Aging-induced formation of the nano-sized clustered carbides in the weld metal of Co-based alloy/AISI 410 stainless steel dissimilar welded joint

The microstructure evolution in Co-based alloy/AISI 410 stainless steel dissimilar welded joints by aging at 566 degrees C for 200, 400, 600, and 800 h was systematically investigated. In particular, the specimen aging treated for 800 h was emphasized in the present study for its nano-sized clustered characteristic microstructure. The results showed that the microstructure of the weld metal (WM) was mainly gamma-Co matrix with dendritic morphology. Before aging treatment, the elements Cr and W segregated slightly in the interdendritic regions. Nevertheless, a large amount of nano-sized clustered carbides rich in elements Cr and W precipitated along grain boundaries after aging treatment. The element segregation during solidification and element diffusion under high-temperature condition could trigger the carbide formation. Though the precipitated carbides revealed a negligible influence on the microhardness of weld (similar to 275 HV), yet a stable performance under high-temperature condition was anticipated for this weldment considering the grain boundary strengthening effect of the nano-sized carbides.