The effect of dendritic structure and secondary phases on the fatigue
crack propagation mechanism of ERNiCrMo-3 weld metal was investigated in
the present study. Element segregation in the weld metal caused severe
lattice distortion in the interdendritic region, which led to the
instability of crack propagation rates, resulting in considerable
differences in mechanical properties between the dendrite core and
interdendritic region. The limited plastic deformation capability of the
interdendritic region caused the contraction of the local plastic
deformation zone at the crack tip, which increased stress concentration
and accelerated crack propagation. Meanwhile, element segregation
promoted the precipitation of a large number of Laves pahse in the
interdendritic region. The interaction between dislocations and Laves
phase was enhanced as the stress increased, which generated micro-voids
and provided fast channels for fatigue crack propagation. Post-weld heat
treatment weakened the non-uniformity of the microstructure and the
fatigue crack showed a stable propagation trend. Moreover, the
dissolution of Laves phase and the precipitation of γ” enhanced the
fatigue property of the weld metal.