PURPOSE: To prevent the occurrence of a crack on weld and further, to prevent the occurrence of a warp on the disk assembly by carrying out postheating repeatedly by a lower temper current than a welding current to delay cooling of a weld zone after welding.

CONSTITUTION: In a drive plate 1 which is formed by subjecting a ring gear 12 and a plate 3 to electric resistance welding and fastening these tightly, the ring gear made of high and medium carbon steel material is welded into the sorbite structure having ≤Hv 500 hardness, further, both are held between electrodes to carry a current thereto and welding is performed so that the lower current of 70-80% of the welding current is added repeatedly to delay cooling of the weld zone after welding.