JPS62151577A - Steel material coated with organic substance having superior corrosion preventing performance - Google Patents

Abstract

PURPOSE:To improve the corrosion preventing performance of an org. coating on a steel material by forming an oxide layer contg. Cr and Sb in a prescribed ratio of Sb/Cr on the steel material as a base for the org. coating by a prescribed extent of sticking. CONSTITUTION:The surface of a steel material is chromated with a chromic acid-base treating soln. contg. Sb to form an oxide layer contg. Cr and Sb in 0.15-4.5 atomic ratio of Sb/Cr on the surface of the steel material by 0.1-10g/m<2> extent of sticking on the dry basis. The steel material having the oxide film on the surface is then coated with an org. substance such as polyethylene or epoxy resin.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a steel material coated with organic materials on the inner and outer surfaces of steel pipes for pipelines and piping, and to steel materials for heavy corrosion-resistant structures such as steel pipe piles, steel sheet piles, and reinforcing bars.

<Prior art and its problems> The conventional base treatment technology for organic coating will be explained by taking polyethylene coating t14Irl as an example. To bond polyethylene to a steel surface, a layer of polyethylene that has been modified by introducing maleic anhydride or the like is placed between the exterior corrosion-resistant polyethylene and the steel surface that has been cleaned by blasting or pickling. However, if this is done alone, it tends to peel off from the edges and flaws of the coating, and the corroded area spreads deep under the coating layer.To deal with this, adhesive modified boethylene In order to improve the adhesion with the steel surface,
Introduction of chemical conversion treatments such as phosphate treatment and chromate treatment has been considered.

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 phosphates (Japanese Patent Publication No. 55-35069, etc.) have been used as phosphorus-effective ingredients, but these were originally used for rust prevention of galvanized steel sheets, decorative steel sheets, and automobiles. It was developed for treating the coating surface of industrial steel plates, and its performance against peeling (hot water peeling, cathodic peeling, etc.) with relatively thick coatings such as polyethylene in hot water environments or under cathodic protection is insufficient. .

On the other hand, apart from chemical conversion treatment, studies have also been conducted to improve the adhesion between the river surface and the polyethylene layer by forming a single layer of organic brimmer between the steel surface and the modified polyethylene layer, but this method When polyethylene is bonded without chemical conversion treatment, the adhesive strength is improved, but the performance with respect to hot water peeling and cathodic peeling is insufficient as in the case of chemical conversion treatment.

In addition, organic coating systems other than polyethylene (epoxy resin,
Even with polyurethane (such as polyurethane), adhesion and anticorrosion performance are insufficient by itself, and improvements have been made by introducing surface treatments, but as with polyethylene, further improvements are needed.

<Purpose of the Invention> The present invention aims to prevent corrosion in splash zones and coastal areas, coating edges, and paper parts in externally coated line pipes, heavy corrosion-resistant steel pipe piles, steel sheet piles, etc. that require long-term corrosion protection performance over several decades. Improved resistance to salt spray and installation in the sea to deal with peeling from the sea.
When buried in wetlands, cathodic peeling resistance has been improved to prevent peeling from defective parts due to electric current during cathodic protection and stray currents.Furthermore, line pipes have improved resistance to peeling, which is a problem associated with high-temperature operation to improve transportation efficiency. The aim is to improve the anti-corrosion performance required of these organic coated steel materials, such as improved hot water releasability.

<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 Cr-like parts (trivalent and hexavalent) of the chromate treatment solution and 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 1 Og/m2 of Sb (Sb/C'r=0.15 to 4.5; in atomic ratio) was found on the surface of the steel material cleaned by blasting or pickling. By coating with a coating material such as polyethylene or epoxy resin after forming, salt spray resistance,
It has been found that an organic coated steel material with excellent anticorrosion properties such as hot water peeling resistance and cathodic peeling resistance can be obtained.

That is, the present invention provides a steel material that is organically coated with an oxide layer containing chromium between the steel material, and the amount of the oxide layer adhered to is 0.1 to 10 g7m2 in terms of dry weight, and the oxide layer The Sb/Cr (atomic ratio) inside is 0.15 to 4.
The present invention provides an organic coated steel material with excellent anti-corrosion performance, characterized in that the corrosion resistance is 5.

The present invention will be explained in more detail below.

The present invention aims to improve the adhesion and anticorrosion performance of organic coatings on steel materials by creating a stable and strong bond between both the steel surface and the organic coating layer. This is achieved by forming a chromate layer that produces The dry weight of the treatment liquid is 0.1-10 g/la2 (preferably 0.3-10 g/la2)
2g/ra2), dried at a temperature range of 50 to 300'', and then coated with an organic coating material such as polyethylene or epoxy to obtain an organic coated steel material with excellent adhesion and anticorrosion performance.

Here, the chromic acid-based treatment liquid is chromic acid in which a part of Cr6+ is reduced to trivalent, S b /Cr = 0.15 to 4.
5 (preferably 0.25 to 1.5) and water, or further 200 parts by weight or less (preferably 1.5 parts by weight) per 100 parts by weight of chromic acid.
(0 to 100 parts by weight) of water-soluble and reducing organic substances such as ethanol, ethylene glycol, glycerin, and starch.

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, the chromate layer (Cr,
Sb composite oxide) has a small oxygen reduction current during cathodic polarization, and suppresses the progress of peeling and corrosion in order to suppress the generation of hydrogen and alkali under cathodic protection or in corroded local cells. Additionally, there is an optimal amount of antimony relative to chromium, making the chromate layer strong and stable. Therefore, the Sb/C:r ratio is 0.
15 to 4.5, particularly preferably a range of 0.25 to 1.5,
Figure 1 shows the influence of the Sb/Cr ratio in the base treatment layer on anticorrosion performance, and Table 1 shows the composition of the test materials.

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 Cr during the formation of the chromate layer and making the chromate layer strong and hardly soluble in water. However, since it is inherently water-soluble when present in excess, the chromate layer is easily dissolved, and the chromate layer after the organic matter itself is eluted becomes network-like and weak.

Therefore, it is necessary to add chromate too3 to the chromate treatment solution.
It is preferably 200 parts by weight or less per 1 part by weight.

Regarding the coating amount of the above chromate treatment liquid, if it is less than 0.1 g/m2 in terms of dry weight, it will have little effect on improving anticorrosion performance, and if it is more than 10 g/112, the chromate layer will be applied from the edge direction on the paper part of the organic coating. In addition, if the upper covering layer 82 is subjected to lateral shrinkage stress like polyethylene, the effect of the anchor pattern on the steel surface will be reduced and peeling will occur more easily. The drying temperature of the treatment liquid is preferably 50 to 300℃, but 50℃
This is because at lower temperatures, the reaction between the treatment liquid and the steel surface is insufficient, and at temperatures above 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, an organic coated steel material with excellent adhesion and anticorrosion 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.
．． 2X150X150■ Intestinal ordinary steel plate (c: 0.12
, Si: 0.27, M! l: 0.45
, P: 0.091°S: 0.004, C
r: 0.44, AJI: 0.033, Cu
The steel surface was cleaned by blasting with alumina #40 and 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 above. Polyethylene compression was applied in an electric furnace at 160°C for 15 molecules of heat and at 180°C for 10 minutes.
It was crimped at 5 kg/cm 2 . The adhesive polyethylene was modified by introducing 2% maleic anhydride, and the outer layer polyethylene was high-density polyethylene with a film thickness ratio of 1=4. Epoxy electrostatic powder coating is done in an electric furnace at 160"C.
After preheating for 5 minutes and painting, it was further cured for 1 minute at 160"0. A phenol curing type epoxy resin was used as the paint.

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

1.1i1 Water Spray Frost Test Specimen size 50 x 50 mm coated steel plate with 30
Make an X30 cross cut up to the steel surface and seal the coated end and back surface. 30 under JIS 22371 conditions
It was exposed for 1 day and evaluated based on the peeling distance from the paper part.

2. Warm salt water immersion test Sample size 50 x 100 m Intestine coated steel plate was cross-cut as it was, without sealing the edges and back, 3% N at 80℃
After being immersed in the aC1 aqueous solution for 30 days, the peel strength was measured and evaluated at room temperature.

3.Cathode peeling test Drill a 5mmφ hole in the center of the coated steel plate of specimen size 10100x100 to the steel surface, and -1.5V vs SCE
The specimens were exposed to a 3% KC,L aqueous solution at room temperature for 30 days while being subjected to cathodic protection, and the peeling distance progressed during that period was measured and evaluated.

As a result, as shown in Table 1 and 3, it was revealed that the organic coated steel material of the present invention has excellent anticorrosion performance.

Table 2 Constituent treatment liquid for organic coated steel materials A Nisilica/Chromic acid = 150 Treatment liquid B Niphosphoric acid/Chromic acid = 0.35 Table 3 Corrosion resistance simple test results Total value Δ Δ × <Effects of the invention> The present invention Organic coated steel materials are provided as externally coated steel pipes for line pipes with excellent corrosion resistance, small-diameter internally and externally coated steel pipes, and steel materials for heavy corrosion-resistant structures (steel pipe piles, steel sheet piles, reinforcing bars, steel frames, etc.).

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the 5bICr ratio in the chromate layer and anticorrosion performance. 0 in 3% KC standing water solution, 30 days, -1,5, v
Peeling distance 1 when cathodic protection is applied with vsSCE is 3%N
The peel strength after immersion in aCl aqueous solution at 80° C. for 30 days is shown. □ □ □

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/C in the oxide layer
An organic coated steel material with excellent anticorrosion performance, characterized in that r (atomic ratio) is 0.15 to 4.5.