Creep-ratcheting effect and lifetime prediction of advanced 9-12% Cr ferritic steel at 600 ℃

Abstract

The creep-ratcheting behavior of advanced 9–12 % Cr ferritic steel at 600 °C under peak holding time of 0 min, 2 min, 5 min, 10 min, 20 min and 30 min were investigated and a creep-ratcheting constitutive model was developed. Results present that the anelastic strain during the whole creep-fatigue life for various holding time approximately keep constant. However, it decreases rapidly during the last several cycles. Moreover, the primary creep regeneration (PCR) behavior during repeated loading and unloading process was observed. It keeps almost the same with increasing number of cycles and changes slightly for different peak holding time under the same stress amplitude and stress ratio. Additionally, a modified plasticity-creep superposition model was established considering the combination effects of creep damage, ratcheting evolution, anelastic recovery and PCR. The comparison between tested and predicted data shows that the proposed model has high accuracy for the prediction of both creep-ratcheting strain and creep-fatigue lifetime. It is of interest that the proposed model can also well simulate the evolution of stress–strain during the whole lifetime, especially for the reproduction of anelastic creep recovery and PCR along the load history.