| 摘要 |
PROBLEM TO BE SOLVED: To provide a crank shaft excellent in workability, in which outer circumferential surfaces of a pin part and of a journal part can be used as a rolling contact surface.SOLUTION: The crank shaft is provided in which outer circumferential surfaces of a pin part 51 and of a journal part 52 are rolling contact surfaces 510 and 520 for a rolling bearing. The chemical component of the crank shaft contains C:0.50 to 0.90%, Si:0.05 to 1.30%, Mn:0.40 to 1.50%, S:0.025% or less, Cr:0.05 to 1.60%, Al:0.001 to 0.050%, O:0.0010% or less, N:0.0200% or less and satisfies formulae (1) and (2). Each of the rolling contact surfaces 510 and 520 is composed of a martensite structure. In each of the rolling contact surfaces, the average of equivalent circle diameter of a maximum inclusion of is 15 μm or less and hardness in at least depth in the range of 1.5 mm from an outermost surface is 650 HV or more. A base material part is a ferrite/perlite structure or a perlite structure and is composed of a metallic structure having no pro-eutectoid cementite and has a hardness of 320 HV or less.SELECTED DRAWING: Figure 1 |
