| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high tensile cold rolled steel sheet having superior ductility and stretch flange workability and a tensile strength of 590 MPa or more, and a method for manufacturing the same. <P>SOLUTION: A cold rolled steel sheet characterized by having a chemical composition containing more than 0.020 mass% and less than 0.20 mass% of C, more than 0.10 mass% and not more than 2.0 mass% of Si, 1.50 to 3.50 mass% of Mn, not more than 0.10 mass% of P, not more than 0.010 mass% of S, not more than 0.10 mass% of sol. Al, and not more than 0.010 mass% of N, and Fe and impurities as the balance. A metallographic structure thereof includes a low-temperature transformation generated phase, which is the main phase, and a second phase containing ferrite and at the same time, contains iron carbide, in which the value of the ratio of Mn content (atom%) to Fe content (atom%) [Mn]/[Fe] is 0.04 or more, in an average number density of 3.0×10<SP POS="POST">-3</SP>pieces/μm<SP POS="POST">2</SP>or more. The average crystal grain size of the ferrite is not more than 5.0 μm. <P>COPYRIGHT: (C)2012,JPO&INPIT |
