| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method for a welded steel tube excellent in a seam part inner face property capable of preventing generation of inner face roughing of a seam part in bead rolling. SOLUTION: In a manufacturing method for the welded steel tube inclusive of a process, in which a seam part S of an open state is heated/welded with pressure and then is smoothed by bead rolling, either one or a combination of two or more of the following items are conducted, 1) bead rolling is conducted at >=1000 deg.C, 2) a tube inside part or tube inside/outside parts including a bead rolling position is subjected to shielding 10 and is purged with non- oxidizing gas 8, 3) the scale stuck to an inner roll 5 or/further to an outer roller 6 is scraped at a roll outlet side 11, 4) non oxidizing gas 14 is blown on an inner face or inner/outer faces of the seam part before bead rolling, 5) in the case of welding with pressure, an thickness increase rate of the seam part is set to <=30%, 6) a lubricant LB is supplied to the inner roll or/further to the outer roll.
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