Iron-chrome aluminium-alloy

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% chromium, and other added materials, namely, 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 tungsten and the usual manufacture-related impurities, the remainder being iron.

Description

[0001] Such alloys are used, inter alia, for the manufacture of electric heating elements and catalyst carriers. These materials form an impenetrable, adhesive aluminium oxide layer, which protects them against 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 the layer growth, as it is described in the “Handbuch der Hochtemperatur-Werkstofflechnik”, Ralf Burgel, Vieweg Verlag, Braunschweig 1998, form page 274 on.

[0002] The aluminium oxide layer protects the metallic material against quick oxidation. Simultaneously, this layer grows but very slowly. During this growth, the aluminium content of the material is consumed. If there is no more aluminium, other oxides will grow (chromium and iron oxides). The metal content of the material is consumed very quickly and then the material fails. The period until failing is called service life. Thus, an increase of the aluminium content increases the service life.

[0003] DE-A 19928842 describes an alloy comprising (in % by 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, the rest being iron as well as manufacture related impurities for the use as carrier foil for exhaust gas catalysts, as heat conductors, as components in the construction of industrial furnaces and in gas burners.

[0004] EP-B 0387670 describes an alloy comprising (in % by 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 approximately the same proportions of 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% sulphur, the rest being reacted iron, the sum of the Ti and Zr contents in % being 1.75 to 3.5 times higher than the C and N contents in % by mass, as well as manufacture related impurities. Ti and Zr can be completely or partially replaced by hafnium and/or tantalum or vanadium.

[0005] EP-B 0290719 describes an alloy comprising (in % by mass) 12 to 30% Cr, 3.5 to 8% Al, 0.008 to 0.10% carbon, max. 0.8% silicium, 0.10 to 0.1% manganese, max. 0.035% phosphorus, max. 0.020% sulphur, 0.1 to 1.0% molybdenum, max. 1% nickel, and the additions of 0.010 to 1.0% zirconium, 0.003 to 0.3% titanium and 0.003 to 0.3% nitrogen, 0.005 to 0.05% calcium plus magnesium, as well as 0.003 to 0.80% rare earths, 0.5% niobium, the rest being iron with usual companion elements, which is for example used as wire of heating elements for electrically heated furnaces and as material for thermally stressed parts and as foil for the manufacture of catalyst carriers.

[0006] U.S. Pat. No. 4,277,374 describes an alloy comprising (in % by mass) up to 26% chromium, 1 to 8% aluminium, 0.02 to 2% hafnium, up to 0.3% yttrium, up to 0.1% carbon, up to 2% silicium, the rest being iron, with a preferred range of 12 to 22% chromium and 3 to 6% aluminium, which is used as foil for the manufacture of catalyst carriers.

[0007] The above documents are based upon traditional manufacturing methods, such as the conventional casting of the alloy and the subsequent hot and cold forming. Since these methods have high failure quota, inter alia due to embrittlements during hot rolling, alternatives have been developed in the last years, in which a chromium steel, which contains reactive elements, is coated with aluminium or aluminium alloys. Such composite materials are then rolled to their final thickness and subsequently homogenized, wherein the setting of suitable annealing parameters leads to a homogenous material.

[0008] Such methods are for example described in the documents EP-B 0640390, EP-B 0204423 and WO 99/18251, and they are extremely suitable to reduce the problems of processing for applications, where a high aluminium content is technically required and the material is used in form of foil or band.

[0009] Another possibility to reduce the failures and costs caused by the embrittlements has been found in the use of iron-chromium-aluminium alloys for household appliances, such as e.g. toaster, hair dryer and the like, which are normally used at lower temperatures beneath 800° C. and manufactured under strict economic conditions. Since the material is usually used in form of wire here, the described solutions by coating are not possible. Because of the low temperature stresses, alloys comprising (in % by mass) a reduced aluminium content of beneath 5% are used here, such as for example an alloy comprising approximately 14.5% Cr, approx. 4.5% Al, additions of reactive elements, the rest being iron, as it is produced and described in the DIN norm 17470 in table 3 with 14% chromium and 4% aluminium, the rest being iron (Cr Al 14 4), as it is known from “Drähte von Krupp VDM für die Elektroindustrie”, publication N563, edition November 1998 on page 24, material Aluchrom W comprising 14 to 16% chromium, 3.5 to 5.0% aluminium, max. 0.08% carbon, max. 0.6% manganese, max. 0.5% silicium, max. 0.3% zirconium, other manufacture related impurities, the rest being iron. In the following, this alloy serves as comparative alloy and is briefly called Cr Al 14 4.

[0010] Due to the aluminium content, which has been reduced to approximately 4 to 4.5% by mass, the iron-chromium-aluminium alloy Cr Al 14 4 can be manufactured more easily than the above described alloys comprising more than 5% by mass aluminium. But it still shows embrittlements, which lead to a higher production effort during hot forming.

[0011] It has been the state of the art, that Fe Cr Al alloys comprising approximately 14 to 15% by mass chromium require a minimum content of approximately 4% by mass Al in order to build up a protective aluminium oxide layer, as it is shown for example in “Handbuch der Hochtemperatur-Werkstofflechnik”, Ralf Burgel, Vieweg Verlag, Braunschweig 1998, on page 272 in image 5.13.

[0012] GB-A 476,115 discloses an iron alloy, which can in particular be used as electric resistance and comprises the following elements: 6.1-30% Cr, 3-12% Al, 0.07-0.2% C, <4% Ti, the rest being Fe as well as manufacture related impurities. Herein, the Ti content is related to the C content, such that it shall not be less than 3 times the C content. Preferred ranges of Cr are >8%, of Al>5%, of C>0.085%.

[0013] DE-A 196 52 399 describes a method for manufacturing a multi-layer metal compound foil as well as the use thereof. The metal compound foil includes a carrier layer made of ferritic steel band, which is provided on both sides with an external layer of aluminium or aluminium alloy. The carrier layer is formed by an alloy comprising (in % by mass) 16-25% Cr, rare earths, Y or Zr contents comprised between 0.01 and 0.1%, the rest being Fe. Furthermore, Al contents comprised between 2 and 6% can be added by alloying. Preferred Cr contents are above 20%.

[0014] Finally, EP-A 0 402 640 discloses a rust-free steel foil as carrier element for catalysts as well as the manufacture thereof. The foil is formed by an alloy having 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, the rest being Fe as well as manufacture related impurities. Preferred contents of Al are comprised between 5,5 and 20%. Furthermore, amounts of up to 0.3% of Y, Sc or rare earths can be added by alloying, wherein contents of up to 2% of at least one of the elements Ti, Nb, Zr, Hf, V, Ta, Mo, W can also be provided. Herein, contents of <4% Al require Cr contents of >25%.

[0015] It is the object of the invention to provide a low cost iron chromium aluminium alloy, which has a similar or better service life than Cr Al 14 4, but has a still lower brittleness and thus improved formability, and simultaneously has the same technical functionality as Cr Al 14 4.

[0016] This aim is achieved by an iron chromium aluminium alloy having a long service life comprising (in % by mass)>2 to 3.6% by mass aluminium and >10 to 20% chromium as well as additions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium and/or 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. 0.01% sulphur, max. 0.05% copper and respectively max. 0.1% molybdenum and/or tungsten as well as manufacture related impurities, the rest being iron.

[0017] Advantageous embodiments of the alloy according to the invention are disclosed in the sub-claims.

[0018] Preferably, the Al content can be set within the limits of 2.5-3.55% and the Cr content within the limits of 13-17%.

[0019] A reduction of the brittleness can be achieved the most efficiently by reducing the aluminium content. But this has the drawback that the specific electric resistance also decreases and the service life becomes shorter.

[0020] The brittleness is also increased by chromium, silicium, carbon and nitrogen, so that these elements should also be kept as low as possible.

[0021] The same technical functionality is achieved for a heat conductor, which serves for the electrical production of heat, when the surface performance, the performance at the heating element, the total resistance of the heating element and the service life of the heating element remain constant in spite of any modification of the material.

[0022] If the specific electric resistance is reduced while keeping the surface performance, the performance and the resistance constant, the diameter of the wire has to be reduced and the wire length has to be increased by the same percentage by which the diameter has been reduced, in order to be able to meet the above requirements. Therewith, the volume is reduced by this percentage. This means, material is saved when the specific electric resistance is reduced. This is also disclosed in H. Pfeifer, H. Thomas “Zuzunderfeste Legierungen”, Springer Verlag, Berlin 1963, on page 387.

[0023] The following calculation illustrates this fact:

[0024] The diameter, length and weight modification caused by the replacement of material A with B is calculated for wires, wherein the surface performance, performance and resistance are kept constant.

[0025] The following formulas are fulfilled under the above conditions:

Diameter DB/DA={cube root}{square root over (&rgr;B/&rgr;A)}

Length LB/LA={cube root}{square root over (&rgr;A/&rgr;B)}

Weight MB/MA={cube root}{square root over (&rgr;B/&rgr;A·&ggr;B/&ggr;A)}

[0026] When the alloy according to the invention is used as wire, for example for a heating element, with a diameter DB, which has been changed according to

DB/DA={cube root}{square root over (&rgr;B/&rgr;A)}

[0027] and a length LB, which has been changed according to

LB/LA={cube root}{square root over (&rgr;A/&rgr;B)}

[0028] a material amount of an alloy B, which is smaller by

MB/MA={cube root}{square root over (&rgr;B/&rgr;A)}·&ggr;B/&ggr;A

[0029] is required for the wire having the specific electric resistance &rgr;B, which has the same functionality in comparison to the wire made of an alloy A and having the specific electric resistance &rgr;A the diameter DA and the length LA, if &rgr;B is smaller than &rgr;B and approximately &ggr;A≈&ggr;B.

[0030] Example: material A: &rgr;A=1.25 &OHgr;mm2/m

[0031] material B: &rgr;B=1.05 &OHgr;mm2/m

[0032] DB/DA=0.94; i.e. reduction of the diameter by 6% by mass

[0033] LB/LA=1.06; i.e. increase of the length by 6% by mass

[0034] MB/MA=0.94; i.e. reduction of the weight by 6% by mass %

[0035] wherein the densities are assumed to be &ggr;A≅&ggr;B in this exemplary theory. In a concrete case, the validity of this assumption has to be verified.

[0036] But this idea has not been realised so far, since the reduction of the diameter leads to a reduction of the service life.

[0037] In the following the service life reduction caused by the reduction of the wire diameter is estimated:

[0038] According to I. Gurrappa, S. Weinbruch, D. Naumenko, W. J. Quadakkers, Materials and Corrosions 51 (2000), pages 224 through 235, the service life t of a wire can be calculated with: 1 t = [ 4.4 × 10 - 3 × ( C 0 - C K ) × γ · f k ] 1 / n ⁢   ⁢ with ⁢   ⁢ f = D 2

[0039] for wire having the diameter D

[0040] &ggr;=density of the alloy

[0041] C0=aluminium concentration of the alloy before start of the oxidation or use of a heating spiral

[0042] CK=critical aluminium concentration, at which the break away oxidation, i.e. the formation of other oxides than the aluminium oxides, starts. This indicates the end of the operativeness of a heat conductor and leads to the rapid fusion of the heat conductor and can thus be regarded as the end of service life.

[0043] k=oxidation constant

[0044] n=oxidation rate exponent having a value of approximately 0.5

[0045] The oxidation constant k is a measuring tool for the quality of the oxide layer. For an oxide layer, which provides a very good protection, k is smaller than for an oxide layer of lower quality. The smaller k is the longer is the service life.

[0046] If, according to the above theory, for one alloy the wire diameter is reduced by the factor 0.94, the service life is reduced as follows, since the oxidation constant k, the density y, C0 and CK remain the same: 2 t 2 t 1 = [ D 2 D 1 ] 1 / n = [ 0 , 95 ] 2 = 0 , 88

[0047] with t1=service life with the greater wire diameter D1

[0048] and t2=service life with the smaller wire diameter D2.

[0049] This means that an alloy with the same functionality would have to have a 12% higher service life, in order to compensate the drawback of the smaller wire diameter. Even higher service lives offer the additional advantage of a longer service life, i.e. an improved functionality.

[0050] Surprisingly it has been found that alloys comprising (in % by mass)>2 to 3.6% aluminium and >10 to 20% chromium, and additions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium, and/or 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, rest iron and the usual manufacture related impurities have a much better service life than the alloy, which has been used so far and which comprises approximately 14.5% Cr, approximately 4.5% Al and additions of max. 0.3% zirconium, max. 0.08% carbon, max. 0.6% manganese, max. 0.5% silicium, rest iron and other manufacture related impurities.

[0051] The subject of the invention can be used, besides for heat conductors for heating elements, e.g. a household appliance, or as material in the construction of furnaces, also as foil, for example as carrier foil for catalysts.

[0052] The advantages of the invention will be explained in detail in the following examples:

EXAMPLES

[0053] In table 1 the different iron chromium aluminium alloys are listed, wherein the table contains both big scale batches and batches produced in the laboratory.

[0054] For heating elements (heat conductors) in form of wire, accelerated service life tests are possible for the comparison of materials with each other, for example under the following conditions:

[0055] The test is carried out with wires having a diameter of 0.40 mm, from which wire spirals having 12 turns, a spiral diameter of 4 mm and a spiral length of 50 mm are manufactured. The wire spirals are clamped between 2 current supplies and heated up to 1200° C. by applying a voltage. They are heated for respectively 2 minutes, then the current supply is interrupted for 15 seconds. At the end of the service life, the wire fails in that the remaining cross section melts. The total period of time, within which the wire was heated, without the interruptions, is indicated as service life and called burning time in the following.

[0056] The big scale batch T1 and the lab scale batches T2 and T3 represent the state of the art for Cr Al 14 4, comprising (in % by mass) approximately 14.5% chromium, 4.5% aluminium, approx. 0.3% manganese, approx. 0.2% silicium, and 0.17% to 0.18% zirconium as reactive element. The lab scale batch T3 has a service life of 49 hours, the lab scale batch T2 has a service life of 63 hours and the big scale batch T1 has a service life of 77 hours. The batches H1 through H6 are batches with an aluminium content of more than 5% by mass and different additions of silicium, manganese, zirconium, titanium, hafnium and yttrium and other additions, such as for example calcium, magnesium, carbon and nitrogen. As it was to expect, they all show a clearly longer service life in comparison to the batches T1 through T3 because of the higher aluminium content. Differences of the service life of H1 through H6 are in particular caused by the different contents of aluminium, silicium, zirconium, titanium, hafnium and yttrium.

[0057] For the lab scale batch K1, the aluminium content has been reduced from 4.5 to 3.55% by mass in comparison to the lab scale batch T2 according to the state of the art. The service life was thus reduced, as expected, from 63 hours to 34 hours.

[0058] This is not the case for the batches L2, L3, M1, M2 and M4 according to the invention and marked with “E”. In comparison to the lab scale batches T3 and T2 according to the state of the art, they have a service life, which is increased by the factor 1.5 to 2, although they comprise clearly lower aluminium contents of 2.5 to 3.6% by mass. Their common characteristic is that they contain, besides zirconium, also yttrium and/or hafnium. Therein, batch L2 comprising an aluminium content (in % by mass) of 2.55% and a zirconium content of 0.05% and a hafnium content of 0.04% and an yttrium content of 0.02% reaches a service life of 109 hours. Batch L3 comprising an aluminium content of 3.55% and a zirconium content of 0.053% and a hafnium content of 0.042% and an yttrium content of 0.02 reaches a service life of 90 hours. Batch M1 comprising an aluminium content of 2.78% and a zirconium content of 0.05% and a hafnium content of 0.03% and an yttrium content of 0.02% reaches a service life of 92 hours. Batch M2 comprising an aluminium 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% reaches a service life of 126 hours. Batch M4 comprising an aluminium 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% reaches a service life of 85 hours.

[0059] These examples show that, in spite of low aluminium contents, very small additions of zirconium, hafnium and yttrium to the iron chromium aluminium alloy make it possible to obtain very high service lives, which correspond to those of iron chromium aluminium alloys comprising more than 5% aluminium.

[0060] Summing up, it may be said that the alloy according to the invention must contain additions of 0.01 to 0.2% yttrium and/or 0.01 to 0.2% Hf and/or 0.01 to 0.3% Zr.

[0061] Batch L1 shows that in spite of an addition of zirconium, hafnium and yttrium, only a service life of 9.3 hours will be obtained with an aluminium content of 1.55%. Batch M3 comprising an aluminium content of only 2.24% also has a service life of only 72 hours in spite of an addition of zirconium, hafnium and yttrium, which service life corresponds to those of the batches according to the state of the art. The alloy according to the invention should thus have an aluminium content of more than 2%.

[0062] Chromium contents comprised between 14 and 17% have no decisive influence on the service life, as it is shown by the comparison of the zirconium, hafnium and yttrium bearing batches Ml comprising 14.85% chromium and 2.78% aluminium and batch L2 comprising 16.86% chromium and 2.55% aluminium. However, a certain chromium content is necessary, since chromium stimulates the formation of the highly stable and protective &agr;-Al2O3 layer. According to H. M. Herbelin, M. Mantel, Colloque C7, Supplement au Journal de Physique III, Vol. 5, November 1995, pages C7-365 through 374, this is still the case for a chromium content of 13%, but a chromium content of 6% is no more sufficient.

[0063] According to J. Klower, Materials and Corrosion 51 (2000), pages 373 through 385, additions of approx. 0.3% by mass silicium and more increase the service life by improving the adhesiveness of the cover layer. Therefore, a content of at least 0.1% silicium is required.

[0064] In table 1 the notched bar impact work at room temperature, 50° C., 100° C. and 150° C. is listed for DMV norm samples (cf. W. Domke, Werkstoffkunde und Werkstoffprüfung, Verlag W. Geradet, Essen 1981, from page 336 on). The notched bar impact work of a ferritic steel is low, when a brittle fracture occurs at low temperatures (low position) and is high for the ductile, easily formable behaviour at higher temperatures (high position) with a steep increase within a few degrees from the low position to the high position. Therein, the notched bar impact work can highly scatter in this range. The temperature, at which the transition from the high position into the low position takes place, is called notch transition temperature. A material is for example the more brittle, the greater the grain size is, or for the iron chromium aluminium materials, the higher the content of alloying elements, such as aluminium, chromium, silicium, nitrogen, carbon, phosphorus and sulphur, is. Due to their preparation as lab scale batch, all notched bar impact samples in table 1 have a very big grain size of about 200 to 400 &mgr;m, which is very unfavourable. Therefore, all samples are in the low position at room temperature, wherein the samples comprising the lowest aluminium content, the lowest chromium content and the lowest carbon content, have the highest notched bar impact work, as the batches M1, M2, M3, M4 and L1 show. Batch M4 has a slightly worse and lower notched bar impact work than batch M2 having a similar aluminium and chromium content, since the first one has a higher carbon content. Batch L2 has a slightly lower notched bar impact work than batch M2, since it has a higher chromium content. Nitrogen, phosphorus and sulphur have a similar effect as carbon, so that their contents should advantageously be kept low. It has been found that the aluminium content may not exceed 3.6% in order to keep the embrittling effect of the aluminium as small as possible.

[0065] The same situation exists for the notched bar impact works measured at 50° C. and 100° C., only that the improvement of the notched bar impact works is still more clear for the low aluminium contents and the reduction of the notched bar impact work due to an increased carbon content of M4 in comparison to M1 and M2 can be seen still more clearly. One can also see here, that batch M1, which differs from batch M2 by a higher silicium content, has a slightly lower notched bar impact work. At 150° C. all notched bar impact works are in the ductile high position, wherein the batches M2, M3 and M4 having an aluminium content of 2.2 to 2.8% present the highest notched bar impact works.

[0066] Summing up, it may be said that the brittle behaviour of the iron chromium aluminium alloys is clearly reduced by decreasing the aluminium content to beneath 3.6%. This is additionally supported by low contents of silicium, carbon, nitrogen, phosphorus and sulphur. 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 sulphur content to max. 0.01% by mass. Phosphorus and sulphur additionally have a negative effect on the service life, so that also from this point of view, low contents of these elements are advantageous.

[0067] For the reason of the embrittling effect, the chromium content should also be provided as low as possible. Because of the requirements concerning the service life, the silicium and chromium contents cannot be reduced to almost zero, but have to be at least 0.1% silicium and 10% chromium. But no more than 20% chromium and 1% silicium should be added, in order to achieve a brittleness, which is as low as possible.

[0068] If an alloy Cr Al 14 4, as it is represented in table 1 for example by the batches T1, T2 and T3, is replaced with an alloy according to the invention, such as for example with the batches M2 or M4, the specific electric resistance is reduced from 1.21 &OHgr;mm2/m (alloy A) to 1.04 &OHgr;mm2/m (alloy B). According to the above statements, the same functionality will be assured, if surface performance, performance and resistance of the heating spiral are kept constant.

[0069] Therein, the following results for

the diameter relation: DB/DA={cube root}{square root over (&rgr;B/&rgr;A)}=0.95

and for the length relation: LB/LA={cube root}{square root over (&rgr;A/&rgr;B)}=1.05

the weight relation MB/MA={cube root}{square root over (&rgr;B/&rgr;A)}·&ggr;B/&ggr;A=0.95 with

approximately &ggr;A≅&ggr;B

[0070] The density of alloy A is &ggr;A=7.12 g/cm2, the density of alloy B is &ggr;B=7.30 g/cm2. Considering the modification of the density, the weight relation results only slightly higher in:

MB/MA={cube root}{square root over (&rgr;B/&rgr;A)}·&ggr;B&ggr;A=0.95

[0071] This means that the approximate estimation of &ggr;A=&ggr;B was admissible in this case.

[0072] The service life estimation according to 1. Gurrappa, S. Weinbruch, D. Naumenko, W. J. Quadakkers, Materials and Corrosions 51 (2000), pages 224 through 235 by reduction of the wire diameter of the alloy B according to the invention results in: 3 t 2 t 1 = [ D 2 D 1 ] 1 / n = [ 0 , 95 ] 2 = 0 , 90

[0073] This means that the alloy according to the invention must have a service life, which is at least 10% longer, in order to compensate the drawback of the smaller wire diameter. But since the batches according to the invention all have an at least 50% higher service life, the use of the alloy according to the invention offers the additional advantage of a longer service life.

[0074] Manganese is limited to 0.5% by mass, since this element reduces the oxidation stability. The same is valid for copper. 1 TABLE 1 Examples of iron chromium aluminium alloys (service life corresponds to burning time) &rgr; in batch Mn Cr Si Al Mg Ca Zr Ti Hf Y N C P S &OHgr;mm2/m1) Big scale batches T1 0.31 14.5  0.2  4.45 0.01 0.17 0.01 — — 0.005 0.02  0.013 0.002 1.21 H1 0.19 20.5  0.32 5.05 0.01 0.003 0.17 0.01 — — 0.007 0.021 0.010 0.002 1.30 H2 0.21 20.85 0.14 5.2  0.01 0.001 0.05 0.06 — 0.06 0.008 0.032 0.013 0.002 1.33 H3 0.22 20.75 0.14 5.1  0.006 0.002 0.05 0.06 — 0.07 0.007 0.036 0.014 0.002 1.32 H4 0.19 20.0  0.30 5.62 0.009 0.004 0.04 0.04  0.06 0.003 0.025 0.013 0.002 1.38 H5 0.10 21.01 0.24 5.65 0.006 0.0006 0.10 0.009 — — 0.014 H6 0.24 22.21 0.03 5.83 0.002 0.003 0.228 0.105 — — 0.026 0.016 0.001 1.39 Lab scale batches T2 0.33 14.4  0.22 4.5  0.0033 3 ppm 0.18 <0.01 — — 0.006 0.026 0.004 0.004 1.21 K1 0.33 14.4  0.44 3.55 0.0033 3 ppm 0.18 <0.01 — — 0.004 0.025 0.004 0.004 1.15 L1 0.26 16.90 0.37 1.55 0.002 0.049 <0.01 0.039 0.02 0.002 0.003 0.002 0.002 0.91 E L2 0.26 16.86 0.38 2.55 0.002 0.050 <0.01 0.040 0.03 0.003 0.002 0.002 0.002 1.06 E L3 0.27 16.61 0.38 3.55 0.002 0.053 <0.01 0.042 0.04 0.003 0.018 0.003 0.003 1.17 T3 0.30 14.70 0.20 4.49 0.0034 5 ppm 0.18 <0.01 — <0.01   0.002 0.002 0.003 0.004 1.21 E M1 0.36 14.85 0.50 2.78 0.0033 6 ppm 0.05 <0.01 0.03  0.02 0.004 0.002 0.003 0.002 1.07 E M2 0.35 14.80 0.28 2.71 0.0034 5 ppm 0.05 <0.01 0.03  0.04 0.004 0.002 0.003 0.004 1.04 M3 0.36 14.80 0.28 2.24 0.0032 4 ppm 0.05 <0.01 0.03  0.02 0.002 0.002 0.003 0.002 0.92 E M4 0.30 14.65 0.3  2.8  <0.001 <0.001 0.03 <0.01 0.03  0.03 0.0015 0.018 0.002 0.002 1.03 Notched bar impact work in J Service life at 13 mm WB2) 1200° C. RT 50° C. 100° C. 150° C. hours 77 119 137 99 117 111 111 7 63 9 34 11 9.3 E 8 109 E 8 90 8 8.1 35 120 49 E 10 20 92 E 10 24 143 272 126 19 102 >300 285 72 E 9 13 85 179 85 1)after 900° C./30 min/OK) 2)after 950° C./15′/PI

Claims

1. An iron chromium aluminium alloy with long service life comprising (in % by mass)>2 to 3.6% aluminium and >10 to 20% chromium as well as additions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium and/or 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. 0.01% sulphur, max. 0.05% copper and respectively max. 0.1% molybdenum and/or tungsten, as well as manufacture related impurities, the rest being iron.

2. An iron chromium aluminium alloy according to claim 1 comprising (in % by mass) 2.5 to 3.55% aluminium, 13 to 17% by mass chromium and additions of 0.1 to 0.5% Si, max. 0.5% Mn, 0.01 to 0.1% yttrium and/or 0.01 to 0.1% Hf and/or 0.01 to 0.2% 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 tungsten, as well as manufacture related impurities, the rest being iron.

3. An iron chromium aluminium alloy according to claim 1 or 2 comprising (in % by mass) 2.5 to 3.0% aluminium and 14 to 17% chromium and additions of 0.1 to 0.5% 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, max. 0.04% nitrogen, max. 0.04% phosphorus, max. 0.01% sulphur, max. 0.05% copper and respectively max. 0.1% molybdenum and/or tungsten, as well as manufacture related impurities, the rest being iron.

4. An 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 can be replaced completely or partly by (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 rare earths, such as in particular lanthanum and/or cerium.

5. An 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 is limited to 0.01%, the phosphorus content is limited to 0.01% and the sulphur content is limited to 0.005%.

6. An iron chromium aluminium alloy according to one of the claims 1 through 5, wherein the following conditions with respect to the diameter, length and weight modification are given, if the alloy is used as wire and if the surface performance, the performance as well as the resistance are kept constant and if a material A is replaced with a material B:

diameter DB/DA={cube root}{square root over (&rgr;B/&rgr;A)}length LA/LB={cube root}{square root over (&rgr;B/&rgr;A)}weight MB/MA={cube root}{square root over (&rgr;B/&rgr;A)}·&ggr;B/&ggr;A

wherein

D is the diameter

p is the specific electric resistance

L is the length

M is the weight

&ggr; is the density

of the respective wire.

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 form of a heating element, for the use in a household appliance.

9. Use of an iron chromium aluminium alloy according to one of the claims 1 through 6 as alloy, especially in form of a heating element or as 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 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 form of wire or band, for the use as braking and starting resistance.