Ausforming of austempered ductile iron alloyed with nickel

The unique properties of austempered ductile iron (ADI) are related to the ausferrite matrix (stable high carbon austenite with fine acicular ferrite) formed during the austempering treatment of ductile iron castings. Ausforming of ADI adds a mechanical processing component to the conventional ADI heat treatment, thus increasing the rate of ausferrite production and therefore leading to a finer and more homogeneous ausferrite product. The present study aims at exploring the potential benefits of ausforming ADI alloyed with Ni, using a rolling operation, with reduction in height up to 25%. The ausforming was introduced into the austempering schedule just after the quench but before any substantial transformation of austenite. Alloying with up to 3·0% nickel as well as varying austempering times were investigated. The kinetics of ausferrite formation was studied using both metallographic and XRD techniques. Ausforming caused a dramatic increase in tensile strength for all investigated alloys and the ductility of Ni-alloyed irons increased, while the ductility of the unalloyed ADI decreased. Ausforming also leads to an increase in both hardness and wear resistance properties.