Iron-based composite powder injection molding material and production process thereof

Abstract

The invention relates to the technical field of alloys, in particular to an iron-based composite powder injection molding material and a production process thereof. The preparation method comprises the following steps: 1) powder mixing and grinding: weighing iron powder, stainless steel 440C material powder and a fluxing agent, uniformly mixing, and grinding to obtain nanoscale composite powder; 2) activating and drying: weighing the nano-scale mixed powder, uniformly stirring the nano-scale mixed powder and the activated dispersion liquid, and drying to obtain iron-based composite powder; 3) injection molding: weighing the iron-based composite powder and the nanoscale injection bonding powder, and performing injection molding to obtain a blank; and 4) degreasing and sintering: degreasing and sintering the blank to obtain the iron-based composite powder injection molding material. Closed-loop synergy is formed through the four steps of powder mixing and grinding, activating and drying, injection blank forming and degreasing and sintering, it is guaranteed that powder is evenly dispersed, the blank forming precision is high, the forming material which is compact in structure and free of pore defects is finally formed, and the synergy effect of hardness and toughness is enhanced.

Description

Technical Field

[0001] This application relates to the field of alloy technology, and more specifically, to an iron-based composite powder injection molding material and its manufacturing process. Background Technology

[0002] Iron, as a widely used metallic material, possesses numerous significant advantages, such as abundant resources, low cost, and good electrical and thermal conductivity, playing an indispensable role in many fundamental fields such as machinery manufacturing, construction, and transportation. However, in some high-end fields with extremely high requirements for material performance, such as railway track manufacturing, rails not only need to withstand the enormous pressure and friction generated by high-speed trains, but also must possess excellent wear resistance, fatigue resistance, and dimensional stability. Existing pure iron materials are insufficient to meet these stringent requirements. In particular, pure iron has relatively low hardness, making it prone to wear and deformation during long-term use, affecting the service life of the rails and operational safety.

[0003] To improve the performance of ferrous materials, alloying with other metals is a common production method. However, due to the complex and irregular structures of components such as railway tracks, traditional compression molding processes (rubber compounding → compression molding → debinding → sintering) have many limitations. They struggle to accurately mold complex structures and have low production efficiency, failing to meet the demands of large-scale production. Therefore, injection molding (rubber compounding → injection molding → debinding → sintering) is now widely used to produce ferrous composite materials. However, existing injection molding processes still result in alloys with relatively low hardness after sintering, making it difficult to simultaneously achieve high hardness and good toughness. This, to some extent, limits the application of ferrous composite materials in high-end fields. Summary of the Invention

[0004] The purpose of this application is to provide an iron-based composite powder injection molding material and its production process, which aims to improve hardness while maintaining good impact toughness, and also take into account good dimensional stability and density.

[0005] Firstly, a production process for an iron-based composite powder injection molding material is obtained by the following method: 1) Mixing and grinding: Weigh iron powder, stainless steel 440C material powder and flux, mix them evenly in a weight ratio of 10:(0.8-1.5):(0.01-0.05), grind them to obtain nano-scale composite powder; 2) Activation and drying: Weigh the nano-sized mixed powder and stir it evenly with the activation dispersion, then dry it to obtain iron-based composite powder; 3) Injection molding: Weigh the iron-based composite powder and mix it with the nano-scale injection bonding powder, and then heat-melt and inject it into the preform to obtain the preform; 4) Degreasing and sintering: The raw material is degreased and sintered to obtain iron-based composite powder injection molding material; The nanoscale injection bonding powder includes wax powder, POM, PTW, and HDPE; the HDPE is composed of type A HDPE and type B HDPE, wherein the relative molecular mass of type A is greater than that of type B; by weight percentage, type B HDPE > type A HDPE > POM > rheology modifier > PTW; the amount of nanoscale injection bonding powder is ≤5.8wt% of the amount of activating powder; the degreasing process includes three stages: the highest temperature of the third stage is 500-510℃, the highest temperature of the second stage is 446-455℃, and the highest temperature of the first stage is 378-385℃; by holding time, the second stage > the third stage > the first stage.

[0006] This application, through the collaborative innovative design of raw material ratio, process steps and key additives, successfully solved the technical problems of existing iron-based composite powder injection molding materials, such as the difficulty in achieving both hardness and toughness and insufficient molding precision of irregular structures, and obtained an iron-based composite powder injection molding material with both excellent comprehensive performance and dimensional stability.

[0007] Specifically, in terms of raw material ratio, iron powder is used as the base material, combined with a specific proportion of stainless steel 440C material powder and trace amounts of flux. The three work together to enable the material to maintain excellent impact toughness on the basis of high hardness.

[0008] In terms of process steps, the four-step closed-loop process of powder mixing and grinding, activation and drying, injection molding, and debinding and sintering improves the dispersion uniformity of each component, avoids the agglomeration of nano-sized powders, results in high-density preforms with stable molding accuracy, and enhances the synergistic effect of material hardness and toughness. For example, in the activation and drying step, the treatment of the dispersion liquid effectively avoids the agglomeration of nano-sized powders, while removing moisture and impurities from the powder, ensuring that the powder is dry and clean, providing good conditions for subsequent mixing with binder powder and injection molding. In the injection molding stage, the use of nano-sized iron-based composite powder and nano-sized injection binder powder has a good particle size matching, which significantly improves the mixing uniformity. Combined with the efficient bonding effect of the binder powder, after melt injection, a preform with high density, compact structure, and regular dimensions is formed, and stable molding accuracy can be maintained in mass production.

[0009] During the debinding and sintering stage, a three-stage gradient heating method is adopted, with the second stage > the third stage > the first stage in terms of heat preservation. This method can not only completely remove the organic components in the nano-scale injection bonding powder and the activated dispersion, avoiding residual impurities from affecting performance, but also promote the full diffusion and densification of powder particles through gradient heating, ultimately forming a molded material with a compact structure and no pore defects, further enhancing the synergistic effect of hardness and toughness. In the nanoscale injection bonding powder raw material system, this application utilizes nanoscale injection bonding powder to achieve a technological breakthrough of "small dosage, high efficiency" through the triple synergy of component selection, ratio design, and dosage control. For example, wax powder adjusts the viscosity of the system and improves injection fluidity; POM (polyoxymethylene) provides excellent bonding strength and dimensional stability, and is easy to degrease without residue; PTW (ethylene-butyl acrylate-glycidyl methacrylate terpolymer) acts as a compatibilizer, significantly improving the compatibility between components, reducing interfacial tension, and further improving injection fluidity and preform uniformity; HDPE (high-density polyethylene) uses a blend of type A and type B, with a ratio design where type A HDPE > type B HDPE. This utilizes the high rigidity of type A HDPE and the high toughness of type B HDPE to synergistically improve the overall bonding performance of the bonding powder, while ensuring melt strength during injection; and through precise proportions, the functions of each component are complementary, avoiding performance defects caused by excessive or insufficient amounts of a single component.

[0010] Furthermore, the amount of binder powder is controlled within 5.8 wt% of the activating powder. Under the premise of ensuring the bonding strength and formability of the blank, the proportion of organic components is reduced, the difficulty of degreasing is reduced, and residues and deformation are avoided. Ultimately, the blank is made of high density, compact structure, and regular size. After sintering, the material maintains a high hardness of about 58 HRC, excellent impact toughness (impact power greater than 30 J), and precise dimensional stability, which meets the needs of mass production of irregular structures and long-term use in high-end scenarios.

[0011] In summary, through the three-dimensional synergistic innovation of materials, processes, and formulations, the iron-based composite powder injection molding material prepared in this application has achieved a breakthrough in comprehensive performance with a hardness of about 58 HRC, an impact energy greater than 30 J, and a density greater than 98%. It is particularly suitable for the precision manufacturing of irregular wear-resistant structural parts such as high-speed railway frogs and switch rails, and effectively solves the technical problems of the inverted hardness-toughness of traditional materials and the difficulty in forming complex structures.

[0012] Preferably, the amount of type A HDPE used accounts for 30-45% of the amount of nano-sized injection adhesive powder.

[0013] By controlling the amount of Type A HDPE to 30-45% of the amount of nano-scale injection bonding powder, and combining it with iron powder, stainless steel 440C material powder, and flux in a weight ratio of 10:(0.8-1.5):(0.01-0.05), grinding it, mixing it with an activated dispersion, drying it, and then mixing it with the nano-scale injection bonding powder for injection molding, followed by debinding and sintering, the components of the nano-scale injection bonding powder can complement each other's functions, avoiding performance defects caused by excessive or insufficient amounts of a single component, synergistically improving the overall bonding performance of the bonding powder, and ensuring the melt strength during the injection process. Ultimately, the resulting blank has high density, compact structure, and regular dimensions. After sintering, the material maintains a high hardness of about 58HRC, excellent impact toughness, and precise dimensional stability, meeting the needs of mass production of irregular structures and long-term use in high-end scenarios.

[0014] Preferably, the relative molecular mass of the type A HDPE is 400,000-500,000, and the relative molecular mass of the type B HDPE is 200,000-300,000.

[0015] By adopting the above technical solution, iron powder, stainless steel 440C material powder, and flux are weighed and mixed evenly at a weight ratio of 10:(0.8-1.5):(0.01-0.05) to obtain nano-scale composite powder. After activation and drying, the nano-scale mixed powder is weighed, mixed with the activated dispersion, and dried to obtain iron-based composite powder. For injection molding, the iron-based composite powder is weighed, mixed evenly with nano-scale injection binder powder, and injection molded to obtain a preform. Finally, the preform is degreased and sintered to obtain an iron-based composite powder injection molded material. The nano-scale injection binder powder includes wax powder, POM, PTW, and HDPE. The HDPE is composed of type A HDPE and type B HDPE, with type A having a higher relative molecular mass than type B. By weight percentage, type B HDPE > type A HDPE. The order of application is PE > POM > rheology modifier > PTW. The amount of nano-scale injection bonding powder used is ≤5.8wt% of the activated powder. The degreasing treatment is divided into three stages. The highest temperature of the third stage is 500-510℃, the highest temperature of the second stage is 446-455℃, and the highest temperature of the first stage is 378-385℃. Based on the heat preservation time, the second stage > the third stage > the first stage. And based on the fact that the amount of type A HDPE accounts for 30-45% of the amount of nano-scale injection bonding powder, type A HDPE with a relative molecular mass of 400,000-500,000 and type B HDPE with a relative molecular mass of 200,000-300,000 are selected. The high rigidity of type A HDPE and the high toughness of type B HDPE are used to synergistically improve the overall bonding performance of the bonding powder, while ensuring the melt strength during the injection process.

[0016] Preferably, the first stage involves raising the temperature from room temperature to 380°C, the second stage involves raising the temperature from 380°C to 450°C, and the third stage involves raising the temperature from 450°C to 505°C.

[0017] A stepped, precise temperature-raising design is employed in the degreasing and sintering process to achieve triple optimization in degreasing efficiency, thorough component removal, and material densification. The first stage involves a slow temperature increase from room temperature to 380℃, precisely matching the volatilization temperature of low-boiling-point organic components in the nano-scale injection binder powder. This avoids defects such as cracking and blistering in the blank, and initially removes volatile components. The second stage raises the temperature to 450℃, designed for the decomposition temperature of non-volatile organic components, allowing for complete decomposition and removal of these components, preventing impact on material hardness and toughness, and initially activating the diffusion capacity of the powder particles. The third stage raises the temperature to 505℃, an optimized sintering temperature for iron powder and 440C stainless steel powder. This lowers the flux melting point, promotes diffusion and fusion between particles, reduces internal porosity and interface defects, and facilitates the formation of a stable reinforcing phase structure in the martensitic stainless steel powder. This allows the material to maintain high hardness while achieving excellent impact toughness and minimal dimensional deformation.

[0018] Preferably, the heating rate of the second stage, the third stage, and the first stage is 2-10℃ / min, and the heating rate of the second stage and the third stage is less than the heating rate of the first stage.

[0019] The first stage employs a relatively high heating rate to quickly reach the volatilization temperature of low-boiling-point volatile organic components such as wax powder and PTW, rapidly forming exhaust channels to prevent volatile components from remaining and permeating inside the blank, ensuring the efficiency of initial degreasing. Simultaneously, it avoids a sudden increase in internal pressure due to excessively high heating rates, ensuring the blank retains its intact structure after initial degreasing and reserving a stable channel for subsequent deep degreasing. The second stage has a lower heating rate than the first stage, combined with the longest holding time, allowing non-volatile organic components such as POM and HDPE to completely decompose into small molecule gases and thoroughly exhaust them. The bottom discharge process avoids the formation of impurity phases due to residual organic components. At the same time, it allows the powder particles to slowly activate their diffusion ability during the degreasing process, achieving a seamless connection between deep degreasing and uniform pre-sintering, ensuring the uniformity of the billet structure. The heating rate in the third stage is also lower than that in the first stage, which allows the iron powder and stainless steel 440C material powder particles to slowly diffuse under the temperature gradient, forming a uniform and fine stable reinforcing phase structure. This results in a stronger metallurgical bond with the iron powder matrix. Meanwhile, the densification rate of the material is precisely controlled to avoid internal stress concentration due to excessive densification, ultimately ensuring that the material density is stabilized at over 98%.

[0020] The impact toughness is further improved compared to conventional rate processes, and the dimensional deformation is further reduced, achieving a triple optimization of high hardness, high toughness, and high dimensional accuracy. The three-stage gradient heating rate design, in deep synergy with the temperature range and holding time, not only solves the multiple contradictions between rapid degreasing and structural shape preservation, deep degreasing and no residue, and densification and performance uniformity, but also further strengthens the overall synergistic effect of raw material ratio, process steps, and additives. This results in a leapfrog improvement in the comprehensive performance, molding accuracy, and stability of the final product compared to existing technologies, fully meeting the adaptation requirements of high-end irregular structural components such as railway tracks for harsh working conditions.

[0021] Preferably, the flux is at least one of ferroboron powder, active Ti powder, and nano zinc oxide, and at least one of them is ferroboron powder.

[0022] The synergistic effects of ferroboron powder, iron-based composite powder, and process system components can form a low-melting-point eutectic phase, reducing intergranular tension and increasing material density. Performance synergy is also achieved through solid solution strengthening, where the powder dissolves in the matrix and reinforces the phase, inhibiting Cr oxidation, stabilizing material hardness, and improving impact toughness. Furthermore, process adaptation synergy is achieved through precise matching of reactivity with the three-stage gradient heating rate, realizing a triple synergy of "fluxing-strengthening-process adaptation." When the flux is ferroboron powder and activated Ti powder, the activated Ti powder purifies the interface, avoiding the influence of oxygen impurities. The combined effect of these two components reduces interfacial defects, improves fatigue resistance, and inhibits particle agglomeration, resulting in a denser billet structure. When the flux is ferroboron powder and nano-zinc oxide, the nano-zinc oxide inhibits grain growth and synergistically enhances the impact toughness and fracture toughness of the material with ferroboron powder, without affecting the formation of the ferroboron eutectic phase or the billet forming accuracy. When the flux is a combination of ferroboron powder, active Ti powder and nano zinc oxide, the three form a comprehensive synergistic system of "interface strengthening + purification + grain refinement", which simultaneously optimizes the material's density, hardness, impact toughness, dimensional accuracy and fatigue resistance.

[0023] Preferably, the flux is a combination of ferroboron powder, active Ti powder, and nano zinc oxide.

[0024] Boron iron powder ensures interfacial bonding and hardness, active Ti powder purifies the interface and resists oxidation, and nano zinc oxide refines grains and improves toughness. The three complement each other without antagonism. This combination is deeply adapted to the "temperature-time-rate" process. Under the synergistic effect of gradient heating and differentiated heat preservation, the functions of each flux are precisely exerted, ultimately improving the material density, stabilizing the hardness at around 58 HRC, improving impact toughness compared to existing technologies, and simultaneously optimizing dimensional accuracy and fatigue resistance. It fully meets the long-term use requirements of high-end irregular structural components such as railway rails under high wear, high impact, and complex working conditions.

[0025] Preferably, the activated dispersion is a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer dispersion, and the content of its active ingredient is ≤1.8%.

[0026] The lipophilic segments of polypropylene oxide can firmly adsorb onto the surface of flux particles such as iron powder, 440C stainless steel powder, and ferroboron powder. The hydrophilic segments of polyethylene oxide extend outward to form a steric hindrance layer, effectively blocking van der Waals forces between nanoparticles, thus improving the dispersion uniformity of the composite powder by more than 40%. The HLB value of this copolymer is precisely matched with the surface polarity of the nanoscale composite powder, forming a uniform adsorption film during the activation and drying process. This ensures that the powder maintains good dispersion after drying and avoids decreased compatibility with injection bonding powder due to excessive adsorption of the dispersant. The decomposition temperature range and three-stage debinding of the triblock copolymer are also discussed. The sintering process temperature design is highly compatible, and the low addition amount can be completely decomposed into small molecule gas during the debinding process, resulting in no carbon residue or impurity phase generation. This avoids the decrease in material hardness or the deterioration of toughness caused by dispersant residue. The low content design ensures the dispersion effect and avoids excessive dispersant occupying space in the preform, thereby increasing the density of the preform after injection molding and laying the foundation for subsequent sintering densification. This content works synergistically with the nano-scale injection binder powder, and the total organic content of the two is low. The internal gas pressure of the preform is smooth during the debinding process, further reducing the risk of cracking and bubbling, and the dimensional deformation is stable within ±0.15%.

[0027] Preferably, the sintering conditions in step 3) are: temperature 1205-1300℃, heating rate 10-25℃ / min, and holding time 2-6 hours.

[0028] Iron powder, stainless steel 440C material powder, and flux were weighed and mixed evenly at a weight ratio of 10:(0.8-1.5):(0.01-0.05) and ground to obtain nano-scale composite powder. After activation, drying, injection molding, and degreasing, the powder was sintered at a temperature of 1205-1300℃, a heating rate of 10-25℃ / min, and a holding time of 2-6 hours. This temperature is higher than the low melting point eutectic phase temperature formed by boron iron powder, which allows the flux to fully melt and spread at the particle interface, eliminating pores and interfacial gaps, promoting metallurgical bonding, increasing material density, and promoting the uniform solid solution of alloying elements in the stainless steel 440C material powder to form a stable martensitic strengthening phase. The heating rate is connected with the gradient rate of the early degreasing stage to avoid internal temperature differences and stress concentration, and reduce powder particle oxidation. The holding time provides sufficient time for element diffusion and phase structure adjustment, improving the uniformity of material hardness.

[0029] At temperatures of 650-900℃ and for 1-4 hours, within the recrystallization temperature range of iron-based materials, sintering internal stress can be eliminated, and martensite decomposition can be avoided. The holding time is tailored to the material to fully release internal stress. Cooling to 590-605℃ at 15-25℃ / h, followed by air cooling to room temperature, slow cooling avoids rapid martensitic transformation that generates structural stress, releases residual stress, and reduces dimensional deformation. Air cooling rapidly crosses the pearlite transformation range, locking in the martensitic strengthening phase structure. The cooling process, combined with pre-forming precision control, improves the material's dimensional stability and fatigue resistance. Simultaneously, the high-temperature sintering decomposes residual triblock copolymers, achieving zero organic residue. The combined effects of ferroboron powder, active Ti powder, and nano-zinc oxide, along with process parameters, enable the material to maintain excellent impact toughness while maintaining high hardness, resulting in improved overall performance. Densification and improved dimensional stability mean that injection-molded irregular structural parts do not require subsequent machining, increasing production efficiency and reducing production costs.

[0030] Secondly, an iron-based composite powder injection molding material is obtained by a production process for an iron-based composite powder injection molding material.

[0031] This research solves the technical problems of existing iron-based composite powder injection molding materials, such as the difficulty in balancing hardness and toughness, and insufficient molding precision for irregular structures. It yields iron-based composite powder injection molding materials with excellent comprehensive performance and dimensional stability. A breakthrough in comprehensive performance is achieved, with a hardness of approximately 58 HRC and a notched impact energy greater than 30 J. This makes it suitable for the precision manufacturing of irregular wear-resistant structural components such as high-speed railway frogs and switch rails, solving the technical challenges of the inverted hardness-toughness ratio and the difficulty in forming complex structures in traditional materials. The degreasing and sintering process employs a stepped, precise heating design combined with a specific holding time ratio, achieving triple optimization of degreasing efficiency, thorough component removal, and material densification. The three-stage gradient heating rate, temperature range, and holding time depth work together to resolve multiple contradictions between rapid degreasing and structural shape preservation, deep degreasing and residue-free processes, and densification and performance uniformity.

[0032] Flux combinations with ferroboron-boron powder as the core solve problems such as insufficient interfacial bonding, poor oxidation resistance, or coarse grains of single fluxes, achieving a comprehensive improvement in hardness, toughness, density, and dimensional stability; specific triblock copolymer activated dispersions solve problems such as nanoparticle agglomeration, dispersant residue, and poor process compatibility, achieving comprehensive optimization of material dispersion uniformity, molding accuracy, and overall performance.

[0033] In summary, this application includes at least one of the following beneficial technical effects: 1. By mixing iron powder, a specific proportion of stainless steel 440C material powder and a trace amount of flux, the material maintains excellent impact toughness while having a high hardness of about 58HRC, meeting the dual requirements of wear resistance and impact resistance in high-end scenarios such as railway tracks. 2. The four-step process of powder mixing and grinding, activation and drying, injection molding, debinding and sintering forms a closed loop and works synergistically to ensure uniform powder dispersion and high precision of the blank forming, ultimately forming a compact material without pore defects, and enhancing the synergistic effect of hardness and toughness. 3. Nanoscale injection bonding powder achieves high density, compact structure, and regular size of the blank through the triple synergy of component selection, ratio design, and dosage control. After sintering, the material maintains a high hardness of about 58HRC, excellent impact toughness, and precise dimensional stability, meeting the needs of mass production of irregular structures and long-term use in high-end scenarios. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] Sources of some raw materials: POM is an abbreviation for polyoxymethylene, with a relative molecular mass of 50,000 to 100,000. PTW is a terpolymer of ethylene-butyl acrylate-glycidyl acrylate, namely DuPont Elvaloy® PTW, with a thermal decomposition temperature of 330°C; The densities of both Type A and Type B HDPE are 0.940-0.976 g / cm³. 3 ; The specification for ferroboron powder is FeB20; The active Ti powder is titanium-iron powder, with a titanium content of 40 wt%. Stainless steel 440C material powder, also known as S44004 (also known as 440C stainless steel), is a high-carbon martensitic stainless steel that conforms to the American UNS ASTM AISI standards. It contains 0.95%-1.20% carbon and 16%-18% chromium, and has both high hardness and wear resistance. The molecular formula of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is as follows:

[0036] Where both n and m are 5-10; The brand and model of maleic anhydride-grafted PE is DuPont 40E529. The wax powder is polyethylene wax with a relative molecular mass of 4000-5000.

[0037] Example Example 1 A production process for an iron-based composite powder injection molding material is obtained by the following method: 1) Mixing and grinding: Weigh iron powder, stainless steel 440C material powder, and flux (boron iron powder) and mix them evenly in a weight ratio of 10:1:0.03. Then put them into a grinder for grinding to obtain nano-scale composite powder with an average particle size of 100nm. 2) Activation and drying: Weigh 10 kg of nano-sized mixed powder and 2 kg of activation dispersion into a planetary mixer and mix them. Stir at 100 r / min for 30 min to ensure thorough mixing. Remove the powder and place it in a vacuum drying oven at 100℃ for 4 h to remove all solvent from the activation dispersion and obtain iron-based composite powder. 3) Injection Molding: Weigh 9.52 kg of iron-based composite powder and 0.43 kg of nano-sized injection bonding powder into a high-speed mixer and stir for 5 minutes at 200 r / min to ensure thorough and uniform mixing. Then transfer the mixture to a metal powder injection molding machine. The feeding zone temperature is 180℃, the compression zone temperature is 195℃, the metering zone temperature is 228℃, and the nozzle temperature is 220℃. The injection pressure is 65 MPa, the holding pressure is 50 MPa, the holding time is 10 s, the mold temperature is 60℃, and the screw speed is 50 rpm to obtain the preform. 4) Degreasing and sintering: The blank is placed in a sintering furnace for degreasing treatment, which includes three stages: the first stage is to raise the temperature from room temperature to 380℃ at a rate of 10℃ / min and hold for 20min; the second stage is to raise the temperature from 380℃ to 450℃ at a rate of 5℃ / min and hold for 80min; the third stage is to raise the temperature from 450℃ to 505℃ at a rate of 2℃ / min and hold for 50min.

[0038] The material is then sintered under the following conditions: the temperature is increased to 1250℃ at a heating rate of 20℃ / min, and then held at that temperature for 4 hours. After that, it is air-cooled to room temperature of 25℃ at a temperature of 25℃, a humidity of 50%, and a wind speed of 0.5m / s to obtain the iron-based composite powder injection molding material.

[0039] The nano-scale injection bonding powder is composed of wax powder (PE wax), POM, PTW, type A HDPE, and type B HDPE in a weight ratio of 0.5:1.4:0.3:3.6:4.8.

[0040] The relative molecular mass of type A HDPE is 400,000, and the relative molecular mass of type B HDPE is 200,000.

[0041] The activated dispersion is a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer dispersion, which is obtained by dissolving the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer in water, and the content of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer is 1.5%.

[0042] Example 2 The difference between Example 2 and Example 1 lies in the dosage and process parameters, as detailed below: Iron powder, stainless steel 440C material powder, and flux (boron iron powder) are mixed in a weight ratio of 10:0.8:0.05. Degreasing: In the first stage, the temperature is increased from room temperature to 385℃ at a rate of 10℃ / min and held for 20min; in the second stage, the temperature is increased from 380℃ to 455℃ at a rate of 5℃ / min and held for 80min; in the third stage, the temperature is increased from 450℃ to 510℃ at a rate of 2℃ / min and held for 50min.

[0043] Sintering: Heat to 1300℃ at a heating rate of 10℃ / min, and then hold for 2 hours.

[0044] Example 3 The difference between Example 3 and Example 1 lies in the dosage and process parameters, as detailed below: Iron powder, stainless steel 440C material powder, and flux (boron iron powder) are mixed in a weight ratio of 10:0.8:0.05. Degreasing: In the first stage, the temperature is increased from room temperature to 385℃ at a rate of 10℃ / min and held for 20min; in the second stage, the temperature is increased from 380℃ to 455℃ at a rate of 5℃ / min and held for 80min; in the third stage, the temperature is increased from 450℃ to 510℃ at a rate of 2℃ / min and held for 50min.

[0045] Sintering: Heat to 1205℃ at a heating rate of 25℃ / min, and then hold for 6 hours.

[0046] Example 4 The difference between Example 4 and Example 1 is that the flux is composed of ferroboron powder and active Ti powder in a weight ratio of 4:1.

[0047] Example 5 The difference between Example 5 and Example 1 is that the flux is composed of ferroboron powder and nano zinc oxide in a weight ratio of 9:1.

[0048] Example 6 The difference between Example 6 and Example 1 is that the flux is composed of ferroboron powder, active Ti powder and nano zinc oxide in a weight ratio of 8.5:1:0.5.

[0049] Example 7 The difference between Example 7 and Example 1 is that the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is replaced with an equal amount of silane coupling agent 550.

[0050] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that POM is replaced with an equal amount of Type A HDPE.

[0051] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that PTW was replaced in equal amounts with maleic anhydride-grafted PE.

[0052] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Type A HDPE is replaced with an equal amount of Type B HDPE.

[0053] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that step 2) is omitted, and the iron-based composite powder in step 3) is directly replaced with the nano-composite powder in step 1).

[0054] Performance testing 1. Hardness; Rockwell hardness (HRC) testing was performed in accordance with GB / T 230.1-2018 standard. The test was conducted on a calibrated Rockwell hardness tester, with at least 5 points tested for each sample and the arithmetic mean was taken, retaining one decimal place.

[0055] 2. Impact toughness; GB / T 19748-2018 "Steel Charpy V-notch Low-Temperature Impact Test Method", when the Charpy V-notch impact energy at room temperature (25℃) is >30J, it is considered qualified.

[0056] 3. Dimensional stability To verify the quality stability of mass production, a sampling inspection was conducted on the obtained iron-based composite powder injection molded material: 20 samples were randomly selected. First, an appearance inspection was performed, and unqualified products with surface defects such as defects, bumps, and bubbles were removed. Then, for the samples that passed the appearance inspection, the dimensions of three different regions on each sample were randomly selected and measured, and the dimensional range (i.e., the difference between the maximum and minimum values) was calculated. Samples with a range greater than 0.20 mm were defined as dimensionally unqualified. Finally, the total number of unqualified products was counted; the fewer the unqualified products, the better the dimensional stability of the material.

[0057] 4) Compactness The bulk density was measured according to ASTM B962 standard using the Archimedes drainage method, and its relative density was calculated relative to the theoretical density (the theoretical density of the iron powder and stainless steel 440C material powder added in this application). The compaction rate is equal to the actual density divided by the relative density, and then multiplied by 100%.

[0058] The specific experimental data are shown in Table 1. Table 1. Experimental data of Examples 1-7 and Comparative Examples 1-3

[0059] Combining Example 1 and Comparative Examples 1-4 with Table 1, it can be seen that the hardness and density of Comparative Examples 1-4 (without POM / using maleic anhydride-grafted PE / without type A HDPE) are lower than those of Example 1. In terms of impact toughness, Comparative Examples 1-4 are unqualified, indicating that the impact energy of Comparative Examples 1-4 does not reach 30J or more. Moreover, the number of unqualified samples in Comparative Examples 1-4 is relatively large, while no unqualified phenomena were observed in Example 1. This indicates that Example 1, using the process and raw materials of this application, produces an iron-based composite powder injection molded material that combines superior dimensional stability, high hardness, good impact toughness, and high density.

[0060] Comparing Examples 1 and 7, it can be seen that when the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer was replaced with an equal amount of silane coupling agent 550 in Example 7, its density decreased from 57.6 to 55.3, the number of unqualified samples increased to 3, and the compactness decreased from 98.5% to 96.7%. This indicates that the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer used in this application, combined with the production process of this application, can achieve better performance. Although silane coupling agent 550 can also play a role in agglomeration and compatibility, it introduces impurities such as silicon, which affects the final alloy performance.

[0061] Comparing Examples 1 and 4-6, it can be seen that the flux in Example 6 is composed of ferroboron powder, active Ti powder and nano zinc oxide. Its hardness and density are higher than those of Examples 1 and 4-5, indicating that the combination of the three components has a synergistic effect and further improves the overall performance.

[0062] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A production process for an iron-based composite powder injection molding material, characterized in that, Obtained by the following method: 1) Mixing and grinding: Weigh iron powder, stainless steel 440C material powder and flux, mix them evenly in a weight ratio of 10:(0.8-1.5):(0.01-0.05), grind them to obtain nano-scale composite powder; 2) Activation and drying: Weigh the nano-sized mixed powder and stir it evenly with the activation dispersion, then dry it to obtain iron-based composite powder; 3) Injection molding: Weigh the iron-based composite powder and mix it with the nano-scale injection bonding powder, and then heat-melt and inject it into the preform to obtain the preform; 4) Degreasing and sintering: The raw material is degreased and sintered to obtain iron-based composite powder injection molding material; The nanoscale injection bonding powder includes wax powder, POM, PTW, and HDPE; the HDPE is composed of type A HDPE and type B HDPE, wherein the relative molecular mass of type A is greater than that of type B; by weight percentage, type B HDPE > type A HDPE > POM > rheology modifier > PTW; the amount of nanoscale injection bonding powder is ≤5.8wt% of the amount of activating powder; the degreasing process includes three stages: the highest temperature of the third stage is 500-510℃, the highest temperature of the second stage is 446-455℃, and the highest temperature of the first stage is 378-385℃; by holding time, the second stage > the third stage > the first stage.

2. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The amount of type A HDPE used accounts for 30-45% of the amount of nano-scale injection adhesive powder used.

3. The production process of an iron-based composite powder injection molding material according to claim 2, characterized in that: The relative molecular mass of the type A HDPE is 400,000-500,000, and the relative molecular mass of the type B HDPE is 200,000-300,000.

4. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The first stage involves raising the temperature from room temperature to 380°C, the second stage involves raising the temperature from 380°C to 450°C, and the third stage involves raising the temperature from 450°C to 505°C.

5. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The heating rates of the second stage, the third stage, and the first stage are all 2-10℃ / min, and the heating rates of the second stage and the third stage are both less than the heating rate of the first stage.

6. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The flux is at least one of ferroboron powder, active Ti powder, and nano zinc oxide, and at least one of them is ferroboron powder.

7. The production process of an iron-based composite powder injection molding material according to claim 6, characterized in that: The flux is a combination of ferroboron powder, active Ti powder, and nano zinc oxide.

8. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The activated dispersion is a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer dispersion, and its active ingredient content is ≤1.8%.

9. The production process of an iron-based composite powder injection molding material according to claim 1, characterized in that: The sintering conditions in step 3) are: temperature 1205-1300℃, heating rate 10-25℃ / min, and holding time 2-6 hours.

10. An iron-based composite powder injection molding material, characterized in that: The iron-based composite powder injection molding material is prepared by the production process of an iron-based composite powder injection molding material as described in any one of 1-9.

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