In this paper, a diffusion model is proposed for studying the bilayer growth kinetics (FeB/Fe2B) on pure iron substrate during the powder-pack boriding in the temperature range of 1023-1273 K. This model based on Fick's laws was solved, under certain assumptions, considering a parabolic growth of iron borides. For this purpose, a computer simulation program was created for predicting the boride layer thickness as a function of process parameters (temperature, time and surface boron content). A fairly good agreement was observed between the simulation calculations and experimental data derived from the literature. (c) 2005 Elsevier B.V. All rights reserved.