US 11,739,866 B2Granted

Electric resistance welded steel pipe for torsion beam

AssigneeNippon Steel Corporation

InventorsTakaaki Fukushi, Noboru Hasegawa, Manabu Wada

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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: Vc90, 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: log Vc90=2.94−0.75βa Formula (i) βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo Formula (ii).

Claims8

Dependent claims

An electric resistance welded steel pipe for a torsion beam, the steel pipe having an outer diameter of from 50 to 150 mm and a wall thickness of from 2.0 to 4.0 mm, and the steel pipe comprising a base metal portion and an electric resistance welded portion,

wherein a chemical composition of the base metal portion consists of, 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 to 0.030% of P,
0 to 0.010% of S,
0.010 to 0.200% of Ti,
0.005 to 0.500% of Al,
0.010 to 0.040% of Nb,
0 to 0.006% of N,
0.0005 to 0.0050% of B,
0 to 1.000% of Cu,
0 to 1.000% of Ni,
0 to 1.00% of Cr,
0 to 0.50% of Mo,
0 to 0.200% of V,
0 to 0.100% of W,
0 to 0.0200% of Ca,
0 to 0.0200% of Mg,
0 to 0.0200% of Zr,
0 to 0.0200% of REM, and,
a balance consisting of Fe and impurities, wherein:
Vc90, defined by the following Formula (i), is from 2 to 150,
a mass ratio of Ti content to N content is 3.4 or more,
a metallographic microstructure of a wall thickness central portion is a tempered martensite structure, and an average aspect ratio of prior austenite grains in the tempered martensite structure is 2.0 or less, in an L cross section at a position deviating by 180° in a circumferential direction of the pipe from the electric resistance welded portion,
a metallographic microstructure of an area within a distance corresponding to a wall thickness from the electric resistance welded portion in a wall thickness central portion in a C cross section includes a tempered martensite and at least one of a tempered bainite or a ferrite,
yield elongation is observed when a tensile test in a pipe axis direction is performed, and
a tensile strength in the pipe axis direction is from 750 to 980 MPa:
log Vc90=2.94−0.75βa Formula (i)
βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo Formula (ii)
wherein, in Formula (i), Pa represents a value defined by Formula (ii), and in Formula (ii), element symbols represent % by mass of respective elements.

28 more elements

wherein a chemical composition of the base metal portion comprising, 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 to 0.030% of P,
0 to 0.010% of S,
0.010 to 0.200% of Ti,
0.005 to 0.500% of Al,
0.010 to 0.040% of Nb,
0 to 0.006% of N,
0.0005 to 0.0050% of B,
0 to 1.000% of Cu,
0 to 1.000% of Ni,
0 to 1.00% of Cr,
0 to 0.50% of Mo,
0 to 0.200% of V,
0 to 0.100% of W,
0 to 0.0200% of Ca,
0 to 0.0200% of Mg,
0 to 0.0200% of Zr,
0 to 0.0200% of REM, and,
a balance comprising Fe and impurities, wherein:
Vc90, defined by the following Formula (i), is from 2 to 150,
a mass ratio of Ti content to N content is 3.4 or more,
a metallographic microstructure of a wall thickness central portion is a tempered martensite structure, and an average aspect ratio of prior austenite grains in the tempered martensite structure is 2.0 or less, in an L cross section at a position deviating by 180° in a circumferential direction of the pipe from the electric resistance welded portion,
a metallographic microstructure of an area within a distance corresponding to a wall thickness from the electric resistance welded portion in a wall thickness central portion in a C cross section includes a tempered martensite and at least one of a tempered bainite or a ferrite,
yield elongation is observed when a tensile test in a pipe axis direction is performed, and
a tensile strength in the pipe axis direction is from 750 to 980 MPa:
log Vc90=2.94−0.75βa Formula (i)
βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo Formula (ii)
wherein, in Formula (i), Pa represents a value defined by Formula (ii), and in Formula (ii), element symbols represent % by mass of respective elements.

28 more elements

Dependencies are inferred from the claim text.