| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a high strength hot-dip plated cold rolled steel sheet having low yield ratio not requiring specific hot rolled sheet firing and the addition of alloy elements such as Nb, Ti and the like, and excellent in extensibility and hole expansion property.SOLUTION: A hot-dip plated cold rolled steel sheet has a chemical composition containing, by mass%, C:0.01 to 0.15%, Si:0.01 to 1.5%, Mn:1.5 to 3.5%, P:0.1% or less, S:0.01% or less, Al:0.005 to 0.10% and N:0.010% or less, and havingαvalue defined in the formula (1) of 1.9 or more, a steel structure having a volume fraction of ferrite of 40% or more and the volume fraction of martensite of 3% or more at a position of 1/4 depth of a sheet thickness from a surface of the steel sheet, and mechanical characteristics such as a yield ratio YR of 70% or less and a tensile strength TS (MPa) and hole expansion property HER (%) satisfying the formula (2). (1)α=Mn+Si×0.5+Al×0.4. (2) TS×HER≥0.9×10.</p> |
