JPH10195678A - Formation of anticorrosive coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly anticorrosive film on a steel material with an aq. soln. by dipping a steel material in an H2 SO4 -acidified soln. contg. MoO4 <2-> , WO4 <2-> , VO4 <3-> and VO3 <-> to form a film and stabilizing the film by the heat treatment at a specified temp. SOLUTION: When a steel material 1 is dipped in an H2 SO4 -acidified soln. contg. >=1 kind among MoO4 <2-> , WO4 <2-> , VO4 <3-> and VO3 <-> , a cathodic reaction such as MoO4 <2-> +4H<+> +2e→MoO2 +2H2 and an anodic reaction such as 2Fe+3H2 O→Fe2 O3 +6H<+> +6e occur at the same time, and a thin and dense passivated MoO3 plus Fe2 O3 moist film 3 is formed. The film 3 is heat-treated at 100-700 deg.C, hence the peroxide group and water are released, and a stable MoO2 plus Fe2 O3 film 4 is formed. Further, the soln. is acidified with sulfuric acid to prevent the dissolution reaction of Fe, to increase the film forming rate and not to precipitate a passivator, and the pH is preferably controlled to 2 to 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an anticorrosion coating for suppressing corrosion of a steel material.

[0002]

2. Description of the Related Art Heretofore, as a technique for controlling corrosion of steel materials, addition of alloying elements for improving corrosion resistance and surface treatment of materials have been performed as controls on the material side. Further, the control on the corrosive environment side has been carried out by adding a corrosion inhibitor to the environment.

A method of subjecting a material to a surface treatment is intended to impart corrosion resistance or other functions to the material while maintaining mechanical properties such as strength. The surface treatment performed for the purpose of improving the corrosion resistance includes a method of coating a metal by plating, thermal spraying, PVD, or the like, or a film of a metal oxide or a hardly soluble salt in an aqueous solution such as an anodizing or chemical conversion treatment. Methods, a method of coating an organic material by coating, etc., a method of coating an inorganic material by a PVD method, a CVD method, and the like.

[0004]

However, when hot-dip plating and thermal spraying of a metal, the metal must be melted at a high temperature, resulting in poor workability. Further, the PVD method and the CVD method are not suitable for surface treatment of a structural material. Coating is the most common anticorrosion measure, but corrosion may progress due to defects in the coating, and it is common to apply a chemical conversion treatment before coating.

[0005] Forming an anticorrosive coating in an aqueous solution is an effective method because a surface treatment of a structural material is possible without requiring high temperatures. Anodization of Al, boehmite treatment, phosphate treatment of steel, chromate treatment of Zn, Al, Mg, and the like are often used. However, such treatment alone is often insufficient from the viewpoint of corrosion resistance. Further, treatment using chromate or chromate, such as chromate treatment, has problems such as toxicity and environmental pollution.

An object of the present invention is to provide a method for forming a coating having good corrosion resistance on a steel material by using an aqueous solution and heat-treating the coating to form a corrosion-resistant coating.

[0007]

Means for Solving the Problems] method of forming a corrosion coating of the present _{^{invention, MoO 4 2-, WO 4 2-}} , VO 4 3-, VO 3 - the H ₂ SO ₄ acid solution containing at least one By immersing the steel material in the surface, at least one of Mo, W and V
Forming a film comprising an oxide and / or a hydroxide and / or an oxyhydroxide containing a seed;
Stabilization by heat treatment at a temperature of 0 to 700 ° C.

Further, a metal and / or metal carbide comprising at least one of Mo, W and V is dissolved in an aqueous solution of H ₂ O _{2, and an} aqueous solution obtained by decomposing and removing excess H ₂ O ₂ is attached to a steel material. Later, by heat treatment at a temperature of 100 to 700 ° C. for stabilization, oxides and / or hydroxides and / or oxyhydroxides of at least one of the metals are formed on the surface of the steel material. .

Further, the present invention resides in a steel material having a corrosion protection coating formed by the above-described method.

According to the present invention, a steel material can be coated with a film having excellent corrosion resistance. Also, a large area material can be coated at a relatively low temperature.

The principle and method will be described below in detail.

MoO ₄ ²⁻ , WO ₄ ²⁻ , VO ₄ ³⁻ , VO ₃ ⁻
Is used as a passivating agent or as an anode inhibitor and suppresses the corrosion of steel materials by putting it in a small amount in a corrosive environment. The mechanism is due to the fact that the corrosion potential is shifted to a noble direction by several hundred mV, and an oxide film having high corrosion resistance, which is called a passive film, is easily formed on the material surface.
That is, since the passivating agent has a unique property that it is rapidly reduced by the cathodic current, it is preferentially adsorbed on the surface of the steel material.

MoO ₄ ²⁻ , WO ₄ ²⁻ , VO ₄ ³⁻ , VO ₃ ⁻
When a steel material is immersed in an H ₂ SO ₄ oxidizing solution containing at least one of the following, the following cathodic reaction and anodic reaction occur simultaneously on the surface, and MoO ₄ ²⁻ + 4H ⁺ + 2e → MoO ₂ + 2H ₂ O: cathodic reaction (Formula 1) WO ₄ ^2- + 4H ⁺ + 2e → WO ₂ + 2H ₂ O: Cathodic reaction (Formula 2) VO ₄ ^3- + 4H ⁺ + e → VO ₂ + 2H ₂ O: Cathode reaction (Formula ₃ ) VO ₃ ⁻ + 2H ⁺ + e → VO ₂ + H ₂ O: Cathode reaction (Formula 4) 2Fe + 3H ₂ O → Fe ₂ O ₃ + 6H + 6e: Anode reaction (Formula 5) MoO ₂ + Fe ₂ O ₃ , WO ₂ + Fe ₂ O ₃ , VO ₂ + Fe ₂ O
Form a thin and dense passive film such as ₃ .

The solution is sulfuric acid in order to promote the dissolution reaction (anode reaction) of Fe to increase the rate of film formation and not to precipitate the passivating agent. The pH is 2
~ 3 is desirable.

Although this film contains a large amount of water because it is prepared in an aqueous solution, it is dehydrated by heat treatment at 100 to 700 ° C., and the base material itself is oxidized and the film thickness is increased, so that the film becomes stable. Note that the heat treatment temperature is 100
C or higher. The temperature is set to 700 ° C. or lower so that the film does not sublime. In order to avoid low-temperature tempering embrittlement, 10
It is desirable to be 0-200 degreeC or 400-700 degreeC.

A metal and / or metal carbide comprising at least one of Mo, W and V is dissolved in an aqueous H ₂ O ₂ solution,
When excess H ₂ O ₂ is decomposed and removed, an aqueous solution of polymolybdic peroxide, polytungstic peroxide, and polyvanadic acid is obtained. When this aqueous solution is spin-coated on a steel material, a thin film is formed on the surface. When this thin film is heat-treated at a temperature of 100 to 700 ° C., it loses a peroxide group and water and becomes a stable film.

[0017]

Next, the present invention will be described specifically with reference to examples.

Example 1 FIG. 1 is a sectional view showing a process of forming an anticorrosion coating according to the present invention. 10 wt% Na ₂ Mo
The case where carbon steel is immersed in an aqueous solution of 50 ° C. at pH = 2 by adding H ₂ SO ₄ to O ₄ for 10 minutes is shown. MoO ₄ ^2- is adsorbed on Fe and is reduced simultaneously with the oxidation of Fe. As a result, a thin and dense MoO ₂ + F
e ₂ O ₃ water-containing film is formed.

By subjecting this to a heat treatment at 200 ° C., it is dehydrated to form an oxide film having high corrosion resistance.

Embodiment 2 FIG. 2 is a sectional view showing a process of forming an anticorrosion coating according to the present invention. The metal W powder is dissolved in an aqueous solution of H ₂ O ₂ , and excess H ₂ O ₂ is decomposed and removed with a platinum catalyst to obtain polytungstic peroxide (2WO ₃ .H ₂ O ₂ .2).
H ₂ O) aqueous solution. When this solution is spin-coated on carbon steel, a film is formed on the surface. When this film is heat-treated at 200 ° C., it becomes a stable WO ₂ + Fe ₂ O ₃ film.

Example 3 FIG. 3 shows current-potential characteristics when carbon steel and carbon steel coated with a MoO ₂ + Fe ₂ O ₃ film by the method for forming an anticorrosive coating of the present invention were electrochemically polarized in the anode direction. FIG. In the case of untreated carbon steel, when the potential is moved in the direction of the anode, a current suddenly flows, and it can be seen that corrosion is extremely likely.

On the other hand, according to the anticorrosion coating forming method of the present invention, M
In the carbon steel coated with the oO ₂ + Fe ₂ O ₃ coating, no sharp increase in current was observed even when the potential was moved toward the anode.
It was confirmed that the corrosion resistance was improved.

[0023]

According to the present invention, an anticorrosion coating having excellent corrosion resistance can be applied to a large area material at a relatively low temperature on the surface of a steel material. Therefore, an inexpensive material such as carbon steel can be made highly corrosion resistant, which is industrially useful.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a process of forming an anticorrosion coating of the present invention.

FIG. 2 is an explanatory view showing a process of forming an anticorrosion coating of the present invention.

FIG. 3 is a graph showing the relationship between carbon steel and M according to the present invention.
FIG. 4 is a current-potential characteristic diagram when the carbon steel coated with the oO ₂ + Fe ₂ O ₃ film is electrochemically polarized in the anode direction.

[Explanation of symbols]

1: Carbon steel, 2: Passivator MoO ₄ ^2- , 3: MoO ₂
+ Fe ₂ O ₃ water-containing film, 4 ... MoO ₂ + Fe ₂ O ₃ film.

Claims (2)

[Claims] A method for forming an anticorrosion coating on a steel material, comprising the steps of:
_{^{oO 4 2-, WO 4 2-,}} VO 4 3-, VO 3 - at least 1
A film made of an oxide and / or a hydroxide and / or an oxyhydroxide containing at least one of Mo, W and V on a surface by immersing a steel material in an H ₂ SO ₄ acidic solution containing a seed. To form a film,
A method for forming an anticorrosion coating, which is stabilized by heat treatment at a temperature of ° C. 2. A method for forming an anticorrosion coating on a steel material, comprising the steps of:
Metals and / or metal carbides of at least one of o, W, and V are dissolved in an aqueous solution of H ₂ O _{2, and an} aqueous solution obtained by decomposing and removing excess H ₂ O ₂ is attached to a steel material.
By stabilizing by heat treatment at a temperature of 0 to 700 ° C., an oxide comprising at least one of the above metals and / or
Alternatively, a method for forming an anticorrosion coating, comprising forming a hydroxide and / or an oxyhydroxide on the surface of a steel material.