Pig iron is a metal material that results when iron ore, charcoal from coal, and limestone are melted together under intense air pressure. When the combined material cools, it forms a high-carbon product known as pig iron. The cooled material is rarely used by itself, as the large amount of carbon makes the material brittle and unstable. Usually, this type of iron is further refined through additional melting and blending processes to create wrought iron, cast iron, or steel.
It is not clear when pig iron first became known in human technology, but some experts believe that it was first used in China around the 11th century BCE. Chinese smiths are believed to have built cannons and weapons out of this form of iron, while also using it for decorative arts such as statues and figurines. Although the use of iron was also common throughout Europe from around the same time, the refining techniques used to make pig iron and resulting alloys may not have spread throughout Europe until many centuries later.
The name for this material comes from an early processing technique. When the hot melted ore was poured out of the blast furnace, it ran into a long tray, called a runner, with several smaller inlets off a main branch. The runner and its small offshoots were said to resemble a sow and piglets, hence the rise of the common name, pig iron.
Many iron products begin with pig iron. Wrought iron was once one of the most formidable building materials in the world, used as the frame of structures like the Eiffel Tower. Today, true wrought iron is rarely available, due to the superior capabilities and strength of steel. To create wrought iron from pig iron, the alloy is remelted and combined with metal oxides that leech away some of the carbon, making the resulting alloy more usable and less brittle.
Cast iron is another type of alloy that can be refined from the initial material. Cast iron is stronger and less breakable than the initial material, thanks to a process that removes carbon, sulfur, and other elements while adding desirable characteristics thanks to melted scrap metal and steel. Once popular as bridge and building material, cast iron is also used to create pots and pans that withstand and distribute high heat evenly.
Pig iron is often used as an intermediary step in creating steel. There are several different ways to get steel from the initial iron product, but all focus on significantly reducing the amount of impurities, particularly carbon, in the material. Until the development of steel, iron was a primary building material throughout the world, for everything from skyscrapers to steam engine components. Steel, which is lighter, more flexible, and stronger than iron, quickly overtook traditional forms of iron to become one of the most widely used materials in the modern world.