Tungsten powder and manufacturing method for tungsten carbide product

Abstract

A tungsten powder based on one aspect of the present disclosure contains tungsten carbide as a main ingredient, oxygen, and nitrogen, and the content ratio of oxygen is smaller than the content ratio of nitrogen in terms of mass%.

Description

Manufacturing method for tungsten powder and tungsten carbide products

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to methods of making tungsten powder and tungsten carbide products used in the manufacture of cutting inserts and the like.

[0002] Tungsten powder is used in the manufacture of tungsten carbide products such as cutting inserts. As described in Patent Document 1, the tungsten carbide powder and cobalt powder are mixed and molded into a predetermined shape, and the molded body produced by this molding is then fired to produce the tungsten carbide product. In recent years, there has been a desire to realize a carbon-neutral society, and as described in Patent Document 2, there has been an increasing need to recycle tungsten in tungsten carbide products.

[0003] Furthermore, as described in Patent Document 3, tungsten carbide powder typically contains various impurities in addition to tungsten carbide, which is the main component. The content ratio of these impurities affects the performance of products manufactured from the tungsten carbide powder.

[0004] JP 2022-060899 A International Publication No. 2015 / 129835 JP 2003-206123 A

[0005] A tungsten powder according to one embodiment of the present disclosure is a tungsten powder containing tungsten carbide as a main component and containing oxygen and nitrogen, and the oxygen content by mass % is smaller than the nitrogen content.

[0006] Figure 1 is a flowchart outlining a method for producing tungsten carbide powder according to a non-limiting example of the present disclosure, Figure 2 is a flowchart outlining an example of a conventional method for producing tungsten carbide powder, and Figure 3 is a flowchart outlining an example of a conventional method for producing tungsten carbide powder.

[0007] Tungsten powder is used in the manufacture of tungsten carbide products such as cutting inserts. As described in Patent Document 1, the tungsten carbide powder and cobalt powder are mixed and molded into a predetermined shape, and the molded body produced by this molding is then fired to produce the tungsten carbide product. In recent years, there has been a desire to realize a carbon-neutral society, and as described in Patent Document 2, there has been an increasing need to recycle tungsten in tungsten carbide products.

[0008] Furthermore, as described in Patent Document 3, tungsten carbide powder typically contains various impurities in addition to tungsten carbide, which is the main component. The content ratio of these impurities affects the performance of products manufactured from the tungsten carbide powder.

[0009] It is desired to further improve the performance of tungsten carbide products made from tungsten carbide powder by adjusting the content ratio of impurities in the tungsten carbide powder. More specifically, it is desired to further improve the performance of cutting inserts by adjusting the content ratio of impurities in the tungsten carbide powder used as the raw material for cutting inserts.

[0010] <Tungsten Powder> A non-limiting example of a tungsten carbide powder according to the present disclosure will be described. In the present disclosure, tungsten carbide powder refers to a powder containing tungsten carbide as the main component, and "main component" means that tungsten carbide accounts for the largest proportion of the components contained in the powder by mass %. Specifically, the powder contains 99 mass % or more of tungsten carbide, while the remainder contains other elements. Examples of other elements include carbon, hydrogen, nitrogen, oxygen, chromium, vanadium, tantalum, niobium, titanium, etc. More specifically, the powder may contain 99.2 mass % or more of tungsten carbide and be substantially free of at least one carbide, nitride, or carbonitride selected from the group IVa, Va, and VIa elements excluding W.

[0011] The tungsten carbide powder shown in this embodiment contains oxygen and nitrogen. In the tungsten carbide powder, the oxygen content by mass% is smaller than the nitrogen content. For example, if the oxygen content by mass% of the tungsten powder is higher than the nitrogen content, the performance of the product using the tungsten carbide powder may be affected.

[0012] For example, when tungsten carbide powder is fired, WC in the tungsten carbide powder reacts with oxygen, and WC becomes W. ２ C, W or WO ３ If the composition changes to these, it may become difficult to obtain the properties of WC, and the liquid phase appearance temperature may increase, making sintering difficult. Furthermore, the WC content in the tungsten carbide product after sintering decreases, making it difficult to obtain the original properties.

[0013] Furthermore, in products containing tungsten carbide and cobalt, such as cutting inserts, cobalt functions as a binder. However, if tungsten carbide powder with a high oxygen content is used, the cobalt may react with oxygen to produce cobalt oxide. This may result in a decrease in the binder function of the cobalt, and a decrease in the properties of the cutting insert (such as Vickers hardness).

[0014] On the other hand, in the case of tungsten powder in which the oxygen content in mass % is smaller than the nitrogen content, the oxygen content is relatively low, so the above-mentioned situation is unlikely to occur. In addition, because the nitrogen content is relatively high, when the tungsten powder is sintered, carbides (e.g., TiC) and carbonitrides / nitrides (TiCN / TiN) derived from inevitable impurities other than tungsten carbide are easily formed, and in this case, a grain growth suppression effect is obtained. In addition, since carbonitrides and nitrides have low affinity with each other, a grain structure uniformity effect is also easily obtained in the tungsten carbide product produced by sintering.

[0015] In addition, when there is more nitrogen than oxygen on the surface of the WC grains, the WC grains repel each other, making it easier to obtain a uniform and fine grain structure when rearranged during the sintering process.

[0016] Here, the oxygen content and nitrogen content in the tungsten carbide powder can be evaluated by, for example, an SEM-EDX method using an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope. The oxygen content ratio and nitrogen content ratio can be calculated as the oxygen content (mass%) and nitrogen content (mass%), respectively, in the entire tungsten carbide powder.

[0017] The nitrogen content of the tungsten carbide powder may be 0.1% by mass or more. In this case, the nitrogen content is relatively high, which makes it easier to obtain the grain growth suppression effect and / or the grain structure uniformity effect. Furthermore, it is more likely that a gradient composition of P-type cemented carbide can be formed. In addition, it is more likely that a de-β phase will be formed.

[0018] The oxygen content of the tungsten carbide powder may be 0.05% by mass or more. In this case, for example, affinity with the solvent is ensured during wet milling, enabling efficient mixing, and the cemented carbide produced from the resulting powder tends to have a uniform composition and structure. In addition, the cohesion of cobalt is also likely to be improved.

[0019] The oxygen content of the tungsten carbide powder may be 0.3 mass% or less. In this case, when the tungsten powder is fired, a reaction between the carbon of the tungsten carbide in the tungsten powder and oxygen is less likely to occur, thereby reducing the risk of a decrease in the carbon content of the tungsten carbide product after firing.

[0020] The tungsten carbide particles constituting the tungsten carbide powder may have an average particle size of 0.8 μm or less. In such a case, the small particle size makes it easier to obtain a cemented carbide having high hardness and strength.

[0021] Here, the average particle size may be, for example, the value obtained by dividing the total area of ​​tungsten particles in a cross-sectional view of the tungsten powder photographed with a scanning electron microscope (SEM) by the number of tungsten particles in the cross-sectional view.

[0022] The tungsten powder may have first particles and second particles having a particle size larger than that of the first particles, and when the content ratio α1 of the first particles is the nitrogen content ratio / oxygen content ratio in mass % and the content ratio α2 of the second particles is the nitrogen content ratio / oxygen content ratio in mass %, α1 may be greater than α2.

[0023] The first particles have a smaller particle size and a larger specific surface area than the second particles. Therefore, even if the oxygen content ratios of the first particles and the second particles are the same, the oxygen contained in the first particles is more likely to affect surrounding components than the oxygen contained in the second particles. For example, in a product containing tungsten carbide and cobalt, the cobalt may be more likely to oxidize.

[0024] In order to suppress the influence of oxygen contained in the tungsten carbide powder on the surrounding components, it is desirable that the oxygen content ratio in both the first particles and the second particles is small, that is, that both α1 and α2 are large. However, simply reducing the oxygen content ratio in both the first particles and the second particles may lead to an increase in production costs.

[0025] However, when α1 is larger than α2, that is, when the oxygen content ratio in the first particles is relatively small, the manufacturing cost of the tungsten carbide powder can be reduced while efficiently suppressing the effect of the oxygen contained in the tungsten carbide powder on surrounding components.

[0026] A particle in the tungsten carbide powder may have two regions separated by a midpoint locus connecting the surface and center of the particle. In this case, the region located on the surface side may be referred to as the surface region, and the region located on the center side may be referred to as the central region. The nitrogen content in the surface region may be greater than the nitrogen content in the central region. In such a case, carbonitrides / nitrides are more likely to be formed, making it easier to achieve grain growth inhibition effects and / or grain structure uniformity effects.

[0027] The nitrogen content in the surface region may decrease toward the center region. In this case, carbonitrides / nitrides are more likely to be formed, which makes it easier to obtain the grain growth suppression effect and / or the grain structure uniformity effect. In addition, since the nitrogen content does not change suddenly, the tungsten carbide powder is more likely to be chemically stable.

[0028] The tungsten carbide powder may contain nitrogen in the central region, which makes the tungsten carbide powder more chemically stable than when nitrogen is contained only in the surface region, since the nitrogen is uniformly distributed throughout the tungsten carbide powder.

[0029] Here, the nitrogen content ratio in the surface region and the nitrogen content ratio in the central region may be compared by mapping a cross-sectional view of the tungsten carbide powder photographed with an SEM.

[0030] When the nitrogen content ratio / oxygen content ratio in the tungsten carbide powder is taken as the content ratio α, α may be 1.2 or more. In such a case, the nitrogen content ratio becomes relatively high, so that the grain growth suppression effect and / or the grain structure uniformity effect are more likely to be obtained.

[0031] <Method for producing (producing) tungsten powder> A method for producing (producing) tungsten powder according to one non-limiting example of the present disclosure will be described.

[0032] 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.

[0033] (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.

[0034] 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 ２ Target 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.).

[0035] (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.

[0036] Examples of methods for oxidizing tungsten include oxidizing roasting. For example, tungsten oxide (WO ３ ) and cobalt tungstate (CoWO ４ ) mixture is obtained.

[0037] 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.

[0038] (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 simultaneously oxidizing and dissolving the metal using a molten salt of sodium salt such as NaOH.

[0039] 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.

[0040] (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.

[0041] [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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] [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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In addition, for example, when the adsorbent is made of microorganisms, 1 ml of a tungsten compound solution adjusted to a tungsten concentration of 0.1 to 10 mmol / L (tungsten concentration of 0.1 to 10 mmol per 1 liter of alkaline solution) is added. ３The adsorbent is added so that the amount of adsorbent is 1 g to 10 kg per 1 mol of metal compound. When the adsorbent is composed of a salt of the 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 adsorbent.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] (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 filtration.

[0075] 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.

[0076] (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 to 2000°C under a predetermined atmosphere for a predetermined time, thereby performing a carbonization treatment, and a tungsten powder containing tungsten carbide as the main component can be obtained (Step G). The predetermined atmosphere may be, for example, a reducing atmosphere containing carbon monoxide, nitrogen, hydrogen, methane, etc.

[0077] 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.

[0078] 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. ３The 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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."

[0086] 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.

[0087] 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 The total amount of CO emitted by using the process of the present invention to produce tungsten carbide may be about 40%. ２ It is possible to significantly reduce the amount of

[0088] In addition, in the above production method, the nitrogen in the tungsten carbide powder may be derived from the nitrogen in the adsorbent. In such a case, it is not necessary to add nitrogen to increase the nitrogen content in the tungsten carbide powder, or the amount of nitrogen added can be reduced, thereby reducing production costs.

[0089] [Examples and Comparative Examples] The production methods of the examples and comparative examples shown in Table 1 will be described below.

[0090]

[0091] Fig. 1 is a flow chart showing an example of a manufacturing process for tungsten carbide powder according to the embodiment, and Fig. 2 is a flow chart showing an example of a manufacturing process for tungsten carbide powder according to a conventional embodiment. As shown in Fig. 1 and Fig. 2, in the manufacturing process for tungsten carbide powder according to the embodiment and the conventional embodiment, first, scrap of cemented carbide was prepared.

[0092] Cemented carbide, a type of cemented carbide, is mainly made of composite carbides such as metallic tungsten or tungsten carbide, with iron, nickel, cobalt, etc. as the binder phase, and TiC, TaC, NbC, VC, Cr, etc. as additive components as needed. ３ C ２ Includes:

[0093] The target materials containing cemented carbide include, for example, cutting tools (cutting inserts, drills, end mills, etc.), molds (forming rolls, forming dies, etc.), and civil engineering and mining tools (oil drilling tools, rock crushing tools, etc.).

[0094] Next, the prepared cemented carbide scrap was oxidized and roasted to produce tungsten oxide (WO ３ ) and cobalt tungstate (CoWO ４ The resulting mixture was refluxed with an aqueous solution of sodium hydroxide (NaOH) and extracted to obtain a mixture of sodium tungstate (Na ２ WO ４ A tungsten compound solution containing tungsten ions was obtained.

[0095] Next, an adsorbent containing lysine was added to the obtained tungsten compound solution to allow the tungsten compound ions to be adsorbed onto the lysine.

[0096] In such an adsorption treatment, for example, the total amount of the salt of the first amino acid added to the adsorbent is added at a content ratio of 0.2 (mol) to 1.1 (mol) per 1 (mol) of the metal component of the tungsten compound, which allows a large amount of the tungsten compound to be adsorbed with a small amount of the adsorbent.

[0097] The total amount of the first amino acid salt added is, for example, 10 (g / L) to 300 (g / L) relative to the tungsten compound solution. This prevents the viscosity of the solution from increasing, and the recovery efficiency of the metal compound from decreasing. In particular, when the adsorbent is made of an amino acid salt, the viscosity of the solution is less likely to increase, resulting in good workability.

[0098] 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 may be 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.

[0099] The pH of the solution may be less than 7 (acidic). When the free amino acids are lysine and arginine, the preferred pH is 4 or less, preferably 0.5 to 3, and more preferably 0.8 to 2.3. When the free amino acid is glutamic acid, the preferred pH is 1.5 or less. In the examples, the pH was adjusted to 1.8.

[0100] It is to be noted that the step of adjusting the pH of the solution and the step of adding the adsorbent to the solution containing the metal compound may be carried out in any order.

[0101] The subsequent steps are different between the manufacturing steps shown in FIG. 1 and those shown in FIG. 2, and will be described separately.

[0102] (Production process in FIG. 1) The adsorbent that adsorbed tungsten compound ions was filtered using filter paper or the like to recover the compound in a slurry form on the filter paper. The recovered compound was then dried and powdered to extract the powdered tungsten compound containing the adsorbent. Here, the tungsten compound containing the adsorbent is lysine, so the adsorbent is lysine-WO ４ etc.

[0103] Next, carbon black is added to and mixed with the recovered tungsten compound, and the mixture is heated for at least one hour in a mixed atmosphere of hydrogen gas and nitrogen gas (1 to 10 L / min) at a temperature as shown in Table 1, to directly carbonize the adsorbent with the tungsten compound ions adsorbed. In the examples, the carbon content of the carbon black was 5 to 6 mass% of the carbon content of the admixture. This allows the tungsten carbide powder of the present application to be used as a raw material for cemented carbide to be obtained. Examples 1 to 9 in Table 1 show tungsten carbide powders produced by this production method.

[0104] (Production process in FIG. 2) Following the lysine adsorption step, the adsorbent with the adsorbed tungsten compound ions was dehydrated by means of filter filtration, centrifugation, etc. Then, if necessary, impurities were removed by washing with pure water, etc.

[0105] The adsorbent with the adsorbed tungsten compound ions was incinerated, for example, in the atmosphere at a temperature of 300°C or higher to oxidize the tungsten compound and remove organic components including the adsorbent. ３ ) was obtained.

[0106] Next, as shown in Figure 2, the obtained tungsten oxide powder is heat-treated in a reducing atmosphere (e.g., a hydrogen gas atmosphere) at a temperature of 800 (°C) to 950 (°C) to reduce the tungsten oxide compound. This allows metallic tungsten (W) to be obtained. Carbon black is then added to and mixed with the obtained metallic tungsten powder, and the mixture is heated and carbonized for at least one hour in a mixed atmosphere of hydrogen gas and nitrogen gas at a temperature shown in Table 1, thereby obtaining tungsten carbide (WC), which is a raw material for conventional cemented carbide alloys. Comparative Examples 1 and 2 in Table 1 show tungsten carbide powders produced by this production method.

[0107] (Manufacturing Process in FIG. 3) FIG. 3 is a flowchart showing an example of the procedure of a conventional method for manufacturing tungsten carbide powder. As shown in FIG. 3, in the process for producing tungsten oxide powder and tungsten carbide in the reference example, first, scrap of cemented carbide was prepared.

[0108] Next, the prepared cemented carbide scrap was oxidized and roasted to produce tungsten oxide (WO ３ ) and cobalt tungstate (CoWO ４ The mixture was extracted with an aqueous solution of sodium hydroxide (NaOH) to obtain a mixture of sodium tungstate (Na ２ WO ４ A tungsten compound solution containing tungsten ions was obtained.

[0109] Next, the obtained tungsten compound solution is subjected to ion exchange with an ion exchange resin or the like to obtain ammonium tungstate ((NH ４ ) ２ WO ４ The resulting aqueous solution was heated and concentrated to crystallize the tungsten compound as ammonium paratungstate (APT).

[0110] Next, carbon powder (carbon black, graphite powder, activated carbon, etc.) is added to and mixed with the obtained APT, and the mixture is heat-treated at a temperature of 1000°C to 1300°C in a reducing atmosphere (e.g., a mixed atmosphere of hydrogen gas and nitrogen gas) as shown in Table 1, to directly carbonize the APT. This allows for the production of tungsten carbide powder, which is a raw material for cemented carbide. Comparative Example 3 in Table 1 shows tungsten carbide powder produced by this production method.

[0111] The items listed in Table 1 will be explained below.

[0112] (Amounts of oxygen and nitrogen in tungsten carbide powder) The obtained tungsten carbide powders of the embodiment and comparative example were subjected to oxygen and nitrogen analysis. The analysis was carried out using a TCH-600 manufactured by LECO. Each powder was measured three times, and the average values ​​of the oxygen amount (amount of O) and nitrogen amount (amount of N) are shown in Table 1.

[0113] (Average particle size) The average particle size of tungsten particles in a tungsten powder was measured by the following method. First, particles in any tungsten powder were observed in an SEM image (10,000x magnification) of a 10 μm × 10 μm area. The total area of ​​the tungsten particles in the SEM image was divided by the number of tungsten particles in the SEM image.

[0114] (Number of Abnormally Grown Particles) The number of abnormally grown particles in tungsten powder was measured using the following method. First, 10 particles of randomly grown tungsten powder were selected. Each of these particles was then observed using an SEM image (10,000x magnification) of a 10 μm × 10 μm area. The number of particles showing abnormal grain growth in the SEM image for each particle was measured, and the total was divided by 10 to obtain the average value, as shown in Table 1. Here, particles showing abnormal grain growth refer to tungsten particles whose area in the SEM image of each tungsten powder is three or more times the value of (total area of ​​tungsten particles) / (number of tungsten particles).

[0115] (Weibull Coefficient) 8% by mass of metallic cobalt (Co) powder with an average particle size of 0.4 μm was added to the tungsten carbide (WC) powder shown in Table 1, methanol was added as a solvent so that the slurry solids ratio was 80 wt%, and 3 mm diameter balls made of ultrafine cemented carbide particles with an average particle size of 0.3 μm were added as grinding media, followed by attritor grinding, mixing, and drying to produce a mixed powder. Subsequently, 1.6% by mass of paraffin wax was added as an organic binder, followed by mold press molding and vacuum firing at a firing temperature of 1380°C to produce a cemented carbide.

[0116] Furthermore, the cemented carbide was processed into a sample shape for measuring three-point bending strength in accordance with JIS R1601, and the three-point bending strength was measured, and the Weibull modulus was calculated in accordance with JIS R1625.

[0117] As a result, the tungsten carbide powder of the above embodiment can further improve the properties of tungsten carbide products made from it, and more specifically, the properties of cutting inserts made from the tungsten carbide powder can further improve.

[0118] <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 production 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 production method of the present disclosure as a raw material will be described in detail as an example.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] The tungsten powder in one embodiment contains (1) tungsten carbide as a main component, oxygen, and nitrogen, and the oxygen content in mass % may be smaller than the nitrogen content.

[0124] (2) In the tungsten powder of (1) above, the nitrogen content in the tungsten powder may be 0.1 mass % or more.

[0125] (3) In the tungsten powder of (1) or (2) above, the oxygen content in the tungsten powder may be 0.05 mass% or more.

[0126] (4) In the tungsten powder according to any one of (1) to (3) above, the oxygen content in the tungsten powder may be 0.3 mass% or less.

[0127] (5) In the tungsten powder according to any one of (1) to (4) above, the tungsten particles constituting the tungsten powder may have an average particle size of 0.8 μm or less.

[0128] (6) In the tungsten powder of any one of (1) to (5) above, the tungsten powder may have first particles and second particles having a particle size larger than the first particles, and when the content ratio α1 is the nitrogen content ratio / oxygen content ratio in mass% in the first particles and the content ratio α2 is the nitrogen content ratio / oxygen content ratio in mass% in the second particles, the content ratio α1 may be larger than the content ratio α2.

[0129] (7) In the tungsten powder of any one of (1) to (6) above, the tungsten powder may have a surface region and a central region located more inward of the tungsten powder than the surface region, and the nitrogen content in the surface region may be greater than the nitrogen content in the central region.

[0130] (8) In the tungsten powder of (7) above, the nitrogen content in the surface region may decrease toward the central region.

[0131] (9) In the tungsten powder according to any one of (1) to (8) above, when the nitrogen content ratio / oxygen content ratio in the tungsten powder is defined as a content ratio α, the content ratio α may be 1.2 or more.

[0132] (10) 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 (9) with cobalt powder to form a molded body, and firing the molded body.

[0133] 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. That is, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure. For example, the above embodiments illustrate the production (recycling) of tungsten oxide powder and tungsten carbide from cemented carbide scrap, but the present disclosure is not limited to such examples and can also be applied to the production of tungsten oxide powder and tungsten carbide from ore.

[0134] Furthermore, embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within 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 within the scope of the present disclosure.

[0135] 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 tungsten powder containing tungsten carbide as a main component and containing oxygen and nitrogen, A tungsten powder having an oxygen content, by mass %, that is smaller than the nitrogen content.

2. 2. The tungsten powder according to claim 1, wherein the nitrogen content in the tungsten powder is 0.1 mass% or more.

3. The tungsten powder according to claim 1 or 2, wherein the oxygen content in the tungsten powder is 0.05 mass% or more.

4. The tungsten powder according to claim 1 or 2, wherein the oxygen content in the tungsten powder is 0.3 mass% or less.

5. 3. The tungsten powder according to claim 1, wherein the average particle size of the tungsten particles constituting the tungsten powder is 0.8 μm or less.

6. The tungsten powder is A first particle; and second particles having a particle size larger than that of the first particles, When the (nitrogen content ratio) / (oxygen content ratio) in mass% in the first particle is defined as a content ratio α1, and the (nitrogen content ratio) / (oxygen content ratio) in mass% in the second particle is defined as a content ratio α2, The tungsten powder according to claim 1 or 2, wherein the content ratio α1 is greater than the content ratio α2.

7. The tungsten powder is a surface area; a central region located more inwardly of the tungsten powder than the surface region; 3. The tungsten powder according to claim 1, wherein the nitrogen content in the surface region is greater than the nitrogen content in the central region.

8. 8. The tungsten powder according to claim 7, wherein the nitrogen content in the surface region decreases toward the central region.

9. 3. The tungsten powder according to claim 1, wherein the content ratio α is 1.2 or more, where α is the nitrogen content ratio / oxygen content ratio in the tungsten powder.

10. A step of preparing the tungsten powder according to claim 1 or 2; mixing the tungsten powder with cobalt powder to form a compact; and sintering the compact.