JP5912839B2 - Spring steel plating pretreatment method and spring steel plating method - Google Patents

Description

  The present invention relates to a pre-plating method for a spring steel material that can suppress hydrogen embrittlement due to hydrogen storage, and a plating method for a spring steel material.

  When a steel material is subjected to a plating treatment, an acid treatment is performed in order to remove surface dirt, oxide film, and the like. By treating the steel with an acid, an oxide film or the like is removed from the surface of the steel, but at the same time, the metal base of the steel is easily dissolved in the acid cleaning solution and the steel is easily corroded. Further, since hydrogen is generated when the metal substrate is dissolved in the acid cleaning solution, the steel material occludes the hydrogen and becomes brittle (hydrogen embrittlement), and delayed fracture is likely to occur.

  For this reason, in the steel material plating method, after the plating process, a baking process is performed to release the hydrogen stored in the steel material.

  On the other hand, in order to suppress corrosion of steel materials during acid treatment, attempts have been made to suppress corrosion of steel materials by adding various additives to the acid cleaning liquid.

  For example, Patent Document 1 discloses performing a film removal treatment by immersing a metal member to be treated in an acid cleaning solution containing a corrosion inhibitor. In the examples, glutamic acid, cysteine, lysine and tryptophan are used as corrosion inhibitors.

JP 2009-144228 A

  In Patent Document 1, a metal material to be treated is immersed in an acid cleaning solution containing a corrosion inhibitor and subjected to a film removal treatment, so that the metal material is corroded, hydrogen brittle, pitting corrosion as described in paragraph 0018 and the like. Although it is said that harmful effects such as generation can be prevented, no specific examination has been made as to how much hydrogen occlusion of metal treated members can be suppressed. Moreover, there is no detailed description regarding a metal to-be-processed member, and attention is not paid about the application to a spring steel material.

  Spring steel materials are often subjected to heat treatments such as quenching, tempering, austempering, strain relief annealing, etc., and therefore oxide films are often firmly attached. For this reason, since it is necessary for spring steel materials to perform acid treatment more strongly than steel materials of other metal products, it was easier to occlude hydrogen. In addition, since the spring product is subjected to a strong load stress during use, delayed fracture due to hydrogen occlusion becomes a major problem, and after plating the spring steel material, it is usually necessary to carefully perform a baking process.

  However, when the baking treatment is performed after the plating treatment, fine cracks are generated on the surface, the corrosion resistance is lowered, the gloss of the plating layer is lowered, and the plating finish is easily lowered.

  Therefore, an object of the present invention is to provide a pre-plating method for a spring steel material that can remove the oxide film on the surface of the spring steel material while suppressing hydrogen occlusion of the spring steel material, and plating of the spring steel material that does not require baking after the plating process. It is to provide a method.

  The pre-plating method for a spring steel material according to the present invention is a pre-plating method for a spring steel material in which the spring steel material is acid-treated to remove an oxide film formed on the surface of the spring steel material, and the acid treatment is performed as a nonion. A hydrogen storage inhibitor containing at least a surfactant and hydrochloric acid, and an acid cleaning solution containing 0.02 to 0.6% by mass of the nonionic surfactant and 10 to 25% by mass of hydrochloric acid. It is characterized by performing.

  In the pretreatment method for plating a spring steel material according to the present invention, the acid cleaning liquid preferably further contains 0.04 to 0.8% by mass of nitric acid.

  In the pretreatment method for plating a spring steel material according to the present invention, the acid treatment is preferably performed by immersing the spring steel material in the acid cleaning solution for 2 to 20 minutes.

  In the pretreatment method for plating a spring steel material of the present invention, it is preferable that the spring steel material subjected to at least one heat treatment selected from quenching, tempering, austempering and strain relief annealing is subjected to the acid treatment.

  The plating method of the spring steel material of the present invention is characterized in that the spring steel material subjected to any of the plating pretreatments is subjected to a plating treatment by electroplating and not subjected to a baking treatment.

  According to the plating pretreatment method for spring steel material of the present invention, the hydrogen storage inhibitor containing at least a nonionic surfactant and hydrochloric acid are contained, 0.02% by mass or more of nonionic surfactant and 10 to 10% of hydrochloric acid. Since the acid treatment is performed using the acid cleaning solution containing 25% by mass, the surface of the spring steel material is protected by the nonionic surfactant, and the elution of the metal base of the spring steel material into the acid cleaning solution can be suppressed. The oxide film can be selectively removed while suppressing the above. For this reason, even if the baking process after a plating process is abbreviate | omitted, the spring product which cannot produce the delayed fracture by hydrogen embrittlement can be obtained. Moreover, since the surface state after an acid treatment is favorable, the finish of plating can be made favorable.

  Moreover, according to the method for plating a spring steel material of the present invention, a delayed spring failure due to hydrogen embrittlement hardly occurs and a spring product excellent in corrosion resistance can be obtained without performing a baking treatment. Further, since no baking process is performed, the running cost can be reduced and the productivity is excellent.

It is the schematic of the hydrogen content measuring apparatus of a spring steel material. It is a figure which shows the relationship between the temperature of a spring steel material, and discharge | release hydrogen amount. 4 is a photograph showing a spring steel material used in Test Example 2. In Example 1, it is a SEM photograph (3000 times) of the spring steel material after acid treatment. In Example 1, it is the surface SEM photograph (3000 times) of the spring steel material after a plating process. It is a cross-sectional SEM photograph (3000 times) of the spring steel material. It is a photograph showing the surface state before and after the salt spray test of the spring steel material. In the comparative example 1, it is a SEM photograph (3000 times) of the spring steel material after acid treatment. In comparative example 1, it is the surface SEM photograph (3000 times) of the spring steel material after baking processing. It is a cross-sectional SEM photograph (3000 times) of the spring steel material. It is a photograph showing the surface state before and after the salt spray test of the spring steel material.

(Pretreatment method for spring steel plating)
First, the plating pretreatment method for the spring steel material of the present invention will be described.

  The pretreatment method for plating a spring steel material according to the present invention is to remove the oxide film formed on the surface of the spring steel material by acid-treating the spring steel material with an acid cleaning solution.

  The spring steel material used for the plating pretreatment method is not particularly limited. A steel material such as carbon-based, silicon-manganese-based, manganese-chromium-based, or chromium-vanadium-based steel that is formed into a laminated leaf spring, a coil spring, or the like and imparted with a spring property can be used. Further, the spring steel material may be subjected to heat treatment such as quenching, tempering, austempering, and strain relief annealing. By performing these heat treatments, an oxide film is firmly formed on the surface of the spring steel material, so it is necessary to perform strong acid cleaning. According to the present invention, even such a strong oxide film is used. Since the oxide film can be removed almost without corroding the metal base of the spring steel material, the effect of the present invention can be obtained more remarkably.

  In the pretreatment method for plating a spring steel material of the present invention, an acid cleaning solution containing a hydrogen storage inhibitor containing at least a nonionic surfactant and hydrochloric acid is used.

  Nonionic surfactants have good permeability and are selectively adsorbed on the metal base of spring steel, so that a protective film containing nonionic surfactant can be formed on the surface of the spring steel while suppressing corrosion of the spring steel. The oxide film can be removed.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid alkanolamide and the like. Polyoxyethylene alkyl ether is preferable. Polyoxyethylene alkyl ether includes polyethylene glycol and the like.

  The number average molecular weight of the nonionic surfactant is preferably from 100 to 1,000, more preferably from 100 to 500, particularly preferably from 100 to 300. If the number average molecular weight is less than 100, corrosion of the spring steel material may not be sufficiently suppressed. When the number average molecular weight exceeds 1000, the permeability tends to decrease.

  The nonionic surfactant is required to be contained in the acid cleaning liquid in an amount of 0.02% by mass or more, preferably 0.02 to 0.6% by mass, and more preferably 0.1 to 0.3% by mass. When the content of the nonionic surfactant is less than 0.02% by mass, the effect of addition is poor, and the hydrogen occlusion of the spring steel material after acid treatment cannot be suppressed. Moreover, even if it exceeds 0.6% by mass, the effect is hardly changed, the acid cleaning liquid tends to foam, and there is a tendency to require time and effort for cleaning and removing the acid cleaning liquid remaining on the spring steel material after the acid treatment. The upper limit is preferably 0.6% by mass. And if content of nonionic surfactant is 0.1-0.3 mass%, an oxide film can be removed efficiently, suppressing the foaming of an acid cleaning liquid.

  In the present invention, the acid cleaning solution further contains 2′-nitrocinnamic acid, 2′-nitrocinnamaldehyde, 3,5-diamino-1,2,4-triazole, 3,5-dimethyl as a hydrogen storage inhibitor. Pyrazole, ethyl 3-aminopyrazole-4-carboxylate, 3′-nitrocinnamic acid, 3-hydroxy-4-methoxycinnamic acid, ethyl 3-phenylpropionate, 3-methyl-1-phenyl-5-pyrazolone, 3-amino-5- (methylmercapto) -1H-1,2,4-triazole, 3-amino-5-mercapto-1,2,4-triazole, ethyl 3-aminopyrazole-4-carboxylate, 3- Nitro-1H-1,2,4-triazole, 4- (dimethylamino) -cinamaldehyde, 4-amino-1,2,4-triazole, 4′-nitrosilicate Cinnamic acid, ethyl 4-nitrocinnamic acid, 4-phenylurazole, 4-fluorocinnamic acid, 4-methylcinnamic acid, t-anethole, α-methylcinnamic acid, α-methylcinnamaldehyde, asparagine, aspartic acid, Arginine, alanine, isoleucine, ethylene glycol diacetate, orotic acid, glycine, glutamine, glutamic acid, cinnamic acid, ethyl cinnamate, benzyl cinnamate, methyl cinnamate, thiamine, cystine, cysteine, cinnamaldehyde, serine, Tyrosine, tryptophan, threonine, valine, histidine, bispyrazolone, proline, pyrazole-3,5-dicarboxylic acid monohydrate, phenylalanine, methionine, methylisoeugenol, lysine, riboflavin, leucine, cinnamoyl chloride and urea 1 type or 2 types or more of compounds selected from (hereinafter referred to as other hydrogen storage inhibiting compounds) may be further contained.

  By using a nonionic surfactant and the other hydrogen storage inhibitor compound in combination as a hydrogen storage inhibitor, the hydrogen storage of the spring steel material after acid treatment can be more effectively suppressed.

  It is preferable to contain 0.001-10 mass% of said other hydrogen storage suppression compounds in an acid washing | cleaning liquid. If it is less than 0.001% by mass, the effect of addition is poor. Even if it exceeds 10% by mass, the effect is not improved so much, which is not economical. In addition, if the hydrogen storage inhibiting compound attached to the surface of the spring steel material is brought into the next process, various adverse effects may occur.

  In the present invention, the hydrochloric acid concentration of the acid cleaning solution needs to be 10 to 25% by mass, more preferably 10 to 20% by mass, and particularly preferably 15 to 20% by mass. Since the oxide film formed on the surface of the spring steel material is strong, if the hydrochloric acid concentration is less than 10% by mass, removal of the oxide film is insufficient, the time required for acid treatment increases, and the productivity decreases. . If it exceeds 25% by mass, the cleaning power of the acid cleaning liquid becomes too strong, the metal base of the spring steel material is dissolved, the hydrogen storage amount of the spring steel material after acid treatment increases, and delayed fracture tends to occur. Further, the surface condition of the spring steel material is deteriorated, and the plating finish tends to be deteriorated.

  In the present invention, the acid cleaning liquid may further contain nitric acid. By containing nitric acid, the cleaning power of the acid cleaning liquid is further increased, and the oxide film on the surface of the spring steel material can be efficiently removed in a shorter time. The acid cleaning solution has a nitric acid concentration of preferably 0.04 to 0.8 mass%, more preferably 0.2 to 0.4 mass%. If it is less than 0.04% by mass, the effect of addition is poor. If it exceeds 0.8%, the detergency becomes too strong, and the hydrogen storage amount of the spring steel material after acid treatment tends to increase or the surface condition tends to deteriorate.

  In the present invention, the acid treatment method for the spring steel material is not particularly limited, and a conventionally known method can be employed. For example, a method of immersing a spring steel material in an acid cleaning solution is an example. The temperature of the acid cleaning solution is preferably 20 to 40 ° C, and more preferably 25 to 35 ° C. Moreover, 2-20 minutes are preferable and, as for immersion time, 5-10 minutes are more preferable. When the temperature of the acid cleaning liquid is less than 20 ° C., the removal of the oxide film is insufficient, the time required for the acid treatment increases, and the productivity is lowered. If it exceeds 40 ° C., the detergency becomes too strong, and the hydrogen occlusion amount of the spring steel material after acid treatment tends to increase or the surface condition tends to deteriorate. Further, if the acid cleaning time is less than 2 minutes, the removal of the oxide film may be insufficient. If it exceeds 20 minutes, the corrosion of the spring steel material tends to proceed, which is not preferable.

  After the acid treatment, the spring steel material is washed with water to remove the acid washing liquid remaining on the surface. In this way, the pre-plating treatment of the spring steel material is performed.

  In the present invention, the spring steel material after the plating pretreatment preferably has a content of diffusible hydrogen in the spring steel material of 3 wt.ppm or less, more preferably 1 wt.ppm or less. When the content of diffusible hydrogen is 1 wt. Ppm or less, a spring product that is unlikely to cause delayed fracture due to hydrogen embrittlement can be obtained without performing a baking process after the plating process.

  In order to reduce the content of diffusible hydrogen in the spring steel after plating pretreatment to 1 wt.ppm or less, it is achieved by adjusting the hydrochloric acid concentration of the acid cleaning solution, the nonionic surfactant concentration, the temperature of the acid cleaning solution, and the cleaning time as appropriate. it can. For example, an acid cleaning solution containing 0.02% by mass or more of a nonionic surfactant and 10 to 25% by mass of hydrochloric acid is used, and the temperature of the acid cleaning solution is adjusted to 20 to 40 ° C. (preferably 25 to 35 ° C.) for cleaning. By setting the time to 2 to 20 minutes (preferably 5 to 10 minutes), the content of diffusible hydrogen can be reduced to 1 wt.ppm or less.

  Note that diffusible hydrogen is atomic hydrogen that can move freely in the crystal lattice. In the present invention, a spring steel material having a thickness of 0.5 mm is heated from 23 ± 3 ° C. to 200 ° C. The total amount of hydrogen released from the spring steel at this time was defined as diffusible hydrogen.

(Spring steel plating method)
Next, the plating method for the spring steel material of the present invention will be described.

  In the method for plating a spring steel material according to the present invention, the spring steel material that has been pre-plated as described above is plated by electroplating. And the baking process is not performed before and after the plating process.

  In the present invention, the spring steel material contains a hydrogen storage inhibitor containing at least a nonionic surfactant and hydrochloric acid, an acid containing 0.02% by mass or more of nonionic surfactant and 10 to 25% by mass of hydrochloric acid. Since the surface treatment of the spring steel material is protected by the nonionic surfactant because the acid treatment is performed using the cleaning liquid, as shown in the examples described later, while suppressing an increase in the amount of diffusible hydrogen in the spring steel material, The oxide film can be selectively removed. For this reason, even if the baking process after a plating process is abbreviate | omitted, the spring product which cannot produce the delayed fracture by hydrogen embrittlement can be obtained.

  Moreover, since corrosion of the spring steel material during the acid treatment can be suppressed, the surface state of the spring steel material after the acid treatment can be improved, and the finish of the plating can be improved. Moreover, since elution to the acid cleaning liquid of the metal base of the spring steel material can be suppressed, the acid cleaning liquid can be used repeatedly, and the waste liquid processing cost can be reduced. Moreover, since the baking process is not performed, the plating process cost can be reduced and it is economical.

  In the spring steel material plating method of the present invention, the electroplating method is not particularly limited, and can be performed using a conventionally known method. For example, there is a method in which a spring steel material is immersed in an electrolytic cell to which an electroplating solution is supplied, and the spring steel material is energized as a cathode. The type of electroplating is not particularly limited, and examples include electrogalvanizing, electrozinc nickel alloy plating, and electrozinc iron alloy plating.

  Further, after electroplating, the chromate treatment may be performed by immersing the plated product in an acid solution containing chromic acid. By performing chromate treatment, the corrosion resistance is further improved.

  Hereinafter, the effects of the present invention will be described in detail using each test example. In each test example, polyoxyethylene alkyl ether having a number average molecular weight of 100 to 200 was used as the nonionic surfactant.

[Test Example 1] (Measurement of hydrogen storage amount)
Acid cleaning liquids 1-1 to 1-4 having the compositions shown in Table 1 were prepared.
Carbon steel (S60CM, bainite Hv450, thickness 0.5 mm) subjected to austempering as a heat treatment is used as a spring steel material, and the spring steel material is immersed in an acid cleaning solution at 25 to 35 ° C. for 10 minutes to be acid-treated, Thereafter, the spring steel material was taken out from the acid cleaning solution, washed with water, and left at room temperature for 1 hour. A spring steel material as a sample was installed in a quartz glass tube of the heating furnace using the hydrogen measuring apparatus shown in FIG. 1 equipped with a heating furnace and a gas chromatograph. Then, Ar gas was supplied as a carrier gas to the quartz glass tube at a flow rate of 50 ml / min, and the temperature was increased from 23 ± 3 ° C. to 800 ° C. at a temperature increase rate of 100 ° C./hr. Hydrogen released from the spring steel was detected with a gas chromatograph, and the total value of hydrogen released up to 200 ° C. (diffusible hydrogen) was determined. The results are shown in Table 1. Further, the relationship between the temperature and the amount of released hydrogen is shown in FIG.

  As shown in Table 1, diffusible hydrogen of spring steel is obtained by acid treatment with acid cleaning solutions 1-1 and 1-2 containing 0.02% by mass or more of nonionic surfactant and 10 to 25% by mass of hydrochloric acid. Was able to suppress occlusion. On the other hand, when acid treatment was performed with the acid cleaning liquids 1-3 and 1-4 in which the nonionic surfactant was less than 0.02% by mass, occlusion of diffusible hydrogen could not be sufficiently suppressed.

[Test Example 2] (Delayed fracture characteristics of spring steel)
Acid cleaning liquids 2-1 to 2-11 having the compositions shown in Table 2 were prepared.
Carbon steel (S60CM, bainite Hv510, thickness 0.5 mm) subjected to austempering as heat treatment was used as a spring steel material, and the spring steel material was bent to prepare a leaf spring having bolt fastening holes. The shape of the leaf spring is shown in FIG.
The bolt was tightened into the bolt tightening hole of the leaf spring so that the displacement amount of the leaf spring was 3 mm. The tightening stress applied to the leaf spring at that time was about 1300 to 2500 MPa in actual measurement. In this state, the plate was immersed in an acid cleaning solution at 25 to 35 ° C. for 90 minutes for acid treatment. Thereafter, the leaf spring was taken out from the acid cleaning solution and washed with water, and the delayed fracture characteristics and the surface cleaning degree in a stress load state were evaluated. The results are shown in Table 2. The delayed fracture characteristics were evaluated as ◯ for those that were not broken, △ for those that were partially broken but not affecting the product characteristics, and x for those that were severely broken. The degree of surface cleanliness was evaluated as ◯ when the scale was almost removed, △ when the scale remained partially, and x when the scale was hardly removed.

  As shown in Table 2, a delay in a stress load state is obtained by acid treatment with an acid cleaning solution 2-1 to 2-10 containing 0.02% by mass or more of nonionic surfactant and 10 to 25% by mass of hydrochloric acid. Destructive properties and surface cleanliness were good. In particular, better results were obtained by acid treatment with acid cleaning solutions 2-3 to 2-6 having a hydrochloric acid concentration of 15 to 20% by mass.

  On the other hand, when the acid treatment was performed with the acid cleaning solution 2-11 containing no nonionic surfactant, the scale could be removed, but even if the displacement amount of the leaf spring was 2 mm, breakage occurred, The delayed fracture characteristics were inferior.

[Test Example 3] (Surface condition after acid treatment, surface condition after plating treatment and corrosion resistance)
Example 1
Carbon steel (S60CM, bainite Hv450, thickness 0.9 mm) subjected to austempering as heat treatment was used as a spring steel material. (% By mass, nonionic surfactant 0.06% by mass) was immersed for 10 minutes for acid treatment, and then the spring steel material was taken out from the acid cleaning solution and washed with water for acid treatment. There was almost no scale on the surface of the spring steel material after the acid treatment, and the surface cleanliness was good.
Moreover, the SEM photograph (3000 times) of the spring steel material after the acid treatment after being left in the atmosphere for 1 hour is shown in FIG. As shown in FIG. 4, the surface condition after the acid treatment was good and there was almost no pitting corrosion.
Moreover, when the diffusible hydrogen content in the spring steel was measured in the same manner as in Test Example 1, the diffusible hydrogen content was 0.41 wt.ppm.
Next, electrogalvanizing was performed under conditions of current and voltage so that the film thickness was about 12 μm, and after forming a galvanized layer, a chromate treatment was performed and a plating treatment was performed. The surface SEM photograph (3000 times) of the spring steel material after the plating treatment is shown in FIG. 5, and the cross-sectional SEM photograph is shown in FIG. 6 (3000 times). As shown in FIGS. 5 and 6, the surface state after the plating treatment was good and almost smooth. Moreover, there was no crack etc. in the plating layer.
Next, the salt water spray test was done for the spring steel material which performed the plating process based on JISZ2371. FIG. 7 shows the initial state and the spring steel material after 72 hours from the salt spray test. As shown in FIG. 7, before and after the salt spray test, there was almost no change in the surface state of the spring steel material, and after the salt spray test, it was glossy and the corrosion resistance was very good.

(Comparative Example 1)
The spring steel used in Example 1 was immersed in an acid cleaning solution (hydrochloric acid 18% by mass) at 25 to 35 ° C. for 10 minutes for acid treatment, and then the spring steel material was taken out from the acid cleaning solution and washed with water for acid treatment. . There was almost no scale on the surface of the spring steel material after the acid treatment, and the surface cleanliness was good.
Further, FIG. 8 shows an SEM photograph (3,000 times) of the spring steel material after acid treatment after being left in the atmosphere for 1 hour. The spring steel material was corroded by the acid treatment, and as shown in FIG. 8, a lot of pitting corrosion was generated in the spring steel material.
Moreover, when the diffusible hydrogen content in the spring steel was measured in the same manner as in Test Example 1, the diffusible hydrogen content was 9.58 wt.ppm.
Next, after electrogalvanizing and chromate treatment under the same conditions as in Example 1, baking treatment was performed in a baking furnace at 200 ° C. × 4 hours. The diffusible hydrogen content after baking was 1.5 wt.ppm. The surface SEM photograph (3000 times) of the spring steel after the baking treatment is shown in FIG. 9, and the cross-sectional SEM photograph is shown in FIG. 10 (3000 times). As shown in FIGS. 9 and 10, fine cracks were generated on the surface by the baking treatment. Further, the plating layer had protrusions due to the shape of the metal base of the spring steel material.
Next, the salt water spray test was done for the spring steel material which performed the plating process based on JISZ2371. FIG. 11 shows the spring steel material in the initial state and 72 hours after the salt spray test. As shown in FIG. 11, after 72 hours of the salt spray test, a lot of white rust was generated in the galvanized layer and there was almost no gloss.

Claims (5)

A method for pre-plating a spring steel material by acid-treating the spring steel material and removing an oxide film formed on the surface of the spring steel material,
The acid treatment includes a hydrogen storage inhibitor containing at least a nonionic surfactant and hydrochloric acid, 0.02 to 0.6 mass% of the nonionic surfactant, and 10 to 25 mass% of the hydrochloric acid. A plating pretreatment method for a spring steel material, which is performed using an acid cleaning solution.   2. The pretreatment method for plating a spring steel material according to claim 1, wherein the acid cleaning liquid further contains 0.04 to 0.8% by mass of nitric acid.   The method for pre-plating a spring steel material according to claim 1 or 2, wherein the acid treatment is performed by immersing the spring steel material in the acid cleaning solution for 2 to 20 minutes.   The plating pretreatment of the spring steel material according to any one of claims 1 to 3, wherein the spring steel material subjected to at least one heat treatment selected from quenching, tempering, austempering, and strain relief annealing is subjected to the acid treatment. Method.   A method for plating a spring steel material, comprising subjecting a spring steel material selected from any one of claims 1 to 4 to a plating treatment by electroplating and no baking treatment.