Improvement of creep and impact resistance of reduced activation ferritic-martensitic steel by the addition of Zr

The influences of Zr addition on the mechanical properties of reduced-activation ferritic-martensitic steel were investigated. 9Cr-based steels with Zr contents varying 0-0.01 wt% were designed and produced by vacuum induction melting, and then formed into a plate by hot rolling, which was followed by normalizing and tempering. The addition of 0.005 wt% Zr improves the impact resistance with a slight sacrifice of yield strength for a given tempering condition. A short-term creep test shows that the addition of 0.01 wt% Zr significantly increases the time to rupture. Such improvement in impact and creep resistances by the addition of small amounts of Zr is attributed to the solution softening effect of Zr, which is associated with a reduced temperature-dependence of the yield strength. It is concluded that Zr has great potential as an alloying element in reduced-activation ferritic-martensitic steel for improving the mechanical properties.