Steel pipe for line pipe with excellent low temperature toughness of welded zone and method for manufacturing the same

A method for manufacturing a steel pipe for a line pipe with excellent low temperature toughness of a welded zone thereof, the method comprising:

• (a) welding the welded zone in an electric resistance welding scheme while shaping a steel sheet for a line pipe containing 0.02 to 0.07% by weight of carbon into a cylindrical shape using a squeeze roll, thereby forming the steel pipe for the line pipe;
• (b) performing selectively high frequency heat-treatment of only the welded zone of the steel pipe for the line pipe;
• (c) rapidly-cooling selectively only the high frequency heat-treated welded zone to 550 to 710° C.;
• (d) air-cooling the rapidly-cooled welded zone to 300 to 400° C.;
• and
• (e) water-cooling the air-cooled welded zone,
• after the (e), wherein a microstructure of the welded zone of the steel pipe for the line pipe has a complex phase including spherical carbide and fine ferrite,
• wherein a shock absorption energy value of the welded zone at −45° C. is 100˜200 J.