Electric-resistance welded steel pipe

Patent metadata

Field	Value
Publication number	US-10738366-B2
Application number	US-201315022004-A
Country	US
Kind code	B2
Filing date	Dec 20, 2013
Priority date	Dec 20, 2013
Publication date	Aug 11, 2020
Grant date	Aug 11, 2020

Abstract

The present invention provides electric-resistance welded steel pipe optimal for applications such as production of shale gas which is comprised of steel having a chemical composition which contains, by mass %, respectively, C: 0.08 to 0.18%, Si: 0.01% to 0.50%, Mn: 1.30 to 2.1%, Al: 0.001 to 0.10%, Nb: 0.005 to 0.08%, and Ti: 0.005 to 0.03%, is limited to N 0.008% or less, P: 0.020% or less, and S: 0.010% or less, and has a balance of Fe and unavoidable impurities, wherein a structure at a center part of thickness is 40% to 70% by area of ferrite phase having a circle-equivalent diameter of 1.0 μm to 10.0 μm and a balance of a low temperature transformation phase comprising a bainite phase, and Ceq satisfies 0.32≤Ceq≤0.60.

First claim

The invention claimed is:

1. Electric-resistance welded steel pipe comprised of steel having a chemical composition which contains, by mass %, respectively
C: 0.08 to 0.18%,
Si: 0.01% to 0.50%,
Mn: 1.30 to 2.1%,
Al: 0.001 to 0.10%,
Nb: 0.005 to 0.08%, and
Ti: 0.005 to 0.03%,
is limited to
N: 0.008% or less,
P: 0.020% or less, and
S: 0.010% or less, and
has a balance of Fe and unavoidable impurities, wherein
a structure at a center part of thickness is 40% to 70% by area of ferrite phase having a circle-equivalent diameter of 1.0 μm to 10.0 μm and a balance of a low temperature transformation phase comprising a bainite phase, and
a Ceq expressed by the following formula (1) satisfies 0.32≤Ceq≤0.60:
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15  (1)

where the “C”, “Mn”, “Cr”, “Mo”, “V”, “Cu”, and “Ni” in formula (1) are values expressing the contents of the respective elements by mass % and where when these elements are not included, the elements are calculated as 0,
wherein an area rate of the bainite phase is 90% or more of the balance other than the ferrite phase,
wherein an area rate of a residual austenite phase is not more than 0.5%,
wherein an area rate of a martensite phase is not more than 0.5%,
wherein a yield strength according to a tensile test in a longitudinal direction using a tensile test piece is 758 MPa to 822 MPa in strength,
wherein a yield ratio according to a tensile test in a longitudinal direction using the tensile test piece is 85 to 95%, and
wherein the tensile test piece is an arc shaped tensile test piece taken from the electric-resistance welded steel pipe in the longitudinal direction thereof on the basis of JIS Z 2241.

2. Electric-resistance welded steel pipe according to claim 1 wherein said chemical composition further contains, by mass %, one or more of
V: 0.08% or less,
Cu: 0.5% or less,
Ni: 0.5% or less,
Cr: 0.5% or less,
Mo: 0.5% or less,
Ca: 0.005% or less, and
REM: 0.005% or less.

3. Electric-resistance welded steel pipe according to claim 2 wherein said chemical composition further is limited to, by mass %,
B: 0.0004% or less.

4. Electric-resistance welded steel pipe according to claim 2 wherein there is no yield elongation in a stress-strain curve of a tensile test.

5. Electric-resistance welded steel pipe according to claim 2 wherein the thickness is 7 to 12.7 mm.

6. Electric-resistance welded steel pipe according to claim 1 wherein said chemical composition further is limited to, by mass %,
B: 0.0004% or less.

7. Electric-resistance welded steel pipe according to claim 1 wherein there is no yield elongation in a stress-strain curve of a tensile test.

8. Electric-resistance welded steel pipe according to claim 1 wherein the thickness is 7 to 12.7 mm.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Hamatani Hideki
• Iguchi Keinosuke
• Ozaki Masakazu
• Fukushi Takaaki
• Asano Takuya

Classifications

• B23K35/30

  with the principal constituent melting at less than 1550°C · CPC title

• C21D8/0426

  Hot rolling · CPC title

• C21D9/50

  for welded joints · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title