U.S. patent application number 12/646756 was filed with the patent office on 2010-07-08 for iron-nickel-chromium-silicon alloy.
Invention is credited to Heike HATTENDORF, Juergen Webelsiep.
Application Number | 20100172790 12/646756 |
Document ID | / |
Family ID | 39790308 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172790 |
Kind Code |
A1 |
HATTENDORF; Heike ; et
al. |
July 8, 2010 |
IRON-NICKEL-CHROMIUM-SILICON ALLOY
Abstract
The invention relates to an iron-nickel-chromium-silicon alloy
comprising (in wt.-%) 19 to 34% or 42 to 87% nickel, 12 to 26%
chromium, 0.75 to 2.5% silicon, and additives of 0.05% to 1% Al,
0.01 to 1% Mn, 0.01 to 0.26% lanthanum, 0.0005 to 0.05% magnesium,
0.04 to 0.14% carbon, 0.02 to 0.14% nitrogen, and further
comprising 0.0005 to 0.07% Ca, 0.002 to 0.020% P, a maximum of
0.01% sulfur, a maximum of 0.005% B, the remainder comprising iron
and the usual process-related impurities
Inventors: |
HATTENDORF; Heike; (Werdohl,
DE) ; Webelsiep; Juergen; (Witten, DE) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET, SUITE 4000
NEW YORK
NY
10168
US
|
Family ID: |
39790308 |
Appl. No.: |
12/646756 |
Filed: |
December 23, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/DE2008/000965 |
Jun 12, 2008 |
|
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12646756 |
|
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Current U.S.
Class: |
420/443 ;
420/581; 420/582; 420/588 |
Current CPC
Class: |
C22C 38/001 20130101;
C22C 19/05 20130101; C22C 38/40 20130101; H05B 3/12 20130101; C22C
38/005 20130101; C22C 19/058 20130101; C22C 38/002 20130101; C22C
38/06 20130101; C22C 38/02 20130101 |
Class at
Publication: |
420/443 ;
420/582; 420/581; 420/588 |
International
Class: |
C22C 19/05 20060101
C22C019/05; C22C 30/02 20060101 C22C030/02; C22C 30/00 20060101
C22C030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2007 |
DE |
10 2007 029 400.1 |
Claims
1. Iron-nickel-chromium-silicon alloy, comprising, in wt. %, 19 to
34% or 42 to 87% nickel, 12 to 26% chromium, 0.75 to 2.5% silicon,
0.05 to 1% AI, 0.01 to 1% Mn, 0.01 to 0.26% lanthanum, 0.0005 to
0.05% magnesium, 0.04 to 0.14% carbon, 0.02 to 0.14% nitrogen,
0.0005 to 0.07% Ca, 0.002 to 0.020% P, max. 0.01% sulfur, max.
0.005% B, iron and usual process-related impurities.
2. Iron-nickel-chromium-silicon alloy in accordance with claim 1,
wherein, by weight, the nickel content is max. 83%, the chromium is
min. 14% the silicon content is min. 1.0% and the lanthanum content
is min. 0.02%.
3. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 19 to 25%, by weight.
4. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 25 to 34%, by weight.
5. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 42 to 44%, by weight.
6. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 44 to 52%, by weight.
7. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 52 to 57%, by weight.
8. Alloy in accordance with claim 1 or 2, wherein the nickel
content of 57 to 65%, by weight.
9. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 65 to 75%, by weight.
10. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 75 to 83%, by weight.
11. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 19 to 22%, by weight.
12. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 23 to 25%, by weight.
13. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 25 to 28%, by weight.
14. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 28 to 31%, by weight.
15. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 31 to 34%, by weight.
16. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 44 to 48%, by weight.
17. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 48 to 52%, by weight.
18. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 57 to 61%, by weight.
19. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 61 to 65%, by weight.
20. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 65 to 70%, by weight.
21. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 70 to 75%, by weight.
22. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 75 to 79%, by weight.
23. Alloy in accordance with claim 1 or 2, wherein the nickel
content is 79 to 83%, by weight.
24. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 14 to 18%, by weight.
25. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 18 to 21%, by weight.
26. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 20 to 26%, by weight.
27. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 21 to 24%, by weight.
28. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 20 to 23%, by weight.
29. Alloy in accordance with claim 1 or 2, wherein the chromium
content is 23 to 26%, by weight.
30. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.5 to 2.5%, by weight.
31. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.0 to 1.5%, by weight.
32. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.5 to 2.0%, by weight.
33. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.7 to 2.5%, by weight.
34. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.2 to 1.7%, by weight.
35. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 1.7 to 2.2%, by weight.
36. Alloy in accordance with claim 1 or 2, wherein the silicon
content is 2.0 to 2.5%, by weight.
37. Alloy in accordance with claim 1 or 2, wherein the aluminum
content is 0.1 to 0.7%, by weight.
38. Alloy in accordance with claim 1 or 2, wherein the manganese
content is 0.1 to 0.7%, by weight.
39. Alloy in accordance with claim 1 or 2, wherein the lanthanum
content is 0.02 to 0.2%, by weight.
40. Alloy in accordance with claim 1 or 2, wherein the lanthanum
content is 0.02 to 0.15%, by weight.
41. Alloy in accordance with claim 1 or 2, wherein the lanthanum
content is 0.04 to 0.15%, by weight.
42. Alloy in accordance with claim 1 or 2, wherein the nitrogen
content is 0.02 to 0.10%, by weight.
43. Alloy in accordance with claim 1 or 2, wherein the nitrogen
content is 0.03 to 0.09%, by weight.
44. Alloy in accordance with claim 1 or 2, wherein the nitrogen
content is 0.05 to 0.09%, by weight.
45. Alloy in accordance with claim 1 or 2, wherein the carbon
content is 0.04 to 0.10%, by weight.
46. Alloy in accordance with claim 1 or 2, wherein the magnesium
content is 0.001 to 0.05%, by weight.
47. Alloy in accordance with claim 1 or 2, wherein the magnesium
content is 0.008 to 0.05%, by weight.
48. Alloy in accordance with claim 1 or 2, wherein maximum content
of sulfur is 0.005%, by weight, and maximum content of the boron is
0.003% B, by weight.
49. Alloy in accordance with claim 1 or 2, wherein the Ca content
is 0.01 to 0.05% Ca, by weight.
50. Alloy in accordance with claim 1 or 2, wherein the Ca content
is 0.001 to 0.05% Ca, by weight.
51. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements Ce, Y, Zr, Hf, Ti, each with a content of
0.01 to 0.3%, by weight.
52. Alloy in accordance with claim 51, wherein the sum
PwE=1.43X.sub.Ce+1.49X.sub.La+2.25X.sub.Y+2.19X.sub.Zr+1.12X.sub.Hf+4.18X-
.sub.Ti.ltoreq.0.38, PwE being the potential of the effective
elements.
53. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements La, Ce, Y, Zr, Hf, Ti, each with a
content of 0.01 to 0.2%, by weight, and wherein the sum
PwE=1.43X.sub.Ce+1.49X.sub.La+2.25X.sub.Y+2.19X.sub.Zr+1.12X.sub.Hf+4.18X-
.sub.Ti.ltoreq.0.36, PwE being the potential of the effective
elements.
54. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements La, Ce, Y, Zr, Hf, Ti, each with a
content of 0.02 to 0.15%, by weight, and wherein the sum
PwE=1.43X.sub.Ce+1.49X.sub.La+2.25X.sub.Y+2.19X.sub.Zr+1.12X.sub.Hf+4.18X-
.sub.Ti.ltoreq.0.36, PwE being the potential of the effective
elements.
55. Alloy in accordance with claim 1 or 2, wherein the phosphorus
content is 0.005 to 0.020%.
56. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements Mo, W, V, Nb, Ta, Co, each with a content
of 0.01 to 1.0%, by weight.
57. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements Mo, W, V, Nb, Ta, Co, each with a content
of 0.01 to 0.2%, by weight.
58. Alloy in accordance with claim 1 or 2, further comprising at
least one of the elements Mo, W, V, Nb, Ta, Co, each with a content
of 0.01 to 0.06%, by weight.
59. Alloy in accordance with claim 1 or 2, wherein the impurities
comprise, by weight, max. 1.0% Cu, max. 0.002% Pb, max. 0.002% Zn,
max. 0.002% Sn.
60. An electrical heating element, comprising the alloy of claim 1
or 2.
61. A tubular heating body, comprising the alloy of claim 1 or
2.
62. A furnace, comprising the alloy of claim 1 or 2.
Description
REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of International Application
PCT/DE2008/000965 filed Jun. 12, 2008.
BACKGROUND OF THE INVENTION
[0002] The invention relates to iron-nickel-chromium-silicon alloys
having a longer service life and enhanced dimensional
stability.
[0003] Austenitic iron-nickel-chromium-silicon alloys having
different nickel, chromium, and silicon contents have been used for
some time as heat conductors in the temperature range up to
1100.degree. C. This alloy group is standardized in DIN 17470
(Table 1) and ASTM B344-01 (Table 2) for use as heat conductor
alloys. There are a number of commercially available alloys, listed
in Table 3, for this standard.
[0004] The sharp increase in the price of nickel in recent years
has resulted in a desire to employ heat conductor alloys that have
the lowest possible nickel content and to significantly increase
the service life of the alloys employed. This makes it possible for
the manufacturer of heating elements either to change to an alloy
that has a lower nickel content or to use greater durability to
justify a higher price to the customer.
[0005] In general it should be noted that the service life and
usage temperature for the alloys listed in Tables 1 and 2 increase
as the nickel content climbs. All of these alloys form a layer of
chromium oxide (Cr.sub.2O3) having a layer of SiO2 thereunder that
is more or less closed. Small additions of elements that have high
affinity for oxygen such as Ce, Zr, Th, Ca, Ta (Pfeifer/Thomas,
Zunderfeste Legierungen [Non-Scaling Alloys] (2nd Edition, Springer
Verlag 1963, pages 258 and 259) increase service life, wherein the
effect of only one single element with affinity for oxygen was
investigated in this case, but no information was provided about
the effect of a combination of such elements. When the heat
conductor is employed, the chromium content is slowly depleted for
building up the protective layer. Therefore a higher chromium
content increases service life since a higher content of chromium,
the element that forms the protective layer, delays the point in
time at which the Cr content drops below the critical limit and
oxides other than Cr.sub.2O.sub.3 form, which are e.g.
iron-containing ferrous oxides.
[0006] Known from EP-A 0 531 775 is a heat-resistant hot-formable
austenitic nickel alloy having the following composition (in wt.
%):
C 0.05-0.15%
Si 2.5-3.0%
Mn 0.2-0.5%
P Max. 0.015%
S Max. 0.005%
Cr 25-30%
Fe 20-27%
Al 0.05-0.15%
Cr 0.001-0.005%
SE 0.05-0.15%
N 0.05-0.20%
[0007] and the remainder Ni and process-related impurities.
[0008] EP-A 0 386 730 describes a nickel-chromium-iron alloy having
very good oxidation resistance and thermal strength, these being
desired for advanced heat conductor applications that proceed from
the known heat conductor alloy NiCr6015 and in which significant
improvements in the usage properties could be attained using
modifications to the composition that were matched to one another.
The alloy is distinguished from the known NiCr6015 material
especially in that the rare earth metals are replaced by yttrium,
in that it also includes zirconium and titanium, and in that the
nitrogen content is matched to the content of zirconium and
titanium in a special manner.
[0009] WO-A 2005/031018 describes an austenitic Fe--Cr--Ni alloy
for use in the high temperature range that essentially has the
following chemical composition (in wt. %):
Ni 38-48%
Cr 18-24%
Si 1.0-1.9%
C<0.1%
Fe Remainder
[0010] With free-hanging heating elements, in addition to the
requirement for a long service life there is also the requirement
for good dimensional stability at the application temperature. If
the coil sags too much during operation, the spacing between the
windings becomes uneven, resulting in uneven temperature
distribution and shortening service life. To compensate for this,
more support points would be necessary for the heating coil, which
increases costs. This means that heat conductor materials must have
adequate dimensional stability and creep resistance.
[0011] Apart from dislocation creep, the creep mechanisms that have
a negative impact on dimensional stability in the application
temperature range (dislocation creep, grain boundary slip, and
diffusion creep) are all influenced by a large grain size to have
greater creep resistance. Displacement creep is not solely a
function of grain size. Producing a wire having a larger grain size
increases creep resistance and thus dimensional stability. In any
considerations grain size should therefore be included as a factor
that has significant influence.
[0012] Also important for a heat conductor material is the greatest
possible specific electrical resistance and the lowest possible
change in the ratio of heat resistance/cold resistance to
temperature (temperature coefficient ct).
SUMMARY OF THE INVENTION
[0013] The underlying object of the invention is to design alloys
with contents of nickel, chromium, and Si similar to the alloys in
accordance with the prior art in Tables 1 and 2, but that have
[0014] a) significantly improved oxidation resistance and
concomitant long service life; [0015] b) significantly improved
dimensional stability at the application temperature; [0016] c)
high specific electrical resistance in conjunction with the least
possible change in the ratio of heat resistance/cold resistance to
temperature (temperature coefficient ct).
[0017] This object is attained using an
iron-nickel-chromium-silicon alloy having (in wt. %) 19 to 34% or
42 to 87% nickel, 12 to 26% chromium, 0.75 to 2.5% silicon, and
additions of 0.05 to 1% Al, 0.01 to 1% Mn, 0.01 to 0.26% lanthanum,
0.0005 to 0.05% magnesium, 0.04 to 0.14% carbon, 0.02 to 0.14%
nitrogen, moreover including 0.0005 to 0.07% Ca, 0.002 to 0.020% P,
max. 0.01% sulfur, max. 0.005% B, the remainder iron and the usual
process-related impurities.
[0018] Due to their special composition, these alloys have a longer
service life than the alloys in accordance with the prior art that
have comparable nickel and chromium contents. In addition, it is
possible to attain enhanced dimensional stability and less sagging
than the alloys in accordance with the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a plot of relative burn time as a function of La
content;
[0020] FIG. 2 is a plot of sagging as a function of N content;
and
[0021] FIG. 3 is a plot of sagging as a function of C content.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The range for the element nickel is either between 19 to 34%
or 42 to 87%, the following nickel contents being possible
depending on use and being adjusted in the alloy regardless of the
use.
[0023] Preferred Ni ranges between 19 and 34% are provided as
follows: [0024] 19 to 25% [0025] 19 to 22% [0026] 23 to 25% [0027]
25 to 34% [0028] 25 to 28% [0029] 28 to 31% [0030] 31 to 34%
[0031] Preferred Ni ranges between 42 and 87% are provided as
follows: [0032] 42 to 44% [0033] 44 to 52% [0034] 44 to 48% [0035]
48 to 52% [0036] 52 to 57% [0037] 57 to 65% [0038] 57 to 61% [0039]
61 to 65% [0040] 65 to 75% [0041] 65 to 70% [0042] 70 to 75% [0043]
75 to 83% [0044] 75 to 79% [0045] 79 to 83%.
[0046] The chromium content is between 12 and 26%, it being
possible for there to be chromium content as follows, again
depending on the area in which the alloy will be employed: [0047]
14 to 26% [0048] 14 to 18% [0049] 18 to 21% [0050] 20 to 26% [0051]
21 to 24% [0052] 20 to 23% [0053] 23 to 26%.
[0054] The silicon content is between 0.75 and 2.5%, it being
possible to adjust defined contents within the range depending on
the area of application: [0055] 1.0-2.5% [0056] 1.5-2.5% [0057]
1.0-1.5% [0058] 1.5-2.0% [0059] 1.7-2.5% [0060] 1.2-1.7% [0061]
1.7-2.2% [0062] 2.0-2.5%.
[0063] The element aluminum is provided as an additive,
specifically in contents of 0.05 to 1%. It can preferably be
adjusted in the alloy as follows: [0064] 0.1-0.7%.
[0065] The same applies to the element manganese, which is added as
0.01 to 1% of the alloy. Alternatively, the following range is also
possible: [0066] 0.1-0.7%.
[0067] The inventive subject matter preferably proceeds from the
fact that the material properties provided in the examples are
essentially adjusted with the addition of the element lanthanum in
contents of 0.01 to 0.26%. In this case, as well, defined values
can be adjusted in the alloy, depending on the area of application:
[0068] 0.02-0.26% [0069] 0.02-0.20% [0070] 0.02-0.15% [0071]
0.04-0.15%.
[0072] This applies in the same manner for the element nitrogen,
which is added in contents between 0.02 and 0.14%. Defined content
can be as follows: [0073] 0.02-0.0% [0074] 0.03-0.09% [0075]
0.05-0.09%.
[0076] Carbon is added to the alloy in the same manner, in contents
between 0.04 and 0.14%. Specifically content can be adjusted in the
alloy as follows: [0077] 0.04-0.10%.
[0078] Magnesium is also among the added elements, in contents of
0.0005 to 0.05%. Specifically, it is possible to adjust this
element in the alloy as follows: [0079] 0.001-0.05% [0080]
0.008-0.05%.
[0081] Moreover, the alloy can include calcium in contents between
0.0005 and 0.07%, especially 0.001 to 0.05% or 0.01 to 0.05%.
[0082] Moreover, the alloy can include phosphorus in contents
between 0.002 and 0.020%, especially 0.005 to 0.02%.
[0083] The elements sulfur and boron can be in the alloy as
follows:
Sulfur Max. 0.005%
Boron Max. 0.003%.
[0084] If the effectiveness of the reactive element lanthanum is
not sufficient alone for producing the material properties
described in the statement of the object, the alloy can moreover
include at least one of the elements Ce, Y, Zr, Hf, Ti, with
contents of 0.01 to 0.3%, wherein when needed the elements may also
be defined additives,
[0085] Adding elements that have affinity for oxygen, such as
preferably La and where needed Ce, Y, Zr, Hf, Ti, improves service
life. These additions do this in that they are also built into the
oxide layer and there block the diffusion paths for the oxygen on
the grain boundaries. The quantity of the elements available for
this mechanism must therefore be adjusted to the atomic weight in
order to be able to compare the quantities of different elements to
one another.
[0086] The potential of the effective elements (PwE) is therefore
defined as
PwE=200.SIGMA.(X.sub.E/atomic weight of E)
where E is the element in question and X.sub.E is the content of
the element in question in percent.
[0087] As already addressed, the alloy can include 0.01 to 0.3% of
one or a plurality of the elements La, Ce, Y, Zr, Hf, Ti,
whereby
[0088]
.SIGMA.PwE=1.43X.sub.Ce+1.49X.sub.La+2.25X.sub.Y+2.19X.sub.Zr+1.12X-
.sub.Hf+4.18X.sub.Ti.ltoreq.0.38, especially .ltoreq.0.36 (at 0.01
to 0.2% of the entire element), wherein PwE is the potential of the
effective elements.
[0089] Alternatively, if at least one of the elements La, Ce, Y,
Zr, Hf, Ti is present in contents of 0.02 to 0.10%, there is the
possibility that the total PwE=1.43
X.sub.Ce+1.49X.sub.La+2.25X.sub.Y+2.19X.sub.Zr+1.12X.sub.Hf+4.18X.sub.Ti
is less than or equal to 0.36, wherein PwE is the potential of the
effective elements.
[0090] Moreover, the alloy can contain between 0.01 to 1.0% of one
or a plurality of the elements Mo, W, V, Nb, Ta, Co, which can
additionally be further limited as follows: [0091] 0.01 to 0.06%
[0092] 0.01 to 0.2%.
[0093] Finally, there can also be the elements copper, lead, zinc,
and tin in impurities in contents as follows:
Cu max. 1.0%
Pb max. 0.002%
Zn max. 0.002%
Sn max. 0.002%.
[0094] The inventive alloy should preferably be used for employment
in electrical heating elements, especially in electrical heating
elements that require good dimensional stability and low
sagging.
[0095] However, it is also possible to use the inventive alloy in
heating elements of tubular heating bodies.
[0096] Another specific application for the inventive alloy is use
in furnace construction.
[0097] The inventive subject matter shall be explained in greater
detail using the following examples.
EXAMPLES
[0098] As already stated in the foregoing, Tables 1 to 3 reflect
the prior art.
[0099] For the alloys smelted on an industrial scale in the
following examples, a commercially produced and soft annealed
specimen having a 1.29 mm diameter was taken. A smaller quantity of
the wire, on a laboratory scale of up to 0.4 mm, was taken for the
service life test.
[0100] For heating elements, especially heat conductors in the form
of wire, accelerated service life tests for comparing materials to
one another are possible and usual for example with the following
conditions:
[0101] The heat conductor service life test is performed on wires
that have a diameter of 0.40 mm. The wire is clamped between 2
power supplies spaced 150 mm apart and is heated to 1150.degree. C.
by applying a voltage. Each heating interval to 1150.degree. C. is
performed for 2 minutes and then the power supply is interrupted
for 15 seconds. The wire fails at the end of its service life in
that the rest of the cross-section melts through. The burn time is
the sum of the "On" times during the service life of the wire. The
relative burn time tb is this figure as a percentage of the burn
time for a reference lot.
[0102] For investigating dimensional stability, the sagging
behavior of heating coils at the application temperature is
investigated in a sagging test. The sagging of heating coils from
the horizontal is determined after a certain period of time. The
less sagging there is, the greater the dimensional stability or
creep resistance of the material.
[0103] For this test, soft annealed wire having a diameter of 1.29
mm is wound into spirals that have an interior diameter of 14 mm.
For each lot, a total of 6 heating coils are produced, each coil
having 31 windings. All heating coils are brought to a uniform
starting temperature of 1000.degree. C. at the beginning of the
test. The temperature is measured with a pyrometer. The test is
performed at constant voltage with a switching cycle of 30 s
"On"/30 s "Off". The test concludes after 4 hours. After the
heating coils have cooled, the sagging of the individual windings
from the horizontal is measured and the mean of the 6 readings for
the heating coils is found.
[0104] Different exemplary alloys having nickel contents of 30 to
34%, or 50 to 60% Ni, 16 to 22% Cr, 1.3 to 2.2% Si, and additions
of 0.2 to 0.5% Al, 0.3 to 0.5% Mn, 0.01 to 0.09% La, 0.005 to
0.014% Mg, 0.01 to 0.065% C, 0.03 to 0.065% N, moreover including
0.001 to 0.04 Ca, 0.005 to 0.013% P, 0.0005 to 0.002% S, max 0.003
B, 0.01 to 0.08% Mo, 0.01 to 0.1% Co, 0.02 to 0.08% Nb, 0.01 to
0.06% V, 0.01 to 0.02% W, 0.01 to 0.1% Cu, the remainder iron and a
PwE value of 0.09 to 0.19 were produced on an industrial scale and
investigated as described in the foregoing.
[0105] The results were evaluated using multiple linear
regression.
[0106] FIG. 1 depicts the relative burn time as a function of La
content, adjusted for the effects of Ni, Cr, and Si content. It can
be seen that the relative burn time increases sharply as La content
increases. An La content of 0.04 to 0.15% is particularly
advantageous.
[0107] When evaluating sagging (of the coils), only specimens
having a grain size of 20 to 25 .mu.m were included so that after
this parameter no regression has to be performed.
[0108] FIG. 2 depicts how sagging is a function of N content,
adjusted for the effects of Ni, Cr, Si and C content. It is already
evident that sagging drops sharply as N content increases. An N
content of 0.05 to 0.09% is especially advantageous.
[0109] FIG. 3 indicates how sagging is a function of C content,
adjusted for the effects of Ni, Cr, Si and N content. It is evident
that sagging drops sharply as C content increases. C content of
0.04 to 0.10% is especially advantageous.
[0110] Alloys having a low nickel content (variant 1) are
particularly cost-effective. Therefore the alloys in the range from
19% to 34% Ni are of great interest, despite the worse temperature
coefficients and lower specific electrical resistances in
comparison to alloys with higher nickel content. The risk of sigma
phase formation, which causes the alloy to become brittle, rises
increasingly at less than 19% nickel. Therefore 19% constitutes the
lower limit for the nickel content.
[0111] The costs for the alloy rise with the nickel content.
Therefore the upper limit for the alloys having a low nickel
content should be 34% (variant 1).
[0112] The temperature coefficient increasingly improves with
greater than 42% Ni. The specific electrical resistance is higher,
as well. At the same time, the nickel portion compared to alloys
having high nickel content is relatively low, approx. 80%.
Therefore 42% is a reasonable lower limit for the alloys having a
higher nickel content (variant 2).
[0113] Alloys with more than 87% no longer include enough Cr and Si
to have adequate oxidation resistance. The upper limit for nickel
content is therefore 87%.
[0114] Cr content that is too low means that the Cr concentration
drops below the critical limit too rapidly. The lower limit for
chromium is therefore 12%. Cr content that is too high has a
negative impact on the alloy's processability. The upper limit for
Cr should therefore be 26%.
[0115] The formation of a silicon oxide layer beneath the chromium
oxide layer reduces the oxidation rate. When less than 0.75%, the
silicon oxide layer has too many gaps for its full effect to be
achieved. Si content that is too high has a negative effect on the
alloy's processability. The upper limit for SI content is therefore
2.5%.
[0116] As stated in the foregoing, additions of elements that have
affinity for oxygen improve service life. They do this in that they
are included in the oxide layer and there block the diffusion paths
of the oxygen on the grain boundaries. The quantity of the elements
available for this mechanism must therefore be adjusted to the
atomic weight in order to be able compare the quantities of
different elements to one another.
[0117] The potential of the effective elements PwE is therefore
defined as
PwE=200.SIGMA.(X.sub.E/atomic weight of E)
[0118] E being the element in question and X.sub.E being the
content of the element in question in %.
[0119] When La and Ce or SE are present, it appears that Ca and Mg
are no longer effective elements.
[0120] Therefore La, Ce, Y, Zr, Hf, and Ti were used for the
addition for the potential of the effective elements PwE. If there
is no information about La and Ce, but due to the addition of Cer
mixed metal there is only all-inclusive information about SE,
Ce=0.6 SE and La=0.35 SE is assumed for calculating the PwE.
PwE=1.49X.sub.La,1.43X.sub.Ce+2.25X.sub.Y+2.19X.sub.Zr+1.12X.sub.Hf+4.18-
X.sub.Ti
[0121] A minimum content of 0.01% La is necessary to retain the
effect La has of increasing oxidation resistance. The upper limit
is set at 0.26%, which equals a PwE of 0.38. Greater values for PwE
do not make sense in this case.
[0122] Al is required for improving the processability of the
alloy. A minimum content of 0.05% is therefore necessary. A content
that is too high again has a negative effect on processability. Al
content is therefore limited to 1%.
[0123] A minimum content of 0.04% C is necessary for good
dimensional stability and low sagging. C is limited to 0.14%
because this element reduces oxidation resistance and
processability.
[0124] A minimum content of 0.02% N is necessary for good
dimensional stability and low sagging. N is limited to 0.14%
because this element reduces oxidation resistance and
processability.
[0125] A minimum content of 0.0005% Mg is necessary; it improves
the processability of the material. The limit is set at 0.05%
because too much Mg has proved to have a negative effect.
[0126] A minimum content of 0.0005% Ca is necessary because it
enhances the processability of the material. The limit is
established at 0.07% because too much CA has proved to have a
negative effect.
[0127] The sulfur and boron contents should be kept as low as
possible because these surfactant elements have a negative effect
on oxidation resistance. Therefore max. 0.01% S and max. 0.005% B
are established.
[0128] Copper is limited to max. 1% because this element reduces
oxidation resistance.
[0129] Pb is limited to max. 0.002% because this element reduces
oxidation resistance. The same applies to Sn.
[0130] A minimum content of 0.01% Mn is necessary for enhancing
processability. Manganese is limited to 1% because this element
also reduces oxidation resistance.
TABLE-US-00001 TABLE 1 Alloys according to DIN 17470 and 17742
(Composition of NiCr8020, NiCr7030, NiCr6015). .rho.(.mu..OMEGA.m)
.rho.(.mu..OMEGA.m) W No. Cr Ni + Co *) Fe Al Si Mn C Cu P S
20.degree. C. 900.degree. C. NiCr8020 2.4869 19-21 >75 <1.0
<0.3 0.5-2.0 <1.0 <0.15 <0.5 <0.020 <0.015 1.12
(1.08) 1.14 NiCr7030 2.4658 29-32 >60 <5.0 <0.3 0.5-2.0
<1.0 <0.10 <0.5 <0.020 <0.015 1.19 (1.16) 1.24
NiCr6015 2.4867 14-19 >59 18-25 <0.3 0.5-2.0 <2.0 <0.15
<0.5 <0.020 <0.015 1.13 (1.11) 1.23 NiCr3020 1.4860 20-22
28.0-31.0 Remainder 2.0-3.0 <1.5 <0.2 <0.045 <0.03 1.02
1.28 NiCr2520 1.4843 22-25 19.0-22.0 Remainder 1.5-2.5 <2.0
<0.2 <0.045 <0.03 0.95 1.24 All figures in wt. % *) max.
Co 1.5%
TABLE-US-00002 TABLE 2 Alloys according to ASTM B 344-01. ct Cr Ni
+ Co *) Fe Si Mn C S .rho.(.mu..OMEGA.m) (at 871.degree. C.) 80Ni,
20Cr 19-21 Remainder <1.0 0.75-1.75 <1.0 <0.15 <0.01
1.081 1.008 60Ni, 16Cr 14-18 >57 0.75-1.75 <1.0 <0.15
<0.01 1.122 1.073 35Ni, 20Cr 18-21 34-37 Remainder 1.0-3.0
<1.0 <0.15 <0.01 1.014 1.214 All figures in wt. %
TABLE-US-00003 TABLE 3 Commercially available alloys. 14862 14862
14862 Nicrofer Nicrofer Nicrofer 3718- Inconel Bright 3718So-
3718So- Nicrofer 353 Ma Alloy330-DB 330 Alloy 35 AlloyDS-DB
AlloyDS-Band 3519Nb Cronifer II Ni 35 33-37 34-37 34-37 34.5-41
35-39 35.2-35.8 57-59 Cr 25 15-17 17-20 18-21 17-19 17-19 19.2-19.8
14-17 Si 1.3 1.-2 0.75-1.5 1.0-3.0 1.9-2.6 1.9-2.5 1.9-2.5 1.0-1.75
Al Max 2 Max 0.3 Mn Max 2 Max 1 0.8-1.5 0.8-1.5 1.5 Nb 0.9 Cu Max
0.5 Max 0.5 Ti Max 0.2 Max 0.2 Max 0.2 1.5 SE Yes 0.03 Max 0.04 Ce
Yes N 0.17 C Max 0.05 Max 0.15 Max 0.08 Max 0.10 Max 0.10 S Max
0.015 Max 0.03 Max 0.15 Max 0.03 P Max 0.045 Max 0.03 Max 0.01 Max
0.03 B Fe Remainder Remainder Remainder Remainder Remainder
Remainder Remainder 24889 Nicrofer Nicrothal WO2005/ WO2005/
Cronifer III Cronifer 45 45TM 40 031018 A8 031018 A9 Ni 30-32 45-48
45-50 37 39-41 44-46 Cr 19.5-21.5 22-24 26-29 20 20-22 20-22 Si
1.8-3 1.5-2.2 2.5-3 2 1.0-1.5 1.0-1.5 Al Max 0.3 Max 0.3 Max 0.2 Mn
Max 1.0 Max 1.0 Max 1 Nb Cu Max 0.3 Ti SE Max 0.10 Max 0.04
0.05-0.15 Ce 0.01-0.04 0.01-0.04 N 0.17 Max 0.15 Max 0.15 C Max
0.01 Max 0.08 0.05-0.12 Max 0.10 Max 0.10 S Max 0.01 P Max 0.015 B
Fe Remainder Remainder Remainder Remainer Remainder Remainder All
information in wt. %
* * * * *