KR20200046238A - Manufacturing method of Tungsten carbide-iron sintered body for metal mold processing - Google Patents

Abstract

Disclosed is a method of manufacturing a tungsten carbide-iron sintered body for processing a metallic material. The method comprises: a feeding step of feeding raw material powder obtained by mixing tungsten carbide with iron in a predetermined ratio into a high-strength stainless accommodation container; a grinding step of feeding the raw material powder and a separate superhard ball into the accommodation container and performing ball milling, such that the raw material powder is mixed, ground, and cold-jointed to be formed into alloyed mixed powder; a drying step of drying the mixed powder in a sealed space in a vacuum atmosphere or in an inert gas atmosphere at a temperature of 50-110°C for a predetermined time; a pre-pressurization step of filling the inside of a graphite mold with the mixed powder ground by completing the grinding step and keeping the graphite mold at a pressure of 10 MPa for 10-30 minutes, such that the mixed powder is evenly distributed; a mounting step of connecting a plurality of electrically-charging means to the pressurization unit or the graphite mold, such that a DC pulse current is applied in a sealable sintering chamber; a vacuuming step of adjusting the inside of the sintering chamber to a vacuum state; a sintering step of pressurizing the mixed powder at a predetermined pressure through the pressurization unit, increasing and reducing a temperature of the mixed powder to a predetermined temperature according to a predetermined pattern by applying a current to each electrically-charging means, and sintering the mixed powder to form a sintered body; and a cooling step of reducing, after the sintering step, the pressure applied to the sintered body, maintaining the reduced pressure, and cooling the graphite mold at a constant temperature of 700-1100°C, wherein the graphite mold is energized multiple times by the plurality of electrically-charging means, such that the mixed powder is heated up to a target temperature within a short time and sintered.

Description

Manufacturing method of tungsten carbide-iron sintered body for metal mold processing

The present invention relates to a method for manufacturing a tungsten carbide-iron sintered body for processing a mold material, and more specifically, a tungsten carbide-iron having high density and uniform internal and external properties in a short time by mixing tungsten carbide and iron powder and using a DC pulse current sintering device. It relates to a method for manufacturing a tungsten carbide-iron sintered body for processing a mold material capable of manufacturing a sintered body.

With the recent industrial development, high-performance, high-precision characteristics are required in all industrial products as well as in the automobile, shipbuilding, aerospace / aviation industry and architecture. Products with excellent characteristics and long life span are widely applied to aircraft, rocket engines and heat-resistant alloys used as parts of the surroundings, lightweight alloys, and medical and general household products that were difficult to use in commercial consumer products.

Due to the excellent mechanical / physical properties of these materials, the workability is greatly deteriorated, and in particular, it is often a major problem in manufacturing parts requiring mass production or high precision.

Materials with poor machinability are generally referred to as difficult-to-cut materials, and when machining difficult-to-cut materials, the wear of the tool is fast, cutting temperature, cutting resistance, surface roughness and cutting chips are fused to the blade. In order to solve these problems, high-efficiency processing of these difficult-to-cut materials greatly contributes to reduction of product manufacturing cost and high-quality, etc., to solve these problems, physical vapor deposition (PVD), chemical vapor deposition (CVD), diamond-like carbon (DLC) film, etc. The coating layer is formed and commercialized, but there is a problem in that the tool unit cost increases due to the increase in the process cost due to the secondary coating process and post-treatment process.

Such a cemented carbide material can be largely divided into a melting / casting method and a powder metallurgy method according to the manufacturing method. Among them, the melting / casting method is the most common method, and it is easy to mass-produce and has the advantage of lowering the manufacturing cost. However, it has limitations in controlling grains, increasing density, and preventing oxidation of materials. There are disadvantages that are required.

On the other hand, when using the powder metallurgy method, a homogeneous phase distribution, fine grain control, high melting point material is easy to manufacture and oxidation prevention is possible, and the range of design freedom of composition and component ratio is large, so that a sintered body having various composition components can be produced. As it has an advantage, it has been actively applied as an alternative to the melting / casting method.

However, as a widely used method of the conventional powder metallurgy method, HIP (Hot Isostatic Pressing) and HP (Hot Pressing) methods that can obtain a relatively high density sintered body by simultaneously applying temperature and pressure have been mainly used. New process technology development is required due to the limitations of grain control, the difference in physical properties inside and outside of the sintered body by external indirect heating method, and costly process cost.

The present invention has been devised to solve the above requirements, and it is possible to control the particle growth of the tungsten carbide powder and the iron powder sintered body using a direct current pulse current-active sintering process, but it is possible to control high-density, uniformity and properties in a short time in a single process. To provide a method of manufacturing a tungsten carbide-iron sintered body for mold material processing using DC pulse current-active sintering, which has characteristics of high strength, has a lower process cost than HP or HIP, and has little difference in properties between inside and outside. There is this.

In order to solve the above problems, the method for manufacturing a tungsten carbide-iron sintered body for processing a mold material according to the present invention includes a high-strength stainless steel container containing a raw material powder obtained by mixing powders of tungsten carbide (WC) and iron (Fe) at a predetermined ratio. In the input step, the raw material powder and a separate cemented carbide ball into the receiving container and performing ball milling to mix and crush and cold bond the raw material powder to produce an alloyed mixed powder, and the mixed powder. Drying step of drying at about 50 to 110 ° C for a predetermined time in a vacuum atmosphere or a closed space of an inert gas atmosphere, filling the mixed powder pulverized through the grinding step inside the graphite mold and mixing the powder with a predetermined pressure. Pre-pressurizing step to pre-pressurize to distribute evenly, DC pulse before sealing inside the sinterable chamber A mounting step of connecting a plurality of energizing means to the pressurizing part or the graphite mold to allow energization, a vacuuming step of adjusting the inside of the sintering chamber to a vacuum state, and pressurizing the mixed powder with a constant pressure through the pressurizing part. , By applying a current to each of the energizing means to increase and decrease the temperature to a set temperature according to a preset pattern and sintering the mixed powder into a sintered body and maintaining the pressure applied to the sintered body under reduced pressure after the sintering step while maintaining the graphite And a cooling step in which the mold is isothermally cooled between 600 and 1000 ° C, and the graphite mold is energized multiple times by a plurality of the energizing means to sinter the mixed powder by heating to a target temperature in a short time.

In addition, the grinding step may be characterized in that the container is rotated at a predetermined speed, the carbide ball is moved separately inside, mixing and grinding the raw material powder.

In addition, in the crushing step, 50 to 100 RPM of inert gas or liquid nitrogen is added to the storage container or a high-energy ball milling method that proceeds for about 10 hours at a rate of 250 to 300 RPM by adding ethanol to the container. Any of the attrition ball milling methods that proceed at a speed of about 10 to 20 hours can be used.

In addition, the input step may be mixed by adding the iron in a weight ratio of 5 to 10 based on the weight part 100 of the tungsten carbide.

In addition, the mounting step may be characterized in that the energizing means has at least three or more engagement points, and is respectively connected to the left and right sides of the pressing part and the graphite mold based on the pressing portion.

In addition, in the sintering step, the current ratios of the DC pulses applied to the energizing means may all be the same, or at least one or more may be differently adjusted.

In addition, the sintering step may be heated to a heating rate of 30 to 100 ° C / min, isothermal for 5 to 10 minutes in a predetermined temperature range, and the graphite mold may be heated to reach a target temperature of 1000 to 1300 ° C.

In addition, the vacuuming step may vacuum the inside of the sintering chamber to 6 Pa or less in order to suppress oxidation of the mixed powder and formation of a second phase due to gas or impurities.

The method for manufacturing a tungsten carbide-iron sintered body for processing a mold material according to the present invention has the following effects.

First, it is possible to manufacture a tungsten carbide-iron sintered body by using a DC pulse current energized sintering, and it is possible to manufacture a sintered body having a uniform structure and high purity with little particle growth in a short time.

Second, there is an advantage in that the sintered body can be stably produced during sintering by performing fine grinding and alloying of the mixed powder through a crushing step using a separate superfine ball before sintering the powder mixed with tungsten carbide and iron.

 The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is a view showing the configuration of a DC pulse current energizing sintering apparatus used in a method for manufacturing a tungsten carbide-iron sintered body for processing a mold material according to an embodiment of the present invention;
2 is an image of a mixed powder obtained by grinding and mixing raw material powders of tungsten carbide and iron in an embodiment of the present invention;
3 is a view showing the shrinkage change of the mixed raw material according to the sintering temperature in the sintering apparatus according to the embodiment of the present invention;
4 is an image of a mixed powder taken at point A in FIG. 3;
5 is an image of a mixed powder taken at point B in FIG. 3;
FIG. 6 is an image of a mixed powder taken at point C in FIG. 3;
7 is a view showing the XRD image analysis results for the mixed powder at point A of Figure 3;
8 is a view showing the results of XRD image analysis of the mixed powder at point B in FIG. 3;
9 is a view showing the results of XRD analysis of the mixed powder at point C in FIG. 3; And
10 is a view showing the overall manufacturing process of a method for manufacturing a tungsten carbide-iron sintered body for mold material processing according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention, in which the object of the present invention can be specifically realized, will be described with reference to the accompanying drawings. In describing this embodiment, the same configuration

The same name and the same code are used, and additional description will be omitted.

First, referring to FIG. 1, the sintering apparatus 100 used in the method for manufacturing a tungsten carbide-iron sintered body for processing a mold material according to the present invention will be described as follows.

The method for manufacturing a tungsten carbide-iron (WC-5Fe) sintered body for cutting tool material according to the present invention is mixed with and crushed tungsten carbide (WC) powder and iron (Fe) powder, which are different materials, and then a DC pulse current conduction sintering device ( 100). Here, the tungsten carbide (WC) powder means a powder of a material in which tungsten (W) and carbon (C) are alloyed.

The DC pulse current energizing sintering apparatus 100 used in the present invention includes a sintering chamber 110, a cooling unit 120, a current supply unit 130, a temperature detection unit 140, a pump 150, a pressurizer 160, and a main It is provided with a controller 170 and an operation unit 180, additionally, the graphite mold 200 into which the mixed powder 205 is loaded, the pressing parts 215 and 216 for pressing the graphite mold 200 and the graphite mold ( 200) and the energizing means 220 connected to the pressing parts 215 and 216 to apply a pulse current.

The sintering chamber 110 is configured to be sealed, and there is provided an energizing means 220 at upper and lower parts spaced apart in the vertical direction, and although not shown, cooling water may be distributed to the energizing means 220 for heat dissipation. It is formed.

The cooling unit 120 is configured to allow cooling water to flow through the cooling water distribution pipe provided on the inner wall of the sintering chamber 110 and the cooling water distribution pipe provided by the energizing means 220.

The current supply unit 130 is controlled to the main controller 170 through the energizing means 220 to apply a pulse current.

The temperature detection unit 140 is preferably applied to the infrared temperature detection method for detecting the temperature through the viewing window provided in the sintering chamber 110.

The pump 150 is configured to discharge the inside air of the sintering chamber 110 to the outside.

The pressurizer 160 may be installed so as to pressurize the mixed powder 205 filled in the graphite mold 200, and in the illustrated example, the support means 212 for supporting the pressurizing portions 215 and 216 is lifted. A cylinder structure that can descend is applied.

The main controller 170 controls the cooling unit 120, the current supply unit 130, the pump 150 and the pressurizer 160 according to the operation command set through the operation unit 180, and is detected by the temperature detection unit 140. The temperature information is received and displayed through a display unit (not shown).

The graphite mold 200 is formed in a cylindrical shape, and a receiving groove is formed to charge the mixed powder 205 in the center. In addition, separate pressing portions 215 and 216 for pressing the mixed powder 205 loaded in the graphite mold 200 are provided.

Here, the pressing portions 215 and 216 are provided on the upper and lower portions of the graphite mold 200, respectively, and are configured to press and lower the mixed powder 205 by selectively raising and lowering.

In this embodiment, the pressing portions 215 and 216 are configured in a pair, and are disposed on the upper and lower portions of the graphite mold 200, at least one of which is raised and lowered, and applies pressure to the mixed powder 205 therein.

In the DC pulse current energizing sintering apparatus 100, a plurality of the energizing means 220 are provided on the pressing parts 215 and 216 and the graphite mold 200 spaced apart from each other on the basis of this. In addition, the mixed powder 205 can be rapidly heated by independently applying a DC pulse current through each of the energizing means 220.

In this embodiment, the energizing means 220 is provided at the upper and lower parts of the center of the pressing parts 215 and 216, and is spaced apart on both sides of the graphite mold 200, and provided at the upper and lower parts, respectively. That is, the energizing means 220 are each paired in the vertical direction, a plurality of pairs are spaced apart.

At this time, all of the current ratios of the DC pulses applied to the energizing means 220 may be the same, or at least one of the current ratios may be adjusted differently, and in this embodiment, the pulses are 5: 1, 12: 1, and 3: 1 respectively. A sintering of the mixed powder 205 is performed by applying a ratio.

As described above, in the present invention, a DC pulse current is applied to the mixed powder 205 through the DC pulse current energizing sintering apparatus 100, and at the same time, the sintered body can be sintered by being pressed by the pressing parts 215 and 216. .

Here, three or more of the energizing means 220 is provided to apply an electric current independently to each other, and thus an ultra-fast rapid sintering process is possible as the rotational combustion speed increases by a pulsed electric current that is energized in large quantities. At this time, the energizing means (220) are respectively spaced apart from each other on the left and right and the pressing portions (215, 216) of the graphite mold 200, as shown in Figure 1, each of which is a pair of terminals in the upper and lower parts It is provided.

Next, referring to FIGS. 2 to 10, the overall process of the method for manufacturing a tungsten carbide-iron sintered body for processing a mold material according to the present invention will be described as follows.

First, the manufacturing method according to the present invention is largely an input step (S100), a crushing step (S200), a drying step (S300), a prepressing step (S400), a mounting step (S500), a vacuuming step (S600), and a sintering step. (S700) and a cooling step (S800).

The input step (S100) is a process for mixing and crushing tungsten carbide and iron, which are raw materials for the production of tungsten carbide-iron sintered body manufactured through the present invention, based on powders having irregular shapes and different melting points. Make a raw material powder mixed at a set ratio.

The raw material powder is sealed in a container (not shown) made of high-strength stainless steel. At this time, ethanol or an inert gas (such as argon or nitrogen) is added together for the progress of the grinding step (S200) described later. The ethanol or inert gas prevents the raw material powder from being unintentionally contaminated or converted into a secondary product.

Here, inside the container is sealed with a separate carbide ball (not shown) inserted.

 And the cemented carbide ball is used to crush and mix the raw material powder of the tungsten carbide and iron in the grinding step (S200) described later.

The carbide ball is crushed and mixed with the raw material powder by rotation of the receiving container inside the receiving container. At this time, the cemented carbide ball is preferably made of a material that may generate friction with the container and does not generate impurities even at high speed rotation. In this embodiment, the cemented carbide ball is made of the same high strength stainless steel as the container.

Basically, in the input step (S100), the particles of the tungsten carbide and the iron powder are irregular, and they are simply mixed at a predetermined weight ratio in a state not evenly mixed.

In this embodiment, in order to prepare a sintered body of tungsten carbide-iron, the mixing ratio of the raw material powder is set at a weight ratio of 5 to 10 based on the weight part of tungsten carbide, and is put in the container. And the weight ratio of the cemented carbide ball and the raw material powder is preferably 15: 1.

As described above, in the input step (S100), the raw material powder and the cemented carbide ball in which the iron and tungsten carbide are mixed at a predetermined ratio are introduced into the container made of high-strength stainless steel, and then mixed in an atmosphere of ethanol or inert gas. And it is a process of sealing so that it can be pulverized to make an uncontaminated alloyed powder.

At this time, when ethanol is added to the container, the weight ratio is preferably 20 to 30 with the mixed raw material powder being 100.

Thus, after the input step (S100), the grinding step (S200) proceeds inside the container.

The crushing step (S200) is a process of crushing and alloying the raw material powder introduced into the receiving container in the input step (S100), and performs a ball milling process using the cemented carbide ball.

Specifically, in the crushing step (S200), the container is rotated at a predetermined speed and the cemented carbide ball is moved inside the container and mixed and crushed and cold bonded to the raw material powder to produce an alloyed mixed powder 205. .

In this embodiment, the grinding step is performed by a high-energy ball milling method, and the milling speed is 250 to 300 RPM, and the milling time is 10 hours (50 min milling / 10 min rest during milling), and the milling and cold bonding are performed. Allow the alloying of the mixed powder to proceed.

At this time, it is preferable to limit to within the range of 250 to 300 RPM in the pulverization step (S200), when the alcohol is gasified at 3000 RPM or more, gas impurities are contained on the powder surface and the pressure inside the stainless container is excessively high and There is a risk of the container being unsealed, and when the RPM is less than 250 RPM, the grinding time becomes too long, causing powder contamination due to wear of the container and the cemented carbide ball.

In addition, when the process time is less than 10 hours, the grinding time of the raw material powder is not appropriate, so that it is not possible to manufacture fine powder.

On the other hand, in the present embodiment, the crushing step (S200) was performed by a high energy ball milling method by mixing ethanol to use a wet milling method. Alternatively, the attrition ball milling method may be performed.

In the case of attrition ball milling, an atmosphere inert gas or liquid nitrogen, etc., may be introduced into the container to carry out the grinding step (S200) under conditions of a milling speed of 50 to 100 RPM and a milling time of 10 to 20 hours.

The pulverization step (S200) is such that the size of the mixed powder 205 is refined and induced to be more easily sintered in the sintering step (S700) described later due to mechanical alloying.

Referring to Figure 2, the image of the mixed powder 205 that has undergone the crushing step (S200) is set, and the tungsten carbide and iron are set at a weight ratio of 95 to 5 to carry out the crushing process at 250 rpm. As shown, the powder is evenly ground and mixed. Accordingly, in the crushing step (S200), it can be seen that the alloying of the raw material powder is performed through a high energy milling method as well as simple crushing.

By producing the mixed powder 205 alloyed by the pulverization step (S200) in this way, sintering can be stably performed even if the materials having different melting points are sintered in the sintering step (S700) described later.

In addition, the grinding step (S200) may additionally proceed to a separate homogenization process in order to homogenize the particles of the mixed powder 205 generated by the receiving container and the cemented carbide ball.

Specifically, the homogenizing process sprays the mixed powder 205 into a separate powder chamber (not shown) equipped with a spray nozzle (not shown) to have a spherical uniform size.

At this time, the outlet of the spray nozzle may be formed of 0.5 to 1 mmØ according to the particle size of the mixed powder 205, the inlet to which the mixed powder 205 is introduced is largely formed in a state, and of the spray nozzle The inlet temperature is 100 to 150 ° C, and the temperature at the outlet where the mixed powder 205 is injected is 80 to 100 ° C. Here, the powder chamber in which the mixed powder 205 is injected is configured to prevent oxidation and contamination of the mixed powder 205 by filling an inert gas such as argon or nitrogen therein in a sealed form.

In the above conditions, the mixed powder 205 is spheroidized by spraying with a pressure of 5 to 15 bar into the powder chamber through the spray nozzle. Accordingly, the crushing step (S200) passes through the additional homogenization process, and the mixed powder 205 subjected to the ball milling process may be produced as a spherical powder having a uniform particle size.

On the other hand, the drying step (S300) is a process of removing impurities and drying in the mixed powder 205 that has been subjected to the grinding step (S200).

Specifically, the drying step (S300) is to remove ethanol and fine gas contained in the mixed powder 205, and dried using separate vacuum drying air or inert gas (argon, hydrogen, nitrogen, etc.).

Here, in the drying step (S300), drying is performed in an enclosed space at about 50 to 110 ° C for 36 to 48 hours to remove ethanol, fine gas, or impurities.

Of course, in this embodiment, ethanol was used as the milling step S200 was performed using a wet milling method. Alternatively, when using the dry milling method, the drying step S300 may be omitted.

Next, the pre-pressurizing step (S400) is a process of filling the graphite mold 200 with a predetermined pressure to sinter the mixed powder 205 as described above at a high density.

The graphite mold 200 used in the direct current pulse current conduction sintering apparatus 100 according to the present invention has a through space that penetrates up and down inside, as shown in FIG. 1, and the mixed powder along the longitudinal direction ( 205) is charged. In addition, pre-pressurization is performed to maintain a predetermined pressure and pressurize the mixed powder 205 loaded inside the graphite mold 200 to be evenly distributed.

In this case, the graphite mold 200 may be configured to press the mixing portions 205 by inserting pressing portions 215 and 216 in the upper and lower portions of the sintering chamber 100.

In the pre-pressurizing step (S400), it is preferable to maintain the pressure of the mixed powder 205 at a pressure of 10 MPa to 20 MPa for 5 to 10 minutes, and sintering that is performed later by uniformly distributing the mixed powder 205 therein. In step S700, sintering is easily performed.

Subsequently, after the preliminary pressing step (S400), the mixed powder 205 is separately supplied to the pressing parts 215, 216 or the graphite mold 200 so that the DC pulse current can be received in the graphite mold 200. The installation step (S500) of connecting the energizing means 220 is performed.

The mounting step (S500) is a process of connecting the energizing means 220 to the pressing parts 215 and 216 and the graphite mold 200 inside the sintering chamber 110, first the graphite mold 200 Is seated inside the sintering chamber 110, and the pressing portions 215 and 216 are disposed in the upper and lower portions. At this time, in the preliminary pressing step 400, the graphite mold 200 may be inserted in the sintering chamber 100, and the pressing portions 215 and 216 may be inserted, otherwise, the mounting step (S500) is performed. It may be.

And the energizing means 220 at three points so that the DC pulse current can be applied to the left and right sides of the graphite mold 200 based on the positions where the pressing parts 215 and 216 and the pressing parts 215 and 216 are fastened. ) To receive DC pulse current. Specifically, the energizing means 220 is connected to the upper and lower portions of the pressing parts 215 and 216, respectively, as shown in FIG. 1 so that the mixed powder 205 is energized and heat is generated. Each of the graphite molds 200 located on both sides of the pressing parts 215 and 216 is additionally connected.

That is, the energizing means 220 is provided at two or more positions on both sides of the graphite mold 200 as well as the pressing parts 215 and 216, and the graphite mold 200 itself is applied by receiving a DC pulse current. Let it heat up. Here, as described above, the energizing means 220 has a pair of electrodes and is coupled to the pressing parts 215, 216 and the upper and lower parts of the graphite mold 200, respectively.

Accordingly, the DC pulse current through each of the energizing means 220 energizes each of the pressing parts 215 and 216 and the graphite mold 200, thereby raising the temperature and thereby increasing the temperature of the mixed powder 205. It can be raised quickly, reducing the overall sintering time.

As described above, in the mounting step (S500), after the graphite mold 200 is mounted inside the sintering chamber 110, the pressing parts 215 and 216 are inserted, and the energizing means 220 is additionally provided at three or more points. Is connected to the pressing parts 215 and 216 and the graphite mold 200.

The vacuuming step (S600) is to make the inner space of the sintering chamber 110 into a vacuum state, and discharge the air inside the sintering chamber 110 through the pump 150 to make it vacuum.

In general, the sintering chamber 110 is configured such that at least a portion is opened and closed to be selectively closed, and the air is discharged by discharging the air therein while the inside is closed.

At this time, the inside of the sintering chamber 110 is vacuumed to 6 Pa or less to suppress oxidation of the mixed powder 205 and formation of a second phase due to gas or impurities, and internal contamination of the sintering chamber 110 occurs. Prevent it.

On the other hand, in the sintering step (S700), while maintaining the mixed powder 205 filled in the graphite mold 200 by the pressurizing portions 215 and 216 at a constant pressure, the temperature is raised to a predetermined temperature according to a set heating pattern. And temperature.

Specifically, the sintering step (S700) is a step of sintering by heating the mixed powder 205, as shown in Figure 1, the mixed powder (205) in the graphite mold 200 through the pressing portion (215, 216) ) To maintain the pressure of 10 to 100MPa initially, and heating the mixed powder 205 in the graphite mold 200 according to the set temperature and isothermal patterns.

At this time, the sintering step (S700) increases the temperature of the graphite mold 200 to a predetermined temperature and then maintains the pressure and temperature for a certain period of time, and repeatedly raises and maintains the temperature to increase the temperature.

Here, in the case of the molding pressure of the mixed powder 205, high density cannot be achieved when applied at a pressure of 10 MPa or less, and the mold may be damaged when 100 MPa or more.

In this embodiment, the sintering step (S700) is heated to 30 to 100 ° C / min to the target temperature, isothermal for 5 to 10 minutes at a constant temperature section, and the temperature is raised to 1000 to 1300 ° C to mix the powder (205). ) To sinter.

In this way, the sintering step (S700) according to the present invention has a temperature rise pattern that maintains the temperature for a certain period of time as the temperature rises in a stair form rather than a linear temperature rise, and sintering is performed along the temperature rise pattern.

Here, due to the process of maintaining the temperature of the mixed powder 205 inside the graphite mold 200 for a period of time during the sintering process, the temperature difference between the central portion and the edge portion of the mixed powder 205 is reduced, and the overall temperature is reduced. It can be evenly distributed.

Meanwhile, in order to increase the temperature of the mixed powder 205, a direct current pulse current is applied through the energizing means 220 connected to each of the graphite mold 200 and the pressing parts 215, 216, and the graphite mold Heat is generated in the 200 and the pressing parts 215 and 216, so that the temperature of the mixed powder 205 increases.

Here, all of the pulse ratios of the DC pulse currents applied to each of the energizing means 220 may be the same, or at least one or more may be adjusted differently, and in this embodiment, pulses are in a ratio of 5: 1, 12: 1, 3: 1. Sintering is performed by applying a ratio.

As described above, when simply applying the direct current by connecting the energizing means 220 only the pressing parts 215 and 216, the temperature of the mixed powder 205 may be increased through the pressing parts 215 and 216, The graphite mold 200 itself heats up and rapidly increases the temperature of the mixed powder 205 by additionally applying a DC pulse current to the graphite mold 200 by configuring three or more of the energizing means 220 as in the present invention. Can be raised.

During such a manufacturing process, a large current in a low voltage pulse flows into a gap between particles of the mixed powder 205 by a current applied through the energizing means 220, and the high energy of the discharge plasma generated instantaneously by a spark discharge phenomenon The sintered body is formed by heat diffusion and electric field diffusion by heat and heat generated by electrical resistance of the graphite mold 200, and pressurized pressure and electrical energy.

In addition, as in the present application, heat is generated in the graphite mold 200 by a direct heating method in which a current is directly flowed to the mixed powder 205 which is a specimen by the pressing parts 215 and 216, and the graphite Direct current also flows in the mold 200 and additional heat is generated in itself.

Therefore, the heating of the graphite mold 200 is simultaneously generated in the mixed powder 205, which is a specimen, and the temperature difference between the inside and the outside of the specimen is small, and the thermal activation reaction generated during the sintering process due to the relatively low temperature and short sintering time. Can be minimized.

On the other hand, in the above-described sintering step (S700), heating the mixed powder 205 in a pattern that repeats the temperature increase and isothermal maintenance is to ensure that the shrinkage and density change according to the elevated temperature of the mixed powder 205 are sufficiently made. to be.

Specifically, referring to FIG. 3, it shows the temperature change inside the graphite mold 200 and the shrinkage change of the mixed powder 205 accordingly. As the temperature increases during the sintering process, the shrinkage rate at point A and point B and C respectively Indicates change.

First, looking at point A in the illustrated drawing, it can be seen that the mixed powder 205 is heated to be adjacent to about 700 ° C, and rapidly expands as the temperature increases. Here, looking at the section of point A, the mixed powder 205 of tungsten carbide and iron is not properly melted, and sintering is starting.

4, the microstructure of the mixed powder 205 of tungsten carbide and iron at point A is an image taken with an electron microscope, and as the sintering of the mixed powder 205 begins, In other words, it was confirmed that some of the particles were changed from spherical to square.

And, referring to FIG. 7, X-ray diffraction (XRD) phase analysis of the mixed powder 205 at the point A was detected, and tungsten carbide and iron were detected, respectively, and the second phase was not detected. Accordingly, it can be seen that impurities that may be mixed during the high-energy ball milling process did not occur in the crushing step (S200), and no impurities were mixed during the sintering step (S700).

Here, it can be seen that in the temperature range of point A (about 700 ° C), it is a low temperature for sintering the mixed powder 205 of tungsten carbide and iron.

On the other hand, looking at point B of Figure 3, it can be seen that the mixed powder 205 is heated to be adjacent to about 950 ° C, and contraction, not expansion, is progressing. However, looking at the section of point B, the mixed powder 205 of tungsten carbide and iron is not sufficiently melted, and the sintering of the mixed powder 205 is in progress, but it has not yet been sufficiently achieved.

5, the image of the microstructure of the mixed powder 205 of tungsten carbide and iron at point B is taken with an electron microscope. As shown in FIG. 4, as the sintering of the mixed powder 205 progresses to some extent, Unlike the image, a quasi-melting phenomenon was found, and it was confirmed that a large number of particles were deformed and particle growth was achieved.

And when looking at the result of the XRD phase analysis of FIG. 8, as in FIG. 7, materials other than tungsten carbide and iron were still not detected, and thus, no contamination occurred.

Of course, since the sintering temperature did not reach the target temperature, the mixed powder 205 was not sufficiently sintered, but it can be seen that sintering is in progress correctly.

Thus, in the sintering step (S700), in the case of sintering at a temperature of the B point (about 950 ° C), some crystals are deformed and contracted, but the sintering is not sufficiently performed.

Subsequently, looking at the point C of FIG. 3, the sintering temperature of the mixed powder 205 increased to about 1100 ° C. Looking at the front, it can be seen that the contraction occurred rapidly compared to the temperature section of the point B (about 950 ° C). In particular, looking at the image of point C shown in FIG. 6, a microstructure of a tungsten carbide-iron (WC-5Fe) sintered body was photographed, and it was confirmed as a high density WC-5Fe sintered body that had undergone a complete densification step.

Here, the shrinkage of the mixed powder 205 means that the gap between the particles becomes narrower, thereby increasing the density of the sintered body, and accordingly, physical properties such as rigidity and durability of the sintered body increase.

At this time, looking at the XRD image analysis result of FIG. 9, it can be seen that most of the tungsten (WC) is detected and the other two-phase substances are not detected, so that the sintering has been properly performed. However, in the production of tungsten carbide-iron (WC-5Fe) sintered body, the content of iron (Fe) is a small amount within 5%, so it is melted during the sintering process and penetrated into the particles of tungsten carbide (WC), thereby substantially It does not detect well.

However, since iron (Fe) was detected at the previous point B and impurities other than tungsten carbide were not detected, it can be seen that sintering of pure tungsten carbide-iron (WC-5Fe) proceeded correctly.

As described above, in the sintering step (S700), sintering of the mixed powder 205 of tungsten carbide and iron is performed through the above-described process, and powder particles are determined by melting as the sintering temperature increases from 700 ° C to 1100 ° C. The mixed powder 205 is completely sintered by changing to a grown plate shape and becoming dense.

Particularly, as the sintering temperature increased to 1100 ° C, iron (Fe) was completely melted, so that rapid crystal growth can be confirmed compared to the existing sintering process, and the relative density of the sintered body greatly increased from about 64% to 99.5%.

Here, as the sintering temperature increases, it can be seen that the relative density increases significantly, but the grain size increases slightly. This is because, as in the present invention, multiple currents were applied through three energizing means 220 when applying a DC pulse current. This is because the sintering proceeds more than three times faster than the sintering apparatus, and the densification speed is increased while the grain growth is suppressed.

In addition, as a result of evaluating the mechanical properties of the sintered body, in the case of hardness and fracture toughness, the WC-5Fe sintered body prepared at the final point C was measured to have a hardness of 2347.5 Hv30 and a fracture toughness of 6.35 MPa.m1 / 2.

When the sintered tungsten carbide-iron sintered body is manufactured as described above, the mixed powder 205 can be stably sintered by performing sintering with a target temperature of about 1100 ° C, and by applying a DC pulse current multiple times at three or more points. The sintering temperature can be rapidly increased by heating the pressing parts 215 and 216 and the graphite mold 200 together.

After the sintering step (S700), the cooling step (S800) is performed to cool the sintered body. Here, the cooling step (S800) also proceeds the process of isothermal cooling while maintaining the pressure acting on the sintered body under reduced pressure according to a predetermined pattern rather than rapid cooling.

When entering the cooling step (S800), while blocking the direct current pulse current applied to the graphite mold 200 and the pressing portion (215, 216) while maintaining the inside of the graphite mold 200 at a constant pressure After cooling at 1000 ° C, 800 ° C and 600 ° C for a cooling pattern that maintains the temperature for about 3 minutes, it is cooled to room temperature while maintaining the basic pressure again.

After the cooling step (S800), the sintered tungsten carbide-iron sintered body from the graphite mold 200 is demolded.

As described above, the method for manufacturing a sintered body according to the present invention is first crushed and alloyed with a raw material powder of tungsten carbide and iron, followed by sintering by heating and pressing according to a preset pattern. At this time, the sintering temperature can be rapidly increased by applying a DC pulse current to both the graphite mold 200 and the pressing parts 215 and 216 through three or more energizing means 220 during sintering.

In addition, due to the rapid temperature rise, the density of the sintered body increases and the structure becomes dense, so that the sintered body having high hardness and wear resistance can be manufactured to be suitable for a cutting tool.

As described above, the preferred embodiments according to the present invention have been examined, and the fact that the present invention can be embodied in other specific forms without departing from the spirit or scope of the embodiments described above has ordinary skill in the art. It is obvious to them. Therefore, the above-described embodiments are to be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description and may be changed within the scope of the appended claims and their equivalents.

100: sintering device
110: sintering chamber
120: cooling unit
130: current supply
140: temperature detection unit
150: pump
160: pressurizer
170: main controller
180: control panel
200: graphite mold
205: mixed powder
215, 216: pressing part
220: energizing means

Claims (8)

A step of introducing a raw material powder obtained by mixing tungsten carbide (WC) and iron (Fe) powders at a predetermined ratio into a high-strength stainless steel storage container;
A pulverization step of introducing a carbide ball separate from the raw material powder into the receiving container and performing ball milling to mix and crush and cold bond the raw material powder to produce an alloyed mixed powder;
A drying step of drying the mixed powder in a vacuum atmosphere or in a closed space in an inert gas atmosphere at a temperature of about 50 to 110 ° C. for a predetermined time;
A pre-pressurizing step of filling the mixed powder pulverized through the crushing step in a graphite mold and pre-pressurizing the mixed powder to be evenly distributed at a preset pressure;
A mounting step of connecting a plurality of energizing means to the pressurizing portion or the graphite mold so that a direct current pulse current can be energized inside the sealable sintering chamber;
A vacuuming step of controlling the inside of the sintering chamber to a vacuum state;
A sintering step of pressing the mixed powder with a constant pressure through the pressing part, applying a current to each of the energizing means to increase and decrease the temperature to a set temperature according to a preset pattern, and sintering the mixed powder with a sintered body; And
A cooling step in which the graphite mold is cooled and isothermal between 600 and 1000 ° C. while maintaining the pressure applied to the sintered body under reduced pressure after the sintering step; It includes,
The graphite mold is a method of manufacturing a tungsten carbide-iron sintered body for mold material processing in which a plurality of energized means are energized multiple times to sinter the mixed powder by heating to a target temperature in a short time. According to claim 1,
The grinding step,
A method of manufacturing a tungsten carbide-iron sintered body for mold material processing, characterized in that the container is rotated at a predetermined speed and the cemented carbide ball is separately moved therein to mix and crush the raw material powder. According to claim 2,
The grinding step,
High-energy ball milling that proceeds for about 10 hours at a rate of 250 to 300 RPM by adding ethanol to the receiving container or inert gas or liquid nitrogen together to the receiving container for about 10 hours to at a rate of 50 to 100 RPM. A method of manufacturing a tungsten carbide-iron sintered body for processing a mold material using any one of the attrition ball milling methods for 20 hours. According to claim 1,
The input step,
A method of manufacturing a tungsten carbide-iron sintered body for mold material processing to be mixed by adding the iron in a weight ratio of 5 to 10 based on the weight part of the tungsten carbide 100. According to claim 1,
The mounting step,
A method of manufacturing a tungsten carbide-iron sintered body for mold material processing, characterized in that the energizing means has at least three or more bonding points, and is respectively connected to the left and right sides of the graphite mold based on the pressing portion and the same. According to claim 1,
The sintering step,
A method of manufacturing a tungsten carbide-iron sintered body for mold material processing in which all of the current ratios of the DC pulses applied to the energizing means are all the same or at least one is differently controlled. According to claim 1,
The sintering step,
Tungsten carbide-iron sintered body for mold material processing for heating at a heating rate of 30 to 100 ° C / min, isothermal for 5 to 10 minutes in a predetermined temperature range, and heating the graphite mold to reach a target temperature of 1000 to 1300 ° C Way. According to claim 1,
The vacuuming step,
A method of manufacturing a tungsten carbide-iron sintered body for mold material processing to vacuum the inside of the sintering chamber to 6 Pa or less to suppress oxidation of the mixed powder and formation of a second phase due to gas or impurities.

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