KR102412428B1 - SURFACE TREATMENT COMPOSITION FOR Ni-Cr-Co ALLOY, SURFACE TREATMENT METHOD AND SURFACE-TREATED Ni-Cr-Co ALLOY - Google Patents

Abstract

An object of the present invention is to provide a Ni-Cr-Co alloy surface treatment composition for reducing friction between a surface of a Ni-Cr-Co alloy and a die surface during a drawing process.
According to the present invention, oxalic acid (C ₂ H ₂ O ₄ ); sodium nitrate (NaNO ₃ ); sodium thiosulfate (Na ₂ S ₂ O ₃ ); zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ .6H ₂ O); and cobalt(II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O). A surface treatment composition for a Ni-Cr-Co alloy is provided.

Description

Surface treatment composition for Ni-Cr-Co alloy, surface treatment method and surface-treated Ni-Cr-Co alloy

The present invention relates to a surface treatment composition for a Ni-Cr-Co alloy, a surface treatment method, and a surface-treated Ni-Cr-Co alloy.

In the drawing process, a pretreatment film is formed on the surface of the material to be drawn before the drawing process so that the lubricant can be applied smoothly during the drawing process. These lubricants act to reduce friction between the surface of the material to be drawn and the surface of the die.

In general, in the case of steel materials, a phosphate film is applied, and the stainless steel material composed of Fe-Cr-Ni does not form a phosphate reaction film due to its high corrosion resistance. A film is formed with a material produced by using the chemical reactivity of the Fe component on the surface of the material with sulfate and oxalate.

For example, Korean Patent No. 10-2006129 discloses 75 to 90% by weight of sulfates such as K ₂ SO ₄ and Na ₂ SO ₄ , 3 to 25% by weight of borate salts such as Na ₂ B ₄ O ₇ , and nonionic surfactants. A stainless steel drawing process pretreatment coating agent containing 2 to 10% by weight is proposed. In addition, US Patent Publication No. 2835616 proposes a pretreatment coating solution for stainless steel containing oxalic acid, active ions, and sodium chloride.

Ni-Cr-Co alloy is used as a material for steam turbines for power generation. The standard components of the Ni-Cr-Co alloy for steam turbines are shown in Table 1 below (Table 1: 740H alloy composition (ASME 2702)). As such, since the Ni-Cr-Co alloy for a steam turbine does not contain an Fe component, there is a problem in that a film cannot be formed through the reaction with the proposed sulfate or oxalate.

Accordingly, there is a need for a coating composition capable of forming a pre-treatment film for drawing on the surface of the Ni-Cr-Co alloy.

It is an object of the present invention to provide a Ni-Cr-Co alloy surface treatment composition for reducing friction between a surface of a Ni-Cr-Co alloy and a die surface during a drawing process.

According to one aspect of the invention, oxalic acid (C ₂ H ₂ O ₄ ); sodium nitrate (NaNO ₃ ); sodium thiosulfate (Na ₂ S ₂ O ₃ ); zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ .6H ₂ O); and cobalt(II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O). A surface treatment composition for a Ni-Cr-Co alloy is provided.

In addition, according to an aspect of the present invention, the solvent is oxalic acid; sodium nitrate; sodium thiosulfate; zinc nitrate hexahydrate; and forming a mixture by adding cobalt (II) sulfate heptahydrate, and immersing a Ni-Cr-Co alloy in the mixture to form a film on at least one surface of the Ni-Cr-Co alloy. -Cr-Co alloy surface treatment method is provided.

In addition, according to one aspect of the present invention, it comprises a Ni-Cr-Co alloy and a film formed on at least one surface of the alloy, wherein the film is oxalic acid; sodium nitrate; sodium thiosulfate; zinc nitrate hexahydrate; And there is provided a surface-treated Ni-Cr-Co alloy comprising cobalt(II) sulfate heptahydrate.

According to the present invention, the surface roughness and friction coefficient of the Ni-Cr-Co alloy surface can be reduced by forming a film by reacting the Ni-Cr-Co alloy with oxalic acid on the surface of the Ni-Cr-Co alloy.

In addition, according to the present invention, friction between the Ni-Cr-Co alloy and the die surface is reduced during the drawing process, so that the drawing process can be smoothly performed.

1 is a SEM (Scanning Electron Microscope) image of observing a film of Example 1-1 according to the present invention.
Figure 2 shows the result of analyzing the component distribution of the cross-sectional layer of the coating film of Example 1-1 according to the present invention using an EPMA (Electron Probe Micro Analyzer) device.
3 is an SEM image of a film of Comparative Example 1-7 observed.
4 and 5 are SEM images of observing the Ni-Cr-Co alloy surface of Comparative Example 2-2 and Comparative Example 3-1, respectively.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

The present invention provides a film capable of reducing friction between a surface of a Ni-Cr-Co alloy and a die surface during a drawing process, and the film can be formed using the composition including oxalic acid according to the present invention.

In the present invention, the Ni-Cr-Co alloy is a super heat-resistant alloy and is mainly used as a material for a steam turbine for power generation. As shown in Table 1, the Ni-Cr-Co alloy, for example, the 740H alloy has a relatively high concentration of Ni or Co component.

Hereinafter, a Ni-Cr-Co alloy surface treatment composition (hereinafter also referred to as 'surface treatment composition' or 'composition') according to an aspect of the present invention will be described. The surface treatment composition is oxalic acid (C ₂ H ₂ O ₄ ), sodium nitrate (NaNO ₃ ), sodium thiosulfate (Na ₂ S ₂ O ₃ ), zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ .6H ₂ O) and Cobalt(II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O) may be included.

In the present invention, oxalic acid may react with the Co component on the surface of the Ni-Cr-Co alloy to form a cobalt oxalate (Co-oxalate, CoC ₂ O ₄ ) film.

The oxalic acid may be included in an amount of 5 to 10% by weight based on the total weight of the composition. If the oxalic acid content is less than 5 wt%, the reactivity with the surface of the Ni-Cr-Co alloy may be weak, so that it may be difficult to form a film. On the other hand, when the oxalic acid content exceeds 10% by weight, the reactivity with the surface of the Ni-Cr-Co alloy is excellent, but there is a problem in that the friction coefficient of the film is greatly increased.

In the present invention, sodium nitrate is a component that generates Co ions on the surface of the Ni-Cr-Co alloy, and may be included in 3 to 5% by weight based on the total weight of the composition. When the sodium nitrate content is less than 3% by weight, the amount of Co ions produced is reduced, and accordingly, the cobalt oxalate film may not be properly formed, and thus the friction coefficient of the film may be greatly increased. On the other hand, when the content of sodium nitrate exceeds 5% by weight, the effect of improving the film performance is insignificant, but it is not preferable because precipitate crystals are formed in the composition to interfere with film formation.

In the present invention, sodium thiosulfate acts as a catalyst for accelerating the reaction of sodium nitrate to produce Co ions. The sodium thiosulfate may be included in an amount of 0.1 to 0.3% by weight based on the total weight of the composition. If the sodium thiosulfate content is less than 0.1% by weight, the amount of Co ions produced decreases and the film crystals are not easily formed. .

In the present invention, zinc nitrate hexahydrate is a component added to supply zinc ions into the cobalt oxalate film. Zinc ions exist in the form of zinc oxide (ZnO) in the film, and can further reduce the friction coefficient of the finally formed film due to the layered structure of zinc oxide.

In this case, the zinc nitrate hexahydrate may be included in an amount of 0.1 to 0.3 wt% based on the total weight of the composition. When the content of zinc nitrate hexahydrate is less than 0.1% by weight, the effect of reducing the friction coefficient of the film is insignificant, whereas when the content of zinc nitrate hexahydrate exceeds 0.3% by weight, a film is formed with a film thickness of 0.1 μm or less, which is suitable for the drawing process. It is difficult to form a film, and there is a problem in that the friction coefficient of the film increases.

The present invention may include a component for additionally supplying Co ions in addition to Co ions generated from the Ni-Cr-Co alloy in order to promote the formation of the cobalt oxalate film. The component for additionally supplying Co ions may be, for example, cobalt(II) sulfate heptahydrate.

In the present invention, cobalt(II) sulfate heptahydrate may be included in an amount of 0.5 to 1% by weight based on the total weight of the composition. If the content of cobalt(II) sulfate heptahydrate is less than 0.5% by weight, the amount of Co ions required to form the cobalt oxalate film is too small, so that the film may not be formed well. On the other hand, when the content of cobalt(II) sulfate heptahydrate exceeds 1% by weight, precipitate crystals are formed in the composition, which is not preferable because it may interfere with film formation.

Next, a method for forming a film on a Ni-Cr-Co alloy using the surface treatment composition according to the present invention will be described.

In order to form a film on the Ni-Cr-Co alloy, first, oxalic acid, sodium nitrate, sodium thiosulfate, zinc nitrate hexahydrate and cobalt(II) sulfate heptahydrate are added to a solvent to form a mixture, and Ni-Cr is added to the mixture. -Co alloy can be immersed.

In the present invention, the solvent is not particularly limited, and may be, for example, distilled water. In this case, the temperature of the solvent may be maintained at 70 to 90° C., and if the temperature of the solvent is less than 70° C., dissolution of the compounds added to the solvent may not be smooth, and thus may not be suitable for film formation. If the temperature of the solvent exceeds 90° C., while it does not significantly affect the film formation, loss may occur due to evaporation of the solution.

The order in which oxalic acid, sodium nitrate, sodium thiosulfate, zinc nitrate hexahydrate and cobalt(II) sulfate heptahydrate are added to the solvent is not particularly limited. However, in the case of sodium thiosulfate, the longer the time it remains in solution after being added to the solvent, the worse the film performance, so it is preferable to add it last.

The mixture comprises, based on the total weight of the mixture, 5 to 10% by weight of oxalic acid; 3 to 5% by weight of sodium nitrate; 0.1 to 0.3% by weight of sodium thiosulfate; 0.1 to 0.3 wt% of zinc nitrate hexahydrate; and 0.5 to 1 wt% of cobalt(II) sulfate heptahydrate.

The immersion time of the Ni-Cr-Co alloy in the present invention may be 45 to 90 minutes. If the immersion time is less than 45 minutes, the preheating time of the material may be insufficient, and thus it may be difficult to form an effective film layer. On the other hand, if the immersion time exceeds 90 minutes, the film is excessively formed, making the surface rough or the coarse film crystals are broken, contaminating the surface treatment solution and forming a precipitate.

By performing the film forming process as described above, it is possible to obtain a Ni-Cr-Co alloy and a surface-treated Ni-Cr-Co alloy including a film formed on at least one surface of the alloy.

The coating may include 5 to 10% by weight of oxalic acid, based on the total weight of the coating; 3 to 5% by weight of sodium nitrate; 0.1 to 0.3% by weight of sodium thiosulfate; 0.1 to 0.3 wt% of zinc nitrate hexahydrate; and 0.5 to 1 wt% of cobalt(II) sulfate heptahydrate.

The film formed according to the present invention may have a surface roughness (Ra) of 5 μm or less, preferably 1 to 3 μm, and a friction coefficient of 3 μm or less, preferably 0.5 to 1 μm. When the film has a surface roughness (Ra) and a coefficient of friction within the above ranges, the Ni-Cr-Co alloy can be easily applied to the drawing process.

Example

Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for understanding of the present invention, and do not limit the present invention.

[Examples 1-1 to 1-2, Comparative Examples 1-1 to 1-16]

1. Preparation of coating solution

1 L of distilled water was put into a beaker and heated to 70 to 90° C. while stirring on a stirrable hot plate. While continuously stirring, when distilled water reaches the solution temperature (70 ℃ ~ 90 ℃) in Table 2 below, oxalic acid, sodium nitrate. Zinc nitrate hexahydrate and cobalt(II) sulfate heptahydrate were sequentially added and dissolved in the amounts shown in Table 2 below. Finally, sodium thiosulfate was added and completely dissolved to prepare a coating solution for a Ni-Cr-Co alloy.

2. Ni-Cr-Co alloy film formation

The surface of the Ni-Cr-Co alloy (740H alloy) specimen was cut using an end mill, and the specimen was washed with alcohol to remove the processing oil and then dried. The specimen was immersed in the prepared film treatment solution for Ni-Cr-Co alloy for 30 to 95 minutes as shown in Table 2 below, and then taken out, washed three times in clear water and dried to form a film.

Furtherance solution
temperature
(℃) immersion
hour
(minute) oxalic acid
(weight%) sodium nitrate
(weight%) thiosulfuric acid
salt
(weight%) zinc nitrate
hexahydrate
(weight%) Cobalt (II) sulfate
heptahydrate
(weight%) Example 1-1 5 4 0.3 0.1 0.5 85 45 Example 1-2 5 4 0.3 0.1 0.5 90 45 Comparative Example 1-1 10 2 0.2 0.1 0.5 85 90 Comparative Example 1-2 10 2 0.4 0.1 One 75 45 Comparative Example 1-3 5 2 0.2 0.2 One 85 45 Comparative Example 1-4 5 2 0.4 0.2 0.5 75 90 Comparative Example 1-5 10 4 0.4 0.2 One 85 90 Comparative Example 1-6 12 2 0.2 0.1 0.5 85 90 Comparative Example 1-7 4 4 0.4 0.1 0.5 70 45 Comparative Examples 1-8 5 2 0.2 0.1 One 75 90 Comparative Example 1-9 10 6 0.4 0.1 One 75 45 Comparative Example 1-10 10 4 0.05 0.2 0.5 75 45 Comparative Example 1-11 5 2 0.3 0.05 One 85 45 Comparative Example 1-12 5 2 0.3 0.35 0.5 75 90 Comparative Example 1-13 10 4 0.3 0.2 0.4 85 90 Comparative Example 1-14 10 4 0.3 0.2 1.5 85 90 Comparative Example 1-15 5 4 0.3 0.1 0.5 85 30 Comparative Examples 1-16 5 4 0.3 0.1 0.5 85 95

[Comparative Examples 2-1 to 2-5]

1 L of distilled water was added to a beaker and heated to 75 to 90° C. while stirring on a stirrable hot plate. While continuously stirring, when distilled water reaches the solution temperature (75 ℃ ~ 90 ℃) of Table 3, a mixture of K ₂ SO4 and Na ₂ SO ₄ , Na ₂ B ₄ O ₇ , and a nonionic surfactant in the table below After adding as in 3, it was dissolved to prepare a solution (A).

The surface of the Ni-Cr-Co alloy (740H alloy) specimen was cut using an end mill, and the specimen was washed with alcohol to remove the processing oil and then dried. The specimen was immersed in the prepared solution (A) for 30 to 90 minutes as shown in Table 3 below, taken out, washed three times in clear water, and dried.

Furtherance solution
temperature
(℃) immersion
hour
(minute) K ₂ SO4+Na ₂ SO ₄
mixture
(weight%) Na ₂ B ₄ O ₇
(weight%) Nonionic surfactant
(weight%) Comparative Example 2-1 85 10 5 85 90 Comparative Example 2-2 75 15 10 85 90 Comparative Example 2-3 90 5 5 85 90 Comparative Example 2-4 85 10 5 90 90 Comparative Example 2-5 85 10 5 75 30

[Comparative Examples 3-1 to 3-4]

1 L of distilled water was added to a beaker and heated to 75 to 90° C. while stirring on a stirrable hot plate. While stirring continuously, when distilled water reaches the solution temperature (75 ℃ ~ 90 ℃) in Table 4, oxalic acid, iron (iron) as activating ions, and sodium chloride (NaCl) are added as shown in Table 4 below and dissolved to dissolve the solution ( B) was prepared.

The surface of the Ni-Cr-Co alloy (740H alloy) specimen was cut using an end mill, and the specimen was washed with alcohol to remove the processing oil and then dried. The specimen was immersed in the prepared solution (B) for 30 to 90 minutes as shown in Table 4 below, taken out, washed three times in clear water, and dried.

Furtherance solution
temperature
(℃) immersion
hour
(minute) oxalic acid
(g/L) Activating ion
(g/L) NaCl
(g/L) Comparative Example 3-1 19.6 7 18.5 85 90 Comparative Example 3-2 19.6 7 18.5 80 90 Comparative Example 3-3 19.6 7 18.5 90 90 Comparative Example 3-4 19.6 7 18.5 75 30

[Evaluation of physical properties of Ni-Cr-Co alloy film]

1. Film thickness measurement

After electron beam etching of the surface layer of the Ni-Cr-Co alloy specimen using FIB (Focused Ion Beam) equipment, the film thickness was repeatedly measured three times at different positions through an electron microscope. It is shown in Table 5 below.

2. Surface roughness measurement

Using Taylor Hobson's Form Talysurf PGI equipment, the Ni-Cr-Co alloy specimen was measured three times with a measuring length of 4 mm (0.8 mm × 5 sections) by the stylus type surface roughness measurement method, and the average roughness (Ra) The values are shown in Table 5 below.

3. Measurement of coefficient of friction

The test material was used as the surface of the Ni-Cr-Co alloy specimen on which the film was formed, and the counter material was a cemented carbide (WC) material with a tip having a diameter of 3 mm, and the surface roughness Ra was polished to a level of 0.02 to 0.03 μm. The friction coefficient was measured three times for each specimen under a friction test load of 80 MPa, a friction speed of 600 mm/min, and a measurement length of 20 mm, and the average values thereof are shown in Table 5 below.

characteristic Film thickness (μm) Film roughness (Ra) (μm) Friction coefficient (μ, 20℃) Example 1 3.5 0.67 0.0747 Example 2 3.6 0.68 0.0847 Comparative Example 1-1 5.3 3.17 0.2674 Comparative Example 1-2 2.3 3.68 0.2631 Comparative Example 1-3 2.2 0.88 0.2506 Comparative Example 1-4 2.5 2.97 0.3148 Comparative Example 1-5 2.2 3.41 0.2770 Comparative Example 1-6 4.0 3.50 0.3255 Comparative Example 1-7 0.5 0.55 0.2745 Comparative Examples 1-8 3.8 3.75 0.2865 Comparative Example 1-9 2.2 3.67 0.2731 Comparative Example 1-10 1.5 1.46 0.1832 Comparative Example 1-11 2.0 1.25 0.2816 Comparative Example 1-12 2.5 3.57 0.3748 Comparative Example 1-13 1.2 1.41 0.2570 Comparative Example 1-14 2.0 2.41 0.2850 Comparative Example 1-15 0.7 1.37 0.1657 Comparative Examples 1-16 4.6 3.25 0.2725 Comparative Example 2-1 0 - - Comparative Example 2-2 0 - - Comparative Example 2-3 0 - - Comparative Example 2-4 0 - - Comparative Example 2-5 0 - - Comparative Example 3-1 0 - - Comparative Example 3-2 0 - - Comparative Example 3-3 0 - - Comparative Example 3-4 0 - -

In Examples 1-1 and 1-2, films having a thickness of 3.5 μm and 3.6 μm, respectively, were formed. In addition, the film had surface roughness of 0.67 μm and 0.68 μm, and friction coefficients of 0.0747 μm and 0.0847 μm, respectively. As such, when a film is formed on the surface of a Ni-Cr-Co alloy using the composition according to the present invention, a film having a low surface roughness and a low coefficient of friction is formed, so that a film suitable for the drawing process can be obtained.

1 is an observation of the coating film of Example 1-1 with a scanning electron microscope (SEM). It can be seen from FIG. 1 that a dense film was formed on the surface of the Ni-Cr-Co alloy specimen.

2 is an electron beam etching process using the FIB (Focused Ion Beam) equipment on the film surface of the Ni-Cr-Co alloy specimen of Example 1-1, and then EPMA (Electron Probe Micro Analyzer) equipment The film layer etched using the equipment The results of component distribution analysis for the cross section are shown. In FIG. 2, (a) to (f) are visual representations of the distribution of component elements present in the area by sensing the intrinsic wavelengths of component atoms emitted from the analysis surface of the cross section of the coating layer, (a): O-KA, (b): S-KA, (c): Co-KA, (d): Fe-KA, (e): Ni-KA, (f): Cr-KA. As shown in Fig. 2(c), a large amount of the wavelength of the Co component element was detected from the surface corresponding to the coating layer, and it was observed as a dark purple region.

On the other hand, in Comparative Examples 1-1 to 1-16, a film having a large surface roughness and a coefficient of friction was formed. 3 is an SEM image of a film of Comparative Example 1-7 observed. Referring to FIG. 3 , it can be seen that when the content of oxalic acid is low, the film is not well formed. The film of Comparative Example 1-7 exhibited a coefficient of friction of 0.2745 μ, which was not suitable for the drawing process.

In Comparative Examples 2-1 to 2-5 and Comparative Examples 3-1 to 3-4, no film was formed. 4 and 5 are SEM images of observing the surface of the Ni-Cr-Co alloy specimen of Comparative Example 2-2 and Comparative Example 3-1, respectively. In FIGS. 4 and 5 , the crystals and contaminants of the surface treatment solution were easily peeled off with only a slight contact in the dry state. Therefore, since the material cannot serve as a film, it cannot be considered that a film is formed.

Claims (8)

oxalic acid (C ₂ H ₂ O ₄ ); sodium nitrate (NaNO ₃ ); sodium thiosulfate (Na ₂ S ₂ O ₃ ); zinc nitrate hexahydrate (Zn(NO ₃ ) ₂ .6H ₂ O); and cobalt(II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O). A surface treatment composition for a Ni-Cr-Co alloy.
According to claim 1,
5 to 10% by weight of oxalic acid, based on the total weight of the composition; 3 to 5% by weight of sodium nitrate; 0.1 to 0.3% by weight of sodium thiosulfate; 0.1 to 0.3 wt% of zinc nitrate hexahydrate; and 0.5 to 1% by weight of cobalt(II) sulfate heptahydrate. A surface treatment composition for a Ni-Cr-Co alloy.
oxalic acid in solvent; sodium nitrate; sodium thiosulfate; zinc nitrate hexahydrate; and cobalt(II) sulfate heptahydrate to form a mixture, and
Forming a cobalt oxalate (Co-oxalate, CoC ₂ O ₄ ) film on at least one surface of the Ni-Cr-Co alloy by immersing the Ni-Cr-Co alloy in the mixture.
A surface treatment method of a Ni-Cr-Co alloy comprising a.
4. The method of claim 3,
The temperature of the solvent is a surface treatment method of a Ni-Cr-Co alloy of 70 to 90 ℃.
4. The method of claim 3,
The mixture, based on the total weight of the mixture, 5 to 10% by weight of oxalic acid; 3 to 5% by weight of sodium nitrate; 0.1 to 0.3% by weight of sodium thiosulfate; 0.1 to 0.3 wt% of zinc nitrate hexahydrate; and 0.5 to 1 wt% of cobalt(II) sulfate heptahydrate.
4. The method of claim 3,
The immersion time of the Ni-Cr-Co alloy is a surface treatment method of a Ni-Cr-Co alloy of 45 to 90 minutes.
Ni-Cr-Co alloy and
Including a cobalt oxalate (Co-oxalate, CoC ₂ O ₄ ) film formed on at least one surface of the alloy,
The coating film is oxalic acid; sodium nitrate; sodium thiosulfate; zinc nitrate hexahydrate; and a surface-treated Ni-Cr-Co alloy comprising cobalt(II) sulfate heptahydrate.
8. The method of claim 7,
The coating may include, based on the total weight of the coating, 5 to 10% by weight of oxalic acid; 3 to 5% by weight of sodium nitrate; 0.1 to 0.3% by weight of sodium thiosulfate; 0.1 to 0.3 wt% of zinc nitrate hexahydrate; and 0.5 to 1% by weight of cobalt(II) sulfate heptahydrate.

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