High-temperature solution annealing as an IASCC mitigation technique

Abstract

Pre-irradiation solution annealing treatments for limited times in the temperature range from 2200{degrees}F (1204{degrees}C) to 2400{degrees}F (1316{degrees}C) were shown to be effective in eliminating irradiation assisted stress corrosion cracking (IASCC) in Type 304 stainless steel (SS), which had been irradiated to fluences between 2.58 and 3.08 {times} 10{sup 21} n/cm{sup 2} (E > 1 MeV). Varying resistance to IASCC as a function of heat treatment parameters was demonstrated in constant extension rate tensile (CERT) tests performed in boiling water reactor (BWR) simulated water. Measures of IASCC susceptibility used in the CERT tests (% IGSCC, % elongation, and maximum stress) could not be correlated with data obtained from HNO{sub 3}/Cr{sup +6} corrosion tests, or from Auger and analytical electron microscopy (AEM) analyses of grain boundary composition. Corrosion test data, however, could be correlated with the Auger and AEM results. The absence of a correlation between IASCC susceptibility and the grain boundary contents of Si, P, and S suggests that other impurities that are known to segregate and undergo nuclear transmutations, such as N and B, may play an important role in the IASCC mechanism. Tensile test data showed that the high temperature solution annealed (HTSA) material had undergone less radiation strengtheningmore » than mill annealed (MA) material. Elongations of approximately 10% were measured in the HTSA material compared to 2% in the MA material. 13 refs., 24 figs., 10 tabs.« less