Normalizing: (Description 2 Marks, Purposes 2 Marks)

Normalizing is the heat treatment which involves heating of the given steel to “austenite temperature range” holding it and there after cooling to room temperature at slow rate of cooling, generally “Air cooling”.

A typical normalizing process involves following steps

1. Heating of steel: The steel, depending upon its type is heated to the normalizing temperature range. For plain carbon steel this range is,

a) Ac3 + 50 for hypo eutectoid steels.

b) Ac1 + 50 for eutectoid steel.

c) Acm + 50 for hyper eutectoid steels. For various alloy steels the normalizing temperature range is around 780 to 850 0c, depending upon the type of steels.

1. Holding of steel: The steel is kept at this normalizing temperature for some time for equalization of temperature depending upon the weight and area of steel part.

2. Cooling of steel: The steel is cooled from this normalizing temperature to room temperature with a slow rate of cooling in the “Air”. Here the austenite in the steel is transformed into the “fine pearlite structure”. The air cooling used may be still air cooling or Forced air cooling. Purposes:

• To eliminate coarse grained structure. • To reduce segregation.

• To refine grain structure.

• To produce harder and stronger steel than annealing. • To obtain required mechanical properties.

• To relieve internal stresses in some cases.