Tempering –
The process of reheating hardened steel to some temp. below its critical range in order to decrease hardness and impart toughness is known as tempering.
Purpose :
1. To impart toughness to an already hardened steel.
2. To improve yeild point of structure steel which have already been hardened by Quenching.
Process :
1. Heating the hardened steel to a desired temperature below lower critical temp. depending upon hardness to be removed and toughness to be imparted.
2. Rapid cooling of hardened steel in water or any quenching medium as soon as the desired temperature is reached. Heating transforms some of martensite into softer constituents like trosite and rapid cooling stops further transformation of martensite into softer constituents.
Read more : Heat Treatment and its effects
