Steel can be given desire property by heat treatment there are three different heat treatment.
This method is done to obtain soft steel. When steel is heated to red hot (about 11000c) and then cooled & lowly, steel becomes soft and the process is called annealing. In annealed steel, carbon is present in free state.
2. Quenching or Hardening:
This process is done to obtain hard steel and brittle steel. When steel is heated to red not and then cooled rapidly by plunging into water or oil, gives hard and brittle steel and the process is called Quenching. In quenched steel, carbon is present in combined form as iron carbide (Fe3C) or Cementite.
This process is done to obtain hard and malleable steel Quenched steel is heated below red hot (about 7000c ) and then cooled slowly to obtain mild steel and the process is called tempering. In tempered steel, carbon is present in both combined and free state.