MANUFACTURE OF WELDED STEEL TUBE AND STEEL TUBE MANUFACTURING LINE

摘要

PROBLEM TO BE SOLVED: To provide a manufacturing method for welded steel tubes by which rolling is executable at lower rolling load, work hardening is suppressed and the tubes having high strength and high ductility are manufactured without deteriorating the surface state and which can deal with the production of many kinds in small lots. SOLUTION: After a base tube 8 is made by continuously forming a band steel 1 into an open tube 7 with forming rolls, heating both edge parts of the open tube 7 to not lower than the fusing point, executing butt-joining with squeeze rolls 6 and cutting the bead, this base tube 8 is heated to not lower than the point Ac3 and rapidly cooled, reheated to the temp. region of 200-700 deg.C and, in this temp. region, drawing is executed with the stretch reducer 21 having plural stands having, preferably, two or more rolls.