Effect of grain size on the irradiation response of grade 91 steel subjected to Fe ion irradiation at 300 °C

Irradiation using Fe ion at 300 °C up to 100 dpa was carried out on three variants of Grade 91 (G91) steel samples with different grain size ranges: fine-grained (FG, with blocky grains of a few micrometers long and a few hundred nanometers wide), ultrafine-grained (UFG, grain size of ~ 400 nm) and nanocrystalline (NC, lath grains of ~ 200 nm long and ~ 80 nm wide). Electron microscopy investigations indicate that NC G91 exhibit higher resistance to irradiation-induced defect formation than FG and UFG G91. In addition, nano-indentation studies reveal that irradiation-induced hardening is significantly lower in NC G91 than that in FG and UFG G91. Effective mitigation of irradiation damage was achieved in NC G91 steel in the current irradiation condition. Graphical abstract