Note: Descriptions are shown in the official language in which they were submitted.
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Applicant: Sandvik Intellectual Property AB
Duplex Stainless Steel
TECHNICAL FIELD OF THE INVENTION AND STATE OF THE
ART
The present invention concerns to a duplex stainless steel alloy
having a high Cr-, Mo- and N- content and a ferrite content of
30-70%.
Duplex stainless steels are characterised by an austenite-ferrite
structure where both phases have different chemical
compositions. They are attractive as structural materials where
both high mechanical strength and excellent resistance to
corrosion are required. Duplex stainless steels are often used as
alternatives to austenitic stainless steels and nickel-based
alloys due to their lower cost, which is a consequence of the
lower nickel content in duplex stainless steels.
Duplex stainless steels are extensively used in the onshore and
offshore sectors of the oil and gas industry due to their corrosive
resistance to the various corrosive media, such as C02, H2S and
chlorides, found in such onshore/offshore environments.
Umbilical pipes, or "umbilicals", that interconnect units on the
land or sea surface with units at the bottom of the sea to
transport substances therebetween, such as to crude oil and gas
from a source to an oil rig, are often made of duplex stainless
steel pipes that are welded together. Downhole tubes, which are
grooved tubes that are generally installed within a drill-hole, and
integrated production tubes (IPUs), which are composite tubes
comprising umbilicals and downhole tubes, are also often made
of duplex steel.
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A downhole tube has to be resistant both to corrosion in the sea
water that surrounds it and to corrosion in the substances that it
transports. Downhole tubes are supplied in threaded finish and
joined to the necessary lengths by means of couplings. Since oil
and gas wells are situated at a considerable depth below sea
level the length of a downhole tube can be quite considerable.
The demands on the material that is used for downhole tubes
can be summarised as follows:
= Yield point in tension; minimum 110 ksi (kilos per square
inch) (760 MPa)
= Resistance to corrosion caused by CO2 or H2S.
= Good impact strength down to -46 C, at least 50J.
= The material has to be capable of being manufactured in
the shape of seamless tubes and in forms in which threads
and fitting couplings for tubes can be produced.
US 6749697 discloses a duplex stainless steel alloy with
austenite-ferrite structure having a high Cr-, Mo- and N- content.
This alloy fulfils the above-mentioned requirements since when
in hot extruded and annealed finish the alloy shows high
strength, good corrosion resistance in several acids and bases
and has especially good pitting resistance in chloride
environments, as well as good weldability. The pitting resistance
of an alloy is often described as a Pitting Resistance Equivalent
number, PRE number = %Cr + 3.3%Mo + 16%N. The alloy is
therefore optimised according to the property. The PRE number
of this alloy is over 40. The alloy contains in weight-% max
0.05% C, 0-2.0% Si 0-3.0% Mn, 25-35% Cr, 4-10% Ni, 2-6% Mo,
0.3-0.6% N, balance Fe and normally occurring impurities
whereby the content of ferrite is 30-70%.
WO 03/020994 describes an alloy characterised by Mn 0-3%, Cr
24-30%, Ni 4.9-10%, Mo 3-5, Cu 0-2%, W 0-3%, N 0.28-0.5%
and Co 0-3.5%. This alloy has a high Cr-, Mo and N content,
which increases the alloy's pitting resistance but on the other
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hand increases the risk of poor structural stability. By alloying
with Co the alloy is considered to be more structurally stable so
at least 0.5% Co, preferably at least 1.5%, max 3.5% Co can be
added to increase the corrosion resistance and this is also
reported to increase structural stability. Since the alloy may
contain W, the PRE number is modified to include the element
W having a weight corresponding to half of the weight for Mo,
namely PREW = %Cr + 3.3% (%Mo+0.5%W) + 16N. This alloy
has a PRE/PREW number over 40.
US 6312532 discloses a duplex stainless steel alloy containing
Mn 0.3-4%, Cr 27-35%, Ni 3-10%, Mo 0-3%, N 0.3-0.55%, Cu
0.5-3% and W 2-5%.The alloy exhibits a relatively high
resistance to corrosion in chloride environments due to alloying
with W. Alloying with Cu in combination with high W or Mo
contents is stated to decrease the precipitation of intermetallic
phases on slow cooling. This property is of great importance
when manufacturing stainless steel products of large dimensions
where the rate of cooling is relatively slow, which in general
increases the risk of intermetallic phases precipitating in the
temperature range of about 700-1000 C. This alloy has a PREW
number over 40. The patent states that at least 2% W should be
added for optimal effect and combinations of Mo + 0.5W should
not exceed 3.52. When using high contents of Mo and W the Cu
content should exceed 1.5% to maximise the structural stability.
If large amounts of Cu are used the Mo content should be low to
ensure good protection against inter-crystalline corrosion.
A disadvantage with duplex stainless steels is that their high
alloy content makes them susceptible to the formation of
intermetallic phases, such as the sigma and chi phases, from
extended exposure to high temperatures. The sigma phase is a
hard, brittle and highly corrodible intermetallic compound that is
rich in Cr and Mo. The chi phase is an intermetallic compound
with a manganese sulphide structure.
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Significant intermetallic precipitation may lead to a loss of
corrosion. resistance and sometimes to a loss of toughness.
Furthermore the production of thick and/or long pipes with large
diameters is adversely affected because of the precipitation of
intermetallic phases inside the products where the cooling rate
is relatively slow after annealing.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a duplex
stainless steel that shows high strength, good corrosion
resistance, good workability and which is weldable.
This object is fulfilled by optimising the alloy described in US
6749697 by utilising knowledge of the influence of the elements
Cu, W and Co on the structural stability of the alloy and its
corrosion properties while retaining or improving the alloy's
tensile properties. The object is fulfilled by a duplex stainless
steel alloy having the composition disclosed herein namely an
alloy that contains (in weight %): Cr 25-35%, Ni 4-10%, Mo 1-
6%, N 0.3-0.6%, Mn greater than 0 to 3%, Si max 1.0% and C
max 0.06%, Cu and/or W and/or Co 0.1-10%, W 0.1-5%,
balance Fe and normally occurring impurities wherein the ferrite
content is 30-70%, and which alloy has a yield point in tension
being minimum 760 MPa.
Such an alloy having high contents of Cr, Mo and N and
containing W or W and Cu and/or Co has surprisingly good
mechanical and corrosion properties, particularly as regards
pitting in a chloride environment. The high contents of Cr, Mo
and N give the alloy a very high strength and simultaneously a
good workability, especially for hot extrusion into articles such
as seamless tubes. The addition of W or W and Cu and/or Co
enhances the alloy's corrosion resistance in acid environments,
improves its structural stability and its weldability and confers
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greater resistance to some types of corrosion attack by
seawater.
Besides exhibiting excellent mechanical properties the inventive
5 alloy has a high resistance to stress corrosion cracking caused
by hydrogen sulphide. The alloy has good hot workability, is
easier to roll and is well suited for applications that require
welding, such as the manufacture of butt-welded seamless tubes
and seam-welded tubes for various coiled tubing applications.
Consequently, the alloy is especially suited for hydraulic tubes,
such as umbilicals, downhole tubes and IPUs. However, the
most remarkable characteristic of the alloy according to the
invention is the extraordinary combination of a high yield point in
tension and a high impact toughness.
The present inventors has found the following relationship be-
tween yield point in tension and composition for a duplex
stainless steel alloy:
Rpo.2 = 31.6% Cr + 34 (% Mo + % W) + 153% N + 10.2% Cu -426.
Tungsten, which is similar to molybdenum in function and effect
in terms of corrosion chemistry, is used to partly replace the
molybdenum in the alloy since tungsten is not as active as
molybdenum in promoting the precipitation of intermetallic
phases such as the sigma phase. Partly substituting
molybdenum with tungsten also increases the alloy's low
temperature impact toughness. The utilization of both
molybdenum and tungsten improves duplex stainless steel
alloy's corrosion resistance. Furthermore since molybdenum is
much more expensive than tungsten the substitution of
molybdenum with tungsten provides a more cost-effective alloy.
An addition of W or W and Cu and/or Co is also essential for
suppressing the precipitation of intermetallic phases. The alloy's
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pitting corrosion properties and its resistance to intergranular
corrosion are furthermore enhanced by a simultaneous addition
of W and Cu, where W at least partly substitutes Mo. However
high contents of W in combination with high contents of Cr and
Mo increase the risk of intergranular precipitations so the
content of W should therefore be limited to max 5 weight %.
According to an embodiment of the invention the alloy contains
0.40-0.55% N. It has been found that this high content of
nitrogen results in a particularly favourable combination of a
high yield point in tension and a high impact toughness.
According to another embodiment of the invention, where the
inventive duplex stainless steel alloy contains tungsten, the
following relationship is satisfied:
0.5(% W)+1(% Mo) =2-10%, or preferably 3-7%.
where (% W) and (% Mo) refer to the content of tungsten and
molybdenum respectively in weight %.
According to another embodiment of the invention the alloy is
manufactured using a conventional metallurgical method, such
as melting in an arc furnace. The inventive alloy may therefore
be readily melted and cast using conventional techniques and
equipment. Alternatively the alloy is manufactured by a powder
metallurgy method.
According to a further embodiment of the invention the alloy
comprises a maximum of 1 weight % alloying additions that are
added for process metallurgical or hot workability reasons.
The present invention also concerns an article in the form of a
tube, wire, strip, rod, sheet or bar or any other article having
high strength andlor good corrosion resistance, which comprises
an alloy according to any of the embodiments disclosed above.
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Such an article may be a seamless tube, a welding wire, a
seam-welded tube, a flange, a coupling, a rotor blade, a fan, a
cargo tank, weld material or high strength highly resistant
wiring. Said article is either made of the inventive alloy or it
comprises a coating of the inventive alloy. Alternatively the
article comprises the inventive alloy metallurgically or
mechanically bonded (or clad) to a base material such as carbon
steel.
Due to the good structural stability and weldability of the
inventive alloy its field of application is much larger than the
fields of application for the alloys constituting the state of the
art.
The alloy and the article according to any of embodiments
described above are intended for use particularly but not
exclusively as a construction material or a mechanical or
structural component, such as an umbilical, a downhole tube or
an integrated production unit (IPU), in sea-water environments,
in chloride environments, in corrosive environments, in chemical
plants, in the paper industry or as welding wire.
Further advantages as well as advantageous features of the in-
vention appear from the following description and the other de-
pendent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Fig 1 is a diagram in the form of a plot of the impact tough-
ness versus the yield point in tension for test charges
of alloys according to embodiments of the invention,
and
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Fig 2 is a diagram showing the relation for test charges of
alloys according to embodiments of the invention at
measured values of yield point in tension and a
prediction according to a formula drawn up by the pre-
sent inventors.
DESCRIPTION OF THE INVENTION
The principles and advantages of the alloy of the present inven-
tion and selection of the desired ranges of the constituent ele-
ments of the alloy which render the unexpected superiority of
the alloy can be stated as follows:
Chromium (Cr) is a very active element that improves the
resistance to a plurality of corrosion types. Moreover chromium
increases the strength of the alloy. High chromium content addi-
tionally implies a very good solubility of N in the material.
Consequently it is desirable to keep the Cr-content as high as
possible in order to improve the strength and resistance to
corrosion. For very good strength properties and resistance to
corrosion the content of chromium should be at least 25 weight
%, preferably at least 28 weight %. However the content should
not exceed 33%. However high contents of Cr increase the risk
of forming intermetallic precipitations. For this reason the
chromium content preferably not exceed 35 weight %.
Nickel (Ni) is used as an austenite-stabilising element and is
added to the alloy at a suitable level in order to attain the desir-
able content of austenite and ferrite, respectively. in order to
attain ferrite contents of between 30-70%, the content of nickel
should be at least 4 weight %, preferably at least 5 weight %
and should not exceed 10 weight %, preferably not exceed 9
we i g ht %.
Molybdenum (Mo) is an active element which improves the
resistance to corrosion in chloride environments as well as in
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reducing acids. An excessive Mo-content in combination with a
high Cr-content means that the risk of forming intermetallic
precipitations increases. Since Mo increases the strength of the
alloy, the content of Mo should be in the range of at least 1
weight %, preferably at least 3%, it should not exceed 6 weight
%, preferably not exceed 5 weight %.
Nitrogen (N) is a very active element which partly increases the
resistance to corrosion and partly increases the structural
stability as well as the strength of the material. Furthermore, a
high N-content improves the reformation of austenite after
welding, which ensures good properties for welded joints. In
order to attain a good effect at least 0.3 weight % N should be
added. High contents of N increase the risk of precipitation of
chromium nitrides, especially when the content of chromium is
also high. Furthermore, a high N-content implies that the risk of
porosity increases because the solubility of N in the steel melt
or weld pool will be exceeded. The N-content should therefore
be limited to max 0.60 weight %, it should preferably be at least
0.40 weight %, and should not exceed 0.55 weight % N.
Manganese (Mn) is added in order to increase the solubility of
N in the material, among other things. There are however other
elements that have a higher influence on the solubility. Mn in
combination with high contents of sulphur can also give rise to
the formation of manganese sulphides, which act as initiation
points for pitting corrosion. The content of Mn should therefore
be limited to being greater than 0 weight %, preferably at least
0.5 weight %, it should not exceed 3 weight %, preferably not
exceed 1.5 weight %.
Silicon (Si) is utilized as a deoxidiser during steel production
and it also increases the floatability under production and
welding. It is known that high silicon contents support the
precipitation of an intermetallic phase. It has been surprisingly
shown that an increased content of silicon favourably reduces
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the precipitation of sigma phase. For this reason a certain
content of silicon should be optionally permitted. The content of
silicon should however be limited to max 1.0 weight %. Silicon
would for example be added up to 0.15 l0 or 0.10%.
5
Carbon (C) strengthens stainless steel but promotes the
formation of precipitates harmful to corrosion resistance and
therefore has to be considered to be a contaminant in this
invention. Carbon has a limited solubility in both ferrite and
10 austenite and this implies a risk of precipitation of chromium
carbides. The carbon content should therefore be limited to max
0.05 weight %, preferably to max 0.03 weight % and most
preferably to max 0.02 weight %.
Copper (Cu) is added in order to improve the duplex stainless
steel's resistance to certain corrosive environments such as in
acid environments, such as sulphuric acid, and it also decreases
the alloy's susceptibility to stress corrosion cracking and
provides age-hardening effects. It has been found that Cu
decreases the precipitation rate of intermetallic phase on slow
cooling in materials with relatively high contents of Mo and/or W.
The reason for this is possibly that the precipitation of a copper-
rich austenite or epsilon phase prevents the precipitation of
other intermetallic phases such as the sigma phase. Since
precipitation of the epsilon phase should not have the same
negative influence on the corrosion properties as the sigma
phase, the appearance of small amounts of copper-rich epsilon
phase is a positive factor in the inventive alloy. However, high
contents of copper mean that the solubility limit is exceeded so
the Cu-content should be limited to max 5 weight %. When
present, the Cu-content should be at least 0.1 weight %,
preferably at least 0.8 weight %, and should not exceed 5 weight
%, preferably not exceed 3.5 weight %.
Tungsten (W) improves the resistance to corrosion in chloride
environments as well as in reducing acids and the alloy's
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resistance to pitting and crevice corrosion. It has been found
that alloying with W as a replacement for Mo increases the
alloy's low temperature impact strength. At the same time
alloying with W and Cu, where W replaces the element Mo in the
alloy with the aim of improving pitting resistance properties, can
take place with the aim of reducing the risk of worsening the
inter-crystalline corrosion resistance. However a too high W-
content in combination with a high Cr-content increases the risk
of precipitation of intermetallic phases, such as the sigma
phase. When present, the W-content should therefore be limited
to at least 0.1 weight %, it should not exceed 5 weight %,
preferably not exceed 3 weight %, and it may be min weight 1%.
Cobalt (Co) is added to reduce the precipitation of sigma phase.
It increases the alloy's corrosion resistance and structural
stability. Cobalt dissolves in the ferrite matrix, like nickel and
silicon, and strengthens the ferrite. Cobalt also tends to stabilise
austenite. When present, the content of cobalt should be greater
than 0%, preferably greater than 0.5% and should not exceed
3.5%, preferably not exceed 2% Co.
Ferrite: The content of ferrite is important in order to obtain
good mechanical properties and corrosion properties as well as
good weldability and workability. From a corrosion and welding
point of view it is desirable to obtain good properties with a
ferrite content between 30-70%. High ferrite contents cause
deterioration in low temperature impact toughness and
resistance to hydrogen embrittlement. The ferrite content is
therefore at least 30%, max 70%, preferably at least 35%, and
should not exceed 55%, the remainder being austenite.
Alloying additions: Elements added -for process metallurgical
reasons, in order to obtain melt purification from S or 0, for
example, or added in order to improve the workability of the
material. Examples of such elements are Al, B, Ca, Ce and Mg.
In order for such elements not to have a harmful effect on the
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properties of the alloy, the levels of each individual element
should be less than 0.1%. The total level of alloying additions
should be less than 1%, preferably max 0.1 %.
Modelling examples
Modelling of 21 different compositions was carried out using the
thermodynamic calculation program ThermoCalc Version Q. The
compositions of the experimental charge-s are given in Table 1.
Table 2 gives the compositions in the ferrite and the austenite
phases respectively. Table 3 contains parameters taken from
the calculated phase diagrams; such as the amount of sigma
phase at 900 C, the maximum temperature for sigma phase
(SIGMA) i.e. the temperature at which the sigma phase starts to
precipitate at thermodynamic equilibrium, which means that this
parameter is a dimension for the structural stability of the alloy,
the maximum temperature for chromium nitrides Cr2N and the
maximum temperature for the precipitation of chromium-rich
austenite phase.
Observations
An increase of the W content in alloys 1-4 increases the balance
in the PREW number (PRENW) between austenite and ferrite.
The Cr content in the austenite phase also decreases. A high Cr
content implies the risk of poor impact strength at low
temperatures (-46 C) so an increasing W content therefore
improves the alloy's impact strength (see Table 2, alloys 1-4).
Cu decreases the maximum temperature for sigma phase in
alloys with W (see Table 3, compare alloys 3 and 4 with alloys 7
and 8). For each weight % Cu Tmaxsigma decreases by 20-30 C.
W as a replacement for Mo should give an increased tensile
yield limit because W is a bigger atom, which should have a
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greater effect on solution hardening. By replacing Mo with W in
the ratio 1:2 the structural stability will be largely unchanged but
a better strength will be achieved.
Co decreases the risk of sigma phase precipitation by lowering
the maximum temperature for sigma phase precipitation. (See
Table 3, compare alloy 10 with alloy 11 and alloy 1 with alloy 9.)
Test examples
Sixteen test charges were produced by casting 170 kg blooms.
The blooms were hot-forged to round bars, from which test
materials for investigations with respect to corrosion, strength
and structural stability were taken.
The composition of the sixteen test charges successfully hot-
forged to round bars with a diameter of 40 mm are given in
Table 4.
For investigating the structural stability of the test charges test
plates from the rods were subjected to solution heat treatment at
7 temperatures between 900-1200 C (in steps of 50 C). The
best possible heat treatment temperature with the lowest degree
of intermetallic phase was determined by studies in a light opti-
cal microscope. The material was then subjected to solution
heat treatment at this temperature during 5 minutes before the
test material was taken out. The ferrite content was determined
by means of point counting in a light optical microscope (LOM).
The results are presented in Table 5.
For determining the structural stability for the test charges the
test material was rapidly heated to the dissolving temperature,
were annealed 3 minutes and cooled with a cooling rate of
-17.5 C/minute and -100 C/minute down to room temperature.
The amount of sigma phase in the test charges was then
determined by picture analysis of pictures from the BSE-detector
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in a Scanning Electron Microscope (SEM). The results are pre-
sented in Table 6.
It has been found that for a good structural stability it is neces-
sary to restrict the amount of the alloying elements as Cr, Mo
and W, while an increased content of N results in an improved
structural stability. Two important relations have been observed,
namely when there is a requirement of a good structural stability
it is advantageous to replace Mo by W. Furthermore, high con-
tents of N are favourable for the structural stability. It is shown
in the example that 5542 has a considerably better structural
stability than 5543, where an essential difference is that W re-
places Mo in a relation 2:1 (2% W for each % Mo).
The mechanical strength of the test charges was determined at
room temperature and the impact toughness was determined at
room temperature and -50 C. The results are presented in Table
7. However, a number of the test bars exhibited cracks. The
results are also shown in diagram form in Figure 1, which is a
plot of the impact toughness versus the yield point in tension.
The yield point in tension Rp0,2 is strongly dependant upon solu-
tion hardening elements. The relation between yield point in ten-
sion and the composition satisfies with a comparatively good
correlation the formula:
Rp0,2=31.6%Cr+34(%Mo+%W)+153%N+10.2%Cu-426
The appended Figure 2 shows the relation for the test charges
at the measured values of Rp0.2 and the prediction according to
this formula. It appears from the formula that for a high yield
point in tension N has the strongest influence, while Cr, Mo and
W have the same influence. Since W is an element which does
not influence the structural stability as negatively as Mo, it is fa-
vourable to alloy with W while lowering the content of Mo for
avoiding problems with the structural stability. However, Mo has
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a greater influence upon the corrosion properties. For a main-
tained structural stability it is possible to alloy with W that re-
places Mo by a factor 2, which means that the content of W may
be increased with 2% if the content of Mo is lowered by
5 1%, for optimizing the yield point in tension.
It appears clearly that for the test charges 5536 in comparison
with 5542 and 5548 it is possible to increase the yield point in
tension for the materials by lowering the content of Mo and N
10 and at the same time increase the content of W and Cu.
A problem for high tensile materials in general is that it is very
difficult to obtain a combination of a good impact toughness and
a high yield point in tension. It has for the present invention
15 been demonstrated that for charges having a very high yield
point in tension, where Rp0,2 exceeds 800 MPa, it is possible to
obtain an acceptable impact toughness at -50 C for charges
where the content of W and Cu is high at the same time as the
content of N has been reduced. lt was by that possible to obtain
a combination of two important properties for construction
materials, which so far has been difficult to obtain for duplex
steels.
A comparison of these charges 5536 with 5542 and 5548 shows
clearly this relationship, where an increase of the content of W
and Cu in combination with a lowering of the content of N results
in an attractive combination of an acceptable low temperature
impact toughness and a high yield point in tension. An optimiza-
tion of the properties may be obtained by further increasing the
content of W and Cu while considering the requirement of a
good structural stability.
The resistance of the test materials to pitting and crevice corro-
sion were measured according to ASTM G48C and MTI-2. The
critical pitting corrosion temperature (CPT) and the critical crev-
ice corrosion temperature (CCT) were determined and are
shown in Table 8. However, several of the test bars had cracks.
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The composition in the ferrite and austenite phase, respectively,
has been determined by means of microprobe analysis (EPMA),
and the results are shown in Table 9. The PRE number may be
calculated according to PRE = % Cr + 3.3 (% Mo + 0.5% W) +
16% N for the respective phase and the total composition. The
PRE number should be as balanced as possible between the
austenite and the ferrite phases.
The properties (positive/negative+0-) of the test material are
compared in Table 10, where also a judgement of the forgea-
bility of the material has been made on a scale from 0 (the
worst) to 5 (the best).
It appears that the charge 5548 is the best one with respect to
the combination of corrosion resistance, yield point in tension
and impact toughness. It appears from Table 4 that this charge
has a content of Cu of about 2%, W about 4% and Co about
0.1% in weight. Thus, it is favourable to have all these three
elements present in the alloy.
An optimum composition of a duplex stainless steel alloy
according to the invention where all the properties are consid-
ered may be as follows:
Alloy with high contents of Cr, Cu and W and with a content of N
which does not negatively influence the low temperature impact
toughness. Restrict the content of Mo so that the requirement of
a good structural stability may be met. A high yield point in ten-
sion is obtained when the content of N is high. It is possible to
lower the content of N without lowering the yield point in tension
if the content of W or Cu is increased. An acceptable low
temperature impact toughness in combination with a high yield
point in tension is obtained when the content of N is compara-
tively low and the content of W and Cu is high.
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1/9
Alloy C Si Mn Cr Ni Mo Cu W N Co
1 0,015 0,15 1,0 31,0 7 81 3,5 0 0 O 5 0
2 0,015 0,15 1,0 31,0 7,98 3,0 0 1,0 05 0
3 0,015 0,15 1,0 31,0 8,15 2,5 0 2,0 05 0
4 0,015 0,15 11,0 31,0 8,46 1 5 0 4,0 0,5 0
0,015 015 1,0 31,0 7,57 25 1,0 2,0 05 0
6 0,015 0,15 1,0 31,0 6,95 2,5 2,0 2,0 0,5 0
7 0,015 0,15 1,0 31,0 721 1,5 20 4,0 0,5 0
8 0 015 0,15 1,0 31,0 6,59 1,5 3,0 4;0 0,5 0
9 0,015 0,15 1,0 31,0 8,54 3,5 0 0 05 1
0,015 0,15 1,0 310 724, 1,5 2,0 4,0 05 1
11 0,015 0,15. 1,0 31,0 685 1,5 20 4,0 0,5 3
12 0015 015 1,0 310 727 35 1,0 0 0,5 0
13 0,015 0,15 10 31,0 6,66 3,5 2,0 0 05 0
14 0015 015 1,0 31,0 602 3,5 3,0 0 05 0
1S 0,015 0,15 1,0 31,0 7,70 3,5 1,0 0 0 5 1
16 0,015 0,15 1,0 31,0 6,86 3,5 210 0 0,5 1
17 0 015 0,15 1,0 31,0 6,05 3,5 3,0 0 0,5 1
18 0015 0,15 1,0 28,0 6,27 2,5 1,5 20 03 0
, 19 0,015 0,15 3,0 28,0 16,23 2,5 1,5 2 0 04 0
~20 0015 0,15 1,0 330 9,27 2,5 15 20 0,4 0
21 0 015 0,15 3,0 33,0 9 12 1,5 1,5 4 0 0,6 0
Table 1
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Alloy Cr Mo W N Cu Co PRENW
Ferr. Aust. Ferr. Aust. Ferr. Aust. Ferr. Aust. Ferr. Aust. Fen. Au6t. Fen.
Aust.
1 32,2 29,2 4,19 2,72 0 0 0,063 0,83 0 0 0 0 47,0 51,4
2 32,3 28,9 3.59 2.32 1,18 0.76 0,065 0,80 0 0 0 0 47,1 50,6
3 32,4 28,6 3,00 1,93 2,35 1,50 0,067 0,76 0 1 0 0 0 47,2 49,6
4 32,7 28,1 1,80 1,14 4,69 2,94 0,071 0,70 0 0 0 0 47,5 47,9
33,1 26,4 2,95 1,90 2,30 1,40 0,069 0,49 0,53 1,57 0 0 47,8 42,9
6 33,9 24.7 2,92 1,91 2,28 1,36 0,072 0,32 0,90 3,36 0 0 48,4 38,4
7 34,1 24,4 1,75 1,14 4,56 2,70 0,077 0.30 0,86 3,42 0 0 48,6 37,4
8 34,8 23,2 1.73 1,17 4,16 2,71 0,081 0,20 1,12 5,35 0 0 49,2 34,8
9 32,5 27,4 4,15 2,65 0 f 0 0,056 0,57 0 0 1,07 0,97 47,1 45,2
34,3 2319 1,75 1,13 4,46 2,72 0,071 0.24 0,81 3,50 0,91 1,19 48,4 35,7
11 = 34,4 23,2 1,76 ; L,1~ 4,3 2,76 0,062= 0,14 0,77 3,58 2,66 3,68 48,3
33,7.=
12 32,9 26;8 4,13 2,67 0 0 0,065 0,53 0,55 1153 0 0. 47 6 441
13 33,6 25,0 4,08 2,68 0 0 0,067 0,35 0,94 3,30 0 0 48 1 39114
14 34,2. 23,6 4,02 2,73 0 0 0,071 0,24 1,22 5,19 0 0 48 6 36,4
33,1 25,6 4,11 2,64 0 0 0,058 0,38 0.50 1,61 1,00 1,06 47,6 40 4
16 33,8 24,3 4,07 2,66 0 0 0,062 0,26 0,88 3,39 0,95 1,13 48.2 37,2
17 34,4 27,2 4,02 2,70 0 0 0,066 0,18 1,18 5,28 0,91 1,18 48.7 35 0
lg 30,8 24,4 3,01 1,94 2,44 1,47 0,068 0,42 0,79 2,26 0 0 45,8 39,9
19 30,4 23,6 2,99 1,90 2,37 1,40 0,070 0,39 0,80 2,31 0 0 45,3 38,4
, 20 37,1 26,9 2,95 1,94 2,37 1,40 0,071 0,37 0,61 2,51 0 0 51,9 41 5
21 36,3 25,3 1,75 1,13 4,49 2,57 0,076 0,32 ~ 0,61 2,67 0 0 50,7 3814
Table 2
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Alloy Mo Cu W Co PRENW PRENVV Sigma at Tmax Tmax Tmax PRENW
ferrite austenite 900 C sigma Cr2N fcc-
Cu
1 3,5 0 0 0 47,0 51 4 10 920 1120 50 5
2 3,0 0 1,0 0 47,1 50 6 15 950 1150 - 50 5
3 2,5 0 2.0 0 47,2 49,6 6 20 950 1175 - 50 5
4 1,5 0 4,0 0 47,5 47 9 25 1000 1220 50 5
2 5 1 0 2 0 0 47 8 42 9 20 950 1250 - 50 5
6 2,5 2,0 2,0 0 48,4 38 4 15 940 1250 850 505
7 15 20 40 0 48,6 374 20 =970 1250 850 505
8 1.5 3,0 4 0 0 49,2 34,8 20 950 1250 1050 50,5
9 3,5 0 0 1 47,1 45,2 0 900 1250 - 50,5
1,5 2 0 4,0 1 48,4 35,7 15 950 1250 850 - 50,5
11 1,5 2,0 4.0 3 48,3 33,7 0 880 1250 850 50,5
12 3,5 1 0 0 0 47,6 44 1 5 910 1250 50 5
13 3 5 2,0 0 0;48 1 39.4 0 900 1250 850 50 5
14 3,5 3,0 0 0 48,6 36,4 0 890 1220 1050 50,5
3,5 1,010 1 147,6 40,4 0 880 1250 - 50.5
16 3,5 2,0 0 1 148,2 37,2 0 ; 880 1250 850 50,5
17 3,5 3 0 0 1 148,7 35,0 0 860 1250 1000 50,5
18 2,5 1 5 2,0 0 45,8 39,9 5 920 1120 - 4413
19 2,5 1,5 2,0 0 45,31 38,4 0 850 1250 - 44,3
2 5 1 5 2,0 0 51 9 41,5 30 990 1250 800 49,3
21 1 5 1,5 14,0 0 50,7 38,4 10 940 1250 - 54,1
Table 3
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Composition of test charges
Table 4
Chargenr C Si Cr Ni Mo Cu W Co N
.5536 0,008 0,12 28,4 7,3 3,51 0,00 0,00 0,00 0,47
5537 0,037 0,42 30,6 7,3 2,27 0,95 2,72 0,98 0,45
5539 0,037 0,51 30,2 7,3 2,23 1,05 2,94 1,06 0,46
5542 0,056 0,89 29,2 7,5 1,54 1,95 3,77 0,01 0,42
5543 0,052 0,11 31,7 7,8 3,50 1,96 0,05 1,96 0,44
5544 0,037 0,48 30,5 7,5 2,26 0,98 2,93 0,99 0,45
5546 0,052 0,13 28,8 6,9 3,46 2,00 0,06 0,01 0,54
5548 0,007 0,11 31,5 9,2 1,47 1,92 3,94 0,10 0,41
5549 0,008 0,71 32,0 8,6 3,44 1,95 0,45 0,02 0,50
5550 0,007 0,12 29,2 6,1 1,57 1,96 4,03 1,98 0,54
=5552 0,061 1,00 29,4 5,1 3,43 0,00 0,00 2,01 0,54
5553 0,011 0,12 32,2 6,9 3,46 0,00 .0,00 2,01 0,53
5554 0,044 0,07' 29,0 5,7 1,53 0,00 3,86 1,95 0,43
5556 0,007 1,02 30,0 6,9 1,46 0,00 4,10 0,00 0,55
5557 0,061 0,10 31,8 6,2 1,47 0,00 3,90 0,00 0,55
6558 0,007 0,94 29,1 6,9 3,36 1,96 0,23 1,93 0,44
Table 5
Annealing temperature Ferrite
Chargenr ( C) (0/4)
5536 1100 56
=5537 1100 47
5539 1100 54
,5542 1150 50
5543 1100 44
5544 1100 47
5546 1025 35
5548 1100 49
5549 1150 47
5550 1100 43
5552 1050 50
5553 1050 18
-5554 1100 48
5556 1075 46
.5557 1050 01
5558 1050 44
Table 6 Sigma phase content ( !o) in dilatomer test and test charges subjected
to solution heat treatment
Chargenr -17,5 C(min -100 C/min
5536 4 0
5537 39 n a
5539 32 5
5542 35 2
5543 39 12
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5544 42 8
5546 2 0
5548 47 3
5549 n a 23
5550 32 1
'5552 15 0
5553 n a 9
5554 5 0
5556 46 1
5557 5 0 n a not analyzed
5558 43 2
Table 7 Impact toughness Elon9 A
(0/0)
Yield point in tension (J) (
Rp 0,2% Ultimate tensile stress
Chargenr (MPa) Rm (MPa) RT -50 C
-5536 660 880 245,0 61,5 46,2
5537 787 955 83,5 28,5 36,9
5539 793 986 78,0 21,0 29,9
5542 826 984 *88,7 *33,3 36,4
5543 756 959 128,7 46,0 38,0
5544 757 937 45,0 17,0 37,5
5546 637 916 65,0 24,7 43,4
5548 839 1014 104,3 33,0 33,3
5549 849 1017 *50,3 *28,3 32,6
,5550 763 972 *19,5 7,0 23,3
5552 n a n a 5,5 5,0 n a
5553 n a n a 4,0 4,0 n a
5554 714 905 49,0 10,5 37,8
5556 820 1063 5,0 4,5 8,2
5557 820 1003 21,5 8,0 22,5
5558 780 .1033 4,0 4,5 10,5
* Rem. Cracks in the test bars
Table 8
Chargenr CPT ( C) CCT ( C)
5536 80 40
5537 **75 50
5538
5539 75 *45
5541
5542 *40 35
5543 55 40
5544 *70 45
5546 65 40
5547
5548 80 40
5549 **50 *42,5
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605550 *40 30
605552 40 30
605553 40 "'30
605554 75 40
605556 45 30
605557 65 35
605558 40 30
*Rem. Cracks in the test bars
**Rem. Wide spread of the test results
Table 9
%Cr %CO %Ni %Cu %MO
aust ferr aust ferr aust ferr aust ferr aust ferr
5536 26,98 29,06 0,00 0,00 8,43 5,70 0,01 0,01 2,75 4,47
5537 29,44 31,39 0,95 0,81 8,68 5,97 1,08 0,77 1,75 2,78
5539 29,25 30,88 0,98 0,92 8,51 5,96 1,17 0,84 1,78 2,76
5542 27,52 30,00 0,00 0,00 9,10 6,00 2,21 1,62 1,06 1,71
.5543 28,33 33,06 1,98 1,63 9,69 6,02 2,31 1,49 2,51 3,97
5544 26,20 29,01 0,91 0,79 9,17 5,81 1,12 0,82 1,54 2,51
5546 27,08 30,16 0,00 0,00 8,01 4,97 2,16 1,49 2,74 4,09
5548 28,94 33,24 0,03 0,02 11,63 7,21 2,38 1,53 1,10 1,80
5549 29,76 32,69 0,00 0,00 10,34 7,02 2,23 1,60 2,50 3,87
cont. Table 9
%W %C %N PRE PRE Total
aust ferr aust ferr aust ferr aust ferr
0,06 0,09 0,016 0,014' 0,645 0,070 46,5 45,1 47,4
2,21 3,50 0,025 -0,008 0,705 0,061 50,1 47,3 49,7
2,44 3,84 0,017 -0,013 0,732 0,070 50,9 47,4 49,8
2,95 4,73 0,11 0,01 0,65 0,08 46,4 44,7 47,2
0,09 0,14 0,08 0,05 0,62 0,16 46,7 49,0 50,3
2,35 3,75 0,09 0,04 0,70 0,09 46,4 45,0 50,0
0,09 0,16 0,06 0,02 0,58 0,07 45,5 45,0 49,0
3,06 5,07 0,03 0,02 0,60 0,08 47,2 48,8 49,5
0,43 0,65 0,04 0,03 0,71 0,07 50,1 47,6 52,1
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Table 10
Yield point
Charge Corrosion in tension Impact toughness
Nr Forg Structural stab. CPT ASTM G48C RpO.2 -50 C
5536 5 ++ + - +
5537 3 0 + 0 0
5538 0
5539 3 0 + 0 0
5541 0
5542 4 0 - + +
5543 2 - - - +
5544 4 - 0 - 0
5546 1 + 0 - 0
5547 0
5548 1 0 + + +
5549 2 -- - + 0
5550 1 0 - - -
5552 5 + - -
5553 4 - - -
5554 2 + +
5556 4 0 - + -
5557 3 + 0 + -
,5558 5 0 - 0 -
