Effects of vanadium additions on microstructure and hardness of hypereutectoid pearlitic steels

An investigation has been carried out on the effects of vanadium additions on the microstructure and hardness values of hyper-eutectoid pearlitic steels with carbon contents up to 1.15 wt.%, for a range of isothermal transformation conditions. As in the case of eutectoid steels with vanadium additions, the predominant carbide species at the grain boundaries is cementite, rather than vanadium carbide, even at the higher vanadium levels (0.2 wt.%). However, the extent of the pro-eutectoid grain boundary cementite network is progressively reduced as the vanadium content is increased, in spite of the hypereutectoid composition. According to SEM and TEM investigations, the morphology of the grain boundary carbide is less continuous in the higher vanadium alloys, and consequently less deleterious to mechanical properties. The microstructural investigation indicates that the cementite particles form independently at many different places on the grain boundary, consistent with vanadium addition increasing the driving force for nucleation. Vanadium additions also effectively decrease the austenite grain sizes. An increment in hardness values has been achieved because of vanadium additions, which has potential to improve other mechanical properties in hypereutectoid pearlitic steels, because of these modifications in microstructure.