High-temperature-resistant and corrosion-resistant cemented carbide and preparation method thereof

Abstract

The application provides a high-temperature-resistant and corrosion-resistant hard alloy and a preparation method thereof. The preparation raw material of the hard alloy comprises a binder phase powder and a hard phase powder; the binder phase powder accounts for 19-36% of the total mass of the preparation raw material, and the hard phase powder accounts for 64-81% of the total mass of the preparation raw material; the hard phase powder is coarse-grained WC powder, and the Fsss particle size of the hard phase powder is 20-26 mu m; and the binder phase powder comprises Co powder, Ni powder, Cr3C2 powder, W powder and Al4C3 powder. The hard alloy of the application contains a nano-sized Ni3Al precipitated phase in the binder phase, which strengthens the binder phase, improves the hardness and strength of the hard alloy, improves the oxidation resistance, improves the wear resistance, simultaneously considers the high-temperature oxidation resistance, corrosion resistance, toughness and wear resistance of the high-binder-phase coarse-grained hard alloy, and improves the service life.

Description

Technical Field

[0001] This invention belongs to the field of cemented carbide technology, specifically relating to a high-temperature and corrosion-resistant cemented carbide and its preparation method. Background Technology

[0002] As a key wear-resistant component required for bar and wire rod rolling in the steel industry, cemented carbide roll rings come into contact with red-hot steel at temperatures of 800–1050°C during the rolling process. They also endure high alternating rolling stress, thermal stress, and torque shear force during temperature-controlled rolling. This is compounded by high-temperature oxidation and corrosion reactions caused by high levels of chloride and sulfate ions during cooling. Therefore, cemented carbide roll rings are required to have high-temperature oxidation resistance, corrosion resistance, high red hardness, impact toughness, and thermal fatigue resistance to ensure that the roll rings do not break, are not prone to corrosion pitting, have high wear resistance, a long service life, and ensure the stability of the rolled material quality.

[0003] The main methods to improve the high-temperature and corrosion resistance of cemented carbide include: changing the composition of the binder phase and adding gain agents such as Ni, Cr, and Mo to modify the properties of the binder phase. For example, patent CN202010701416.1 discloses a method for preparing a bicrystalline corrosion-resistant cemented carbide by adding nickel powder, aluminum powder, vanadium carbide powder, chromium carbide powder, molybdenum powder, and tungsten carbide powder to WC cemented carbide without adding Co, which has poor corrosion resistance, in an attempt to effectively improve the high corrosion resistance of cemented carbide. Patent 202011204906.7 introduces Ni3Al precipitation strengthening by adding AlB2, providing a metal-ceramic material with dual strengthening of the binder phase, namely Ni-Cu solid solution strengthening and Ni3Al precipitation strengthening, and its preparation method, to obtain a metal-ceramic material with high strength, high wear resistance, oxidation resistance, and high hardness. Patent CN202211280930.8 discloses a wear-resistant and corrosion-resistant valve seat composed of titanium carbonitride solid solution, nickel, cobalt, chromium, and other trace elements ≤2%. Patent CN201811274139.X discloses a high-temperature resistant and wear-resistant cemented carbide with good strength and hardness by scientifically adjusting the proportions of cobalt powder, nickel powder, iron powder, tungsten carbide, titanium carbide, tantalum carbide, and silicon carbide, and then mixing, vacuum high-temperature pressing, and sintering the above raw materials. Patent CN201610964405.6 uses a rhenium-molybdenum-nickel alloy as the binder phase and tungsten carbide as the hard phase, adding a small amount of Cr3C2 and TaC additives to prepare a WC-Ni-Mo-Re cemented carbide, giving the product strong resistance to high-temperature oxidation and corrosion, for use in the production of nuclear-grade sealing rings.

[0004] Traditional WC-Ni cemented carbide and higher technologies primarily offer superior corrosion and wear resistance, enabling them to withstand high-temperature environments of around 120°C and high-pressure acidic water environments when used in nuclear-grade sealing rings. However, these technologies cannot produce corrosion-resistant cemented carbide roll rings with excellent impact toughness and resistance to thermal cracking because the following issues significantly reduce the roll ring's service life:

[0005] 1) Ni has poorer wettability to WC than Co, and micropores are easily formed in pure nickel or high-nickel alloys, which can lead to fracture sources;

[0006] 2) Pure nickel cemented carbide is non-magnetic or has very low magnetic properties, and cannot be monitored by cobalt magnetism or magnetic force, thus effectively ensuring the stability of mass production processes;

[0007] 3) In nickel-containing cemented carbide, the face-centered cubic structure of nickel is prone to forming nickel flakes during ball milling, causing the aggregated and segregated binder phase in the cemented carbide, resulting in poor uniformity of the binder phase distribution in the microstructure of the alloy.

[0008] 4) Nickel is less hard than cobalt. In Co+Ni binder phase cemented carbide, as the nickel content increases, the alloy hardness decreases, which leads to a decrease in the alloy's wear resistance and causes premature product failure.

[0009] The existing cemented carbide with certain corrosion resistance and toughness is the WC-Co-Ni-Cr grade with high binder phase and high cobalt content. However, it suffers from binder phase aggregation, resulting in poor product stability. Furthermore, in environments with controlled temperature and rolling and poor rolling cooling water quality, the poor wear resistance of cemented carbide leads to frequent roll changes, and corrosion causes pitting, resulting in poor surface quality of steel products.

[0010] Therefore, there is an urgent need to develop a high-binder phase high-temperature corrosion resistant cemented carbide that simultaneously improves high-temperature oxidation resistance, corrosion resistance, toughness, and wear resistance. Summary of the Invention

[0011] To address the aforementioned problems in the prior art, this invention proposes a high-temperature and corrosion-resistant cemented carbide and its preparation method. The cemented carbide prepared using this invention effectively solves the problem of simultaneously achieving high-temperature oxidation resistance, corrosion resistance, toughness, and wear resistance in high-binder cemented carbides. This simultaneously improves the toughness, wear resistance, high-temperature resistance, and corrosion resistance of the cemented carbide, thereby increasing its service life.

[0012] In a first aspect, the present invention proposes a high-temperature and corrosion-resistant cemented carbide, the raw materials for which are prepared include binder phase powder and hard phase powder; the binder phase powder accounts for 19-36 wt% of the total mass of the raw materials, and the hard phase powder accounts for 64-81 wt% of the total mass of the raw materials.

[0013] The hard phase powder is coarse-grained WC powder, and the Fsss particle size of the hard phase powder is 20-26 μm; the binder phase powder includes Co powder, Ni powder, Cr3C2 powder, W powder and Al4C3 powder.

[0014] According to the present invention, the coarse-grained WC powder is coarse-grained WC powder without the use of alkali metals or other coarsening agents, and has a lower content of alkali metal impurities at the ppm level, which can reduce the micropores in the alloy.

[0015] As a specific embodiment of the present invention, the relationship between the mass of Co powder and Ni powder in the binder phase powder and the total mass of the raw materials is: Co + Ni = 16.8-30 wt%, and Ni:Co ≥ 1.5, Co ≥ 5 wt%.

[0016] According to the present invention, the Co powder and Ni powder in the binder phase powder account for 16.8-30 wt% of the total mass of the raw materials, and the mass ratio of Ni powder to Co powder is ≥1.5, and the mass ratio of Co powder is not less than 5 wt% of the total mass of the raw materials.

[0017] As a specific embodiment of the present invention, in the binder phase powder, W powder accounts for 0.2-3 wt% of the total mass of the raw materials, Al4C3 powder accounts for 1-1.5 wt% of the total mass of the raw materials, and Cr3C2 powder accounts for 1-1.5 wt% of the total mass of the raw materials.

[0018] As a specific embodiment of the present invention, the average grain size of tungsten carbide in the cemented carbide is 2.4-3.2 μm.

[0019] In a second aspect, the present invention provides a method for preparing the high-temperature resistant and corrosion-resistant cemented carbide described in the first aspect, comprising the following steps:

[0020] S1: Wet-mill the hard phase powder, the binder phase powder (excluding Ni powder), and the forming agent to obtain the first mixture;

[0021] S2: Add Ni powder to the first mixture obtained in step S1, mix and wet grind to obtain the second mixture;

[0022] S3: Filter, dry, shape, and sinter the second mixture obtained in step S2 to obtain the high-temperature and corrosion-resistant hard alloy.

[0023] In a specific embodiment of the present invention, step S1, the wet milling includes wet milling using a ball mill; the conditions for wet milling include: a ball-to-material ratio of (2-4):1, a ball milling rate of 30-40 rpm, and a ball milling time of 8-18 h; the ball milling medium is alcohol, and the volume-to-mass ratio of alcohol to the raw material is 220-400 ml: 1 kg. The ball-to-material ratio refers to the ratio of the weight of the grinding media to the weight of the material being ground.

[0024] In a specific embodiment of the present invention, in step S1, the molding agent includes paraffin wax, and the amount of molding agent added is 1-5% of the total mass of the raw materials, preferably 2%.

[0025] As a specific embodiment of the present invention, in step S2, the conditions for wet milling include: a ball-to-material ratio of (2-4):1, a ball milling rate of 30-40 rpm, and a ball milling time of 8-12 h.

[0026] According to the present invention, in the conventional ball milling process, all raw materials are added to the ball mill together at the beginning of the ball milling process and wet milled until unloading. The ball milling process of the present invention first wet mills the raw materials except for Ni powder, and then adds nickel powder to continue wet milling. The addition time of Ni powder in the wet milling process is adjusted to shorten the ball milling time of the face-centered cubic structure nickel powder. This can avoid plastic deformation and cold welding agglomeration caused by prolonged ball milling of nickel powder, and effectively improve the problem of uneven distribution of binder phase in high-binding-phase cemented carbide.

[0027] As a specific embodiment of the present invention, in step S3, the sintering includes pressure sintering, preferably, pressure sintering in an inert atmosphere.

[0028] In a specific embodiment of the present invention, in step S3, the inert atmosphere includes argon and helium; preferably, the inert atmosphere is argon; and the pressure is increased to 50-90 bar.

[0029] As a specific embodiment of the present invention, in step S3, the sintering method includes segmented sintering, which includes a dewaxing stage, a pre-firing stage and a sintering stage, wherein the dewaxing temperature in the dewaxing stage is 240℃-550℃, the pre-firing temperature in the pre-firing stage is 860℃-1160℃, and the sintering temperature in the sintering stage is 1350℃-1520℃.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The high-temperature and corrosion-resistant cemented carbide of this invention has a binder phase content of 19%-36% by weight, classifying it as a high-binder-phase cemented carbide. Furthermore, metallographic analysis shows an average grain size of 2.4-3.2 μm, classifying it as a coarse-grained cemented carbide. Both factors contribute to the high toughness of the cemented carbide. The high nickel content in the cemented carbide enhances its corrosion resistance. Electrochemical experiments, using polarization curves to calculate the self-corrosion potential and corrosion current density, reveal a higher self-corrosion potential, making corrosion less likely; the corrosion current density is significantly reduced by 70%-95%, slowing the corrosion rate. The cemented carbide binder phase contains nano-sized Ni3Al precipitates, which strengthen the binder phase, improving not only the hardness and strength of the cemented carbide but also its oxidation resistance and wear resistance. This allows the high-binder-phase coarse-grained cemented carbide to simultaneously maintain its high-temperature oxidation resistance, corrosion resistance, toughness, and wear resistance, thus extending its service life.

[0032] 2. The high-temperature and corrosion-resistant cemented carbide of this invention uses coarse-grained WC powder without alkali metal or other thickening agents, resulting in low impurity content and reduced microporosity in the alloy. In the high-temperature and corrosion-resistant cemented carbide of this invention, the main component of the binder phase raw material has Co ≥ 5%, ensuring wettability between the binder phase and WC. Furthermore, cobalt magnetism and magnetic force monitoring can be used to ensure stable, simple, and controllable production quality.

[0033] 3. The ball milling process of the present invention adjusts the addition time of nickel powder in the wet milling process to shorten the ball milling time of face-centered cubic nickel powder, which can avoid plastic deformation and cold welding agglomeration caused by long-term ball milling of nickel powder, and effectively improve the problem of uneven distribution of binder phase in high-binder phase cemented carbide. Attached Figure Description

[0034] Figure 1 Metallographic image of the high-temperature and corrosion-resistant hard alloy of the present invention;

[0035] Figure 2 A scanning electron microscope image of the precipitated phase in the high-temperature and corrosion-resistant hard alloy binder phase of the present invention;

[0036] Figure 3 This is a comparison graph of the polarization curves of Example 3 and Comparative Example 1, which were tested for corrosion performance in the same rolling cooling water. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0038] Example 1

[0039] This embodiment provides a high-temperature and corrosion-resistant cemented carbide and its preparation method, with specific details as follows:

[0040] S1: Based on the total mass percentage of the raw materials, 81% WC powder with an Fsss particle size of 25μm, 5.5% Co powder, 1% Cr3C2 powder, 1% Al4C3 powder, 0.3% W powder, and 2% forming agent paraffin are mixed in a ball mill and wet-milled. The wet milling conditions include: the ball milling medium is alcohol, the alcohol dosage is 240ml of alcohol per kilogram of powder, the ball-to-material ratio is 3:1, and the ball milling is carried out for 8 hours to obtain the first mixture.

[0041] S2: Add 11.2% Ni powder to the first mixture obtained in step S1, and then ball mill for 12 hours to obtain the second mixture;

[0042] S3: The second mixture obtained in step S2 is filtered and dried to obtain the third mixture. The third mixture is then pressed on a hydraulic press with a molding pressure of 160 MPa. Finally, it is sintered in a pressure furnace with a final dewaxing temperature of 550°C, a final pre-firing temperature of 1160°C, and a final sintering temperature of 1480°C. The furnace pressure for sintering is 50 bar, and the holding time is 1.5 h, to obtain a high-temperature and corrosion-resistant hard alloy.

[0043] The high-temperature and corrosion-resistant cemented carbide obtained in Example 1 is a coarse-grained cemented carbide, and its metallographic structure is as follows: Figure 1 As shown.

[0044] Scanning electron microscope (SEM) images of the precipitated phase in the binder phase of the high-temperature and corrosion-resistant cemented carbide obtained in Example 1 are shown below. Figure 2 As shown, the large gray-white particles are the WC phase, the dark gray particles are the binder phase, and the small gray-white particles in the binder phase are the nano phase (Ni3Al) in the binder phase.

[0045] Example 2

[0046] This embodiment provides a high-temperature and corrosion-resistant cemented carbide and its preparation method, with specific details as follows:

[0047] S1: Based on the total mass percentage of the raw materials, 64% WC powder with an Fsss particle size of 22μm, 10% Co powder, 1.5% Cr3C2 powder, 1.5% Al4C3 powder, 2% W powder, and 2% of the molding agent paraffin wax are mixed in a ball mill and wet-milled. The wet milling conditions include: the ball milling medium is alcohol, the alcohol dosage is 340ml per kilogram of powder, the ball-to-material ratio is 2.2:1, and the ball milling is carried out for 16 hours to obtain the first mixture.

[0048] S2: Add 21% Ni powder to the first mixture obtained in step S1, and continue ball milling for 9 hours to obtain the second mixture;

[0049] S3: Filter and dry the second mixture obtained in step S2 to obtain the third mixture. Then press the third mixture on a hydraulic press with a molding pressure of 180MPa. Finally, sinter it in a pressure sintering furnace with a final dewaxing temperature of 550℃, a final pre-sintering temperature of 1060℃, a final sintering temperature of 1390℃, a sintering furnace pressure of 60bar, and a holding time of 2h to obtain a high-temperature and corrosion-resistant hard alloy.

[0050] Example 3

[0051] This embodiment provides a high-temperature and corrosion-resistant cemented carbide and its preparation method, with specific details as follows:

[0052] S1: Based on the total mass percentage of the raw materials, 74% WC powder with an Fsss particle size of 20μm, 8.5% Co powder, 1.2% Cr3C2 powder, 1% Al4C3 powder, 0.8% W powder, and 2% forming agent paraffin are mixed in a ball mill and wet-milled. The wet milling conditions include: the ball milling medium is alcohol, the alcohol dosage is 300ml alcohol per kilogram of powder, the ball-to-powder ratio is 3.2:1, and the ball milling is carried out for 18 hours to obtain the first mixture.

[0053] S2: Add 14.5% Ni powder to the first mixture obtained in step S1, and continue ball milling for 8 hours to obtain the second mixture;

[0054] S3: Filter and dry the second mixture obtained in step S2 to obtain the third mixture. Then press the third mixture on a hydraulic press with a molding pressure of 160 MPa. Finally, sinter it in a pressure sintering furnace with a final dewaxing temperature of 550℃, a final pre-sintering temperature of 1120℃, a final sintering temperature of 1430℃, a sintering furnace pressure of 70 bar, and a holding time of 2 hours to obtain a high-temperature and corrosion-resistant hard alloy.

[0055] Comparative Example 1

[0056] This comparative example provides a high-temperature and corrosion-resistant cemented carbide and its preparation method, with specific details as follows:

[0057] S1: Based on the total mass percentage of the raw materials, 74% WC powder with an Fsss particle size of 20μm, 12.4% Co powder, 1.2% Cr3C2 powder, 12.4% Ni powder, and 2% forming agent paraffin wax are mixed in a ball mill and wet-milled. The wet milling conditions include: the ball milling medium is alcohol, the alcohol dosage is 300ml per kilogram of powder, the ball-to-powder ratio is 3.2:1, and the ball milling is carried out for 26 hours to obtain the first mixture.

[0058] S2: Filter and dry the first mixture obtained in step S1 to obtain the second mixture;

[0059] S3: The second mixture obtained in step S2 is pressed on a hydraulic press with a molding pressure of 160 MPa. Finally, it is sintered in a pressure sintering furnace with a final dewaxing temperature of 550°C, a final pre-sintering temperature of 1120°C, a final sintering temperature of 1430°C, a furnace pressure of 7 bar, and a holding time of 2 hours to obtain the cemented carbide.

[0060] Test Example 1

[0061] The high-temperature and corrosion-resistant cemented carbides prepared in Examples 1-3 and Comparative Example 1 were subjected to performance tests. The test items included hardness, density, bending strength, WC average grain size, and surface weight gain per unit area after oxidation at 900℃ for 1 hour. The test results are shown in Table 1.

[0062] Table 1

[0063]

[0064] Test Example 2

[0065] The corrosion performance of the high-temperature and corrosion-resistant cemented carbides prepared in Example 3 and Comparative Example 1 was tested in the same rolling cooling water. The test results are as follows: Figure 3 As shown.

[0066] Depend on Figure 3 It can be seen that the polarization curve of Example 3 shifts to the lower right compared to Comparative Example 1, indicating that the high-temperature and corrosion-resistant hard alloy of Example 3 has a higher self-corrosion potential, is more difficult to corrode, has a lower corrosion current density, and a slower corrosion rate.

[0067] In summary, the cemented carbide of this invention uses coarse-grained WC powder without alkali metal or other coarsening agents, resulting in low impurity content and reduced microporosity. The high nickel content enhances the alloy's corrosion resistance. Electrochemical experiments using polarization curves to calculate the self-corrosion potential and corrosion current density show that a higher self-corrosion potential makes corrosion more difficult, while a significantly lower corrosion current density (70%-95%) slows down the corrosion rate. Furthermore, the cemented carbide's binder phase contains nano-sized Ni3Al precipitates, which strengthen the binder phase, improving not only the hardness and strength but also oxidation resistance and wear resistance. This allows the high-binder coarse-grained cemented carbide to simultaneously maintain its high-temperature oxidation resistance, corrosion resistance, toughness, and wear resistance, thus extending its service life.

[0068] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0069] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a high-temperature and corrosion-resistant hard alloy, characterized in that, The raw materials for preparing the cemented carbide include binder phase powder and hard phase powder; the binder phase powder accounts for 19-36 wt% of the total mass of the raw materials, and the hard phase powder accounts for 64-81 wt% of the total mass of the raw materials. The hard phase powder is coarse-grained WC powder, and the Fsss particle size of the hard phase powder is 20-26 μm; the binder phase powder includes Co powder, Ni powder, Cr3C2 powder, W powder and Al4C3 powder. The method for preparing the cemented carbide includes the following steps: S1: Wet-mill the hard phase powder, the binder phase powder (excluding Ni powder), and the forming agent to obtain the first mixture; S2: Add Ni powder to the first mixture obtained in step S1, mix and wet grind to obtain the second mixture; S3: Filter, dry, shape, and sinter the second mixture obtained in step S2 to obtain the high-temperature and corrosion-resistant hard alloy.

2. The preparation method according to claim 1, characterized in that, The relationship between the mass of Co powder and Ni powder in the binder phase powder and the total mass of the raw materials is as follows: Co + Ni = 16.8-30 wt%, and Ni:Co ≥ 1.5, Co ≥ 5 wt%.

3. The preparation method according to claim 1, characterized in that, In the binder phase powder, W powder accounts for 0.2-3 wt% of the total mass of the raw materials, Al4C3 powder accounts for 1-1.5 wt% of the total mass of the raw materials, and Cr3C2 powder accounts for 1-1.5 wt% of the total mass of the raw materials.

4. The preparation method according to any one of claims 1-3, characterized in that, The average grain size of tungsten carbide in this cemented carbide is 2.4-3.2 μm.

5. The preparation method according to any one of claims 1-3, characterized in that, In step S1, the wet milling includes wet milling using a ball mill; the conditions for wet milling include: a ball-to-material ratio of (2-4):1, a ball milling rate of 30-40 rpm, and a ball milling time of 8-18 h; the ball milling medium is alcohol, and the volume-to-mass ratio of alcohol to the raw material is 220-400 ml: 1 kg; The molding agent includes paraffin wax, and the amount of molding agent added is 1-5% of the total mass of the raw materials.

6. The preparation method according to claim 5, characterized in that, The amount of the molding agent added is 2% of the total mass of the raw materials.

7. The preparation method according to any one of claims 1-3, characterized in that, In step S2, the conditions for wet milling include: a ball-to-material ratio of (2-4):1, a ball milling rate of 30-40 rpm, and a ball milling time of 8-12 h.

8. The preparation method according to any one of claims 1-3, characterized in that, In step S3, the sintering includes pressure sintering.

9. The preparation method according to claim 8, characterized in that, The sintering process includes pressure sintering in an inert atmosphere.

10. The preparation method according to claim 9, characterized in that, In step S3, the inert atmosphere includes argon and helium; the pressure is increased to 50-90 bar.

11. The preparation method according to claim 10, characterized in that, The inert atmosphere is argon.

12. The preparation method according to any one of claims 1-3, characterized in that, In step S3, the sintering method includes segmented sintering, which includes a dewaxing stage, a pre-firing stage, and a sintering stage. The dewaxing temperature in the dewaxing stage is 240℃-550℃, the pre-firing temperature in the pre-firing stage is 860℃-1160℃, and the sintering temperature in the sintering stage is 1350℃-1520℃.

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