The growth kinetics of Fe2B layers formed at the surface of AISI 1018 was simulated. The paste-boriding (with a paste thickness of 4 mm) was applied to produce the Fe2B phase at the material surface; considering four temperatures (1123, 1173, 1223 and 1273 K) for 2, 4, 5, 6 and 8 h. The suggested model was based on the mass balance equation at the (Fe2B /substrate) interface. As a fitting parameter of the model, the surface boron concentration (12.16 wt. %B) was obtained in order to predict with a good agreement the experimental parabolic growth constants at the (Fe2B /substrate) interface derived from the literature. An expression of the parabolic growth constant at the (Fe2B /substrate) interface was obtained as a function of the two parameters: and . In addition, a relationship of the Fe2B layer thickness was also deduced that showed a good concordance with the experimental results from the literature.