| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a steel as the stock before hardening and a steel having excellent fatigue properties after hardening which is provided with a hardened layer by induction hardening on the surface and suitably applied to an automobile drive shaft, a constant velocity joint or the like, and to provide their production methods. <P>SOLUTION: The steel 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, has a base metal structure composed of a bainitic structure and/or a martensitic structure, and in which the total structural fraction of the bainitic structure and the martensitic structure is≥10%, further, the degree of ruggedness in old austenite grain boundaries in a hardened layer after induction hardening is≥0.05, and the thickness of the hardened layer is≥2 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
