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Abstract

An electric resistance welded steel pipe for a torsion beam, in which a chemical composition of a base metal portion contains, in terms of % by mass, 0.05 to 0.30% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.010 to 0.200% of Ti, 0.005 to 0.500% of Al, 0.010 to 0.040% of Nb, and 0.0005 to 0.0050 % of B, the balance containing Fe and impurities, wherein: V_c90, defined by the following Formula (i), is from 2 to 150, a mass ratio Ti/N is 3.4 or more, a microstructure of a wall thickness central portion in an L cross section at a base metal 1800 position is a tempered martensite, an average aspect ratio of prior γ grains in the tempered martensite is 2.0 or less, and a tensile strength in the pipe axis direction is from 750 to 980 MPa:

description='In-line Formulae' end='lead'log V_c90=2.94−0.75βa  Formula (i)description='In-line Formulae' end='tail'

description='In-line Formulae' end='lead'βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo  Formula (ii).description='In-line Formulae' end='tail'

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