Why Carbon is used in making of steel?

Because it works as a hardening agent. So, basically the impurity of Carbon in Iron stops the dislocation of the Iron atoms in the lattice from sliding past one another. The amount of this impurity is used to control the hardness, ductility and tensile strength.

  • The Steel which has Carbon as alloy is called “Carbon Steel”. The Steel which has Non-carbon alloy is called “Alloy 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 till 16th century.
  • 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%). So it is Brittle, Non-malleable and used only in limited applications.
  • Iron alloy which has impurity more than 2.1% but less than the Pig Iron is called “Cast Iron“. They are mostly brittle but there are Malleable Cast Irons. The Cast Iron because of more impurities has a lower melting point.
  • Historically cast Iron has been used in “Bridge making” all over the word. The famous “Iron Bridge” of England is made up of Cast Iron.
  • “Wrought iron” has very low carbon content. It is also known as “Slag‘. 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 iss considered to be commercially pure. The “Eiffel Tower ” is made up of Wrought Iron.
  • Following table compares the Pig Iron, Carbon Steel and Wrought Iron.