METHOD OF MANUFACTURING LARGE DIAMETER WELDED STEEL PIPE HAVING HIGH STRENGTH AND TOUGHNESS

摘要

Submerged arc welding is performed in a single layer on both sides so that chemical composition of weld metal produced in seam welding using steel sheet, a low oxygen flux and a low carbon based weld wire provides a structure which contains PWM defined by a formula PWM = Pcm + 3.19Ti - 1.020 and being in the range of 0.18 to 0.33, and in which acicular ferrite has an area ratio of 55 % or more. Further, for an application requiring a crack resistance, submerged arc welding is performed so that in addition to the above condition, chemical composition of weld metal contains Prh defined by a formula Prh = Cr + Cu + Ni + 2Mo + 10V + 7Nb + 5Ti and being 2.8 or less.