Kinetics of the δ/γ interface in the massive-like transformation in Fe-0.3C-0.6Mn-0.3Si alloys

In Fe-C alloys, it has been considered that the peritectic reaction occurs during solidification. Recently, the massive-like transformation, in which δ phase undercooled below the peritectic temperature transforms into γ phase, has been observed by X-ray imaging. It is of interest to know how the δ phase transforms into the γ phase, because the transformation is related to deformation of solidifying shell. Time-resolved and in-situ X-ray imaging with frame rate up to 500 fps was performed to know the δ/γ interface motion in the massive-like transformation in Fe-0.3C-0.6Mn-0.3Si alloys (mass%). The moving velocity of the δ/γ interface locally fluctuated. The average velocity ranged from several mm/s to 200 mm/s. However, no relationship between the moving velocity and the undercooling from the peritectic temperature was observed. The interface was not planar and the morphology continuously changed. The results showed that the stress / strain induced though the transformation from the δ phase to the γ phase in the steel solidification was not simply explained by the conventional peritectic reaction.