Induction heating allows the treating of a particular area of the part, so as to obtain surface hardening localised in particular zones. In fact, most induction hardening operations are superficial. This surface treatment is obtained by controlling the power applied, the frequency of the inductor current and the heating and cooling times. The treatment can be done in two different ways: either static or progressive (by scanning).

Static treatment consists of setting the part in front of the inductor and carrying out the operation without moving either the part or the inductor. This type of operation is very fast, requires only simple mechanics and enables a very accurate localisation of the treated area, even with parts with complicated geometry.

The scanning treatment consists of going over the part with a continuous operation, moving either the part or the inductor. This kind of operation means that parts with large surfaces to be treated and large sizes can be processed with lower powers.

The traditional tempering system consists of heating the parts at relatively low temperatures (from 150 to 700ºC) for a time normally a little over an hour and leaving these to cool slowly.

Induction tempering lies in obtaining the same or very similar metallurgical effects to the ones acquired by tempering in a conventional furnace but at higher temperatures and for shorter time.

The tempering temperatures normally used in induction are from 200 to 400ºC.

Heating times for induction tempering are closely connected with the part’s geometry. It is highly important for the whole area to be tempered to be at the same temperature. Consequently, in parts with a simple geometry, the tempering times tend to be lower than those of more complicated parts.

At the end of the induction heating process, the part is normally cooled in air until its temperature drops to about 100ºC. Under this temperature the tempering process is complete. Then cooling tends to be speeded up by means of quenching or immersion in a liquid.