| 摘要 |
When the amount of C, the amount of Si and the amount of Mn are respectively represented by [C], [Si] and [Mn] in unit mass%, the cold rolled steel sheet satisfies a relationship of (5×[Si]+[Mn])/[C]>10, the metallographic structure contains, by area ratio, 40% to 90% of a ferrite and 10% to 60% of a martensite, further contains one or more of 10% or less of a pearlite by area ratio, 5% or less of a retained austenite by volume ratio and 20% or less of a bainite by area ratio, the hardness of the martensite measured using a nanoindenter satisfies H20/H10<1.10 and ÃHM0<20, and TS×» representing the product of TS that is a tensile strength and » that is a hole expansion ratio is 50000 MPa·% or more. |
