Normalising
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Normalizing is a heat treatment process that increases the toughness of steels. It involves heating steel above a certain temperature, soaking, then air cooling to refine the grain structure, relieve internal stresses, and improve toughness. Normalizing produces a finer grain structure and stronger, harder steel compared to annealing, though it is slightly less ductile. It is commonly the last heat treatment applied before use to enhance the mechanical properties of steels.
Normalising
- 1. NORMALIZING
- 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 hypereutectoid 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.
- 12. THANKS