A method for producing medium-grained tungsten carbide

Abstract

The application belongs to the technical field of powder metallurgy, and particularly relates to a preparation method of medium-granularity tungsten carbide, which comprises the following steps: placing tungsten oxide powder in a rotary heating device, introducing sufficient methane into the rotary heating device, then starting rotation, heating to 1400-1600 DEG C for reaction, and screening after cooling to obtain the medium-granularity tungsten carbide. In the application, the nanoscale carbon black powder generated by high-temperature cracking of methane is fully contacted with the tungsten oxide powder, which is beneficial to complete carbonization of the tungsten oxide and accurate control of the carbon content; hydrogen generated by high-temperature cracking of the methane combines with oxygen in the tungsten oxide to generate water vapor, which promotes the growth of the generated tungsten carbide grains, and ensures the uniformity of the tungsten carbide grain size; by using the tungsten oxide and the methane as raw materials for one-step carbonization, the intermediate process of tungsten powder production is reduced, and safe and efficient production of the tungsten carbide powder is realized.

Description

Technical Field

[0001] This application belongs to the field of powder metallurgy technology, specifically a method for preparing medium-particle tungsten carbide. Background Technology

[0002] Tungsten carbide, due to its high hardness, high wear resistance, good chemical stability, and excellent high-temperature mechanical properties, has become a core raw material for the preparation of cemented carbides, wear-resistant components, and cutting tools, and is widely used in machinery manufacturing, mining, aerospace, and other fields. Based on particle size differences, tungsten carbide can be divided into four categories: ultrafine, fine, medium, and coarse particles. Among them, medium-particle tungsten carbide has irreplaceable advantages in the preparation of high-toughness cemented carbides and large-size wear-resistant parts—especially in the cemented carbides prepared with it exhibiting outstanding wear resistance and impact resistance, making it suitable for harsh working conditions such as heavy-duty cutting and mining crushing, leading to continuous growth in market demand.

[0003] Currently, the mainstream production method for medium-particle tungsten carbide is the solid-phase carbonization method using tungsten powder and carbon powder (or carbon black). The basic process involves uniformly mixing tungsten powder and carbon powder according to a stoichiometric ratio, carbonizing them in a high-temperature carbonization furnace at 1400-1600℃, and then crushing and classifying them to obtain the finished product. However, the existing process still faces many technical bottlenecks in actual production. First, the particle uniformity is poor, easily leading to abnormal growth and agglomeration: uneven mixing easily causes differences in reaction rates and abnormal grain growth, and at high temperatures, particles adhere to form hard agglomerates, resulting in defects during crushing and reducing the processing performance of tungsten carbide powder and the mechanical properties of the final product. Second, the carbon content control precision is low, with prominent issues of free carbon or insufficient carbon: carbon content is a key factor determining the stoichiometric ratio of tungsten carbide. Excessive carbon will generate free carbon, which forms a graphite phase after sintering, reducing the alloy's hardness and wear resistance; insufficient carbon will generate a metastable W2C phase, increasing the brittleness of tungsten carbide. Existing processes rely heavily on experience in carbon formulation, resulting in large fluctuations in carbon content, which makes it difficult to meet the requirements for preparing high-end cemented carbide.

[0004] Patent CN109867286A uses a CH4 / H2 mixed gas for a secondary carburizing reaction, optimizing the carbonization accuracy problem of the traditional solid-phase method through gas-phase carburizing. However, it still suffers from the inherent limitations of the two-step method, such as a long process and high energy consumption. Patent CN108675299A uses a 10% CH4 / 90% H2 mixed gas to directly carburize blue tungsten into tungsten carbide in one step, but the grain growth and agglomeration problems caused by water vapor limit the product quality. In addition, both patents add hydrogen as a reducing gas to the reaction, increasing the safety and management costs of industrial production.

[0005] Therefore, there is an urgent need to develop a process for preparing particulate tungsten carbide that is short, complete in carbonization, and has high control precision. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a method for preparing medium-sized tungsten carbide. By introducing methane into a rotary heating device containing tungsten oxide powder, a one-step carbonization reaction is carried out, thereby obtaining medium-sized tungsten carbide powder that is fully carbonized and has uniform particle size.

[0007] The present application discloses a method for preparing medium-particle tungsten carbide, which involves placing tungsten oxide powder in a rotary heating device and introducing sufficient methane, then turning on the device and heating it to 1400~1600℃ for reaction, and then cooling and sieving to obtain the medium-particle tungsten carbide.

[0008] In the above technical solution, tungsten oxide powder is first placed in a rotary heating device, and methane gas is introduced. The device is then heated to 1400~1600℃. The methane rapidly decomposes at high temperature to produce nano-sized carbon black powder and hydrogen. As the rotary heating device rotates, the tungsten oxide powder and carbon black can come into full contact. The high surface activity of the nano-sized carbon black powder can promote the complete carbonization of the tungsten oxide powder. At the same time, hydrogen combines with oxygen in tungsten oxide to generate water vapor, which can promote the growth of tungsten carbide grains at high temperature to form medium-sized tungsten carbide powder with uniform particle size.

[0009] Furthermore, the molar ratio of the tungsten oxide powder (WO3) to the methane is 1:(2.1~2.2).

[0010] Furthermore, the heating process specifically involves: first, heating to 750~850℃ at a rate of 10℃ / min for a first heat preservation, and then heating to 1400~1600℃ at a rate of 5℃ / min for a second heat preservation. Segmented heating is used to make the temperature rise faster and more uniform. The initial stage has a lower temperature and a faster heating rate, which can improve efficiency, while the later stage has a higher temperature and a slower heating rate, which can ensure that the powder or gas is heated evenly.

[0011] Furthermore, the first heat preservation time is 20-40 minutes, and the second heat preservation time is 2-4 hours.

[0012] Furthermore, the rotational speed of the rotary heating device is 10~18 r / min.

[0013] Furthermore, the furnace pressure of the rotary heating device should be adjusted to ≤10Pa before introducing methane.

[0014] Furthermore, the tungsten oxide powder has a purity of ≥99.8% and a particle size of 10~20μm.

[0015] Furthermore, the purity of the methane is ≥99.9%, and the water content and carbon monoxide content in the methane are ≤5ppm and ≤1ppm, respectively.

[0016] Furthermore, after the reaction is complete, the pressure inside the rotary heating device is adjusted to ≤10Pa, and nitrogen gas is introduced into the rotary heating device for cooling.

[0017] Furthermore, the sieving is carried out using a negative pressure airflow sieve at a vacuum degree of -5 to -10 kPa.

[0018] Furthermore, the medium-sized tungsten carbide has a Fisher particle size of 1.8~9.5μm, a combined carbon content of ≥6.10%, and a free carbon content of ≤0.02%, wherein the combined carbon content is calculated by subtracting the free carbon content from the total carbon content obtained by detection.

[0019] This application proposes a method for preparing medium-sized tungsten carbide, which produces the following beneficial effects: by fully contacting the nano-sized carbon black powder generated from high-temperature methane cracking with tungsten oxide powder, it is beneficial to achieve complete carbonization of tungsten oxide and precise control of carbon content; by combining the hydrogen gas generated from high-temperature methane cracking with the oxygen in tungsten oxide to generate water vapor, the generated tungsten carbide grains grow, ensuring the uniformity of tungsten carbide particle size; by using tungsten oxide and methane as raw materials for one-step carbonization, intermediate steps in the production of tungsten powder are reduced, achieving safe and efficient production of tungsten carbide powder. Detailed Implementation

[0020] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] The present application discloses a method for preparing medium-particle tungsten carbide, which involves placing tungsten oxide powder in a rotary heating device and introducing sufficient methane, then turning on the device and heating it to 1400~1600℃ for reaction, and then cooling and sieving to obtain the medium-particle tungsten carbide.

[0022] Preferably, in order to fully carbonize tungsten oxide to obtain tungsten carbide powder with a carbon content close to 6.13% and without introducing excessive free carbon, the molar ratio of the tungsten oxide powder (WO3) to the methane is 1:(2.1~2.2). Specifically, the molar ratio can be any one of 1:2.1, 1:2.11, 1:2.12, 1:2.13, 1:2.14, 1:2.15, 1:2.16, 1:2.17, 1:2.18, 1:2.19, 1:2.2, or a range between any two.

[0023] Preferably, the heating process specifically involves: first, raising the temperature to 750~850℃ at a rate of 10℃ / min for a first holding period, and then raising the temperature to 1400~1600℃ at a rate of 5℃ / min for a second holding period. The first holding period lasts for 20~40 minutes, and the second holding period lasts for 2~4 hours. Specifically, the temperature can be raised to any one or any two of 750℃, 780℃, 800℃, 820℃, and 850℃, and then raised to any one or any two of 1400℃, 1450℃, 1500℃, 1550℃, and 1600℃. The first holding period lasts for any one or any two of 20 minutes, 25 minutes, 30 minutes, 35 minutes, and 40 minutes, and the second holding period lasts for any one or any two of 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours.

[0024] Preferably, the tungsten oxide powder has a purity of ≥99.8% and a particle size of 10~20μm; the methane has a purity of ≥99.9%, and the water content in the methane is ≤5ppm and the carbon monoxide content is ≤1ppm; in some preferred embodiments, the tungsten oxide powder is further passed through a 60-mesh sieve, and the impurity content (such as iron, silicon, calcium, etc.) is ensured to be ≤0.01%, so as to avoid impurities affecting the carbonization reaction efficiency and the purity of the final product; to ensure the purity of methane, impurities such as water and carbon monoxide can be removed in advance by a gas purification device to prevent impurities from reacting with tungsten oxide at high temperature and affecting the carbon content control accuracy.

[0025] In some preferred embodiments of this application, the rotary heating device includes a furnace body, a material inlet and outlet, an air inlet and an exhaust outlet. Preferably, the furnace body is provided with raised ribs, which can fully and uniformly mix the tungsten oxide powder and the carbon black powder obtained by methane cracking during the rotation of the device. The prepared tungsten oxide powder is added to the rotary heating device furnace body through the inlet and outlet. After feeding, the inlet and outlet are closed, and the exhaust port is opened. The gas inside the device is extracted through the exhaust port, and the furnace pressure is adjusted to ≤10Pa. Then, the exhaust port is closed, the inlet port is opened, and all the methane is introduced. After that, the inlet port is closed, and the device is turned on to rotate and heat until the temperature inside the device stabilizes at the target temperature. The methane and tungsten oxide powder are kept at a certain temperature in the furnace for a period of time to carry out the carbonization reaction. Preferably, the rotation speed of the rotary heating device can be controlled at 10~18 r / min during heating and reaction. After the reaction is completed, the gas in the furnace is extracted, the furnace pressure is adjusted to ≤10Pa, and nitrogen is introduced until the furnace temperature drops below 200℃. At this time, the rotation speed of the device can be adjusted appropriately to accelerate cooling. After cooling, the obtained tungsten carbide is graded by a negative pressure airflow sieve under a vacuum of -5~-10kPa to obtain medium-particle tungsten carbide with a Fisher particle size of 1.8~9.5μm, a combined carbon content of ≥6.10%, and a free carbon content of ≤0.02%. Preferably, the screen mesh of the negative pressure airflow sieve is 100 mesh.

[0026] The technical solution of this application will be further described below with reference to specific embodiments. In the raw materials used in the following embodiments and comparative examples, the purity of tungsten trioxide powder is ≥99.8%, its particle size is 10~20μm, it passes through a 60-mesh sieve, and the impurity content is ≤0.01%; the purity of methane is ≥99.9%, the water content is ≤5ppm, and the CO content is ≤1ppm; the rotary heating device used is a 4.0MPa-grade high-temperature resistant alloy container with raised ribs inside, and the heating program can be set.

[0027] Example 1

[0028] 1. Add tungsten trioxide powder into the rotary heating device furnace body through the feed inlet. After feeding, close the feed and discharge inlets, open the exhaust port, and extract the gas inside the device through the exhaust port to make the pressure inside the device ≤10Pa. Close the exhaust port, open the gas inlet, introduce methane, and then close the gas inlet. Start the device rotation and heating. The furnace rotation speed is 10r / min. The molar ratio of tungsten trioxide powder (WO3) to methane is 1:2.17. 2. The temperature is increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, and then increased to 1400℃ at a rate of 5℃ / min and held for 3 h to carry out the reaction. 3. After the carbonization reaction is complete, turn off the heating, adjust the furnace rotation speed to 15 r / min, and simultaneously turn on the vacuum pump to extract the internal gas until the pressure inside the device is ≤10 Pa, and then move the vacuum pump at an 8 m speed. 3 Nitrogen gas is introduced at a flow rate of / h until the furnace temperature drops below 200℃, then the nitrogen supply is stopped and the furnace body is rotated. 4. The cooled tungsten carbide powder is classified using a negative pressure airflow sieve with a mesh size of 100 mesh and a vacuum degree of -10 kPa to obtain medium-particle tungsten carbide.

[0029] The average Fisher particle size of the medium-sized tungsten carbide in this embodiment was measured to be 2.1 μm, with uniform particle size distribution; the total carbon content was 6.12%, and the free carbon content was 0.01%, which meets the quality requirements for medium-sized tungsten carbide.

[0030] Example 2

[0031] 1. Add tungsten trioxide powder into the rotary heating device furnace body through the feed inlet. After feeding, close the feed and discharge inlets, open the exhaust port, and extract the gas inside the device through the exhaust port to make the pressure inside the device ≤10Pa. Close the exhaust port, open the gas inlet, introduce methane, and then close the gas inlet. Start the device rotation and heating. The furnace rotation speed is 15r / min. The molar ratio of tungsten trioxide powder (WO3) to methane is 1:2.17. 2. The temperature is increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, then increased to 1500℃ at a rate of 5℃ / min and held for 4 h to carry out the reaction. 3. After the carbonization reaction is complete, turn off the heating, adjust the furnace rotation speed to 15 r / min, and simultaneously turn on the vacuum pump to extract the internal gas until the pressure inside the device is ≤10 Pa, and then move the vacuum pump at an 8 m speed. 3 Nitrogen gas is introduced at a flow rate of / h until the furnace temperature drops below 200℃, then the nitrogen supply is stopped and the furnace body is rotated. 4. The cooled tungsten carbide powder is graded using a negative pressure airflow sieve with a mesh size of 100 mesh and a vacuum degree of -6 kPa to obtain medium-sized tungsten carbide particles.

[0032] The average Fisher particle size of the medium-sized tungsten carbide in this embodiment was measured to be 5.1 μm, with uniform particle size distribution; the total carbon content was 6.13%, and the free carbon content was 0.02%, which meets the quality requirements for medium-sized tungsten carbide.

[0033] Example 3

[0034] 1. Add tungsten trioxide powder into the rotary heating device furnace body through the feed inlet. After feeding, close the feed and discharge inlets, open the exhaust port, and extract the gas inside the device through the exhaust port to make the pressure inside the device ≤10Pa. Close the exhaust port, open the gas inlet, introduce methane, and then close the gas inlet. Start the device rotation and heating. The furnace rotation speed is 18r / min. The molar ratio of tungsten trioxide powder (WO3) to methane is 1:2.17. 2. The temperature is increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, then increased to 1600℃ at a rate of 5℃ / min and held for 2 h to carry out the reaction. 3. After the carbonization reaction is complete, turn off the heating, adjust the furnace rotation speed to 15 r / min, and simultaneously turn on the vacuum pump to extract the internal gas until the pressure inside the device is ≤10 Pa, and then move the vacuum pump at an 8 m speed. 3 Nitrogen gas is introduced at a flow rate of / h until the furnace temperature drops below 200℃, then the nitrogen supply is stopped and the furnace body is rotated. 4. The cooled tungsten carbide powder is graded using a negative pressure airflow sieve with a mesh size of 100 mesh and a vacuum degree of -5 kPa to obtain medium-particle tungsten carbide.

[0035] The average Fisher particle size of the medium-sized tungsten carbide in this embodiment was measured to be 9.35 μm, with uniform particle size distribution; the total carbon content was 6.13%, and the free carbon content was 0.02%, which meets the quality requirements for medium-sized tungsten carbide.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: In step 2: the temperature is increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, and then increased to 1300℃ at a rate of 5℃ / min and held for 3 h to carry out the reaction. All other conditions remain the same as in Example 1.

[0037] The average Fisher particle size of the medium-sized tungsten carbide in this comparative example was measured to be 1.2 μm, with a uniform particle size distribution; however, the total carbon content was only 6.03%, and the free carbon content was 0.03%. Due to the low carbonization temperature, the methane was not completely decomposed, resulting in a low total carbon content and a high free carbon content, meaning that the content did not meet the standard value and did not meet the quality requirements for medium-sized tungsten carbide.

[0038] Comparative Example 2 The difference between this comparative example and Example 2 is as follows: In step 2: the temperature is increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, and then increased to 1700℃ at a rate of 5℃ / min and held for 4 h to carry out the reaction. All other conditions remain the same as in Example 2.

[0039] The average Fisher particle size of the medium-sized tungsten carbide in this comparative example was measured to be 10.5 μm, with uneven particle size distribution; the total carbon content was 6.13%, and the free carbon content was 0.03%; due to the excessively high carbonization temperature, the tungsten carbide grains grew excessively, resulting in excessively large particles, which did not meet the quality requirements for medium-sized tungsten carbide.

[0040] Comparative Example 3 The difference between this comparative example and Example 3 is as follows: In step 1: without closing the exhaust port, the inlet port was opened directly to introduce methane and then the inlet port was closed. The temperature was increased from room temperature to 800℃ at a rate of 10℃ / min and held for 30 min, and then increased to 1600℃ at a rate of 5℃ / min and held for 2 h to carry out the reaction. All other conditions remain the same as in Example 3.

[0041] The average Fisher particle size of the medium-sized tungsten carbide in this comparative example was measured to be 5.0 μm, with uniform particle size distribution; the total carbon content was 1.93%, and the free carbon content was 0.01%; due to the unsealed exhaust port when methane gas was introduced, methane overflowed, reducing the carbon produced by cracking and the water produced by the reaction, resulting in a decrease in both carbon content and Fisher particle size, and some tungsten oxide did not react, which does not meet the quality requirements for medium-sized tungsten carbide.

[0042] Comparative Example 4 The difference between this comparative example and Example 1 is as follows: The device rotation was not activated throughout the entire reaction process; All other conditions remain the same as in Example 1.

[0043] The average Fisher particle size of the medium-sized tungsten carbide in this comparative example was measured to be 2.1 μm, with a uniform particle size distribution; the total carbon content was 5.90%, and the free carbon content was 0.03%; due to the fact that the device was not turned on for rotation, the carbon black produced by methane cracking did not come into full contact with the tungsten oxide powder, resulting in incomplete carbonization of some tungsten oxide, uneven carbon content, and excessively high free carbon content, which did not meet the quality requirements for medium-sized tungsten carbide.

[0044] Comparative Example 5 The difference between this comparative example and Example 1 is as follows: In step 1: After adding tungsten trioxide powder to the rotary heating device, the exhaust port and the inlet port are closed. Then the device is turned on to rotate and heat. After the temperature rises to 1400℃, all the methane is introduced and the reaction is carried out at 1400℃ for 3 hours. All other conditions remain the same as in Example 1.

[0045] The average Fisher particle size of the medium-sized tungsten carbide particles in this comparative example was measured to be 2.0 μm, with a uniform particle size distribution; the total carbon content was 6.02%, and the free carbon content was 0.01%; due to the introduction of methane gas at high temperature, the methane gas expanded rapidly upon heating, causing the device to automatically release pressure due to overpressure, which posed a safety hazard and would reduce the amount of methane participating in the reaction due to pressure release, thus lowering the carbon content.

[0046] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing medium-sized tungsten carbide, characterized in that, Tungsten oxide powder was placed in a rotary heating device and sufficient methane was introduced. Then the rotation was turned on and heated to 1400~1600℃ for reaction. After cooling, it was sieved to obtain the medium-particle tungsten carbide. The medium-sized tungsten carbide has a Fisher particle size of 1.8~9.5μm, a combined carbon content of ≥6.10%, and a free carbon content of ≤0.02%.

2. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, The molar ratio of the tungsten oxide powder (WO3) to the methane is 1:(2.1~2.2).

3. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, The heating process specifically involves: first, raising the temperature to 750~850℃ at a rate of 10℃ / min for the first heat preservation, and then raising the temperature to 1400~1600℃ at a rate of 5℃ / min for the second heat preservation.

4. The method for preparing medium-sized tungsten carbide according to claim 2, characterized in that, The first heat preservation time is 20~40 minutes, and the second heat preservation time is 2~4 hours.

5. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, The rotational speed of the rotary heating device is 10~18 r / min.

6. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, Before introducing methane, adjust the furnace pressure of the rotary heating device to ≤10Pa.

7. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, The tungsten oxide powder has a purity of ≥99.8% and a particle size of 10~20μm; The methane has a purity of ≥99.9%, and the water content in the methane is ≤5ppm and the carbon monoxide content is ≤1ppm.

8. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, After the reaction is complete, the pressure inside the rotary heating device is adjusted to ≤10Pa, and nitrogen gas is introduced into the rotary heating device for cooling.

9. The method for preparing medium-sized tungsten carbide according to claim 1, characterized in that, The sieving was carried out using a negative pressure airflow sieve at a vacuum of -5 to -10 kPa.