Table of Contents
In this article we will discuss hot and cold working process of metals. First, we will learn hot working and then we will learn cold working of metals.
Before moving further let us understand concept of recrystallisation, it would be very helpful to us later.
What is recrystallisation temperature?
The temperature at which new stress-free grains are formed in a metal is known as recrystallisation temperature.
What is Hot working process?
Metal deformation process which is carried out above recrystallisation temperature is known as hot working process.
Examples of hot working processes of metals are hot rolling, hot forging, hot spinning, hot extrusion, hot drawing etc.
Advantages of hot working process
- It reduces strain hardening
- Its components have better toughness
- Its components have better ductility
- Its components have better resistance to shocks and vibrations
- Its components have better strength particularly the forged parts
- It reduces residual stress in the component
Disadvantages of hot working process
- Rapid oxidation of surface due to high temperature
- Its components have poor surface finish compared with cold rolled parts
- It requires expensive tools
What is cold working process?
Metal deformation process which is carried out below recrystallisation temperature is known as cold working process.
Examples of cold working processes of metals are cold rolling, cold forging, cold spinning, cold extrusion, cold drawing etc.
Advantages of cold working
- Its components have high hardness
- Its components have high strength
- Its components have better surface finish compared with the components made by hot working process
- Its components have high dimensional accuracy
- Tooling required is comparatively inexpensive
Disadvantages of cold working process
- It reduces toughness of components
- It reduces ductility of components
- Its components have poor resistance to shocks and vibrations
- It induces residual stress in the parts and proper heat treatment is required to relieve this stress
Comparison between hot working and cold working
| Sr. no. | Cold Working | Hot Working |
| 01 | It is carried out below recrystallisation temperature | It is carried out above recrystallisation temperature |
| 02 | Residual stresses remain after cold working | Residual stresses do not remain after cold working |
| 03 | Stress required for deformation is relatively higher | Stress required for deformation is relatively lower |
| 04 | Tooling required is relatively cheaper | Tooling required is relatively costly |
| 05 | It gives better surface finish | It gives poor surface finish |
| 06 | It gives us close tolerances | It does not gives us close tolerances |
| 07 | It may develop new cracks and propagate existing cracks | It does not develop new cracks or propagate existing cracks |
Featured image attribution: By Metoc – selftaken, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=1105603
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