Relationship between hardening and damage structure in austenitic stainless steel 316LN irradiated at low temperature in the HFIR

An austenitic stainless steel 316LN irradiated to damage levels of about 3 dpa at irradiation temperatures of about 90 C and 250 C has been examined by transmission electron microscopy. The irradiation at 90 C and 250 C induced a dislocation loop density of 3.5 x 1022 and 5.2 x 1022 m-3, and a black dot density of 2.2 x 1023 and 1.1 x 1023 m-3, respectively, in the steel. A low density (<1 x 1019 m-3) of radiation-enhanced precipitates was observed in the matrix. No cavities were observed. These features are correlated with the changes in tensile properties. It is concluded that the dislocation loops and the black dots cause irradiation hardening and a decrease in the uniform elongation in the 316LN steel irradiated at low temperatures. (orig.)