Improving IASCC resistance of austenitic stainless steel by oversized solute addition; Amelioration de la resistance a la corrosion sous contrainte assistee par l'irradiation d'aciers inoxydables austenitiques par l'addition de solutes

The effect of hafnium oversized solute addition on the radiation-induced microstructure, radiation-induced grain boundary segregation and post-irradiation intergranular stress corrosion cracking (IGSCC) behavior of ultra high purity (UHP) 316SS alloy was investigated. Irradiations were conducted with 3.2 MeV protons at 400 C to a dose of 2.5 dpa on a UHP 316SS base alloy and a UHP 316SS alloy doped with hafnium. Radiation-induced microstructure was characterized in transmission electron microscopy (TEM). Addition of hafnium suppressed swelling and significantly decreased the mean loop diameter relative to the base alloy. Grain boundary composition was measured by means of scanning TEM coupled with energy dispersive x-ray spectrometry. Hafnium addition effectively suppressed the radiation-induced grain boundary segregation observed in the UHP 316SS base alloy. Constant elongation rate tensile (CERT) tests performed in normal water chemistry at 288 C showed that the hafnium doped alloy was not sensitive to post-irradiation IGSCC, in contrast to the base alloy. The mechanisms by which hafnium oversized solute addition mitigates radiation-induced damages as well as the link between radiation-induced damages and irradiation-assisted stress corrosion cracking (IASCC) are discussed. (authors)