PEARLITE PHASE-TRANSFORMATION IN SI AND V STEEL

Systematic research has been undertaken on the effects of single and c ombined additions of vanadium and silicon on the phase transformation and microstructure of pearlitic steels. Both alloy additions were foun d to result in the formation of nonlamellar products in the vicinity o f austenite grain boundaries in hypereutectoid compositions (0.77 to 0 .95 wt pet C). The products comprise discrete initial cementite partic les and grain boundary ferrite, which is embedded with interphase prec ipitates of vanadium carbide. As the carbon content is increased furth er (up to 1.05 wt pet), the amount of grain boundary ferrite gradually decreases without any dramatic change in the morphology of the initia l cementite particles. No continuous embrittling grain boundary cement ite network was formed. The aspect ratios of the grain boundary cement ite particles were decreased from 60:1 to 25:1 by the addition of the alloy elements. A comprehensive model has been suggested to explain th ese effects. Other effects of these alloy elements on the microstructu re of pearlitic steels have also been examined. For given austenitizat ion conditions, an increase in carbon and vanadium content produced a decrease in austenite grain size. Silicon was found to increase the ra te of interphase precipitation of vanadium carbides.