Investigation of boriding kinetics of AISI D2 steel

A diffusion model was suggested to analyse the growth kinetics of Fe2B layers formed on AISI D2 steel by the pack-boriding process. It was used to estimate the boron diffusion coefficients of Fe2B in the temperature range of 1123?1273 K by applying the mass balance equation at the (Fe2B/substrate) interface. The proposed model was validated experimentally at 1253 K for a treatment time of 5 h by comparing the experimental Fe2B layer thickness with the predicted value. Furthermore, the pack-borided AISI D2 steel was characterised by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. A contour diagram describing the evolution of Fe2B layer thickness as a function of the process variables was also proposed. In addition, the boron activation energy for AISI D2 steel was found to be equal to 201.50 kJ mol?1, on the basis of our experimental results.