Formulación numérica de la difusión del boro en capas duras de boruros de hierro formadas en una configuración cilíndrica de acero AISI D2

Abstract

In this work, the growth kinetics of borided layer (FeB + Fe2B) formed at the surface of AISI D2 borided steel (with cylindrical and linear geometry) was evaluated. The powder –pack boriding process was carried out at temperatures of 1173, 1193,1223 and 1243 K with exposure times of 4, 5 and 8 h for each temperature. The growth of boride layer was established from two models that consider the mass balance equations at the layer /substrate. The models consider the parabolic law r t   l k  t to T  -  , taking into account the boride incubation time and the boron concentration profile along the surface layer. Furthermore, the boron diffusion coefficients in the boride layer were estimated for both geometrical configurations ( rtot (D ) for cylindrical geometry and ctot (D ) for linear geometry). To validate the diffusion models, the thickness of boride layer was estimated and verified experimentally for the boriding conditions of AISI D2 steels, obtained an accuracy of 2.57% error between the experimental and the theoretical depth of boride layer. Finally, it was verified that the activation energy that stimulates the boron diffusion in the boride layers is independent of the geometrical configuration, and is a function of the chemical composition of the substrate