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What Is Ductile Iron?

Manhole covers are made from ductile iron.
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  • Written By: Lori Kilchermann
  • Edited By: Lauren Fritsky
  • Last Modified Date: 21 September 2014
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Ductile iron is a type of cast iron that has superior strength when compared to common cast iron. Often called nodular iron or ductile cast iron, the key in the strength comes from the addition of spherical graphite into the cast-iron mixture. The graphite allows for a more flexible and elastic iron, which resists breaking and cracking far greater than the common cast-iron materials. Carbon, silicone and manganese are all components of ductile iron and are used to give the iron its strength. Often used in automobiles and machinery when more strength is required than aluminum can produce and solid steel is not needed, ductile iron is a strong and affordable option.

In automotive use, ductile iron is commonly used in high-performance rear gear and cylinder sleeve applications. In the case of the rear-end gear case, the common name for the high-performance unit is a nodular case. This stems from the term nodular iron, which is based on the nodular graphite particles that give ductile iron its strength. When used in cylinder wall sleeves, ductile iron produces a cylinder that is strong enough to contain the extreme pressures generated by a racing engine. The material makeup of the ductile sleeves also promotes increased ring seal and better compression and oil control.

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Due to the increased strength of the cylinder sleeves, installing sleeves into an engine block can actually increase the strength of the block. This was not always the case, and as such, sleeving an engine block used to carry a certain misconception that the block was somehow inferior to a non-sleeved unit. Advances in metallurgy and machining process and techniques have replaced that school of thought among knowledgeable racers and engine builders. The majority of the most powerful engines in the world, the nitro-methane burning drag racing engines, feature replaceable ductile iron cylinder sleeves.

In a manufacturing application, ductile iron is easily drilled and tapped, producing threaded holes that do not strip out easily when a fastener is torqued in place. The corrosion resistance of ductile iron pipe makes it a better choice than gray iron pipe for waterlines as well as valve assemblies. This is also the preferred pipe of many plumbers when the terrain is not optimal for plastic pipe. Manhole covers are also manufactured from the ductile material due to its tremendous strength and durability. The iron alloy is well-suited to high-heat applications.

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