Special features of transformation of supercooled austenite under continuous cooling of Si - Mn steels with nickel content reduced with respect to that in the traditional engineering steels are studied. The temperature ranges of occurrence of phase transformations under heating and cooling are determined by dilatometry. Thermokinetic diagrams of transformation of supercooled austenite are plotted. The components of the microstructure formed in the steels are assessed qualitatively and quantitatively. The chemical composition of a steel with high stability of supercooled austenite and high hardenability is suggested.