To understand how austenite forms in high-formability steels during the heating step of intercritical annealing, calculations based on atomic diffusion and local equilibrium assumption were used to simulate the transformation kinetics. It appears that chromium must be considered in the calculations to allow for a good fit with the austenite formation kinetics obtained by dilatometry. Indeed, Cr has a strong delaying effect on this kinetics, even though it is a minor element in the steel chemistry. The parametric study reveals that cementite initial radius is the most influential parameter on transformation kinetics. Mn and Cr enrichments also prove to be important parameters to consider.