JPH03177506A - Production of superhard alloy or cermet alloy - Google Patents

Abstract

PURPOSE:To prevent the deformation of a molded body and the occurrence of defects at the time of removing an org. binder and to improve quality by successively treating the molded body made of a powdery mixture of alloy powder with the binder in an inert gas and in vacuum and then carrying out sintering. CONSTITUTION:Superhard alloy powder or cermet alloy powder is mixed and kneaded with an org. binder. A molded body formed by injection-molding the kneaded material is heated in an inert gaseous atmosphere to remove the org. binder and the residual org. binder is perfectly removed by further heating in vacuum of <=1 Torr pressure. The molded body is then sintered to obtain a dense alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for manufacturing cemented carbide or cermet alloy, and in particular, it relates to a method for manufacturing cemented carbide or cermet alloy, and in particular, manufacturing cemented carbide powder or cermet alloy powder into a predetermined shape by injection molding. The present invention relates to a method for producing a cemented carbide or a cermet alloy, which is formed by molding, removing an organic binder, and sintering.

[Conventional technology] Cemented carbide and cermet alloys are high melting point materials.

Therefore, when obtaining cemented carbide sintered bodies or cermet alloy sintered bodies, powder raw materials have traditionally been press-formed or C
A powder metallurgy method is used in which sintering is performed after IP molding. However, this method has many restrictions on the shapes that can be manufactured. In order to obtain a complex final shape, it is necessary to grind the sintered body with a diamond grindstone after sintering, resulting in an extremely high cost.

It is widely known that plastics are molded by injection molding. Japanese Patent Publication No. 62-33282 discloses that metal powder or ceramic powder is kneaded with an organic binder,
A method of molding this into a complex-shaped article by injection molding is disclosed.

[Problems to be Solved by the Invention] However, when powder injection molding technology is applied to cemented carbide or cermet alloy, the following problems occur.

That is, cemented carbide powder and cermet alloy powder are fine powders with a particle size of about 1 μm. Furthermore, these alloys have a high specific gravity.

Furthermore, the tolerance for carbon concentration in the alloy is small. Due to the material properties of such cemented carbide and cermet alloy, deformation and defects are likely to occur during the binder removal process. Moreover, a good quality alloy cannot be obtained due to the influence of residual carbon due to decomposition of the organic binder. In order to avoid such problems, it is necessary to perform the binder removal process for a very long time. Due to the above-mentioned problems, injection molding technology for cemented carbide and cermet alloys has hardly been put into practical use yet.

[Summary of the Invention] The object of the present invention is to efficiently mold cemented carbide powder or cermet alloy powder by injection molding, and then to produce high quality cemented carbide or cermet alloy through a subsequent debinding process and sintering process. The goal is to provide a method that can be used to obtain the desired results.

Another object of the present invention is to provide a method that does not cause deformation or defects in the molded body during binder removal treatment.

Still another object of the present invention is to provide a method that can perform binder removal treatment in a short time.

The manufacturing method of cemented carbide or cermet alloy, which is a prerequisite for this invention, includes the steps of mixing and kneading cemented carbide powder or cermet alloy powder with an organic binder, and molding this mixed powder into a predetermined shape by injection molding. and then a step of removing the organic binder from the molded body and sintering it. In such a method,
The present invention is characterized in that the organic binder is first removed in an inert gas atmosphere as a first removal step, and then in a vacuum below ITo r r as a second removal step.

In one aspect of the invention, the organic binder includes multiple types of binders classified into a group that can be removed at low temperatures and a group that can be removed at high temperatures.

The composition of each binder in the organic binder was determined in an inert gas atmospheric pressure heating weight loss test (TG) of only the organic binder - when the low temperature removal group lost 30% of the total weight loss, the high temperature removal group had a weight loss rate of within 5%. selected to meet the following conditions. Preferably, the proportion of the binder belonging to the low-temperature removal group to the total organic binder is 30
% or more and 90% or less.

In another aspect of the invention, the temperature at which the transition from the first (removal step) to the second removal step is performed is selected to satisfy the following conditions. The condition is that the amount removed is 30% or more of the total organic binder, and the residual proportion of the binder belonging to the high temperature removal group is 5% or more of the total organic binder.Main component of the low temperature removal group The binder has a hydrophilic polar group with a melting point of 80
'C or lower waxes are preferred.

After the organic binder in the molded body is removed by the method described above, the molded body may be subsequently subjected to a sintering treatment. Alternatively, after removing the organic binder, the material may be cooled by -0.degree. and then sintered.

The injection molded product is composed of powder and a binder, and has almost no voids. When the temperature of the molded body is raised in this state, the binder first flows out due to expansion of the binder, and then the binder is removed by evaporation from the surface. When 30% of the binder is removed through this process, pores are formed inside the molded body that communicate with the surface. Gas generated inside the molded body is removed through the pores, and debinding further progresses. However, if gas is generated inside the molded article with less than 30% binder removed, the molded article will crack or bulge. In order to prevent such cracking and blistering of the molded product, it is necessary to suppress the generation of gas inside the molded product at a slow temperature increase rate until the binder removal reaches 30%.

Therefore, the binder removal process requires a long time. As the binder, waxes as a plasticizer and polymer resins as a binder are required. Since waxes evaporate at low temperatures without being decomposed, binder removal can be performed relatively easily. On the other hand, since polymeric resins generate a large amount of gas when decomposed, defects are likely to occur in the molded product at the initial stage of binder removal.

The inventor of the present application has focused on the above-mentioned points and has accomplished the present invention. Specifically, a polymer resin that does not start decomposing even when a temperature at which 30% or more of the waxes are removed is selected, and the polymer resin and the waxes are mixed. In the initial state of the binder removal process,
By evaporating only the waxes, 30% or more of the binder is removed and continuous pores are formed inside the molded body. After the pores are formed, the decomposition of the polymer resin is started.

The main component waxes of the low-temperature removal group include Hoechst wax, carnauba wax, montan wax, osikerite wax, ouricuri wax, candelilla wax, beeswax, microcrystalline wax, and the like.

Binders in the high temperature removal group include low density polyethylene, low molecular weight polyethylene, ethylene vinyl acetate, polypropylene, acrylic resin, and the like.

In the initial state of the binder removal process, the atmospheric pressure is maintained above atmospheric pressure to prevent defects from occurring in the molded body. After continuous pores have been formed inside the compact, the atmospheric pressure is reduced to a vacuum state or close to vacuum to allow the gas to evaporate from the surface or to release the gas generated inside the compact. promote.

Let's focus on the strength of injection molded products. If the polymeric resin that is the binder is removed, the bonding force between powder particles will be extremely reduced, and cemented carbide, etc. with a high specific gravity will collapse.

In order to prevent this, it is necessary to bond the powders forming the alloy to obtain strength. However, since the surface of the alloy powder is covered with a thin oxide film, bonding by diffusion is difficult to occur. The inventors of the present invention have discovered that if the binder is removed in a vacuum, the surface of the alloy powder is reduced by the surrounding carbon, resulting in a bonding force between the powders. Thus, in the present invention, powder particles are bonded together by promoting binder removal in a vacuum state. If the powder particles are bonded together, the molded body will not collapse until the binder removal is completed. In a preferred embodiment of the present invention, the binder removal process is performed in two stages: a first removal process and a second removal process. The first removal step is performed under an atmospheric pressure atmosphere, and the second removal step is performed under a vacuum atmosphere. At least 5% of the binder must remain when moving from the first removal step to the second removal step. If the residual amount of binder is less than 5%, the compact will collapse before the bonding force between the powder particles is generated.

Next, the atmosphere of the binder removal process will be described.

The first removal step is preferably performed in an inert gas atmosphere such as N2 or Ar. When debinding is performed in an oxidizing atmosphere such as air, Co,
Surface oxidation of Ni, etc. progresses. If such a surface oxidation layer exists, the bonding strength due to reduction will decrease in the second removal step. In addition, as binder removal progresses, oxidation progresses only in the parts exposed to the surrounding atmosphere, resulting in uneven carbon concentration within the alloy, resulting in uneven liquid phase appearance temperature during sintering, which reduces dimensional accuracy. It will decrease significantly. It is possible to reduce the oxide film on the surface of the alloy powder by performing the second removal process not in a vacuum (in an H2 atmosphere). However, if the binder removal process is performed in an H2 atmosphere, Carbide C, which is a hard phase forming component of the alloy, reacts with hydrogen to form CH4
At the same time, the reaction that produces . Therefore, the carbon content of the alloy will be reduced.

Next, we will discuss the types of wax. The surfaces of cemented carbide powder and cermet alloy powder are hydrophilic.

On the other hand, waxes such as n-paraffin are hydrophobic. Therefore, the wettability between wax such as n-paraffin and cemented carbide powder or cermet alloy powder is poor. Therefore,
In order to obtain the viscosity required for injection molding, it becomes necessary to use more wax. The inventor of this application is
After investigating various waxes, we found that the amount of binder can be reduced by using a certain type of natural wax that has hydrophilic polar groups. Further, when the molded product is removed from the mold during injection molding, the molded product is easily broken because the wax is brittle.

In order to prevent such destruction, it is desirable to use a wax with a melting point of at least 80° C. or lower. If it is a wax with a hydrophilic polar group and a melting point of 80°C or less,
Whether it is synthetic or natural, its effectiveness remains the same. Incidentally, stearic acid or the like may be used as a lubricant, but even if such a small amount of additive is used, the effects of the present invention will not change.

[Example] Example 1 80% WC powder with a particle size of 2 to 4 μm, T with a particle size of 1 to 2 μm
IC powder 10%, C with particle size 2-4 μm.

10% of the powder was mixed in a wet ball mill for 3 hours and dried. Beeswax 6.0% for this mixed powder 100%
%, low molecular weight polyethylene added 1.0%, 120℃
They were kneaded for 30 minutes.

Next, this raw material mixture is cooled and solidified, and then pulverized to have a particle size of 0. Raw material grains of 5 to 2.0 mm were produced. Next, a mold in the shape of an indexable chip (20x20x6m
A molded article was produced by injection molding in step m). The molded body was placed in a furnace, and the inside of the furnace was maintained at 1 atmosphere with an Ar atmosphere.

The temperature inside the furnace was raised to 425° C. at a temperature increase rate of 8° C./hour under the condition that the flow rate of Ar was 3 t/min, and the binder removal process was performed. Next, the temperature inside the furnace was raised to 700° C. at a temperature increase rate of 50° C./hour while keeping the inside of the furnace at 0.5 Torr or less using a vacuum pump, and the temperature was maintained at that temperature for 1 hour and then cooled. In this way, the binder removal process was completed. Next, the inside of the furnace is 0.05
A vacuum of Torr was applied, the temperature was raised to 1400° C. at a rate of 200° C./hour, and the temperature was maintained at that temperature for 1 hour, followed by cooling. The sintered body thus obtained had no defects and had good alloy properties. When the binder used in this example was subjected to a heating weight loss test, the beeswax lost weight by 95% by 425° C. under the condition of 1 atm of N2. Furthermore, the weight loss of low molecular weight polyethylene at 425°C is 13
%Met.

Example 2 90% WC powder with particle size 0.5-2 pm, particle size 2-4 μm
10% of Co powder was mixed in a wet ball mill for 20 hours and dried. 5.5% carnauba wax and 0% low molecular weight polypropylene were added to 100% of this mixed powder, and kneaded at 40° C. for 30 minutes. Next, this raw material mixture is cooled and solidified, then pulverized, and the particle size is approximately 0.5 to 2.0.
Raw material grains of mm size were produced. Next, injection molding was performed using a mold (20 x 20 x 6 mm) in the shape of an indexable tip. This molded body was placed in a furnace.

The interior of the furnace was at industrial pressure in an Ar atmosphere, and the temperature was raised to 430'C at a rate of 10°C/hour under conditions of a flow rate of 3L/min to perform an initial binder removal process.

Next, use a vacuum pump to pump the inside of the furnace to zero. ．． Raise the temperature to 700°C at a heating rate of 50°C/hour while maintaining the temperature below 2 Torr,
It was held at that temperature for ↓ hours. In this way, the binder removal process was completed. Thereafter, the temperature inside the furnace was raised to 1350° C. at a rate of 200° C./hour under a vacuum of 0°05 Torr, and after being maintained at that temperature for 1 hour, it was cooled. The sintered body thus obtained had no defects and had good alloy properties. In addition, when a heating loss test was conducted on the binder used in this example, it was found that N2 was heated to 43% at atmospheric pressure.
By 0°C, the carnauba wax had lost 92% weight. Further, the weight loss of the low molecular weight polypropylene at 430°C was 8%.

Example 3 88% WC powder with a particle size of 0.1% or more μm, a particle size of 2 to 4 μm
6% CO powder and 6% Ni powder having a particle size of 2 to 4 μm were heated in a wet ball mill for 25 hours and then dried. 0.0% beeswax for 100% of this mixed powder. 5%, n-paraffin 4.5%, stearic acid 0. 2%, ethylene vinyl acetate 0. 5%, low molecular weight polyethylene 1. 0%
was added and kneaded for 30 minutes at 20°C. Next, this raw material mixture is cooled and solidified, then pulverized, and the particle size is about 0. 5～
2. Raw material grains with a diameter of 0 mm were produced. Next, injection molding was performed using a mold (20 x 20 x 6 mm) in the shape of an indexable tip. This molded body was placed in a furnace. The inside of the furnace was set to L atmospheric pressure in a N2 atmosphere, and the temperature was raised to 380'C at a temperature increase rate of 13°C/hour under conditions of a flow rate of 2L/min, and an initial binder removal process was performed. Next, while keeping the inside of the furnace at 0.5 Torr or less using a vacuum pump, the temperature was increased at a rate of 50°C/
The temperature was raised to 70,000 in hours, maintained at that temperature for 1 hour, and then cooled. In this way, the binder removal process was completed.

Next, the inside of the furnace was vacuumed to 0.05 Torr and heated to 1350°C.
The temperature was raised at a rate of 200° C./hour to 200° C., maintained at that temperature for 1 hour, and then cooled. The sintered body thus obtained had no defects and had good alloy properties. When the binder used in this example was subjected to a heat loss test, the weight loss of beeswax was 60% and the weight loss of n-paraffin was 100% by 380° C. under the condition of N2.1 atm. Further, at 380°C, the weight loss of low molecular weight polyethylene was 7.0%, and the weight loss of ethylene vinyl acetate was 10%.

Example 4 88% of WC powder and 12% of Co powder with a particle size of 1 to 2 μm were mixed in a wet ball mill for 5 hours and dried. Based on 100% of this mixed powder, 5.5% of montan wax and 0.0% of low density polyethylene. 8% was added and kneaded at 120°C for 3 hours. Next, this raw material mixture was cooled and solidified, and then pulverized to produce raw material particles having a particle size of about 0.5 to 2.0 mm. Next, a mold in the shape of an indexable tip (20x20
Injection molding was performed at This molded body was placed in a furnace. The inside of the furnace is set to 1 atmosphere with Ar atmosphere, and the flow is ff.
The temperature was raised to 350° C. at a rate of 10° C./hour under the conditions of 13 L/min, and an initial binder removal process was performed. Next, while keeping the inside of the furnace at Q, 5 Torr or less using a vacuum pump, the temperature was raised to 650° C. at a heating rate of 50'C/hour, and after being maintained at that temperature for a working time, the binder removal process was completed by cooling. Next, the inside of the furnace was vacuumed to 0.05 Torr and 140
The temperature was raised to 0°C at a rate of 200°C/hour, maintained for 1 hour, and then cooled. The sintered body thus obtained had no defects and had good alloy properties. When the binder used in this example was subjected to a heating loss test, it was found that N
Under the condition of 2.1 atm, the weight loss of montan wax was 93% by 350°C, and the measured weight loss of low density polyethylene was 0% at 350°C.

Ta.

Example 5 Cermet powder (TaC 10%,
TaC10%, Mo2C12%, WCl5%, Ni5%
, C010%) for 10 hours in a wet ball mill,
Dry. To 100% of this mixed powder, 7.8% of montan wax, 2.7% of n-paraffin, 2.7% of low density polyethylene, and 0.3% of stearic acid were added.
The mixture was kneaded at ℃ for 3 hours. Next, this raw material mixture is cooled and solidified, then pulverized, and the particle size is about 0. Raw material grains of 5 to 2.0 mm were produced. Next, injection molding was performed into a ball end mill-shaped mold having a diameter of IQ mm to obtain a molded product. This molded body was placed in a furnace. The inside of the furnace is set to t atmosphere in Ar atmosphere,
The temperature was raised to 350° C. at a rate of 10° C./hour under conditions of a flow rate of 3 and 7 minutes to perform an initial binder removal treatment.

Next, while keeping the inside of the furnace at 0.5 Torr or less using a vacuum pump, the temperature was raised to 650 °C at a temperature increase rate of 50 °C/hour, and after being held at that temperature for 1 hour, it was cooled to complete the binder removal process. . Next, the inside of the furnace was evacuated to 0.05 Torr, and the temperature was raised to 1400°C at a rate of 200°C/hour, held for 1 hour, and then cooled, and then HIP treatment was performed at 1350°C. The sintered body thus obtained had no defects and had good alloy properties. When a heat loss test was conducted on the binder used in this example, N2.
Under the condition of 1 atm, the weight loss of montan wax is 93%, and the weight loss of n-paraffin is 100% by 350°C.
Furthermore, the weight loss of the low density polypropylene at 350°C was measured to be 0%.

Example 6 A plurality of molded raw material particles were produced under the same conditions as in Example 1. The state of these compacts after binder removal was examined by varying the temperature increase rate in the first removal step of the binder removal treatment and the transition temperature to the second removal step. The results are shown in Table 2. Table 1 also shows the results of heat loss tests for beeswax and low molecular weight polyethylene (PE).

As is clear from the results in Tables 1 and 2, according to the method of the present invention, the condition after binder removal is good and the binder removal time can be shortened.

(Leaving space below) Table Ⅰ Heating loss rate (N21ata 10℃/min! Temperature) Table 2 Temperature test results for transition to the second removal step ○ mark Method of the present invention 6 4 Example 7 The same alloy powder as in Example 1 was used. Test No.
10 to 17), a binder removal test was conducted. The results are shown in Table 3.

The transition temperature from the first removal step to the second removal step is 450
℃. As is clear from the results in Table 3, it is recognized that the composition of the present invention is good.

(Margins below) Table 3 (Note) ○ Marked method of the present invention The binder composition is the ratio to 100% of the alloy powder Example 8 Binder removal test using the same alloy powder as in Example 3 and changing the binder type and composition was carried out. The results are shown in Table 4. Note that the binder removal conditions were the same as in Example 3. Test NQ.

For samples No. 8 to No. 20, good injection and binder removal were possible. However, test N0921 with n-paraffin
could not achieve good injection without increasing the amount of n-paraffin. Further, in test No. 22, deformation occurred during the binder removal process. Test No. 23, in which beeswax and n-paraffin were mixed at a ratio of 1:1, required addition of a small amount of binder, but no deformation was observed during binder removal.

(Leaving space below) Table 4 Wax types and results (Note) O mark The composition of the isotropic binder of the present invention is the ratio to 100% of the alloy powder Example 9 In the same manufacturing method as Test No. 5 in Table 2, the first removal The atmosphere of the process and the second removal process was changed as shown in Test Nos. 24 to 30 in Table 5. As is clear from the results in Table 5, it is recognized that the atmosphere of the present invention is effective.

Samples of test Nos. 26 and 29 collapsed during binder removal, so they could not proceed to the sintering step. Other samples were able to proceed to the sintering process.

(Margin below) O mark: method of the present invention

Claims (5)

[Claims] (1) Mixing and kneading cemented carbide powder or cermet alloy powder with an organic binder, molding this mixed powder into a predetermined shape by injection molding, and then removing the organic binder from this molded body and sintering it. In a method for manufacturing a cemented carbide or cermet alloy, in which a dense alloy is obtained by Characterized by being carried out in a vacuum,
Method of manufacturing cemented carbide or cermet alloy. (2) The organic binder includes multiple types of binders classified into a group that can be removed at low temperature and a group that can be removed at high temperature, and the organic binder of each binder in the low temperature removal group including the i type of binder is The proportion a_1, a_2,...
, a_i, and the proportion of each binder in the high-temperature removal group containing j types of binders to the total organic binder is b_
1, b_2, ..., b_j (Σa_i+Σb_j=1
), a certain temperature T in the inert gas atmospheric pressure heating weight loss test (TG) of each binder belonging to the low temperature removal group.
Let xT_1, xT_2, ..., xT_i be the weight loss rate at a certain temperature T in the inert gas atmospheric pressure heating weight loss test of each binder belonging to the high temperature removal group, then let yT_1, yT_2, ..., yT_j be the weight loss rate at The composition of each binder in the organic binder is selected to satisfy the following conditions: Σ(b_j×yT_j)≦0.05 Σb_j≧0.1 at a temperature T such that Σ(a_i×xT_i)=0.3 A method for producing a cemented carbide or a cermet alloy according to claim 1. (3) The temperature T at which the first removal step shifts to the second removal step is selected to satisfy the following conditions: Σa_i×xT_i>0.3 Σb_j×(1−yT_j)>0.05; A method for producing a cemented carbide or cermet alloy according to claim 2. (4) The method for producing a cemented carbide or cermet alloy according to claim 2, wherein the low-temperature removal group includes waxes having a hydrophilic polar group and a melting point of 80° C. or lower. (5) The method for producing a cemented carbide or cermet alloy according to claim 3, wherein the low-temperature removal group includes a wax having a hydrophilic polar group and a melting point of 80° C. or lower.