ESTIMATION OF THE BORON DIFFUSION COEFFICIENTS IN FeB AND Fe_2B LAYERS DURING THE PACK-BORIDING OF A HIGH-ALLOY STEEL

摘要

In this work we propose a diffusion model to estimate the boron diffusion coefficients in FeB and Fe_2B layers during the pack-boriding of AISI M2 steel in the temperature range 1173-1323 K for a treatment time of 4-8 h. The proposed model is based on the mass-balance equations at the two growth fronts - FeB/Fe_2B and Fe_2B/substrate - under certain assumptions. The estimated values of the boron activation energies in the FeB and Fe_2B layers were compared with the literature data. The present model was extended to predict the thickness of each boride layer for the borided samples at different temperatures for 10 h. Iso-thickness diagrams were established to be used as a tool for predicting the thickness of each boride layer as a function of the two parameters: temperature and time. Finally, a simple equation was proposed to estimate the required time to obtain a single Fe_2B layer by diffusion annealing.