EP1381701B1 - Iron-chrome-aluminium-alloy - Google Patents

Abstract

The invention relates to an iron-chrome-aluminium-alloy with a high service life, comprising (in mass %) >2 3.6 % aluminium and >10 - 20 % chrome and other added materials, 0.1 -1 % Si, max. 0.5 % Mn, 0.01 0.2 % Yttrium and/or 0.01 0.2 % Hf and/or 0.01 0.3 % Zr, max. 0.01 % Mg, max. 0.01 % Ca, max. 0.08 % carbon, max. 0.04 % nitrogen, max. 0.04 % phosphorus max. 0.01 % sulphur, max. 0.05 % copper and respectively max. 0.1 % molybdenum and/or wolfram and the usual manufacture-related impurities, the remainder being iron.

Description

The invention relates to a deformable, ferritic steel alloy.

Such alloys are used inter alia for the production of electrical Heating elements and catalyst supports used. These materials form one dense, adherent alumina layer that protects it from destruction. This Protection is improved by additions of so-called reactive elements such as for example, Ca, Ce, La, Y, Zr, Hf, Ti, Nb, which improve the adhesiveness and / or reduce layer growth, as described in the "Handbook of the High-temperature materials technology, Ralf Bürgel, Vieweg Verlag, Braunschweig 1998 ", from page 274 onwards.

The aluminum oxide layer protects the metallic material from faster Oxidation. At the same time she is growing herself, albeit very slowly. This growth takes place using consumption of the aluminum content of the material. Is not a Aluminum more present, so grow other oxides (chromium and iron oxides). The metal content of the material is consumed very quickly and the material failed. The time to failure means life. An increase in the Aluminum content thus extends the life.

In DE-A 19928842 an alloy with (in mass%) 16 to 22% Cr, 6 to 10% Al and additions of 0.02 to 1.0% Si, max. 0.5% Mn, 0.02 to 0.1% Hf, 0.02 to 0.1% Y, 0.001 to 0.01% Mg, max. 0.02% Ti, max. 0.03% Zr, max. 0.02 % SE, max. 0.1% Sr, max. 0.1, max. 0.5% Cu, max. 0.1% V, max. 0.1% Ta, Max. 0.1% Nb, max. 0.03% C, max. 0.01% N, max. 0.01% B, balance iron as well Contamination-related contaminants for use as a carrier film for Catalytic converters, as heat conductor, as component in industrial furnace construction and in Gas burners described.

In EP-B 0387670 an alloy with (in mass%) 20 to 25% Cr, 5 to 8 % Al and additions of 0.03 to 0.08% yttrium 0.004 to 0.008% nitrogen, 0.020 to 0.040% carbon, as well as about equal parts 0.035 to 0.07% Ti and 0.035 to 0.07% zirconium, and max. 0.01% phosphorus, max. 0.01% magnesium, Max. 0.5% manganese, max. 0.005% sulfur, residual iron is addressed, the Sum of the contents of Ti and Zr in% from 1.75 to 3.5 times as large as the sum the contents of C and N in mass% as well as melting Impurities. Ti and Zr may be wholly or partially hafnium and / or Tantalum or vanadium are replaced.

In EP-B 0290719 is an alloy with (in mass%) 12 to 30% Cr, 3.5 to 8% Al, 0.008 to 0.10% carbon, max. 0.8% silicon, 0.10 to 0.1% manganese, Max. 0.035% phosphorus, max. 0.020% sulfur, 0.1 to 1.0% molybdenum, max. 1 % Nickel, and the additives 0.010 to 1.0% zirconium, 0.003 to 0.3% titanium and 0.003 to 0.3% nitrogen, calcium plus magnesium 0.005 to 0.05%, as well rare earth metals from 0.003 to 0.80%, nlob from 0.5%, remaining iron with usual Accompanying elements described, for example, as a wire for heating elements for electrically heated ovens and as a construction material for thermally loaded Parts and is used as a film for the preparation of catalyst supports.

In US Pat. No. 4,277,374, an alloy having (in% by mass) up to 26% chromium, 1 up to 8% aluminum, 0.02 to 2% hafnium, up to 0.3% yttrium, up to 0.1% Carbon, up to 2% silicon, balance iron, with a preferred range of 12 to 22% chromium and 3 to 6% aluminum treated as a foil to the Production of catalyst supports is used.

The above documents are based on traditional production methods, namely the conventional casting of the alloy and the subsequent hot and Cold forming. Since these methods with high failures u. a. by Embrittlement phenomena associated with hot rolling have been reported in the In recent years, alternatives have been developed in which a chromium steel, the reactive Contains elements coated with aluminum or even aluminum alloys becomes. Such composites are then rolled to final thickness and subsequently diffusion annealed, wherein when setting suitable annealing parameters a homogeneous material is created.

Such methods are described for example in the publications EP-B 0640390, EP-B 0204423 and WO 99/18251 and are excellent suitable, the processing problems, for the applications where a high Aluminum content is technically required and the application in the form of Folle or band occurs, decrease.

Another way the failures and the costs by the Embrittlement phenomena will decrease in the use of iron-chromium-aluminum alloys for household appliances such. B. toaster, Hairdryer, u. Ä., which is usually practiced at lower temperatures be used below 800 ° C and very much under Costs are produced. Since here the use is usually in Form of wire, the solutions described by coating are not possible. There are due to the lower temperature loads Alloys with (in% by mass) a reduced aluminum content of less than 5% used, such. B. an alloy with about 14.5% Cr, about 4.5% Al, additions of reactive elements, residual iron, as in the DIN standard 17470 in Table 3 with 14% chromium and 4% aluminum, residual iron (Cr Al 14 4) is described and produced as "wires from Krupp VDM for the electrical industry", Publication N563, issue November 1998 on page 24, Material Aluchrom W, with 14 to 16% chromium, 3.5 to 5.0% aluminum, max. 0.08% carbon, max. 0.6% manganese. Max. 0.5% silicon, max. 0.3% zirconium, others melting-related impurities, residual iron is known. These In the following, alloy serves as a comparative alloy and becomes short with Cr Al 14 4 designated.

The iron - chromium - aluminum alloy Cr Al 14 4 can indeed by the to about 4 to 4.5 mass% lowered aluminum content easier than the alloys described above with more than 5% by weight of aluminum. She shows, however still embrittlement, which increased to an Manufacturing costs during hot forming lead.

So far, it has been state of the art that in Fe Cr Al alloys with approximately 14 to 15 Mass% chromium a minimum content of about 4 mass% Al is needed to make a protective aluminum oxide layer, build up, for example, in "Manual High Temperature Materials Technology, Ralf Bürgel, Vieweg Verlag, Braunschweig 1998 "on page 272 in Fig. 5.13.

GB-A 476,115 is an iron alloy, in particular usable as electrical resistance, which includes the following elements: 6.1 - 30 % Cr, 3 - 12% Al, 0.07 - 0.2% C, ≤ 4% Ti, balance Fe as well melting impurities. The Ti content is in this case on the C content is bound to be not less than 3 times the C content should be. Preferred ranges for Cr are> 8%, for Al> 5%, for C> 0.085 %.

In DE-A 196 52 399 is a method for producing a multilayer Metal composite film and their use described. The metal composite foil includes a carrier layer of ferritic steel strip, the both sides with a Outer layer of aluminum or an aluminum alloy is provided. The Carrier layer is formed of an alloy with (in mass%) 16-25% Cr, Rare earths, Y or Zr, in contents between 0.01 - 0.1%, Fe remainder. Femer Al may be added in levels between 2 and 6%. Preferred Cr contents are above 20%.

Finally, EP-A 0 402 640 discloses a stainless steel foil as a carrier element for catalysts and their preparation. The film is formed from a Alloy of the following composition (in% by mass): 1.0 -20% Al, 5 - 30% Cr, Up to 2% Mn, up to 3% Si, up to 1% C, balance Fe and production-related Impurities. Preferred ranges for Al are between 5.5 and 20%. Of Further, Y, Sc or rare earths can be added within limits of 0.3% wherein at least one of the elements Ti, Nb, Zr, Hf, V, Ta, Mo, W in Levels up to 2% can be provided. Contents <4% Al require in this case Cr contents > 25%.

JP-A 06330248 is an alloy having the following composition from 2.5 to 4.5% Al, 9 to <18% Cr, ≤1% Si, ≤1% Mn, ≤0.02% C, ≤0.02 % N, balance Fe. As a reactive element should Hf in limits of 0.01 - 0.2% to Get used.

JP-A 0611 6686 discloses an iron-chromium-aluminum alloy Composition: 1 - 6% Al, 10 - 28% Cr, <1% Si, <1.5% Mn, ≤0.05% Ti + Nb, ≤0.01% Ce, ≤0.05% C, ≤0.02% N, Fe as the remainder Zr in contents of 0.01 - 1.0% and La in contents of 0.01 - 0.2% be added.

Finally, JP-A 08269730 discloses an alloy of the following Composition: 3 - 8% Al, 9 - 30% Cr, ≤1.0% Si, ≤1.0% Mn, ≤0.05% C, ≤ 0.05% N, Fe as the remainder. The alloy can have in excess of> 1% elements such as Nb, Ti, Zr, V, Hf, Mo, Ta and Co are added.

The invention is based on the object, a cost-effective iron-chromium-aluminum Alloy to provide a similar or better life as Cr Al 14 4 has, but even less brittleness and therefore improved Formability has, but at the same time the same technical functionality as Cr Al 14 has 4.

This object is achieved by an iron-chromium-aluminum alloy with high durability, with (in mass%) 2.5 to 3.0% aluminum and> 10 to <20% Chromium and additions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium and 0.01 to 0.2% Hf and / or 0.01 to 0.3% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon, max. 0.04% nitrogen, max. 0.04% phosphorus max. DE-A-198 34 552 discloses: an iron-chromium-aluminum alloy as a metal foil for Heizleiterwiederstände or as a carrier for Catalytic converters is used, wherein the film has the following composition Al: 4-10%; Cr: 18-25%; Si: 0.5-1.5%; Y: 0:03 to 12:08%; Zr: 0:01 to 12:05%; Hf: 0.01-0.05%; Ti: max. 00:01% and balance Fe and common impurities. 0.01% sulfur, max. 0.05% copper and max. 0.1% molybdenum and / or Tungsten and production-related impurities, the rest iron

Advantageous developments of the alloy according to the invention are the Subclaims refer.

Preferably, the Al content in limits of 2.5 - 3.55% and the Cr content in Set limits of 13 -17%.

A reduction in brittleness is most effective by reducing reach the aluminum content. However, this has the disadvantage that the Specific electrical resistance also decreases and the service life decreases.

The brittleness is also due to chromium, silicon, carbon and nitrogen increased, which is why these elements are kept as low as possible should.

The same technical functionality for a heating conductor used for electrical Generation of heat is achieved when the surface power, the Power at the heating element, the total resistance of the heating element and the Service life of the heating element in any change of the material remains constant.

Decreasing now at constant surface power, constant power and constant resistance to the specific electrical resistance, so you have to order above conditions to reduce the diameter of the wire and increase the wire length by the same percentage as the diameter. Overall, this reduces the volume by this percentage. This means, you save material while reducing the electrical resistivity. This is also in H. Pfeifer, H. Thomas, Zunderfeste alloys, Springer Verlag, Berlin 1963, on page 387 read.

The following calculation demonstrates this situation:

With wires, the diameter, length and weight change are added Exchange of the material A calculated by B, whereby surface performance, Power and resistance are kept constant.

The following formulas apply with the above boundary conditions Diameter D B / D A = 3 ρ B / ρ A Length L B / L A = 3 ρ A / ρ B Weight M B / M A = 3 ρ B / ρ A • γ B / γ A

Beispiel: Material A: ρ_A = 1,25 Ωmm²/m

Material B: ρ_B = 1,05 Ωmm²/m

   D_B/D_A = 0,94;   d. h. Verringerung des Durchmessers um 6 Masse %
   L_B/L_A = 1,06;   d. h. Erhöhung der Länge um 6 Masse %
   M_B/M_A = 0,94;   d. h. Verringerung des Gewichts um 6 Masse %
wobei für diese beispielhafte Vorüberlegung für die Dichten noch γ_A ≅ γ_B angenommen wird. Die Gültigkeit dieser Annahme ist im konkreten Fall zu prüfen. When using the alloy according to the invention as a wire z. B. for a heating element with a after D B / D A = 3 ρ B / ρ A changed diameter D _B and one after L B / L A = 3 ρ A / ρ B changed lengths L _B , in the wire with the electrical resistivity ρ _B , which has the same functionality as compared to that of an alloy A with the electrical resistivity ρ _A , the diameter D _A and the length L _A , however if ρ _{B is} smaller than ρ _A and approximately γ _A ≅ γ _B , one um M B / M A = 3 ρ B / ρ A · γ B / γ A requires less material amount of an alloy B.

Example: Material A: ρ _A = 1.25 Ωmm ² / m

Material B: ρ _B = 1.05 Ωmm ² / m

D _B / D _A = 0.94; ie reduction of the diameter by 6 mass%
L _B / L _A = 1.06; ie increasing the length by 6%
M _B / M _A = 0.94; ie reduction of weight by 6%
whereby γ _A ≅ γ _{B is} assumed for this exemplary consideration for the densities. The validity of this assumption must be checked in the specific case.

This path has not yet been followed, because with the reduction of the Diameter associated with a reduction in the life.

In the following, the life reduction by reducing the Wire diameter estimated:

γ = Dichte der Legierung

C₀ = Aluminiumkonzentration der Legierung vor Beginn der Oxidation bzw. des Einsatzes einer Heizwendel

C_K = kritische Aluminiumkonzentration bei der die "Break away" Oxidation, das heißt die Bildung anderer Oxide als der Aluminiumoxide, startet. Dies zeigt das Ende der Funktionsfähigkeit eines Heizleiters an und führt zum schnellen Durchschmelzen des Heizleiters und ist somit als Lebensdauerende anzusehen ist.

k = Oxidationskonstante

n = Oxidationsratenexponent, mit einer Größe von circa 0,5

According to I. Gurrappa, S. Weinbruch, D. Naumenko, WJ Quadakkers, Materials and Corrosion 51 (2000), pages 224 to 235, the service life t of a wire can be calculated

γ = density of the alloy

C ₀ = aluminum concentration of the alloy before the beginning of the oxidation or the use of a heating coil

C _K = critical aluminum concentration at which "break away" oxidation, that is the formation of oxides other than the aluminas, starts. This indicates the end of the functioning of a heating element and leads to rapid melting of the heating element and is thus to be regarded as end of life.

k = oxidation constant

n = oxidation rate exponent, with a size of approximately 0.5

The oxidation constant k is a measure of the quality of the oxide layer. At a Oxide layer with very good protective effect, k is smaller than a worse one Oxide layer. The smaller k is, the longer the life.

mit   t₁ = Lebensdauer beim größerem Drahtdurchmesser D₁.

und   t₂ = Lebensdauer beim kleineren Drahtdurchmesser D₂.

If one reduces the wire diameter by a factor of 0.94 in an alloy, as in the above consideration, the lifetime is reduced, since the oxidation constant k, the density γ, C ₀ and C _K remain unchanged, as follows:

with t ₁ = service life with larger wire diameter D ₁ .

and t ₂ = life at the smaller wire diameter D ₂ .

That is, an alloy with the same functionality would have a minimum of 12% have longer life, to the disadvantage of smaller wire diameter to compensate. Additional lifetimes offer even more the advantage of a longer life, that is an improved functionality.

Surprisingly, it was found that alloys with (in% by mass)> 2.5 to 3.0% Aluminum and> 10 to 20% chromium, and additions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.08% yttrium, and / or 0.01 to 0.08% Hf and / or 0.01 to 0.08% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon, balance iron and the usual process-related impurities a much better Have lifespan than the previously used alloy with approximately 14.5% Cr, about 4.5% Al, and additions of max. 0.3% zirconium, max. 0.08% carbon, Max. 0.6% manganese, max. 0.5% silicon, balance iron and others melting impurities.

The subject invention is in addition to heating conductors for heating elements, eg. B. one Household appliance, or as a construction material in the furnace construction as a film, For example, used as a carrier film for catalysts.

The advantages of the invention are explained in more detail in the following examples:

EXAMPLES Table 1 lists various iron-chromium-aluminum alloys, the table containing both large-scale and laboratory molten batches.

For heating elements (heating conductors) in the form of wire are accelerated Lifetime tests to compare materials with each other, for example, with following conditions possible:

The test is carried out on wires with a diameter of 0.40 mm, from which Wire spirals with 12 turns, a spiral diameter of 4 mm and a Spiral length of 50 mm can be made. The wire spirals are between 2 Power supply clamped and by applying a voltage up to 1200 ° C. heated. The heating takes place for 2 minutes, then the power supply for 15 Seconds interrupted. At the end of the life of the wire fails, that the remaining cross section melts through. As a lifetime, the Total time the wire was heated, without the break times indicated in the following burning time.

The large-scale batch T1 and the laboratory batches T2 and T3 represent the state technology for Cr Al 14 4, with (in% by mass) approx. 14.5% chromium, 4.5% Aluminum, about 0.3% manganese, about 0.2% silicon and as a reactive element 0.17 to 0.18% zirconium. They have 49-hour lifetimes for the lab batch T3, 63 hours for the laboratory batch T2 and 77 hours for the large-scale Batch T1. Batches H1 to H6 are batches with an aluminum content of over 5 mass% and different additions of silicon, manganese, zirconium, Titanium, hafnium and yttrium and other admixtures such as calcium, Magnesium, carbon and nitrogen. They show, as one would expect, all one significantly increased lifetime compared to the batches T1 to T3 Reason of the increased aluminum content. Differences in the lifetime at H1 to H6 are in particular the different contents of aluminum, Silicon, zirconium, titanium, hafnium and yttrium due.

The laboratory batch K1 is compared to the laboratory batch according to the state of Technique T2 the aluminum content has been lowered from 4.5 to 3.55 mass%. The Lifespan decreased, as expected, from 63 hours to 34 hours.

This is different in the case of the batches according to the invention labeled "E", M1, M2 and M4. You have compared to the laboratory batches T3 and T2 after the prior art increased by a factor of 1.5 to 2 life, although they have significantly reduced aluminum contents of 2.5 to 3.0% by mass contain. Their common characteristic is that they, in addition to zirconium yet Yttrium and / or hafnium included. In this case, batch L2 reaches with one Aluminum content of (in% by mass) 2.55% and a zirconium content of 0.05% and a hafnium content of 0.04% and an yttrium content of 0.02% Life of 109 hours. The batch M1 achieved with an aluminum content of 2.78% and a Zirconium content of 0.05% and a hafnium content of 0.03% and a Yttrium content of 0.02% a life of 92 hours. The batch M2 achieved with an aluminum content of 2.71% and a zirconium content of 0.05% and a hafnium content of 0.03% and an yttrium content of 0.04% Life of 126 hours. The batch M4 reaches with an aluminum content of 2.8% and a zirconium content of 0.03% and a hafnium content of 0.03 % and an yttrium content of 0.03%, a life of 85 hours.

These examples show that with very small additions of zirconium, hafnium and Yttrium to the iron - chromium - aluminum alloy even at low Aluminum contents of 2.5% have very high lifetimes, those of iron - Chromium - aluminum alloys with over 5% aluminum correspond can be.

In summary, it can be said that the alloy according to the invention Additions of 0.01 to 0.08% yttrium, and / or 0.01 to 0.08% Hf and / or 0.01 to 0.08% Zr must contain.

Charge L1 shows that even with the addition of zirconium, hafnium and yttrium at a Aluminum content of 1.55% only reached a life of 9.3 hours becomes. Even Charge M3, despite the addition of zirconium, hafnium and yttrium at one Aluminum content of only 2.24% only a life of 72 hours, the in the range of batches according to the prior art. The alloy according to the invention should therefore have an aluminum content of more than 2% to have.

Chromium contents between 14 and 17% have no significant effect on the lifetime as compared to the zirconium, hafnium and yttrium containing batches M1 with 14.85% chromium and 2.78% aluminum and batch L2 with 16.86% chromium and 2.55 % Aluminum shows. However, a certain chromium content is necessary because chromium promotes the formation of the particularly stable and protective α - Al ₂ O ₃ layer. After HM Herbelin, M coat, Colloque C7, Supplement au Journal de Physique III, Vol 5, Novembre 1995, pages C7-365 to 374 this is still done with a chromium content of 13%, a chromium content of 6% is no longer sufficient ,

According to J. Klöwer, Materials and Corrosion 51 (2000), pages 373-385 Additions of silicon of about 0.3 mass% and more through the life an improvement in the adhesion of the topcoat. It is therefore a content of at least 0.1 mass% silicon required.

In Table 1, the impact work is at room temperature, 50 ° C, 100 ° C and 150 ° C on DMV standards (See W. Domke, Werkstoffkunde and Material Testing, Verlag W. Gerardet, Essen, 1981, from page 336). The Impact energy is low at a ferritic steel Temperatures occurring brittle fracture low (low position), in the case of higher Temperatures ductile, well deformable behavior high (high) with a steep rise within a few degrees from the low altitude to the high altitude. there can strongly spread the impact work in this area. The temperature, at the transition from high to low is made Notch impact transition temperature. For example, a material is all the more brittle, depending the grain size is larger or in the case of the iron-chromium-aluminum materials, the higher the content of alloying elements such as aluminum, chromium, silicon, Nitrogen, carbon, phosphorus and sulfur is. Because of your Production path as a laboratory batch, all notched specimens in Table 1 have a very large grain size of about 200 to 400 microns, which is very unfavorable. Therefore all samples are at room temperature in the low position, with the samples with the lowest aluminum content, the lowest chromium content and the lowest carbon content have the highest impact energy, as is the Batches M1, M2, M3, M4 and L1 show. The batch M4 has a bit worse lower impact work than the batch M2 with a similar one Aluminum and chromium content, as it has a higher carbon content. The Charge L2 has a slightly lower impact performance than the Charge M2, as it does has a higher chromium content. Similar to carbon, nitrogen, Phosphorus and sulfur, whose contents therefore advantageously kept low should be. It turns out that the aluminum content does not exceed 3.0% may be used to minimize the embrittling effect of aluminum hold.

The same picture is shown at those measured at 50 ° C and 100 ° C Kurbschlagarbeiten, only that the improvement of the impact tests in the low aluminum content is even more pronounced and also reducing the impact strength due to an increased C content in M4 compared to M1 and M2 is even better to recognize. It can also be seen here that batch M1, which differs from the batch M2 by a higher silicon content, one has slightly lower impact energy. At 150 ° C are all Impact work in the ductile elevated area, batches M2, M3 and M4 with an aluminum content of 2.2 to 2.8%, the highest impact tests exhibit.

In summary, it can be said that the brittle behavior of the iron - chromium - Aluminum alloys is significantly reduced by lowering the Aluminum content to less than 3.0%. This is additionally supported by low levels of silicon, carbon, nitrogen, phosphorus and sulfur. Of the Carbon content is therefore limited to max. 0.08%, the nitrogen content to max. 0.04 %, the phosphorus content to max. 0.04% and the sulfur content to max. 0.01 Mass% limited. Phosphorus and sulfur are additionally unfavorable on the life, so that the lowest possible content of these elements are also advantageous from this perspective.

Because of the embrittling effect, the chromium content should be as low as be provided possible. Because of the life requirements can the silicon and chromium levels are not lowered to near zero, but must be at least 0.1% silicon and 10% chromium. It should but not more than 20% chromium and 1% silicon are added to one to achieve the lowest possible brittleness.

When replacing an alloy Cr Al 14 4, as represented in Table 1 for example by the batches T1, T2 and T3, by an alloy according to the invention, for example by batches M2 or M4, the specific electrical resistance of 1, 21 Ωmm ² / m (Alloy A) to 1.04 Ωmm ² / m. (Alloy B). Same functionality is ensured according to the foregoing, if surface power, power and resistance of the heating coil are kept constant.

This results for the diameter ratio D B / D A = 3 ρ B / ρ A = 0.95 and for the aspect ratio L B / L A = 3 ρ A / ρ B = 1.05 the weight ratio M B / M A = 3 ρ B / ρ A • γ B / γ A = 0.95 with approximate γ A ≅ γ B

The density of alloy A is γ _A = 7.12 g / cm ² , the density of alloy B is γ _B = 7.30 g / cm ² . Taking into account the change in density, the weight ratio is only marginally greater M B / M A = 3 ρ B / ρ A • γ B / γ A = 0.97

That is, the approximate estimation with γ _A ≅ γ _B was allowed in this case.

The life estimate according to I. Gurrappa, S. Weinbruch, D. Naumenko, WJ Quadakkers, Materials and Corrosion 51 (2000), pages 224 to 235 by reducing the wire diameter in the inventive alloy B gives:

That is, the alloy of the invention must be at least 10% larger Lifespan to have the disadvantage of smaller wire diameter too compensate. However, since the batches of the invention all at least one 50% longer life, brings the use of the alloy according to the invention additionally has the advantage of increased Lifespan.

Manganese is limited to 0.5% by weight, as this element reduces the oxidation resistance. The same applies to copper.

Claims (11)

1. Iron-chromium-aluminium alloy having a high service life, comprising (in % by mass):

   2.5 to 3.0% Al

   > 10 to < 20% Cr

   as well as addition of

   0.1 to 1% Si

   max. 0.5% Mn

   Y and Hf and Zr, each within the limits of 0.01 to 0.08% or

   0.01 to 0.03% Y and 0.01 to 0.03% Hf or

   0.01 to 0.03% Y and 0.01 to 0.08% Zr

   max. 0.01% Mg

   max. 0.01 % Ca

   max. 0.08% C

   max. 0.04% N

   max. 0.04% P

   max. 0.01% S

   max. 0.05% Cu and

   max. 0.1 % Mo and/or W, respectively

   rest Fe

   as well as impurities resulting from the manufacturing.
2. Iron-chromium-aluminium alloy according to claim 1 comprising (in % by mass):

   2.5 to 3.0% Al

   13 to 17% Cr

   as well as addition of

   0.1 to 0.5% Si

   max. 0.5% Mn

   Y and Hf and Zr, each within the limits of 0.01 to 0.08% or

   0.01 to 0.08% Y and 0.01 to 0.08% Hf or

   0.01 to 0.08% Y and 0.01 to 0.08% Zr

   max. 0.01% Mg

   max. 0.01% Ca

   max. 0.08% C

   max. 0.04% N

   max. 0.04% P

   max. 0.01% S

   max. 0.05% Cu and

   max. 0.1 % Mo and/or W, respectively

   rest Fe

   as well as impurities resulting from the manufacturing.
3. Iron-chromium-aluminium alloy according to claim 1 or 2 comprising (in % by mass):

   2.5 to 3.0% Al

   14 to 17% Cr

   as well as addition of

   0.1 to 0.5% Si

   max. 0.5% Mn

   Y and Hf and Zr, each within the limits of 0.01 to 0.08% or

   0.01 o 0.08% Y and 0.01 to 0.08% Hf or

   0.01 to 0.08% Y and 0.01 to 0.08% Zr

   max. 0.01% Mg

   max. 0.01% Ca

   max. 0.08% C

   max. 0.04% N

   max. 0.04% P

   max. 0.01% S

   max. 0.05% Cu and

   max. 0.1 % Mo and/or W, respectively

   rest Fe

   as well as impurities resulting from the manufacturing.
4. Iron-chromium-aluminium alloy according to one of the claims 1 through 3, in which one or more of the elements yttrium, hafnium or zirconium are completely or partially replaced with (in % by mass) 0.01 to 0.1% of one or more of the elements scandium and/or titanium and/or vanadium and/or niobium and/or tantalum and/or cerium.
5. Iron-chromium-aluminium alloy according to one of the claims 1 through 4, characterized in that the carbon content is limited to 0.02%, the nitrogen content to 0.01%, the phosphorous content to 0.01% and the sulphur content to 0.005%.
6. Iron-chromium-aluminium alloy according to one of the claims 1 through 5,
   wherein when the alloy is used as wire and when the surface capacity, the capacity as well as the resistance are kept constant and when a material A is replaced with a material B, the following boundary conditions with respect to diameter, length and weight changes are given: diameter   DB /DA = 3 ρ B /ρ A length   LB /LA = 3ρ A /ρ B weight   MB /MA = 3ρ B /ρA •γ B /γ A wherein

   D is the diameter

   ρ is the specific electric resistance

   L is the length

   M is the weight

   γ is the density

   of the respective wire, which in case of ρ_B is smaller than ρ_A and approximately γ _A ≅ γ _B leads to a smaller amount requirement of alloy B, wherein alloy B stands out for a clearly longer service life than alloy A and thus the service life reducing reduction of the diameter is overcompensated.
7. Use of an iron-chromium-aluminium alloy according to one of the claims 1 through 6 as heat conductor in a heating element.
8. Use of an iron-chromium-aluminium alloy according to one of the claims 1 through 6 as alloy, especially in the form of a heating element for the use in household appliances.
9. Use of an iron-chromium-aluminium alloy according to one of the claims 1 through 6 as alloy, especially in the form of a heating element or a construction material for the use in the construction of furnaces.
10. Use of an iron-chromium-aluminium alloy according to one of the claims 1 through 6 as alloy, especially in the form of a foil for the use as carrier foil of catalysts.
11. Use of an iron-chromium-aluminium alloy according to one of the claims 1 through 6 as alloy, especially in the form of wire or band for the use as braking and starting resistance.