Deoxidizing agent for metal smelting and preparation process thereof

Abstract

The invention discloses a deoxidizer for metal smelting and a preparation process thereof, and belongs to the technical field of steel for high-strength fasteners, and the deoxidizer comprises aluminum powder, silicon powder, titanium powder, zirconium powder and carbon-coated lanthanum nano powder in a mass ratio of (45-50): (20-25): (15-20): (8-12): (0.2-0.4). In a sol crystallization stage, lanthanum nitrate and a composite ligand form a directionally growing metal organic framework under the assistance of an external field, and a regular pore structure of the metal organic framework provides a nano-scale template for subsequent carbon coating, so that the decomposed organic ligand is gradually carbonized in a segmented heating process and forms a gradient structure; the low-temperature section promotes the carbon layer to be converted from an amorphous state to an ordered state so as to enhance the electron conduction capability, and the high-temperature section forms a through mesoporous network through external energy etching, so that excessive agglomeration of lanthanum nanoparticles is limited, and a controllable release channel is constructed. The preheating and pre-pressurizing process provides support for the nanostructure on the macroscopic scale, and the aluminum powder is softened through low-temperature plastic deformation to fill gaps of the titanium-zirconium powder, so that a compact initial blank structure is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength fastener steel, and particularly to a deoxidizer for metal smelting and its preparation process. Background Art

[0002] In the field of metal smelting, the performance of the deoxidizer directly affects the quality of steel. Especially for high-strength fastener steel, the deoxidation efficiency, inclusion control and process stability of the deoxidizer are crucial.

[0003] Although traditional aluminum-based deoxidizers (such as pure aluminum and silicon-aluminum-iron alloy) have strong deoxidation ability, the generated Al2O3 inclusions have a melting point as high as 2030°C and are distributed in the grain boundaries in the form of chains or strings, significantly reducing the toughness and fatigue strength of the steel. Although calcium-based composite deoxidizers can convert Al2O3 into low-melting calcium aluminates or spherical inclusions, they are prone to introducing residual elements and affecting the performance of the steel grade. The rare earth modification process can refine inclusions and improve the deformation ability, but its cost is high and the process is complex, making it difficult to be applied on a large scale.

[0004] Based on this, the present invention designs a deoxidizer for metal smelting and its preparation process to solve the above problems. Summary of the Invention

[0005] Aiming at the above-mentioned shortcomings of the existing technology, the present invention provides a deoxidizer for metal smelting and its preparation process.

[0006] A preparation method of a deoxidizer for metal smelting includes the following steps: S1. Pretreatment of lanthanum powder; Dissolve lanthanum nitrate in an ethanol / water mixed solvent, stir to form a transparent solution, dropwise add a composite ligand solution, and simultaneously add a dispersant, and continuously stir until a uniform sol is formed; Crystallize the sol while applying a pulsed magnetic field; After natural cooling, centrifuge, wash and dry to obtain a white powder-like precursor; S2. Thermal decomposition and carbon coating modification; Thermally decompose the organic ligand of the precursor to form an amorphous carbon layer while applying plasma-assisted enhancement of the graphitization degree of the carbon layer; Raise the temperature to promote the agglomeration of lanthanum atoms, and simultaneously remove volatile by-products by purging with high-flow argon, and apply plasma etching to the carbon layer to form nanoscale pores; S3. Freeze-mill and sieve to obtain carbon-coated lanthanum nanoflakes; S4. Mechanically alloy the mixed powder; Sieve aluminum powder, silicon powder, titanium powder and zirconium powder and put them into a ball mill together with the carbon-coated lanthanum nanoflakes, and ball mill and mix to obtain a mixed powder; S5. Press under segmented temperature increase and pressure; Step 1: Pour the mixed powder into a mold, place it in a press for pre-pressing, then put the mold into a heating furnace, heat and keep it warm while introducing argon for protection. Step 2: Transfer it to a multi-functional hot press furnace to continue heating up; meanwhile, apply pressure in stages. S6. Cooling and finished product treatment; After the heat preservation and pressure holding are completed, stop heating and let the mold cool naturally in the furnace to room temperature. During the cooling process, maintain a certain inert gas atmosphere to prevent oxidation on the surface of the deoxidizer. After cooling, demold the finished product using a hydraulic demolding machine, remove the demolding agent powder adhering to the surface with a soft brush, then put it into an ultrasonic cleaner for 15 min to remove residual impurities, and obtain the deoxidizer for metal smelting.

[0007] Furthermore, S1 is specifically as follows: Dissolve lanthanum nitrate in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 1 - 3:1), stir at 400 - 600 r / min and form a 20 wt% transparent solution at 35 - 45 °C. Dropwise add the composite ligand solution at a rate of 0.3 - 0.7 mL / min, and simultaneously add polyvinylpyrrolidone, a dispersant, accounting for 0.5 - 0.8% of the mass of the composite ligand solution, and continuously stir at a speed of 150 - 200 r / min until a uniform sol is formed. Transfer the sol to a high-pressure reaction kettle, crystallize at 110 - 130 °C for 5 - 8 h, and apply a pulsed magnetic field of 0.4 - 0.6 T (frequency 4 - 6 Hz) during the crystallization process to promote the oriented growth of MOFs (metal-organic frameworks) along the crystal direction. After natural cooling, perform centrifugal separation, wash with ethanol and deionized water three times each, and vacuum dry at 60 - 80 °C to obtain a white powdery precursor.

[0008] Furthermore, the composite ligand solution is composed of 3,4-dihydroxycinnamic acid and a nitrogen-containing carboxylic acid with a molar ratio of 2 - 4:1.

[0009] Furthermore, S2 is specifically as follows: Place the precursor in a porcelain boat, put it into a three-stage tubular furnace, evacuate to ≤10 -3 Pa, and then fill with high-purity argon. Heat up to 550 - 650 °C at a rate of 8 - 12 °C / min, keep it warm for 1.5 - 2.5 h to decompose the organic ligand at low temperature to form an amorphous carbon layer, assisted by 100 - 200 W plasma etching. Heat up to 750 - 850 °C at a rate of 10 - 15 °C / min, keep it warm for 0.8 - 1.2 h to promote the agglomeration of lanthanum atoms at high temperature, and simultaneously remove volatile by-products through high-flow argon purging, assisted by 200 - 300 W plasma etching.

[0010] Further, S3 specifically includes: freezing in liquid nitrogen for 30 min, transferring to a planetary cryogenic ball mill, with a ball-to-material ratio of 8 - 12:1, selecting zirconia ceramic balls with a hardness ≥ 1500 HV as grinding balls, grinding at 500 - 700 r / min for 20 - 40 min, and passing through a 200 - 300 mesh sieve to obtain carbon-coated lanthanum nanopowder.

[0011] Further, S4 specifically includes: by weight, passing 45 - 50 parts of aluminum powder (purity ≥ 99%, particle size 30 - 80 μm), 20 - 25 parts of silicon powder (purity ≥ 98%, particle size 30 - 80 μm), 15 - 20 parts of titanium powder (purity ≥ 97%, particle size 20 - 60 μm), and 8 - 12 parts of zirconium powder (purity ≥ 96%, particle size 10 - 50 μm) through a 200 - 300 mesh sieve and putting them together with 0.2 - 0.4 parts of carbon-coated lanthanum nanopowder into a ball mill, controlling the ball-to-material ratio at 5 - 10:1, and selecting zirconia ceramic balls with a hardness ≥ 1500 HV as grinding balls.

[0012] Further, in S4, the mass ratio of the aluminum powder, silicon powder, titanium powder, zirconium powder, and carbon-coated lanthanum nanopowder is 45 - 50:20 - 25:15 - 20:8 - 12:0.2 - 0.4.

[0013] Further, S5 specifically includes: pouring the mixed powder into a mold, putting it into a press for pre-pressing, with a pre-pressing pressure of 50 - 100 MPa, maintaining the pressure for 5 - 10 min to preliminarily form the powder, then putting the mold into a heating furnace, heating at a heating rate of 5 - 10 °C / min to 200 - 300 °C, holding for 1 - 2 h, and simultaneously introducing argon for protection at a rate of 5 L / min; Transferring to a multi-functional hot press furnace to continue heating, heating at a heating rate of 10 - 15 °C / min to 800 - 1000 °C; simultaneously applying pressure in stages to 400 - 500 MPa, and holding the pressure and temperature for 2 - 3 h at this temperature and pressure.

[0014] Further, the step of applying pressure in stages specifically includes: increasing the pressure at a rate of 40 - 50 MPa / h to 280 - 300 MPa and then maintaining the pressure constant, and when the temperature rises to 550 - 600 °C, increasing the pressure at a rate of 16 - 20 MPa / h to the final temperature.

[0015] A deoxidizer prepared by the preparation process of the deoxidizer for metal smelting as described above.

[0016] The beneficial effects of the present invention compared with the prior art are as follows: 1. During the sol crystallization process of the present invention, lanthanum nitrate and the composite ligand form a metal-organic framework (MOFs) through coordination. The introduction of a pulsed magnetic field promotes the oriented growth of MOFs along the crystal direction, forming a highly ordered porous crystal structure, which significantly increases the exposure area of active sites. This ordered structure not only shortens the diffusion path of lanthanum atoms but also enhances the migration ability of lanthanum atoms through lattice defect regulation. After crystallization treatment, lanthanum is uniformly dispersed in the carbon coating layer in the form of nanoscale particles, and its high specific surface area characteristics significantly improve the interfacial reaction efficiency with oxides in the molten steel, thereby accelerating the deoxidation kinetics process.

[0017] 2. The preheating and pre-pressurization process of the present invention combines low-temperature plastic deformation and diffusion, enabling the formation of a tight mechanical bite and atomic-level bonding interface between the internal particles of the deoxidizer, and constructing a dense microstructure. This structure exhibits stable dissolution behavior in the molten steel, avoiding the reaction runaway caused by the fragmentation of traditional deoxidizers. At the same time, the densification process promotes the formation of nanoscale mixed interfaces among the metal components in the deoxidizer, and gradually reduces the oxygen content in the molten steel through the synergistic deoxidation effect (rapid deoxidation of aluminum and deep deoxidation of titanium and zirconium).

[0018] 3. The present invention constructs a three-level collaborative system of "nanostructure regulation - release behavior control - macroscopic structure stability" through the process coupling of sol crystallization - segmented heating - preheating and pre-pressurization, realizing the precise regulation of the deoxidation process and the in-depth optimization of inclusion evolution.

[0019] In the sol crystallization stage, lanthanum nitrate and the composite ligand form a metal-organic framework with directional growth assisted by an external field. Its regular pore structure provides a nanoscale template for subsequent carbon coating, enabling the decomposed organic ligand to gradually carbonize during the stepwise temperature increase and form a gradient structure - the low-temperature stage promotes the transformation of the carbon layer from amorphous to ordered to enhance the electron conduction ability, and the high-temperature stage forms a through mesoporous network through external energy etching, which not only restricts the excessive aggregation of lanthanum nanoparticles but also constructs a controllable release channel, ultimately generating carbon-coated lanthanum nanoparticles with high reaction activity and stable release characteristics. The preheating and pre-pressurization process provides support for the above nanostructure at the macroscopic scale. By low-temperature plastic deformation, the aluminum powder softens and fills the gaps between titanium and zirconium powders, forming a dense green body structure, uniformly embedding nanoscale lanthanum particles in the metal matrix, avoiding aggregation and strengthening the synergistic deoxidation effect between metal components - the rapid deoxidation of aluminum reduces the dissolved oxygen in the molten steel, and the deep deoxidation of titanium and zirconium removes the inclusion oxygen, creating a low-oxygen environment for the selective inclusion modification of lanthanum. This dense structure exhibits a stable dissolution behavior in the molten steel. Its surface micropores first release the free lanthanum on the surface of the carbon layer, which quickly adsorbs on the oxide nuclei generated by aluminum deoxidation to reduce the surface energy. Subsequently, the mesoporous network drives the lanthanum nanoparticles to diffuse through the concentration gradient and react with the oxide cores formed by titanium and zirconium to form composite inclusions, while the lanthanum particles inside the structure slowly migrate through the diffusion channels of the metal matrix and maintain a constant release rate by means of the confinement effect of the carbon layer pores, achieving continuous spheroidization modification of the residual inclusions. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 Comparison diagram of XRD diffraction patterns of the deoxidizers prepared in Example 3 and Comparative Examples 1-4; Figure 2 Curve graph of the change in oxygen content in the molten steel acted upon by the deoxidizers prepared in Example 3 and Comparative Examples 1-4. Detailed Embodiments

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0023] Example 1: This example provides a deoxidizer for metal smelting, which includes the following components: 50% aluminum powder, 25% silicon powder, 20% titanium powder, 12% zirconium powder, 0.4% carbon-coated lanthanum nanoflakes; The preparation method includes the following steps: S1. Pretreatment of lanthanum powder; Dissolve lanthanum nitrate in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 3:1), form a 20wt% transparent solution under stirring at 600r / min and 45°C, dropwise add the composite ligand solution at a rate of 0.7mL / min, and simultaneously add 0.8% of the dispersant polyvinylpyrrolidone based on the mass of the composite ligand solution, and continuously stir at a speed of 200r / min until a homogeneous sol is formed; The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid with a molar ratio of 4:1; Transfer the sol to a high-pressure reaction kettle, crystallize at 130°C for 8h, and apply a 0.6T pulsed magnetic field (frequency 6Hz) during the crystallization process to promote the oriented growth of MOFs (metal-organic frameworks) along the crystal direction; After natural cooling, centrifuge and separate, wash 3 times with ethanol and deionized water respectively, and vacuum dry at 80°C to obtain a white powdery precursor; S2. Thermal decomposition and carbon coating modification; Place the precursor in a porcelain boat and put it into a three-zone tube furnace. First, evacuate to ≤10 -3 Pa, and then fill with high-purity argon (cycle 3 times); First stage: Heat up to 650°C at a rate of 12°C / min, keep the temperature for 2.5h to decompose the organic ligand at low temperature to form an amorphous carbon layer, and use 200W plasma to assist in enhancing the graphitization degree of the carbon layer; Second stage: Heat up to 850°C at a rate of 15°C / min, keep the temperature for 1.2h to promote the agglomeration of lanthanum atoms at high temperature, and at the same time remove volatile by-products by purging with high-flow argon, and use 300W plasma to etch the carbon layer to form nano-scale pores; S3. Freeze-crushing; Freeze in liquid nitrogen for 30min, transfer to a planetary freeze ball mill, with a ball-to-material ratio of 12:1, select grinding balls with a hardness ≥1500HV and a material of zirconia ceramic balls (Φ10mm:Φ8mm:Φ5mm = 6:3:4), grind at 700r / min for 40min, and pass through a 300-mesh sieve to obtain carbon-coated lanthanum nanoflakes; S4. Mechanically alloy the mixed powder; By weight ratio, aluminum powder (purity ≥ 99%, particle size 30 - 80 μm), silicon powder (purity ≥ 98%, particle size 30 - 80 μm), titanium powder (purity ≥ 97%, particle size 20 - 60 μm), and zirconium powder (purity ≥ 96%, particle size 10 - 50 μm) are passed through a 300 - mesh sieve and then put into a ball mill (a stainless - steel ball mill QM - 3SP2 with a tungsten carbide - plated inner wall, ultrasonically cleaned with anhydrous ethanol for 30 min before use, dried, and purged with argon 3 times) together with carbon - coated lanthanum nanoflakes. The ball - to - material ratio is controlled at 10:1, and zirconia ceramic balls with a hardness ≥ 1500 HV are selected as grinding balls (Φ10mm:Φ5mm:Φ3mm = 5:3:2); The rotation speed of the ball mill is set at 500 r / min, and ball - milling mixing is carried out for 2 h under the protection of inert gas (after the ball mill is sealed, it is evacuated to ≤ 10 Pa, and then filled with high - purity argon to atmospheric pressure, and the cycle is repeated 3 times to ensure an oxygen - free environment) to obtain a mixed powder. During the mechanical alloying process, the powder particles are continuously refined and mixed under the impact, rolling, and shearing actions of the grinding balls, enabling the uniform mixing of each metal powder to reach the nanometer or sub - micron level and improving the mixing uniformity; S5. Pressing with stepped heating and pressurization; First stage: Pour the mixed powder into a mold (a graphite mold with a 10 - μm - thick boron nitride release agent coated on the inner wall. Before the mold is placed in the heating furnace, it is pre - heated in an oven at 150 °C for 2 h to remove adsorbed moisture), and then put it into a press (a servo - hydraulic press with a parallelism of the press head ≤ 0.01 mm / m and an accuracy of ± 1% F.S.) for pre - pressing. The pressing rate is 10 mm / min, the pre - pressing pressure is 100 MPa, and the pressure is maintained for 10 min to initially form the powder. Then, the mold is placed in a heating furnace (a box - type resistance furnace of model SX2 - 8 - 13) and heated to 300 °C at a heating rate of 10 °C / min and held for 2 h. At the same time, argon is introduced at a speed of 5 L / min for protection to slightly soften the aluminum (the melting point of aluminum is 660 °C), further promoting the bonding between powder particles and forming a preliminary green body structure; Second stage: Transfer to a multi-functional hot press furnace (model HP-2000, maximum pressure 1000 MPa, temperature 1500 °C, equipped with a K-type thermocouple with a temperature measurement accuracy of ±2 °C and a pressure sensor with an accuracy of ±0.5% F.S.) and continue heating. Heat at a heating rate of 15 °C / min to 1000 °C (the melting point of titanium is 1668 °C, and that of zirconium is 1852 °C, control the temperature below the melting point of the main components); at the same time, pressurize in stages to 500 MPa (increase the pressure to 300 MPa at a rate of 50 MPa / h and then keep the pressure constant. When the temperature rises to 600 °C, increase the pressure to the final temperature at a rate of 20 MPa / h). Insulate and hold the pressure at this temperature and pressure for 3 h. Under high temperature and high pressure conditions, diffusion and recrystallization occur between powder particles, forming a denser organizational structure, improving the density and strength of the deoxidizer, enabling it to play a more stable deoxidizing role after being added to the molten steel, and reducing process instability factors caused by problems such as the breaking of the deoxidizer; S6. Cooling and finished product treatment; After the insulation and pressure holding are completed, stop heating and let the mold cool naturally in the furnace to room temperature. Maintain a certain inert gas atmosphere during the cooling process (keep the argon flowing at a rate of 10 L / min) to prevent the surface of the deoxidizer from oxidizing. After cooling, demold the finished product using a hydraulic demolding machine. After removing the mold release agent powder adhering to the surface with a soft brush, put it into an ultrasonic cleaner (frequency 40 kHz, solvent is anhydrous ethanol) and clean for 15 min to remove residual impurities, obtaining the deoxidizer for metal smelting.

[0024] Example 2: This example provides a deoxidizer for metal smelting, including the following components: 45% aluminum powder, 20% silicon powder, 15% titanium powder, 8% zirconium powder, 0.2% carbon-coated lanthanum nanoflakes; The preparation method includes the following steps: S1. Pretreatment of lanthanum powder; Dissolve lanthanum nitrate in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 1:1), form a 20 wt% transparent solution under stirring at 400 r / min and 35 °C, dropwise add the composite ligand solution at a rate of 0.3 mL / min, and simultaneously add 0.5% of the dispersant polyvinylpyrrolidone based on the mass of the composite ligand solution. Continuously stir at a speed of 150 r / min until a uniform sol is formed; The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid with a molar ratio of 2:1; Transfer the sol to a high-pressure reaction kettle, crystallize at 110 °C for 5 h, and apply a 0.4 T pulsed magnetic field (frequency 4 Hz) during the crystallization process to promote the directional growth of MOFs (metal-organic frameworks) along the crystal direction; After natural cooling, centrifuge and separate, wash 3 times each with ethanol and deionized water, and vacuum dry at 60 °C to obtain a white powdery precursor; S2. Thermal decomposition and carbon coating modification; Place the precursor in a porcelain boat and put it into a three - zone tube furnace. First, evacuate to ≤ 10 -3 Pa, and then fill with high - purity argon gas (cycle 2 times); Zone 1: Heat up to 550 °C at a rate of 8 °C / min, hold for 1.5 h to decompose organic ligands at low temperature to form an amorphous carbon layer, and use 100 W plasma to assist in enhancing the graphitization degree of the carbon layer; Zone 2: Heat up to 750 °C at a rate of 10 °C / min, hold for 0.8 h to promote the agglomeration of lanthanum atoms at high temperature. At the same time, remove volatile by - products by purging with high - flow argon gas, and use 200 W plasma to etch the carbon layer to form nano - scale pores; S3. Freeze - crushing; Freeze in liquid nitrogen for 30 min, transfer to a planetary freeze - ball mill. With a ball - to - material ratio of 8:1, select zirconia ceramic balls with a hardness ≥ 1500 HV as grinding balls (Φ10 mm:Φ8 mm:Φ5 mm = 6:3:4), grind at 500 r / min for 20 min, and pass through a 200 - mesh sieve to obtain carbon - coated lanthanum nanoflakes; S4. Mechanically alloying mixed powder; By weight ratio, pass aluminum powder (purity ≥ 99%, particle size 30 - 80 μm), silicon powder (purity ≥ 98%, particle size 30 - 80 μm), titanium powder (purity ≥ 97%, particle size 20 - 60 μm), and zirconium powder (purity ≥ 96%, particle size 10 - 50 μm) through a 200 - mesh sieve and put them together with the carbon - coated lanthanum nanoflakes into a ball mill (a stainless - steel ball mill QM - 3SP2 with a tungsten carbide - plated inner wall, ultrasonically clean with absolute ethanol for 30 min before use, and purge with argon gas 3 times after drying). Control the ball - to - material ratio at 5:1, and select zirconia ceramic balls with a hardness ≥ 1500 HV as grinding balls (Φ10 mm:Φ5 mm:Φ3 mm = 5:3:2); Set the ball - mill rotation speed at 300 r / min, and carry out ball - milling mixing for 1 h under inert gas protection (after the ball mill is sealed, evacuate to ≤ 10 Pa, then fill with high - purity argon gas to atmospheric pressure, cycle 3 times to ensure an oxygen - free environment) to obtain the mixed powder. During the mechanical alloying process, the powder particles are continuously refined and mixed under the impact, rolling, and shearing actions of the grinding balls, which can make the metal powders reach nano - scale or sub - micron - scale uniform mixing and improve the mixing uniformity; S5. Pressing with segmented temperature rise and pressure; Section 1: Pour the mixed powder into a mold (a graphite mold with an inner wall coated with 5 μm thick boron nitride release agent. Before putting the mold into the heating furnace, preheat it in an oven at 150 °C for 2 h to remove adsorbed moisture), and place it in a press (a servo-hydraulic press with a press head parallelism ≤ 0.01 mm / m and an accuracy of ±1% F.S.) for pre-pressing. The pressing rate is 10 mm / min, the pre-pressing pressure is 50 MPa, and the pressure is maintained for 5 min to initially form the powder. Then place the mold into a heating furnace (a box-type resistance furnace of model SX2-8-13), heat it to 200 °C at a heating rate of 5 °C / min, and keep it at this temperature for 1 h. At the same time, introduce argon for protection at a speed of 5 L / min to slightly soften the aluminum (the melting point of aluminum is 660 °C), further promoting the bonding between powder particles to form a preliminary green body structure; Section 2: Transfer it to a multi-functional hot press furnace (model HP-2000, with a maximum pressure of 1000 MPa and a temperature of 1500 °C, equipped with a K-type thermocouple with a temperature measurement accuracy of ±2 °C and a pressure sensor with an accuracy of ±0.5% F.S.) to continue heating. Heat it to 800 °C at a heating rate of 10 °C / min (the melting point of titanium is 1668 °C, and that of zirconium is 1852 °C, controlling the temperature below the melting point of the main components); at the same time, apply pressure in stages up to 400 MPa (increase the pressure to 280 MPa at a speed of 40 MPa / h and then keep the pressure constant. When the temperature rises to 550 °C, increase the pressure to the end temperature at a speed of 16 MPa / h), and keep it at this temperature and pressure for 2 h. Under high temperature and high pressure conditions, diffusion and recrystallization occur between powder particles to form a denser tissue structure, improving the density and strength of the deoxidizer, enabling it to play a more stable deoxidation role after being added to the molten steel, and reducing process instability factors caused by problems such as deoxidizer fragmentation; S6. Cooling and finished product treatment; After the heat preservation and pressure holding are completed, stop heating and let the mold cool naturally in the furnace to room temperature. During the cooling process, maintain a certain inert gas atmosphere (keep argon flowing at a speed of 10 L / min) to prevent the surface of the deoxidizer from oxidizing. After cooling, demold the finished product with a hydraulic demolding machine. After removing the release agent powder adhering to the surface with a soft brush, place it in an ultrasonic cleaner (frequency 40 kHz, solvent is anhydrous ethanol) for cleaning for 15 min to remove residual impurities, and obtain the deoxidizer for metal smelting.

[0025] Example 3: This example provides a deoxidizer for metal smelting, which includes the following components: 48% aluminum powder, 23% silicon powder, 17% titanium powder, 11% zirconium powder, 0.3% carbon-coated lanthanum nanoflakes; The preparation method includes the following steps: S1. Lanthanum powder pretreatment; Dissolve lanthanum nitrate in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 2:1) to form a 20 wt% transparent solution under stirring at 480 r / min and 39 °C. Dropwise add the composite ligand solution at a rate of 0.4 mL / min, and simultaneously add polyvinylpyrrolidone, a dispersant, accounting for 0.6% of the mass of the composite ligand solution. Continuously stir at a speed of 180 r / min until a uniform sol is formed; The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and a nitrogen-containing carboxylic acid with a molar ratio of 3:1; Transfer the sol to a high-pressure reactor and crystallize it at 122 °C for 6 h. Apply a 0.5 T pulsed magnetic field (frequency 5 Hz) during the crystallization process to promote the oriented growth of MOFs (metal-organic frameworks) along the crystal direction; After natural cooling, perform centrifugal separation, wash it 3 times each with ethanol and deionized water, and vacuum dry at 72 °C to obtain a white powdery precursor; S2. Thermal decomposition and carbon coating modification; Place the precursor in a porcelain boat and put it into a three-zone tube furnace. First, evacuate to ≤10 -3 Pa, and then fill it with high-purity argon (cycle 3 times); Zone 1: Heat it to 620 °C at a rate of 11 °C / min and hold for 2 h to decompose the organic ligand at low temperature to form an amorphous carbon layer, and use 140 W plasma to assist in enhancing the graphitization degree of the carbon layer; Zone 2: Heat it to 820 °C at a rate of 13 °C / min and hold for 1 h to promote the agglomeration of lanthanum atoms at high temperature. At the same time, remove volatile by-products by purging with high-flow argon, and use 230 W plasma to etch the carbon layer to form nanoscale pores; S3. Freeze crushing; Freeze it in liquid nitrogen for 30 min, transfer it to a planetary freeze ball mill, with a ball-to-material ratio of 9:1. Select zirconia ceramic balls with a hardness ≥1500 HV and a material of zirconia ceramic balls as grinding balls (Φ10 mm:Φ8 mm:Φ5 mm = 6:3:4), and grind at 610 r / min for 35 min. Pass through a 240-mesh sieve to obtain carbon-coated lanthanum nanoflakes; S4. Mechanically alloy the mixed powder; According to the weight ratio, pass aluminum powder (purity ≥99%, particle size 30 - 80 μm), silicon powder (purity ≥98%, particle size 30 - 80 μm), titanium powder (purity ≥97%, particle size 20 - 60 μm), and zirconium powder (purity ≥96%, particle size 10 - 50 μm) through a 260-mesh sieve and put them together with the carbon-coated lanthanum nanoflakes into a ball mill (a stainless-steel ball mill QM-3SP2 with a tungsten carbide coating on the inner wall, ultrasonically clean it with anhydrous ethanol for 30 min before use, and purge it with argon 3 times after drying). Control the ball-to-material ratio at 8:1, and select zirconia ceramic balls with a hardness ≥1500 HV and a material of zirconia ceramic balls as grinding balls (Φ10 mm:Φ5 mm:Φ3 mm = 5:3:2); Set the rotational speed of the ball mill to 420 r / min, and carry out ball milling and mixing for 1.5 h under the protection of inert gas (after the ball mill is sealed, evacuate to ≤10 Pa, then fill with high-purity argon to normal pressure, and cycle 3 times to ensure an oxygen-free environment) to obtain the mixed powder. During the mechanical alloying process, the powder particles are continuously refined and mixed under the impact, rolling and shearing of the grinding balls, which can make each metal powder reach a uniform mixture at the nanometer or sub-micron level, improving the mixing uniformity; S5. Press in stages with temperature increase and pressure increase; First stage: Pour the mixed powder into a mold (a graphite mold with an inner wall coated with 7 μm thick boron nitride release agent, and preheat it in an oven at 150 °C for 2 h to remove adsorbed moisture before putting the mold into the heating furnace), and put it into a press (a servo hydraulic press with a parallelism of the press head ≤0.01 mm / m and an accuracy of ±1% F.S.) for pre-pressing. The pre-pressing rate is 10 mm / min, the pre-pressing pressure is 80 MPa, and the pressure is maintained for 6 min to initially form the powder. Then put the mold into a heating furnace (a box-type resistance furnace of model SX2-8-13), heat it to 260 °C at a heating rate of 6 °C / min, and keep it warm for 1.8 h. At the same time, introduce argon for protection at a speed of 5 L / min to slightly soften the aluminum (the melting point of aluminum is 660 °C), further promoting the combination between powder particles and forming a preliminary green body structure; Second stage: Transfer to a multi-functional hot press furnace (model HP-2000, with a maximum pressure of 1000 MPa and a temperature of 1500 °C, equipped with a K-type thermocouple with a temperature measurement accuracy of ±2 °C and a pressure sensor with an accuracy of ±0.5% F.S.) to continue heating, and heat it to 900 °C at a heating rate of 12 °C / min (the melting point of titanium is 1668 °C, zirconium is 1852 °C, and the temperature is controlled below the melting point of the main component); at the same time, press in stages to 470 MPa (increase the pressure to 295 MPa at a speed of 45 MPa / h and then keep the pressure unchanged. When the temperature rises to 580 °C, increase the pressure to the end temperature at a speed of 18 MPa / h), keep the temperature and pressure for 2.5 h at this temperature and pressure. Under high temperature and high pressure conditions, diffusion and recrystallization occur between powder particles, forming a denser tissue structure, improving the density and strength of the deoxidizer, enabling it to play a more stable deoxidation role after being added to the molten steel, and reducing process instability factors caused by problems such as the breakage of the deoxidizer; S6. Cooling and finished product treatment; After the heat preservation and pressure holding are completed, stop heating, let the mold cool naturally in the furnace to room temperature, and maintain a certain inert gas atmosphere during the cooling process (keep the argon flowing at a speed of 10 L / min) to prevent the surface oxidation of the deoxidizer. After cooling, demold the finished product with a hydraulic demolding machine, remove the release agent powder adhered to the surface with a soft brush, and then put it into an ultrasonic cleaning machine (frequency 40 kHz, solvent is anhydrous ethanol) for cleaning for 15 min to remove residual impurities, obtaining the deoxidizer for metal smelting.

[0026] Comparative Example 1: The difference between this comparative example and Example 3 is that the sol was not crystallized in S1. Specifically: Lanthanum nitrate was dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water was 2:1), and a 20 wt% transparent solution was formed under stirring at 480 r / min and 39 °C. The composite ligand solution was added dropwise at a rate of 0.4 mL / min, and a dispersant polyvinylpyrrolidone accounting for 0.6% of the mass of the composite ligand solution was added synchronously. Stirring was continued at a speed of 180 r / min until a uniform sol was formed; The composite ligand solution was composed of 3,4-dihydroxycinnamic acid and a nitrogen-containing carboxylic acid with a molar ratio of 3:1; After the sol was naturally cooled, it was centrifuged and separated, washed 3 times each with ethanol and deionized water, and vacuum dried at 72 °C to obtain a white powdery precursor.

[0027] Comparative Example 2: The difference between this comparative example and Example 3 is that in S2, the temperature was not raised in segments but directly raised to 820 °C. Specifically: The precursor was placed in a porcelain boat and put into a three-stage tubular furnace. First, the vacuum was pumped to ≤10 -3 Pa, and then high-purity argon was filled (circulated 3 times); The temperature was raised to 820 °C at a rate of 13 °C / min and held for 3 h. High temperature promoted the agglomeration of lanthanum atoms, and at the same time, volatile by-products were removed by purging with high-flow argon, and 230 W plasma etching was carried out.

[0028] Comparative Example 3: The difference between this comparative example and Example 3 is that in S5, the first-stage preheating and pre-pressurization were not carried out, and only the second-stage temperature increase and pressurization were carried out. Specifically: The mixed powder was poured into a mold (a graphite mold with an inner wall coated with a 7-μm-thick boron nitride release agent. Before the mold was put into the heating furnace, it was preheated in an oven at 150 °C for 2 h to remove adsorbed moisture), and then placed in a multi-functional hot press furnace (model HP-2000, maximum pressure 1000 MPa, temperature 1500 °C, equipped with a K-type thermocouple with a temperature measurement accuracy of ±2 °C and a pressure sensor with an accuracy of ±0.5% F.S.) and the temperature was continued to be raised. The temperature was raised to 900 °C at a heating rate of 12 °C / min (the melting point of titanium is 1668 °C, and that of zirconium is 1852 °C, and the temperature was controlled below the melting point of the main components); At the same time, the pressure was increased in segments to 470 MPa (the pressure was increased to 295 MPa at a speed of 45 MPa / h and then the pressure was kept constant. When the temperature rose to 580 °C, the pressure was increased to the end temperature at a speed of 18 MPa / h), and the temperature and pressure were kept constant for 2.5 h. Under high temperature and high pressure conditions, diffusion and recrystallization occurred between the powder particles, forming a denser organizational structure, improving the density and strength of the deoxidizer, enabling it to play a more stable deoxidation role after being added to the molten steel, and reducing process instability factors caused by problems such as the breaking of the deoxidizer.

[0029] Comparative Example 4: The difference between this comparative example and Example 3 is that: 1. The sol was not crystallized in S1; 2. There is no stepwise temperature increase in S2; 3. There is no primary preheating and pre-pressing in S5.

[0030] Experimental example: 1. Draw XRD patterns for the deoxidizers for metal smelting prepared in Example 3 and Comparative Examples 1-4; 1.1 Sample grinding: Use an agate mortar to grind the sample to a particle size <5 μm, ensure that the powder particles are uniform, and avoid uneven diffraction intensity caused by coarse particles; 1.2 Drying treatment: Place the ground powder in a vacuum drying oven and dry it at 60 °C for 2 hours to remove adsorbed water and volatile substances; 1.3 Anti-oxidation treatment: For easily oxidized samples (such as metal matrix composites), grinding and sample preparation need to be carried out under the protection of an inert atmosphere (nitrogen); 1.4 Tablet pressing for sample preparation; Use a stainless steel sample holder with a diameter of 10 mm and a sample cell depth of 0.5 mm; Fill 200 mg of the powder sample evenly into the sample cell, apply a pressure of 15 MPa using a manual tablet press, hold the pressure for 30 seconds to form a flat sample surface, and scrape off the excess powder with a blade to ensure that the sample surface is flush with the sample holder; 1.5 Equipment: Bruker D8 Advance X-ray diffractometer (equipped with a Vantec-500 detector); Light source: CuKα radiation (Kα1 = 0.15406 nm, Kα2 = 0.15444 nm), separated by a graphite monochromator; Tube voltage: 40 kV; Tube current: 40 mA; Divergence slit: 1°, anti-scattering slit: 0.3 mm, receiving slit: 0.1 mm; 1.6 Instrument calibration: 2θ calibration: Use a standard Si powder (NIST SRM 640c) to calibrate the diffraction angle at 2θ = 28.44°, with an error ≤0.02°; Intensity calibration: Use a corundum ( ) standard sample to calibrate the linearity of the detector response; 1.7 Scanning parameter settings: Scanning range: 10° - 80° (2θ), covering the common crystal diffraction peak region; Scanning step: 0.02°; Scanning speed: 5° / min (balancing data quality and acquisition time, total scanning time is about 14 minutes); Acquisition mode: Continuous scanning mode, counting time per step is 0.5 seconds; 1.8 Background collection: Collect background data of an empty sample rack under the same conditions for subsequent subtraction; 1.9 Repeated experiments: Collect 3 independent data for each sample, with RSD (relative standard deviation) ≤ 2%.

[0031] Data analysis: As can be seen from the XRD pattern, the peak intensity of Example 3 is the highest, and the peak shape is sharp and symmetric; the peak intensities of Comparative Examples 1-4 decrease in sequence, and the peak width gradually increases; the positions of the main peaks of all samples are almost the same, indicating that the crystal diffraction plane spacing (d value) remains unchanged.

[0032] The peak intensity of Example 3 is significantly higher than that of other samples, indicating that the long-range order of the atomic arrangement inside the crystal is optimal, probably due to: an optimized sintering temperature curve, which promotes atomic diffusion to form a complete lattice; the introduction of a seed-induced growth technique, which reduces the nucleation barrier and reduces the residual amorphous phase; the sharp peak shape indicates good grain size uniformity.

[0033] In Comparative Example 1, due to insufficient atomic diffusion, a glass phase remains at the grain boundaries, and the scattering of the amorphous phase weakens the diffraction intensity; the grain size is uneven, and the broadened diffraction peak masks part of the intensity.

[0034] In Comparative Example 2, due to too fast cooling rate, the lattice distortion is aggravated, the diffraction peak is broadened and the intensity is dispersed; a metastable intermediate phase may be formed (a weak miscellaneous peak appears at 2θ = 38° in the XRD pattern), consuming the content of the main phase.

[0035] In Comparative Example 3, due to insufficient pressing pressure, the formed low-density green body results in poor contact between grains. During sintering, the neck growth is hindered, forming a porous and loose structure. A large number of microcracks and pores cause multiple scattering effects, significantly attenuating the main peak intensity.

[0036] As a comprehensive experimental group that simultaneously integrates the process defects of Comparative Examples 1-3, the XRD pattern of Comparative Example 4 shows a superimposed structural deterioration feature, specifically manifested as: the attenuation amplitude of the main peak intensity compared to Example 3 is greater than the linear superposition of the single-factor effects; the full width at half maximum (FWHM) of the main peak increases by 40%, and the peak shape shows obvious asymmetric broadening. New miscellaneous peaks appear at 2θ = 38.2° and 43.5°, corresponding to the diffraction of the unreacted raw material phase.

[0037] 2. Construction of simulated smelting environment: Use an intermediate frequency induction furnace (power 50 kW, capacity 5 kg) to melt a 40Cr steel billet, heat it up to 1620 ± 10 °C, and introduce argon for stirring for 10 min to homogenize the composition.

[0038] Take an initial molten steel sample (200 g), and refer to GB / T 11261-2006. Use the pulse heating inert gas fusion-infrared absorption method to measure the initial oxygen content as 50 ppm.

[0039] Add the deoxidizers for metal smelting prepared in Examples 1 - 3 and Comparative Examples 1 - 4 respectively at a ratio of 1.2 kg of deoxidizer per ton of steel.

[0040] Immediately start electromagnetic stirring (frequency 50 Hz, intensity 0.4 T) after addition, and measure the dissolved oxygen content in the molten steel with an oxygen probe (model OX - 2000) for 5 minutes.

[0041] Draw a curve graph showing the change of oxygen content over time (as Figure 2 , where the ordinate in the graph is the oxygen content in ppm), and calculate the deoxidation rate (Δ[O] / Δt) and the final oxygen content.

[0042] The results are shown in the following table: As can be seen from the above table, by crystallizing the sol in S1, the deoxidation rate of the molten steel is increased; by preheating and pre - pressurizing in S5, the final oxygen content in the molten steel is reduced; by crystallizing the sol in S1, preheating and pre - pressurizing in S5, and combining with the step - by - step heating in S2, the synergistic effect of increasing the deoxidation rate and reducing the final oxygen content is achieved.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements will not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation process of a deoxidizer for metal smelting, characterized in that, It includes the following steps: S1. Pretreatment of lanthanum powder; Dissolve lanthanum nitrate in an ethanol / water mixed solvent, stir to form a transparent solution, dropwise add a composite ligand solution, synchronously add a dispersant, and continuously stir until a uniform sol is formed; Crystallize the sol while applying a pulsed magnetic field synchronously; After natural cooling, centrifuge, wash, and dry to obtain a white powdery precursor; S2. Thermal decomposition and carbon coating modification; Decompose the organic ligand of the precursor at a low temperature while applying plasma assistance synchronously; Raise the temperature to promote the agglomeration of lanthanum atoms, and at the same time remove volatile by-products by purging with high-flow argon, while applying plasma etching synchronously; S3. Freeze-mill and screen to obtain carbon-coated lanthanum nanoflakes; S4. Mechanically alloy the mixed powders; Screen aluminum powder, silicon powder, titanium powder, and zirconium powder and then ball-mill them with the carbon-coated lanthanum nanoflakes to obtain mixed powders; S5. Press in stages with temperature increase and pressure application; First stage: Pour the mixed powders into a mold for pre-pressing, heat and keep warm, while introducing argon for protection; Second stage: Continue to increase the temperature; and apply pressure in stages; S6. Cooling and finished product treatment; Naturally cool to room temperature, and demold after cooling to obtain a deoxidizer for metal smelting.

2. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, Specifically, for S1: Dissolve lanthanum nitrate in an ethanol / water mixed solvent, stir at 400 - 600 r / min and at 35 - 45 °C to form a 20 wt% transparent solution, dropwise add the composite ligand solution at a rate of 0.3 - 0.7 mL / min, synchronously add a dispersant polyvinylpyrrolidone accounting for 0.5 - 0.8% of the mass of the composite ligand solution, and continuously stir at a speed of 150 - 200 r / min until a uniform sol is formed; Transfer the sol to an autoclave, crystallize at 110 - 130 °C for 5 - 8 h, and apply a 0.4 - 0.6 T pulsed magnetic field during the crystallization process to promote the oriented growth of MOFs along the crystal direction; After natural cooling, centrifuge and separate, wash with ethanol and deionized water, and dry in vacuum at 60 - 80 °C to obtain a white powdery precursor.

3. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and a nitrogen-containing carboxylic acid with a molar ratio of 2 - 4:

1.

4. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that Specifically, S2 is as follows: Place the precursor in a porcelain boat, put it into a three-zone tube furnace, evacuate to ≤ 10 -3 Pa, and then fill with high-purity argon; Raise the temperature at a rate of 8 - 12 °C / min to 550 - 650 °C, keep warm for 1.5 - 2.5 h to decompose the organic ligand at a low temperature to form an amorphous carbon layer, and assist with 100 - 200 W plasma etching; Raise the temperature at a rate of 10 - 15 °C / min to 750 - 850 °C, keep warm for 0.8 - 1.2 h to promote the agglomeration of lanthanum atoms at a high temperature, and at the same time remove volatile by-products by purging with high-flow argon, and assist with 200 - 300 W plasma etching.

5. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, Specifically, for S3: Freeze in liquid nitrogen, transfer to a planetary freeze mill, with a ball-to-material ratio of 8 - 12:1, select grinding balls made of zirconia ceramic with a hardness ≥ 1500 HV as the grinding balls, grind at 500 - 700 r / min for 20 - 40 min, and pass through a 200 - 300 mesh sieve to obtain carbon-coated lanthanum nanoflakes.

6. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, Specifically, S4 is as follows: By weight ratio, 45 - 50 parts of aluminum powder, 20 - 25 parts of silicon powder, 15 - 20 parts of titanium powder, and 8 - 12 parts of zirconium powder are sieved through a 200 - 300 mesh sieve and then put into a ball mill together with 0.2 - 0.4 parts of carbon-coated lanthanum nanoflakes. The ball-to-material ratio is controlled at 5 - 10:1, and zirconia ceramic balls with a hardness ≥ 1500 HV are selected as grinding balls.

7. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, Specifically, S5 is as follows: The mixed powder is poured into a mold and put into a press for pre-pressing. The pre-pressing pressure is 50 - 100 MPa, and the pressure is maintained for 5 - 10 min to initially form the powder. Then the mold is put into a heating furnace and heated to 200 - 300 °C at a heating rate of 5 - 10 °C / min, and held for 1 - 2 h while argon is introduced at a rate of 5 L / min for protection; It is transferred to a multi-functional hot press furnace for further heating, and heated to 800 - 1000 °C at a heating rate of 10 - 15 °C / min; at the same time, it is pressurized in stages to 400 - 500 MPa, and held at this temperature and pressure for 2 - 3 h.

8. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that, The specific steps of the staged pressurization are as follows: The pressure is increased to 280 - 300 MPa at a rate of 40 - 50 MPa / h and then the pressure is kept constant. When the temperature rises to 550 - 600 °C, the pressure is increased to the final temperature at a rate of 16 - 20 MPa / h.

9. A deoxidizer prepared by the preparation process of the deoxidizer for metal smelting according to any one of claims 1 - 8.

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