| 摘要 |
PROBLEM TO BE SOLVED: To produce a non-heat treated steel by saving steps and energy, the steel composed of components which require no desulfurization and include no expensive alloy element, the steel having high strength and high toughness equivalent to S45C or higher. SOLUTION: A steel comprising, by mass, 0.30 to 0.65% of C, 0.10-0.50% of Si, 0.50-1.50% of Mn, 0.003-0.100% of S, 0.20% or less (0 is included) of Cr, 0.005-0.060% of Al and the balance Fe with inevitable impurities is subjected to solution heat treatment at temperatures ranging from above 1,300°C to the solidus temperature or less and quench treatment at 5°C/sec or higher. Subsequently, age heat treatment is applied to the resulting steel at a parameter P value of 24,200-27,000, P being represented by the formula: P=(T+273)ä20+log(t/60)}, wherein T is retention temperature (°C) inγ-temperature range, and t is retention time (min), so that particles mainly composed of MnS and having a particle size of 200 nm or less are dispersedly precipitated in ferrite. Thus, the non-heat treated ferrite-pearlite steel material having a Vickers hardness of 210 or more, even 240 or more, is obtained. COPYRIGHT: (C)2009,JPO&INPIT
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