JPH0525606A - Chromium oxide thermal spraying material and production thereof - Google Patents

Abstract

PURPOSE:To provide the thermal spraying material from which a thermally sprayed film having excellent wear resistance and corrosion resistance and excellency in terms of finish surface roughness can be formed and the process for production of such material by providing the process for production for obtaining the calcined chromium oxide thermal spraying material at a relatively low calcination temp. to obtain the chromium oxide thermal spraying material having a lower content of metal chromium without secondary treating stages and by providing the chromium oxide thermal spraying material suitable for thermal spraying in grain size distribution and particle size. CONSTITUTION:The sintered chromium oxide thermal spraying material consisting of the chromium oxide having >=97.5wt.% purity and titanium oxide having 0.05 to 2.0wt.% and having <=0.5wt.% metal chromium content is obtd. by selecting chromium oxide raw materials in the process for production consisting in uniformly coating the surface of the chromium oxide with the titanium oxide and calcining the chromium oxide for 10 minutes to 10 hours at 1100 to 1500 deg.C, then disintegrating and sizing the chromium oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal spray material for forming a thermal spray coating having excellent wear resistance, corrosion resistance and finished surface roughness as compared with a conventional thermal spray coating using a chromium oxide thermal spray material. The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art Chromium oxide has a high melting point (2435).
°), high hardness (formerly Mohs hardness of 8.5) and chemically stable, the chromium oxide sprayed coating is expected to have excellent performance as a wear-resistant and corrosion-resistant protective coating.

Chromium oxide sprayed materials are generally manufactured by melting raw materials, solidifying, crushing and sizing. However, since this chromium oxide has a property of releasing oxygen at a high temperature and easily producing metallic chromium, 1 to 5% by weight of metallic chromium is usually produced in the above melting step. It is difficult to remove this metallic chromium due to the manufacturing method of the powder material for thermal spraying, and it is inevitable that most of the mixed metallic chromium remains as it is in the thermal spray coating even in the end. The presence of this metallic chromium significantly deteriorates the quality characteristics required for the chromium oxide sprayed coating, that is, high hardness, wear resistance, and corrosion resistance, and makes it difficult to form a sprayed coating having excellent finished surface roughness.

For example, a chromium oxide sprayed coating is expected to have its original properties, and is used for corrosion resistance and wear resistance at 200 ° C. or lower, that is, the inner wall of a pump component for transporting chemicals having a strong corrosive power, and fibers. It is used in a wide range of fields, such as industrial transport roll surfaces and general mechanical parts, but the presence of metallic chromium, which has low hardness and is vulnerable to abrasion resistance and chemical corrosion, reduces wear resistance and causes thermal spraying. It is known that the original chemical corrosion resistance of the coating is significantly deteriorated.

In order to improve such problems, the present inventors have previously provided the following production method capable of reducing the content of metallic chromium.

JP-A-62-63659 Japanese Patent Laid-Open No. 62-63659 discloses a method in which an oxide powder containing a chromium oxide powder is melted, solidified, crushed and classified, and then the melted melt and an oxygen-containing gas are contacted and reacted with each other, and The method of reducing the content of metallic chromium in the above item to 0.5% by weight or less.

Japanese Laid-Open Patent Publication No. 62-63660 discloses that when oxide powder containing chromium oxide powder is melted and solidified, and then pulverized and classified, 5-10 by pulverization and classification.
A method of obtaining a powder material of 0 μm, baking the powder material in a high temperature oxidizing atmosphere, and making the content of metallic chromium in the powder 0.5 wt% or less.

[Patent Document 1] JP-A-62-63661 When the oxide powder containing the chromium oxide powder is melted and solidified, and then pulverized and classified, 5 to 10 are obtained by the pulverization and classification.
A method for obtaining a powder material of 0 μm and pickling the powder material so that the content of metallic chromium in the powder is 0.5% by weight or less.

Japanese Patent Laid-Open No. 62-63662 discloses that oxide powder containing chromium oxide powder is melted and solidified, and then pulverized and classified.
A powder material of 0 μm was obtained, and the content of metallic chromium in the powder was 0.5% by weight by separating the powder material by specific gravity.
How to: Further, in general, a thermal spray material is sprayed by using a flame or a plasma spray system, and in order to form a spray coating having excellent adhesion strength, it is necessary to sufficiently melt the flame flame and the plasma flame, and the particle size thereof. Distribution width is 105-5 μm, average particle size is 50-1
0 μm is desirable. Further, since the thermal spray powder is supplied to the thermal spray gun using a carrier tube or the like, the fluidity affects the quality of the coating, and if the fluidity is poor, the coating of the desired quality cannot be obtained. In order to improve the fluidity during transportation,
It is desired that there is no edge surface in the particle shape and that the particle shape is substantially spherical, that is, spherical or blocky.

[0010]

Since chromium oxide is difficult to sinter, it is difficult to obtain an appropriate particle size that enables thermal spraying, and the firing temperature becomes high when the sintering method is used. Therefore, there is a problem in terms of equipment.

Further, when the melting step is used, as described above, usually 1 to 5% by weight of metallic chromium is produced in the sprayed powder, and the quality characteristics inherent to chromium oxide are significantly deteriorated. As a manufacturing method for removing metallic chromium of a thermal spray material in order to improve these, as described in JP-A-62-63659.
Of reacting the melt of No. 3 with an oxygen-containing gas, JP-A-62-62
No. 63660, a bi-baking treatment method in a high temperature oxidizing atmosphere,
The pickling treatment method of JP-A-62-63661 and the specific gravity separation method of JP-A-62-63661 are provided, and all of these production methods use an electromelt pulverized product as a starting material. Therefore, there is a problem that a complicated secondary process is required to remove the chromium metal in the starting material, and there is a problem in the fluidity of the sprayed powder obtained.

As will be described later, these thermal spray materials have a chemical composition of 50% by weight of Al ₂ O ₃ and Cr ₂ O _3.
Is a thermal spray material containing 50% by weight of chromium oxide and does not contain chromium oxide as a main component.

Therefore, the object of the present invention is to firstly provide a manufacturing method and a thermal spray obtained by which a chromium oxide spray material having a low metal chromium content can be directly obtained without requiring a complicated secondary treatment step. We are in the area of providing materials.

Another object of the present invention is to provide a thermal spray material having a particle size distribution suitable for melting in a flame flame and a plasma flame and having a particle shape suitable for fluidity.

Further, by this, it is possible to solve all the problems in the above-mentioned conventional chromium oxide sprayed material, and to form a sprayed coating excellent in wear resistance and corrosion resistance and also in terms of finished surface roughness. It is intended to provide a new thermal spray material and a method for manufacturing the same.

[0016]

SUMMARY OF THE INVENTION The inventors of the present invention firstly proposed that a chromium oxide spray material can be manufactured by a sintering method at a relatively low firing temperature by selecting an additive material that can serve as a sintering aid. I got the knowledge. That is, it was confirmed that when titanium oxide was selected as a sintering aid and titanium oxide was uniformly coated on the surface of chromium oxide and fired, firing could be performed at a relatively low temperature.

That is, the present invention has developed a method for producing a sintered chromium oxide sprayed material, in which the surface of chromium oxide is uniformly coated with titanium oxide and is fired at a temperature of 1100 to 1500 ° C. for 10 minutes to 10 hours. After that, it is characterized by crushing and sizing.

If the purity of chromium oxide used as the starting material is 98% or more and the content of metallic chromium is 0.5% by weight or less, preferably 0.1% by weight or less, the purity of chromium oxide is 97.5% by weight or more. And has a metallic chromium content of 0.
5% by weight or less, preferably 0.1% by weight or less, of a sintered chromium oxide spray material is obtained.

The average particle size of chromium oxide used as a starting material is preferably 1 to 5 μm in order to uniformly coat the surface of the raw material with titanium oxide fine powder added as a sintering aid. When the average particle size is smaller than 1 μm, the particle size is almost the same as the titanium oxide fine powder of the sintering aid to be coated,
Titanium oxide is not uniformly coated on the surface of chromium oxide, and chromium oxide raw materials are bonded to each other, which makes sintering difficult. Further, since it becomes difficult to uniformly disperse the titanium oxide, agglomerated particles of titanium oxide which are not coated are generated on the surface of the chromium oxide, which deteriorates the film characteristics. When the average particle diameter exceeds 5 μm, sintering itself does not proceed unless a large amount of titanium oxide is added, and excess titanium oxide remaining in the coating deteriorates the coating characteristics.

Chromium oxide as a starting material is produced by a dry method, that is, a product obtained by adding a reducing agent to anhydrous sodium dichromate and baking it is used. The amount of chromium as well as the average particle size can be obtained. If the content of metallic chromium is more than 0.5% by weight, the content of metallic chromium in the thermal spray coating also increases and the coating properties are significantly deteriorated, so that further secondary treatment is required. Titanium oxide added as a sintering aid uniformly coats the chromium oxide surface as described above,
In order to improve the sinterability of the chromium oxide raw material and not to lose the original film characteristics of chromium oxide, it is necessary to make the average particle diameter fine and to add a small amount. If the amount added is less than 0.05% by weight, sintering will not proceed. If it is more than 2% by weight, the coating properties are deteriorated. Further, it is desirable that the average particle diameter is 1.0 μm or less, preferably 0.3 μm or less in order to uniformly coat the chromium oxide surface.
When the average particle size is larger than 1.0 μm, it becomes difficult to uniformly coat the surface of chromium oxide.

As a method for uniformly coating the surface of chromium oxide with titanium oxide, mixing may be performed using a stirrer such as a universal stirrer.

The firing atmosphere is preferably an oxidizing atmosphere in order to prevent the reduction reaction of chromium oxide to metallic chromium. If the firing temperature is selected within the range of 1100 to 1500 ° C., satisfactory results can be obtained, preferably 1300 to 145.
0 ° C is suitable.

If the temperature is 1100 ° C. or lower, the firing time must be long in order to sufficiently advance the sintering and obtain the particle diameter and particle shape suitable for thermal spraying.

On the other hand, if the temperature exceeds 1500 ° C., the sintering proceeds excessively and the average particle size becomes coarse, and a post-process such as pulverization is required. In addition, equipment costs such as a firing furnace also increase.

The firing time is not particularly limited, but it is preferable that the firing time is long when firing at a low temperature, and the firing time is short when firing at a high temperature. Usually, it can be selected within the range of 10 minutes to 10 hours.

The particle shape of the obtained thermal spray material does not have an edge surface because it has not undergone a crushing step unlike conventional electromelted products and sintered products, and has a spherical or elliptical spherical shape, which is excellent in fluidity. ing. Also, its particle size distribution range is 1
The average particle size is 05 to 5 μm, and the average particle size is 10 to 50 μm. The yield does not decrease due to the pulverizing step as in the conventional method, and the yield is improved to 115 to 140% as compared with the conventional method.

[0027]

According to the manufacturing method of the present invention, by using chromium oxide and titanium oxide as starting materials, 1100
Directly sintered chromium oxide thermal spray materials can be produced at firing temperatures of ~ 1500C.

Therefore, by selecting the purity of chromium oxide and the content of metal chromium, it is possible to easily obtain a sintered chromium oxide spray material having a low content of metal chromium and high purity of chromium oxide.

After firing, only crushing and sizing are required, and no secondary treatment step is required. Further, the obtained sintered chromium oxide exhibits a spherical shape or an approximately spherical shape of an elliptic sphere, is excellent in fluidity, is easy to obtain a good quality coating, and has a particle size distribution range of 105 to 5 μm and an average particle diameter of 10-. Since a particle size of 50 μm is obtained, a particle size suitable for melting in a flame flame and a plasma flame is obtained, and the yield does not decrease due to the pulverization process.

Therefore, it is possible to form a sprayed coating excellent in high hardness, abrasion resistance, and corrosion resistance as compared with a conventional sprayed coating using a sprayed material, and also in terms of finished surface roughness.

[0031]

EXAMPLES The present invention will now be described in detail with reference to examples.

[Example 1] Commercially available dry process chromium oxide ("Chromium oxide No. 80" manufactured by Nippon Denko KK, Cr ₂ O)
₃ : 98.5% or more, average particle size: 1.0, 3.0 and 5.0 μm and commercially available titanium oxide (TiO ₂ : 99.0).
% Or more, average particle size: 0.3 and 1.0 μm),
Each was stirred and mixed using a universal stirrer to coat the surface of chromium oxide with titanium oxide.

After the coating was completed, a firing treatment was carried out using an electric furnace for a silicon carbide based heating element at 1350 ° for a holding time of 3 hours. The obtained sintered powder is crushed, and after removing 75 μm above using a sieving mesh without going through a crushing step, 10 μm or less is also removed using a wet classification method 75-10 μm
A thermal spray material having an average particle diameter of 26-34 μm was obtained. The quality characteristics of the starting material and the thermal spray material are shown in Tables 1 and 2.

For the thermal spraying, a plasma spraying apparatus was used, and argon and hydrogen were used as working gases, and the thermal spraying was carried out on a substrate of SUS-304 steel plate of 50 × 50 × 10 mm so that the film thickness was 200 μm.

Further, sample numbers 1 to 6 were prepared as comparative examples. In Sample Nos. 1 to 5, the chromium oxide raw material was the same as that of the product of the present invention, but the average particle diameter thereof was different (Sample Nos. 1 and 2), and the average particle diameter of titanium oxide was different ( Sample No. 3) The samples (Sample Nos. 4 and 5) having different amounts of titanium oxide added were prepared.

Sample No. 1: Starting material having a small average particle diameter of chromium oxide of 0.5 μm Sample No. 2: Starting material having an average particle diameter of 7.0
μm and Coarse Sample No. 3: Titanium oxide used for coating has an average particle size of 2.0 μm and Coarse Sample No. 4: Titanium oxide addition is as small as 0.03% Sample No. 5: Titanium oxide addition As many as 3.00% Sample No. 6: Conventional product (commercial electrofused pulverized product) As the quality characteristics of the sprayed powder, as shown in Tables 1 and 2, chemical composition, metallic Cr content, particle size distribution, average The particle size, yield, and fluidity were measured.

The metal Cr was analyzed by immersing the sample in 50 cc of a 1: 1 (volume ratio) solution of hydrochloric acid of a reagent grade and pure water, leaving it for one day and night, then boiling for 15 minutes, cooling and filtering. After that, the filtered water was quantitatively analyzed by an atomic absorption spectrometer and measured.

The yield was obtained by measuring the ratio of 75-10 μm suitable for thermal spraying in the total amount of the obtained sintered powders, and the value of sample No. 6 was set to 100 and expressed as an index. The fluidity was measured according to JIS Z-2502 (metal powder fluidity test method).

[0039]

[Table 1]

[0040]

[Table 2]

The quality characteristics of the thermal spray coating include hardness (Hv
₃₀₀ ), diamond grinding wheel (#
At 600), the average surface roughness (Ra) after grinding and finishing, the specific wear amount and the corrosion resistance were measured. The results are shown in Table 3.
Shown in.

The specific wear amount was measured using an Ogoshi rapid wear tester at room temperature under the following measurement conditions.

Polishing rotator material: SUJ-2 (H _RC 60) Abrasion speed: 1.37 m / sec Abrasion distance: 200 m Final load: 12.6 kg Corrosion resistance test was conducted with concentrated nitric acid. Apply and 100 at room temperature
After standing for a period of time, the cross section of the coating film was cut and the degree of erosion of the base material was measured.

[0044]

[Table 3]

Sample Nos. 1 to 4 used as comparative examples have the same chromium oxide as that of the present invention and are manufactured by the sintering method. No progress was made, and all of the obtained thermal spray powders were as fine as 30 μm or less, and the yield was 35 to 45%, which is worse than that of the conventional electrofused pulverized product (Comparative Example 6). In addition, since the sintering was incomplete even during the thermal spraying, the fluidity was poor, and the nozzle was clogged to make the thermal spraying impossible. The thermal spray coating using sample number 5 is
Conventional product (Sample No. 6, electro-fused crushed product with metallic Cr 1.52)
%, And has a large number of edge faces. 2), the amount of metallic Cr is reduced and the corrosion resistance is improved,
Since 3% solid solution of titanium oxide, the coating hardness is 112
It is as low as 0 and the specific wear amount is 20 × 10 ⁻⁸ mm ³ / kg · m, which is almost the same as the conventional product.

On the other hand, sample No. 7 to
No. 13 does not have an edge surface because the particle shape of the obtained thermal spray material does not go through a crushing step like a conventional electromelted product, and exhibits a spherical shape or an approximately elliptic spherical shape (sample number 8, see FIG. 1), Excellent fluidity and 1 yield compared to conventional products
It is improved to 15 to 140%.

The product of the present invention has a chromium oxide purity of 9%.
It has a high hardness of 7.5% or more, a low content of metallic chromium of 0.08% or less, and an excellent particle shape. Therefore, the thermal spray coating using these thermal spray materials has a high hardness of 1200 or more, Specific wear amount is also 5-10 × 10 ^-8 mm ³ / kg ・ m
And improve. In addition, the corrosion resistance is about 2 compared to the conventional electrofused crushed product.
Improved by 5%. Further, the surface average roughness (Ra) is also 0.2.
It is as small as 5 μm or less, and the appearance after grinding is excellent.

[0048]

As described in detail above, the present invention can provide a method for producing a chromium oxide spray material which can be produced by a sintering method at a relatively low firing temperature, and a sintered chromium oxide spray material obtained thereby. Therefore, by selecting the purity of chromium oxide, it is possible to easily obtain a chromium oxide spray material having a low content of metallic chromium without going through a complicated secondary treatment step.

The obtained sintered chromium oxide thermal spray material has a preferable particle size distribution as a thermal spray material,
In addition to improving the yield, the desired product particles are obtained by crushing and sizing, so the particle shape is approximately spherical,
It has excellent fluidity and also has the advantage that it is easy to obtain a good quality coating.

Therefore, the thermal spray coating using this thermal spray material exhibits high hardness, wear resistance, and corrosion resistance, so that the service life of the base alloy can be extended and the finished surface can be improved. It is a thing.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle shape of a sintered chromium oxide spray material according to the present invention,

FIG. 2 is an electron micrograph showing the particle shape of a conventional electrofused pulverized product,

Claims (6)

[Claims] 1. A calcination characterized by comprising chromium oxide having a purity of 97.5% by weight or more and titanium oxide of 0.05 to 2.0% by weight, and having a metal chromium content of 0.5% by weight or less. Chromium oxide oxide thermal spray material. 2. The sintered chromium oxide spray material according to claim 1, wherein the content of metallic chromium is 0.1% by weight or less. 3. The sintered chromium oxide thermal spray material according to claim 1, wherein the particle shape is substantially spherical and the average particle diameter is 10 to 50 μm. 4. The surface of chromium oxide is uniformly coated with titanium oxide, and the temperature is 1100 to 1500 ° C. for 10 minutes to 1 minutes.
A method for producing a sintered chromium oxide spray material, which comprises crushing and sizing after firing for 0 hour. 5. Chromium oxide as a starting material has a purity of 9
The method for producing a sintered chromium oxide thermal spray material according to claim 4, wherein the content of metallic chromium is 8% or more, the content of metallic chromium is 0.5% by weight or less, and the average particle diameter is 1 to 5 μm. 6. Titanium oxide as a starting material has a purity of 9
The average particle size is 8% or more and the average particle size is 1.0 μm or less.
A method for producing a sintered chromium oxide thermal spray material as described.