| Austempered Ductile Iron (ADI) is produced by heat-treating Ductile (Nodular) Iron using the austempering Process, (as exemplified in A.5), a specialized, isothermal heat treatment. When compared to conventional ductile iron, ADI can have over twice the strength for a given level of ductility. ADI can have fatigue strength comparable to that of cast and forged steels and that strength can be greatly enhanced by subsequent grinding, fillet rolling or shot peening. Although the first commercial application of ADI did not occur until 1972, the material has found applications in virtually every industrial market segment. Its principal attribute is its ability to replace steel forgings, castings and weldments at equal or lesser weight and at a reduced cost. It is also typically much less costly than aluminum and, with its high strength-to-weight ratio it has replaced cast aluminum parts at equal weight in some automotive applications. The ausferrite matrix in ADI undergoes a strain transformation hardening when exposed to a high normal force. That effect makes machining of ADI challenging, but knowledge of this effect allows the machinist to adjust the feeds, speeds and tool angles to adequately compensate. This same strain transformation hardening is what gives ADI wear resistance better than its bulk hardness would indicate. Other attributes of the material include, good noise dampening, fracture toughness and low temperature properties, and reasonable stiffness. Applications
AD750 is a more readily machinable grade of ADI. It has tensile and fatigue strengths that are slightly lower than that of grade AD900, but may be an economical alternative for parts that require extensive machining AFTER austempering. Information provided by Applied Process Inc. |
