| 摘要 |
Provided are a high-strength, cold-rolled steel sheet having a tensile strength of 1,300 MPa or above, and excellent chemical conversion treatability and workability, and a method for manufacturing the same. The steel sheet contains C: 0.15%-0.22%, Si: 1.0%-2.0%, Mn: 1.7%-2.5%, P: 0.05% or less, S: 0.02% or less, Al: 0.01%-0.05%, N: 0.005% or less, and O: 0.01% or less, and satisfies the relationship [Si]/[Mn] ≥ 0.5 (where [Si] is the Si content and [Mn] is the Mn content), with the remainder comprising iron and unavoidable impurities. The structure, in area percent, is 60% to less than 100% of tempered martensite, and 5% or less (including 0%) of retained austenite, with the remainder being ferrite, the average crystal grain size of the ferrite being 3.5 μm or less, the number of Si-Mn compound oxides having equivalent circular diameter of 5 μm or less at the steel sheet surface being less than 10/100 μm2, and the steel sheet surface coverage of oxides comprising mainly Si being 1% or less. |
