JP2006124796A - Corrosion resistant coated steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corrosion resistant coated steel exhibiting excellent corrosion resistance when used under a severe open air environment, maintaining corrosion resistance over a long period even when widely applied to a bridge or the like, and capable of elongating the cycle of recoating. <P>SOLUTION: The corrosion resistant coated steel is obtained by forming a film comprising ≥50 wt.% zinc and having an average film thickness of ≥10 μm on the surface of a steel comprising, by weight, ≤0.20% C, 0.03 to 1.0% Si, ≤2.5% Mn, 0.05 to 3.0% Cu, 0.05 to 6.0% Ni, ≤0.02% S, ≤0.02% P, ≤0.20% Cr, 0.03 to 1.0% Ti and 0.0001 to 0.01% Ca, and satisfying Ti/P>2.0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steel material for bridges, ships, offshore structures, and other applications that require weather resistance in harsh environments, and to a steel material having a coating for imparting a high degree of corrosion resistance to the outside air.

  Various steel materials that can be easily rust-proof when used in a harsh outdoor environment include a weather-resistant steel that can be used barely and a coated steel material. However, in March 1993, the former Ministry of Construction published a policy on the application of weathering steel, “Joint Research Report on the Application of Weathering Steel to Bridges”. After being regulated, unpainted steel was virtually unusable. For this reason, it is necessary to recoat phthalic acid resin, chlorinated rubber, tar epoxy resin, etc. on steel materials for multi-salt environments, and it is also necessary to repaint within a relatively short period of about 10 years, There are problems with man-hours and costs.

With respect to such problems, research has been carried out from the material side of steel materials and the component side of paints, and a few inventions have been published.
JP-A-10-330881 JP 2002-129282 A Japanese Patent Application Laid-Open No. 2002-332537 Patent Documents 1 and 2 are both inventions that have improved the weather resistance with a focus on improving the components of steel materials, and the third method is based on both the components of steel materials and the formulation of paints. ing. However, these inventions still have insufficient weather resistance or corrosion resistance when used in a recent severe environment. In other words, the coating steel material of Patent Document 1 is made chromium-free and improves weather resistance by blending Cu, Ni, Ti, and further Ca. The coated steel material of Patent Document 2 attempts to improve the corrosion resistance by devising the painted surface after adjusting the same steel components. Moreover, while the coated steel material of patent document 3 is adding Al to steel materials, the corrosion resistance is improved by increasing zinc in a coating material 75% or more.

  The coated steel materials disclosed in the above-mentioned patent documents show temporary anticorrosion or corrosion resistance when used in the open air environment, but the increasingly severe natural environment and severe conditions from the viewpoint of manufacturing, use, maintenance, etc. There is always room for satisfaction. That is, when this kind of coated steel material is placed in a harsh environment, it is a major problem that corrosion progresses locally such as coating film defects, scratches, edges, and thin parts of the coating film. . It has become a big subject to suppress such corrosion and to prolong the repainting cycle.

  Therefore, in order to solve this problem, the present invention seeks to provide an improved corrosion-resistant coated steel material that is satisfactory from both technical and economic aspects by improving both the composition of the steel and the coating components. .

In order to solve the above problems, the present invention
(1) C: 0.20% or less, Si: 0.01 to 1.0%, Mn: 2.5% or less, Cu: 0.05 to 3.0%, Ni: 0.005 to 6.0 %, S: 0.02% or less, P: 0.2% or less, Cr: 0.20% or less, Ca: 0.0001 to less than 0.01% and Ti: 0.03 to 1.0% And Ti / P> 20. In addition, on the surface of the steel material composed of the remaining iron and inevitable impurities, a coating containing an organic or inorganic resin as a main component and containing 50% or more of zinc was formed so that the average film thickness was 10 μm or more. Corrosion resistant coated steel material, characterized by
(2) The steel material described in (1) above, wherein Cr: 0.10% or less corrosion-resistant coated steel material,
(3) The steel material described in the above (1) or (2), wherein Ca: 0.005% or less, corrosion-resistant coated steel material,
(4) The steel material according to any one of the above (1) to (3), which additionally contains Al: 0.05 to 0.50%,
(5) The steel material described in any one of (1) to (4) above, wherein La: 0.0001-0.05% and Ce: 0.0001-0.05% Corrosion-resistant coated steel material additionally containing,
(6) The steel material described in any one of (1) to (5) above, wherein Nb ≦ 0.10%, V ≦ 0.10%, Zr ≦ 0.05%, Mo ≦ 0.25% , Mg ≦ 0.010%, REM ≦ 0.010%, additionally containing one or more types of corrosion-resistant coated steel materials,
(7) The corrosion-resistant coated steel material according to any one of the above (1) to (6), wherein a coating containing 50 to 90% of zinc and a metal salt of an electrochemically base metal than zinc is formed,
(8) The corrosion-resistant coated steel material according to (7), wherein the metal salt is magnesium phosphate or aluminum polyphosphate,
(9) The corrosion-resistant coated steel described in (7) or (8) above, wherein the average particle size of the metal salt is 1 μm or less,
(10) One type of Group IIA metal oxides or hydroxides on the surface of a steel material, the main component of which is an organic or inorganic resin, 50% or more of zinc and a saturated aqueous solution having a pH value of 10.5 or more A corrosion-resistant coated steel material according to any one of (1) to (9), wherein a coating film containing the above is formed;
(11) The corrosion-resistant coated steel material according to (10), wherein a coating containing one or more of calcium oxide, magnesium oxide, or calcium hydroxide is formed as the IIA metal-based oxide or hydroxide.

  The present invention ensures a protective iron rust due to the iron rust densification effect under severe environmental conditions by combining a steel material with a specific composition and a zinc-containing paint, and at the same time has an environmental barrier effect due to the zinc rust densification. Strengthen and reliably improve the corrosion resistance of the coated steel. And since the corrosion resistance of the coated steel material can be maintained over a long period of time, it can be used for a wide range of buildings, structures, industrial machines, etc., and the repainting cycle can be extended even when exposed to the outside air. Very large.

  As described above, the corrosion-resistant coated steel material of the present invention is characterized by the respective component compositions of the base steel and the coating, and both improve the corrosion resistance synergistically. First, the good component composition of the steel material will be described.

  In addition to C, Si, Mn, Cu, Ni, S, P, and Cr that are usually included, the steel material that is the basis of the present invention includes Ti: 0.03 to 1.0% and Ti / P> 2.0. Add Ca: 0.0001 to 0.01%. A steel material having this component composition, combined with a zinc-containing paint containing a large amount of 50% or more, significantly improves the corrosion resistance of the coated steel material.

  This steel material requires C: 0.20% or less for securing steel strength, but 0.15% or less is desirable from the viewpoint of weldability and corrosion resistance. Moreover, in order to promote the formation of stable rust of steel and promote the improvement of corrosion resistance, Si: 0.01 to 1.0% is added as a solid solution strengthening element, but this is a limit to guarantee good weldability. It is. Further, the addition of Mn: 2.5% or less is for securing the steel strength, but the limit was set to 2.5% from the viewpoints of deterioration of workability and toughness and deterioration of corrosion resistance due to MnS formation. Further, in order to densify the generated rust and promote the formation of stable rust, Cu: 0.05 to 3.0% is essential added, but in the presence of S: 0.02% or less, 3. Acceptable up to 0%. Further, in order to expect the effect of improving the corrosion resistance of the steel and to suppress the hot brittleness which is feared by the co-addition of Cu, Ni: 0.05 to 6.0% is also essentially added. : Acceptable up to 6.0% in the presence of 0.02% or less. In view of corrosion of iron and zinc, Cr: 0.20% or less, preferably 0.01% or less is desirable.

  In addition, Ti: 0.03 to 1.0% is added in the hope of promoting the formation of a stable rust layer by densification of the generated rust, excellent corrosion resistance, and steel cleaning. From the competitive relationship with P that contributes to Ti / P> 2.0, an additional condition was set. If the ratio is less than this ratio, the zinc rust is not sufficiently densified, the environmental barrier effect is not achieved, and the weldability is also deteriorated.

  Furthermore, Ca 0.0001 to less than 0.01%, desirably 0.005% or less is present in the steel. This is because a small amount of Ca dissolves in the progress of corrosion under the anticorrosion film and exhibits alkalinity, and exhibits a solution pH buffering effect at the so-called anodic dissolution tip, and suppresses crevice corrosion at a defective portion of the coating.

  Furthermore, when Al: 0.05 to 0.50% is added to the steel, the suppression of the Cr amount is supplemented, the generated rust is densified and the formation of a stable rust layer is promoted, and in particular, the combined addition with Ti is More effective. However, the upper limit is made 0.50% in order not to deteriorate the weldability of the steel material.

  Moreover, in this invention, in addition to Ca, La or Ce: 0.0001-0.05% of the same effect may be added, and it is more convenient than Ca on steelmaking. Furthermore, the present invention provides one type of Nb ≦ 0.10%, V ≦ 0.10%, Zr ≦ 0.05%, Mo ≦ 0.25%, Mg ≦ 0.010%, and REM ≦ 0.010%. The above may be accompanied. These are for imparting other properties and functions required for the objective steel material to the steel, and the addition in the above range does not reduce the expected effect of the present invention.

  Next, the coating in the present invention will be described. Any inorganic and organic resin coatings may be used, provided that a coating containing 50% or more of zinc is used. As an organic system, brown, ocher, titanium white, titanium yellow, chrome oxide green, phthalocyanine blue, phthalocyanine green, etc. are blended as coloring pigments in epoxy, urethane, polyester resin and the like. As extender pigments, talc, mica, silica, calcium carbonate, barium sulfate and the like may be blended. In addition, additives such as thixotropic agents and dispersants may be blended, and it is optional to use a solvent during coating. As the inorganic system, an alkyl silicate resin, for example, an ethyl silicate resin paint is preferable.

  By adding 50% or more of zinc to these resin-based main components, the corrosion resistance of the coating is surely improved in combination with the steel component. FIG. 1 schematically shows the above functions. Step 1 shows a situation in which zinc contained in the coating 1 is dissolved 3 in the steel material 2 for electrochemical sacrificial protection. . Further, the presence of Ca in the steel has an effect of suppressing the corrosion of not only iron but also zinc by alkalizing and extending the life of both. Next, the atmosphere protection action of zinc rust, which is the corrosion product 4 of zinc, is step 2, and the corrosion resistance of the steel material is maintained. In the present invention, by adding Ti in steel in the above-mentioned amount range, a zinc corrosion product formed by densifying zinc rust effectively repairs a defective portion.

  In the present invention, by controlling the contents of Cu, Ni, and Ti in steel as described above, iron rust that is noticeable in the presence of chlorine ions in the outside air, particularly iron such as β rust, can be obtained. Improves corrosion resistance by promoting densification of corrosion products. Further, as shown in step 3, this dense corrosion product 4 is precipitated 5 so as to fill the gaps that will occur in the zinc rust, thereby repairing the coating defects and improving the corrosion resistance of the coated steel material. Contribute to.

  If the zinc content is 50% or less, the above-described electrochemical sacrificial protective action against iron, that is, corrosion inhibition under the anticorrosion film becomes insufficient, and the pitting corrosion inhibiting effect on the heel portion cannot be expected. However, when the blending amount of zinc exceeds 90% and reaches 95%, the resin binder is insufficient, and the film forming property and the film adhesion are deteriorated. Further, the thickness of the zinc-containing coating needs to be 10 μm or more, and if it is thinner than this, the corrosion suppression under the coating is insufficient and the pitting corrosion of the heel portion cannot be sufficiently prevented.

  Further, in the present invention, a metal salt that is electrochemically lower than zinc, such as zinc phosphate, magnesium phosphate or aluminum phosphomolybdate, may be blended together with 50 to 90% zinc. When these salts coexist with zinc in the coating, they raise the pH and resist acidification by elution ionization of zinc, and the zinc ions are insolubilized by changing to zinc hydroxide, basic zinc chloride or the like. Thus, if zinc elution is suppressed, as a result, the corrosion resistance and durability of the coated steel sheet are further improved. These salt compounds are preferably fine particles having an average particle size of 1 μm or less, and the blending amount is preferably 0.1 to 30% in view of the amount of zinc.

  As described above, the elution of zinc in the coating containing a large amount of zinc is due to sacrificial anodization of zinc, and as a result, the pH is lowered by the hydrolysis reaction of the following formula.

Zn → Zn ²⁺ + 2e ⁻
Zn ²⁺ + H ² O⇔ZnOH ⁺ + H ⁺
Although dissolution of zinc tends to continue in a state where the pH is lowered, addition of the above metal salt to the coating suppresses acidification by zinc ions as shown in the following formula. It becomes insolubilized as basic zinc chloride.

ZnOH ⁺ + H ⁺ + 2OH ⁻ → Zn (OH) 2 + H 2 O
In this way, the corrosion resistance of the coating is improved.

For the same purpose, the present invention provides one or two oxides or hydroxides of Group IIA metal of the periodic table in which a saturated aqueous solution has a pH value of 10.5 or more in a film containing 50% or more of zinc. The above may be blended. For example, calcium oxide / magnesium or calcium hydroxide is preferable. If this compound is additionally added, the saturated aqueous solution is increased to the alkali side, and as a result, elution of zinc is suppressed. The particle size of this compound is 10 μm or less to increase the specific surface area, thereby making it easier to effectively suppress acidification in the coating film.

  Further, when the above-mentioned IIA-based metal oxide / hydroxide is used together with a salt compound of a metal that is less basic than zinc as described above, a synergistic effect can be expected.

(Example)
Table 1 shows the component compositions of the steels according to the present invention and comparative steels, Tables 2 and 3 show coating types and coating specifications for forming coatings on these steels, and Table 4 shows the results of the corrosion resistance test of the coated steels. Respectively.

  First, each steel material in Table 1 was melted by a conventional method and processed into a test material. After descaling by shot blasting, various coatings (Tables 2 and 3) were applied by spraying. Next, the surface of each coating test material was creased with a cutter knife to reach the substrate, and an artificial film defect was made.

  Next, the edge portions of these test materials were sealed with another paint, and the evaluation test was carried out after processing so that the corrosion resistance evaluation was not affected by the thickness of the coating.

  First, the coating corrosion test was performed for the following four steps in the order of 1 to 4 for a total of 6 hours and 1 cycle, which was repeated 4 cycles per day and continued for 6 months.

1. Salt spray
5% NaCl aqueous solution, 30 ± 2 ° C., 0.5 hours 2. Wet
95 ± 3% RH, 30 ± 2 ° C, 1.5 hours 3. Hot air drying
20% RH, 50 ± 2 ° C, 2 hours 4. Drying with warm air
20% RH, 30 ± 2 ° C., 2 hours After 6 months, the blister width from the film defect was measured and evaluated. That is, the corrosion amount of a test piece obtained by coating the comparative steel A in Table 1 with (Table 2) lead-based rust inhibitor (without zinc) was set to 100, and each corrosion amount was classified into the following four types and evaluated. .

◎ <70%, ○ <80%, △ <90%, × 90% or more
In Table 2, “Lead-based rust prevention” is zinc-free, and Tables A to D are examples in which a large amount of zinc of the present invention is blended. In addition, “New Zinc” in Table O is an example in which zinc and a base metal salt compound are combined, and also an IIA metal oxide / hydroxide is blended. 3 shows the breakdown.

  Tests 1 to 5 in Table 4 are comparative materials outside the specified conditions of the present invention for both the steel component and the coating composition, and the test results are all poor. In Tests 6 to 12, the base steel within the conditions of the present invention was coated with a lead-based paint, and the test results were unsatisfactory with Δ. On the other hand, the test pieces 18-27 are the film | membrane which mix | blended 85% zinc, and a test result is good. Furthermore, the test pieces 28 to 35 are films in which zinc and a metal salt are added together, and the corrosion resistance is even better. In addition, the test piece 36 and below are coatings in which zinc, metal salt, and IIA metal oxide / hydroxide are co-added, and it is understood that the corrosion resistance is most excellent.

It is sectional drawing which represented typically the corrosion phenomenon from the coating-film layer to the steel interface part in the highly corrosion-resistant coating steel material of this invention.

Explanation of symbols

1: Coating 2: Steel material 3: Zinc dissolution 4: Zinc corrosion product 5: Iron corrosion product

Claims (11)

  C: 0.20% or less (representing weight%, the same shall apply hereinafter), Si: 0.01 to 1.0%, Mn: 2.5% or less, Cu: 0.05 to 3.0%, Ni: 0.05 to 6.0%, S: 0.02% or less, P: 0.2% or less, Cr: 0.20% or less, Ca: 0.0001 to less than 0.01%, and Ti: 0.03 On the surface of a steel material containing ~ 1.0% and Ti / P> 2.0, the balance being iron and inevitable impurities, the main component is an organic or inorganic resin, and 50% or more of zinc A corrosion-resistant coated steel material, wherein the coating film is formed so as to have an average film thickness of 10 μm or more.   The steel material according to claim 1, wherein Cr: 0.10% or less.   The steel material according to claim 1 or 2, wherein Ca: 0.005% or less.   The steel material according to any one of claims 1 to 3, further comprising Al: 0.005 to 0.50%.   The steel material according to any one of claims 1 to 4, further comprising one or two of La: 0.0001 to 0.05% and Ce: 0.0001 to 0.05%. Corrosion-resistant coated steel material.   The steel material according to any one of claims 1 to 5, wherein Nb≤0.10%, V≤0.10%, Zr≤0.05%, Mo≤0.25%, Mg≤0.010. % And REM ≦ 0.010% are additionally contained.   The corrosion-resistant coated steel material according to any one of claims 1 to 6, wherein a coating film containing 50 to 90% zinc and further containing a metal salt of a metal that is electrochemically less basic than zinc is formed. .   The corrosion-resistant coated steel material according to claim 7, wherein the metal salt is magnesium phosphate or aluminum polyphosphate.   9. The corrosion-resistant coated steel sheet according to claim 7, wherein the metal salt has an average particle diameter of 1 μm or less.   The surface of the steel material contains organic or inorganic resin as a main component, and contains 50% or more of zinc and one or more of Group IIA metal oxides or hydroxides having a pH value of 10.5 or more of saturated aqueous solution. A corrosion-resistant coated steel material according to any one of claims 1 to 9, wherein a coating film is formed. 11. The corrosion-resistant coated steel material according to claim 10, wherein a coating containing at least one of calcium oxide, calcium hydroxide, or magnesium oxide is formed as the IIA metal-based oxide or hydroxide.

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