PURPOSE: To lower the hardness of weld zones without generating oxidation scale by welding a member and a member by a high-density energy source and subjecting the welded member obtd. in such a manner to a heating treatment in a nitriding atmosphere of a specific temp. or below.
CONSTITUTION: The respective pieces A, B, C of an S48C material of an assembled crack shaft are formed and molded and are subjected to required working. Projecting parts 5 of the piece A are press-fitted into a shaft hole 6 of the pieces B, C and the weld zones 4 of the respective pieces A, B, C are welded by a CO2 laser beam machine. The welding is executed under the conditions of prescribed output and welding speed and the preheating is also executed under the conditions of the prescribed output and welding speed (3 turn beam irradiation). Pin shafts 1 and journal shafts 2 are polished and the resulted crank shaft is heated for a prescribed period of time in the nitriding atmosphere of 580°C (≤700°C). No problems arise with the resulted crank shaft in the durability test made at a prescribed rotating speed by assembling the crank shaft to an actual engine. Since the crank shaft is subjected to the heating treatment in the nitriding atmosphere of ≤700°C after the welding in this way, the generation of the oxidation scale is obviated and th hardness of th weld zones is lowered, while the strength and wear resistance as the members are improved.
FUJIWARA YOSHINARI
KISHIMOTO MASANORI
MOCHITO HIROSHI
