The development of low-activation martensitic 9 and 11%Cr, W, V stainless steels for fusion reactor applications

The effects of increasing tempering temperature on the room and elevated temperature tensile strengths and impact toughness of 9% and 11%Cr, 0.65%W, 0.25%V steels have been established and compared with those in the higher strength 3%W, 0.25%V alloy. The use of tantalum and titanium to promote austenite grain refinement and modify the precipitation sequence has been examined, together with the effects of variations in carbon and nitrogen contents. Creep tests have been conducted to 16000 h at temperatures of 500-5750C for the 9% and 11%Cr, 3%W, 0.25%V steels. The creep strain rates of the latter are higher than those of the commercial steel FV448, despite the similarity of the elevated temperature tensile strengths. The rupture lives of these steels are appreciably lower for all except the lowest stress conditions at 5000C but equal or exceed those obtained with FV448 at 550 and 5750C. (orig.)