EFFECTS OF VANADIUM ADDITIONS ON MICROSTRUCTURE AND HARDNESS OF HYPEREUTECTOID PEARLITIC STEELS

An investigation has been carried out on the effects of vanadium addit ions on the microstructure and hardness values of hypereutectoid pearl itic steels with carbon contents up to 1.15 wt.%, for a range of isoth ermal transformation conditions. As in the case of eutectoid steels wi th vanadium additions, the predominant carbide species at the grain bo undaries is cementite, rather than vanadium carbide, even at the highe r vanadium levels (0.2 wt.%). However, the extent of the pro-eutectoid grain boundary cementite network is progressively reduced as the vana dium 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 microstru ctural investigation indicates that the cementite particles form indep endently at many different places on the grain boundary, consistent wi th vanadium addition increasing the driving force for nucleation. Vana dium additions also effectively decrease the austenite grain sizes. An increment in hardness values has been achieved because of vanadium ad ditions, which has potential to improve other mechanical properties in hypereutectoid pearlitic steels, because of these modifications in mi crostructure.