JPS58153708A - Manufacture of alloy powder with fine structure - Google Patents

Abstract

PURPOSE:To obtain the alloy powder with fine structure in the wide range of chemical composition by following method in which molten metal is dropped on the rotary surface of the roll made of the material hard to be wet with molten metal and is separated into fine molten metal drops and then they are rapidly solidified by collision with the surface of the rotary body rotating at high speed. CONSTITUTION:The roll 4 with the surface hard to be wet with molten metal is rotated at the peripheral speed of above 2m/sec. Molten alloy 2 in a crucible 1 is dropped on said rotary surface through a nozzle 3 and is separated into fine molten metal drops. Then, these metal drops 6 are thrown out by centrifugal force and are caused to collide with the rotary surface of a metallic rotary body 7 which has the peripheral rotary speed of above 10m/sec and high heat conductivity, thereby rapidly solidifying and cooling said drops. The alloy powder 8 is collected in a vessel 9. By this process, the alloy powder used for sintered body having fine crystal grain is industrially obtained.

Description

[Detailed description of the invention] The present invention relates to an improvement in a method for producing alloy powder.

In recent years, in the field of powder metallurgy, when adding alloying elements to improve the properties of products, a method has been adopted in which pre-mixed and melted alloy powder, called pre-alloyed powder, is blended into raw material powder. -It's coming. This type of alloy powder has traditionally been produced by the pulverization method or the atomization method, but since the alloy powder produced by the pulverization method is not rapidly solidified during melting, the grain size is very large, especially for high-speed tool steel. In alloys containing such carbides in their structure, there is a problem in that the carbides are formed in a network shape, impairing the toughness of the sintered body. Since the alloy powder produced by the atomization method is rapidly solidified, it solves the problems encountered with the pulverization method, but the solidification rate varies depending on the size of the alloy powder particles, and powder particles with large diameters are difficult to solidify. The alloy powder produced by the above-mentioned pulverization method has the drawback that the speed is somewhat slow, and in order to obtain a sintered body having sufficient toughness, the fine powder must be sieved before use.

It is an object of the present invention to solve the above-mentioned problems and to provide a method for producing an alloy powder having a structure consisting of fine crystal grains regardless of the size of the powder particles.

The inventor previously proposed a method for producing amorphous metal powder, in which the metal powder has a surface layer with low wettability to molten metal and rotates at a circumferential speed of 2 m 7 seconds or more. After the metal is dropped through the nozzle and the molten metal beam is broken into fine molten metal droplets, the molten metal droplets are continuously spread over a distance of 10 m.
A method for producing amorphous metal powder is proposed in which the amorphous metal powder is collided with a metal rotating body rotating at a circumferential speed of F to rapidly solidify it. (hereinafter referred to as the prior invention). The prior invention is an IE with low wettability for the molten metal rotating at high speed.
Molten metal is dropped onto the surface of the roll, and cavitation is generated by applying negative pressure to the molten metal using a roll circumferential speed that is significantly faster than the falling speed, breaking the molten metal into fine molten metal droplets, which are then VC is a method of obtaining amorphous metal powder by colliding it with a rotating body such as a high-speed rotating metal drum and cooling it at an extremely high rate. Metals and alloys (hereinafter referred to as However, at the time of completion of the earlier invention, the inventor discovered that if a general alloy other than the target alloy μ is rapidly solidified as in the earlier invention, extremely fine particles would be formed. It has been found that an alloy powder consisting of crystal grains can be obtained.

The present invention was made based on the knowledge described in F.

As in the previous example, the alloy powder that has been cooled from the molten state at an extremely high rate and solidified has a structure consisting of fine crystal grains of several microns or smaller, regardless of the size of the powder particles, and it is difficult to crystallize. The phases are also extremely fine, or the phases that would crystallize in the conventional method are solid dissolved in the rc supersaturated matrix and do not crystallize, and the precipitated phases that precipitate during sintering or heat treatment are also extremely fine. Moreover, the growth of crystal grains during sintering in green compacts using water powder is inhibited by fine crystallized and precipitated phases.
Coarsening of crystal grains is slight, and a tough sintered body can be obtained.

The above roll has a surface force of 4 and 1ρ'? 41b In order to be able to split into fine particles instantly and release them, it is necessary to use a material that has low wettability with respect to the molten metal, in other words.
□It is necessary to use a material that is not easy to get rid of, or at least the surface layer is made of a material that has low wettability.
Those made of ceramics, such as, or those having a surface V (having these layers) are suitable.

When the circumferential speed of the roll is 2 m/sho J] J, the roll-&
In order to prevent cavitation from occurring on the surface, the circumferential speed of the roll is set to 2 rn/sec or more, and VC is applied so that the molten metal is finely divided after colliding with the surface of the Ll.

Further, the number of rolls may be one, or two rolls facing each other with a narrow roll interval may be used. In the former case, the molten metal comes into contact with the surface of the roll rotating in the falling direction, and the action of the centrifugal force is effectively absorbed. In order to prevent the molten metal from scattering over a wide area, it is preferable to let the molten metal fall close to the tangential direction of the roll surface. For this purpose, it is preferable to supply the molten metal to the roll via a nozzle. In the latter case, VC is 1" - If the molten metal is supplied near the roll gap, it will easily become negative pressure between the surfaces of the rolls rotating at high speed while facing each other while passing through the narrow roll gap, causing cavitation. By the centrifugal force of both rolls, it is easily and finely divided and released. The distance between both rolls is 03
The effect is great if it is less than that. If the two rolls have the same diameter and the same circumferential speed, they will be discharged in a direction perpendicular to the line connecting the centers of both rolls, making it convenient to introduce them into the rotating body for the next process.

The fine molten droplets separated by the rotating roll as described above then collide with the outer or inward surface of the rotating body located below, that is, the rotating surface, and are rapidly solidified and cooled into powder. At this time, the cooling rate necessary to form the above-mentioned fine structure varies depending on the chemical composition of the alloy, but the critical cooling rate is considered to be, for example, on the order of about 106° C./second. If a rotating body such as a rotating drum is made of copper, copper alloy, or steel, has sufficient heat capacity, is rotated at a circumferential speed of 1 Qrn/sec or more, and collides with it, it can spread over a considerable area. A molten alloy having a chemical composition of can be solidified as an alloy powder having a fine structure.

In this case, the collision surface can be either the inner or outer surface of the rotating drum to achieve the same effect, and it may also be a cylindrical body instead of a hollow cylinder. 'Next, embodiments of the present invention will be described with reference to the accompanying drawings.

A molten alloy 2 is placed in a crucible 1, and the molten metal 2 is supplied from a sprue at the bottom of the crucible through a nozzle 3 to a call 4 provided below.

The roll 4 is rotated at high speed by a drive device (not shown), and the nozzle 3 is preferably externally cooled by a water cooling jacket 5 to prevent it from melting.

As mentioned above, an example in which there is only one roll 4 is shown in Fig. 1.
FIG. 2 shows an example of a pair of rolls 4a and 4b.

A rotating body 7 is provided on each side of the roll 4.
The broken molten droplets 6 collide with the rotating body 7 and are rapidly solidified and cooled. The rotating body 7 is a cylindrical body as shown in Figs.
The rotating body 7a may have a shape that straightens the truncated conical surface symmetrically from the center as shown in C.

1 and 2 show an example in which the outer circumferential surface of the cylindrical body is used for one cycle, and FIG. 4 shows an example in which the inner circumferential surface of the cylindrical body is used.

A container 9 containing alloy powder 8 is provided on the f side of the rotating body 6.

In addition, when producing alloy powder continuously, one rotating body 7.
It is desirable to operate while forcibly cooling the tubes 7ai and 7b in order to ensure a cooling rate higher than the critical cooling rate.

Next, an example of implementing the method of the present invention using the apparatus shown in FIG. 3 will be described.

High speed tool steel 5KH9, alloy tool steel S K D 61,
stainless steel 5US304, iron-based super heat-resistant alloy A, -2
The molten metal of Inconel 600, a nickel-based superheat-resistant alloy, is passed through a quartz tube nozzle 3 to a graphite roll 4a,
It was supplied toward the gap 4b.

The I-knolls 4a and 4b have a diameter of 80 alII and face each other with a gap of 0.1 m, and have a diameter of 6000 r, p, rn, respectively.
(peripheral speed of 25.1'm/sh). Roll 4a.

'::1 The molten metal droplets that passed between 4b are ejected downward at high speed,
250 (1r, p, m, maximum diameter 200
During this time, the powder was rapidly cooled by colliding with the circumferential surface of a copper rotating body 7a having a diameter of 180 M on both ends and a thickness of 20 m, to obtain alloy powder 8.

The alloy powder obtained had a size of 20 to 500 microns. As a result of microscopic examination of these alloy powders, regardless of the size of the powder particles, the grain size of the crystal grains is approximately 5.
The crystal grains were significantly finer and more uniform than the alloy powder of the same chemical composition produced by the conventional method.

As explained above, according to the method of the present invention, a roll made of a material that does not easily get wet with molten metal is rotated at high speed,
The molten metal is dropped and supplied to the rotating surface 7, and the negative pressure generated within the molten metal causes cavitation to break up into fine molten droplets, which are then released at high speed by centrifugal force onto the rotating surface of the rotating body, which has good thermal conductivity. Since the particles are collided and rapidly solidified and cooled at a rate higher than the critical cooling rate, it is possible to easily obtain an alloy powder having a fine crystal structure with small variations. In addition, since rapid solidification occurs by colliding with the rotating surface of a metal rotating body with good thermal conductivity, the cooling rate can be significantly faster than that of the conventional method of rapid cooling using a cooling liquid, allowing for a wider range of chemical composition. Its industrial utility value is extremely large, as it has become possible to turn the alloy into an alloy powder having a microstructure iIk.

[Brief explanation of drawings]

Fig. 1 is a partially cut-away elevation view schematically showing the main parts of an embodiment of the method of the present invention, and Fig. 2 is a similar elevation view showing an embodiment in the case of two identical []-rules. , FIG. 3 is a similar elevational view showing another embodiment of the rotating body, and FIG. 4 is a similar elevational view showing another embodiment using the inner peripheral surface of the rotating body. ■... Crucible, 2... Molten metal, 3... Nozzle,
4...Roll, 4a14b...Roll pair, 5...
Cooling jacket, 6... Molten metal droplets, 7.7a, 7
b...Rotating body, 8...Metal powder, 9...Container Patent attorney Patent attorney FL Kamoshi (second son, Figure 7, Figure 2, Ward 3, Figure 4)

Claims (1)

[Claims] The molten metal is dropped through a nozzle onto the surface of a roll that has a surface layer with low wettability for the molten metal and is rotating at a circumferential speed of 2 m/sec or more -F, and the molten metal is finely dispersed. After dividing the molten metal droplets into 10
A method for producing microstructured alloy powder, in which it is collided with a metal rotating body that rotates at a circumferential speed of m/s or more and is rapidly solidified.