Effect of magnetism on kinetics of "gamma"-"alpha" transformation and pattern formation in iron

Kinetics of polymorphous "gamma"-"alfa" transformation in Fe is studied numerically within a model taking into account both lattice and magnetic degrees of freedom, based on first-principle calculations of the total energy for different magnetic states. It is shown that magnetoelastic phenomena, namely, a strong sensitivity of the potential relief along the Bain deformation path to the magnetic state, are crucial for the picture of the transformation. With the temperature increase, a scenario of the phase transformation evolves from a homogeneous lattice instability at T<Ms (Ms is the temperature of the beginning of the martensitic transformation) to the growth and nucleation of embryos of the new phase at T>Ms. In the latter case, a stage of formation of a tweed-like structure occurs, with a strong short-range order and slow interphase fluctuations.