Importance of Grain Growth during Intercritical Anneal of Advanced High-strength Dual-phase Steels

Grain growth behavior in the two-phase austenite plus ferrite region was studied for an advanced high-strength dual-phase steel. It was revealed that the grain growth of ferrite depends on the intercritical annealing temperature and the presence of austenite islands, where these two factors compete with each other. By increasing the annealing temperature, initially the rate of grain growth increased, which indicates the high-temperature dependency. However, after formation of a certain amount of austenite and the attaining the chin-network morphology, the increase of temperature resulted in a decreased growth rate. This suggested that the pinning effect counteracts the temperature effect in this stage. Moreover, the effect of grain size on mechanical properties and work-hardening behavior was 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.