High-chromium polyhedral grinding medium and preparation method thereof

Abstract

The invention discloses a high-chromium polyhedral grinding medium and a preparation method thereof, and belongs to the technical field of material processing. A strengthening area is limited in a spherical crown body with the vertex as the center and the radius not larger than 0.5 mm, a WC-Co particle array gradient strengthening structure is constructed in the area, and the concentration of the WC-Co particle array gradient strengthening structure is in exponential attenuation distribution C (x) = C0.e-0. 2x from the vertex center to the edge direction. The diameter of the WC-Co particles is controlled within the range of 0.05-0.1 mm, and the surfaces of the WC-Co particles are wrapped with transition interface layers which are composed of Cr3C2 particles and have the thickness of 0.02-0.05 mm. The problem of fracture caused by vertex stress concentration is effectively solved, the wear resistance and the service life of the grinding medium are remarkably improved, meanwhile, interface stripping failure caused by a strengthening structure is avoided, the method is compatible with an existing high-chromium iron process, the industrialization implementation cost is increased limitedly, and the method is suitable for industrial production. And a more reliable and efficient grinding medium solution is provided for an industrial ball milling system.

Description

Technical Field

[0001] This invention belongs to the field of materials processing technology, specifically relating to a high-chromium polyhedral grinding media and its preparation method. Background Technology

[0002] High-chromium polyhedral grinding media are key consumables in ball mill systems, and their geometry and material properties directly affect grinding efficiency, energy consumption, and product purity. Currently, high-chromium cast iron (hardness HRC 58–62) with a Cr content of 12%–18% is widely used in industry, combined with cubic, dodecahedral, and other polyhedral structures to enhance the impact crushing ability of materials. However, in actual operation, the stress concentration effect at the vertices of the polyhedrons makes them prone to early brittle fracture, leading to a shortened media life and the generation of micron-sized debris that contaminates the grinding products.

[0003] Utility model CN206046190U discloses a soccer ball-shaped grinding media with multiple facets on its surface, made of ceramic materials such as zirconium oxide, alumina, or silicon carbide, which improves grinding efficiency by increasing the shear area. While this design optimizes the geometry and material system of the media, it does not offer an effective solution to the apex fracture problem of high-chromium cast iron-based metal media. Furthermore, the low density of the ceramic material used makes it difficult to meet the high impact kinetic energy requirements under heavy-duty ball milling conditions, limiting its applicability in large-scale mining or cement grinding applications.

[0004] Patent application CN102732212A discloses a composite abrasive media formed by sintering a mixture of metallic (e.g., tungsten) and ceramic (e.g., alumina) materials, achieving uniform strengthening through injection molding and sintering. While this approach balances hardness and toughness to some extent, its overall strengthening strategy fails to consider the stress gradient differences between vertices, edges, and faces in a polyhedral structure, thus failing to specifically control the initiation and propagation paths of cracks in high-stress regions. Furthermore, this method relies on complex powder metallurgy processes, resulting in high manufacturing costs, and the introduction of heterogeneous phases into a high-chromium cast iron matrix may lead to insufficient interfacial bonding strength, posing a risk of localized spalling under dynamic impact loads.

[0005] In summary, existing technologies still have limitations in the structure-material co-design of high-chromium polyhedral grinding media, especially lacking precise means to control the micro-stress field and crack propagation behavior in the vertex region, and have not yet formed a systematic solution that takes into account high hardness, high toughness and long life. Summary of the Invention

[0006] One of the objectives of this invention is to provide a high-chromium polyhedral grinding media to solve the problem of brittle fracture caused by stress concentration at the apex during ball milling of existing high-chromium cast iron grinding media.

[0007] The second objective of this invention is to provide a method for preparing a high-chromium polyhedral abrasive media, which is used to prepare the aforementioned high-chromium polyhedral abrasive media.

[0008] The objective of this invention can be achieved through the following technical solutions: A high-chromium polyhedral abrasive media, wherein the abrasive media has a polyhedral structure with a Cr content of not less than 12%, and its vertex region has a gradient-reinforced microparticle composite structure; the vertex region is defined as a spherical cap with a radius r not exceeding 0.5 mm centered at the vertex; the gradient-reinforced microparticle composite structure includes a WC-Co (tungsten-cobalt alloy) microparticle array, the concentration of which decreases exponentially from the vertex center towards the edge, and the concentration function is C(x) = C0·e -0.2x Where C0 is the concentration at the vertex center and x is the radial distance from the vertex center; the WC-Co particles have a diameter of 0.05-0.1 mm and are covered with a transition interface layer; the transition interface layer is composed of Cr3C2 nanoparticles and has a thickness of 0.02-0.05 mm.

[0009] Furthermore, the concentration C0 at the vertex center is 1100-1300 particles / mm². 3 .

[0010] Furthermore, at a radial distance x = 0.5 mm at the edge boundary, the concentration is 220-260 particles / mm. 3 .

[0011] Furthermore, the WC-Co particles contain 85%-90% WC and 10%-15% Co binder phase.

[0012] Furthermore, the Cr3C2 nanoparticles in the transition interface layer have a particle size of 40-60 nanometers.

[0013] Furthermore, the polyhedron is a cube or octahedron with a side length of 50-150 mm.

[0014] A method for preparing a high-chromium polyhedral abrasive media includes the following steps: S1. High-carbon ferrochrome, ferromolybdenum and scrap steel are added to a medium-frequency induction furnace for smelting in proportion. When the temperature of the molten steel rises to 1520-1550℃, a carbon raiser is added to adjust the carbon content. After refining, the mixture is allowed to stand for 5-8 minutes to obtain high-chromium molten iron. The high-chromium molten iron is poured into a polyhedral metal mold preheated to 300-350℃. After solidification, the mold is demolded to obtain the billet. S2. A WC-Co suspension is injected into the apex region of the cast billet through a microfluidic nozzle. The volume percentage of WC-Co particles in the suspension is 12%-18%, and the volume ratio of ethanol to acetone in the ethanol-acetone mixed solvent is (2.5-3.5):1. The nozzle flow rate is expressed as a function v(x)=v0·e -0.2xControl, where v0 = 0.10 - 0.14 ml / s, and x is the radial distance from the center of the vertex; S3. Place the mold in a centrifuge and centrifuge at 2800-3200 rpm for 4-6 minutes; S4. Spray Cr3C2 sol with a spray gun pressure of 0.35-0.45 MPa and a spraying distance of 140-160 mm to form a pre-coating layer with a thickness of 0.02-0.05 mm; S5. Place the mold in a vacuum sintering furnace and sinter according to the following procedure: The temperature was increased from room temperature to 300℃ at a rate of 1.5-2.5℃ / min. The temperature was increased from 300℃ to 1150℃ at a rate of 4.5-5.5℃ / min. Keep warm at 1150℃ for 1.8-2.2 hours; Immerse in hot oil at 100-110℃ for quenching for 10-15 minutes; immediately after quenching, transfer to a tempering furnace and heat to 290-330℃ at 4.5-5.5℃ / min, hold for 6-8 hours, remove from the furnace and air cool to obtain high-chromium polyhedral grinding media.

[0015] Furthermore, the components of the high-chromium molten iron in S1, by weight percentage, include: Cr 15.0%-18.0%, C 2.5%-3.0%, Mo 1.0%-2.0%, Si≤0.8%, Mn≤1.0%, S≤0.05%, P≤0.05%, with the balance being Fe.

[0016] Furthermore, the WC-Co suspension in S2 contains 0.4%-0.6% polyvinylpyrrolidone dispersant.

[0017] Furthermore, the positioning accuracy of the microfluidic nozzle in S2 is ±10μm.

[0018] Furthermore, 0.3%-0.7% triethanolamine is added to the ethanol-acetone mixed solvent in S2 to adjust the pH to 6.5-7.5.

[0019] Furthermore, the Cr3C2 sol in S4 is prepared by mixing Cr(NO3)3·9H2O and citric acid in a molar ratio of 1:(1.8-2.2).

[0020] Furthermore, after step S4, the process includes drying at a temperature of 110°C-130°C for 1.8-2.2 hours.

[0021] Furthermore, the vacuum degree of the vacuum sintering furnace in S5 does not exceed 8×10⁻⁶. -3 Pa.

[0022] The beneficial effects of this invention are: (1) This invention provides a high-chromium polyhedral grinding media, wherein the grinding media adopts a polyhedral structure with a Cr content of not less than 12%. This composition design ensures that the matrix has sufficient hardness and wear resistance, while the polyhedral geometry enhances the impact crushing ability of materials. The vertex region is precisely defined as a spherical cap with a radius r not exceeding 0.5 mm centered on the vertex, ensuring that the reinforcing structure only acts on the high stress concentration area, avoiding the introduction of redundant reinforcement in non-critical areas and increasing manufacturing costs.

[0023] Within this defined region, a gradient-enhanced microparticle composite structure was constructed, wherein the concentration of the WC-Co microparticle array exhibited an exponentially decreasing distribution from the vertex center towards the edges, with the concentration function being C(x) = C0·e -0.2x This specific exponential function is optimized to closely match the actual stress field distribution. This concentration gradient design allows impact energy to dissipate layer by layer in the apex region, effectively avoiding the reflection and superposition of stress waves, and causing a reasonable deflection of the crack propagation path, thereby suppressing the rapid propagation of cracks in high-stress areas. The diameter of WC-Co particles is strictly controlled within the range of 0.05-0.1 mm. This size provides sufficient strengthening effect while avoiding the problem of local rigidity abrupt changes caused by excessively large particles, ensuring the coordinated deformation capability between the particles and the matrix.

[0024] (2) The present invention coats the surface of WC-Co particles with a layer of C The transition interface layer composed of nanoparticles, with a thickness limited to 0.02-0.05 mm, serves multiple functions: C The material's coefficient of thermal expansion falls between that of WC-Co and the high-chromium matrix, effectively buffering the thermal expansion mismatch between the two. The nanoscale particle structure facilitates a sufficient interfacial reaction with the matrix during sintering, promoting metallurgical bonding. The specific thickness range ensures sufficient stress buffering capacity while avoiding interfacial weakening due to excessive thickness. This structure-material synergistic design fundamentally solves the common interfacial delamination failure problem in traditional composite structures, ensuring long-term interfacial stability under dynamic impact loads.

[0025] (3) Through the organic combination of the above-mentioned technical features, the present invention achieves precise strengthening of the vertex region of the polyhedral grinding media, which not only maintains the excellent properties of the high-chromium cast iron matrix, but also specifically solves the problem of early fracture caused by stress concentration at the vertex, significantly improving the overall service life and reliability of the grinding media, while maintaining good compatibility with existing manufacturing processes, and providing a more efficient and durable grinding media solution for industrial ball milling systems. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0027] In some embodiments, a high-chromium polyhedral abrasive media is provided, wherein the abrasive media has a polyhedral structure with a Cr content of not less than 12%, and its vertex region is provided with a gradient-reinforced microparticle composite structure; the vertex region is defined as a spherical cap with a radius r not exceeding 0.5 mm centered at the vertex; the gradient-reinforced microparticle composite structure includes a WC-Co microparticle array, the concentration of which decreases exponentially from the vertex center towards the edge direction, and the concentration function is C(x) = C0·e -0.2x Where C0 is the concentration at the vertex center and x is the radial distance from the vertex center; the WC-Co particles have a diameter of 0.05-0.1 mm and are covered with a transition interface layer; the transition interface layer is composed of Cr3C2 nanoparticles and has a thickness of 0.02-0.05 mm.

[0028] This invention provides a high-chromium polyhedral grinding media, wherein the grinding media has a polyhedral structure with a Cr content of not less than 12%, and its vertex region has a gradient-reinforced microparticle composite structure; the vertex region is defined as a spherical cap with a radius r not exceeding 0.5 mm centered at the vertex. This spatial limitation is based on measured data of the stress distribution at the vertex during ball milling. Finite element analysis determines that 0.5 mm is the boundary of the region with significant stress concentration effect. Beyond this range, the stress rapidly decays. Precisely defining the effective domain avoids redundant reinforcement in non-critical areas, reduces manufacturing costs, and ensures that the reinforced structure covers the high stress concentration area.

[0029] The gradient-enhanced microparticle composite structure comprises a WC-Co microparticle array, the concentration of which decreases exponentially from the vertex center towards the edges, with the concentration function being C(x) = C0·e -0.2x ,in Here, is the concentration at the vertex center, and x is the radial distance from the vertex center. This effectively suppresses the rapid propagation of cracks in high-stress regions.

[0030] The WC-Co microparticles have a diameter of 0.05-0.1 mm, which ensures that the microparticles provide sufficient reinforcement while avoiding insufficient reinforcement due to excessively small particles or local rigidity abrupt changes due to excessively large particles. This ensures the coordinated deformation capability between the microparticles and the matrix and maintains the integrity of the overall structure.

[0031] The WC-Co microparticles are coated with a transition interface layer; this transition interface layer is composed of Cr3C2 nanoparticles with a thickness of 0.02-0.05 mm. Cr3C2 was chosen instead of traditional oxides as the interface layer material because of its coefficient of thermal expansion (5.5 × 10⁻⁶). 6 / ℃) is between WC-Co (5.2×1 6 / ℃) and high chromium substrate (12×1 6 Between 0.67°C and 0.67°C, it can effectively buffer thermal expansion mismatch. This thickness range ensures sufficient stress buffering capacity while avoiding the problems of insufficient buffering effect due to excessive thinness or interface weakening caused by excessive thickness.

[0032] In some embodiments, the apex center concentration C0 is 1100-1300 particles / mm. 3 .

[0033] when <1100 grains / mm 3 At that time, the energy dissipation efficiency is insufficient, and it cannot effectively suppress crack propagation; when >1300 grains / mm 3 At this point, excessively high particle density can lead to sudden changes in local rigidity, which may in turn trigger microcracks. This concentration range ensures sufficient crack-blocking capability while avoiding negative effects.

[0034] In some embodiments, when the radial distance at the edge boundary is x = 0.5 mm, the concentration is 220-260 particles / mm. 3 .

[0035] When the concentration is below 220 particles / mm 3 At this point, a significant concentration abrupt change exists between the particle distribution tip and the matrix, leading to secondary stress concentration; above 260 particles / mm 3 This indicates that the gradient attenuation is insufficient and a smooth transition of stress cannot be achieved. This range ensures a smooth transition between the particle distribution end and the matrix.

[0036] In some embodiments, the WC-Co particles contain 85%-90% WC and 10%-15% Co binder phase.

[0037] WC provides high hardness and wear resistance, while Co, as a metallic binder phase, melts and diffuses during sintering, promoting metallurgical bonding with the matrix. This ratio achieves an optimal balance between hardness and toughness, avoiding the problems of insufficient hardness due to too low WC content or increased brittleness due to too high WC content, as well as the issues of insufficient interfacial bonding due to too low Co content or decreased overall hardness due to too high Co content.

[0038] In some embodiments, the Cr3C2 nanoparticles in the transition interface layer have a particle size of 40-60 nm. Too small a particle size (<40 nm) will lead to severe agglomeration during sintering, affecting the uniformity of distribution; too large a particle size (>60 nm) will prevent the formation of a continuous and dense interface layer. This range ensures that the nanoparticles are uniformly dispersed during the sol-gel process and form a dense interface layer during subsequent sintering.

[0039] In some embodiments, the polyhedron is a cube or octahedron with a side length of 50-150 mm. A side length that is too small (<50 mm) will alter the stress distribution characteristics at the vertices, requiring adjustment of the strengthening parameters; a side length that is too large (>150 mm) will cause excessive stress concentration at the vertices, exceeding the design range of this strengthening scheme.

[0040] In some embodiments, a method for preparing a high-chromium polyhedral abrasive media includes the following steps: S1. High-carbon ferrochrome, ferromolybdenum and scrap steel are added to a medium-frequency induction furnace for smelting in proportion. When the temperature of the molten steel rises to 1520-1550℃, a carbon raiser is added to adjust the carbon content. After refining, the mixture is allowed to stand for 5-8 minutes to obtain high-chromium molten iron. The high-chromium molten iron is poured into a polyhedral metal mold preheated to 300-350℃. After solidification, the mold is demolded to obtain the billet. S2. A WC-Co suspension is injected into the apex region of the cast billet through a microfluidic nozzle. The volume percentage of WC-Co particles in the suspension is 12%-18%, and the volume ratio of ethanol to acetone in the ethanol-acetone mixed solvent is (2.5-3.5):1. The nozzle flow rate is expressed as a function v(x)=v0·e -0.2x The control is defined as follows: v0 = 0.10-0.14 mL / s, x is the radial distance from the center of the apex; the particle volume ratio is the optimal balance between suspension stability and enhancement effect; the ethanol-acetone ratio ensures good particle dispersion and rapid solvent evaporation; and the nozzle flow rate function is a precise spatial mapping of the concentration gradient.

[0041] S3. Place the mold in a centrifuge and centrifuge at 2800-3200 rpm for 4-6 minutes. This parameter range ensures that the WC-Co particles settle in the gaps between the high-chromium powders according to the preset concentration gradient. After centrifugation, the particle positions are locked by the powder skeleton to prevent displacement in subsequent operations. This avoids insufficient sedimentation caused by too low a speed or too short a time, as well as damage to the gradient distribution caused by too high a speed or too long a time.

[0042] S4. Spray Cr3C2 sol at a spray gun pressure of 0.35-0.45 MPa and a spraying distance of 140-160 mm to form a pre-coating layer with a thickness of 0.02-0.05 mm. This combination of parameters ensures that the sol uniformly covers the surface of WC-Co particles, forming a continuous pre-coating layer. This lays the foundation for a good interface to be formed during subsequent sintering and avoids problems such as uneven coating or splashing caused by improper pressure or distance.

[0043] S5. Place the mold in a vacuum sintering furnace and sinter according to the following procedure: The temperature was increased from room temperature to 300℃ at a rate of 1.5-2.5℃ / min. The temperature was increased from 300℃ to 1150℃ at a rate of 4.5-5.5℃ / min. Keep warm at 1150℃ for 1.8-2.2 hours; Immerse in hot oil at 100-110℃ for quenching for 10-15 minutes; immediately after quenching, transfer to a tempering furnace and heat to 290-330℃ at 4.5-5.5℃ / min, hold for 6-8 hours, remove from the furnace and air cool to obtain high-chromium polyhedral grinding media.

[0044] The segmented heating program is carefully designed based on material properties and process requirements to ensure the slow removal of organic matter, sufficient interfacial reaction, complete diffusion of the Co phase to form a three-phase metallurgical bonding interface, and effective control of thermal stress.

[0045] In some embodiments, the components of the high-chromium molten iron in S1 include, by weight percentage: Cr 15.0%-18.0%, C 2.5%-3.0%, Mo 1.0%-2.0%, Si≤0.8%, Mn≤1.0%, S≤0.05%, P≤0.05%, with the balance being Fe.

[0046] This composition system represents the optimal balance between wear resistance and toughness in high-chromium cast iron. The Cr content ensures the formation of sufficient M7C3 type carbides to provide basic wear resistance, while the C content is matched with Cr to avoid the presence of free graphite or excessive residual austenite. The Mo element refines the eutectic carbide size and improves the fracture toughness of the matrix.

[0047] In some embodiments, the WC-Co suspension in S2 contains 0.4%-0.6% polyvinylpyrrolidone dispersant. This ensures that the dispersant effectively prevents particle aggregation while avoiding the problem of organic residue caused by excessive amounts, thus guaranteeing uniform delivery of particles in the microfluidic system.

[0048] In some embodiments, the positioning accuracy of the microfluidic nozzle in S2 is ±10 μm. This accuracy is achieved through a high-resolution servo motor and a laser feedback system, ensuring that the flow rate function is accurately mapped to the concentration gradient in space, avoiding gradient distribution deviations caused by insufficient accuracy, while also considering the economic feasibility of industrial implementation.

[0049] In some embodiments, 0.3%-0.7% triethanolamine is added to the ethanol-acetone mixed solvent in step S2 to adjust the pH to 6.5-7.5. This pH range imparts a negative charge to the surface of the WC-Co particles, enhancing their interaction with the dispersant and ensuring the long-term stability of the suspension in the microfluidic system, thus avoiding particle aggregation caused by improper pH.

[0050] In some embodiments, the Cr3C2 sol in S4 is prepared by mixing Cr(NO3)3·9H2O and citric acid in a molar ratio of 1:(1.8-2.2). This ratio controls the proportion of metal ions to complexing agents, thereby regulating the hydrolysis and polymerization rate of the sol and ensuring the acquisition of Cr3C2 precursor particles, laying the foundation for the formation of a high-quality interface layer.

[0051] In some embodiments, step S4 is followed by drying at 110°C-130°C for 1.8-2.2 hours. This drying process removes residual solvent from the sol, allowing Cr3C2 nanoparticles to be initially fixed on the surface of WC-Co microparticles, forming a continuous pre-coating. This avoids problems such as insufficient solvent removal or nanoparticle agglomeration caused by improper temperature or time.

[0052] In some embodiments, the vacuum degree of the vacuum sintering furnace in S5 does not exceed 8 × 10⁻⁶. -3 The vacuum level is verified by oxygen partial pressure measurement to ensure the suppression of oxidation reactions and to guarantee that the Co phase can fully diffuse and form a metallurgical bond with the matrix when it melts at 1150℃. At the same time, the economic feasibility of industrial implementation is taken into account, avoiding oxidation problems caused by excessively low vacuum or increased costs caused by excessively high vacuum.

[0053] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0054] Example 1

[0055] This embodiment provides a high-chromium polyhedral abrasive media, which is prepared through the following steps: S1. High-carbon ferrochrome, ferromolybdenum, and scrap steel are added to a medium-frequency induction furnace for smelting in a certain proportion. When the temperature of the molten steel rises to 1520-1550℃, a carbon raiser is added to adjust the carbon content. After refining, the mixture is allowed to stand for 5-8 minutes to obtain high-chromium molten iron. Its components by weight percentage include: Cr 16%, C 2.8%, Mo 1.5%, Si≤0.8%, Mn≤1.0%, S≤0.05%, P≤0.05%, with the balance being Fe. The high-chromium molten iron is poured into a cubic metal mold preheated to 330℃. After solidification, it is demolded to obtain a billet. S2. Select 88% WC-12% Co microparticles (average particle size 0.080±0.005 mm, particle size distribution D90≤0.10 mm), add 15% by volume to an ethanol-acetone mixed solvent (volume ratio 3:1), add 0.5% polyvinylpyrrolidone (molecular weight 40000) as a dispersant, and then add 0.5% triethanolamine to adjust the pH to 7.0±0.1; the suspension is ultrasonically dispersed for 30 minutes to obtain a WC-Co suspension; Microfluidic injection system setup: Employs a five-axis linkage microfluidic nozzle (positioning accuracy ±10 micrometers), with an inner diameter of 0.1 mm. Based on the concentration gradient function C(x) = C0·e -0.2x Let the flow velocity function be v(x) = v0·e -0.2x (v0 = 0.12 ml / s). The nozzle moves layer by layer along the vertex normal in steps of 0.05 mm, and the residence time of each layer is calculated as t = V / v(x) (V is the required suspension volume for a single layer). In actual operation, starting from the vertex center (x=0), the flow rate is 0.12 ml / s at x=0, 0.096 ml / s at x=0.25 mm, and 0.072 ml / s at x=0.5 mm. The total injection volume for each billet vertex region is 0.85 ml, and the injection process is carried out under nitrogen protection with humidity ≤30%.

[0056] S3. Place the coated mold in a centrifuge and centrifuge at 3000 rpm for 5 minutes; S4. Dissolve Cr(NO3)3·9H2O and citric acid in deionized water at a molar ratio of 1:2, add 0.1% polyethylene glycol (molecular weight 2000) as a stabilizer, and stir in a water bath at 60°C for 4 hours to obtain Cr3C2 sol; Cr3C2 sol was sprayed using an air atomizing spray gun with a spray gun pressure of 0.40±0.02 MPa and a spraying distance of 150±5 mm. During the spraying process, the mold rotated at a speed of 10 rpm. After spraying, a pre-coating layer with a thickness of 0.035±0.005 mm was formed. It was then dried in an oven at 120±5℃ for 2.0 hours. S5. Place the mold in a vacuum sintering furnace and evacuate to a vacuum level of 5×1 3 Pa; sinter according to the following heating program: 1.8℃ / min to 300℃ (removal of organic solvent); 5.0℃ / min to 600℃ (interfacial reaction stage); 5.0℃ / min to 1150℃ (holding for 2 hours); quench in 105℃ hot oil for 12 minutes; immediately after quenching, transfer to a tempering furnace, heat to 320℃ at 5℃ / min and hold for 6-8 hours, remove from the furnace and air cool to obtain high-chromium polyhedral grinding media.

[0057] Example 2

[0058] The difference between this embodiment and Example 1 is that the chemical composition of the high-chromium matrix, by mass percentage, is 17% Cr, 2.6% C, 1.8% Mo, and the balance is Fe; The WC-Co microparticles consist of 87% WC and 13% Co. The flow rate of the microfluidic nozzle is v0 = 0.13 ml / s; The remaining raw materials and preparation process are the same as in Example 1.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that an octahedral mold (side length 80 mm) is used. The chemical composition of the high-chromium matrix, by mass percentage, is Cr 15.5%, C 2.9%, Mo 1.2%, with the balance being Fe; WC-Co particles have a diameter of 0.060 ± 0.005 mm; The volume fraction of particles in the suspension was 14%. The remaining raw materials and preparation process are the same as in Example 1.

[0061] Example 4

[0062] The difference between this embodiment and Embodiment 1 is that the side length of the medium is 45 mm (less than 50 mm). The radius of the vertex region has been adjusted to 0.3 mm; The chemical composition of the high-chromium matrix, by mass percentage, is Cr 21%, C 2.7%, Mo 1.6%, with the balance being Fe; In the WC-Co microfluidic nozzle with a Co content of 10%, the maximum x value is 0.3 mm, and v0 = 0.11 ml / s. The remaining processes are performed on a scaled-down basis.

[0063] Example 5

[0064] The difference between this embodiment and Example 1 is that 0.5% V is added to the high-chromium matrix; Add 1% TiC to WC-Co particles; The centrifugation phase is divided into two parts: 2800 rpm for the first 3 minutes and 3200 rpm for the next 3 minutes; Nitrogen protection was added during the sintering and heat preservation stage (flow rate 2 L / min); The remaining raw materials and preparation process are the same as in Example 1.

[0065] Example 6

[0066] The difference between this embodiment and Embodiment 1 is that a dodecahedral mold (90 mm on each side) is used. The radius of the vertex region has been increased to 0.6 mm; Add 0.2% graphene (mass fraction) to the suspension; The sintering rate decreased to 4.0℃ / min during the heating stage to 1150℃; The remaining raw materials and preparation process are the same as in Example 1.

[0067] Example 7

[0068] The difference between this embodiment and Example 1 is that the ratio of citric acid in the Cr3C2 sol is adjusted to 1:1.8; The remaining raw materials and preparation process are the same as in Example 1.

[0069] Example 8

[0070] The difference between this embodiment and Embodiment 1 is that the radius of the vertex region is reduced to 0.4 mm; WC-Co particles have a diameter of 0.090 ± 0.005 mm; Centrifugation speed: 3200 rpm; time: 4.5 minutes; The quenching temperature has been changed to 110℃, and the tempering temperature has been changed to 290℃. The remaining raw materials and preparation process are the same as in Example 1.

[0071] Example 9

[0072] The difference between this embodiment and Example 1 is that the chemical composition of the high-chromium matrix, by mass percentage, is 22% Cr, 2.7% C, 1.6% Mo, and the balance is Fe; The Co content of WC-Co particles decreased to 8%; The pH of the suspension was adjusted to 6.5; The sintering holding time is extended to 2.2 hours; The remaining raw materials and preparation process are the same as in Example 1.

[0073] Example 10

[0074] The difference between this embodiment and Embodiment 1 is that a composite gradient design is adopted: C(x) = 1250·e in the 0-0.2 mm segment. -0.25x For the 0.2-0.5 mm segment, C(x) = 800·e -0.15x Thickness gradient of Cr3C2 layer: 0.05 mm at the vertex center, 0.02 mm at the boundary; The centrifugation process increases radial vibration (frequency 20 Hz); The remaining raw materials and preparation process are the same as in Example 1.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that it uses a conventional high-chromium cast iron cube (100 mm side length, chemical composition by mass percentage: Cr 16%, C 2.8%, Mo 1.5%, balance Fe), with no vertex reinforcement structure, and is heat-treated after integral casting. The specific implementation steps are as follows: The high-chromium alloy was melted and poured into a cubic mold; it was held at 1000°C for 2 hours and then air-cooled; it was then tempered at 500°C for 2 hours; the remaining raw materials and preparation process were the same as in Example 1.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that the Cr3C2 transition layer is omitted, and WC-Co particles are directly sintered with the matrix. The specific implementation steps are as follows: Steps S1-S3 are the same as in Example 1; Step S4 is omitted, and sintering is performed directly in step S5. The remaining raw materials and preparation process are the same as in Example 1.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that WC-Co microparticles were uniformly distributed throughout the entire apex spherical cap (concentration was kept constant at 1200 particles / mm²). 3 The specific implementation steps are as follows: Step S1 is the same as in Example 1; In step S2, the nozzle flow rate is kept constant at 0.12 ml / s (without gradient control); Steps S3-S5 are the same as in Example 1; The remaining raw materials and preparation process are the same as in Example 1.

[0081] Comparative Example 4

[0082] The difference between this comparative example and Example 1 is that Cr2O3 is used instead of Cr3C2 in the transition interface layer. The specific implementation steps are as follows: Steps S1-S3 are the same as in Example 1; In step S4, Cr2O3 sol (prepared from Cr(NO3)3·9H2O and urea) is sprayed. Step S5 is the same as in Example 1; The remaining raw materials and preparation process are the same as in Example 1.

[0083] Comparative Example 5

[0084] The difference between this comparative example and Example 1 is that the particle concentration gradient function is changed to a linear distribution C(x) = 1200-1960x. The specific implementation steps are as follows: Step S1 is the same as in Example 1; in Step S2, the nozzle flow rate is controlled according to the linear function v(x) = 0.12-0.24x. Steps S3-S5 are the same as in Example 1; The remaining raw materials and preparation process are the same as in Example 1.

[0085] Comparative Example 6

[0086] The difference between this comparative example and Example 1 is that the diameter of the WC-Co particles is 0.15 mm (exceeding the upper limit of 0.1 mm).

[0087] The remaining raw materials and preparation process are the same as in Example 1.

[0088] Performance testing

[0089] The grinding media obtained from the various embodiments and comparative examples of this application were subjected to the following tests, the specific items of which are as follows: 1. Wear resistance test: A Φ500×500 laboratory ball mill was used, with the following parameters set: rotation speed: 28±0.5 rpm; material: quartz sand (particle size 2-5 mm, SiO2≥99.5%); filling rate: 35±1%; running time: 100 hours; lubrication conditions: dry grinding; and mass loss rate was tested. 2. Interface bond strength test: YB / T 5349-2014 "Test Methods for Bending Mechanical Properties of Metallic Materials"; 3. Fracture toughness test: GB / T 23806-2009 "Test method for fracture toughness of fine ceramics - single-sided pre-cracked beam (SEPB) method"; 4. Hardness Test: GB / T 230.1-2018 "Metallic Materials - Rockwell Hardness Test - Part 1: Test Method" The results are shown in Table 1: Table 1

[0090] As shown in Table 1, the test results demonstrate that the high-chromium polyhedral grinding media prepared in this embodiment significantly outperforms the comparative example in all key performance indicators. The gradient-reinforced microparticle composite structure employed in this embodiment, through its exponentially decaying concentration distribution, allows impact energy to dissipate layer by layer within the apex region, effectively avoiding the superposition effect of stress wave reflection and significantly improving the wear resistance of the media. This concentration distribution design closely matches the actual stress field distribution, causing a reasonable deflection of the crack propagation path, thereby inhibiting rapid crack propagation in high-stress regions and significantly extending the service life of the grinding media.

[0091] The key innovation of this invention lies in the design of the Cr3C2 nano-transition interface layer, which forms an effective stress buffer region between the WC-Co particles and the high-chromium matrix. The performance of Comparative Examples 2 and 4 showed a significant decline, verifying the shortcomings of traditional interface designs or schemes without an interface layer. The thermal expansion coefficient of Cr3C2 material lies between that of WC-Co and the high-chromium matrix, effectively buffering thermal expansion mismatch. During sintering, it undergoes an interfacial reaction with the matrix to form a stable metallurgical bond, fundamentally solving the problem of interfacial delamination failure. This interface design ensures the long-term stability of the interface under dynamic impact loads and significantly improves the interfacial bonding strength.

[0092] The synergistic application of microfluidic injection and centrifugal positioning technologies enabled precise control of the particle concentration gradient, which is the key reason why the performance of this example is superior to Comparative Example 5 (linear gradient) and Comparative Example 3 (uniform distribution). Flow rate function v(x) = ·e -0.2x With the concentration gradient function C(x) = C0·e -0.2x The precise mapping ensures the reasonable spatial distribution of particles and avoids secondary stress concentration caused by sudden changes in concentration.

[0093] This invention also demonstrates good parameter adaptability and process compatibility. Example 4, after parameter adjustments for small-sized media, still maintains excellent performance, proving that the invention can be optimized for parameters of different media specifications. The composite gradient design in Example 10 further improves performance, indicating that the invention has room for continuous optimization. While maintaining the hardness of the high-chromium matrix, all embodiments significantly improve impact resistance and fracture toughness, achieving a synergistic improvement in wear resistance and toughness, providing a systematic solution to the technical challenge of easy fracture at the vertices of high-chromium polyhedral grinding media.

[0094] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A high-chromium polyhedral abrasive media, characterized in that, The grinding media is a polyhedral structure with a Cr content of not less than 12%, and its vertex region has a gradient-reinforced microparticle composite structure; the vertex region is defined as a spherical cap with a radius r not exceeding 0.5 mm centered at the vertex; the gradient-reinforced microparticle composite structure includes a WC-Co microparticle array, the concentration of which decreases exponentially from the vertex center towards the edge direction, and the concentration function is C(x) = C0·e -0.2x Where C0 is the concentration at the vertex center and x is the radial distance from the vertex center; the WC-Co particles have a diameter of 0.05-0.1 mm and are covered with a transition interface layer; the transition interface layer is composed of Cr3C2 nanoparticles and has a thickness of 0.02-0.05 mm.

2. The high-chromium polyhedral abrasive media according to claim 1, characterized in that, The concentration C0 at the apex center is 1100-1300 particles / mm. 3 .

3. The high-chromium polyhedral abrasive media according to claim 1, characterized in that, At a radial distance x = 0.5 mm at the edge boundary, the concentration is 220-260 particles / mm. 3 .

4. The high-chromium polyhedral abrasive media according to claim 1, characterized in that, The WC-Co particles contain 85%-90% WC and 10%-15% Co binder phase.

5. The high-chromium polyhedral abrasive media according to claim 1, characterized in that, The Cr3C2 nanoparticles in the transition interface layer have a particle size of 40-60 nanometers.

6. The high-chromium polyhedral abrasive media according to claim 1, characterized in that, The polyhedron is a cube or octahedron with a side length of 50-150 mm.

7. A method for preparing a high-chromium polyhedral abrasive media, characterized in that, The preparation of the high-chromium polyhedral grinding media according to any one of claims 1-6 includes the following steps: S1. High-carbon ferrochrome, ferromolybdenum and scrap steel are added to a medium-frequency induction furnace for smelting in proportion. When the temperature of the molten steel rises to 1520-1550℃, a carbon raiser is added to adjust the carbon content. After refining, the mixture is allowed to stand for 5-8 minutes to obtain high-chromium molten iron. The high-chromium molten iron is poured into a polyhedral metal mold preheated to 300-350℃. After solidification, the mold is demolded to obtain the billet. S2. A WC-Co suspension is injected into the apex region of the cast billet through a microfluidic nozzle. The volume percentage of WC-Co particles in the suspension is 12%-18%, and the volume ratio of ethanol to acetone in the ethanol-acetone mixed solvent is (2.5-3.5):

1. The nozzle flow rate is expressed as a function v(x)=v0·e -0.2x Control, where v0 = 0.10 - 0.14 ml / s, and x is the radial distance from the center of the vertex; S3. Place the mold in a centrifuge and centrifuge at 2800-3200 rpm for 4-6 minutes; S4. Spray Cr3C2 sol with a spray gun pressure of 0.35-0.45 MPa and a spraying distance of 140-160 mm to form a pre-coating layer with a thickness of 0.02-0.05 mm; S5. Place the mold in a vacuum sintering furnace and sinter according to the following procedure: The temperature was increased from room temperature to 300℃ at a rate of 1.5-2.5℃ / min. The temperature was increased from 300℃ to 1150℃ at a rate of 4.5-5.5℃ / min. Keep warm at 1150℃ for 1.8-2.2 hours; Immerse in hot oil at 100-110℃ for quenching for 10-15 minutes; immediately after quenching, transfer to a tempering furnace and heat to 290-330℃ at 4.5-5.5℃ / min, hold for 6-8 hours, remove from the furnace and air cool to obtain high-chromium polyhedral grinding media.

8. The method for preparing a high-chromium polyhedral grinding media according to claim 7, characterized in that, The high-chromium molten iron in S1 comprises, by weight percentage: Cr 15.0%-18.0%, C 2.5%-3.0%, Mo 1.0%-2.0%, Si≤0.8%, Mn≤1.0%, S≤0.05%, P≤0.05%, with the balance being Fe.

9. The method for preparing a high-chromium polyhedral grinding media according to claim 7, characterized in that, The WC-Co suspension in S2 contains 0.4%-0.6% polyvinylpyrrolidone dispersant; The positioning accuracy of the microfluidic nozzle in S2 is ±10μm; In the S2 mixture, 0.3%-0.7% triethanolamine is added to adjust the pH to 6.5-7.

5.

10. The method for preparing a high-chromium polyhedral grinding media according to claim 7, characterized in that, The Cr3C2 sol in S4 is prepared by mixing Cr(NO3)3·9H2O and citric acid in a molar ratio of 1:(1.8-2.2); after S4, the mixture is dried at 110℃-130℃ for 1.8-2.2 hours. The vacuum degree of the vacuum sintering furnace in S5 does not exceed 8×10⁻⁶. -3 Pa.

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