Production method for cemented carbide powders

Abstract

To provide cemented carbide powders using a simple production method.SOLUTION: A production method for cemented carbide powders comprises a step of mixing base powders containing tungsten oxide powders, cobalt oxide powders, and carbon powders, a step of spray drying, and a step of heat treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing powders such as raw materials for powder metallurgy and raw materials for thermal spraying, and particularly to a method for producing cemented carbide powders suitable for additive manufacturing.

Background Art

[0002] Cemented carbides containing high melting point carbides such as WC are hard, have high strength, have physical properties such as a large Young's modulus and specific gravity, and these physical properties are stable. Therefore, the powders are used as raw materials for powder metallurgy, raw materials for thermal spraying, and the like. On the other hand, as a method for producing powder materials, an atomization method is used. According to this atomization method, powders with high sphericity and density can be obtained. However, it is difficult to produce the above-mentioned cemented carbide powders by the atomization method of melting raw materials. Therefore, methods for producing cemented carbide powders by devising the manufacturing process have been proposed.

[0003] For example, Patent Document 1 describes a method of mixing tungsten carbide powder and cobalt powder, spray-drying them, and obtaining sintered cemented carbide powder through two vacuum sintering processes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above circumstances and proposals, and an object thereof is to obtain cemented carbide powder by a simple manufacturing method.

Means for Solving the Problems

[0006] The method for producing cemented carbide powder according to an embodiment of the present invention is It includes, in this order, a step of mixing raw material powders including tungsten oxide powder, cobalt oxide powder, and carbon powder, a spray drying step, and a heat treatment step.

Advantages of the Invention

[0007] The cemented carbide powder manufacturing method according to the above embodiment can obtain cemented carbide powder by a simple manufacturing method.

Modes for Carrying Out the Invention

[0008] When the inventor studied the manufacturing method of the cemented carbide powder described in the above Patent Document 1, the inventor found the following preferable improvements (1) and (2). (1) Since WC powder and Co powder are used as raw material powders, oxygen and moisture are adsorbed on the surfaces of these raw material powders, which causes oxidation of the raw material powders during the manufacturing process of the cemented carbide powder. Therefore, it is necessary to manage the temperature and humidity for storage and the manufacture of the cemented carbide powder, and it is preferable to reduce the labor of handling the raw material powders. (2) There are two sintering steps that consume energy, and it is preferable to suppress energy consumption.

[0009] Therefore, in order to improve these points (1) and (2), the inventor conducted intensive studies. As a result, the inventor obtained the finding that if oxide powders are used as the raw material powders, point (1) can be improved, and if the sintering step is made into one step, point (2) can be improved, and thus the present invention was derived.

[0010] Hereinafter, the manufacturing method of the cemented carbide powder according to the embodiment of the present invention will be described in detail, particularly focusing on the case where it is applied to the manufacture of cemented carbide powder suitable for laminated manufacturing. In the description of this specification and the claims, when a numerical range is expressed as "A to B" (both A and B are numerical values), it is synonymous with "A or more and B or less", and the range includes the upper limit value (B) and the lower limit value (A). Also, when only the unit is described for the upper limit value (B), the units of the upper limit value (B) and the lower limit value (A) are the same.

[0011] The manufacturing method of cemented carbide powder according to an embodiment of the present invention includes, as described above, a step of mixing raw material powders including tungsten oxide powder, cobalt oxide powder, and carbon powder, a spray drying step, a heat treatment step, and a sintering step in this order.

[0012] 1. Preparation of raw material powders As the raw material powders, oxide powders are used as the WC source and the Co source, respectively. As the WC source, tungsten oxide powder As the Co source, cobalt oxide powder As the carbon source, graphite powder are essential, and at least one of Cr2O3 powder, VC powder, TiC powder, TaC powder, and NbC powder is used as necessary to suppress the growth of WC particles in the sintering step.

[0013] Here, the composition of the tungsten oxide powder as the WC source may be any known tungsten oxide. Also, the composition of the cobalt oxide powder as the Co source may be any known cobalt oxide.

[0014] The average particle size of the primary particles of these raw material powders is 10 μm or less, preferably 5 μm or less, more preferably 1 μm or less, and the average particle size of the primary particles as the lower limit is about 10 nm in order to allow the reduction and carbonization reactions to proceed efficiently.

[0015] 2. Step of mixing raw material powders Weigh the raw material powders prepared above so as to have a predetermined blending ratio. Here, the blending amount of each raw material powder is preferably as follows. After weighing, it is preferable to put the mixed powder into a pot of an attritor mixer together with media (for example: cemented carbide balls) and a solvent (for example: an alcohol-based solvent), and perform mixing and pulverization to obtain a slurry.

[0016] (1) Cobalt oxide powder Co improves sinterability in the sintering process and enhances the density and strength of cemented carbide powder. For this purpose, the blending ratio of cobalt oxide powder is determined by the use of the cemented carbide powder. In many cases, it is advisable to blend the Co content in the cemented carbide powder to be 3 - 26 mass%. The reason is that when the Co content is less than 3 mass%, the density of the cemented carbide powder after the sintering process is low and it does not have sufficient strength due to the low Co content. On the other hand, when it exceeds 26 mass%, the sintered powders fuse together and it becomes difficult to crush them.

[0017] Here, when Cr2O3 powder, VC powder, TiC powder, TaC powder, and NbC powder are not blended, the blending ratio of cobalt oxide powder to make the Co content 3 - 26 mass% is as shown in Table 1.

[0018]

Table 1

[0019] (2) Carbon powder Carbon powder is necessary to cause a reduction and carbonization reaction of tungsten oxide, for example, WO3 powder, to obtain WC powder. Therefore, it is preferable that the carbon powder has a blending amount of generally more than 1 / 10 times and less than 1 / 4 times the blending amount of tungsten oxide powder so that the carbon amount in the cemented carbide powder becomes 5.8 - 6.2 mass%. When the carbon powder is insufficient, the carbonization reaction of WO3 powder becomes insufficient and tungsten oxide remains in the cemented carbide powder. On the other hand, when it is excessive, a large amount of carbon remains in the cemented carbide powder.

[0020] (3) Cr2O3 powder, VC powder, TiC powder, TaC powder, NbC powder Cr2O3 powder, VC powder, TiC powder, TaC powder, and NbC powder play a role in suppressing the grain growth of WC powder during the heat treatment process. The blending of these powders is not essential, but when blending, the blending ratio is preferably 0.1 to 5.0% by mass in total of at least one of Cr2O3 powder, VC powder, TiC powder, Ta powder, and Nb powder. The reason is that when the blending ratio is less than 0.1% by mass, the suppression of WC grain growth is not sufficient, while when it exceeds 5.0% by mass, the sinterability of the obtained cemented carbide powder decreases.

[0021] (4) Tungsten oxide powder As long as a cemented carbide powder corresponding to the use of the cemented carbide powder according to this embodiment can be manufactured, there is no particular restriction on the blending amount of tungsten oxide powder, and it becomes the remainder of the blending amounts of the various powders described above. In other words, since the content of the tungsten oxide powder is determined by the reason for determining the content of the components of the various powders described above that should be contained in the cemented carbide powder, the content of the tungsten oxide powder is the remainder of the cemented carbide powder, that is, 74 to 97% by mass. And the amount of WC powder resulting from the content of this tungsten oxide powder is the amount of cemented carbide powder suitable for additive manufacturing in addition to powders such as raw materials for powder metallurgy and raw materials for thermal spraying.

[0022] 3. Spray drying process The slurry obtained in the step of mixing the raw material powders in 2 above is spray-dried with a spray dryer to obtain spherical granulated powder. Here, the set temperature of the spray dryer is set to 80°C to 200°C according to the solvent used. When using an alcohol-based solvent, this set temperature is set to 100°C and spray drying is carried out. Also, the rotation speed of the atomizer is adjusted to correspond to the size (average particle diameter) determined according to the use of the cemented carbide powder.

[0023] 4. Screening process It is preferable to provide a screening process in which the spherical granulated powder obtained by the spray drying process is crushed as necessary and made into a size determined according to the use of the cemented carbide powder. For example, if the use of the cemented carbide powder is for additive manufacturing, pass it through a sieve of -45μm to +5μm and recover the powder with a size of 5μm to 45μm.

[0024] 5. Heat treatment process Perform heat treatment on the granulated powder that has undergone the sieving process, and perform sintering as necessary. By this heat treatment, carbonization is carried out following reduction, and tungsten carbide and cobalt are formed from tungsten oxide and cobalt oxide respectively. The heat treatment is carried out, for example, by charging it into a carbon crucible, flowing an inert gas such as nitrogen or argon, and if the use of the cemented carbide powder is for additive manufacturing, hold it at 700 to 1500°C, for 30 minutes to 2 hours, and at 0.1 to 1000 Pa at which the carbonization reaction occurs.

[0025] Sinter the granulated powder that has undergone the heat treatment process as necessary. In the production of cemented carbide powders that do not require high strength as cemented carbide powders, that is, in the production of cemented carbide powders for powder metallurgy or thermal spraying, sintering is not necessarily required. By the sintering process, the powder that has become tungsten carbide and cobalt from tungsten oxide and cobalt oxide by the heat treatment is sintered, and these powders are partially fused together to form a mass. The sintering conditions are, for example, if the use of the cemented carbide powder is for additive manufacturing, hold it at 1100 to 1400°C, for 30 minutes to 2 hours, and at 0.1 to 1000 Pa. Note that the aforementioned inert gas may be flowed during the heat treatment.

[0026] 6. Crushing process The crushing process is carried out to loosen the mass when the powders are partially fused together to form a mass after the sintering process. In other words, if the sintering process is not carried out or if the powders do not fuse together to form a mass even after the sintering process, there is no need to carry it out. The crushing process can be exemplified by using a crusher or a mill.

Example

[0027] Next, examples will be described. The examples will be mainly described centering on the manufacturing method of cemented carbide powder for laminated modeling.

[0028] 1. Preparation of raw material powder As the raw material powder, WO3 powder, Co3O4 powder, and graphite powder with an average primary particle diameter of 0.5 μm were all prepared.

[0029] 2. Step of mixing raw material powders The raw material powders prepared in 1 above were CoO powder: 17% by mass Graphite powder: 17.1% by mass WO3 powder: the balance were blended at the following blending ratios (the blending ratios were the same in all examples).

[0030] 3. Spray drying step The rotation speed of the atomizer was adjusted to produce powders with different average particle diameters (D50). In all examples, the crushing step immediately after the spray drying step was not performed.

[0031] 3. Heat treatment step In all examples, nitrogen gas was passed and held at 1100 °C for 60 minutes at 67 Pa.

[0032] 4. Sintering step Subsequently, in all examples, nitrogen gas was passed and held at 1250 °C for 60 minutes at 67 Pa.

[0033] 5. Crushing step Subsequently, the crushing step was performed to loosen the mass in which the powders were partially fused together by the sintering step.

[0034] Table 2 shows the D50 and Hausner ratio of the powders of Examples 1 to 4 that have undergone the above steps. In Table 2, for comparison, the cemented carbide powder manufactured according to the process described in Prior Art Document 1 is shown as Comparative Example 1.

[0035]

Table 2

[0036] Examples 1 and 2 in Table 2 are cemented carbide powders for laminated manufacturing, Example 3 is a cemented carbide powder for thermal spraying, and Example 4 is a cemented carbide powder for blasting. Thus, the method for manufacturing a cemented carbide powder according to the present invention can manufacture cemented carbide powders for various applications. Further, the cemented carbide powders for laminated manufacturing in Examples 1 and 2 have a Hausner ratio equivalent to that of Comparative Example 1 manufactured according to Prior Art Document 1, and it can be said that the manufacturing method according to the present invention can obtain a cemented carbide powder, particularly a cemented carbide powder for laminated manufacturing, by a simple manufacturing method.

Claims

【Claim 1】 A method for manufacturing cemented carbide powder, comprising in this order: a step of mixing raw material powders including tungsten oxide powder, cobalt oxide powder, and carbon powder; a spray drying step; and a heat treatment step.

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