JP3613891B2 - Method for producing Fe-Cr-Al alloy foil for exhaust gas purification catalyst carrier - Google Patents

Description

【００２６】
【表２】

【００２７】
表２から本発明例のNo.1〜３は、熱延コイルの表面状態は良好であり、箔圧延性、耐酸化性も良好であった。一方、本発明の範囲を外れる比較例のNo.4、No.5、No.7は、箔圧延性が５〜８と高く、極薄箔への圧延中に破断が多発している。また、比較例のNo.5は熱間圧延時の圧下率が高すぎ表面欠陥が多発し長時間のグラインダ研摩を必要とした。また、No.6はスラブ加熱温度が低すぎ表面欠陥、耳割れが多発し、製品にすることができなかった。
【００２８】
【発明の効果】
本発明によれば、排ガス浄化触媒担体に用いて好適な耐酸化性に優れ、使用中の耐縮み性に優れた極薄のＦｅ−Ｃｒ−Ａｌ合金箔が、コイル破断も少なく歩留り良く製造でき、著しい産業上の効果が期待できる。
【図面の簡単な説明】
【図１】縮み測定試験片形状と製作方法を示す説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a Fe-Cr-Al alloy foil, in particular a method of manufacturing a Fe-Cr-Al alloy foil used for the carrier of the exhaust gas purifying catalyst.
[0002]
[Prior art]
As one of the sources of air pollution, pollutants discharged from automobiles have been regarded as problems, and catalysts have been used to reduce these pollutants. An exhaust gas purifying catalyst converter is used NO X generated when mixing the fuel and air is burned in an automobile or the _like, HC, to detoxify harmful gases such as CO. Conventionally, a ceramic has been used as a support for supporting the catalyst. However, in order to increase the exhaust gas purification efficiency, it is necessary to mount the catalyst close to the engine, and the carrier is exposed to a higher temperature exhaust gas, making it difficult to use the ceramic carrier from the structural aspect. Instead, metal carriers assembled from Fe-Cr-Al alloy foils that can improve purification characteristics and reduce airflow resistance have been used.
[0003]
Such an alloy foil is usually used with a thickness of about 50 μm, but recently, particularly for those used in catalytic converters for automobiles, a thickness of about 35 μm is used for the purpose of further reducing airflow resistance and improving purification characteristics. The use of ultrathin foil is being studied.
Since the exhaust gas purifying catalytic converter is heated by high-temperature exhaust gas and catalytic reaction heat, the material used is required to have excellent oxidation resistance. As a carrier material used for this converter, for example, Fe-Cr-Al alloys to which La and Zr are added have been proposed in Japanese Patent Application Laid-Open Nos. 64-11946 and 5-202449.
[0004]
However, the above-mentioned material can be rolled without any trouble at a thickness of about 50 μm, but it is difficult to roll to a thinner thickness.
For example, if the thickness is less than about 40 μm, the material breaks during cold rolling, and further rolling becomes difficult, and even if rolling can be performed, the yield is low and only a small amount of product can be obtained. Fe—Cr—Al alloys have low hot workability, and surface defects such as baldness occur frequently due to microcracks that occur during hot rolling. When a hot-rolled sheet having a surface defect is cold-rolled, a hole is formed in the product foil, or the material is broken during foil rolling starting from the hole. Therefore, when there is a surface defect, the surface must be polished and removed with a grinder or the like. However, such polishing care increases costs, and when the amount of polishing is large, the shape of the material deteriorates, the material is easily broken during foil rolling, and the foil cannot be produced.
[0005]
Further, when the thickness of the catalyst carrier is reduced, the volume ratio with respect to the surface area is decreased, and the carrier is easily destroyed due to abnormal oxidation in a shorter time. For this reason, the material used for the ultra-thin foil carrier is required to have higher oxidation resistance than before.
Further, in order to improve the purification characteristics, that is, to promote the catalytic reaction, the exhaust gas purification catalytic converter is preferably installed at a location close to the engine, but the carrier is heated to a higher temperature as it approaches the engine. As a result, the carrier shrinks and a gap is formed between the carrier and the outer cylinder. Since the exhaust gas passing through the gap is not purified, there is a problem that the amount of harmful substances discharged increases.
[0006]
[Problems to be solved by the invention]
The present invention advantageously solves the above problems, can be made into an ultrathin foil with excellent workability, and also has excellent oxidation resistance without causing abnormal oxidation as an ultrathin foil, and has little shrinkage during use. It aims at proposing the manufacturing method of the Fe-Cr-Al alloy foil for exhaust gas purification catalyst carriers.
[0007]
[Means for Solving the Problems]
The present inventors have determined that the fracture in cold rolling of Fe—Cr—Al alloy foil is caused by precipitates present in the material, and suppresses the formation of precipitates in the Fe—Cr—Al alloy foil. As a result of finding a new composition and manufacturing conditions, and intensively examining the shrinkage of the carrier that occurs during use in the exhaust gas purification catalytic converter, it was discovered that the addition of Ti is effective in reducing shrinkage during use. The present invention is configured.
[0008]
That is , the present invention includes, by weight, Cr: 15.0 to 25.0%, Al: 4.0 to 6.5%, Zr: 0.005 to 0.10%, Ti: 0.005 to 0.05%, and Ti / Zr: 2 or less. Furthermore, a material containing one or more selected from rare earth elements in a total of 0.01 to 0.20% and the balance consisting of Fe and unavoidable impurities is heated to a temperature range between 1050 ° C. and less than 1150 ° C. This is a method for producing an Fe-Cr-Al alloy foil for an exhaust gas purifying catalyst carrier having excellent oxidation resistance after annealing and cold rolling to form an alloy foil. The hot rolling is the first 3 It is preferable that rolling of at least one pass up to the pass is a reduction ratio: 10% or less, and the material is wt%, Cr: 15.0 to 25.0%, Al: 4.0 to 6.5%, Zr: 0.005 to 0.05 %, Ti: 0.005 to 0.05%, Ti / Zr: 0.2 to 2, and one or more selected from rare earth elements It is preferable that the total content is 0.01 to 0.20%, with the balance being Fe and inevitable impurities.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
First, the reasons for limiting the present invention will be described.
Cr: 15.0-25.0%
Cr is an element that improves the oxidation resistance. However, if it is less than 15.0%, its effect is small. On the other hand, if it exceeds 25.0%, toughness deteriorates and cold rolling becomes difficult. For this reason, Cr is taken as 15.0 to 25.0% of range. In addition, Preferably, it is 18.0-22.0%.
[0010]
Al: 4.0 to 6.5%
Al forms a highly protective Al ₂ O ₃ film on the surface of the alloy foil, and improves oxidation resistance. However, if it is less than 4.0%, the formation of an effective Al ₂ O ₃ film is small and the oxidation resistance is inferior, and in the case of an ultrathin foil, it is consumed in a short period of oxidation and abnormal oxidation occurs, leading to the destruction of the support. Therefore, the lower limit of the Al content is set to 4.0%. Further, if it exceeds 6.5%, the toughness deteriorates and rolling becomes difficult, so 6.5% was made the upper limit of the Al content. In addition, Preferably, it is 4.5 to 6.0%.
[0011]
Zr: 0.005 to 0.10%
Zr is an element that improves the oxidation resistance. However, if it is less than 0.005%, its effect is small, and if it exceeds 0.10%, the oxidation rate is increased and the oxidation resistance is lowered. , Zr was in the range of 0.005 to 0.10%. If it exceeds 0.05%, shrinkage during use increases, and even if Ti is added, shrinkage cannot be prevented. Therefore, when considering shrinkage during use, Zr is 0.005 to 0.05%. The range of is preferable. More preferably, it is 0.01 to 0.03%.
[0012]
Ti: 0.005 to 0.05%
Ti fixes N and C in the alloy as TiN and TiC, and prevents the precipitation of harmful ZrN and ZrC during foil rolling. Furthermore, Ti penetrates into the Al ₂ O ₃ film formed on the surface during use, and prevents shrinkage that occurs during use. If it is less than 0.005%, these effects are small, and if it exceeds 0.05%, the oxidation resistance is lowered. Therefore, Ti is set in the range of 0.005 to 0.05%. In addition, Preferably, it is 0.01 to 0.03%.
[0013]
Ti / Zr: 2 or less In the present invention, Ti is further restricted in relation to the Zr content. When Ti / Zr 2 exceeds 2, the oxidation resistance decreases, so Ti / Zr = 2 was set as the upper limit. Further, in order to prevent shrinkage during use, Ti / Zr is preferably 0.2 or more. More preferably, Ti / Zr is 0.5 or more and 1.5 or less.
[0014]
Total of rare earth elements: 0.01-0.20%
In the present invention, the rare earth element includes Y, and refers to La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu. One or more selected from the group of rare earth elements can be added. A rare earth element is an element that improves oxidation resistance, and its effect is recognized by addition of 0.01% or more. However, when it exceeds 0.20%, hot workability deteriorates and ear cracks occur during rolling. Arise. Therefore, the rare earth element is set in the range of 0.01 to 0.20%. When two or more rare earth elements are added, the total amount of these elements may be within this range.
[0015]
Among the rare earth elements, La is most preferable. Ce remarkably promotes a decrease in hot workability, so its addition is preferably 0.05% or less. In addition, the addition amount of rare earth elements is more preferably 0.05 to 0.12% in total.
The balance is Fe, and impurities other than the above components are impurities. As impurity elements, C, Si, Mn, P, S, and N are respectively C: 0.02% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, N: 0.02% or less.
[0016]
Moreover, since Hf is contained as an impurity in Zr, it may be mixed with the addition of Zr and contained in an amount of about 0.01 to 0.05%. Hf is an element that improves oxidation resistance, and even if contained, it does not impair the object of the present invention.
The material having the above composition is melted by a normal melting method, converter, electric furnace, vacuum melting furnace or the like, and an RH degassing method, AOD method, VOD method, or the like is suitable. As the casting method, the continuous casting method is desirable in terms of productivity and quality, but an ingot-making method can also be applied.
[0017]
The material manufactured by the above-described method is hot-rolled and then annealed and cold-rolled to obtain an alloy foil.
The heating temperature of the hot rolling is set to a temperature range between 1050 ° C. and less than 1150 ° C.
Below 1050 ° C, the material cracks during hot rolling, making rolling difficult, and at 1150 ° C and above, large ZrC and ZrN precipitate, and the material breaks during foil rolling. The temperature range was 1050 ° C. and less than 1150 ° C. The heating time is preferably 1 to 3 hours because the longer the time is, the more the precipitate grows.
[0018]
The rolling of at least one pass up to the first three passes of hot rolling is set to a reduction ratio of 10% or less.
When the amount of reduction per pass of all passes up to the first three passes exceeds 10%, micro cracks that cause surface defects frequently occur. Such a microcrack becomes a surface defect and induces fracture of the material during cold rolling. By rolling at least one pass up to the first three passes to a rolling reduction of 10% or less, a hot-rolled sheet with a good surface can be obtained, and ultrathin foil rolling becomes possible.
[0023]
【Example】
A Fe—Cr—Al alloy having the composition shown in Table 1 was melted in a VOD furnace and formed into a slab by continuous casting. These slabs (200 mm thick × 1000 mm × 7000 mm) were hot-rolled under the hot rolling conditions shown in Table 2 to obtain hot-rolled coils having a thickness of 3 mm. Among the hot rolling conditions shown in Table 2 , the hot rolling reduction ratio indicates the amount of reduction in each of the first three passes of hot rolling. Next, these hot-rolled coils were annealed at 900 ° C., pickled and trimmed at the end, and then cold-rolled to form cold-rolled coils having a thickness of 100 μm. Furthermore, after these cold-rolled coils were annealed at 850 ° C. in a nitrogen gas atmosphere, the end portions were further trimmed and cold-rolled to obtain 35 μm-thick foils.
[0024]
The number of times the material coil broke during cold rolling from a 100 μm-thick cold rolled coil to a 35 μm-thick foil was defined as the foil rollability, and the rollability of the material coil was evaluated. The results are shown in Table 2 .
Moreover, about these foil, oxidation resistance and shrinkage resistance were evaluated by the following test , and the result is shown in Table 2 .
(1) Oxidation resistance test
A 20 × 30 mm test piece was taken from the foil , subjected to an oxidation test for 72 hours at a temperature of 1150 ° C. in the atmosphere, and the weight before and after the oxidation test was measured to determine the increase in oxidation. ○ where oxidation weight gain is less than 1.0 mg / cm ^2, the case where oxidation weight gain is less than 1.0 mg / cm ² than 2.0mg / cm ² △, oxidized amount was evaluated as × in the case of exceeding 2.0 mg / cm ² .
(2) Shrinkage resistance test
A test piece of 50 × 50 mm taken from the foil in the form indicating the test piece 1 (about 5 mm phi cylindrical), the size of about 5 mm phi to the rolling direction coincides with the longitudinal direction of the cylinder The end was fixed by spot welding and used as a shrinkage measurement test piece. This shrinkage measurement specimen was held at 1100 ° C. for 100 hours, and the amount of shrinkage (%) in the longitudinal direction was measured.
[0025]
[Table 1]

[0026]
[Table 2]

[0027]
From Table 2 , Nos. 1 to 3 of the examples of the present invention were good in the surface condition of the hot-rolled coil, and the foil rolling property and oxidation resistance were also good. On the other hand, Comparative Examples No. 4, No. 5, and No. 7, which are out of the scope of the present invention, have high foil rollability of 5 to 8, and many breaks occur during rolling to an ultrathin foil. In addition, No. 5 of the comparative example required excessive grinding for a long time because the rolling reduction during hot rolling was too high and surface defects occurred frequently. In No. 6, the slab heating temperature was too low, and surface defects and ear cracks occurred frequently, making it impossible to produce a product.
[0028]
【The invention's effect】
According to the present invention, an ultra-thin Fe-Cr-Al alloy foil having excellent oxidation resistance suitable for use in an exhaust gas purification catalyst carrier and excellent in shrinkage resistance during use can be produced with low coil breakage and high yield. A significant industrial effect can be expected.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a shrinkage measurement test piece shape and a manufacturing method.

Claims (3)

% By weight
Cr: 15.0-25.0%,
Al: 4.0-6.5%,
Zr: 0.005 to 0.10%,
Ti: 0.005 to 0.05% included, and
Ti / Zr: 2 or less,
A material containing one or more selected from rare earth elements in a total of 0.01 to 0.20%, with the balance consisting of Fe and inevitable impurities, heated to a temperature range between 1050 ° C and less than 1150 ° C. A method for producing an Fe-Cr-Al alloy foil for an exhaust gas purification catalyst carrier having excellent oxidation resistance, wherein the alloy foil is subjected to annealing and cold rolling after rolling. The hot rolling, rolling reduction rate of at least one pass to the first three pass: exhaust gas superior in oxidation resistance according to claim 1, wherein the 10% or less purification catalyst carrier for Fe-Cr -Manufacturing method of Al alloy foil. The material is weight percent,
Cr: 15.0-25.0%,
Al: 4.0-6.5%,
Zr: 0.005 to 0.05%,
Ti: 0.005 to 0.05% included, and
Ti / Zr: 0.2-2,
The oxidation resistance according to claim 1 or 2, wherein one or more selected from rare earth elements are contained in a total of 0.01 to 0.20%, and the balance is composed of Fe and inevitable impurities. A method for producing an Fe-Cr-Al alloy foil for an exhaust gas purification catalyst carrier.

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