Transformation Behavior in Austempering Nodular Iron

Abstract

Interest in austempered bainitic ductile irons has increased dramatically in the past few years as more and more successful applications are being reported. The remarkable combination of properties attainable has caused this material to emerge as a new class of ductile iron. Austempered ductile irons achieve strength levels as high as twice those of standard ductile iron grades at the same level of toughness and ductility, see Figure 1. In addition they respond to work-hardening treatments at the surface and thus have exceptionally high bending fatigue strength and wear resistance. These good properties are directly related to the unique bainite-austenite microstructure produced by austempering.