DE102007005605B4 - Iron-nickel-chromium-silicon alloy - Google Patents

Abstract

Iron-nickel-chromium-silicon alloy having (in % by weight) 34 to 42% nickel, 18 to 26% chromium, 1.0 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, 0.01 to 0.14% carbon, 0.01 to 0.14% nitrogen, max. 0.01% sulfur, max. 0.005% B, remainder iron and the usual impurities resulting from the production process.

Description

The The invention relates to an iron-nickel-chromium-silicon alloy with improved life and dimensional stability.

austenitic Iron-nickel-chromium-silicon alloys with different nickel, chromium and silicon contents have long been used as heat conductors in the temperature range up to 1100 ° C used. For the use as heating conductor alloy is this alloy group standardized in DIN 17470 (Table 1) and ASTM B344-83 (Table 2). There are a number of commercially available alloys to this standard, which are listed in Table 3.

Of the strong rise in nickel prices in recent years leaves the Request emerge, Heizleiterlegierungen with the lowest possible nickel contents use. In particular, the desire arises the hochnickelhaltigen Variants NiCr8020, NiCr7030 and NiCr6015 (Table 1), which are characterized by particularly advantageous properties, by materials to replace with reduced nickel content, without too much loss in the capacity to accept the materials.

In general, it should be noted that the service life and service temperature of the alloys indicated in Tables 1 and 2 increase with increasing nickel content. All these alloys form a chromium oxide layer (Cr ₂ O ₃ ), with an underlying, more or less closed, SiO ₂ layer. Small additions of strongly oxygen affine elements such as Ce, Zr, Th, Ca, Ta (Pfeifer / Thomas, Zunderfeste alloys 2nd edition, Springer Verlag 1963, pages 258 and 259) increase the life, in the cited case, only the influence of a investigated individual oxygen affinity element, but no information on the effect of a combination of such elements were made. The chromium content is slowly consumed in the course of using a heat conductor to build up the protective layer. Therefore, a higher chromium content increases the lifetime because a higher content of the protective layer-forming element chromium retards the time at which the Cr content is below the critical limit and forms oxides other than Cr ₂ O ₃ , e.g. B. iron-containing oxides.

By the EP 0 531 775 A1 a heat-resistant thermoformable austenitic nickel alloy of the following composition (in wt .-%) has become known:
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%
Balance Ni and impurities caused by melting.

In the EP 0 386 730 A1 describes a nickel-chromium-iron alloy with very good oxidation resistance and high temperature resistance, as desired for advanced heat conductor applications, which emanates from the known NiCr6015 Heizleiterlegierung and in which by matching modifications of the composition considerable improvements in performance could be achieved. The alloy differs from the known material NiCr6015 in particular in that the rare earth metals are replaced by yttrium, that it additionally contains zirconium and titanium, and that the nitrogen content is specially adapted to the contents of zirconium and titanium.

Of the WO 2005/031018 A1 an austenitic Fe-Cr-Ni alloy for use in the high-temperature range is to be taken, which has essentially the following chemical composition (in% by weight):
Ni 38-48%
Cr 18-24%
Si 1.0-1.9%
C <0.1%
Fe rest.

Of the CH 345745 For example, a nickel-chromium alloy containing 10 to 30% chromium, 0.2 to 2% silicon and 0.01 to 0.5% rare earth metals has been disclosed, which contains up to 0.02% boron.

The EP 0 381 121 A1 discloses a steel of the following composition:
C 0.05-0.3%
Mn not> than 10%
Ni 15-50%
Si not> than 3%
Cr 15-35%
Mg 0.001-0.2%
B 0.001-0.1% and / or
Zr 0.001-0.1%
at least one of the elements
Ti 0.05-1.0%
Nb 0.1-2.0% and
Al 0.05-1.0%
Mo 0-3%
W 0-6%
(Mo + ½B = 3% or less)
Remaining iron and unavoidable impurities.

Finally describes the Handbuch der Sonderstahlkunde 2nd volume 1956, Springer-Verlag on page 1466/1467 that on the heat resistant steels and alloys on it has been pointed out that by low additions of some elements, the life considerably extended by the heating conductor can be. Cerium or mischmetal should act favorably here.

at free hanging Heating elements in addition to the demand for a long life also the demand for a good dimensional stability at the application temperature. Too much slumping of the helix (sagging) during operation has one uneven distance the turns with an uneven temperature distribution result, whereby the life is shortened. To compensate for this would be more support points for the Heating coil required, which increases the cost. This means that the Heizleitermaterial a sufficiently good dimensional stability or creep resistance must have.

The in the range of application temperature affecting the dimensional stability Creep mechanisms (dislocation creeping, grain boundary slipping or Diffusion creep) all but the dislocation creep through a big one Grain size in the direction greater creep resistance affected. The dislocation creep does not depend on the grain size. The Producing a wire with a large grain size increases creep resistance and thus the dimensional stability. For all considerations, therefore, the grain size as important Influence factor taken into account become.

Farther important for a Heizleitermaterial is as possible high specific electrical resistance and one possible small change of the relationship Hot resistance / cold resistance with temperature (temperature coefficient ct).

The Lower Ni content variants NiCr3020 or 35Ni, 20Cr (Table 1 and Table 2), which are characterized by significantly lower costs excel, fulfill In particular, the life requirements only inadequate.

• a) eine hohe Oxidationsbeständigkeit und eine damit einhergehende hohe Lebensdauer
• b) eine ausreichend gute Formstabilität bei der Anwendungstemperatur
• c) einen hohen spezifischen elektrischen Widerstand in Verbindung mit einer möglichst geringen Änderung des Verhältnisses Warmwiderstand/Kaltwiderstand mit der Temperatur (Temperaturkoeffizient ct) hat.

The task is therefore to design an alloy that has a much lower nickel content than NiCr6015 and therefore significantly lower costs

• a) a high oxidation resistance and a concomitant long life
• b) a sufficiently good dimensional stability at the application temperature
• c) has a high electrical resistivity in conjunction with the smallest possible change in the ratio of heat resistance / cold resistance with the temperature (temperature coefficient ct).

This object is achieved by an iron-chromium-nickel-silicon alloy, with (in wt .-%)
Ni 34- <38%
Cr 20-24%
Si 1.5-2.0%
Fe rest
and additions of
Al 0.05-1%
Mn 0.1-0.7%
La 0.02-0.15%
Mg 0.001-0.05%
C 0.04-0.14%
N 0.02-0.10%
S max. 0.005%
B max. 0.003%
and the usual process-related impurities.

advantageous Further developments of the subject invention are the associated claims remove.

These Due to its special composition, alloy has a longer service life as the alloys of the prior art with the same Nickel and chromium contents. additionally let yourself an increased dimensional stability or a lower Sagging than the alloys of the prior art reach 0.04 to 0.10% carbon.

• – 34–37%
• – 37–< 38%.

The spreading range for the element nickel is between 34 and <38%, whereby, depending on the application, nickel contents can be given as follows:

• - 34-37%
• - 37- <38%.

• – 21–24%.

The chromium content is between 20 and 24%, although here too, depending on the area of use of the alloy, chromium contents can be given as follows:

• - 21-24%.

Of the Silicon content is between 1.5 and 2.0%, depending on Range of application, defined contents within the spreading range can be adjusted.

• – 0,1–0,7%.

The element aluminum is provided as an addition and in amounts of 0.05 to 1%. Preferably, it may also be adjusted in the alloy as follows:

• - 0.1-0.7%.

The same applies to the element manganese, which is added with 0.1 to 0.7% of the alloy becomes.

• – 0,04–0,15%.

The subject invention is preferred assume that the material properties given in the examples essentially set with the addition of the element lanthanum in amounts of 0.02 to 0.15%. Depending on the field of application, defined values in the alloy can also be set here:

• - 0.04-0.15%.

• – 0,03–0,09%.

This applies equally to the element nitrogen, which is added in amounts between 0.02 and 0.10%. Defined contents can be given as follows:

• - 0.03-0.09%.

• – 0,04–0,10%.

Carbon is added to the alloy in the same manner, at levels between 0.04 and 0.14%. Specifically, contents can be adjusted in the alloy as follows:

• - 0.04-0.10%.

• – 0,001–0,05%
• – 0,008–0,05%.

Also, magnesium is one of the addition elements in levels of 0.0005 to 0.05%. Specifically, it is possible to adjust this element in the alloy as follows:

• - 0.001-0.05%
• - 0.008-0.05%.

• Schwefel max. 0,005%
• Bor max. 0,003%.

The elements sulfur and boron may be given in the alloy as follows:

• Sulfur max. 0.005%
• Boron max. 0.003%.

The Alloy can further contain calcium in levels between 0.0005 and 0.07%, especially 0.001 to 0.05% or 0.01 to 0.05%.

Provided the effectiveness of the lanthanum reactive element alone is insufficient should, to the material properties set out in the task In addition, the alloy may further comprise at least one of Contain elements Ce, Y, Zr, Hf, Ti with a content of 0.01 to 0.3%, which, if necessary, can also be defined additions.

Additions from Improve oxygen affinity elements such as La, Ce, Y, Zr, Hf, Ti the life. They do this by putting in the oxide layer be installed and there on the grain boundaries, the diffusion paths of oxygen. The amount of available for this mechanism Elements must therefore be normalized to the atomic weight to the To compare sets of different elements with each other.

The potential of the active elements (PwE) therefore becomes too high PwE = 200 · Σ (X e / Atomic weight of E) where E is the relevant element and X _{E is} the content of that element in percent.

As already mentioned, the alloy may contain 0.01 to 0.3% of one or more of the elements La, Ce, Y, Zr, Hf, Ti, respectively
ΣPwE = 1.43 × X _Ce + 1.49 × X _La + 2.25 × X _Y + 2.19 × X _Zr + 1.12 × _Xf + 4.18 × X _Ti ≤ 0.38, in particular ≤ 0.36 (at 0.01 to 0.2% of the total element), where PwE corresponds to the potential of the active elements.

Alternatively, in the presence of at least one of the elements La, Ce, Y, Zr, Hf, Ti in contents of 0.02 to 0.10%, there is a possibility that the sum PwE = 1.43 · X _Ce + 1.49 · X _La + 2.25 • X _Y + 2.19 • X _Zr + 1.12 • X _Hf + 4.18 • X _Ti is less than or equal 0.36, wherein PwE corresponds to the potential of the active elements.

The Alloy can do that In addition, a phosphorus content between 0.01 to 0.20%, in particular from 0.005 to 0.020%.

• – 0,01 bis 0,2%
• – 0,01 bis 0,06%.

Furthermore, the alloy may contain between 0.01 to 1.0% each of one or more of the elements Mo, W, V, Nb, Ta, Co, which may be further limited as follows:

• - 0.01 to 0.2%
• - 0.01 to 0.06%.

Finally, impurities may still contain the elements copper, lead, zinc and tin in amounts as follows:
Cu max. 1.0%
Pb max. 0.002%
Zn max. 0.002%
Sn max. 0.002%.

The alloy according to the invention should for the Use in electrical heating elements can be used, in particular in electrical heating elements, which have a high dimensional stability and a require low sagging.

One concrete application for the alloy according to the invention is the use in furnace construction.

Based The following examples illustrate the subject matter of the invention.

Examples:

The Tables 1 to 3 reflect - how already mentioned at the beginning - the stand the technology.

In Tables 4a and 4b, large scale electroless iron-nickel-chromium-silicon alloys of the prior art T1 to T7 are an alloy melted on a laboratory scale in the prior art T8 and several laboratory scale melted inventive experimental alloys V771 to V777, V1070 to V1076, V1090 to V1093 for optimizing the alloy composition shown.

at the laboratory scale molten alloys T8, V771-V777, V1070-V1076, V1090-V1093 out of blocks discharged material by means of hot rolling, cold drawing and matching Intermediate or final annealing which one annealed Wire made with the diameter of 1.29 mm.

at the industrially molten alloys T1-T7 was from the large-scale production a factory made and which annealed pattern with the diameter 1.29 mm removed. For the life test was a smaller subset of the wire respectively in the laboratory scale drawn to 0.4 mm.

For heating conductors in the form of wire accelerated life tests for comparing materials with each other, for example, with the following conditions are possible and common:
The heat conductor life test is carried out on wires with a diameter of 0.40 mm. The wire is clamped between 2 power supply lines at a distance of 150 mm and heated by applying a voltage up to 1150 ° C. The heating at 1150 ° C takes place for 2 minutes, then the power supply is interrupted for 15 seconds. At the end of the life of the wire fails by the fact that the remaining cross-section melts through. The burning time is the addition of the "on" times during the life of the wire. The relative burning time tb is the indication in% related to the burning time of a reference batch.

For the investigation the dimensional stability is in a Saggingtest the lowering behavior (Sagging) of Heating coils examined at the application temperature. This is on heating coils, the sagging of the coils from the horizontal to recorded at a certain time. The lower the bagging, the more is larger the dimensional stability or creep resistance of the material.

For this Try using soft annealed wire with the diameter of 1.29 mm to spirals with the inside diameter 14 mm wound In total, 6 heating coils are produced for each batch each made with 31 turns. All heating coils are at the beginning of the experiment regulated to a uniform outlet temperature of 1000 ° C. The temperature is determined with a pyrometer. The attempt will with a switching cycle of 30 s "on" / 30 s "off" at constant voltage. To 4 hours the experiment is ended. After cooling the heating coils is measured the sagging of the individual turns from the horizontal and the mean of the 6 values formed. These values (mm) are in Table 4b entered.

In Tables 4a and 4b are examples of the prior art alloys the technique T1 to T7 listed. T1 and T2 are alloys with about 30% nickel, about 20% Cr and about 2% Si. They contain encores of rare earths (SE) in this case cerium misch metal, which means that SE consists of about 60% Ce, about 35% La and the rest Pr and Nd. The relative burning time is 24% and 35% respectively.

The Example T3 is an alloy with about 40% nickel, about 20% Cr and about 1.3% Si. It contains additions of rare earths (SE) in this case cerium misch metal, which means that SE is about 60% Ce, about 35% La and the rest Pr and Nd. The relative burning time is 72%.

The Examples T4 to T7 are alloys with approx. 60% nickel, approx. 16% Cr and about 1.2-1.5% Si. They contain rare earth (SE) additions in this case Cerium mischmetal, which means that SE is about 60% Ce, about 35% La and the rest is Pr and Nd. The relative burning time is in the range from about 100 to 130%.

Of Further, Tables 4a and 4b contain a number of alloys melted on a laboratory scale. The laboratory scale Prior Art Melted Alloy T8 is an alloy with 36.2% nickel, 20.8% Cr and 1.87% Si. It contains like the industrially produced alloys T1-T7 Rare earth (SE) additions in the form of cerium mischmetal, what means that SE about 60% Ce, about 35% La and the rest Pr and Nd is and was, apart from the Ni, Cr, and Si content, after the same Specifications such as the large-scale Batches melted. The batches of the prior art T1 bis T8 are thus directly comparable. The relative burning time T8 is 53%.

at the laboratory scale melted experimental alloys according to the invention V771 to V777, V1070 to V1076, V1090 to V1093 is the Ni content about 36%, the Cr content about 20% and the Si content about 1.8%. The additions were varied on Ce, La, Y, Zr, Hf, Ti, Al, Ca, Mg C, N. Leave these batches Therefore directly with alloys according to the state of Compare technology T8, which thus serves as a reference alloy for optimization serves.

The addition of Ce and La in V771 to V777, V1070, V1071 and V1076 is carried out by adding cerium mischmetal. These batches therefore contain, in addition to Ce and La, even minor amounts of Pr and Nd, which, however, because of their small amounts of gene shares have not been explicitly listed in Table 4a.

As already mentioned improve additives Of oxygen affine elements the life span. They do this by being incorporated in the oxide layer and there on the Grain boundaries block the diffusion paths of oxygen. The amount the one for this one Mechanism available standing elements must therefore be normalized to atomic weight, to compare the amounts of different elements with each other to be able to.

The potential of the active elements PwE therefore becomes too high PwE = 200 · sum (X e / Atomic weight of E) where E is the element in question and X _{E is} the content of the relevant element in%.

1 shows a graphical representation of the relative burning time tb and the potential PwE for the indicated in the tables 4a and 4b different alloys. Range A: typical content of active elements, range B: possible content of active elements, range C: too high content of active elements.

At the Comparison of T6 with T7 drops On the fact that the content of SE is the same, T7, however, despite a slight longer life has a smaller content of Ca and Mg. In the presence of SE or Ce or La, Ca and Mg no longer appear to be the active elements To belong. Because in the laboratory melts without SE or Ce or La Ca or Mg always less than or equal to 0.001%, these two elements are not in included the potential of the active elements.

The addition for the potential of the active elements PwE has therefore been carried out over Ce, La, Y, Zr, Hf and Ti. If there is no information for Ce and La, but due to the addition of cerium mischmetal only the flat rate SE given, it is assumed for the calculation of PwE Ce = 0.6 SE and La = 0.35 SE. PwE = 1.43 x Ce + 1.49 x La + 2.25 x Y + 2.19 x zr + 1.12 x Hf + 4.18 x Ti

at In the prior art alloys T1 to T8, PwE is intermediate 0.11 (T2 and T4) and 0.15 (T6 and T7). The alloy according to the state the T8 technology, which is also the reference alloy for the trial melts is, has a PwE of 0.12.

The Test melts V1090 and V1072 which do not contain cerium misch metal, d. H. no Ce and La were added, but Y instead, show one lower relative burn time than T8, though V1090 is 0.10 slightly lower PwE, for that but V1072 with 0.18 a higher PwE has. Y does not seem to work as well as Ce and / or La, so that replacement of SE by Y leads to a deterioration compared to State of the art leads. Further additions of Zr and Ti (V1074) or Zr and Hf (V1092, V1073, V1091, V1093) in different proportions is managed to reach the life of T8 again. But that was it in all cases a PwE of greater than 0.28 required (0.28 for V1092 and V1073; 0.50 for V1074; 0.33 for V1091 and 0.42 for V1093). This increases the cost by a higher Need for expensive oxygen affine elements and is therefore no favorable way.

The test melts V771 to V777, V1070, V1071 have all been melted with cerium mischmetal, V1075 contains only La. The experimental melts V1075 and V777 achieved the highest relative burning time of about 70% of these experimental melts. The PwE of V777 is significantly larger at 0.36 than in V1075 at 0.20, which is at the limit of the PwE of the prior art alloys. As a result, it can be seen that a high amount of oxygen affinity elements is not essential to achieve a high relative burning time, but it is much more important to add defined oxygen affine elements. A similar good burning time was achieved with V777 with a combination of 0.06% Ce, 0.02% La, 0.03% Zr and 0.04% Ti. However, this requires a much larger PwE of 0.36 than V1075. For V772, the relative burn time is slightly lower than for V1075 and V777, although the same amount of La as in V1075 is included. PwE is very high at 0.53. Too high a content of oxygen affine elements leads to increased internal oxidation and thus in the end to a shortening of the relative burning time. A clear overshoot of a PwE of 0.36 does not seem to make sense. At 0.23 V771 has only a slightly larger PwE like V1075, but a much lower relative burning time. In V771, most of the oxygen affinity elements are Ce and only the smaller part is La. Thus, it appears that La as a burn-time improving additive is much more effective than Ce. It also appears that this can not be compensated for by a sharp increase of both Ce to 0.17% and La to 0.08%, as shown by V773 with an almost equal relative burn time of 58% and an increased PwE of 0.36. This confirms the previously made statement that a PwE of significantly greater than 0.36 does not make sense. However, even at a PwE of 0.22 as in V776 with a relative burning time of 59%, a combination of Ce = 0.06% and La = 0.02% and Zr = 0.05% does not seem as effective as the addition from just La at V1075, which means that too Zr is not as effective as La. The same applies to an additional addition of Y to Ce and La, as shown by V774 (PwE = 0.28) and showing a combination of Ce, La, Zr and Hf, such as V1070 (PwE = 0.19). A 1.7 fold increase in PwE to 0.32 for the Ce, La, Zr, and Hf combination only adds 1.15 times the relative burn time to V1076, again indicating that the PwEs are too high not so effective anymore. This becomes clear once again when comparing V1071 with V777. V1071 has the same content of Ce, La, Zr, as V777, only a much higher Ti content, which means a PwE of 0.44 and compared to V777 significantly reduced burning time of only 49%. V775 with 0.07% Ce and 0.03% La, 0.05% Y and 0.03% Hf with a PwE of 0.30 only has a relative burning time of 46%, indicating that additional doses of Y and Zr to Ce and La are not as effective.

2 is a plot of relative burn time and PwE to illustrate the previously described. 2 shows the relative burning time of the alloys Ti to T8 according to the prior art as a function of the nickel content. The straight lines limit the scattering band in the relative burning time into which the alloys of the prior art fall as a function of the nickel content. Additionally marked is the trial alloy V1075 with the addition of the best acting element La. Their life is well above the scattering range.

In Table 4b summarizes sagging along with the grain size of the wires. The prior art alloys T1 to T8 indicate Sagging between 4.5 and 6.2 mm at comparable grain sizes between 20 and 25 μm.

3 shows a plot of the nickel content. However, this does not seem to be decisive for sagging.

4 shows a plot of the alloys T1 to T8 and the experimental alloys on the C content. Since the experimental alloys have different particle sizes, they were divided into 2 classes: particle sizes from 19 to 26 μm and particle sizes from 11 to 16 μm. The alloys T1 to T8 and the trial alloys with a grain size of 19 microns to 26 microns, which have comparable grain sizes, all show a similar sagging in the range of 4.5 to 6.2 mm. The experimental alloys, which have a particle size of 11 to 16 microns and a carbon content less than 0.042% have a larger Sagging of about 8 mm, as it is to be expected due to the smaller grain size. The experimental alloys with a grain size of 11 to 16 microns and a carbon content of greater than 0.044% unexpectedly show a lower sagging of 2.8 to 5 mm.

5 shows a plot of the alloys T1 to T8 and the experimental melts on the N content. The alloys T1 to T8 and the trial alloys with a grain size of 19 microns to 26 microns, all of which have comparable grain sizes, show a reduction in sagging with increasing N content. The experimental alloys, which have a particle size of 11 to 16 microns and an N content less than 0.010%, show, as expected due to the grain size, a larger Sagging than all alloys with a particle size of 19 to 26 microns. The experimental alloys with a grain size of 11 to 16 microns and a carbon content of greater than 0.044%, which also have a nitrogen content greater than 0.045%, show unexpectedly the same to less sagging than all alloys with a grain size of 19 to 26 microns.

6 shows a plot of the sum C + N. It illustrates once again how C + N significantly reduce sagging. The alloys T1 to T8 and the trial alloys with a grain size of 19 microns to 26 microns, all of which have comparable grain sizes, show a reduction in sagging with increasing C + N content. The experimental alloys, which have a particle size of 11 to 16 microns and a C + N content less than 0.060%, show, as expected due to the grain size, a larger Sagging than all alloys with a particle size of 19 to 26 microns. The experimental alloys with a grain size of 11 to 16 microns and a C + N content of greater than 0.09%, consisting of a carbon content greater than 0.044% and at the same time have a nitrogen content greater than 0.045%, show unexpectedly the same to less sagging than all Alloys with a grain size of 19 to 26 microns.

One higher C- or N-content thus reduces sagging so much that the Sagging increasing Effect of a smaller grain size not Completely is compensated. The trial alloys are all a standard heat treatment been subjected.

As Table 4b shows arise especially at a C content greater than 0.04% smaller particle sizes. at change the standard heat treatment too slightly higher Temperatures at which larger particle sizes are created can in these alloys with a C content greater than 0.04% will achieve a further reduction of the Saggings.

The alloy V777 shows the lowest sagging of all alloys. It has the highest C content and an N content in the upper third. A high C content therefore seems particularly effective to be in the reduction of the Saggings.

nickel contents below 34% deteriorate the life (relative burning time), the specific electrical resistance and the ct value too much. Therefore is 34% the lower limit for the nickel content. Too high nickel contents cause due to the high nickel price higher costs. Therefore, 42% should be the upper limit for the nickel content.

To low Cr contents mean that the Cr concentration is too fast falls below the critical limit. That is why 18% Cr is the lower one Border for chrome. Too high Cr contents deteriorate the workability of the alloy. Therefore, 26% Cr is the upper limit.

The Formation of a silicon oxide layer below the chromium oxide layer reduces the oxidation rate. Below 1% is the silicon oxide layer too sketchy, to fully develop your effect. Too much Si content the processability of the alloy. Therefore, a Si content of 2.5% the upper limit.

It is a minimum content of 0.01% La necessary to maintain the oxidation resistance to get increasing effect of the La. The upper limit is 0.26% which corresponds to a PwE of 0.38. Larger values of PwE are how explained in the examples, not useful.

al is needed to improve the processability of the alloy. It Therefore, a minimum content of 0.05% is necessary. Too high contents in turn impair the processability. The Al content is therefore limited to 1%.

It is a minimum content of 0.01% C for a good dimensional stability or a slight sagging necessary. C is limited to 0.14% since this Element the oxidation resistance and reduced processability.

It is a minimum content of 0.01% N for a good dimensional stability or a slight sagging necessary. N is limited to 0.14% since this Element the oxidation resistance and reduced processability.

For Mg's a minimum content of 0.001% is required, as this is the processability of the material is improved. The limit is set at 0.05%, so as not to soften the positive effect of this element.

The Keep sulfur and boron levels as low as possible since these are surfactant Elements impair the oxidation resistance. It will therefore max. 0.01% S and max. 0.005% B is set.

copper is set to max. 1% limited, since this element's oxidation resistance reduced.

pb is set to max. 0.002% limited because this element's oxidation resistance reduced. The same applies Sn.

It is a minimum content of 0.01% Mn to improve processability necessary. Manganese is limited to 1% because this element's oxidation resistance reduced.

Claims (25)

Iron-chromium-nickel-silicon alloy, with (in Wt .-%) Ni 34- <38% Cr 20-24% Si 1.5-2.0% Fe rest and additions of Al 0.05-1% Mn 0.1-0.7% La 0.02-0.15% mg 0.001-0.05% C 0.04 to 0.14% N 0.02-0.10% S Max. 0.005% B max. 0.003% and the usual procedural Impurities. An alloy according to claim 1, having a nickel content from 34 to 37%. An alloy according to claim 1, having a nickel content from 37 to <38%. An alloy according to any one of claims 1 to 3, having a chromium content from 21 to 24%. An alloy according to any one of claims 1 to 4, having an aluminum content from 0.1 to 0.7%. An alloy according to any one of claims 1 to 5, having a lanthanum content from 0.04 to 0.15%. An alloy according to any one of claims 1 to 6, having a nitrogen content from 0.03 to 0.09%. An alloy according to any one of claims 1 to 7, having a carbon content from 0.04 to 0.10% An alloy according to any one of claims 1 to 8, having a magnesium content from 0.008 to 0.05%. Alloy according to one of claims 1 to 9, further containing 0.0005 to 0.07% Ca. An alloy according to any one of claims 1 to 9, further comprising 0.001 to 0.05% approx. An alloy according to any one of claims 1 to 9, further comprising 0.01 to 0.05% approx. An alloy according to any one of claims 1 to 12, further if necessary as an addition containing at least one of the elements Ce, Y, Zr, Hf, Ti at a content of 0.01 to 0.3%. An alloy according to any one of claims 1 to 13, wherein 0.01 to 0.3% each of one or more of the elements La, Ce, Y, Zr, Hf, Ti, wherein the sum PwE = 1.43 · X _Ce + 1, 49 × X _La + 2.25 × X _Y + 2.19 × X _zr + 1.12 × X _Hf + 4.18 × X _{Ti is} less than or equal to 0.38, where PwE corresponds to the potential of the active elements. Alloy according to one of claims 1 to 13, wherein 0.01 to 0.2% in each case one or more of the elements La, Ce, Y, Zr, Hf, Ti, the sum PwE = 1.43 × X _Ce + 1, 49 × X _La + 2.25 × X _y + 2.19 × X _zr + 1.12 × X _Hf + 4.18 × X _{Ti is} less than or equal to 0.36, in which PwE corresponds to the potential of the active elements. Alloy according to one of Claims 1 to 13, with 0.02 to 0.15% each of one or more of the elements La, Ce, Y, Zr, Hf, Ti, the sum being PwE = 1.43 × X _Ce + 1, 49 × X _La + 2.25 × X _y + 2.19 × X _zr + 1.12 × X _Hf + 4.18 × X _{Ti is} less than or equal to 0.36, in which PwE corresponds to the potential of the active elements. An alloy according to any one of claims 1 to 16, having a phosphorus content from 0.001 to 0.020%. An alloy according to any one of claims 1 to 16, having a phosphorus content from 0.005 to 0.020%. An alloy according to any one of claims 1 to 18, further containing 0.01 to 1.0% in each case one or more of the elements Mo, W, V, Nb, Ta, Co. An alloy according to any one of claims 1 to 18, further containing 0.01 to 0.2% in each case one or more of the elements Mo, W, V, Nb, Ta, Co. An alloy according to any one of claims 1 to 18, further containing 0.01 to 0.06% each one or more of the elements Mo, W, V, Nb, Ta, Co. An alloy according to any one of claims 1 to 21, wherein the impurities in contents of max. 1.0% Cu, max. 0.002% Pb, max. 0.002% Zn, max. 0.002% Sn are set. Use of the alloy according to one of claims 1 to 22 for use in electrical heating elements. Use of the alloy according to one of claims 1 to 22 for the use in electrical heating elements, which have a high dimensional stability or a low Require sagging. Use of the alloy according to one of claims 1 to 22 for the use in furnace construction.