The mechanical properties and microstructure of the OPTIMAX series of low activation ferritic-martensitic steels

Polycrystalline specimens of the ferritic-martensitic OPTIMAX A steel have been irradiated on the one hand with neutrons at 523 K to a dose of 2.5 dpa and with 590 MeV protons at ambient temperature and 523 K to doses of abou t 0.3 and 1 dpa on the other. Charpy tests reveal a shift of the ductile-to -brittle transition temperature from about 190 to 268 K in the neutron-irra diated steel. Proton irradiations at ambient temperature lead to hardening and reduction of tensile ductility of the material. Both phenomena are stro ngly and positively dependent on dose. After irradiation at 523 K, they app ear negligible (at least for the dose of 0.75 dpa). Transmission electron m icroscopy observations reveal that neutron irradiation leads to the formati on of only a few Visible black dots, together with a few faceted cavities, while proton irradiations also produce few visible defect clusters with siz es of about 1-2 nm, with no clear difference in size and density with dose and temperature. As a particular result, from proton irradiations performed at ambient temperature, the embedded carbides become amorphous, while at 5 23 K they remain crystalline. (C) 2000 Elsevier Science B.V. All rights res erved.