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Ductile Iron Castings

Cast iron is an alloy of iron, carbon and silicon with carbon levels of about 3.2% and silicon at about 2.2%. If molten cast iron is allowed to cool normally the carbon forms flakes of graphite which run through the iron matrix, hence the term flake graphite iron. These flakes are at the microscopic level, the ends of which form stress points in the cast iron. 

Ductile Iron Castings & Ductile Cast Iron

If cast iron is subject to a compressive load, these stress points are not particularly detrimental and flake graphite cast iron is excellent under compression. However, tensile loading above the natural tensile strength of the cast iron can cause rapid tensile failure as cracks propagate rapidly out from these stress points. The result of this is that cast iron has virtually no elongation, is a brittle material and is therefore limited in its use in tensile and shock loading applications. For years foundrymen and metallurgists tried to develop a new type of cast iron that would withstand bending and shock loading and would have the characteristics more of malleable cast iron but could be produced at the lower cost of grey cast iron. This resulted in the development of Ductile Cast Iron. Call Durham Foundry on 0114 249 4977 to discuss your Ductile Iron Castings and Ductile Cast Iron project.

Ductile Cast Iron At Durham Foundry

At Durham Foundry we have been producing ductile iron castings since the early 1960’s and were one of the first jobbing foundries in the UK to do so. As well as ductile iron castings, our customer base also covers grey iron 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 moulders can work from complex loose pattern equipment, particularly where low volumes are required, whilst our moulding 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 ductile iron castings and continue to be so.

All our ductile iron castings are produced to the current ISO material specification, ISO 1083 2004, along with any further certification which a customer may require. Durham Foundry is accredited with ISO9001 & ISO14001 management systems to ensure the highest quality in ductile casting production.

Ductile Iron Castings & Ductile Cast Iron Applications

Our diverse customer base has also given us experience in a wide range of applications for 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.

The History Of Ductile Cast Iron

In 1943, at the International Nickel Company Research Laboratory, Keith Dwight Millis made a ladle addition of magnesium (as a copper-magnesium alloy) to cast iron – the solidified castings contained not flakes, but nearly perfect spheres of graphite. Ductile iron was born. The advantage of ductile iron is that the spheres of graphite don’t act as stress raisers but as crack arresters and are what give ductile iron its ductility.

This new form of cast iron immediately found uses where malleable iron, forgings, cast steel or steel fabrications would have been used. From this start, ductile cast iron has grown into a world class material offering cast solutions at a competitive price compared to traditional alternatives.

Ductile Cast Iron Production

At Durham Foundry we produce our ductile iron by the addition magnesium, in the form of ferro silicon magnesium, to the melt as it is tapped from the furnace to the casting ladle. The magnesium is used to remove as much sulphur from the molten metal as possible in the form of magnesium sulphide. In a normal grey iron, sulphur is controlled at a level of about 0.06 to 0.08%. Sulphur is a surface active material, which means it tends to come out of solution at surface boundaries during the cooling process. In cast iron these boundaries are between the graphite and the ferrite/pearlite matrix.

The presence of sulphur at these boundaries also lowers the surface tension of the graphite as it comes out of solution which allows it to form an irregular shape, in this case flakes. By removing the sulphur from the molten metal the graphite forms with a much higher surface tension which “pulls” the graphite into a tighter shape, in this case a sphere.

Ductile Cast Iron Properties

Ductile iron can be alloyed with small amounts of copper to produce increasingly stronger irons as the copper levels are increased. These copper alloyed ductile irons can also be heat treated, being particularly suited to induction and flame hardening. With the addition of nickel up to 30% and chrome at smaller levels a range of austenitic ductile irons can be produced which have improved properties at elevated temperatures and in aggressive atmospheres and environments.

One area of potential confusion is the number of ways ductile iron is described. All of the following are used and are interchangeable – Ductile Iron, Ductile Cast Iron, SG, SG Iron, Spheroidal Graphite and Spheroidal Graphite Cast Iron.

Please browse our website for more information about Durham Foundry and our ability to manufacture Ductile Iron Castings & Ductile Cast Iron then contact us on 0114 249 4977 or e-mail us on castings@durhamfoundry.com or visit our dedicated website www.ductilecastiron.com for more information.

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