Production and properties of iron and steel

Before proceeding to a study of iron and steel it will be well to understand how they are produced.

Iron is found in the natural form as iron ores. These ores are of four main types:

1. (1) Haematite, red or brown Fe2O3, containing 40–60% iron.

2. (2) Magnetite or magnetic oxide of iron, Fe3O4, containing up to 70% iron.

3. (3) Limonite, a hydrated ore, Fe2O3·3H2O, containing 20–50% iron.

4. (4) Siderite, a carbonate, FeCO3, with iron content 20–30%.

Limonite and siderite are termed lean ores since they are so low in iron. The ore found in England in Lincolnshire, Northamptonshire, Leicestershire and Oxfordshire is one of low iron content and is generally obtained by opencast working.

Iron ore, as mined, contains appreciable amounts of earthy waste material known as gangue, and if this were fed into the furnace with the ore, more fuel would be consumed to heat it up and it would reduce the furnace capacity. Ores are washed, or magnetically separated in the case of the magnetic ores, to remove much of this waste material. They are roasted or calcined to drive off the moisture and carbon dioxide and to remove some of the sulphur by oxidation to sulphur dioxide, and crushed to bring the lumps to a more uniform size.