JPS62267477A - Steel material coated with organic coat having superior corrosion preventing performance - Google Patents

Abstract

PURPOSE:To improve the stripping resistance and corrosion preventing performance of an org. coat by using an optimum total amount of Sb and Si based on the amount of Cr in an oxide layer contg. Cr formed as a base layer for the org. coat and by specifying the amount of the oxide layer stuck. CONSTITUTION:A chromate layer (oxide layer) having 0.1-2.0atom ratio of (Sb+Si)/Cr is formed on the blasted or cleaned surface of a steel material by 0.1-10g/m<2> on dry basis. A coat is then formed with an org. coating material such as polyethylene or epoxy resin. By this method, a steel material coated with an org. coat having superior corrosion preventing performance is obtd. The org. coat is proof against sprayed brine and has resistance to stripping in warm water and cathodic stripping.

Description

[Detailed Description of the Invention] <Field of Application in Industry 1> This invention applies to the inner and outer surfaces 4'T of steel pipes for vibration lines and piping.
This product relates to steel materials for heavy corrosion protection structures such as machine wL steel cladding materials, steel pipe piles, steel shafts, and reinforcing bars.

<Prior art and its problems> Conventional surface treatment technology for organic coating will be explained using a polyethylene coated steel pipe as an example.

To glue polyethylene to the inner or outer surface of a steel pipe,
A layer of polyethylene that has been modified by introducing maleic anhydride or the like is sandwiched between the anti-corrosion polyethylene for the exterior and the steel surface that has been cleaned by plastic treatment or pickling, and then they are bonded together under heat. In this case, peeling is likely to occur from the covered V end portion or eaves portion, and the corrosion area spreads deep beneath the coating layer. In order to cope with this problem, it has been considered to subject steel to chemical conversion treatments such as phosphate treatment and chromate treatment in order to improve the adhesion between the adhesive modified polyethylene and the steel surface.

Among them, chromate treatment is relatively superior, and along with chromic acid, silica or alumina sol (Japanese Patent Application Laid-Open No. 57-16
9092, etc.) and lysates (Japanese Patent Publication No. 55-35069, etc.) have been used as active ingredients, but these were originally 111! This product was developed for use as a base treatment for coating of lead-plated steel sheets, etc., for rust prevention or decorative steel sheets, and for steel sheets used in Japan (IJJ). The performance against peeling and cathodic peeling is insufficient.

On the other hand, apart from chemical conversion treatment, studies have also been conducted to form a single layer of organic brima between the steel surface and the modified polyethylene layer to improve the adhesion between the steel surface and the polyethylene layer, but this method does not When polyethylene is bonded without chemical conversion treatment, the adhesive strength is improved, but the performance with respect to hot water separation and cathode peeling is insufficient, as in the case of chemical conversion treatment.

In addition, organic coating systems other than polyethylene (epoxy resin,
Even with polyurethane, polyvinyl chloride, etc., adhesion and anti-corrosion performance are insufficient, and improvements have been made to the introduction of IA embedding, but as with polyethylene, further improvements are needed. be.

<Purpose of the Invention> The present invention aims to prevent corrosion in splash zones and seaside areas, coating edges, and eaves areas in externally coated line pipes, heavy corrosion-resistant steel pipe piles, steel sheet piles, etc. that require corrosion protection performance for several seven years. Improved salt spray resistance to prevent peeling from seawater, and underwater installation.
When buried in wetlands, cathode peeling resistance has been improved to prevent peeling from defective parts due to electric current during cathodic protection and stray currents, and for line pipes, it has been improved to prevent problems with high-temperature operation to improve transportation efficiency. The improvement in corrosion resistance required of these organic coated steel materials, such as improvement in hot water peeling resistance, is considered to be LI.

<Structure of the Invention> The present inventors focused on the fact that among chemical conversion treatments, chromate treatment is inexpensive and has relatively excellent anti-corrosion and rust-preventing performance for steel materials by itself, and developed an improvement in chromate treatment. I tried.

The state of Cr (trivalent and hexavalent) in the chromate treatment solution and the additives, i.e. metal oxide sol with film-forming effect (in addition to conventionally used silica and alumina, iron oxide, tin oxide, oxidized antimony, titania, zirconia, etc.)
and water-soluble organic substances (ethanol, ethylene glycol, glycerin,
The effects of starch, etc.) were examined in detail.

As a result, a chromate layer containing 0.1 to 10 g/m2 of sb and Si [(Sb+Si)/Cr=0] was formed on the surface of steel materials cleaned by blasting or pickling.
．． 1 to 2.0: at an atomic ratio] and then coated with a coating material such as polyethylene or epoxy resin, resulting in excellent corrosion resistance in terms of salt spray resistance, hot water peeling resistance, and cathodic peeling resistance. It was discovered that an organically coated steel material can be obtained.

That is, the present invention provides a steel material that is organically coated with a chromium-containing oxide layer between it and a copper material, in which the amount of the oxide layer attached is 0.1 to 10 g/m2 in terms of dry weight, and (Sb+Si)/Cr (atomic ratio) in the oxide layer is 0.1
The purpose of the present invention is to provide an organic coated steel material with excellent anticorrosion performance, characterized in that the corrosion resistance is 2.0.

Incidentally, the applicant of the present application has disclosed in Japanese Patent Application No. 60-296118 an organic coated steel material with excellent corrosion resistance that achieves the same object as the present invention. The present invention uses Si in the oxide layer.
This is different from the above-mentioned Japanese Patent Application No. 60-296118 in that it contains .

Hereinafter, the organic coated steel material with excellent corrosion resistance of the present invention will be explained in detail.

The present invention aims to improve the adhesion and 1νi corrosion performance of organic coatings on steel materials by providing stable and strong bonding between the steel surface and the organic coating layer. This is achieved by forming a chromate layer that forms a bond. The dry weight of the acid-based treatment liquid is 0.1 to 10 g/m2 (preferably 0.3
~2germ2), dried at a temperature range of 50 to 300°C, and coated with a perforation coating material such as polyethylene or epoxy, an organic coated steel material with excellent adhesion and anticorrosion performance can be obtained.

Here, the chromic acid-based treatment II liquid removes a portion of Cr6'' by 3
Chromic acid reduced to valence and (Sb+Si)/Cr=
colloidal antimony oxide and silica in an amount of 0.1 to 2.0 (in atomic ratio) and water or further chromic acid 1
An aqueous dispersion containing 200 parts by weight or less (preferably 10 to 100 parts by weight) of a water-soluble and reducing organic substance such as ethanol, ethylene glycol, glycerin, or starch based on the total weight of the dispersion.

It is believed that the excellent anti-corrosion performance of the organic coated steel of the present invention is due to the following factors.

First, (:r, Sb oxide and composite oxide are
During cathodic polarization, the reduction current of oxygen is small, and under cathodic protection,
Alternatively, in order to suppress the generation of hydrogen and alkali in corroded local cells, the progress of peeling and corrosion is suppressed.

Silica has good compatibility with chromic acid and antimony oxide as a dispersion, makes the dispersion stable, and plays the role of forming a strong film in the dried composite oxide.

Furthermore, an optimum Sb+Sim exists for Cri, and the chromate layer becomes strong and stable. For this reason, Sb+
The 5j/Cr ratio is preferably in the range of 0.1 to 2.0 in terms of atomic ratio. Note that the Si/Sb ratio is not particularly limited, but is preferably in the range O<Si/Sb≦10.

FIG. 1 shows the influence of the (Sb+Si)/Cr ratio in the base treatment layer on anticorrosion performance (representatively cathodic peeling resistance), and Table 1 shows the composition of the test material.

Table 1 Composition of test material On the other hand, ethylene glycol, glycein, etc. in the treatment liquid have the function of increasing the reduction ratio of Gr during the formation of the chromate layer and making the chromate layer strong and hardly soluble in water. However, since it is originally water-soluble when present in excess, the chromate layer will not be dissolved, and the chromate layer after the organic matter itself has been eluted will form a network and become weak.

Therefore, the addition to the chromate treatment solution is chromic acid 100@
It is better to have 200 city weights for Kabe.

Regarding the amount of the chromate treatment liquid applied, if it is less than 0.1 g/rn2 in terms of dry weight, the effect of improving anticorrosion performance will be small, and if it exceeds 10 g7m2, the chromate layer will be exposed to water from the end surface direction at the eaves of the organic coating. In addition, if the upper coating layer is subjected to lateral shrinkage stress as in the case of polyethylene, the effect of the anchor pattern on the steel surface becomes less effective, making peeling even more likely.

The drying temperature of the treatment liquid is preferably 50 to 300°C. 5
This is because at a temperature lower than 0°C, the reaction between the treatment liquid and the steel surface is insufficient, and at a temperature exceeding 300°C, the chromate layer rapidly shrinks and cracks occur on the surface.

The coating material for the organic coated steel of the present invention includes all kinds of resins such as polyethylene, epoxy resin, polyurethane, polyvinyl chloride, nylon, and polyester, and can be coated at temperatures up to 300°C at which the chromate layer is destroyed. By covering, a perforated steel material with excellent adhesion and anti-corrosion performance can be obtained.

<Example> Examples will be shown below to explain the excellent anticorrosion performance of the organic coated steel material of the present invention.

Table 2 shows the composition of each organic coated steel material. All steel materials are 3
．． 2 x l 50 x 150 mm Shinatsu steel plate SS41
(C: 0.12, Si: 0.27,
Mn: 0.45.

P: 0.09+, S: 0.004
, Cr: 0.44, 8Q=0.0:]
:l, (:u: 0.26wt!k), and the steel surface was cleaned by blasting using alumina #46.

An organic coating was applied on the base treatment layer under the conditions shown in Table 2. The chromate treatment solution was applied at room temperature and dried at 100°C or higher. After that, polyethylene was heated in an electric furnace at 160°C for 15 minutes.
A: Pressure bonding was carried out at 180°C for 10 minutes at 2.5 kg/r and m 2 . Adhesive polyethylene is modified polyethylene by introducing 2% maleic anhydride 5 Outer layer polyethylene is high density polyethylene 1=4 II! 2J2 ratio was used.

The epoxy electrostatic powder coating was heated in an electric oven at 160° C. for 15 minutes, and then cured at 160° C. for 10 minutes. A phenol curing type epoxy resin was used for the paint.

The evaluation of anti-corrosion performance was as follows: 1. Salt spray test, 2, mixed salt water immersion B
7 exams, 3. This was done by cathodic peel test. Each test condition is as follows.

1. Place 3 in the center of the coating of the IW steel plate with a salt spray test specimen size of 50 x 50 mm.
Make a 0x30 cross cut to the steel surface and seal the coated end and back surface.

It was exposed for 30 days under JIS 22371 conditions and evaluated based on the peeling distance from the eaves.

2. Warm salt water immersion test A coated fJA plate of specimen size 50 x 10011III+ was immersed as is at 3% at 80°C without sealing the edges or back side.
After being immersed in an Na Cl aqueous solution for 30 days, the peel strength was measured and evaluated at room temperature.

3.Cathode peel test Drill a 5!101φ hole in the center of the coating of a coated copper plate with sample size 10100 x 100 to the steel surface and -1.5V vsS
The specimen was exposed to a 3% KCR aqueous solution at room temperature for 30 days while being cathodic-protected with CE, and the peeling distance progressed during that period was measured and evaluated.

As can be seen from Table 3, the organic coated steel materials of Examples 1 to 3 of the present invention received high evaluations in all of the salt spray test, warm salt water immersion test, and cathode peeling test, and were excellent overall. It was confirmed that it has anti-corrosion performance.

Table 2 Composition of organic coated steel (Part 1) Table 2 Composition of organic coated steel (Part 2) Treatment liquid A Nisilica/Chromic acid = 1.0 Treatment liquid B Niphosphoric acid/Chromic acid = O-: 15 Table 3 Corrosion prevention performance Test results <Effects of the invention> The organic coated steel material of the present invention can be used for externally coated line pipe steel pipes with excellent corrosion resistance, small diameter inner and outer coated steel pipes, steel materials for heavy corrosion protection structures ('JJA pipe piles, ° steel sheet piles, reinforcing bars, steel frame, etc.).

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the (Sb+Si)/Cr ratio in the chromate layer and anticorrosion performance. Same patent attorney Yo Ishii −7, τ−゛′go・°
:: 1 ・ I-t ni-j1

Claims (1)

[Claims] In a steel material coated with an organic material through an oxide layer containing chromium between the steel material and the oxide layer, the amount of the oxide layer deposited is 0.
1 to 10 g/m^2, and (Sb+
An organic coated steel material with excellent anticorrosion performance, characterized in that Si)/Cr (atomic ratio) is 0.1 to 2.0.