Metastable Equilibrium between Cubic and Tetragonal Ferrites in Fe–C Alloys with Excluded Carbide Formation

Abstract

Metastable equilibrium of the α- and α'-phases comprising solid solutions of carbon in iron with cubic and tetragonal lattices, respectively, has been analyzed using the Zener–Khachaturyan theory of tetragonality of martensite of Fe–C alloys. The condition of the absence of carbide precipitates was imposed, as in the case of very low tempering or the formation of non-carbide bainite. A phase equilibrium diagram has been plotted in the region of low temperatures between 300–600 K. The violation of the linear dependence of the degree of tetragonality c/a on the carbon concentration in the concentration range 0.17–0.61 wt % C, established by Academician G.V. Kurdyumov for higher carbon concentrations, is explained.