| 摘要 |
A steel sheet having the following chemical composition, in mass%: 0.06-0.13% of C, 1.2-2.3% of Si, 0.6-1.6% of Mn, 0.10% or less of P, 0.010% or less of S, 0.01-0.10% of Al, and 0.010% or less of N, the remainder comprising Fe and inevitable impurities. The microstructure of the steel sheet includes, in volume fraction, 90% or more of ferrite having a mean grain size of less than 20 mum, and 1.0-10% of perlite having a mean grain size less than 5 mum. A high-yield-ratio high-strength cold-rolled steel sheet of excellent elongation and stretch-flangeability where the ferrite has a mean Vickers hardness of 130 or higher, the yield ratio is 65% or higher, and the tensile strength is 590 MPa or greater. |
