[en] To establish boundary conditions of pit formation energy at crack top γsub(d) for steels of different structural classes, and to choose steels for low operation temperatures, fracture microrelief is investigated at static and dynamic types of loading at 20 and 196 deg C. For investigation austenitic and ferritic steels used at low temperatures up to -196 deg C (77K) were taken. The minimum (critical) fracture quantum determining the boundary of ductile-brittle transition (T₅₀) at the state of semibrittleness characterized by the change of fracture mechanism, transition from fracture according to the breakaway mechanism to fracture according to the shear type is determined. A new approach to the choice of materials and optimization of the structural states for low temperatures is suggested. On the basis of mathematical processing of eXperimental data the uniform dependence of the average pit size in the fracture on the square of yield strength for steels of different structural classes and crystal lattices, is established. The value of the local energy spent for a single fracture quantum at a given temperature of loading conditions can be accepted as stable which opens the prospects for developing heterogeneous systems