Induction heat treatment

Heating a metal by holding it in an alternating electric field which induces an electric current in it.

A medium-frequency or high-frequency alternating current is passed through an induction coil and creates a magnetic field around the coil. When a conducting material, such as steel, is held in the centre of the coil, the magnetic field causes a current to flow in the surface of the steel, which heats it up. The temperature to which the steel is heated can be controlled readily and so induction heating can be used to harden or soften steel, as required.

See also eddy currents.