The effect of stress on the microstructure of neutron irradiated type 316 stainless steel

Abstract

Examination was performed on pressurized tube specimens stressed during irradiation at 500°C. The hoop stress levels ranged from 0 to 327 MN/m 2, with fluences between 2.0 and 3.0 × 10 22 n/cm 2 . The data showed that applied tensile stresses enhance swelling in the annealed steel. The number densities of both voids and Frank loops were sensitive to the stress level. While cold working suppressed swelling, nucleation and growth of Frank loops were unaffected by the cold worked microstructure. The individual planar loop densities were dependent upon the magnitude of the stress component normal to the loop plane, in both cold worked and annealed steels. The mean loop sizes were limited by the probability of loop intersection with other microstructural components. The stress dependence of void and loop densities allowed determination of the critical nuclei sizes. The observations support models predicting a coupling of swelling and irradiation creep phenomena through the stress state.