Preparation method of sub-fine grain WC hard alloy

Abstract

The invention discloses a preparation method of a sub-fine grain WC hard alloy, which comprises the following steps: directly adopting fine particle or sub-fine particle W powder as a raw material, wet-grinding and mixing with Co / Ni powder, C black and an inhibitor to prepare a mixture, molding the mixture, and completing the W powder carbonization and alloy sintering densification process in one step in a low-pressure sintering furnace. According to the method, the working procedure steps of independently carrying out carbon blending mixing and carbonization on the W powder are reduced, the alloy production technological process is greatly shortened, the production cost is reduced, and the method can be suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing cemented carbides by powder metallurgy, and provides a method for preparing submicron-grained WC cemented carbides. Background Art

[0002] Submicron-grained WC cemented carbides (WC grain size 0.5 - 0.8 μm) are widely used in cutting tools and wear-resistant parts due to their excellent hardness, wear resistance, good fracture strength and toughness. The traditional preparation method of submicron-grained WC cemented carbides is to use submicron WC powder (Fsss grain size 0.6 - 1.0 μm), fine-grained (Fsss grain size 1.0 - 1.3 μm) cobalt powder / nickel powder, transition metal carbide inhibitors (such as VC, Cr3C2, Mo2C, NbC, TaC, TiC and ZrC, etc.) and molding agents (such as paraffin, PEG, etc.), and obtain submicron-grained WC cemented carbides through steps such as wet grinding and mixing, vacuum drying, pressing and sintering. The preparation process of submicron WC powder includes: 1) Carbon mixing is carried out using submicron W powder, and in some cases, carbide inhibitors or metal element inhibitors are also added for mixing simultaneously during the carbon mixing stage. 2) The mixed powder after carbon mixing (W + C or W + C + inhibitor) is carbonized. 3) The carbonized WC is sieved and classified or air-milled and classified to obtain submicron WC powder. Therefore, the preparation process flow of submicron-grained WC cemented carbides is relatively complex, with many input devices and high production costs (energy consumption, labor). In addition, the longer the preparation process flow of submicron-grained WC cemented carbides, the more process quality control points there are, and the greater the difficulty of quality stability control. The invention patent with the patent number CN101285134B (a preparation method of WC-Co cemented carbide) uses a dielectric barrier discharge plasma-assisted high-energy ball milling method to ball mill W, C, Co powder and carbon supplementation to obtain a W, C, Co mixed powder, and the mixed powder is pressed, vacuum sintered or pressure sintered to obtain WC-Co cemented carbide. The patent application document with the application number CN 102181679 A provides a preparation method of W-C-Co powder containing inhibitors and its cemented carbide. The mixed powder of W, C, Co powder, grain growth inhibitor VC or V2O5 and additional carbon supplementation is ball milled by a dielectric barrier discharge plasma-assisted high-energy ball milling method to obtain a W, C, Co mixed powder containing grain growth inhibitors, and the mixed powder is pressed, vacuum sintered or pressure sintered to obtain WC-Co cemented carbide. Both of these methods use dielectric barrier discharge plasma-assisted high-energy ball milling to improve the powder activity and achieve the purpose of reducing the carbonization temperature of W powder. However, this method belongs to the dry powder preparation method, with a relatively high ball-to-material ratio (16 - 200:1). It is difficult to synchronously add the molding agent during the ball milling process, resulting in great difficulty in forming the mixed powder in the later stage and being unsuitable for industrial production. Moreover, the powder activity is relatively high after high-energy ball milling, and a large number of lattice distortions, dislocations, atomic vacancies and other defects are generated at the same time. Coupled with the presence of Co powder, even if the inhibitor VC is contained in the mixed powder, some W powder will still grow into coarse plate-like WC grains during the high-temperature sintering process, and it is difficult to obtain WC-Co cemented carbides with uniform fine grains or submicron grains in terms of microstructure. Summary of the Invention

[0003] Aiming at the deficiencies of the above-mentioned existing process technologies, the present invention provides a submicron-grained WC cemented carbide and a preparation method thereof. This method selects fine-grained or submicron-grained W powder, fine-grained Co / Ni powder, ultrafine carbon black, and carbide inhibitors, and mixes them by wet milling to ensure that the mixed powder has a certain sintering activity. Under the coexistence of ultrafine carbon black and diffusion-assisted metal Co / Ni, a specific sintering process is used to integrate the W powder carbonization process with the alloy solid-phase sintering, realizing the complete carbonization of W powder at a lower temperature (1150°C - 1280°C), and avoiding the abnormal grain growth caused by the carbonization of W powder in the high-temperature liquid phase stage. At the same time, a heat preservation section (1320°C) is set before the liquid phase appears after the carbonization of W powder is completed to allow the full exclusion of gases in the alloy, ensuring the smooth progress of the alloy high-temperature densification process. The method of the present invention has a simple process flow, low production cost, is suitable for industrial production, and has low difficulty in process quality control. The prepared submicron-grained WC-Co cemented carbide has a uniform organizational structure and a relatively high density, and the alloy properties are equivalent to those of the submicron-grained WC-Co cemented carbide prepared by the traditional method.

[0004] In order to achieve the above invention objectives, a preparation method of a submicron-grained WC cemented carbide provided by the present invention includes the following steps:

[0005] S1: Ball milling: Weigh the raw materials according to weight percentages, including 83.63 - 87.77 wt% tungsten carbide, 6 - 10 wt% cobalt powder or nickel powder, 0.4 - 0.5 wt% chromium carbide, 0 - 0.3 wt% vanadium carbide, and 5.55 - 5.85 wt% carbon black; after ball milling the raw materials, a mixed material is obtained.

[0006] S2: Compression molding;

[0007] S3: Sintering; The sintering process sequentially includes the following stages:

[0008] 3-1: Heat up from room temperature to 280°C at a rate of 3 - 5°C / min and hold for 30 min, then heat up to 380°C at a rate of 1 - 2°C / min and hold for 3 h, and then heat up to 420°C at a rate of 1.0 - 1.2°C / min and hold for 1 h;

[0009] 3-2: Heat up from 420°C to 1150°C at a rate of 4 - 6°C / min and hold for 0.5 h, then heat up to 1280°C at a rate of 1.0 - 1.5°C / min and hold for 1.5 - 2 h, and then heat up from 1280°C to 1320°C at a rate of 2 - 3°C / min and hold for 0.5 - 1 h. After the heat preservation ends, introduce argon to adjust the vacuum degree in the furnace to 2.0 - 3.0 KPa, and heat up from 1320°C to 1440°C - 1470°C at a rate of 3.5 - 5°C / min.

[0010] 3-3 Close the vacuum valve, introduce argon gas into the furnace to make the pressure in the furnace reach 4 - 5 MPa. The argon gas filling time is 0.5 h, and keep the temperature and pressure at 1440°C - 1470°C for 1 h.

[0011] 3-4 Cool the furnace to room temperature with the furnace to obtain submicron-grained WC cemented carbide.

[0012] A further improvement is that in step S1, VC and Cr3C2 can be replaced by one or several components selected from Mo2C, NbC, TaC, TiC, and ZrC.

[0013] A further improvement is that the carbon content in tungsten carbide is 6.21 - 6.27 wt%, the Fisher particle size is 0.5 - 2.0 μm; for Co powder, the Fisher particle size is 0.8 - 1.3 μm; the Fsss particle size of the transition metal carbide inhibitor (VC, Cr3C2, Mo2C, NbC, TaC, TiC, and ZrC) is 1.0 - 2.0 μm, and the average particle size of carbon black is 0.3 - 0.6 μm.

[0014] A further improvement is that the wet milling process parameters are as follows: the rotation speed of the ball mill is 72 r / min, the grinding media are WC-6wt%Co cemented carbide balls with a diameter The ball-to-material ratio is 4 - 5:1, the wet milling medium is hexane, the addition amount of hexane is (410 - 460) ml / Kg, the addition amount of the molding agent (paraffin) is 2.0 ± 0.2 wt%, and the ball milling time is 36 - 48 h.

[0015] In the traditional cemented carbide sintering process, during the solid-phase sintering process after removing the molding agent (450°C - 1230°C), the heating rate is relatively fast (4°C - 7°C / min). Usually, vacuum insulation is carried out at 1200°C - 1230°C for 1 h to remove the gases (CO or CO2) generated during the sintering process of the product. Through experiments, it is found that there are serious pores and uneven WC in the alloy after sintering the mixed powder (W powder, fine-grained Co / Ni powder, ultrafine carbon black, and carbide inhibitor) of the present invention under the conditions of the traditional sintering process. Analyzing the reasons, it is because the carbonization temperature of W powder is too low and the carbonization time is too short during the solid-phase sintering stage of the traditional sintering process, resulting in incomplete carbonization of W powder. The carbonization reaction continues until the liquid-phase sintering process, leading to abnormal growth of some WC grains. At the same time, the gases generated by the continuous carbonization of W or W2C in the liquid phase cannot be discharged and are sealed in the alloy to form serious pores or holes. By optimizing the composition and particle size of various powders and matching a suitable sintering process, the submicron-grained WC-Co cemented carbide prepared by the present invention has a uniform microstructure and a high density. The alloy properties are equivalent to those of the submicron-grained WC-Co cemented carbide prepared by traditional methods. This preparation method has a simple process flow, low production cost, is suitable for industrial production, and has low difficulty in process quality control.

[0016] The present invention mainly consists of W powder, Co / Ni powder, and one or several of VC, Cr3C2, Mo2C, NbC, TaC, TiC, and ZrC. The Fsss particle size of the Co / Ni powder is 0.8 - 1.3 μm; the Fsss particle size of the transition metal carbide inhibitors (VC, Cr3C2, Mo2C, NbC, TaC, TiC, and ZrC) is 1.0 - 2.0 μm, and the mass percentage is 0.3% - 1.2%. The balance is W powder and carbon black. The Fsss particle size of the W powder is 0.5 - 2.0 μm, and the average particle size of the carbon black is 0.3 - 0.6 μm. According to different Co / Ni contents, W powder particle sizes, and ball milling times, carbon is added in the range of 6.21 wt% - 6.27 wt% based on the carbon content of WC. <@

[0017] (1) In the present invention, fine-grained or sub-fine-grained W powder is directly used as a raw material and wet-milled and mixed with Co / Ni powder, C black, and inhibitors to prepare a mixture. After the mixture is formed, the processes of W powder carbonization and alloy sintering densification are completed in one step in a low-pressure sintering furnace. This method reduces the process steps of separately mixing and carbonizing W powder, greatly shortens the alloy production process flow, reduces production costs, and is applicable to industrial production.

[0018] (2) By selecting fine-grained or sub-fine-grained W powder, ultra-fine C black, and fine-grained Co powder for ball milling and matching a suitable sintering process (setting a suitable carbonization temperature range of 1100°C - 1280°C in the solid-phase sintering stage), complete carbonization of the fine-grained W powder is achieved at a lower temperature (1100°C - 1280°C) under the condition of coexistence of diffusion-assisted metals Co / Ni (ultra-fine C black and diffusion-assisted metals Co / Ni can significantly reduce the W powder carbonization temperature). Due to the lower carbonization temperature and the presence of carbide inhibitors, the tendency of WC grain growth during the W powder carbonization process and the subsequent liquid-phase sintering stage is greatly reduced, and sub-fine-grained cemented carbide with fine and uniform WC grains can be obtained. Description of the Drawings

[0019] The following will clearly and completely describe the technical solutions in conjunction with the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0020] Figure 1 It is a photograph of the sub-fine-grained WC cemented carbide in Example 1 of the present invention;

[0021] Figure 2 It is a metallographic photograph of the sub-fine-grained WC cemented carbide in Example 2 of the present invention;

[0022] Figure 3 It is a metallographic photograph of the sub-fine-grained WC cemented carbide in Example 3 of the present invention;

[0023] Figure 4It is the metallographic photograph of the fine-grained WC cemented carbide in Example 4 of the present invention;

[0024] Figure 5 It is the metallographic photograph of the fine-grained WC cemented carbide in Comparative Example 1;

[0025] Figure 6 It is the metallographic photograph of the fine-grained WC cemented carbide in Comparative Example 2. Specific Embodiments

[0026] The following further elaborates on the above content of the present invention in combination with the specific embodiments of the examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. Without departing from the above technical idea of the present invention, various substitutions or modifications made according to ordinary technical knowledge and customary means in the art shall be included within the scope of the present invention.

[0027] Example 1:

[0028] A method for preparing fine-grained WC cemented carbide includes the following steps:

[0029] 1. Raw material ratio: Weigh the raw materials according to the following parts by weight. The total mass of the powder is 1 Kg

[0030] Powder Name W08 Powder Co Powder <![CDATA[Cr3C2]]> VC C Black Proportion (wt%) 83.63 10 0.5 0.3 5.57

[0031] Note: The Fsss particle size of W08 powder is 0.70 μm. The carbon content in WC is 6.244%

[0032] 2. Ball milling: Weigh each powder component and add it to a 1.0 L ball milling barrel. After adding hexane, paraffin, and stearic acid, place it on a cantilever ball mill for rolling ball milling. The rotational speed of the ball mill is 72 r / min; the addition amount of hexane is 440 ml / kg, the addition amount of paraffin is 2 wt%, the addition amount of stearic acid is 0.1 wt%, and the grinding medium is WC-6 wt% Co cemented carbide balls with a diameter of The ball-to-powder ratio is 4:1, and the ball milling time is 36 h; place the slurry in a drying cabinet and vacuum dry it at �0℃ for 2 h. After the material cools to below 40℃, sieve it (80 mesh) and granulate it to obtain a mixed material.

[0033] 3. Pressing: Press the prepared mixed material into a green compact with the corresponding size requirements, and the pressing pressure is 7 MPa.

[0034] 4. Sintering: Sinter the green compact. The specific process implementation is divided into four stages:

[0035] ① First, heat from room temperature to 280℃ at a rate of 3℃ / min and hold for 30 min, then heat to 380℃ at a rate of 1.5℃ / min and hold for 3 h, and then heat to 420℃ at a rate of 1.0℃ / min and hold for 1 h to complete dewaxing;

[0036] ② After the hydrogen dewaxing at 420 °C is completed with heat preservation, vacuum sintering is carried out. It is heated from 420 °C to 1150 °C at a rate of 4 °C / min and kept warm for 0.5 h, then heated to 1280 °C at a rate of 1.0 °C / min and kept warm for 1.5 h, and then heated from 1280 °C to 1320 °C at a rate of 2 °C / min and kept warm for 0.5 h. After the heat preservation is completed, argon is introduced to adjust the vacuum degree in the furnace to 2.0 KPa, and it is heated from 1320 °C to 1440 °C at a rate of 3.5 °C / min.

[0037] ③ When the temperature rises to 1440 °C, the vacuum valve is closed, and argon is introduced into the furnace to make the pressure in the furnace reach 4 MPa. The argon filling time is 0.5 h, and it is kept warm and under pressure at 1440 °C for 1 h.

[0038] ④ After the heat preservation and pressure holding at 1440 °C are completed, it is cooled to room temperature with the furnace, and submicron-grained WC cemented carbide is obtained.

[0039] The physical properties and microstructures of the alloy specimens prepared in this example are shown in Table 1.

[0040] Example 2

[0041] A method for preparing submicron-grained WC cemented carbide is the same as that in Example 1 except for the following process steps.

[0042] 1. Raw material ratio: Weigh the raw materials according to the following parts by weight.

[0043] Powder Name W11 Powder Co Powder <![CDATA[Cr3C2]]> VC C Black Proportion (wt%) 83.65 10 0.5 0.3 5.55

[0044] Note: The Fsss particle size of W11 powder is 1.06 μm. The carbon content in WC is 6.222%.

[0045] 2. Ball milling: The ball milling time is 40 h;

[0046] 4. Sintering:

[0047] ① First, it is heated from room temperature to 280 °C at a rate of 4.5 °C / min and kept warm for 30 min, then heated to 380 °C at a rate of 1.5 °C / min and kept warm for 3 h, and then heated to 420 °C at a rate of 1.2 °C / min and kept warm for 1 h to complete dewaxing;

[0048] ② After the hydrogen dewaxing at 420 °C is completed with heat preservation, vacuum sintering is carried out. It is heated from 420 °C to 1150 °C at a rate of 5 °C / min and kept warm for 0.5 h, then heated to 1280 °C at a rate of 1.5 °C / min and kept warm for 1.5 h, and then heated from 1280 °C to 1320 °C at a rate of 2.5 °C / min and kept warm for 0.5 h. After the heat preservation is completed, argon is introduced to adjust the vacuum degree in the furnace to 2.5 Kpa, and it is heated from 1350 °C to 1440 °C at a rate of 3.5 °C / min.

[0049] ③ When the temperature rises to 1440 °C, close the vacuum valve, introduce argon into the furnace to make the pressure in the furnace reach 5 MPa, the argon filling time is 0.5 h, and keep the temperature and pressure at 1440 °C for 1.5 h.

[0050] ④ After the heat preservation and pressure maintenance at 1440 °C are completed, cool the furnace to room temperature.

[0051] Example 3

[0052] A preparation method of submicron-grained WC cemented carbide, except for the following process steps, the rest are the same as in Example 1.

[0053] 1. Raw material ratio: Weigh the raw materials according to the following parts by weight.

[0054] Powder Name W15 Powder Co Powder <![CDATA[Cr3C2]]> VC C Black Proportion (wt%) 83.65 10 0.5 0.3 5.55

[0055] Note: The Fsss particle size of W15 powder is 1.75 μm. The carbon content in WC is 6.222%.

[0056] 2. Ball milling: The ball milling time is 48 h;

[0057] 4. Sintering:

[0058] ① First, raise the temperature from room temperature to 280 °C at a rate of 5 °C / min and keep it for 30 min, then raise the temperature to 380 °C at a rate of 2 °C / min and keep it for 3 h, and then raise the temperature to 420 °C at a rate of 1.2 °C / min and keep it for 1 h to complete dewaxing;

[0059] ② After the hydrogen dewaxing and heat preservation at 420 °C are completed, carry out vacuum sintering. Raise the temperature from 420 °C to 1150 °C at a rate of 6 °C / min and keep it for 0.5 h, then raise the temperature to 1280 °C at a rate of 1.5 °C / min and keep it for 2 h, and then raise the temperature from 1280 °C to 1320 °C at a rate of 3 °C / min and keep it for 1 h. After the heat preservation is completed, introduce argon to adjust the vacuum degree in the furnace to 3 Kpa, and raise the temperature from 1320 °C to 1470 °C at a rate of 4 °C / min.

[0060] ③ When the temperature rises to 1470 °C, close the vacuum valve, introduce argon into the furnace to make the pressure in the furnace reach 5 MPa, the argon filling time is 0.5 h, and keep the temperature and pressure at 1470 °C for 1 h.

[0061] ④ After the heat preservation and pressure maintenance at 1470 °C are completed, cool the furnace to room temperature.

[0062] The physical properties and microstructural morphology of the alloy specimens prepared in this example are shown in Table 1.

[0063] Example 4:

[0064] A preparation method of sub - fine - grained WC cemented carbide, except for the following process steps, the rest is the same as in Example 1.

[0065] 1. Raw material ratio: Weigh the raw materials according to the following parts by weight in the table.

[0066] Powder Name W08 Powder Co Powder <![CDATA[Cr3C2]]> VC C Black Proportion (wt%) 87.55 6 0.4 0.2 5.85

[0067] Note: The Fsss particle size of W08 powder is 0.7μm. The carbon content of WC is 6.263%.

[0068] 2. Ball - milling time: 36h;

[0069] 4. Sintering:

[0070] ① First, heat from room temperature to 280℃ at a rate of 4℃ / min and hold for 30min, then heat to 380℃ at a rate of 1.5℃ / min and hold for 3h, and then heat to 420℃ at a rate of 1.0℃ / min and hold for 1h to complete dewaxing;

[0071] ② After the hydrogen dewaxing and holding at 420℃ is completed, carry out vacuum sintering. Heat from 420℃ to 1150℃ at a rate of 6℃ / min and hold for 0.5h, then heat to 1280℃ at a rate of 1.0℃ / min and hold for 1.5h, then heat from 1280℃ to 1320℃ at a rate of 2℃ / min and hold for 0.5h. After the holding is completed, introduce argon to adjust the vacuum degree in the furnace to 3.0Kpa, and heat from 1320℃ to 1440℃ at a rate of 5℃ / min.

[0072] ③ When the temperature rises to 1440℃, close the vacuum valve, introduce argon into the furnace to make the furnace pressure reach 5MPa, the argon - filling time is 0.5h, and hold at 1440℃ with pressure for 1.5h.

[0073] ④ After the holding and pressure - holding at 1440℃ are completed, cool the furnace to room temperature.

[0074] The physical properties and micro - structures of the alloy specimens prepared in this example are shown in Table 1.

[0075] Comparative examples

[0076] The properties of the alloys (Comparative Example 1 and Comparative Example 2) prepared from the mixed powders of Example 3 and Example 4 under traditional sintering process conditions are shown in Table 1.

[0077] Table 1 Physical properties and micro - structures of alloys in each example and comparative example

[0078]

[0079]

[0080] To further confirm the phase composition in the alloy, XRD diffraction analysis was performed on the alloys of Example 1 and Example 3 (as shown in the figure). Only WC and Co phases were present in the two alloys, and no W2C phase or W phase was detected.

[0081] As described above, the above are only the preferred embodiments of the present invention, and do not impose any formal limitations on the present invention. Any simple modifications and equivalent changes made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the present invention.

Claims

1. A preparation method of submicrocrystalline WC cemented carbide, characterized in that, It includes the following steps: S1: Ball milling: Weigh the raw materials according to weight percentages, including 83.63 - 87.77 wt% tungsten carbide, 6 - 10 wt% cobalt powder or nickel powder, 0.4 - 0.5 wt% chromium carbide, 0 - 0.3 wt% vanadium carbide, and 5.55 - 5.85 wt% carbon black; After ball milling the raw materials, a mixture is obtained; S2: Compression molding; S3: Sintering; The sintering process sequentially includes the following stages: 3 - 1 Heat from room temperature to 280 °C at a rate of 3 - 5 °C / min and hold for 30 min, then heat to 380 °C at a rate of 1 - 2 °C / min and hold for 3 h, and then heat to 420 °C at a rate of 1.0 - 1.2 °C / min and hold for 1 h; 3 - 2 Heat from 420 °C to 1150 °C at a rate of 4 - 6 °C / min and hold for 0.5 h, then heat to 1280 °C at a rate of 1.0 - 1.5 °C / min and hold for 1.5 - 2 h, and then heat from 1280 °C to 1320 °C at a rate of 2 - 3 °C / min and hold for 0.5 - 1 h. After the holding ends, introduce argon to adjust the vacuum degree in the furnace to 2.0 - 3.0 KPa, and heat from 1320 °C to 1440 °C - 1470 °C at a rate of 3.5 - 5 °C / min; 3 - 3 Close the vacuum valve, introduce argon into the furnace to make the pressure in the furnace reach 4 - 5 MPa, the argon filling time is 0.5 h, and hold the pressure and temperature at 1440 °C - 1470 °C for 1 h; 3 - 4 Cool with the furnace to room temperature to obtain sub - fine - grained WC cemented carbide.

2. The method according to claim 1, characterized in that, In step S1, VC and Cr3C2 can be replaced by one or several components selected from Mo2C, NbC, TaC, TiC, and ZrC.

3. The method according to claim 1 or 2, wherein, In step S1, the carbon content of tungsten carbide is 6.21 - 6.27 wt%, the Fisher particle size is 0.5 - 2.0 μm; the Fisher particle size of Co powder is 0.8 - 1.3 - μm; the Fsss particle size of VC, Cr3C2, Mo2C, NbC, TaC, TiC, and ZrC is 1.0 - 2.0 μm, and the particle size of carbon black is 0.3 - 0.6 μm.

4. The method according to claim 1, wherein, In step S1, the ball milling process parameters are as follows: the rotational speed of the ball mill is 72 r / min, the grinding media is WC - 6 wt% Co cemented carbide balls with a diameter of φ6.35 mm, the ball - to - material ratio is 4 - 5:1, the wet - milling medium is hexane, the addition amount of hexane is (410 - 460) ml / Kg, the addition amount of the forming agent (paraffin) is \(2.0\pm0.2\) wt%, and the ball milling time is 36 - 48 h.

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