METHOD FOR PRODUCING LASER-WELDED STEEL TUBE

摘要

Provided is a method of stably manufacturing a laser welded steel pipe having a high quality weld portion at a high yield ratio by laser welding while a typical problem of the laser welding of frequent occurrence of undercut or underfill is solved. Specifically, a method of manufacturing a laser welded steel pipe by forming a steel strip into a cylindrical open pipe with forming rolls and performing laser welding on edges of the open pipe by emitting a laser beam while pressing the edges with squeeze rolls, the laser welding including: emitting two laser beams along the edges from an upper surface side of the open pipe, the two laser beams being transmitted through different optical fibers and having in-focus spot diameters exceeding 0.3 mm; emitting the laser beams such that a leading laser beam of the two laser beams and a trailing laser beam of the two laser beams are each inclined toward a direction in which welding proceeds at an incident angle with respect to a direction perpendicular to an upper surface of the open pipe, the leading laser beam being ahead of the trailing laser beam on the upper surface of the open pipe in the direction in which welding proceeds, the trailing laser beam being behind the leading laser beam; setting the incident angle of the leading laser beam to be larger than the incident angle of the trailing laser beam; and setting a gap between a center point of the leading laser beam and a center point of the trailing laser beam on a back surface of the open pipe to 1 mm or larger.