Medium-coarse tungsten carbide and preparation method thereof

Abstract

The invention belongs to the technical field of powder metallurgy, and particularly relates to high-performance tungsten carbide and a preparation method thereof. A preparation method of medium-coarse tungsten carbide comprises the following steps that tungsten oxide is subjected to high-temperature reduction through a reverse hydrogen reduction method, and tungsten powder is obtained; and the tungsten powder is subjected to carbon blending, uniform mixing and high-temperature carbonization in a reducing atmosphere, a product is pre-crushed and then subjected to airflow crushing, and the tungsten carbide is obtained. According to the preparation method of the medium-coarse tungsten carbide, the particle size of the prepared tungsten carbide is 1-3 microns, the total carbon content is 6.12-6.18%, the combined carbon content is larger than or equal to 6.10%, the free carbon content is smaller than or equal to 0.06%, the oxygen content is smaller than or equal to 0.12%, and the impurity content is smaller than 0.5%; the particle size distribution is narrow, the particles are uniform, and the performance of the tungsten carbide powder is greatly improved.

Description

Technical Field

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

[0002] In the cemented carbide industry, tungsten carbide particles with a particle size of 1 to 3 μm are called coarse-grained tungsten carbide. Because of their high hardness, good wear resistance and excellent compressive strength, they are widely used in cutting tools, cemented carbide materials, mining tools and other fields. Compared with ultrafine tungsten carbide, this type of coarse-grained tungsten carbide has stronger bending strength and higher impact toughness, especially in application scenarios that require impact resistance and high strength. Therefore, tungsten carbide particles of 1 to 3 μm occupy an important position in cemented carbide production.

[0003] The cemented carbide prepared by medium-grained and coarse-grained tungsten carbide produced by traditional technology has good strength and impact toughness, but it is difficult to meet the needs of high-strength and high-toughness tools. In addition, in the process of producing 1-3μm coarse-grained tungsten carbide, although the process is relatively mature, it still faces the problem of how to further improve the uniformity of particles and combined carbon. If the tungsten carbide powder particles are unevenly distributed, the local grains grow abnormally or coarse grains aggregate during the sintering process of the cemented carbide, and if the combined carbon of the tungsten carbide powder is low, the local carbon balance of the cemented carbide will be affected. Coarse inclusions, coarse grain aggregation, or local carbon imbalance in cemented carbide will reduce the strength and impact toughness of cemented carbide, and may even cause the alloy to fail during use. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned shortcomings and provide a medium-coarse tungsten carbide and a preparation method thereof.

[0005] In the first aspect, a method for preparing medium-coarse tungsten carbide adopts the following technical scheme:

[0006] A method for preparing medium-coarse tungsten carbide comprises the following steps:

[0007] The tungsten oxide is reduced by reverse hydrogen reduction to obtain tungsten powder;

[0008] The tungsten powder is carbonized, mixed evenly, carbonized at high temperature in a reducing atmosphere, and the product is subjected to air flow milling and screening to obtain the tungsten carbide.

[0009] Furthermore, the tungsten oxide is blue tungsten or yellow tungsten, or blue tungsten or yellow tungsten doped with alkali metal;

[0010] The oxygen index of the blue tungsten is 2.90-2.98, and the specific surface area is 6m 2 / g~18m 2 / g, the particle size of Fisher is 10μm~35μm;

[0011] The specific surface area of ​​the yellow tungsten is 4m 2 / g~16m 2 / g, the particle size of Fisher is 12μm~40μm;

[0012] The alkali metal doped in the blue tungsten or yellow tungsten is hydroxide, carbonate, bicarbonate, oxalate or tungstate of lithium, sodium or potassium, which may be one of them or a mixture of several thereof, with a content of 0.0010% to 0.10%.

[0013] Furthermore, the tungsten oxide is reduced at high temperature by reverse hydrogen reduction method, which specifically includes the following process: the tungsten oxide is reduced at a temperature of 750°C to 1100°C and a hydrogen flow rate of 30m 3 / h~60m 3 / h, and the boat loading amount is 0.30kg / boat to 1kg / boat, and high-temperature reduction is performed for 2.5h to 4h to obtain the tungsten powder.

[0014] Furthermore, the temperature of the reverse hydrogen reduction method is divided into three reduction temperature zones, including the following temperature zones: zone one temperature is 750°C to 850°C, zone two temperature is 850°C to 950°C and zone three temperature is 950°C to 1050°C.

[0015] Furthermore, the tungsten powder has a Fisher particle size of 0.9 μm to 2.8 μm.

[0016] Furthermore, the carbon mixing time is 1 hour to 3 hours.

[0017] Furthermore, the high temperature carbonization process is carried out at a temperature of 1800°C to 2300°C under a reducing atmosphere, the reducing atmosphere is hydrogen, carbon monoxide or methane, and the carbonization time is 2h to 4h.

[0018] Furthermore, the air flow mill screening process specifically includes: air flow crushing under the action of dry gas at a pressure of 0.5MPa to 1.0MPa.

[0019] Furthermore, the dry gas is dry nitrogen or dry compressed air (water content is not more than 0.5%) or a mixed gas of dry nitrogen and dry compressed air (water content is not more than 0.5%).

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

[0021] A tungsten carbide prepared by the method for preparing tungsten carbide as described in any one of the above items.

[0022] Beneficial effects of the present invention:

[0023] The invention provides a method for preparing medium-coarse tungsten carbide. The prepared tungsten carbide has a particle size of 1 to 3 μm, a total carbon content of 6.12-6.18%, a combined carbon content of ≥6.10%, a free carbon content of ≤0.06%, an oxygen content of ≤0.12%, and an impurity content of <0.5%. The particle size distribution is narrow, the particle uniformity is excellent, and the quality of the tungsten carbide powder is greatly improved. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present application will be further described in detail below. The described embodiments should not be regarded as limiting the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Example

[0032] Example 1

[0033] Embodiment 1 provides a method for preparing medium-coarse tungsten carbide, comprising the following steps:

[0034] Step 1: prepare the granular material with oxygen index of 2.90 and specific surface area of ​​6 m 2 / g, the temperature of blue tungsten with a Fisher particle size of 10μm in the three zones is 750℃ in the first zone, 850℃ in the second zone, 950℃ in the third zone, and the hydrogen flow rate is 60m 3 / h, high temperature reduction was carried out, the boat loading was 0.30kg / boat, and the reduction time was 2.5h, to obtain tungsten powder, the ground tungsten powder had a Fischer-Marshal particle size of 0.9μm;

[0035] Step 2, carbonizing the tungsten powder with a mass fraction of 6.15 wt.%, mixing for 1 hour, and carbonizing for 2 hours at a temperature of 1800° C. in a hydrogen reducing atmosphere to obtain tungsten carbide;

[0036] Step 3, air flow crushing the tungsten carbide, the air flow crushing equipment is introduced with a mixed gas of dry nitrogen and dry compressed air, the ratio of dry nitrogen to dry compressed air is 8:1, the pressure is 1.0 MPa, and the air flow crushing time is 1.5 hours, so as to obtain tungsten carbide.

[0037] Example 2

[0038] Embodiment 2 provides a method for preparing medium-coarse tungsten carbide, comprising the following steps:

[0039] Step 1: prepare the granular material with oxygen index of 2.98 and specific surface area of ​​18 m 2 / g, the temperature of blue tungsten with a particle size of 35μm in the three zones is 850℃ in the first zone, 950℃ in the second zone, 1050℃ in the third zone, and the hydrogen flow rate is 30m 3 / h, high temperature reduction was carried out, the boat loading was 1kg / boat, and the reduction time was 4h, to obtain tungsten powder, the ground tungsten powder had a Fischer-Matz particle size of 2.8μm;

[0040] Step 2, carbonizing the tungsten powder with a mass fraction of 6.18 wt.%, mixing for 3 h, and carbonizing for 4 h at a temperature of 2300° C. in a hydrogen reducing atmosphere to obtain tungsten carbide;

[0041] Step 3, the tungsten carbide is subjected to air flow crushing, and a mixed gas of dry nitrogen and dry compressed air is introduced into the air flow crushing equipment, the ratio of dry nitrogen to dry compressed air is 8:1, the pressure is 0.5MPa, and the air flow milling time is 40min, so as to obtain tungsten carbide.

[0042] Example 3

[0043] Embodiment 3 provides a method for preparing medium-coarse tungsten carbide, comprising the following steps:

[0044] Step 1: prepare the granular material with oxygen index of 2.94 and specific surface area of ​​12 m 2 / g, the temperature of blue tungsten with a Fisher particle size of 23μm in the three zones is 800℃ in the first zone, 900℃ in the second zone, 1000℃ in the third zone, and the hydrogen flow rate is 45m 3 / h, high temperature reduction was carried out, the boat loading was 0.6kg / boat, and the reduction time was 3h, to obtain tungsten powder, the ground tungsten powder had a Fischer-Matz particle size of 2μm;

[0045] Step 2, carbonizing the tungsten powder with a mass fraction of 6.16 wt.%, mixing for 2 h, and carbonizing for 8 h at a temperature of 2100° C. in a hydrogen reducing atmosphere to obtain tungsten carbide;

[0046] Step 3, the tungsten carbide is subjected to air flow crushing, and a mixed gas of dry nitrogen and dry compressed air is introduced into the air flow crushing equipment, the ratio of nitrogen to compressed air is 8:1, the pressure is 0.8MPa, and the air flow milling time is 1h, so as to obtain tungsten carbide.

[0047] Example 4

[0048] Embodiment 4 provides a method for preparing medium-coarse tungsten carbide, comprising the following steps:

[0049] Step 1: The oxygen index is 3.0 and the specific surface area is 4m 2 / g, and the Feldspar particle size is 12μm. The temperatures of the three zones of yellow tungsten are 750℃ for the first zone, 850℃ for the second zone, and 950℃ for the third zone. The hydrogen flow rate is 60m 3 / h, high temperature reduction was carried out, the boat loading was 0.30kg / boat, and the reduction time was 2.5h, to obtain tungsten powder, the ground tungsten powder had a Fischer-Marshal particle size of 0.9μm;

[0050] Step 2, carbonizing the tungsten powder with a mass fraction of 6.15 wt.%, mixing for 1 hour, and carbonizing for 2 hours at a temperature of 1800° C. in a hydrogen reducing atmosphere to obtain tungsten carbide;

[0051] Step 3, air flow crushing the tungsten carbide, the air flow crushing equipment is introduced with a mixed gas of dry nitrogen and dry compressed air, the ratio of dry nitrogen to dry compressed air is 8:1, the pressure is 1.0 MPa, and the air flow crushing time is 1.5 hours, so as to obtain tungsten carbide.

[0052] Example 5

[0053] Embodiment 5 provides a method for preparing medium-coarse tungsten carbide, comprising the following steps:

[0054] Step 1: The oxygen index is 3.0 and the specific surface area is 16m 2 / g, the temperature of yellow tungsten with a Fisher particle size of 40μm in the three zones is 850℃ in the first zone, 950℃ in the second zone, and 1050℃ in the third zone, and the hydrogen flow rate is 30m 3 / h, high temperature reduction was carried out, the boat loading was 1kg / boat, and the reduction time was 4h, to obtain tungsten powder, the ground tungsten powder had a Fischer-Matz particle size of 2.8μm;

[0055] Step 2, carbonizing the tungsten powder with a mass fraction of 6.18 wt.%, mixing for 3 h, and carbonizing for 4 h at a temperature of 2300° C. in a hydrogen reducing atmosphere to obtain tungsten carbide;

[0056] Step 3, the tungsten carbide is subjected to air flow crushing, and a mixed gas of dry nitrogen and dry compressed air is introduced into the air flow crushing equipment, the ratio of dry nitrogen to dry compressed air is 8:1, the pressure is 0.5MPa, and the air flow milling time is 40min, so as to obtain tungsten carbide.

[0057] Comparative Example

[0058] Comparative Example 1

[0059] Comparative Example 1 provides a method for preparing medium-coarse tungsten carbide, which is different from Example 1 in that the blue tungsten reduction temperature in step 1 adopts a single temperature of 750°C, and the other steps are the same as Example 1.

[0060] Comparative Example 2

[0061] Comparative Example 2 provides a method for preparing medium-coarse tungsten carbide, which differs from Example 1 in that the blue tungsten reduction temperature in step 1 adopts a single temperature of 900°C, and the other steps are the same as Example 1.

[0062] Comparative Example 3

[0063] Comparative Example 3 provides a method for preparing medium-coarse tungsten carbide, which is different from Example 1 in that the blue tungsten reduction temperature in step 1 adopts a single temperature of 1050°C, and the other steps are the same as Example 1.

[0064] Comparative Example 4

[0065] Comparative Example 4 provides a method for preparing medium-coarse tungsten carbide. The difference from Example 1 is that the hydrogen flow rate in step 1 is 25m 3 / h, and the other steps are the same as in Example 1.

[0066] Comparative Example 5

[0067] Comparative Example 5 provides a method for preparing medium-coarse tungsten carbide, which is different from Example 1 in that the carbon mixing time in step 2 is 0.5 h, and the other steps are the same as Example 1.

[0068] Comparative Example 6

[0069] Comparative Example 6 provides a method for preparing medium-coarse tungsten carbide, which is different from Example 1 in that the carbonization temperature in step 2 is 1600° C., and the other steps are the same as Example 1.

[0070] Comparative Example 7

[0071] Comparative Example 7 provides a method for preparing medium-coarse tungsten carbide, which differs from Example 1 in that the carbonization time in step 2 is 1 hour, and the other steps are the same as Example 1.

[0072] Comparative Example 8

[0073] Comparative Example 8 provides a method for preparing medium-coarse tungsten carbide, which differs from Example 1 in that the air flow milling time in step 3 is 20 minutes, and the other steps are the same as Example 1.

[0074] Performance Testing

[0075] The particle size distribution, free carbon, oxygen content and impurity content of the tungsten carbides provided in Examples 1-5 and Comparative Examples 1-8 were tested, and the test results are shown in Table 1 below.

[0076] Table 1 Physical and chemical properties of tungsten carbide provided by Examples 1-5 and Comparative Examples 1-8

[0077]

[0078] It can be seen from the data in Table 1 that the comparative sample is not as good as the example in terms of particle size, oxygen content, free carbon content and impurity content. The particle size distribution of the comparative sample is uneven, ranging from 0.8 μm to 9.0 μm. Such large particle size fluctuations may lead to unstable performance of the material in use, especially in applications with high requirements for mechanical strength and wear resistance.

[0079] The oxygen content of the comparative samples is relatively high, and some data even reach 0.3%, indicating that the oxidation degree of the material is relatively high. This high oxygen content may affect the material's antioxidant properties, especially in application environments that require high temperature or corrosion resistance, where a higher oxygen content will reduce the material's stability.

[0080] The free carbon content of the comparative samples is relatively high, with some samples reaching 0.28%. Excessive free carbon content may lead to a decrease in the physical properties of the material, especially hardness and toughness. In contrast, the free carbon content of the embodiment is controlled below 0.05%, ensuring the purity of the material and the stability of its performance.

[0081] The impurity content in the comparative samples also showed obvious disadvantages, with the impurity content of some samples reaching 3.5%. The increase in impurity content usually affects the mechanical properties of the material, increases brittleness, and reduces wear resistance and corrosion resistance. The stricter control of the impurity content in the examples further demonstrates the advantages of the material in purity and quality.

[0082] In summary, the larger particle size distribution, high oxygen content, high free carbon content and high impurity content of the comparative example all show that its quality control is poor, resulting in large fluctuations in the performance of the material, which is not as stable and reliable as the embodiment.

[0083] 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 medium-coarse tungsten carbide, characterized in that: The process includes: The tungsten oxide is reduced at high temperature by reverse hydrogen reduction method to obtain tungsten powder; The tungsten powder is carbonized, mixed evenly, and carbonized at high temperature in a reducing atmosphere. The product is pre-crushed and then air flow crushed to obtain the tungsten carbide.

2. The method for preparing medium-coarse tungsten carbide according to claim 1, characterized in that: The tungsten oxide is blue tungsten or yellow tungsten, or blue tungsten or yellow tungsten doped with alkali metal; The oxygen index of the blue tungsten is 2.90-2.98, and the specific surface area is 6m 2 / g~18m 2 / g, the particle size of Fisher is 10μm~35μm; The specific surface area of ​​the yellow tungsten is 4m 2 / g~16m 2 / g, the particle size of Fisher is 12μm~40μm; The alkali metal doped in the blue tungsten or yellow tungsten is hydroxide, carbonate, bicarbonate, oxalate or tungstate of lithium, sodium or potassium, which may be one of them or a mixture of several thereof, with a content of 0.0010% to 0.10%.

3. The method for preparing medium-coarse tungsten carbide according to claim 1, characterized in that: The tungsten oxide is reduced at high temperature by reverse hydrogen reduction method, which specifically includes the following process: the tungsten oxide is reduced at a temperature of 750°C to 1100°C and a hydrogen flow rate of 30m 3 / h~60m 3 / h, and the boat loading amount is 0.30kg / boat to 1kg / boat, and high-temperature reduction is performed for 2.5h to 4h to obtain the tungsten powder.

4. The method for preparing medium-coarse tungsten carbide according to claim 3, characterized in that: The temperature of the reverse hydrogen reduction method is divided into three reduction zones, including the following temperature zones: zone one temperature is 750°C to 850°C, zone two temperature is 850°C to 850°C and zone three temperature is 950°C to 1050°C.

5. The method for preparing medium-coarse tungsten carbide according to claim 4, characterized in that: The tungsten powder has a Fisher particle size of 0.9 μm to 2.8 μm.

6. The method for preparing medium-coarse tungsten carbide according to claim 1, characterized in that: The carbon mixing time is 1 hour to 3 hours.

7. The method for preparing medium-coarse tungsten carbide according to claim 1, characterized in that: The high temperature carbonization process is carried out at a temperature of 1800°C to 2300°C in a reducing atmosphere, the reducing atmosphere being hydrogen, carbon monoxide or methane, and the carbonization time being 2h to 4h.

8. The method for preparing medium-coarse tungsten carbide according to claim 1, characterized in that: The air flow mill screening process specifically includes: air flow crushing under the action of dry gas (water content is not more than 0.5%) with a pressure of 0.5MPa to 1.0MPa.

9. The method for preparing medium-coarse tungsten carbide according to claim 8, characterized in that: The dry gas is dry nitrogen or dry compressed air (water content is not more than 0.5%) or a mixed gas of dry nitrogen and dry compressed air (water content is not more than 0.5%).

10. Tungsten carbide obtained by the method for preparing tungsten carbide according to any one of claims 1 to 9.

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