Microstructural origins of radiation-induced changes in mechanical properties of 316 L and 304 L austenitic stainless steels irradiated with mixed spectra of high-energy protons and spallation neutrons

A number of candidate alloys were exposed to a particle flux and spectrum a t Los Alamos Neutron Science Center (LANSCE) that closely match the mixed h igh-energy proton/neutron spectra expected in accelerator production of tri tium (APT) window and blanket applications. Austenitic stainless steels 316 L and 304 L are two of these candidate alloys possessing attractive streng th and corrosion resistance for APT applications. This paper describes the dose dependence of the irradiation-induced microstructural evolution of SS 316 L and 304 L in the temperature range 30-60 degreesC and consequent chan ges in mechanical properties. It was observed that the microstructural evol ution during irradiation was essentially identical in the two alloys, a beh avior mirrored in their changes in mechanical properties. With one expectio n, it was possible to correlate all changes in mechanical properties with v isible microstructural. features. A late-term second abrupt decrease in uni form elongation was not associated with visible microstructure, but is post ulated to be a consequence of large levels of retained hydrogen measured in the specimens. In spite of large amounts of both helium and hydrogen retai ned, approaching I at.% at the highest exposures, no visible cavities were formed, indicating that the gas atoms were either in solution or in subreso lvable clusters. Published by Elsevier Science B.V.