Cast iron is an alloy of iron and carbon, and is popular because of its low cost and ability to make complex structures.
The carbon content in cast iron is 3% to 4.5% by weight. Silicon and small amounts of Manganese, Sulfur, and Phosphorus are also present in it.
The products of cast iron exhibit reasonable resistance against corrosion.
The cast iron is neither malleable nor ductile, and it cannot be hardened like steel. It melts at about 2100 °F, and has either a crystalline or a granular fracture. The mechanical properties of cast iron are very much dependent on the morphology of its carbon content. Carbon is present in the form of plates in gray cast iron, whereas, it is incorporated in compound Fe3C (cementite) in white cast iron. Nodular cast iron, which show better tensile strength and strain than gray cast iron, carry carbon in the form of sphere shaped graphite particles. Following are some of the properties of cast iron.
Different varieties of cast iron are used in the construction of machines and structures. Cast iron having a tensile strength of 5 tons per square inch, or less, is of no value for the purpose where strength is required. This type may however be used for balance weights, foundation blocks, or for purposes where weight alone is of consequence. Some varieties of cast iron show a tensile strength as high as 19 tons per square inch, but on an average, the strength is 7 tons per square inch. Addition of vanadium can increase the strength of cast iron.
High Compressive Strength
Compressive strength is defined as the ability of a material to withstand forces which attempt to squeeze or compress it. Cast iron shows high compressive strength, which makes it desirable for use in columns and posts of buildings. The compressive strength of gray cast iron can be almost as high as that of some mild steels.
Resistance to Deformation
Cast iron structures show resistance to deformation and provide a rigid frame. However, if one part of the casting after the iron is poured into the molds, is very thin, and another very thick, the problem of the structure breakdown becomes prominent. The reason for this is when the thin part cools first and contracts, the thick part which cools down afterward causes stress in the thin part, offering sufficient force to break it.
Resistance to Oxidation
Rust is formed by the reaction of iron and oxygen, in the presence of water or air moisture. It leads to the corrosion of iron and its alloys, and any iron mass in presence of water and oxygen, can eventually convert into rust and later disintegrate. As cast iron offers resistance to oxidations, it provides a solution to the problem of rust.