| 摘要 |
PROBLEM TO BE SOLVED: To proide a high tensile strength steel sheet for welded structure having remarkably improved fatigue strength while maintaining good weldability by controlling the steel components and to provide its production method. SOLUTION: This high tensile strength steel for welded structure has a composition containing, by mass, 0.005 to 0.1% C, 0.01 to 1.6% Si, 0.5 to 2% Mn, <=0.01% P, <=0.005% S, 0.001 to 0.05% Al, 0.001 to 0.05% Ti, 0.001 to 0.01% Mg, 0.0001 to 0.008% O and 0.001 to 0.008% N, further containing one or two kinds of 0.05 to 0.3% Nb and 0.05 to 0.3% V, and the balance Fe with inevitable impurities. In this steel, Ceq and Pcm defined by the following formula satisfy Ceq: >0.24 to 0.55%, and Pcm: <=0.025%: Ceq=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5+Nb/3, and Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B.
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