JPH05247663A - Steel material subjected to rust stabilization treatment and its treating method - Google Patents

Abstract

PURPOSE:To form a rust stable in weather resistance in an early period without generating a floating scale or peelable scale such as red rust, yellow rust, etc. CONSTITUTION:An aq. solution of alkaline such as an aq. solution of sodium hydroxide, aq. solution of ammonia or aq. solution of pottasium hydroxide is applied on a rust layer formed on the surface of a steel material by spraying or brushing to supply OH<->, and, at the same time, to make an environment to be > PH7 by which the rust layer is changed to alpha-FeOOH in an early period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust-stabilized steel material having a rust layer which is stable in an atmospheric corrosive environment and has an excellent anticorrosion property, and a rust stabilization method.

[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 self-form rust (hereinafter referred to as weather resistant rust) that is protective against corrosion in a few years outdoors.
It is a so-called maintenance-free steel that does not require any subsequent corrosion resistance treatment such as painting. In the weather resistant steel, it takes several years for the weather resistant rust having corrosion resistance to be formed on the surface of the steel material, so floating rust or flow rust such as red rust or yellow rust occurs during the period up to that time. However, there is a problem that not only it is unfavorable in appearance, but it also causes pollution of the surrounding environment.

Regarding this problem, for example, Japanese Patent Laid-Open No. 1-1420
In the '88 publication, Fe ions of 0.1 to 0.1 are previously formed on the surface of the steel material.
P containing 390.0 g / l and 0.1 to 175.0 g / l of one or more of P, Cu, Cr, Ni, Mn ions
It discloses a method of forming stable protective rust on the surface of a steel material in a short period of time by forming a film by treating with an acidic aqueous solution of H2.3 or less and then forming a phosphate film.

[0004]

However, in the above-mentioned prior art, the contents of the treatment are complicated, such as the necessity of performing an appropriate pretreatment before forming the phosphate film, and the welding of steel materials is required. In this case, it is difficult to apply the treatment only to the welded portion, and there is a problem that it is difficult to apply it to a building structure or the like. Further, conventionally, a surface treatment method such as applying a coating film on the surface of weather resistant steel or applying a coating after forming a phosphate film is known, but the formation of weather resistant rust is slow due to the coating. In addition, there is a problem that the coating film itself deteriorates and the appearance is impaired. Furthermore, the weather resistant steel is visually unsightly for several years until it exhibits a beautiful dark brown color when used so-called "naked", and even weather resistant steel is placed under a specific environment. In that case, there is a problem that the occurrence of the weather resistant rust cannot be expected.

Therefore, the main object of the present invention is to perform a simple and place-free treatment, which causes almost no floating rust or flow rust such as red rust or yellow rust, and a corrosive environment in the atmosphere in a short period of time. It is intended to provide a rust stabilization promoting method for forming a stable weather-resistant rust.

[0006]

The present invention SUMMARY OF] is, OH rust layer formed on the stabilizing process steel, and the steel surface rust with stable alpha-FeOOH at atmospheric corrosion environment on the steel surface ^-
To provide an environment in which the pH exceeds 7 to convert the rust layer into α-FeOOH, thereby providing a method for promoting stabilization of rust.

The OH ^- supply can be carried out by spraying or brushing the surface of the steel material with an alkaline aqueous solution such as an aqueous NaOH solution, an aqueous ammonia solution or an aqueous KOH solution.

The steel material of the present invention has a surface covered with α-FeOOH before it is used as a building, and a steel material already used as a building is treated with the α-FeOOH layer by the treatment method of the present invention. Includes both steel materials with.

The term "rust layer formed on the surface of the steel material before treatment" as used herein means a precipitation type film formed by corrosion involving an aqueous solution. Not included. Also, the rust layer is easily formed by exposing it to the atmosphere outdoors, but by artificially placing the surface of the steel material in a dry-wet repeated environment using various aqueous solutions, the Formed in.

[0010]

[Function] Although various reasons have been discussed as to why weatherproof rust exhibits the above-mentioned excellent corrosion resistance, conventionally, when weatherproof steel is used as a building, after several years have passed. The reason why floating rust such as red rust or yellow rust was not generated was thought to be that amorphous rust was formed on the surface of the steel material. However, as a result of diligent research by the present inventors, it was found that α-FeOOH self-formed on the surface of the steel material greatly contributes to the excellent corrosion resistance of the weather resistant steel material.
Even if the weather-resistant steel material is left in an atmospheric corrosive environment, the α-FeOO is partially formed on the surface of the steel material after several years.
Although H is generated, it takes a very long time until the entire surface of the steel material is covered, and generally it takes about 10 to 20 years depending on the components of the weather resistant steel material and the corrosive environmental conditions to be placed. It seems to be.

The present invention has been made based on the finding that the anticorrosive action of the weather-resistant steel material is due to α-FeOOH formed on the surface of the steel material as described above.

[0012] OH respect rust layer formed on the surface of the steel material ^-
Is supplied to obtain an environment in which the pH exceeds 7, it is possible to convert into a stable α-FeOOH layer having excellent weather resistance. In the present invention, as described above, by supplying OH ⁻ to the rust layer and setting the environment to exceed pH 7, the Fe ions eluted from the steel are converted into α-FeOOH stable to the environment at an early stage. , And the already formed rust layer is converted into stable α-FeOOH. As the OH ^- supplying means, it suffices to apply an alkaline aqueous solution such as an aqueous solution of NaOH, an aqueous solution of ammonia or an aqueous solution of KOH to the surface of the steel material, so that it can be easily performed anywhere without any special equipment. In addition, if the pH during processing exceeds 7, stable α
-FeOOH can be converted, but if it is desired to shorten the processing time, pH 9 to 1
By setting it under the environment of No. 4, it is possible to further promote the stabilization of rust. However, if importance is placed on improving the working environment, it is preferable to perform the treatment in a neutral environment even if the stabilization of rust is delayed. The steel targeted in the present invention is
Materials such as stainless steel and Ni-based alloys that do not generally generate rust are excluded from the present invention because they do not require treatment, and mainly contain elements such as P, Cu, Cr, and Ni, such as weather-resistant steel. In addition to low alloy steel, carbon steel is also targeted.

When applying the alkaline aqueous solution,
Any method such as air spray, airless spray, or brush coating can be used. In addition, it is desirable to wait for drying after application and repeat application multiple times in order to generate stable rust at an early stage, but a sufficient acceleration effect can be expected even with a single application. It is desirable to select it after considering the surrounding corrosive environment, work efficiency, and economic efficiency.

Since the method of the present invention does not require special equipment and can easily perform rust stabilization promotion treatment, it has already been used for railway vehicles, industrial machinery, plant equipment, bridges, buildings and the like. It can be easily applied to weather resistant steel, etc., and can be partially processed during local cutting and welding of steel materials.

[0015]

EXAMPLES The effects of the present invention will be described in detail below with reference to examples. In this example, first, two types of chemical-resistant weather-resistant steel (A) and ordinary steel (B) shown in Table 1 were used, and 150 mm × 60 mm × 5 mm test pieces No. 1 to 1 for each steel type.
No. 1 is manufactured, and No. 1 to 4 are No.
7 is an aqueous ammonia solution, and K for Nos. 8 to 10
A coating treatment was performed with an aqueous OH solution after exposure to the atmosphere for a predetermined period of time, and the test piece No. 11 was subjected to the test as a comparative example without treatment. The surface of the test piece was mirror-finished by emery paper polishing and buffing, and the pH value of each treatment solution was set to the value shown in Table 2.

[0016]

[Table 1]

[0017]

[Table 2]

Test pieces No. 1 to 11 which have been subjected to the above treatment
Under the same conditions, they were exposed to the coastal zone of Kitakyushu City, Fukuoka Prefecture, in a severe atmospheric corrosive environment for 70 days and 335 days, respectively, and their surface properties and the amount of reduction in plate thickness due to corrosion were investigated. As a result, with regard to Nos. 1 to 10 of the present invention, almost no flow rust was observed, and the surface color tone was a uniform dark brown color. On the other hand, Comparative Example No
A large amount of flow rust was generated in the test piece of No. 11, the color tone of the surface was reddish brown, and the distribution of red rust was observed in dots. In addition, as a result of investigating the identification and the distribution of the constituents in the rust layer by X-ray diffraction, Fourier transform infrared spectroscopy and microscopic laser Raman spectroscopy, for the test pieces Nos. 1 to 10,
Both the 70-day exposure test piece and the 335-day exposure test piece had a pH value of
Although the lower the value is, the smaller the tendency is, the entire surface of each test piece was uniformly covered with α-FeOOH. On the other hand, in the case of the untreated No. 11 test piece, the exposure period from the start of exposure was 100% for about 5%.
And the range of about 15% in 365 days is α-
It was only covered with FeOOH, and in other areas, it was covered with β-FeOOH and γ-FeOOH in almost equal amounts. In the case of the weather resistant steel (A), α-FeOOH was slightly present near the steel surface, but it was generally said that they were mixed in the rust layer.

Tables 3 and 4 show the results of the reduction of the plate thickness of each test piece for each exposure period. As is clear from Tables 3 and 4, the test pieces of Nos. 1 to 10, which are within the scope of the present invention, have a reduction in sheet thickness as compared with untreated No. 11 for both the corrosion resistant steel (A) and the ordinary steel (B). Is suppressed to almost half or less, and the effect of the rust stabilization promoting treatment of the present invention is remarkably exhibited. Further, in comparison between the corrosion resistant steel (A) and the ordinary steel (B), the corrosion resistant steel (A)
The result is that the corrosion resistance is superior, but even the ordinary steel (B) has a remarkable corrosion protection effect as compared with the untreated No11.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

As is apparent from the above description, the steel material treated according to the method of the present invention does not cause floating rust or flow rust such as red rust or yellow rust after the treatment, and has stable weather resistance and rust in a short period of time. Can be formed. In addition, because the treatment is easy and can be done in a short period of time at any place, it is possible to produce steel materials covered with a stable rust layer with high corrosion resistance at the factory stage and to cut steel materials locally. It can also be suitably used for processing after processing such as welding.

Claims (2)

[Claims] 1. A α-Fe stable on a steel surface in an atmospheric corrosive environment.
A rust-stabilized steel material having OOH. 2. A method for promoting stabilization of rust, which comprises converting rust layer into α-FeOOH by supplying OH ⁻ to the rust layer formed on the surface of steel material to make the environment exceed pH 7. ..