| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a high tensile strength steel sheet whose TS is 780 MPa or more, and which does not cause a weld crack even if the preheating temperature in a welding procedure is a low temperature of 50°C or lower, and a manufacturing method thereof. <P>SOLUTION: The high tensile strength steel sheet has tensile strength of 780 MPa or more and contains, by mass%, 0.02-0.10% of C, 0.01-0.2% of Si, 1.0-2.0% of Mn, 0.01% or less of P, 0.002% or less of S, 0.1-0.5% of Cu, 0.1-1.0% of Ni, 0.5-1.5% of Cr, 0.01-0.05% of Nb, 0.005-0.03% of Ti, 0.0005-0.0025% of B, 0.03-0.08% of Al, 0.0005-0.0050% of N and the balance being Fe and impurities, wherein the C content in the sheet thickness center is 0.10% or less, the aspect ratio of prior austenite particles in the sheet thickness center is 2.0 or more, the M-A structure in the sheet thickness center is 5.0% or less, and Mo, V or Sn may be contained. The manufacturing method thereof is provided. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
