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

摘要

Utilizing the chemical composition of a steel plate, a low-oxygen welding flux, and a low carbon welding wire, seam welding is conducted by submerged arc welding so that the resulting weld metal has a chemical composition, in which PWM value defined as below is in a range of from 0.18 to 0.33, and a micro-structure containing acicular ferrite not less than 55% by area ratio: $where,$ Furthermore,\; when\; cracking\; resistance\; is\; required,\; submerged\; arc\; welding\; is\; conducted\; such\; that\; the\; chemical\; composition\; of\; the\; weld\; metal\; satisfies\; Prh\; value\; of\; less\; than\; 2.8,\; in\; addition\; to\; fulfilling\; the\; above\; conditions:$ \mathop{\mathrm{image}}$$$