Composite WC-Co powder material containing plate-shaped grain WC and coarse-grain plate-shaped WC crystal hard alloy prepared from composite WC-Co powder material

Abstract

The invention relates to the technical field of hard alloys, in particular to a composite WC-Co powder material containing plate-shaped crystal grains WC and a coarse-grain plate-shaped WC crystal hard alloy prepared from the composite WC-Co powder material, and the content of plate-shaped WC crystals in the powder material is larger than 75%; the average grain size is greater than or equal to 2.0 mu m, preferably 2.0 mu m to 6 mu m; and the length-diameter ratio of the crystal grains is greater than or equal to 3, preferably 3-6. The content of tabular crystals in the prepared composite WC-Co powder material containing the tabular crystal grains WC is larger than 75%; the content is far more than 20%. Hydroxycellulose is adopted to replace conventionally used carbon powder, the hydroxyl modified cellulose has a large number of-OH bonds and is adsorbed on the surfaces of W particles and the like, in the drying treatment process, the cellulose is curled to enable the W particles to be in close contact, steric hindrance is eliminated, and the W particles are promoted to merge and grow to generate granules; in the subsequent heat treatment process of the pellets, the element diffusion path is short, and thick plate-shaped tungsten carbide crystal grains can be obtained easily.

Description

Technical Field

[0001] The invention relates to the technical field of cemented carbides, and in particular to a composite WC-Co powder material containing plate-shaped WC grains and a coarse-grained plate-shaped WC crystal cemented carbide prepared therefrom. Background Art

[0002] Cemented carbide is widely used in cutting tools, mining tools and wear-resistant parts due to its good wear resistance. It is mainly composed of hard phase WC that provides wear resistance and bonding phase Co that provides toughness. The hardness and fracture toughness of cemented carbide are a pair of contradictions. Synergistically improving the hardness and fracture toughness of cemented carbide has always been the goal pursued by materials workers.

[0003] For products used in mining and rolling mills, cemented carbide is required to have better impact resistance and fracture toughness. This type of product often uses coarse-grained cemented carbide as the material. As the market's requirements for product service life become higher and higher, it is more and more urgent to coordinate the wear resistance and fracture toughness of coarse-grained cemented carbide materials. Prior art shows that by optimizing the grain morphology of cemented carbide, that is, introducing plate-like WC grains, the hardness and toughness of cemented carbide materials can be doubled. In particular, when the content of plate-like WC grains in cemented carbide exceeds 20%, this alloy will exhibit a series of excellent mechanical properties including high hardness, high toughness, excellent high-temperature creep and high-temperature fatigue strength. Therefore, the preparation of coarse-grained plate-like WC cemented carbide is an effective method.

[0004] WC with an average grain size of ≥2.0μm is generally called coarse-grained WC. At present, the preparation of existing coarse-grained plate-like WC cemented carbide mainly includes the following methods: First, coarse-grained plate-like WC cemented carbide is prepared by adding plate-like seeds, such as the Chinese patent CN101376931A that publishes "a method for preparing cemented carbide containing (large) plate-like tungsten carbide grains". This method uses high-energy ball milling to prepare a mixture by ball milling plate-like WC seeds and Co, and then hot pressing and sintering to obtain a mixed crystal structure composed of plate-like WC and conventional WC grains. It is prepared by adding plate-like WC single crystal particles as a variety, so that the cemented carbide contains large plate-like WC grains due to the dissolution of fine WC particles during the sintering process and the subsequent precipitation on the surface of the plate-like WC seeds. This method requires reliance on plate-like seeds. Second, by allowing WC nucleation and growth in the solid or liquid phase of the bonding phase to prepare a coarse-grained plate-shaped WC crystal cemented carbide, such as CN 114318040A, a rare earth-added cemented carbide and its preparation method, it is pointed out that the formation of WC grains mainly depends on the decomposition of η phase powder (such as Co3W3C and Co6W6C). Specifically, a small amount of η phase powder and an equal amount of carbon black are added to WC-Co powder, and a cemented carbide containing plate-shaped WC grains can be prepared by a traditional powder metallurgy process. However, this method has extremely high quality requirements for CoxWyCz powder, and it is necessary to prepare this powder in advance. It is essential to prepare this powder that the W powder needs to be flattened. In addition, the η phase often cannot be completely decomposed during the sintering process, and a W2C brittle phase may also be produced, which has an adverse effect on the overall performance of the alloy. In general, the process steps are long, the process is complex, the production cost is high, and the control difficulty is large. At the same time, the WC grains are uncontrollable during the η phase decomposition process, causing the WC grain size distribution to be difficult to meet the set requirements.

[0005] In summary, there are some technical difficulties in the preparation process of existing coarse-grained plate-like WC cemented carbide, such as the difficulty in forming plate-like WC grains, the high requirements of the preparation process and the difficulty in controlling the comprehensive properties of the alloy; moreover, the particle size of the prepared plate-like WC crystals is difficult to control and is uneven; furthermore, it is difficult to obtain large-size plate-like WC grains. Summary of the invention

[0006] In view of the problems existing in the preparation process of coarse-grained plate-shaped WC grain cemented carbide at present, the present invention provides a coarse-grained plate-shaped WC crystal cemented carbide, which has plate-shaped and coarse grains, good impact performance and is suitable for use in high-impact environments.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a composite WC-Co powder material containing plate-like WC grains, wherein the content of plate-like WC crystals in the powder material is greater than 75%; the average grain size is ≥2.0 μm; and the grain aspect ratio is ≥3.

[0009] As a specific embodiment of the present invention, the content of plate-like WC crystals in the powder material is greater than 75%; the average grain size is 2.0 μm-6 μm; and the grain aspect ratio is 3-6.

[0010] The composite WC-Co powder material containing plate-like crystal grains WC prepared by the present invention has a grain size of ≥2.0 μm, meeting the requirement of coarse crystals, an aspect ratio of ≥3, meeting the requirement of plate-like crystals, and a plate-like crystal content of more than 75%; the content far exceeds 20%.

[0011] As a specific embodiment of the present invention, the atomic ratio of W:C in the coarse-grained plate-like WC cemented carbide is 1:0.8-1.2.

[0012] The second aspect of the present invention provides a method for preparing a composite WC-Co powder material containing plate-like grains of WC, comprising obtaining a mixture of W powder, Co powder and hydroxy-modified cellulose, wet grinding, drying, heat treatment, and pulverizing and granulating.

[0013] In the present invention, hydroxy cellulose is used to replace conventional carbon powder. Hydroxyl modified cellulose has a large number of -OH bonds, which are adsorbed on the surface of W particles, etc. During the drying process, the cellulose curls up to make the W particles closely contact each other, eliminating the steric hindrance and promoting the merger and growth of W particles to form agglomerates. In the subsequent heat treatment process, the agglomerates have a short element diffusion path, which is conducive to obtaining coarse plate-like tungsten carbide grains.

[0014] As a specific embodiment of the present invention, the particle size of the W powder is 0.2-0.8 μm.

[0015] The present invention adopts W powder with finer particle size to prepare composite WC-Co powder material. W powder with this particle size has high activity and is conducive to the formation of coarse plate-like WC in the subsequent calcination process. If W powder with a coarser particle size of more than 0.8 microns is used, the plate-like WC will be difficult to grow thick due to insufficient activity. If W powder with a finer particle size of less than 0.2 microns is used, the cost is high and it is not easy to crush after heat treatment.

[0016] As a specific embodiment of the present invention, the mass percentage of W powder in the mixture is 75-90wt%; the mass percentage of Co powder in the mixture is 6-15wt%; the mass percentage of hydroxyl modified cellulose in terms of C in the mixture is 2-8wt%, preferably 5-6wt%.

[0017] As a specific embodiment of the present invention, the mass percentage of W powder in the raw material mixture is 79.8-88.2wt%.

[0018] As a specific embodiment of the present invention, the cellulose includes at least one of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose and carboxymethyl hydroxyethyl cellulose.

[0019] As a specific embodiment of the present invention, the cellulose includes hydroxyethyl cellulose and / or hydroxypropyl cellulose.

[0020] As a specific embodiment of the present invention, the conditions for wet grinding include: a ball-to-material ratio of 2-10:1, and a time of 40 to 100 hours; preferably, a ball-to-material ratio of 3-8:1, and a time of 50 to 100 hours.

[0021] As a specific embodiment of the present invention, the drying is carried out by spray drying.

[0022] As a specific embodiment of the present invention, the heat treatment conditions include: 1000-1400° C. vacuum insulation for 2-8 hours; preferably, 1100-1300° C. vacuum insulation for 3-5 hours.

[0023] The invention adopts wet grinding-spray drying granulation to prepare W+Co+C granules (C is derived from hydroxy-modified cellulose), wherein wet grinding allows the three elements to be fully mixed and evenly mixed; spray drying is conducive to forming granules and ensuring the uniformity of the three components; after heat treatment, the composite WC-Co powder containing plate-like WC grains can be obtained through crushing and screening.

[0024] In a third aspect, the present invention provides a coarse-grained plate-like WC crystal cemented carbide, wherein the content of plate-like WC crystals in the coarse-grained plate-like WC crystal cemented carbide is greater than 80%; the average grain size is ≥2.4 μm; and the grain aspect ratio is ≥3.

[0025] As a specific embodiment of the present invention, the average grain size of the plate-like WC crystals is 2.4 μm-10 μm.

[0026] As a specific embodiment of the present invention, the aspect ratio of the plate-like WC crystal is 3-10, for example, the aspect ratio of the grain can be 3, 4, 5, 6, 7, 8, 9, 10 or a range thereof.

[0027] A fourth aspect of the present invention provides a method for preparing coarse-grained plate-like WC cemented carbide.

[0028] The method for preparing the coarse-grained plate-shaped WC-crystal cemented carbide provided by the present invention can adopt the existing cemented carbide powder metallurgy preparation method.

[0029] As a specific embodiment of the present invention, the method for preparing the coarse-grained plate-like WC cemented carbide is prepared by using the above-mentioned composite WC-Co powder material containing plate-like grains of WC;

[0030] As a specific embodiment of the present invention, the preparation method of the coarse-grained plate-like WC cemented carbide comprises:

[0031] The method comprises the following steps: subjecting the composite WC-Co powder material to wet grinding II, pressing treatment and sintering treatment in sequence.

[0032] As a specific embodiment of the present invention, the conditions of wet grinding II include: a ball-to-material ratio of 2-4:1, and a time of 50 to 90 hours.

[0033] As a specific embodiment of the present invention, the sintering treatment conditions include 1450-1550°C.

[0034] The fifth aspect of the present invention is to protect the use of the coarse-grained plate-shaped WC cemented carbide prepared by the above method in cutting tools, mining tools or wear-resistant parts.

[0035] Beneficial effects of the present invention

[0036] (1) Hydroxyl cellulose is used to replace the conventional carbon powder. Hydroxyl modified cellulose has a large number of -OH bonds, which are adsorbed on the surface of W particles. During the drying process, the cellulose curls up to make the W particles closely contact each other, eliminating the steric hindrance and promoting the merger and growth of W particles to form agglomerates. In the subsequent heat treatment process, the element diffusion path of the agglomerate is short, which is conducive to obtaining coarse plate-like tungsten carbide grains.

[0037] (2) Using finer-grained W powder, which has high activity and helps the formation of coarse-grained plate-like WC during the subsequent calcination process;

[0038] (3) The present invention adopts wet grinding-dry granulation to prepare W+Co+C granules, and wet grinding allows the three elements to be fully mixed and uniform.

[0039] (4) The plate-like crystals prepared by the existing methods generally have small particles, which have limited effects on improving the impact toughness of the material. Compared with the existing technology, the plate-like crystals prepared by the present invention have coarse particles, and the prepared material has good impact effect, which is suitable for use in high-impact environments. In addition, the present method does not require flattening of W powder, and the plate-like WC in the obtained cemented carbide is randomly distributed, which is more conducive to the uniformity of product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The microstructure of W+Co+C pellets after drying and granulation in Example 1 (50 times);

[0041] Figure 2This is the microstructure of the W+Co+C pellet after calcination in Example 1 (500 times);

[0042] Figure 3 The microstructure of the plate-like WC grains in the pellets after calcination in Example 1 (3000 times);

[0043] Figure 4 The microstructure of the coarse-grained plate-shaped WC grain cemented carbide provided in Example 1 (1500 times);

[0044] Figure 5 The microstructure diagram of the ordinary coarse-grained cemented carbide provided for Comparative Example 1 (1500 times). DETAILED DESCRIPTION

[0045] In order to make the present invention more easily understood, the present invention will be described in detail below in conjunction with embodiments. These embodiments are only for illustration and are not intended to limit the application scope of the present invention.

[0046] Example 1

[0047] A method for preparing coarse-grained plate-shaped WC grain cemented carbide comprises the following steps:

[0048] (1) 88.2 kg of W powder with a particle size of 0.2 μm, 6 kg of Co powder, and 5.8 g (based on carbon content) of hydroxyethyl cellulose were mixed;

[0049] (2) After mixing, the pellets were wet-milled at a ratio of 6:1 and alcohol as the grinding medium for 96 hours, and then spray-dried and granulated at 90-100°C and a spray pressure of 1.1 MPa;

[0050] (3) calcining the particles at 1100° C. under vacuum for 5 h to form plate-like WC particles; after crushing through a 200-mesh sieve, composite WC-Co powder containing plate-like WC particles was obtained;

[0051] (4) The composite WC-Co powder containing plate-like WC grains of step (3) is used as a raw material, with a ball-to-material ratio of 3:1, wet-milled, pressed, and then sintered at 1520° C. to obtain a coarse-grained plate-like WC grain cemented carbide.

[0052] The coarse-grained plate-like WC grain cemented carbide has a Co binder phase content of 6 wt %.

[0053] Example 2

[0054] A method for preparing coarse-grained plate-shaped WC grain cemented carbide comprises the following steps:

[0055] (1) 82.1 kg of W powder with a particle size of 0.5 μm, 12.5 kg of Co powder, and 5.4 g (based on carbon content) of hydroxyethyl cellulose were mixed;

[0056] (2) After mixing, the pellets were wet-milled at a ratio of 6:1 and alcohol as the grinding medium for 72 hours, and then spray-dried and granulated at 90-100°C and a spray pressure of 1.1 MPa;

[0057] (3) the particles are kept in vacuum at 1200° C. for 4 h to form plate-like WC particles; after being crushed through a 200-mesh sieve, composite WC-Co powder containing plate-like WC particles is obtained;

[0058] (4) Using the composite WC-Co powder containing plate-like WC grains of step (3) as a raw material, the existing cemented carbide powder metallurgy preparation method is adopted, according to the required target alloy composition and carbon content, wet grinding under the condition of a ball-to-material ratio of 3:1, pressing, and then sintering at 1480° C. to obtain a coarse-grained plate-like WC grain cemented carbide.

[0059] The coarse-grained plate-like WC grain cemented carbide has a Co binder phase content of 12.5 wt %.

[0060] Example 3

[0061] A method for preparing coarse-grained plate-shaped WC grain cemented carbide comprises the following steps:

[0062] (1) 79.8 kg of W powder with a particle size of 0.8 μm, 15 kg of Co powder and 5.2 g (based on carbon content) of hydroxyethyl cellulose were mixed;

[0063] (2) After mixing, the pellets were wet-milled at a ratio of 6:1 and alcohol as the grinding medium for 48 hours, and then spray-dried and granulated at 90-100°C and a spray pressure of 1.1 MPa;

[0064] (3) calcining the particles at 1300° C. under vacuum for 3 h to form plate-like WC particles; after crushing through a 200-mesh sieve, composite WC-Co powder containing plate-like WC particles was obtained;

[0065] (4) Using the composite WC-Co powder containing plate-like WC grains of step (3) as a raw material, the existing cemented carbide powder metallurgy preparation method is adopted, according to the required target alloy composition and carbon content, wet grinding under the condition of a ball-to-powder ratio of 3:1, pressing, and then sintering at 1450° C. to obtain a coarse-grained plate-like WC grain cemented carbide.

[0066] The coarse-grained plate-like WC grain cemented carbide has a Co binder phase content of 15 wt %.

[0067] Comparative Example 1

[0068] 94 kg WC powder (commercially purchased) with a particle size of 10 μm and 6 kg Co powder were wet-milled at a ball-to-material ratio of 3:1, pressed, and then sintered at 1520° C. to obtain a cemented carbide with a Co binder phase content of 6 wt%.

[0069] Comparative Example 2

[0070] Same as Example 2, except that carbon powder was added instead of cellulose, and the prepared WC powder was the same as that in Example 2.

[0071] Comparative Example 3

[0072] Similar to Example 2, step (3) does not include the vacuum insulation condition at 1200° C. for 4 h.

[0073] Implementation effect example

[0074] 1. Plate-shaped WC grain content test

[0075] (1) Metallographic examination was performed using a German Leica DMI5000M optical microscope. The microstructure of the cemented carbide prepared in Example 1 and Comparative Example 1 was examined, and the microstructure diagrams were as follows: Figure 4 and Figure 5 shown.

[0076] pass Figure 3 , Figure 4 The comparison shows that after the composite WC-Co powder material is prepared into cemented carbide, the plate-like WC grains will become larger and the aspect ratio will remain the same.

[0077] according to Figure 4 , Figure 5 It can be seen that the coarse-grained plate-like WC grain cemented carbide provided by the present invention has plate-like WC grains compared with the cemented carbide provided by Comparative Example 1.

[0078] (2) The content of plate-like WC grains was tested on the cemented carbides prepared in Example 1 and Comparative Example 1: WC grains with an aspect ratio greater than 3 were plate-like WC grains, and the content was measured using WC grain statistical analysis software Image J.

[0079] Table 1 Property analysis of composite WC-Co powder materials prepared in various embodiments and comparative examples

[0080]

[0081] Table 2 Property analysis of cemented carbides prepared in various embodiments and comparative examples

[0082]

[0083] The plate-like WC grain content in the table refers to the mass ratio of the plate-like WC grains to the whole WC.

[0084] It can be seen from Table 1 and Table 2 that after the powder material of the present application is used to prepare cemented carbide, the proportion of plate-like WC grains increases and their size also increases.

[0085] The difference between Comparative Example 1 and Example 1 is the source of WC powder. It can be seen from the results in Table 2 that the cemented carbide prepared by the composite WC-Co powder material prepared by the present invention contains plate-like WC grains, and the content of the plate-like WC grains can reach 95%; while the content of the plate-like WC grains in the cemented carbide prepared by commercially available WC powder is basically negligible.

[0086] The difference between Comparative Example 2 and Example 2 is that the source of the carbon powder is different. From the results in Table 2, it can be found that the present invention uses cellulose to replace the carbon powder to obtain plate-like WC grains.

[0087] The difference between Comparative Example 3 and Example 2 is that no heat treatment is performed during the preparation of the composite WC-Co powder material. The cemented carbide prepared using the composite WC-Co powder material that has not been heat treated cannot obtain plate-shaped WC grains with an aspect ratio greater than 3.

[0088] Any numerical value mentioned in the present invention includes all values ​​that increase by one unit each time from the lowest value to the highest value if there is only an interval of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In the present invention, in a similar manner, all possible combinations of numerical values ​​between the listed lowest and highest values ​​are considered to have been disclosed.

[0089] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A composite WC-Co powder material containing plate-like grains of WC, characterized in that: The content of plate-like WC crystals in the powder material is greater than 75%; the average grain size is ≥2.0 μm, preferably 2.0 μm-6 μm; and the grain aspect ratio is ≥3, preferably 3-6.

2. The composite WC-Co powder material containing plate-like grains of WC according to claim 1, characterized in that: The atomic ratio of W:C in the composite WC-Co powder material is 1:0.8-1.

2.

3. A method for preparing a composite WC-Co powder material containing plate-like grains of WC according to claim 1 or 2, characterized in that: A mixture of W powder, Co powder and hydroxy-modified cellulose is obtained, wet-ground, dried, heat-treated, crushed and granulated to obtain the product.

4. The preparation method according to claim 3, characterized in that: The W powder particle size is 0.2-0.8 μm; And / or, the mass percentage of W powder in the mixture is 75-90wt%; the mass percentage of Co powder in the mixture is 6-15wt%; the mass percentage of hydroxyl-modified cellulose in terms of C in the mixture is 2-8wt%, preferably 5-6wt%.

5. The preparation method according to claim 3 or 4, characterized in that: The hydroxy-modified cellulose includes at least one of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl hydroxyethyl cellulose; More preferably, the hydroxy-modified cellulose includes hydroxyethyl cellulose and / or hydroxypropyl cellulose.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The conditions of wet grinding I include: a ball-to-material ratio of 2-10:1, and a time of 40 to 100 hours; preferably, a ball-to-material ratio of 3-8:1, and a time of 50 to 100 hours; And / or, the drying is carried out by spray drying; The heat treatment conditions include: 1000-1400° C. vacuum insulation for 2-8 hours; preferably, the heat treatment conditions include: 1100-1300° C. vacuum insulation for 3-5 hours.

7. A coarse-grained plate-shaped WC cemented carbide, characterized in that: The content of plate-like WC crystals in the coarse-grained plate-like WC crystal cemented carbide is greater than 80%; the average grain size is ≥2.4 μm, preferably 2.4 μm-10 μm; and the grain aspect ratio is ≥3, preferably 3-10.

8. A method for preparing coarse-grained plate-shaped WC cemented carbide, characterized in that: Prepared by using the composite WC-Co powder material containing plate-shaped grains of WC as described in claim 6 or 7; Preferably, the process comprises: subjecting the composite WC-Co powder material to wet grinding II, pressing treatment, and sintering treatment in sequence.

9. The method for preparing coarse-grained plate-shaped WC cemented carbide according to claim 8, characterized in that: The conditions for wet grinding II include: ball-to-material ratio 2-4:1, time 50-90h; And / or, the sintering process conditions include 1450-1550°C.

10. Use of the composite WC-Co powder material containing plate-shaped WC grains according to claim 1 or 2 or the coarse-grained plate-shaped WC cemented carbide according to claim 7 in cutting tools, mining tools or wear-resistant parts.

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