JP4259225B2 - Metal material for fuel cell and solid oxide fuel cell - Google Patents

Description

  The present invention relates to a metal material for a fuel cell, and in particular, a metal material for an interconnector of a solid oxide fuel cell (Fe-Cr alloy) having both excellent oxidation resistance and electrical conductivity during use at high temperatures. Material) and a solid oxide fuel cell using the metal material.

  Fuel cells are expected to be applied to a wide range of power generation systems, such as large-scale power generation, cogeneration systems, and automobile power supplies, because they emit less harmful gases and have high power generation efficiency. Among them, solid oxide fuel cells (also referred to as solid oxide fuel cells) operate at 700 to 1000 ° C. and do not require the use of a catalyst for electrode reaction, and various fuel gases such as coal reformed gas. And can be combined with a gas turbine or a steam turbine using high-temperature exhaust heat, and has attracted attention as a next-generation energy source.

As shown in FIG. 1, this solid oxide fuel cell is composed of an electrolyte 1, electrodes 2 and 3, and an interconnector 4 (also referred to as a separator). An ion-conducting solid electrolyte such as stabilized zirconia (YSZ) is used, anode (air electrode) 2 made of (La, Sr) MnO _3, etc. on both sides and Ni / YSZ (Ni and yttria stabilized zirconia cermet), etc. A cathode (fuel electrode) 3 is attached to form an electrolyte-electrode assembly, and electricity is supplied by supplying a fuel gas 5 such as hydrogen gas to one side and an oxidizing gas 6 such as air to the other side using the electrolyte 1 as a partition. I'm taking it out. The interconnector 4 supports the three layers of the electrolyte 1, the anode 2, and the cathode 3, forms a gas flow path 7, and plays a role of flowing current.

  Such solid oxide fuel cells still have many problems to be put into practical use. In particular, the interconnector 4 which is an important constituent material has many problems. This is because the interconnector is used at a high temperature of 700-900 ° C., which is close to 1000 ° C., so that it has excellent oxidation resistance and electrical conductivity, as well as characteristics such as a small difference in thermal expansion from the electrolyte. Because.

Conventionally, conductive ceramics such as (La, Sr) CrO ₃ have been used to satisfy such required characteristics. However, ceramics have poor workability and are expensive, so there is a problem in terms of increasing the size and practical use of fuel cells. Therefore, as an alternative material, an interconnector made of an inexpensive and highly reliable metal material is being developed.

  By the way, when using a metal material at high temperature, there exists a problem that the surface is oxidized and an oxide film is produced. Therefore, in order to use as an interconnector, it is necessary that the growth of this oxide film is slow and does not peel off. Furthermore, this oxide film has electrical conductivity, that is, high temperature oxidation resistance and electrical conductivity. It is necessary to have two characteristics.

As a technology that meets such a requirement, for example, in Patent Document 1, as a metal material for a solid oxide fuel cell, C: 0.1 mass% or less, Si: 0.5 to 3.0 mass%, Mn: 3.0 mass% or less, An austenitic stainless steel is disclosed in which Cr: 15 to 30 mass%, Ni: 20 to 60 mass%, Al: 2.5 to 5.5 mass%, and the balance being substantially Fe. However, since this metal material contains a considerable amount of Al and Cr, an oxide film mainly composed of an Al-based oxide is generated. As will be described later, since the Al-based oxide has low electrical conductivity, it is not suitable for use in an interconnector for a solid oxide fuel cell. Furthermore, the austenitic stainless steel has a coefficient of thermal expansion from 20 ° C. to 900 ° C. of 16 to 20 × 10 ⁻⁶ / ° C., that of yttria stabilized zirconia used in the electrolyte (9 to 12 × 10 ⁻⁶ / ° C.). ), The electrolyte and the electrode may be cracked due to a difference in thermal expansion due to a temperature change at the time of starting and stopping. Moreover, expensive Ni needs to be added in a large amount of 20 to 60 mass%.

  Patent Document 2 discloses that a solid oxide fuel cell interconnector is made of a material composed of Fe: 60 to 82 mass% and Cr: 18 to 40 mass%, and contact between the air electrode of a single cell (cell). A technique in which an element (La, Y, Ce or Al) for reducing resistance is added is disclosed. However, this interconnector material does not have oxidation resistance that can withstand long-term use at high temperatures, and inevitably increases the electrical resistance of the oxide film.

  Patent Document 3 discloses, as a metal material for a solid oxide fuel cell, a material consisting of Cr: 5 to 30 mass%, Co: 3 to 45 mass%, La: 1 mass% or less, and the balance being substantially Fe. Has been. However, it does not have sufficient characteristics in terms of oxidation resistance, particularly in terms of increase in oxidation.

  Moreover, in patent document 4, as steel for interconnectors for solid oxide fuel cells, C: 0.2 mass% or less, Si: 0.2-3.0 mass%, Mn: 0.2-1.0 mass%, Cr: 15-30 mass% , Y: 0.5 mass% or less, REM: 0.2 mass% or less, Zr: 1 mass% or less, and the balance substantially including Fe is disclosed. However, although this material has been evaluated for the amount of scale peeling with respect to oxidation resistance, the effect of suppressing an increase in the thickness of the oxide film is insufficient, and an increase in electrical resistance due to the growth of the oxide film can be avoided. Absent. Moreover, the reduction of the thermal expansion coefficient is insufficient.

Furthermore, in Patent Document 5, as steel for an interconnector for a solid oxide fuel cell, C: 0.2 mass% or less, Si: 3.0 mass% or less, Mn: 1.0 mass% or less, Cr: 15 to 30 mass%, Hf : 0.5 mass% or less, the material which the remainder substantially consists of Fe is disclosed. However, as in Patent Document 4, this technique also evaluates the amount of scale peeling with respect to oxidation resistance, but the effect of suppressing the growth of the oxide film is small, and an increase in electrical resistance is inevitable. Moreover, the reduction of the thermal expansion coefficient is insufficient.
As described above, any of the conventionally disclosed metal materials for fuel cells does not necessarily have sufficient oxidation resistance and electrical conductivity for an interconnector of a solid oxide fuel cell.
JP-A-6-264193 Japanese Unexamined Patent Publication No. 7-166301 JP 7-145454 A JP-A-9-157801 Japanese Patent Laid-Open No. 10-280103

  As described above, the solid oxide fuel cell operates in a high temperature environment of 700 to 900 ° C., which is close to 1000 ° C. Therefore, the metal material used for the interconnector of this solid oxide fuel cell needs to have excellent oxidation resistance, and for that purpose, formation of a protective oxide film is indispensable. However, since it is also a member that requires electrical conductivity at the same time, it is desired to reduce the thickness of the oxide film together with the electrical conductivity of the oxide. In this respect, an Al-based oxide that forms an excellent protective film has a low electric conductivity, and the cell performance is greatly degraded due to an increase in electric resistance due to the formation of an oxide film. Therefore, a metal material containing a large amount of Al cannot be used for an interconnector.

In addition, the interconnector of the solid oxide fuel cell is required to form a protective film having a small thermal expansion difference from yttria-stabilized zirconia (YSZ), which is an electrolyte, and excellent in electrical conductivity. Therefore, for example, a ferritic metal material that produces a protective film mainly composed of Cr ₂ O ₃ is considered promising. However, a material obtained by simply adding REM or the like to a Fe-Cr alloy as in the prior art. Then, the characteristics are insufficient, and further improvement in oxidation resistance is necessary. In other words, even if a Fe-Cr alloy is used and a Cr-based oxide film with high electrical conductivity is formed, if the film adhesion cannot be improved or the film growth rate cannot be reduced, it can be applied to the application of the present invention. There is a problem that you can not.

  The object of the present invention is to have excellent oxidation resistance even under a high temperature use environment of 700 to 900 ° C., that is, the oxidation rate is low, and the formed oxide film has excellent peeling resistance and good electrical conductivity. And a metal material (Fe-Cr alloy) for an interconnector of a solid oxide fuel cell that has a small difference in thermal expansion from an electrolyte and can be manufactured at low cost, and a fuel cell using the metal material It is in.

  In order to solve the above-mentioned problems of the prior art, the inventors focused on the influence of additive elements on the oxidation resistance, and conducted intensive studies. As a result, it has been found that the oxidation resistance is greatly improved by the combined addition of Mo and Nb, and the present invention has been completed. That is, the greatest feature of the present invention is that a large amount of Mo, Nb intermetallic compound (a kind of precipitate) is used in a high temperature and long-time use environment of 700 to 900 ° C. where the solid oxide fuel cell operates. The purpose is to precipitate at the grain boundary of the base material and to improve the oxidation resistance by the effect of controlling the diffusion of alloy elements by the precipitate. In other words, the intermetallic compound precipitates even when Mo or Nb is added alone, but only when the combined addition of Mo and Nb, the intermetallic compound precipitates in large amounts at the grain boundary of the base metal, and Cr, Fe, Si, etc. Thus, it is possible to control the diffusion of each element and to significantly improve the oxidation resistance.

Furthermore, the Mo-Nb-based material-specific, a problem that peeling of the oxide increases at high temperatures, Sc, Y, La, Ce , Pr, Nd, Pm, 1 or more either S m Contact and Hf It was found that this can be prevented by addition of these elements. Even if these additions are made, the oxide film formed is mainly composed of Cr ₂ O ₃ , so there is no significant increase in electrical resistance, and only an increase in oxidation can be suppressed purely. It can be effectively suppressed.

The present invention developed based on the above findings is C: 0.20 mass% or less, Si: 0.02 to 1.0 mass%, Mn: 2.0 mass% or less, Cr: 10 to 40 mass%, Mo: 0.03. -5.0mass%, Nb: 0.1-3.0mass% is contained, and Mo and Nb are following Formula;
0.1 ≦ Mo / Nb ≦ 6.81 is satisfied and contained,
Furthermore, Sc, Y, La, Ce , Pr, Nd, Pm, containing 0.03～1.0Mass% in a total amount of one or more selected from among S m Contact and Hf, the balance being Fe And a metal material for a fuel cell comprising inevitable impurities.

The metal material for an interconnector of the solid oxide fuel cell of the present invention contains a precipitate, and the total amount of Fe, Cr, and Si contained in the precipitate is 0.02 mass% with respect to the metal material. The above is preferable .

The metal material for an interconnector of the solid oxide fuel cell of the present invention is preferably a hot rolled material or a cold rolled material.

The total amount of Fe, Cr and Si contained in the deposit of the metal material for an interconnector of the solid oxide fuel cell according to the present invention is based on the metal material after power generation at an operating temperature of 800 ° C. for 1000 hours or more. It is preferable that it is 0.03 mass% or more.

  The metal material for a fuel cell of the present invention is preferably used for a solid oxide fuel cell, particularly for an interconnector of a solid oxide fuel cell.

Further, the present invention is a solid oxide fuel cell characterized by using the above Symbol of the solid oxide fuel cell interconnector metallic material.

According to the present invention, the Fe-Cr alloy, the Mo and Nb added in combination, further, Sc, Y, La, Ce , Pr, Nd, Pm, 1 kind selected from among S m Contact and Hf or 2 By adding seeds or more, it is possible to obtain a metal material for an interconnector of a solid oxide fuel cell that is excellent in oxidation resistance and excellent in electrical conductivity. In addition, by using the metal material of the present invention for an interconnector of a solid oxide fuel cell, it is possible to suppress the deterioration of the power generation characteristics of the cell even when used at high temperatures and for a long time, and to reduce the cost of the fuel cell. Can greatly contribute to the practical application of fuel cells.

Hereinafter, the component composition of the metal material for fuel cells according to the present invention will be described.
Mo: 0.03-5.0 mass%, Nb: 0.1-3.0 mass% and 0.1 ≦ Mo / Nb ≦ 30
The metal material of the present invention is based on an Fe-Cr alloy, and is obtained by further adding Mo and Nb to this component system. By adopting this component system, Mo, Nb and Cr, Fe, Si, etc. are combined during long-time use at a high temperature of 700-900 ° C, which is the operating environment of solid oxide fuel cells. A large amount of intermetallic compounds are precipitated at the grain boundaries of the base material, and the oxidation resistance can be improved by the effect of controlling the diffusion of elements such as Cr, Fe and Si by the precipitates. However, excessive addition of Mo and Nb deteriorates the workability, so that Mo is limited to 0.03-5.0 mass%, Nb: 0.1-3.0 mass%, and 0.1 ≦ Mo / Nb ≦ 30. Here, the reason for limiting the value of Mo / Nb to the above range is that when Mo / Nb <0.1 and Mo / Nb> 30, the amount of precipitation of these intermetallic compounds at the grain boundary is not sufficient, and oxidation resistance This is because the effect of improving the property cannot be obtained. More preferably, Mo: 0.1 to 3.0 mass%, Nb: 0.1 to 2.0 mass%, and 0.5 ≦ Mo / Nb ≦ 30.

C: 0.20 mass% or less C is an element that forms carbides and increases high-temperature strength. In order to obtain this effect, it is desirable to add 0.001 mass% or more. However, if the addition amount exceeds 0.20 mass%, the workability is deteriorated, and the Cr amount effective for oxidation resistance is reduced by combining with Cr, so the amount is limited to 0.20 mass% or less. More preferably, it is 0.10 mass% or less.

Si: 0.02 to 1.0 mass%
Si has an action of promoting precipitation of intermetallic compounds. However, excessive addition causes deterioration of workability and also generates SiO ₂ with low electrical conductivity near the interface between the oxide film and the base material to lower the electrical conductivity, so it is limited to 0.02 to 1.0 mass%. To do. Preferably it is 0.05-1.0 mass%.

Mn: 2.0 mass% or less
Mn is an element necessary for improving the adhesion of the oxide film. In order to obtain this effect, it is desirable to add 0.05 mass% or more. However, excessive addition causes an increase in oxidation rate, so it is limited to 2.0 mass% or less.

Cr: 10-40 mass%
Cr is an element necessary for producing a Cr ₂ O ₃ film and maintaining oxidation resistance and electrical conductivity. However, excessive addition causes deterioration of workability, so it is limited to 10 to 40 mass%. More preferably, it is 10-30 mass%.

Sc, Y, La, Ce, Pr, Nd, Pm, Sm , Hf : 0.03 to 1.0 mass% in total of 1 type or 2 types or more
Sc, Y, La, Ce, Pr, Nd, Pm, S m Contact and Hf is to improve the adhesion of the oxide film when added in a small amount, improves the oxidation resistance. To obtain the effect, it added 0.03 mass% or more in a total amount of one or more of them. However, excessive addition degrades hot workability, so it is limited to 1.0 mass% or less. More preferably 0.03 ~0.5mass%.

In addition, in this invention, you may contain the following elements other than said essential component as needed.
Al: 2.0 mass% or less, Cu: 0.20 mass% or less, Ni: 1.0 mass% or less, V: 1.0 mass% or less, W: 3.0 mass% or less, Ta: 2.0 mass% or less, Ti: 0.5 mass% or less, Mg : 0.05 mass% or less, Ca: 0.05 mass% or less, Co: 5.0 mass% or less In addition to the components described above, Fe and unavoidable impurities. If the impurities P, S, and N are P: 0.05 mass% or less, S: 0.05 mass% or less, and N: 0.5 mass% or less, respectively, the characteristics of the present invention are not particularly affected.

Next, the total amount of Fe, Cr, and Si contained in the precipitate deposited in the metal material of the present invention will be described.
In the metal material of the present invention, it is one of the most important requirements to deposit an intermetallic compound of Mo and Nb, which is a kind of precipitate, at the crystal grain boundary of the base material. That is, the present invention allows a large amount of intermetallic compounds to precipitate at the grain boundaries of the metal material base material when used for a long time at a high temperature of 700 ° C. to 900 ° C., which is the operating environment of the solid oxide fuel cell, It is characterized by improving the oxidation resistance by controlling the diffusion mechanism of each element such as Cr, Fe and Si. In the component range of the present invention, Mo and Nb intermetallic compounds and carbon / nitrides such as Nb exist as precipitates, but most of Fe, Cr and Si contained in the precipitates are the above Mo. , Nb intermetallic compound, the amount of precipitation of Mo, Nb intermetallic compound can be controlled by controlling the total amount of Fe, Cr and Si contained in the precipitate.

  In order for the metal material to exhibit excellent oxidation resistance as an interconnector in the operating environment of a solid oxide fuel cell, the material before being used for the interconnector, that is, a hot rolled material or cold rolled In the material stage, the total amount of Fe, Cr and Si contained in the precipitate is preferably 0.01 mass% or more based on the metal material. If the total amount of Fe, Cr and Si in the precipitate is less than 0.01 mass% with respect to the metal material, a large amount will result from long-term use at 700 ° C to 900 ° C, which is the operating environment of the solid oxide fuel cell This is because it is difficult to precipitate precipitates (that is, intermetallic compounds) at the crystal grain boundaries of the base material. In order to ensure the amount of precipitation, it is effective to subject the hot rolled material or cold rolled material to annealing at 700 to 1200 ° C. for 30 seconds or more. When it is required to have excellent oxidation resistance from the beginning of use of the fuel cell, the total amount of Fe, Cr and Si in the precipitate is 0.02 mass% or more based on the metal material. For this purpose, for example, it is effective to subject the hot-rolled material, the cold-rolled material or the annealed material to a precipitation treatment at 500 to 900 ° C. for 1 to 200 hours. . In addition, in a fuel cell that has generated power for 1000 hours or more at an operating temperature of 800 ° C, the total amount of Fe, Cr, and Si contained in the precipitates of the metal material for which excellent heat resistance is recognized is compared to the metal material. From this point of view, it can be said that the total amount of Fe, Cr and Si in the precipitate is more preferably 0.03 mass% or more with respect to the metal material. .

Next, characteristics that the metal material of the present invention should have will be described.
Thermal expansion coefficient: 13.0 × 10 ⁻⁶ / ° C. or less in the range of 20 ° C. to 900 ° C. The thermal expansion coefficient of the metal material for fuel cell according to the present invention is 13.0 × 10 ⁻⁶ / ° C. in the range of 20 ° C. to 900 ° C. The following is preferable. This is because if the thermal expansion coefficient exceeds 13.0 × 10 ⁻⁶ / ° C., the electrolyte and the metal material may be separated due to the difference in thermal expansion from the electrolyte. It is preferably 12.6 × 10 ⁻⁶ / ° C. or less.

Electrical resistance: electric resistance of 50 m [Omega · cm ² or less metallic material for a fuel cell according to the present invention, since the battery performance is significantly decreased and when it exceeds 50 m [Omega · cm ^2, that is 50 m [Omega · cm ² or less preferable. More preferably, it is 30 mΩ · cm ² or less.

  As described above, the metal material for a fuel cell according to the present invention preferably has a small thermal expansion coefficient, and for that purpose, the area ratio of the austenite phase having a large thermal expansion coefficient is preferably suppressed to 10% or less. . More preferably, a ferrite single phase (partially precipitated) or a two-phase structure of ferrite and martensite (partially precipitated) is advantageous in reducing the thermal expansion coefficient.

Next, the manufacturing method of the metal material of this invention is demonstrated easily.
The metal material melting method according to the present invention is not particularly limited since all known methods can be generally applied. For example, the steelmaking process is performed in a converter, an electric furnace, etc. It is preferable that the steel adjusted to be melted and further subjected to secondary refining by strong stirring and vacuum oxygen decarburization treatment (SS-VOD). The casting method is preferably continuous casting in terms of productivity and quality. It is preferable that the slab obtained by casting is hot-rolled after reheating if necessary to obtain a hot-rolled material, and if necessary, hot-rolled sheet annealed at 700 to 1200 ° C. and then pickled.

  The hot-rolled material that has been hot-rolled or further annealed and pickled can be suitably used as a material for forming an interconnector by forming a gas flow path by a cutting method. On the other hand, when an interconnector is produced by a press working method, the hot-rolled material is further cold-rolled, or is further cold-rolled (700 ° C to 1200 ° C annealed / pickled). It is preferable to use the material. Of course, a hot-rolled material may be used as a pressing material, and a cold-rolled material may be used as a cutting material. In addition, the groove processing for forming the gas flow path may be performed by a method other than the cutting method or the pressing method, for example, another method such as a corrugate method or an etching method. In addition, the hot-rolled material or the cold-rolled material is preliminarily subjected to a precipitation treatment at 500 to 900 ° C. for 1 to 200 hours in an arbitrary atmosphere such as argon gas or air, before being incorporated into the interconnector. It is desirable to adjust so that the total amount of Fe, Cr and Si contained in the precipitate is 0.01 mass% or more, preferably 0.02 mass% or more, more preferably 0.03 mass% or more based on the metal material.

  Moreover, the said hot-rolled material or cold-rolled material can be used suitably also for members (for example, a heat exchanger, a reformer, etc.) which comprise fuel cells other than an interconnector. The welding method in the case of welding these members is not particularly limited. For example, normal arc welding such as MIG (Metal Inert Gas), MAG (Metal Active Gas), TIG (Tungsten Inert Gas), spot, etc. Any method such as electric resistance welding such as welding and seam welding, high frequency resistance welding, high frequency induction welding and brazing can be applied.

  Various metal materials having the composition shown in Table 1 were melted in the converter-secondary refining process, and slabs having a thickness of 200 mm were formed by continuous casting. After heating these slabs to 1250 ° C, they were hot-rolled to obtain hot-rolled materials having a thickness of 5 mm, and subjected to hot-rolled sheet annealing and pickling treatment at 700 to 1200 ° C to obtain hot-rolled annealed materials. Then, after making the plate thickness 1 mm by cold rolling, annealing was performed at 700 to 1200 ° C., and pickling treatment was performed to obtain a cold rolled material (cold rolled annealed material). From this cold-rolled annealed material, a 1 mm × 30 mm × 30 mm test piece was cut out and subjected to the following test.

<Oxidation resistance test>
An oxidation resistance test was conducted in which the test piece was heated and held in an air atmosphere furnace heated to 800 ° C. for 1000 hours, and the oxide generated on the steel sheet surface was identified by X-ray diffraction. Further, the weight of the test piece before and after the test was measured, and this change was divided by the total surface area of the test piece to obtain the increase in oxidation. Furthermore, regarding the peelability of the oxide film, brushing is performed by rubbing the surface of the sample after the oxidation test with a nylon brush 5 times, and the difference in weight before and after that is 0.1 mg or less without peeling (○), with peeling exceeding 0.1 mg Evaluated as “Yes” (×).

<Oxidation resistance acceleration test>
In order to evaluate long-term oxidation resistance, an accelerated oxidation resistance test was performed in the atmosphere at 1000 ° C x 600 hours (equivalent to 800 ° C x 1 million hours or more). Similarly, the increase in oxidation and the peelability of the oxide film were measured and evaluated.

<Measurement of amount of precipitated elements>
The amount of precipitation of each element of Fe, Cr and Si is a non-aqueous solvent solution using 10% AA electrolyte (10% acetylacetone-1% tetramethylammonium chloride-residual methanol) as the test material before and after the oxidation resistance test. The amount of Fe, Cr and Si in the remaining residue was quantitatively analyzed by Inductively Coupled Plasma-Atomic Emission, and from this result, Fe, Cr and The amount of each Si element deposited (mass% relative to the metal material) was determined.

<Measurement of thermal expansion coefficient>
The coefficient of thermal expansion is the following formula when a sample of plate thickness × 20 mm × 5 mm is heated from 20 ° C. to 5 ° C./min in an argon atmosphere and the longitudinal dimension when reaching 900 ° C. is L mm:
(L-20) / {20 × (900-20)}
Determined by Three measurements were performed under each condition, and the average of these was taken as the thermal expansion coefficient.

<Measurement of electrical resistance value>
As shown in Fig. 2, the electrical resistance value is obtained by sandwiching the sample after the oxidation resistance test (plate thickness: 1 mm or 5 mm x 20 mm square) between two Pt plates (thickness: 1 mm x 20 mm square). After connecting Pt wires for current application and voltage measurement to the plate, leave it in an oven at 800 ° C for 1 hour under a 0.2 MPa load, and then apply a 1.2 A current to the voltage between the upper and lower Pt plates. Was measured, and an electrical resistance value (area resistivity) was determined by multiplying the obtained resistance value by an area of 4 cm ² . The measurement was performed three times under each condition, and the average value thereof was defined as the electric resistance value.

The results of these tests are summarized in Tables 2 and 3.
No. shown in Table 1. 2-No. 12 (excluding No. 4) and No. 4 36-No. All 47 materials (excluding Nos. 4, 44 and 46) are Fe—Cr alloys to which Mo and Nb within the range of the composition of the present invention are added in combination. In these materials, as shown in Table 3, the total amount of Fe, Cr and Si contained in the precipitate in the metal material before the oxidation resistance test is 0.01 mass% or more, and the oxidation resistance. The total amount of Fe, Cr and Si contained in the precipitate after the test is 0.03 mass% or more. Further, as shown in Table 2, the increase in oxidation by the oxidation resistance test of these materials shows a small value, and the effect of improving the oxidation resistance by the combined addition of Mo and Nb is remarkably recognized. Further, the generated oxide is mainly composed of Cr ₂ O ₃ , and it is expected that the performance degradation when used as an interconnector is small. Furthermore, as shown in Table 2, the results of the accelerated oxidation resistance test (1000 ° C. × 600 hr) were selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm , and Hf . By adding a small amount of seeds or more, the peel resistance of the oxide film is remarkably improved. In addition, since the thermal expansion coefficients of these materials in the temperature range of 20 ° C. to 900 ° C. are 13.0 × 10 ⁻⁶ / ° C. or less as shown in Table 3, yttria stabilized zirconia, etc. It is considered that the possibility of peeling due to the difference in thermal expansion from other members is small. Moreover, as shown in Table 3, the electric resistance values of these materials are all 50 mΩ · cm ² or less, and the effect of reducing the growth rate of the oxide film and suppressing the increase in electric resistance is remarkable. Appears.

On the other hand, when the composition range is out of the range of the present invention, it cannot be used as an interconnector as described below.
For example, No. 33 and No. 34 are examples in which tests similar to the above were performed on the conventional materials described in No. 5 of Table 2 of Patent Document 4 and No. 3 of Table 1 of Patent Document 5, respectively. However, the growth rate of the oxide film is large, so that the electrical resistance value is extremely high. The materials of No. 27 and No. 52 were not oxidized, because of the small amount of Cr, so that the protective film was not formed, and it was impossible to measure the electrical resistance value. In addition, materials with excessive addition of Cr, such as No. 28 and No. 53, are not only inferior in workability but also in oxidation resistance. Further, materials having a high C amount such as No. 24 and No. 49 have low oxidation resistance because C is combined with Cr and the effective Cr amount is reduced. Further, the materials No. 25 and No. 50 containing a large amount of Si cannot be confirmed by X-ray diffraction, but as a result of the generation of a large amount of SiO _{2 on the} surface, the electric resistance value is greatly increased.

Mn has an effect of suppressing the exfoliation of the oxide, but generates an oxide on the surface layer because the diffusion rate in the Cr ₂ O ₃ film is fast. Therefore, no. 26, no. If the amount of Mn is large like the material 51, the oxide film becomes too thick, which adversely affects the electrical resistance. No. 29, no. Like the material No. 54, addition of excessive Mo not only deteriorates workability, but also has poor peeling resistance and is not very effective in improving oxidation resistance. The same applies to Nb (No. 30, No. 55) .

No. Sc, Y, La, Ce, Pr, Nd, Pm, Sm , and Hf are not added, or the composition of the selectively added component is out of the scope of the present invention. 1, no. With respect to the materials 13 to 32, in the results of the acceleration test at a high temperature shown in Table 2, the increase in oxidation shows-(minus). These materials mean that the oxide film is peeled off and cannot be used as an interconnector. Further, No. in which the increase in oxidation does not show minus. 16, 23 and 26 also have large electric resistance values.

A 5 mm hot-rolled sheet having the composition described in No. 2 of Table 1 is annealed at 1050 ° C., dipped in a mixed acid of 60 ° C. (15 mass% nitric acid + 5 mass% hydrofluoric acid), and descaled. A hot-rolled annealed material was used. About this hot-rolled annealing board, the oxidation resistance test, the oxidation resistance acceleration test, the thermal expansion coefficient measurement, and the electrical resistance measurement were performed under the same conditions as in Example 1. The results of these tests, the oxidation resistance test: 1.6 g / m ^2, oxidation resistance acceleration test: 60.2g / m ^2, Fe in the precipitates before and after oxidation resistance test, the total amount of Cr and Si: 0.03 mass% (front), 0.50 mass% (rear), coefficient of thermal expansion: 12.6 × 10 ⁻⁶ / ° C., and electric resistance: 28 mΩ · cm ² . From this result, it is found that the properties of the hot-rolled annealed material having the composition No. 2 in Table 1 are almost the same as the properties of the cold-rolled materials (cold-rolled annealed materials) shown in Table 2 and Table 3. It could be confirmed.

Precipitation at 800 ° C. for 10 hours with respect to a cold-rolled material (cold-rolled annealed material) having the composition of No. 5 in Table 1 and No. 2 hot-rolled annealed material in Table 1 used in Example 2 The properties of these steel sheets were examined in the same manner as in Example 1. The results of the test, cold-rolled annealed material, oxidation resistance test: 1.7 g / m ^2, oxidation resistance acceleration test: 64.3g / m ^2, Fe in the precipitates before and after oxidation resistance test, Cr and Si Total amount: 0.05 mass% (front), 0.54 mass% (rear), coefficient of thermal expansion: 12.4 × 10 ^-6 / ° C and electrical resistance: 28 mΩ · cm ² , and hot-rolled annealed materials are subjected to oxidation resistance test: 1.5 g / m ² , oxidation resistance acceleration test: 58.4 g / m ² , total amount of Fe, Cr and Si in the precipitate before and after the oxidation resistance test: 0.05 mass% (front), 0.51 mass% (back) The thermal expansion coefficient was 12.6 × 10 ⁻⁶ / ° C. and the electric resistance was 27 mΩ · cm ² . From this result, it was confirmed that the cold-rolled annealed material and the hot-rolled annealed material that had been subjected to the precipitation treatment in advance also had substantially the same characteristics as the material that was not subjected to the precipitation treatment.

Using a cold-rolled material (cold-rolled annealed material) having the composition of No. 2 in Table 1, a power generation characteristic testing device consisting of a single cell as shown in FIG. The changes in power generation characteristics were investigated. The interconnector that constitutes a single cell is made by cutting 10 grooves at 5mm intervals on a cold-rolled annealed material with a thickness of 1mm x 105mm square and a width of 5mm x depth of 0.5mm as shown in Fig. 3. The processed one was used. As the electrolyte, a 0.2 mm × 105 mm square plate obtained by sintering yttria-stabilized zirconia (YSZ) was used, and NiO powder and YSZ powder were mixed at a mass ratio of 4: 6 on one surface. The cathode (fuel electrode) material mixed in 1) and the anode (air electrode) material in which La _0.8 Sr _0.2 MnO ₃ powder and YSZ powder were mixed at a mass ratio of 8: 2 on the other side, respectively. Was printed to a thickness of 50 μm and fired at 1400 ° C. to form an electrolyte-electrode assembly, and the interconnector was placed on both sides to form a single cell. Electric power is generated at a current density of 0.2 A / cm ² and a temperature of 750 ° C. by flowing ultrahigh purity hydrogen (purity 99.9999%) on the fuel electrode side of this single cell and air with a dew point of 30 ° C. on the air electrode side. The output voltage after 1000 hours was measured to evaluate the battery performance. As a result, the decrease in the output voltage was as small as 1.8% on average in three measurements, and it was confirmed that the metal material of the present invention has sufficient characteristics for an interconnector of a solid oxide fuel cell. .

  The metal material of the present invention is suitably used not only for an interconnector of a solid oxide fuel cell that requires oxidation resistance but also for a member constituting the fuel cell (for example, a heat exchanger or a reformer). Can do.

It is the figure which showed typically the structural example of the solid oxide fuel cell. It is the figure which showed typically the apparatus which measures the electrical resistance value of an interconnector. It is the figure which showed typically the apparatus which measures the electric power generation characteristic of a solid oxide fuel cell.

Explanation of symbols

1: Electrolyte 2: Electrode (Anode, Air electrode)
3: Electrode (cathode, fuel electrode)
4: Interconnector 5: Fuel gas (hydrogen gas)
6: Oxidizing gas (air)
7: Gas flow furnace (groove)
8: Electronics (electricity)

Claims (6)

C: 0.20 mass% or less,
Si: 0.02 to 1.0 mass%,
Mn: 2.0 mass% or less,
Cr: 10 to 40 mass%,
Mo: 0.03-5.0 mass%,
Nb: 0.1 to 3.0 mass%, and Mo and Nb are the following formulas:
0.1 ≦ Mo / Nb ≦ 6.81
In addition, one or more selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm and Hf are contained in a total amount of 0.03 to 1.0 mass%. The balance includes Fe and inevitable impurities , and the total amount of Fe, Cr and Si includes a precipitate of 0.01 mass% or more with respect to the metal material.
Metal material for interconnectors of solid oxide fuel cells. 2. The solid oxide type according to claim 1, wherein the total amount of Fe, Cr, and Si contained in the deposit of the fuel cell metal material is 0.02 mass% or more with respect to the metal material. Metal materials for fuel cell interconnectors . The metal material for an interconnector of a solid oxide fuel cell according to claim 1 or 2 , wherein the metal material for a fuel cell is a hot rolled material. The metal material for an interconnector of a solid oxide fuel cell according to claim 1 or 2 , wherein the metal material for a fuel cell is a cold rolled material. The total amount of Fe, Cr and Si contained in the deposit of the metal material for fuel cell is 0.03 mass% or more with respect to the metal material after generating power for 1000 hours or more at an operating temperature of 800 ° C. The metal material for an interconnector of a solid oxide fuel cell according to any one of claims 1 to 4 . 請 Motomeko 1-5 solid oxide fuel cell characterized by using a solid oxide fuel cell interconnector metal material according to any one.

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