Preparation method of high-toughness ultra-coarse grain hard alloy

Abstract

The invention discloses a preparation method of a high-toughness ultra-coarse grain hard alloy, and belongs to the field of powder metallurgy materials. The high-toughness ultra-coarse grain hard alloy provided by the invention comprises the following raw materials: tungsten carbide and a binder. The tungsten carbide is tungsten carbide powder of which the FSSS particle size is greater than 25 microns; the binder is cobalt-containing binder powder formed by mixing 99%-100% of cobalt, 0%-0.2% of cobalt phosphide and 0%-1% of cobalt silicide. The method disclosed by the invention comprises the steps of mixing, pressing and sintering. According to the invention, the multi-sintering process is designed by stages, so that the uniform growth of crystal grains in the alloy is promoted. Through the design of the alloy raw material formula and the preparation process, grain coarsening is promoted, martensite phase transformation of a binding phase during alloy sintering is inhibited, and the toughness of the alloy is synergistically improved.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy materials, and in particular relates to a method for preparing high-toughness ultra-coarse-grained cemented carbide. Background Art

[0002] Cemented carbide is an alloy material made through a powder metallurgy process using tungsten carbide as a hard phase, cobalt as a binder phase, and other functional elements. Cemented carbide offers advantages such as high hardness, high wear resistance, high strength, and good toughness, making it widely used in cutting tools, molds, mining tools, and wear-resistant parts. When cold heading fasteners, especially drywall screws, the low impact forces allow the toughness of medium- and coarse-grained carbides to meet requirements and provide a long service life. However, when heading large-diameter bolts, the high impact forces make it difficult for medium- and coarse-grained carbides to meet toughness requirements, leading to chipping during the heading process and mold failure before wear is achieved. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention aims to provide a method for preparing high-toughness ultra-coarse-grained cemented carbide.

[0004] A second object of the present invention is to provide a method for preparing the high-toughness ultra-coarse-grained cemented carbide.

[0005] The present invention provides a high-toughness ultra-coarse-grained cemented carbide, wherein the raw materials of the high-toughness ultra-coarse-grained cemented carbide include tungsten carbide and a binder; the content of the tungsten carbide in the raw material is 70% to 85%, and the content of the binder in the raw material is 15% to 30%; The tungsten carbide is tungsten carbide powder with a FSSS particle size greater than 25 microns; The binder is a cobalt-containing binder powder; the cobalt-containing binder powder is a mixture of 99-100% cobalt, 0-0.2% cobalt phosphide, and 0-1% cobalt silicide; The WC grain size of the high-toughness ultra-coarse-grained cemented carbide is 6-12 μm.

[0006] The present invention also provides a method for preparing the high-toughness ultra-coarse-grained cemented carbide, comprising the following steps: S1 according to the high toughness ultra coarse-grained cemented carbide raw material formula weighed tungsten carbide and binder as raw materials; S2. The tungsten carbide and binder obtained in step S1 are mixed uniformly by wet grinding and dried to obtain a high toughness ultra-coarse-grained cemented carbide mixture; S3 The high toughness ultra-coarse-grained cemented carbide mixture obtained in step S2 is pressed to obtain a cemented carbide body; S4. Sintering the cemented carbide blank obtained in step S3 to obtain the high-toughness ultra-coarse-grained cemented carbide.

[0007] In step S2, the process conditions of the wet grinding are as follows: the dispersion medium is anhydrous ethanol, the forming agent is polyethylene glycol, the grinding balls are made of cemented carbide, the ball-to-material ratio is (2-4):1, the solid-liquid ratio is (3-6):1, the mass fraction of the forming agent is 1-2%, the rotation speed is 10-40 r / min, and the ball milling time is 12-30 hours.

[0008] The drying step specifically involves separating and recovering the anhydrous ethanol from the mixed material in the wet-grinding slurry.

[0009] In step S3, the process conditions for the press molding are: placing the high-toughness ultra-coarse-grained cemented carbide mixture into a mold and pressing it under a pressure of 100-150 MPa.

[0010] In step S4, the sintering includes a degreasing stage, a vacuum sintering stage, a pressure sintering stage, a heat treatment stage, and a post-processing stage; the cemented carbide blank is placed in a sintering furnace and sequentially undergoes the degreasing stage, the vacuum sintering stage, the pressure sintering stage, and the heat treatment stage to obtain the high-toughness ultra-coarse-grained cemented carbide.

[0011] The degreasing stage is specifically as follows: placing the cemented carbide blank into a sintering furnace, evacuating the furnace to a vacuum degree of ≤10 -3 Pa, heating to 500~800℃ at a heating rate of 5~20℃ / min, keeping the temperature for 1~10 hours to perform degreasing treatment to remove the forming agent in the cemented carbide blank; The vacuum sintering stage is specifically as follows: after degreasing is completed, the temperature is continuously raised to 1250-1350°C at a rate of 2-20°C / min and kept at this temperature for 1-5 hours to allow the components in the alloy body to fully diffuse and react; The pressure sintering stage is specifically as follows: after vacuum sintering, argon is introduced into the sintering furnace to increase the pressure in the furnace to 5-20 MPa, and then the temperature is increased to 1450-1550° C. at a heating rate of 2-10° C. / min and kept at this temperature for 1-5 hours.

[0012] The heat treatment stage specifically comprises: cooling the product to 750°C to 1320°C at a rate of 2-5°C / min after pressure sintering, and then rapidly cooling it to room temperature at a rate of 10-50°C / min; The principle of this invention: The binder in the raw material formula designed in this invention utilizes cobalt phosphide and cobalt silicide. Cobalt phosphide modifies the binder phase, lowering the binder phase liquidus temperature during alloy sintering, extending the high-temperature liquidus sintering time and promoting grain coarsening. Cobalt silicide increases the binder phase liquidus viscosity during alloy sintering, indirectly promoting uniform grain coarsening.

[0013] The pressure sintering stage of the sintering process in the present invention can promote the elimination of pores in the alloy, improving the density and toughness of the alloy. At the same time, the heat treatment stage can inhibit the martensitic phase transformation of the binder phase during sintering, thereby increasing the toughness of the alloy.

[0014] Beneficial effects of the present invention: The present invention promotes alloy grain coarsening and synergistically improves the toughness of the alloy by designing the alloy raw material formula and preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a grain map of the ultra-coarse-grained cemented carbide obtained in an embodiment of the present invention; Figure 2 This is a metallographic diagram of an ultra-coarse-grained cemented carbide obtained in an embodiment of the present invention; Figure 3 This is a diagram showing the results of a Babbitt toughness test according to an embodiment of the present invention; Figure 4 This is a grain map of the product in Comparative Example 4 of the present invention; Figure 5 This is a graph showing the results of a Babbitt toughness test of the product in Comparative Example 4 of the present invention; Figure 6 This is a grain map of the product in Comparative Example 5 of the present invention; Figure 7 This is a graph showing the results of the Babbitt toughness test of the product in Comparative Example 5 of the present invention. DETAILED DESCRIPTION

[0016] In order to provide a more detailed understanding of the features and technical content of the embodiments of the present disclosure, the implementation of the embodiments of the present disclosure is described in detail below. This is for reference only and is not intended to limit the embodiments of the present disclosure. In the following technical description, for the sake of convenience, multiple details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details.

[0017] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other.

[0018] The method of the present invention is further described below with reference to the following embodiments: Example 1: A cemented carbide mix was prepared using WC powder (FSSS) with a particle size of 26.7 μm and 27% binder powder. The binder contained 0.1% cobalt phosphide, 0.02% cobalt silicide, and 99.88% cobalt. The wet milling parameters were: ball-to-material ratio of 2:1, solid-to-liquid ratio of 6:1, forming agent mass fraction of 2%, rotation speed of 10 rpm, and milling time of 14 hours. The resulting mix was pressed into a φ30x30 green body at a pressure of 120 MPa. The green body is placed in a sintering furnace and heated to 600°C at a rate of 5°C / min, and kept at this temperature for 2 hours for degreasing. The temperature is then raised to 1280°C at a rate of 5°C / min and kept at this temperature for 2 hours. Argon is then introduced into the sintering furnace to increase the pressure in the furnace to 5MPa. The temperature is then raised to 1480°C at a rate of 2°C / min and kept at this temperature for 1 hour. Finally, the product is cooled to 1200°C at a rate of 5°C / min and then rapidly cooled to room temperature at a rate of 30°C / min. Through the above process, an ultra-coarse-grained cemented carbide with a WC grain size of 8.1μm can be obtained. The grain diagram is shown in FIG. Figure 1 shown.

[0019] The obtained ultra-coarse-grained cemented carbide was tested, and the metallographic diagram is as follows: Figure 2 shown.

[0020] According to GB / T 33819-2017 Cemented Carbide Babbitt Toughness Test, the indentation method is used to test the Babbitt toughness of cemented carbide. The calculation method is: in, is the Babbitt toughness; P is the indentation load; is the length of the first diagonal line of the crack; is the length of the second diagonal of the crack; is the length of the first diagonal of the indentation; is the length of the second diagonal of the indentation.

[0021] The conventional test of the Babbitt toughness of cemented carbide in the prior art usually uses a load of 30 kgf. The Babbitt toughness of cemented carbide is usually 7 MN·m -3 / 2 ~25MN·m -3 / 2 between.

[0022] In this embodiment, the maximum load of 150kgf is used to test the babbitt toughness of the obtained ultra-coarse-grained cemented carbide. The results are as follows: Figure 3 As shown in the figure, it was found that even if the applied load was as high as 150 kgf, no obvious cracks were generated at the diagonal corners of the Vickers hardness indentation under an optical microscope, and the fracture toughness could not be calculated.

[0023] Example 2: A cemented carbide mix was prepared using WC powder with a 35-μm FSSS particle size and 22% binder powder. The binder contained 0.03% cobalt phosphide, 0.06% cobalt silicide, and 99.91% cobalt. The wet milling parameters were: ball-to-material ratio of 3.2:1, solid-to-liquid ratio of 3.5:1, forming agent mass fraction of 1.5%, rotation speed of 22 rpm, and milling time of 12 hours. The resulting mix was pressed into a φ30x30 green body at 150 MPa. The green body is placed in a sintering furnace and heated to 600°C at a rate of 2°C / min. The temperature is then held at this temperature for 1.5 hours for degreasing. The temperature is then raised to 1320°C at a rate of 5°C / min and held at this temperature for 1.5 hours. Argon is then introduced into the sintering furnace to raise the pressure to 10 MPa. The temperature is then raised to 1520°C at a rate of 5°C / min and held at this temperature for 2 hours. Finally, the product is cooled to 1150°C at a rate of 8°C / min and then rapidly cooled to room temperature at a rate of 20°C / min. This process yields an ultra-coarse-grained cemented carbide with a WC grain size of 9.5 μm.

[0024] The Babbitt toughness of cemented carbide was tested using a Vickers hardness tester with a maximum load of 150kgf. The results showed that even when the applied load was as high as 150kgf, no obvious cracks were produced at the diagonal corners of the Vickers hardness indentation of the alloy under an optical microscope, and the fracture toughness could not be calculated.

[0025] Example 3: A cemented carbide mix was prepared using WC powder with a FSSS particle size of 41 μm and 25% binder powder added. The binder contained 0.15% cobalt phosphide, 0.08% cobalt silicide, and 99.77% cobalt. The wet milling parameters were: ball-to-material ratio of 4:1, solid-to-liquid ratio of 5:1, forming agent mass fraction of 1%, rotation speed of 18 rpm, and milling time of 18 hours. The resulting mix was pressed into a φ30x30 green body at a pressure of 150 MPa. The green body is placed in a sintering furnace and heated to 700°C at a rate of 5°C / min. The temperature is then held for one hour for degreasing. The temperature is then raised to 1220°C at a rate of 5°C / min and held for two hours. Argon is then introduced into the sintering furnace to raise the pressure to 12 MPa. The temperature is then raised to 1500°C at a rate of 5°C / min and held for three hours. Finally, the product is cooled to 1150°C at a rate of 5°C / min and then rapidly cooled to room temperature at a rate of 25°C / min. This process yields an ultra-coarse-grained cemented carbide with a WC grain size of 10.6 μm.

[0026] The Babbitt toughness of cemented carbide was tested using a Vickers hardness tester with a maximum load of 150kgf. The results showed that even when the applied load was as high as 150kgf, no obvious cracks were produced at the diagonal corners of the Vickers hardness indentation of the alloy under an optical microscope, and the fracture toughness could not be calculated.

[0027] Comparative Example 1: Cemented carbide was prepared using the patent publication number CN101985717B, "Preparation Method of High-Toughness Ultra-Coarse-Grained Tungsten-Cobalt Cemented Carbide," specifically as follows: (1) Tungsten carbide powder is coarse-grained tungsten carbide powder with a Fsss particle size of 13.0-18.5 μm, and the particle size of cobalt powder is 1.4-2.0 μm; (2) When mixing ingredients, cobalt powder and tungsten carbide powder are selected for mixing, and the mass ratio of cobalt powder to tungsten carbide powder is 2.4~2.6:97.4~97.6; (3) Wet-grinding the above-mentioned mixture, drying it, and then pre-calcining it; (4) adding metallic cobalt powder and Co2W4C nanoparticles to the pre-sintered mixture, the amount of cobalt powder added to achieve a mass ratio of cobalt to tungsten carbide in the mixture of 8 to 13:87 to 92; (5) Adopt vacuum low-pressure integrated sintering with a maximum temperature of 1440-1460°C; The average particle size of WC in the final cemented carbide reaches 4.0-5.2 μm.

[0028] The average WC grain size in the cemented carbide obtained in Comparative Example 1 is 4.0-5.2 μm, which is only a coarse-grained cemented carbide. The cobalt content in the alloy is 8-13%, which is lower than the 15-30% of the present invention. There is no relevant description on suppressing martensitic transformation, so its toughness is lower than that of the ultra-coarse-grained cemented carbide of the present invention.

[0029] Comparative Example 2: Cemented carbide was prepared using the patent publication number CN113699406A, "High-strength and toughness extra-coarse-grained WC cemented carbide with an average grain size greater than 8 microns and its preparation method", specifically: (1) Prepare a cemented carbide mixture by mass percentage, including the following components: 78% to 95% WC powder, 3% to 15% Co powder, 0% to 15% Ni powder, 0% to 1.5% W4Co2C powder, 0% to 1.5% NbC powder, 0% to 1.5% TaC powder, 0% to 1.5% TiC powder, 0% to 1.5% VC powder, and 0% to 1.5% Cr2C3 powder; CN101985717B (2) The WC powder has two types of FSSS characteristics. The first type is used for performance activation, and its FSSS is 1 micron or less, that is, fine WC powder, and the total amount of ingredients is less than or equal to 10%. The second type is used for extra coarsening of hard phase powder, and its FSSS mean is 25 microns or more, and the total amount of ingredients ranges from 78% to 95%. W4Co2C powder has a FSSS of 1 micron or less. Co, Ni powder and other added powders NbC, TaC, TiC, VC, Cr2C3 powder are characterized by a FSSS of 0.1 to 3.0 microns. (3) The above powders are batched, pre-ground to activate fine powder, mixed, ball-milled, and slurry-dried to obtain a mixture, which is then pressed into shape and sintered; (4) Raise the temperature from room temperature to the dewaxing or degumming sintering temperature at a rate of 3 to 5 °C / min. The dewaxing or degumming sintering temperature is 420 to 500 °C and the holding time is 1 to 3.5 h. (5) After dewaxing or degumming, the formed blank is solid-phase sintered in a sintering furnace. The holding temperature of solid-phase sintering is 1100-1350℃, and the heating rate is less than 5℃ / min. When the required temperature is set, it is kept warm for 1-3.5h. After solid-phase sintering, liquid-phase sintering is carried out. The liquid-phase sintering temperature is 1450-1550℃, and when the required temperature is set, it is kept warm for 1-4h. At the same time, 1-10MPa argon gas is introduced, and the purity of argon gas is greater than 99.995%. After the liquid-phase sintering and holding stage is completed, the furnace is cooled to room temperature to obtain a high-strength and toughness extra-coarse-grained WC cemented carbide block with an average grain size greater than 8 microns.

[0030] The average grain size is greater than 8 microns, and the fracture toughness of the high-strength and toughness extra-coarse-grained WC cemented carbide block is between 18.3 and 19.8 MPa / m 2 The calculation method of fracture toughness is to calculate by crack length. As shown in the results of Examples 1 to 3, the alloy prepared by the method of the present invention will not produce cracks under the Babbitt toughness test. Therefore, the ultra-coarse-grained cemented carbide prepared by the method of the present invention is significantly superior to the cemented carbide prepared by the method of Comparative Example 2 in terms of toughness.

[0031] Comparative Example 3: Cemented carbide was prepared using the patent publication number CN102732768A, "A high-toughness, corrosion-resistant, ultra-coarse-grained cemented carbide and its preparation method", specifically: (1) Using powder with a grain size of >4.5μm as raw material, by adding Cr3C2 alone or jointly adding Cr3C2 and rare earth, and using Co / Ni densely coated WC type composite powder process; (2) Nano-assembled Co / Ni-coated WC composite powders were prepared by hydrothermal high-pressure hydrogen reduction or hydrazine hydrate aqueous phase atmospheric pressure reduction. The composite powders were then subjected to thermal diffusion homogenization and Co / Ni coating densification in a hydrogen atmosphere at 600°C-700°C using the nano-diffusion sintering effect. PEG or paraffin-based forming agents accounting for 2.0-2.5% of the total mass fraction of the composite powders were then added to the densely coated WC composite powders. The composite powders with the forming agents were dried and granulated, the granulated composite powders were formed, and the pressed green compacts were liquid-phase sintered in a pressure sintering furnace at 1430°C-1480°C. The resulting alloy had a grain size of 7.5μm-8.5μm.

[0032] The Brinell toughness test of cemented carbide was conducted using a Vickers hardness tester with a maximum load of 50 kgf. This method is performed under a load of 50 kgf. The greater the load, the more likely it is to crack.

[0033] The average WC grain size in the cemented carbide obtained in Comparative Example 3 is 7.5-8.5 μm, which is lower than that of the ultra-coarse-grained cemented carbide disclosed in the present invention, and the cobalt content in the alloy is lower than 15-30% of the present invention. There is no relevant description on suppressing martensitic transformation, so its toughness is lower than that of the ultra-coarse-grained cemented carbide of the present invention.

[0034] Comparative Example 4: Compared with Example 1, the only difference in this comparative example is that the binder powder is replaced with cobalt powder.

[0035] Finally, a coarse-grained cemented carbide with a WC grain size of 7.4 μm was obtained, and its grain map is shown in Figure 4 shown.

[0036] The Vickers hardness tester was used to test the toughness of cemented carbide with a maximum load of 100kgf. The results showed that under a load of 100kgf, there were obvious cracks at the corners, such as Figure 5 shown.

[0037] It can be seen from Comparative Example 4 that the cobalt phosphide and cobalt silicide contained in the alloy formulation binder have a significant promoting effect on improving the toughness of the alloy.

[0038] Comparative Example 5: Compared with Example 2, the only difference of this comparative example is that after the sintering process is carried out at 1520°C for 2 hours, no heat treatment is performed and the sintering process is directly cooled in the furnace.

[0039] Finally, a coarse-grained cemented carbide with a WC grain size of 9.0 μm was obtained, and its grain map is shown in Figure 6 shown.

[0040] The Vickers hardness tester was used to test the toughness of cemented carbide with a maximum load of 100kgf. The results showed that cracks appeared on some corners under the load of 100kgf. Figure 7 shown.

[0041] It can be seen from Comparative Example 5 that in the preparation process, the heat treatment after pressure sintering has a significant promoting effect on improving the toughness of the alloy.

Claims

1. A method for preparing high-toughness ultra-coarse-grained cemented carbide, characterized in that: The following steps are involved: S1. Weigh tungsten carbide and a binder as raw materials; the binder is a cobalt-containing binder powder; the cobalt-containing binder powder is a mixture of cobalt, cobalt phosphide, and cobalt silicide; the tungsten carbide is tungsten carbide powder with a FSSS particle size greater than 25 microns; the cobalt-containing binder powder is a mixture of 99-100% cobalt, 0-0.2% cobalt phosphide, and 0-1% cobalt silicide; S2. The tungsten carbide and binder obtained in step S1 are mixed uniformly by wet grinding and dried to obtain a high toughness ultra-coarse-grained cemented carbide mixture; S3 The high toughness ultra-coarse-grained cemented carbide mixture obtained in step S2 is pressed to obtain a cemented carbide body; S4. Sintering the cemented carbide body obtained in step S3 to obtain a sintered cemented carbide body; immediately heat-treating the sintered cemented carbide body to suppress martensitic transformation and obtain the high-toughness ultra-coarse-grained cemented carbide.

2. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: In step S1, the content of the tungsten carbide in the raw material is 70% to 85%, and the content of the binder in the raw material is 15% to 30%.

3. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: The WC grain size of the high-toughness ultra-coarse-grained cemented carbide is 6-12 μm.

4. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: In step S2, the process conditions of the wet grinding are as follows: the dispersion medium is anhydrous ethanol, the forming agent is polyethylene glycol, the grinding balls are made of cemented carbide, the ball-to-material ratio is (2-4):1, the solid-liquid ratio is (3-6):1, the mass fraction of the forming agent is 1-2%, the rotation speed is 10-40 r / min, and the ball milling time is 12-30 hours.

5. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: In step S2, the drying step specifically involves separating and recovering the anhydrous ethanol from the mixed material in the wet-grinding slurry.

6. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: In step S3, the process conditions for the press molding are: placing the high-toughness ultra-coarse-grained cemented carbide mixture into a mold and pressing it under a pressure of 100-150 MPa.

7. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 1, characterized in that: In step S4, the sintering includes a degreasing stage, a vacuum sintering stage, a pressure sintering stage, and a heat treatment stage; the cemented carbide blank is placed in a sintering furnace and sequentially undergoes the degreasing stage, the vacuum sintering stage, the pressure sintering stage, and the heat treatment stage to obtain the high-toughness ultra-coarse-grained cemented carbide.

8. The method for preparing high-toughness ultra-coarse-grained cemented carbide according to claim 7, characterized in that: The degreasing stage is specifically as follows: placing the cemented carbide blank into a sintering furnace, evacuating the furnace to a vacuum degree of ≤10 -3 Pa, heating to 500~800℃ at a heating rate of 5~20℃ / min, keeping the temperature for 1~10 hours to perform degreasing treatment to remove the forming agent in the cemented carbide blank; The vacuum sintering stage is specifically as follows: after degreasing is completed, the temperature is continuously raised to 1250-1350°C at a rate of 2-20°C / min and kept at this temperature for 1-5 hours to allow the components in the alloy body to fully diffuse and react; The pressure sintering stage is specifically as follows: after vacuum sintering, argon is introduced into the sintering furnace to increase the pressure in the furnace to 5-20 MPa, and then the temperature is increased to 1450-1550°C at a heating rate of 2-10°C / min and kept at this temperature for 1-5 hours; The heat treatment stage is specifically as follows: after pressure sintering, the product is cooled to 750°C~1320°C at a speed of 2~5°C / min, and then rapidly cooled to room temperature at a speed of 10~50°C / min.

Images