iron: Cast Iron

Cast iron is made when pig iron is remelted in small cupola furnaces (similar to the blast furnace in design and operation) and poured into molds to make castings. It usually contains 2% to 6% carbon. Scrap iron or steel is often added to vary the composition. Cast iron is used extensively to make machine parts, engine cylinder blocks, stoves, pipes, steam radiators, and many other products. Gray cast iron, or gray iron, is produced when the iron in the mold is cooled slowly. Part of the carbon separates out in plates in the form of graphite but remains physically mixed in the iron. Gray iron is brittle but soft and easily machined. White cast iron, or white iron, which is harder and more brittle, is made by cooling the molten iron rapidly. The carbon remains distributed throughout the iron as cementite (iron carbide, Fe₃C). A malleable cast iron can be made by annealing white iron castings in a special furnace. Some of the carbon separates from the cementite; it is much more finely divided than in gray iron. A ductile iron may be prepared by adding magnesium to the molten pig iron; when the iron is cast the carbon forms tiny spherical nodules around the magnesium. Ductile iron is strong, shock resistant, and easily machined.

Sections in this article:

• Introduction
• Wrought Iron
• Cast Iron
• Production and Refining
• Natural Occurrence
• Compounds
• Properties
• Bibliography

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