A new preparation method for cemented carbide

Abstract

The present invention provides a new preparation method for cemented carbide. Step 1: Mix carbides, iron-group metal oxides and a forming agent in a ratio of 50-97 wt% of carbides, 2-50 wt% of iron-group metal oxides, and 0.2-9 wt% of the forming agent. Step 2: Put them into a ball mill in sequence and use anhydrous ethanol as the ball-milling medium to mix the materials. Step 3: Obtain a mixed powder through vacuum drying. Step 4: Obtain a formed blank from the mixed powder through a forming device. Step 5: Remove the forming agent from the blank under a hydrogen atmosphere with a certain flow rate at 20-550 °C, and simultaneously remove the oxygen in the iron-group metal oxides in the blank. The present invention not only reduces the energy consumption and production cost generated by separately reducing iron-group metal oxides with hydrogen, but also avoids the phenomenon that metal atoms between adjacent particles diffuse at high temperature during the reduction of pure metal oxides to form a bonding surface, ultimately causing the growth of metal particles, and avoids the uneven distribution of the binder phase in the cemented carbide, further improving the quality of the product.

Description

Technical Field

[0001] The present invention relates to a cemented carbide, and particularly to a novel preparation method of a cemented carbide. Background Art

[0002] German scientist Karl Schroter first proposed a patent for producing hard alloys by powder metallurgy in 1923, that is, mixing carbide with a small amount of iron-group metal (iron, nickel, cobalt) powder, then pressing into shape and sintering in hydrogen at a temperature above 1300 °C. Up to now, although all cemented carbide companies at home and abroad have continuously improved the alloy formula, production process and production equipment, resulting in continuous optimization of the alloy performance and an increasingly wide range of applications of its products; its production essentially still adopts Karl Schroter's production method;

[0003] At present, the domestic and foreign production still adopts traditional production methods such as Figure 2 As shown: First, the iron-group metal oxide is subjected to reduction and deoxidation treatment to form sponge-like metal particles, and then pulverized by a high-speed pulverizer to obtain ultrafine iron-group metal powder. Then, the carbide is mixed with a certain amount of iron-group metal (iron, nickel, cobalt) powder and an appropriate amount of molding agent by ball milling with anhydrous ethanol. After drying, it goes through processes such as molding, removing the molding agent, and sintering. Taking cobalt powder of iron-group metal element as an example: The preparation of ultrafine cobalt powder generally uses a slide rail tube furnace to reduce ultrafine grain cobalt oxide at 400 - 500 °C with a certain hydrogen flow rate. During the process of reducing cobalt oxide to metallic cobalt, metal atoms between adjacent particles diffuse at high temperature to form a bonding surface, eventually causing the growth of metal particles or the generation of branched sponge cobalt. Then, the sponge cobalt is crushed into ultrafine cobalt powder by a high-speed pulverizer. Coarse dendritic cobalt powder exists in the cobalt powder after crushing; due to the good ductility of cobalt, the coarse dendritic cobalt powder cannot be eliminated during the ball milling process, and finally, the phenomenon of cobalt lake or cobalt pool occurs in the cemented carbide. Summary of the Invention

[0004] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0005] In view of the above, the object of the present invention is to provide a novel preparation method of a cemented carbide,

[0006] Step 1: Mix the carbide, iron-group metal oxide and molding agent according to the ratio of 50 - 97 wt% of carbide, 2 - 50 wt% of iron-group metal oxide, and 0.2 - 9 wt% of molding agent;

[0007] Step 2: Put them into a ball mill in sequence, and use anhydrous ethanol as the ball milling medium to mix the materials;

[0008] Step 3: Obtain the mixed powder after vacuum drying;

[0009] Step 4: Obtain a formed blank from the mixed powder through a forming device;

[0010] Step 5: Remove the forming agent from the blank by stepwise temperature control and heat preservation in a hydrogen atmosphere at 20 - 550°C, and simultaneously remove the oxygen in the iron-group metal oxides in the blank;

[0011] Step 6: Sinter the blank from which the forming agent has been removed under a partial pressure in high-purity argon at 0 - 1000 Pa, raise the temperature to 1300 - 1600°C, and then keep it warm for 30 - 120 min; or sinter it under pressure with a protective gas at a pressure of 10 - 100 bar at a sintering temperature of 1300 - 1600°C, and then cool it after heat preservation sintering.

[0012] As a further improvement of the above solution:

[0013] Preferably, the iron-group metal oxides include any one or two or a combination of three of iron oxide, nickel oxide, and cobalt oxide.

[0014] Preferably, the carbides include all tungsten carbides or carbonitrides used for making cemented carbides, etc.

[0015] Preferably, the particle size of the cobalt oxide powder is ≤ 3.5 μm, the particle size of the iron oxide powder is ≤ 5.0 μm, and the particle size of the nickel oxide powder is ≤ 5.0 μm.

[0016] Preferably, in Step 2, alloy balls are added in a certain proportion for ball milling, the ball milling time is 15 - 100 h, and a mixed powder with uniform distribution of each component is obtained after ball milling.

[0017] Preferably, Step 3 is heated in a vacuum device, the vacuum degree is 4×10 -1 -4×10 -3 Pa, keep it warm within 100°C until anhydrous ethanol is completely removed, or use a drying method of spray granulation in an inert gas.

[0018] Preferably, in Step 4, it is compacted by a cold isostatic press, then the mixed powder is placed in a special forming jacket, the pressure of the cold isostatic press is 100 - 2000 MPa, and the pressure holding time is 5 - 30 min; if it is compacted by a mechanical press, the mixed powder is placed in a mold for forming; if it is extruded by an extruder for forming.

[0019] Preferably, Steps 5 and 6 are staged sintering.

[0020] S1. Gradually heat up to 550 °C in a hydrogen atmosphere at a heating rate of 0.1 - 5 °C / min with stage temperature control, and keep the temperature for 30 - 200 min to remove the forming agent in the green compact and oxygen in the metal oxide.

[0021] S2. Then, with a heating rate of 2 - 8 °C / min, sinter and heat up to 1300 - 1600 °C in high-purity argon with a partial pressure of 0 - 1000 Pa with stage temperature control, and keep the temperature for 30 - 120 min.

[0022] S3. At a sintering temperature of 1300 - 1600 °C, a protective gas can be introduced to keep the temperature at a pressure of 10 - 100 bar.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention not only reduces the energy consumption and production cost generated when separately reducing iron group metal oxides in a hydrogen or reducing gas atmosphere at 400 - 500 °C, but also, since the iron group metal oxides are basically dispersed in the carbide in the hard alloy blank, it avoids the possibility that metal atoms between adjacent particles diffuse at high temperature to form a bonding surface during the reduction of pure metal oxides, ultimately causing the growth of metal particles or the generation of a sponge-like structure, and avoids the phenomenon of non-uniform binder phase in the hard alloy, further improving the quality and performance of the hard alloy product. Description of the Drawings

[0025] Figure 1 is the preparation process flow of the hard alloy of the present invention.

[0026] Figure 2 is the existing preparation process flow of the hard alloy. Detailed Embodiments

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0028] As Figure 1-2 shown, a new preparation method of a hard alloy

[0029] Step 1. Mix carbides, iron group metal oxides, and forming agents according to the ratio of 50 - 97 wt% of carbides, 2 - 50 wt% of iron group metal oxides, and 0.2 - 9 wt% of forming agents.

[0030] Step 2: Put them into a ball mill in sequence, use absolute ethanol as the ball milling medium to mix the materials. The iron-group metal oxides are basically dispersed in the carbide in the cemented carbide blank, thus avoiding the possibility that during the reduction process of pure metal oxides, metal atoms between adjacent particles diffuse at high temperature to form a bonding surface, which may ultimately cause the growth of metal particles or the formation of a spongy state, and avoiding the phenomenon of uneven binder phase in the cemented carbide, further improving the quality and performance of the cemented carbide product;

[0031] Step 3: Obtain the mixed powder after vacuum drying;

[0032] Step 4: Obtain a formed blank from the mixed powder through a forming device;

[0033] Step 5: Gradually control the temperature step by step and keep warm in a hydrogen atmosphere at 20 - 550 °C to remove the forming agent, and at the same time remove the oxygen in the iron-group metal oxides;

[0034] Step 6: Gradually control the temperature step by step to raise the temperature of the blank after removing the forming agent to 1300 - 1600 °C, or keep warm and sinter under a protective gas pressure of 10 - 100 bar at the sintering temperature and then cool down.

[0035] The iron-group metal oxides include any one or two or a combination of three of iron oxide, nickel oxide, and cobalt oxide.

[0036] The particle size of the cobalt oxide powder is ≤ 5.0 μm, the particle size of the iron oxide powder is ≤ 5.0 μm, and the particle size of the nickel oxide powder is ≤ 5.0 μm.

[0037] In Step 2, a certain proportion of alloy balls are added for ball milling, the ball milling time is 15 - 100 h, and a mixed powder with uniform distribution of each component is obtained after ball milling, so that each component in the mixed powder can be kept balanced and consistent in each tiny area;

[0038] Step 3 is heated in a vacuum device, and the vacuum degree is 4×10 -1 -4×10 -3 Pa, keep warm within 100 °C until the absolute ethanol is completely removed, or adopt a drying method of spray granulation in an inert gas;

[0039] In step 4, if cold isostatic pressing is used for compaction, the mixed powder is placed in a special forming sleeve; the elastic die sleeve filled with powder is placed in a sealed high-pressure container, and a fluid medium is pumped into it by means of a high-pressure pump. By utilizing the properties of uniform pressure transmission and incompressibility of the fluid medium, the powder is uniformly pressed in all directions simultaneously, thereby obtaining a green body with higher density and strength. The pressure of the cold isostatic press is 100 - 2000 MPa, and the pressure holding time is 5 - 30 min; if mechanical pressing is used for compaction, the mixed powder is placed in a mold and pressed into shape; if an extruder is used for extrusion molding.

[0040] In step 5, the formed blank is stepwise temperature-controlled in a hydrogen atmosphere at 20 - 550 °C and stage-insulated to remove the forming agent, and simultaneously remove the oxygen in the iron-group metal oxides.

[0041] The said step 6 is stage sintering.

[0042] S1. Stepwise temperature-control and stepwise heating to 550 °C in a hydrogen atmosphere at a heating rate of 0.1 - 5 °C / min, and the stage insulation time is 30 - 200 min to remove the forming agent in the green compact and the oxygen in the metal oxides.

[0043] S2. Then, with a heating rate of 2 - 8 °C / min, in high-purity argon at 0 - 1000 Pa, partial pressure stage temperature-control sintering is carried out to heat up to 1300 - 1600 °C, and the stage insulation time is 30 - 120 min.

[0044] S3. At a sintering temperature of 1300 - 1600 °C, a protective gas can be introduced to a pressure of 10 - 100 bar for heat preservation sintering.

[0045] Example 1:

[0046] The cemented carbide of this factual example is prepared from the following raw materials: 72 wt% tungsten carbide, 2 wt% cobalt oxide powder, 18 wt% iron oxide powder, 5 wt% nickel oxide powder, 3 wt% forming agent.

[0047] Among them, the particle size of the tungsten carbide powder is 5.0 μm, the particle size of the cobalt oxide powder is 1.5 μm, the particle size of the iron oxide powder is 3.0 μm, and the particle size of the nickel oxide powder is 2.0 μm. The forming agent is polyethylene glycol, paraffin, rubber, etc.

[0048] Weigh tungsten carbide powder, cobalt oxide powder, iron oxide powder, nickel oxide powder and the forming agent, and put them into a ball mill in sequence. Use anhydrous ethanol as the ball milling medium to mix the materials, add a certain proportion of alloy ball rods, and then carry out ball milling. The ball milling time is 30 h, and the mixed material slurry obtained after ball milling.

[0049] After vacuum drying, the mixed powder is obtained and heated in a vacuum device, and the vacuum degree is 4×10-1 -4×10 -3 Pa, keep it warm within 100 °C until all the absolute ethanol is removed, or adopt the drying method of spray granulation in an inert gas;

[0050] Obtain a formed blank from the mixture powder through a forming device;

[0051] Keep the formed blank under a hydrogen atmosphere at 20 - 550 °C with step - by - step temperature control and hold for 20.0 - 120 min to remove the forming agent, and at the same time remove the oxygen in the iron - group metal oxides;

[0052] Then, heat the blank after removing the forming agent by step - by - step temperature control method and hold at 1300 - 1600 °C, or keep it warm and sinter under a protective gas at a pressure of 10 - 100 bar at the sintering temperature and then cool down.

[0053] Among them, the heat - preservation sintering is stage - by - stage sintering,

[0054] S1: Heat it by step - by - step temperature control method at a heating rate of 2 - 10 °C / min under vacuum conditions to 1300 °C, and then hold for 20.0 - 120 min;

[0055] S2: Then heat it by step - by - step temperature control method at a heating rate of 2 - 8 °C / min in a protective atmosphere to 1300 - 1600 °C, and then hold for 30 - 120.0 min; or keep it warm and sinter under a protective gas at a pressure of 10 - 100 bar at the sintering temperature and then cool down.

[0056] Example 2:

[0057] The cemented carbide of this example is prepared from the following raw materials: 92 wt% tungsten carbide, 6 wt% cobalt oxide powder and 2 wt% forming agent;

[0058] Among them, the particle size of the tungsten carbide powder is 1.0 μm, the particle diameter of the cobalt oxide powder is 0.5 μm, and the forming agent is polyethylene glycol, paraffin or rubber, etc. Weigh the tungsten carbide powder, cobalt oxide powder and forming agent, put them into a ball mill in sequence, use absolute ethanol as the ball - milling medium to mix the materials, add a certain proportion of alloy ball rods, and then carry out ball - milling. The ball - milling time is 30 h, and the obtained mixture slurry;

[0059] After vacuum drying, obtain the mixture powder, heat it in a vacuum device, and the vacuum degree is 4×10 -1 -4×10 -3 Pa, keep it warm within 100 °C until all the absolute ethanol is removed, or adopt the drying method of spray granulation in an inert gas;

[0060] Obtain a formed blank from the mixture powder through a forming device;

[0061] The formed blank is stepwise temperature-controlled and heat-insulated in a hydrogen atmosphere at 20-550 °C to remove the forming agent, and at the same time, the oxygen in the iron-group metal oxides is removed.

[0062] Then, the blank after removing the forming agent is heated to 1300-1600 °C by the stepwise temperature control method, or heat-insulated and sintered under a pressure of 10-100 bar with a protective gas at the sintering temperature and then cooled.

[0063] Among them, the heat-insulated sintering is stage sintering.

[0064] S1: Heat up to 1300 °C at a heating rate of 2-10 °C / min under vacuum conditions, and then keep the temperature for 20.0-120 min.

[0065] S2: Then heat up to 1300-1600 °C at a heating rate of 2-8 °C / min in a protective atmosphere, and then keep the temperature for 30-120.0 min; or heat-insulated and sintered under a pressure of 10-100 bar with a protective gas at the sintering temperature and then cooled.

[0066] Example 3:

[0067] The cemented carbide of this factual example is prepared from the following raw materials: 70 wt% tungsten carbide, 20 wt% cobalt oxide powder, 8 wt% nickel oxide powder, and 2 wt% forming agent.

[0068] Among them, the particle size of the tungsten carbide powder is 5.0 μm, the particle size of the cobalt oxide powder is 0.8 μm, the particle size of the nickel oxide powder is 1.2 μm, and the forming agent is polyethylene glycol, paraffin wax, rubber, etc. Weigh the tungsten carbide powder, cobalt oxide powder, nickel oxide powder, and forming agent, and put them into the ball mill in sequence. Use anhydrous ethanol as the ball milling medium to mix the materials, add a certain proportion of alloy ball rods, and then carry out ball milling. The ball milling time is 30 h, and the mixed material slurry obtained after ball milling.

[0069] After vacuum drying, the mixed material powder is obtained, heated in a vacuum equipment, and the vacuum degree is 4×10 -1 -4×10 -3 Pa, keep the temperature within 100 °C until the anhydrous ethanol is completely removed, or adopt the drying method of spray granulation in an inert gas.

[0070] The mixed material powder is formed into a formed blank through a forming equipment.

[0071] The formed blank is stepwise temperature-controlled and heat-insulated in a hydrogen atmosphere at 20-550 °C to remove the forming agent, and at the same time, the oxygen in the iron-group metal oxides is removed.

[0072] Then, the blank from which the binder has been removed is heated to 1300 - 1600 °C by the stepwise temperature control method, or is sintered under protection gas at a pressure of 10 - 100 bar at the sintering temperature and then cooled.

[0073] Among them, the heat preservation sintering is stage sintering.

[0074] S1. Heat to 1300 °C at a heating rate of 2 - 10 °C / min under vacuum conditions, and then keep the temperature for 20.0 - 120 min.

[0075] S2. Then heat to 1300 - 1600 °C at a heating rate of 2 - 8 °C / min in a protective atmosphere, and then keep the temperature for 30 - 120.0 min; or sinter under protection gas at a pressure of 10 - 100 bar at the sintering temperature and then cool.

[0076] The above embodiments are only the preferred embodiments of the present invention, and the scope of the rights of the present invention cannot be limited by the above. Therefore, the modifications, equivalent changes, improvements, etc. made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention. In addition, the carbides described in the present invention cover all tungsten carbides or carbonitrides used for making cemented carbides, etc.

Claims

1. A new preparation method of cemented carbide, characterized in that: Step 1: Mix carbide, iron-group metal oxide and molding agent in a ratio of 50-97 wt% of carbide, 2-50 wt% of iron-group metal oxide, and 0.2-9 wt% of molding agent; Step 2: Put them into a ball mill in sequence, and use anhydrous ethanol as the ball milling medium to mix the materials; Step 3: Obtain the mixed powder after vacuum drying; Step 4: Obtain a formed blank from the mixed powder through a forming device; Step 5: Gradually control the temperature step by step and keep the temperature in a hydrogen atmosphere at 20-550 °C to remove the molding agent, and at the same time remove the oxygen in the iron-group metal oxide in the blank; Step 6: Then, heat the blank after removing the molding agent and oxygen to 1300-1600 °C by stepwise temperature control vacuum sintering method or partial pressure sintering method and keep the temperature for sintering, or keep the temperature for sintering under a pressure of 10-100 bar with a protective gas at this temperature and then cool.

2. The novel preparation method of cemented carbide according to claim 1, characterized in that: The iron-group metal oxide includes any one or two or a combination of three of iron oxide, nickel oxide, and cobalt oxide.

3. The novel preparation method of cemented carbide according to claim 2, characterized in that: The particle size of the cobalt oxide powder is ≤3.5 μm, the particle size of the iron oxide powder is ≤5.0 μm, and the particle size of the nickel oxide powder is ≤5.0 μm.

4. The novel preparation method of cemented carbide according to claim 1, characterized in that: In Step 2, a certain proportion of alloy balls are added for ball milling, the ball milling time is 15-100 h, and a uniformly distributed mixed powder of each component is obtained after ball milling.

5. The novel preparation method of cemented carbide according to claim 1, characterized in that: Step 3 is to heat in a vacuum device with a vacuum degree of 4×10 -1 -4×10 -3 Pa, and keep it warm within 100°C until absolute ethanol is completely removed, or adopt the drying method of spray granulation in an inert gas.

6. The novel preparation method of cemented carbide according to claim 1, characterized in that: In Step 4, if it is compacted by a cold isostatic press, the mixed powder is placed in a special forming jacket, the pressure of the cold isostatic press is 100-2000 MPa, and the pressure holding time is 5-30 min; if it is compacted by a mechanical press, the mixed powder is pressed into shape in a mold; if it is extruded by an extruder.

7. The novel preparation method of cemented carbide according to claim 1, characterized in that: Steps 5 and 6 are staged sintering, S1: Heat and control the temperature step by step in a hydrogen atmosphere at a heating rate of 0.1-5 °C / min to 550 °C, and the stage heat preservation time is 30-200 min to remove the molding agent in the blank and the oxygen in the metal oxide; S2: Then, heat and sinter under partial pressure in high-purity argon at a heating rate of 2-8 °C / min to 1300-1600 °C at 0-1000 Pa, and then keep the temperature for 30-120 min; S3: At the sintering temperature of 1300-1600 °C, a protective gas can be introduced to keep the temperature for sintering under a pressure of 10-100 bar.

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