The objective of this work is to study the process of phosphatizing with manganese by immersion. In the literature there is not enough information on the phosphate process with manganese phosphate, hence the main contribution of the present. The methodology involves an electrochemical study, using open circuit potential techniques in order to follow the kinetics of the process. In the same way, the characterization of the coating formed on the surface of each steel used was carried out using scanning electron microscopy and X-ray energy dispersion spectroscopy. Through this technique, the time was found in which the internal layer of the coating developed on the phosphatized substrates, both on the rough and the rough sides of the steel samples. The results obtained show that the formation of the manganese phosphate coating on the steels depends both on the grain size of the steels at the beginning of the process, as well as on the surface finish to which the steel surface is subjected, resulting in an increase in the size of the crystals, and affecting the rate of disintegration and growth of the same.