A Diffusion Model for the Fe₂B Layers Formed on a Ductile Cast Iron

Abstract

In this work, a diffusion model was applied to estimate the boron diffusion coefficients in the Fe2B layers on the ASTM A-536 ductile iron in the temperature range 1173-1273 K by the powder-pack boriding. The mass balance equation at the (Fe2B/substrate) interface was formulated considering the effect of boride incubation times. As a result, the value of activation energy for boron diffusion in the ductile iron was estimated and compared with the literature. To verify the validity of the present model, the experimental Fe2B layer thickness obtained at 1173 K for 10 h was compared to the predicted value. A good concordance was observed between the predicted value of Fe2B layer thickness and the experimental data.

Characterization and Boronizing Kinetics of EN-GJL-250 Lamellar Gray Cast Iron

“…The three time-dependent unknowns a(t), b(t) and u(t) are subjected to the boundary conditions given by Eqns. 2and (3). Eq.…”

“…(13) was obtained from the graph displayed in Figure 6 by a linear fitting of data with a coefficient of determination close to unity. In Table 3 are gathered the values of activation energies for boron diffusion in some pack-borided cast irons [3,6,11,25] with the value of activation energy for boron diffusion in EN-GJL-250 lamellar gray cast iron estimated in this work. The found value of activation energy for boron diffusion (=163.86 kJ mol -1 ) is required to overcome the energetic barrier allowing the diffusion of boron atoms inside the material substrate.…”

“…The boriding process requires high temperatures to be carried out (between 800 and 1050°C) and a treatment time from 0.5 to 10 h. Various methods of boriding can be found in the literature. Among them, the powder pack-boriding as the frequently used method, owing to its simplicity and cost effectiveness [2,3]. For instance, Sen et al [4] have used the liquid boriding (in salts bath) to produce the boride layers on GGG-80 ductile cast iron and investigate the wear behaviour.…”

Simulation of the incubation time for the formation of (FeB/Fe2B) bilayer on pure iron

“…In a recent work, published by Keddam et al [19], a kinetic model has been proposed to study the growth kinetics of FeB and Fe 2 B layers on AISI D2 steel where the effect of diffusion annealing process was taken into account. Keddam et al [20] suggested another approach to investigate the boronizing kinetics of a cast iron by using a different mathematical model. Some of these models are developed without considering the presence of incubation times of borided layer.…”

Application of integral method for investigating the boriding kinetics of AISI 316 steel

“…For these reasons, the modeling of boriding kinetics is crucial for optimizing the desired boride layer thickness that matches the practical utilization of borided steels at industrial scale. To reach this objective, several studies were devoted in the literature for modeling the boriding kinetics of ferrous alloys: (Armco iron [3][4][5][6], steels [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and cast irons [25][26][27][28]) by using different approaches.…”