New As-Cast Ductile Iron Raises Bar for Properties

Ductile iron has a wide range of mechanical properties, depending on its metallic matrix. The material can replace cast and forged steel in a large number of applications due to its combination of high strength and toughness, in addition to lower density.

Because of this, the search for new ductile iron alloys with improved mechanical properties and lowered production costs is an important research field. The ductile iron with the highest resistance/ductility rate is austempered ductile iron (ADI), which gets its superior properties from its microstructure. This microstructure, called «ausferritic,» is different than that of conventional irons. Fine grains of ferrite yield high strength, and the distribution of austenite and ferrite together make ADI more ductile and tougher than conventional irons.

ADI achieves its microstructure through a heat treatment process called austempering. This is a well-established method, and ADI parts have replaced hundreds of steel forgings and fabrications in production volume levels.

As a secondary operation, austempering adds cost and time to casting production. Researchers are investigating a new process to achieve castings with the same microstructure as ADI (ausferritic) without heat treatment. In this process, engineered cooling is used to coerce the metal to form the desirable ausferritic microstructure. For end-users, it could mean lower cost, high strength parts with shorter lead times.