Method for preparing super-coarse and extra-coarse grain hard alloy

Abstract

The invention discloses a method for preparing super-coarse and extra-coarse grain hard alloy, which comprises the following steps of: ball-milling high-temperature carbonized coarse tungsten carbide powder with Fisher particle size of 35-40 mu m and cobalt powder according to a bar-to-material ratio; 1: 1-1.5: 1; the filling coefficient is 50%-70%, and the ball milling time is 16-20 hours; a grinding body used for ball milling is a rod-like alloy with the diameter phi of 5-10 mm, and a grinding rod with the diameter phi of 5 mm accounts for more than 50% of the total mass of the grinding body; carrying out compression molding on the ball-milled mixture, and sintering to obtain the super-coarse and extra-coarse grain hard alloy. According to the method, a conventional hard alloy method is adopted, the bar-to-material ratio, the filling coefficient and the mass ratio of grinding bars with the diameter phi being 5 mm to a total grinding body in the ball milling process are controlled, and the ultra-thick and extra-thick hard alloy with the required grain size can be prepared in batches. The method is low in cost and simple in process, and the prepared alloy is large in grain size and uniform in structure.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a method for preparing ultra-coarse and extra-coarse-grained cemented carbide. Background Art

[0002] WC-Co alloy is a very traditional cemented carbide material. It is widely used in rock excavation, energy drilling and other fields due to its excellent comprehensive properties such as wear resistance, strength and toughness. With the development of modern science and technology, users' requirements for the cost and efficiency of cemented carbide are gradually increasing. Compared with alloys with ordinary grain size, extra coarse grain alloys have better thermal shock resistance, thermal conductivity, higher fatigue strength and fracture toughness; therefore, super coarse and extra coarse WC-Co alloys with coarse grains and uniform structure are particularly suitable for the field of hard rock excavation. According to Sandvik's cemented carbide classification standards, super coarse and extra coarse refer to cemented carbides with an average WC cross-sectional grain size of 5.0 to 7.9 μm and 8 μm or more, respectively.

[0003] In order to break through the performance limit of conventional coarse-grained WC-Co alloys and make the alloy grain size reach the ultra-coarse grain level of 5-8μm or the extra-coarse level of 8μm and above, the main methods reported so far are: coating method, nano-activation method, and mild ball milling method.

[0004] CN97114712.4 is a classic patent for the powder coating method. Co salt is coated on the surface of WC particles by sol-gel method. After a series of process treatments, a coarse-grained alloy containing 5% to 7% cobalt and an average grain size of 8 to 30 μm is prepared. The preparation process of the sol-gel patent technology is complex and requires proprietary equipment. The waste generated during the preparation process is difficult to handle and has strict requirements on the production environment.

[0005] Patent CN201210045580.7 discloses a hydrothermal high-pressure hydrogen reduction process to prepare nano-assembled Co / Ni coated WC powder, and the ultra-coarse alloy prepared with the coated powder as raw material has an average grain size of 11.8μm. This process method has high technical requirements, the process may be difficult to control, and mass production is difficult.

[0006] Patents CN201010588351.0 and CN201210549232.3 disclose a physical coating method, which first crushes and grades the coarse WC, then puts the pretreated coarse WC into a physical vapor deposition powder coating machine for Co coating, and obtains Co-coated WC powder. The WC-10Co hard alloy prepared with this as raw material has an average grain size of 6 to 10 μm. The application effect of the super-coarse and extra-coarse alloys prepared by this method needs to be tested by the market, and the physical coating method also has the problem of developing industrial-grade and production-type equipment.

[0007] CN202010909593.9 adopts liquid phase reduction method to introduce Co and P elements into coarse WC powder, and Co and P coat WC particles, then heat treat the coarse WC powder containing Co and P to obtain coarse WC powder with Co-P eutectic structure, and then mix it with Co powder by ball milling, and filter, dry, sieve, press, and sinter to prepare a WC alloy with uniform structure, no abnormal growth, and WC grain size of 6 to 10μm. The same type of technical patent CN202010909601.X adopts liquid phase reduction method to introduce Cu and P elements into coarse WC powder, so that Cu and P elements are deposited on the surface of WC particles, and the coarse WC powder coated with Cu and P is solid solution treated to form coarse WC powder containing Cu-P solid solution, and then mixed with Co powder, and filtered, dried, sieved, pressed, and sintered to obtain a WC alloy with low grain distribution dispersion, no abnormal growth, and WC grain size of 6 to 10μm. These two patented technologies introduce Cu and P elements into the alloy composition. Whether they have any impact on the performance of the alloy needs further study.

[0008] Patent CN201210416414.3 ball-mills part of the coarse-grained WC powder to obtain fine-grained WC powder with high activity, and then adds the remaining coarse-grained WC powder and Co powder into the ball mill to prepare ultra-coarse-grained cemented carbide. However, the grain size obtained is 4.0 to 8.0 μm, and the grain size of the alloy has not yet exceeded 8 μm.

[0009] Patent CN201110035634.7 is a patented method for preparing ultra-coarse grain mixture by combining premixing and mild ball milling. First, coarse WC powder (particle size 18-22μm) and Co powder (4-20%) are processed in a Y-type or double cone mixer in proportion for 0.5-2h. The uniformity of WC powder and Co powder mixing is enhanced by premixing. Then the premixed powder is added to the ball mill and lightly ball milled at a critical speed of 20-55% to reduce the degree of damage to WC grains by ball milling. After ball milling for 8-24h, the material is unloaded, followed by drying, granulation, pressing, and sintering to obtain WC cemented carbide with an average grain size of 6-10μm. The solution requires premixing first and then wet grinding. Compared with conventional processes, the premixing process is added, which correspondingly increases the production process and cost.

[0010] At present, the industrialized manufacture of coarse-grained WC-Co alloy still uses coarse WC powder as raw material, and the coarse-grained cemented carbide is prepared in a liquid medium through standard powder metallurgy process such as ball milling, drying and granulation, pressing, sintering, etc. Ball milling mixing equipment - ball mill, is still the mainstream equipment for the production of cemented carbide because of its mature technology, low investment cost, easy operation, and convenient mass production of cemented carbide. Summary of the invention

[0011] The object of the present invention is to provide a process method for preparing ultra-coarse grain alloys in batches in view of the shortcomings and difficulties of the prior art. The WC grain size in the WC-Co alloy is related to the original particle size of tungsten carbide. The idea of ​​the present invention is to use high-temperature carbonized coarse WC powder as raw material, and the ball mill is designed with a low rod-to-material ratio (mass ratio of the grinding body to the mixed powder) and a high filling factor (total volume of the grinding body and the mixed powder to the volume ratio of the ball mill barrel), so as to maximize the mixing effect of the traditional ball milling equipment, and at the same time control the crushing effect of the ball milling equipment on the coarse WC grains, so as to prepare an alloy with coarse grain size and uniform organization. From the aspect of ball milling mixing intensity, the coarse grains in the original WC particles are retained without being excessively crushed, and the alloy microstructure is defect-free.

[0012] The method for preparing ultra-coarse and extra-coarse-grained cemented carbide of the present invention adopts the standard method for producing cemented carbide to prepare ultra-coarse and extra-coarse-grained cemented carbide, with WC powder carbonized at 2000°C as the main raw material, the Fisher particle size is 35μm-40μm, and the cobalt content of the cemented carbide is 8%. The specific steps are as follows:

[0013] Ingredients: Mix tungsten carbide powder and cobalt powder according to the mass composition ratio:

[0014] Ball milling and drying: Use ball milling equipment commonly used in the cemented carbide industry. The grinding body is a rod-shaped alloy with a diameter of φ5 to φ10 mm and a length twice the diameter. The grinding rod with a diameter of φ5 mm accounts for more than 50% of the total grinding body mass. Put the prepared tungsten carbide powder and cobalt powder materials, paraffin wax, and cosolvent (stearic acid) into the ball mill for ball milling and mixing. The ball milling medium is hexane, and the liquid-solid ratio of hexane to materials (tungsten carbide powder and cobalt powder) is 0.15 to 0.20 L / Kg. The ball milling time is controlled at 16 to 20 hours. The mass ratio of the grinding rod to the material (tungsten carbide powder and cobalt powder) (rod-to-material ratio) is 1:1 to 1.5:1, and the total volume of the grinding rod and the material (tungsten carbide powder and cobalt powder) accounts for 50% to 70% of the ball mill barrel volume (filling factor). After ball milling, drying, and granulation, a mixed powder of ultra-coarse and extra-coarse grain alloys is obtained.

[0015] The method of the present invention adopts ultra-coarse high-temperature tungsten carbide, and in the ball milling process, obtains a suitable ball milling mixing intensity by adjusting the rod-to-material ratio and the filling factor, controls the crushing effect of the ball milling equipment on the coarse WC grains, and prepares an alloy with coarse grain size and uniform structure. Specifically, the lower the rod-to-material ratio, the higher the percentage of the φ5mm diameter grinding rod in the total grinding body mass, the higher the filling factor, and the cemented carbide with extra-coarse grain size can be obtained; and the higher the rod-to-material ratio, the lower the percentage of the φ5mm diameter grinding rod in the total grinding body mass, and the cemented carbide with ultra-coarse grain size can be obtained.

[0016] The mixed powder is pressed into a green body and sintered to obtain ultra-coarse and extra-coarse grained cemented carbide. The sintering temperature is 1480℃~1520℃ and the sintering time is 0.5-1.0h. This method can produce cemented carbide with a grain size of 4~6um, 6~8μm and 8~10μm, with no defects in the metallographic structure and a porosity of A02B00.

[0017] The present invention has the following characteristics:

[0018] (1) Using high-temperature carbonized coarse WC powder as raw material, the grains in the WC particles are fully developed, the WC grain strength is high, and the WC grain size is easy to control during ball milling.

[0019] (2) By adopting a low rod-to-material ratio and high filling method, the degree of crushing of coarse-grained WC particles during ball milling is alleviated and controlled. This method can obtain an alloy with coarse grains and uniform distribution.

[0020] (3) Ball milling equipment is a common equipment in the cemented carbide industry. The ball mill is used to complete the alloy structure and grain size design without the investment of additional new equipment. The production process and technology are the same as the traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The technical solution will be described clearly and completely below in conjunction with the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0022] 1. Figure 1-6 The metallographic microstructures corresponding to the alloys prepared in Examples 1-6 of the present invention at a magnification of 200 times. DETAILED DESCRIPTION

[0023] The above contents of the invention are further described in detail below in conjunction with the specific implementation methods of the embodiments. However, this should not be understood as the scope of the above subject matter of the invention being limited to the following examples. Various substitutions or changes made according to common technical knowledge and customary means in the art without departing from the above technical ideas of the invention should be included in the scope of the invention.

[0024] In the following examples, high temperature carbonized coarse WC powder is used as raw material, the cobalt powder content is 8%, and the grinding body used in the ball mill is a rod-shaped alloy with a diameter of φ5 to φ10 mm.

[0025] Example 1

[0026] Take 92 parts of WC powder with a Fisher particle size of 40.0μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.15L, the amount of paraffin added is 0.2g, and the amount of solvent added is 0.02g. The WC powder, Co powder, paraffin, solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1:1, the φ5mm grinding rod accounts for 100%, and the volume of the grinding rod and the mixed powder (WC powder and Co powder) accounts for 70% of the total volume of the ball mill barrel. The ball milling time is 16h. After the ball milling is completed, the compact is obtained by unloading, drying, granulating and pressing. It is sintered at 1520℃ for 0.5h to 1h to obtain an alloy with a grain size of 10.2um and a porosity of A02B00. The metallographic structure is as follows Figure 1 .

[0027] Example 2

[0028] Take 92 parts of WC powder with a Fisher particle size of 40.0μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.15L, the amount of paraffin added is 0.2g, and the amount of co-solvent added is 0.02g. The WC powder, Co powder, paraffin, co-solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1.3:1, the φ5mm grinding rod accounts for 100%, and the volume of the grinding rod and the mixed powder accounts for 60% of the total volume of the ball mill barrel. The ball milling time is 18h. After the ball milling is completed, the compact is obtained by unloading, drying, granulating, and pressing. It is sintered at 1520℃ for 0.5h to 1h to obtain an alloy with a grain size of 9.1um and a porosity of A02B00. The metallographic structure is as follows Figure 2 .

[0029] Example 3

[0030] Take 92 parts of WC powder with a Fisher particle size of 35.2μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.15L, the amount of paraffin added is 0.2g, and the amount of co-solvent added is 0.02g. The WC powder, Co powder, paraffin, co-solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1.3:1, the φ5mm grinding rod accounts for 100%, the volume of the grinding rod and the mixed powder accounts for 60% of the total volume of the ball mill barrel, and the ball milling time is 20h. After the ball milling is completed, the compact is obtained by unloading, drying, granulating, and pressing. It is sintered at 1480℃ for 0.5 to 1h to obtain an alloy with a grain size of 8.2um and a porosity of A02B00. The metallographic structure is as follows Figure 3 .

[0031] Example 4

[0032] Take 92 parts of WC powder with a Fisher particle size of 35.2μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.20L, the amount of paraffin added is 0.2g, and the amount of co-solvent added is 0.02g. The WC powder, Co powder, paraffin, co-solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1.5:1, the φ5mm grinding rod accounts for 50%, the volume of the grinding rod and the mixed powder accounts for 70% of the total volume of the ball mill barrel, and the ball milling time is 16h. After the ball milling, the compact is obtained by unloading, drying, granulating and pressing. It is sintered at 1480℃ for 0.5 to 1h to obtain an alloy with a grain size of 7.5um and a porosity of A02B00. The metallographic structure is as follows Figure 4 .

[0033] Example 5

[0034] Take 92 parts of WC powder with a Fisher particle size of 35.2μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.20L, the amount of paraffin added is 0.2g, and the amount of co-solvent added is 0.02g. The WC powder, Co powder, paraffin, co-solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1.5:1, the φ5mm grinding rod accounts for 50%, the volume of the grinding rod and the mixed powder accounts for 60% of the total volume of the ball mill barrel, and the ball milling time is 16h. After the ball milling, the compact is obtained by unloading, drying, granulating and pressing. It is sintered at 1480℃ for 0.5 to 1h to obtain an alloy with a grain size of 6.0um and a porosity of A02B00. The metallographic structure is as follows Figure 5 .

[0035] Example 6

[0036] Take 92 parts of WC powder with a Fisher particle size of 35.2μm and 8 parts of Co powder for component proportioning. For every kilogram of mixed powder, the amount of hexane added is 0.20L, the amount of paraffin added is 0.2g, and the amount of co-solvent added is 0.02g. The WC powder, Co powder, paraffin, co-solvent, etc. are mixed and transferred into a ball mill. The rod-to-material ratio is 1.5:1, the φ5mm grinding rod accounts for 50%, the volume of the grinding rod and the mixed powder accounts for 50% of the total volume of the ball mill barrel, and the ball milling time is 16h. After the ball milling, the compact is obtained by unloading, drying, granulating and pressing. It is sintered at 1480℃ for 0.5 to 1h to obtain an alloy with a grain size of 5.5um and a porosity of A02B00. The metallographic structure is as follows Figure 6 .

[0037] The present invention adopts a conventional cemented carbide method, and by controlling the rod-to-material ratio, filling coefficient, ball milling time, and the mass ratio of the grinding rod with a diameter of φ5 mm to the total grinding body in the ball milling process without adding any new equipment, it can realize the batch preparation of ultra-coarse and extra-coarse cemented carbides with the required grain size without changing any equipment. The method of the present invention has low cost and simple process, and can prepare alloys with coarse grain size and uniform structure.

[0038] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing ultra-coarse and extra-coarse grain cemented carbide, characterized in that: The steps include: (1) Ingredients: tungsten carbide powder and cobalt powder are mixed according to the mass composition ratio: the tungsten carbide powder is a coarse tungsten carbide powder carbonized at high temperature, and the Fisher particle size is 35 μm to 40 μm; (2) ball milling and drying: the material of step (1) is loaded into a ball mill for ball milling, wherein the ball milling process is as follows: the rod-to-material ratio is 1:1 to 1.5:1; the filling factor is 50% to 70%; the ball milling time is 16 to 20 hours; the ball milling medium is hexane; the liquid-to-solid ratio of hexane to the material is 0.15L-0.20L / Kg; the grinding body used for ball milling is a rod-shaped alloy with a diameter of φ5 to φ10mm, and the grinding rod with a diameter of φ5mm accounts for more than or equal to 50% of the total grinding body mass; after ball milling, the mixed powder of ultra-coarse and extra-coarse grain alloy is obtained by drying and granulation; (3) Pressing and forming; (4) Sintering: After sintering, ultra-coarse and extra-coarse grain cemented carbides are obtained; the sintering process is as follows: sintering temperature is 1480° C. to 1520° C., and holding time is 0.5 to 1.0 h.

2. The method according to claim 1, characterized in that The mass percentage of the cobalt powder in step (1) is 8%, and the remainder is tungsten carbide powder.

3. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 40 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.15 L / Kg, the proportion of φ5 mm grinding rods is 100%, the rod-to-material ratio is 1:1, the filling factor is 70%, and the ball milling time is 16 h; In the step (4), the sintering temperature is 1520° C. and the holding time is 0.5-1.0 h.

4. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 40 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.15 L / Kg, the proportion of φ5 mm grinding rods is 100%, the rod-to-material ratio is 1.3:1, the filling factor is 60%, and the ball milling time is 18 h; In the step (4), the sintering temperature is 1520° C. and the holding time is 0.5-1.0 h.

5. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 35.2 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.15 L / Kg, the proportion of φ5 mm grinding rods is 100%, the rod-to-material ratio is 1.3:1, the filling factor is 60%, and the ball milling time is 20 h; In the step (4), the sintering temperature is 1480° C. and the holding time is 0.5-1.0 h.

6. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 35.2 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.20 L / Kg, the proportion of φ5 mm grinding rods is 50%, the rod-to-material ratio is 1.5:1, the filling factor is 70%, and the ball milling time is 16 h; In the step (4), the sintering temperature is 1480° C. and the holding time is 0.5-1.0 h.

7. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 35.2 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.20 L / Kg, the proportion of φ5 mm grinding rods is 50%, the rod-to-material ratio is 1.5:1, the filling factor is 60%, and the ball milling time is 16 h; In the step (4), the sintering temperature is 1520° C. and the holding time is 0.5-1.0 h.

8. The method according to claim 2, characterized in that In the step (1), the tungsten carbide powder has a Fisher particle size of 35.2 μm; In the step (2), the liquid-solid ratio of hexane to material is 0.20 L / Kg, the proportion of φ5 mm grinding rods is 50%, the rod-to-material ratio is 1.5:1, the filling factor is 50%, and the ball milling time is 16 h; In the step (4), the sintering temperature is 1480° C. and the holding time is 0.5-1.0 h.

9. The method according to any one of claims 3 to 8, characterized in that: In the step (1), paraffin wax and stearic acid are further added, wherein the mass ratio of paraffin wax to tungsten carbide powder and cobalt powder is 0.2 g / kg, and the mass ratio of stearic acid to tungsten carbide powder and cobalt powder is 0.02 g / kg.

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