Pig iron

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Casting pig iron, Iroquois smelter, Chicago, between 1890 and 1901.

The Chinese were making pig iron by the later Zhou Dynasty (1122–256 BC).[2] In Europe, the process was not invented until the Late Middle Ages (1325–1500).[3] Actually, the phase transition of the iron into liquid in the furnace was an avoided phenomenon, as decarburizing the pig iron into steel was an extremely tedious process using medieval technology.


Traditionally pig iron was worked into wrought iron in finery forges, later puddling furnaces, and more recently into steel.[4] In these processes, pig iron is melted and a strong current of air is directed over it while it is stirred or agitated. This causes the dissolved impurities (such as silicon) to be thoroughly oxidized. An intermediate product of puddling is known as refined pig iron, finers metal, or refined iron.[5]

Pig iron can also be used to produce gray iron. This is achieved by remelting pig iron, often along with substantial quantities of steel and scrap iron, removing undesirable contaminants, adding alloys, and adjusting the carbon content. Some pig iron grades are suitable for producing ductile iron. These are high purity pig irons and depending on the grade of ductile iron being produced these pig irons may be low in the elements silicon, manganese, sulfur and phosphorus. These types of pig irons are used to dilute all the elements in a ductile iron charge (except carbon) which may be harmful to the ductile iron process.

Modern uses[edit]

Until recently, pig iron/slag was typically poured directly out of the bottom of the blast furnace through a trough into a ladle car for transfer to the steel mill in mostly liquid form; in this state, the pig iron was referred to as hot metal. The hot metal was then poured into a steelmaking vessel to produce steel, typically with an electric arc furnace, induction furnace or basic oxygen furnace, by burning off the excess carbon in a controlled fashion and adjusting the alloy composition. Earlier processes for this included the finery forge, the puddling furnace, the Bessemer process, and the open hearth furnace.

Modern steel mills and direct-reduction iron plants transfer the molten iron to a ladle for immediate use in the steel making furnaces or cast it into pigs on a pig-casting machine for reuse or resale. Modern pig casting machines produce stick pigs, which break into smaller 4–10 kg pieces at discharge.

Pig iron was used as ballast on the NASA's Shuttle Carrier Aircraft, a modified Boeing 747 used for transporting Space Shuttle orbiters.[6]


  1. ^ Camp, James McIntyre; Francis, Charles Blaine (1920). The Making, Shaping and Treating of Steel (2nd ed. ed.). Pittsburgh: Carnegie Steel Co. p. 174. OCLC 2566055. 
  2. ^ Wagner, Donald. Iron and Steel in Ancient China. Leiden 1996: Brill Publishers
  4. ^ R. F. Tylecote, A history of metallurgy (2nd edition, Institute of Materials, London, 1992).
  6. ^ Gravel Haulers: NASA's 747 Shuttle Carriers

External links[edit]