Effect of Intercritical Annealing Conditions on Grain Growth Kinetics of Dual Phase Steel

Abstract

The study of grain coarsening and its kinetics during intercritical annealing is of vital importance for the production of dual phase (DP) steels with appropriate microstructure and properties required for industrial applications. In the present work, the kinetics of grain growth in the two-phase austenite plus ferrite region was studied based on the parabolic grain growth law. It was revealed that the thermally-activated grain growth of ferrite depends on the soaking temperature and the presence of austenite islands, where these two factors compete with each other. As a result, by increasing the temperature, initially the rate of growth increases and the activation energy of grain growth (Q) was determined as 615\xa0kJ/mol, which indicates the high-temperature dependency. However, after the formation of a certain amount of austenite and the formation of chain-network morphology of austenite, the increase of temperature results in a decreased growth rate with the Q value of −\u2009258\xa0kJ/mol. This suggests that the pinning effect counteracts the temperature effect in this stage. The effect of grain size on mechanical properties and work-hardening behavior was also discussed. Higher work-hardening rate was observed for the fine-grained DP microstructures, which was found to be responsible for the better strength–ductility trade off.