Mechanical properties and microstructure of steels with carbide-intermetallic strengthening phases containing 0.12 and 0.21% C; 9.5% Ni; 1.0-3.5% Mo; 0.3 and 0.8% Al; 0.2% V; 1.2% Cu and 0.05% Nb were studied. Heat treatment consisted of quenching from 900-1050°C and tempering at 200-700°C (1 hour). It was established, that hardness rises at tempering temperatures above 300°C. The peak of hardness lies at 400-500°C. Increase of Mo content increased the strength properties, but decreased the impact toughness. Optimal heat treatment consists of quenching from 900°C and tempering at 550°C, 1 hour. Results of X-ray, electron microscopic and chemical analysis are presented.