KR20110114249A - Method for manufacturing high speed steel powder compact - Google Patents

Abstract

A method for producing high speed tool steel specimens is disclosed. The method includes injecting the high speed tool steel powder into a chamber in a discharge plasma sintering system and compressing the high speed tool steel powder under preset sintering conditions to sinter the high speed tool steel specimen. This makes it possible to produce high speed tool steel specimens in a minimal process.

Description

Method for manufacturing High Speed Steel powder compact}

The present invention relates to a high speed tool steel specimen manufacturing method, and more particularly to a method for manufacturing a high speed tool steel specimen using the discharge plasma sintering method.

As the industry diversifies, various types of products are being developed and distributed, and various industrial devices for manufacturing these products are also being developed.

In particular, the quality of the machines making the various machines, ie machine tools, has also been significantly improved. Therefore, research into the quality of the materials making these machines is also underway.

One such material is High Speed Steel (HSS). The high speed tool steel was named because it was a revolutionary tool material that, when invented, could be used at a higher speed than previous carbon tool steels or alloy tool steels. High-speed tool steels contain tungsten-based tungsten (T system) containing 12 to 18% of tungsten and chromium vanadium cobalt, and molybdenum system (M system) to which tungsten is reduced and molybdenum is added.

High speed tool steels are often used for high speed cutting because they have high wear resistance, strength, hardness, ductility and especially high temperature characteristics. High speed tool steels can generally be produced by powder metallurgy rather than casting. However, in general powder metallurgy, it was difficult to manufacture complex and small parts.

In particular, among these high speed tool steels, especially the T42 tool steel has a high Vickers hardness of more than 500, and the density of the tissue should also be manufactured to a density close to 100% with almost no pores or defects.

To this end, conventionally, a high-speed tool steel specimen was manufactured by a special sintering process using a powder metallurgy method, followed by a subsequent heat treatment process to improve hardness while maintaining the structure unchanged.

However, such a prior art has a difficulty in that the process is complicated, and in particular, a detailed heat treatment operation is required through several steps, making it difficult to produce a high speed tool steel specimen of a desired quality.

Thus, there is a need for a method that can produce high quality tool steel specimens in a more convenient way.

The present invention is in accordance with the above-described needs, an object of the present invention is to provide a method for producing a high speed tool steel specimen using the discharge plasma sintering method.

According to an embodiment of the present invention for achieving the above object, a method for manufacturing a high speed tool steel specimen includes the steps of injecting a high speed tool steel powder into a chamber in a discharge plasma sintering system, compressing the high speed tool steel powder under a predetermined sintering condition. Sintering the high speed tool steel specimen.

In this case, the sintering conditions,

Temperature: 900 ℃ ~ 1150 ℃

Pressure: 3000 ~ 4000kgf

Temperature rise rate: 100 ℃ / min

Sintering time: 10 minutes

Mold: Graphite

Sintering atmosphere: can be 10 ^-2 torr vacuum,

The high speed tool steel powder may be a T42 high speed tool steel powder.

According to the present invention, the specimen of the high speed tool steel can be easily manufactured by using the discharge plasma sintering method. In particular, it provides an optimum sintering condition that can utilize discharge plasma sintering.

1 is a view showing the configuration of a high speed tool steel specimen manufacturing system according to an embodiment of the present invention,
2 is a photograph for explaining the shape of the T42 high speed tool steel powder,
3 is a view showing the current flow between the high speed tool steel powder in the sintering process,
4 is a graph comparing the hardness and density according to the sintering temperature, and
5 shows a FESEM photograph of the surface of the specimen sintered at 1100 ° C.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

1 is a view showing the configuration of a high speed tool steel specimen manufacturing system according to an embodiment of the present invention.

The system of FIG. 1 includes a DC pulse generator 10, an upper compression unit 20, a lower compression unit 30, a side support 40, and a chamber 50.

The chamber 50 refers to a configuration in which high-speed tool steel powder is injected into the specimen. In FIG. 1, the portion surrounded by the upper compression unit 20, the lower compression unit 30, and the side support part 40 is referred to as a chamber 50, but the upper compression unit 20 and the lower compression unit 30 are referred to as chambers 50. The outer chamber including all of the side supports 40 and the like may be referred to as a chamber. For convenience of description, the portion designated by the reference numeral 50 will be referred to as a chamber.

Meanwhile, the chamber 50 may be provided with an air valve (not shown) or an exhaust pump (not shown) for vacuuming the inside of the chamber. In addition, a temperature sensor may be attached to accurately sense the temperature inside the internal chamber 50. As shown in FIG. 1, the temperature sensor may be connected to the inside of the inner chamber 50 through the side support 40.

In addition, the shape of the side support portion 40 and the shape of the upper compression unit 20, the lower compression unit 30 may be variously changed. That is, in order to produce a cylindrical specimen, the side support portion 40 may be in the form of a hollow cylindrical tube, and the punch portion coupled to the upper and lower compression portions 20 and 30 may have a cylindrical shape for compressing the inside of the side support portion 40. It can be a structure. On the other hand, in order to produce a square or rectangular specimen, the side support portion 40 may be in the form of a tube having a square cross section, and the punches of the upper and lower compression portions 20 and 30 may also have a square columnar structure corresponding thereto. have. In addition, of course, it can be implemented in a variety of shapes.

In this state, the high speed tool steel powder is introduced into the internal chamber 50. As the material of the high speed tool steel powder, T42 high speed tool steel may be used. T42 high speed tool steel means that the high speed tool steel material contains more Co and V than conventional materials. According to one embodiment of the invention, the chemical composition of the high speed tool steel powder may be made as shown in the following table.

ingredient C Cr Mo Co V W wt% 1.27 4.18 3.50 9.50 3.36 9.59

As shown in Table 1, the composition of the high speed tool steel may be made of C, Cr, Mo, Co, V, W. The composition and composition ratio are not limited to Table 1, and may be changed in various forms.

That is, the chemical composition of the T42 high speed tool steel powder may be configured as follows.

CHEMICAL COMPOSITIONS (mass%) SPECIFICATION RESULTS C 1.200-1.350 1.271 Si MAX 0.40 0.30 Mn MAX 0.40 0.28 P MAX 0.030 0.008 S MAX 0.030 0.006 Ni MAX 0.25 0.06 Cr 3.80-4.50 4.18 Mo 3.00-4.00 3.50 Cu MAX 0.25 0.03 Co 9.00 to 11.00 95.0 V 3.00 to 3.70 3.36 W 9.00 to 11.00 9.59         O (ppm) REPORT 2,100

In addition, the characteristics of the T42 high speed tool steel powder may be configured as shown in the following table.

SCREEN ANALYSIS
(mass%) SPECIFICATION RESULTS +30 MAX 10.0 5.7 30 to 20 MAX 15.0 11.8 20 to 10 MAX 45.0 31.5 -10 MIN 40.0 51.0 MEAN SIZE D50 9.00-11.00 9.78 TAP DENSITY REPORT 4.31

2 is a photograph showing an example of the shape of the T42 high speed tool steel powder. According to FIG. 2, the powder may be provided in various sizes and shapes.

As such, when the high-speed tool steel powder is introduced into the internal chamber 50, sintering is performed under preset sintering conditions. Accordingly, a specimen of high speed tool steel is manufactured by the spark plasma sintering method.

The discharge plasma sintering method refers to a method in which sintering proceeds by thermally diffusing or electric field diffusion of high energy of a high-temperature discharge plasma instantaneously generated by spark discharge by applying pulse electric energy directly between particles while applying mechanical pressure. do. It is similar to the pressure sintering (HIP: Hot Isostatic Press) method in that pressure and heating are performed at the same time, but has the advantage of being capable of sintering at low temperature and in a short time.

When the high speed tool steel powder is provided in the inner chamber 50, the exhaust pump (not shown) or the air valve (not shown) connected to the inner chamber 50 is adjusted to appropriately adjust the atmosphere inside the inner chamber 50. . For example, the atmosphere inside the inner chamber may be controlled to about 10 ⁻² torr vacuum.

When sintering is started in such a state, compression is performed while the punch provided in each of the upper compression part 20 and the lower compression part 30 moves in the inner direction of the inner chamber 50. In this case, the side support portion 40 disposed on the inner chamber 50 side supports the compression, so that the high-speed tool steel powder is compressed in all directions.

In addition, the electrical energy generated by the DC pulse generator 10 along with the compression is applied to the upper compression unit 20 side. That is, current flows between the upper compression unit 20 and the lower compression unit 30. In this process, some current flows along the side support 40, but some current flows through the high speed tool steel powder inside the inner chamber 50. This is because the high speed tool steel powder itself has conductivity.

According to one embodiment of the present invention, the sintering conditions may be implemented as follows.

Temperature: 900 ℃ ~ 1150 ℃

Pressure: 3000 ~ 4000kgf

Temperature rise rate: 100 ℃ / min

Sintering time: 10 minutes

Mold: Graphite

Sintering atmosphere: 10 ^-2 torr vacuum

Accordingly, the hardness of the sintered high speed tool steel specimen may be realized up to about Hv 600 when the relative density is 99% and about Hv 400 when the relative density is 88%.

In addition, the particle size of the sintered state may be on the order of 20 microns on average.

3 is a view showing a current state flowing through the high speed tool steel powder particles in the sintering process.

According to FIG. 3, the electric current is transferred to the surrounding particles along the surface of each particle and flows toward the lower compression part 30. As a result, Joule's heat is generated as shown in FIG. 3 where the particles are in contact with each other. The particle surface is activated, so atoms move easily and spread heat. In addition, the temperature at which the particles contact each other increases due to Joule's heat, causing plastic flow, etc., from the initial point of sintering, and densifying at a very high speed. Thereby, sintering advances rapidly.

When the sintering is completed, the upper compression unit 20, the lower compression unit 30 is moved back to the original position, to release the compression. As a result, the sintered specimen of the high speed tool steel existing in the inner chamber 50 is output to the system. In this case, the upper compression portion 20, the lower compression portion 30, the side support portion 40 may be made of graphite (Graphite) so that the high-speed tool steel specimen can be easily derived.

4 shows a graph comparing hardness and relative density according to sintering temperature.

According to FIG. 4, when the sintering temperature is 900 ° C., the relative density is about 76% and the hardness is 200 Hv. Moreover, when sintering temperature is 1000 degreeC, a relative density will be about 90% and hardness will be about 400 Hv. Moreover, when sintering temperature is 1100 degreeC, a relative density will be nearly 100% and hardness will be about 600 Hv level.

As described above, referring to the graph of FIG. 4, by controlling the sintering temperature appropriately, a high speed tool steel specimen having a desired hardness and relative density can be manufactured.

FIG. 5 shows a FESEM (Field Emission Scanning Electron Microscopy) photograph of the surface of a high speed tool steel specimen obtained at a sintering temperature of 1100 ° C. FIG. The photograph of FIG. 5 is the photograph taken in the state which expanded 10000 times. In FIG. 5, a portion indicated as a white dot means a carbide formed inside a particle forming a specimen. As can be seen in Figure 5, the high-speed tool steel specimen prepared according to the present method can be seen that the structure is dense, the hardness is high.

Thus, according to the present invention, it is possible to produce a high hardness, high density material, that is, a high speed tool steel specimen in a single process.

As a result of the experiment compared to the conventional manufacturing method, the following experimental results were confirmed.

Manufacturing method Conventional PM method MIM method MIM method HIP Sintering Law Discharge Plasma Sintering Discharge plasma sintering method
Hardness (Hv) 530 500 350 600 600 400 Relative density (%) 99 95 88 99 99 88 MC Carbide Distribution Precipitation Precipitation Precipitation No precipitation M6C Carbide Distribution Grain boundary precipitation Grain boundary precipitation Grain boundary precipitation Precipitation in the mouth

According to Table 4, when the discharge plasma sintering method, a much simpler process than the other sintering method, it is possible to obtain the same or better hardness and relative density characteristics compared to the other sintering method. In addition, when the 600Hv, 99% relative density, MC carbide is not precipitated, it can be seen that M6C carbide also has the property of precipitation inside the particle, not the grain boundary.

Thus, according to the present invention, it is possible to produce a high-density, high-hardness tool steel specimen in a much more convenient way than in the prior art.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the above-described specific embodiment, the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

10: DC pulse generator
20: upper compression part
30: lower compression part
40: side support
50: inner chamber

Claims (2)

In the high speed tool steel specimen manufacturing method,
Injecting the high speed tool steel powder into a chamber in a discharge plasma sintering system; And
And compressing the high speed tool steel powder under a predetermined sintering condition to sinter the high speed tool steel specimen. The method of claim 1,
The sintering conditions,
Temperature: 900 ℃ ~ 1150 ℃
Pressure: 3000 ~ 4000kgf
Temperature rise rate: 100 ℃ / min
Sintering time: 10 minutes
Mold: Graphite
Sintering atmosphere: 10 ^-2 torr vacuum,
The high speed tool steel powder is a high speed tool steel powder manufacturing method, characterized in that the T42 high speed tool steel powder.

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