Formation of aligned two-phase microstructures by applying a magnetic field during the austenite to ferrite transformation in steels

Abstract Application of a magnetic field during the ferrite to austenite transformation in Fe–C alloys was found to yield a two-phase microstructure with the paramagnetic austenite grains aligned as chains or columns along the direction of the field in the matrix of ferromagnetic ferrite phase. The underlying mechanism of dipolar interactions suggests that similar alignment of microstructures should take place during the austenite to ferrite transformation under a magnetic field. In the present investigation, an experimental setup has been designed to study the magnetic alignment. Its concept is characterized by deforming steels prior to the austenite to ferrite transformation to introduce ample nucleation sites in addition to applying magnetic fields up to 12 T. Experiments have revealed successful conditions for aligned two-phase microstructures in carbon steels. The formation mechanism of the aligned structures is discussed from the viewpoint of the nucleation and growth of ferrite grains in austenite phase under a magnetic field. Furthermore, it is shown that the shape of the aligned ferrite grains is determined by a balance of the magnetostatic and the interfacial energies.