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 B.H. Sencer a,b, * , G.M. Bond a , M.L. Hamilton b , F.A. Garner b , S.A. Maloy c , W.F. Sommer c a New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA b Materials Resources Department, Paci®c Northwest National Laboratory, P.O. Box 999, Building #326, Battelle Boulevard, P8-15, Richland, WA 99352, USA c Los Alamos National Laboratory, Los Alamos, NM 87545, USA Abstract A number of candidate alloys were exposed to a particle ¯ux and spectrum at Los Alamos Neutron Science Center LANSCE) that closely match the mixed high-energy proton/neutron spectra expected in accelerator production of tritium APT) window and blanket applications. Austenitic stainless steels 316 L and 304 L are two of these candidate alloys possessing attractive strength 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°C and consequent changes in mechanical properties. It was observed that the microstructural evolution during irradiation was essentially identical in the two alloys, a behavior mirrored in their changes in mechanical properties. With one expection, it was possible to correlate all changes in mechanical properties with visible microstructural features. A late-term second abrupt decrease in uniform elongation was not associated with visible microstructure, but is postulated to be a consequence of large levels of retained hydrogen measured in the specimens. In spite of large amounts of both helium and hydrogen retained, approaching 1 at.% at the highest exposures, no visible cavities were formed, indicating that the gas atoms were either in solution or in subresolvable clusters. Published by Elsevier Science B.V. 1. Introduction An understanding of the response of candidate ma- terials to the irradiation conditions they will experience in the accelerator production of tritium APT) facility is essential to proper development of its components [1]. Very limited information was previously available for application of 300-series steels in such severe environ- ments. Accelerator-driven spallation environments such as APT will produce high radiation damage levels, concurrent with high rates of helium and hydrogen generation, and in APT, at relatively low irradiation temperatures. Irradiation data on these steels that are already available were derived, in general, from situa- tions involving relatively low particle energies, much lower gas He/H) generation rates, and much lower doses, compared to those expected in APT. Therefore specimens of APT candidate materials were irradiated at the 800 MeV 100 mA Los Alamos Neutron Science Center LANSCE) accelerator in o- beam neutron furnaces to relatively low exposures, and to displacement levels as high as 15 dpa in the direct proton beam in order to simulate various APT condi- tions [1]. Nevertheless, even the high exposure data www.elsevier.com/locate/jnucmat Journal of Nuclear Materials 296 2001) 112±118 * Corresponding author. Tel.: +1-509 376 0156; fax: +1-509 376 0418. E-mail address: bulent.sencer@pnl.gov B.H. Sencer). 0022-3115/01/$ - see front matter. Published by Elsevier Science B.V. PII:S0022-311501)00512-8