JPH0480746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a catalyst carrier used for decomposing harmful gas components contained in exhaust gas.

(Prior art) Many methods have been known for producing catalyst carriers for decomposing harmful components of automobile exhaust gas.Especially in recent years, as exhaust gas regulations have become stricter, there has been a need to develop catalyst carriers that are lightweight, highly efficient, and durable. There is a growing need for superior catalyst supports. Ceramic was used as the catalyst carrier due to its heat resistance, but metal carriers were proposed due to its durability and poor exhaust gas permeability.
A method for producing alumina on the metal surface using a metal base as a special component was published in 1971, and a method for producing whiskers on the surface was published in Japanese Patent Publication No.
57-71898, etc., but the former has poor workability and productivity, while the latter has poor heat resistance, especially at high temperatures of 900°C or higher, where it oxidizes severely and cannot withstand use.

In addition, the technology described in Japanese Patent Publication No. 51-47157 coats a base material with iron as a substrate with Al, and through heat treatment forms a rough surface layer with an iron-aluminum compound as the substrate, making it easier to support the catalyst. It is something that has been trained. However, the iron made in this way
Because aluminum compounds are hard and brittle,
Many cracks occur during high-temperature use, and oxygen enters from these cracks and oxidizes the base material, resulting in an oxidized layer between the compound and the base material, causing problems such as peeling of the compound.

In addition, aluminum is added to the substrate whose main component is iron.
Various methods have been proposed in the past for coating aluminum alloys to form metal carriers. For example, Tokukai Akira
50-66492, JP-A-54-97593, etc. However, in this method, the composition of the steel is not specified, and if the steel is simply coated with aluminum, the heat resistance is at most 600 to 700 degrees Celsius, and the temperature of automobile exhaust gas is 900 degrees Celsius to 1100 degrees Celsius. is completely unbearable.
In addition, there is a method of aluminum plating using SUS430, 303, and 316 for the board, as disclosed in Japanese Patent Application Laid-Open No. 58-55815.
It is difficult to plate aluminum using normal methods, and some special treatment is required.
Even if the plating is successful, there are problems such as the fact that the stainless steel component has a heat resistance of up to 800°C.

Furthermore, as an example of using a steel sheet containing iron, chromium, and other metals as a substrate for a metal carrier, Japanese Patent Application Laid-Open No. 53-122693 describes Cr3~40, Al1~10%, Co0
~5% Ni, composition examples of Ni0~72% are disclosed in Japanese Patent Application Laid-Open No. 1986-
126692 discloses a composition example of 0 to 20% Cr, 0.5 to 12% Al, and 0 to 3% yttrium. The problem with these components is that they require the addition of expensive metal components such as yttrium and Co, and even components that do not contain expensive metals have high oxidation resistance.
Al component materials are hard and cannot withstand rolling, processing, etc.

The biggest problem with metal carriers is how to expand the surface area and how much catalyst can be supported to increase the catalytic effect, and how long the catalyst can withstand high temperatures, vibrations, etc. and retain its catalytic effect. be. These component systems are hard, brittle, and break easily, so
It has become clear that it is difficult to maximize the catalytic effect by processing it into nets, foils, etc., and that it is difficult to put it into practical use as a catalyst.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the problems of conventional metal carriers and provide a method for efficiently and inexpensively manufacturing metal carriers that have excellent heat resistance and workability. There is a particular thing.

(Means and effects for solving the problems) In order to achieve the above-mentioned object, the present invention uses a steel plate having a specific steel composition based on chromium and aluminum as a substrate, and after pretreatment, melts Al or melts. Al alloy is plated, at which time the total amount of aluminum contained in the steel sheet and the plating film is maintained above a certain level, and the thickness of the alloy layer formed on the steel sheet surface is suppressed, and then cold rolling, By heat-treating after processing, the plated Al does not remain as an intermetallic compound, but is actively dissolved into the substrate.The main points are (1) C0.1% or less by weight. , Si2.0% or less, Mn2.0%
Hereinafter, 0.3 to 5.0 g/m ² (per one side) of Ni is plated on the surface of a steel plate containing 9.0% to 25.0% Cr, 0.01 to 6.0% Al, the balance being iron, and unavoidable impurities, and then The amount of melting specified by the following formula (1)
Along with applying Al or molten Al alloy plating,
In order to suppress the thickness of the Al and iron alloy formed on the steel plate surface during plating to 7 μm or less, and to increase the contact area with gas, the plated steel plate is cold rolled to 0.1 mm or less. A method for manufacturing a metal carrier characterized by processing and then heat treatment, and (2) a weight ratio of C0.1% or less, Si2.0% or less, and Mn2.0%.
The following contains Cr9.0%~25.0%, Al0.01~6.0%,
And (A): 2.0% or less of Ti, Zr, Nb, Hf in total
One or more of the following, (B): 0.01% or less in total
One or more of Mg, Ca, Ba, (C): 0.5% or less Y in total, one or two rare earth elements,
(D): 1 or 2 types of Mo and W with a total content of 5% or less
Ni is applied to the surface of a steel sheet containing one or more of the following groups (A), (B), (C), and (D), with the remainder being iron and unavoidable impurities. 5.0g/ ^m2
(on one side), then apply molten Al or molten Al alloy plating in an amount specified by formula (1) below, and measure the thickness of the Al and iron alloy formed on the steel sheet surface during plating. suppressed to 7μm or less,
This method of manufacturing a metal carrier is characterized in that a plated steel plate is cold rolled to a thickness of 0.1 mm or less, processed to increase the contact area with gas, and then heat treated.

Melt plating weight (μm: one side) >T×f(1780/t-Crb-2a)/G(4b+2Crm-3560
/t)...(1) T: Thickness of steel plate for plating (μm) t: Thickness of foil to be rolled (μm) Crb: Cr content of steel plate for plating (wt%) Crm: Plating bath Cr content (wt%) in the plating steel plate (wt%) b: Al content in the plating bath (wt%) f: Specific gravity of the plating steel plate G: plating bath Specific Gravity Hereinafter, the present invention will be explained in more detail.

Catalyst supports for automobile exhaust gas purification are exposed to high-temperature exhaust gas for long periods of time, and are made of metal foil several tens of microns thick, so it is necessary to provide them with sufficient oxidation resistance over a long period of time. There is. In general, when heat-resistant stainless steel becomes a foil with a diameter of several tens of microns, the absolute amount of Cr and Al held in the foil decreases, resulting in a decrease in oxidation resistance. need to be added.

The present inventors melted stainless steel with various amounts of Cr and Al on a small scale, rolled it into a 50 μm thick foil, and attempted to evaluate its oxidation resistance in automobile exhaust gas. Figure 1 shows their Cr and Al content and oxidation resistance in exhaust gas at 1200°C.
The components of the foil that were abnormally oxidized within 70 hours in exhaust gas at ℃ are shown, and the white circles indicate the components of the foil that remained in a healthy oxidation state even after 70 hours. 1200℃× in this exhaust gas
Although the 70-hour test is an accelerated test, the present inventors prototyped metal carriers using 50 μm foil of several component systems and subjected them to various engine bench tests lasting up to 1000 hours. ×
Products based on ingredients that withstood the 70-hour oxidation resistance test passed all bench tests, but those that did not withstand the accelerated test mentioned above had problems due to insufficient oxidation resistance in at least one bench test. We have confirmed that this has occurred. Therefore, this accelerated test at 1200°C for 70 hours in exhaust gas is a fair evaluation of whether it can withstand actual use as a metal carrier.

The evaluation results shown in FIG. 1 are for a 50 μm foil, but as mentioned above, the oxidation resistance of the foil depends on the absolute amount of Cr and Al held in the foil. Therefore
40 μm foil requires 20% higher Cr and Al concentrations to exhibit the same oxidation resistance as 50 μm foil.
That is, the Cr and Al content (wt%) necessary for the metal carrier foil needs to satisfy (2Al+Cr)t/50>32, assuming the foil thickness is tμm.

However, in order to satisfy the above formula with a foil of 20 to 80 μm, it is necessary to have a certain amount of high Cr and high Al.
Although it is barely possible to melt and roll these on a small scale, it is almost impossible to melt and roll them on a large scale for the purpose of mass production.

The present inventors have developed a method for obtaining a high Cr-high Al foil that maintains sufficient oxidation resistance over a long period of time for use as a metal carrier.
A thin plate containing Cr-Al content (Cr≧9%) is plated with Ni in advance at 0.3 to 5.0 g/m ² (per one side),
If Al plating is applied on top of this and then rolled into foil, the adhesion of the Al plating layer will be good, and the Al plated layer will have good adhesion during rolling.
It was found that there was no peeling of the layers, and the thickness ratio between the Al plating layer and the base material after rolling was almost the same as before rolling. They also discovered that when this foil is heated in a non-oxidizing environment in a vacuum, more than 90% of the plated Al diffuses into the base material without forming iron-aluminum intermetallic compounds.

Therefore, in order to maintain workability and heat resistance by controlling the total amount of Al in the plated material and the amount of Al in the plated coating layer, the amount of Al or Al alloy plating required should be increased. Calculating based on the formula and the above-mentioned knowledge, we find that: Melt welding area weight (μm per side) >T×f(1780/t-Crm-2a)/G(4b+2Crm-3560
/t) T: Thickness of base material (μm) t: Thickness of foil after rolling (μm) Crb: Cr content of base material (wt%) Crm: Cr content in plating bath (wt%) ) A: Al content (wt%) of the base material b: Cr content (wt%) in the plating bath f: Specific gravity of the steel plate for plating G: The relationship between the specific gravity of the plating bath is obtained. In the above formula, if the right side is 5 μm or less, aluminum plating with a minimum thickness of 5 μm shall be performed. Also, the non-oxidizing atmosphere here means
Inert gas such as Ar, _N2 , N2 _{- H2} gas, etc. are suitable.

In the present invention, a steel plate with a time-determined composition based on chromium and aluminum is used as a substrate for a metal carrier, but the reason for limiting the composition of the steel plate will be explained here.

C is unavoidably mixed in and has a negative effect on the toughness, ductility, and oxidation resistance of steel materials, so it is preferable to keep it low, but in the present invention, actual damage can be tolerated if it is 0.1% or less, so the upper limit is set at 0.1%. .

Si is also inevitably mixed in, reducing the toughness and ductility of steel materials and generally improving oxidation resistance, but unlike the present invention, oxidation resistance cannot be maintained with Al ₂ O ₃ .
High Si content deteriorates the adhesion of the Al ₂ O ₃ film, so Si
A lower value is preferable. However, in the present invention, if it is 2% or less, there is little actual damage, so the upper limit is set at 2%.

Mn is also inevitably mixed in, and if it exceeds 2%, the oxidation resistance of the steel material deteriorates, so the upper limit was set at 2%. (However, since Mn improves the plating properties of steel materials, its most desirable range is 0.5 to 1.0%.) In the present invention, Cr is used to form a metal plated Al with Fe by heat treatment after Al plating. Al ₂ O ₃ can be actively dissolved in the substrate without forming intermediate compounds, and
It is added to stabilize the film and improve its oxidation resistance, but if it is less than 9%, the effect is insufficient, and
If it exceeds 25%, the steel becomes brittle and cannot withstand cold rolling or processing, so the range was set at 9 to 25%.

Al lowers the oxygen level of steel materials during steelmaking, so
It promotes the desulfurization reaction, increases the purity of steel, and improves toughness and ductility, so it is added to steel so that it remains at least 0.01%. In particular, in the present invention, Al in the steel material promotes diffusion of Al to be plated into the steel material. For this purpose, it is desirable to add 0.5% or more. However, if it is added in excess of 6%, the steel becomes brittle and cannot withstand cold rolling or processing, so the upper limit was set at 6%.

Ti, Zr, Nb, and Hf fix C and N in steel within the grains and substantially purify the matrix, improving workability. They also stabilize the Al ₂ O ₃ film and improve oxidation resistance. Improve. However, if the total amount exceeds 2%, precipitation of intermetallic compounds increases in the steel material, making the steel material brittle, so the upper limit for the total amount is set at 2%.

Mg, Ca, and Ba are strong deoxidizers that reduce the oxygen level during steelmaking, and also directly participate in desulfurization reactions to improve the purity of the steel, which improves the toughness and ductility of steel as well as its oxidation resistance. also contributes. However, in total
If it exceeds 0.01%, the toughness of the steel material will deteriorate, so the total upper limit was set at 0.01%.

Y and rare earth elements have the same effect as Mg, Ca, and Ba mentioned above, and in particular, they fix S in the grains, eliminate the effect of S that is harmful to oxidation resistance, and promote the diffusion of Cr and Ar. It has a remarkable effect of improving oxidation resistance, such as improving the adhesion of the film. However, since the precipitation of these intermetallic compounds exceeding 0.5% in total increases and the embrittlement of the steel material becomes severe, the upper limit of the total of these compounds must be set.
It was set at 0.5%.

Both Mo and W are effective in improving the high temperature and strength of steel materials. However, even if the total amount exceeds 5%, the effect will not increase much and various precipitated phases will increase, resulting in embrittlement, so the upper limit of the total amount is set at 5%.

When plating aluminum or aluminum alloy using such steel sheets for plating, any method may be used as long as it is a melting method, but it is preferable to use a non-oxidizing furnace (NOF) suitable for mass production. ) The best method is the Sendzimer method, which involves heating → heating in a reducing furnace → dipping (Al molten bath). Since aluminum is a metal that oxidizes very easily, hot-dip plating is extremely difficult with conventional methods. This is because aluminum is added to the original plate, so the original plate is easily oxidized, and this oxide cannot be reduced by normal plating. The present inventors discovered a method of plating Ni as a treatment before plating. As shown in Figure 2, the relationship between the amount of Ni and the adhesion properties requires at least 0.3 g/m ² and 5 g/m ^{2 .}
Even if it exceeds 5, the effect will not change and the cost will increase.
g/m ² or less is preferable. Ni basis weight is 0.3~2.0g/
In the case of m ² , some dissatisfaction occurs. However, in the subsequent aluminum plating layer diffusion process, the foil components become uniform, so there is no problem in practical use. Al
The surface of steel sheets containing steel sheets is very easily oxidized, and the surface is oxidized during heating in a non-oxidizing furnace, and it is very difficult to reduce the oxide film in a reducing furnace. Adopt the method of plating. Nickel promotes alloying between aluminum and the plating base material, and since nickel itself is easily reduced, aluminum can be completely coated on the plating base material.

On the other hand, when plating, the next processing step is to keep the amount of alloy between aluminum and iron below a certain level.
It is absolutely necessary to prevent plating from peeling off during processing as a metal carrier. Even in the molten aluminum plating method using flux, complete coverage cannot be obtained unless nickel is plated in the same way. If it is not completely coated, oxidation will progress during use as a metal carrier, resulting in poor gas flow and failure to perform its original function. Such defects can be fatal, especially at the stage where the final product with the honeycomb structure is used as a metal carrier. As the oxidation of this unmet part progresses, the flow of gas in that part becomes turbulent, and the oxidation further increases and the hole becomes clogged. Therefore, defects must be completely removed.

In order to roll the incomplete steel sheet obtained in this manner after being tempered into foil, it is necessary to suppress the aluminum-iron alloy as described above. FIG. 3 shows the relationship between the thickness of this alloy and the peeling of plating during rolling into foil. If the alloy layer is not kept below 7 μm, the plating layer will peel off and the desired plating coating will not be obtained. When the alloy layer is usually melt-dipped in a pure aluminum bath, a very thick alloy layer grows and the above-mentioned problem occurs.
Even with the plating method using NOF-RF, the alloy layer becomes 20 μm or more in plating time of 10 seconds.

Therefore, it is necessary to control the plating bath temperature and immersion time to suppress the formation of the alloy layer. In order to suppress the growth of this alloy layer, by adding 10% silicon to the aluminum bath,
It can be suppressed to 7μm on one side or less. Although it is better to add a small amount of silicon, it is necessary to add the minimum amount to suppress the formation of an alloy layer. Usually 7
Addition of % to 10% is desirable. In addition to Si, it can also be used as a glazing bath.
The alloy layer can also be suppressed by adding Cu or Be.

In the present invention, a composition based on Al is adopted as the plating film, or an aluminum alloy is used in addition to pure aluminum. As the alloy composition, an alloy in which the above-mentioned alloy suppressing metal is added to aluminum, or an alloy in which magnesium is blended alone or together with an alloy suppressing metal in aluminum can also be used.

The aluminum or aluminum alloy plated steel sheet produced in this way is then rolled into foil.
This rolling may be performed by a conventional method.
If the plating coating is not uniform, the plate cannot be rolled in the rolling process. If it is not uniform, it is necessary to lightly roll the plated layer to make it uniform before rolling.
The plating original plate is usually 0.2 to 0.7 mm,
It is rolled into a foil of 100 μm or less, preferably 20-80 μm. The foil is processed into structures having various shapes as shown in FIG. 4 so as to exhibit the maximum effect as a catalyst. Roll this into a spiral
Use a metal carrier as shown in the figure. This metal carrier can be used in a neutral atmosphere such as vacuum, argon, helium, etc.
In a reducing atmosphere such as hydrogen or hydrogen-nitrogen gas
When diffusion treatment is performed at a temperature of 500 to 1300℃, most of the plated Al diffuses into the base material and becomes Fe-Cr-
A solid solution of Al is created, and the iron-aluminum intermetallic compound that occurs when ordinary steel is plated with Al does not remain. Note that this diffusion treatment can also be performed as a brazing treatment for fixing the honeycomb.
The processing time for the sole purpose of Al diffusion is determined by the relationship with temperature. It is necessary to heat the material until no aluminum remains on the surface layer. Therefore, the heating time must be changed depending on the amount of aluminum deposited and the amount of rolling of the base steel onto the component foil. An example of the relationship between temperature and time is shown in FIG. This is 15%Cr−4.5%Al
This is the result of a 0.4 mm original plate coated with Al-10% Si to 40 μm on one side and then rolled into a 50 μm foil.

Example 1 C=0.004%, Cr=15.0%, by continuous casting method
Steel containing Ti = 0.15%, Al = 4.5% and other unavoidable impurities is manufactured, and a steel strip with a thickness of 0.4 mm is manufactured by hot rolling and cold rolling, which is degreased and pickled. , 2g/ ^m2 per side of nickel plating,
Aluminum was plated to a thickness of 45 μm on one side using the Sendzimer method using an Al-10Si melt plating bath, and then cold rolled to a thickness of 50 μm to form a foil. This is processed into a honeycomb structure as shown in Figure 4 A, and then
Heat treatment was performed at 900°C for 30 minutes.

Heat resistance test of the metal carrier obtained in this way
Tested in air at 1200℃ for 300 hours, the surface showed no change at all and had good heat resistance.
The product supporting the alumina catalyst was used in an automobile exhaust gas decomposition test, and no abnormalities were observed even after 1,000 hours of testing.

Example 2 C=0.006%, Cr=17.0%, by continuous casting method
A steel containing Ti=0.15%, Al=4.0% and other unavoidable impurities is manufactured, and a steel strip with a thickness of 0.3 mm is manufactured by hot rolling and cold rolling, which is degreased and pickled. , 1g/ ^m2 per side of nickel plating,
Aluminum was plated to a thickness of 30 μm on one side using the Sendzimer method using an Al-7%Si melt plating bath, and then cold rolled to a thickness of 45 μm to form a foil. This was processed into a honeycomb structure and then heat treated at 850°C for 20 minutes. A product coated with a catalyst for purifying automobile exhaust gas using this as a carrier showed no abnormalities even during a 100-hour test in exhaust gas at 1200°C. For comparison, steel with the same composition but without aluminum plating developed abnormal oxidation within 3 hours and the test was discontinued.

(Effects of the Invention) According to the present invention, it has become possible to efficiently and inexpensively produce a metal carrier with excellent workability and heat resistance.

[Brief explanation of drawings]

Figure 1 shows the relationship between Cr and Al contents in steel sheets and oxidation resistance. Figure 2 shows the amount of Ni pre-plated and the uniformity of the plating after hot-dip Al plating is applied to the surface. Figure 3 shows the relationship between molten steel and steel plate.
Fe− formed on the steel sheet surface during Al plating
A diagram showing the relationship between the thickness of the Al alloy layer and the state of peeling of the plating film after cold rolling, Figure 4 A, B and C,
Figure 5 shows a metal carrier manufactured by spirally winding the processed foil, and Figure 6 shows the heating temperature and heating of the metal carrier. It is a figure which shows the example of time.

Claims (1)

[Claims] 1 Weight%: C0.1% or less, Si2.0% or less, Mn2.0% or less, Cr9.0% to 25.0%, Al 0.01 to 6.0%, the balance being iron, and unavoidable 0.3 to 5.0 g/m ² (per side) of Ni is plated on the surface of the steel plate, which contains impurities, and then melted in an amount specified by the following formula (1).
Along with applying Al or molten Al alloy plating,
In order to suppress the thickness of the Al and iron alloy formed on the steel plate surface during plating to 7 μm or less, and to increase the contact area with gas, the plated steel plate is cold rolled to 0.1 mm or less. A method for producing a metal carrier, characterized by processing and then heat treatment. Melt plating weight (μm: one side) >T×f(1780/t-Crm-2a)/G(4b+2Crm-3560
/t)...(1) T: Thickness of steel plate for plating (μm) t: Thickness of foil to be rolled (μm) Crb: Cr content of steel plate for plating (wt%) Crm: Plating bath Cr content (wt%) in the plating steel plate (wt%) b: Al content in the plating bath (wt%) f: Specific gravity of the plating steel plate G: plating bath Specific gravity 2 Contains C0.1% or less, Si2.0% or less, Mn2.0% or less, Cr: 9.0% to 25.0%, Al: 0.01 to 6.0%, and (A): 2.0 in total % or less of one or more of Ti, Zr, Nb, Hf, (B): One or more of Mg, Ca, Ba, or less of 0.01% in total, (C): 0.5% or less in total Y, one or two kinds of rare earth elements, (D): 5% or less Mo in total, one or two kinds of W, each of (A), (B), (C), (D) Ni is plated on the surface of a steel plate containing one or more of ^the following, the balance being iron and unavoidable impurities, and then the following (1) In addition to applying molten Al or molten Al alloy plating in the amount specified by the formula, the thickness of the Al and iron alloy formed on the steel plate surface during plating is suppressed to 7 μm or less, and the plated steel plate is cold rolled. A method for producing a metal carrier, which is characterized in that the metal carrier is rolled to 0.1 mm or less, processed to increase the contact area with gas, and then heat treated. Melt plating weight (μm: one side) >T×f(1780/t-Crm-2a)/G(4b+2Crm-3560
/t)...(1) T: Thickness of steel plate for plating (μm) t: Thickness of foil to be rolled (μm) Crb: Cr content of steel plate for plating (wt%) Crm: Plating bath Cr content (wt%) in the plating steel plate (wt%) b: Al content in the plating bath (wt%) f: Specific gravity of the plating steel plate G: plating bath specific gravity.