| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a thick high-tensile-strength steel sheet suitable for use in a large-sized steel structure, excellent in low temperature toughness at a multi-layer welding portion, and having a yield strength of 630 MPa or more and a sheet thickness of 75 mm or more; and to provide a method for producing the thick high-tensile-strength steel sheet. <P>SOLUTION: The steel sheet contains, by mass%, 0.02-0.05% of C, 0.3% or less of Si, 0.5-3% of Mn, 0.015% or less of P, 0.005% or less of S, 0.5-5% of Ni, 0.01-0.08% of Al, 0.007% or less of Ni, 0.0003-0.003% of B, and, if required, one or more selected from among Cu, Mo, Cr, V, Nb, Ca and REM (rare-earth metal), with the remainder being Fe and unavoidable impurities. A slab containing the constituents is subjected to hot rolling starting at a temperature region from the Ac<SB POS="POST">3</SB>point to 1,150°C. The hot rolling is performed so that a cumulative draft is 50% or more. After the slab is formed to have a predetermined sheet thickness, the slab is quenched and then tempered at a temperature of 450 to 650°C. <P>COPYRIGHT: (C)2012,JPO&INPIT |
