| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing carburizing (or carbonitriding)-treated parts having excellent torsional fatigue strength and usable, e.g., for automobile driving system parts such as shafts each having a cave (oil hole) at the shaft part. SOLUTION: The chemical composition of steel is composed of, by mass, 0.15 to 0.3% C, 0.2 to 1.0% Mn,≤0.35% Si,≤0.015% P, 0.01 to 0.03% S, 0.005 to 0.05% Al, 0.002 to 0.05% N and 0.0005 to 0.005% B, and the balance substantially Fe, and the cooling rate at the time of steel casting and heating temperature/finishing temperature/draft at the time of hot rolling are regulated, thus the average aspect ratio of inclusion particles with a major length of≥3μm in the steel is controlled to≤6.0, also the area ratio of the inclusion particles is controlled to≤0.6%, and further, carburizing time to the steel is regulated to control the ratio of the effective depth of a hardened layer at the inside face of a cave to the radius of the shaft part to 0.015 to 0.08. COPYRIGHT: (C)2005,JPO&NCIPI
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