| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a steel sheet having a high yield ratio and an ultrahigh tensile strength, which can stably show the TS of 1,180 MPa or higher, has the high YR of 0.7 or more and is superior also in ductility, and to provide a method for manufacturing the same. <P>SOLUTION: The steel sheet having the high yield ratio and the ultrahigh tensile strength superior in the ductility has a component composition comprising, by mass%, 0.5-1.5% C, 0.1% or less Si, 10-25% Mn, 0.1% or less P, 0.05% or less S, 0.1% or less Al, 0.1-5.0% Mo, 0.01% or less N and the balance Fe with unavoidable impurities; and has a microstructure in which an austenite phase occupies 95% or more by an area rate in the whole structure, not-yet-recrystallized austenite grains with an aspect ratio of 3 or more occupy 70% or more by the area rate in the whole structure, and recrystallized austenite grains occupy 5% or more by the area rate in the whole structure. <P>COPYRIGHT: (C)2010,JPO&INPIT |
