Abstract
Martensitic stainless steels are much more considered using in many applications relating high loading and wear. A boride layer on martensitic stainless steel is generally accepted against wear and oxidation occurred during services. Boronizing processes, salt bath and powder pack, were performed on a martensitic stainless steel AISI 420 at a temperature range of 1123–1223 K with boronizing time up to 9 h. Boride layer thicknesses were measured using an optical microscope with an image analyzer program. An X-ray diffraction (XRD) and a scanning electron microscope with energy dispersive X-ray spectroscopy (SEM–EDS) were performed to characterize the boride layers. Kinetics of boronizing processes was analyzed using diffusion and Arrhenius equations. Activation energies and empirical data of the boronizing processes will be determined. It was found that the thicknesses of the boride layers increase with increasing boronizing temperature and time taking into account diffusion theory. Activation energies of 233.5 and 185.2 kJ mol^–1 were determined and discussed for martensitic stainless steel AISI 420 boride in a salt bath and powder pack, respectively. Finally, empirical relationships of boride thickness as a function of boronizing temperature and time are presented.

Key words
thermochemical surface treatment, boronizing process, stainless steel, diffusion, kinetics

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