A method for refining molten steel using die steel fines

Abstract

The present application belongs to the field of metal material recycling and green metallurgy technology, and particularly relates to a method for refining molten steel by using die steel coarse powder. The die steel coarse powder is mixed with a purifying agent to form a core material, the core material is coated by an aluminum or aluminum-based alloy strip and drawn into shape to form an alloy cored wire; the alloy cored wire is fed into a molten steel bath below a slag line at a position of 300mm-600mm below the slag line at a speed of 3m / s-12m / s when the oxygen activity of the molten steel is less than 20ppm. The present application utilizes the characteristic that the aluminum-based coating layer melts earlier than the core material to form a local low-oxygen micro area in the molten steel, and at the same time, the built-in purifying agent completes the synchronous deep purification of the molten steel. The method can increase the yield of Cr, Mo and V alloy elements to more than 95%, control the total oxygen content of the molten steel to be less than 14ppm, and control the sulfur content to be less than or equal to 0.003%, and the process is stable and controllable, and is suitable for large-scale and high-value recycling of additive manufacturing die steel coarse powder.

Description

Technical Field

[0001] This invention belongs to the field of metal material recycling and green metallurgy technology, specifically relating to a method for refining molten steel using mold steel coarse powder. Background Technology

[0002] Utilizing electric arc furnace technology to produce high-quality steel materials from recycled steel raw materials in a low-carbon manner has become an important development direction. Simultaneously, the industrial application of metal additive manufacturing technology in high-end fields such as mold making and aerospace has significantly increased the demand for metal powder raw materials. In actual production, a considerable proportion of coarse metal powder (accounting for 60%–70% of the powder composition and having a particle size greater than 53μm) cannot be used directly due to its physical properties, such as particle size and flowability, not meeting the requirements for additive manufacturing. Taking mold steel coarse powder as an example, it is rich in high-value alloying elements such as Cr, Mo, and V, representing a potential high-quality alloy resource. However, currently, most of this coarse powder is either stockpiled or treated as solid waste, resulting in resource waste and significant environmental pressure. Therefore, how to efficiently reuse this type of coarse powder in the steel metallurgical process to achieve its resource utilization and high-value use has become a crucial issue of concern in the industry.

[0003] In existing technologies, mold steel coarse powder is usually recycled as ordinary scrap steel for remelting. Specifically, during the smelting process in an electric arc furnace or medium-frequency induction furnace, the mold steel coarse powder is mixed with other scrap steel and added to the molten pool. The high temperature of the molten steel melts the coarse powder, thereby recovering the iron matrix and alloying elements from the mold steel coarse powder.

[0004] However, due to the extremely high specific surface area of ​​the coarse powder for mold steel, its contact area with air, slag, and oxygen in the molten steel is enormous during the addition to the molten pool. This leads to severe burn-off of easily oxidized alloying elements such as Cr, Mo, and V, resulting in typically low and highly volatile alloying element yields. Simultaneously, oxides, moisture, and adsorbed gases adhering to the surface of the coarse powder directly enter the molten steel, increasing the oxygen, nitrogen, and inclusion content and deteriorating the purity of the molten steel. Furthermore, the direct addition of powder easily causes molten pool splashing and compositional fluctuations, resulting in poor process stability and controllability, making it difficult to meet the smelting requirements for high-quality mold steel.

[0005] To reduce oxidation losses caused by directly remelting mold steel powder, existing technologies further propose using mold steel powder as a conventional alloying additive. For example, the powder can be pressed into blocks after simple reduction treatment, or it can be wrapped with ordinary steel strip to form a cored wire, which is then added to the molten steel during the refining stage to improve the recovery rate of alloying elements.

[0006] While the aforementioned methods reduce the macroscopic exposure of coarse powder to some extent, they do not solve the problem of interfacial oxidation during the addition of coarse powder to molten steel. When the ordinary coating layer melts in the molten steel, the core coarse powder is instantly exposed and undergoes a violent localized oxidation reaction with trace amounts of dissolved oxygen and interfacial oxides in the molten steel. This results in significant burn-off of core alloying elements such as Cr, Mo, and V, making it difficult to consistently improve the recovery rate of alloying elements. Simultaneously, oxide inclusions and gases introduced by the coarse powder are difficult to remove in a timely manner, leading to poor cleanliness of the molten steel. These problems severely restrict the high-value, large-scale recycling and utilization of additive manufacturing die steel coarse powder in the iron and steel metallurgical field. Summary of the Invention

[0007] To address the technical problems of low alloy element recovery rate of mold steel coarse powder, poor cleanliness of molten steel caused by introducing mold steel coarse powder into molten steel, and insufficient process stability in the prior art, this invention provides a method for refining molten steel using mold steel coarse powder.

[0008] This invention uses mold steel coarse powder as raw material, mixes the mold steel coarse powder with a purifying agent to form a core material, and uses aluminum strip or aluminum-based alloy strip to coat the core material and draw it to prepare an alloy cored wire with the core material as the core and the aluminum-based coating layer as the outer layer. Subsequently, the alloy cored wire is refined. By controlling the insertion depth and feeding speed of the alloy cored wire, it is ensured that the alloy cored wire penetrates the slag layer with appropriate kinetic energy and reaches the high-temperature active zone in the middle of the molten steel pool, so that the aluminum-based coating layer melts and reacts first, forming a stable local high-temperature and low-oxygen protective environment, thereby inhibiting the instantaneous oxidation of alloy elements in the mold steel coarse powder when entering the molten steel. Without requiring major modifications to existing smelting equipment, this method fundamentally overcomes the problems of interfacial oxidation and contamination during the addition of mold steel coarse powder to molten steel. It achieves high yields of key alloying elements Cr, Mo, and V in mold steel coarse powder, high purity of molten steel, and precise control of the smelting process. This transforms mold steel coarse powder from an industrial byproduct into a "low-carbon precision alloy material" that can be used to produce high-quality mold steel, thus realizing resource recycling.

[0009] This invention provides a method for refining molten steel using mold steel powder, comprising the following steps: The core material is formed by mixing coarse mold steel powder with a purifying agent. The core material is then coated with aluminum strip or aluminum-based alloy strip and drawn into shape to form an aluminum-based cladding layer on the outside of the core material, resulting in an alloy cored wire. The purifying agent is a calcium-based purifying agent or a rare earth-based purifying agent. Under the condition that the oxygen activity of the molten steel is less than 20 ppm, the alloy cored wire is fed into the molten steel at a speed of 5 m / s to 12 m / s, with an insertion depth of 300 mm to 600 mm below the refining slag layer covering the surface of the molten steel. This allows the aluminum-based cladding layer to melt before the core material and react with the residual oxygen in the molten steel, forming a local high-temperature and low-oxygen protection zone in the molten steel. Subsequently, the core material melts and decomposes, and the purifying agent is used to perform deep deoxidation and desulfurization on the molten steel to obtain purified molten steel.

[0010] Preferably, the purifying agent is silicon-calcium alloy powder, metallic calcium particles, or rare-earth silicon-iron alloy powder. This invention achieves simultaneous purification at the alloying source by adding a purifying agent to the core. Simultaneously, while the core melts and releases alloying elements, the purifying agent deeply deoxidizes and desulfurizes the molten steel, and modifies the generated Cr, Mo, and V oxide inclusions, causing them to spheroidize and float.

[0011] Preferably, the mass of the purifying agent accounts for 0.5% to 3% of the mass of the die steel coarse powder. The dosage range of the purifying agent is crucial for achieving high alloy element recovery and high steel purity. If the dosage is less than 0.5%, its deoxidation, desulfurization, and modification treatment capabilities for oxide inclusions are insufficient. It cannot completely eliminate the adverse effects of residual oxygen and sulfur in the steel on alloying, nor can it fully spheroidize and float Al2O3 and inclusions generated by alloy element oxidation, leading to a decrease in steel purity and making it difficult to maintain an alloy recovery rate above 95%. If the dosage exceeds 3%, excessive purifying agent will react violently, causing excessive local agitation of the steel, increased temperature drop, and the generation of excessive high-melting-point modification products, which in turn affects the cleanliness and process stability of the steel, while also increasing raw material costs. By controlling the dosage of the purifying agent within the range of 0.5% to 3%, it can be ensured that when the purifying agent is released in the core of the alloy cored wire, it can fully achieve deep purification (deoxidation and desulfurization) of the molten steel and effective modification treatment of inclusions, without causing drastic process fluctuations. Thus, while efficiently recovering alloying elements, it can also synergistically ensure the high purity of the molten steel.

[0012] Preferably, the diameter of the alloy cored wire is 8mm to 16mm; the thickness of the aluminum-based cladding layer is 0.5mm to 2mm. This invention uses aluminum strip or aluminum-based alloy strip as the cladding material. Based on the strong affinity of aluminum for oxygen, after the molten steel is fed in, the outer aluminum-based cladding layer melts first and reacts with the residual oxygen in the steel, forming a momentary high-temperature, low-oxygen partial-pressure micro-protective atmosphere at the front end of the core wire. This greatly inhibits the oxidation and burn-off of Cr, Mo, and V elements in the coarse powder particles of the mold steel in the core. Furthermore, as a strong deoxidizer, aluminum's reaction product, Al2O3, can be effectively denatured by the built-in purifying agent.

[0013] This invention utilizes the significant difference in melting kinetics between the aluminum-based cladding layer and the coarse powder particles of mold steel in molten steel to achieve a "time-sharing protection" mechanism that "first creates a protective atmosphere, then releases alloying elements," and further achieves a "synergistic effect of alloying-purification." The specific mechanism is as follows: In molten steel at approximately 1600°C, the melting of the aluminum-based cladding layer and the accompanying intense exothermic reaction are completed within seconds, rapidly forming a high-temperature, low-oxygen partial pressure local "protective micro-zone" at the front end of the alloy-core wire. The duration of this protective micro-zone (i.e., the "protective window") can be precisely controlled by matching the thickness of the aluminum-based cladding layer with the wire feeding speed. In contrast, the coarse powder particles of mold steel in the core require tens of seconds from the start of melting to complete uniform diffusion in the molten steel. This invention fully utilizes this crucial time difference: by controlling the duration of the protective window, it completely covers the initial stage of the melting and release of alloying elements from the coarse powder particles of mold steel. During this stage, oxidation kinetics are fastest, and easily oxidized elements such as Cr, Mo, and V are most prone to burn-off. Thus, a protective micro-zone is pre-established before the coarse powder particles of the mold steel are exposed to the molten steel, fundamentally inhibiting the oxidation of alloying elements at the most vulnerable moment upon entering the molten steel. Before the protective micro-zone completely dissipates, the purifying agent in the core melts and releases. This purifying agent performs deep desulfurization and deoxidation on the molten steel, and immediately modifies the Al2O3 produced by the reaction of the aluminum-based coating layer and the oxide inclusions remaining in the coarse powder, transforming them into low-melting-point, easily floating spherical inclusions.

[0014] This invention utilizes the matching of the insertion depth and feeding speed of the alloy cored wire to ensure the effective operation of the "structural time-sharing protection" mechanism of the alloy cored wire in the active zone of the molten steel. As the alloy cored wire travels through the molten steel, the outer aluminum-based cladding layer melts and reacts first, creating a localized protective atmosphere. Subsequently, the core, containing purifying agent-containing coarse mold steel powder, rapidly melts into the molten steel under this protection, completing the addition and initial diffusion of Cr, Mo, and V alloying elements.

[0015] Preferably, the feed rate of alloy cored wire, based on the weight of molten steel, is 25 kg / t steel to 40 kg / t steel.

[0016] Preferably, during the wire feeding process, bottom-blown argon is used for stirring, with an argon flow rate of 5 NL / min to 15 NL / min. At the same time, high-basicity (CaO / SiO2>3) and low-oxidizing (FeO<1%) refining slag is used to cover the molten steel pool to further adsorb floating inclusions and stabilize the pool atmosphere.

[0017] Preferably, before preparing alloy cored wire, the die steel powder is heat-treated at 350℃~550℃ for 1 hour to 4 hours in a reducing atmosphere. This effectively reduces the unstable oxides of Cr2O3 and MoO3 on the surface of the die steel powder and removes adsorbed impurities. The oxygen content of the treated die steel powder is significantly reduced, providing qualified raw materials for subsequent alloy cored wire preparation.

[0018] Compared with the prior art, the present invention has the following technical effects: This invention uses die steel powder as raw material, mixes the die steel powder with a purifying agent to form a core material, and then coats the core material with aluminum strip or aluminum-based alloy strip and draws it to prepare an alloy cored wire with a core material and an outer aluminum-based cladding layer. The alloy cored wire is then refined. By controlling the insertion depth and feeding speed of the alloy cored wire, it is ensured that the alloy cored wire penetrates the slag layer with appropriate kinetic energy and reaches the high-temperature active zone in the middle of the molten pool. This allows the aluminum-based cladding layer to melt before the core material and react with residual oxygen in the molten steel, forming a stable local high-temperature, low-oxygen protection zone. This inhibits the instantaneous oxidation of alloying elements in the die steel powder upon entering the molten steel, and stably increases the yield of key alloys Cr, Mo, and V in the die steel powder to over 95%. Subsequently, the core material melts and desulfurizes, and the purifying agent built into the core performs deep deoxidation and desulfurization on the molten steel, synergistically acting with the reaction products of the aluminum-based cladding layer to complete the simultaneous deep refining of the molten steel. While adding alloys, deep deoxidation, desulfurization, and modification of inclusions are carried out, so that the total oxygen content of the final purified molten steel can be stably controlled at 12ppm to 14ppm and the sulfur content ≤0.003%. The purity of the steel meets the requirements of high-end mold steel, and the performance is improved rather than decreased.

[0019] This invention, based on a cored wire feeding method, achieves uniform, stable, and precise addition of alloying elements by controlling the feeding speed and depth, completely avoiding splashing and drastic composition fluctuations. The entire recycling process can be seamlessly integrated into existing refining processes, offering stable technology, high composition control precision, and the potential for large-scale application on a scale of tens of thousands of tons. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0021] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0022] Example 1 A method for refining molten steel using mold steel powder includes the following steps: Step 1: Take 2 tons of H13 coarse powder (D50=100μm) and load it into a controlled atmosphere roller kiln. Heat treat it at 480℃ for 2.5 hours under a protective atmosphere of 5% H2 and 95% N2 (volume ratio). After treatment, sample analysis showed that the oxygen content of the coarse powder decreased from 0.25% before treatment to 0.12%.

[0023] Step 2: Mix the pretreated coarse powder with 1.5% (by weight) silicon-calcium alloy powder (Ca). 28 Si 60 The particles (≤0.3mm) are uniformly mixed to obtain the core material. Using a 1mm thick pure aluminum strip, the core material is coated and drawn into shape on the cored wire production line to produce an alloy cored wire with a diameter of 13mm and a core filling density ≥92%.

[0024] Step 3: During the smelting cycle of the 50-ton electric arc furnace, the scrap steel raw material is melted by electricity to form molten steel. Oxygen is blown into the molten steel for decarburization, controlling the carbon content of the molten steel to decrease to 0.1%–0.15%. Oxidized slag in the electric arc furnace is removed. The oxidized molten steel is then tapped into a ladle. For every ton of steel, 2.5 kg / t of aluminum ingot (i.e., 125 kg) is added to the ladle for deep deoxidation. After standing for 3 minutes, the temperature and oxygen content are measured. When the molten steel temperature reaches 1580℃ and the dissolved oxygen [O] is measured to be 18 ppm, the oxygen content requirement for the feed line is met. At this point, the ladle surface is covered with high-basicity (CaO / SiO2>3) and low-oxidizing (FeO<1%) refining slag. Alloy cored wire is fed into the molten steel via a top feeder at a speed of 8 m / s, vertically inserting it into the molten pool from above the ladle to a depth of 450 mm below the refining slag layer (molten pool slag line) covering the ladle surface. This ensures the alloy cored wire penetrates the slag layer and enters the molten steel, while simultaneously ensuring it is positioned within the active zone created by bottom-blown argon stirring. The target feed rate is set at 35 kg per ton of steel (i.e., a total feed rate of 1.75 tons). Throughout the feeding process, bottom-blown argon is maintained with weak stirring (flow rate 8 NL / min) to promote uniform composition and the flotation of inclusions. The feeding process is smooth and free of splashing.

[0025] After wire feeding, the steel was stirred for 3 minutes, and a steel sample was taken for analysis. The results showed that the alloy element recovery rates were: Cr 96.5%, Mo 96.1%, and V 95%. The purity of the molten steel was: total oxygen content [TO] 13 ppm and sulfur content [S] 0.003%. The subsequent continuous casting billet exhibited excellent low-magnification microstructure. After rolling, its room temperature impact toughness, hardness, and tempering stability all met the requirements for high-grade H13 die steel in GB / T 1299 standard.

[0026] Example 2 This embodiment aims to verify that even with a higher proportion of coarse powder added, the cored wire process of the present invention can still achieve excellent composition control and yield.

[0027] A method for refining molten steel using mold steel powder includes the following steps: Step 1: Take 1.5 tons of H13 coarse powder with a relatively fine particle size (D50=65μm) and load it into a controlled atmosphere roller kiln. Heat treat it at 480℃ for 2.5 hours under a protective atmosphere of 5%H2 and 95%N2 (volume ratio).

[0028] Step 2: Mix the pretreated coarse powder with 2% (by weight) silicon-calcium alloy powder (Ca). 28 Si 60 The particles (≤0.3mm) are uniformly mixed to obtain the core material. Using a 1mm thick pure aluminum strip, the core material is coated and drawn into shape on the cored wire production line to produce an alloy cored wire with a diameter of 13mm and a core filling density ≥92%.

[0029] Step 3: In another 50-ton electric arc furnace smelting cycle, the scrap steel raw material is smelted to form molten steel. Oxygen is blown into the molten steel for decarburization, controlling the carbon content of the molten steel to decrease to 0.1%–0.15%. Oxidized slag in the electric arc furnace is removed. The oxidized molten steel is then tapped into a ladle. For every ton of steel, 2.5 kg / t of aluminum ingot (i.e., 125 kg) is added to the ladle for deep deoxidation. After standing for 3 minutes, temperature and oxygen levels are measured. When the molten steel temperature reaches 1580℃ and the dissolved oxygen [O] is measured to be 18 ppm, the oxygen content requirement for wire feeding is met. At this point, the ladle surface is covered with high-basicity (CaO / SiO2>3), low-oxidizing (FeO<1%) refining slag. Alloy cored wire is then fed in through the top wire feeder of the ladle. The target feed rate per ton of steel is set at 40 kg (total feed rate 2 tons). To precisely control the composition, the wire feeding process is divided into two stages: In the first stage, 60% of the total amount is fed in, with the alloy cored wire vertically inserted into the molten pool from above the ladle at a feeding speed of 8 m / s, to a depth of 450 mm below the refining slag layer (molten pool slag line) covering the ladle surface, and samples are taken for rapid analysis; Based on the analysis results, in the second stage, the feeding speed is reduced to 3 m / s to 5 m / s, and the remaining 40% is fed in segments (50 kg to 100 kg each time, with sampling and testing before continuing), to ensure that the final composition hits the target middle limit.

[0030] Even with a high proportion of coarse powder and finer powder, the smelting process remained highly stable in this embodiment through segmented wire feeding and online fine-tuning. Ultimately, the yields of Cr, Mo, and V remained at 95.8%, 95.2%, and 94.5%, respectively. The steel composition was precisely controlled, with a target Cr content of 5% actually achieved at 5.02%. The purity of the steel remained at a high level, with total oxygen content [TO] = 14 ppm and sulfur content [S] = 0.002%. This demonstrates the effectiveness of this method in high-intensity, refined recovery.

[0031] Example 3 This embodiment uses P20 mold steel coarse powder to illustrate the process adaptability of the present invention to mold steel coarse powder with different compositions.

[0032] A method for refining molten steel using mold steel powder includes the following steps: Step 1: Take 1 ton of P20 steel coarse powder (C 0.28%–0.4%, Si 0.2%–0.80%, Mn 0.6%–1%, Cr 1.4%–2%, Mo 0.3%–0.55%, P≤0.03%, S≤0.03%, balance Fe), with a particle size range of 100μm–200μm, and load it into a controlled atmosphere roller kiln. Considering its predominantly chromium and manganese oxide composition, adjust the pretreatment atmosphere to 8% H2 and 92% N2 (volume ratio), and heat-treat at 450℃ for 2 hours to efficiently reduce chromium oxides.

[0033] Step 2: Due to the strict requirements for sulfur content control in P20 steel, rare earth ferrosilicon alloy powder with stronger desulfurization capabilities is selected as the purification agent during the wire forming process. The pretreated coarse powder is mixed with 2% (by weight) of rare earth ferrosilicon alloy powder (FeSiRe). 21 The particles (≤0.3 mm) are uniformly mixed to obtain the core material. Using a 1 mm thick pure aluminum strip, the core material is coated and drawn into shape on the cored wire production line to produce an alloy cored wire with a diameter of 13 mm and a core filling density ≥92%.

[0034] Step 3: In a 30-ton ladle refining furnace, the molten steel that has undergone preliminary LF treatment is fed with wire alloy, with a feed rate of 25 kg per ton of steel.

[0035] The yields of key alloying elements Cr and Mn reached 97% and 96.5%, respectively. Thanks to the strong desulfurization effect of the rare earth purifier, the sulfur content of the molten steel was reduced to [S]=0.001%. The key performance characteristics of the steel, such as polishability and uniformity of etched patterns, reached the level of high-end P20 steel, verifying the wide material adaptability of this invention.

[0036] Example 4 To verify the necessity of the core structural design of the "aluminum-based composite coating layer" and "built-in purifying agent" proposed in this invention, three sets of comparative experiments were set up in adjacent heats of the same 50-ton electric arc furnace. The subjects treated in all three sets of experiments were the same batch of pretreated H13 coarse powder (D50=100μm, oxygen content 0.12%), and the target addition amount of coarse powder per ton of steel was 30kg. Except for the experimental variables, all other process conditions (such as initial steel temperature, deoxidation degree, and bottom blowing agitation) remained consistent.

[0037] The treatment method for the experimental group was: 1. Alloy cored wire preparation: Pretreated H13 coarse powder is mixed with 2% (by weight) silicon-calcium alloy powder (Ca).28 Si 60 The particles (≤0.3 mm) are uniformly mixed to obtain the core material. Using pure aluminum strip with a thickness of 1 mm, the core material is coated and drawn into shape on the cored wire production line to produce an alloy cored wire with a diameter of 13 mm and a core filling density ≥92%.

[0038] 2. Deoxidation pretreatment of molten steel: After the oxidation period of the 50-ton electric arc furnace is completed, the molten steel is tapped into the ladle, and aluminum ingots of 2.5 kg / t steel are added into the ladle for deep deoxidation. The ladle is allowed to stand for 3 minutes to allow the deoxidation reaction to be fully completed. After the temperature reaches 1580℃, the oxygen content is determined, and the dissolved oxygen [O] is measured to be 18 ppm, which meets the oxygen content requirements of the feed line. At this time, the surface of the ladle is covered with refining slag with high basicity (CaO / SiO2>3) and low oxidizing power (FeO<1%).

[0039] 3. Wire Feeding Operation: Alloy cored wire is fed into the ladle via a top wire feeder. The feeding speed is set to 8 m / s, the target feed rate is 30 kg per ton of steel, and the insertion depth is 450 mm below the refining slag layer (molten pool slag line) covering the ladle surface. Weak stirring with bottom-blown argon is maintained throughout the feeding process, with an argon flow rate of 8 NL / min.

[0040] The treatment method for control group A was as follows: after the molten steel was deoxidized by aluminum and the oxygen activity [O] was reduced to 22 ppm, 1.5 tons of pretreated H13 coarse powder were directly added to the molten steel.

[0041] The treatment method for control group B was as follows: using ordinary low-carbon steel strip with a thickness of 0.6 mm, pretreated H13 coarse powder was coated into ordinary cored wire with a diameter of 13 mm on a cored wire production line, and the core wire filling density was ≥92%. After the molten steel was deoxidized by aluminum and the oxygen activity [O] was reduced to 20 ppm, it was fed into the molten steel at a speed of 8 m / s to a depth of 450 mm below the refining slag layer (molten pool slag line) covering the surface of the molten steel, with a target feed rate of 30 kg per ton of steel.

[0042] The difference between control group B and experimental group is that control group B only uses cored wire feeding and the covering material is ordinary low carbon steel strip; no purifying agent is added to the core mixture.

[0043] Table 1. Experimental results of different groups in Example 4 As shown in Table 1, the Cr and Mo yields in control group A were only 78.3% and 75.1%, respectively, with a final total oxygen content of 45 ppm. Control group B (ordinary cored wire) achieved yields of 85.6% and 84.2%, respectively, with a total oxygen content of 28 ppm. However, the experimental group of this invention achieved a breakthrough: Cr and Mo yields reached as high as 96.2% and 95.5%, respectively, with a deep purification of the total oxygen content to 13 ppm, and the inclusion morphology in the steel was optimized into small spherical shapes.

[0044] Example 5 To verify the necessity of matching the wire feeding speed and insertion depth parameters proposed in this invention, three sets of comparative experiments were set up in adjacent heats of the same 50-ton electric arc furnace. The three sets of experiments all used the same batch of pretreated H13 coarse powder (D50=100μm, oxygen content 0.12%), and alloy cored wires of identical specifications (core consisting of a mixture of H13 coarse powder and 1.5% silicon-calcium alloy powder, covered with a 1mm thick pure aluminum strip, 13mm in diameter) were manufactured using the same method. The initial conditions of the molten steel (temperature, oxygen activity after deoxidation), total feed rate (30 kg per ton of steel), and bottom blowing stirring conditions were kept consistent across the three sets of experiments. The difference lies in:

[0045] Control group A was formed by feeding alloy cored wire into molten steel at a feeding speed of 3 m / s after the molten steel was deoxidized and the oxygen activity [O] was reduced to 18 ppm, and the insertion depth was controlled to be 450 mm below the refining slag layer covering the surface of the molten steel.

[0046] Control group B was formed under the same molten steel conditions, in which alloy cored wire was fed into the molten steel at a feeding speed of 15 m / s and its insertion depth was controlled to be 200 mm below the refining slag layer covering the surface of the molten steel.

[0047] The experimental group was fed into the molten steel at a feeding speed of 8 m / s under the same molten steel conditions, and its insertion depth was controlled to be 450 mm below the refining slag layer covering the surface of the molten steel.

[0048] Table 2 Experimental results of different groups in Example 5 As shown in Table 2, the process of control group A was stable, but there was continuous flue gas at the wire feeding point. Due to the low wire feeding speed, the outer aluminum-based cladding layer of the alloy cored wire melted and was consumed prematurely when it reached a depth of 450 mm because it stayed in the molten steel for too long. This resulted in the core powder losing its effective protection when it was released, leading to a low recovery rate of alloying elements (Cr recovery rate: 86.5%). In addition, the deoxidation products of aluminum were not fully modified, resulting in a high total oxygen content in the molten steel (25 ppm). The process of control group B was characterized by violent splashing and instability. Due to the excessively high wire feeding speed (15 m / s) and insufficient insertion depth (200 mm), the cored wire impacted the shallow area of ​​the molten steel with extremely high kinetic energy, causing splashing. The aluminum-based cladding layer did not have enough time to fully react and form an effective protective micro-zone in the shallow low-temperature zone before the core material was dispersed and exposed, resulting in the lowest alloy recovery rate (Cr recovery rate: 82.1%) and an unstable process, as well as the worst cleanliness of the molten steel. In contrast, the experimental group of this invention employed an optimized match between speed (8 m / s) and depth (450 mm), resulting in a smooth wire feeding process without splashing and a gentle, continuous reaction. These parameters ensured that the alloy cored wire penetrated the slag layer with appropriate kinetic energy, reaching the high-temperature active zone in the center of the molten pool. Furthermore, the aluminum-based cladding layer had sufficient time (approximately 1 second) to melt and react first at this location, forming a stable localized high-temperature, low-oxygen micro-region. This created perfect conditions for the subsequent zero-oxidation recovery and simultaneous purification of the core material. Therefore, its experimental results were comprehensively superior to the control group: the recovery rate of alloying elements was greater than 95.5%, the total oxygen content of the molten steel was deeply purified to 12 ppm, and the morphology of inclusions was effectively improved.

[0049] This embodiment demonstrates through direct comparison that wire feeding speed and insertion depth are interrelated and must be controlled in a coordinated manner as core process parameters. Only when the wire feeding speed (5m / s to 12m / s) and insertion depth (300mm to 600mm below the refining slag layer covering the molten steel surface) are matched within the range defined by this invention can the "structural time-sharing protection" mechanism of "aluminum-based cladding layer melting first to form a local protective micro-region" be effectively realized, thereby achieving high alloy yield and high molten steel purity. Too slow a speed, too fast a speed, or too shallow a depth will cause this mechanism to fail, and the technical effects of this invention cannot be achieved.

[0050] In summary, this invention, through the sacrificial protection of the "aluminum-based composite coating layer" and the dual action of the built-in purifying agent, creates a localized, high-temperature, low-oxygen "micro-reaction zone" around the coarse powder particles the moment they enter the molten steel. This physically isolates the molten steel from the slag's erosion and chemically inhibits the oxidation of key alloying elements such as Cr, Mo, and V. This allows the average yield of alloying elements to be stably increased to over 95%.

[0051] This invention achieves synergistic refining of molten steel while efficiently adding alloying elements. The active components in the cored wire can deeply deoxidize and desulfurize, and transform introduced oxide inclusions into low-melting-point, easily floating spherical inclusions. The molten steel produced using this process has high purity, with its total oxygen content stably controlled below 15 ppm and sulfur content ≤0.005%.

[0052] This invention, through specific design of the alloy cored wire's structure and composition, makes its melting, powder release, and reaction processes in molten steel highly controllable and synchronized. By matching and optimizing the wire feeding parameters, the composition control accuracy of the entire recycling alloying process can reach ±0.05%, and the uniform, stable, and precise transfer of alloying elements into the molten steel is achieved, avoiding molten pool splashing and drastic composition and temperature fluctuations caused by material addition. This allows the coarse powder-based alloying process to be seamlessly integrated into existing continuous refining processes, significantly improving composition control accuracy and providing a reliable guarantee for the large-scale, stable industrial consumption of tens of thousands of tons of coarse powder.

[0053] This invention provides a replicable and standardized end-to-end technology system, from waste powder to high-quality alloy wire and then to high-end steel. Simultaneously, by completely replacing expensive primary Fe-Cr, Fe-Mo, and other alloys with high-quality recycled alloy raw materials, it significantly reduces carbon emissions and raw material costs in steel production from the source, resulting in outstanding economic and environmental benefits.

[0054] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0055] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If these modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for refining molten steel using mold steel powder, characterized in that, Includes the following steps: The core material is formed by mixing coarse powder of mold steel with a purifying agent. The core material is then coated with aluminum strip or aluminum-based alloy strip and drawn into shape to form an aluminum-based coating layer on the outside of the core material, thus obtaining an alloy cored wire. The purifying agent is a calcium-based purifying agent or a rare earth-based purifying agent; When the oxygen activity of the molten steel is below 20 ppm, the alloy cored wire is fed into the molten steel at a speed of 5 m / s to 12 m / s and inserted to a depth of 300 mm to 600 mm below the refining slag layer covering the surface of the molten steel. This allows the aluminum-based coating layer to melt before the core material and react with the residual oxygen in the molten steel, forming a local high-temperature and low-oxygen protection zone in the molten steel. Subsequently, the core material melts and desulfurizes, and the molten steel is deeply deoxidized and desulfurized using a purifying agent to obtain purified molten steel.

2. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, The purifying agent is silicon-calcium alloy powder, metallic calcium particles, or rare earth silicon-iron alloy powder.

3. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, The mass of the purifying agent accounts for 0.5% to 3% of the mass of the coarse powder of the mold steel.

4. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, The diameter of the alloy cored wire is 8mm to 16mm.

5. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, The thickness of the aluminum-based cladding layer is 0.5mm to 2mm.

6. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, Before preparing alloy cored wire, the rough mold steel powder is heat-treated at 350℃~550℃ for 1 hour to 4 hours in a reducing atmosphere.

7. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, During the wire feeding process, bottom-blown argon gas is used for stirring, with an argon gas flow rate of 5 NL / min to 15 NL / min.

8. The method for refining molten steel using mold steel powder according to claim 1, characterized in that, The total oxygen content of the purified molten steel is 12ppm to 14ppm, and the sulfur content is ≤0.003%.

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