| 摘要 |
Provided is a cold-rolled steel sheet having excellent delayed fracture resistance for laser welds and suitable for use in automobiles, electronics, and the like, said cold-rolled steel sheet having a steel composition containing, in mass%, 0.05-0.15% of C, 0.05-2.0% of Si, 1.2-3.5% of Mn, 0.05% or less of P, 0.005% or less of S, 0.01-0.10% of Al, 0.010-0.070% of Nb, 0.005-0.040% of Ti, and 0.0005-0.0065% of N, with the mass ratio of Ti and N (Ti/N) being 2.5-7.5 inclusive, the addition of B being kept to 0.0003% or less, and the remainder comprising Fe and unavoidable impurities, wherein 70 mass% or more of Ti in said steel is present as a precipitate while 15-65 mass% inclusive of Nb in said steel is present as solid Nb, and the tensile strength is 980 MPa or more. |
