Tungsten carbide-cobalt hard alloy and preparation method thereof

Abstract

The preparation method of the tungsten carbide-cobalt hard alloy comprises the following steps that S1, raw materials are taken according to the raw material formula amount and are subjected to wet grinding to be uniform, and a mixture is obtained; s2, the wet grinding medium in the mixture is gasified and separated through drying equipment, and a dried material is obtained; s3, pressing the dried material into a blank material with the size required by the process by using a pressing mold; s4, performing vacuum sintering on the blank material to obtain a primary sintered material; s5, the sintered material is subjected to secondary sintering through the low-pressure furnace, and a secondary sintered material is obtained; and S6, performing post-treatment on the secondary sintered material to obtain a finished product. The raw material formula comprises the following components in parts by mass: 100 parts of tungsten carbide powder, 6-20 parts of cobalt powder, 1-8 parts of a wet grinding medium, 0.3-5 parts of a forming agent and 0.6-1.8 parts of a composite inhibitor. The method has the advantage that the problem that the porosity of the tungsten carbide-cobalt hard alloy is high can be obviously solved.

Description

Technical Field

[0001] The present invention relates to a production technology of non-ferrous metal alloys, in particular to a production technology of tungsten carbide-cobalt alloys. Background Art

[0002] Tungsten carbide-cobalt (WC-Co) cemented carbide is known as the "industrial tooth" due to its high hardness, wear resistance and toughness, and is widely used in fields such as cutting tools, mining tools, wear-resistant components, etc. The traditional production process of WC-Co cemented carbide mainly includes steps such as wet ball milling, drying, forming, debinding and sintering.

[0003] At present, in fields such as automobiles and aerospace, the requirements for tool life and machining efficiency are increasing, and materials with both high hardness and high toughness are needed. For example, medium-grained WC is required for rough turning, while ultra-fine-grained WC is required for finish turning. The traditional process cannot take both into account, resulting in waste of resources. In addition, under extreme working conditions (such as deep mining), higher requirements are put forward for the wear resistance and impact resistance of coarse-grained / ultra-coarse-grained cemented carbide, making the traditional production process of tungsten carbide-cobalt (WC-Co) cemented carbide face great challenges.

[0004] Studies have shown that during the solid-phase sintering stage of tungsten carbide-cobalt cemented carbide, the solid solution diffusion rate of ultra-fine / nano-crystalline tungsten carbide particles into the binder phase cobalt is relatively large; during the liquid-phase sintering stage, the liquid-phase mass transfer through the Ostwald ripening mechanism is also relatively fast, and tungsten carbide particles are prone to abnormal grain growth of recrystallization through dissolution and reprecipitation. On the one hand, the fine-grained hard-phase tungsten carbide relies on the contact and aggregation of grains with each other to combine into large-grained tungsten carbide, or large-grained tungsten carbide swallows small-grained tungsten carbide and then grows. On the other hand, after the liquid phase is generated during the sintering process of tungsten carbide-cobalt cemented carbide, the saturation solubility of small-grained tungsten carbide is relatively large, and it dissolves first, and then precipitates on the surface of large-grained tungsten carbide, so the large-grained tungsten carbide tends to grow.

[0005] Based on the above problems, currently, grain growth inhibitors are usually added to inhibit the growth of tungsten carbide grains. Some researchers add VC, Cr3C2, TiC, etc. during powder making to inhibit the grain growth during sintering, hoping to obtain ultra-fine-grained tungsten carbide. Research shows that these inhibitors do have good effects in inhibiting grain growth, but the side effect is that they will precipitate at the grain boundaries of tungsten carbide-cobalt, increasing the porosity of the alloy. Summary of the Invention

[0006] In order to solve the problem of relatively high porosity of tungsten carbide-cobalt cemented carbide in the prior art, the present invention provides a tungsten carbide-cobalt cemented carbide and a preparation method thereof.

[0007] The technical solution adopted by the present invention is: a preparation method of tungsten carbide-cobalt cemented carbide, comprising the following steps:

[0008] S1. Weigh each raw material according to the raw material formula, wet grind them evenly to obtain a mixture.

[0009] S2. Use a drying device to vaporize and separate the wet grinding medium in the mixture to obtain a dried material.

[0010] S3. Use a pressing die to press the dried material into a blank material with the dimensions required by the process.

[0011] S4. The blank material is vacuum sintered to obtain a primary sintered material.

[0012] S5. The sintered material is secondary sintered in a low-pressure furnace to obtain a secondary sintered material.

[0013] S6. The secondary sintered material is post-treated to obtain a finished product.

[0014] The raw material formula includes the following components in parts by mass: 100 parts of tungsten carbide powder, 6 - 20 parts of cobalt powder, 1 - 8 parts of wet grinding medium, 0.3 - 5 parts of forming agent, and 0.6 - 1.8 parts of composite inhibitor.

[0015] As a further improvement of the present invention, the composite inhibitor is composed of vanadium carbide and hexagonal boron nitride in a mass ratio of 1:0.1 - 0.6.

[0016] As a further improvement of the present invention, the tungsten carbide powder meets the following requirements: particle size 100 - 300 nm, free carbon content 0.05 - 0.1 wt%. The cobalt powder meets the following requirements: particle size 1.5 - 2.5 μm, purity ≥ 99.5 wt%.

[0017] As a further improvement of the present invention, the wet grinding medium is ethanol. Ethanol can effectively prevent the cobalt powder and tungsten carbide powder from being oxidized due to heat generation during wet grinding. Wet grinding can be carried out using a ball mill, and the purpose is to evenly mix the two metal powders and evenly distribute the forming agent, which is beneficial for subsequent pressing and forming. The drying device can use a drying device with stirring, and adopt an electric heating method to vaporize and separate ethanol to achieve a drying effect. The volatilized ethanol can also be recycled through condensation recovery.

[0018] As a further improvement of the present invention, the forming agent is paraffin wax. The advantages of paraffin wax are that it allows a relatively high pressing pressure without delamination, is not easily aged, has no ash content, does not introduce impurities to the alloy, can be stored for a long time, is suitable for spray drying, and has a relatively high production efficiency. It is easy for those skilled in the art to understand that in addition to paraffin wax, rubber, polyethylene glycol, etc. can also be used as the forming agent.

[0019] It is easy for those skilled in the art to understand that in step S3, corresponding pressing and forming parameters can be set according to specific product requirements. For example, we propose a preferred implementation scheme: the strength of the pressing die ≥ 100 MPa, the pre-pressing pressure is 50 - 80 MPa, and the pressure holding time is 15 - 40 s; the density of the blank ≥ 6.5 g / cm 3 . It is easy to understand that the above scheme is not the only one, and technicians can adjust it according to product requirements.

[0020] It is easy for those skilled in the art to understand that the vacuum sintering in step S4 can be carried out in a vacuum sintering furnace. Under vacuum conditions, sintering processing is realized by using the principle of intermediate frequency induction heating. The vacuum sintering furnace uses electricity as the energy source and can adopt a PCL automatic control system, with flexible operation. The specific sintering conditions can be set as follows: the vacuum degree ≤ 1×10 -2 Pa, the heating rate is 65 - 140 °C / min, the sintering temperature is 1650 - 1750 °C, and the heat preservation time is 10 - 20 min.

[0021] After the vacuum sintering of the present invention, secondary sintering in a low-pressure furnace is also carried out. Specifically, it can be implemented according to the following steps: putting the primary sintered material into the low-pressure furnace, raising the temperature to 1350 - 1450 °C, keeping the temperature for 3 - 8 min, and then introducing argon into the low-pressure furnace at a rate of 0.04 - 0.06 Mpa / min until the pressure in the low-pressure furnace reaches 0.45 - 0.55 Mpa; then gradually increasing the argon flow rate so that the pressure in the low-pressure furnace reaches 5.2 - 5.7 Mpa within the subsequent 35 - 40 min; continuing to keep the temperature for 30 - 60 min and then stopping heating, and taking out the furnace after the furnace temperature drops below 80 °C.

[0022] It is easy to understand that the secondary sintered material after taking out the furnace can be obtained as the finished tungsten carbide-cobalt hard alloy after post-treatment. The above post-treatment can include: performing outer circle grinding on the outer circle according to the size required by the product using a centerless grinder; performing precision machining using equipment such as a machining center grinder; performing deburring, flattening, and polishing and passivation treatment on the product by means such as a brush and drag polishing.

[0023] The present invention also discloses a tungsten carbide-cobalt hard alloy, which is obtained by the preparation method of the tungsten carbide-cobalt hard alloy of the present invention.

[0024] The present invention also discloses a tool, which is characterized in that the production material includes the tungsten carbide-cobalt hard alloy of the present invention.

[0025] The beneficial effect of the present invention is: Experiments show that the method of the present invention can significantly improve the problem of relatively high porosity of tungsten carbide-cobalt hard alloys. Specific Embodiments

[0026] The present invention will be further described below in conjunction with embodiments.

[0027] Example 1:

[0028] Tungsten carbide-cobalt hard alloy is produced according to the following steps:

[0029] (1) Weigh each raw material according to the following raw material formula: 100 parts of tungsten carbide powder (particle size 210 nm, free carbon content 0.06 wt%), 8 parts of cobalt powder (particle size 2.3 μm, purity 99.9 wt%), 5 parts of wet grinding medium (ethanol), 3 parts of forming agent (paraffin), 1.2 parts of composite inhibitor. Wet grind evenly to obtain a mixed material; the composite inhibitor is composed of vanadium carbide and hexagonal boron nitride according to a mass ratio of 1:0.5.

[0030] (2) Use a drying device to vaporize and separate the wet grinding medium in the mixed material to obtain a dried material; the volatilized ethanol can also be recycled through condensation recovery.

[0031] (3) Use a pressing die to press the dried material into a blank material with the dimensions required by the process; the strength of the pressing die is 150 MPa, the pre-pressing pressure is 65 MPa, and the pressure holding time is 30 s; the density of the blank material is 6.9 g / cm 3

[0032] (4) The blank material is vacuum sintered to obtain a first sintered material; the vacuum sintering conditions are: vacuum degree 0.85×10 - 2 Pa, heating rate 100 °C / min, sintering temperature 1700 °C, heat preservation time 13 min.

[0033] (5) Put the first sintered material into a low-pressure furnace, raise the temperature to 1400 °C, keep it warm for 6 min, and then introduce argon into the low-pressure furnace at a rate of 0.05 Mpa / min until the pressure of the low-pressure furnace reaches 0.5 Mpa; then gradually increase the argon flow rate so that the pressure of the low-pressure furnace reaches 5.5 Mpa in the subsequent 40 min; continue to keep it warm for 40 min and then stop heating. Wait for the furnace temperature to drop to 70 °C and then take it out of the furnace;

[0034] (6) The second sintered material is polished to obtain a finished product.

[0035] Example 2:

[0036] Tungsten carbide-cobalt hard alloy is produced according to the following steps:

[0037] (1) Weigh each raw material according to the following raw material formula: 100 parts of tungsten carbide powder (particle size 205 nm, free carbon content 0.05 wt%), 6 parts of cobalt powder (particle size 2.1 μm, purity 99.7 wt%), 4 parts of wet grinding medium (ethanol), 3.5 parts of molding agent (paraffin), 1.5 parts of composite inhibitor. Wet grind evenly to obtain a mixture; the composite inhibitor is composed of vanadium carbide and hexagonal boron nitride in a mass ratio of 1:0.35.

[0038] (2) Use a drying device to vaporize and separate the wet grinding medium in the mixture to obtain a dry material; the volatilized ethanol can also be recycled through condensation recovery.

[0039] (3) Use a pressing die to press the dry material into a blank with the dimensions required by the process; the strength of the pressing die is 120 MPa, the pre-pressing pressure is 60 MPa, and the pressure holding time is 40 s; the density of the blank is 6.4 g / cm 3

[0040] (4) The blank is vacuum sintered to obtain a primary sintered material; the vacuum sintering conditions are: vacuum degree 0.8×10 - 2 Pa, heating rate 100℃ / min, sintering temperature 1650℃, heat preservation time 15 min.

[0041] (5) Put the primary sintered material into a low-pressure furnace, raise the temperature to 1350℃, keep it warm for 8 min, then introduce argon into the low-pressure furnace at a rate of 0.05 Mpa / min until the pressure of the low-pressure furnace reaches 0.45 Mpa; then gradually increase the argon flow rate so that the pressure of the low-pressure furnace reaches 5 Mpa in the subsequent 38 min; continue to keep it warm for 45 min and then stop heating. Wait for the furnace temperature to drop to 75℃ and then take it out of the furnace;

[0042] (6) The secondary sintered material is polished to obtain a finished product.

[0043] Example 3:

[0044] Produce tungsten carbide-cobalt hard alloy according to the following steps:

[0045] (1) Weigh each raw material according to the following raw material formula: 100 parts of tungsten carbide powder (particle size 220 nm, free carbon content 0.06 wt%), 7 parts of cobalt powder (particle size 2.4 μm, purity 99.8 wt%), 7 parts of wet grinding medium (ethanol), 5 parts of molding agent (paraffin), 1 part of composite inhibitor. Wet grind evenly to obtain a mixture; the composite inhibitor is composed of vanadium carbide and hexagonal boron nitride in a mass ratio of 1:0.6.

[0046] (2) Use a drying device to vaporize and separate the wet grinding medium in the mixture to obtain a dried material; the volatilized ethanol can also be recycled through condensation recovery.

[0047] (3) Use a pressing mold to press the dried material into a blank material with the dimensions required by the process; the strength of the pressing mold is 160 MPa, the pre-pressing pressure is 75 MPa, and the pressure holding time is 25 s; the density of the blank material is 7.3 g / cm 3

[0048] (4) The blank material is vacuum sintered to obtain a primary sintered material; the vacuum sintering conditions are: vacuum degree 0.8×10 - 2 Pa, heating rate 100 °C / min, sintering temperature 1750 °C, heat preservation time 11 min.

[0049] (5) Put the primary sintered material into a low-pressure furnace, raise the temperature to 1450 °C, keep it warm for 5 min, and then introduce argon into the low-pressure furnace at a rate of 0.05 Mpa / min until the pressure in the low-pressure furnace reaches 0.55 Mpa; then gradually increase the argon flow rate so that the pressure in the low-pressure furnace reaches 4.8 Mpa in the subsequent 37 min; continue to keep it warm for 50 min and then stop heating, and take it out of the furnace when the furnace temperature drops to 80 °C;

[0050] (6) The secondary sintered material is polished to obtain a finished product.

[0051] Comparative Example 1:

[0052] This comparative example is a control experiment of Example 1, which is carried out according to the same steps and conditions as Example 1, and the only difference is that: only vanadium carbide is used as the inhibitor, and the total amount of the inhibitor used remains unchanged. The specific steps are as follows:

[0053] Produce tungsten carbide-cobalt hard alloy according to the following steps:

[0054] (1) Weigh each raw material according to the following raw material formula: 100 parts of tungsten carbide powder (particle size 210 nm, free carbon content 0.06 wt%), 8 parts of cobalt powder (particle size 2.3 μm, purity 99.9 wt%), 5 parts of wet grinding medium (ethanol), 3 parts of molding agent (paraffin), 1.2 parts of inhibitor (vanadium carbide), and wet grind evenly to obtain a mixture.

[0055] (2) Use a drying device to vaporize and separate the wet grinding medium in the mixture to obtain a dried material; the volatilized ethanol can also be recycled through condensation recovery.

[0056] (3) Use a pressing mold to press the dried material into a blank material with the dimensions required by the process; the strength of the pressing mold is 150 MPa, the pre-pressing pressure is 65 MPa, and the pressure holding time is 30 s; the density of the blank material is 6.9 g / cm3

[0057] (4) The green compact is sintered in vacuum to obtain a first sintered product; the vacuum sintering conditions are: a vacuum degree of 0.85×10 - 2 Pa, a heating rate of 100 °C / min, a sintering temperature of 1700 °C, and a holding time of 13 min.

[0058] (5) The first sintered product is placed in a low-pressure furnace, the temperature is raised to 1400 °C, held for 6 min, and then argon is introduced into the low-pressure furnace at a rate of 0.05 Mpa / min until the pressure of the low-pressure furnace reaches 0.5 Mpa; then the argon flow rate is gradually increased so that the pressure of the low-pressure furnace reaches 5.5 Mpa in the subsequent 40 min; after continuing to hold for 40 min, heating is stopped, and the furnace is taken out after the furnace temperature drops to 70 °C;

[0059] (6) The second sintered product is polished to obtain the finished product.

[0060] Comparative Example 2:

[0061] This comparative example is a control experiment of Example 1, which is carried out according to the same steps and conditions as Example 1, and the difference is only that: only hexagonal boron nitride is used as the inhibitor, and the total amount of the inhibitor used remains unchanged. The specific steps are as follows:

[0062] Tungsten carbide-cobalt hard alloy is produced according to the following steps:

[0063] (1) Weigh each raw material according to the following raw material formula: 100 parts of tungsten carbide powder (particle size 210 nm, free carbon content 0.06 wt%), 8 parts of cobalt powder (particle size 2.3 μm, purity 99.9 wt%), 5 parts of wet grinding medium (ethanol), 3 parts of molding agent (paraffin), 1.2 parts of inhibitor (hexagonal boron nitride), and wet grind evenly to obtain a mixture.

[0064] (2) The wet grinding medium in the mixture is gasified and separated using a drying device to obtain a dried material; the volatilized ethanol can also be recycled through condensation recovery.

[0065] (3) The dried material is pressed into a green compact with the dimensions required by the process using a pressing die; the strength of the pressing die is 150 MPa, the pre-pressing pressure is 65 MPa, and the pressure holding time is 30 s; the density of the green compact is 6.9 g / cm 3

[0066] (4) The green compact is sintered in vacuum to obtain a first sintered product; the vacuum sintering conditions are: a vacuum degree of 0.85×10 - 2 Pa, a heating rate of 100 °C / min, a sintering temperature of 1700 °C, and a holding time of 13 min.

[0067] (5) Put the primary sintered material into a low-pressure furnace, raise the temperature to 1400 °C, hold for 6 min, and then introduce argon into the low-pressure furnace at a rate of 0.05 Mpa / min until the pressure of the low-pressure furnace reaches 0.5 Mpa; then gradually increase the argon flow rate so that the pressure of the low-pressure furnace reaches 5.5 Mpa in the subsequent 40 min; continue to hold for 40 min and then stop heating. After the furnace temperature drops to 70 °C, take out the product from the furnace;

[0068] (6) The secondary sintered material is polished to obtain the finished product.

[0069] Experiment on detecting the porosity and grain size of tungsten carbide-cobalt hard alloy:

[0070] Use the method of GB / T 3489-2015 to detect the porosity of the tungsten carbide-cobalt hard alloy products obtained in the above Examples 1 to 3, Comparative Example 1 and Comparative Example 2;

[0071] Use the method of ISO 4499-2:2008 to detect the grain size of the tungsten carbide-cobalt hard alloy products obtained in the above Examples 1 to 3, Comparative Example 1 and Comparative Example 2;

[0072] The test results are shown in Table 1.

[0073] Table 1 Test results of porosity and grain size of tungsten carbide-cobalt hard alloy

[0074] Grain size (μm) Porosity Example 1 0.27 0.14％ Example 2 0.34 0.11％ Example 3 0.29 0.12％ Comparative Example 1 (Vanadium carbide) 0.25 0.46％ Comparative Example 2 (Hexagonal boron nitride) 0.41 0.31％

[0075] It can be seen from the test results of Examples 1 to 3 in Table 1 that the tungsten carbide-cobalt hard alloy prepared by the method of the present invention has relatively low grain size and porosity, indicating that the method of the present invention can prepare tungsten carbide-cobalt hard alloy products with excellent performance, especially suitable for products such as high-end cutting tools that have high requirements for the wear resistance and strength of the alloy.

[0076] It can be seen from the comparison of Examples 1, Comparative Example 1 and Comparative Example 2 in Table 1 that when the total amount of inhibitors used is exactly the same, Example 1 using the composite inhibitor can control the porosity at 0.14%; while Comparative Example 1 using vanadium carbide inhibitor alone is 0.46%, and Comparative Example 2 using hexagonal boron nitride inhibitor alone is 0.31%. It can be seen that the porosity of the product in Example 1 using the composite inhibitor is much lower than that of the alloy products prepared in Comparative Example 1 and Comparative Example 2 using a single inhibitor alone. It can be seen that the components in the composite inhibitor of the present invention have an obvious synergistic effect of reducing the porosity of tungsten carbide-cobalt hard alloy.

Claims

1. A method for preparing tungsten carbide-cobalt hard alloy, comprising the following steps: S1. Weigh each raw material according to the raw material formula, and wet grind them evenly to obtain a mixture; S2. Use a drying device to vaporize and separate the wet grinding medium in the mixture to obtain a dried material; S3. Use a pressing die to press the dried material into a blank material with the size required by the process; S4. Vacuum sinter the blank material to obtain a primary sintered material; S5. Secondarily sinter the sintered material in a low-pressure furnace to obtain a secondary sintered material; S6. Post-treat the secondary sintered material to obtain a finished product; The raw material formula includes the following components in the following mass fraction ratios: 100 parts of tungsten carbide powder, 6-20 parts of cobalt powder, 1-8 parts of wet grinding medium, 0.3-5 parts of forming agent, and 0.6-1.8 parts of composite inhibitor.

2. The preparation method of tungsten carbide-cobalt hard alloy according to claim 1, characterized in that: The composite inhibitor is composed of vanadium carbide and hexagonal boron nitride in a mass ratio of 1:0.1-0.

6.

3. The method for preparing tungsten carbide-cobalt hard alloy according to claim 1 or 2, characterized in that: The tungsten carbide powder meets the requirements: particle size of 100-300 nm, free carbon content of 0.05-0.1 wt%; the cobalt powder meets the requirements: particle size of 1.5-2.5 μm, purity ≥ 99.5 wt%.

4. The method for preparing tungsten carbide-cobalt hard alloy according to claim 1 or 2, characterized in that: The wet grinding medium is ethanol.

5. The method for preparing tungsten carbide-cobalt hard alloy according to claim 1 or 2, characterized in that: The forming agent is paraffin.

6. The method for preparing tungsten carbide-cobalt hard alloy according to claim 1 or 2, characterized in that: In step S3, the strength of the pressing die is ≥100 MPa, the pre-pressing pressure is 50 - 80 MPa, and the pressure holding time is 15 - 40 s; the density of the blank material is ≥6.5 g / cm 3 .

7. The method for preparing tungsten carbide-cobalt hard alloy according to claim 6, characterized in that: The vacuum sintering conditions in step S4 are as follows: the degree of vacuum ≤ 1×10 -2 Pa, the heating rate is 65 - 140 °C / min, the sintering temperature is 1650 - 1750 °C, and the holding time is 10 - 20 min.

8. The preparation method of tungsten carbide-cobalt hard alloy according to claim 7, characterized in that: Step S5 is specifically as follows: Put the primary sintered material into a low-pressure furnace, raise the temperature to 1350-1450 °C, keep it warm for 3-8 min, and then introduce argon into the low-pressure furnace at a rate of 0.04-0.06 Mpa / min until the pressure in the low-pressure furnace reaches 0.45-0.55 Mpa; then gradually increase the argon flow rate so that the pressure in the low-pressure furnace reaches 5.2-5.7 Mpa within the subsequent 35-40 min; continue to keep it warm for 30-60 min and then stop heating. After the furnace temperature drops below 80 °C, take it out of the furnace.

9. A tungsten carbide-cobalt hard alloy prepared by the method for preparing tungsten carbide-cobalt hard alloy according to any one of claims 1-8.

10. A cutting tool, characterized in that: The production material includes the tungsten carbide-cobalt hard alloy of claim 9.