Diffusion model and characterisation of Fe_{2B layers on AISI 1018 steel

An approach was suggested to study the kinetics of formation of Fe2B layers grown at the surface of AISI 1018 steel by the pack-boriding process. The kinetic model considered the principle of mass conservation at the (Fe2B/substrate) interface to evaluate the boron diffusion coefficient of Fe2B in the temperature range of 1,123-1,273 K. Validation of the model was made by comparing the experimental Fe2B layer thickness with the predicted value for the borided sample at 1,253 K during 5 h. In addition, the generated boride layers were analysed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis. Finally, a contour diagram describing the evolution of Fe2B layer thickness as a function of treatment time and temperature was also proposed. Finally, the boron activation energy for AISI 1018 steel was estimated as 159.3 kJ mol−1 basing on our experimental results.