MICROSTRUCTURE AND MECHANICAL PROPERTIES OF PM STEELS ALLOYED WITH SILICON AND VANADIUM

The effects of silicon and vanadium additions on the mechanical properties and microstructures of PM alloy steels have been investigated. It has been demonstrated that the addition of these two elements increases the strength in both the sintered and heat-treated conditions. With a pearlitic microstructure, silicon strengthens the pearlite by solid-solution strengthening of the ferrite while vanadium increases the strength of the pearlite by precipitation hardening of the ferrite. In addition, vanadium limits grain growth during austentitizing prior to oil quenching. By limiting austenite grain growth, the precipitates result in significant improvement in both strength and ductility. The effects of silicon and vanadium on hardenability were investigated by performing Jominy end-quench tests and metallographic analysis. The addition of silicon and vanadium to high-carbon (>0.8 w/o) PM steels suppresses the formation of grain-boundary carbides, which permits carbon levels that are higher than those commonly used for commercial PM applications.