Pig iron

Pig iron is the immediate product of smelting iron ore with coke and limestone in a blast furnace. Pig iron has a very high carbon content, typically 3.5%, which makes it very brittle and not useful directly as a material except for limited applications.

Pig iron is typically poured directly out of the bottom of the blast furnace through a trough into a ladle car for transfer to the steel plant in liquid form, referred to as "hot metal." The hot metal is then charged into a steel-making vessel to produce steel, typically with an electric arc 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 Bessemer Process, open hearth furnace, finery forge, and the puddling furnace.

The traditional shape of the molds used for these ingots was a branching structure formed in sand, with many individual ingots at right angles to a central channel or runner. Such a configuration is similar in appearance to a litter of piglets suckling on a sow. When the metal had cooled and hardened, the smaller ingots (the pigs) were simply broken from the much thinner runner (the sow), hence the name pig iron. As pig iron is intended for remelting, the uneven size of the ingots and inclusion of small amounts of sand was insignificant compared to the ease of casting and of handling.

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.

Cast iron is made by remelting pig iron, often along with substantial quantities of scrap iron, and removing undesirable contaminants, adding alloys, and adjusting the carbon content.

The Chinese were making pig iron by the later Zhou Dynasty (1122 BC - 256 BC). In Europe, the process did not become common until the 14th century.

Additional recommended knowledge

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Refining

Pig iron is melted and a strong current of air is directed over it while it is being stirred or agitated. This causes the dissolved impurities (such as silicon) to be thoroughly oxidized (and thus released into the atmosphere). The metal is then cast into molds or used in other processes. This is known as refined pig iron, finers metal or refined iron.^[1]

Popular References

• The Lehigh Valley IronPigs, a AAA-level Minor league baseball team based in Allentown, Pennsylvania and affiliated with the Philadelphia Phillies, is named for pig iron. Allentown and its surrounding Lehigh Valley region of Pennsylvania have historically been a major manufacturing site for steel.
• Episode 7 of the spoof science BBC television show Look Around You showed pig iron as being manufactured by specially-trained pigs.
• In Leadbelly's song, "Rock Island Line" the train conductor was actually transporting Pig Iron, not livestock.
• In the 1977 Clint Eastwood movie "The Gauntlet", Pat Hingle refers to the armour Eastwood has attached to a bus as pig iron.
• Brazil's Carajas region in the Amazon is one of the world's major pig iron exporting centers, with exports of around 6 million tonnes per year. The Carajas region has a total of 1,500 charcoal works, according to the ICC.
• In Episode 4 Series 4 of the Channel Four comedy Peep Show, Jez admonishes his old fashioned flatmate Mark by saying: "We don't make steam engines out of pig iron in this country any more, yeah?"
• In Eoin Colfer's novel "The Supernaturalist", pig iron is the major building material of the corrupt and decaying Satellite City.
• In the computer role-playing game Ultima VIII, pig iron is used as a reagent in sorcery rituals.
• Australian Prime Minister Sir Robert Menzies was given the nickname 'Pig Iron Bob' after breaking a strike to ensure its export to Japan in the 1930's.

See also

• Steelmaking
• Wrought iron

References