Tungsten powder manufacturing method, and tungsten carbide product manufacturing method

Abstract

A tungsten powder manufacturing method according to a non-restricting example of the present disclosure is for manufacturing a tungsten powder in which tungsten carbide is the main component, the method comprising: a step for preparing a raw material containing tungstic oxide; a step for obtaining a solution having eluted therein tungstic oxide from the raw material by using an alkali solvent; a step for obtaining a compound including tungsten and an adsorbent, by adding the adsorbent to the solution and reacting the adsorbent with the solution containing the eluted tungsten; a step for extracting the compound from the solution; a step for generating a mixture material by mixing the compound and carbon powder; and a step for baking the mixture material.

Description

Method for producing tungsten powder and method for producing tungsten carbide products

[0001] The present disclosure relates to methods for producing tungsten powder for use in the manufacture of cutting inserts and the like, and methods for producing tungsten carbide products.

[0002] Tungsten powder is used in the manufacture of tungsten carbide products, such as cutting inserts. Tungsten powder is obtained by extracting tungsten-containing ores (e.g., scheelite CaWO ４ , Wolframite MnWO ４ and ferrite FeWO ４ ), or by recovery from tungsten-containing products, as described in US Pat. No. 5,649,999.

[0003] International Publication No. 2015 / 129835

[0004] A method for producing tungsten powder according to one non-limiting example of the present disclosure includes the steps of preparing a raw material containing tungsten oxide, obtaining a solution by eluting the tungsten oxide from the raw material using an alkaline solvent, adding an adsorbent to the solution and allowing the adsorbent to adsorb the tungsten oxide, extracting the adsorbent with the tungsten oxide adsorbed thereon from the solution, mixing the adsorbent with the tungsten component adsorbed thereon with carbon powder to produce a mixture, and heating the mixture.

[0005] FIG. 1 is a flowchart outlining a method for producing tungsten powder according to one non-limiting example of the present disclosure.

[0006] Tungsten powder is used in the manufacture of tungsten carbide products, such as cutting inserts. Tungsten powder is obtained by extracting tungsten-containing ores (e.g., scheelite CaWO ４ , Wolframite MnWO ４ and ferrite FeWO ４ ), or by recovery from tungsten-containing products, as described in US Pat. No. 5,649,999.

[0007] There is a demand for further reduction in the manufacturing cost of tungsten carbide powder.

[0008] <Method for Producing Tungsten Powder> A method for producing (producing) tungsten powder according to one non-limiting example of the present disclosure will be described.

[0009] As shown in Figure 1, a method for producing tungsten powder according to one embodiment includes the following steps (A) to (G): (A) preparing a raw material containing tungsten; (B) oxidizing tungsten in the raw material to obtain tungsten oxide; (C) using an alkaline solvent to obtain a solution in which tungsten oxide is eluted from the raw material; (D) adding a metal compound adsorbent (hereinafter sometimes referred to as an adsorbent) to the solution and reacting the adsorbent with the solution containing the eluted tungsten to obtain a compound containing the adsorbent and tungsten; (E) extracting the compound from the solution; (F) mixing the compound with carbon powder to produce a mixture; and (G) heating the mixture.

[0010] (Step A) First, a raw material containing tungsten is prepared. Examples of the raw material include ore and scrap containing tungsten. Examples of the ore containing tungsten include scheelite (CaWO ４ ), Wolframite (MnWO ４ ), ferrite (FeWO ４ ) and Wolframite ((Fe,Mn)WO ４ Scrap containing tungsten is waste generated during the production process of products whose main components are metallic tungsten, tungsten carbide (WC), etc. Specific examples include scrap generated during the manufacturing process of cemented carbide tools, hard scrap such as used tools, and powdery soft scrap such as grinding sludge.

[0011] Cemented carbide, a type of cemented carbide, is mainly composed of composite carbides such as metallic tungsten and tungsten carbide. This composite carbide-based material contains iron, nickel, cobalt, etc. as a binder phase, and TiC, TaC, NbC, VC, Cr, etc. as additive components as needed. ３ C ２Target materials containing cemented carbide include cutting tools (cutting inserts, drills, end mills, etc.), dies (forming rolls, forming dies, etc.), and civil engineering and mining tools (oil drilling tools, rock crushing tools, etc.).

[0012] (Step B) When tungsten is contained in the raw material in a non-oxide state, the tungsten in the raw material is oxidized to obtain tungsten oxide. For example, when preparing a used cutting tool as the raw material, the cutting tool contains tungsten in the form of tungsten carbide. Therefore, the tungsten carbide is oxidized to obtain tungsten oxide.

[0013] Examples of methods for oxidizing tungsten include oxidizing roasting. For example, tungsten oxide (WO ３ ) and cobalt tungstate (CoWO ４ ) mixture is obtained.

[0014] As described above, the purpose of step A and step B is to obtain tungsten oxide from a raw material, and therefore these steps may be collectively expressed as a step of preparing a raw material containing tungsten oxide.

[0015] (Process C) The recovery method is an alkali extraction / alkali fusion process in which metal components of the cemented carbide scrap are eluted in an alkali solution to obtain a tungsten compound solution in which tungsten compound ions are dissolved. Methods for obtaining the metal compound solution include an alkali extraction method and an alkali fusion method. The alkali extraction method is a method in which scrap that has been previously oxidized and roasted is subjected to alkali extraction with, for example, an aqueous NaOH solution. The alkali dissolution method is a method in which NaNO ３ , Na ２ SO ４ , Na ２ CO ３ This method involves oxidizing and dissolving the metal by using a molten salt of sodium salt such as NaOH.

[0016] For example, soft scrap is highly reactive and difficult to control, so it is more efficient to use the alkaline extraction method, while hard scrap is more efficient to use the alkaline dissolution method, as only the surface can be oxidized by oxidizing roasting.

[0017] (Step D) The adsorbent of this embodiment is added to the tungsten compound solution obtained in Step C. The adsorbent of this embodiment adsorbs metal compounds present as anions in the solution. Here, as the adsorbent of this embodiment, for example, the first adsorbent and / or the second adsorbent shown below can be used.

[0018] [First Adsorbent] The first adsorbent contains at least one first amino acid selected from the group consisting of alanine, cystine, methionine, tyrosine, lysine, valine, glutamic acid, histidine, proline, threonine, asparagine, glycine, isoleucine, ornithine, arginine, serine, citrulline, and cystathionine as a free amino acid. The first adsorbent may contain 10 mol% or more of the first amino acid as a free amino acid (sometimes referred to as the first free amino acid) relative to the total amount of free amino acids.

[0019] This allows metal compounds to be recovered through a simple process, and because it does not require the use of large amounts of chemicals, it reduces environmental pollution.

[0020] The free amino acids in the adsorbent may exist as a solid or may exist as free amino acids when dissolved in a solution. In either case, the solution contains free amino acids, and by using these adsorbents, metal compounds can be recovered through a simple treatment process.

[0021] An example of the first adsorbent is a substrate having free amino acids supported on its surface. The substrate may be, for example, an organic substance such as a peptide containing free amino acids, a protein, or a substance that forms a living organism such as a microorganism (hereinafter sometimes referred to as a biological substance), or a resin, or an inorganic substance.

[0022] Examples of microorganisms include bacteria such as E. coli (Escherichia coli), Bacillus sp., Thiobacillus ferrooxidans, Streptomyces rimosus, Pseudomonas sp., Bacillus thuringiensis, Arthrobacternicotianae, Shewanella algae, and Shewanella oneidensis, yeasts such as Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida albicans, Yarrowia ipolytica, Pichiapastoris, Hansenula polymorpha, and Kluyveromyces lactis, and koji mold.

[0023] Adsorbents made from biological substances come in various forms, such as powders, pellets formed from powders, gels, and aqueous solutions. Powders and pellets are easy to store and handle. When the adsorbent is a solid, such as a powder or pellets, the solid can be dissolved in another liquid, such as water, and then added to a solution containing the metal compound. Alternatively, the solid can be directly added to a solution containing the metal compound and stirred.

[0024] The first adsorbent preferably contains, as free amino acids, at least one amino acid selected from alanine, cystine, methionine, tyrosine, lysine, valine, glutamic acid, histidine, and proline (hereinafter sometimes referred to as the 1-1 amino acid), at least one amino acid selected from threonine, asparagine, glycine, isoleucine, ornithine, and arginine (hereinafter sometimes referred to as the 1-2 amino acid), and at least one amino acid selected from serine, citrulline, and cystathionine (hereinafter sometimes referred to as the 1-3 amino acid). Furthermore, the first adsorbent may contain, as free amino acids, at least one second amino acid selected from phosphoserine, aspartic acid, leucine, and phenylalanine, in a ratio of 40 mol% or less relative to the total amount of free amino acids.

[0025] An adsorbent containing the 1-1 amino acid, the 1-2 amino acid, and the 1-3 amino acid as free amino acids can increase the recovery efficiency of metal compounds.

[0026] When such an adsorbent is used and the 1-1 amino acid consists of two or more types, the 1-1 amino acid may be contained in a ratio of 5 mol% or more as free amino acids when the total amount of free amino acids is 100 mol%. In particular, lysine may be contained in a ratio of 10 mol% or more as free amino acids. In such cases, the recovery efficiency of metal compounds is improved. Furthermore, the total amount of the 1-1 amino acids is contained in a ratio of 10 mol% or more as free amino acids. This improves the recovery efficiency of metal compounds.

[0027] The adsorbent may contain a total amount of free amino acids consisting of the first amino acid of 0.5% by mass or more relative to the total amount of solid matter obtained by drying the adsorbent, i.e., the solid content of the adsorbent, which improves the recovery efficiency of metal compounds.

[0028] Furthermore, when the free amino acids contain aspartic acid and at least one amino acid selected from glutamic acid and valine as free amino acids, the content of at least one amino acid selected from glutamic acid and valine may be greater than that of aspartic acid. The free amino acids selected from glutamic acid and valine have a positive zeta potential when the pH of the solution is adjusted to the acidic side, and adsorb metal compound ions (anions) in the solution. On the other hand, aspartic acid has a low ability to adsorb metal compounds (ions). Therefore, when the content of at least one amino acid selected from glutamic acid and valine in the free amino acids is greater than that of aspartic acid, the adsorption efficiency of metal compounds can be improved.

[0029] The type and content of free amino acids contained in the adsorbent can be confirmed by free amino acid analysis (also known as biological amino acid analysis). The content ratio of the total amount of free amino acids to the solid content of the adsorbent can be calculated from the mass of free amino acids in the adsorbent and the mass of the solid content of the adsorbent. When the adsorbent is a solid such as a powder, for example, the adsorbent is added to pure water at a liquid temperature of 25°C, and the adsorbent is suspended by stirring for 10 minutes while rotating with a magnetic stirrer at a rotation speed of 500 rpm. Free amino acid analysis is performed using this suspension. When the adsorbent is a solution, free amino acid analysis is performed in the solution, and the total amount of free amino acids can be calculated from the mass of the solid content of the adsorbent obtained by centrifuging the adsorbent solution. The mass of the solid content of the adsorbent is measured after it has been thoroughly dried under drying conditions, such as at 60°C for 24 hours.

[0030] In addition, the free amino acids contained in the biological material are supported on the surface of a substrate, which is a peptide or protein. Supporting free amino acids on a peptide or protein with a large molecular weight makes the adsorbent easier to handle, and when recovering the adsorbent to which the metal compound has been adsorbed from a solution containing the metal compound, the adsorbent can be concentrated by a simple method such as filtration. The substrate may be a biological material or a resin or inorganic material, but if it is a biological material, the free amino acids can be easily increased. In the first adsorbent, free amino acids are supported on the body surface of a microorganism.

[0031] When the substrate of the adsorbent is a resin or an inorganic substance, a large number of free amino acids can be supported on the surface of the substrate if the substrate has a large specific surface area, such as a powder or a porous body. In the case of a porous body, amino acids can also be supported on the inner walls of the pores.

[0032] When the adsorbent is made of a biological substance, in addition to free amino acids, there are amino acids that do not contribute to the adsorption reaction (hereinafter, sometimes referred to as inactive amino acids). Examples of inactive amino acids include amino acids located at intermediate positions among amino acids linked by peptide bonds, and amino acids located at internal positions that are not exposed on the surface of the adsorbent.

[0033] When the adsorbent is made of a biological substance, it is effective to perform a treatment to cleave the peptide bonds of the inactive amino acids present in the adsorbent and convert the inactive amino acids into free amino acids in order to increase the content of free amino acids in the adsorbent.

[0034] For example, when the organic matter is a microorganism, the peptide bonds present in the microorganism can be cleaved using existing treatment methods. Specifically, the proteins constituting the microorganism are decomposed with proteolytic enzymes such as trypsin, LYSYLENDOPEPTIDASE (registered trademark), and V8 protease. This allows at least a portion of the inactive amino acids contained within the microorganism to be converted into free amino acids. Another effective method for converting inactive amino acids into free amino acids is to subject the adsorbent to, for example, heating at 60°C or higher, boiling, or heat and pressure treatment using an autoclave or the like to decompose the proteins. Note that if the adsorbent is a living organism such as a microorganism, and does not need to be stored in a solution but can be stored as a solid like a decomposed inanimate object, large-scale facilities for cultivation and storage and their maintenance are not required, and the facilities can be made smaller.

[0035] [Second Adsorbent] The second adsorbent contains at least one first amino acid selected from the group consisting of alanine, cystine, methionine, tyrosine, lysine, valine, glutamic acid, histidine, proline, threonine, asparagine, glycine, isoleucine, ornithine, arginine, serine, citrulline, and cystathionine, and at least a portion of the first amino acid exists as a free amino acid in the solution. The second adsorbent may also contain a total amount of the first amino acid in the form of free amino acid of 10 mol% or more relative to the total amount of the free amino acids.

[0036] That is, the second adsorbent exists as a solid and does not contain free amino acids in the solid state, but has free amino acids in solution.

[0037] An example of the second adsorbent is a salt of a first amino acid. Examples of salts include hydrochloride, nitrate, sulfate, acetate, and carbonate. An adsorbent made of an amino acid salt dissolves in a liquid to provide free amino acids. Then, as with the first adsorbent, the adsorbent is added to a solution in which a metal compound has been dissolved, and the pH is adjusted so that the zeta potential of the free amino acids on the adsorbent is positive. At this time, since the metal compound exists as an anion, the anion of the metal compound is adsorbed to the positively charged free amino acids on the adsorbent.

[0038] In the second adsorbent, the content ratio of free amino acids in the adsorbent can be increased compared to a form in which free amino acids are supported on the surface of a substrate. Therefore, the adsorption efficiency of metal compounds is high, and a large amount of metal compounds can be adsorbed with a small amount of adsorbent. Furthermore, when recovering metal compounds after adsorption, the content of unnecessary materials that need to be disposed of is small, making handling easy and reducing production costs. Furthermore, since the adsorbent is not a living organism like bacteria or microorganisms, it is easy to store and manage the adsorbent.

[0039] The second adsorbent, which is an adsorbent made of a salt, may be in the form of a solution, but is easier to handle, store, and manage when it is solid, and in particular, when it is in powder form, it can be easily dissolved in a solution. Furthermore, the adsorbent may be in the form of pellets to facilitate handling of the adsorbent.

[0040] When the salt of the first amino acid is a salt of at least one of lysine and arginine as the main component, the adsorbent has good adsorption efficiency. For example, a salt containing lysine may be used as the adsorbent. Here, examples of the salt containing lysine include lysine hydrochloride, lysine sulfate, lysine nitrate, and lysine acetate.

[0041] Among these, lysine hydrochloride (e.g., L-lysine hydrochloride) is stable and inexpensive. Furthermore, when lysine hydrochloride is used as an adsorbent, it is less likely that unnecessary elements will be introduced during acid treatment in a subsequent step. Note that "containing at least one salt of lysine or arginine as the main component" means that the total mass ratio of the lysine salt or arginine salt in the adsorbent is 50 mass% or more relative to the total mass of the adsorbent.

[0042] The total amount of the lysine salt and the arginine salt present in the adsorbent is preferably 90% by mass or more. This allows a large amount of metal compound to be adsorbed with a small amount of the adsorbent. The total amount of the lysine salt and the arginine salt present in the adsorbent is more preferably 95% by mass or more.

[0043] When a salt of glutamic acid is contained as the salt of the first amino acid, the cost of the adsorbent can be reduced. Among them, sodium glutamate is stable and inexpensive.

[0044] The content of glutamic acid salts in the adsorbent is preferably 90% by mass or more, which allows for inexpensive recovery of metal compounds. The total amount of glutamic acid salts in the adsorbent is preferably 95% by mass or more.

[0045] The free amino acid is not limited to one type, and for example, salts of other first amino acids such as lysine and arginine can be added together with the salt of glutamic acid.

[0046] Furthermore, for example, when the adsorbent is made of a microorganism, 1 g to 10 kg of the adsorbent is added per 1 m3 of a tungsten compound solution adjusted to a tungsten concentration of 0.1 to 10 mmol / L (0.1 to 10 mmol of tungsten per 1 liter of alkaline solution). When the adsorbent is made of a salt of a first amino acid, for example, the total amount of the salt of the first amino acid added in the adsorbent is added at a content ratio of 0.2 to 1.1 mol per 1 mol of the metal component of the metal compound. This allows a large amount of metal compound, such as a tungsten compound, to be adsorbed with a small amount of the adsorbent.

[0047] The total amount of the salt of the first amino acid added may be 10 to 300 g / L relative to the metal compound solution. In such a case, the viscosity of the solution does not increase, and the recovery efficiency of the metal compound is less likely to decrease. In particular, when the adsorbent is made of a salt of an amino acid, the viscosity of the solution does not increase easily, and workability is good.

[0048] The temperature can be adjusted depending on the activity of the free amino acid, and is usually room temperature. The tungsten compound solution to which the adsorbent has been added is adjusted using hydrochloric acid or the like so that the zeta potential of the free amino acid becomes positive. This allows the adsorbent to adsorb anionic tungsten compound ions.

[0049] The pH of the solution is less than 7 (acidic). When the free amino acids are lysine and arginine, the preferred pH is 4 or less, preferably 1 to 3, and desirably 1 to 2.3. When the free amino acid is glutamic acid, the preferred pH is 1.5 or less. This can increase the recovery rate of the tungsten compound. Note that the step of adjusting the pH of the solution and the step of adding an adsorbent to the solution containing the metal compound can be carried out in either order.

[0050] When the adsorbent is a salt of the first amino acid, the recovery efficiency of the adsorbent is higher if the adsorption reaction is carried out within one hour. In other words, if the adsorption reaction exceeds one hour, a portion of the adsorbed metal compound may be desorbed from the free amino acid.

[0051] (Step E) Next, the adsorbent that has adsorbed the tungsten compound ions is extracted from the solution. Here, "extracting" includes a step of filtering the compound from the solution and a step of drying and powdering the compound recovered by filtering.

[0052] Specifically, the adsorbent that has adsorbed tungsten compound ions is filtered with filter paper or the like to recover the compound in a slurry form on the filter paper. The recovered compound is then dried and powdered to extract the powdered tungsten compound containing the adsorbent. Here, the tungsten compound containing the adsorbent is, for example, lysine-WO ４ etc.

[0053] (Steps F and G) A predetermined amount of carbon powder (carbon black, graphite powder, activated carbon, etc.) or carbon slurry is added as a reducing agent to the extracted tungsten compound and mixed (Step F). Then, this mixture is heated to 1100-2000°C under a predetermined atmosphere for a predetermined time, resulting in a carbonization treatment to obtain a tungsten powder primarily composed of tungsten carbide (Step G). Here, "main component" means that tungsten carbide is the largest component, by mass, among the components contained in the powder. Specifically, tungsten carbide is contained in an amount of 99% by mass or more, while unavoidable impurities of less than 1% by mass may be contained. Examples of unavoidable impurities include carbon, hydrogen, nitrogen, oxygen, chromium, vanadium, tantalum, niobium, and titanium. More specifically, the powder may contain 99.2% by mass or more of tungsten carbide and be substantially free of at least one carbide, nitride, or carbonitride selected from Groups IVa, Va, and VIa elements, excluding W. The predetermined atmosphere may be, for example, a reducing atmosphere containing carbon monoxide, nitrogen, hydrogen, methane, and the like.

[0054] In the carbonization step shown in this embodiment, the carbonization treatment is performed in a mixed atmosphere containing nitrogen and hydrogen as the main components. In this way, when the mixed atmosphere containing nitrogen and hydrogen as the main components is used, the production cost is further reduced compared to when the nitrogen and hydrogen are treated separately in their respective atmospheres. Note that "main component" means that, among the components contained in the gas, nitrogen and hydrogen are more abundant than components other than nitrogen and hydrogen in terms of mole percent. More specifically, this refers to a case where the proportions of nitrogen and hydrogen are 40 mole percent or more and 10 mole percent or more, respectively.

[0055] Generally, the powder extracted in step E is incinerated to remove the adsorbent, and WO ３ is taken out. ３ Metallic tungsten is extracted by removing oxygen from the tungsten by reduction treatment. Then, this metallic tungsten is carbonized to obtain tungsten carbide powder. However, for example, when the adsorbent is removed, WO ３ The process of extracting WO requires incineration at a temperature of 300°C or higher. ３ The reduction treatment of tungsten carbide powder requires heat treatment in a reducing atmosphere (e.g., a hydrogen gas atmosphere) at a temperature of 800°C to 950°C, which places a heavy burden on the user.

[0056] On the other hand, in the production method of this embodiment, the tungsten compound extracted in the above-mentioned step E is directly carbonized to produce WC without undergoing the above-mentioned oxidation and reduction treatments. Therefore, the burden of producing tungsten carbide powder is reduced. Furthermore, when carbonizing the above-mentioned tungsten compound, carbon powder is mixed to produce a mixture, and then this mixture is heated.

[0057] When the adsorbent is an organic material as described above, the carbon component contained in the adsorbent can be used to carbonize tungsten to obtain WC. However, since the carbon component contained in the adsorbent alone is likely to be insufficient in the G step of carbonizing tungsten, in the G step, not only WC but also W can be obtained. ２ C is also easily produced.

[0058] In the step F of the production method of this embodiment, carbon powder is mixed with the tungsten compound, so the above-mentioned carbon shortage is resolved, and W ２ C is less likely to be produced, and it is possible to produce high-purity WC powder.

[0059] The amount of carbon powder added in the F step may be adjusted so that the carbon content in the mixture is 5 mass % or more. In this case, tungsten is easily carbonized stably in the G step, so that W ２ C is less likely to be produced, and WC is more likely to be produced.

[0060] Furthermore, the amount of carbon powder added in step F may be adjusted so that the carbon content in the mixture is 6% by mass or less. While the greater the carbon content in the mixture, the more stable the carbonization of tungsten becomes, if the carbon content in the mixture is too high, the step of removing the excess carbon that has not bonded to tungsten after step G may become complicated. However, if the carbon content in the mixture is 6% by mass or less, the load required to remove the excess carbon is small.

[0061] In addition, when the adsorbent is an organic substance as described above, the amount of carbon powder may be adjusted taking into account the amount of carbon components contained in the adsorbent. From another perspective, the carbon components in tungsten carbide may not only be derived from the carbon powder, but also from the carbon components in the adsorbent. That is, the carbon in the tungsten powder may contain the carbon in the adsorbent. When the adsorbent is an organic substance as described above and contains carbon, and the carbon in the tungsten powder contains the carbon in the adsorbent, the amount of carbon powder added in step F can be reduced.

[0062] When the mixing atmosphere in the G step is mainly composed of nitrogen and hydrogen, the hydrogen content (mol %) may be less than or equal to that of nitrogen. When there is less hydrogen than nitrogen, coarse particles are less likely to form. Note that the nitrogen and hydrogen content ratios being equal do not necessarily have to be strictly the same. A ratio of (nitrogen content ratio) / (hydrogen content ratio) between 0.9 and 1.1 is considered to be "equal."

[0063] In the method for recovering a metal compound of the present embodiment, the number of steps can be reduced, and the amounts of chemicals used and waste liquid can be reduced, compared to conventional methods for recovering a metal compound, and tungsten compounds can be recovered at low cost.

[0064] Furthermore, CO emitted in the conventional ion exchange method for producing tungsten carbide via ammonium paratungstate and W metal powder ２ CO emitted by the process of this application relative to the total amount (energy equivalent) ２ In this case, by using the process of the present invention to produce tungsten carbide, the total amount of CO emitted ２ It is possible to significantly reduce the amount of

[0065] <Method for manufacturing a tungsten carbide product> Next, a method for manufacturing a tungsten carbide product according to one non-limiting example of the present disclosure will be described. Specifically, a method for manufacturing a tungsten carbide product using tungsten carbide powder obtained by the method of the present disclosure as a raw material will be described. Here, a method for manufacturing a cutting insert using tungsten carbide powder obtained by the method of the present disclosure as a raw material will be described in detail as an example.

[0066] A method for manufacturing a machined product according to one embodiment includes the following steps (X) and (Y): (X) mixing tungsten carbide powder with cobalt powder to form a compact; and (Y) firing the compact.

[0067] More specifically, cobalt powder is first added to the tungsten carbide powder obtained by the production method of the present disclosure. Metal powders other than cobalt powder and / or carbon powder may also be added. The resulting mixture is then wet-mixed in a ball mill for a predetermined period of time, dried, and then molded into a desired tool shape using a known molding method such as press molding, slip casting, extrusion molding, or cold isostatic pressing to obtain a molded body.

[0068] The compact is then fired in a vacuum or a non-oxidizing atmosphere to produce a cutting insert. The surface of the produced cutting insert may be subjected to polishing or honing.

[0069] The surface of the cutting insert may be coated with a coating by chemical vapor deposition (CVD) or physical vapor deposition (PVD). The coating composition may be titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), and alumina (Al ２ O ３ ) etc.

[0070] In one embodiment, (1) a method for producing a tungsten powder containing tungsten carbide as a main component may include the steps of preparing a raw material containing tungsten oxide, obtaining a solution by eluting the tungsten oxide from the raw material using an alkaline solvent, adding an adsorbent to the solution and reacting the adsorbent with the solution containing the eluted tungsten to obtain a compound containing the adsorbent and tungsten, extracting the compound from the solution, mixing the compound with carbon powder to produce a mixture, and heating the mixture.

[0071] (2) In the method for producing tungsten powder described above in (1), the adsorbent may be a salt containing lysine.

[0072] (3) In the method for producing tungsten powder described above in (2), the adsorbent may be lysine hydrochloride.

[0073] (4) In any one of the methods for producing tungsten powder described above in (1) to (3), the atmosphere in the step of heating the admixture may be a mixed atmosphere containing nitrogen and hydrogen as main components.

[0074] (5) In any of the methods for producing tungsten powder described above in (1) to (4), the carbon in the tungsten powder may contain carbon in the adsorbent.

[0075] (6) In any of the methods for producing tungsten powder described above in (1) to (5), the carbon content in the admixture may be 6 mass % or less.

[0076] (7) In any of the methods for producing tungsten powder described above in (1) to (6), the carbon content in the admixture may be 5 mass % or more.

[0077] (8) A method for producing a tungsten carbide product may include the steps of mixing tungsten powder obtained by any of the methods for producing tungsten powder described above in (1) to (7) with cobalt powder to form a molded body, and firing the molded body.

[0078] The invention according to the present disclosure has been described above based on the embodiments. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art would easily be able to make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure.

[0079] The above provides examples of embodiments of the present disclosure, but it goes without saying that the present disclosure is not limited to the above-described embodiments and can be any embodiment as long as it does not deviate from the gist of the present disclosure.

Claims

1. A method for producing tungsten powder containing tungsten carbide as a main component, comprising: providing a raw material containing tungsten oxide; a step of obtaining a solution by dissolving the tungsten oxide from the raw material using an alkaline solvent; adding an adsorbent to the solution and reacting the adsorbent with the eluted tungsten-containing solution to obtain a compound containing the adsorbent and tungsten; removing the compound from the solution; mixing the compound with carbon powder to form a mixture; and heating the mixed material.

2. 2. The method for producing tungsten powder according to claim 1, wherein the adsorbent is a salt containing lysine.

3. 3. The method for producing tungsten powder according to claim 2, wherein the adsorbent is lysine hydrochloride.

4. The method for producing tungsten powder according to any one of claims 1 to 3, wherein the atmosphere in the step of heating the admixture is a mixed atmosphere mainly composed of nitrogen and hydrogen.

5. The method for producing a tungsten powder according to any one of claims 1 to 3, wherein the carbon in the tungsten powder includes carbon in the adsorbent.

6. The method for producing tungsten powder according to any one of claims 1 to 3, wherein the carbon content in the admixture is 6 mass% or less.

7. The method for producing tungsten powder according to any one of claims 1 to 3, wherein the carbon content in the admixture is 5 mass% or more.

8. A step of mixing the tungsten powder obtained by the method for producing tungsten powder according to any one of claims 1 to 3 with cobalt powder to form a compact; and sintering the compact.