SUBMERGED ARC WELDING METHOD, WELD JOINT FORMED BY THE WELDING METHOD, AND STEEL PIPE OR TUBE HAVING THE WELD JOINT

摘要

A welding method for welding the upper surface side of a steel plate after welding the lower surface side thereof when butt welding is performed in submerged arc welding, wherein an angle (θ1) which an upper surface side boundary straight line that connects a meeting point at which a fusion boundary line of a lower surface side weld metal and a fusion boundary line of an upper surface side weld metal intersect, and a first intersection point at which a first parallel line that passes a position at a distance of 5 mm from the meeting point toward the upper surface of the steel plate and is parallel to the upper surface and the fusion boundary line of the upper surface side weld metal intersect forms with a line perpendicular to the first parallel line is set to 15° or more, an angle (θ2) which a lower surface side boundary straight line that connects the meeting point and a second intersection point at which a second parallel line that passes a position at a distance of 5 mm from the meeting point toward the lower surface of the steel plate and is parallel to the lower surface and the fusion boundary line of the lower surface side weld metal intersect forms with a line perpendicular to the second parallel line is set to 15° or more, and the total heat input (Q (kJ/cm)) of welding heat input on the lower surface side of the steel plate and welding heat input on the upper surface side thereof satisfies the relationship of Q≤1.3×t^1.37 with the thickness (t (mm)) of the steel plate, thereby making it possible to stably obtain a weld heat-affected zone with high toughness.