Advances in the Metallurgy and Applications of ADI

The excellent property combination of ADI has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications with considerable cost benefits. Thanks to the extensive research efforts made over the past few years, new processing techniques have opened even more opportunities for this very prospective material to acquire better combinations of strength, ductility, toughness, wear resistance as well as machinability. This review analyses the key features of those novel processing techniques and the resulted new applications of ADI. The survey firstly discusses the possible strengthening mechanism of ADI with special emphasis on the TRIP phenomena, associated with the deformation of ADI. Strength and toughness properties could be improved through the development of: Ausformed ADI; where mechanical processing component was added to the conventional heat treatment as a driving force to accelerate the rate of stage I austempering. Squeeze cast ADI; where superior quality ADI castings were produced through squeeze casting of molten iron in a permanent mold, followed by in-situ heat treatment of the hot knocked-out castings in the austenite range followed by normal austempering in a salt bath. Two step austempering to achieve finer ausferrite at higher undercooling during austempering treatment followed by austempering at higher temperature where higher austenitic carbon is promoted. The machinability and ductility of ADI may be considerably enhanced through the development of dual phase microstructures (ferrite + ausferrite or ferrite-martensite by partial austenitization in the (? + ? + graphite) region followed by normal austempering. The abrasion resistance could be remarkably increased through the development of: Carbidic ADI-ductile iron containing carbides subsequently austempered to form ausferritic matrix with an engineered amounts of carbides Bainitic/martensitic (B/M) ADI containing less expensive alloying elements such as Si and Mn in the range of 2.5 - 3.0% This report discusses as well the recent trials to produce thin-wall ADI castings.