Radiation hardening and IASCC susceptibility of extra high purity austenitic stainless steel

Ioka, Ikuo  ; Ishijima, Yasuhiro ; Usami, Koji; Sakuraba, Naotoshi; Kato, Yoshiaki; Kiuchi, Kiyoshi

Fe-25Cr-35Ni EHP alloy was developed with conducting the countermeasure for IASCC. It is composed to adjust major elements, to remove harmful impurities and so on. The specimens were irradiated at 553 K for 25000h using JRR-3. The fluence was estimated to be 1.510n/m. Type 304SS was also irradiated as a comparison material. SSRT test was conducted in oxygenated water at 561 K in 7.7 MPa. The fracture mode of EHP alloy was ductile. IGSCC was not observed in the fracture surface. On the other hand, the fraction of IGSCC on the fracture surface of type 304 was about 70%. Microstructural evolution of EHP and type 304 after irradiation was examined by TEM. The defects induced by irradiation mostly consisted of black dots and frank loops in both specimens. No void was also observed in grain and grain boundary of both specimens. There was a little difference in microstructure after irradiation. It is believed that EHP alloy is superior to type 304 in irradiation.