Improved properties of dual-phase steel via pre-intercritical annealing treatment and thermal cycling

Abstract

The synergistic effects of pre-intercritical annealing treatments and multiple heating to the two-phase region (followed by quenching) on the microstructure and mechanical properties of dual-phase (DP) steel were studied. Intercritical annealing of ferritic-pearlitic, martensitic, and cold-rolled martensitic microstructures was investigated. The effects of tempering, austenitisation, grain growth, and recrystallisation were unravelled and an optimum holding time was characterised for each initial microstructure. Grain refinement by recrystallisation of cold-rolled martensitic microstructure resulted in the enhancement of tensile properties. Thermal cycling through multi-step intercritical annealing resulted in grain refinement and enhanced mechanical response. It was revealed that thermal cycling combined with the carefully controlled pre-intercritical microstructure could be simply used for the improvement of mechanical properties of DP steel.