JPH0830254B2 - Ferritic stainless steel with excellent high temperature oxidation resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel excellent in high temperature oxidation resistance, which is suitable for use in an automobile exhaust gas purifying apparatus, a combustion tube of a stove, an electric heating element and the like.

[0002]

2. Description of the Related Art In general, ferritic stainless steel containing a high concentration of Al is a material suitable for applications requiring oxidation resistance in a high temperature range such as an automobile exhaust gas purifying device and a stove combustion cylinder. It is known. In recent years, the environment surrounding the automobile exhaust gas purifying apparatus tends to accelerate the catalytic reaction by reducing the thickness of the plate material used and reduce exhaust resistance to reduce the load on the engine. Further, in the combustion cylinder of the stove, there is a strong demand to increase the operating temperature in order to improve the combustion efficiency, and to reduce the thickness of the plate material used in order to reduce the cost. However, the above ferritic stainless steel is not sufficiently durable under these environments, and there is a problem that the material life is inevitably shortened when used in such an environment.

On the other hand, conventionally, a method of increasing the Al content of the stainless steel has been adopted as a means for avoiding the above-mentioned shortening of the material life. However, this method promotes embrittlement of the hot rolled steel strip, and
In particular, there has been a problem that cracks and fractures are likely to occur during cold rolling, making it difficult to manufacture by a normal manufacturing method. For these reasons, it has been desired to develop a technique for improving the high-temperature oxidation resistance of Al-containing ferritic stainless steel by a means different from the above method of increasing the Al content.

As a technique for fulfilling this demand, conventionally, there is a method of adding a rare earth element or the like. For example, a technique has been proposed in which a lanthanoid excluding Ce is added to enable rolling without cracks and to improve oxidation resistance (see Japanese Patent Publication No. 4-8502).

[0005]

However, in the above-mentioned prior art, since the rare earth element as an additive element is an active metal, the additive yield is poor, and thus the product yield is deteriorated, which causes another problem that the cost is increased. Occurred.
Furthermore, recently, due to automobile exhaust gas regulations, it is desired to shorten the time required to reach the catalytic action temperature in an automobile exhaust gas purifying device, or to increase the output of the engine, and the exhaust gas temperature tends to become higher and higher. Therefore, as the exhaust gas purifying apparatus, the exhaust gas atmosphere to which the ferritic stainless steel is exposed becomes a more severe condition,
It has become necessary to develop ferritic stainless steel that has even higher high-temperature oxidation resistance than before.

Therefore, an object of the present invention is to advantageously overcome the above-mentioned problems of the prior art, and in particular, it is possible to obtain a high temperature oxidation resistance superior to that of the prior art, without adding a rare earth element more than necessary. To provide ferritic stainless steel.

[0007]

Means for Solving the Problems The inventors of the present invention have earnestly studied in order to overcome the above-mentioned problems, and have obtained the following findings. (1) Ni, which was considered to be a component element having poor toughness and oxidation resistance, is effective in improving oxidation resistance, and the addition of an appropriate amount of Ni can secure oxidation resistance. (2) Oxidation resistance and toughness can be further improved by adding an appropriate amount of Ti. (3) Oxidation resistance can be further improved by adding an appropriate amount of one or two of La and Y, which are effective in improving oxidation resistance. (4) With the addition of an appropriate amount of Ti, La which is effective in improving oxidation resistance
By adding an appropriate amount of any one or two of Y and Y,
Further excellent oxidation resistant steel can be obtained. The present invention is a ferritic stainless steel having higher high-temperature oxidation resistance than ever before, and is based on the above findings.

That is, the gist of the present invention is as follows. C: 0.030 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt%
% Or less, Cr: 15.0~25.0wt%, Ni: 0.32~5.0 wt%, Al: 2.
5 to 15.0 wt% and N: 0.03 wt% or less and L
a: 0.01 to 0.3 wt% and Y: 0.01 to 0.3 wt%
At the same time as including one or two types, this La and Y
When it is contained in the oil, the total amount of them should be 0.3 wt% or less.
Contained, the balance consisting of Fe and unavoidable impurities
Featuring stainless steel with excellent high temperature oxidation resistance
Steel . C: 0.030 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt%
% Or less, Cr: 15.0 to 25.0 wt%, Ni: 0.32 to 5.0 wt%, Al:
2.5-15.0 wt%, N: 0.03 wt% or less, and Ti: 0.
010 to 0.30 wt%, and La: 0.01 to 0.3 wt% and
Y: contains any one or two of 0.01 to 0.3 wt%
At the same time, when it contains both La and Y,
Contains 0.3 wt% or less in total, and the balance is Fe and
Excellent in high temperature oxidation resistance, which is characterized by consisting of contraceptive impurities.
Ferritic stainless steel .

[0009]

The reason why the composition of the steel is limited to the above range in the present invention will be described below. C: 0.030 wt% or less When C exceeds 0.030 wt%, the toughness of the hot rolled steel strip is significantly reduced. Therefore, the content of C is 0.03
0 wt% or less.

Si: 1.0 wt% or less Si is a component element effective for improving the oxidation resistance of stainless steel, but although the effect is not as great as Al, the drawback that deteriorates the toughness is remarkable. Is. Therefore,
The Si content was 1.0 wt% or less.

Mn: 1.0 wt% or less If the content of Mn exceeds 1.0 wt%, the oxidation resistance deteriorates. Therefore, the Mn content is set to 1.0 wt% or less.

Cr: 15.0 to 25.0 wt% Cr is a very important element in ensuring the oxidation resistance and corrosion resistance of stainless steel. However, if the content is less than 15.0 wt%, the above-mentioned oxidation resistance and corrosion resistance are not sufficient, while if it exceeds 25.0 wt%, the toughness of the hot-rolled steel strip is significantly reduced. Therefore, the Cr content is
It was limited to the range of 15.0 to 25.0 wt%.

Ni: 0.32 to 5.0 wt%, Ni is an element that plays an extremely important role in the present invention, and as described above, it has been conventionally disadvantageous to oxidation resistance, but 0.32 wt% or more is required. If added, it is surprisingly effective in improving the oxidation resistance. This effect becomes remarkable when the amount added is 1.0 wt% or more, and more preferably 1.5 wt% or more is the desirable amount added. However, if it exceeds 5.0 wt%, an austenite phase is generated, which deteriorates the oxidation resistance and the toughness. Therefore, the Ni content is limited to the range of 0.32 wt% to 5.0 wt%.

Al: 2.5-15.0 wt% Al is an element effective for improving the high temperature oxidation resistance of stainless steel. However, its content is 2.5 wt%
When the content is less than 1, it is not sufficient to secure the high temperature oxidation resistance, while when it exceeds 15.0 wt%, the toughness of the hot rolled steel strip is significantly reduced and the production becomes difficult by the ordinary production method. . Therefore, the Al content is limited to the range of 2.5 to 15.0 wt%.

N: 0.03 wt% or less N significantly reduces the toughness of the hot-rolled steel strip and reacts with Al to form AlN, which causes abnormal oxidation. Therefore,
The N content is 0.03 wt% or less.

Ti: 0.010 to 0.3 wt% Ti is an element effective as a carbide to fix N and C and improve the oxidation resistance and toughness. However, in order to exert this effect, it is necessary to add 0.010 wt%, and addition of more than necessary adversely deteriorates toughness and further deteriorates oxidation resistance. Therefore, the content of Ti is
It was limited to the range of 0.010 to 0.3 wt%.

La: 0.01 to 0.3 wt% La is an element effective for improving the oxidation resistance of stainless steel. However, if the content is less than 0.01 wt%, the effect of improving the oxidation resistance is not sufficient, while 0.3 wt%
If it is contained in excess of%, the workability deteriorates. Therefore,
The content of La is limited to the range of 0.01 to 0.3 wt%.

Y: 0.01 to 0.3 wt% Y, like La, is an element effective for improving the oxidation resistance of stainless steel. However, its content is 0.
If it is less than 01 wt%, the effect of improving the oxidation resistance does not appear, while
If the content exceeds 0.3 wt%, hot workability deteriorates. Therefore, the Y content is limited to the range of 0.01 to 0.3 wt%.

La + Y: 0.3 wt% or less When both La and Y are contained, their total amount is
Considering both aspects of improvement of oxidation resistance and prevention of deterioration of hot workability, the content is set to 0.3 wt% or less.

[0020]

[Example] 10 kg of a steel ingot having the composition shown in Table 1 was obtained by melting and refining in the atmosphere. Next, the obtained steel ingot is forged into a plate having a thickness of 40 mm and a width of 50 mm, which is then hot-rolled, and then cold-rolled and annealed (900 ° C x 1 min) to repeat the plate. The foil was 50 μm thick. The ferritic stainless steel foil thus obtained was subjected to a high temperature oxidation resistance test. This test is 50μm ^t × 25mm ^w × 50mm ^l
The above foil was used for the following method. Sand
> Then, the oxidation resistance test is 1150 ℃ × 8 in the air in the above foil.
One cycle consists of heating for 1 hour, cooling to room temperature, and then measuring the change in weight, and repeating this operation. The oxidation resistance is evaluated by the total oxidation time until abnormal oxidation or scale peeling on the foil surface occurs. I went there. The abnormal oxidation means that the oxidation curve greatly deviates from the parabolic law or the linear law to increase the oxidation weight gain, and the scale peeling means that the weight of the test piece sharply decreases due to the oxide film peeling off. Say.

[0021]

[Table 1]

The results of the high temperature oxidation resistance test are shown in Table 2 and FIG.
Shown in As is clear from these results, it was confirmed that the invention steel exhibited a longer time until abnormal oxidation than that of the comparative steel and exhibited excellent high temperature oxidation resistance. In particular, invention steel No. 4
Indicates that the time until abnormal oxidation is extremely longer than that of Comparative Steel Nos. 12 and 14 , and that abnormal oxidation does not occur even after 192 hours. As is clear from the results shown in FIG. 1, it was found that the effect of Ni addition on the high temperature oxidation resistance was extremely large. Inventive steel No. 2 is Ni
Is contained in a larger amount, the time until abnormal oxidation shifts to the long-term side.

[0023]

[Table 2]

[0024]

As described above, according to the present invention,
It is possible to provide a ferritic stainless steel having higher high-temperature oxidation resistance than conventional steels without excessively adding rare earth elements having extremely low addition yield.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of Ni addition on high temperature oxidation resistance.

Front Page Continuation (72) Inventor Yuji Ikegami 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Metallurgical Industry Co., Ltd. R & D Headquarters Technical Research Laboratory (56) References ) JP-A-49-102512 (JP, A) JP-A-2-254136 (JP, A)

Claims (2)

[Claims] 1. C: 0.030 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15.0 to 25.0 wt%, Ni: 0.32 to 5.0 wt%, Al: 2.5 to 15.0 wt%, N: 0.03 wt% or less, and La: 0.01 to 0.3 wt% and Y: 0.01 to 0.3 wt%, and when both La and Y are contained, A ferritic stainless steel having excellent high temperature oxidation resistance, characterized by containing 0.3 wt% or less of the total amount thereof, and the balance being Fe and inevitable impurities. 2. C: 0.030 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, Cr: 15.0 to 25.0 wt%, Ni: 0.32 to 5.0 wt%, Al: 2.5 to 15.0 wt%, N: 0.03 wt% or less, Ti: 0.010 to 0.30 wt%, and La: 0.01 to 0.3 wt% and Y: 0.01 to 0.3 wt%. When both La and Y are contained, the total content of La and Y is 0.3 wt% or less, and the balance is Fe and unavoidable impurities, and the ferritic stainless steel excellent in high temperature oxidation resistance is characterized. .