Ultrahigh-strength steel powder for injection molding, part and preparation method and application of ultrahigh-strength steel powder

Abstract

The invention provides ultrahigh-strength steel powder for injection molding, a part and a preparation method and application of the ultrahigh-strength steel powder. The ultrahigh-strength steel powder for injection molding comprises the following components in percentage by mass: 9%-11% of Cr, 6.5%-8.5% of Ni, 7%-9% of Co, 3.5%-5.5% of Mo, 0.01%-1.0% of Nb, 0 < C < = 0.03%, and the balance of Fe and inevitable impurities. The yield strength of an ultrahigh-strength steel part prepared by taking the steel as a raw material reaches 1800 MPa to 2000 MPa, and the tensile strength of the ultrahigh-strength steel part reaches 1800 MPa to 2100 MPa.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of powder injection molding, and particularly provides a component design and preparation method of powder injection molding super high strength steel, a super high strength steel part and a high-throughput preparation method and application thereof. BACKGROUND

[0002] Powder injection molding is a near-net shaping technology that can efficiently and mass-produce small metal parts with complex shapes and precise dimensions. This technology combines the advantages of powder metallurgy and plastic injection molding and has wide applications in consumer electronics, medical devices, aerospace precision parts, etc. However, traditional super high strength steel is mostly produced by casting and forging, and its application in powder injection molding process is limited. This is mainly because traditional super high strength steel, such as typical secondary hardening super high strength steel, needs to add alloying elements such as chromium (Cr), molybdenum (Mo), vanadium (V), and carbon (C) to form nanoscale carbides, achieve precipitation strengthening and fine-grain strengthening, but the high carbon content affects the flowability of the feedstock and the sintering performance of the powder, easily causing carbide aggregation and reducing material toughness; super low carbon high alloy martensitic age hardening steel relies on the addition of elements such as cobalt (Co), nickel (Ni), Mo, titanium (Ti), and aluminum (Al) to form intermetallic compounds, and uses precipitation strengthening to improve strength. This type of steel has good sintering performance, but the high content of Co and Ni increases the cost of the material, and Ti and Al elements are prone to form oxides during powdering and sintering, leading to an increase in oxygen content, and Ti element is also prone to react with carbon in the binder decomposed during thermal debinding, increasing the inclusion content and thus reducing the material performance.

[0003] For example, in patent CN118650159A "Composite age hardening stainless steel powder injection molding preparation method", the cobalt content is 14-18%, and the aluminum content is 0.1-1%; in patent CN118341972A "Cobalt-containing alloy steel powder injection molding feedstock and cobalt-containing alloy steel processing method", the cobalt content reaches 18%. These materials all contain a high content of cobalt, which is costly, and aluminum easily adsorbs oxygen, increasing the oxygen content. In addition, in patent CN103981436A "Metal powder injection molding high-strength martensitic age hardening steel and its manufacturing method", the nickel content is 17-19%, and the cobalt content is 8-10%, which is high in cost, and the lack of chromium results in poor corrosion resistance and limited comprehensive performance.

[0004] Based on the above status, there is an urgent need in the field to develop a new type of super high strength steel component design suitable for powder injection molding, which can balance the strength, toughness, and corrosion resistance while controlling the cost of the material. SUMMARY

[0005] The present application aims to design and optimize components by high-throughput methods to prepare a powder injection molding part with low cost, good sintering performance, low inclusions and oxygen content, high corrosion resistance and high strength.

[0006] To achieve the above object, the technical scheme adopted by the present application is as follows: The present application provides an ultra-high strength steel powder for injection molding, which comprises the following components in percentage by mass: Cr 9%~11%, Ni 6.5%~8.5%, Co 7%~9%, Mo 3.5%~5.5%, Nb 0.01%~1.0%, 0<C≤0.03%, and the rest is Fe and inevitable impurities.

[0007] The present application provides a preparation method of the above-mentioned ultra-high strength steel powder for injection molding, which comprises: after grading baking the bearing container, placing the master alloy in the bearing container for vacuum induction atomization to obtain the ultra-high strength steel powder for injection molding.

[0008] Further, the preparation method specifically comprises the following steps: S11, grading baking the bearing container in the vacuum induction melting furnace by using graphite core combined with induction, with the parameters of 25 KW~35 KW baking for 0.5 h~1.5 h, gradually increasing the temperature to 35 KW~45 KW baking for 0.5 h~1.5 h, to obtain the pretreated bearing container; S12, placing the master alloy in the bearing container and performing induction heating under the conditions of inert gas protection and a temperature of 1650℃~1750℃; after the master alloy is completely melted, obtaining the molten metal liquid; S13, gas atomizing the molten metal liquid, and cooling and collecting the obtained atomized metal powder to obtain the ultra-high strength steel powder for injection molding.

[0009] Further, S12 specifically comprises: when the pressure in the melting chamber is reduced to below 5 Pa, filling high-purity argon into the melting chamber to restore it to standard atmospheric pressure, and then vacuumizing it to below 5 Pa; when the oxygen content in the melting chamber is less than 50 ppm, performing induction heating on the master alloy. It should be noted that, in order to obtain a stable state of the molten metal liquid, after the master alloy is completely melted, it is further heat preserved for 3~5 minutes.

[0010] Further, S13 specifically comprises: pouring the molten metal liquid into a tundish, flowing out through a nozzle under the tundish and performing supersonic gas atomization to make powder; wherein the diameter of the nozzle is 5 mm~6 mm, the gas atomization medium is high-purity argon at 80℃~150℃, and the atomization pressure is 4 MPa~10 MPa. It can be understood that the cooling of the obtained atomized metal powder is carried out in a cooling chamber and collected in a powder collecting tank.

[0011] Further, in order to facilitate the preparation of subsequent ultra-high strength steel parts, the preparation method of the injection molding ultra-high strength steel powder further comprises: S14, under the protection of inert gas, the atomized metal powder is classified and screened to obtain a metal powder with a particle size range of >0 and ≤25 µm, that is, the injection molding ultra-high strength steel powder. The obtained injection molding ultra-high strength steel powder is vacuum sealed and packaged for standby use. The classified and screened method can be realized by mechanical vibration screening and airflow classification screening.

[0012] The third aspect of the present application provides an ultra-high strength steel part, which is prepared from the above-mentioned injection molding ultra-high strength steel powder.

[0013] The fourth aspect of the present application provides a preparation method of an ultra-high strength steel part based on component high-throughput optimization, which is used to prepare the above-mentioned ultra-high strength steel part; the method comprises: S21, mixing the injection molding ultra-high strength steel powder and the binder to obtain an ultra-high strength steel feedstock; mixing the reduced carbonyl iron powder and the binder to obtain a reduced carbonyl iron powder feedstock; S22, adjusting the delivery flow rates of the ultra-high strength steel feedstock and the reduced carbonyl iron powder feedstock respectively, so that the ultra-high strength steel feedstock and the reduced carbonyl iron powder feedstock are mixed and injection molded to obtain a rough blank with a continuously gradient change in component volume fraction; S23, catalytically debinding the rough blank to obtain a debound blank; S24, sintering the debound blank to obtain a sintered blank; and S25, heat treating the sintered blank to obtain the ultra-high strength steel part.

[0014] Further, in S21, the binder is one or more of polyformaldehyde, polyethylene, EVA, stearic acid, and modified montmorillonite; the selected polyethylene is high-density polyethylene. The addition amount of the binder in the ultra-high strength steel feedstock is 55% to 70% of the volume of the injection molding ultra-high strength steel powder, and the addition amount of the binder in the reduced carbonyl iron powder feedstock is 55% to 70% of the volume of the reduced carbonyl iron powder. The particle size of the injection molding ultra-high strength steel powder is greater than 0 and less than or equal to 25 µm. The reduced carbonyl iron powder has a purity of 99.9% and a particle size distribution in the range of 5 µm to 25 µm. The mixing temperature is 170°C to 190°C, and the mixing time is 1 h to 2 h.

[0015] Further, in S22, the injection molding specifically includes the following parameters: the mold temperature is 120°C to 140°C, the injection molding temperature is 175°C to 185°C, and the injection molding pressure is 120 bar to 130 bar.

[0016] It can be understood that the volume ratio of the reduced carbonyl iron powder feed in the rough blank along the gradient direction is from 0 to 100%, or from 100% to 0.

[0017] It can also be understood that the mixing of the ultra-high strength steel feed and the reduced carbonyl iron powder feed is completed in a mixing device, the mixing device comprising two hoppers with flow meters and a barrel with a rotor. By precisely adjusting the conveying flow of the feeds in the two hoppers, the two feeds are synchronized into the barrel, and after stirring by the rotor, the two feeds are uniformly mixed and continuously conveyed to an injection molding machine, and finally a rough blank with a continuously gradient change in volume fraction is prepared.

[0018] Preferably, in S23, the catalytic debinding is carried out in an oxalic acid atmosphere at a temperature of 120-130 DEG C, and the catalytic debinding time is 4-6 h.

[0019] Preferably, in S24, the sintering is divided into two stages, the operation parameters of the first stage including: a debinding temperature of 500-700 DEG C, a holding time of 30-120 min, a gas pressure of 0.001-0.1 Pa, and a flow rate of the protective gas of 80-120 L / min; the operation parameters of the second stage including: a sintering temperature of 1340-1390 DEG C, a holding time of 120-240 min, and a controlled gas pressure of 0.001-0.1 Pa, followed by forced cooling; wherein the protective gas is preferably argon.

[0020] Preferably, in S25, the solid solution treatment temperature is 1100-1250 DEG C, the solid solution time is 0.5-2 h, the brine is cooled to room temperature, the aging temperature is 400-600 DEG C, the aging time is 0.5-4 h, and the cooling to room temperature is in the furnace.

[0021] The fifth aspect of the present application provides an application of the above-mentioned ultra-high strength steel part in the field of precise and complex components of unmanned aerial vehicle supports, robot finger joints, precision gears and folding screen mobile phone hinges.

[0022] Compared with the prior art, the technical solution provided by the present application has at least the following advantages: The application provides an injection-molding super-high-strength steel powder, which is characterized by the following aspects: first, the content of Co and Ni elements is optimized and reduced, thereby greatly reducing the cost of the steel material; second, the content of C element is reduced, because C is easy to form carbide to hinder the diffusion of atoms and the growth of grains, thereby causing high porosity, and a low content of C can guarantee the sintering performance of the powder and also guarantee the good flowability of the feed material; and third, the content of Ti and Al elements is reduced, thereby reducing the traditional Ni3Ti and NiAl precipitated phases. By adding appropriate amounts of Nb and Mo elements, the original austenite grains are refined, and high-density and small-size Laves phases and Ni3Mo composite precipitated structures are formed in the martensite matrix, thereby exhibiting excellent composite precipitated strengthening effect and simultaneously improving the strength and plastic deformation capacity of the steel material, so that the yield strength of the super-high-strength steel part prepared by using the steel material as a raw material reaches 1800 MPa-2000 MPa, and the tensile strength reaches 1800 MPa-2100 MPa. In addition, by adding a certain amount of Cr element in the alloy composition, the corrosion resistance of the steel material is guaranteed, and the Mo element can also significantly improve the oxidation resistance, seawater corrosion resistance and atmospheric corrosion resistance of the steel material.

[0023] The application also provides a preparation method of the injection-molding super-high-strength steel powder.

[0024] The application also provides a preparation method of a super-high-strength steel part based on high-throughput optimization of components, which uses the injection-molding super-high-strength steel powder as a raw material. In the injection molding stage, the content of Laves phases and Ni3Mo precipitated phases in the super-high-strength steel is accurately controlled by adjusting the proportion of the reduced carbonyl iron powder feed material in the injection process, thereby realizing effective control of the strength and toughness of the material and providing an efficient way for high-throughput screening of the optimal alloy composition of strength and toughness. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A preparation method flow chart of the injection-molding super-high-strength steel powder and parts is provided for the embodiments of the application. Figure 2 A sample schematic diagram of the super-high-strength steel part with a continuously gradient change in the component volume fraction is provided for the embodiments of the application. Figure 3Microstructure morphology photos of the ultra-high strength steel parts provided for example 1, example 2, example 3 and comparative example 1 of the present application under scanning electron microscope. (a) Microstructure morphology photo of the sample prepared in example 1 under scanning electron microscope (b) Microstructure morphology photo of the sample prepared in example 2 under scanning electron microscope (c) Microstructure morphology photo of the sample prepared in example 3 under scanning electron microscope (d) Microstructure morphology photo of the sample prepared in comparative example 1 under scanning electron microscope. DETAILED DESCRIPTION

[0026] Based on the above background technology, the present application provides a new type of ultra-high strength steel suitable for powder injection molding. The present application realizes the target by precisely designing alloy composition, controlling element content and optimizing powdering and sintering process. Specifically, Cr is used to provide corrosion resistance and replace part of the Ni element; by controlling the content of Ni and Co to be relatively low, a lath martensite matrix with toughness is obtained; at the same time, Ti and Al are abandoned to reduce the oxidation tendency in the powdering process and reduce non-metallic inclusions; and elements such as Co, Mo and Nb form intermetallic compounds during aging to achieve composite strengthening effect.

[0027] The present application can reduce the cost while keeping good sintering performance of the material, and realize low oxygen content and low inclusion level, and finally obtain powder injection molded parts with high corrosion resistance and high strength. In addition, the present application also uses injection molding for high-throughput optimization, and by adjusting the content of base element Fe, the precipitation behavior of Laves phase and Ni3Mo intermetallic compound is controlled directionally, so as to realize effective regulation of the strength and toughness of the ultra-high strength steel.

[0028] As shown in Figure 1 The present application provides a preparation method of an ultra-high strength steel powder and parts for injection molding, comprising: after the composition design of the ultra-high strength steel is completed, the ultra-high strength steel powder for injection molding is prepared by gas atomization powdering; the ultra-high strength steel powder and the reduced carbonyl iron powder after reduction are respectively mixed with a binder to obtain ultra-high strength steel feedstock and reduced carbonyl iron powder feedstock, and then the two are mixed and injection molded to obtain a rough casting with a continuous gradient change in composition volume fraction; and the rough casting is sequentially subjected to debinding, sintering and heat treatment to obtain an ultra-high strength steel part.

[0029] The preparation method specifically comprises the following steps: S11, in a vacuum induction melting furnace, a graphite core is used in combination with induction to perform staged baking on the bearing container at parameters of 25 KW~35 KW baking for 0.5 h~1.5 h, gradually increasing the temperature to 35 KW~45 KW baking for 0.5 h~1.5 h, to obtain a pretreated bearing container.

[0030] S12, put the master alloy into a bearing container, and perform induction heating under the conditions of inert gas protection and a temperature of 1650-1750°C; after the master alloy is completely melted, a molten metal liquid is obtained.

[0031] S13, perform gas atomization on the metal liquid, and perform cooling and collection on the obtained atomized metal powder to obtain an ultra-high-strength steel powder for injection molding.

[0032] S14, perform grading screening on the atomized metal powder under inert gas protection to obtain metal powder with a particle size interval of >0 and ≤25 µm, i.e., an ultra-high-strength steel powder for injection molding. The obtained ultra-high-strength steel powder for injection molding is vacuum sealed and packaged for standby use.

[0033] S21, mix the ultra-high-strength steel powder for injection molding and the binder to obtain an ultra-high-strength steel feedstock; mix the reduced carbonyl iron powder and the binder to obtain a reduced carbonyl iron powder feedstock.

[0034] S22, by respectively adjusting the delivery flow rates of the ultra-high-strength steel feedstock and the reduced carbonyl iron powder feedstock, the ultra-high-strength steel feedstock and the reduced carbonyl iron powder feedstock are mixed and injection molded to obtain a blank with a continuous gradient change in component volume fraction.

[0035] S23, perform catalytic debinding on the rough blank to obtain a debound blank.

[0036] S24, perform sintering on the debound blank to obtain a sintered blank.

[0037] S25, perform heat treatment on the sintered blank to obtain an ultra-high-strength steel part, and the component gradient change is as shown in Figure 2

[0038] and perform mechanical property analysis on the obtained ultra-high-strength steel part.

[0039] The application will be described in detail below in conjunction with specific embodiments.

[0040] Embodiment 1: The embodiment provides a preparation method of an ultra-high-strength steel powder for injection molding, and the steps are as follows: The chemical components of the master alloy include, in mass percentage: Cr 10.0%, Ni 7.5%, Co 8.0%, Mo 4.5%, Nb 0.8%, C 0.03%, the balance Fe and impurities; (1) a graphite core is used in combination with an induction furnace to perform staged temperature rising roasting on the crucible, 30 kW heating for 1 h, and then gradually heating to 40 kW and maintaining for 1 h; (2) the master alloy block is placed into the crucible of the vacuum induction melting furnace; ​(3) The melting chamber is vacuumed, when the pressure is reduced to 5 Pa or less, 99.999% high-purity argon is filled to standard atmospheric pressure, and then vacuumed to 5 Pa or less; (4) When the oxygen content in the vacuum melting chamber is less than 50 ppm, the master alloy is inductively heated at 1650°C; (5) After the master alloy is completely melted, the metal liquid is poured into a tundish, and is atomized by supersonic gas to prepare powder through a nozzle, the atomizing medium is 120°C high-purity argon, the pressure is 5 MPa, and the size of the nozzle is φ5 (5 mm in diameter); (6) The cooled powder is sieved (particle size > 0 and ≤ 25 µm) under inert gas protection, vacuum sealed and packaged to obtain the super-high-strength steel powder for injection molding.

[0041] The embodiment also provides a preparation method of a super-high-strength steel part based on component high-throughput optimization, and the steps are as follows: (1) 66% of the volume of the super-high-strength steel powder and the reduced carbonyl iron powder is added with a binder (in the embodiment, the binder is one or a mixture of several of polyformaldehyde, polyethylene, EVA, stearic acid and modified montmorillonite, preferably the following raw materials in mass fraction: 60%-70% of polyformaldehyde, 10-20% of polyethylene, 0-10% of EVA, 0-10% of stearic acid and 0-3% of modified montmorillonite, the same below), the mixing temperature is 180°C, and the time is 1.5 h to obtain two kinds of feedstocks; (2) The super-high-strength steel feedstock and the reduced carbonyl iron powder feedstock are mixed in a mixing device at a flow ratio of 6:1 (super-high-strength steel feedstock:reduced carbonyl iron powder feedstock, wherein the flow meter unit is kg / h, the total flow is controlled to be 2.5-3.5 kg / h, the same below), and injection molding is performed at a mold temperature of 130°C, an injection temperature of 185°C and an injection pressure of 125 bar to obtain an injection rough casting with a continuous gradient change in the volume fraction of components; specifically, the injection rough casting has a continuous gradient change in the volume fraction of components along the injection direction in the injection machine.

[0042] (3) The rough casting is catalytically debound in an oxalic acid atmosphere at 120°C for 4 h to obtain a debound blank; (4) Two-stage sintering: the debound blank is debound at a negative pressure of 600°C for 60 min, the gas pressure is 0.001 Pa, the argon gas flow is 120 L / min; then sintering is performed at a vacuum sintering temperature of 1365°C for 120 min, the gas pressure is 0.001 Pa, and then cooling is performed to obtain a sintered blank.

[0043] (5) The sintered blank is heat treated at a solid solution temperature of 1100°C for 1 h, salt water cooling, an aging temperature of 500°C for 4 h and furnace cooling to obtain the super-high-strength steel part.

[0044] It can be understood that the sintering treatment of step (4) and the heat treatment of step (5) are respectively completed in different reaction furnaces. After the reaction in step (4) is completed and cooled, the sintering treatment is completed, and a sintered blank is obtained. The sintered blank is transferred from the reaction furnace of step (4) to the reaction furnace for performing step (5), and after the reaction and cooling, the heat treatment is completed.

[0045] It should be noted that the mixing device includes two hoppers with flow meters, and a barrel with a rotor. By precisely adjusting the conveying flow of the two feed materials in the two hoppers, the two feed materials are synchronized into the barrel, and after stirring by the rotor, the homogenized mixture is continuously conveyed to the injection molding machine, and finally the rough blank with continuously changing volume fraction of components is prepared.

[0046] It should also be noted that in the injection molding, debinding and sintering stages, the surface roughness and dimensional accuracy of the complex component are closely related to the uniformity of the feed material. In the present application, a small amount of modified montmorillonite is added to the original plastic-based binder system, which can act as a nano-scale thixotropic agent to form a weak three-dimensional network, prevent powder settling, and improve the uniformity of the feed material; and in the debinding stage of the sintering stage, vacuum debinding is used, and the gas flow during the thermal debinding process is increased to remove the carbon and oxygen content residues of the binder in the blank, thereby obtaining an ultra-high strength steel part with low carbon and oxygen inclusions.

[0047] Example 2: The present embodiment provides a method for preparing an ultra-high strength steel powder for injection molding, the steps being as follows: The chemical composition of the master alloy (mass percent): Cr 9.5%, Ni 7.0%, Co 8.5%, Mo 5.0%, Nb 0.6%, C 0.02%, the balance Fe and impurities; (1) The graphite core is used to roast the crucible in stages with an induction furnace, heating at 30 kW for 1 h, and then gradually heating to 40 kW for 1 h; (2) The master alloy block is placed in the crucible of the vacuum induction melting furnace; (3) The melting chamber is evacuated, and when the pressure drops to below 5 Pa, 99.999% high-purity argon gas is charged to standard atmospheric pressure, and then vacuumed to below 5 Pa; (4) When the oxygen content in the vacuum melting chamber is less than 50 ppm, the master alloy is heated to 1700°C by induction; (5) After the master alloy is completely melted, the metal liquid is poured into the tundish, and the powder is prepared by supersonic gas atomization through the nozzle, the atomization medium is 150°C high-purity argon gas, the pressure is 5 MPa, and the nozzle size is φ5; (6) The cooled powder is sieved (particle size > 0 and ≤ 25 µm) under inert gas protection, vacuum sealed and packaged to obtain the ultra-high-strength steel powder for injection molding.

[0048] The embodiment also provides a preparation method of an ultra-high-strength steel part based on component high-throughput optimization, and the steps are as follows: (1) 70% of the volume of the ultra-high-strength steel powder and the reduced carbonyl iron powder is added with a binder, and the mixing temperature is 185°C, and the time is 1 h; (2) The flow rate ratio of the ultra-high-strength steel feedstock and the reduced carbonyl iron powder feedstock is adjusted to 9:1 (it can be understood that, in the case that the flow rate of the ultra-high-strength steel feedstock is set to 2.7 kg / h, the flow rate of the reduced carbonyl iron powder feedstock can be set to 0.3 kg / h), the mold temperature is 125°C, the injection temperature is 180°C, and the injection pressure is 125 bar; (3) Catalytic degreasing in an oxalic acid atmosphere at 125°C for 4 h; (4) Two-stage sintering: negative pressure degreasing at 600°C for 60 min, the gas pressure is 0.001 Pa, the argon gas flow rate is 120 L / min, vacuum sintering at 1350°C for 180 min, the gas pressure is 0.001 Pa, and then cooling.

[0049] (5) Solution temperature 1050°C, holding time 1 h, salt water cooling, aging temperature 550°C, holding time 5 h, furnace cooling, to obtain the ultra-high-strength steel part.

[0050] Example 3: The embodiment provides a preparation method of an ultra-high-strength steel powder for injection molding, and the steps are as follows: The chemical composition (mass percentage) of the master alloy is as follows: Cr 11.0%, Ni 8.0%, Co 7.5%, Mo 4.0%, Nb 1.0%, C 0.01%, the balance Fe and impurities; (1) The graphite core is used in cooperation with the induction furnace to perform stage-by-stage heating roasting on the crucible, 30 kW heating for 1 h, and then gradually heating to 40 kW and then holding for 1 h; (2) The master alloy block is placed into the crucible of the vacuum induction melting furnace; (3) The melting chamber is vacuumized, when the pressure is reduced to below 5 Pa, 99.999% high-purity argon is filled to the standard atmospheric pressure, and then vacuumized to below 5 Pa; (4) When the oxygen content in the vacuum melting chamber is less than 50 ppm, the master alloy is inductively heated at 1650°C; (5) After the master alloy is completely melted, the metal liquid is poured into the tundish, and the powder is prepared by ultrasonic speed gas atomization through the nozzle, the atomization medium is 100°C high-purity argon, the pressure is 4.5 MPa, and the nozzle size is φ6; (6) The cooled powder is sieved (particle size > 0 and ≤ 25 pm) under inert gas protection, vacuum sealed and packaged to obtain the ultra-high strength steel powder for injection molding.

[0051] The embodiment also provides a preparation method of an ultra-high strength steel part based on component high-throughput optimization, and the steps are as follows: (1) 60% of the volume of the ultra-high strength steel powder and the reduced carbonyl iron powder is added with a binder, the mixing temperature is 175°C, and the time is 2 h; (2) The flow ratio of the ultra-high strength steel feedstock and the reduced carbonyl iron powder feedstock is adjusted to 4:1, the mold temperature is 130°C, the injection temperature is 185°C, and the injection pressure is 125 bar; (3) Catalytic degreasing in an oxalic acid atmosphere at 130°C for 5 h; (4) Two-stage sintering: degreasing at a negative pressure of 600°C for 60 min, an argon gas flow of 120 L / min, vacuum sintering at 1390°C for 90 min, and an argon gas flow of 0.001 Pa; and then cooling.

[0052] (5) Solution temperature 1150°C, holding time 1 h, salt water cooling, aging temperature 500°C, holding time 6 h, furnace cooling, to obtain the ultra-high strength steel part.

[0053] Comparative Example 1: The comparative example provides a preparation method of an ultra-high strength steel powder for injection molding, and the steps are as follows: The chemical composition of the master alloy (mass percent) is: Cr 10.0%, Ni 7.5%, Co 8.0%, Mo 4.5%, C 0.03%, and the balance Fe and impurities; (1) The graphite core is used in combination with the induction furnace to perform stage-by-stage temperature rising roasting on the crucible, 30 kW heating for 1 h, and then gradually heating to 40 kW for 1 h; (2) The master alloy block is placed in the crucible of the vacuum induction melting furnace; (3) The melting chamber is vacuumed, when the pressure drops to below 5 Pa, 99.999% high-purity argon gas is filled to standard atmospheric pressure, and then vacuumed to below 5 Pa; (4) When the oxygen content in the vacuum melting chamber is less than 50 ppm, the master alloy is inductively heated at 1650°C; (5) After the master alloy is completely melted, the metal liquid is poured into the tundish, and the powder is prepared by supersonic gas atomization through the nozzle, the atomization medium is 120°C high-purity argon gas, the pressure is 5 MPa, and the nozzle size is φ5; (6) Under the protection of inert gas, the cooled powder is sieved (particle size > 0 and ≤ 25 μm), vacuum sealed and packaged to obtain the super-high-strength steel powder for injection molding.

[0054] The present comparative example also provides a preparation method of a super-high-strength steel part, comprising the following steps: (1) 70% of the super-high-strength steel powder is added with a binder, and the mixing temperature is 185°C and the mixing time is 1h; (2) The super-high-strength steel feedstock is injection molded with the parameters of a mold temperature of 125°C, an injection temperature of 180°C and an injection pressure of 125 bar; (3) Catalytic debinding under an oxalic acid atmosphere, 120°C for 4h; (4) Two-stage sintering: negative pressure debinding at 600°C for 60min, with an argon gas flow of 120L / min and a gas pressure of 0.001Pa, vacuum sintering at 1365°C for 120min, with a gas pressure of 0.001Pa; and then cooling.

[0055] (5) Solid solution at 1100°C for 1h, salt water cooling, aging at 500°C for 4h, furnace cooling, to obtain the super-high-strength steel part.

[0056] Figure 3 The microstructure morphology photos of the super-high-strength steel parts provided by the example 1, the example 2, the example 3 and the comparative example 1 under a scanning electron microscope are shown in the following figures. Figure 3 The microstructure morphology photo of the sample prepared by the example 1 under a scanning electron microscope is shown in the figure a, Figure 3 The microstructure morphology photo of the sample prepared by the example 2 under a scanning electron microscope is shown in the figure b, Figure 3 The microstructure morphology photo of the sample prepared by the example 3 under a scanning electron microscope is shown in the figure c, Figure 3 The microstructure morphology photo of the sample prepared by the comparative example 1 under a scanning electron microscope is shown in the figure d.

[0057] The physical properties of the materials prepared by the example 1, the example 2, the example 3 and the comparative example 1 are shown in the following table 1. Table 1. Partial physical property parameters of the super-high-strength steel parts of the examples 1-3 and the comparative example 1

[0058] From the above table 1 and Figure 3It can be seen that by adjusting the proportion of the reduced carbonyl iron powder feed, the tensile strength and yield strength of the samples of embodiments 1-3 are all above 1800 MPa, and the elongation is kept above 5%, showing excellent matching of strength and toughness, and with the increase of the proportion of the reduced carbonyl iron powder feed, the composition cost is reduced, the mechanical properties show a trend of decreasing strength and increasing elongation. In one experiment, the performance and cost of multiple composition points can be evaluated at the same time, providing a basis for selecting composition windows for industrialization.

[0059] Compared with example 1, the comparative example 1 does not add additional Fe powder (except the Fe in the powder composition of the injection-molded ultrahigh-strength steel), and the composition is also adjusted slightly, the alloying compound precipitates too much, the structure is coarse, and the toughness decreases significantly, proving the feasibility of the present application.

[0060] Those skilled in the art can understand that the above-mentioned embodiments are specific embodiments for realizing the present application, and in actual application, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make respective changes and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. A type of ultra-high strength steel powder for injection molding, characterized in that, The ultra-high strength steel powder for injection molding comprises the following components by mass percentage: Cr 9%~11%, Ni 6.5%~8.5%, Co 7%~9%, Mo 3.5%~5.5%, Nb 0.01%~1.0%, 0<C≤0.03%, with the remainder being Fe and unavoidable impurities.

2. A method for preparing ultra-high strength steel powder for injection molding according to claim 1, characterized in that, The preparation method includes: baking the carrier container in stages, and then placing the master alloy in the carrier container for vacuum induction atomization to obtain the ultra-high strength steel powder for injection molding.

3. The method for preparing ultra-high strength steel powder for injection molding according to claim 2, characterized in that, The preparation method specifically includes the following steps: S11. In a vacuum induction melting furnace, a graphite core is used in conjunction with induction to bake the carrier container in stages with parameters of 25 KW~35 KW for 0.5 h~1.5 h and gradually increasing the temperature to 35 KW~45 KW for 0.5 h~1.5 h, so as to obtain a pre-treated carrier container. S12. Place the master alloy into the supporting container and perform induction heating under inert gas protection and at a temperature of 1650℃~1750℃; after the master alloy is completely melted, molten metal is obtained. S13. The molten metal is atomized into a gas, and the resulting atomized metal powder is cooled and collected to obtain the ultra-high strength steel powder for injection molding.

4. The method for preparing ultra-high strength steel powder for injection molding according to claim 2, characterized in that, S12 specifically includes: evacuating the melting chamber until the pressure drops below 5 Pa, then filling it with high-purity argon gas until the melting chamber returns to standard atmospheric pressure, and then evacuating it again to below 5 Pa; and induction heating the master alloy when the oxygen content in the melting chamber is <50 ppm.

5. The method for preparing ultra-high strength steel powder for injection molding according to claim 2, characterized in that, S13 specifically includes: pouring the molten metal into an intermediate tundish, allowing it to flow out through a leak at the bottom of the intermediate tundish and undergoing ultrasonic gas atomization to produce powder; wherein the leak has a diameter of 5 mm to 6 mm, the atomization medium is high-purity argon gas at 80℃ to 150℃, and the atomization pressure is 4 MPa to 10 MPa.

6. A type of ultra-high strength steel component, characterized in that, The ultra-high strength steel component is prepared from the ultra-high strength steel powder for injection molding as described in claim 1.

7. A method for preparing ultra-high strength steel parts based on high-throughput composition optimization, characterized in that, This method is used to prepare the ultra-high strength steel parts as described in claim 6; the method includes: S21. The ultra-high strength steel powder for injection molding as described in claim 1 is mixed with a binder to obtain an ultra-high strength steel feedstock; the reduced carbonyl iron powder is mixed with a binder to obtain a reduced carbonyl iron powder feedstock. S22. By adjusting the conveying flow rates of the ultra-high strength steel feed and the reduced carbonyl iron powder feed respectively, the ultra-high strength steel feed and the reduced carbonyl iron powder feed are mixed and then injection molded to obtain a rough blank with a continuous gradient change in the volume fraction of the composition. S23. The rough blank is subjected to catalytic degreasing to obtain a degreased blank; S24. The degreased blank is sintered to obtain a sintered blank; S25. The sintered billet is heat-treated to obtain the ultra-high strength steel parts.

8. The method for preparing ultra-high strength steel parts based on high-throughput composition optimization according to claim 7, characterized in that, In S21, the adhesive is one or more of polyoxymethylene, polyethylene, EVA, stearic acid, and modified montmorillonite; The amount of binder added in the ultra-high strength steel feed is 55% to 70% of the volume of ultra-high strength steel powder for injection molding, and the amount of binder added in the reduced carbonyl iron powder feed is 55% to 70% of the volume of carbonyl iron powder after reduction. The particle size of the ultra-high strength steel powder used for injection molding is greater than 0 and less than or equal to 25 µm; The reduced carbonyl iron powder is a 99.9% pure metal powder with a particle size distribution in the range of 5 µm to 25 µm. The mixing temperature is 170℃~190℃, and the time is 1 h~2 h.

9. The method for preparing ultra-high strength steel parts based on high-throughput composition optimization according to claim 7, characterized in that, In S22, the injection molding specifically includes the following parameters: mold temperature is 120℃~140℃, injection molding temperature is 175℃~185℃, and injection molding pressure is 120 bar~130 bar. Preferably, in S23, the catalytic degreasing is carried out in an oxalic acid atmosphere at a temperature of 120°C to 130°C for a time of 4 to 6 hours. Preferably, in S24, the sintering is divided into two stages. The operating parameters of the first stage include: degreasing temperature of 500℃~700℃, holding time of 30 min~120 min, gas pressure of 0.001 Pa~0.1 Pa, and protective gas flow rate of 80 L / min~120 L / min. The operating parameters of the second stage include: sintering temperature of 1340℃~1390℃, holding time of 120 min~240 min, controlling gas pressure of 0.001 Pa~0.1 Pa, followed by forced cooling. Preferably, in S25, the solution treatment temperature is 1100℃~1250℃, the solution treatment time is 0.5 h~2 h, the brine is cooled to room temperature, the aging temperature is 400℃~600℃, the aging time is 0.5 h~4 h, and the furnace is cooled to room temperature.

10. The application of an ultra-high strength steel component according to claim 6 in the field of precision and complex components such as drone brackets, robot joints, precision gears, and hinges for foldable screen phones.

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