The dynamic transformation (DT) of austenite to ferrite phase at high temperatures was studied in a medium-carbon low-alloy steel. The study involved hot compression tests followed by microstructural examinations using electron microscopy. Mathematical calculation of the data indicated that Cr atoms increases the driving force for the transformation of austenite to ferrite; however, when the influence of stress and thermodynamic analysis are considered, it was observed that Cr increases the barrier energy and therefore, emerges as a barrier to the transformation. An in-depth atomic analysis, based on lattice and pipe diffusion theories quantifies the role of stress on the diffusivity of Cr and is compared with other the main alloying elements such as C, Si and Mn and its impact, positive or negative, on the DT barrier energy. Finally, a comparison is made on the differential effects of temperature and stress on the initiation of DT in medium-carbon low-alloy steels.