Nucleation and growth of creep cavities in a Type 347 steel

Abstract

The nucleation and growth of intergranular creep cavities has been studied in a Type 347 austenitic steel tested at 550 and 650°C over a limited range of stress. It was found that the number of cavities per unit volume is linearly related to the time-dependent creep strain, being independent of stress or temperature over the conditions tested. The results indicate that cavity nucleation is controlled by a deformation process. Studies on cavity growth show that the cavity diameter increases approximately linearly with time, with a stress dependence for growth similar to that for secondary creep. These results are consistent with a diffusion growth model when a simple deformation-controlled nucleation law is incorporated. Using this growth model the observed stress and time dependence for the total void volume can be predicted, and the rupture life has been estimated reasonably well using a simple fracture criterion.