ELECTRIC-RESISTANCE WELDED STEEL PIPE

摘要

The present invention is an electric resistance welded steel pipe which is most suitable for use in the mining of shale gas and the like, and which has a chemical composition containing, in % by mass, 0.08 to 0.18% of C, 0.01% to 0.50% of Si, 1.30 to 2.1% of Mn, 0.001 to 0.10% of Al, 0.005 to 0.08% of Nb and 0.005 to 0.03% of Ti, wherein the amounts of N, P and S are limited to 0.008% or less, 0.020% or less and 0.010% or less, respectively, and the remainder is made up by Fe and unavoidable impurities. The steel pipe is characterized as follows: the structure of a thick central part of the steel pipe is a low-temperature transformation product phase comprising a ferrite phase and a remainder made up by a bainite phase, wherein the ferrite phase has an area ratio of 40% to 70% and an equivalent circle diameter of 1.0 to 10.0 µm; and the Ceq value satisfies the formula: 0.32 = Ceq = 0.60.