Formation of ultrafine grained ferrite in low carbon steel by heavy deformation in ferrite or dual phase region

The microstructural refinement supplies an alternative approach to improve the strength of low carbon steel without loss of room temperature ductility. This paper reports the methods to obtain the ultrafine grained ferritic microstructure by the heavy deformation of low carbon steel in ferrite or dual phase region. Various initial microstructures before deformation were selected. The deformation microstructure was analyzed by optical microscopy and electron back-scattered diffraction (EBSD) technique. It has been demonstrated that the equiaxed ferritic microstructure with a grain size of around 3 μm was obtained. The coarse pre-eutectoid ferrite dynamically recrystallized to form the ultrafine grained ferrite and the undercooled austenite was transformed to the ultrafine ferrite by the strain-induced austenite to ferrite transformation.