A deoxidizer for metal smelting and its preparation process

Abstract

The present invention discloses a deoxidizer for metal smelting and a preparation process thereof, which belongs to the technical field of high-strength fastener steel, wherein the mass ratio of 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. In the sol crystallization stage of the present invention, lanthanum nitrate and composite ligands form a directionally grown metal organic framework with the assistance of an external field, and its regular pore structure provides a nanoscale template for subsequent carbon coating, so that the decomposed organic ligand is gradually carbonized and forms a gradient structure during the segmented heating process. The low-temperature section promotes the carbon layer to transform from amorphous to ordered to enhance the electron conduction ability, and the high-temperature section is etched by external energy to form a through-mesoporous network, which not only limits the excessive agglomeration of lanthanum nanoparticles but also constructs a controlled release channel. The preheating and pre-pressurization process provides support for the above-mentioned nanostructure on a macro scale, and the aluminum powder is softened and filled into the gaps between the titanium and zirconium powders by low-temperature plastic deformation to form a dense pre-blank structure.

Description

Technical Field

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

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

[0003] While traditional aluminum-based deoxidizers (such as pure aluminum and silicon-aluminum-iron alloys) offer strong deoxidation capabilities, the resulting Al2O3 inclusions have a melting point as high as 2030°C and are distributed in chains or strings at grain boundaries, significantly reducing the toughness and fatigue strength of the steel. Calcium-based composite deoxidizers can convert Al2O3 into low-melting calcium aluminates or spherical inclusions, but they can easily introduce residual elements, impacting the steel's performance. Rare earth modification processes can refine inclusions and improve deformability, but their high cost and complex process make them difficult to apply on a large scale.

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

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a deoxidizer for metal smelting and a preparation process thereof.

[0006] A method for preparing a deoxidizer for metal smelting comprises the following steps:

[0007] S1. Lanthanum powder pretreatment;

[0008] Dissolve lanthanum nitrate in an ethanol / water mixed solvent, stir to form a transparent solution, add the composite ligand solution dropwise, add the dispersant simultaneously, and continue stirring until a uniform sol is formed;

[0009] The sol is crystallized and a pulsed magnetic field is applied synchronously;

[0010] After natural cooling, the precursor was centrifuged, washed and dried to obtain a white powder;

[0011] S2. Thermal decomposition and carbon coating modification;

[0012] The precursor is decomposed into organic ligands at low temperature to form an amorphous carbon layer, and plasma is simultaneously applied to enhance the graphitization degree of the carbon layer;

[0013] Increasing the temperature promotes the agglomeration of lanthanum atoms, while high-flow argon gas is used to remove volatile byproducts. Simultaneously, plasma is applied to etch the carbon layer to form nanoscale pores.

[0014] S3. Freeze-ball milling and sieving to obtain carbon-coated lanthanum nanopowder;

[0015] S4. Mechanical alloying mixed powder;

[0016] Aluminum powder, silicon powder, titanium powder and zirconium powder are sieved and put into a ball mill together with carbon-coated lanthanum nanopowder, and ball milled to obtain a mixed powder;

[0017] S5. Staged heating and pressurization;

[0018] Stage 1: Pour the mixed powder into the mold, put it into the press for pre-pressing, put the mold into the heating furnace, heat and keep it warm, and introduce argon gas for protection;

[0019] Second stage: transfer to the multifunctional hot pressing furnace to continue heating; at the same time, pressurize in sections;

[0020] S6. Cooling and finished product processing;

[0021] After the heat preservation and pressure holding is completed, the heating is stopped and the mold is allowed to cool naturally to room temperature in the furnace. A certain inert gas atmosphere is maintained during the cooling process to prevent oxidation of the deoxidizer surface. After cooling, the finished product is demoulded by a hydraulic demoulding machine. The release agent powder adhering to the surface is removed with a soft brush, and then the mold is placed in an ultrasonic cleaning machine for cleaning for 15 minutes to remove residual impurities to obtain a deoxidizer for metal smelting.

[0022] Furthermore, S1 is specifically as follows: lanthanum nitrate is dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 1-3:1), stirred at 400-600 r / min and 35-45° C. to form a 20 wt% transparent solution, the composite ligand solution is added dropwise at a rate of 0.3-0.7 mL / min, and 0.5-0.8% of the mass of the composite ligand solution of dispersant polyvinyl pyrrolidone is simultaneously added, and the mixture is continuously stirred at a speed of 150-200 r / min until a uniform sol is formed;

[0023] The sol was transferred to a high-pressure reactor and crystallized at 110-130°C for 5-8 hours. During the crystallization process, a 0.4-0.6T pulsed magnetic field (frequency 4-6Hz) was applied to promote the directional growth of MOFs (metal organic frameworks) along the crystal direction.

[0024] After natural cooling, the product was centrifuged, washed with ethanol and deionized water three times respectively, and dried in vacuo at 60-80° C. to obtain a white powder precursor.

[0025] Furthermore, the composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 2-4:1.

[0026] Furthermore, S2 is specifically as follows: the precursor is placed in a porcelain boat, placed in a three-stage tube furnace, and vacuumed to ≤10 -3 After Pa, high-purity argon gas is filled in;

[0027] Raise the temperature to 550-650℃ at a rate of 8-12℃ / min, keep warm for 1.5-2.5h to decompose the organic ligand at low temperature to form an amorphous carbon layer, and use 100-200W plasma etching as an auxiliary;

[0028] The temperature is raised to 750-850°C at a rate of 10-15°C / min and maintained for 0.8-1.2 hours to promote the agglomeration of lanthanum atoms. At the same time, volatile by-products are removed by high-flow argon purge, assisted by 200-300W plasma etching.

[0029] Furthermore, S3 is specifically as follows: freezing in liquid nitrogen for 30 minutes, transferring to a planetary refrigerated ball mill, with a ball-to-material ratio of 8-12:1, selecting zirconia ceramic balls with a hardness ≥1500HV as grinding balls, grinding at 500-700r / min for 20-40 minutes, and passing through a 200-300 mesh sieve to obtain carbon-coated lanthanum nanopowder.

[0030] Furthermore, S4 is specifically as follows: by weight, 45-50 parts of aluminum powder (purity ≥99%, particle size 30-80μm), 20-25 parts of silicon powder (purity ≥98%, particle size 30-80μm), 15-20 parts of titanium powder (purity ≥97%, particle size 20-60μm) and 8-12 parts of zirconium powder (purity ≥96%, particle size 10-50μm) are passed through a 200-300 mesh sieve and put into a ball mill together with 0.2-0.4 parts of carbon-coated lanthanum nanopowder, the ball-to-material ratio is controlled at 5-10:1, and zirconium oxide ceramic balls with a hardness ≥1500HV are selected as grinding balls.

[0031] Furthermore, 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.

[0032] Furthermore, S5 is specifically as follows: pouring the mixed powder into a mold, placing it in a press for pre-pressing, the pre-pressing pressure is 50-100 MPa, maintaining the pressure for 5-10 minutes, so that the powder is initially formed, and then placing the mold in a heating furnace, heating it to 200-300°C at a heating rate of 5-10°C / min, keeping it warm for 1-2 hours, and at the same time, passing argon protection at a rate of 5L / min;

[0033] Transfer to a multifunctional hot pressing furnace and continue heating to 800-1000°C at a heating rate of 10-15°C / min; at the same time, pressurize to 400-500 MPa in sections and keep at this temperature and pressure for 2-3 hours.

[0034] Furthermore, the step of stepwise pressurization is specifically as follows: increasing the pressure to 280-300 MPa at a rate of 40-50 MPa / h and then maintaining the pressure unchanged; when the temperature rises to 550-600°C, increasing the pressure to the terminal pressure at a rate of 16-20 MPa / h.

[0035] A deoxidizer prepared according to the preparation process of the deoxidizer for metal smelting.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] During the sol crystallization process, lanthanum nitrate and complex ligands form metal-organic frameworks (MOFs) through coordination. The introduction of a pulsed magnetic field promotes the directional growth of the MOFs along the crystallographic direction, forming a highly ordered porous crystal structure that significantly increases the exposed area of ​​active sites. This ordered structure not only shortens the diffusion path of lanthanum atoms but also enhances their mobility through lattice defect manipulation. After crystallization, lanthanum is uniformly dispersed in the carbon coating as nanoparticles. Its high specific surface area significantly enhances the efficiency of interfacial reactions with oxides in the molten steel, thereby accelerating the deoxidation kinetics.

[0038] 2. The preheating and pre-pressurizing process of this invention combines low-temperature plastic deformation with diffusion to create a tight mechanical bond and atomic-level interface between the deoxidizer particles, creating a dense microstructure. This structure exhibits stable dissolution behavior in molten steel, avoiding the runaway reaction caused by fragmentation of traditional deoxidizers. Simultaneously, the densification process promotes the formation of nanoscale mixed interfaces among the metal components in the deoxidizer, gradually reducing the oxygen content of the molten steel through a synergistic deoxidation effect (rapid deoxidation of aluminum and deep deoxidation of titanium and zirconium).

[0039] 3. The present invention constructs a three-level synergistic system of "nanostructure regulation-release behavior control-macrostructure stabilization" through the process coupling of sol crystallization-stage heating-preheating and pre-pressurization, realizing precise regulation of the deoxidation process and deep optimization of inclusion evolution.

[0040] During the sol crystallization stage, lanthanum nitrate and complex ligands form a directionally grown metal-organic framework (MOF) assisted by an external field. Its regular pore structure provides a nanoscale template for subsequent carbon coating, allowing the decomposed organic ligands to gradually carbonize and form a gradient structure during the staged heating process. The low-temperature stage promotes the transformation of the carbon layer from amorphous to ordered, enhancing electron conductivity. The high-temperature stage, through external energy etching, forms a perforated mesoporous network, which both limits excessive agglomeration of lanthanum nanoparticles and creates controlled release channels, ultimately generating carbon-coated lanthanum nanoparticles with high reactivity and stable release properties. The preheating and pre-pressurization process provides macroscopic support for this nanostructure. Low-temperature plastic deformation softens the aluminum powder, filling the gaps between the titanium and zirconium powders to form a dense preform structure. This uniformly embeds the nanoscale lanthanum particles into the metal matrix, preventing agglomeration and strengthening the synergistic deoxidation effect between the metal components. Rapid deoxidation of the aluminum reduces dissolved oxygen in the molten steel, while deep deoxidation of the titanium and zirconium removes included oxygen, creating a low-oxygen environment for selective inclusion modification of lanthanum. This dense structure exhibits stable dissolution behavior in molten steel. Its surface micropores first release free lanthanum on the surface of the carbon layer, which is quickly adsorbed on the oxide nuclei generated by aluminum deoxidation to reduce the surface energy. Then, the mesoporous network drives the lanthanum nanoparticles to diffuse through the concentration gradient, and undergoes interfacial reaction with the oxide core formed by titanium and zirconium to form composite inclusions. The lanthanum particles inside the structure slowly migrate through the metal matrix diffusion channel, maintaining a constant release rate with the help of the confinement effect of the carbon layer pores, thereby achieving continuous spheroidization modification of the residual inclusions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0042] Figure 1 The XRD diffraction patterns of the deoxidizers prepared in Example 3 and Comparative Examples 1-4 are compared;

[0043] Figure 2 The graph is a graph showing the change in oxygen content in molten steel after the deoxidizers prepared in Example 3 and Comparative Examples 1-4 act on the molten steel. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] Example 1: This example provides a deoxidizer for metal smelting, comprising the following components:

[0046] 50% aluminum powder, 25% silicon powder, 20% titanium powder, 12% zirconium powder, 0.4% carbon-coated lanthanum nanopowder;

[0047] The preparation method comprises the following steps:

[0048] S1. Lanthanum powder pretreatment;

[0049] Lanthanum nitrate was dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water was 3:1), stirred at 600 r / min and 45°C to form a 20 wt% transparent solution, the composite ligand solution was added dropwise at a rate of 0.7 mL / min, and 0.8% of the mass of the composite ligand solution as a dispersant polyvinyl pyrrolidone was added simultaneously, and the mixture was stirred continuously at a speed of 200 r / min until a uniform sol was formed;

[0050] The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 4:1;

[0051] The sol was transferred to a high-pressure reactor and crystallized at 130°C for 8 h. During the crystallization process, a 0.6 T pulsed magnetic field (frequency 6 Hz) was applied to promote the directional growth of MOFs (metal organic frameworks) along the crystal direction.

[0052] After natural cooling, the product was centrifuged, washed with ethanol and deionized water three times each, and dried in vacuo at 80°C to obtain a white powder precursor;

[0053] S2. Thermal decomposition and carbon coating modification;

[0054] Place the precursor in a porcelain boat and place it in a three-stage tube furnace. First, evacuate the vacuum to ≤10 -3 Pa, and then filled with high-purity argon (cycle 3 times);

[0055] Stage 1: Heating to 650°C at a rate of 12°C / min, keeping the temperature for 2.5 hours to decompose the organic ligand at low temperature to form an amorphous carbon layer, and 200W plasma assisted to enhance the graphitization degree of the carbon layer;

[0056] Stage 2: The temperature was raised to 850°C at a rate of 15°C / min and kept at this temperature for 1.2 hours to promote the agglomeration of lanthanum atoms. At the same time, volatile by-products were removed by high-flow argon purge, and the carbon layer was etched with 300W plasma to form nano-scale pores.

[0057] S3. Freeze-crushing;

[0058] The mixture was frozen in liquid nitrogen for 30 min, transferred to a planetary cryogenic ball mill, and ground at 700 r / min for 40 min with a ball-to-batch ratio of 12:1. Zirconia ceramic balls with a hardness of ≥1500 HV and a material of 6:3:4 were selected as grinding balls (Φ10 mm:Φ8 mm:Φ5 mm=6:3:4). The powder was passed through a 300-mesh sieve to obtain carbon-coated lanthanum nanopowder.

[0059] S4. Mechanical alloying mixed powder;

[0060] 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) were sieved through a 300-mesh sieve and placed together with carbon-coated lanthanum nanopowder in a ball mill (QM-3SP2 stainless steel ball mill with tungsten carbide coating on the inner wall, ultrasonically cleaned with anhydrous ethanol for 30 minutes before use, dried, and purged with argon three times). The ball-to-material ratio was controlled at 10:1, and zirconia ceramic balls with a hardness ≥1500 HV were selected as grinding balls (Φ10 mm:Φ5 mm:Φ3 mm = 5:3:2).

[0061] The ball mill speed was set at 500 r / min, and ball milling was performed for 2 hours under inert gas protection (after sealing the ball mill, vacuum was evacuated to ≤10 Pa, and then filled with high-purity argon gas to normal pressure, and the cycle was repeated three times to ensure an oxygen-free environment) to obtain a mixed powder. During the mechanical alloying process, the powder particles were continuously refined and mixed under the collision, rolling and shearing action of the grinding balls, which can achieve uniform mixing of the metal powders at the nanometer or submicron level, thereby improving the mixing uniformity;

[0062] S5. Staged heating and pressurization;

[0063] Stage 1: The mixed powder is poured into a mold (a graphite mold with a 10μm thick boron nitride release agent coated on the inner wall. Before being placed in a heating furnace, the mold is preheated in a 150℃ oven for 2 hours to remove adsorbed moisture). The mold is then placed in a press (a servo hydraulic press with a punch parallelism ≤0.01mm / m and an accuracy of ±1%FS) for pre-pressing at a pressing rate of 10mm / min and a pre-pressing pressure of 100MPa. The pressure is maintained for 10 minutes to achieve initial molding of the powder. The mold is then placed in a heating furnace (SX2-8-13 box-type resistance furnace) and heated to 300℃ at a heating rate of 10℃ / min. The temperature is maintained for 2 hours. At the same time, argon gas is introduced at a rate of 5L / min to slightly soften the aluminum (the melting point of aluminum is 660℃), further promoting the bonding between the powder particles and forming a preliminary green body structure.

[0064] Stage 2: Transfer to a multifunctional hot pressing furnace (model HP-2000, maximum pressure 1000MPa, temperature 1500℃, built-in K-type thermocouple with temperature measurement accuracy of ±2℃, and pressure sensor with accuracy of ±0.5%FS). Continue heating at a rate of 15℃ / min to 1000℃ (the melting point of titanium is 1668℃, and that of zirconium is 1852℃; the temperature is controlled below the melting point of the main components). Simultaneously, pressurize to 500MPa in stages (increase the pressure at a rate of 50MPa / h to 300MPa and then maintain the pressure constant. When the temperature reaches 600℃, increase the pressure at a rate of 20MPa / h to the final pressure). Maintain the pressure at this temperature and pressure for 3h. Under the conditions of high temperature and high pressure, diffusion and recrystallization occur between the powder particles, forming a denser microstructure, increasing the density and strength of the deoxidizer, enabling it to more stably perform its deoxidation function after adding the molten steel, and reducing process instability factors caused by problems such as deoxidizer breakage.

[0065] S6. Cooling and finished product processing;

[0066] After the heat preservation and pressure holding is completed, the heating is stopped and the mold is allowed to cool naturally to room temperature in the furnace. During the cooling process, a certain inert gas atmosphere is maintained (argon is circulated at a rate of 10L / min) to prevent oxidation of the deoxidizer surface. After cooling, the finished product is demolded by a hydraulic demolding machine. After removing the release agent powder adhering to the surface with a soft brush, it is placed in an ultrasonic cleaning machine (frequency 40kHz, solvent is anhydrous ethanol) for cleaning for 15 minutes to remove residual impurities to obtain a deoxidizer for metal smelting.

[0067] Example 2: This example provides a deoxidizer for metal smelting, comprising the following components:

[0068] 45% aluminum powder, 20% silicon powder, 15% titanium powder, 8% zirconium powder, 0.2% carbon-coated lanthanum nanopowder;

[0069] The preparation method comprises the following steps:

[0070] S1. Lanthanum powder pretreatment;

[0071] Lanthanum nitrate was dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water was 1:1), stirred at 400 r / min and 35°C to form a 20 wt% transparent solution, the composite ligand solution was added dropwise at a rate of 0.3 mL / min, and 0.5% of the mass of the composite ligand solution was added simultaneously with the dispersant polyvinyl pyrrolidone, and the mixture was stirred continuously at a speed of 150 r / min until a uniform sol was formed;

[0072] The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 2:1;

[0073] The sol was transferred to a high-pressure reactor and crystallized at 110°C for 5 h. During the crystallization process, a 0.4 T pulsed magnetic field (frequency 4 Hz) was applied to promote the directional growth of MOFs (metal organic frameworks) along the crystal direction.

[0074] After natural cooling, the product was centrifuged, washed with ethanol and deionized water three times each, and dried in vacuum at 60°C to obtain a white powder precursor;

[0075] S2. Thermal decomposition and carbon coating modification;

[0076] Place the precursor in a porcelain boat and place it in a three-stage tube furnace. First, evacuate the vacuum to ≤10 -3 Pa, then fill with high-purity argon (cycle 2 times);

[0077] Stage 1: Heating to 550°C at a rate of 8°C / min, keeping the temperature for 1.5 hours to decompose the organic ligand at low temperature to form an amorphous carbon layer, and 100W plasma assisted to enhance the graphitization degree of the carbon layer;

[0078] Stage 2: The temperature was raised to 750°C at a rate of 10°C / min and kept at this temperature for 0.8h to promote the agglomeration of lanthanum atoms. At the same time, volatile by-products were removed by high-flow argon purge, and the carbon layer was etched with 200W plasma to form nano-scale pores.

[0079] S3. Freeze-crushing;

[0080] The mixture was frozen in liquid nitrogen for 30 min, transferred to a planetary cryogenic ball mill, and ground at 500 r / min for 20 min with a ball-to-material ratio of 8:1. Zirconia ceramic balls with a hardness of ≥1500 HV and a material of 6:3:4 were selected as grinding balls (Φ10 mm:Φ8 mm:Φ5 mm=6:3:4). The powder was passed through a 200-mesh sieve to obtain carbon-coated lanthanum nanopowder.

[0081] S4. Mechanical alloying mixed powder;

[0082] 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) were sieved through a 200-mesh sieve and placed together with carbon-coated lanthanum nanopowder in a ball mill (QM-3SP2 stainless steel ball mill with tungsten carbide coating on the inner wall, ultrasonically cleaned with anhydrous ethanol for 30 minutes before use, dried, and purged with argon three times). The ball-to-material ratio was controlled at 5:1, and zirconia ceramic balls with a hardness ≥1500 HV were selected as grinding balls (Φ10 mm:Φ5 mm:Φ3 mm = 5:3:2).

[0083] The ball mill speed was set at 300 r / min, and ball milling was performed for 1 hour under inert gas protection (after sealing the ball mill, vacuum was evacuated to ≤10 Pa, and then high-purity argon was filled to normal pressure, and the cycle was repeated three times to ensure an oxygen-free environment) to obtain a mixed powder. During the mechanical alloying process, the powder particles were continuously refined and mixed under the collision, rolling and shearing action of the grinding balls, which can achieve uniform mixing of the metal powders at the nanometer or submicron level, thereby improving the mixing uniformity;

[0084] S5. Staged heating and pressurization;

[0085] Stage 1: The mixed powder is poured into a mold (a graphite mold with a 5μm thick boron nitride release agent coated on the inner wall. Before being placed in a heating furnace, the mold is preheated in a 150℃ oven for 2 hours to remove adsorbed moisture). The mold is then placed in a press (a servo hydraulic press with a punch parallelism of ≤0.01mm / m and an accuracy of ±1%FS) for pre-pressing at a pressing rate of 10mm / min and a pre-pressing pressure of 50MPa. The pressure is maintained for 5 minutes to achieve initial shaping of the powder. The mold is then placed in a heating furnace (SX2-8-13 box-type resistance furnace) and heated to 200℃ at a heating rate of 5℃ / min. The temperature is maintained for 1 hour. At the same time, argon gas is introduced at a rate of 5L / min to slightly soften the aluminum (the melting point of aluminum is 660℃), further promoting the bonding between the powder particles and forming a preliminary green body structure.

[0086] Stage 2: Transfer to a multifunctional hot pressing furnace (model HP-2000, maximum pressure 1000MPa, temperature 1500℃, built-in K-type thermocouple with temperature measurement accuracy of ±2℃, and pressure sensor with accuracy of ±0.5%FS). Continue heating at a rate of 10℃ / min to 800℃ (the melting point of titanium is 1668℃, and that of zirconium is 1852℃, and the temperature is controlled below the melting point of the main components). Simultaneously, pressurize to 400MPa in stages (increase the pressure at a rate of 40MPa / h to 280MPa and maintain the pressure constant. When the temperature reaches 550℃, increase the pressure at a rate of 16MPa / h to the final pressure). Maintain the pressure at this temperature and pressure for 2h. Under the conditions of high temperature and high pressure, diffusion and recrystallization occur between the powder particles, forming a denser microstructure, increasing the density and strength of the deoxidizer, enabling it to more stably perform its deoxidation function after adding the molten steel, and reducing process instability factors caused by problems such as deoxidizer breakage.

[0087] S6. Cooling and finished product processing;

[0088] After the heat preservation and pressure holding is completed, the heating is stopped and the mold is allowed to cool naturally to room temperature in the furnace. During the cooling process, a certain inert gas atmosphere is maintained (argon is circulated at a rate of 10L / min) to prevent oxidation of the deoxidizer surface. After cooling, the finished product is demolded by a hydraulic demolding machine. After removing the release agent powder adhering to the surface with a soft brush, it is placed in an ultrasonic cleaning machine (frequency 40kHz, solvent is anhydrous ethanol) for cleaning for 15 minutes to remove residual impurities to obtain a deoxidizer for metal smelting.

[0089] Example 3: This example provides a deoxidizer for metal smelting, comprising the following components:

[0090] 48% aluminum powder, 23% silicon powder, 17% titanium powder, 11% zirconium powder, 0.3% carbon-coated lanthanum nanopowder;

[0091] The preparation method comprises the following steps:

[0092] S1. Lanthanum powder pretreatment;

[0093] Lanthanum nitrate was dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water was 2:1), stirred at 480 r / min and 39°C to form a 20 wt% transparent solution, the composite ligand solution was added dropwise at a rate of 0.4 mL / min, and 0.6% of the mass of the composite ligand solution was added simultaneously with the dispersant polyvinyl pyrrolidone, and the mixture was stirred continuously at a speed of 180 r / min until a uniform sol was formed;

[0094] The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 3:1;

[0095] The sol was transferred to a high-pressure reactor and crystallized at 122°C for 6 h. During the crystallization process, a 0.5 T pulsed magnetic field (frequency 5 Hz) was applied to promote the directional growth of MOFs (metal organic frameworks) along the crystal direction.

[0096] After natural cooling, the product was centrifuged, washed with ethanol and deionized water three times each, and dried in vacuo at 72°C to obtain a white powder precursor;

[0097] S2. Thermal decomposition and carbon coating modification;

[0098] Place the precursor in a porcelain boat and place it in a three-stage tube furnace. First, evacuate the vacuum to ≤10 -3 Pa, and then filled with high-purity argon (cycle 3 times);

[0099] Stage 1: Heating to 620°C at a rate of 11°C / min, holding for 2 hours to decompose the organic ligand at low temperature to form an amorphous carbon layer, and 140W plasma assisted to enhance the graphitization degree of the carbon layer;

[0100] Stage 2: The temperature was raised to 820°C at a rate of 13°C / min and kept at that temperature for 1 hour to promote the agglomeration of lanthanum atoms. At the same time, volatile by-products were removed by high-flow argon purge, and the carbon layer was etched by 230W plasma to form nano-scale pores.

[0101] S3. Freeze-crushing;

[0102] The mixture was frozen in liquid nitrogen for 30 min, transferred to a planetary cryogenic ball mill, and ground at 610 r / min for 35 min with a ball-to-batch ratio of 9:1. Zirconia ceramic balls with a hardness of ≥1500 HV and a material of 6:3:4 were selected as grinding balls (Φ10 mm:Φ8 mm:Φ5 mm=6:3:4). The powder was passed through a 240-mesh sieve to obtain carbon-coated lanthanum nanopowder.

[0103] S4. Mechanical alloying mixed powder;

[0104] 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) were sieved through a 260-mesh sieve and placed together with carbon-coated lanthanum nanopowder in a ball mill (QM-3SP2 stainless steel ball mill with tungsten carbide coating on the inner wall, ultrasonically cleaned with anhydrous ethanol for 30 minutes before use, dried, and purged with argon three times). The ball-to-material ratio was controlled at 8:1, and zirconia ceramic balls with a hardness ≥1500 HV were selected as grinding balls (Φ10 mm:Φ5 mm:Φ3 mm = 5:3:2).

[0105] The ball mill speed was set at 420 r / min, and ball milling was performed for 1.5 hours under inert gas protection (after sealing the ball mill, vacuum was evacuated to ≤10 Pa, and then filled with high-purity argon gas to normal pressure, and the cycle was repeated three times to ensure an oxygen-free environment) to obtain a mixed powder. During the mechanical alloying process, the powder particles were continuously refined and mixed under the collision, rolling and shearing action of the grinding balls, which can achieve uniform mixing of the metal powders at the nanometer or submicron level, thereby improving the mixing uniformity;

[0106] S5. Staged heating and pressurization;

[0107] Stage 1: The mixed powder is poured into a mold (a graphite mold with a 7μm thick boron nitride release agent coated on the inner wall. Before being placed in a heating furnace, the mold is preheated in a 150℃ oven for 2 hours to remove adsorbed moisture). The mold is then placed in a press (a servo hydraulic press with a punch parallelism of ≤0.01mm / m and an accuracy of ±1%FS) for pre-pressing at a pressing rate of 10mm / min and a pre-pressing pressure of 80MPa. The pressure is maintained for 6 minutes to achieve initial shaping of the powder. The mold is then placed in a heating furnace (SX2-8-13 box-type resistance furnace) and heated to 260℃ at a heating rate of 6℃ / min. The temperature is maintained for 1.8 hours. At the same time, argon gas is introduced at a rate of 5L / min to slightly soften the aluminum (the melting point of aluminum is 660℃), further promoting the bonding between the powder particles and forming a preliminary green body structure.

[0108] Stage 2: Transfer to a multi-functional hot pressing furnace (model HP-2000, maximum pressure 1000MPa, temperature 1500℃, built-in K-type thermocouple with temperature measurement accuracy of ±2℃, and pressure sensor with accuracy of ±0.5%FS). Continue heating at a rate of 12℃ / min to 900℃ (the melting point of titanium is 1668℃, and that of zirconium is 1852℃, and the temperature is controlled below the melting point of the main components). Simultaneously, pressurize to 470MPa in stages (increase the pressure to 295MPa at a rate of 45MPa / h, then maintain the pressure constant. When the temperature reaches 580℃, increase the pressure to the endpoint at a rate of 18MPa / h). Maintain the pressure at this temperature and pressure for 2.5h. Under the high temperature and high pressure conditions, diffusion and recrystallization occur between the powder particles, forming a denser microstructure, increasing the density and strength of the deoxidizer, enabling it to more stably perform its deoxidation function after adding the molten steel, and reducing process instability factors caused by problems such as deoxidizer breakage.

[0109] S6. Cooling and finished product processing;

[0110] After the heat preservation and pressure holding is completed, the heating is stopped and the mold is allowed to cool naturally to room temperature in the furnace. During the cooling process, a certain inert gas atmosphere is maintained (argon is circulated at a rate of 10L / min) to prevent oxidation of the deoxidizer surface. After cooling, the finished product is demolded by a hydraulic demolding machine. After removing the release agent powder adhering to the surface with a soft brush, it is placed in an ultrasonic cleaning machine (frequency 40kHz, solvent is anhydrous ethanol) for cleaning for 15 minutes to remove residual impurities to obtain a deoxidizer for metal smelting.

[0111] Comparative Example 1: The difference between this comparative example and Example 3 is that the sol is not crystallized in S1. Specifically, lanthanum nitrate is dissolved in an ethanol / water mixed solvent (the volume ratio of ethanol to water is 2:1), stirred at 480 r / min and 39°C to form a 20 wt% transparent solution, the composite ligand solution is added dropwise at a rate of 0.4 mL / min, and 0.6% of the mass of the composite ligand solution as a dispersant polyvinyl pyrrolidone is simultaneously added, and stirring is continued at a speed of 180 r / min until a uniform sol is formed;

[0112] The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 3:1;

[0113] The sol was cooled naturally and then centrifuged, washed with ethanol and deionized water three times each, and dried in vacuo at 72° C. to obtain a white powder precursor.

[0114] Comparative Example 2: The difference between this comparative example and Example 3 is that the temperature is directly raised to 820°C without stepwise heating in S2. Specifically, the precursor is placed in a porcelain boat, placed in a three-stage tube furnace, and vacuumed to ≤10 -3 Pa, and then filled with high-purity argon (circulated 3 times); heated to 820℃ at a rate of 13℃ / min, kept at high temperature for 3 seconds to promote the agglomeration of lanthanum atoms, and at the same time removed volatile by-products by high-flow argon purge, and 230W plasma etching.

[0115] Comparative Example 3: The difference between this comparative example and Example 3 is that, in S5, no preheating and prepressurization is performed, and only two stages of heating and pressurization are performed. Specifically, the mixed powder is poured into a mold (a graphite mold with a 7 μm thick boron nitride release agent coated on the inner wall, and the mold is preheated in a 150°C oven for 2 h before being placed in a heating furnace to remove adsorbed moisture), and then placed in a multi-functional hot pressing furnace (model HP-2000, maximum pressure 1000 MPa, temperature 1500°C, built-in K-type thermocouple with a temperature measurement accuracy of ±2°C, and a pressure sensor with an accuracy of ±0.5%FS). The temperature is continued to rise at a heating rate of 12°C / min to 900°C ( The melting points of titanium are 1668°C and zirconium are 1852°C, and the temperature is controlled to be lower than the melting points of the main components. At the same time, the pressure is increased in stages to 470 MPa (the pressure is increased to 295 MPa at a rate of 45 MPa / h and then maintained constant. When the temperature rises to 580°C, the pressure is increased to the terminal pressure at a rate of 18 MPa / h). The temperature and pressure are maintained at this temperature and pressure for 2.5 hours. Under the conditions of high temperature and high pressure, diffusion and recrystallization occur between the powder particles, forming a denser organizational structure, improving the density and strength of the deoxidizer, so that it can more stably exert its deoxidation effect after being added to the molten steel, and reducing process instability factors caused by problems such as deoxidizer breakage.

[0116] Comparative Example 4: The difference between this comparative example and Example 3 is that:

[0117] 1. The sol was not crystallized in S1;

[0118] 2. No staged heating in S2;

[0119] 3. No preheating or prepressing is performed in S5.

[0120] Experimental Example: 1. The XRD patterns of the deoxidizers for metal smelting prepared in Example 3 and Comparative Examples 1-4 were drawn;

[0121] 1.1 Sample grinding: Use an agate mortar to grind the sample to a particle size of less than 5 μm to ensure uniform powder particles and avoid uneven diffraction intensity caused by coarse particles;

[0122] 1.2 Drying treatment: Place the ground powder in a vacuum drying oven at 60°C for 2 hours to remove adsorbed water and volatile substances;

[0123] 1.3 Anti-oxidation treatment: For easily oxidized samples (such as metal-based composite materials), grinding and sample preparation must be carried out under the protection of an inert atmosphere (nitrogen);

[0124] 1.4 Sample preparation: Use a stainless steel sample holder with a diameter of 10 mm and a sample slot depth of 0.5 mm.

[0125] Fill 200 mg of powder sample evenly into the sample slot, apply 15 MPa pressure using a manual tablet press, hold the pressure for 30 seconds to form a flat sample surface, and scrape off excess powder with a blade to ensure that the sample surface is flush with the sample holder;

[0126] 1.5 Equipment: Bruker D8 Advance X-ray diffractometer (equipped with Vantec-500 detector);

[0127] Light source: CuKα radiation (Kα1=0.15406nm, Kα2=0.15444nm), separated by a graphite monochromator;

[0128] Tube voltage: 40kV;

[0129] Tube current: 40mA;

[0130] Divergence slit: 1°, anti-scatter slit: 0.3mm, receiving slit: 0.1mm;

[0131] 1.6 Instrument Calibration:

[0132] 2θ calibration: Using standard Si powder (NIST SRM 640c), the diffraction angle was calibrated at 2θ = 28.44° with an error of ≤ 0.02°;

[0133] Intensity calibration: using corundum ( ) Standard samples, to calibrate the detector response linearity;

[0134] 1.7 Scan parameter settings:

[0135] Scanning range: 10°-80° (2θ), covering the common crystal diffraction peak area;

[0136] Scanning step: 0.02°;

[0137] Scan speed: 5° / min (balance between data quality and acquisition time, total scan time approximately 14 minutes);

[0138] Acquisition mode: continuous scanning mode, counting time per step is 0.5 seconds;

[0139] 1.8 Background collection: Collect background data of empty sample rack under the same conditions for subsequent subtraction;

[0140] 1.9 Repeat experiment: collect data for each sample three times independently, and the RSD (relative standard deviation) should be ≤2%.

[0141] Data analysis: From the XRD spectrum, it can be seen that Example 3 has the highest peak intensity and the peak shape is sharp and symmetrical; the peak intensities of Comparative Examples 1-4 decrease successively, and the peak widths gradually increase; the main peak positions of all samples are almost the same, indicating that the crystal diffraction plane spacing (d value) has not changed.

[0142] 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, which may be due to: the optimized sintering temperature curve promotes atomic diffusion to form a complete crystal lattice; the introduction of seed-induced growth technology reduces the nucleation barrier and reduces the residual amorphous phase; the sharp peak shape indicates good grain size uniformity.

[0143] In Comparative Example 1, insufficient atomic diffusion resulted in residual glass phase at the grain boundary, and the amorphous phase scattering weakened the diffraction intensity; the grain size was uneven, and the broadened diffraction peak masked part of the intensity.

[0144] In Comparative Example 2, the lattice distortion is aggravated due to the excessively fast cooling rate, and the diffraction peak is broadened and the intensity is dispersed; a metastable intermediate phase may be formed (a weak impurity peak appears at 2θ=38° in the XRD pattern), which consumes the main phase content.

[0145] In Comparative Example 3, due to insufficient pressing pressure, the low-density green body formed results in loose contact between grains, and the neck growth is hindered during sintering, forming a porous and loose structure. A large number of microcracks and pores induce multiple scattering effects, which significantly attenuates the main peak intensity.

[0146] Comparative Example 4 is a comprehensive experimental group that simultaneously integrates the process defects of Comparative Examples 1-3. Its XRD spectrum shows superimposed structural degradation characteristics, which are specifically manifested as follows: the attenuation of the main peak intensity compared with Example 3 is greater than the linear superposition of the influence of a single factor; the half-maximum width (FWHM) of the main peak increases by 40%, the peak shape shows obvious asymmetric broadening, and new miscellaneous peaks appear at 2θ=38.2° and 43.5°, corresponding to the diffraction of the incompletely reacted raw material phase.

[0147] 2. Construction of simulated smelting environment: A medium frequency induction furnace (power 50kW, capacity 5kg) was used to melt the 40Cr steel billet, the temperature was raised to 1620±10℃, and argon was introduced and stirred for 10 minutes to homogenize the composition.

[0148] An initial molten steel sample (200 g) was taken and the initial oxygen content was determined to be 50 ppm using the pulse heating inert gas fusion-infrared absorption method according to GB / T 11261-2006.

[0149] The deoxidizers for metal smelting prepared in Examples 1-3 and Comparative Examples 1-4 were added at a ratio of 1.2 kg of deoxidizer per ton of steel.

[0150] Immediately after addition, electromagnetic stirring (frequency 50 Hz, intensity 0.4 T) was started, and the dissolved oxygen content in the molten steel was measured using an oxygen probe (model OX-2000) for 5 minutes.

[0151] Draw a graph of oxygen content versus time (e.g. Figure 2, where the vertical axis is oxygen content in ppm), calculate the deoxygenation rate (Δ[O] / Δt) and the final oxygen content.

[0152] The results are shown in the following table:

[0153]

[0154] It can be seen from the above table that the deoxidation rate of the molten steel is improved by crystallizing the sol in S1; the final oxygen content in the molten steel is reduced by preheating and prepressurizing in S5; and the sol crystallization in S1, preheating and prepressurizing in S5, and staged heating in S2 achieve a synergistic effect of improving the deoxidation rate and reducing the final oxygen content.

[0155] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A process for preparing a deoxidizer for metal smelting, characterized in that: The following steps are involved: S1. Lanthanum powder pretreatment; Dissolve lanthanum nitrate in an ethanol / water mixed solvent, stir to form a transparent solution, add the composite ligand solution dropwise, add the dispersant simultaneously, and continue stirring until a uniform sol is formed; The composite ligand solution is composed of 3,4-dihydroxycinnamic acid and nitrogen-containing carboxylic acid in a molar ratio of 2-4:1; The sol was transferred to a high-pressure reactor and crystallized at 110-130°C for 5-8 hours, with a 0.4-0.6T pulsed magnetic field applied during the crystallization process; After natural cooling, the precursor was centrifuged, washed and dried to obtain a white powder; S2. Thermal decomposition and carbon coating modification; The precursor is heated to 550-650°C at a rate of 8-12°C / min and kept at this temperature for 1.5-2.5 hours to decompose the organic ligand at low temperature to form an amorphous carbon layer, assisted by 100-200W plasma etching; Raise the temperature to 750-850°C at a rate of 10-15°C / min and keep it at that temperature for 0.8-1.2h to promote the agglomeration of lanthanum atoms. At the same time, remove volatile by-products by purging with high-flow argon gas, and use 200-300W plasma etching as an auxiliary. S3. Freeze-ball milling and sieving to obtain carbon-coated lanthanum nanopowder; S4. Mechanical alloying mixed powder; The sieved aluminum powder, silicon powder, titanium powder, zirconium powder and carbon-coated lanthanum nanopowder are ball-milled in a mass ratio of 45-50:20-25:15-20:8-12:0.2-0.4 to obtain a mixed powder; S5. Staged heating and pressurization; Stage 1: Pour the mixed powder into the mold and pre-press it at 50-100 MPa, heat it to 200-300°C, keep it warm for 1-2 hours, and introduce argon protection at the same time; Stage 2: Continue heating to 800-1000°C; at the same time, pressurize to 280-300 MPa, and continue pressurizing to 400-500 MPa; S6. Cooling and finished product processing; The mixture is naturally cooled to room temperature, and demoulded 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: S1 is specifically as follows: lanthanum nitrate is dissolved in an ethanol / water mixed solvent, stirred at 400-600 r / min and 35-45° C. to form a 20 wt% transparent solution, the composite ligand solution is added dropwise at a rate of 0.3-0.7 mL / min, and 0.5-0.8% of the mass of the composite ligand solution of dispersant polyvinyl pyrrolidone is simultaneously added, and the mixture is continuously stirred at a speed of 150-200 r / min until a uniform sol is formed; The sol was transferred to a high-pressure reactor and crystallized at 110-130°C for 5-8 hours. During the crystallization process, a 0.4-0.6T pulsed magnetic field was applied to promote the directional growth of MOFs along the crystal direction. After natural cooling, the product was centrifuged, washed with ethanol and deionized water, and dried in vacuo at 60-80° C. to obtain a white powder precursor.

3. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that: S2 also includes: placing the precursor in a porcelain boat, placing it in a three-stage tube furnace, and evacuating it to ≤10 -3 After Pa, high-purity argon gas is filled in.

4. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that: S3 is specifically as follows: freezing in liquid nitrogen, transferring to a planetary refrigerated ball mill, using 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.

5. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that: S4 is specifically as follows: by weight, 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 passed through a 200-300 mesh sieve and put into a ball mill together with 0.2-0.4 parts of carbon-coated lanthanum nanopowder. The ball-to-material ratio is controlled at 5-10:1, and zirconia ceramic balls with a hardness ≥1500HV are selected as grinding balls.

6. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that: S5 is specifically as follows: pour the mixed powder into the mold, put it into the press for pre-pressing, the pre-pressing pressure is 50-100MPa, and the pressure is maintained for 5-10min to make the powder initially formed, then put the mold into the heating furnace, heat it to 200-300℃ at a heating rate of 5-10℃ / min, keep it warm for 1-2h, and at the same time, introduce argon protection at a rate of 5L / min; Transfer to a multifunctional hot pressing furnace and continue heating to 800-1000°C at a heating rate of 10-15°C / min; at the same time, pressurize to 400-500 MPa in sections and keep at this temperature and pressure for 2-3 hours.

7. The preparation process of the deoxidizer for metal smelting according to claim 1, characterized in that: The step of stepwise pressurization is specifically as follows: increasing the pressure to 280-300 MPa at a rate of 40-50 MPa / h and then maintaining the pressure unchanged; when the temperature rises to 550-600°C, increasing the pressure to the terminal pressure at a rate of 16-20 MPa / h.

8. A deoxidizer prepared according to the process for preparing a deoxidizer for metal smelting according to any one of claims 1 to 7.

Images