DE102016103313A1 - Process for producing a coated steel foil - Google Patents

Abstract

In order to provide a process for the production of a steel foil and a coated film which can be produced cost-effectively by the process, which dispenses with the use of rare earth elements which contain only small amounts of alloying elements, the oxidation resistance and corrosion resistance at temperatures of up to to 1200 ° C, which has a functional surface in this temperature range, that is, an effect against diffusion bonding and a good coating adhesion, in which further dispenses with a diffusion annealing, which is thus suitable as a support material for engine-near exhaust gas catalysts of internal combustion engines is proposed that a 15 to 28 wt .-% chromium, 0.5-3.0 wt .-% aluminum and 0.5-2.5 wt .-% silicon-containing steel strip with a strip thickness of up to 3 mm on both sides with a layer of aluminum or an aluminum alloy coated with a silicon content of ≤ 16% wi rd, wherein the layers on both sides have an amount of at least 60 g / m2 and a coating thickness of at least 10 microns and wherein the coated steel strip is then rolled to a thickness of 20 to 200 microns and a coated steel foil is produced by this method.

Description

The invention relates to a method for producing a coated steel foil. In addition, the invention relates to a steel foil produced by the process.

Due to the incomplete combustion of the fuels, the engine produces approximately 1% additional combustion products, other than water and CO ₂ , which are referred to as exhaust gases.
For gasoline engines: CO, HC and NOx,
for diesel engines: CO, HC, NOx, SO ₂ and PM (soot particles).

In order to achieve the legal limit values for the emissions of internal combustion engines, innovative exhaust aftertreatment systems consisting of catalytic converters and diesel particulate filters must be used.

• 1. Umwandlung von CO in CO₂,
• 2. Umwandlung von HC in H₂O + CO₂ und
• 3. Umwandlung von NOx in N₂.

The pollutants in the exhaust gas are transformed by catalysts and particle filters into water, CO ₂ and N ₂ . As standard equipment for petrol cars 3-way catalysts are used with the following functions:

• 1. conversion of CO into CO ₂ ,
• 2. Conversion of HC to H ₂ O + CO ₂ and
• 3. Conversion of NOx to N ₂ .

For diesel engines today's system configurations to achieve the Euro 5/6 limits are largely comparable and consist of a DOC (Diesel Oxidation Catalyst) with a downstream cDPF (Coated Diesel Particulate Filter) and SCR (Selective Catalytic Reduction) system to control the nitrogen oxides (NO _x ) to a high percentage.

As support material for such exhaust aftertreatment systems, such as catalysts and diesel particulate filter, both ceramic and metallic materials are used. Compared to ceramic substrates metal substrates have better physical and mechanical properties, such as. B. high shock resistance and high thermal conductivity. Metallic catalyst supports heat up faster and also offer the possibility of electric preheating and electrostatic deposition of nanoparticles. In addition, they show a good temperature resistance and a higher conversion performance due to the turbulence-generating structure and thus make less demands on the space size compared to ceramic systems. A lower exhaust back pressure also allows a lower fuel consumption in economical driving.

Compared to ceramic, however, metallic catalyst supports have the disadvantage of higher material costs. Usually steel foils with thicknesses of 30-80 microns of FeCrAl alloys are used as support materials for metallic automotive exhaust catalysts. Due to the high contents of chromium of usually 16-23 wt .-% and aluminum of 3-8 wt .-%, these ferritic steels have a high oxidation resistance in the high temperature range of 800-1200 ° C, by a dense, slow growing alumina layer (α-Al ₂ O ₃ ) whose adhesion or growth is improved or slowed down by additional elements of rare earths (Ce, La, Y, Hf).

However, the fabrication of conventional FeCrAl alloys is difficult and associated with high failures (eg, holes, shell strips) due to the high alloying elements of Cr and Al as well as rare earths. Due to the high oxygen affinity of Al and Cr, scales rapidly form during steelmaking processes. Complex melt management and forming as well as multiple surface treatments (belt grinding after continuous casting and hot rolling) are necessary to remove scales and shells and to ensure surface quality.

For applications close to the engine, the catalyst support materials must have good oxidation resistance at temperatures of more than 1000 ° C. A conventional material for close-coupled catalysts (3-way catalysts and DOC) is from the DIN CrAl 20-5 (Material No. 1.4767) Among other things, it has ~ 20% Cr and ~ 5% Al and rare earths. Of the Standard material 1.4767 Although shows good oxidation resistance at temperatures of 1000-1200 ° C, tends to diffusion bonding, which affects the flexibility of the components. The material is thus brittle at these high temperatures of 1000-1200 ° C, so that cracks can occur, which significantly shortens the life of such catalysts. This is undesirable to the consumer because such catalysts would have to be renewed after only a relatively short cycle.

In order to avoid the high losses in the conventional manufacturing process, native varieties have been developed in which a chromium steel containing rare earth elements is coated with aluminum or Al alloys. Such composites are then rolled and then diffusion annealed, with setting of suitable annealing parameters a homogeneous alloy similar to the Material no. 1.4767 or in another known Material with the number 1.4725 should arise. Such diffusion annealing is usually carried out at high temperatures of 900-1000 ° C for a sufficient period of time (> 10 h) and is therefore very expensive.

An aluminum-plated stainless steel foil with chromium content of 18 to 20 wt .-% and rare earth is, for example, from the DE 694 09 886 T2 known, wherein a diffusion annealing is necessary. An aluminum-coated, titanium-alloyed steel foil containing no chromium elements and having a cold-rolled, flame-aluminized surface is known, for example, from US Pat DE 35 19 492 A1 known. Other alternatives are chromium steel that is aluminum-free, free of Al and rare earth elements, and aluminum-alloyed with Al or an Al alloy ( DE 10 2012 111 954 B3 ). However, such a coated chromium steel is only suitable for applications at temperatures ≤ 850 ° C due to the lack of Al content in chromium steel, so it can only be used as a carrier material for the non-motor catalysts (diesel particulate filter and SCR).

The object of the invention is to provide a process for producing a steel foil and a coated foil which can be produced cost-effectively by the process and which dispenses with the use of rare earth elements which contain only small amounts of alloying elements which have high oxidation states. and corrosion resistance at temperatures of up to 1200 ° C, which has a functional surface in this temperature range, that is, an effect against diffusion bonding and a good coating adhesion, in which further dispenses with a diffusion annealing, thus the support material for close-coupled catalytic converters of internal combustion engines is suitable.

To solve this problem, the invention proposes the method that a 15 to 28 wt .-% chromium, 0.5-3.0 wt .-% aluminum and 0.5-2.5 wt .-% silicon-containing steel strip with a Strip thickness of up to 3 mm is coated on both sides with a layer of aluminum or an aluminum alloy with a silicon content of ≤ 16%, wherein the layers on both sides of an amount of at least 60 g / m ² and a coating thickness of at least 10 microns and wherein the coated Steel strip is then rolled to a thickness of 20 to 200 microns.

Advantageous developments of the method according to the invention are specified in the dependent claims 2 to 7.

In addition, the invention proposes a steel foil according to claim 8.

An advantageous embodiment of this steel foil is shown in claim 9.

In the process according to the invention is a 15 to 28 wt .-% chromium, 0.5-3.0 wt .-% aluminum and 0.5-2.5 wt .-% silicon-containing steel strip having a strip thickness of up to 3 mm coated on both sides by hot dipping or roll cladding in such a way with a layer of aluminum or an aluminum alloy with a silicon content of ≤ 16%, that the layers after the hot dipping treatment on both sides an amount of at least 60 g / m ² and a coating thickness of at least 10 microns, wherein the coated steel strip is then rolled to a thickness of 20 to 200 microns.

The process according to the invention makes it possible to produce steel foils which are particularly suitable as carrier material for close-coupled catalysts which are subjected to high-speed vibration at the temperature range from 1000 to 1200 ° C. The coated film has a high oxidation and corrosion resistance in the high temperature range of 1000-1200 ° C due to the thin aluminum oxide layer on the surface, with a thin layer of Fe-Al intermetallic phases good adhesion between the pads and the core material and anti-diffusion bonding and ensures good coating adhesion. Such a coated film also exhibits insensitivity to the action of sulfur-containing gases, which is often a problem by sulfur-containing fuels used in Asia, which produce gases containing sulfur in combustion.

Any suitable standard method known in the art, such as, in particular, fire aluminizing and roll cladding, may be used for the coating. A cost-effective and therefore economical process is the fire aluminizing, this preferably in a continuous coating process, preferably in a continuous in-line plant, for example in a continuous annealing and coating system, is performed. The continuous coating process is characterized by the fact that a consistently formed coating can be achieved economically with particularly high reliability.

In principle, the coated steel strip can be brought to its final dimensions in any rolling process, whereby the rolling process does not have to follow directly the hot-dip treatment. Preferably, the deformation is achieved by rolling and more preferably by cold rolling. In a preferred embodiment of the invention it is provided that the coated steel strip is rolled to its final dimensions to intermediate thicknesses of 0.08-0.15 mm before the rolling process and optionally after an intermediate annealing to the desired final thickness of 20-200 .mu.m, preferably to a Final thickness of 30-100 microns, is rolled. The degree of deformation achieved by the rolling process of the coated steel strip to the hot-dip aluminized film is at least 50%. A fire-aluminized film produced in this way is distinguished by the fact that it can be used directly in accordance with its intended use, without the need for further post-processing, such as, for example, diffusion annealing or preoxidizing. Also here are no further intermediate steps, which cause additional costs necessary. In the hot-dip aluminized film produced in this way, there are no tensions which, for example, could promote crack formation later in use in the temperature range from 1000 to 1200 ° C.

According to a development of the method according to the invention, it is provided that the finish-rolled film is annealed over a short period of time (<10 min). This embodiment of the invention also allows the production of critical components, since the film can be brought in a particularly simple manner in the given forms.

The film thus has a high degree of flexibility, which allows improved adaptation to given surfaces or contours, particularly in the production of catalysts.

As the core material for fire aluminizing, any steel having Cr content of 15-28 wt%, Al content of 0.5-3.0 wt%, and Si content of 0.5-2.5 wt. -% be used. Preferably, a band-shaped steel sheet is used. The core material is also free of rare earth elements, so that a particularly economical and thus cost-effective production of a hot-dip aluminized steel foil according to the invention is made possible.

As the coating material for the process according to the invention, aluminum or any aluminum alloy can be selected, the silicon content of which is in each case less than or equal to 16% by weight. In a preferred embodiment, the hot dip process is carried out in an aluminum alloy comprising 8-12% by weight of silicon and less than 5% by weight of iron. The film which can be produced in this way is characterized in a particular way by being able to be used as a carrier material for engine-related catalytic converters.

The process according to the invention for producing a hot-dip aluminized steel foil is illustrated below using an exemplary embodiment of a hot-aluminized steel foil produced by way of example in comparison with the films not produced according to the invention.

For the coating by fire aluminizing two different core materials with different Cr contents are used as not according to the invention (NEF1 and NEF2) and a core material as according to the invention (EF).

The chemical compositions of the two steel core materials and the aluminum overlays are reproduced in Tab. Tab. 1. Chemical composition of the materials selected in the exemplary embodiment (% by weight) Core material C Si Mn P S Cr al Ti Nb NEF1 ≤ 0.03 ≤ 1.00 ≤ 1.00 ≤ 0.040 ≤ 0.015 10.50 to 12.50 6 × (C + N) - 0.65 NEF2 ≤ 0.03 ≤ 1.00 ≤ 1.00 ≤ 0.040 ≤ 0.015 17.50 to 18.50 0.10-0.60 3 × C + 0.30-1.00 EF ≤ 0.12 0.70 to 1.40 ≤ 1.00 ≤ 0.040 ≤ 0.015 23.00 to 26.00 1.20-1.70 Al Pads Si = 10%; Fe = 3%; Rest al

The Cr-alloyed steel strip (NEF1 and NEF1) deviating from the method according to the invention and the Cr-Al-Si-alloyed steel strip (EF) according to the invention having a thickness of 1.0 mm were subjected to a hot-dip aluminizing process by means of the standard process in an 8-11% Si aluminum bath. The hot-dip aluminized steel strips were further rolled to thicknesses of 50 μm. From the rolling trials, two comparative samples V-NEF1 and V-NEF2 and a sample E-EF according to the invention were divided.

With increasing Cr contents in the core material, the oxidation resistance of the hot-dip aluminized steel foil is significantly improved. The ~ 11.5% Cr alloyed hot-dip aluminized steel foil (V-NEF1) is resistant to oxidation up to 750 ° C and with ~ 18% Cr alloyed foil (V-NEF2) up to 850 ° C. However, this is not sufficient for applications close to the motor (T> 1000 ° C). With additional alloying elements of Al and Si and increased Cr content in the core material, the steel foil produced according to the invention can be oxidation resistant up to at least 1150 ° C. The results can be summarized in Tab. 2. Tab. 2. Oxidation resistance of the produced in the exemplary embodiment hot-dip aluminized films. sample Film thickness [mm] material oxidation resistance V-NEF1 0.05 NEF1 ≤ 750 ° C V-NEF2 0.05 NEF2 ≤ 850 ° C E-FE 0.05 EF ≤ 1150 ° C

In addition to the high oxidation resistance, the steel foil produced according to the invention has a significantly higher surface roughness, which ensures an anti-diffusion effect and good coating adhesion, which makes it particularly suitable for the use of internal combustion engines as support material for the exhaust gas catalytic converters close to the engine.

The rough surface which brings about the stated advantages arises from the material composition of the steel foil according to the invention. In particular, by increasing the surface roughness, the life of the catalytic converters can be further improved.

Thus, the invention provides a coated steel foil which has both an operating temperature range which is higher than known coated steel foils, which moreover can be produced less expensively than the known foils and, in particular, has a significantly increased service life compared to known foils due to their anti-diffusion effect. In addition, the aluminum-coated steel foil according to the invention is free of rare earths and has only low aluminum contents. In addition, the steel foil according to the invention can be produced by a particularly simple and thus cost-effective production method, so that further cost advantages over known foils arise. The oxidation resistance of the steel foil according to the invention is at least comparable to the known steel foils.

The invention is not limited to the embodiments, but in the context of the disclosure often variable.

All individual and combination features disclosed in the description are considered to be essential to the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 69409886 T2 [0011]
• DE 3519492 A1 [0011]
• DE 102012111954 B3 [0011]

Cited non-patent literature

• DIN CrAl 20-5 (Material No. 1.4767) [0009]
• Standard material 1.4767 [0009]
• Material No. 1.4767 [0010]
• Material No.. 1.4725 [0010]

Claims (9)

Process for producing a hot-dip aluminized steel foil, characterized in that a steel strip comprising 15 to 28% by weight of chromium, 0.5-3.0% by weight of aluminum and 0.5 to 2.5% by weight of silicon has a steel strip Strip thickness of up to 3 mm is coated on both sides with a layer of aluminum or an aluminum alloy with a silicon content of ≤ 16%, wherein the layers on both sides of an amount of at least 60 g / m ² and a coating thickness of at least 10 microns and wherein the coated Steel strip is then rolled to a thickness of 20 to 200 microns. A method according to claim 1, characterized in that the steel strip is coated by hot dipping or roll cladding. A method according to claim 1 or claim 2, characterized in that the coated steel strip is rolled to intermediate thicknesses of 0.08 to 0.15 mm and then finish rolled, wherein particularly preferably the intermediate thickness rolled coated steel strip is annealed prior to finish rolling. Method according to one of claims 1 to 3, characterized in that the steel strip is annealed prior to coating. Method according to one of claims 1 to 4, characterized in that the finish-rolled steel foil is annealed. Method according to one of claims 1 to 5, characterized in that for the steel strip, a core material is used which has the following chemical composition: C: ≤ 0.15 wt .-%, Si: 0.5-2.0 wt. %, Mn: ≤ 1.20 wt%, P: ≤ 0.06 wt%, S: ≤ 0.018 wt%, Cr: 15-28 wt%, Al: 0.5-3 , 0 wt .-% and a balance iron with the usual impurities to an amount of 100 wt .-%. Method according to one of claims 1 to 6, characterized in that the steel strip is coated with an aluminum alloy having the following chemical composition: Si: 8-12 wt .-%, Fe: ≤ 5 wt .-%, AL: Rest. Hot-dip aluminized steel foil, preferably produced by a process according to one or more of claims 1 to 7, characterized by A 15 to 28 wt .-% chromium, 0.5-3.0 wt .-% aluminum and 0.5-2.5 wt .-% silicon, on both sides with a layer of aluminum or an aluminum alloy with a silicon content of ≤ 16% coated steel foil, and wherein - The coated steel foil has a thickness of 20 to 200 microns. Fire-aluminized steel foil according to claim 8, characterized in that the steel foil has a particularly high surface roughness.