JP2012136751A - Surface treatment liquid for steel material, and surface treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical conversion treatment liquid free from generation of sludge.SOLUTION: A surface treatment liquid for steel materials contains an oxalic acid and a trivalent iron ion, and is an acid aqueous solution with an oxidation-reduction potential of 100-500 mV.

Description

  The present invention relates to a surface treatment liquid and a surface treatment method for steel materials, and more particularly, to a surface treatment liquid and a surface treatment method for chemical forming that exhibit excellent performance as a base film of a lubricant for cold forging.

  Conventionally, as a lubricating film for cold forging on steel materials, a composite film in which a zinc phosphate film as a lubricating base film on a material and a metal soap film and a sodium soap film as a lubricating film are laminated on the material has been widely used. This film is formed by applying soap treatment after zinc phosphate treatment.

  Zinc phosphate treatment has long been widely used as a lubricating base treatment for cold forging of steel materials. However, a considerable amount of sludge is generated at the time of processing, and the generated sludge is difficult to reuse, so it is almost always landfilled as industrial waste. In recent years, the increase in industrial waste treatment costs, that is, sludge disposal costs in this case, has pushed up the overall cost of zinc phosphate conversion treatment, which is strongly desired not only for environmental reasons but also for economic reasons. ing.

  Further, when zinc phosphate treatment is used as a cold forging lubrication base treatment, it may not always produce a beneficial result for the subsequent manufacturing process and quality. For example, the problem of phosphorus immersion, which is a concern with high-strength bolts, is said to be caused by brittle fracture due to the phosphorus in the zinc phosphate coating entering the steel during heat treatment. Furthermore, the appearance of the steel material after heat treatment may be poor, or in vacuum heat treatment or the like, the piping that draws a vacuum may be clogged with phosphate coating carbides, which may reduce the degree of vacuum.

  On the other hand, oxalate treatment is known as a lubricating ground treatment other than zinc phosphate treatment. Oxalic acid, which is the main component of the oxalate treatment solution, has a function of inhibiting the formation of a stainless passive film, and can be treated not only on steel materials but also on stainless steel materials. However, since the conventional oxalate film has insufficient adhesion to the material, the lubricating performance is inferior to that of the zinc phosphate film. Therefore, the cases used for steel materials are rare, and the usage is almost limited to stainless steels to which the zinc phosphate treatment is difficult to apply.

  In addition, the reaction mechanism of the conventional oxalate treatment with respect to steel materials is as follows. When a steel material is immersed in an aqueous oxalic acid solution, divalent iron ions eluted from the substrate by etching and oxalic acid in the treatment liquid become insoluble ferrous oxalate and precipitate on the material. Therefore, when etching is insufficient, film deposition is also insufficient. Usually, in order to obtain a sufficient coating amount, it is necessary to set the pH to around 1.0 or less and to treat at a high temperature of about 80 ° C. for 5 minutes or more. Further, in this case, not all of the divalent iron ions eluted by etching become a healthy film, but part of the film becomes brittle and the part forms sludge in the treatment liquid.

Although there are few recent development examples regarding the oxalate treatment technology and the description in the literature is limited, for example, Table 1.12 (p142) of the literature 1 shows H ₂ C ₂ O ₄ , as a component of the oxalate treatment solution. F, SO ₄ , Cl, stainless steel as the target metal, steel, FeC ₂ O ₄ , NiC ₂ O ₄ , Cr ₂ (C ₂ O ₄ ) ₃ as coating components, processing temperature: 65 to 95 ° C, processing time: 5 to There is a description of 20 minutes, treatment method: immersion, film weight: 5 to 20 g / m ² .

  There are also few patent documents related to oxalate treatment, and there are few inventions related to treatment solutions. In Patent Document 1 (Japanese Patent Laid-Open No. 6-220651), after performing a shot blast treatment with steel particles on the surface of a steel material, an oxalate film is formed without performing a pickling treatment, and then a lubrication treatment is performed. Although a high-corrosion-resistant metal material lubrication method characterized by this is described, this relates to a pretreatment of oxalate treatment, and is not an invention of an oxalate treatment solution itself.

Latest Surface Treatment Technology Overview Editorial Committee, Latest Surface Treatment Technology Overview, Industrial Technology Service Center Co., Ltd., p142 (1987)

JP-A-6-220651

  As described above, zinc phosphate treatment is a method for depositing a chemical conversion film with good adhesion to steel materials, but the generation of sludge cannot be avoided, and the film inevitably contains phosphorus. Therefore, it becomes a factor that causes a phosphorus immersion problem particularly during heat treatment after application as a lubricating base. On the other hand, in the oxalate treatment, although there is no concern about phosphorus immersion, the generation of sludge is still unavoidable and the adhesion of the deposited film is insufficient.

  That is, until now, there is no method for forming a chemical conversion film that does not contain phosphorus and has good adhesion without generation of sludge. An object of this invention is to provide the processing liquid and processing method which can solve these various subjects.

  The present inventor focuses on the solution to the above problem, specifically, the oxalate treatment that does not contain phosphorus in the coating, and the improvement of coating adhesion and the reduction of sludge generation in conventional oxalate treatment We studied diligently. As a result, a proper amount of a soluble trivalent iron compound as a reaction accelerator is added to the treatment solution, and trivalent iron ions are dissolved under an acidic and appropriate oxidation-reduction potential, so that the shoe has good adhesion. It was found that an iron oxide film can be deposited without generation of sludge. In addition, the trivalent iron ions in the treatment liquid are effective in lowering the treatment temperature and shortening the treatment time.

  The greatest discovery in the present invention is that trivalent iron ions are dissolved in the treatment liquid. Since ferric oxalate is soluble unlike ferrous oxalate, it is possible to dissolve a certain concentration of trivalent iron ions when added as a salt of trivalent iron ions. Trivalent iron ions themselves are oxidizing agents and promote the etching of steel materials. In addition, it receives electrons generated by etching the steel material and is reduced to divalent iron ions.

When processing a steel material, if 1 mol of iron is converted into divalent iron ions by etching, 2 mol of trivalent iron ions in the treatment liquid are converted into divalent iron ions by 2 mol of electrons generated along with this. Reduced. That is, 3 mol of divalent iron ions are generated on the iron material by 1 mol of etching.
Etching reaction of the iron material: Fe → Fe ²⁺ + 2e ^-
Reduction of trivalent iron ions in the processing solution: 2Fe ³⁺ + 2e ⁻ → 2Fe ²⁺
Total reaction: Fe + 2Fe ³⁺ → 3Fe ²⁺

  By this action, it has become possible to efficiently form a film with a minimum amount of etching even under mild processing solution conditions that have been difficult to form in the past, such as a relatively low processing temperature and a relatively short time. . And since a divalent iron ion concentrated layer having a high concentration and a thin layer is formed on the surface of the base metal, a uniform and dense iron oxalate film with good adhesion is formed.

  However, when divalent iron ions of a certain concentration or more exist while containing oxalic acid and trivalent iron ions, iron oxalate sludge in which oxalic acid and divalent iron ions are insoluble in the treatment liquid is formed. End up. More specifically, by continuously treating the steel material, divalent iron ions gradually accumulate in the treatment liquid, and the iron oxalate sludge forms at a stage where the allowable amount of divalent iron ions is exceeded. It occurs. In order to avoid this, it is necessary to keep the divalent iron ion concentration within an allowable range. As a method for realizing this, oxidation is an index derived from (trivalent iron ion concentration / divalent iron ion concentration). A method of appropriately adding a redox potential adjusting agent selected from oxidizing agents according to the treatment so as to keep the reduction potential within a certain range has been devised, and this method can be said to be another important discovery of the present invention.

  In addition, the total acidity (neutralization titration with phenolphthalein as an indicator), which has been applied as a method for controlling the concentration of oxalate treatment solutions, can measure the concentration of simple oxalic acid aqueous solutions. (Nitrate ion, sulfate ion, etc.) and cations (divalent iron ion, trivalent iron ion, etc.) are not suitable as a management method in the treatment liquid of the present invention in which a non-negligible concentration is mixed.

  Oxalic acid, which is the main component of the treatment liquid, needs to be measured not as total acidity but also as oxalic acid concentration. Since oxalic acid is a reducing agent, redox titration with an oxidizing agent is considered to be an effective means. However, divalent iron ions, which are another reducing agent, may be present in the treatment liquid of the present invention. In this case, the titration value in the oxidation-reduction titration is a value that takes into account the divalent iron ion concentration. However, in fact, it has been found that by adding the concentration of divalent iron ions rather than the concentration of oxalic acid alone, it becomes an index that can be more reflected in the actual chemical conversion properties. This index specifically indicates the permanganate ion consumption up to the end point when the permanganate is selected as the oxidizing agent, and this is one of the discoveries of the present invention.

The film deposited by the treatment liquid of the present invention is thin and dense and has good adhesion to the material. By applying and drying a lubricant on the film, it is extremely good as a base coating film for a plastic working lubricant film. The inventors have found that the present invention exhibits performance, and have completed the present invention.
That is, the present invention includes the following (1) to (8).

(1) An acidic aqueous solution containing oxalic acid and trivalent iron ions, the total iron ion concentration of the total of divalent iron ions and trivalent iron ions is 10 to 110 mmol / L, and the redox potential is 100 to 100 A surface treatment solution for steel materials characterized by 500 mV.
(2) When performing redox titration of the treatment liquid of (1) using permanganate, the permanganate titration amount at the end point is 0.02 to 0.15 mmol with respect to 1 mL of the treatment liquid. Surface treatment liquid for steel materials.
(3) The surface treatment liquid for steel materials according to (1) or (2), which is for a lubricating film for plastic working.
(4) When the iron oxalate film is deposited by the chemical conversion method by immersing the steel material in the surface treatment solution of any one of (1) to (3), a redox potential regulator according to the treatment load A surface treatment method for a steel material, characterized in that the oxidation-reduction potential is maintained at 100 to 500 mV by adding.
(5) The surface treatment method for a steel material according to (4), wherein one or more selected from hydrogen peroxide, organic peroxides, persulfates and nitrites are used as a redox potential regulator. .
(6) The steel according to (4) or (5), wherein the steel material is immersed in a surface treatment solution of any one of (1) to (3) whose temperature is adjusted to 20 to 70 ° C. for 1 to 10 minutes. Surface treatment method for materials.
(7) As a method for treating a lubricating film for cold forging on a steel material, the steel is characterized by further applying a lubricant to the surface of the steel material after the surface treatment of any one of (4) to (6) is performed. Surface treatment method for materials.
(8) The surface treatment for a steel material according to (7), wherein one or more selected from fatty acids, fatty acid metal salts, waxes, graphite, molybdenum disulfide, calcium sulfate and talc are used as a lubricant. Method.

In Example 11 and Comparative Example 8, when the treatment liquid was continuously used, the change of the oxidation-reduction potential between when the oxidation-reduction potential adjusting agent was added (Example 11) and when it was not (Comparative Example 8). It is the figure which showed a mode.

  The steel material to be treated with the treatment liquid of the present invention is not particularly limited. For example, carbon steel for machine structure (JISG4051) such as S45C, and alloy steel for machine structure (JISG4053) such as SCM415 and SCM435. In addition, various steel materials such as cold-rolled steel plates, hot-rolled steel plates, cast materials, and steel pipes can be suitably applied. However, the present invention can also be applied to zinc-based alloys, aluminum-based alloys, steel plates or steel materials plated with these.

  The treatment liquid of the present invention is a treatment liquid for depositing an iron oxalate film by chemical conversion treatment on the surface of a cleaned steel material, which contains oxalic acid and trivalent iron ions as essential components, and is oxidation-reduction. It contains a potential regulator and / or divalent iron ions.

  The divalent iron ion concentration in the treatment solution is preferably about 0 to 50 mmol, the trivalent iron ion concentration is about 10 to 60 mmol, and the total iron ion concentration is preferably 10 to 110 mmol. When the divalent iron ion concentration exceeds 50 mmol, iron oxalate sludge is generated in the treatment liquid. If the trivalent iron ion concentration is less than 10 mmol, the chemical reaction promoting effect of the trivalent iron ions becomes insufficient, and the film deposition becomes incomplete. If it exceeds 60 mmol, the amount of the film becomes excessive and the adhesion of the film is impaired. Due to the above complex factors, the total iron ion concentration is preferably 10 to 110 mmol, more preferably 15 to 90 mmol, and most preferably 20 to 70 mmol.

  Since the divalent iron ion is not an essential component in the treatment liquid of the present invention, it is not necessary to supply it artificially. However, if it is intentionally supplied, iron (II) sulfate heptahydrate, ammonium iron sulfate (II) 6 water Japanese products can be applied. In actual processing, the iron component eluted from the steel material surface by etching and the trivalent iron ions in the processing solution reduced by etching become divalent iron ions, which diffuse into the processing solution without forming a film. For this reason, the concentration of divalent iron ions in the treatment liquid gradually increases according to the treatment load unless the oxidation-reduction potential regulator is continuously added.

  Trivalent iron ions are an essential component in the treatment liquid of the present invention, and must be supplied artificially. The source of trivalent iron ions is not limited, but is usually a salt or salt of iron (III) nitrate nonahydrate, iron sulfate (III) n hydrate, iron (III) fluoride, etc. An aqueous solution is used. As a method for obtaining an aqueous solution of a salt, not only a method of dissolving a salt in water, but also a method of dissolving iron in an acid and oxidizing iron dissolved with an oxidizing agent such as hydrogen peroxide into trivalent iron ions is used. Can do. It is also possible to supply divalent iron ions generated during actual treatment by oxidation by adding a redox potential adjusting agent.

  The total iron ion concentration can also be measured by instrumental analysis such as atomic absorption spectrometry or ICP emission spectroscopy, or chelate titration. An example of the chelate titration method is described below. If necessary, permanganate is added to the treatment solution to which sulfuric acid has been added until reddish purple is exhibited, whereby oxalic acid is decomposed and divalent iron ions are oxidized to convert all iron ions to trivalent iron ions. Excess permanganate ions are reduced with hydrogen peroxide (add hydrogen peroxide until the reddish brown color derived from permanganate ions disappears), and the color changes from blue-purple to colorless with variamin blue B as the indicator and EDTA as the titrant. Convert to the total iron ion concentration from the titration amount until

  The oxidation-reduction potential of the treatment liquid in the present invention needs to be 100 to 500 mV. 150 to 450 mV is more preferable, and 200 to 400 mV is even more preferable. If the lower limit is not reached, iron oxalate sludge is generated from the treatment liquid, and if the upper limit is exceeded, the coating crystal becomes coarse due to excessive etching of the material, which is not preferable. In addition, the oxidation-reduction potential of the treatment liquid consisting only of oxalic acid and trivalent iron ions is approximately in the range of 300 to 400 mV, and when the oxidation-reduction potential exceeds the upper limit value, the oxidation-reduction potential adjusting agent was added excessively. It can only happen at times. That is, excessive etching is caused by the addition of an excessive redox potential adjusting agent.

  The redox potential can be measured without problems by using a commercially available redox electrode. A redox electrode generally measures the electrode potential of an inert metal selected as a working electrode based on the potential difference from the reference electrode. For example, a platinum electrode is used as the working electrode, and a silver-silver chloride electrode is used as the reference electrode. Can do.

The oxidation-reduction potential is an index derived from (trivalent iron ion concentration / divalent iron ion concentration), and is specifically derived from the following Nernst equation.
E = E ₀ + RT / F ・ ln ([Fe ³⁺ ] / `` Fe ²⁺ ])
・ Redox potential: E
Standard redox potential: E ₀
・ R: Gas constant (8.314JK ^-1 mol ^-1 )
・ T: Absolute temperature
・ F: Faraday constant (6.02 × 10 ²³ electrons are 96,500 coulomb)
・ [Fe ³⁺ ]: Trivalent iron ion activity (activity approximates concentration)
・ [Fe ²⁺ ]: Bivalent iron ion activity (activity approximates concentration)

  Therefore, in order to reduce the oxidation-reduction potential, a divalent iron salt, for example, iron (II) sulfate heptahydrate, can be added or the steel material can be treated. Further, it can be increased by adding a salt of trivalent iron such as iron (III) nitrate nonahydrate or adding a redox potential regulator. However, since the oxidation-reduction potential is unilaterally reduced by performing the target treatment, it is compensated by the addition of the oxidation-reduction potential adjusting agent by the amount that decreases with the treatment.

  The oxalic acid concentration in the treatment liquid of the present invention is about 50 to 300 mmol. The source of oxalic acid is not limited, but oxalic acid dihydrate is usually used. Although it is difficult to measure the concentration of oxalic acid itself, the titration value in the oxidation-reduction titration using permanganate is an index that takes into account the concentration of divalent iron ions in addition to the concentration of oxalic acid. It is an index that can be reflected in actual chemical conversion performance. The deposited film is ferrous oxalate, that is, a salt of oxalic acid and divalent iron ions. That is, it is considered that the divalent iron ions in the treatment liquid have an effect of improving the chemical conversion treatment property as long as it can be dissolved.

Redox titration using permanganate is a drop of permanganate solution in a 1 mL treatment solution until a reddish purple color is obtained. This is a method for calculating the titer. In addition, the oxidation-reduction ability of 1 mol of permanganate is 5 equivalents, oxalic acid is 2 equivalents, and divalent iron ions are 1 equivalent, so the titration value is simply the sum of molar concentrations of oxalic acid and divalent iron ions. It will not be. The oxidation-reduction reaction formula of each component is shown below.
_{^{· MnO 4 - + 8H + +}} 5e - → Mn 2+ + 4H 2 O
_{· (COOH) 2 → 2CO 2} + 2e - + 2H +
^{· Fe 2+ → Fe 3+ + e} -

  In redox titration using permanganate, the permanganate titration at the end point is preferably 0.02 to 0.15 mmol, more preferably 0.03 to 0.12 mmol, and 0.05 to 0.10 mmol with respect to 1 mL of the treatment liquid. Is most preferred. When the value is below the lower limit, the concentration of oxalic acid is mainly insufficient, and a sufficient film amount cannot be obtained. When the upper limit is exceeded, it is conceivable that the concentration of divalent iron ions is excessive or the concentration of oxalic acid is excessive. In the former case, sludge is generated in the treatment liquid. As the effect is saturated, it is economically disadvantageous.

In the oxidation-reduction titration, the amount of the treatment liquid collected is not necessarily 1 mL. The upper and lower limits of the permanganate titer are only for 1 mL of the processing solution. For example, when 2 mL of processing solution is collected, the upper and lower limits are simply doubled. Although the permanganate to be used is not particularly limited, a potassium permanganate aqueous solution is usually used. The concentration of the aqueous potassium permanganate solution is not particularly limited as long as it is known. For example, reagents having concentrations of 40 mmol / L, 20 mmol / L, 5 mmol / L, and the like are commercially available for analysis. When the titer of 40 mmol of potassium permanganate aqueous solution is 10.0 mL with respect to 5 mL of the treatment liquid, the permanganate titration in the present invention is 0.08 mmol because it is converted to 1 mL of the treatment liquid.
Note that the treatment liquid needs to be sufficiently acidic during the oxidation-reduction titration. For this reason, sulfuric acid can also be added to the processing solution after collection as required.

つまりシュウ酸は水溶液のpHに応じて０価のシュウ酸、１価のシュウ酸イオン、２価のシュウ酸イオンの３形態を取るため、厳密にはこれらの形態を区別して呼称すべきであるが、本発明においてはこの煩雑さを回避するため、これら全てをシュウ酸と呼ぶ。なお、濃度に関しては単位にモル濃度を使用しているため問題ない。 I will add here the definition of words for oxalic acid. Oxalic acid dissociates in an aqueous solution as shown by the following formula.

In other words, oxalic acid takes three forms, 0-valent oxalic acid, 1-valent oxalate ion, and 2-valent oxalate ion, depending on the pH of the aqueous solution. However, in order to avoid this complexity in the present invention, these are all called oxalic acid. There is no problem with the concentration because the molar concentration is used for the unit.

  When a steel material is treated using the treatment liquid of the present invention, the concentration of divalent iron ions in the treatment liquid increases and the oxidation-reduction potential decreases. When the oxidation-reduction potential finally falls below the lower limit, divalent iron ions cannot be completely dissolved and iron oxalate sludge is generated. In order to prevent this, it is necessary to add a redox potential adjusting agent in accordance with the processing load and maintain the redox potential in a predetermined range.

  The type of oxidation-reduction potential regulator in this case is not particularly limited, but for the purpose of application of the oxidation-reduction potential regulator, it oxidizes and treats a divalent iron ion generated in a small amount by the treatment of the steel material. The characteristic which does not oxidize and decompose the oxalic acid in the liquid is required. For example, nitrate ions and permanganate ions belong to the oxidizing agent, but nitrate ions are poor in the ability to oxidize divalent iron ions, and permanganate ions are the main component of the treatment liquid, although the ability to oxidize divalent iron ions is sufficient. Since oxalic acid is also oxidatively decomposed, it is not preferable.

  Preferably, one or more selected from hydrogen peroxide, organic peroxides, persulfates and nitrites are selected. Hydrogen peroxide can be used as an aqueous solution of any concentration. The organic peroxide is not particularly limited, but is preferably water-soluble such as t-butyl hydroperoxide, acetylacetone peroxide, and can be used as an aqueous solution having an arbitrary concentration. As persulfate (peroxodisulfate) and nitrite, sodium salt, potassium salt, ammonium salt and the like can be used, and an aqueous solution of any concentration can be used.

  Since the oxidation-reduction potential adjusting agent excluding nitrite has a relatively strong oxidizing power, it cannot coexist with divalent iron ions. Therefore, even after addition of the redox potential adjuster, if the redox potential is below about 300 mV, only some divalent iron ions are present and basically no redox potential adjuster remains. On the other hand, when the oxidation-reduction potential exceeds about 300 mV, divalent iron ions do not exist and only the oxidation-reduction potential regulator exists. In addition, since the redox potential increases according to the concentration of the redox potential regulator, if the relationship between the redox potential regulator concentration and the redox potential is examined in advance, the redox potential can be adjusted by measuring the redox potential. The agent concentration can be determined.

  Nitrite is also a redox potential regulator, which eventually oxidizes divalent iron ions and reduces itself to ammonia, but the redox reaction rate is relatively slow, and in the short term divalent. Since iron ions and nitrite can coexist, the nitrite concentration cannot be predicted from the redox potential like other redox potential regulators.

Nitrite ion concentration can be measured by the amidosulfuric acid method. In the amidosulfuric acid method, a U-shaped glass container (Einhorn fermentation tube) with a repair volume of 50 mL is filled with a sample solution, and the gas volume generated when about 2 g of amidosulfuric acid is charged therein is measured. The gas generation reaction by nitrite ions and amidosulfuric acid is as follows, and the nitrite ion concentration can be converted from the generated gas capacity.
・ HNO ₂ + NH ₂ SO ₃ H → H ₂ SO ₄ + H ₂ O + N ₂ ↑

  However, even if any redox potential regulator including nitrite is used, it is not particularly meaningful to directly measure the redox potential regulator concentration, and the redox potential is measured to a predetermined value. If it is within the range, the object of the present invention can be sufficiently achieved.

  The treatment liquid of the present invention contains essentially no phosphoric acid. This is because trivalent iron ions, which are essential components in the treatment liquid of the present invention, form sludge by forming insoluble iron phosphate due to the presence of phosphoric acid. When it is inevitably mixed in due to bringing in from the previous step, it is slightly acceptable, but 1.0 mmol is the upper limit, and 0.5 mmol or less is preferable.

  The liquid medium of the treatment liquid according to the present invention is preferably water (for example, deionized water or pure water). In addition, you may contain liquid media other than water as a liquid medium (for example, alcohol), In this case, it is suitable to set it as 10 mass% or less on the basis of the total mass of a liquid medium.

  The pH of the treatment liquid is preferably adjusted as appropriate. Although the chemical | medical agent used for pH adjustment is not specifically limited, For example, acids, such as nitric acid, a sulfuric acid, hydrofluoric acid, an organic acid, lithium hydroxide, potassium hydroxide, sodium hydroxide, sodium carbonate, aqueous ammonia, ammonium carbonate, Examples include alkalis such as ammonium hydrogen carbonate and triethanolamine. These alkalis or acids can be used after being dissolved in water or diluted with water in advance. The pH of the treatment solution of the present invention can be measured without problems with a pH meter using a commercially available pH electrode.

  The treatment solution pH is preferably 0.8 to 3.5, more preferably 1.0 to 3.0, and most preferably 1.5 to 2.5. Below the lower limit, overetching occurs, and not only the film amount is reduced, but also iron oxalate sludge is generated in the treatment liquid. If the upper limit is exceeded, the etching power is reduced, and a sufficient amount of film cannot be obtained, and trivalent iron ions in the treatment liquid are hydrolyzed to generate iron hydroxide sludge.

  When processing a steel material using the processing liquid of the present invention, the temperature of the processing liquid needs to be adjusted to 20 to 70 ° C. A more preferred temperature is 30-60 ° C, and a most preferred temperature is 35-50 ° C. Good film deposition is possible in this temperature range. Below the lower limit, the reactivity is lowered and a sufficient amount of film cannot be obtained, and when it exceeds the upper limit, overetching occurs and adhesion of the film is impaired, which is not preferable. Considering that the conventional oxalate treatment was performed at 65 to 95 ° C., a dramatic reduction in temperature could be achieved.

  Trivalent iron ions are also effective in shortening the processing time. A preferred treatment time is 1 to 10 minutes. The conventional oxalate treatment required a treatment time of 5 minutes or more. However, when the treatment solution of the present invention is used, the chemical precipitation reaction is almost completed in about 1 minute, and the film is completely formed in about 2 minutes. Complete. Further, there is no technical problem of long-time processing, but if it exceeds 5 minutes, productivity is reduced. Therefore, a more preferable treatment time is about 2 to 5 minutes.

  The treatment of the present invention is a chemical conversion treatment, and basically the reaction proceeds and the film is deposited by the contact between the steel material and the treatment liquid. In general, the liquid contact method can be roughly divided into a spray method and an immersion method, but the immersion method is preferable. The treatment liquid of the present invention is characterized by the fact that, as described above, a trivalent iron ion concentrated layer having a high concentration and a thin layer can be formed on the surface of the base metal by the action effect of the trivalent iron ions. Excessive stirring by the spray method may cause this concentrated layer to diffuse into the treatment liquid, making it difficult to obtain the effects of the present invention. Although the treatment of the present invention is premised on chemical conversion treatment, the effect of the present invention is not impaired even if the cathode electrolysis using a steel material as a cathode is partially applied.

  After the chemical conversion treatment, it is preferable to wash with water. The method of washing with water is not particularly limited, and methods such as a dipping method and a spray method can be applied. The treatment liquid of the present invention contains various salts. If these salts remain, the corrosion resistance decreases, and the coating performance when applied later and the lubricating performance when a lubricant is applied are reduced. The washing step can be multi-staged to improve washing efficiency.

  The film deposited by the treatment liquid of the present invention can be applied as a rust preventive film or a paint base film. When applied as a rust preventive film, by applying the rust preventive oil after the treatment of the present invention, a further rust preventive effect can be obtained by improving the retention of the rust preventive oil. When applied as a coating undercoat, the coating film adhesion and post-coating corrosion resistance can be improved in any coating system such as solvent coating, powder coating, and electrodeposition coating.

  However, it can be said that the most suitable application of the film deposited by the treatment liquid of the present invention is a lubricating base film for plastic working. Compared to the zinc phosphate coating that has been generally used as a conventional lubricant base coating, it does not contain phosphorus, so there is no problem of phosphorus immersion, sludge does not occur, and the coating can be formed at a low temperature in a short time. It is an advantage. In addition, the lubricity of the zinc phosphate film alone is inadequate, but if the lubricant applied in the case of zinc phosphate is applied as it is, it will exhibit equivalent lubricating performance as an alternative to zinc phosphate. . As the lubricant, one or more selected from fatty acids, fatty acid metal salts, waxes, graphite, molybdenum disulfide, calcium sulfate and talc are selected.

  Furthermore, the treatment liquid of the present invention can directly contain a surfactant in the treatment liquid, and the degreasing treatment can be omitted. As the surfactant, any of nonionic, anionic, cationic, and amphoteric types can be used, but the nonionic type is most preferable. A suitable surfactant can be selected according to the oil type and the amount of oil adhering to the material, and the concentration is generally about 100 to 2000 ppm.

Examples of the present invention will be given together with comparative examples, and the effects will be described more specifically.
<Steel materials>
The following two types were used as steel materials. The cold rolled steel sheet was used for sludge generation amount evaluation, film adhesion evaluation and film amount measurement. Carbon steel was used for evaluation of cold forging workability.
-Cold-rolled steel sheet: JIS G 3141 SPCC: SD 0.8 x 70 x 150 mm
・ Carbon steel (cylindrical): JIS G 4051 S45C Diameter 25mmφ, Height 30mm

<Chemical conversion treatment>
A commercially available alkaline degreasing agent manufactured by Nihon Parkerizing Co., Ltd .: Fine cleaner 4360 (20 g / L) was used to remove dirt and oil adhering to the surface of the steel material by dipping at 60 ° C. for 10 minutes. Next, the plate was washed with tap water for 30 seconds, and then treated by immersion for 2 minutes using the chemical conversion liquids of Examples and Comparative Examples. Only Comparative Example 7 was treated for 10 minutes. After the chemical conversion treatment, it was further immersed in tap water for 30 seconds, washed with water and dried by air blow.

<Preparation of treatment liquid>
Oxalic acid dihydrate as oxalic acid source, iron (II) sulfate heptahydrate or iron (III) nitrate nonahydrate as iron ion source, 28% ammonia water as pH adjuster, redox potential adjustment Using 35% hydrogen peroxide, 20% sodium nitrite aqueous solution or 69% t-butyl hydroperoxide as the agent, the treatment liquids of Examples and Comparative Examples were prepared, heated to a predetermined temperature, and then treated for steel materials Provided.
In Example 1, the iron (II) sulfate heptahydrate and the redox potential regulator were not added, but a predetermined amount of iron (III) nitrate nonahydrate iron ion was added. In Examples 2, 3, 5, 6, 7, and 9 and Comparative Examples 2 and 4, iron (II) sulfate heptahydrate was not added, but a predetermined amount of iron (III) nitrate nonahydrate iron ion was added. The redox potential was adjusted using a redox potential regulator. In Examples 4, 8, and 10 and Comparative Examples 1 and 3, a predetermined amount of iron (II) sulfate heptahydrate was added without adding iron (III) nitrate nonahydrate, and an oxidation-reduction potential regulator was added. Was used to adjust the redox potential. In Comparative Examples 5 and 6, neither iron ions nor redox potential modifiers were added.

<Measurement of total iron ion concentration in processing solution>
It was measured by ICP emission spectroscopy. The results are shown in Table 1.

<Measurement of redox potential (ORP) in processing solution>
It measured using the commercially available ORP meter. The results are shown in Table 1.

<Permanganate titration measurement>
The measurement was performed by the following procedure.
1. Collect 1.0 mL of treatment solution.
2. Add 15 mL of water.
3. Add 10mL of 50wt% sulfuric acid and add water so that the total volume is about 50mL.
4). Warm in a boiling water bath.
5. Titrate until 0 mmol / L potassium permanganate solution is used as a titrant until a slight red color is observed.
6). The titration volume is calculated from the amount and concentration of titrant required for titration.
The results are shown in Table 1.

<PH measurement>
It measured using the commercially available pH meter. The results are shown in Table 1.

<Evaluation of sludge generation>
Ten sheets of cold-rolled steel sheet were treated for 5.0 L of the treatment liquid, and the appearance of the amount of generated sludge was evaluated. The processing load is 0.042 m ² / L. The amount generated was evaluated according to the following evaluation criteria. The results are shown in Table 1.
○: No sludge △: Some sludge ×: Clearly sludge is generated and cloudy

<Measurement of coating amount>
The coated cold-rolled steel sheet was weighed, and a 5% chromic anhydride aqueous solution at room temperature was prepared as a stripping solution, and the coating was stripped for 5 minutes. Thereafter, it was washed and dried with water, weighed again, and the coating amount [g / m ² ] was calculated from the mass difference before and after peeling and the peeled area. Only in the case of Comparative Example 3, the temperature of the stripping solution was 75 ° C., and stripping was performed for 15 minutes. The results are shown in Table 1.

<Evaluation of film adhesion>
Adhesive tape was affixed to the cold-rolled steel sheet that had been subjected to the film treatment, and the amount of film adhered to the tape side after peeling was visually determined. The film adhesion was evaluated according to the following evaluation criteria. In addition, the film | membrane whose film amount was less than 0.5 g / m < ² > was excluded from the evaluation object. The results are shown in Table 1.
◎: No film peeling ○: Slightly peeling △: Slightly peeling ×: Remarkably peeling

<Processability evaluation>
Carbon steel was coated with a lubricant after chemical conversion treatment, and the workability was evaluated by a spike test. As a lubricant, a lubricant manufactured by Nihon Parkerizing Co., Ltd .: Palube 4612 (500 g / L) containing calcium soap as a main component was used, dipped up at room temperature, and then dried in an electric oven at 100 ° C. for 10 minutes. The spike test was carried out in accordance with the invention of Japanese Patent No. 3227721, and the degree of film follow-up to the protrusions of the test piece after processing and the presence or absence of seizure portions were visually evaluated. Those having good followability have sufficient seizure resistance against the surface area expansion during cold plastic working, and those that do not follow the film tend to cause seizure. Workability was evaluated according to the following evaluation criteria. The results are shown in Table 1.
A: The film follows up to the protrusion, and there is no seizure part. ○: The film does not follow up to the protrusion, but there is no seizure part. : The film does not follow the protrusions and there is intense seizure.

  As can be seen from the sludge generation amount and film performance evaluation results of Examples 1 to 10 in Table 1, if the total iron ion concentration and oxidation-reduction potential in the oxalate treatment liquid are within the range of the present invention, the temperature is relatively low and short. In time, it became clear that a film with good adhesion could be obtained without generation of sludge, and good workability could be secured.

  In Example 6, since the permanganate titer was small and the oxalic acid concentration was low, the coating amount and workability were slightly reduced. In Example 7, the permanganate titer was high, and the oxidation-reduction potential exceeded 300 mV, so the oxalic acid concentration was excessive and the film adhesion was slightly reduced. In Example 8, both the total iron ion concentration and the oxidation-reduction potential were lower, and as a result, the trivalent iron ion concentration seemed to be insufficient, and as a result of the decrease in the amount of film, the workability was slightly reduced.

In Comparative Example 1 in Table 1, the total iron ion concentration is below the lower limit value, and the film deposition amount is insufficient due to insufficient trivalent iron ion concentration.
On the contrary, in Comparative Example 2, the total iron ion concentration exceeds the upper limit, and due to the effect of promoting the formation of excess trivalent iron ions, a film with good adhesion cannot be obtained, and the workability is also lowered.
In Comparative Example 3, the oxidation-reduction potential was lower than the lower limit value, and the divalent iron ions reached the saturation concentration, and sludge was generated quickly by the treatment. Further, due to insufficient trivalent iron ion concentration, the coating amount could not be obtained sufficiently and the workability was insufficient.
In Comparative Example 4, the 7 redox potential exceeds the upper limit, and a film with good adhesion cannot be obtained due to excessive etching of the redox potential adjusting agent, and the workability is also deteriorated.

Comparative Example 5 and Comparative Example 6 are simple oxalate treatment solutions that do not contain iron ions and correspond to the prior art. In Comparative Example 5, a film is obtained by the temperature effect, but the adhesion is poor and the processability is insufficient, and sludge is generated quickly due to excessive etching.
Comparative Example 6 is a treatment liquid having the same composition as Comparative Example 5, but no film deposition is observed because the treatment temperature is low.
In Comparative Example 7, a zinc phosphate treatment was performed using a zinc phosphate treating agent: Palbond 181X (90 g / L) manufactured by Nippon Parkerizing Co., Ltd. The treatment temperature was set to 80 ° C., and 0.25 g / L of accelerator 131 was added immediately before the treatment, and the treatment was performed for 10 minutes. A film with good adhesion was obtained, and the workability was good, but a large amount of sludge was generated.

The amount of sludge generated in the above Examples and Comparative Examples was evaluated with 10 cold-rolled steel sheets, that is, a treatment load of 0.042 m ² / L with respect to a 5 L treatment liquid. However, the oxidation-reduction potential after treating 10 cold-rolled steel sheets in Example 1 decreased from the initial 300 mV to 185 mV, suggesting that divalent iron ions have accumulated gradually. Therefore, the continuous processing is continued up to 120 sheets as it is, and at that time, a 35% hydrogen peroxide aqueous solution is added as an oxidation-reduction potential regulator, and the oxidation-reduction potential regulator is added as long as the oxidation-reduction potential is maintained at the initial value. The case of no addition was compared. The case where the oxidation-reduction potential adjusting agent was used was Example 11, and the case where it was not used was Comparative Example 8, and the results are shown in Table 2 and FIG.

As a result, in Comparative Example 8, sludge started to be generated at a processing number of 40 sheets (processing load 0.168 m ² / L), and then the sludge generation amount continued to increase. In addition, almost no film deposition was observed on the 120th steel plate due to insufficient trivalent iron ion concentration in the treatment liquid.

On the other hand, in the case of Example 11, no sludge was observed even after the continuous treatment, and both the amount of deposited film and the adhesion of the film were maintained at the initial values. When the oxidation-reduction potential adjusting agent was kept constant by the oxidation-reduction potential adjusting agent, it was confirmed that the production of divalent iron ions was suppressed, and if the necessary components were replenished, it could be treated semipermanently without sludge generation.

Claims (8)

  An acidic aqueous solution containing oxalic acid and trivalent iron ions, the total iron ion concentration of divalent iron ions and trivalent iron ions is 10 to 110 mmol / L, and the redox potential is 100 to 500 mV The surface treatment liquid for steel materials characterized by the above-mentioned.   When the treatment liquid according to claim 1 is subjected to oxidation-reduction titration using permanganate, the steel is characterized in that the permanganate titration amount at the end point is 0.02 to 0.15 mmol with respect to 1 mL of the treatment liquid. Surface treatment liquid for materials.   The surface treatment liquid for steel material according to claim 1 or 2, which is for a lubricating film for plastic working.   In order to deposit an iron oxalate film by a chemical conversion method by immersing a steel material in the surface treatment liquid according to any one of claims 1 to 3, an oxidation-reduction potential regulator is added according to the treatment load. A surface treatment method for a steel material, characterized in that the oxidation-reduction potential is maintained at 100 to 500 mV.   The surface treatment method for a steel material according to claim 4, wherein one or more selected from hydrogen peroxide, organic peroxides, persulfates and nitrites are used as the redox potential regulator.   The steel material surface according to claim 4 or 5, wherein the steel material is immersed in the surface treatment liquid according to any one of claims 1 to 3 adjusted to a temperature of 20 to 70 ° C for 1 to 10 minutes. Processing method.   A surface treatment for a steel material, characterized in that a lubricant is applied to the surface of the steel material after the surface treatment according to any one of claims 4 to 6 is applied as a lubricating film treatment method for plastic working on the steel material. Method.   The surface treatment method for a steel material according to claim 7, wherein one or more selected from fatty acids, fatty acid metal salts, waxes, graphite, molybdenum disulfide, calcium sulfate and talc are used as the lubricant. .

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