Pig iron

Pig iron is a very important material used by the iron industry to make steel. It is created by heating iron ore in a special building called a blast furnace. This process is known as smelting.

Pig iron contains a lot of carbon, usually between 3.8% and 4.7%, along with silica and other waste materials. Because of this, pig iron is very hard and not easy to shape. This means it can't be used directly to make most things, except for a few special uses.

Even though pig iron isn't perfect, it is a key step in making steel, which is used in many everyday objects like buildings, cars, and appliances.

Etymology

The name "pig iron" comes from the way the metal was shaped when it cooled. Workers made molds in sand that looked like a litter of baby pigs, with a main channel like a mother pig and smaller channels for the piglets. After the metal hardened, they broke the smaller pieces (the "pigs") from the main piece (the "sow"). This made it easier to handle and melt the metal again later.

History

See also: Ferrous metallurgy

People in China were making pig iron a long time ago, during the later Zhou dynasty, which ended in 256 BC. In Europe, places like Lapphyttan in Sweden and some areas in the County of Mark, now part of Westphalia, Germany, had furnaces as early as the 12th and 13th centuries. It is not clear if these European methods came from China or were discovered separately.

Making pig iron needed special furnaces and strong materials to handle very high heat, more than 1538°C, which is the temperature iron melts at. Before the Middle Ages in Europe, people made a type of iron called wrought iron in smaller furnaces called bloomeries, but they avoided making pig iron because it was too hard to work with. Turning pig iron into steel was very difficult with old methods, so the small pieces of pig iron were usually thrown away with waste material.

Uses

Traditionally, pig iron was changed into wrought iron using special furnaces. Later, it was turned into steel. In these processes, pig iron is melted, and air is blown over it to remove impurities like silicon.

Pig iron can also be used to make gray iron. This is done by melting pig iron together with steel and old iron pieces, removing unwanted materials, and adjusting the amount of carbon. Special types of pig iron can be used to make ductile iron, depending on the quality needed.

In the past, pig iron was poured from the bottom of a blast furnace into a container for transport to a steel mill. This hot liquid pig iron was then used to make steel in special furnaces where extra carbon was removed.

Today, steel factories and iron plants either use the molten iron right away or pour it into smaller pieces for later use. Modern machines create small pieces of pig iron that break into 4–10-kilogram (9–22 lb) chunks when they come out.