austempered ductile iron (ADI) is a group of ductile irons offering the design engineers remarkable mechanical properties. It exhibits an excellent combination of high strength, ductility, toughness, fatigue strength, and exceptional wear resistance that is unavailable in other grades of cast iron. Austempered ductile iron is almost twice as strong as the regular ASTM grades of ductile iron, whilst still retaining high elongation and toughness characteristics. In addition to the exceptional wear resistance and fatigue strength, it enables designers to reduce a component's weight and costs for equivalent or improved performance. Therefore, ADI has become an attractive and economic substitute for forged steel and cast steel in many engineering applications.
Austempered ductile iron (ADI) has been used since the late 1970s and significant developments have been made since then, being now possible to produce high-resistance ADIs. Among the Fe?CC alloys products, ADI presents a very interesting combination of mechanical properties. Actually, some ADIs are only surpassed by high-resistance alloyed steels when tensile strength is considered.
Replacing conventional steel parts by ADIs results in several advantages which strongly promoted the acceptance and use of these materials, namely in the automotive industry. The first economical reason to use ADIs is that the base material (nodular iron) is cheaper than steel, the second is that ADIs are casting materials, thus products can be molded, allowing significant cost reduction of the manufacturing process when compared to conventional steel machining. The heat-treatments are also low-energy consumers (austempering is done at about 300 ?C) and allowing cost-savings when compared to steel quenching or other conventional heat-treatments. ADIs are also very interesting for the automotive industry as they allow considerable weight reduction (10% lighter than steel), high vibration absorption (more than 6 dB attenuation can be achieved in a gearbox, per instance) and a very high wear and scuffing resistance, avoiding malfunctions under unpredicted unfavorable working conditions (a momentaneous failure of a lubrication system, per instance). ADIs?? tribological performance is not dependent of the presence of AW and EP additives in the lubricants, allowing the use of slightly doped oils, a major ecological benefit.