1. HEAT TREATMENT PROCESS
Joshi Mayur

2. What is heat treatment?
Heat treatment is a stage in the fabrication of structure and is often forgotten; but it has perhaps more wide- reaching and important ramifications than many of the other stages in the fabrication of structures or components.

3. Classification of heat treatment process
Annealing
Normalising
Hardening
Tempering
Martempering
Austempering

4. Heat Treating Processes

5. Annealing Definition :-
Annealing is the primary process of heating a metal which is in a metastable or distorted structural state, to a temperature which will remove the instability or distortion and then cooling is so that the room temperature structure is stable or strain free.

6. Process annealing
Process annealing is usually subcritical annealing and is applied to remove the effects of cold work , to soften and permit further cold work as in sheet and wire industries.
Ferrous alloy are heated to
a temperature close to but below the lower limit of the transformation rang °C are held at that temperature.
Fig are shows temperature for various heat treating process.

7. Purpose of Annealing Inducing a completely stable structure.
Refining and homogenising the structure.
Reducing hardness.
Improving machinability.
Producing desired microstructure.
Removing gases.

8. Normalizing
Normalizing is a technique used to provide uniformity in grain size and composition throughout an alloy. The term is often used for ferrous alloys that have been austenitized and then cooled in open air.
Normalizing not only produces pearlite , but also bainite sometimes martensite , which gives harder and stronger steel, but with less ductility for the same composition than full annealing.

9. Purpose of Normalizing
Produces a uniform structure.
Reduces internal stresses.
Improving structures.
Produces a harder and stronger steel than full annealing.

10. Hardening(by quenching)
Quenching is a process of cooling a metal at a rapid rate. This is most often done to produce a martensite transformation. In ferrous alloys, this will often produce a harder metal, while non-ferrous alloys will usually become softer than normal.
To harden by quenching, a metal (usually steel or cast iron) must be heated above the upper critical temperature and then quickly cooled

11. Tempering
Tempering may also be performed on normalized steels. Other methods of tempering consist of quenching to a specific temperature, which is above the martensite start temperature, and then holding it there until pure bainite can form or internal stresses can be relieved.
Tempering colors of steel

12. Purpose of tempering Relieve residual stresses. Improving ductility.
Improving toughness.
Reduces hardness.
Increase elongation.

13. Differential hardening
Flame hardening
Induction hardening
Case hardening
Cold and cryogenic treating

14. Case hardening
Case hardening is a thermochemical diffusion process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal.
The resulting interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing toughness

15. Purpose of case hardening
Improve corrosion , heat or wear resistance.
Rebuild worn or undersized parts.
Serve as an ornamental finish.