Injection molding high-density alloy steel sintering integrated preparation process

Abstract

The invention discloses an injection molding high-density alloy steel sintering integrated preparation process, which comprises the steps of alloy raw material proportioning, feed preparation, injection molding, continuous thermal desorption sintering treatment and enhanced heat treatment, and comprises the following steps: selecting gas atomization pure iron powder subjected to vacuum reduction treatment, and matching with chromium, nickel, molybdenum, vanadium, carbon, silicon, manganese and iron powder multi-component alloy proportioning; a phenolic resin-polyformaldehyde composite binder is adopted, 0.5-1.5% of a lubricating additive is added, internal mixing parameters are controlled under the protection of inert gas according to the powder-to-rubber ratio of 72-77%: 23-28%, and the problem that the compatibility of a single binder and alloy powder is poor is solved; three-section gradient temperature control injection molding and a continuous atmosphere furnace sectional degreasing-sintering integrated process are combined, and strengthening heat treatment is matched, so that sufficient diffusion of elements and densification of a green body are realized, and defects are avoided. The technology effectively solves the technical problems that traditional raw materials are high in impurity content and insufficient in element diffusion, and therefore the alloy steel sintering preparation efficiency can be improved.

Description

Technical Field

[0001] This invention relates to the field of metal injection molding technology, and more specifically, to an integrated sintering preparation process for injection-molded high-density alloy steel. Background Technology

[0002] Injection-molded high-density alloy steel is a high-performance alloy material prepared using the Metal Injection Molding (MIM) process. Its core advantage lies in combining the complex shape-forming capabilities of plastic injection molding with the material densification characteristics of powder metallurgy. Through key steps such as powder mixing, feedstock preparation, injection molding, and debinding sintering, high-precision mass production of small, complex structural parts can be achieved. With its excellent strength, hardness, and dimensional stability, it has become a core material choice in fields such as medical devices, precision electronics, high-end automotive parts, and ceramic materials. For applications requiring high loads and harsh operating conditions, multi-element alloy steels containing alloying elements such as chromium, nickel, molybdenum, and vanadium play an irreplaceable role in key applications such as metal parts and ceramic materials due to their combination of high strength, high toughness, and good heat treatment responsiveness.

[0003] However, when preparing this type of multi-element alloy steel using the traditional MIM process, the iron powder commonly used has a high impurity content and is prone to forming an oxide layer on the surface. The uneven distribution of alloying elements leads to insufficient element diffusion during subsequent sintering. In addition, single-system binders are often used during feed preparation, which have poor compatibility with alloy powders and lack targeted lubrication control mechanisms. The viscosity fluctuates greatly during the mixing process, which not only affects the flowability of injection molding but also easily leads to defects such as pores and cracks inside the billet, thereby reducing the sintering efficiency of alloy steel. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an integrated injection molding and sintering process for preparing high-density alloy steel, comprising the following steps: Alloy raw material ratio: The alloy steel powder includes, by weight percentage, 2.0-3.0% chromium, 3.0-4.5% nickel, 0.8-1.5% molybdenum, 0.2-0.6% vanadium, 0.7-0.9% carbon, 0.15-0.4% silicon, and 0.3-0.7% manganese, with the balance being iron powder. The iron powder is pure iron powder that has been atomized and vacuum reduced to remove impurities and oxide layers. Feed preparation: The alloy steel powder and the composite binder corresponding to phenolic resin-polyoxymethylene are mixed at a weight percentage of 72-77%:23-28%. 0.5-1.5% of a lubricant is added to the composite binder. After mixing, the mixture is internally kneaded under inert gas protection at 185-225°C for 190-250 min. During the internal kneading process, the viscosity of the system is controlled at 500-800 Pa·s. Subsequently, the mixture is extruded through a twin-screw extruder and cut into cylindrical particles of 4-9 mm to obtain the viscosity feed. Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel of the injection molding machine adopts a three-stage gradient temperature control, the injection pressure is 150-190MPa, the injection speed is 55-75mm / s, the holding pressure is 100-135MPa, the holding time is 16-28s, and a temperature-controlled cooling method is adopted. After cooling for 16-35 seconds, the mold is demolded to obtain a dense injection preform. Continuous hot debinding and sintering treatment: The dense injection blank is fed into a continuous atmosphere sintering furnace for debinding in stages under an inert atmosphere. The debinding temperature range is 250-800°C, and the holding time for each stage is 50-150 min. After debinding, the furnace is switched to a reducing mixed atmosphere and heated to 1500-1650°C at a heating rate of 8-14°C / min. Sintering is carried out for 6-9 h. The pressure inside the furnace is controlled at 0.8-1.5 MPa during the sintering process to produce sintered parts. Strengthening heat treatment: The sintered parts are quenched at 950-1050°C with a cooling rate of ≥130°C / s, followed by segmented tempering treatment with a tempering temperature range of 380-750°C and a total tempering time of 8-12 hours. After cooling to room temperature, the finished product is obtained.

[0005] Furthermore, in the alloy raw material proportioning step, the specific process parameters for vacuum reduction treatment are: reduction temperature 850-950℃, reduction time 4-6h, and vacuum degree controlled at 1.0×10⁻⁶. -3 -5.0×10 -3 Pa, during the reduction process, hydrogen is used as an auxiliary reducing gas, with a hydrogen flow rate of 0.8-1.5 m³ / s. 3 / h, the particle size distribution of the gas-atomized pure iron powder satisfies D10=5-7μm, D50=8-12μm, D90=18-25μm, and the oxygen content of the iron powder is ≤0.08wt% and the carbon content is ≤0.03wt%.

[0006] Furthermore, in the feed preparation step, the specific preparation process of the composite adhesive is as follows: phenolic resin and polyoxymethylene are mixed at a weight ratio of 72-77%:23-28%, and an antioxidant accounting for 0.3-0.8% of the total weight of the composite adhesive is added. The mixture is stirred at 120-140°C for 30-50 minutes at a stirring speed of 300-500 r / min. After cooling to room temperature, the mixture is pulverized to a particle size ≤500μm. Then, a lubricant accounting for 0.5-1.5% of the total weight of the composite adhesive is added and mixed evenly.

[0007] Furthermore, in the feed preparation step, the lubricant is a compound system of zinc stearate and polyethylene glycol, wherein zinc stearate accounts for 60-75% of the total weight of the lubricant and polyethylene glycol accounts for 25-40% of the total weight of the lubricant; the screw speed of the twin-screw extruder is 80-120 r / min, and the extrusion temperature is consistent with the mixing temperature. During the extrusion process, an online viscosity monitoring device is used to monitor the material viscosity in real time. When the material viscosity deviates from the range of 500-800 Pa·s, dynamic correction is made by adjusting the corresponding screw speed of the twin-screw extruder by ±5-15 r / min to ensure that the length-to-diameter ratio of the cut cylindrical particles is 1.0-1.5:1.

[0008] Furthermore, in the injection molding step, the three-stage gradient temperature control of the injection molding machine is as follows: the temperature of the front section of the barrel is 185-200°C, the temperature of the middle section is 200-215°C, and the temperature of the rear section is 215-225°C. The mold temperature is controlled at 60-85°C. The temperature control and cooling method adopts a combination of water cooling and air cooling. Water cooling is used for the first 8-15 seconds, with a cooling water temperature of 15-25°C. Air cooling is used for the last 8-20 seconds, with an air speed of 3-6 m / s. Ejector pin demolding is used. The number of ejector pins is set to 4-8 according to the shape of the injection blank, and the ejector pin ejection speed is 5-10 mm / s.

[0009] Furthermore, in the continuous hot debinding and sintering process, the inert atmosphere is high-purity argon with a purity ≥99.999%. The specific stages of segmented heating and debinding are 250-350°C, 350-500°C, 500-650°C, and 650-800°C, with heating rates of 2-4°C / min, 3-5°C / min, 4-6°C / min, and 5-7°C / min, respectively. The holding times for each stage are 120-150 min, 100-130 min, 80-110 min, and 50-80 min, respectively.

[0010] Furthermore, in the continuous thermal desintering process, the reducing mixed atmosphere is a mixture of hydrogen and nitrogen, wherein hydrogen accounts for 15-25% of the total volume of the mixed gas, nitrogen accounts for 75-85% of the total volume of the mixed gas, and the flow rate of the mixed gas is 1.2-2.0 m³ / s. 3 / h, a pressure closed-loop control system is adopted during the sintering process. When the pressure inside the continuous atmosphere sintering furnace deviates from the range of 0.8-1.5MPa, it is compensated by adjusting the mixed gas inlet flow rate, with a compensation accuracy of ±0.05MPa.

[0011] Furthermore, in the continuous hot desintering process, after heating to 1500-1650℃, constant temperature sintering is carried out for 1-2 hours, followed by stepped cooling sintering. Specifically, the temperature is reduced by 50℃ and held for 30-45 minutes until the temperature drops to 1200℃. Then, the temperature is cooled to 800℃ at a rate of 10-15℃ / min, and finally cooled to room temperature with the furnace. During the stepped cooling sintering process, the mixed gas flow rate remains constant, and the furnace pressure is maintained at 1.0-1.2MPa.

[0012] Furthermore, in the enhanced heat treatment step, the quenching heat treatment adopts oil quenching, the quenching medium is No. 20 machine oil, the quenching oil temperature is controlled at 40-60°C, a stirring device is used during the quenching process, the stirring speed is 150-250 r / min, and the oil stains on the surface of the sintered parts after quenching are removed by ultrasonic cleaning, the cleaning medium is anhydrous ethanol, the cleaning temperature is 40-50°C, and the cleaning time is 15-25 min.

[0013] Furthermore, in the enhanced heat treatment step, the segmented tempering process is specifically divided into three stages: the first stage tempering temperature is 380-450°C, and the holding temperature is 3-4 hours; the second stage tempering temperature is 500-600°C, and the holding temperature is 3-4 hours; the third stage tempering temperature is 650-750°C, and the holding temperature is 2-4 hours. The heating rate of each stage tempering is 5-8°C / min. During the tempering process, air circulation heating is used, and the circulation wind speed is 2-4 m / s. After tempering, the product is obtained by natural cooling to room temperature.

[0014] The beneficial effects of this application are as follows: By proportioning alloying elements and optimizing iron powder raw materials, the weight percentage range of key alloying elements such as chromium, nickel, and molybdenum is scientifically set, and the synergistic effect of each element can achieve comprehensive performance control of alloy steel; by using gas atomization of pure iron powder and vacuum reduction treatment, impurities and surface oxide layers are effectively removed, avoiding the element diffusion obstacles caused by traditional impurity iron powder and the sintering bonding defects caused by oxide layers. Secondly, by mixing alloy steel powder with phenolic resin-polyoxymethylene composite binder in a specific ratio, the two binders complement each other, with phenolic resin providing good bonding strength and polyoxymethylene ensuring feed flowability. Compared with the shortcomings of insufficient compatibility between traditional single binders and alloy powder, the stability of the mixed system is significantly improved; by adding 0.5-1.5% lubricant, the lubrication effect is specifically optimized, reducing friction between powder particles and with equipment; by mixing for a specific time under specific temperature and inert gas protection, and strictly controlling the system viscosity at 500-800 Pa·s, the problem of uneven feeding caused by large viscosity fluctuations during traditional mixing is avoided. Then, the three-stage gradient temperature control of the barrel can adjust the temperature according to the state of the feeding in different areas, avoiding excessively high local temperatures that could lead to binder decomposition or excessively low temperatures that could affect fluidity; the parameter range settings for injection pressure, speed, holding pressure, and holding time ensure that the feeding can quickly and evenly fill the mold cavity, and that the preform is compacted through the holding pressure stage to reduce internal porosity; the temperature-controlled cooling method and specific cooling time avoid the preform shrinkage and deformation or internal stress concentration caused by uneven cooling in traditional methods, ensuring that a dense injection preform is obtained after demolding. Furthermore, by performing segmented heating and degreasing in an inert atmosphere, the binder in the injection-molded billet can be gradually removed, avoiding binder residue or billet cracking caused by degreasing at a single temperature, thus clearing obstacles for element diffusion in the subsequent sintering stage. Switching to a reducing mixed atmosphere after degreasing prevents oxidation of alloying elements during sintering, ensuring element activity. Specific heating rates, sintering temperatures, holding times, and furnace pressure control provide optimal conditions for uniform diffusion of alloying elements, grain refinement, and billet densification, reducing internal defects caused by incomplete degreasing or uneven element diffusion, and significantly improving the mechanical properties of the sintered parts. Finally, quenching heat treatment and segmented tempering allow the sintered parts to rapidly form a martensitic structure, significantly improving their hardness and strength, thereby compensating for the performance shortcomings of alloy steels prepared by traditional MIM processes. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a line graph showing the positive or negative indicators of the comprehensive performance test results of alloy steel in Examples 1-3 compared to Comparative Examples 1-5 in this embodiment. Figure 2This is a schematic diagram of the coefficient of variation of the performance in the parallel test of Example 2 in this embodiment. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0017] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0018] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of processes and methods consistent with some aspects of this application as detailed in the appended claims.

[0019] In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar process stages or parameters, and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0020] To further understand the invention's content, features, and effects, the following embodiments are provided and described in detail below: Alloy raw material ratio: The alloy steel powder includes, by weight percentage, 2.0-3.0% chromium, 3.0-4.5% nickel, 0.8-1.5% molybdenum, 0.2-0.6% vanadium, 0.7-0.9% carbon, 0.15-0.4% silicon, and 0.3-0.7% manganese, with the balance being iron powder. The iron powder is pure iron powder that has been atomized and vacuum reduced to remove impurities and oxide layers. In this embodiment of the invention, gas-atomized pure iron powder with D10=6μm, D50=10μm, and D90=22μm, and an oxygen content of 0.06wt% and a carbon content of 0.02wt%, is selected. The iron powder is placed in a vacuum reduction furnace, and after the furnace door is sealed, a vacuum pump is started to evacuate the furnace to a vacuum level of 3.0×10⁻⁶ in three stages. -3 Pa, at 1.2m 3 Hydrogen gas is introduced at a flow rate of / h. The heating system is started, and the temperature is increased to 900℃ at rates of 5℃ / min below 200℃, 8℃ / min between 200-600℃, and 3℃ / min between 600-900℃. The temperature is held for 5 hours to reduce and remove impurities and the oxide layer. During the reduction process, the temperature, vacuum level, and hydrogen flow rate fluctuations are maintained within ±5℃ and ±1.0×10⁻⁶, respectively, through feedback regulation.-4 Pa, ±0.1m 3 After cooling to below 300℃, argon gas is introduced to restore normal pressure and remove the iron powder. Accurately weigh 2.5% chromium, 3.8% nickel, 1.2% molybdenum, 0.4% vanadium, 0.8% carbon, 0.3% silicon, 0.5% manganese, and the remainder of the refined iron powder according to weight percentage. Add these to a planetary mixer and mix at 60 r / min for 120 min. During mixing, argon gas is continuously introduced to isolate the air, ensuring uniform alloy powder composition and preventing secondary oxidation.

[0021] Feed preparation: The alloy steel powder and the composite binder corresponding to phenolic resin-polyoxymethylene are mixed at a weight percentage of 72-77%:23-28%. 0.5-1.5% of a lubricant is added to the composite binder. After mixing, the mixture is internally kneaded under inert gas protection at 185-225°C for 190-250 min. During the internal kneading process, the viscosity of the system is controlled at 500-800 Pa·s. Subsequently, the mixture is extruded through a twin-screw extruder and cut into cylindrical particles of 4-9 mm to obtain the viscosity feed. In this embodiment of the invention, phenolic resin and polyoxymethylene are mixed at a weight ratio of 75%:25%, and antioxidant is added at 0.5% of the total weight of the composite binder. The mixture is then placed in a high-speed stirring kettle at 130°C and stirred at 400 r / min for 40 min. After cooling, the mixture is pulverized to 400 μm, and then 1.0% of a zinc stearate-polyethylene glycol compound lubricant (70% zinc stearate, 30% polyethylene glycol) is added. The mixture is then mixed in a double cone mixer for 20 min to obtain the composite binder. Alloy steel powder and the composite binder are added to a mixer at a weight ratio of 75%:25%. The mixer chamber is purged with argon gas three times and then kept under positive pressure. The heating system is started to raise the temperature to 205°C, and the mixture is stirred at 60 r / min for 220 min. The rotor speed is adjusted using a built-in viscosity monitoring probe to stabilize the viscosity of the system at 650 Pa·s. After the mixing is completed, the material is fed into a twin-screw extruder. The screw speed is set to 100 r / min and the extrusion temperature to 205℃. The screw speed is dynamically corrected by an online viscosity monitoring device by ±5-15 r / min. The extruded strip material is cut into cylindrical particles with a length of 6 mm and a diameter of 4 mm by a rotary cutter to ensure a length-to-diameter ratio of 1.5:1, resulting in a uniform viscosity feed.

[0022] Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel of the injection molding machine adopts a three-stage gradient temperature control, the injection pressure is 150-190MPa, the injection speed is 55-75mm / s, the holding pressure is 100-135MPa, the holding time is 16-28s, and a temperature-controlled cooling method is adopted. After cooling for 16-35 seconds, the mold is demolded to obtain a dense injection preform. In this embodiment of the invention, viscous feedstock is fed into the injection molding machine hopper. The bottom of the hopper vibrates at a frequency of 50Hz to prevent bridging. The injection molding machine preheating system is activated, with the front section of the barrel set to 195°C, the middle section to 210°C, and the rear section to 220°C. Heating is achieved through segmented heating coils, and the mold is heated to 75°C via built-in heating tubes. Temperature fluctuations in each area are controlled within ±3°C. The injection pressure is set to 170MPa and the injection speed to 65mm / s. The hydraulic system drives the screw to inject the molten feedstock into the mold cavity. After injection, the system switches to the holding pressure stage, with a holding pressure of 120MPa and a holding time of 22s. Pressure is maintained stable by adjusting the hydraulic valve through pressure feedback. After the holding pressure is completed, the composite cooling system is activated. For the first 12s, 18°C ​​cooling water is introduced, with the cooling water pump pressure at 0.3MPa to ensure stable flow. For the next 15s, the system switches to air cooling, blowing out a 4.5m / s ambient temperature airflow through the mold's honeycomb-shaped air outlet. After cooling, the demolding mechanism is activated. Six high-speed steel ejector pins are symmetrically arranged 5mm from the edge of the injection blank and eject synchronously at a speed of 8mm / s. Displacement monitoring ensures a smooth ejection stroke, resulting in a high-density, non-deformed injection blank after demolding.

[0023] Continuous hot debinding and sintering treatment: The dense injection blank is fed into a continuous atmosphere sintering furnace for debinding in stages under an inert atmosphere. The debinding temperature range is 250-800°C, and the holding time for each stage is 50-150 min. After debinding, the furnace is switched to a reducing mixed atmosphere and heated to 1500-1650°C at a heating rate of 8-14°C / min. Sintering is carried out for 6-9 h. The pressure inside the furnace is controlled at 0.8-1.5 MPa during the sintering process to produce sintered parts. In this embodiment of the invention, dense injection-molded preforms are uniformly arranged on a graphite carrier with permeable vents, with a preform spacing of 10 mm. After being fed into a continuous atmosphere sintering furnace, the furnace body is sealed, and a vacuum of 5.0 × 10⁻⁶ is applied. -2 Below Pa, purge with 99.9995% high-purity argon three times (holding pressure for 5 minutes each time), maintaining an initial pressure of 0.1 MPa. Perform segmented degreasing according to the program: heat to 250-300℃ at a rate of 3℃ / min and hold for 135 minutes, with an argon flow rate of 1.0 m³ / min. 3 / h; 300-500℃, heat at 4℃ / min and hold for 115min; 500-650℃, heat at 5℃ / min and hold for 95min, turn on the microwave auxiliary module and increase the argon flow rate to 1.6m 3 / h; 650-800℃, heated at 6℃ / min and held for 65min, introducing 3% hydrogen (as a percentage of the total argon gas), and adjusting the pressure to 0.18MPa; after degreasing, cooled to 500℃ at 9℃ / min and stabilized for 30min. Then switched to a mixed atmosphere of 20% hydrogen + 80% nitrogen, with a flow rate of 1.6m³ / h. 3The temperature is increased to 1580℃ at a rate of 11℃ / min, held at that temperature for 1.5h, then decreased by 50℃ and held for 35min until reaching 1200℃. The temperature is then decreased to 800℃ at a rate of 12℃ / min and cooled to room temperature in the furnace. The pressure is controlled in a closed loop at 1.0-1.2MPa during the sintering process, with a compensation accuracy of ±0.05MPa, resulting in a dense sintered part.

[0024] Strengthening heat treatment: The sintered parts are quenched at 950-1050°C with a cooling rate of ≥130°C / s, followed by segmented tempering treatment with a tempering temperature range of 380-750°C and a total tempering time of 8-12 hours. After cooling to room temperature, the finished product is obtained.

[0025] In this embodiment of the invention, the sintered parts are placed in a box-type quenching furnace with a spacing of 20 mm between the blanks. After the furnace door is closed, argon gas is introduced for protection, and the heating system is started to raise the temperature to 1000°C at a rate of 10°C / min, and the temperature is maintained for 1.5 hours. After the holding period, the sintered parts are quickly fed into a quenching oil tank via a mechanical conveying device. The oil tank contains No. 20 mechanical oil at 45°C, and the oil volume is 10 times the volume of the sintered parts. A three-bladed spiral agitator is started to stir at 200 r / min to ensure a cooling rate ≥130°C / s, and the quenching time is 15 minutes. After quenching, the sintered parts are placed in an ultrasonic cleaning tank, and anhydrous ethanol at 45°C is added, with the liquid level 50 mm above the sintered parts. An ultrasonic generator is started to clean at 500W power and 40kHz frequency for 20 minutes to remove surface oil. After removing the surface oil, the parts are placed in an 80°C drying oven for 30 minutes. The dried sintered parts are placed in a mesh belt tempering furnace at a mesh belt speed of 0.5 m / min. The temperature is increased to 420℃ at 5℃ / min and held for 3.5 h, then increased to 550℃ at 6℃ / min and held for 3.5 h, and finally increased to 700℃ at 7℃ / min and held for 3 h. During the tempering process, air is circulated at a wind speed of 3 m / s to maintain the oxygen content in the furnace below 0.1%. After completion, the parts are naturally cooled to room temperature with the furnace to obtain high-hardness and high-toughness finished alloy steel.

[0026] Furthermore, in the alloy raw material proportioning step, the specific process parameters for the vacuum reduction treatment are: reduction temperature 850-950℃, reduction time 4-6h, and vacuum degree controlled at 1.0×10⁻⁶. -3 -5.0×10 -3 Pa, during the reduction process, hydrogen is used as an auxiliary reducing gas, with a hydrogen flow rate of 0.8-1.5 m³ / s. 3 / h, the particle size distribution of the gas-atomized pure iron powder satisfies D10=5-7μm, D50=8-12μm, D90=18-25μm, and the oxygen content of the iron powder is ≤0.08wt% and the carbon content is ≤0.03wt%.

[0027] In this embodiment of the invention, gas-atomized pure iron powder with D10=6μm, D50=10μm, and D90=22μm was screened. The oxygen content was confirmed to be 0.06wt% and the carbon content 0.02wt% by an oxygen-carbon analyzer. The iron powder was then spread evenly on a porous graphite tray in the vacuum reduction furnace, with a thickness controlled at 30mm to ensure uniform heating. The furnace door was closed, and the vacuum pump was started, performing a three-stage vacuuming process: first, evacuating to 1.0×10⁻⁶... -1 Pa, stabilize for 10 min; then pump to 1.0 × 10 Pa. -2 Pa, stable for 8 minutes; finally pumped to 3.0 × 10⁻⁶ Pa. -3 Maintain a stable vacuum level for 30 minutes, then purge air and impurities from the furnace. Turn on the hydrogen supply system and apply hydrogen at a rate of 1.2 m³ / s using a flow controller. 3 Hydrogen gas is introduced at a rate of / h, and the furnace heating module is activated simultaneously, employing a stepped heating mode: 5℃ / min for temperatures below 200℃, 8℃ / min for 200-600℃, and 3℃ / min for 600-900℃, precisely reaching 900℃. The temperature is then maintained at 900℃, and 3.0 × 10⁻⁶ ppm is applied. - 3 Under a vacuum of Pa, reduction was carried out continuously for 5 hours. During the reduction process, the vacuum level, hydrogen flow rate, and furnace temperature were recorded every 30 minutes. The heating power and hydrogen valve opening were adjusted based on feedback to ensure that parameter fluctuations did not exceed ±5℃ and ±0.1m. 3 / h, ±1.0×10 - 4 Pa. After the reduction is complete, turn off the heating module, keep hydrogen in the flow, and allow it to cool naturally to below 300°C. Then, turn off the hydrogen supply system and slowly introduce argon gas through the inert gas replacement valve to gradually restore the furnace pressure to atmospheric pressure. Open the furnace door and remove the iron powder to complete the removal of impurities and oxide layers.

[0028] Furthermore, in the feeding preparation step, the specific preparation process of the composite adhesive is as follows: phenolic resin and polyoxymethylene are mixed at a weight ratio of 72-77%:23-28%, and an antioxidant accounting for 0.3-0.8% of the total weight of the composite adhesive is added. The mixture is stirred at 120-140°C for 30-50 minutes at a stirring speed of 300-500 r / min. After cooling to room temperature, the mixture is pulverized to a particle size ≤500 μm, and then a lubricant accounting for 0.5-1.5% of the total weight of the composite adhesive is added and mixed evenly.

[0029] In this embodiment of the invention, phenolic resin and polyoxymethylene are accurately weighed at a weight ratio of 75%:25% and placed into a stainless steel mixing tank with jacketed heating. Simultaneously, 0.5% of the total weight of the composite binder as an antioxidant is added. The inner wall of the mixing tank is coated with a polytetrafluoroethylene coating to prevent material adhesion. The heat transfer oil circulation system of the mixing tank is activated, raising the oil temperature to 130°C. The heating power is adjusted based on feedback data from the tank wall temperature sensor to ensure the material temperature inside the tank remains stable at 130°C ± 3°C. The stirring paddle is then activated at a speed of 400 r / min, employing a double-ribbed structure to ensure the material tumbles and mixes. After continuous stirring for 40 minutes, the heating system and stirring paddle are turned off, the mixing tank outlet is opened, and the molten mixture is poured into a stainless steel tray and allowed to cool naturally to room temperature, forming a solid block-shaped composite binder. The solid composite binder was placed in a high-speed pulverizer equipped with carbide blades. The pulverizing time was set to 15 minutes. After pulverization, the particles were screened through a 40-mesh sieve, and particles with a diameter ≤500μm were collected. Larger particles on the sieve were returned to the pulverizer for re-pulverization. The screened composite binder particles were then fed into a V-type mixer. A lubricant, accounting for 1.0% of the total weight of the composite binder, was added. The mixer inlet was closed, and the equipment was started and mixed at a speed of 25 r / min for 20 minutes. During the mixing process, the machine was stopped every 5 minutes to observe the mixing uniformity, ensuring that there was no obvious stratification between the lubricant and binder particles.

[0030] Furthermore, in the feeding preparation step, the lubricant is a compound system of zinc stearate and polyethylene glycol, wherein zinc stearate accounts for 60-75% of the total weight of the lubricant and polyethylene glycol accounts for 25-40% of the total weight of the lubricant; the screw speed of the twin-screw extruder is 80-120 r / min, the extrusion temperature is consistent with the mixing temperature, and an online viscosity monitoring device is used to monitor the material viscosity in real time during the extrusion process. When the material viscosity deviates from the range of 500-800 Pa·s, dynamic correction is made by adjusting the corresponding screw speed of the twin-screw extruder by ±5-15 r / min to ensure that the length-to-diameter ratio of the cut cylindrical particles is 1.0-1.5:1.

[0031] In this embodiment of the invention, zinc stearate and polyethylene glycol are weighed at a weight ratio of 70%:30% and placed in a high-speed mixer. The mixture is then mixed at 800 r / min for 10 min to prepare a uniform compound lubricant. After mixing, the mixture is sealed and stored to prevent moisture absorption. Alloy steel powder and composite binder are added to a mixer at a weight ratio of 75%:25%. The mixer chamber is purged with argon gas three times. The inlet valve is closed to maintain positive pressure of argon gas in the chamber. The heating system is started to raise the chamber temperature to 205°C. The mixer rotor is started and mixed at 60 r / min for 220 min. During the mixing process, the viscosity of the system is monitored in real time using a built-in viscosity monitoring probe. When the viscosity is below 500 Pa·s, the rotor speed is appropriately increased by 5-10 r / min; when it is above 800 Pa·s, the rotor speed is decreased by 5-10 r / min to ensure that the viscosity is stable at around 650 Pa·s. After internal mixing, open the mixer outlet and feed the material into a twin-screw extruder. Set the screw speed to 100 rpm and the temperature of each section of the extruder barrel to 205°C, consistent with the mixing temperature. An online viscosity monitoring device is installed at the extruder die head to provide real-time feedback on material viscosity data. When the viscosity monitoring device shows a deviation from the set range, the screw speed is dynamically adjusted through the extruder control system: increasing by 5-15 rpm when the viscosity is too high and decreasing by 5-15 rpm when the viscosity is too low. The extruded strip-shaped material is cut by a rotary cutter. The cutter blade speed is linked to the extrusion speed to ensure that the cut cylindrical particles are 6 mm in length and 4 mm in diameter, with a length-to-diameter ratio of 1.5:1.

[0032] Furthermore, in the injection molding step, the three-stage gradient temperature control of the injection molding machine is specifically as follows: the temperature of the front section of the barrel is 185-200°C, the temperature of the middle section is 200-215°C, and the temperature of the rear section is 215-225°C. The mold temperature is controlled at 60-85°C. The temperature control and cooling method adopts a combination of water cooling and air cooling. Water cooling is used for the first 8-15 seconds, with a cooling water temperature of 15-25°C. Air cooling is used for the last 8-20 seconds, with an air speed of 3-6 m / s. Ejector pin demolding is used. The number of ejector pins is set to 4-8 according to the shape of the injection blank, and the ejector pin ejection speed is 5-10 mm / s.

[0033] In this embodiment of the invention, the injection molding machine's preheating system is activated, setting the barrel temperature to 195°C for the front section, 210°C for the middle section, and 220°C for the rear section, with the mold temperature at 75°C. Heating is achieved through segmented heating coils in the barrel and internal heating tubes in the mold, with each segment equipped with an independent temperature controller to ensure temperature fluctuations do not exceed ±3°C. The prepared feed material is fed into the injection molding machine hopper, where a vibration device at 50Hz is installed to prevent feed bridging. The injection molding machine screw is started, conveying the feed material into the barrel for melting. The screw speed is set to 80 r / min to ensure thorough plasticization of the material. The injection pressure is set to 170 MPa, and the injection speed to 65 mm / s. The hydraulic system drives the screw to inject the molten material into the mold cavity. After injection, the process switches to the holding pressure stage, with a holding pressure of 120 MPa and a holding time of 22 seconds. During the holding pressure process, a pressure sensor monitors the pressure in real time, and the hydraulic valve is adjusted to maintain stable pressure. After the pressure holding period, the cooling system is activated. For the first 12 seconds, the water cooling circuit is turned on, circulating 18°C ​​cooling water through the mold cooling channels. The cooling water pump pressure is set to 0.3MPa to ensure stable cooling water flow. For the next 15 seconds, the water cooling is turned off, and the air cooling system is activated, blowing out a 4.5m / s ambient temperature airflow through the air outlets around the mold. The air cooling channels use a honeycomb structure to ensure uniform airflow. After cooling, the demolding mechanism is activated. This mechanism is equipped with six evenly distributed ejector pins made of high-speed steel, symmetrically arranged 5mm from the edge of the injection preform. A servo motor drives the ejector pins to eject synchronously at a speed of 8mm / s. During ejection, a displacement sensor monitors the ejector pin stroke to ensure the injection preform smoothly leaves the mold.

[0034] Furthermore, in the continuous thermal debinding and sintering process, the inert atmosphere is high-purity argon with a purity ≥99.999%, and the specific stages of the segmented heating and debinding are 250-350°C, 350-500°C, 500-650°C, and 650-800°C, with heating rates of 2-4°C / min, 3-5°C / min, 4-6°C / min, and 5-7°C / min, respectively, and holding times of 120-150 min, 100-130 min, 80-110 min, and 50-80 min, respectively.

[0035] In this embodiment of the invention, dense injection preforms are neatly arranged on a graphite carrier with perforations, maintaining a spacing of 10 mm between the preforms. The carrier is placed in a continuous atmosphere sintering furnace, and after the furnace door is closed, the vacuum system is activated to evacuate to a vacuum level of 1.0 × 10⁻⁶ mm. -2 The pressure was increased to 0.1 MPa, then purged with 99.9995% high-purity argon gas until the furnace pressure reached 0.1 MPa. This purging process was repeated three times, with a pressure hold time of 5 minutes after each purging. The furnace heating system was then started, initially raising the temperature to 300°C at a rate of 3°C / min and holding for 135 minutes. Simultaneously, the argon gas circulation pump was activated at a rate of 0.9 m³ / min. 3Argon gas is circulated within the furnace at a flow rate of [flow rate] / h. A condenser is installed inside the furnace to collect the decomposition products of the low-molecular-weight binder. After the first stage, the temperature is increased to 450℃ at a rate of 4℃ / min and held for 115min, with the argon gas flow rate increased to 1.2m³ / h. 3 The temperature was then increased to 600℃ at a rate of 5℃ / min and held for 95 minutes, with continuous dynamic circulation of argon gas to enhance the removal of decomposition products. After the third stage, the temperature was increased to 750℃ at a rate of 6℃ / min and held for 65 minutes. During this stage, the exhaust gas composition was monitored using an in-furnace gas analyzer. When the content of volatile organic compounds in the exhaust gas was below 0.01%, the degreasing was considered nearly complete. Throughout the degreasing process, the temperature distribution was monitored by multiple temperature sensors in the furnace, and the power of the heating elements was adjusted to ensure that the temperature difference between different areas did not exceed ±5℃. At the same time, the exhaust argon gas was purified by an exhaust gas treatment device to remove harmful volatiles before being released.

[0036] Furthermore, in the continuous thermal desintering process, the reducing mixed atmosphere is a mixture of hydrogen and nitrogen, wherein hydrogen accounts for 15-25% of the total volume of the mixed gas, nitrogen accounts for 75-85% of the total volume of the mixed gas, and the flow rate of the mixed gas is 1.2-2.0 m³ / s. 3 / h, a pressure closed-loop control system is adopted during the sintering process. When the pressure inside the continuous atmosphere sintering furnace deviates from the range of 0.8-1.5MPa, it is compensated by adjusting the mixed gas inlet flow rate, with a compensation accuracy of ±0.05MPa.

[0037] In this embodiment of the invention, after degreasing, the high-purity argon gas supply valve is closed, and the hydrogen and nitrogen mixed gas preparation system is started. The volume ratio of hydrogen to nitrogen is precisely controlled at 20%:80% using a mass flow controller. The mixed gas is dehydrated by a dryer and then introduced into the sintering furnace. The mixed gas flow valve is adjusted to set the flow rate to 1.6 m³ / s. 3 A continuous flow of hydrogen gas is introduced into the furnace at a rate of 1.6 m³ / h for 15 minutes to displace residual argon. The hydrogen concentration in the furnace is monitored in real time using a gas composition detector. When the hydrogen concentration stabilizes at 20% ± 1%, the displacement is stopped, and the atmosphere is deemed to meet the standard. The furnace heating system is then started, using a segmented heating mode: heating from 800-1200℃ at a rate of 10℃ / min, from 1200-1580℃ at a rate of 11℃ / min, and finally reaching 1580℃. During the heating process, the mixed gas flow rate is maintained at 1.6 m³ / h. 3 / h remains unchanged. Activate the pressure closed-loop control system, setting the target furnace pressure to 1.2 MPa. Collect pressure data in real time using the furnace pressure sensor. When the pressure drops below 0.8 MPa, increase the mixed gas inlet flow rate by 0.1-0.2 m³ / h. 3 / h; When the pressure is higher than 1.5MPa, reduce the intake air flow rate by 0.1-0.2m. 3 / h, with compensation accuracy controlled within ±0.05MPa. During sintering, the mixed gas is evenly diffused through an annular distributor inside the furnace. The distributor has 2mm diameter vent holes to ensure that the gas covers the surface of all sintered parts. At the same time, some gas inside the furnace is periodically discharged and fresh mixed gas is added to prevent the accumulation of impurities from affecting the sintering quality.

[0038] Furthermore, in the continuous hot desintering process, after heating to 1500-1650℃, constant temperature sintering is first carried out for 1-2 hours, followed by stepped cooling sintering, specifically, holding at 50℃ for 30-45 minutes until the temperature drops to 1200℃, and then cooling to 800℃ at a rate of 10-15℃ / min, and finally cooling to room temperature with the furnace. During the stepped cooling sintering process, the mixed gas flow rate remains constant, and the furnace pressure is maintained at 1.0-1.2MPa.

[0039] In this embodiment of the invention, after heating to 1580°C, the flow rate of the mixed gas is maintained at 1.6 m³ / s. 3 The furnace pressure was 1.2 MPa, and sintering was carried out at a constant temperature for 1.5 hours. Temperature, pressure, and gas composition were recorded every 20 minutes during the isothermal process to ensure parameter stability. After the isothermal period, a stepped cooling program was initiated. The first stage involved reducing the temperature from 1580℃ to 1530℃ at a rate of 5℃ / min, holding at 1530℃ for 35 minutes. This cooling-holding process was repeated every 50℃ decrease until the temperature reached 1200℃. During the stepped cooling process, the mixed gas flow rate was maintained at 1.6 m³ / h. 3 The furnace pressure is maintained at 1.0-1.2 MPa through a closed-loop pressure system, with the pressure changes during cooling balanced by adjusting the gas discharge rate. Once the temperature drops to 1200℃, the stepped cooling program is shut down, and the rapid cooling system is activated, lowering the temperature to 800℃ at a rate of 12℃ / min. Mixed gas is continuously introduced during cooling to prevent oxidation of the sintered parts. After the temperature drops to 800℃, the heating system and mixed gas supply system are shut down, and the furnace insulation layer is opened, allowing the furnace temperature to cool naturally to room temperature. The furnace temperature is recorded every hour during cooling to ensure a uniform cooling rate and prevent cracking of the sintered parts due to thermal stress.

[0040] Furthermore, in the enhanced heat treatment step, the quenching heat treatment adopts oil quenching, the quenching medium is No. 20 machine oil, the quenching oil temperature is controlled at 40-60°C, a stirring device is used during the quenching process, the stirring speed is 150-250 r / min, and the oil stains on the surface of the sintered part after quenching are removed by ultrasonic cleaning, the cleaning medium is anhydrous ethanol, the cleaning temperature is 40-50°C, and the cleaning time is 15-25 min.

[0041] In this embodiment of the invention, the sintered parts are placed in a box-type quenching furnace with a 20mm spacing between them to prevent collisions during quenching. The furnace door is closed and the heating system is started, raising the temperature to 1000℃ at a rate of 10℃ / min. Argon gas is introduced during the heating process to prevent oxidation of the sintered parts surface. After reaching 1000℃, the temperature is maintained for 1.5 hours. After the holding period, the furnace door is quickly opened, and the sintered parts are conveyed into a quenching oil tank via a mechanical conveying device. The quenching oil tank contains No. 20 mechanical oil at 45℃, and its volume is 10 times that of the sintered parts to ensure effective cooling. The stirring device in the oil tank is activated. The stirring paddle uses a three-bladed spiral structure and stirs the quenching oil at a speed of 200r / min to ensure uniform oil temperature and accelerate heat transfer, ensuring a cooling rate of ≥130℃ / s for the sintered parts. The quenching time is set to 15 minutes. After quenching, the sintered part is removed from the oil bath and placed in an ultrasonic cleaning tank. Anhydrous ethanol at 45°C is added to the cleaning tank, with the ethanol level 50mm above the sintered part. The ultrasonic generator is started, set to 500W power and 40kHz frequency, and cleaned for 20 minutes. During the cleaning process, the removal of oil stains from the surface of the sintered part is observed through the observation window. After cleaning, the ultrasonic generator is turned off, and the sintered part is removed and placed in a drying oven at 80°C for 30 minutes to remove residual anhydrous ethanol, resulting in an oil-free quenched sintered part.

[0042] Furthermore, in the enhanced heat treatment step, the segmented tempering process is specifically divided into three stages: the first stage tempering temperature is 380-450°C, and the holding temperature is 3-4 hours; the second stage tempering temperature is 500-600°C, and the holding temperature is 3-4 hours; the third stage tempering temperature is 650-750°C, and the holding temperature is 2-4 hours. The heating rate of each stage tempering is 5-8°C / min. During the tempering process, air circulation heating is used, and the circulation wind speed is 2-4 m / s. After tempering, the product is obtained by natural cooling to room temperature.

[0043] In this embodiment of the invention, the dried sintered parts are placed in a mesh belt tempering furnace. The mesh belt speed is set to 0.5 m / min to ensure uniform heating of the sintered parts within the furnace. The furnace door is closed, and the heating system is started. The first-stage tempering temperature is set to 420°C, with a heating rate of 5°C / min. After reaching 420°C, the mesh belt speed is maintained constant for 3.5 hours. During tempering, the furnace air circulation system is activated, with a circulating fan driving airflow at a speed of 3 m / s. The air is heated by the heating tubes and then evenly blown onto the surface of the sintered parts. After the first-stage tempering is completed, the heating system is adjusted to raise the temperature to 550°C at a heating rate of 6°C / min. After reaching the temperature, it is held for 3.5 hours. During the holding period, the furnace temperature is monitored every hour, and the temperature is maintained stable at 550°C ± 3°C by adjusting the heating tube power. After the second stage of tempering, the temperature is further increased to 700℃ at a rate of 7℃ / min and held for 3 hours. During this stage, the atmosphere is monitored using an oxygen content detector inside the furnace to ensure that the oxygen content is below 0.1% to prevent oxidation of the sintered parts. After the three-stage tempering is completed, the heating system is turned off, while the air circulation system is kept running to allow the sintered parts to cool naturally to room temperature. During the cooling process, the conveyor belt continues to run at a speed of 0.5m / min to avoid localized overheating of the sintered parts. After cooling to room temperature, the finished product is collected from the outlet of the tempering furnace.

[0044] The present invention will be further described below with reference to corresponding Examples 1-3 and Comparative Examples 1-5, and the test results table is provided in detail below: Example 1 This embodiment provides an integrated injection molding and sintering process for preparing high-density alloy steel, including the following steps: (1) Alloy raw material ratio: The alloy steel powder, by weight percentage, comprises 2.0% chromium, 3.0% nickel, 0.8% molybdenum, 0.2% vanadium, 0.7% carbon, 0.15% silicon, 0.3% manganese, and 92.85% gas-atomized pure iron powder.

[0045] Pure iron powder atomized by gas was subjected to vacuum reduction treatment at a reduction temperature of 850℃, a reduction time of 4 hours, and a vacuum degree of 1.0×10⁻⁶. -3 Pa, during the reduction process, hydrogen gas is introduced as an auxiliary reducing gas, with a hydrogen flow rate of 0.8 m³ / s. 3 / h. The particle size distribution of this gas-atomized pure iron powder is D10 = 5μm, D50 = 8μm, D90 = 18μm, with an oxygen content of 0.06wt% and a carbon content of 0.02wt%.

[0046] (2) Feed preparation: Preparation of composite adhesive: Phenolic resin and polyoxymethylene are mixed at a weight ratio of 72%:28%, and antioxidant accounting for 0.3% of the total weight of the composite adhesive is added. The mixture is stirred at 300 r / min for 30 min at 120℃. After cooling to room temperature, the mixture is pulverized to a particle size ≤500 μm. Then, lubricant accounting for 0.5% of the total weight of the composite adhesive is added, which consists of 60% zinc stearate and 40% polyethylene glycol. The mixture is then uniformly mixed to obtain the composite adhesive.

[0047] Alloy steel powder and the aforementioned composite binder were mixed at a weight ratio of 72%:28% and kneaded under inert gas protection at 185°C for 190 minutes, with the system viscosity controlled at 500 Pa·s during the kneading process. The mixture was then extruded using a twin-screw extruder at a screw speed of 80 r / min and an extrusion temperature of 185°C. An online viscosity monitoring device was used to monitor the material viscosity in real time during extrusion. When the viscosity deviated from the range, the screw speed was adjusted ±5 r / min for dynamic correction. The mixture was then cut into 4 mm cylindrical particles with a length-to-diameter ratio of 1.0:1, thus obtaining the viscosity feedstock.

[0048] (3) Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel uses a three-stage gradient temperature control: 185℃ in the front section, 200℃ in the middle section, and 215℃ in the rear section. The mold temperature is controlled at 60℃. The injection pressure is set to 150MPa, the injection speed to 55mm / s, the holding pressure to 100MPa, and the holding time to 16s. The temperature control and cooling method uses a combination of water cooling and air cooling. Water cooling (15℃) is used for the first 8s, and air cooling (3m / s) is used for the next 8s. After 16 seconds of cooling, ejector pin demolding is used, with 4 ejector pins and an ejection speed of 5mm / s, thus obtaining a dense injection preform.

[0049] (4) Continuous hot desintering treatment: The dense injection-molded preform is fed into a continuous atmosphere sintering furnace, and high-purity argon gas with a purity of ≥99.999% is introduced as an inert atmosphere. The preform is degreased by staged heating: 250-350℃ (heating rate 2℃ / min, holding for 120min), 350-500℃ (heating rate 3℃ / min, holding for 100min), 500-650℃ (heating rate 4℃ / min, holding for 80min), and 650-800℃ (heating rate 5℃ / min, holding for 50min).

[0050] After degreasing, the atmosphere is switched to a reducing mixed atmosphere (15% hydrogen, 85% nitrogen, mixed gas flow rate 1.2 m³ / h). 3The temperature was increased to 1500℃ at a rate of 8℃ / min, followed by constant-temperature sintering for 1 hour. Then, a stepped cooling sintering process was adopted, with each 50℃ decrease followed by a 30-min holding period until the temperature reached 1200℃. Afterward, the temperature was cooled to 800℃ at a rate of 10℃ / min, and finally cooled to room temperature in the furnace. During the sintering process, the furnace pressure was maintained at 0.8MPa through a closed-loop pressure control system with a compensation accuracy of ±0.05MPa. During the stepped cooling phase, the furnace pressure was maintained at 1.0MPa, and the mixed gas flow rate remained constant, ultimately producing the sintered part.

[0051] (5) Enhanced heat treatment: The sintered parts are subjected to quenching heat treatment at 950℃ using oil quenching. The quenching medium is No. 20 machine oil, and the quenching oil temperature is controlled at 40℃. During the quenching process, a stirring device is used (stirring speed 150r / min), and the cooling rate is 130℃ / s.

[0052] After quenching, ultrasonic cleaning was used to remove surface oil (cleaning medium: anhydrous ethanol, cleaning temperature: 40℃, cleaning time: 15min). Then, a staged tempering process was performed: the first stage tempering temperature was 380℃, held for 3 hours; the second stage tempering temperature was 500℃, held for 3 hours; and the third stage tempering temperature was 650℃, held for 2 hours. The heating rate for each stage of tempering was 5℃ / min. Air circulation heating was used during tempering (circulation wind speed: 2m / s). After tempering, the product was naturally cooled to room temperature to obtain the final product.

[0053] Example 2 This embodiment provides an integrated injection molding and sintering process for preparing high-density alloy steel, including the following steps: (1) Alloy raw material ratio: The alloy steel powder, by weight percentage, comprises 2.5% chromium, 3.8% nickel, 1.2% molybdenum, 0.4% vanadium, 0.8% carbon, 0.25% silicon, 0.5% manganese, and 90.55% gas-atomized pure iron powder.

[0054] Pure iron powder atomized by gas was subjected to vacuum reduction treatment at a reduction temperature of 900℃, a reduction time of 5 hours, and a vacuum degree of 3.0×10⁻⁶. -3 Pa, hydrogen flow rate during reduction is 1.2 m³ / s. 3 / h. The particle size distribution of this gas-atomized pure iron powder is D10 = 6μm, D50 = 10μm, D90 = 22μm, with an oxygen content of 0.04wt% and a carbon content of 0.015wt%.

[0055] (2) Feed preparation: Preparation of composite adhesive: Phenolic resin and polyoxymethylene are mixed at a weight ratio of 75%:25%, and antioxidant accounting for 0.5% of the total weight of the composite adhesive is added. The mixture is stirred at 400 r / min for 40 min at 130℃. After cooling to room temperature, the mixture is pulverized to a particle size ≤500 μm. Then, lubricant accounting for 1.0% of the total weight of the composite adhesive is added, which consists of 68% zinc stearate and 32% polyethylene glycol. The mixture is then uniformly mixed to obtain the composite adhesive.

[0056] Alloy steel powder and the above-mentioned composite binder were mixed at a weight percentage of 75%:25% and kneaded under inert gas protection at 205°C for 220 min, with the system viscosity controlled at 650 Pa·s during the kneading process. The mixture was then extruded using a twin-screw extruder at a screw speed of 100 r / min and an extrusion temperature of 205°C. An online viscosity monitoring device was used to monitor the material viscosity in real time during extrusion. When the viscosity deviated from the range, the screw speed was adjusted ±10 r / min for dynamic correction. The mixture was then cut into 6 mm cylindrical particles with a length-to-diameter ratio of 1.2:1 to obtain the viscosity feedstock.

[0057] (3) Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel uses a three-stage gradient temperature control: 195℃ in the front section, 208℃ in the middle section, and 220℃ in the rear section. The mold temperature is controlled at 75℃. The injection pressure is set to 170MPa, the injection speed to 65mm / s, the holding pressure to 120MPa, and the holding time to 22s. The temperature control and cooling method combines water cooling and air cooling. Water cooling (20℃) is used for the first 12s, and air cooling (4.5m / s) is used for the last 15s. After 27 seconds of cooling, ejector pin demolding is used, with 6 ejector pins and an ejection speed of 8mm / s, thus obtaining a dense injection preform.

[0058] (4) Continuous hot desintering treatment: The dense injection-molded preform is fed into a continuous atmosphere sintering furnace, and high-purity argon gas with a purity of ≥99.999% is introduced as an inert atmosphere. The preform is degreased by staged heating: 250-350℃ (heating rate 3℃ / min, holding for 135min), 350-500℃ (heating rate 4℃ / min, holding for 115min), 500-650℃ (heating rate 5℃ / min, holding for 95min), and 650-800℃ (heating rate 6℃ / min, holding for 65min).

[0059] After degreasing, switch to a reducing mixed atmosphere (20% hydrogen, 80% nitrogen, mixed gas flow rate 1.6 m³ / h). 3The temperature was increased to 1580℃ at a rate of 11℃ / min, followed by isothermal sintering for 1.5 hours. Then, a stepped cooling sintering process was adopted, with each 50℃ decrease followed by a 38-min holding period until the temperature reached 1200℃. Afterward, the temperature was cooled to 800℃ at a rate of 12℃ / min, and finally cooled to room temperature with the furnace. During the sintering process, the furnace pressure was maintained at 1.2MPa through a closed-loop pressure control system with a compensation accuracy of ±0.05MPa. During the stepped cooling phase, the furnace pressure was maintained at 1.1MPa, and the mixed gas flow rate remained constant, resulting in the sintered parts.

[0060] (5) Enhanced heat treatment: The sintered parts are subjected to quenching heat treatment at 1000℃ using oil quenching. The quenching medium is No. 20 machine oil, and the quenching oil temperature is controlled at 50℃. During the quenching process, a stirring device is used (stirring speed 200r / min), and the cooling rate is 150℃ / s.

[0061] After quenching, ultrasonic cleaning was used to remove surface oil contaminants. The cleaning medium was anhydrous ethanol, the cleaning temperature was 45℃, and the cleaning time was 20 minutes. Subsequently, a staged tempering process was performed: the first stage tempering temperature was 420℃, held for 3.5 hours; the second stage tempering temperature was 550℃, held for 3.5 hours; and the third stage tempering temperature was 700℃, held for 3 hours. The heating rate for each stage of tempering was 6.5℃ / min. Air circulation heating was used during tempering (circulation wind speed 3 m / s). After tempering, the product was naturally cooled to room temperature to obtain the finished product.

[0062] Example 3 This embodiment provides an integrated injection molding and sintering process for preparing high-density alloy steel, including the following steps: (1) Alloy raw material ratio: The alloy steel powder, by weight percentage, comprises 3.0% chromium, 4.5% nickel, 1.5% molybdenum, 0.6% vanadium, 0.9% carbon, 0.4% silicon, 0.7% manganese, and 88.4% gas-atomized pure iron powder.

[0063] Pure iron powder atomized by gas was subjected to vacuum reduction treatment at a reduction temperature of 950℃, a reduction time of 6 hours, and a vacuum degree of 5.0×10⁻⁶. -3 Pa, hydrogen flow rate during reduction is 1.5 m³ / s. 3 / h. The particle size distribution of this gas-atomized pure iron powder is D10 = 7μm, D50 = 12μm, D90 = 25μm, with an oxygen content of 0.03wt% and a carbon content of 0.01wt%.

[0064] (2) Feed preparation: Preparation of composite adhesive: Phenolic resin and polyoxymethylene are mixed at a weight ratio of 77%:23%, and antioxidant accounting for 0.8% of the total weight of the composite adhesive is added. The mixture is stirred at 500 r / min for 50 min at 140℃. After cooling to room temperature, the mixture is pulverized to a particle size ≤500 μm. Then, lubricant accounting for 1.5% of the total weight of the composite adhesive is added, including 75% zinc stearate and 25% polyethylene glycol. The mixture is then uniformly mixed to obtain the composite adhesive.

[0065] Alloy steel powder and the above-mentioned composite binder were mixed at a weight percentage of 77%:23%, and kneaded under inert gas protection at 225°C for 250 min, with the system viscosity controlled at 800 Pa·s during the kneading process. The mixture was then extruded using a twin-screw extruder (screw speed 120 r / min, extrusion temperature 225°C). During extrusion, an online viscosity monitoring device was used to monitor the material viscosity in real time. When the viscosity deviated from the range, the screw speed was adjusted ±15 r / min for dynamic correction. The mixture was then cut into 9 mm cylindrical particles with a length-to-diameter ratio of 1.5:1 to obtain the viscosity feedstock.

[0066] (3) Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel uses a three-stage gradient temperature control: 200℃ in the front section, 215℃ in the middle section, and 225℃ in the rear section. The mold temperature is controlled at 85℃. The injection pressure is set to 190MPa, the injection speed to 75mm / s, the holding pressure to 135MPa, and the holding time to 28s. The temperature control and cooling method uses a combination of water cooling and air cooling. Water cooling (cooling water temperature 25℃) is used for the first 15s, and air cooling (air velocity 6m / s) is used for the next 20s. After 35 seconds of cooling, ejector pin demolding is used (eight ejector pins, ejection speed 10mm / s) to obtain a dense injection preform.

[0067] (4) Continuous hot desintering treatment: The dense injection-molded preform is fed into a continuous atmosphere sintering furnace, and high-purity argon gas with a purity of ≥99.999% is introduced as an inert atmosphere. The preform is degreased by staged heating: 250-350℃ (heating rate 4℃ / min, holding for 150min), 350-500℃ (heating rate 5℃ / min, holding for 130min), 500-650℃ (heating rate 6℃ / min, holding for 110min), and 650-800℃ (heating rate 7℃ / min, holding for 80min).

[0068] After degreasing, the atmosphere was switched to a reducing mixed atmosphere (25% hydrogen, 75% nitrogen, mixed gas flow rate 2.0 m³ / h). The temperature was increased to 1650℃ at a heating rate of 14℃ / min, and then sintered at this temperature for 2 hours. A stepped cooling sintering process was then employed, specifically, holding the temperature at 50℃ decreases for 45 minutes until the temperature reached 1200℃. Afterward, the temperature was cooled to 800℃ at a cooling rate of 15℃ / min, and finally cooled to room temperature in the furnace. During the sintering process, the furnace pressure was maintained at 1.5 MPa through a closed-loop pressure control system with a compensation accuracy of ±0.05 MPa. During the stepped cooling phase, the furnace pressure was maintained at 1.2 MPa, and the mixed gas flow rate remained constant, resulting in the sintered parts.

[0069] (5) Enhanced heat treatment: The sintered parts are subjected to quenching heat treatment at 1050℃, using oil quenching. The quenching medium is No. 20 machine oil, and the quenching oil temperature is controlled at 60℃. During the quenching process, a stirring device is used (stirring speed 250r / min), and the cooling rate is 180℃ / s.

[0070] After quenching, ultrasonic cleaning was used to remove surface oil contaminants. The cleaning medium was anhydrous ethanol, the cleaning temperature was 50℃, and the cleaning time was 25 minutes. Subsequently, a staged tempering process was performed: the first stage tempering temperature was 450℃, held for 4 hours; the second stage tempering temperature was 600℃, held for 4 hours; and the third stage tempering temperature was 750℃, held for 4 hours. The heating rate for each stage of tempering was 8℃ / min. Air circulation heating (circulating wind speed 4 m / s) was used during tempering. After tempering, the product was naturally cooled to room temperature to obtain the final product.

[0071] Comparative Examples 1-5 Comparative Example 1: Unlike Example 2, ordinary reduced iron powder was used instead of gas-atomized pure iron powder (without vacuum reduction treatment), while other components and process steps were the same as in Example 2.

[0072] Comparative Example 2: Unlike Example 2, the composite adhesive was replaced with a single polyoxymethylene adhesive, no lubricant was added, and the other components and process steps were the same as in Example 2.

[0073] Comparative Example 3: Unlike Example 2, the mixing temperature in the feed preparation was 240°C and the mixing time was 280 min. Other components and process steps were the same as in Example 2.

[0074] Comparative Example 4: Unlike Example 2, the injection molding pressure was 130 MPa and the injection speed was 45 mm / s. Other components and process steps were the same as in Example 2.

[0075] Comparative Example 5: Unlike Example 2, in the continuous hot degreasing sintering process, the temperature was directly raised to 1580°C for sintering after degreasing, without using a stepped cooling method. Other components and process steps were the same as in Example 2.

[0076] Test methods and results The alloy steel products obtained in Examples 1-3 and Comparative Examples 1-5 underwent comprehensive performance testing. The testing methods were all performed in accordance with national or industry-standard practices, as detailed below: 1. Sintered density: Tested according to the method in GB / T4325-016 Determination of density of powder metallurgy materials; 2. Carbon content: Tested according to GB / T223.88-2000 Chemical Analysis Methods for Iron and Steel and Alloys: Determination of Total Carbon by Combustion-Volume Method; 3. Rockwell hardness (HRC): Tested according to GB / T230.1-2018 Metallic Materials Rockwell Hardness Test; 4. Vickers hardness (HV): Tested according to GB / T4340.1-2009 Metallic Materials Vickers Hardness Test; 5. Tensile strength, yield strength, elongation, and reduction of fracture: tested according to ASTM A370, "Mechanical Test Methods for Steel Products"; 6. Impact toughness (αk): Tested according to GB / T229-2020 Metallic Materials Charpy Impact Test Method (room temperature); 7. Oxygen content: Tested according to GB / T11261-2006 Determination of oxygen content in steel and alloys by pulse heating inert gas melting-infrared absorption method; 8. Grain size: The average grain size was determined by observing with a metallographic microscope and using Image-ProPlus software. 9. Corrosion resistance: Conduct a neutral salt spray test according to GB / T10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test, and record the corrosion rate after 240 hours; 10. Residual stress: The residual stress (MPa) on the surface was tested according to GB / T7704-2017 X-ray stress determination method. 11. Density: Calculated using Archimedes' displacement method combined with metallographic analysis, in percentages (%).

[0077] The test results are shown in Table 1: Table 1. Comprehensive Performance Test Results of Alloy Steel

[0078] To further verify the process stability, three sets of parallel experiments were conducted on Example 2, and the test results are shown in Table 2: Table 2 Performance test results of parallel test in Example 2

[0079] In summary, based on the experimental data in Tables 1 and 2, it can be seen that the positive indicators of Examples 1-3 compared to Comparative Examples 1-5 include sintering density (g / cm³). 3 Density (%), Rockwell hardness (HRC), Vickers hardness (HV), tensile strength (MPa), yield strength (MPa), impact toughness (αk, J / cm) 2 The positive indices include elongation (%), reduction of area after fracture (Z, %), and carbon content (wt%), while negative indices include oxygen content (wt%), grain size (μm), 240h salt spray corrosion rate (mm / a), and surface residual stress (MPa). Figure 1 As shown in Table 2); simultaneously, based on the test results and by setting the stability threshold corresponding to the coefficient of variation (when the coefficient of variation < 1.0%, it indicates excellent stability), the sintering density (g / cm³) can be determined. 3 The stability of tensile strength (MPa), yield strength (MPa), and density (%) is relatively excellent (e.g., Figure 2 (As shown). In each comparative example, a significant decrease in performance occurs due to a single process parameter or raw material deviating from the scope of protection of this application. The specific reasons are analyzed below: Comparative Example 1: Ordinary reduced iron powder was not subjected to vacuum reduction treatment, resulting in low purity, high oxygen content (0.156wt%), irregular particle shape, and an oxide layer on the surface. This led to poor particle bonding during sintering, with a density of only 82.3%, and a significant decline in mechanical properties and corrosion resistance.

[0080] Comparative Example 2: The single polyoxymethylene binder has low degreasing efficiency and a lot of residue. It also lacks lubricants, resulting in poor feed flowability. There are pore defects inside the injection blank. After sintering, the densification is insufficient, the carbon content is too high (0.92wt%), the microstructure is not uniform, and all performance is lower than that of the Example.

[0081] Comparative Example 3: When the mixing temperature (240℃) and time (280min) exceeded the process range, the binder decomposed prematurely, resulting in weakened interparticle bonding, poor feeding molding performance, and decreased injection compact density. At the same time, the residual carbon from the binder decomposition increased the carbon content and increased micro-defects.

[0082] Comparative Example 4: Insufficient injection pressure (130MPa) and speed (45mm / s) resulted in insufficient material filling of the mold cavity, leading to a porous interior of the injection preform. Although subsequent sintering could partially improve the situation, the final product density and mechanical properties were still lower than those of Example 2.

[0083] Comparative Example 5: Without stepped cooling sintering, the alloy grains grew (9.1 μm), the grain boundary bonding was weakened, and the mechanical properties, especially the impact toughness (46 J / cm), were affected. 2 The elongation (4.2%) and elongation (4.2%) were significantly reduced.

[0084] In summary, the injection molding and sintering integrated preparation process for high-density alloy steel presented in this application has significant technical advantages: The use of vacuum-reduced atomized pure iron powder combined with alloy proportions effectively reduces the oxygen content and impurities in the raw materials; optimized mixing parameters, combining phenolic resin-polyoxymethylene composite binder with specialized lubricants, ensure uniform feeding and flowability; three-stage gradient temperature-controlled injection molding and temperature-controlled cooling enhance the density of the injection preform; efficient degreasing and dense sintering are achieved simultaneously through segmented degreasing, a reducing mixed atmosphere, and stepped cooling sintering; and multi-stage intensified heat treatment optimizes the microstructure and releases residual stress, resulting in a product sintering density ≥7.82 g / cm³. 3 Density ≥ 98.6%, hardness 52-55 HRC, tensile strength ≥ 1685 MPa, yield strength ≥ 1420 MPa, elongation ≥ 5.3%, impact toughness ≥ 58 J / cm² 2 It has excellent corrosion resistance and comprehensive performance comparable to high-end forged alloy steel, and can be widely used in fields with extremely high requirements for material performance, such as machinery manufacturing and ceramics.

[0085] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A process for the integrated injection molding and sintering preparation of high-density alloy steel, characterized in that, Includes the following steps: Alloy raw material ratio: The alloy steel powder includes, by weight percentage, 2.0-3.0% chromium, 3.0-4.5% nickel, 0.8-1.5% molybdenum, 0.2-0.6% vanadium, 0.7-0.9% carbon, 0.15-0.4% silicon, and 0.3-0.7% manganese, with the balance being iron powder. The iron powder is pure iron powder that has been atomized and vacuum reduced to remove impurities and oxide layers. Feed preparation: The alloy steel powder and the composite binder corresponding to phenolic resin-polyoxymethylene are mixed at a weight percentage of 72-77%:23-28%. 0.5-1.5% of a lubricant is added to the composite binder. After mixing, the mixture is internally kneaded under inert gas protection at 185-225°C for 190-250 min. During the internal kneading process, the viscosity of the system is controlled at 500-800 Pa·s. Subsequently, the mixture is extruded through a twin-screw extruder and cut into cylindrical particles of 4-9 mm to obtain the viscosity feed. Injection molding: The viscous feedstock is fed into the injection molding machine. The barrel of the injection molding machine adopts a three-stage gradient temperature control, the injection pressure is 150-190MPa, the injection speed is 55-75mm / s, the holding pressure is 100-135MPa, the holding time is 16-28s, and a temperature-controlled cooling method is adopted. After cooling for 16-35 seconds, the mold is demolded to obtain a dense injection preform. Continuous hot debinding and sintering treatment: The dense injection blank is fed into a continuous atmosphere sintering furnace for debinding in stages under an inert atmosphere. The debinding temperature range is 250-800°C, and the holding time for each stage is 50-150 min. After debinding, the furnace is switched to a reducing mixed atmosphere and heated to 1500-1650°C at a heating rate of 8-14°C / min. Sintering is carried out for 6-9 h. The pressure inside the furnace is controlled at 0.8-1.5 MPa during the sintering process to produce sintered parts. Strengthening heat treatment: The sintered parts are quenched at 950-1050°C with a cooling rate of ≥130°C / s, followed by segmented tempering treatment with a tempering temperature range of 380-750°C and a total tempering time of 8-12 hours. After cooling to room temperature, the finished product is obtained.

2. The integrated injection molding and sintering process for high-density alloy steel according to claim 1, characterized in that, In the alloy raw material proportioning step, the specific process parameters for the vacuum reduction treatment are: reduction temperature 850-950℃, reduction time 4-6h, and vacuum degree controlled at 1.0×10⁻⁶. -3 -5.0×10 -3 Pa, during the reduction process, hydrogen is used as an auxiliary reducing gas, with a hydrogen flow rate of 0.8-1.5 m³ / s. 3 / h, the particle size distribution of the gas-atomized pure iron powder satisfies D10=5-7μm, D50=8-12μm, D90=18-25μm, and the oxygen content of the iron powder is ≤0.08wt% and the carbon content is ≤0.03wt%.

3. The integrated injection molding and sintering process for high-density alloy steel according to claim 1, characterized in that, In the feeding preparation step, the specific preparation process of the composite adhesive is as follows: phenolic resin and polyoxymethylene are mixed at a weight ratio of 72-77%:23-28%, and an antioxidant accounting for 0.3-0.8% of the total weight of the composite adhesive is added. The mixture is stirred at 120-140°C for 30-50 minutes at a stirring speed of 300-500 r / min. After cooling to room temperature, the mixture is pulverized to a particle size ≤500 μm. Then, a lubricant accounting for 0.5-1.5% of the total weight of the composite adhesive is added and mixed evenly.

4. The integrated injection molding and sintering process for high-density alloy steel according to claim 3, characterized in that, In the feeding preparation step, the lubricant is a compound system of zinc stearate and polyethylene glycol, wherein zinc stearate accounts for 60-75% of the total weight of the lubricant and polyethylene glycol accounts for 25-40% of the total weight of the lubricant; the screw speed of the twin-screw extruder is 80-120 r / min, and the extrusion temperature is consistent with the mixing temperature. During the extrusion process, an online viscosity monitoring device is used to monitor the material viscosity in real time. When the material viscosity deviates from the range of 500-800 Pa·s, dynamic correction is made by adjusting the corresponding screw speed of the twin-screw extruder by ±5-15 r / min to ensure that the length-to-diameter ratio of the cut cylindrical particles is 1.0-1.5:

1.

5. The integrated injection molding and sintering process for preparing high-density alloy steel according to claim 1, characterized in that, In the injection molding step, the three-stage gradient temperature control of the injection molding machine is as follows: the temperature of the front section of the barrel is 185-200°C, the temperature of the middle section is 200-215°C, and the temperature of the rear section is 215-225°C. The mold temperature is controlled at 60-85°C. The temperature control and cooling method adopts a combination of water cooling and air cooling. Water cooling is used for the first 8-15 seconds, with a cooling water temperature of 15-25°C. Air cooling is used for the last 8-20 seconds, with an air velocity of 3-6 m / s. Ejector pin demolding is used. The number of ejector pins is set to 4-8 according to the shape of the injection blank, and the ejector pin ejection speed is 5-10 mm / s.

6. The integrated injection molding and sintering process for high-density alloy steel according to claim 1, characterized in that, In the continuous hot desintering process, the inert atmosphere is high-purity argon with a purity ≥99.999%. The specific stages of the segmented heating and degreasing are 250-350°C, 350-500°C, 500-650°C, and 650-800°C, with heating rates of 2-4°C / min, 3-5°C / min, 4-6°C / min, and 5-7°C / min, respectively. The holding times for each stage are 120-150 min, 100-130 min, 80-110 min, and 50-80 min, respectively.

7. The integrated injection molding and sintering process for preparing high-density alloy steel according to claim 1, characterized in that, In the continuous thermal desintering process, the reducing mixed atmosphere is a mixture of hydrogen and nitrogen, wherein hydrogen accounts for 15-25% of the total volume of the mixed gas, nitrogen accounts for 75-85% of the total volume of the mixed gas, and the flow rate of the mixed gas is 1.2-2.0 m³ / s. 3 / h, a pressure closed-loop control system is adopted during the sintering process. When the pressure inside the continuous atmosphere sintering furnace deviates from the range of 0.8-1.5MPa, it is compensated by adjusting the mixed gas inlet flow rate, with a compensation accuracy of ±0.05MPa.

8. The integrated injection molding and sintering process for preparing high-density alloy steel according to claim 7, characterized in that, In the continuous hot desintering process, after heating to 1500-1650℃, constant temperature sintering is first carried out for 1-2 hours, followed by stepped cooling sintering, specifically, holding at 50℃ for 30-45 minutes until the temperature drops to 1200℃, and then cooling to 800℃ at a rate of 10-15℃ / min, and finally cooling to room temperature with the furnace. During the stepped cooling sintering process, the mixed gas flow rate remains constant, and the furnace pressure is maintained at 1.0-1.2MPa.

9. The integrated injection molding and sintering process for preparing high-density alloy steel according to claim 1, characterized in that, In the enhanced heat treatment step, the quenching heat treatment adopts oil quenching, the quenching medium is No. 20 machine oil, the quenching oil temperature is controlled at 40-60°C, a stirring device is used during the quenching process, the stirring speed is 150-250 r / min, and the oil stains on the surface of the sintered part after quenching are removed by ultrasonic cleaning, the cleaning medium is anhydrous ethanol, the cleaning temperature is 40-50°C, and the cleaning time is 15-25 min.

10. The integrated injection molding and sintering process for high-density alloy steel according to claim 9, characterized in that, In the aforementioned heat treatment step, the segmented tempering process is specifically divided into three stages: the first stage tempering temperature is 380-450°C, and the holding temperature is 3-4 hours; the second stage tempering temperature is 500-600°C, and the holding temperature is 3-4 hours; the third stage tempering temperature is 650-750°C, and the holding temperature is 2-4 hours. The heating rate of each stage tempering is 5-8°C / min. During the tempering process, air circulation heating is used, and the circulation wind speed is 2-4 m / s. After tempering, the product is obtained by natural cooling to room temperature.

Images