THE ROLE OF DYNAMIC STRAIN‐AGEING IN THE ENVIRONMENT ASSISTED CRACKING OBSERVED IN PRESSURE VESSEL STEELS

Abstract

Abstract— The dynamic strain ageing (DSA) behaviour of A533B Class 1 reactor pressure vessel (RPV) steel, containing 5 ppm of free nitrogen, has been investigated over a wide range of strain rates from 3 × 10−7 to 3−10−3s−1 and temperatures from 20 to 350°C. The DSA was observed within certain temperature ranges at all strain rates tested and its hardening effect in terms of the maximum strengthening stress (s̀p) decreased linearly with the increase of log strain rate. The temperature to stimulate DSA was observed to increase with increasing strain rate. The apparent activation energies of the characteristic strain rates for the onset, and peak of DSA have been determined, and their implications have been discussed. Compared with the available data, a positive effect of free nitrogen content on s̀p has been evaluated. It has been found that the occurrence of susceptible environment assisted cracking (EAC) of A533B steel in high temperature water is co‐related to the DSA behaviour. The results suggest that DSA reduces the ductility of RPV steel and its role in enhancing the EAC of RPV steels should not be neglected, in view of the coincidence with susceptibility zones for DSA and EAC in terms of strain rate and temperature.