Pure iron is soft and easily shaped. This is because its atoms are arranged in a regular way that lets layers of atoms slide over each other. Pure iron is too soft for many uses.
Iron from the blast furnace is an alloy of about 96 per cent iron together with carbon and some other impurities. It is hard, but too brittle for most uses. So, most iron from the blast furnace is converted into steel by removing some of the carbon.
Carbon is removed by blowing oxygen into the molten metal. The oxygen reacts with the carbon producing carbon monoxide and carbon dioxide. These escape from the molten metal. Enough oxygen is used to produce steel with the desired carbon content. Often, other metals are often added, such as vanadium and chromium.
There are many different types of steel, depending on the other elements mixed with the iron. The table below summarises the properties of some different steels.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science