Microstructures resulting from the interaction between ferrite recrystallization and austenite formation in dual-phase steels

The present work investigates the interactions between ferrite recrystallization and austenite formation in dual-phase steels by experiments performed at high heating rate (100 degrees C/s). It was shown that both ferrite recrystallization and austenite formation are strongly coupled and interdependent. The kinetics of ferrite recrystallization is strongly affected by the formation of austenite and can be even inhibited in some cases. The microstructure is more heterogeneous and anisotropic when both the austenite formation and the ferrite recrystallization overlap. It was highlighted that the degree of anisotropy depends on the volume fraction of austenite at a given temperature. Furthermore, an unusual behavior for austenite growth was highlighted. It is characterized by a much higher volume fraction than those obtained under OrthoEquilibrium and ParaEquilibrium. The results, especially those at 715 degrees C close to the eutectoid plateau, at which the driving force for austenite growth is classically low, suggest a diffusionless transformation for austenite.