Preparation method of coarse-grained chromium carbide powder

Abstract

The invention relates to a preparation method of coarse-grained chromium carbide powder. The preparation method comprises the following steps: firstly, carrying out preliminary stirring, ball milling, pre-drying, low-temperature drying and medium-temperature pyrolysis on chromium sesquioxide powder, a dispersing agent and glycerol, so that the glycerol is pyrolyzed into solid carbon, and coating the surface of chromium sesquioxide with the solid carbon to form first-stage carbon source coated powder; mixing the powder with graphite powder and glycerol, carrying out pre-drying and low-temperature drying and shaping to obtain a two-stage carbonization column, carrying out gradient heating carbonization under a protective atmosphere to enable chromium sesquioxide and carbon to fully react to generate a chromium carbide phase mainly comprising Cr3C2, and then carrying out post-treatment to obtain the coarse-grained chromium carbide powder. According to the invention, glycerol is introduced as a main carbon source in the early stage and microcosmic coating is realized, so that the contact between the carbon source and chromium sesquioxide is more sufficient, and the reaction efficiency is improved; and meanwhile, the graphite powder is subjected to independent ball milling in advance to control the granularity, so that carbon source demolding is avoided, and better granularity control is realized. The method is flexible in process, and the product is coarse, uniform and stable in granularity.

Description

Technical Field

[0001] The present invention relates to the technical field of carbide material preparation, and particularly relates to a method for preparing coarse-grained chromium carbide powder. Background Art

[0002] Chromium carbide is an important functional material. Due to its excellent wear resistance, high hardness, corrosion resistance and high-temperature stability, it has been widely used in the fields of metallurgy, chemical engineering, aerospace, etc. Chromium carbide powder, as a key raw material, is usually used to make wear-resistant coatings, composite materials and corrosion-resistant alloys. Its properties are not only related to the chemical composition, but also significantly affected by the particle size distribution and particle morphology.

[0003] Coarse-grained chromium carbide powder has significant advantages in certain applications due to its unique properties. For example, coarse-grained particles can significantly improve the densification and wear resistance of the coating in plasma spraying or thermal spraying processes, while reducing processing losses. However, the current research on the preparation process of coarse-grained chromium carbide powder is less, and it is difficult for the existing technology to simultaneously achieve uniform particle distribution and particle size control, resulting in large fluctuations in product performance and difficult to meet the actual industrial requirements. Therefore, developing an efficient and controllable method for preparing coarse-grained chromium carbide powder is of great significance for improving the actual application effect of chromium carbide powder.

[0004] The main methods for preparing coarse-grained chromium carbide powder in the prior art and the existing defects include:

[0005] 1. High-temperature carbonization method: After thoroughly mixing chromium powder and a carbon source (such as graphite, carbon black or acetylene black) in a certain proportion, the mixture is placed in a high-temperature furnace for carbonization reaction. Usually, the reaction temperature is above 1500°C and the reaction time is relatively long to produce chromium carbide powder. In order to obtain a coarse-grained product, usually larger-sized raw materials are required and sieving is carried out after the reaction.

[0006] Existing defects: It is difficult to accurately control the particle size distribution of the powder. Especially when reacting at high temperatures, particles are prone to agglomeration, resulting in a large number of irregular particles in the product. In addition, due to the excessively high temperature, it is easy to cause excessive grain growth, affecting the morphological uniformity of the powder, and also significantly increasing the energy consumption, thus leading to a relatively high preparation cost.

[0007] 2. Arc method: The arc method uses a high-temperature arc (the temperature can reach above 3000°C) to heat the mixture of chromium and the carbon source, melt it and then generate chromium carbide powder through rapid cooling. This method relies on the high energy density of the arc and can complete the carbonization and cooling processes of the material in a short time.

[0008] There are defects: the particle size distribution of the obtained powder is usually relatively wide, and a large number of fine particles are often mixed in the coarse-grained powder. The cooling rate and reaction conditions of the arc method are difficult to precisely control, which may lead to incomplete reactions, generating uncompletely carbonized raw materials or impurities, thereby affecting the purity and performance of the powder.

[0009] 3. Mechanical alloying method: In the mechanical alloying method, chromium powder and carbon powder are put into a high-energy ball mill, and the mechanical energy generated by ball milling is used to make the raw material powder react to generate chromium carbide powder in the cold or warm state. This method can process coarse-grained raw materials to the target particle size range and promote the progress of the carbonization reaction.

[0010] There are defects: the mechanical alloying method is prone to generating powders with too fine particle sizes, which are difficult to meet the requirements of coarse-grained chromium carbide powder. The high-intensity impact during the ball milling process may lead to irregular particle morphology and even cause powder agglomeration. Long-term ball milling operations are likely to introduce impurities, reducing the product purity. At the same time, there are also problems of equipment wear and high energy consumption, limiting its prospects for industrial application.

[0011] 4. Chemical vapor deposition method: In the chemical vapor deposition method, the precursors of chromium-containing compounds and carbon sources are decomposed at high temperatures, or chromium carbide particles are generated through gas-phase chemical reactions and deposited into powders. This method can precisely control the reaction conditions and the chemical composition of the generated powder by utilizing the uniformity of gas-phase reactions.

[0012] There are defects: Although the chemical vapor deposition method has high chemical purity and good composition control ability, its process is complex, the equipment cost is high, and the preparation efficiency is low. At the same time, the particle size of the chromium carbide powder generated by the chemical vapor deposition method is usually small, mainly concentrated below the micron level, and it is difficult to directly meet the coarse-grained requirements.

[0013] 5. Plasma spraying method: In the plasma spraying method, the raw material particles of chromium carbide powder are melted by a high-temperature plasma arc and then cooled by spraying to form coarse-grained chromium carbide powder. This method can quickly cool the material from the high-temperature state to the solid state, avoiding excessive grain growth.

[0014] There are defects: When preparing coarse-grained powders by the plasma spraying method, the cooling rate is fast, but it is difficult to obtain powders with a uniform particle size distribution. The generated particles often have large differences in particle size. Since it is difficult to precisely control the energy density and spraying speed of the plasma arc, some particles may not be completely melted, thus affecting the performance of the powder. Summary of the Invention

[0015] In view of the above problems, the object of the present invention is to propose:

[0016] A preparation method of coarse-grained chromium carbide powder, comprising the following steps:

[0017] S1. Prepare the first-stage slurry: Prepare chromium(III) oxide powder of a first predetermined mass, a dispersant of a second predetermined mass, and glycerol of a third predetermined mass. After mixing and ball milling, obtain the first-stage slurry.

[0018] S2. Prepare the first-stage carbon source-coated powder: Subject the first-stage slurry to pre-drying, low-temperature drying, medium-temperature pyrolysis, and crushing to obtain the first-stage carbon source-coated powder.

[0019] S3. Prepare the second-stage slurry; Mix the first-stage carbon source-coated powder, graphite powder of a fourth predetermined mass, and glycerol of a fifth predetermined mass to obtain the second-stage slurry.

[0020] S4. Prepare the second-stage carbonized column; Pour the second-stage slurry into a cylindrical mold, and after pre-drying and low-temperature drying, obtain the second-stage carbonized column.

[0021] S5. Gradient temperature carbonization; Subject the demolded second-stage carbonized column to gradient temperature carbonization to obtain a chromium carbide product column.

[0022] S6. Post-treatment: Cool, crush, and screen the chromium carbide product column to obtain coarse chromium carbide powder with a target particle size.

[0023] Further, step S1 specifically includes:

[0024] S11. Stir the chromium(III) oxide powder: Pour the chromium(III) oxide powder into a mixer and perform preliminary stirring to break up obvious lumps.

[0025] S12. After preliminarily mixing the dispersant into the glycerol, pour it into the mixer and stir at a speed of 50 - 100 rpm for 10 - 30 min until it is preliminarily infiltrated and there are no obvious dry powders or flying powders.

[0026] The dispersant is one or a mixture of more than one of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol octylphenyl ether, Tween 20, Tween 80, and Span 80.

[0027] S13. Increase the stirring speed to 200 - 300 prm and stir for 20 - 30 min until there is no obvious agglomeration and the whole uniformly presents a stable slurry state, then stop stirring.

[0028] S14. Transfer the slurry to a planetary ball mill, select a ball-to-material ratio of 5:1 - 10:1, the rotational speed of the planetary ball mill is 200 - 300 rpm, and the ball milling time is 12 - 36 h; If the slurry becomes viscous and causes the equipment to heat up, add an appropriate amount of deionized water for dilution; Conduct sampling inspection, and stop ball milling after reaching the predetermined particle size to obtain the first-stage slurry.

[0029] Further, in step S1: the chromium sesquioxide powder of the first predetermined mass, the dispersant of the second predetermined mass, and the glycerol of the third predetermined mass are 100 parts by mass, 0.5 - 2 parts by mass, and 40 parts by mass respectively.

[0030] Further, step S2 specifically includes:

[0031] S21. Pre-drying: Pour the first-stage slurry into a drying tray, transfer it to a vacuum drying oven, and perform vacuum drying at 60 - 100 °C, maintaining the vacuum degree below 7 kPa until the weight is constant to remove free water.

[0032] S22. Low-temperature drying: Under a protective atmosphere, heat the dried first-stage slurry at a heating rate of 3 - 5 °C / min to 150 °C, hold for 1 h, remove residual moisture, and cause the glycerol to start preliminary decomposition.

[0033] S23. Medium-temperature pyrolysis: Continue to heat from 150 °C to 600 °C at a heating rate of 5 °C / min, hold for 1 - 2 h; cause the glycerol to complete pyrolysis and obtain a glycerol pyrolysis mass mainly composed of chromium sesquioxide powder coated with a glycerol carbon source, and part of Cr 2 O 3 comes into in-situ contact with carbon; the reaction path is:

[0034]

[0035] S24. Crushing: Crush the glycerol pyrolysis mass to a predetermined particle size to obtain the first-stage carbon source-coated powder material.

[0036] Further, in step S3: the graphite powder of the fourth predetermined mass and the glycerol of the fifth predetermined mass are 20 parts by mass and 10 parts by mass respectively; among them, the graphite powder is pre-milled to a predetermined particle size.

[0037] Further, in step S4:

[0038] Pre-drying means: Transfer the cylindrical mold containing the second-stage slurry to a vacuum drying oven, and perform vacuum drying at 60 - 100 °C, maintaining the vacuum degree below 7 kPa until the weight is constant to remove free water;

[0039] Low-temperature drying means: Under a protective atmosphere, heat the dried second-stage slurry at a heating rate of 3 - 5 °C / min to 150 °C, hold for 1 h, remove residual moisture and shape the second-stage slurry, and demold to obtain the second-stage carbonized column.

[0040] Further, step S5 specifically includes:

[0041] S51, placing the second-stage carbonization column under a protective atmosphere, heating to 1000°C at a heating rate of 10°C / min, and keeping the temperature for 1-2h;

[0042] S52, the furnace temperature is raised from 1000°C to 1400°C at a heating rate of 10°C / min, and kept at this temperature for 4 hours; the reaction mechanism is;

[0043]

[0044] Chromium trioxide or reduced chromium reacts with excess carbon to convert the second-stage carbonization column into a column containing Cr 3 C 2 The product column is mainly composed of chromium carbide phase.

[0045] Furthermore, step S6 specifically includes: after the reaction is completed, the product column is cooled to room temperature in a protective atmosphere, the furnace is opened, the product column is taken out, and it is crushed and sieved to obtain coarse chromium carbide powder of target particle size.

[0046] Furthermore, the protective atmosphere refers to a nitrogen atmosphere or an inert gas atmosphere.

[0047] Furthermore, the protective atmosphere refers to an argon atmosphere.

[0048] The invention also provides a coarse-grained chromium carbide powder, which is prepared by the method described.

[0049] The beneficial effects of the present invention are:

[0050] 1. The dry preparation method in the prior art uses graphite powder as the main carbon source and uses a small amount of glycerol or carboxymethyl cellulose as a binder. In this preparation method, the contact area between chromium trioxide as a metal oxide and the carbon source is small, and the reaction rate is low. The present invention uses glycerol as the main carbon source instead, and does not add solid carbon sources such as graphite in the first stage, so that glycerol adheres and coats the chromium trioxide particles. Through the first stage of heating, the glycerol is cracked into solid carbon, so that the carbon source can fully coat the chromium trioxide particles in a more microscopic form.

[0051] 2. The prior art is to mix chromium trioxide powder and graphite powder for ball milling. This will make it difficult to achieve differentiated control of ball milling particle size due to the different crushing strengths of different substances. The chromium trioxide powder and graphite powder of the present invention are ball milled separately, and the particle size can be independently controlled. Moreover, after the chromium trioxide powder of the present invention is coated with the glycerol carbon source, it will not be ball milled again to avoid the glycerol carbon source from de-membrane.

[0052] 3. The protective atmosphere of the present invention is filled in after low-temperature drying, which can avoid the residual water vapor and the like from affecting the purity of the protective atmosphere. Description of the Drawings

[0053] Figure 1 It is a schematic flow chart of the method of the present invention;

[0054] Figure 2 It is a schematic sub - flow chart of step S2 of the present invention;

[0055] Figure 3 It is a schematic sub - flow chart of step S5 of the present invention. Detailed Description of the Invention

[0056] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0057] Embodiment 1

[0058] According to Figures 1 - 3 shown, this embodiment provides a method for preparing coarse - grained chromium carbide powder, including the following steps:

[0059] S1. Prepare the first - stage slurry: Prepare a first predetermined mass of chromium trioxide powder, a second predetermined mass of dispersant, and a third predetermined mass of glycerol, and obtain the first - stage slurry through mixing and ball - milling; specifically including:

[0060] S11. Stir the chromium trioxide powder: Pour the chromium trioxide powder into a mixer and conduct preliminary stirring to break obvious lumps;

[0061] S12. After preliminarily mixing the dispersant into the glycerol, pour it into the mixer and stir at a speed of 50 - 100 rpm for 10 - 30 min until it is preliminarily infiltrated without obvious dry powder and flying powder;

[0062] The dispersant is one or a mixture of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol octyl phenyl ether, Tween 20, Tween 80, Span 80;

[0063] S13. Increase the stirring speed to 200 - 300 prm and stir for 20 - 30 min until there is no obvious agglomeration and the whole is uniformly and stably in a slurry state, then stop stirring;

[0064] S14. Transfer the slurry to a planetary ball - mill, select a ball - to - material ratio of 5:1 - 10:1, the rotational speed of the planetary ball - mill is 200 - 300 rpm, and the ball - milling time is 12 - 36 h; if the slurry becomes viscous and causes the equipment to heat up, add an appropriate amount of deionized water for dilution; conduct sampling inspection, and stop ball - milling after reaching the predetermined particle size to obtain the first - stage slurry.

[0065] S2. Prepare the first-stage carbon source-coated powder: Subject the first-stage slurry to pre-drying, low-temperature drying, medium-temperature pyrolysis, and crushing to obtain the first-stage carbon source-coated powder; specifically including:

[0066] S21. Pre-drying: Pour the first-stage slurry into a drying tray, transfer it to a vacuum drying oven, and perform vacuum drying at 60 - 100 °C, maintaining the vacuum degree below 7 kPa until the weight is constant to remove free water.

[0067] S22. Low-temperature drying: Under a protective atmosphere, heat the dried first-stage slurry at a heating rate of 3 - 5 °C / min to 150 °C, hold for 1 h, remove residual moisture, and cause glycerol to start preliminary decomposition.

[0068] S23. Medium-temperature pyrolysis: Continue heating from 150 °C to 600 °C at a heating rate of 5 °C / min, hold for 1 - 2 h; cause glycerol to complete pyrolysis and obtain a glycerol pyrolysis mass mainly composed of chromium sesquioxide powder coated with glycerol carbon source, and part of Cr 2 O 3 comes into in-situ contact with carbon; the reaction path is:

[0069]

[0070] S24. Crushing: Crush the glycerol pyrolysis mass to a predetermined particle size to obtain the first-stage carbon source-coated powder;

[0071] S3. Prepare the second-stage slurry; Mix the first-stage carbon source-coated powder, the fourth predetermined mass of graphite powder, and the fifth predetermined mass of glycerol to obtain the second-stage slurry;

[0072] S4. Prepare the second-stage carbonization column; Pour the second-stage slurry into a cylindrical mold, and obtain the second-stage carbonization column through pre-drying and low-temperature drying;

[0073] S5. Gradient temperature carbonization; Perform gradient temperature carbonization on the demolded second-stage carbonization column to obtain a chromium carbide product column; specifically including:

[0074] S51. Place the second-stage carbonization column under a protective atmosphere, heat it to 1000 °C at a heating rate of 10 °C / min, and hold for 1 - 2 h;

[0075] S52. Raise the furnace temperature from 1000 °C to 1400 °C at a heating rate of 10 °C / min, and hold at this temperature for 4 h; the reaction mechanism is;

[0076]

[0077] Chromium sesquioxide or reduced chromium reacts with excess carbon to convert the second-stage carbonization column into one containing Cr 3 C2 A product column mainly composed of chromium carbide phase;

[0078] S6. Post-treatment: After the reaction is completed, the product column is cooled to room temperature in the furnace under a protective atmosphere, the furnace is opened, the product column is taken out, crushed and sieved to obtain coarse chromium carbide powder with the target particle size.

[0079] In step S1: The first predetermined mass of chromium trioxide powder, the second predetermined mass of dispersant and the third predetermined mass of glycerol are 100 parts by mass, 0.5 - 2 parts by mass, and 40 parts by mass respectively.

[0080] In step S3: The fourth predetermined mass of graphite powder and the fifth predetermined mass of glycerol are 20 parts by mass and 10 parts by mass respectively; among them, the graphite powder is pre-milled to a predetermined particle size.

[0081] In step S4:

[0082] Pre-drying means: Transfer the cylindrical mold filled with the two-stage slurry to a vacuum drying oven, evacuate and dry at 60 - 100 °C, maintain the vacuum degree below 7 kPa, and dry until the weight is constant to remove free water;

[0083] Low-temperature drying means: Under a protective atmosphere, heat the dried two-stage slurry at a heating rate of 3 - 5 °C / min to 150 °C, hold for 1 h, remove residual moisture and shape the two-stage slurry, and demold to obtain a two-stage chromium carbide column.

[0084] The protective atmosphere refers to a nitrogen atmosphere or an inert gas atmosphere, and it can be an argon atmosphere. Specific Example 2

[0086] This embodiment provides a method for preparing coarse-grained chromium carbide powder. The method includes the following steps:

[0087] Step A: Prepare the primary slurry

[0088] A1. Preparation: Weigh the first predetermined mass of chromium trioxide powder (100 parts by mass) and put it into a mixer, stir at a low speed (about 50 - 100 rpm) for 10 - 30 minutes to preliminarily dissociate the obviously agglomerated chromium oxide particles.

[0089] A2. Premixing of dispersant and glycerol: Dissolve or uniformly disperse the second predetermined mass of 0.5 - 2 parts by mass of dispersant (the dispersant can be a single or composite system of PEG, PVP, PVA, polyethylene glycol octyl phenyl ether, Tween 20, Tween 80, Span 80) in 40 parts by mass of glycerol in advance, and slowly add it to the mixer after sufficient stirring. Continue to stir at 50 - 100 rpm for 10 - 30 min to preliminarily wet the surface of the chromium trioxide powder, and there is no obvious dry powder and flying powder.

[0090] A3. Enhanced stirring: Increase the stirring speed to 200 - 300 rpm and continue stirring for 20 - 30 min to ensure no obvious particle agglomeration and obtain a uniform and stable primary slurry.

[0091] A4. Wet ball milling: Place the primary slurry into a planetary ball mill and perform wet milling for 12 - 36 h at a ball - to - material ratio of 5:1 - 10:1 and a rotation speed of 200 - 300 rpm. To avoid the slurry becoming viscous and heating up during the grinding process, an appropriate amount of deionized water can be added timely to regulate the viscosity. Stop ball milling when the sampling inspection meets the predetermined particle size requirements to obtain a first - stage slurry with suitable particle size.

[0092] Step B: Prepare the first - stage carbon - source - coated powder

[0093] B1. Vacuum drying: Spread the first - stage slurry evenly on a drying tray, transfer it to a vacuum drying oven, keep the vacuum degree less than 7 kPa at 60 - 100 °C, and dry to constant weight to remove free moisture.

[0094] B2. Preliminary heat treatment (low - temperature drying): Under a protective atmosphere (such as argon or nitrogen), increase the temperature to about 150 °C at a heating rate of 3 - 5 °C / min and hold for 1 h to further remove a small amount of residual moisture and promote the preliminary decomposition of glycerol.

[0095] B3. Medium - temperature pyrolysis: Continue to increase the temperature to about 600 °C (heating rate is 5 °C / min), hold for 1 - 2 h, so that glycerol is basically pyrolyzed, and carbonaceous residues are deposited on the surface of Cr 2 O 3 particles to form chromium oxide lumps with a carbon - source - coated layer. This process is accompanied by the decomposition of C_3H_8O_3 to generate C (solid carbon residue) and gaseous H 2 、CO、CO 2 and other products.

[0096] B4. Crushing: Slightly crush and grind the obtained pyrolyzed mass to obtain a relatively uniform first - stage carbon - source - coated powder with a particle size meeting the requirements for subsequent use.

[0097] Step C: Prepare the secondary slurry

[0098] Mix the above - obtained first - stage carbon - source - coated powder with graphite powder (about 20 parts by mass) pre - ball - milled to a predetermined particle size and additional glycerol (about 10 parts by mass), and stir well to form a second - stage slurry. At this time, the second - stage slurry has better wettability and uniformity, laying a foundation for subsequent forming.

[0099] Step D: Prepare the carbonized column blank

[0100] D1. Transfer the two-stage slurry into a cylindrical mold. First, perform vacuum drying at 60 - 100 °C (vacuum degree below 7 kPa) until free moisture is removed.

[0101] D2. Under a protective atmosphere, heat it at a heating rate of 3 - 5 °C / min to 150 °C and hold for 1 h to further remove low-boiling components, shape the slurry, and achieve solidification and demolding to obtain a two-stage carbonized column blank.

[0102] Step E: Gradient heating carbonization

[0103] E1. In a protective atmosphere, heat the two-stage carbonized column blank from room temperature to 1000 °C at a heating rate of 10 °C / min and hold for 1 - 2 h to achieve partial reduction of Cr 2 O 3 and preliminary carbonization reaction.

[0104] E2. Then increase the temperature from 1000 °C to 1400 °C at the same heating rate (about 10 °C / min) and hold for 4 h. At this high temperature, Cr 2 O 3 further reacts with excessive carbon to form a chromium carbide phase mainly composed of Cr 3 C 2 . The reaction mechanism includes:

[0105]

[0106]

[0107] Finally, a chromium carbide product column is formed.

[0108] Step F: Post-treatment

[0109] After the reaction is completed, cool it to room temperature in the furnace under a protective atmosphere. Take out the product column and perform mild crushing and sieving to obtain chromium carbide powder with coarse particle size and the expected crystal phase distribution.

[0110] This embodiment, through staged slurry preparation, step-by-step drying and pyrolysis treatment, and secondary forming and gradient heating carbonization processes, enables the carbon sources provided by glycerol and graphite to fully contact and react with Cr 2 O 3 , and realizes the preparation of coarse-grained chromium carbide powder. At the same time, by optimizing the dispersant and multi-stage ball milling process, the material uniformity is improved, providing favorable conditions for obtaining a final product with stable performance.

[0111] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing coarse-grained chromium carbide powder, characterized in that: The following steps are involved: S1. Preparing a first-stage slurry: preparing a first predetermined mass of chromium trioxide powder, a second predetermined mass of a dispersant, and a third predetermined mass of glycerol, and mixing and ball milling them to obtain a first-stage slurry; S2. Preparing a first-stage carbon source coated powder: pre-drying the first-stage slurry, drying at low temperature, pyrolyzing at medium temperature, and crushing the first-stage carbon source coated powder; S3, preparing a second-stage slurry; mixing the first-stage carbon source coated powder, the fourth predetermined mass of graphite powder and the fifth predetermined mass of glycerol to obtain a second-stage slurry; S4, preparing a two-stage carbonized column; pouring the two-stage slurry into a cylindrical mold, pre-drying and low-temperature drying to obtain a two-stage carbonized column; S5, gradient temperature carbonization; subjecting the demoulded two-stage carbonization column to gradient temperature carbonization to obtain a chromium carbide product column; S6. Post-processing: cooling, crushing and sieving the chromium carbide product column to obtain coarse chromium carbide powder of target particle size.

2. The method for preparing a coarse-grained chromium carbide powder according to claim 1, characterized in that: Step S1 specifically includes: S11. Stirring chromium trioxide powder: pouring chromium trioxide powder into a mixer and performing preliminary stirring to break up obvious lumps; S12, pour the dispersant into the glycerin for preliminary mixing, pour into the mixer, stir at a speed of 50-100 rpm for 10-30 min, and initially soak until there is no obvious dry powder or flying dust; The dispersant is a mixture of one or more of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol octylphenyl ether, Tween 20, Tween 80, and Span 80; S13, increase the stirring speed to 200-300prm, stir for 20-30min, until there is no obvious agglomeration and the whole is in a uniform and stable slurry state, then stop stirring; S14, move the slurry to a planetary ball mill, select a ball-to-material ratio of 5:1-10:1, a planetary ball mill speed of 200-300rpm, and a ball milling time of 12-36h; if the slurry becomes viscous and causes the equipment to heat up, add an appropriate amount of deionized water for dilution; perform sampling inspection, and stop ball milling when the predetermined particle size is reached to obtain a first-stage slurry.

3. The method for preparing a coarse-grained chromium carbide powder according to claim 2, characterized in that: In step S1 , the first predetermined mass of chromium oxide powder, the second predetermined mass of dispersant, and the third predetermined mass of glycerol are 100 parts by mass, 0.5-2 parts by mass, and 40 parts by mass, respectively.

4. The method for preparing a coarse-grained chromium carbide powder according to claim 1, characterized in that: Step S2 specifically includes: S21. Pre-drying: Pour the first-stage slurry into a drying tray, transfer it to a vacuum drying oven, and dry it at 60-100°C, maintaining the vacuum degree below 7kPa, and dry it until the weight is constant to remove free water. S22, low temperature drying: put the dried first-stage slurry into a heating furnace, heat it to 150°C at a heating rate of 3-5°C / min, keep it warm for 1 hour, remove residual moisture, and start the initial decomposition of glycerol. S23, medium temperature pyrolysis: fill the furnace with protective gas to build a protective atmosphere, continue to heat from 150°C to 600°C, the heating rate is 5°C / min, and keep warm for 1-2h; pyrolysis of glycerol is completed to obtain a glycerol pyrolysis block whose main component is chromium trioxide powder coated with glycerol carbon source, and part of Cr2O3 is in situ contact with carbon; the reaction path is: S24, crushing: crushing the glycerol pyrolysis block to a predetermined particle size to obtain a first-stage carbon source coated powder.

5. The method for preparing coarse-grained chromium carbide powder according to claim 1, characterized in that: In step S3: the fourth predetermined mass of graphite powder and the fifth predetermined mass of glycerol are 20 parts by mass and 10 parts by mass respectively.

6. The method for preparing coarse-grained chromium carbide powder according to claim 1, characterized in that: In step S4: Pre-drying means: transferring the cylindrical mold containing the second-stage slurry into a vacuum drying oven, vacuum drying at 60-100°C, maintaining the vacuum degree below 7kPa, and drying until the weight is constant to remove free water; Low-temperature drying means: heating the dried second-stage slurry to 150°C at a heating rate of 3-5°C / min under a protective atmosphere, keeping the temperature for 1 hour, removing residual moisture and shaping the second-stage slurry, and demolding to obtain a second-stage carbonized column.

7. The method for preparing coarse-grained chromium carbide powder according to claim 1, characterized in that: Step S5 specifically includes: S51, placing the second-stage carbonization column under a protective atmosphere, heating to 1000°C at a heating rate of 10°C / min, and keeping the temperature for 1-2h; S52, the furnace temperature is raised from 1000°C to 1400°C at a heating rate of 10°C / min, and kept at this temperature for 4 hours; the reaction mechanism is; The chromium trioxide or reduced chromium reacts with excess carbon to convert the second-stage carbide column into a product column containing a chromium carbide phase mainly composed of Cr3C2.

8. The method for preparing coarse-grained chromium carbide powder according to claim 1, characterized in that: Step S6 specifically includes: after the reaction is completed, cooling the product column to room temperature in a protective atmosphere, opening the furnace, taking out the product column, crushing and sieving it to obtain coarse chromium carbide powder with a target particle size.

9. A method for preparing coarse-grained chromium carbide powder according to any one of claims 4, 6, 7 and 8, characterized in that: The protective atmosphere refers to a nitrogen atmosphere or an inert gas atmosphere.

10. A coarse-grained chromium carbide powder, characterized in that: The coarse-grained chromium carbide powder is prepared by the method according to any one of claims 1 to 9.

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