JPH04308072A - Aluminum diffusion coating agent and treatment using the same - Google Patents

Abstract

PURPOSE:To form a fine aluminide layer at a low cost by diffusion coating with Al powder. CONSTITUTION:An Al diffusion coating agent is composed of 5-15wt.% Al powder, Cr powder in 1-2 weight ratio to the Al powder, 0.1-5wt.% ammonium chloride and the balance sintering inhibitor. A body to be treated is embedded in above coating agent and heated in a non-oxidizing atmosphere.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an aluminum diffusion coating using a powder method, which is widely adopted for the purpose of imparting heat resistance, corrosion resistance, sulfidation resistance, and carburization resistance to metal parts and extending the life of the parts. This invention relates to a processing agent and a processing method using the same.

0002

2. Description of the Related Art In general, an aluminum diffusion coating treatment method using a powder pack method is widely employed for the purpose of improving the oxidation resistance and high temperature corrosion resistance of heat-resistant members and extending the life of the members.

Among them, Ni-Cr heat-resistant steel, typically JIS steel, has been used as a reaction tube material for heating and thermally decomposing hydrocarbons such as naphtha to high temperatures, such as cracking tubes used in ethylene production equipment in the petroleum industry. N.C.
F800H steel or heat-resistant cast steel containing Ni and Cr, typically ASTM HP material (equivalent to JIS SCH24), is used as the reaction tube material, and aluminum diffusion coating is used to further strengthen carburization resistance and extend the life of the reaction tube. The treated steel pipes are now in practical use.

In recent years, in order to increase the efficiency of thermal decomposition and improve the yield of ethylene, operating conditions have become harsher, and the reaction tube temperature has decreased to 1.
Although the temperature reaches as high as 100°C, carbon produced by thermal decomposition of hydrocarbons adheres to the surface of the reaction tube and causes coking, which lowers the temperature of the surface of the reaction tube and impairs the efficiency of thermal decomposition.

As a countermeasure, generally a reaction tube material with a smooth surface is used to prevent the generated carbon from adhering to the surface of the reaction tube. Furthermore, a decoking operation is carried out at regular intervals to flush oxidizing gas such as air into the reaction tube and burn and remove attached carbon, thereby preventing a decrease in thermal decomposition efficiency.

Regarding reaction tubes that have been treated with aluminum diffusion coating, the conventional method significantly increases the surface roughness of the smoothed surface of the reaction tube, creating a surface condition that is easy for carbon to adhere to, resulting in insufficient coking resistance and heat resistance. It had the disadvantage that the decomposition efficiency was not sufficient.

[0007] A typical aluminum diffusion coating treatment method using a powder method uses an appropriate amount of an aluminum source such as aluminum or an aluminum alloy as a treatment agent, a mixed powder of a halide such as ammonium chloride as an activator, and a sintering prevention powder such as alumina. The object to be treated is embedded inside and heated to a high temperature of 700°C to 1100°C in a non-oxidizing atmosphere for an appropriate period of time to precipitate and diffuse aluminum on the surface of the object to form an aluminide layer with the base material. . The methods currently being used industrially can be roughly classified based on the processing agent, and the following three methods are representative.

1) Al-Al2 O3 powder method Al2
A method of performing aluminum diffusion coating by embedding the object to be treated in a mixed treatment agent in which metal aluminum powder is mixed with O3 and a halide is added.

2) Fe-Al alloy powder method New Fe-Al alloy powder having an aluminum concentration of about 50% by weight is mixed with repeatedly used Fe-Al alloy powder having an aluminum concentration of about 30% by weight, and then several A method of performing aluminum diffusion coating treatment by embedding the base material of the object to be treated in a mixed treatment agent to which % of halide has been added.

3) A method using Al alloy powder other than Fe. A other than Fe as an aluminum source in Al2 O3 etc.
l alloy powder, e.g. Cr-Al alloy powder, Ni3Al
A method that uses aluminum diffusion coating by embedding the object to be treated in a mixed treatment agent containing alloy powder, Co2Al5 alloy powder, etc., and further adding a halide.

The above-mentioned conventional methods have the following drawbacks. (1) Disadvantages of the Al-Al2 O3 powder method (a) During the aluminum diffusion coating treatment, the aluminum powder in the treatment agent melts and adheres to the surface of the object to be treated, resulting in a rough finished surface and poor surface roughness. (b) Variations in the thickness and aluminum concentration of the aluminide layer occur between the aluminum powder melt-adhered area and other areas.

(2) Disadvantages of the Fe-Al alloy powder method (
b) When aluminum diffusion coating is applied to a base material with low Fe content such as Co-based or Ni-based superalloys, concentration of Fe due to Fe diffusion and intrusion of Fe-Al alloy powder occur in the aluminide layer. Decreases high temperature strength and adversely affects corrosion resistance of the base material. (b) The new Fe-Al powder and the surface of the object to be treated are likely to sinter, resulting in roughness and worsening of the surface roughness after treatment.

(3) Disadvantages of the method using Al alloy powder other than Fe (a) Alloying elements with Al are inactive or have very low activity during the aluminum diffusion coating treatment, and the treatment agent is not active during repeated use. , a decrease in the concentration of only Al occurs, and it is difficult to restore the treatment agent to an appropriate composition by adding new Al alloy, and the use of the treatment agent is limited to repeated use several times. The processing cost is higher than the high price.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aluminum diffusion coating treatment method that solves the above-mentioned drawbacks of the conventional method and forms a smooth and beautiful aluminide layer on a metal workpiece at low cost. be.

[0015]

The above object is achieved by embedding a metal workpiece in an aluminum diffusion coating treatment agent having the following composition and heating it in a non-oxidizing atmosphere. Below, the former coating treatment agent will be treated as a specific invention, and an aluminum diffusion coating treatment method using the same will be explained as a related invention.

The specified invention comprises 5 to 15% by weight of aluminum powder, chromium powder in a weight ratio of 1 to 2 to the aluminum powder, 0.1 to 5% by weight of ammonium chloride, and the balance anti-sintering powder. It is an aluminum diffusion coating treatment agent,

The related invention comprises 5 to 15% by weight of aluminum powder, chromium powder in a weight ratio of 1 to 2 to the aluminum powder, 0.1 to 5% by weight of ammonium chloride, and the balance anti-sintering powder. This is an aluminum diffusion coating treatment method characterized by embedding a metal workpiece in a treatment agent and heating it in a non-oxidizing atmosphere.

[0018]

[Function] The treatment agent of the specified invention contains aluminum powder and chromium powder in a weight ratio of 1 to 2 to the aluminum powder, so this chromium causes high temperature heating during aluminum diffusion coating treatment. In some cases, part or all of the aluminum powder forms a Cr-Al alloy having a higher melting point than aluminum to prevent molten aluminum from adhering to the workpiece. The reasons for limiting the contents of aluminum powder and chromium powder will be described later.

Ammonium chloride is 0 based on the total powder weight.
．． It is necessary to contain 1 to 5% by weight. If the ammonium chloride content is less than 0.1% by weight, sufficient Al concentration and uniform aluminum diffusion coating of the aluminide layer cannot be achieved, and if it exceeds 5% by weight, ammonium chloride sublimes during heating and the volume of the powder agent decreases. Because of this decrease, it becomes difficult to retain the processed material in the processing agent. For industrial use, the most suitable amount of ammonium chloride is 0.2 to 1% by weight.

The anti-sintering powder used in the present invention is as follows:
Stable oxides such as alumina and kaolin can be used. Its content ranges from 50 to 90% by weight of the normal range.

In the present invention, materials to be treated include stainless steel, heat-resistant cast steel, Fe-based superalloys, Ni-based superalloys, and Co-based superalloys.

Heating in the present invention involves embedding the object to be processed in a processing agent and placing it in a non-oxidizing atmosphere, such as H2 or Ar.
Diffusion treatment may be performed in an atmosphere at 700° C. to 1100° C. for 1 to 20 hours.

Next, the present invention will be explained in more detail with reference to Examples. In the examples, alumina was used as the sintering prevention powder. Further, percentages indicate weight %.

[0024]

[Example] (Example 1) In the mixed treatment agent of aluminum powder, chromium powder, 1% ammonium chloride, and the balance alumina, which are the powder components of the present invention, the weight % of the aluminum powder in the total powder is 2.5%. %, 5%, 10%
, 15%, 20%, and 30%, and the chromium powder content for each aluminum powder is the ratio of chromium powder weight/aluminum powder weight (hereinafter referred to as Cr/Al ratio).
The mixture was added in varying amounts of 0.5, 1, 2, and 3 to form a post-mixing treatment agent.

[0025] The sample material has a width of 20 mm and a length of 20 mm.
Using JIS standard NCF800H material with a thickness of 3 mm, the surface is polished with #1500 emery paper and then buffed to finish JI.
S surface roughness test method, 0.5 at maximum height (Rmax)
A sample adjusted to μm was used (hereinafter referred to as surface roughness according to JIS
(means the standard maximum height).

[0026] In the aluminum diffusion coating treatment, the above treatment agents are placed in a mild steel container, the test material is embedded in the powder agent, and
It was heated at 900° C. for 10 hours in an Ar gas atmosphere. The surface roughness of the sample material subjected to the aluminum diffusion coating treatment described above was measured. From this result, each surface roughness limit shown in FIG. 1 was obtained.

Curve 1 in FIG. 1 shows the limit of stable aluminum diffusion coating, curve 2 shows the range of surface roughness of 3 μm or less, curve 3 shows the limit of surface roughness of 6 μm, and curve 4 shows the limit of surface roughness of 6 μm. It shows a limit of 12 μm.

The following findings were obtained from FIG. 1 and the observation results of the surface and cross-section of the aluminized layer.

1) If the amount of aluminum powder exceeds 15%, the aluminum grains in the powder will melt and adhere to the surface of the specimen material, resulting in increased surface roughness.

2) Even if the Cr/Al ratio is less than 1, the aluminum grains in the powder agent will strongly melt and adhere to the surface of the specimen, resulting in increased surface roughness, similar to the case in item 1).

3) When the Cr/Al ratio exceeds 2,
Sintering of the chromium powder on the surface of the test material becomes intense, increasing the surface roughness.

4) If the Cr/Al ratio is 0.5 or more and the amount of aluminum powder in the powder is less than 5%, an aluminide layer with a uniform thickness cannot be formed.

Based on the findings from 1) to 4) above, the required composition of the aluminum diffusion coating powder to form a beautiful aluminide layer with a smooth surface is that the amount of aluminum powder is 5 to 1.
5%, and the chromium powder content ranges from 1 to 2 in Cr/Al ratio.

Table 1 compares the properties of an aluminide layer prepared using the treatment agent in the above-mentioned optimum range according to the method of the present invention and an aluminide layer prepared according to the conventional method as a comparative example. The concentration of the aluminide layer in the table indicates the outermost surface aluminum concentration determined by EPMA.

[0035]

[Table 1]

As shown in Table 1, the aluminide layer thickness of the inventive example was slightly thinner than that of the comparative example under the same heating conditions, but the Al concentration on the surface of the aluminide layer was the same, and a significant improvement in surface roughness was observed. .

(Example 2) Width 25 mm, length 25 mm,
The sample surface of a JIS standard NCF600 Ni-based superalloy with a thickness of 3 mm was polished with #1500 emery paper and then buffed to a surface roughness of 0.5 μm. Aluminum diffusion coating was performed using a powder composition treatment agent and a comparative example treatment agent. For aluminum diffusion coating treatment, put each of the above treatment agents into a mild steel container,
The test material was embedded in the treatment agent and heated at 9°C in an Ar gas atmosphere.
It was heated at 50°C for 10 hours.

Table 2 compares the properties of an aluminide layer prepared using the treatment agent of Example 2 and an aluminide layer prepared by a conventional method as a comparative example. The aluminide layer concentration in Table 2 indicates the outermost surface aluminum concentration determined by EPMA.

[0039]

[Table 2]

As shown in Table 2, in the inventive example, the surface Al concentration of the aluminide layer was the same as in the comparative example under the same heating conditions, and a significant improvement in surface roughness was observed.

Although not shown, a surface photograph (×100) taken by a scanning electron microscope (SEM) showing the surface properties of the aluminide layer according to Example 2, and a surface photograph taken by SEM showing the surface properties of the aluminide layer according to the comparative example in Table 2. Photo (×10
0), remarkable swelling due to fusion of Al powder in the treatment agent was observed in the comparative example, whereas no such swelling was observed in Example 2, and an improvement in the surface condition due to the addition of Cr powder was observed.

[0042]

[Effects of the Invention] As is clear from the descriptive description, the present invention has the following advantages:
By mixing chromium powder with a processing agent containing aluminum powder and ammonium chloride, part or all of the aluminum powder forms a Cr-Al alloy with a higher melting point than aluminum, and molten aluminum adheres to the object to be treated. As a result, an aluminide layer with a smooth and beautiful surface can be formed at low cost.

[Brief explanation of drawings]

[Fig. 1] Total weight percentage of aluminum powder, chromium powder, ammonium chloride, and alumina in the aluminum diffusion coating powder, stable coating limit and surface roughness range of the surface-polished NCF800H material after the aluminum diffusion coating treatment. FIG.

[Explanation of symbols]

1. Curve showing the limit of stable aluminum diffusion coating. 2. Curve showing the range of surface roughness of 3 μm or less. 3. Curve showing the limit of surface roughness of 6 μm. 4. Curve showing the limit of surface roughness of 12 μm.

Claims (2)

[Claims] Claim 1: Consisting of 5 to 15% by weight of aluminum powder, chromium powder in a weight ratio of 1 to 2 to the aluminum powder, 0.1 to 5% by weight of ammonium chloride, and the balance being anti-sintering powder. Aluminum diffusion coating treatment agent. 2. Consisting of 5 to 15% by weight of aluminum powder, chromium powder in a weight ratio of 1 to 2 to the aluminum powder, 0.1 to 5% by weight of ammonium chloride, and the balance being anti-sintering powder. An aluminum diffusion coating treatment method characterized by embedding a metal workpiece in a treatment agent and heating it in a non-oxidizing atmosphere.