JPH07275715A - Metal honeycomb for catalyst - Google Patents

Abstract

PURPOSE:To obtain an inexpensive metal honeycomb for a catalyst by a simple joining method by doing mutual diffusion joining or liquid phase joining of a flat plate and a corrugated plate consisting of ferrite stainless steel foil having specified Mo and forming a coating film of chrome oxide at high temp. CONSTITUTION:A flat plate and a corrugated plate consisting of ferrite stainless steel foil contg. 0.3-3% Mo and on which surface a coating film comprising primarily chrome oxide is formed at high temp. are subjected to mutual diffusion joining or liquid phase joining, allowing a metal honeycomb for a catalyst to be constituted. For example, in a honeycomb body housed in an outer cylinder 1, a diffusion stop material consisting essentially of titania is applied to a shadowed portion 3 when the honeycomb body is wound to prevent the diffusion joining from occurring. The part 2 indicated by a dotted line is the area to be joined. In this way, a foil material of low manufacturing cost is used, the joining is accelerated and oxidation resistance is secured, and also an assembling process is simplified to attain cost reduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal honeycomb used in a catalyst device for exhaust gas purification of an internal combustion engine or a catalyst device of a chemical plant.

[0002]

2. Description of the Related Art In recent years, there has been an increasing number of cases where a metal honeycomb is used in a catalyst device for exhaust gas purification of an internal combustion engine, especially a gasoline engine for automobiles. This is because the metal honeycomb has a larger opening ratio than the ceramic honeycomb that has been conventionally used, and the metal honeycomb has excellent durability even in an environment where the temperature rises and falls sharply. This metal honeycomb is made of stainless steel foil having excellent heat resistance, flat foil having a thickness of about 50 μm, and corrugated flat foil, which are superposed and bonded to each other.

As a stainless steel foil, Japanese Patent Publication No. 58-23
As described in Japanese Patent Publication No. 138, Japanese Patent Publication No. 54-15035, Japanese Patent Publication No. 56-96726, and the like,
An Fe-Cr-Al alloy foil excellent in oxidation resistance is used. These foils form an aluminum oxide film on the surface at high temperature and retain extremely excellent oxidation resistance. Further, as a joining method, there are brazing as described in JP-A-61-199574, resistance welding as described in JP-A-64-40180, and description in JP-A-54-13462. Various types such as laser beam welding and electron beam welding are used.

[0004]

An Fe-Cr-Al alloy foil used as a honeycomb material, for example, 20Cr-5.
Although the Al steel foil has excellent resistance to oxidation, its manufacturability is extremely poor and its manufacturing cost is high. In most cases, the actual use environment is about 800 ° C. at most, and the oxidation resistance of this material is often of excessive quality. Also, the brazing material used in brazing is expensive, and the process of performing this is complicated by coating the binder, adhering the brazing material, and vacuum heat treatment. Resistance welding is a low-productivity manufacturing method and is not suitable for mass production. Further, laser beam welding has the drawback that the welding equipment becomes extremely expensive.

US Pat. No. 4 as a relatively inexpensive joining method
There are also diffusion bonding methods described in the specification of No. 300956 and JP-A No. 1-270947, but when it is attempted to secure the oxidation resistance required for a catalyst substrate in a foil material, the material used is the above-mentioned material. In the Fe-Cr-Al-based alloy described in (1), an extremely thin aluminum oxide film is formed on the foil surface by reacting with a slight amount of oxygen sources (CO, H ₂ O) in the furnace in the vacuum heat treatment for diffusion bonding. Therefore, even if it is heated to a high temperature of 1200 ° C. or higher, these coatings become an obstacle to diffusion bonding, and the bonding must be locally and unstable. The SU described in JP-A 1-270947
Ordinary stainless steels such as S410L, 430, and 434 lack the oxidation resistance and high-temperature strength as a foil material, and thus lack heat resistance as a base material for automobile exhaust gas catalysts. Further, in the case of a catalyst for a diesel engine, sulfuric acid dew point corrosion may occur in the honeycomb due to the high concentration of S in the fuel. In this case, the above stainless steel lacks the corrosion resistance of the foil material and is used as a base material for a catalyst for automobile exhaust gas. Is insufficient.

The present invention has been made to solve the above-mentioned current problems, and provides an inexpensive metal honeycomb for catalyst by a relatively simple joining method using Cr-Mo type stainless steel foil. With the goal.

[0007]

The present invention has been made to achieve the above object, and the gist thereof is as follows. (1) A flat plate and a corrugated plate of a ferritic stainless steel foil containing 0.3 to 3% of Mo and forming a film mainly composed of chromium oxide at a high temperature by diffusion bonding or liquid phase bonding. Metal honeycomb for catalyst formed by joining. (2) The metal honeycomb for catalyst according to the above item (1), wherein the content of Al in the ferritic stainless steel foil is from the impurity level to 0.8% and an aluminum oxide film is not formed at a high temperature. (3) The chemical composition of the stainless steel foil is C:
0.2% or less, Si: 1% or less, Cr: 11 to 25%,
Mo: 0.3 to 3%, Al: impurity level to 0.8%,
The catalyst metal honeycomb according to item (1), wherein the balance is Fe and inevitable impurities. (4) The chemical composition of the stainless steel foil is C: 0.
2% or less, Si: 1% or less, Cr: 11 to 25%, M
o: 0.3 to 3%, Al: impurity level to 0.8%, and 0.01 to 0.2% in total of one or more rare earth elements including Y, and the balance being Fe and unavoidable. The catalyst metal honeycomb according to the above (1), which comprises impurities. (5) The chemical composition of the stainless steel foil is C:
0.2% or less, Si: 1% or less, Cr: 11 to 25%,
Mo: 0.3 to 3%, Al: impurity level to 0.8%,
Furthermore, Ti: 0.05-0.5%, Zr: 0.05-0.
5%, V: 0.03-0.5%, W: 0.5-3%
The metal honeycomb for a catalyst according to the above item (1), which contains any one or more of the above and the balance is Fe and inevitable impurities. (6) The chemical composition of the stainless steel foil is C: 0.
2% or less, Si: 1% or less, Cr: 11 to 25%, M
o: 0.3 to 3%, Al: impurity level to 0.8%, Y
1 or 2 or more of rare earth elements including
1 to 0.2%, Ti: 0.05 to 0.5%, Z
r: 0.05 to 0.5%, V: 0.03 to 0.5%,
W: 0.5 to 3% of any one kind or two or more kinds, and the balance is Fe and inevitable impurities, The metal honeycomb for catalyst according to claim 1.

The present inventors previously disclosed in Japanese Patent Application No. 5-24517 that diffusion while maintaining the oxidation resistance required for a foil material.
In order to improve the liquid phase bondability, it has been proposed to limit Al to a low level and add more than 1% to 3.5% of Si.
As a result of subsequent research, even if the Si content is 1% or less, the Mo content becomes 0.
The present invention has been made on the finding that the addition of 3 to 3% can improve the diffusion-liquid phase bonding while maintaining the required oxidation resistance. Further, the present inventors have found that addition of Mo is effective for sulfuric acid dew point corrosion, which may be a problem with a diesel catalyst, and arrived at the present invention. That is, the present invention, as a metal honeycomb foil material,
By using a stainless steel foil containing 0.3 to 3% Mo, diffusion or liquid phase bonding can be facilitated, and at the same time, necessary oxidation resistance can be secured, and further considering the use as a catalyst for a diesel, Al content is 0.8% to ensure sulfuric acid corrosiveness and not to form an alumina film that may be a hindrance when using relatively simple diffusion process or liquid phase bonding.
By suppressing the amount to the following, diffusion or liquid phase bonding can be smoothly performed at a lower temperature. The present invention, however, uses a Cr-Mo-based stainless steel foil, which is far more manufacturable than the Fe-Cr-Al alloy-based stainless steel foil, to perform a relatively simple process of diffusion or liquid phase bonding at a lower temperature. It is possible to provide a low-cost metal honeycomb.

Next, the reasons for limiting the components of the stainless steel foil of the honeycomb in the present invention will be described. Mo is Al or Si
In ferritic stainless steel that does not contain
It reinforces the oxidation resistance and improves the high temperature strength to improve the thermal fatigue resistance of the honeycomb, and at the same time, prevents the formation of the aluminum oxide film even in the steel material containing a low amount of aluminum and facilitates diffusion bonding. However, if it is less than 0.3%, the effect of addition thereof is insufficient, and if it exceeds 3%, the material deteriorates, so the addition amount was made 0.3 to 3%. In addition, sulfuric acid dew point corrosion may occur in the honeycomb with the catalyst for diesel.
In this case, adding Mo in an amount of 0.5% or more improves the dew point corrosion resistance. Si is an element that is inevitably contained, and if it is added in a higher amount, it has the effect of improving the oxidation resistance of the steel material and inhibiting the formation of an aluminum oxide film, thus facilitating diffusion bonding. However, in the present invention, Mo is Since it plays this role, the range of Si was made 1% or less. However, Cr is 18%
In the following cases, the Si content is preferably 0.6% or more in order to reinforce the oxidation resistance of the foil.

When 1% of Al is added to Cr-based stainless steel, it forms a protective film of aluminum oxide at high temperature to improve oxidation resistance, but in the present invention, it hinders diffusion or liquid phase bonding. Exclude. However, in order to shift the transformation point of the foil material to the higher temperature side than the operating temperature, within the range where the aluminum oxide film is not formed, that is, 0.8% or less Al
Can be added.

C lowers the melting point of the foil material to facilitate diffusion or liquid phase bonding, but if added in excess, it deteriorates the material, so the upper limit was made 0.2%. Cr is a basic element that maintains the oxidation resistance of stainless steel. If it is less than 11%, the oxidation resistance is insufficient, and if it exceeds 25%, the material becomes hard and the productivity deteriorates.

Since the rare earth element containing Y improves the oxidation resistance of the foil material, it is added as necessary in the present invention.
However, if it is less than 0.01% in total of one kind or two or more kinds thereof, there is no effect, and if it exceeds 0.2%, scratches are caused on the material, so 0.01 to 0.2% is set. Ti, Zr, V, and W each improve the high-temperature strength of the foil material, so they are added as necessary. Below the respective lower limits, the effect of addition is insufficient, and above the respective upper limits, the material becomes hard and the manufacturability deteriorates. Also, N
b can be added in an amount of 0.1 to 0.6% for improving the high temperature strength.

Table 1 shows examples of foil material compositions that can be used in the honeycomb of the present invention. Of the chemical composition of the foil material used in the present invention, Mn, P, S are not particularly specified,
There is no problem as long as they are contained in ordinary stainless steel.

The diffusion bonding referred to in the present invention means that the top surface of the corrugated foil and the contact surface of the flat foil are solid phase and mutual diffusion occurs to bond them. Further, the liquid phase bonding referred to in the present invention means that both surfaces become a liquid phase and are bonded by a melting point depressant such as graphite powder applied to the contact surface.

[0015]

[Table 1]

[0016]

[Examples] [Example-1] A foil having a thickness of 50 µm and having a chemical composition of A, G, N, and R in Table 1 was prepared, and a part of the foil was corrugated to obtain a corrugated foil. Outer diameter is 97mmφ and length is 10
A 0 mm honeycomb was prepared. Furthermore, as an outer cylinder, 19% Cr
Outer diameter is 100mmφ, made of stainless steel with a thickness of 1.5mm
A cylinder having a length of 100 mm was prepared, and the above honeycomb was inserted therein. This was heat-treated at 1200 ° C. for 30 minutes in a vacuum, and the outer cylinder, the outermost periphery of the honeycomb, and the corrugated plate and the flat plate in the honeycomb were diffusion-bonded to each other. At this time, if the corrugated foil and the flat foil are bonded to each other in the entire area of the honeycomb, thermal fatigue failure is likely to occur during use in the engine. Therefore, as shown in the cross-sectional view of FIG. A diffusion stop material containing titania as a main component was applied to the portion 3 shown when it was wound around the honeycomb so that diffusion bonding did not occur in this portion. In the figure, 1 is an outer cylinder accommodating the honeycomb body, and 2 is a region where the honeycomb bodies are joined. As a comparative example, a 50 μm thick foil material of SUS430 (16% Cr steel) was used and the honeycomb was inserted into the outer cylinder and vacuum heat treated in the same manner as above.

The exhaust capacity of these two types of metal substrates is 2000
Installed in the middle of the exhaust pipe of a cc, 4-cylinder engine, operated at full load at 5000 mpm, 800 ° C x 10
A cooling / heating test of heating for 20 minutes and cooling for 20 minutes with the engine stopped was performed 900 times. As a result, in the case of using the foils of A, G, N, and R in Table 1, no particular abnormality was observed after 900 thermal tests, while in the case of the comparative example using the foil of 20Cr-5Al. When checking the cold heat 600 times, the 3 in the center of the honeycomb
About two-thirds caused a deviation on the outlet side of the exhaust gas. As a result of the investigation, in the former honeycomb, the apex of the corrugated foil and the flat foil were surely diffusion-bonded, and the bonding had a planar spread.
In the latter case, the joining was performed only sparsely, and moreover, only the spot-like joining was performed even in the joined portion. That is, it is shown that the 20Cr-5Al foil was not sufficiently diffusion-bonded because the aluminum oxide film was formed during the vacuum heat treatment.

Example 2 A foil having a chemical composition of A, G, M, and S in Table 1 and having a thickness of 50 μm was prepared, and a metal substrate was prepared in the same manner as in Example 1. However, in this case, graphite powder was applied in a paste form to the tops of the corrugated foils to be joined, and the vacuum heat treatment was performed at 1150 ° C. At the same time, when a honeycomb for heat treatment was examined, it was found that when the graphite powder was applied, the foil surface was melted and liquid phase bonding was performed. As a comparative example, a 50 μm thick foil of SUS430 (16% Cr steel) was prepared and a metal substrate was prepared in the same manner as described above.

These two types of metal substrates were subjected to the cold heat test by the engine bench in the same manner as in Example-1. As a result, no special abnormality was found in the former metal substrate after 900 times of cold heat, but in the latter case, the foil on the honeycomb surface on the exhaust gas inlet side was partially blackened during 600 times of cold heat inspection. The test was discontinued because part of it had disappeared and disappeared. As a result of the investigation, although the latter metal-base honeycomb was sufficiently diffusion-bonded, the inside of the honeycomb was considerably oxidized and some cavities were formed. That is, SUS4 of the comparative example
It is shown that the foil No. 30 has insufficient oxidation resistance.

[Example 3] A foil having a chemical composition of A, B, G, and M shown in Table 1 and having a thickness of 50 µm was prepared, and a metal substrate was prepared in the same manner as in Example-1. SUS430 as a comparative example
A (16% Cr steel) foil having a thickness of 50 μm was prepared, and a metal substrate was prepared in the same manner as described above. 1 from these metal substrates
Carefully cut into strips of 0 mm x 10 mm x 50 mm to prepare test samples, and a sulfuric acid corrosion test was conducted to simulate the corrosive environment that occurs in the case of a catalyst carrier for a diesel engine. In the test, after carrying out a pre-oxidation treatment in the atmosphere of 700 ° C. × 1 hr, 50 cycles of a cycle test in which one cycle was 4 hr until dipping in a low pH solution containing sulfuric acid at 150 ° C. and drying were performed. As a result, no particular abnormality was observed in the metal substrate of the present invention after 50 cycles, but in the comparative example, the corrosion deterioration was severe and the holes penetrated the foil. That is, it is shown that the SUS430 foil of the comparative example lacks sulfuric acid corrosion resistance.

As shown in the above embodiments, the present invention provides a low-cost catalyst honeycomb by a simple joining method using a relatively inexpensive foil material, and greatly contributes to pollution control technology. Is.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an example of a metal base joint structure for carrying out the present invention.

[Explanation of symbols]

 1 outer cylinder 2 area where honeycomb is joined 3 area where honeycomb is not joined

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location C22C 38/18 (72) Inventor Hitoshi Ohta 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Corporation Ceremony Company Nagoya Steel Works

Claims (6)

[Claims] 1. A flat plate and a corrugated plate of a ferritic stainless steel foil containing 0.3 to 3% of Mo and forming a film mainly composed of chromium oxide at high temperature on the surface thereof by diffusion bonding or liquid phase. A metal honeycomb for a catalyst, characterized by being bonded by bonding. 2. The metal honeycomb for catalyst according to claim 1, wherein the content of Al in the ferritic stainless steel foil is at an impurity level of 0.8% and an aluminum oxide film is not formed at a high temperature. 3. The chemical composition of the stainless steel foil has a weight ratio of C: 0.2% or less, Si: 1% or less, Cr: 11-25%, Mo: 0.3-3%, Al: Impurity level. The metal honeycomb for catalyst according to claim 1, wherein the balance is Fe and unavoidable impurities. 4. The chemical composition of the stainless steel foil has a weight ratio of C: 0.2% or less, Si: 1% or less, Cr: 11-25%, Mo: 0.3-3%, Al: impurity level. ~ 0.8% and 0.01 to 0.2% in total of one or more rare earth elements including Y, and the balance being Fe and inevitable impurities. Metal honeycomb for catalyst. 5. The chemical composition of the stainless steel foil has a weight ratio of C: 0.2% or less, Si: 1% or less, Cr: 11-25%, Mo: 0.3-3%, Al: impurity level. To 0.8%, Ti: 0.05 to 0.5%, Zr: 0.05 to 0.5%, V: 0.03 to 0.5%, and W: 0.5 to 3%. The metal honeycomb for a catalyst according to claim 1, characterized in that it contains one or more kinds, and the balance is Fe and unavoidable impurities. 6. The chemical composition of the stainless steel foil has a weight ratio of C: 0.2% or less, Si: 1% or less, Cr: 11-25%, Mo: 0.3-3%, Al: Impurity level. ~ 0.8%, 1 or 2 or more of rare earth elements including Y in total of 0.
01: 0.2%, Ti: 0.05-0.5%, Zr: 0.05-0.5%, V: 0.03-0.5%, W: 0.5-3% 2. The catalyst metal honeycomb according to claim 1, wherein the catalyst metal honeycomb includes any one or more of the above, and the balance is Fe and inevitable impurities.