JP5858424B2 - Stainless steel for polymer electrolyte fuel cell separator and method for producing the same - Google Patents

Description

  The present invention relates to a stainless steel for a polymer electrolyte fuel cell separator used as a separator for a polymer electrolyte fuel cell and a method for producing the same.

  The polymer electrolyte fuel cell is, for example, a separator in which grooves on both sides of a membrane / electrode assembly (MEA) in which electrodes are bonded to both sides of a solid polymer electrolyte membrane are provided as reaction gas supply channels. The unit cell is the basic unit. A cell stack in which high voltages can be obtained by stacking single cells and connecting them in series is called a cell stack.

The polymer electrolyte fuel cell separator functions as a flow path for uniformly supplying the reaction gas over the entire surface of the cell, and the water generated on the cathode side is efficiently combined with a carrier gas such as air and oxygen after the reaction. A role as a flow path for discharging outside, a role as an electrical connector that maintains low electrical resistance and good conductivity for a long time as an electrode, and a role of separating the anode chamber and the cathode chamber of stacked and adjacent single cells Is required.
The solid polymer electrolyte membrane is made of a polymer having a large number of sulfonic acid groups, and the inside of the cell becomes a strong acid environment in a wet state. Therefore, the separator is required to have high corrosion resistance as well as conductivity.
In addition, a solid polymer fuel cell separator that is being studied for application to a mobile body represented by a fuel cell vehicle is required to have durability against impact and weight reduction.

  Until now, carbon materials were generally used as separator materials for polymer electrolyte fuel cells. However, carbon materials have a problem that they have poor ductility and are easily broken, and the cost of machining the reaction gas supply channel is low. There is a problem that becomes very high. Therefore, in order to realize cost reduction and durability, use of metal separators such as stainless steel and titanium has been studied.

Stainless steel is cheaper than non-ferrous alloys containing titanium or aluminum as a main element, and has a corrosion resistance because a passive film is formed on the surface thereof. However, since the passive film on the surface has a large contact resistance, it is not suitable for an electrical component that requires low contact resistance such as a separator. If the contact resistance of stainless steel can be reduced, it can be used as a separator for a polymer electrolyte fuel cell that requires excellent corrosion resistance and low contact resistance.
In order to solve this problem, various proposals have been conventionally made.

Patent Document 1 discloses a technique for reducing contact resistance and ensuring high output by performing gold plating on the surface of a stainless steel, aluminum, or nickel alloy separator. Patent Document 2 discloses a method of obtaining a separator having reduced contact resistance by dispersing carbon powder in ferritic stainless steel. Further, in Patent Document 3, a first layer containing M ₄ N type and M _2-3 N type nitride on the surface of stainless steel and Cr ₂ N, CrN, M _2-3 N type, and M ₄ N type nitride are included. A method of reducing the contact resistance by forming a second layer containing any one of them is disclosed.
Patent Document 4 discloses a method for reducing contact resistance by depositing M ₂₃ C ₆ type carbide or M ₂ B type boride, which is a conductive precipitate, on the surface of a stainless steel plate. Discloses a method for reducing contact resistance by precipitating σ phase by an area ratio of 1% or more on the surface of stainless steel by aging heat treatment.

JP-A-10-228914 JP 2000-277133 A JP 2010-3417 A Japanese Patent No. 4078966 JP 2009-235478 A

  However, in the technique proposed in Patent Document 1, there is a high risk of pin pole defects occurring in thin gold plating and impairing corrosion resistance, and the cost is very high in thick gold plating.

  The techniques proposed in Patent Document 2 and Patent Document 3 require a reasonable cost for the surface treatment, and if there is a defect on the surface, there is a high possibility that the corrosion resistance will be impaired.

  Furthermore, in the technique proposed in Patent Document 4, since carbides or borides precipitated by a large amount of C or B are hard particles, there is a problem that it is difficult to produce a stainless steel plate. When Cr, which is the main metal element of the precipitate, is deficient from the base to form a Cr-deficient layer, the corrosion resistance may be significantly deteriorated.

  Furthermore, in the technique proposed in Patent Document 5, since the ductility of the material is impaired because the σ phase which is an embrittlement phase is actively used, it is difficult to manufacture the steel plate as in Patent Document 4, and the mobile body It is difficult to satisfy the impact resistance and durability required for the polymer electrolyte fuel cell separator used.

  The present invention has been made against the background of the above circumstances, and aims to provide a stainless steel for a polymer electrolyte fuel cell separator having excellent strength and corrosion resistance while ensuring ductility, and low contact resistance, and a method for producing the same. To do.

That is, among the stainless steels for polymer electrolyte fuel cell separators of the present invention, the first present invention is mass%, C: 0.01 to 0.1%, Si: 0.1 to 1.0% , Mn: 0.1 to 3.0%, Ni: 6.0 to 20.0%, Cr: 17.0 to 30.0%, Mo: 0.5 to 4.0%, N: 0.86 -1.5%, with the balance being Fe and inevitable impurities, P: 0.03% or less, S: 0.01% or less, Al: 0.01% or less, O: 0 in the inevitable impurities In the stainless steel having a composition limited to 0.02% or less, conductive metal nitride is dispersed, and a part of the dispersed metal nitride is exposed on the surface of the stainless steel. And

The stainless steel for the polymer electrolyte fuel cell separator according to the second aspect of the present invention is the above-mentioned first aspect of the present invention, wherein the metal nitride is M ₄ N type, M ₂ N type, MN type nitride (where M is It is one or more of (metal elements).

  In the stainless steel for a polymer electrolyte fuel cell separator according to the third aspect of the present invention, in the first or second aspect of the present invention, the metal element in the nitride contains one or more of chromium, molybdenum, and vanadium. It is characterized by that.

  The stainless steel for the polymer electrolyte fuel cell separator according to the fourth aspect of the present invention is characterized in that, in any of the first to third aspects of the present invention, the stainless steel base is an austenitic phase.

The stainless steel for the polymer electrolyte fuel cell separator according to the fifth aspect of the present invention is the composition according to any one of the first to third aspects of the present invention, in addition to the composition, in mass%, V: 0.01 to 1.5. % .

The stainless steel for a polymer electrolyte fuel cell separator according to the sixth aspect of the present invention is the above composition according to any one of the first to fifth aspects of the present invention, in addition to the composition by mass%, Nb: 0.05 to 1.5. %, Ti: 0.01-0.05%, Zr: 0.01-0.1% of 1 type or 2 types or more are contained.

The stainless steel for a polymer electrolyte fuel cell separator according to the seventh aspect of the present invention is the above-mentioned composition according to any one of the first to sixth aspects, wherein the composition further comprises, in mass%, Co: 0.5 to 3.0. %, Cu: 0.5 to 3.0%, W: 0.05 to 0.5%, or one or more thereof.

The method for producing stainless steel for a polymer electrolyte fuel cell separator according to the eighth aspect of the present invention comprises an electroslag remelting electrode having the composition according to any one of the first and fifth to seventh aspects as a target composition, and a pressure type Using an electroslag remelting furnace, a nitrogen gas partial pressure in the furnace is set to 0.8 MPa or more to obtain an ingot of the target composition by electroslag remelting.

In the ninth method of producing a stainless steel for a polymer electrolyte fuel cell separator according to the present invention, one or both of annealing and aging treatment at 800 to 1000 ° C. are performed on the ingot obtained by remelting the electroslag. It is characterized by that.

The method for producing stainless steel for a polymer electrolyte fuel cell separator according to the tenth aspect of the present invention is the center line average roughness defined in JIS B 0633-2001 by acid-treating the surface in the eighth or ninth aspect of the present invention. The rough surface is 0.5 to 2.5 μm.

That is, according to the present invention, the conductivity of stainless steel is improved without deteriorating the corrosion resistance and strength, and the characteristics suitable for a polymer electrolyte fuel cell separator are exhibited.
Below, each condition in prescription | regulation of this invention is demonstrated.

Dispersion of metal nitride Metal nitride has higher conductivity than carbides conventionally used to improve the conductivity of stainless steel, and it disperses more finely than carbides and borides, thus impairing workability. Therefore, the conductivity can be remarkably improved. Further, since the metal nitride is finely precipitated, there is almost no influence on the corrosion resistance.
In the present invention, the size of metal nitride and the degree of dispersion are not particularly limited. Moreover, the kind of metal nitride should just have electroconductivity, and is not limited to a specific thing. In addition, as what has electroconductivity here, electrical conductivity 120 * 10 < ⁴ > (omega ^| ohm) ^-1 * m < ^-1 > or more can be mentioned suitably.
Examples of the metal nitride include M ₄ N type, M ₂ N type, and MN type (where M is a metal element), and examples of the metal element include chromium, molybdenum, and vanadium. One kind of metal nitride may be used, or two or more kinds may be mixed. Further, the metal nitride may contain a plurality of metals as constituent elements.

Austenitic Phase Base In the present invention, the structure of austenitic steel is not limited to a specific one, but is preferably composed of an austenitic phase. Austenitic stainless steel has excellent corrosion resistance, good ductility, and excellent workability.

The reason for limitation of the composition prescribed | regulated by the following one form of this invention is demonstrated.
Content of each component demonstrated below is shown by the mass% altogether. In the following composition, 0.6 to 1.5% nitrogen is added as a stainless steel for polymer electrolyte fuel cell separators exposed to harsh environments to increase strength and corrosion resistance, and to stabilize strong austenite phase The contact resistance is reduced by dispersing and exposing a highly conductive nitride on the surface of the stainless steel while keeping the base in the austenite phase by utilizing the characteristics of nitrogen which is an element.

C: 0.01 to 0.1%
C is a strong austenite stabilizing element and at the same time is very effective as a solid solution strengthening component, and is contained in an amount of 0.01% or more. However, if the content exceeds 0.1%, the nitrogen solubility of the molten steel is reduced, and the formation of Cr carbide reduces the amount of Cr in the matrix and significantly deteriorates the intergranular corrosion. The upper limit is 0.1%.
For the same reason, it is desirable that the lower limit is 0.03% and the upper limit is 0.07%.

Si: 0.1 to 1.0%
Si is indispensable for the steelmaking process as an effective deoxidizer, and if Al, which is a stronger deoxidizer than Si, may cause generation of AlN that adversely affects high-temperature strength and ductility, It is desirable to use it as a main deoxidizing agent, and 0.1% or more is contained. However, if it exceeds 1.0%, wrinkles and cracks are likely to occur during production, so the upper limit is made 1.0%.
For the same reason, it is desirable to set the lower limit to 0.2% and the upper limit to 0.8%.

Mn: 0.1 to 3.0%
Mn acts as a deoxidizing and desulfurizing agent, and is an austenite phase stabilizing element and significantly increases the nitrogen solubility of the molten steel. However, if the content exceeds 3.0%, the corrosion resistance is deteriorated, so the upper limit is made 3.0%. For the same reason, it is desirable to set the lower limit to 0.5% and the upper limit to 2.5%.

Ni: 6.0 to 20.0%
Ni is an important element for obtaining corrosion resistance and an austenite phase stabilizing element. Therefore, in the stainless steel for a polymer electrolyte fuel cell separator of the present invention, at least 6.0% or more is necessary to obtain an austenite single phase. However, if the content is more than necessary, the strength is impaired and the cost of raw materials is increased, so the upper limit is made 20.0%. For the same reason, it is desirable to set the lower limit to 7.0% and the upper limit to 18.0%.

Cr: 17.0 to 30.0%
Cr significantly increases the nitrogen solubility of molten steel and greatly contributes to the improvement of the corrosion resistance and strength of the matrix. On the other hand, when metal nitride such as M ₄ N type, M ₂ N type, and MN type deposits, although the contact resistance is reduced, Cr in the steel is consumed as the metal element of the nitride, so that the corrosion resistance is improved. The amount of Cr in the steel that contributes may decrease and corrosion resistance may deteriorate. Therefore, in the stainless steel for a polymer electrolyte fuel cell separator of the present invention, it is necessary to contain 17.0% or more of Cr in order to secure a nitrogen amount of 0.6% or more and ensure corrosion resistance. However, since Cr is a ferrite phase stabilizing element and causes instability of the austenite phase, the upper limit is made 30.0%. For the same reason, it is desirable to set the lower limit to 18.0% and the upper limit to 28.0%.

Mo: 0.5-4.0%
Mo significantly increases the nitrogen solubility of molten steel and is very effective as a solid solution strengthening component. Furthermore, since there exists an effect which improves corrosion resistance in a small quantity rather than Cr, in order to acquire the effect, it contains 0.5% or more in this invention. However, if the content is more than necessary, the raw material cost is increased, and the ductility is reduced due to the formation of an embrittled phase such as the σ phase, and the hot workability is impaired, so the upper limit is made 4.0%. For the same reason, it is desirable to set the lower limit to 1.0% and the upper limit to 3.5%.

V: 0.01 to 1.5%
V is a metal element in M ₄ N type, M ₂ N type, and MN type nitride that significantly increases the nitrogen solubility of the molten steel and reduces the contact resistance of the stainless steel for the polymer electrolyte fuel cell separator of the present invention. It is a major component and is desirably contained. If the V amount is less than 0.01%, a sufficient contact resistance reduction effect cannot be expected. However, since V is a ferrite-forming element, the austenite phase is destabilized, and the ductility is reduced due to the formation of an embrittled phase such as the σ phase, so that the hot workability is impaired. And For the same reason, the lower limit is preferably 0.1% and the upper limit is 1.2%, and more preferably 0.5%.
In addition, what does not contain V is also contained in this invention.

N: 0.6-1.5%
N is an interstitial solid solution element and has an extremely high solid solution strengthening ability, and is an additive component serving as the basis of the present invention effective for stabilizing the austenite phase and improving corrosion resistance. In addition, M ₄ N-type, M ₂ N-type, and MN-type nitrides having N as a constituent element have conductivity superior to carbides. Therefore, in the stainless steel for polymer electrolyte fuel cell separator of the present invention, the austenite phase becomes unstable when the amount of nitrogen is less than 0.6%, and the contact resistance is sufficiently reduced in addition to causing a decrease in strength and a deterioration in corrosion resistance. Precipitation of nitride sufficient to obtain the effect cannot be expected. However, if it exceeds 1.5%, a melting facility stored in a high-pressure environment of 10 atm or more is required to suppress the formation of nitrogen blowholes. .5%. For the same reason, it is desirable to set the lower limit to 0.7% and the upper limit to 1.3%.

(Inevitable impurities)
In the inevitable impurities, it is desirable to regulate the contents of P, S, Al, and O as described below.

P: 0.03% or less When P is contained in excess of 0.03%, P segregated at grain boundaries significantly deteriorates hot workability and corrosion resistance, so it is necessary to limit it to 0.03% or less.
S: 0.01% or less If S is contained in excess of 0.01%, hot workability deteriorates and corrosion resistance is significantly impaired by the formation of sulfides such as MnS, so it is limited to 0.01% or less. There is a need to.
Al: 0.01% or less Al is an element that is effective as a deoxidizer, but in steels containing a large amount of nitrogen, if Al is added excessively, AlN is formed, and hot workability deteriorates and corrosion resistance decreases significantly. Therefore, it is necessary to limit it to 0.01% or less.
O: 0.02% or less O, if the content is excessive, lowers the cleanness of the ingot, leading to a reduction in ductility and a deterioration in corrosion resistance, so it is necessary to limit it to 0.02% or less.

  Hereinafter, components that can be further added to the stainless steel for a polymer electrolyte fuel cell separator of the present invention will be described.

Nb: 0.05 to 1.5%
Nb, like V, increases the nitrogen solubility of molten steel, and forms metal nitrides such as M ₄ N type, M ₂ N type, and MN type to contribute to improvement of strength and reduce contact resistance. . In order to obtain this effect, 0.05% or more must be contained. However, if the content exceeds the upper limit, the nitride becomes stable at high temperatures, which causes deterioration of hot workability and corrosion resistance. For the same reason, it is desirable that the lower limit is 0.06% and the upper limit is 1.0%.

Ti: 0.01 to 0.05%
Ti has the effect of increasing the nitrogen solubility of molten steel and forming metal nitrides such as M ₄ N type, M ₂ N type, and MN type to contribute to improving strength and reducing contact resistance. In order to obtain this effect, a content of 0.01% or more is required. However, if it exceeds 0.05%, nitrides crystallize from the molten steel, and hot as nonmetallic inclusions in the steel. It causes deterioration of workability and corrosion resistance. For the same reason, it is desirable that the lower limit is 0.02% and the upper limit is 0.04%.

Zr: 0.01 to 0.1%
Zr has the effect of increasing the nitrogen solubility of molten steel, like Ti, and forming metal nitrides such as M ₄ N type, M ₂ N type, and MN type to reduce contact resistance. In order to obtain this effect, it is necessary to contain 0.01% or more. However, if it exceeds 0.1%, nitride will crystallize from the molten steel, and it is hot as a nonmetallic inclusion in the steel. It causes deterioration of workability and corrosion resistance. For the same reason, it is desirable that the lower limit is 0.02% and the upper limit is 0.08%.
The Nb, Ti, and Zr can contain one or more of them in a content within the above range if desired.

Co: 0.5-3.0%
Co, like Ni, is an austenite phase stabilizing element and a component contributing to corrosion resistance. If the content is less than 0.5%, the effect is poor, but if the content exceeds 3.0% more than necessary, the raw material cost increases, so the upper limit is made 3.0%.

Cu: 0.5 to 3.0%
Cu is an austenite phase stabilizing element and contributes to the stabilization of the austenite phase like Ni and Co. If it is less than 0.5%, the effect is poor, but if it exceeds 3.0%, hot workability is impaired, so the upper limit is made 3.0%.

W: 0.05-0.5%
W, like Mo, is effective as a component for enhancing corrosion resistance and strengthening the solid solution. For this reason, it is necessary to contain 0.05% or more, but the ductility decreases due to the formation of an embrittlement phase such as σ phase. The hot workability is impaired, and undissolved Cr carbonitride during the solution treatment is grown to significantly reduce the yield strength. Therefore, the upper limit is set to 0.5%.
The Co, Cu, and W can contain one or more of them in a content within the above range as desired.

Melting equipment Stainless steel for polymer electrolyte fuel cell separators of the present invention having the above-mentioned form is characterized by containing a large amount of nitrogen. However, when melting in a normal atmospheric pressure environment, nitrogen blowholes are contained in the steel during solidification. Occurs, leading to a deterioration in yield and an increase in costs for subsequent processes. Therefore, it is desirable that the stainless steel for the polymer electrolyte fuel cell separator of the present invention is manufactured using a pressurized electroslag remelting furnace having at least a pressure resistance of 0.8 MPa or more. The use of various melting furnaces capable of pressurization makes it possible to produce the stainless steel for the polymer electrolyte fuel cell separator of the present invention, but metal nitriding such as M ₂ N type and MN type that crystallizes during solidification. In consideration of uniformly dispersing the material in the steel, it is most effective to use a pressurized electroslag remelting furnace. Furthermore, since the desired nitrogen amount cannot be obtained when the nitrogen gas partial pressure in the furnace is less than 0.8 MPa, it is desirable to adjust the nitrogen gas partial pressure to 0.8 MPa or more.
The pressurization type electroslag remelting furnace is not limited to a specific one as long as it can perform electroslag remelting in a predetermined pressurized atmosphere.

  The method of adding nitrogen is not particularly limited, and a method of adding a nitride alloy such as ferromanganese nitride or ferrochromium nitride together with the electrode at the time of electroslag melting or adding to the molten steel by gas absorption at the time of electrode preparation Various methods such as a method for performing the above can be used.

Annealing or aging treatment Since the stainless steel for polymer electrolyte fuel cell separator of the present invention in the above form contains a large amount of nitrogen such as Cr, V, etc., metal nitrides such as M ₂ N type and MN type Crystallizes from the time of solidification and is present in the steel. Although not specified in the present invention, it is possible to further reduce the contact resistance by increasing the amount of precipitation of metal nitrides such as M ₄ N type and M ₂ N type by aging treatment. It is also possible to ease the subsequent hot working or cold working by relaxing the strain in the stainless steel by annealing treatment. At this time, since an embrittlement phase such as σ phase precipitates at an annealing or aging temperature of less than 800 ° C. and impairs hot workability, it is desirable to carry out the annealing or aging temperature in the temperature range of 800 ° C. to 1000 ° C. In addition, at an annealing temperature of 1000 ° C. or higher or an aging temperature, the amount of M ₄ N-type and M ₂ N-type nitrides deposited is small, and MN-type nitrides that have already existed in the steel will be dissolved, reducing contact resistance. Insufficient effect is obtained.

As described above, the stainless steel for a polymer electrolyte fuel cell separator of the present invention disperses metal nitrides such as M ₄ N type, M ₂ N type, and MN type having higher conductivity than carbide on the surface of stainless steel.・ It can be exposed to reduce contact resistance.

  Further, if nitrogen is contained in a large amount, the austenite phase is stabilized, and there is a large amount of nitrogen in the base that improves corrosion resistance together with Cr and Mo without impairing strength and ductility. It can have strength, ductility and corrosion resistance higher than those of stainless steel on which intermetallic compounds are deposited.

  Furthermore, since the amount of expensive austenite phase stabilizing elements such as Ni and Co is reduced, the increase in raw material costs is suppressed, and an appropriate amount of nitrogen addition is adopted, so high pressure equipment exceeding 10 atm is not required. The stainless steel for polymer electrolyte fuel cell separator of the present invention can produce a large ingot by using a pressurized electroslag remelting furnace having a pressure resistance of less than 10 atm. be able to.

It is a schematic sectional drawing which shows the electroslag remelting furnace used for one Embodiment of the manufacturing method of this invention. Similarly, it is a figure which shows a process flow. It is the schematic which shows the measuring method of the contact resistance in the Example of this invention. Similarly, in Example No. 2 and Example No. The SEM photograph of the surface of 6 is shown. Similarly, Comparative Example No. 18 shows SEM photographs of 18 surfaces.

Hereinafter, an embodiment for producing stainless steel for a polymer electrolyte fuel cell separator of the present invention will be described with reference to the accompanying drawings.
First, in mass%, C: 0.01 to 0.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 3.0%, Ni: 6.0 to 20.0%, Cr: 17.0-30.0%, Mo: 0.5-4.0%, N: 0.6-1.5%, optionally in mass%, V: 0.01-1 1%, Nb: 0.05-1.5%, Ti: 0.01-0.05%, Zr: 0.01-0.1% Or 2 or more, and, if desired, 1% by mass, Co: 0.5-3.0%, Cu: 0.5-3.0%, W: 0.05-0.5% It contains seeds or two or more, and the balance consists of Fe and unavoidable impurities. P: 0.03% or less, S: 0.01% or less, Al: 0.01% or less, O: 0 Target composition limited to 0.02% or less It is prepared the ESR electrode 10 where the component adjustment so as to obtain a minute.

The electroslag remelting furnace 1 is a closed type, and the ESR electrode 10 can be installed so as to be movable up and down by a hanging jig 10a. The electroslag remelting furnace 1 has a gas introduction part 2 for introducing nitrogen gas into the furnace. doing. The electroslag remelting furnace 1 is provided with a power source 3 and one end is connected to the ESR electrode installed in the furnace. In the electroslag remelting furnace 1, the other end of the power source 3 is connected to a conductive hearth. Although not shown, an appropriate cooling means such as water cooling can be provided on the furnace wall of the electroslag remelting furnace 1.
In operation, the electroslag remelting furnace 1 is charged with a slag 11 having an appropriate composition. The ESR electrode 10 is positioned such that its tip is immersed in the slag 11. Further, nitrogen is introduced into the furnace from the gas introduction part 2 to make the inside of the furnace a pressurized atmosphere having a nitrogen partial pressure of 0.8 MPa or more.

  When the power source 3 is energized through the ESR electrode 10 and the slag 11, the slag 11 and the tip of the ESR electrode 10 are melted by the resistance heat of the slag 11. The molten metal is dropped in the slag 11, and at that time, impurities such as P, S and O in the molten metal are taken into the slag and refined to form a molten pool 12 below the slag. The ESR ingot 13 is generated by cooling from the furnace bottom. As the ESR ingot 13 and the molten pool 12 are generated, the slag 11 gradually floats and moves upward. Accordingly, the electrode 10 is lowered in accordance with this, and the ESR electrode 10 is continuously remelted. As described above, the molten metal descends through the slag 11 and is effectively desulfurized, and is cooled from the furnace wall and the furnace bottom, whereby an ingot having a good casting surface and internal properties is obtained.

FIG. 2 shows an embodiment of the process flow of the manufacturing method of the present invention.
The ingot obtained by electroslag remelting can be annealed as desired. In the annealing, the strain in the stainless steel is relaxed to facilitate subsequent hot working or cold working. As described above, the annealing temperature is desirably performed in a temperature range of 800 ° C to 1000 ° C.

  The ESR ingot 13 can be made into a plate material by hot forging or hot rolling after the annealing or while remelting the electroslag. The conditions at this time are not particularly limited in the present invention.

  The stainless steel plate can be processed into a shape used for a separator by hot working or cold working, but may be subjected to an aging treatment as desired before or after working. In the aging treatment, precipitation of metal nitride can be promoted. As described above, the temperature of the aging treatment is preferably performed in the temperature range of 800 ° C to 1000 ° C.

  The stainless steel plate having a separator shape can be roughened by acid treatment. Thereby, the surface exposure of the metal nitride can be ensured and the conductivity can be further increased. In the present invention, it is desirable that the center line average roughness specified in JIS B 0633-2001 is 0.5 to 2.5 μm by acid treatment. In the present invention, the kind of acid used for the acid treatment and the treatment time are not particularly limited as long as the rough surface can be obtained, but the acid used includes hydrofluoric acid. Things are desirable.

  The obtained stainless steel can be used as a separator incorporated in a polymer electrolyte fuel cell.

Examples of the present invention will be described below with reference to the drawings.
The raw materials were mixed and melted in a vacuum induction melting furnace so that the finally obtained ESR ingot had the component composition shown in Table 1 (the balance being Fe and other impurities), and an alloy steel was produced. Next, an ESR electrode was produced from the obtained alloy steel and remelted in a pressurized electroslag remelting furnace equipped with a pressure vessel so that the nitrogen partial pressure was 0.8 MPa or more. An example ESR ingot was obtained. This ingot was made into a plate having a thickness of 25 mm by hot forging and subjected to a solution treatment by water cooling after heating at 1200 ° C. for 4 hours.

  Then, the test piece was cut out from the said board | plate material and the normal temperature tension test was implemented. Table 2 shows the results. As shown in Table 2, the 0.2% proof stress of the example of the present invention is about 2-3 times higher than that of the comparative example, and the tensile strength is about 1.5-2 times higher than that of the comparative example. Moreover, although elongation becomes lower than a comparative example, since 30% or more was ensured, it had the ductility which can also endure thinning by hot processing or cold processing.

Moreover, the pitting corrosion resistance evaluation test was implemented using the test piece of width 20mm, length 25mm, and thickness 3mm cut out from the said board | plate material by machining. The test was conducted in Example No. 2 and Comparative Example No. 17 and no. At 18, the pitting potential in a 3.5% sodium chloride solution at 30 ° C. was measured. At that time, the pitting corrosion potential was measured as a potential reaching 10 μA / cm ² and a potential reaching 100 μA / cm ² .
Table 3 shows the results. As shown in Table 3, Example No. 2 is Comparative Example No. No pitting corrosion was generated even at a potential much higher than the potential at which 18 suffered from pitting corrosion. 17 and no. It had a corrosion resistance better than 18.

Furthermore, a contact resistance measurement test was performed using a test piece having a width of 50 mm, a length of 55 mm, and a thickness of 0.8 mm cut out from the plate material by machining. Among the test pieces, the No. of the example. 1, no. 4, no. 6, no. 7, no. 9, no. 10, no. 11, no. 12, no. In No. 13, the specimen was heated at 1000 ° C. for 30 hours and then subjected to an aging treatment in which the specimen was cooled. And the test piece removed the oxide scale by sand blasting using Al ₂ O ₃ sand, and immersed in a pickling solution of 3% hydrofluoric acid, 8% nitric acid and 89% water, and the surface roughness was JIS B 0633. In 2001, the average center line roughness was set to 0.5 to 2.5 μm. The pickling temperature was fixed at 60 ° C., and the immersion time was 20 minutes for the solution-treated test piece and 5 minutes for the aging-treated test piece.

The contact resistance measurement was carried out in the form of simulating a single cell of a polymer electrolyte fuel cell as shown in FIG. That is, while the gas diffusion layers (GDL) 21 and 21 are sandwiched between current collector plates 22 and 22 made of Ni on both sides of the test piece 20, packing 23 and end plates 24 are arranged on both sides of the outer side of the test piece 20. A load of 1000 N was applied. At that time, the contact area was 10 cm ² . And it supplies with electricity with the power supply 25 between the current collecting plates 22 and 22, and a contact resistance value is obtained by measuring the overvoltage value in each regulation current value (1-5A) between the current collecting plates 22 and 22 with the measuring device 26. It was. In this measurement, a test piece in which a commercially available aluminum plate (JIS A1050) was subjected to zinc-substituted Ni plating having a thickness of 0.1 μm was also used as a comparative example. Prepared as 20.
Table 4 shows the contact resistance measurement results. As shown in Table 4, the embodiment of the present invention has a contact resistance that is 1/2 to 1/3 times that of the comparative example, and has a surface conductivity that is superior to that of a conventional steel or Ni-plated aluminum surface. Was confirmed.

FIG. 4 shows Example No. used for contact resistance. 2 and Example No. 6 shows a scanning electron micrograph of the surface of the test piece. In the examples of the present invention, it was observed that many nitrides were dispersed and exposed on the surface. On the other hand, in FIG. A scanning electron micrograph of the surface of 18 test pieces is shown, but almost no precipitate was observed in the comparative example.
As described above, since the present invention contains a large amount of nitrogen, it has excellent room temperature strength and corrosion resistance while ensuring ductility capable of cold working, and contact resistance is reduced by the dispersion and exposure of nitride on the surface. Has reduced properties.

DESCRIPTION OF SYMBOLS 1 Electroslag remelting furnace 2 Gas introduction part 10 ESR electrode 13 ESR ingot

Claims (10)

  In mass%, C: 0.01 to 0.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 3.0%, Ni: 6.0 to 20.0%, Cr: 17.0 to 30.0%, Mo: 0.5 to 4.0%, N: 0.86 to 1.5%, with the balance being Fe and inevitable impurities, P: Conductive metal nitride is dispersed in stainless steel having a composition limited to 0.03% or less, S: 0.01% or less, Al: 0.01% or less, and O: 0.02% or less. Stainless steel for a polymer electrolyte fuel cell separator, wherein a part of the dispersed metal nitride is exposed on the surface of the stainless steel. _{2. The} polymer electrolyte fuel according to claim 1, wherein the metal nitride is at least one of M ₄ N type, M ₂ N type, and MN type nitride (where M is a metal element). Stainless steel for battery separator.   3. The stainless steel for a polymer electrolyte fuel cell separator according to claim 1, wherein the metal element in the nitride contains one or more of chromium, molybdenum, and vanadium.   The stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 3, wherein the stainless steel base is an austenite phase.   The stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 3, wherein the composition further contains V: 0.01 to 1.5% by mass%.   The composition further contains one or more of Nb: 0.05 to 1.5%, Ti: 0.01 to 0.05%, and Zr: 0.01 to 0.1% by mass%. The stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 5.   Further, the composition contains one or more of Co: 0.5 to 3.0%, Cu: 0.5 to 3.0%, and W: 0.05 to 0.5% by mass%. The stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 6. A method for producing stainless steel for a polymer electrolyte fuel cell separator according to any one of claims 1 to 7,
Using an electroslag remelting electrode having a composition of stainless steel as a target composition and a pressurized electroslag remelting furnace, the nitrogen gas partial pressure in the furnace is set to 0.8 MPa or more by remelting the electroslag. A method for producing stainless steel for a polymer electrolyte fuel cell separator, comprising obtaining an ingot of a target composition.   The ingot obtained by remelting the electroslag is subjected to one or both of annealing and aging treatment at 800 to 1000 ° C. 9. The stainless steel for polymer electrolyte fuel cell separator according to claim 8, Production method.   The solid polymer fuel according to claim 8 or 9, wherein the surface is acid-treated to have a centerline average roughness of 0.5 to 2.5 µm as defined in JIS B 0633-2001. A method for producing stainless steel for battery separators.