JPH089725B2 - Manufacturing method of powder with low argon content - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a powder having an argon content of 1.5 ppm or less in an argon gas atomizing method.

More specifically, the present invention relates to a method for producing a powder for use in a powder molded article produced by the powder metallurgy method, which has a particularly clean structure and high properties, and more specifically, it is produced by an argon gas atomizing method. The present invention relates to a method for producing a high-performance powder in which the maximum value of argon gas contained in the produced powder is specified.

(Prior Art) In the field of powder metallurgy, when manufacturing a powder metallurgy product, first, a metal or alloy powder is filled in a capsule, and a filling hole and / or a lid at an end is welded to the capsule body by means such as welding. After sealing and assembling a powder capsule with an airtight structure into a powder billet, the powder billet is subjected to hot working such as hot extrusion processing or hot forging processing to form a tubular or rod-shaped product. are doing.

Nitrogen gas, helium gas, argon gas, or air is used as the atomizing medium, cooling medium, or atomizing and cooling medium when producing the above metal powder. Argon gas is often used because of its limited content and because helium gas is very expensive and has limited industrial use.

Therefore, a method of producing powder by using argon gas, more specifically, a metal powder produced by an argon gas atomizing method or a rotating electrode method using argon gas as a cooling medium is generally used.

In this specification, an atomizing method using argon gas as a spray medium, a cooling medium, or a spraying and cooling medium is referred to as an “argon gas-using atomizing method”.

At this time, the powder molded material that has been subjected to hot extrusion processing or hot forging processing may have a structure in which pores are partially left, and although it does not lead to characteristic deterioration, the commercial value may be significantly impaired.

Also, when circumferentially welding a powder product formed into a tubular shape,
Welded blowholes also appeared.

In particular, in today's applications such as piping for the chemical industry and oil well piping that are used under high stress, it is required to eliminate the defects of such products.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for producing powder by an atomizing method using argon gas, which solves the above-mentioned problems.

A specific object of the present invention is to develop a technique for eliminating the generation of welding blowholes and voids in the metal structure, which are found in powder molded products obtained by hot forming powder by an atomizing method using argon gas.

(Means for Solving the Problems) In order to achieve these objects, the inventors of the present invention noted that the above-mentioned problem is a case where the powder contains a relatively large amount of argon gas.

Therefore, the amount of argon allowed to avoid such a problem was clarified, and the correlation between the occurrence of defects in the powder molded product and the content of argon was examined to complete the present invention.

Although the powder partially contains oxygen and nitrogen, the powder is sufficiently clean and the content of oxygen and nitrogen at which blowholes are generated is less than that of the powder.

That is, the powder molded product processed by the hot extrusion or hot forging method, even when using a metal powder having a clean surface, when it contains an argon gas that does not form a solid solution in the metal structure, the welding process Therefore, holes are generated in the weld metal part or the heat affected part. The limit that does not generate voids is when the argon gas contained in the powder is 1.7 ppm or less.

In addition, when pores are generated in the structure of the powder molded product and further heat treatment is performed at a high temperature for the purpose of solid solution or the like, the size of the pores inside the metal structure increases and becomes remarkable. The limit of generation of such voids is that there are no voids of about 5 μm or more inside the powder, which varies depending on the steel type, but the content of argon gas contained in the powder is generally less than 1.5 ppm. Correspond.

In order to generate a powder having an argon content of not more than a specified value by the atomizing method using argon gas, the temperature of the molten metal at the time of supplying the atomizing nozzle differs from its liquidus temperature, that is, the degree of superheat is within 50 ° C. And the injection gas flow velocity in the region where the molten metal stream is divided into powder is 150 m / sec or less. Preferably, the gas flow rate at this time is 14
It is 0 to 100 m / sec.

The metal or alloy targeted by the present invention is not particularly limited, but in general, high Ni alloys and Co-based alloys having high corrosion resistance are mainly targeted.

(Operation) Next, the reason why the argon content and the spraying conditions at the time of manufacturing are limited as described above in the present invention will be described in detail.

As already mentioned repeatedly, when a powder molded product processed by hot extrusion or hot forging contains an argon gas that does not form a solid solution in the metallographic structure, it does not become a weld metal or heat affected zone during the welding process. Creates voids. When the argon gas contained in the powder is 1.5 ppm or less, the above-mentioned holes do not occur.

Further, in the same manner as described above, when the inside of the powder compact processed by hot extrusion or hot forging contains an argon gas that does not form a solid solution in the metallographic structure, voids are generated in the structure of the compacted body, and further solidification occurs. When heat treatment is performed at a high temperature for the purpose of solubilization or the like, the size of pores inside the metal structure increases and becomes conspicuous.

Similar to the blowholes, the pores of this structure occur when the surface of the powder is significantly contaminated, but in the case of a metal powder having a clean surface, when there are no pores of 5 μm or more inside the powder, as described above. No holes are generated. This means that no holes are generated when the argon gas contained in the powder is 1.5 ppm or less, although it depends on the steel type.

In order to produce a powder with the above-mentioned argon content not more than the specified value while ensuring high productivity by the argon gas atomizing method, the temperature of the molten metal is different from its liquidus temperature, that is, the degree of superheat is within 50 ° C. As a relatively low temperature,
The injection gas flow velocity in the region where the molten metal stream is divided into powder is approximately 15
This can be achieved by keeping the speed relatively low at 0 m / sec or less. If this superheat exceeds 50 ° C, the entrainment of argon gas will increase, while the jet gas flow velocity will exceed 150 m / sec.
Similarly, the involvement of argon gas increases.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.

Example 1 This example is a manufacturing example of powder by an argon gas atomizing method and a molding example using the same.

FIG. 1 is a schematic diagram of a powder manufacturing apparatus by a gas atomizing method. In the figure, a molten metal 3 is contained in a molten metal tundish 2 provided in a vacuum chamber 1. The molten metal 3 reaches the atomizing nozzle 5 through the molten metal pipe 4 provided at the lower portion, and is atomized by the high-pressure argon gas from the atomizing nozzle 5 connected to the high-pressure gas pipe. 7
Is a powder recovery tank. The powder that has become a powder and is collected in the powder recovery tank 7 is recovered from below, but the powder entrained in the gas is then separated from the argon gas by the cyclone separator 8 and recovered.

Powder having the composition shown in Table 1 was produced by the apparatus shown in FIG. The particle size of the resulting powder was 63 microns on average.

Next, the powder produced by the above method is vibration-filled into the mild steel double cylindrical container 11 shown in FIG. 2, and then the lid 14 having the degassing pipe 13 is welded to the position corresponding to the powder-filled portion 12. I attached it at. After operating the degassing pipe 13 by connecting it to a vacuum device as appropriate, the mild steel cylindrical container 11 was inserted into an electric furnace (not shown) held at 500 ° C. for 2 hours and then taken out, and the degassing pipe 13 was heated. After forging in between, it was air cooled to room temperature.

The above powder billet is heated to 1200 ° C in an electric furnace (not shown).
Then, it was hot-extruded at an extrusion ratio of 10.5.

FIG. 3 is a graph showing the relationship between the argon content of the powder thus obtained and the detectability of blowholes.

The powders used in the test were powders having different argon contents by changing the molten metal temperature by the argon gas atomizing method.

The relationship between the argon content of the extruded product and the presence or absence of void-like defects in the metallographic structure and the presence or absence of weld blowholes due to TIG tanning were investigated.

FIG. 2 is a graph showing the relationship between the content of argon in the powder and the presence or absence of holes in the metal structure.

The powder used in this test was also produced by changing the temperature of the molten metal as described above.

Table 2 shows the relationship between the gas content of the powder extruded material and the holes and blowholes.

It has been previously confirmed that there is a good correlation between the occurrence of blowholes in circumferential welding and the occurrence of weld blowholes in TIG tanning.

From the results shown in Table 2, it was found that blowholes were not detected in the powder molded product processed by the hot extrusion method when the amount of argon contained in the powder was about 1.7 ppm or less. No constant correlation is found between oxygen (O) and nitrogen (N) gas contents and defects.

Moreover, it was found that the limit of generation of voids inside the metallographic structure is when argon is less than about 1.5 ppm.

Next, a powder having an argon content of not more than a specified value is
The correlation between the Ar content, the temperature of the molten metal and the flow velocity of the injection gas was investigated in order to produce it while ensuring high productivity by the atomization method.

That is, FIG. 5 shows the relationship between the melting temperature supplied to the atomizing nozzle and the argon content of the powder using the powder having the composition shown in Table 1. As can be seen from this, the argon content of the powder is The higher the temperature, the higher the tendency. In order to suppress the occurrence of defects in the metal structure as described above, in order to make the argon content of the powder 1.5 ppm or less, the difference between the liquidus temperature and the temperature of the molten metal, that is, the degree of superheat is within 50 ° C. It is necessary.

Further, FIG. 6 shows the relationship between the virtual powdering point of the molten metal, that is, the gas flow rate at the geometrical focus of the atomizing nozzle and the argon content of the powder. The argon content of the powder tends to increase as the gas flow rate increases. In order to suppress the occurrence of defects in the metal structure as described above, the content of powdered argon should be controlled.
In order to reduce the concentration to 1.5 ppm or less, it is necessary to keep the injection gas flow velocity in the region where the molten metal is split into powder at a relatively low speed of about 150 m / sec or less. The gas flow rate is preferably at least 50 m / sec for atomization.

Example 2 In addition, as another example, a powder whose main chemical components are shown in Table 3 was produced according to Example 1 by an argon gas atomizing method.

The relationship between the temperature of the molten metal supplied to the atomizing nozzle at this time and the argon content of the powder is shown in FIG. 7, and the relationship between the gas flow rate and the argon content of the powder is shown in FIG.

From FIGS. 7 and 8 as well, in order to reduce the argon content of the powder to 1.5 ppm or less, it is necessary that the temperature of the molten metal be different from its liquidus temperature, that is, the degree of superheat is within 50 ° C. It was found that it is necessary to keep the injection gas velocity in the region where the molten metal stream is divided into powder at a relatively low speed of approximately 150 m / sec or less.

(Effect of the Invention) According to the method of the present invention, even if there is a powder manufacturing method in which argon gas is used as a spraying medium or a cooling medium or a spraying and cooling medium, a metal powder containing argon at an allowable value or less is atomized. It is possible to produce with a high productivity, and as a result, it is possible to prevent the formation of a structure in which voids remain partially in the molding material produced from the obtained metal and alloy powder and to form it into a tubular shape. It is possible to prevent welding blowholes from occurring in the circumferential welding of the powdered product.

[Brief description of drawings]

1 is a schematic configuration diagram of an apparatus for producing a fine powder according to the method of the present invention; FIG. 2 is a schematic explanatory diagram showing the structure of a powder billet; FIG. 3 is a diagram showing the argon content of powder and whether or not blowholes can be detected. FIG. 4 is a graph showing the relationship between the argon content of the powder and the presence or absence of holes in the metal structure; FIG. 5 is the melt temperature supplied to the atomizing nozzle and the argon content of the powder. Relationship (for the components shown in Table 1)
FIG. 6 is a graph showing the relationship between the gas flow rate at the geometrical focus of the atomizing nozzle and the argon content of the powder (in the case of the components shown in Table 1); FIG. 7 is the atomizing nozzle. Between the temperature of the molten metal supplied to the furnace and the content of argon in the powder (for the components shown in Table 2)
FIG. 8 is a graph showing the relationship between the gas flow rate at the geometrical focus of the atomizing nozzle and the argon content of the powder (in the case of the components shown in Table 2). 1: Vacuum chamber, 2: Molten tundish 3: Molten metal, 4: Molten metal pipe 5: Atomizing nozzle, 6: High pressure gas piping 7: Atomizing tank (powder recovery tank) 8: Cyclone separator

Claims (1)

[Claims] 1. A method for producing a powder of a metal or an alloy by an atomizing method using argon gas, wherein a difference between a melt temperature when a melt serving as a raw material of the powder is supplied to an atomizing nozzle and a liquidus temperature of the melt is determined. A method for producing a powder having an argon content of 1.5 ppm or less, which is within 50 ° C., and a gas flow velocity injected into the molten metal is 150 m / sec or less immediately before collision with the molten metal.