Forms/Classification of Iron
Based on the varying percentages of carbon, iron is broadly classified into the following:
1. Pig iron:
Pig iron is the product of smelting iron ore. It contains up to 5% carbon. This carbon content is quite high and it makes the pig iron hard and brittle, and thus difficult to work with.
Consequently, pig iron is not very useful in technology for fabrication purposes. However, pig iron is refined to produce other forms of iron such as cast iron, wrought iron, steel, etc.
2. Cast iron:
This is produced by refining pig iron in a furnace called cupola. it contains 2% to 5% of carbon.
The pig iron scraps and some limestone are put in the furnace and burnt together with coke fire. The molten pig iron is then put into moulds to form either white cast iron (in form of iron carbide) or grey cast iron (in form of graphite)
Cast iron is brittle, and can easily break if given a hard blow.
3. Wrought iron:
This is produced by removing the impurities that come with the pig iron. As it melts in the furnace, it is stirred with a puddling pole so that the carbon content escapes as carbon II oxide gas. Wrought iron has fibrous nature. It is able to withstand sudden shock. It can resist corrosion. It is used for making couplings, chains, gates, railings, etc.
Steel is a strong metal that is made up of a mixture of iron and carbon. Steel is the product obtained when the carbon content of pig iron is reduced to 2% or less.
To make steel from pig iron, the excess carbon in the pig iron is reduced by a process known as oxidation and other impurities burnt out. This means that carbon is made to combine with oxygen and is blown off as slag. Then the amount of carbon needed for a particular grade of steel is now added, and the steel is produced.
There are different types of steel based on carbon content. They are;
1. Low Carbon or Mild Steel: Low carbon steel contains 0.05% to 0.3% carbon. Mild steel is ductile, highly formable, and can be used for automobile body parts, plates, and wire products.
2. Medium Carbon Steel: Medium carbon steel contains 0.3% to 0.6% carbon. They are also produced from pig iron in an open furnace. They could be black or white.
3. High Carbon Steel: High carbon steel contains 0.6% to 1.5% carbon. This is harder than mild or medium carbon steel, because it contains a higher carbon content.
4. Tool Steel: Tool steel contains carbon content between 0.7% and 1.5%. The strength of steel depends on the quantity of carbon it contains. When the carbon content of steel is increased beyond 0.8%, it means it can be hardened by heating. It is also called cast steel. It is produced by a high induction furnace.
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