Cemented carbide and method for producing the same

Abstract

This invention belongs to the field of powder metallurgy technology, specifically relating to a cemented carbide and its preparation method. The preparation method includes the following steps: S1, preparing a premix according to a formula, ball milling the premix to obtain a slurry, and dividing it into a first slurry and a second slurry; S2, subjecting the first slurry to a first drying process to obtain a first mixture, and subjecting the second slurry to a second drying process to obtain a second mixture; S3, placing the first mixture and the second mixture into a preset mold according to a preset mass ratio and pressing them to obtain a compact. This invention prepares two mixtures of the same composition using different methods, and then uniformly mixes these two mixtures in different proportions to press small-sample compacts. This solves the problem of mold and material matching limitations during the pressing process, reduces mold manufacturing costs, ensures the quality of the compacted product, is easy to adjust, and is suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically a cemented carbide and its preparation method. Background Technology

[0002] Hard alloys are alloy materials made from hard compounds of refractory metals and binder metals through powder metallurgy. Powder metallurgy is a process technology that uses metal powders (or mixtures of metal and non-metal powders) as raw materials, followed by forming and sintering, to manufacture metallic materials, composite materials, and various types of products. Among these, compression molding is widely used in the hard alloy industry due to its advantages such as high production efficiency, high material utilization, and excellent surface quality.

[0003] Compression molding has relatively high requirements for powder raw materials. The industry usually uses spray granulation to obtain powder raw materials with a certain bulk ratio, flow rate, and good particle morphology. By using powder raw materials with stable bulk ratio, flow rate, and good particle morphology, and a mold with a suitable shrinkage coefficient, a compact with good density is pressed out, and after sintering, a cemented carbide with excellent appearance and performance is prepared.

[0004] However, this method is highly dependent on raw materials and molds, resulting in relatively poor applicability. For example: 1. Pressing the same product with different raw materials requires molds with different shrinkage coefficients to produce compacts with good density. However, due to the high cost of mold manufacturing, mass production of molds is not conducive to long-term production development, especially for products with small order volumes; 2. Pressing the same product with different raw materials using a specific mold can only produce compacts with good density by adjusting the raw material bulk ratio. However, the adjustment range of the bulk ratio of raw materials obtained by spray granulation is limited. How to prepare cemented carbide with excellent appearance and performance using different raw materials under a mold with a specific shrinkage coefficient has become a technical research challenge. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing cemented carbide, comprising the following steps:

[0006] S1. Prepare a premix according to the formula, ball mill the premix to obtain a slurry, and divide it into a first slurry and a second slurry;

[0007] S2. The first slurry is dried in the first stage to obtain a first mixture, and the second slurry is dried in the second stage to obtain a second mixture. The D50 particle size of the first mixture is 80~150μm, and the D50 particle size of the second mixture is less than or equal to 30μm.

[0008] S3. The first mixture and the second mixture are placed into a preset mold according to a preset mass ratio and pressed to obtain a pressed blank;

[0009] S4. The pressed blank is sintered to obtain a cemented carbide.

[0010] In step S1, the tungsten carbide content in the premix is ​​90wt%~94wt%, with the remainder being cobalt powder. The Fisher particle size of the tungsten carbide is 2~3μm, and the ball milling medium is 94wt%~96wt% ethanol.

[0011] Specifically, step S2 involves drying the first slurry with inert gas in a spray device at an outlet temperature of 90-100°C, and then cooling it with a vibrating table to obtain the first mixture with particle morphology, wherein the temperature of the first mixture is less than or equal to 26°C; and then heating, vacuuming, stirring and drying, and cooling the second slurry in a vacuum stirring dryer, and then crushing it with a vibrating grating screen to obtain the second mixture.

[0012] In step S3, the preset mass ratio and the preset mold are determined by the following method:

[0013] S31. The first mixture and the second mixture are mixed at a mass ratio of a:(10-a) to prepare a small sample, wherein 1≤a<10;

[0014] S32. Select a mold with any shrinkage coefficient, and place the small sample into the mold to press it to obtain the pressed blank;

[0015] S33. Detect the density of the pressed blank, select a qualified pressed blank that meets the standard, take the mass ratio of the first mixture and the second mixture in the sample used to prepare the qualified pressed blank as the preset mass ratio, and take the mold as the preset mold;

[0016] Preferably, step S31 specifically involves: mixing the first mixture and the second mixture in mass ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9 to prepare small samples.

[0017] In step S32, the shrinkage coefficient of the preset mold is 1.19~1.22.

[0018] In step S33, the density of the qualified pressed blank is 8.0~9.0 g / cm³. 3 ;

[0019] Furthermore, the surface of the qualified pressed blank is flat and smooth, with regular particle accumulation patterns.

[0020] In step S4, the sintering temperature is 1400~1500℃ and the sintering time is 90~100min.

[0021] To solve the above-mentioned technical problems, the present invention also provides a cemented carbide, which is prepared by the above-described cemented carbide preparation method.

[0022] The metallographic microstructure of the cemented carbide (detected using the national standard (GB / T 3488.4-2022 Metallographic determination of cemented carbide microstructure - Part 4: Metallographic determination of porosity, non-combined carbon defects and decarburized phases)) has a porosity of A00B00, a non-combined carbon structure of C00, and a decarburized phase of E00.

[0023] This invention prepares two mixtures of the same composition using different methods. These two mixtures are then mixed evenly in different proportions and pressed into small blanks. A mixing ratio with excellent density and appearance is selected for the small blanks. The two mixtures are then mass-produced and mixed evenly in a batching machine according to this ratio to obtain a mixed material. The mixed material is then used to press blanks and sinter to obtain alloy products with excellent appearance and performance. This invention solves the problem of mold and material matching limitations during the pressing process, reduces mold manufacturing costs, ensures the quality of the pressed blanks, is easy to adjust, and is suitable for mass production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a morphological image of the first mixture in Example 1;

[0026] Figure 2 This is an image showing the appearance of the second mixture in Example 1;

[0027] Figure 3 This is a microscopic view of the qualified pressed blank obtained in Example 1;

[0028] Figure 4 Metallographic images of the cemented carbide obtained in Example 1;

[0029] Figure 5 This is a microscopic view of the pressed blank used in Comparative Example 1;

[0030] Figure 6 The image shows the microscopic appearance of the compact used in Comparative Example 2.

[0031] Figure 7Metallographic images of the cemented carbide obtained in Comparative Example 2;

[0032] Figure 8 The image shows the metallographic examination results of the cemented carbide obtained in Comparative Example 3.

[0033] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0034] 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.

[0035] This invention provides a method for preparing cemented carbide, comprising the following steps:

[0036] S1. Prepare a premix according to the formula, ball mill the premix to obtain a slurry, and divide it into a first slurry and a second slurry;

[0037] In an embodiment of the present invention, after preparing the premixed material according to the formula and ball milling it to obtain a slurry, it is divided into two slurries with completely identical components.

[0038] In a preferred embodiment of the present invention, the content of tungsten carbide powder is 90wt%~94wt%, the balance is cobalt powder, and the Fisher particle size of tungsten carbide is 2~3μm.

[0039] S2. The first slurry is dried in the first stage to obtain a first mixture, and the second slurry is dried in the second stage to obtain a second mixture. The D50 particle size of the first mixture is 80~150μm, and the D50 particle size of the second mixture is less than or equal to 30μm.

[0040] In an embodiment of the present invention, the first slurry and the second slurry are subjected to different drying treatments to obtain two mixtures with different particle sizes;

[0041] In an embodiment of the present invention, the first slurry is dried by convection with high-temperature inert gas in a spray device, with an outlet temperature of 90~100°C. It is then cooled by a vibrating table to obtain the first mixture with particle morphology. The temperature of the first mixture after cooling is less than or equal to 26°C. The outlet and cooling temperatures of the material affect the morphology of the mixture, causing agglomeration, clumping, and defects such as product porosity and bulging. The second slurry is heated, vacuumed, stirred, dried, and cooled in a vacuum stirring dryer in sequence, and then crushed by a vibrating crushing screen to obtain the second mixture.

[0042] S3. The first mixture and the second mixture are placed into a preset mold according to a preset mass ratio and pressed to obtain a pressed blank;

[0043] In an embodiment of the present invention, in order to ensure that the density of the compacts prepared by molds with different shrinkage coefficients can meet the requirements, a method is adopted to prepare small samples of the first mixture and the second mixture in different mass ratios in advance. The compacts are prepared by using the small samples, and their density and appearance are tested to determine whether they are qualified. This determines the mass ratio of the first mixture and the second mixture corresponding to the mold, that is, to obtain the preset mass ratio and the preset mold, and then large-scale production can be carried out.

[0044] S4. The pressed blank is sintered to obtain a cemented carbide.

[0045] This invention enables the preparation of cemented carbide without appearance defects for molds with different shrinkage coefficients. The metallographic microstructure of the cemented carbide conforms to the standard of GB / T3488.4-2022, which specifies porosity of A00B00, non-combined carbon structure of C00, and decarburized phase of E00. This solves the problem of limited matching between mold and material during the pressing process, reduces mold manufacturing costs, and ensures the quality of pressed products.

[0046] Example 1

[0047] The premix was prepared according to the formula, put into a ball mill and added an appropriate amount of ball milling media. After ball milling and mixing evenly, a slurry was obtained, which was then divided into a first slurry and a second slurry. The premix contained 92 wt% tungsten carbide and the remainder was cobalt powder. The tungsten carbide had a Fisher particle size of 3.0 μm and the ball milling media was 95 wt% ethanol.

[0048] The first slurry was dried by convection with inert gas in a spray device, and then cooled by a vibrating table to obtain a first mixture with a particle morphology. The D50 particle size of the first mixture was 94.84 μm. The inert gas was nitrogen, the material outlet temperature was 95℃, and the temperature of the cooled first mixture was 23℃. Please refer to [link / reference]. Figure 1 , Figure 1 The image shows the appearance of the first mixture in Example 1, which consists of regular spherical particles.

[0049] The second slurry was sequentially heated, vacuumed, stirred, dried, and cooled in a vacuum mixer-dryer, and then crushed through a vibrating sieve to obtain the second mixture. The D50 particle size of the second mixture was 25 μm. The heating method was to pass water at 95°C. Please refer to [link to relevant documentation]. Figure 2 , Figure 2 This is an image showing the appearance of the second mixture in Example 1, with irregular particle morphology.

[0050] A mold with a shrinkage coefficient of 1.20 was selected. Small samples were prepared by mixing the first and second mixtures at mass ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9. These samples were then pressed using the mold to obtain compacts. The surface condition of each compact was observed under an optical microscope, and its density was measured. The compact pressed from the sample with a first and second mixture mass ratio of 7:3 was deemed a qualified compact with a density of 8.51 g / cm³. 3 Please see Figure 3 , Figure 3 The image shows the appearance of the compact with a mass ratio of 7:3 under an optical microscope in Example 1. Its surface is flat and smooth with regular particle accumulation patterns. Using 7:3 as the preset mass ratio, the above mold is used as the preset mold for mass production of compacts. The compacts are sintered to obtain cemented carbide at a temperature of 1440°C and a sintering time of 95 minutes.

[0051] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0052] Please see Figure 4 , Figure 4 The image shows a metallographic photograph of the cemented carbide obtained in Example 1, which shows no internal defects.

[0053] Example 2

[0054] Unlike Example 1, the premix contained 94 wt% tungsten carbide with a Fisher particle size of 2.0 μm, and the ball milling media consisted of 96 wt% ethanol. The discharge temperature of the material was 97°C, and the cooling temperature was 25°C. A sample with a mass ratio of 7:3 of the first mixture and the second mixture was pressed into a qualified compact with a density of 8.64 g / cm³. 3 The preset mass ratio is 7:3.

[0055] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0056] Example 3

[0057] Unlike Example 1, the premix contained 90 wt% tungsten carbide with a Fisher particle size of 2.5 μm, and the ball milling media consisted of 94 wt% ethanol. The discharge temperature of the material was 93°C, and the temperature after cooling was 22°C. A sample with a mass ratio of 8:2 of the first mixture and the second mixture was pressed into a qualified compact with a density of 8.39 g / cm³. 3 The preset mass ratio is 8:2.

[0058] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, and the decarburized phase is E00, that is, there are no internal defects such as pores and carburized phases.

[0059] Example 4

[0060] Unlike Example 1, the shrinkage coefficient of the mold was 1.19, and the sample with a mass ratio of the first mixture to the second mixture of 8:2 was pressed into a qualified compact with a density of 8.73 g / cm³. 3 The preset mass ratio is 8:2.

[0061] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0062] Example 5

[0063] Unlike Example 1, the shrinkage coefficient of the mold was 1.22, and the sample with a mass ratio of the first mixture to the second mixture of 5:5 was pressed into a qualified compact with a density of 8.1 g / cm³. 3 The preset mass ratio is 5:5.

[0064] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0065] Example 6

[0066] Unlike Example 1, the particle size of the first mixture is 140 μm, and the particle size of the second mixture is 15 μm.

[0067] The obtained cemented carbide has no external defects. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0068] Comparative Example 1

[0069] Unlike Example 1, the first mixture was placed in a mold and directly pressed to form a compact and prepare cemented carbide. Please refer to [link to example]. Figure 5 , Figure 5 The image shows the appearance of the compact obtained in Comparative Example 1 under an optical microscope. Its surface is rough and has obvious pores.

[0070] The obtained cemented carbide exhibits cracks on its surface. In its metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and macroscopic pores are present. Please refer to [link / reference needed]. Figure 7 , Figure 7 The metallographic image of the cemented carbide obtained in Comparative Example 1 shows numerous pore defects.

[0071] Comparative Example 2

[0072] Unlike Example 1, a second mixture was placed in a mold and directly pressed to form a compact and prepare cemented carbide. Please refer to [link to relevant documentation]. Figure 6 , Figure 6 The image shows the appearance of the compact obtained in Comparative Example 2 under an optical microscope. Its surface has wrinkles and irregular particle accumulation patterns.

[0073] The obtained cemented carbide has wrinkled appearance. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are no internal defects such as pores or carburized phases.

[0074] Comparative Example 3

[0075] Unlike Example 1, a density of 7.7 g / cm³ was used. 3 The compact is formed when the mass ratio of the first mixture to the second mixture is 4:6. The surface of the compact is smooth and has regular particle accumulation patterns. 4:6 is used as the preset mass ratio.

[0076] The obtained cemented carbide had no visible defects. In its metallographic microstructure, the porosity was A00B00, the non-combined carbon structure was C00, and the decarburized phase was E00. The alloy size was 20.21 mm. 5.28mm 7.17mm, compared to the target size of 20.89mm 5.46mm The difference is significant at 6.71mm.

[0077] Comparative Example 4

[0078] Unlike Example 1, a density of 9.8 g / cm³ was used. 3 The pressed blanks were produced with a mass ratio of 9:1 between the first and second mixtures. The pressed blanks all exhibited wrinkles and delamination, and were not used for the preparation of cemented carbide.

[0079] Comparative Example 5

[0080] Unlike Example 1, the material discharge temperature was 110°C, and the temperature after cooling was 23°C.

[0081] The obtained cemented carbide has a defect-free appearance. In its metallographic microstructure, the porosity is A04B00, the non-combined carbon structure is C00, and the decarburized phase is E00. Please refer to [link / reference needed]. Figure 8 , Figure 8 The metallographic image of the cemented carbide obtained in Comparative Example 4 shows porosity.

[0082] Comparative Example 6

[0083] Unlike Example 1, the discharge temperature of the material is 80°C, and the temperature after cooling is 23°C.

[0084] The resulting cemented carbide exhibits bubbling on its surface. In its metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, and the decarburized phase is E00.

[0085] Comparative Example 7

[0086] Unlike Example 1, the discharge temperature of the material is 95°C, and the temperature after cooling is 40°C.

[0087] The resulting cemented carbide exhibits deformation in appearance. In its metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and macroscopic pores are present.

[0088] Comparative Example 8

[0089] Unlike Example 1, the D50 particle size of the first mixture is 68.23 μm;

[0090] The resulting cemented carbide has a wrinkled appearance. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, and the decarburized phase is E00.

[0091] Comparative Example 9

[0092] Unlike Example 1, the D50 particle size of the second mixture is 50 μm;

[0093] The metallographic microstructure of the obtained cemented carbide has a porosity of A00B00, a non-combined carbon structure of C00, a decarburized phase of E00, and macroscopic pores.

[0094] Comparative Example 10

[0095] Unlike Example 1, the shrinkage coefficient of the mold is 1.17;

[0096] The resulting cemented carbide has a wrinkled appearance. In the metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, and the decarburized phase is E00.

[0097] Comparative Example 11

[0098] Unlike Example 1, the shrinkage coefficient of the mold is 1.24;

[0099] The obtained cemented carbide exhibits cracks on its surface. In its metallographic microstructure, the porosity is A00B00, the non-combined carbon structure is C00, the decarburized phase is E00, and there are macroscopic pores.

[0100] This invention prepares two mixtures of the same composition using different methods. These two mixtures are then mixed evenly in different proportions and pressed into small blanks. A mixing ratio with excellent density and appearance is selected for the small blanks. The two mixtures are then mass-produced and mixed evenly in a batching machine according to this ratio to obtain a mixed material. The mixed material is then used to press blanks and sinter to obtain alloy products with excellent appearance and performance. This invention solves the problem of mold and material matching limitations during the pressing process, reduces mold manufacturing costs, ensures the quality of the pressed blanks, is easy to adjust, and is suitable for mass production.

[0101] 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 preparing a cemented carbide, characterized in that, Includes the following steps: S1. Prepare a premix according to the formula, ball mill the premix to obtain a slurry, and divide it into a first slurry and a second slurry; S2. The first slurry is dried in the first stage to obtain a first mixture, and the second slurry is dried in the second stage to obtain a second mixture. The D50 particle size of the first mixture is 80~150μm, and the D50 particle size of the second mixture is less than or equal to 30μm. S3. The first mixture and the second mixture are placed into a preset mold according to a preset mass ratio and pressed to obtain a pressed blank; S4. Sinter the pressed blank to obtain a cemented carbide; In step S1, the tungsten carbide content in the premix is ​​90wt%~94wt%, with the remainder being cobalt powder, and the tungsten carbide has a Fisher particle size of 2~3μm. Specifically, step S2 involves drying the first slurry with inert gas in a spray device at an outlet temperature of 90-100°C, and then cooling it with a vibrating table to obtain the first mixture with particle morphology, wherein the temperature of the first mixture is less than or equal to 26°C; and then heating, vacuuming, stirring and drying, and cooling the second slurry in a vacuum stirring dryer, and then crushing it with a vibrating grating screen to obtain the second mixture. In step S3, the preset mass ratio and the preset mold are determined by the following method: S31. The first mixture and the second mixture are mixed at a mass ratio of a:(10-a) to prepare a small sample, wherein 1≤a<10; S32. Select a mold with any shrinkage coefficient, and place the small sample into the mold to press it to obtain the pressed blank; S33. Detect the density of the pressed blank, select a qualified pressed blank that meets the standard, take the mass ratio of the first mixture and the second mixture in the sample used to prepare the qualified pressed blank as the preset mass ratio, and take the mold as the preset mold.

2. The method for preparing a cemented carbide according to claim 1, characterized in that, The ball milling medium used in the ball mill is 94wt%~96wt% ethanol.

3. The method for preparing a cemented carbide according to claim 1, characterized in that, In step S32, the shrinkage coefficient of the preset mold is 1.19~1.

22.

4. The method for preparing a cemented carbide according to claim 1, characterized in that, In step S33, the density of the qualified pressed blank is 8.0~9.0 g / cm³. 3 .

5. The method for preparing a cemented carbide according to claim 1, characterized in that, In step S4, the sintering temperature is 1400~1500℃ and the sintering time is 90~100min.

6. A cemented carbide, characterized in that, The cemented carbide is prepared by the cemented carbide preparation method according to any one of claims 1 to 5.

Images