Method for preventing sintering distortion of high cobalt cemented carbide

Abstract

The present application belongs to the technical field of cemented carbide production, and particularly relates to a method for preventing sintering deformation of high-cobalt cemented carbide. In the method, spherical metal oxides after carbon supplementing and calcination are filled around the green compact of high-cobalt cemented carbide. When the green compact shrinks with the removal of the forming agent in the sintering process, the spherical metal oxides around the green compact are displaced with the shrinkage of the green compact under the action of gravity, and the displacement of the spherical metal oxides is caused by the instability of the spherical metal oxides. The displacement of the spherical metal oxides can support the green compact at any time, so that the downward and bending deformation of the high-cobalt cemented carbide caused by the excessive cobalt content in the sintering process can be significantly reduced, and the problem of low cobalt magnetism or decarburization of the product can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of cemented carbide production technology, specifically a method for preventing sintering deformation of high-cobalt cemented carbide. Background Technology

[0002] Cemented carbide, often referred to as the "teeth" of industry, is widely used across various sectors. It is a composite material made from refractory metal carbides and binder metals (cobalt, nickel, iron) through powder metallurgy. High-cobalt (cobalt content ≥15wt%) cemented carbide is particularly prevalent in cold heading and stamping. Cemented carbide production typically involves preparing a mixture, pressing it into a compact using a mold, and then sintering it at high temperatures (1380℃~1500℃), exceeding the melting point of the binder metal. As the sintering temperature increases, more liquid binder metal is produced, especially noticeable in high-cobalt alloys. With increased liquid cobalt, the liquid cobalt is prone to downward displacement under gravity. After cooling and solidification, the final product may exhibit unevenness, with larger aspect ratios leading to bending deformation, ultimately affecting the product's dimensional accuracy. Summary of the Invention

[0003] To address the problems existing in the prior art, the main objective of this invention is to propose a method for preventing sintering deformation of high-cobalt cemented carbide.

[0004] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0005] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0006] S1, carbon supplementation and calcination of spherical metal oxides;

[0007] S2. During the sintering of high cobalt cemented carbide, spherical metal oxides after carbon supplementation and calcination are filled around the high cobalt cemented carbide blank, and the filling height of the spherical metal oxides is 60-70% of the high cobalt cemented carbide blank.

[0008] As a preferred embodiment of the method for preventing sintering deformation of high-cobalt hard alloys according to the present invention, in step S1, the spherical metal oxide includes aluminum oxide, zirconium oxide, and yttrium oxide.

[0009] As a preferred embodiment of the method for preventing sintering deformation of high cobalt cemented carbide according to the present invention, in step S1, spherical metal oxide and carbon black are mixed at a mass ratio of 1:1 to 2 and then placed in a graphite box for calcination at a calcination temperature of 1450 to 1500°C for a calcination time of 25 to 35 minutes.

[0010] As a preferred embodiment of the method for preventing sintering deformation of high cobalt hard alloys according to the present invention, in step S1, the calcined spherical metal oxide and carbon black mixture is sieved and then separated by compressed air purging.

[0011] As a preferred embodiment of the method for preventing sintering deformation of high-cobalt cemented carbide according to the present invention, in step S2, the cobalt content of the high-cobalt cemented carbide is ≥15wt%.

[0012] As a preferred embodiment of the method for preventing sintering deformation of high cobalt cemented carbide according to the present invention, in step S2, during the sintering of high cobalt cemented carbide, spherical metal oxides after carbon calcination are first laid flat at the bottom of the container, and then the high cobalt cemented carbide blank is placed.

[0013] As a preferred embodiment of the method for preventing sintering deformation of high-cobalt hard alloys according to the present invention, in step S2, the particle size of the spherical metal oxides after carbon supplementation and calcination is 0.4 to 0.6 mm.

[0014] As a preferred embodiment of the method for preventing sintering deformation of high cobalt hard alloys according to the present invention, in step S2, the thickness of the spherical metal oxide after carbon calcination is first spread flat at the bottom of the container, which is 0.4 to 3.0 mm.

[0015] As a preferred embodiment of the method for preventing sintering deformation of high-cobalt cemented carbide according to the present invention, in step S2, the aspect ratio of the high-cobalt cemented carbide blank is ≥2.

[0016] As a preferred embodiment of the method for preventing sintering deformation of high-cobalt cemented carbide according to the present invention, in step S2, the sintering temperature is 1380~1420℃.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention proposes a method to prevent sintering deformation of high-cobalt cemented carbide. During the sintering of high-cobalt cemented carbide, spherical metal oxides after carbon supplementation and calcination are filled around the high-cobalt cemented carbide compact. As the compact shrinks due to the removal of the forming agent during sintering, the spherical metal oxides filling the compact shrink under the influence of gravity. As the compact shrinks, the spherical metal oxides become unstable and shift, filling the gaps created by the shrinkage of the compact and providing constant support. This significantly reduces the sagging and bending deformation caused by excessive cobalt liquid phase during sintering due to the high cobalt content of the product. It also avoids problems such as low cobalt magnetic properties or even decarburization in the product. Detailed Implementation

[0019] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0020] The main objective of this invention is to propose a method to prevent sintering deformation of high-cobalt cemented carbide, thereby solving the problems of uneven size and bending deformation caused by liquid phase flow during the sintering process.

[0021] According to one aspect of the present invention, the present invention provides the following technical solution:

[0022] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0023] S1, carbon supplementation and calcination of spherical metal oxides;

[0024] S2. During the sintering of high cobalt cemented carbide, spherical metal oxides after carbon supplementation and calcination are filled around the high cobalt cemented carbide blank, and the filling height of the spherical metal oxides is 60-70% of the high cobalt cemented carbide blank.

[0025] Preferably, in step S1, the spherical metal oxide includes alumina, zirconium oxide, and yttrium oxide; more preferably, the spherical metal oxide and carbon black are mixed at a mass ratio of 1:1 to 2 and then placed in a graphite box for calcination at a temperature of 1450 to 1500°C for 25 to 35 minutes; the calcined mixture of spherical metal oxide and carbon black is then sieved and separated by compressed air purging. Specifically, the mass ratio of spherical metal oxide to carbon black can be, for example, but not limited to, any one or a range between any two of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, and 1:2; the calcination temperature can be, for example, but not limited to, any one or a range between any two of 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, and 1500℃; and the calcination time can be, for example, but not limited to, any one or a range between any two of 25min, 26min, 27min, 28min, 29min, 30min, 31min, 32min, 33min, 34min, and 35min.

[0026] Preferably, in step S2, the cobalt content of the high-cobalt cemented carbide is ≥15wt%; during the sintering of the high-cobalt cemented carbide, spherical metal oxides after carbon supplementation and calcination are first spread evenly at the bottom of the container, and then the high-cobalt cemented carbide compact is placed; the particle size of the spherical metal oxides after carbon supplementation and calcination is 0.4-0.6mm; the thickness of the spherical metal oxides after carbon supplementation and calcination spread evenly at the bottom of the container is 0.4-3.0mm; the aspect ratio of the high-cobalt cemented carbide compact is ≥2; and the sintering temperature is 1380-1420℃. Specifically, the particle size of the spherical metal oxide after carbon supplementation and calcination can be, for example, but not limited to, any one or any two of 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, and 0.6 mm; the thickness of the spherical metal oxide after carbon supplementation and calcination first spread at the bottom of the container can be, for example, but not limited to, any one or any two of 0.4 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm; the filling height of the spherical metal oxide can be, for example, but not limited to, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, and 70% of the high-cobalt cemented carbide compact; and the sintering temperature can be, for example, but not limited to, any one or any two of 1380℃, 1390℃, 1400℃, 1410℃, and 1420℃.

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0030] S1. After thoroughly mixing 0.6mm alumina spherical particles and high-purity carbon black at a mass ratio of 1:1, the mixture is placed in a graphite box and calcined at a temperature of 1450℃ for 30 minutes. The calcined alumina and carbon black mixture is then sieved and purged with compressed air to separate the two. The separated alumina is then packaged in a sealed container.

[0031] S2. Alternatively, select a graphite box with one open side. Lay 0.6mm calcined alumina spherical particles from step S1 on the bottom of the graphite box, with a thickness of 0.6mm. Place the pressed high-cobalt (cobalt content equal to 15wt%) cemented carbide billet on the laid alumina. The billet has an outer diameter of 20mm, a length of 60mm, and an aspect ratio of 3:1. Fill the high-cobalt cemented carbide billet with 0.6mm calcined alumina spherical particles from step S1, with a particle size of 0.6mm, at a height of about 60% of the billet height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1420℃. After completion, remove the product.

[0032] Example 2

[0033] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0034] S1. After thoroughly mixing 0.5mm alumina spherical particles and high-purity carbon black at a mass ratio of 1:1.5, the mixture is placed in a graphite box and calcined at a temperature of 1450℃ for 35 minutes. The calcined alumina and carbon black mixture is then sieved and purged with compressed air to separate the two. The separated alumina is then sealed in a sealed container.

[0035] S2. Alternatively, select a graphite box with one open side. Lay 0.5mm calcined alumina spherical particles from step S1 on the bottom of the graphite box, with a thickness of about 1.5mm. Place the pressed high-cobalt (cobalt content equal to 20wt%) cemented carbide blank on the laid alumina. The blank has an outer diameter of 20mm, a length of 60mm, and an aspect ratio of 3:1. Fill the high-cobalt cemented carbide blank with 0.5mm calcined alumina spherical particles from step S1, with a particle size of about 65% of the blank height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1400℃. After completion, the product can be removed.

[0036] Example 3

[0037] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0038] S1. After thoroughly mixing the mixture of alumina and zirconia spherical particles with a particle size of 0.4mm and high-purity carbon black at a mass ratio of 1:2, the mixture is placed in a graphite box and calcined at a temperature of 1450℃ for 25 minutes. The calcined mixture of alumina and zirconia spherical particles and carbon black is then sieved and purged with compressed air to separate the two. The separated mixture of alumina and zirconia spherical particles is then sealed in a sealed container.

[0039] S2. Alternatively, select a graphite box with one open side. Lay a mixture of 0.4mm spherical alumina and zirconia particles obtained from step S1 on the bottom of the graphite box, with a thickness of about 2.0mm. Place the pressed high-cobalt (cobalt content equal to 25wt%) cemented carbide blank on the mixture of spherical alumina and zirconia particles. The blank has an outer diameter of 20mm, a length of 40mm, and an aspect ratio of 2:1. Fill the high-cobalt cemented carbide blank with the mixture of 0.4mm spherical alumina and zirconia particles obtained from step S1, with the particle size of the particles, at a height of about 70% of the blank height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1400℃. After completion, remove the product.

[0040] Example 4

[0041] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0042] S1. After thoroughly mixing 0.6mm zirconia spherical particles and high-purity carbon black at a mass ratio of 1:1, the mixture is placed in a graphite box and calcined at a temperature of 1500℃ for 30 minutes. The calcined zirconia and carbon black mixture is then sieved and purged with compressed air to separate the two. The separated zirconia is then sealed in a sealed container.

[0043] S2. Alternatively, select a graphite box with one open side. Lay 0.6mm zirconia spherical particles (calcined in step S1) on the bottom of the graphite box, with a thickness of about 3.0mm. Place the pressed high-cobalt (cobalt content equal to 15wt%) cemented carbide blank on the laid zirconia. The blank has an outer diameter of 20mm, a length of 60mm, and an aspect ratio of 3:1. Fill the high-cobalt cemented carbide blank with 0.6mm zirconia spherical particles (calcined in step S1) around it, with a laying height of about 60% of the blank height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1400℃. After completion, remove the product.

[0044] Example 5

[0045] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0046] S1. Mix 0.5mm yttrium oxide spherical particles and high-purity carbon black at a mass ratio of 1:1.5, then load them into a graphite box for calcination at a temperature of 1480℃ for 30 minutes. After calcination, the yttrium oxide and carbon black mixture is sieved and purged with compressed air to separate the two. The separated yttrium oxide is then sealed in a sealed container.

[0047] S2. Alternatively, select a graphite box with one open side. Lay 0.5mm yttrium oxide spherical particles (calcined in step S1) on the bottom of the graphite box, with a thickness of about 1.5mm. Place the pressed high-cobalt (cobalt content equal to 20wt%) cemented carbide blank on the laid yttrium oxide. The blank has an outer diameter of 20mm, a length of 60mm, and an aspect ratio of 3:1. Fill the high-cobalt cemented carbide blank with 0.5mm yttrium oxide spherical particles (calcined in step S1) around it, with a particle size of about 65% of the blank height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1380℃. After completion, the product can be removed.

[0048] Example 6

[0049] A method for preventing sintering deformation of high-cobalt cemented carbide includes the following steps:

[0050] S1. A mixture of alumina, zirconium oxide, yttrium oxide spherical particles with a particle size of 0.5 mm and high-purity carbon black are thoroughly mixed at a mass ratio of 1:1.5. The mixture is then placed in a graphite box and calcined at a temperature of 1450℃ for 30 minutes. The calcined mixture of alumina, zirconium oxide, yttrium oxide spherical particles and carbon black is then sieved and purged with compressed air to separate the two. The separated mixture of alumina, zirconium oxide, yttrium oxide spherical particles is then sealed in a sealed container.

[0051] S2. Alternatively, select a graphite box with one open side. Lay a mixture of 0.5mm spherical alumina, zirconium oxide, and yttrium oxide spherical particles obtained from step S1 on the bottom of the graphite box, with a thickness of about 1.5mm. Place the pressed high-cobalt (cobalt content equal to 20wt%) cemented carbide blank on the laid mixture of alumina, zirconium oxide, and yttrium oxide spherical particles. The blank has an outer diameter of 20mm, a length of 60mm, and an aspect ratio of 3:1. Fill the high-cobalt cemented carbide blank with the mixture of alumina, zirconium oxide, and yttrium oxide spherical particles obtained from step S1, with a particle size of 0.5mm, and lay it to a height of about 65% of the blank height. Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1400℃. After completion, remove the product.

[0052] Comparative Example 1

[0053] A method for sintering high-cobalt cemented carbide includes the following steps:

[0054] A graphite box with one open side was selected, and 0.6 mm calcined alumina spherical particles were laid flat at the bottom of the graphite box with a thickness of 0.6 mm.

[0055] The pressed high-cobalt (cobalt content equals 15wt%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20mm, a length of 60mm, and a length-to-diameter ratio of 3:1.

[0056] Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1420℃. Once completed, remove the product.

[0057] Comparative Example 2

[0058] A method for sintering high-cobalt cemented carbide includes the following steps:

[0059] A graphite box with one open side is selected. The bottom of the graphite box is laid flat with 0.5mm calcined alumina spherical particles from Example 2, with a thickness of about 1.5mm.

[0060] The pressed high-cobalt (cobalt content equals 20wt%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20mm, a length of 60mm, and a length-to-diameter ratio of 3:1.

[0061] Completely cover the graphite box with a graphite plate, place it in a dewaxing vacuum sintering furnace, and sinter at a final temperature of 1400℃. Once completed, remove the product.

[0062] Comparative Example 3

[0063] A method for sintering high-cobalt cemented carbide includes the following steps:

[0064] A graphite box with one open side is selected. The bottom of the graphite box is covered with 0.5mm calcined alumina spherical particles from Example 2, with a thickness of about 3mm.

[0065] The pressed high-cobalt (cobalt content equals 25wt%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20mm, a length of 40mm, and a length-to-diameter ratio of 2:1.

[0066] Completely cover the graphite box with a graphite plate, place it in a dewaxing vacuum sintering furnace, and sinter at a final temperature of 1400℃. Once completed, remove the product.

[0067] Comparative Example 4

[0068] A method for sintering high-cobalt cemented carbide includes the following steps:

[0069] A graphite box with one open side is selected, and the bottom of the graphite box is covered with 0.6mm alumina polyhedrons with a thickness of 0.6mm.

[0070] The pressed high-cobalt (cobalt content equals 15%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20 mm, a length of 60 mm, and a length-to-diameter ratio of 3:1.

[0071] Polyhedral alumina with a particle size of 0.6 mm is filled around the high cobalt cemented carbide blank, and the height of the filling is about 60% of the blank height.

[0072] Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1420℃. Once completed, remove the product.

[0073] Comparative Example 5

[0074] A method for sintering high-cobalt cemented carbide includes the following steps:

[0075] Select a graphite box with one open side, and lay 0.5mm alumina polyhedrons on the bottom of the graphite box with a thickness of about 1.5mm.

[0076] The pressed high-cobalt (cobalt content equals 20%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20 mm, a length of 60 mm, and a length-to-diameter ratio of 3:1.

[0077] Polyhedral alumina particles with a diameter of 0.5 mm are filled around the high-cobalt cemented carbide blank, and the particle height is about 65% of the blank height.

[0078] Completely cover the graphite box with a graphite plate, place it in a dewaxing vacuum sintering furnace, and sinter at a final temperature of 1400℃. Once completed, remove the product.

[0079] Comparative Example 6

[0080] A method for sintering high-cobalt cemented carbide includes the following steps:

[0081] Select a graphite box with one open side, and lay 0.4mm alumina polyhedrons on the bottom of the graphite box with a thickness of about 3mm.

[0082] The pressed high-cobalt (cobalt content equals 25%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20 mm, a length of 40 mm, and a length-to-diameter ratio of 2:1.

[0083] Polyhedral alumina particles with a particle size of 0.4 mm are filled around the high-cobalt cemented carbide blank, and the particle height is about 70% of the blank height.

[0084] Completely cover the graphite box with a graphite plate, place it in a dewaxing vacuum sintering furnace, and sinter at a final temperature of 1400℃. Once completed, remove the product.

[0085] Comparative Example 7

[0086] A method for sintering high-cobalt cemented carbide includes the following steps:

[0087] Select a graphite box with one open side, and lay uncalcined 0.6mm alumina spherical particles on the bottom of the graphite box with a thickness of 0.6mm.

[0088] The pressed high-cobalt (cobalt content equals 15%) cemented carbide billet is placed on the laid alumina. The billet has an outer diameter of 20 mm, a length of 60 mm, and a length-to-diameter ratio of 3:1.

[0089] Uncalcined spherical alumina particles with a particle size of 0.6 mm are filled around the high cobalt cemented carbide blank, and the height of the filling is about 60% of the blank height.

[0090] Completely cover the graphite box with a graphite plate and place it in a dewaxing vacuum sintering furnace for sintering at a final sintering temperature of 1420℃. Once completed, remove the product.

[0091] The high-cobalt cemented carbides of each embodiment and comparative example after sintering were tested, and the test results are shown in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] In this invention, during the sintering of high-cobalt cemented carbide, spherical metal oxides, after carbon supplementation and calcination, are filled around the high-cobalt cemented carbide compact. During the sintering process, the compact shrinks as the forming agent is removed. Under the influence of gravity, the spherical metal oxides filling the compact shrink and their volume decreases. As the compact shrinks, the spherical metal oxides become unstable and shift, filling the gaps created by the shrinking compact and providing constant support. This significantly reduces the sagging and bending deformation caused by excessive cobalt liquid phase during sintering due to the high cobalt content in the product. It also avoids problems such as low cobalt magnetic properties or even decarburization in the product.

[0096] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preventing sintering deformation of high-cobalt cemented carbide, characterized in that, Includes the following steps: S1. Carbon supplementation calcination of spherical metal oxides: Spherical metal oxides and carbon black are mixed at a mass ratio of 1:1~2 and then placed in a graphite box for calcination at a temperature of 1450~1500℃ for 25~35min. The calcined mixture of spherical metal oxides and carbon black is sieved and then separated by compressed air. The separated spherical metal oxides are then sealed in a sealed container. S2. Sintering of high-cobalt cemented carbide in a dewaxing vacuum sintering furnace: First, spread spherical metal oxides after carbon supplementation and calcination on the bottom of the graphite box, then place the high-cobalt cemented carbide blank. The cobalt content of the high-cobalt cemented carbide is ≥15wt%. Fill the high-cobalt cemented carbide blank with the spherical metal oxides after carbon supplementation and calcination. The filling height of the spherical metal oxides is 60~70% of the length of the high-cobalt cemented carbide blank. The length-to-diameter ratio of the high-cobalt cemented carbide blank is ≥2. Completely cover the graphite box with a graphite plate and place it in the dewaxing vacuum sintering furnace for sintering.

2. The method for preventing sintering deformation of high-cobalt cemented carbide according to claim 1, characterized in that, In step S1, the spherical metal oxide is any one of aluminum oxide, zirconium oxide, and yttrium oxide; or the spherical metal oxide is aluminum oxide and zirconium oxide; or the spherical metal oxide is aluminum oxide, zirconium oxide, and yttrium oxide.

3. The method for preventing sintering deformation of high-cobalt cemented carbide according to claim 1, characterized in that, In step S2, the particle size of the spherical metal oxide after carbon supplementation and calcination is 0.4~0.6mm.

4. The method for preventing sintering deformation of high-cobalt cemented carbide according to claim 1, characterized in that, In step S2, the thickness of the spherical metal oxides after carbon calcination laid flat at the bottom of the graphite box is 0.4~3.0 mm.

5. The method for preventing sintering deformation of high-cobalt cemented carbide according to claim 1, characterized in that, In step S2, the sintering temperature is 1380~1420℃.

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