that theWC-Co/45steel EBW joints were mainly composed of martensite, residual austeniteand herringbone carbides Fe3W3C, and brittle phase Fe3W3C formed around the WCparticle. As a result, the plastic deformation capacity of the joint was poor andbecomes the microstructure factors for joint cracking.Electron beam welding experiments of WC-Co and45steel with Ni-Fe fillermetal were then carried out. Results showed that macroscopic cracks would noteasily occur in WC-Co/Ni-Fe/45steel joints. And effective bonding without cracksbetween WC-Co and45steel could be obtained by optimizing the weldingparameters.Analysis of the microstructure and mechanical properties of WC-Co/Ni-Fe/45steel joint was carried out, and the crack arrestment mechanism of the filler metalwas analyzed. The joint was mainly composed of γ-Fe solid solution andherringbone carbides, and no brittle phase such as Fe3W3C formed around WC particles at the WC-Co interface. Thus, the plastic deformation capacity of the jointwas improved. Furthermore, stress field analysis results showed that the stress valueis small in the weld beam and at the WC-Co interface. According to the results ofjoint microstructure and stress distribution, the tendency of joint crack decreased.Average tensile strength of the WC-Co/Ni-Fe/45steels joint exceeded541.48MPa,and fracture occurred at the WC-Co interface. Average shear strength of the jointsexceeded432.64MPa, and fracture occurred at the45steel interface, andobservation of the fractures showed that all the fractures are brittle fracture.