A carburizing agent and a method for preparing ultra-coarse tungsten carbide powder

Abstract

The present invention belongs to the technical field of powder metallurgy or waste tungsten wire recycling, and specifically relates to a carburizing agent and a method for preparing ultra-coarse tungsten carbide powder. The preparation method comprises: activating the tungsten wire in an inert atmosphere and then performing a first carburizing treatment, using an organic solvent with a high carbon-oxygen atomic ratio and an activator; then crushing the obtained tungsten carbide wire to obtain tungsten carbide powder, using a gaseous carbon source for a second carburizing treatment, and then performing a sintering treatment to obtain ultra-coarse tungsten carbide powder. The present invention uses tungsten wire as a raw material, and the tungsten wire is composed of single crystal tungsten particles, which are not easy to crack. When preparing tungsten carbide powder, the particle size of the ultra-coarse tungsten carbide powder will not be affected by transcrystalline fracture. The present invention uses an organic solvent with a high carbon-oxygen ratio for carburizing treatment, and the active carbon atoms can penetrate into the core of the tungsten wire; then the carburized tungsten wire is crushed, and then subjected to a secondary carburizing and sintering treatment, and the partially decarburized phase in the tungsten carbide powder is carbonized to form a complete crystal, which promotes the sintering and growth of the tungsten carbide powder at a high temperature to obtain an ultra-coarse tungsten carbide powder.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy or waste tungsten wire recycling, and in particular relates to a carburizing agent and a preparation method of ultra-coarse tungsten carbide powder. Background Art

[0002] As a non-renewable scarce resource, tungsten has physical properties such as high density, high melting point, high wear resistance, high conductivity, and high hardness. Tungsten-based steel wire is more resistant to high temperatures, has stronger tensile strength, and can be made thinner at the same breaking force. It has replaced the traditional photovoltaic diamond wire busbar (carbon steel wire). However, tungsten wire is prone to breakage during the wire drawing process, and the scrap rate reaches 50%. How to reuse waste tungsten wire is of great significance.

[0003] At present, the main methods for recycling tungsten wire are electrolysis and hydrometallurgy. First, tungsten oxide is prepared and then tungsten powder is prepared. The process is complicated and requires the use of a large amount of chemical reagents, which is not environmentally friendly. When tungsten wire is oxidized to prepare tungsten oxide by pyrometallurgy, the surface oxide skin will wrap the unoxidized tungsten wire inside, making it difficult to oxidize the internal tungsten wire. Multiple oxidations are required to completely oxidize the tungsten wire, which will increase energy consumption. Otherwise, the recycled tungsten powder will contain more short tungsten wires and tungsten fibers, making it difficult to ensure the quality of the recycled tungsten powder.

[0004] Ultra-coarse tungsten carbide powder is the key raw material for preparing high-quality ultra-coarse-grained cemented carbide. Ultra-coarse tungsten carbide powder is usually obtained by mixing ultra-coarse tungsten powder with a solid carbon source and then subjecting it to carburization treatment. In addition, ultra-coarse tungsten carbide powder is also prepared by adding alkali metal elements to promote the growth of tungsten particles or by high-temperature reduction and carburization processes. The addition of alkali metal elements will deteriorate the performance of tungsten carbide powder and affect the subsequent coarse-grained cemented carbide performance; while the high-temperature reduction and high-temperature carburization processes require briquetting before reduction and carburization. The reduction temperature and carburization temperature are usually 1500°C and higher than 2100°C, respectively. The required temperature is high, the time is long, and the requirements for equipment are harsh. In addition, mechanical crushing is required after carburization. During the crushing process, the tungsten carbide powder cracks, making the particle size smaller. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing a carburizing agent and ultra-coarse tungsten carbide powder. The preparation method of the present invention does not require the addition of alkali metal elements, the ultra-coarse tungsten carbide powder obtained has a large particle size, and can be carburized at a relatively low temperature.

[0006] The present invention provides a carburizing agent, comprising an organic solvent and an activator which are liquid at normal temperature and pressure;

[0007] The carbon-oxygen atomic ratio of the organic solvent which is liquid at normal temperature and pressure is ≥3;

[0008] The activator includes ammonium bicarbonate and / or ammonium carbonate.

[0009] Preferably, the mass ratio of the organic solvent that is liquid at room temperature and pressure to the activator is (8-17):(1-5).

[0010] Preferably, the organic solvent that is liquid at room temperature and pressure includes one or more of acetone, isopropanol and ether.

[0011] The present invention also provides a method for preparing ultra-coarse tungsten carbide powder, comprising the following steps:

[0012] Activating the tungsten wire in an inert atmosphere to obtain an activated tungsten wire;

[0013] The activated tungsten wire is subjected to a first carburizing treatment using an activated liquid carburizing agent as a carbon source to obtain a tungsten carbide wire; the activated liquid carburizing agent is the carburizing agent described in the above technical solution;

[0014] crushing the tungsten carbide wire to obtain tungsten carbide powder;

[0015] Carburizing the tungsten carbide powder using a gaseous carbon source at room temperature and pressure to obtain carbon-replenished tungsten carbide powder;

[0016] The carbon-filled tungsten carbide powder is sintered to obtain ultra-coarse tungsten carbide powder.

[0017] Preferably, the temperature of the first carburizing treatment is 900° C. to 1100° C., and the time is 6 h to 10 h.

[0018] Preferably, the gaseous carbon source at normal temperature and pressure includes one or more of methane, propane, butane and carbon monoxide.

[0019] Preferably, the temperature of the second carburizing treatment is 1300° C. to 1500° C., and the time is 2 h to 4 h.

[0020] Preferably, the tungsten wire comprises waste tungsten wire, which is tungsten wire broken during the wire drawing process.

[0021] Preferably, the activation temperature is 800° C. to 1000° C., and the holding time is 0.5 h to 1.5 h.

[0022] Preferably, the sintering treatment temperature is 1600° C. to 1800° C., and the holding time is 1 h to 2 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a carburizing agent, including an organic solvent that is liquid at room temperature and pressure and an activator; the carbon-oxygen atomic ratio of the organic solvent that is liquid at room temperature and pressure is ≥3; the activator includes ammonium bicarbonate and / or ammonium carbonate. The present invention uses a self-made activated liquid carburizing agent for carburizing treatment, the carburizing agent includes an activator and an organic solvent, the activator includes ammonium bicarbonate and / or ammonium carbonate, the grain boundaries of tungsten wire particles are activated at high temperature, and can react and decompose with lanthanum oxide on the grain boundaries of tungsten wire particles, effectively reducing the pinning effect of lanthanum oxide particles on tungsten grain boundaries, which is beneficial to subsequent grain boundary migration to make tungsten carbide particles grow. The present invention uses an organic solvent with a high carbon-oxygen ratio for carburizing treatment. The organic solvent with a high carbon-oxygen ratio can crack highly active carbon atoms at high temperature to quickly increase the carbon potential, which is beneficial to the gradient diffusion of carbon atoms to the core of the tungsten wire, and the active carbon atoms can penetrate into the core of the tungsten wire until the tungsten carburization is completed.

[0025] The present invention also provides a method for preparing ultra-coarse tungsten carbide powder. The present invention uses tungsten wire as a raw material. The tungsten wire is composed of single crystal tungsten particles. The single crystal tungsten particles are tightly combined and not easy to crack. The energy required for transcrystalline fracture is higher than the energy of grain boundary fracture. Therefore, in the process of preparing tungsten carbide powder, the particle size of ultra-coarse tungsten carbide powder will not be affected by transcrystalline fracture, and the obtained ultra-coarse tungsten carbide powder has a large particle size. The present invention crushes the carburized tungsten wire, and then performs secondary carburization and sintering treatment, and carbonizes part of the decarburized phase in the tungsten carbide powder to form a complete crystal, which promotes the sintering and growth of the tungsten carbide powder at high temperature to obtain ultra-coarse tungsten carbide powder.

[0026] Furthermore, the present invention uses waste tungsten wire as raw material to prepare ultra-coarse tungsten carbide powder, which has two advantages: first, the waste tungsten wire can be recycled to ensure the recycling of tungsten resources, providing a new idea for the recycling of waste tungsten wire; second, the tungsten wire is mainly composed of single-crystal tungsten particles, which is not easy to break, and the single-crystal tungsten particles are tightly combined, which is conducive to sintering and growing, and is conducive to the preparation of ultra-coarse tungsten carbide powder; and the tungsten wire itself has a small wire diameter, and the carburizing treatment of the present invention can be achieved at a lower temperature. The present invention adopts a step-by-step carburizing process, which can complete the carburizing process at a lower temperature to obtain ultra-coarse tungsten carbide powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 is a scanning electron microscope image of the waste tungsten wire used in the examples;

[0029] Figure 2This is a process flow chart for preparing ultra-coarse tungsten carbide powder in the embodiment;

[0030] Figure 3 This is a process schematic diagram of the first carburizing treatment in the embodiment;

[0031] Figure 4 The scanning electron microscope images of the ultra-coarse tungsten carbide powder prepared in Example 2, wherein (a) is 200X and (b) is 1000X;

[0032] Figure 5 The XRD patterns of the ultra-coarse tungsten carbide powders prepared in Example 1 and Comparative Examples 1-3 are shown. DETAILED DESCRIPTION

[0033] The present invention provides a carburizing agent, comprising an organic solvent and an activator which are liquid at normal temperature and pressure;

[0034] The carbon-oxygen atomic ratio of the organic solvent which is liquid at normal temperature and pressure is ≥3;

[0035] The activator includes ammonium bicarbonate and / or ammonium carbonate.

[0036] In the present invention, the organic solvent that is liquid at room temperature and pressure preferably includes one or more of acetone, isopropanol and diethyl ether, the organic solvent that is liquid at room temperature and pressure is an organic solvent with a high carbon-oxygen atomic ratio (C / O), and the carbon-oxygen atomic ratio of the organic solvent that is liquid at room temperature and pressure is preferably 3 or 4. The present invention uses an organic solvent with a high carbon-oxygen atomic ratio (C / O) as a carburizing agent, which can crack more highly active carbon atoms at high temperatures, can effectively carburize, and is not prone to the occurrence of a decarburized phase (W2C).

[0037] In the present invention, the mass ratio of the liquid organic solvent at room temperature and pressure to the activator is preferably (8-17):(1-5), specifically 8:1, 11:3 or 17:5. The mass ratio of the present invention is conducive to obtaining ultra-coarse tungsten carbide powder with large particle size and will not hinder carburization.

[0038] In the present invention, the carburizing agent preferably includes the following components in mass fractions: 8 parts of acetone and 1 part of ammonium bicarbonate; or 11 parts of isopropyl alcohol and 3 parts of ammonium carbonate; or 17 parts of ether and 5 parts of ammonium bicarbonate. The activator of the present invention activates the grain boundaries of tungsten wire particles at high temperatures, and can react and decompose with lanthanum oxide on the grain boundaries of tungsten wire particles, effectively reducing the pinning effect of lanthanum oxide particles on tungsten grain boundaries, which is beneficial to the subsequent grain boundary migration to make tungsten carbide particles grow.

[0039] The present invention also provides a method for preparing ultra-coarse tungsten carbide powder, comprising the following steps:

[0040] Activating the tungsten wire in an inert atmosphere to obtain an activated tungsten wire;

[0041] The activated tungsten wire is subjected to a first carburizing treatment using an activated liquid carburizing agent as a carbon source to obtain a tungsten carbide wire; the activated liquid carburizing agent is the carburizing agent described in the above technical solution;

[0042] crushing the tungsten carbide wire to obtain tungsten carbide powder;

[0043] Carburizing the tungsten carbide powder using a gaseous carbon source at room temperature and pressure to obtain carbon-replenished tungsten carbide powder;

[0044] The carbon-filled tungsten carbide powder is sintered to obtain ultra-coarse tungsten carbide powder.

[0045] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0046] The present invention activates the tungsten wire in an inert atmosphere to obtain the activated tungsten wire.

[0047] In the present invention, the tungsten wire preferably includes waste tungsten wire, and the waste tungsten wire is preferably tungsten wire broken during the wire drawing process.

[0048] In the present invention, the tungsten wire preferably includes a tungsten wire with a wire diameter less than 100 μm, greater than or equal to 100 μm and less than 500 μm, or greater than or equal to 500 μm and less than 1000 μm. The tungsten wire of the present invention has a relatively thin wire diameter, and it is effective to recycle the waste tungsten wire through carburizing treatment to prepare ultra-coarse tungsten carbide powder.

[0049] In the present invention, the tungsten wire is preferably a cleaned waste tungsten wire, which is preferably obtained by sequentially washing the tungsten wire with alkali, water, alcohol and supercritical CO2 and then drying; the reagent for the alkali washing is preferably a saturated sodium hydroxide solution, which is used to remove graphite emulsion and oil stains on the surface of the tungsten wire; the water washing is used to remove alkali liquid and dust; the alcohol washing is used to remove moisture, which is beneficial to subsequent drying; and the supercritical CO2 is used to purify the waste tungsten wire as a whole. The cleaning method of the present invention is beneficial to subsequent carburizing treatment.

[0050] In the present invention, the activation temperature is preferably 800°C to 1000°C, specifically 900°C, and the holding time is preferably 0.5h to 1.5h, specifically 0.5h, 1h or 1.5h. The activation process of the present invention can ensure uniform temperature between the core and the surface of the tungsten wire, increase the energy of the tungsten wire, expand the tungsten wire, facilitate the penetration of active carbon atoms into the core of the tungsten wire, facilitate subsequent carbonization, and improve carburizing efficiency.

[0051] In the present invention, the inert atmosphere is preferably an argon atmosphere or a nitrogen atmosphere.

[0052] In the present invention, the activation is preferably carried out in a drum-type resistance furnace, and the drum-type resistance furnace is preferably subjected to a gas scrubbing treatment before use to discharge oxidizing gases.

[0053] After obtaining the activated tungsten wire, the present invention performs a first carburizing treatment on the activated tungsten wire using an activated liquid carburizing agent as a carbon source to obtain a tungsten carbide wire; the activated liquid carburizing agent is the carburizing agent described in the above technical solution.

[0054] In the present invention, the conditions of the first carburizing treatment include: the flow rate of the activated liquid carburizing agent is preferably 1 mL / min to 3 mL / min, specifically 2 mL / min; the temperature is preferably 900°C to 1100°C, specifically 980°C or 1050°C; the total time is preferably 6h to 10h, specifically 7h or 8h; the first carburizing treatment preferably includes a strong carburizing stage and an active carbon atom diffusion stage (such as Figure 3 As shown in the figure, the time of the strong carburizing stage (the time of introducing the liquid carbon source) is preferably 2h~4h, specifically 3h; the time of the activated carbon atom diffusion stage (the time after stopping the introduction of the liquid carbon source) is preferably 4h~6h, specifically 5h.

[0055] In the present invention, the first carburizing treatment preferably further includes cooling, and the cooling is preferably furnace cooling.

[0056] After obtaining the tungsten carbide wire, the present invention crushes the tungsten carbide wire to obtain tungsten carbide powder.

[0057] In the present invention, the crushing preferably includes grinding and ball milling in sequence, wherein the grinding is to crush the tungsten carbide wire, and the ball milling is to further crush the crushed tungsten carbide wire; the ball milling is preferably dry grinding, and the ball-to-material ratio of the ball milling is preferably (3-7):1, specifically 5:1 or 6:1, the time is preferably 3h-9h, specifically 6h or 7h, and the speed of the ball milling is preferably 150 rpm-250 rpm, specifically 200 rpm. The purpose of crushing the tungsten carbide wire in the present invention is to break up the pseudo particles that are not firmly bonded.

[0058] After obtaining the tungsten carbide powder, the present invention uses a gaseous carbon source at normal temperature and pressure to perform a second carburizing treatment on the tungsten carbide powder to obtain carbon-supplemented tungsten carbide powder.

[0059] In the present invention, the gaseous carbon source at normal temperature and pressure preferably includes one or more of methane, propane, butane and carbon monoxide.

[0060] In the present invention, a mixed gas is preferably introduced during the second carburizing treatment, and the mixed gas preferably includes a gaseous carbon source and hydrogen at room temperature and pressure. The volume ratio of the gaseous carbon source and hydrogen at room temperature and pressure is preferably 98:2.

[0061] In the present invention, the conditions of the second carburizing treatment include: the flow rate of the mixed gas is preferably 0.5L / min~2L / min, specifically 1L / min or 1.5L / min; the temperature is preferably 1300℃~1500℃, specifically 1400℃; the time is preferably 2h~4h, specifically 3h. After the second carburizing treatment, a tungsten carbide powder with complete crystallization is obtained.

[0062] In the present invention, the second carburizing treatment is preferably performed in a carbon tube furnace.

[0063] After obtaining the carbon-filled tungsten carbide powder, the present invention performs a sintering treatment on the carbon-filled tungsten carbide powder to obtain an ultra-coarse tungsten carbide powder.

[0064] In the present invention, the sintering temperature is preferably 1600° C. to 1800° C., specifically 1700° C., and the holding time is preferably 1 h to 2 h.

[0065] In the present invention, hydrogen is preferably introduced during the sintering process.

[0066] In the present invention, the sintering treatment preferably further includes air flow crushing, and the conditions of the air flow crushing preferably include: 10m 3 / min, nitrogen.

[0067] The particle size of the ultra-coarse tungsten carbide powder prepared by the present invention is preferably 28 μm to 40 μm (FSSS particle size), specifically 28.76 μm, 38.36 μm, 34.62 μm or 32.45 μm. The ultra-coarse tungsten carbide powder prepared by the present invention has complete crystallization and pure physical phase.

[0068] In order to further illustrate the present invention, the carburizing agent and the preparation method of the ultra-coarse tungsten carbide powder provided by the present invention are described in detail below in combination with the accompanying drawings and examples, but they should not be understood as limiting the protection scope of the present invention.

[0069] Embodiment 1~4

[0070] The ultra-coarse tungsten carbide powder is prepared according to the process parameters in Table 1, including the following steps:

[0071] 1. Classify the waste tungsten wire according to the wire diameter range, and divide it into waste tungsten wire with a wire diameter less than 100μm, greater than or equal to 100μm and less than 500μm, and greater than or equal to 500μm and less than 1000μm. Then, the waste tungsten wires with different wire diameter ranges are washed with alkali (saturated sodium hydroxide solution), water, and alcohol in turn, and then washed with supercritical CO2, and finally dried to obtain clean waste tungsten wires.

[0072] 2. Place the cleaned waste tungsten wire obtained in step 1 in a drum-type resistance furnace, perform gas washing on the resistance furnace, and discharge the oxidizing gas; increase the temperature of the resistance furnace to 900°C and keep it warm for 0.5h~1.5h to obtain activated tungsten wire.

[0073] 3. Use a peristaltic pump to deliver the homemade activated liquid carburizing agent to the resistance furnace, perform the first carburizing treatment on the activated tungsten wire to obtain tungsten carbide wire, and cool it with the furnace after carburizing. Among them, the homemade activated liquid carburizing agent is homemade liquid a (mixing 8 parts by mass of acetone and 1 part by mass of ammonium bicarbonate), homemade liquid b (mixing 11 parts by mass of isopropanol and 3 parts by mass of ammonium carbonate) or homemade liquid c (mixing 17 parts by mass of ether and 5 parts by mass of ammonium bicarbonate), the flow rate is 1 mL / min~3 mL / min, the first carburizing temperature is 900℃~1100℃, the strong carburizing stage time (time of introducing liquid carbon source) is 2h~4h, and the active carbon atom diffusion time (after stopping the introduction of liquid carbon source) is 4h~6h.

[0074] 4. The tungsten carbide wire obtained in step 3 is ground and crushed, and then further crushed by ball milling to obtain tungsten carbide powder. The ball-to-material ratio of the ball milling is 3-7:1, the ball milling time is 3h-9h, and the ball milling speed is 150 rpm-250 rpm.

[0075] 5. Place the tungsten carbide powder obtained in step 4 in a carbon tube furnace for secondary carburizing treatment. During the process, a mixture of a gaseous carbon source and hydrogen (hydrogen volume ratio is 2%) is introduced to form a crystalline tungsten carbide powder, and finally obtain a carbon-filled tungsten carbide powder. Among them, the secondary carburizing treatment temperature is 1300℃~1500℃, the secondary carburizing time is 2h~4h, the mixed gas flow rate is 0.5 L / min~2.0 L / min, and the gaseous carbon source for secondary carburizing is methane, propane, butane or carbon monoxide.

[0076] 6. Sinter the carbon-filled tungsten carbide powder obtained in step 5. Raise the temperature to the sintering temperature based on the secondary carburizing treatment in step 5, stop introducing the gaseous carbon source, and only introduce hydrogen. Finally, perform air flow crushing (10m 3 / min, nitrogen), to obtain ultra-coarse tungsten carbide powder. The sintering temperature is 1600℃~1800℃, and the holding time is 1h~2h.

[0077] Table 1 Process parameters of Examples 1 to 4

[0078]

[0079] Comparative Example 1

[0080] The difference from Example 1 is that only the first carburizing treatment is performed, and the second carburizing treatment is not performed (ie, step 5 is not performed), and the remaining steps and conditions are the same.

[0081] Comparative Example 2

[0082] The difference from Example 4 is that the ether in the homemade solution c is replaced by ethanol, and the remaining steps and conditions are the same.

[0083] Comparative Example 3

[0084] The difference from Example 2 is that the first carburizing treatment uses methane as the gaseous carbon source, and the remaining steps and conditions are the same.

[0085] Comparative Example 4

[0086] The difference from Example 3 is that isopropanol is used in the first carburizing treatment (to remove the activating agent ammonium carbonate), and the remaining steps and conditions are the same.

[0087] Comparative Example 5

[0088] Ammonium paratungstate is used as raw material to prepare ultra-coarse tungsten carbide powder through high-temperature reduction and high-temperature carbonization processes.

[0089] First, ammonium paratungstate is calcined at 800℃ for 2h to prepare tungsten trioxide, and then ultra-coarse tungsten powder is prepared by high-temperature reduction. The high-temperature reduction temperature is 1500℃, the hydrogen flow rate is 2 L / min, and the reduction time is 4h. The ultra-coarse tungsten powder is then carbonized and briquette-treated, and high-temperature carbonization is performed at 2200℃ for 6h. Mechanical crushing is used, and finally air flow crushing is performed to obtain ultra-coarse tungsten carbide powder.

[0090] Figure 1 This is a scanning electron microscope image of the waste tungsten wire (wire diameter is less than 100 μm) used in the example. It can be seen from the image that the waste tungsten wire is composed of single crystal tungsten particles, and the grains are tightly combined.

[0091] Figure 2 The process flow chart of preparing ultra-coarse tungsten carbide powder in the embodiment is as follows: the waste tungsten wire is washed to obtain the washed waste tungsten wire, and then high-temperature activation is performed, the tungsten carbide wire is carburized for the first time to obtain the tungsten carbide wire, and the tungsten carbide powder is obtained after crushing, the secondary carburization is performed to obtain the carbon-replenished tungsten carbide powder, and then high-temperature sintering is performed to obtain ultra-coarse tungsten carbide powder.

[0092] Figure 3 Schematic diagram of the process of the first carburizing treatment in the embodiment, which is divided into a strong carburizing stage and a diffusion stage, with time ranges of 2h~4h and 4h~6h respectively.

[0093] Figure 4 The scanning electron microscope images of the ultra-coarse tungsten carbide powder prepared in Example 2, wherein (a) is 200X and (b) is 1000X. It can be seen that the ultra-coarse tungsten carbide powder prepared in Example 2 has good dispersibility and coarse particles.

[0094] Figure 5 The XRD spectra of the ultra-coarse tungsten carbide powder prepared in Example 1 and Comparative Examples 1 to 3. As can be seen from the figure, the ultra-coarse tungsten carbide powder prepared in Example 1 is completely carburized, and only the characteristic peak of tungsten carbide appears in the XRD spectrum (the physical phase of the ultra-coarse tungsten carbide powder in Examples 2 to 4 is also pure WC); while the characteristic peaks of tungsten and ditungsten carbide appear in the XRD spectrum of the ultra-coarse tungsten carbide powder in the comparative example, indicating that the comparative example experiment is not completely carburized. The step-by-step carburizing process of the present invention must be adopted to ensure the complete carburization of tungsten powder. The tungsten carbide powder after only the first carburizing process is prone to decarburization phase (W2C), see the XRD spectrum of Comparative Example 1; in addition, the use of general liquid carbon sources (such as ethanol) cannot be effectively carburized, and the carburizing efficiency is greatly reduced. See Comparative Example 2 for a large amount of ditungsten carbide phase and pure tungsten phase; using commonly used methane as a carburizing agent, the concentration of active carbon atoms is insufficient, it is difficult to complete carburization, and the carburizing effect is almost non-existent, see Comparative Example 3. Therefore, the present invention adopts an organic solvent with a high carbon-oxygen atomic ratio (with an activator added) as a carbon source, which can provide more active carbon atoms, is beneficial to the effective carburization of the tungsten wire, and combines the reaction and decomposition process of the activator and lanthanum oxide at high temperature to effectively reduce the pinning effect of lanthanum oxide on the grain boundaries of tungsten particles. In addition, the combination of secondary carburization and sintering process can ensure the crystal integrity and particle size of the ultra-coarse tungsten carbide powder.

[0095] Table 2 shows the FSSS particle size results of the tungsten carbide powders obtained in Examples 1 to 4 and Comparative Examples 4 to 5. From the data in the table, it can be seen that the FSSS particle size of the tungsten carbide powder of Example 1 is 28.76 μm, the FSSS particle size of the tungsten carbide powder of Example 2 is 38.36 μm, the FSSS particle size of the tungsten carbide powder of Example 3 is 34.62 μm, the FSSS particle size of the tungsten carbide powder of Example 4 is 32.45 μm, the FSSS particle size of the tungsten carbide powder of Comparative Example 4 is 23.93 μm, and the FSSS particle size of the tungsten carbide powder of Comparative Example 5 is 28.26 μm. It can be seen that the FSSS particle size of the ultra-coarse tungsten carbide powder prepared by two-step carburization at a lower temperature using tungsten wire as a raw material in all embodiments can be greater than the ultra-coarse tungsten carbide powder prepared in Comparative Example 5, thanks to the use of waste tungsten wire of single crystal tungsten particles as a raw material in the present invention, the energy required for single crystal transcrystalline fracture is high, and it is not easy to crack. In addition, the tungsten particles are tightly combined, which is conducive to the growth of particles. Comparing Example 3 with Comparative Example 4, it can be clearly seen that the activator effectively reduces the inhibitory effect of rare earth lanthanum oxide on the growth of tungsten carbide, which is beneficial to the growth of ultra-coarse tungsten carbide powder.

[0096] Table 2 FSSS particle size results of tungsten carbide powders obtained in Examples 1 to 4 and Comparative Examples 4 to 5

[0097]

[0098] The present invention provides a method for preparing ultra-coarse tungsten carbide powder by recycling waste tungsten wire. The present invention selects waste tungsten wire as raw material, and the transgranular fracture energy of single crystal tungsten particles is large, which can avoid transgranular fracture of ultra-coarse tungsten carbide powder; and the compact tungsten particles are conducive to sintering and growth, which is conducive to the preparation of ultra-coarse tungsten carbide powder. Secondly, the present invention adopts a liquid-gas step-by-step carburizing process. The first carburizing uses an organic solvent with a high carbon-oxygen atomic ratio (with an activator added) as a carburizing agent to quickly increase the concentration of active carbon atoms. The first carburizing process is divided into a strong carburizing stage and a diffusion stage to ensure that the two stages have sufficient time and temperature to achieve rapid carburizing; the second carburizing uses a gas carburizing agent to replenish the decarburized phase of the ultra-coarse tungsten carbide particles with carbon to make the crystallization complete, and then the tungsten carbide particles are grown by sintering, and finally the ultra-coarse tungsten carbide powder is prepared.

[0099] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-coarse tungsten carbide powder, characterized in that: The following steps are involved: Activating the tungsten wire in an inert atmosphere to obtain an activated tungsten wire; Carrying out a first carburizing treatment on the activated tungsten wire using an activated liquid carburizing agent as a carbon source to obtain a tungsten carbide wire; The activated liquid carburizing agent comprises an organic solvent which is liquid at room temperature and pressure and an activator; the carbon-oxygen atomic ratio of the organic solvent which is liquid at room temperature and pressure is ≥3; the activator comprises ammonium bicarbonate and / or ammonium carbonate; crushing the tungsten carbide wire to obtain tungsten carbide powder; Carburizing the tungsten carbide powder using a gaseous carbon source at room temperature and pressure to obtain carbon-replenished tungsten carbide powder; The carbon-filled tungsten carbide powder is sintered to obtain ultra-coarse tungsten carbide powder; The FSSS particle size of the ultra-coarse tungsten carbide powder is 28 μm to 40 μm.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the organic solvent that is liquid at normal temperature and pressure to the activator is (8-17):(1-5).

3. The preparation method according to claim 1 or 2, characterized in that: The organic solvent that is liquid at normal temperature and pressure includes one or more of acetone, isopropanol and ether.

4. The preparation method according to claim 1, characterized in that: The temperature of the first carburizing treatment is 900° C. to 1100° C., and the time is 6 h to 10 h.

5. The preparation method according to claim 1, characterized in that: The gaseous carbon source at normal temperature and pressure includes one or more of methane, propane, butane and carbon monoxide.

6. The preparation method according to claim 1 or 5, characterized in that: The temperature of the second carburizing treatment is 1300° C. to 1500° C., and the time is 2 h to 4 h.

7. The preparation method according to claim 1, characterized in that: The tungsten wire includes waste tungsten wire, which is tungsten wire broken during the wire drawing process.

8. The preparation method according to claim 1, characterized in that: The activation temperature is 800° C. to 1000° C., and the insulation time is 0.5 h to 1.5 h.

9. The preparation method according to claim 1, characterized in that: The sintering treatment temperature is 1600° C. to 1800° C., and the heat preservation time is 1 h to 2 h.

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