| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a high tensile strength steel sheet excellent in toughness in which yield strength is 400 MPa or more, CTOD value is 0.3 mm or more, and sheet thickness is 40 mm or more, and a manufacturing method thereof. <P>SOLUTION: The high tensile strength steel sheet excellent in toughness has a chemical composition containing, by mass%, 0.01-0.08% of C, 0.01-0.3% of Si, 1.0-2.0% of Mn, 0.012% or less of P, 0.005% or less of S, 0.8-2.0% of Cu, 0.1-2.5% of Ni, 0.01-0.5% of Cr, 0.005-0.03% of Ti, 0.001-0.050% of Al, 0.001-0.01% of N, and the balance being Fe and impurities including 0.001% or less of Nb, 0.0003% or less of B, and 0.003% or less of O, wherein the ferrite fraction with a grain size of 20μm or less in the sheet thickness center is 60% or more, the area ratio of an island-like martensite structure in the sheet thickness center is 4.0% or less, the amount of inclusion in the sheet thickness center is 0.020% or less by JIS G 0555 point counting method, the C content in the sheet thickness center is 0.12% or less, and yield strength in the sheet thickness center is 400 MPa or more. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
