A comprehensive study of temperature-time parameters and structural changes during aging of pearlitic class steel 25KH1MF was carried out. It was found that aging at a temperature of 450 °C after heat improvement leads to a decrease of the lattice parameter of ferrite. This provides a reduction in carbon content in the ferritic matrix due to the allocation of excess carbon in the form of cementite and subsequent coagulation of carbide particles. It is shown that aging at a temperature of 450 °C with exposure for 5 hours allows to increase the cold resistance of the investigated steel by more than 2.5 times. The critical brittleness temperature of the 25KH1MF steel decreased from -15...-17 to -43...-45 °C, while impact strength increased by 2.5-3 times at a temperature of -20 °C.