JPH0668154B2 - Chromium alloy surface treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for a chromium alloy, and more particularly, chromium having one or more main metals such as iron, cobalt and nickel, such as stainless steel. An oxide film is formed to color the surface of the alloy.
The present invention relates to a surface treatment method for a chromium alloy that cures this oxide film.

(Prior Art) Conventionally, as a method for coloring a chromium alloy such as stainless steel, coloring is performed by forming a porous oxide film on the surface of the chromium alloy using an aqueous solution containing chromic acid and sulfuric acid. There is a method (first method).

Further, as a method of curing such a porous oxide film, as disclosed in, for example, Japanese Patent Publication No. 53-31817 and Japanese Patent Publication No. 56-24040,
An aqueous solution containing sulfuric acid and chromic acid at a concentration lower than the concentration of sulfuric acid used for coloring was separately prepared, and cathodic electrolysis was performed on the surface of the chromium alloy on which a porous oxide film was previously formed in the aqueous solution. There is a method of curing the porous oxide film by performing the treatment (second method).

Furthermore, conventional electrolytic coloring method of chromium alloy, for example,
As disclosed in Japanese Examined Patent Publication No. 52-32621, this method involves immersing stainless steel as a chromium alloy in an aqueous solution containing chromic acid and sulfuric acid, and subjecting the stainless steel to anodic electrolytic treatment to remove stainless steel. This is a method of coloring the surface by forming a porous oxide film on the surface (third method).

(Problems to be Solved by the Invention) However, in the first method, since the oxide film formed is porous, the wear resistance of the oxide film is poor.

Therefore, a method of curing the second oxide film was created. In this second method, the oxide film is formed separately from the aqueous solution for forming the porous oxide film on the surface of the chromium alloy. At least two aqueous solutions for hardening
Requires a kind of aqueous solution. Therefore, two or more baths for storing the aqueous solution are required, which complicates the manufacturing apparatus, and the work of moving the chromium alloy between the baths becomes very complicated. Moreover, in the second method, the color tone of the oxide film is not sufficiently adjusted, and further, the color tone is slightly changed by the film hardening treatment performed after the coloring, so that the color tone becomes unstable. It has drawbacks.

Further, in the third method, as the treatment time of the anodic electrolytic treatment elapses, the color tone of the oxide film formed by the treatment abruptly changes, which makes it difficult to adjust the color tone and the color tone is unstable. Becomes Moreover, in the third method, the wear resistance of the oxide film formed by the anodic electrolytic treatment is not sufficient and the strength thereof is weak.

Therefore, the main object of the present invention is to adjust the color tone formed on the surface of a chromium alloy uniformly and with good reproducibility, to enhance the effect of film hardening, to improve the strength of the oxide film, and to form an oxide film. It is an object of the present invention to provide a surface treatment method for a chromium alloy, which makes it possible to carry out the step and the step of performing cathodic electrolysis treatment in the same aqueous solution, and which can simplify the manufacturing apparatus and remove the complexity of workability.

(Means for Solving Problems) The present invention relates to a surface treatment method for a chromium alloy which forms an oxide film for coloring the surface of the chromium alloy and further hardens the oxide film. A chromium alloy is immersed in an aqueous solution containing 500 g / and sulfuric acid of 300 to 1,000 g /, and an anodic electrolysis treatment step is performed continuously or intermittently until the coloring start point, and after reaching the coloring start point, A surface treatment method for a chromium alloy, comprising: a step of forming an oxide film on the surface of an aqueous solution; and a step of performing cathodic electrolysis, which is alternately repeated in the aqueous solution, of forming an oxide film. .

(Function) An oxide film that is not visible as a color is previously generated by an anodic electrolytic treatment step that is continuously or intermittently performed until the coloring start point.

Alternatingly repeated, by the step of forming an oxide film on the surface of the chromium alloy and the step of cathodic electrolytic treatment,
A change in color tone is given to the surface of the chromium alloy little by little, and the oxide film formed up to that time is stably strengthened and hardened each time the above two steps are repeated.

(Effects of the Invention) According to the present invention, an anodic electrolytic treatment step that is continuously or intermittently performed up to the coloring start point and a step of forming an oxide film on the surface of the chromium alloy after reaching the coloring start point The color tone formed on the surface of the chromium alloy can be adjusted uniformly and with good reproducibility by alternately repeating the step of performing the cathodic electrolysis treatment. Further, the effect of hardening treatment is great, and the oxide film formed up to that time can be stably strengthened each time both steps are repeated, and the strength of the oxide film can be remarkably improved.

Moreover, since the same aqueous solution can be used as the aqueous solution necessary for the anodic electrolytic treatment step, the step of forming an oxide film on the surface of the chromium alloy, and the step of performing the cathodic electrolytic treatment,
It becomes possible to perform a series of treatments in the same aqueous solution.
Therefore, there is no need to prepare two types of baths, an aqueous solution for forming a porous oxide film and an aqueous solution for curing the oxide film, and both steps can be performed in one bath during production. Therefore, the manufacturing process can be simplified, and the complexity of work such as the movement of the chromium alloy between the baths can be avoided.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

(Embodiment) FIGS. 1A and 1B show an example of an apparatus for carrying out the present invention, FIG. 1A is an illustration of the whole, and FIG. 1B is an illustration showing a bath and its peripheral portion. It is a figure.

FIG. 2A shows a case where the anodic electrolytic treatment step is continuously performed until the coloring start point, and after the coloring start point is reached, the oxide film forming treatment step and the cathodic electrolytic treatment step are alternately repeated in a constant cycle. It is a graph which shows the time-current value relationship.

The device 10 includes a constant current power supply 12. This constant current power supply 12 has, for example, AC 100 to 20 at its input end.
By connecting a 0V power source, an arbitrary constant current is output from the output terminal. The constant current power supply 12 can output a DC constant current having an arbitrary current value of 0 to 20.0 A, and has a current passage area of 1 d, for example.
A current having a current density of 0 to 20.0 A / dm ² can be passed through the conductor of m ² .

The output terminal of the constant current power supply 12 is connected to the input terminal of the polarity conversion switch 14. The polarity conversion switch 14 is for switching the polarity of the current input to its input end as it is or with the lapse of arbitrary time, and outputting it from its output end. This polarity change switch 14
Then, the polarity of the current input thereto can be arbitrarily switched and output in a time period of, for example, 1 second or more.

Therefore, the constant current input to the input end of the polarity changing switch 14 can output a current for intermittent cathodic electrolysis as shown in FIG. 2A from the output end according to the method of the present invention. At the same time, the polarity is switched and output so that the current for continuously performing the anodic electrolysis can be output during the time until the coloring start point.

One output end of the polarity changing switch 14 is connected to the plate 20 to be colored through, for example, an ammeter 16 for digital display or analog display and a connector 18a made of copper. As the colored plate 20, for example, a chromium alloy such as SUS304 stainless steel is used.

It should be noted that this colored plate 20 is, as a pretreatment of the coloring treatment,
For example, it is preferable that treatments such as degreasing treatment, washing treatment and neutralization treatment have been performed. As this degreasing treatment, a colored plate 2 such as a stainless steel plate as a chromium alloy is used.
0 is, for example, of a sodium orthosilicate system, for example, 70 ° C.
It is performed by immersing in the solution. The washing process with water is performed by ultrasonically washing the plate 20 to be colored in a water bath, for example. Furthermore, the neutralization treatment is performed by immersing the plate 20 to be colored in, for example, a 20% HNO ₃ solution for 30 to 60 seconds.

On the other hand, the other output end of the polarity conversion switch 14 is connected to a counter electrode plate 22 as a counter electrode of the colored plate 20 via a copper connector 18b. The counter electrode plate 22 is made of lead in this embodiment, but may be made of other conductive metal such as platinum, titanium, niobium, carbon and stainless steel.

The colored plate 20 and the counter electrode plate 22 are arranged so as to face each other in the aqueous solution 26 in the bath 24 with a predetermined space therebetween.

That is, in this embodiment, the inner surface of the bath 24 is divided into lead, and the inner volume of the bath 24 is, for example, 250, and 200 aqueous solutions 26, for example, are stored in the bath 24.

The to-be-colored plate 20 and the counter electrode plate 22 are suspended by the copper-made connecting tools 18a and 18b, and immersed in the aqueous solution 26 so as to face ^each other with an area of, for example, 12 dm ^2. .

The colored plate 20 and the counter electrode plate 22 are suspended by the connecting tools 18a and 18b so that the upper portions thereof are not soaked in the aqueous solution 26. If the connectors 18a and 18b are made of a metal material such as titanium or stainless steel that is not easily corroded by the aqueous solution 26, the connectors 18a and 18b may be dipped in the aqueous solution 26.

The aqueous solution 26 stored in the bath 24 contains, for example, 250 g / chromic acid as a main component and 490 g / sulfuric acid as an electrolyte.

In addition, as a preferable example of the aqueous solution 26 in this invention, chromic acid is 50 to 500 g / and sulfuric acid is 300.
The thing containing-1,000g / is mentioned.

That is, the chromic acid contained in the aqueous solution contains 50
If it is less than g /, the step of forming an oxide film and the step of curing the oxide film take too long to be put to practical use, and if it is more than 500 g /,
Chromic acid is difficult to dissolve and is economically disadvantageous. Therefore, it is preferable that the chromic acid contained in the aqueous solution 26 in the present invention is contained within the above range.

Furthermore, the sulfuric acid contained in the aqueous solution contains 300 g /
If it is less than 1, the reaction of the electrolytic treatment is too slow to be put to practical use, and if it exceeds 1,000 g /,
Since the surface of the plate to be colored is dissolved and a remarkably porous oxide film is formed on the surface of the plate to be colored and the oxide film cannot be cured, the aqueous solution 26 of the present invention is used.
The sulfuric acid contained in 1) is preferably contained within the above range.

The temperature of the aqueous solution 26 is room temperature (20 ° C.).
If it is lower, the electrolytic treatment takes too much time to be put into practical use, and if it is higher than 100 ° C., aging due to corrosion of the bath occurs, so that it is preferably in the range of 20 to 100 ° C.

Furthermore, it is preferable that the temperature of the aqueous solution is in the range of 60 to 90 ° C.

Further, in the present invention, in order to color the chromium alloy (plate 20 to be colored) such as stainless steel in the aqueous solution 26 containing chromic acid and sulfuric acid within the above range, the anodic electrolysis treatment is performed before the coloring start point. Performing the step of forming an oxide film after reaching the coloring start point, and further repeating the step of performing cathodic electrolysis treatment in this homogeneous aqueous solution with the step of forming the oxide film by alternately coloring and It cures the oxide film.

Next, with this device 10, on the surface of the plate 20 to be colored,
An operation of performing the anodic electrolysis treatment step and thereafter alternately repeating the step of forming an oxide film after reaching the coloring start point and the step of performing the cathodic electrolysis treatment will be described in detail.

First, as shown in FIGS. 1A and 1B, the device 10
The colored plate 20 and the counter electrode plate 22 are connected to the colored plate 20, and the colored plate 20 and the counter electrode plate 2 are immersed in the aqueous solution 26 in the bath 24.
2 and the like are connected, and further, the plate 20 to be colored and the counter electrode plate 22 are immersed in an aqueous solution 26 in a bath 24 so as to face each other.

Then, the anodic electrolysis treatment is continuously performed in the aqueous solution 26 until the oxide film reaches a film thickness sufficient to start coloring in the aqueous solution 26, that is, a coloring start point.

In this example, the current density was 0.03 A / dm ^2.
Then, the anodic electrolysis treatment was performed for 300 seconds. In this case, the time until the coloring start point was reached was obtained by previously immersing the same quality chromium alloy in the aqueous solution 26 as a preliminary test, or by
It can be easily obtained by performing an anodic electrolytic treatment in the inside and observing the surface successively. For the same quality chromium alloy, the anodic electrolysis treatment may be continuously performed during the time until the coloring start point thus obtained is reached. It should be noted that the time to reach the coloring start point does not require so strict control, and may be replaced with the meaning such as the time to reach the vicinity of the coloring start point, during which anodic electrolytic treatment may be performed. .

In the anodic electrolytic treatment step, after reaching the coloring start point, for example, a dipping step of forming an oxide film is performed for 50 seconds in 1 minute, and further, for example, 0.6
The step of outputting the constant current of A from the output end of the polarity conversion switch 14 and subjecting the plate 20 to be colored in the aqueous solution 26 in one bath 24 to cathodic electrolysis is performed for 10 seconds. Then, the step of forming the oxide film and the step of performing the cathodic electrolytic treatment are alternately repeated for a total of 22 minutes. By the treatment, the colored plate 20 was colored gold.

When performing this cathodic electrolysis treatment, the current density of the current flowing through the plate 20 to be colored is such that the current value output from the constant current power supply 12 is 0.6 A, and the plate 20 to be colored and the counter electrode plate 22 are in an aqueous solution 26. Since they are facing each other with an area of 12 dm ² ,
It is set to 0.05 A / dm ² .

During this cathodic electrolysis treatment, the plate 20 to be colored is at a negative potential with respect to the counter plate 22, so that the sealing treatment is repeatedly performed, and the surface of the plate 20 to be colored is colored and the oxide film is formed. Is cured. The colored plate 2 of the present invention
The current density flowing in 0 is 0.01 to 20.0 A
It is preferably in the range of / dm ² .

The current for performing this cathodic electrolysis treatment can be performed at a low current density as compared with the case where the cathodic electrolysis treatment is continuously performed after coloring as described in the conventional method.

However, if it is less than 0.01 A / dm ² , the sealing effect is small and the effect of curing the oxide film is poor. In addition, although increasing the current density does not hinder one direction,
If it exceeds 20.0 A / dm ² , the pore-sealing effect becomes too large, and the color tone of coloring due to the oxide film may be impaired.

Thus, according to the present invention, an oxide film can be formed on the surface of the chromium alloy in one kind of aqueous solution, and the oxide film can be further hardened. Therefore, in the present invention, an oxide film can be formed on the surface of the chromium alloy with one bath, and the oxide film can be further hardened.

In the above embodiment has been performed for a predetermined time anodic electrolysis at a constant current density, for example, as shown in Figure 2B, the current value of the constant current and 0.2 A / dm ^2, energized 10 seconds The anodic electrolytic treatment may be intermittently performed, for example, turning off for 20 seconds and repeating this 10 times.

Further, in the above example, the immersion treatment time for forming the oxide film and the treatment time for the cathodic electrolysis treatment were alternately repeated at the same time intervals in each treatment step,
For example, as shown in FIG. 2B, a constant current value of 0.
The immersion treatment time for forming the oxide film is 3 A / dm ^2, and the immersion treatment time for forming the oxide film is changed between 300 and 60 seconds. The present invention also includes a method in which the step of forming an oxide film and the step of performing cathodic electrolysis are alternately repeated. As a method of changing the immersion treatment time, for example, 300 seconds, 240
Seconds, 180 seconds, 150 seconds, 120 seconds, 90 seconds, 60 seconds, and the like are gradually decreased and vice versa.

Further, as shown in FIG. 2C, the current value of the cathodic electrolysis treatment is changed between 0.05 and 2.0 A / dm ² , and
A treatment method in which the time interval is changed in each treatment step such that the immersion treatment time for forming an oxide film is changed between 270 and 5 seconds, and the current density in the cathodic electrolysis treatment is also changed in each step. Also included in the present invention. As a method of changing the current value,
For example, 0.05 A / dm ² , 0.1 A / dm ² , 0.3
A / dm ^2, or is gradually increased as such ^{0.6 / dm 2 ··· 2.0A / dm} 2, includes a method of decreasing the reverse. Further, as a method of changing the immersion treatment time, for example, there is a case where it is gradually decreased, such as 270 seconds, 240 seconds, 180 seconds ... 5 seconds, and gradually increased.

In addition, a method of changing only the current value can be selected.

Experimental Example 1 First, an aqueous solution 26 containing 250 g / chromic acid and 490 g / sulfuric acid was prepared. Furthermore, the beaker 30 of 5 was prepared as a bath, and the aqueous solution 26 was poured into the beaker 30.

As the plate to be colored, a SUS304 stainless specular plate 32 having a length of 150 mm, a width of 140 mm and a thickness of 1.5 mm was prepared. Furthermore, a lead counter plate 3 made of lead 150 mm long and 140 mm wide 3
Prepared 4.

Then, as shown in FIG. 3, in the beaker 30 in which the aqueous solution 26 was poured, the counter electrode plate 34 was arranged so as to face the stainless plate 32 with a distance of 10 cm.

Then, in order to color the surface of the stainless plate 32 in the aqueous solution 26, an anodic electrolytic treatment step is performed until the coloring start point, and after the coloring start point is reached, an immersion treatment step of forming an oxide film, and a cathode. The process of electrolytic treatment was repeated alternately.

In this case, as shown in the table, samples 1, 3, 9, 11
Samples 2, 4, 5, 6, 7, 8, 10, 12, 13, 15, ² and 14 were continuously energized at a current density of 0.03 A / dm ² for 5 minutes for anodic electrolysis.
For 1 and 24, a current density of 0.2 A / dm ² was applied for 10 seconds and then turned off for 20 seconds, and the number of repetitions was 1
The anodic electrolytic treatment was carried out by energizing for 0 minutes for a total of 5 minutes.

And in this case, as shown in the table, samples 1 to 1
For each of the stainless steel plates 32 of 5, 24, and 25, after the coloring start point was reached in the aqueous solution 26, the oxide film formation and the cathodic electrolysis treatment were repeated under the predetermined conditions, the number of times indicated by the number of repetitions (N). Were alternately repeated.

The temperature of the aqueous solution 26 was maintained at 70 ° C. for samples 1 to 15, 24 and 25, and 85 ° C. for sample 21.

Samples 1 to 15, 21, 24 and 25 thus obtained
For each of these, the color tone was observed, and the surface thereof was rubbed with an eraser 100 times to perform a test for examining the abrasion resistance thereof.

As a result of this test, in the table, those having little change in color tone after being rubbed 100 times were evaluated as having good wear resistance, and those having slightly changed color tone after being rubbed 100 times were resistant. The abrasion resistance was slightly poor, and the abrasion resistance was markedly changed, and the abrasion resistance was poor. As a result shown in this table, Samples 1 and 2 were out of the scope of the present invention because their oxide films had poor wear resistance.

Further, Samples 24 and 25 were out of the scope of the present invention because of the difficulty in the color tone of the oxide film.

Further, it was found that Samples 3 to 15 and 21 obtained by the method within the scope of the present invention had good wear resistance of the oxide film and excellent color uniformity. Further, it is understood that these samples 3 to 15 and 21 were able to form an oxide film in one kind of aqueous solution and further cure the oxide film. Therefore, in the present invention, it is understood that an oxide film can be formed on the surface of the chromium alloy and the oxide film can be cured by using one bath.

Experimental Example 2 The same aqueous solution 26, stainless mirror plate 32, and counter electrode plate 34 as those in Experimental Example 1 were prepared. And the third
As shown in the figure, the stainless plate 32 and the counter electrode plate 34 were arranged.

Then, in order to color the surface of the stainless steel plate 32 in the aqueous solution 26, an anodic electrolytic treatment step is performed until the coloring start point is reached, and after the coloring start point is reached, an immersion film forming step and a cathode step are performed. The step of performing the electrolytic treatment and the step of performing the cathodic electrolytic treatment while changing the immersion treatment time for forming the oxide film were alternately repeated.

Then, with respect to Samples 16, 17 and 20, the temperature of the aqueous solution was maintained at 70 ° C. Sample 2
Regarding No. 3, the temperature of the aqueous solution was kept at 85 ° C.

In this case, as shown in the table, for Samples 17 and 23, a current density of 0.03 A / dm ² was continuously applied for 5 minutes to carry out an anodic electrolysis treatment.
For 0, a current density of 0.2 A / dm ² was applied for 10 seconds, turned off for 20 seconds, and repeated 5 times for a total of 5 times.
It was energized for a minute and subjected to anodic electrolytic treatment.

In this case, as shown in the table, samples 16, 1
For each of the stainless steel plates 32, 7, 20, and 23, after the coloring start point was reached in the aqueous solution 26, the number of times indicated by the number of repetitions (N) of the oxide film formation and the cathodic electrolysis treatment was performed under predetermined conditions. Were alternately repeated.

With respect to the samples 16, 17, 20 and 23 thus obtained, the color tone was observed, and the surface thereof was rubbed with an eraser 100 times to carry out a test for examining the abrasion resistance thereof. The same observation as in Experimental Example 1 was performed, and the test results are shown in the table.

It was found that the samples 16, 17, 20 and 23 obtained by the method within the scope of the present invention had good wear resistance of the oxide film and excellent color tone uniformity. In addition, these samples 16, 17, 20
Regarding Nos. 23 and 23, it can be seen that an oxide film was formed in one kind of aqueous solution, and the oxide film could be cured. Therefore, in the present invention, it is understood that an oxide film can be formed on the surface of the chromium alloy and the oxide film can be cured by using one bath.

Experimental Example 3 The same aqueous solution 26, stainless steel mirror plate 32, and counter electrode plate 34 as in Experimental Example 1 were prepared. And the third
As shown in the figure, the stainless plate 32 and the counter electrode plate 34 were arranged.

Then, in order to color the surface of the stainless steel plate 32 in the aqueous solution 26, an anodic electrolytic treatment step is performed until the coloring start point is reached, and after the coloring start point is reached, a dipping treatment time for oxide film formation and The treatment process for forming an oxide film and the cathodic electrolysis process were alternately repeated while changing any of the current densities for the cathodic electrolysis process.

Samples 18 and 19 had an aqueous solution temperature of 70
Each treatment step was carried out while maintaining the temperature at ℃.

In this case, as shown in the table, for sample 19,
Energize continuously for 5 minutes at a current density of 0.03 A / dm ² ,
0.2A for sample 18 after anodic electrolysis
At a current density of / dm ^2, a current was applied for 10 seconds, turned off for 20 seconds, and then repeated 10 times for a total of 5 minutes to carry out an anodic electrolysis treatment.

Then, in this case, as shown in the table, for each of the stainless steel plates 32 to be the samples 18 and 19,
After reaching the coloring start point in the aqueous solution 26, the oxide film formation and the cathodic electrolysis treatment were alternately repeated under the predetermined conditions for the number of times indicated by the number of repetitions (N).

With respect to the samples 18 and 19 thus obtained, the color tone was observed, and the surface thereof was rubbed with an eraser 100 times to carry out a test for examining the abrasion resistance thereof. The same observation as in Experimental Example 1 was performed, and the test results are shown in the table.

It was found that the samples 18 and 19 obtained by the method within the scope of the present invention had good wear resistance of the oxide film and excellent uniformity of color tone.
Also, for these samples 18 and 19, 1
It can be seen that it was possible to form an oxide film in various kinds of aqueous solutions and further to cure the oxide film. Therefore, in the present invention, it is understood that an oxide film can be formed on the surface of the chromium alloy and the oxide film can be cured by using one bath.

Experimental Example 4 The same aqueous solution 26, stainless steel mirror plate 32, and counter electrode plate 34 as in Experimental Example 1 were prepared. And the third
As shown in the figure, the stainless plate 32 and the counter electrode plate 34 were arranged.

Then, in order to color the surface of the stainless plate 32 in the aqueous solution 26, the sample 22 has a current density of 0.03 A /
dc ² for 5 minutes continuously, anodic electrolytic treatment,
While changing the current density of the cathodic electrolysis treatment, the immersion treatment step for forming an oxide film and the cathodic electrolysis treatment step were repeated alternately under the predetermined conditions, the number of times indicated by the repeating number.

Sample 22 was subjected to each surface treatment step while maintaining the temperature of the aqueous solution at 85 ° C.

With respect to the sample 22 thus obtained, the color tone was observed, and the surface thereof was rubbed with an eraser 100 times to perform a test for examining the abrasion resistance thereof. The same observation as in Experimental Example 1 was performed, and the test results are shown in the table.

In the cathodic electrolysis process, for example, electrolysis is performed with a direct current rectified by a rectifier including a transistor, the duration is, for example, 1 msec, and the separation is, for example, 3 msec, that is, the duty ratio is 1: 3. The electrolytic treatment may be performed with a pulse wave. Further, the electrolytic treatment may be performed with a pulsating flow obtained by rectifying, for example, three-phase alternating current of 60 cycles by a rectifying device including a thyristor.

In addition to the pulse wave described above, its duration is 0.1 m.
sec ~ 100msec, the separation is 10
Even if a pulse wave having a time shorter than 0 msec is used, the same color tone can be obtained if the average value of the current density is the same as the above-mentioned value.

Further, in each of the above-mentioned Examples or Experimental Examples, the plate-shaped chromium alloy was treated, but the present invention is, for example, linear,
It goes without saying that the present invention can be applied to a chromium alloy having any shape such as an annular shape and a coil shape.

In particular, in the case of a long coil, for example, a rectifier set to each current density is used for each current density of the cathodic electrolysis process that is performed alternately with the dipping process of forming an oxide film in the line. It may be prepared on the line and subjected to cathodic electrolysis treatment at a predetermined current density.

[Brief description of drawings]

1A and 1B show an example of an apparatus for carrying out the present invention, FIG. 1A is a schematic illustration of the whole, and FIG. 1B is a schematic illustration showing a bath and its peripheral portion. FIG. 2A shows a time-current value relationship in the case where the anodic electrolysis treatment is continuously performed for a certain period of time and after reaching the coloring start point, the oxide film forming treatment step and the cathodic electrolysis treatment step are alternately repeated. It is a graph which shows an example. FIG. 2B shows that the anodic electrolysis is intermittently performed for a certain period of time, and after the coloring start point is reached, the constant current value is constant,
It is a graph which shows the time-current relationship when the oxide film formation time is changed. FIG. 2C shows the time when the anodic electrolysis treatment is continuously performed for a certain period of time, the current value of the cathodic electrolysis treatment is changed after the coloring start point is reached, and the oxide film formation time is changed.
It is a graph which shows the relationship of an electric current value. FIG. 3 is an illustrative view showing a positional relationship between a stainless plate and a counter plate in an experimental example. In the figure, 10 is a device, 12 is a constant current power supply, 14 is a polarity change switch, 18a and 18b are connectors, 20 is a stainless plate, 22 is a counter plate, 24 is a bath, and 26 is an aqueous solution.

Claims (5)

[Claims] 1. A surface treatment method for a chromium alloy, which comprises forming an oxide film for coloring on the surface of the chromium alloy and further hardening the oxide film, which comprises 50 to 500 g of chromic acid and 300 to 1, of sulfuric acid. 0
In an aqueous solution containing 00 g /, a chromium alloy is immersed, and an anodic electrolytic treatment step is carried out continuously or intermittently up to the coloring start point, and in the aqueous solution after the coloring start point is reached,
A surface treatment method for a chromium alloy, comprising: a step of forming an oxide film on the surface; and a step of performing a cathodic electrolysis treatment, which is alternately repeated in the aqueous solution, a step of forming the oxide film. 2. The step of performing the cathodic electrolysis treatment comprises performing cathodic electrolysis treatment at a current density of 0.01 to 20.0 A / dm ² in performing the cathodic electrolysis treatment in the aqueous solution. A method for surface treatment of a chromium alloy according to claim 1. 3. The method according to claim 1, wherein the time interval for forming the oxide film, which is alternately repeated with the step of performing the cathodic electrolytic treatment, is changed in each step of forming the oxide film. Surface treatment method for chromium alloys. 4. The chromium alloy according to claim 1 or 2, wherein the current density in the step of performing the cathodic electrolysis treatment alternately repeated with the step of forming the oxide film is changed in each step. Surface treatment method. 5. The method according to claim 1, wherein the time intervals and the current densities in the step of performing the cathodic electrolysis treatment alternately repeated with the step of forming the oxide film are changed in each step. Alternatively, the surface treatment method of the chromium alloy according to the second item.