Contact fatigue resistance of austempered and partially chilled ductile irons

This study reports the results of laboratory tests carried out to evaluate the rolling contact fatigue (RCF) resistance of ductile iron with different treatments. Tests were conducted in a flat washer type RCF apparatus, at loading and lubricating conditions leading to the interaction of surface microasperities, i.e. with specific oil film thickness, λ<1. The microstructures evaluated correspond to different austempered ductile iron (ADI) grades, obtained at different austempering temperatures, and one variant of a partially chilled ductile iron (PCDI). The ADI variants have shown the highest RCF resistance for the lowest austempering temperature evaluated. The PCDI samples, in the as-cast condition, have shown the highest RCF resistance among the different ductile iron variants evaluated. It was observed that nodules play an important role on the nucleation stage of the failure process, and also the reduced nodule size of the PCDI could be responsible for its high RCF life.