# US 11,028,456 B2 · Electric resistance welded steel pipe for torsion beam

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- Number: US 11,028,456 B2
- Document ID: US11028456B2
- Status: Granted
- Kind: B2
- Application number: 16/327,066
- Filed: 2017-08-23
- Published: 2019-07-18
- Granted: 2021-06-08
- Earliest claimed: 2016-10-03
- Assignees: Nippon Steel & Sumitomo Metal Corporation
- Applicants: Nippon Steel & Sumitomo Metal Corporation
- Inventors: Takaaki Fukushi; Yasuhiro Shinohara; Hideki Hamatani
- Web page: https://patentgrep.com/patent/US11028456B2

## CPC

- C21D 8/10: during manufacturing of tubular bodies
- B23K 35/3073: {with Mn as next major constituent}
- C21D 9/08: for tubular bodies or pipes
- C21D 9/46: for sheet metals
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/20: with copper
- C22C 38/26: with niobium or tantalum
- C22C 38/28: with titanium or zirconium
- C22C 38/58: with more than 1.5% by weight of manganese
- B23K 11/002: {specially adapted for particular articles or work}
- C21D 2211/005: Ferrite
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

An electric resistance welded steel pipe for a torsion beam, in which a base metal portion includes, in terms of % by mass, 0.04 to 0.12% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.08 to 0.24% of Ti, 0.005 to 0.500% of Al, 0.01 to 0.06% of Nb, and 0.0005 to 0.0100% of N, a balance including Fe and impurities, wherein Vc90, defined by the following Formulae (i) and (ii), is 200 or more, a mass ratio of Ti content to C content is from 0.85 to 5.00, an areal ratio of ferrite is 80% or more, an average crystal grain size of ferrite crystal grains is 10 μm or less, and an average aspect ratio of ferrite crystal grains is 2.0 or less, in a metallographic microstructure of a central portion in a wall thickness direction of the base metal portion; log Vc90=2.94−0.75(βa−1) Formula (i); βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo Formula (ii).

## Claims

### Claim 1

An electric resistance welded steel pipe for a torsion beam, the steel pipe comprising a base metal portion and an electric resistance welded portion,
wherein a chemical composition of the base metal portion comprises, in terms of % by mass:
0.04 to 0.12% 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,
0.08 to 0.24% of Ti,
0.005 to 0.500% of Al,
0.01 to 0.06% of Nb,
0.0005 to 0.0100% of N,
0 to 1.00% of Cu,
0 to 1.00% of Ni,
0 to 1.00% of Cr,
0 to 0.50% of Mo,
0 to 0.20% of V,
0 to 0.10% 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 200 or more,
a mass ratio of Ti content to C content is from 0.85 to 5.00,
an areal ratio of ferrite is 80% or more, an average crystal grain size of ferrite crystal grains is 10 μm or less, and an average aspect ratio of ferrite crystal grains is 2.0 or less, in a metallographic microstructure of a central portion in a wall thickness direction of an L cross section of the base metal portion, and
a tensile strength in a pipe axis direction is from 750 to 1000 MPa;
log Vc90=2.94−0.75(βa−1) Formula (i)
βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+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.

### Claim 2 (depends on 1)

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 1.00% of Cu,
more than 0% but equal to or less than 1.00% 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 0.20% of V,
more than 0% but equal to or less than 0.10% 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.

### Claim 3 (depends on 1)

The electric resistance welded steel pipe for a torsion beam according to claim 1, which has an outer diameter of from 50 to 150 mm and a wall thickness of from 2.0 to 4.0 mm.

### Claim 4 (depends on 2)

The electric resistance welded steel pipe for a torsion beam according to claim 2, which has an outer diameter of from 50 to 150 mm and a wall thickness of from 2.0 to 4.0 mm.

### Claim 5

An electric resistance welded steel pipe for a torsion beam, 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:
0.04 to 0.12% 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,
0.08 to 0.24% of Ti,
0.005 to 0.500% of Al,
0.01 to 0.06% of Nb,
0.0005 to 0.0100% of N,
0 to 1.00% of Cu,
0 to 1.00% of Ni,
0 to 1.00% of Cr,
0 to 0.50% of Mo,
0 to 0.20% of V,
0 to 0.10% 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 200 or more,
a mass ratio of Ti content to C content is from 0.85 to 5.00,
an areal ratio of ferrite is 80% or more, an average crystal grain size of ferrite crystal grains is 10 μm or less, and an average aspect ratio of ferrite crystal grains is 2.0 or less, in a metallographic microstructure of a central portion in a wall thickness direction of an L cross section of the base metal portion, and
a tensile strength in a pipe axis direction is from 750 to 1000 MPa;
log Vc90=2.94−0.75(βa−1) Formula (i)
βa=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+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.

### Claim 6 (depends on 5)

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 1.00% of Cu,
more than 0% but equal to or less than 1.00% 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 0.20% of V,
more than 0% but equal to or less than 0.10% 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.

### Claim 7 (depends on 5)

The electric resistance welded steel pipe for a torsion beam according to claim 5, which has an outer diameter of from 50 to 150 mm and a wall thickness of from 2.0 to 4.0 mm.

### Claim 8 (depends on 6)

The electric resistance welded steel pipe for a torsion beam according to claim 6, which has an outer diameter of from 50 to 150 mm and a wall thickness of from 2.0 to 4.0 mm.