Electric resistance welded steel pipe for torsion beam

Patent metadata

Field	Value
Publication number	US-11739866-B2
Application number	US-201817268285-A
Country	US
Kind code	B2
Filing date	Oct 12, 2018
Priority date	Oct 12, 2018
Publication date	Aug 29, 2023
Grant date	Aug 29, 2023

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).

First claim

The invention claimed is:

1. 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:
V c90 , 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 V c90 =2.94−0.75 βa   Formula (i)

β a =2.7 C+ 0.4 Si+Mn+ 0.45 Ni+ 0.8 Cr+ 2 Mo   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.

2. The electric resistance welded steel pipe for a torsion beam according to claim 1 , wherein the chemical composition of the base metal portion contains, in terms of % by mass, at least one selected from the group consisting of:
more than 0% but equal to or less than 1.000% of Cu,
more than 0% but equal to or less than 1.000% of Ni,
more than 0% but equal to or less than 1.00% of Cr,
more than 0% but equal to or less than 0.50% of Mo,
more than 0% but equal to or less than 0.200% of V,
more than 0% but equal to or less than 0.100% of W,
more than 0% but equal to or less than 0.0200% of Ca,
more than 0% but equal to or less than 0.0200% of Mg,
more than 0% but equal to or less than 0.0200% of Zr, and
more than 0% but equal to or less than 0.0200% of REM.

3. The electric resistance welded steel pipe for a torsion beam according to claim 1 , wherein packet grains in the tempered martensite structure have an average grain size of 10 μm or less.

4. The electric resistance welded steel pipe for a torsion beam according to claim 1 , wherein the wall thickness central portion in the L cross section has a dislocation density of 2.0×10 14 m −2 or less.

5. 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 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:
V c90 , 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 V c90 =2.94−0.75 βa   Formula (i)

β a =2.7 C+ 0.4 Si+Mn+ 0.45 Ni+ 0.8 Cr+ 2 Mo   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.

6. The electric resistance welded steel pipe for a torsion beam according to claim 5 , wherein the chemical composition of the base metal portion contains, in terms of % by mass, at least one selected from the group consisting of:
more than 0% but equal to or less than 1.000% of Cu,
more than 0% but equal to or less than 1.000% of Ni,
more than 0% but equal to or less than 1.00% of Cr,
more than 0% but equal to or less than 0.50% of Mo,
more than 0% but equal to or less than 0.200% of V,
more than 0% but equal to or less than 0.100% of W,
more than 0% but equal to or less than 0.0200% of Ca,
more than 0% but equal to or less than 0.0200% of Mg,
more than 0% but equal to or less than 0.0200% of Zr, and
more than 0% but equal to or less than 0.0200% of REM.

7. The electric resistance welded steel pipe for a torsion beam according to claim 5 , wherein packet grains in the tempered martensite structure have an average grain size of 10 μm or less.

8. The electric resistance welded steel pipe for a torsion beam according to claim 5 , wherein the wall thickness central portion in the L cross section has a dislocation density of 2.0×10 14 m −2 or less.

Assignees

• Nippon Steel Corp

Inventors

• Fukushi Takaaki
• Hasegawa Noboru
• Wada Manabu

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• F16L13/0281 Primary

  cold welded · CPC title

• C21D6/002

  containing Cr (C21D6/004 takes precedence) · CPC title

• C21D6/005

  containing Mn · CPC title

• C21D6/008

  containing Si · CPC title