JPH02179851A - Heat resisting steel for monolythic use - Google Patents

Abstract

PURPOSE:To improve the blister resistance, gas corrosion resistance, heat- and cold-resisting durability, and oxidation resistance of the steel by combinedly adding La and Ce into a steel and also specifying respective contents of Cr, Al, Ti, etc. CONSTITUTION:A heat resisting steel has a composition which consists of, by weight ratio, <=0.3% C, <=1.5% Si, <=1.5% Mn, 19.0-25.0% Cr, 5.0-8.0% Al, 0.01-0.50% Ce, 0.01-0.50% La, <=0.04% Ti, and the balance Fe with impurity elements and in which (La+Ce) is regulated to 0.02-0.80%. If necessary, 0.05-2.0% Co, 0.10-2.0% Ni, and. 0.05-0.20% V are incorporated to the above composition. This steel is used for a honeycomb structure for monolithic catalyst device. By the above composition, blister in the case of 1100 deg.C and 600hr is reduced to <= about 1%, and abnormal oxidation does not occur until >=1000hr elapse in exhaust gas of 950 deg.C, and further, >= about 3000 times heat- and cold-resisting durability and >= about 600hr oxidation resistance can be satisfactorily satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat-resistant steel for a monolith forming a honeycomb structure of a monolith catalyst device used as an exhaust gas purification device.

[Background Art] With the tightening of automobile exhaust gas regulations, automobiles have come to be equipped with exhaust gas purification devices. Exhaust gas purification methods include thermal reactor method, lean burn method,
There are engine modification methods and catalytic methods, but the majority use the catalytic method.

Pt and Pd-based catalysts are used as catalysts for automobiles, and the shape of the catalysts is roughly divided into granular and monolithic. Although monolithic catalysts have excellent installation and warm-up properties, they are said to be inferior to granular catalysts in terms of economy and impact resistance.

Monolithic catalysts include those made of ceramics and those made of metal. For ceramic products, the carrier is made by firing ceramics into a honeycomb shape, the carrier is placed in a metal cylinder, and the γ-A I 203 powder supporting a catalyst metal such as PT is attached to the carrier. It is something. However, this ceramic monolith is vulnerable to mechanical shock.
Recently, metal monoliths have been attracting attention because they have drawbacks such as high exhaust resistance.

The metal monolith catalytic converter is Fe-Cr-
A1 type @ thermal material (20Cr-6AI) is rolled into a foil with a thickness of several tens of microns, and this foil is processed into a corrugated sheet and a flat sheet are alternately laminated, or the foil is wound into a roll. , the base is a honeycomb structure housed in a metal tube,
A1□03 film is formed by high-temperature oxidation,
γ-AI203 supporting a catalyst metal such as PT is deposited by coating.

[Issues to be solved by the inventionffl] Conventionally, Fe-Cr-A used in this metal monolith
L-based electrical heating materials (20Cr-6Al) still do not have sufficient high-temperature corrosion resistance. In other words, the catalytic converter is repeatedly heated and cooled by exhaust gas at around 1000°C, so the entire foil is oxidized and the honeycomb structure tends to move toward the cells. 5-10%
The honeycomb structure swells and protrudes forward and backward from the metal tube, which deforms the honeycomb structure and peels off the coating that supports the catalyst metal, shortening the life of the catalytic converter.

In addition, gas corrosion resistance (950'C in exhaust gas), cold and heat resistance (repeated heating and cooling at 1000°C and room temperature), and oxidation resistance (1100'C) are not sufficient, and gas corrosion resistance is 30°C. In terms of time, cold and heat resistance is S.

The oxidation resistance is 0 times and the oxidation resistance is 150 hours. Due to abnormal oxidation, lump-like oxide scales are formed on the surface of the foil constituting the honeycomb structure, which causes the coating to peel off and impede air permeability.

The present invention was made in view of the above-mentioned problems of conventional heat-resistant steel for monoliths.
00 hours) is 1% or less, gas corrosion resistance is 1000 hours or more, cold and heat resistance is 3000 times or more, oxidation resistance is 600
The objective is to provide a heat-resistant steel for monoliths that satisfies the required characteristics over time.

[Means for Solving the Problems] In order to solve the above-mentioned problems, intensive research has been carried out on the influence of various elements on the blistering resistance of heat-resistant steel for monoliths. As a result, it has been found that the combined addition of rare earth elements, particularly La and Ce, significantly improves the blistering resistance. In addition, gas corrosion resistance can be improved by increasing the amount of C added and adding rare earth elements, and oxidation resistance can be improved by increasing the amount of Cr and A1 added, adding rare earth elements, and adding Ti.
We obtained the knowledge that this can be improved by reducing the Furthermore, it has been found that the cold and heat resistance durability is improved by adding rare earth elements, particularly Ce. The present invention was completed based on these new findings.

The heat-resistant steel for monoliths of the present invention is the first invention steel, and has a weight ratio of C: 0.3% or less, Si: 1.5% or less, Mn: 1.
5% or less, Cr; 19.0-25.0%, Al; 5°0
~8.0%, Ce; 0.01~0.50%, La; 0
.

01~0.50%, La+Ce・0.02~0.80%
, Ti: 0.04% or less, and the remainder consists of Fe and its impurity elements. Moreover, in order to improve the cold workability of the first invention steel, the second invention steel further includes Co;
0.05~2.0%, Ni; 0.10~2゜0%, V
, 0.05 to 0.20%, and the remainder consists of Fe and its impurity elements.

[Function] The heat-resistant steel for monoliths of the present invention has markedly improved blistering resistance due to the combined addition of Ce and La.
Blistering after 600 hours at 00°C is less than 1%. Also,
By increasing the Cr content and adding rare earth elements Ce and La, gas corrosion resistance is improved and the 950"C
Abnormal oxidation does not occur until more than 1000 hours in the exhaust gas.

In addition, by increasing the content of AI and Cr,
A thickness of A1□O1 is produced that provides sufficient oxidation resistance.

Furthermore, the added Ce and La stabilize the Al2O film. Therefore, abnormal oxidation does not occur even if held at 1100''C for 600 hours or more.

The cold and heat resistance durability is significantly improved by adding rare earth elements, especially Ce, and the number of repetitions of heating and cooling at 1000'C and room temperature is 3.
Blistering due to abnormal oxidation does not occur until 000 times or more.

Next, the reason for limiting the composition range of the chemical components of the present invention will be explained.

C: 0.3% or less C is an element that is inevitably contained in steel, and if it is too high, the structure will become martensite.

In addition, if carbide is formed with the contained C, the corrosion resistance will be lowered, so the lower the content, the better, and the upper limit was set at 0.3%.

Si: 1.5% or less Si generally has the effect of improving oxidation resistance and stabilizes ferrite. However, if the content exceeds 1.5%, the toughness decreases and cold workability is inhibited, so the upper limit was set at 1.5%.

Mn: 1.5% or less Mn is added as a deoxidizing agent during steelmaking and fixes S, but
If the content exceeds 1.5%, the toughness will be reduced.
The upper limit was set at 1.5%.

Coco, 05-2.0% Adding Co prevents recrystallization, refines crystal grains, and improves cold workability. To obtain the above effect, 0.05
It is necessary to add more than %. However, even if it is added in excess of 2.0%, the effect will be saturated and the price will increase, so the upper limit was set at 2.0%.

Ni: 0.10 to 2.0% Adding Ni prevents recrystallization, refines crystal grains, and improves cold workability. To obtain the above effect, 0.1%
The above additions are necessary. However, even if it is added in excess of 2.0%, the effect will be saturated and the price will increase, so the upper limit was set at 2.0%.

Cr: 19.0 to 25.0% Cr is an element that imparts oxidation resistance and gas corrosion resistance to steel, and unless it is contained in an amount of 19.0% or more, sufficient gas corrosion resistance cannot be obtained. However, if the content exceeds 25%, the cold workability will be inhibited and the σ phase will precipitate, so the upper limit should be set to 25%.
%.

A1・5.0~8.0% A1 is the most important element for forming an A I20 z skin on the surface of steel. In order to form an A I20 y film and obtain sufficient oxidation resistance, it is necessary to add 5.0% or more. However, if the content exceeds 8.0%,
Since hot rolling properties become difficult, the upper limit was set at 8.0%.

V: 0.005 to 0.2% ■ is 0.0 because it refines the crystal grains and improves cold workability.
0.5% or more is added. However, if it is added in an amount exceeding 0.2%, it tends to crack under hot conditions, so the upper limit was set at 0.2%.

Ce・0.01-0.5% Ce is an element that improves blistering resistance, and in order to obtain this effect, it is necessary to add at least 0.01% or more. However, if added in excess of 0.5%, hot workability deteriorates, so the upper limit was set at 0.5%.

La: 0.01 to 0.5% La is an element that improves oxidation resistance, and in order to obtain this effect, it is necessary to add at least 0.01% or more. However, if added in excess of 0.5%, hot working becomes impossible, so the upper limit was set at 0.15%.

La+Ce: 0.03 to 0.8% The combined addition of La and Ce stabilizes the AI203 protective film, but in order to obtain this effect, it is necessary to add at least 0.03% or more in total.

However, if the total amount added exceeds 0.8%, cracks will occur during hot rolling, so the upper limit should be set to 0.8%.
．． It was set at 8%.

Ti: 0.04% or less Since T; destabilizes the A120i protective film and deteriorates oxidation resistance, it is desirable that it be as small as possible, and its upper limit is set to 0.04% or less.

[Example] Next, an example of the present invention will be described together with a conventional example and a comparative example to clarify the effects of the present invention.

Table 1 shows the chemical composition of these test steels. In Table 1, steels A to H are steels of the present invention, steels A to D are steels of the first invention,
E-H steel is the second invention. M-M steel is comparative steel,
IW4 does not contain Ce and La, J steel has a high content of Ce and La, K steel has a high content of Ti, L steel has a low content of A1, and M steel has a low content of C. In addition, N steel is a conventional steel.

(Left below) The test steels shown in Table 1 were processed into 50μ steel foils, and then tested for blistering resistance, gas corrosion resistance, cold and heat resistance, and oxidation resistance.

The blistering resistance is 110 after forming the foil into a honeycomb structure.
The elongation in the cell direction was measured by passing exhaust gas at 0° C. for 600 hours.

Regarding gas corrosion resistance, the sample was kept in exhaust gas at 950°C and the time required for abnormal oxidation to occur was measured.

Regarding cold and heat resistance durability, heating and cooling between 1000° C. and room temperature were repeated, and the number of times abnormal oxidation occurred was measured.

Regarding oxidation resistance, the sample was kept in an oxidizing atmosphere at 1100°C and the time for abnormal oxidation to occur was measured.

The results obtained are shown in Table 2.

(Left below) As is clear from Table 2, the comparison steel that does not contain Ce and La [1m] has a blistering resistance of 13% and is also extremely inferior in properties such as gas corrosion resistance. is T
Due to the high i content, it is inferior in oxidation resistance and other properties, while the comparative steel has a low A1 content, so although it is excellent in blistering resistance, it is inferior in gas corrosion resistance and oxidation resistance. Since steel M has a low C content, it similarly has poor gas corrosion resistance and oxidation resistance. Comparative steel J has a low C content.
Also, the La content was too high, causing cracks during cold working, making it impossible to process into foil.

Furthermore, conventional steel has a high blistering resistance of 13% and is inferior in other heat resistance properties.

On the other hand, steels A to H, which are the steels of the present invention, had a blistering resistance of 1% or less, and a gas corrosion resistance of 11%.
00-1550 hours, cold and heat resistance 3000-520
0 times and oxidation resistance for 600 to 1000 hours, excellent results were obtained for all properties, confirming the effects of the present invention.

[Effects of the Invention] As explained above, the heat-resistant steel for monoliths of the present invention has gas corrosion resistance and gas corrosion resistance by adding Ce and La to improve blistering resistance and increasing the amount of AI and C. It has improved oxidation resistance and cold and heat resistance by adding Ce, and has a blistering resistance (1100℃, 600 hours) of 1% or less, which is a required property as a heat-resistant steel for monoliths. It fully satisfies gas corrosion resistance of 1000 hours or more, cold and heat resistance durability of 3000 times or more, and oxidation resistance of 600 hours or more.

Claims (2)

[Claims] (1) Weight ratio of C: 0.3% or less, Si: 1.5% or less, Mn: 1.5% or less, Cr: 19.0 to 25.0%,
Al; 5.0-8.0%, Ce; 0.01-0.50%
, Li; 0.01-0.50%, La+Ce; 0.02
~0.80%, Ti; Contains 0.04% or less, balance F
A heat-resistant steel for monoliths characterized by consisting of e and its impurity elements. (2) Weight ratio of C: 0.3% or less, Si: 1.5% or less, Mn: 1.5% or less, Cr: 19.0 to 25.0%,
Al; 5.0-8.0%, Ce; 0.01-0.50%
, La; 0.01 to 0.50%, La+Ce; 0.02
~0.80%, Ti; 0.04% or less, further Co; 0.05 to 2.0%, Ni; 0.10 to 2.0%.
, V; 0.05 to 0.20%, and the remainder consists of Fe and its impurity elements.