A method for atomizing preparation of high-carbon chromium bearing steel powder for metal additive manufacturing

Abstract

The application discloses a kind of atomization preparation methods of high-carbon chromium bearing steel powder for metal additive manufacturing, belong to the technical field of manufacturing metal powder with plasma method.The method comprises: S1 vacuum induction melting GCr15 alloy of specific component, and ZrN, AlN and Se are added at the end of refining;S2 finish machining into high-precision electrode rod;S3 rod loading, vacuum pumping and filling Ar:He=4:1 protective gas and local N2 injection;S4 PREP atomization powder is carried out under the synergistic assistance of gradient current, gradient nitrogen (2~8L / min), gradient ultrasonic (500~2000W) and radial electrostatic field (-200~‑800V);S5 cooling collection and implementation corona charging dispersion desorption;S6 ultrasonic vibration screening grading and carrying out 200~300 DEG C vacuum annealing;S7 vacuum packaging.The application is through "Se surface modification+ZrN / AlN heterogeneous nucleation and solid-state isolation+nitriding shell+electrostatic repulsion+ultrasonic degassing and shrinkage+corona desorption" multiple effects, effectively inhibit satellite powder, eliminate internal porosity, meet the requirement of high-quality powder for additive manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of metal powder manufacturing technology using plasma method, specifically relating to a method for preparing metal powder for additive manufacturing (3D printing). Background Technology

[0002] Additive manufacturing technology, due to its unique layer-by-layer deposition molding method and excellent component performance, has been widely used in industries such as industrial production, aerospace, and medical devices. With the continuous development of the metal additive manufacturing industry, the demand for high-quality spherical metal powders has increased significantly.

[0003] Compared to other powder metallurgy technologies, additive manufacturing technology has more stringent requirements for powders, demanding high sphericity, high bulk density, and good flowability. Currently, the commonly used powder particle size range for metal additive manufacturing is 15–150 μm. Sphericity directly affects powder flowability; higher sphericity makes powder spreading and feeding processes easier to control, contributing to the production of high-quality printed parts.

[0004] High carbon chromium bearing steel (GCr) 15 Due to its high hardness, high wear resistance, and good fatigue strength, GCr is widely used in the manufacture of key components such as bearing rings, rolling elements, and plungers. However, GCr prepared by traditional casting methods... 15 Bearing steel suffers from defects such as coarse grains, macroscopic segregation of alloying elements, and coarse network carbides at grain boundaries. Powder metallurgy and additive manufacturing offer the potential to address these issues, but only if high-quality GCr steel meeting additive manufacturing requirements can be produced. 15 Spherical powder.

[0005] In the existing technology, some researchers have attempted to prepare GCr using the plasma rotating electrode atomization (PREP) method. 15 Spherical powder for bearing steel. However, existing PREP technology has the following shortcomings: 1) As the PREP speed increases, at high speeds (such as above 18,000 r / min), medium and fine particles collide and agglomerate during flight, forming a large number of "satellite powder" particles (small particles adhering to the surface of large particles). The increase in satellite powder reduces the powder's flowability and bulk density, while additive manufacturing processes have extremely high requirements for powder flowability—powder with poor flowability is prone to defects such as uneven thickness and powder shortages during powder spreading.

[0006] 2) Although PREP powder has high sphericity, some particles still contain micron-sized pores. The formation of these pores is related to factors such as the release of dissolved gases from the molten metal and solidification shrinkage. The pore size decreases as the powder particle size decreases, but pore defects are more significant in large-particle-size powders. Internal pores can become stress concentration sources and crack initiation points during additive manufacturing, severely reducing the fatigue life and density of printed parts.

[0007] The aforementioned defects make it difficult for existing PREP powder preparation technology to meet the requirements of additive manufacturing for high-quality powders. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and provide an atomization preparation method for high-carbon chromium bearing steel powder for metal additive manufacturing. By optimizing the alloy composition, electrode rod preparation process, plasma rotating electrode atomization parameters, and post-processing, a GCr powder with high sphericity, low oxygen content, concentrated particle size distribution, and good flowability is prepared. 15 The bearing steel spherical powder meets the requirements for use in additive manufacturing (especially selective laser melting (SLM) processes).

[0009] The specific plan is as follows: A method for preparing high-carbon chromium bearing steel powder for metal additive manufacturing by atomization includes the following steps: S1. Alloy smelting and ingot preparation; S2, Electrode rod processing; S3, loading rods, vacuuming and working pressure regulation; S4, Plasma rotating electrode atomization powder production; S5. Powder cooling and collection; S6. Powder sieving and grading; S7, vacuum packaging; In step S1, the alloy composition by mass percentage includes C 0.95–1.05, Si 0.15–0.35, Mn 0.25–0.45, Cr 1.40–1.65, Mo ≦0.10, P ≦0.025, S ≦0.025, Ni ≦0.3, Cu ≦0.25, Zr 0.0173–0.0434, Al 0.0132–0.0329, N 0.0094%–0.0237, Se 0.005–0.01, and Fe balance.

[0010] Furthermore, the raw materials added during smelting in step S1 include (wt% refers to mass percentage, the same throughout): Industrial pure iron, with an iron content of ≥99.8wt%, serves as the base metal, providing the Fe balance; High carbon ferrochrome FeCr 55 C 10 It contains 55%–65 wt% Cr and 7%–10 wt% C, and is used as a chromium source and part of a carbon source. The amount added is calculated based on the target Cr content of 1.40 wt%–1.65 wt%. The carbon raiser is made of high-purity graphite with a carbon content ≥98wt%, used to precisely adjust the carbon content to 0.95wt%~1.05wt%. Industrial-grade silicon, containing ≥98wt% Si, used to adjust the Si content to 0.15%–0.35wt%; Electrolytic manganese, containing ≥99.5 wt% Mn, is used to adjust the Mn content to 0.25%–0.45 wt%. Micro-carbon ferrochrome is added according to the target components to finely adjust the Cr content without introducing excessive carbon. Ni and Cu are derived from residues in pure iron and ferrochrome raw materials and are not specifically added. They are controlled to be within 0.30 wt% and 0.25 wt% respectively by selecting the raw material grade. Al is added in the form of nano-aluminum nitride (AlN) powder, and the amount added is calculated based on the target Al content of 0.0132 to 0.0329 wt%. Se is added in the form of ferro-selenium alloy, and the amount added is calculated based on the target Se content of 0.005 to 0.01 wt%. Zr is added in the form of zirconium nitride powder ZrN, and the amount added is calculated based on the target Zr content of 0.0173 to 0.0434 wt%. N comes from ZrN powder and AlN powder.

[0011] Furthermore, the smelting process parameters in step S1 are as follows: The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1580~1650℃; Refining time: 30-60 minutes; Casting temperature: 1520~1560℃.

[0012] Further, step S3 includes: A high-carbon chromium bearing steel alloy electrode rod is clamped onto the rod rotation drive device of a plasma rotating electrode atomization powder making equipment. The diameter of the atomization chamber of the equipment is 2.0 to 3.0 m. The entire powder-making equipment was pre-vacuumed. Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes for leak detection; After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached: Protective gas: a mixture of high-purity argon (≥99.999%) and high-purity helium (≥99.999%), with a volume ratio of Ar:He = 4:1; Working air pressure: 0.10~0.15MPa (absolute pressure); Gas circulation flow rate: 5~15Nm 3 / min; Pre-evacuation vacuum degree ≤ 5.0 × 10 -3 Pa.

[0013] Furthermore, step S3 also includes: While maintaining the original Ar:He = 4:1 mixed atmosphere, the total flow rate is 5-15 Nm³. 3 Based on the flow rate of [flow rate] / min, high-purity nitrogen (N2) with a purity ≥99.999% is precisely introduced into the atomization chamber via a mass flow controller, with the following control parameters: Nitrogen flow rate: 2–8 L / min; Gas circulation flow rate: The sum of the original Ar and He flow rates and the nitrogen flow rate is 5.002~15.008 Nm³. 3 / min; Controlling the gradient nitrogen flow rate: During the initial 0-2 minutes of atomization, the nitrogen flow rate is 2-3 L / min, and the low flow rate is used for preheating to avoid excessive nitriding in the initial unstable stage. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, reduce the nitrogen flow rate to 3-4 L / min to avoid excessive reaction in the feed head area.

[0014] Furthermore, the process parameters for plasma rotating electrode atomization powder production in step S4 include: Electrode rod rotation speed: 15000~26000 r / min; Preferred rotational speed: 18000~22000 r / min; Plasma operating voltage: 150~200V; Plasma melting current: 1500~2200A; Preferred current: 1700~2000A Distance between plasma gun and electrode rod end face: 3-8mm; Electrode rod feed speed: 0.5~2.0mm / s; During the atomization process, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled to be ≤50ppm; Specifically, when producing fine powder of 15–53 μm, the electrode rod rotation speed is controlled at 22,000–26,000 r / min; when producing coarse powder of 53–150 μm, the electrode rod rotation speed is controlled at 15,000–20,000 r / min. Gradient control of plasma current is implemented: during the first 5 minutes of atomization, the melting current is controlled at 1800-2000A; during the stable atomization period, the melting current is controlled at 1600-1800A; and during the last 3 minutes of the final atomization period, the melting current is controlled at 1500-1700A. During atomization, an inert gas forced circulation cooling system is used in the atomization chamber, with a gas circulation flow rate of 5–15 Nm³. 3 / min.

[0015] Furthermore, step S4 also includes: Electrostatic assistance is implemented during the atomization process, and a radial electrostatic field is established between the atomization chamber wall and the central grounding rod of the atomization chamber. The central grounding rod is grounded at 0V, and the atomization chamber wall is connected to a negative potential of -200 to -800V.

[0016] Furthermore, step S4 also includes: During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 20–40 kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process; Gradient ultrasonic power control is used for different atomization stages: During the initial 0-2 minutes of atomization, the ultrasonic power is 500-800W. During the stable phase of atomization, the ultrasonic power is 1200-2000W; At the end of the atomization stage, the ultrasonic power is 600-1000W.

[0017] Further, step S5 includes: After atomization, the powder particles are naturally cooled to room temperature under inert gas protection, and then collected under inert gas protection to prevent oxidation of the powder during the collection process. The cooled and collected powder is fed into a corona-charged dispersion device via a vacuum conveying device. The powder flows through a vertically installed electrostatic dispersion tube with an inner wall coated with PTFE insulation, which is 1-2m in length. The powder flows through the corona-charged zone at the inlet of the tube by gravity. Under the action of corona discharge, the powder particles acquire the same negative charge on their surface. The corona-charged zone at the inlet of the tube is equipped with a tungsten needle electrode with a voltage of -10 to -30kV. The oxygen content in the corona-charged zone is ≤30ppm under argon protection.

[0018] Further, the screening parameters for step S6 are: Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 20–40 kHz; Screening time: 30-60 minutes per batch; Grading criteria (based on particle size requirements for additive manufacturing powders): Fine powder: 15~53μm (suitable for SLM process); Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor under each layer of screen monitors the cumulative powder mass curve in real time. When the mass change is less than 0.5% of the total powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be complete. The sieved powder is subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 200-300℃ for 2-4 hours.

[0019] Compared with the prior art, the present invention has at least one of the following technical effects: 1) This invention first adds Se, a surface-active element, to the alloy formulation to reduce the surface tension of droplets (by about 10% to 15%), thereby reducing the driving force for the adhesion of fine droplets from the source. ZrN (melting point 2980℃) and AlN (melting point > 2200℃) are thermodynamically stable and have a low decomposition rate in molten steel at 1580~1630℃. The nanoparticles (ZrN≤80nm, AlN≤50nm) dispersed on the droplet surface form discontinuous "protrusion pinning points". When two droplets approach each other, these rigid particles preferentially contact rather than directly contact the droplet surface, reducing the effective contact area and capillary adhesion (Pickering effect), thus physically preventing the merging of fine droplets. At the same time, the ZrC and AlN / CrN precipitates decomposed from both refine the solidification structure, making the droplet surface smoother and more regular. Se, as a surface-active element, agglomerates on the droplet surface to reduce surface tension (chemical modification), forming a complementary "chemical de-adhesion + physical isolation" effect with the physical barrier of ZrN / AlN. Se works by "reducing the driving force of adhesion," while ZrN / AlN works by "setting up contact barriers." The two act on the chemical environment and physical structure of the droplet surface, respectively, to jointly inhibit satellite powder formation. The synergistic effect is greater than that of a single method.

[0020] 2) This invention utilizes GCr to locally spray nitrogen gas at a rate of 2-8 L / min onto the end face of the electrode rod during the atomization process. 15 The high-temperature nitriding reaction of Cr element generates a CrN / Cr2N "rigid shell" of about 50~200nm on the droplet surface in situ. This high-melting-point (about 1500℃) nitride shell reduces the adhesion coefficient of the droplet surface, thereby reducing the effective contact area and adhesion force when particles collide, and effectively reducing the number of satellite powders.

[0021] 3) At the alloy formulation level, this invention adds ZrN and AlN. ZrN partially decomposes into active Zr and N in high-temperature molten steel. Zr reacts with C in the molten steel to generate ZrC particles. At the same time, AlN decomposes into Al and N, which react with Cr in the steel to generate AlN / CrN dispersed precipitates. These high-melting-point nitride precipitates (particle size 20-100nm) act as heterogeneous nucleation nuclei during droplet solidification, increasing nucleation density and refining dendrite spacing. This allows the solidification shrinkage volume to be effectively filled by uniformly distributed fine grains. Meanwhile, the precipitation reaction consumes dissolved C and N, reducing the driving force for CO / N2 bubble formation, which is beneficial for reducing powder porosity.

[0022] 4) During the atomization process, this invention activates an ultrasonic field-assisted system (1200~2000W high power during the stable period). Ultrasonic vibration is transmitted to the flying droplets through coupling with an inert gas medium: the cavitation effect generates violent oscillations inside the droplets, accelerating the escape of dissolved gas; mechanical vibration breaks down the droplet's "shell solidifies first, interior solidifies later" feeding barrier, allowing residual melt inside to continuously fill shrinkage cavities; simultaneously, vibration refines the solidification structure, further reducing porosity. The synergistic effect of these two methods reduces the internal porosity of the powder from 0.55% in Comparative Example 5 to 0.28% in Example 2, effectively reducing the risk of stress concentration and crack initiation caused by internal pores during additive manufacturing.

[0023] 5) At the physical level, this invention establishes a radial electrostatic field between the atomization chamber wall (-200 to -800V) and the central grounding rod (0V). The negatively charged droplets are subjected to a centripetal electrostatic force pointing towards the axis. At the same time, all droplets are separated from each other due to the Coulomb repulsion of the same charge. The two work together to keep the droplets in a monodisperse state throughout the flight, reducing the chance of collision.

[0024] 6) In the post-processing stage, the cooled and collected powder is sent to a corona-charged dispersion device (tungsten needle electrode -10 to -30kV) so that the physically adhered satellite particles and the main particles acquire the same charge, generating a very strong Coulomb repulsion force to "eject" the satellite particles away.

[0025] 7) This invention quantifies all process parameters (electrode rod geometric accuracy, rotation speed, current, gas flow rate, etc.) into a clear numerical range and introduces gradient current control (1800~2000A in the initial stage, 1600~1800A in the stable stage, and 1500~1700A in the final stage) so that the molten pool temperature and liquid film thickness are always within the optimal window throughout the atomization process, eliminating the arbitrariness of manual experience operation. In each embodiment, D50 is stabilized in an extremely narrow range of 31.8~32.2μm, and batch-to-batch consistency is improved.

[0026] 7) This invention constructs a process from vacuum melting (≤1.0×10⁻⁶) -2From atomization (≤50ppm), cooling, collection, and sieving (≤30ppm) to vacuum packaging (≤1.0×10⁻⁶ Pa), the entire process continues. -1 The entire process of low oxygen control system (Pa) is progressive and seamless, ensuring that the oxygen content of the finished powder is stably controlled at 292~298ppm (various examples), which is far below the industry standard requirement of 350ppm.

[0027] 8) The overnitrided shell of this invention makes the powder surface smoother, electrostatic field and corona desorption eliminate satellite powder, and ultrasonic vibration improves particle morphology. The combined effect of these three mechanisms improves the Hall flow rate from 14.5 s / 50 g in Comparative Example 5 to 12.7 s / 50 g in Example 2, and increases the bulk density from 4.38 g / cm³ to 4.57 g / cm³. 3 This provides flowability assurance for the powder spreading process in additive manufacturing.

[0028] 9) This invention addresses the residual stress characteristics of micro-scale powders in the micro-area by developing a "low-temperature long-time" annealing process at 200~300℃ for 2~4 hours (far lower than the 600~700℃ for bulk materials). This process effectively releases the micro-area stress generated by rapid solidification and avoids powder surface oxidation and interparticle sintering adhesion caused by high-temperature annealing, thus maintaining the high sphericity and flowability of the powder.

[0029] 10) In Comparative Example 5, the broken fine droplets collided and agglomerated during flight, forming satellite powder. The rough particle surface caused agglomeration during sieving, resulting in a large amount of fine powder leaving the target range of 15-53 μm, with a yield of only about 18%. In contrast, Example 3 reduced surface tension and adhesion driving force with Se, blocked droplet merging with the solid isolation effect of ZrN / AlN, reduced the surface adhesion coefficient with the nitrided shell, maintained droplet monodispersion and reduced collisions with the electrostatic field, desorbed the already adhered satellite powder with corona charge, optimized particle size distribution concentration with gradient current, and improved particle density with ultrasonic assistance, making sieving more accurate. These seven measures ensured that the large amount of fine particles that would have been lost due to adhesion, merging, and agglomeration were effectively retained within the target range of 15-53 μm, reducing the cumulative loss of fine powder in each stage and increasing the yield to 35%, which is about twice that of Comparative Example 5. Detailed Implementation

[0030] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0031] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0032] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0033] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0034] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0035] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0036] This invention uses plasma rotating electrode atomization (PREP) to prepare high-carbon chromium bearing steel powder, specifically including the following steps: Step 1: Alloy smelting and ingot preparation.

[0037] High-carbon chromium bearing steel alloy ingots were prepared by vacuum induction melting (VIM). The alloy composition by mass percentage (wt%) was: C 0.95–1.05, Si 0.15–0.35, Mn 0.25–0.45, Cr 1.40–1.65, Mo ≤0.10, P ≤0.025, S ≤0.025, Ni ≤0.3, Cu ≤0.25, Zr 0.0173–0.0434, Al 0.0132–0.0329, N 0.0094%–0.0237, Se 0.005–0.01, Fe balance.

[0038] The sum of the mass percentages of all components is 100%.

[0039] The raw materials added during smelting include: pure iron (industrial pure iron, with an iron content of ≥99.8%, used as the base metal to provide the Fe balance); High carbon ferrochrome (FeCr) 55 C 10 It contains 55%–65% Cr and 7%–10% C, serving as a chromium source and part of a carbon source (the amount added is calculated based on a target Cr content of 1.40%–1.65%). Carbon raiser (high-purity graphite or electrode powder, carbon content ≥98%, used to precisely adjust the carbon content to 0.95%~1.05%) Metallic silicon (industrial grade silicon, containing ≥98% Si, used to adjust the Si content to 0.15%–0.35%). Electrolytic manganese (containing ≥99.5% Mn, used to adjust the Mn content to 0.25%–0.45%). And micro-carbon ferrochrome (used to finely adjust Cr content without introducing excessive carbon) as needed according to the target components. For impurity elements such as P and S, we control them from the source by selecting high-quality raw materials with low P and low S (P≤0.025%, S≤0.025%), and do not add raw materials containing P and S. Mo is a high-carbon ferrochrome (FeCr) 55 C 10 The trace beneficial elements introduced as by-products in raw materials such as iron and pure iron can be controlled within the range of ≤0.10% by selecting raw materials with low Mo content.

[0040] Ni and Cu are derived from residues in pure iron and ferrochrome raw materials and are not specifically added. Their content is controlled within ≤0.30% for Ni and ≤0.25% for Cu by selecting the raw material grade.

[0041] Al is added in the form of nano-aluminum nitride (AlN) powder (particle size ≤ 50 nm, calculated based on Al target content of 0.0132~0.0329 wt%). Se is added in the form of ferro-selenium alloy (the amount added is calculated based on the target Se content of 0.005 to 0.01 wt%). Zr is added as zirconium nitride powder ZrN (particle size ≤ 80 nm, purity ≥ 99.9%, calculated based on the target Zr content of 0.0173~0.0434 wt%). N comes from ZrN powder and AlN powder.

[0042] All raw materials must be dried (200-300℃, held for 2-4 hours) before entering the furnace to remove surface adsorbed moisture and oil. After being accurately weighed according to the above proportions, they are added to the vacuum induction melting furnace in the order of "pure iron → high carbon ferrochrome → metallic silicon → electrolytic manganese → carbon raiser" to ensure that the high melting point ferrochrome is fully melted and diffused after the molten iron is cleared. Easily oxidized silicon and manganese are added later to reduce burn-off.

[0043] During the final refining stage of vacuum induction melting (5-10 minutes before tapping), when the molten steel has been fully degassed, has a uniform composition, and its temperature is stable at 1580-1630℃, nano-ZrN, AlN powder (wrapped in nickel foil and pressed in), and ferroselenium alloy are added sequentially. The common point of these three additions is that the vacuum environment (≥10Pa) at the end of refining minimizes burn-off and oxidation.

[0044] The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1580~1650℃; Refining time: 30-60 minutes; Casting temperature: 1520~1560℃; Vacuum degree (≤1.0×10) -2 The function of Pa is to remove active gases such as oxygen and nitrogen in the melting space, prevent alloying elements from being oxidized and burned off at high temperatures or forming non-metallic inclusions, and at the same time reduce the content of dissolved gases in the melt, thus ensuring the purity of the alloy from the source. The melting temperature (1580~1650℃) needs to ensure that all alloying elements (especially high carbon ferrochrome, with a melting point of about 1400-1500℃) are fully melted and diffused evenly. However, excessively high temperatures will exacerbate crucible reactions and element burn-off. Therefore, the temperature is set in this range to balance complete melting and composition control. The refining time (30-60 minutes) provides sufficient kinetic time for the degassing reaction inside the melt and the flotation of inclusions, ensuring that the gas and inclusions in the molten steel are fully removed, while allowing the alloying elements to achieve a uniform molecular-level distribution in the liquid phase. The casting temperature (1520~1560℃) needs to be maintained above the liquidus temperature (GCr15 about 1450℃) to ensure that the molten steel has good fluidity during the casting process and fills the mold. However, it is also necessary to avoid excessive superheat, which may cause severe dendrite segregation and shrinkage defects when the ingot solidifies. In GCr 15 In the classic composition design of steel, each element plays a specific role: Carbon (C) is the main strengthening element, with its content controlled in the high-carbon region (0.95%~1.05%) near the eutectoid point to ensure a high-hardness martensitic matrix after quenching and to retain sufficient undissolved carbides, thus giving bearing steel excellent wear resistance; Chromium (Cr) is the core alloying element, not only combining with carbon to form (Fe,Cr)3C composite carbides to improve wear resistance, but also significantly improving the hardenability of the steel, enabling large-section parts to achieve overall hardening, while also possessing... The role of silicon (Si) and manganese (Mn) in improving corrosion resistance; as auxiliary strengthening elements, the main function of silicon (Si) and manganese (Mn) is to improve the hardenability of steel. At the same time, manganese can react with sulfur in steel to form MnS, which "encapsulates" harmful sulfides into plastic inclusions to reduce their damage to the matrix. Nickel (Ni) and copper (Cu) are residual elements in the standard rather than intentionally added alloying elements. Their upper limits (Ni≤0.30%, Cu≤0.25%) must be strictly controlled through raw material selection to avoid reducing the toughness and hot working performance of steel when they are in excess.

[0045] The proportions of various alloying elements (C 0.95-1.05%, Cr 1.40-1.65%, etc.) jointly determine the hardness, wear resistance, and hardenability of the final powder product. Among them, carbon and chromium are key elements in the formation of M7C3 type carbides, which directly affect the wear resistance of bearing steel. At the same time, chromium can also increase the electrode potential of the matrix, thereby improving corrosion resistance.

[0046] In high-temperature molten steel, ZrN partially decomposes into active Zr and N. Zr reacts with C in the molten steel to form ZrC particles, which serve as heterogeneous nucleation sites, promoting equiaxed grain refinement and dendrite filling, thereby eliminating shrinkage cavities. Simultaneously, N reacts with Al and Cr in the steel to form dispersed nitride precipitates such as AlN and CrN, further increasing nucleation sites and consuming dissolved N to reduce the driving force for bubble formation. Furthermore, undecomposed ZrN nanoparticles (due to ZrN's high melting point of 2980℃, in GCr...) 15 The steel melt is thermodynamically stable at temperatures of 1580–1630℃ and has a low decomposition rate. It is dispersed on the surface of the droplets as a "solid spacer" to form a physical barrier that prevents the fine droplets from merging and adhering, thus reducing satellite dust at the source.

[0047] Se, as a surface-active element, agglomerates on the surface of droplets in the molten state, significantly reducing GCr. 15The surface tension of molten steel is reduced by about 10% to 15%, which reduces the tendency for fine droplets to adhere and form satellite powder due to surface energy. At the same time, the addition of Se makes the droplet surface easier to spheroidize.

[0048] In high-temperature molten steel, AlN partially decomposes into Al and N. N reacts with Al and Cr in the molten steel to generate dispersed AlN and CrN nanoprecipitates (particle size 20-100 nm). These high-melting-point nitride precipitates act as heterogeneous nucleation nuclei during droplet solidification, promoting the formation of equiaxed crystals within the crystal and refining the dendrite spacing. This allows the solidification shrinkage volume to be effectively filled by uniformly distributed ultrafine grains, thereby eliminating shrinkage cavities. At the same time, undecomposed AlN nanoparticles are dispersed on the droplet surface as "physical barrier points" (Pickering effect), further hindering the merging and adhesion of fine droplets. The three factors—Se-dominated surface tension reduction (satellite powder suppression), AlN-dominated solidification nucleation and shrinkage compensation (shrinkage cavity elimination), and AlN surface particles assisting in barrier (dual suppression of satellite powder)—constitute a three-dimensional synergistic network of "surface + volume + interface".

[0049] Se agglomerates on the droplet surface to reduce surface tension and decrease the tendency of fine droplets to adhere (surface modification); ZrC produced by ZrN decomposition and AlN / CrN precipitates produced by AlN decomposition act as heterogeneous nucleation cores to refine grains and eliminate shrinkage cavities (volume modification); undecomposed ZrN (melting point 2980℃) and AlN (melting point > 2200℃) nanoparticles are dispersed on the droplet surface as "solid spacers" to form a physical barrier and prevent droplet merger (interfacial isolation) - the three act on different scales and different stages of droplet formation respectively, "connecting in time and combining in space", together achieving the synergistic effect of "non-sticky surface, dense interior, and non-merging interface".

[0050] Step 2: Electrode rod processing.

[0051] The alloy ingot obtained in step one is forged (forging ratio ≥3:1) and heat-treated, then precision machined into a high-carbon chromium bearing steel alloy electrode rod, removing the black iron oxide scale and surface defect layer from the surface.

[0052] Electrode rod specifications: Diameter: 50–90 mm; Length: 200–350 mm; Roundness deviation: ≤0.05mm; Straightness deviation: ≤0.1mm / m; Surface roughness: ≤1.2μm; Density: ≥99.5%.

[0053] By controlling the forging ratio to ≥3:1 and subsequent heat treatment processes, the alloy ingot is ensured to be fully densified. Then, the surface defect layer is removed by precision machining, so that the electrode rod density reaches ≥99.5%. The end face of the electrode rod needs to be ground, and the flatness of the end face is ≤0.02mm to ensure the uniformity of melting during atomization.

[0054] The electrode rod diameter (50-90mm) and length (200-350mm) must be matched with the clamping range of the roller assembly and the power of the electric spindle of the PREP equipment. If the diameter is too small, the powder output of a single rod will be low and the production efficiency will decrease. If the diameter is too large, it will exceed the clamping capacity of the equipment and require higher power to melt. Controlling roundness deviation (≤0.05mm) and straightness deviation (≤0.1mm / m) is crucial because at ultra-high speeds of 15,000 to 25,000 r / min, any geometric deviation of the electrode rod will be amplified into a huge centrifugal force, causing severe vibration of the equipment and accelerated wear of the bearings. At the same time, end face runout will cause instability of the molten pool and increased fluctuation of the atomized droplet size, directly damaging the concentration of powder particle size distribution and batch consistency. Surface roughness (≤1.2μm) affects the frictional stability between the electrode rod and the roller assembly. Excessive roughness will lead to accelerated roller wear and axial movement, while insufficient roughness may cause slippage. Both of these factors will affect the accurate transmission of rotational speed. Density (≥99.5%) ensures that there are no pores or loose defects inside the electrode rod. Otherwise, under the dual effects of high-speed rotation and high-temperature melting, internal defects will become stress concentration sources, causing the electrode rod to break during atomization. At the same time, the molten metal in the loose area will carry gas out, causing the liquid film to break and become unstable. The flatness of the end face (≤0.02mm) directly affects the uniformity of the initial molten pool formation. If the end face is not flat, uneven phenomena such as local overheating and local undermelting will occur during plasma arc heating, resulting in uneven distribution of liquid film thickness along the circumference and increased dispersion of droplet size after breakage.

[0055] Step 3: Loading the rod and vacuuming.

[0056] The high-carbon chromium bearing steel alloy electrode rod obtained in step two is clamped onto the rod rotation drive device of the plasma rotating electrode atomization powder making equipment. The diameter of the atomization chamber of the equipment is 2.0 to 3.0 m.

[0057] The entire powder-making equipment was pre-vacuumed. Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes (leak detection); After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached: Protective gas: a mixture of high-purity argon (purity ≥99.999%) and high-purity helium (purity ≥99.999%), with a volume ratio of Ar:He = 4:1; Working air pressure: 0.10~0.15MPa (absolute pressure); Gas circulation flow rate: 5~15Nm 3 / min; Pre-evacuation vacuum degree (≤5.0×10) -3 The goal of GCr15 is to eliminate residual air (mainly oxygen and moisture) in the atomization chamber to the greatest extent possible, and reduce the basic oxygen content of the atomization environment to an extremely low level. This is because chromium and carbon in GCr15 have a high affinity for oxygen at high temperatures. If the residual oxygen content in the atmosphere is too high, a dense chromium oxide film will immediately form on the surface of the molten metal droplets. This will not only cause the loss of alloying elements and increase the oxygen content of the powder, but also change the surface tension of the droplets, thereby hindering their spheroidization process. The pressure holding time (≥30 minutes) is used for leak detection verification because the atomization chamber of the PREP equipment needs to maintain a slightly positive pressure state when it is running at high speed. If there is a slight leak, the dynamic seal at high speed will draw in air due to the periodic change of the sealing gap caused by shaft sway, causing the oxygen content to run out of control. The working air pressure (0.10~0.15MPa, absolute pressure) provides the gas resistance environment during the droplet flight process. If the air pressure is too low, the gas cooling capacity will be insufficient, and the droplets will not be able to fully solidify during flight and will hit the atomization chamber wall, resulting in irregular powder shape or adhesion. If the air pressure is too high, the resistance will increase, which may change the droplet flight trajectory, while increasing gas consumption and equipment sealing burden. The Ar:He = 4:1 mixed atmosphere design balances cooling rate and cost. Helium has a higher thermal conductivity (about 10 times that of argon). Adding 20% ​​helium can significantly improve the droplet solidification rate, thereby inhibiting grain growth, while also significantly reducing costs compared to a pure helium atmosphere. Gas circulation flow rate (5-15 Nm) 3 The / min) is used for forced convection heat transfer to avoid the formation of local high-temperature zones in the atomization chamber due to plasma heating (the temperature near the plasma gun can reach tens of thousands of degrees), ensuring that the temperature gradient and atmosphere composition of the entire atomization space remain uniform, so that the droplets ejected at different times experience the same cooling and solidification conditions, thereby ensuring the concentration of particle size distribution.

[0058] As a further improvement to the technical solution, while maintaining the original Ar:He = 4:1 mixed atmosphere (total flow rate 5-15 Nm³), 3 Based on the mass flow rate ( / min), high-purity N2 is precisely introduced into the atomization chamber through a mass flow controller, and the high-purity N2 is concentrated and sprayed onto the droplet generation and initial flight area (a local space with a diameter of about 50mm) on the end face of the electrode rod through an annular nozzle.

[0059] The control parameters are as follows: Nitrogen flow rate: 2–8 L / min; Total gas flow rate: Original total Ar and He flow rates plus nitrogen flow rate (5.002~15.008 Nm³) 3 / min).

[0060] Gradient nitrogen flow control strategy: In the initial stage of atomization (0-2 minutes), the nitrogen flow rate is 2-3 L / min, and the low flow rate is used for preheating to avoid excessive nitriding in the initial unstable stage. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, reduce the nitrogen flow rate to 3-4 L / min to avoid excessive reaction in the feed head area.

[0061] During the atomization process, GCr 15 The Cr element in the droplet undergoes the following nitriding reaction with N2 at high temperature (droplet temperature approximately 1500–1600℃): 2Cr + 1 / 2N2 → Cr2N (preferential reaction, when nitrogen content is low); Cr + 1 / 2N2 → CrN (when nitrogen content is sufficient); The reaction preferentially occurs at the droplet surface, forming a nanoscale (approximately 50–200 nm) CrN / Cr2N micro / nano shell. This shell has the following characteristics: Nitrogen is evenly distributed on the surface of the powder; The shell hardness is much higher than that of GCr 15 Matrix (CrN hardness approximately HV1800~2000); It has a high melting point (CrN decomposition temperature is about 1500℃) and remains solid at the atomization temperature; Dual mechanism of action: 1) Suppress satellite dust formation.

[0062] The nitride shell forms a "rigid shell" on the droplet surface, which has the following effect in suppressing satellite dust: Reduced surface adhesion: The high-melting-point nitride shell significantly reduces the adhesion coefficient of the droplet surface; Reduced effective contact area: The hard shell reduces the contact area when particles collide, thus reducing adhesion. Shortening the effective bonding time window: The high thermal conductivity of the shell accelerates the solidification of the particle surface, allowing the particles to form a complete shell before collision.

[0063] 2) Improve powder flowability.

[0064] The micro-etching effect of reactive gases makes the powder surface smoother, specifically manifested in the following ways: Surface roughness decreases, and interparticle friction decreases; The sphericity of the particles has been further improved; Both packing density and flowability improved simultaneously.

[0065] Studies have shown that when the nitrogen flow rate increases from 3 L / min to 8 L / min, the powder particle size exhibits a trend of first decreasing and then increasing. When the flow rate is too low (<2 L / min), the nitriding reaction is insufficient, resulting in a discontinuous shell; when the flow rate is too high (>8 L / min), it leads to the appearance of elongated and poorly spherical irregular powder particles. Therefore, 2–8 L / min is the optimal process window.

[0066] The CrN / Cr2N micro / nano shell (approximately 50-200 nm thick) generated in situ on the powder surface after introducing 2-8 L / min of nitrogen is essentially a "surface modification" rather than an "overall degradation." This shell increases the powder surface hardness from approximately HV700-800 of the original GCr15 matrix to HV1200-1500, enhancing the wear resistance of powder particles and reducing the generation of fine debris during additive manufacturing powder spreading. The final performance is comparable to that of the original GCr... 15 Certain changes will indeed occur—the oxygen content may increase slightly (due to the introduction of trace amounts of water and oxygen in the nitrogen), the surface hardness may increase, and the measured values ​​of some performance indicators may deviate slightly, but such changes are perfectly acceptable in this invention.

[0067] The key is that the presence of the shell makes the particle surface smoother, reduces satellite powder, further improves the Hall flow rate, and the increased flowability makes the powder perform far better than untreated powder in the additive manufacturing powder spreading process; during the laser melting process of additive manufacturing, the nanoscale shell accounts for less than 0.1% of the total particle volume, and the total nitrogen content is only at the ppm level. It melts into the molten pool along with the matrix and is evenly distributed in the matrix during rapid solidification, without forming harmful coarse nitride inclusions—the final printed part has the same density, hardness, and wear resistance as untreated GCr. 15 The powder itself doesn't change much, but the increased surface hardness makes the powder more wear-resistant during storage, transport, and spreading, reducing the generation of fine dust and facilitating cleanliness control in the printing environment.

[0068] Step 4: Plasma rotating electrode atomization powder production.

[0069] The rod rotation drive is activated, causing the electrode rod to rotate at high speed. The plasma generator is ignited, and the plasma gun heats and melts the end face of the high-speed rotating electrode rod. The molten metal is thrown out and broken into fine droplets under centrifugal force. As the droplets fly in the inert gas environment, they spherize under the action of surface tension, and at the same time, they rapidly cool and solidify into spherical particles, which fall into the bottom of the atomization chamber for collection.

[0070] Core process parameters: Electrode rod rotation speed: 15000~26000 r / min; Preferred rotational speed: 18000~22000 r / min; Plasma operating voltage: 150~200V; Plasma melting current: 1500~2200A; Preferred current: 1700~2000A Distance between plasma gun and electrode rod end face: 3-8mm (adjustable online); Electrode rod feeding speed: 0.5~2.0mm / s (automatically adjusted according to the melting process); During the atomization process, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled at ≤50ppm.

[0071] As a preferred option, when producing fine powder of 15–53 μm, the electrode rod rotation speed is controlled at 22,000–26,000 r / min; when producing coarse powder of 53–150 μm, the electrode rod rotation speed is controlled at 15,000–20,000 r / min. As a preferred approach, gradient control of the plasma current is performed: preferably, the melting current is controlled at 1800-2000A in the initial stage of atomization (first 5 minutes); preferably, the melting current is controlled at 1600-1800A in the stable atomization period; and preferably, the melting current is controlled at 1500-1700A in the final stage of atomization (last 3 minutes), in order to avoid overheating of the electrode rod tip, which would lead to deterioration of powder quality.

[0072] The core function of gradient control of plasma current is to dynamically match the heat input according to the changes in the physical state of the atomization process, so as to maintain the stability of the molten pool state throughout the process. In the initial stage of atomization (the first 5 minutes), the electrode rod end face heats up rapidly from room temperature, requiring a large current of 1800-2000A to quickly establish a stable molten pool and form a continuous liquid film, so as to avoid atomization interruption or the generation of a large number of irregular particles due to insufficient heat input in the initial stage. After entering the stable period, the molten pool has entered a thermal equilibrium state. Reducing the current to 1600-1800A can avoid the melt from overheating and viscosity reduction caused by continuous high current, thereby preventing the liquid film from being too thin and the satellite powder and flaky powder generated by excessive fragmentation of droplets. In the final stage of atomization (the last 3 minutes), the remaining length of the electrode rod is shortened and the heat conduction path is shortened. The heat of the plasma arc is more likely to accumulate at the end. At this time, the current needs to be further reduced to 1500-1700A to compensate for the end "self-heating" effect, prevent the electrode rod end from local melting out of control or droplet splashing due to overheating, thereby avoiding the generation of a large number of trailing particles and excessively fine powder in the final stage of atomization. This gradient strategy keeps the liquid film thickness and melt temperature within the optimal window throughout the atomization process, effectively improving the fine powder yield and batch consistency.

[0073] As a preferred option, during the atomization process, an inert gas forced circulation cooling system is used in the atomization chamber, with a gas circulation flow rate of 5–15 Nm³. 3 / min, to ensure a uniform temperature gradient in the atomization chamber and to ensure that the powder particles receive a consistent cooling rate during flight.

[0074] The rotational speed of the electrode rod (15000~25000 r / min) is the most critical parameter determining the powder particle size. Its physical essence lies in the fact that the rotational speed determines the magnitude of the centrifugal force (F=ω) experienced by the molten metal droplet on the electrode rod's end face. 2 The higher the rotational speed, the greater the centrifugal force, resulting in finer droplets being ejected. However, higher rotational speed is not always better. Exceeding a critical value can lead to excessively fine droplets, increasing the probability of adjacent droplets colliding and merging during flight. Furthermore, extremely high rotational speeds place stringent requirements on the mechanical precision and dynamic balance of the equipment. Therefore, precise selection is necessary based on the target particle size range—high rotational speed (≥22000 r / min) corresponds to fine powder production, while low rotational speed (15000~20000 r / min) corresponds to coarse powder production. The plasma working voltage (150-200V) and melting current (1500-2200A) together determine the heating power input to the electrode rod end face (P=U×I). Among them, the current is the main adjustment quantity, and the voltage plays an auxiliary matching role. The appropriate power input should melt the amount of metal that matches the feed rate in a unit time, while keeping the molten pool temperature within a suitable superheat range of 200-300℃ above the melting point of GCr15 (about 1450℃). If the power is too high, the melt will be overheated and the viscosity will decrease. The droplets will spread excessively before spheroidizing in flight, forming flakes or irregular powders. If the power is insufficient, the melting amount will be insufficient, the atomization yield will be low, or even interrupted. The distance (3-8mm) between the plasma gun and the end face of the electrode rod needs to be balanced between arc length stability and thermal efficiency. If the distance is too close, the arc column will be too short, the heat will be highly concentrated, and the end face of the electrode rod will be easily burned to form a pit. If the distance is too far, the arc column will diverge, the thermal efficiency will be reduced, and the plasma arc will be easily affected by gas flow and deflect. The feeding speed (0.5~2.0mm / s) needs to be precisely matched with the melting rate. If the feeding is too fast, the electrode rod will push against the molten pool, causing the liquid film to accumulate too thickly and the size of the broken droplets to be too large. If the feeding is too slow, the molten pool will move backward and the end face of the electrode rod will be burned into a cone shape, which will destroy the stability of atomization. The continuous control of oxygen content (≤50ppm) ensures that no oxide film will form on the surface of newly generated metal droplets throughout the atomization process. This is because even ppm-level oxygen will react instantaneously on the droplet surface to generate oxides. These oxides both increase the oxygen content of the powder (degrading the fatigue performance of the material) and change the surface tension of the droplets, thereby reducing their sphericity.

[0075] In practice, an ultrasonic field generator is placed outside the atomization chamber, so that ultrasonic vibration is transmitted to the molten droplets in flight through an inert gas medium. By utilizing the cavitation effect and mechanical vibration effect of ultrasound, the internal dissolved gas is accelerated out and replenished while the droplets are still in a molten state, thereby further eliminating the internal pores of the powder.

[0076] The ultrasonic radiation plate is installed in the lower middle part of the atomization chamber (i.e., the middle area of ​​the droplet flight trajectory), arranged in a ring around the atomization chamber. It does not come into contact with the high-temperature area inside, nor does it come into direct contact with the molten metal, thus avoiding contamination.

[0077] During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 20–40 kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process (from plasma arc ignition to the end of atomization); Gradient ultrasonic power control is used for different atomization stages: In the initial stage of atomization (0-2 minutes), the ultrasonic power is 500-800W, starting at low power to avoid interfering with the initial stability of the molten pool; During the stable phase of atomization, the ultrasonic power is 1200-2000W, with high power enhancing degassing and compression. Towards the end of the atomization stage, reduce the ultrasonic power to 600-1000W to avoid excessive vibration in the material head area.

[0078] Mechanism of action of ultrasonic field: 1) When ultrasound propagates in a gaseous medium, it generates periodic compressive and tensile stresses on the surface and inside of the droplet, causing cavitation resonance in the bubble nuclei formed by dissolved gas inside the droplet. The bubbles undergo a violent oscillation process of "expansion-compression-collapse" in the ultrasonic field, accelerating the diffusion and escape of dissolved gas from the inside of the droplet to the surface. At the same time, the cavitation effect generates microjets on the droplet surface, further promoting gas desorption.

[0079] 2) Mechanical vibration promotes shrinkage compensation: Ultrasonic vibration is transmitted to the droplets in flight through the gas medium, causing the droplets to generate micro-amplitude mechanical vibration. This vibration disrupts the "shell-core" structure formed by the preferential solidification of the outer shell during the droplet solidification process, allowing the residual melt inside to continuously replenish the tiny cavities generated by volume shrinkage, thereby effectively eliminating shrinkage cavities.

[0080] 3) Refines the solidified structure: Ultrasonic vibration also plays a role in refining the grains, making the solidified structure of the droplets more dense and uniform, and further reducing the porosity.

[0081] The core function of gradient ultrasonic power control is to dynamically match the ultrasonic power input according to the different ultrasonic energy requirements at each stage of the atomization process. This maximizes the ultrasonic cavitation and mechanical vibration effects to eliminate internal pores in the powder while avoiding negative impacts on atomization stability and powder quality.

[0082] In the initial stage of atomization (0-2 minutes), the plasma arc has just been ignited and the molten pool is in a non-equilibrium stage transitioning from room temperature to steady state. If high-power ultrasound is applied at this time, its vibration energy may disturb the uniform formation of the liquid film on the surface of the molten pool and the stable ejection of the initial droplets, resulting in increased fluctuations in powder particle size in the initial stage of atomization. Therefore, a low-power start-up of 500-800W is used to provide only the initial melt vibration to preheat the ultrasonic system and ensure that the atomization stability in the initial stage is not disturbed.

[0083] After entering the stable period, the droplet generation rate is the highest and the flight trajectory is the most dense. The droplets undergo a complete solidification process from liquid at 1500℃ to solid at room temperature. At this time, the power is increased to 1200~2000W. The ultrasonic vibration is efficiently coupled to the flying droplets through the gas medium. The cavitation effect generates violent oscillations inside the droplets, which accelerates the escape of dissolved gas. The mechanical vibration destroys the feeding barrier of "the outer shell solidifies first and the inside solidifies later" of the droplets, so that the residual melt inside can continuously fill the shrinkage cavities. The two work together to achieve the maximum degassing and feeding effect, effectively reducing the internal porosity of the powder.

[0084] In the final stage of atomization (the last 2-3 minutes), the remaining length of the electrode rod is less than 10%-15% of its initial length. At this point, the "self-heating of the feed head" effect caused by the shortened heat conduction path has resulted in a higher end-face temperature. In addition, the mechanical vibration of the feeding mechanism increases slightly as it approaches the end of its stroke. If the high-power ultrasound of 1200-2000W is maintained, the vibration energy combined with the overheating effect of the feed head may induce micro-cracks or abnormal particle shedding and contamination of the powder at the end of the feed head. Therefore, the power is reduced to 600-1000W to avoid excessive vibration impact on the feed head while maintaining a certain degassing effect. This gradient strategy ensures that the ultrasonic assistance plays its maximum role in the stable atomization period, while actively "avoiding" the non-steady-state stages in the initial and final stages. This reduces the internal porosity and increases the density of the powder without sacrificing the powder production efficiency, while avoiding the introduction of new quality defects and achieving the best overall effect throughout the process.

[0085] This invention further enhances the original PREP equipment by adding an electrostatic field auxiliary system, including: DC high voltage power supply: output voltage 0~±1000V, power 500W, function is to establish an electrostatic field between the atomization chamber wall and the central grounding rod; Atomizing chamber wall electrode: The stainless steel wall of the atomizing chamber itself is used as the counter electrode. Its function is to apply a bias voltage between the wall and the central grounding rod to form a radial electric field region. High-voltage isolator: withstands voltage ≥2kV, installed on the sensor signal line, its function is to protect the sensor from high-voltage interference; Grounding system: resistance ≤ 4Ω, its function is to ensure equipment safety.

[0086] Voltage application method: The center grounding rod is grounded (0V), and the wall of the atomizing chamber is connected to a negative potential, so that the droplet (negatively charged) is subjected to a radial electric field pointing towards the axis of the atomizing chamber (i.e. the axis of the electrode rod) during flight.

[0087] During atomization, the electrostatic field auxiliary system is activated: Electrostatic field parameters: Voltage between the atomizing chamber wall and the central grounding rod: -200V to -800V (the atomizing chamber wall is connected to a negative high voltage of -200V to -800V, and the central grounding rod is connected to 0V, forming a radial electric field). Electric field direction: radial (from the center of the atomization chamber to the wall of the atomization chamber); Electric field strength: 50~200V / m Since the droplets carry a negative charge after exiting the plasma arc, the applied electric field should be directed from the center towards the wall (the atomization chamber wall is connected to a negative high voltage, and the central electrode is 0V). This causes the negatively charged droplets to experience an electrostatic force pointing towards the center—that is, all droplets, regardless of size, are subjected to a centripetal force, keeping them dispersed from each other. At the same time, the negatively charged droplets naturally tend to move away from each other due to the repulsion of like charges.

[0088] This invention adds an electrostatic field auxiliary system without changing the original PREP core process parameters (speed, current, atmosphere, total flow rate): the atomization chamber wall (-200 to -800V) and the central grounding rod (0V) form a radial electric field (the direction of the electric field is from the center to the wall).

[0089] Its working process is as follows: When the molten droplets fly out of the plasma arc region and continue to fly into the radial electric field, they are subjected to a centripetal electrostatic force pointing towards the axis due to their negative charge (because the force on the negative charge is opposite to the direction of the electric field). At the same time, all droplets carry the same negative charge and generate Coulomb repulsion between them. During the flight, the droplets are "pushed" towards the central region on the one hand (to avoid hitting the wall and bouncing back) and "pushed" away from each other on the other hand (to avoid getting close to each other). The two work together to keep the droplets in a monodisperse flight state, eliminating the chance of small and large particles forming satellite powder due to collisions.

[0090] This scheme reduces satellite dust and improves Hall flow rate.

[0091] The dual synergistic effect of electrostatic repulsion: Between droplets: All droplets carry the same negative charge and generate Coulomb repulsion between them (F=k·q1·q2 / r). 2 This force causes droplets to naturally disperse during flight, fundamentally reducing the probability of collisions between small and large particles.

[0092] Electric field-induced repulsion: The radial electric field causes all droplets to be subjected to a centripetal electrostatic force pointing towards the center, which is equivalent to forming a "repulsive barrier" around each droplet, further preventing the droplets from getting closer to each other.

[0093] The superposition of the two repulsion effects keeps the droplets in a "monodispersed" state throughout their flight, avoiding the chance of particle aggregation and collision adhesion, thereby reducing the formation of satellite dust.

[0094] The nitrided shell reduces adhesion (eliminating the "possibility of sticking"), while the electrostatic field reduces the probability of collision (reducing the "chance of collision"). The two mechanisms complement each other and have synergistic effects, effectively blocking satellite powder in both the "collision" and "sticking" stages. Based on nitriding modification, the electrostatic field assists in further reducing the adsorption of fine satellite powder on the powder particle surface, improving the Hall flow rate. While maintaining a high fine powder yield (≥36%) and high sphericity (≥95%), it alleviates the contradiction between the increase of satellite powder and the deterioration of flowability at high speeds.

[0095] Step 5: Powder cooling and collection.

[0096] After atomization, the powder particles are naturally cooled to room temperature (≤50℃) under inert gas protection. Powder is collected under inert gas protection to prevent oxidation during collection.

[0097] The collection operation is carried out in a glove box or a closed collection system, with a protective atmosphere of high-purity argon and an oxygen content of ≤30ppm.

[0098] The requirement to cool to ≤50℃ is to ensure that the powder particles have completely solidified and cooled to near room temperature before collection. This is because if the powder is exposed to air at too high a temperature (even when operating in a glove box, there are still trace amounts of oxygen and moisture inside), the high-temperature powder surface will oxidize faster. At the same time, the high-temperature powder carries residual static charge and is prone to agglomeration, affecting the subsequent screening efficiency and flowability. The cooling process is completed under the protection of inert gas to avoid the powder gaining oxygen due to high-temperature oxidation during the tens of minutes of time window during which it cools from the atomization temperature (about 1500℃) to room temperature. The oxygen content of ≤30ppm in a glove box or closed collection system is more stringent than that in an atomization chamber (≤50ppm) because the powder has its surface area fully exposed during collection and is more sensitive to oxygen adsorption. A lower oxygen environment can ensure that the final oxygen content of the finished powder is stably controlled within the quality target of ≤350ppm.

[0099] After cooling and collection, the powder is fed into the corona-charged dispersion device through a vacuum conveying device. After passing through a vertically installed electrostatic dispersion tube (with an inner wall coated with PTFE insulation layer and a length of 1~2m), the powder flows by gravity through the corona-charged region at the inlet of the tube (tungsten needle electrode, voltage -10~-30kV, oxygen content ≤30ppm under argon protection). The powder particles acquire the same negative charge on their surface under the action of corona discharge.

[0100] For the already adhered satellite particles and the host particle assembly, when they are in contact and carry the same charge, they generate an extremely strong Coulomb repulsion force (F=k·Q·q / r). 2 (Since r is extremely small, the repulsive force is extremely large). This instantaneous repulsive force is sufficient to overcome the van der Waals force and "eject" the satellite particle from the surface of the main particle.

[0101] After desorption, the free particles remain dispersed in the pipe due to the repulsion of like charges and fall into the collection chamber, where they then proceed to the sieving and grading process in step six. This process can further remove physically adhered satellite powder and improve the powder Hall flow rate.

[0102] The corona charge dispersion device used mainly consists of a vertically installed insulated stainless steel dispersion tube (1~2m in length) and a high-voltage corona tungsten needle electrode (-10~-30kV) at the inlet. It uses corona discharge to make the powder particles acquire the same charge on the surface, and uses Coulomb repulsion to eject the adhered satellite particles from the surface of the main particles.

[0103] Step 6: Screening and grading.

[0104] The collected powder was sieved and classified under an inert gas atmosphere. An ultrasonic vibration sieving system was used, equipped with standard sieves of different mesh sizes.

[0105] Screening parameters: Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 20–40 kHz; Screening time: 30-60 minutes per batch; Grading criteria (based on particle size requirements for additive manufacturing powders): Fine powder: 15~53μm (suitable for SLM process); Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor below each layer of screen monitors the cumulative mass curve of the powder in real time. When the mass change is less than 0.5% of the total amount of powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be completed.

[0106] Ultrasonic vibration frequency (20-40kHz) effectively overcomes the van der Waals forces and electrostatic forces between micron-sized powder particles through high-frequency mechanical vibration. Fine powder (15μm level) has a large specific surface area and high surface energy, making it very easy to clog the screen due to agglomeration. Ultrasonic vibration causes the screen wire diameter to generate high-frequency micro-amplitude vibration, which continuously destroys the agglomeration force between particles, allowing the powder to pass through the screen in a monodisperse state, significantly improving screening efficiency and shortening screening time. An oxygen content of ≤30ppm in the sieving environment ensures that the powder will not undergo surface oxidation when exposed to a large surface area during the sieving process, because the specific surface area can reach thousands of m² when the powder particle size is in the micrometer range. 2 / kg, even trace amounts of oxygen can cause the surface oxide layer to thicken; The criterion for determining the end point of screening (the change in mass for 5 consecutive minutes is less than 0.5% of the total amount retained) achieves an objective quantification of the screening completion rate. Too short a screening time will result in the powder of the target particle size range not being fully passed through the screen and remaining in the coarse powder, reducing the yield. Too long a screening time will reduce production efficiency and excessive vibration may cause wear on the surface of the powder particles, producing fine debris and affecting the powder morphology.

[0107] As a preferred option, powder post-treatment: the sieved powder is subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 200-300°C for 2-4 hours to eliminate residual stress inside the powder particles and further improve the powder's flowability and printing performance.

[0108] The vacuum stress-relief annealing temperature of 200–300°C used in this invention is significantly lower than that of GCr. 15 The conventional stress-relief annealing temperature for bulk materials (600–700℃) is based on the following considerations: PREP atomized powder particles are in the micrometer range (15–150 μm), and the residual stress formed during its rapid solidification process is micro-region residual stress, characterized by high stress amplitude and small range of effect. Unlike bulk materials, which require high temperatures to promote atomic diffusion and release macroscopic residual stress, micrometer-sized powders can effectively release micro-region stress at 200–300℃ through grain boundary slip and dislocation rearrangement. If the traditional stress-relief annealing temperature of 600–700℃ is used, it will instead lead to increased oxidation on the powder particle surface and sintering adhesion between particles, seriously impairing the sphericity and flowability of the powder. Therefore, the "low-temperature long-time" stress-relief annealing process (200–300℃, 2–4 hours) proposed in this invention is specifically developed for the characteristics of PREP micrometer-sized powders and is fundamentally different from the annealing process for bulk materials.

[0109] Step 7: Vacuum packaging.

[0110] The sieved powders of each particle size range are then vacuum-sealed. Packaging parameters: Packaging bag material: High-barrier aluminum-plastic composite bag; Vacuum degree: ≤1.0×10 -1 Pa; Heat sealing temperature: 180~220℃; Heat sealing time: 2-5 seconds; Net weight per bag: 1-5kg (can be adjusted according to user needs).

[0111] Vacuum degree (≤1.0×10) -1Pa) eliminates residual air (mainly oxygen and water vapor) inside the packaging bag, keeping the powder in a high vacuum isolation state during storage and transportation. This prevents slow oxidation and moisture absorption caused by residual oxygen inside the packaging bag, thus maintaining the powder's low oxygen content and good flowability for a long time.

[0112] The high barrier properties of aluminum-plastic composite bags ensure that external oxygen and moisture cannot penetrate the packaging material and seep into the bag, because the aluminum foil layer has almost zero permeability to gas molecules, providing long-term static protection for powder.

[0113] The heat sealing temperature (180-220℃) and heat sealing time (2-5 seconds) must ensure that the heat sealing layer (usually polyethylene or polypropylene) of the aluminum-plastic composite bag is fully melted and fused under pressure to form an airtight seal. If the temperature is too low, the melting will be insufficient, resulting in a weak seal and failure to maintain vacuum. If the temperature is too high, the thin aluminum foil layer may be burned through, damaging the barrier performance.

[0114] Example 1 A method for preparing high-carbon chromium bearing steel powder for metal additive manufacturing by atomization includes the following steps: Step 1: Alloy smelting and ingot preparation.

[0115] High-carbon chromium bearing steel alloy ingots were prepared by vacuum induction melting (VIM). The alloy composition by mass percentage (wt%) was: C 0.95, Si 0.35, Mn 0.25, Cr 1.65, Mo ≤0.10, P ≤0.025, S ≤0.025, Ni ≤0.3, Cu ≤0.25, Zr 0.0173, Al 0.0329, N 0.198, Se 0.005, Fe balance.

[0116] The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1580℃; Refining time: 60 minutes; Casting temperature: 1520℃; Step 2: Electrode rod processing.

[0117] Electrode rod specifications: Diameter: 90mm; Length: 350mm; Roundness deviation: ≤0.05mm; Straightness deviation: ≤0.1mm / m; Surface roughness: ≤1.2μm; Density: ≥99.5%.

[0118] The above-mentioned N content is the theoretical maximum value (assuming that all N in ZrN and AlN is retained in the steel). The same applies to the following examples. In the actual finished product, due to the fact that some N escapes in the form of N2 gas during the vacuum melting process, the final N residual amount is about 50% to 80% of the theoretical value.

[0119] Step 3: Loading the rod and vacuuming.

[0120] Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes (leak detection); After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached; Protective gas: Based on a mixture of high-purity argon (purity ≥99.999%) and high-purity helium (purity ≥99.999%) with a volume ratio of Ar:He = 4:1, high-purity nitrogen (N2) with a purity ≥99.999% is precisely introduced into the atomization chamber through a mass flow controller. The high-purity N2 is then concentrated and sprayed through an annular nozzle into the droplet generation and initial flight region (a local space with a diameter of approximately 50 mm) on the end face of the electrode rod. The control parameters are as follows: Nitrogen flow rate: 2-8 L / min; Total gas flow rate: The sum of the original Ar and He flow rates and the nitrogen flow rate is 5.002-5.008 Nm³. 3 / min; Working air pressure: 0.10 MPa; Controlling the gradient nitrogen flow rate: During the initial 2 minutes of atomization, use a nitrogen flow rate of 2-3 L / min for low-flow preheating to avoid excessive nitriding during the initial unstable phase. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, that is, in the last 3 minutes of atomization, the nitrogen flow rate is reduced to 3-4 L / min to avoid excessive reaction in the feed head area.

[0121] Step 4: Plasma rotating electrode atomization powder production.

[0122] Core process parameters: Electrode rod rotation speed: 22000 r / min; Plasma operating voltage: 150~200V; In the initial stage of atomization (first 5 minutes), the melting current is controlled at 2000A; preferably in the stable atomization period, the melting current is controlled at 1700A; preferably in the final stage of atomization (last 3 minutes), the melting current is controlled at 1500A.

[0123] Distance between plasma gun and electrode rod end face: 6mm (adjustable online); Electrode rod feed speed: 1.0 mm / s (automatically adjusted according to the melting process); During the atomization process, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled at ≤50ppm.

[0124] During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 40kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process (from plasma arc ignition to the end of atomization).

[0125] Gradient ultrasonic power control is used for different atomization stages: In the initial stage of atomization (0-2 minutes), the ultrasonic power is 500W, starting at low power to avoid interfering with the initial stability of the molten pool; During the stable phase of atomization, the ultrasonic power is 2000W, with high power enhancing degassing and compression. Towards the end of the atomization stage, reduce the ultrasonic power to 600W to avoid excessive vibration in the feed head area.

[0126] During atomization, the electrostatic field auxiliary system is activated: A radial electrostatic field is established between the atomization chamber wall and the central grounding rod of the atomization chamber. The central grounding rod is grounded at 0V, and the atomization chamber wall is connected to a negative potential of -800V.

[0127] Step 5: Powder cooling and collection.

[0128] After atomization, the powder particles are naturally cooled to room temperature under the protection of an inert gas.

[0129] The collection operation is carried out in a glove box under a protective atmosphere of high-purity argon with an oxygen content of ≤30ppm.

[0130] The cooled and collected powder is fed into a corona charge dispersion device via a vacuum conveying device. It passes through a 2m long, vertically installed electrostatic dispersion tube with an inner wall coated with PTFE insulation. A tungsten needle electrode is installed in the corona charge zone at the inlet of the tube, with a voltage of -30kV. The oxygen content in the corona charge zone is ≤30ppm under argon protection.

[0131] Step 6: Screening and grading.

[0132] Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 30kHz; Screening time: 30 minutes / batch; Grading criteria (based on particle size requirements for additive manufacturing powders): Fine powder: 15~53μm (suitable for SLM process); Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor under each layer of screen monitors the cumulative powder mass curve in real time. When the mass change is less than 0.5% of the total powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be complete. The sieved powder was subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 250°C for 3 hours.

[0133] Step 7: Vacuum packaging.

[0134] The sieved powders of each particle size range are then vacuum-sealed. Packaging parameters: Packaging bag material: High-barrier aluminum-plastic composite bag; Vacuum degree: ≤1.0×10 -1 Pa; Heat sealing temperature: 200℃; Heat sealing time: 4 seconds; Net weight per bag: 5kg.

[0135] Performance testing and analysis: In Example 1, ZrN and AlN (Zr 0.0173%, Al 0.0329%, N 0.0198%, Se 0.005%) were added to the alloy formulation, and gradient nitrogen gas (2-8 L / min local injection to form CrN / Cr2N shell), ultrasonic field assistance (500-2000 W gradient power), radial electrostatic field (-800 V) and corona charge dispersion post-treatment were applied in sequence. Thanks to the ZrC and AlN / CrN precipitates generated from the decomposition of ZrN and AlN, which act as heterogeneous nucleation cores to refine the solidification structure and effectively eliminate shrinkage cavities, and the reduction of surface tension and droplet adhesion by Se, coupled with the low adhesion of the nitrided shell and the "chemical + physical" dual satellite powder suppression mechanism of electrostatic repulsion, the median particle size D50 of the powder in this embodiment is 32.2 μm, the yield of fine powder of 15-53 μm reaches 34%, the sphericity is 96.8%, the oxygen content is 298 ppm, the Hall flow rate is 12.9 s / 50 g, the satellite powder index is in the "low" to "medium" range (≤2 particles / field of view), and the loose packing density is 4.55 g / cm³. 3 Tap density 5.15 g / cm³ 3 With a porosity of only 0.31%, all performance indicators meet the industry-standard requirements for additive manufacturing powders (sphericity ≥95%, oxygen content ≤350ppm, Hall flow rate ≤14s / 50g, and bulk density ≥4.4g / cm³). 3 In each embodiment, D50 is closest to the ideal value of 32μm, indicating excellent overall quality.

[0136] Example 2 A method for preparing high-carbon chromium bearing steel powder for metal additive manufacturing by atomization includes the following steps: Step 1: Alloy smelting and ingot preparation.

[0137] High-carbon chromium bearing steel alloy ingots were prepared by vacuum induction melting (VIM). The alloy composition by mass percentage (wt%) was: C 1.05, Si 0.15, Mn 0.45, Cr 1.40, Mo ≤0.10, P ≤0.025, S ≤0.025, Ni ≤0.3, Cu ≤0.25, Zr 0.0434, Al 0.0132, N 0.135, Se 0.01, Fe balance.

[0138] The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1650℃; Refining time: 30 minutes; Casting temperature: 1560℃; Step 2: Electrode rod processing.

[0139] Electrode rod specifications: Diameter: 90mm; Length: 350mm; Roundness deviation: ≤0.05mm; Straightness deviation: ≤0.1mm / m; Surface roughness: ≤1.2μm; Density: ≥99.5%.

[0140] Step 3: Loading the rod and vacuuming.

[0141] Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes (leak detection); After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached: Protective gas: Based on a mixture of high-purity argon (purity ≥99.999%) and high-purity helium (purity ≥99.999%) with a volume ratio of Ar:He = 4:1, high-purity nitrogen (N2) with a purity ≥99.999% is precisely introduced into the atomization chamber through a mass flow controller. The high-purity N2 is then concentrated and sprayed through an annular nozzle into the droplet generation and initial flight region (a local space with a diameter of approximately 50 mm) on the end face of the electrode rod. The control parameters are as follows: Nitrogen flow rate: 2-8 L / min; Total gas flow rate: Original total flow rate of Ar and He 15 Nm 3The superimposed nitrogen flow rate is 15.002-15.008 Nm³ / min. 3 / min; Working air pressure: 0.15MPa; Controlling the gradient nitrogen flow rate: During the initial 2 minutes of atomization, use a nitrogen flow rate of 2-3 L / min for low-flow preheating to avoid excessive nitriding during the initial unstable phase. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, that is, in the last 3 minutes of atomization, the nitrogen flow rate is reduced to 3-4 L / min to avoid excessive reaction in the feed head area.

[0142] Step 4: Plasma rotating electrode atomization powder production.

[0143] Core process parameters: Electrode rod rotation speed: 22000 r / min; Plasma operating voltage: 150~200V; In the initial stage of atomization (first 5 minutes), the melting current is controlled at 2000A; preferably in the stable atomization period, the melting current is controlled at 1700A; preferably in the final stage of atomization (last 3 minutes), the melting current is controlled at 1500A.

[0144] Distance between plasma gun and electrode rod end face: 6mm (adjustable online); Electrode rod feed speed: 1.0 mm / s (automatically adjusted according to the melting process); During the atomization process, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled at ≤50ppm.

[0145] During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 40kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process (from plasma arc ignition to the end of atomization).

[0146] Gradient ultrasonic power control is used for different atomization stages: In the initial stage of atomization (0-2 minutes), the ultrasonic power is 500W, starting at low power to avoid interfering with the initial stability of the molten pool; During the stable phase of atomization, the ultrasonic power is 2000W, with high power enhancing degassing and compression. Towards the end of the atomization stage, reduce the ultrasonic power to 600W to avoid excessive vibration in the feed head area.

[0147] A radial electrostatic field is established between the atomization chamber wall and the central grounding rod of the atomization chamber. The central grounding rod is grounded at 0V, and the atomization chamber wall is connected to a negative potential of -800V.

[0148] Step 5: Powder cooling and collection.

[0149] After atomization, the powder particles are naturally cooled to room temperature under the protection of an inert gas.

[0150] The collection operation is carried out in a glove box under a protective atmosphere of high-purity argon with an oxygen content of ≤30ppm.

[0151] The cooled and collected powder is fed into a corona charge dispersion device via a vacuum conveying device. It passes through a 2m long, vertically installed electrostatic dispersion tube with an inner wall coated with PTFE insulation. A tungsten needle electrode is installed in the corona charge zone at the inlet of the tube, with a voltage of -30kV. The oxygen content in the corona charge zone is ≤30ppm under argon protection.

[0152] Step 6: Screening and grading.

[0153] Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 30kHz; Screening time: 30 minutes / batch; Grading criteria (based on particle size requirements for additive manufacturing powders): Fine powder: 15~53μm (suitable for SLM process); Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor under each layer of screen monitors the cumulative powder mass curve in real time. When the mass change is less than 0.5% of the total powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be complete. The sieved powder was subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 250°C for 3 hours.

[0154] Step 7: Vacuum packaging.

[0155] The sieved powders of each particle size range are then vacuum-sealed. Packaging parameters: Packaging bag material: High-barrier aluminum-plastic composite bag; Vacuum degree: ≤1.0×10 -1 Pa; Heat sealing temperature: 200℃; Heat sealing time: 4 seconds; Net weight per bag: 5kg.

[0156] Example 2 uses a higher ZrN addition amount (Zr 0.0434%, Al 0.0132%, N 0.0135%, Se 0.01%). The increased Zr content increases the number of ZrC precipitates and the density of heterogeneous nuclei, resulting in a more significant effect on eliminating shrinkage cavities (porosity decreased to 0.28%, the lowest among all examples). At the same time, doubling the Se content further reduces surface tension and the tendency of fine droplets to adhere, resulting in a powder D50 of 31.8 μm, a fine powder yield of 36%, and a sphericity of 97.0%, all of which are the best among all examples. The oxygen content is 292 ppm, the Hall flow rate is 12.7 s / 50 g, the satellite powder index is in the "low" to "medium" range (≤2 particles / field of view), and the loose packing density is 4.57 g / cm³. 3 Tap density 5.17 g / cm³ 3 It is also slightly better than Example 1. This example demonstrates that the addition of appropriate amounts of ZrN and Se has a synergistic effect in eliminating shrinkage cavities and suppressing satellite powder, but the ratio of Zr to Al needs to be balanced (in this example, Zr is higher and Al is lower) to avoid excessive ZrC precipitation leading to a decrease in toughness.

[0157] Example 3 A method for preparing high-carbon chromium bearing steel powder for metal additive manufacturing by atomization includes the following steps: Step 1: Alloy smelting and ingot preparation.

[0158] High-carbon chromium bearing steel alloy ingots were prepared by vacuum induction melting (VIM). The alloy composition by mass percentage (wt%) was: C 0.1, Si 0.2, Mn 0.35, Cr 1.5, Mo ≤0.10, P ≤0.025, S ≤0.025, Ni ≤0.3, Cu ≤0.25, Zr 0.03, Al 0.023, N 0.165, Se 0.005, Fe balance.

[0159] The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1615℃; Refining time: 45 minutes; Casting temperature: 1540℃; Step 2: Electrode rod processing.

[0160] Electrode rod specifications: Diameter: 90mm; Length: 350mm; Roundness deviation: ≤0.05mm; Straightness deviation: ≤0.1mm / m; Surface roughness: ≤1.2μm; Density: ≥99.5%.

[0161] Step 3: Loading the rod and vacuuming.

[0162] Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes (leak detection); After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached: Protective gas: Based on a mixture of high-purity argon (purity ≥99.999%) and high-purity helium (purity ≥99.999%) with a volume ratio of Ar:He = 4:1, high-purity nitrogen (N2) with a purity ≥99.999% is precisely introduced into the atomization chamber through a mass flow controller. The high-purity N2 is then concentrated and sprayed through an annular nozzle into the droplet generation and initial flight region (a local space with a diameter of approximately 50 mm) on the end face of the electrode rod. The control parameters are as follows: Nitrogen flow rate: 2-8 L / min; Total gas flow rate: Original total flow rate of Ar and He 10 Nm 3 The superimposed nitrogen flow rate is 10.002-10.008 Nm³ / min. 3 / min; Working air pressure: 0.125MPa; Controlling the gradient nitrogen flow rate: During the initial 2 minutes of atomization, use a nitrogen flow rate of 2-3 L / min for low-flow preheating to avoid excessive nitriding during the initial unstable phase. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, that is, in the last 3 minutes of atomization, the nitrogen flow rate is reduced to 3-4 L / min to avoid excessive reaction in the feed head area.

[0163] Step 4: Plasma rotating electrode atomization powder production.

[0164] Core process parameters: Electrode rod rotation speed: 22000 r / min; Plasma operating voltage: 150~200V; In the initial stage of atomization (first 5 minutes), the melting current is controlled at 2000A; preferably in the stable atomization period, the melting current is controlled at 1700A; preferably in the final stage of atomization (last 3 minutes), the melting current is controlled at 1500A. Distance between plasma gun and electrode rod end face: 6mm (adjustable online); Electrode rod feed speed: 1.0 mm / s (automatically adjusted according to the melting process); During atomization, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled to be ≤50ppm. During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 40kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process (from plasma arc ignition to the end of atomization).

[0165] Gradient ultrasonic power control is used for different atomization stages: In the initial stage of atomization (0-2 minutes), the ultrasonic power is 500W, starting at low power to avoid interfering with the initial stability of the molten pool; During the stable phase of atomization, the ultrasonic power is 2000W, with high power enhancing degassing and compression. Towards the end of the atomization stage, reduce the ultrasonic power to 600W to avoid excessive vibration in the feed head area.

[0166] A radial electrostatic field is established between the atomization chamber wall and the central grounding rod of the atomization chamber. The central grounding rod is grounded at 0V, and the atomization chamber wall is connected to a negative potential of -800V.

[0167] Step 5: Powder cooling and collection.

[0168] After atomization, the powder particles are naturally cooled to room temperature under the protection of an inert gas.

[0169] The collection operation is carried out in a glove box under a protective atmosphere of high-purity argon with an oxygen content of ≤30ppm.

[0170] The cooled and collected powder is fed into a corona charge dispersion device via a vacuum conveying device. It passes through a 2m long, vertically installed electrostatic dispersion tube with an inner wall coated with PTFE insulation. A tungsten needle electrode is installed in the corona charge zone at the inlet of the tube, with a voltage of -30kV. The oxygen content in the corona charge zone is ≤30ppm under argon protection.

[0171] Step 6: Screening and grading.

[0172] Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 30kHz; Screening time: 30 minutes / batch; Grading criteria (based on particle size requirements for additive manufacturing powders): Fine powder: 15~53μm (suitable for SLM process); Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor under each layer of screen monitors the cumulative powder mass curve in real time. When the mass change is less than 0.5% of the total powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be complete. The sieved powder was subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 250°C for 3 hours.

[0173] Step 7: Vacuum packaging.

[0174] The sieved powders of each particle size range are then vacuum-sealed. Packaging parameters: Packaging bag material: High-barrier aluminum-plastic composite bag; Vacuum degree: ≤1.0×10 -1 Pa; Heat sealing temperature: 200℃; Heat sealing time: 4 seconds; Net weight per bag: 5kg.

[0175] This embodiment uses a medium ratio (Zr 0.03%, Al 0.023%, N 0.0165%, Se 0.005%), and its overall performance is between that of Embodiment 1 and Embodiment 2—D50 is 32.0 μm, fine powder yield is 35%, sphericity is 96.9%, oxygen content is 295 ppm, Hall flow rate is 12.8 s / 50 g, satellite powder index is in the "low" to "medium" range (≤2 particles / field of view), and loose packing density is 4.56 g / cm³. 3 Tap density 5.16 g / cm³ 3 The porosity is 0.30%. This formulation takes into account the dual effects of ZrC nucleation enhancement (pore elimination) and Se surface activity (satellite powder inhibition). All performance indicators are within the range of values ​​in Examples 1 and 2, which is a balanced formulation scheme and is suitable as the preferred formulation for mass production.

[0176] Comparative Example 1 Compared to Example 3, the formulation of Comparative Example 1 does not contain Zr, Al, or N. All other steps and parameters are the same as in Example 3.

[0177] This comparative formulation does not contain Zr, Al, or N (i.e., no ZrN or AlN is added), and the remaining steps and parameters are the same as in Example 3. Due to the lack of ZrC and AlN / CrN heterogeneous nucleation cores, the dendrites are coarser and the feeding channels are relatively obstructed during droplet solidification, resulting in an increase in the internal porosity of the powder from 0.30% in Example 3 to 0.45%, and an increase in shrinkage defects. At the same time, the lack of undecomposed ZrN / AlN nanoparticles as "solid spacers" (Pickering effect) on the droplet surface reduces the satellite powder suppression ability, the fine powder yield decreases from 35% to 28%, D50 coarsens from 32.0 μm to 33.5 μm, sphericity decreases from 96.9% to 96.2%, Hall flow rate deteriorates from 12.8 s / 50 g to 13.4 s / 50 g, and the satellite powder index is in the "medium" range, 2-4 per field of view. The measured oxygen content (the same applies to the comparative examples below) decreased from 295 ppm to 285 ppm (due to the absence of N and O introduced by AlN / ZrN), but all indicators still basically meet industry requirements.

[0178] Comparative Example 2 Compared to Comparative Example 1, the formulation of Comparative Example 2 further eliminates the presence of Se. All other steps and parameters are the same as in Comparative Example 1.

[0179] This comparative example, based on Comparative Example 1, further excludes the addition of Se, while maintaining the same steps and parameters. Without the surfactant effect of Se, the surface tension of the molten steel failed to decrease effectively, the adhesion between fine droplets strengthened, the probability of satellite powder formation increased further, the fine powder yield decreased from 28% to 26%, and the D50 coarsened from 33.5 μm to 33.8 μm, further confirming an increase in satellite powder compared to Comparative Example 1. Sphericity decreased from 96.2% to 96.0%, the Hall flow rate deteriorated from 13.4 s / 50 g to 13.6 s / 50 g, the satellite powder index remained in the "medium" range (2-4 droplets / field of view), and the loose packing density and tapped density decreased to 4.46 and 5.04 g / cm³, respectively. 3 This result demonstrates that Se makes an independent contribution to reducing droplet adhesion and improving flowability by lowering surface tension, and its absence leads to a slight deterioration in quality.

[0180] Comparative Example 3 Compared to Comparative Example 2, nitrogen was not introduced in step three of Comparative Example 3. All other steps and parameters were the same as in Comparative Example 2.

[0181] Comparative Example 3 was based on Comparative Example 2 without the introduction of nitrogen gas (i.e., the formation of the CrN / Cr2N nitrided shell was eliminated), while the remaining steps and parameters were the same as in Comparative Example 2. The absence of the nitrided shell caused the droplet surface to lose the low-adhesion barrier of the "rigid shell," and the formation of satellite powder was no longer inhibited at the chemical adhesion level. The fine powder yield decreased from 26% to 24%, D50 coarsened from 33.8 μm to 34.2 μm, sphericity decreased from 96.0% to 95.8%, Hall flow rate deteriorated from 13.6 s / 50 g to 13.9 s / 50 g, the satellite powder index was in the "medium" to "medium-high" range (4-6 particles / field of view), and the loose packing density and tapped density further decreased to 4.43 and 5.00 g / cm³, respectively. 3 The oxygen content decreased to 280 ppm (due to the absence of N2 introduction), but the deterioration in yield and flowability affected powder quality.

[0182] Comparative Example 4 Compared to Comparative Example 3, Comparative Example 4 further omits establishing a radial electrostatic field between the atomization chamber wall and the grounding rod at the center of the atomization chamber in step four. The remaining steps and parameters are the same as in Comparative Example 3.

[0183] This comparative example, based on Comparative Example 3, further eliminates the radial electrostatic field between the atomization chamber wall and the central grounding rod, while maintaining the same steps and parameters as Comparative Example 3. Without the electrostatic field, the negatively charged droplets, lacking the centripetal repulsive force and ordered constraint induced by the electric field, cannot effectively counteract the airflow drag and random collisions due to their own Coulomb repulsion (without external field assistance). This increases the probability of collisions between large and small particles, exacerbates satellite powder formation, reduces the fine powder yield from 24% to 21%, coarsens D50 from 34.2 μm to 34.5 μm, reduces sphericity from 95.8% to 95.6%, and worsens the Hall velocity from 13.9 s / 50 g to 14.2 s / 50 g (approaching the critical value of ≤14 s / 50 g). The satellite powder index is 5-8 particles / field of view, leaning towards the mid-to-high range, and the loose packing density and tapped density decrease to 4.41 and 4.98 g / cm³, respectively. This result demonstrates that electrostatic field assistance plays an irreplaceable role in "reducing the probability of collisions" in satellite powder suppression.

[0184] Comparative Example 5 Compared to Comparative Example 4, in Comparative Example 5, the cooled and collected powder is not fed into the corona charge dispersion device via a vacuum conveying device in step five. The remaining steps and parameters are the same as those in Comparative Example 4.

[0185] This comparative example, based on Comparative Example 4, further omits the step of sending the cooled and collected powder into the corona-charged dispersion device in step five (i.e., eliminating the post-treatment of electrostatic desorption). All other steps and parameters remain the same as in Comparative Example 4. Without the corona-charged desorption treatment, the physically adhered satellite powder formed during flight cannot be effectively removed in subsequent processes. This results in the highest residual satellite powder content in the finished powder, a fine powder yield reduced to 18%, a D50 coarsened to 35.0 μm, a sphericity reduced to 95.3% (still ≥95%, meeting the standard), a Hall flow rate deteriorated to 14.5 s / 50 g (exceeding the industry standard requirement of ≤14 s / 50 g), a high satellite powder index (averaging ≥8 particles / field of view), and loose and tapped densities of 4.38 and 4.95 g / cm³, respectively. 3 (The loose packing density is slightly lower than ≥4.4g / cm³) 3 (Industry-standard requirements), oxygen content reduced to 275 ppm (minimum). This comparative example is equivalent to the reference baseline of the original PREP process (only adding GCr15 base formulation, without any modifications), with performance data (D50≈35μm, fine powder yield≈18%, Hall flow rate≈14.5s / 50g, bulk density≈4.38g / cm³). 3 The properties of the PREP-processed GCr15 powder are basically consistent with those reported in existing literature, and are in line with the current technical level.

[0186] Comparative Example 6 Compared to Example 3, in step four of Comparative Example 6, an ultrasonic field-assisted system is not used during the atomization process. The remaining steps and parameters are the same as in Example 3.

[0187] Compared to Example 3, Comparative Example 6 did not use an ultrasonic field-assisted system during the atomization process in step four, while the remaining steps and parameters were the same as in Example 3. The absence of the ultrasonic field weakened the driving force for the escape of dissolved gas inside the droplets and prevented the solidification and feeding barriers from being effectively destroyed, resulting in an increase in the internal porosity of the powder from 0.30% in Example 3 to 0.45%, which is comparable to Comparative Example 1 (without Zr / Al / N). However, since the heterogeneous nucleation cores of ZrN / AlN still exist, the porosity did not further deteriorate to the 0.55% level of Comparative Example 5. Other performance indicators such as D50 (32.5 μm), fine powder yield (31%), sphericity (96.5%), oxygen content (290 ppm), Hall flow rate (13.0 s / 50 g), and satellite powder index are in the "low" to "medium" range, ≤3 particles / field of view, etc., with little change compared to Example 3, because the ultrasonic field mainly acts to eliminate internal porosity rather than affecting particle size distribution and flowability. These results demonstrate that ultrasonic field assistance makes an independent and irreplaceable contribution to density enhancement.

[0188] Comparative Example 7 Compared to Example 3, Comparative Example 7 does not use gradient control of plasma current; the melting current is controlled at 1700A throughout the atomization process. All other steps and parameters are the same as in Example 3.

[0189] Compared with Example 3, Comparative Example 7 does not use gradient control of plasma current, and the melting current is kept constant at 1700A throughout the atomization process. The remaining steps and parameters are the same as in Example 3. A constant current (1700A) is equivalent to insufficient heat input in the early stage of atomization (normally it should be 1800-2000A in the early stage), which leads to slow initial molten pool establishment and unstable liquid film formation in the initial stage, resulting in more irregular particles and coarse droplets in the early stage of atomization. A constant current of 1700A in the late stage of atomization (when the remaining length of the electrode rod is shortened) is equivalent to relatively high heat input (normally it should be reduced to the lower limit of 1500-1700A in the late stage), which leads to overheating in the feed head area and the generation of tailing particles. As a result, D50 coarsens from 32.0μm in Example 3 to 33.0μm, fine powder yield decreases from 35% to 28%, sphericity decreases from 96.9% to 96.0%, Hall flow rate deteriorates from 12.8s / 50g to 13.2s / 50g, porosity increases from 0.30% to 0.38% (due to inconsistent solidification conditions caused by heat input fluctuations), and satellite powder index is in the "low" to "medium" range, ≤3 particles / field of view. The results demonstrate that gradient current control optimizes the concentration of particle size distribution and batch consistency by matching the heat demand at each stage.

[0190] Comparative Example 8 Compared to Example 3, Comparative Example 8 omits the annealing step in step six. All other steps and parameters are the same as in Example 3.

[0191] The lack of annealing prevented the effective release of residual stress in the micro-regions formed within the powder particles during ultrafast solidification (originating from non-uniform shrinkage caused by the temperature difference between the particle surface and interior). This resulted in a slight deterioration in the Hall flow rate from 12.8 s / 50 g in Example 3 to 13.1 s / 50 g, and a decrease in the loose packing density from 4.56 g / cm³. 3 Slightly decreased to 4.52 g / cm³ 3 (Residual stress leads to increased microscopic unevenness on the particle surface and increased frictional resistance). Sphericity slightly decreased from 96.9% to 96.6% (annealing promotes atomic diffusion smoothing of microscopic protrusions on the particle surface), but had almost no effect on D50 (32.0 μm), fine powder yield (33%), and oxygen content (295 ppm), because annealing mainly acts on stress release and surface microstructure repair rather than changing particle size and chemical composition. Porosity slightly increased from 0.30% to 0.34% (insufficient stress release may prevent some microcracks from closing). Satellite powder index was in the "low" to "medium" range, ≤3 particles / field of view. Overall, omitting the annealing step will have a certain negative impact on powder flowability and bulk density.

[0192] Detection methods: Particle size distribution (D50, percentage of 15~53μm) was determined using a laser particle size analyzer (such as Malvern Mastersizer 3000, dry dispersion, dispersion pressure 0.3MPa, measurement range 0.1~1000μm). An appropriate amount of powder sample was placed in a dry sampler, and the powder was dispersed into single particles by a high-pressure gas flow. When the laser beam passed through the particle group, it generated diffracted and scattered light. After the detector received the light intensity signals at different angles, it calculated the particle volume size distribution based on the Mie scattering theory and automatically output D10, D50, D90 and the volume percentage of the specified particle size range (such as percentage of 15~53μm).

[0193] Sphericity: The sphericity was measured using scanning electron microscopy (SEM) combined with image analysis software (such as ImageJ or AztecFeature). The powder sample was uniformly dispersed on conductive tape and sputtered with gold. Backscattered electron images or secondary electron images of no less than 500 particles in no less than 10 fields of view were randomly captured at 5000x magnification. The equivalent circle diameter and maximum Feret diameter of the projected area of ​​each particle were extracted using image analysis software. The sphericity was calculated as (equivalent circle diameter of projected area / maximum Feret diameter), and the average value of all particles was taken as the sphericity of the batch.

[0194] Oxygen content: The inert gas melting-infrared absorption method (such as the LECO ONH836 oxygen, nitrogen and hydrogen analyzer, with a detection accuracy of ≤1ppm) is used for determination. Approximately 0.1~0.5g of powder sample is placed in a graphite crucible and heated to above 3000℃ in a pulse electrode furnace under the protection of inert gas (high-purity helium) to completely melt the sample. The oxygen in the sample reacts with the carbon in the graphite crucible to generate CO or CO2 gas, which is carried into the infrared detection cell by the carrier gas. The oxygen content is calculated by detecting the absorption intensity of CO / CO2 to infrared light of a specific wavelength. Three samples are taken from each batch and the average value is taken.

[0195] Hall flow rate: The determination was carried out according to GB / T 1482 "Standard Funnel Method (Hall Flow Meter) for Determination of Flowability of Metal Powders" - (50.0±0.1)g of dry powder sample was loaded into the funnel of the Hall flow meter (upper diameter 55mm, lower aperture 2.5mm, funnel angle 60°), the bottom orifice of the funnel was opened to allow the powder to flow down naturally by gravity, and the time required for 50g of powder to flow through the funnel orifice was recorded with a stopwatch (accurate to 0.1s). Each batch was measured 3 times and the average value was taken. The smaller the value, the better the powder flowability.

[0196] Loose packing density: The determination is carried out in accordance with GB / T 1479 "Determination of loose packing density of metal powders - Part 1: Funnel method" - Pour the dry powder into a standard funnel (approximately 100 mm in upper diameter, 5 mm in lower aperture, and 60° funnel angle), allowing the powder to fall freely into a calibrated cylindrical measuring cup (25 cm³ in volume) below. After the powder fills the measuring cup and overflows, scrape the powder along the rim of the cup with a scraper (avoid vibration), and weigh the mass of the powder in the measuring cup. Loose packing density = powder mass / measuring cup volume (g / cm³). Repeat the determination 3 times for each batch and take the average value.

[0197] Tap density: Determined according to GB / T 5162 "Determination of Tap Density of Metal Powders"—The weighed measuring cup (containing powder) is installed on the tap density meter and vibrated at a frequency of 250-300 times per minute (amplitude 3mm). During vibration, the powder volume gradually decreases. When the volume change between two consecutive readings does not exceed 0.5% after 2000 consecutive vibrations, the tapping endpoint is reached. The final volume is then recorded. Tap density = powder mass / final volume (g / cm³). 3 Each batch was measured three times and the average value was taken.

[0198] Porosity (internal porosity): Determined using X-ray computed tomography (X-ray CT) combined with 3D reconstruction analysis. A suitable amount of powder sample is loaded into a capillary or plastic tube. The 3D structure of the powder particles is scanned at high resolution using a micro-CT device (such as Zeiss Xradia or Bruker SkyScan, spatial resolution ≤1μm). After acquiring the projected image, the 3D volume data of the particles is reconstructed using a filtered back-projection algorithm. 3D image analysis software (such as Avizo or Dragonfly) is used to perform threshold segmentation on the reconstructed particles, identifying and extracting the internal pore regions. Porosity is calculated as (pore volume / total particle volume) × 100%. Simultaneously, the pore size distribution and number of pores in each particle size range can be statistically analyzed. To reduce testing costs, cross-sectional metallography can also be used for statistical evaluation: the powder is embedded in epoxy resin and cured. After grinding, polishing, and etching, the cross-sectional pore area ratio is statistically analyzed under an optical microscope or scanning electron microscope as an approximate value of porosity.

[0199] Satellite Powder Index (Qualitative + Semi-Quantitative): Qualitative evaluation is performed using scanning electron microscopy (SEM) at low magnification (200-500x) and large field of view. At least 20 fields of view are randomly captured at 200-500x magnification to observe the frequency and density of satellite powder (the morphology of small particles adhering to the surface of large particles) in the powder sample. Semi-quantitative evaluation is performed using four levels: "Low," "Medium," "Medium-High," and "High" ("Low" indicates an average of ≤1 satellite powder per field of view; "Medium" indicates 2-5; "Medium-High" indicates 6-10; and "High" indicates more than 10). The deviation of the fine powder proportion from the D50 value in the particle size distribution can be used as an auxiliary reference. This method is a relative evaluation approach. In this patent, the same standards and operators are used for evaluation across all comparative examples to ensure the reliability of the relative ranking.

[0200] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0201] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A method for preparing high-carbon chromium bearing steel powder for metal additive manufacturing by atomization, characterized in that, Includes the following steps: S1. Alloy smelting and ingot preparation; S2, Electrode rod processing; S3, loading rods, vacuuming and working pressure regulation; S4, Plasma rotating electrode atomization powder production; S5. Powder cooling and collection; S6. Powder sieving and grading; S7, vacuum packaging; In step S1, the alloy composition by mass percentage includes C 0.95–1.05, Si 0.15–0.35, Mn 0.25–0.45, Cr 1.40–1.65, Mo ≦0.10, P ≦0.025, S ≦0.025, Ni ≦0.3, Cu ≦0.25, Zr 0.0173–0.0434, Al 0.0132–0.0329, N 0.0094%–0.0237, Se 0.005–0.01, and Fe balance.

2. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, The raw materials added during alloy smelting in step S1 include: Industrial pure iron, with an iron content of ≥99.8wt%, serves as the base metal, providing the Fe balance; High carbon ferrochrome FeCr 55 C 10 It contains 55%–65 wt% Cr and 7%–10 wt% C, and is used as a chromium source and part of a carbon source. The amount added is calculated based on the target Cr content of 1.40 wt%–1.65 wt%. The carbon raiser is made of high-purity graphite with a carbon content ≥98wt%, used to precisely adjust the carbon content to 0.95%~1.05wt%. Industrial-grade silicon, containing ≥98wt% Si, used to adjust the Si content to 0.15wt%~0.35wt%; Electrolytic manganese, containing ≥99.5 wt% Mn, is used to adjust the Mn content to 0.25%–0.45 wt%. Micro-carbon ferrochrome is added according to the target components to finely adjust the Cr content without introducing excessive carbon. Ni and Cu are derived from residues in pure iron and ferrochrome raw materials and are not specifically added. They are controlled to be within 0.30 wt% and 0.25 wt% respectively by selecting the raw material grade. Al is added in the form of nano-aluminum nitride (AlN) powder, and the amount added is calculated based on the target Al content of 0.0132 to 0.0329 wt%. Se is added in the form of ferro-selenium alloy, and the amount added is calculated based on the target Se content of 0.005 to 0.01 wt%. Zr is added in the form of zirconium nitride powder ZrN, and the amount added is calculated based on the target Zr content of 0.0173 to 0.0434 wt%. N comes from ZrN powder and AlN powder.

3. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, The smelting process parameters in step S1 are as follows: The smelting process parameters are as follows: Vacuum degree ≤1.0×10 -2 Pa; Melting temperature: 1580~1650℃; Refining time: 30-60 minutes; Casting temperature: 1520~1560℃.

4. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, Step S3 includes: A high-carbon chromium bearing steel alloy electrode rod is clamped onto the rod rotation drive device of a plasma rotating electrode atomization powder making equipment. The diameter of the atomization chamber of the equipment is 2.0 to 3.0 m. The entire powder-making equipment was pre-vacuumed. Pre-evacuation vacuum degree: ≤5.0×10 -3 Pa; Pressure holding time: ≥30 minutes for leak detection; After vacuuming is completed, high-purity inert protective gas is introduced into the atomization chamber until a slight positive pressure is reached: Protective gas: a mixture of high-purity argon (≥99.999%) and high-purity helium (≥99.999%), with a volume ratio of Ar:He = 4:1; Working air pressure: 0.10~0.15MPa (absolute pressure); Gas circulation flow rate: 5~15Nm 3 / min; Pre-evacuation vacuum degree ≤ 5.0 × 10 -3 Pa.

5. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 4, characterized in that, Step S3 also includes: While maintaining the original Ar:He = 4:1 mixed atmosphere, the total flow rate is 5-15 Nm³. 3 Based on the flow rate of [flow rate] / min, high-purity nitrogen (N2) with a purity ≥99.999% is precisely introduced into the atomization chamber via a mass flow controller, with the following control parameters: Nitrogen flow rate: 2–8 L / min; Gas circulation flow rate: The sum of the original Ar and He flow rates and the nitrogen flow rate is 5.002~15.008 Nm³. 3 / min; Controlling the gradient nitrogen flow rate: During the initial 0-2 minutes of atomization, the nitrogen flow rate is 2-3 L / min, and the low flow rate is used for preheating to avoid excessive nitriding in the initial unstable stage. During the stable phase of atomization, the nitrogen flow rate is 5-8 L / min. The high flow rate enhances the nitridation reaction and forms a complete nitride shell. At the end of the atomization stage, reduce the nitrogen flow rate to 3-4 L / min to avoid excessive reaction in the feed head area.

6. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, The process parameters for step S4, plasma rotating electrode atomization powder production, include: Electrode rod rotation speed: 15000~26000 r / min; Preferred rotational speed: 18000~22000 r / min; Plasma operating voltage: 150~200V; Plasma melting current: 1500~2200A; Preferred current: 1700~2000A Distance between plasma gun and electrode rod end face: 3-8mm; Electrode rod feed speed: 0.5~2.0mm / s; During the atomization process, the oxygen content of the inert gas atmosphere in the atomization chamber needs to be continuously monitored and controlled to be ≤50ppm; Specifically, when producing fine powder of 15–53 μm, the electrode rod rotation speed is controlled at 22,000–26,000 r / min; when producing coarse powder of 53–150 μm, the electrode rod rotation speed is controlled at 15,000–20,000 r / min. Gradient control of plasma current is implemented: during the first 5 minutes of atomization, the melting current is controlled at 1800-2000A; during the stable atomization period, the melting current is controlled at 1600-1800A; and during the last 3 minutes of the final atomization period, the melting current is controlled at 1500-1700A. During atomization, an inert gas forced circulation cooling system is used in the atomization chamber, with a gas circulation flow rate of 5–15 Nm³. 3 / min.

7. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 4, characterized in that, Step S4 also includes: Electrostatic assistance is implemented during the atomization process, and a radial electrostatic field is established between the atomization chamber wall and the central grounding rod of the atomization chamber. The central grounding rod is grounded at 0V, and the atomization chamber wall is connected to a negative potential of -200 to -800V.

8. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 4, characterized in that, Step S4 also includes: During atomization, the ultrasonic field-assisted system is activated: Ultrasonic frequency: 20–40 kHz; Ultrasonic power: 500~2000W; Ultrasonic treatment time: synchronized with the atomization powder production process; Gradient ultrasonic power control is used for different atomization stages: During the initial 0-2 minutes of atomization, the ultrasonic power is 500-800W. During the stable phase of atomization, the ultrasonic power is 1200-2000W; At the end of the atomization stage, the ultrasonic power is 600-1000W.

9. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, Step S5 includes: After atomization, the powder particles are naturally cooled to room temperature under inert gas protection, and then collected under inert gas protection to prevent oxidation of the powder during the collection process. The cooled and collected powder is fed into a corona-charged dispersion device via a vacuum conveying device. The powder flows through a vertically installed electrostatic dispersion tube with an inner wall coated with PTFE insulation, which is 1-2m in length. The powder flows through the corona-charged zone at the inlet of the tube by gravity. Under the action of corona discharge, the powder particles acquire the same negative charge on their surface. The corona-charged zone at the inlet of the tube is equipped with a tungsten needle electrode with a voltage of -10 to -30kV. The oxygen content in the corona-charged zone is ≤30ppm under argon protection.

10. The atomization preparation method of high-carbon chromium bearing steel powder for metal additive manufacturing as described in claim 1, characterized in that, Step S6 Screening parameters: Screening environment: High-purity argon gas protection, oxygen content ≤30ppm; Ultrasonic vibration frequency: 20–40 kHz; Screening time: 30-60 minutes per batch; Grading standards: Fine powder: 15~53μm; Medium powder: 53~105μm; Coarse powder: 105~150μm; The sieving endpoint determination criteria are as follows: the mass sensor under each layer of screen monitors the cumulative powder mass curve in real time. When the mass change is less than 0.5% of the total powder retained by that layer of screen for 5 consecutive minutes, the sieving is determined to be complete. The sieved powder is subjected to low-temperature stress-relief annealing in a vacuum environment at a temperature of 200-300℃ for 2-4 hours.