JP4941320B2 - Catalyst support for exhaust gas purification device and Fe-Cr-Al alloy foil used therefor - Google Patents

Description

  The present invention relates to a catalyst support having a honeycomb structure used for exhaust gas purification apparatuses such as automobiles and motorcycles, and more particularly to a catalyst support excellent in high temperature durability and an Fe—Cr—Al alloy foil used therefor.

  Fe-Cr-Al alloy foils are excellent in oxidation resistance at high temperatures, and are therefore used as catalyst carriers for exhaust gas purification apparatuses such as automobiles and motorcycles. As shown in FIG. 3, the catalyst carrier made of this alloy foil usually has a honeycomb structure in which flat foils and corrugated foils having a thickness of 0.10 mm or less are alternately wound in a cylindrical shape and spot-welded at the outer periphery. The surface of the alloy foil is covered with an alumina-based coating agent, and a noble metal catalyst for purifying exhaust gas is supported. In addition, the catalyst carrier made of such alloy foil has a smaller heat capacity and is easier to warm than ceramics, so it has excellent purification efficiency at the start-up, is resistant to impacts, and can be thinned to reduce weight and pressure reduction resistance. Because it has the advantage of being able to do so, it is also attracting attention from the aspect of improving engine performance and fuel efficiency.

However, in the case of a catalyst carrier made of an alloy foil, in order to ensure the strength of the honeycomb structure, a Ni-based brazing agent is usually applied to the contact portion between the flat foil and the corrugated foil, and then in a vacuum or a non-oxidizing atmosphere. A brazing process is performed to join by heating to ~ 1200 ° C. At this time, diffusion bonding occurs even at the part where the flat foil and the corrugated foil are in contact with each other, and the temperature change during use There is a problem that it becomes impossible to alleviate the thermal strain caused by this, and the carrier is likely to be deformed or broken, that is, the diffusion resistance is poor. Therefore, in Patent Document 1, the atomic% ratio satisfies the condition of N% / (Fe% + Cr% + Al% + O% + N%) ≧ 0.10, that is, resistance to having a high N concentration region on the surface layer. An Al-containing ferritic stainless steel sheet (corresponding to an Fe—Cr—Al alloy foil) excellent in diffusion bonding has been proposed.
Japanese Patent Laid-Open No. 2001-32051

  However, in the Fe-Cr-Al alloy foil described in Patent Document 1, it is difficult to control the region where the N concentration is high, the N concentration is too high or becomes uneven depending on the location, and the subsequent alumina whiskers and dense There is a problem that the formation of an oxide film is hindered and the coating property and the oxidation resistance of the coating agent are lowered, that is, the high temperature durability is inferior.

  The present invention has been made to solve such problems, and provides a catalyst carrier for an exhaust gas purifying apparatus excellent in diffusion bonding resistance and high-temperature durability, and an Fe-Cr-Al alloy foil used therefor The purpose is to do.

  As a result of detailed investigations on the catalyst carrier of the exhaust gas purification apparatus using the Fe—Cr—Al based alloy foil excellent in diffusion bonding resistance and high temperature durability, the present inventors have obtained the following knowledge.

  i) When the average roughness measured in the winding direction of the flat foil differs from the average roughness measured in the winding direction of the corrugated foil on the contact surface between the flat foil and corrugated foil constituting the honeycomb structure of the carrier, the contact area Can be reduced, and excellent diffusion bonding resistance can be obtained.

  ii) When the average roughness of the smaller foil and the average roughness of the larger foil are controlled within a predetermined range, it is possible to prevent a decrease in the coating property and oxidation resistance of the coating agent and to obtain excellent high temperature durability. .

  The present invention has been made based on such knowledge, and has a honeycomb structure in which flat and corrugated foils of Fe-Cr-Al alloy foil are alternately wound in a cylindrical shape, and the flat foil and the corrugated foil On the contact surface with the foil, the average roughness Ra (1) measured in the winding direction of one foil is 0.10 to 0.50 μm, and the average roughness Ra (2) measured in the winding direction of the other foil is Ra Provided is a catalyst carrier for an exhaust gas purifying apparatus characterized by being 0.30 to 0.80 μm larger than (1).

The catalyst carrier of the exhaust gas purification apparatus of the present invention, the average roughness Ra measured in the direction wound in a cylindrical shape is different between the front and back surfaces, the smaller average roughness Ra (S) is 0.10 to 0.50 μm, large It is preferable to use an Fe—Cr—Al based alloy foil characterized in that the average roughness Ra (L) is larger than Ra (S) by 0.30 to 0.80 μm.

  As the Fe-Cr-Al alloy foil of the present invention, for example, in mass%, C ≦ 0.02%, Si ≦ 0.3%, Mn ≦ 0.2%, P ≦ 0.05%, S ≦ 0.003%, N ≦ 0.02%, Ni ≦ 0.3%, Cr: 17.0 to 21.0%, Al: 2.6 to 7.0%, and at least one element of rare earth elements: 0.03 to 0.20% in total, and at least one element of Zr, Hf, Ti : Fe-Cr-Al alloy foil characterized by containing 0.02 to 0.15% in total and the balance being Fe and inevitable impurities is preferable.

  According to the present invention, it has become possible to produce a catalyst carrier for an exhaust gas purifying apparatus having excellent diffusion bonding resistance and high temperature durability. The catalyst carrier of the exhaust gas purifying apparatus of the present invention is suitable for exhaust gas purifying apparatuses such as automobiles and motorcycles.

  Hereinafter, the catalyst carrier of the exhaust gas purifying apparatus according to the present invention and the Fe—Cr—Al alloy foil used therein will be described in detail.

1) About the average roughness Ra measured in the winding direction at the contact surface between the flat foil and the corrugated foil FIG. 1 schematically shows the contact state of the contact surface between the flat foil and the corrugated foil in the catalyst carrier of the present invention. FIG. 2 schematically shows the contact state of the contact surface between the flat foil and the corrugated foil in the conventional catalyst carrier. As shown in FIG. 1, the average roughness measured in the winding direction of the flat foil is different from the average roughness measured in the winding direction of the corrugated foil on the contact surface between the flat foil and the corrugated foil in the catalyst carrier of the present invention. Therefore, the unevenness on the surface of the flat foil and the corrugated foil becomes difficult to mesh with each other, the contact area between the two foils is reduced, and the diffusion bonding resistance is improved. On the other hand, as shown in FIG. 2, in the conventional catalyst carrier, since the average roughness of the flat foil and the average roughness of the corrugated foil are almost the same, the irregularities on the surface of the flat foil and corrugated foil are easy to mesh, The contact area increases and the diffusion bonding resistance is inferior.

  At this time, in order to make it difficult to mesh the irregularities on the surface of the flat foil and the corrugated foil, contact occurs at the crests and valleys of the corrugated foil, so that the average roughness measured in the axial direction of the cylindrical carrier is more in the axial direction of the carrier. It is more effective to control the average roughness measured in the direction perpendicular to the winding direction.

  In addition, even if the average roughness of the flat foil and the corrugated foil is different, if the average roughness of both foils is large, the foil softens at high temperatures and receives a force due to thermal expansion, so that the large convex portion is easily deformed. As a result, the contact area is increased, the diffusion bonding resistance is deteriorated, the coating property and the oxidation resistance of the coating agent are lowered, and the high temperature durability is deteriorated. Furthermore, if the average roughness is large, the carrier may be deformed during the brazing process due to residual stress, and purification performance may be reduced. To prevent this, the smaller average roughness Ra (S) is set to 0.10 to 0.50 μm, and the larger average roughness Ra (L) is set to 0.30 from the smaller average roughness Ra (S). It needs to be increased by ~ 0.80μm. In order to obtain higher temperature durability, it is preferable that the sum of the smaller average roughness Ra (S) and the larger average roughness Ra (L) be 1.6 μm or less. Here, the average roughness Ra of the foil is measured according to JIS B 0601.

2) About Fe-Cr-Al alloy foil By using two types of Fe-Cr-Al alloy foils with different average roughness Ra for flat and corrugated foils, a contact surface with a small contact area is formed. However, as shown in Fig. 1, flat and corrugated foils were prepared using one type of Fe-Cr-Al alloy foil with different average roughness Ra on the front and back surfaces, and different Ra on the contact surface. Even if these surfaces are brought into contact with each other, the object of the present invention is achieved. In this case, since only one type of Fe—Cr—Al alloy foil needs to be produced, productivity can be improved and costs can be reduced.

  In addition, as the Fe-Cr-Al alloy foil having different average roughness Ra on the front and back surfaces, the mass%, C ≦ 0.02%, Si ≦ 0.3%, Mn ≦ 0.2%, P ≦ 0.05% for the following reasons , S ≦ 0.003%, N ≦ 0.02%, Ni ≦ 0.3%, Cr: 17.0-21.0%, Al: 2.6-7.0%, and at least one element among rare earth elements: 0.03-0.20% in total, and Zr An Fe—Cr—Al alloy foil containing at least one element of H, Hf, and Ti: 0.02 to 0.15% in total, with the balance being Fe and inevitable impurities is preferable.

C ≦ 0.02%
If the amount of C exceeds 0.02%, the workability of the alloy is lowered, making the production of the alloy foil difficult, and also reducing the oxidation resistance. Therefore, the C content is 0.02% or less, preferably 0.01% or less.

Si ≦ 0.3%
When the amount of Si exceeds 0.3%, the growth of the alumina oxide film is inhibited, and the adhesion of the oxide film is also reduced, and in particular, the oxidation resistance in the temperature range of 900 ° C. or higher is reduced. Therefore, the Si content is set to 0.3% or less.

Mn ≦ 0.2%
Similar to Si, if the Mn content exceeds 0.2%, the growth of the alumina oxide film is inhibited and the oxidation resistance is lowered. For this reason, the Mn content is 0.2% or less.

P ≦ 0.05%
If the amount of P exceeds 0.05%, the workability of the alloy is remarkably reduced, making the production of the alloy foil difficult, inhibiting the growth of the alumina oxide film, and reducing the oxidation resistance. Therefore, the P content is 0.05% or less, preferably 0.03% or less.

S ≦ 0.003%
As with P, when the S content exceeds 0.003%, the workability of the alloy is remarkably lowered, making the production of the alloy foil difficult, inhibiting the growth of the alumina oxide film, and reducing the oxidation resistance. For this reason, the S content is 0.003% or less, preferably 0.001% or less.

N ≦ 0.02%
As with C, when the N content exceeds 0.02%, the workability of the alloy is lowered, making the production of the alloy foil difficult, and the oxidation resistance also being lowered. Therefore, the N content is 0.02% or less, preferably 0.01% or less.

Ni ≦ 0.3%
Ni is an element that improves the high-temperature strength, but increases the thermal expansion coefficient of the alloy foil and decreases the durability of the carrier. Therefore, the Ni content is 0.3% or less, preferably 0.1% or less.

Cr: 17.0-21.0%
Cr is a basic element necessary for ensuring oxidation resistance and rigidity at high temperatures. If the amount is less than 17.0%, the oxidation resistance in a high temperature range exceeding 900 ° C. is not sufficient, and if it exceeds 21.0%, the workability of the alloy is lowered and the production of the alloy foil becomes difficult. For this reason, the Cr content is 17.0 to 21.0%.

Al: 2.6-7.0%
Al is an element that improves the oxidation resistance at high temperatures by forming an alumina oxide film on the foil surface. In order to obtain sufficient oxidation resistance, the Al content needs to be 2.6% or more. On the other hand, if the Al content exceeds 7.0%, the workability of the alloy is lowered, making it difficult to produce the alloy foil. For this reason, the Al content is set to 2.6 to 7.0%.

At least one element among rare earth elements: 0.03 to 0.20% in total
Rare earth elements, particularly Y and lanthanoids, are elements that improve the adhesion resistance of the alumina oxide film, suppress the diffusion of oxygen into the alloy foil, and effectively improve the oxidation resistance. If the total amount of rare earth elements is less than 0.03%, such an effect cannot be obtained.If it exceeds 0.20%, the grain boundary in the oxide film and the concentration at the interface between the oxide film and the alloy foil become significant, and the oxidation rate is reduced. Increase to reduce oxidation resistance. For this reason, at least one element among the rare earth elements is 0.03 to 0.20% in total, preferably 0.04 to 0.15%.

At least one element of Zr, Hf, Ti: 0.02 to 0.15% in total
At least one element of Zr, Hf, and Ti is an element that combines with C and N to improve the workability of the alloy and effectively improve the oxidation resistance by coexisting with a rare earth element. If at least one element of Zr, Hf, Ti is less than 0.02% in total, such an effect cannot be obtained, and if it exceeds 0.15%, as in the case of rare earth elements, the grain boundaries in the oxide film and Concentration at the interface between the oxide film and the alloy foil becomes significant, increasing the oxidation rate and lowering the oxidation resistance. For this reason, at least one element of Zr, Hf, and Ti is 0.02 to 0.15% in total, preferably 0.03 to 0.10%.

  The balance is Fe and inevitable impurities, but Ta, W, Mo, V, Ca, Mg, B, etc. can be added in the following range.

At least one element of Ta, W, Mo, V: 2% or less in total
Ta, W, Mo, and V are effective in improving the high-temperature strength, but reduce the oxidation resistance. Therefore, the total of at least one element of Ta, W, Mo, and V is 2% or less.

At least one element of Ca, Mg, B: 0.006% or less in total
Ca, Mg, and B improve the hot workability and toughness and are effective in improving the manufacturability of the alloy foil, but reduce the oxidation resistance. Therefore, the total of at least one element of Ca, Mg, and B is 0.006% or less.

  The Fe-Cr-Al alloy foil of the present invention is a conventional method, for example, alloy steel having the above component composition is melted in a converter or electric furnace, refined with VOD, AOD, etc. It is made into a slab by continuous casting, heated to 1050-1250 ° C., hot rolled to form a hot rolled sheet, and after scale removal, annealing and cold rolling or warm rolling are repeated a plurality of times, and an alloy foil having a predetermined thickness is obtained. It can manufacture by the method to do.

  At this time, the average roughness Ra of the front and back surfaces of the alloy foil can be adjusted by changing the surface roughness of the upper and lower work rolls in cold rolling or warm rolling, but the surface roughness can be adjusted only by pickling or grinder. It can also be adjusted, or can be adjusted by appropriately combining rolls, pickling, and grinders.

Alloys No. 1 and 2 with chemical components shown in Table 1 were melted in a 100 kg small vacuum melting furnace to form an alloy lump, then heated to 1200 ° C and hot rolled in the temperature range of 900 to 1200 ° C A hot-rolled sheet having a thickness of 3 mm was used. Next, this hot-rolled sheet was repeatedly annealed at 900 to 1000 ° C. and cold-rolled to produce an alloy foil having a sheet thickness of 0.05 mm. At this time, change the surface roughness of the upper and lower work rolls in the final pass at the time of the last cold rolling and the pass before it, and perpendicular to the rolling direction of the front and back surfaces (surface 1, surface 2) of the alloy foil The average roughness (Ra, Rz) in the direction was changed as shown in Table 2. A flat foil cut into a size of 80 mm in the rolling direction and 300 mm in the width direction from the obtained alloy foil, and a flat foil of the same size with a gear-shaped roll with a pitch of 5 mm in the longitudinal direction (300 mm direction) and a height of 3 mm After corrugated foil is wound under the conditions shown in Table 2 and wound in a cylindrical shape in the longitudinal direction, the outer periphery is spot welded to have a honeycomb structure as shown in FIG. 3 having a diameter of 20 mm and a height of 80 mm. Catalyst carriers No. 1 to 15 were produced. The produced catalyst carrier was evaluated for diffusion bonding resistance and high temperature durability by the following methods.
Diffusion bonding resistance: The prepared catalyst carrier was heat-treated in vacuum at 1150 ° C for 1 hour, then only the outer spot welded part was cut with a cutter, and flat foil and corrugated foil were pulled in the outer circumferential direction to dismantle A test to (separate) was performed. At this time, three test pieces were prepared under each condition, and if the number of pieces that could disassemble 80% or more of the length of the alloy foil was two, the diffusion-bonding resistance was extremely good (◯), and even one piece. It was evaluated as good (Δ) if it was 0, and bad (×) if it was 0. The case of (circle) and (triangle | delta) satisfy | filled the objective of this invention.
High temperature durability: Oxidation test of the prepared catalyst support at 1150 ° C for 150 hours in the atmosphere. If the amount of change in the height of the support exceeds 5% compared to the initial height, the high temperature durability is Poor (x), 3-5%, high temperature durability is good (△), less than 3%, high temperature durability is very good (○), ○, △ satisfy the purpose of the present invention It was said that

  The results are shown in Table 2. It can be seen that the catalyst carrier of the present invention has good evaluation with respect to both diffusion-bonding resistance and high-temperature durability, with good or no evaluation, and no x.

It is a figure which shows typically the contact state of the contact surface of flat foil and corrugated foil in the catalyst carrier of this invention. It is a figure which shows typically the contact state of the contact surface of the flat foil and corrugated foil in the conventional catalyst support | carrier. It is a figure which shows typically an example of the catalyst support | carrier which has the honeycomb structure which consists of metal foil.

Claims (3)

  Fe-Cr-Al alloy foil has a honeycomb structure in which flat foil and corrugated foil are alternately wound in a cylindrical shape, and measured in the winding direction of one foil at the contact surface between the flat foil and corrugated foil The average roughness Ra (1) is 0.10 to 0.50 μm, and the average roughness Ra (2) measured in the winding direction of the other foil is 0.30 to 0.80 μm larger than the Ra (1). Catalyst carrier for exhaust gas purification device. The average roughness Ra measured in the direction of winding in a cylindrical shape is different between the front and back surfaces, the smaller average roughness Ra (S) is 0.10 to 0.50 μm, and the larger average roughness Ra (L) is the Ra 2. The Fe—Cr—Al alloy foil used for the catalyst carrier of the exhaust gas purifying apparatus according to claim 1, wherein the Fe—Cr—Al alloy foil is 0.30 to 0.80 μm larger than (S).   % By mass, C ≦ 0.02%, Si ≦ 0.3%, Mn ≦ 0.2%, P ≦ 0.05%, S ≦ 0.003%, N ≦ 0.02%, Ni ≦ 0.3%, Cr: 17.0 to 21.0%, Al: 2.6 to 7.0% and at least one element of rare earth elements: 0.03 to 0.20% in total, and at least one element of Zr, Hf, Ti: 0.02 to 0.15% in total, the balance being Fe and inevitable 3. The Fe—Cr—Al based alloy foil according to claim 2, comprising impurities.

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