| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide an ultra-high-strength thin steel sheet which is excellent in workability and corrosion resistance and has tensile strength of≥980 MPa. <P>SOLUTION: (1) The ultra-high-strength thin steel sheet which is excellent in workability and corrosion resistance and has tensile strength of≥980 MPa includes, by mass, 0.10-0.18% C, 1.0-3.0% Si, 1.0-3.5% Mn, 0.05-0.2% P,≤0.02% (not including 0%) S,≤0.5% (not including 0%) Al and the balance being Fe and unavoidable impurities and has such a composite structure that bainitic ferrite and martensite occupy≥80% of the area in total and retained austenite occupies≥1% of the area, wherein the average axial ratio (long axis/short axis) of the retained austenite crystal grains is≥5 and the average length of the short axis of the retained austenite crystal grains is≤1μm. (2) The steel sheet further includes 0.0002-0.01 mass% B. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
