The impact toughness of a martensitic 12 Cr-0.6 Mo-2.2 W-4 Co-0.8 Cu-VNb (in wt pct) steel subjected to tempering at 770°C for 3 hours and aging at 650°C for 643 hours was examined in the temperature range of 20 to 250°C. The steel in the tempered condition exhibits a ductile-brittle transition temperature (DBTT) of 41°C and a Charpy V-notch impact energy of 100 J/cm2 at a temperature of 20°
