In-situ investigations on the dynamic transformation in steel near the Ae3 temperature

The austenite to ferrite transformation during high-temperature deformation, called dynamic transformation, was investigated by means of in-situ high energy x-ray diffraction experiments for a Fe-0.1C-6Ni (wt%) model alloy. Hot compression tests ranging from the paraequilibrium (Ap3 = 675 °C) to the orthoequilibrium (Ae3 = 729 °C) temperatures, with 50 % reduction in length and strain rates of 0.14 s-1, 1.4 s-1, and 14 s-1, revealed that the dynamic transformation was only possible at the lowest strain rate for temperatures up to 700 °C. The fraction of dynamic ferrite that formed was always less than 1 %. By comparing the fraction of ferrite observed in-situ and that observed in the room temperature microstructure for this alloy, it was demonstrated that traditional methods can overestimate the fraction of ferrite and the upper temperature limit of dynamic transformation. Additionally, the obtained results were compared to existing models for the dynamic transformation.