Commonly used current frequencies for induction heating surface quenching are:

1. High-frequency heating: 100-500KHZ, commonly used 200-300KHZ, it is tube type high-frequency or solid-state high-frequency heating, the hardened layer depth is 0.5-2.5mm, suitable for small and medium-sized parts.

2. Intermediate frequency heating: the current frequency is 0.5KHZ ~ 15KHZ, commonly used 2.5KHZ ~ 8KHZ, the power supply equipment is a solid-state intermediate frequency heating device or a thyristor intermediate frequency heating device. The depth of the hardened layer is 1 to 10 mm. Suitable for larger diameter shafts, medium and large gears, etc.

3.Power frequency heating: the current frequency is 50HZ. Using mechanical power frequency heating power supply equipment, the depth of the hardened layer can reach 10-20mm, which is suitable for surface quenching of large-diameter workpieces.