| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heattreated steel capable of being produced without reducing finishing temperature excessively and having a high strength of≥800 MPa and further having excellent toughness. SOLUTION: The high strength/high toughness non-heattreated steel contains, by mass, 0.35 to 0.70% C, 0.1 to 1.5% Si, 0.5 to 2.0% Mn,≤1.5% Cr, 0.2 to 1.0% V and 0.005 to 0.05% Al, and the balance Fe with inevitable impurities. The steel is provided with a ferrite-pearlite structure, and provided that the number of precipitates of >10 nm is defined as A and the number of precipitates of≤10 nm as B, A/B satisfies≥1/20. The above components may further comprise one or more kinds of elements selected from each group of (1) 0.005 to 0.05% Nb and (2) 0.2 to 1.0% Ni, 0.2 to 1.0% Cu and 0.1 to 0.5% Mo alone or in combination. COPYRIGHT: (C)2006,JPO&NCIPI
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