High-frequency and induction heating technologies currently offer the highest efficiency and fastest speed for heating metallic materials, while also being low-energy and environmentally friendly. They are widely used in various industries for hot processing, heat treatment, hot assembly, welding, and smelting of metallic materials. They can heat workpieces both as a whole and in a targeted manner; they can achieve deep heating or concentrate heating only on the surface or outer layer; they can directly heat metallic materials as well as indirectly heat non-metallic materials. Therefore, induction heating technology will undoubtedly see increasingly widespread application across various industries.

Surface heat treatment processes that use induced current to locally heat workpieces. This heat treatment process is commonly used for surface hardening, but can also be used for local annealing or tempering, and sometimes for overall hardening and tempering.

The workpiece is placed inside an inductor (coil). When an alternating current of a certain frequency is passed through the inductor, an alternating magnetic field is generated around it. The electromagnetic induction effect of the alternating magnetic field induces a closed induced current—eddy current—within the workpiece. The induced current distribution across the workpiece cross-section is highly uneven, with a very high current density at the surface that gradually decreases inwards; this phenomenon is called the skin effect. The electrical energy of the high-density current at the workpiece surface is converted into heat energy, raising the surface temperature, thus achieving surface heating. The higher the current frequency, the greater the difference in current density between the workpiece surface and interior, resulting in a thinner heated layer. Rapid cooling after the heated layer temperature exceeds the critical temperature of the steel achieves surface hardening.