| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel material, even in the case a drive shaft or the like with small diameters are produced, which can secure excellent strength, toughness or the like, and also has satisfactory machinability, and to provide its production method. SOLUTION: A steel material comprising prescribed amounts of C, Si, Mn, S, Ti, Cr and B, and the balance iron with inevitable impurities, and in which the occupancy area ratio of ferrite is≥30% and H<SB>RB</SB>is 85 to 93 is subjected to induction hardening. The surface of the steel material after being subjected to the hardening shows 650 to 730 by H<SB>V</SB>. Further, provided that the distance from the surface to a part showing 392 by H<SB>V</SB>is defined as effective hardened layer depth (t), and the radius or thickness of the steel material is defined as (r), the hardened layer ratio t/r is≥0.5. COPYRIGHT: (C)2007,JPO&INPIT
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