WO2008092419A2

WO2008092419A2 - Iron-nickel-chromium- silicon alloy

Info

Publication number: WO2008092419A2
Application number: PCT/DE2008/000060
Authority: WO
Inventors: Heike Hattendorf; Jürgen WEBELSIEP
Original assignee: Thyssenkrupp Vdm Gmbh
Priority date: 2007-01-31
Filing date: 2008-01-15
Publication date: 2008-08-07
Also published as: PL2115179T3; ATE463589T1; JP2010516902A; CN101595236B; CN101595236A; JP5404420B2; EP2115179B1; WO2008092419A3; EP2115179A2; DE102007005605B4; ES2341151T3; DE502008000536D1; DE102007005605A1; US20090285717A1; MX2009007535A

Abstract

Iron-nickel-chromium-silicon alloy having (in percentage by weight) 34-42% nickel, 18-26% chromium, 1.0-2.5% silicon, to which 0.05-1% Al, 0.01-1% Mn, 0.01-0.26% lanthanium, 0.0005-0.05% magnesium, 0.01-0.14% carbon, 0.01-0.14% nitrogen, maximum 0.01% sulphur, maximum 0.005% B are added, the remainder being iron and the usual impurities due to processing.

Description

Iron-nickel-chromium-silicon alloy

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 heating conductors in the temperature range up to 1100 ^° C. For use as a heating conductor alloy, this alloy group is standardized in DIN 17470 (Table 1) and ASTM B344-83 (Table 2). There are a number of commercially available alloys listed in Table 3 for this standard.

The sharp increase in the price of nickel in recent years gives rise to the desire to use heat conductor alloys with the lowest possible nickel contents. In particular, there is a desire to replace the high-nickel NiCr8020, NiCr7030 and NiCr6015 (Table 1), which are characterized by particularly advantageous properties, with materials with a reduced nickel content, without having to accept large losses in the performance of 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 (C ^ Os), with an underlying, more or less closed, Siθ 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, the lifetime is increased by a higher chromium content, since a higher content of the protective layer forming element chromium Time delays at which the Cr content is below the critical limit and form other oxides than Cr ₂ O ₃ , which are, for example, iron-containing oxides.

By EP-A O 531 775 is a heat-resistant austenitic heat-deformable

Nickel alloy of the following composition (in% by weight):

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.

EP-A-0 386 730 describes a nickel-chromium-iron alloy with very good oxidation resistance and high temperature resistance, as desired for advanced heat conductor applications, starting from the known NiCr6015 heating conductor alloy and making significant modifications to the composition 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. WO-A 2005/031018 discloses an austenitic Fe-Cr-Ni alloy for use in the high-temperature range, 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 remainder.

In free-hanging heating elements in addition to the demand for a long life and the requirement for good dimensional stability at the application temperature. Too much sagging during operation results in uneven spacing of the turns with uneven temperature distribution, thereby shortening the life. To compensate this would require more support points for the heating coil, which increases the cost. This means that the heating conductor material must have a sufficiently good dimensional stability or creep resistance.

The creeping mechanisms affecting the dimensional stability in the area of the application temperature (dislocation creeping, grain boundary slipping or

Diffusion creep) are all influenced by the creep, except for the dislocation creeping by a large grain size in the direction of greater creep resistance. The dislocation creep does not depend on the grain size. The production of a wire with a large grain size increases the creep resistance and thus the dimensional stability. For all considerations, grain size should therefore also be taken into account as an important influencing factor.

Another important factor for a heat conductor material is the highest possible specific electrical resistance and the smallest possible change in the ratio of the thermal resistance / cold resistance to the temperature (temperature coefficient et). The variants with lower nickel content NiCr3020 or 35Ni, 20Cr (Table 1 and Table 2), which are characterized by significantly lower costs, meet in particular the requirements of the life only inadequate.

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 et).

This object is achieved by an iron-nickel-chromium-silicon alloy, with (in wt .-%) 34 to 42% nickel, 18 to 26% chromium, 1, 0 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, 0.01 to 0.14% carbon, 0.01 to 0, 14% nitrogen, max. 0.01% sulfur, max. 0.005% B, balance iron and the usual process-related impurities.

Advantageous developments of the subject invention can be found in the associated dependent claims.

This alloy, due to its special composition, has a longer service life than the alloys of the prior art with the same nickel and chromium contents. In addition, increased dimensional stability or sagging can be achieved than the prior art alloys with 0.04 to 0.10% carbon. The spreading range for the element nickel is between 34 and 42%, whereby, depending on the application, nickel contents can be given as follows:

34 - 39%

34 - 38%

34 - 37%

37 - 38%.

The chromium content is between 18 and 26%, although here too, depending on the area of use of the alloy, chromium contents can be given as follows:

20 - 24%

21-24%.

The silicon content is between 1.0 and 2.5%, whereby, depending on the field of application, defined contents within the spread range can be set:

1.5-2.5%

1.0-1.5%

1.5-2.0%

1.7-2.5%

1.2-1.7%

1.7-2.2%

2.0-2.5%.

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 0.01 to 1% of the alloy. Alternatively, the following spread range is conceivable:

0.1-0.7%. The subject of the invention preferably assumes that the material properties specified in the examples are essentially set with the addition of the element lanthanum in contents of 0.01 to 0.26%. Depending on the field of application, defined values in the alloy can also be set here:

0.01 - 0.2%

0.02 - 0.15%

0.04 - 0.15%.

This applies equally to the element nitrogen, which is added in amounts between 0.01 and 0.14%. Defined contents can be given as follows:

0.02 - 0.10%

0.03-0.09%.

Carbon is added to the alloy in the same manner, at levels between 0.01 and 0.14%. Specifically, contents can be adjusted in the alloy as follows:

0.04 - 0.14%

0.04 - 0.10%.

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%.

The elements sulfur and boron may be given in the alloy as follows: sulfur max. 0.005% boron max. 0.003%.

The alloy may further include calcium at levels between 0.0005 and 0.07%, especially 0.001 to 0.05% or 0.01 to 0.05%. If the effectiveness of the reactive element lanthanum alone should not be sufficient to produce the material properties set out in the problem, the alloy may further comprise at least one of the elements Ce, Y, Zr, Hf, Ti with a content of 0.01 to 0, 3%, which can also be defined supplements as needed.

Additions of oxygen-affinity elements such as La, Ce, Y, Zr, Hf, Ti improve the lifetime. They do this by incorporating them into the oxide layer and blocking the diffusion paths of the oxygen there on the grain boundaries. The amount of elements available for this mechanism must therefore be normalized to the atomic weight in order to be able to compare the amounts of different elements among 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 element in question and XE 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

Σ PwE = 1, 43 'XCe ⁺ 1, 49 - XL ₈ + 2.25 - XY + 2.19 ^•) <& + 1, 12 ^• X _Hf + 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 the possibility that the sum PwE =

1, 43 • Xc _e + 1, 49 • X _La + 2.25 • X _γ + 2.19 • X _zr +1, 12 • X _Hf + 4.18 • X _{Ti is} less than or equal to 0.36, where PwE corresponds to the potential of the active elements. In addition, the alloy may have a phosphorus content between 0.01 to 0.20%, in particular from 0.005 to 0.020%.

Furthermore, the alloy may contain between 0.01 to 1.0% 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 is to be used for use in electric heating elements, in particular in electrical heating elements which require high dimensional stability and low sagging.

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

Based on the following examples, the subject invention will be explained in more detail.

Examples:

Tables 1 to 3 reflect - as already mentioned at the beginning - the state of the art.

In Tables 4a and 4b are industrially molten iron-nickel-chromium-silicon alloys according to the prior art T1 to T7, one on a laboratory scale Prior art molten alloy T8 and a plurality of bench scale inventive experimental alloys V771 to V777, V1070 to V1076, V1090 to V1093 melted to optimize the alloy composition.

For the T8, V771-V777, V1070-V1076, V1090 - V1093 alloys melted on a laboratory scale, a soft annealed wire with a diameter of 1.29 mm was produced from the material cast in blocks by hot rolling, cold drawing and appropriate intermediate or final annealing.

For the large-scale molten alloys T1-T7, a factory-made and soft-annealed sample with a diameter of 1.29 mm was taken from large-scale production. For the life test, a smaller subset of the wire was drawn on a laboratory scale up 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 ⁰ C. The heating at 1150 ⁰ C takes place in each case 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 of dimensional stability, the sagging behavior of heating coils at the application temperature is investigated in a sagging test. This is on heating coils, the sagging of the helices of the Horizontal captured after a certain time. The lower the sag, the greater the dimensional stability or creep resistance of the material.

For this test, soft annealed wire with a diameter of 1.29 mm is wound into spirals with an inner diameter of 14 mm. In total, 6 heating coils each with 31 turns are produced for each batch. All heating coils are controlled at the start of the experiment to a uniform outlet temperature of 1000 ° C. The temperature is determined with a pyrometer. The test is carried out with a switching cycle of 30 s "on" / 30 s "off" at constant voltage. After 4 hours, the experiment is terminated. After the heating coils have cooled, the sagging of the individual turns from the horizontal is measured and the mean value of the 6 values is formed. These values (mm) are listed in Table 4b.

Examples of the alloys according to the prior art T1 to T7 are listed in Tables 4a and 4b. T1 and T2 are alloys with about 30% nickel, about 20% Cr and about 2% Si. They contain rare earth (SE) additions 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% or 35%.

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

The examples T4 to T7 are alloys with about 60% nickel, about 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 Pr and Nd. The relative burning time is in the range of about 100 to 130%.

Furthermore, Tables 4a and 4b contain a number of alloys melted on a laboratory scale. The laboratory-scale melted prior art alloy T8 is an alloy of 36.2% nickel, 20.8% Cr, and 1.87% Si. Like the industrially produced alloys T1-T7, it contains rare earth (SE) additions in the form of cerium misch metal, which means that SE is and was about 60% Ce, about 35% La and the rest Pr and Nd, apart from the Ni, Cr, and Si contents, melted to the same specifications as the large-scale batches. The batches according to the prior art T1 to T8 are thus directly comparable. The relative burning time of T8 is 53%.

In the case of the pilot scale inventive experimental alloys V771 to V777, V1070 to V1076, V1090 to V1093, the Ni content is about 36%, the Cr content about 20% and the Si content about 1, 8%. The additions to Ce, La, Y, Zr, Hf, Ti, Al, Ca, Mg C, N were varied. These batches can therefore be compared directly with the prior art alloys T8, thus serving 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. Therefore, these batches contain not only Ce and La but also minor amounts of Pr and Nd, but because of their minor proportions have not been explicitly listed in Table 4a.

As already mentioned, additions of oxygen-affine elements improve the lifetime. They do this by incorporating them into the oxide layer and blocking the diffusion paths of the oxygen there on the grain boundaries. The amount of elements available for this mechanism must therefore be normalized to the atomic weight in order to be able to compare the amounts of different elements among each other.

The potential of the active elements PwE therefore becomes too high

PwE = 200 ^* Sum (X _E / atomic weight of E) defined, where E is the element concerned and XE is the content of the relevant element

Element is in%. Fig. 1 shows a graph of the relative burning time tb and the potential PwE for the different alloys indicated in Tables 4a and 4b. Range A: typical content of active elements, range B: possible content of active elements, range C: too high content of active elements.

When comparing T6 with T7, it is noticeable that the content of SE is the same, 11 however, despite a slightly longer service life, it has a smaller content of Ca and Mg. In the presence of SE, Ce or La, Ca and Mg no longer appear to belong to the active elements. Since in laboratory melts without SE or Ce or La Ca or Mg is always less than or equal to 0.001%, these two elements are not included in 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 _γ + 2.19 • X _zr +1, 12 • X _Hf + 4.18 • X _Ti

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

Trials V1090 and V1072, which did not add cerium misch metal, ie, Ce and La, but Y instead, show a lower relative burn time than T8, although V1090 at 0.10 has a slightly lower PwE but V1072 at 0, 18 has a higher PwE. Y does not appear to work as well as Ce and / or La, so replacement of SE by Y leads to a deterioration over the prior art. Further additions of Zr and Ti (V1074) or Zr and Hf (V1092, V1073, V1091, V1093) in different proportions have succeeded in achieving the service life of T8 again. However, in all cases a PwE of greater than 0.28 was 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 increasing the demand for expensive oxygen affinity elements and is therefore not an advantageous route.

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 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 a combination of Ce, La, Zr and Hf, such as V1070 (PwE = 0.19). Increasing PwE by 1.7 times to 0.32 for the combination of Ce, La, Zr and Hf only increases the relative burning time by a factor of fifteen at V1076, which in turn indicates 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.

Figure 2 is a plot of relative burn time and PwE to illustrate the previously described. Figure 2 shows the relative burning time of the alloys T1 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.

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

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

Figure 4 shows a plot of the alloys T1 to T8 and the experimental alloys over 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, the 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.

Figure 5 shows a plot of the alloys T1 to T8 and the experimental melts over 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 equal to less sagging than all alloys with a particle size of 19 to 26 microns.

Figure 6 shows a plot over 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 test 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 a nitrogen content greater than 0.045 %, unexpectedly show an equal to lesser sagging than all alloys with a grain size of 19 to 26 μm.

A higher C- or N-content thus reduces sagging so much that the sagging-enhancing effect of a smaller grain size is not fully compensated. The trial alloys have all been subjected to a standard heat treatment.

As Table 4b shows, especially at a C content greater than 0.04% smaller particle sizes. By changing the standard heat treatment to slightly higher temperatures, which then results in larger grain sizes, a further reduction of the sagging can be achieved in these alloys with a C content greater than 0.04%.

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 to be particularly effective in reducing sagging.

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

Too low Cr contents mean that the Cr concentration falls too fast below the critical limit. That is why 18% Cr is the lower limit for chromium. 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%, the silicon oxide layer is too patchy to your To be fully effective. Too high Si contents impair the processability of the alloy. Therefore, an Si content of 2.5% is the upper limit.

A minimum content of 0.01% La is necessary to obtain the oxidation resistance-enhancing effect of La. The upper limit is set at 0.26%, which corresponds to a PwE of 0.38. Larger values of PwE are not meaningful as explained in the examples.

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

A minimum content of 0.01% C is necessary for good dimensional stability or low sagging. C is limited to 0.14% because this element reduces oxidation resistance and processability.

A minimum content of 0.01% N is necessary for good dimensional stability or low sagging. N is limited to 0.14% because this element reduces oxidation resistance and processability.

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

The levels of sulfur and boron should be kept as low as possible, since these surface-active elements affect the oxidation resistance. It will therefore max. 0.01% S and max. 0.005% B is set.

Copper is heated to max. 1% limited as this element reduces the oxidation resistance. Pb is set to max. 0.002% limited because this element reduces the oxidation resistance. The same applies to Sn.

A minimum content of 0.01% Mn is required to improve processability. Manganese is limited to 1% because this element reduces oxidation resistance.

Table 1 Alloys according to DIN 17470 and 17742 (composition of NiCr8020, NiCr7030, NiCr6015). All data in% by weight

^* ) max. Co 1, 5%

Table 2: Alloys according to ASTM B 344-83. All data in% by weight

Cr Ni + Co *) Fe S Mn CSP (μΩm) Ct (at 871 ⁰ C)

80Ni, 20Cr 19-21 radical <1.0 0, 75-1.75 <1, 0 <o, 15 <o, 01 1, 081 1, 008

60Ni, 16Cr 14-18> 57 0, 75-1.75 <1, 0 <o, 15 <o, 01 1, 122 1, 073

35Ni, 20Cr 18-21 34-37 residue 1, 0-3,0 <1, 0 <o, 15 <o, 01 1, 014 1, 214

Table 3: Commercially available alloys. All data in% by weight

kt

O

Table 4a: Relative burning time tb and composition of test batches (batch number starts with V) and prior art batches (T1 to T8). All data in% by weight. SE = sum (Ce ₁ La ₁ Pr, Nd). If there is no information for Ce or La

Table 4b: Continuation: Relative burning time tb and composition of test batches (batch number starts with V) and prior art batches (T1 to T8). All data in% by weight.

Kt Kt

Claims

claims

1. iron-nickel-chromium-silicon alloy, with (in wt%) 34 to 42% nickel, 18 to 26% chromium, 1, 0 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, 0.01 to 0.14% carbon, 0.01 to 0.14% nitrogen, Max. 0.01% sulfur, max. 0.005% B, balance iron and the usual process-related impurities.

2. An alloy according to claim 1, having a nickel content of 34 to 39%.

3. The alloy of claim 1, having a nickel content of 34 to 38%.

4. The alloy of claim 1, having a nickel content of 34 to 37% nickel

5. The alloy of claim 1, having a nickel content of 37 to 38%.

6. An alloy according to any one of claims 1 to 5, having a chromium content of

20 to 24%.

7. An alloy according to any one of claims 1 to 5, having a chromium content of

21 to 24%.

8. The alloy of any one of claims 1 to 7, having a silicon content of 1, 5 to 2.5%.

9. An alloy according to any one of claims 1 to 7, having a silicon content of 1, 0 to 1, 5%.

10. An alloy according to any one of claims 1 to 7, having a silicon content of 1, 5 to 2.0%.

11. An alloy according to any one of claims 1 to 7, having a silicon content of 1.7 to 2.5%.

12. An alloy according to any one of claims 1 to 7, having a silicon content of 1, 2 to 1, 7%.

13. An alloy according to any one of claims 1 to 7, having a silicon content of 1.7 to 2.2%.

14. An alloy according to any one of claims 1 to 7, having a silicon content of 2.0 to 2.5%.

An alloy according to any one of claims 1 to 14, having an aluminum content of 0.1 to 0.7%.

16. An alloy according to any one of claims 1 to 15, having a manganese content of 0.1 to 0.7%.

17. An alloy according to any one of claims 1 to 16, having a lanthanum content of 0.01 to 0.2%.

18. An alloy according to any one of claims 1 to 16, having a lanthanum content of 0.02 to 0.15%.

19. An alloy according to any one of claims 1 to 16, having a lanthanum content of 0.04 to 0.15%.

20. An alloy according to any one of claims 1 to 19, having a nitrogen content of 0.02 to 0.10% nitrogen.

An alloy according to any one of claims 19 to 19, having a nitrogen content of 0.03 to 0.09%.

22. An alloy according to any one of claims 1 to 21, having a carbon content of 0.04 to 0.14%.

23. An alloy according to any one of claims 1 to 21, having a carbon content of 0.04 to 0.10%.

24. An alloy according to any one of claims 1 to 23, having a magnesium content of 0.001 to 0.05%.

25. An alloy according to any one of claims 1 to 23, having a magnesium content of 0.008 to 0.05%.

26. Alloy according to one of claims 1 to 25, with max. 0.005% sulfur and max. 0.003% B.

An alloy according to any one of claims 1 to 26, further containing 0.0005 to 0.07% Ca.

An alloy according to any one of claims 1 to 26, further containing 0.001 to 0.05% Ca.

29. An alloy according to any one of claims 1 to 26, further comprising 0.01 to 0.05% Ca.

The alloy according to any one of claims 1 to 29, further comprising, if necessary, an addition containing at least one of Ce, Y, Zr, Hf, Ti at a content of 0.01 to 0.3%.

31. An alloy according to any one of claims 1 to 30, wherein 0.01 to 0.3% in each case one or more of the elements La, Ce, Y, Zr, Hf, Ti, wherein the sum PwE = 1, 43 - X ₀₆ + 1, 49 • X _La + 2.25 ^• X _γ + 2.19 - X ^ +1, 12 - X ^ + 4.18 ^• X _T i is less than or equal to 0.38, where PwE corresponds to the potential of the active elements.

32. An alloy according to any one of claims 1 to 30, wherein 0.01 to 0.2% 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 ^« Xγ + 2.19 ^« Xzr +1, 12 ^« X _Hf + 4.18 • Xu is less than or equal to 0.36, where PwE corresponds to the potential of the active elements.

33. An alloy according to any one of claims 1 to 30, wherein 0.02 to 0.15% each one or more of the elements La, Ce, Y, Zr, Hf, Ti, wherein the sum PwE = 1, 43 'X _C e ⁺ 1, 49 • X _La + 2.25 • X _γ + 2.19 ^• X _zr +1, 12 • X _Hf + 4.18 ^• X _T i is less than or equal to 0.36, where PwE is the potential of the active elements equivalent.

An alloy according to any one of claims 1 to 33, having a phosphorus content of 0.001 to 0.020%.

35. An alloy according to any one of claims 1 to 33, having a phosphorus content of 0.005 to 0.020%.

An alloy according to any one of claims 1 to 35, further comprising 0.01 to 1.0% each of one or more of Mo, W, V, Nb, Ta, Co.

An alloy according to any one of claims 1 to 35, further comprising 0.01 to 0.2% each of one or more of Mo, W, V, Nb, Ta, Co.

38. The alloy according to any one of claims 1 to 35, further comprising 0.01 to 0.06% each of one or more of Mo, W, V, Nb, Ta, Co.

39. An alloy according to any one of claims 1 to 38, wherein the impurities are present in levels of max. 1, 0% Cu, max. 0.002% Pb, max. 0.002% Zn, max. 0.002% Sn are set.

40. Use of the alloy according to one of claims 1 to 39 for use in electrical heating elements.

41. Use of the alloy according to one of claims 1 to 39 for use in electrical heating elements that require a high dimensional stability or a low sagging.

42. Use of the alloy according to one of claims 1 to 39 for use in furnace construction.