PURPOSE: To produce a track bushing which is hardened at a high depth and has excellent durability by subjecting the track bushing to oil hardening over the entire part, low-temp. tempering, induction tempering and high-frequency hardening of the bore party, and low-temp. tempering of the entire part, successively.

CONSTITUTION: The entire part of the track bushing 1 is heated to about 800°C and is oil- hardened in an oil tank 5; thereafter, the bushing is tempered at about 180°C to form the hardened layer uniform from the surface of the outside diameter part down to the core part. The bushing is then subjected to the induction tempering by a moving coil 6 from the bottom to the bottom end of the bore part. The completely hardened and tempered layer is thereby formed from the bore part to the core part. The outside diameter part is cooled with a water cooling jacket 7 so that the prescribed cured layer remains in the outside diameter part at this time. The bore part is then subjected to the high-frequency hardening by the moving coil 6 and a water cooling jacket 8 for the bore part from the bottom to the top end. The outside diameter part is cooled at this time. The prescribed cured layer is thereby formed in the bore part and the residual stress is provided thereto. The entire part of the track bushing material 1 is thereafter charged into a tempering furnace 9 where the bushing is subjected to the low-temp. tempering at about 180°C. The track bushing hardened at the high depth is thereby obtd.