Hard alloy sintering rapid carburizing process

Abstract

The invention relates to the field of metal powder material processing, and particularly discloses a hard alloy sintering rapid carburizing process which comprises the following steps: S1, weighing required raw material powder in percentage by weight: 5-15wt% of Co, 6-10wt% of Mo, 3-5wt% of W and the balance of WC, and preparing a hard alloy blank; s2, core / shell structure powder with TiH2 coated with Al2O3, multi-walled carbon nanotubes and BaCO3 are mixed and subjected to ball milling, and then a hydrogen-containing carburizing medium is prepared; and S3, embedding the hard alloy blank without the forming agent into a hydrogen-containing carburizing medium, putting the hard alloy blank into a vapor deposition furnace, keeping the temperature at 1350-1500 DEG C for 1-2 hours, cooling to 1000-1200 DEG C, inputting hydrocarbon gas, and keeping the temperature for 1-2 hours to obtain a finished product. Carburization of sintering of the hard alloy is carried out in the vapor deposition furnace, a carburized layer is rapidly formed through a hydrogen-containing carburizing medium in direct contact in the early stage, and hydrocarbon gas is evenly input through micropores formed by the hydrogen-containing carburizing medium in the later stage to consolidate the carburized layer.

Description

Technical Field

[0001] The invention relates to the field of metal powder material processing, in particular to a hard alloy sintering rapid carburizing process. Background Art

[0002] The performance of cemented carbide can be improved by surface carburizing. Since the surface can achieve self-lubrication after carburizing, the wear resistance is improved. However, currently, carburizing of cemented carbide is generally carried out after sintering, which results in a long carburizing time. In addition, carburizing after sintering of cemented carbide materials is prone to grain growth, resulting in reduced hardness, wear resistance and toughness of cemented carbide. Summary of the invention

[0003] In order to solve the problems in the prior art of carburizing cemented carbide after sintering, such as long carburizing time and easy grain growth, the present invention provides a rapid carburizing process for sintering cemented carbide.

[0004] The technical solution adopted by the present invention is:

[0005] A cemented carbide sintering rapid carburizing process comprises the following steps:

[0006] S1. Weigh the required raw material powders according to weight percentage, wherein Co accounts for 5-15wt%, Mo accounts for 6-10wt%, W accounts for 3-5wt%, and the balance is WC; mix the weighed powders, ball mill, filter, and dry them, then add a molding agent, and then press to form a cemented carbide green body; place the cemented carbide green body in a vacuum sintering furnace for sintering to form a cemented carbide body;

[0007] S2, weigh TiH2 powder and add it to anhydrous ethanol to form a mixed solution in which TiH2 accounts for 35wt%, and then perform ultrasonic dispersion treatment and vacuum drying; prepare a solution using a mixed solution of deionized water and anhydrous ethanol as a solvent, add Al(NO3)3 at a concentration of 0.1-0.8mol / L, add the ultrasonically dispersed TiH2 powder, and adjust the pH value to 3-6 with CH3COOH, and then stir with a stirrer and dry to obtain a core / shell structure powder of TiH2 coated with Al2O3; then, the core / shell structure powder of TiH2 coated with Al2O3 having an outer diameter of less than 8nm, a length of less than 30μm and a specific surface area of ​​more than 350m 2 / g multi-walled carbon nanotubes, BaCO3 three substances were mixed and ball-milled to prepare hydrogen-containing carburizing medium;

[0008] S3. First, load the hydrogen-containing carburizing medium into a graphite crucible, and then bury the cemented carbide blank from which the forming agent has been removed; put the cemented carbide blank from which the forming agent has been removed and the graphite crucible containing the hydrogen carburizing medium into a vapor deposition furnace and keep it at 1350-1500°C for 1-2 hours, then cool it to 1000-1200°C, input carbon hydrogen gas and keep it at this temperature for 1-2 hours to obtain a finished product.

[0009] Preferably, in step S1, the ball milling time is 24 to 72 hours, a 400-mesh screen is used for filtration, the drying temperature is 85 to 100°C, the molding agent is sodium butadiene rubber, the amount of the molding agent added is 50 to 120% of the total weight of Co, Mo, W and WC powders, and the molding is performed under a pressure of 300 to 400 MPa; during sintering, the temperature is raised to 550 to 700°C in a vacuum sintering furnace, the heating rate is 1 to 5°C / min, the vacuum degree is 5 to 15 Pa, and the temperature is kept for 1 to 2 hours to remove the molding agent to form a cemented carbide blank.

[0010] Preferably, in step S2, the particle size of the weighed TiH2 powder is 0.5-1.5 μm, and the ultrasonic frequency of the ultrasonic dispersion treatment is 4×10 4 Hz, power of 100W, time of 20-40min, vacuum drying temperature of 85-100°C, vacuum degree of 10-20Pa, drying time of 1-2h; the amount of ultrasonically dispersed TiH2 powder added is 5-7 times the concentration of Al(NO3)3, stirred at 60-80°C for 8-24h with a magnetic stirrer, the speed is 20-50r / min, and dried at 120-150°C for 1-3h; Al2O3 coated TiH2 core / shell structure powder, with an outer diameter of less than 8nm, a length of less than 30μm and a specific surface area of ​​more than 350m 2 / g of multi-walled carbon nanotubes and BaCO3 are mixed in a weight ratio of 2:3:1 and milled in a planetary ball mill for 1 to 2 hours at a rotation speed of 250 to 300 r / min.

[0011] Preferably, in step S2, the volume ratio of deionized water to anhydrous ethanol is 1:10.

[0012] Preferably, in step S3, the weight ratio of the cemented carbide blank from which the forming agent is removed and the hydrogen-containing carburizing medium is 5:1, and the thickness of the hydrogen-containing carburizing medium around the cemented carbide blank from which the forming agent is removed is less than 5 mm.

[0013] Preferably, in step S3, the temperature in the vapor deposition furnace is first increased to 550-700°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours, then increased to 1100-1250°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours, then increased to 1350-1500°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours, and before that, the vacuum degree in the vapor deposition furnace is 1-5Pa, and then the temperature is reduced to 1000-1200°C at a rate of 5-10°C / min, hydrocarbon gas is input and kept at this temperature for 1-2 hours, and finally, the input of hydrocarbon gas is stopped, the temperature is reduced to room temperature at a rate of 1-8°C / min, and then the product is taken out.

[0014] The beneficial effects of the present invention are:

[0015] 1. In the initial sintering stage, the cemented carbide blank containing carbide-forming elements is used as the carburizing matrix, and surface carburization is achieved during the sintering process. Metal hydride TiH2 is introduced into the hydrogen-containing carburizing medium, and H2 is decomposed during the sintering process and reacts with multi-walled carbon nanotubes to form C+2H2=CH4 (CH4=[C]+H2). The formed activated carbon atoms enter the metal to achieve carburization; Al2O3 is coated on the surface of TiH2 to control the H2 release rate and avoid rapid depletion; the carbide-forming elements in the hydrogen-containing carburizing medium react with carbon elements to form carbides during the sintering process, which can promote the diffusion of activated carbon atoms from the carburizing medium to the surface of the cemented carbide matrix, which is beneficial to the adsorption of activated carbon atoms and the improvement of carburizing efficiency;

[0016] 2. In the initial sintering stage, multi-walled carbon nanotubes are used as the carbon source, which has a small particle size, greater reaction activity and high carburizing efficiency;

[0017] 3. In the initial sintering stage, although the hydrogen-containing carburizing medium in direct contact with the cemented carbide blank can quickly achieve preliminary carburizing, the direct contact with the hydrogen-containing carburizing medium is limited, which will lead to insufficient carbon source in the later stage. By sintering and carburizing in a vapor deposition furnace, carbon-hydrogen gas can be input for later continuous carburizing, and as the sintering proceeds, the hydrogen-containing carburizing medium will form a large number of microporous structures, which is conducive to the uniform coverage of the blank by carbon-hydrogen gas. Since the carbon-hydrogen gas is input in the vapor deposition furnace in the later stage to further consolidate the carburizing effect, the carbon source is more sufficient, which can increase the Mo content, promote the formation of Mo2C, hinder grain boundary migration, limit grain growth, refine WC grains, increase the relative density and hardness of cemented carbide, and significantly improve the mechanical properties of cemented carbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0020] Example 1, a cemented carbide sintering rapid carburizing process, such as Figure 1 As shown, the following steps are included:

[0021] S1. Weigh the required raw material powders by weight percentage, wherein Co accounts for 5wt%, Mo accounts for 6wt%, W accounts for 3wt%, and the balance is WC; mix the weighed powders and ball mill for 24h, filter through a 400-mesh sieve, and dry at 85°C, then add a butyl rubber molding agent according to 50% of the total weight of the Co, Mo, W and WC powders, and press mold under a pressure of 300MPa to obtain a cemented carbide green body; place the cemented carbide green body in a vacuum sintering furnace and heat it to 550°C at a heating rate of 1°C / min and a vacuum degree of 5Pa, and keep it warm for 1h to remove the molding agent to form a cemented carbide green body, and sinter it to form a cemented carbide green body;

[0022] S2. Weigh TiH2 powder with a particle size of 0.5 μm and add it to anhydrous ethanol to form a mixed solution with TiH2 accounting for 35 wt%. Then, perform ultrasonic dispersion treatment for 20 min at an ultrasonic frequency of 4×10 4 Hz, the power is 100 W, and it is vacuum dried at 85°C and the vacuum degree is 10 Pa for 1 hour; then a solution is prepared using a mixed solution of deionized water and anhydrous ethanol in a volume ratio of 1:10 as a solvent, Al(NO3)3 is added at a concentration of 0.1 mol / L, and TiH2 powder that has been ultrasonically dispersed is added at 5 times the concentration of Al(NO3)3, and the pH value is adjusted to 3 with CH3COOH, and then stirred at 60°C with a magnetic stirrer at a speed of 20 r / min for 8 hours, and then dried at 120°C for 1 hour to obtain a core / shell structure powder of TiH2 coated with Al2O3; then the core / shell structure powder of TiH2 coated with Al2O3 having an outer diameter of less than 8 nm, a length of less than 30 μm and a specific surface area of ​​more than 350 m 2 / g multi-walled carbon nanotubes, BaCO3 and the like were mixed in a weight ratio of 2:3:1, and milled in a planetary ball mill at a speed of 250 r / min for 1 h to prepare a hydrogen-containing carburizing medium;

[0023] S3. First, load the hydrogen-containing carburizing medium into a graphite crucible, and then bury the cemented carbide blank without the forming agent. The weight ratio of the cemented carbide blank without the forming agent and the hydrogen-containing carburizing medium is 5:1. The thickness of the hydrogen-containing carburizing medium around the cemented carbide blank without the forming agent is less than 5mm. Put the graphite crucible containing the cemented carbide blank without the forming agent and the hydrogen carburizing medium into a vapor deposition furnace, first heat it to 550°C at a rate of 5°C / min and keep it warm for 1h, then heat it to 1100°C at a rate of 5°C / min and keep it warm for 1h, then heat it to 1350°C at a rate of 5°C / min and keep it warm for 1h. Before that, the vacuum degree in the vapor deposition furnace is 1Pa, then cool it to 1000°C at a rate of 5°C / min, input hydrocarbon gas and keep it warm for 1h, finally stop inputting hydrocarbon gas, cool it to room temperature at a rate of 1°C / min and take it out.

[0024] Example 2, S1, weigh the required raw material powders by weight percentage, wherein Co accounts for 10wt%, Mo accounts for 8wt%, W accounts for 4wt%, and the balance is WC; mix the weighed powders and ball mill for 48h, filter through a 400-mesh sieve, and dry at 90°C, then add a sodium butadiene rubber molding agent according to 80% of the total weight of the Co, Mo, W and WC powders, and press mold under a pressure of 350MPa to obtain a cemented carbide green body; put the cemented carbide green body into a vacuum sintering furnace and heat it to 600°C at a heating rate of 3°C / min and a vacuum degree of 10Pa, and keep it warm for 1.5h to remove the molding agent to form a cemented carbide green body, and sinter it to form a cemented carbide green body;

[0025] S2. Weigh TiH2 powder with a particle size of 1 μm and add it to anhydrous ethanol to form a mixed solution with TiH2 accounting for 35 wt%. Then, perform ultrasonic dispersion treatment for 30 min at an ultrasonic frequency of 4×10 4 Hz, the power is 100 W, and it is vacuum dried at 90°C and the vacuum degree is 15 Pa for 1.5 hours; then a solution is prepared with a mixed solution of deionized water and anhydrous ethanol in a volume ratio of 1:10 as a solvent, Al(NO3)3 is added at a concentration of 0.4 mol / L, and TiH2 powder dispersed by ultrasound is added at 6 times the concentration of Al(NO3)3, and the pH value is adjusted to 5 with CH3COOH, and then stirred at 70°C with a magnetic stirrer at a speed of 30 r / min for 16 hours, and then dried at 130°C for 2 hours to obtain a core / shell structure powder of TiH2 coated with Al2O3; then the core / shell structure powder of TiH2 coated with Al2O3, having an outer diameter of less than 8 nm, a length of less than 30 μm and a specific surface area of ​​more than 350 m 2 / g multi-walled carbon nanotubes, BaCO3 and the like were mixed in a weight ratio of 2:3:1, and milled in a planetary ball mill at a speed of 280 r / min for 1.5 h to prepare a hydrogen-containing carburizing medium;

[0026] S3, firstly put the hydrogen-containing carburizing medium into a graphite crucible, and then bury the cemented carbide blank without the forming agent, the weight ratio of the cemented carbide blank without the forming agent and the hydrogen-containing carburizing medium is 5:1, and the thickness of the hydrogen-containing carburizing medium around the cemented carbide blank without the forming agent is less than 5mm; put the graphite crucible containing the cemented carbide blank without the forming agent and the hydrogen-containing carburizing medium into a vapor deposition furnace, first heat it to 600°C at a speed of 8°C / min and keep it warm for 10 minutes. 1.5h, then increase the temperature to 1150°C at a rate of 8°C / min and keep it for 1.5h, then increase the temperature to 1400°C at a rate of 8°C / min and keep it for 1.5h. Before that, the vacuum degree in the vapor deposition furnace is 3Pa. Then, reduce the temperature to 1100°C at a rate of 8°C / min, input hydrocarbon gas and keep it for 1.5h. Finally, stop inputting hydrocarbon gas, reduce the temperature to room temperature at a rate of 4°C / min and take it out.

[0027] Example 3, S1, weigh the required raw material powders by weight percentage, wherein Co accounts for 15wt%, Mo accounts for 10wt%, W accounts for 5wt%, and the balance is WC; mix the weighed powders and ball mill for 72h, filter through a 400-mesh sieve, and dry at 100°C, then add a sodium butadiene rubber molding agent according to 120% of the total weight of the Co, Mo, W and WC powders, and press mold under a pressure of 400MPa to obtain a cemented carbide green body; put the cemented carbide green body into a vacuum sintering furnace and heat it to 700°C at a heating rate of 5°C / min and a vacuum degree of 15Pa, and keep it warm for 2h to remove the molding agent to form a cemented carbide green body, and sinter it to form a cemented carbide green body;

[0028] S2, weigh TiH2 powder with a particle size of 1.5 μm and add it to anhydrous ethanol to form a mixed solution with TiH2 accounting for 35 wt%, and then perform ultrasonic dispersion treatment for 40 min at an ultrasonic frequency of 4×10 4 Hz, power of 100 W, and vacuum drying at 100°C and vacuum degree of 20 Pa for 2 h; then a solution was prepared using a mixture of deionized water and anhydrous ethanol in a volume ratio of 1:10 as a solvent, Al(NO3)3 was added at a concentration of 0.8 mol / L, and ultrasonically dispersed TiH2 powder was added at 7 times the concentration of Al(NO3)3, and the pH value was adjusted to 6 with CH3COOH, and then stirred at 80°C with a magnetic stirrer at a speed of 50 r / min for 24 h, and then dried at 150°C for 3 h to obtain a core / shell structure powder of TiH2 coated with Al2O3; then the core / shell structure powder of TiH2 coated with Al2O3 having an outer diameter of less than 8 nm, a length of less than 30 μm and a specific surface area of ​​more than 350 m 2 / g multi-walled carbon nanotubes, BaCO3 were mixed in a weight ratio of 2:3:1, and milled in a planetary ball mill at a speed of 300r / min for 2h to prepare a hydrogen-containing carburizing medium;

[0029] S3. First, load the hydrogen-containing carburizing medium into a graphite crucible, and then bury the cemented carbide blank without the forming agent. The weight ratio of the cemented carbide blank without the forming agent and the hydrogen-containing carburizing medium is 5:1. The thickness of the hydrogen-containing carburizing medium around the cemented carbide blank without the forming agent is less than 5mm. Put the graphite crucible containing the cemented carbide blank without the forming agent and the hydrogen carburizing medium into a vapor deposition furnace, first heat it to 700°C at a rate of 10°C / min and keep it warm for 2h, then heat it to 1250°C at a rate of 10°C / min and keep it warm for 2h, then heat it to 1500°C at a rate of 10°C / min and keep it warm for 2h. Before that, the vacuum degree in the vapor deposition furnace is 5Pa, then cool it to 1200°C at a rate of 10°C / min, input hydrocarbon gas and keep it warm for 2h, finally stop inputting hydrocarbon gas, cool it to room temperature at a rate of 8°C / min and take it out.

[0030] The carbide-forming elements in the hydrogen-containing carburizing medium react with carbon elements to form carbides during the sintering process, which can promote the diffusion of activated carbon atoms from the carburizing medium to the surface of the cemented carbide matrix, which is beneficial to the adsorption of activated carbon atoms and the improvement of carburizing efficiency. In the initial sintering stage, the cemented carbide blank containing carbide-forming elements is used as the carburizing matrix, and surface carburization is achieved during the sintering process. Metal hydride TiH2 is introduced into the hydrogen-containing carburizing medium, and H2 is decomposed during the sintering process and reacts with multi-walled carbon nanotubes to form C+2H2=CH4 (CH4=[C]+H2). The formed activated carbon atoms enter the metal to achieve carburization. Multi-walled carbon nanotubes are used as carbon sources. They have small particle size, greater reaction activity, and high carburizing efficiency. Al2O3 coated on the surface of TiH2 can control the H2 release rate and avoid rapid depletion.

[0031] In the initial sintering stage, although the hydrogen-containing carburizing medium in direct contact with the cemented carbide blank can quickly achieve preliminary carburizing, the direct contact with the hydrogen-containing carburizing medium is limited, which will lead to insufficient carbon source in the later stage. By sintering and carburizing in a vapor deposition furnace, carbon-hydrogen gas can be input for later continuous carburizing, and as the sintering proceeds, the hydrogen-containing carburizing medium will form a large number of microporous structures, which is conducive to the uniform coverage of the blank by the carbon-hydrogen gas, and the hydrogen-containing carburizing medium can also effectively support the cemented carbide blank to avoid dead corners that cannot be covered by the carbon-hydrogen gas. Since the carbon-hydrogen gas is input in the vapor deposition furnace in the later stage to further consolidate the carburizing effect, the carbon source is more sufficient, which can increase the Mo content, promote the formation of Mo2C, hinder grain boundary migration, limit grain growth, refine WC grains, increase the relative density and hardness of cemented carbide, and significantly improve the mechanical properties of cemented carbide.

[0032] Compared with the traditional method of sintering before carburizing, the present invention uses a cemented carbide blank containing carbide-forming elements as a carburizing matrix, realizes surface carburizing in situ during the sintering process, and is supplemented by vapor deposition to consolidate the carburizing. This method not only has high carburizing efficiency and good quality, but also can increase the Mo content, thereby significantly improving the performance of the cemented carbide.

[0033] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A cemented carbide sintering rapid carburizing process, characterized in that: The steps include: S1. Weigh the required raw material powders according to weight percentage, wherein Co accounts for 5-15wt%, Mo accounts for 6-10wt%, W accounts for 3-5wt%, and the balance is WC; mix the weighed powders, ball mill, filter, and dry them, then add a molding agent, and then press to form a cemented carbide green body; place the cemented carbide green body in a vacuum sintering furnace for sintering to form a cemented carbide body; S2, weigh TiH2 powder and add it to anhydrous ethanol to form a mixed solution in which TiH2 accounts for 35wt%, and then perform ultrasonic dispersion treatment and vacuum drying; prepare a solution using a mixed solution of deionized water and anhydrous ethanol as a solvent, add Al(NO3)3 at a concentration of 0.1-0.8mol / L, add the ultrasonically dispersed TiH2 powder, and adjust the pH value to 3-6 with CH3COOH, and then stir with a stirrer and dry to obtain a core / shell structure powder of TiH2 coated with Al2O3; then, the core / shell structure powder of TiH2 coated with Al2O3 having an outer diameter of less than 8nm, a length of less than 30μm and a specific surface area of ​​more than 350m 2 / g multi-walled carbon nanotubes, BaCO3 three substances were mixed and ball-milled to prepare hydrogen-containing carburizing medium; S3. First, load the hydrogen-containing carburizing medium into a graphite crucible, and then bury the cemented carbide blank from which the forming agent has been removed; put the cemented carbide blank from which the forming agent has been removed and the graphite crucible containing the hydrogen carburizing medium into a vapor deposition furnace and keep it at 1350-1500°C for 1-2 hours, then cool it to 1000-1200°C, input carbon hydrogen gas and keep it at this temperature for 1-2 hours to obtain a finished product.

2. The cemented carbide sintering rapid carburizing process according to claim 1, characterized in that: In step S1, the ball milling time is 24 to 72 hours, a 400-mesh screen is used for filtering, the drying temperature is 85 to 100°C, the molding agent is sodium butadiene rubber, the amount of the molding agent added is 50 to 120% of the total weight of Co, Mo, W and WC powders, and the molding is performed under a pressure of 300 to 400 MPa; during sintering, the temperature is raised to 550 to 700°C in a vacuum sintering furnace, the heating rate is 1 to 5°C / min, the vacuum degree is 5 to 15 Pa, and the temperature is kept for 1 to 2 hours to remove the molding agent to form a cemented carbide blank.

3. The cemented carbide sintering rapid carburizing process according to claim 2, characterized in that: In step S2, the particle size of the weighed TiH2 powder is 0.5-1.5 μm, and the ultrasonic frequency of the ultrasonic dispersion treatment is 4×10 4 Hz, power of 100W, time of 20-40min, vacuum drying temperature of 85-100°C, vacuum degree of 10-20Pa, drying time of 1-2h; the amount of ultrasonically dispersed TiH2 powder added is 5-7 times the concentration of Al(NO3)3, stirred at 60-80°C for 8-24h with a magnetic stirrer, the speed is 20-50r / min, and dried at 120-150°C for 1-3h; Al2O3 coated TiH2 core / shell structure powder, with an outer diameter of less than 8nm, a length of less than 30μm and a specific surface area of ​​more than 350m 2 / g of multi-walled carbon nanotubes and BaCO3 are mixed in a weight ratio of 2:3:1 and milled in a planetary ball mill for 1 to 2 hours at a rotation speed of 250 to 300 r / min.

4. The cemented carbide sintering rapid carburizing process according to claim 3, characterized in that: In step S2, the volume ratio of deionized water to anhydrous ethanol is 1:

10.

5. The cemented carbide sintering rapid carburizing process according to claim 4, characterized in that: In step S3, the weight ratio of the cemented carbide blank from which the forming agent is removed and the hydrogen-containing carburizing medium is 5:1, and the thickness of the hydrogen-containing carburizing medium around the cemented carbide blank from which the forming agent is removed is less than 5 mm.

6. The cemented carbide sintering rapid carburizing process according to claim 5, characterized in that: In step S3, the temperature in the vapor deposition furnace is first increased to 550-700°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours, then increased to 1100-1250°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours, then increased to 1350-1500°C at a rate of 5-10°C / min and kept at this temperature for 1-2 hours. Prior to this, the vacuum degree in the vapor deposition furnace is 1-5Pa. Then, the temperature is reduced to 1000-1200°C at a rate of 5-10°C / min, hydrocarbon gas is introduced and kept at this temperature for 1-2 hours, and finally, the hydrocarbon gas introduction is stopped, the temperature is reduced to room temperature at a rate of 1-8°C / min, and then the product is taken out.

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