STEEL SHEET HAVING EXCELLENT WELDABILITY

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PURPOSE : A high tensile strength steel sheet with excellent high speed weldability is provided to form beads with wide width even at a high arc welding speed of 100 cm/min or above.CONSTITUTION : A steel sheet comprises, by mass percent, 0.20 to 2%% of Si, and 1 to 2.5%% of Mn, a total mass of Si and Mn being 1.5%% or more, and further comprises 0.002%% or less(exclusive of 0%%) of O, 0.02 to 0.25%% of C, 0.1%% or less(exclusive of 0%%) of P, 0.05%% or less(exclusive of 0%%) of S, 0.02 to 0.2%% of Al, and 0.0015 to 0.015%% of N. The steel sheet has an inner oxide layer with a thickness of 5 μm or thinner that exists in a surface layer thereof. The steel sheet further comprises at least one element selected from 0.03 to 2%% of Cr, 0.03 to 1%% of Mo, and 0.0003 to 0.005%% of B. The steel sheet further comprises at least one element selected from 0.005 to 0.1%% of Nb, 0.005 to 0.3%% of Ti, 0.005 to 0.5%% of V, and 0.005 to 0.5%% of W. The steel sheet further comprises 0.03 to 0.5%% of Cu. The steel sheet further comprises at least one of 0.0005 to 0.005%% of Ca and 0.0005 to 0.005%% of REM(rare earth elements). The steel sheet further comprises 0.0005 to 0.005%% of Zr and Mg in total. The steel sheet further comprises 0.03 to 1%% of Co. The steel sheet further comprises 0.015 to 0.5%% of Ni.? KIPO 2007