A graphite boat device for sintering cemented carbide and a sintering method

Abstract

This invention provides a graphite boat apparatus and sintering method for cemented carbide sintering. The graphite boat apparatus includes a graphite boat assembly, a graphite cover, and a graphite cap. The graphite boat assembly is located inside the graphite cover. The graphite cap is disposed on top of the graphite cover. The graphite cover has a closed side and open ends, and several first through holes are formed at the bottom of each side wall of the graphite cover. Several second through holes are formed at the center of the graphite cap. The inner walls of both the graphite cover and the graphite cap are coated with a carbon conditioning coating. Using the graphite boat apparatus provided by this invention for sintering cemented carbide products, the relative magnetic saturation difference of the resulting alloy product can be controlled within 7%, thereby stabilizing the alloy microstructure within the two-phase region and achieving stable and controllable hardness, toughness, and strength.

Description

Technical Field

[0001] This invention belongs to the field of cemented carbide sintering technology, and relates to a graphite boat apparatus and sintering method for cemented carbide sintering. Background Technology

[0002] Hard alloys are highly sensitive to the carbon atmosphere during sintering. Oxygen and water absorption are unavoidable during production, leading to large fluctuations in magnetic saturation during sintering, and even decarburization or carburization. This is particularly true for products with lower weight, lower cobalt content, and finer grains, where the magnetic saturation difference between the center and edges of the graphite plate is significant. Using conventional sintering methods, the edge products are prone to decarburization and scrapping. While increasing the carbon content of the alloy can solve the decarburization problem at the edges, it causes carburization and scrapping of the center products.

[0003] CN119794351A discloses a method and apparatus for controlling the carbon atmosphere during the sintering of cemented carbide billets. The apparatus includes a graphite base plate, a spraying boat, graphite carbon-increasing columns, and alumina carbon-reducing columns. The graphite base plate is divided into multiple sections. The graphite carbon-increasing columns and alumina carbon-reducing columns are used to increase or decrease the carbon atmosphere during sintering in different sections. However, its range of action is limited, and multiple types of columns need to be arranged over a large area to achieve uniform atmosphere throughout the furnace, which makes furnace loading and unloading operations inconvenient and difficult to promote and apply.

[0004] CN102002606A discloses a graphite boat and a graphite boat assembly for cemented carbide sintering processes, comprising a disc-shaped graphite boat body surrounded by sidewalls and a bottom plate, wherein a plurality of through holes are uniformly arranged on the bottom plate. Due to the need for drilling holes in the graphite boat and its disc-shaped structure, it is only suitable for products of specific sizes, has poor versatility, and limits its production and promotion.

[0005] CN120947346A discloses a sintering stack with controllable insert height, and a system and method for controlling the magnetic property fluctuations of cemented carbide rods. The sintering stack with controllable insert height comprises several sintering boats and several insert groups; the sintering boats and insert groups are arranged alternately; the minimum height difference between the inserts in the several insert groups is 1mm~2mm. It mainly adjusts the atmosphere by changing the size of the sintering space, and is suitable for rod products, but not for products with small individual weight and fine low-cobalt crystals.

[0006] In summary, there is an urgent need to provide a novel graphite boat and sintering method to effectively solve the problems of decarburization, carburization, or large fluctuations in magnetic saturation after product sintering. Summary of the Invention

[0007] The purpose of this invention is to provide a graphite boat apparatus and sintering method for hard alloy sintering, which can effectively solve the problems of decarburization, carburization, or large fluctuations in magnetic saturation after product sintering.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a graphite boat apparatus for sintering cemented carbide, the graphite boat apparatus comprising a graphite boat assembly, a graphite cover, and a graphite cap. The graphite boat-and-vessel assembly is located inside the graphite cover; The graphite cap is disposed on top of the graphite cover; The graphite cover has closed sides and open ends, and several first through holes are provided at the bottom of the side walls of the graphite cover. The graphite cap has several second through holes in its center; The inner walls of both the graphite cover and the graphite cap are provided with a carbon conditioning coating.

[0009] Using the graphite boat-and-dish apparatus provided by this invention for sintering cemented carbide products, the relative magnetic saturation difference of the resulting alloy products can be controlled within 7%, thereby stabilizing the alloy microstructure within the two-phase region and achieving stable and controllable hardness, toughness, and strength.

[0010] It should be noted that by adding a graphite shroud and a graphite cap to the outside of the graphite boat assembly, and combining this with the placement of the first and second through holes, the direction of hydrogen flow during the product sintering process is standardized, ensuring the effectiveness of the release agent and the uniformity of the carbon atmosphere. By providing a carbon conditioning coating on the inner walls of the graphite shroud and the graphite cap, the carbon atmosphere within the graphite shroud is stabilized and homogenized, ensuring a carbon balance between the sintered product and the interior of the graphite shroud.

[0011] Preferably, the graphite boat assembly comprises several graphite boats stacked on top of each other.

[0012] Preferably, the graphite boat includes a graphite base plate.

[0013] In this invention, the graphite substrate is coated with a high-temperature resistant coating, and various graphite substrate shapes can be selected according to the needs of the sintered products.

[0014] Preferably, graphite support points are provided at the four corners of the graphite base plate.

[0015] Preferably, the graphite fulcrum is used to support and connect the stacked graphite boats.

[0016] Preferably, the height difference between the graphite support and the cemented carbide product to be sintered is 2mm-10mm, for example, it can be 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm, 8.5mm, 9mm or 9.5mm, etc.

[0017] Preferably, the weight of the cemented carbide product to be sintered is <10g, for example, it can be 9g, 8g, 7g, 6g, 5g, 4g, 3g, 2g or 1g, etc.; the Co content is <5wt%, for example, it can be 4.8wt%, 4.5wt%, 4.2wt%, 4wt%, 3.8wt%, 3.5wt%, 3.2wt% or 3wt%, etc.; the average WC grain size is <1μm, for example, it can be 0.9μm, 0.8μm, 0.6μm, 0.5μm, 0.4μm or 0.3μm, etc.

[0018] Preferably, the wall thickness of the graphite cover is 5mm-10mm, for example, it can be 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm, 8.5mm, 9mm or 9.5mm, etc.

[0019] Preferably, at least two first through holes are provided on the bottom of the sidewall of the graphite cover.

[0020] Preferably, the length of the first through hole is 25mm-35mm, for example, it can be 26mm, 27mm, 28mm, 29mm, 30mm, 31mm, 32mm, 33mm or 34mm, etc.; the width is 15mm-25mm, for example, it can be 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm or 24mm, etc.

[0021] Preferably, the thickness of the graphite cap is 5mm-10mm, for example, it can be 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm, 8.5mm, 9mm or 9.5mm, etc.

[0022] Preferably, the number of the second through holes is ≥6, for example, it can be 7, 8, 9 or 10, etc.

[0023] In this invention, the arrangement of the second through holes includes, but is not limited to, single-row and multi-row arrangements, which can be flexibly configured according to actual needs.

[0024] Preferably, the diameter of the second through hole is 3mm-7mm, for example, it can be 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm or 6.5mm.

[0025] Preferably, the graphite cover is provided with a groove for sealing with the graphite cover.

[0026] Preferably, the thickness of the carbon conditioning coating is 100μm-300μm, for example, it can be 120μm, 140μm, 150μm, 160μm, 180μm, 200μm, 220μm, 240μm, 250μm, 260μm or 280μm, etc.

[0027] In this invention, a carbon conditioning coating is coated on the inner wall of both the graphite cover and the graphite cap, and after drying, a carbon conditioning coating with a thickness of 100μm-300μm is formed.

[0028] Preferably, the raw materials of the carbon conditioning coating slurry include, by mass percentage: 20%-35% high-temperature oxides, 15%-30% carbon-containing materials, 9%-11% binder, 3%-5% dispersant and 0.1%-1.5% thickener.

[0029] It should be noted that the high-temperature oxides and carbon-containing materials in the carbon conditioning coating provide an adjustable carbon concentration for the carbon atmosphere during sintering. This effectively replenishes the carbon consumed during sintering by removing adsorbed water and oxygen from the product, ensuring carbon balance within the product and uniformity of the sintering atmosphere in the furnace. The binder in the carbon conditioning coating acts to bond the high-temperature oxides, carbon-containing materials, and graphite walls, preventing the coating from detaching from the graphite walls. Because both the graphite cover and graphite cap are porous, the coating adheres well to the graphite walls even at high temperatures.

[0030] In this invention, the high-temperature oxide accounts for 20%-35% of the mass of the carbon-modified coating, for example, 22%, 24%, 25%, 26%, 28%, 30%, 32%, or 34%; the carbon-containing material accounts for 15%-30% of the mass of the carbon-modified coating, for example, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, or 29%; and the binder accounts for 9%-11% of the mass of the carbon-modified coating, for example, 9.2%, 9.5%, or 9%. The dispersant has a mass percentage of 3%-5% in the carbon conditioning coating, for example, 3.2%, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.5%, 4.6%, or 4.8%; the thickener has a mass percentage of 0.1%-1.5% in the carbon conditioning coating, for example, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, or 1.4%.

[0031] Preferably, the high-temperature oxide includes any one or a combination of at least two of aluminum oxide, zirconium oxide, or yttrium oxide.

[0032] Preferably, the carbon-containing material includes carbon black and / or acetylene black.

[0033] Preferably, the binder comprises orthosilicate and / or sodium silicate.

[0034] Preferably, the dispersant comprises polyethylene glycol and / or Tween.

[0035] Preferably, the thickener includes a cellulose-based thickener.

[0036] In this invention, the cellulose thickener includes methylcellulose and / or ethylcellulose.

[0037] Preferably, the slurry raw material for the carbon conditioning coating further includes 30%-40% solvent, such as 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, or 39%.

[0038] In this invention, the solvent includes deionized water.

[0039] Secondly, the present invention provides a sintering method for cemented carbide, the sintering method comprising: Several cemented carbide products to be sintered are placed in the graphite boat apparatus for cemented carbide sintering described in the first aspect for sintering. The sintering process includes a first heating, a first holding, a second heating, and a second holding in sequence.

[0040] The sintering method provided by this invention is applicable to furnaces of various volumes, is easy to operate, has low production costs, and is suitable for industrial production.

[0041] Preferably, the first heating and the first heat preservation are carried out in a hydrogen atmosphere.

[0042] Preferably, the hydrogen flow rate is 5m³. 3 / h-10m 3 / h, for example, could be 5.5m 3 / h、6m 3 / h, 6.5m 3 / h、7m 3 / h, 7.5m 3 / h、8m 3 / h, 8.5m 3 / h、9m 3 / h or 9.5m 3 / h etc.

[0043] Preferably, the heating rate of the first heating is 1℃ / min-3℃ / min, for example, it can be 1.2℃ / min, 1.5℃ / min, 1.6℃ / min, 1.8℃ / min, 2℃ / min, 2.2℃ / min, 2.5℃ / min, 2.6℃ / min or 2.8℃ / min, etc.

[0044] Preferably, the endpoint of the first temperature rise is 400℃-500℃, for example, it can be 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃ or 490℃, etc.

[0045] Preferably, the first heat preservation time is 90min-150min, for example, it can be 95min, 100min, 105min, 110min, 115min, 120min, 125min, 130min, 135min or 140min.

[0046] Preferably, the second heating is carried out under vacuum conditions, with a vacuum degree ≤20Pa, such as 18Pa, 15Pa, 12Pa, 10Pa, 8Pa or 5Pa.

[0047] Preferably, the heating rate of the second heating is 2℃ / min-5℃ / min, for example, it can be 2.2℃ / min, 2.5℃ / min, 2.6℃ / min, 2.8℃ / min, 3℃ / min, 3.2℃ / min, 3.5℃ / min, 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.5℃ / min, 4.6℃ / min or 4.8℃ / min, etc.

[0048] Preferably, the endpoint of the second temperature rise is 1380℃-1500℃, for example, it can be 1390℃, 1400℃, 1420℃, 1450℃, 1460℃, 1480℃ or 1490℃, etc.

[0049] Preferably, an inert gas is introduced during the second heat preservation process.

[0050] In this invention, the inert gas includes argon and / or nitrogen.

[0051] Preferably, the pressure of the inert gas is 5MPa-10MPa, for example, it can be 5.5MPa, 6MPa, 6.5MPa, 7MPa, 7.5MPa, 8MPa, 8.5MPa, 9MPa or 9.5MPa, etc.

[0052] It should be noted that hydrogen is introduced during the first heating and first holding stages. By controlling the hydrogen flow rate, the removal of the forming agent from the compact can be ensured without causing excessive carbon loss inside the alloy. The second heating is carried out under vacuum conditions and the second holding is carried out under a high-pressure inert atmosphere, which effectively eliminates porosity in the alloy and ensures the compactness of the alloy.

[0053] Preferably, the second heat preservation time is 30-60 minutes, for example, it can be 35 minutes, 40 minutes, 45 minutes, 50 minutes or 55 minutes.

[0054] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects: (1) The graphite boat device provided by the present invention, by adding a graphite cover and a graphite cap with a specific structure and coating outside the graphite boat assembly, not only regulates the direction of hydrogen flow during the product sintering process and ensures the effect of the release agent, but also achieves the effect of stabilizing and homogenizing the carbon atmosphere inside the graphite cover, and ensures the carbon balance between the sintered product and the inside of the graphite cover.

[0056] (2) The method provided by the present invention is designed with two heating stages. The first stage is pre-sintering in a hydrogen atmosphere, and the second stage combines vacuum sintering and high-pressure sintering under argon protection. This can ensure that the forming agent of the compact is removed without causing excessive loss of carbon inside the alloy, and can effectively eliminate the porosity in the alloy and ensure the compactness of the alloy.

[0057] (3) When the graphite boat device provided by the present invention is used to sinter hard alloy products, the relative magnetic saturation difference of the resulting alloy products can be controlled within 7%, thereby stabilizing the alloy microstructure within the two-phase region and achieving stable and controllable hardness, toughness and strength. Attached Figure Description

[0058] Figure 1 This is an external view of the graphite boat apparatus for sintering hard alloys provided in Example 1.

[0059] Figure 2 This is a cross-sectional view of the graphite boat apparatus for sintering cemented carbide provided in Example 1.

[0060] Among them, 1-graphite cover, 2-graphite cap, 3-graphite boat, 4-graphite fulcrum, 5-hard alloy blank, 11-first through hole, 21-second through hole. Detailed Implementation

[0061] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0063] All materials used in the specific embodiments of this invention are commercially available or prepared using conventional methods in the prior art. All methods employed are conventional techniques in the field. In the following examples and comparative examples, the graphite substrates are coated with a high-temperature resistant coating with a thickness of 0.15 mm. The coating composition is a mixture of zirconium oxide and yttrium oxide (weight percentage 8:2).

[0064] Example 1 This embodiment provides a graphite boat / dining device and a sintering method for sintering cemented carbide. The graphite boat / dining device (such as...) Figure 1-2 (As shown) includes a graphite boat-shaped container assembly, a graphite cover 1, and a graphite cap 2; The graphite boat assembly comprises several graphite boats 3 stacked in layers; each graphite boat 3 includes a graphite base plate; graphite support points 4 are provided at the four corners of the graphite base plate; the graphite support points 4 are used to support and connect the stacked graphite boats 3; the height difference between the graphite support points 4 and the cemented carbide blank 5 is 2 mm; the cemented carbide blank 5 has a weight of 2.0 g, a Co content of 3.8 wt%, and an average WC grain size of 0.6 μm; The graphite boat assembly is located inside the graphite cover 1; the graphite cover 1 has a closed side and open ends, and two first through holes 11 are provided at the bottom of the side wall of the graphite cover 1; the wall thickness of the graphite cover 1 is 8mm; the length of the first through hole 11 is 30mm and the width is 20mm. The graphite cover 2 is disposed on the top of the graphite cover 1; the thickness of the graphite cover 2 is 8mm; the center of the graphite cover 2 is provided with 9 second through holes 21; the diameter of the second through holes 21 is 5mm; the second through holes 21 are evenly distributed in a 3×3 matrix; the graphite cover 2 is provided with a groove for sealing with the graphite cover 1. The inner walls of both the graphite cover 1 and the graphite cap 2 are provided with a carbon conditioning coating with a thickness of 200 μm; the carbon conditioning coating is prepared by the following method: applying a slurry to the inner wall surface of the graphite cover and the graphite cap and drying it at 150°C. The raw materials for the carbon-modified coating slurry, by weight percentage, include: 30% high-temperature oxides, 20% carbon-containing materials, 10% binder, 4.2% dispersant, 0.8% thickener, and 35% solvent; The high-temperature oxide comprises aluminum oxide and zirconium oxide in a mass ratio of 1:1; The carbon-containing material includes carbon black; The binder comprises orthosilicate and sodium silicate in a mass ratio of 3:7; The dispersant comprises polyethylene glycol and Tween in a mass ratio of 1:1.1; The thickener includes ethyl cellulose; The solvent includes deionized water.

[0065] The sintering method includes: Several cemented carbide blanks are placed in the graphite boat apparatus for cemented carbide sintering and sintering is performed. The sintering includes a first heating, a first holding, a second heating and a second holding in sequence. The first heating and the first heat preservation are carried out in a hydrogen atmosphere; the hydrogen flow rate is 7 m³ / s. 3 / h; the heating rate of the first heating is 1.5℃ / min; the heating endpoint of the first heating is 450℃; the holding time of the first heating is 120min; The second heating is carried out under vacuum conditions with a vacuum degree of 10 Pa; the heating rate of the second heating is 3.5 °C / min; the heating endpoint of the second heating is 1410 °C. Argon gas is introduced during the second heat preservation process; the pressure of the argon gas is 6 MPa; the second heat preservation time is 40 min.

[0066] Example 2 This embodiment provides a graphite boat device and sintering method for cemented carbide sintering. The graphite boat device includes a graphite boat assembly, a graphite cover, and a graphite cap. The graphite boat assembly comprises several graphite boats stacked on top of each other; each graphite boat includes a graphite base plate; graphite support points are provided at the four corners of the graphite base plate; the graphite support points are used to support and connect the stacked graphite boats; the height difference between the graphite support points and the cemented carbide blank is 5 mm; the cemented carbide blank has a weight of 1.0 g, a Co content of 4.5 wt%, and an average WC grain size of 0.8 μm; The graphite boat assembly is located inside the graphite cover; the graphite cover has closed sides and open ends, and two first through holes are provided at the bottom of the side walls of the graphite cover; the wall thickness of the graphite cover is 8mm; the length of the first through hole is 30mm and the width is 20mm. The graphite cap is disposed on top of the graphite cover; the graphite cap is 8mm thick; nine second through holes are opened in the center of the graphite cap; the diameter of the second through holes is 5mm; the second through holes are evenly distributed in a 3×3 matrix; the graphite cap is provided with a groove for sealing with the graphite cover. The inner walls of both the graphite cover and the graphite cap are provided with a carbon conditioning coating with a thickness of 150 μm; the carbon conditioning coating is prepared by the following method: applying a slurry to the inner wall surface of the graphite cover and the graphite cap and drying it at 150°C. The raw materials of the carbon-modified coating slurry, by weight percentage, include: 25% high-temperature oxide, 25% carbon-containing material, 10% binder, 4% dispersant, 1% thickener, and 35% solvent; The high-temperature oxide comprises aluminum oxide, zirconium oxide, and yttrium oxide in a mass ratio of 2:2:1; The carbon-containing material includes acetylene black; The binder comprises orthosilicate and sodium silicate in a mass ratio of 1:3; The dispersant comprises polyethylene glycol and Tween in a mass ratio of 5:3; The thickener includes ethyl cellulose; The solvent includes deionized water.

[0067] The sintering method is performed in accordance with the method provided in Example 1.

[0068] Example 3 This embodiment provides a graphite boat device and sintering method for cemented carbide sintering. The graphite boat device includes a graphite boat assembly, a graphite cover, and a graphite cap. The graphite boat assembly comprises several graphite boats stacked on top of each other; each graphite boat includes a graphite base plate; graphite support points are provided at the four corners of the graphite base plate; the graphite support points are used to support and connect the stacked graphite boats; the height difference between the graphite support points and the cemented carbide blank is 8 mm; the cemented carbide blank has a weight of 5.0 g, a Co content of 3.8 wt%, and an average WC grain size of 0.6 μm; The graphite boat assembly is located inside the graphite cover; the graphite cover has a closed side and open ends, and two first through holes are provided at the bottom of the side wall of the graphite cover; the wall thickness of the graphite cover is 6mm; the length of the first through hole is 30mm and the width is 20mm. The graphite cap is disposed on the top of the graphite cover; the thickness of the graphite cap is 6mm; the center of the graphite cap has 9 second through holes; the diameter of the second through holes is 7mm; the second through holes are evenly distributed in a 3×3 matrix; the graphite cap is provided with a groove for sealing with the graphite cover. The inner walls of both the graphite cover and the graphite cap are provided with a carbon conditioning coating with a thickness of 300 μm; the carbon conditioning coating is prepared by the following method: applying a slurry to the inner wall surface of the graphite cover and the graphite cap and drying it at 150°C. The raw materials for the carbon-modified coating slurry, by weight percentage, include: 35% high-temperature oxides, 15% carbon-containing materials, 10% binder, 3.5% dispersant, 1.5% thickener, and 35% solvent; The high-temperature oxide includes aluminum oxide; The carbon-containing material includes carbon black; The binder comprises orthosilicate and sodium silicate in a mass ratio of 3:7; The dispersant includes polyethylene glycol; The thickener includes ethyl cellulose; The solvent includes deionized water.

[0069] The sintering method includes: Several cemented carbide blanks are placed in the graphite boat apparatus for cemented carbide sintering and sintering is performed. The sintering includes a first heating, a first holding, a second heating and a second holding in sequence. The first heating and the first heat preservation are carried out in a hydrogen atmosphere; the hydrogen flow rate is 10 m³ / s. 3 / h; the heating rate of the first heating is 2℃ / min; the heating endpoint of the first heating is 450℃; the holding time of the first heating is 120min; The second heating is carried out under vacuum conditions with a vacuum degree of 10 Pa; the heating rate of the second heating is 3 °C / min; the heating endpoint of the second heating is 1410 °C. Argon gas is introduced during the second heat preservation process; the pressure of the argon gas is 6 MPa; the second heat preservation time is 40 min.

[0070] Example 4 This embodiment provides a graphite boat apparatus and sintering method for hard alloy sintering. Except that the mass ratio of high-temperature oxides in the slurry is 10% and the mass ratio of carbon-containing materials is 40%, all other conditions are the same as in Embodiment 1.

[0071] Example 5 This embodiment provides a graphite boat apparatus and sintering method for hard alloy sintering. Except that the mass ratio of high-temperature oxides in the slurry is 45% and the mass ratio of carbon-containing materials is 5%, all other conditions are the same as in Embodiment 1.

[0072] Example 6 This embodiment provides a graphite boat apparatus and sintering method for hard alloy sintering, except that the hydrogen flow rate is 2m³ / s. 3 Except for / h, all other conditions are the same as in Example 1.

[0073] Example 7 This embodiment provides a graphite boat apparatus and sintering method for cemented carbide sintering. Except that the pressure of the argon gas is 2 MPa, all other conditions are the same as in Embodiment 1.

[0074] Comparative Example 1 This comparative example provides a graphite boat apparatus and sintering method for hard alloy sintering. Except that the bottom sidewall of the graphite cover does not have a first through hole, all other conditions are the same as in Example 1.

[0075] Comparative Example 2 This comparative example provides a graphite boat apparatus and sintering method for sintering cemented carbide. Except that the graphite cap does not have nine second through holes in its center, all other conditions are the same as in Example 1.

[0076] Comparative Example 3 This comparative example provides a graphite boat apparatus and sintering method for hard alloy sintering. Except that the inner walls of the graphite cover and the graphite cap are not provided with a carbon conditioning coating, all other conditions are the same as in Example 1.

[0077] Comparative Example 4 This comparative example provides a graphite boat device and sintering method for sintering cemented carbide. Except that the graphite boat device uses conventional graphite strip enclosure sintering, all other conditions are the same as in Example 1.

[0078] Comparative Example 5 This comparative example provides a graphite boat device and sintering method for sintering cemented carbide. Except that the graphite boat device uses conventional graphite strip enclosure sintering, all other conditions are the same as in Example 2.

[0079] The sintered alloy products obtained in the above embodiments and comparative examples were subjected to metallographic structure and relative magnetic saturation performance tests. Relative magnetic saturation was measured using a cobalt magnetic analyzer and calculated using the following formula: Where e is the measured specific saturation magnetization of the sintered alloy product, and W coThe cobalt content (by weight) in the cemented carbide is indicated by the metallographic structure, which is observed under a 100x or 200x microscope after the sintered cemented carbide product has been prepared, polished, and then examined.

[0080] The test results are shown in Table 1.

[0081] Table 1 As shown in Table 1: The graphite boat apparatus and sintering method for cemented carbide sintering provided in Embodiments 1-3 of this invention, by adding graphite covers and graphite caps with specific structures and coatings, combined with optimized sintering methods, ensure the demolding effect while maintaining the carbon balance within the product and the uniformity of the sintering atmosphere in the furnace, and control the relative magnetic saturation difference of the cemented carbide product to within 7%, thereby stabilizing the microstructure of the cemented carbide within the two-phase region and achieving stable and controllable hardness, toughness, and strength.

[0082] A comparison of Examples 1 and 4-5 reveals that if the content of high-temperature oxides in the carbon-conditioned slurry is too low, the overall magnetic saturation strength will be too high due to the excessively high carbon concentration within the graphite boat device, posing a risk of carburization. Conversely, if the content of carbon-containing materials in the carbon-conditioned slurry is too low, the magnetic saturation strength of the edge products will be too low due to the excessively low carbon concentration within the graphite boat device, resulting in a significant difference between the magnetic saturation strength of the edge products and that of the core products.

[0083] A comparison of Examples 1 and 6 shows that if the flow rate of hydrogen gas introduced into the sintering dewaxing section is too low, the forming agent of the compact cannot be fully removed, resulting in residual carbon in the cemented carbide product and the appearance of a carburized phase.

[0084] A comparison of Examples 1 and 7 shows that if the pressure during high-pressure sintering is too low, the pressure during sintering is insufficient to make the product dense, resulting in Class A porosity in the cemented carbide product.

[0085] A comparison of Example 1 and Comparative Examples 1-2 shows that if the graphite cover does not have through holes, the removed molding agent cannot be effectively discharged, resulting in the presence of a carburized phase in the cemented carbide product.

[0086] A comparison of Example 1 and Comparative Example 3 shows that if no carbon conditioning coating is provided, the low carbon atmosphere concentration at the edge will result in decarburization phase in the edge cemented carbide product.

[0087] A comparison of Examples 1 and 2 and Comparative Examples 4 and 5 shows that when conventional graphite strips are used for sintering, the magnetic saturation intensity of the products at the edge and the core differs too much, and decarburization occurs in the products at the edge.

[0088] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A graphite boat apparatus for sintering cemented carbide, characterized in that, The graphite boat-and-vessel device includes a graphite boat-and-vessel assembly, a graphite cover, and a graphite cap. The graphite boat-and-vessel assembly is located inside the graphite cover; The graphite cap is disposed on top of the graphite cover; The graphite cover has a closed side and open ends, and several first through holes are provided at the bottom of the side wall of the graphite cover. The graphite cap has several second through holes in its center; The inner walls of both the graphite cover and the graphite cap are provided with a carbon conditioning coating.

2. The graphite boat apparatus for sintering cemented carbide according to claim 1, characterized in that, The graphite boat assembly comprises several graphite boats stacked on top of each other. Preferably, the graphite boat includes a graphite base plate; Preferably, graphite support points are provided at the four corners of the graphite base plate; Preferably, the graphite fulcrum is used to support and connect the stacked graphite boats; Preferably, the height difference between the graphite support and the cemented carbide product to be sintered is 2mm-10mm; Preferably, the weight of the cemented carbide product to be sintered is <10g, the Co content is <5wt%, and the average grain size of WC is <1μm.

3. The graphite boat apparatus for sintering cemented carbide according to claim 1 or 2, characterized in that, The graphite cover has a wall thickness of 5mm-10mm; Preferably, at least two first through holes are provided on the bottom of the sidewall of the graphite cover; Preferably, the length of the first through hole is 25mm-35mm and the width is 15mm-25mm.

4. The graphite boat apparatus for sintering cemented carbide according to any one of claims 1-3, characterized in that, The thickness of the graphite cap is 5mm-10mm; Preferably, the number of the second through holes is ≥6; Preferably, the diameter of the second through hole is 3mm-7mm; Preferably, the graphite cover is provided with a groove for sealing with the graphite cover.

5. The graphite boat apparatus for sintering cemented carbide according to any one of claims 1-4, characterized in that, The thickness of the carbon conditioning coating is 100μm-300μm; Preferably, the raw materials of the carbon conditioning coating slurry include, by mass percentage: 20%-35% high-temperature oxides, 15%-30% carbon-containing materials, 9%-11% binder, 3%-5% dispersant and 0.1%-1.5% thickener.

6. The graphite boat apparatus for sintering cemented carbide according to claim 5, characterized in that, The high-temperature oxide includes any one or a combination of at least two of aluminum oxide, zirconium oxide, or yttrium oxide; Preferably, the carbon-containing material includes carbon black and / or acetylene black.

7. The graphite boat apparatus for sintering cemented carbide according to claim 5 or 6, characterized in that, The binder comprises orthosilicate and / or sodium silicate; Preferably, the dispersant comprises polyethylene glycol and / or Tween; Preferably, the thickener includes a cellulose-based thickener; Preferably, the slurry raw material for the carbon conditioning coating further includes 30%-40% solvent.

8. A sintering method for cemented carbide, characterized in that, The sintering method includes: Several cemented carbide products to be sintered are placed in the graphite boat apparatus for cemented carbide sintering as described in any one of claims 1-7 for sintering. The sintering process includes a first heating, a first holding, a second heating, and a second holding in sequence.

9. The sintering method according to claim 8, characterized in that, The first heating and the first heat preservation are carried out in a hydrogen atmosphere; Preferably, the hydrogen flow rate is 5m³. 3 / h-10m 3 / h; Preferably, the heating rate of the first heating is 1℃ / min-3℃ / min; Preferably, the endpoint of the first temperature rise is 400℃-500℃; Preferably, the first heat preservation time is 90 min to 150 min.

10. The sintering method according to claim 8 or 9, characterized in that, The second heating is carried out under vacuum conditions, with a vacuum degree ≤20 Pa; Preferably, the heating rate of the second heating is 2℃ / min-5℃ / min; Preferably, the endpoint of the second temperature rise is 1380℃-1500℃; Preferably, an inert gas is introduced during the second heat preservation process; Preferably, the pressure of the inert gas is 5 MPa-10 MPa; Preferably, the second heat preservation time is 30-60 minutes.

Images