Continuous cooling transformations in two medium carbon microalloyed forging steels have been studied. The influence of austenite grain size and molybdenum content on diffusion-controlled transformations and displacive transformations has been thoroughly analyzed. Moreover, a study of the austenite grain structure previous to the transformation has been carried out. In this sense, the evolution of austenite grain size with austenitization temperature has been experimentally analyzed. That allowed to detect the temperature at which an undesirable microstructure with a duplex grain morphology starts to form. Finally, continuous cooling conditions to reach a final microstructure formed mainly of acicular ferrite in industrial forging processes has been determined.