The paper presents the results of studies of the combined effect of strain rate and low temperatures on the flow of martensitic transformations in steel 12X18H10T after heat treatment in an austenitized state. Metastable austenitic steels are widely used in low-temperature equipment, including for manufacturing of gas carrier tanks. Operation of components at low temperatures may impact both static and dynamic loads. It is known that the combined effect of temperature and deformation factors in metastable austenitic steels may result in martensitic transformations, which, on the one hand, can lead to hardening of the material but cause embrittlement of the material of low-temperature equipment parts on the other hand. The steel was smelted in an open way in an induction steelmaking capacity of 150 kg, poured into iron molds with a capacity of 50 kg. The obtained ingots were forged into square and round billets. The temperature for forging was 1050–1250 °C. Further, the billets were subjected to thermal treatment: austenitization under 1050–1100 °C and cooling in water. After heat treatment, samples were made from forgings for mechanical tests and subsequent additional metallographic and X-ray studies. Tests were carried out to assess the strength and ductility characteristics after testing of smooth samples for static tension in the temperature range from 20 to -196 °C in accordance with GOST 11150–75, as well as studies to assess the impact viscosity after impact bending tests in a wide temperature range (GOST 9454–78). After the tests, the share of martensitic component in the surface area of the destroyed sample was determined. Conclusions are made about the influence of the deformation rate on the phase transformations in metastable austenitic steels at low temperatures. We have established the dependence of deformed volume and the parameters characterizing the process of phase transformations at the stages of sufficiently developed plastic deformation on temperature.