Why Carbon is used in making of steel?

Steel is one of the most important materials used in construction, manufacturing and various other industries. It is made by adding certain elements to iron to improve its properties. Carbon is one of the most commonly used elements in making steel. In this article, we will discuss why carbon is used in the making of steel and the different types of iron alloys.

Carbon as a Hardening Agent

Carbon is added to iron to make it harder and stronger. The impurity of carbon in iron stops the dislocation of the iron atoms in the lattice from sliding past one another. The amount of carbon added to iron is used to control the hardness, ductility and tensile strength of steel. The steel that has carbon as an alloy is called “carbon steel”.

Types of Steel Alloys

There are different types of steel alloys based on the amount and type of alloying element added to iron. The steel that has non-carbon alloy is called “alloy steel”.

Crucible Steel

The iron which was used in earlier times using techniques in crucible is called “crucible steel”. In India, Konasamudram and Gatihosahalli were the most important sources of crucible steel until the 16th century.

Pig Iron

The immediate product of the iron alloy found in mines is “pig iron”. Pig iron has a very high carbon content (3.5-4.5%), making it brittle and non-malleable. Therefore, it is used only in limited applications.

Cast Iron

Iron alloy that has an impurity more than 2.1% but less than pig iron is called “cast iron”. Cast iron is mostly brittle, but there are malleable cast irons. Due to its high impurity content, cast iron has a lower melting point. Historically, cast iron has been used in “bridge making” all over the world. The famous “Iron Bridge” of England is made up of cast iron.

Wrought Iron

Wrought iron has very low carbon content, making it less brittle and more malleable than cast iron. When it is bent to the point of breaking, it gives texture which resembles wood. Wrought iron was earlier known as “pure iron”, but not now because now the iron, which has less than 0.008% impurity, is considered to be commercially pure. The “Eiffel Tower” is made up of wrought iron.

Comparison

The following table compares the properties of pig iron, carbon steel, and wrought iron:

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