Method for preparing Cr-containing superfine WC powder with uniform crystal grains

Abstract

The invention discloses a method for preparing Cr-containing superfine WC (wolfram carbide) powder with uniform grains, which comprises the following steps: preparing superfine chromic oxide with BET (Brunauer, Emmett and Teller) granularity of 80-150nm, doping chromium in tungsten oxide in a way of adopting the superfine chromic oxide and carrying out two-time solid-solid mixing, reducing, uniformly mixing tungsten powder, carbonizing and carrying out airflow crushing to prepare WC-Cr3C2 powder, and the distribution in tungsten carbide is uniform. The WC-Cr3C2 powder prepared through the method is prepared into the superfine hard alloy, Cr3C2 is evenly distributed in the alloy and free of segregation or aggregation, abnormal grain growth of WC grains in the sintering process can be effectively restrained, and the grain size of the alloy is obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of cemented carbide, and in particular relates to a method for preparing ultrafine WC powder containing Cr and having uniform grains. Background Art

[0002] Ultrafine cemented carbide has the advantages of high hardness, high strength, and good toughness. It is called "double high" cemented carbide and is widely used in high-efficiency precision tools, micro-drills, micro-milling, blades, precision molds, etc. The key technical difficulty in preparing ultrafine cemented carbide lies in how to effectively inhibit the growth and coarsening of WC grains during the sintering process, and adding inhibitors is a common means. The main factors affecting the effect of inhibitors are the particle size of the inhibitor and the uniformity of the inhibitor's distribution in cemented carbide, and the main factors affecting the particle size and distribution uniformity of the inhibitor in cemented carbide are the particle size of the inhibitor itself and the way it is added. At present, there are two major methods commonly adopted in the industry, as follows:

[0003] The first type is the addition of inhibitor Cr at the alloy preparation end 3 C 2 The main method is wet grinding doping, that is, by adding inhibitors during the wet grinding process of the alloy mixture, the solubility of WC grains in the liquid phase cobalt is reduced during the sintering process, thereby reducing the dissolution and precipitation process of WC grains in the liquid phase cobalt, thereby avoiding the coarsening of WC grains. 3 C 2 The particle size is about 1.0μm, which cannot reach the ultrafine level, affecting the particle size of the inhibitor in the cemented carbide, thereby affecting the inhibition effect.

[0004] The second type is the addition of inhibitors at the preparation end of ultrafine tungsten carbide powder. Currently, the main methods of adding inhibitors are: liquid-liquid doping method, general solid-solid doping method and liquid-solid doping method.

[0005] Liquid-liquid doping method: In the production process of ammonium paratungstate (APT), a soluble ammonium dichromate solution is added to the ammonium paratungstate solution, or the APT crystal is dissolved in water and then a soluble ammonium dichromate solution is added, and then crystallized, dried, and calcined to form tungsten oxide, and then reduced and carbonized to obtain Cr-containing tungsten oxide. 3 C 2 Tungsten carbide powder is then prepared by alloy preparation process to obtain Cr-containing 3 C 2Inhibitor ultrafine cemented carbide. Although the ammonium dichromate solution and the ammonium paratungstate solution are evenly mixed in the solution state in the liquid-liquid doping method, the solubility of ammonium dichromate and APT is different during the crystallization process, resulting in the precipitation time of ammonium dichromate being different from that of APT, which causes the uneven distribution of ammonium dichromate grains in the APT crystals. At the same time, the ammonium dichromate solution will grow thicker during the crystallization process to form ammonium dichromate crystals with coarser grains. Correspondingly, the chromium oxide powder formed during the APT calcination process is coarser in particle size, generally with a specific surface area of ​​1-2m. 2 / g, that is, the BET particle size is about 550-1150 nanometers. During the carbonization process of tungsten powder, coarser Cr 3 C 2 Powder, causing Cr 3 C 2 The effect of inhibiting the coarsening of WC grains in the alloy cannot reach the best.

[0006] Solid-solid doping method: This method is to add chromium oxide or Cr in the process of tungsten powder and carbon. 3 C 2 , mixed evenly with tungsten powder and carbon black, and then carbonized and ball-milled to obtain Cr-containing 3 C 2 Ultrafine tungsten carbide, and then obtain Cr-containing 3 C 2 Inhibitor ultrafine cemented carbide. The general solid-solid doping method is mixed under dry mixing conditions, and it is difficult to ensure that the tungsten powder and chromium oxide or Cr 3 C 2 The mixing uniformity of Cr 3 C 2 The uniformity of the mixture with tungsten carbide and the final Cr 3 C 2 The particle size depends on the added chromium oxide or Cr 3 C 2 The particle size of chromium oxide or Cr 3 C 2 The particle size is about 1.0μm. Since the added mass ratio is generally less than 1%, the volume ratio is small, which affects the Cr 3 C 2 Uniformity of distribution in ultrafine tungsten carbide.

[0007] Liquid-solid doping method: This method is to add a certain amount of ammonium dichromate solution to tungsten oxide powder, and then mix them to achieve solid-liquid mixed doping; then after hydrogen reduction, carbonization, carbonization, cooling, ball milling, and screening, ultrafine WC powder containing Cr is obtained. However, the amount of ammonium dichromate solution added is small, the solid-liquid ratio is small, and under the action of gravity, the added liquid gathers at the bottom of the mixer, resulting in incomplete wetting of the tungsten oxide powder as a whole, uneven dryness and wetness of the material, and due to the residual liquid, the water content of the tungsten oxide powder is increased, the fluidity of the oxide is reduced, resulting in the coarsening of the tungsten powder particle size during reduction, and also reducing the Cr 3 C 2 The distribution uniformity in the ultrafine tungsten carbide. At the same time, ammonium dichromate begins to decompose at about 500°C in the reduction stage to generate chromium oxide, and its particle size is basically the same as that of calcination, that is, the BET particle size is about 550-1150 nanometers. Therefore, the particle size of chromium oxide added in the preparation stage of tungsten carbide by this method is coarse, and the mixing uniformity is poor, which ultimately affects the Cr 3 C 2 The effect of inhibiting the growth of tungsten carbide grains during the sintering process. Summary of the invention

[0008] In order to overcome the problems in the prior art, the present invention provides a method for preparing ultrafine WC powder containing Cr with uniform grains, and obtains Cr 3 C 2 Very fine grain size, WC-Cr evenly distributed in ultrafine tungsten carbide 3 C 2 Mixed powder, the mixed powder is used to prepare ultrafine cemented carbide, Cr 3 C 2 It is evenly distributed in the alloy without segregation or aggregation, which can effectively inhibit the abnormal grain growth of WC grains during sintering and significantly reduce the grain size of the alloy.

[0009] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0010] The invention provides a method for preparing ultrafine WC powder containing Cr and having uniform grains, comprising the following steps: premixing ultrafine chromium oxide with a BET particle size of 80-150nm with part of tungsten oxide, then adding the remaining tungsten oxide for diffusion mixing to achieve solid-solid mixed doping, and finally obtaining the ultrafine WC powder containing Cr and having uniform grains after hydrogen reduction, tungsten powder mixing, carbonization, cooling, crushing and screening.

[0011] The present invention prepares nano-scale ultrafine chromium oxide. A certain amount of ultrafine chromium oxide is added to tungsten oxide, and solid-solid doping is performed twice to uniformly mix the ultrafine chromium oxide with tungsten oxide powder. Then, the ultrafine chromium oxide is reduced with hydrogen, mixed with tungsten powder, carbonized, and crushed with airflow to obtain Cr 3 C 2Very fine grain size, WC-Cr evenly distributed in ultrafine tungsten carbide 3 C 2 Mixed powder. This mixed powder is used to prepare ultrafine cemented carbide, Cr 3 C 2 Excellent effect of suppressing the growth of carburized grains.

[0012] The preparation method of the ultrafine chromium oxide is as follows: after the chromium anhydride is crushed to a diameter of ≤0.8um, a pressure of ≥5000Pa and a flow rate of 2-8m are introduced at a temperature of 700-900°C. 3 / h of compressed air, calcined for 2-5h, to prepare ultrafine chromium oxide with a BET particle size of 80-150nm

[0013] In the present invention, the chromic anhydride is uniformly crushed to a diameter of ≤0.8um, providing extremely fine chromic anhydride raw materials for subsequent calcination, and calcination at a low temperature (700-900℃) ensures the control of Cr 2 O 3 The growth trend is controlled by controlling the BET particle size to 80-150 nanometers and the flow rate to 2-8m 3 / h, compressed air with a pressure of ≥5000Pa can accelerate the reaction to produce O 2 Exhaust, accelerate CrO 3 →Cr 2 O 3 +O 2 The reaction of a chemical process ensures that the reaction is complete.

[0014] As an optional embodiment, in the method provided by the present invention, the crushing process is to crush the chromic anhydride in a ball mill with a ball-to-material ratio of 10:1.

[0015] In the present invention, the chromic anhydride can be evenly crushed to a diameter of ≤0.8um by means of a high ball-to-material ratio.

[0016] As an optional embodiment, in the method provided by the present invention, the bulk density of the ultrafine chromium oxide is 40-80 g / L.

[0017] In the present invention, the nano-level ultrafine chromium oxide has a low bulk specific gravity and a large volume, which is beneficial to increasing the mixing contact area with tungsten oxide and improving the mixing uniformity.

[0018] As an optional embodiment, in the method provided by the present invention, the mass ratio of ultrafine chromium oxide to tungsten oxide during premixing is 1:10-1:20, and the mixing is performed for 30-60 minutes.

[0019] In the present invention, the "mixed seed" is prepared by mixing ultrafine chromium oxide and tungsten oxide powder at a solid-solid mass ratio of 1:10 to 1:20 for 30 to 60 minutes. The chromium oxide content is greatly increased to 5-10%, the contact area with tungsten oxide is increased, and the uniformity of the prepared "mixed seed" is greatly improved.

[0020] As an optional embodiment, in the method provided by the present invention, during diffusion mixing, the mass ratio of the mixture of the completely doped and mixed ultrafine chromium oxide and tungsten oxide to the remaining tungsten oxide is 1:30-1:10, and the mixing is carried out for 1-3 hours.

[0021] In the present invention, the first "mixed seeds" are mixed with tungsten oxide powder, and the chromium oxide in the "mixed seeds" is better dispersed into the tungsten oxide by taking advantage of the ratio of the "mixed seeds" to the tungsten oxide powder being 1:30 to 1:10, thereby greatly improving the mixing uniformity.

[0022] As an optional embodiment, in the method provided by the present invention, the reduction temperature during the hydrogen reduction process is 600-900°C, the reduction time is 4-9h, and tungsten powder and Cr are obtained after reduction. 2 O 3 A mixture of powders.

[0023] In the present invention, the tungsten oxide powder can be reduced to obtain tungsten powder under the condition of 600-900°C without affecting the Cr 2 O 3 Powder produces an effect, making it easier to obtain tungsten powder and Cr 2 O 3 A mixture of powders.

[0024] As an optional embodiment, in the method provided by the present invention, the BET particle size of the tungsten powder obtained after hydrogen reduction is 40-250nm, and the tungsten powder and Cr obtained after hydrogen reduction are 2 O 3 The powder mixture was mixed for another 0.5-1 h.

[0025] As an optional embodiment, in the method provided by the present invention, the tungsten oxide is selected from yellow tungsten oxide WO 3 、Blue tungsten oxide WO 2.9 Or purple tungsten oxide WO 2.72 One or more of .

[0026] As an optional embodiment, in the method provided by the present invention, the Fsss particle size of the tungsten oxide is 9-13um, the mass content of particles larger than 120 mesh in the tungsten oxide is less than 0.5%, and the mass content of particles between 200 mesh and 325 mesh is 45-65%.

[0027] As an optional embodiment, in the method provided by the present invention, the carbon blending is to mix the tungsten powder and Cr 2 O 3 The powder mixture is mixed with carbon black.

[0028] As an optional embodiment, in the method provided by the present invention, the carbonization is to load the carbon mixed powder into a graphite boat and carry out carbonization in a carbonization furnace. The carbonization atmosphere is a non-oxidizing atmosphere, the carbonization temperature is 1200-1600°C, and the carbonization time is 1-3h.

[0029] As an optional embodiment, in the method provided by the present invention, the cooling is natural cooling under non-oxidizing atmosphere conditions after the carbonization is completed.

[0030] As an optional embodiment, in the method provided by the present invention, the crushing is to subject the carbonized and cooled materials to air flow crushing, with a crushing pressure of 6.5-9.0 kPa and a classifying wheel speed of 3000-5000 r / min, to air flow crushing of the block materials, and the crushed materials are passed through a fine screen to remove impurities.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention crushes chromic anhydride to a diameter of ≤0.8 μm and then calcines it at 700-900° C. for 2-5 hours to prepare ultrafine chromium oxide. The ultrafine chromium oxide with a BET particle size of nanometer level is beneficial to increase the mixing contact area with tungsten oxide and improve the mixing uniformity.

[0033] (2) Since the proportion of chromium oxide added to tungsten oxide is relatively low, generally less than 1%, it is difficult to disperse and mix chromium oxide and tungsten oxide evenly. Therefore, the present invention adopts two solid-solid doping mixing methods to greatly improve the mixing uniformity. The first doping is pre-mixing, which is used to prepare "mixed seeds", so that the chromium oxide content is greatly increased to 5-10%, the contact area with tungsten oxide is increased, and the uniformity of the prepared "mixed seeds" is greatly improved. The second doping is diffusion mixing, using the first "mixed seeds" to mix with tungsten oxide powder, so that the chromium oxide in the "mixed seeds" is better dispersed into the tungsten oxide, which greatly improves the mixing uniformity.

[0034] (3) Since the particle size difference between chromium oxide and tungsten oxide powders is large, which affects the uniform dispersion and mixing of the two, the particle size and screening of tungsten oxide Fsss are controlled in this application. By optimizing the particle size and screening of tungsten oxide, its coarse particles are strictly controlled to reduce the particle size difference between chromium oxide and tungsten oxide powders.

[0035] (4) Traditional method: tungsten powder and Cr 2 O 3The powder is mixed and arranged in the carbon preparation process. However, during the carbon preparation process, the fluidity of the ultrafine tungsten powder drops sharply due to the strong crushing and deagglomeration effect, which seriously affects the tungsten powder and Cr 2 O 3 Powder mixing effect. This method uses tungsten powder and Cr to obtain 2 O 3 The powder mixture is placed in a mixer for light mixing to loosen and break up large agglomerates, but ensure that small agglomerates and fluidity of the tungsten powder are not greatly damaged, which can further improve the tungsten powder and Cr 2 O 3 Powder mixing uniformity.

[0036] (5) The present invention uses air flow crushing to 3 C 2 The particle size is further reduced and the Cr 3 C 2 In WC-Cr 3 C 2 The uniformity of dispersion in the mixed powder lays the foundation for subsequent alloy production.

[0037] (6) The present invention prepares ultrafine chromium oxide, uses ultrafine chromium oxide in tungsten oxide, and dopes chromium in a solid-solid mixing method twice, and then prepares WC-Cr through reduction, uniform mixing of tungsten powder, carbonization and air flow crushing. 3 C 2 Powder, Cr 3 C 2 The powder has fine particle size and is evenly distributed in tungsten carbide. 3 C 2 Powder is prepared into ultrafine cemented carbide, Cr 3 C 2 It is evenly distributed in the alloy without segregation or aggregation, can effectively inhibit the abnormal grain growth of WC grains during sintering, and significantly reduce the grain size of the alloy. Moreover, the present invention can be fully realized on conventional ultrafine tungsten carbide production equipment, the product quality is controllable, and it is easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 WC-Cr prepared in Example 2 3 C 2Typical SEM analysis results of powder re-prepared alloys;

[0040] Figure 2 In the preparation of Comparative Example 1, Cr was added during the wet grinding stage. 3 C 2 Typical SEM analysis results of the prepared alloys. DETAILED DESCRIPTION

[0041] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0043] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0044] Example 1

[0045] (1) Chromic anhydride (CrO 3 ) The ball-to-material ratio is 10:1, and the ball mill is used for 8 hours to crush the diameter to 0.75um, and then calcined at 750℃ in a four-tube furnace, while the pressure is ≥5000Pa and the flow rate is 2-8m 3 / h of compressed air, the calcination time is 3 hours, the BET particle size of the prepared ultrafine chromium oxide is 120 nanometers, and the bulk density (HB) is 46 g / L.

[0046] (2) Take 3 kg of chromium oxide with a BET particle size of 120 nanometers and 60 kg of blue tungsten with a Fsss particle size of 10.5 μm, put them together in a mixer, mix for 30 minutes, and prepare a uniform mixture of ultrafine chromium oxide and tungsten oxide powder, namely "mixed seeds". Take 63 kg of "mixed seeds" and 600 kg of blue tungsten with a Fsss particle size of 10.5 μm, put them together in a mixer, mix for 2 hours, and prepare a uniform mixture of ultrafine chromium oxide and tungsten oxide powder.

[0047] (3) The mixed ultrafine chromium oxide and tungsten oxide powder mixture is discharged from the mixer and reduced in a reduction furnace under H 2 The reduction was carried out in an atmosphere at 700 °C for 7 h to obtain tungsten powder and Cr 2 O 3 Powder mixture. Tungsten powder and Cr 2 O 3The powder mixture was blended in a double cone blender for 1 hour.

[0048] (4) Then tungsten powder and Cr 2 O 3 The powder mixture is mixed with carbon black in a plowshare carbon mixer for 2 hours, and then carbonized in a carbonization furnace under a non-oxidizing atmosphere (such as hydrogen, nitrogen) and 1400°C for 2 hours. The carbonized powder is kept in a non-oxidizing atmosphere and naturally cooled. Then, the powder is air-broken with a crushing pressure of 6.5-9.0 kPa and a classifying wheel speed of 5000 r / min. The powder is sieved through a fine sieve of 80-120 meshes to remove impurities after air-broken powder. Finally, the powder containing Cr is obtained. 3 C 2 Ultrafine WC-Cr 3 C 2 powder.

[0049] The preparation methods of Examples 2-7 are the same as those of Example 1, except for the solid-solid ratio of chromium oxide to tungsten oxide, the BET particle size of chromium oxide, and the type and particle size of tungsten oxide. The specific contents are shown in Table 1.

[0050] Comparative Example 1

[0051] No inhibitors are added during the production of tungsten carbide, and Cr is added during the wet grinding stage of alloy preparation. 3 C 2 Alloys prepared as inhibitors.

[0052] Comparative Example 2

[0053] (1) Take 3 kg of chromium oxide with a BET particle size of 500 nanometers and 600 kg of blue tungsten with a Fsss particle size of 10.5 μm, put them into a mixer, and mix them for 30 minutes to prepare a uniform mixture of chromium oxide and tungsten oxide powder.

[0054] (2) The mixed chromium oxide and tungsten oxide powder mixture is discharged from the mixer and reduced in a reduction furnace under H 2 The reduction was carried out in an atmosphere at 700 °C for 7 h to obtain tungsten powder and Cr 2 O 3 A mixture of powders.

[0055] (3) Then tungsten powder and Cr 2 O 3The powder mixture is mixed with carbon black in a plowshare carbon mixer for 2 hours, and then carbonized in a carbonization furnace under a non-oxidizing atmosphere (such as hydrogen, nitrogen) and 1400°C for 2 hours. The carbonized powder is kept in a non-oxidizing atmosphere and naturally cooled. Then, the powder is air-broken with a crushing pressure of 6.5-9.0 kPa and a classifying wheel speed of 5000 r / min. The powder is sieved through a fine sieve of 80-120 meshes to remove impurities after air-broken powder. Finally, the powder containing Cr is obtained. 3 C 2 Ultrafine WC-Cr 3 C 2 powder.

[0056] Table 1: Raw material ratios, process parameters and corresponding results of the examples and comparative examples

[0057]

[0058]

[0059] The chromium content of tungsten oxide after mixing the raw materials of Comparative Example 2 and Examples 1-7 is shown in Table 2.

[0060] Table 2 Chromium content of tungsten oxide after mixing the raw materials of Comparative Example 2 and Examples 1-7 %

[0061]

[0062] 11 sampling points were randomly selected from the mixtures of (tungsten oxide + chromium oxide) of various proportions to test the Cr content. As shown in Table 2, the chromium in the tungsten oxide + chromium oxide in Examples 1-7 was more evenly mixed.

[0063] The ultrafine WC-Cr prepared in Examples 1-7 3 C 2 The powder and the samples of comparative examples 1-2 were prepared into alloys, and the performance was tested. The test results are shown in Table 3 below. 3 C 2 The alloy prepared from the powder was subjected to scanning electron microscopy, and the results were as follows Figure 1 The typical SEM analysis results of the alloy prepared in the comparative example are shown in Figure 2 shown.

[0064] Table 3: Performance results of alloys prepared from examples and comparative examples

[0065]

[0066] The metallographic roughness detection in Table 3 is to observe 10 different fields of view at 1000 times. If the average number of roughness in each field is 3-6, it is judged as "more", if the average number of roughness in each field is 1-3, it is judged as "less", and if it is less than 1, it is judged as "trace". Figure 1-2 It can be seen that when the ultrafine tungsten powder containing chromium oxide prepared by the embodiment of the present invention and the ultrafine tungsten powder without chromium oxide added in comparative example 1 have the same BET particle size, the loading amount of embodiment 2 is 30% more, and the production increase benefit is obvious. From Table 2, the fluctuation extreme value of the Cr content of the (tungsten oxide + chromium oxide) mixture prepared by the embodiment of the present invention is 0.019-0.024%, while the fluctuation extreme value of comparative example 2 is 0.069%, indicating that the Cr content distribution of the embodiment is more uniform.

[0067] The Cr-containing 3 C 2 The alloy is prepared from ultrafine tungsten carbide. The magnetic force and hardness of the alloy are significantly higher than those of the sample in Comparative Example 1. The grain size of the alloy is finer, and the metallographic inclusion phenomenon is less and smaller, which shows that the WC-Cr prepared by the present invention 3 C 2 Powder is used to prepare alloy, Cr 3 C 2 The effect of inhibiting the growth and coarsening of alloy grains is significantly better than that of the traditional method. Compared with the chromium oxide group with a BET particle size of 500nm added in Comparative Example 2, the ultrafine tungsten powder containing chromium oxide prepared by the embodiment of the present invention shows that the BET particle size of the tungsten powder and tungsten carbide in Comparative Example 2 is coarser, and the results in Table 3 show that the metallographic inclusions of Comparative Example 2 are more 3-4u, and the inclusions are more serious. It also shows that the mixture (tungsten oxide + chromium oxide) with uniform Cr content prepared by ultrafine chromium oxide can better prepare tungsten carbide with fine BET particle size, and the metallographic inclusions prepared by it are also less.

[0068] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine WC powder containing Cr and having uniform grains, characterized in that: The method comprises the following steps: pre-mixing ultrafine chromium oxide with a BET particle size of 80-150nm with part of tungsten oxide, then adding the remaining tungsten oxide for diffusion mixing to achieve solid-solid mixed doping, and finally obtaining ultrafine WC powder containing Cr and having uniform grains after hydrogen reduction, tungsten powder mixing, carbonization, cooling, crushing and screening.

2. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: The preparation method of the ultrafine chromium oxide is as follows: after the chromium anhydride is crushed to a diameter of ≤0.8um, a pressure of ≥5000Pa and a flow rate of 2-8m are introduced at a temperature of 700-900°C. 3 / h of compressed air and calcined for 2-5h to prepare ultrafine chromium oxide with a BET particle size of 80-150nm.

3. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1 or 2, characterized in that: The crushing process is to crush the chromic anhydride in a ball mill with a ball-to-material ratio of 10:

1.

4. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: The bulk density of the ultrafine chromium oxide is 40-80 g / L.

5. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: During premixing, the mass ratio of ultrafine chromium oxide to tungsten oxide is 1:10-1:20, and the mixture is mixed for 30-60 minutes.

6. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: During diffusion mixing, the mass ratio of the mixture of the completely doped and mixed ultrafine chromium oxide and tungsten oxide to the remaining tungsten oxide is 1:30-1:10, and the mixing is performed for 1-3 hours.

7. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: During the hydrogen reduction process, the reduction temperature is 600-900°C, the reduction time is 4-9h, and a mixture of tungsten powder and Cr2O3 powder is obtained after reduction; the BET particle size of the tungsten powder obtained after hydrogen reduction is 40-250nm, and the mixture of tungsten powder and Cr2O3 powder obtained after hydrogen reduction is continuously mixed for 0.5-1h.

8. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: The tungsten oxide is selected from yellow tungsten oxide WO3, blue tungsten oxide WO 2.9 Or purple tungsten oxide WO 2.72 One or more of .

9. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: The Fsss particle size of the tungsten oxide is 9-13um, the mass content of particles larger than 120 mesh in the tungsten oxide is less than 0.5%, and the mass content of particles between 200 mesh and 325 mesh is 45-65%.

10. The method for preparing ultrafine WC powder containing Cr and having uniform grains according to claim 1, characterized in that: The carbon blending is to mix the mixture of tungsten powder and Cr2O3 powder obtained after mixing with carbon black; the carbonization is to load the mixed powder into a graphite boat and carbonize it in a carbonization furnace. The carbonization atmosphere is a non-oxidizing atmosphere, the carbonization temperature is 1200-1600°C, and the carbonization time is 1-3h; the cooling is to maintain natural cooling under non-oxidizing atmosphere conditions after carbonization; the crushing is to air flow crush the carbonized and cooled materials, the crushing pressure is 6.5-9.0kPa, the classification wheel speed is 3000-5000r / min, the block materials are air flow crushed, and the crushed materials are passed through a fine screen to remove impurities.

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