The basic principle of induction heating surface quenching:

Put the workpiece in the inductor made of hollow copper tube, and after passing the intermediate frequency or high frequency alternating current, an induced current of the same frequency is formed on the surface of the workpiece, and the surface of the part is rapidly heated (the temperature can be increased by 800~ 1000 degrees, the core is still close to room temperature), and then spray cooling (or oil immersion quenching) immediately to harden the surface layer of the workpiece.