1. The optimum tempering conditions of steel 30KhGT are 180°–200° C for 90 minutes' holding. 2. The impact toughness of such steel case-hardened to a 1.1–1.2 mm depth by carburizing and tempered at 120°–150° C/90 min. is by 20%–40% less than that obtained for the optimum tempering conditions. 3. The same steel, when carburized and quenched but not tempered, shows impact toughness values 50% less than after the best tempering procedure.