A high-hardness, low-expansion, low-oxidation cemented carbide and its preparation method

Abstract

This invention belongs to the field of powder metallurgy technology, specifically relating to a high-hardness, low-expansion, and low-oxidation cemented carbide and its preparation method. Doping is achieved through liquid mixing-evaporation crystallization, with precise control of the dopant element content achieved by coordinating temperature and pH control of the crystallization mother liquor. Furthermore, ball milling is eliminated, allowing the incorporated cobalt and chromium to undergo intermolecular mixing, which not only improves doping efficiency but also reduces impurities introduced by ball milling, ensuring the cemented carbide's low expansion coefficient and low oxidation increment. The powder is stored and mixed in a nitrogen atmosphere and at low temperature, reducing the probability of spontaneous combustion and ensuring production safety. Reduction carbonization using a nitrogen and hydrogen mixture not only promotes rapid one-step carbonization but also, by increasing the nitrogen flow rate, promptly removes the water vapor generated during reduction, reducing the risk of powder growth and ensuring the hardness of the cemented carbide.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically a high-hardness, low-expansion, and low-oxidation cemented carbide and its preparation method. Background Technology

[0002] Binderless WC-based cemented carbide refers to a cemented carbide product containing little or no metallic binder phase (≤0.5 wt.%). It possesses unparalleled superior wear resistance, corrosion resistance, excellent polishability, oxidation resistance, and low thermal expansion thermodynamic properties compared to traditional cemented carbides. Utilizing its excellent wear and corrosion resistance, it can be used to manufacture sandblasting nozzles, electronic packaging materials, and heavy-duty sliding seal wear-resistant parts. Its excellent cutting performance makes it suitable for cutting tools and drill bits, particularly for machining titanium / titanium alloys, significantly improving work efficiency. Furthermore, its oxidation resistance, excellent polishability, and low coefficient of thermal expansion make it suitable for precision molds and high-end decorative materials.

[0003] However, the application of binderless cemented carbide has not been widespread and is still only being tested in various fields. This is mainly due to the high difficulty in producing binderless cemented carbide, the unstable product performance, and the high production cost. Insufficient purity of raw materials or impurities introduced during the production process, such as environmental factors or equipment, can lead to changes in various properties of binderless cemented carbide. For example, the intake of metallic elements can cause abnormal grain growth and may also reduce the alloy's wear resistance, corrosion resistance, and oxidation resistance. The intake of non-metallic elements may lead to unstable carbon content in the alloy, causing decarburization problems and potentially resulting in porosity. Summary of the Invention

[0004] To address the problems existing in the prior art, the main objective of this invention is to propose a high-hardness, low-expansion, and low-oxidation cemented carbide and its preparation method. By utilizing liquid-phase doping and adjusting the evaporation and crystallization temperature and the pH value of the mother liquor, the precipitation of Co and Cr elements can be precisely controlled to ensure the Co and Cr content of the cemented carbide, thereby guaranteeing the stability of cemented carbide production. Furthermore, by controlling the raw materials and the production process, the product performance of the binderless cemented carbide can be ensured.

[0005] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0006] A method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide includes the following steps:

[0007] S1. Preparation of W-Co-Cr crystals

[0008] A mother liquor for crystallization was prepared using ammonium tungstate, cobalt acetate, and chromium acetate. The solution was then evaporated and crystallized at a temperature of 90–100°C. Crystallization was stopped when the pH of the solution reached 6.5–7.0, and the solution was filtered to obtain W-Co-Cr crystals.

[0009] S2. Preparation of WO3-Co-Cr composite powder

[0010] The W-Co-Cr crystals were calcined and cooled to obtain WO3-Co-Cr composite powder. Nitrogen gas was introduced and the WO3-Co-Cr composite powder was stored in an environment below 10°C.

[0011] S3. Preparation of WO3-Co-Cr+C mixed powder

[0012] WO3-Co-Cr composite powder and C powder are mixed to obtain WO3-Co-Cr+C mixed powder;

[0013] S4. Preparation of WC-Co-Cr composite powder

[0014] WO3-Co-Cr+C mixed powder is carbonized in one step to obtain WC-Co-Cr composite powder; the carbonization atmosphere is a mixture of hydrogen and nitrogen gas, the volume ratio of hydrogen to nitrogen is (4~7):1, and the carbonization temperature is three temperature zones, from the inlet to the outlet: 510~650℃, 780~820℃, and 980~1250℃ respectively.

[0015] S5. Preparation of cemented carbide

[0016] The WC-Co-Cr composite powder was rapidly sintered: the temperature was raised to 1400-1800℃ under vacuum, held for 10-15 minutes, and then cooled to room temperature in the furnace to obtain a hard alloy with high hardness, low expansion and low oxidation.

[0017] In a preferred embodiment of the method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S1, the concentration of ammonium tungstate in the mother liquor is 220–270 g / L, the concentration of cobalt acetate is 1.2–1.7 g / L, and the concentration of chromium acetate is 8–11 g / L.

[0018] As a preferred embodiment of the method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S2, W-Co-Cr crystals are placed in a calcining furnace for calcination at a temperature of 600–800°C.

[0019] As a preferred embodiment of the preparation method of a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S2, after calcination, the WO3-Co-Cr composite powder is obtained by cooling under a nitrogen atmosphere.

[0020] As a preferred embodiment of the preparation method of a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S3, WO3-Co-Cr composite powder and C powder are mixed in a nitrogen atmosphere at a mass ratio of (5-7):1.

[0021] In a preferred embodiment of the method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S4, a one-step carbonization is carried out in a rotary kiln, and the rotation speed of the rotary kiln is 1.5 to 5.0 r / min.

[0022] In a preferred embodiment of the method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, in step S4, the flow rate of the hydrogen + nitrogen mixed gas is 550–900 m³ / h. 3 / h.

[0023] In a preferred embodiment of the method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide according to the present invention, the sintering pressure in step S5 is 50-80 MPa.

[0024] To solve the above-mentioned technical problems, according to another aspect of the present invention, the present invention provides the following technical solution:

[0025] A high-hardness, low-expansion, and low-oxidation cemented carbide was prepared using the above-described method.

[0026] As a preferred embodiment of the high-hardness, low-expansion, and low-oxidation cemented carbide described in this invention, the cemented carbide has a hardness ≥ 2750 HV3 and a coefficient of thermal expansion ≤ 5.0 × 10⁻⁶ at 400℃. -6 K -1 Oxidation increment ≤ 0.090 g / cm³ 2 .

[0027] This invention proposes a high-hardness, low-expansion, and low-oxidation cemented carbide and its preparation method, which has the following advantages:

[0028] (1) This invention uses liquid mixing-evaporation crystallization for doping, and coordinates the control of temperature and pH value of crystallization mother liquor to achieve precise control of the content of doping elements. Furthermore, it abandons ball milling doping, which allows the doped cobalt and chromium to complete the intermolecular mixing, which not only improves the doping efficiency but also reduces the intake of impurities introduced by ball milling, ensuring the low expansion coefficient and low oxidation increment of cemented carbide.

[0029] (2) The powder is stored and mixed in a nitrogen atmosphere and at low temperature, which reduces the probability of spontaneous combustion of the powder and ensures the safety of production.

[0030] (3) The present invention uses a mixture of nitrogen and hydrogen gas for reduction carbonization, which not only promotes the rapid progress of one-step carbonization, but also increases the flow rate of nitrogen gas to carry away the water vapor generated during reduction in time, reducing the risk of powder growth and ensuring the hardness of cemented carbide. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0032] Figure 1 Image of the cemented carbide prepared in Example 1 of this invention;

[0033] Figure 2 Image of the cemented carbide prepared in Comparative Example 1 of this invention;

[0034] Figure 3 This is an image of the cemented carbide prepared in Comparative Example 4 of this invention. Detailed Implementation

[0035] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention proposes a high-hardness, low-expansion, and low-oxidation cemented carbide and its preparation method. By utilizing liquid-phase doping and adjusting the evaporation and crystallization temperature and the pH value of the mother liquor, the precipitation of Co and Cr elements is precisely controlled to ensure the Co and Cr content of the cemented carbide and guarantee the stability of cemented carbide production. Furthermore, by controlling the raw materials and production process, the product performance of the binderless cemented carbide is ensured.

[0037] According to one aspect of the present invention, the present invention provides the following technical solution:

[0038] A method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide includes the following steps:

[0039] S1. Preparation of W-Co-Cr crystals

[0040] A mother liquor for crystallization was prepared using ammonium tungstate, cobalt acetate, and chromium acetate. The solution was then evaporated and crystallized at a temperature of 90–100°C. Crystallization was stopped when the pH of the solution reached 6.5–7.0, and the solution was filtered to obtain W-Co-Cr crystals.

[0041] S2. Preparation of WO3-Co-Cr composite powder

[0042] The W-Co-Cr crystals were calcined and cooled to obtain WO3-Co-Cr composite powder. Nitrogen gas was introduced and the WO3-Co-Cr composite powder was stored in an environment below 10°C.

[0043] S3. Preparation of WO3-Co-Cr+C mixed powder

[0044] WO3-Co-Cr composite powder and C powder are mixed to obtain WO3-Co-Cr+C mixed powder;

[0045] S4. Preparation of WC-Co-Cr composite powder

[0046] WO3-Co-Cr+C mixed powder is carbonized in one step to obtain WC-Co-Cr composite powder; the carbonization atmosphere is a mixture of hydrogen and nitrogen gas, the volume ratio of hydrogen to nitrogen is (4~7):1, and the carbonization temperature is three temperature zones, from the inlet to the outlet: 510~650℃, 780~820℃, and 980~1250℃ respectively.

[0047] S5. Preparation of cemented carbide

[0048] The WC-Co-Cr composite powder was rapidly sintered: the temperature was raised to 1400-1800℃ under vacuum, held for 10-15 minutes, and then cooled to room temperature in the furnace to obtain a hard alloy with high hardness, low expansion and low oxidation.

[0049] Preferably, in step S1, the concentration of ammonium tungstate in the crystallization mother liquor is 220–270 g / L, the concentration of cobalt acetate is 1.2–1.7 g / L, and the concentration of chromium acetate is 8–11 g / L. Specifically, the evaporation crystallization temperature can be, for example, but not limited to, any one or any two of 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, and 100°C; the pH value of the solution at the end of crystallization can be, for example, but not limited to, any one or any two of 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0; and the concentration of ammonium tungstate in the crystallization mother liquor can be, for example, but not limited to, 220 g / L, 230 g / L, 240 g / L, and 250 g / L. The concentration of cobalt acetate in the crystallization mother liquor may be, for example, but not limited to, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, 1.6 g / L, 1.7 g / L, or any two of these concentrations; the concentration of chromium acetate in the crystallization mother liquor may be, for example, but not limited to, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L, 10 g / L, 10.5 g / L, 11 g / L, or any two of these concentrations.

[0050] Preferably, in step S2, the W-Co-Cr crystals are placed in a calcination furnace for calcination at a temperature of 600–800°C, and then cooled under a nitrogen atmosphere to obtain WO3-Co-Cr composite powder. Specifically, the calcination temperature can be, for example, but not limited to, any one or a range between any two of 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, and 800°C.

[0051] Preferably, in step S3, WO3-Co-Cr composite powder and C powder are mixed in a nitrogen atmosphere using a mixer at a mass ratio of (5-7):1. Specifically, the mass ratio of WO3-Co-Cr composite powder and C powder can be, for example, but not limited to, any one of 5:1, 5.5:1, 6:1, 6.5:1, 7:1, or any range between any two.

[0052] Preferably, in step S4, carbonization is carried out in a rotary kiln at a rotation speed of 1.5–5.0 r / min. Specifically, the rotation speed of the rotary kiln can be, for example, but not limited to, any one or a range between any two of 1.5 r / min, 2.0 r / min, 2.5 r / min, 3.0 r / min, 3.5 r / min, 4.0 r / min, 4.5 r / min, and 5.0 r / min.

[0053] Preferably, in step S4, the flow rate of the hydrogen + nitrogen mixed gas is 550-900 m³ / h. 3 / h. Specifically, the flow rate of the hydrogen + nitrogen mixture can be, for example, but not limited to, 550 m³ / h. 3 / h, 600m 3 / h, 650m 3 / h, 700m 3 / h, 750m 3 / h、800m 3 / h, 850m 3 / h、900m 3 The range of any one or any two of the following values ​​per hour; the hydrogen to nitrogen volume ratio can be, for example, but not limited to, any one or any two of the following: 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1; the carbonization temperature consists of three temperature zones, from the inlet to the outlet: the first temperature zone is 510–650℃, the second temperature zone is 780–820℃, and the third temperature zone is 980–1250℃. Specifically, the first temperature zone temperature can be, for example, but not limited to, 510℃. The temperature range of the second temperature zone can be, for example, but not limited to, any one or any two of the following: 0℃, 530℃, 550℃, 570℃, 590℃, 610℃, 630℃, 650℃; the temperature range of the third temperature zone can be, for example, but not limited to, any one or any two of the following: 780℃, 790℃, 800℃, 810℃, 820℃; the temperature range of the third temperature zone can be, for example, but not limited to, any one or any two of the following: 980℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃.

[0054] Preferably, in step S5, the sintering pressure is 50–80 MPa. Specifically, the sintering pressure can be, for example, but not limited to, any one or any two of 50 MPa, 60 MPa, 70 MPa, and 80 MPa; the temperature under vacuum can be, for example, but not limited to, any one or any two of 1400°C, 1500°C, 1600°C, 1700°C, and 1800°C; and the holding time can be, for example, but not limited to, any one or any two of 10 min, 11 min, 12 min, 13 min, 14 min, and 15 min.

[0055] According to another aspect of the present invention, the present invention provides the following technical solution:

[0056] A high-hardness, low-expansion, and low-oxidation cemented carbide is prepared using the above-described method. The cemented carbide has a hardness ≥2750 HV3 and a coefficient of thermal expansion ≤5.0 × 10⁻⁶ at 400℃. -6 K-1 Oxidation increment ≤ 0.090 g / cm³ 2 .

[0057] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0058] Example 1

[0059] A method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide includes the following steps:

[0060] S1. Preparation of W-Co-Cr crystals

[0061] A crystallization mother liquor was prepared using ammonium tungstate, cobalt acetate, and chromium acetate. The concentrations of ammonium tungstate, cobalt acetate, and chromium acetate in the mother liquor were 220 g / L, 1.2 g / L, and 8 g / L, respectively. Evaporation crystallization was carried out at a temperature of 90 °C. Crystallization was stopped when the pH of the solution reached 6.5, and the solution was filtered to obtain W-Co-Cr crystals.

[0062] S2. Preparation of WO3-Co-Cr composite powder

[0063] W-Co-Cr crystals were placed in a calcination furnace and calcined at a temperature of 600℃. After cooling under a nitrogen atmosphere, WO3-Co-Cr composite powder was obtained. Nitrogen gas was then introduced, and the WO3-Co-Cr composite powder was stored in an environment below 10℃.

[0064] S3. Preparation of WO3-Co-Cr+C mixed powder

[0065] WO3-Co-Cr composite powder and C powder were mixed in a nitrogen atmosphere using a mixer at a mass ratio of 5:1 to obtain WO3-Co-Cr+C mixed powder.

[0066] S4. Preparation of WC-Co-Cr composite powder

[0067] WO3-Co-Cr+C mixed powder was placed in a rotary kiln for one-step carbonization to obtain WC-Co-Cr composite powder; the rotary kiln speed was 1.5 r / min, the carbonization atmosphere was a hydrogen + nitrogen mixture, and the flow rate of the hydrogen + nitrogen mixture was 550 m³ / min. 3 / h, the volume ratio of hydrogen to nitrogen is 4:1, and the carbonization temperature has three temperature zones, from the inlet to the outlet: 510℃, 780℃, and 980℃ respectively.

[0068] S5. Preparation of cemented carbide

[0069] WC-Co-Cr composite powder was rapidly sintered: the sintering pressure was 50 MPa, the temperature was raised to 1400℃ under vacuum, held for 10 min, and then cooled to room temperature in the furnace to obtain a high-hardness, low-expansion, and low-oxidation cemented carbide. Figure 1 As shown, the hardness of the cemented carbide is 2782HV3, and its coefficient of thermal expansion at 400℃ is 4.6×10⁻⁶. -6 K -1 The oxidation increment was 0.081 g / cm³. 2 .

[0070] Example 2

[0071] A method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide includes the following steps:

[0072] S1. Preparation of W-Co-Cr crystals

[0073] A crystallization mother liquor was prepared using ammonium tungstate, cobalt acetate, and chromium acetate, with concentrations of 250 g / L for ammonium tungstate, 1.5 g / L for cobalt acetate, and 9.5 g / L for chromium acetate. Evaporation crystallization was carried out at a temperature of 95°C. Crystallization was stopped when the pH of the solution reached 6.7, and the solution was filtered to obtain W-Co-Cr crystals.

[0074] S2. Preparation of WO3-Co-Cr composite powder

[0075] W-Co-Cr crystals were placed in a calcination furnace and calcined at 700℃. After cooling under a nitrogen atmosphere, WO3-Co-Cr composite powder was obtained. Nitrogen gas was then introduced and the WO3-Co-Cr composite powder was stored in an environment below 10℃.

[0076] S3. Preparation of WO3-Co-Cr+C mixed powder

[0077] WO3-Co-Cr composite powder and C powder were mixed in a nitrogen atmosphere using a mixer at a mass ratio of 6:1 to obtain WO3-Co-Cr+C mixed powder.

[0078] S4. Preparation of WC-Co-Cr composite powder

[0079] WO3-Co-Cr+C mixed powder was placed in a rotary kiln for one-step carbonization to obtain WC-Co-Cr composite powder; the rotary kiln speed was 3.0 r / min, the carbonization atmosphere was a hydrogen + nitrogen mixed gas, and the flow rate of the hydrogen + nitrogen mixed gas was 700 m³ / min. 3 The hydrogen to nitrogen volume ratio is 5.5:1, and the carbonization temperature has three temperature zones, from the inlet to the outlet: 580℃, 800℃, and 1125℃.

[0080] S5. Preparation of cemented carbide

[0081] WC-Co-Cr composite powder was rapidly sintered at a pressure of 65 MPa under vacuum, heated to 1600℃, held for 10 minutes, and then cooled to room temperature in the furnace to obtain a high-hardness, low-expansion, and low-oxidation cemented carbide. The hardness of the cemented carbide was 2832 HV3, and its coefficient of thermal expansion at 400℃ was 4.3 × 10⁻⁶. -6 K -1 The oxidation increment was 0.089 g / cm³. 2 .

[0082] Example 3

[0083] A method for preparing a high-hardness, low-expansion, and low-oxidation cemented carbide includes the following steps:

[0084] S1. Preparation of W-Co-Cr crystals

[0085] A crystallization mother liquor was prepared using ammonium tungstate, cobalt acetate, and chromium acetate. The concentrations of ammonium tungstate, cobalt acetate, and chromium acetate in the mother liquor were 270 g / L, 1.7 g / L, and 11 g / L, respectively. Evaporation crystallization was carried out at a temperature of 100 °C. Crystallization was stopped when the pH of the solution reached 7, and W-Co-Cr crystals were obtained by filtration.

[0086] S2. Preparation of WO3-Co-Cr composite powder

[0087] W-Co-Cr crystals were placed in a calcination furnace and calcined at 800℃. After cooling under a nitrogen atmosphere, WO3-Co-Cr composite powder was obtained. Nitrogen gas was then introduced and the WO3-Co-Cr composite powder was stored in an environment below 10℃.

[0088] S3. Preparation of WO3-Co-Cr+C mixed powder

[0089] WO3-Co-Cr composite powder and C powder were mixed in a nitrogen atmosphere using a mixer at a mass ratio of 7:1 to obtain WO3-Co-Cr+C mixed powder.

[0090] S4. Preparation of WC-Co-Cr composite powder

[0091] WO3-Co-Cr+C mixed powder was placed in a rotary kiln for one-step carbonization to obtain WC-Co-Cr composite powder; the rotary kiln speed was 5.0 r / min, the carbonization atmosphere was a hydrogen + nitrogen mixed gas, and the flow rate of the hydrogen + nitrogen mixed gas was 900 m³ / min. 3 / h, the volume ratio of hydrogen to nitrogen is 7:1, and the carbonization temperature has three temperature zones, from the inlet to the outlet: 650℃, 820℃, and 1250℃ respectively.

[0092] S5. Preparation of cemented carbide

[0093] WC-Co-Cr composite powder was rapidly sintered: the sintering pressure was 80 MPa, the temperature was raised to 1800℃ under vacuum, held for 10 min, and then cooled to room temperature in the furnace to obtain a high-hardness, low-expansion, and low-oxidation cemented carbide. The hardness of the cemented carbide was 2765 HV3, and the coefficient of thermal expansion at 400℃ was 4.5 × 10⁻⁶. -6 K -1 The oxidation increment was 0.060 g / cm³. 2 .

[0094] Comparative Example 1

[0095] The difference from Example 1 is that,

[0096] In step S1, the evaporation and crystallization temperature is 110℃;

[0097] The prepared cemented carbide, such as Figure 2 As shown, the cemented carbide exhibits porosity, has a hardness of 2530 HV3, and a coefficient of thermal expansion of 7.1 × 10⁻⁶ at 400℃. -6 K -1 The oxidation increment was 0.099 g / cm³. 2 .

[0098] Comparative Example 2

[0099] The difference from Example 1 is that,

[0100] Step S1: Stop crystallization when the pH of the solution reaches 5.

[0101] The prepared cemented carbide has an increased cobalt content, a hardness of 2555 HV3, and a coefficient of thermal expansion of 6.7 × 10⁻⁶ at 400℃. -6 K -1 The oxidation increment was 0.117 g / cm³. 2 .

[0102] Comparative Example 3

[0103] The difference from Example 1 is that,

[0104] In step S2, nitrogen is not introduced, and the WO3-Co-Cr composite powder is stored at room temperature.

[0105] The experiment was repeated 5 times, but the powder spontaneously combusted in 2 of them, and the experiment could not be continued.

[0106] Comparative Example 4

[0107] The difference from Example 1 is that,

[0108] In step S4, the carbonization atmosphere is pure hydrogen.

[0109] The prepared cemented carbide has larger grains, a hardness of 2493 HV3, and a coefficient of thermal expansion of 6.3 × 10⁻⁶ at 400℃. - 6 K -1 The oxidation increment was 0.203 g / cm³. 2 .

[0110] Comparative Example 5

[0111] The difference from Example 1 is that,

[0112] In step S4, the carbonization temperature consists of three temperature zones, which are 700℃, 1000℃, and 1400℃ from the feed inlet to the discharge outlet, respectively.

[0113] The prepared cemented carbide, such as Figure 3 As shown, the cemented carbide has enlarged grains, a hardness of 2261HV3, and a coefficient of thermal expansion of 5.8×10⁻⁶ at 400℃. -6 K -1 The oxidation increment was 0.190 g / cm³. 2 .

[0114] Comparative Example 6

[0115] The difference from Example 1 is that,

[0116] In step S5, the temperature is raised to 2000°C under vacuum conditions;

[0117] The prepared cemented carbide exhibits abnormally large grain size and significant differences in internal and external morphology. Its hardness is 1740 HV3, and its coefficient of thermal expansion at 400℃ is 8.8 × 10⁻⁶. -6 K -1 The oxidation increment was 0.173 g / cm³. 2 .

[0118] Comparative Example 7

[0119] The difference from Example 1 is that,

[0120] W powder was produced using conventional methods, and WC-Co-Cr composite powder was prepared by adding Cr and Co as used in Example 1 at a carbon content of 6.13 wt.% during carbon formulation.

[0121] Traditional methods introduce more impurity elements, resulting in larger grains and increased oxidation in the prepared cemented carbide. Its hardness is 2193 HV3, and its coefficient of thermal expansion at 400℃ is 1.02 × 10⁻⁶. -5 K -1 The oxidation increment was 0.285 g / cm³. 2 .

[0122] Comparative Example 8

[0123] The difference from Example 1 is that,

[0124] According to the component ratio in Implementation 1, WC powder, chromium carbide and cobalt powder are ball-milled to prepare a mixed powder;

[0125] The prepared cemented carbide exhibited WC grain inhomogeneity and some abnormally large grains. This was due to the ball milling process failing to evenly distribute the small amounts of chromium carbide and cobalt powder, and the prolonged ball milling time introducing excessive impurity elements. The cemented carbide had a hardness of 2359 HV3 and a coefficient of thermal expansion of 1.26 × 10⁻⁶ at 400℃. -5 K -1 The oxidation increment was 0.351 g / cm³. 2 .

[0126] This invention employs liquid mixing-evaporation crystallization for doping, and through coordinated control of temperature and pH of the crystallization mother liquor, it achieves precise control of the dopant element content. Furthermore, it eliminates the need for ball milling, allowing the incorporated cobalt and chromium to undergo intermolecular mixing. This not only improves doping efficiency but also reduces impurities introduced by ball milling, ensuring a low coefficient of thermal expansion and low oxidation increment in the cemented carbide. The powder is stored and mixed in a nitrogen atmosphere at low temperatures, reducing the probability of spontaneous combustion and ensuring production safety. Reduction carbonization using a nitrogen and hydrogen mixture not only accelerates the one-step carbonization process but also increases the nitrogen flow rate, promptly removing moisture generated during reduction and reducing the risk of powder growth, thus ensuring the hardness of the cemented carbide.

[0127] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a high-hardness, low-expansion, low-oxidation binderless cemented carbide, characterized in that, Includes the following steps: S1. Preparation of W-Co-Cr crystals A crystallization mother liquor was prepared using ammonium tungstate, cobalt acetate, and chromium acetate. The concentration of ammonium tungstate in the mother liquor was 220-270 g / L, the concentration of cobalt acetate was 1.2-1.7 g / L, and the concentration of chromium acetate was 8-11 g / L. Evaporation crystallization was carried out at a temperature of 90-100℃. When the pH of the solution reached 6.5-7.0, crystallization was stopped, and the solution was filtered to obtain W-Co-Cr crystals. S2. Preparation of WO3-Co-Cr composite powder W-Co-Cr crystals were placed in a calcination furnace and calcined at a temperature of 600~800℃. After calcination, the crystals were cooled under a nitrogen atmosphere to obtain WO3-Co-Cr composite powder. The powder was then filled with nitrogen and stored in an environment below 10℃. S3. Preparation of WO3-Co-Cr+C mixed powder WO3-Co-Cr composite powder and C powder are mixed in a nitrogen atmosphere using a mixer at a mass ratio of (5~7):1 to obtain WO3-Co-Cr+C mixed powder; S4. Preparation of WC-Co-Cr composite powder WO3-Co-Cr+C mixed powder was carbonized in a rotary kiln in one step to obtain WC-Co-Cr composite powder; the rotation speed of the rotary kiln was 1.5~5.0 r / min, the carbonization atmosphere was a mixture of hydrogen and nitrogen gas, the volume ratio of hydrogen to nitrogen was (4~7):1, and the flow rate of the hydrogen + nitrogen mixture was 550~900 m³ / min. 3 / h, the carbonization temperature has three temperature zones, from the feed inlet to the discharge outlet: 510~650℃, 780~820℃, 980~1250℃; S5. Preparation of cemented carbide WC-Co-Cr composite powder was rapidly sintered: the sintering pressure was 50~80MPa, the temperature was raised to 1400~1800℃ under vacuum, held for 10~15min, and cooled to room temperature with the furnace to obtain a binderless cemented carbide with high hardness, low expansion and low oxidation. The hardness of the cemented carbide is ≥2750HV3, and the coefficient of thermal expansion at 400℃ is ≤5.0×10. -6 K -1 Oxidation increment ≤ 0.090 g / cm³ 2 .

2. A high-hardness, low-expansion, low-oxidation binderless cemented carbide, characterized in that, The high-hardness, low-expansion, and low-oxidation binderless cemented carbide was prepared using the method described in claim 1.

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