| 摘要 |
PROBLEM TO BE SOLVED: To enhance a pitching fatigue life in order to cope with an increased load surface pressure which becomes higher as automobile components becomes smaller, or as the output power becomes higher. SOLUTION: A gear is made of a material containing, by a weight percent, 0.1 to 0.3% of C, 0.01 to 0.5% of Si, 0.3 to 1.5% of Mn, 0.01 to 0.06% of S, 0.03 to 1.5% of Cr and the remainder of Fe and impurities, and the shape of MnS has a maximum ratio (L/D) between the major diameter length L and the minor diameter length D, which is not more than 7 or having a maximum length of not more than 12μm, an incomplete quenching layer in the skin layer part having a thickness of not more than 12μm. Aβ' value which is obtained by dividing a half power band width of X-ray diffraction at the outer surface, with a half power band width after the steel there is annealing, so as to be non-dimensioned, is not less than 1.65, and thisβvalue and the surface roughness Rmax (unit:μm) satisfyβ'<=2.23+0.8561n (Rmax). Further, the residual austenite is in a range of 2 to 10%.
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