JP2009046718A - Alloy foil and catalyst carrier for exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alloy foil for a catalyst carrier in which the increasing amount of oxidization and deformation volume at high temperature are reduced compared with the conventional Fe-20Cr-5Al series alloy, and to provide a catalyst carrier for an exhaust gas purifying apparatus using the alloy foil. <P>SOLUTION: The alloy foil has a componential composition including, by mass, ≤0.015%C, ≤0.3% Si, ≤0.2% Mn, ≤0.05% P, ≤0.003% S, ≤0.015% N, 19.0 to 21.0% Cr, 4.6 to 7.0% Al, 0.03 to 0.20% La, one or two kinds selected from Zr and Hf by 0.02 to 0.15% in total and 1.5 to 3.5% W, and further including <0.15% Nb, <0.20% Mo, <0.5% Ta, <0.20% Ni and <0.10% Ti. Also a catalyst carrier for an exhaust gas purifying apparatus is provided by using the alloy foil. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an alloy foil suitable for use in a member that requires high-temperature strength (rigidity) and oxidation resistance, such as a metal honeycomb catalyst carrier of an exhaust gas purifying apparatus for automobiles and motorcycles, and the alloy foil. The present invention relates to a catalyst carrier for an exhaust gas purification device.

  Fe-Cr-Al alloys are excellent in oxidation resistance at high temperatures, and are therefore used in exhaust gas purifying members (catalyst carriers, various sensors, etc.) for internal combustion engines such as automobiles, motorcycles, and motor boats. In addition, it is also used as a heater, a gas burner, a heating furnace member, or a heater heating element, taking advantage of its high electrical resistivity.

  Among the above applications, the catalyst carrier of the exhaust gas purification device for automobiles and motorcycles has a cylindrical honeycomb structure using an alloy foil having a plate thickness of 0.10 mm or less. Continues to be subjected to engine vibration and impact from running for a long time. For this reason, the alloy foil is required to have a high level of high-temperature strength (rigidity) and oxidation resistance because of the need to ensure the long-term durability of the catalyst carrier. This is because when the alloy foil is consumed or embrittled due to oxidation at a high temperature, the carrier is broken or deformed, and the purification performance is significantly reduced.

  Furthermore, with the recent tightening of exhaust gas regulations, in order to further improve the purification efficiency, the carrier installation location is changed to a position where the exhaust gas and the catalyst are in contact with each other at a higher temperature than before, or the structure of the carrier is changed. Design changes and modifications such as a honeycomb structure provided with a large number of openings have been made. As a result, the load on the material constituting the carrier is in the direction of increasing as compared with the conventional case, and the demand for improvement with respect to high-temperature rigidity and oxidation resistance is further increased.

Several proposals have been made for alloy foil materials having both high-temperature rigidity and oxidation resistance. For example, in Patent Document 1, repeated thermal stress at high temperature, in which Young's modulus is increased by adding Ni, Mo and W to an Fe-20Cr-5Al-based alloy to which Zr, Hf and rare earth elements are added, and Ferritic stainless steel that can be used for applications requiring resistance to oxidation and high mechanical strength is disclosed in Patent Document 2 as Fe-20Cr-5Al alloy with Y misch added, Nb and An alloy foil for a metal carrier is disclosed in which the proof strength and the oxidation resistance at high temperature are improved by adding / or Ta or, further, Mo and / or W. Furthermore, in Patent Document 3, a predetermined amount of Ta is added with respect to C + N to an Fe-20Cr-5Al alloy to which La, Ce, Pr, and Nd are added, and Mo, W, and Nb are added. Discloses a heat-resistant stainless steel foil having improved durability at high temperatures.
JP-T-2005-504176 JP 05-277380 A Japanese Patent Publication No. 06-104879

  A material in which one or more of Nb, Ta, Mo, or W as a strengthening element is added to an Fe-20Cr-5Al-based alloy as disclosed in Patent Documents 1 to 3 to increase high-temperature strength and Young's modulus. Many other proposals have been made. However, since none of these materials has been studied on the suppression of the increase in oxidation and the suppression of the deformation amount, these materials are of an insufficient level to satisfy the high demand for oxidation resistance in recent years.

  Therefore, in order to develop a catalyst carrier with high purification efficiency that can sufficiently meet the exhaust gas regulations that will be further strengthened in the future, There is a need to develop a material (alloy foil) that is more durable than an Fe-20Cr-5Al-based alloy, that is, has a small amount of oxidation increase and a small amount of deformation (dimensional change). Also, high rigidity is a necessary requirement for reducing the amount of deformation.

Therefore, the object of the present invention is superior to conventional Fe-20Cr-5Al-based alloys in high-temperature durability even under higher-temperature usage environments than before, that is, with a small amount of oxidation increase and deformation (dimensional change), and rigidity. It is an object to provide a catalyst carrier for an exhaust gas purifying apparatus using the material (alloy foil) for the catalyst carrier having a high level. The specific target characteristics of the alloy foil that the present invention aims to develop are that the increase in oxidation when the oxidation test at 1100 ° C. × 500 hr in the atmosphere is 15 g / m ² or less, and the deformation at this time is 5% or less. Furthermore, the Young's modulus at 900 ° C. is 110 GPa or more.

  In order to achieve the above-mentioned problems, the inventors added Nb, Mo, W and Ta as elements having an effect of increasing the Young's modulus at a high temperature to the Fe—Cr—Al-based alloy alone or in combination. The effect on the rate and high temperature durability (oxidation increase and deformation) was investigated in detail. As a result, it has been found that the effect of increasing the Young's modulus at a high temperature is great. However, regarding oxidation resistance, when Nb, Mo and Ta are added in a predetermined amount or more, even if an oxidation resistance improving element such as La, Zr, or Hf is added, abnormal oxidation occurs at a temperature of 900 ° C. or higher. It was found that oxidation resistance deteriorated remarkably, particularly at high temperatures exceeding 1000 ° C.

  Therefore, in order to obtain high durability (oxidation resistance, deformation resistance) while securing rigidity even at a higher use temperature than before, after adding W as a strengthening (improvement of Young's modulus) element, Other impurity elements that inevitably contain the contents of Nb, Mo, Ta that are harmful to the improvement of oxidation resistance by adding La, Zr, and Hf, and that are harmful to the improvement of oxidation resistance. It was found that it was necessary to strictly limit the composition range to a predetermined amount or less, and the present invention was developed.

  That is, the present invention includes C: 0.015 mass% or less, Si: 0.3 mass% or less, Mn: 0.2 mass% or less, P: 0.05 mass% or less, S: 0.003 mass% or less, N: 0.00. 015 mass% or less, Cr: 19.0 to 21.0 mass%, Al: 4.6 to 7.0 mass%, La: 0.03 to 0.20 mass%, one or two selected from Zr and Hf Total: 0.02 to 0.15 mass%, W: 1.5 to 3.5 mass%, Nb: less than 0.15 mass%, Mo: less than 0.20 mass%, Ta: 0.5 mass% Less than, Ni: less than 0.20 mass% and Ti: less than 0.10 mass%, and the balance is an alloy foil having a component composition composed of Fe and inevitable impurities.

  Moreover, this invention is C: 0.015 mass% or less, Si: 0.3 mass% or less, Mn: 0.2 mass% or less, P: 0.05 mass% or less, S: 0.003 mass% or less, N: 0.00. 015 mass% or less, Cr: 19.0 to 21.0 mass%, Al: 4.6 to 7.0 mass%, La: 0.03 to 0.20 mass%, one or two selected from Zr and Hf Total: 0.02 to 0.15 mass%, W: 1.5 to 3.5 mass%, Nb: less than 0.15 mass%, Mo: less than 0.20 mass%, Ta: 0.5 mass% Exhaust gas purifying apparatus using an alloy foil having a composition of less than Ni, less than 0.20 mass% and less than Ti: 0.10 mass%, the balance being Fe and inevitable impurities A catalyst support.

  According to the present invention, it is possible to obtain an alloy foil that has high rigidity even at a high temperature of 900 ° C. or higher and excellent oxidation resistance and deformation resistance even at a high temperature of 1100 ° C. Therefore, the alloy foil of the present invention is suitable for use as a catalyst carrier for exhaust gas purifying apparatuses such as automobiles and motorcycles used under severe exhaust gas regulations in the future.

In order to obtain high durability (oxidation resistance, deformation resistance) while ensuring high rigidity even in a use environment at a higher temperature than before, the present invention provides W as a strengthening (Young's modulus improvement) element. In addition, La, Zr, and Hf are added to improve the oxidation resistance, and the contents of Nb, Mo, Ta, which are harmful to the improvement of the oxidation resistance, are inevitably mixed in production. It is characterized in that the composition range is limited to a predetermined amount or less including other impurity elements.
Hereinafter, the component composition that the alloy foil of the present invention should have will be specifically described.

C: 0.015 mass% or less, N: 0.015 mass% or less When both C and N are contained excessively, not only does the processability deteriorate and the production of the alloy foil becomes difficult, but also the oxidation resistance deteriorates. Let Therefore, the contents of C and N are each 0.015 mass% or less. Desirably, it is 0.010 mass% or less.

Si: 0.3 mass% or less Si, when contained in excess, inhibits the growth of an Al ₂ O ₃ oxide film that serves as a protective film and plays an important role. Moreover, to reduce the adhesion of the Al ₂ O ₃ oxide film, in particular, it deteriorates the oxidation resistance at 900 ° C. or higher. Therefore, the Si content is set to 0.3 mass% or less. Preferably it is 0.2 mass% or less.

Mn: 0.2 mass%
When Mn is contained excessively, like Si, Mn is a component that inhibits the growth of the Al ₂ O ₃ oxide film and deteriorates the oxidation resistance. Therefore, the Mn content is 0.2 mass% or less. Preferably it is 0.1 mass% or less.

P: 0.05 mass% or less, S: 0.003 mass% or less P and S are inevitably mixed impurity components, both of which deteriorate the workability and make it difficult to produce an alloy foil. In addition, it is an element that inhibits the growth of the Al ₂ O ₃ oxide film and deteriorates the oxidation resistance. Therefore, in the present invention, it is desirable to reduce as much as possible, P is 0.05 mass% or less, and S is 0.003 mass% or less. Preferably, P is 0.03 mass% or less, and S is 0.001 mass% or less.

Cr: 19.0 to 21.0 mass%
Cr is a basic element necessary for ensuring oxidation resistance and rigidity at high temperatures. If it is less than 19.0 mass%, it is insufficient to satisfy the target oxidation resistance and Young's modulus of the present invention. On the other hand, if it exceeds 21.0 mass%, the workability deteriorates, so the alloy foil is rolled. Since it becomes difficult to carry out, and durability after corrugation processing for forming a honeycomb is deteriorated, the range is set to 19.0 to 21.0 mass%. Preferably, it is in the range of 19.5 to 20.5 mass%.

Al: 4.6-7.0 mass%
Al is an element that forms a highly protective Al ₂ O ₃ oxide film on the surface of the alloy foil and improves the oxidation resistance at high temperatures. However, when the Al content is less than 4.6 mass%, when the alloy foil is 0.1 mm, sufficient oxidation resistance cannot be obtained due to early consumption of Al due to oxidation. On the other hand, when Al is added excessively, workability deteriorates, rolling and passing through a production line become difficult, and high temperature strength and Young's modulus are reduced. Therefore, the upper limit of Al is 7.0 mass%. In addition, it is preferable that it is the range of 5.0-6.4 mass% from a viewpoint of ensuring the balance with oxidation resistance, rigidity, and manufacturability.

W: 1.5-3.5 mass%
W has an action of improving strength and Young's modulus at high temperatures, and is an extremely important component in the present invention. In particular, W is the most suitable strengthening element for the alloy foil of the present invention because it has a smaller adverse effect on the oxidation resistance compared to Nb, Mo, and Ta. In order to set the Young's modulus at 900 ° C. to 110 GPa or more, it is necessary to add W by 1.5 mass% or more. However, if it exceeds 3.5 mass%, workability and oxidation resistance are lowered. Therefore, in this invention, W shall be the range of 1.5-3.5 mass%. Preferably, it is in the range of 1.5 to 2.5 mass%.

La: 0.03 to 0.20 mass%, and one or two of Zr and Hf are combined: 0.02 to 0.15 mass%
La, Zr, and Hf are extremely important elements in the present invention that enhance the oxidation resistance of Fe—Cr—Al alloys at high temperatures. That is, La is an element that improves the adhesion between the Al ₂ O ₃ oxide film and the alloy and improves the oxidation resistance by suppressing the inward diffusion of oxygen. Zr and Hf are elements that improve workability by binding and fixing with C and N. Moreover, by adding simultaneously with La, there exists a function which raises the oxidation resistance improvement effect of La further. However, if the content of La is less than 0.03 mass% and the total content of Zr or Hf is less than 0.02 mass%, the excellent oxidation resistance aimed by the present invention cannot be obtained, When these elements are added excessively, the grain boundary in the oxide film and the concentration at the interface between the oxide film and the base iron become excessive, and on the contrary, the oxidation rate is increased, so that the oxidation resistance is lowered. Therefore, in the present invention, La is added in the range of 0.03 to 0.20 mass%, and one or two of Zr and Hf are added in the range of 0.02 to 0.15 mass% in total. Preferably, the range is La: 0.04 to 0.15 mass%, and the total of Zr and Hf: 0.03 to 0.10 mass%.

Nb: less than 0.15 mass%, Mo: less than 0.20 mass%, Ta: less than 0.5 mass%, Ni: less than 0.20 mass% and Ti: less than 0.10 mass% Nb, Mo and Ta Ni and Ti are components that have the effect of increasing the Young's modulus and have the effect of increasing the strength at high temperatures. However, if Nb and Mo are added in excess, the amount of oxidation increases, and Ta, Ni, and Ti increase the thermal expansion coefficient of the alloy by concentrating on the surface layer of the steel, thereby reducing material consumption and deformation. Promotes and shortens carrier life. In particular, if these components are added excessively, the oxidation increase when the oxidation test at 1100 ° C. × 500 hr in the air exceeds 15 g / m ² or the deformation (dimension increase) exceeds 5%. When a honeycomb carrier is produced from these alloy foils, the purification function is deteriorated at an early stage due to deformation or fracture of the alloy foil. Therefore, the upper limit of the content of these components must be strictly controlled, Nb is less than 0.15 mass%, Mo is less than 0.20 mass%, Ta is less than 0.5 mass%, Ni is less than 0.20 mass%, and Ti is limited to less than 0.10 mass%. Desirably, Nb, Mo, and Ti are less than 0.05 mass%, Ta is less than 0.1 mass%, and Ni is less than 0.15 mass%.

  In addition to the above essential components, the alloy foil of the present invention may contain Ca, Mg, and B as elements that reduce the adverse effects of S that are harmful to oxidation resistance. Ca, Mg, and B suppress S from concentrating on the grain boundaries and the surface layer of the alloy foil, improve high-temperature toughness, and improve resistance to oxidation such as La, Zr, and Hf. By coexisting, there is an effect of further improving oxidation resistance. In order to obtain the effect, it is preferable to contain one or more of Ca, Mg and B in a total amount of 0.0010 mass%. However, if the content exceeds 0.0080 mass%, the workability and the oxidation resistance are deteriorated. Therefore, when these elements are added, Ca, Mg and B are desirably in a range of 0.0010 to 0.0080 mass% in total. More preferably, it is 0.0020 to 0.0060 mass%. Desirable ranges of the individual elements are 0.0003 to 0.0040 mass% for Ca, 0.0020 to 0.0030 mass% for Mg, and 0.0005 to 0.0050 mass% for B.

  Further, in addition to the above components, a trace amount of rare earth elements Ce, Nd, Sm and Y may be added to improve oxidation resistance. However, a significant improvement in oxidation resistance cannot be expected, and depending on the amount added, it may deteriorate instead. In addition, the raw materials for these elements are expensive and difficult to control the composition, resulting in a significant increase in manufacturing costs. Therefore, when adding rare earth elements other than La, it is desirable that the total be 0.02 mass% or less, more preferably 0.01 mass% or less.

Next, the manufacturing method of the alloy foil which concerns on this invention is demonstrated.
Since the alloy foil of the present invention is designed in consideration of workability, the alloy foil can be sufficiently manufactured by applying a conventional manufacturing method, and is not particularly limited. For example, steel containing the above component composition is melted in a converter, electric furnace or the like, secondarily refined by VOD or AOD, and then made into a steel slab by ingot-bundling rolling or continuous casting, and then , Heated to 1050 to 1250 ° C. and hot-rolled to obtain a hot-rolled steel sheet. Subsequently, the scale on the surface of the steel sheet is removed by pickling, shot blasting, grinding, etc., and annealing and cold rolling are repeated a plurality of times to obtain an alloy foil having a predetermined sheet thickness (0.03 to 0.1 mm). preferable.

  In addition, in order to ensure desired oxidation resistance, it is important for the alloy foil of the present invention to control the surface roughness of the alloy foil in addition to controlling the component composition within an appropriate range. When the thickness of the alloy foil is 0.10 mm or less, when the surface roughness is large, that is, when the surface area is increased, oxidation is accelerated by use at a high temperature, and Al is oxidized and consumed in a short time. It is easy to wake up. For this reason, it is desirable to control the surface roughness of the alloy foil so as to be as small as possible without causing problems in manufacturing. Specifically, in order to ensure the target oxidation resistance of the present invention, the arithmetic average roughness Ra of the alloy foil surface is 0.3 μm or less, and the ten-point average roughness Rz is 1.5 μm or less. Preferably there is. In particular, when the plate thickness is 0.05 mm or less, Ra is preferably 0.2 μm or less and Rz is preferably 1.2 μm or less. Here, Ra, which is a parameter for the roughness, is defined by JIS B0601 (2001), and Rz is defined by JIS B0601 (1998).

  No. shown in Table 1. An alloy having a component composition of 1 to 24 is melted in a vacuum melting furnace to form a 50 kg steel ingot, and then the steel ingot is heated to 1200 ° C. and then hot-rolled in a temperature range of 900 to 1200 ° C. A hot-rolled steel sheet with a thickness of 3 mm is obtained, and then the surface scale is removed, and one or two annealings and cold rolling are performed to obtain a cold-rolled steel sheet with a thickness of 1 mm, and further, annealing at 950 to 1100 ° C Then, cold rolling was performed to obtain an alloy foil having a final thickness of 0.05 mm, a surface roughness Ra of 0.3 μm or less, and an Rz of 1.5 μm or less.

The hot-rolled steel sheet and alloy foil obtained as described above were subjected to the following test.
<Measurement of Young's modulus>
A hot-rolled steel sheet having a thickness of 3 mm during the production was annealed at a temperature of 950 to 1100 ° C. and sufficiently recrystallized, and then a specimen having a thickness of 2 mm × width: 10 mm × length: 60 mm was cut out. After finishing all the end faces to smooth surfaces, Young's modulus at 900 ° C. was measured using a bending resonance method. The measurement results of Young's modulus were evaluated as x for less than 110 MPa, ◯ for 110 MPa or more and less than 120 MPa, and ◎ for 120 MPa or more.
<Evaluation of oxidation resistance>
The alloy foil having a thickness of 0.05 mm obtained as described above was further annealed at 1050 to 1200 ° C. and sufficiently recrystallized, and then used for measuring the amount of increase in oxidation: width: 20 mm × length: 30 mm. Three test pieces having dimensions of width: 50 mm × length: 50 mm were taken from each alloy foil for measuring the amount of deformation, and for measuring the amount of deformation. Next, using these test pieces, an oxidation test was performed by heating in an air atmosphere furnace at 1100 ° C. for 500 hours, and the amount of increase in oxidation and the amount of deformation were measured.
Oxidation weight gain, and the weight change before and after the oxidation test was divided by the initial surface area, determined the oxidation weight gain per unit area, three mean values, 15 g / m ² exceeds × a, 10 g / m ² greater than 15 g / m ² or less a 〇, was evaluated 10g / ^{m 2} or less ◎ with. In measuring the weight change before and after the test, the scale peeled from the test piece was also collected and added to the oxidation increase. In addition, the amount of deformation is measured at three locations for each test piece at three locations, the amount of dimensional change (%) is determined, the average value of the three test pieces is obtained, and the average amount of deformation is 5%. Exceeding item was rated as x, exceeding 3% and 5% or less, and ◯ and 3% or less.

  The results of the above measurements are shown together in Table 1. From this result, the alloy No. in which the component composition of the alloy is within the scope of the present invention is shown. In the alloys 1 to 9, the evaluation of Young's modulus at high temperature, the amount of oxidation increase, and the amount of deformation are all good or better, indicating that the strength and durability at high temperature are excellent. In contrast, Alloy No. whose component composition is outside the scope of the present invention. For the alloys of 10 to 24, one or more of the Young's modulus, the amount of increase in oxidation, and the amount of deformation is evaluated as x. From these results, it can be seen that the alloy foil of the present invention has preferable characteristics as a catalyst carrier for an exhaust gas purifying device used in a higher temperature environment than the conventional material.

  The alloy foil of the present invention is suitable as a member for exhaust gas purification devices such as motorcycles and automobiles, particularly as an alloy foil for a metal metal carrier for a catalyst. Furthermore, since the alloy having the component composition of the present invention is excellent in oxidation resistance and rigidity at high temperatures, it is not only used as a foil, but also for heater heating elements, stoves, burners and heating furnaces used in plate thicknesses exceeding 0.10 mm. It can also be used for members.

Claims (2)

C: 0.015 mass% or less, Si: 0.3 mass% or less, Mn: 0.2 mass% or less, P: 0.05 mass% or less, S: 0.003 mass% or less, N: 0.015 mass% or less, Cr: 19.0 to 21.0 mass%, Al: 4.6 to 7.0 mass%, La: 0.03 to 0.20 mass%, a total of one or two selected from Zr and Hf: 0.02 -0.15 mass%, W: 1.5-3.5 mass%, Nb: less than 0.15 mass%, Mo: less than 0.20 mass%, Ta: less than 0.5 mass%, Ni: 0.00. An alloy foil having a composition of less than 20 mass% and Ti: less than 0.10 mass%, with the balance being Fe and inevitable impurities. C: 0.015 mass% or less, Si: 0.3 mass% or less, Mn: 0.2 mass% or less, P: 0.05 mass% or less, S: 0.003 mass% or less, N: 0.015 mass% or less, Cr: 19.0 to 21.0 mass%, Al: 4.6 to 7.0 mass%, La: 0.03 to 0.20 mass%, a total of one or two selected from Zr and Hf: 0.02 -0.15 mass%, W: 1.5-3.5 mass%, Nb: less than 0.15 mass%, Mo: less than 0.20 mass%, Ta: less than 0.5 mass%, Ni: 0.00. A catalyst carrier for an exhaust gas purifying apparatus using an alloy foil having a composition of less than 20 mass% and Ti: less than 0.10 mass%, the balance being Fe and inevitable impurities.