Patent ID: 6532995
Filing Date: 2003-03-18
Classification: C22C,Y10T

Abstract:
A super-high-strength line pipe excellent in low temperature toughness characterized in that:a tensile strength of said steel pipe at a base metal steel plate portion in a circumferential direction is from 900 to 1,100 MPa; a submerged arc seam weld portion comprising a weld metal disposed between abutting ends of said steel plate portion shaped into a pipe shape at a U&O step; a mean tensile strength of said weld metal of said submerged arc seam weld portion being at least the tensile strength of said steel plate minus 100 MPa; said pipe having an expanded diameter of about 450 to about 1,500 mm and a wall thickness of about 10 to about 40 mm, said pipe having been expanded after forming said submerged arc seam weld portion by submerged arc welding; wherein said steel plate contains, as components thereof: C: 0.04 to 0.10%, Si: not greater than 0.6%, Mn: 1.7 to 2.5%, P: not greater than 0.015%, S: not greater than 0.003%, Ni: 0.1 to 1.0%, Mo: 0.15 to 0.60%, Nb: 0.01 to 0.10%, Ti: 0.005 to 0.030%, and Al: not greater than 0.06%, and â€ƒcontaining selectively at least one of the following elements: B: not greater than 0.0020%, N: 0.001 to not greater than 0.006%, V: not greater than 0.10%, Cu: not greater than 1.0%, Cr: not greater than 0.8%, Ca: not greater than 0.01%, REM: not greater than 0.02%, and Mg: not greater than 0.006%, and â€ƒthe balance of iron and unavoidable impurities; and wherein said weld metal contains: C: 0.04 to 0.14%, Si: 0.05 to 0.40%, Mn: 1.2 to 2.2%, P: not greater than 0.010%; S: not greater than 0.010%, Ni: 1.3 to 3.2%, Cr+Mo+V: 1.0 to 2.5%, B: not greater than 0.005%, and the balance of iron and unavoidable impurities; and wherein the Ni content of said weld metal is higher by at least 1% than the Ni content of said steel plate.