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 mum 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. (C) 2002 Elsevier Science B.V. All rights reserved.