D2 is an air-hardening tool steel and due to its high chromium content provides very good protection against wear and oxidation, especially at elevated temperatures. Boriding of D2 steel can further enhance its surface mechanical and tribological properties. Unfortunately, it has been very difficult to achieve a very dense and uniformly thick boride layers on D2 steel using traditional boriding processes. In an attempt to overcome such a deficiency, we explored the suitability and potential usefulness of electrochemical boriding for achieving thick and hard boride layers on this tool steel in a molten borax electrolyte at 850, 900, 950 and 1000 degrees C for durations ranging from 15 min to 1 h. The microstructural characterization and phase analysis of the resultant boride layers were performed using optical, scanning electron microscopy and X-ray diffraction methods. Our studies have confirmed that a single phase Fe(2)B layer or a composite layer consisting of FeB+Fe(2)B is feasible on the surface of D2 steel depending on the length of boriding time. The boride layers formed after shorter durations (i.e., 15 min) mainly consisted of Fe(2)B phase and was about 30 mu m thick. The thickness of the layer formed in 60 min was about 60 mu m and composed mainly of FeB and Fe(2)B. The cross sectional micro-hardness values of the boride layers varied between 14 and 22 GPa, depending on the phase composition. Published by Elsevier B.V.