Iron is obtained by extracting it from iron ore in a large container, called a blast furnace. The blast furnace is necessary to smelt the iron out of the ore.
Smelting is a process in which the iron ore is heated until it becomes spongy and the chemicals in the ore begin to break down. The most important part of the process is that it releases the oxygen from the ore, which makes up most of the ore. In a blast furnace, pure carbon reacts with the oxygen to form carbon monoxide. The carbon monoxide then reacts with the iron ore to form pure iron and carbon dioxide. Limestone is added to help remove impurities from the iron ore, creating what is called slag. The molten iron, also known as pig iron, is then drawn off the bottom of the furnace. The slag is less dense than the iron, so it is drawn off just above the molten iron. The pig iron was too brittle to be used for most things, so inventors started working on ways to toughen the pig iron. One of the ways pig iron is made tougher is by remelting the pig iron and burning off the remaining carbon. A blast of hot air is blown through the pig iron, which results in stronger forms of iron, cast and wrought iron. When additional elements, such as chromium and manganese, are added, steel is formed.