JP5315576B2 - Si-containing ferritic stainless steel conductive member and method for producing the same - Google Patents

Description

  The present invention relates to a Si-containing ferritic stainless steel conductive member and a method for producing the same, in which the contact electrical resistance is remarkably improved while maintaining the surface design, workability and spring characteristics of the ferritic stainless steel.

  Conventionally, copper-based alloys have been used for contact parts such as switches, relays, and connectors used in electronic parts and base materials for casings that require grounding characteristics. However, due to demands for reducing the weight and thickness of conductive members, stainless steel has been widely used as a base material for conductive materials instead of copper-based alloys.

A passive film showing low electrical conductivity exists on the surface of stainless steel, and this increases the contact electrical resistance, which causes a problem when a stainless steel member is used for a component requiring an electrical contact function. In particular, in a Si-containing ferritic stainless steel, an oxide of Si, such as SiO ₂ , is concentrated in the passive film during annealing, which significantly increases the contact electrical resistance.

  Even if the passive film of stainless steel is removed by pickling or mechanical polishing, it is regenerated in the air in a short time. For this reason, after removing the passive film formed on the surface of stainless steel, the base layer with excellent adhesion (for example, strike Ni plating) is applied while preventing its regeneration, and the upper layer is electrically conductive. Excellent tin-lead (solder), tin, precious metal silver, gold, etc. are plated and used with improved contact electrical resistance. In addition to metal plating, stainless steel (Patent Document 1) with excellent electrical conductivity provided by a carbonaceous coating layer, and stainless steel with a Cu rich layer deposited or Cu concentrated layer formed on the surface (Patent Document 1) 2) is known.

  As described above, when stainless steel is used as the base material for electrical contact parts, tin-lead (solder), tin, silver, gold, etc., which have excellent electrical conductivity, are plated on the stainless steel surface to reduce contact electrical resistance. There is a need to improve. However, in tin, whiskers (whisker-like crystals) are likely to occur during the plating process, and in the lead-tin alloy plating that can prevent the generation of whiskers, the draining process of lead becomes a problem. In addition, in silver plating, after being incorporated as a part, ion migration is likely to occur, and there is a possibility of causing contact failure or dielectric breakdown. Further, since gold often uses cyan as a plating solution, drainage treatment becomes a problem as in the case of lead, which is not environmentally preferable as a manufacturing process.

Gold plating is often used with a plating thickness of about 0.5μm, but the plating film has many defects, and when used in a highly corrosive environment, gold is eluted from the base metal. Promote. In order to prevent this, there is a measure to reduce the defects of the film by increasing the plating thickness to 3 μm or more, but this causes an increase in manufacturing cost.
In general, electrical contact parts are processed into target parts by press punching after plating on a stainless steel plate or coil material. However, there is an internal stress in the plating film, which may cause a warp after press molding and a desired shape may not be obtained. The higher the requirements for reducing the weight and thickness of the conductive member, the thinner the substrate thickness, and the greater the influence of the internal stress of the plating film.

  Furthermore, in stainless steel (Patent Document 1) to which excellent electrical conductivity is imparted by a carbonaceous coating layer, a stainless steel plate having a large number of pit surfaces is used as a base material, and the carbonaceous coating layer is provided on the base material surface. It has been. Stainless steel base material and carbonaceous coating layer are said to exhibit excellent adhesion due to the increased anchor effect and effective surface area due to pits, but the carbonaceous coating layer can follow press molding and other processing It is unthinkable, especially in shallow pits, the anchor effect is low, and it is considered that there are problems in adhesion and durability.

  Stainless steel with a Cu-rich layer precipitation or Cu-enriched layer formed on the surface (Patent Document 2) requires a long time for Cu precipitation heat treatment, resulting in an increase in manufacturing costs and stainless steel that does not contain Cu as a base material. Then there are many problems such as impossible processing.

JP 2001-243839 A JP 2001-234296 A

Therefore, the object of the present invention is to improve the passive film on the surface of the Si-containing ferritic stainless steel while maintaining the design properties of the appearance-like ferritic stainless steel surface, and to have excellent conductivity and low contact electric resistance. It is to provide a conductive member made of ferritic stainless steel containing Si.
Another object of the present invention is to modify the passive film on the surface of the Si-containing ferritic stainless steel while maintaining the design properties of the appearance-like ferritic stainless steel surface, and to have excellent conductivity and low contact electric resistance. It is providing the manufacturing method of the Si containing ferritic stainless steel electroconductive member which has this.
Still another object of the present invention is that there are few problems with the treatment liquid drainage treatment, and it is less likely to cause ion migration, poor contact, or dielectric breakdown due to the plating film after being assembled as a part, and the manufacturing cost is low. Another object of the present invention is to provide a method for producing a conductive member made of Si-containing ferritic stainless steel that generates little internal stress during processing.

In the present invention, after removing Si oxide concentrated in the surface passive film of Si-containing ferritic stainless steel, at least one of fluoride ions and lithium ions is chemically and / or electrochemically applied to the passive film. In addition, the iron in the passive film is preferentially eluted to form a chromium oxide and hydroxide-based film, thereby improving the electronic conductivity and corrosion resistance of the passive film, and leaving it in the atmosphere. The present invention also provides a Si-containing ferritic stainless steel conductive member that does not cause time-series degradation of surface contact electrical resistance.
In the present invention, after removing Si oxide concentrated in the surface passive film of Si-containing ferritic stainless steel, at least one of fluoride ions and lithium ions is chemically and / or electrochemically applied to the passive film. In addition, the iron in the passive film is preferentially eluted to form a chromium oxide and hydroxide-based film, thereby improving the electronic conductivity and corrosion resistance of the passive film, and leaving it in the atmosphere. The present invention also provides a method for producing a Si-containing ferritic stainless steel conductive member that does not cause time-series degradation of surface contact electrical resistance.

The present invention provides the following Si-containing ferritic stainless steel conductive member and method for producing the same.
1． In a conductive member made of ferritic stainless steel containing Si, the Cr / Fe ratio (atomic%) in the passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 2 or more, and surface X-ray photoelectron spectroscopy Stainless steel conductive member characterized in that the Si content in the passive state film analyzed by the method (XPS) is 0.1 atomic% or less.
2． 2. The stainless steel conductive member according to 1 above, wherein Cr / Fe (atomic%) is 3 or more.
3． 3. The stainless steel conductive member according to 1 or 2 above, wherein the F concentration in the passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 0.1 atomic% or more.
Four. 4. The stainless steel conductive member according to any one of 1 to 3 above, wherein the Li concentration in the passive film analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is 0.01 atomic% or more.
Five. 5. The stainless steel conductive member according to any one of 1 to 4 above, wherein the stainless steel is SUS430, SUS434, SUS430J1L, or SUS444.
6． The stainless steel conductivity according to any one of 1 to 5 above, wherein the stainless steel is bright annealed finish (BA), pickled finish (2D), pickled and lightly rolled (2B), or temper rolled finish steel Element.
7． Production method of Si-containing ferritic stainless steel conductive member including the following step (A), step (B) and / or step (C):
(A) The process of removing Si from the passive film (B) The process of injecting fluorine into the passive film (C) The process of injecting lithium into the passive film.
8. The method for producing a stainless steel conductive member according to 7 above, further comprising (D) a step of eluting iron in the passive film.
9． 9. The method for producing a stainless steel conductive member according to 8 above, wherein the steps (A), (B) and (C) are repeated once or more in this order, and finally the step (D) is performed.
Ten. The manufacturing method of the stainless steel electroconductive member of any one of said 7-9 including the process of heat-processing stainless steel before a process (A).
11． The manufacturing method of the stainless steel electroconductive member of any one of said 7-9 including the process of heat-processing stainless steel before a process (B).
12． The manufacturing method of the stainless steel electroconductive member of any one of said 7-9 including the process of heat-processing stainless steel before a process (C).
13. 9. The method for producing a stainless steel conductive member according to 8 above, wherein the step (D) is performed before the step (B).
14. 14. The stainless steel conductive member according to any one of 7 to 13 above, wherein the step (A) includes a step of subjecting stainless steel to anodic electrolysis or alternating electrolysis in an aqueous solution of an alkali metal compound that exhibits alkalinity when dissolved in water. Manufacturing method.
15． 15. The method for producing a stainless steel conductive member according to any one of 7 to 14, wherein the step (B) includes a step of subjecting stainless steel to anodic electrolysis in an aqueous solution containing fluoride ions.
16． The stainless steel conductive member according to any one of 7 to 15 above, wherein the step (B) includes a step of immersing stainless steel in an aqueous solution of hydrogen fluoride or an aqueous solution containing an oxidizing agent and fluoride ions. Production method.
17． 17. The method for producing a stainless steel conductive member according to any one of 7 to 16, wherein the step (C) includes a step of cathodic electrolysis or immersion treatment of stainless steel in an aqueous solution or a non-aqueous solution containing lithium ions.
18． 18. The process according to any one of 8 to 17 above, wherein the step (D) comprises a step of immersing stainless steel in an aqueous solution containing nitric acid and fluoride ions, a thioglycolate salt, or a triammonium citrate solution. A method for producing a stainless steel conductive member.
19. 19. The method for producing a stainless steel conductive member according to any one of 7 to 18 above, wherein the stainless steel is SUS430, SUS434, SUS430J1L, or SUS444.

The Si-containing ferritic stainless steel conductive member of the present invention is excellent in conductivity, exhibits low contact electric resistance, and has high contact sensitivity. The Si-containing ferritic stainless steel conductive member of the present invention maintains a low contact electric resistance for a long period of time and has excellent corrosion resistance.
In addition, according to the present invention, the original surface finish state of stainless steel is not changed in appearance, and there are few problems of drainage treatment such as plating treatment. Therefore, it is possible to provide a Si-containing ferritic stainless steel conductive member that is less likely to cause contact failure and dielectric breakdown, and has a low manufacturing cost.

  The stainless steel used in the present invention is a ferritic stainless steel containing Si as a component. Since this Si is contained in the raw material of stainless steel and is also used as a deoxidizer in the steel making process, it is contained as a component in ferritic stainless steel. Specific examples thereof include SUS430, SUS430J1L, SUS434, and SUS444. Surface finish conditions include bright annealing finish (BA), pickling finish (2D), light rolling finish after pickling (2B), temper rolling finish, and the like.

The Si-containing ferritic stainless steel conductive member of the present invention can be produced, for example, by a method including the following step (A), step (B) and / or step (C).
(A) The process of removing Si from the passive film (B) The process of injecting fluorine into the passive film (C) The process of injecting lithium into the passive film.
The present invention preferably further includes (D) a step of eluting iron in the passive film.
In order to remove Si from the passive film, anodic electrolysis or alternating electrolysis may be carried out in an aqueous solution of an alkali metal compound that is dissolved in water and exhibits alkalinity. Examples of the alkali metal compound include sodium hydroxide, sodium carbonate, trisodium phosphate, potassium hydroxide, alkali metal hydroxides, carbonates, phosphates, etc., which are alkalis that dissolve in water and exhibit alkalinity. Any metal compound can be used.
In order to inject fluorine into the passive film, stainless steel may be dipped (chemical treatment) or electrolytic treatment (electrochemical treatment) in an aqueous solution containing fluoride ions.
In order to inject lithium into the passive state film, stainless steel may be dipped (chemical treatment) or electrolytically treated (electrochemical treatment) in an aqueous solution or a non-aqueous solution containing lithium ions.
In order to preferentially elute iron in the passive film, it may be dipped in a nitric acid solution, an aqueous solution containing fluoride ions, or in a thioglycolate or triammonium citrate solution.
Before this treatment, it is effective to perform a heat treatment in the air or in an inert gas atmosphere such as nitrogen gas or Ar gas. This is because Fe is concentrated on the outermost surface layer of the passive film by heat treatment, and then complexed with Fe easily by the immersion treatment in the above solution and eluted from the passive film. is there. By preferentially eluting Fe from the passive film, the film is modified to a composition mainly composed of Cr oxide and hydroxide.

As described above, by injecting Li and F, which are electron carriers, into the passive film, the electron conductivity of the passive film is improved, and the contact electrical resistance of the conventional passive film is significantly improved. can do.
Furthermore, the corrosion resistance is improved by modifying the passive film to a composition mainly composed of Cr oxide and hydroxide, and the film does not change even when left in the atmosphere for a long time, and the surface contact electrical resistance is deteriorated over time. It can be prevented or suppressed.

(A) Step of removing Si from the passive film In order to remove Si from the passive film, a method of anodic electrolysis or alternating electrolysis in an aqueous solution of an alkali metal compound exhibiting alkalinity by dissolving in water is preferable. It is. The aqueous solution should be an alkali metal hydroxide, carbonate, phosphate, such as sodium hydroxide, sodium carbonate, trisodium phosphate, potassium hydroxide, etc., which can be dissolved in water to show alkalinity. All can be used. These compounds may be used alone or as a mixture. The concentration of these alkali metal compounds is preferably 0.001 kmol · m ⁻³ or more and is suitable up to the saturation concentration. The aqueous solution temperature is preferably room temperature to 90 ° C, more preferably 30 ° C to 70 ° C. The electrolysis current density is preferably 0.01 to 50 A / dm ² , more preferably 0.1 to 10 A / dm ² , and the electrolysis time is preferably 5 to 600 seconds, more preferably 10 to 300 seconds.
In the case of alternating electrolysis, the electrolysis time of each cycle of anode electrolysis and cathode electrolysis is preferably 10 ms to 120 s, more preferably 100 ms to 60 s, within the range of the above current density and aqueous solution temperature. The total electrolysis time is preferably 5 to 600 seconds, more preferably 10 to 300 seconds.
In anodic electrolysis and alternating electrolysis, the higher the current density, the shorter the treatment is possible. However, when the concentration of the alkali metal compound is increased, the stainless steel is dissolved in a passive state in the high current density region, and originally Therefore, it is preferably 0.1 to 10 A / dm ² , 10 to 120 seconds, and more preferably about 60 seconds. By these electrolytic treatments, the Si oxide in the passive film becomes metasilicate. Ions and orthosilicate ions are discharged from the passive film.

(B) Step of injecting fluorine into passive film As fluoride ion source in fluoride injection, any compound can be used as long as it is hydrofluoric acid or a fluorine compound that dissolves in water to generate fluoride ions it can. For example, alkali metal fluoride (for example, sodium fluoride, potassium fluoride, etc.), ammonium fluoride, antimony trifluoride, copper fluoride, sodium hydrogen difluoride, potassium hydrogen difluoride, and the like can be given. Of these, alkali metal fluorides, particularly sodium fluoride and potassium fluoride are preferred.

In order to electrochemically inject fluoride, stainless steel is subjected to anodic electrolysis in an aqueous hydrogen fluoride solution or in an acidic aqueous solution obtained by adding nitric acid, sulfuric acid, phosphoric acid or the like to the fluoride ion source. The pH of the treatment liquid is preferably 0 to 3, more preferably 0 to 2. The fluoride concentration is preferably 0.001 kmol · m ⁻³ or more and is suitable up to the saturation concentration. The aqueous solution does not need to be heated, and can be used, for example, at 10 to 30 ° C., preferably at room temperature. The electrolysis current density is preferably 0.01 to 50 A / dm ² , more preferably 0.5 to 10 A / dm ² , and the electrolysis time is preferably 5 to 600 seconds, more preferably 10 to 60 seconds. The higher the current density, the shorter the treatment is possible, but the higher the fluoride ion concentration, the more the stainless steel may be passively dissolved in the high current density region, which may damage the original appearance. Is 0.1 to 10 A / dm ² , 10 to 120 seconds, preferably about 60 seconds is suitable.

In order to chemically inject fluoride, immersion treatment is performed in a solution in which an oxidizing agent is added to hydrofluoric acid and the above fluoride ion source. The fluoride concentration is preferably 0.001 kmol · m ⁻³ or more and is suitable up to the saturation concentration.
Examples of the oxidizing agent include nitric acid, potassium permanganate, hydrogen peroxide acid, and the like. The concentration is preferably 0.1 to 10 kmol · m ⁻³ , more preferably 1 to 5 kmol · m ⁻³ . The aqueous solution temperature is preferably 20 to 80 ° C, more preferably 30 to 60 ° C. The dipping time is preferably 10 seconds to 10 minutes, more preferably 1 to 10 minutes.

(C) Step of Injecting Lithium into Passive Film Any compound can be used as the lithium ion source in lithium injection as long as it is a lithium compound that dissolves in water or a non-aqueous solvent to generate lithium ions. For example, examples of the oxygen compound include lithium hydroxide and lithium oxide, examples of the halide include lithium chloride, lithium bromide, and lithium iodide. Examples of the oxyacid salt include lithium nitrate and lithium sulfate. Examples of the non-aqueous solvent include ethanol, methanol, dimethyl ether, diethyl ether, methyl ethyl ether and the like. A mixture of water and a water-miscible non-aqueous solvent can also be used.

The concentration of the lithium compound in the aqueous solution or non-aqueous solution containing the lithium ion source is preferably 0.01 kmol · m ⁻³ or more, and is suitable up to a saturated solution. The solution does not need to be warmed and is preferably 10-30 ° C., for example room temperature. In the case of immersion treatment, the treatment time is preferably 10 seconds to 10 minutes, more preferably 30 seconds to 5 minutes. In the case of cathodic electrolysis, the current density is preferably 0.01 A / dm ^{2 to} 10 A / dm ² , more preferably 0.1 to 5 A / dm ² , and the electrolysis time is preferably 10 seconds to 10 minutes, more preferably 20 seconds to About 5 minutes is appropriate.

  An effective method for injecting fluoride ions and lithium ions into the passive film is to repeat the above-described steps (B) and (C). Any of the order of the step (B) and the step (C) may be performed first, but it is preferable that the step (B) is performed first and then the step (C) is performed.

(D) The process of eluting iron in the passive film To preferentially elute the iron in the passive film, immerse it in a nitric acid solution, thioglycolate, triammonium citrate solution or an aqueous solution containing fluoride ions. You just have to process it.
When a nitric acid solution is used, the concentration is preferably 1 kmol · m ⁻³ or more, and is suitable up to a saturated solution. The aqueous solution temperature is preferably from room temperature to 90 ° C, more preferably from 30 ° C to 70 ° C. The immersion time is preferably 10 seconds to 120 minutes, more preferably 30 seconds to 60 minutes.
As the thioglycolate, in the case of thioglycolic acid, the mass% is preferably 0.1% to 90%, more preferably 1 to 50%. The solution temperature does not need to be heated, and can be used, for example, at 10 to 50 ° C., preferably at room temperature. The immersion time is preferably 5 seconds to 120 minutes, more preferably 10 seconds to 30 minutes. The ammonium thioglycolate and monoethanolamine thioglycolate are preferably 0.1% to 50%, more preferably 1% to 30% as mass%. The solution temperature can be, for example, 10 to 50 ° C., preferably at room temperature.

The concentration of triammonium citrate is preferably 0.1 kmol · m ⁻³ or more, and is suitable up to a saturated concentration. The aqueous solution temperature is preferably room temperature to 50 ° C, more preferably 30 ° C to 40 ° C. The dipping time is preferably 10 seconds to 120 minutes, more preferably 30 seconds to 30 minutes.
When using an aqueous solution containing fluoride ions, hydrofluoric acid or an aqueous solution made acidic by adding an acid to the fluoride ion source is suitable. The pH is preferably 0-3, more preferably 0-2. The fluoride concentration is preferably 0.001 kmol · m ⁻³ or more, and is suitable up to the saturation concentration. Examples of the acid for adjusting pH include nitric acid, sulfuric acid, phosphoric acid, and the like. The concentration is preferably 0.01 to 10 kmol · m ⁻³ , more preferably 0.1 to 5 kmol · m ⁻³ . The aqueous solution temperature is preferably 10 to 80 ° C, more preferably 20 to 60 ° C. The dipping time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 10 minutes.

  Furthermore, in order to efficiently preferentially elute iron in the passive film, before the immersion treatment in the aqueous solution containing nitric acid, thioglycolate and fluoride ions in step (D), the atmosphere or nitrogen Alternatively, it is desirable to perform heat treatment in an inert gas atmosphere such as Ar. A suitable heat treatment temperature is preferably 100 ° C. to 600 ° C., more preferably 140 ° C. to 500 ° C., and the treatment time is preferably 1 second to 30 minutes, more preferably 10 seconds to 20 minutes.

By this heat treatment, an iron concentrated layer is formed on the outermost surface layer of the passive film, and in the subsequent step (D), Fe and complex ions are easily formed and eluted into the solution.
By this treatment, the passive film has a Cr-based composition, so the corrosion resistance is improved, and even if left in the air for a long time, the film does not change, and the time-series degradation of surface contact electrical resistance is considered to be small. It is done.

Hereinafter, the present invention will be described in detail with reference to examples.
Example 1

Contact electrical resistance measurement method Contact electrical resistance was measured using an electrical contact simulator (CRS-113-mold) manufactured by Yamazaki Seiki Laboratory Co., Ltd. The measurement probe used was a PU-05 gold wire contactor, 0.5 mmΦ. The applied constant current was 10 mA. The contact load was measured with a maximum contact load of 100 gf and a moving distance of 1 mm, and a contact load-contact electric resistance distribution curve was obtained.

Specimen SUS430BA (BA: bright annealed material) having a thickness of 0.2 mm was used as the specimen. This was cut into 15 mm × 50 mm to obtain test pieces.
Experimental method After immersing the test piece in acetone and subjecting it to ultrasonic cleaning, it was subjected to anodic electrolytic treatment at 1 A / dm ² for 1 minute in 20 g / L NaOH aqueous solution (30 ° C), and then 1 kmol · m ^{− 3} Cathodic electrolysis was performed at 1 A / dm ² for 1 minute in a LiOH aqueous solution (25 ° C.), and the contact electrical resistance was measured. In addition, after each electrolytic treatment and immersion treatment, distilled water washing and cold air drying steps are included. Fig. 1 shows the contact pressure-contact electrical resistance distribution curve of the material and the specimen after treatment.

  In the material (SUS430BA), although the behavior that the contact electrical resistance decreases instantaneously is recognized, the contact electrical resistance remains at 300 mΩ or more up to a contact load of 100 gf. On the other hand, the contact electrical resistance of the test piece subjected to the above treatment started to decrease from a contact load of about 45 gf (decrease load) and decreased to about 80 mΩ at a contact load of 100 gf. Thus, it has been found that the contact electrical resistance is lowered even if only Li as an electron carrier.

Example 2
Specimen Same as used in Example 1.
Experimental Method After immersing the test piece in acetone and subjecting it to ultrasonic cleaning, it was subjected to anodic electrolysis at 20 A / dm ² for 1 minute in 20 g / L NaOH aqueous solution (30 ° C.), and then 2.5 mass%. Immersion treatment was performed for 1 minute in an HF aqueous solution (25 ° C.), and the contact electric resistance was measured. In addition, after each electrolytic treatment and immersion treatment, distilled water washing and cold air drying steps are included. The contact pressure-contact electric resistance distribution curve of the test piece after the treatment is shown in FIG.

  The contact electrical resistance of the test piece subjected to the above treatment began to decrease from about 20 gf (decrease load), and decreased to about 60 mΩ at a contact load of 100 gf.

Example 3
Specimen Same as used in Example 1.
Experimental Method After immersing the test piece in acetone and subjecting it to ultrasonic cleaning, in a mixed solution of 20 g / L NaOH and 30 g / L Na ₃ PO ₄ · 12H ₂ O (30 ° C.) at 1 A / dm ² After performing an anodic electrolytic treatment for 1 minute, atmospheric heating was performed at 300 ° C. for 1 minute. Subsequent immersion treatment in 2.5% HF aqueous solution (25 ° C) for 1 minute, cathodic electrolytic treatment at 1A / dm ² for 1 minute in 1kmol · m ^-3 LiOH aqueous solution (25 ° C), and contact electrical resistance Was measured. In addition, after each electrolytic treatment and immersion treatment, distilled water washing and cold air drying steps are included. FIG. 3 shows a contact pressure-contact electric resistance distribution curve of the test piece after the treatment.

  The contact electrical resistance of the test piece subjected to the above treatment started to decrease from a contact load of about 5 gf (decrease load), and decreased to about 30 mΩ at a contact load of 100 gf.

Example 4
Specimen Same as used in Example 1.
Experimental method After immersing the test piece in acetone and subjecting it to ultrasonic cleaning, the anode is 1A / dm ² for 1 minute in a mixed solution (25 ° C) of 20g / L NaOH and 40g / L Na ₂ CO ₃ After the electrolytic treatment, atmospheric heating was performed at 300 ° C. for 5 minutes. Thereafter, in 1.5kmol · m ^-3 HNO ₃ and 5 × 10 ^-3 kmol · m ^-3 mixed solution of NaF (25 ° C.), has been dipped in 10 minutes. Furthermore, immersion treatment in 2.5 mass% HF aqueous solution (25 ° C.) for 10 seconds, cathodic electrolysis treatment at 1 A / dm ² in 1 kmol · m ⁻³ LiOH aqueous solution, and 30 mass% HNO ₃ , 60 An immersion treatment was performed at a temperature of 10 minutes. The contact electrical resistance of the test piece after the treatment was measured. In addition, after each electrolytic treatment and immersion treatment, distilled water washing and cold air drying steps are included. Fig. 4 shows the contact pressure-contact electrical resistance distribution curve.

  The contact electrical resistance of the test piece began to decrease from about 7 gf at the contact load (decrease load), and decreased to about 20 mΩ at a contact load of 100 gf. In this way, it was found that the contact electrical resistance was greatly reduced by removing the Si oxide in the passive film, further reducing the iron concentration in the film, and injecting Li and F as electron carriers.

Example 5
Specimen Same as used in Example 1.
Experimental Method After immersing the test piece in acetone and subjecting it to ultrasonic cleaning, a mixed solution of 20 g / L NaOH, 30 g / L Na ₃ PO ₄ .12H ₂ O, 40 g / L Na ₂ CO ₃ ( The anode was subjected to an anodic electrolysis treatment at 1 A / dm ² at 25 ° C. for 1 minute, followed by atmospheric heating at 300 ° C. for 5 minutes. Thereafter, an immersion treatment was performed in a 10% by mass thioglycolic acid aqueous solution at 25 ° C. for 5 minutes, a 30% by mass HNO ₃ aqueous solution in 60 ° C. for 10 minutes. Then, 2.5 in mass% in aqueous HF solution (25 ° C.) 1 minute immersion treatment and 1 kmol · m ^-3 LiOH aqueous solution in the cathode electrolytic treatment for 1 minute at 1A / dm ^2, further 30% by weight HNO ₃ solution Then, immersion treatment was performed at 60 ° C. for 5 minutes. In addition, after each electrolytic treatment and immersion treatment, distilled water washing and cold air drying steps are included. FIG. 5 shows a contact pressure-contact electric resistance distribution curve.

The contact electrical resistance of the test piece suddenly decreased from a contact load of about 5 gf (decrease load). This behavior is comparable to the contact pressure-contact electric resistance distribution curve of the semi-bright Ni plating film (base material SUS430) generally used as an electric contact part shown in FIG.
As a result of analyzing the passive film of the test piece by X-ray photoelectron spectroscopy (XPS), Si having high electrical resistance from the passive film by anodic electrolysis in a mixed aqueous solution of NaOH, Na ₃ PO ₄ and Na ₂ CO ₃ It was found that the oxide could be completely removed, and that the iron concentrated layer formed on the outermost surface layer of the passive film by atmospheric heating could be removed by dipping treatment in a thioglycolic acid aqueous solution and a nitric acid solution. With this treatment, the Si content in the passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) was below the detection limit (0.1 atomic%). The Si concentration in the material (SUS430) passive film was 2.5 atomic%. It was also found that the Fe concentration in the passive film decreased significantly, the Cr concentration increased, and the Cr / Fe ratio (atomic%) of the material increased to 5.5 after processing, compared to 0.5. . In this way, the Cr / Fe ratio increased and the corrosion resistance of the film was improved, so there was no deterioration in contact electrical resistance over time even in a 50% test at a constant temperature and humidity environment of 95% RH and 60 ° C. Conceivable.
In addition, the presence of Li and F in the passive film can be confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) by HF immersion treatment and cathodic electrolysis in LiOH, and X-ray photoelectron spectroscopy As a result of obtaining F concentration by (XPS), it was 1.2 atomic%. As a result of various studies, it was found that the contact electrical resistance decreased at an F concentration of 0.1 atomic% or more. As for Li, it was 0.5 atomic% when the test piece after treatment was analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). As a result of various investigations, it was found that the contact electric resistance was lowered when contained in the passive film at 0.01 atomic% or more.

Example 6
Test materials SUS430 (2B), SUS434 (BA), SUS430J1L (BA), and SUS444 (BA) were used as test materials. This was cut into 15 mm × 50 mm to obtain test pieces. The test piece was immersed in acetone and subjected to ultrasonic cleaning, and then treated by the method shown in Example 5. From the contact pressure-contact electrical resistance distribution curve of the material and the treated specimen, the contact load (decrease load) at which the contact electrical resistance decreases to 300 mΩ or less was determined. Table 1 shows the material (before treatment) and contact resistance after treatment (shows the drop load).

  As described above, even if the surface state of the material of SUS430 steel is different or other steel types such as SUS434, SUS430J1L, and SUS444, the contact electric resistance is lowered.

2 is a contact pressure-contact electric resistance distribution curve of a test piece obtained by treating a SUS430BA material in the process shown in Example 1. FIG. 3 is a contact pressure-contact electric resistance distribution curve of a test piece obtained by processing a SUS430BA material in the process shown in Example 2. FIG. 3 is a contact pressure-contact electric resistance distribution curve of a test piece obtained by treating a SUS430BA material in the process shown in Example 3. FIG. 6 is a contact pressure-contact electric resistance distribution curve of a test piece obtained by processing a SUS430BA material in the process shown in Example 4. FIG. 6 is a contact pressure-contact electric resistance distribution curve of a test piece obtained by treating a SUS430BA material in the process shown in Example 5. FIG. It is a contact pressure-contact electric resistance distribution curve of a semi-bright Ni plating film (base material SUS430) generally used as an electric contact part.

Claims (19)

  In a conductive member made of ferritic stainless steel containing Si, the Cr / Fe ratio (atomic%) in the passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 2 or more, and surface X-ray photoelectron spectroscopy Stainless steel conductive member characterized in that the Si content in the passive state film analyzed by the method (XPS) is 0.1 atomic% or less.   2. The stainless steel conductive member according to claim 1, wherein Cr / Fe (atomic%) is 3 or more.   3. The stainless steel conductive member according to claim 1, wherein the F concentration in the passive film analyzed by surface X-ray photoelectron spectroscopy (XPS) is 0.1 atomic% or more.   The stainless steel conductive member according to any one of claims 1 to 3, wherein a Li concentration in the passive film analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) is 0.01 atomic% or more.   The stainless steel conductive member according to any one of claims 1 to 4, wherein the stainless steel is SUS430, SUS434, SUS430J1L, or SUS444.   The stainless steel conductive material according to any one of claims 1 to 5, wherein the stainless steel is a bright annealing finish (BA), a pickling finish (2D), a light rolling finish after pickling (2B), or a temper rolled finish steel. Sexual member. Production method of Si-containing ferritic stainless steel conductive member including the following step (A), step (B) and / or step (C):
(A) The process of removing Si from the passive film (B) The process of injecting fluorine into the passive film (C) The process of injecting lithium into the passive film.   8. The method for producing a stainless steel conductive member according to claim 7, further comprising (D) a step of eluting iron in the passive film.   9. The method for producing a stainless steel conductive member according to claim 8, wherein the steps (A), (B) and (C) are repeated once or more in this order, and the step (D) is finally performed.   The manufacturing method of the stainless steel electroconductive member of any one of Claims 7-9 including the process of heat-processing stainless steel before a process (A).   The manufacturing method of the stainless steel electroconductive member of any one of Claims 7-9 including the process of heat-processing stainless steel before a process (B).   The manufacturing method of the stainless steel electroconductive member of any one of Claims 7-9 including the process of heat-processing stainless steel before a process (C).   9. The method for producing a stainless steel conductive member according to claim 8, wherein the step (D) is performed before the step (B).   The stainless steel conductive material according to any one of claims 7 to 13, wherein the step (A) includes a step of subjecting stainless steel to anodic electrolysis or alternating electrolysis in an aqueous solution of an alkali metal compound that exhibits alkalinity when dissolved in water. Manufacturing method of member.   15. The method for producing a stainless steel conductive member according to any one of claims 7 to 14, wherein the step (B) includes a step of subjecting stainless steel to anodic electrolysis in an aqueous solution containing fluoride ions.   The stainless steel conductive member according to any one of claims 7 to 15, wherein the step (B) includes a step of immersing the stainless steel in an aqueous solution of hydrogen fluoride or an aqueous solution containing an oxidizing agent and fluoride ions. Manufacturing method.   The method for producing a stainless steel conductive member according to any one of claims 7 to 16, wherein the step (C) includes a step of cathodic electrolysis or immersion treatment of stainless steel in an aqueous solution or a non-aqueous solution containing lithium ions. .   18. The step (D) includes a step of immersing stainless steel in an aqueous solution containing nitric acid and fluoride ions, a thioglycolate salt, or a triammonium citrate solution. Method for producing a stainless steel conductive member.   The method for producing a stainless steel conductive member according to any one of claims 7 to 18, wherein the stainless steel is SUS430, SUS434, SUS430J1L, or SUS444.

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