JP5644046B2 - Underground steel - Google Patents

Description

  The present invention relates to a steel material having excellent corrosion resistance in a buried environment.

  Underground environment is an environment where the corrosion of steel is easy to progress because the soil contains moisture, but conventionally steel structures are often used in deep areas such as foundation piles. Therefore, a corrosion allowance of about 1 mm (per one side of steel material) per year has been considered sufficient.

  When foundation piles are used as the foundation structure of buildings, there are many cases where RC structures are used for beams etc. that exist at shallow embedding depths. Conventionally, corrosion of steel is a problem except for extremely special soils. It was never taken.

  However, recently, it has been required to shorten the construction period of building construction, and integration of buildings and foundation structures with steel structures has been required. Therefore, it is required to improve the corrosion resistance of steel materials even in a shallow embedding environment, and electrocorrosion protection, coating, or corrosion resistance steel has been studied.

  Patent Document 1 relates to a corrosion-resistant steel for underground, in order to give the steel itself a general corrosion resistance and a macrocell corrosion resistance as corrosion resistance in the soil, so as to limit the Cr content and add appropriate amounts of Ni, Mo, and Cu. It is described that the composition is a component.

Patent Document 2 discloses a method in which a surface of a steel material is coated with a metal that is lower than the steel material by plating, thermal spraying, or the like, and Zn powder or Zn oxide powder is added to the soil. Patent Documents 3 and 4 disclose techniques for coating the surface of a steel material with a butyral resin containing Ni sulfate, Cr sulfate, and carbonate ions.
JP 2000-336463 A Japanese Patent Laid-Open No. 10-183386 JP 2002-167544 A JP 2002-59076 A

  However, although anticorrosion is well known as a method for preventing corrosion in soil, in the case of the galvanic anode type, it is necessary to secure the electrode mounting site in the soil quite finely, and the conventional RC structure is required in terms of cost. In the case of painting, it is effective at a thickness of several hundreds of μm or more. Therefore, management of coating, cost, and measures for scratches at the time of backfilling are problems.

  On the other hand, corrosion products that have a denser structure than the corrosion products of general steel, such as weather resistant steel, and prevent the diffusion of oxygen and the diffusion of ions necessary for the electrochemical reaction of corrosion, prevent corrosion of steel materials. The mechanism used to reduce the corrosion rate of steel materials is said to have little or very little effect in the buried soil environment because no corrosion products are generated in the atmosphere due to the high moisture content in the soil. ing.

  The steel material described in Patent Document 1 contains a large amount of Cr, Ni, Mo, and Cu, so that the cost of the steel material increases, and the method described in Patent Document 2 also increases the cost, and there remains a problem in the processing of the joining site and the like. .

  In the method of coating with butyral resin described in Patent Documents 3 and 4, sufficient corrosion resistance cannot be obtained only by adding Ni and Cr into the organic coating, and when the steel material does not contain a corrosion-resistant element, Small effect.

  Then, an object of this invention is to provide the steel material which is excellent in corrosion resistance in the shallow embedding environment where a corrosive environment is severer than a deep region.

The present inventors pay attention to the fact that corrosion products are easily retained on the steel surface by earth pressure in the soil, and in order to reduce the corrosion rate of the steel materials using the corrosion products, moisture is present as in a shallow buried environment. The following findings were obtained by intensively studying the corrosion products that suppress the corrosion reaction in an environment with a large amount of corrosion weight loss and the mechanism for retaining the corrosion products.
(1) Corrosion is suppressed when vanadate, metavanadate, molybdate, tungstate, niobate, and tantalate ions are present in the corrosion product.
(2) These ions supply the element group of V, Mo, W, Nb, and Ta to the steel surface in the form of oxyacid salt (oxide hydrolysis) contained in the butyral resin. If it is contained as an additive element, it can be contained in the corrosion product. This is because ions discharged with the progress of corrosion of the steel material change to the oxyacid salt.
(3) In the case of moist soil in a shallow buried environment, corroded iron ions and the like are likely to flow out of the system, but the presence of an organic layer is effective in maintaining the corrosion product layer.

The present invention has been made by further study based on the above knowledge, that is, the present invention,
1. When exposed to embedded soil environment, vanadate ions in the corrosion products of steel surfaces, ground burial steel materials having a mechanism for the presence of one or more niobium ion and tantalum ion.
2. The mechanism, on the surface of the steel material, water absorption during resin layer formed of 10% or more, in 300% or less of the water-soluble butyral resin, vanadate ions, one or more niobate ion and tantalum ion containing Yes 2. The steel material for embedding in soil according to 1, wherein the resin layer is coated with a thickness of 10 to 100 μm.
3. In the water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less when the resin layer is formed on the surface of the steel material, the mechanism is a resin solid containing one or more of sodium vanadate, sodium niobate and potassium tantalate. 3. The steel material for embedding in soil according to 1 or 2, wherein the resin layer contained at 1 mass% to 30 mass% with respect to 100 mass% is coated with a thickness of 10 to 100 μm.
4 . Before Symbol chemical composition of the steel, V, Mo, W, soil burying steel 2 or 3, wherein a is intended to include one or more elements of Nb and Ta.
5. A buried underground steel structure made using the steel material for buried in earth according to any one of 1 to 4 .
6). Buried when exposed to soil environment, soil, characterized in that provided vanadate ions in the corrosion products of steel surfaces, the mechanism for the presence of one or more of niobium ion and tantalum ion to the steel sheet surface Manufacturing method for steel materials for underground use.
7). Buried when exposed to soil environment, vanadate ions in the corrosion products of steel surfaces, for supplying one or more niobium ion and tantalum ion, soil forming the corrosion-resistant resin layer on the surface of the steel material a method of manufacturing a medium for embedding steel, the corrosion-resistant resin layer, water absorption during resin layer formed of 10% or more, in 300% or less of the water-soluble butyral resin, vanadate ions, niobium ions, and method for producing a soil burying steel 6, wherein the forming by coating a resin layer containing one or more tantalate ions 10~100μm thickness.
8). The corrosion-resistant resin layer has a resin solid content of 100 mass with at least one of sodium vanadate, sodium niobate, and potassium tantalate in a water-soluble butyral resin having a water absorption rate of 10% to 300% when the resin layer is formed. The method for producing a steel material for embedding in soil according to 6 or 7, wherein a resin layer contained at 1 mass% to 30 mass% with respect to% is coated with a thickness of 10 to 100 μm.
9. The chemical component of the steel material includes one or more elements of V, Mo, W, Nb, and Ta. Manufacturing of a steel material for embedding in soil according to any one of 6 to 8, Method.

According to the present invention, the following effects can be obtained, which is extremely useful industrially.
1. Even in a shallow embedding environment, it is possible to take measures against corrosion of steel materials by a corrosion allowance as in a deep embedding environment.
2. Corrosion weight loss can be suppressed to about 1/3 or less of steel materials used as conventional steel materials for civil engineering materials.
3. Moreover, it can process with a thin film compared with the conventional coating, and can suppress the anticorrosion cost low.

  The steel material for buried in the soil according to the present invention corrodes when exposed to the environment in the buried soil, and vanadate ion, metavanadate ion, molybdate ion, tungstate ion, niobate ion in the corrosion product on the steel surface. And a function of supplying tantalate ions (referred to as a mechanism in the present invention).

[Mechanism 1]
The mechanism 1 is a mechanism for supplying one or more element groups of V, Mo, W, Nb, and Ta in the form of oxyacid salt (oxide hydrolysis) to the surface of the steel material in the buried soil environment. .

  The oxyacid salt of the element group is at least one of sodium vanadate, sodium metavanadate, sodium molybdate, ammonium molybdate, sodium tungstate, sodium niobate and potassium tantalate. This is because these oxyacid salts adsorb on the steel surface to inhibit the corrosion reaction, and these salts are incorporated into the iron oxide (so-called rust) structure to form a composite rust layer. The reason for this is that these substances inhibit the corrosion reaction, and, unlike oxides, have high solubility in water, that is, they can be supplied to the steel surface relatively easily.

  Since the oxyacid salt needs to be supplied to the steel material surface as the corrosion reaction proceeds, it is mixed with a water-soluble organic resin and applied to the steel material surface.

  The water-soluble organic resin is a water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less when the resin layer is formed.

Under the organic resin, it is easy to store corrosion products, and in the case of a water-soluble resin layer, even when scratched, the inorganic compound present inside (the above oxyacid salt) is water-soluble and easily diffuses, A water-soluble organic resin is used, and in the present invention, a water-soluble butyral resin is used.
To do.

  FIG. 1 is a graph showing a change in the amount of sodium metavanadate eluted when sodium metavanadate is mixed as an oxyacid salt with a water-soluble butyral resin and the water absorption rate is changed. Oxyacid salt added at 10% or more The amount of elution increases significantly, but if it exceeds 300%, water enters between the butyral resin molecules and the resin swells to increase the amount of elution, so the effect of retaining the rust layer is lost. The water absorption at the time is 10% or more and 300% or less.

  Sodium vanadate, sodium molybdate, ammonium molybdate, sodium tungstate, sodium niobate and potassium tantalate show similar trends.

  When mixing one or more of sodium vanadate, sodium metavanadate, sodium molybdate, ammonium molybdate, sodium tungstate, sodium niobate and potassium tantalate with water-soluble butyral resin, the resin solid content is 100 mass%. It is contained at 1 mass% to 30 mass%.

  The effect appears remarkably at 1 mass% or more with respect to the resin solid content of 100 mass%, and if it is added at 30 mass% or more, it becomes impossible to form a film with a water-soluble resin. Therefore, it is preferably 30 mass% or less, more preferably 20 mass% or less. . When adding a plurality of inorganic compounds, it is preferable to add so that the total does not exceed 20 mass%. In addition, the one where there is much addition amount exists in the tendency for the effect which reduces corrosion weight loss to be large.

  A resin obtained by mixing an oxyacid salt with a water-soluble butyral resin covers the surface of a steel material with a thickness of 10 to 100 μm. The thickness of the organic resin layer applied to the surface of the steel material is less than 10 μm, and the effect of the organic resin layer is not obtained. In the structure of the organic layer of 100 μm or more, the effect is saturated and economically disadvantageous. . In addition, the weight loss of corrosion is reduced as the thickness increases, and a preferable film thickness range is 10 to 30 μm.

The method for applying the water-soluble organic resin to the steel material may be any method that can ensure a predetermined thickness, such as spraying, brushing, or pouring the solution on the surface. Further, the water-soluble organic resin organic layer may be formed on the rust layer already formed without the necessity of pretreatment of the steel material. Although the durability is inferior, an aqueous solution in which these oxyacid salts are dissolved may be applied to the surface of the steel material.
[Mechanism 2]
Mechanism 2 uses steel containing one or more of V, Mo, W, Nb, and Ta as a steel composition for buried soil environment. Vanadate ion, metavanadate ion, molybdate ion, tungstate ion, niobate ion and tantalate ion eluted from the inside of steel containing one or more of V, Mo, W, Nb and Ta in the steel composition One or more are oxidized and converted to oxyacid salts.

  The oxyacid salt is supplied from the inside of the corrosion product (rust layer), and the effect of reducing the corrosion weight loss is obtained in the same manner as the oxyacid salt supplied from the outside of the mechanism 1. When mechanism 1 and mechanism 2 are used in combination, an oxyacid salt is supplied from the upper layer and lower layer of the corrosion product (rust layer), so that a more excellent effect can be obtained.

  In addition, as for content (mass%) of 1 or more types of V, Mo, W, Nb, and Ta in a steel composition, V is 0.05 mass% or more and 1.0 mass% or less, Mo is 0.05 mass% or more and 0.00. 5 mass% or less, W is preferably 0.01 mass% or more and 0.2 mass% or less, Nb is preferably 0.01 mass% or more and 0.1 mass% or less, and Ta is preferably 0.01 mass% or more and 0.1 mass% or less. Components other than V, Mo, W, Nb and Ta may be used as long as they have a component composition that ensures the price and performance as structural steel. For example, 0.1 mass% C-0.65 mass% Si-0.95 mass% Mn system It is assumed that an alloy element is appropriately added to the above. As steel containing at least one of V, Mo, W, Nb and Ta in steel composition, JFE trade names JFE-HITEN540, 570, 610, 780, JFE ACL 400A Type1, JFE LT415, JFE-EH360, materials, etc. are used. Is possible. Hereinafter, the present invention will be described in detail with reference to examples.

<Production of test steel plate>
The test steel plate was a 100 × 50 × 6 t (mm) steel plate, and the black skin was removed by blasting, and the test steel plate was tested. With the black skin removed by blasting, the weight was measured to 0.1 mg, which was the initial weight. Table 1 shows chemical components. The treating agent applied to the surface was prepared as follows.
1. An aqueous dispersion of butyral resin was prepared by mixing 400 g / l of butyral resin by weight in ion-exchanged water. As the butyral resin, those having different molecular weights from 1000 to 1000000 were used, and those having different water absorption rates were used. For the water absorption, a free film of 300 μm × 10 cm × 10 cm was prepared, dried at 40 ° C. for 10 days, then immersed in room temperature ion-exchanged water for 24 hours, and the water absorption was determined from the weight difference before and after the immersion.
2. Various inorganic materials (sodium vanadate, sodium metavanadate, sodium molybdate, ammonium molybdate, sodium tungstate, sodium niobate, potassium tantalate) with the composition shown in Table 2 were added to the aqueous dispersion of the resulting butyral resin. In each case, a reagent having a purity of 99.9% was mixed) (the content of the inorganic material is an amount based on 100 mass% of the resin solid content).

The inorganic mixture is mainly a powder, but this is ground in a mortar, and a powder of approximately 1 μm or less is put into a predetermined amount of the above aqueous dispersion and stirred vigorously with a stirrer (in the input inorganic material). Some of them are soluble in an aqueous solution, and others have low solubility.
3. The dispersion was poured over the steel surface while stirring was continued, and the water film of the dispersion was made constant (adjusted so that the film thickness after water drying was 20 μm) with a bar coater. When the water film is 5 μm or 1 μm, the water dispersion is further diluted 4 times or 20 times with ion-exchanged water, and the dispersion is poured on a steel plate leaning at an angle of 45 °. The film thickness was adjusted.
4). Water was evaporated by drying for 1 week at room temperature. FIG. 2 shows a macro sectional explanatory view of the test material obtained.

<Investigation of corrosion resistance>
In the investigation of the corrosion resistance of the steel material, masking was performed so that the back and end surfaces of the steel material subjected to the above surface treatment were not corroded by the seal tape so that only the target area (80 × 40 mm) was corroded. After that, the prepared test material was embedded in a beaker with 200 mm Φ × 200 mm height containing Kanto loam (soil), and after adding 20 mass% of 0.5 mass% NaCl solution to the soil, the temperature was maintained at a constant temperature of 30 ° C. Left in a constant temperature room.

  Thereafter, 10 mass% of ion exchange water was added to the soil every week. After 91 days, the test material was taken out, washed with water, the film was peeled off with a coating film remover, the rust layer was removed with a solution containing an inhibitor in hydrochloric acid, and the weight of the steel material was measured to 0.1 mg. The average corrosion thickness (corrosion weight loss (mm / 90 days)) was determined by the following formula with respect to the assumed area (80 × 40 mm) corroded from the difference between the initial weight and the weight after the test.

Corrosion amount of steel material = (initial weight−weight after corrosion test) / (32 cm ² × 7.8 g / cm ³ )
Tables 2 to 4 show the test results. No. 1-42 is an example of this invention, and corrosion weight loss (mm / 90 days) is 0.41 (mm / 90 days) or less. Nos. 43 to 53 were comparative examples, and the corrosion weight loss (mm / 90 days) was 0.52 (mm / 90 days) or more.

  No. No. 16 of the present invention shows the result when combined with a steel material containing the same kind of element. It is recognized that the corrosion resistance superior to the result in the case of combining with 15 steel materials not containing the same kind of element is ensured.

The figure which shows the change of the elution amount of sodium metavanadate when sodium metavanadate as an oxyacid salt is mixed with water-soluble butyral resin, and a water absorption is changed. Macro sectional explanatory drawing of a test material.

Explanation of symbols

1 Steel plate 2 Organic resin + inorganic mixture layer

Claims (9)

  When exposed to the environment in the buried soil, it has a mechanism that causes one or more of niobate ions and tantalate ions to be present in the corrosion product of the steel surface, and the mechanism is formed on the surface of the steel material when the resin layer is formed. A steel material for embedding in soil, which is to coat a water-soluble butyral resin having a water absorption of 10% or more and 300% or less with a resin layer containing at least one of niobate ions and tantalate ions in a thickness of 10 to 100 μm. .   In the water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less when the resin layer is formed on the surface of the steel material, the mechanism has at least one kind of sodium niobate and potassium tantalate at a resin solid content of 100 mass%. The steel material for embedding in soil according to claim 1, wherein the resin layer contained at 1 mass% to 30 mass% is coated with a thickness of 10 to 100 µm.   The steel material for embedding in soil according to claim 1 or 2, wherein the chemical component of the steel material includes one or more elements of V, Mo, W, Nb and Ta.   A buried underground steel structure made using the steel material for buried in earth according to any one of claims 1 to 3.   When exposed to the environment in the buried soil, a mechanism is provided on the steel surface to cause one or more of niobate ions and tantalate ions to be present in the corrosion products on the steel surface, and the mechanism forms a resin layer on the surface of the steel material. A water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less is formed by coating a resin layer containing at least one of niobate ions and tantalate ions with a thickness of 10 to 100 μm. A method of manufacturing steel materials for underground use.   Manufacture of steel for underground use that forms a corrosion-resistant resin layer on the surface of steel to supply one or more of niobate ions and tantalate ions to the corrosion products on the steel surface when exposed to the environment in the buried soil The corrosion-resistant resin layer is a resin containing at least one of niobate ions and tantalate ions in a water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less when forming the resin layer. A method for producing a steel material for embedding in soil, wherein the layer is formed by covering with a thickness of 10 to 100 μm. The Organization has water absorption during resin layer formed of 10% or more, in 300% or less of the water-soluble butyral resin, 1 mass sodium niobate, and one or more potassium tantalate solid content of the resin 100 mass% The method for producing a steel material for embedding in soil according to claim 5, wherein the resin layer is contained by coating with a thickness of 10 to 100 μm. In the water-soluble butyral resin having a water absorption rate of 10% or more and 300% or less when the resin layer is formed, the corrosion-resistant resin layer contains at least one kind of sodium niobate and potassium tantalate with respect to 100 mass% of the resin solid content. The method for producing a steel material for embedding in soil according to claim 6, wherein the resin layer contained at 1 mass% to 30 mass% is coated and formed with a thickness of 10 to 100 µm. The steel material for embedding in soil according to any one of claims 5 to 8 , wherein the chemical component of the steel material includes one or more elements of V, Mo, W, Nb, and Ta. Manufacturing method.

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