Threaded core head double crystal high cobalt hard alloy and preparation method thereof

Abstract

The application discloses a double-crystal high-cobalt hard alloy for a threaded core head and a preparation method thereof, raw materials of which include coarse-grained WC powder, fine-grained WC powder and Co powder, wherein the Co powder accounts for 18-26% of the proportion of the main raw materials, and the rest is the coarse-grained WC powder and the fine-grained WC powder.The double-crystal high-cobalt hard alloy for the threaded core head and the preparation method thereof have the following advantages: the microstructure of the double-crystal hard alloy contains coarse-grained and fine-grained WC grains in a certain proportion, and the coarse-grained and fine-grained WC grains are uniformly distributed, so that the technical problem that an ordinary hard alloy is difficult to simultaneously meet high toughness and high hardness can be solved.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide technology, and in particular to a dual-crystal high-cobalt cemented carbide for threaded mandrels and its preparation method. Background Technology

[0002] The main components of cemented carbide include various hard phases and binder phases. Hard phases (such as WC phase and solid solution phase) play a crucial role in the alloy's hardness and wear resistance, while binder phases significantly influence the alloy's strength and toughness. Traditional methods to improve the toughness of cemented carbide include increasing the Co content and enlarging the WC grain size; however, this simultaneously reduces hardness and wear resistance. Conversely, cemented carbides prepared using fine-grained WC and low Co content can improve hardness and wear resistance, but at the expense of bending strength and toughness. There is a sharp contradiction between hardness and toughness in cemented carbide materials; therefore, achieving high hardness and toughness simultaneously is not easy with traditional cemented carbide methods.

[0003] The processing of internally threaded copper pipes (including air conditioning pipes, grooved pipes, etc.) all utilizes thread mandrel dies. These dies have a certain number and shape of slots for forming internal threads or grooves. Thread mandrel dies have high requirements for the hardness and toughness of the material. Low hardness leads to rapid wear of the mandrel dies, reducing their service life; poor toughness causes the slots of the dies to easily break, resulting in scrap. The limitation of traditional uniform-structure cemented carbide, where hardness and toughness are inversely proportional, restricts its application areas and makes it difficult to meet the high hardness and high toughness requirements of cemented carbide for thread mandrels.

[0004] Therefore, it is particularly important to develop a new type of cemented carbide material that can simultaneously meet the requirements of high hardness and high toughness for threaded mandrels. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention proposes a dual-crystal high-cobalt cemented carbide for threaded cores and its preparation method. The microstructure of the dual-crystal cemented carbide contains a certain ratio of coarse and fine WC grains, and the coarse and fine WC are evenly distributed. This can solve the technical problem that ordinary cemented carbide is difficult to simultaneously satisfy in terms of high toughness and high hardness.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a dual-crystal high-cobalt cemented carbide for threaded cores, comprising coarse-grained WC powder, fine-grained WC powder and Co powder, wherein the Co powder accounts for 18% to 26% of the main raw materials, and the remainder is the coarse-grained WC powder and the fine-grained WC powder.

[0008] Furthermore, the average particle size of the coarse WC powder is 23~26μm, accounting for 20%~30% of the total WC powder raw material;

[0009] The fine WC powder has an average particle size of 0.5~0.6μm and accounts for 70%~80% of the total WC powder raw material.

[0010] Secondly, the present invention also provides a method for preparing a dual-crystal high-cobalt cemented carbide for threaded mandrels, comprising the following steps:

[0011] (1) Fine WC powder and Co powder with an average particle size of 0.5~0.6μm are added to a ball mill for grinding and mixing for a certain period of time;

[0012] (2) Add coarse WC powder with an average particle size of 23~26μm to the mixed material in step (1), and add 1wt%~2wt% of paraffin wax. Mix the mixture in a ball mill for a certain period of time to obtain the mixture.

[0013] (3) The mixture in step (2) is dried, sieved, and hot-pressed to obtain the double-crystal high-cobalt hard alloy.

[0014] Furthermore, the grinding process in step (1) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (6~10):1, and the ball milling time is 20~30h.

[0015] Furthermore, the grinding process in step (2) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (2~4):1, and the ball milling time is 8~12h.

[0016] Furthermore, in step (3), the drying method is spray drying, the air inlet temperature is 80~100℃, and the hot pressing sintering process is as follows: the dried WC-Co mixed powder is filled into the mold, and pressure is applied while heating is applied so that the forming and sintering are completed simultaneously. The sintering temperature is 1280~1320℃, the mechanical pressure is 20~50MPa, and the sintering time is 1~2h.

[0017] In summary, the beneficial effects of the present invention are as follows:

[0018] The present invention relates to a dual-crystal high-cobalt cemented carbide for threaded cores and its preparation method. During the mixing process, fine WC powder and Co powder are first ground for a longer time to further refine the fine WC powder. Then, coarse WC powder is added and ball-milled for a shorter time to control the coarse WC powder from being crushed too finely and to ensure the proportion of coarse grains after sintering.

[0019] In addition, the hot-pressing sintering process involves heating and pressurizing simultaneously, keeping the powder in a thermoplastic state, which facilitates particle contact diffusion and mass transfer. Compared to the low-pressure sintering process, the cold-pressing step can be eliminated. Hot-pressing sintering can also lower the sintering temperature and shorten the sintering time, ensuring that fine-grained WC does not grow during sintering and improving the alloy density. No sintering aids or forming aids are needed to obtain cemented carbide products with higher purity. Attached Figure Description

[0020] Figure 1 This is a SEM image of Example 1;

[0021] Figure 2 This is a particle size distribution diagram of Example 1;

[0022] Figure 3 This is a particle size distribution diagram for Example 2;

[0023] Figure 4 This is a particle size distribution diagram for Example 3. Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In a first aspect, the present invention provides a dual-crystal high-cobalt cemented carbide for threaded cores, comprising coarse-grained WC powder, fine-grained WC powder and Co powder, wherein the Co powder accounts for 18% to 26% of the main raw materials, and the remainder is the coarse-grained WC powder and the fine-grained WC powder.

[0026] Furthermore, the average particle size of the coarse WC powder is 23~26μm, accounting for 20%~30% of the total WC powder raw material;

[0027] The fine WC powder has an average particle size of 0.5~0.6μm and accounts for 70%~80% of the total WC powder raw material.

[0028] Secondly, the present invention also provides a method for preparing a dual-crystal high-cobalt cemented carbide for threaded mandrels, comprising the following steps:

[0029] (1) Fine WC powder and Co powder with an average particle size of 0.5~0.6μm are added to a ball mill for grinding and mixing for a certain period of time;

[0030] (2) Add coarse WC powder with an average particle size of 23~26μm to the mixed material in step (1), and add 1wt%~2wt% of paraffin wax. Mix the mixture in a ball mill for a certain period of time to obtain the mixture.

[0031] (3) The mixture in step (2) is dried, sieved, and hot-pressed to obtain the double-crystal high-cobalt hard alloy.

[0032] Furthermore, the grinding process in step (1) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (6~10):1, and the ball milling time is 20~30h.

[0033] Furthermore, the grinding process in step (2) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (2~4):1, and the ball milling time is 8~12h.

[0034] Furthermore, in step (3), the drying method is spray drying, the air inlet temperature is 80~100℃, and the hot pressing sintering process is as follows: the dried WC-Co mixed powder is filled into the mold, and pressure is applied while heating is applied so that the forming and sintering are completed simultaneously. The sintering temperature is 1280~1320℃, the mechanical pressure is 20~50MPa, and the sintering time is 1~2h.

[0035] After the above preparation steps, a bicrystalline high-cobalt cemented carbide is obtained. The microstructure of the alloy includes coarse-grained WC with a grain size of 6-10 μm and fine-grained WC with a grain size of 0.1-0.5 μm. Based on the total weight of WC grains as 100%, the content of fine-grained WC (0.1-3 μm) is 60-70 wt%, and the content of coarse-grained WC (6-10 μm) is 10-20%.

[0036] In this invention, coarse-grained WC in the bicrystalline cemented carbide enhances the alloy's toughness, while fine-grained WC improves its hardness and wear resistance. This is related to the γ-phase (a Co-based Co-WC solid solution) formed during the liquid-phase sintering process of the cemented carbide. The fracture toughness of the WC-Co cemented carbide mainly depends on the volume fraction and mean free path of the γ-phase, which increases with the γ-phase content and average grain size. With a fixed cobalt content, increasing the coarse-grained WC content not only increases the γ-phase mean free path but also improves the alloy's toughness; however, simultaneously, the contact area between the WC and Co phases decreases, and the number of bonded phases along the mean free path increases, which to some extent reduces the hardness of the cemented carbide. This invention employs an appropriate ratio of coarse / fine-grained WC to improve the toughness of the cemented carbide while maintaining its hardness. Example

[0037] (1) Take 2.56 kg of fine WC powder with an average particle size of 0.5~0.6 μm and 0.8 kg of cobalt powder for grinding. Use anhydrous ethanol as the medium for wet grinding. The solid-liquid ratio is 25%, the ball-to-material ratio is 10:1, and the ball milling time is 30 h to obtain mixture 1.

[0038] (2) Mix mixture 1 and 0.64 kg of coarse WC powder with an average particle size of 23~26 μm, and add 1 wt% paraffin for grinding. Use anhydrous ethanol as the medium for wet grinding, with a solid-liquid ratio of 25%, a ball-to-material ratio of 3:1, and a ball milling time of 10 h to obtain mixture 2.

[0039] (3) The mixture 2 is spray-dried and granulated at an air inlet temperature of 90°C. After drying and granulation, the material is sieved and then hot-pressed at 1280°C and 40MPa pressure for 1.5 hours to obtain the double-crystal high-cobalt hard alloy. Example

[0040] (1) Take 2.4 kg of fine WC powder with an average particle size of 0.5~0.6 μm and 0.8 kg of cobalt powder for grinding. Use anhydrous ethanol as the medium for wet grinding. The solid-liquid ratio is 25%, the ball-to-material ratio is 10:1, and the ball milling time is 30 h to obtain mixture 1.

[0041] (2) Mix mixture 1 and 0.8 kg of coarse WC powder with an average particle size of 23~26 μm, and add 1 wt% paraffin for grinding. Use anhydrous ethanol as the medium for wet grinding, with a solid-liquid ratio of 25%, a ball-to-material ratio of 3:1, and a ball milling time of 10 h to obtain mixture 2.

[0042] (3) The mixture 2 is spray-dried and granulated at an air inlet temperature of 90°C. After drying and granulation, the material is sieved and then hot-pressed at 1300°C and 35MPa pressure for 1.5 hours to obtain the double-crystal high-cobalt hard alloy. Example

[0043] (1) Take 2.24 kg of fine WC powder with an average particle size of 0.5~0.6 μm and 0.8 kg of cobalt powder for grinding. Use anhydrous ethanol as the medium for wet grinding. The solid-liquid ratio is 25%, the ball-to-material ratio is 10:1, and the ball milling time is 30 h to obtain mixture 1.

[0044] (2) Mix 1 and 0.96 kg of coarse WC powder with an average particle size of 23~26 μm, and add 1 wt% paraffin for grinding. Use anhydrous ethanol as the medium for wet grinding, with a solid-liquid ratio of 25%, a ball-to-material ratio of 3:1, and a ball milling time of 10 h to obtain 2.

[0045] (3) The mixture 2 is spray-dried and granulated with an air inlet temperature of 90°C. After drying and granulation, the material is sieved and then hot-pressed and sintered at 1280°C and 40MPa for a time of h to obtain the double-crystal high-cobalt hard alloy.

[0046] Table 1 Comparison of Examples and Comparative Examples

[0047] Examples and Comparative Examples Hardness (HRA) <![CDATA[Flexural strength (N / mm 2 )]]> <![CDATA[Fracture toughness (MPa / m 2 ).]]> Wear rate Example 1 86 2250 15.3 16% Example 2 85 2146 14.7 15% Example 3 85 2150 14.6 17%

[0048] The present invention relates to a dual-crystal high-cobalt cemented carbide for threaded cores and its preparation method. During mixing, fine-particle WC powder and Co powder are first ground for a longer time to further refine the fine WC powder. Then, coarse-particle WC is added and ball-milled for a shorter time to prevent the coarse WC from being broken down too finely, thus ensuring the proportion of coarse grains after sintering.

[0049] In addition, the hot-pressing sintering process involves heating and pressurizing simultaneously, keeping the powder in a thermoplastic state, which facilitates particle contact diffusion and mass transfer. Compared to the low-pressure sintering process, the cold-pressing step can be eliminated. Hot-pressing sintering can also lower the sintering temperature and shorten the sintering time, ensuring that fine-grained WC does not grow during sintering and improving the alloy density. No sintering aids or forming aids are needed to obtain cemented carbide products with higher purity.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a double-crystal high-cobalt cemented carbide for threaded mandrels, characterized in that: The threaded mandrel using a dual-crystal high-cobalt hard alloy comprises coarse-grained WC powder, fine-grained WC powder, and Co powder. The Co powder accounts for 18% to 26% of the main raw materials, with the remainder being the coarse-grained WC powder and the fine-grained WC powder. The average particle size of the coarse-grained WC powder is 23 to 26 μm, accounting for 20% to 30% of the total WC powder raw materials. The average particle size of the fine-grained WC powder is 0.5 to 0.6 μm, accounting for 70% to 80% of the total WC powder raw materials. The method for preparing the threaded mandrel using a dual-crystal high-cobalt cemented carbide includes the following steps: (1) Fine WC powder and Co powder with an average particle size of 0.5~0.6μm are added to a ball mill for grinding and mixing for a certain period of time; (2) Add coarse WC powder with an average particle size of 23~26μm to the mixed material in step (1), and add 1wt%~2wt% of paraffin wax. Mix the mixture in a ball mill for a certain period of time to obtain the mixture. (3) The mixture in step (2) is dried, sieved, and hot-pressed to obtain the double-crystal high-cobalt cemented carbide; the grinding process in step (1) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (6~10):1, and the ball milling time is 20~30h; the grinding process in step (2) is wet grinding, the wet grinding medium is anhydrous ethanol, the solid-liquid ratio is 20%~30%, the ball-to-material ratio is (2~4):1, and the ball milling time is 8~12h; the drying method in step (3) is spray drying, the air inlet temperature is 80~100℃, and the hot-pressing sintering process is to fill the dried WC-Co mixed powder into the mold, pressurize and heat at the same time so that the forming and sintering are completed simultaneously, the sintering temperature is 1280~1320℃, the mechanical pressure is 20~50MPa, and the sintering time is 1~2h.

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