U.S. patent application number 10/385837 was filed with the patent office on 2004-04-01 for nickel-base alloy for the electro-welding of nickel alloys and steels, welding wire and use.
This patent application is currently assigned to Framatome ANP. Invention is credited to Chabenat, Alain, Faure, Francois, Guyon, Claude, Pierron, Dominique, Thomas, Andre.
Application Number | 20040062677 10/385837 |
Document ID | / |
Family ID | 31985268 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040062677 |
Kind Code |
A1 |
Chabenat, Alain ; et
al. |
April 1, 2004 |
Nickel-base alloy for the electro-welding of nickel alloys and
steels, welding wire and use
Abstract
The alloy contains, by weight, less than 0.05% of carbon, from
0.015% to 0.5% of silicon, from 0.4% to 1.4% of manganese, from 28%
to 31.5% of chromium, from 8% to 12% of iron, from 2% to 7% of
molybdenum, from 0.05% to 0.75% of aluminium, from 0.1% to 0.8% of
titanium, from 0.6% to 2% in total of niobium and tantalum, the
ratio of percentages of niobium plus tantalum and of silicon being
at least 4, less than 0.04% of nitrogen, from 0.0008% to 0.0120% of
zirconium, from 0.0010% to 0.0100% of boron, less than 0.01% of
sulphur, less than 0.020% of phosphorus, less than 0.30% of copper,
less than 0.15% of cobalt and less than 0.10% of tungsten, the
remainder of the alloy, with the exception of unavoidable
impurities of which the total content is at most 0.5%, consisting
of nickel. The alloy is used, in particular, for the production of
wires for the electro-gas welding of units or components of nuclear
reactors and, more particularly, of pressurised water-cooled
nuclear reactors.
Inventors: |
Chabenat, Alain;
(Chabeat-sur-Saone, FR) ; Pierron, Dominique;
(Saint Martin En Bresse, FR) ; Thomas, Andre;
(Lyon, FR) ; Faure, Francois; (Satnt-Cloud,
FR) ; Guyon, Claude; (Charrecey, FR) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Assignee: |
Framatome ANP
|
Family ID: |
31985268 |
Appl. No.: |
10/385837 |
Filed: |
March 12, 2003 |
Current U.S.
Class: |
420/448 |
Current CPC
Class: |
B23K 35/304 20130101;
C22C 19/053 20130101; B23K 35/0261 20130101; C22C 19/055
20130101 |
Class at
Publication: |
420/448 |
International
Class: |
C22C 019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2002 |
FR |
02 11 937 |
Claims
1. Nickel-base alloy for the electro-welding of nickel alloys and
steels and, in particular, of stainless steels, wherein the alloy
contains, by weight, less than 0.05% of carbon, from 0.015% to 0.5%
of silicon, from 0.4% to 1.4% of manganese, from 28% to 31.5% of
chromium, from 8% to 12% of iron, from 2% to 7% of molybdenum, from
0.05% to 0.75% of aluminium, from 0.1% to 0.8% of titanium, from
0.6% to 2% in total of niobium and tantalum, the ratio of
percentages of niobium plus tantalum and of silicon being at least
4, less than 0.04% of nitrogen, from 0.0008% to 0.0120% of
zirconium, from 0.0010% to 0.0100% of boron, less than 0.01% of
sulphur, less than 0.020% of phosphorus, less than 0.30% of copper,
less than 0.15% of cobalt and less than 0.10% of tungsten, the
remainder of the alloy, with the exception of unavoidable
impurities of which the total content is at most 0.5%, consisting
of nickel.
2. Alloy according to claim 1, and preferably containing less than
0.05% of silicon, about 4% of molybdenum, 0.006% of zirconium and
0.004% of boron.
3. Alloy according to claim 1, and containing about 0.15% of
aluminium.
4. Alloy according to claim 2, and containing about 0.15% of
aluminium.
5. Alloy according to claim 1, and containing about 0.30% of
titanium.
6. Alloy according to claim 2, and containing about 0.30% of
titanium.
7. Alloy according to claim 3, and containing about 0.30% of
titanium.
8. Welding wire for the electro-gas welding of nickel alloys and
steel, in particular of stainless steels, wherein it is produced
from an alloy according to claim 1.
9. Welding wire for the electro-gas welding of nickel alloys and
steel, in particular of stainless steels, wherein it is produced
from an alloy according to claim 2.
10. Welding wire for the electro-gas welding of nickel alloys and
steel, in particular of stainless steels, wherein it is produced
from an alloy according to claim 3.
11. Welding wire for the electro-gas welding of nickel alloys and
steel, in particular of stainless steels, wherein it is produced
from an alloy according to claim 4.
12. Use of an alloy according claim 1, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear
reactor.
13. Use of an alloy according claim 2, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear
reactor.
14. Use of an alloy according claim 3, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear
reactor.
15. Use of an alloy according claim 4, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear
reactor.
16. Use of an alloy according claim 5, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear
reactor.
17. Use of an alloy according claim 8, for the welding of units or
components of a nuclear reactor during construction, assembly or
repair operations on a unit or component of the nuclear reactor.
Description
TECHNICAL FIELD
[0001] The invention relates to a nickel-base alloy for the
electro-welding of nickel alloys and steels, in particular
non-alloyed or low alloy steels and stainless steels.
[0002] The invention also relates to wires and electrodes for the
electro-welding of parts made of nickel alloy and/or steel, in
particular in the field of the construction, assembly and repair of
components of nuclear reactors.
BACKGROUND TO THE INVENTION
[0003] It is known to use chromium-containing nickel-base alloys
for the production of certain components or units of nuclear
reactors.
[0004] In particular, a nickel alloy containing approximately 15%
of chromium, known as alloy 600, has been used for the production
of units or components of pressurised water-cooled nuclear
reactors.
[0005] To improve the corrosion resistance of the units or
components of pressurised water-cooled nuclear reactors, there is a
tendency to replace the alloy 600 containing approximately 15% of
chromium by an alloy 690 containing approximately 30% of chromium
and approximately 10% of iron.
[0006] Electro-welding wires or electrodes of nickel alloy of which
the composition is adapted to the welding of the alloy 600 or the
alloy 690 are used to produce welds on these nickel alloy units or
components.
[0007] Table 1 below shows typical compositions of commercially
available wires for the welding of the alloy 690 and for the
welding of the alloy 600 (alloy 52 or alloy 82).
[0008] The first four columns of Table 1 show the compositions of
alloy 52 wires known by the trade name Inconel 52 from the American
company, Special Metals, produced on the basis of four separate
castings and used to weld the alloy 690.
[0009] The last column of the table gives a typical analysis of an
alloy 82 wire with the trade name Phyweld 82 made by Sprint Metal,
for welding the alloy 600.
[0010] Alloy 52 wires or 82 may be used, in particular, for the
inert gas electro-welding of the alloy 690 or the alloy 600.
1TABLE 1 Analysis of wires for welding the alloys 600 and 690 Alloy
Alloy Alloy Alloy 52 52 52 52 Comparison Comparison wire wire wire
wire example CF example CF Inconel Casting 1 2 3 4 52 wire 52 wire
82 wire C 0.022 0.020 0.020 0.020 0.022 0.020 0.030 S 0.001 0.001
0.001 0.001 0.002 0.001 0.002 P 0.004 0.004 0.003 0.004 <0.003
0.003 0.003 Si 0.150 0.140 0.140 0.170 0.020 0.03 0.170 Mn 0.25
0.24 0.25 0.25 0.88 0.92 3.04 Ni 61.13 60.46 60.40 59.13 58.20
60.10 70.54 Cr 29.00 28.97 28.91 28.94 30.93 30.13 20.99 Cu 0.010
0.010 0.010 0.010 0.03 0.005 Co 0.040 0.010 0.010 0.010 0.010 Mo
0.010 0.010 0.010 0.010 0.012 0.02 Nb 0.021 0.010 0.010 0.010 0.918
0.93 2.287 Al 0.660 0.690 0.670 0.680 0.065 0.08 Ti 0.560 0.580
0.560 0.530 0.193 0.22 0.200 Fe 8.14 8.86 9.03 10.25 9.12 8.50 2.72
Zr 0.0013 0.006 B 0.0028 0.0040 Nb/Si 0.14 0.07 0.00 0.00 45.90
31.0 13.45
[0011] The alloy 52 welding wires are used, in particular, in the
nuclear field, to produce welds in zones of the nuclear reactor
components in contact with the primary fluid, which is water at a
very high temperature (approximately 310.degree. C.) and under very
high pressure (approximately 155 bars), in the case of pressurised
water-cooled nuclear reactors.
[0012] Alloy 52 is used for the homogeneous welding of alloy 690
parts and for producing heterogeneous welds. These heterogeneous
welds may be, for example, welds on an alloy 600 containing 15% of
chromium in solid form or deposited on a base metal, wherein the
chromium content of the deposited metal may be from 15% to 20%.
[0013] Another application for alloy 52 in heterogeneous welding is
the coating of low alloy steels such as the steels 16MND5, 18MND5
or 20MND5 or the welding of low alloy steels to austenitic
stainless steels.
[0014] The alloy 52 may also be used to repair zones of nuclear
reactor units or components consisting of various metals such as
low alloy steels (for example of the type 18MND5), stainless steels
of the type 304L (for example in solid form), of the type 308L (in
deposited form) or else 316L (in solid or deposited form). These
zones may comprise a plurality of these materials on which
heterogeneous welds made of alloy 52 are produced.
[0015] Certain defects, mainly in the form of small cracks, have
been demonstrated when using commercial alloys 52 such as the
alloys 52 from Special Metals.
[0016] In particular, when the molten welding wire is deposited on
a layer consisting of a nickel alloy deposited by welding, hot
cracking was observed and may be due to one of the following
phenomena: solidification, liquation, reassignment or else lack of
hot ductility. It was noted that a single type or a plurality of
types of crack may be found in a weld. Small-dimension cracks
formed in these conditions will be called type 1 cracks.
[0017] Tests were carried out on welding wires of different
compositions under variable welding conditions, in particular by
fusing these wires on various base metals such as: nickel alloys as
mentioned above and stainless steels, in the form of solid metals
or of layers pre-deposited by welding.
[0018] During these tests, it was demonstrated that commercially
available wires, in particular alloys 52 for the welding of nickel
690 alloys, gave poor results when they were deposited on nickel
alloys containing 15% or 30% of chromium or else stainless steels
deposited by welding, in the form of a coating of low alloy steel
components.
[0019] In addition to small type 1 cracks, other larger cracks,
which will be called type 2 hot cracks, were observed in certain
cases.
[0020] Type 2 cracks were observed, in particular, in the zones of
pronounced dilution of the welding alloy (in the metal deposited
during the first welding passes or in the region of the parts to be
joined) or more generally in the case of the welding of stainless
steels.
[0021] Commercial welding wires of which the grades had been
modified to improve the resistance to hot cracking and the
resistance to oxidation were also used during these tests.
[0022] The modified composition of these commercially available
wires is given in columns 5 and 6 of Table 1. Grades modified to
improve the resistance to hot cracking and defects due to oxidation
have a substantially higher niobium content (higher than 0.9%) and
substantially lower aluminium and titanium contents than unmodified
commercial grades.
[0023] In these improved grades, the niobium to silicon ratio is
high (higher than 30 or even 45). Finally, these grades contain
boron and zirconium as complementary elements.
[0024] It has been found that the improved commercially available
alloys gave good results in the diluted zones during the welding of
nickel alloys containing 15% or 30% of chromium, these zones being
virtually free of hot cracking, but poor results in diluted zones
in the case of welding on stainless steels, the type 2 hot cracks
being detected in these diluted zones.
[0025] The tests carried out showed that there are no commercially
available wires for producing homogeneous or heterogeneous
electro-welds, which are free of cracking and oxidation, on nickel
alloys and on steels.
SUMMARY OF THE INVENTION
[0026] The object of the invention is therefore to propose a
nickel-base alloy for the electro-welding of nickel alloys and
steels, in particular stainless steels, which allow the production
of homogeneous or heterogeneous welds on these materials, which are
free of hot-cracking and of traces of oxidation.
[0027] Accordingly, the alloy according to the invention contains,
by weight, less than 0.05% of carbon, from 0.015% to 0.5% of
silicon, from 0.4% to 1.4% of manganese, from 28% to 31.5% of
chromium, from 8% to 12% of iron, from 2% to 7% of molybdenum, from
0.1% to 0.8% of titanium, from 0.6% to 2% in total of niobium and
tantalum, the ratio of percentages of niobium plus tantalum and of
silicon being at least 4, from 0.05% to 0.75% of aluminium, less
than 0.04% of nitrogen, from 0.0008% to 0.0120% of zirconium, from
0.0010% to 0.010% of boron, less than 0.01% of sulphur, less than
0.020% of phosphorus, less than 0.30% of copper, less than 0.15% of
cobalt and less than 0.10% of tungsten, the remainder of the alloy,
with the exception of unavoidable impurities of which the total
content is at most 0.5%, consisting of nickel.
[0028] The invention also relates to a welding wire for the
electro-gas welding of nickel-base alloy according to the
invention.
[0029] The invention additionally relates to the application of the
alloy and of the electro-welding wire to the welding of units or
components of nuclear reactors, in particular pressurised
water-cooled nuclear reactors, for the realization of joints during
the construction of nuclear reactors, the coating of components by
metal deposition and for making repairs, wherein these welding
operations may be operations for the homogeneous or heterogeneous
welding of any nickel alloy or steel component.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] To assist understanding of the invention, a plurality of
grades of alloy according to the invention used for the production
of wires will be described by way of examples which have been used
during homogeneous and heterogeneous welding tests on nickel alloys
and stainless steels.
[0031] In Table 2, column 1 shows the minimum contents of the
various elements of the alloy, column 2 the maximum contents of
these elements and column 3 the preferred contents.
[0032] Columns 4 and 5 of the table give alloy compositions
according to two embodiments which will be described
hereinafter.
[0033] The effect of the various elements of the alloy and the
reasons for the claimed ranges or the limitations of these elements
will be explained hereinafter.
2TABLE 2 Elements in the alloy Mini Maxi Preferred Example 1
Example 2 C / 0.05 0.020 0.015 S / 0.010 0.001 0.001 P / 0.020
0.003 0.003 Si 0.015 0.5 <0.05 0.025 0.15 Mn 0.4 1.4 1 1 Ni
balance balance balance balance balance Cr 28 31.5 30.0 29.0 Cu /
0.30 0.020 0.020 Co / 0.15 0.01 0.01 Mo 2 7 4 4.00 5.50 Nb (+Ta)
0.6 2 0.80 1.2 Al 0.05 0.75 0.15 0.07 0.25 Ti 0.1 0.8 0.30 0.35
0.20 Zr 0.0008 0.012 0.006 0.0015 0.006 B 0.001 0.010 0.004 0.003
0.004 N / 0.040 0.01 0.01 W / 0.10 0.01 0.01 Fe 8 12 9.00 8.5 Nb/Si
4 32 8
[0034] Carbon, Sulphur, Phosphorus
[0035] These elements are residual elements of which the contents
have to be limited as far as possible and, in any case, fixed below
0.05% in the case of carbon, 0.010% in the case of sulphur and
0.020% in the case of phosphorus. Depending on the methods of
production and the starting products for preparation of the alloys,
the effective contents of carbon, sulphur and phosphorus may be
substantially lower than the given maximum limits. As shown in
columns 4 and 5 relating to the examples 1 and 2, the effective
carbon, sulphur and phosphorus contents of the castings carried out
are substantially lower than the maximum values given
hereinbefore.
[0036] Silicon
[0037] Silicon is an element which is always present in the alloy
but of which the content is to be limited to a low value,
preferably lower than 0.05%. In all cases, this content must be
lower than 0.5% to limit hot cracking of the welding metal.
However, the silicon must be present in a content of at least
0.015% to obtain good weldability on account of the fact that it
influences the wetting and the viscosity of the bath during
welding.
[0038] It will be seen hereinafter, with respect to niobium, that
the important parameter for resistance to fissuration in heat is
the ratio of the percentage by weight of niobium and silicon.
[0039] Manganese
[0040] The manganese must be at least 0.4% to achieve satisfactory
conditions for the production of the alloy in the presence of
sulphur (limited to the value of 0.01% mentioned hereinafter).
[0041] The manganese contributes to the resistance to fissuration
in heat, but this effect is rapidly saturated as a function of the
manganese content, and a manganese content limited to 1.4% leads to
satisfactory results.
[0042] Chromium
[0043] The chromium must be close to the percentage of chromium in
the alloy 690, and the composition range of 28% to 31.5%, which is
also that of the alloys 52, has been found to be satisfactory in
the case of homogeneous and heterogeneous welds employing the alloy
690 or stainless steels. This level of chromium is required for
achieving good anti-corrosion behaviour in a primary PWR
medium.
[0044] Copper
[0045] Copper must be strictly limited to less than 0.30% to avoid
a deterioration in the properties of the alloy.
[0046] Cobalt
[0047] The cobalt must necessarily be limited to a value below
0.15%. In fact, this element, which is activated in the presence of
radiation in a nuclear reactor, must be avoided as far as possible
in any application to the construction or repair of nuclear
reactors.
[0048] Molybdenum
[0049] Molybdenum is a particularly important element in the
production of the alloys according to the invention, and this
represents a significant difference relative to previously known
alloys (see Table 1) which have only very low molybdenum
contents.
[0050] Tests carried out by the Applicant of the present patent
application have shown that the molybdenum had a decisive influence
on the resistance to cracking of the metal deposited by fusion of a
nickel alloy welding wire, in particular when the welding wire is
deposited on stainless steels, for example steels containing 18% of
chromium and 8% of nickel with or without an addition of
molybdenum, in solid form or in the form of a deposit obtained by
covered electrode or TIG electro-welding.
[0051] The tests carried out showed that:
[0052] the formation of type 2 cracks is observed with low levels
of molybdenum in the molten metal of the welding wire, typically
lower than 0.5%, in particular when welding stainless steels,
[0053] as the molybdenum content increases, for example to 1% in
the molten metal, it is found that the cracking resistance of the
welding alloy is substantially improved if the alloy contains
sufficient quantities of titanium (and/or of aluminium). A minimal
titanium and/or aluminium content of 0.3% to 0.4%, with a
molybdenum content of 1% in the alloy, limits the number of type 2
cracks in the welding metal to a low level, particularly in the
case of the welding of stainless steels; these results suggest that
the molybdenum, titanium and/or aluminium contents should be
increased beyond these limits in order to limit or eliminate
crackings,
[0054] when the molybdenum content increases to at least 2% in the
molten metal, the tests show that the type 2 cracks completely
disappear and that the titanium and/or the aluminium have less
influence on the cracking resistance than in the case of a
molybdenum of about 1%.
[0055] The molybdenum contents have been fixed in the alloy welding
wire or rod according to the invention while agreeing that, in the
region of the defects, the dilution is high and may reach 50% but
does not exceed this limit which has been considered as respected
in all the work forming the basis of the present patent application
and corresponds to normal welding conditions.
[0056] As a result of the tests, it has been possible to establish
that the molybdenum content has to be at least 2% in order to
obtain, in all cases of use in welding, very high resistance to
cracking and, in particular, a total disappearance of type 2
cracks, while limiting the total titanium and aluminium content to
a level at which oxidation of the welding metal is avoided.
[0057] A molybdenum content higher than 7% is possible, but not
essential, in so far as the influence of the molybdenum on the
cracking resistance is saturated at a value of approximately 7%. A
content higher than 7% increases the price of the alloy and may
undesirably modify the properties of the welding metal.
[0058] The molybdenum should preferably be in the region of 4%.
[0059] Aluminium and Titanium
[0060] As mentioned hereinbefore, the presence of titanium and/or
aluminium improves the cracking resistance, but this effect
diminishes if the molybdenum content is higher than 1%.
[0061] The aluminium and titanium are used, in particular, as
deoxidising and denitriding agents and lead to the formation of
oxide films. These elements also reduce the grain size of the
welding alloy during solidification. The oxides and nitrides formed
in the form of fine particles in the liquid metal initiate the
germination of the solidification grains and refine the
structure.
[0062] It is therefore necessary to have a certain proportion of
titanium and aluminium in the welding metal and to limit the
proportion of aluminium to a value at which the undesirable
oxidation effects of the molten bath are avoided during
welding.
[0063] The titanium must be present in the alloy in a proportion of
between 0.1% and 0.8% and, for example, close to 0.30%.
[0064] The aluminium must be present in the alloy in a proportion
of between 0.05% and 0.75% and, for example, in the region of
0.15%.
[0065] Zirconium and Boron
[0066] When combined, these elements have a favourable influence on
the cracking resistance owing to the ductility dip cracking.
However, these elements alone are not sufficient to solve the
cracking problems which the alloy according to the invention
rectifies. Furthermore, zirconium, like aluminium, affects the
oxidation of the molten bath during welding. The zirconium and
boron must therefore be present in the alloy but in limited
quantities.
[0067] The zirconium must be present in the alloy according to the
invention in a proportion of between 0.0008% and 0.012% and
preferably in a proportion of approximately 0.006%.
[0068] In relation to these proportions of zirconium, the boron
must be between 0.001% and 0.010% and, preferably, in the region of
0.004%.
[0069] Niobium and Tantalum
[0070] Niobium affects the resistance to hot cracking. To avoid
increasing the risks of hot cracking and undesirably modifying the
characteristics of the deposited metal, this element must not be
present in an excessively large quantity.
[0071] As a result, the proportion of niobium must be at least 0.6%
to obtain the desirable effects of resistance to hot cracking and
at most 2%.
[0072] The proportion of niobium within this range must be fixed at
a value which is such that the ratio of the percentage of niobium
to the percentage of silicon is higher than 4 to obtain a
satisfactory effect on the resistance to hot cracking.
[0073] Iron
[0074] As in commercial alloys, the iron is fixed at a content of
between 8% and 12% for good resistance to stress corrosion in a PWR
medium.
[0075] Nitrogen
[0076] Nitrogen, which is a residual element, is not necessary in
the alloy. The nitrogen will be limited, in all cases, to a value
of less than 0.040%.
[0077] Tungsten
[0078] Tungsten is an element which is not desired in the alloy,
this residual element being limited to 0.10% in any case to avoid
undesirable modification of the properties of the welding
metal.
[0079] The alloy may contain small proportions of other residual
elements; these elements may be, for example, tin, vanadium, lead,
cadmium, magnesium, zinc, antimony, tellurium, calcium or cerium.
These elements, which are in a very small quantity in the alloy,
are in a total proportion with the other residual elements
considered above (carbon, sulphur, phosphorus, copper, cobalt,
nitrogen and tungsten) of less than 0.5% by weight.
[0080] Nickel
[0081] As a base alloy, it makes up the remainder of the
composition to 100%.
[0082] The compositions of two welding alloys according to the
invention are shown in Table 2 under columns 5 and 6 (example 1 and
example 2).
EXAMPLE 1
[0083] In the case of example 1, the molybdenum content is at the
optimum value (4%). The aluminium content is in the region of the
lower limit of the range of aluminium and the titanium content has
a value close to the typical value of 0.30%.
[0084] The silicon content of the alloy is low (0.025%) and is
clearly below the preferred upper limit. Although the niobium
content is only 0.80%, the niobium/silicon ratio is high and is
approximately the same as in commercial alloys of the improved type
shown in Table 1 (32). The value of this ratio is much higher than
the lower limit imposed. The zirconium and boron contents lie
towards the bottom of the claimed range.
EXAMPLE 2
[0085] In the case of example 2, the molybdenum content is higher
than the mean content considered as preferred (4%). The aluminium
content which is substantially higher than in the case of example 1
is fixed above the typical value of 0.15% and the titanium content
is lower than the typical value, the entirety of the aluminium and
titanium representing a percentage by weight which is substantially
identical in the case of example 1 and in the case of example
2.
[0086] The boron content is higher than in the case of example 1
and corresponds to the preferred values.
[0087] The silicon content is substantially higher than in the case
of example 1. The niobium content is also slightly higher than in
the case of example 1. Owing to the presence of a fairly large
quantity of silicon, the niobium to silicon ratio is substantially
lower in the case of example 1.
[0088] However, this ratio is twice as high as the minimum required
value.
[0089] Welding wires in the two grades corresponding to examples 1
and 2 were produced. The welding wires were used for diverse
homogeneous or heterogeneous welding of nickel alloys containing
30% and 15% of chromium and stainless steels.
[0090] The total absence of type 2 cracks in the deposited metal
was observed, even in the diluted zones of the weld.
[0091] The deposited metal is also virtually exempt from type 1
cracks in all cases.
[0092] No trace of oxidation which could lead to deterioration of
the deposited metal was found.
[0093] It has never been possible to obtain results of this type in
the case of alloy wires according to the prior art.
[0094] Considering the comparison examples in columns 5 and 6 of
Table 1, it can be seen that the comparison alloy in column 5 (CF
52) has a silicon content comparable to that of example 1 according
to the invention and a slightly higher niobium content, the niobium
to silicon ratio being 50% higher than the niobium to silicon ratio
of example 1. However, this alloy according to the prior art
contains only a very small proportion of molybdenum (0.012%)
whereas the alloys according to the invention contain more than 2%
and generally 4% or more of molybdenum. Despite a higher niobium to
silicon ratio and similar contents of aluminium and titanium, the
alloy CF 52 does not result in a resistance to cracking which is
comparable to that of the alloys according to the invention.
[0095] In the case of the second comparison example (alloy 52 M) in
column 6 of Table 2, the silicon and niobium contents and the
niobium to silicon ratio are similar to those of the alloy of
example 1. The aluminium and the titanium, on the other hand, are
limited to values comparable to those of the examples according to
the invention. The zirconium and boron contents of the comparison
alloys are, moreover, similar to those of the alloys of examples 1
and 2 according to the invention respectively.
[0096] It is perfectly clear that a quasi-absence of molybdenum
(0.02%) in the second comparison alloy explains the differences in
welding behaviour and the good results achieved with the examples
of alloy according to the invention and, in particular, example
1.
[0097] A comparison of the examples according to the invention and
the examples of alloys according to the prior art therefore shows
that a welding alloy having a molybdenum content of approximately
4% or slightly higher, an adequate niobium content to obtain a
niobium to silicon ratio substantially higher than 4 and moderate
aluminium and titanium contents solves the welding problems of
nickel alloys containing approximately 15% and 30% of chromium as
well as stainless steels.
[0098] The alloy according to the invention leads to electro-gas
welding wires for the perfect homogeneous or heterogeneous welding
of nickel alloys and stainless steels for the construction and
repair of nuclear reactor components.
[0099] The invention is not strictly limited to the described
embodiments.
[0100] The contents of the various elements of the alloys for
electro-welding in the considered applications may be adapted
within the claimed ranges to optimise the properties of the welding
metal and the welding conditions.
[0101] The alloy according to the invention may be used not only in
the form of electro-gas welding wires or rods but also in other
forms, for example in the form of coated electrodes.
[0102] Although the alloy is intended, in particular, for
applications in the field of the construction and repair of nuclear
reactors, its use in other industries may be considered.
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