Abstract
Interfacial creep failure was strongly affected by the solidified grain boundary (SGB) for steel/nickel dissimilar metal welded joints, especially at higher temperatures and lower stresses. Short, long, and mixed length SGBs were found as three distinct characteristics adjacent to the interface. These characteristics were attributed to the heterogeneous nucleation, multi-layer thermal cycle, and pre-solidified macrosegregation inducing local cooling rate differences, respectively. Because of the diffusion of elements C and N across the interface, short SGBs were more likely to be occupied completely by coarsening granular carbides (M23C6 and M6C) and acicular nitrides (AlN and TiN), which promoted the relative sliding of SGBs. This resulted in a large number of cavities at the interface with short SGBs, while few cavities were observed for long SGBs. Besides, the shorter side of mixed length SGBs also tended to form cavities in macrosegregation. These findings indicated that controlling the presence of short SGBs and macrosegregation could improve the creep life of the dissimilar metal welded joints.
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