| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet excellent in heat spot resistance, wear resistance and punchability.SOLUTION: The cold rolled steel sheet contains, by mass%, 0.03 to 0.08% of C, 0 to 1.0% of Si, 0.2 to 0.8% of Mn, 0.03% or less of P, 0.01% or less of S and 0.05% or less of Al so as to satisfy 5×C%-Si%+Mn%-1.5×Al%<1, and further contains at least one kind of 0.03 to 0.4% of Nb, 0.01 to 0.3% of V and 0.01 to 0.3% of Ti so as to satisfy 0.04<(Nb%÷1.4)+(V%÷1.1)+Ti%<0.3. An average particle diameter of carbide as a precipitate is regulated so as to be 20 to 100 nm. An area ratio of a second phase structure having a major axis of 5 μm or more in a sectional structure is also regulated so as to be 5% or less. |
