Helium implantation effects on low activation 9Cr martensitic steels

Tensile specimens of low activation 9Cr-0.5V and 9Cr-2W martensitic steels were implanted with helium up to 500 appm at 673-873 K using a 26 MeV3He beam. After implantation, tensile behavior was investigated at test temperatures equal to the implantation temperatures. While implantation of 100 appm He at 673 K and 773 K caused no visible effect on the tensile behavior, implantation of 100 and 500 appm at 873 K reduced the strength slightly. The fracture mode was found to remain ductile and transgranular in all the 9Cr steels examined. Small bubbles, mainly nucleated at laths-boundaries and sub-boundaries in the laths, were observed in all the implanted specimens. The bubble size increased with increasing implantation temperatures. Comparing the results of the low activation 9Cr-2W steel with those of the modified 9Cr-1Mo steel, no visible difference was observed in bubble formation behavior and fracture mode. (orig.)