The characterization of vanadium boride coatings on AISI 8620 steel

Thermodiffusion coatings containing boron and vanadium (B+V) on AISI 8620 steel have been carried out by an initial boronizing in a salt bath consisting of borax, boric acid and ferro-silicon and followed by saturation with vanadium. The properties of the diffusion layer, namely microstructure, phase composition and elemental distribution of the vanadium boride layer, have been studied. The influence of temperature and the duration of vanadizing on the thickness of the metallized layer and its phase composition have been determined. Boronizing treatment was performed at 900 °C for 4 h. Then, the vanadizing treatment was performed by pack method in the powder mixture consisting of ferro-vanadium, ammonium chloride and alumina at 950 and 1000 °C for 1-6 h. The phases formed on the boronized steel and boro-vanadized steel are FeB and FeB, and VB and V2B3 which were confirmed by X-ray diffraction (XRD) analysis. Longer vanadizing times and the higher treatment temperatures result in thicker vanadium boride layers. The thickness of vanadium boride layer is between 3 and 25 μm as a function of treatment time and temperature. The distribution of alloying elements from the surface to the interior was determined using energy-dispersive X-ray spectroscopy (EDS).