High-hardness tungsten carbide-cobalt hard alloy and preparation method thereof

Abstract

The invention discloses a high-hardness tungsten carbide-cobalt hard alloy and a preparation method thereof. A production raw material formula comprises the following components in parts by mass: 100 parts of tungsten carbide powder, 6-20 parts of cobalt powder, 0.2-1.3 parts of a composite sintering aid, 0.5-4 parts of a wet grinding medium and 0.2-4 parts of a forming agent, the composite sintering aid is composed of rare earth oxide and cobalt phosphide according to the mass ratio of (1-5): 1. The method has the advantages that on the premise that the toughness of the tungsten carbide-cobalt hard alloy is slightly improved, the hardness and wear resistance of the alloy are remarkably improved, and the industrial problems that the hardness improvement of the tungsten carbide-cobalt hard alloy with a single sintering aid is limited and the toughness of the alloy is lost are solved.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide materials technology, and specifically to a method for producing tungsten carbide-cobalt cemented carbide. Background Technology

[0002] Tungsten carbide-cobalt (WC-Co) cemented carbide, renowned for its high hardness, high wear resistance, and good toughness, is widely used in cutting tools, molds, mining drills, and other fields. Hardness is one of the key indicators for evaluating the performance of cemented carbide. To improve hardness, the industry typically employs two approaches: reducing the cobalt (Co) content and refining the WC grain size.

[0003] However, reducing the cobalt content significantly impairs the toughness of the alloy, making the tool prone to brittle fracture under impact loads. While adding grain growth inhibitors (such as VC, Cr3C2, etc.) to prepare ultrafine or nanocrystalline cemented carbides can effectively improve hardness, these additives often form a brittle film at the WC / Co interface, which also adversely affects toughness. Furthermore, the process control window is narrow, and the additives are extremely sensitive to sintering temperature.

[0004] Sintering aids are important means to optimize the sintering process and improve the microstructure and properties of alloys. Rare earth oxides (such as Y2O3 and La2O3) have been extensively studied as sintering aids. They can refine grains by "purifying" grain boundaries and improving the wettability of the cobalt phase, but experiments have shown that their effect on improving the hardness of tungsten carbide-cobalt alloys is limited.

[0005] Cobalt phosphide (Co2P) additives have been attempted to regulate the properties of the binder phase in alloys, but experiments have shown that they contribute little to grain refinement and have no significant effect on hardness improvement.

[0006] Therefore, developing a novel additive system that can significantly improve the hardness of an alloy while maintaining or even optimizing its toughness has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the problems of low hardness in existing tungsten carbide-cobalt alloys and the lack of significant performance improvement from traditional sintering aids, this invention provides a high-hardness tungsten carbide-cobalt cemented carbide and its preparation method.

[0008] The technical solution adopted in this invention is: a method for preparing high-hardness tungsten carbide-cobalt cemented carbide. The raw material formula includes the following components in the following mass proportions: 100 parts of tungsten carbide powder, 6-20 parts of cobalt powder, 0.2-1.3 parts of composite sintering aid, 0.5-4 parts of wet grinding media, and 0.1-3 parts of forming agent; the composite sintering aid is composed of rare earth oxides and cobalt phosphide in a mass ratio of 1-5:1.

[0009] As will be readily understood by those skilled in the art, the rare earth oxides in this invention can be selected from common rare earth oxides in the art, such as one or any combination of yttrium oxide, lanthanum oxide, and cerium oxide.

[0010] As will be readily understood by those skilled in the art, the specific preparation method of the tungsten carbide-cobalt cemented carbide in this invention can be referenced from conventional methods. To enable those skilled in the art to better utilize this invention, we propose a preferred embodiment, for example, which can be prepared according to the following specific steps:

[0011] S1. According to the production raw material formula, measure each component, and place tungsten carbide powder, cobalt powder, composite sintering aid and wet grinding media in a ball mill for ball milling and mixing to obtain a mixture.

[0012] S2. The mixture is dried, then the molding agent is added and stirred, and then granulated by sieving to obtain the molding material;

[0013] S3. Place the molding material in a mold and press it to form a pressed blank;

[0014] S4. The pressed blank is sintered in a vacuum sintering furnace. The sintering process is as follows: first, the forming agent is removed, and then low-pressure sintering or pressure sintering is carried out at a sintering temperature of 1380-1450°C for 40-90 minutes. After that, it is cooled to room temperature with the furnace to obtain a high-hardness tungsten carbide-cobalt cemented carbide.

[0015] In the above specific preparation method, the wet grinding medium is ethanol, and the molding agent is paraffin or polyethylene glycol.

[0016] In the above specific preparation method, step S1 can be carried out by high-energy ball milling, for example, the ball-to-material ratio used in the ball milling is 3 to 6:1, and the ball milling time is 12 to 48 hours.

[0017] As a further improvement to this scheme, the sintering described in step S4 is carried out in a low-pressure sintering furnace, and argon gas at 0.3 to 0.6 MPa is introduced during the sintering stage.

[0018] As a further improvement to this scheme, the particle size of the tungsten carbide powder is 0.4 to 1.2 μm.

[0019] It is particularly important to note that the particle size of the rare earth oxides and cobalt phosphide used in this invention needs to meet certain conditions. Experiments show that the technical effect can be achieved when the particle size of the rare earth oxides is 1 to 100 nm and the particle size of the cobalt phosphide is 0.5 to 10 μm.

[0020] The present invention also discloses a high-hardness tungsten carbide-cobalt cemented carbide product, which is prepared by the preparation method of the high-hardness tungsten carbide-cobalt cemented carbide of the present invention.

[0021] The present invention also discloses an alloy product, characterized in that the raw materials include the high-hardness tungsten carbide-cobalt cemented carbide of the present invention. For example, the alloy product can be an alloy cutting tool, an alloy drill bit, etc.

[0022] The beneficial effects of this invention are: 1) The tungsten carbide-cobalt cemented carbide prepared by this invention significantly improves hardness (HRA) while maintaining or even slightly increasing bending strength (TRS), breaking the traditional trade-off relationship between hardness and toughness and achieving excellent comprehensive mechanical properties. 2) Strong process applicability: The preparation method is simple, compatible with existing cemented carbide production processes, requires no special or expensive equipment, and is easy to scale up for mass production. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments.

[0024] Example 1:

[0025] Tungsten carbide-cobalt cemented carbide is produced according to the following steps:

[0026] (1) The following raw material formula is used to measure each component: 100 parts of tungsten carbide powder with a particle size of 0.8 μm, 15 parts of cobalt powder with a particle size of 2.5 μm, 0.8 parts of composite sintering aid, 2 parts of ethanol, and 1.5 parts of paraffin; the composite sintering aid is composed of yttrium oxide with a particle size of 24 nm and cobalt phosphide with a particle size of 7.8 μm in a mass ratio of 3:1.

[0027] (2) Tungsten carbide powder, cobalt powder, composite sintering aid and ethanol are placed in a ball mill for ball milling and mixing. The ball-to-material ratio is 5:1 and the ball milling time is 24 hours to obtain a mixture.

[0028] (3) The mixture is dried and gasified to separate the wet grinding media, then paraffin wax is added and stirred, and then granulated by sieving to obtain the molding material;

[0029] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0030] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: 0.5 MPa of argon gas is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1420°C for 60 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0031] Example 2:

[0032] Tungsten carbide-cobalt cemented carbide is produced according to the following steps:

[0033] (1) The following raw material formula is used to measure each component: 100 parts of tungsten carbide powder with a particle size of 0.5 μm, 18 parts of cobalt powder with a particle size of 3 μm, 0.9 parts of composite sintering aid, 2.4 parts of ethanol, and 1.7 parts of paraffin; the composite sintering aid is composed of cerium oxide with a particle size of 18 nm and cobalt phosphide with a particle size of 8.2 μm in a mass ratio of 2.5:1.

[0034] (2) Tungsten carbide powder, cobalt powder, composite sintering aid and ethanol were placed in a ball mill for ball milling and mixing. The ball-to-material ratio was 4.8:1 and the ball milling time was 18 hours to obtain the mixture.

[0035] (3) The mixture is dried and gasified to separate the wet grinding media, then paraffin wax is added and stirred, and then granulated by sieving to obtain the molding material;

[0036] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0037] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: 0.6 MPa of argon gas is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1390°C for 75 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0038] Example 3:

[0039] Tungsten carbide-cobalt cemented carbide is produced according to the following steps:

[0040] (1) The following raw material formula is used to measure each component: 100 parts of tungsten carbide powder with a particle size of 1.1 μm, 33 parts of cobalt powder with a particle size of 5.2 μm, 1.2 parts of composite sintering aid, 2.8 parts of ethanol, and 0.9 parts of paraffin; the composite sintering aid is composed of lanthanum oxide with a particle size of 34 nm and cobalt phosphide with a particle size of 6.8 μm in a mass ratio of 4:1.

[0041] (2) Tungsten carbide powder, cobalt powder, composite sintering aid and ethanol were placed in a ball mill for ball milling and mixing. The ball-to-material ratio was 6.5:1 and the ball milling time was 28 hours to obtain the mixture.

[0042] (3) The mixture is dried and gasified to separate the wet grinding media, then polyethylene glycol is added and stirred, and then granulated by sieving to obtain the molding material;

[0043] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0044] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: argon gas of 0.45 MPa is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1430°C for 50 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0045] Comparative Example 1:

[0046] This comparative example serves as a control experiment for Example 1, conducted according to the same steps and conditions as Example 1. The raw materials used are from the same batch as in Example 1. The difference lies in the absence of sintering aids. The specific procedure is as follows:

[0047] (1) Take the following components according to the production raw material formula: 100 parts of tungsten carbide powder with a particle size of 0.8μm, 15 parts of cobalt powder with a particle size of 2.5μm, 2 parts of ethanol, and 1.5 parts of paraffin.

[0048] (2) Tungsten carbide powder, cobalt powder and ethanol were placed in a ball mill for ball milling and mixing. The ball-to-material ratio was 5:1 and the ball milling time was 24 hours to obtain a mixture.

[0049] (3) The mixture is dried and gasified to separate the wet grinding media, then paraffin wax is added and stirred, and then granulated by sieving to obtain the molding material;

[0050] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0051] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: 0.5 MPa of argon gas is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1420°C for 60 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0052] Comparative Example 2:

[0053] This comparative example serves as a control experiment for Example 1, conducted according to the same steps and conditions as Example 1. The raw materials used are from the same batch as in Example 1, with the difference being that all sintering aids are yttrium oxide (i.e., cobalt phosphide is not used), and the total amount of sintering aids used remains constant. The specific scheme is as follows:

[0054] (1) Take the following components according to the production raw material formula: 100 parts of tungsten carbide powder with a particle size of 0.8 μm, 15 parts of cobalt powder with a particle size of 2.5 μm, 0.8 parts of sintering aid, 2 parts of ethanol, and 1.5 parts of paraffin; wherein the sintering aid is yttrium oxide with a particle size of 24 nm.

[0055] (2) Tungsten carbide powder, cobalt powder, sintering aid and ethanol are placed in a ball mill for ball milling and mixing. The ball-to-material ratio is 5:1 and the ball milling time is 24 hours to obtain a mixture.

[0056] (3) The mixture is dried and gasified to separate the wet grinding media, then paraffin wax is added and stirred, and then granulated by sieving to obtain the molding material;

[0057] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0058] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: 0.5 MPa of argon gas is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1420°C for 60 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0059] Comparative Example 3:

[0060] This comparative example serves as a control experiment for Example 1, conducted according to the same steps and conditions as Example 1. The raw materials used are from the same batch as in Example 1, with the difference being that all sintering aids are cobalt phosphide (i.e., yttrium oxide is not used), and the total amount of sintering aids used remains unchanged. The specific scheme is as follows:

[0061] (1) Take the following components according to the production raw material formula: 100 parts of tungsten carbide powder with a particle size of 0.8μm, 15 parts of cobalt powder with a particle size of 2.5μm, 0.8 parts of sintering aid, 2 parts of ethanol, and 1.5 parts of paraffin; wherein the sintering aid is cobalt phosphide with a particle size of 7.8μm.

[0062] (2) Tungsten carbide powder, cobalt powder, sintering aid and ethanol are placed in a ball mill for ball milling and mixing. The ball-to-material ratio is 5:1 and the ball milling time is 24 hours to obtain a mixture.

[0063] (3) The mixture is dried and gasified to separate the wet grinding media, then paraffin wax is added and stirred, and then granulated by sieving to obtain the molding material;

[0064] (4) The molding material is placed in a mold and pressed into shape. The mold strength is 95MPa, the pre-pressing pressure is 67MPa, and the holding time is 30s to obtain a pressed blank.

[0065] (5) The pressed blank is sintered in a vacuum low-pressure sintering furnace. The sintering process is as follows: 0.5 MPa of argon gas is introduced during the sintering stage, and then low-pressure sintering is carried out at a sintering temperature of 1420°C for 60 minutes. After that, it is cooled to room temperature with the furnace to obtain tungsten carbide-cobalt cemented carbide.

[0066] Mechanical property testing of tungsten carbide-cobalt cemented carbide:

[0067] The hardness (HRA), bending strength, and coercivity of the tungsten carbide-cobalt cemented carbide products of the above embodiments and comparative examples were tested as follows:

[0068] I. Hardness Testing:

[0069] Detection indicator: HRA.

[0070] Testing standard: Complies with GB / T 3849.1 (equivalent to or equivalent to ISO 3738-1) "Hard alloys Rockwell hardness test (A scale) Part 1: Test method".

[0071] Testing equipment: Rockwell hardness tester.

[0072] Test method: Using a diamond conical indenter (120° apex angle, 0.2 mm tip curvature radius), after applying an initial test force (98.07 N, 10 kgf) and a total test force (588.4 N, 60 kgf) successively, the main test force is removed, and the residual increment of the indentation depth (h) is measured while retaining the initial test force. The HRA value is directly displayed on the hardness tester dial.

[0073] Sample requirements:

[0074] The sample surface is finely ground or polished to ensure it is smooth, flat, and free of oxide scale and dirt.

[0075] The sample thickness is 10 times the indentation depth.

[0076] Five points were tested at different locations for each sample, and the arithmetic mean was taken as the final result.

[0077] II. Bending Strength Testing

[0078] Testing index: Transverse fracture strength (TRS).

[0079] Testing standard: in accordance with GB / T 3851 (equivalent to or equivalent to ISO 3327) "Determination of transverse fracture strength of cemented carbide".

[0080] Testing equipment: Universal testing machine.

[0081] Testing principle: The three-point bending method is used. Samples of the same size are placed on two support rollers, and a loading roller applies pressure at a constant rate from the middle until the sample breaks. The maximum load (F) at the point of fracture is recorded.

[0082] Sample requirements:

[0083] The standard sample dimensions are: length (20 ± 1) mm, width (6.5 ± 0.2) mm, and thickness (5.25 ± 0.2) mm. All edges must be chamfered, and the surface must be polished to remove any defects.

[0084] The support roller span is (15 ± 0.2) mm.

[0085] Loading rate: Control the descent speed of the loading roller to make the sample break within 30 seconds.

[0086] Calculation formula:

[0087] TRS = (3 * F * L) / (2 * w * t²)

[0088] in:

[0089] F = Fracture load (N)

[0090] L = Support roller span (mm)

[0091] w = Sample width (mm)

[0092] t = Sample thickness (mm).

[0093] III. Coercive Magnetic Force Testing

[0094] Detection indicator: Hc, unit kA / m (kiloampere / meter).

[0095] Testing standard: in accordance with GB / T 3849.2 (equivalent to or equivalent to ISO 3326) "Determination of coercivity of cemented carbide".

[0096] Testing equipment: coercive magnetometer.

[0097] Detection method:

[0098] The sample is placed in a strong magnetic field until it is magnetized to saturation.

[0099] After the magnetizing field was removed, the sample retained remanence due to the presence of the ferromagnetic cobalt phase (Co).

[0100] A demagnetizing field with the opposite direction is applied to the sample, and its intensity is gradually increased.

[0101] When the strength of the reverse magnetic field is sufficient to reduce the remanence of the sample to zero, this magnetic field strength value is the coercive force Hc.

[0102] Sample requirements:

[0103] Before measurement, the sample needs to be demagnetized to eliminate the influence of its historical magnetization state.

[0104] The test results are shown in Table 1.

[0105] Table 1. Test Results of Mechanical Properties of Tungsten Carbide-Cobalt Cemented Carbide

[0106] Hardness (HRA) Flexural strength (MPa) Coercive force (kA / m) Example 1 93.6 3350 25.2 Example 2 92.9 3320 24.8 Example 3 92.5 3290 23.4 Comparative Example 1 87.2 3270 18.1 Comparative Example 2 91.3 2940 20.1 Comparative Example 3 88.0 3250 19.2

[0107] As can be seen from the comparison of Examples 1, 2, and 3 and Comparative Example 1 in Table 1, the present invention, through the use of composite sintering aids, increases the hardness of tungsten carbide-cobalt cemented carbide from 87.2 HRA to 93.6 HRA; the bending strength from 3270 MPa to 3350 MPa; and the coercivity from 18.1 kA / m to 25.2 kA / m. It is evident that the composite sintering aid of the present invention can significantly improve the hardness of tungsten carbide-cobalt cemented carbide while maintaining or even slightly improving the bending strength of the alloy material; simultaneously, the high coercivity also demonstrates that the grain size of the tungsten carbide-cobalt cemented carbide has been effectively refined.

[0108] As can be seen from the comparison of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 in Table 1, under the premise that the proportion of sintering aids remains completely unchanged, the hardness improvement value of tungsten carbide-cobalt cemented carbide is 4.1 HRA when using rare earth oxide yttrium oxide alone as a sintering aid, and 0.8 HRA when using cobalt phosphide alone as a sintering aid. Theoretically, when the two are combined in a 3:1 ratio to form a composite sintering aid, the hardness improvement value of tungsten carbide-cobalt cemented carbide should not exceed 3.3 HRA, while the actual measured improvement value in Example 1 is 6.4 HRA, which is 93.9% higher than the theoretical value. It can be seen that rare earth oxides and cobalt phosphide in the composite sintering aid of the present invention have a significant synergistic effect in improving the hardness of tungsten carbide-cobalt cemented carbide. At the same time, based on the coercivity test results, the inventors believe that the reason is related to the fact that rare earth oxides and cobalt phosphide can synergistically promote the grain refinement of tungsten carbide-cobalt cemented carbide during the sintering process.

Claims

1. A method for preparing high-hardness tungsten carbide-cobalt cemented carbide, characterized in that: The raw material formula includes the following components in the following mass proportions: 100 parts tungsten carbide powder, 6-20 parts cobalt powder, 0.2-1.3 parts composite sintering aid, 0.5-4 parts wet grinding media, and 0.1-3 parts forming agent; the composite sintering aid is composed of rare earth oxides and cobalt phosphide in a mass ratio of 1-5:

1.

2. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 1, characterized in that: The rare earth oxide is selected from one or more of yttrium oxide, lanthanum oxide, and cerium oxide.

3. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 1 or 2, characterized in that, Includes the following steps: S1. According to the production raw material formula, measure each component, and place tungsten carbide powder, cobalt powder, composite sintering aid and wet grinding media in a ball mill for ball milling and mixing to obtain a mixture. S2. The mixture is dried, then the molding agent is added and stirred, and then granulated by sieving to obtain the molding material; S3. Place the molding material in a mold and press it to form a pressed blank; S4. The pressed blank is sintered in a vacuum sintering furnace. The sintering process is as follows: first, the forming agent is removed, and then low-pressure sintering or pressure sintering is carried out at a sintering temperature of 1380-1450°C for 40-90 minutes. After that, it is cooled to room temperature with the furnace to obtain a high-hardness tungsten carbide-cobalt cemented carbide.

4. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 3, characterized in that: The wet grinding medium is ethanol, and the molding agent is paraffin or polyethylene glycol.

5. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 3, characterized in that: In step S1, the ball milling process uses a ball-to-material ratio of 3 to 6:1 and a milling time of 12 to 48 hours.

6. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 3, characterized in that: The sintering described in step S4 is carried out in a low-pressure sintering furnace, and argon gas at 0.3 to 0.6 MPa is introduced during the sintering stage.

7. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 1 or 2, characterized in that: The particle size of the tungsten carbide powder is 0.4–1.2 μm.

8. The method for preparing high-hardness tungsten carbide-cobalt cemented carbide according to claim 1 or 2, characterized in that: The particle size of the rare earth oxide is 1–100 nm; the particle size of the cobalt phosphide is 1–10 μm.

9. A high-hardness tungsten carbide-cobalt cemented carbide prepared by any one of the high-hardness tungsten carbide-cobalt cemented carbide preparation methods according to any one of claims 1 to 8.

10. An alloy product, characterized in that: The raw materials used in the production include the high-hardness tungsten carbide-cobalt cemented carbide as claimed in claim 9.