Kinetics and Boron Diffusion in the FeB/Fe2B Layers Formed at the Surface of Borided High-Alloy Steel

In the present study, boron diffusion in the surface layers of AISI M2 borided steels and the growth kinetics of the FeB/Fe2B layers were estimated. The boriding of AISI M2 steel was performed according to the powder-pack method and was conducted at 1173-1323 K and at various exposure times. As a result of the boriding process, the diffusion-controlled growth of the FeB/Fe2B layers was obtained at the surface of the high-alloy steel, and the kinetics of the growth process changed parabolically over time. The boron diffusion coefficients were estimated by solving two simultaneous equations based on the limits of the boron concentration in each layer, the boride incubation time, and the parabolic growth constant. With the proposed diffusion model, an expression, which describes the evolution of the FeB/Fe2B layers, was obtained. Moreover, the proposed model and diverse empirical models presented in the literature provided a good fit to the experimental data obtained for 10 h of exposure and different boriding temperatures.