JPH1088391A - Treatment of surface of stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase affinity and the thermal conductivity of a stainless steel to vapor or liquid to promote its dispersion and evaporation in the case liquid is brought into contact therewith and to improve coating adhesion thereof by immersing a stainless steel in an iron oxide ion and chromium oxide ion-contg. treating soln. prepd. by specified treatment and forming iron oxide coating film thereon. SOLUTION: A stainless steel immersed in an iron oxide ion (FeO4 <2-> ) and chromium oxide ion-contg. treating soln. obtd. by executing electrolytic treatment with a chromium-iron alloy as the anode in an alkali aq. soln. to form iron oxide coating on the surface. As the chromium-iron alloy to be used as the anode, a ferritic stainless steel contg., by weight, about 0.12% C and about 12 to 25% Cr or a martensitic stainless steel contg. about 0.10 to 1.00% C and about 11 to 17% Cr is suitable. As for the cathode material, limitation is not particularly placed, and the one same as the anode material, the other alkali resistant conductive material or the like may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a stainless steel material having a surface with an affinity for vapor or liquid to promote dispersion and evaporation when the liquid is brought into contact with the surface of the material, as well as heat transfer, coating adhesion, and the like. The present invention relates to a novel surface treatment method for a stainless steel material for improving corrosion resistance.

[0002]

2. Description of the Related Art Stainless steel is a steel containing chromium as a main alloy element, and five types of austenitic, ferritic, austenitic / ferritic, martensitic and precipitation hardening are known. Since these stainless steel materials are excellent in corrosion resistance, heat resistance, chemical resistance, surface brightness and gloss, water repellency, etc., in many fields,
Widely used.

However, since the stainless steel material has high water repellency, it is difficult for a uniform liquid thin film to be formed on the surface thereof. As a result, heat transfer is impaired, and the material used in the operation of condensing vapor or evaporating the liquid is difficult. It has drawbacks such as low efficiency of heat transfer and heat transfer, and low adhesion of the coating when coated.

[0004] Further, stainless steel materials are susceptible to erosion due to electrochemical reactions via solids and droplets attached to the surface, and as a result, the corrosion resistance characteristics of stainless steel materials are impaired, such as salt water damage. The problem is the progress of corrosion of stainless steel in coastal areas where there is a lot of water, or the progress of spot corrosion due to high-concentration nitric acid and sulfuric acid-based liquids generated by repeated water droplet formation and evaporation / condensation due to exhaust gas in high-speed tunnels. I have.

[0005] In order to improve the disadvantages of the stainless steel material, for example, it is necessary to impart lyophilicity to the surface of the stainless steel material and form a liquid thin film without deteriorating the corrosion resistance to improve the heat transfer characteristics. Has been attempted, but has not been practically used because of insufficient effect and industrial implementation. In addition, in the case of painting a stainless steel material to improve its corrosion resistance and to color the stainless steel material, a surface treatment by a chemical conversion treatment is usually performed before the painting in order to improve the adhesion of the coating film. Conventionally, as a surface treatment by such a chemical conversion treatment, a phosphate method, a chromate method, and the like are generally performed. However, in these methods, preparation of a treatment liquid is complicated and a stable effect is obtained. There is a disadvantage that there is no.

[0006]

SUMMARY OF THE INVENTION Under such circumstances, the present invention improves the affinity and heat transfer to a vapor or a liquid on the surface of a stainless steel material, and prevents dispersion and evaporation when a liquid is brought into contact with the surface. The object of the present invention is to provide a surface treatment method for a stainless steel material for accelerating and improving coating film adhesion.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies on a method for modifying the surface of a stainless steel material, and as a result, a treatment solution containing iron oxide ions and chromium oxide ions prepared by a specific treatment has been developed. By immersing a stainless steel material and forming an iron oxide film on its surface, it was possible to improve the affinity and heat transfer to vapor or liquid, and to improve the adhesion of the coating film. Thus, the present invention has been completed.

That is, the present invention provides a treatment solution containing iron oxide ions and chromium oxide ions obtained by electrolytically treating a chromium-iron alloy as an anode in an aqueous alkaline solution.
An object of the present invention is to provide a method for treating a surface of a stainless steel material, characterized by immersing a stainless steel material and forming an iron oxide film on the surface.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, first, a treatment liquid for forming an iron oxide film on the surface of a stainless steel material is prepared. This treatment liquid is subjected to electrolytic treatment in an aqueous alkaline solution using a chromium-iron alloy as an anode,
The iron and chromium in the alloy are eluted and iron oxide ions (Fe
This is an alkaline aqueous solution containing O ₄ ^2- ) and chromium oxide ions. At this time, the chromium-iron alloy used as the anode is a ferritic stainless steel having a carbon content of about 0.12% by weight or less and a chromium content of about 12 to 25% by weight (SUS430, SUS405, SUS).
444) or a martensitic stainless steel having a carbon content of about 0.10 to 1.00% by weight and a chromium content of about 11 to 17% by weight (SUS410JI, SUS
403, SUS410, etc.) are preferred. Carbon content 0.03-0.15
Alloys with a high nickel content, such as austenitic stainless steels (SUS304L, SUS316L, SUS304, etc.) having a weight percent of about 16% by weight or more and a chromium content of about 16% by weight or more and a nickel content of about 6% by weight or more, are made of alkali metals of iron and chromium. Elution into an aqueous solution is unlikely (see FIG. 1).

The cathode material used in the electrolytic treatment is not particularly limited, and may be the same as the anode material, or may be another alkali-resistant conductive material such as iron, titanium, or carbon material. . Examples of the aqueous alkali solution include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide.
Those containing about 10 to about 10 mol / l are used.
There are no particular restrictions on the electrolysis conditions, for example, a bath temperature of about 10 to 40 ° C, preferably 15 to 30 ° C, and a current of 50 to 30 ° C.
DC current is applied under conditions of about 200 mA, preferably about 70 mA to 150 mA, and an electrolysis time of about 10 to 300 minutes, preferably 30 to 240 minutes.

As a result of this electrolytic treatment, iron and chromium are eluted from the alloy of the anode into the alkaline aqueous solution, and a treatment solution containing mainly iron oxide ions (FeO ₄ ^2- ) and containing a small amount of chromium oxide ions is obtained. can get. The concentration of iron oxide ion (FeO ₄ ²⁻ ) in the treatment liquid varies depending on the type of anode material, electrolytic treatment conditions, and the like.
A range of -3000 ppm is preferred.

[0012] This processing solution is treated with the reaction formula 2FeO ₄ ²⁻ + 2CrO ₂ ⁻ + 2H ₂ O → Fe (OH) _{3 over time.}
+ CrO ₄ ^2- + OH ^- in side reactions occur, such as shown, since the iron hydroxide tends to precipitate, After the treatment solution is prepared immediately, that subjected to a surface treatment of the stainless steel desired. If iron hydroxide precipitates due to the above reaction, an oxidizing agent such as sodium hypochlorite is added to the precipitate, and the same electrolytic treatment is performed again to return to the original state. Can be.

Next, the stainless steel material to be surface-treated is immersed in the thus-prepared treatment liquid containing mainly iron oxide ions (FeO ₄ ^2- ) and containing a small amount of chromium oxide ions. Then, an iron oxide film is formed on the surface. There is no particular limitation on the type of stainless steel material to be subjected to such surface treatment, and any of austenitic, ferritic, austenitic / ferritic, martensitic, and precipitation hardening types can be used. The processing conditions at this time are 0-8.
A temperature of about 0 ° C., preferably in the range of 20 to 60 ° C., and a processing time of about 10 minutes to 5 hours, preferably about 30 minutes to 3 hours are used, but there is no particular limitation.

By such a treatment, iron oxide ions (FeO ₄ ²⁻ ) in the treatment liquid chemically react with the surface of the stainless steel material, and a dense, stable and strong Fe ₂ O ₃ (γ-Fe
₍ Probably ₂ O ₃ ) layer.

[0015] The iron oxide film formed on the surface of the stainless steel material in this manner has an affinity for vapor or liquid, promotes dispersion and evaporation when the liquid is brought into contact, and enhances heat transfer and thermal conductivity. Improves coating film adhesion and also improves corrosion resistance.

[0016]

According to the treatment method of the present invention, dispersion and evaporation when a liquid is brought into contact with the surface of a stainless steel material are promoted, heat conductivity and coating film adhesion are improved, and corrosion resistance is improved. It is possible to easily form an iron oxide film having an excellent affinity for vapor or liquid, which also improves the temperature.

The stainless steel material surface-treated by the method of the present invention is excellent in mass transfer and heat transfer.
Applications related to heat transfer and mass transfer, such as distillation, evaporation, absorption, crystallization, humidity control, drying, extraction equipment and combustion, refrigeration equipment, specifically brewing fermentation equipment, chemical manufacturing equipment, bio-related equipment, etc. It is useful for coatings and has excellent coating adhesion, so it is required to improve corrosion resistance by painting and to be colored or multicolored, such as stainless steel for painting of building materials, home appliances, vehicles, ships, etc. Useful. further,
Because of its excellent corrosion resistance, it is useful as a corrosion-resistant building material used in atmospheres such as dust, corrosive pulverized liquid, scattered salt water, condensable gas and steam, and condensable / evaporable exhaust gas.

[0018]

Next, the present invention will be described in more detail with reference to examples.

Reference Example As a chromium-iron alloy, ferrite stainless steel S
US444, SUS3 of austenitic stainless steel
04L and SUS316L were used. The above stainless steel (both electrodes are the same) was immersed as an anode and a cathode in 200 ml of an aqueous solution of potassium hydroxide at a concentration of 6 mol / liter, and a voltage of 1.999 V was applied at a bath temperature of 24 ° C. to apply a direct current. Was passed at 100 mA, and an electrolytic treatment was performed for 240 minutes. Electrolysis treatment time 10 minutes, 20 minutes, 40 minutes, 8
The iron oxide ion (FeO ₄ ²⁻ ) concentration in the aqueous potassium hydroxide solution was measured at 0, 160, and 240 minutes.
FIG. 1 shows SUS444 as A, SUS3
04L is shown as B and SUS316L is shown as C.

FIG. 1 is a graph showing the relationship between the electrolytic treatment time and the concentration of FeO ₄ ²⁻ in the aqueous KOH solution. As can be seen from this figure, SUS304L and SUS316L of austenitic stainless steels having a high nickel content are shown.
Indicates that iron in the alloy hardly elutes.

Example 1 Electrolytic treatment was performed for 120 minutes in the same manner as in the reference example, using SUS444 as the anode and the cathode.
The O ₄ ^2-) treatment solution containing 1000ppm was prepared.
Next, as stainless steel to be surface-treated, SUS4
Using 44, SUS304 and SUS316, each was immersed in the above-mentioned treatment solution and subjected to surface treatment at 40 ° C. for 30 minutes.

The surface hydrophilicity of the surface-treated stainless steel material was compared with that of the untreated stainless steel material. That is, JIS K6768 wetting index standard solution No. Using 32 (surface tension of 32 dyne / cm) and tap water (surface tension of about 72 dyne / cm), about 0.02 ml of each was dropped on the surface of a stainless steel material, and the average length of the major axis and minor axis of the droplet after 1 minute The length was measured and the hydrophilicity was compared. Table 1 shows the results.

[0023]

[Table 1] [Note] (a), (b), (c) and (d) show the average length of the major axis and minor axis of the droplet.

As can be seen from Table 1, the surface-treated product is superior to the untreated product in all types of steel.

Example 2 Electrolytic treatment was performed for 120 minutes in the same manner as in the reference example, using SUS444 as the anode and the cathode.
eO ₄ ^2- ) A treatment liquid containing 3000 ppm was prepared. Next, a SUS316L stainless steel flat plate was immersed in the above treatment liquid, and subjected to a surface treatment at 40 ° C. for 30 minutes.
The wettability of the surface-treated product, the untreated product for comparison, and the treated product by the chromate method were compared by measuring the contact angle with water at several tens of places. Table 2 shows the results.

[0026]

[Table 2]

As can be seen from Table 2, the treated article according to the method of the present invention is more effective than the untreated article, exhibits the same performance as the treated article according to the conventional method, and has a contact angle. The dispersion of the numerical values of is small, and stable wettability is exhibited.

The surface-treated stainless steel plate and the untreated stainless steel plate were each applied to a vertical falling liquid film type evaporator, the cold water outlet temperature and the refrigerating capacity were determined, and the heat transfer properties were compared. The result is shown in FIG. 2 as a graph showing the relationship between the chilled water outlet temperature and the refrigeration capacity. In FIG. 2, the solid line is a processed product, and the broken line is an unprocessed product. As can be seen from FIG.
The refrigeration capacity of the surface-treated product was clearly higher than that of the untreated product. That is, by surface treatment,
It was confirmed that heat transfer was improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the electrolytic treatment time of various chromium-iron alloys and the concentration of iron oxide ions in an alkaline aqueous solution.

FIG. 2 is a graph showing the relationship between the chilled water outlet temperature and the refrigerating capacity in a vertical falling film evaporator to which a surface-treated stainless steel plate and an untreated stainless steel plate according to the method of the present invention are applied.

Claims (2)

[Claims] 1. A stainless steel material is immersed in a treatment solution containing iron oxide ions and chromium oxide ions obtained by electrolytic treatment in an alkaline aqueous solution using a chromium-iron alloy as an anode, and an iron oxide film is formed on the surface thereof. A surface treatment method for a stainless steel material. 2. The chromium-iron alloy is ferritic stainless steel or martensitic stainless steel.
The surface treatment method for the stainless steel material described in the above.