KR0163992B1 - Method for powder of wc-co alloy - Google Patents

Abstract

The present invention relates to a method for producing an ultrafine WC / Co alloy powder by a chemical method, and more particularly, to an ultrafine WC / Co alloy by a chemical method for improving the mechanical properties of the alloy and improving wear resistance. It relates to a method for producing a powder.

In the method for preparing ultra-fine WC / Co alloy powder according to the chemical method of the present invention, an AMT-Co (NO ₃ ) ₂ solution is prepared using a spray dryer to prepare starting powder in which CoWO ₄ and WO ₂ phases of porous spherical bodies are present. A first step of reducing the initial powder into a porous W / Co powder at a low process temperature using N ₂ / H ₂ gas in a reaction tube furnace, and CO / H of the W / Co powder A third step of carburizing with ₂ gas to produce WC / Co powder, and a fourth step of controlling and removing carbon activity in a CO / CO ₂ atmosphere by removing free carbon present in the ultrafine WC / Co powder after carburizing is completed. The process takes place.

Description

Manufacturing method of ultra fine WC-Co alloy powder

1 is a process block diagram showing a manufacturing process according to the manufacturing method of ultra-fine WC-Co alloy powder by the chemical method according to the present invention.

Figure 2 is a SEM photograph of the starting powder powder chemically pulverized according to the manufacturing method of ultra-fine WC-Co alloy powder by the chemical method according to the present invention.

Figure 3 is a graph showing the weight loss change of the powder particles with the temperature change when reducing the initial powder in accordance with the manufacturing method of ultrafine WC-Co alloy powder by the chemical method according to the present invention.

(A) of FIG. 4 is a graph showing the intensity of the XRD peaks of the CoWO ₄ powder and the WO ₂ powder forming the initial powder under a state in which reduction is not initiated.

(B) of FIG. ₄ shows the intensity of XRD peak of CoWO ₄ powder and WO ₂ powder and W-Co powder reduced with CoWO ₄ powder and WO ₂ powder after heating the initial powder to a temperature of 750 ° C. for 1 hour. Graph showing.

Figure 4 (c) is a graph showing the intensity of the XRD Peak of the W-Co powder CoWO ₄ powder and WO ₂ powder reduced after the initial powder is heated to a temperature of 750 ℃ for 3 hours.

Figure 4 (d) is a graph showing the intensity of the XRD peak of the reduced W-Co powder after heating the starting powder to a temperature of 750 ℃ for 4 hours.

(A) of FIG. 5 is a graph showing the weight change when the carburizing temperature of the WC-Co powder is 700 ° C.

FIG. 5B is a graph showing the weight change when the carburizing temperature of the WC-Co powder is set at 750 ° C.

(C) of FIG. 5 is a graph showing the weight change when the carburizing temperature of the WC-Co powder is set at 800 ° C.

6 is a TEM photograph showing the shape and size of a WC-Co powder containing 10% Co by weight percent.

The present invention relates to a method for producing an ultrafine WC-Co alloy powder by a chemical method, and more particularly, to a method of preparing ultrafine WC-Co alloy powder by a chemical method for improving mechanical properties and improving wear resistance of a cemented carbide. It relates to a manufacturing method.

In general, cemented carbide is manufactured by mixing and molding TiC, TaC, Mo ₂ C, and VC together with a binder or by sintering alloy powder containing tungsten carbide (WC) by powder metallurgy. It is used for dice materials.

In the case of WC-Co cemented carbide, the chemical composition, the particle size distribution of the WC powder particles and the carbon content in the alloy, the porosity of the microstructure and the degree of inclusion of foreign substances are known to affect the mechanical properties. The distribution of WC powder and Co acts as a major factor in determining the properties of cemented carbide.

In this case, as the WC powder is distributed in a small particle size and the WC powder and Co are uniformly distributed and distributed, mechanical properties such as hardness, compressive strength, and tensile strength (TRS) can be improved.

On the other hand, the above-described method for producing a WC-Co-based cemented carbide is usually prepared by grinding WC powder having a particle size of 0.5 μm through pulverization, mixing Co and the like, and then sintering at high temperature and for a long time.

However, since the conventional method for producing a WC-Co-based cemented carbide is manufactured by a physical method through pulverized mixing of the WC powder, the grain size cannot reach the nano grain level of 0.1 μm or less. It is difficult to miniaturize, uniformly distributed with a mixture such as Co, not only requires a long process time and a high process temperature, but also has problems such as incorporation of process impurities, thereby limiting the improvement of mechanical properties and wear resistance of the cemented carbide.

Therefore, there is a need for a method and means capable of producing particles of WC at nanocrystalline levels of 0.1 μm or less.

The present invention has been made to meet the above-described conventional requirements, an object of the present invention is to require a method and means for producing particles of WC powder by the chemical method to a nanocrystalline level of 0.1 μm or less. have.

The present invention has been made in order to meet the above-described conventional requirements, the object of the present invention is to produce a particle of WC powder by a chemical method to a nanocrystalline level of 0.1μm or less, and also uniform distribution of Co and the like In addition to improving the mechanical properties of the cemented carbide, and to provide a method for producing ultra-fine WC-Co alloy powder by a chemical method that can maximize the improvement of wear resistance.

In order to realize this, the present invention provides a step of preparing an initial powder containing CoWO ₄ and WO ₂ phases using an AMT-Co (NO ₃ ) ₂ solution using a spray dryer, and adding the initial powder to a N ₂ / H ₂ comprising the steps of reduction to the porous W / Co powder using a gas mixture, comprising the steps of: preparing a WC / Co powder by carburization of the W / Co powder with CO / H ₂ gas mixture, wherein the carburizing is finished WC / It provides a method for producing an ultra-fine WC-Co alloy powder, characterized in that the step of controlling the carbon activity in the CO / CO ₂ mixed gas atmosphere to remove the free carbon present in the Co powder.

And, in order to remove the salt in the initial powder is heat-treated at a temperature of 350 ~ 400 ℃, the reduction step of the initial powder is characterized in that it proceeds for 3 to 4 hours at a temperature of 350 ~ 800 ℃ in a hydrogen atmosphere.

In addition, the carburizing step is performed for 20 to 25 minutes at a temperature of 750 ~ 800 ℃, characterized in that the average particle size of WC in the WC-Co alloy powder is 0.1μm or less.

Hereinafter, the reason for numerical limitation of this invention is demonstrated.

First, the reason for limiting the temperature range for removing the salt of the starting powder is 350 to 400 ° C., as shown in FIG. 3, when the salt of the starting powder is removed, a rapid weight loss starts from 350 ° C. and the weight is lost after 400 ° C. This is because it is gradually decreasing. This sudden change in weight means that salts are being removed from the starting powder.

In addition, the reduction of the starting powder in the hydrogen atmosphere is for the reduction of the starting powder by reducing the reactivity with oxygen, that is, reducing the hydrogen atmosphere with a strong reducing power, and the temperature range is limited to 350 to 800 ° C. This is because the change in weight of the specimen begins to occur at 350 ° C and remains constant at 800 ° C, as shown in FIG.

In other words, this indicates that the reduction of the starting powder starts at 350 ° C and ends at 800 ° C.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

EXAMPLE

FIG. 1 is a block diagram showing a manufacturing process of the ultrafine cemented carbide powder according to the present invention. In the first process, a starting powder is prepared by spray drying the AMT-Co (NO ₃ ) ₂ solution.

Here, Ammonium Meta Tungstate (AMT) represents (NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ ) 4H ₂ O.

The starting powder prepared as described above has a spherical shape with an average particle size of 30 to 40 μm, as shown in FIG. 2. In the starting powder, some water is present, and the amount of water is large when the amount of the solution flowing into the spray dryer is large. Increased.

In addition, since the initial powder contains salts having strong affinity with water, when stored in the air, it is necessary to remove salts having strong affinity with water because it absorbs moisture rapidly. For this, it is heated in air at 400 ° C.

Accordingly, water and most salts in the starting powder, that is, NH ₄ , NO _3, etc. are removed, and the starting powder is present in the form of an oxide. In the process, the weight of the starting powder is reduced by about 30%.

As described above, the initial powder in the form of an oxide in which water and salts are removed is reduced in a N ₂ -H ₂ mixed gas atmosphere.

W-Oxide (WO ₂ ), Co-Oxide + H ₂ → W-Co + H ₂ O ↑

In addition to the H ₂ gas directly participating in the reduction in the above N ₂ gas was added in a ratio of 3: 1, for the purpose of cost reduction.

According to this scheme, the TGA results of the weight loss of the specimen when the starting powder is reduced in the hydrogen atmosphere are shown in FIG.

According to FIG. 3, the weight of the specimen decreases rapidly as most salts are removed below 400 ° C., and oxygen remaining in the powder is almost removed at 800 ° C., and the reduction is completed. The weight of the powder is about 40% after the final reduction treatment. It can be seen that the decrease.

4 shows that CoWO ₄ and WO ₂ phases are reduced as the reduction proceeds as a result of XRD of the initial powder and the W-10% Co powders reduced at 750 ° C.

(A) of FIG. 4 shows that CoWO ₄ and WO ₂ phases are present in the powder as the initial powder under the condition that no reduction is initiated.

(B) of FIG. ₄ shows the XRD results of CoWO ₄ powder and WO ₂ powder and W-Co powder with reduced CoWO ₄ powder and WO ₂ powder after the initial powder was heated to a temperature of 750 ° C. for 1 hour. .

(C) of FIG. 4 shows the intensity of the XRD peak of the W-Co powder in which the CoWO ₄ powder and the WO ₂ powder are reduced after the initial powder is heated to a temperature of 750 ° C. for 3 hours.

(D) of FIG. 4 shows the intensity of the XRD peak of the reduced W-Co powder after the initial powder was heated to a temperature of 750 ° C. for 4 hours.

As shown in FIG. 4, when the spray dried raw powder is heated to a temperature of 750 ° C. for 4 hours, both CoWO ₄ powder and WO ₂ powder are reduced to W-Co powder, and the reduced powder is spherical like the initial powder. Although it is maintained, it can be seen that the size is reduced by about 20 to 30% as a porous material.

This is thought to be due to the removal of oxygen in the powder by reduction, the pore size increases with the reduction temperature.

In addition, the W-Co powder has a difference in reducing conditions for the complete reduction to WC according to the content of Co contained in the double, the reduction is completed in TGA as Co content increases from 3% by weight to 18% by weight The time gradually decreases.

That is, heating time for 90 minutes is required when Co is 3% by weight, heating time is 50 minutes when Co is 6% by weight, and 45 minutes when Co is 10% by weight. The complete reduction is completed through the heating time.

In this way, the spherical porous W-Co powder having the reduction effect is carburized.

In other words, the spherical porous W-Co powder is carburized in a CO-H ₂ mixed gas atmosphere, and the ultra-fine W-Co micropores are filled with the excess decomposition carbon, and the carbon reacts rapidly with the W particles, thus providing the following reaction formula: According to WC.

W + 2CO → WC + CO ₂ ↑

The addition of H ₂ gas in a ratio of about 4: 1 in addition to the CO gas directly acting on the carburizing action is for cost reduction in addition to the action of cleaning the surface of the powder to be carburized.

W-Co powders containing 10% Co by weight were still present in Co ₃ W ₃ C intermediate carbide phases when maintained for 10 minutes at a temperature of 800 ° C. It was confirmed that the carburizing was completed by XRD, carburizing time required about 25 minutes at the carburizing temperature 750 ℃.

The carburized ultrafine WC-Co powder is decarburized to remove free carbon remaining in the WC-Co powder.

Free carbon is produced during the carburization process and can be removed by fixing the carbon activity to 0.4 in a CO-CO ₂ mixed gas atmosphere.

At this time, the reaction formula is WC + C + CO ₂ → WC + 2CO, was added by adjusting the ratio of CO-CO ₂ to prevent the decarburization of C in the WC generated when CO ₂ alone.

The fifth turning WC-10 wt% Co powder with 700 ℃, when 750 ℃, decarburization treatment carburization at a temperature of 800 ℃, illustrates the reaction time and the weight change when the done decarburization in the CO-CO ₂ atmosphere further weight The decarburization reaction is completed in the section where the decrease does not occur, and the time taken for the reaction decreases as the reaction temperature increases.

However, comparing the half-widths of the XRD peaks of the ultra-fine WC-Co powders prepared at each temperature, the process time was decreased as the reaction temperature was higher, but the size of the prepared powder was greatly increased. .

Ni plating on the wc-10 wt% Co powder prepared at a temperature of 700 to 800 ° C. followed by electrolytic polishing, and the photograph observed by TEM is shown in FIG. 5. WC-10 wt% Co prepared at 700 to 750 ° C. The cemented carbide powder can have a particle size of about 30 to 50 nm, but at 800 ° C., the WC particles grow considerably.

Therefore, in consideration of both the reaction rate and the size of the WC particles, the time required for carburizing and decarburizing at 750 ° C. in the reaction tube furnace was 3.5 hours and 5 hours, respectively. Was about 50 nm.

In addition, as the Co content decreases, the time required to complete carburization increases rapidly, and a carburizing time of about 30 minutes is required for 3 wt% Co.

However, in the case of Co content of 12% by weight and 18% by weight, carburization and decarburization time were drastically reduced compared to 10% by weight.

The reason is that Co increases the catalytic decomposition effect of Co gas during carburization.

The ultrafine cemented carbide powder according to the chemical method according to the present invention and the manufacturing method thereof produce particles of WC powder at the level of nanocrystal grains of 0.1 μm or less, and make uniform distribution of Arler Co and the like to mechanically produce cemented carbide. In addition to improving the properties, there is an advantage that can maximize the improvement of wear resistance.

Claims (5)

Preparing an initial powder containing CoWO ₄ and WO ₂ phases using an AMT-Co (NO ₃ ) ₂ solution using a spray dryer, and using the N ₂ -H ₂ mixed gas in a reaction tube furnace. Reducing the porous W-Co powder, carburizing the W-Co powder with a CO-H ₂ mixed gas to produce a WC-Co powder, and free carbon present in the carburized WC-Co powder. Method for producing an ultra-fine WC-Co alloy powder, characterized in that consisting of the step of controlling the carbon activity in the CO-CO ₂ mixed gas atmosphere. The method for producing ultrafine WC-Co alloy powder according to claim 1, characterized in that heat treatment is performed at a temperature of 350 to 400 ° C. to remove salts in the starting powder. The method of claim 1, wherein the reducing step is performed for 3 to 4 hours at a temperature of 350 to 800 ℃ in a hydrogen atmosphere. According to claim 1, wherein the carburizing step is a method for producing ultra-fine WC-Co alloy powder, characterized in that performed for 20 to 25 minutes at a temperature of 750 ~ 800 ℃. The method for producing ultrafine WC-Co alloy powder according to claim 1, wherein the average particle size of WC in the WC-Co alloy powder is 0.1 µm or less.