Determination of the Diffusion Coefficients of Boron in the FeB and Fe₂B Layers Formed on AISI D2 Steel

In the present work, a diffusion model was applied to estimate the boron diffusion coefficients in the FeB and Fe₂B layers during the pack-boriding of AISI D2 steel in the temperature range of 1223-1323 K during a variable exposure time between 1 and 8 h. The mass balance equations were formulated at each growing interface by considering the effect of boride incubation times. The estimated values of boron activation energies in the FeB and Fe₂B layers were compared with the literature data. Validation of the present model was made by comparing the experimental thickness of each boride layer, taken from the literature data, with the predicted values. In addition, a simple equation was suggested to estimate the required time to obtain a single Fe₂B layer by diffusion annealing.