Formation Mechanisms for (Cr,Co)7C3/(Cr,Co)23C6 Heterogeneous Precipitates and Stacking Faults Around Carbides in Surfacing Welding of Stellite Alloy on Stainless Steel

The formation mechanisms for two carbides with co-existence and increasing stacking faults nearby the carbides during surfacing welding were investigated in this study. The results indicated that the surfacing layer had a two-phase structure of a matrix phase and a second phase, the density of the second phase was relatively small and the second phase was discontinuous, by contrast with the as-received welding wire. Relatively uniform microstructure of surfacing layer and the welding interface without melting of base metal were obtained, resulting in an inapparent change in the microhardness. A few carbides with blocky shape were identified in the surfacing layer. The mechanisms for (Cr,Co)23C6 of face-centered cubic crystal structure co-existing with (Cr,Co)7C3 of hexagonal close-packed crystal structure and (Cr,Co)23C6 subsequently forming close to the pre-formed (Cr,Co)7C3 during the cooling process were discussed in alloying element, calculated equilibrium phase diagram, Gibbs energy, etc. The relatively higher density of the stacking fault present around the carbides was understood from forming energy of stacking faults.