| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile fire resistant steel having excellent weldability and gas cutting properties, and having high temperature strength in case of a fire or the like, and to provide its production method. SOLUTION: The high tensile refractory steel has a composition comprising, by mass, 0.04 to 0.14% C,≤0.50% Si, 0.50 to 2.00% Mn,≤0.020% P,≤0.010% S, 0.01 to 0.05% Nb, 0.30 to <0.70% Mo,≤0.060% Al and 0.0010 to 0.0060% N, and in which welding crack sensitivity composition: P<SB>CM</SB>=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B is≤0.25%, and the balance iron with inevitable impurities, and the area fraction of polygonal ferrite or pseudo polygonal ferrite in the position of the 1/4 thickness in the sheet thickness direction of the steel sheet upon final rolling is≤10%. COPYRIGHT: (C)2006,JPO&NCIPI
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