A three-dimensional mixed-mode cellular automaton model [C. Bos, M. G. Mecozzi, and J. Sietsma. Computational Materials Science 48.3 (2010): 692-699] for the austenite to ferrite transformation in low-carbon steel has been analyzed and improved. A comparison between the new and conventional model has been made and the improvements found are significant. Interface velocity is based on diffusion of carbon atoms and determined by the local density of carbon. A higher grain boundary carbon diffusion coefficient is applied. The conventional model has been revised and stabilized. Real dilatometry tests have been used to mirror the transformation behaviour of the model with reality. For a one-dimensional model it has been shown that the space-discretizing cellular automaton model converges to the space-continuous method of Murray-Landis.