KR20190040574A - Austenitic stainless steel excellent in electric conductivity and method of manufacturing the same - Google Patents

Abstract

The present invention relates to an austenite-based stainless steel having an excellent electric conductivity and a method for manufacturing the same, which are capable of removing a non-conductive film formed on the surface of the stainless steel, forming a new conductive film, and securing a superior conductive surface layer. According to an embodiment of the present invention, the austenite-based stainless steel having excellent electric conductivity comprises: a stainless steel basic material composed of 0.1 wt% or lower of C, 0.1-1.0 wt% of Si, 0,1-2.0 wt% of Mn, 15-24 wt% of Cr, 6-12 wt% of Ni, 2.5 wt% or lower of Mo, 0.3 wt% or lower of N, 0.003 wt% or lower of S, remaining Fe, and other inevitable impurities; and a passive film formed on the stainless steel basic material. The thickness of the passive film is greater than 0 nm and less than or equal to 4 nm. The atomic weight ratio of Ni to Fe in an area with a thickness of 2 nm or lower from the surface of the passive film is 0.1 or higher.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel having excellent electrical conductivity and a method of manufacturing the same. 2. Description of the Related Art Austenitic stainless steels,

The present invention relates to an austenitic stainless steel having excellent electrical conductivity and a method of manufacturing the same. More particularly, the present invention relates to an austenitic stainless steel which is excellent in electrical conductivity and which can remove a nonconductive film formed on a surface of a stainless steel and form a new conductive film, An austenitic stainless steel having excellent conductivity, and a method of manufacturing the same.

Electrical contacts are used in a wide variety of electronic products. The most important characteristic is electrical conductivity. Copper (Cu) and nickel (Ni) are excellent in surface electrical conductivity, but copper (Cu) or nickel (Ni), which is a soft metal, can not be used solely for the electrical contact portion requiring a hardness higher than a certain level.

On the other hand, stainless steels having a relatively high hardness use stainless steel thin plates less than 0.3 mm in thickness for electrical contacts, and these stainless steel thin plates are manufactured through a cold rolling and bright annealing process. Stainless steel cold-rolled coils of less than 0.3 mm thickness are subjected to cold annealing in an oxidizing atmosphere to prevent surface defects such as difficulties in control of coil tension, %) And a heat treatment in a reducing atmosphere containing nitrogen.

Since the heat treatment of the brass annealing is performed in a reducing atmosphere, the stainless steel sheet is formed into a stainless steel sheet having a passive film having a thickness of several nm, which has a smooth surface state and is not a high temperature oxidation scale of several micrometers thick formed in a normal oxidizing atmosphere. Since the passive film formed through the brightness annealing process exhibits a high resistance value, it is difficult to use the stainless steel alone in the electrical contact portion without plating the conductive material. In order to use it for the electric point contact application, the interface contact resistance and the electric conductivity A post-treatment process is required.

In order to solve this problem, a stainless steel having high hardness is plated with a conductive metal such as copper (Cu) or nickel (Ni), and the manufacturing cost and manufacturing time are increased due to the additional process for plating, It is difficult to mass-produce it.

Embodiments of the present invention provide an austenitic stainless steel capable of removing a nonconductive film formed on a stainless steel surface and forming a new conductive film to secure an excellent contact resistance.

According to an embodiment of the present invention, there is also provided a method of manufacturing an austenitic stainless steel excellent in electrical conductivity.

The austenitic stainless steel excellent in electrical conductivity according to an embodiment of the present invention may contain 0.1% or less of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 15 to 24% of Cr, Ni : 6 to 12%, Mo: 2.5% or less, N: 0.3% or less, S: 0.003% or less, the balance Fe and other unavoidable impurities, and a passive film formed on the stainless steel base material, The coating has a thickness of more than 0 nm and 4 nm or less, and a Ni / Fe atomic ratio of 0.1 or more in a thickness region of 2 nm or less from the surface of the passive film.

According to an embodiment of the present invention, the Cr ratio in the Cr / base material in the thickness region of 2 nm or less from the surface of the passive film may be 1.0 or more.

According to an embodiment of the present invention, the ratio of Cr hydroxide / Cr oxide in the thickness region of 2 nm or less from the surface of the passive film may be 0.6 or more.

According to an embodiment of the present invention, the interface contact resistance of the passive film may be 20 m? Cm ² or less.

According to an embodiment of the present invention, there is provided a method of manufacturing an austenitic stainless steel having excellent electrical conductivity, which comprises 0.1% or less of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 15 to 24% , 6 to 12% of Ni, 2.5% or less of Mo, 0.3% or less of N, 0.003% or less of S, the balance Fe and other unavoidable impurities to form a first passive film, Removing the first passivation film, and forming a second passivation film on the stainless steel base material.

According to an embodiment of the present invention, the step of removing the first passivation film may be electrolytically treated in a sulfuric acid solution having a concentration of 10 to 20%.

According to an embodiment of the present invention, the temperature of the sulfuric acid solution may be 40 to 80, and the current density of the electrolytic treatment may be 0.05 to 0.45 A / cm ² .

Also, according to an embodiment of the present invention, the step of removing the first passive film may be performed for 45 to 60 seconds in a hydrochloric acid solution having a concentration of 10 to 15%.

According to an embodiment of the present invention, the step of forming the second passivation film may include a step of forming a second passivation film on the surface of the first passivation film by a nitric acid solution having a concentration of 10 to 20% or a nitric acid solution having a concentration of 10 to 20% Stainless steel base material can be immersed.

Also, according to an embodiment of the present invention, the temperature of the nitric acid solution and the mixed acid solution may be 40 to 60 ° C.

According to an embodiment of the present invention, in the step of forming the second passive film, the thickness of the second passive film may be greater than 0 and less than 4 nm.

According to an embodiment of the present invention, the step of forming the second passive film may be performed such that the Ni / Fe atomic ratio in the thickness region of 2 nm or less from the surface of the second passive film is 0.1 or more have.

According to an embodiment of the present invention, the step of forming the second passive film may be performed such that the Cr ratio in the Cr / base material in the thickness region of 2 nm or less from the surface of the passive film is 1.0 or more .

According to an embodiment of the present invention, the step of forming the second passivation film may include forming a second passivation film so that a ratio of Cr hydroxide / Cr oxide in a thickness region of 2 nm or less from the surface of the second passivation film is 0.6 or more .

According to the embodiment of the present invention, it is possible to manufacture austenitic stainless steel having excellent conductivity without performing a separate plating process on the heat-treated stainless steel by the brightness annealing, thereby reducing the manufacturing cost and improving the productivity.

1 is a cross-sectional view of an austenitic stainless steel having excellent electrical conductivity according to an embodiment of the present invention.
FIGS. 2 to 4 are cross-sectional views for explaining a method of manufacturing austenitic stainless steel excellent in electrical and electrical conductivity according to an embodiment of the present invention.
5 is a schematic view of an apparatus for manufacturing austenitic stainless steel according to an embodiment of the present invention.
6 and 7 are photographs of a passive film of stainless steel according to Example 3 and Comparative Example 3, respectively, observed using a transmission electron microscope (TEM).

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

Since the stainless steel cold rolled steel sheet produced through the brass annealing process exhibits a high contact resistance due to the passive oxide film on the surface formed after annealing, the passive film must be removed in order to use the brass annealed stainless steel as the electrical contact.

If the nonconductive passivation oxide film is removed and then exposed to air, a nonconductive oxide film of several nm thickness is formed again by bonding with oxygen in the air. The oxidation film produced in the air is not suitable for use in applications where the content of Fe is high and the thickness thereof is thick and conductivity is required. Therefore, after the non-conductive oxide film is removed, an oxide film having conductivity should be formed in a state in which contact with air is suppressed. The conductive oxide film should be thin, and the content of Cr and Ni should be higher than other metal elements in the oxide film.

To this end, the present invention provides an austenitic stainless steel excellent in electrical conductivity which does not require the plating of a conductive material by removing the nonconductive oxide film existing on the surface of stainless steel and forming an oxide film having excellent conductivity, and a method for manufacturing the same .

1 is a cross-sectional view of an austenitic stainless steel having excellent electrical conductivity according to an embodiment of the present invention.

1, an austenitic stainless steel excellent in electrical conductivity according to an embodiment of the present invention includes a stainless steel base material 10 and a passive film 30 formed on a stainless steel base material 10.

The stainless steel base material 10 contains, by weight%, 0.1% or less of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 15 to 24% of Cr, 6 to 12% , N: not more than 0.3%, S: not more than 0.003%, the balance Fe and other unavoidable impurities.

Hereinafter, the reasons for limiting the numerical values of the alloy component content in the examples according to the present invention will be described. Unless otherwise stated, the unit is wt% (wt%).

The content of carbon (C) is 0.1% or less. Carbon as austenite phase stabilizing element is more effective in stabilizing the austenite phase, but when it is contained in an amount of 0.1% or more, the corrosion resistance of the layer lacking chromium (Cr) is impaired.

The content of silicon (Si) is 0.1 to 1.0%. Silicon in steel is added as deoxidizer in steelmaking process, and it is effective to improve corrosion resistance of steel by forming silicon oxide in passive film when bright annealing process is performed when adding a certain amount. However, There is a problem of deteriorating ductility.

The content of manganese (Mn) is 0.1 to 2.0%. As manganese in the steel is added as austenite phase stabilizing element, the austenite phase is stabilized to 0.1% or more, but when it is added excessively, the corrosion resistance is impaired, so it is limited to 2.0% or less.

The content of chromium (Cr) is 15.0 to 24.0%. Chromium in steel is an essential element for improving the corrosion resistance. In order to secure corrosion resistance in the atmospheric environment, chromium is required to be added in an amount of 15.0% or more. However, when added excessively, chromium is an element for producing ferrite phase and excessive delta (δ) ferrite phase remains, It is preferable to limit 24.0% to the upper limit.

The content of nickel (Ni) is 6.0 to 12.0%. Nickel in steel is an essential element as an austenite phase stabilizing element and is added by 6.0% or more because it facilitates the concentration of chromium (Cr) to form a conductive passive film by suppressing extreme dissolution of the base material during sulfuric acid electrolysis or hydrochloric acid immersion. However, excessive use of expensive nickel limits the cost to 12.0%.

The content of molybdenum (Mo) is 2.5% or less. Molybdenum in the steel has the effect of improving the corrosion resistance and workability, but excessive addition is accompanied by an increase in cost, so it is limited to 2.5% or less.

The content of nitrogen (N) is 0.3% or less. As the amount of nitrogen in the steel increases as the austenite phase stabilizing element is added, the effect of stabilizing the austenite phase and the corrosion resistance such as the formal dislocation are improved, but when it is added excessively, the hot workability is lowered.

The content of sulfur (S) is 0.003% or less. Since sulfur in the steel is a trace element of impurities, it is segregated at crystal grain boundaries and is the main element causing cracking during hot rolling, so it is limited to 0.003% or less, which is as low as possible.

The austenitic stainless steel excellent in electrical conductivity according to an embodiment of the present invention includes a stainless steel base material 10 and a conductive passivation film 30 formed on the stainless steel base material 10, (t ₁ ) may be more than 0 and 4 nm or less.

As the thickness t ₁ of the passive film 30 is reduced to 4 nm or less, the passive film having semiconductor characteristics close to normal insulation can be thinned to reduce the contact resistance.

The ratio of the Ni / Fe atomic ratio of the thickness (t ₂ ) region 35 of ₂ nm or less from the surface of the passive film 30 is 0.1 or more.

The Cr / base material Cr ratio of the thickness (t ₂ ) region 35 of ₂ nm or less from the surface of the passive film 30 is 1.0 or more.

Further, the ratio of Cr hydroxide / Cr oxide in the thickness (t ₂ ) region 35 of ₂ nm or less from the surface of the passive film 30 is 0.6 or more.

In the process of manufacturing the austenitic stainless steel excellent in electrical conductivity according to an embodiment of the present invention, the nonconductive passive film formed by the heat treatment of the brightness annealing is removed, and in the region adjacent to the surface of the stainless steel base material 10, Fe Eluted and Cr and Ni are concentrated. The ratio of Ni / Fe in the thickness (t ₂ ) region 35 of ₂ nm or less from the surface of the passive film 30 may be 0.1 or more, Cr / The Cr ratio in the base material is 1.0 or more, and the Cr hydroxide / Cr oxide ratio is 0.6 or more.

The formation of an insulating void in the passive film 30 can be suppressed as the ratio of Ni / Fe in the passive film 30, the Cr ratio in the Cr / base material, and the Cr hydroxide / Cr oxide ratio are increased. Accordingly, the interface contact resistance of the passive film 30 can be 20 m? Cm 2 (100 N / cm 2) or less. More preferably, the interface contact resistance of the passive film 30 is 15 m? Cm 2 (100 N / cm 2) or less.

FIGS. 2 to 4 are cross-sectional views illustrating a method of manufacturing austenitic stainless steel excellent in electrical conductivity according to an embodiment of the present invention. 5 is a schematic view of an apparatus for manufacturing austenitic stainless steel according to an embodiment of the present invention.

Hereinafter, a process for manufacturing an austenitic stainless steel having excellent electrical conductivity according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG.

According to an embodiment of the present invention, there is provided a method of manufacturing an austenitic stainless steel having excellent electrical conductivity, which comprises 0.1% or less of C, 0.1 to 1.0% of Si, 0.1 to 2.0% of Mn, 15 to 24% Of the stainless steel base material 10 containing 6 to 12% of Ni, not more than 2.5% of Mo, not more than 0.3% of N and not more than 0.003 of S and the balance of Fe and other unavoidable impurities, ); Removing (100) the first passive coating (20); And forming (300) a second passivation film (30) on the stainless steel base material (10).

The reason for limiting the numerical value of the alloy component content is as described above.

Referring to FIG. 2, a stainless steel cold rolled thin plate is manufactured through hot rolling, annealing, pickling, cold rolling, and light annealing steps of the stainless steel casting having the alloy composition. In the cold rolling step, the stainless steel plate is rolled by using a Z-mill cold rolling mill, and then the cold rolled thin plate is subjected to a light annealing treatment in the heat treatment step to form a first passive coating 20 on the surface of the cold rolled thin plate .

The heat treatment of the brass annealing means that annealing is performed in a non-oxidizing atmosphere. In the case of a coil of 0.3 mm or less, a brass annealing heat treatment is performed in a reducing atmosphere containing hydrogen and nitrogen to prevent coil tension control and surface defects. The hydrogen content is preferably 70% or more.

Since the annealing for the brightness annealing is performed in a reducing atmosphere, a passive film having a thickness of several nm and having a smooth surface state can be formed. Cr-Fe oxide, Mn oxide, Si oxide and the like can be formed on the passive film.

The interface contact resistance is increased by the first passive film 20 having a thickness of several nm formed on the surface of the cold rolled thin plate which has undergone the heat annealing process of the brightness annealing.

Therefore, in order to use the thin-walled stainless steel thin plate as the electrical contact portion application, the first non-conductive passive film 20 present on the surface of the thin stainless steel sheet must be removed to form a new conductive film.

Accordingly, a method for manufacturing an austenitic stainless steel excellent in electrical conductivity according to the present invention comprises the steps of: removing a first nonconductive passive film 20 on a stainless steel base material 10 through a process described below, 30 can be formed.

In the step 100 of removing the first passive film 20, electrolytic treatment is performed in a sulfuric acid solution having a concentration of 10 to 20% or immersion in a hydrochloric acid solution having a concentration of 10 to 15% to form a first passive film (20) can be removed.

Referring to FIG. 3, the first passive film 20 can be completely removed through the sulfuric acid electrolytic treatment or the hydrochloric acid immersion process. In the region adjacent to the surface of the stainless steel base material 10 from which the first passive film 20 has been removed, The Fe may be eluted selectively to concentrate Cr and Ni on the surface of the stainless steel base material 10. At this time, the present invention containing 6.0 to 12.0% by weight of Ni can suppress the extreme dissolution of the stainless steel base material 10 due to the presence of Ni.

The electrolytic treatment in the sulfuric acid solution may be performed at a current density of 0.05 to 0.45 A / cm ² , and the temperature of the sulfuric acid solution may be 40 to 80 ° C.

If the concentration of the sulfuric acid solution is less than 10%, the removal of the first passivation film 20 on the surface may be insufficient. On the contrary, even if the concentration exceeds 20%, the removal effect of the first passivation film 20 becomes saturated and is not economical. Therefore, the concentration of the sulfuric acid solution is preferably controlled to 10 to 20%.

If the temperature of the sulfuric acid solution is too low, it is difficult to remove the first passive film 20 on the surface. Conversely, if the temperature is too high, safety concerns and damage to the stainless steel base material 10 may be caused. .

If the current density is lower than 0.05 A / cm ² , the dissolution of the passive film may be removed uniformly over the entire surface to reduce the contact resistance reduction efficiency. If the current density is higher than 0.45 A / cm ² , And the surface concentration effect of Ni are hardly expected.

The immersion in the hydrochloric acid solution can be carried out for 45 to 60 seconds in a 10 to 15% hydrochloric acid solution.

If the concentration of the hydrochloric acid solution is less than 10%, the removal of the first passive film 20 on the surface may be insufficient. On the contrary, even if the concentration exceeds 15%, the removal effect of the first passive film 20 is saturated and is not economical. Therefore, it is preferable to control the concentration of the hydrochloric acid solution to 10 to 15%.

If the immersion time is less than 45 seconds, it is difficult to remove the first passive film 20, and if it exceeds 60 seconds, the stainless base material 10 may be damaged.

After the step 100 of removing the first passive film 20, the second passive film 30 is formed on the stainless steel base material 10 through the step 200 of washing the stainless steel.

4, in the step 300 of forming the second passivation film 30 on the stainless steel base material 10, a new film of Cr (4 nm) is formed on the surface of the stainless steel base material 10 in which Cr and Ni are concentrated, A second passivation film 30 having a thickness t ₁ is formed.

The newly formed second passive film 30 is formed by Cr and Ni concentrated on the surface of the stainless steel base material 10 and has a thickness t ₂ region 35 ) Of 0.1 or more, a Cr / Cr ratio in the base material of 1.0 or more, and a Cr hydroxide / Cr oxide ratio of 0.6 or more.

In the step 300 of forming the second passivation film 30, the stainless steel base material 10 is immersed in a mixed solution of 10 to 20% nitric acid solution or 10 to 20% nitric acid and 5% It can be immersed.

If the concentration of nitric acid is too low, the effect of decreasing the contact resistance is lowered because the efficiency of Cr and Ni on the surface is increased or the efficiency of forming a new passive film is low. Even if the concentration is increased, the effect of increasing the Cr / Ni ratio on the surface is saturated or rather, The erosion of the base material 10 is severe and the contact resistance reducing effect is lowered. Therefore, the concentration of the nitric acid solution is preferably limited to 10 to 20%.

Hydrofluoric acid increases the effect of nitric acid by helping to remove metal ions through reaction with eluted metal ions. Therefore, when the insoluble oxide is not present or the effect of nitric acid can be sufficiently exhibited, the concentration of hydrofluoric acid is set to 0 in the step 300 of forming the second passivation film 30. If the concentration of hydrofluoric acid is too high, erosion of the stainless steel base material 10 becomes severe, so that the upper limit of the hydrofluoric acid concentration is preferably 5%.

In addition, the temperature of the nitric acid solution or mixed acid solution in the step 300 of forming the second passivation film 30 may be 40 to 60 캜. If the temperature of the nitric acid or mixed acid solution is lower than 40 占 폚 or higher than 60 占 폚, the effect of forming a new passivation film is lowered and it is preferable to limit the temperature to the above range.

After forming the second passivation film 30, the stainless steel may be washed 400 (step 400).

The austenitic stainless steel excellent in electrical conductivity produced according to the above-described method can exhibit an interface contact resistance of 10 m? Cm 2 or less at a contact pressure of 100 N / cm 2. That is, the austenitic stainless steel having excellent electrical conductivity according to an embodiment of the present invention may include a highly conductive passive film.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

Invented steel and comparative steel

The austenitic stainless steels containing the component contents shown in the following Table 1 were cold-rolled through a Z-mill cold rolling mill and subjected to a heat treatment in a reducing atmosphere containing hydrogen (75 vol%) and nitrogen (25 vol% A cold rolled thin plate having a thickness of 0.1 mm was produced.

division C Si Mn Cr Ni Mo N Inventive Steel 1 0.03 0.5 0.8 18.1 8.2 0.03 Invention river 2 0.05 0.6 1.1 16.3 9.8 2.1 0.04 Invention steel 3 0.03 0.5 1.7 21.2 11.3 0.13 Inventive Steel 4 0.04 0.4 1.5 18.2 6.3 0.10 Invention steel 5 0.02 0.2 0.7 15.4 10.6 1.5 0.03 Comparative River 1 0.03 0.4 0.9 16.2 3.6 0.04 Comparative River 2 0.02 0.3 1.0 15.7 5.1 0.05

Next, the cold rolled thin plates of the inventive steel and the comparative steel were subjected to a process of removing the first non-conductive passivation film and a process of forming the second conductive passivation film according to the conditions shown in Table 2 below.

Table 3 shows the Ni / Fe atomic ratio, the Cr / Cr ratio in the base material, and the Cr hydroxide / Cr oxide ratio in the thickness region of 2 nm or less from the passive film surface, which is a main parameter after formation of the conductive passivation film.

division Steel grade The first passivation film removal step The second passive film forming step Acid solution density Current density
(time) Acid solution Temperature time Example 1 Inventive Steel 1 Sulfuric acid electrolysis 15% 0.15 A / cm ² 15% nitric acid
+ 5% hydrofluoric acid 50 ℃ 60 seconds Example 2 Inventive Steel 1 Sulfuric acid electrolysis 15% 0.05 A / cm ² 15% nitric acid
+ 5% hydrofluoric acid 40 ℃ 60 seconds Example 3 Inventive Steel 1 Sulfuric acid electrolysis 15% 0.20 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 50 ℃ 30 seconds Example 4 Inventive Steel 1 Sulfuric acid electrolysis 15% 0.45 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 55 ° C 60 seconds Example 5 Inventive Steel 1 Sulfuric acid electrolysis 15% 0.20 A / cm ² 15% nitric acid 50 ℃ 60 seconds Example 6 Invention river 2 Sulfuric acid electrolysis 15% 0.15 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 50 ℃ 60 seconds Example 7 Invention river 2 Sulfuric acid electrolysis 15% 0.20 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 55 ° C 60 seconds Example 8 Invention steel 3 Hydrochloric acid immersion 10% (60 seconds) 15% nitric acid
+ 1% hydrofluoric acid 50 ℃ 60 seconds Example 9 Invention steel 3 Hydrochloric acid immersion 15% (45 seconds) 15% nitric acid 55 ° C 60 seconds Example 10 Inventive Steel 4 Sulfuric acid electrolysis 15% 0.15 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 50 ℃ 60 seconds Example 11 Invention steel 5 Hydrochloric acid immersion 10% (60 seconds) 15% nitric acid 55 ° C 60 seconds Comparative Example 1 Comparative River 1 Sulfuric acid electrolysis 15% 0.25 A / cm ² 15% nitric acid
+ 1% hydrofluoric acid 50 ℃ 60 seconds Comparative Example 2 Comparative River 2 Hydrochloric acid immersion 10% (60 seconds) 15% nitric acid 50 ℃ 60 seconds Comparative Example 3 Comparative River 2 - -

division The second passive film thickness (nm) From the second passive coating surface
A thickness region of 2 nm or less Contact resistance
(m? cm ² ) Ni / Fe
Atomic weight
ratio Cr
/ Cr in the base material
ratio Cr hydroxide / Cr oxide ratio Example 1 2.1 0.17 1.8 1.3 10.1 Example 2 2.7 0.15 1.3 1.0 12.1 Example 3 2.6 0.13 1.1 0.8 11.6 Example 4 2.4 0.14 1.5 1.0 10.6 Example 5 2.3 0.13 1.4 1.1 10.4 Example 6 2.7 0.12 1.3 0.9 11.8 Example 7 2.2 0.14 1.3 0.9 10.3 Example 8 3.2 0.11 1.1 0.7 12.6 Example 9 2.5 0.13 1.3 0.9 11.1 Example 10 2.4 0.14 1.5 1.0 10.7 Example 11 2.3 0.14 1.4 1.1 10.3 Comparative Example 1 3.8 0.04 0.7 0.7 24.8 Comparative Example 2 2.9 0.05 0.6 0.5 22.7 Comparative Example 3 5.4 0.01 0.2 0.2 60.2

At this time, in order to evaluate the contact resistance, the manufactured 0.1 mm thick material was cut to an area of 25 cm2 and two sheets were prepared. Thereafter, carbon paper (SGL-10BA) of 4 cm2 area used as a gas diffusion layer was placed therebetween , And the interface contact resistance was evaluated four times at a contact pressure of 100 N / cm 2.

As shown in Table 2 and Table 3, Invention steels 1 to 5 all control the removal of the nonconductive passive film and the formation of the conductive passive film through Examples 1 to 11, so that the thickness of the region of less than 2 nm from the passive film surface The Ni / Fe atomic ratio was 0.1 or more, the Cr / Cr ratio in the base material was 1.0 or more, the Cr hydroxide / Cr oxide ratio was 0.6 or more, and at the same time, the contact resistance was low and high conductivity was secured.

Invention steels 1 to 5 show that the nonconductive passivation film was completely removed through electrolysis of sulfuric acid or hydrochloric acid according to Examples 1 to 11, and Cr and Ni were concentrated through selective elution of Fe. In particular, the concentration of Ni represented by the Ni / Fe atomic ratio shows that the comparative steels 1 and 2 contain less than 6% by weight of Ni and did not inhibit the violent dissolution of the stainless steel base material during the sulfuric acid electrolytic treatment or hydrochloric acid immersion.

In the second passivation film formation step, a highly conductive passive film having a thickness of 4 nm or less was formed by immersing it in a mixed acid solution of nitric acid or nitric acid and hydrofluoric acid, and the contact resistance was 13 m? Cm ² or less, .

On the other hand, in Comparative Example 3 of Table 3, the cold rolled thin sheet having a thickness of 0.1 mm and subjected to the heat-annealing treatment as a result of the removal of the first passive film and the step of forming the second passive film, And the ratio of Cr in the film is low, so that the contact resistance is higher than 60 m? Cm ² .

Further, comparative steels 1 and 2 were performed according to the process conditions of Comparative Examples 12 to 14, but due to the low Ni content, sufficient Cr and Ni enrichment occurred not only in the passive film but also in the extreme melting of the stainless steel base material during the first passive film removal process A thick passive film was formed. In addition, the ratio of Ni / Fe in the thickness region of 2 nm or less from the passive film surface, the Cr / Cr ratio in the Cr / base material, and the Cr hydroxide / Cr oxide ratio exceeded the range of the present invention and the high conductivity of 20 mΩcm ² or less could not be ensured .

6 and 7 are photographs of a passive film of stainless steel according to Example 3 and Comparative Example 3, respectively, observed using a transmission electron microscope (TEM).

The passive film of Comparative Example 3, which has not undergone the manufacturing process according to the present invention, has a thickness of 5 nm or more and is nonconductive. However, the passive film of Example 3 shows that a thin conductive thin passive film is newly formed by the manufacturing process according to the present invention .

As described above, the austenitic stainless steel excellent in electrical conductivity produced according to the embodiment of the present invention produces a passive film having a low interface contact resistance by using Cr and Ni concentration, It can have excellent conductivity.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited thereto. Those skilled in the art will recognize that other embodiments may occur to those skilled in the art without departing from the scope and spirit of the following claims. It will be understood that various changes and modifications may be made.

10: stainless steel base material 20: first passive film
30: second passive film 100: first passive film removing step
200: first water washing step 300: second passive film forming step
400: second washing step

Claims (14)

0.1 to 2.0% of Cr; 15 to 24% of Cr; 6 to 12% of Ni; 2.5% or less of Mo; 0.3% or less of N; S: 0.003% or less, the balance Fe and other unavoidable impurities, and a passive film formed on the stainless steel base material,
Wherein the passive film has a thickness of more than 0 nm and 4 nm or less,
An austenitic stainless steel excellent in electric conductivity having a Ni / Fe atomic ratio of 0.1 or more in a thickness region of 2 nm or less from the surface of the passive film. The method according to claim 1,
A Cr / Cr ratio in a thickness region of 2 nm or less from the surface of the passive film is 1.0 or more, and an excellent austenitic stainless steel having excellent electrical conductivity. The method according to claim 1,
And a Cr oxide / Cr oxide ratio of 0.6 or more in a thickness region of 2 nm or less from the surface of the passive film is superior to the austenitic stainless steel. The method according to claim 1,
Wherein an interface contact resistance of the passive film is 20 m? Cm ² or less. 0.1 to 2.0% of Cr; 15 to 24% of Cr; 6 to 12% of Ni; 2.5% or less of Mo; 0.3% or less of N; S: 0.003% or less, the balance Fe, and other unavoidable impurities to form a first passivation film;
Removing the first passivation film; And
And forming a second passivation film on the stainless steel base material. The method of manufacturing austenitic stainless steel according to claim 1, 6. The method of claim 5,
Wherein the step of removing the first passive film comprises:
A method for producing an austenitic stainless steel excellent in electrical conductivity, which is electrolytically treated in a sulfuric acid solution having a concentration of 10 to 20%. The method according to claim 6,
The temperature of the sulfuric acid solution is 40 to 80,
Wherein the electrolytic treatment has a current density of 0.05 to 0.45 A / cm < ² >. ^{2. A} method for producing an austenitic stainless steel according to claim 1, 6. The method of claim 5,
Wherein the step of removing the first passive film comprises:
Wherein the substrate is immersed in a hydrochloric acid solution having a concentration of 10 to 15% for 45 to 60 seconds to obtain an austenitic stainless steel having excellent electrical conductivity. 6. The method of claim 5,
The forming of the second passive film may include:
Wherein the stainless steel base material is immersed in a nitric acid solution having a concentration of 10 to 20% or a mixed acid solution of 10 to 20% of nitric acid and 5 to less than 5% of hydrofluoric acid. 10. The method of claim 9,
Wherein the nitric acid solution and the mixed acid solution have a temperature of 40 to 60 占 폚. 6. The method of claim 5,
The forming of the second passive film may include:
Wherein the thickness of the second passivation film is greater than 0 nm and equal to or less than 4 nm. 6. The method of claim 5,
The forming of the second passive film may include:
Wherein the ratio of the Ni / Fe atomic ratio in the thickness region of 2 nm or less from the surface of the second passive film is 0.1 or more. 6. The method of claim 5,
The forming of the second passive film may include:
Wherein a Cr ratio in a thickness region of 2 nm or less from the surface of the passive film is 1.0 or more. 6. The method of claim 5,
The forming of the second passive film may include:
Wherein a ratio of Cr hydroxide / Cr oxide in a thickness region of 2 nm or less from the surface of the second passivation film is 0.6 or more.

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