Electric resistance welded steel pipe

Patent metadata

Field	Value
Publication number	US-9726305-B2
Application number	US-201314420971-A
Country	US
Kind code	B2
Filing date	Sep 27, 2013
Priority date	Sep 27, 2012
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

An electric resistance welded steel pipe which has sufficient strength and low-temperature toughness and a low yield ratio and which is suitable as a line pipe to be laid in depths of the sea, characterized in that: the composition of the base material contains, in mass %, 0.05 to 0.10% of C, 1.00 to 1.60% of Mn, and 0.005 to less than 0.035% of Nb, and has a Ceq value of 0.23 to 0.38; and the metal microstructure of the base material contains 3 to 13% of martensite in area fraction with the balance being ferrite.

First claim

The invention claimed is:

1. An electric resistance welded pipe comprising a base material having a chemical composition comprising, by mass %,
C: 0.05 to 0.10%,
Mn: 1.00 to 1.60%,
Ti: 0.005 to 0.030%,
Nb: 0.005% to less than 0.035%, and
N: 0.001 to 0.008%,

further comprising one or both of
Si: 0.01 to 0.60% and
Al: 0.001 to 0.10%, and
a balance of iron and unavoidable impurities, wherein contents are restricted to
P: 0.02% or less and
S: 0.005% or less, and

a Ceq, represented by the following formula 1, satisfies 0.23≦Ceq≦0.38, and having a metal microstructure comprising, by area ratio, 3 to 13% of martensite, and a balance of ferrite, an average value of an equivalent circle diameter of the martensite being 0.5 to 1.5 μm:
Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15  (formula 1)

where, in formula 1, C, M, Cr, Mo, V, Ni, and Cu are values which represent the contents of the elements by mass %.

2. The electric resistance welded pipe according to claim 1 wherein the chemical composition of the base material further comprises, by mass %, one or more of
Ni: 1.0% or less,
Cu: 1.0% or less,
Cr: 1.0% or less,
Mo: 0.5% or less,
V: 0.2% or less,
Ca: 0.006% or less, and
REM: 0.006% or less.

3. The electric resistance welded pipe according to claim 1 wherein the chemical composition of the base material satisfies
Mn: 1.00 to 1.50% and
Si: 0.40% or less and
further satisfies
0.23≦Ceq≦0.30,
and
a tensile strength of the steel pipe is 490 to 760 MPa.

4. The electric resistance welded pipe according to claim 3 wherein the chemical composition of the base material satisfies
Nb: 0.005 to 0.020%.

5. The electric resistance welded pipe according to claim 3 wherein the chemical composition of the base material further comprises, by mass %, one more of
Ni: 0.5% or less,
Cu: 0.5% or less,
Cr: 0.5% or less,
Mo: 0.2% or less,
V: 0.1% or less,
Ca: 0.006% or less, and
REM: 0.006% or less.

6. The electric resistance welded pipe according to claim 4 wherein the chemical composition of the base material further comprises, by mass %, one more of
Ni: 0.5% or less,
Cu: 0.5% or less,
Cr: 0.5% or less,
Mo: 0.2% or less,
V: 0.1% or less,
Ca: 0.006% or less, and
REM: 0.006% or less.

7. The electric resistance welded pipe according to claim 1 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

8. The electric resistance welded pipe according to claim 2 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

9. The electric resistance welded pipe according to claim 3 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

10. The electric resistance welded pipe according to claim 4 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

11. The electric resistance welded pipe according to claim 5 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

12. The electric resistance welded pipe according to claim 6 , wherein the electric resistance weld pipe has a Charpy absorption energy at −30° C. of 190 J or more.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Shinohara Yasuhiro
• Nagai Kensuke
• Ozaki Masakazu

Classifications

• C22C38/18

  containing chromium · CPC title

• C22C38/08

  containing nickel {(C22C38/105 takes precedence)} · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title

• C21D9/46

  for sheet metals · CPC title

• Y10T428/12292

  Workpiece with longitudinal passageway or stopweld material [e.g., for tubular stock, etc.] · CPC title