Method for producing a support film for catalytic converters

Abstract

Method for producing a support film for catalytic converters with application temperatures < 900°C, consisting of an iron-chromium-aluminium alloy containing 8-14% by weight Cr, 1-4% by weight Al and iron as the remainder, along with melting impurities, by the alloy being cast in the form of ingots, the ingots being hot-rolled or forged into slabs of thicknesses between 150 and 400 mm, the slabs in the hot state either being cooled down to room temperature in air / oil / water or first placed with an insert into an oven installation in the temperature range of 475°C to 700°C and, following a heat-retention phase for a holding period of between 0.5 and 100 hours at a defined holding temperature of between 475°C and 700°C, cooled down to room temperature outside the furnace installation.

Description

[0001] Process for producing a carrier film for catalysts

[0002] The invention relates to a method for producing a carrier film for catalysts.

[0003] Iron-chromium-aluminum alloys with chromium contents > 10 wt.% and aluminum > 2 wt.% are used as metallic carrier foils for catalysts at application temperatures of 1000°C and above. Typically, these alloys contain > 18 wt.% chromium and > 4.5 wt.% aluminum. Due to these alloy compositions, these alloys exhibit very good oxidation resistance at high temperatures (> 1000°C). However, the high chromium and aluminum contents are responsible for the formation of a brittle phase (so-called 475°C embrittlement) during the production of the cast ingot in hot forming processes on slabs, hot strip, cold strip, and foil, provided that temperatures below approximately 500°C occur during the process. This brittle phase, in conjunction with material stresses, can lead to significant material fractures.

[0004] For catalysts used up to a maximum temperature of < 900°C, a sufficiently good oxidation resistance of the metallic carrier foil (about 50 pm foil thickness) is necessary, which must be present up to this lower application temperature.

[0005] DE 10 2012 004 488 A1 discloses an iron-chromium-aluminum alloy with improved high-temperature strength, low chromium evaporation rate and good processability with (in mass %) 2.0 - 4.5% AI, 12 - 25% Cr, 1.0 - 4.0% W, 0.25 - 2.0% Nb, 0.05 - 1.2% Si, 0.001 - 0.70% Mn, 0.001 - 0.030% C, 0.0001 - 0.05% Mg, 0.0001 - 0.03% Ca, 0.001 - 0.030% P, max. 0.03% N, max. 0.01% S, balance iron and the usual impurities resulting from the melting process. If necessary, the elements Y, Hf, and Zr can be added to the alloy. Applications for this alloy include interconnector plates and / or components in auxiliary components of a solid oxide fuel cell, particularly in heat exchangers, as well as carrier foil and / or wire mesh in metallic exhaust catalysts.

[0006] DE 103 10865 B3 describes the use of an iron-chromium-aluminum alloy with good oxidation resistance containing (in mass %) 2.5 - 5.0% Al, 10 - 25% Cr, and 0.05 - 0.8% Si, as well as additions of > 0.01 - 0.1% Y and / or > 0.01 - 0.1% Hf and / or > 0.01 - 0.2% Zr and / or > 0.01 - 0.2% cerium mischmetal (Ce, La, Nd), as well as manufacturing-related impurities, for components in diesel vehicles and two-stroke engines, particularly in diesel and two-stroke engines. Components produced from the alloy exhibit a change in length of < 4% after annealing at 1100°C for 400 hours at a metal thickness of 50 μm. Components that can be considered here include carrier foils in metallic exhaust gas catalysts and components in exhaust gas purification systems.

[0007] DE 101 57 749 A1 relates to an iron-chromium-aluminium alloy with a long service life, with (in mass%) > 2 - 2.6% aluminium and > 10 - 20% chromium as well as additions of 0.1 - 1% Si, max. 0.5% Mn, 0.01 - 0.2% Y 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% C, max. 0.04% N, max. 0.04% P, max. 0.01% S, max. 0.05% Cu and each max. 0.1% Mo and / or W, the remainder being iron and impurities resulting from the manufacturing process. The alloy can be used as a heating element, for example, in a household appliance, or as a construction material for furnace construction. Furthermore, the alloy can be used in foil form as a carrier film for catalysts.

[0008] The materials referred to in the state of the art are manufactured industrially as follows:

[0009] The alloys are melted in melting plants, such as arc or induction melting furnaces, and then cast into ingots. The ingots are hot rolled onto slabs, and the slabs are hot rolled onto hot strip. The further forming processes involve several cold rolling steps with intermediate annealing of hot strip onto strip or foil. Between the individual hot and cold rolling steps, surfaces are ground and slab ends are trimmed. Each transport step from the rolling mill locations takes place in a so-called hot transport, during which the material temperature must be kept above 500°C to above 700°C to suppress the embrittling phase. After hot transport, the material pieces are placed in a furnace at a temperature of > 500°C upon arrival at the plant where the subsequent rolling process takes place and heated to rolling temperature.Even during longer waiting periods for a hot-rolled piece before being transported to the next process step, these pieces are kept in furnaces at higher temperatures and then, for logistical reasons, transported to the next process location at a later time using hot transport. The individual process steps, hot transport, and reloading in a furnace at temperatures > 500°C include the following stations and transports:

[0010] Hot transport of the cast block

[0011] Furnace loading of the block at > 500°C and heating to rolling temperature Hot rolling of the block to slab

[0012] Furnace loading of the slab at > 500°C and heating and holding at higher holding temperature Hot transport of the slab

[0013] Furnace loading of the slab at > 500°C and heating to rolling temperature Hot rolling of the slab on hot strip Hot transport of the hot strip

[0014] Furnace insert of the hot strip at > 500°C

[0015] Hot rolling of the hot strip to a specific pre-dimension, cold rolling of the strip with further intermediate annealing, and finally cold rolling of the foil. Hot rolling of the ingot to a slab can be replaced by a forging process if required. Hot grinding processes can also be performed during the process sequence.

[0016] The aim of the subject matter of the invention is to provide a method for producing a carrier film for catalysts with application temperatures < 900°C, in which the previously described complex production process, in particular the hot transport, is unnecessary.

[0017] Furthermore, the use of the procedure for specific applications should be protected.

[0018] This object is achieved by a process for the production of a carrier foil for catalysts with application temperatures < 900°C, consisting of an iron-chromium-aluminium alloy with contents (in wt%) of Cr 8 - 14%

[0019] AI 1 - 4%

[0020] Fe residue as well as melting-related impurities by casting the alloy into blocks, hot-rolling or forging the blocks into slabs with thicknesses between 150 and 400 mm, cooling the slabs in the hot state either in air / oil / water to room temperature or first placing them with an insert in a furnace in the temperature range from 475°C to 700°C and cooling them to room temperature outside the furnace after a holding phase with a holding time of between 0.5 and 100 hours at a defined holding temperature between 475°C and 700°C.

[0021] Advantageous developments of the process according to the invention can be found in the associated subclaims. The contents of the elements Cr, Al, and Fe can be modified as follows within the original range: Cr 10 - 13% 9 - 13% 9 - 12%

[0022] AI 1 - 4%

[0023] 1 - 3.5%

[0024] 2 - 3.5% 1.5 - 3%

[0025] Fe residue and melting-related impurities.

[0026] In addition, it is possible to optionally include the following elements in the alloy:

[0027] Y up to 0.3% and / or

[0028] Hf up to 0.3% and / or

[0029] La to 0.3% and / or

[0030] Cerium up to 0.3%, whereby cerium can be present in the form of mixed metals (Ce, La, Nd).

[0031] Furthermore, it is possible to optionally add the element Zr to the alloy, with contents of > 0 - max. 0.5 wt.% being conceivable.

[0032] With the method according to the invention it is now possible, in the case of a material with an alloy composition of 8 - 14% by weight chromium, as well as 1 - 4% by weight aluminum, the remainder being iron and impurities, to dispense with a longer holding phase of several hours or even days in a furnace at a holding temperature well above 500°C. In the manufacturing process according to the subject matter of the invention, in contrast to the prior art, the slab is either rolled in thicknesses of 150 - 400 mm, preferably 150 and 250 mm, in the hot state after the hot rolling process orForging process: From ingot to slab, the steel is placed directly in air / oil / water and cooled to room temperature, or placed in a furnace at a temperature between 475°C and 700°C, cooled from the final rolling / forging temperature to a temperature between 475°C and 700°C, and held at a defined holding temperature between 475°C and 700°C with a holding time between 0.5 and 100 hours to allow temperature equalization across the slab cross-section. The slab is then removed from the furnace and further cooled to room temperature in air / oil / water.

[0033] This process eliminates the need for complex holding heat processes (sometimes involving long holding phases at temperatures well above 500°C), significantly simplifying the manufacturing process. Furthermore, the film exhibits sufficiently good oxidation resistance in a 400-hour oxidation test at temperatures ranging from 750°C to approximately 900°C, which particularly meets the requirements as a carrier film for catalysts with maximum application temperatures between 750 and 900°C.

[0034] Furthermore, the use of the process according to one or more of claims 1 to 7 for producing carrier films for catalysts with application temperatures < 900°C is claimed.

[0035] Table 1 discloses the chemical composition (in wt%) of an exemplary batch 155408

[0036] Table 1

[0037] Range limits of a preferred chemical composition of an alloy that can be selected for the inventive manufacturing process and for the described applications are listed in Table 2.

[0038] Table 2

[0039] The alloys described may optionally contain a selection of additional elements such as yttrium and / or hafnium and / or lanthanum and / or cerium.

Claims

Patent claims 1. Method for producing a support film for catalysts with application temperatures < 900°C, consisting of an iron-chromium-aluminium alloy with contents (in wt.%) of Cr 8 - 14% AI 1 - 4% Iron residue and melting-related impurities are removed by casting the alloy into blocks, hot-rolling or forging the blocks into slabs with thicknesses between 150 and 400 mm, cooling the slabs in their hot state either in air / oil / water to room temperature or first placing them with a lining in a furnace system at a temperature range of 475°C to 700°C and, after a holding phase of between 0.5 and 100 hours at a defined holding temperature between 475°C and 700°C, cooling them to room temperature outside the furnace system.

2. The method according to claim 1, wherein the content of the elements Cr is 9-13%. AI 1.0 - 3.5% Iron residue and melting-related impurities in the alloy are adjusted.

3. Method according to claim 1 or 2, wherein the content of the elements Cr is 10-13%. AI 2 - 3.5% Iron residue and melting-related impurities in the alloy are adjusted. Method according to claim 1 or 2, wherein the content of the elements Cr is 9-12%. AI 1.5 - 3% Iron residue and melting-related impurities in the alloy are adjusted. Method according to any one of claims 1 to 4, wherein the following elements are optionally added to the alloy: Y up to 0.3% and / or Hf up to 0.3% and / or La up to 0.3% and / or Cer up to 0.3%. A process according to any one of claims 1 to 5, wherein the element Zr is optionally added to the alloy in amounts > 0.0 to 0.5%. A process according to any one of claims 1 to 6, characterized in that the slab, after cooling to room temperature, is rolled into strip and film by hot and cold rolling processes, wherein at least one heat treatment process of the strip or film is carried out as required. Use of the process according to one or more of claims 1 to 7 for the production of carrier films for catalysts with application temperatures < 900°C.

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