Microstructure and properties of austempered ductile cast iron with refined graphite nodules

The present study examined the influence of refinement of graphite nodules on microstructure and tensile properties of austempered ductile cast iron (ADI). A casting technique using deoxidation treatment enabled manufacture of thin walled castings made of ductile cast iron without ledebulite. The thin walled casting (t=2 mm) was subjected to extreme refinement of graphite nodules, where the number of graphite nodules was 1750 mm(-2). Decrease in graphite nodule diameter resulted in refinement of ausferrite and gamma-pool structures in ADI and rapid reaction of austempering. The significant increase in the number of graphite nodules resulted in a remarkable drop in the tensile strength and elongation of ADI. These results can be explained by the graphite nodule distance.