JP2001001443A - Coated steel material excellent in water-resisting adhesion and cathode separation resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated steel material with a coating demonstrating good, water-resisting adhesion even after a long term use in humid environment and, at the same time, having good cathode separation resistance even after electrical corrosion protection is applied. SOLUTION: By forming a coating on a low alloy steel containing 0.5 wt.% or more, preferably 0.5 to 5 wt.% of chromium, so as to obtain an insulation resistance of 104 Ω.m2 or higher, a coated steel material with a coating demonstrating good, water-resisting adhesion even after a long term use in humid environment and, at the same time, having good cathode separation resistance even after electrical corrosion protection is applied. Further, by adding at least one of 0.1 to 2 wt.% of molybdenum and 0.1 to 1.5 wt.% of aluminum, an alloy having good, water-resisting adhesion, the good cathode separation resistance and satisfying the conditions of the mechanical characteristics such as toughness or the like, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel material mainly used in a wet environment, and more particularly, to a low alloy steel and an optimized coating to greatly improve water adhesion and cathodic peeling resistance. The present invention relates to a coated steel material that has been improved.

[0002]

2. Description of the Related Art Civil engineering materials used in humid environments, such as steel pipe piles, steel sheet piles, steel pipe sheet piles, floating structures, and other steel structures used in marine environments, pipelines, and steel pipes for piping, are used in wet environments. Extension of service life in the environment is required. Therefore, a coated steel material is used for such an application. Generally, when a coated steel material is used in a humid environment, its adhesion strength is greatly reduced.

In such an environment, it is important to suppress a decrease in the adhesive strength between the steel material and the coating. Particularly, when the electrolytic protection is used in combination, the cathodic peeling resistance is an important problem. The technique of applying cathodic protection is common in marine structures, but when performing anticorrosion for a long period of time, it is necessary to provide a large number of galvanic anode materials (anodes), so the cost is enormous.

[0004] As a method of cathodic protection for marine structures, there are cases where the method is used in combination with painting and cases where painting is not performed. In the former case, the portion where the coating film is present is inhibited from being corroded by the coating film and has high electric resistance, so that the necessary anticorrosion current is suppressed and the cost can be reduced. However, when the coating is used in combination, the coating film develops a defect with the passage of time and peels off, so that the cost of the cathodic protection is governed by the progress speed of the peeling of the coating film.

That is, it is necessary to supply a sufficient anticorrosion current to the portion where the coating film has peeled off in order to suppress corrosion. For this reason, the required anticorrosion current increases with time with the peeling of the coating film. When the speed of the peeling of the coating film is high, the anticorrosion current required for maintaining the anticorrosion of the structure increases, and the required number of anodes and the required current increase, thereby increasing the anticorrosion cost.

As a countermeasure against such a problem, for example, Japanese Unexamined Patent Publication No. Hei 7-11455 proposes a technique of subjecting a coated steel material to a chromate treatment on the surface of the steel material as a chemical conversion treatment in order to improve the water adhesion resistance and the cathodic peeling resistance. Have been. Japanese Patent Application Laid-Open No. 61-40151 proposes a treatment method using a silane coupling agent. Further, JP-A-8-11258
The publication also proposes a method of adding a rust preventive salt to the primer.

[0007] Further, as a technique for providing cathodic protection, Japanese Unexamined Patent Publication No.
No. 176791 proposes a method of applying an alkali-resistant paint to chromium (Cr) -containing steel.

[0008]

The above-mentioned prior art is disclosed in Japanese Patent Application Laid-Open No. 7-11455, a chromate treatment technology, and Japanese Patent Application Laid-Open No. 61-4015.
Patent Document 1: Method for treating silane coupling agent
Although any of the methods for adding a rust-preventive salt to a primer disclosed in -11258 are effective in a short-term cathodic peeling test environment, they have been studied in a highly corrosive humid environment represented by a marine environment. No, long-term effects cannot be expected.

The method of applying an alkali-resistant paint to chromium (Cr) -containing steel disclosed in Japanese Patent Application Laid-Open No. 9-176791 is a technique intended only for electrolytic protection. Therefore, the effect of not applying cathodic protection is not specified.

[0010] It is an object of the present invention to provide a coated steel material having good water adhesion of a coating even when used in a wet environment for a long period of time, and having good cathodic peeling resistance even when electrolytic protection is applied. And

[0011]

SUMMARY OF THE INVENTION According to the present invention, a coating is formed on a low alloy steel containing chromium, so that the coating has good water adhesion even when used for a long time in a humid environment, and Provided is a coated steel material having good cathodic peeling resistance even when electrolytic protection is applied.

The invention according to claim 1 is characterized in that a low alloy steel containing chromium of 0.5 wt% or more is coated so as to have an insulation resistance of 10 ⁴ Ω · m ² or more. A coated steel material with excellent adhesion and cathodic peel resistance.

In the present invention, an essential condition required for a steel material component having excellent water adhesion and cathodic peel resistance is that chromium be contained in an amount of 0.5 wt% or more. During the review process,
It has been found that when the chromium content of the steel material is 0.5 wt% or more, the coating has improved water adhesion resistance and cathode peeling resistance. Further, even during the cathodic protection, the inclusion of chromium causes the atmospheric oxide coating formed on the surface of the steel to contain chromium, so that it is difficult to be reduced under the cathodic protection environment. In this way, a decrease in the adhesion between the coating film and the steel material is prevented.

Further, the coating has an insulation resistance of 10 ⁴ Ω · m ²
It is necessary to do above. If the insulation resistance of the coating is less than 10 ⁴ Ω · m ² , even if a steel material containing 0.5% by weight or more of chromium is used as the base steel material, the water adhesion and cathode peeling resistance of the coating are not improved.

The invention according to claim 2 is the coated steel material according to claim 1, wherein the low alloy steel forming the coated steel material contains 0.5 to 5 wt% of chromium.

In the present invention, the upper limit of the chromium content is set to 5% by weight because it has been found that even if chromium is added, the effect is saturated when it exceeds 5% by weight.

According to a third aspect of the present invention, the low alloy steel forming the coated steel material contains 0.5 to 5% by weight of chromium and at least one of 0.1 to 2% by weight of molybdenum and 0.1 to 1.5% by weight of aluminum. 2. The coated steel material according to claim 1, wherein:

Molybdenum (Mo) and aluminum (Al)
Has the same effect as chromium, and if necessary, one or two of them may be added to chromium. here,
If the amount of molybdenum added is less than 0.1 wt%, there is no effect, and 2 wt%
If it exceeds, the effect is saturated. Also, aluminum is 0.1w
Addition of less than t% has no effect, and exceeding 1.5 wt% saturates the effect and adversely affects the mechanical properties.
Add t% or less. In addition, other alloying elements may be added to satisfy conditions such as mechanical properties and toughness.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The main object of the present invention is civil engineering construction materials used in a humid environment, such as steel pipes, steel sheet piles, steel pipe piles, steel pipe sheet piles and floating structures. Hereinafter, embodiments of the present invention will be described in detail.

<Steel Material Component> As the base steel material, one obtained by adding at least one or two of molybdenum and aluminum in addition to chromium and, if necessary, chromium is used within the scope of the present invention.

In the case where the cathodic protection is applied, when the lowest potential portion is set to a value lower than -1.05 V (vs. SCE: based on a saturated luster electrode), molybdenum or molybdenum is added in addition to chromium. A steel material to which one or two types of aluminum are added is preferable.

<Base and Surface Treatment of Steel> It is important to keep the surface of the steel clean in order to secure the adhesion between the surface of the steel and the coating. As the method, pickling treatment or blast treatment is generally used. In particular, in blast treatment, a ten-point average roughness (Rz) of 20 to 150 μm is desirable. If the surface roughness is less than 20 μm, there is no effect, and if it exceeds 150 μm, the effect remains the same.

After the blasting treatment, it is desirable to coat within 48 hours. In particular, when the coating is applied within 24 hours, the adhesion is further improved.

In the present invention, good water adhesion and cathode peeling resistance can be obtained without chemical conversion treatment. However, by applying a chromate treatment or applying a silane coupling agent to the steel material surface, the water adhesion and cathode resistance can be further improved. Peelability can be improved. In the case of the chromate treatment, the one to which silica such as aqueous colloidal silica is added is preferable. The coating amount is preferably 30 to 1000 mg / m ^{2 in} total chromium amount. If it is less than 30 mg / m ² , there is no effect, and if it exceeds 1000 mg / m ² , a strong film is not formed, and the adhesion is reduced. Silane coupling agent 50-2000mg / m
A coating amount of ² is desirable. No effect is less than 50mg / m ^2, 20
It becomes brittle exceeding 00 mg / m ² and there is a risk of peeling.

Further, separately from or in combination with the chromate treatment and the silane coupling treatment, an acid such as phosphoric acid, molybdic acid, tungstic acid, vanadic acid, phosphonic acid, tannic acid, citric acid or a salt thereof, etc. By treating with an acidic solution containing one or more of the above, water adhesion resistance and cathode peeling resistance can be further improved.

<Coating> The coating in the present invention means a coating applied to the surface of a steel material including a so-called primer layer.
Although an inorganic coating may be used, an organic resin coating is more preferable.

By setting the insulation resistance of the coating within the range of the invention, the water adhesion resistance and the cathode peeling resistance are improved.

It is more preferable that the surface of the steel material be excellent in oxygen permeability and water vapor permeability.
If the oxygen transmission rate of the coating is 15 × 10 ⁻¹⁵ mol / (cm ・ sec) or less and the water vapor transmission rate is 5 × 10 ⁻¹² mol / (cm Cathodic peelability is further improved.

As the organic resin coating, there is one coated with a coating material alone or several types. The paint is not particularly limited, but includes, for example, zinc rich primer (organic and inorganic), thick film type zinc rich paint (organic and inorganic), epoxy resin paint, modified epoxy resin paint, tar epoxy resin paint, and glass flake Paints (vinyl ester resins, polyester resins, epoxy resins), chlorinated rubber paints, polyurethane resin paints, silicone-modified acrylic resin paints, fluorine resin paints, and the like. Particularly, a combination of a zinc rich primer and an epoxy resin paint or a tar epoxy resin paint is preferable. The form of the paint is not limited to the organic solvent type, but may be an aqueous type (aqueous, emulsion type, etc.), powder, NAD (non-aqueous dispersion type emulsion), or the like. The coating method is not limited to brush coating, air spray, airless spray, electrostatic coating, electrodeposition coating, etc., but airless spray is preferred.

The organic lining is not limited, but may be, for example, polyolefin lining (polyethylene, polypropylene, etc.), urethane elastomer lining, vinyl chloride resin lining, nylon lining, polyester lining, AAS (acrylic,
It may be lined with a resin lining such as (butadiene acrylate, styrene) resin or a polymer alloy blended with a plurality of resins and a filler or the like.

Other linings include an ultra-thin film lining (epoxy resin type, polyurethane resin type, acrylic resin type), underwater construction type lining (putty type, paint type), anticorrosion tape lining, FRP
There are lining, rubber lining, petrolatum lining and so on.

In particular, it is preferable to apply an epoxy primer layer, a modified polyolefin adhesive layer, and a polyolefin layer sequentially coated from the steel surface side, or a primer layer and a polyurethane layer sequentially coated from the steel surface side. Particularly, the polyurethane layer is preferably a urethane elastomer, and more preferably a polyurethane layer comprising liquid MDI (diphenylmethane diisocyanate) as a diisocyanate component and PBD (polybutadiene) polyol as a polyol component.

The lining method is not particularly limited, and includes extrusion coating, spray coating, powder lining, lamination of a resin sheet, and the like.

It is preferable to add a rust-preventive pigment to the organic resin coating.
It is particularly preferable to contain 0 wt%. Zinc chromate (ZPC: basic zinc chromate, ZTO:
Tetrabasic zinc chromate), strontium chromate,
There are barium chromate and calcium chromate.

The coating thickness is not particularly limited as long as the insulation resistance is 10 ⁴ Ω · m ^2. However, in consideration of impact resistance, scratch resistance and the like, the coating thickness of the organic resin coating is not limited. If
It is desirable that the thickness be 100 μm or more.

The entire surface of the steel material may be covered or may be partially covered. For example, in the case of a harbor structure such as a steel pipe pile, a steel sheet pile, a steel pipe sheet pile, etc., LWL is said to cause intensive corrosion. (Low Water Level) It is permissible to cover only the portion of -1 m or more.

[0037]

EXAMPLES Table 1 shows the component compositions of the test steel materials. The low alloy steel was set to 9 levels indicated by A to I, and the ordinary steel was set to 1 level indicated by J.

[0038]

[Table 1]

First, shot blasting was performed using the test steel materials shown in Table 1 as base steel materials. The surface roughness (Rz) after blasting was 40-60 μm.

Next, coating was performed within 48 hours after the blast treatment. Table 2 shows the types of coatings applied to the above base steel materials and their insulation resistance values.

[0041]

[Table 2]

Finally, with respect to various steel materials to which the various coatings shown in Table 2 were applied, the water resistance and the peeling width of the cathode were measured.

Here, the water-resistant adhesion was determined by immersing in hot water at 60 ° C. for 60 days, followed by a pull-off test (ASTM D4541-85) or 9
The adhesion strength of the coating layer was measured by a 0 ° peel test (23 ° C.). In addition, in the cathode peeling test, an artificial defect with a 9 mmφ steel surface exposed at the center of the test material was provided, and a potential was applied at −1.05 V (vs. SCE) for 60 days in a 3 wt% NaCl aqueous solution at 60 ° C. Thereafter, the cathode peeling width was measured and evaluated. Table 3 shows the measurement results.

[0044]

[Table 3]

After immersion in hot water at 60 ° C. for 60 days, the adhesion of the coating layer measured by a pull-off test (ASTM D4541-85) exceeds 300 N / cm ² or a 90 ° peel test (23
It has been confirmed that when the adhesion of the coating layer measured at 100 ° C.) exceeds 100 N / cm, the water-resistant adhesion is maintained for a long time under a natural environment in a humid environment. In addition, it has been confirmed that when the cathode peeling width after the cathode peeling test is less than 2.0 mm, cathodic peeling does not occur for a long time when the cathodic protection is performed in a natural environment.

FIG. 1 shows the scope of the present invention in the case where the horizontal axis represents the chromium content of the steel material and the vertical axis represents the insulation resistance of the coating applied to the steel material. Each point shown in the figure corresponds to each of the test materials shown in Table 3.

In the drawing, those indicated by ● have adhesive strengths exceeding 300 N / cm ² in the pull-off test or exceeding 100 N / cm in the peel test, and further, the peeling width of the cathode was 2.0 N / cm ^2.
mm. In addition, those indicated by × have an adhesive force of 300 N / cm ² or less in a pull-off test or 100 N / cm or less in a peel test, and further, a cathode peeling width.
It is 2.0 mm or more.

From this, it can be seen that by combining a low alloy steel containing chromium of 0.5 wt% or more with a coating having an insulation resistance of 10 ⁴ Ω · m ² or more, the water adhesion resistance and the cathode peeling resistance are improved. .

[0049]

According to the present invention, the insulation resistance is 10 ⁴ Ω on a low alloy steel containing 0.5% by weight or more of chromium, preferably 0.5 to 5% by weight.
· M by ² or more and the coating so that, even if used for a long time in a humid environment, has good water resistance adhesion of the coating, and, a good coating shade pole peelable even when applying the cathodic protection Provide steel products.

Further, by adding at least one of molybdenum and aluminum in a predetermined amount, water adhesion is good, cathode peeling resistance is good, and mechanical properties,
An alloy satisfying conditions such as toughness can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the chromium content of steel and the insulation resistance of a coating on the adhesion and the cathode peeling properties.

──────────────────────────────────────────────────の Continued on the front page (51) Int. Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 28/00 C23C 28/00 C C23F 13/00 C23F 13/00 Z (72) Inventor Shiro Miyata Tokyo 1-1-2, Marunouchi, Chiyoda-ku Nihon Kokan Co., Ltd. F-term (reference) 4F100 AA25 AB03A AB10A AB13A AB20A AB31A AK53 AR00B BA02 BA03 EJ34 EJ65 GB07 GB90 JB02 JB07 JG04B JK06 YY00A YY00B 4K0BA BB07 CA20 CA26 CA29 CA30 CA31 CA38 CA39 CA41 DA02 DA06 EA02 EB08 EB11 4K044 AA02 AB03 AB04 AB10 BA14 BA15 BA17 BA19 BA21 BB03 BB11 BC02 BC04 BC05 CA16 CA31 CA53 4K060 AA01 BA19 BA22 BA26 BA33 BA39 DA07 EA05 EB01 FA03

Claims (3)

[Claims] 1. A low alloy steel containing chromium of 0.5 wt% or more.
On top, insulation resistance is 10 ^FourΩ ・ m^TwoAnd cover it so that
Water resistance and cathodic peeling resistance
Excellent coated steel material. 2. The low alloy steel forming the coated steel material forms chromium.
2. The coated steel material according to claim 1, comprising 0.5 to 5% by weight. 3. The low alloy steel forming the coated steel material forms chromium.
2. The coated steel material according to claim 1, wherein the coated steel material contains 0.5 to 5% by weight and at least one of 0.1 to 2% by weight of molybdenum and 0.1 to 1.5% by weight of aluminum is added.