Normalising

          Normalizing is the term applied to the process of heating the steel approximately 4 above the critical temperature followed by cooling below this range in still air. This is one of the simplest treatment.

          Due to air cooling which is slightly fast as compared to furnace cooling employed in full annealing, normalised components show slightly different structure and properties than annealed components. 

• The steel produced by this treatment is harder and stronger but less ductile than annealed steel having the same composition.
• This treatment is frequently applied to castings, forgings, etc., to refine grain structure and to relieve stresses set up in previous operations.
• It is commonly applied after cold working, overheating, or any other operation resulting in non-uniform heating or cooling.

The objects of normalising are:

1. To eliminate  coarse gain structure obtained during forging, rolling, and stamping.
2. To reduce internal stresses.
3. To improve machinability of low carbon steels.
4. To increase strength of medium carbon steel.
5. To improve structure of welds.
6. To achieve desired results in mechanical and electrical properties.  

Distinction between Annealing and Normalising

ANNEALING	NORMALISING
Main purpose of annealing is to  relieve internal stresses	Main purpose of normalising is to  improve mechanical properties.
Less hardness, more T.S & Toughness	Slightly more hardness, less T.S & Toughness.
Pearlite is coarse	Pearlite is fine and usually appears  unresolved with optical microscope.
Grain size distribution is more.	Grain size distribution is less.
Internal stresses are least.	Internal stresses are slightly more.
Furnace cooling is employed.	Air cooling is employed.
Cooling rate is slow.	Cooling rate is high.
Costly and inconvenient.	Economical and more convenient.