| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide steel products for heat treatment, having excellent workability before heat treatment and having high strength and excellent toughness after heat treatment. <P>SOLUTION: The steel products have a chemical composition including, by mass%, more than 0.35% and 0.6% or less of C, 0.5% or less of Si, 0.5% or more and 1.5% or less of Mn, 0.03% or less of P, 0.01% or less of S, 0.1% or less of sol. Al, 0.01% or less of N, 0.005% or less of B and 0.1% or less of T, with the remainder being Fe and impurities, and have a steel structure which comprises ferrite, carbide and an inclusion while an average line segment length of the ferrite is 5 μm or longer, and has an effective spheroidizing ratio of 0.6 or more and 0.85 or less when a ratio of coarse carbide is 0.5 or more and an effective spheroidizing ratio of 0.7 or more and 0.91 or less when the ratio of coarse carbide is less than 0.5. <P>COPYRIGHT: (C)2012,JPO&INPIT |
