To provide a crankshaft which has an excellent bending fatigue life.
In the crankshaft having quench-hardened layers on the surfaces of crank pin parts and journal parts, the steel structure has a composition comprising, by mass, 0.35 to 0.7% C, 0.30 to 1.1% Si, 0.2 to 2.0% Mn, 0.005 to 0.25% Al, 0.005 to 0.1% Ti, 0.05 to 0.6% Mo, 0.0003 to 0.006% B, ≤0.06% S, ≤0.02% P and ≤0.2% Cr, and the balance Fe with inevitable impurities, and further, the base metal has a bainitic structure and/or a martensitic structure, and in which the total structural fracture of the bainitic structure and the martensitic structure is controlled to ≥10%, and further, the old austenite grain size in the hardened layers after induction hardening is controlled to ≤12 μm over the whole thickness of the hardened layers.
COPYRIGHT: (C)2005,JPO&NCIPI
Akihiro Matsuzaki
Yasuhiro Omori
Takaaki Toyooka
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Kenji Sugimura
Kiyoshi Kuruma