| 摘要 |
PURPOSE:To obtain a welded steel pipe having high tensile strength and low temp. toughness, by tempering the same under limited conditions under submerged arc welding by a wire of the specific compsn. consisting of C, Si, Mn, Ni, Cu, P, S, Fe, etc. and a flux having specific basicity. CONSTITUTION:A steel pipe is welded by submerged arc welding by using a welding wire consisting of 0.05-0.15% C, <=0.1% Si, 1.0-2.0% Mn, 3.0-9.0% Ni, <=1.0% Cu, <=0.015% P, <=0.010% S, and the balance Fe and unavoidable impurities, and a flux having about >=1.5, more preferably about 1.5-2.5 basicity B expressed by the equations. The welded steel pipe is quenched after heating to 900-1,100 deg.C and is then tempered for >=5min at 600-700 deg.C, whereby the welded steel pipe having the weld metal of high low temp. toughness wherein the Charpy transition temp. is about <=-50 deg.C and the tensile strength at ordinary temp. is about >=50kg/mm.<2> is obtd. |
