The effects of neutron irradiation and temperature on the mechanical properties of AISI 348 and 304 stainless steels have been determined using smooth and notched tension specimens containing different amounts of cold-work. Smooth tension specimens were irradiated at about 50, 290, and 750 C. Room temperature and 300 C tests on specimens in both the annealed and 25 percent cold-worked conditions show a marked reduction in ductility with increasing exposure and increasing test temperature. Damage accumulation, as measured by changes in mechanical properties, occurs more rapidly at the intermediate irradiation temperature. Control specimens exposed in an out-of-reactor loop at 282 C for times in excess of 5000 hr showed a significant change in mechanical properties.

Notched tension specimens of AISI 348 stainless steel in the annealed, 10, 20, and 40 per cent cold-worked conditions were irradiated at about 290 C and tested at room temperature. The mode of fracture was ductile in nature throughout the range of cold-work and neutron exposures studied. A transition from notch-strengthening to a notch-sensitive behavior was observed for specimens in the 20 and 40 per cent cold-work levels after an exposure of about 1.0 x 10²⁰ neutrons/cm² (>1 Mev).

The effects of cold-work, temperature, and chemical composition on the metallurgical stability of these materials were examined using magnetic measurements and X ray diffraction. The magnetic susceptibility of both materials containing up to 70 per cent cold-work was determined prior to irradiation. No measurable change was noted in the magnetic susceptibility of either the annealed or 25 per cent cold-worked materials which could be attributed to irradiation alone, after exposures of 1.5 x 10²¹ neutrons/cm2 ( > 1 Mev). Optical and electron microscopy studies on both materials revealed no changes in structure due to the combined effects of irradiation and temperature.