Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~ 212S~35.-
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HIGH STRENGTH AUSTENITIC STAINLESS STEEL
SHAVING EXCELLENT GALLINC~ RESISTANCE
BACKGROUND OF THE INVENTION
This invention relates to nonmagnetic, austenitic, stainless steels
which are balanced in composition to provide high yield strength in the hot
10 worked, forged or cold worked condition, improved resistance to galling,
good resistance to intergranular stress corrosion cracking and good general
corrosion resistance. The steels are particularly suited for the production of
down-hole stabilizers and drill collars fabricated therefrom.
In view of the considerable depths to which the average oil fields are
15 drilled, thc requirements for the tubular alloys have changed dramatically
over the years. The materials must withstand greater stresses and are
required to have greater strength levels. Deeper drilling has required the
use of sensitive measuring equipment to ensure the desired course of
drilling is being maintained. This requires the alloy to be completely
2 0 nonmagnetic to avoid any interference with the instruments. At these greaterdepths, the steels have encountered very aggressive chloride and sulfide
environments which has required alloy modifications to improve resistance
to stress corrosion crachng. The drill collars have threaded connections
and must also possess reasonably good machinability. Drill collar alloys
2 5 have been continuously improved for various properties while attempting to
maintain the previous combination of properties because the loss of one
property would make the drill collar unacceptable for use in the industry.
~ 212~535 -'
During drilling, the total length of drill pipe down to the drill bit must be
regularly withdrawn to substitute new drill bits for the worn members. All ot
the pipe and drill collar joints must be threaded and disconnected many
times over the entire drilling depth. The joints encounter severe conditions
S which contribute to galling and wear. The make up torques at drilling sites,
in most cases, are excessive and cause premature galling damage at the
connections. When these drill collars are returned from the field after a
journey or two into the hole (short usage), they must be repaired extensively
or the damaged connections removed and new ones remachined on
10 shortened collars. Many users employ short pieces of galling resistant
beryllium-copper to minimize the joint damage. However, this alternative is
very costly. In order to insure that the relatively expensive threaded drill
collars can be used many times before being replaced and minimize any
downtime required for making and breaking the connections, the material
1 5 needs to be able to resist galling and wear.
Galling may be defined as the condition where the friction developed
between two rubbing surfaces results in localized welding at the high spots
on the surfaces. As more localized welding occurs during the making and
breaking of the joints, the metal-to-metal contact results in the destnuction of2 0 the threads which then require remachining.
The materials used for drill collars have not been modified
significantly tor the purpose of improving the resistance to wear and galling.
This may appear quite surprising when one stops to consider that there has
been a great deal of alloy development in austenitic stainless steels to
2 5 improve these properties. The major explanation for the lack of
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development work in this area is the influence of alloy changes on the other
properties required for these products.
The galling resistance of austenitic stainless steels has been relatsd
to many theories. Patents such as U.S. Patent 3,912,503 have modified the
5 surface oxide and increased the work hardening rate with a typical steel
having a composition of 16% Cr, 8% Ni, 8% Mn, 4% Si, 0.08% C, 0.15% N
and balance essentially iron. This alloy with good galling resistance was
also designed to provide good corrosion resistance as a replacement for
Type 304 stainless steel. Ni at these levels can impair stress corrosion
1 0 cracking resistance.
U.S. 3,663,215 relies on hard silicides of Mo, n, v or W which are
finely dispersed in the matrix to improve wear and galling. These steels
have 5 - 12% Si, 10 - 22% Cr, from about ~% up to about 10% of the silicide
former, 14 - 25% Ni, up to 0.15% C, less than 0.05% N and balance iron.
15 However, these steels do not have adequate strength for drill collars. They
also use high levels of expensive elements like Ni, Mo and W.
U.S. Patent 4,146,412 has excellent galling resistance and has a
broad chemistry composition of 13 - 19% Cr, 13 - 19% Ni, up to 4% Mn, 3.5 -
7% Si, up to 0.1~% C, less than 0.04% N and balance essentially iron.
20 These steels also have good resistance to stress corrosion cracking and
chloride environments but do not have adequate strength for drill collars.
Vanadium is restricted to residual amounts because of its strong ferrite
forming characteristics and the added cost to balance the alloy with more
nickel. Silicon and manganese were believed to lower the stacking fault
2 5 energy at the planes of atom disarray within the matrix of the steel. Under
' '' 2125535
loading conditions, the lower stacking fault energy promoted the
development of numerous stacking faults which produced much greater
strain hardening rates in the material. Silicon was believed to diffuse rapidly
to points or planes of stress and thereby promote excellent galling
5 resistance.
A standard grade which is regarded as having improved galling
resistance is the straight chrome grade known as AISI Typs 440C which
contains about 16 - 18% Cr, 1% max Mn, 1% max Si, 0.75% max Mo, about
0.95 - 1.20% C and remainder iron. This steel is heat hardenable but has
1 0 poor corrosion resistance, is magnetic and has poor formability.
From the work done previously, it is apparent that the balance
between the levels of chromium, manganese, nickel, carbon, nitrogen,
silicon and other elements has varied considerably.
Galling resistance in austenitic stainless steels has frequently been
15 improved by the addition of silicon in amounts up to 5% or more. However,
a close look at the alloy discussion for drill collar applications will reveal that
silicon is a very strong ferrite former and this element has been typically
maintained at levels below 1%. The desired composition balance for
maintaining a nonmagnetic condition (a magnetic permeability below 1.02
20 and preferably below 1.004), requires that any increases in silicon be
balanced by the addition of austenite stabilizing elements (carbon,
manganese, nitrogen or nickel) and/or the reduction of the chromium. This
is not an easy matter to resolve since the carbon is controlled to a very low
level to avoid intergranular corrosion. Manganese is a weak austenite
25 former but does increase the solubility limit of the alloy for nitrogen.
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Nitrogen is already at the highest level which can be kept in solution. Nickel
is very expensive and is maintained at the lowest level possible which will
preserve a low stacking fauit energy and provide good resistance to stress
corrosion cracking. Lowering the chromium decreases the corrosion
S resistance. All of these elements are balanced to provide the required levels
of strength, magnetic permeability, corrosion resistance, and intergranular
corrosion resistance. With all of these requirements, the industry has not
made, much of an attempt to change the chemistry balance to improve the
problems relating to galling and wear in the threaded connections.
Applicants are aware of only two patents which address the problem
of galling and wear in drill collar alloys. One is U.S. Patent 4,337,088 which
simply thought that any austenitic stainless having good resistance to galling
(U.S. Patent 3,912,503) would make a good drill collar alloy and made no
changes in the composition of an existing alloy. This steel does not provide
l S the desired level of strength required for these applications. The other
austenitic stainless steel developed with good galling properties for the oil
drilling applications is U.S. Patent 4,840,768. This patent relates to an
expensive, high nickel alloy (27 - 32%) having high chromium (24 - 28%),
low nitrogen (0.015% max) and low manganese (2% max). The steel has
20 1.5 - 2.75% silicon added for improved resistance to stress corrosion
cracking, but there is no relationship taught between the silicon and the
galling resistance, and there is no discussion on what features of the
composition balance provide the improved galling resistance. There is no
teaching which relates to a low nickel, high manganese, and high nitrogen
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alloy with typical chromium contents for these applications and does not
suggest how these elements would be balanced.
There is thus a need in the oil drilling business for an austenitic
stainless steel which possesses high strength, low magnetic permeability,
5 good corrosion resistance, good resistance to intergranular corrosion and
improved resistance to galling and wear. The steels of the invention are well
suited for other applications as well.
BRIEF SUMMARY OF THE INVENTION
10The present invention has found the composition balance within
critical ranges of the essential elements chromium, manganese, nickel,
carbon, nitrogen, vanadium and silicon in a ferrous alloy which develops a
steel alloy particularly suited for drill collars. The nonmagnetic austenitic
steel in the hot-worked or forged condition will have a 0.2% yield strength of
15at least 690 N/mm2 (100 ksi), and typically greater than 760 N/mm2 (110
ksi), resistance for at least 24 hours in the ASTM A262E test for intergranular
corrosion, a magnetic permeability not greater than 1.004 at 500 oersteds
and resistance to galling up to a stress level of at least 138 N/mm2 (20 ksi)
and preferably at least 170 N/mm2 (25 ksi) when mated against itself. The
20 steels preferably are further characterized by a % reduction in area of at
least 40%, a % elongation in 5 cm(2 inches) of at least 25%, a minimum
hardness of 290 HBN and a minimum tensile strength of at least 895 N/mm2
(130 ksi). The steels of the invention have been found to provide a galling
resistance up to a stress level of at least 138 N/mm2 (20 ksi) when mated
2 5 with other alloys tested.
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The steels of the invention consist essentially of, in weight percent,
greater than 0.05% to about 0.10% carbon, greater than about 16% to about
22% manganese, about 12.5% to about 17% chromium, about 0.2% to
about 0.4% nitrogen, about 1.5% to about 5% nickel, about 0.2% to about
5 0.7% vanadium, about 1% maximum copper, about 1% maximum
molybdenum, about 2% to about 4% silicon, about 0.05% maximum
phosphorus, about 0.03% maximum sulfur and balance essentially iron with
minor amounts of unavoidable impurities which do not adversely affect the
properties.
It is an object of the present invention to increase the galling
resistance of an austenitic stainless steel while maintaining the strength,
corrosion resistance, intergranular corrosion resistance and magnetic
permeability required for articles such as drill collars used in oil drilling.
It is a feature of the present invention to improve the galling resistance
15 of an austenitic stainless steel by increasing the silicon content and still
provide a composition balance which maintains the other required
properties for drill collars.
It is an advantage of the present invention that when the threaded
connections of drill collars made from the steel of the present invention are
20 made and broken during service, the damage to the threads of the drill
collars caused by galling is drastically reduced.
It is a further advantage of the present invention that the composition
balance for the steel of the present invention is obtained without the need for
large amounts of nickel which would significantly increase the cost.
5 3 ~ ;
,
It is a still further advantage of the present
invention that when the composition balance of the steel of
the present invention is provided, the material may be
processed and fabricated into drill collars with the
desired combination of properties.
Accordingly, in one aspect the present invention
resides in an austenitic stainless steel having a 0.2%
yield strength of at least 690 N/mm2 (100 ksi), a magnetic
permeability not greater than 1.004 at 500 oersteds,
acceptable intergranular corrosion resistance as measured
by ATSM A-262 Practice E and a resistance to galling up to
a stress level of at least 138 N/mm2 (20 ksi) when self
mated, said steel consisting essentially of, in weight
percent, from greater than 0.05% to about 0.10% carbon,
greater than 16% to about 22% manganese, about 12.5% to
about 17% chromium, about 1.5% to about 5% nickel, greater
than about 0.2% to about 0.4% nitrogen, about 0.2% to about
0.7% vanadium, about 1% maximum copper, about 1% maximum
molybdenum, greater than 2% to about 4% silicon, about
0.05% maximum phosphorus, about 0.03% maximum sulfur and
balance essentially iron.
In another aspect, the present invention resides
in a nonmagnetic drill collar produced by hot forging an
austenitic stainless steel consisting essentially of, in
weight %. greater than 0.05% to about 0.10% carbon, greater
than 16% to about 22% manganese, about 12.5% to about 17%
chromium, about 1.5% to about 5% nickel, about 0.2% to
about 0.4% nitrogen, about 0.2% to about 0.7% vanadium,
about 1% maximum copper, about 1% maximum molybdenum,
greater than 2% to about 4% silicon, about 0.05% maximum
phosphorus, about 0.03% maximum sulfur and balance
essentially iron with said collar having a 0.2% yield
strength of at least 690 N/mm2 (100 ksi), a magnetic
permeability not greater than 1.004 at 500 oersteds, a
2 ~ ~5 ~3~ ~
resistance to galling up to a stress level of at least 138
N/mm2 (20 ksi) when self mated and acceptable intergranular
corrosion resistance as measured by the ASTM A-262 Practice
E test.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Most austenitic stainless steels, which have been
developed for improved galling resistance, have not been
designed for high strength applications that also require
the magnetic permeability of the articles fabricated from
the steel to be critically controlled, as in drill collars.
The composition of the present invention is
balanced to provide a stable austenitic structure having a
significantly improved resistance to galling. The
austenitic structure is maintained during all conditions of
manufacture and use. The use of vanadium and a controlled
combination of carbon and nitrogen results in improved
resistance to intergranular attack and sensitization while
maintaining excellent strength and a nonmagnetic structure.
The desired combination of properties for the steel of the
present invention is obtained with the addition of about 2~
to about 4% silicon which has provided a galling resistance
which is typically at least 50~ improved over previous
drill collar levels.
Ingots or billets having a composition in
accordance with the present invention may be heated to a
temperature above 1095~C (2000~F) and hot reduced by
forging to the desired outside diameter which typically
ranges up to about 0.3 meters (1 foot) in diameter and to
lengths from about 4.5 meters (15 feet) to over 9 meters
(30 feet). The forged material is then trepanned to
8a
" 2i25~35
form the desired bore diameter. Drill collars may also vary in properties
depending on the diameter, processing and where the properties are
measured. Stress corrosion cracking is reduced if the stress in the drill
collars resulting from processing is minimized.
The steel of the invention consists essentially of, in weight percent,
greater than 0.05% to about 0.10% carbon, greater than 16% to about 22%
manganese, about 12.5% to about 17% chromium, greater than 0.2% to
about 0.4% nitrogen, about 1.5% to about 5% nickel, about 0.2% to about
0.7% vanadium, about 1% maximum copper, about 1% maximum
molybdenum, about 2% to about 4% silicon, about 0.05% maximum
phosphorus, about 0.03% maximum sulfur and balance essentially iron with
minor amounts of unavoidable impurities which do not adversely affect the
properties. A more preferred chemistry consists essentially of, in weight %,
0.06% to 0.10% carbon, greater than 18% to about 21% manganese, about
1 S 14.5% to about 16.5% chromium, about 0.22% to 0.4% nitrogen, about 2%
to about 4.6% nickel, about 0.2% to about 0.6% vanadium, up to 1% copper,
about 0.5% maximum molybdenum, about 2.5% to about 3.5% silicon, about
0.05% maximum phosphorus, about 0.03% maximum sulfur and balance
essentially iron with minor amounts of unavoidable impurities which do not
2 0 adversely affect the properties
Carbon is required for its function as a strong austenite former and its
contribution to strength. In order to also provide good resistance to inter-
granular corrosion, the level of carbon must be balanced to avoid excessive
amounts of grain boundary carbides. While carbon in many austenitic
2 5 stainless steels is normally maintained below 0.03% for excellent resistance
~ 21255~
to intergranular attack, the present carbon level of above 0.05% to about
0.10% and preferably 0.06% to 0.10% provides good resistance to
intergranular corrosion and sensitization while providing high strength and
austenite stability. A more preferred level of carbon is from 0.065% to
5 0.085%. The addition of vanadium to the steels of the present invention will
form fine precipitates with the carbon to impede dislocation slip and increase
strength. It must also be considered in the balance of the composition that
any removal of the carbon (and nitrogen) by the vanadium addition will
remove the strong austenite forming and stabilizing effect of the carbon
1 0 which would have been present if the carbon were in solid solution.
Vanadium is also a very strong ferrite former.
Several patents, such as U.S. 4,341,555, U.S. Patent 4,502,886, U.S.
3,645,725 and U.S. 3,926,620 have taught manganese should be restricted
to levels below the present range to provide an alloy with good intergranular
1 5 corrosion resistance. U.S. Patent 4,822,556 taught manganese levels
should be restricted to an amount below about 18% to avoid hot shortness
when copper is present and to avoid the formation of precipitates which
lower the intergranular corrosion resistance. There are many patents
including U.S. Patent 4,822,556 which taught that high levels of manganese
2 0 contribute to the formation of ferrite which is a serious concern for the steels
of the present invention. Contrary to this teaching, it is believed by the
applicants that manganese will form some austenite but is added primarily to
stabilize the austenite and provide the basis for holding large amounts of
nitrogen in solution. Manganese greater than 16% and typically greater
2 5 than 18% is required in the steels of the present invention to keep the nitro-
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gen in solution and stabilize the austenite. The upper limit for manganeseis about 22% and preferably about 21%. Contrary to the teachings of U.S.
4,502,886, manganese above 14% does not adversely affect the
mechanical properties but allows the levels of strength to be improved
5 because higher nitrogen contents may be kept in solution. U.S. Patent
3,912,503 states that manganese above 16% hurts the composition balance
and lowers the general corrosion resistance. Preferably, the manganese in
this patent is restricted to a level below 8.5% and this is in combination with
an alloy having twice the nickel content of the present invention. The upper
10 limit of manganese in the present invention is restricted to about 22% to
minimize the risk of hot shortness when high residual copper is present.
Higher levels of manganese also tend to form undesirable precipitates
which lower the intergranular corrosion resistance. Higher levels of
manganese may also contribute to the presence of ferrite. A preferred range
1 5 of manganese is from 18.5% to 21% and more preferably from about 19.5%
to 20.5%. It is also important to note that the high levels of manganese in the
steel of the present invention are also related to the silicon additions used
since silicon decreases nitrogen solubility and manganese additions are
relied upon to keep the nitrogen in solution. Previous levels of manganese
2 0 which kept the nitrogen in solution are not acceptable with silicon contents of
2% to 4%. Steels developed in U.S. Patent 3,912,503 were limited to
nitrogen contents below about 0.2% with the high level of silicon present.
The present invention has increased the amount of nitrogen in solution by
increasing the amount of manganese to levels higher than those used in
2 5 U.S. Patent 3,912,503.
2125~3~
Chromium is present from about ~2.5% to 17% to insure good
general corrosion resistance. A preferred chromium range of 13% to less
than 16% provides the optimum properties when balanced with the other
elements in the composition and particularly the higher levels of nitrogen. A
5 more preferred range ot chromium is from 13% to 14.5%. Chromium is
lower in the steels of the present invention compared to some drill collar
alloys in order to maintain the desired austenitic structure and compensate
for the increased silicon contents. The lower amounts of chromium in the
steels of the present invention must be supplemented with the higher levels
10 of manganese to insure that there is adequate solubility for nitrogen.
Nitrogen is a key element in developing the high strength level of this
alloy while stabilizing the austenitic structure. Nitrogen is present from
above about 0.2% to about 0.4%. Nitrogen will typically be from 0.22 % to
0.4% and preferably from 0.25% to 0.35%. The level of nitrogen must not
l S exceed the solubility limits of the alloy. The higher than normal levels of
manganese allow these higher levels of nitrogen to be in solution with the
reduced chromium contents. Since silicon decreases the nitrogen solubility,
the level of manganese must be even higher than the amount used to
replace chromium for maintaining the nitrogen in solution. The nitrogen
20 solubility limit for galling resistant steels such as taught in U.S. Patent
3,912,503 is about 0.2%. Previous drill collar alloys having high nitrogen
contents but low silicon contents have not been faced with the influence of
silicon on nitrogen solubility. Nitrogen is also a grain boundary corrosion
sensitizing element although not as aggressive as carbon. Achieving
2 S complete stabilization for the control of intergranular corrosion involves the
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consideration of the high levels of nitrogen as well as the carbon. The high
levels of nitrogen allow the silicon content to be increased while maintaining
an austenitic structure.
Vanadium has been considered with niobium and titanium as a
5 strengthening element but has not been used much because it is not as
strong a carbide former as the other elements. Niobium is generally
regarded as a better strengthening agent. Strengthening elements must be
used with caution in drill collar alloys for several reasons. Niobium, titanium,vanadium, tantalum, zirconium and others are very strong ferrite formers and
10 are usually avoided in a nonmagnetic alloy. Additionally, when these
elements combine with carbon or nitrogen, they remove these strong
austenite formers and stabilizers from the system which must be rebalanced
to insure a nonmagnetic structure. The formation of carbides and nitrides
will also remove the ferrite former (Nb, n, v, Ta and Zr). The addition of
about 0.2% to about 0.7% vanadium, preferably 0.2% to 0.6% and more
preferably about 0.25% to about 0.5% provides improved strength properties
when balanced properly with manganese and nitrogen additions.
Vanadium helps to provide a grain size of ASTM 6 or smaller which
improves strength and reduces intergranular stress corrosion. Vanadium
2 0 carbides and nitrides are very fine and uniformly distributed, as compared to
niobium carbides, which are massive and not uniformly distributed. The
vanadium addition for optimum results is 0.25% to 0.4% to provide the best
balance of grain size, precipitation strengthening, resistance to intergranular
stress corrosion, a stable austenitic structure and good forging
2 5 characteristics.
7 ~ ~ 3
U.S. Patent 4,822,556 relates to drill collars having a vanadium
addition.
Nickel is an element normally relied heavily upon for providing an
austenitic structure. The upper limit of nickel in this invention is about 5% tomaintain sufficient stress corrosion cracking resistance. A minimum level of
about 1.5% is required to provide an austenitic structure. A preferred range fornickel is about 2.5% to 4.5%. For the purposes of galling resistance, nickel
increases the stacking fault energy and should be minimized. Silicon lowers the
stacking fault energy which is favorable for galling resistance. A critical balance
of silicon and nickel is necessary to maximize austenite formation stability andresistance to galling. Lower nickel helps to keep the overall cost of the alloy
down. With the nitrogen added to the solubility limit of the alloy, the nickel will
be added in an amount which is just enough to maintain the alloy completely
austenitic.
Molybdenum and copper are commonly present as impurities and
are restricted to a maximum of 1.0% and preferably a maximum of 0.75% .
Molybdenum may be added to provide additional strengthening but its use will
require the addition of austenite formers to maintain the nonmagnetic balance
of the alloy since molybdenum is a ferrite former and also tends to remove
carbon from solution. While copper is beneficial in forming austenite, stabilizing
austenite to resist matensite transformation and lowering the work hardening
rate, it could cause a problem with hot shortness due to the high levels of
manganese and is thus limited to a maximum of 1%.
14
212553S
The critical magnetic permeability requirement for steels of the
present invention makes the addition of silicon a serious concern. Silicon
has a very high ferrite forming capability and requires the addition of
austenite formers above the existing levels used for drill collars. Silicon is
relied upon in the present invention to provide the improved galling
resistance, but the addition of silicon requires a rebalancing of the alloy
composition. Silicon is critical to the present invention and must be present
in an amount greater than about 2% to about 4%. Preferably, the silicon is
present in an amount ranging from 2.25% to 3.75% and more preferably
from 2.5% to 3.5%. With silicon contents below 2%, the alloy does not
possess good galling resistance and at levels higher than 4%, the alloy
does not have the desired combination of properties required for drill collars
and other articles.
Phosphorus and sulfur are commonly present as impurities.
1 5 Phosphorus is limited to about 0.05% maximum and sulfur is limited to about
0.03% maximum.
Any one or more of the preferred or more preferred ranges indicated
above can be used with any one or more of the broad ranges for the
remaining elements in this iron base alloy.
2 0 Drill collars produced according to the invention typically will have the
following properties determined at the 75% radius position:
1 ) Magnetic permeability of 1 .004 maximum.
2) 0.2% yield strength of 690 N/mm2 (100 ksi ) minimum.
3) Resistance to intergranular attack (as measured by the ASTM
2 5 A262E test) for at least 24 hours.
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4) % elongation in 5 cm (2 inches) of at least 25%.
5) % reduction in area of at least 40%.
6) Resistance to galling up to a stress level of at least 138 MN/m2
(20 ksi) on the surface.
The nonmagnetic alloy of the present invention is particularly suited
for down-hole equipment such as drill collars or stabilizers but may be
produced into various product forms such as plate, sheet, strip, bar, rod, wire
and castings. Applications, while not limiting, include boat shafts and other
marine products such as rudders, pump shafts and piston rods. The
stainless steel articles have particular utility in applications requiring high
strength, austenitic stability under all conditions, and good resistance to
intergranular and stress corrosion cracking. The alloy is also well suited for
the production of nonmagnetic generator rings.
A series of heats was processed and tested. The compositions for
these heats are reported in TABLE 1 and the properties reported in TABLES
2 and 3. The properties were on laboratory plate 1.6 cm (5/8 inch) thick
which simulated drill collars fabricated using the forging practice discussed
previously. The results represent delayed cooling prior to the last reduction.
All of the material was water quenched. The steels of the invention met the
desired combination of properties for yield strength, galling resistance,
nonmagnetic permeability and resistance to intergranular corrosion. The
composition also provided excellent properties for forging as measured by
the reduction of area and elongation results.
ASTM A-262 Practice E is a test procedure which is used to
2 5 detect susceptibility to intergranular corrosion. It is more sensitive than the
16
21~5~3~
. .~
previously used Strauss test. The test requires th~ material b~ immersed for
24 hours in a boiling solution of 10% sulfuric acid - 10% copper sulfate
solution while the test sample is in contact with metallic copper. After
exposure for 24 hours, the samples are bent 180~ and visually examined for
5 intergranular cracking. All of the steels of the inv~ntion containing vanadiumwithin the range of thè present invention and carbon below 0.11% passed
the ASTM A262E test for good resistance to intergranular corrosion.
TABLE 1
STAINLESS STEEL COMPOSITIONS (WEIGHT %)
I~L % C %Mn % Ni % N ~C ~/OV ~ ~ ~Q ~
.150 10.5 2.03 0.27 13.4 0.47 2.63 0.76 0.40 BAL
1 5 2 .067 15.1 2.07 0.34 13.4 0.50 2.52 0.77 0.44 BAL
3 .064 17.7 2.09 0.37 13.5 0.50 2.60 0.77 0.40 BAL
4~ .081 19.8 2.07 0.38 13.5 0.52 2.48 0.76 0.40 BAL
5~ .070 19.6 2.08 0.32 13.7 0.37 2.72 0.42 0.31 BAL
6~ .076 19.9 2.09 0.32 13.6 0.35 2.81 0.42 0.30 BAL
2 0 7~ .080 20.1 2.09 0.27 13.4 0.37 2.89 0.42 0.30 BAL
8 .083 21.0 2.06 0.48 13.6 0.34 3.02 0.61 0.40 BAL
9 .054 20.2 2.14 0.44 13.5 0.35 3.50 0.61 0.40 BAL
.079 13.6 4.60 0.31 17.8 0.05 3.80 <.01 <.01 BAL.
11 .081 14.2 4.52 0.27 17.5 0.02 3.85 <.01 <.01 BAL
2 5 12 .082 20.4 4.60 0.28 16.1 0.01 3.60 RES. RES. BAL
13t .076 20.3 4.60 0.28 16.2 0.30 3.60 RES. RES. BAL
14 .080 14.6 3.10 0.26 16.7 0.32 2.92 0.52 0.34 BAL.
.079 15.2 3.10 0.27 16.7 0.33 3.11 0.52 0.31 BAL.
16 .083 15.2 3.06 0.30 16.6 0.36 3.08 0.52 0.30 BAL
3 0 17 .069 15.3 3.05 0.31 16.6 0.30 3.28 0.51 0.31 BAL
1 8 .079 15.1 4.04 0.28 16.6 0.36 3.24 0.32 0.30 BAL
19 .070 15.2 2.13 0.43 17.3 0.34 0.48 0.50 0.20 BAL
20## .070 8.22 8.18 0.13 16.4 RES. 3.96 0.41 0.20 BAL
21 .066 15.0 3.97 0.26 16.5 0.36 3.07 0.30 0.30 BAL
3 5 22 .075 15.9 4.09 0.25 16.4 0.34 3.27 0.43 0.31 BAL.
23~ .075 17.0 4.10 0.22 16.4 0.33 3.21 0.43 0.31 BAL
24~ .086 20.2 4.18 0.26 16.0 0.35 3.40 0.42 0.31 BAL.
25# .070 15.0 2.00 0.42 16.5 0.36 0.50 0.50 RES. BAL
4 0 26 .073 14.9 3.04 0.33 16.6 0.35 3.21 0.51 0.31 BAL
~= STEELS OF THE INVENTION RES. = RESIDUAL
#= STEEL OF US 4,822,556 ##= STEEL OF US3,912,503
BAL.= BALANCE EXCEPT NORMAL RESIDUAL ELEMENTS
212~3~
._
The steels of TABLE 1 were examined for mechanical properties,
corrosion resistance, hardness and magnetic permeability. Th~ soundness
of the cast material was also checked for nitro~en porosity to see if the alloy
was also balanced to enable the nitrogen to stay in solution. The results of
5 these properties are shown in TABLE 2 and TABLE 3. Heats 1-3, 8-10 and
26 were gassy and not processed. Heat 16 was slightly gassy.
TABLE 2 - MECHANICAL PROPERTIES
10 ~ Gassy ~ TS % % ~ ~g, A262F Gall.
Qerst. Self/L80
Yes
1 5 2 Yes
4~ No 112 143 30 51 302 1.002 Pass 27 / 27
5~ No 1.002 Pass 28
6~ No 318 1.002 Pass
2 0 7~ No 318 1.002 Pass
8 Yes
g Yes
Yes ~1.1 39
11 No 127 150 28 34 353 1.024 Pass 39
2 5 12 No 108 137 43 67 289 1.001 Pass 34
13~ No 122 146 34 54 311 1.002 Pass 33 / 39
1 4 No 113 140 40 63 292
1 5 No 11 3 140 38 61 311 >1.01
16 Slight 120 147 38 58 306 1.015
3 ~ 17 No 11 4 143 39 60 306 1.06
18 No 315 <1 05
19 No 11 7 143 33 297 1.002 Pass
20## N0 96 127 37 61 279 1.003 41
21 No 307 1.03 34
3 5 22 Split
23~ No 318 1.002 Pass 32
24~ No 318 1.002 Pass 28
25# No ~100 >130 ~25 >40 >285 1.003 Pass 15 / 4
26 Yes
1 8
n 2 1 2 5 5 3 ~
L80 is a carbon steel used in the oil industry for casing and tubing. It
typically has about 0.2% - 0.25 % carbon and in the quenched and
tempered condition has about a 550N/m2 (80 ksi) yield strength.
The importance of the addition of vanadium is clearly shown by
comparing Heat 13 with Heat 12. The addition of 0.30% vanadium in Heat
13 provided a significant improvement in yield strength enabling the steel of
the invention to exceed the minimum required yield strength level of 690
MN/m2 (100 ksi ) whereas Heat 12 with 0.01% vanadium produced a
significantly lower minimum yield strength. Heat 12 was not considered a
steel of the invention because the properties were developed on plate
samples and the addition of at least 0.2% vanadium is believed to be
required to consistently develop the required minimum properties.
A study was made to determine the amount of nitrogen which could
be added to increase the strength of the drill collar alloy. In this study the
nickel was maintained at about 2% and the chromium was held at about
13.5%. The manganese was adjusted between 10% and 21% to determine
the effect on the austenitic structure and nitrogen solubility. The silicon was
maintained between 2% and 4% to provide the improved galling resistance.
The higher nitrogen containing heats (greater than about 0.4%) were
porous, especially when the manganese contents were below about 19%.
At low levels o~ manganese (Heat 1), porosity was a problem even at 0.27%
nitrogen. When manganese was increased to about 19% to 21%, nitrogen
solubility was increased and nitrogen levels as high as 0.38% (Heat 4) did
not develop porosity problems. These higher manganese levels also
19
~ : 212553S
promoted very stable austenitic stnuctures having magnetic permeabilities of
about 1.002. The results of this study revealed that higher levels of
manganese were required to maintain the austenitic structure and that an
austenitic alloy which was economical to melt and process would provide
S adequate properties for drill collars. An improved chemistry with slightly
higher nickel and chromium would provide better properties but at a higher
melt cost. It is to be noted that the results from the 3~/O silicon heat (Heat 21 )
provided an unacceptable magnetic permeability and helped to establish
the critical need for manganese contents of greater than 16%. Even though
10 the material had 0.26% N and 3.97% Ni, the balance with 16.46% Cr and
15% Mn produced a permeability of 1.03 at 500 oersteds which is
unacceptable for drill collars. One can easily see from this data that the
combination of properties is critical to control and that one can not change
the composition with the thought of enhancing a single property, such as
l S galling resistance (Heat 21), without balancing the chemistry in
consideration for the other properties of interest. Although the magnetic
permeability for Heat 14 was not determined, it was assumed that the
material would behave very similar to Heat 15 and would not have a
permeability within the required range.
2 0 The results shown in TABLE 3 show the delicate balance required to insure
that the nitrogen present remains in solution and does not cause a gassy
condition due to nitrogen evolution. The only heats above which did not
have a serious nitrogen porosity problem were Heats 4, 5, 6, 7 and 17.
While it is desired to increase the amount of nitrogen to the highest possible
2 5 level without having a porosity problem, the above heats show that very high
~ -- 2~25535 ~-
.._
levels of manganese are required for the low levels of chromium used with
the steels of the present invention in order to keep the nitrogen in solution.
Higher levels of chromium promote the formation of chromium nitrides and
cause a higher permeability. The differences between Heats 3 and 4 are
S very slight and show that for a nitrogen content of 0.37% or 0.38%, a level ofmanganese above 17.7% is required to keep the nitrogen in solution for
steels having from 2.48% to 2.60% silicon. One can also see from a
comparison between Heat 8 and Heat 4 that a reduction in silicon from
3.02% to 2.48% could be critical in keeping the nitrogen in solution even
1 0 with manganese contents above 20% with the chromium levels of the
present invention for high nitrogen near about 0.4%.
TABLE 3 - NITROGEN POROSITY (WEIGHT %)
Heat ~ %Mn ~ ~Ç~ .%Ni ~ ~L ~
0.150 10.46 2.63 13.41 2.03 0.76 0.47 0.27 P
1 5 2 0.067 15.03 2.52 13.44 2.07 0.77 0.50 0.34 P
3 0.064 17.68 2.60 13.53 2.09 0.77 0.50 0.37 P
4 0.081 19.84 2.48 13.53 2.07 0.76 0.52 0.38 OK
5~ 0.070 19.64 2.72 13.70 2.08 0.42 0.37 0.32 OK
6~ 0.076 19.92 2.81 13.61 2.09 0.42 0.35 0.32 OK
2 0 7' 0.080 20.09 2.89 13.39 2.09 0.42 0.37 0.27 OK
8 0.083 20.99 3.02 13.62 2.06 0.61 0.34 0.48 P
9 0.054 20.20 3.50 13.63 2.14 0.61 0.35 0.44 P
16 0.083 15.2 3.08 16.6 3.06 0.52 0.36 0.30 P~
17 0.069 15.3 3.28 16.6 3.05 0.51 0.30 0.31 OK
2 5 26 0.073 14.9 3.21 16.6 3.04 0.51 0.35 0.33 P
' ' 212553S
.,_.
P = Porosity Problems; P~ = Only A Slight Porosity Problem; ok = no porosity
Within the preferred ranges ot the present invention, there were
identified two groups of alloys which provide excellent combinations of
properties for drill collars and other related articles. One preferred chemistry5 (Heats 4-7) for less corrosive environments consists essentially of, in weightpercent, from greater than 0.05% to about 0.10% carbon, greater than 18%
to about 22% manganese, about 12.5% to about 15% chromium, about
1.5% to about 3% nickel, about 0.2% to about 0.4% nitrogen, about 0.2% to
about 0.7% vanadium, about 1% maximum copper, about 1% maximum
10 molybdenum, about 2% to about 3% silicon, about 0.05% maximum
phosphonus, about 0.03% maximum sulfur and the balance essentially iron.
This steel is basically a low nickel version balanced with low silicon and low
chromium to provide an economical alloy with a good balance of properties
along with improved galling and wear resistance.
A second alloy (Heats 13 and 24) for use in more corrosive
environments has a chemistry which consists essentially of, in weight
percent, from greater than 0.05% to about 0.10% carbon, greater than 18%
to about 22% manganese, about 15% to about 17% chromium, about 3% to
about 5% nickel, about 0.2% to about 0.4% nitrogen, about 0.2% to about
2 0 0.7% vanadium, about 1% maximum copper, about 1% maximum
molybdenum, about 3% to about 4% silicon, about 0.05% maximum
phosphorus, about 0.03% maximum sulfur and the balance essentially iron.
This alloy is a higher chromium and silicon alloy balanced with higher nickel
to provide a good combination of properties including improved resistance
2 5 to wear and galling.
21255~
While the invention has been described primarily with reference to the
production of nonmagnetic drill collars, it will be understood that the
invention has utility for other applications requiring a combination of
strength, resistance to intergranular stress corrosion, freedom from magnetic
S effects and good galling resistance. Modifications to the alloys shown may
be made by those skilled in the art without departing from the spirit of the
invention. Accordingly, no limitations are to be inferred except as set forth inthe appended claims.
