A method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder

Abstract

This invention relates to a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method includes the following steps: (1) sampling the mixture of tungsten carbide powder and cobalt powder and sealing and storing the sample; (2) preparing the sealed sample into an identification compact, storing the compact in a fixed environment until the expiration date, then placing it in a graphite boat and sintering it together with a large batch of products; (3) testing the magnetic properties of the sintered identification compact. The identification method simulates the actual production cycle to the greatest extent possible. The graphite boat isolates the sample from atmospheric influences without causing carbon buildup, and the identification results can reliably guide large-scale production.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide raw material testing technology, and in particular to a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. Background Technology

[0002] Currently, before mass production of WC-Co cemented carbide products, it is usually necessary to sample and identify the mixture of tungsten carbide and cobalt powder to ensure the quality of the batch products. This involves testing the material properties to determine if they meet standards, with magnetic properties being a key indicator for evaluating the quality of the mixture. The current identification method typically involves extracting a small amount of powder from a large batch of tungsten carbide and cobalt powder mixture, preparing an identification compact using conventional forming methods, and then sintering this compact along with the batch products. However, due to atmospheric differences between sintering furnaces, and the dynamic changes in the specifications, quantity, and weight of batch sintered products at different locations and in different furnace cycles, the sintering environment of the identification samples is extremely unstable. This instability is particularly significant for fine-grained grades (grain size ≤ 1 μm) and low cobalt content (cobalt content ≤ 6% wt), easily leading to large fluctuations in the magnetic properties of the identification samples. For example, the relative fluctuation of the magnetic saturation value of the same batch of 0.4μm WC-6%Co material in different furnaces can reach 12%, while the fluctuation value of 0.4μm WC-3%Co material can even reach 16%. The large fluctuation of the magnetic properties of the test samples makes it difficult for the test results to accurately reflect the true quality of a large batch of raw materials, thus failing to effectively guide subsequent mass production.

[0003] In existing technologies, besides the aforementioned fluctuations in the sintering environment, inadequate sampling and storage conditions for the tungsten carbide and cobalt powder mixture are also a significant cause of deviations in identification results. On one hand, in the powder storage stage, existing technologies generally use ordinary plastic sample bags for sealing. However, PE / PP bags have limited airtightness, making it difficult to completely isolate air, leading to easy oxidation of the tungsten carbide and cobalt powder mixture during storage. Actual measurement data shows that after 24 hours of storage, the oxygen content of the tungsten carbide and cobalt powder mixture packaged in PE / PP bags significantly increases from the initial 0.89% to 1.36% and 1.54%, respectively, severely affecting the initial performance of the samples. On the other hand, in the sintering protection stage, existing technologies typically only use a fixed-position furnace loading method. While this can reduce atmospheric differences within the furnace space to some extent, it cannot effectively isolate the atmospheric interference of the sintered products on the identification samples. For example, the fluctuation value of the same batch of 0.4μm WC-6%Co material in different heats was still as high as 14%, and the fluctuation value of 0.4μm WC-2.3%Co material also reached 15%.

[0004] Existing technologies suffer from drawbacks such as insufficient representativeness of identification samples, easy oxidation of powders, significant interference from sintering atmosphere, and poor magnetic property stability. Therefore, how to effectively prevent oxidation and preserve the identification samples made from a mixture of tungsten carbide powder and cobalt powder, and how to construct a relatively independent and stable microenvironment during sintering to significantly improve the stability and accuracy of the magnetic properties of the identification samples, has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. Through a synergistic design of multi-point sampling, aluminum foil sealing for oxidation prevention, and sintering protection using a sealed graphite tube boat with vents, the method achieves high representativeness, low oxidation rate, and stable sintering microenvironment for the identified samples. This effectively avoids problems such as insufficient sample representativeness, oxygenation during powder storage, and interference from the sintering atmosphere, thereby significantly improving the accuracy and reliability of the magnetic property identification results and providing reliable guidance for quality control in the mass production of WC-Co cemented carbide.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder, the method comprising the following steps:

[0008] (1) Take a sample of the mixture of tungsten carbide powder and cobalt powder and seal and preserve the sample;

[0009] (2) The sealed and preserved sample is prepared into an identification compact. After the identification compact has been stored in a fixed environment for an extended period, it is placed in a graphite boat and sintered together with a large batch of products.

[0010] (3) Perform magnetic property testing on the sintered identification compact.

[0011] The term "mass production" refers to cemented carbide blanks that originate from the same batch of tungsten carbide and cobalt powder mixture, are prepared using the same forming process, and are used for mass production, as the identified blanks.

[0012] The identification compacts described in this invention are stored in a fixed environment. The specific temperature, humidity, and storage time of the fixed environment are determined according to the production cycle of a large number of samples to ensure that the identification results can be used to guide the production of a large number of products.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] As a preferred technical solution of the present invention, the sampling in step (1) is multi-point sampling.

[0015] The multi-point sampling method described in this invention specifically involves selecting sub-samples from multiple different locations within a large batch of tungsten carbide and cobalt powder mixture. At least three of these locations are selected, and the samples are mixed to form an identification sample, ensuring that the sampled powder represents the overall quality of the large batch of tungsten and cobalt powder mixture. The selection of these multiple sampling locations needs to be determined in conjunction with the stacking pattern of the large batch of material. For example, when the pile is cone-shaped, the sampling locations should at least cover the apex, waist, and bottom of the cone; when the pile is flat, the sampling locations should at least cover the edge, center, and corners. During sub-sample mixing, uniform stirring must be ensured. The mixing time is selected and optimized based on the total mass of the sub-samples, and no further limitations are imposed here.

[0016] As a preferred technical solution of the present invention, the sealing and preservation in step (1) uses an aluminum foil sealed bag.

[0017] The aluminum foil sealing bag described in this invention can be heat-sealed or sealed with a self-sealing strip to ensure sufficient airtightness after sealing to isolate air. The specific sealing method can be selected according to the actual production efficiency requirements, and no further limitations are made here.

[0018] As a preferred technical solution of the present invention, the graphite boat is tubular, and graphite plugs are provided at both ends of the tube.

[0019] The graphite boat of this invention is preferably tubular, which results in a more uniform temperature and atmosphere field and a more stable sintering effect compared to the rectangular graphite boats of the prior art.

[0020] The graphite plug of the graphite boat of the present invention has a shape and size that matches the size of the inner wall of the tubular structure to form a structure in which the graphite plug seals both ends of the tubular structure.

[0021] The graphite plug of this invention, with its matching size, enables seamless fitting between the two ends of the tubular graphite boat, effectively blocking the intrusion of fluctuating atmosphere in the furnace and impurity gases released from the fired products, reducing the interference of external factors on the identification of the pressed sintering process, and improving the stability of the magnetic property identification results.

[0022] As a preferred technical solution of the present invention, the graphite boat has through holes.

[0023] As a preferred technical solution of the present invention, the opening area of ​​the through hole is 2% to 10% of the cross-sectional area of ​​the graphite tube, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0024] The present invention preferably has an opening ratio within the above range to avoid the large resistance to the removal of the forming agent during the sintering process, which would prevent the forming agent from being discharged smoothly and causing high-temperature decomposition of residual carbon, thus increasing the carbon content and magnetic saturation of the sample; or the atmosphere inside the furnace and the atmosphere inside the graphite tube are fully exchanged, so the atmosphere inside the furnace directly affects the sample inside the graphite tube, resulting in fluctuations in the magnetic saturation of the sample.

[0025] As a preferred embodiment of the present invention, the through hole is provided on the tube wall and / or graphite plug of the graphite boat.

[0026] The through hole described in this invention can be opened on the graphite plug or tube wall of the graphite boat. The position design of the opening on the tube wall is more flexible, and it has greater flexibility in sintering atmosphere control. The opening is set on the graphite plug, which has better positional stability and is easier to operate.

[0027] As a preferred technical solution of the present invention, the inner wall of the graphite boat is coated with an anti-sintering adhesive coating.

[0028] As a preferred technical solution of the present invention, the size of the identified compact is the same as the size of the compact of a large batch of products.

[0029] The anti-sintering bonding coating described in this invention can be a common anti-sintering bonding coating in the art, including but not limited to boron nitride coatings or silicon carbide coatings, to prevent the identification compact from bonding to the inner wall of the tubular graphite boat.

[0030] As a preferred technical solution of the present invention, the magnetic performance test includes performing a magnetic saturation / or coercivity test on the sintered identification compact.

[0031] As a preferred technical solution of the present invention, the magnetic property identification method is applicable to tungsten carbide powder and cobalt powder mixture with a grain size ≤1μm and a cobalt content ≤6wt%.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] (1) The identification method provided by the present invention solves the problems of large fluctuations in the magnetic properties of the identified samples and inaccurate identification results in the prior art by combining the sample preservation process and the sintering process. The identification compact is preserved in a fixed environment, simulating the normal batch production cycle of molding products. The graphite boat with vent holes constructs a relatively independent and stable sintering environment, which not only isolates the interference of fluctuating atmosphere in the furnace, but also allows the molding agent to be discharged smoothly to avoid carbonization of the sample. In the end, the magnetic property stability of the identified sample is significantly improved. It is especially suitable for fine-grained grades (grain size ≤ 1 μm) and low cobalt content (cobalt content ≤ 6 wt%) WC-Co mixtures. The identification results can accurately guide the batch production of WC-Co cemented carbide.

[0034] (2) The present invention further preferably uses aluminum foil sealing bags for sample sealing and preservation, which reduces the amount of oxygen added during sample preservation. In addition, the shape and opening size of the graphite boat dish during sintering are preferred to further balance the influence of the isolation atmosphere and discharge the molding agent, thereby further improving the reliability of the identification results. Attached Figure Description

[0035] Figure 1This is a schematic diagram of the graphite boat used in Embodiment 1 of the present invention;

[0036] Figure 2 These are comparison diagrams of magnetic saturation obtained from tests in Embodiment 1 and Comparative Example 1 of the present invention;

[0037] Figure 3 These are comparison diagrams of magnetic saturation obtained from tests in Embodiment 2 and Comparative Example 2 of the present invention;

[0038] Figure 4 These are comparison diagrams of magnetic saturation obtained from tests in Embodiment 3 and Comparative Example 3 of the present invention;

[0039] Figure 5 These are comparison diagrams of magnetic saturation obtained from tests conducted in Examples 1 and 4-6 of this invention;

[0040] Figure 6 These are comparison diagrams of magnetic saturation obtained from tests conducted in Embodiments 1 and 7 of this invention. Detailed Implementation

[0041] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0042] Example 1

[0043] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder, the method comprising the following steps:

[0044] (1) Samples of 1.0μm WC-3%Co mixture were taken from the four edges, the middle and the four corners of the rectangular flat material and mixed evenly. The samples were then sealed and stored in aluminum foil bags.

[0045] (2) The sealed and preserved sample is prepared into an identification compact with dimensions of φ10×75mm, a single compact weight of 22g, a holding time of 15 seconds, and a molding pressure of 130MPa. The identification compact is then stored at an ambient temperature of 25±2℃ and a relative humidity of 35~55% for 24 hours before being loaded into the sample. Figure 1The graphite boat shown has a graphite plug porosity of 2%. The inner wall of the graphite boat is coated with a boron nitride anti-sintering adhesive coating, and it is sintered together with a large batch of products. The sintering adopts a gradient heating method with the following parameters: 30℃~250℃, heating rate 5℃ / min, pressure 200mbar, argon atmosphere; 250℃~450℃, heating rate 1℃ / min, pressure 200mbar, argon atmosphere; 450℃, holding for 2 hours, pressure 200mbar, argon atmosphere; 450℃~1200℃, heating rate 5℃ / min, pressure 0; 1200℃, holding for 1.5 hours, pressure 0; 1200℃~1420℃, heating rate 5℃ / min, pressure 0; 1420℃, holding for 1.5 hours, pressure 50bar; cooling is performed with the furnace.

[0046] (3) Perform a magnetic saturation test on the sintered identification compact;

[0047] Repeat steps 1-3 above a total of 10 times. The test results are as follows: Figure 2 As shown, the magnetic saturation fluctuation was identified in multiple different furnace cycles.

[0048] Example 2

[0049] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder, the method comprising the following steps:

[0050] (1) Samples of 0.4μm WC-6wt%Co mixture were taken from the four edges, the middle and the four corners of the rectangular flat material and mixed evenly. The samples were then sealed and stored in aluminum foil bags.

[0051] (2) The sealed and preserved sample was prepared into an identification compact with a size of φ10×75mm. The compact weighed 22.5g, the holding time was 18 seconds, and the forming pressure was 140MPa. The identification compact was stored at an ambient temperature of 25±2℃ and a relative humidity of 35~55% for 24 hours and then placed in a graphite boat. The graphite boat was the same as in Example 1 except that the graphite plug opening rate was 5%. It was sintered together with a large batch of products. The sintering adopted a gradient heating method with the following specific parameters: 30℃~250℃, heating rate 5℃ / 250℃~450℃, heating rate 1℃ / min, pressure 200mbar, atmosphere argon; 450℃, hold for 2.5 hours, pressure 200mbar, atmosphere argon; 450℃~1200℃, heating rate 5℃ / min, pressure 0; 1200℃, hold for 1.5 hours, pressure 0; 1200℃~1450℃, heating rate 5℃ / min, pressure 0; 1450℃, hold for 1.5 hours, pressure 60bar; cooling with the furnace.

[0052] (3) Perform a magnetic saturation test on the sintered identification compact;

[0053] Repeat steps 1-3 above a total of 8 times. The test results are as follows: Figure 3 As shown, magnetic saturation fluctuations were identified in multiple different furnace cycles.

[0054] Example 3

[0055] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method is identical to that in Example 1, except that the graphite boat dish has a 10% open-pore ratio for the graphite plug. The sampling, pressing, sintering, and magnetic saturation testing are repeated five times. The test results are as follows: Figure 4 As shown, the magnetic saturation fluctuation was identified in multiple different furnace cycles.

[0056] Example 4

[0057] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method is identical to that in Example 1, except that the graphite boat dish has a 15% open-pore ratio for the graphite plug. The test results are as follows: Figure 5 As shown, the magnetic saturation fluctuation was identified in multiple different furnace tests at 15°C.

[0058] Example 5

[0059] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method is identical to that in Example 1, except that the graphite boat dish has a 1% open-pore ratio for the graphite plug. The test results are as follows: Figure 5 As shown, magnetic saturation fluctuations were identified in multiple different furnace batches.

[0060] Example 6

[0061] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method is identical to that in Embodiment 1, except that the graphite boat and container are completely sealed, with no holes in the graphite plug. The test results are as follows: Figure 5 As shown, magnetic saturation fluctuations were identified in multiple different furnace cycles.

[0062] Example 7

[0063] This embodiment provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method is identical to that in Example 1, except that a PP sealed bag is used to preserve the sample powder. The test results are as follows: Figure 6 As shown, magnetic saturation fluctuations were identified in multiple different furnace cycles.

[0064] Comparative Example 1

[0065] This comparative example provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method employs a conventional fixed-position loading method, without the use of a graphite boat. All other aspects are the same as in Example 1. The test results are as follows: Figure 2 As shown, magnetic saturation fluctuations were identified in multiple different furnace tests.

[0066] Comparative Example 2

[0067] This comparative example provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method employs a conventional fixed-position loading method, without the use of a graphite boat. All other aspects are the same as in Example 2. The test results are as follows: Figure 3 As shown, magnetic saturation fluctuations were identified in multiple different furnace cycles.

[0068] Comparative Example 3

[0069] This comparative example provides a method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder. The method employs a conventional fixed-position furnace loading method, without the use of a graphite boat. All other aspects are the same as in Example 3. The test results are as follows: Figure 4 As shown, magnetic saturation fluctuations were identified in multiple different furnace tests.

[0070] Test methods

[0071] The magnetic saturation test method adopts GB / T 23369-2009 "Standard Test Method for Determination of Magnetic Saturation (MS) of Hard Alloy". The magnetic saturation fluctuation is calculated as the difference between the maximum and minimum magnetic saturation values ​​of multiple batches of tests.

[0072] The test results show that:

[0073] (1) As can be seen from Examples 1 to 3, the present invention ensures the stability of sample preservation and provides a stable sintering microenvironment for the identification of compacts by using appropriate graphite boat structure and sample preservation conditions, thereby significantly improving the stability of magnetic property identification.

[0074] (2) As can be seen from Examples 1, 4, 5 and 6, the present invention can achieve better magnetic performance stability by further limiting the open porosity of the graphite plug to 2%~10%. When the open porosity is less than 2%, the poor discharge of the forming agent leads to local carbon increase, and the fluctuation value rises to 9. When the open porosity is greater than 10%, the sealing effect is weakened, the interference of the furnace atmosphere is aggravated, and the fluctuation value rises to 15. When there is no open porosity at all, the forming agent is retained, and the fluctuation value rises significantly to 12, all of which are inferior to the technical effect of the preferred range.

[0075] (3) As can be seen from Examples 1 and 7, the present invention can effectively reduce the risk of powder oxidation and ensure the stability of magnetic properties by using aluminum foil sealed bags to preserve samples; when using PP sealed bags, the fluctuation value increased from 3 to 12, indicating that the airtight performance of aluminum foil sealed bags is more suitable for the needs of mixed material preservation and can avoid deviation of the original performance of the sample.

[0076] (4) As can be seen from Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, the present invention can obtain significantly lower magnetic saturation fluctuation values ​​by using a graphite boat with vent holes for furnace sintering. When the graphite boat is not used, the fluctuation value corresponding to Example 1 increases from 3 to 7, the fluctuation value corresponding to Example 2 increases from 4 to 12, and the fluctuation value corresponding to Example 3 increases from 3 to 7, proving that the graphite boat can effectively isolate the fluctuating atmosphere in the furnace and the interference of the fired products, which is a key technical feature to improve the accuracy of identification.

[0077] In summary, this invention, through a collaborative design of multi-point sampling, aluminum foil sealing and preservation, and graphite boat sintering with ventilated holes, can effectively solve the problems of large magnetic saturation fluctuations and inaccurate identification results in the prior art, so that the magnetic saturation fluctuation value of WC-Co mixture is stabilized within 5, and the identification results can accurately guide mass production.

[0078] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for identifying the magnetic properties of a mixture of tungsten carbide powder and cobalt powder, characterized in that, The identification method includes the following steps: (1) Take a sample of the mixture of tungsten carbide powder and cobalt powder and seal and preserve the sample; (2) The sealed and preserved sample is prepared into an identification compact. After the identification compact has been stored in a fixed environment for an extended period, it is placed in a graphite boat and sintered together with a large batch of products. (3) Perform magnetic property testing on the sintered identification compact.

2. The identification method according to claim 1, characterized in that, The sampling in step (1) is multi-point sampling.

3. The identification method according to claim 1 or 2, characterized in that, The sealed storage in step (1) uses an aluminum foil sealed bag.

4. The identification method according to any one of claims 1 to 3, characterized in that, The graphite boat is tubular, with graphite plugs at both ends.

5. The identification method according to any one of claims 1 to 4, characterized in that, The graphite boat has through holes.

6. The identification method according to claim 5, characterized in that, The opening area of ​​the through hole is 2% to 10% of the cross-sectional area of ​​the graphite tube.

7. The identification method according to claim 5, characterized in that, The through-hole is provided on the tube wall and / or graphite plug of the graphite boat.

8. The identification method according to any one of claims 1 to 7, characterized in that, The inner wall of the graphite boat is coated with an anti-sintering adhesive coating.

9. The identification method according to any one of claims 1 to 8, characterized in that, The dimensions of the identified compact are the same as those of the compacts used in a large batch of products.

10. The identification method according to any one of claims 1 to 9, characterized in that, The magnetic performance test includes performing a magnetic saturation / or coercivity test on the sintered identification compact.

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