JP4687231B2 - Structural steel and surface treatment agent with excellent beach weather resistance - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention can suppress the corrosion of steel materials in a highly corrosive environment such as a high-flying chloride environment, such as an atmospheric corrosion, particularly a coastal area where salinity flies and a region where anti-freezing agents such as rock salt are sprayed. The present invention relates to a steel material surface treatment agent and a structural steel material surface-treated with the surface treatment agent.

  The surface treatment agent of the present invention is weather resistant in the sense that it can be used as a minimum maintenance material even in a high-flying chloride environment with a large amount of incoming salt, such as a beach area or an area where snow melting salt / freezing agent is sprayed. (Seaside weather resistance) can be imparted to steel materials, particularly structural steel materials.

  In general, when weathering steel is exposed to an atmospheric corrosive environment, a protective rust layer is formed on the surface, and the subsequent corrosion of steel is suppressed, thereby exhibiting weather resistance. Therefore, the weather-resistant steel is used for structures such as bridges as a minimum maintenance steel that can be used as it is without being painted.

  However, in environments where there is a large amount of incoming salt (that is, under high-flying chloride environments), such as beach areas and areas where snow melting salt is scattered even in the inland areas, the surface of the weathering steel is protected. The layer is not formed, and the effect of suppressing corrosion is not exhibited. For this reason, it was not possible to use a weather-resistant steel material that has not been painted on the beach.

Also in the standard of weather resistant steel (JIS G3114: weather resistant hot rolled steel for welded structure) of Japanese Industrial Standard (JIS), the amount of incoming salt is 0.05 mg / dm ² / day (0.05 mdd) or more as NaCl. In areas such as beach areas and areas where snowmelt salt / freezing agents are sprayed (hereinafter collectively referred to as beach areas), 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・ Guidelines for construction (revised version-1993.3)).

  For this reason, in the beach area, it is common to use ordinary steel that is coated with ordinary steel. However, in bridges constructed in the coastal area near the river mouth and roads such as mountainous areas where snow melt is salted, the corrosion is significant and the coating film deteriorates due to corrosion, so it is necessary to repaint every 10 years. Since repainting takes a lot of man-hours and enormous costs for maintenance, there is a strong demand for steel materials with excellent beach weather resistance that can be used without painting even in the beach area.

  Recently, a Ni-based high weathering steel added with about 1 to 3% of Ni has been developed and put into practical use. For example, see Patent Document 1 below. However, it has been proved that application of Ni alone to such steel is difficult in an area where a high salinity chloride environment in which the salinity content exceeds 0.3 to 0.4 mdd.

  Since corrosion of steel materials becomes more severe as the amount of flying salt increases, a weather-resistant steel material corresponding to the amount of flying salt is required from the viewpoint of corrosion resistance and economy. Moreover, even if it is called a bridge, the corrosive environment of steel materials is not the same by the place and site | part used. For example, outside the girders, they are exposed to rainfall, condensed water and sunlight. On the other hand, inside the girders, they are exposed to condensed water, but there is no rain. In general, in an environment with a large amount of incoming salt, it is said that corrosion is more severe inside the girders than outside the girders that are washed with rain.

  In addition, in an environment where snow melting salt is sprinkled on the road, the salt is wound up on a running car and adheres to the bridge supporting the road, creating a severe corrosive environment. Furthermore, the eaves under the eaves a little away from the coast are also exposed to severe salt damage environments, and in such areas, the amount of incoming salt becomes a severe corrosive environment with 1 mdd or more.

  Steel materials that prevent corrosion in environments with a high amount of incoming salt have also been developed. For example, Patent Document 2 discloses a method for growing stable rust at an early stage by coating an organic resin paint containing 1 to 65% by mass of chromium sulfate or copper sulfate. In Patent Document 3, an organic resin coating film having a dry film thickness of 5 to 50 μm containing 0.1 to 15% by mass of chromium sulfate in the lower layer is formed, and a dry film thickness of 5 to 20 μm not containing chromium sulfate in the upper layer. A treatment method for forming an organic resin coating film is disclosed. Both of these methods have been demonstrated to facilitate the formation of a protective rust layer and to exhibit high corrosion resistance at an early stage, so that weatherability can be significantly improved.

Patent Document 4 discloses a weather-resistant steel material in which a film having a dry film thickness of 5 μm or more and 150 μm or less is formed on the surface of a steel material or a rust layer of the steel material with an organic resin paint containing 1 to 65% by mass of aluminum sulfate in a dry mass. It is disclosed. Prior to the formation of the coating film, a ground treatment may be performed in which an aqueous solution containing Al and optionally one or more metal ions of Cu, Fe, P, Cr, and Ni is applied and dried.
JP-A-11-172370 JP-A-6-226198 JP 2001-81575 A JP-A-8-13158

  The present invention aims to solve the problems of conventional weathering steel and the like, and is in an environment with a large amount of incoming salt (especially exceeding 1 mdd) such as a beach area or an area where snowmelt salt is sprayed. Surface treatment agent that can give steel materials excellent weather resistance even in the environment of high-flying chlorides that are severely corrosive) and in tanks that store crude oil, and for applications such as civil engineering, construction, and oil tanks An object of the present invention is to provide a low-cost structural steel material excellent in weather resistance that can be applied to the above.

As already reported by one of the present inventors ("Materials and the Environment", Vol. 43 (1994), No. 1, page 26), the rust layer has a protective property in weathering steel. This is because a rust layer composed of fine α- (Fe _1-X Cr _x ) OOH in which part is replaced with Cr is formed. 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 mmd or more, Conversely, it has been found that the weather resistance deteriorates. On the other hand, it has been considered that the addition of Ni is effective for improving the weather resistance in an area where the amount of incoming salt is large.

Based on these findings, the present inventors examined corrosion in an environment with a large amount of incoming salt. As a result, in such an environment, the FeCl ₃ solution was repeatedly dried and wet (this solution was dried and redissolved with water). of repetition) is an essential condition, while pH is lowered by hydrolysis of Fe ^3+, and by the Fe ³⁺ acts as an oxidizing agent, it has been found that the corrosion is accelerated. 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, for the above reduction reaction, anode reaction: Fe → Fe ²⁺ + 2e ⁻ (Fe dissolution reaction)
Also happens. Therefore, the overall reaction of corrosion is
2Fe ³⁺ + Fe → 3Fe ²⁺ ... Reaction 1
It becomes.

The Fe ²⁺ generated by the reaction 1 is oxidized to Fe ³⁺ by air oxidation, and the generated Fe ³⁺ again accelerates corrosion as an oxidant. 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 solution, and Fe ³⁺ is easily generated. It was found that due to such a cyclic reaction, in an environment where the amount of incoming salt is very large, Fe ³⁺ is constantly supplied, the corrosion of steel is accelerated, and the corrosion resistance is significantly deteriorated.

  In this way, in an environment where the amount of incoming salt is very large, protection by the rust layer cannot be expected, so it is effective to slow the anodic dissolution reaction of the steel itself. That is, in an environment where the amount of flying salt is very large, the steel containing Cr accelerates the anode reaction (Fe dissolution reaction), so the weather resistance deteriorates, whereas the steel containing Ni does not react with the anode reaction. It is estimated that the weather resistance is improved.

  As a result of examining the influence of various alloying elements on the weather resistance based on the above-mentioned corrosion mechanism in an environment with a large amount of incoming salt, it was found that Sn is effective in suppressing corrosion of steel by the above mechanism. Completed the invention.

  In one aspect, the present invention includes a binder resin and an acid-soluble Sn ion source material in an amount of 1 to 54% by mass in terms of metal Sn based on the total solid content of the surface treatment agent. It is a surface treatment agent for imparting weather resistance to structural steel materials.

  From another aspect, the present invention provides an acid-soluble Sn ion supply in an amount of 1 to 54% by mass in terms of metal Sn in a binder resin on the surface of a structural steel material or on a rust layer formed on the steel material. A weatherable structural steel material having a surface treatment layer having a thickness of 5 to 50 μm containing a source material. The structural steel material may further have an organic resin layer having a dry film thickness of 10 μm or more and less than 100 μm on the surface treatment layer.

The surface treatment agent and the surface treatment layer supply at least one additional acid-soluble metal ion serving as a source of Cu ²⁺ ions, Ni ²⁺ ions or Cr ³⁺ ions in addition to the Sn ion source material. It may further contain a source material. In this case, the total amount of the metal ion source material and the Sn ion source material in terms of metal is set to 65% by mass or less.

“Acid-soluble Sn ion source material” means a material that can be dissolved in an acidic solution to supply one or both of Sn ²⁺ ions and Sn ⁴⁺ ions. Such Sn ion source materials specifically include divalent Sn compounds, tetravalent Sn compounds, and metal Sn. As will be described below, in an acidic solution containing iron ions generated by contact of water with steel in a chloride environment, reactions in both directions of Sn⇔Sn ²⁺ ions⇔Sn ⁴⁺ ions can occur.

The inhibitory effect of Sn on the corrosion of steel materials in a high flying chloride environment is considered to be due to the following mechanism.
(a) When Sn is dissolved as Sn ²⁺ , the concentration of Fe ³⁺ is decreased by a reaction of 2Fe ³⁺ + Sn ²⁺ → 2Fe ²⁺ + Sn ⁴⁺ , thereby suppressing the reaction 1 described above. Sn also has an effect of suppressing anodic dissolution.

(b) Of the Sn dissolved as Sn ²⁺ , the excess not receiving the reaction described in (a) above is deposited as metal Sn on the steel material surface.
(c) The precipitated Sn significantly suppresses the reaction of 2H ⁺ + 2e ⁻ → H ₂ , which is a counter reaction (cathode reaction) of the steel elution reaction (anode reaction). This is thought to be due to high hydrogen overvoltage.

(d) Since precipitation of Sn concentrates on the elution part of steel, the eluted Sn ^<2+ > precipitates as Sn efficiently only in the corroded part.
(e) Once the deposited Sn is corroded directly under or near the deposited portion, it re-elutes as Sn ^{2+ and} precipitates as Sn only on the corroded portion, thereby suppressing the corrosion. To do.

(f) Sn ⁴⁺ also becomes Sn ^{2+ in the} vicinity of the steel surface due to the reaction of Sn ⁴⁺ + 2e ⁻ → Sn ²⁺ , and thus has the effects (c) to (e).
Therefore, if a Sn ion source material that is a source of Sn ²⁺ ions and / or Sn ⁴⁺ ions is contained in the steel surface treatment layer, corrosion of the steel material can be suppressed repeatedly without being depleted, The effect is exhibited semi-permanently.

  The weather-resistant steel material of the present invention can maintain corrosion resistance for a long time even in a highly corrosive high-flying chloride environment in which a large amount of chlorides fly. In particular, when the present invention is applied as a steel material for civil engineering or building structures or oil tanks constructed in a beach area, the maintenance cost related to the corrosion prevention of the steel material is remarkably reduced, so the economic effect of the present invention is high.

As described above, in the concentrated chloride environment where thickening of Cl, wet and dry repetition of FeCl ₃ solution is an essential condition, while pH is lowered by hydrolysis of Fe ^3+, and Fe ³⁺ oxidation By acting as an agent, corrosion is accelerated. That is, when water contacts the steel material interface, Fe as a base material is eluted to produce Fe ²⁺ , and a part thereof is oxidized to Fe ³⁺ . If chloride ions are present there, hydrolysis is accelerated and the pH is significantly reduced.

According to the present invention, when the surface treatment layer contains a Sn ion source material capable of supplying Sn ²⁺ ions and / or Sn ⁴⁺ ions, the surface treatment is performed when moisture reaches the steel surface through the surface treatment layer. Sn ²⁺ ions and / or Sn ⁴⁺ ions are generated from the Sn ion source material in the layer, and are preferentially deposited as Sn on the surface of the corroded portion. On the deposited Sn, the hydrogen reduction reaction (cathode reaction) is remarkably suppressed, and corrosion is suppressed. Furthermore, some of the Sn ²⁺ ions react with the Fe ³⁺ ions reduces the concentration of Fe ³⁺ ions, suppressing the reaction 1.

  In order to acquire the said effect by Sn, the quantity of Sn ion supply source material in a surface treatment layer must be 1 mass% or more in Sn metal conversion amount. On the other hand, if this amount exceeds 54% by mass, the amount of the binder resin that binds the Sn ion source material is insufficient, the surface treatment layer becomes brittle, and through-holes reaching the steel surface from the surface treatment layer surface are formed. This causes flow rust. Therefore, the amount of Sn ion source material is in the range of 1 to 54% by mass in terms of Sn metal. A preferred range for this amount is 2-40% by weight.

When the Sn ion source material is an Sn compound, the Sn metal equivalent mass can be calculated according to the following formula:
(Addition amount of Sn compound) × [(Sn atomic weight) / (Molecular weight of Sn compound)].

The Sn ion source material used is an Sn compound that dissolves and ionizes in a low pH region to generate Sn ²⁺ ions or Sn ⁴⁺ ions, that is, acid-soluble divalent and tetravalent Sn compounds, and metal Sn. At least one selected from the above may be used. A divalent Sn compound is preferable. The divalent Sn compound decreases the Fe ³⁺ concentration directly by the reaction of 2Fe ³⁺ + Sn ²⁺ → 2Fe ²⁺ + Sn ⁴⁺ without going through the reaction of Sn ⁴⁺ + 2e ⁻ → Sn ²⁺ . This is because the reaction 1 can be suppressed. Specific examples of the divalent Sn compound include tin (II) sulfate, tin (II) oxide, and tin (II) pyrophosphate. Halides such as tin (II) chloride are acid-soluble, but are not preferred because they are sources of corrosive chloride ions or other halogen ions. Among them, tin (II) oxide is difficult to dissolve in the neutral region and dissolves in the low pH region, so it dissolves only in the chloride-concentrated portion and exerts its effect and is used in the present invention. Particularly preferred Sn ion source material.

In addition to the Sn ion source material, the surface treatment agent includes a metal ion source material that serves as a source of metal cations, such as Cu ²⁺ ions, Ni ²⁺ ions, Cr ³⁺ ions, and the like, which has a weather resistance improving effect. It is possible to coexist and is preferable. An acid-soluble metal compound (or metal) is also used for the metal ion source material. Specific examples of such a metal compound include Cu (NO ₃ ) ₂ , CuSO ₄ , Ni (NO ₃ ) ₂ , NiSO ₄ , Cr (NO ₃ ) ₃ , Cr ₂ (SO ₄ ) _{3 and the} like.

  These additional metal ion source materials can be used alone or in combination of two or more in order to further improve the weather resistance, and the total amount added in terms of metal is the total solid content of the surface treatment agent. The amount is preferably in the range of 1 to 20% by mass based on the minute. In this case, if the total amount of the additional metal ion source material and the Sn ion source material is too large, the amount of the binder resin is insufficient and the strength of the surface treatment layer is insufficient. It is preferable to be 65% by mass or less in terms of metal based on the total solid content.

  The surface treatment agent may further contain a pigment and various additives in addition to the Sn ion source material, the above-described additional metal ion source material which can be optionally added, and the binder resin. The solvent for the surface treatment agent can be either water or an organic solvent, and one or more solvents can be used. The resin may be dissolved in a solvent or may be in an emulsion state.

  The binder resin is not particularly limited, and various organic resins used for paints can be used. Specific examples include epoxy resin, urethane resin, vinyl resin, polyester resin, acrylic resin, alkyd resin, phthalic acid resin, butyral resin, melamine resin, phenol resin, and the like. These may be in the state of either a solution or an emulsion. If necessary, a curing agent is added to the binder resin. In particular, a butyral resin alone or a mixture of a butyral resin and another resin compatible with the butyral resin (for example, melamine resin or phenol resin) is preferable from the viewpoint of moisture permeability of the formed film. An inorganic resin that can form a metal oxide type film such as ethyl silicate resin can also be used as the binder resin.

  The amount of the binder resin as a solid content is preferably at least 25% by mass, more preferably at least 30% by mass based on the total solid content of the surface treatment agent from the viewpoint of ensuring the strength of the surface treatment layer. is there.

  In addition to the above components, the surface treatment agent includes colored pigments such as bengara, titanium dioxide, carbon black, phthalocyanine blue, α-FeOOH, and iron oxide; and extender pigments such as talc, silica, mica, barium sulfate, and calcium carbonate. One or more of each can be added.

  Further, as a known anti-rust pigment, an anti-corrosion pigment such as chromium oxide, zinc chromate, lead chromate, basic lead sulfate and the like, further chromium compounds such as chromium sulfate, and nickel compounds such as nickel sulfate are included. It is not excluded. However, considering the environmental load, the amount of these compounds added (total amount in the case of two or more) is desirably 20% by mass or less based on the total solid content of the surface treatment agent.

In addition, conventional additives such as thixotropic agents, dispersants, antioxidants, etc. may be added. Moreover, it is also possible to contain phosphoric acid, which is effective for preventing the initial flow rust outflow.
The concentration of the surface treatment agent may be adjusted by diluting with a suitable solvent so that the viscosity of the surface treatment agent is suitable for the coating operation. The coating on the steel surface can be performed according to a conventional method. For example, in the case of an existing structure, an air spray method, an airless spray method, a brush coating method, or the like is appropriate. When painting at the factory, other coating methods such as roll coating and dipping can be employed.

  Since the solvent is preferably evaporated by natural drying after coating, it is preferable to select such a solvent. The coating is performed so that a surface treatment layer having a thickness of 5 to 50 μm is formed after drying. When the thickness of the surface treatment layer is in the range of 5 to 50 μm, Sn ions are appropriately supplied to the surface of the steel material even in a high-flying chloride environment, and the weather resistance of the steel material is improved. The thickness of the surface treatment layer is preferably in the range of 20 to 50 μm.

On top of the Sn-containing layer containing Sn ²⁺ ions and / or Sn ⁴⁺ ions that supply Sn ²⁺ ions thus formed, the organic resin layer has a dry film thickness of 10 μm or more and less than 100 μm as an upper layer. It can be formed, and is suitable when the initial appearance is important. A preferable thickness of the upper organic resin layer is 10 to 50 μm in terms of a dry film thickness.

  The upper organic resin layer is not particularly limited. For example, an epoxy resin, a urethane resin, a vinyl resin, a polyester resin, an acrylic resin, an alkyd resin, a phthalic resin, a butyral resin, a melamine resin, a phenol resin, or the like is used as the organic resin layer. Can be used for forming. Also, coloring pigments such as bengara, titanium dioxide, carbon black, phthalocyanine blue, α-FeOOH, and iron oxide; and one or more extender pigments such as talc, silica, mica, barium sulfate, and calcium carbonate are added. be able to.

  Furthermore, it does not exclude the inclusion of rust preventive pigments such as chromium oxide, zinc chromate, lead chromate and basic lead sulfate as known rust preventive pigments in the organic resin layer. However, considering the environmental load, the addition amount is preferably 20% by mass or less of the organic resin layer. In addition, additives commonly used in paints such as thixotropic agents, dispersants, antioxidants and the like may be included in the organic resin layer. When the organic resin layer contains one or more kinds of pigments and other solid particles as described above, the total amount of the solid particles is preferably 30% by mass or less in order to ensure the film strength.

  The organic resin layer may be diluted with an organic solvent as necessary so that the viscosity becomes suitable for the coating work before coating, after adding optional components to the organic resin liquid (which may be a solution or an emulsion) as desired. Can be adjusted and used for painting. Painting can be performed according to a conventional method, and in the case of an existing structure, methods such as air spray, airless spray, and brush coating are suitable. When painting at a factory, other methods such as roll coating and dipping can be employed. Thereafter, the solvent is evaporated to form an organic resin layer. About the solvent to be used, it is the same as that of the surface treating agent.

  The structural steel material on which the surface treatment layer of the present invention is formed is not particularly limited in the steel type. Although ordinary steel may be used, it is advantageous from the viewpoint of long-term durability if it is a weather resistant steel or a low alloy steel containing Ni, Al, Sn or the like. The form of the steel material is not particularly limited, and may be any form including a plate, a rod, a shaped steel, a pipe, a cast product, and the like. Here, the structural steel material means a steel material that can be used for civil engineering and architectural purposes. Further, since it can sufficiently withstand use in a crude oil tank environment, it can also be applied to an oil tank. As described above, the structural steel material may be an existing steel structure.

  When applying to existing structural steel materials such as existing bridges and buildings, the surface treatment agent of the present invention may be coated on the rust layer generated on the surface of the steel material, or the rust layer is shot. You may paint after removing by suitable methods, such as blasting. The same applies to the case where rust has already occurred in the steel material when painting at the factory.

  In addition, as steel materials surface-treated with Sn, there are the following steel materials in the prior art, but these are not related to structural steel materials, and the purpose of the surface treatment is not imparting weather resistance, so the present invention and Have different technical ideas.

  (1) As antifouling paints for ship hulls and fish nets, paints containing organotin compounds, that is, tin compounds such as TBT (tributyltin) and TPT (triphenyltin) have been used. However, since this is added for the purpose of antifouling due to adhesion of shellfish or the like, the technical idea is different from the present invention.

(2) Although there is surface treatment by Sn plating performed on the inner surface of canned foods, the steel material is not a structural steel material, and the purpose of the surface treatment is also different.
(3) As a surface treatment of electrical steel sheets used for generators, transformers, motors, etc., it is known to form a coating of Sn-treated surface treatment agent on steel, but the steel is not structural. Further, the purpose of the surface treatment is to prevent nitriding of the steel material from the atmosphere during annealing to prevent deterioration of magnetic characteristics, and the technical idea is different from the present invention.

  Four types of test steel materials (all 100 × 60 × 3 mm thick plate materials) having the chemical composition shown in Table 1 were removed by shot blasting and used for coating. The steel materials (A) in Table 1 are so-called weather resistant steels (JIS 3114, SMA), (B) is ordinary steel, (C) is high Ni weather resistant steel, and (D) is Sn-added corrosion resistant steel.

  In the types and blending ratios shown in Table 2, resin, Sn ion source material (Sn added species), other metal ion source material coexisting in some cases (coexisting cation species), pigment [barium sulfate / talc (by mass ratio) 4/1) Mixture and iron oxide (Bengara)], and other additives (thixotropic agent, anti-settling agent) are added with an appropriate amount of solvent so that the viscosity (B-type viscometer measurement) is 200 to 1000 cps, By thoroughly stirring, a surface treatment agent was prepared. Content (mass%) of each component in a table | surface is the mass% based on the total solid of the surface treating agent except the solvent.

As the coexisting cation source materials, Cu ²⁺ ions were copper sulfate (II), Ni ²⁺ ions were nickel nitrate (II), and Cr ³⁺ ions were chromium (III) nitrate. As the solvent, a mixed solvent in which toluene and xylene as aromatic hydrocarbon solvents and isopropyl alcohol as an alcohol solvent were mixed at a volume ratio of 2/1 was used.

  When forming the resin layer in the upper layer, the same resin as that used for the surface treatment agent was used. The upper resin layer consisted essentially of a resin and contained no metal compound, pigment, or other additives.

  The prepared surface treatment agent is applied to the entire surface of the specified test steel by air spray so that it has a predetermined dry thickness, and the coating is dried by allowing the solvent to evaporate to form a surface treatment layer on the surface of the test steel. did. Some test materials were directly coated with an organic resin coating.

The specimens thus prepared were exposed for 12 months to the horizontal position under the eaves (the environment where there was no rain and salt accumulated) on the factory roof in Amagasaki City, Hyogo Prefecture. In the meantime, once a week, artificial seawater diluted three times was suspended on the surface using a syringe. The salt accumulation amount in this environment is equivalent to 10 mmd (mg-NaCl / dm ² / day). The steel material weight before painting was measured. On the other hand, the steel weight after exposure for 3, 6, 12 months was measured after removing the film and rust with an ammonium citrate solution. From the corrosion weight loss determined from the weight difference before and after coating, the average plate thickness corrosion weight loss thickness during each exposure period was determined. The results are also shown in Table 2.

  In Test Nos. 1 to 12 according to the present invention, corrosion is remarkably suppressed even in an environment where a large amount of chloride is present, and it is confirmed that the corrosion weight loss is 100 μm or less even after 12 months and is highly corrosion resistant. It was. On the other hand, as seen in Test No. 13, with the bare steel material, even the weather resistant steel was corroded remarkably, resulting in delamination rust. As shown in Test Nos. 14 and 15, when the addition amount of the Sn ion source material is zero or too small, the corrosion resistance can be maintained by the environmental barrier effect of the coating film at the initial stage, but it corrodes significantly from the middle of the exposure, and after 12 months. Then, like bare steel, it became layered peeling rust. Further, as shown in Test No. 16, when the film thickness was thin, the effect of adding Sn was not sufficiently obtained. As in test number 17, when the content of Sn ion source material in the coating exceeds 60% by mass in terms of metal, there is almost no adhesion of the resin coating immediately after coating, and the coating peeled off at the beginning of exposure. The exposure test was discontinued

Claims (5)

  A structural steel material characterized by containing a binder resin and an acid-soluble Sn ion source material in an amount of 1 to 54% by mass in terms of metal Sn based on the total solid content of the surface treatment agent. Surface treatment agent for imparting And further comprising at least one additional acid-soluble metal ion source material that provides Cu ²⁺ ions, Ni ²⁺ ions, or Cr ³⁺ ions, the metal ion source material and the Sn ion source material; The surface treatment agent according to claim 1, wherein the total amount in terms of metal is 65% by mass or less based on the total solid content of the surface treatment agent.   On the surface of the structural steel material or on the rust layer formed on the steel material, the binder resin contains an acid-soluble Sn ion source material in an amount of 1 to 54% by mass in terms of metal Sn, and has a film thickness of 5 A weatherable structural steel material having a surface treatment layer of 50 μm. The surface treatment layer further includes at least one additional acid-soluble metal ion source material that serves as a source of Cu ²⁺ ions, Ni ²⁺ ions, or Cr ³⁺ ions, The structural steel material according to claim 3, wherein the total amount in terms of metal with the Sn ion source material is 65 mass% or less. The weatherable structural steel material according to claim 3 or 4, further comprising an organic resin layer having a dry film thickness of 10 µm or more and less than 100 µm on the surface treatment layer.