JP2001089865A - Stainless steel sheet low in contact resistance and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stainless steel in which contact resistance is reduced by the precipitation of a Cu-enriched phase or the high concentration of Cu in the surface layer. SOLUTION: In this stainless steel sheet, stainless steel containing Cu of >=1.0 wt.%, and in which a secondary phase essentially consisting of Cu is dispersedly precipitated into a matrix in the ratio of >=0.2 vol.% is used as a base material 1, and a passive film 3 is deposited on the surface of the base material 1 other than the surface part in which the second phase 2 essentially consisting of Cu has been precipitated. Alternatively, also, by concentrating Cu contained in the outermost surface layer or the passive film 3 in the stainless steel sheet in such a manner that the weight ratio of the Cu concentration to the Si concentration and Mn concentration, i.e., Cu/(Si+Mn) is controlled to >=0.5, its contact resistance can be reduced. Moreover, in the case the exposure of the second phase essentially consisting of Cu and the concentration of Cu on the passive film or the outermost surface layer are combined, its contact resistance is furthermore reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel sheet used for electric parts, electronic parts and the like which require a low contact resistance and a method for producing the same.

[0002]

2. Description of the Related Art Conventional stainless steels represented by SUS430 and SUS304 exhibit excellent corrosion resistance due to a passive film formed on the surface. The passive film is made of Cr
And oxide and hydroxide films containing Si, Mn, etc. Oxides and hydroxides constituting the passivation film have a high specific electrical resistance and poor conductivity. For example, battery can bodies, spring materials for fixing batteries, etc., electric circuit contacts such as electromagnetic relays, etc. Not preferred for use. With an emphasis on conductivity, Cu alloys are used as materials for electric circuit contacts. However, Cu alloys have insufficient corrosion resistance,
There is also a problem of conductivity deterioration due to rusting. Therefore, in order to utilize the excellent corrosion resistance inherent in stainless steel, a method of partially eliminating a defect derived from a passive film by Ni plating or the like has been partially adopted (Japanese Patent Application Laid-Open No. 63-145793).

[0003]

The Ni plating is applied to the surface of the stainless steel plate by electroplating or electroless plating, and both are expensive plating methods. Further, since a plating step is required, the number of steps is increased, and the burden of waste liquid treatment is also increased. Furthermore, if the adhesion of the formed Ni plating layer to the stainless steel sheet surface is insufficient,
Peeling occurs during molding and handling, and the advantages of the Ni plating layer are lost. The present invention has been devised to solve such a problem. By modifying a surface layer including a passivation film of a stainless steel sheet, it is not necessary to add a process such as plating, and the stainless steel sheet itself is not required. The purpose of the present invention is to reduce the contact resistance.

[0004]

In order to achieve the object, the stainless steel sheet of the present invention has a Cu content of 1.0% by weight or more.
The base material is a stainless steel in which a second phase mainly composed of Cu is dispersed and precipitated in a matrix at a rate of 0.2% by volume or more, and a surface portion where a second phase mainly composed of Cu is precipitated is excluded. A passive film is formed on the surface of the substrate. The passivation film may be formed on the entire surface of the stainless steel plate. In this case, the contact resistance is increased by enriching the Cu contained in the outermost layer or the passive film of the stainless steel sheet so that the weight ratio of the Cu concentration to the Si concentration and the Mn concentration Cu / (Si + Mn) becomes 0.5 or more. Can be lowered. Furthermore, when the exposure of the second phase mainly composed of Cu (hereinafter, referred to as Cu-rich phase) and the concentration of Cu in the passivation film or the outermost layer are combined, the contact resistance is further reduced.

[0005] As the stainless steel sheet, various stainless steel sheets such as ferritic, austenitic, martensitic, and duplex stainless steels are used without any particular restrictions on the type of steel as long as the steel contains 1.0% by weight or more of Cu. You. By performing bright annealing in an atmosphere having a dew point of −30 ° C. or less as final annealing, Cu is concentrated on the surface layer of the stainless steel sheet. Alternatively, after final annealing in an air atmosphere, Cu can be concentrated by pickling with a mixed acid such as hydrofluoric acid-nitric acid or sulfuric acid-nitric acid. When a stainless steel sheet in which a Cu-rich phase is precipitated is used as a substrate, it is necessary to reduce the contact resistance on the surface of the stainless steel sheet by performing an aging treatment at, for example, about 800 ° C. for 1 hour or more in the process up to final annealing. The amount of precipitation is obtained.

[0006]

The passivation film is effective in improving the corrosion resistance of stainless steel, but it is made of an oxide or the like having a high specific electric resistance, and is a cause of increasing the contact resistance of the stainless steel plate. Therefore, the present inventors have investigated and studied a method of modifying the passivation film by including a conductive substance in the passivation film or concentrating it on the surface layer of stainless steel to reduce the contact resistance. . During the investigation process,
It has been found that Cu-containing stainless steel exhibits low contact resistance. Among them, Cu containing 1.0% by weight or more and C
In stainless steel in which the u-rich phase was dispersed and precipitated at a rate of 0.2% by volume or more, the contact resistance was remarkably reduced. The content of Cu contained in the stainless steel as the base material is set to 1.0% by weight or more from the viewpoint of ensuring a surface Cu concentration and / or a Cu-rich phase effective for reducing the contact resistance. As the Cu content increases, the amount of the Cu-rich phase dispersed and precipitated increases, and the Cu concentration of the passivation film or the surface layer progresses.
The addition of u causes a reduction in hot workability, which may impair the manufacturability. Therefore, the upper limit of the Cu content is 5% by weight.
It is preferable that

[0007] Based on this finding, C contained in the base material
Investigating and studying the effects of the u-content and the dispersed and precipitated Cu-rich phase on the contact resistance, the Cu-rich phase 2 was deposited on the surface layer of the substrate 1 as schematically shown in FIG. The passivation film 3 containing Cr, Si, Mn, etc. was not formed thereon, and the pinhole 4 opened in the passivation film 3 was not formed.
Revealed that the Cu-rich phase 2 was exposed to the atmosphere. From this result, it is inferred that the exposed Cu-rich phase 2 became a part of the conduction path and the contact resistance decreased. The contact resistance is remarkably reduced when the ratio of the Cu-rich phase 2 precipitated on the substrate 1 becomes 0.2% by volume or more.

[0008] Even when a Cu-rich phase is not precipitated on the surface layer of the base material, the outermost layer or the passivation film is formed so that the weight ratio of the Cu concentration to the Si concentration and the Mn concentration Cu / (Si + Mn) becomes 0.5 or more. When Cu was concentrated, the contact resistance showed a low value. The low contact resistance is presumed to be due to the fact that the concentrated Cu is dispersed in the outermost layer or the passive film as metal Cu or an oxide having a low specific electric resistance. Further, when Cu is concentrated in the passivation film 3 or the outermost layer in addition to the exposure of the Cu-rich phase 2, the contact resistance shows a lower value. The heat treatment for dispersing and precipitating the Cu-rich phase 2 varies depending on the Cu content.
By performing aging treatment at about 00 ° C. for 1 to 24 hours, the fine Cu-rich phase 2 can be dispersed and precipitated.

A stainless steel sheet having a Cu-rich phase 2 dispersed and precipitated on the surface of a base material or a passive steel film 3 or a stainless steel sheet having Cu concentrated on the outermost layer has a dew point of -30 ° C. or less when subjected to bright annealing as final annealing. It is manufactured by bright annealing in an annealing atmosphere of When the dew point of the annealing atmosphere is lowered, the oxidation reaction is suppressed, and the increase in the amount of the metal oxide having a high specific electrical resistance is suppressed. As a result, the metal Cu or Cu oxide is concentrated in the passive film 3 or the outermost layer. On the other hand, in an annealing atmosphere having a dew point exceeding −30 ° C., the diffusion of Si, Mn, etc. from the inside of the base material to the surface layer is promoted as the oxidation of Si, Mn, etc. progresses, and a large amount of metal oxide having a high specific electric resistance is produced. , A passivation film 3 or the outermost layer is formed.

[0010] Instead of bright annealing, Cu can be concentrated in the passive film 3 or the outermost layer by air annealing and pickling. Cr, F when stainless steel plate is annealed in air
Scales containing oxides such as e, Mn, Si, and Cu are formed on the surface of the steel sheet, but the scales are removed by pickling, and then the passivation film 3 is formed. At this time, when the anodized stainless steel sheet is electrolytically pickled, Cu or a Cu-rich phase present on the steel sheet surface after the scale exfoliation is preferentially eluted from the base material by the electrolytic reaction. Therefore, the passive film 3 having a low Cu concentration is formed on the surface of the steel sheet after the electrolytic pickling. On the other hand, in pickling using a mixed acid such as hydrofluoric acid-nitric acid or sulfuric acid-nitric acid, there is no preferential elution of Cu or a Cu-rich phase, and the passivation film 3 generated after pickling has a reduced Cu concentration. Absent. As the mixed acid, there is no particular restriction on the type and concentration of the acid, but generally a mixed solution of sulfuric acid, hydrofluoric acid and nitric acid having a concentration of about 10% by volume is used.

[0011]

EXAMPLES Some of the stainless steel sheets having the compositions shown in Table 1 were kept at 800 ° C. for 24 hours to precipitate a Cu-rich phase, and then subjected to bright annealing or atmospheric annealing. In bright annealing,
Annealing atmospheres with different dew points were used. Electrolytic pickling using 5% nitric acid and 6%
Pickling was performed using a mixed acid of% nitric acid + 2% hydrofluoric acid. The remaining various stainless steel sheets were similarly bright annealed without being subjected to a Cu-rich phase precipitation treatment, or pickled after being air-annealed.

[0012]

The surface of each stainless steel plate was observed with a transmission electron microscope, and the ratio of the Cu-rich phase precipitated in the matrix was calculated. Further, the concentrations of Cu, Si and Mn with respect to the total amount of the analyzed elements were determined by glow emission analysis, and the weight ratio Cu / (Si + Mn) of the passive film or the outermost layer was calculated. Further, a contact electrode made of pure gold and a measuring terminal were brought into contact with the surface of the test piece, and a contact resistance was measured after a load of 100 g was applied to the measuring terminal to obtain a contact resistance.

As can be seen from the investigation results in Table 2, SUS304 (test numbers 1 and 2), SUS430 (test number 3) and SUS430 in which the Cu content does not reach 1.0% by weight.
J1L (test number 4) showed a high contact resistance of 20Ω or more. Even if Cu is added in an amount of 1.0% by weight or more,
The weight ratio Cu / (Si + Mn) of the passivation film or the outermost layer is less than 0.5, or the precipitation amount of the Cu-rich phase is 0.2
The stainless steel plates (test numbers 5 to 7) that did not reach volume% still showed high values of contact resistance. On the other hand, a stainless steel sheet having a Cu content of 1.0% by weight or more was used as a base material, and the precipitation amount of a Cu-rich phase was 0.2% by volume or more, or the weight ratio Cu / (Si + Mn) of the outermost layer was 0.5%. The stainless steel plates of the present invention described above (test numbers 8 to 17) all exhibited sufficiently low contact resistance. Above all, C
u-rich phase 0.2% by volume or more and Cu / (Si + Mn)
Stainless steel sheets satisfying both of ≧ 0.5 (test numbers (10, 13 to 15, 17)) showed lower contact resistance.

[0015]

[0016]

As described above, in the stainless steel sheet of the present invention, a Cu-rich phase having a Cu content of 1.0% by weight or more and 0.2% by volume or more is dispersed and precipitated.
(Si + Mn) stainless steel in which the passive film or the outermost layer is Cu-enriched so as to satisfy ≧ 0.5 as a base material,
The contact resistance is greatly reduced irrespective of the passivation film on the surface. For this reason, the corrosion resistance inherent in stainless steel is ensured, and materials used as various electric parts, electronic parts, and the like are provided by utilizing low contact resistance.

[Brief description of the drawings]

FIG. 1 is a schematic view of a surface of a stainless steel plate in which a Cu-rich phase is exposed through a pinhole of a passive film.

Claims (4)

[Claims] 1. A stainless steel containing 1.0% by weight or more of Cu and a second phase mainly composed of Cu dispersed and precipitated in a matrix at a rate of 0.2% by volume or more. A stainless steel sheet having a low contact resistance, wherein a passivation film is formed on the surface of the base material excluding a two-phase precipitation portion. 2. A passive film or outermost layer comprising a stainless steel containing 1.0% by weight or more of Cu as a base material and a weight ratio of Cu concentration to Si concentration and Mn concentration of Cu / (Si + Mn) of 0.5 or more. A stainless steel sheet having a low contact resistance, characterized by having a surface formed thereon. 3. A final annealing of a stainless steel sheet containing at least 1.0% by weight of Cu is performed by bright annealing in an atmosphere having a dew point of −30 ° C. or less, whereby a weight ratio of Cu concentration to Si concentration and Mn concentration is Cu / ( A method for producing a stainless steel sheet having a low contact resistance, wherein Cu is concentrated in a passive film or an outermost layer so that (Si + Mn) becomes 0.5 or more. 4. A stainless steel sheet containing 1.0% by weight or more of Cu is finally annealed in an air atmosphere, and then pickled with a mixed acid to obtain a Cu / (Si + Mn) weight ratio of Cu concentration to Si concentration and Mn concentration. A method for producing a stainless steel sheet having a low contact resistance, comprising enriching Cu in a passivation film or an outermost layer so as to be 0.5 or more.