LAUSR

Austempered ductile irons (ADIs) have remarkable properties such as high strength with good toughness, high wear resistance and fatigue strength owing to their ausferritic microstructures as compared to conventional ductile irons. Because of unique combinations of these properties, ADIs are preferred as an engineering material in many structural applications in the automotive and defense industries and in earth-moving machinery.1–3) Ductile irons containing silicon in the range of 2.8– 4.5 wt% can be categorized as high-silicon grades. Silicon, as a ferrite-forming element, encourages the formation of a fully ferritic microstructure in high silicon ductile irons, and decreases total shrinkage during solidification as well.4) On the other hand, silicon makes a solid solution by replacing iron in the lattice, contributes to lattice distortion and finally makes dislocation motion more difficult. The mechanical properties of ADIs depend on microstructural features such as ferrite morphology, retained austenite volume fraction and the carbon content of the retained austenite. For example, lower ausferritic microstructure and higher carbon content in the retained austenite enhances fracture toughness, while optimum fracture toughness is obtained when retained austenite was around 25%.5) High fatigue strength, on the other hand, is attributed to low carbon content and high volume fraction of retained austenite due to possible transformation of low carbon retained austenite into martensite during straining.6) The magnetic properties of materials strongly depend on their microstructure, chemical composition, and heat-treatment Effect of Microstructural Features on Mechanical and Magnetic Properties of Austempered High-silicon Ductile Irons