| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength steel having excellent weldability and joint toughness at a low cost by improving the toughness of the welded joint of a high tensile strength steel having a tensile strength of≥780 N/mm<SP>2</SP>without the addition of large quantities of alloy elements. SOLUTION: The high tensile strength steel has a composition comprising, by mass, 0.02 to 0.1% C,≤0.3% Si, 1 to 2% Mn,≤0.015% P,≤0.005% S,≤1% Cr,≤1% Mo, 0.005 to 0.05% Nb, 0.0003 to 0.003% B, 0.03 to 0.09% Al, 0.003 to 0.015% Ti, and≤0.004% N, and, if necessary, further comprising either or both of≤0.7% Cu and≤1% Ni, and the balance Fe with inevitable impurities, and satisfying Al/Ti≥6 (wherein, each atomic symbol denotes the content thereof in mass%). The high tensile strength steel can be used as quenched without performing tempering. COPYRIGHT: (C)2006,JPO&NCIPI
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