According to American Society of Material Testing, it is defined as the process in which iron base alloys are heated 40 to 50°C above the upper transformation range and held there for a specified period and followed by cooling in still air at room temperature.
The heating of hypo-eutectoid as well as hyper-eutectoid steel is done above the upper critical temperature. The normalised steel consists of ferrite and pearlite for hypo-eutectoid, and pearlite and cementite for hyper-eutectoid steel.
The parts on which normalising treatment is carried out are:
(a) Normalising is generally carried out on large castings and forgings as it is cheap process. It is also applied to low and medium carbon steel parts.
(b) It is frequently applied as the final heat-treatment process on items which are subjected to relatively high stresses.
The objects of normalising are:
(1) To eliminate coarse grain structure obtained during forging, rolling and stamping.
(2) To increase the strength of medium carbon steel.
(3) To improve the machinability of low carbon steel.
(4) To improve the structure of welds.
(5) To reduce internal stresses.
(6) To achieve desired results in machanical and electrical properties.
The parts subjected to normalising treatment have higher yield strength, ultimate tensile strength and impact strength but ductility is somewhat reduced.