Behavior of creep cavity growth in Cr-Mo-V forged steel

The creep damage characteristics of a commercial Cr-Mo-V steam turbine rotor material have been studied at 550 and 600 degrees C, to understand the creep mechanism under plant service condition. The mean cavity length at the grain boundaries increased linearly with increasing creep strain during the secondary creep stage. In this condition the growth of creep cavities was found to depend mainly on grain boundary diffusion and cavities retained a similarity in shape. Assuming that all cavities were distributed homogeneously in the matrix and cavity density vs creep strain was a parabolic relationship, mean cavity length could be approximately predicted with a theoretical model of grain boundary diffusion growth