| The main stages |
| The main steps in making steel are shown on the left. You can find more information about each step by clicking on it. In this section we’ll summarise the chemistry that is important in changing iron ore into steel.
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| Reactivity of metals |
| Iron is a moderately reactive metal which joins readily with non-metals such as oxygen. This is why we do not find pure iron in the Earth’s crust. Instead it is found as an ore, in which iron is chemically combined with oxygen or other non-metals. Most workable iron ores are rich in iron (III) oxide, Fe2O3. Making iron by removing oxygen from the ore is the first step in the manufacture of steel.
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| Reduction and oxidation |
| Removing oxygen chemically from a substance is called reduction. The industrial production of iron involves reducing iron (III) oxide in a Blast Furnace. Most of the iron (III) oxide is reduced using carbon monoxide gas. This gas is a reducing agent which takes the oxygen away from iron (III) oxide. | | | | | | | | iron (III) oxide | + | carbon monoxide |  | iron | + | carbon dioxide |  | | Fe2O3(s) | + | 3 CO(g) | | 2 Fe(l) | + | 3 CO2(g) |
Notice that carbon monoxide gas in this reaction is changing into carbon dioxide. We call this oxidation, because each molecule of carbon monoxide gains an oxygen atom. The overall process is a redox reaction, in which iron (III) oxide is reduced and carbon monoxide is oxidised.
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| Another redox reaction |
| Not all the iron (III) oxide is reduced by carbon monoxide in this way. Between 20% and 30% of the iron is produced by direct reduction, when the ore is directly reduced by carbon. | | | | | | | | iron (III) oxide | + | carbon | | iron | + | carbon monoxide | | | Fe2O3(s) | + | 3 C(g) | | 2 Fe(l) | + | 3 CO(g) |
In this reaction unburned carbon, not carbon monoxide, is the reducing agent. This carbon is oxidised to form carbon monoxide. |
| Oxidising iron |
| Iron is a moderately reactive metal and is easily changed back into its oxide. This is what happens during rusting. This everyday reaction affects most kinds of iron and steel. Steels are usually treated in some way during their manufacture to slow down the rate at which rusting takes place.
Iron is changed into steel by blowing oxygen through the molten metal from the Blast Furnace. This oxidises the impurities in the molten metal. |
