Modelling the Boronizing Kinetics in AISI 316 Stainless Steel

This work deals with the simulation of the growth kinetics of the $(FeB//Fe_2B)$ bilayer and the diffusion zone on a substrate of AISI 316 stainless steel exposed to the powder-pack boriding process, in the temperature range of 1123-1273 K and a time duration ranging from 2 to 10 h. The developed diffusion model employs a set of mass balance equations at the three growth fronts: [$(FeB//Fe_2B),$ (FeB/diffusion zone) and (diffusion zone/substrate)] under certain assumptions, including the effect of the incubation times during the formation of iron borides and the diffusion zone. For this purpose, a computer code written in Matlab (version 6.5) was created to simulate the boriding kinetics. A good concordance was obtained when comparing the experimental parabolic growth constants taken from the literature and the simulated values of the parabolic growth constants: ($k_{FeB},$ $k_1$ and $k_2$). Moreover, the present model was also used to predict the thicknesses of the $FeB$ and $Fe_2B$ layers and the diffusion zone thickness at various treatment times and boriding temperatures. The simulated values were in good agreement with the experimental borided layers thicknesses.