Effect of high-carbon austenite content at different niobium concentrations on the mechanical properties of austempered ductile iron

Abstract

This study explores the influence of high-carbon retained austenite content, as modulated by niobium additions and austempering time, on the hardness, wear resistance and impact toughness of ductile iron. Four alloys containing 0, 0.1, 0.2 and 0.3 wt.% niobium were austempered at a constant temperature of 350 °C for 15, 30, 60 and 90 minutes. Alloys with higher niobium contents (0.2 and 0.3%) reached their maximum retained austenite fractions at 30 minutes (40.67 and 41.98%, respectively), while peak values for the 0 and 0.1% niobium alloys were observed at 60 minutes. A clear inverse relationship was found between hardness and retained austenite content, with lower hardness values corresponding to higher austenite fractions enriched in carbon.