page contents

Heat Treatment Process-Definition,Purpose And Types

Heat Treatment 

Heat Treatment Process


  • Heat treatment process is defined as an operation involving the heating of sample to suitable temperature, followed by cooling at different rate(fast ,moderate & slow).
  • Heat treatment process is a series of operations involving the Heating and Cooling of metals in the solid state.
  • It is very important manufacturing process that can not only help the manufacturing process but can also improve the product, it’s performance , and it’s characteristics .

Purpose of Heat Treatment

  • Increase the mechanical properties of materials.
  • Relief the internal stress.
  • To change the structure and size of grain.
  • Improve mach-inability.

Types of Heat Treatment Process

  1. Annealing (Furnace cool)
  2. Normalising(Air cool)
  3. Hardening
  4. Tempering
  5. Case Hardening

1. Annealing (Furnace cool)

  • Annealing is a heat treatment process which involves the heating of steel sample above critical temperature(727 degree) and holding it there for about 1 hours so that their complete austenization take place.
  • Then, it allow to cool slowly in the furnace.
  • It is also known as Furnace cooling process.

Benefits of Annealing

  1. To improve the ductility of the sample.
  2. It enhances the mach-inability of the sample.
  3. It reduces the internal resting force (internal stress).

2. Normalising

  • Normalising is a process which is similar to annealing process. Here ,the specimen is heating beyond the upper -critical limit temperature(227-912)degree while lower critical temperature(227)degree and cool in open air.
  • In this process,the rate of cooling will be more as compare to annealing process.
  • The strength of sample as well as its mach inability is enhance.

3. Hardening

  • In this process, steel is cooling in water and oil baths.
  • The rate of cooling is very fast as compare to annealing and normalising process.
  • The hardness of a metal is directly proportional to the uni-axial yield stress at the location of the imposed strain.
  • It reduces the mach inability of the sample.

4. Tempering

  • This process is using to increase the mach inability of harden steel.
  • In this process,sample is heating below the lower critical temperature(227)degree and holding it for some time and then cooling it slowly.
  • The process has the effect of toughening by lessening brittleness and reducing internal stresses.

5. Case Hardening

  • It is also known as chemical heat treatment process.
  • In this process,steel surface is processing by the addition of carbon.

    Types of Case Hardening

  1. Carburizing
  2. Nitriding
  3. Cyaniding
  4. Induction hardening
  5. Flame hardening

A. Carburizing

  • In this process,steel is heating in contact with charcoal,wood.
  • After heating it will be followed by rapid cooling.

B. Nitriding

  • Nitriding is a heat treatment process in which steel will heating in atmosphere of ammonia gas(NH3) at the temperature(1|2-1|3) carburizing process.
  • At this temperature NH3 gas dissociate in nascent nitrogen and hydrogen.
  • After this nitrogen will get diffused into steel in form of nit-rides.

Advantages of Nitriding

  • High fatigue life.
  • High hardness than carburised and hardened components.
  • Better corrosion resistance than carburised and hardened components.

Disadvantages of Nitriding

  • No heat treatment can be done after nitriding.
  • White layer.
  • Thin case depth.

C. Cyaniding

  • Cyaniding is a process in which steel sample is heated in atmosphere of sodium cyanide.
  • Both carbon and nitrogen will get diffused into steel sample.
  •  The nitrides are form during heating and cyanides are form during cooling.

D. Induction Hardening

  • This process is applicable to high carbon steel.
  • In this process,steel sample is heating to red hot condition by induction hardening.
  • Then steel sample is quenching into water.

Advantages of Induction Hardening

  • Increase fatigue strength.
  • Localized areas can be heat treated.
  • Low operating costs.
  • May be incorporate into cell manufacture.

Disadvantages of Induction Hardening

  • High capital investment.
  • Only certain steels can be induction hardened.

D. Flame Hardening

  • Flame hardening is a surface hardening method that involves heating a metal with a high temperature flame,followed by quenching.
  • It is used on medium carbon, mild or alloy steels or cast iron to produce a hard, wear-resistant surface.

 Benefits of Flame hardening

  • Increase wear resistance.
  • Reduce processing time.
  • To reduce cost by hardening only selective areas.
  • Less distortion.
  • Ability to use low to medium carbon steels.

 Thanks for reading. If the articles help you then please spread your love and don’t forget to share it on social network’s.

Leave a Reply

Your email address will not be published. Required fields are marked *