JP5641000B2 - Surface-treated steel with excellent corrosion resistance - Google Patents

Description

The present invention relates to a steel material used in a concentrated chloride environment having a high chloride ion (Cl ⁻ ) content, such as a beach area where salt is splashed, or a snow melting salt (freezing agent) such as rock salt. Even in environments where corrosion can be suppressed or prevented, and where cooling and heating are repeated due to seasonal changes in temperature or due to temperature changes (hereinafter referred to as “cooling and cycling environment”), surface-treated steel materials can be peeled off. The present invention relates to a surface-treated steel material with excellent corrosion resistance that suppresses or prevents and realizes minimum maintenance.

Steel materials are widely used in various fields such as marine structures, harbor facilities, ships, construction / civil engineering structures, automobiles, etc., but there is a problem that they corrode when exposed to the natural environment. As a method for preventing or suppressing corrosion, there are a case where anticorrosion / corrosion prevention coating is performed and a case where an alloying element is added to the steel material to improve corrosion resistance. Examples of the latter include low-alloy steels that generate protective rust (stable rust layer) in an atmospheric corrosive environment and suppress the subsequent corrosion, so-called weather-resistant steels, etc. Used in steel structures. For example, Patent Document 1 below describes a steel material in which the corrosion resistance of the steel material is enhanced by stable rust (α-FeOOH). In the invention described in Patent Document 1, α-FeOOH is obtained on the steel material surface by supplying OH ⁻ to the rust layer and placing it in a high pH environment exceeding pH 7.

  However, a protective rust layer is not formed on the surface of the weathering steel material in a concentrated chloride environment with a high chloride ion concentration, such as a beach area or an inland area where snow melting salt is scattered. The effect of suppressing corrosion is not exhibited. For this reason, it has not been possible to use a weather-resistant steel material that has not been painted in the seaside area.

Even in weathering steel standardized by Japanese Industrial Standards (JIS) (JIS G3114: weathering hot rolled steel for welded structures), the amount of incoming salt is 0.05 mg / dm ² / day (0.05 mdd) as NaCl. In the above areas, that is, beach areas and areas where snow melting salt is sown (hereinafter sometimes collectively referred to as beach areas, etc.), corrosion loss due to the occurrence of scale-like rust, layered rust, etc. is so large that it cannot be used without painting. (Ministry of Construction Public Works Research Institute, Steel Club, Japan Bridge Construction Association: Joint Research Report on the Application of Weatherproof Steel to Bridges (XX)-Design of Uncoated Weatherproof Bridges・ Construction Procedure (Revised Version-1993.3).

  For this reason, in a concentrated chloride environment such as a beach area, it is common to use ordinary steel with a corrosion-resistant coating. However, even in the coastal area, especially in the vicinity of the estuary where the humidity is high, the environment is severely corroded, and the corrosion of steel structures such as bridges is fast. Also, in inland areas where snowmelt salt is spilled in large quantities, such as mountainous areas, snowmelt salt is rolled up on the running car and scattered and easily adheres to bridges, creating a severely corrosive environment and steel structures such as bridges. The progress of corrosion is fast. Furthermore, even in areas a little away from the coast, under the eaves where no salt deposits are washed away due to rain, a severe salt damage / corrosion environment with an incoming salt content of 1 mdd or more is obtained. Under such a severe corrosive environment, repair coating (repainting) is required about every 10 years due to coating film deterioration due to corrosion. Since this repair coating requires a great amount of man-hours and enormous costs for maintenance, there is a high demand for extending the life of the coating film.

  A chromate treatment may be performed as a coating ground treatment for improving the corrosion resistance. However, although the chromate treatment has a high effect of improving corrosion resistance, the coating formed by the treatment (chromate coating) also contains hexavalent chromium because an aqueous solution mainly containing chromic acid, which is a hexavalent chromium compound, is used for the treatment. Its harmfulness is a problem from the standpoint of environmental protection.

  The corrosion resistance, durability, adhesion and adhesion of the steel material after aging of the rust / corrosion protection coating are greatly influenced by the properties of the steel surface. When the existing steel structure is repainted, rust is usually generated on the surface of the steel material, and even if the paint is repainted on such a surface, the coating film is swelled or peeled off, and the steel material cannot be protected from rust for a long time.

Therefore, conventionally, after rusting the surface of steel using a moving tool such as blasting or grinder before painting, paint is applied, or floating rust on the surface of steel is removed before painting, and then rust conversion is performed. An agent was applied, brittle iron oxyhydroxide, the main component of red rust, was converted to hard Fe ₃ O ₄ , the main component of black rust, and a paint was applied.

  However, the former method has a problem that not only the working environment is deteriorated, but also the working efficiency is very bad when the rust is removed. The latter method is also time-consuming and has the problems that it cannot be applied unless a certain amount of time is spent after applying the rust conversion agent.

In the case of general repainting, 1 to 3 types of kelen are applied to the surface of steel before coating to remove rust. However, it is difficult to remove rust at the indentations and narrow areas of steel structures. Corrosive ionic substances such as Cl ⁻ and SO ₄ ²⁻ are likely to remain at the interface between the rust layer and the iron base, and moisture is also likely to exist. Therefore, even if it is repainted, the anticorrosion properties at those locations are greatly reduced. If the rust removal is not sufficient, the coating film is poorly adhered, and the coating film is peeled off and rusted very quickly. Therefore, the highest possible rust removal (10 mg / m ² ) is standardized in the construction of rust and anticorrosion coatings.

  However, in reality, depending on conditions such as the environment and parts of steel structures such as offshore structures, harbor facilities, ships, construction and civil engineering structures, automobiles, mechanical equipment, railway vehicles, generators, large transformers, etc. The rust removal work itself is difficult, and there are a lot of painting problems due to inadequate pretreatment. In recent years, due to the shortage of workers engaged in rust removal work, simplification of rust removal work has been strongly demanded.

  Corrosion and repainting are also a major problem in the ship field. Ships such as tankers and freighters are loaded with seawater in a ballast tank so that the hull is stable even when empty. However, seawater has a corrosive action on steel, and promotes corrosion of the steel material constituting the ballast tank. It is known that the corrosion of the steel constituting the ballast tank is not so much at the inner wall of the tank where the seawater injected and loaded into the ballast tank is in direct contact, but at the part in contact with the space (gas phase) on the seawater surface. It has been. This is because the tank inner wall of the space portion is always in a wet state, and oxygen causing corrosion (promoting) is continuously supplied from the air. In order to prevent corrosion of the inner wall surface of the ballast tank, conventionally, tar epoxy paint is coated on the inner wall surface of the ballast tank with a relatively thick film thickness of about 200 μm to prevent corrosion. However, even in this method, the corrosive environment is severe, the life of the coating film is as short as about 10 years, and repair coating is necessary.

  In addition, coastal and offshore structures, bridges, and ship structural members are painted as described above, but in addition to seasonal differences in temperature, the coating film and steel material interface are subject to cohesive failure due to changes in steel temperature due to sunshine. Wake up and paint peels off. It is known that corrosion proceeds from the peeled portion. The coating peeling due to this cooling and heating cycle occurs due to the difference in thermal expansion coefficient between the steel material and the coating film resin. Therefore, the larger the coating film thickness on the steel material surface, the greater the difference between the thermal expansion and contraction of the steel material and the coating film, and the easier the peeling progresses. When a thick coating film is designed in consideration of only corrosion resistance and the steel surface is coated, the peeling of the coating progresses due to the thermal cycle, and rather the corrosion progresses. In order to cope with this corrosion resistance and paint peeling due to the thermal cycle, the corrosion resistance and the thermal cycle resistance due to the ground treatment have been required.

In the following Patent Document 2, an acidic aqueous solution containing Sn ²⁺ ions and having a pH of 3 or less is applied on the surface of a structural steel material having a surface roughness Rzjis of 30 to 100 μm or on a rust layer formed on the steel material. In a concentrated chloride environment with a high chloride ion concentration by forming a Sn-containing layer with a metal Sn equivalent adhesion amount of 15 to 400 mg / m ² and applying a resin coating for corrosion protection with a dry film thickness of 20 μm or more on it. Also discloses a resin-coated steel material that exhibits excellent long-term durability and can significantly extend the coating life until repainting, and an invention relating to its manufacturing method. As the film thickness of the Sn-containing layer increases, the corrosion resistance improves. However, in a cold cycle environment, this Sn-containing layer becomes a starting point of cohesive failure at the interface between the coating film and the steel material, and there is a possibility that coating peeling will increase.

Japanese Patent Laid-Open No. 5-247663 JP 2007-230088

  The present invention aims to improve steel material corrosion that is unavoidable for steel materials widely used as structural materials in offshore structures, harbor facilities, ships, construction / civil engineering structures, automobiles, and the like. More specifically, it exhibits excellent corrosion resistance even in coastal areas, areas where snowmelt salt is sprayed, and even in concentrated chloride environments with high chloride ion concentration where seawater scatters or contacts, such as ship tanks. Another object of the present invention is to provide a surface-treated steel material having excellent long-term durability, which can exhibit excellent durability even in an environment of a cooling / heating cycle depending on sunlight and temperature.

As already reported by one of the present inventors ("Materials and Environment", Vol. 43 (1994), No. 1, p. 26), in rust-resistant steel materials, the rust layer has a protective property of Fe. This is because a rust layer made of fine α- (Fe _1-x Cr _x ) OOH in which part is replaced with Cr is generated. However, the addition of Cr to the steel to promote the formation of this rust layer is effective in improving the weather resistance in an environment where the amount of incoming salt is relatively small, but in an environment where the amount of incoming salt is as high as 1 mdd or more, It has been found that such a stable rust layer is not formed and the weather resistance is deteriorated.

  In chloride environments, such as beaches and coastal areas where salt comes in, or mountains or cold areas where rock salt is sprayed as a snow melting agent, anti-freezing agent, etc., the formation of the protective rust layer is inhibited by chlorides. The steel material is significantly corroded. That is, in a chloride environment, β-FeOOH (mineral name: akaganeite) that has a stable crystal structure is easily generated by taking in chloride ions. Therefore, instead of generating a protective rust layer mainly composed of α-FeOOH, corrosion is progressed as a result of formation of rust with poor protection containing a large amount of β-FeOOH, represented by layered peeling rust. Become. Unlike α-FeOOH, which is electrochemically inactive, β-FeOOH is electrochemically active. Therefore, β-FeOOH is produced by cathodic reaction (reduction) as a counter reaction of Fe elution reaction (oxidation reaction). Reaction), which is believed to promote corrosion. In particular, in a concentrated chloride environment in which the amount of salt attached to the steel material surface is 1 mdd or more per year, the steel material is severely corroded, and a large amount of β-FeOOH is generated in the rust layer formed on the steel material surface.

Based on this knowledge, the present inventors examined corrosion in a concentrated chloride environment. As a result, in such an environment, repeated drying and wetting of the FeCl ₃ solution became an essential condition for corrosion, and due to the hydrolysis of Fe ³⁺ It has been found that corrosion is accelerated by an acidic environment with a reduced pH and by Fe ³⁺ acting as an oxidant. The corrosion reaction at this time is expressed by the following equation.

Cathode reaction: Fe ³⁺ + e ⁻ → Fe ²⁺ (reduction reaction of Fe ³⁺ )
Of course, besides this reaction,
2H ₂ O + O ₂ + 2e ⁻ → 4OH ⁻ ,
2H ⁺ + 2e ⁻ → H ₂
The cathodic reaction also occurs.

On the other hand, Fe → Fe ²⁺ + 2e ⁻ (anode reaction: Fe dissolution reaction)
Also happens. More specifically, this Fe dissolution reaction is
Fe → FeCl _ad or FeOH _ad → Fe ²⁺
As shown by the adsorption intermediate FeCl _ad or FeOH _ad (ad is adsorption) in the chloride or hydroxide form.

Therefore, the overall reaction of corrosion is
2Fe ³⁺ + Fe → 3Fe ²⁺ [Reaction 1]
It becomes.

Fe ²⁺ generated by the reaction 1 is oxidized to Fe ³⁺ by air oxidation, and the generated Fe ³⁺ accelerates corrosion as an oxidizing agent again. At this time, the reaction rate of air oxidation of Fe ²⁺ is generally slow in a low pH environment, but is accelerated in a concentrated chloride environment, and Fe ³⁺ is easily generated. It was found that due to such a cyclic reaction, in an environment where the chloride ion concentration is high, Fe ³⁺ is always supplied, corrosion of the steel is accelerated, and corrosion resistance is significantly deteriorated.

  Thus, protection by formation of a rust layer made of α-FeOOH that is stable in a concentrated chloride environment with a high chloride ion concentration cannot be expected. However, if it is possible to appropriately form a protective rust layer in a concentrated chloride environment, it is considered that high corrosion resistance can be imparted to the steel material. Therefore, the inventors conducted a basic experiment based on inorganic synthesis of iron oxyhydroxide (rust) using an aqueous chloride solution of Sn, and can form α-FeOOH which is protective rust even in a concentrated chloride environment. I knew.

  Table A shows the experimental conditions and results. After adjusting the pH of a solution in which Sn chloride shown in Table A was added at a molar ratio to 0.05 to 0.1 mol / L of iron (III) chloride, the solution was heated at 80 ° C. for about 2 days. , Accelerated rust generation. The generated rust was qualitatively analyzed by X-ray diffraction. As shown in Table A, when the concentration of Sn chloride was within a certain range, α-FeOOH as protective rust was generated. In particular, with respect to divalent Sn chloride, it has been clarified that only α-FeOOH is produced in a wider concentration range.

  Furthermore, when Sn was investigated in detail, it discovered that Sn itself was effective in suppression of corrosion of steel materials. The inhibitory effect of Sn on the corrosion of steel in a concentrated chloride environment, that is, an environment in which the pH is significantly lowered, is considered to be due to the mechanism shown in the following (a) to (g).

(a) Sn on the surface of the steel material dissolves as Sn ²⁺ ions in a concentrated chloride environment,
Fe → FeCl _ad or FeOH _ad → Fe ²⁺
The anodic reaction (Fe dissolution reaction) indicated by is suppressed, so that elution of iron can be prevented. This is because, as shown in the left diagram of FIG. 1, Sn ²⁺ ions preferentially bind to the adsorption active sites on the steel surface, and the adsorption intermediate or FeOH _ad (ad is adsorbed) in the form of chloride or hydroxide. This is because the generation is disturbed. That is, the decrease in active sites (FeCl _ad , FeOH _ad ) due to Sn ²⁺ ions suppresses the anode reaction.

(b) In addition, after Sn is dissolved as Sn ²⁺ ions, in a low pH solution, it is reduced by the electrode potential on the steel surface and precipitates as Sn on the steel surface.

(c) Sn deposited on the surface of the steel material is a counter reaction of the dissolution reaction (anodic reaction) of Fe in an acidic environment, as shown in the right diagram of FIG.
2H ⁺ + 2e ⁻ → H ₂
The cathode reaction (reduction reaction) of hydrogen ions represented by That is, since H ⁺ ions are not adsorbed on Sn deposited on the steel surface, the hydrogen generation reaction is not suppressed, and the cathode reaction is suppressed. This is thought to be due to high hydrogen overvoltage.

(d) Since precipitation of Sn concentrates on the elution part of steel, dissolved Sn2 ⁺ precipitates as Sn only in the part which is corroding efficiently.

(e) Once deposited, Sn re-elutes as Sn ²⁺ when corrosion progresses, exerts a corrosion-inhibiting effect, and precipitates again as Sn on the corroded portion.

(f) In an environment where the dissolved oxygen concentration is high, it is known that the rate of air oxidation from Sn ^{2+ to} Sn ⁴⁺ is fast. Sn ⁴⁺ which is an air oxide is reduced again to Sn ²⁺ by electrons supplied by the anode reaction of Fe, and further precipitated as Sn. The cyclic reaction of Sn using the Fe anode reaction as an electron source suppresses corrosion.

(g) Therefore, when Sn or Sn ²⁺ or Sn ⁴⁺ ions are present on the surface of the steel material, repeated corrosion can be suppressed without depletion, that is, a semi-permanent corrosion suppressing effect can be obtained. In order to make Sn or Sn ²⁺ or Sn ⁴⁺ ions exist on the surface of the steel material, an acidic aqueous solution having a pH of 3.0 or less containing one or both of Sn ²⁺ ions and Sn ⁴⁺ ions is applied to the surface of the steel material, or The surface of the steel material may be covered with an organic resin film containing Sn, Sn ²⁺ or Sn ⁴⁺ ions.

Thus, when Sn or Sn ^<2+> or Sn ^<4+> ion exists on the steel material surface, not only the anticorrosion effect of the protective rust layer by (alpha) -FeOOH but the corrosion inhibitory effect of Sn itself can be anticipated. Therefore, formation of α-FeOOH can be promoted even in a concentrated chloride environment, and corrosion of the steel material can be suppressed by corrosion resistance due to protective rust.

  The present invention has been completed based on such knowledge, and the gist thereof is a surface-treated steel material having excellent corrosion resistance as shown in the following (1) to (7).

(1) A surface-treated steel material obtained by coating the surface of a steel material having a surface roughness Rzjis of 30 to 100 μm with a rust layer containing α-FeOOH, and Sn or Sn compound is converted into metal Sn in the rust layer. In a range of 0.05 mg / m ² or more and less than 15.0 mg / m ² .

  (2) The surface-treated steel material according to (1) above, wherein an organic resin film having a dry film thickness of 20 μm or more is coated on the rust layer.

  (3) The surface-treated steel material according to (1) above, wherein an organic resin film having a dry film thickness of 20 μm or more containing Sn or a Sn compound is coated on the rust layer.

  (4) The surface treatment according to (1) above, wherein an organic resin film having a dry film thickness of 20 μm or more is coated on the rust layer through an organic resin film containing Sn or a Sn compound. Steel material.

  (5) The surface-treated steel material according to any one of (1) to (4) above, which contains β-FeOOH in addition to α-FeOOH in the rust layer, and X-ray diffraction of α-FeOOH in the rust layer A surface-treated steel material, wherein a ratio (α / β ratio) between an integral value obtained by X-ray diffraction and an integral value obtained by X-ray diffraction of β-FeOOH is 0.6 or more.

(6) The rust layer is formed by applying an acidic aqueous solution having a pH of 3.0 or less containing one or both of Sn ²⁺ ions and Sn ⁴⁺ ions to the surface of the steel material. The surface-treated steel material according to any one of (1) to (5).

  The surface-treated steel material according to the present invention exhibits excellent corrosion resistance even in a concentrated chloride environment with a high chloride ion concentration, and is excellent in being able to remarkably suppress paint peeling even in an environment of a cold cycle caused by sunlight or temperature. Shows long-term durability. Therefore, when the present invention is applied to steel materials used for bridges, shipbuilding, and offshore structures, the paint repainting interval can be extended, and maintenance costs can be greatly reduced.

It is explanatory drawing which illustrates typically the effect of Sn or a Sn compound. The left figure shows the suppression of the anode reaction (Fe dissolution reaction), and the right figure shows the suppression of the cathode reaction which is the counter reaction.

  The steel material to which the present invention is applied is not particularly limited, but is preferably a structural steel material, particularly a steel material used as a structural material in marine structures, port facilities, ships, construction / civil engineering structures, automobiles, railways, and the like. is there. The material of the steel material is not particularly limited, and may be alloy steel such as carbon steel or low alloy steel. A weather resistant steel or a low alloy steel containing Ni, Al, Sn, etc. is advantageous from the viewpoint of long-term durability.

  The form of the steel material is not particularly limited, and may be any form including a plate, a rod, a shape steel, a pipe, a cast product, etc. In addition to a steel pipe used for a line pipe or a pipe, a steel pipe pile, a steel sheet pile, a reinforcing bar, etc. It can also be applied to steel materials of various shapes. The present invention can also be applied to various existing steel materials including bridges, land tanks, and ballast tanks.

  The steel material to be treated according to the present invention has an outer surface whose surface is obtained by a known physical means such as shot blasting, grid blasting or sand blasting, chemical means such as pickling or alkaline degreasing, or an appropriate combination thereof. It may have a clean surface from which rust is removed substantially completely. In this case, the steel material surface is processed. Even in the case of a new steel material, it is preferable to clean the surface in advance before the treatment.

Forming a rust layer rich in α-FeOOH on the entire surface of the steel material by applying an acidic aqueous solution containing one or both of Sn ²⁺ and Sn ⁴⁺ to the steel material with a pH of 3.0 or less. Can do. The lower limit of the pH of the acidic aqueous solution is preferably 0, and more preferably 0.5.

When Sn solution supplied to the steel surface is coated with an aqueous solution containing Sn ²⁺ , it is considered that the divalent Sn compound remains on the surface of the steel material due to evaporation of water, but some of the corrosion (Fe Elution) and can be reduced to Sn and exist as metallic Sn. When an aqueous solution containing Sn ⁴⁺ is applied, it is reduced to Sn ²⁺ and further reduced to metal Sn. Therefore, Sn can exist as a tetravalent Sn compound, a divalent Sn compound, or metal Sn.

In the case of a steel material coated with an organic resin film, if Sn, a divalent Sn compound, or a tetravalent Sn compound is present as an underlayer, ionization occurs when moisture reaches the steel surface by impregnating the organic resin coating. Or by dissolving in water, Sn ²⁺ ions or Sn ⁴⁺ ions are generated, and these Sn ions suppress the formation of an adsorption reaction intermediate on the Fe surface, thereby suppressing the dissolution of Fe.

Furthermore, the generated Sn ²⁺ and its air oxide Sn ⁴⁺ are preferentially deposited as Sn on the corroded partial surface, and the reduction reaction (cathode reaction) of hydrogen ions on the deposited Sn is remarkably suppressed, Corrosion will be suppressed. Thus, Sn and Sn ions repeatedly dissolve and precipitate to exert a corrosion inhibiting effect semipermanently.

Here, if an acidic aqueous solution having a high acidity of pH 3.0 or less is used, the corrosion inhibiting action by Sn ions can be effectively functioned, while the steel surface is etched with an acid to form a protective rust layer. Can do. Fe ²⁺ eluted in a low pH environment is immediately oxidized into air to become Fe ³⁺ , and α-FeOOH containing Sn ions is generated as the hydrolysis reaction proceeds. It was found that Sn ²⁺ and Sn ⁴⁺ were incorporated into the rust layer when the rust layer was dissolved with a strong acid and examined by an induction spectroscopic plasma method. Although it is unclear in what state it is taken in, it is contained in the rust layer in a state where α-FeOOH adsorbs Sn or the like, or in a state where Fe of α-FeOOH is replaced with Sn It is guessed.

When an organic resin coating is further applied on the layer subjected to the aqueous solution coating treatment, a Sn ²⁺ or Sn ⁴⁺ compound is present under the resin coating. While these Sn compounds exhibit a strong anchoring action when present between the steel surface and the resin film, when water impregnates the resin coating and reaches the steel surface, Sn ions are eluted and Sn ²⁺ or Sn ⁴⁺ is generated. The corrosion reaction at the steel material surface and the resin interface is suppressed by the action of the Sn ions described above.

In a concentrated chloride environment, a rust layer is formed along with a corrosion reaction on a part of the steel material surface, but when Sn ²⁺ and Sn ⁴⁺ are present when rust is formed, α-FeOOH is preferentially formed. Conventionally, α-FeOOH was not formed in a concentrated chloride environment of 1 mdd or more. However, when Sn is present, not only in a chloride environment of less than 1 mdd but also in a concentrated chloride environment of 1 mdd or more. -The formation of rust composed of FeOOH is promoted.

  The organic resin film formed on the upper layer of the rust layer made of α-FeOOH has an effect of physically blocking the steel material from the external corrosion environment and improving the corrosion resistance. Even if the organic resin coating is damaged, the corrosion resistance is maintained because α-FeOOH and a Sn compound are present in the lower layer. If the organic resin film has a dry film thickness of 20 μm or more, it exhibits a sufficient shielding effect from the external corrosive environment.

  Sn ions are likely to be deposited in the recesses on the surface of the steel material, which greatly contributes to the above-described corrosion-inhibiting action by Sn ions and the promoting action of forming a protective rust layer. On the other hand, in the convex part on the surface of the steel material, the deposition of Sn ions is small, and when the organic resin coating is applied, the film thickness of the organic resin coating on the convex part becomes thin, so that corrosion starts from the convex part. Cheap.

  Further, the adhesion between the steel material surface and the resin film when the organic resin film is coated is strongly related to the durability of the resin film steel plate in a cold cycle environment. For example, paint peeling in a cold cycle environment is caused by cohesive failure occurring at the interface between the steel surface and the resin due to a difference in thermal expansion coefficient between the steel material and the resin due to a rapid temperature change. Generally, when the roughness of the steel material surface becomes high, the anchoring action of the resin film is exhibited by the unevenness of the steel material surface.

  Thus, the surface roughness Rzjis of the steel material before the surface treatment greatly affects the characteristics of the surface-treated steel material. The surface roughness Rzjis of the steel material is preferably 30 to 100 μm. The surface roughness Rzjis may be adjusted by the above-described shot blasting.

In the above description, the surface-treated steel material in which α-FeOOH is formed by applying an acidic aqueous solution containing Sn ions has been described. However, the organic resin film has a function of generating α-FeOOH by containing Sn or a Sn compound. May be. If the Sn or Sn compound contained in the organic resin film elutes as Sn ions to promote the formation of α-FeOOH and a protective rust layer is appropriately formed on the steel material, it is simpler than the aqueous solution coating method. This is because a surface-treated steel material with high corrosion resistance can be formed. In this case as well, although the form is unknown, Sn ²⁺ or Sn ⁴⁺ is taken into the rust layer on the steel surface. As a result, a rust layer composed of α-FeOOH containing Sn is formed at the interface between the organic resin film and the steel material, and the surface-treated steel material coated with the organic resin coating containing Sn is formed thereon.

  Sn or Sn compounds contained in the organic resin film are eluted as Sn ions by moisture impregnating the organic resin film. The eluted Sn ions suppress the corrosion reaction by the above-described action and promote the formation of protective rust α-FeOOH.

  On the organic resin film containing Sn or Sn compound, an organic resin film may be further coated as an overcoat. By applying the top coating, it is possible to physically block corrosion factors such as water and chloride. As the coating film thickness increases, the protective rust layer formation rate at the interface between the resin film and the steel material is expected to decrease. However, when the eluted Sn ions are contained, the acidity of the resin film is slightly increased, but it provides a starting point for the formation of protective rust to etch the steel surface, and immediately protects when moisture impregnates the resin film. A rust layer is formed. Even if the organic resin film is deteriorated or scratched, Sn ions are supplied from the resin film containing Sn or the Sn compound to the scratched portion of the resin film, thereby suppressing corrosion by Sn and forming protective rust. Can suppress the progress of corrosion.

  In addition, since the eluted Sn ions in the organic resin film etch the surface of the steel material, a Sn compound is formed at the interface between the resin film and the steel material, and exerts a stronger anchoring action. The phenomenon can be suppressed.

The acidic aqueous solution containing one or both of Sn ²⁺ ions and Sn ⁴⁺ ions used for applying to the steel material surface of the present invention can be prepared as follows.

Sn ²⁺ can be prepared by dissolving tin (II) sulfate or tin (II) chloride in water or by dissolving tin (II) oxide in an aqueous acid solution. An acidic aqueous solution containing Sn ²⁺ may be oxidized by air to contain Sn ^4+, and when oxidized to Sn ⁴⁺ , white precipitation of tin hydroxide [Sn (OH) ₄ ] may occur. In this case, when the metal Sn is allowed to coexist in the solution, this precipitation can be suppressed.

Sn ⁴⁺ can be adjusted by dissolving tin (IV) chloride in water or by dissolving tin (IV) oxide in an aqueous acid solution. The aqueous solution containing only Sn ⁴⁺ is more stable as the pH is lower, and when precipitation of tin hydroxide occurs, the precipitation can be dissolved by lowering the pH of the aqueous solution with hydrochloric acid.

In the case of an acidic aqueous solution in which Sn ²⁺ and Sn ⁴⁺ are mixed, if Sn ⁴⁺ is made equal to or less than Sn ²⁺ , the equilibrium of Sn ²⁺ ⇔Sn ⁴⁺ is maintained, and precipitation of tin hydroxide is caused by air oxidation of Sn ^2+. Suppresses and becomes a uniform aqueous solution, which is effective.

  The pH of the acidic aqueous solution is adjusted to 3.0 or less. When the pH exceeds 3.0, Sn ions precipitate and do not function effectively. The pH can be adjusted by adding an acid or a base as necessary. The lower limit of the pH is preferably 0, more preferably 0.5.

This acidic aqueous solution cannot contain a large amount of organic resin that functions as a binder, but a small amount of organic resin (eg, 10% or less of the total solid content in the liquid) for making the aqueous solution into an emulsion state. Inclusion is allowed. However, it is preferable that the organic resin is not substantially contained (the content of the organic resin is 1% by mass or less of the total solid content in the liquid). The aqueous solution to be applied can be colored by adding a pigment or a dye. In this case, it becomes easy to distinguish the application portion of the aqueous solution, which is particularly convenient when applying to an existing structure. Moreover, in order to accelerate | stimulate the drying after application | coating, volatile organic solvents, such as alcohol which does not inhibit stability of Sn2 ⁺ , can also be added as a part of solvent. In addition, other additive components can be contained in the aqueous solution to be applied as long as the effects of the present invention are not substantially adversely affected.

  The application method of the acidic aqueous solution is not particularly limited as long as a necessary adhesion amount is obtained. For example, brushing, ironing, and air spraying are possible. Since the coating aqueous solution has a viscosity lower than that of a normal paint, the surface of the steel material to be applied or the rust surface is a relatively rough surface having a surface roughness Rzjis of 30 to 100 μm.

  When the surface roughness Rzjis is 30 to 100 μm, the difference in the amount of adhesion between the top / bottom portions of the unevenness is not large, appropriate coating uniformity can be maintained, and dripping of the applied aqueous solution can be easily prevented. This is advantageous because the production efficiency of the resin-coated steel material can be increased. Therefore, in particular, when the rust layer is not formed, it is preferable that the steel material surface has the surface roughness Rzjis. The surface roughness Rzjis is more preferably 40 to 90 μm. The surface roughness Rzjis of the steel material can be adjusted, for example, by changing the particle diameter of a steel ball used in shot blasting. Even if a rust layer is generated, the original roughness is basically reflected in the surface roughness Rzjis.

When the surface of a steel material having such a surface roughness Rzjis is coated with a rust layer containing α-FeOOH, the Sn or Sn compound content in the rust layer is 0.05 mg / m ^{2 in} terms of metal Sn. It is necessary to make it the range above and below 15 mg / m ² . When the content of Sn or Sn compound is less than 0.05 mg / m ² , the corrosion inhibiting effect by the Sn or Sn compound and the durability of the thermal cycle cannot be sufficiently obtained. On the other hand, even if the Sn or Sn compound content is 15 mg / m ² or more, the corrosion inhibiting effect can be expected. However, when the content is 15 mg / m ² or more, the rust layer may cause cohesive failure in a thermal cycle environment, and the resin film may be largely peeled off. The upper limit of the Sn or Sn compound content is preferably 12 mg / m ^2, and the lower limit is preferably 0.07 mg / m ² .

When an acidic aqueous solution containing an aqueous solution containing one or both of Sn ²⁺ and Sn ⁴⁺ is applied, a Sn-containing layer is formed on the surface or rust surface of the applied steel after drying. As described above, the Sn-containing layer contains metal Sn or tetravalent Sn compound in addition to the divalent Sn compound. The Sn-containing layer is preferably formed uniformly on the surface or rust surface of the steel material, but even if it is non-uniform, it has a sufficient corrosion inhibiting effect. As described above, when Sn ²⁺ ions are precipitated as Sn, precipitation is concentrated on the steel elution portion, that is, the corrosion portion, and further corrosion of the corrosion portion is suppressed. In addition, Fe ions and Sn ions eluted during the surface treatment form a reaction compound, and α-FeOOH is generated in the rust generation process.

  In addition to the surface treatment in this way, an anti-corrosion resin coating may be formed as an upper layer with a dry film thickness of 20 μm or more. This resin coating is generally formed by painting, but can also be performed by resin coating lining to which a pre-formed organic resin film (eg, polyethylene or polyurethane film) is attached.

  If the dry film thickness of the resin coating is 20 μm or more, the steel material surface can be completely covered, so that corrosion resistance can be exhibited. The upper limit of the dry film thickness of the resin coating is not particularly limited, but from the viewpoint of economy, it is preferably 2000 μm or less in the case of a general paint and 5000 μm or less in the case of a resin coating lining.

  The thickness of the resin coating may be selected according to the corrosive strength of the surrounding environment of the steel material. The present invention can be applied to a steel material installed in a place where the corrosiveness is not so strong. In that case, a thickness of 20 to 50 μm is sufficient for the resin coating. On the other hand, from the viewpoint of corrosion protection, it is preferable that the thickness of the resin coating is 100 μm or more for an environment having a strong corrosive property such as a sea or beach area or a region where a large amount of snow melting salt is poured.

  The resin species to be coated is not particularly limited, and a resin suitable for the anticorrosion resin coating may be used. For example, in the case of paint, epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin, alkyd resin, phthalic acid resin, butyral resin, melamine resin, phenol resin and the like can be used. For paint, color pigments such as bengara, titanium dioxide, carbon black, phthalocyanine blue, α-FeOOH, iron oxide, etc .; and one or more extender pigments such as talc, silica, mica, barium sulfate, calcium carbonate, etc. Can be added. It does not exclude inclusion of chromium oxide, zinc chromate, lead chromate, basic lead sulfate or the like as the anticorrosive pigment. However, considering the environmental load, the amount added is preferably 20% by mass or less, more preferably 10% by mass or less, based on the total solid content in the paint. In addition, conventional additives such as thixotropic agents, dispersants, antioxidants, etc. may be added to the paint.

  For resin coating with paint, if necessary, use a paint whose concentration is adjusted by diluting with an organic solvent so that it has a viscosity suitable for the painting work. If necessary, air spray, airless spray, brush painting, etc. It can be done by the method. When painting in a factory, it may be carried out by other methods such as roll coating and dipping. After coating, the coated film is dried by heating as necessary, or baked in some cases. Painting can be performed more than once.

  Also in the case of resin-coated lining, it can be performed by a known method. The resin-coated lining is preferably applied to the surface of a steel material without a rust layer, and is preferably implemented in a factory even in the case of an existing structure. Therefore, painting is more suitable for existing bridges.

Moreover, the organic resin film containing Sn or Sn compound used in order to implement this invention can be adjusted as follows. Sn ²⁺ can be procured from tin (II) sulfate, tin (II) chloride or tin (II) oxide. In general, tin chloride is highly reactive and the possibility of reacting with the organic resin component to be contained is taken into consideration. Therefore, it is preferable to procure from tin (II) sulfate. Sn ⁴⁺ can be procured from tin (IV) chloride or tin (IV) oxide.

  These inorganic salts are preferably dispersed in an amount of 0.05 to 10.0% by mass with respect to the total weight of the organic resin. Although it is considered that an excellent effect is exhibited even when the amount of the inorganic salt added exceeds 10.0% by mass, it is difficult to uniformly disperse in the paint when the organic resin is applied, and spray coating is performed. In some cases, the tip of the spray may become clogged. On the other hand, when the addition amount is 0.05% or less, a sufficient Sn-containing layer is not formed on the steel material surface.

The Sn or Sn compounds is contained in 0.05 mg / ^{m 2} or more and 15.0 mg / ^{m 2} less than the range of metal Sn terms, to achieve a rust layer containing alpha-FeOOH is the amount of the inorganic salt The organic resin may be adjusted and applied so that the dry film thickness is 20 μm or more and less than 200 μm.

When the content of Sn or Sn compound is less than 0.05 mg / m ² , it is not possible to sufficiently obtain the corrosion inhibition effect and the durability of the thermal cycle due to the inclusion of Sn or Sn compound. On the other hand, if the content is 15.0 mg / m ² or more, the rust layer causes cohesive failure in a cold cycle environment, and there is a high possibility that resin film peeling will increase.

The content of Sn or Sn compounds, preferably 0.07 mg / ^{m 2} or more and 12.0 mg / ^{m 2} or less. In order to achieve such a content, the inorganic salt may be added in an amount of 0.1 to 8.0% by mass, and the organic resin may be applied so that the dry film thickness is 20 μm or more and less than 200 μm.

  The type of resin to which Sn or Sn compound is added is not particularly limited, and may be suitable as a resin coating for anticorrosion. For example, in the case of paint, epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin, alkyd resin, phthalic acid resin, butyral resin, melamine resin, phenol resin and the like can be used.

  The method for applying the resin is not particularly limited. If necessary, the resin is diluted with an organic solvent so that the viscosity is suitable for the coating operation at the time of use. It can be performed by spraying, airless spraying, brushing, or the like. When applying at a factory, you may implement by other methods, such as roll coating and immersion. After coating, the coated film is dried by heating, if necessary, or baked as necessary. The application can be performed twice or more.

  Further, a resin coating may be further applied on the resin film containing Sn or Sn compound. The coating can be performed in the same manner as described above.

Test steel materials having three kinds of chemical compositions shown in Table 1 (all 100 × 60 × 3 mm thick plate materials) were used. Here, the test steel (1) is plain steel, the test steel (2) is Cr-Sn composite added corrosion resistant steel, and the test steel (3) is Sn added corrosion resistant steel. When shot blasting these steel materials, the surface roughness Rzjis of the steel materials was changed by changing the size of the steel balls used.

1. Surface-treated steel material having no organic resin film On the surface of the steel material having the above-mentioned surface roughness Rzjis changed, as a surface treatment, various Sn-containing aqueous solutions shown in Tables 2 and 3 were adjusted to pH 2.12. Or it ironed so that content of Sn compound might become the value shown in Table 2 and Table 3 in conversion of Sn metal. The content of Sn or Sn compound was changed by changing the aqueous solution concentration. As a guide, when stannous sulfate is used as the Sn ion source, the content is about 6 to 7 mg / m ^{2 in} a 0.1% strength aqueous solution. After the application, it was dried by natural drying to form a Sn-containing rust layer. Here, SnSO ₄ or SnCl ₂ was used as Sn ²⁺ and SnCl ₄ was used as Sn ⁴⁺ as a Sn ion supply source. Test numbers 3 and 6 contained both Sn ²⁺ and Sn ⁴⁺ Sn ions.

  The test steel materials that were surface-treated with the inorganic salt of Sn thus produced were evaluated by a chloride / dry moisture repeat test. Chloride / wet repeat test: salt adhesion: 0.01 mol / L NaCl was dropped to form a 500 μm liquid film on the steel surface, dried (40 ° C., 40% RH, 4 hours) and wet (40 ° C., 100% RH, 4 hours) This is a test in which 3 cycles per day are carried out, and salt is deposited every other week. The salinity adhering to the steel material surface for a test period of 3 months is 2.2 mdd.

After conducting a chloride / wet repeat test for 3 months, the rust layer formed on the surface of the test piece was removed, and the amount of corrosion was measured by the following equation (1) as the thickness reduction.
Corrosion amount = (test piece mass after rust layer removal-test piece mass before test) / test piece surface area / iron density ... Equation (1)

Moreover, the rust layer produced | generated on each test material after the chloride wet and dry repetition test was extract | collected with the cutter knife. The collected rust sample was dried in a desiccator for more than one week, and then quantitative analysis of rust constituent compounds was performed by powder X-ray diffraction method using ZnO powder (made by Wako Pure Chemical, particle size of about 5 μm) as an internal standard substance. . The sample for powder X-ray diffraction was mixed with ZnO at a constant weight ratio (30% in this example) with respect to the rust weight collected in advance, and mixed with an agate mortar so that rust and ZnO were uniformly dispersed. X-ray diffraction measurement was performed using a RU200 model manufactured by Rigaku Corporation, with a Co target and a voltage-current of 30 kV-100 mA, and a scanning speed of 2 ° / min. Α-FeOOH, γ-FeOOH (manufactured by Rare Metallic), Fe _{3 -δ} O ₄ (manufactured by High-Purity Chemical), and β-FeOOH synthesized by hydrolyzing an aqueous FeCl ₃ solution at 100 ° C. A quantitative analysis was performed from the intensity of the obtained X-ray diffraction pattern using the calibration curve prepared. The amounts (mass%) of β-FeOOH and α-FeOOH in the rust thus determined were compared.

  In Table 2 and Table 3, the result of the test material which carried out the aqueous solution process on the steel material surface was shown collectively.

  As shown in Table 2, in test numbers 1 to 3 according to the present invention, the corrosion amount was small due to the surface treatment of Sn ions, and all were 0.25 mm or less.

  As shown in Table 3, in Test No. 4 with no ground treatment and Test No. 5 with a small Sn content, the corrosion amount was 0.37 mm or more, and the corrosion proceeded. On the other hand, in the test number 6 having a large Sn content, Sn oxide was deposited on the surface of the steel material after the surface treatment.

  Moreover, as shown in Table 2 and Table 3, the rust produced | generated to the test material by the chloride and the wet and dry repetition test was quantitatively analyzed by said X-ray-diffraction measuring method, and ratio (alpha) -FeOOH and (beta) -FeOOH produced | generated ( Hereinafter, “α / β ratio”) was obtained.

  In Test Nos. 1 to 3, the α / β ratio was relatively high at 0.61 to 1.30, the production of β-FeOOH was suppressed, and α-FeOOH was produced.

  In Test No. 4 with no ground treatment and Test No. 5 with a small Sn content, the α / β ratio was as low as 0.35 and 0.39, respectively, and a large amount of β-FeOOH was produced. For test No. 6, the chloride / wet repeat test was not performed as described above, so the α / β ratio was not determined.

2. Surface-treated steel material having organic resin film The aqueous solution containing various Sn ion sources shown in Tables 4 and 5 is adjusted to pH 2.12. Then, the Sn or Sn compound content was ironed so as to have the values shown in Tables 4 and 5 in terms of Sn metal. The content of Sn or Sn compound was changed by changing the aqueous solution concentration. As a guide, when stannous sulfate is used as the Sn ion source, the content is about 6 to 7 mg / m ^{2 in} a 0.1% strength aqueous solution. After the application, it was dried by natural drying to form a Sn-containing rust layer. Here, as the Sn ion supply source, Sn ²⁺ used SnSO ₄ or SnCl ₂ , and Sn ⁴⁺ used SnCl ₄ . In test numbers 16-18 and 24, both Sn ²⁺ and Sn ⁴⁺ Sn ions were included.

  Separately, instead of Sn, an aqueous chloride solution of Cu, Cr, or Ni was used, and ironing was performed so that the values shown in Table 6 were obtained in terms of metal. In addition, about these test materials, it was able to confirm visually that a rust layer will be formed on the steel material surface if it is left to stand after ironing.

  For test numbers 7 to 27 in Tables 4 to 6, the entire surface of the steel material was coated with an epoxy paint (Neo Gosei # 2300: manufactured by Shinto Paint) by air spray so that the dry film thickness of the epoxy resin was 200 μm. It was applied, the solvent was evaporated and the resin film was dried to form a coating resin layer.

Next, an organic resin film (butyral resin or epoxy resin) containing an inorganic salt of Sn (Sn ion supply source) shown in Table 7 and Table 8 on the surface of the steel material in which the surface roughness Rzjis is changed, is displayed. As shown in Table 7 and Table 8, it was applied by air spray so as to have various dry film thicknesses, and the solvent was evaporated to dry the resin film. As an indication of the film thickness to be formed, when 2.0 mass% of stannous sulfate is added to the butyral resin coating film manufactured by Shinto Paint Co., Ltd. and the dry film thickness is 200 μm, The adhesion amount of Sn formed at the interface is about 2.0 to 3.0 mg / m ² . Here, SnSO ₄ or SnCl ₂ was used as Sn ²⁺ and SnCl ₄ was used as Sn ⁴⁺ as a source of Sn ions eluted into the resin film. In test number 33, both SnSO ₄ and SnCl ₄ were included in the organic resin film in order to elute both Sn ²⁺ and Sn ⁴⁺ Sn ions.

  In addition, for test numbers 28, 29 and 31 in Table 7 and test numbers 35 and 37 in Table 8, an epoxy paint (Neo Gosei # 2300: manufactured by Shinto Paint) was further sprayed by air spray with a dry film thickness of the epoxy resin. The entire surface was applied onto an organic resin film containing an inorganic salt of Sn so as to have a thickness of 100 μm or 200 μm, and the solvent was evaporated to dry the resin film to form a coating resin layer.

  A test material coated with an organic resin film containing an inorganic salt of Sn thus prepared, or a test material further coated with an organic resin film via an organic resin film containing an inorganic salt of Sn After making a crosscut at a depth that reached the substrate, it was evaluated by a chloride / wet repeat test. Chloride / wet repeat test: salt adhesion: 0.01 mol / L NaCl was dropped to form a 500 μm liquid film on the steel surface, dried (40 ° C., 40% RH, 4 hours) and wet (40 ° C., 100% RH, 4 hours) This is a test in which 3 cycles per day are carried out, and salt is deposited every other week. The salinity adhering to the steel material surface for a test period of 3 months is 2.2 mdd.

  After conducting a chloride / dry moisture repeated test for 3 months, the film peeling corrosion part after the test was peeled off and photographed with a digital camera, and then the photograph was binarized to calculate the peeled area ratio. The test results are shown in Tables 4-8.

  In addition, the resin-coated specimen prepared by the above method was evaluated by a cooling and heating cycle test after putting a flaw having a length of 1 cm in length to reach the steel substrate. The cold cycle test is a test in which one cycle is a high temperature (50 ° C., humidity 95% RH, 8 hours) and a low temperature (−30 ° C., 8 hours).

  After carrying out 20 cycles of the cooling and heating cycle test, the same method for calculating the peeled area ratio was used as in the chloride / dry cycle test.

Moreover, the rust layer produced | generated on each test material after the chloride wet and dry repetition test was extract | collected with the cutter knife. The collected rust sample was dried in a desiccator for more than one week, and then quantitative analysis of rust constituent compounds was performed by powder X-ray diffraction method using ZnO powder (made by Wako Pure Chemical, particle size of about 5 μm) as an internal standard substance. . The sample for powder X-ray diffraction was mixed with ZnO at a constant weight ratio (30% in this example) with respect to the rust weight collected in advance, and mixed with an agate mortar so that rust and ZnO were uniformly dispersed. X-ray diffraction measurement was performed using a RU200 model manufactured by Rigaku Corporation, with a Co target and a voltage-current of 30 kV-100 mA, and a scanning speed of 2 ° / min. Α-FeOOH, γ-FeOOH (manufactured by Rare Metallic), Fe _{3 -δ} O ₄ (manufactured by High-Purity Chemical), and β-FeOOH synthesized by hydrolyzing an aqueous FeCl ₃ solution at 100 ° C. A quantitative analysis was performed from the intensity of the obtained X-ray diffraction pattern using the calibration curve prepared. The amounts (mass%) of β-FeOOH and α-FeOOH in the rust thus determined were compared.

  Tables 4 to 6 show the results of the test materials in which the steel surface was treated with an aqueous solution.

  As shown in Table 4, in the test materials of test numbers 7 to 18 according to the present invention, peeling from the scratched part (cross-cut part) was suppressed in the chloride / wet repeated test, and the peeling area ratio was 25 to 25. The value was 42%, and in the thermal cycle test, peeling from the scratch portion was suppressed, and the peel area ratio was 15 to 30%.

  As shown in Table 5, in the absence of the ground treatment as in test number 19, peeling progressed remarkably in both the chloride / dry cycle test and the thermal cycle test. In Test Nos. 20 and 22 having a small Sn content, peeling progressed remarkably in both the chloride / dry moisture test and the thermal cycle test, as in the case of no surface treatment (Test No. 19). On the other hand, as shown in Test Nos. 21, 23 and 24, if the Sn content is too much, the resin film peeling in the chloride / wet repeat test can be suppressed, but the resin film peeling in the thermal cycle test can be suppressed. Became larger.

  As shown in Table 6, when using an aqueous chloride solution other than Sn (test numbers 25 to 27), compared to test numbers 7 to 18 according to the present invention, a chloride / wet and humidity repeat test, a cooling and cycling test The resin film peeling at is slightly higher. However, as will be described later, these test materials cannot obtain sufficient α-FeOOH and do not have good corrosion resistance.

  In addition, as shown in Tables 4 to 6, rust produced in the resin film scratch portion of the test material in the chloride / wet repeat test was quantitatively analyzed by the above X-ray diffraction measurement method, and the produced α-FeOOH and β The ratio of -FeOOH (hereinafter referred to as “α / β ratio”) was determined.

  In test numbers 7 to 18, the α / β ratio was relatively high at 0.61 to 1.30, the production of β-FeOOH was suppressed, and α-FeOOH was produced. In Test No. 19 having no base treatment, the α / β ratio was as low as 0.37, and a large amount of β-FeOOH was produced. Considering the relationship between the Sn content and the α / β ratio in these test numbers 7 to 18 and test numbers 19 to 24, the α / β ratio tends to increase as the Sn adhesion amount increases. It can be seen that the formation of -FeOOH depends largely on the Sn content.

  Tables 7 and 8 show the results of test materials obtained by applying a resin film treatment (paint coating) to the steel material surface.

  As shown in Table 7, in test numbers 28 to 33 according to the present invention, peeling from the scratched part (cross cut part) was suppressed in the chloride / wet repeated test, and the peel area ratio was 19 to 38%. Thus, in the thermal cycle test, peeling from the scratch portion was suppressed, and the peel area ratio was 19 to 30%.

  As shown in Table 8, in test number 34 where a paint containing no Sn was applied, and in test number 35 where the Sn adhesion amount was small even if Sn was contained, both the chloride / wet cycle test and the thermal cycle test were significantly peeled off. Progressed. In Test No. 36 having a large Sn content, peeling of the resin film in the chloride / wet repeat test could be suppressed, but peeling of the resin film in the cooling / heating cycle test increased. Furthermore, even in test number 37 where the surface roughness Rzjis of the steel material was small, the peeling progressed remarkably in both the chloride / wet repeat test and the cold cycle test. In these test numbers 34 to 37, the α / β ratio was as low as 0.35 to 0.45.

  The surface-treated steel material according to the present invention exhibits excellent corrosion resistance even in a concentrated chloride environment with a high chloride ion concentration, and is excellent in being able to remarkably suppress paint peeling even in an environment of a cold cycle caused by sunlight or temperature. Shows long-term durability. Therefore, when the present invention is applied to steel materials used for bridges, shipbuilding, and offshore structures, the paint repainting interval can be extended, and maintenance costs can be greatly reduced.

Claims (6)

It is a surface-treated steel material obtained by coating the surface of a steel material having a surface roughness Rzjis of 30 to 100 μm with a rust layer containing α-FeOOH, and Sn or Sn compound in the rust layer is converted to a metal Sn value of 0.00. A surface-treated steel material characterized by being contained in a range of 05 mg / m ² or more and less than 15.0 mg / m ² .   The surface-treated steel material according to claim 1, wherein an organic resin film having a dry film thickness of 20 μm or more is coated on the rust layer.   2. The surface-treated steel material according to claim 1, wherein an organic resin film having a dry film thickness of 20 μm or more formed by containing Sn or a Sn compound is coated on the rust layer.   2. The surface-treated steel material according to claim 1, wherein an organic resin film having a dry film thickness of 20 μm or more is coated on the rust layer via an organic resin film containing Sn or a Sn compound.   The surface-treated steel material according to any one of claims 1 to 4, which contains β-FeOOH in addition to α-FeOOH in the rust layer, and is an integrated value by X-ray diffraction of α-FeOOH in the rust layer. A surface-treated steel material in which the ratio of the integral value (α / β ratio) by X-ray diffraction of β-FeOOH is 0.6 or more. The rust layer is formed by applying an acidic aqueous solution having a pH of 3.0 or less containing one or both of Sn ²⁺ ions and Sn ⁴⁺ ions to the surface of the steel material. The surface-treated steel material according to any one of 5 to 5.

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