Effect of helium implantation on mechanical properties and microstructure evolution of reduced-activation 9Cr-2W martensitic steel

A reduced-activation martensitic steel was implanted with helium up to 580 at. ppm by using 36 MeV alpha -beam between 353 and 423 K along with displa cement damage up to 0.226 dpa. The implantation-induced increase in ductile -brittle transition temperature (DBTT) was estimated to be 98 K for the sta ndard charpy V-notched (CVN) specimen implanted with 580 at. ppm. He, throu gh the conversion of small punch (SP) test results by an empirical relation ship. It is clarified from comparison with neutron irradiation data that th e increase in DBTT as well as implantation-induced hardening is interpreted simply in terms of displacement damage, suggesting that there is no signif icant effect of helium on both the irradiation hardening and the fracture t oughness of the steel. No fracture mode change by the helium implantation w as observed in the SP tests, showing a complete cleavage fracture mode in t he lower shelf energy region. (C) 2001 Elsevier Science B.V. All rights res erved.