The effects of substituting W for Mo in a quenched and tempered martensitic steel (US Steel "T-1" alloy) on tensile and impact properties have been investigated. The tungsten content (w/o) varied from 0.25 to 1.00 for the 0.5 w/o Mo, while the remaining alloy compositions were kept constant. It was found that both yield strength and ultimate tensile strength increased with the increasing tungsten content, reaching a plateau strength above 0.75 W. The tensile properties of 0.75 W alloy were about equal to those of 0.50 Mo alloy. On the other hand, the substitution of W for Mo in the alloy greatly enhanced the Charpy impact energy. At the test temperature of -20℃, the impact energies of 0.75-1.00 W alloys were 20-40% higher than that of 0.5 Mo alloy. It was also observed that the addition of W was as potent as Mo in preventing temper embrittlement in the alloy.
