Chemical potentials of tetragonal ferrite and its equilibrium with -phase in steels

For steels with non-carbide bainite equilibrium of tetragonal ferrite/austenite occurring in the decay of γ-phase on the basis of Fe-C alloys is considered. Chemical potentials of the components are calculated by summing the corresponding expressions for α-phase with the cubic lattice and tetragonal additive according to Zener-Khachaturyan theory. The condition of equality of chemical potentials of the components for two phases makes it possible to calculate the boundary concentrations of carbon in α- and γ-phases. It is determined that in a tetragonal α-phase the calculated carbon concentration is 40-60 times higher than for conventional cubic ferrite. This opens up new possibilities for the construction of high-strength steel with non-carbide bainite structure.