History of Ductile Iron
In the past 400 years cast iron has been used in every conceivable situation where strength and corrosion resistance were needed. From manhole covers to fire hydrants, water pipe, sewer pipe, bridges and buildings, cast iron has weathered the elements and has survived the test of time. The oldest operating cast iron water main is in Versailles, France and was installed in 1664. In North American alone, there are more than 500 municipalities with cast iron pipe that has been in service for more than 100 years. With hundreds of years of underground and above ground service, cast iron is well-known for its longevity and durability.
Ductile iron, which was first used in the 1960's, continues this excellent record of underground and above ground service. Ductile iron is only different from cast iron in its ability to bend without breaking. Ductile iron contains the same ingredients as cast iron. The difference is not the quantity of carbon, but the configuration of the carbon molecules. In cast iron, carbon is in flake form, while in ductile iron, the carbon is in nodular form.
The Science of Ductile Iron
Ductile iron is produced by adding magnesium alloy to a molten iron of low phosphorous and low sulfur content. The magnesium alloy addition produces a remarkable change in the microstructure by causing the carbon in the iron to assume a spheroidal or nodular shape, compared to the flake form of graphite in gray cast iron, and at the same time producing a finer grained iron matrix in the surrounding ferrite structure. As a result of this remarkable change, a far stronger, tougher, and ductile material is obtained.
Ductile iron has excellent mechanical and corrosion resistant properties. It can be formed, machined and heat treated for use in a wide variety of structural applications. Its history of service is unmatched by any other material. It is for these reasons that ductile iron is the material of choice for utility poles in the future.