A method for producing a cemented carbide

Abstract

The application relates to the technical field of hard alloys, and discloses a preparation method of a hard alloy, which comprises the following steps: raw material preparation, selecting tungsten carbide powder, cobalt powder and additives, mixing treatment, placing the dried tungsten carbide powder, cobalt powder and additives into a planetary ball mill, adding organic solvents such as ethanol or acetone, the ball-to-material ratio is 5:1-10:1, the ball milling speed is 200-400 r / min, the ball milling time is 12-24 hours, the mixed slurry is obtained after uniform mixing, the initial particle diameter of the tungsten carbide powder and the cobalt powder is accurately controlled and vacuum drying pretreatment is carried out, and the planetary ball mill is combined to be used for mixing under specific ball-to-material ratio, speed and time, and a dispersing agent is added at the same time, so that the raw material powder can reach a highly uniform mixing state, the problem of uneven powder mixing caused by insufficient ball milling process can be solved, and the uniformity and compactness of the microstructure of the hard alloy are ensured.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide technology, specifically to a method for preparing cemented carbide. Background Technology

[0002] Cemented carbide is an alloy material made from hard compounds of refractory metals and binder metals through powder metallurgy. Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, and corrosion resistance, and is widely used as a cutting tool material.

[0003] Currently, due to the multiple processes involved in cemented carbide preparation, the ball milling process used during raw material mixing and molding is difficult to achieve uniform powder dispersion. When the ball milling time and energy input are insufficient, it can lead to uneven distribution of tungsten carbide particles and binder phase, which can easily cause compositional segregation and porosity defects in the alloy after sintering, making it impossible to guarantee the compactness of the microstructure. At the same time, during the sintering process, the inability to monitor and adjust the heating curve and atmosphere in real time can cause abnormal grain growth and discontinuous distribution of binder phase in cemented carbide. Furthermore, sintering defects cannot be corrected in time. In the post-processing stage of the alloy, due to the lack of targeted heat treatment and surface strengthening processes, it is difficult to achieve a synergistic improvement in the toughness and hardness of cemented carbide, resulting in premature failure and excessive wear of the finished product in application, further affecting the overall performance and production efficiency of cemented carbide.

[0004] Therefore, a method for preparing cemented carbide is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing cemented carbide, which solves the problems mentioned in the background art, such as abnormal grain growth and discontinuous distribution of the binder phase in cemented carbide, and the inability to correct sintering defects in a timely manner.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing cemented carbide, comprising the following steps:

[0007] Step 1: Raw material preparation. Select tungsten carbide powder, cobalt powder, and additives. The particle size of the tungsten carbide powder is 0.5-2.0 micrometers, the particle size of the cobalt powder is 1.0-3.0 micrometers, and the additives include grain growth inhibitors and strengthening phases. The tungsten carbide powder accounts for 80-90 parts by weight, the cobalt powder accounts for 5-15 parts by weight, and the additives account for 1-5 parts by weight. The raw materials are subjected to vacuum drying treatment at a temperature of 100-150℃ for 2-4 hours.

[0008] Step 2: Mixing treatment. Place the dried tungsten carbide powder, cobalt powder and additives in a planetary ball mill, add organic solvent ethanol or acetone, the ball-to-material ratio is 5:1-10:1, the ball milling speed is 200-400 r / min, the ball milling time is 12-24 hours, and after mixing evenly, a mixed slurry is obtained.

[0009] Step 3: Molding process. The mixed slurry is spray-granulated into spherical powder at a temperature of 150-200℃ and a particle size of 50-150 micrometers. Then, it is pressed into shape using a cold isostatic press at a pressure of 100-300MPa to obtain a green body.

[0010] Step 4: Sintering treatment. Place the green blank in a vacuum sintering furnace. First, heat to 600-800℃ at a rate of 5-10℃ / min for degreasing and hold for 1-2 hours. Then, heat to 1350-1450℃ at a rate of 10-15℃ / min for sintering, holding for 1-3 hours. The sintering atmosphere is vacuum or argon protection, with a vacuum degree better than 1×10⁻⁶. -2 Pa;

[0011] Step 5: Post-treatment. The sintered cemented carbide is subjected to heat treatment, including quenching and tempering. The quenching temperature is 1000-1100℃, and the oil quenching is used for cooling. The tempering temperature is 500-600℃, and the temperature is held for 2-4 hours. The cemented carbide is then air-cooled to room temperature to obtain the finished cemented carbide product.

[0012] In step two, the amount of organic solvent added is 20-30% of the total weight of the mixed powder, and 0.1-0.5 parts by weight of dispersant is added during ball milling. The dispersant is polyvinyl alcohol or zinc stearate.

[0013] Preferably, the raw material preparation in step one includes the following sub-steps: placing tungsten carbide powder and cobalt powder separately in a vacuum drying oven and drying them at 110°C for 3 hours, then sieving them with a sieve mesh size of 400-600 mesh. The additive is composed of the following parts by weight of raw materials: 0.5-1.5 parts of vanadium carbide, 0.3-1.0 parts of chromium carbide, and 0.2-0.8 parts of rare earth oxides, wherein the rare earth oxides are either yttrium oxide or lanthanum oxide. Before mixing the raw materials, the additive is pretreated using an ultrasonic disperser with an ultrasonic power of 500-1000W for 10-20 minutes.

[0014] Preferably, the mixing process in step two includes the following conditions: the planetary ball mill uses a stainless steel grinding jar and tungsten carbide grinding balls with a diameter of 5-10 mm; the temperature is controlled at 20-30°C during the ball milling process and maintained by a circulating water cooling system; the viscosity of the mixed slurry is adjusted to 1000-2000 cP and monitored by a rotational viscometer; after the ball milling is completed, the slurry is vacuum filtered to remove some of the solvent, so that the solid content reaches 70-80%; and then it is placed in an oven and dried at 80°C for 1 hour to obtain a mixed powder.

[0015] Preferably, the molding process in step three includes the following methods: during spray granulation, the inlet temperature is 180℃, the outlet temperature is 80℃, the atomization pressure is 0.2-0.5MPa, the molding adopts a bidirectional pressing method, first pre-pressed at 50MPa for 1 minute, then main pressed at 200MPa for 2 minutes, with a holding time of 30 seconds, the density of the green body is controlled to be 50-60% of the theoretical density, and the green body is placed in the air to dry naturally for 24 hours to avoid cracking. For complex shaped workpieces, injection molding is used instead of cold isostatic pressing, the injection temperature is 150-170℃, and the injection pressure is 80-120MPa.

[0016] Preferably, the sintering treatment in step four includes the following sintering curve: the heating stage is divided into three segments: from room temperature to 400°C at a rate of 5°C / min, from 400°C to 800°C at a rate of 8°C / min, and from 800°C to the sintering temperature of 1400°C at a rate of 12°C / min. During the sintering holding period, the pressure inside the furnace is maintained below 5 × 10⁻⁶. -3 Pa, and argon gas is introduced as a protective gas at a flow rate of 10-20 L / min. After sintering, the temperature is cooled to 800°C at a rate of 5°C / min, and then cooled to room temperature with the furnace.

[0017] Preferably, the post-processing in step five includes the following steps: before heat treatment, the sintered body is surface-ground to remove the oxide layer, with a grinding depth of 0.1-0.3 mm; quenching is performed using a salt bath quenching medium at a quenching cooling rate of 50-100℃ / s; after tempering, shot peening is performed at a pressure of 0.4-0.6 MPa and a shot diameter of 0.2-0.4 mm for 10-20 minutes; finally, polishing is performed using diamond polishing paste until the surface roughness Ra is less than 0.1 micrometers.

[0018] Preferably, the grain growth inhibitor in the additive is prepared by the following method: vanadium carbide and chromium carbide powders are selected, mixed in a weight ratio of 1:1, added to a ball mill and ball-milled at 300 r / min for 5 hours, then placed in a tube furnace and heat-treated at 1200℃ for 2 hours under a hydrogen atmosphere with a hydrogen flow rate of 5 L / min to obtain composite inhibitor powder with a particle size of 0.5-1.0 micrometers. The reinforcing phase is either titanium nitride or titanium carbide, and is activated by plasma treatment before addition, with a plasma power of 500 W and a treatment time of 10 minutes.

[0019] Preferably, in step four, the sintering furnace employs a multi-zone temperature control system, with the temperature difference between each zone controlled within ±5℃. During the sintering process, the oxygen content inside the furnace is monitored in real time, and the oxygen partial pressure is controlled to be below 1×10⁻⁶ via an oxygen probe. -5 Pa, after the sintered body is taken out of the furnace, it is immediately transferred to a slow cooling tank, which is filled with nitrogen and the cooling rate is controlled below 2℃ / min. The hardness of the sintered body is tested using a Vickers hardness tester with a load of 10kg and the hardness value is not less than 1600HV.

[0020] Preferably, the preparation method further includes a quality inspection step: performing non-destructive testing on the cemented carbide finished product, including ultrasonic testing and X-ray diffraction analysis, with an ultrasonic frequency of 5MHz, detecting defect sizes greater than 0.1mm, and X-ray diffraction analysis of phase composition.

[0021] Preferably, in step two, 0.05-0.1 parts by weight of lubricant are added during the mixing process. The lubricant is paraffin or polyethylene glycol. Before molding, the mixed powder is aged in an environment with 50% humidity for 12 hours. After sintering, the cemented carbide is carburized at a temperature of 900°C for 4 hours, with the carbon potential controlled at 1.0-1.2%, to form a carbon-rich layer 5-10 micrometers thick on the surface.

[0022] Compared with the prior art, the present invention provides a method for preparing cemented carbide, which has the following beneficial effects:

[0023] 1. In this invention, during the preparation of cemented carbide, the initial particle size of tungsten carbide powder and cobalt powder is precisely controlled and vacuum drying pretreatment is performed. Combined with the use of a planetary ball mill at a specific ball-to-powder ratio, rotation speed and time for mixing, and the addition of a dispersant, the raw material powder can be ensured to achieve a highly uniform mixing state. This solves the problem of uneven powder mixing caused by insufficient ball milling process, thereby avoiding compositional segregation and porosity defects in the alloy after sintering, and ensuring the uniformity and density of the cemented carbide microstructure.

[0024] 2. In this invention, during the sintering process of cemented carbide, by formulating a sintering curve with multi-stage precise temperature control and strictly controlling the vacuum degree and protective gas flow rate of the sintering atmosphere, and by utilizing a multi-zone temperature control system and real-time oxygen content monitoring, precise control of the thermal field and atmosphere throughout the sintering process can be achieved. This enables the system to ensure the stability of the sintering environment in real time, suppress abnormal growth of tungsten carbide grains, avoid defects caused by discontinuous distribution of the binder phase due to fluctuations in sintering parameters and environmental interference, and correct deviations from ideal sintering conditions through parameter adjustment, ensuring that the cemented carbide obtains the expected fine and uniform grain structure and high sintering density.

[0025] 3. In this invention, when performing post-sintering treatment of cemented carbide, by introducing a composite post-treatment process including specific quenching, tempering, shot peening, and optional carburizing treatment, the matrix and surface of cemented carbide can be synergistically strengthened. This method can achieve a synergistic improvement in the toughness and hardness of cemented carbide, reduce the risk of early fracture and excessive wear during use, and further improve the comprehensive mechanical properties and reliability of cemented carbide. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1: A method for preparing a cemented carbide includes the following steps:

[0028] Step 1: Raw material preparation. Select tungsten carbide powder, cobalt powder, and additives. The particle size of the tungsten carbide powder is 0.5 micrometers, the particle size of the cobalt powder is 1.0 micrometer, and the additives include grain growth inhibitors and strengthening phases. Tungsten carbide powder accounts for 80 parts by weight, cobalt powder accounts for 5 parts by weight, and additives account for 1 part by weight. Vacuum dry the raw materials at a temperature of 100°C for 2 hours.

[0029] Step 2: Mixing treatment. Place the dried tungsten carbide powder, cobalt powder and additives in a planetary ball mill, add organic solvent ethanol or acetone, the ball-to-material ratio is 5:1, the ball milling speed is 200 r / min, the ball milling time is 12 hours, and after mixing evenly, a mixed slurry is obtained.

[0030] Step 3: Molding process. The mixed slurry is spray-granulated into spherical powder at a temperature of 150°C and a particle size of 50 micrometers. Then, it is pressed into shape using a cold isostatic press at a pressure of 100 MPa to obtain a green body.

[0031] Step 4: Sintering treatment. Place the green blank in a vacuum sintering furnace. First, heat to 600℃ at a rate of 5℃ / min for degreasing and hold for 1 hour. Then, heat to 1350℃ at a rate of 10℃ / min for sintering and hold for 1 hour. The sintering atmosphere is vacuum or argon protection, with a vacuum degree better than 1×10⁻⁶. -2 Pa;

[0032] Step 5: Post-treatment. The sintered cemented carbide is subjected to heat treatment, including quenching and tempering. The quenching temperature is 1000℃, and the oil quenching is used for cooling. The tempering temperature is 500℃, and the temperature is held for 2 hours. The carbide is then air-cooled to room temperature to obtain the finished cemented carbide product.

[0033] In step two, the amount of organic solvent added is 20% of the total weight of the mixed powder, and 0.1 parts by weight of dispersant is added during ball milling. The dispersant is polyvinyl alcohol or zinc stearate.

[0034] Step 1, raw material preparation, includes the following sub-steps: Tungsten carbide powder and cobalt powder are placed in a vacuum drying oven and dried at 110°C for 3 hours, then sieved with a sieve mesh of 400 mesh. The additive consists of the following parts by weight of raw materials: 0.5 parts of vanadium carbide, 0.3 parts of chromium carbide, and 0.2 parts of rare earth oxides. The rare earth oxides are either yttrium oxide or lanthanum oxide. Before mixing the raw materials, the additive is pretreated with an ultrasonic disperser with an ultrasonic power of 500W for 10 minutes.

[0035] The mixing process in step two includes the following conditions: the planetary ball mill uses a stainless steel grinding jar and tungsten carbide grinding balls with a diameter of 5 mm. The temperature is controlled at 20°C during the ball milling process and maintained by a circulating water cooling system. The viscosity of the mixed slurry is adjusted to 1000 cP and monitored by a rotational viscometer. After the ball milling is completed, the slurry is vacuum filtered to remove some of the solvent, so that the solid content reaches 70%. Then it is placed in an oven and dried at 80°C for 1 hour to obtain a mixed powder.

[0036] Step 3 molding process includes the following methods: During spray granulation, the inlet temperature is 180℃, the outlet temperature is 80℃, the atomization pressure is 0.2MPa, the molding adopts a bidirectional pressing method, first pre-pressed at 50MPa for 1 minute, then main pressed at 200MPa for 2 minutes, the holding time is 30 seconds, the density of the green body is controlled to 50% of the theoretical density, and the green body is placed in the air to dry naturally for 24 hours to avoid cracking. For complex shaped workpieces, injection molding is used instead of cold isostatic pressing, the injection temperature is 150℃, and the injection pressure is 80MPa.

[0037] Step four, the sintering process, includes the following sintering curves: the heating stage is divided into three segments: from room temperature to 400℃ at a rate of 5℃ / min, from 400℃ to 800℃ at a rate of 8℃ / min, and from 800℃ to the sintering temperature of 1400℃ at a rate of 12℃ / min. During the sintering holding period, the pressure inside the furnace is maintained below 5 × 10⁻⁶. -3 Pa, and argon gas is introduced as a protective gas at a flow rate of 10 L / min. After sintering, it is cooled to 800°C at 5°C / min, and then cooled to room temperature with the furnace.

[0038] The post-treatment in step five includes the following steps: Before heat treatment, the sintered body is surface-ground to remove the oxide layer. The grinding depth is 0.1 mm. The quenching is performed using a salt bath quenching medium at a quenching cooling rate of 50℃ / s. After tempering, shot peening is performed at a pressure of 0.4 MPa and a shot diameter of 0.2 mm for 10 minutes. Finally, polishing is performed using diamond polishing paste until the surface roughness Ra is less than 0.1 micrometers.

[0039] The grain growth inhibitor in the additive is prepared by the following method: Vanadium carbide and chromium carbide powders are selected, mixed in a weight ratio of 1:1, added to a ball mill and ball-milled at 300 r / min for 5 hours, and then placed in a tube furnace and heat-treated at 1200℃ for 2 hours under a hydrogen atmosphere with a hydrogen flow rate of 5 L / min to obtain composite inhibitor powder with a particle size of 0.5 micrometers. The reinforcing phase is either titanium nitride or titanium carbide. Before addition, it is activated by plasma with a plasma power of 500 W and a treatment time of 10 minutes.

[0040] In step four, the sintering furnace employs a multi-zone temperature control system, with the temperature difference between each zone controlled within ±5℃. During the sintering process, the oxygen content inside the furnace is monitored in real time, and the oxygen partial pressure is controlled to be below 1×10⁻⁶ via an oxygen probe. -5 Pa, after the sintered body is taken out of the furnace, it is immediately transferred to a slow cooling tank. The tank is filled with nitrogen and the cooling rate is controlled below 2℃ / min. The hardness of the sintered body is tested using a Vickers hardness tester with a load of 10kg and the hardness value is not less than 1600HV.

[0041] The preparation method also includes a quality inspection step: non-destructive testing of the cemented carbide finished product, including ultrasonic testing and X-ray diffraction analysis, with an ultrasonic frequency of 5MHz, detecting defects larger than 0.1mm, and X-ray diffraction analysis of phase composition;

[0042] In step two, 0.05 parts by weight of lubricant, which is paraffin or polyethylene glycol, is added during the mixing process. Before molding, the mixed powder is aged in an environment with 50% humidity for 12 hours. After sintering, the cemented carbide is carburized at a temperature of 900°C for 4 hours with a carbon potential controlled at 1.0% to form a 5-micron-thick carbon-rich layer on the surface.

[0043] Example 2: A method for preparing a cemented carbide includes the following steps:

[0044] Step 1: Raw material preparation. Select tungsten carbide powder, cobalt powder, and additives. The particle size of the tungsten carbide powder is 1.0 micrometer, the particle size of the cobalt powder is 2.0 micrometer, and the additives include grain growth inhibitors and strengthening phases. Tungsten carbide powder accounts for 85 parts by weight, cobalt powder accounts for 10 parts by weight, and additives account for 3 parts by weight. Vacuum dry the raw materials at a temperature of 120°C for 3 hours.

[0045] Step 2: Mixing treatment. Place the dried tungsten carbide powder, cobalt powder and additives in a planetary ball mill, add organic solvent ethanol or acetone, the ball-to-material ratio is 7:1, the ball milling speed is 300 r / min, the ball milling time is 18 hours, and after mixing evenly, a mixed slurry is obtained.

[0046] Step 3: Molding process. The mixed slurry is spray-granulated into spherical powder at a temperature of 180°C and a particle size of 100 micrometers. Then, it is pressed into shape using a cold isostatic press at a pressure of 200 MPa to obtain a green body.

[0047] Step 4: Sintering treatment. Place the green blank in a vacuum sintering furnace, first heat to 700℃ at a rate of 7℃ / min for degreasing and hold for 1.5 hours, then heat to 1400℃ at a rate of 12℃ / min for sintering, holding for 2 hours. The sintering atmosphere is vacuum or argon protection, with a vacuum degree better than 1×10⁻⁶. -2 Pa;

[0048] Step 5: Post-treatment. The sintered cemented carbide is subjected to heat treatment, including quenching and tempering. The quenching temperature is 1050℃, followed by oil quenching and cooling. The tempering temperature is 550℃, and the temperature is held for 3 hours. The carbide is then air-cooled to room temperature to obtain the finished cemented carbide product.

[0049] In step two, the amount of organic solvent added is 25% of the total weight of the mixed powder, and 0.3 parts by weight of dispersant is added during ball milling. The dispersant is polyvinyl alcohol or zinc stearate.

[0050] Step 1, raw material preparation, includes the following sub-steps: Tungsten carbide powder and cobalt powder are placed in a vacuum drying oven and dried at 110°C for 3 hours, then sieved with a sieve mesh of 500 mesh. The additive consists of the following parts by weight of raw materials: 1.0 part of vanadium carbide, 0.7 parts of chromium carbide, and 0.5 parts of rare earth oxides. The rare earth oxides are either yttrium oxide or lanthanum oxide. Before mixing the raw materials, the additive is pretreated with an ultrasonic disperser with an ultrasonic power of 800W for 15 minutes.

[0051] The mixing process in step two includes the following conditions: the planetary ball mill uses a stainless steel grinding jar and tungsten carbide grinding balls with a diameter of 7 mm. The temperature is controlled at 25°C during the ball milling process and maintained by a circulating water cooling system. The viscosity of the mixed slurry is adjusted to 1500 cP and monitored by a rotational viscometer. After the ball milling is completed, the slurry is vacuum filtered to remove some of the solvent, so that the solid content reaches 75%. Then it is placed in an oven and dried at 80°C for 1 hour to obtain a mixed powder.

[0052] Step 3 molding process includes the following methods: During spray granulation, the inlet temperature is 180℃, the outlet temperature is 80℃, the atomization pressure is 0.3MPa, the molding adopts a bidirectional pressing method, first pre-pressed at 50MPa for 1 minute, then main pressed at 200MPa for 2 minutes, the holding time is 30 seconds, the density of the green body is controlled to 55% of the theoretical density, and the green body is placed in the air to dry naturally for 24 hours to avoid cracking. For complex shaped workpieces, injection molding is used instead of cold isostatic pressing, the injection temperature is 160℃, and the injection pressure is 100MPa.

[0053] Step four, the sintering process, includes the following sintering curves: the heating stage is divided into three segments: from room temperature to 400℃ at a rate of 5℃ / min, from 400℃ to 800℃ at a rate of 8℃ / min, and from 800℃ to the sintering temperature of 1400℃ at a rate of 12℃ / min. During the sintering holding period, the pressure inside the furnace is maintained below 5 × 10⁻⁶. -3 Pa, and argon gas is introduced as a protective gas at a flow rate of 15 L / min. After sintering, it is cooled to 800°C at 5°C / min, and then cooled to room temperature with the furnace.

[0054] The post-treatment in step five includes the following steps: Before heat treatment, the sintered body is surface-ground to remove the oxide layer. The grinding depth is 0.2 mm. The quenching is performed using a salt bath quenching medium at a quenching cooling rate of 80℃ / s. After tempering, shot peening is performed at a pressure of 0.5 MPa and a shot diameter of 0.3 mm for 15 minutes. Finally, polishing is performed using diamond polishing paste until the surface roughness Ra is less than 0.1 micrometers.

[0055] The grain growth inhibitor in the additive is prepared by the following method: Vanadium carbide and chromium carbide powders are selected, mixed in a weight ratio of 1:1, added to a ball mill and ball-milled at 300 r / min for 5 hours, and then placed in a tube furnace and heat-treated at 1200℃ for 2 hours under a hydrogen atmosphere with a hydrogen flow rate of 5 L / min to obtain composite inhibitor powder with a particle size of 0.7 micrometers. The reinforcing phase is either titanium nitride or titanium carbide. Before addition, it is activated by plasma with a plasma power of 500 W and a treatment time of 10 minutes.

[0056] In step four, the sintering furnace employs a multi-zone temperature control system, with the temperature difference between each zone controlled within ±5℃. During the sintering process, the oxygen content inside the furnace is monitored in real time, and the oxygen partial pressure is controlled to be below 1×10⁻⁶ via an oxygen probe. -5 Pa, after the sintered body is taken out of the furnace, it is immediately transferred to a slow cooling tank. The tank is filled with nitrogen and the cooling rate is controlled below 2℃ / min. The hardness of the sintered body is tested using a Vickers hardness tester with a load of 10kg and the hardness value is not less than 1600HV.

[0057] The preparation method also includes a quality inspection step: non-destructive testing of the cemented carbide finished product, including ultrasonic testing and X-ray diffraction analysis, with an ultrasonic frequency of 5MHz, detecting defects larger than 0.1mm, and X-ray diffraction analysis of phase composition;

[0058] In step two, 0.07 parts by weight of lubricant, which is paraffin or polyethylene glycol, is added during the mixing process. Before molding, the mixed powder is aged in an environment with 50% humidity for 12 hours. After sintering, the cemented carbide is carburized at a temperature of 900°C for 4 hours with a carbon potential controlled at 1.1% to form a 7-micron-thick carbon-rich layer on the surface.

[0059] Example 3: A method for preparing a cemented carbide includes the following steps:

[0060] Step 1: Raw material preparation. Select tungsten carbide powder, cobalt powder, and additives. The particle size of the tungsten carbide powder is 2.0 micrometers, the particle size of the cobalt powder is 3.0 micrometers, and the additives include grain growth inhibitors and strengthening phases. Tungsten carbide powder accounts for 90 parts by weight, cobalt powder accounts for 15 parts by weight, and additives account for 5 parts by weight. Vacuum dry the raw materials at a temperature of 150°C for 4 hours.

[0061] Step 2: Mixing treatment. Place the dried tungsten carbide powder, cobalt powder and additives in a planetary ball mill, add organic solvent ethanol or acetone, the ball-to-material ratio is 10:1, the ball milling speed is 400 r / min, the ball milling time is 24 hours, and after mixing evenly, a mixed slurry is obtained.

[0062] Step 3: Molding process. The mixed slurry is spray-granulated into spherical powder at a temperature of 200°C and a particle size of 150 micrometers. Then, it is pressed into shape using a cold isostatic press at a pressure of 300 MPa to obtain a green body.

[0063] Step 4: Sintering treatment. Place the green blank in a vacuum sintering furnace. First, heat to 800℃ at a rate of 10℃ / min for degreasing and hold for 2 hours. Then, heat to 1450℃ at a rate of 15℃ / min for sintering and hold for 3 hours. The sintering atmosphere is vacuum or argon protection, with a vacuum degree better than 1×10⁻⁶. -2 Pa;

[0064] Step 5: Post-treatment. The sintered cemented carbide is subjected to heat treatment, including quenching and tempering. The quenching temperature is 1100℃, and the oil quenching is used for cooling. The tempering temperature is 600℃, and the temperature is held for 4 hours. The carbide is then air-cooled to room temperature to obtain the finished cemented carbide product.

[0065] In step two, the amount of organic solvent added is 30% of the total weight of the mixed powder, and 0.5 parts by weight of dispersant is added during ball milling. The dispersant is polyvinyl alcohol or zinc stearate.

[0066] Step 1, the raw material preparation includes the following sub-steps: Tungsten carbide powder and cobalt powder are placed in a vacuum drying oven and dried at 110°C for 3 hours, and then sieved with a sieve mesh of 600 mesh. The additive is composed of the following parts by weight of raw materials: 1.5 parts of vanadium carbide, 1.0 part of chromium carbide, and 0.8 parts of rare earth oxides. The rare earth oxides are either yttrium oxide or lanthanum oxide. Before mixing the raw materials, the additive is pretreated with an ultrasonic disperser with an ultrasonic power of 1000W for 20 minutes.

[0067] The mixing process in step two includes the following conditions: the planetary ball mill uses a stainless steel grinding jar and tungsten carbide grinding balls with a diameter of 10 mm. The temperature is controlled at 30°C during the ball milling process and maintained by a circulating water cooling system. The viscosity of the mixed slurry is adjusted to 2000 cP and monitored by a rotational viscometer. After the ball milling is completed, the slurry is vacuum filtered to remove some of the solvent, so that the solid content reaches 80%. Then it is placed in an oven and dried at 80°C for 1 hour to obtain a mixed powder.

[0068] The molding process in step three includes the following methods: During spray granulation, the inlet temperature is 180℃, the outlet temperature is 80℃, the atomization pressure is 0.5MPa, and the molding adopts a bidirectional pressing method. First, it is pre-pressed at 50MPa for 1 minute, then the main pressure is 200MPa for 2 minutes, and the holding time is 30 seconds. The density of the green body is controlled to be 60% of the theoretical density, and the green body is placed in the air to dry naturally for 24 hours to avoid cracking. For complex shaped workpieces, injection molding is used instead of cold isostatic pressing. The injection temperature is 170℃ and the injection pressure is 120MPa.

[0069] Step four, the sintering process, includes the following sintering curves: the heating stage is divided into three segments: from room temperature to 400℃ at a rate of 5℃ / min, from 400℃ to 800℃ at a rate of 8℃ / min, and from 800℃ to the sintering temperature of 1400℃ at a rate of 12℃ / min. During the sintering holding period, the pressure inside the furnace is maintained below 5 × 10⁻⁶. -3 Pa, and argon gas is introduced as a protective gas at a flow rate of 20 L / min. After sintering, it is cooled to 800°C at 5°C / min, and then cooled to room temperature with the furnace.

[0070] The post-treatment in step five includes the following steps: Before heat treatment, the sintered body is surface-ground to remove the oxide layer. The grinding depth is 0.3 mm. The quenching is performed using a salt bath quenching medium at a quenching cooling rate of 100℃ / s. After tempering, shot peening is performed at a pressure of 0.6 MPa and a shot diameter of 0.4 mm for 20 minutes. Finally, polishing is performed using diamond polishing paste until the surface roughness Ra is less than 0.1 micrometers.

[0071] The grain growth inhibitor in the additive is prepared by the following method: Vanadium carbide and chromium carbide powders are selected, mixed in a weight ratio of 1:1, added to a ball mill and ball-milled at 300 r / min for 5 hours, and then placed in a tube furnace and heat-treated at 1200℃ for 2 hours under a hydrogen atmosphere with a hydrogen flow rate of 5 L / min to obtain composite inhibitor powder with a particle size of 1.0 micrometers. The reinforcing phase is either titanium nitride or titanium carbide. Before addition, it is activated by plasma with a plasma power of 500 W and a treatment time of 10 minutes.

[0072] In step four, the sintering furnace employs a multi-zone temperature control system, with the temperature difference between each zone controlled within ±5℃. During the sintering process, the oxygen content inside the furnace is monitored in real time, and the oxygen partial pressure is controlled to be below 1×10⁻⁶ via an oxygen probe. -5 Pa, after the sintered body is taken out of the furnace, it is immediately transferred to a slow cooling tank. The tank is filled with nitrogen and the cooling rate is controlled below 2℃ / min. The hardness of the sintered body is tested using a Vickers hardness tester with a load of 10kg and the hardness value is not less than 1600HV.

[0073] The preparation method also includes a quality inspection step: non-destructive testing of the cemented carbide finished product, including ultrasonic testing and X-ray diffraction analysis, with an ultrasonic frequency of 5MHz, detecting defects larger than 0.1mm, and X-ray diffraction analysis of phase composition;

[0074] In step two, 0.1 parts by weight of lubricant, which is paraffin or polyethylene glycol, is added during the mixing process. Before molding, the mixed powder is aged in an environment with 50% humidity for 12 hours. After sintering, the cemented carbide is carburized at a temperature of 900°C for 4 hours with a carbon potential controlled at 1.2% to form a 10-micron-thick carbon-rich layer on the surface.

[0075] Comparative Example 1: The difference between this comparative example and Example 1 is that this comparative example did not use planetary ball milling process when mixing raw materials, but instead used a regular drum mixer to mix at 100 r / min for 2 hours.

[0076] Comparative Example 2 differs from Example 2 in that: this comparative example does not use a multi-stage controllable heating curve and precise atmosphere control during sintering, but instead directly heats to 1400°C at a rate of 15°C / min and holds for 1 hour, and sinters in an air atmosphere.

[0077] Comparative Example 3 differs from Example 3 in that the sintered cemented carbide was not subjected to post-heat treatment of quenching and tempering.

[0078] Comparative Example 4 differs from Example 3 in that no grain growth inhibitors or strengthening phase additives were added during the preparation process of this comparative example.

[0079] The cemented carbides prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests. The test items and test methods are as follows:

[0080] Density test: The relative density was calculated using Archimedes' method of displacement.

[0081] Hardness test: A Vickers hardness tester was used to apply a 10 kgf load and hold the pressure for 15 seconds to determine the hardness value.

[0082] Fracture toughness test: The stress intensity factor KIC was determined on a universal testing machine using the single-sided notched beam method.

[0083] Bending strength test: The three-point bending method was used, with a span of 30 mm and a loading rate of 0.5 mm / min.

[0084] Abrasion resistance test: The volumetric wear was measured using the wet sand rubber wheel abrasion test method.

[0085] The test data of the cemented carbides prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0086] Group Relative density (%) Vickers hardness (HV) <![CDATA[Fracture toughness (MPa·m 1 / 2 )]]> Flexural strength (MPa) <![CDATA[Wear amount (mm 3 )]]> Example 1 99.2 1650 11.8 2800 0.025 Example 2 99.5 1690 12.5 2950 0.021 Example 3 99.8 1720 13.0 3100 0.018 Comparative Example 1 95.5 1450 9.5 1850 0.065 Comparative Example 2 97.0 1550 8.2 2200 0.048 Comparative Example 3 99.3 1680 10.0 2500 0.030 Comparative Example 4 98.8 1580 11.0 2700 0.040

[0087] By comparing and analyzing the data in the table, it can be seen that the cemented carbide prepared using the processes in Examples 1-3 has significantly better performance than that prepared using the processes in Comparative Examples 1-4. This indicates that during the preparation of cemented carbide, by precisely controlling the initial particle size of tungsten carbide and cobalt powders and performing vacuum drying pretreatment, combined with mixing using a planetary ball mill at a specific ball-to-powder ratio, rotation speed, and time, and adding a dispersant, a highly uniform mixing state of the raw material powders can be ensured. This solves the problem of uneven powder mixing caused by insufficient ball milling, thereby avoiding component segregation and porosity defects inside the alloy after sintering, and ensuring the uniformity and density of the cemented carbide microstructure. During the sintering process of the cemented carbide, by developing a sintering curve with multi-stage precise temperature control and strictly controlling the vacuum degree of the sintering atmosphere and the protective gas flow rate, and by utilizing a multi-zone temperature control system... The integrated real-time oxygen content monitoring system enables precise control of the thermal field and atmosphere throughout the sintering process. This ensures the stability of the sintering environment in real time, suppresses abnormal growth of tungsten carbide grains, and avoids defects such as discontinuous binder phase distribution caused by fluctuations in sintering parameters and environmental interference. Furthermore, deviations from ideal sintering conditions can be corrected through parameter adjustments, ensuring that the cemented carbide achieves the expected fine and uniform grain structure and high sintering density. During the post-sintering treatment of cemented carbide, the introduction of a composite post-treatment process including specific quenching, tempering, shot peening, and optional carburizing treatment can synergistically strengthen the matrix and surface of the cemented carbide. This method can achieve a synergistic improvement in the toughness and hardness of cemented carbide, reducing the risk of early fracture and excessive wear during use, and further improving the comprehensive mechanical properties and reliability of cemented carbide.

[0088] By comparing and analyzing the relevant data in the table, it can be seen that the cemented carbide prepared by the forming process of the present invention has high hardness and high wear resistance, while also having good toughness. This indicates that the cemented carbide preparation method provided by the present invention has superior comprehensive performance.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cemented carbide, characterized in that, Includes the following steps: Step 1: Raw material preparation. Select tungsten carbide powder, cobalt powder, and additives. The particle size of the tungsten carbide powder is 0.5-2.0 micrometers, and the particle size of the cobalt powder is 1.0-3.0 micrometers. The additives include grain growth inhibitors and reinforcing phases. The grain growth inhibitors include vanadium carbide, chromium carbide, and rare earth oxides. The rare earth oxides are either yttrium oxide or lanthanum oxide. The reinforcing phase is either titanium nitride or titanium carbide. The tungsten carbide powder accounts for 80-90 parts by weight, the cobalt powder accounts for 5-15 parts by weight, and the additives account for 1-5 parts by weight. The raw materials are vacuum dried at a temperature of 100-150°C for 2-4 hours. Step 2: Mixing treatment. Place the dried tungsten carbide powder, cobalt powder and additives in a planetary ball mill, add organic solvent ethanol or acetone, the ball-to-material ratio is 5:1-10:1, the ball milling speed is 200-400 r / min, the ball milling time is 12-24 hours, and after mixing evenly, a mixed slurry is obtained. Step 3: Molding process. The mixed slurry is spray-granulated into spherical powder at a temperature of 150-200℃ and a particle size of 50-150 micrometers. Then, it is pressed into shape using a cold isostatic press at a pressure of 100-300MPa to obtain a green body. Step 4: Sintering treatment. Place the green blank in a vacuum sintering furnace. First, heat to 600-800℃ at a rate of 5-10℃ / min for degreasing and hold for 1-2 hours. Then, heat to 1350-1450℃ at a rate of 10-15℃ / min for sintering, holding for 1-3 hours. The sintering atmosphere is vacuum or argon protection, with a vacuum degree better than 1×10⁻⁶. -2 Pa; Step 5: Post-treatment. The sintered cemented carbide is subjected to heat treatment, including quenching and tempering. The quenching temperature is 1000-1100℃, and the oil quenching is used for cooling. The tempering temperature is 500-600℃, and the temperature is held for 2-4 hours. The cemented carbide is then air-cooled to room temperature to obtain the finished cemented carbide product. In step two, the amount of organic solvent added is 20-30% of the total weight of the mixed powder, and 0.1-0.5 parts by weight of dispersant is added during ball milling. The dispersant is polyvinyl alcohol or zinc stearate.

2. The method for preparing a cemented carbide according to claim 1, characterized in that, The raw material preparation in step one includes the following sub-steps: tungsten carbide powder and cobalt powder are placed in a vacuum drying oven and dried at 110°C for 3 hours, then sieved with a mesh size of 400-600. The additive consists of the following parts by weight: 0.5-1.5 parts vanadium carbide, 0.3-1.0 parts chromium carbide, and 0.2-0.8 parts rare earth oxides, wherein the rare earth oxides are either yttrium oxide or lanthanum oxide. Before mixing the raw materials, the additive is pretreated using an ultrasonic disperser with an ultrasonic power of 500-1000W for 10-20 minutes.

3. The method for preparing a cemented carbide according to claim 1, characterized in that, The mixing process in step two includes the following conditions: the planetary ball mill uses a stainless steel grinding jar and tungsten carbide grinding balls with a diameter of 5-10 mm. During the ball milling process, the temperature is controlled at 20-30℃ and maintained by a circulating water cooling system. The viscosity of the mixed slurry is adjusted to 1000-2000 cP and monitored by a rotational viscometer. After the ball milling is completed, the slurry is vacuum filtered to remove some of the solvent, so that the solid content reaches 70-80%. Then, it is placed in an oven and dried at 80℃ for 1 hour to obtain a mixed powder.

4. The method for preparing a cemented carbide according to claim 1, characterized in that, The molding process in step three includes the following methods: During spray granulation, the inlet temperature is 180℃, the outlet temperature is 80℃, the atomization pressure is 0.2-0.5MPa, and the molding adopts a bidirectional pressing method, first pre-pressing at 50MPa for 1 minute, then pressing at 200MPa for 2 minutes, with a holding time of 30 seconds. The density of the green body is controlled to be 50-60% of the theoretical density, and the green body is placed in the air to dry naturally for 24 hours to avoid cracking. For complex shaped workpieces, injection molding is used instead of cold isostatic pressing, with an injection temperature of 150-170℃ and an injection pressure of 80-120MPa.

5. The method for preparing a cemented carbide according to claim 1, characterized in that, The sintering process in step four includes the following sintering curve: the heating stage is divided into three segments: from room temperature to 400℃ at a rate of 5℃ / min, from 400℃ to 800℃ at a rate of 8℃ / min, and from 800℃ to the sintering temperature of 1400℃ at a rate of 12℃ / min. During the sintering holding period, the pressure inside the furnace is maintained below 5×10⁻⁶. -3 Pa, and argon gas is introduced as a protective gas at a flow rate of 10-20 L / min. After sintering, it is cooled to 800℃ at 5℃ / min, and then cooled to room temperature with the furnace.

6. The method for preparing a cemented carbide according to claim 1, characterized in that, The post-treatment in step five includes the following steps: Before heat treatment, the sintered body is surface-ground to remove the oxide layer. The grinding depth is 0.1-0.3 mm. Quenching is performed using a salt bath quenching medium at a quenching cooling rate of 50-100℃ / s. After tempering, shot peening is performed at a pressure of 0.4-0.6 MPa and a shot diameter of 0.2-0.4 mm for 10-20 minutes. Finally, polishing is performed using diamond polishing paste until the surface roughness Ra is less than 0.1 micrometers.

7. The method for preparing a cemented carbide according to claim 1, characterized in that, The grain growth inhibitor in the additive is prepared by the following method: vanadium carbide and chromium carbide powders are selected, mixed in a weight ratio of 1:1, added to a ball mill and ball-milled at 300 r / min for 5 hours, then placed in a tube furnace and heat-treated at 1200℃ for 2 hours under a hydrogen atmosphere with a hydrogen flow rate of 5 L / min to obtain composite inhibitor powder with a particle size of 0.5-1.0 micrometers. The reinforcing phase is either titanium nitride or titanium carbide, and is activated by plasma treatment before addition with a plasma power of 500 W and a treatment time of 10 minutes.

8. The method for preparing a cemented carbide according to claim 1, characterized in that, In step four, the sintering furnace employs a multi-zone temperature control system, with the temperature difference between each zone controlled within ±5℃. During the sintering process, the oxygen content inside the furnace is monitored in real time, and the oxygen partial pressure is controlled to be below 1×10⁻⁶ via an oxygen probe. -5 Pa, after the sintered body is taken out of the furnace, it is immediately transferred to a slow cooling tank, which is filled with nitrogen and the cooling rate is controlled below 2℃ / min. The hardness of the sintered body is tested using a Vickers hardness tester with a load of 10kg and the hardness value is not less than 1600HV.

9. The method for preparing a cemented carbide according to claim 1, characterized in that, The preparation method also includes a quality inspection step: non-destructive testing of the cemented carbide finished product, including ultrasonic testing and X-ray diffraction analysis, with an ultrasonic frequency of 5MHz, detecting defects larger than 0.1mm, and X-ray diffraction analysis of phase composition.

10. The method for preparing a cemented carbide according to claim 1, characterized in that, In step two, 0.05-0.1 parts by weight of lubricant, which is paraffin or polyethylene glycol, is added during the mixing process. Before molding, the mixed powder is aged in an environment with 50% humidity for 12 hours. After sintering, the cemented carbide is carburized at a temperature of 900°C for 4 hours, with the carbon potential controlled at 1.0-1.2%, to form a carbon-rich layer of 5-10 micrometers thick on the surface.