What is heat treatment?
Heat treatment process is the controlled heating or cooling of plain carbon steel or alloy steel.
Heat treatment of steel is used to change its structure in order to obtain certain mechanical properties. These mechanical properties could be hardness, strength or ductility.
Note: For heat treatment there should be some quantity of carbon in the iron.
There are basically four main types of heat treatment processes.
Types of heat treatment processes
In annealing steel is heated to a temperature which is slightly above the critical temperature, followed by slow cooling.
Annealing is used to reduce hardness and increases ductility.
Normalizing is similar to annealing, but in normalizing the heated steel is cooled in air.
Normalizing is used to remove the effect of all the previous heat treatment processes.
In quenching steel is heated to the critical temperature and then cooled rapidly in water or air.
Quenching is used to increase hardness and wear resistance. In this process steel becomes brittle and its ductility is reduced.
Tempering is reheating of quenched component to a temperature which is below transformation range, followed by cooling at a desired rate.
Tempering is used to restore ductility and reduce the brittleness due to quenching.
Selection of a suitable heat treatment process always depends on the required properties of the steel.
Featured image attribution: By Laurens Sanders – Industrial Gears Watteeuw, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=41262166