Stress and Temperature Dependence of Irradiation Creep of Selected FCC and BCC Steels at Low Swelling

Abstract

Abstract A large amount of data on irradiation creep of face centered cubic (FCC) and body centered cubic (BCC) steels have been analyzed and published by the present authors, but a recent reanalysis of these data have provided further insight into irradiation creep behavior. The present paper looks at the stress and temperature dependence of creep at low swelling for selected 316 stainless steels and HT9 steels irradiated at temperatures from 400–670°C. Analysis of the creep data has revealed that a transition from a lower creep rate with a stress exponent of one to a higher creep rate with an unknown stress exponent occurs in FCC and BCC steels at moderate stresses, and the transition stress is approximately the same for both classes of steels. Due to limited data at higher stresses, the nature of the creep behavior at stresses greater than the transition stress cannot be unambiguously defined. One possibility is that the stress exponent is transitioning from a value of one to a value greater than one. Another possibility is that the creep compliance value is transitioning to a higher value while the stress exponent remains at a value of one. The creep compliance coefficients of the FCC and BCC steels have also been carefully reanalyzed in the regime where the stresses are lower than the transition stress, and in this regime there is a clear delineation in the creep compliance values between 316 stainless steels, titanium-modified 316 steels, and HT9 steels as a function of temperature.