JP5077207B2 - Stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive stainless steel material having a low contact resistance suitable as a material for conductive parts. <P>SOLUTION: The conductive stainless steel material is characterized in that it contains a substance derived from a base material formed from stainless steel, has an electrical conductivity, and has conductive deposits deposited on the surface of the base material, wherein the conductive deposits are electrically conductive with the base material. It is preferable that the conductive deposits are conductive smuts formed from a solution containing a non-oxidizing acid, and that a coating layer containing graphitic carbon is provided on the stainless steel material having the conductive deposits. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention is suitable as a material for conductive parts such as electrical parts and electronic parts that require low contact resistance, high productivity (excellent workability), and high economic efficiency, specifically, wiring terminals, connectors, etc. Related to stainless steel.

  Stainless steel represented by SUS430 and SUS304 exhibits excellent corrosion resistance due to the passive film formed on the surface. On the other hand, this passive film is an oxide or hydroxide film mainly composed of Cr and containing Si, Mn, etc., and therefore has high electrical resistance and poor conductivity.

  Therefore, for example, wiring terminals, connectors, battery cans, spring materials for fixing batteries, electrical circuit contact members such as electromagnetic relays, etc. A stainless steel material whose passivating film increases the contact resistance is not usually used, and a material made of a Cu alloy in which a passivating film is not formed on the surface is generally used.

  However, the Cu alloy has insufficient corrosion resistance, and there is a problem that conductivity is deteriorated by rusting. Therefore, in order to apply stainless steel materials for applications as conductive parts while taking advantage of the excellent corrosion resistance inherent in stainless steel, Ni plating is applied on stainless steel materials to eliminate the disadvantages (high contact resistance) derived from passive films. The method to do is employ | adopted (for example, patent document 1).

In addition to Patent Document 1, various methods for solving the above problems have been proposed. For example, Patent Documents 2 and 3 include a stainless steel material having a chemical composition containing 1.0 mass% or more of Cu. And a method of ensuring conductivity by depositing a Cu-rich phase on the substrate and exposing a part of the deposited Cu-rich phase to the surface of a stainless steel material.
JP-A 63-145793 JP 2001-89865 A JP 2004-10993 A

  However, in the method of forming Ni plating on the surface of a stainless steel material as disclosed in Patent Document 1, since a step of performing plating is added together with steps before and after that (pretreatment, washing, drying, etc.), the production of parts Man-hours required for the increase. In addition, both the electroplating method and electroless plating method for plating formation require dedicated equipment for that purpose, and the running cost is high. Furthermore, since waste liquid is inevitably generated, this processing cost is also required. For this reason, the production cost per part will rise remarkably compared with the part manufactured by the method which does not use plating.

  In the stainless steel materials disclosed in Patent Documents 2 and 3, the Cu-rich phase precipitated in the base material significantly reduces secondary workability such as press molding. This becomes a restriction for increasing the amount of precipitation of the Cu-rich phase, and as a result, a decrease in the contact resistance of the stainless steel material is limited. Further, in order to form a Cu-rich phase, heat treatment at a high temperature for a long time (for example, at 800 ° C. for 24 hours) is necessary, and this treatment makes it difficult to reduce the running cost of the entire process. Moreover, since this heat treatment must be performed by batch processing, it is impossible to perform continuous processing by making the entire process into a line. For this reason, it is also difficult to improve productivity by heat treatment. On the other hand, when the conductive material is included in the non-conductive film without precipitating the Cu rich phase inside the stainless steel material, it is difficult to uniformly contain the conductive material such as Cu, so that the conductivity is poor. There is also a problem that the electrical conductivity of the stainless steel material increases with time with the growth of the nonconductive film, which is not sufficiently stable.

  The present invention has been devised to solve such a problem, and reprecipitation and / or redeposition of a steel-derived substance on the surface of a stainless steel material does not require additional steps such as plating. And it is providing the stainless steel material which ensured the stable electroconductivity.

The present invention has been completed based on the above findings and is as follows.
(1) Originating from a base material made of stainless steel, after the surface of the base material is once dissolved by pickling the base material with a pickling solution, a substance that has been subjected to at least one of reprecipitation and reattachment A conductive deposit that has electrical conductivity and is deposited on the surface of the base material, the conductive precipitate is in electrical communication with the base material, and the conductive property precipitates, O, S, Fe, including as constituent elements Cr and C, non-metal polycrystal der is, the conductive parts for stainless steel, wherein the conductive deposit is characterized that you have exposed.

(2) The stainless steel material for conductive parts according to (1) above, wherein a coating layer made of a nonmetallic conductive material is further formed on the stainless steel material provided with the conductive precipitate.

(3) The stainless steel material for conductive parts as described in (2) above, wherein the coating layer contains graphitic carbon.

(4) The stainless steel material for conductive parts as described in (3) above, wherein the interplanar spacing of the graphitic carbon contained in the coating layer is d002 ≦ 3.390 mm.

(5) The intensity ratio between the peak intensity I (110) of the (110) diffraction line and the peak intensity I (004) of the (004) diffraction line in wide-angle X-ray diffraction from the graphitic carbon crystal in the coating layer. The stainless steel material for conductive parts according to (4) above, wherein I (110) / I (004) is less than 0.1.

(6) From the above (3) to (5), the coating layer containing graphitic carbon is formed by sliding a member containing graphitic carbon against a stainless steel material provided with the conductive precipitate. ) A stainless steel material for conductive parts as described in any of the above.

(7) The coating layer containing the conductive precipitate and the graphitic carbon slides the member containing the graphitic carbon with respect to the base material, and uses the member containing the graphite carbon as a counter electrode. The stainless steel material for conductive parts as described in (6) above, which is formed on the surface of the base material by subjecting the material to sulfuric acid electrolytic treatment.

(8) The average surface roughness of the stainless steel material provided with the conductive precipitate is 0.10 as Ra.
The stainless steel material for conductive parts according to the above (6) or (7), which is μm or more.

  According to the present invention, there is provided a conductive stainless steel material that has excellent conductive properties (low contact resistance) with little change over time, while having no need for an expensive surface treatment such as Ni plating, and is excellent in economy. The A conductive part using such a conductive stainless steel material is inexpensive but has a low contact resistance and a little change with time in resistance.

1. Conductive precipitate The stainless steel material according to the present invention contains a substance originating from a base material made of stainless steel, has electrical conductivity, and has a conductive precipitate deposited on the surface of the base material. This conductive deposit is in electrical communication with the substrate.

  In the present invention, a portion made of stainless steel (metal) in the stainless steel material is referred to as a “base material” and does not include a passive film formed on the surface. The composition of the base material is not particularly limited as long as it is a stainless steel capable of forming a passive film on the surface, and may be austenitic or ferrite based on the component ranges shown in JIS G4305.

  An example of the chemical composition of the stainless steel forming the substrate is C: 0.15 mass% or less, Si: 1 mass% or less, Mn: 2.0 mass% or less, Al: 0.05 mass% or less, P : 0.06 mass% or less, S: 0.003 mass% or less, N: 0.03 mass% or less, Cr: 16-26 mass%, Ni: 30 mass% or less, Mo: 5 mass% or less, Cu: 3% by mass or less and the balance Fe and impurities.

  Further, Ti, Nb, W, Zr, B, Ca and / or Rem (rare earth metal) may be contained for the purpose of improving mechanical properties, corrosion resistance, etc. and reducing impurities. % Or less is desirable. Further, when Mn is used as an alternative to Ni, it may be contained in an amount of 10% by mass or less.

  “Contains a material originating from the base material” means that the material constituting the base material stainless steel, specifically Fe, Cr, Ni, C, Si, Mn, Cu, Mo, W, etc. It means that the composition is different from that of stainless steel, and the chemical and physical properties are different while containing one or more kinds of substances.

  “Precipitated on the surface of the substrate” means that it is deposited on the surface of the substrate and is present on the surface of the substrate, and that the material deposited on the surface other than the surface of the substrate adheres to the surface of the substrate. It exists on the substrate surface.

  Specifically, the conductive precipitates are conductive carbides formed by combining Fe and Cr, which are mainly metal bonds in stainless steel, with, for example, carbon contained in the steel, carbon alone, and stainless steel. An example is one in which metal ions such as Cu, Mo, W, and Ni eluted from the metal are precipitated again as metal.

  Among such conductive precipitates, the conductive precipitates will be described in detail below by taking as an example a conductive smut obtained by bringing a stainless steel material into contact with a solution containing a non-oxidizing acid.

  Here, the “solution containing a non-oxidizing acid” means a non-oxidizing acid, that is, an acid other than an acid having oxidizing power (oxidizing acid) such as nitric acid, for example, a hydrogen halide such as hydrochloric acid or hydrofluoric acid. A solution containing acid and sulfuric acid, which can remove the passive film of the stainless steel material and expose the substrate. The non-oxidizing acid contained in the solution containing the non-oxidizing acid may be one kind or plural kinds, and contains a component effective for removing the passive film in addition to the non-oxidizing acid. May be. Moreover, an oxidizing acid may be included as will be described later.

  In the study of reducing the contact resistance of the present inventors, it has been found that some smuts generated when a stainless steel material is brought into contact with a solution containing a non-oxidizing acid have electrical conductivity. It was.

  Here, “smut” is generated when a stainless steel material is brought into contact with a solution containing a non-oxidizing acid, and a substance constituting the stainless steel in a metal or passive state is a non-oxidizing acid. Dissolved and / or released (hereinafter collectively referred to as “dissolved”), and then re-deposited and / or re-attached to the surface of the substrate as a material having a composition different from stainless steel (metal) or passive (Hereinafter collectively referred to as “reprecipitation”).

  Depending on the type of non-oxidizing acid contained in the solution to be contacted, this smut may stain the surface of the stainless steel material and impair the beauty of the surface. It was customary to select at least no coloration.

  The present inventor derives from the passive film as long as the smut having electrical conductivity (hereinafter referred to as “conductive smut”) can be deposited on the surface of the substrate among the smuts that are normally avoided. The idea that the contact resistance can be reduced while maintaining the corrosion resistance is obtained. Further studies were made based on this idea, and the conductive smut was found to be excellent in three points: (1) electrical conductivity to the substrate, (2) adhesion to stainless steel, and (3) chemical resistance. .

The conductive smut has such excellent characteristics for the following reason.
That is, when a stainless steel material is immersed in a solution containing a non-oxidizing acid, the passive film formed on the surface of the base material made of stainless steel is dissolved by the non-oxidizing acid, and the exposed base material is also exposed to the acid. Partly dissolved. Since the material containing the dissolved stainless steel-derived material is again deposited on the base material, it is a smut. Therefore, the smut is deposited on the surface of the base material. Therefore, when the smut has conductivity, the top of the conductive smut deposited on the substrate is electrically connected to the substrate.

  Such a state in which the base material is exposed can exist stably only when immersed in a solution containing a non-oxidizing acid, and is taken out from the solution and left in the atmosphere, or by washing with water, etc. If immersed in a non-acidic solution, a passive film is rapidly formed on the exposed portion of the substrate. Although this passive film has poor electrical conductivity as described above and is excellent in corrosion resistance, the obtained stainless steel material has corrosion resistance based on the passive film and low contact resistance based on the conductive smut. It will have characteristics.

  In addition, since the smut is a component in which the components constituting the stainless steel once dissolved are precipitated again on the surface of the base material made of stainless steel in a non-oxidizing acid having corrosive properties, The potential difference with respect to is small. Therefore, it is difficult for the conductive smut to form a local battery with the base material, and the conductive smut may be corroded, or the base material around the conductive smut may be corroded and the conductive smut may fall off. Hateful. On the other hand, when a conductive material is present from the outside so that the stainless steel material penetrates the passive film and reaches the base material, local battery corrosion between the conductive material and the base material is almost eliminated. Inevitably, the conductive material often corrodes in a short period of time or the adhesion to the base material decreases.

  Moreover, the passive film formed so as to cover the exposed substrate once is formed so as to surround the conductive smut so as to cover the contact portion between the conductive smut and the substrate. For this reason, it is suppressed also by a passive film that a conductive smut falls from a base material.

  The composition of the conductive smut according to the present invention is not particularly limited as long as it has electrical conductivity. Composition of stainless steel as base material, type of non-oxidizing acid contained in the solution to be contacted, type of substance coexisting with non-oxidizing acid as required when contacting stainless steel with non-oxidizing acid, non-oxidizing This is because the composition varies greatly depending on the conditions (concentration, temperature, time, electrolysis conditions, etc.) for bringing the stainless steel material into contact with the solution containing the acidic acid.

  In addition, the size is required to be larger than the thickness of the passive film, but since the thickness of the passive film varies depending on the composition of the stainless steel, the lower limit is the thickness of the passive film. What is necessary is just to set suitably according to. On the other hand, when the conductive smut is excessively larger than the thickness of the passive film, there is a concern that the conductive smut may fall off from the base material during secondary processing to various conductive parts or during use as a conductive part. . From the viewpoint of preventing the dropout, the upper limit of the size of the conductive smut may be appropriately determined according to the thickness of the passive film.

Further, the crystal structure is not particularly limited as long as electrical conductivity can be realized.
An example of the conductive smut according to the present invention having the above characteristics will be described in detail below together with an example of a manufacturing method.

  A typical example of the method for forming the conductive smut according to the present invention is a treatment immersed in sulfuric acid (hereinafter also referred to as “sulfuric acid washing”). When a stainless steel material used for conductive parts is immersed in dilute sulfuric acid, the passive film formed on the surface is removed and a conductive smut is generated. The conductive smut can be generated so as to be sparsely present on the surface of the stainless steel material or can be deposited so as to substantially cover the surface of the stainless steel material by appropriately changing the processing conditions.

  There are various types of conductive smuts thus obtained with respect to size, composition, precipitation state, and the like. Therefore, by removing from the sulfuric acid and cleaning with water, preferably brushing or ultrasonic cleaning, the smut that is not retained on the stainless steel material, specifically, the powdered smut generated excessively is removed. Therefore, it is realized that only the conductive smut as the conductive precipitate having excellent adhesion is present on the surface of the stainless steel.

  Further, prior to washing with water, when a conductive smut is produced by dipping in sulfuric acid, a stainless steel material having the conductive smut may be subjected to anodic electrolysis. Since the conductive smut inferior in corrosion resistance is dissolved and removed by this anode electrolysis, it is realized that only the conductive smut in excellent corrosion resistance exists on the surface of the stainless steel as a conductive precipitate.

  Alternatively, electrolytic treatment in sulfuric acid (hereinafter, also referred to as “sulfuric acid electrolytic treatment”) may be performed instead of immersion in sulfuric acid. This electrolytic treatment may be performed by direct current or alternating current. Further, the stainless steel material may be directly energized as an electrode, or the stainless steel material may be indirectly energized without directly contacting the terminal from the power source. When the sulfuric acid electrolytic treatment is performed in this way, the smut inferior in corrosion resistance is dissolved during electrolysis on the surface of the base material, so that only those having excellent corrosion resistance are formed.

  In the case of sulfuric acid electrolytic treatment, as in the case of sulfuric acid washing, a conductive smut having excellent corrosion resistance and adhesion may be present on the surface of stainless steel by washing with water, preferably brushing or ultrasonic washing. Realized.

  The conductive smut thus formed by the sulfuric acid electrolysis treatment is shown in FIGS. 1 (1) and (2) according to component analysis and surface analysis using STEM-EDX and ESCA for the sample extracted by the blank replica method. As shown, it is an amorphous precipitate of 1 μm or less.

  Moreover, as shown in Table 1 showing the results of quantitative analysis of the outermost surface based on the narrow scan spectrum, the conductive smut contains O, S, Fe, Cr and C as main constituent elements.

The apparatus and measurement conditions used for this analysis are as follows.
Equipment used: Quantera SXM manufactured by ULVAC-PHI
X-ray source: mono-AlKα (hν = 1486.6 eV)
Detection depth: several nm (photoelectron extraction angle 45 °)
X-ray beam diameter: 100 μm in diameter (point analysis)
Charge neutralization gun: 1.0V, 20μA
Further, “*” of N and Mo shown in Table 1 means that the quantitative analysis could not be performed because the peaks of these elements overlapped with the peaks of other elements.

  The chemical composition of stainless steel, which is the base material on which the conductive smut to be analyzed is most precipitated, is as follows. C: 0.02 mass%, Si: 0.21 mass%, Mn: 1.8 mass%, P: 0.018 mass%, S: 0.002 mass%, N: 0.015 mass%, Cr: 17.5% by mass, Ni: 12.2% by mass, Mo: 2.20% by mass and the balance Fe and impurities.

  Of these main constituent elements in the conductive smut, Fe, Cr and C are derived from stainless steel, and O and S are mainly derived from sulfuric acid. Further, as shown in FIG. 1 (3), the crystalline state of the conductive smut is microcrystalline according to the electron diffraction of the sample extracted by the blank replica method, and the conductive smut is a multicrystal composed of microcrystals. It is a crystal.

  Although the conductive smut has been described above as an example, the method for generating the conductive precipitate according to the present invention on the surface of the conductive stainless steel base material is not limited to the above. Any method may be used as long as it removes the passive film with a non-oxidizing acid solution or the like and deposits conductive precipitates containing exposed stainless steel-derived substances.

  In addition, the present invention reprecipitates a conductive substance containing a substance originating from a base material, for example, dissolved as ions, once detached from the base material so as to be in electrical contact with the base material. This ensures electrical continuity between the conductive substance and the base material, suppresses local battery corrosion between the conductive substance and the base material, and changes the electrical continuity over time. Therefore, the reprecipitated material is not limited to O, S, Fe, Cr and C. For example, an element having a smaller ionization tendency than hydrogen, for example, steel containing copper may be brought into contact with an acid to precipitate copper on the surface of the steel, or by electrolysis of a stainless steel material including cathode electrolysis, Elements having a greater ionization tendency than hydrogen, such as Mo and W, may be reprecipitated on the substrate.

  Furthermore, when the conductive smut is reprecipitated by bringing the stainless steel material into contact with a solution containing a non-oxidizing acid, the solution containing the non-oxidizing acid may contain an oxidizing acid such as nitric acid.

  Generally speaking, when stainless steel is brought into contact with a solution mainly containing an oxidizing acid (for example, nitric acid), the surface of the stainless steel material is oxidized by the oxidizing acid, and a passive film is formed during pickling. For this reason, even if the element which becomes the basis of the conductive substance is once dissolved or released into the solution by contact with the solution, they are re-deposited on the non-conductive film instead of on the substrate, and further oxidation proceeds. And will be taken into the non-conductive film. Therefore, in the case of a solution mainly containing an oxidizing acid, the contact resistance of the stainless steel material is difficult to decrease. Further, in the case of a solution mainly containing an oxidizing acid, the smut tends not to adhere to the stainless steel, and also in this respect, it is difficult to reduce the contact resistance.

  However, even in the case where an oxidizing acid is contained in the solution that comes into contact with the stainless steel material, other components that suppress the formation of the passive film or remove the passive film are included. When the influence of the component is dominant, the non-conductive film is not formed on the stainless steel material, and a good conductive smut may be formed. For example, in the case of a mixed acid having a high dissolution rate, such as 5% hydrofluoric acid + 10% hydrochloric acid + 10% nitric acid, a non-conductive film is not easily formed during pickling, and the conductive material reprecipitates directly on the substrate.

  Thus, even an oxidizing acid generally recognized that it should not be used as a component of a solution for reprecipitating a conductive smut on a substrate for the purpose of forming a passive film, Depending on the composition of the entire solution, the conductive smut may be contained as a component of the solution for reprecipitation on the substrate.

2. Non-metallic conductive material coating layer Protects the conductive deposits according to the present invention deposited on the surface of the base material made of stainless steel, preferably deposited so as to cover, or uses the stainless steel material according to the present invention. For the purpose of further reducing the contact resistance of the conductive parts manufactured in this way, a conductive coating layer comprising a nonmetallic conductive material on a stainless steel material (hereinafter referred to as “nonmetallic conductive material coating layer”) May be formed.

  Non-metallic conductive materials include carbon black, conductive paint, and compound-based conductive materials such as ITO (Indium Tin Oxide) and WC. It can be achieved and is preferred. Accordingly, the coating layer containing graphitic carbon (hereinafter referred to as “graphitic carbon coating layer”) among the nonmetallic conductive material coating layers will be described in detail below.

  Since graphitic carbon is excellent in corrosion resistance, it is generally used in parts where corrosion resistance is required. In the present invention, the graphitic carbon contained in the graphite carbon coating layer may be any type of scaly graphite, scaly graphite, expanded graphite, natural graphite, artificial graphite, etc., as will be described later. From the viewpoint of maximizing the anisotropic conductivity of graphitic carbon, it is preferable to use a graphite having a shape with a large aspect ratio, such as scaly graphite or scaly graphite.

  Here, the graphitic carbon to be coated is required to be (1) highly conductive. Furthermore, a preferable manufacturing method (to be described later) (sliding a stainless steel material and a member containing graphitic carbon, scraping off the graphitic carbon by the relief effect of the uneven surface of the stainless steel surface and the conductive precipitate, From the viewpoint of (a method of adhering to the surface so that the a-axis direction is preferentially parallel to the surface), (2) it is preferably a soft material with high plasticity and easy to cover by sliding.

  From the viewpoint of satisfying these requirements at the same time, it is preferable to use graphitic carbon having high crystallinity as follows, and it is particularly preferable if the C-plane spacing of the graphitic carbon is d002 ≦ 3.390 mm.

(1) Electrical conductivity The electrical resistance value of highly crystalline graphitic carbon has anisotropy (Characteristics of graphite and technical development, Hitachi Powdered Metallurgy Technical Report No. 3 (2004), Table 1). The volume resistivity in the a-axis direction is as low as 4 to 7 × 10 ⁻⁵ Ωcm, and the c-axis direction is as high as ^{1 to} 5 × 10 ⁻¹ Ωcm. Since the electrical conduction in the a-axis direction is caused by conjugation of π bonds in sp2 bonds, the higher the crystallinity, the lower the volume resistivity. For this reason, by using graphitic carbon with high crystallinity of d002 ≦ 3.390%, the volume resistivity in the a-axis direction is particularly low, the volume resistivity of the entire graphitic carbon is lowered, and the contact resistance is reduced. Brought about. Taking into account that the average resistance of carbon is 1375 × 10 ⁻⁶ Ωcm (mechanical and metal material for young engineers Maruzen Co., Ltd., page 325), the low volume of graphitic carbon in the a-axis direction It is preferable to actively utilize the resistivity (4-7 × 10 ⁻⁵ Ωcm).

  Here, as described later, when a member containing highly crystalline graphite carbon is slid with respect to the stainless steel material, the graphite carbon is torn into a scaly powder, and the stainless steel provided with conductive precipitates. Adhere on steel. At this time, the graphitic carbon adhering to the stainless steel material is a scaly powder having a high aspect ratio, so that the a-axis direction is parallel to the stainless steel surface so that the influence of the shearing force due to sliding is minimized. There are more things that are oriented.

  In this case, the graphitic carbon coating layer forming the outermost surface of the stainless steel material is particularly easy to move charges in a direction parallel to the surface. For this reason, if another conductive part (hereinafter referred to as “other conductive part”) contacts the conductive part having this surface to form a contact, a base material made of stainless steel is contacted with the contact part. Even when there is no conductive deposit that is directly conducting and in contact with the graphitic carbon, the charge is deposited through the graphitic carbon coating layer, which has a particularly low volume resistivity. It is possible to quickly move to the vicinity and move to the base material (current collection phenomenon).

  That is, as long as other conductive parts come into contact with the highly crystalline graphitic carbon present on the surface of the conductive parts made of the stainless steel material according to the present invention, the conductive precipitates formed by this graphitic carbon coating layer are formed. Electrical contact is achieved by the current collecting action. This means that, in the stainless steel material according to the present invention, the electrical contact area has increased dramatically and has changed from a point contact to a state close to a surface contact. In particular, when a graphitic carbon with d002 ≦ 3.390 mm having a particularly low volume resistivity in the a-axis direction as described above is used, this current collection phenomenon becomes remarkable, and the contact resistance becomes extremely low. Such a conductive stainless steel material according to the present invention exhibits a resistance value equivalent to that of Ni plating at the surface portion thereof, and is realized to have conductivity equivalent to that of the Ni plating conductive stainless steel material.

The orientation of graphitic carbon in the graphitic carbon coating layer according to the present invention is the peak intensity I (110) of the (110) diffraction line in wide-angle X-ray diffraction from the graphitic carbon crystal in the graphitic carbon coating layer. And I (110) / I (004), which is the intensity ratio between the peak intensity I (004) of the (004) diffraction line. If this index I (110) / I (004) is less than 0.1, the a-axis direction of graphitic carbon in the graphitic carbon coating layer is substantially parallel to the stainless steel surface, and the a-axis direction of graphitic carbon. The low volume resistivity (4-7 × 10 ⁻⁵ Ωcm) can be actively utilized, that is, the current collection phenomenon can be effectively realized.

  As described above, it is assumed that the graphitic carbon coating layer realizes high conductivity as a conductive stainless steel material due to the current collection phenomenon. It is thought that it contributes to improving the electrical conductivity as a steel material.

  The graphitic carbon coating layer has a higher thermal conductivity than the passive film that is an oxide, particularly high crystallinity of the graphitic carbon, and when the a-axis direction of the graphitic carbon is substantially parallel to the stainless steel surface, It is assumed that a thermal conductivity of 100 W / mK or more is achieved in the direction parallel to the surface of the graphitic carbon coating layer. For this reason, it is expected that Joule heat generated in the conductive precipitate due to the current collecting phenomenon during use is quickly diffused into the graphitic carbon coating layer. Therefore, the volume resistivity of the conductive precipitate is prevented from increasing due to Joule heat, and the volume resistivity is prevented from increasing due to thermal denaturation of the conductive precipitate, and the conductivity as the conductive stainless steel material is suppressed. The decrease in the temperature is suppressed. In a power system connector in which a large current needs to be applied, the influence of Joule heat at the contact point becomes large. Therefore, when the stainless steel material according to the present invention is applied to this application, a particularly remarkable effect is expected.

(2) Plasticity (i) The plasticity of graphitic carbon becomes better as the C-plane spacing becomes smaller and the ideal crystal state approaches 3.354%. In the present invention, the graphitic carbon having a C-plane spacing of d002 ≦ 3.390 mm has a good plasticity, so that it is easy to coat the stainless steel surface.

  The coating method for realizing the graphitic carbon coating state as described above is not particularly limited. A dispersion liquid in which graphitic carbon is dispersed in an appropriate dispersion medium may be applied to the surface of stainless steel, and the dispersion medium may be removed by a technique such as volatilization, or may be formed by a technique such as sputtering or plasma CVD. Also good. Among such fixing methods, sliding adhesion is preferable from the viewpoint of productivity and the characteristics of the formed graphitic carbon. The method for forming the graphitic carbon coating layer by sliding adhesion will be described in detail below.

  Sliding a stainless steel material having conductive precipitates on the surface and a block-shaped member containing graphitic carbon, and scraping the surface layer of the member by the filed effect of the convex portions of the surface irregularities and conductive precipitates, Graphite carbon is adhered to the surface of the stainless steel material. When the graphitic carbon is coated in this manner, the graphitic carbon peels off from the block due to the shearing force due to sliding, and adheres to almost the entire surface of the stainless steel material with exposed conductive precipitates. To do. And since this graphitic carbon is scaly, the a-axis of the fixed graphitic carbon tends to be parallel to the surface of the steel material. For this reason, the above-mentioned current collecting action tends to occur, and a conductive stainless steel material having particularly excellent characteristics can be obtained.

  Here, the block-like member containing the graphitic carbon may contain other components such as a resinous binder in addition to the graphitic carbon, but from the viewpoint of increasing the conductivity of the graphitic carbon coating layer, It is preferable that it consists only of carbonaceous.

  The sliding conditions between the stainless steel material and the block of the member containing graphitic carbon are not particularly limited. The contact surface pressure and relative movement speed are determined in consideration of the surface roughness of the stainless steel material, the precipitation state of the conductive precipitates on the surface of the stainless steel material, the hardness of the graphitic carbon, the thickness of the graphitic carbon coating layer, and its characteristics. do it.

  The method of slidingly attaching graphite is not limited to the above sliding. For example, rolling is performed with a rolling machine with a roll material of graphite while applying back tension, the tool part of the milling machine is replaced with a graphite round bar, the graphite is rotated and pressed while applying a certain load, and graphite powder is adhered. A method such as rubbing the surface with a brush and rubbing with a cloth (felt etc.) to which graphite powder is adhered can be used.

  However, in order to improve the adhesion of the graphitic carbon coating layer of the stainless steel material, the surface roughness of the stainless steel material provided with the conductive precipitate is preferably 0.10 μm or more as the average surface roughness Ra. The upper limit of the surface roughness of the stainless steel material is not particularly limited from the viewpoint of adhesion. However, it is preferable to set the average surface roughness Ra to 1/10 or less of the plate thickness from the viewpoint of reducing the possibility of cracking when processed into a conductive part by press molding or the like. Usually, when surface roughness is imparted by pickling, the upper limit of the average surface roughness Ra is 2 to 3 μm. When applying the roughness by dull roll, a roughness of about several tens of μm can be sufficiently provided, but there are problems of saturation of the effect and cracking at the time of press molding, and about 0.1 to 3 μm is practically sufficient.

In addition, this surface roughness is a suitable aspect which should have only the surface which needs electrical conduction, when a conductive stainless steel material is comprised.
Moreover, the method of adjusting the stainless steel material to the above surface roughness is not particularly limited, and some examples are as follows.

  (1) Surface treatment: For example, a known etchant for etching a stainless steel material such as iron chloride is used, and etching is performed by setting the etchant concentration, the etchant temperature, the etching time, etc. according to the etching amount.

  (2) Polishing by belt grinding; surface polishing is performed using a belt grinder in which polishing grains such as diamond, silicon carbide, and alumina are embedded on the surface, and the surface roughness is adjusted to a predetermined level.

(3) Surface roughness control by adjusting the surface roughness of the rolling roll; the roughness of the rolling roll grinding finish is adjusted, and the surface roughness of the material to be rolled is adjusted.
The conductive deposit and nonmetallic conductive material coating layer described above are schematically shown in FIG.

3. Resinous Binder Layer When a graphitic carbon is coated on a substrate, a method is generally used in which a conductive paint containing graphitic carbon is prepared and this paint is applied. However, this paint is specifically a mixture of graphitic carbon powder and a resinous binder, and the resin that serves as the binder does not have electrical conductivity, so compared with the case of coating with graphite carbon alone, Contact resistance tends to increase.

  Therefore, in order to form a graphitic carbon coating layer and achieve particularly low contact resistance, it is desirable not to use a resinous binder when coating graphitic carbon. However, use of a resinous binder facilitates management of manufacturing conditions in the coating step, and therefore it may be preferable to use it from the viewpoint of productivity.

  Therefore, the resinous binder is not mixed with the graphitic carbon to form a conductive paint, but the resinous binder is applied by itself on a stainless steel material having conductive precipitates. Layer (hereinafter referred to as “resinous binder layer”), and then coated with graphitic carbon by sliding as described above to suppress the increase in contact resistance as much as possible. Carbon adhesion may be improved. In the present invention, the resinous binder layer is a part of the graphitic carbon coating layer, and the resinous binder layer obtained by laminating the graphitic carbon coating layer is also called a graphitic carbon coating layer.

  Even in this case, the coating amount of the resinous binder is desirably 2% by mass or less based on the mass of the graphitic carbon to be coated. This is due to the following reason. That is, when a member containing graphitic carbon is slid with respect to the stainless steel material on which the resinous binder layer is formed, the resinous binder layer is partially peeled by the shear stress. For this reason, even if the member containing graphitic carbon is composed of only graphitic carbon, the graphite carbon coating layer inevitably contains a region where the graphitic carbon and the resinous binder are mixed. As a result, the conductivity of the graphitic carbon coating layer is lowered by this region. Therefore, an upper limit is applied to the application amount of the resinous binder to suppress the influence of the decrease in conductivity due to this mixed region.

  The resinous binder to be used is not limited as long as it has excellent water resistance, oxidation resistance and chemical resistance, but PTFE (polytetrafluoroethylene), PVDF used for forming a catalyst layer of a fuel cell. Fluororesin binders such as (polyvinylidene fluoride) are preferred, and among these, PTFE is particularly preferred.

Examples for showing the superiority of the present invention will be described below.
1. Preparation of stainless steel plate (1) Steel plate Four types of general-purpose stainless steel plates available in the city were obtained as materials used in the examples. Table 2 shows the composition. The thickness of the obtained material is about 4 mm and / or 0.15 mm.

(2) Adjustment of surface roughness Surface roughness adjustment and surface roughness adjustment of the obtained conductive stainless steel sheet material are (A) surface treatment, (B) polishing by belt grinding, (C) rolling roll roughness. The method of roughing and cold rolling was used.

(A) Surface treatment raw material; ferric chloride anhydride (manufactured by Wako Pure Chemical Industries, Ltd.),
Pure water surface treatment solution; 45 Baume ferric chloride aqueous solution Surface treatment conditions; Washing and drying conditions after 40 seconds immersion of conductive stainless steel plate in 60 ° C treatment solution; And then thoroughly dried in an oven at 70 ° C.

(B) Polishing by Belt Grinding The surface was polished by a belt grinder in which abrasive grains were embedded on the surface, and adjusted to a predetermined surface roughness.

(C) Surface roughness control by adjusting the rolling roll surface roughness The roughness of the rolling roll grinding was adjusted to adjust the surface roughness of the material to be rolled.
2. Contact Resistance Measurement Method Contact resistance was measured using the apparatus schematically shown in FIG. 3 according to the method reported in papers (eg, Titanium Vol. 54 No. 4 P259). The conductive stainless steel plate material is sandwiched between carbon papers having an area of 1 cm ² (TGP-H-90 manufactured by Toray Industries, Inc.) and sandwiched between gold-plated electrodes. Next, a load (5 kgf / cm ² or 20 kgf / cm ² ) is applied to both ends of the gold-plated electrode, and then a constant current is passed between the electrodes, resulting in a voltage generated between the carbon paper and the conductive stainless steel plate. The drop was measured and the contact resistance was measured based on this result. In addition, since the obtained resistance value becomes the value which added the contact resistance of both sides sandwiched, it divided by 2 and evaluated by the contact resistance value per one side.
A digital multimeter (KEITLEY 2001 manufactured by Toyo Technica Co., Ltd.) was used to measure the current value and the voltage drop.

3. Measurement of interplanar spacing of coated graphite Interplanar spacing of graphite to be coated was determined by analyzing data measured using an X-ray diffractometer (RINT 2000, manufactured by Rigaku Corporation) using the Gakushin method. In the analysis, Carbon-X Ver1.4.2 carbon material X-ray diffraction data analysis program manufactured by Realize Science and Technology Center was utilized.

  Here, when the graphite was covered by sliding, the graphite block itself was measured by X-ray diffraction. In the case of coating, the graphite powder used was measured by X-ray diffraction. When the graphitic carbon was coated by vacuum deposition, it was difficult to measure the surface spacing as it was, so a thick sample was deposited until the d002 peak appeared clearly, and a sample exclusively for XRD measurement was prototyped. Used for measurement.

4). Measurement of Adhesion of Coated Graphite For the measurement of the adhesion of a prototype carbonaceous carbon-coated stainless steel sheet, a cross-cut tape peeling test was performed in accordance with JIS D0202-1988. Using cellophane tape (CT24 manufactured by Nichiban Co., Ltd.), the film was adhered to the film with the belly of the finger and then peeled off. Judgment is represented by the number of squares that do not peel out of 100 squares (10 × 10). The case where the functional layer does not peel is represented as 100/100, and the case where the functional layer peels completely is represented as 0/100.

5. Measurement of surface resistance The resistance value measured by the measurement method shown in FIG. 3 is a value including the contact resistance component to the carbon paper and the bulk resistance component in the thickness direction of the material, and is different from the surface resistance of the material itself. is there. Therefore, the surface resistance of the material according to the present invention was measured by the following apparatus and method, and compared with the surface resistance of the material obtained by the method according to the prior art (Patent Documents 1 to 3).
Measuring device: Mitsubishi Chemical Corporation resistivity meter (low resistivity meter) Lorester GP
Measurement probe: AS probe (4 probes, 5 mm between probes, applied pressure 210 g / piece)
Measurement method: Conforms to JIS K6911

Example 1
Test number 1 (commercially available SUS): SUS316L (4 mmt) obtained in the city was used.

Test numbers 2 to 6: An evaluation sample was prepared by the following procedure.
As the surface roughness adjustment, the surface roughness of the surface portion of the processed stainless steel plate was polished and adjusted by a belt grinding method. The obtained surface roughness was about 0.25 μm as Ra.

Then, in the present Example, the electroconductive smut which is an electroconductive precipitate was produced | generated by the method shown below.
(A) Sulfuric acid washing method It adjusted with the sulfuric acid solution shown in Table 3, and pickling conditions.

(B) Sulfuric acid electrolysis The sulfuric acid electrolysis was performed using a graphite electrode for the cathode electrode and stainless steel as the anode electrode. The sulfuric acid electrolytic treatment conditions are shown in Table 4. Electrolysis was performed after immersion in the solution for 60 seconds.

  Among the steel plates on which the conductive precipitates were formed in this way, a part (test number 14) was brought into contact with block graphite (diameter 100 mm d002 = 3.365 mm made by Nippon Steel Technocarbon) to adjust the surface roughness. By sliding the surface of the stainless steel plate, a graphitic carbon coating layer was formed.

  Table 5 shows the results of the above evaluation performed on the obtained test members.

  Here, the carbon dispersion paint of Comparative Prior Art 5 is obtained by adding carbon black at a ratio of 10% by weight to the acrylic aqueous resin diluted to 10% by weight and sufficiently dispersing it.

Based on the above results, the effectiveness of the present invention will be described below.
In Invention Examples 1 to 5 (Test Nos. 2 to 6), the contact resistance when a load of 5 kgf / cm ² is applied is less than ²⁰ mΩ · cm ² , and the test No. 1 according to the comparative prior art is performed. The resistance value is smaller than 1.

  The graphitic carbon coating fixing method of the present invention 5 shows that the contact resistance value is greatly improved as compared with the conventional technique.

(Example 2)
As a preferred range of the present invention, the following experiment was conducted in order to confirm a preferred interplanar spacing range of the graphitic carbon contained in the graphitic carbon coating layer.

  By preparing mesophase microspheres produced by heat treatment of petroleum pitch and bulk mesophase, which is the matrix of these microspheres, and carbonizing carbonized material, and then changing the graphitization heat treatment heating temperature and time, various aspects are obtained. Graphite carbon with spacing was adjusted.

  Table 6 shows the heating temperature and the interplanar spacing of the obtained graphitic carbon. Carbons 1 to 3 are outside the preferred range of the present invention, and carbons 4 to 9 are within the preferred range of the present invention.

  A graphite carbon coating layer is formed by sliding a block material composed of nine types of graphitic carbon shown in Table 6 on the contact portion of the conductive stainless steel plate subjected to the same treatment as that of the present invention 5 of Example 1. did. The results of evaluating the separator having this coating layer are shown in Table 7.

  It was shown that the 316L stainless steel plate coated with graphitic carbon having an interplanar spacing exceeding 3.390 mm has a lower contact resistance, and a better performance is obtained as the interplanar spacing d002 of the graphitic carbon is smaller.

  Based on the above results, a preferred range of the present invention is the one in which a graphitic carbon coating layer in which the interplanar spacing of graphitic carbon is d002 ≦ 3.390 mm is formed on a stainless steel plate on which conductive precipitates are formed. (Inventions 5 and 7-13).

(Example 3)
The following experiment was conducted to confirm a desirable range in the surface roughness of the stainless steel plate. The raw materials having various surface roughnesses were obtained by adjusting the abrasive roughness of the belt grinder and the ferric chloride etching time.

  Table 8 shows changes in contact resistance and fuel cell characteristics when the surface roughness is changed.

  When the average surface roughness Ra is smaller than 0.10 μm (Invention 15), the contact resistance is low, but the conductive precipitate and / or the graphite pressure-bonded to the upper part thereof peeled off.

If the average surface roughness Ra is 1.0 μm or more (Invention 16), cracks may occur at the severe R portion during press molding.
On the other hand, if Ra is in the range of 0.10 to 1.0 μm, particularly good low contact resistance can be obtained without worrying about cracks during press working.

Example 4
When performing a sulfuric acid electrolysis treatment on the stainless steel plate before the conductive precipitate is formed, O, S, Fe, Cr and the like covering the stainless steel plate surface by sliding the stainless steel plate using graphitic carbon as a counter electrode. Example for verifying the effect when a graphitic carbon coating layer is formed on an electrically conductive precipitate (conductive smut) which is a polycrystalline body comprising C as an essential constituent element. Indicates.

As conceptually shown in FIG. 4, a graphitic carbon coating layer was formed in a sulfuric acid solution.
A graphitic carbon coating layer was formed by applying a voltage of 0.4 V using stainless steel subjected to surface roughening with a belt grinder as a material to be treated. Table 9 shows the results of the above evaluation performed on the obtained stainless steel plate.

  As shown in Table 9, test numbers 23 and 24 obtained in this example had particularly low contact resistance.

(Example 5)
In order to confirm a preferable range in the present invention, the influence of the orientation of graphitic carbon in the graphitic carbon coating layer was investigated. Wide angle X-ray diffraction measurement is performed on the surface of the conductive stainless steel plate on which the graphitic carbon coating layer is formed, and the peak intensity I (110) of the in-plane diffraction line (110) plane of the graphitic carbon crystal obtained by the measurement is obtained. I (110) / I (004), which is the intensity ratio with the peak intensity I (004) of the diffraction line (004) plane in the C-axis direction, was used as an index that quantitatively represents the orientation.

The used material is SUS316L shown in Table 2. The sulfuric acid washing method shown in Table 2 was applied, and then graphitic carbon (d002 = 3.360 Å) was deposited by various methods shown in Table 10.
Table 10 shows the relationship between orientation and contact resistance.

  In the present invention, the contact resistance was low when the intensity ratio = I (110) / I (004) <0.10.

(Example 6)
A comparative study with the conventional method was carried out. The materials used in the examples were prepared according to the following procedure according to the patent literature.

(1) Method of Patent Document 1 The material used was austenitic stainless steel SUS304 shown in Table 2. Strike nickel plating with the following bath composition was performed as the base plating under the following conditions, the thickness of the plated product was measured, and the thickness of the base material was subtracted from this to determine the plating thickness.

<Bath composition>
Nickel chloride 240g / l
Hydrochloric acid 100ml / l
<Plating conditions>
Current density 3A / dcm ²
Time 15 seconds The thickness of the plating film formed by strike nickel plating was 0.44 μm. Hereinafter, this plated material is referred to as the conventional invention 1 material.

(2) Methods of Patent Documents 2 and 3 NAR304LA manufactured by Sumitomo Metals Naoetsu Co., Ltd. was used as the material. The composition of this material is shown in Table 11.

  A plate material having the composition shown in the above table was held at 800 ° C. for 24 hours to precipitate a Cu-rich phase. Thereafter, atmospheric annealing was performed, and pickling was performed using a mixed acid of 6% nitric acid + 2% hydrofluoric acid.

  The surface of the obtained material was observed with SEM-EPMA, and EDX analysis of Cu-rich phase Cu, Si, Mn was performed. Table 11 shows the ratio of Cu / (Si + Mn) calculated based on the measurement results of the contents. The material in which this Cu-rich phase is formed is referred to as Conventional Invention Material 2.

  The surface resistivity was compared for the inventive material and the inventive material. The results are shown in the table below.

  Since the material of the present invention does not require a process for increasing running costs such as plating treatment or heat treatment for precipitating a Cu-rich phase, a stainless steel material having high conductivity and suitable as a material for conductive parts is used. Can be provided economically.

It is a SEM image (1), a STEM image (2), and an electron beam diffraction image (3) of the conductive smut formed on the surface of SUS316. It is a figure which shows the outline | summary of this invention typically. It is a figure which shows the measurement principle of the contact resistance which concerns on an Example. It is a figure which shows the principle of the sulfuric acid electrolysis process which concerns on an Example.

Claims (8)

It originates from a base material made of stainless steel, and comprises a substance that has been subjected to at least one of reprecipitation and reattachment after the surface of the base material is once dissolved by pickling the base material with a pickling solution. Conductive deposits having electrical conductivity and deposited on the surface of the substrate, the conductive deposits being electrically connected to the substrate, and the conductive deposits being , O, S, Fe, including as constituent elements Cr and C, non-metal polycrystal der is, the conductive parts for stainless steel, wherein the conductive deposit is characterized that you have exposed. The stainless steel material for conductive parts according to claim 1, wherein a coating layer made of a nonmetallic conductive material is further formed on the stainless steel material provided with the conductive precipitate. The stainless steel material for conductive parts according to claim 2, wherein the coating layer contains graphitic carbon. The stainless steel material for conductive parts according to claim 3, wherein the interplanar spacing of graphitic carbon contained in the coating layer is d002≤3.390mm. I (110) is the intensity ratio of the peak intensity I (110) of the (110) diffraction line and the peak intensity I (004) of the (004) diffraction line in wide-angle X-ray diffraction from the graphitic carbon crystal in the coating layer. ) / I (004) is less than 0.1. The stainless steel material for conductive parts according to claim 4. The coating layer containing the graphitic carbon is formed by sliding a member containing the graphitic carbon with respect to a stainless steel material having the conductive precipitate. Stainless steel material for conductive parts . The coating layer containing the conductive precipitate and the graphitic carbon slides the member containing the graphitic carbon with respect to the base material, and the sulfuric acid is sulfated using the member containing the graphitic carbon as a counter electrode. The stainless steel material for conductive parts according to claim 6, which is formed on the surface of the base material by electrolytic treatment. The stainless steel material for conductive parts according to claim 6 or 7, wherein an average surface roughness of the stainless steel material provided with the conductive precipitate is 0.10 µm or more as Ra.