The Effects of Molybdenum and Manganese on the Mechanical Properties of Austempered Ductile Iron

In this review paper an insight is given on how alloying elements and heat treatment parameters affect mechanical properties of austempered ductile irons (ADI).To elevate hardenability or austemperability of large sections, alloying is required during production of ADI. Conventional ductile iron should be enriched with certain alloying elements to obtain ADIs with desired strength and ductility. These elements must ensure that pearlite formation is avoided as well as that austenite is stabilized during the austempering heat treatment. It has been shown that both single alloying elements and also combinations of different alloying elements affect the mechanical properties of ADI. Also, it has been shown that strength, hardness, elongation and fracture toughness strongly depend on the amount of ausferritic ferrite and stable, high carbon enriched retained austenite. A combination of Ni, Cu, Mn and Mo is usually added. To increase hardenability of ductile irons,Mo should be added. Addition of Mn in ductile irons may influence tensile strength and hardenability of ADIs. During the selection of chemical composition, both for DIs and ADIs, alloying elements which negatively affect casting quality, such as formation of non-spheroidal graphite, inclusions and carbides should be limited. The standard processing window depends on the austempering parameters and alloying elements, as well as the method used to produce ADI