Hardening with Induction Heating

Many types of steel are treated with heat to increase toughness and resistance to wear. The effectiveness of this process depends on the steel's carbon content. When the steel is heated above its transformation temperature (720°C), the carbon changes the steel's crystalline structure to an austenite. The harder, more brittle steel is then quickly cooled or quenched.

To make the steel less brittle and more usable, another process called tempering is used; the steel is slowly heated to just below the transformation temperature and then slowly cooled.

There are two general types of hardening processes: through- hardening treats the entire part, while case-hardening generally treats the part surface area and some of the interior area, according to the depth of hardening requirements for a specific application.

Modern induction heating provides reliable, repeatable, non-contact and energy-efficient heat in a minimal amount of time. For hardening, induction provides the necessary control and accuracy to focus the heat to a specific area of the part. Solid state systems are capable of heating very small areas within precise production tolerances, without disturbing individual metallurgical characteristics.

For case-hardening, typical frequencies are 450 kHz for case-depths of 0.030" to 0.080"; thicker case-depths of 0.100 to 0.150" are typically hardened at 10 kHz. It is important to heat the part quickly with high power density, and then quench the part rapidly to prevent the inside of the part from exceeding the transformation temperature. Through hardening is generally defined more by the time required to heat through the part than the by the frequency of the power supply

Typical RF power supplies for hardening range from 5 to 120 kW, depending on the material and application requirements.