A recycled powder for titanium microalloy steel injection smelting, a preparation method and application thereof

Abstract

This invention discloses a recycled powder for the injection smelting of titanium microalloyed steel, its preparation method, and its application, belonging to the field of metal material recycling and green metallurgy technology. The method targets additive manufacturing titanium alloy coarse powder with an oxygen content of 1000ppm–1500ppm, sequentially subjecting it to partial hydrogen permeation treatment at 350℃–500℃, mechanical stripping treatment at 750℃–850℃, and dehydrogenation and deoxidation treatment at 550℃–700℃, yielding recycled powder with an oxygen content <500ppm. The recycled powder exhibits uniform density, lacks a dense oxide shell, and does not violently splash with molten steel at high temperatures, allowing it to be directly added to molten steel through the injection system. This solves the problems of easy nozzle clogging, low yield, and numerous inclusions associated with traditional titanium alloy scrap injection, significantly improving the precise control of titanium microalloyed steel composition and production economy, and promoting the greening and resource recycling of iron and steel metallurgy.

Description

Technical Field

[0001] This invention relates to the field of metal material recycling and green metallurgy technology, and more specifically to a recycled powder for titanium microalloy steel injection smelting, its preparation method and application. Background Technology

[0002] Titanium microalloying is a key technology for improving the overall performance of low-alloy high-strength steel and pipeline steel. By adding trace amounts of titanium (typically 0.01%–0.1%) to form TiC and TiN precipitates, grain refinement and improved strength and toughness can be effectively achieved. Traditional titanium microalloying methods mainly rely on adding ferrotitanium alloys or ferrotitanium cored wires, which are costly. Furthermore, ferrotitanium alloys contain many impurities and have high melting points, resulting in titanium yields that are generally only 50%–75%, leading to large compositional fluctuations and limiting the performance stability of high-grade steels.

[0003] The industrial application of metal additive manufacturing (3D printing) technology has driven a surge in demand for titanium alloy powder raw materials. Taking TC4 (Ti-6Al-4V) titanium alloy coarse powder as an example, its high titanium content (up to 90% or more) and low cost make it a potentially high-quality alloying resource. However, in actual production, over 50% of titanium alloy coarse powder cannot be directly utilized due to severe surface oxidation, excessive oxygen content (1000ppm–1500ppm), and reduced fluidity. The yield of powder particles smaller than 45μm during the preparation process is only 20%–30%, resulting in a high proportion of byproducts with low value, low utilization rate, and high recycling costs. Reusing these titanium, aluminum, and vanadium-rich coarse powders in the steel metallurgical process is key to solving the recycling problem and achieving a green circular economy. Currently, the focus of industry technological research is on how to directly, efficiently, and cost-effectively transform this solid waste into high-quality raw materials for titanium microalloying, a technical challenge that urgently needs to be overcome in this field. The main research directions include physical shaping and chemical reduction pretreatment of coarse powder, or the development of new steelmaking alloying processes to directly utilize its high titanium content advantage to replace traditional titanium-iron alloys or titanium wires, thereby reducing the cost of titanium microalloying and improving steel performance.

[0004] Currently, the main technical solutions for treating titanium alloy coarse powder include the following: remelting as ordinary titanium waste, plasma spheroidization for return to additive manufacturing processes, traditional hydrogenation dehydrogenation (HDH) method for crushing and reuse, and surface purification by pickling or mechanical grinding.

[0005] Remelting titanium scrap as ordinary titanium waste involves treating additive manufacturing titanium alloy powder as general titanium alloy recyclable material and remelting it with other titanium scrap in a vacuum arc remelting (VAR) furnace or electron beam cold hearth furnace (EB). The technical principle relies on high-temperature vacuum melting, where the titanium alloy powder is melted, and some gaseous impurities are removed through vacuum degassing before casting into titanium alloy ingots for further processing. However, this method suffers from problems such as the inability to remove the oxide layer and the loss of high-value elements. The dense TiO2 (rutile type, melting point 1840℃) and Al2O3 (melting point 2050℃) oxide layers formed on the surface of the titanium alloy powder have melting points much higher than the titanium alloy matrix (~1650℃). Under conventional vacuum melting temperatures, the oxide layer cannot melt and remains in the ingot as solid inclusions. Even after the ingot is crushed into powder, oxide inclusions remain, hindering the wetting of titanium and molten steel during injection, resulting in a yield of only 35%–55%. In addition, the high vapor pressure of Al under high temperature and vacuum causes severe Al burn-off during the remelting process, resulting in the composition deviating from the standard range and failing to meet the compositional accuracy requirements of titanium microalloying.

[0006] Plasma spheroidization for return to additive manufacturing involves feeding coarse powder into a high-temperature plasma jet (>5000 ℃) for instantaneous melting, followed by re-spheroidization under surface tension and rapid cooling. This yields a clean alloy raw material with high sphericity and good flowability, specifically designed for titanium microalloyed steel spraying, which can then be directly returned to the additive manufacturing process. However, this approach faces significant technical and economic hurdles: extremely high energy consumption and oxidation issues. Plasma spheroidization requires heating the powder to over 10000℃, consuming over 5000 kW·h per ton, with processing costs reaching 200-300 RMB / kg, far exceeding the value of the coarse powder itself. Furthermore, plasma spheroidization only improves morphology and does not remove existing oxide layers; instead, the oxygen content increases after spheroidization, making it more prone to reaction and splashing with molten steel during spraying.

[0007] Traditional hydrogenation-dehydrogenation (HDH) pulverization and reuse utilizes the embrittlement property of titanium after absorbing hydrogen. Coarse titanium powder is completely hydrogenated at 600℃–800℃ to generate titanium hydride (TiH2). After mechanical crushing to the desired particle size, it is then dehydrogenated under vacuum to obtain fine-grained recycled titanium powder for use in powder metallurgy or chemical industries. However, this method suffers from several drawbacks: the oxide layer is not removed, resulting in poor deoxidation; the product morphology is damaged, losing the advantages of coarse powder; and there are risks related to hydrogen content, leading to safety concerns. The traditional HDH method uses high-temperature hydrogenation at 600℃–800℃ to completely convert titanium into TiH2 for overall embrittlement, facilitating mechanical crushing. However, during this process, TiH2 coats the oxide layer, which remains firmly attached to the particle surface after dehydrogenation, resulting in no significant reduction in oxygen content. This fails to meet the low-oxygen requirements of titanium microalloying or additive manufacturing. Furthermore, mechanical crushing after complete embrittlement in the HDH method results in irregular polygonal powder shapes. This results in a large specific surface area of ​​the recovered powder, making it susceptible to oxidation by furnace gas during injection and prone to clogging of the injection pipeline, leading to unstable recovery rates. Furthermore, high-temperature hydrogenation allows hydrogen to penetrate deep into the matrix, and incomplete dehydrogenation can cause hydrogen embrittlement, affecting the safety of subsequent use; the hydrogenation process also carries the risk of hydrogen explosion. Finally, energy consumption is high. High-temperature, long-duration hydrogenation and subsequent dehydrogenation result in high overall energy consumption and poor economic efficiency.

[0008] Pickling or mechanical grinding for surface purification involves using a mixed hydrofluoric acid-nitric acid pickling method or mechanical ball milling to remove the oxide layer on the surface of coarse powder, reducing the oxygen content before further utilization. However, this approach presents environmental and efficiency challenges: severe pickling pollution, poor mechanical grinding performance, and issues with fine powder loss and injection failure. The mixed hydrofluoric acid-nitric acid pickling generates a large amount of fluoride-containing waste liquid, resulting in high treatment costs and significant environmental pressure. Furthermore, the pickling process corrodes the titanium matrix, reducing yield. In addition, ball milling only removes the surface protruding oxide layer, failing to thoroughly remove the dense oxide shell and introducing iron contamination (due to ball wear). Moreover, mechanical processing leads to particle breakage, drastically increasing the proportion of fine powder (<100μm), severely deteriorating powder flowability and causing frequent nozzle blockage and bridging during pneumatic conveying. Simultaneously, the large specific surface area of ​​fine powder makes it easily oxidized by furnace gas or escape with flue gas when injected into molten steel, causing the titanium yield to drop below 60%, and a surge in inclusions in the steel, completely failing to meet the smelting requirements for high-quality titanium microalloyed steel.

[0009] In conclusion, the recycled powder obtained after processing titanium alloy coarse powder using existing methods cannot be directly used for steel molten injection alloying. Summary of the Invention

[0010] To address the above issues, there is an urgent need for an innovative solution that can accommodate large-scale processing capabilities and fundamentally open up a technological pathway for the direct use of additive manufacturing titanium alloy coarse powder in steel injection alloying, thereby realizing the high-value transformation of this solid waste into high-quality raw material for titanium microalloying. Based on this, this invention provides a recycled powder for titanium microalloy steel injection smelting, its preparation method, and its application.

[0011] The first objective of this invention is to provide a method for preparing recycled powder for the injection smelting of titanium microalloyed steel, comprising the following steps: In a hydrogen atmosphere, additive manufacturing titanium alloy coarse powder is subjected to partial hydrogen permeation treatment at 350℃~500℃, allowing hydrogen atoms to permeate to the interface between the surface oxide layer and the internal matrix of the additive manufacturing titanium alloy coarse powder, resulting in hydrogen-permeated coarse powder; the oxygen content of the additive manufacturing titanium alloy coarse powder is 1000ppm~1500ppm; under a vacuum degree <10 -1 Under vacuum conditions of Pa, the hydrogen-permeable coarse powder is mechanically exfoliated at 750℃~850℃ to remove the surface oxide layer of the hydrogen-permeable coarse powder, resulting in coarse powder with weakened interface after exfoliation treatment; under vacuum conditions <10 -3 Under vacuum conditions of Pa, the coarse powder after interface weakening and stripping treatment is subjected to dehydrogenation and deoxidation treatment at 550℃~700℃ to obtain recycled powder for titanium microalloy steel injection smelting.

[0012] In the process of this invention, hydrogen atoms are first controlled to permeate into the oxide layer-matrix interface through partial hydrogen permeation treatment, thereby reducing the interfacial bonding energy and creating conditions for subsequent stripping. At the same time, this avoids the overall embrittlement and particle size destruction caused by the high-temperature complete hydrogenation of the traditional HDH method.

[0013] Then, in the mechanical stripping process, the dense TiO2 / Al2O3 oxide layer is mechanically stripped from the substrate surface based on the interface weakening caused by partial hydrogen permeation, rather than relying on traditional chemical reduction. The stripped oxide layer fragments are in the form of flakes or powder, separating from the particle body and exposing a clean metal substrate surface. It should be noted that in the prior art, for pressed blanks, multiple thermal cycles (usually 3 to 10 times) are used to promote diffusion sintering, grain refinement, and densification; while in this step of the present invention, for loose coarse powder particles, the mechanical stripping of the oxide layer is achieved by using the phase change volume effect through a limited number of temperature-controlled cycles (1 to 2 times).

[0014] The dehydrogenation and deoxygenation treatment simultaneously achieves the triple functions of dehydrogenation, deep deoxygenation, and surface activation, as detailed below: Dehydrogenation: The dissolved hydrogen atoms diffuse out under high vacuum and medium temperature conditions and are removed by the vacuum pump in the form of H2, reducing the hydrogen content of the coarse powder to <150ppm, thus avoiding the risk of hydrogen embrittlement in subsequent use.

[0015] Deep deoxidation: Under vacuum conditions, trace oxides remaining on the particle surface undergo a reduction reaction with active hydrogen atoms diffused from the matrix to the surface: TiO2 + 4[H] → Ti + 2H2O↑. Due to the extremely high vacuum level (<10), -3 The partial pressure of H2O in the gas phase is extremely low (Pa), and the reaction continues to proceed to the right, further reducing the residual TiO2 that is difficult to remove by conventional thermodynamic reduction, ultimately reducing the oxygen content of the coarse powder to <500ppm.

[0016] Surface activation: The clean metal surface exposed after dehydrogenation does not undergo re-oxidation under high vacuum, forming an active surface with low oxygen content, which is beneficial for subsequent direct use in titanium microalloying steelmaking or additive manufacturing processes.

[0017] In a preferred embodiment of the present invention, the partial hydrogen permeation treatment lasts for 1 to 3 hours, and the hydrogen pressure is 0.05 MPa to 0.3 MPa. This temperature range in the partial hydrogen permeation treatment is much lower than the hydrogenation temperature (600°C to 800°C) of the traditional HDH method, and the hydrogen pressure is controlled at a low pressure. The purpose is to allow hydrogen atoms to preferentially diffuse and accumulate along grain boundaries and the oxide layer-matrix interface in a solid solution state (interstitial atoms), rather than forming an integral titanium hydride (TiH2) compound with titanium. After this treatment, the hydrogen content of the coarse powder is controlled at 0.3 wt% to 1.5 wt%, and the particles retain their original mechanical strength, but the bonding energy at the oxide layer-matrix interface is significantly reduced (by more than 60%), achieving the key effect of "weakening the interface without making the bulk brittle."

[0018] It should be noted that partial hydrogen permeation treatment is key to achieving interfacial weakening rather than overall embrittlement. Specifically, the hydrogen permeation temperature (350℃~500℃), hydrogen pressure (0.05MPa~0.3MPa), hydrogen content control target (0.3wt%~1.5wt% dissolved hydrogen), and hydrogen purity requirements (>99.999%, dew point <-70℃) collectively ensure that hydrogen atoms preferentially accumulate in a solid solution state at the oxide layer-matrix interface, rather than forming TiH2 compounds. This creates conditions for subsequent interfacial exfoliation while preserving the original mechanical strength of the coarse powder.

[0019] In a preferred embodiment of the present invention, the mechanical peeling process is as follows: after holding at 750℃~850℃ for 10min~30min, the temperature is lowered to 650℃~750℃; The mechanical peeling process is repeated 1 to 2 times; the heating rate is 5℃ / min to 15℃ / min, and the cooling rate is 5℃ / min to 15℃ / min. The number of peeling cycles can be selected based on the oxide layer thickness.

[0020] It should be noted that in the mechanical exfoliation process, the temperature range of 750℃ to 850℃ causes the α↔β phase transition point of titanium to decrease from 995℃ to approximately 800℃ due to the solid solution effect of hydrogen. When the temperature crosses the α↔β phase transition point after the hydrogen reduction, the titanium matrix undergoes an hcp↔bcc structural transformation, accompanied by a volume change of approximately 5%, generating shear stress at the oxide layer-matrix interface. This shear stress is sufficient to mechanically exfoliate the oxide layer from the matrix surface. The purpose of this temperature-controlled process is clearly "oxide layer exfoliation" rather than "bulk densification" or "grain refinement." The temperature range is limited to the vicinity of the α↔β phase transition point after the hydrogen reduction (750℃ to 850℃), and the heating-cooling rate (5℃ / min to 15℃ / min) and the number of cycles (1 to 2 times) both serve the specific mechanism of "interfacial shear stress generated by phase transformation volume change."

[0021] In a preferred embodiment of the present invention, the dehydrogenation and deoxygenation treatment time is 3h to 6h.

[0022] It should be noted that dehydrogenation and deoxygenation are key steps in achieving an oxygen content of <500ppm. This is especially true for vacuum levels (<10). -3 The matching of Pa), dehydrogenation temperature (550℃~700℃) and holding time (3h~6h) allows the dehydrogenation process to proceed simultaneously with the reduction of residual oxides: active hydrogen atoms reduce TiO2 to generate H2O, which is then removed by vacuum, breaking through the thermodynamic limit that simple vacuum degassing cannot reduce the oxygen content of oxides.

[0023] In a preferred embodiment of the present invention, the titanium content of the additively manufactured titanium alloy coarse powder is >85%, and the original particle size is 150μm to 600μm.

[0024] A second objective of this invention is to provide a recycled powder, which is prepared using the aforementioned method for preparing recycled powder for titanium microalloy steel injection smelting; the recycled powder has an oxygen content of <500ppm, a hydrogen content of <150ppm, a particle size of 150μm to 600μm, a sphericity ≥0.7, and a bulk density ≥2.0g / cm³. 3 .

[0025] The recycled powder prepared by this invention has uniform density, no dense oxide shell, and does not splash violently with molten steel at high temperatures. It can be directly added to molten steel through the blowing system. The titanium element recovery rate is ≥90%, and the fluctuation of titanium content in steel is controlled within ±0.002%. This solves the problems of easy clogging of the blowing gun, low recovery rate, and many inclusions in traditional titanium alloy waste blowing.

[0026] It should be noted that, based on the actual production status of additive manufacturing titanium alloy powder, during the gas atomization powder preparation process, the original coarse powder typically contains widely distributed particles ranging from 100μm to 1000μm, with the 150μm to 600μm range accounting for ≥80%. In other words, the particle size of the raw material, additive manufacturing titanium alloy coarse powder, is 100μm to 1000μm. Before preparing the recycled powder, the additive manufacturing titanium alloy coarse powder is sieved to obtain coarse powder with a particle size concentrated in the 150μm to 600μm range. After preparation according to the method of this invention, the resulting product still retains the original particle size.

[0027] The third objective of this invention is to provide the application of the above-mentioned recycled powder in the spraying smelting of titanium microalloy steel. The recycled powder is sprayed into molten steel at 1600°C to 1700°C. Under the drive of a carrier gas, nitrogen or argon is used as the carrier gas to spray the recycled powder into the molten steel. After the spraying is completed, the titanium microalloy steel is obtained through post-treatment.

[0028] The post-processing includes calming, purification, casting, and rolling.

[0029] It should be noted that during the blowing process, bottom blowing argon stirring is used, with a flow rate of 2NL / (min‧t) to 5NL / (min‧t); after blowing, the sample is settled for 3 to 5 minutes, and then analyzed to obtain titanium microalloyed steel with a titanium content of 0.01% to 0.10%.

[0030] During injection, the injection gun should be inserted to a depth of 1.5m to 3.0m, penetrating the slag layer and entering the molten steel. The specific insertion depth is adjusted according to the ladle capacity: for large-capacity ladles of 150 tons or more, the insertion depth is controlled at 2.5m to 3.0m; for small and medium-capacity ladles, the insertion depth is controlled at 1.5m to 2.0m. This depth ensures that the recycled powder avoids the high-oxygen zone at the slag-metal interface and directly enters the turbulent zone of the molten steel, preventing powder from floating and oxidizing.

[0031] In a preferred embodiment of the present invention, the amount of recycled powder added to each ton of molten steel is 0.5 kg / t to 3 kg / t, and the temperature of the molten steel is 1620℃ to 1680℃; during the injection of recycled powder, the conveying speed of recycled powder is 10 m / s to 15 m / s, and the injection pressure is 0.3 MPa to 0.5 MPa.

[0032] It should be noted that 1620℃~1680℃ is the preferred initial temperature range within the range of 1600℃~1700℃.

[0033] The initial temperature was set to ensure that after the heat is removed during the blowing process, the final temperature of the molten steel can still be maintained above 1600℃, which meets the requirements of the casting process.

[0034] In a preferred embodiment of the present invention, the molten steel is molten steel for engineering and building structures, pipeline steel or automotive structures, and the titanium content in the molten steel is 0.01wt% to 0.10wt% based on the total mass of the molten steel.

[0035] Compared with the prior art, the present invention has the following beneficial effects: To address the bottlenecks in existing recycling technologies for additive manufacturing titanium alloy coarse powder, such as difficulty in removing the oxide layer, high oxygen content, low recovery rate of alloying elements, and insufficient process economy, this invention innovatively proposes a hydrogenation deoxidation regeneration method. Compared with existing technologies, this invention can produce the following significant and verifiable beneficial effects:

[0036] This invention employs a three-step synergistic approach: low-temperature partial hydrogen permeation, temperature-controlled interface weakening, and vacuum dehydrogenation reduction. It leverages the high diffusion capacity of hydrogen atoms within the matrix of additively manufactured titanium alloy powder to preferentially enrich hydrogen at the interface between the oxide layer on the surface of the powder and the internal matrix, thereby reducing the interfacial bonding energy. Subsequently, during the temperature-controlled interface weakening process, hydrogen is used at 750℃–850℃ to reduce the volume change caused by the phase transition after the α↔β phase transition point of titanium, leading to the mechanical exfoliation of the dense TiO2 / Al2O3 oxide layer. Finally, during the vacuum dehydrogenation process, active hydrogen atoms reduce the residual oxides to metallic titanium and remove them as gaseous water. This allows the oxygen content in titanium alloy coarse powder to be stably reduced from 1000ppm to 1500ppm to <500ppm, and the oxide layer removal rate to >85%. This achieves a fundamental transformation of additive manufacturing coarse powder from oxidized waste to clean raw material, laying a quality foundation for its return to additive manufacturing or use in titanium micro-alloying steelmaking. It overcomes the difficulties in peeling and reducing the dense oxide layer, and realizes deep deoxidation and regeneration of coarse powder.

[0037] Unlike the traditional HDH method, which completely embrittles coarse powder and then mechanically pulverizes it into fine powder <45 μm, this invention employs low-temperature (350℃~500℃) controlled hydrogen permeation. This allows hydrogen to exist only in a solid solution state within the crystal lattice, without generating a bulk TiH2 compound, thus preserving the original mechanical strength of the coarse powder. Subsequent temperature-controlled processing only removes the surface oxide layer, without damaging the particle itself. The treated clean alloy raw material maintains a particle size within the range of 150μm~600μm, retaining the near-spherical characteristics of the original coarse powder, with an angle of repose ≤26° and a Hall flow rate ≥28 g / s. This prevents bridging and nozzle blockage during pneumatic conveying and blowing. Simultaneously, the absence of a dense oxide shell on the surface prevents electrostatic agglomeration due to friction within the conveying pipeline, making it suitable for industrial blowing systems. Furthermore, high-value elements such as Ti, Al, and V are not lost due to burning, with a compositional deviation of <±3%, allowing direct use in titanium microalloying steelmaking, avoiding the drawbacks of traditional methods that "destroy the shape for deoxidation." This preserves the original particle size and alloy composition of the coarse powder, ensuring its applicability to downstream processes.

[0038] This invention achieves deep deoxidation while maintaining a process temperature below 900℃ (far below the melting point of titanium alloys and the significant volatilization temperature of Al and V elements). This avoids the Al burn-off and V segregation problems caused by traditional plasma melting or high-temperature remelting. The Al and V content in the powder deviates from the original coarse powder by <±3%. Ti and Al, which exist in oxide form in the coarse powder, are released into active metallic states, significantly improving the effective utilization rate of elements. The regenerated coarse powder has an oxygen content of <500ppm and maintains the original Ti content (>85%), and can directly replace part of the titanium-iron alloy or titanium wire for titanium microalloying of low-alloy high-strength steel. The cost of coarse powder is only 60% to 70% of that of commercial titanium-iron alloys, reducing the alloying cost of low-alloy high-strength steel by 40 to 60 yuan per ton, significantly lowering alloying costs. The removal of the oxide layer increases the titanium yield when added to molten steel from the traditional 35% to 85% to >90%, reducing ineffective burn-off and inclusion formation. The molten steel has high purity, with finely dispersed TiC / TiN precipitates, resulting in better grain refinement and a better balance of strength and toughness in the steel. The process according to this invention achieves synergistic deoxidation and titanium preservation, improving the economics of titanium microalloying.

[0039] This invention features a hydrogen permeation temperature of 350℃~500℃ (significantly lower than the 600℃~800℃ of traditional HDH) and a vacuum dehydrogenation temperature of 550℃~700℃. The entire process is completed in a conventional vacuum heat treatment furnace or hydrogenation furnace, eliminating the need for energy-intensive equipment like plasma spheroidization and wastewater treatment systems like those used in acid washing. The three steps can be completed continuously within the same furnace, resulting in a compact process. Energy consumption per ton is approximately 60% of that of the traditional HDH method and 15% of that of plasma spheroidization. This invention boasts low energy consumption, highly versatile equipment, low investment, and simple operation. It is highly compatible with existing titanium powder metallurgy or steel refining equipment, making it suitable for large-scale industrial application. It provides an economically feasible technical path for the large-scale industrial consumption of tens of thousands of tons of additive manufacturing coarse powder. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Given that titanium alloy coarse powder (rich in high-value alloying elements such as Ti, Al, and V) generated from additive manufacturing cannot be directly utilized due to severe surface oxidation and excessive oxygen content, existing technologies (such as direct remelting, plasma spheroidization, traditional hydrogenation dehydrogenation, and pickling) suffer from fundamental drawbacks such as difficulty in removing the oxide layer, persistently high oxygen content, low effective utilization rate of alloying elements, and poor process economics, thus failing to achieve high-value recycling. The purpose of this invention is to provide a customized regeneration solution specifically for this type of high-specific-surface-area, high-oxygen-content titanium alloy coarse powder.

[0042] Specifically, this invention aims to overcome the bottlenecks of difficult peeling and oxygen removal from the dense oxide layer on the surface of coarse powder by designing a synergistic process of low-temperature partial hydrogen permeation, temperature-controlled interface weakening, and vacuum dehydrogenation reduction, without requiring major modifications to existing vacuum heat treatment equipment. This achieves the goals of deep deoxidation of coarse powder (oxygen content <500ppm), preservation of original particle size and alloy composition, and improved yield of titanium microalloying. As a result, additive manufacturing titanium alloy coarse powder is directly transformed from industrial solid waste into a "clean alloy raw material" that can be used for titanium microalloying steelmaking or returned to additive manufacturing, thus opening up its resource recycling path.

[0043] The technical solution of the present invention is as follows: (1) Raw material preparation and testing: Collect titanium alloy coarse powder generated during the additive manufacturing process, with a particle size distribution of 100μm to 1000μm. Perform preliminary sieving to remove powder particles with a diameter >600μm and <150μm and obvious foreign matter. Analyze the composition and oxygen content of the coarse powder to confirm that the titanium content is >85% and the oxygen content is 1000ppm to 1500ppm. Place the coarse powder in a vacuum drying oven and dry it at 80℃ to 120℃ for 2h to 4h to remove adsorbed moisture.

[0044] This invention requires the raw materials to have a titanium content >85%, an oxygen content of 1000ppm to 1500ppm, and a particle size distribution of 150μm to 600μm. This is to match the core logic of hydrogen permeation, interface weakening, and dehydrogenation and deoxygenation in this invention.

[0045] The titanium content >85% is to eliminate foreign metal impurities, avoiding incompatibility in subsequent hydrogenation processes and the introduction of harmful elements into the molten steel, which would degrade the steel's performance. The oxygen content of 1000ppm to 1500ppm is a range specifically suited for this invention. Below 1000ppm, the oxide layer of coarse powder is extremely thin, requiring no complete process and can be used directly after simple drying, avoiding unnecessary cost waste. Above 1500ppm, the oxide layer is too thick, and the bonding force with the matrix is ​​too strong. At low temperatures, some hydrogen penetration cannot reach the deep interface, and the phase transformation shear stress is insufficient to completely peel off the oxide layer, ultimately failing to meet the deoxidation requirements. The particle size distribution of 150μm to 600μm matches the original morphological characteristics of additive manufacturing coarse powder, eliminating fine powder that is prone to excessive hydrogen absorption and embrittlement, as well as large particles with slow penetration rates and uneven dissolution, retaining near-spherical characteristics, which can be directly used for injection after subsequent sieving.

[0046] If the raw material does not fall within this range after testing, it can be classified and processed according to the rules: Materials with a titanium content ≤85% should be directly rejected. If impurities are locally mixed in, they can be retested after magnetic separation or density separation, and only those meeting the standards can enter the process; Materials with an oxygen content <1000ppm only need vacuum drying at 80℃~120℃ for 2h~4h to remove adsorbed water, and after sieving, can be used directly as a blowing material; Materials with an oxygen content of 1500ppm~2000ppm can have their process parameters adjusted to suit the requirements, such as setting the hydrogen permeation temperature to the upper limit of 500℃, the hydrogen pressure to the upper limit of 0.3MPa, and the heat preservation time... The holding time is extended to 3 hours, the temperature control interface is weakened and one more cycle is added, the dehydrogenation and deoxygenation temperature is taken as the upper limit of 700℃, and the holding time is extended to 6 hours. After treatment, the oxygen content is retested and it is <500ppm, which can be used normally. If it still exceeds the standard, it is converted into low-grade metallurgical raw material. The oxygen content >2000ppm is directly rejected and is used as ordinary titanium waste for remelting. For particles with a particle size <150μm accounting for more than 20% or >600μm accounting for more than 10%, the oversized particles can be pre-screened with the corresponding aperture screen to remove them before entering the process, so as to avoid uneven treatment or excessive embrittlement of fine powder.

[0047] It should be noted that the above parameter adjustment scheme for raw materials with a content of 1500ppm to 2000ppm is a remedial process under special circumstances. Its energy consumption and processing cost are significantly higher than those of the standard oxygen content (1000ppm to 1500ppm). Therefore, based on the consideration of economic efficiency and stability in industrial production, this invention still protects 1000ppm to 1500ppm as the optimal raw material range.

[0048] (0) Low-temperature partial hydrogen permeation: The dried coarse powder is loaded into a hydrogenation furnace (such as a vertical or rotary hydrogenation furnace), and high-purity hydrogen gas (purity >99.999%, dew point <-70℃) is introduced. The temperature is raised to 350℃~500℃, and the hydrogen pressure is adjusted to 0.05MPa~0.3MPa. The temperature is maintained for 1h~3h. During the hydrogen permeation process, a programmed temperature control is used, with a heating rate of 2℃ / min~5℃ / min to avoid particle cracking caused by thermal stress. After the hydrogen permeation is completed, the powder is cooled to room temperature under hydrogen protection, and a sample is taken to test the hydrogen content, confirming that it reaches 0.3wt%~1.5wt%.

[0049] (3) Mechanical stripping (temperature-controlled interface weakening stripping): The hydrogen-permeated coarse powder is transferred to a vacuum heat treatment furnace (such as a vertical vacuum sintering furnace) and vacuumed to <10 -1 Pa. Increase the temperature to 750℃~850℃ at a rate of 5℃ / min~15℃ / min, hold for 10min~30min, then cool to 650℃~750℃ at a rate of 5℃ / min~15℃ / min, completing one round-trip temperature control process. Determine whether to repeat the process 1~2 times based on the original oxygen content of the coarse powder and the thickness of the oxide layer. During the peeling process, check the oxide layer peeling progress through the observation window or sampling port inside the furnace.

[0050] (4) Vacuum dehydrogenation and deep deoxygenation: In the same vacuum furnace, continue to evacuate to <10 -3 Pa, heat to 550℃~700℃, hold for 3h~6h. Continuously monitor the vacuum level during dehydrogenation. When the vacuum level stabilizes and the furnace pressure does not rise significantly, dehydrogenation is basically complete. After dehydrogenation, cool the furnace to below 200℃ under vacuum, then introduce high-purity argon (or nitrogen) to atmospheric pressure, and remove the powder.

[0051] (5) Post-processing and testing: The powder is sieved under inert gas protection to remove the oxide layer fragments that have been peeled off. The powder is tested for oxygen content, hydrogen content, particle size distribution, and composition analysis to confirm that the oxygen content is <500ppm, the hydrogen content is <150ppm, the particle size is 150μm~600μm, and the Ti / Al / V content deviates from the original coarse powder by <±3%. After passing the tests, the powder is vacuum-sealed or stored under inert gas protection for later use.

[0052] This invention, through the synergistic process of low-temperature partial hydrogen permeation, temperature-controlled interface weakening, and vacuum dehydrogenation reduction described above, specifically addresses the core challenges raised in the background art, achieving the following verifiable and significant effects: (1) Overcoming the bottleneck of chemical reduction of dense oxide layer and pioneering a new physical stripping path: Traditional methods rely on high-temperature chemical reduction of TiO2 / Al2O3, which is extremely difficult thermodynamically. This invention uses a physical stripping mechanism that weakens the interface through low-temperature partial hydrogen permeation and generates shear stress through temperature-controlled phase transition. First, the oxide layer is mechanically stripped from the substrate surface, and then residual trace oxides are reduced through vacuum dehydrogenation. This achieves efficient removal and deep deoxidation of the oxide layer, breaking through the thermodynamic limit of reducing oxide oxygen that traditional vacuum melting and HDH methods cannot achieve.

[0053] (2) Breaking the "embrittlement and crushing" dilemma of the HDH method and achieving deoxidation and shape preservation synergy: The traditional HDH method mechanically crushes the coarse powder after complete hydrogenation at 600-800 ℃, which crushes the coarse powder into irregular powder, destroying the convenience of adding it to steelmaking. The present invention adopts low-temperature controllable hydrogen permeation at <500 ℃, in which hydrogen exists in solid solution without generating integral TiH2, and the coarse powder maintains its original mechanical strength; the temperature-controlled treatment only peels off the surface oxide layer without damaging the particle body, and the particle size is still maintained at 150μm~600μm after regeneration, retaining the advantages of moderate coarse powder dissolution rate and easy addition control. There is no burning loss of Al and V throughout the process, and the composition deviation is <±3%.

[0054] (3) Lowering the threshold for energy consumption in recycling and opening up a path for large-scale industrial consumption: The temperature of the whole process of this invention is <900℃, the energy consumption per ton is about 60% of that of the traditional HDH method and 15% of that of plasma spheroidization, and there is no need for an acid washing waste liquid treatment system; the three steps can be completed continuously in the same furnace, with low equipment investment and good compatibility with existing vacuum heat treatment equipment, providing an economical and feasible technical path for the large-scale industrial consumption of 10,000 tons of additive manufacturing coarse powder.

[0055] The following describes the implementation of the present invention in detail through three preferred embodiments.

[0056] Example 1: Standardized regeneration of TC4 coarse powder.

[0057] This embodiment provides a hydrogenation deoxidation method for TC4 titanium alloy coarse powder generated during additive manufacturing. The specific process flow is as follows: Step 1, Raw material preparation: Take 50 kg of TC4 titanium alloy coarse powder, and after sieving, obtain coarse powder with a particle size concentrated in 150 μm to 600 μm. The oxygen content of the original TC4 titanium alloy coarse powder is 1380 ppm and the hydrogen content is 38 ppm. The TC4 titanium alloy coarse powder is composed of the following components by mass percentage: Ti 89.5 wt%, Al 6.1 wt%, V 4.0 wt%.

[0058] Step 2, Low-Temperature Partial Hydrogen Permeation: The coarse powder was loaded into a vertical hydrogenation furnace, and high-purity hydrogen gas (purity ≥99.99%, dew point -75℃) was introduced. The temperature was increased to 420℃ at a heating rate of 3℃ / min, the hydrogen pressure was 0.15MPa, and the temperature was maintained for 2 hours to obtain coarse powder treated with low-temperature hydrogen permeation. A sample of the low-temperature hydrogen permeation treated coarse powder was taken and its hydrogen content was measured: 0.85wt%. There was no change in particle appearance, and no obvious pulverization was observed.

[0059] Step 3, Temperature-controlled interface weakening and peeling: Transfer the coarse powder treated with low-temperature hydrogen permeation to a vacuum heat treatment furnace, and evacuate to 8×10 -2 Pa. The temperature is increased to 820℃ at a heating rate of 10℃ / min, held for 20 min, and then cooled to 700℃ at a cooling rate of 10℃ / min. The furnace is then allowed to cool naturally to room temperature, completing one round of temperature control. The resulting coarse powder, after interface weakening and peeling treatment, is sampled and observed: the original bright metallic oxide film on the particle surface has turned grayish-brown, and flaky peeling is visible in some areas, with a peeling rate of approximately 87%.

[0060] Step 4, Vacuum Dehydrogenation and Deep Deoxidation: The coarse powder after the interface weakening and stripping treatment is placed in the same furnace, and the furnace is further evacuated to 5×10⁻⁶. -3 Pa was heated to 650℃ at a heating rate of 10℃ / min and held for 5 hours. The furnace was then cooled to 150℃, and argon gas was introduced before exiting the furnace to obtain recycled TC4 powder. The recycled TC4 powder can be directly used as a raw material for blowing clean alloys.

[0061] Performance testing: The oxygen content of the powder decreased to 380 ppm, the hydrogen content to 105 ppm, and the particle size distribution to 140 μm–580 μm (close to the original). The composition was: Ti 89.8 wt%, Al 6.0 wt%, and V 3.9 wt%. The oxygen content decreased by 72.5%, and there was no loss of Al and V, meeting the requirements for titanium microalloying powder used in steelmaking.

[0062] Example 2: Deep deoxidation of high oxygen content TA7 titanium alloy coarse powder.

[0063] This embodiment provides a hydrogenation deoxidation method for additive manufacturing of TA7 titanium alloy coarse powder with higher oxygen content. The specific process flow is shown below, verifying the ability of this invention to handle high-oxygen materials.

[0064] Step 1, Raw material preparation: Take 30 kg of TA7 titanium alloy coarse powder, and after sieving, obtain coarse powder with a particle size concentrated in 200 μm to 600 μm. The oxygen content of the original TA7 titanium alloy coarse powder is 1520 ppm and the hydrogen content is 42 ppm. The TA7 coarse powder is composed of the following components by mass percentage: Ti 90.0 wt% and Al 5.0 wt%.

[0065] Step 2, Low-Temperature Partial Hydrogen Permeation: The coarse powder was loaded into a vertical hydrogenation furnace, and high-purity hydrogen gas (purity ≥99.99%, dew point -75℃) was introduced. The temperature was increased to 450℃ at a heating rate of 3℃ / min, the hydrogen pressure was 0.2MPa, and the temperature was maintained for 2.5h to obtain coarse powder treated with low-temperature hydrogen permeation. A sample of the low-temperature hydrogen permeation treated coarse powder was taken and its hydrogen content was measured: 1.2wt%. There was no change in particle appearance, and no obvious pulverization was observed.

[0066] Step 3, Temperature-controlled interface weakening and peeling: Transfer the coarse powder treated with low-temperature hydrogen permeation to a vacuum heat treatment furnace, and evacuate to 6×10 -2 Pa. The temperature was increased to 820℃ at a heating rate of 10℃ / min, held for 20 min, and then cooled to 700℃ at a cooling rate of 10℃ / min. The furnace was then allowed to cool naturally to room temperature, completing one round of temperature control. The temperature was then increased to 840℃ at a heating rate of 10℃ / min, held for 25 min, and then cooled to 720℃ at a cooling rate of 10℃ / min. The resulting coarse powder, after interface weakening and peeling treatment, was sampled and observed. The original bright metallic oxide film on the particle surface turned grayish-brown, and flaky peeling was visible in some areas, with a peeling rate of approximately 92%.

[0067] Step 4, Vacuum Dehydrogenation and Deep Deoxygenation: The coarse powder after the interface weakening and stripping treatment is placed in the same furnace, and the furnace is further evacuated to 3×10⁻⁶. -3 Pa was heated to 680°C at a heating rate of 10°C / min and held at that temperature for 6 hours. The furnace was then cooled to 150°C and purged with argon gas before being removed from the furnace.

[0068] Results testing: The oxygen content of the powder decreased to 420 ppm (a reduction of 72.4%), and the hydrogen content was 88 ppm. Two temperature-controlled stripping processes were also effective for high-oxygen coarse powders, proving that this method is applicable to coarse powders with oxygen contents ranging from 1000 ppm to 1500 ppm.

[0069] Example 3 This embodiment provides a hydrogenation deoxidation method for TC4 titanium alloy coarse powder generated during additive manufacturing. The specific process flow is as follows: Step 1, Raw material preparation: Take 50 kg of TC4 titanium alloy coarse powder, and after sieving, obtain coarse powder with a particle size concentrated in 150 μm to 600 μm. The oxygen content of the original TC4 titanium alloy coarse powder is 1380 ppm and the hydrogen content is 38 ppm. The TC4 titanium alloy coarse powder is composed of the following components by mass percentage: Ti 89.5 wt%, Al 6.1 wt%, V 4.0 wt%.

[0070] Step 2, Low-temperature partial hydrogen permeation: The coarse powder is loaded into a vertical hydrogenation furnace, and high-purity hydrogen gas (purity ≥99.99%, dew point -75℃) is introduced. The temperature is increased to 350℃ at a heating rate of 3℃ / min, the hydrogen pressure is 0.3MPa, and the temperature is maintained for 3h to obtain coarse powder treated with low-temperature hydrogen permeation.

[0071] Step 3, Temperature-controlled interface weakening and peeling: Transfer the coarse powder treated with low-temperature hydrogen permeation to a vacuum heat treatment furnace, and evacuate to 8×10 -2 Pa. The temperature is increased to 750℃ at a heating rate of 5℃ / min, held for 30min, and then cooled to 650℃ at a cooling rate of 5℃ / min. The mixture is then allowed to cool naturally to room temperature in the furnace. This completes one round of temperature control and yields coarse powder after the interface weakening and exfoliation treatment.

[0072] Step 4, Vacuum Dehydrogenation and Deep Deoxidation: The coarse powder after the interface weakening and stripping treatment is placed in the same furnace, and the furnace is further evacuated to 5×10⁻⁶. -3 Pa was heated to 550℃ at a heating rate of 10℃ / min and held for 3 hours. The furnace was then cooled to 150℃, and argon gas was introduced before exiting the furnace to obtain recycled TC4 powder. The recycled TC4 powder can be directly used as a raw material for blowing clean alloys.

[0073] Example 4 This embodiment provides a hydrogenation deoxidation method for TC4 titanium alloy coarse powder generated during additive manufacturing. The specific process flow is as follows: Step 1, Raw material preparation: Take 50 kg of TC4 titanium alloy coarse powder, and after sieving, obtain coarse powder with a particle size concentrated in 150 μm to 600 μm. The oxygen content of the original TC4 titanium alloy coarse powder is 1380 ppm and the hydrogen content is 38 ppm. The TC4 titanium alloy coarse powder is composed of the following components by mass percentage: Ti 89.5 wt%, Al 6.1 wt%, V 4.0 wt%.

[0074] Step 2, Low-temperature partial hydrogen permeation: The coarse powder is loaded into a vertical hydrogenation furnace, and high-purity hydrogen gas (purity ≥99.99%, dew point -75℃) is introduced. The temperature is increased to 500℃ at a heating rate of 3℃ / min, the hydrogen pressure is 0.05MPa, and the temperature is maintained for 1h to obtain coarse powder treated with low-temperature hydrogen permeation.

[0075] Step 3, Temperature-controlled interface weakening and peeling: Transfer the coarse powder treated with low-temperature hydrogen permeation to a vacuum heat treatment furnace, and evacuate to 8×10 -2 Pa. The temperature is increased to 850℃ at a heating rate of 15℃ / min, held for 10min, and then cooled to 750℃ at a cooling rate of 15℃ / min. The mixture is then allowed to cool naturally to room temperature in the furnace. This completes one round of temperature control. The resulting coarse powder after interface weakening and peeling treatment is then obtained.

[0076] Step 4, Vacuum Dehydrogenation and Deep Deoxidation: The coarse powder after the interface weakening and stripping treatment is placed in the same furnace, and the furnace is further evacuated to 5×10⁻⁶. -3 Pa was heated to 700℃ at a heating rate of 10℃ / min and held for 4 hours. The furnace was then cooled to 150℃, and argon gas was introduced before exiting the furnace to obtain recycled TC4 powder. The recycled TC4 powder can be directly used as a raw material for blowing clean alloys.

[0077] To verify the necessity of the core parameters for low-temperature hydrogen permeation in step 2 of this invention, the same batch of TC4 titanium alloy coarse powder with an original oxygen content of 1350ppm was used, and the following comparative examples were set up for comparison with Example 1.

[0078] Comparative Example 1 Take 50kg of TC4 titanium alloy coarse powder from the same batch, and after sieving, obtain coarse powder with a particle size of 150μm~600μm, original oxygen content of 1350ppm, hydrogen content <50ppm, composition of Ti 89.5wt%, Al 6.1wt%, V 4.0wt%.

[0079] The coarse powder was loaded into a vertical hydrogenation furnace, and hydrogen gas with a purity of 99.99% and a dew point of -75℃ was introduced. The temperature was increased to 650℃ at a heating rate of 5℃ / min, the hydrogen pressure was 0.5MPa, and the temperature was maintained for 4 hours to obtain hydrogenated coarse powder. After this step, the coarse powder was completely hydrogenated to TiH2 and was in a completely embrittled state.

[0080] The hydrogenated coarse powder is mechanically crushed in a jaw crusher to a particle size of <45μm, and then transferred to a vacuum heat treatment furnace, where it is evacuated to a vacuum of 5×10⁻⁶. -3 Pa was heated to 600°C at a heating rate of 10°C / min, held at that temperature for 4 hours to remove hydrogen, cooled to 150°C in the furnace, and then purged with argon gas to obtain powder produced by the conventional HDH method.

[0081] Comparative Example 2 This comparative example addresses TC4 titanium alloy coarse powder generated during additive manufacturing, and provides a hydrogenation deoxidation method for additive manufacturing titanium alloy coarse powder. The preparation method is basically the same as in Example 1, except that the process parameters for hydrogen permeation in step 2 are different. The specific process flow is as follows: Step 1: Raw material preparation: Take 50kg of TC4 titanium alloy coarse powder, and after sieving, obtain coarse powder with a particle size concentrated in 150μm~600μm. The oxygen content of the original TC4 coarse powder is 1380ppm, the hydrogen content is <50ppm, and the composition is: Ti 89.5wt%, Al 6.1wt%, V 4.0wt%.

[0082] Step 2, Medium-temperature hydrogen permeation: The coarse powder was loaded into a vertical hydrogenation furnace, and high-purity hydrogen gas (purity ≥99.99%, dew point -75℃) was introduced. The temperature was increased to 550℃ at a heating rate of 3℃ / min, the hydrogen pressure was 0.3MPa, and the temperature was maintained for 2 hours to obtain hydrogen-permeated coarse powder. A sample of the hydrogen-permeated coarse powder was taken and its hydrogen content was measured: 0.85wt%. There was no change in particle appearance, and no obvious pulverization was observed.

[0083] Step 3, Temperature-controlled interface weakening and peeling: Transfer the coarse powder treated with low-temperature hydrogen permeation to a vacuum heat treatment furnace, and evacuate to 8×10 -2 Pa. The temperature was increased to 820℃ at a rate of 10℃ / min, held for 20 min, and then cooled to 700℃ at a rate of 10℃ / min, completing one round of temperature control. The resulting coarse powder, after interface weakening and peeling treatment, was sampled and observed: the original bright metallic oxide film on the particle surface turned grayish-brown, and flaky peeling was visible in some areas, with a peeling rate of approximately 87%.

[0084] Step 4, Vacuum Dehydrogenation and Deep Deoxidation: The coarse powder after the interface weakening and stripping treatment is placed in the same furnace, and the furnace is further evacuated to 5×10⁻⁶. -3 Pa, heat to 650℃, hold for 5 hours. Cool to 150℃ in the furnace, then purge with argon gas before removing from the furnace.

[0085] Table 1. Comparison of products from Example 1 and Comparative Examples 1 to 2 As shown in Table 1, Comparative Example 1 was completely hydrogenated at a high temperature of 650℃ to generate integral TiH2 and achieve full particle embrittlement. During the hydrogenation process, the oxide layer was wrapped by TiH2. Subsequent mechanical crushing could only break the particle body and could not remove the dense TiO2 / Al2O3 oxide layer on the surface. Therefore, after dehydrogenation, the oxygen content only decreased from 1350ppm to 1280ppm, a decrease of only 5.2%. Moreover, after crushing, the proportion of fine powder <45μm reached 70%, completely destroying the original particle size of the coarse powder, making it unsuitable for injection.

[0086] Comparative Example 2 used a medium-temperature infiltration at 550℃, which is close to the α→β phase transition point after hydrogen doping (approximately 520℃). In some areas, a surface TiH2 layer was formed. Although hydrogen atoms could diffuse, the penetration depth was uneven. In the thick oxide layer area, hydrogen did not reach the interface, and the interfacial binding energy was reduced by only about 30%. The shear stress generated by the phase transition at the same controlled temperature of 820℃ could not completely peel off the oxide layer, with a peeling rate of only 72%. The final oxygen content dropped to 680ppm, and a small amount of TiH2 caused the particle surface to become embrittled, with a particle size retention rate of only 65%. The remaining powder became embrittled and broke during the temperature control process, producing a large amount of fine powder (<45μm) and fragments that could not be used for spraying. If used directly for industrial spraying, it would clog the spray gun and affect the yield.

[0087] In Example 1 of this invention, a low-temperature permeation at 420℃ was used, which is within the stable α-phase range. Hydrogen was preferentially enriched only in a solid solution state at the oxide layer-matrix interface, without generating overall TiH2. The hydrogen content was controlled at 0.85wt%, and the interfacial bonding energy was reduced by more than 60%. The 5% volume change generated when the temperature was controlled at 820℃ to cross the hydrogen-induced phase transition point (about 800℃) could be completely applied to interfacial shearing, with a stripping rate of 87%. The final oxygen content was reduced to 360ppm, a reduction of more than 73%, and the particles did not become embrittled, with a particle size retention rate of more than 82%. At the same time, the temperature was kept below 900℃ throughout the process, and there was no burn-off of Al and V. This fully verified the core value of the three-step synergistic approach of low-temperature hydrogen control, interfacial stripping, and vacuum deoxidation.

[0088] Application Example 1 This application example verifies the process compatibility of the recycled TC4 powder prepared in Example 1 with direct injection into molten steel via a pneumatic conveying system. The specific implementation process is as follows: Step 1: Preparation of raw materials for blowing: Take the regenerated TC4 powder prepared in Example 1. The test indicators are as follows: oxygen content 380 ppm, hydrogen content 105 ppm, particle size distribution 140 μm~580 μm, of which the main particle size range of 150 μm~500 μm accounts for 88%, angle of repose 24°, Hall flow rate 29 g / s, and loose packing density 2.1 g / cm³. 3 The composition of the regenerated TC4 powder is: Ti 89.8wt%, Al 6.0wt%, V 3.9wt%, which meets the requirements of pneumatic blowing for powder flowability and particle size uniformity.

[0089] Step 2, Injection Process Implementation: A direct injection test was conducted in a 150 t LF refining furnace at the steel plant. The molten steel grade was Q690D (C 0.14wt%, Si 0.30wt%, Mn 1.45wt%, Nb 0.035wt%, V 0.04wt%, Ti≤0.002wt%, P≤0.020wt%, S≤0.005wt%). The initial temperature of the molten steel was 1660℃, the oxygen activity [O] = 16ppm, and the target titanium content was 0.015%. Nitrogen was used as the carrier gas. The injection gun was inserted 2.8m below the surface of the molten steel. The recycled TC4 powder obtained in Example 1 was injected into the depth of the molten steel through a pneumatic conveying system at a conveying speed of 12m / s and an injection pressure of 0.4 MPa. The injection process was combined with bottom blowing argon stirring at a flow rate of 3NL / (min·t). The amount of recycled TC4 powder added per ton of steel was 1.2kg.

[0090] During the injection process, the recycled powder comes into stable contact with the molten steel without violent splashing or gun clogging. After the injection is completed, the titanium element recovery rate in the molten steel is ≥90%, and the deviation between the final titanium composition and the target composition is ≤±0.002%.

[0091] After the blasting is completed, the molten steel is allowed to settle for 3 minutes, and then the following procedures are performed in sequence: Soft blowing purification: Start the soft blowing argon operation in the LF furnace at a flow rate of 0.5 NL / (min·t) for 10 min to promote the floating of inclusions and avoid the trace residual inclusions brought in by TC4 recycled powder from affecting the purity of the molten steel.

[0092] Casting and billet formation: After soft blowing, the temperature of the molten steel is adjusted to 1510℃ (the liquidus temperature of Q690D is 1485~1490℃, which is 20~25℃ above the liquidus). The casting process is protected throughout. Electromagnetic stirring (stirring current 300A, frequency 2Hz) is used to suppress segregation during continuous casting. The water content in the secondary cooling section is controlled at 0.25L / kg. The process is controlled according to the conventional weak cooling regime. The billet pulling speed is 1.2m / min to obtain the billet of the target specifications.

[0093] Rolling process: The above-mentioned billet is heated to 1220℃ and held for 2 hours. After being taken out of the furnace, it is subjected to two-stage controlled rolling.

[0094] The rolling conditions for the first stage are as follows: initial rolling temperature 1150℃, three rolling passes in total, deformation controlled at 20% per pass, total deformation controlled at 60%, 30-second warm-up before each pass, and final rolling temperature 980℃.

[0095] The rolling conditions for the second stage are as follows: initial rolling temperature 880℃, three rolling passes in total, deformation per pass controlled at 10%, final rolling temperature 830℃, and total rolling deformation reaching 30%; Immediately after rolling, accelerated laminar flow cooling is performed at a cooling rate of 15℃ / s and a coiling temperature of 580℃ to obtain a 12mm thick titanium microalloyed steel hot-rolled coil.

[0096] Step 3, Effect Detection: After blowing, the steel was cooled for 3 minutes and then sampled for testing. The total oxygen content [TO] of the molten steel was 12 ppm, and the nitrogen content [N] was 38 ppm. No significant increase in inclusions was observed. As shown in Table 2, after rolling, the microstructure of the titanium microalloyed steel was uniform, and the average size of the TiN precipitate was 1.1 μm. Mechanical property testing showed that the steel's yield strength reached 725 MPa, tensile strength reached 810 MPa, and longitudinal Charpy impact energy at -20℃ was 172 J. All indicators were superior to those of the same grade of steel smelted using primary titanium-iron alloy, and the steel plate had good surface quality with no subcutaneous bubble defects.

[0097] Application Comparative Example 1 Step 1: In this comparative application, commercially available FeTi30 titanium-iron alloy (Ti 28wt%~32wt%, oxygen content ≤1200ppm) was used for injection after being crushed by jaw crusher and screened to 150μm~500μm.

[0098] Step 2, Injection Process Implementation: A direct injection test was conducted in a 150 t LF refining furnace at the steel plant. The molten steel grade was Q690D (C 0.14%, Si 0.30%, Mn 1.45%, Nb 0.035%, V 0.04%, Ti≤0.002%, P≤0.020%, S≤0.005%). The initial temperature of the molten steel was 1660℃, the oxygen activity [O] = 16ppm, and the target titanium content was 0.015%. Nitrogen was used as the carrier gas. The injection gun was inserted 2.8m below the surface of the molten steel. A commercially available FeTi30 titanium-iron alloy was injected into the depth of the molten steel through a pneumatic conveying system at a conveying speed of 12 m / s and an injection pressure of 0.4 MPa. The injection process was combined with bottom blowing argon stirring at a flow rate of 3NL / (min·t). The amount of FeTi30 titanium-iron alloy added per ton of steel was 1.2 kg.

[0099] After the blasting is completed, the molten steel is allowed to settle for 3 minutes, and then the following procedures are performed in sequence: Soft blowing purification: Start the soft blowing argon operation in the LF furnace at a flow rate of 0.5 NL / (min·t) for 10 min to promote the floating of inclusions and avoid the trace residual inclusions brought in by TC4 recycled powder from affecting the purity of the molten steel.

[0100] Casting and billet formation: After soft blowing, the temperature of the molten steel is adjusted to 1510℃ (the liquidus temperature of Q690D is 1485~1490℃, which is 20~25℃ above the liquidus). The casting process is protected throughout. Electromagnetic stirring (stirring current 300A, frequency 2Hz) is used to suppress segregation during continuous casting. The water content in the secondary cooling section is controlled at 0.25L / kg. The process is controlled according to the conventional weak cooling regime. The billet pulling speed is 1.2m / min to obtain the billet of the target specifications.

[0101] Rolling process: The above-mentioned billet is heated to 1220℃ and held for 2 hours. After being taken out of the furnace, it is subjected to two-stage controlled rolling. The rolling conditions for the first stage are as follows: initial rolling temperature 1150℃, three rolling passes in total, deformation controlled at 20% per pass, total deformation controlled at 60%, 30-second warm-up before each pass, and final rolling temperature 980℃.

[0102] The rolling conditions for the second stage are as follows: initial rolling temperature 880℃, three rolling passes in total, deformation per pass controlled at 10%, final rolling temperature 830℃, and total rolling deformation reaching 30%; Immediately after rolling, accelerated laminar flow cooling is performed at a cooling rate of 15℃ / s and a coiling temperature of 580℃ to obtain a 12mm thick titanium microalloyed steel hot-rolled coil.

[0103] As shown in Table 2, intermittent lance blockage occurred during the injection process (1 time / 10 heats), accompanied by slight splashing; the titanium yield was only 76%; the average size of the TiN precipitates in the steel grew to 2.4 μm; and the final longitudinal Charpy impact energy of the steel at -20℃ was 142 J.

[0104] Application Comparative Example 2 Step 1: In this comparative application, commercially available conventional HDH fine titanium powder (Ti≥99.2wt%, particle size 45μm~150μm, oxygen content≤800ppm) is used for subsequent blowing.

[0105] Step 2, Injection Process Implementation: A direct injection test was conducted in a 150 t LF refining furnace at the steel plant. The molten steel grade was Q690D (C 0.14%, Si 0.30%, Mn 1.45%, Nb 0.035%, V 0.04%, Ti≤0.002%, P≤0.020%, S≤0.005%). The initial temperature of the molten steel was 1660℃, the oxygen activity [O] = 16ppm, and the target titanium content was 0.015%. Nitrogen was used as the carrier gas. The injection gun was inserted 2.8m below the surface of the molten steel. Commercially available conventional HDH fine titanium powder was injected into the depth of the molten steel through a pneumatic conveying system at a conveying speed of 12m / s and an injection pressure of 0.4MPa. The injection process was combined with bottom blowing argon stirring at a flow rate of 3 NL / (min·t). The amount of conventional HDH fine titanium powder added per ton of steel was 1.2kg.

[0106] After the blasting is completed, the molten steel is allowed to settle for 3 minutes, and then the following procedures are performed in sequence: Soft blowing purification: Start the soft blowing argon operation in the LF furnace at a flow rate of 0.5 NL / (min·t) for 10 min to promote the floating of inclusions and avoid the trace residual inclusions brought in by TC4 recycled powder from affecting the purity of the molten steel.

[0107] Casting and billet formation: After soft blowing, the temperature of the molten steel is adjusted to 1510℃ (the liquidus temperature of Q690D is 1485~1490℃, which is 20~25℃ above the liquidus). The casting process is protected throughout. Electromagnetic stirring (stirring current 300A, frequency 2Hz) is used to suppress segregation during continuous casting. The water content in the secondary cooling section is controlled at 0.25L / kg. The process is controlled according to the conventional weak cooling regime. The billet pulling speed is 1.2m / min to obtain the billet of the target specifications.

[0108] Rolling process: The above-mentioned billet is heated to 1220℃ and held for 2 hours. After being taken out of the furnace, it is subjected to two-stage controlled rolling. The rolling conditions for the first stage are as follows: initial rolling temperature 1150℃, three rolling passes in total, deformation controlled at 20% per pass, total deformation controlled at 60%, 30-second warm-up before each pass, and final rolling temperature 980℃.

[0109] The rolling conditions for the second stage are as follows: initial rolling temperature 880℃, three rolling passes in total, deformation per pass controlled at 10%, final rolling temperature 830℃, and total rolling deformation reaching 30%; Immediately after rolling, accelerated laminar flow cooling is performed at a cooling rate of 15℃ / s and a coiling temperature of 580℃ to obtain a 12mm thick titanium microalloyed steel hot-rolled coil.

[0110] As shown in Table 2, the injection process was extremely unstable, with the frequency of gun blockage reaching 4 times per 10 heats, and the titanium yield plummeted to 58%. The TiN precipitates in the steel were coarse, with an average size of 3.3 μm. Furthermore, due to severe oxidation of the fine powder, the total oxygen content in the molten steel rose to 45 ppm, and the final longitudinal Charpy impact energy of the steel at -20℃ was only 108 J.

[0111] Table 2 Comparison of spraying in Application Example 1 and Comparative Examples 1 to 2 This invention eliminates the need for cored wire preparation and allows for direct pneumatic injection into molten steel. The wire feeding process avoids issues such as nozzle blockage and splashing. The titanium yield is increased by 15% compared to traditional titanium-iron alloys (comparative example 1), the size of TiN precipitates in the steel is reduced by 54.2%, and the toughness of the steel is significantly improved. At the same time, it eliminates the cost of cored wire processing, reducing the alloying cost per ton of steel by 39.5%. This invention achieves high-value utilization of additive manufacturing titanium alloy coarse powder through direct injection.

[0112] Currently, existing technologies for deoxidizing titanium powder or titanium alloys generally involve complete hydrogenation, crushing, and chemical reduction. Complete hydrogenation, in this step, generates TiH2 compounds or increases the weight by ≥3.2%, aiming to embrittle the material for mechanical crushing. Subsequent mechanical crushing relies on high-energy ball milling or air jet milling. After crushing, the original particle size is inevitably damaged, failing to meet the process requirements for subsequent titanium microalloying steelmaking. In the chemical reduction step, existing technologies require external reducing agents (such as TiH2 or Mg) for chemical reduction, resulting in a relatively high oxygen content in the final product.

[0113] Compared to existing technologies, the core of this invention lies in addressing the physicochemical characteristics of titanium alloy coarse powder, such as the difficulty in reducing the dense TiO2 / Al2O3 oxide layer on the surface and the elemental loss caused by traditional high-temperature treatment. A synergistic process was designed, involving low-temperature controllable hydrogen permeation to induce interface weakening, hydrogen-induced phase change volume effect to achieve mechanical stripping of the oxide layer, and simultaneous deep deoxidation via vacuum dehydrogenation. This process is further matched with refined process parameter control. This yields a specialized injection raw material with high sphericity, high packing density, and no dense oxide shell, thus realizing a complete technological closed loop for the conversion of solid waste powder into clean alloy raw material and its final use in the precise injection of molten steel.

[0114] First, this invention employs partial hydrogen permeation (0.3wt%–1.5wt% dissolved hydrogen) to weaken only the oxide layer-matrix interface while preserving the bulk strength. Oxide layer removal utilizes phase transformation mechanical stripping caused by hydrogen-induced interface weakening and the self-reduction of residual oxides by active hydrogen during vacuum dehydrogenation. No mechanical crushing is required; the oxide layer automatically peels off through phase transformation interface shear stress. After processing, the powder retains its original coarse particle size of 150μm–600μm, meeting the process requirements for titanium microalloying steelmaking. The titanium element recovery rate is consistently ≥90%, and the final titanium composition of the molten steel deviates from the target composition by ≤±0.002%, achieving precise, stable, and low-cost smelting of titanium microalloyed steel. Simultaneously, the entire process is conducted at temperatures below 900℃, with no loss of high-value elements such as Al and V, and a compositional deviation of ≤±3%.

[0115] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0116] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing recycled powder for the injection smelting of titanium microalloyed steel, characterized in that, Includes the following steps: In a hydrogen atmosphere, the additive manufacturing titanium alloy coarse powder is subjected to partial hydrogen permeation treatment at 350℃~500℃, so that hydrogen atoms permeate to the interface between the surface oxide layer and the internal matrix of the additive manufacturing titanium alloy coarse powder, and hydrogen permeation treatment coarse powder is obtained; the oxygen content of the additive manufacturing titanium alloy coarse powder is 1000ppm~1500ppm. Vacuum degree <10 -1 Under vacuum conditions of Pa, the hydrogen-permeable coarse powder is mechanically exfoliated at 750℃~850℃ to remove the surface oxide layer of the hydrogen-permeable coarse powder, and obtain coarse powder after interface weakening exfoliation treatment. Vacuum degree <10 -3 Under vacuum conditions of Pa, the coarse powder after interface weakening and stripping treatment is subjected to dehydrogenation and deoxidation treatment at 550℃~700℃ to obtain recycled powder for titanium microalloy steel injection smelting.

2. The method for preparing recycled powder for titanium microalloyed steel injection smelting according to claim 1, characterized in that, In partial hydrogen permeation treatment, the treatment time is 1h to 3h, and the hydrogen pressure is 0.05MPa to 0.3MPa.

3. The method for preparing recycled powder for titanium microalloyed steel injection smelting according to claim 1, characterized in that, The mechanical peeling process involves maintaining the temperature at 750℃~850℃ for 10min~30min, then cooling it down to 650℃~750℃. The mechanical peeling process is repeated 1 to 2 times; the heating rate is 5℃ / min to 15℃ / min, and the cooling rate is 5℃ / min to 15℃ / min.

4. The method for preparing recycled powder for titanium microalloyed steel injection smelting according to claim 1, characterized in that, The dehydrogenation and deoxygenation treatment time is 3h to 6h.

5. The method for preparing recycled powder for titanium microalloyed steel injection smelting according to claim 1, characterized in that, The titanium content of the additively manufactured titanium alloy coarse powder is >85%, and the particle size is 150μm~600μm.

6. A recycled powder, characterized in that, The recycled powder is prepared using the method for preparing recycled powder for titanium microalloy steel injection smelting as described in any one of claims 1 to 5; the recycled powder has an oxygen content of <500ppm, a hydrogen content of <150ppm, a particle size of 150μm to 600μm, a sphericity of ≥0.7, and a bulk density of ≥2.0g / cm³. 3 .

7. The application of the recycled powder according to claim 6 in the injection smelting of titanium microalloyed steel, characterized in that, Recycled powder is sprayed into molten steel at 1600℃~1700℃, using nitrogen or argon as the carrier gas. Driven by the carrier gas, the recycled powder is sprayed into the molten steel. After the spraying is completed, the titanium microalloyed steel is obtained through post-treatment.

8. The application of the recycled powder according to claim 7 in the spraying smelting of titanium microalloyed steel, characterized in that, The amount of recycled powder added to each ton of molten steel is 0.5 kg / t to 3 kg / t, and the temperature of the molten steel is 1620℃ to 1680℃. During the injection of recycled powder, the conveying speed of recycled powder is 10 m / s to 15 m / s, and the injection pressure is 0.3 MPa to 0.5 MPa.

9. The application of the recycled powder according to claim 8 in the spraying smelting of titanium microalloyed steel, characterized in that, The molten steel is molten steel used for engineering and building structures, pipeline steel, or automotive structures; The titanium content in the molten steel is 0.01wt% to 0.10wt% based on the total mass of the molten steel.

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