Evolution of microstructure and mechanical properties under different austempering holding time of cast Fe–1.5Si–1.5Mn–V steels

The present investigation was carried out to examine the influence of austempering holding time on the microstructure and mechanical properties of low carbon, high silicon cast steels. Austempering treatment was carried out at a temperature of 400 °C with varying holding time from 10 to 60 min. The austempered microstructure showed the presence of bainite and retained austenite. The high carbon retained austenite was identified by X-ray diffraction and confirmed by transmission electron microscopy (TEM) analysis. It is observed that ultimate tensile strength (UTS) increased but percentage of elongation (%El) decreased with increasing austempering time. Increase in austempering time changed the morphology of bainite from fine to coarse lath. The carbide was formed when austempering time increased from 30 min to 60 min and resulted in decrease in ductility but increase in strength. The best combination of strength and ductility was observed at 400 °C austempering temperature and 10–30 min holding time. The fracture surface showed that dimple could not grow with increasing holding time and formation of carbide resulting in decreased ductility with increased holding time.