| 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 material 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%, and further, regarding the old austenite grain boundaries in the hardened layer after induction hardening, the value of grain boundary ruggedness A obtained from the total value Le (μm) of grain boundary lengths and the total value L (μm) of the lengths of straight lines connecting the adjoining grain boundary triple junctions is controlled to a prescribed range. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
