EFFECT OF COMPOSITION AND HEAT-TREATMENT PARAMETERS ON THE CHARACTERISTICS OF AUSTEMPERED DUCTILE IRONS

The discovery of Ductile Iron (DI) in 1948 provided new growth markets to the iron foundry industry. Precipitating the graphite phase as nod ules in a continuous ''pseudo-steel'' matrix provided the mechanical s trength and impact toughness lacking in gray cast irons. This new clas s of engineering materials was well suited to replace steel castings, forgings and assemblies, resulting in a North American production leve l exceeding four million tons (including pipe) of DI in 1995. This mar ket growth was concurrent with the development of a family of material s which found applications in most industrial fields. Austempered Duct ile Irons (ADI) are the most recently developed materials of the DI fa mily. By adapting the austempering treatment initially introduced for steels to DI, it has been shown that the resulting metallurgical struc tures provide properties that favorably compare to those of steel whil e taking advantage of a near-net-shape manufacturing process. The obje ctives of this paper are to review the metallurgical aspects of ADI pr oduction and to discuss the effects of chemical composition, heat trea tment variables and initial casting quality on the structure and prope rties of ADI castings. (C) 1998 Canadian Institute of Mining and Metal lurgy. Published by Elsevier Science Ltd. All rights reserved.