An experimental study of the surface carbon saturation process of the steel plates during catalytic gas carburizing is carried out. The rate of the carburizing is determined as well as the hardness distribution in the diffusion layer after quenching. A mathematical model based on the experimental data and the results of numerical modeling has been obtained that makes it possible to determine the variation of the carbon concentration in the diffusion layer on the steel surface during the carburizing process. A simplified technique for simulation of the steel carburizing is proposed.