It was experimentally shown, using Auger-spectroscopy method, that there is a certain temperature interval of forming surface segregations of an element (C, N, B, P, Mo, Ti, Al, S, Sn, Cu) solved in α-Fe of low-carbon steels and ferrous-based alloys. Proposed mathematical approach based on traditional relationships of the equilibrium thermodynamics and diffusion kinetics models has determined the temperature scale positions of the intervals of forming segregations of the solved elements in α-Fe.