Development of Reduced-Activation Martensitic 9Cr Steels for Fusion Reactor.

In order to develop reduced-activation ferritic/martensitic steels potentially suitable for fusion reactor applications, the effect of principal alloying elements Cr, W and V on the micro- structural evolution, toughness and high-temperature creep strength was systematically investigated for relatively simple Cr-W-V steels. Based on the results on the simple steels, two kinds of martensitic 9Cr steels with low and high levels of W were alloy-designed: 9Cr-1WVTa and 9Cr-3WVTa. They exhibited excellent toughness and high-temperature strength. Irradiation hardening was the smaller for the reduced-activation 9Cr-1WVTa and 9Cr-3WVTa steels than for the conventional 9Cr-lMoVNb and it was smaller for the low W steel than for the high W steel. It is concluded that from the aspect of toughness the 9Cr-1WVTa steel is the most promising alloy for the first wall and blanket structures which will be operated at low temperatures below 773 K (500°C). Another 9Cr-3WVTa steel is the most promising in terms of high- temperature creep strength for the future power reactor structures which will be operated at temperatures higher than 773 K.