Forging Heat Treatment Process – Hardening for Open and Closed Die Forgings


Hardening process performs on tools and important parts of some heavy duty machineries; it also performs on every machinery part of steel alloys. Hardening process immediately follows by tempering process. This process does for following reasons.

(1) To increase friction resistance.
(2) To increase strength, elasticity, tensile stress and toughness.

In this process steel has to heat at the point above the critical temperature and maintain the part on this temperature for very long time. For quick cooling part has to quench in bath of water, oil or liquid salt. Hypoeutectoid steel has to heat at 30 0C to 40 0 more than AC3 temperature and hypereutectoid steel has to heat at C 30 0C to 40 0C more than AC1 temperature. Here AC3 is upper critical temperature and AC1 is lower critical temperature.
For hardening alloy steel and high speed steel it heated till 1100 0C to 1300 0C and cooled through air flow. Alloy steel element’s stability gains better austenite does not converts in marten site.

Following requirements has to consider for good hardening process.

  • Content of carbon elements and alloys.
  • Homogenity of austenite.
  • Grain size of austenite.
  • Rate and time of heating.
  • State of quenching.
  • Rate of quenching.
  • Size and mass of a part.
  • Condition of surface.

Hardening process is performs for following purposes:

  • To increase hardness of steel.
  • To make tools and machine parts useful for heavy duties.
  • To increase friction resistance.
  • To make tool able to cut another material.
  • To increase strength, toughness and ductility of steel.


     In case hardening-Carbon elements at the surface layer take to very higher percentage this process calls case hardening. The deep till the carbon percentage could found higher calls case depth.  Gets hard surface but remaining core of a part remains with original mechanical properties after this process. This process name suggests that it is a process to harden outer surface (case) then inner surface (core).

     This process is important to make the parts which needs tough core, hard surface anfriction resistant like cam, change over switch, shaft, drive worm, brake drum and gears.

Benefits of Surface Hardening & Case Hardening are as follows:

  • Very less heating time.
  • No scaling and no cracks generation on part.
  • Possibility of change in shape due to heat treatment is very rare.
  • This is an automatic process.
  • Material gains property of friction resistance.
  • Fatigue limit increases.
  • This process doesn’t harm surface finish.
  • Impact strength increases.
  • We can use cheap materials to make parts.
  • Price of equipment is cheaper.
  • This process is simple.
  • This process can perform on long parts too.
  • It is very suitable process for mass production of medium size parts.


Various types of surface hardening and case hardening processes:

  • Induction Hardening.
    Flame Hardening.


Various types of surface hardening and case hardening processes:
In induction hardening-Parts has to put between the induction coil and current of proper frequency passes through inductor coil. At that time magnetic lines passes through part and AC current induces. As a result of these parts get heating due to hysteresis loses. This induce current circulates over parts surface. Induction hardening can do on the parts having 0.35 to 0.55% carbons.
Parts heated by electrical induction heating in this process. High frequency induction current used for the process is generates with help of motor generator set and spark gap oscillator or tube oscillator. Frequency is around 1000 to 10000 cycle per second. We can get frequency of 100000 to 400000 cycles per second with help of gap oscillator.

Cam shaft, Gears, Axles, Automobile Forgings and Tractor parts and some parts having friction are harden by induction hardening process.

Hardening Heat Treatment Process by Emerson forge

In flame hardening- The part heating with the help of gas torch and then quenching and gets friction resistance layer on tough core. This process performs over steel having 0.4 % to 0.6 % carbon elements. Surface heating process perform by oxy acetylene flame till acquired more than AC3 (Upper critical) temperature and fast quenching. We can harden some required surfaces of big parts too. This is an advantage of this process. We cannot maintain proper temperature is disadvantage of this process. Part can be damage or have crack due to overheating is also disadvantage of this process.

So, up till now we detailed Forging Heat Treatment Process with Annealing Heat Treatment Process, Normalizing Heat Treatment Process, Tempering Heat Treatment Process and Hardening Heat Treatment Process.

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 Heat Treatment Process for Open and Closed Die Forgings

Forging Heat Treatment Process – Annealing

Forging Heat Treatment Process – Normalising

Forging Heat Treatment Process – Tempering

Forging Heat Treatment Process – Hardening


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