Low-carbon Cr-Ni-Mo steels widely used in mechanical engineering were studied: 0.18C2Cr4NiMo; 0.25C2Cr4Ni1,5Mo; 0.25C2Cr3Ni0.5Mo. The CCT diagrams have been plotted by the dilatometric method. The temperature-time ranges for the formation of microstructure constituents have been established. It was shown that bainite in the studied steels can be formed both above and below the M s temperature. The features of the isothermal bainite transformation are investigated, the kinetics of bainite transformation is determined, as well as the quantitative ratio of the microstructure constituents formed as a result of austempering. It has been established that the largest amount of bainite in the structure of the studied steels (80-95%) is achieved at the temperature near M s. The mechanical properties (strength, ductility, impact toughness) of the steels under study are analyzed after various heat treatment modes: various cooling intensities, upper and lower bainite austempering. It has been shown that the formation of upper bainite has an ambiguous effect on the impact strength of steels.