Influence of deformation induced ferrite transformation on grain refinement of dual phase steel

A controlled rolling process was simulated by thermomechanical simulator (Gleeble1500) to produce as-hot-rolled dual phase steel. The microstructure of as-hot-rolled dual phase steel using deformation induced ferrite (DIF) transformation could be refined to as fine as that of Intermediate Quenching (martensite as a starting microstructure). DIF transformation was influenced by austenite grain size, amount of strain and strain rate, and the grain of about 2 μm could be produced by heavy deformation of 80%. However, the ferrite growth occurred during the intercritical isothermal holding after deformation. Microalloying such as Nb, V was effective for suppressing the ferrite growth. Thus, microalloying elements that could restrain ferrite grain coarsening were required to produce fine grained dual phase steel.