Kinetics of V(N,C) coating produced by a duplex surface treatment

A duplex surface treatment has been developed involving the pre-nitrocarburising of annealed DIN 1.2367 die steel followed by vanadium thermo-reactive diffusion (TRD) coating and then hard and temper treatment. TRD process performed by pack method at 1223, 1323 and 1423 K for 1–5 h in an electrical resistance furnace. The TRD process formed a thin (5 to 40 µm) and hard (2220 ± 40 HV) vanadium carbonitride surface layer above a hardened diffusion zone. Characterization of the coating by means of microstructure and X-ray diffraction analysis indicates that the vanadium carbonitride coating consists of V–C–N, V–C and V–N phases which produced a single, undifferentiated layer. Moreover, the results showed a parabolic relationship (d2 = Kt) between carbonitride layer thickness (d) and treatment time (t). The mean activation energy for the TRD process was estimated to be 145.5 kJ/mol and the growth rate constant (K) changed between 4.16 × 10− 10 to 1.02 × 10− 9 cm2/s depending on the process temperature.