DIFFERENCE BETWEEN COLD AND HOT WORKING PROCESS EXPLAINED !!

The metal working processes are divided into hot working and cold working processes. The division is on the basis of the amount of heating applied to the metal before applying the mechanical force.Re-crystallization temperature is defined as the approximate minimum temperature at which complete re-crystallization of a cold work metal occurs with in a specified time.

In other words,The lowest level of heat at which the distorted grain structure of a metal is replaced by a strain-free grain structure.

HOT WORKING PROCESS:-

• Hot working is carried out above the recrystallization temperature and below the melting point. Hence the deformation of metal and recovery take place simultaneously.
• No internal or residual stresses are set-up in the metal in hot working process.
• If cracks and blow boles are present in the metal, they can be finished through hot working.
• Close tolerance can not be maintained.
• Surface finish of hot working process is comparatively not good.
• It results in improvements of properties like impact strength and elongation.
• Due to recrystallisation very negligible hardening of metal takes place.

COLD WORKING PROCESS:-

• Cold working is carried out below the recrystallization temperature. As such, there is no appreciable recovery.
• In cold working process internal or residual stresses are set-up in the metal.
• In cold working the existing cracks propagate and new cracks may develop.
• Better tolerance can be easily maintained.
• Surface finish of cold working process is better.
• It also results in improvements of properties like impact strength and elongation.
• It improves ultimate tensile strength, hardness, yield strength but reduces the corrosion resistance of strength of the metal.
• The stress required to cause deformation is much higher.