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Austempered Ductile Iron

Austempered ductile iron, also known as ADI or ausferritic ductile iron, is the most recent addition to the ductile iron family. It is produced by giving the conventional ductile iron a special austempering heat treatment. Nearly twice as strong as pearlitic ductile iron, ADI still retains high elongation and toughness. 

About Austempered Ductile Iron Castings

ADI provides a material with superior wear resistance and fatigue strength to conventional ductile iron, cast and forged aluminum and many cast and forged steels. The mechanical properties of ductile iron and ADI are primarily determined by the metal matrix. The matrix in conventional ductile iron is a controlled mixture of pearlite and ferrite. The properties of ADI are due to its unique matrix of acicular ferrite and carbon stabilized austenite called ausferrite.

The austempering process is neither new nor novel and has been utilized since the 1930’s on a cast and wrought steels. The austempering process was first commercially applied to ductile iron in 1972 and by 1998 worldwide production was approaching 100,000 tonnes annually. All our austempered ductile iron castings are produced to the current ISO material specification, BS ISO 17804, along with any further certification that a customer requires.

Austempered Ductile Iron Castings Production

At Durham Foundry we have been producing austempered ductile iron castings for the last 30 years. As well as austempered ductile iron castings, our customer base also covers grey, ductile and alloyed irons for the engineering, decorative, architectural and artistic sectors and we can supply castings from one-off up to small to medium batch production using Alkali Phenolic resin bonded sands. Our workforce of highly skilled molders can work from complex loose pattern equipment, particularly where low volumes are required, whilst our molding line is suited for batch production. Our long trading history, coupled with an investment programme that has enabled us to keep up with modern production methods and environmental legislation has meant that we have been involved with many projects requiring austempered ductile iron castings and continue to be so.

Our diverse customer base has also given us experience in a wide range of applications for austempered ductile iron castings, including pumps and valves, forges, foundries and rolling mills, automotive and aerospace, a wide range of OEM’s, quarries and mines, railways and rolling stock, local authorities and artists and sculptors. We also have long-term trading relationships with local pattern makers, machine shops and surface finishers which enable us to quote for the complete supply of the finished casting.

Austempered Ductile Iron Castings Properties

ADI is a group of materials whose mechanical properties can be varied over a wide range by a suitable choice of heat treatment. A high austempering temperature, 750F (400°C), produces ADI with high ductility, a yield strength in the range of 500 MPa with good fatigue and impact strength. These grades of ADI also respond well to a surface strain transformation which greatly increases their bending fatigue strength. A lower transformation temperature, 500F (260°C), results in ADI with very high yield strength (1400 MPa (200 MPa)), high hardness, excellent wear resistance and contact fatigue strength. This high strength ADI has lower fatigue strength as-austempered but it can be greatly improved with the proper rolling or grinding process. Thus, through relatively simple control of the austempering conditions, ADI can be given a range of properties unequaled by any other material. Small amounts of alloying elements such as nickel, copper and molybdenum are used to produce the desired heat treated result.

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