Energetics of the fcc $\left(\gamma \right)$-bcc $\left(\alpha \right)$ lattice transformation by the Bain tetragonal deformation is calculated for both magnetically ordered and paramagnetic (disordered local moment) states of iron. The first-principles computational results manifest a relevance of the magnetic order in a scenario of the $\gamma \text{−}\alpha$ transition and reveal a special role of the Curie temperature of $\alpha \text{-Fe}$, $T_C$, where a character of the transformation is changed. At a cooling down to the temperatures $T<T_C$ one can expect that the transformation is developed as a lattice instability whereas for $T>T_C$ it follows a standard mechanism of creation and growth of an embryo of the new phase. It explains a closeness of $T_C$ to the temperature of start of the martensitic transformation, $M_s$.

• Received 14 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.094111