JP3414364B2 - Rust stabilization treatment method for steel material, steel material subjected to this rust stabilization treatment, and steel structure constructed from this steel material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust stabilizing treatment method for steel materials used in areas with a large amount of incoming salt, such as coastal areas.
Rust having high anticorrosion performance on the surface of weather resistant steel, that is, stable rust at an early stage, relating to a rust stabilization treatment method, a steel material subjected to this rust stabilization treatment, and a steel structure constructed by this steel material Is.

[0002]

2. Description of the Related Art Weather-resistant steel materials include Cu, Ni, Cr, P,
It is made of low alloy steel containing a small amount of elements such as Mo, and when it is exposed to the air without coating, rust excellent in anticorrosion property, that is, stable rust is naturally formed in the process of corrosion and rusting. After stable rust is formed, corrosion of steel hardly progresses.
Weather-resistant steel does not need to be repaired like painted steel, that is, it is maintenance-free.
It is applied to various steel materials such as steel pipes and has a wide range of applications as structures such as bridges and steel towers.

However, in areas with a large amount of incoming salt, such as coastal areas and snow-melting salt-sprayed areas, stable rust is unlikely to form on the weathering steel, and therefore the areas where the weathering steel can be applied are areas with a low amount of incoming salt. Has been limited to.

To cope with this problem, weather-resistant steel containing Ni as a main additive element, which has no coating and has sufficient corrosion resistance even in an environment with a large amount of flying salt, is disclosed in JP-A-9-165647 and JP-A-3-158436. Etc.

[0005]

However, even in the case of these weather resistant steels containing Ni as a main additive element, it takes a long time of 5 years or more before stable rust is formed.
During the period until stable rust is formed, especially flow rust and floating rust in the initial stage of use, the appearance of steel materials and structures may be lost, and further environmental pollution of the environment may occur.

Therefore, an object of the present invention is to provide a method of rust stabilizing treatment of steel material capable of forming stable rust at an early stage in an area having a large amount of flying salt, a steel material subjected to this rust stabilization treatment, and this steel material. To provide a steel structure constructed by.

[0007]

The invention according to claim 1 is
Cr ≦ 0.1 mass%, Ni: 0.4 to 5.0 mass% included
The surface of the weather resistant steel material has trivalent chromium ions
From a resin composition containing water-soluble or trivalent chromium ions
It is characterized by applying the following rust stabilizer .

The invention according to claim 2 is the trivalent chromium.
The amount of ions applied to the weather resistant steel is 1 to 200 μm.
It is characterized by being within the range of ol / cm ² .

The invention according to claim 3 is the invention according to claim 1 or 2.
It is characterized by being subjected to rust stabilization treatment by the method described .

The invention according to claim 4 is the steel according to claim 3.
It is characterized by being constructed of wood .

[0011]

[0012]

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the rust stabilizing treatment method for steel materials according to the present invention will be described.

(Steel) In the present invention, the range of Ni and Cr among the elements contained in the base steel is particularly important from the viewpoint of weather resistance in an area having a large amount of flying salts. Other elements are not particularly limited. Further, it is preferable that the treated surface has scales and rust removed by blasting or the like, but it is not always necessary.

Ni Ni has an effect of forming rust excellent in stable rust formation and excellent in anticorrosion in an environment with a large amount of incoming salt. However, if the added amount of Ni is less than 0.4% by mass, the above-described effects of Ni cannot be obtained, while
If the addition amount exceeds 5.0% by mass, it is disadvantageous from the economical point of view, and a bainite structure is apt to occur, and mechanical properties, particularly toughness are deteriorated. Therefore, the amount of Ni added is
It is preferable to limit it to the range of 0.4 to 5.0 mass%.

Cr Cr is an element that promotes the occurrence of pitting corrosion in an environment with a large amount of flying salts. The perforated corrosion inhibits the generation of stable rust due to the concentration of corrosive anions such as chloride ions. In addition, the amount of flow rust increases due to perforation corrosion.
Therefore, Cr is not substantially contained in the steel material. Here, “not substantially containing” means that 0.1 mass% or less may be contained.

(Rust Stabilizing Agent) The rust stabilizing agent in the present invention is an aqueous solution or resin composition containing trivalent chromium ions. The aqueous solution is a solution of salts of trivalent chromium ions and counter anions. Examples of such salts are trivalent chromium acetate, chromium formate, chromium hydroxide, chromium nitrate, chromium phosphate, and chromium sulfate. And hydrates thereof and the like, but not limited thereto. Among these, chromium acetate, chromium formate, chromium nitrate, chromium sulfate and the like, which have appropriate solubility, are preferable. The resin composition is preferably a resin that can dissolve or disperse the salt and / or aqueous solution containing the trivalent chromium ion, and specifically, an epoxy resin, a urethane resin, a vinyl resin, an amino resin, a polyester resin. , Acrylic resin, alkyd resin, butyral resin, phthalic resin, phenol resin and the like. Further, it is also possible to use those modified with a drying oil or the like as appropriate.

Trivalent chromium ions are generated in rust defects and pores.
Has the function of permeating and densifying rust to form stable rust
ing. However, in order to contribute to the densification of rust
The coating amount of trivalent chromium ions is the steel material unit area (c
m²) 1 μmol / cm²It should be above. one
On the other hand, the coating amount of trivalent chromium ions is the steel material unit area (cm
²), The effect is saturated even if it exceeds 200 μmol
To do. Therefore, the coating amount of trivalent chromium ions is 1 to 2
00 μmol / cm²Limited to within the range.

(Coating Method of Rust Stabilizing Agent) The coating method of the rust stabilizing agent may be a publicly known coating method, that is, air spray, airless spray, brush coating, etc., and the treating method is not particularly limited. In addition, since it does not require treatment such as aging and baking, it can be used for both factory construction and on-site construction.

(Effect of Combination of Steel Material and Rust Stabilizing Agent) Both Ni and Cr have the effect of densifying rust and improving anticorrosion performance of rust. The rates of concentration of these elements in the rust layer are different, and Cr is relatively early in Ni.
Thickens over time. Therefore, by supplying Cr from the rust stabilizing treatment agent, it is possible to stabilize rust at an early stage. Further, as described above, Cr promotes the occurrence of perforated corrosion when included in the steel material, and increases the flow rust amount. From this point as well, it is desirable that Cr is supplied from the rust stabilization treatment agent.

On the other hand, if Ni is supplied from the treating agent, the effect is reduced due to weathering of the rust stabilizing agent before it is concentrated in the steel. Therefore, Ni is preferably added to the steel material and slowly concentrated in rust.

From the above, a dense rust layer in which Cr and Ni are concentrated is obtained by a combination of applying a rust stabilizing treatment agent containing no Ni and Cr to a steel material containing Ni and Cr. Once formed, this makes it possible to form a rust layer having excellent anticorrosion performance.

[0023]

Next, the effects of the present invention will be described in more detail with reference to Examples.

First, a steel material having the chemical composition shown in Table 1 was prepared. In Table 1, A is the steel material of the present invention, and B, C and D are comparative steel materials. 150 for each steel
It was cut into a size of mm × 70 mm × 6 mm, and the surface was shot blasted. The steel materials A, B, C and D thus prepared were coated with the rust stabilizing treatment in the combinations shown in Table 2. Then, each steel material coated with the rust stabilization treatment is tilted at an angle of 30 ° to the south in the coastal area.
It was exposed for a year, and the presence or absence of flow rust and the presence or absence of stable rust formation were evaluated. Average flying salt content during the exposure period was approximately 0.4 mdd
(Mg · NaCl / dm ² / day). The formation of stable rust at this time was evaluated as follows.

[0025]

[Table 1]

For the flow rust, white paint was applied to the lower end of the sample steel material, and from the contamination state of the white paint due to the flow rust,
The following four grades were used for evaluation.

⊚: Not seen at all

◯: Almost no visible

Δ: Some are seen.

X: Remarkably observed.

Stable rust formation was evaluated by peeling the coating film, examining the appearance of rust under the coating film, and evaluating it in the following four stages.

⊚: Rust is dense, has few defects, and is continuously formed.

◯: Rust is dense, but some are defective and discontinuous.

Δ: Rust formation was non-uniform, and powdery rust that was easily peeled off was formed.

X: A layered rust which is easily peeled off is formed.

A ferroxyl test was performed on the rust under the coating. The ferroxyl test evaluates the stability of rust, and a filter paper dipped in a test solution (mixed aqueous solution of potassium ferrocyanide, potassium ferricyanide, and sodium chloride) is attached to the test surface, and the filter paper corresponding to the corrosion active point is attached. This is to investigate the blue spots appearing on. The number density of spots was counted and evaluated according to the following four grades.

⊚: The number of color development points is less than 50 / dm ² .

◯: Number of coloring points is 50 / dm ² or more 100
It is less than the number of pieces / dm ² .

Δ: The number of coloring points is 100 / dm ² or more 20
It is less than 0 / dm ² .

X: The number of coloring points is 200 / dm ² or more.

A cellotape® peel test was performed on the rust under the coating. Cellotape peeling test
The amount of floating rust is evaluated, and the rust surface (test area is 250
A cellophane tape is adhered to 0 mm ² ) and peeled off, and the number density and size of the rust particles attached to the cellophane tape are examined. The same portion was repeated 3 times, and the total amount of floating rust was evaluated according to the following 3 grades.

◯: The amount of floating rust is less than 10 mg.

Δ: The amount of floating rust is 10 mg or more and less than 50 mg.

X: The amount of floating rust is 50 mg or more.

Table 2 shows the above evaluation results.

[0046]

[Table 2]

As is clear from Table 2, all of Invention Examples 1 to 12, which are the rust-stabilized steel materials of the present invention, provided good results in an environment with a large amount of incoming salt. That is,
It has been found that the combination of the steel material of the present invention and the treating agent can prevent flow rust, stabilize rust at an early stage, further improve the paint film peeling property, and greatly improve weather resistance and appearance. This is due to the densification of rust due to Ni of the base steel material and the trivalent chromium ions in the treatment agent, and the flow rust prevention effect due to the fact that the steel material does not substantially contain Cr.

Further, the combination of the present invention gave excellent results in the coating property, which is presumed to be due to the following mechanism. (1) Pitting corrosion occurs in the Cr-added steel, and as a result, a portion having a large rust thickness locally occurs. (2) Local rust thickness growth presses the coating film, resulting in
Peeling occurs in the coating film. (3) If Cr is not added but Ni is not added, the rust is not sufficiently densified, so that the rust layer becomes thick and irregularities become large, resulting in uneven appearance.

On the other hand, each of the comparative examples had the following problems.

In Comparative Example 1, since the coating amount of trivalent chromium ions was out of the range of the present invention, the rust densification was insufficient, and therefore stable rust formation and cellotape peeling test results were inferior. Was there.

In Comparative Example 2, the coating amount of trivalent chromium ions is within the range of the present invention, but since the Cr content in the steel material is large, local corrosion due to Cr in the steel material occurs,
Since the number of defects in the rust increased, the flow rust resistance and the ferroxyl test results were poor.

In Comparative Example 3, the coating amount of trivalent chromium ions was out of the range of the present invention, and the C content in the steel material was small.
Since the r content was high, all the evaluation items were inferior.
In particular, local corrosion caused by Cr in the steel material occurred and the number of defects in the rust increased, so that the flow rust resistance and the ferroxyl test result were remarkably poor.

In Comparative Example 4, the amount of trivalent chromium ions applied was within the range of the present invention, but the amount of Ni added in the steel material was outside the range of the present invention, and the Cr content in the steel material was small. However, it was inferior in all evaluation items. In particular, since the Ni content in the steel material was small, the rust densification was insufficient, and the result of the cellophane tape peeling test was extremely poor.

In Comparative Example 5, the amount of trivalent chromium ions applied was small outside the scope of the present invention, the amount of Ni added in the steel material was outside the scope of the present invention, and the content of C in the steel material was small.
Since the r content was large, all the evaluation items were significantly inferior.

In Comparative Example 6, the coating amount of trivalent chromium ions was within the range of the present invention, and the Cr content in the steel material was small, but the Ni addition amount in the steel material was outside the range of the present invention. Therefore, the flow rust resistance was excellent, but the other evaluation items were inferior. In particular, since the amount of Ni added to the steel material was small, the rust densification was insufficient, which resulted in a markedly poor cellophane tape peel test result.

[0056]

As described above, according to the rust-stabilized steel material of the present invention, stable rust can be formed early in an environment with a large amount of flying salt. Moreover, by using the rust-stabilized steel material of the present invention in a structure, the structure can be maintenance-free even in an environment with a large amount of incoming salt, so that the cost of repainting the conventional coating is unnecessary. , Industrially useful effects are brought about.

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Claims (4)

(57) [Claims] 1. Cr ≦ 0.1% by mass, Ni: 0.4 to
The surface of the weather-resistant steel material containing 5.0% by mass is trivalent
Including water-soluble or trivalent chromium ion containing rom ion
A rust stabilizing treatment method for a steel material, which comprises applying a rust stabilizer comprising a resin composition . 2. The weathering steel containing the trivalent chromium ions.
The amount applied to the material is within the range of 1 to 200 μmol / cm ² .
And characterized in that, in claim 1, wherein, rust stabilization method of the steel material. 3. Rust by the method according to claim 1 or 2.
A steel material characterized by being subjected to stabilization treatment. 4. Constructed from the steel material according to claim 3.
A steel structure characterized by the above.