Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium

Definitions

• 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 - Maschinenstofflechnik” , Ralf Burgel, Vieweg Verlag, Braunschweig 1998, form page 274 on.
• reactive elements such as for example Ca, Ce, La, Y, Zr, Hf, Ti, Nb
• 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.
• 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.
• 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.
• 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.
• nickel 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.
• 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.
• 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.
• 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 - Maschinenstofflechnik” , Ralf Burgel, Vieweg Verlag, Braunschweig 1998, on page 272 in image 5.13.
• 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.
• 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%.
• 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.
• Al contents comprised between 2 and 6% can be added by alloying.
• Preferred Cr contents are above 20%.
• 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%.
• 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.
• contents of ⁇ 4% Al require Cr contents of >25%.
• 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.
• the Al content can be set within the limits of 2.5-3.55% and the Cr content within the limits of 13-17%.
• the brittleness is also increased by chromium, silicium, carbon and nitrogen, so that these elements should also be kept as low as possible.
• Diameter D B /D A ⁇ cube root ⁇ square root over ( ⁇ B / ⁇ A ) ⁇
• Weight M B /M A ⁇ cube root ⁇ square root over ( ⁇ B / ⁇ A ⁇ B / ⁇ A ) ⁇
• M B /M A ⁇ cube root ⁇ square root over ( ⁇ B / ⁇ A ) ⁇ B/ ⁇ A
• [0029] is required for the wire having the specific electric resistance ⁇ B , which has the same functionality in comparison to the wire made of an alloy A and having the specific electric resistance ⁇ A the diameter D A and the length L A , if ⁇ B is smaller than ⁇ B and approximately ⁇ A ⁇ B .
• Example: material A: ⁇ A 1.25 ⁇ mm 2 /m
• L B /L A 1.06; i.e. increase of the length by 6% by mass
• M B /M A 0.94; i.e. reduction of the weight by 6% by mass %
• C 0 aluminium concentration of the alloy before start of the oxidation or use of a heating spiral
• C K 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.
• n oxidation rate exponent having a value of approximately 0.5
• the oxidation constant k is a measuring tool for the quality of the oxide layer.
• k is smaller than for an oxide layer of lower quality. The smaller k is the longer is the service life.
• 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.
• 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.
• table 1 the different iron chromium aluminium alloys are listed, wherein the table contains both big scale batches and batches produced in the laboratory.
• heating elements heat conductors
• accelerated service life tests are possible for the comparison of materials with each other, for example under the following conditions:
• 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.
• 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
• 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.
• 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.
• batches L2, L3, M1, M2 and M4 are not the case for the batches L2, L3, M1, M2 and M4 according to the invention and marked with “E”.
• 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.
• 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.
• 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.
• 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%.
• 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.
• a certain chromium content is necessary, since chromium stimulates the formation of the highly stable and protective ⁇ -Al 2 O 3 layer.
• 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.
• 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 ⁇ 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.
• 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.
• 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.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Resistance Heating (AREA)
• Conductive Materials (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=7682876

Family Applications (1)

Country Status (2)

Cited By (10)

Families Citing this family (6)

Citations (7)

Family Cites Families (5)

• 2001
  • 2001-11-24 DE DE10157749A patent/DE10157749B4/de not_active Expired - Fee Related
• 2002
  • 2002-04-25 US US10/476,170 patent/US20040131493A1/en not_active Abandoned
  • 2002-04-25 DE DE50200904T patent/DE50200904D1/de not_active Expired - Lifetime

Patent Citations (7)

Also Published As

Similar Documents

Legal Events