| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel plate having excellent weld zone toughness in a thick material with a plate thickness of≥18 mm, and to provide a method for advantageously producing the same. SOLUTION: The hot rolled steel plate has a steel composition comprising, by mass, 0.01 to <0.05% C,≤1.0% Si, 0.3 to 2.0% Mn,≤0.025% P,≤0.015% S, 0.005 to 0.10% Al,≤0.0050% N, 0.001 to 0.0050% B, 0.005 to 0.05% Ti and 0.030 to 0.10% Nb, also comprising the Si and Mn so as to satisfy 0.8Si≤Mn≤Si+1.2, and the Ti, Nb and C so as to satisfy 0.5<(Ti+Nb/2)/C<4.0, and the balance Fe with inevitable impurities, and has a structure composed of bainitic ferrite and/or ferrite. By the above, an electric resistance welded tube having high strength and having excellent base metal toughness, electric resistance welded zone toughness and circumferential weld zone toughness can be produced. Further, by controlling the composition in such a manner that the amount of precipitation of B to be precipitated reaches≤10 ppm, the remarkable improvement of strength and weld zone toughness are imparted, and also, a difference between the electric resistance weld zone hardness and the base metal hardness after seam annealing can be reduced. COPYRIGHT: (C)2007,JPO&INPIT
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