Induction is the most versatile method for heat treating steel. Uniform surface hardening, localized surface heating, through hardening, and tempering of pre-hardened pieces is effectively achieved with induction heating.
A part is heated by placing it into a magnetic field generated by a high frequency alternating current passing through a water cooled copper coil. The rapidly alternating magnetic field established within the coil induces current within the steel, and that induced current then generates heat. The depth of heating produced is related to the frequency of the alternating current. By varying the frequency the depth of heating is accurately controlled. The higher the frequency, the more shallow the heating protrudes. Conversely, deeper case depths and even through hardening are produced by using lower frequencies