Irradiation-induced evolution of mechanical properties and microstructure of Eurofer 97

Specimens of ferritic/martensitic (FM) steel Eurofer 97 were irradiated to doses ranging from 9.5 dpa/760 appm He to 20.4 dpa/1795 appm He at temperatures between 150 and 360 °C in the second experiment of the SINQ Target Irradiation Program (STIP-II). The results of tensile tests and hardness measurements demonstrated strong effect of irradiation-induced hardening and embrittlement in the steel. Specimens irradiated to 19.8 dpa/1750 appm He at 345 °C exhibited a fully brittle fracture mode regardless testing at 25 or 400 °C. Transmission electron microscopy (TEM) investigation showed that the visible defect features produced by irradiation were mainly small clusters and dislocation loops. High-density helium bubbles with sizes of 1–3 nm were also observed in the specimens irradiated to 20.4 dpa/1795 appm He.