JP2000051786A - Surface-treated steel material excellent in weather resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make early formable a stabilized rust layer having corrosion resistance in a corrosive air environment, especially to obtain excellent corrosion resistance even in an environment near the seashore where sea salt particles fly, by providing an org. resin coating film containing a specified amt. of nickel sulfate and having a specified range in the thickness on the surface of a steel material or on the surface of its rust layer. SOLUTION: An org. resin coating film containing nickel sulfate is provided on the surface of a steel material or its rust layer surface in order to increase the corrosion resistance of the steel material. The amt. of the nickel sulfate is made to 1 to 65 mass % of the coating film and the thickness of the coating film is made to 5 to 150 μm. When water permeates through such the org. resin coating film, the nickel sulfate is dissociated into a nickel ion and a sulfate ion and the both reach the surface of the steel material or the interface with the rust layer. The sulfate ion corrodes the steel to produce an iron ion which transforms into α-FeOOH (goethite). The nickel ion is trapped by the goethite grains to make the grains into a fine and dense structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel surface-treated steel material, which is capable of forming a rust layer (so-called weathering-stable rust) having a protective effect on the steel material in an atmospheric corrosion environment without loss of aesthetic appearance due to flowing rust or the like. The present invention relates to a surface-treated steel material which can be formed early and has excellent weather resistance.

[0002]

2. Description of the Related Art As is generally known as weathering steel, the corrosion resistance of steel in the atmosphere can be improved by adding elements such as P, Cu, and Cr to the steel. These weather-resistant steels form weather-resistant stable rust (hereinafter simply referred to as "stable rust") that protects against corrosion when exposed outdoors for several years. It is used as a maintenance free steel that does not require

However, since it takes several years to form stable rust, floating rust and flowing rust such as red rust and yellow rust occur during this time, impairing the appearance and polluting the surrounding environment. There is a problem that it also causes. In particular, this tendency was a serious problem in the environment where sea salt particles flew.

To solve this problem, for example, Japanese Patent Laid-Open No. 1-1
No. 42088 discloses a surface treatment method for weather-resistant steel, wherein a surface of a steel material is treated with an acidic aqueous solution containing ions such as a metal to form a film, and further a phosphate film is formed. Is disclosed. However, the above-mentioned method has problems in that the contents of the treatment are complicated, and it is not easy to apply these treatments to a welded portion of steel material, and it is difficult to apply the method to a building structure.

The present inventors have disclosed in Japanese Patent Application Laid-Open No. Hei 6-226198 a weather resistance characterized in that an organic resin coating containing chromium sulfate and / or copper sulfate is provided on the surface of a steel material or the surface of a steel rust layer. A surface-treated steel excellent in heat resistance is disclosed. Although this steel material can easily form stable rust, it is necessary to contain chromium sulfate and / or copper sulfate in the organic resin coating film, and chromium sulfate and copper sulfate are eluted by rainwater. was there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to form a stable rust at an early stage on a surface of weather-resistant steel or ordinary steel without causing floating rust or flowing rust. It is an object of the present invention to provide a surface-treated steel material that is economical and has excellent weather resistance.

[0007]

If the structure of rust is dense, it is easy to physically shut off the atmospheric corrosion environment, and the elution of Fe ions, which is a fundamental cause of floating rust and flowing rust, is reduced.
However, if there are cracks or pores in the rust, it becomes a supply path for water or oxygen, and the corrosion resistance of the rust is reduced. For this reason, it is necessary to form a dense and continuous rust layer as stable rust.

The inventors of the present invention have analyzed stable rust formed by exposing for more than 20 years and found that stable rust is mainly α-Fe
It has been found that it is constituted by a dense set of fine crystals composed of OOH. Therefore, it has been found that the point of the technology for generating stable rust at an early stage lies in a method for promoting the generation of dense α-FeOOH.

Further, in order to generate stable rust at an early stage, it is necessary to promote oxidation of the steel material surface. On the other hand, in order to prevent generation of flowing rust and floating rust until stable rust is generated, It is necessary to prevent the generation of excessive rust. These seemingly contradictory problems can be solved by providing an organic resin-based coating film containing an appropriate amount of nickel sulfate on the steel material surface or the steel material rust layer surface.

When moisture permeates the organic resin coating film, nickel sulfate dissociates into nickel ions and sulfate ions, and reaches the interface between the coating film and the surface of the steel material. Sulfate ions and moisture corrode the steel, producing iron ions. Sulfate ion is α-FeOO whose iron ion is the main component of stable rust.
It has the effect of catalytically accelerating the transformation to H (ge-site).

The nickel ions are incorporated into the α-FeOOH crystal grains and become nickel-substituted gausite, which makes the crystal grains fine and dense. The detailed structure is unknown, and when the amount of nickel taken in is large, the structure may be amorphous by X-ray diffraction. In any case, the corrosion prevention performance of the rust layer is remarkably improved by the action of nickel ions and sulfate ions.

That is, the coating of the present invention allows a suitable amount of moisture or oxygen to permeate the surface of the steel material or the surface of the rust layer, thereby promoting stable rust generation or transformation reaction on the surface and the Fe ion to the outside. It has the function of preventing seepage and completing stable rust generation without flowing rust.

The present invention has been completed based on these findings, and the gist of the present invention is a surface-treated steel material having excellent weather resistance described below.

A surface-treated steel material excellent in weather resistance, comprising an organic resin-based coating film containing nickel sulfate of 1 to 65% by mass and having a thickness of 5 to 150 μm on the surface of the steel material or the surface of the rust layer.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail. In the following, percentages representing chemical compositions mean mass% unless otherwise indicated.

The steel material of the present invention has an organic resin film containing nickel sulfate on the surface of the steel material or the surface of the rust layer. The content of the above nickel sulfate is 1 to 65% based on the weight of the coating film, and the thickness of the coating film is 5 to 150 µm.

When moisture penetrates into the organic resin-based coating film, nickel sulfate dissociates into nickel ions and sulfate ions and reaches the interface between the surface of the steel material or the surface of the rust layer. And a catalytic action to accelerate the transformation of this iron ion into α-FeOOH (goethite).

Further, the nickel ions are incorporated into the goethite crystal grains, so that the goethite becomes nickel-substituted goethite, and the crystal grains have a fine and dense structure. By these actions, the anticorrosion performance of the rust layer is dramatically improved. As described above, nickel sulfate has an extremely excellent effect as a stable rust formation promoter.

In order to obtain these effects, the coating film contains 1% or more of nickel sulfate based on the weight of the coating film. It is preferably at least 5%. If the content of nickel sulfate exceeds 65%, the organic resin component that plays a role in binding these inorganic substances is insufficient, so that the coating becomes brittle and a through-hole is formed from the coating surface to the steel surface, and the flow rust is reduced. May occur. Therefore, the content of nickel sulfate is set to 65% or less. Preferably it is 35% or less.

The organic resin-based coating film has an effect of preventing excessive rust of the steel material and preventing flow rust and floating rust until stable rust is formed. 5μ
m or more.

When the thickness of the coating is less than 5 μm,
The leaching of Fe ions generated by corrosion of the steel material cannot be completely prevented, and there is a possibility that flow rust may occur. Further, in a corrosive environment in which sea salt particles fly, chlorine ions easily penetrate the coating film and cause excessive corrosion, thereby inhibiting the formation of a continuous stable rust coating. The thickness of the coating is preferably 10 μm or more.

If the thickness of the coating film is excessively large, it becomes difficult for water and ions generated by dissociation of nickel sulfate to reach the surface of the steel material, and it takes a long time to form stable rust or the formation of rust is hindered. May be done. This often becomes a problem especially when there is no rust layer on the surface of the steel material. Also,
If the coating film comes off due to impact or the like before stable rust is formed, rust is generated from that part, and the aesthetics and environment are impaired. It is not preferable that the cost is increased and the economic efficiency is impaired. For these reasons, the thickness of the coating film is 150 μm or less. Preferably it is 50 μm or less.

The organic resin used in the paint is not particularly limited, and examples thereof include an epoxy resin, a urethane resin, a vinyl resin, a polyester resin, an acrylic resin, an alkyd resin, a butyral resin, and a phthalic acid resin. Can be. When the above resin is formed into a paint and applied, either a solvent-based paint or an aqueous paint may be used.

Coloring pigments such as red iron oxide, titanium dioxide, carbon black, ocher, and phthalocyanine blue; extender pigments such as talc, silica, mica, barium sulfate, and calcium carbonate; chromium oxide; zinc chromate , A conventional additive such as a thixotropic agent, a dispersant, an antioxidant and the like. The rust-preventive pigment may be included to improve the anti-corrosion property when the steel material is used in a place where the corrosive environment is severe, but even in such a case, the amount of the anti-rust pigment should be added in order not to give an excessive anti-corrosion property. The content is preferably 10% by mass or less.

Further, the organic resin-based coating film preferably contains copper sulphate, iron sulphate, chromium sulphate, phosphoric acid and the like as a stable rust generation promoter in addition to nickel sulfate. Iron ions, chromium ions, or phosphoric acid have an effect of promoting the formation of stable rust by coexisting with nickel ions.

Further, it is preferable to use a coloring pigment to make brown or chocolate of the same color as stable rust so that the organic resin-based coating film will not lose its appearance even if it is partially worn or peeled off.

The content of the additive in the organic resin-based paint is as follows:
The content after drying and solidification is shown. The surface treatment having excellent weather resistance of the present invention can be applied by the following method.

The steel material used as the base metal is not particularly limited in steel type, and may be any of ordinary steel and weather-resistant steel.
Even if the base material is ordinary steel, if an organic resin-based coating film that satisfies the conditions specified in the present invention is provided, the rust is chemically stable and dense due to the action of nickel sulfate in the coating film. Transforms into stable rust and exhibits a protective effect.

However, when any external force acts on the protective rust layer thus generated to cause cracking or peeling, ordinary steel has a self-healing ability to generate stable rust again at the damaged portion. Inferior. Therefore, it is preferable to use weathering steel as the base material.

The state of the surface of the steel material may be either one having a rust layer on the surface or one having the rust layer removed from the surface.
However, in order to generate dense stable rust at an early stage, it is better to remove floating rust and dust on the surface of the base material, and remove floating rust with a brush etc. and clean the surface by air blow or water washing. It is preferable to keep it.

It is also preferable to perform a pretreatment for cleaning the surface such as degreasing, pickling, or shot blasting, which is usually performed.

[0032] The paint is prepared by adding nickel sulfate in an amount such that a coating film of a desired composition can be obtained at the solid content after drying the coating film, and, if necessary, an appropriate amount of a coloring pigment, extender pigment, rust-preventive pigment and other thixotropy pigments. Agents, dispersants, antioxidants and other conventional additives, and mixed with toluene, xylene, isopropyl alcohol, isobutyl alcohol, methyl ethyl ketone, 1-
The viscosity may be adjusted with a known solvent such as butanol or the like or water so as to be suitable for the coating operation to obtain a coating.

These paints can be applied by a known method, for example, a conventional method such as air spray, airless spray, or brushing. The coating can be performed at an arbitrary place and under an arbitrary condition, and can also be applied after processing such as cutting and welding of a steel material on site. After painting, the solvent or moisture of the paint evaporates by natural drying after painting to form a coating film. The thickness of the coating film specified by the present invention is a thickness that can be applied in one coating operation, and therefore is excellent in economy.

[0034]

EXAMPLES The chemical composition shown in Table 1 has a width of 150.
A hot-rolled steel sheet having a length of 70 mm and a thickness of 3.2 mm was used as a base material, and its surface was subjected to a pretreatment by any of the methods X or Y shown in Table 2. . The degree of rust removal of the shot blasted material (Y) was Sa2.
5. The surface roughness was 50 μm as a ten-point average roughness (Rz) specified in JIS-B-0601.

Table 3 shows the contents of the resin composition as the coating composition. The resin-based types B and C using a curing agent are two-pack types, and a main agent (base resin + additive) and a curing agent were mixed and used immediately before coating.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

An appropriate amount of a solvent was added to the coating composition in which the resin system and the additive compounding ratio were variously changed, and a coating composition adjusted to a viscosity of 200 to 1000 CPS using a B-type viscometer was prepared. Was applied to both surfaces of each test piece to produce a coated test piece. Under the same conditions, these painted test specimens were 100m from the coast of Joetsu City, Niigata Prefecture.
On the inland side, they were exposed for up to 5 years, and the occurrence of run-off rust and corrosion weight loss were investigated.

The state of generation of flowing rust was evaluated by visually observing the surface of the test piece with the passage of time and evaluating the result according to the following criteria. ○: No flowing rust, △: Small flowing rust, ▲: Medium flowing rust, ×: Large flowing rust.

The state of formation of stable rust was examined by cutting a test piece exposed for 5 years into a 20 mm square, polishing the cut surface, and observing the cross section with a polarizing microscope. When observed with a polarizing microscope, γ-FeOOH having low anticorrosion properties is polarized, and stable rust becomes a quenching layer, so that the state of formation of stable rust can be confirmed. The rate at which the stable rust covered the steel material was determined and evaluated as follows.

：: stable rust coverage of 90% or more, Δ: less than 90%, 60% or more, ：: less than 60%, 30% or more, ×: less than 30%.

The corrosion state of the base material was determined by measuring the weight of the test piece after removing the coating film remaining on the surface and the generated rust using a solvent or ammonium citrate from the samples exposed for 2 years and 5 years. From the difference from the weight of the test piece before the start of exposure, the weight loss of corrosion of the base steel sheet during this period was determined, and this value was converted to the thickness loss of the base steel sheet and evaluated. Further, the average annual thickness reduction during the three years from the third year to the end of the fifth year was determined from the thickness reductions of the exposure periods of 2 years and 5 years. These results show that the thickness reduction after 5 years is 50μ.
m or less, and the case where the annual average corrosion amount in 3 years was 5 μm / year or less was determined to be good. Table 4 shows the preparation conditions and evaluation results of each test piece.

[0044]

[Table 4]

As can be seen from Table 4, in Test Nos. 1 to 19, which are examples of the present invention, generation of flowing rust was not observed and stable rust was generated at a high rate on the surface of the base material. It was confirmed that the progress of corrosion was almost stopped, with the average annual corrosion amount for 3 years being 5 μm / year or less.

In particular, those containing chromium sulfate, copper sulfate, etc., in comparison with those containing nickel sulfate alone, have a high corrosion inhibiting effect of rust generated due to their synergistic effect, and have a high rate of speed. The effect of promoting stable rust formation was remarkable.

On the other hand, as shown in the results of Test Nos. 20 to 25, the content of nickel sulfate in the coating film was less than 1%, and the thickness of the coating film was out of the range specified by the present invention. In the test piece, flow rust was generated, and formation of stable rust was insufficient. Test number 2 without organic resin coating
6 was not good.

The test pieces after the two-year exposure of Test No. 1 and Test No. 14 were scratched with a knife to reach the steel base, and the exposure was continued for another three years. Test number 14
In the test piece of No. 5, the flow rust was generated from the scratched portion, but in the test piece of Test No. 9, almost no flow rust was observed. This is presumably because the base steel is preferably a weather-resistant steel, and the weather-resistant steel has a self-healing function with respect to stable rust formation.

[0049]

The surface-treated steel material provided with the organic resin-based coating film of the present invention can form a stable rust layer having anticorrosion properties in an atmospheric corrosion environment without causing floating rust such as red rust and yellow rust and flowing rust. ,
It can be formed early. In particular, the effect is exhibited even in the sea salt particle flying environment near the coast. Further, the painting operation is easy, and the surface-treated steel sheet of the present invention can be obtained economically and easily even at the construction site. Therefore, it is extremely useful as a steel material that can be made maintenance-free for buildings requiring corrosion resistance, such as bridges and buildings.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Kazuyuki Kashima 4-53, Kitahama, Chuo-ku, Osaka-shi F-term in Sumitomo Metal Industries, Ltd. 4D075 BB92Y CA32 CA33 CA47 DB02 DC02 DC05 EA06 EA07 EB19 EB22 EB33 EB35 EB36 EB38 EC01

Claims (1)

[Claims] 1. A steel material or a rust layer surface containing nickel sulfate of 1 to 65% by mass and having a thickness of 5 to 150 μm.
A surface-treated steel material with excellent weather resistance provided with an organic resin-based coating film.