An indispensable tool to choose the suitable process parameters for obtaining boride layer of an adequate thickness is the modeling of the boriding kinetics. In this work, two mathematical approaches were used in order to determine the value of activation energy in the Fe2B layers on ASTM A36 steel during the iron powder-pack boriding in the temperature range of 1123–1273 K for treatment times between 2 and 8 h. The first approach was based on the mass balance equation at the interface (Fe2B/substrate) and the solution of Fick’s second law under steady state (without time dependent). The second approach was based on the same mathematical principles as the first approach for one-dimensional analysis under non-steady-state condition. The measurements of the thickness (Fe2B), for different temperatures of boriding, were used for calculations. As a result, the boron activation energy for the ASTM A36 steel was estimated as 161 kJ·mol−1. This value of energy was compared between both models and with other literature data. The Fe2B layers grown on ASTM A36 steel were characterized by use of the following experimental techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray Spectroscopy (EDS). Finally, the experimental value of Fe2B layer’s thickness obtained at 1123 K with an exposure time of 2.5 h was compared with the predicted thicknesses by using these two approaches. A good concordance was achieved between the experimental data and the simulated results.

In this work, American Iron and Steel Institute (AISI) O1 steel was pack borided in the temperature range of 1123-1273 K for treatment times between 2 and 8 hours. A kinetic model was proposed for estimating the boron diffusion coefficients through the Fe 2 B layers. As a result, the boron activation energy for the AISI O1 steel was estimated as 197?2 kJ mol 21 . This value of energy was compared to the literature data. In addtion, to extend the validity of the present model, two additional boriding conditions were done. The Fe 2 B layers grown on AISI O1 steel were characterised by use of the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and Daimler-Benz Rockwell-C indentation technique. Finally, the scratch and pin on disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions.

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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.

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The nitriding of iron and steel is of considerable technological importance, because it can make a pronounced improvement in the fatigue, the wear, and the corrosion resistance of these materials. Nitriding on the surface of ferrous alloys results in the formation of a compound layer of γ´-Fe4N1-x and ɛ-Fe3N nitrides or a mixture of γ´ and ɛ with a nitrogen diffusion zone beneath the nitride layer. The broad range of nitride layer properties needed for different applications requires good control of nitriding process [1-3]. In the powder-pack nitriding process, which is similar to the powder-pack carburizing process, samples are placed in an annealing box with a powder mixture that consists of nitrogen-rich material and an activator. The nitriding temperatures are between 723 K and 823 K, a range in which the nitriding potential is a function of the mount of activator used in the powder mixture. The powder-pack method is a low-cost process particularly suited for the formation of uniform nitride layers on structural alloy components with complex shapes and of various sizes [4-5]. In this study, the microstructure of the γ´-Fe4N1-x and ɛ-Fe3N layers formed on an ARMCO pure iron surface have been investigated at different temperatures by the powder-pack process.