A polycrystalline CBN magnetic abrasive and its preparation method

Abstract

The invention belongs to the technical field of preparation of composite materials and specifically discloses a polycrystalline CBN magnetic abrasive and a preparation method thereof. In the invention, polycrystalline CBN abrasive grains formed by sintering single crystal CBN particles and an AlN binder under high temperature and high pressure are used as a grinding phase of the magnetic abrasive. The polycrystalline CBN abrasive grains have higher wear resistance, high hardness and self-sharpening properties, and can improve the grinding performance and grinding life of the magnetic abrasive. The polycrystalline CBN abrasive grains are mechanically ball-milled with ferromagnetic spherical iron powder, the grinding phase is uniformly distributed on the surface of the ferromagnetic phase, the abrasive grains and the spherical iron powder are mechanically bonded, and the ball-milled abrasive is heat-treated to form the polycrystalline CBN magnetic abrasive. The preparation process is simple, and the grinding life of the prepared polycrystalline CBN magnetic abrasive is increased to 80 minutes.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of composite materials, and in particular relates to a polycrystalline CBN magnetic abrasive and a preparation method thereof. Background Art

[0002] The principle of magnetic grinding technology is that abrasive particles are attracted to the workpiece surface by a magnetic field and linked together along the magnetic field lines to form a flexible "magnetic brush." ​​This interaction creates a squeezing, rolling, and micro-cutting effect on the workpiece surface, removing surface defects and improving surface finish and precision. This demonstrates the importance of magnetic abrasives in this process, and is central to the development, promotion, and application of this technology.

[0003] Magnetic abrasives, as grinding tools for magnetic finishing, play a key role in this process. The core of magnetic finishing technology lies in the preparation of high-performance magnetic abrasive particles. Magnetic abrasives are basically composed of two parts: a magnetic conductive phase matrix and a hard abrasive phase. The ferromagnetic phase enables the abrasive to generate sufficient grinding pressure on the workpiece surface under the influence of the magnetic field, while the hard abrasive phase is responsible for producing a micro-cutting effect.

[0004] At present, the main methods used in China to prepare magnetic abrasives are sintering, bonding, chemical composite plating, and sol-gel methods. However, the sintering and bonding methods require the sintered blocks to be crushed in the later stage. Since the crushing force is difficult to control, the abrasive morphology and particle size are uncontrollable, the abrasive phase distribution is unreasonable, and there are a large number of cracks in the abrasive, which ultimately affects the processing quality of the abrasive. The chemical composite plating and sol-gel methods have poor two-way bonding in the abrasive on the one hand, and low efficiency in abrasive preparation on the other hand, which pollutes the environment and is not suitable for mass production. However, the problems of complex process, poor abrasive processing accuracy, and short grinding life are the key to limiting the widespread promotion and application of this method. Therefore, how to select a method with simple process and low cost to prepare magnetic abrasives with high surface hardness and long life from the perspective of abrasive structure design is a difficulty in the research of magnetic grinding technology in recent years. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a polycrystalline CBN magnetic abrasive and a preparation method thereof, so as to solve the problems of the existing magnetic abrasive having a short grinding life and a complicated preparation process.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a polycrystalline CBN magnetic abrasive, comprising:

[0008] After uniformly mixing single crystal CBN particles and AlN binder, they are sintered under high temperature and high pressure to form polycrystalline CBN abrasive grains, which serve as the grinding phase of magnetic abrasives.

[0009] The grinding phase and the ferromagnetic phase are mixed and then mechanically ball milled to obtain an abrasive, and the abrasive after mechanical ball milling is heat treated to obtain a polycrystalline CBN magnetic abrasive; spherical iron powder is used as the ferromagnetic phase.

[0010] Furthermore, the particle size of the single crystal CBN is less than 3 μm, the mass percentage of AlN binder in the mixture of single crystal CBN particles and AlN binder is 3-10 wt.%, and the particle size of the polycrystalline CBN abrasive grains is 5-20 μm.

[0011] Furthermore, the particle size of the ferromagnetic phase is 200-300 μm, the particle size ratio of the ground phase to the ferromagnetic phase is 1:8, and the volume ratio is 1:3.

[0012] Furthermore, the time for uniformly mixing the single crystal CBN particles and the AlN binder is 3 to 5 hours.

[0013] Furthermore, the high temperature and high pressure sintering time is 1 to 5 hours, the sintering temperature is 1200 to 1800° C., the heating rate is 3 to 5° C. / min, and the pressure applied during sintering is 4 to 12 GPa.

[0014] Furthermore, the ball milling is carried out in a ball milling jar, and the ball milling jar is evacuated to a vacuum degree of less than 1×10 - 3 Pa, ball mill speed is 350~550r / min, and ball mill time is 6~10h.

[0015] Furthermore, the ball milling balls used in the mechanical ball milling are stainless steel balls, and the volume ratio of the ball milling balls to the abrasive is (11-12):1.

[0016] Furthermore, the grinding phase and the ferromagnetic phase are mixed for 60 minutes.

[0017] Furthermore, the heating rate of the heat treatment is 3-5°C / min, the heat treatment temperature is 1200-1300°C, the heat treatment time is 5-7h, and the cooling rate is 5°C / min.

[0018] In a second aspect, the present invention provides a polycrystalline CBN magnetic abrasive, characterized in that the polycrystalline CBN magnetic abrasive is prepared according to any one of the above-mentioned methods for preparing a polycrystalline CBN magnetic abrasive.

[0019] The present invention has at least the following beneficial effects:

[0020] 1. The polycrystalline CBN abrasive grains formed by sintering single-crystal CBN particles and an AlN binder under high temperature and high pressure in the present invention are used as the grinding phase of the magnetic abrasive. The polycrystalline CBN abrasive grains have higher wear resistance, high hardness and self-sharpening properties, which can improve the grinding performance and grinding life of the magnetic abrasive. The polycrystalline CBN abrasive grains are mechanically ball-milled with ferromagnetic spherical iron powder. The grinding phase is uniformly distributed on the surface of the ferromagnetic phase, and the abrasive grains and the spherical iron powder are mechanically bonded. The milled abrasive is then heat-treated to form the polycrystalline CBN magnetic abrasive. The preparation process is simple. The grinding life of the prepared polycrystalline CBN magnetic abrasive is increased to 80 minutes.

[0021] 2. The mechanical ball milling-heat treatment process provided by the present invention has the characteristics of simple process, good bonding, and long service life. The polycrystalline CBN abrasive grains are exposed on the surface of the microcrystalline CBN through the wear and tear of the AlN binder, so that the surface of the polycrystalline CBN abrasive grains has more micro-cutting edges. The abrasive can be self-sharpened, which can achieve better workpiece surface quality. The fracture toughness of the polycrystalline CBN abrasive grains is about 4 times that of single-crystal CBN particles.

[0022] 3. The polycrystalline CBN abrasive grains of the present invention are substantially uniform in height on the sphere surface, and the cutting depth formed during grinding is also substantially uniform, which ensures the isoenergeticity between the magnetic abrasive grains, thereby maintaining good processing stability and excellent processing effect during the grinding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 Schematic diagram of the wear characteristics of polycrystalline CBN and single crystal CBN magnetic abrasives;

[0025] Figure 2 This is the SEM image of single crystal CBN magnetic abrasive prepared by sintering method;

[0026] Figure 3 This is the SEM image of polycrystalline CBN magnetic abrasive prepared by mechanical ball milling-heat treatment;

[0027] Figure 4 This is the SEM image observed by low-power microscope after 80 minutes of grinding with polycrystalline CBN magnetic abrasive;

[0028] Figure 5 This is the SEM image observed by high magnification microscope after polycrystalline CBN magnetic abrasive grinding for 80 minutes;

[0029] Figure 6 is the initial zirconium alloy tube wall roughness;

[0030] Figure 7 The roughness of the zirconium alloy tube wall after machining with single crystal CBN abrasive prepared by sintering method;

[0031] Figure 8 This is the roughness of the zirconium alloy tube wall after processing with the polycrystalline CBN abrasive prepared by the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0033] The following detailed description is an exemplary description and is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0034] A method for preparing polycrystalline CBN magnetic abrasive, comprising:

[0035] After single crystal CBN (cubic boron nitride) particles and AlN (aluminum nitride) binder are uniformly mixed and sintered under high temperature and high pressure to form polycrystalline CBN abrasive grains. The polycrystalline CBN abrasive grains serve as the grinding phase of magnetic abrasives. The polycrystalline CBN abrasive grains are exposed on the surface through the wear and tear of the AlN binder, so that the surface of the polycrystalline CBN abrasive grains has more micro-cutting edges. The abrasive can be self-sharpened, which can achieve better workpiece surface quality.

[0036] The abrasive phase is mixed with a ferromagnetic phase and then mechanically ball-milled to obtain an abrasive. The milled abrasive is then heat-treated to produce a polycrystalline CBN magnetic abrasive, in which the abrasive phase and the ferromagnetic phase are evenly embedded and tightly bonded on the surface. The ferromagnetic phase is composed of spherical iron powder, with a particle size ratio of 1:8 and a volume ratio of 1:3. Because the polycrystalline CBN abrasive grains are essentially uniform in height across the sphere, the depth of cut achieved during grinding is also essentially uniform. This ensures isoenergetic properties between the magnetic abrasive particles, resulting in excellent processing stability and results during the grinding process.

[0037] like Figure 1 As shown in the figure, for single-crystal CBN and polycrystalline CBN magnetic abrasives produced by mechanical ball milling and heat treatment, the grinding phase is evenly distributed on the surface of the ferromagnetic phase, and the abrasive particles form a tight mechanical bond with the spherical iron powder. During the grinding process, single-crystal CBN abrasive particles tend to fall off in large pieces, losing their grinding ability. However, polycrystalline CBN magnetic abrasives are less likely to break during the grinding process, and after breaking, they form a large number of micro-cutting edges, which improves grinding accuracy and achieves high-precision machining of the workpiece surface.

[0038] The specific steps are:

[0039] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 3-5 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 1-5 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0040] The sintering temperature is 1200-1800° C., the heating rate is 3-5° C. / min, and the pressure applied during sintering is 4-12 GPa.

[0041] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3 and added to a ball mill for ball milling to obtain abrasives. The ball milling balls were 316 stainless steel balls (2 mm in diameter) with a ball-to-material ratio of (11-12):1. The ball mill was evacuated (vacuum degree less than 1×10 -3 Pa), the ball milling speed is 350-550 r / min, and the ball milling time is 6-10 h.

[0042] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0043] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0044] The heating rate of the heat treatment is 3-5°C / min, the heat treatment temperature is 1200-1300°C, the heat treatment time is 5-7h, and the cooling rate is 5°C / min.

[0045] like Figure 2 The figure shows the single crystal CBN magnetic abrasive prepared by sintering method. Figure 3 The figure shows the polycrystalline CBN magnetic abrasive prepared by mechanical ball milling-heat treatment method.

[0046] Example 1

[0047] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 3 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 1 hour, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0048] The sintering temperature was 1200°C, the heating rate was 3°C / min, and the pressure applied during sintering was 4 GPa.

[0049] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 350 r / min, and the ball milling time was 6 h.

[0050] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0051] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0052] The heating rate of the heat treatment is 3°C / min, the heat treatment temperature is 1200°C, the heat treatment time is 5h, and the cooling rate is 5°C / min.

[0053] Example 2

[0054] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 4 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 2 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0055] The sintering temperature was 1300°C, the heating rate was 4°C / min, and the pressure applied during sintering was 5 GPa.

[0056] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 400 r / min, and the ball milling time was 7 h.

[0057] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0058] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0059] The heating rate of the heat treatment is 4°C / min, the heat treatment temperature is 1210°C, the heat treatment time is 6h, and the cooling rate is 5°C / min.

[0060] Example 3

[0061] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 5 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 3 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0062] The sintering temperature was 1400°C, the heating rate was 5°C / min, and the pressure applied during sintering was 6 GPa.

[0063] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 450 r / min, and the ball milling time was 8 h.

[0064] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0065] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0066] The heating rate of the heat treatment is 3-5°C / min, the heat treatment temperature is 1250°C, the heat treatment time is 7h, and the cooling rate is 5°C / min.

[0067] Example 4

[0068] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 3 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 4 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0069] The sintering temperature was 1500°C, the heating rate was 3°C / min, and the pressure applied during sintering was 7 GPa.

[0070] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 500 r / min, and the ball milling time was 9 h.

[0071] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0072] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0073] The heating rate of the heat treatment is 3°C / min, the heat treatment temperature is 1300°C, the heat treatment time is 5h, and the cooling rate is 5°C / min.

[0074] Example 5

[0075] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 4 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 5 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0076] The sintering temperature was 1600°C, the heating rate was 4°C / min, and the pressure applied during sintering was 8 GPa.

[0077] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 550 r / min, and the ball milling time was 10 h.

[0078] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0079] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0080] The heating rate of the heat treatment is 4°C / min, the heat treatment temperature is 1280°C, the heat treatment time is 6h, and the cooling rate is 5°C / min.

[0081] Example 6

[0082] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 5 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 1 hour, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0083] The sintering temperature was 1700°C, the heating rate was 5°C / min, and the pressure applied during sintering was 10 GPa.

[0084] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed was 370 r / min, and the ball milling time was 8 h.

[0085] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0086] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0087] The heating rate of the heat treatment is 5°C / min, the heat treatment temperature is 1230°C, the heat treatment time is 7h, and the cooling rate is 5°C / min.

[0088] Example 7

[0089] S1: Single crystal CBN with a particle size of less than 3 μm is uniformly mixed with 3-10 wt.% AlN binder for 4 hours, the mixture is pressed into a blank, the blank is sintered under high temperature and high pressure conditions for 4 hours, cooled to room temperature with the furnace, and crushed and sieved to obtain polycrystalline CBN abrasive grains with a particle size of 5-20 μm.

[0090] The sintering temperature was 1800°C, the heating rate was 3°C / min, and the pressure applied during sintering was 12 GPa.

[0091] S2: Polycrystalline CBN abrasive grains and spherical iron powder were uniformly mixed in a volume ratio of 1:3, and added to a ball mill for ball milling to obtain abrasives; the ball milling balls were 316 stainless steel balls (2 mm in diameter), and the ball-to-material ratio was (11-12):1. The ball mill was evacuated (vacuum degree less than 10 -3 ), the ball milling speed is 550r / min, and the ball milling time is 6 to 10h.

[0092] The particle size of the spherical iron powder is 200-300 μm, and the mixing time of the polycrystalline CBN abrasive grains and the spherical iron powder is 60 min.

[0093] S3: The abrasive after mechanical ball milling is heat treated to make the surface of the spherical iron powder slightly melted, and the grinding phase and ferromagnetic are more closely combined to obtain polycrystalline CBN magnetic abrasive.

[0094] The heating rate of the heat treatment is 5°C / min, the heat treatment temperature is 1300°C, the heat treatment time is 7h, and the cooling rate is 5°C / min.

[0095] Application Examples

[0096] For the zirconium alloy tube wall with initial Ra = 0.317 ± 0.01 μm, Figure 6 As shown, the single crystal CBN magnetic abrasive prepared by sintering and the polycrystalline CBN magnetic abrasive prepared by the present invention were processed, the processing time was 10min, and the processing length was 10mm; the roughness of the single crystal CBN magnetic abrasive prepared by sintering was Ra = 0.214 ± 0.01μm after processing. Figure 7 As shown; the roughness of the polycrystalline CBN magnetic abrasive prepared by the present invention after processing is Ra = 0.189 ± 0.01 μm, as Figure 8 As shown in the figure, the grinding life is increased to 80 min, and the grinding life of the magnetic abrasive prepared by sintering method is about 40 to 60 min.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for preparing polycrystalline CBN magnetic abrasive, characterized in that: include: After uniformly mixing single crystal CBN particles and AlN binder, they are sintered under high temperature and high pressure to form polycrystalline CBN abrasive grains, which serve as the grinding phase of magnetic abrasives. The grinding phase and the ferromagnetic phase are mixed and then subjected to mechanical ball milling to obtain an abrasive, and the abrasive after mechanical ball milling is heat treated to obtain a polycrystalline CBN magnetic abrasive; spherical iron powder is used as the ferromagnetic phase; The particle size of the single crystal CBN is less than 3 μm, the mass percentage of the AlN binder in the mixture of the single crystal CBN particles and the AlN binder is 3 to 10 wt.%, and the particle size of the polycrystalline CBN abrasive grains is 5 to 20 μm; The high temperature and high pressure sintering time is 1 to 5 hours, the sintering temperature is 1200 to 1800°C, the heating rate is 3 to 5°C / min, and the pressure applied during sintering is 4 to 12 GPa; The ball milling is carried out in a ball milling jar, and the ball milling jar is evacuated to a vacuum degree of less than 1×10 -3 Pa, ball mill speed is 350-550 r / min, and ball milling time is 6-10 h; The heating rate of the heat treatment is 3-5°C / min, the heat treatment temperature is 1200-1300°C, the heat treatment time is 5-7h, and the cooling rate is 5°C / min.

2. The method for preparing a polycrystalline CBN magnetic abrasive according to claim 1, characterized in that: The particle size of the ferromagnetic phase is 200-300 μm, the particle size ratio of the grinding phase to the ferromagnetic phase is 1:8, and the volume ratio is 1:

3.

3. The method for preparing a polycrystalline CBN magnetic abrasive according to claim 1, characterized in that: The time for uniformly mixing the single crystal CBN particles and the AlN binder is 3 to 5 hours.

4. The method for preparing a polycrystalline CBN magnetic abrasive according to claim 1, characterized in that: The ball-to-material ratio of the ball mill is (11-12):

1.

5. The method for preparing a polycrystalline CBN magnetic abrasive according to claim 1, characterized in that: The mixing time of the grinding phase and the ferromagnetic phase is 60 minutes.

6. A polycrystalline CBN magnetic abrasive, characterized in that: The polycrystalline CBN magnetic abrasive is prepared according to the preparation method of polycrystalline CBN magnetic abrasive according to any one of claims 1-5.

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