JP2006233282A - Stainless steel for energizing electric parts with superior electric conductivity and corrosion resistance, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stainless steel which is used for energizing electric parts and has superior electric conductivity and corrosion resistance, and to provide a manufacturing method therefor. <P>SOLUTION: The ferritic stainless steel for energizing electric parts includes predetermined components, one or two elements of Ti in a range of 0.15 to 0.50% and Nb in a range of 0.20 to 0.50%, while controlling the amounts of Cr and Mo so as to satisfy 23≤[Cr]+3.3×[Mo] (wherein [Cr] represents a content (%) of Cr contained in the steel; and [Mo] represents a content (%) of Mo contained in the steel), and the balance Fe with unavoidable impurities. Furthermore, the stainless steel includes TiN or NbN with diameters between 50 nm and 50,000 nm in the density of 2,000 pieces/mm<SP>2</SP>or more by average. The method for manufacturing the stainless steel for energizing electric parts includes annealing the steel in an atmosphere containing 20% or more nitrogen at 800 to 1,300°C for 24 hours or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a stainless steel for energized electrical parts excellent in electrical conductivity and corrosion resistance suitable for, for example, a polymer electrolyte fuel cell separator and a method for producing the same.

  Stainless steel is excellent in corrosion resistance because a passive film is formed on the surface thereof, but the passive film on the surface has a large electric resistance, so that it is not suitable for a component requiring a small contact electric resistance. If the contact electrical resistance can be reduced, stainless steel can be used as a current-carrying electrical component that requires corrosion resistance. For example, one of the parts that require excellent corrosion resistance and small contact electric resistance is a separator for a polymer electrolyte fuel cell.

Since fuel cells are excellent in power generation efficiency and do not emit CO ₂ , they have been developed in recent years from the viewpoint of global environmental conservation. This fuel cell reacts H ₂ and O ₂ to generate electricity, and its basic structure is an electrolyte membrane (ie, an ion exchange membrane), two electrodes (ie, a fuel electrode and an air electrode), and O ₂ ( That is, it comprises a diffusion layer of air) and H ₂ and two separators. Depending on the type of electrolyte membrane used, phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, alkaline fuel cells, solid polymer fuel cells, and the like have been developed.

  Among these fuel cells, the polymer electrolyte fuel cell (A) has a power generation temperature of about 80 ° C. compared with a phosphoric acid fuel cell and a molten carbonate fuel cell, and generates power at a significantly lower temperature. (B) The fuel cell body can be reduced in weight and size, (C) can be started up in a short time, (D) has high fuel efficiency and high power density. For this reason, the polymer electrolyte fuel cell is the fuel cell that is attracting the most attention today for use as a power source for mounting an electric vehicle, a stationary generator for home use, and a small portable generator.

This polymer electrolyte fuel cell takes out electricity from H ₂ and O ₂ through a polymer membrane. As shown in FIG. 1, gas diffusion layers 2 and 3 (for example, carbon paper) and a separator 4 are used. , 5 sandwiches the membrane-electrode assembly 1 to form a single component (a so-called single cell), and generates an electromotive force between the separator 4 and the separator 5. The membrane-electrode assembly 1 is called MEA (that is, membrane-electron assembly), which is a polymer film integrated with an electrode material such as carbon black carrying a platinum-based catalyst on the front and back surfaces of the membrane. The thickness is several tens of μm to several hundreds of μm. In many cases, the gas diffusion layers 2 and 3 are integrated with the membrane-electrode assembly 1.

  When the polymer electrolyte fuel cell is applied to the above-described use, a fuel cell stack is formed by connecting several tens to several hundreds of such single cells in series.

As the separators 4 and 5, (E) In addition to the role as a partition wall that separates single cells, (F) a conductor that carries generated electrons, (G) an air flow through which O ₂ (ie, air) and H ₂ flow A function as a channel, a hydrogen channel, and (H) a discharge channel for discharging generated water and gas is required. Furthermore, in order to put the polymer electrolyte fuel cell into practical use, it is necessary to use separators 4 and 5 having excellent durability and electrical conductivity.

  Regarding durability, when used as a power source for mounting an electric vehicle, it is assumed that the time is about 5000 hours. Alternatively, when used as a home-use stationary generator or the like, it is assumed that the time is about 40000 hours. Therefore, the separators 4 and 5 are required to have characteristics such as corrosion resistance that can withstand long-time power generation. Regarding electrical conductivity, it is desirable that the contact resistance between the separators 4 and 5 and the gas diffusion layers 2 and 3 is as low as possible. This is because when the contact resistance between the separators 4 and 5 and the gas diffusion layers 2 and 3 increases, the power generation efficiency of the polymer electrolyte fuel cell decreases. That is, the smaller the contact resistance, the better the electrical conductivity.

  To date, polymer electrolyte fuel cells using a graphite material as a separator have been put into practical use. The separator made of this graphite material has an advantage that contact resistance is relatively low and corrosion does not occur. However, since it is easily damaged by impact, it is difficult to reduce the size and the processing cost for forming the air channel 6 and the hydrogen channel 7 is high. These drawbacks of the separator made of graphite are a cause of hindering the spread of solid polymer fuel cells.

  In order to solve the above problems, an attempt has been made to apply a metal material as a separator material instead of a graphite material. In particular, from the viewpoint of improving durability, various studies have been made toward the practical application of separators made of stainless steel.

  For example, Patent Document 1 discloses a technique in which a metal that easily forms a passive film is used as a separator. However, the formation of a passive film causes an increase in contact resistance, leading to a decrease in power generation efficiency. For this reason, these metal materials have a large contact resistance and inferior corrosion resistance compared to carbon materials.

  For example, Patent Document 2 discloses a technique for reducing contact resistance and ensuring high output by performing gold plating on the surface of a metal separator such as SUS304. However, it is difficult to prevent pinholes with thin gold plating, and conversely with thick gold plating, the problem of cost remains.

  For example, Patent Document 3 discloses a method of obtaining a separator having improved electrical conductivity by dispersing carbon powder in a ferritic stainless steel substrate. However, even when carbon powder is used, a cost problem still remains because the surface treatment of the separator requires a corresponding cost. Further, it has been pointed out that the separator subjected to the surface treatment has a problem that the corrosion resistance is remarkably lowered when scratches or the like are generated during assembly.

Attempts have also been made to reduce the contact resistance of the separator by using precipitates having electrical conductivity. For example, Patent Document 4 discloses a separator in which M23C6 type carbide or M2B type boride is deposited on the surface. However, in order to obtain a sufficient amount of precipitation with this technique, a large amount of C and B must be added, so that the stainless steel as the separator material becomes hard. In addition, these M23C6 type carbides and M2B type borides also have a high hardness, so that there is a problem that the formability is remarkably deteriorated when stainless steel is processed into a separator. Further, since the metal element (that is, M) of the M23C6 type carbide and M2B type boride is mainly composed of Cr, there is a problem that when these precipitate, Cr in the stainless steel decreases and the corrosion resistance deteriorates.
Japanese Patent No. 3460346 Japanese Patent Laid-Open No. 10-228914 JP 2000-277133 A Japanese Patent No. 3365385

  As described above, when selecting a material as a separator for a polymer electrolyte fuel cell, the conventional method has the above-mentioned problems, and a material excellent in both electrical conductivity and corrosion resistance has not been obtained. It is. A metal material that has excellent corrosion resistance and satisfies the characteristics required for a current-carrying electric component has not been put to practical use so far.

  In view of such circumstances, an object of the present invention is to provide a stainless steel for energized electrical parts excellent in electrical conductivity and corrosion resistance and a method for producing the same when used as a separator of a polymer electrolyte fuel cell.

  The present inventors have conducted intensive research to solve the above problems. As a result, stainless steel is excellent in corrosion resistance because a passive film is formed on the surface thereof. Therefore, in the present invention, first, stainless steel is selected as a base material, and a conductive substance is present on the surface of stainless steel. The basic idea was that the contact resistance of stainless steel would be lowered and the electrical conductivity would be improved. Based on these, paying attention to nitride-based precipitates as conductive materials, by depositing TiN or NbN in the passive film formed on the surface of stainless steel, both electrical conductivity and corrosion resistance characteristics can be obtained. I found it to improve.

  Further, when depositing TiN or NbN in the passive film, 1) forming and depositing TiN or NbN from N existing as an atmosphere and Ti and Nb in steel by performing surface nitriding treatment. 2) It was found that it is important from the viewpoint of improving electrical conductivity to define the optimum size and density of TiN or NbN.

  As described above, in the present invention, by specifying the amount of Ti and Nb, the size of nitride inclusions, and the density, stainless steel having sufficient electrical conductivity and corrosion resistance for energized electrical parts can be obtained. .

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: 0.02% or less, N: 0.01% or less, Cr: 11 to 45%, Mo: 7.0% or less, Si: 1.5% or less, Mn: 1. 5% or less, P: 0.05% or less, S: 0.03% or less, and one or two of Ti and Nb are Ti: 0.15-0.50, Nb: 0.20-0. It is contained in a range of 50%, and the Cr and Mo contents are 23 ≦ [Cr] + 3.3 × [Mo] (where [Cr]: the amount of Cr contained in the steel (%) [Mo]: in the steel The amount of Mo contained (%)), the balance being stainless steel made of Fe and inevitable impurities, and the diameter of TiN or NbN contained in the steel is 50 nm to 50000 nm and the average density is 2000 pieces / mm Ferrite stainless steel for current-carrying electrical components with excellent electrical conductivity and corrosion resistance, characterized by being ² or more Less steel.

  [2] In the above [1], further containing one or two kinds of Cu: 1% or less and Ni: 1% or less in mass%, which is excellent in electric conductivity and corrosion resistance, Ferritic stainless steel for parts.

[3] By mass%, C: 0.01% or less, N: 0.01% or less, Cr: 15-26%, Ni: 6-28%, Si: 5.0% or less, Mn: 5.0 % Or less, P: 0.05% or less, S: 0.03% or less, Ti or Nb, one or two of Ti: 0.15-0.50%, Nb: 0.20-0. It is contained in the range of 50%, and the Cr and Mo contents are 20 ≦ [Cr] + 3.3 × [Mo] (where [Cr]: the amount of Cr contained in the steel (%) [Mo]: in the steel The amount of Mo contained (%) is satisfied, the balance is made of Fe and inevitable impurities, and the diameter of TiN or NbN contained in the steel is 50 nm or more and 50000 nm or less, and the average density is 2000 pieces / mm ² or more. An austenitic stainless steel for energized electrical parts with excellent electrical conductivity and corrosion resistance.

  [4] In the above [3], the composition further comprises one or two of Cu: 2% or less and Mo: 7.0% or less in mass%, and is excellent in electrical conductivity and corrosion resistance Austenitic stainless steel for energized electrical parts.

  [5] Surface nitriding treatment is performed within 24 hours at 800 to 1300 ° C. in a nitrogen atmosphere having a concentration of 20% or more using the steel having the chemical component according to any one of [1] to [4]. A method for producing stainless steel for energized electrical parts having excellent electrical conductivity and corrosion resistance.

  In addition, in this specification, all% which shows the component of steel is the mass% (mass%).

  According to the present invention, stainless steel for energized electrical parts having excellent electrical conductivity and corrosion resistance can be obtained. Since the stainless steel of the present invention has a low contact resistance value and excellent corrosion resistance, it is optimal for a polymer electrolyte fuel cell separator. In addition, it is possible to provide an inexpensive stainless steel separator to a solid polymer fuel cell that has conventionally used an expensive graphite separator due to durability problems. It can be said that it is an industrially useful invention that can be widely used not only as a separator but also as a stainless steel electrical component having electrical conductivity.

  The first feature of the stainless steel of the present invention is that it is defined by the composition shown below centering on Ti and Nb. The second feature is to define the size and density of TiN or NbN precipitated in the passive film. Thus, by defining the composition, the size and density of TiN or NbN, the present invention provides a stainless steel for energized electrical parts that is excellent in electrical conductivity and corrosion resistance.

  In addition, the above characteristics can be obtained by performing surface nitriding treatment under conditions that allow TiNb nitride concentration to occur on the surface. In the present invention, specific conditions in the surface nitriding treatment are characteristic of the manufacturing method.

  Hereinafter, the present invention will be described in detail.

  First, the reasons for limiting the chemical composition (composition) of steel in the present invention are as follows.

  C is preferably as small as possible because it has a small solid solubility limit in ferritic and austenitic stainless steels and mainly precipitates as Cr carbides to cause intergranular corrosion. Furthermore, in the austenitic stainless steel, C is an element that precipitates in the form of Cr carbide during use at high temperatures or during welding and degrades oxidation resistance. Therefore, C is 0.02% or less for ferritic stainless steel, and C is 0.01% or less for austenitic stainless steel.

  Si is an element necessary as a deoxidizer, but it is desirable to refrain from addition as much as possible in materials that require softening in order to significantly increase the yield strength. Therefore, it is 1.5% or less for ferritic stainless steel and 5.0% or less for austenitic stainless steel.

  Mn is generally used as a deoxidizer in ferritic stainless steel, but it is desirable that the content of Mn be low because it forms sulfides in the steel and significantly deteriorates the corrosion resistance. However, it is acceptable if the upper limit is up to 1.5% in consideration of economics at the time of manufacture. Therefore, in ferritic stainless steel, Mn is 1.5% or less. Further, since Mn is an austenite-forming element, there is no problem that it is added in the austenitic stainless steel to stabilize the structure. However, Mn is not more than 5.0% because a large amount of addition deteriorates hot workability.

  P is preferably less in terms of hot workability in ferritic and austenitic stainless steels. Therefore, P is set to 0.05% or less.

  S is preferable to be less in terms of hot workability and corrosion resistance in ferritic and austenitic stainless steels. Therefore, S is set to 0.03% or less.

  Cr and Mo are basic elements that ensure corrosion resistance in ferritic and austenitic stainless steels, and are particularly effective in suppressing pitting corrosion. In order to obtain such an effect, Cr needs to be contained in an amount of 11% or more for ferritic stainless steel and 15% or more for austenitic stainless steel. Mo has an effect approximately 3.3 times as high as the pitting corrosion potential in 3.5% sodium chloride, and by adding Cr as a supplement, it is possible to prevent harmful effects caused by high alloying. On the other hand, addition of a large amount of both Cr and Mo is undesirable because it causes a decrease in workability and an increase in manufacturing cost. Therefore, in ferritic stainless steel, Cr is 45% or less, and Mo is 7.0% or less. In the austenitic stainless steel, Cr is added to 26% or less, and Mo is added to 7.0% or less as required. Furthermore, in the present invention, it is essential and important that nitride inclusions (TiN, NbN) are precipitated in the passive film on the surface in order to give stainless steel electrical conductivity. Therefore, in order to ensure corrosion resistance even in the state where nitride inclusions are precipitated, Cr and Mo should be 23 ≦ [Cr] + 3.3 × [Mo] for ferritic stainless steel, and for austenitic stainless steel. It should be contained so as to satisfy the condition of 20 ≦ [Cr] + 3.3 × [Mo].

  N precipitates on the surface as TiN or NbN and acts as an electric conductor, but on the other hand, since addition of a large amount is difficult in the process, the upper limit is 0.01%. In addition, nitrogen contained in TiN or NbN used as an electric conductor in the present invention is added mainly by nitriding from the outside, and is not added at the molten steel stage. In addition, the said range of N and the reason for limitation are object in any case of a ferritic stainless steel and an austenitic stainless steel.

  Ti is necessary for bonding with N and depositing on the surface as TiN. Surface precipitation of TiN or NbN, so-called nitride inclusions, is important in the present invention in terms of improving electrical conductivity. Thus, Ti is one of the important elements in the present invention. In order to obtain an excellent electrical conductivity effect by depositing on the surface as TiN or NbN, addition of Ti: 0.15% or more is necessary. is necessary. However, if these elements are added in a large amount, the workability is impaired, so 0.50% is made the upper limit. Accordingly, Ti is set to be 0.15% or more and 0.50% or less. In addition, the said range of Ti and the reason are object in any case of a ferritic stainless steel and an austenitic stainless steel.

  Nb, like Ti, is necessary for bonding with N and precipitating as NbN, and is one of the important elements in the present invention. In order to obtain an excellent electrical conductivity effect, it is necessary to add Nb: 0.20% or more. However, if these elements are added in a large amount, the workability is hindered, so Nb: 0.50% is made the upper limit. Accordingly, Nb is set to 0.20% or more and 0.50% or less. In addition, the said range of Nb and its reason are object in any case of a ferritic stainless steel and an austenitic stainless steel.

  Ni is necessary for stabilizing the austenitic structure in the austenitic stainless steel, but adding a large amount increases the manufacturing cost, so the content is made 6 to 28%. Moreover, in ferritic stainless steel, although it is not an essential element, the effect of improving corrosion resistance and toughness can be obtained by inclusion. However, if the content exceeds 1%, the production cost increases, which is undesirable. Therefore, in a ferritic stainless steel, when it contains Ni, it is 1% or less.

  The steel sheet of the present invention can achieve the desired characteristics with the above-mentioned essential additive elements, but can contain the following elements depending on the desired characteristics.

  Since Cu is a solid solution at least in a small amount in ferritic and austenitic stainless steels, it can be contained. However, if it exceeds 1% for ferritic stainless steel and 2% for austenitic stainless steel, the hot workability deteriorates, which is not preferable. Therefore, when it contains Cu, it is 1% or less for ferritic stainless steel and 2% or less for austenitic stainless steel.

  The balance other than the above is Fe and inevitable impurities. In the present invention, an element that effectively contributes to improvement of toughness and workability can be contained in a range of 1% or less without greatly changing electrical conductivity and corrosion resistance.

  Next, TiN or NbN, which is one of the important requirements for the present invention, will be described. TiN or NbN is formed of N in the heat treatment atmosphere, Ti and Nb, and precipitates as nitride inclusions in the passive film formed on the surface of the stainless steel. By having TiN or NbN in the passive film as described above, TiN and NbN act as electrical conductors, lowering the contact resistance, and improving the electrical conductivity as stainless steel. In the present invention, since the base material is stainless steel, the passive film formed on the surface is strong and has sufficient corrosion resistance. Therefore, as described above, by depositing TiN and NbN as nitride inclusions in the passive film, it is possible to improve the electrical conductivity while exhibiting the corrosion resistance effect of the passive film. .

At this time, the size and density of TiN or NbN in the passive film are 50 nm or more in diameter and 2000 / mm ² or more in average density. The contact electrical resistance depends on the contact area per unit area with the conductive material when energized, that is, the number of contact points and the total area of the contact points. In this respect, the TiN and NbN in the passive film It is important to define the size and density. If the diameter is less than 50 nm, TiN and NbN are buried in the passive film, so that they do not sufficiently function as an electric conductor, and as a result, the electric conductivity is not improved. On the other hand, if it exceeds 50000 nm, the corrosion resistance may deteriorate. Therefore, the upper limit is preferably 50000 nm or less. Thus, by defining the sizes of TiN and NbN in the passive film, the diameters of TiN and NbN become larger than the normal passive film thickness, and in the passive film on the surface, TiN For example, when the present invention is used as a separator of a fuel cell, the contact portion is concentrated on TiN and NbN when the electrode and the separator are in contact with each other, and the contact resistance is further reduced. Further, by defining the average density of TiN and NbN in the passive film, it becomes possible to secure a sufficient contact area, and the contact resistance is further lowered. In the present invention, the nitride inclusions are TiN or NbN. Examples of the nitride inclusions include CrN in addition to TiN or NbN, but TiN or NbN is preferable from the viewpoint of ensuring intergranular corrosion resistance. However, within the range where the effects of the present invention are exhibited, it is possible to precipitate the CrN or the like as long as the intergranular corrosion resistance does not deteriorate. Further, as inclusions precipitated in the passive film formed on the surface of the stainless steel, carbide inclusions can be used in addition to nitride inclusions. However, although the carbide inclusions are conductive like the nitride inclusions, they must contain a certain amount of C in order to obtain an excellent electrical conductivity effect. Then, problems such as deterioration of weldability remain. Therefore, in the present invention, the inclusions precipitated in the passive film formed on the surface of the stainless steel are TiN or NbN which are nitride inclusions. It is also possible to precipitate carbon within a range where the weldability is not deteriorated as long as the effect of the present invention is achieved. Next, a method for producing stainless steel for energized electrical parts having excellent electrical conductivity and corrosion resistance according to the present invention will be described.

  In producing the stainless steel of the present invention, it is not necessary to specifically limit the production technique, and any conventionally known production technique can be applied. However, in the present invention, it is important that the chemical components described above and the size and density of TiN or NbN are within the range, and that the passive film on the stainless steel surface has TiN or NbN. In order to precipitate NbN in the passive film on the surface of stainless steel, surface nitriding treatment is performed in a nitrogen atmosphere having a concentration of 20% or more and at a temperature of 800 to 1300 ° C. and a holding time of 24 hours. Excessive heating is undesirable because it causes surface roughness. This is an essential item in the manufacturing conditions in the present invention.

  For example, in the steelmaking process, it is preferable to melt the stainless steel having the above-described chemical composition in a converter, electric furnace, or the like and perform secondary refining by a strong stirring vacuum oxygen decarburization method. In addition, the casting of molten stainless steel is preferably continuous casting from the viewpoint of productivity and quality.

  The obtained slab is hot rolled into a hot rolled stainless steel sheet. The conditions for hot rolling are not particularly limited.

  Next, surface nitriding is performed at 800 to 1300 ° C. in a gas containing nitrogen having a concentration of 20% or more. By performing the surface nitriding treatment under such conditions, TiN or NbN can be deposited in the passive film on the stainless steel surface. In order to prevent the oxidation of the surface while absorbing nitrogen, it is performed in a non-oxidizing atmosphere containing 20% or more of nitrogen. The surface nitriding temperature is set to 800 ° C. or higher and 1300 ° C. or lower. If it is less than 800 ° C., the deposition rate is slow, and sufficient nitride inclusions for obtaining the effect of electrical conductivity cannot be deposited. On the other hand, if it exceeds 1300 ° C., the crystal grains become coarse, which is not preferable. Also, it becomes thermally unstable and re-dissolves. The surface nitriding time is 24 hours or less. Exceeding 24 hours is not preferable because coarsening of crystal grains and surface oxidation proceed.

  It is preferable to perform pickling or electrolytic pickling after the surface nitriding treatment. By performing the pickling treatment, it becomes possible to expose a part of TiN and NbN deposited in the passive film on the surface of the stainless steel to the outer surface, which works effectively in reducing the contact resistance value. The pickling treatment is not particularly limited as long as the surface of the stainless steel can be slightly dissolved. Even if it immerses in an acidic solution, an acidic solution may be sprayed or sprayed with a nozzle. Among these, pickling by electrolysis is preferable from the viewpoint of surface uniformity.

  As described above, the stainless steel for energized electrical parts having excellent electrical conductivity and corrosion resistance according to the present invention can be obtained. In addition, following the said process, it is also possible to cold-roll as needed and to give the cold-rolled stainless steel plate obtained by annealing (800-1150 degreeC), and to perform a pickling process.

Production Method 100 kg of stainless steel having the components shown in Table 1 was melted by lab vacuum melting to form a steel ingot having a thickness of 150 mm. After heating this ingot to 1250 ° C., a hot rolled stainless steel sheet having a thickness of 4 mm was formed by hot rolling. Furthermore, the obtained hot-rolled stainless steel plate was annealed and pickled under conditions of 950 ° C. × 4 minutes for the ferrite type and 980 ° C. × 4 minutes for the austenite type. Subsequently, the thickness was reduced to 1.0 mm by cold rolling, and further subjected to annealing and pickling treatment at 925 ° C. for 1 minute to obtain a cold rolled stainless steel sheet. The pickling treatment was performed using a pickling solution containing nitric acid and hydrofluoric acid.

  A 200 mm × 200 mm sample was cut out one by one from the center portion and the center portion in the longitudinal direction of the obtained cold-rolled stainless steel plate. Further, the scale was removed by polishing the sample, and then pickling treatment was performed using a pickling solution containing 5% by mass of nitric acid and 2.5% by mass of hydrofluoric acid.

With respect to the cold-rolled annealed pickled board produced as described above, the following observation of precipitates by SEM, contact resistance measurement, and corrosion resistance test were performed to evaluate the performance. The obtained results are shown in Table 2.
Precipitation observation: quantification of the number of precipitates One test piece of 10 mm × 10 mm was cut out from the center of each of the inventive sample and the comparative sample. After buffing the surface of the central part of this sample with 1 μm alumina and grains, using a scanning electron microscope, 5 fields of view were taken at a magnification of 5000 times, and the number of precipitate images was measured using image processing. Extracted. The separation of NbN and TiN was determined from the difference in shape.
Measurement of Contact Resistance Four test pieces each having a size of 30 mm × 30 mm were cut out from the samples of the present invention sample and the comparative example sample, and from the central portion of each sample. Further, as shown in FIG. 2, one test piece 8 is alternately sandwiched between two carbon papers (TGP-H-120 made by Toray Industries, Inc.) 9 of the same size from both sides, and a copper plate is plated with gold. 10 is contacted, a pressure of 137.2 N / cm ² (ie, 14 kgf / cm ² ) is applied per unit area, the resistance between the test pieces 8 is measured, multiplied by the area of the contact surface, and the number of contact surfaces (= The value divided by 2) was taken as the measured value of contact resistance.

The contact resistance value was calculated four times while exchanging the test pieces, and the average value is shown in Table 2. As reference examples, contact resistance values were similarly calculated for a stainless steel plate (equivalent to SUS304) having a surface plated with gold of approximately 0.1 μm and a graphite plate having a thickness of 5 mm.
Corrosion resistance test Evaluation of corrosion resistance: A 5% by mass sulfuric acid corrosion test was carried out in accordance with JIS G0591. A 30 mm × 30 mm test piece used for measurement of contact resistance was immersed in 5% by mass sulfuric acid, and the weight change after being held at 80 ° C. for 7 days was measured. Corrosion resistance was evaluated by evaluating that the average value of the weight loss per unit area of the four test pieces was 0.1 g / m ² or less as good (◯), and that exceeding 0.1 g / m ² was not possible (x). It shows in Table 2.

From Table 2, many precipitates are observed on the surface of the cold-rolled annealed pickling plate in the examples, whereas almost no precipitates are observed in the comparative example not containing TiNb. As a result, in the present invention, the contact resistance value was 10 mΩ · cm ² or less, and a contact resistance value equivalent to that of the gold-plated stainless steel plate or graphite plate was obtained, whereas in the comparative example, the contact resistance value was 10 mΩ · cm. ^It can be seen that the electrical conductivity is inferior, greatly exceeding ² .

  Furthermore, all the stainless steel plates of the present invention had good (◯) evaluation of corrosion resistance.

  The stainless steel of the present invention can be widely used not only as a polymer electrolyte fuel cell separator but also as a stainless steel electrical component that requires good corrosion resistance and low contact electric resistance.

It is a perspective view which shows the example of a solid polymer type fuel cell typically. It is sectional drawing which shows typically the sample used for the measurement of contact resistance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane-electrode assembly 2 Gas diffusion layer 3 Gas diffusion layer 4 Separator 5 Separator 6 Air flow path 7 Hydrogen flow path 8 Test piece 9 Carbon paper 10 Electrode

Claims (5)

In mass%, C: 0.02% or less, N: 0.01% or less, Cr: 11 to 45%, Mo: 7.0% or less, Si: 1.5% or less, Mn: 1.5% or less , P: 0.05% or less, S: 0.03% or less,
1 or 2 types of Ti and Nb are contained in the range of Ti: 0.15 to 0.50, Nb: 0.20 to 0.50%,
Cr, Mo content is 23 ≦ [Cr] + 3.3 × [Mo] (However, [Cr]: Cr amount contained in steel (%) [Mo]: Mo amount contained in steel (%)) And the balance is stainless steel consisting of Fe and inevitable impurities,
Furthermore, the ferritic stainless steel for current-carrying electrical parts excellent in electrical conductivity and corrosion resistance, characterized in that the diameter of TiN or NbN contained in the steel is 50 nm or more and 50000 nm or less and the average density is 2000 pieces / mm ² or more. .   The ferrite for current-carrying electrical components having excellent electrical conductivity and corrosion resistance according to claim 1, further comprising one or two of Cu: 1% or less and Ni: 1% or less in mass%. Stainless steel. In mass%, C: 0.01% or less, N: 0.01% or less, Cr: 15-26%, Ni: 6-28%, Si: 5.0% or less, Mn: 5.0% or less, P: 0.05% or less, S: 0.03% or less,
1 or 2 types of Ti and Nb are contained in the range of Ti: 0.15 to 0.50%, Nb: 0.20 to 0.50%,
Cr, Mo content 20 ≦ [Cr] + 3.3 × [Mo] (However, [Cr]: Cr content contained in steel (%) [Mo]: Mo content contained in steel (%)) And the balance consists of Fe and inevitable impurities,
Furthermore, the diameter of TiN or NbN contained in the steel is 50 nm or more and 50000 nm or less, and the average density is 2000 pieces / mm ² or more. Austenitic stainless steel for current-carrying electrical parts excellent in electrical conductivity and corrosion resistance. .   Furthermore, it contains 1 type or 2 types of Cu: 2% or less and Mo: 7.0% or less by mass%, The electricity supply electrical component excellent in the electrical conductivity and corrosion resistance of Claim 3 characterized by the above-mentioned For austenitic stainless steel. Using the steel having the chemical component according to any one of claims 1 to 4,
A method for producing stainless steel for current-carrying electrical parts excellent in electrical conductivity and corrosion resistance, characterized in that surface nitriding is performed in a nitrogen atmosphere at a concentration of 20% or more at 800 to 1300 ° C. within 24 hours.

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