AS-ROLLED TYPE ELECTRIC-RESISTANCE-WELDED STEEL PIPE FOR LINE PIPES

• Main Authors: FUKUSHI, Takaaki, ASAHI, Hitoshi, ISHITSUKA, Tetsuo, TASHIMA, Kenzo, SAKAMOTO, Shinya
• Format: Patent
• Language: English; French; German
• Published: 02.10.2019
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

An as-rolled electric resistance welded steel pipe for a line pipe has a base metal portion that includes, in terms of % by mass, 0.01 to 0.10% of C, 0.01 to 0.40% of Si, 0.50 to 2.00% of Mn, 0 to 0.030% of P, 0 to 0.0015% of S, 0.010 to 0.050% of Al, 0.0030 to 0.0080% of N, 0.010 to 0.050% of Nb and 0.005 to 0.020% of Ti, the balance comprising Fe and impurities, and in a metallographic microstructure of the base metal portion, an areal ratio of polygonal ferrite is 80% to 98% and the balance is composed of at least one of bainite or pearlite, a yield strength in a pipe axis direction is 415 to 550 MPa, a tensile strength in the pipe axis direction is 461 to 625 MPa, and a maximum Vickers hardness of an inner surface layer of the base metal portion is 248 HV or less and is smaller than a maximum Vickers hardness of an outer surface layer of the base metal portion by 5 HV or more.