JP2718337B2 - Rust stabilization evaluation method for weathering steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating rust stabilization of weathering steel, and more particularly to a method for accurately and easily evaluating the degree of stabilization of a stable rust layer exhibiting a protective action against an atmospheric corrosion environment. .

[0002]

2. Description of the Related Art Generally, corrosion resistance in the atmosphere can be improved by adding elements such as P, Cu, Cr, and Ni to steel. These low-alloy steels are called weather-resistant steels and form rust (hereinafter referred to as stable rust) that protects against corrosion in the outdoors for several years to several decades. This is a so-called maintenance-free steel that does not require processing.

However, it takes a long time for stable rust to be formed on weathering steel, and the time required for stabilization varies greatly depending on environmental conditions. Further, stable rust may not be formed depending on environmental conditions. In other words, when weather-resistant steel is used for structures, etc., the time required for the formation of stable rust varies depending on the individual use environment, but it is important to know the time required for anticorrosion treatment at an appropriate time. Important from a point of view, but with significant difficulty.

[0004] By the way, during the period until the rust layer formed by atmospheric corrosion is stabilized and becomes stable rust, floating rust such as red rust and yellow rust and flowing rust are generated, which is not only externally undesirable. It also causes pollution of the surrounding environment. Therefore, it is necessary to accurately understand the degree of stabilization of the rust layer in order to take measures against the contamination.

On the other hand, it has been pointed out that as a conventional method of evaluating the degree of stabilization of a rust layer, a change with time in the amount of corrosion is measured and evaluated from the weight reduction of a base steel material (Nippon Kokan Technical Report, N
o. 46,250 (1969)).

[0006]

However, this method is
Although effective in the laboratory, it is virtually impossible to measure the weight loss of a structure once constructed.

Accordingly, an object of the present invention is to make it possible to accurately evaluate the degree of stabilization of a rust layer of a weather-resistant steel material, and to evaluate the rust layer of a weather-resistant steel material of a constructed structure. It is in.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for collecting a very small amount of a rust layer of a weather-resistant steel material, the ratio of the amount of α-FeOOH to the total amount of the collected powder, and The constitution is to evaluate the degree of stabilization of the rust layer by measuring at least one of the average crystal grain diameters of α-FeOOH present.

[0009] The degree of stabilization of the rust layer referred to in the present invention is:
The meaning includes both the presence or absence or the process of formation of stable rust, and the degree of formation of stable rust or the level of corrosion resistance.

The term “weather-resistant steel material” as used in the present invention refers to all steel materials capable of forming stable rust on the surface.
3114 (Weather-resistant steel: SMA) and JIS G 3125 (High weather-resistant steel: SPA) Stable rust due to surface treatment, etc., in addition to weather-resistant hot-rolled steel and highly weather-resistant rolled steel for welded structures And the like, which can form steel.

[0011]

[Action]

(Regarding the evaluation method based on the ratio of the amount of α-FeOOH to the total amount of the rust layer-collected powder) According to a long-term study of the present inventors, α-FeOOH has a high anticorrosion property formed by exposing a weather-resistant steel material for a long period of time. It is a major constituent of stable rust, and is known to be chemically stable in normal atmospheric corrosion environments without phase transformation or dissolution. In addition, through many exposure tests, α-F
It has been found that there is a close correlation between the ratio of the eOOH amount and the degree of stabilization of the rust layer.

Therefore, at an appropriate time, the degree of stabilization of the rust layer can be evaluated by measuring the ratio of the amount of α-FeOOH to the total amount of the rust layer collected powder, and the effectiveness of this method is remarkable.

(Evaluation Method Based on Average Crystal Particle Size of α-FeOOH in Powder Collected from Rust Layer) Further, as a result of diligent research conducted by the present inventors, the average crystal grain size of α-FeOOH in the powder collected from the rust layer was small. As the density of the rust layer increased, the higher the degree of stabilization, the higher the degree of stabilization.
That is, as described above, α-
The rust layer is stabilized when the ratio of the amount of FeOOH is equal to or more than a certain amount. Even in such a case, the smaller the average crystal grain size of α-FeOOH is, the more the stable rust layer is densified and the degree of stabilization is further improved. It is.

Therefore, after confirming the formation of stable rust by the above method, α-FeOOH
By measuring the average crystal grain size, the corrosion resistance of stable rust can be accurately evaluated.

In the above method, a very small amount of a rust layer of a weather-resistant steel material is sampled, and the ratio of the amount of α-FeOOH to the total amount of the sampled powder is determined by X-ray powder diffraction or the like. -The average crystal grain size of FeOOH can be easily implemented by transmission electron microscopy or the like. Furthermore, only a small amount of rust layer is collected on site, and the workability is good. Therefore, it is easy to evaluate the rust layer of the weather-resistant steel material of the constructed structure. In addition, in collecting the rust layer, it is preferable to collect the rust layer until a part of the steel surface is exposed in order to obtain average information of the rust layer.

[0016]

The effects of the present invention will be described below with reference to examples. The test steel (weather resistant steel (steel type symbol S
MA) JIS G 3114, high weather resistance steel (Steel type symbol SPA) JIS
G 3125) is shown in Table 1. The dimensions of the test piece were 150 mm × 60 mm × 3 mm, and the surface thereof was polished with emery paper and buffed.

[0017]

[Table 1]

Under the same conditions, each of the test pieces shown in Table 1 was exposed to an industrial area in Amagasaki City, Hyogo Prefecture, 4 km from the coast, for 20 years, and the corrosion rate (plate per unit time) was determined at regular intervals. The thickness reduction) was evaluated by measuring the weight of the steel sheet. Further, about 100 mg of the rust layer of the same test piece was sampled with a cutter knife until the steel surface was confirmed and ground to obtain a powder sample. Using this, the ratio of the amount of α-FeOOH to the total amount of the powder sample was determined by X-ray powder diffraction. Measurement and α-FeO in the powder sample by transmission electron microscopy.
The average crystal grain size of OH was measured (at this time, α-FeOO
H was identified by an electron diffraction pattern).

FIG. 1 shows α-FeOO with respect to the total amount of the powder sample.
The relationship between the ratio of the amount of H and the corrosion rate of the steel sheet is shown. Referring to FIG. 1, the amount of α-FeOOH is approximately 50% of the total amount of the powder sample.
Above the above, the corrosion rate was significantly reduced, indicating that the rust layer was stabilized.

FIG. 2 shows α-FeOOH in the powder sample.
Shows the relationship between the average grain size and the corrosion rate of the steel sheet. In addition,
○ indicates the results when the weight ratio of α-FeOOH is 50 ± 5%, and ● indicates that the weight ratio of α-FeOOH is 7%.
The results are for 5 ± 5%. α-FeOOH
When the amount ratio is 50% or more, the rust layer becomes stable rust as described above. However, even in this case, when the average crystal grain size of α-FeOOH is 100 nm or less, the corrosion rate further decreases. This confirms that the stable rust is denser and has a higher degree of stabilization.

[0021]

As described above, according to the present invention, the degree of stabilization of the rust layer of the weathering steel can be accurately evaluated, and the rust layer of the weathering steel of the constructed structure can be easily evaluated. it can.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of the amount of α-FeOOH to the total amount of a powder sample and the corrosion rate of a steel sheet.

FIG. 2 is a graph showing the relationship between the average crystal grain size of α-FeOOH in a powder sample and the corrosion rate of a steel sheet.

Claims (1)

(57) [Claims] A rust layer of a weather-resistant steel material is sampled in a very small amount, and at least one of a ratio of an amount of α-FeOOH to the total amount of the sampled powder and an average crystal grain size of α-FeOOH present in the sampled powder is determined. A rust stabilization evaluation method for weathering steel, wherein the degree of stabilization of the rust layer is evaluated by measuring.