DESIGNATION OF ALLOY COMPOSITION OF REDUCED-ACTIVATION MARTENSITIC STEEL

An alloy composition of reduced-activation martensitic steel for fusio n reactor is designed on the basis of the experimental results of post irradiation microstructure, mechanical properties, such as creep, frac ture toughness and tensile properties, hydrogen effects and corrosion. At present, a desired composition of the steel is i-0.5Mn-9Cr-2W-0.25 V-0.02Ti-0.05Ta-<0.002S-<0.002P by weight percent. Effects of the othe r minor elements such as Al, Zr and B are also inspected. An addition of 0.05 wt% Ta increases the high temperature strength but seduces the fracture toughness. Susceptibility to hydrogen-induced cracking is re duced by an addition of 0.03 wt% Al, though it results in a severe deg radation of the fracture toughness. An addition of 30 wppm B together with the addition of 0.02 wt% Ti increases the fracture toughness. Voi d nucleation at grain boundaries, however, is enhanced by the B additi on under the FFTF irradiation at 638 K in 10 dpa.