| 摘要 |
PROBLEM TO BE SOLVED: To stably provide steel which has high twisting fatigue strength. SOLUTION: The steel having excellent fatigue properties 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,≤0.020% P and≤0.2% Cr, and the balance Fe with inevitable impurities. The steel has a bainitic structure and/or a martensitic structure as a base metal structure, in which the total structural fraction of the bainitic structure and the martensitic structure is≥10%, also, the old austenite grain size in a hardened layer after induction hardening is controlled to≤12μm over the whole thickness of the hardened layer, and further, the degree of dispersion in the grain size is reduced. COPYRIGHT: (C)2005,JPO&NCIPI
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