| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To stably provide a steel material having high fatigue strength. <P>SOLUTION: The steel material has a composition comprising, by mass, 0.35 to 0.7% C,≤1.1% Si, 0.1 to 2.0% Mn,≤0.25% Al, 0.005 to 0.1% Ti, 0.05 to 0.6% Mo, 0.0003 to 0.006% B,≤0.10% S,≤0.03% P and≤0.2% Cr, and the balance Fe with inevitable impurities, and its base metal structure has a bainitic structure and/or a martensitic structure. Also, the total structural fraction of the bainitic structure and the martensitic structure is≥10%, further, regarding old austenite grain boundaries in a hardened layer after induction hardening, the average value of the frequencies for which the code of the curvature in each grain boundary changes at the parts other than grain boundary triple junctions per old austenite grain is≥5, and the thickness of the hardened layer is≥2 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
