Ferrous metals all contain some proportion of iron. It is very difficult to obtain absolutely pure iron in commercial quantities, but iron of a high purity is very ductile, of fairly low tensile strength(154 N/mm2) and resists rust formation. Other substances such as carbon, manganese, silicon, sulphur, phosphorus, nickel and molybdenum may be added to iron, and will have considerable effects on the properties of the resulting material. However, it is not intended to discuss here the various methods of manufacture of these materials or their internal structure. The aim is to give an indication of the general properties of the more common materials with indication of their main fields of application.