Difference between Flame and Induction Hardening

 Difference between Flame and Induction Hardening

Flame hardening and induction hardening methods have the same purpose of obtaining hard and wear surface whilst the core remains soft. The main difference between them is in the manner or the mode of heating.


In the induction hardening high frequency current of about 1000 to 10000 cycles per is passed through a copper inductor block which acts as a primary coil of the transformer. Heating by high frequency current is accomplished by the thermal effect of the current induced in the article being heated in this process. This way 750°C to 800°C temperature is obtained in the metal. Now, the heated surface is quenched by the water. In the flame hardening process, the metal surface is heated by means of oxy-acetylene flame. Heating is carried for sufficient time so as to raise the temperature of the portion of the surface of the specimen above the critical temperature. Then surface is cooled rapidly by spray of water.

Flame hardening method is cheaper as initial investment in this process is less in comparison to induction hardening method. However, same equipments can be used for all sizes of specimen in induction hardening process.

In induction hardening, the hardness depth is controlled very accurately by using different frequencies and a method is very clean and quick in comparison of flame hardening method.

Induction hardening method is generally used for crank shaft shafts, gears, pinions and a wide range of automobile and tractor components. Flame hardening method is generally used for local hardening of components such as hardening of gear wheel teeth only.

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