A method for producing modified high-carbon ferrochrome

Abstract

The application discloses a preparation method of modified high-carbon ferrochrome and belongs to the technical field of nano modification. The method comprises the following steps: ultrasonic dispersion and heating stirring of Fe-Cr alloy powder, nano carbon material, nitrogen source precursor and nano ceramic particles in an alcohol solvent, sintering, hydrofluoric acid etching to obtain core-shell particles; mechanical stirring of the core-shell particles into a high-carbon ferrochrome matrix, followed by addition of graphene powder for smelting to obtain a modified melt; pouring of the modified melt and directional solidification to obtain a modified casting; immersion of the casting into a hexamethylenetetramine ethanol solution, pyrolysis treatment and laser remelting to form a surface wear-resistant layer; quenching and tempering treatment of the casting to obtain a modified casting with a surface nanocrystalline structure. The application remarkably improves the comprehensive performance of the high-carbon ferrochrome through nano heterogeneous nucleation, graphene reinforcement and surface nanocrystallization synergistic modification.

Description

Technical Field

[0001] This invention belongs to the field of nanotechnology, specifically, it relates to a method for preparing modified high-carbon ferrochrome. Background Technology

[0002] High-carbon ferrochrome is a ferroalloy made by mixing elements such as iron, chromium, and carbon in specific proportions. Its carbon content is typically controlled within the range of 4.0-6.0 wt%, chromium content is 60-70 wt%, and the balance is iron. This material is mainly used as an indispensable alloying additive in the production of stainless steel and special steels. During the steelmaking process, it is added to molten steel according to the steel grade composition requirements, significantly improving the hardenability, wear resistance, hardness, and corrosion resistance of the steel, thereby producing a variety of high-strength, corrosion-resistant, wear-resistant, high-temperature resistant, and oxidation-resistant special steels. In downstream applications, high-carbon ferrochrome is widely used in the manufacture of ball bearing steel, tool steel, high-speed steel, and various wear-resistant cast iron parts. It is a key raw material for core components in large-scale industrial manufacturing fields such as coal mining, oil extraction, power generation, shipbuilding, textiles, and steel.

[0003] However, the performance of traditional high-carbon ferrochrome materials under extreme working conditions remains significantly limited, making it difficult to meet the increasingly stringent requirements of modern industry for the comprehensive performance of materials. Firstly, the inherent contradiction between hardness and toughness in high-carbon ferrochrome has long constrained its application expansion. Materials science research shows that there is a complex correlation between hardness and toughness, not a simple inverse relationship. However, when increasing the hardness of traditional high-carbon ferrochrome by increasing the carbon and chromium content, it often leads to a sharp decrease in impact toughness. The hardness range of standard high-carbon ferrochrome is typically 800-900 HV, but its impact toughness is generally below 4 J / cm². 2 This "hard and brittle" characteristic makes the material prone to brittle fracture under impact loads, severely shortening the service life of equipment. Secondly, the wear resistance of traditional high-carbon ferrochrome still has significant room for improvement. Under heavy-load wear conditions in mining machinery, cement equipment, and crushing equipment, the surface wear rate of the material is typically as high as 0.5-0.8 mg / cm². 2 This leads to frequent replacements of key components, resulting in significant economic and efficiency losses. Third, high-carbon ferrochrome has inherent structural defects; during solidification, it easily forms coarse network carbides. These brittle phases are continuously distributed at grain boundaries, becoming channels for crack initiation and propagation, further deteriorating the material's overall mechanical properties.

[0004] To address the aforementioned issues, researchers both domestically and internationally have conducted extensive research on modification technologies, primarily focusing on traditional processes such as alloying strengthening, modification treatment, plastic deformation, and heat treatment optimization. Alloying strengthening, by adding alloying elements such as Mo, Ni, V, Ti, and Nb, can refine grains and improve carbide morphology to some extent. However, excessive addition of alloying elements not only significantly increases material costs but may also induce compositional segregation and the precipitation of new brittle phases. Modification treatment technology, by adding rare earth and alkali metal elements to alter the thermodynamic conditions of carbide growth, optimizes carbide morphology and refines size. However, the absorption rate of the modifier is unstable, resulting in poor process repeatability. Plastic deformation methods, through high-temperature forging or rolling, break up and uniformly distribute carbides, improving impact toughness. However, this is extremely difficult to implement on large castings and is energy-intensive. Heat treatment processes, through high-temperature solution treatment and tempering, can isolate and round the edges of network carbides, but the microstructure improvement effect is limited by the solubility of carbides. Furthermore, while directional solidification technology can control the directional growth of carbides and improve material anisotropy, it requires huge equipment investment, involves complex process control, and is only applicable to castings of specific shapes. Although these traditional modification methods have achieved some success, they generally suffer from problems such as narrow process windows, high costs, limited effects, or difficulty in large-scale application, failing to fundamentally solve the hardness-toughness inversion problem of high-carbon ferrochrome.

[0005] In recent years, with the rapid development of nanotechnology, nanomaterials have provided a new approach to breaking through the performance limits of traditional materials in metal matrix composites. Carbon nanomaterials (such as carbon nanotubes and graphene) have become ideal reinforcing phases for metal matrix composites due to their ultra-high strength, excellent toughness, and huge specific surface area. Studies have shown that the main strengthening mechanisms of carbon nanomaterials in metal matrices include load transfer strengthening, grain refinement strengthening, Orowan strengthening, and thermal residual stress strengthening, among which load transfer and grain refinement strengthening contribute the most significantly. For example, adding a small amount of carbon nanotubes or graphene to magnesium-based composites can increase the yield strength by 78% and the tensile strength by 48%. In titanium-based composites, interface optimization of carbon nanomaterials can simultaneously improve strength and plasticity. However, the application of carbon nanomaterials in iron-based alloys faces severe challenges: carbon nanomaterials are prone to react with the iron matrix at high temperatures, leading to structural damage; insufficient interfacial bonding strength results in low load transfer efficiency; and nanomaterials are difficult to disperse in molten metal and are prone to agglomeration. Existing research has focused on low-melting-point non-ferrous metal matrices. For high-melting-point, high-carbon-content ferroalloy systems such as high-carbon ferrochrome, nano-reinforcement technology has not yet formed a systematic solution.

[0006] Surface nanocrystallization, as another cutting-edge modification technique, prepares nanocrystalline structures on the surface of materials through methods such as intense plastic deformation, high-energy shot peening, or laser shock, simultaneously improving surface hardness, wear resistance, and corrosion resistance. The nanocrystalline surface possesses numerous highly active dislocations and grain boundaries, promoting the formation of a protective passivation film that is thicker, denser, more uniform, and has fewer defects. In medical metal materials such as stainless steel and titanium alloys, surface nanocrystallization treatment can increase corrosion potential, reduce corrosion current density, and improve wear resistance by 2-3 times. However, existing surface nanocrystallization technologies are mostly applicable to sheet metal or simple-shaped parts, and suffer from problems such as uneven treatment, weak bonding between the nanolayer and the substrate, and high processing costs for complex castings like high-carbon ferrochrome. Furthermore, single surface modification cannot improve the core toughness of the material, making it difficult to achieve a synergistic improvement in overall performance.

[0007] In summary, although some progress has been made in the research on high-carbon ferrochrome modification, the following core issues still urgently need to be addressed: First, there is a lack of a systematic solution that can simultaneously achieve the synergistic effect of "high hardness, high toughness, and high wear resistance"; second, the structural stability and interfacial bonding mechanism of nano-reinforcing phases in high-temperature iron-based alloys are still unclear; third, surface modification technology and matrix microstructure control have not been effectively coupled, making it difficult to exert a synergistic strengthening effect; fourth, traditional processes lack the ability to control the multi-scale microstructure of materials, making it impossible to construct a gradient functional structure from the matrix to the surface. Therefore, developing a new high-carbon ferrochrome modification technology that can break through traditional performance limits, achieve multi-scale structural control, and possess both excellent comprehensive performance and good process adaptability is of great strategic significance and broad application prospects for promoting my country's high-end equipment manufacturing and enhancing the self-sufficiency of key components. Summary of the Invention

[0008] Compared to existing technologies, this invention systematically solves key technical problems such as the inverted hardness-toughness, insufficient wear resistance, and coarse microstructure of high-carbon ferrochrome by constructing a multi-scale synergistic modification system of "nanocore-shell intermediate alloy - graphene melt reinforcement - surface nanocrystallization," achieving a breakthrough improvement in material properties. This invention innovatively uses a nanocore-shell structure as the heterogeneous nucleation core. Through multi-component composites of Fe-Cr alloy powder with nano-carbon materials, nitrogen source precursors, and nano-ceramic particles, core-shell particles with precisely controllable shell thickness (10-20 nm) are prepared via sintering-etching processes. This structure possesses both structural stability and interfacial activity in high-temperature melts, effectively avoiding the agglomeration and burn-off problems of the nano-reinforcing phase. It achieves uniform dispersion and efficient load transfer of nano-carbon materials in the iron matrix, fundamentally solving the bottleneck of weak interfacial bonding and poor reinforcement effect in traditional nano-reinforced ferroalloys. In the preparation of nano-carbon materials, this invention makes a breakthrough by using coconut shell powder as raw material. Through an integrated process of potassium hydroxide activation, hexamethylenetetramine nitrogen pre-doping, supercritical carbon dioxide-assisted exfoliation, and vacuum calcination, nano-carbon materials with a particle size of 20-50 nm and a specific surface area of ​​150-200 nm are prepared. 2 This invention presents a specialized nano-carbon material with a density of / g. Rich in nitrogen-active sites, this material exhibits excellent wettability with the iron matrix, significantly enhancing the interfacial bonding strength between the reinforcing phase and the matrix. Addressing the structural stability challenge of graphene in high-temperature molten iron, this invention develops a chemical modification technique based on graphene oxide. Through the synergistic grafting reaction of dicyclohexylcarbodiimide, 1-hydroxybenzotriazole, and 2-aminothiazole, stable functional groups are introduced onto the graphene surface, effectively suppressing structural damage and interfacial reactions at high temperatures, ensuring the integrity of the graphene and the full realization of its strengthening effect during the melting process. This invention organically couples melt internal modification, directional solidification microstructure control, and surface nanocrystallization treatment, forming a gradient functional structure from the matrix to the surface. Directional solidification technology optimizes the carbide distribution morphology, and the surface hexamethylenetetramine pyrolysis-laser remelting composite treatment constructs a 10-20μm thick nanocrystalline wear-resistant layer, achieving a synergistic improvement in matrix toughness and surface hardness. By precisely controlling the laser power (500-1500W), scanning speed (5-15mm / s), and spot diameter (1-3mm), the metallurgical bonding between the nanolayer and the substrate is ensured, avoiding the problems of insufficient bonding strength and easy peeling in traditional surface modification techniques. This invention further refines the substrate microstructure and stabilizes the surface nanocrystalline structure by systematically optimizing heat treatment process parameters, achieving a precise match between quenching temperatures of 950-1050℃ and tempering temperatures of 200-400℃. Ultimately, this results in a surface hardness >1000HV and a wear rate ≤0.3mg / cm². 2 Impact toughness ≥5J / cm 2 Its superior overall performance, with all indicators significantly outperforming existing technologies.

[0009] The present invention adopts the following technical solution: a method for preparing modified high-carbon ferrochrome, which, by weight, includes the following steps: (1) preparation of nano-core-shell intermediate alloy: 60-100 parts of Fe-Cr alloy powder, 5-15 parts of nano-carbon material, 3-10 parts of nitrogen source precursor, and 2-8 parts of nano-ceramic particles are ultrasonically dispersed and heated and stirred in 80-120 parts of alcohol solvent to obtain a slurry. After sintering, a nano-shell structure is obtained. Then, the core-shell particles are obtained by etching with hydrofluoric acid solution; (2) preparation of modified melt: first, 20-50 parts of the core-shell particles obtained in step (1) are added to 1000-1500 parts of high-carbon ferrochrome matrix at 1600-1650℃, and mechanical stirring is performed to obtain a dispersed nano-heterogeneous structure. (2) Core, then add 20-30 parts of graphene powder and melt to obtain a modified melt; (3) Casting forming treatment: pour and directional solidify the modified melt obtained in step (2) to obtain a modified casting; (4) Surface modification treatment: immerse the modified casting obtained in step (3) in an ethanol solution of 5-15wt% hexamethylenetetramine (CAS No.: 100-97-0), then pyrolyze to form a nano-thin layer with a thickness of 10-20μm, and then perform laser remelting to obtain a modified casting with a surface wear-resistant layer; (5) Heat treatment optimization: quench and temper the modified casting with a surface wear-resistant layer obtained in step (4) to form a modified casting with a surface nanocrystalline structure.

[0010] Preferably, the parameters of the Fe-Cr alloy powder in step (1) are as follows: particle size 10-50 μm, chromium content 60-70 wt%, carbon content 4.0-6.0 wt%, and the balance being iron; the preparation method of the nano-carbon material in step (1) is as follows: take 80-100 parts of coconut shell powder with a particle size ≤100 μm, soak it in 20 wt% potassium hydroxide solution for 24 h, wash it until neutral, vacuum dry it at 110℃ for 12 h to obtain an activated carbon source, and add an equal mass of 5 wt% hexamethylenetetramine solution (HMTA, CAS) to the activated carbon source. (No.: 100-97-0) The N-predoped carbon source was obtained by ball milling ZrO2 balls at 300 rpm for 2 h. Then, triethanolamine with a mass of 3-5 times that of the N-predoped carbon source was added and placed in a high-pressure reactor. Liquid carbon dioxide was injected to 15 MPa, the temperature was set to 45℃ and the mixture was stirred at 300 rpm for 2 h. After decompression, nano-carbon materials were obtained and finally calcined at 400℃ for 2 h. The nano-carbon materials obtained in step (1) had a particle size of 20-50 nm and a specific surface area of ​​150-200 m². 2 / g; the nitrogen source precursor in step (1) is hexamethylenetetramine (CAS No.: 100-97-0), melamine (CAS No.: 108-78-1), dicyandiamide (CAS No.: 461-58-5) or polyaniline (CAS No.: 25233-30-1); the nano-ceramic particles in step (1) are selected from nano-silica (CAS No.: 7631-86-9) or nano-alumina (CAS No.: 1344-28-1), with a particle size of 30-50nm; the alcohol solvent in step (1) is anhydrous ethanol or isopropanol; the concentration of hydrofluoric acid solution in step (1) is 0.5-2mol / L.

[0011] Preferably, in step (1), the ultrasonic dispersion power is 200-600W, the frequency is 20-60kHz, and the time is 20-45min; in step (1), the heating and stirring temperature is 60-80℃, and the heating and stirring speed is 100-200rpm; the sintering parameters in step (1) are as follows: the temperature is raised to 5℃ in an argon inert gas atmosphere, and then sintered at 500-800℃ for 2-6h; the etching time in step (1) is 20-30min, and the shell thickness of the core-shell particles after etching is 10-20nm.

[0012] Preferably, the grade of the high carbon ferrochrome matrix in step (2) is FeCrHC64C4.0; the preparation method of graphene powder in step (2) is as follows: take graphene oxide and disperse it in N,N-dimethylformamide at 1 mg / mL, mix it to obtain a brownish-yellow suspension, then add dicyclohexylcarbodiimide (CAS No.: 538-75-0) and 1-hydroxybenzotriazole (CAS No.: 2592-95-2) to the suspension, the mass ratio of the three is (20-40): (1-2): (2-4), stir at 100 rpm for 2 h at room temperature to obtain a reaction solution, then add 2-4 times the mass of the reaction solution of 2-aminothiazole (CAS No.: 96-50-4), and in an oil bath at 80-90℃ for 12 h, after the reaction is completed, cool to room temperature, and vacuum dry at 60-80℃ for 12 h.

[0013] Preferably, the mechanical stirring parameters in step (2) are as follows: rotation speed 100-200 rpm, time 5-15 min; the melting equipment in step (2) is a medium frequency induction furnace, the melting power is 200 kW, and the melting time is 60 min.

[0014] Preferably, the pouring temperature in step (3) is 1450-1550℃; the parameters for directional solidification in step (3) are as follows: the pulling speed is 100-200μm / s, the solidification temperature gradient is 50℃ / cm, the solidification thickness is 5-15mm, and the molding sand is zircon sand.

[0015] Preferably, the ethanol solution in step (4) is anhydrous ethanol; the laser power of the laser remelting in step (4) is 500-1500W, the scanning speed is 5-15mm / s, and the spot diameter is 1-3mm.

[0016] Preferably, the immersion parameters in step (4) are as follows: vacuum degree 0.05-0.09MPa, temperature 60-80℃, time 30-60min; the pyrolysis treatment temperature in step (4) is 400℃, and the pyrolysis treatment time is 1-2h.

[0017] Preferably, in step (5), the quenching heating rate is 10℃ / min, the quenching temperature is 950-1050℃, and the quenching holding time is 3h; in step (5), the cooling rate before tempering is 50℃ / min, the tempering temperature is 200-400℃, and the tempering holding time is 2-6h.

[0018] Preferably, the modified casting with a surface nanocrystalline structure obtained in step (5) has the following parameters: surface hardness > 1000 HV, wear rate ≤ 0.3 mg / cm². 2 Impact toughness ≥5J / cm 2 .

[0019] Compared to existing technologies, this invention introduces a multi-scale synergistic modification system, achieving overall optimization of the matrix-interface-surface and significantly improving the comprehensive performance of high-carbon ferrochrome. Specific technical effects include the following key points: Breaking the hardness-toughness inversion: Through a coupling path of nano-core-shell intermediate alloy-graphene melt reinforcement-surface nanocrystallization, a gradient functional structure from the matrix to the surface is formed, significantly improving surface hardness while maintaining matrix toughness, solving the problem of brittleness and vulnerability of traditional high-carbon ferrochrome under high hardness conditions. Compared with existing single modification methods, the overall toughness improvement is more significant and the adaptability is stronger. Synergistic strengthening of surface and bulk phases: Under the combined effect of directional solidification and surface nanocrystallization, a 10-20 μm thick nanocrystalline wear-resistant layer is formed on the material surface, significantly improving wear resistance and surface hardness. Simultaneously, through the synergistic effect of matrix microstructure refinement and reinforcing phase distribution, overall fatigue resistance and impact toughness are improved. This coupling strategy overcomes the limitation of surface modification alone in improving core toughness. Enhanced stability of phase dispersion and interfacial bonding: Using a nano-core-shell structure as the heterogeneous nucleation core ensures uniform dispersion of the nano-reinforcing phase in the high-temperature melt and improves interfacial load transfer efficiency, reducing nanomaterial agglomeration and reaction losses at high temperatures, thereby significantly improving the toughening effect and wear resistance stability. Compared with traditional nano-reinforced ferroalloys, the interfacial bonding strength and thermal stability are reliably improved. Synergistic effect of advanced carbon materials and modified interfaces: Using chemically modified graphene / carbon materials and nano-carbon materials co-doped with highly active nitrogen sources achieves better wettability and interfacial bonding strength, enhances the load transfer capacity relative to the matrix, and improves the overall performance of high-temperature oxidation resistance and wear resistance. These modification strategies work together to significantly enhance the stability and continuous strengthening ability of the reinforcing phase in high-carbon ferrochrome. Process Coupling and Enhanced Process Controllability: By organically coupling melt internal modification, directional solidification microstructure control, and surface nanocrystallization treatment, a gradient structure from the matrix to the surface is established. Key process parameters such as welding / laser processing power, scanning speed, and quenching / tempering temperature are precisely controlled, enabling high-performance output under repeatable, large-scale production conditions. Compared to single-process methods, multi-process coupling provides a larger process window and better process robustness. Significantly Superior Overall Performance Compared to Existing Technologies: After gradient structure design and multi-scale modification, surface hardness exceeds 1000 HV, wear resistance is significantly improved, impact toughness and fatigue life are significantly enhanced, and various indicators achieve synergistic optimization, resulting in overall performance surpassing existing technologies. Compared to traditional single-process paths, performance improvements exhibit advantages in simultaneity and stability, making it suitable for key component applications in high-end equipment manufacturing. Attached Figure Description

[0020] Figure 1 This is a transmission electron microscope image of the core-shell particles prepared in Example 1 of this invention.

[0021] Figure 2This is the energy dispersive X-ray spectrum of Fe element in the core-shell particles prepared in Example 1 of this invention.

[0022] Figure 3 This is the energy dispersive X-ray spectrum of Cr element in the core-shell particles prepared in Example 1 of this invention.

[0023] Figure 4 This is the energy-dispersive X-ray spectrum of carbon element in the core-shell particles prepared in Example 1 of this invention.

[0024] Figure 5 This is the energy-dispersive X-ray spectrum of nitrogen element in the core-shell particles prepared in Example 1 of this invention. Detailed Implementation

[0025] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0026] Example 1.

[0027] The preparation method of modified high-carbon ferrochrome includes the following steps: (1) Preparation of nano-core-shell intermediate alloy: 80g of Fe-Cr alloy powder (particle size 30μm, chromium content 65wt%, carbon content 5.0wt%, balance iron), 10g of nano-carbon material (particle size 35nm, specific surface area 175m²) 2 / g, its preparation method is as follows: Take 90g of coconut shell powder with a particle size ≤100μm, soak it in 20wt% potassium hydroxide solution for 24h, wash until neutral, and vacuum dry at 110℃ for 12h to obtain activated carbon source. Add an equal mass of 5wt% hexamethylenetetramine solution (HMTA, CAS No.: 100-97-0) to the activated carbon source, and ball mill it at 300rpm for 2h using ZrO2 balls to obtain N-predoped carbon source. Then, add 4 times the mass of triethanolamine of N-predoped carbon source, place it in a high pressure vessel, inject liquid carbon dioxide to 15MPa, set the temperature to 45℃ and treat it with a stirring speed of 300rpm for 2h. After depressurization release, obtain nano-carbon material, and finally vacuum dry at 400℃. The following ingredients were prepared by ultrasonic dispersion (400W power, 40kHz frequency, 32min time) in 100g of anhydrous ethanol, followed by heating and stirring (70℃ temperature, 150rpm speed) to obtain a slurry. The slurry was then sintered (heating at 5℃ / min under an inert argon atmosphere, followed by sintering at 650℃ for 4h) to obtain a nanoshell structure. This structure was then etched for 25min using hydrofluoric acid solution (concentration 1.25mol / L) to obtain core-shell particles (shell thickness 15nm). The slurry was prepared as follows: (1.25mol / L calcination for 2h), 6.5g nitrogen source precursor (hexamethylenetetramine, CAS No.: 100-97-0), and 5g nano-ceramic particles (nano-silica, CAS No.: 7631-86-9, particle size 40nm). Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5As shown. (2) Preparation of modified melt: First, 35g of the core-shell particles obtained in step (1) were added to 1250g of high carbon ferrochrome matrix (grade FeCrHC64C4.0) at 1625℃ and mechanically stirred (150rpm, 10min) to obtain a dispersed nano-heterogeneous core. Then, 25g of graphene powder was added (the preparation method is: take graphene oxide and disperse it in N,N-dimethylformamide at 1mg / mL, mix well to obtain a brownish-yellow suspension, and then add dicyclohexylcarbodiimide (C) to the suspension. AS No.: 538-75-0) and 1-hydroxybenzotriazole (CAS No.: 2592-95-2), with a mass ratio of 30:1.5:3, were stirred at 100 rpm for 2 h at room temperature to obtain a reaction solution. Then, 2-aminothiazole (CAS No.: 96-50-4) with a mass of 3 times that of the reaction solution was added. The mixture was then heated in an oil bath at 85℃ for 12 h. After the reaction was completed, the mixture was cooled to room temperature, dried under vacuum at 70℃ for 12 h, and then smelted (using a medium-frequency induction furnace with a power of 200 kW and a time of 60 min) to obtain a modified melt. (3) Casting and forming treatment: The modified melt obtained in step (2) was poured (temperature 1500℃) and directional solidified (pulling speed 150 μm / s, solidification temperature gradient of 50℃ / cm, solidification thickness 10 mm, and zircon sand) to obtain a modified casting. (4) Surface modification treatment: The modified casting obtained in step (3) is immersed in an ethanol solution (anhydrous ethanol) of 10wt% hexamethylenetetramine (CAS No.: 100-97-0) (vacuum degree 0.07MPa, temperature 70℃, time 45min), followed by pyrolysis treatment (temperature 400℃, time 1.5h) to form a nano-thin layer with a thickness of 15μm. Then, laser remelting treatment is performed (laser power 1000W, scanning speed 10mm / s, spot diameter 2mm) to obtain a modified casting with a surface wear-resistant layer. (5) Heat treatment optimization: The modified casting with a surface wear-resistant layer obtained in step (4) is quenched (heating rate 10℃ / min, temperature 1000℃, holding time 3h) and tempered (cooling rate before tempering 50℃ / min, tempering temperature 300℃, holding time 4h) to form a modified casting with a surface nanocrystalline structure. The parameters of the obtained modified casting are: surface hardness 1050 HV, wear rate 0.25 mg / cm². 2 Impact toughness 6J / cm 2 .

[0028] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progression of the steps, with each table reflecting different parameter values ​​for the examples / comparative examples, covering all endpoint and intermediate values. Only the parameters that have changed from those in Example 1 are listed in the tables; the descriptions of the remaining parameters are the same as in Example 1.

[0029] Table 1: Preparation parameters of step (1) nano-core-shell intermediate alloy (Fe-Cr alloy powder, nano-carbon material, nitrogen source precursor, nano-ceramic particles, alcohol solvent)

[0030]

[0031] Table 2: Step (1) Preparation parameters of nano-core-shell intermediate alloy (ultrasonic dispersion, heating and stirring, sintering, etching, hydrofluoric acid concentration)

[0032]

[0033] Table 3: Comparative parameters for step (1) (adjusted based on Example 1)

[0034]

[0035] Table 4: Preparation parameters of the modified melt in step (2) (high carbon ferrochrome matrix, core-shell particles, graphene powder)

[0036]

[0037] Table 5: Step (2) Preparation Parameters of Modified Melt II (Temperature, Mechanical Stirring, Melting)

[0038]

[0039] Table 6: Step (2) Comparative parameters (adjusted based on Example 1)

[0040]

[0041] Table 7: Casting and forming parameters for step (3)

[0042]

[0043] Table 8: Step (3) Comparative parameters (adjusted based on Example 1)

[0044]

[0045] Table 9: Parameters for surface modification in step (4) (concentration of hexamethylenetetramine, immersion, pyrolysis)

[0046]

[0047] Table 10: Step (4) Surface modification parameters 2 (laser remelting)

[0048]

[0049] Table 11: Step (4) Comparative parameters (adjusted based on Example 1)

[0050]

[0051] Table 12: Optimization parameters for heat treatment in step (5)

[0052]

[0053] Table 13: Step (5) Comparative parameters (adjusted based on Example 1)

[0054]

[0055] To verify the performance of the modified high-carbon ferrochrome described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included surface hardness, wear rate, and impact toughness. The test methods are as follows: Surface hardness test: Measured using a Vickers hardness tester (model: HV-1000), with a load of 500g and a loading time of 10s. Wear rate test: According to GB / T3960-2016 standard, a friction and wear testing machine (model: MM-200) was used, with a load of 200N, a rotation speed of 200r / min, and a time of 30min. The wear rate (mg / cm²) was calculated. 2 Impact toughness test: According to GB / T229-2007 standard, a Charpy impact testing machine (model: JB-300B) was used, with sample size 10mm×10mm×55mm. The impact toughness (J / cm²) was calculated. 2 ).

[0056] Table 14: Performance Test Results

[0057]

[0058] Table 15: Performance Test Results II

[0059]

[0060] The test results show that the surface hardness of the products in the examples ranges from 1002.7 to 1105.9 HV, and the wear rate ranges from 0.21 to 0.29 mg / cm². 2 Impact toughness is 5.1-7.4 J / cm. 2 The original sample exhibited excellent performance; however, the comparative sample showed a significant decrease in performance due to missing components or parameter deviations (e.g., hardness decreased to 795.6-850.9 HV, and wear rate increased to 0.45-0.53 mg / cm²). 2 This demonstrates the superiority of the preparation method of the present invention.

[0061] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A method for preparing modified high-carbon ferrochrome, characterized in that: The following steps are included by weight: (1) Preparation of nano-core-shell intermediate alloy: 60-100 parts of Fe-Cr alloy powder, 5-15 parts of nano-carbon material, 3-10 parts of nitrogen source precursor, and 2-8 parts of nano-ceramic particles are ultrasonically dispersed and heated and stirred in 80-120 parts of alcohol solvent to obtain a slurry. After sintering, a nano-shell structure is obtained. Then, the core-shell particles are obtained by etching with hydrofluoric acid solution. The parameters of Fe-Cr alloy powder are as follows: particle size 10-50μm, chromium content 60-70wt%, carbon content 4.0-6.0wt%, and the balance is iron. The preparation method of nano-carbon material is as follows: 80-100 parts of coconut shell powder with a particle size ≤100μm are soaked in 20wt% potassium hydroxide solution for 24h. Wash until neutral, vacuum dry at 110℃ for 12h to obtain activated carbon source, add 5wt% hexamethylenetetramine solution of equal mass to activated carbon source, ball mill mix at 300rpm for 2h using ZrO2 balls to obtain N-predoped carbon source, then add triethanolamine 3-5 times the mass of N-predoped carbon source, place in high pressure vessel, inject liquid carbon dioxide to 15MPa, set temperature to 45℃ and treat at 300rpm for 2h, release under reduced pressure to obtain nano-carbon material, and finally calcine at 400℃ for 2h; the nitrogen source precursor in step (1) is hexamethylenetetramine, melamine, dicyandiamide or polyaniline; the nano-ceramic particles are selected from nano-silica or nano-alumina, with a particle size of 30-50 mm. nm; (2) Preparation of modified melt: First, add 20-50 parts of the core-shell particles obtained in step (1) to 1000-1500 parts of high carbon ferrochrome matrix at 1600-1650℃, mechanically stir to obtain a dispersed nano-heterogeneous core, then add 20-30 parts of graphene powder and melt to obtain a modified melt; The preparation method of graphene powder is as follows: Take graphene oxide and disperse it in N,N-dimethylformamide at 1mg / mL, mix well to obtain a brownish-yellow suspension, then add dicyclohexylcarbodiimide and 1-hydroxybenzotriazole to the suspension, the mass ratio between the three is (20-40): (1-2): (2-4), stir at 100rpm for 2h at room temperature to obtain a reaction solution, then add 2-4 times the mass of 2-aminothiazole in the reaction solution, oil bath at 80-90℃ for 12h, after the reaction is completed, cool to room temperature, vacuum dry at 60-80℃ for 12h; (3) Casting forming treatment: pour and directional solidify the modified melt obtained in step (2) to obtain the modified casting; (4) Surface modification treatment: immerse the modified casting obtained in step (3) in an ethanol solution of 5-15wt% hexamethylenetetramine, then pyrolyze to form a nano-thin layer with a thickness of 10-20μm, and then perform laser remelting to obtain the modified casting with a surface wear-resistant layer; (5) Heat treatment optimization: quench and temper the modified casting with a surface wear-resistant layer obtained in step (4) to form a modified casting with a surface nanocrystalline structure.

2. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: The nano-carbon material obtained in step (1) has a particle size of 20-50 nm and a specific surface area of ​​150-200 m². 2 / g; the alcohol solvent in step (1) is anhydrous ethanol or isopropanol; the concentration of hydrofluoric acid solution in step (1) is 0.5-2mol / L.

3. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: In step (1), the ultrasonic dispersion power is 200-600W, the frequency is 20-60kHz, and the time is 20-45min; in step (1), the heating and stirring temperature is 60-80℃, and the heating and stirring speed is 100-200rpm; in step (1), the sintering parameters are as follows: the temperature is raised to 5℃ in an argon inert gas atmosphere, and then sintered at 500-800℃ for 2-6h; in step (1), the etching time is 20-30min, and the shell thickness of the core-shell particles after etching is 10-20nm.

4. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: In step (2), the grade of the high-carbon ferrochrome matrix is ​​FeCrHC64C4.

0.

5. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: The parameters for mechanical stirring in step (2) are as follows: rotation speed 100-200 rpm, time 5-15 min; the equipment for melting in step (2) is a medium frequency induction furnace, the melting power is 200 kW, and the melting time is 60 min.

6. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: The pouring temperature in step (3) is 1450-1550℃; the parameters for directional solidification in step (3) are as follows: the pulling speed is 100-200μm / s, the solidification temperature gradient is 50℃ / cm, the solidification thickness is 5-15mm, and the molding sand is zircon sand.

7. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: In step (4), the ethanol solution is anhydrous ethanol; in step (4), the laser power of laser remelting is 500-1500W, the scanning speed is 5-15mm / s, and the spot diameter is 1-3mm.

8. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: The parameters for immersion in step (4) are as follows: vacuum degree 0.05-0.09MPa, temperature 60-80℃, time 30-60min; the temperature of pyrolysis treatment in step (4) is 400℃, and the time of pyrolysis treatment is 1-2h.

9. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: In step (5), the quenching heating rate is 10℃ / min, the quenching temperature is 950-1050℃, and the quenching holding time is 3h; in step (5), the cooling rate before tempering is 50℃ / min, the tempering temperature is 200-400℃, and the tempering holding time is 2-6h.

10. The method for preparing modified high-carbon ferrochrome according to claim 1, characterized in that: The parameters of the modified casting with a surface nanocrystalline structure obtained in step (5) are as follows: surface hardness > 1000 HV, wear rate ≤ 0.3 mg / cm². 2 Impact toughness ≥5J / cm 2 .

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