JPH06146011A - Austenite stainless steel material and its manufacture - Google Patents

Abstract

PURPOSE:To provide are austenite stainless steel which has superior oxidation resistance and high-temperature mechanical strength and also has basic characteristics and advantages of austenite stainless steel as they are and is superior in high-temperature electric conductivity and its manufacture. CONSTITUTION:The surface of an austenite stainless steel plate containing 10-30% Cr and 10-60% Ni is coated with an Ni layer or an oxide layer is formed by a plasma treatment as necessary, then the surface is coated with a conductive oxide to improve the electric conductivity and oxidation resistance in a high-temperature oxidative atmosphere. Further, an annealing treatment wherein the plate is held at 400-1,200 deg.C temperatures for >=1 second in a nonoxidative atmosphere whose dewing point is -15 to -60 deg.C may be carried out.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an austenitic stainless steel having excellent oxidation resistance and electrical conductivity in a high temperature environment of, for example, 400 ° C. or higher and having good compatibility with a material having a small coefficient of thermal expansion such as ceramics. Steel and its manufacturing method.

[0002]

2. Description of the Related Art Due to environmental problems including depletion of petroleum resources and air pollution in the 21st century, fuel cells that can use coal reformed gas as a next-generation power supply source have come into the limelight. There are various types of fuel cells, such as phosphoric acid type, molten carbonate type, and solid electrolyte type, depending on the electrolyte that generates electromotive force.
The operating temperature is also different. For both the molten carbonate type with an operating temperature of 650 ° C and the solid electrolyte type with an operating temperature of 1000 ° C, reducing fuel cell manufacturing costs and extending their lifespan are extremely important development issues for future practical application. Therefore, inexpensive and high-performance metallic materials are required.

Particularly, in the solid electrolyte type, which can be said to be developed including the fuel cell structure, the constituent members such as the interconnector and the corrugated support layer, which have been studied in a laboratory scale, are extremely expensive ceramics having electric conductivity. Therefore, there is a strong demand for the development of inexpensive high-performance metal materials that can be used instead. Now, when applying stainless steel as a constituent member such as an interconnector or a corrugated support layer of such a solid oxide fuel cell,
It is necessary to give the stainless steel a performance that distinguishes it from conventional stainless steels in securing the oxidation resistance in the extremely harsh oxidizing environment of 1000 ° C and the electrical conductivity at high temperature.

By the way, in comparison with conventional component materials used at high temperatures, such as automobile exhaust manifolds, automobile exhaust gas reforming catalyst carriers, heat exchanger members, heating furnace members, heating device combustion members, etc. Ferritic stainless steel is an inexpensive material. For example, for exhaust manifolds for automobiles, 12% Cr-based stainless steel such as SUH409, N
b, Cu-containing 17% Cr-based ferritic stainless steel, or the same system of 19% Cr-based ferritic stainless steel is used. In addition, 20% Cr-5% Al-based ferritic stainless steel foil with Ca or REM added is used for automobile exhaust gas reforming catalyst carriers. It is also well known that 18% Cr-based ferritic stainless steel containing 2.5% Si is often used for the combustion member of the stove.

In the austenitic type, 25Cr-20Ni typified by SUS 310S and 21Cr known as Incoloy 800
−32.5Ni series, SUSXM15J1 with Si added, etc.
Each is used according to the purpose of use. In general,
To ensure the oxidation resistance of stainless steel at high temperatures,
12% or more of Cr is added, and 0.5% or more of Si or A1 is not added. Due to the addition of these alloying elements, SiO ₂ and A1 ₂ O are formed on the steel surface during use in a high temperature oxidizing atmosphere.
Oxide scale mainly composed of ₃ or Cr ₂ O ₃ is generated, and further progress of oxidation is significantly suppressed.

Further, REM addition of Y, La, etc. is carried out for the purpose of fixing sulfide in steel as sulfide more stable than MnS. By adding more than 0.001% of these elements, preferably about 0.008%, local abnormal oxidation around the surface-exposed sulfide is suppressed, and the adhesion of oxide scale is improved, so that the oxidation resistance is improved. It will be strengthened.

As for the oxidation resistance, it is possible to improve the oxidation resistance to some extent by adding an appropriate amount of the oxidation resistance improving elements such as A1 and Si to the steel. Oxide scale formed on the steel surface at that time significantly lowers the electric conductivity at high temperature, and therefore it is necessary to devise a method for ensuring the electric conductivity at high temperature. In particular, the A1 ₂ O ₃ film that is most desirable for improving the oxidation resistance under conditions exceeding 1000 ° C is an insulating oxide.
^It has only a conductivity of about ^-6 S / cm. On the other hand, it is a P-type semiconductor and has an electric conductivity of about 2 × 10 ⁻³ S / cm at 1000 ° C.
Cr ₂ O _3, which is relatively good, has a fast scale growth rate, and the scale thickness at a certain time is significantly thicker than A 1 ₂ O ₃ . Therefore, in the case of Cr ₂ O ₃ oxide scale, it is necessary to improve the oxidation resistance while ensuring the conductivity.

Further, when considering use as a constituent member of a fuel cell, mechanical strength at high temperature is required. Deformation of the material after long-term use not only prevents stable electricity extraction but also damages the battery body. Mechanical strength at 1000 ° C. is 1.5 kgf / mm ² in ferritic is 8.5 kgf / mm ² in austenitic.

Further, if the difference in thermal expansion from the ceramics constituting the electrolyte is large, it is easily expected that the electrolyte will be damaged. 1000 ℃ of Fe-Cr ferritic stainless steel
The coefficient of thermal expansion in the vicinity is about 13 × 10 ^-6 / ℃, about 20 × 10 ^-6 / ℃ for Fe-Cr-Ni austenitic stainless steel, 10 × 10 ^{-6 of the} ceramic that constitutes the electrolyte. It is larger than / ℃ and may cause damage to the battery. Desirably, the coefficient of thermal expansion is about the same as that of the ceramic constituting the electrolyte. Now, in the austenitic stainless steel containing the above-mentioned oxidation resistance improving element, without impairing its basic characteristics, if it is possible to ensure the electrical conductivity at high temperature, in terms of practicality and convenience A huge profit is expected.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to provide the basic characteristics and advantages of austenitic stainless steel excellent in oxidation resistance and mechanical strength at high temperature as they are, and to have electrical conductivity at high temperature. To provide an excellent austenitic stainless steel and a manufacturing method thereof.

[0011]

Means for Solving the Problems The present inventors have conducted studies for the purpose of developing a material having excellent oxidation resistance and good electric conductivity at high temperatures, and have obtained the following findings. When Cr, A1, Si, etc. are added to austenitic stainless steel as an alloying element to improve oxidation resistance, it can be used at 900 ° C or higher to some extent from the viewpoint of high temperature oxidation progress rate. Along with this, the electrical conductivity at high temperature decreases. In particular, when applied beyond 1000 ° C. is is most effective to add the A1 from the point of view of oxidation resistance secured at least 3%, A1 A1 ₂ O insulating the steel surface by adding
_{3 As a} film is formed, the electrical conductivity is significantly reduced.

When a high A1 added austenitic stainless steel is applied to a portion such as an interconnector of a solid oxide fuel cell, the electric resistance becomes high and the cell characteristics may be greatly deteriorated with time. It is possible, to some extent, to improve the electrical conductivity by changing the oxide scale composition during use by optimizing the components in the steel, but in that case, the oxide scale produced by the environment to which the material is exposed More practical than changing. Therefore, based on the above knowledge and consideration, the present inventors have studied the improvement of oxidation resistance and the improvement of electrical conductivity at high temperature by various methods, and have obtained the following knowledge to provide the present invention. I arrived.

(1) Conventionally, an interconnector for a fuel cell is made of an extremely expensive conductive ceramic having oxidation resistance, good electrical conductivity, and thermal expansion comparable to that of the conductive ceramic constituting the electrolyte. It is used. (2) Stainless steel containing 10% or more of Cr can be applied for a long time without exceeding its excellent oxidation resistance even in the temperature range of over 850 ° C and 950 ° C. It is promising as an interconnector material for fuel cells.

(3) The austenitic stainless steel containing 10% or more of Ni in addition to the above components has sufficient mechanical strength even in a high temperature environment near 1000 ° C. (4) By covering the surface of a steel material having good oxidation resistance at high temperature with a conductive oxide by a method such as vapor deposition or plasma spraying, oxygen reaches the surface of the steel material in a high temperature oxidizing atmosphere more slowly It has excellent oxidation resistance and good electrical conductivity.

(5) By coating Ni as an intermediate layer before coating the surface of the steel material with the conductive oxide, the adhesion of the conductive oxide at the time of coating is improved, and at the same time the steel material and the oxide are oxidized. It plays the role of alleviating the difference in thermal expansion from the product. (6) Prior to the coating treatment, low-temperature plasma treatment is performed on the surface of the steel material in an atmosphere in which plasma is generated.
It is possible to form an oxide layer containing A1 and mainly composed of Cr oxide. By providing a coating of a conductive oxide on the oxide layer thus produced, it is possible to further improve the oxidation resistance and also improve the adhesion of the vapor-deposited or plasma sprayed film.

In the present invention, the weight ratio of Cr is 10 to 30.
%, Ni: 10 to 60%, and the surface thereof is coated with a conductive oxide, which is an oxidation resistant austenitic stainless steel material excellent in electrical conductivity in a high temperature oxidizing atmosphere.
From another aspect, the present invention provides Cr: 10 to 10% by weight.
30%, Ni: 10-60% contained steel plate surface coated with Ni layer,
Then, a conductive oxide is coated on the Ni layer, which is a method for producing an oxidizable austenitic stainless steel material having excellent electric conductivity in a high temperature oxidizing atmosphere.

In yet another aspect, the present invention provides a weight percent.
Then, an oxide layer is formed on the surface of a steel sheet containing Cr: 10 to 30% and Ni: 10 to 60% by low temperature plasma treatment, and then a conductive oxide is coated on the oxide layer. It is a method for producing an oxidation resistant austenitic stainless steel material having excellent electrical conductivity in a high temperature oxidizing atmosphere. According to a preferred aspect, after coating the conductive oxide,
400 ~ in a non-oxidizing atmosphere with a dew point temperature of -15 to -60 ℃
You may perform the heat processing hold | maintained at the temperature of 1200 degreeC for 1 second or more.

The above-mentioned "austenitic stainless steel material" refers to general members made of austenitic stainless steel, specifically, plate materials, bar materials, pipe materials,
Examples include foil materials.

[0019]

Next, the reason why the present invention is limited to the above range will be described. Cr: The subject of the present invention is to treat, that is, the base material is austenitic stainless steel, Cr: 10 ~
There is no particular limitation as long as it contains 30% and Ni: 10 to 60%. That is, in the present invention, the austenitic stainless steel was selected as the target, and the surface was treated with Cr by the low temperature plasma treatment or Ni coating as desired.
Alternatively, it is sufficient that an oxide layer mainly containing Cr oxide containing Al can be formed. Therefore, in the present invention, Cr: 10
It is limited to ~ 30%, Ni: 10 to 60%.

Therefore, Cr is a basic element necessary for obtaining oxidation resistance at high temperature together with A1. In the present invention, the lower limit is 10% and the upper limit is 30%. This is 400
10 to produce Cr ₂ O ₃ -based oxide scales above ℃
This is because Cr of more than% is required. On the other hand, addition of more than 30% does not not only improve the oxidation resistance, but also makes it difficult to maintain the austenite phase, and is particularly sensitive to σ embrittlement and 475 ° C embrittlement. Formability,
It adversely affects workability.

Ni: Ni is an important element that gives the basic properties of austenitic steel. If it is less than 10.0%, it becomes difficult to maintain the austenite structure. On the other hand, if it exceeds 60%, it will be difficult to put it into practical use in terms of cost.
The upper limit is 60%.

Conductive oxide: The conductive oxide used as the coating material in the present invention has excellent oxidation resistance and electrical conductivity even in a high temperature oxidizing atmosphere as found in, for example, a solid oxide fuel cell. If it is not particularly limited as long as it is, according to its preferred embodiment, both are oxygen ion conductive oxides or mixed conductive oxides, in the present invention YSZ, LaCrO ₃ , LaCoO ₃ , La _1-x Sr. _x CrO ₃ ,
La _1-x Sr _x MnO ₃ , La _1-x Cr _x CoO _3, a mixture thereof, and a complex oxide were used.

Next, some explanation will be made on these conductive oxides used in the present invention. YSZ is a conductive ceramic in which low-valent oxide Y ₂ O ₃ is solid-solved in ZrO ₂ having a fluorite structure so that a fluorite-type cubic crystal can exist stably from high temperature to room temperature. This fluorite type solid solution shows that oxygen ions are not the closest packing, and that the substitutional solid solution range with alkaline earth or rare earth atoms is wide and the vacancy concentration at the oxygen atom position is high and the oxygen ion conductivity is large. .

On the other hand, the oxide represented by ABO ₃ is an oxide called a perovskite type oxide, and exhibits mixed ion conductivity by the movement of oxygen ions and electrons or holes. The coating method is preferably a vapor deposition method or a plasma spraying method, but any coating thermal decomposition method may be used as long as it can coat the above-mentioned conductive oxide in the present invention. Therefore, the coating method used in the present invention is not particularly limited, but preferred embodiments of the vapor deposition method and the plasma spraying method will be described below.

The vapor deposition method is already known per se,
The treatment operation may be a conventional one, but it is necessary to optimize the alloying components and the oxygen potential of the atmosphere for each treatment condition so as to obtain a proper oxide composition. As the thermal spraying method, one already known per se may be used. Plasma spraying under reduced pressure is desirable from the viewpoint of the denseness of the sprayed film, but the impact of the powder colliding with the base material during film formation is large and mechanical stress occurs, which destroys the crystal structure of the powder. Leading to. Therefore, in the preferred embodiment of the present invention, plasma spraying under atmospheric pressure was used.

In the case of thermal spraying, the blasting treatment before the coating treatment is extremely effective in reducing the residual stress to reduce the grain size and improve the adhesion of the coating material to the base material.
This process is performed as needed. Prior to coating the oxide layer by such vapor deposition or thermal spraying method, Ni was used as a kind of pretreatment.
Formation of a film and low temperature plasma treatment may be performed.

The thickness of the vapor-deposited layer and the thermal sprayed layer may be appropriately determined according to the purpose and is not particularly limited, but preferably the vapor-deposited layer is 10 μm or less and the thermal sprayed layer is 100 μm or less. By forming the Ni layer between the base material and the conductive oxide in this way, it is expected that the adhesion will be improved. The method is not particularly limited. Although the vapor deposition method is used in the present invention, its basic characteristics are not impaired even when it is coated by electroplating, hot dipping or plasma spraying.

The low-temperature plasma treatment is, for example, an austenitic stainless steel which is subjected to an ion bombardment treatment by applying a bias voltage of 0 to -500 V in a state where it is preheated to room temperature or higher than room temperature and 450 ° C. or lower. The preheating temperature was set to 450 ° C. or lower at which high temperature oxidation due to thermal diffusion became remarkable. The bias voltage is 0 to -500V. When the bias voltage is too large, the degree to which the atoms turned into plasma hit the surface becomes strong and the low-temperature plasma treatment effect decreases. In addition, when a small amount of air or oxygen is introduced into the chamber during the treatment, there is a behavior that a specific element is concentrated and oxidized on the surface of the steel sheet during the low temperature plasma treatment. The oxide film composed of a specific element is effective in improving the oxidation resistance and the adhesiveness of the sprayed film, and therefore is performed as necessary.

The heat treatment after coating with the conductive oxide is, if necessary, 400 to 400 in a non-oxidizing atmosphere having a dew point of -15 to -60 ° C.
It is performed by keeping the temperature at 1200 ° C for 1 second or more. The treatment temperature of 400 to 1200 ° C does not cause thermal diffusion below 400 ° C, and above 1200 ° C, the austenitic stainless steel, which is the component range of the steel of the present invention, has a low melting point compound due to mutual diffusion. Will be generated. Further, the atmosphere in the furnace is extremely important in performing such an annealing treatment. It is necessary to maintain the dew point at −15 to −60 ° C. in a non-oxidizing atmosphere mainly containing Ar, N ₂ , H ₂ or the like or a reduced pressure atmosphere.

The composition of the austenitic stainless steel to which the present invention is applied is not particularly limited as long as it has the above composition, but from a practical point of view, more specifically, the austenitic stainless steel according to the present invention is Is
% By weight, C: 0.0001 to 0.10%, N: 0.0001 to 0.10%,
S: 0.0001 to 0.0020%, Cr: 10.00 to 30.00%, Ni: 1
0.00 to 60.00%, A1: 0.001 to 2.0%, Si: 0.01 to 6.0
%, Mn: 0.01% to 3.00%, P: 0.03% or less, Ti or N
1 or 2 of b in total is more than 4 times the amount of C + N, 3.0%
Below, if necessary, rare earth elements (REM) such as Ce, La, or
One or two or more of Y and Ca is 0.20% or less, and if necessary, Mo: 0.01 to 10.0%, and a steel composition containing 0.8% or less of Cu in the steel and the balance Fe and unavoidable impurities. Is an austenitic stainless steel.

Further, the austenitic stainless steel according to the present invention which can be applied to the production of oxides mainly containing A1 is, by weight%, C: 0.0001 to 0.10%, N: 0.0001 to 0.
10%, S: 0.0001 to 0.0020%, Cr: 10.00 to 30.00%,
Ni: 10.00 to 60.00%, A1: 2.00 to 6.00%, Si: 0.01 to
6.00%, Mn: 0.01% to 3.00%, P: 0.03% or less, one or two of Ti or Nb in total of 4 times or more the amount of C + N, 3.
0% or less, if necessary, rare earth elements (REM) such as Ce, La, etc., or one or more of Y, Ca, 0.20% or less, and if necessary, Mo: 0.01 to 10.0% Other, in steel Is an austenitic stainless steel containing 0.8% or less of Cu and having a balance of Fe and inevitable impurities.

Although the present invention is not limited to such a steel composition, the reason why the steel composition is limited as described above will be described as a suitable example. C: C is an element that significantly reduces the toughness at room temperature, and when used at high temperatures or in the heat-affected zone of the weld, forms Cr ₂₃ C ₆ type carbides, which improves the oxidation resistance of Cr. Has the effect of significantly reducing In addition, it is preferable that the lower limit is 0.10% because it causes scale peeling. However, when importance is attached to mechanical strength, it may be contained up to near the upper limit. The lower limit is practically set to 0.0001%.

A1 A1 is an important basic element in the steel of the present invention. When forming an oxide mainly composed of A1 (oxide having the highest content of metallic Al in all oxides), 2.0% or more is required to form a uniform scale. However, if it is added in excess of 6.0%, the toughness at room temperature will be significantly reduced, so the upper limit is made 6.0%. However, Cr ₂ O ₃ , CrFe ₂ O ₄
When producing oxides mainly composed of Cr, such as 0.001 ~
Limit to 2.0%.

Si: Si is a deoxidizing element and 0.1% or more is necessary to ensure its effect. It acts as an oxidation resistance improving element during the formation of Cr-based oxides, but in the case of A1-based oxide formation, the effect of Si for improving the oxidation resistance is not significant and the upper limit is set due to the problem of toughness reduction. 6.0%

N: N, like C, is an element that significantly reduces toughness at room temperature. Further, by forming a nitride by combining with Cr and A1 in the steel, there is an adverse effect that Cr and Al reduce the oxidation resistance at high temperature. The upper limit is 0.10%. For the purpose of reducing the adverse effects of C and N in steel, Ti and Nb stabilizing elements with a stronger affinity for C and N than Cr or A1 are added. In order to improve the toughness at room temperature and the oxidation resistance at high temperature, there is a desirable amount of addition. In order to fix C and N in steel, C + N (%) in steel must be more than 4 times
Ti or Nb is required. In addition, since excessive addition of Ti and Nb also causes deterioration of toughness due to precipitation of intermetallic compounds, the upper limit is set to 3.00% for Ti + Nb (%).

S: The upper limit of S is regulated to 0.002%, and if necessary, it is fixed by adding a rare earth element such as Ce, La, or Y, which forms a more stable sulfide at a temperature higher than Mn, or Ca. Turn into. For the purpose of enhancing these effects, the O concentration in steel is preferably low. This is because these additive elements tend to form oxides and are consumed as oxides before they function as S-fixing elements in steel, reducing the effective amount. Lower S + O (%) value in steel is preferable, but S + O (%) ≤ 0.008, more preferably S + O
(%) ≤ 0.005 is required.

Mo: Mo may be added to secure strength at high temperature or to secure corrosion resistance. However, the upper limit is set to 10.0% due to the problem of reduced toughness. Mn: Mn may be added to secure strength at high temperatures. It is also effective for stabilizing the austenite phase. 0.
It is desirable that the content is 01 to 3.00%.

P: P is not positively added. In principle, it is an impurity. Contains 0.03% or less. La, Ce, Y, Ca: These are S in steel as described above.
It is an immobilizing element. Although it has a strong affinity with oxygen in steel and is also consumed as an oxide, excessive addition adversely affects the oxidation resistance due to the formation of coarse oxide.
If necessary, it is added within the range of not more than%.

Cu: Cu in steel may improve the corrosion resistance of the base material. If it is contained as an impurity in 0.8% or less, there is no adverse effect. Next, the effects of the present invention will be further described with reference to specific examples.

[0040]

【Example】

(Example 1) Steel Nos. 1 to 14 having the compositions shown in Table 1 are melted in a vacuum melting furnace and cast, hot-rolled and cold-rolled to a plate thickness of 1 mm. The various steel plates thus produced were used as vapor deposition or thermal spray substrates, degreased and washed with an organic solvent, and then coated with the conductive oxide in the amounts shown in Table 2 by vapor deposition or thermal spray.

The vapor deposition was carried out using an electron beam method at a degree of vacuum in the vacuum chamber of 1 × 10 ⁻³ to 10 ⁻⁵ torr. The oxygen potential depends on the partial pressure adjustment in the vacuum chamber and / or the residual water content.
The thermal spraying was performed by a reduced pressure plasma system with an arc voltage of 25 V and an arc current of 400 A. The working gas is Ar or Ar.
And a mixed gas of N ₂ + H ₂ was used. Various test materials were cut out from the steel plate thus obtained and subjected to an oxidation test by continuous heating at 1000 ° C. in the atmosphere.

FIG. 1 shows the changes with time (in mg / cm ² ) of the increase in oxidation at 1000 ° C. of the steels No. 1 to 11 of the present invention and the comparative steel No. 13 coated with LaCrO ₃ by vapor deposition among the steel types shown in Table 1. Show. Among the present invention steels, the present invention steel Nos. 1 and 6, the coating method, the coating material and the treatment conditions of the coating layer thickness, the strength by the tensile test at 1000 ° C. in the atmosphere, and the increase change after oxidation at 1000 ° C. × 1000 hr The results are summarized in Table 2. In addition, in the oxidation test, the oxidation resistance was evaluated based on the magnitude of the increase in the amount of oxidation after the oxidation including scale peeling.

FIG. 2 shows that LaCrO ₃ , LaSrCrO ₃ and La were deposited by vapor deposition.
₃ is a graph showing the results of electric resistance of various kinds of steel No. 1 of the present invention coated with CoO ₃ , Al ₂ O _{3 and the} like after oxidation at 1000 ° C. for 1000 hours in the atmosphere. The measurement was performed in the thickness direction of the steel sheet, and the result was converted to sheet resistance (Ω · cm ² ). From the change over time in the amount of increased oxidation shown in FIG. 1, it can be seen that each steel type having the proper chemical composition shown in the present invention has excellent oxidation resistance. Further, from Table 2, the austenitic stainless steel of the present invention is a ferritic stainless steel N even in a high temperature environment around 1000 ° C.
It has sufficient strength compared to o.12. Also, those coated with a conductive oxide have better oxidation resistance than steel without coating. From the result of resistance measurement shown in FIG. 2, it can be seen that the conductivity is extremely improved by the coating treatment with the conductive oxide.

(Example 2) Steel No. of the present invention used in Example 1
For austenitic stainless steel sheets 1 and 6, Table 3
The Ni layer was coated under the conditions shown in. An oxidation test was conducted on the steel sheet of Steel No. 1 of the present invention thus obtained. FIG. 3 is a graph showing the results of the increase in the amount of oxidation during the repeated oxidation test of 1000 ° C. × 30 min heating and −10 min cooling in the atmosphere. It can be seen that by interposing the Ni layer between the base material and the conductive oxide layer, a steel sheet with more excellent adhesion can be obtained.

(Example 3) Steel No. of the present invention used in Example 2
The austenitic stainless steel sheets 1 and 6 were subjected to low temperature plasma treatment, heat treatment after oxide coating, or blast treatment under the conditions shown in Table 4. An oxidation test was conducted on the steel plate of Steel No. 1 thus obtained. In the air
The graph shows the results of the time course of the increase in the amount of oxidation when heated at 1000 ° C. It can be seen that the oxidation resistance is further improved particularly when oxygen or air is introduced in the low temperature plasma treatment. This is due to the presence of Cr on the steel plate surface under proper low temperature plasma conditions.
This is because the main oxide or the main oxide of Cr containing A1 is densely formed.

Furthermore, by performing heat treatment after coating, the oxidation resistance is further improved. It is considered that the oxide scale becomes dense due to the high temperature heat treatment accompanied by thermal diffusion.
In particular, since oxides coated by plasma spraying under body pressure have many pores and facilitate the ingress of oxygen, it is extremely effective to seal the pores by heat treatment. According to the present invention, by covering the LaCrO _3, LaMnO ₃ such as a conductive ceramic ferritic stainless steel, in the temperature range of 500 to 1000 ° C., takes on the example LaMnO _3, expansion coefficient close to YSZ, Good compatibility with ceramics.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

[0051]

As described above, according to the present invention, by coating an austenitic stainless steel having mechanical strength at high temperature with a conductive oxide, high temperature can be achieved without sacrificing oxidation resistance. Since the electric conductivity of the steel is secured, and the steel material thus obtained has good compatibility with ceramics having a small coefficient of thermal expansion, it is useful as a constituent member of a fuel cell.

[Brief description of drawings]

FIG. 1 is a graph showing the oxidation resistance of the material obtained in Example 1.

FIG. 2 is a graph showing the electric conductivity of a material coated with each conductive oxide.

FIG. 3 is a graph showing the effect of a Ni layer as an intermediate material on the adhesion of the material obtained in Example 2.

FIG. 4 is a graph showing the oxidation resistance of a material that has been subjected to a low temperature plasma treatment and a heat treatment after coating in Example 3.

Claims (4)

[Claims] 1. By weight%, Cr: 10 to 30%, Ni: 10 to 60%
An oxidation-resistant austenitic stainless steel material having excellent electrical conductivity in a high-temperature oxidizing atmosphere, characterized by containing a conductive oxide on the surface. 2. By weight, Cr: 10 to 30%, Ni: 10 to 60%
A method for producing an oxidizable austenitic stainless steel material excellent in electrical conductivity in a high temperature oxidizing atmosphere, characterized by coating a Ni layer on the surface of a steel sheet containing it, and then coating a conductive oxide on the Ni layer . 3. By weight%, Cr: 10 to 30%, Ni: 10 to 60%
An electrically conductive oxide is formed in a high temperature oxidizing atmosphere according to claim 2, wherein an oxide layer is formed on the surface of the steel sheet containing the same by a low temperature plasma treatment, and then a conductive oxide is coated on the oxide layer. Excellent oxidation resistance A method for manufacturing austenitic stainless steel. 4. After the conductive oxide is coated, the conductive oxide is further applied in a non-oxidizing atmosphere having a dew point temperature of −15 to −60 ° C.
The method for producing an oxidation-resistant austenitic stainless steel material excellent in electrical conductivity in a high temperature oxidizing atmosphere according to claim 2 or 3, characterized in that the temperature is maintained at 0 to 1200 ° C for 1 second or more.