The finished product can have some internal stresses or uneven properties. The solution lies in reheating. The product is reheated under controlled conditions.. After heating, the part is cooled at specific rates. Well, it gives the desired strength and toughness to the steel part.
Common heat treatment processes include:
Annealing: Annealing can soften the material, which makes the machining easier. Moreover, it improves the ductility of the metal.
Normalising: To enhance the uniform strength and refine the grain structure, normalising is preferred.
Quenching and Tempering: To make the metal further hard, it is cooled rapidly, which is called quenching. And, if you want to reduce the brittleness of the metal, tempering is the right technique.
You can understand it with the example that automotive crankshafts are quenched and tempered, so that they can handle constant stress without cracking.
