JPWO2009060900A1 - Stainless steel material for polymer electrolyte fuel cell separator and polymer electrolyte fuel cell - Google Patents

Abstract

A stainless steel material for a polymer electrolyte fuel cell separator that realizes sufficiently low contact resistance and long-term corrosion resistance, and a polymer electrolyte fuel cell including a stainless steel separator using the same. An austenitic stainless steel material having a Ni content of 50% by mass or more, a conductive precipitate exposed on the surface, and a surface exposure rate of the precipitate of 3% by area, and its steel material A polymer electrolyte fuel cell comprising a separator comprising: The precipitate preferably contains Ni3X type (X is one or more selected from the group consisting of Al, Ti, V, Nb, Ta, and Zr), and includes a Ni3Nb phase and / or a Ni3Ti phase. It is particularly preferable to include it.

Description

  The present invention relates to a solid polymer fuel cell current-carrying component material that has a low contact electric resistance and excellent corrosion resistance when incorporated in a battery body, and a solid state using a separator manufactured from the stainless steel material. The present invention relates to a molecular fuel cell.

  A fuel cell is a battery that generates direct-current power using hydrogen and oxygen, and includes various fuel cells such as a solid electrolyte type, a molten carbonate type, a phosphoric acid type, and a solid polymer type. Among these, the fuel cells that have reached the commercial stage are phosphoric acid fuel cells and molten carbonate fuel cells. The approximate operating temperatures of these fuel cells are 1000 ° C for solid oxide fuel cells, 650 ° C for molten carbonate fuel cells, 200 ° C for phosphoric acid fuel cells, and 80 ° C for solid polymer fuel cells. Before and after.

  As described above, the polymer electrolyte fuel cell has a low operating temperature, can be easily started and stopped, and can be expected to have an energy efficiency of about 40%. Therefore, as an emergency distributed power source for small offices, telephone offices, etc., a small distributed power source for households that uses city gas as fuel, and a power source for low-pollution electric vehicles that uses hydrogen gas, methanol or gasoline as fuel, worldwide Practical use is expected.

  FIG. 1 is a diagram showing the structure of a polymer electrolyte fuel cell (hereinafter also simply referred to as “fuel cell”). FIG. 1 (a) is an exploded view of a single cell constituting the fuel cell, and FIG. b) is a perspective view of the whole fuel cell made by combining a number of single cells.

  As shown in FIG. 1, the fuel cell 1 is an assembly (stack) of single cells. In the single cell, as shown in FIG. 1A, a gas diffusion electrode layer (also referred to as a fuel electrode membrane, hereinafter referred to as “anode”) 3 acting as an anode on one surface of the solid polymer electrolyte membrane 2 is provided. A gas diffusion electrode layer (referred to as an oxidizer electrode film, hereinafter referred to as “cathode”) 4 acting as a cathode is laminated on each surface, and separators (bipolar plates) 5a and 5b are laminated on both surfaces. It has a structure.

  In addition, there is a water-cooled fuel cell in which a water separator having a cooling water passage is disposed between the single cells or between several single cells. The present invention is also directed to such a water-cooled fuel cell.

  As the solid polymer electrolyte membrane (hereinafter simply referred to as “electrolyte membrane”) 2, a fluorine-based proton conductive membrane having a hydrogen ion (proton) exchange group is used. In some cases, the anode 3 and the cathode 4 are provided with a catalyst layer made of a particulate platinum catalyst, graphite powder, and, if necessary, a fluororesin having a hydrogen ion (proton) exchange group. Then, the fuel gas or the oxidizing gas and the catalyst layer come into contact with each other to promote the reaction.

  A fuel gas (hydrogen or hydrogen-containing gas) A is flowed from the flow path 6 a provided in the separator 5 a to supply hydrogen to the fuel electrode film 3. Also, an oxidizing gas B 2 such as air is flowed from the flow path 6b provided in the separator 5b, and oxygen is supplied. The supply of these gases causes an electrochemical reaction to generate DC power.

The main functions required for a separator of a polymer electrolyte fuel cell are as follows.
(1) Function as a “flow path” for uniformly supplying fuel gas and oxidizing gas into the battery surface,
(2) A function as a “flow path” for efficiently discharging water generated on the cathode side from the fuel cell together with a carrier gas such as air and oxygen after reaction,
(3) The function of becoming an electrical path in contact with the electrode films (anode 3 and cathode 4), and further serving as an electrical “connector” between single cells,
(4) A function as a “partition” between the anode chamber of one cell and the cathode chamber of the adjacent cell between adjacent cells, and (5) In the water-cooled fuel cell, the cooling water flow path and the adjacent cell Function as a “partition wall”.

  As a material for a polymer electrolyte fuel cell separator (hereinafter simply referred to as “separator”) that is required to fulfill such a function, excellent workability, low electrical resistivity, low surface contact resistance, high strength, Excellent corrosion resistance is required at the same time, and mass productivity is a big problem. Conventionally, a carbon-based material has been used as the separator material, but the carbon-based material has a problem in strength. In addition, there is a drawback that the processing cost for the separator increases. Specifically, in the case of a carbon plate material, machining for flattening the surface and forming a flow path is not easy, and in the case of thermally expandable graphite, resin impregnation is performed to reduce gas permeability. It is necessary to repeat firing.

  There is a need for the development of press-moldable metal-based separator materials that enable the design of lighter and more compact fuel cells than conventional carbon-based materials. In response to these demands, the use of stainless steel has been studied.

  Stainless steel is a material that can realize high corrosion resistance by an oxide film (passive film) formed on its surface, and is expected to maintain sufficient corrosion resistance even in a polymer electrolyte fuel cell environment. However, since the contact resistance is increased by the passive film formed on the surface, if the stainless steel is applied as it is as a current-carrying part such as a separator, the effective power generation efficiency as a fuel cell is reduced by this contact resistance. This is not preferable.

Therefore, some stainless steels specially developed as separator materials have been proposed. For example, Patent Document 1 discloses a technique in which a conductive contact layer made of a noble metal such as gold is formed on the surface of a separator substrate with a thickness of less than 0.0005 to 0.01 μm by plating or the like. Patent Document 2 discloses a technique for dispersing and exposing metal inclusions such as conductive carbides and borides having a conductive surface on a stainless steel surface so as to break through the passive film, and bringing the surface roughness into a predetermined range. Is disclosed. At this time, the carbide or boride-based metal inclusion functions as an “electric path”, so that the contact electrical resistance is greatly reduced, and the contact electrical resistance is maintained low over time. As a technique based on the same idea, Patent Document 3 describes a method of utilizing an Fe ₂ Mo type Laves phase as a conductive precipitate. These are all precipitates mainly composed of Cr, Fe and Mo.
JP 2004-158437 A JP 2001-32056 A JP 2004-124197 A

  However, the laminated structure as disclosed in Patent Document 1 has a thin conductive layer on the surface and is relatively soft. Therefore, when assembling as a fuel cell, the separator comes into contact with other component elements to form a conductive layer. There is concern about peeling. Moreover, a local battery is formed between a noble metal part and a base material, and there exists a possibility that the corrosion resistance by the side of a base material may fall.

  The techniques disclosed in Patent Documents 2 and 3 do not cause the above problems. However, in order to expose a predetermined metal inclusion so as to break through the passive film responsible for corrosion resistance, when the separator is exposed to a moisture-rich atmosphere such as a portion facing the cathode, it has high corrosion resistance over a long period of time. It is unclear whether it will be maintained.

  Therefore, the present invention uses a stainless steel material for a polymer electrolyte fuel cell current-carrying component, which has a contact resistance low enough to operate as a separator and can maintain corrosion resistance for a long time even at a cathode facing portion, and the same. An object of the present invention is to provide a polymer electrolyte fuel cell including a stainless steel separator.

  As a result of intensive studies by the inventor in order to solve the above problems, Ni-based precipitates, which are Ni precipitates having a Ni content of 50% by mass or more and having conductivity, are exposed from a dense Cr oxide film. Thus, it has been found that stainless steel having a structure dispersed in such a manner has excellent current resistance and high corrosion resistance. The present invention completed based on such knowledge is as follows.

  (1) An austenitic stainless steel material, in which the Ni content is 50% by mass or more and one or more conductive precipitates are exposed on the surface, and the surface exposure rate of the precipitates is 3% by area or more. A stainless steel material for a polymer electrolyte fuel cell separator.

(2) The precipitate includes a Ni ₃ X-type precipitate (X is one or more selected from the group consisting of Al, Ti, V, Nb, Ta, and Zr). The stainless steel material for a polymer electrolyte fuel cell separator according to (1) above.

(3) The stainless steel material for a polymer electrolyte fuel cell separator as described in (2) above, wherein the precipitate contains a Ni ₃ Nb phase.
(4) The stainless steel material for a polymer electrolyte fuel cell separator as described in (2) above, wherein the precipitate contains a Ni ₃ Ti phase.

  (5) The stainless steel material which comprises a separator is the mass%, C: 0.001-0.2%, Si: 0.01-1.5%, Mn: 0.01-2.5%, P: 0.04% or less, S: 0.01% or less, Cr: 15-30%, Ni: 20-60%, Cu: 2% or less, Al: 3.1% or less, N: 0.4% or less Mo: 7% or less, W: 4% or less, Ti: 5% or less, Nb: 6% or less, V: 5% or less, Ta: 10% or less, and Zr: 6% or less Characterized in that it is an austenitic stainless steel material containing one or more of the above, the balance being Fe and impurities, and having a chemical composition in which Al, Ti, V, Nb, Ta and Zr satisfy the following formula: The polymer electrolyte fuel cell separator according to any one of (1) to (4) above Over data for stainless steel.

2% <8 × Al + 4 × Ti + 4 × V + 2 × Nb + 2 × Zr + Ta <25%
However, the element symbol in a formula shows content (unit: mass%) of each element.
(6) A polymer electrolyte fuel cell comprising a polymer electrolyte membrane, an electrode and a separator, wherein the polymer electrolyte fuel cell separator described in any one of (1) to (5) above is used as a material for the separator A solid polymer type fuel cell characterized by using stainless steel for the battery.

  ADVANTAGE OF THE INVENTION According to this invention, a solid polymer fuel cell provided with the stainless steel material for a polymer electrolyte fuel cell electricity supply component with low contact resistance and excellent corrosion resistance, and a stainless steel separator using the same.

It is a figure which shows notionally the structure of a polymer electrolyte fuel cell. It is a figure which shows notionally the state which contacted the surface of the stainless steel material which the deposit exposed, and the other electrically-conductive body surface. It is an observation image by SEM of the surface of the stainless steel material which concerns on this invention.

  A solid polymer fuel cell including a stainless steel material for a polymer electrolyte fuel cell energizing component according to the present invention, a method for producing the same, and a stainless steel separator using the material will be described in detail with specific examples. In the present specification, “%” relating to the content of steel components means “mass%”.

1. Surface structure of stainless steel material (1) Ni-based precipitate The stainless steel material according to the present invention is exposed on a dense Cr oxide film (passive film) formed on the surface of the steel material. It has the structure to do.

Here, the “Ni-based precipitate” is a precipitate having a Ni content of 50% by mass or more and having conductivity.
The chemical composition of the Ni-based precipitate is not particularly limited as long as it has conductivity. It may be an intermetallic compound or a carbide. The intermetallic compound has a plurality of structures such as NiX type, Ni ₂ X type, Ni ₃ X type (where X is one or more of elements such as Al, Ti, V, Nb, Ta, Zr, etc.) Is).

  Since stainless steel generally contains Cr in its chemical composition, Cr-based precipitates (precipitates with a Cr content of 50% by mass or more) may be deposited in addition to Ni-based precipitates. Since the thickness of the oxide film formed on the surface of the Ni-based precipitate according to the present invention is thinner than that of the oxide film formed on the surface of the Cr-based precipitate, the Ni-based precipitate exhibits a lower contact resistance than the Cr-based precipitate. Moreover, although it is relatively thinner than the Cr-based precipitate oxide film, the Ni-based precipitate oxide film is dense, and therefore exhibits a sufficient degree of corrosion resistance in a polymer electrolyte fuel cell environment. Therefore, when the separator made of the steel material comes into contact with the electrode member made of carbon paper or the like, the Ni-based precipitate exposed on the surface comes into contact with the electrode member. Therefore, the separator has good conductivity. In addition, this separator maintains high corrosion resistance even when exposed to an atmosphere containing a large amount of moisture on the cathode side.

  FIG. 2 is a diagram conceptually showing a state in which the surface of the stainless steel material with the Ni-based precipitate exposed on the surface is brought into contact with another current-carrying member surface. The stainless steel material 10 according to the present invention has an oxide film 12 on its surface and the above-mentioned Ni-based precipitates. A part 13 of this Ni-based precipitate is inside thereof, and another part 14 is an oxide film 11. Is partially exposed on the surface so as to break through, and another portion 15 exists directly under the oxide film. In use, the electrode member 11 having a gas diffusion function is brought into contact with the stainless steel material. At this time, the Ni-based precipitate 14 exposed on the surface of the stainless steel material 10 and the electrode member 11 come into contact with each other, thereby reducing the contact resistance. The electrical connection is realized.

  The shape of the Ni-based precipitate is not particularly limited, but if it is excessively large, the Ni-based precipitate exposed on the surface tends to fall off, and if it is excessively small, the base material of the stainless steel material is exposed even if it is exposed on the surface. Ni-based precipitates cannot protrude from the oxide film (passive film) formed on the surface, making it difficult to function as an “electric path”. Therefore, the particle size is preferably about 10 nm to 1 μm, and more preferably 20 to 100 nm.

  The formation method of the Ni-based precipitate is not limited. Formed when the molten stainless steel solidifies, formed during the primary processing such as forging or rolling, and formed by heat treating the primary processed product or the secondary processed product Any of those may be used. From the viewpoint of easy control of the chemical composition and shape of the precipitate, it is preferable to deposit by precipitation.

(2) Ni ₃ X-type precipitate The Ni-based precipitate exposed on the surface of the stainless steel material according to the present invention includes a precipitation phase of a Ni-based alloy and having a Ni ₃ X-type structure. It is preferable from the viewpoint of achieving both conductivity and corrosion resistance. Here, X is one or more of elements such as Al, Ti, V, Nb, Ta, and Zr as described above. Specifically, Ni ₃ Nb phase and Ni ₃ Ti phase are exemplified as Ni ₃ X type precipitates. In this precipitate, a part of the Ni site in the Ni ₃ X-type structure may be substituted with a metal other than Ni, for example, Fe. Such substitution of Ni sites is likely to occur when X consists of a plurality of elements.

(3) Volume distribution of precipitates The composition of the Ni-based precipitates in the stainless steel material according to the present invention is Ni ₃ X (X: one or more selected from the group consisting of Al, Ti, V, Nb, Ta and Zr) ), And if all the elements that are elements of X in the steel are taken into the precipitate, the volume% (hereinafter referred to as “A”) of the precipitate in the stainless steel material is approximately expressed by the following equation: Can do.

A (volume%) = 8 x Al + 4 x Ti + 4 x V + 2 x Nb + 2 x Zr + Ta
However, the element symbol in a formula shows content (mass%) in steel of each element.
In the range of A, Ni-based precipitates require a certain amount of precipitation in order to cause the surface of the steel material to be cut by an acid so that the precipitates are dispersedly exposed on the surface and function as electric paths. For this reason, the lower limit of the precipitation amount of the Ni-based precipitate is defined, and according to the result of detailed examination, the lower limit Amin is 2% by volume, and A is preferably 10% by volume or more. On the other hand, the upper limit is determined by manufacturability such as workability of the material, and the upper limit Amax is preferably 25% by volume.

(4) Surface distribution of precipitate As described above, the Ni-based precipitate of the stainless steel material according to the present invention reduces the surface resistance of the steel material by being exposed to the surface. The ratio of the exposed Ni-based precipitates on the surface (unit: area%, in the present invention, this ratio is referred to as “surface exposure rate”) may be 3% or more, and is preferably approximately 5% or more. . Since an electric current flows into the member (carbon paper) which contacts through the deposit exposed on the surface, the higher the surface exposure rate, the lower the contact resistance, which is preferable. A surface exposure rate of 5% or more is sufficient. Even if it is lower than 5%, it is effective as long as a current flows through the deposited portion, and if it is 3% or more, generally minimum conductivity is ensured. Therefore, the surface exposure rate is 3% or more. A particularly preferable surface exposure rate is 12% or more. On the other hand, the upper limit of the area ratio is not defined from the viewpoint of contact resistance, but the upper limit may be defined from the viewpoint of workability. Since this upper limit depends on the composition and processing method, it is difficult to set a specific numerical value as the upper limit without these restrictions. If a numerical value is mentioned as an example, the upper limit of a preferable surface exposure rate is 20 area%.

  The method for measuring the surface exposure rate is not particularly limited, but an example is as follows. That is, considering that the diameter of the Ni-based precipitate is generally several tens to several hundreds of nanometers, using an electron microscope such as SEM or TEM, the field of view is 500 nm × 500 nm to 5 μm × 5 μm, preferably Observe the precipitates on the surface of the stainless steel material as 500 nm × 500 nm to 2 μm × 2 μm. The chemical composition of the precipitate in the observation field is measured by an elemental analysis means such as EPMA or AES, and the Ni-based precipitate is specified from these. The area ratio of the Ni-based precipitate in the observation visual field thus specified is calculated by using an image processing means.

2. Chemical composition of stainless steel material The stainless steel material according to the present invention capable of stably obtaining the above precipitate is a steel material made of austenitic stainless steel, and a preferred chemical composition thereof is as follows.

C: 0.001 to 0.2%
In order to suppress precipitation of various carbides that affect workability and corrosion resistance, the C content is preferably 0.001 to 0.2%.

Si: 0.01 to 1.5%
It is preferable to contain Si in steel in the range of 0.01 to 1.5%. Si is a deoxidizing element as effective as Al in mass-produced steel. If it is less than 0.01%, there is a concern that deoxidation will be insufficient. On the other hand, if it exceeds 1.5%, the moldability tends to decrease.

Mn: 0.01 to 2.5%
Mn is preferably contained in the range of 0.01 to 2.5%. Mn is an effective austenite phase stabilizing element. However, it is not necessary to contain 2.5% or more.

P: 0.04% or less The P content in the steel is preferably 0.04% or less. In the steel material according to the present invention, P is the most harmful impurity along with S. The lower the better.

S: 0.01% or less The S content in steel is preferably 0.01% or less. In the steel material according to the present invention, since S is the most harmful impurity along with P, the lower the S content, the better. Depending on the coexisting elements in steel and the amount of S in steel, Mn-based sulfides, Cr-based sulfides, Fe-based sulfides, or composite non-metallic inclusions with these composite sulfides and oxides are mostly precipitated. To do. However, in the environment where the separator of a polymer electrolyte fuel cell is placed, non-metallic inclusions of any composition can act as a starting point for corrosion to a certain extent, maintaining a passive film and suppressing corrosion elution. It is harmful. In general mass-produced steel, the S content in steel is more than 0.005% and not more than 0.008%, but it is desirable to reduce it to 0.004% or less in order to prevent the harmful effects described above. The more desirable S content in steel is 0.002% or less, and the most desirable S content level in steel is less than 0.001%, and the lower the better. If it is less than 0.001% at the industrial mass production level, if the current refining technology is used, the increase in production cost is slight, and there is no problem at all.

Cr: 15-30%
Cr is a basic alloy element that is extremely important in securing the corrosion resistance of the base material. As a basic tendency, the higher the content, the higher the corrosion resistance. If the Cr content is less than 15%, it may be difficult to ensure the corrosion resistance necessary for the separator even if other elements are changed. On the other hand, if it exceeds 30%, the austenite phase becomes unstable due to adjustment of other alloy components. Therefore, the Cr content is preferably 15 to 30%, particularly preferably 15 to 20%.

Ni: 20 to 60%
Ni is an essential element for forming Ni inclusions having conductivity, and is an important element having a function of stabilizing the austenite phase. In particular, in a steel containing a large amount of Nb or Ti as in the steel material according to the present invention, it is preferable to contain 20% or more of Ni in order to stabilize the austenite phase. On the other hand, since manufacture will become difficult when it contains excessively, it is preferable that the upper limit of content shall be 60%. A particularly preferred range is 25 to 50%.

Al: 3.1% or less Al is generally added as a deoxidizing element at the molten steel stage. On the other hand, in the steel material according to the present invention, Al also acts as a constituent element of a conductive precipitate that becomes a path of electricity. However, if the content exceeds 3.1%, the influence due to the decrease in workability becomes significant. Therefore, the Al content is preferably 3.1% or less. A particularly preferable Al content is 1% or less.

Cu: 2% or less Cu is an effective austenite phase stabilizing element, and works effectively in maintaining the passive state. However, if it exceeds 2%, hot workability will be reduced, and it will be difficult to ensure mass productivity. Therefore, the Cu content is preferably 2% or less.

N: 0.4% or less N is an element effective for adjusting the austenite phase balance as an austenite forming element. However, there is concern about deterioration of workability if contained excessively. Therefore, it is preferable that the upper limit of the N content is 0.4%.

One or two selected from the group consisting of Mo: 7% or less, W: 4% or less, Ti: 5% or less, Nb: 6% or less, V: 5% or less, Ta: 10% or less, and Zr: 6% or less More than seeds Mo has the effect of improving corrosion resistance in a small amount compared to Cr. It is preferably contained in an amount of 7% or less if necessary. If the content exceeds 7%, it is difficult to avoid precipitation of intermetallic compounds such as sigma phase, and the problem of embrittlement of steel becomes obvious, which may make production difficult. Therefore, the upper limit of the Mo content is preferably 7%.

  W has an effect of improving the corrosion resistance like Mo and can be contained if necessary. However, since the workability deteriorates when contained in a large amount, the upper limit is preferably made 4%.

  The other elements in the above group are constituent elements of conductive precipitates that serve as a path for electricity, like Al. In order to ensure workability, one or more selected from the group consisting of Ti: 5% or less, Nb: 6% or less, V: 5% or less, Ta: 10% or less, and Zr: 6% or less are satisfied. It can be made to contain.

Other than the above elements, Fe and impurities.
In addition, as mentioned above, about Al, Ti, V, Nb, Ta, and Zr contained in steel, it is preferable to satisfy | fill the following formula from a viewpoint of the suitable range of the volume of a precipitate.

2% <8 × Al + 4 × Ti + 4 × V + 2 × Nb + 2 × Zr + Ta <25%
However, the element symbol in a formula shows content (mass%) of each element.
3. Manufacturing method of stainless steel material The stainless steel material according to the present invention is within the range in which the surface exposure rate of Ni-based precipitates is defined in the present invention as described above, and preferably has the chemical composition as described above. For example, the manufacturing method is not particularly limited. However, if the following manufacturing method is employed, it is possible to efficiently and stably obtain the stainless steel material according to the present invention.

(1) Manufacturing method of steel material The stainless steel material according to the present invention may be manufactured in accordance with a normal manufacturing method of austenitic stainless steel material before depositing Ni-based precipitates. An example is as follows. First, a metal raw material is heated and melted in a furnace, and the obtained molten steel is made into a slab by continuous casting, which is hot-rolled and annealed. A steel material obtained by annealing is pickled, cold-rolled, and annealed to obtain a stainless steel material. In addition, without performing continuous casting, ingots may be obtained from molten steel to obtain ingots, which may be forged and subjected to hot rolling.

(2) Precipitate formation by heat treatment The stainless steel material according to the present invention has conductive precipitates mainly composed of Ni (specifically, 50% by mass or more), that is, Ni-based precipitates. Although this precipitation method is not particularly limited, it is preferable to deposit the precipitate by performing a heat treatment on the stainless steel material obtained by the above production method. The chemical composition, shape, and precipitation amount of Ni-based precipitates depend not only on the chemical composition of the stainless steel material but also on the heat treatment conditions, so the heat treatment conditions are set appropriately so that the Ni-based precipitates have the desired surface exposure rate. Is done. For example, it is about 700 ° C. to 800 ° C., several hours to several tens of hours.

  The timing of this heat treatment may be before or after the molding process (press molding, cutting process, etc.) into the separator shape. Since precipitates precipitated in the steel material do not cause deterioration of workability, it is particularly preferable to perform precipitation heat treatment after forming.

(3) Hot-cutting Once the precipitates are deposited in the steel material, the precipitates uniformly deposited inside the steel material are exposed on the surface in order to secure the passage of electricity on the surface. Therefore, in general, the surface is pickled after the precipitation heat treatment. Since the base material has a higher dissolution rate with respect to the acid than the precipitate, pickling preferentially dissolves the base material over the precipitate, and as a result, a part of the precipitate is exposed on the surface of the steel (indexing). .

The treatment liquid used for pickling for cueing is not particularly limited, and examples thereof include an aqueous treatment liquid containing 8 to 15% by volume of nitric acid and 3 to 8% by volume of hydrofluoric acid.
Since the treatment conditions with the treatment liquid vary depending on the composition of the treatment liquid, it may be set as appropriate so that the Ni-based precipitate has the target surface exposure rate. For example, in the case of an aqueous processing solution having 8% by volume of nitric acid and 3% by volume of hydrofluoric acid, the processing time may be about 1 to 5 minutes at a liquid temperature of 60 ° C.

4). Stainless steel separator and polymer electrolyte fuel cell The structure of the stainless steel material according to the present invention having the deposit as described above, the processing method thereof, and the structure of the polymer electrolyte fuel cell using the obtained separator The assembly method is not particularly limited.

As an example of the structure of the separator, there are separators 5a and 5b shown in FIG. 1, and as the structure of the polymer electrolyte fuel cell, there is the fuel cell 1 shown in FIG.
The manufacturing method of the separator may be a method of forming a groove by cutting a stainless steel material or a method of forming irregularities by pressing a stainless steel plate.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

  Ten kinds of alloys having the chemical composition shown in Table 1 were melted by adjusting impurities in steel using a commercially available metal raw material in a high-frequency induction heating method 20 kg vacuum melting furnace, and ingot was obtained. . The balance in the chemical composition shown in Table 1 is Fe and impurities. A cold-rolled steel sheet was produced from each ingot by the following process.

Ingot->forging-> hot rolling->annealing->pickling-> cold rolling (intermediate annealing)->annealing-> cold-rolled steel sheet For some alloys, the steel sheet at the end of hot rolling in the above process, that is, hot The rolled steel plate was machined, and the processed member was subjected to heat treatment to be evaluated.

The details in each manufacturing process are as follows.
Forging was performed in the press method by heating the ingot to 1100 ° C. by heating in the atmosphere, and a steel material after forging having a thickness of 25 to 30 mm × 110 mm was obtained. The steel material after forging was heated to 1100 ° C. by heating in the atmosphere, and what was 25-30 mm thick was hot-rolled to 6 mm thick. The steel sheet after hot rolling was annealed by heating to 1050 ° C. by heating in the air. Subsequently, the steel material after annealing was pickled and then cold-rolled from a thickness of 6 mm to a thickness of 0.5 to 0.2 mm. The cold-rolled steel sheet was obtained by annealing the steel sheet after cold rolling under the same conditions as described above.

Table 1 shows the calculation results of the volume ratio (volume%) of the cold-rolled steel sheet finished in the above process when the precipitate is Ni ₃ X type.
The dispersion and cueing of the precipitate on the surface of the cold-rolled steel sheet was carried out by uniformly depositing the precipitate in the material by heat treatment under the conditions shown in Table 2 and then pickling the surface. . The composition of the treatment solution used for pickling was a 5% HCl solution, and cueing was performed by immersion at 60 ° C. for 10 minutes.

For the cold-rolled steel sheet on which the precipitates were dispersed / cueed on the surface, a plurality of arbitrary measurement locations were selected, and the area ratio of the precipitates in the observation image of the field of view of 580 nm × 580 nm obtained by SEM observation was calculated. . In addition, the identification of the deposit was performed by SEM observation, X-ray observation, and TEM observation (and attached EDX). An example of the obtained SEM image is shown in FIG. The white or gray portion of the circle or ellipse in FIG. 3 is a precipitate (the precipitate observed in FIG. 3A is Ni ₃ Ti, and the precipitate in FIG. 3A is Ni ₃ Nb. .)

Moreover, the contact resistance with a carbon member was measured about the cold-rolled steel plate which performed dispersion | distribution / cueing of the precipitate to the surface. A test piece of 20 mm × 20 mm was cut out from the cold-rolled steel sheet subjected to the predetermined treatment. A carbon paper (TGP-H120 manufactured by Toray Industries Inc.) was sandwiched between ^two test pieces with a load of 5 kg / cm ² , and the resistance was measured. Since the measured value is derived from the contact resistance of two test pieces, the contact resistance (unit: mΩcm ² ) of one contact surface of the test piece and the carbon paper is calculated based on the half of the measured value. did. In addition to the contact resistance initial value thus obtained, the contact resistance after the test piece was held in an environment of 75 ° C. and 95% relative humidity for 200 hours was measured.

  Table 2 shows the results of the cold-rolled steel sheet after cueing the precipitate.

No. 3 is an evaluation result of a material (surface exposure rate 16%) obtained by cueing precipitates by hot-melting the alloy a shown in Table 1 after heat treatment at 720 ° C. × 16 h. The initial resistance was a low value of 8.8 mΩcm ² . On the other hand, no. No. 1 was not subjected to precipitation treatment (heat treatment), and resistance did not decrease even when pickling corresponding to cueing was performed. No. In No. 2, precipitates were deposited by precipitation treatment (heat treatment), but the surface pickling treatment at the surface cueing level was not performed, so that the contact resistance was high.

Hereinafter, no. 5 and no. In Nos. 7 to 14, the exposure rate of the precipitates was 10% or more, and low contact resistance values of about 10 mΩcm ² were exhibited. No. In Nos. 4 and 6, since no precipitation treatment (heat treatment) was performed, no precipitate was deposited, and the contact resistance was high. No. For comparison, 15 is a result obtained by subjecting SUS316L to a treatment equivalent to surface cutting, and it was confirmed again that the contact resistance was high.

  When the sample shown in Table 2 was left in an atmosphere of 75 ° C. and a relative humidity of 95% for 200 hours and then contact resistance was measured, no. 3, 5, and no. 7 to 14 showed almost no increase in resistance. On the other hand, the resistances of all the comparative examples increased about twice.

  The above results show that the precipitates on the surface of the stainless steel plate according to the present invention effectively act as a path for electricity, and the deterioration under a high temperature and high humidity environment is small.

A plate cut out from the hot rolled steel sheets of alloys a, b, and g shown in Table 1 was subjected to a flow path by cutting and processed into a separator. The width of the groove serving as the gas flow path was 1.5 mm and the depth was 1.0 mm. The separator was subjected to heat treatment at 720 ° C. for 16 hours, and further subjected to a pickling treatment similar to the treatment shown in Example 1, thereby performing surface cueing of the precipitate. A membrane electrode assembly (MEA) having an electrode effective area of 25 cm ² in which a polymer membrane, an electrode, and a gas diffusion layer were integrated was sandwiched between the separators to produce a single cell fuel cell. Air (utilization rate 50%) was passed to the cathode side, pure hydrogen (utilization rate 70%) was passed to the anode side, the output voltage was monitored at a current density of 0.5 A / cm ² , and the battery performance was evaluated. The results are shown in Table 3. The voltage drop rate after 100 hours of operation was less than 3%, and it was confirmed that the separator made of the steel of the present invention functioned well when incorporated in a battery.

A fuel cell similar to the fuel cell according to Example 2 was manufactured using hot-rolled steel sheets of alloys b and g shown in Table 1. The separator was subjected to the same heat treatment and cue pickling treatment as in Example 2 after machining. The fuel used methanol aqueous solution, and the electrode effective area was 16 cm < ² >. The cathode side was exposed to the atmosphere, and a 3% methanol solution was flowed to the anode side. The battery performance was evaluated by maintaining the current density at 5 mA / cm ² and monitoring the output voltage. The results are shown in Table 4.

  The voltage drop rate after 100 hours of operation is still less than 3%, and it has been confirmed that the stainless steel separator according to the present invention functions sufficiently even when incorporated in a battery using methanol as a fuel.

Claims (6)

  It is an austenitic stainless steel material, the Ni content is 50% by mass or more, and one or more types of conductive precipitates are exposed on the surface, and the surface exposure rate of the precipitates is 3% by area or more. A stainless steel material for solid polymer fuel cell separators. The precipitates include Ni ₃ X-type precipitates (X is one or more selected from the group consisting of Al, Ti, V, Nb, Ta, and Zr). Item 2. A stainless steel material for a polymer electrolyte fuel cell separator according to Item 1. The stainless steel material for a polymer electrolyte fuel cell separator according to claim 2, wherein the precipitate contains a Ni ₃ Nb phase. The stainless steel material for a polymer electrolyte fuel cell separator according to claim 2, wherein the precipitate contains a Ni ₃ Ti phase. The stainless steel material constituting the separator is mass%, C: 0.001 to 0.2%, Si: 0.01 to 1.5%, Mn: 0.01 to 2.5%, P: 0.04. %: S: 0.01% or less, Cr: 15-30%, Ni: 20-60%, Cu: 2% or less, Al: 3.1% or less, N: 0.4% or less Mo: 7% or less, W: 4% or less, Ti: 5% or less, Nb: 6% or less, V: 5% or less, Ta: 10% or less, and Zr: 6% or less An austenitic stainless steel material containing two or more, comprising the balance Fe and impurities, and Al, Ti, V, Nb, Ta and Zr having a chemical composition satisfying the following formula: The solid polymer fuel cell separator step according to any one of 1 to 4 Less steel.
2% <8 × Al + 4 × Ti + 4 × V + 2 × Nb + 2 × Zr + Ta <25%
However, the element symbol in a formula shows content (unit: mass%) of each element.   A solid polymer fuel cell comprising a solid polymer membrane, an electrode, and a separator, wherein the separator is made of stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 5. A polymer electrolyte fuel cell characterized by the above.

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