Stress rupture initiated by the carbides in the grain boundaries of the multi-pass weld metal

The weld metal (WM) was generally regarded as one of the weakest zones in the dissimilar welded joints. The microstructure and fracture mechanism of the multi-pass WM are systematically probed in the present study. The scanning electron microscopy (SEM) results show more voids in the equiaxed grain zone (EGZ) adjacent to the fracture than those in the columnar grain zone (CGZ). The transmission electron microscopy (TEM) results reveal that the precipitates are mainly Cr-rich M23C6 and Mo-rich M6C phases. The voids were initiated by the mismatch deformation between the precipitates and matrix during the stress rupture test. Moreover, the voids could easily extend and converge to form the macro cracks in the EGZ.