Kinetics of Formation of Fe2B Layers on AISI S1 Steel

Abstract

In the present work, the AISI S1 steel was pack-borided in the temperature range 1123-1273 K for 2-8 h to form a compact layer of Fe 2 B at the material surface. A recent kinetic approach, based on the integral method, was proposed to estimate the boron diffusion coefficients in the Fe 2 B layers formed on AISI S1 steel in the temperature range 1123-1273 K. In this model, the boron profile concentration in the Fe 2 B layer is described by a polynomial form based on the Goodman's method. As a main result, the value of activation energy for boron diffusion in AISI S1 steel was estimated as 199.15 kJmol-1 by the integral method and compared with the values available in the literature. Three extra boriding conditions were used to extend the validity of the kinetic model based on the integral method as well as other diffusion models. An experimental validation was made by comparing the values of Fe 2 B layers' thicknesses with those predicted by different diffusion models. Finally, an iso-thickness diagram was proposed for describing the evolution of Fe 2 B layer thickness as a function of boriding parameters.

Analysis of the growth kinetics of Fe2B layers by the integral method

“…C 0 is the solubility limit of boron within the material substrate which can be neglected (0 wt.%) [29,30]. The following assumptions considered during the establishment of diffusion model can be found elsewhere [23][24][25].…”

“…This resulting DAE system can be solved either analytically [23][24][25] or numerically [32].To get the expression of boron diffusion coefficients in Fe 2 B, an analytic solution exists for this diffusion problem by setting: (11) and by choosing the expressions for a(t) and b(t) as :…”

“…After substitution of Equations (11), (12) and 13into Equation 7and derivation with respect to the time, Equation (19) was deduced [23][24][25]. This last equation allows us to calculate the value of boron diffusion coefficient in Fe 2 B at the considered boriding temperature.…”

“…In the current study, an alternative diffusion model [23][24][25] using the integral method was applied to determine the boron diffusivity in the Fe 2 B layers on the Armco iron substrate in the range of 1123 to 1273 K.…”

Boriding Kinetics of FeB and Fe2B Layers on AISI M2 Steel by the Integral Diffusion Model

“…The two ordinary differential equations given by Equations (18) and (19) are obtained from the integration of Second Fick's law between the two limits 0 and u(t) for FeB, and between u(t) and v(t) for Fe2B.…”