Cast iron is an iron-carbon alloy that also contains small amounts of other elements, such as manganese, silicon sulphur or phosphorus. The quantity of carbon in cast iron is generally 2.5 to 3 per cent. This saturation of carbon gives the material certain properties that can be both advantages and disadvantage. Cast iron is used in a variety of products, including cookware, engine blocks and components, pipe, ornamental metalwork and decorative objects.
According to Machine Design, the carbon content in cast iron in the form of graphite provides good machinability of the material. It counteracts the normal shrinkage of the metal casting, reduces vibration and aids lubrication on wear surfaces. Most of the carbon stays combined with the iron in the material, yet the presence of hard iron carbines on the surface provides abrasion resistance. Cast iron has a lower melting point than other metals which makes it ideal for casting. The exact chemical composition of the cast iron used in the casting process is determined by the size and shape of the end product.
Cast iron offers a good strength to weight ratio, as well as a lower cost per unit of strength compared to other materials. The addition of other chemical components can increase the strength capability of the cast iron material as needed for certain engineering designs.
The ability of cast iron to resist wear makes it good choice for engine blocks and disc brake rotor components where constant movement of parts and resulting friction are a problem for other types of metals. Both grey cast iron and white cast iron have good wear resistance, and other elements can be added to the material to increase the wear resistant properties for particular uses. Heat treating is also used to increase the wear resistance of cast iron.
According to the Cast Iron Soil Pipe Institute, cast iron is preferred around the world for draining, waste, water distribution and water vent pipe applications. Though the material initially corrodes, this layer of corrosion products is very dense and adherent, sealing the material against further corrosion. Internal corrosion of cast iron pipes can be caused by strong acids, but the rinsing action of other discharges works to counteract the corrosion
One of the disadvantages of cast iron products is the tendency to crack under certain conditions. Gray iron, one of the most commonly-used cast irons, contains graphite that makes the material easy to machine, but gives it almost no ductility, according to Esabna. Therefore, the metal breaks before any appreciable amount of stretch or elongation can occur. This means cast iron cannot be wrought or hammered like other types of metal. Welding cast iron can also be a problem because the material can crack under the heating and cooling stresses of the operation. Preheating cast iron parts to distribute the heat more widely can help to prevent this problem.