Diffusion model and characterization of Fe2B 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 1123-1273 K. Validation of the model was made by comparing the experimental Fe2B layer thickness with the predicted value for the borided sample at 1253 K during 5 h. In addition, the generated boride layers were analyzed 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.