JP2018131643A - Separator excellent in heat resistance for solid oxide type fuel cell and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a solid oxide type fuel cell which maintains excellent oxidation resistance and electrical conduction property under a long period high temperature oxidation environment without involving increase in material cost and impairment of versatility, and in which surface damage caused by heat stress is suppressed, and a fuel cell using the separator for a solid oxide type fuel cell.SOLUTION: Structure having an austenite phase composed of an austenite grain having an average particle size of 1-10 μm is formed on at least one surface of a ferritic stainless steel containing, by mass%, C: 0.030% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.045% or less, S: 0.0050% or less Cr: 19.0-25.0%, Mo: 0.2-2.0% or less, N: 0.040% or less, Al: 0.50% or less, Nb: 0.001-0.5% and/or Ti: 0.001-0.5%, and the balance Fe with inevitable impurities. The Co concentration of the austenite phase may be 10-95 mass%, and the balance Ni, Fe, Cr with inevitable impurities.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a solid oxide fuel cell separator that maintains excellent oxidation resistance and electrical conductivity in a long-term high-temperature oxidation environment, and suppresses surface damage caused by thermal stress, and the surrounding high-temperature members, and these The present invention relates to a solid oxide fuel cell using

In recent years, the spread of new systems replacing conventional power generation systems is accelerating due to problems such as the depletion of fossil fuels represented by petroleum and global warming due to CO ₂ emissions. As one of them, “fuel cell”, which has high practical value as a distributed power source and a power source for automobiles, is attracting attention. There are several types of fuel cells. Among them, solid oxide fuel cells (hereinafter referred to as SOFC) have high energy efficiency, and are expected to be widely used in the future.

  In recent years, SOFC systems operating at 600 to 900 ° C. have become mainstream due to improvements in solid electrolyte membranes. In this temperature range, an inexpensive and poorly workable ceramic material to a cheap and good workable metal material separator can be applied.

  The characteristics required for a fuel cell separator are that it first has excellent “oxidation resistance” and “electric conductivity” in a temperature range of 600 to 900 ° C. Next, a ceramic solid oxide and It has the same “thermal expansion coefficient”. For example, conventionally, Patent Documents 1 to 3 disclose steels for SOFC having both oxidation resistance and electrical conductivity. These SOFC steels are high Cr type ferritic stainless steels containing one or more selected from the group of (Y, REM (rare earth elements), Zr).

However, when the above-described solid stainless steel material is used for the separator, an oxide having a high Cr concentration is generated during the operation of the SOFC, the electrical resistance of the contact portion is increased, and power generation loss occurs. Further, due to the problem of chromium poisoning of the air electrode material, it is necessary to practically apply a spinel oxide of MnCo as a chromium poisoning prevention coating on the surface of the SOFC steel as in Patent Document 4.
When MnCo-based spinel oxide is used as a coating, a sintering step of the oxide powder is required, and since it is fired at a high temperature at 1000 ° C., there arises a problem that the base material is not resistant to oxidation. In order to lower the sintering temperature, there is a method of adding a sintering aid such as Li, but there are concerns about the cracking of the coating due to shrinkage and the influence of the sintering aid on the base material. Here, the MnCo-based spinel oxide refers to a material typified by MnCo ₂ O ₄ .

  On the other hand, Patent Document 5 discloses a SOFC separator material that is excellent in electric conductivity and oxidation resistance and suppresses chromium poisoning without depending on the addition of expensive rare earth elements. These separator materials have Cr: 11 to 40% by mass of ferritic stainless steel as a base material, and a TiN coating layer having a film thickness of 0.05 to 100 μm and a Ti concentration of 40 atomic% or more is formed on the surface of the base material. It is characterized by being. In addition, as in Patent Document 6, a technique for improving the electrical conductivity and oxidation resistance of a separator material has been studied. Ag is used for the coating of the separator material, and the aim is to prevent oxidation of the material surface and to ensure electrical conductivity. Recently, an interconnect structure, a device and a method have been disclosed in which a diffusion barrier layer made of an austenite phase is formed on the surface of an interconnect structure formed of ferritic stainless steel containing chromium. These techniques are directed to minimizing the formation of a thick chromium oxide layer by forming an austenite phase with a low chromium diffusion rate on the surface.

Japanese Patent No. 4310723 Japanese Patent No. 4737600 Japanese Patent No. 4385328 Japanese Patent No. 5283896 Japanese Patent No. 4756905 Japanese Patent No. 5417935 Japanese Patent Application Laid-Open No. 2010-3629

Since the technology of Patent Document 4 for coating the MnCo-based spinel oxide uses stainless steel added with expensive rare earth elements disclosed in Patent Documents 1 to 3, the material cost and versatility are reduced from the viewpoint of widespread use. There are challenges.
The technology of Patent Document 5 that coats TiN is extremely hard and durable in addition to the thermal expansion coefficient at a high temperature that is about an order of magnitude smaller than that of ferritic stainless steel (for example, 22Cr steel) as a base material. From this point of view, there are concerns about delamination and microscopic surface damage due to thermal stress at start and stop.
The technique of Patent Document 6 that coats Ag has problems of heat resistance and material cost when Ag is used for a long time.
Regarding the technique of Patent Document 6 for forming an austenite phase on the surface, there is no specific description or disclosure relating to the components of the ferritic stainless steel of the base material or the surface structure during power generation.
As described above, conventionally, as a separator for SOFC, in a high Cr type ferritic stainless steel, (1) an expensive rare earth element (Y, REM, Zr, etc.) is added to coat a MnCo based spinel type oxide. (2) A TiN coating layer or an Ag coating is applied to improve oxidation resistance and electrical conductivity. The former separator has problems in material cost and versatility from the viewpoint of widespread use of SOFC. In the latter case, it is unknown about oxidation resistance, heat resistance, electrical conductivity and surface damage due to thermal stress in a long-term high-temperature oxidation environment.

  As described above, the SOFC maintains excellent oxidation resistance and electrical conductivity in a long-term high-temperature oxidation environment and suppresses surface damage due to thermal stress without sacrificing material cost or versatility. At present, no separator has appeared.

  The present invention has been devised to solve the above-mentioned problems, and is excellent in a long-term high-temperature oxidation environment without relying on the addition of expensive rare earth elements or the coating of a MnCo-based spinel oxide. The present invention provides a SOFC separator that maintains high oxidation resistance and electrical conductivity and suppresses surface damage caused by thermal stress.

The gist of the present invention is as described below.
(1) In mass%, C: 0.030% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.045% or less, S: 0.0050% or less, Cr: 19.0-25.0%, Mo: 0.2-2.0%, N: 0.040% or less, Al: 0.50% or less, Nb: 0.001-0.5% and / or Ti : Austenite containing 0.001 to 0.5%, the balance being ferritic stainless steel made of Fe and inevitable impurities, and having an average particle size of 1 to 10 μm on at least one surface of the stainless steel substrate A separator for a solid oxide fuel cell, wherein a structure having a phase is formed.
(2) The solid oxide fuel cell separator according to (1), wherein the Co concentration of the austenite phase of the structure is 10 to 95% by mass, and the balance is Ni, Fe, Cr, and inevitable impurities.
(3) The solid oxide form described in (1) or (2), wherein the average value of the aspect ratio (plate width direction / plate thickness direction) of the austenite grains forming the austenite phase is 0.1 to 0.9. Fuel cell separator.
(4) The base material is further mass%, V: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, Cu: 1% or less, W : 1% or less, Co: 1% or less, B: 0.010% or less, Ga: 0.010% or less, Mg: 0.010% or less, Ca: 0.010% or less, Zr: 0.1% or less , La: 0.1% or less, Y: 0.1% or less, REM: 0.1% or less, Ta: 0.1% or less. A separator for a solid oxide fuel cell according to any one of 1) to (3).
(5) A fuel cell configured by laminating a plurality of power generation elements, wherein the power generation element includes a plate-shaped cell in which an anode is connected to one main surface and a cathode is connected to the other main surface; And a separator laminated so as to be electrically connected to the cathode, and the separator for a solid oxide fuel cell according to any one of (1) to (4) is used for at least a part of the separator. Was a fuel cell.

  Hereinafter, the inventions related to the separators (1), (2), (3), and (4) are referred to as the present invention. The inventions (1) to (5) may be collectively referred to as the present invention.

  According to the present invention, without depending on the addition of expensive rare earth elements or coating of MnCo-based spinel type oxides, excellent oxidation resistance and electrical conductivity can be maintained in a long-term high-temperature oxidation environment, It is possible to obtain a SOFC separator that suppresses surface damage due to thermal stress and a solid oxide fuel cell using the same.

It is a disassembled perspective view of a power generation unit. It is a disassembled perspective view of a separator. It is a figure which shows the example of an EBSD measurement result of the structure | tissue which has the austenite phase formed in the base-material surface. It is an example of a measurement result of a power generation evaluation test, and is a diagram showing a relationship between a voltage drop rate and time.

In order to solve the above-mentioned problems, the present inventors have earnestly studied an SOFC separator that suppresses oxidation resistance and electrical conductivity required in a long-term high-temperature oxidation environment, and surface damage caused by thermal stress due to starting and stopping. Experiments and studies were repeated to complete the present invention.
Below, the knowledge acquired by this invention is demonstrated.
(A) The long-term high-temperature oxidation environment in the SOFC separator is assumed to be 1 to 100,000 hours (hours) of exposure at 700 to 750 ° C. at the SOFC air electrode. In the laboratory, exposure is performed at 800 to 850 ° C. for 100 to 1000 hours in an atmosphere of air or humidified air, and the oxidation characteristics and microstructure of the separator, and the degradation behavior of power generation efficiency are evaluated.
(B) In the accelerated evaluation described above, in order to suppress the deterioration behavior of the separator, a high Cr type ferritic stainless steel containing Mo is used as a base material, and the surface has an austenite phase composed of fine crystal grains. It is very effective to form a tissue. That is, the above-described oxidation resistance, electrical conductivity, and surface damage caused by thermal stress are completely new knowledge that crystal grains composed of an austenite phase having an average grain size of 10 μm or less are remarkably improved. Won.
(C) Further, in order to improve oxidation resistance and electrical conductivity, the Co concentration of the structure having an austenite phase formed on the substrate surface is increased, and the aspect ratio of the austenite grains (plate width direction / plate thickness direction) is increased. It has also been found that reducing the average value is effective.
(D) Although there are still many unclear points about the above-described substrate surface modification action, the following action mechanism is presumed based on experimental facts. The austenite phase having a high Co concentration produces a highly conductive spinel oxide represented by Co ₃ O ₄ on the outer layer side in a high-temperature oxidation environment. In the lower layer, a reaction layer of Fe and Co diffused from the base material is formed to suppress oxidation of Cr which leads to a decrease in conductivity. At that time, the refinement of austenite grains on the substrate surface promotes selective oxidation of Fe and suppresses oxidation of Cr. In addition, by using high Cr type ferritic stainless steel containing Mo as a base material, a Cr ₂ O ₃ film is formed at the interface between the Co-based oxide layer and the base material to prevent oxidation of the base material. Maintain sex. Furthermore, by using high Cr type ferritic stainless steel containing Mo as the base material, the difference in thermal expansion coefficient from the ceramic electrode is reduced, and the structure with fine austenite grains is generated on the surface with the start and stop. It also works effectively to relieve thermal stress.
(E) When a spinel oxide mainly composed of Co ₃ O ₄ is formed on the outer layer side, scattering of Cr gas due to volatilization of the lower layer Cr oxide is prevented, and chromium poisoning of the air electrode material is prevented. Furthermore, since spinel oxides are less likely to change the valence of elements, oxidation of Cr (III) oxide to Cr (VI) can be suppressed, and chromium coating of the air electrode material due to Cr gasification can be suppressed. Poison can also be prevented. In addition, the spinel type oxide has a slow movement of + ions such as metal ions due to its crystal structure, so that diffusion of metal ions from the substrate to the surface layer is also slow, which is suitable from the viewpoint of oxidation resistance.

  As mentioned above, surface modification based on high Cr type ferritic stainless steel containing Mo maintains excellent oxidation resistance and electrical conductivity, and suppresses surface damage associated with thermal stress. New properties can be achieved without resorting to the addition of expensive rare earth elements or MnCo-based spinel oxide coatings. The present inventions (1) to (4) have been completed based on the above-described examination results.

  Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element in the base material means "mass%".

(I) The reason for limitation of the base component will be described below.

  C is an inevitable impurity element contained in the steel, and inhibits the oxidation resistance and electrical conductivity of the base material. Therefore, the lower the amount of C, the better. However, excessive reduction leads to a decrease in creep resistance under a high temperature environment and a significant increase in refining costs. Therefore, the upper limit is 0.030%. A preferable range is 0.001 to 0.02% from the above-described characteristics and manufacturability.

  Si has the effect of increasing the oxidation resistance and high-temperature strength of the base material, but excessive addition inhibits electrical conductivity. From the viewpoint of these basic characteristics, the upper limit is 1.0%. The lower limit is preferably set to 0.01% because of an increase in manufacturing cost considering inevitable impurities from the deoxidizer and chromium raw material. From the viewpoint of achieving both the basic characteristics of the substrate and the manufacturing cost, the preferred range is 0.05 to 0.5%, and the more preferred range is 0.10 to 0.30%.

  In addition to effectively acting as a deoxidizing element, Mn has an effect of improving the electrical conductivity of the substrate. In order to obtain these effects, the lower limit is preferably 0.05%. On the other hand, excessive addition may inhibit the oxidation resistance of the substrate, so the upper limit is made 1.0%. From the viewpoint of the basic characteristics and manufacturability of the substrate, the preferred range is 0.05 to 0.5%, and the more preferred range is 0.10 to 0.30%.

  P is an element that inhibits manufacturability and oxidation resistance, and the lower the content, the better. Therefore, the upper limit is made 0.045%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.003%. From the basic characteristics and manufacturability of the substrate, the preferred range is 0.005 to 0.035%, more preferably 0.010 to 0.030%.

  S is an inevitable impurity element contained in the steel, and lowers the oxidation resistance and electrical conductivity of the substrate. In particular, the presence of Mn inclusions and solute S acts as a starting point for reducing the protective properties of the Cr-based oxide film in a long-term high-temperature oxidation environment. Therefore, the lower the amount of S, the better. Therefore, the upper limit is made 0.0050%. However, excessive reduction leads to an increase in raw materials and refining costs, so the lower limit is made 0.0001%. A preferable range is 0.0001 to 0.0030%, more preferably 0.0002 to 0.0020% from the viewpoint of basic characteristics and manufacturability of the substrate.

  Cr is an element that is fundamental in securing the oxidation resistance and electrical conductivity of the substrate, as well as the thermal expansion coefficient and creep resistance. In the present invention, if the content is 19.0% or less, the basic characteristics of the substrate are not sufficiently ensured. Therefore, the lower limit is 19.0%. However, excessive addition of Cr may not only promote the formation of the σ phase, which is an embrittlement phase, but also promote the oxidation and evaporation of Cr and impair the electrical conductivity when exposed to a high temperature environment. . The upper limit is 25.0% from the viewpoint of the basic characteristics targeted by the present invention. A preferable range is 20 to 24%, more preferably 21 to 23% from the viewpoint of the basic characteristics of the substrate and the manufacturing cost.

  Mo is a constituent element effective in securing the oxidation resistance and thermal expansion coefficient of the base material. Furthermore, it acts as a solid solution strengthening element, and acts effectively as a high temperature member in ensuring creep resistance. In order to obtain these effects, the lower limit is made 0.2%. However, excessive addition promotes the formation of the σ phase, which is an embrittlement phase, and causes an increase in raw material cost. The upper limit is set to 2.0% from the viewpoint of the basic characteristics targeted by the present invention. A preferable range is 0.3 to 1.5%, more preferably 0.5 to 1.3% from the viewpoint of basic characteristics of the substrate and cost effectiveness.

  N is an unavoidable impurity element contained in the steel and inhibits the oxidation resistance and electrical conductivity of the base material. For this reason, the N content is preferably as low as possible, but excessive reduction leads to a decrease in creep resistance under a high temperature environment and a significant increase in refining costs. Therefore, the upper limit is 0.040%. A preferable range is 0.001 to 0.02% from the above-described characteristics and manufacturability.

  In addition to being effective as a strong deoxidizing element, Al has an effect of increasing the oxidation resistance of the substrate. In order to obtain these effects, the lower limit is preferably 0.01%. Excessive addition may lower the electrical conductivity of the substrate and increase the thermal expansion coefficient. From the viewpoint of these basic characteristics, the upper limit is 0.50%. From the viewpoint of achieving both basic characteristics and manufacturability of the substrate, the preferred range is 0.02 to 0.30%, more preferably 0.05 to 0.15%.

  Nb and Ti fix C and N as carbonitrides and increase the oxidation resistance and electrical conductivity of the base material, and also increase the strength required as a high temperature member. In order to obtain these effects, the lower limit is made 0.001%. Excessive addition saturates the effect and hinders increase in raw material cost and processability, so the upper limit is 0.5%. From the viewpoint of cost effectiveness, a preferable range is 0.05 to 0.40%, and a more preferable range is 0.15 to 0.35%. Nb and Ti may be added alone or in combination.

  V is an element effective for fixing C and N as carbonitrides and enhancing the oxidation resistance and high-temperature strength of the substrate, and may be added as necessary. However, excessive addition inhibits oxidation resistance and causes an increase in alloy cost, so the upper limit is made 0.5%. The lower limit is preferably set to 0.005% because of an increase in raw material cost in consideration of inevitable impurities from the chromium raw material. A preferable range is 0.01 to 0.2%, more preferably 0.01 to 0.1% from the viewpoint of achieving both the basic characteristics of the substrate and the raw material cost.

  Sn, Sb, Ni, Cu, W, and Co are elements effective for increasing the oxidation resistance and creep resistance strength of the substrate, and may be added as necessary. However, excessive addition leads to an increase in alloy costs and obstructs manufacturability, so the upper limit of Sn and Sb is 0.3%, and the upper limit of Ni, Cu, W and Co is 1%. The lower limit of the preferred contents of Sn and Sb is 0.01%, and the preferred lower limit of Ni, Cu, W, and Co is 0.1%.

  B, Ga, Mg, and Ca are effective elements for improving the oxidation resistance, creep resistance, and hot workability of the substrate, and may be added as necessary. On the other hand, excessive addition causes a decrease in manufacturability and oxidation resistance of the substrate. For this reason, each upper limit is made into B: 0.010%, Ga: 0.010%, Mg: 0.010%, Ca: 0.010%. The preferred lower limit is 0.0002% for all elements. The contents of Mg and Ca can also be controlled by refining conditions.

  Zr, La, Y, REM, and Ta are elements that have been conventionally effective in increasing the oxidation resistance and electrical conductivity of the substrate, and may be added as necessary. However, the addition of these elements is not relied on because of the technical idea of the present invention, the idea, and the alloy cost reduction. When added, the upper limit is preferably 0.1%, and the lower limit is preferably 0.001%. Here, REM is an element belonging to atomic numbers 57 to 71, such as Ce, Pr, and Nd.

  In addition to the elements described above, the elements of the present invention can be contained within a range not impairing the effects of the present invention. It is preferable to reduce as much as possible Zn, Bi, Pb, Se, H, Tl, etc. as well as the aforementioned P and S, which are general impurity elements. On the other hand, the content ratio of these elements is controlled within the limit of solving the problems of the present invention, and, if necessary, Zn ≦ 100 ppm, Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, H ≦ 100 ppm, Tl One or more of ≦ 500 ppm may be contained.

  The base material of the present invention is mainly intended for a cold-rolled annealed sheet obtained by annealing a hot-rolled steel strip or omitting annealing and then cold-rolling after descaling, followed by finish annealing and descaling. . In some cases, a hot-rolled annealed plate that is not subjected to cold rolling may be used. The finish annealing is preferably 800 to 1050 ° C. If it is less than 800 degreeC, softening and recrystallization of steel become inadequate, and a predetermined material characteristic may not be acquired. On the other hand, if it exceeds 1050 ° C., it becomes coarse particles, which may impair the toughness and ductility of steel.

(II) The reason for limiting the metal structure in the structure formed on the substrate surface will be described below. In the present invention, a structure having an austenite phase described below is formed on the surface of the base material having the above-described components in order to impart the target heat resistance of the present invention.

  The average grain size of the austenite crystal grains constituting the structure having the austenite phase is, as described in [0015] (b) and (d), the upper limit for expressing the surface modification action in a high temperature oxidation environment. Is 10 μm. If the average particle size exceeds 10 μm, selective oxidation of Fe may be accelerated and oxidation resistance may be impaired. In addition, there is a case in which durability is hindered by inducing damage such as fine cracks on the surface without exerting an effect on relaxation of the thermal stress generated along with starting and stopping. Here, in the structure having an austenite phase, the lower limit of the average particle diameter is not particularly specified, but is preferably 1 μm from the viewpoint of an industrial production method and effects. From the viewpoint of cost effectiveness, a preferable average particle diameter is 1 to 8 μm, and a more preferable range is 2 to 6 μm.

  As described in the paragraphs [0015] (d) and (e), it is extremely effective to increase the Co concentration in order to impart the target heat resistance of the present invention. The lower limit of the Co concentration is 10%. When the Co concentration is less than 10%, it is difficult to maintain electrical conductivity in a long-term high-temperature oxidation environment. The upper limit of the Co concentration is 95% from the viewpoint of the manufacturing method and effects. From the viewpoint of cost effectiveness, a preferable range is 30 to 95%, and a more preferable range is 60 to 90%. The balance may be Ni that forms an intermetallic compound with Co, or Fe or Cr that forms spinel oxide with Co in a high-temperature oxidizing environment. In addition, inevitable impurities such as Ti, Mn, Sn, Cu, Zn, Nb, and Mo may be mixed as long as the target heat resistance of the present invention is not impaired.

  The average value of the aspect ratio (plate width direction / plate thickness direction) of the austenite crystal grains is preferably small as described in [0015] items (c) and (d). In particular, it effectively works to relieve thermal stress generated with starting and stopping. In order to obtain these functions and effects, the upper limit of the average aspect ratio is preferably 0.9, and the lower limit is preferably 0.1 from the viewpoints of effects and manufacturing method. From the viewpoint of cost effectiveness, a more preferable range is 0.3 to 0.6.

  The thickness of the structure having an austenite phase is not particularly specified, but the lower limit is 1 μm corresponding to the lower limit of the average particle diameter described in the item [0036], and the upper limit is 50 μm from the viewpoint of cost effectiveness. preferable. From the viewpoint of cost effectiveness, a more preferable range is 2 to 20 μm, and a further preferable range is 3 to 15 μm.

  The average particle size, composition, aspect ratio, and thickness of the structure having the austenite phase described above are not limited to the initial state, but can be applied to the state remaining after operation in a high-temperature oxidizing environment.

Regarding the formation method of the structure having an austenite phase, a Co metal film is formed to 2 to 20 μm, preferably 3 to 15 μm on at least one surface of a high Cr type ferritic stainless steel base material containing Mo. . As a forming method, a dry or wet plating method can be considered, but a wet plating method with high productivity is preferable. After forming the Co metal film, a structure having an austenite phase can be formed in the vicinity of the surface of the high Cr type ferritic stainless steel containing Mo by performing a vacuum heat treatment. The vacuum heat treatment forms a structure having an austenite phase by processing under conditions of 850 ° C. to 1100 ° C. and holding time of 2 to 6 hours under a reduced pressure of 10 to 100 Pa in an argon or nitrogen gas atmosphere. can do.
(III) The configuration of the solid oxide fuel cell will be described below. The fuel cell is configured by stacking a plurality of power generation units 10. The power generation unit 10 is configured to flow so that the fuel gas and the oxidant (air) face each other (counter flow).

  As shown in FIG. 1, in the power generation unit 10, the separator 20, the insulating member 30, the cell 50, and the cell presser 60 are stacked in this order from the lower side (Z2 direction side).

  As shown in FIG. 2, in the separator 20, the current collecting plate 21, the cathode plate 22, the separator body 23, the anode plate 24, and the cell holder 25 are stacked in this order from the lower side (Z2 direction side). Has been.

  The current collecting plate 21 is configured to come into contact with the cathode of the cell 50. The current collecting plate 21 is provided with a hole 21a through which fuel gas flows, and a hole 21b and hole 21c through which an oxidant flows. Further, the current collecting plate 21 is provided with a plurality of holes 21d for guiding the oxidant to the cathode.

  The cathode plate 22 is provided with a hole 22a through which fuel gas flows, and a hole 22b and a hole 22c through which an oxidant flows. The cathode plate 22 is provided with an oxidant flow path 22d along the X direction. Specifically, the oxidant flows on the lower surface side (Z2 direction side) of the flow path 22d.

  The separator body 23 is provided with a hole 23a through which the fuel gas flows, and a hole 23b and a hole 23c through which the oxidant flows. Further, the surface of the separator body 23 is formed into a flat surface.

  The anode plate 24 is provided with a hole 24a and a hole 24d through which fuel gas flows, and a hole 24b and a hole 24c through which an oxidant flows. The anode plate 24 is provided with a fuel gas flow path 24e along the X direction. The fuel gas flows through the upper surface side of the flow path 24e. The current collecting plate 21, the cathode plate 22, the separator body 23, and the anode plate 24 are formed of conductive members. Thereby, the cell 50 arrange | positioned at the upper surface side of the separator 20 and the cell 50 arrange | positioned at the lower surface side conduct | electrically_connect. That is, the cell 50 disposed on the upper surface side of the separator 20 and the cell 50 disposed on the lower surface side are electrically connected.

  The cell holder 25 is provided with a hole 25a through which the fuel gas flows, and a hole 25b and a hole 25c through which the oxidant flows. In addition, an opening 25d is provided at the center of the cell holder 25.

  The insulating member 30 is provided with a hole 30a through which the fuel gas flows, and a hole 30b and a hole 30c through which the oxidant flows. The insulating member 30 is configured to insulate between the cells 50 adjacent in the stacking direction.

  As shown in FIG. 2, the cell retainer 60 is provided with a hole 60a through which the fuel gas flows, and a hole 60b and a hole 60c through which the oxidant flows. In addition, an opening 60d is provided at the center of the cell presser 60.

  As shown in FIG. 1, a separator 20 a that includes a top plate but does not include an anode plate is provided on the upper surface of the power generation unit 10 that is disposed at the uppermost position. A separator 20b that includes a bottom plate but does not include a cathode plate is provided on the lower surface of the power generation unit 10 that is disposed at the lowermost position.

  As shown in FIG. 2, the fuel gas supplied to the anode of the cell 50 (FIG. 1) passes through the hole 23 a on the X1 direction side of the separator main body 23 through the hole 24 d of the anode plate 24. It flows into the upper surface side (Z1 direction side surface side). The reacted fuel gas flows out through the hole 24a on the X2 direction side of the anode plate 24. Further, the oxidant (air) supplied to the cathode 53 of the cell 50 flows into the upper surface side (the lower surface side of the cathode plate 22) of the current collecting plate 21 from the hole 22 b on the X2 direction side of the cathode plate 22. Further, the oxidant after the reaction flows out through the hole 21c on the X1 direction side of the current collecting plate 21.

  In the above embodiment, the fuel cell (power generation unit) is an example of a counter-flow fuel cell that flows so that the fuel gas and air face each other. However, the present invention is not limited to this. For example, the present invention can be applied to a cross-flow fuel cell in which fuel gas and air flow so as to intersect each other.

  Examples of the present invention will be described below.

  The base material which shows a component in Table 1 is melted, hot-rolling, annealing pickling, and cold-rolling are performed, and it anneals according to above-mentioned heat processing conditions, The cold-rolled steel plate with a plate thickness of 0.2-1.0 mm is then carried out. Manufactured. Steels A to J have a component range defined by the present invention, and steels K to R deviate from the component ranges defined by the present invention. Next, test pieces were cut out from these cold-rolled steel sheets, coated with Co by wet Co plating to form a metal film, and then subjected to vacuum heat treatment to form a structure having an austenite phase near the substrate surface. Produced. The structure having an austenite phase formed on the surface of the substrate was analyzed, and the oxidation resistance by the oxidation test and the evaluation of the surface damage by the repeated test at high temperature were used. In addition, a cell stack was prepared and a power generation evaluation test was performed using the SOFC separator of the present invention.

  The average particle diameter and aspect ratio of the structure having an austenite phase formed in the vicinity of the substrate surface can be evaluated using an electron beam backscatter diffraction method (EBSD). The EBSD is a device that measures the crystal structure (austenite phase, ferrite phase) and the shape (aspect ratio) and crystal orientation of each crystal grain at high speed. From the analysis system for EBSD measurement, the crystal grain size and aspect ratio of the austenite phase were displayed in a histogram format, and the average value was adopted. In addition, EBSD can be measured with the sample which finished the cross section of the test piece by colloidal silica grinding | polishing. FIG. 3 shows an example of an EBSD measurement result of a structure having an austenite phase formed on the surface of a base material that realizes a remarkable improvement in characteristics to be described later. The composition (Co concentration) of the austenite phase can be measured by elemental analysis using an energy dispersive X-ray spectrometer (EDS) of an electron microscope. EDS produced and analyzed the cross-section sample of the test piece.

In the oxidation test, a Co-coated substrate was prepared, and cooled to room temperature after being kept at 800 ° C. for 100 hours in 20 ° C. humidified air (water vapor concentration: 2.3%). The evaluation index of oxidation resistance is “◎”, which indicates that a continuous film of Cr ₂ O ₃ was formed at the substrate / coating interface from the observation of the cross section of the structure without observing the peeling of the oxide visually. Although the exfoliation of the object was seen, “○” indicates that the Cr ₂ O ₃ continuous film was formed at the substrate / coating interface, and “x” indicates that the oxide exfoliation and the Cr ₂ O ₃ breakout were observed. " The target oxidation resistance of the present invention is “◯” and “◎”.

  In the power generation test, a cell stack was produced using the SOFC separator of the present invention, and the change with time in voltage value caused by continuous power generation at 700 ° C. and 1000 h was evaluated. The voltage change with time was measured, and the case where the voltage drop rate per 1000 h was 0.125% / kh or less was marked with ◯, and the case where it exceeded 0.125% / kh was marked with x. FIG. 4 shows an example of a measurement result in which good power generation performance was obtained by the power generation evaluation test.

  In the high temperature repetition test, a coated substrate was prepared, and heating in the air at 800 ° C. for 24 hours and cooling to room temperature was repeated 30 times. The evaluation index of surface damage is that the oxide does not peel off visually, and from the cross-sectional observation of the embedded sample, the coating was neither peeled nor lifted up, and the oxide peeling was seen visually. “○” indicates that the coating was peeled off and floated from the observation of the cross section, while “×” indicates that the coating was peeled off and floated both by visual observation and cross-sectional observation. In addition, the grade of the surface damage made into the target of this invention makes "(circle)" and "(double-circle)" pass.

  The obtained results are also shown in Table 2. No. 1, 2, 4 to 16 have the components of the base material defined in the present invention, satisfy the properties of the structure having the austenite phase in the vicinity of the base material surface defined in the present invention, and target oxidation resistance of the present invention. The evaluation of the property, the power generation performance and the surface damage is “◯” or “◎”. Among these, No. 7 and 12, the base component is in a more preferable range, and the structure having an austenite phase in the vicinity of the base surface is in the range of the more preferable average particle diameter, Co concentration, and aspect ratio of the present invention, and remarkable oxidation resistance. Both showed “◎” as a result of the improvement in surface resistance and the effect of suppressing surface damage.

  No. 3 and 17 have the components of the base material defined in the present invention, but the austenite grain size of the structure in the vicinity of the surface of the base material is out of the scope of the present invention, and the power generation performance and surface damage targeted by the present invention Could not be obtained, and the evaluation was “x”. No. 18 to 25 are deviated from the base material component of the present invention, and the structure having the austenite phase in the vicinity of the base material surface is within the specified range of the present invention, but the target oxidation resistance, power generation performance of the present invention, Not all of the surface damage could be achieved, and either evaluation was “x”.

  From the above results, if the average particle size, Co concentration, and aspect ratio of the structure having the austenite phase formed in the vicinity of the components of the base material defined in the present invention are satisfied, oxidation resistance and power generation in a high-temperature oxidation environment are satisfied. It was found that the performance was sustained and it was extremely effective in suppressing surface damage caused by thermal stress.

  According to the present invention, an SOFC that maintains excellent oxidation resistance and electrical conductivity in a long-term high-temperature oxidation environment and suppresses surface damage due to thermal stress without impairing the cost of materials and versatility. Can be obtained. Moreover, the SOFC separator of the present invention can be industrially produced regardless of a special production method. Therefore, it is suitable for all high-temperature members used in fuel cells, gas turbines, power generation systems and the like.

DESCRIPTION OF SYMBOLS 10 Electric power generation unit 20 Separator 21 Current collecting plate 21a, 21b, 21c, 21d, Hole part 22 Cathode plate 22a, 22b, 22c Hole part 22d Flow path (for oxidizing gas)
23 Separator body 23a, 23b, 23c Hole 24 Anode plate 24a, 24b, 24c, 24d Hole 24e Flow path (for fuel gas)
25 cell holder 25a, 25b, 25c hole 25d opening 30 insulating member 30a, 30b, 30c hole 30d opening 50 (fuel cell) cell 60 cell holder 60a, 60b, 60c hole 60d opening

Claims (5)

  In mass%, C: 0.030% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.045% or less, S: 0.0050% or less, Cr: 19.0 To 25.0%, Mo: 0.2 to 2.0%, N: 0.040% or less, Al: 0.50% or less, Nb: 0.001 to 0.5% and / or Ti: 0.00. The base material is ferritic stainless steel containing 001 to 0.5%, the balance being Fe and inevitable impurities, and has an austenite phase having an average particle diameter of 1 to 10 μm on at least one surface of the stainless steel base material. A solid oxide fuel cell separator in which a structure is formed.   2. The solid oxide fuel cell separator according to claim 1, wherein the Co concentration of the austenite phase of the structure is 10 to 95 mass%, and the balance is Ni, Fe, Cr, and inevitable impurities.   3. The solid oxide fuel cell separator according to claim 1, wherein an average value of aspect ratios (plate width direction / plate thickness direction) of austenite grains forming the austenite phase is 0.1 to 0.9.   The base material is further mass%, V: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, Cu: 1% or less, W: 1% Hereinafter, Co: 1% or less, B: 0.010% or less, Ga: 0.010% or less, Mg: 0.010% or less, Ca: 0.010% or less, Zr: 0.1% or less, La: One or two or more of 0.1% or less, Y: 0.1% or less, REM: 0.1% or less, Ta: 0.1% or less are contained. A separator for a solid oxide fuel cell according to item 1.   A fuel cell configured by laminating a plurality of power generation elements, the power generation element comprising: a plate-like cell having an anode on one main surface and a cathode connected to the other main surface; and the anode and the cathode A separator using the separator for a solid oxide fuel cell according to any one of claims 1 to 4 as at least a part of the separator. battery.