Effect of rare earth oxides on the morphology of carbides in hardfacing metal of high chromium cast iron

The flux cored wires with different amounts of rare earth (RE) oxides additions for hardfacing (harden-face-welding) the workpieces of high chromium cast iron were studied in this work. The morphology of carbides in hardfacing metal was observed, and the type of the carbides was determined by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). Based on the data of effect of RE on carbides morphology, the refined reason for carbide by RE oxide was discussed with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of martensite, residual austenite and M7C3 carbides. With the increasing amount of RE oxide additions, the volume fraction and roundness of the carbides were increased, however, the area and perimeter of carbides were decreased. It indicated that carbides in hardfacing metal could be refined and spheroidized by adding RE oxides in flux cored wires.