Microstructural evolution and kinetics for post-dynamic transformation in a plain low carbon steel

The post-dynamic transformation (post-DT), which could occur during isothermal holding after hot deformation, was investigated by using both dilatometry method and optical microstructural observation in a plain low carbon steel. The results indicates that the kinetics of post-DT at deformation temperature between Ae(3) and Ar-3 can be well described by the Avrami equation: X=1 -exp(-kt(n)), but the n value is lower than that of the corresponding static transformation due to the early impingement of formed ferrite grains. Furthermore, the ferrite-to-austenite re-transformation was measured by dilatometry during the isothermal holding after hot deformation above Ae(3) temperature, which suggests that dynamic transformation can indeed occur even above Ae(3).