Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• • 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
• • 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
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • 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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/16—Selection of particular materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2370/00—Selection of materials for exhaust purification
  • F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
  • F01N3/28—Construction of catalytic reactors
  • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
  • F01N3/2807—Metal other than sintered metal

Definitions

• the invention relates to an iron chromium aluminum alloy manufactured by metallurgic melting and having a long service life.
• Such alloys are used for producing electric heating elements and catalyst carriers. These materials form a dense, highly adhesive aluminum oxide layer that protects them against destruction at high temperatures (for example up to 1400° C.). This protection is still improved by adding so called reactive elements, such as for example Ca, Ce, La, Y, Zr, Hf, Ti, Nb, W, which inter alia improve the adhesiveness of the oxide layer and/or reduce the layer growth, as it is for example described in “Ralf Bürgel, Handbuch der Hochtemperatur-Werkstofftechnik, Vieweg-Verlag, Braunschweig 1998” from page 274 onwards.
• reactive elements such as for example Ca, Ce, La, Y, Zr, Hf, Ti, Nb, W
• the aluminum oxide layer protects the material against quick oxidation. Herein, it grows itself, but only very slowly. This growth consumes the aluminum content of the material. If no more aluminum is present, other oxides (chromium and iron oxides) will grow, the metal content of the material will be very quickly consumed and the material will fail due to destructive corrosion. The time period until failing is defined as service life. An increase of the aluminum content increases the service life.
• a ferritic rustproof steel alloy is known, in particular for the use as heat conductor element.
• the alloy is formed by a FeCrAl alloy manufactured by powder metallurgy and comprising (in % by mass) less than 0.02% C, ⁇ 0.5% Si, ⁇ 0.2% Mn, 10.0 to 40.0% Cr, ⁇ 0.6% Ni, ⁇ 0.01% Cu, 2.0 to 10.0% Al, one or more element(s) from the group of the reactive elements, such as Sc, Y, La, Ce, Ti, Zr, Hf, V, Nb, Ta, in contents comprised between 0.1 and 1.0%, the rest being iron as well as unavoidable impurities.
• EP-B 0 387 670 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 in about the same portions 0.035 to 0.07% Ti and 0.035 to 0.07% zirconium, and max. 0.01% phosphorous, max. 0.01% magnesium, max. 0.5% manganese, max. 0.005% sulphur, the rest being iron, is described, wherein the sum of the contents of Ti and Zr is 1.75 to 3.5% greater than the percentage sum of the contents of C and N as well as impurities resulting from the melting process.
• Ti and Zr can be completely or partially replaced by hafnium and/or tantalum or vanadium.
• EP-B 0 290 719 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 0.4% manganese, max. 0.035% phosphorous, max. 0.020% sulphur, 0.1 to 1.0% molybdenum, max.
• 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 is described, which is for example used as wire for heating elements of electrically heated furnaces and as construction material for thermally stressed parts as well as foil for the manufacture of catalyst carriers.
• t B 4 , 4 ⁇ 10 - 3 ⁇ ( C 0 - C B ) ⁇ p ⁇ d ⁇ k - 1 n ⁇ ( ⁇ ⁇ ⁇ m * ) 1 n - 1 wherein ⁇ m* is the critical change in weight with which spalling starts.
• thermal cycle defines the combination of heating up period, holding time at the temperature, cooling down period, and waiting time until a new heating up.
• Thermal cycles presenting a short heating up period, a short cooling down period and an only short holding time at the high temperature will be called short and rapid thermal cycles in the following.
• Heat conductors made of thin films stand out for a great surface-to-volume ratio.
• This is advantageous if fast heating up and cooling down times shall be achieved, as they are for example required for the heat conductors used in glass-ceramic cooking zones in order to make the heating up quickly visible and to obtain a fast temperature rise, similar to a gas cooker.
• the great surface-to-volume ratio is disadvantageous for the service life of the heat conductor (see above).
• the temperature has to be limited below the glass in this application, in order to protect it against deterioration. This can be achieved by switching off the current repeatedly and for short periods of time. Both measures will cause stress for the heat conductor due to short heating up periods and fast cooling down and only short holding times, which further reduces the service life, as described above.
• the addition may not be too high, since otherwise a higher oxidation rate will occur which means an increased consumption of aluminum and thus a shortened service life.
• This higher oxidation rate is for example caused by an addition of only 0.11% hafnium to an iron chromium aluminum alloy comprising 20% Cr, 7% aluminum and 0.01% yttrium.
• a higher oxidation rate caused by a too high addition of a reactive element examples include an iron chromium aluminum alloy comprising 18.8% Cr, 7% Al and an addition of 0.11% Y or an iron chromium aluminum alloy comprising 20% Cr, 7% Al and additions of 0.04% yttrium, 0.05% Zr and 0.05% Ti.
• the range in which a higher oxidation rate is caused by a too high addition of a reactive element varies with the aluminum content. According to J. Klöwer, Materials and Corrosion 51 (2000), pages 373 through 385, 0.04% Zr in an iron chromium aluminum alloy comprising 20% Cr, 7% Al and 0.05% Y already causes an increased oxidation rate.
• an iron chromium aluminum alloy manufactured by metallurgic melting and having a long service life comprising (in % by mass) 4 to 8% aluminum, 16 to 24% chromium and additions of 0.05 to 1% Si, max. 0.5% Mn, 0.02 to 0.2% yttrium and 0.1 to 0.3% Zr and/or 0.02 to 0.2% Hf, 0.003 to 0.05% C, 0.0002 to 0.05% Mg, 0.0002 to 0.05% Ca, max. 0.04% N, max. 0.04% P, max. 0.01% S, max. 0.5% Cu and the usual impurities resulting from the melting process, the rest being iron.
• the element Hf can be completely or partly replaced by at least one of the elements Sc and/or Ti and/or V and/or Nb and/or Ta and/or La and/or cerium, wherein ranges comprised between 0.02 and 0.15% by mass are preferred for a partial substitution.
• the alloy according to the invention shall be molten with (in % by mass) max. 0.02% N, max. 0.02% P as well as max. 0.005% S.
• Preferred FeCrAl alloys have the following composition (in % by mass): Al 5-6% 5-6% Cr 18-22% 18-22% Si 0.05-0.7% 0.05-0.7% Mn 0.001-0.4% 0.001-0.4% Y 0.03-0.1% 0.03-0.1% Zr 0.15-0.25% Hf 0.02-0.15% 0.02-0.15% C 0.003-0.03% 0.003-0.3% Mg 0.0002-0.03% 0.0002-0.03% Ca 0.0002-0.03% 0.0002-0.03% N max. 0.04% max. 0.04% P max. 0.04% max. 0.04% S max. 0.01% max. 0.01% Cu max. 0.5% max. 0.5%
• the range of the following elements can be set as follows: Hf 0.03-0.11% C 0.003-0.025% Mg 0.0002-0.01% Ca 0.0002-0.01%
• the alloys according to the invention can be preferably used for electric heating elements having short heating up and cooling down periods, short holding times at the temperature and short waiting times until a new heating up period starts.
• the alloys according to the invention can also be used for heating elements which require a high dimensional stability or a low sagging.
• the alloys according to the invention can also be used for heat conductors made of films having a thickness comprised between 20 and 100 ⁇ m.
• alloys according to the invention as heat conductors for the use in cooking zones.
• the service life test of heat conductors is carried out with wires having a diameter of 0.40 mm, the wire coils of which have 12 windings, a coil diameter of 4 mm and a coil length of 50 mm.
• the wire coils are fixed between two current supplies and heated up to 1200° C. by applying an electric tension. The heating up to 1200° C. is respectively realized for 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 fuses thoroughly.
• An analogue service life test can be carried out with film strips.
• film strips having a thickness of 50 ⁇ m and a width of 6 mm are fixed between two current supplies and heated up to 1050° C. by applying an electric tension. The heating up to 1050° C. is respectively realized for 15 seconds, then, the current supply is interrupted for 5 seconds. At the end of the service life the film fails in that the remaining cross section fuses thoroughly.
• the service life indicates the total period of time in which the wire or the film are at the mentioned temperature without interruption times.
• the temperature is measured by an optical pyrometer and, if necessary, corrected to the nominal temperature.
• the results of the service life test are indicated in table 1.
• the mean values indicated in the table are respectively the mean values of at least 3 samples.
• the coils are fixed horizontally at the beginning. In the course of the service life test they start sagging. The smaller the sagging the higher is the dimensional stability of the material. A high dimensional stability is an advantageous technological characteristic, since this means that the parts made of the material present a small modification of their shape when being used at higher temperatures.
• the alloys G1 and G2 that have been industrially molten and the alloy L2 molten in the laboratory show an iron chromium aluminum alloy comprising (in % by mass) about 20% Cr, about 5% Al and additions of 0.04 to 0.07% Y, 0.04 to 0.07% Zr and 0.04 to 0.05% Ti and a carbon content of 0.033 to 0.037%, a Si content of 0.15 to 0.34%, a Mn content of about 0.24% and little contents of N, S, Ce, La, Pr, Ne, P, Mg, Ca, as indicated in table 1 according to the state of the art.
• the service life of a wire made of L2 and having a thickness of 0.4 mm at 1200° C. in a cycle of 120 s “on” and 15 s “off” serves as reference and is indicated as 100%.
• the service life of 50 ⁇ m thick film at 1050° C. and in a cycle of 15 s “on” and 5 s “off” is comprised between 102 and 124% of the service life of the laboratory batch L1.
• the industrially molten alloy G3 also shows an iron chromium aluminum alloy comprising about 20% Cr, about 5% Al and additions of 0.06% Y, 0.04% Zr, 0.02% Hf, a carbon content of 0.029%, a Si content of 0.28%, a Mn content of 0.20% and little contents of P, Mg, Ca, as indicated in table 1 according to the state of the art.
• the alloys according to the state of the art show values of about 100% to about 150% of L1 in the service life test of 50 ⁇ m thick film at 1050° C. and in a cycle of 15 s “on” and 5 s “off”.
• the contents of Si, C, Zr, Ti and Hf have been varied.
• the Mn content has not been varied and is comprised between 0.24 and 0.28% in all laboratory melts and the little admixtures of P, Mg, Ca, Ce, La, Pr, Ne are as indicated in table 1.
• the variant L1 comprising 0.03% Y, 0.04% Zr and 0.02% Hf and a carbon content of 0.007% and a Si content of 0.35% shows a relatively long service life of 116% in a service life test of 0.4 mm thick wire at 1200° C. in a cycle of 120 s “on” and 15 s “off”.
• the variants L3 and L7 with an addition of Y of only 0.06% or 0.05% and a carbon content of 0.002 or 0.031% and a Si content of 0.34 or 0.35% have a service life of only 41% or 51% in the service life test of wire.
• the variants L4 and L5 with an addition of 0.04 or 0.05% Y and 0.05 or 0.014% Zr and carbon contents of 0.002 or 0.003% and the Si contents of 0.33 or 0.35% have a service life of 79% or 86%, which is better than the one of L3 and L7, but does not reach the service lives of L2 or L1.
• the variant L6 with an addition of 0.05% Y and 0.05% Hf and carbon contents of 0.010% and a Si content of 0.36% has a service life of 85%, which is also better than the one of L3 and L7, but does not reach the service lives of L2 or L1.
• the laboratory batch L8 comprises additions of 0.05% Y, 0.21% Zr and 0.11% Ti and a carbon content of 0.018% and a Si content of only 0.02%.
• this alloy due to the high Zr and Ti content, is already situated in the concentration range of the higher oxidation rate in the service life test with long cycles of for example 100 h or 96 h in the furnace. Nevertheless, it shows a service life of 105% in the heat conductor service life test of wire, which means it is situated between L1 and L2.
• the alloys according to the invention E1 comprising 0.05% Y, 0.18% Zr, 0.04% Hf, 0.006% C and 0.35% Si and E2 comprising 0.03% Y, 0.20% Zr, 0.11% Ti instead of hafnium, 0.020% C and 0.61% Si are within the range of the higher oxidation rate in the life service test with long cycles of for example 100 h or 96 h in the furnace. Both alloys have long service lives of 96% for E2 and even 118% for E1 in the heat conductor service life test of wire. Thus, the following ranking of service life results for the laboratory melts (respectively classified according to decreasing service life):
• Peak group E1, L1, L8, L2, E2, characterized by additions of Y and Zr and furthermore by an addition of Ti or Hf.
• the alloy L2 for example corresponds to the industrially molten alloys G1 and G2 according to the state of the art.
• the picture is different, if one looks at the heat conductor service life test of 50 ⁇ m thick film at 1050° C. in a cycle of 15 s “on” and 5 s “off”:
• the alloys L3 and L7 which show a short service life in the test of wire, show a service life of 94% and 110% of L1, which is within the range of the service lives of the alloys according to the state of the art.
• the alloys L5, L6, L4 which show a medium service life in the test of wire show a service life of 145% or 113% of L1, which is also within the range of the service lives of the alloys according to the state of the art.
• the alloys L1 and L2 which are in the peak group for the wire test show a service life of 100% or 125% of L1, the alloy L8 shows a service life of 140% of L1, which is only within the range of the service lives of the alloys according to the state of the art.
• Group with service lives comprised between about 100% and 150% of L1, which corresponds to the state of the art: G3, L5, L8, L2, G2, L4, L6, G1, L1, L7, L3, characterized by a smaller addition of Y and Zr and/or Hf and/or Ti outside the range of the higher oxidation rate in the service life test with long cycles of for example 100 h or 96 h in the furnace or in the case of L8 by a too low Si content with an addition of Y, Zr and Hf in the range of the higher oxidation rate.
• the alloys according to the invention E1, E2 and L8 show values comprised between 5 and 7 mm and are thus in the peak group in comparison to the other alloys L1 through L7 according to the state of the art which show values comprised between 17 and 19 mm.
• the alloys according to the invention also present the advantage of a high dimensional stability.
• a minimum content of 0.02% Y is necessary in order to maintain the effect of Y to increase the oxidation stability.
• the upper limit is set to 0.2% by mass for the reason of costs.
• a minimum content of 0.1% Zr is required in order to reach the range of high service lives with short and quick temperature cycles.
• the upper limit is set to 0.3% by mass Zr for the reason of costs.
• a minimum content of 0.02% Hf is necessary in order to maintain the effect of Hf to increase the oxidation stability.
• the upper limit is set to 0.2% by mass Hf for the reason of costs.
• a minimum content of 0.02% Ti is necessary in order to maintain the effect of Ti to increase the oxidation stability.
• the upper limit is set to 0.2% by mass Ti for the reason of costs.
• the carbon content should be 0.003% to 0.05% in order to assure the working properties.
• the nitrogen content should be maximum 0.04% in order to avoid the formation of nitrides that deteriorate the working properties.
• Chromium contents comprised between 16 and 24% by mass have no decisive influence on the service life, as it can be read in J. Klöwer, Materials and Corrosion 51 (2000), pages 373 through 385.
• a certain chromium content is required, since chromium stimulates the formation of the especially stable and protecting ⁇ -Al 2 O 3 layer. This is assured from about 16% onwards. Therefore, the lower limit is 16%.
• Chromium contents of >24% degrade the working properties of the alloy.
• the aluminum content of the alloy according to the invention should be comprised between 4 and 8%. According to the “Handbuch der Hochtemperatur-Werkstofftechnik, Ralf Bürgel, Vieweg Verlag, Braunschweig 1998”, page 272 picture 5.13 about 4% aluminum are required in order to form a closed ⁇ -Al 2 O 3 layer. Higher aluminum contents than 8% degrade the working properties.
• Manganese is limited to 0.5%. by mass, since this element reduces the oxidation stability. The same is true for copper.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Heat Treatment Of Steel (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Resistance Heating (AREA)
• Soft Magnetic Materials (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Materials For Medical Uses (AREA)
• Cookers (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Laminated Bodies (AREA)

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• 2005
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