PURPOSE:To increase resistance to fatigue and reduce the whole weight of a crankshaft by extending high frequency induction hardened end edges of each outer periphery of a crankpin part and a journal part to each web side near each fillet part, and forming a hardened boundary face so that it exists in machined surfaces of the side faces of the web. CONSTITUTION:High frequency induction hardening is applied to the outer peripheries of a crankpin part Cp and a journal part Jo, and hardened end edges are formed to extend to a fillet part Rp on the pin side and the side face of a web part near a fillet part Rj on the journal side. The side faces of the webs are machined, and hardened boundary surfaces of high frequency induction hardened end faces are formed to exist in each machined surfaces of the webs. The whole weight of a crankshaft can be reduced, and thereby resistance to fatigue can also be increased.
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