Electroseamed steel pipe for line pipe

Abstract

An electroseamed steel pipe for line pipe wherein: the chemical composition of the base metal section comprises, in mass%, C: 0.030% to less than 0.080%, Mn: 0.30-1.00%, Ti: 0.005-0.050%, Nb: 0.010-0.100%, N: 0.001-0.020%, Si: 0.010-0.450% and Al: 0.001-0.100%, the balance comprising Fe and impurities; CNeq represented by equation (1) is 0.190-0.320; Mn/Si ratio is at least 2.0; LR represented byequation (2) is at least 0.210; and when the metal structure of the base metal section is viewed at a 1000-fold magnification using SEM, the ferrite area ratio is 40-80% and the balance comprises tempered bainite. CNeq=C+Mn/6+Cr/5+(Ni+Cu)/15+Nb+Mo+V... Equation (1) LR=(2.1*C+Nb)/Mn... Equation (2)

Description

technical field [0001] The present invention relates to an electric resistance welded steel pipe (electroseamed steel pipe: electric seam steel pipe) for a line pipe. Background technique [0002] In recent years, the importance of mainline pipes, which are mainly one of the transportation means of crude oil or natural gas, has increased. [0003] Various studies are being conducted on electric resistance welded steel pipes used as line pipes (ie, electric resistance welded steel pipes for main line pipes). [0004] For example, Patent Document 1 proposes a hot-rolled steel sheet for a sour resistance high-strength electric resistance welded steel pipe in which bainitic ferrite in the steel structure is 95 vol% or more. [0005] Patent Document 2 discloses a technique of inducing a Bauschinger effect by repeatedly deforming a steel strip as a raw material by, for example, bending-return processing before pipe forming, thereby enabling The yield ratio in the pipe axis direc...

AI Technical Summary

Problems solved by technology

In paragraph 0019 of this patent document 3, it is described that "in the conventional electric resistance welded steel pipe with a large amount of Nb, under the action

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