STEEL SHEET AND STEEL PIPE FOR ELECTRON BEAM WELDING, AND PIPELINE HAVING EXCELLENT LOW TEMPERATURE TOUGHNESS IN WELD METAL ZONE

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet for an electron beam welding, a steel pipe for an electron beam welding, and a pipeline in which the variation of toughness at low temperatures in a weld metal zone welded by an electron beam can be reduced, and to provide an electron beam welding method for the steel pipe.;SOLUTION: The steel sheet has a composition containing, by mass, 0.03 to 0.06% C, 0.1 to 0.4% Si, 0.8 to 2.0% Mn, ≤0.015% P, 0.005 to 0.025% Ti, 0.020 to 0.050% Al, and ≤0.0030% O, and also satisfying [O]0.019×[Si]+0.009×[Al], and in which the number of inclusions of ≥3 μm is ≤5.0 pieces/mm². The steel pipe is obtained by using the steel sheet. As for the pipeline, in the weld metal zone in the circumferential direction of the steel pipe obtained by welding the respective steel pipes in the circumferential direction by electron beam welding, the number of inclusions of ≥3 μm is ≤3.0 pieces/mm², or the ratio of bainite packets with dimensions of ≥30,000 μm² occupied in the whole weld metal structure is ≤10%.;COPYRIGHT: (C)2003,JPO