U.S. patent application number 12/285032 was filed with the patent office on 2009-02-05 for oil country tubular good for expansion in well and duplex stainless steel used for oil country tubular good for expansion.
Invention is credited to Kunio Kondo, Taro Ohe, Hideki Takabe, Masakatsu Ueda.
Application Number | 20090032246 12/285032 |
Document ID | / |
Family ID | 39788416 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090032246 |
Kind Code |
A1 |
Takabe; Hideki ; et
al. |
February 5, 2009 |
Oil country tubular good for expansion in well and duplex stainless
steel used for oil country tubular good for expansion
Abstract
An oil country tubular good for expansion according to the
invention is expanded in a well. The oil country tubular good for
expansion according to the invention is formed of duplex stainless
steel having a composition containing, in percentage by mass,
0.005% to 0.03% C, 0.1% to 1.0% Si, 0.2% to 2.0% Mn, at most 0.04%
P, at most 0.015% S, 18.0% to 27.0% Cr, 4.0% to 9.0% Ni, at most
0.040% Al, and 0.05% to 0.40% N, and the balance consisting of Fe
and impurities, a structure including an austenite ratio in the
range from 40% to 90%. The oil country tubular good for expansion
according to the invention has a yield strength from 256 MPa to 655
MPa, and a uniform elongation more than 20%. Therefore, the oil
country tubular good for expansion according to the invention has a
high pipe expansion characteristic.
Inventors: |
Takabe; Hideki; (Osaka-shi,
JP) ; Ueda; Masakatsu; (Osaka-shi, JP) ;
Kondo; Kunio; (Osaka-shi, JP) ; Ohe; Taro;
(Osaka-shi, JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
39788416 |
Appl. No.: |
12/285032 |
Filed: |
September 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2008/054747 |
Mar 14, 2008 |
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12285032 |
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Current U.S.
Class: |
166/206 ; 420/34;
420/57; 420/61; 420/67 |
Current CPC
Class: |
C22C 38/46 20130101;
C22C 38/001 20130101; C22C 38/44 20130101; C22C 38/004 20130101;
C22C 38/40 20130101; C22C 38/58 20130101; C22C 38/04 20130101; C22C
38/42 20130101; C22C 38/02 20130101 |
Class at
Publication: |
166/206 ; 420/57;
420/61; 420/67; 420/34 |
International
Class: |
E21B 17/00 20060101
E21B017/00; C22C 38/58 20060101 C22C038/58; C22C 38/44 20060101
C22C038/44; C22C 38/42 20060101 C22C038/42; C22C 38/18 20060101
C22C038/18; C22C 38/54 20060101 C22C038/54 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2007 |
JP |
2007-078691 |
Claims
1-10. (canceled)
11. An oil country tubular good for expansion in a well formed of
duplex stainless steel having a composition comprising, in
percentage by mass, 0.005% to 0.03% C, 0.1% to 1.0% Si, 0.2% to
2.0% Mn, at most 0.04% P, at most 0.015% S, 18.0% to 27.0% Cr, 4.0%
to 9.0% Ni, at most 0.040% Al, and 0.05% to 0.40% N, and the
balance consisting of Fe and impurities, and a structure comprising
an austenite ratio in the range from 40% to 90%, said oil country
tubular good having a yield strength from 276 MPa to 655 MPa, and a
uniform elongation more than 20%.
12. The oil country tubular good for expansion according to claim
11, wherein said duplex stainless steel further contains at most
2.0% Cu.
13. The oil country tubular good for expansion according to claim
11, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 4.0% Mo and at
most 5.0% W.
14. The oil country tubular good for expansion according to claim
12, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 4.0% Mo and at
most 5.0% W.
15. The oil country tubular good for expansion according to claim
11, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.8% Ti, at most
1.5% V, and at most 1.5% Nb.
16. The oil country tubular good for expansion according to claim
12, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.8% Ti, at most
1.5% V, and at most 1.5% Nb.
17. The oil country tubular good for expansion according to claim
13, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.8% Ti, at most
1.5% V, and at most 1.5% Nb.
18. The oil country tubular good for expansion according to claim
14, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.8% Ti, at most
1.5% V, and at most 1.5% Nb.
19. The oil country tubular good for expansion according to claim
11, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
20. The oil country tubular good for expansion according to claim
12, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
21. The oil country tubular good for expansion according to claim
13, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
22. The oil country tubular good for expansion according to claim
14, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
23. The oil country tubular good for expansion according to claim
15, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
24. The oil country tubular good for expansion according to claim
16, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
25. The oil country tubular good for expansion according to claim
17, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
26. The oil country tubular good for expansion according to claim
18, wherein said duplex stainless steel further contains one or
more selected from the group consisting of at most 0.02% B, at most
0.02% Ca and at most 0.02% Mg.
27. Duplex stainless steel used for oil country tubular goods for
expansion, comprising, in percentage by mass, 0.005% to 0.03% C,
0.1% to 1.0% Si, 0.2% to 2.0% Mn, at most 0.04% P, at most 0.015%
S, 18.0% to 27.0% Cr, 4.0% to 9.0% Ni, at most 0.040% Al, and 0.05%
to 0.40% N, and the balance consisting of Fe and impurities, said
duplex stainless steel comprising an austenite ratio from 40% to
90%, and having a yield strength from 276 MPa to 655 MPa and a
uniform elongation more than 20%.
28. The duplex stainless steel according to claim 27, further
comprising at most 2.0% Cu.
29. The duplex stainless steel according to claim 27, further
comprising one or more selected from the group consisting of at
most 4.0% Mo and at most 5.0% W.
30. The duplex stainless steel according to claim 27, further
comprising one or more selected from the group consisting of at
most 0.8% Ti, at most 1.5% V, and at most 1.5% Nb.
31. The duplex stainless steel according to claim 27, further
comprising one or more selected from the group consisting of at
most 0.02% B, at most 0.02% Ca, and at most 0.02% Mg.
Description
TECHNICAL FIELD
[0001] The present invention relates to an oil country tubular good
and duplex stainless steel, and more specifically, to an oil
country tubular good to be expanded in a well and duplex stainless
steel to be used for such an oil country tubular good for
expansion.
BACKGROUND ART
[0002] When a well (oil well or gas well) that yields oil or gas is
drilled in general, a plurality of oil country tubular goods called
"casings" are inserted into a well drilled using a drill pipe in
order to prevent the wall of the well from being collapsed. A
conventional method of constructing a well is as follows. To start
with, when a well is drilled for a prescribed distance, a first
casing is inserted. Then, when the well is further drilled for a
prescribed distance, a second casing having an outer diameter
smaller than the inner diameter of the first casing is inserted. In
this way, according to the conventional construction method, the
outer diameters of casings to be inserted are sequentially reduced
as the well is drilled deeper. Therefore, as the oil well is
deeper, the inner diameters of casings used in the upper part of
the well (near the surface of the ground) increase. As a result,
the drilling area increases, which pushes up the drilling cost.
[0003] A new technique for reducing the drilling area and thus
reducing the drilling cost is disclosed by JP 7-507610 A and the
pamphlet of International Publication WO 98/00626. The technique
disclosed by these documents is as follows. A casing C3 having a
smaller outer diameter than the inner diameter ID1 of casings C1
and C2 already provided in a well is inserted into the well. Then,
the inserted casing C3 is expanded, so that its inner diameter is
equal to the inner diameter ID1 of the previously provided casings
C1 and C2 as shown in FIG. 1. According to the method, the casing
is expanded inside the well and therefore it is not necessary to
increase the drilling area if the oil well to construct is deep.
Therefore, the drilling area can be reduced. Furthermore, the
number of necessary steel pipes can be reduced because large size
casings are not necessary.
[0004] In this way, the oil country tubular good expanded in a well
must have a uniformly deforming characteristic when expanded
(hereinafter referred to as "pipe expansion characteristic.") In
order to obtain a high pipe expansion characteristic, the deforming
characteristic without local constriction during working is
required, in other words, uniform elongation that can be evaluated
by tensile testing must be high.
[0005] As shown in FIG. 1 in particular, in the bell part 10 where
casings vertically placed on each other overlap, the pipe expansion
ratio is maximized. In consideration of the expansion ratio at the
bell part, the uniform elongation of the oil country tubular good
for expansion is preferably more than 20%.
[0006] JP 2005-146414 A discloses a seamless oil country tubular
good for expansion. The structure of the disclosed oil country
tubular good includes a ferrite transformation phase and low
temperature transformation phases (such as bainite, martensite, and
bainitic ferrite), and has a high pipe expansion characteristic.
However, the uniform elongation of each test piece in the disclosed
embodiment is not more than 20% (see JP 2005-146414 A, u-E1 in
Tables 2-1 and 2-2). Therefore, the bell part described above may
not deform uniformly.
DISCLOSURE OF THE INVENTION
[0007] It is an object of the invention to provide an oil country
tubular good for expansion having a high pipe expansion
characteristic. More specifically, it is to provide an oil country
tubular good having a uniform elongation more than 20%.
[0008] In order to achieve the above-described object, the
inventors examined the uniform elongation of various types of
steel. As a result, the inventors have found that duplex stainless
steel having prescribed chemical components has a uniform
elongation significantly higher than those of carbon steel and
martensitic stainless steel.
[0009] The inventors have further studied and found that in order
to produce an oil country tubular good having a uniform elongation
more than 20%, the following requirements must be fulfilled.
[0010] (1) The austenite ratio in the duplex stainless steel is in
the range from 40% to 90%. Herein, the austenite ratio is measured
by the following method. A sample is taken from an arbitrary
position of an oil country tubular good for expansion. The sample
is mechanically polished and then subjected to electrolytic etching
in a 30 mol % KOH solution. The etched surface of the sample is
observed using a 400.times. optical microscope with a 25-grating
ocular lens, and the austenite ratio is measured by a point count
method according to ASTM E562.
[0011] (2) The yield strength is adjusted in the range from 276 MPa
to 655 MPa. The yield strength herein is 0.2% proof stress
according to the ASTM standard. When an oil country tubular good
for expansion is kept as-solution treated, the yield strength is
within the above-described range. Herein, "as-solution treated"
means the state in which after the solution treatment, no other
thermal treatment or no other cold working is carried out except
for cold straightening.
[0012] The present invention was made based on the above-described
findings and the invention can be summarized as follows.
[0013] An oil country tubular good for expansion according to the
invention is expanded in a well. The oil country tubular good for
expansion according to the invention is formed of duplex stainless
steel having a composition containing, in percentage by mass,
0.005% to 0.03% C, 0.1% to 1.0% Si, 0.2% to 2.0% Mn, at most 0.04%
P, at most 0.015% S, 18.0% to 27.0% Cr, 4.0% to 9.0% Ni, at most
0.040% Al, and 0.05% to 0.40% N, and the balance consisting of Fe
and impurities, and a structure including an austenite ratio in the
range from 40% to 90%. The oil country tubular good has a yield
strength from 256 MPa to 655 MPa, and a uniform elongation more
than 20%.
[0014] Herein, the "uniform elongation" means the distortion (%) at
the maximum load point in a tensile test. The austenite ratio is an
austenite area ratio.
[0015] The duplex stainless steel may further contain at most 2.0%
Cu. The duplex stainless steel may further contain one or more
selected from the group consisting of at most 4.0% Mo and at most
5.0% W. The duplex stainless steel may further contain one or more
selected from the group consisting of at most 0.8% Ti, at most 1.5%
V, and at most 1.5% Nb. The duplex stainless steel may further
contain one or more selected from the group consisting of at most
0.02% B, at most 0.02% Ca and at most 0.02% Mg.
[0016] The duplex stainless steel according to the invention is
used for the above-described oil country tubular good for
expansion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic view for use in illustrating a new
method of constructing a well that yields oil or gas.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] Now, embodiments of the invention will be described in
detail.
[0019] An oil country tubular good according to an embodiment of
the invention is formed of duplex stainless steel having the
following chemical composition and metal structure. Hereinafter,
"%" related to elements means "% by mass."
[0020] 1. Chemical Composition
[0021] C: 0.005% to 0.03%
[0022] Carbon stabilizes the austenite phase. In order to
effectively secure the effect, the C content is not less than
0.005%. Meanwhile, if the C content exceeds 0.03%, carbide is more
easily precipitated, which lowers the grain boundary corrosion
resistance. Therefore, the C content is from 0.005% to 0.03%.
[0023] Si: 0.1% to 1.0%
[0024] Silicon deoxidizes the steel. In order to secure the effect,
the Si content is not less than 0.1%. Meanwhile, if the Si content
exceeds 1.0%, intermetallic compounds are acceleratingly generated,
which lowers the hot workability. Therefore, the Si content is from
0.1% to 1.0%.
[0025] Mn: 0.2% to 2.0%
[0026] Manganese deoxidizes and desulfurizes the steel and improves
the hot workability as a result. Manganese also increases the solid
solubility of N. In order to effectively secure the effect, the Mn
content is not less than 0.2%. Meanwhile, if the Mn content exceeds
2.0%, the corrosion resistance is lowered. Therefore, the Mn
content is from 0.2% to 2.0%.
[0027] P: 0.04% or less
[0028] Phosphorus is an impurity that promotes central segregation
and degrades the sulfide stress cracking resistance. Therefore, the
P content is preferably as small as possible. Therefore, the P
content is not more than 0.04%.
[0029] S: 0.015% or less
[0030] Sulfur is an impurity and lowers the hot workability.
Therefore, the S content is preferably as small as possible. The S
content is therefore not more than 0.015%.
[0031] Cr: 18.0% to 27.0%
[0032] Chromium improves the carbon dioxide corrosion resistance.
In order to secure sufficient carbon dioxide corrosion resistance
for duplex stainless steel, the Cr content is not less than 18.0%.
Meanwhile, if the Cr content exceeds 27.0%, intermetallic compounds
are acceleratingly generated, which lowers the hot workability.
Therefore, the Cr content is from 18.0% to 27.0%, preferably from
20.0% to 26.0%.
[0033] Ni: 4.0% to 9.0%
[0034] Nickel stabilizes the austenite phase. If the Ni content is
too small, the amount of ferrite in the steel is excessive, and the
characteristic of the duplex stainless steel does not result. The
solid solubility of N in the ferrite phase is small, and the
increase in the ferrite amount causes nitride to be precipitated,
which degrades the corrosion resistance. Meanwhile, an excessive Ni
content reduces the ferrite amount in the steel, and the
characteristic of the duplex stainless steel does not result. In
addition, an excessive Ni content causes a .sigma. phase to be
precipitated. Therefore, the Ni content is from 4.0% to 9.0%,
preferably from 5.0% to 8.0%.
[0035] Al: 0.040% or less
[0036] Aluminum is effective as a deoxidizing agent. However, if
the Al content exceeds 0.040%, inclusions in the steel increase,
which degrades the toughness and the corrosion resistance.
Therefore, the Al content is not more than 0.040%.
[0037] N: 0.05% to 0.40%
[0038] Nitrogen stabilizes the austenite phase and also improves
the thermal stability and the corrosion resistance of the duplex
stainless steel. In order to achieve an appropriate ratio between
the ferrite phase and the austenite phase in the steel, the N
content is not less than 0.05%. Meanwhile, if the N content exceeds
0.40%, a defect attributable to a generated blow hole is caused.
The toughness and corrosion resistance of the steel are degraded as
well. Therefore, the N content is from 0.05% to 0.40%, preferably
from 0.1% to 0.35%.
[0039] Note that the balance of the duplex stainless steel
according to the invention consists of Fe and impurities.
[0040] The duplex stainless steel for an oil country tubular good
for expansion according to the embodiment further contains Cu in
place of part of Fe if necessary.
[0041] Cu: 2.0% or less
[0042] Copper is an optional element and improves the corrosion
resistance of the steel. However, an excessive Cu content lowers
the hot workability. Therefore, the Cu content is not more than
2.0%. Note that in order to effectively secure the above-described
effect, the Cu content is preferably not less than 0.2%. However,
if the Cu content is less than 0.2%, the above-described effect can
be obtained to some extent.
[0043] The duplex stainless steel for an oil country tubular good
for expansion according to the embodiment further contains one or
more selected from the group consisting of Mo and W in place of
part of Fe if necessary.
[0044] Mo: 4.0% or less
[0045] W: 5.0% or less
[0046] Molybdenum and tungsten are optional elements. These
elements improve the pitting corrosion resistance and the deposit
corrosion resistance. However, an excessive Mo content and/or an
excessive W content causes a .sigma. phase to be more easily
precipitated, which embrittles the steel. Therefore, the Mo content
is not more than 4.0% and the W content is not more than 5.0%. In
order to effectively secure the above described effect, the Mo
content is preferably not less than 2.0% and the W content is
preferably not less than 0.1%. However, if the Mo content and the W
content are less than the described lower limits, the
above-described effect can be obtained to some extent.
[0047] The duplex stainless steel for an oil country tubular good
for expansion according to the embodiment further contains one or
more selected from the group consisting of Ti, V, and Nb in place
of part of Fe if necessary.
[0048] Ti: 0.8% or less
[0049] V: 1.5% or less
[0050] Nb: 1.5% or less
[0051] Titanium, vanadium, and niobium are optional elements. These
elements improve the strength of the steel. However, if the
contents of these elements are excessive, the hot workability is
lowered. Therefore, the Ti content is 0.8% or less, the V content
is 1.5% or less, and the Nb content is 1.5% or less. In order to
more effectively secure the above-described effect, the Ti content
is preferably not less than 0.1%, and the V content is preferably
not less than 0.05%. The Nb content is preferably not less than
0.05%. However, if the Ti, V, and Nb contents are less than the
above-described lower limits, the above effect can be obtained to
some extent.
[0052] The duplex stainless steel for an oil country tubular good
according to the embodiment further contains one or more selected
from the group consisting of B, Ca, and Mg in place of part of
Fe.
[0053] B: 0.02% or less
[0054] Ca: 0.02% or less
[0055] Mg: 0.02% or less
[0056] Boron, calcium, and magnesium are optional elements. These
elements improve the hot workability. However, if the contents of
these elements are excessive, the corrosion resistance of the steel
is lowered. Therefore, the B content, the Ca content, and the Mg
content are each not more than 0.02%. In order to more effectively
secure the above-described effect, the B content, the Ca content,
and the Mg content are each preferably not less than 0.0002%.
However, if the B, Ca, and Mg contents are less than the lower
limits, the above-described effect can be obtained to some
extent.
[0057] 2. Metal Structure
[0058] The duplex stainless steel that forms an oil country tubular
good for expansion according to the invention has a metal structure
including a ferrite phase and an austenite phase. It is considered
that the austenite phase as a soft phase contributes to improvement
of the uniform elongation.
[0059] The austenite ratio in the steel is from 40% to 90%. Herein,
the austenite ratio is an area ratio measured by the following
method. A sample is taken from an arbitrary position of an oil
country tubular good for expansion and mechanically polished, and
then the polished sample is subjected to electrolytic etching in a
30 mol % KOH solution. The etched surface of the sample is observed
using a 400.times. optical microscope with a 25 grating ocular
lens, and the austenite ratio is measured by the point count method
according to ASTM E562.
[0060] If the austenite ratio is less than 40%, the uniform
elongation is reduced to 20% or less. Meanwhile, if the austenite
ratio exceeds 90%, the corrosion resistance of the steel is
degraded. Therefore, the austenite ratio is from 40% to 90%. The
austenite ratio is preferably from 40% to 70%, more preferably from
45% to 65%.
[0061] 3. Manufacturing Method
[0062] The oil country tubular good for expansion according to the
invention is produced by the following method.
[0063] Molten steel having the above-described composition is cast
and then formed into billets. The produced billet is subjected to
hot working and made into an oil country tubular good for
expansion. As the hot working, for example, the Mannesmann method
is carried out. As the hot working, hot extrusion may be carried
out, or hot forging may be carried out. The produced oil country
tubular good for expansion may be a seamless pipe or a welded
pipe.
[0064] The oil country tubular good for expansion after the hot
working is subjected to solution treatment. The solution treatment
temperature at the time is from 1000.degree. C. to 1200.degree. C.
If the solution treatment temperature is less than 1000.degree. C.,
a .sigma. phase is precipitated, which embrittles the steel. The
yield strength is raised and exceeds 655 MPa because of the
precipitation of the .sigma. phase, and therefore the uniform
elongation is 20% or less. On the other hand, if the solution
treatment temperature exceeds 1200.degree. C., the austenite ratio
is significantly lowered and becomes less than 40%. The solution
treatment temperature is preferably from 1000.degree. C. to
1175.degree. C., more preferably from 1000.degree. C. to
1150.degree. C.
[0065] The oil country tubular good for expansion according to the
invention is in an as-solution-treated state (so-called
as-solution-treated material). More specifically, the tubular good
is used as a product right after the solution treatment without
being subjected to other heat treatment and cold working (such as
cold reduction or pilger rolling) except for cold straightening. In
this way, since the oil country tubular good for expansion
according to the invention is in an as-solution-treated state, and
therefore the yield strength may be in the range from 276 MPa to
655 MPa (40 ksi to 95 ksi). It is considered that in this way, the
uniform elongation exceeds 20% and a high expansion characteristic
is obtained even in a well. Note that if the yield strength exceeds
655 MPa, the uniform elongation is 20% or less. The oil country
tubular good for expansion needs strength in a certain level, and
the yield strength is 276 MPa or more.
[0066] Note that if cold working is carried out after the solution
treatment, the yield strength exceeds 655 MPa. Therefore, the
uniform elongation is less than 20%.
EXAMPLE
[0067] A plurality of steel products having the chemical
compositions in Table 1 were cast and formed into billets. The
produced billets were subjected to hot forging and hot rolling and
a plurality of steel plates for testing having a thickness of 30
mm, a width of 120 mm, and a length of 300 mm were formed.
TABLE-US-00001 TABLE 1 heat ST test chemical composition (in % by
mass, the balance consisting of Fe and impurities) treat- temp.
.gamma. TS YS UE No. C Si Mn P S Cr Ni Al N Cu Mo W Ti V Nb B Ca Mg
structure ment (.degree. C.) (%) (MPa) (MPa) (%) inventive 1 0.016
0.35 0.49 0.023 0.0005 24.90 6.94 0.020 0.2900 0.50 3.07 2.11 --
0.11 -- 0.0025 -- -- D ST 1085 56 867 623 28.5 steel 2 0.010 0.25
0.39 0.017 0.0007 22.00 5.40 0.032 0.1400 0.10 2.90 -- -- -- -- --
-- -- D ST 1070 58 735 490 48.0 3 0.022 0.40 0.90 0.016 0.0008
25.19 6.20 0.030 0.1400 0.25 3.16 -- -- 0.07 -- -- -- -- D ST 1080
55 821 605 34.0 4 0.020 0.55 1.10 0.016 0.0012 26.12 6.50 0.020
0.1500 -- -- -- -- -- -- -- -- -- D ST 1050 62 600 430 50.2 5 0.014
0.29 0.46 0.023 0.0003 24.88 6.59 0.005 0.2715 0.45 3.08 2.00 --
0.04 -- 0.0023 0.0016 -- D ST 1100 50 849 625 32.8 6 0.018 0.38
0.57 0.025 0.0005 25.37 6.82 0.016 0.2898 0.52 3.17 2.15 0.005 0.08
0.017 0.0028 0.0023 -- D ST 1150 48 893 645 26.6 7 0.020 0.48 1.51
0.022 0.0011 22.39 5.74 0.034 0.1650 -- 3.20 -- -- -- -- -- -- -- D
ST 1050 55 734 484 48.4 8 0.018 0.45 1.56 0.021 0.0009 22.45 5.75
0.025 0.1665 -- 3.21 -- -- -- -- -- -- -- D ST 1050 56 754 531 43.5
9 0.017 0.31 0.87 0.017 0.0009 24.59 5.66 0.018 0.1200 0.26 3.07 --
-- -- -- -- -- 0.002 D ST 1050 58 780 560 40.3 10 0.024 0.49 0.95
0.027 0.0020 25.53 6.37 0.031 0.1700 0.48 3.18 -- -- -- -- -- -- --
D ST 1060 58 830 610 33.5 11 0.018 0.45 0.85 0.022 0.0007 25.10
7.18 0.028 0.1600 -- 3.20 0.42 -- -- -- -- 0.0021 -- D ST 1060 55
805 605 37.5 comparative 12 0.070 0.28 1.27 0.008 0.0007 0.20 0.02
0.020 0.0040 -- 0.04 -- 0.007 0.04 -- -- -- -- C QT -- -- 596 520
9.5 steel 13 0.080 0.33 1.32 0.014 0.0009 0.18 0.06 0.030 0.0050 --
0.05 -- 0.009 0.05 -- -- -- -- C QT -- -- 528 445 11.0 14 0.007
0.23 1.20 0.019 0.0005 0.15 -- 0.031 0.0060 -- -- -- -- -- -- -- --
-- C QT -- -- 535 348 17.0 15 0.009 0.20 0.42 0.012 0.0014 11.90
5.33 0.020 0.0087 -- 1.91 -- 0.086 0.06 -- -- -- -- M QT -- -- 914
751 2.00 16 0.007 0.20 0.44 0.017 0.0009 12.03 5.44 0.025 0.0077
0.24 1.92 -- 0.071 0.06 -- -- -- -- M QT -- -- 955 948 6.12 17
0.007 0.20 0.42 0.015 0.0006 11.87 5.82 0.030 0.0076 -- 1.91 --
0.100 -- -- -- -- -- M QT -- -- 890 843 9.15 18 0.007 0.20 0.44
0.017 0.0009 12.05 5.43 0.022 0.0065 0.24 1.92 -- 0.069 0.06 -- --
-- -- M QT -- -- 860 616 8.34 19 0.006 0.22 0.42 0.016 0.0005 11.89
5.42 0.021 0.0080 0.24 1.91 -- 0.097 0.06 -- -- -- -- M QT -- --
904 670 4.00 20 0.008 0.21 0.41 0.013 0.0007 11.94 5.41 0.030
0.0090 0.23 1.91 -- 0.095 0.06 -- -- -- -- M QT -- -- 917 705 3.20
21 0.021 0.55 1.08 0.016 0.0012 26.12 6.54 0.020 0.1700 -- 2.94
1.55 -- -- -- -- -- -- D ST 980 60 970 701 15.0 22 0.020 0.55 1.10
0.016 0.0012 26.01 6.50 0.020 0.1600 -- 2.87 1.95 -- -- -- -- -- --
D ST 1250 32 930 643 18.0 23 0.016 0.33 0.49 0.023 0.0005 24.60
6.85 0.020 0.2900 0.50 3.04 2.05 -- 0.09 -- 0.0022 -- -- D ST +
1085 52 1110 1075 1.6 CW D: duplex stainless steel, C: carbon
steel, M: martensitic stainless steel, QT: quenching &
tempering, ST: solution-treatment, ST + CW: solution-treatment +
cold working, UE: uniform elongation
[0068] In Table 1, steel types for test numbers are given in the
"structure" column. In the table, "D" represents duplex stainless
steel, "C" represents carbon steel, and "M" represents martensitic
stainless steel. With reference to Table 1, test Nos. 1 to 11 and
21 to 23 were duplex stainless steel. Test Nos. 12 to 14 were
carbon steel and test Nos. 15 to 20 were martensitic stainless
steel.
[0069] Steel plates with test Nos. 1 to 23 were subjected to heat
treatment as described in the "heat treatment" column and cold
working in Table 1. More specifically, the steel plates with test
Nos. 1 to 11 were subjected to solution treatment in the
temperature range from 1050.degree. C. to 1150.degree. C. ("ST" in
the "heat treatment" column in Table 1). The solution treatment
temperature for each of the steel plates is shown in the "ST
temperature" in Table 1. The steel plates with test Nos. 1 to 11
were each a so-called as-solution-treated material without being
subjected to other heat treatment or cold working such as cold
reduction after the solution treatment.
[0070] The steel plates with test Nos. 12 to 20 were quenched at
920.degree. C. and then tempered in the temperature range from
550.degree. C. to 730.degree. C. ("QT" in the "heat treatment"
column in Table 1). The steel plate with test No. 21 was subjected
to solution treatment at a temperature less than 1000.degree. C.,
and the steel plate with test No. 22 was subjected to solution
treatment at a temperature higher than 1200.degree. C. The steel
plates with test Nos. 21 and 22 are as-solution-treated materials.
The steel plate with test No. 23 was subjected to solution
treatment at 1085.degree. C. followed by cold drawing.
[0071] Measurement of Austenite Ratio
[0072] For the steel plates of duplex stainless steel with test
Nos. 1 to 11 and 21 to 23, the austenite ratio was obtained after
the heat treatment. More specifically, a test piece was taken from
each of these steel plates. The sampled test pieces were
mechanically polished and the polished test pieces were subjected
to electrolytic etching in a 30 mol % KOH solution. The etched
surfaces of the samples were observed using a 400.times. optical
microscope with 25 grating ocular lens in 16 fields. The austenite
ratio (%) was obtained for each of the observed fields. The
austenite ratios were obtained by the point count method according
to ASTM E562. The average of the austenite ratios (%) obtained for
each of the fields is given in the ".gamma." column in Table 1.
[0073] Tensile Testing
[0074] A round bar specimen having an outer diameter of 6.35 mm,
and a parallel part length of 25.4 mm was taken from each of the
steel plates 1 to 23 in the lengthwise direction and subjected to a
tensile test at room temperature. The yield strengths (MPa)
obtained by the tensile tests are given in the "YS" column in Table
1, the tensile strengths (MPa) are given in the "TS" column in
Table 1, and the uniform elongations (%) are given in the "UE"
column in Table 1. The 0.2% proof stress according to the ASTM
standard was defined as the yield strength (YS). The distortion of
a specimen at the maximum load point was defined as the uniform
elongation (%).
[0075] Test Result
[0076] With reference to Table 1, the steel plates with test Nos. 1
to 11 each had a chemical composition, a metal structure and a
yield strength within the ranges defined by the invention, and
therefore their uniform elongations all exceeded 20%.
[0077] Meanwhile, the steel plates with test Nos. 12 to 20 were not
made of duplex stainless steel and therefore their uniform
elongations were not more than 20%.
[0078] The steel plate with test No. 21 is made of duplex stainless
steel and has a chemical composition within the range defined by
the invention, but its solution-treatment temperature was less than
1000.degree. C. Therefore, the yield strength exceeded the upper
limit by the invention and the uniform elongation was not more than
20%. It was probably because the solution-treatment temperature was
low and therefore a .sigma. phase was precipitated, which raised
the yield strength.
[0079] Since the steel plate with test No. 22 exceeded 1200.degree.
C., the austenite ratio was less than 40% and the uniform
elongation was not more than 20%. The steel plate with test No. 23
was not an as-solution-treated material, but subjected to cold
working after the solution-treatment. Therefore, the yield strength
exceeded the upper limit of the range defined by the invention and
the uniform elongation was not more than 20%.
[0080] Although the embodiments of the present invention have been
described and illustrated in detail, it is clearly understood that
the same is by way of illustration and example only of how to carry
out the invention and is not to be taken by way of limitation. The
invention may be embodied in various modified forms without
departing from the spirit and scope of the invention.
INDUSTRIAL APPLICABILITY
[0081] The oil country tubular good for expansion and duplex
stainless steel according to the invention are applicable to an oil
country tubular good and particularly applicable as an oil country
tubular good for expansion in a well.
* * * * *