Tungsten powder and method for producing tungsten carbide product

Abstract

A tungsten powder according to one embodiment of the present invention is a tungsten powder containing tungsten carbide as a main component and containing oxygen and nitrogen, the content of oxygen being less than the content of nitrogen in mass%.

Description

Technical Field

[0001] The present invention relates to a method for producing tungsten powder and tungsten carbide products used in the production of cutting inserts and the like. Background Art

[0002] Tungsten powder is used in the manufacture of tungsten carbide products such as cutting inserts. As described in Patent Document 1, this tungsten carbide powder is mixed with cobalt powder and shaped into a predetermined shape. The resulting shaped body is then fired to produce the tungsten carbide product. In recent years, with the desire to achieve a carbon-neutral society, as described in Patent Document 2, the need for recycling tungsten in tungsten carbide products has increased.

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

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-060899

[0007] Patent Document 2: International Publication No. 2015 / 129835

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-206123 Summary of the Invention

[0009] The tungsten powder according to one embodiment of the present invention comprises tungsten carbide as a main component and contains oxygen and nitrogen, wherein the oxygen content, expressed in mass %, is lower than the nitrogen content. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a flow chart schematically showing a non-limiting example of a method for producing tungsten carbide powder according to the present invention.

[0011] Figure 2 This is a flowchart schematically showing an example of a conventional method for producing tungsten carbide powder.

[0012] Figure 3 This is a flowchart schematically showing an example of a conventional method for producing tungsten carbide powder. DETAILED DESCRIPTION

[0013] Tungsten powder is used in the manufacture of tungsten carbide products such as cutting inserts. As described in Patent Document 1, this tungsten carbide powder is mixed with cobalt powder and shaped into a predetermined shape. The resulting shaped body is then fired to produce the tungsten carbide product. In recent years, there has been a desire to achieve a carbon-neutral society, and as described in Patent Document 2, the need for recycling tungsten in tungsten carbide products has increased.

[0014] Furthermore, as described in Patent Document 3, tungsten carbide powder generally contains various impurities in addition to tungsten carbide as a main component. The content ratio of these impurities affects the performance of products manufactured from the tungsten carbide powder.

[0015] It is required to further improve the performance of tungsten carbide products using tungsten carbide powder as a raw material by adjusting the impurity content ratio in tungsten carbide powder, etc. More specifically, it is required to further improve the performance of cutting inserts by adjusting the impurity content ratio in tungsten carbide powder as a raw material for cutting inserts, etc.

[0016] Tungsten powder

[0017] A non-limiting example of tungsten carbide powder of the present invention is described. The so-called tungsten carbide powder in the present invention refers to a powder with tungsten carbide as the main component. The so-called "main component" means that among the components contained in the powder, tungsten carbide is the largest in terms of mass%. Specifically, it contains tungsten carbide by more than 99% by mass, and on the other hand, it contains other elements as the rest. Examples of other elements include carbon, hydrogen, nitrogen, oxygen, chromium, vanadium, tantalum, niobium, titanium, etc. More specifically, it contains tungsten carbide by more than 99.2% by mass, and it can also be a case where it does not substantially contain at least one carbide, nitride, or carbonitride selected from Groups Iva, Va, and VIa except W.

[0018] The tungsten carbide powder described in this embodiment contains oxygen and nitrogen. Furthermore, the oxygen content, measured by mass%, of the tungsten carbide powder is lower than the nitrogen content. For example, if the tungsten carbide powder contains a higher oxygen content than nitrogen, the performance of products using the tungsten carbide powder may be affected.

[0019] For example, when sintering tungsten carbide powder, the WC in the powder reacts with oxygen, potentially converting it into W2C, W, or WO3. These compositions can make it difficult to achieve the properties of WC, or the liquid phase temperature can rise, making sintering difficult. Furthermore, the WC content in the sintered tungsten carbide product decreases, making it difficult to achieve its original properties.

[0020] Furthermore, in products containing tungsten carbide and cobalt, such as cutting inserts, cobalt functions as a binder. Using tungsten carbide powder with a high oxygen content can lead to a reaction between the cobalt and oxygen, potentially forming cobalt oxide. This can reduce the cobalt's ability to act as a binder, potentially lowering the cutting insert's properties (such as Vickers hardness).

[0021] On the other hand, in the case of tungsten powders in which the oxygen content is lower than the nitrogen content (in mass %), the aforementioned situation is less likely to occur due to the relatively low oxygen content. Furthermore, the relatively high nitrogen content facilitates the formation of carbides (e.g., TiC) and carbonitrides / nitrides (TiCN / TiN)—unavoidable impurities other than tungsten carbide—during sintering. This suppresses grain growth. Furthermore, carbonitrides and nitrides have low affinity for each other, making it easier to achieve uniform grain size in the sintered tungsten carbide product.

[0022] Furthermore, when nitrogen is present on the surface of the WC particles in a larger amount than oxygen, the WC particles repel each other, and a uniform and fine-grained structure is easily obtained during rearrangement during sintering.

[0023] The oxygen and nitrogen contents in the tungsten carbide powder can be evaluated, for example, using the SEM-EDX method using an energy dispersive X-ray spectrometer (EDX) attached to a scanning electron microscope. Furthermore, the oxygen and nitrogen content ratios can be calculated from the oxygen and nitrogen content (mass %) in the entire tungsten carbide powder, respectively.

[0024] The nitrogen content in the tungsten carbide powder can be 0.1% by mass or more. In this case, because the nitrogen content is relatively high, it is easier to obtain a grain growth inhibition effect and / or a uniform grain structure effect. In addition, the possibility of forming a gradient composition of P-type hardness increases. Moreover, the possibility of generating a de-β phase increases.

[0025] The oxygen content in the tungsten carbide powder can be 0.05% by mass or more. In this case, for example, during wet grinding, the affinity with the solvent can be ensured and efficiently mixed, and the cemented carbide made from the obtained powder easily forms a uniform composition and structure. In addition, the cohesiveness of cobalt is also easily improved.

[0026] The oxygen content in the tungsten carbide powder may be 0.3% by mass or less. In this case, when the tungsten powder is sintered, the carbon in the tungsten carbide in the tungsten powder is less likely to react with the oxygen, thereby reducing the risk of a decrease in the carbon content in the sintered tungsten carbide product.

[0027] The average particle size of the tungsten carbide particles constituting the tungsten carbide powder may be 0.8 μm or less. In this case, since the particle size is small, a cemented carbide having high hardness and high strength can be easily obtained.

[0028] Here, the average particle size may be, for example, a value obtained by dividing the total area of ​​tungsten particles by the number of tungsten powder particles in a cross-sectional view of the tungsten powder photographed by a scanning electron microscope (SEM).

[0029] The tungsten powder may include first particles and second particles having a larger particle size than the first particles. Furthermore, when the (nitrogen content ratio) / (oxygen content ratio) in the first particles is represented by a content ratio α1, and the (nitrogen content ratio) / (oxygen content ratio) in the second particles is represented by a content ratio α2, α1 may be greater than α2.

[0030] Compared to the second particles, the first particles have a smaller particle size and a larger specific surface area. Therefore, assuming the oxygen content ratios in the first and second particles are the same, the oxygen contained in the first particles is more likely to affect the 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 susceptible to oxidation.

[0031] To minimize the effect of oxygen in the tungsten carbide powder on surrounding components, it is desirable to minimize the oxygen content ratio between the first and second particles. This means that both α1 and α2 are large. However, simply minimizing the oxygen content ratio between the first and second particles can increase manufacturing costs.

[0032] However, when α1 is larger than α2, that is, the oxygen content ratio in the first particles is relatively small, the production cost of the tungsten carbide powder can be suppressed while effectively suppressing the influence of oxygen contained in the tungsten carbide powder on surrounding components.

[0033] The particles in the tungsten carbide powder may have two regions divided by a midpoint trajectory connecting the center of the particle from the surface of the particle. In this case, the region on the surface side can be used as the surface region, and the region on the center side can be used as the center region. The nitrogen content ratio of the surface region can be greater than the nitrogen content ratio of the center region. In this case, because carbonitrides / nitrides are more likely to form, it is easier to obtain a grain growth inhibition effect and / or a uniform grain size effect.

[0034] In addition, the nitrogen content in the surface area can decrease as it approaches the center area. In this case, carbonitrides / nitrides are more easily formed, thereby more easily achieving grain growth suppression and / or uniform grain size. In addition, because the nitrogen content does not fluctuate drastically, the tungsten carbide powder is chemically stable.

[0035] The tungsten carbide powder may contain nitrogen in the central region. In this case, the nitrogen is evenly distributed in the tungsten carbide powder, making the tungsten carbide powder more chemically stable compared to the case where the nitrogen is contained only in the surface region.

[0036] Here, the comparison between the nitrogen content ratio in the surface region and the nitrogen content ratio in the central region can be confirmed by mapping a cross-sectional image of the tungsten carbide powder photographed by SEM.

[0037] When the content ratio α is defined as (nitrogen content ratio) / (oxygen content ratio) in the tungsten carbide powder, α may be 1.2 or greater. In this case, the nitrogen content ratio is relatively high, making it easier to achieve grain growth suppression effects and / or uniform grain size effects.

[0038] <Method for producing tungsten powder (production method)>

[0039] A non-limiting example of a method for producing (manufacturing method of) tungsten powder according to the present invention will be described.

[0040] A method for producing tungsten powder according to one embodiment of the present invention is as follows: Figure 1 As shown, the following steps (A) to (G) are included.

[0041] (A) Process of preparing raw materials containing tungsten

[0042] (B) Process of oxidizing the tungsten in the raw material to obtain tungsten oxide

[0043] (C) Step of dissolving tungsten oxide from the raw material using an alkaline solvent to obtain a solution

[0044] (D) A step of adding a metal compound adsorbent (hereinafter sometimes referred to as an adsorbent) to the solution and reacting the adsorbent with the solution containing the dissolved tungsten to obtain a compound containing the adsorbent and tungsten.

[0045] (E) Step of obtaining a compound from a solution

[0046] (F) Process of mixing the compound and carbon powder to produce a mixed material

[0047] (G) Process of heating mixed materials

[0048] (Process A)

[0049] First, prepare raw materials containing tungsten. Examples of raw materials include tungsten-containing ores and scrap. Examples of tungsten-containing ores include scheelite (CaWO4), manganese tungsten ore (MnWO4), ferromagnetite (FeWO4), and ferromagnetite ((Fe,Mn)WO4). Tungsten-containing scrap is waste generated during the production of products primarily composed of metallic tungsten or tungsten carbide (WC). Specifically, it includes scrap generated during the manufacturing process of superhard tools, hard scrap from used tools, and powdered soft scrap such as grinding sludge.

[0050] Cemented carbide, a type of super-hard alloy, is primarily composed of a composite carbide of metallic tungsten and tungsten carbide. Components primarily composed of this composite carbide have a binder phase composed of iron, nickel, cobalt, and other materials, and may contain additives such as TiC, TaC, NbC, VC, and Cr3C2 as needed. Materials containing cemented carbide that are suitable for treatment include cutting tools (cutting inserts, drills, end mills, etc.), molds (forming rollers, forming dies, etc.), and civil engineering and mining tools (such as oil drilling tools and rock crushing tools).

[0051] (Process B)

[0052] When tungsten is present in a non-oxide state in the raw material, the tungsten in the raw material is oxidized to produce tungsten oxide. For example, when a used cutting tool is used as the raw material, tungsten is present in the cutting tool as tungsten carbide. Therefore, this tungsten carbide is oxidized to produce tungsten oxide.

[0053] As a method for oxidizing tungsten, for example, oxidative baking can be used. For example, by oxidative baking a cutting tool containing tungsten carbide and cobalt, a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4) can be obtained.

[0054] As described above, the purpose of step A and step B is to obtain tungsten oxide from the raw material. Therefore, these steps can be collectively expressed as a step of preparing a raw material containing tungsten oxide.

[0055] (Process C)

[0056] The recovery method involves an alkaline extraction / alkaline melting step, where the metal components of the cemented carbide scrap are dissolved in an alkaline solution to produce a tungsten compound solution containing dissolved tungsten compound ions. Examples of methods for producing the metal compound solution include alkaline extraction and alkaline melting. The alkaline extraction method involves performing alkaline extraction on pre-oxidized and roasted scrap using, for example, an aqueous NaOH solution. The alkaline dissolution method involves simultaneously oxidizing and dissolving the scrap using a molten sodium salt such as NaNO3, Na2SO4, Na2CO3, or NaOH.

[0057] For example, soft waste is difficult to control due to its high reactivity, so the alkali extraction method is more effective. Hard waste can only partially oxidize the surface through oxidative roasting, so the alkali dissolution method is more effective.

[0058] (Process D)

[0059] The adsorbent of this embodiment is added to the tungsten compound solution obtained in step C. The adsorbent of this embodiment adsorbs the metal compound present as anions in the solution. Here, as the adsorbent material of this embodiment, for example, the first adsorbent and / or the second adsorbent described below can be used.

[0060] [First adsorbent]

[0061] The first adsorbent contains at least one first amino acid selected from 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. Furthermore, the first adsorbent may contain at least 10 mol% of the first amino acid as a free amino acid (also referred to as a "first free amino acid") relative to the total amount of free amino acids.

[0062] This allows the metal compound to be recovered in a simple processing step and eliminates the need to use large amounts of chemicals, thereby reducing environmental pollution.

[0063] In addition, the free amino acid in the adsorbent may exist as a solid or as a free amino acid when dissolved in a solution. In either case, the free amino acid is contained in the solution, and by using these adsorbents, the metal compound can be recovered in a simple processing step.

[0064] An example of the first adsorbent is a substrate with free amino acids supported on its surface. Suitable substrates include peptides and proteins containing free amino acids, substances forming organisms such as microorganisms (hereinafter referred to as "biological substances"), and organic or inorganic substances such as resins.

[0065] Examples of the microorganisms include Escherichia coli, Bacillus sp., Thiobacillus ferrooxidans, Streptomyces rimosus, Pseudomonas sp., Bacillus thuringiensis, Arthrobacter truncatus, Shewanella algae, and Shewanella oneida. Bacteria such as Shewanella oneidensis, yeasts such as Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida albicans, Yarrowia lipolytica, Pichia pastoris, Hansenula polymorpha, and Kluyveromyces lactis, and Aspergillus fungi.

[0066] Adsorbents made from biomass come in a variety of forms, including powders, pellets formed from powders, gels, and aqueous solutions. Powders and pellets are easy to store and handle. When the adsorbent is a solid substance, such as a powder or pellet, it can be dissolved in water or other liquids before adding it to the solution containing the metal compound, or the solid can be added directly to the solution containing the metal compound and stirred.

[0067] The first adsorbent may contain, as free amino acids, at least one of alanine, cystine, methionine, tyrosine, lysine, valine, glutamic acid, histidine, and proline (hereinafter referred to as the first amino acid); at least one of threonine, asparagine, glycine, isoleucine, ornithine, and arginine (hereinafter referred to as the first second amino acid); and at least one of serine, citrulline, and cystathionine (hereinafter referred to as the first third amino acid). Furthermore, the first adsorbent may contain, as a free amino acid, at a ratio of 40 mol% or less of at least one of phosphoserine, aspartic acid, leucine, and phenylalanine as a second amino acid relative to the total amount of free amino acids.

[0068] An adsorbent containing the 1-1 amino acid, the 1-2 amino acid, and the 1-3 amino acid as free amino acids can improve the recovery efficiency of the metal compound.

[0069] When using such an adsorbent, if the first amino acid is composed of two or more species, the content of each free amino acid in the first amino acid can be 5 mol% or more, based on the total amount of free amino acids being 100 mol%. In particular, lysine can be contained at a rate of 10 mol% or more as a free amino acid. This improves the recovery efficiency of the metal compound. Furthermore, if the total amount of the first amino acid is 10 mol% or more as a free amino acid, the recovery efficiency of the metal compound is improved.

[0070] The free amino acid composed of the first amino acid may be contained in an amount of 0.5% by mass or more relative to the total amount of the solid matter obtained by drying the adsorbent, that is, relative to the solid content of the adsorbent. In this case, the recovery efficiency of the metal compound is improved.

[0071] Furthermore, when the free amino acids include at least one of glutamic acid and valine and asparagine, the content of at least one of glutamic acid and valine may be greater than that of asparagine. Free amino acids composed of glutamic acid and valine, by adjusting the pH of the solution toward the acidic side to a positive zeta potential, adsorb metal compound ions (anions) in the solution. On the other hand, asparagine has a low adsorption capacity for metal compounds (ions). Therefore, increasing the content of at least one of glutamic acid and valine in the free amino acids relative to that of asparagine can improve the adsorption efficiency of the metal compound.

[0072] The types and contents of free amino acids contained in the adsorbent can be confirmed through free amino acid analysis (also known as bioamino acid analysis). The ratio of the total free amino acid content to the adsorbent's solid content can be calculated based on the mass of the free amino acids in the adsorbent and the mass of the adsorbent's solid content. If the adsorbent is a solid, such as a powder, the adsorbent is added to pure water at a temperature of 25°C and stirred for 10 minutes with a magnetic stirrer at 500 rpm to suspend the adsorbent. This suspension is then used for free amino acid analysis. If the adsorbent is a solution, free amino acid analysis is performed in the solution and can be calculated based on the total free amino acid content and the mass of the adsorbent's solid content obtained by centrifuging the adsorbent solution. The mass of the adsorbent's solid content can be measured after it has been thoroughly dried, for example, at 60°C for 24 hours.

[0073] Furthermore, the free amino acids contained in biological substances are supported on the surface of peptides and proteins as a matrix. Since the free amino acids are supported on high-molecular-weight peptides and proteins, the adsorbent is easy to handle. Furthermore, when recovering the adsorbent adsorbed with metal compounds from a solution containing metal compounds, simple methods such as filtration separation can be used to concentrate the adsorbent. Besides biological substances, the matrix can also be resins and inorganic substances, but biological substances can easily increase the free amino acids. In the first adsorbent, the free amino acids are supported on the surface of the microorganism.

[0074] When the adsorbent matrix is ​​a resin or inorganic substance, if the matrix is ​​in a form with a large specific surface area, such as a powder or porous body, a large amount of free amino acids can be supported on the surface of the matrix. If it is a porous body, the inner walls of the pores can also support amino acids.

[0075] When the adsorbent is composed of a biological substance, in addition to free amino acids, there may also be amino acids that do not contribute to the adsorption reaction (hereinafter referred to as inert amino acids). Examples of inert amino acids include amino acids located at intermediate positions among amino acids bound by peptide bonds, and amino acids located at internal positions that are not exposed to the adsorbent surface.

[0076] When the adsorbent is composed of a biological substance, in order to increase the content ratio of free amino acids in the adsorbent, it is effective to perform a treatment to cleave the peptide bonds of inert amino acids present in the adsorbent to convert the inert amino acids into free amino acids.

[0077] For example, when the organic matter is a microorganism, the peptide bonds present in the microorganism can be cleaved using existing treatment methods. Specifically, proteolytic enzymes such as trypsin, lysyl endopeptidase (registered trademark), and V8 protease can be used to degrade the proteins that make up the microorganism. This can convert at least a portion of the inert amino acids contained in the microorganism into free amino acids. Other effective methods for converting inert amino acids into free amino acids include heating the adsorbent at 60°C or above, boiling it, or applying heat and pressure using an autoclave to decompose the protein. Furthermore, since the adsorbent is a living organism such as a microorganism and does not necessarily need to be stored in solution, if it can be stored as a solid, inanimate object like the decomposed product, large-scale equipment and maintenance for cultivation and storage are unnecessary, allowing for miniaturization of the equipment.

[0078] [Second adsorbent]

[0079] 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, wherein at least a portion of the first amino acid is present as a free amino acid in the solution. Alternatively, the second adsorbent may contain the first amino acid in an amount of 10 mol % or more relative to the total amount of the free amino acids.

[0080] That is, the second adsorbent exists as a solid and does not contain free amino acids in the solid, but contains free amino acids in the solution.

[0081] An example of a second adsorbent is a salt of the first amino acid. Examples of salts include hydrochlorides, nitrates, sulfates, acetates, and carbonates. The adsorbent composed of the amino acid salt is dissolved in a liquid to provide free amino acids. Then, similar to the first adsorbent, the adsorbent is added to a solution containing a metal compound, and the pH is adjusted to a level where the zeta potential of the free amino acids in the adsorbent is positive. At this point, since the metal compound acts as an anion, the anion of the metal compound adsorbs onto the positively charged free amino acids in the adsorbent.

[0082] Compared to a form in which free amino acids are supported on the surface of a substrate, the second adsorbent can increase the free amino acid content in the adsorbent. Consequently, the adsorption efficiency of the metal compound is high, enabling a large amount of metal compound to be adsorbed with a small amount of adsorbent. Furthermore, when the metal compound is recovered after adsorption, the amount of waste that needs to be discarded is low, making it easier to handle and reducing manufacturing costs. Furthermore, because the adsorbent is not a living organism like bacteria or microorganisms, it is easy to store and manage.

[0083] The salt-based adsorbent serving as the second adsorbent may be in the form of a solution, but solid forms are easier to handle, store, and manage, and powder forms are particularly easy to dissolve in solutions. Furthermore, the adsorbent may be in the form of pellets for easier handling.

[0084] If the salt of the first amino acid contains at least one salt of lysine or arginine as a main component, the adsorbent has a high adsorption efficiency. For example, a salt containing lysine can be used as the adsorbent. Here, the so-called salt containing lysine refers to, for example, lysine hydrochloride, lysine sulfate, lysine nitrate, lysine acetate, etc.

[0085] Among them, lysine hydrochloride (e.g., L-lysine hydrochloride) is stable and inexpensive. Furthermore, when lysine hydrochloride is used as an adsorbent, it is difficult for unwanted elements to enter during the subsequent acid treatment step. Furthermore, the phrase "containing at least one salt of lysine or arginine as a main component" means that the total mass of the lysine salt or arginine salt in the adsorbent is 50% or more by mass relative to the total mass of the adsorbent.

[0086] The total amount of the lysine salt and the arginine salt present in the adsorbent may be 90% by mass or greater. This allows a large amount of metal compounds to be adsorbed using a small amount of adsorbent. The total amount of the lysine salt and the arginine salt present in the adsorbent is more preferably 95% by mass or greater.

[0087] If a salt of glutamic acid is included as the first amino acid salt, the cost of the adsorbent can be reduced. Among them, sodium glutamate is stable and inexpensive.

[0088] The content of the glutamic acid salt present in the adsorbent can be 90% by mass or more. This allows for inexpensive recovery of the metal compound. The desired range of the total amount of the glutamic acid salt present in the adsorbent is 95% by mass or more.

[0089] The free amino acid is not limited to one type. For example, a salt of another first amino acid such as lysine or arginine may be added together with a salt of glutamic acid.

[0090] For example, when the adsorbent is composed of microorganisms, the tungsten concentration is adjusted to 0.1 to 10 mmol / l (0.1 to 10 mmol per liter of alkaline solution). 3 The adsorbent is added to the tungsten compound solution in an amount of 1 g to 10 kg. When the adsorbent is composed of a salt of a first amino acid, for example, the total amount of the first amino acid salt added to the adsorbent is 0.2 to 1.1 mol per 1 mol of the metal component of the metal compound. This allows a small amount of adsorbent to adsorb a large amount of a metal compound, such as a tungsten compound.

[0091] The total amount of the first amino acid salt added can be 10 to 300 g / L relative to the metal compound solution. In this case, the viscosity of the solution does not increase, and the recovery efficiency of the metal compound is unlikely to decrease. In particular, when the adsorbent is composed of an amino acid salt, the viscosity of the solution is unlikely to increase, resulting in improved workability.

[0092] The temperature can be adjusted according to the activity of the free amino acid and can generally be room temperature. The tungsten compound solution to which the adsorbent is added is adjusted using hydrochloric acid or the like so that the zeta potential of the free amino acid is positive. This allows the tungsten compound ions, which serve as anions, to be adsorbed on the adsorbent.

[0093] The pH of the solution is below 7 (acidic). When the free amino acids are lysine and arginine, the optimal pH is 4 or below, preferably 1 to 3, and desirably 1 to 2.3. When the free amino acid is glutamic acid, the optimal pH is 1.5 or below. This can improve the recovery rate of the tungsten compound. The pH adjustment step or the step of adding the adsorbent to the solution containing the metal compound can be performed first.

[0094] When the adsorbent is a salt of the first amino acid, the adsorption reaction takes place within 1 hour, and the recovery efficiency of the adsorbent is high. However, if the adsorption reaction takes longer than 1 hour, part of the adsorbed metal compound may be released from the free amino acid.

[0095] (Process E)

[0096] Next, the adsorbent having adsorbed the tungsten compound ions is removed from the solution. The term "removal" herein includes the steps of separating the compound from the solution by filtration and drying the recovered compound to powder form.

[0097] Specifically, the adsorbent containing the tungsten compound ions is filtered through filter paper, and the slurry of the compound on the filter paper is recovered. The recovered compound is then dried and powdered to obtain a powdered tungsten compound containing the adsorbent. Here, the term "tungsten compound containing the adsorbent" refers to, for example, lysine-WO4 when the adsorbent is lysine.

[0098] (F, G process)

[0099] A predetermined amount of carbon powder (carbon black, graphite powder, activated carbon, etc.) or carbon slurry is added to the extracted tungsten compound as a reducing agent and mixed (step F). This mixture is then heated to 1100-2000°C for a predetermined time under a predetermined atmosphere to undergo carbonization, yielding tungsten powder primarily composed of tungsten carbide (step G). The predetermined atmosphere described above may be, for example, a reducing atmosphere containing carbon monoxide, nitrogen, hydrogen, and methane.

[0100] In the carbonization step described in this embodiment, the carbonization treatment is performed in a mixed atmosphere primarily composed of nitrogen and hydrogen. This allows for further reductions in manufacturing costs compared to treating the gas in separate atmospheres. The term "primary component" refers to the presence of nitrogen and hydrogen in a gaseous atmosphere, where the proportions of nitrogen and hydrogen exceed those of other components, measured in mole percent. More specifically, this refers to a situation where the proportions of nitrogen and hydrogen are 40 mole percent or greater and 10 mole percent or greater, respectively.

[0101] Generally, the powder obtained in step E is incinerated to remove the adsorbent, producing WO3. A reduction treatment removes oxygen from the WO3, yielding metallic tungsten. This metallic tungsten is then carbonized to produce tungsten carbide powder. However, for example, the process of removing the adsorbent and obtaining WO3 requires incineration at temperatures above 300°C. Furthermore, the reduction of the WO3 requires heat treatment in a reducing atmosphere (e.g., a hydrogen atmosphere) at temperatures between 800°C and 950°C. Consequently, producing tungsten carbide powder requires significant effort.

[0102] On the other hand, in the production method of this embodiment, the tungsten compound obtained in step E is directly carbonized to produce WC without undergoing the aforementioned oxidation and reduction treatments. This reduces the burden of producing tungsten carbide powder. Furthermore, when carbonizing the tungsten compound, carbon powder is mixed to produce a mixed material, which is then heated.

[0103] When the adsorbent is an organic substance as described above, WC can be obtained by carbonizing tungsten using the carbon component contained in the adsorbent. However, in the G step, which carbonizes tungsten using only the carbon component contained in the adsorbent, carbon is often insufficient, and therefore, not only WC but also W2C is easily generated in this G step.

[0104] In step F of the production method of this embodiment, since carbon powder is mixed with the tungsten compound, the above-mentioned carbon deficiency is eliminated, W2C is hardly produced, and a high-purity WC powder can be produced.

[0105] The amount of carbon powder added in step F can be adjusted so that the carbon content in the mixed material is 5% by mass or more. In this case, in step G, tungsten is stable and easily carbonized, so W2C is less likely to form and WC is more likely to form.

[0106] Furthermore, the amount of carbon powder added in step F can be adjusted to keep the carbon content in the mixed material at 6% by mass or less. The higher the carbon content in the mixed material, the more stable the tungsten becomes, making it easier to carbonize. On the other hand, if the carbon content in the mixed material is too high, removing the remaining carbon that has not bonded to the tungsten after step G may be cumbersome. However, when the carbon content in the mixed material is 6% by mass or less, the burden of removing the excess carbon is minimal.

[0107] Furthermore, when the adsorbent is an organic substance as described above, the amount of carbon powder can be adjusted by adding the carbon content of the adsorbent. From another perspective, the carbon content in the tungsten carbide can come not only from the carbon powder but also from the carbon content in the adsorbent. In other words, the carbon in the tungsten powder can include 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 includes the carbon in the adsorbent, the amount of carbon powder added in step F can be reduced.

[0108] When the mixed atmosphere in step G primarily consists of nitrogen and hydrogen, the hydrogen content (mol %) may be lower than that of nitrogen, or may be of equal proportion. When the hydrogen content is lower than the nitrogen content, coarse particles are less likely to form. Furthermore, the phrase "nitrogen and hydrogen content ratios are equal" does not necessarily mean they are strictly identical. "Equal proportions" are considered acceptable when the ratio (nitrogen content ratio) / (hydrogen content ratio) is between 0.9 and 1.1.

[0109] The metal compound recovery method of this embodiment can reduce man-hours, reduce the amount of chemicals used and the amount of waste liquid, and recover tungsten compounds at low cost, compared to conventional metal compound recovery methods.

[0110] Furthermore, the total amount of CO₂ emitted by the process of the present invention is approximately 40% of the total amount of CO₂ emitted by the conventional ion exchange method for producing tungsten carbide via ammonium metatungstate and W metal powder (in terms of energy conversion). By adopting the process of the present invention, CO₂ emissions can be significantly reduced when producing tungsten carbide.

[0111] Furthermore, in the case of the above-mentioned production method, the nitrogen in the tungsten carbide powder can be derived from the nitrogen in the adsorbent. In this case, there is no need to add nitrogen to increase the nitrogen content in the tungsten carbide powder, or the nitrogen content can be reduced, thereby reducing production costs.

[0112] [Examples and Comparative Examples]

[0113] Hereinafter, the method for producing the examples and comparative examples shown in Table 1 will be described.

[0114]

Table 1

[0115]

[0116] Figure 1 1 is a flowchart showing an example of the steps of a tungsten carbide powder production process according to an embodiment. Figure 2 This is a flow chart showing an example of the steps of a conventional tungsten carbide powder production process. Figure 1 and Figure 2 As shown, in the manufacturing process of the tungsten carbide powder of the embodiment and the conventional method, first, scrap of cemented carbide is prepared.

[0117] Cemented carbide, a type of super-hard alloy, is mainly composed of composite carbides such as metal tungsten and tungsten carbide, with iron, nickel, cobalt, etc. as a binder phase, and contains TiC, TaC, NbC, VC, Cr3C2, etc. as additives as needed.

[0118] Examples of target carbide-containing materials to be treated include cutting tools (cutting inserts, drills, end mills, etc.), dies (forming rolls, forming dies, etc.), and civil engineering and mining tools (oil mining tools, rock crushing tools, etc.).

[0119] Next, the prepared cemented carbide scrap is oxidatively roasted to produce a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). This mixture is then refluxed with a sodium hydroxide (NaOH) aqueous solution and extracted to produce a tungsten compound solution containing sodium tungstate (Na2WO4).

[0120] Next, an adsorbent containing lysine is added to the obtained tungsten compound solution to allow the tungsten compound ions to be adsorbed on the lysine.

[0121] In such an adsorption treatment, for example, the total amount of the first amino acid salt added to the adsorbent is 0.2 to 1.1 mol per mol of the metal component of the tungsten compound. This allows a large amount of tungsten compound to be adsorbed by a small amount of adsorbent.

[0122] Furthermore, 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 solution viscosity from increasing, minimizing the reduction in metal compound recovery efficiency. In particular, when the adsorbent is composed of an amino acid salt, the solution viscosity is minimized, resulting in improved operability.

[0123] The temperature can be adjusted according to the activity of the free amino acid and can generally be room temperature. The tungsten compound solution to which the adsorbent is added can be adjusted by using hydrochloric acid or the like to make the zeta potential of the free amino acid positive. This allows the tungsten compound ions, which are anions, to be adsorbed on the adsorbent.

[0124] The solution pH can be below 7 (acidic). When the free amino acids are lysine and arginine, the pH is preferably below 4, preferably between 0.5 and 3, and desirably between 0.8 and 2.3. When the free amino acid is glutamic acid, the pH is preferably below 1.5. In the examples, the pH was adjusted to 1.8.

[0125] It should be noted that either the step of adjusting the pH of the solution or the step of adding the adsorbent to the solution containing the metal compound may be performed first.

[0126] In the subsequent process, because Figure 1 The manufacturing process and Figure 2 The manufacturing processes are different, so they are explained separately.

[0127] ( Figure 1 manufacturing process)

[0128] The adsorbent containing the tungsten compound ions is filtered through filter paper, etc., thereby recovering the compound in a slurry on the filter paper. The recovered compound is then dried and powdered to obtain a powdered tungsten compound containing the adsorbent. Here, the term "tungsten compound containing the adsorbent" refers to, for example, lysine-WO4, since the adsorbent is lysine.

[0129] Next, carbon black is added to and mixed with the recovered tungsten compound, and heated for at least one hour in a mixed atmosphere of hydrogen and nitrogen (1 to 10 L / minute) at the temperature shown in Table 1. This allows the adsorbent, which has adsorbed the tungsten compound ions, to be directly carbonized. In the examples, the carbon content of the carbon black is 5 to 6% by mass of the carbon content of the mixed material. This yields the tungsten carbide powder of the present application, which serves as a raw material for cemented carbide. Examples 1 to 9 in Table 1 represent tungsten carbide powders produced using this production method.

[0130] ( Figure 2 Manufacturing process)

[0131] Following the lysine adsorption step, the adsorbent containing the tungsten compound ions is dehydrated by filtration, centrifugation, etc., and then, if necessary, washed with pure water to remove impurities.

[0132] The adsorbent that adsorbed the tungsten compound ions is burned in the air at a temperature of 300° C. or higher, for example, to oxidize the tungsten compound and remove organic components contained in the adsorbent. Thus, the tungsten oxide powder (WO 3 ) of the embodiment can be obtained.

[0133] Then as Figure 2 As shown in Table 1, the resulting tungsten oxide powder is heat-treated at 800°C to 950°C in a reducing atmosphere (e.g., a hydrogen atmosphere) to reduce the tungsten oxide compound. This produces metallic tungsten (W). Carbon black is then added and mixed into the resulting metallic tungsten powder, and the mixture is heated in a mixed atmosphere of hydrogen and nitrogen at the temperatures shown in Table 1 for at least one hour to produce tungsten carbide (WC), a conventional raw material for cemented carbide. Comparative Examples 1 and 2 in Table 1 show tungsten carbide powders produced using this production method.

[0134] ( Figure 3 Manufacturing process)

[0135] Figure 3 This is a flow chart showing an example of the steps of a conventional method for producing tungsten carbide powder. Figure 3 As shown, in the production process of tungsten oxide powder and tungsten carbide of the reference example, first, scrap of cemented carbide is prepared.

[0136] Next, the prepared cemented carbide scrap is oxidatively roasted to produce a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). This mixture is then extracted with an aqueous sodium hydroxide (NaOH) solution to produce a tungsten compound solution containing sodium tungstate (Na2WO4).

[0137] The resulting tungsten compound solution is then ion-exchanged using an ion exchange resin or the like to produce an aqueous solution of ammonium tungstate ((NH4)2WO4). The resulting aqueous solution is then heated and concentrated to crystallize the tungsten compound as ammonium metatungstate (APT).

[0138] Next, carbon powder (such as carbon black, graphite powder, and activated carbon) is added and mixed into the resulting APT. The APT is then heat-treated at a temperature of 1000°C to 1300°C in a reducing atmosphere (e.g., a mixture of hydrogen and nitrogen) as shown in Table 1 to directly carbonize it. This yields tungsten carbide powder, a raw material for cemented carbide. Comparative Example 3 in Table 1 shows tungsten carbide powder produced using this method.

[0139] Hereinafter, the items shown in Table 1 will be described.

[0140] (Amount of oxygen and nitrogen in tungsten carbide powder)

[0141] Oxygen and nitrogen analysis was performed on the obtained tungsten carbide powders of the embodiment and comparative example. The analysis was performed using a TCH-600 manufactured by LECO. The oxygen (O) and nitrogen (N) content values, averaged over three measurements for each powder, are shown in Table 1.

[0142] (Average particle size)

[0143] The average particle size of tungsten particles in tungsten powder is measured using the following method. First, observe particles in any tungsten powder using a SEM image (10,000x magnification) covering a 10 μm x 10 μm area. The average particle size is calculated by dividing the total area of ​​the tungsten particles in the SEM image by the number of tungsten particles in the image.

[0144] (Number of abnormally growing particles)

[0145] The number of abnormally grown particles in tungsten powder is measured using the following method. First, 10 random pieces of tungsten powder are selected. Each particle is then observed in a 10 μm x 10 μm SEM image (10,000x magnification). The number of particles with abnormal grain growth in the SEM image is measured for each particle, and the average value, calculated by dividing the total by 10, is shown in Table 1. Particles with abnormal grain growth are defined as tungsten particles with an area greater than or equal to three times the value of (total area of ​​tungsten particles) / (number of tungsten particles) in the SEM image of each tungsten powder.

[0146] (Weibull coefficient)

[0147] 8% by mass of cobalt (Co) powder with an average particle size of 0.4 μm was added to the tungsten carbide (WC) powder listed in Table 1. Methanol was added as a solvent to a slurry solid content of 80% by weight. 3 mm diameter grinding balls composed of ultrafine cemented carbide particles with an average particle size of 0.3 μm were added as a grinding medium. The mixture was pulverized in an attritor, mixed, and dried to produce a mixed powder. Subsequently, 1.6% by mass of paraffin wax was added as an organic binder. The mixture was press-formed using a mold and then vacuum-sintered at a sintering temperature of 1380°C to produce a cemented carbide.

[0148] Furthermore, the cemented carbide was processed into a sample shape for three-point bending strength measurement in accordance with JIS R1601, the three-point bending strength was measured, and the Weibull modulus was calculated in accordance with JIS R1625.

[0149] Therefore, the tungsten carbide powder of the above embodiment can further improve the properties of tungsten carbide products made from the tungsten carbide powder, and more specifically, can further improve the properties of cutting inserts made from the tungsten carbide powder.

[0150] <Method for manufacturing tungsten carbide products>

[0151] Next, a method for manufacturing a tungsten carbide product according to a non-limiting example of the present invention will be described. Specifically, a method for manufacturing a tungsten carbide product using tungsten carbide powder obtained by the production method of the present invention as a raw material will be described. Here, a method for manufacturing a cutting blade using tungsten carbide powder obtained by the production method of the present invention as a raw material will be described in detail as an example.

[0152] A method for producing a machined product according to one embodiment includes the following steps (X) and (Y).

[0153] (X) Step of mixing tungsten carbide powder and cobalt powder to form a compact

[0154] (Y) Step of firing the molded body

[0155] More specifically, first, cobalt powder is suitably added to the tungsten carbide powder obtained by the production method of the present invention. Metal powders other than cobalt powder and / or carbon powder may also be added at this time. Then, wet mixing is performed using a ball mill for a predetermined time. After drying, the mixed powder is formed into a predetermined tool shape using a known forming method such as stamping, casting, extrusion, or cold isostatic pressing to obtain a formed body.

[0156] Thereafter, the formed body is fired in a vacuum or non-oxidizing atmosphere to produce a cutting insert. The surface of the produced cutting insert may be subjected to a grinding process or a honing process.

[0157] The surface of a cutting insert can be coated using chemical vapor deposition (CVD) or physical vapor deposition (PVD). Examples of coating compositions include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), and aluminum oxide (Al2O3).

[0158] A tungsten powder according to one embodiment (1) contains tungsten carbide as a main component and contains oxygen and nitrogen, wherein the oxygen content is smaller than the nitrogen content in mass %.

[0159] (2) In the tungsten powder of (1) above, the nitrogen content of the tungsten powder may be 0.1% by mass or more.

[0160] (3) In the tungsten powder of (1) or (2) above, the oxygen content of the tungsten powder may be 0.05 mass % or more.

[0161] (4) In any one of the tungsten powders described in (1) to (3) above, the oxygen content of the tungsten powder may be 0.3 mass % or less.

[0162] (5) In any one of the tungsten powders described in (1) to (4) above, the average particle size of the tungsten particles constituting the tungsten powder may be 0.8 μm or less.

[0163] (6) In any one of the tungsten powders of (1) to (5) above, the tungsten powder comprises a first particle and a second particle having a particle size larger than that of the first particle, and when the (nitrogen content ratio) / (oxygen content ratio) in the first particle is expressed in mass % as a content ratio α1 and the (nitrogen content ratio) / (oxygen content ratio) in the second particle is expressed in mass % as a content ratio α2, the content ratio α1 may be larger than the content ratio α2.

[0164] (7) In any one of the tungsten powders of (1) to (6) above, the tungsten powder has a surface region and a central region located inside the tungsten powder relative to the surface region, and the nitrogen content ratio of the surface region may be greater than the nitrogen content ratio of the central region.

[0165] (8) In the tungsten powder of (7) above, the nitrogen content ratio in the surface region may decrease as it approaches the center region.

[0166] (9) In any one of the tungsten powders described in (1) to (8), 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 greater.

[0167] (10) A method for producing a tungsten carbide product may include the following steps: a step of mixing tungsten powder obtained by the method for producing tungsten powder according to any one of (1) to (9) above with cobalt powder to form a compact; and a step of sintering the compact.

[0168] The present invention has been described above based on embodiments. However, the present invention is not limited to the aforementioned embodiments. That is, the present invention can be modified in various ways within the scope of the present invention. For example, the above embodiments illustrate the production (recycling) of tungsten oxide powder and tungsten carbide from cemented carbide scrap. However, the present invention is not limited to this example and is also applicable to the production of tungsten oxide powder and tungsten carbide from ore.

[0169] In addition, embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. In other words, it should be noted that if a person skilled in the art can easily make various variations or modifications based on the present invention. It should also be noted that such variations or modifications are included in the scope of the present invention.

[0170] Although the embodiments of the present invention have been exemplified above, the present invention is not limited to the above-described embodiments, and any embodiments may be employed without departing from the spirit of the present invention.

Claims

1. A tungsten powder comprising tungsten carbide as a main component and containing oxygen and nitrogen, wherein: The content ratio of oxygen in mass % is smaller than the content ratio of nitrogen.

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 any one of claims 1 to 3, wherein The oxygen content in the tungsten powder is 0.3 mass % or less.

5. The tungsten powder according to any one of claims 1 to 4, wherein The average particle size of the tungsten particles constituting the tungsten powder is 0.8 μm or less.

6. The tungsten powder according to any one of claims 1 to 5, wherein The tungsten powder has: 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 the first particles is expressed in mass % as content ratio α1 and the (nitrogen content ratio) / (oxygen content ratio) in the second particles is expressed in mass % as content ratio α2, The content ratio α1 is greater than the content ratio α2.

7. The tungsten powder according to any one of claims 1 to 6, wherein The tungsten powder has: surface area; and A central region located inside the tungsten powder compared to the surface region, The nitrogen content ratio of the surface region is greater than the nitrogen content ratio of the central region.

8. The tungsten powder according to claim 7, wherein The nitrogen content ratio in the surface region decreases as it approaches the central region.

9. The tungsten powder according to any one of claims 1 to 8, wherein When the (nitrogen content ratio) / (oxygen content ratio) in the tungsten powder is defined as a content ratio α, the content ratio α is 1.2 or greater.

10. A method for manufacturing a tungsten carbide product, wherein: The process is as follows: A step of preparing the tungsten powder according to any one of claims 1 to 9; The step of mixing the tungsten powder and the cobalt powder to form a compact; and A step of firing the molded body.

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