JPH04143294A - How to color stainless steel materials - Google Patents

Abstract

PURPOSE:To form colored films having excellent corrosion and wear resistances on the surfaces of stainless steel products by subjecting the stainless steel products to a cathodic electrolytic treatment at a specific current density in an electrolyte which contains sulfuric acid and chromic acid and at specific concn. and temp. CONSTITUTION:The stainless steel products are subjected to the cathodic electroytic treatment within the range of 0.5 to 50A/dm<2> current density in the electrolyte which contains 3 to 7mol/l sulfuric acid and 1 to 5mol/l chromic acid and is kept at 85 to 120 deg.C, by which the colored films are formed on the surfaces of the steel products. The colored films having the high corrosion and wear resistances are formed in a short period of time by one process in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a colored film with excellent corrosion resistance and abrasion resistance on the surface of a stainless steel material.

[Conventional technology]

The surface of a stainless steel material is colored by forming a colored film on the surface of the stainless steel material, and the following method is known as a method for forming such a colored film.

(A method for forming a colored film on the surface of a chromium alloy material, disclosed in 11 Japanese Patent Publication No. 52-32621, consisting of the following force A, an electrolytic solution containing chromic acid or chromate and sulfuric acid. In this method, the chromium alloy material is subjected to anodic electrolysis treatment to form a colored film on the surface of the chromium alloy material (hereinafter referred to as prior art 1).

(2) A method for processing stainless steel material consisting of the following, 25 to 850 g, disclosed in Japanese Patent Publication No. 53-31817.
In an electrolytic solution at a temperature of 20 to 80 ° C. containing chromic acid of /j7 and sulfuric acid of 0.1 to 1 Og / l,
A stainless steel material having a porous colored film on its surface is subjected to cathodic electrolysis treatment at a current density of 0.6 to 30 A/dm' to harden the colored film of the stainless steel material (hereinafter referred to as Prior Art 2). ).

(3) Disclosed in Japanese Patent Application Laid-open No. 61-139681,
Method for forming a hardened colored film on stainless steel material consisting of the following: 2 to 5 m01/1 of hexavalent chromium and 2.5 to 7°2
A stainless steel material is immersed in an aqueous solution at a temperature of 30 to 90 ° C. containing mol / f sulfuric acid to form a colored film on the surface of the stainless steel material, and then in an aqueous solution having the same components as the aqueous solution, The stainless steel material on which the colored film has been formed is subjected to cathodic electrolysis treatment at a current density of 0.5 A/dm'' to harden the colored film on the stainless steel material (hereinafter referred to as prior art 3).

(4) A method for manufacturing a colored stainless steel material disclosed in JP-A No. 63-8198, consisting of the following: Stainless steel in an electrolytic solution containing 2 moles or more of hexavalent chromium and 2.5 moles or more of sulfuric acid. For steel materials, 0.01 to 3.
Anodic electrolysis with a current density of OA/dm2 and 0.03~
5. A colored film is formed on the surface of the stainless steel material by performing alternating current electrolysis treatment at a repetition rate of 100 Hz or less, consisting of cathodic electrolysis with a current density of OA/dm2 (
(hereinafter referred to as prior art 4).

[Problem to be solved by the invention]

The applicant of Prior Art 1 and 2 is the same, and the two are usually implemented in combination, and together they are commonly referred to as the 1NC0 method.

That is, in the case of the 1NC0 method, after a colored film is formed on a stainless steel material using prior art 1, the colored film must be hardened using prior art 2. Therefore, two steps are required: the step of forming a colored film according to Prior Art #Il and the step of curing the colored film according to Prior Art 2, resulting in unavoidable problems of complication of the process and increase in product cost.

Prior arts 3 and 4 are lN consisting of prior arts 1 and 2.
This was done to solve the above-mentioned interlayer point of the C0 method. However, in the case of Prior Art 3, it is necessary to form a colored film on the stainless steel material in an aqueous solution containing hexavalent chromium and sulfuric acid, and to harden the colored film in the aqueous solution. Requires a long time to process.

In recent years, when applying coloring to the surface of stainless steel materials, it is desired to increase the depth of coloring in order to reduce costs. Can not.

In the case of Prior Art 4, as is clear from the examples, it takes about 20 minutes to form a colored film. Therefore, similar to prior art 3, there is a problem in that it is not possible to increase the speed of coloring. Furthermore, in Prior Art 4, if the thickness of the formed colored film is thin (and the color is blue, gold, black, etc.), the abrasion resistance of the film is sufficient, but When the colored film is thick and its color is reddish-purple (red), green, etc., there is a problem that the abrasion resistance of the colored film is insufficient.

Therefore, an object of the present invention is to provide a method capable of forming a colored film having excellent wear resistance and corrosion resistance on the surface of a stainless steel material in one step and in a short time.

[Means to solve the problem]

The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, we obtained the following knowledge. That is, when a stainless steel material is immersed in an electrolytic solution containing a predetermined concentration of sulfuric acid and chromic acid at a predetermined temperature, a porous oxide film, that is, a colored film, is formed on the surface of the stainless steel material due to a perpassivation dissolution reaction. It is formed. At this time, if the stainless steel material is subjected to cathodic electrolytic treatment at a predetermined current density, Cr"→C
Due to the reaction at r, 0°, chromium oxide is precipitated on the surface of the stainless steel material. The chromium oxide thus deposited fills the pores of the porous colored coating described above. Therefore, the colored coating is cured simultaneously with the formation of the colored coating, and a colored coating with excellent corrosion resistance and abrasion resistance can be formed.

This invention was made based on the above findings, and in an electrolytic solution containing 3 to 7 mol/f of sulfuric acid and 1 to 5 mol/l of chromic acid at a temperature of 85 to 120°C, The stainless steel material is subjected to cathodic electrolytic treatment at a current density within the range of .5 to 50 A/dm' to form a colored film with excellent corrosion resistance and abrasion resistance on the surface of the stainless steel material. It has the following.

[Effect]

Next, the principle of this invention will be explained. When a stainless steel material is immersed in an electrolytic solution containing chromic acid and sulfuric acid, a partial anodic reaction and a partial cathodic reaction occur in the stainless steel material. The partial anodic reaction is a hyperpassive dissolution reaction of the stainless steel material, and this perpassive dissolution reaction forms an oxide film, that is, a colored film, on the surface of the stainless steel material. On the other hand, the partial cathode reaction is a precipitation reaction of chromium oxide (Cr'+→Cr*Os), and the colored film is hardened by this precipitation reaction.

The figure is a graph showing the two reactions mentioned above. In the drawings, the horizontal axis represents the potential generated when a stainless steel material is immersed in an electrolytic solution containing chromic acid and sulfuric acid, and the vertical axis represents the current value at that time. Line A represents the partial anodic reaction rate or partial anodic current value, and line B represents the partial cathodic reaction rate or partial cathodic current value.

As is clear from the drawings, the partial anode reaction rate, that is, the partial anode current value A, and the partial cathode reaction rate, that is, the partial cathode current value B, are the same when the external current is 0, that is, the potential E.
When , there is balance at point a where line A and line B intersect.

In this state, when a cathode current is applied to the stainless steel material, the potential shifts to El. At potential El, the partial cathodic reaction, that is, the hardening reaction of the coating, is significantly accelerated;
The partial cathode reaction rate moves to point b. On the other hand, the partial anodic reaction, that is, the reaction for forming a colored film, decreases, and the partial anodic reaction rate drops to zero.

Therefore, the content of sulfuric acid in the aqueous solution and the temperature of the aqueous solution are increased to promote the partial anodic reaction. As a result,
The partial anode reaction rate, that is, the partial anode current value A moves to A' shown by the dotted line, and the partial anode reaction rate increases from point 0 to point C°.

Therefore, a sufficient anode reaction rate is obtained, and both the colored film forming reaction and the colored film curing reaction are promoted. Note that, as the content of sulfuric acid in the aqueous solution and the temperature of the aqueous solution are increased, the partial anodic reaction, that is, the reaction for forming a colored film is accelerated.

Based on the above, in this invention, the conditions for optimizing the partial anode current value for forming a colored film on the surface of a stainless steel material, that is, the formation rate of the colored film, are determined as follows.

(1) Content of sulfuric acid in electrolyte: 3 mol/i' or more, preferably 4 mol/j' or more (
2) Temperature of electrolyte: 85°C or higher, preferably 90°C or higher (3) Cathode electrolytic current density: 50A/dm or lower, preferably 12A/dm2 or lower Also, the partial cathode current value for curing the colored film, that is, the colored film The conditions for making the curing speed appropriate were determined as follows.

(1) Content of chromic acid in electrolyte: 1+ol/1
or more, preferably 2 mol# or more (2) Electrolyte temperature: 85°C or more, preferably 90°C or more (3) Cathode electrolysis current density: 0.5 A/dm or more, preferably 2 A/dm or more The conditions for preventing color unevenness from occurring in the colored film were determined as follows.

(1) The content of sulfuric acid in the electrolyte is less than about mol/f, preferably less than 6 mol/i' (2
) Content of chromic acid in the electrolyte: 5 mol/l or less, preferably 4 mol/l or less (3 mol/l or less)
) Temperature of electrolyte: 120°C or less, preferably 110"C or less Based on the above conditions, in this invention, the content of sulfuric acid and chromic acid in the electrolytic solution for cathode electrolysis applied to stainless steel material, The temperature of and the current density for cathodic electrolysis were limited as described below.

That is, the content of sulfuric acid in the electrolyte for cathode electrolysis is 3
It should be limited within the range of ~7 mol/l. If the content of sulfuric acid is less than 3 mol/f, a desired colored film cannot be formed. On the other hand, the content of sulfuric acid is 7 mol/i
If it exceeds ', color unevenness will occur in the colored film. The preferred content of sulfuric acid is within the range of 4 to 6 mol/l.

The content of chromic acid in the electrolyte for cathode electrolysis is between 1 and
5mol/I! should be limited within the range of

If the content of chromic acid is less than 1 mol/1, the colored coating will be insufficiently cured. On the other hand, the content of chromic acid is 5 mo
If it exceeds l/l, color unevenness will occur in the colored film. The preferred content of chromic acid is within the range of 2 to 4 mol/l.

The temperature of the electrolyte for cathodic electrolysis should be limited within the range of 85-120°C. If the temperature of the electrolytic solution is less than 85° C., the colored coating will not be sufficiently cured.

On the other hand, when the temperature of the electrolytic solution exceeds 120° C., evaporation of the electrolytic solution occurs, causing color unevenness in the colored film. A preferred temperature is within the range of 90-110°C.

The current density of cathodic electrolysis should be limited within the range of 0.5 to 50 A/dm.
If it is less than that, the colored film will not be sufficiently cured. On the other hand, if the current density exceeds 5 OA/dm, it becomes impossible to form the desired colored film.
It is within the range of 12A/dm'.

Next, the method of the present invention will be explained using examples and comparing with comparative examples.

〔Example〕

1 mm thick stainless steel plate (SUS 304)
It was degreased by immersion in 0% NaOH solution for 30 minutes, and then washed with water. The stainless steel plate thus degreased and then washed with water is subjected to cathodic electrolysis treatment using a constant DC current under the conditions shown in Table 1 and within the scope of the present invention to form a colored film on the surface of the stainless steel plate. did. Note that platinum was used as the anode. In this way, a specimen Nllll-11 of the present invention (hereinafter referred to as "specimen of the present invention") having a colored film formed on its surface was prepared.

For comparison, a colored film was formed on the surface of the stainless steel plate described above under conditions outside the scope of the present invention as shown in Table 2, and a comparative specimen (hereinafter referred to as "comparative specimen") was prepared.
Ncl-11 was prepared.

Tables 1 and 2 show the time required to form a colored film,
The color tone of the colored film, the corrosion resistance and abrasion resistance of the colored film are also shown. Incidentally, cases in which the time required to form a colored film was less than 10 minutes were marked with a circle, and cases with a time required for formation of a colored film of 10 minutes or more were marked with an X.

The corrosion resistance and abrasion resistance of the colored coating were investigated by the performance tests described below.

(1) Corrosion resistance test A length of 20 m111. A sample with a width of 30 mm was cut out, and this sample was immersed in a 10% PeCl* solution at a temperature of 40° C. for 8 hours. The sample was visually inspected for discoloration and presence of holes, and evaluated as follows.

O: No discoloration or holes, △: Discoloration, but no holes, ×: Discoloration and holes.

(2) Abrasion resistance test The surface of each of the above-mentioned specimens of the present invention and comparative specimens was rubbed 50 times with a 3H pencil lead, and the presence or absence of discoloration in the colored film was visually examined, and The following evaluation was made.

○: No discoloration, △: Slight discoloration, ×: Extremely discolored.

Comparative specimen No. 1, in which the temperature of the electrolyte was lower than the range of this invention, required 25 minutes to form a colored film, and the content of sulfuric acid in the electrolyte was outside of the range of this invention. Comparative specimen fish 2, which was small in number, required 30 minutes to form a colored film.

Comparative specimen Oni 3, in which the current density for cathodic electrolytic treatment was higher than the range of the present invention, was unable to form a colored film.

Comparative specimen Fish 4, in which the current density for cathodic electrolytic treatment is lower than the range of this invention, and Comparative specimen Arashi 5, in which the content of chromic acid in the electrolyte is lower than the range of this invention. Both had poor abrasion resistance and somewhat poor corrosion resistance.

Comparative specimen No. 6, in which the content of sulfuric acid in the electrolytic solution is higher than the range of this invention, Comparative specimen fish 7, in which the content of chromic acid in the electrolytic solution is higher than the range of this invention, and In both comparative specimen No. 8, in which the temperature of the electrolytic solution was higher than the range of the present invention, color unevenness occurred in the colored film.

Comparative specimen Oni 9, in which a colored film was formed by the two steps of forming a colored film and curing the colored film, according to the INC0 method consisting of Prior Art 1 and 2, and colored film according to Prior Art 3. Comparative specimen fish 10, in which a colored film was formed by forming and curing the same, and comparative specimen &11, in which a colored film was formed by alternating current electrolysis in accordance with prior art 4, were: 1 for forming a colored film
It took more than 0 minutes. Furthermore, the corrosion resistance of Prior Art 9 was slightly inferior.

On the other hand, in all of the present invention specimen fishes 1 to 11, the formation time of the colored film was extremely short at maximum of 4 minutes, there was no color unevenness in the colored film, and the film had excellent corrosion resistance and abrasion resistance. Ta.

〔Effect of the invention〕

As described above, according to the present invention, a colored film having high wear resistance and corrosion resistance can be formed on the surface of a stainless steel material in a short time in a single step, which is an industrially useful effect. It can be done.

[Brief explanation of drawings]

The drawing is FIG. 1 is a diagram showing the principle of the invention.

Claims (1)

[Claims] In an electrolytic solution containing 1, 3 to 7 mol/l of sulfuric acid and 1 to 5 mol/l of chromic acid, at a temperature of 85 to 120°C, an amount of 0.5 to 50 A/dm^2 A method for coloring a stainless steel material, comprising subjecting the stainless steel material to cathodic electrolysis treatment at a current density within a range to form a colored film with excellent corrosion resistance and abrasion resistance on the surface of the stainless steel material. 2. The content of the sulfuric acid in the electrolyte is 4 to 6 mol/
l, the content of the chromic acid is 2 to 4 mol/l, and the temperature of the electrolytic solution is 90 to 110°C,
And, the current density of the cathode electrolysis is 2 to 12 A/dm^
2. The method according to claim 1.