Mild carbon containing engineering steels based on Cr-Ni-Mo with low addition of silicon and aluminum (up 1,6 % of alloying element) were investigated. Distribution of alloying elements in structure of experimental steels was shown by the method of scanning electron microscopy. Using the method of dilatometry in high temperature region it was shown that aluminum and silicon extends intercritical temperature range. Also new heat treatment was developed. It consisted of quenching from 920 °С + tempering on 580 or 650 °С; quenching from 920 °С + quenching from two-phase region from 820 °С + tempering 580 or 650 °С. Analysis of mechanical properties showed that quenching from two-phase region leads to an increase in impact elasticity, what is necessary for achievement of optimum structural strength. Analysis of micro fractures after various tests was made and it was shown, that with decreasing experimental temperature from 20 to –60 °C viscous character of fissures changes on brittle character.