| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet combining high strength with excellent workability, and a production method therefor.SOLUTION: The cold rolled steel sheet is provided which has a chemical composition that contains, by mass%, C:0.05 to 0.30%, Si:0.5 to 2.5%, Mn:0.5 to 3.5%, P:0.1% or less, S:0.05% or less, sol.Al:0 to 1.0%, Ti:0 to 0.050%, Nb:0 to 0.030%, Cr:0 to 1.0%, Mo:0 to 0.3%, V:0 to 0.3%, B:0 to 0.005%, Ca:0 to 0.003%, REM:0 to 0.003% and the balance Fe with impurities, and that satisfies [0≤Ti+Nb≤0.070]. The cold rolled steel sheet having the above chemical composition has metallographic structure that contains, by area ratio, 50% or more of bainite and tempered martensite in total and 3.0% or more of retained austenite and that has a ratio of the retained austenite in which other retained austenite having crystal orientation with difference of 10° or more is present in a range of most proximity distance of 1 μm or less, to the retained austenite of 50% or more.SELECTED DRAWING: None |
