| 摘要 |
PROBLEM TO BE SOLVED: To provide a soft-nitrided crankshaft excellent in manufacturability without sacrificing mechanical strength, and a method of manufacturing the same.SOLUTION: There is provided the soft-nitrided crankshaft obtained by forging and machining a bainitic non-heat treated steel, at least subjecting the forged/machined steel to strain-relief heat treatment, then to soft nitridation. The bainitic non-heat treated steel contains, by mass%, C:0.10 to 0.40%, Si:0.10 to 1.0%, Mn:1.0 to 2.0%, Mo:0.05 to 0.40%, V:0.05 to 0.40% as essential elements, and may contain, by mass%, S:0.01 to 0.1%, Ti:0.005 to 0.2%, Al:0.001 to 0.03%, Cr:≤0.50%, Cu:≤0.5%, Ni:≤0.5% as optional additional elements, and the balance Fe with inevitable impurities. P as the inevitable impurity is suppressed to at least less than 0.025%, retained γ quantity is set to less than 5.0% and a core part hardness is set to 270 Hv or more. |
