JP2009231149A - Ferrite system roughened surface stainless steel plate for separator, and separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite system stainless steel plate having a roughened surface to be extremely effective for reducing contact resistance at a contact part as is used for a structure member of a platy member complex separator of a polymer electrolyte fuel cell. <P>SOLUTION: In the roughened surface stainless steel plate for a separator of a polymer electrolyte fuel cell, the steel plate includes a coarse surface of its surface roughness SPa of 0.3 to 2 μm on at least one surface of a steel plate made of ferrite system stainless steel type containing Cr of 16 to 40 mass% and Mo of 0.2 to 5 mass%. When the coarse surface of the steel plate and a coarse surface of another steel plate having the surface with the same condition as above are made in contact with each other with a contact surface pressure of 1 MPa, a contact resistance is ≤10 mΩ cm<SP>2</SP>, preferably ≤3 mΩ cm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a roughened ferritic stainless steel plate for constituting a metal separator of a solid polymer fuel cell, and a solid polymer fuel cell configured using the ferritic stainless steel plate as a member. It relates to a separator.

  Among fuel cells, a polymer electrolyte fuel cell can operate at a low temperature of 100 ° C. or less, and has an advantage of starting in a short time. In addition, since each member is made of a solid structure, maintenance is easy, and it can also be applied to applications that are exposed to vibration and impact. In addition, it has advantages such as high output, suitable for downsizing, high fuel efficiency and low noise.

  Since a polymer electrolyte fuel cell has a small power generation amount per cell, it is necessary to stack a large number of cells with one cell having a polymer electrolyte membrane sandwiched between separators in order to extract practical power. is there. The polymer electrolyte fuel cell utilizes the function of a solid polymer resin having a proton exchange group in the molecule as a proton conductive electrolyte. Like other types of fuel cells, the polymer electrolyte fuel cell The fuel gas such as hydrogen is flowed on one side and the oxidizing gas such as air is flowed on the other side.

  FIG. 1 schematically illustrates a cross-sectional structure of an in-vehicle solid polymer fuel cell using a metal separator. Separators are arranged on both sides of the solid polymer membrane with electrodes (a negative electrode and a positive electrode, respectively) interposed therebetween. The separator is in a state in which a pair of separator member 1 and separator member 2 formed by processing a metal plate into a shape having a bowl-shaped concavo-convex cross section by pressing (that is, a contact surface pressure is applied to the contact portion). It has a contact and integrated structure. The separator member 1 is in electrical contact with a negative electrode (for example, carbon paper), and a channel through which fuel gas (mainly hydrogen) passes is formed between the negative electrode and the member. On the other hand, the separator member 2 is in electrical contact with a positive electrode (for example, carbon paper) in an adjacent cell, and a flow path through which an oxidant gas (for example, mainly air) passes between the positive electrode and the member. Is formed. And a pair of separator member 1 and separator member 2 which constitute a separator have electrical contact mutually, and a channel through which cooling water passes is often provided between both members.

  FIG. 2 schematically illustrates a cross-sectional structure of a polymer electrolyte fuel cell that is assumed for stationary use in homes and the like. In this case, since it is less likely to be operated at a higher current as in-vehicle use, for example, a structure in which cooling water is passed between the separator members at a rate of about 1 cell per 3 cells is assumed. In the cell through which the cooling water passes, a separator member 3 and a separator member 4 formed by processing a metal plate into a shape having a bowl-shaped concavo-convex cross section by pressing are combined in contact with each other in a pressed state. Constitute. Also in this case, the pair of separator members 3 and the separator members 4 are in electrical contact with each other, and a flow path through which cooling water passes is provided between the members.

  A separator of a type in which a pair of press-molded plate-like members are brought into contact with each other in a pressed state as shown in FIGS. 1 and 2 is simply referred to as a “plate-like member composite separator” hereinafter. is there.

  The separator of the polymer electrolyte fuel cell needs to be made of a material that can withstand an acidic atmosphere having a pH of about 2 to 3. A metal material that can withstand such a strong acidic atmosphere and satisfies the characteristics required for the separator has not been put to practical use so far. For example, an acid-resistant material such as stainless steel can be considered as a metal material that can withstand a strong acid atmosphere. These materials exhibit acid resistance due to a strong passive film formed on the surface, but surface resistance and contact resistance are increased due to the presence of the passive film. In particular, in the plate-shaped member composite separator having the above-described structure in which the cooling water flow path is partitioned by combining a pair of separator members, good conductivity must be ensured at the contact point between both members. When the contact resistance increases, a large amount of Joule heat is generated at the contact portion, resulting in a large heat loss, which reduces the power generation efficiency of the fuel cell. Therefore, it is not easy to apply a metal material of a type that ensures acid resistance by a passive film such as stainless steel to a separator material having a practical structure. On the other hand, a noble metal is mentioned as a metal material which exhibits high corrosion resistance irrespective of a passive film, and if this is coated on the separator member surface, it is possible to reduce contact resistance. However, such a method cannot be adopted in terms of cost.

  So far, various methods for reducing the contact resistance of the stainless steel surface have been studied with the intention of being a separator for a polymer electrolyte fuel cell. Patent Documents 1 to 3 disclose separator materials that improve conductivity and contact resistance while ensuring acid resistance by distributing carbon particles in an island shape on the surface of stainless steel. However, it is not always easy to stably and sufficiently secure the adhesion of the carbon particles to the stainless steel surface, and there is a concern that the carbon particles may fall off the stainless steel surface during handling or processing. In addition, a process for attaching the carbon particles with a good degree of adhesion is required, resulting in an increase in production man-hours.

  Patent Document 4 describes a method of reducing contact resistance by attaching a noble metal or an alloy of noble metal after removing an oxide layer on the surface of stainless steel or titanium. However, this method inevitably increases costs due to the use of noble metals.

  On the other hand, only acid dipping without electrolysis results in insufficient dissolution and a good roughening cannot be achieved. Also, known anode electrolysis is not effective in reducing contact resistance.

Japanese Patent Laid-Open No. 11-12018 Japanese Patent Laid-Open No. 11-126621 JP-A-11-126622 JP 2001-6713 A

  In view of the present situation, the present invention is a ferritic stainless steel sheet having a roughened surface that is extremely effective in reducing contact resistance at the contact portion when used in the plate-shaped member composite separator as described above. Is to provide. Moreover, it aims at providing the separator using the stainless steel plate.

The purpose is to provide a rough surface having a surface roughness SPa of 0.3 to 2 μm on at least one surface of a steel plate made of ferritic stainless steel containing Cr: 16 to 40% by mass and Mo: 0.2 to 5% by mass. When the roughened surface of the steel plate is brought into contact with the roughened surface of another steel plate having the roughened surface under the same conditions at a contact surface pressure of 1 MPa. Further, it is achieved by a roughened stainless steel plate for a separator of a polymer electrolyte fuel cell having a contact resistance of 10 mΩ · cm ² or less, preferably 3 mΩ · cm ² or less, more preferably 1 mΩ · cm ² or less. The roughened surface is roughened by, for example, alternating electrolysis or anodic electrolysis in a ferric chloride aqueous solution.

Here, “surface roughness SPa” is obtained by measuring the arithmetic average height Pa of a cross-sectional curve defined in JIS B0601-2001 for a surface area of a certain area and taking the average value. Specifically, SPa is one of surface roughness parameters obtained by analyzing data of a three-dimensional surface profile measured by a scanning laser microscope, and the absolute value of the elevation of the cross-sectional curved surface with respect to the average surface of the cross-sectional curved surface Mean value of The surface region for measuring the three-dimensional surface profile is a rectangular surface region having a side of 50 μm or more. That is, a measurement area of 50 μm × 50 μm or more is ensured. The depth resolution of the scanning laser microscope is desirably 0.01 μm or more. “Contact surface pressure” is a stress component in a direction perpendicular to the contact surface applied between the surfaces of both steel plates in contact. “Contact resistance” is obtained by multiplying the contact area by a resistance value calculated from a voltage drop when a direct current (for example, a current density of 1 A / cm ² at the contact surface) flows between both steel plates through the contact portion. It is a thing.

  Examples of the ferritic stainless steel types include those corresponding to the ferritic steel types defined in JIS G4305: 2005, and having Cr and Mo contents in the above ranges. Based on these standard steel types, it is also possible to adopt steel types whose characteristics are improved by adding various elements as necessary. In particular, P is allowed to contain up to 0.08% by mass. The component composition range is exemplified by C: 0.12% or less, Si: 1% or less, Mn: 2% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16 -40%, Mo: 0.2-5%, N: 0.025% or less, Ni: 0-0.6%, Cu: 0-1%, Al: 0-1%, Ti: 0 0.8%, Nb: 0 to 0.8%, V: 0 to 1%, Ca: 0 to 0.1%, REM (rare earth element): 0 to 0.1%, B: 0 to 0.1 %, The balance Fe, and a steel type having a composition that is an inevitable impurity. Here, the element whose lower limit is 0% is an optional component, and 0% means that the element is not added and is below the measurement limit in the analysis method in the normal steelmaking process.

  Further, in the present invention, a pair of separator members formed by press-forming the roughened steel sheet as described above are integrated so that contact points pressed between the respective roughened surfaces are formed. A separator for a polymer electrolyte fuel cell is provided. In particular, one having a cooling water flow path partitioned by the contact portion between the pair of separator members is a suitable target. In the example of FIG. 1 and FIG. 2, the roughened surface is applied to a portion indicated by a thick line.

  According to the present invention, a roughened stainless steel sheet is provided in which the contact resistance when the surfaces of ferritic stainless steel sheets are brought into contact with each other is significantly reduced. Therefore, the roughened stainless steel sheet of the present invention is extremely useful as a member constituting a solid polymer fuel cell separator having a reasonable structure in which a cooling water flow path is incorporated. The plate-shaped member composite separator made of the roughened stainless steel plate of the present invention is made of a relatively inexpensive ferritic stainless steel and is low in cost because it uses no precious metal and has a cooling function. However, since high conductivity can be maintained, it contributes to the spread of practical solid polymer fuel cells for in-vehicle use and stationary use.

[Ferrite stainless steel grade]
In the present invention, as a stainless steel exhibiting high durability in an acidic environment to which a separator of a polymer electrolyte fuel cell is exposed, a ferritic stainless steel species containing Mo: 0.2 to 5% by mass is targeted. As such a steel type, an existing known steel type can be adopted. For example, a ferritic steel type specified in JIS G4305: 2005, which contains Mo in the above range can be exemplified.

  Specific component composition ranges are shown, for example, in mass%, C: 0.12% or less, preferably 0.025% or less, Si: 1% or less, preferably 0.5% or less, and Mn: 2% or less, preferably 1% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16-40%, preferably 16-35%, more preferably 16-32%, Mo: 0.2-5%, preferably 1 to 3%, N: 0.025% or less, Ni: 0 to 0.6%, Cu: 0 to 1%, preferably 0 to 0.5%, Al: 0 to 1%, preferably 0 to 0 .3%, Ti: 0 to 0.8%, preferably 0 to 0.3%, Nb: 0 to 0.8%, preferably 0 to 0.3%, V: 0 to 1%, Ca: 0 to 0 0.1%, preferably 0-0.01%, REM (rare earth element): 0-0.1%, preferably 0-0.01%, B: 0-0.1%, preferably 0-0.01%, Balance Fe and Compositions consisting avoidable impurities like.

The main component elements will be briefly described.
C can be tolerated up to 0.12% by mass, but it is preferably 0.12% by mass or less because it lowers the workability and low temperature toughness of ferritic stainless steel. When emphasizing those characteristics, it is more desirable to set it as 0.05 mass% or less, and it is still more preferable that it is 0.025 mass% or less.

  When Si is contained in a large amount, it hardens the steel and impairs workability, so it is preferably 1% by mass or less, and more preferably 0.5% by mass or less.

  When Mn is contained in a large amount, workability, corrosion resistance, and contact resistance are increased. Therefore, Mn is preferably 2% by mass or less, and more preferably 1% by mass or less.

  P is an element effective for improving the corrosion resistance in the internal environment of the fuel cell to which the separator is exposed. However, since the workability decreases as the P content increases, it is preferably 0.08% by mass or less.

  S is an element harmful to corrosion resistance, and is preferably 0.03 mass% or less.

  Cr is an important element for ensuring the corrosion resistance of stainless steel, and generally the corrosion resistance improves as the Cr content increases. In view of the in-cell environment of the polymer electrolyte fuel cell, it is desirable to ensure a Cr content of 16% by mass or more. However, since a large amount of Cr causes a decrease in workability, the Cr content must be suppressed to 40% by mass or less. It is desirable to set it as 35 mass% or less, and 30 mass% or less is more preferable.

  Mo is an element that improves the corrosion resistance of stainless steel by coexistence with Cr. In the present invention, an austenitic stainless steel having a Mo content of 0.2% by mass or more is targeted so as to exhibit excellent durability when exposed to the in-cell environment. The Mo content is more preferably 1% by mass or more. However, a large amount of Mo hardens stainless steel and causes deterioration of workability, and is also disadvantageous in terms of cost, so the upper limit of the Mo content is limited to 5% by mass. More preferably, the content is 3% by mass or less.

  N is preferably 0.025% by mass or less because it lowers workability and low temperature toughness.

  Since Ni and Cu have the effect of improving the general corrosion resistance in an acidic atmosphere and improving the low temperature toughness of the ferritic stainless steel, one or more of these can be added as necessary. In order to sufficiently exhibit the above-described action, it is desirable to secure a content of 0.15% by mass or more in the case of Ni and 0.2% by mass or more in the case of Cu. However, these elements have a property of easily eluting, and battery performance is likely to deteriorate when the eluted Ni ions reach the catalyst layer. Therefore, when adding 1 or more types of Ni and Cu, it is desirable to carry out Ni in the range of 0.6 mass% or less and Cu in the range of 0.8 mass% or less.

  Al functions as a deoxidizer for steel and is also useful for fixing N. Therefore, Al can be added as necessary. In this case, it is more effective to secure a content of 0.04% by mass or more. However, when adding Al, it is desirable to set it as 1 mass% or less, and 0.3 mass% or less is more preferable.

  Ti and Nb have the effect of fixing C and N and improving workability, and are added as necessary. For that purpose, it is effective to add one or more of Ti: 0.03 mass% or more and Nb: 0.03 mass% or more. However, when adding 1 or more types of Ti and Nb, it is desirable to make content of both Ti and Nb into 0.8 mass% or less, and 0.3 mass% or less is more preferable.

  V has an effect of improving the corrosion resistance in the internal environment of the fuel cell, and is added as necessary. In order to obtain the effect sufficiently, it is desirable to secure a V content of 0.2% by mass or more. However, when adding V, it is desirable to make it content of 1 mass% or less.

  In addition, various elements can be added as long as the effects of the present invention are not impaired. For example, Ca: 0.1 mass% or less, preferably 0.01 mass% or less, REM (rare earth element): 0.1 mass% or less, preferably 0.01 mass% or less, B: 0.1 mass% or less, preferably Addition of one or more of 0.01 mass% or less is permitted.

(Roughened form)
In FIG. 3, the SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which the roughening surfaces of the roughening steel plate of this invention are contacting with the contact pressure of 1 Mpa is illustrated. Both roughened steel sheets were obtained under the conditions of No. 305 in the examples described later. The edge of the pit boundary observed as a sharp protrusion shape undergoes plastic deformation under a large load due to pressing, and the passive film on the surface breaks along with the plastic deformation, and the fresh surfaces come into contact with each other and have a good energized state. It is considered to be.

  In FIG. 4, the SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which the surfaces of the steel plate which is not roughened is contacting with the contact pressure of 1 Mpa is illustrated. In this case, even when subjected to a contact pressure of 1 MPa, it can be seen that when viewed microscopically, there are few portions where both the steel plates are in contact and there are many portions where gaps are formed. Further, the surface passive film is not easily destroyed. In such a state, contact resistance is high and a good energized state cannot be expected.

According to the study by the inventors, in a plate-shaped member composite type separator, in order to ensure sufficient energization between the plate-shaped members constituting the separator, the contact resistance when contacting at a contact surface pressure of 1 MPa is It has been found that it is necessary to use a plate-like member in which a contact state such as 10 mΩ · cm ² or less is formed. When plate-like members that do not satisfy such characteristics are combined, it is difficult to ensure stable and good energization. In particular, the steel sheet is preferably a roughened steel sheet having a contact resistance of 3 mΩ · cm ² or less when contacted at a contact surface pressure of 1 MPa, and more preferably 1 mΩ · cm ² or less.

As a result of detailed examination, in order to realize a contact state with a contact resistance of 10 mΩ · cm ² or less by contact between fresh surfaces as shown in FIG. A unique roughening form obtained by roughening (roughness formed with a high density of about 80% or more in terms of the ratio of spherical pits with deep openings to the projected area of the steel sheet surface, although the openings are small. It has been found that a roughened surface having a surface roughness SPa of 0.3 μm or more is extremely effective. If SPa is less than 0.3 μm, the ratio of the pit non-occurrence area to the projected area of the steel sheet surface is too large, or the pit is too shallow and the pit boundary is not sharp enough. It is difficult to achieve stable reduction of contact resistance stably.

[Stainless steel plate]
As the stainless steel material used for the electrolytic surface roughening treatment, a general pickling finish material or a temper rolled finish material can be applied.

[Preliminary processing]
Before being subjected to the electrolytic surface roughening treatment, it is preferable to carry out normal electrolytic degreasing as a preliminary treatment, or further, hydrochloric acid pickling can be carried out as necessary. As the electrolytic degreasing, for example, anode electrolysis in a sodium orthosilicate aqueous solution having a concentration of 1 to 10% by mass can be suitably employed. The liquid temperature and anode current density of electrolytic degreasing can be set to, for example, 60 ° C. ± 5 ° C., ² to 10 A / dm ^2, and the treatment time may be adjusted in the range of, for example, 5 to 30 seconds. As the hydrochloric acid pickling, a method of immersing in an aqueous hydrochloric acid solution at room temperature can be suitably employed. The hydrochloric acid concentration may be, for example, 1 to 10% by mass, and the immersion time may be adjusted in the range of about 5 to 30 seconds.

[Electrolytic roughening treatment]
In order to obtain the roughened form as described above, alternating electrolytic treatment or anodic electrolytic treatment in an aqueous ferric chloride solution can be suitably applied. As the electrolyte, ferric chloride containing Fe ³⁺ ions is suitable. The fact that the electrolyte does not contain ions such as NO ³⁻ and SO ₄ ²⁻ that promote the oxidation action of stainless steel also facilitates pitting, that is, the formation of pits, and roughens the surface for a short time. Is important to finish with. In the case of ferritic stainless steel containing Mo, alternating electrolysis is relatively suitable for steel types having a Cr content of approximately 25% by mass or less, and anode for high corrosion resistance steel types having a higher Cr content. Electrolysis is relatively suitable.

It is necessary to set the concentration of the electrolytic solution and the electrolysis conditions in an appropriate range in which the above roughened form can be obtained according to the stainless steel type. For example, in the case of alternating electrolysis, in a ferric chloride aqueous solution having an Fe ³⁺ concentration of 5 to 100 g / L, the current density during anode electrolysis is 1 to 10 kA / m ² , and the current density during cathode electrolysis 0.03 to ² kA / Optimum conditions may be determined in a condition range in which alternating electrolysis of 1 to 20 Hz with m ² is performed for 10 to 300 seconds. In the case of anodic electrolysis, when optimum conditions are determined in a condition range in which anodic electrolysis with a current density of 1 to 10 kA / m ² is performed for 10 to 300 seconds in an aqueous ferric chloride solution with an Fe ³⁺ concentration of 50 to 100 g / L, Good.

[Separator]
The roughened stainless steel plate of the present invention as described above can be a separator member having predetermined bowl-shaped irregularities formed by pressing. It has been experimentally confirmed that even after the press working, the contact resistance between the pair of members constituting the plate-shaped member composite separator is not inferior to that when the sample before the press working is used. The pair of separator members are usually integrated by brazing or caulking the peripheral portion, and a plate-shaped member composite separator in a state where the contact portions of both members are pressed is constructed.

A ferritic stainless steel plate having a 2B finish and a thickness of 0.4 mm corresponding to SUS436J1L (18Cr-0.5Mo) was prepared.
As a pretreatment, a steel plate as a test material was immersed in a sodium orthosilicate solution having a concentration of 5 mass% and a liquid temperature of 60 ° C., and anodic electrolytic degreasing was performed at a current density of 5 A / dm ² for 10 seconds.

The surface of the steel sheet after electrolytic degreasing was subjected to a roughening treatment by performing an alternating electrolytic treatment in a ferric chloride aqueous solution. The treatment conditions were: Fe ³⁺ : ferric chloride aqueous solution of 20 g / L, anode current density: 3.0 kA / m ² , alternating electrolysis cycle 5 Hz, treatment time: 60 seconds, cathode current density and liquid temperature Alternating electrolytic treatment was performed by changing. Fine pits were formed on the entire surface under all conditions, and sharp edges with a cross-sectional shape were formed at the pit boundaries. As a comparative material, a 2B-finished material that was not subjected to electrolytic surface roughening was also prepared (the same applies to Examples 2 to 4).

  The surface roughness SPa and contact resistance of the material that had been subjected to the roughening treatment and the comparative materials that were not subjected to the roughening treatment (hereinafter referred to as sample steel plates) were examined as follows.

[Surface roughness SPa]
Using a scanning confocal laser microscope (Olympus Co., Ltd .; OLS1200) on the roughened surface of each sample steel plate (the surface of the comparative material that was not roughened was a 2B-finished surface), 51 μm × 51 μm For the surface region, the surface roughness SPa was measured at a resolution of 0.01 μm. Specifically, the objective lens is set to 100 × (depth resolution: 0.01 μm) and the zoom is set to 2.5 × magnification, and after removing the rough surface of the 51 μm × 51 μm field of view, peak noise is removed. Then, a three-dimensional surface profile was obtained by performing image processing for image luminance averaging, and a surface roughness SPa calculated based on the data was obtained.

[Contact resistance]
The sample steel plate was left in the room for about 72 hours, and then a circular sample having a diameter of 15 mm was punched from the steel plate. Two round specimens (both of which are punched from the same type of steel sheet specimens) are superposed so that the roughened surfaces face each other, Cu blocks are placed on the top and bottom, and 1 MPa is obtained by autograph. The load which becomes the contact pressure of was added. Then, a current of 1.77 A (1 A / cm ² ) was passed from the DC power source between the upper and lower Cu blocks, and the voltage drop E (mV) between the two stacked circular samples was measured with a digital multimeter, Contact resistance R (mΩ · cm ² ) = E / I was determined.
The results are shown in Table 1.

No. 118 not subjected to electrolytic surface roughening treatment had a contact resistance of 25 mΩ · cm ² , whereas the contact resistance of the present invention in which the surface roughness SPa was 0.3 to 2 μm had a margin. Cleared 10 mΩ · cm ² or less.

The steel plate used for the electrolytic surface roughening treatment is a ferritic stainless steel plate having a 2B finish and a plate thickness of 0.15 mm corresponding to SUS444 (18Cr-2Mo). ³⁺ : 27.5 to 48 g / L, liquid temperature: 40 to 60 ° C., anode current density: 3.0 kA / m ² , cathode current density: 0.3 to 1.0 A / m ² , alternating electrolysis cycle 5 Hz, Treatment time: An experiment was performed under the same conditions as in Example 1 except that the alternating electrolytic treatment was performed for 60 seconds. The results are shown in Table 2.

The example of the present invention in which the surface roughness SPa was 0.3 to ² μm was able to realize a contact resistance of 10 mΩ · cm ² or less with a margin.

The steel plate used for the electrolytic surface roughening treatment is a ferritic stainless steel plate having a 2D finish and a thickness of 0.2 mm corresponding to SUS445J1 (22Cr-1.2Mo). , Fe ³⁺ : 30 g / L, liquid temperature: 50 ° C., anode current density of 3.5 kA / m ² , cathode current density of 0.8 kA / m ² , alternating electrolysis cycle of 10 Hz, and alternate electrolysis with various treatment times The experiment was performed under the same conditions as in Example 1 except that the above was performed. The results are shown in Table 3.

The example of the present invention in which the surface roughness SPa was 0.3 to ² μm was able to realize a contact resistance of 10 mΩ · cm ² or less with a margin.

The steel plate used for the electrolytic surface roughening treatment is a ferritic stainless steel plate having a 2B finish and a thickness of 0.25 mm, which corresponds to SUS447J1 (30Cr-2Mo). ³⁺ : 70 g / L, liquid temperature: 40-50 ° C., anode current density: ³ kA / m ² , treatment time: 30-60 seconds It was. The results are shown in Table 4.

The example of the present invention in which the surface roughness SPa was 0.3 to ² μm was able to realize a contact resistance of 10 mΩ · cm ² or less with a margin.

The figure which illustrated typically the cross-sectional structure of the polymer electrolyte fuel cell for vehicles using a metal separator. The figure which illustrated typically the cross-sectional structure of the polymer electrolyte fuel cell for stationary use using metal separators. The SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which is contacting in the state by which the roughening surfaces of the roughening steel plate of this invention were pressed. The SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which is contacting in the state where the surfaces of the steel plate which is not roughened are pressed.

Claims (6)

At least one surface of a steel sheet made of a ferritic stainless steel containing Cr: 16 to 40% by mass and Mo: 0.2 to 5% by mass has a roughened surface with a surface roughness SPa of 0.3 to 2 μm. When the roughened surface of the steel plate is brought into contact with the roughened surface of another steel plate having the roughened surface under the same conditions, the contact resistance is 1 MPa. A roughened stainless steel sheet for a separator of a polymer electrolyte fuel cell exhibiting 10 mΩ · cm ² or less.   The roughened stainless steel sheet for a separator according to claim 1, wherein the roughened surface is roughened by alternating electrolysis or anodic electrolysis in a ferric chloride aqueous solution.   The roughened stainless steel sheet for a separator according to claim 1 or 2, wherein the ferritic stainless steel type corresponds to a ferritic steel type specified in JIS G4305: 2005.   The ferritic stainless steel type is, by mass, C: 0.12% or less, Si: 1% or less, Mn: 2% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16 -40%, Mo: 0.2-5%, N: 0.025% or less, Ni: 0-0.6%, Cu: 0-1%, Al: 0-1%, Ti: 0 0.8%, Nb: 0 to 0.8%, V: 0 to 1%, Ca: 0 to 0.1%, REM (rare earth element): 0 to 0.1%, B: 0 to 0.1 The roughened stainless steel sheet for a separator according to claim 1 or 2, which is a steel type having a composition of%, balance Fe and inevitable impurities.   The solid which integrated the pair of separator members formed by press-molding the roughened steel plate in any one of Claims 1-4 so that a contact location may be formed between each said roughened surface Polymer fuel cell separator.   The separator according to claim 5, further comprising a cooling water passage partitioned by the contact portion between the pair of separator members.