JPH03180497A - Surface treatment of steel - Google Patents

Abstract

PURPOSE:To smoothen and purify the surface of a steel member used to treat a high purity substance, to form a corrosion preventive film on the surface of the memer and to prevent impurities from entering the high purity substance by electropolishing the surface of the steel member and washing it with a soln. of a water-repellent organometallic compd. in an alcohol. CONSTITUTION:A member used to produce, store, transfer and treat a high purity substance is made of ordinary carbon steel or low-alloy steel, electropolished with an aq. soln. of phosphoric acid or sulfuric acid as an electrolytic soln. and washed with a washing soln. prepd. by dissolving a water- repellent organometallic compd. such as a perfluoroalkylsilane in an alcohol such as ethanol or methanol. The surface of the steel member is coated with a polymer film having high surface smoothness and superior corrosion resistance and the components of the steel member are prevented from entering the high purity substance as impurities during handling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for surface treatment of steel, and in particular, a method for surface treatment of steel for smoothing and cleaning the steel surface and forming an anticorrosive film on the steel surface. and, in particular, equipment, equipment for the production, storage, transport or processing of highly pure substances that are averse to impurities;
The present invention relates to a steel surface treatment method suitable for surface treatment of ordinary steel and low alloy @ (hereinafter referred to as steel) constituting structures etc. (hereinafter referred to as high purity material processing equipment etc.).

(Conventional technology) The high-purity substance processing equipment, etc. includes cylinders and piping.

There are many parts, such as reaction towers, in a so-called sealed state that are isolated from the outside air, and since corrosion is difficult to occur in these sealed parts, steel is used as a constituent material. The steel constituting the sealed portion comes into contact with the high-purity substance itself or with raw materials or intermediates for producing the high-purity substance (hereinafter referred to as high-purity substance, etc.). In such devices, contamination with impurities is naturally disliked, and it is necessary to prevent such contamination as much as possible.

As part of the measures to prevent the contamination of impurities, the steel constituting the high-purity substance processing equipment, etc. must be treated before using the equipment, etc.
A smoothing cleaning process is performed to smooth and clean the surface. This treatment aims to improve adhesion resistance and suppress contamination of impurities by smoothing the surface and reducing the actual surface area.

Conventionally, the above-mentioned smooth cleaning treatment of the steel surface has been carried out by mechanically polishing the surface. The mechanical polishing method involves, for example, polishing with a whetstone or abrasive paper and then finishing with puff polishing, which can smooth the surface. However, due to this polishing, so-called sharp protrusions are formed in some areas, and abrasive grains and buffing powder remain in the polished area, which causes impurities to easily enter the polishing area. be. That is,
The above-mentioned paris increases adhesion in that area, and residues from the polishing part such as buff powder are themselves mixed in as impurities. Further, in the case of a cylinder having a narrow opening, it is difficult to smooth the opening, and it takes a long time to smooth the opening.

Therefore, instead of the mechanical polishing method described above, attempts have been made to adopt an electrolytic polishing method. The electrolytic polishing method uses steel as an anode and applies a voltage between it and a cathode in an electrolytic solution to cause lightning decomposition to smooth the surface of the steel, and is an aerochemical method. As the electrolyte, a phosphoric acid-based strong acid aqueous solution is often used from the viewpoint of workability. For example, an aqueous solution containing 65 parts of phosphoric acid is used. After the electrolytic polishing treatment, the substrate is washed using ordinary water such as tap water or industrial water as a cleaning liquid, and then dried.

(Problems to be Solved by the Invention) The electrolytic polishing method described above has the advantage that the steel surface can be made smooth without producing any flying spots as in the case of the mechanical fishing bait zero method.

However, in the above-mentioned electropolishing method, since the electrolytically polished surface is extremely chemically active, it is corroded especially during washing with water or drying after electrolytic polishing, and a film-like corrosion product remains attached to the steel surface. This is particularly likely to occur when the electrolyte is highly acidic. Therefore, the conventional electrolytic polishing method described above has
The steel surfaces that make up high-purity material processing equipment, etc. cannot be sufficiently cleaned, and the film-like corrosion products described above are attached to them.
There is a problem that they are mixed into high purity substances as impurities.

The present invention has been made in view of these circumstances, and its purpose is to solve the above-mentioned problems of conventional methods, and to sufficiently cover the surface of steel constituting high-purity material processing equipment, etc. It is an object of the present invention to provide a method for smoothing and cleaning the surface of steel, which can clean the surface of steel and prevent contamination of high-purity substances with impurities.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for surface treatment of steel having the following configuration.

That is, the steel surface treatment method according to the present invention is a steel surface treatment method characterized in that after the surface of the steel is computer-polished, the surface of the steel is cleaned using an alcohol solution containing a water-repellent organometallic compound as a cleaning liquid. be.

(Function) As explained above, the method for surface treatment of steel according to the present invention,
Since the steel is electrolytically polished, the copper surface is smoothed and, as mentioned above, is highly chemically activated. Note that the electrolytic solution remains attached to the steel surface after electrolytic polishing.

After the electrolytic polishing, cleaning is performed using an alcohol solution containing a water-repellent organic metal compound (hereinafter referred to as an organic cleaning liquid) as a cleaning liquid. The liquid in the organic cleaning solution is alcohol, and alcohol has an affinity with an aqueous solution of 4I.
The electrolytic solution that remains on the steel surface after electrolytic polishing is water stone solution as described above. Therefore, by the above cleaning, the TL solution on the steel surface is replaced with the organic cleaning solution and removed (i.e., ?jc cleaning).
can be done. As a result of the cleaning, the cleaning fluid comes into contact with a highly chemically active steel surface.

The organic cleaning liquid is an alcohol solution containing a 10-aqueous organometallic compound, and the water-repellent organometallic compound has excellent affinity with metals, and when it comes into contact with a chemically active metal surface,
It has the effect of strongly bonding to the metal surface and forming a polymer film that coats the metal surface smoothly and uniformly. In addition, if the metal surface is chemically inert, the above-mentioned coating is difficult to form, and even if it is coated, it tends to be uneven, and the bonding force between the coating film and the metal is weak, resulting in poor adhesion. becomes worse.

In this way, if the metal surface that comes into contact with the organic cleaning solution is chemically active, coating will occur smoothly as described above, and the metal surface will be smoothly covered with a uniform polymer film.
Corrosion products are generated in the HB that is in contact with the organic cleaning solution. In addition, since the lFj in the cleaning solution is an alcohol with almost no corrosive properties, it does not produce corrosion products. Furthermore, since the coating is coated with a polymer film having excellent corrosion resistance, no corrosion products are generated.

Since the coating with the polymer film does not impair the surface smoothness, the smoothness of the surface after the coating is equal to or higher than the smoothness of the steel surface after electrolytic polishing.

Therefore, when the organic cleaning solution comes into contact with a highly chemically active steel surface as described above, it is coated with a highly corrosion-resistant polymer film without producing any corrosion products, and the surface of this film layer remains intact after electrolytic polishing. The smoothness is equal to or better than that of steel surfaces.

Therefore, according to the steel surface treatment method according to the present invention, the surface smoothness is high without producing corrosion products, and
It becomes possible to coat the steel surface with a polymer film with excellent corrosion resistance. Therefore, it is possible to sufficiently smooth and clean the surfaces of the parts constituting the high-purity substance processing equipment, etc., and to prevent the contamination of the high-purity substances with impurities. Furthermore, since the steel surface is coated with the above-mentioned corrosion-resistant polymer film, steel elution is extremely difficult to occur compared to conventional electrolytic polishing, water washing, and drying treatments, and as a result, contamination with impurities due to controlled elution is extremely difficult. becomes less likely to occur.

Cleaning of the steel surface after electropolishing with the organic cleaning liquid can be performed by immersing the steel in the organic cleaning liquid, flowing the organic cleaning liquid onto the steel surface, spraying the organic cleaning liquid onto the surface, etc. The cleaning method is not limited.

After cleaning the steel surface, the steel surface may be washed with water to remove the organic cleaning liquid, and then dried. During washing and drying, the steel surface is coated with the above-mentioned corrosion-resistant polymer film, so corrosion does not occur and corrosion products do not remain on the surface, and impurities caused by such corrosion products do not occur. It does not cause the problem of 'l contamination.

Regarding the organic cleaning liquid, the water-repellent organometallic compound therein is not limited, and includes, for example, a silane coupling agent, perfluoroalkylsilane, methyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, amino Type silanes, epoxy type silanes, chlorosilanes, etc. can be used. As for the above-mentioned silane camping agents, those having perfluoro groups have particularly good affinity with the steel surface, improve the adhesion between the polymer film and the steel surface, and have excellent not only water repellency but also oil repellency. Therefore, it is desirable to use a material having a perfluoro group.

The alcohol in the cleaning liquid is not limited, and methanol, ethanol, etc. can be used.

The material to be subjected to the electrolytic polishing and cleaning treatment is ordinary copper or low alloy, and the types thereof are not limited, such as 5541
Targets include Cl1A, Mn steel1, chromium molybdenum steel, etc.

The method of surface treatment of steel according to the present invention is particularly suitable as a method of surface treatment of steel constituting high-purity substance processing equipment, etc., but the application is not limited to this only, and it can be used to prepare a smooth surface. It can also be effectively used as a surface treatment method for steel and its materials that require good corrosion resistance, and for steel and its materials that have a smooth surface and are required to be aesthetically pleasing.

(Example) Arsenal - Soil thickness: 2 mm + width: 20 mm, length: 100 mm steel plate (SS41), 85% phosphoric acid: 65 parts and 9
An aqueous solution (50°C) containing 35 parts of 6% sulfuric acid was used as an electrolyte, and after electrolytic polishing was carried out by applying current for 10 minutes at a current density of 2OA/dm, perfluoroalkyl silane: 0.2
It was washed by immersing it in an ethanol solution (20°C) containing X for 2 minutes, then washed with water, and then dried.

In this way, a steel plate coated with a silicone-based polymer film was obtained without any occurrence of corrosion or residual corrosion products adhering to the surface.

The surface roughness of the steel plate obtained above was measured to determine the smoothness and
When examined, the smoothness was found to be at a high level equivalent to that of the steel surface after electrolytic polishing.

In addition, the above-mentioned steel plate (hereinafter referred to as A material), the same electrolytic polishing as above, then washed and dried (hereinafter referred to as B material), and the same steel plate as above without electropolishing under the same conditions as above. After being washed with water and dried, the mouthpieces (hereinafter referred to as mouthpieces) were simultaneously left in the air at room temperature for 3 days to conduct an estrus test. It should be noted that since the spout was not electrolytically polished, the polymer coating was uneven, and microscopic observation confirmed that the steel surface was partially exposed.

As a result of the above-mentioned rust development test, material B was completely rusted. The spout was partially rusted starting from the exposed steel surface. On the other hand, material A does not rust at all! ,It did not fit.

The same steel plate as in Example 1 was electrolytically polished under the same conditions, then washed by immersion in a 0.1x alcohol solution of methyltrimethynesilane for 2 minutes, then washed with water, and then dried.

In this way, a steel plate coated with a silicon-based polymer film was obtained without any occurrence of corrosion or residual corrosion products adhering to the surface.

When the surface roughness of the obtained steel plate was measured and the smoothness was examined, the smoothness was found to be at a high level equivalent to that of the steel surface after electrolytic polishing.

In addition, the above-mentioned steel plate (hereinafter referred to as A material), the same electrolytic polishing as above, then washed and dried (hereinafter referred to as mouth material), and the steel plate without electrolytic polishing under the same conditions as above. After washing, washing and drying (hereinafter referred to as material) were separately immersed in 80°C ion-exchanged water for 240 flr, the amount of iron in the water was analyzed to determine the amount of iron eluted. On the other hand, since the steel material was not electrolytically polished, the polymer film coating was uneven, and microscopic observation revealed that the steel surface was partially exposed. 2 was given.

As a result, the amount of iron eluted from the mouth material was 200 PPM, and the amount of iron eluted from the material C was 100 PP)'I, and iron elution was observed in every shot. In the case of wood, the detection limit of the analysis (
Iron m: less than 0.01 PPM), and no elution of iron could be observed in the analysis.

(Effects of the Invention) According to the steel surface treatment method according to the present invention, the surface of steel constituting a high-purity substance processing device etc. can be sufficiently smoothed and cleaned.
This will prevent the introduction of impurities into high-purity substances and the like. In addition to the above, since the copper surface is coated with a corrosion-resistant polymer film, steel elution is extremely difficult to occur compared to conventional electrolytic polishing, water washing, and drying treatments, and as a result, contamination with impurities due to copper elution is reduced. It also has the effect of making it extremely unlikely to occur.

In addition, steel other than the steel constituting the above-mentioned high-purity substance processing equipment, etc., such as nets and their materials that have a smooth surface and are required to have good corrosion resistance, and those that have a smooth surface and are required to have good appearance. The surface of steel and its materials can be cleaned and smoothed, and the corrosion resistance of the steel can be improved by coating it with a polymer film.

Claims (1)

[Claims] (1) A method for surface treatment of steel, which comprises electrolytically polishing the surface of steel and then cleaning the surface using an alcohol solution containing a water-repellent organic metal compound as a cleaning liquid.