Superfine tungsten carbide and preparation method thereof

Abstract

The invention belongs to the technical field of powder metallurgy, and particularly relates to superfine tungsten carbide and a preparation method thereof. A preparation method of superfine tungsten carbide comprises the following steps that blue tungsten is reduced through a reverse hydrogen reduction method, and tungsten powder is obtained; the tungsten powder is subjected to carbon blending and uniform mixing, high-temperature carbonization is conducted, and tungsten carbide is obtained; and carrying out crushing airflow classification on the tungsten carbide to obtain the superfine tungsten carbide. According to the preparation method of the superfine tungsten carbide, the particle size range of the prepared tungsten carbide powder is that D10 ranges from 0.361 [mu] m to D90 ranges from 0.929 [mu] m, D50 is 0.585 [mu] m, the ratio of (D90-D10) to D50 is 0.971, particle size distribution is narrow, particle uniformity is good, the phenomenon that crystal grains grow up abnormally is avoided, and the quality of the powder is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to ultrafine tungsten carbide and a preparation method thereof. Background Art

[0002] In the cemented carbide industry, tungsten carbide particles with a size of 0.2 to 0.5 μm are called ultrafine tungsten carbide. Due to its excellent physical and chemical properties, it is widely used in high-speed cutting tools, cemented carbide, top hammers, dense ceramic products and other fields. Especially in the field of cemented carbide, it is known as the "teeth of modern industry". Ultrafine tungsten carbide not only has excellent electrical and thermal conductivity, extremely high hardness, but also has good high temperature tolerance, so it has become a key raw material for manufacturing high-strength and high-wear-resistant cemented carbide.

[0003] The mechanical properties of cemented carbide are mainly determined by the size of tungsten carbide particles. By reducing the size of tungsten carbide particles, especially when reaching the nanometer level, the hardness, modulus, wear resistance and compressive strength of the alloy are significantly improved. However, the production of nanometer-level tungsten carbide powder is currently limited by both cost and technology, and large-scale industrial production cannot be achieved. Therefore, ultrafine tungsten carbide powder is still widely used in the industry. Although the performance is slightly lower than that of nanometer-level, the cost-effectiveness of ultrafine tungsten carbide makes it occupy an important position in the production of mid-to-high-end cemented carbide.

[0004] However, in the production process of ultrafine tungsten carbide powder, the uniformity problem seriously affects the quality of the final cemented carbide product. Tungsten carbide powder with poor uniformity is prone to abnormal particle growth during sintering, and coarse grains will significantly reduce the bending strength and thermal sensitivity of cemented carbide. When the sintering temperature increases, powder with poor uniformity is prone to abnormal grain growth, which leads to an increase in coarse grain defects in cemented carbide and a decrease in the mechanical properties of the product.

[0005] At present, due to the easy coarsening phenomenon in the preparation process of ultrafine tungsten carbide powder, the powder uniformity is difficult to control, which makes the final alloy product molding quality poor, the product rework rate is high, and the production cost is increased. Therefore, how to improve the uniformity of ultrafine tungsten carbide powder and reduce the abnormal growth of grains has become a technical problem that needs to be solved in the industry, and is also the key to improving the performance of cemented carbide products and reducing production costs. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned shortcomings and provide an ultrafine tungsten carbide and a preparation method thereof.

[0007] In the first aspect, a method for preparing ultrafine tungsten carbide adopts the following technical scheme:

[0008] A method for preparing ultrafine tungsten carbide, characterized in that it includes the following steps:

[0009] The blue tungsten is reduced by reverse hydrogen reduction to obtain tungsten powder;

[0010] The tungsten powder is mixed with carbon uniformly, and carbonized at high temperature to obtain tungsten carbide;

[0011] The tungsten carbide is crushed and air flow classified to obtain ultrafine tungsten carbide.

[0012] Furthermore, the oxygen index of the blue tungsten is 2.94-2.97, the specific surface particle size is 10 μm-35 μm, and the loose ratio is 2.5 g / cm 3 ~4.5g / cm 3 .

[0013] Furthermore, the blue tungsten is reduced by reverse hydrogen reduction method, which specifically includes the following process: the blue tungsten is reduced at a temperature of 600°C to 950°C and a hydrogen flow rate of 310m 3 / h~350m 3 / h and a rotation speed of 15Hz to 25Hz to obtain tungsten powder.

[0014] Furthermore, the temperature of the reverse hydrogen reduction method is divided into six reduction temperature zones, including the following temperature zones: zone one temperature is 590°C to 610°C, zone two temperature is 610°C to 630°C, zone three temperature is 640°C to 660°C, zone four temperature is 690°C to 710°C, zone five temperature is 880°C to 900°C and zone six temperature is 890°C to 950°C.

[0015] Furthermore, the six zone temperatures of the reverse hydrogen reduction method are: zone one temperature is 600°C, zone two temperature is 620°C, zone three temperature is 650°C, zone four temperature is 700°C, zone five temperature is 890°C and zone six temperature is 920°C.

[0016] Furthermore, the ground specific surface area of ​​the tungsten powder is 5.0 m 2 / g~5.5m 2 / g.

[0017] Furthermore, the carbon mixing time is 2h to 5h.

[0018] Furthermore, the high temperature carbonization process has a temperature of 1300° C. to 1500° C. and a high temperature carbonization time of 10 min to 15 min.

[0019] Furthermore, the air flow crushing and classification specifically includes the following process: when the air flow rate in the gap is 200m 3 / h~300m 3 / h, grinding gas flow rate is 400m 3 / h~600m 3 / h, and air flow crushing and dispersion are carried out under the conditions of the classifying wheel speed being 3000rpm~4000rpm.

[0020] In the second aspect, a tungsten carbide adopts the following technical solution:

[0021] Ultrafine tungsten carbide prepared by any of the above-mentioned methods for preparing ultrafine tungsten carbide.

[0022] Beneficial effects of the present invention:

[0023] The present invention provides a method for preparing ultrafine tungsten carbide, wherein the prepared tungsten carbide powder has a particle size range of D 10 0.361μm to D 90 is 0.929μm, where D 50 is 0.585 μm, and (D 90 -D 10 ) / D 50 The ratio is 0.971, the particle size distribution is narrow, the particle uniformity is good, the abnormal grain growth phenomenon is avoided, and the quality of the powder is greatly improved; most of the tungsten carbide grains are single crystals, the crystal growth is complete, the metallographic interface particle coarseness reaches the first-class standard (> 4μm particles ≤ 5), and the abnormal grain growth phenomenon is greatly reduced; the coercive force is 21.84kA / m, with strong magnetic properties, which meets the requirements of high-quality tungsten carbide powder; the grinding specific surface area is 2.51m 2 / g, showing good surface area characteristics, which is beneficial to improving the sintering performance and mechanical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The SEM image of tungsten carbide provided in Example 1;

[0025] Figure 2 The particle size distribution diagram of tungsten carbide provided in Example 1;

[0026] Figure 3 The metallographic structure diagram of tungsten carbide provided in Example 1. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. The described embodiments should not be regarded as limiting the present invention. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0028] In the following description, reference is made to "some embodiments", which describe a subset of all possible embodiments, but it is understood that "some embodiments" may be the same subset or different subsets of all possible embodiments, and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the present invention have the same meaning as those commonly understood by those skilled in the art to which the embodiments of the present invention pertain. The terms used in the embodiments of the present invention are only for the purpose of describing the embodiments of the present invention and are not intended to limit the present invention.

[0029] Those skilled in the art should understand that in the following description of the embodiments of the present invention, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0030] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "an" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0031] It will be appreciated by those skilled in the art that the numerical ranges in the embodiments of the present invention are to be understood as also specifically disclosing each intermediate value between the upper and lower limits of the range. Each smaller range between the intermediate values ​​in any stated value and stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded in the range.

[0032] Unless otherwise specified, the technical / scientific terms used herein have the same meanings as those generally understood by those skilled in the art in the art. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the embodiments or test cases of the present invention. All documents mentioned in this specification are generally incorporated by reference to disclose and describe methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this application shall prevail.

[0033] It should be noted that all raw materials and / or reagents in the examples of the present invention are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0034] The physical and chemical properties of the blue tungsten raw materials used in the following examples are as follows:

[0035] The oxygen index of blue tungsten is 2.94-2.97, the specific surface particle size is 10μm-35μm, and the loose ratio is 2.5g / cm 3~4.5g / cm 3 .

[0036] Example

[0037] Example 1

[0038] Embodiment 1 provides a method for preparing ultrafine tungsten carbide, comprising the following steps:

[0039] Step 1: The oxygen index is 2.96, the specific surface particle size is 20 μm, and the loose ratio is 3.0 g / cm 3 The temperature of the six zones of blue tungsten is 600℃~620℃~650℃~700℃~890℃~920℃, and the hydrogen flow rate is 320m 3 / h and a rotation speed of 20Hz to obtain tungsten powder. The specific surface area of ​​the ground tungsten powder is 5.2-5.3m 2 / g;

[0040] Step 2, carbonizing the tungsten powder, adding carbon black in an amount of 6.18% of the total weight, mixing for 3.5 hours, and carbonizing at 1400° C. for 12 minutes to obtain tungsten carbide;

[0041] Step 3: When tungsten carbide is treated with nitrogen as the gas source, the gap gas flow rate is controlled to be 240m 3 / h~250m 3 / h, grinding gas flow rate is 500m 3 / h~550m 3 / h, and the rotating speed of the classifying wheel is 3500rpm~3600rpm to carry out air flow crushing and classification, so as to obtain ultrafine tungsten carbide.

[0042] like Figure 1 The figure shows the SEM image of the tungsten carbide powder provided in Example 1. The tungsten carbide grains grow relatively completely, and most of the grains are single crystal grains.

[0043] like Figure 2 The tungsten carbide particle size distribution diagram provided in Example 1 is shown in FIG. 10 0.361μm, D 50 0.585μm, D 90 0.929 μm, (D 90 -D 10 ) / D 50 It is 0.971, the tungsten carbide has good uniformity and narrow particle size distribution.

[0044] The metallographic phase of the tungsten carbide provided in Example 1 was prepared and measured according to GB / T3489-2015 standard, and the results are as follows: Figure 3As shown in the figure, the alloy grain coarsening degree of the entire metallographic interface reaches the first-class standard (>4μm grains ≤5) and the number of grains >3μm in any three adjacent fields is ≤1. Its coercive force HCP is 21.84kA / m, and the specific surface area of ​​the ground state is 2.51m 2 / g.

[0045] Example 2

[0046] Embodiment 2 provides a method for preparing ultrafine tungsten carbide, comprising the following steps:

[0047] Step 1: The oxygen index is 2.94, the specific surface particle size is 10 μm, and the loose ratio is 4.5 g / cm 3 The temperature of the six zones of blue tungsten is 600℃~620℃~650℃~700℃~890℃~920℃, and the hydrogen flow rate is 310m 3 / h and a rotation speed of 15 Hz to obtain tungsten powder. The specific surface area of ​​the ground tungsten powder is 5.1 m 2 / g~5.2m 2 / g;

[0048] Step 2, carbonizing the tungsten powder, adding carbon black in an amount of 6.18% of the total weight, mixing for 2 hours, and carbonizing at 1300° C. for 10 minutes to obtain tungsten carbide;

[0049] Step 3: Place tungsten carbide in a nitrogen gap with a gas flow rate of 200m 3 / h~250m 3 / h, grinding gas flow rate is 550m 3 / h~600m 3 / h, and the rotating speed of the classifying wheel is 3000rpm~3100rpm, and air flow crushing and classification are carried out to obtain ultrafine tungsten carbide.

[0050] Example 3

[0051] Embodiment 3 provides a method for preparing ultrafine tungsten carbide, comprising the following steps:

[0052] Step 1: The oxygen index is 2.97, the specific surface particle size is 35 μm, and the loose ratio is 2.5 g / cm 3 The temperature of the six zones of blue tungsten is 600℃~620℃~650℃~700℃~890℃~920℃, and the hydrogen flow rate is 350m 3 / h and a rotation speed of 25Hz to obtain tungsten powder. The specific surface area of ​​the ground tungsten powder is 5.4m 2 / g~5.5m 2 / g;

[0053] Step 2, carbonizing the tungsten powder, adding carbon black in an amount of 6.18% of the total weight, mixing for 5 hours, and carbonizing at 1500° C. for 15 minutes to obtain tungsten carbide;

[0054] Step 3: Place tungsten carbide in a nitrogen gap with a gas flow rate of 250m 3 / h~300m 3 / h, grinding gas flow rate is 500m 3 / h~550m 3 / h, and the rotating speed of the classifying wheel is 3900rpm~4000rpm, and air flow crushing and classification are carried out to obtain ultrafine tungsten carbide.

[0055] Example 4

[0056] Embodiment 4 provides a method for preparing ultrafine tungsten carbide, comprising the following steps:

[0057] Step 1: The oxygen index is 2.95, the specific surface particle size is 25 μm, and the loose ratio is 3.5 g / cm 3 The temperature of the six zones of blue tungsten is 600℃~620℃~650℃~700℃~890℃~920℃, and the hydrogen flow rate is 330m 3 / h and a rotation speed of 22Hz to obtain tungsten powder. The specific surface area of ​​the ground tungsten powder is 5.2m 2 / g~5.3m 2 / g;

[0058] Step 2, carbonizing the tungsten powder, adding carbon black in an amount of 6.18% of the total weight, mixing for 4 hours, and carbonizing at 1450° C. for 13 minutes to obtain tungsten carbide;

[0059] Step 3: Place tungsten carbide in a nitrogen gap with a gas flow rate of 250m 3 / h~280m 3 / h, grinding gas flow rate is 450m 3 / h~550m 3 / h, and the rotating speed of the classifying wheel is 3700rpm~3800rpm, and air flow crushing and classification are carried out to obtain ultrafine tungsten carbide.

[0060] Comparative Example

[0061] Comparative Example 1

[0062] Comparative Example 1 provides a method for preparing tungsten carbide, which differs from Example 1 in that the physical and chemical properties of the blue tungsten raw material are different, and the other steps are the same as Example 1, which are specifically as follows:

[0063] The physical and chemical properties of blue tungsten raw materials: oxygen index is 2.92, specific surface particle size is 20μm, and loose ratio is 3.0g / cm 3.

[0064] Comparative Example 2

[0065] Comparative Example 2 provides a method for preparing tungsten carbide, which differs from Example 1 in that the physical and chemical properties of the blue tungsten raw material are different, and the other steps are the same as Example 1, which are specifically as follows:

[0066] The physical and chemical properties of blue tungsten raw materials: oxygen index is 2.96, specific surface particle size is 5μm, loose ratio is 8g / cm 3 .

[0067] Comparative Example 3

[0068] Comparative Example 3 provides a method for preparing tungsten carbide, which is different from Example 1 in that the temperature of the reverse hydrogen reduction method in step 1 is a single temperature, that is, the temperature is 920°C, and the other steps are the same as Example 1.

[0069] Comparative Example 4

[0070] Comparative Example 4 provides a method for preparing tungsten carbide, which is different from Example 1 in that the temperature of the reverse hydrogen reduction method in step 1 is a three-zone temperature, i.e., the temperature of zone 1 is 600°C, the temperature of zone 2 is 700°C and the temperature of zone 3 is 920°C, and the other steps are the same as Example 1.

[0071] Comparative Example 5

[0072] Comparative Example 5 provides a method for preparing tungsten carbide, which differs from Example 1 in that the temperature of the reverse hydrogen reduction method in step 1 is a four-zone temperature, i.e., the temperature of zone 1 is 600°C, the temperature of zone 2 is 650°C, the temperature of zone 3 is 890°C and the temperature of zone 4 is 920°C, and the other steps are the same as Example 1.

[0073] Comparative Example 6

[0074] Comparative Example 6 provides a method for preparing tungsten carbide, which is different from Example 1 in that the hydrogen flow rate of the reverse hydrogen reduction method in step 1 is 300m 3 / h, and the other steps are the same as in Example 1.

[0075] Comparative Example 7

[0076] Comparative Example 7 provides a method for preparing tungsten carbide. The difference from Example 1 is that the hydrogen flow rate of the reverse hydrogen reduction method in step 1 is 280m 3 / h, and the other steps are the same as in Example 1.

[0077] Comparative Example 8

[0078] Comparative Example 8 provides a method for preparing tungsten carbide. The difference from Example 1 is that the hydrogen flow rate of the reverse hydrogen reduction method in step 1 is 250m 3 / h, and the other steps are the same as in Example 1.

[0079] Comparative Example 9

[0080] Comparative Example 9 provides a method for preparing tungsten carbide, which differs from Example 1 in that the hydrogen flow rate of the reverse hydrogen reduction method in step 1 is 200 m 3 / h, and the other steps are the same as in Example 1.

[0081] Comparative Example 10

[0082] Comparative Example 10 provides a method for preparing tungsten carbide. The difference from Example 1 is that the nitrogen gap gas flow rate in step 3 is 180m 3 / h, and the other steps are the same as in Example 1.

[0083] Comparative Example 11

[0084] Comparative Example 11 provides a method for preparing tungsten carbide. The difference from Example 1 is that the grinding gas flow rate in step 3 is 370m 3 / h, and the other steps are the same as in Example 1.

[0085] Comparative Example 12

[0086] Comparative Example 12 provides a method for preparing tungsten carbide, which is different from Example 1 in that the rotation speed of the classifying wheel in step 3 is 2500 rpm, and the other steps are the same as Example 1.

[0087] Performance Testing

[0088] The particle size distribution, metallographic structure analysis, coercive force HCP and ground specific surface area of ​​the tungsten carbides provided in Examples 1-6 and Comparative Examples 1-12 were tested, and the test results are shown in Table 1 below.

[0089] Table 1 Physical and chemical properties of tungsten carbide provided by Examples 1-6 and Comparative Examples 1-15

[0090]

[0091]

[0092] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing ultrafine tungsten carbide, characterized in that: The process includes: The blue tungsten is reduced by reverse hydrogen reduction to obtain tungsten powder; The tungsten powder is mixed with carbon uniformly, and carbonized at high temperature to obtain tungsten carbide; The tungsten carbide is crushed and air flow classified to obtain ultrafine tungsten carbide.

2. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that: The oxygen index of the blue tungsten is 2.94-2.97, the specific surface particle size is 10 μm-35 μm, and the loose ratio is 2.5 g / cm 3 ~4.5g / cm 3 .

3. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that: The blue tungsten is reduced by reverse hydrogen reduction method. The process includes: heating the blue tungsten at a temperature of 600°C to 950°C and a hydrogen flow rate of 310m 3 / h~350m 3 / h and a rotation speed of 15Hz to 25Hz to obtain tungsten powder.

4. The method for preparing ultrafine tungsten carbide according to claim 3, characterized in that: The temperature of the reverse hydrogen reduction method is divided into six reduction zones, including the following temperature zones: zone one temperature is 590°C to 610°C, zone two temperature is 610°C to 630°C, zone three temperature is 640°C to 660°C, zone four temperature is 690°C to 710°C, zone five temperature is 880°C to 900°C and zone six temperature is 890°C to 950°C.

5. The method for preparing ultrafine tungsten carbide according to claim 4, characterized in that: The six zone temperatures of the reverse hydrogen reduction method are: zone one temperature is 600°C, zone two temperature is 620°C, zone three temperature is 650°C, zone four temperature is 700°C, zone five temperature is 890°C and zone six temperature is 920°C.

6. The method for preparing ultrafine tungsten carbide according to claim 5, characterized in that: The ground specific surface area of ​​the tungsten powder is 5.0 m 2 / g~5.5m 2 / g.

7. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that: The carbon mixing time is 2h to 5h.

8. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that: The high temperature carbonization process has a temperature of 1300° C. to 1500° C. and a high temperature carbonization time of 10 min to 15 min.

9. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that: The air flow crushing and classification specifically includes the following process: when the gap air flow is 200m 3 / h~300m 3 / h, grinding gas flow rate is 400m 3 / h~600m 3 / h, and air flow crushing and dispersion are carried out under the conditions of the classifying wheel speed being 3000rpm~4000rpm.

10. Ultrafine tungsten carbide prepared by the method for preparing ultrafine tungsten carbide according to any one of claims 1 to 9.

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