JPS6160807A - Production of metallic powder having narrow width of grain size - Google Patents

Abstract

PURPOSE:To obtain easily metallic powder having a narrow width of grain size at a good yield by cooling the molten metal drops by a gap or liquid at a specific solidifying rate in such a manner that the size of the crystal grains of the formed powder and granular material attains a prescribed grain size then pulverizing mechanically such material and breaking the material at the grain boundary. CONSTITUTION:The molten metal obtd. by melting the metals [e.g.; Si-Al-Fe(9%-6%-Bal)] in a melting furnace is discharged from the hole provided to the bottom of, for example, a refractory vessel to manufacture the molten metal drops. The molten metal drops are then cooled at 10-10<4> deg.C/sec cooling rate by the refrigerant consisting of the gas or liquid, i.e., water, inert gas, molten salt, etc. in such a manner that the size of the crystal grain of the resulted powder and granular material attains 50-200mum. The resulted powder and granular material is broken at the grain boundary of the powder and granular material by using an ordinary ball mill, rod mill, etc. The metallic powder having the narrow width of grain size is thus obtd. at a good yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for easily producing metal powder having a narrow particle size range with good yield.

[Conventional technology]

Among the uses of metal powders, those that require a particularly narrow particle size range include those used for filters, clutches, carriers, thermal spraying, and magnetic materials.

Conventionally, metal powder with a narrow particle size width has been produced by pulverizing an ingot cast piece or by a spraying method to produce a powder, which is then sieved. However, when producing metal powder by crushing an ingot cast piece, powders of 200 μm or more can be easily produced using this method, but the yield of metal powders with a narrow particle size range is very poor. This is because the crystal grains are 200 μm or more, so when producing metal powder of 200 μm or less, the crystal grains themselves must be crushed. In other words, the crystal grains themselves must undergo plastic processing,
Since the powder undergoes a process of deformation such as work hardening that leads to destruction, the resulting powder has a wide particle size range and is irregular. When producing powder by the spraying method, powders with a diameter of 50 μm or less have a relatively good yield (it can be produced, but powders with a narrow particle size width of 50 μm or more may have a yield of less than 10%,
Not the preferred method.

[Problems to be solved by the present invention]

The present invention has been made in consideration of the problems of the conventional technology, and has been made by various studies to easily and simply produce metal powder with a narrow particle size width, and has been developed by making a powder having crystal grains of a certain size. The present invention was completed based on the knowledge that metal powder with a narrow particle size width can be produced in good yield by crushing granules at grain boundaries.

[Means for solving problems]

That is, in the present invention, metal droplets are cooled with gas or liquid at a temperature of 10 to 100 m so that the crystal grain size of the obtained powder becomes 50 to 200 μm, and then the obtained powder is machined. This is a method for producing metal powder with a narrow particle size range, which is characterized by pulverizing the metal powder and destroying it at the grain boundaries.

[Effect]

In the present invention, it is important to control the crystal grains of the granular material before pulverization. The size of the crystal grains of this granular material is
It is known that it is influenced by the material, solidification rate, additives, etc. Among these, the solidification rate is an especially important factor.

In the present invention, since the purpose is to obtain powder having crystal grains of 50 to 200 μm, the solidification rate of the droplets is set to 10 to 200 μm.
If the solidification rate is slower than 10 to 104℃/sec, it is difficult to reduce the grain size to 200μm or less;
When the solidification rate is faster than /sec, the grain size is 50μ.
This is because even if it is crushed, powder with a narrow particle size width of 50 μm or more cannot be obtained. for example,
When a powder material having crystal grains of 40 μm is crushed at its grain boundaries, 40 μm powder is easily obtained, but 80 μm powder is easily obtained.
In order to obtain a powder of m, it is necessary to grind so that two crystal grains exist, and such grinding is actually difficult.

Usually, powders having one or two to three crystal grains coexist, and therefore powder with a narrow particle size width of 50 μm or more cannot be obtained.

Note that this solidification rate is considerably influenced by the size of the droplets and the material of the refrigerant.

Droplets can be created by melting the desired material composition in a melting furnace, and then flowing the molten metal through a hole provided at the bottom of a refractory container. A method in which the molten metal flows out from a hole and is crushed using a low-pressure refrigerant;
There is a method of forming droplets using a metal wire or rod as a heating source, such as a gas banner.

The droplets preferably have a diameter of approximately 20 mm or less, 20II
When the temperature exceeds IIm, the difference in the solidification rate between the outer surface and the center of the droplet becomes large, which causes variations in the size of crystal grains, and the resulting powder has a large particle size range.

The coolant may be appropriately selected from water, inert gas, molten salt, etc. depending on the material of the droplets and the desired size of crystal grains.

Alloys such as 5i-AI-Fe (9%-6%-Bal) alloy, which tend to have large crystal grains, need to be solidified quickly to make the crystal grains fine. In this case, water is used as a coolant. It is appropriate to use it as

On the other hand, if the crystal grains are relatively fine, such as the Fe-N1 (18%-Bal) alloy, the solidification rate is fast, so it is best to solidify it using a coolant with low cooling capacity, such as molten salt. Note that it is also possible to add additives to each refrigerant to adjust its cooling capacity, and in the case of a molten salt, to adjust the temperature to adjust the solidification rate of the droplets.

In the present invention, the powder particles having a crystal grain size of 50 to 200 μm are destroyed at the grain boundaries, and in this case, a conventional ball mill, rod mill, crusher, attritor, jet mill, etc. can be used for pulverization.

For example, in a 5t-AI-Fe alloy, fracture at the grain boundaries can usually occur when using a crusher, but in a Fe-Ni alloy, even if the same crusher is used, it will not be crushed. This alloy can be easily fractured at grain boundaries by using a ball mill. However, if a pulverizer with too large a pulverizing capacity is used, not only the grain boundary fracture but also the intracrystalline fracture occurs, so it is necessary to select the pulverizer according to the material of the granular material.

In addition, if there is not much difference between the strength of the grain boundaries and the strength of the grains depending on the material of the powder or grains, or if the strength of the grain boundaries is strong, additives that precipitate brittle precipitates at the grain boundaries, such as S, may be added. By adding s P , S + , etc. and precipitating a compound with the base material, fracture at grain boundaries can be facilitated. Even if powder and granules are manufactured from molten metal for cars, if the brittle precipitates do not precipitate at the grain boundaries,
The obtained powder may be heat-treated to precipitate the brittle precipitates at the grain boundaries.

Hereinafter, typical examples of the present invention will be shown.

〔Example〕

Example (1) Si 9wt%, Al 6nt%, balance Fe alloy was melted, and the molten metal at 1550°C was poured into a hole in the bottom of a refractory container with a diameter of 10
III+, and the solidification rate of the droplet is 10"C
/sec, spray pressure cuff kg/cal, spray water 15j! /5ecT: The molten metal stream was pulverized, dropped into water, and cooled to produce granular material. The obtained powder has a particle size of 1
~5II1m, average grain size 3II1)1, and crystal grain size was 70~1)0 μm.

Next, the powder obtained as described above was crushed for 6 hours using a crusher, and powder having a width of 63 to 149 μm was collected, and the yield was 80%.

Example (2) An alloy rod with a diameter of 201) m consisting of 13 wt% Cr, 3 wt% AI Q, and the balance Fe was melted with a gas burner, and the temperature of the droplet was 1600'C, and the size of the droplet was about 21) 1)
The gas burner was adjusted so that the temperature was 1, and the resulting droplets were dropped into water, cooled and solidified at about 103°C/sec.

The particle size of the obtained powder is 1 to 4 mm, and the average particle size is 2 m+
It was ++. In addition, the crystal grain size is 80 to 120 μm
Met.

Next, the powder obtained as described above was pulverized in a ball mill for 5 hours, and powder with a diameter of 74 to 149 μm was collected, and the yield was 65%.

Example (3) An alloy of 18 wt% Fe, 1 wt% SO, and the balance Ni was melted, and the molten metal at 1500°C was flowed out from a hole with a diameter of 15 mm at the bottom of a refractory container, and the solidification rate of the droplets was 102°C. 8e
Spray pressure 5kg/cd, spray water 1) 3 so that it becomes c.
The molten metal stream is crushed at R/sec, cooled by dropping into water,
The powder and granular material obtained by producing the powder and granular material has a particle size of 2 to 71I.
lffl, the average grain size is 41, and the crystal grain size is 1)
It was 0 to 150 μm.

Next, the powder obtained as described above was pulverized for 10 hours using an attritor, and then powder having a diameter of 88 to 177 μm was collected, and the yield was 80%.

Example (4) A 1550°C molten metal containing SUS316L with SO, i% added was flowed out from a hole with a diameter of 10 mm at the bottom of a refractory container, and NaCl was added so that the solidification rate of the droplets was 10°C/sec.
50 wt% of CL was added dropwise to 50 wt% of 750°C molten salt. When the powder and granules recovered from the molten salt were thoroughly washed with water and dried, the particle size of the obtained powder and granules was 1 to 1.
The particle size was 5 mm, and the average particle size was 31. Moreover, the size of crystal grains of the powder and granular material was 150-190 μm.

Next, the powder obtained as described above was crushed for 8 hours using a crusher, and a powder having a diameter of 125 to 210 μm was collected, and the yield was 70%.

Comparative Example (1) An alloy having the same composition as the alloy used in Examples 1 to 4 was prepared using a normal water spray method, that is, a spray pressure of 10 kg/cut and an amount of sprayed ice of 20
Table 1 shows the yield when spraying at β/sec and sieving the obtained powder to match the particle size of Examples 1 to 4, respectively.

Note that Table 1 also shows the yields of Examples 1 to 4.

Table 1 Comparative Example (2) An alloy having the same composition as the alloy used in Examples 1 to 4 was melted,
A mold cast piece of 10 x 30 x 200ff+m was produced, and after crushing it in advance to a particle size of about 3 mmc with a crusher, it was crushed using the same crushing method and conditions as in Examples 1 to 4,
Table 1 shows the yields when powders having particle sizes of Examples 1 to t were collected.

〔effect〕

As shown in Table 1 above, according to the method of the present invention, it is possible to produce metal powder with a narrow particle size width in good yield, and the obtained powder has a uniform particle size, so it can be used in filters and fluids. Useful for clutches, copier carriers, etc. Further, since the powder obtained by the method of the present invention is made up of a single crystal grain that forms a single particle, there is little variation in magnetic properties, and the powder can be used as a powder useful for magnetic materials.

Claims (1)

[Claims] (1) Cool the metal droplets with gas or liquid at a solidification rate of 10 to 10^4°C/sec so that the crystal grain size of the obtained powder becomes 50 to 200 μm, and then A method for producing metal powder with a narrow particle size width, characterized by mechanically crushing powder particles and destroying them at grain boundaries.