Induction surface hardening is used when not every zone of a part must have the same hardness. Zones that must be hard are raised to hardening temperature by the magnetic field of a copper coil and quenched. Puntaş, one of Türkiye’s early heat-treatment shops, runs medium-to-high frequency induction machines for both series and tight-tolerance work. Coil design is held to a high standard so the surface heats evenly.