Heat Treatment Process
Heat Treatment Process are as follows:-
Annealing is a process of heating the steel slowly to a temperature of 800 degree celsius to 1000 degree celsius and then holding it for sufficient time so it is unable the internal changes to take place and then pulling it in slow rate while cooling the heated steel is taken out of the furnish and embedded in stand .
The main objective of annealing are as given below :
(a) To soften the metal.
(b) To increase ductility.
(c) To improve machine ability.
(d) To improve or refine grain size.
(e) To remove entrapped air formed during varies metallurgical work.
The types of annealing are as given below :
(i) Full annealing
(ii) Iso-thermal annealing
(iii) Sub-critical annealing
( iv) Spheroidization annealing
It is a process of heating the steel approximately 4 degree celsius above the critical temperature follow by cooling below this range in steel air.
The objective of normalization are as given below :
-> To reduce internal stresses.
-> To remove course grain structure obtain during forging,rolling etc.
-> To increase the strain of steel.
-> To achieve desire result in mechanical and electrical properties.
The steel produce by this treatment is harder and stronger but less ductile then annealed steel having the same composition.
Quenching is the process of heat treatment in which process of steel is heated above it’s upper critical temperature and alloy to pull rapidly by plunging it into the liquid bath.This formed extremely hard niddle shape structure known as martensitie. In other word,in sudden quenching of steel greatly increases it’s hardness in clear cold water,salty water or oil is used as quenching media to obtain desire hardness.
Martensite structure formed by direct quenching of steel are hard and strong but also brittle which can’t be plastically deformed and have very little toughness.Also,they are unable to resist impact load.So some of hardness and strain most be scarified to obtain by tempering martensite steel.Tempering process increase toughness,decrease hardness,relieve the stress.The process include heating quench in martensite condition to some predetermine between room temperature and critical temperature of steel followed by air cooling.
5) Surface hardening
It is specific process of heat treatment in which only the outer part of produced is made extra hard while inner parts remain soft.The process involve heating the process above the critical temperature for 1 to 8 hours and then plunged into the cold water.This result in a hard outer surface all throw inner part or the core remain soft.
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