| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength and high-toughness steel sheet with a low yield ratio, which is inexpensively manufactured without adding a large quantity of alloying elements, and to provide a manufacturing method therefor. SOLUTION: The high-strength and high-toughness steel sheet with a low yield ratio comprises, by mass%, 0.02% or more but less than 0.07% C, 0.01-0.5% Si, 0.5-2.0% Mn, 0.05-0.5% Mo, 0.005-0.04% Ti, 0.01-0.08% Al, and the balance substantially Fe, has the ratio of a C content to the total content of Mo and Ti, by atom%, C/(Mo+Ti) of 0.5 to 3.0, and has a two-phase metal structure substantially consisting of ferrite and bainite, in which carbides containing Ti and Mo are dispersingly precipitated in a bainite phase. COPYRIGHT: (C)2004,JPO&NCIPI
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