Patent Application
20250215540
The invention relates to a method for the manufacture of a support foil for catalytic converters.
Iron-chromium-aluminum alloys with contents of chromium >10 wt-% and aluminum >2 wt-% are used as metallic support foils for catalytic converters at application temperatures of 1000° C. and above. Typically, the contents of these alloys are then chromium >18 wt-% and aluminum >4.5 wt-%. On the basis of these alloy compositions, these alloys indeed have a very good oxidation resistance at high temperatures (>1000° C.), but on the other hand the high contents of chromium and aluminum mean that a brittle phase (known as 475° C. embrittlement) may form during the course of fabrication of the cast ingot in processes of hot-forming to obtain slab, hot strip, cold strip and foil, as long as temperatures below approximately 500° C. occur in process control. The brittle phase in association with material stresses may lead to considerable material fracturing.
For catalytic converters, which are used up to a maximum temperature of ≤900° C., a sufficiently good for oxidation resistance of the metallic support foil (approximately 50 μm foil thickness) is needed, which must exist up to this lower application temperature.
DE 10 2012 004 488 A1 discloses an iron-chromium-aluminum alloy with improved hot strength, low chromium evaporation rate and good processability with (in mass-%) 2.0-4.5% Al, 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, the rest iron and the usual melting-related impurities. If necessary, the elements Y, Hf, Zr may be added to the alloy. Areas of use for this alloy are interconnector plates and/or component parts in additional assemblies of a solid oxide fuel cell, such as in a heat exchanger in particular as well as support foil and/or wire mesh in metallic exhaust-gas catalytic converters.
From DE 103 10 865 B3, it is possible to learn the use of an iron-chromium-aluminum alloy with good oxidation resistance with (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 mixed metal (Ce, La, Nd) as well as manufacturing-related impurities for components in diesel vehicles and two-cycle devices, especially in diesel and two-cycle engines. Component parts produced from the alloy have, after an annealing at 1100° C. for 400 hours, a length change of <4% for a metal thickness of 50 μm. In this context, support foils in metallic exhaust-gas catalytic converters as well as components in exhaust-gas purification systems may be regarded as component parts.
DE 101 57 749 A1 relates to an iron-chromium-aluminum alloy with long lifetime, with (in mass-%)>2-2.6% aluminum 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 respectively max. 0.1% Mo and/or W, the rest iron as well as manufacturing-related impurities. The alloy can be used as a heating element, for example for use in a household appliance or as construction material for the use in furnace construction. Furthermore, the alloy may be used in the form of a foil for the use as support foil for catalytic converters.
The materials cited in the prior art are manufactured industrially as follows:
The alloys are melted in melting systems, such as, for example, arc or induction-melting furnaces, and then cast in the form of ingots. The ingots are hot-rolled to slabs and the slabs are hot-rolled to hot strip. The further forming processes provide several steps of cold-rolling with intermediate annealings from hot strip to strip or foil. Between the individual hot-rolling and cold-rolling steps, processes of grinding of the surfaces are carried out, as is the removal of the slab ends by cutting off. Each transport step from the sites of the rolling systems takes place in a so-called hot transport, in which the material temperature must be maintained above 500° C. up to above 700° C. in order to suppress the embrittling phase. After the hot transport, the material pieces, upon arrival in the mill in which the subsequent rolling process takes place, are introduced into a furnace system at a temperature of >500° C. and heated to rolling temperature. Even during longer phases of waiting of a hot-rolled piece until further transport to the next process step, these pieces are kept in furnace systems at higher temperatures so that subsequently, for logistical reasons, they can be transported at a later time by means of hot transport to the next process site. The individual process steps and the hot transports as well as reintroduction into a furnace system at temperatures of >500° C. comprise the following stations and transports:
The hot-rolling of the ingot to slab may be replaced if necessary by a forging process. In the course of the process sequence, hot-grinding processes may also take place.
The objective of the subject matter of the invention is to provide, for the manufacture of a support foil for catalytic converters with application temperatures of ≤900° C., a method in which the expensive manufacturing process described in the foregoing, especially the hot transport, is unnecessary.
Furthermore, it is intended that protection be claimed for the use of the method for specific application situations.
This task is accomplished by a method for the manufacture of a support foil for catalytic converters with application temperatures of ≤900° C., consisting of an iron-chromium-aluminum alloy with contents (in wt-%) of
Advantageous further developments of the method according to the invention can be inferred from the associated dependent claims.
The contents of the elements Cr, Al, Fe may be modified as follows within the original range of values, namely
Beyond that, the possibility exists of optionally also providing the following elements in the alloy:
Furthermore, the possibility exists of optionally also adding the element Zr to the alloy, wherein contents of >0-max. 0.5 wt-% are conceivable.
With the method according to the invention, it is now possible, in the case of a material with an alloy composition of 8-14 wt-% chromium, as well as 1-4% wt-% aluminum, the rest iron and impurities, that a longer holding phase of several hours or even days in a furnace system at a holding temperature significantly above 500° C. can be dispensed with. In the fabrication process existing according to the subject matter of the invention, and in contrast to the prior art, either the slab in thickness dimensions of 150-400 mm, preferably 150 and 250 mm, while in the hot condition after the process of hot-rolling or the process of forging from ingot to slab, is placed directly in air/oil/water and cooled to room temperature, or is introduced into a furnace system at a temperature between 475° C. and 700° C., cooled from final temperature of rolling/forging to a temperature between 475° C. and 700° C. and held at a defined holding temperature between 475° C. and 700° C. for a hold time between 0.5 and 100 hours for equalization of temperature over the slab cross section. Then the slab is removed from the furnace system and the further cooling to room temperature takes place in air/oil/water.
With this process, it is possible to dispense with the expensive holding heating processes (in some cases, long-lasting holding phases at a holding temperature significantly above 500° C.), wherein a considerable simplification of the fabrication process is established. Beyond that, the foil has a sufficiently good oxidation resistance in a 400-hour oxidation test at temperatures of 750° C. to approximately 900° C., which in particular satisfies the requirements as support foil for catalytic converters with maximum application temperatures between 75° and 900° C.
Furthermore, the use of the method according to one or more of claims 1 to 7 for production of support foils for catalytic converters with application temperatures of ≤900° C. is claimed.
Table 1 discloses the chemical composition (in wt-%) of an exemplary batch 155408
Range limits of a preferred chemical composition of an alloy that may be selected for the inventive fabrication process and for the described conditions are listed in Table 2.
The described alloys may optionally contain, in a selection, contents of additional elements such as yttrium and/or hafnium and/or lanthanum and/or cerium.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 109 883.4 | Apr 2022 | DE | national |
| 10 2023 104 526.1 | Feb 2023 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2023/100264 | 4/6/2023 | WO |
