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Changes in mechanical properties induced by irradiation of AISI Type 347 stainless steel at about 60 C were determined after integrated fast-flux (>1 Mev) exposures of 1.6 × 1022 and 2.1 × 1022 n/cm2. Tension tests were performed at room temperature, 316, and 750 C. The results indicated that the ultimate tensile strength and yield strength were greater after irradiation, with the yield strength showing the greater increase. After an exposure of 2.1 × 1022 n/cm2, the ratio of yield strength to ultimate strength was approximately 1. The decreases in ductility as measured by total and uniform elongation at 20 C were about the same magnitude for both levels of irradiation. The ductility at 316 C continued to decrease as a function of increasing neutron exposure. Radiation-induced property changes differed only slightly from those observed after irradiation to 5.5 × 1021 n/cm2 with the exception of the uniform and the total elongation at 316 C, suggesting that saturation of displacement damage occurred prior to this exposure. The fracture mode for both unirradiated and irradiated specimens was transgranular. Annealing of irradiated specimens for 1 hr at 982 C restored the preirradiation mechanical properties at 316 C. A severe reduction in ductility was noted for specimens tested at 750 C after irradiation to 2.1 × 1022 n/cm2, showing only about 0.5 per cent as uniform and total elongation. The fracture mode was intergranular. Annealing for 1 hr at 982 and 1350 C did not change the as-irradiated ductility.
Room-temperature cyclic-strain fatigue tests were made on Type 347 stainless steel specimens after irradiation to 5.5 × 1021, 1.1 × 1022, and 1.6 × 1022 n/cm2. The results indicated that the fatigue life at room temperature for stainless steel decreased at high strains, >1.5 per cent total strain per cycle, and increased at low strains, >0.5 per cent total strain per cycle, as a result of irradiation. The stress to produce the same total strain per cycle was greater after irradiation and increased with increasing irradiation levels. The failure time was a function of the total plastic strain and appeared to follow the relationship NmΔϵt = C, where N is the number of cycles to failure. Δϵt is the total strain range, and m and C are constants.
stainless steels, neutron irradiation, tensile properties, fatigue properties, ductility, steels, fracture, radiation effects, metals
Research engineer, Environmental Engineering Division, Battelle Memorial Inst., Columbus, Ohio
Shober, F. R.
manager, Nuclear Metallurgy, Pacific Northwest Laboratory, Battelle Memorial Inst., Richland, Wash