| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To attain a high tensile cold-rolled steel sheet excellent in ductility, work-hardenability, and stretch flange formability. <P>SOLUTION: The cold-rolled steel sheet contains, by mass%, >0.020 and <0.30% C, >0.10% and≤3.00% Si, and >1.00 and≤3.50% Mn, and optionally further contains one or more elements selected from <0.050% Ti, <0,050% Nb,≤0.50% V,≤1.0% Cr,≤0.50% Mo,≤0.010% B,≤0.010% Ca,≤0.010% Mg,≤0.050% REM, and≤0.050% Bi, and has a metallic structure in which a main phase is a low-temperature transformation-produced phase and a second phase includes retained austenite. The retained austenite counts for >4.0% and <25.0% by a volume fraction relative to the entire structure, and has an average diameter of <0.80μm, and a number density of the retained austenite particles having a particle size of≥1.2μm is≤3.0×10<SP POS="POST">-2</SP>pieces/μm<SP POS="POST">2</SP>. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
