Mechanical response of irradiated thermally-sensitized type 304 stainless steels

Thermally sensitized type 304 stainless steels, together with solution annealed materials, were irradiated in inert gas environment to neutron fluences up to 5 x 10(23) n/m(2) (E > 1 MeV) at 563 K, and to 1 x 10(24) n/m(2) at 613 K, and then examined by a slow strain rate (SSR) tensile test and a microhardness test. The SSR tensile test results showed that 0.2% proof stress of the thermally sensitized materials unirradiated and irradiated to lower neutron fluences of similar to 2 x 10(23) n/m(2) was larger than that for the solution annealed one, whereas the former irradiated to the high neutron fluence above similar to 2 x 10(23) n/m(2) was smaller than the latter at the same neutron fluences. Microhardness at grain boundary regions was larger than that for grain centers in the irradiated as well as unirradiated thermally sensitized materials. The larger grain boundaries hardening could be attributed to radiation induced segregation of interstitial impurity elements and their interaction with radiation defects. The hardening of the grain boundaries relative to the grain centers increased with neutron fluence. The above neutron fluence dependent 0.2% proof stress of the thermally sensitized and solution annealed materials would primarily be ascribable to the larger hardening of the grain boundary area than that for the grain center. Radiation anneal hardening appeared at 600-650 K and 700-750 K upon post irradiation annealing of thermally sensitized materials.