AISI D2 cold work tool steel is usually used for the purpose of hardness and wear resistance. Thermo reactive diffusion coatings (TRD) treatment is usually applied to this type of tool steel to improve the surface hardness. Since the rollers made of D2 tool steels are susceptible to wear fatigue, its surface hardness is of critical importance. In first stage, a heat treatment route has been proposed for D2 tool steel which results in a combination of high hardness and toughness. For this purpose two heat treatment routes were adopted. In the first one, the preheated steel samples were held in a molten salt bath of 990 °C for a certain time followed by tempering at different temperatures. This heat treatment cycle resulted in a steel of 56 HRC and microstructure containing the primary carbides, tempered martensite, retained austenite, and transition carbides. In the second heat treatment route, the preheated samples were held in a BaCl 2 molten bath of 1070 °C for 30 minutes and then oil quenched. The two stages tempering treatment were then applied to the quenched specimens in which the samples were first tempered at 560 °C followed by tempering at 530 °C . The latter heat treatment resulted in a hardness of 60 HRC and an increase of D2 working time up to 15% in rolling mill. In the second stage, a vanadium carbide coating was applied to the D2 tool steel samples by immersion in borax liquid bath containing ferro vanadium, aluminum and boric acid. Coating process hardening heat treatment were carried out simultaneously as follows: Firstly the samples were preheated up to 500 °C and then TRD coating was performed on the samples at various temperatures for different times. Finally a specific mar-tempering treatment route was carried on the samples. The surface hardness of coated sample was evaluated as 2300-3200 HV at various positions while the hardness of the bulk was measured as (59-61) HRC. XRD analysis of coating showed that main component was vanadium carbide (V 8 C 7 ). Finally the kinetic of coating was studied based on determined rate curves. Kinetic study of Formation Coating showed that the diffusion of Carbon atoms in the Coating layer controlled the Coating process and the activation energy 114.5 kJ/mole was obtained.
