Pig iron is an intermediate product obtained during the smelting of iron ore using high-carbon fuel, such as coke, charcoal or anthracite. In addition to iron, pig iron consists of varying amounts of phosphorus, sulfur, manganese, silicon, and carbon. Its high carbon content makes it brittle and, hence, it is used for very limited applications. Gray iron can be produced from pig iron by remelting pig iron, removing undesirable contaminants, adding alloys, and adjusting the carbon content.
The traditional method of casting iron using a blast furnace involves arranging molds in sand beds, such that the mold could be fed from a common runner. The shape of the molds is a branching structure formed in sand, with several ingots at right angles to a runner. This configuration resembles a litter of suckling pigs, hence the term “pig iron”. With the cooling and hardening of the cast iron metal, the smaller ingots, referred to as the pigs, are simply broken from the thinner runner, referred to as the sow.
Types of Pig Iron
Pig iron is classified into the following three grades, based on the chemical composition:
- Ferro-alloys – These alloys of pig iron have high proportion of iron content, and are used as additives in iron and steel industries to control the properties of iron and steel
- Foundry pig iron – These alloys consist of 3 to 4.5% of carbon, 0.5 to 3.5% of silicon, 0.4 to 1.25% of manganese, and varying amounts of sulfur, phosphorus, and iron. They are mainly used in the production of iron castings
- Basic pig iron – Carbon content of this type varies from 3.5 to 4.4%, phosphorus is usually less than 1%, and manganese ranges from 1 to 2%. This type of pig iron is low in sulfur, which is an active impurity in steel. It is widely used in the steel-making process and manufacture of refractory linings