The History and Develpment of ADI
Austempering is an isothermal heat treatment process, which allows good control of the transformation process and leaves the part free from residual stress, distortion and cracking, often associated with conventional quenching techniques.
The austempering process was first discovered by Bain et al in 1933. Initially, it was applied to steel and produced an acicular microstructure (now known as Bainite), which gave superior mechanical properties, compared with conventionally quenched and tempered steel.
In 1937, the austempering process was applied to grey cast iron. Although the mechanical properties were enhanced, the full potential was not realised due to the limiting factor of the graphite shape.
Shortly after discovery of Spheroidal Graphite Iron (or Ductile Iron as it is now more commonly known), the first documented reference to what we now call ADI, was made by von Hummel in Germany, in 1951.
However, it was not until 1972 that the first ADI part was produced commercially. This was a small (0.4 Kg) crankshaft for a compressor, which remained in continuous production for over twenty years.
In the mid 1970s, General Motors announced that ADI would replace case carburised, forged steel for the manufacture of crown wheel and pinion gears for a range of vehicles. This decision followed nine years of development and six years of field-testing in taxicabs.
During the 1980s, research work in the UK, Japan and the USA continued to provide more data for design engineers and in 1989 the American Society for Testing Materials (ASTM) published the first specification for ADI, which contained five grades. This standard (A 897) was revised in 2003.
The first European Standard, EN 1564, was published in 1997, which covered four grades. Details of the mechanical properties can be viewed here.
By the 1990s, ADI components were being used for numerous applications worldwide and total output exceeded 100,000 tonnes by the end of the century. Rapid growth has continued as customers appreciate the excellent combination of mechanical properties and the commercial advantages of this material.
Anticipated growth in ADI throughout the world.
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