Cold work and temperature dependence of stress corrosion crack growth of austenitic stainless steels in hydrogenated and oxygenated high-temperature water

The rate of stress corrosion cracking (SCC) was measured for nonsensitized. cold-worked Type 316 (UNS S31600) and Type 304 (UNS S30400) in both hydrogenated pressurized water reactor (PWR) primary water and oxygenated water, each containing standard boron and lithium additions. First, the stress dependence of 5% to 20% cold-worked Type 316 (CW316) was determined in the PWR primary environment at 320 degrees C. The rate of crack growth increased both with increasing cold work and stress intensity. Intergranulur morphology was observed for 5%. 10%. 15%. and 20% CW316. Second, the dependence of crack growth rates on temperature in the range from 250 degrees C to 320 degrees C were measured in both hydrogenated PWR primary and oxygenated water. More rapid crack growth rates were observed in oxygenated water than that in hydrogenated PWR water. The crack growth rates Could be correlated with a I IT dependence on temperature for both hydrogenated PWR primary and oxygenated water: apparent activation energies of crack growth were similar in both environments. To assess what appeared to be common dependencies on temperature and cold work in both hydrogenated and oxygenated water. grain boundary creep (GB creep) was studied in air using CW316: intergranular creep cracking (IG creep cracking) was observed after low-temperature creep tests in air. The apparent activation energy of IG creep cracking was similar to that of intergranular stress corrosion cracking (IGSCC in high-temperature water. The similar dependencies on temperature, cold work, and rolling direction of SCC and creep suggest that creep by grain boundary diffusion plays a critical role in the growth of SCC The extent to which grain boundary diffusion interacts with other electrochemical processes is probably important but is not defined.