Normalizing is a heat treatment process used to increase the toughness of steels. It involves heating steel to a temperature above its critical point, soaking, then air cooling to produce a finer grain structure. This refines the grain size and relieves internal stresses to improve toughness while making the steel harder and stronger compared to annealing. The objective is to counter the effects of processes like casting or rolling and enhance properties for the steel's intended use.
2. Aim
• The aim of normalizing is to increase the
toughness of steels.
3. Objective of Normalizing
• The objective of the treatment is to counter
the effects of prior processes, such as
casting, forging or rolling into one which
enhances toughness or, in certain product
forms, meets final mechanical property
requirements by
– Refining the existing non-uniform structure
– Relieving internal stresses
– Refining the grain size and
– Improving toughness.
4. Normalizing
• Normalizing consists of heating a suitable steel
to a temperature 50-1000 C above Ae3
temperature in case of hypoeutectoid steels
and above Acm temperature in case of hyper-
eutectoid steel, soaking for sufficient time and
then cooling in still air.
5. Fe-Fe3C Phase Diagram Indicating Heat Treating Temperature
Ranges for Plain Carbon Steel
7. Normalizing
• Average transformation temperature during
cooling is lower in normalizing compared to
annealing resulting in finer grains in
normalizing compared to annealing.
• Therefore normalised steels are harder and
stronger than annealed steels.
8. Normalising
• Heating is usually carried out in air, so
subsequent machining or surface finishing is
required to remove scale or decarburised
layers.
• Normalising is a type of heat treatment
applicable to ferrous metals only.
• In many cases, it is the last treatment given to
steel before it is put to use.
9. Normalising of cold worked steel
• Cold working and casting are manufacturing processes
that produce grain structures that may require
normalising before the component is put into service.
• Normalizing relieves internal stresses caused by cold
work.
• The resultant fine grain structure after normalizing is
stress free and the mechanical properties generally
show a decrease in hardness, improved ductility and
increased overall toughness, i.e. impact strength
compared to cold work state.
10. Advantages
• Grain growth is limited by the relatively high cooling
rate therefore the strength, and hardness of a
normalized steel are better than in an annealed steel.
• For example, a normalised 0.4%C steel will have a
tensile strength of 580 MPa compared to an annealed
steel of 510 MPa. Its ductility will be 27% compared to
30%, and its hardness will be 165 BHN compared to
145 BHN. That is, the normalised steel will be stronger,
and harder, but slightly less ductile than the annealed
steel.
• Quality of surface after machining of a normalized part
is also better than in an annealed part.
11. Limitation
• Since the cooling rate in a steel part may be
different at different depths during
normalizing, the resulting structure is
dependent on the thickness of the steel part.
