JP3083292B1 - Aluminum diffusion method to steel surface - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To be applicable to various structural parts and mechanical parts that require high-temperature characteristics and oxidation resistance, and to be subjected to treatments such as nitriding and carburizing to thereby obtain various structural parts that require wear resistance and corrosion resistance. Establish a simple steel surface treatment method applicable to machine parts, various tools and molds. SOLUTION: A mixture of powder of aluminum or an alloy mainly composed of aluminum and powder of a metal (for example, titanium metal) which easily forms an intermetallic compound with aluminum is applied to a steel surface, and this is applied in a vacuum or in an inert state. In a gas or reducing gas atmosphere, aluminum is diffused by heating to a temperature higher than the melting point of aluminum or the liquidus of aluminum alloy to diffuse aluminum into the steel surface and form a layer with high aluminum concentration on the steel surface. Is the way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be applied to various structural parts and machine parts that require high-temperature characteristics and oxidation resistance, and requires abrasion resistance and corrosion resistance by performing treatments such as nitriding and carburizing. The present invention relates to a method for diffusing aluminum to a steel surface using powder applicable to various structural parts, machine parts, various tools, and molds.

[0002]

2. Description of the Related Art Conventionally, as a so-called aluminizing surface reforming method for forming a high-concentration layer of aluminum on a steel surface, (1) a hot-dip plating method in which an object to be processed is immersed in molten aluminum or an aluminum alloy and pulled up (for example, (2) A powder packing method in which an object to be processed is immersed in a mixed powder obtained by adding an alumina powder or a volatile halide to aluminum or an aluminum alloy powder and heated to a high temperature (for example, Japanese Patent Application Laid-Open No. 3-180461). Kaihei 7-109579), (3)
There is a method in which aluminum or an aluminum film is formed on the surface of an object by vapor deposition, sputtering, ion plating, electroplating, or the like, and the aluminum is diffused by heating (for example, JP-A-8-319557).

Also, (4) an aluminum alloy powder of iron, cobalt, nickel, zirconium or the like having a melting point of at least 1100 ° C. and an aluminum content of 40 to 60 at%, which is close to the aluminum diffusion method of the present invention. A halide (for example, ammonium chloride) and an organic resin binder (for example, a xylene solution of polybutyl methacrylate)
Is applied to a steel surface, dried and heated to 800 to 1100 ° C. in an inert gas to generate volatile aluminum halide, and the steel surface is subjected to diffusion treatment. Seen in No. 50-57037.

[0004]

Since the hot-dip plating method (1) is originally a plating method, an aluminum or aluminum alloy film having a thickness of several tens of microns is formed in addition to the diffusion layer. For this reason, nitriding after plating becomes difficult. Further, it is difficult to precisely control the thickness of the plating, and the surface of the object is roughened due to the incorporation of the object into the molten metal, and dimensional changes occur.

In the case of the powder pack (2), the surface of the object to be treated is roughened due to the reaction between the surface of the object and the powder and the adhesion of the powder. It takes a long time to heat and cool the object to be processed, and it is difficult to control the diffusion layer. The method (3) has no surface roughness of the object to be treated and can control the surface aluminum concentration,
Post-processing such as nitriding can be performed without forming a brittle compound layer. However, a large-scale processing apparatus is required to form a film of aluminum or an aluminum alloy, and the shape of an object to be processed is greatly restricted. Further, in the case of plating, an aqueous plating bath cannot be used, so that it is industrially difficult and there is a drawback that the adhesion of the film is poor.

As described above, the methods (1) and (2) involve forming a high-concentration, fragile aluminum-enriched layer on the surface, and also cause the surface of the workpiece to be roughened. It is not suitable as an aluminizing method. On the other hand, the method (3) is a high-precision aluminum diffusion method, but the method of forming an aluminum or aluminum alloy film on the surface of the object to be treated is greatly restricted.

The method of (4) uses a special alloy containing 40 to 60% of aluminum, and furthermore, performs a treatment at a high temperature of 1100 ° C. in the presence of a halide.
This method is troublesome and inferior in versatility.

Accordingly, as a result of intensive studies on a simple method of diffusing aluminum into the steel surface, a new method for solving the problems of the existing method of diffusing aluminum into the steel surface has been found.

[0009]

According to the method of the present invention, a slurry of a mixture of aluminum powder and titanium powder is applied to a steel surface and heated in a vacuum or reducing atmosphere, or in an inert gas. This is a very simple processing method.

That is, a slurry of a mixture of powder of aluminum or an alloy mainly composed of aluminum and a metal powder which easily forms an intermetallic compound with aluminum is applied to the steel surface, and this is applied in a vacuum or in an inert gas or In a reducing gas atmosphere, a temperature of about the melting point of aluminum or the liquidus of aluminum alloy or higher (for example, 65
(0 ~ 1000 ℃), selective aluminum on steel surface
This is a method of diffusing aluminum into the steel surface using a slurry of powder , characterized by forming a layer having a high aluminum concentration on the steel surface by diffusing and penetrating into the steel surface.

The alloy mainly composed of aluminum used herein is a commercially available alloy of 70 at% or more of aluminum, and is composed of Si, Fe, Cu, Mn, Mg, Cr, Zn, Zr, and Zr.
Alloy with Ti, Ca, V, etc. Above all, pure aluminum, Al-Ti (0.25% or less), Al- (Zr + Ti (6.25%)
%), Al-Mg (5.0% or less), Al-Mg (3.0% or less) -Zn (7.0% or less) and the like. Further, a metal which is easily mixed with aluminum or an alloy powder mainly containing aluminum to form an intermetallic compound is titanium (T
i), titanium alloys are preferred, but in addition, Cu, Mn,
It is also possible to select a metal powder such as Mg or Ca.

According to this method, aluminum can be diffused on the steel surface, and the surplus coating material easily falls off.
This is because (1) excess aluminum powder and metal powder such as titanium react to form an intermetallic compound with aluminum such as aluminum-titanium, and (2) the formed compound hardly forms a compound with the steel base. Or hard to form a solid solution, (3)
This is because titanium and the like react more easily with aluminum than with iron.

Furthermore, it was confirmed that even if the amount of the mixture applied was changed, a substantially constant diffusion thickness was obtained, and that the aluminum concentration in the diffusion layer could be changed by the mixing ratio of aluminum powder / titanium powder. . This is because the composition of the intermetallic compound formed by the reaction of aluminum and titanium changes depending on the mixing ratio of aluminum and titanium, thereby exhibiting a function of controlling the aluminum concentration on the steel surface.

In order to control the diffusion of aluminum to the steel surface, an intermetallic compound is formed with aluminum, which reacts with aluminum more easily than iron, and the reactant does not form a compound with iron or form a solid solution. Although it is possible to select a metal powder other than titanium as described above, in order to further improve the characteristics of the diffusion layer, boron,
Post-treatment such as addition of a third element such as silicon or chromium, quenching, or annealing is also possible.

The particle size of each powder used is not particularly limited, but from the viewpoint that the mixture is easily held on the surface of the object to be treated, the particle size is preferably about 0.1 μm to 50 mesh (0.3 mm), preferably 1 μm to 0.2 mm. desirable. If it is 0.1 μm or less, it is too fine to handle, and if it is 50 mesh or more, it is too coarse to make uniform coating difficult.

In order to efficiently adhere and hold the mixture on the surface of the object, water, an organic solvent, and an organic binder can be used for the mixed powder. Specific examples include alcohols and polyvinyl alcohol.
Although the method of adhering the mixed powder to the material to be treated is not particularly specified,
Methods such as coating, spraying and dipping can be applied.

The steel to be processed according to the present invention does not matter on the type, shape and size of the steel to be processed. Depending on the application, it can be applied to alloy steels such as carbon steel, tool steel, mold steel, and stainless steel.

Hereinafter, a method for diffusing aluminum to a steel surface using the powder of the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 Aluminum powder (particle size 3 μm) and titanium powder (particle size)
10 μm) were mixed at a volume ratio of 5: 5, and a slurry obtained by adding ethyl alcohol was applied to steel (S45C) having a diameter of 50 mm and a thickness of 5 mm in a sufficient thickness. After drying, the coating was heated at 950 ° C. for 1 hour in vacuum. FIG. 1 shows a photograph of the appearance of the processed product. The right is a reaction product of the mixed powder peeled from the processed product, and the left is an appearance surface state of the processed product peeled.
FIG. 2 shows a scanning electron micrograph of this sample cross section and the result of line analysis by an X-ray microanalyzer. The surplus powder was peeled off from the steel while maintaining the shape of the disk as shown in the photograph of FIG. On the surface of the steel from which excess powder has been peeled,
Although some roughening was observed, it was possible to sufficiently polish it with the degree of paper clinging. Further, the aluminum diffusion layer was clearly observed from the cross-sectional micrograph and the result of the line analysis. Although traces of titanium were found on the outermost surface, no diffusion into the substrate was observed.

Example 2 A slurry obtained by mixing the powder shown in Example 1 with Ti: Al = 7: 3 was used, and the amount to be applied to the steel sheet was changed variously, and diffusion treatment was performed under the same conditions as in Example 1 to obtain aluminum. The thickness of the diffusion layer was measured. The result is shown in FIG. It was found that even if the amount of application was changed, the diffusion thickness was almost constant, and the diffusion thickness was insensitive to the mixed powder application thickness.

Example 3 A slurry obtained by changing the mixing ratio of aluminum powder and titanium powder with ethyl alcohol to a thickness of 5 was used.
It was applied to a steel sheet (S45C) having a thickness of 0.5 mm and subjected to a diffusion treatment under the same conditions as in Example 1. At this time, for the sample containing only aluminum powder, the amount of application was carefully restricted so that no extra aluminum layer remained. FIG. 4 shows the relationship between the mixing ratio of the powder and the diffusion thickness, and FIG. 5 shows the aluminum concentration in the diffusion layer at a typical mixing ratio. It has been found that the thickness of the diffusion layer and the aluminum concentration in the diffusion layer can be controlled by the mixing ratio of the aluminum powder and the titanium powder. In particular, the aluminum concentration in the diffusion layer can be suppressed to 30 at% or less, and it is possible to prevent the formation of a fragile compound in the diffusion layer.

[0022]

The method of the present invention for diffusing aluminum to the surface of steel using powder is extremely simple and easy to form an intermetallic compound such as titanium in the aluminum powder. The diffusion thickness of aluminum into the steel material becomes substantially constant in a wide range of conditions due to the presence of, and excess material can be peeled off and removed, so that process control is easy and uniform surface treatment can be performed. Therefore, it is possible to easily obtain a steel excellent in high-temperature characteristics and a high-quality steel that can be subjected to a composite treatment with the nitriding treatment.

The thickness and concentration of the aluminum diffusion layer can be changed by changing the mixing ratio of aluminum or an easily available general-purpose aluminum-based alloy powder and a metal powder, and the thickness of the aluminum diffusion layer can be changed to 1000 ° C. or higher. It can be said that this is an excellent aluminum diffusion method also in that a high temperature is not required.

[Brief description of the drawings]

FIG. 1 is a comparison photograph of the appearance of a steel sheet after diffusion treatment (left) and a reactant of separated excess powder (right).

FIG. 2 is a scanning electron micrograph of a cross section of a sample and a chart of a line analysis result by an X-ray microanalyzer corresponding to the cross section.

FIG. 3 is a graph showing a relationship between a mixed powder application amount and a diffusion thickness.

FIG. 4 is a graph showing a relationship between a mixing ratio of powder and a diffusion thickness.

FIG. 5 is a graph showing a relationship between a powder mixing ratio and an aluminum concentration in a diffusion layer.

Claims (2)

(57) [Claims] 1. A slurry of a mixture of aluminum or an aluminum-based alloy powder and a metal powder that easily forms an intermetallic compound with aluminum is applied to a steel surface, and the slurry is applied in a vacuum or in an inert gas or Heating to a temperature higher than the melting point of aluminum or the liquidus of aluminum alloy in a reducing gas atmosphere to selectively diffuse and infiltrate aluminum onto the steel surface, forming a layer with high aluminum concentration on the steel surface. Aluminum diffusion method to steel surface to be used. 2. The method according to claim 1, wherein the metal that easily forms an intermetallic compound with aluminum is one of titanium, a titanium alloy, or a mixture of two or more of them.