Abstract This work is dedicated to the study of the growth kinetics of the borided layers obtained by the paste-boriding process. A diffusion model based on Fick’s laws and coupled with a thermodynamic description of the Fe–B binary system was suggested to simulate the growth kinetics of the borided layers consisting only of Fe2B phase and containing 8.83 wt.% B onto the iron substrate within the temperature range of 1223–1323 K. The validation of the diffusion model was achieved by comparing the simulation results with the experimental data taken from the literature and a good agreement was observed. Furthermore, the model was able to predict the boron-depth–concentration profile for Fe2B phase as well as the thickness of the borided layers depending on the boriding parameters.