Correlation of Intergranular Stress Corrosion Cracking Susceptibility with Mechanical Response of Irradiated, Thermally Sensitized Type 304 Stainless Steel

Intergranular stress corrosion cracking (IGSCC) susceptibility of irradiated, thermally sensitized type 304 (UNS S30400) stainless steels (SS) was studied as a function of neutron fluence and correlated with mechanical responses of the materials. Neutron irradiation was carried out to neutron fluences up to 5.4 x 10²³ n/m² (E > 1 MeV) at 290°C and to 1.1 x 10²⁴ n/m² (E > 1 MeV) at 340°C in the Japan Material Test Reactor. Irradiated specimens were examined by slow strain rate tensile testing (SSRT) in 290°C pure water of 0.2 ppm dissolved oxygen (DO) concentration, by SSRT at 290°C in argon gas, and by microhardness measurements. IGSCC susceptibility increased with neutron fluences up to 1.1 x 10²⁴ n/m² regardless of irradiation temperatures. The 0.2% proof stress (PS) and the grain-boundary (GB_HV) and grain-center microhardness (GC_HV) increased. The uniform elongation (UE) decreased with neutron fluences up to 5.4 x 10²³ n/m², but 0.2% PS and GB_HV and GC_HV decreased, and UE increased at 1.1 x 10²⁴ n/m². However, the 1.1 x 10²⁴ n/m² fluence was achieved at 340°C. Excellent correlation was identified between IGSCC susceptibility and microhardness increments at the grain boundary relative to the grain center. Incremental grain-boundary hardening presumably may be a major factor affecting IGSCC.