Hot working vs Cold working

What is hot working?

Metal deformation process that is carried out above the recrystallization temperature is called a hot working process.

What is cold working?

Metal deformation process that is carried out below the recrystallization temperature is called a cold working process.

Now one question arises in your mind that what is re-crystallization temperature?

The temperature at which the metal formed new stress-free grains is called the temperature of re-crystallisation.

Let us have a deep insight into the comparison between the hot and cold working process. 

Difference between hot and cold working : 

• Hot rolled components have higher toughness and ductility while cold rolled components have higher hardness and strength.
• The dimensions of cold-rolled parts are very accurate as compared to hot rolled.
• Hot-working requires expensive tools while tooling required for cold working is comparatively inexpensive.
• Hot-working reduces residual stresses in the component while cold working induces residual stresses in the component.
• Cold worked components have a better surface finish than hot rolled parts.
• In the hot working process risk of the crack is less while in the cold working risk of the crack is more.
• Internal and residual stresses are produced in the cold working process while not produced in hot working.
• Hot-working requires less energy for plastic deformation because at higher temperature metal become more ductile and soft while cold working requires more energy for plastic deformation.
• Heavy oxidation occurs during hot working so pickling is required to remove oxide while pickling is not required in cold working because no oxidation takes place in this process.
• Material is uniform after the hot working process while the material is not uniform after the cold working process.
• The cold working process can easily maintain better tolerance while hot working not. 
• Hot-working refines metal grains resulting in improved mechanical properties while most of the cold-working processes lead to distortion of grains. 
• Due to recrystallization, very negligible Harding of metal takes place in hot-working on the other hand, metal gets work hardened in cold-working. 
• The stress required for deformation is much less in case of hot-working due to higher deformation temperature and stress required is more in cold-working for deformation.