MADI™: Introducing a New, Machinable, Austempered Ductile Iron

A unique combination of metal chemistry and heat treatment has lead to the invention of MADI (machinable austempered ductile iron). Two MADI grades have been developed: chassis grade for fatigue critical applications and crankshaft grade for high strength applications. The mechanical properties, fatigue life of components and quantitative machinability data of MADI, regular ADI and pearlitic ductile iron are presented. Since the design strength of MADI is 50-100% higher than currently used as-cast ductile irons, significantly lighter weight components can now be produced. MADI may lead the way to the increased use of low cost, ductile iron castings since, for the first time, both improved mechanical properties (fatigue resistance or high strength) and improved machinability have been obtained.