A method for producing high-cleanliness steel by tundish diffusion deoxidation

Abstract

The application discloses a high-cleanliness steel production method of tundish diffusion deoxidization, and relates to the technical field of steel smelting. The high-cleanliness steel production method of tundish diffusion deoxidization realizes the synergistic effect of 'upper-layer acid covering agent oxygen isolation and heat preservation and lower-layer alkaline covering agent inclusion adsorption' through the design of the upper-and-lower-layer double-layer functionalized covering agent structure, thereby inhibiting the secondary oxidation and oxygen increase of molten steel in the continuous casting process from the source; the deoxidizer is stably suspended in the lower-layer alkaline covering agent, efficient and continuous diffusion deoxidization is realized, endogenous inclusions are not introduced into the molten steel, the oxygen activity of a slag phase is stably reduced, and the deep deoxidization of the molten steel is indirectly realized. Without the need of reforming the existing continuous casting production line, the process operation is simple and controllable, is not limited by the tundish shape and steel type, and under the premise of not changing the original main smelting process, the oxygen content of the molten steel can be stably reduced, the non-metallic inclusions in the steel can be greatly reduced, and the cleanliness of the steel can be effectively improved.

Description

Technical Field

[0001] This application belongs to the field of iron and steel smelting technology, and in particular relates to a method for producing high-cleanliness steel by diffusion deoxidation in an tundish. Background Technology

[0002] Clean steel refers to high-grade steel with extremely low levels of impurity elements, few and small-sized non-metallic inclusions, and uniform distribution. To meet the high-quality requirements of clean steel, especially to reduce oxygen content, deoxidizers such as aluminum, silicon, and manganese are added to the molten steel to generate oxide inclusions, which are then floated to the surface and discharged. Deoxidation methods include precipitation deoxidation and diffusion deoxidation. These methods, along with other smelting processes, directly affect the type, distribution, and quality of inclusions in the steel. Taking bearing steel as an example, according to the national standard GB / T18254-2016, high-carbon chromium bearing steel is divided into three grades: high-quality steel, high-grade high-quality steel, and special-grade high-quality steel. Non-metallic inclusions are one of the important indicators; the higher the cleanliness, the smaller the size and the fewer the number of non-metallic inclusions, and the higher the grade of the steel.

[0003] Protective casting in continuous casting is a key technology for ensuring the cleanliness of molten steel in the continuous casting process. It uses inert gases or physical barriers to isolate the molten steel from air, preventing secondary oxidation and nitrogen absorption. The tundish, as a buffer container connecting the ladle and the crystallizer in continuous casting, is the last crucial step before the molten steel enters the crystallizer, where deoxidation and inclusion adsorption can significantly improve its cleanliness. If efficient deoxidation and inclusion removal can be achieved in the tundish, the cleanliness of the molten steel can be further significantly improved, ultimately enhancing the quality of the final steel product. In actual industrial production, controlling the cleanliness of molten steel in the tundish stage faces a difficult technical bottleneck: as the molten steel flows from the ladle to the crystallizer, it inevitably undergoes secondary oxidation due to contact with air and corrosion from refractory materials, leading to oxygenation of the molten steel. This problem is difficult to completely eliminate in existing conventional processes. Meanwhile, as the continuous casting process continues, non-metallic inclusions that float to the steel-slag interface, although wetted and captured by the liquid slag layer and entering the slag phase through chemical reactions or direct dissolution, simultaneously cause a continuous accumulation and increase of oxidizing components such as FeO in the slag. This not only directly weakens the slag's ability to continuously capture inclusions but also disrupts the oxygen balance at the steel-slag interface, leading to oxygen transfer into the molten steel and further exacerbating the deterioration of steel cleanliness. Current technologies have not yet developed an effective solution to simultaneously address these issues, making it difficult to reliably meet the demands of large-scale production of high-end clean steel. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this application provides a method for producing high-cleanliness steel using tundish diffusion deoxidation.

[0005] This application provides a method for producing high-purity steel through tundish diffusion deoxidation, comprising the following steps: Step S1: During the continuous casting process, a lower layer of alkaline covering agent and an upper layer of acidic covering agent are sequentially added to the surface of the molten steel in the tundish. The density difference between the two covering agents is used to form a stable double-layer covering agent structure on the surface of the molten steel. The density of the upper acidic covering agent is lower than that of the lower alkaline covering agent. Step S2: During continuous casting and balanced pouring, a diffusion deoxidizer with a density between the upper and lower layers of the covering agent is added to the double-layer covering agent, so that the diffusion deoxidizer passes through the upper acidic covering agent and is stably suspended in the lower alkaline covering agent. Step S3: Throughout the continuous casting process, the layered structure of the double-layer covering agent and the suspension state of the diffusion deoxidizer are maintained. The oxygen activity of the lower layer covering agent is continuously reduced by the diffusion deoxidizer, while the non-metallic inclusions floating on the molten steel are adsorbed by the lower alkaline covering agent to obtain high-cleanliness molten steel. Step S4: The high-purity molten steel is fed into the crystallizer for continuous casting to obtain a high-purity steel billet.

[0006] Preferably, the upper acidic covering agent has a hollow spherical structure with a density of 0.9-1.2 g / cm³. 3 .

[0007] Preferably, the chemical composition of the upper acidic covering agent, by mass percentage, includes 50%≤SiO2≤75%; 5%≤CaO≤25%; Al2O3≤5%; MgO≤5%; Fe2O3≤1.5%, with the remainder being flux and unavoidable impurities.

[0008] Preferably, the liquid phase density of the lower alkaline covering agent is 2.5-2.8 g / cm³. 3 .

[0009] Preferably, the lower alkaline covering agent, by mass percentage, comprises 20%≤Al2O3≤50%; SiO2≤6%; 35%≤CaO≤55%; MgO≤8%; Fe2O3≤1.5%, with the remainder being flux and unavoidable impurities.

[0010] Preferably, the thickness ratio of the upper acidic covering agent to the lower alkaline covering agent is 1:2 to 1:4.

[0011] Preferably, the diffusion deoxidizer is an aluminum-calcium alloy with a density of 2.25-2.70 g / cm³. 3 By mass percentage, its calcium content is 0%-40%, with the remainder being aluminum and unavoidable impurities.

[0012] The high-purity steel production method using tundish diffusion deoxidation in this application has the following advantages and positive effects: (1) Through the design of the double-layer functionalized covering agent structure with upper and lower layers, the synergistic effect of "the upper layer acidic covering agent isolating oxygen and heat preservation, and the lower layer alkaline covering agent adsorbing inclusions" is realized, which inhibits the secondary oxidation and oxygenation of the molten steel during continuous casting from the source; through the design of diffusion deoxidizer with precise density matching, the deoxidizer is stably suspended in the lower layer alkaline covering agent, realizing efficient and continuous diffusion deoxidation, which will not introduce endogenous inclusions into the molten steel, and can stably reduce the oxygen activity of the slag phase, thus indirectly achieving deep deoxidation of the molten steel.

[0013] (2) No need to modify the existing continuous casting production line, the process operation is simple and controllable, and it is not limited by the shape of the tundish or the type of steel. It can stably adapt to the continuous casting production of various high-end clean steels such as bearing steel and gear steel. Without changing the original main smelting process, it can stably reduce the oxygen content of the molten steel, greatly reduce non-metallic inclusions in the steel, and effectively improve the cleanliness of the steel. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0015] The method for producing high-purity steel by diffusion deoxidation in an intermediate ladle according to this application includes the following steps: Step S1: During the continuous casting process, a lower layer of alkaline covering agent and an upper layer of acidic covering agent are added sequentially to the surface of the molten steel in the tundish. The density difference between the two covering agents is used to form a stable double-layer covering agent structure on the surface of the molten steel. The density of the upper acidic covering agent is lower than that of the lower alkaline covering agent. Step S2: During the continuous casting balance pouring, a diffusion deoxidizer with a density between the upper and lower covering agents is added to the double-layer covering agent, so that the diffusion deoxidizer passes through the upper acidic covering agent and is stably suspended in the lower alkaline covering agent; the diffusion deoxidizer is added evenly according to the tonnage of molten steel.

[0016] Step S3: Throughout the continuous casting process, the layered structure of the double-layer covering agent and the suspension state of the diffusion deoxidizer are maintained. The oxygen activity of the lower layer covering agent is continuously reduced by the diffusion deoxidizer, while the non-metallic inclusions floating on the molten steel are adsorbed by the lower alkaline covering agent to obtain high-cleanliness molten steel. Step S4: The high-purity molten steel is fed into the crystallizer for continuous casting to obtain a high-purity steel billet.

[0017] The upper acidic covering agent has a hollow spherical structure with a density of 0.9-1.2 g / cm³. 3The upper acidic covering agent, by mass percentage, comprises 50% ≤ SiO2 ≤ 75%; 5% ≤ CaO ≤ 25%; Al2O3 ≤ 5%; MgO ≤ 5%; Fe2O3 ≤ 1.5%, with the remainder being flux and unavoidable impurities. The lower alkaline covering agent has a liquid phase density of 2.5-2.8 g / cm³. 3 The lower alkaline covering agent, by mass percentage, comprises 20% ≤ Al₂O₃ ≤ 50%; SiO₂ ≤ 6%; 35% ≤ CaO ≤ 55%; MgO ≤ 8%; Fe₂O₃ ≤ 1.5%, with the remainder being flux and unavoidable impurities. The thickness ratio of the upper acidic covering agent to the lower alkaline covering agent is 1:2 to 1:4.

[0018] The diffusion deoxidizer is an aluminum-calcium alloy with a density of 2.25-2.70 g / cm³. 3 By mass percentage, its calcium content is 0%-40%, with the remainder being aluminum and unavoidable impurities.

[0019] This application provides the following two sets of embodiments, and also includes one set of comparative examples. The comparative examples employ existing conventional single-layer covering agent processes for continuous casting, and are used to compare the technical effects with the embodiments of this application, in order to verify the advancement and effectiveness of the proposed solution.

[0020] Comparative example (existing conventional continuous casting process) This comparative example uses the conventional tundish single-layer alkaline covering agent continuous casting process in the steel industry, without diffusion deoxidation treatment. The specific implementation steps are as follows: Pre-smelting process: Based on the target steel grade, conventional converter / electric furnace smelting + LF refining process is adopted to complete the pre-deoxidation, composition adjustment and temperature control of molten steel, so as to obtain molten steel that meets the composition requirements of the target steel grade, and then transfer it to the continuous casting station for pouring.

[0021] Covering agent application: During the continuous casting process, after the molten steel surface in the tundish stabilizes, a single layer of alkaline covering agent is added to the surface of the molten steel in one go, so that the covering agent completely covers the surface of the molten steel. There is no layered structure design throughout the process, and the same type of covering agent is only added according to the consumption of the covering agent.

[0022] Continuous casting: After the continuous casting enters the stable equilibrium casting stage, no diffusion deoxidizer is added. The entire process adopts the conventional protective casting process, and no additional deoxidation and inclusion control operations are performed.

[0023] Continuous casting: Molten steel flows into the crystallizer through the tundish to complete continuous pouring, and after cooling and demolding, a continuously cast billet is obtained.

[0024] This comparative example represents a conventional production process with inherent technical flaws: a single-layer alkaline covering agent cannot simultaneously provide oxygen isolation and heat preservation while also adsorbing inclusions; during continuous casting, the molten steel is prone to secondary oxidation and oxygenation upon contact with air; without diffusion deoxidation treatment, as continuous casting progresses, oxidizing components such as FeO in the slag continuously increase, failing to achieve deep deoxidation of the molten steel and even transferring oxygen back into the molten steel; simultaneously, the slag's adsorption capacity for non-metallic inclusions continuously decreases; ultimately, the resulting molten steel billet has a high oxygen content, a large number and size of non-metallic inclusions, and insufficient steel cleanliness, failing to meet the quality requirements for high-end bearing steel and gear steel.

[0025] Example 1: Continuous casting production of bearing steel The specific implementation steps are as follows: Pre-smelting process: conventional converter smelting + LF refining process is adopted, and then the material is transferred to the continuous casting station.

[0026] Construction of double-layer covering agent: During the continuous casting process, after the molten steel enters the tundish and the liquid surface stabilizes, the lower layer of alkaline covering agent is first evenly added to the surface of the molten steel in the tundish, and then the upper layer of acidic covering agent is added. Relying on the density difference between the two layers of covering agent, a stable upper and lower layer double-layer covering agent structure is formed on the surface of the molten steel. The upper acidic covering agent has a hollow spherical structure and a density of 1.0 g / cm³. 3 By mass percentage, its chemical composition is SiO2: 62%, CaO: 20%, Al2O3: 4%, MgO: 4%, with the remainder being flux and unavoidable impurities. The hollow spherical structure significantly reduces the thermal conductivity of the covering agent, achieving excellent heat preservation. It also possesses excellent spreadability, completely covering the surface of the molten steel to isolate it from air, inhibiting secondary oxidation and nitrogen absorption of the molten steel from the source. The high SiO2 content prevents the covering agent from reacting with air, ensuring long-term stability of the oxygen barrier effect, and is suitable for the full-cycle casting requirements of bearing steel continuous casting.

[0027] The liquid phase density of the lower alkaline covering agent is 2.6 g / cm³. 3 It has a significantly higher concentration than the upper acidic covering agent, allowing it to remain stably between the molten steel and the upper covering agent, directly contacting the molten steel surface. By mass percentage, its chemical composition is: CaO: 50%, Al2O3: 30%, SiO2: 5%, MgO: 5%, with the remainder being flux and unavoidable impurities. This high CaO and high Al2O3 design provides extremely strong adsorption capacity for the most common Al2O3 brittle inclusions in bearing steel. It can quickly wet, capture, and fix inclusions floating in the molten steel into the slag phase, preventing them from re-entering the molten steel and causing secondary contamination. Simultaneously, it provides a stable liquid-phase reaction site for the diffusion deoxidation reaction.

[0028] The upper layer of acidic covering agent is 4 mm thick, and the lower layer of alkaline covering agent is 15 mm thick, with a thickness ratio of 1:3.75. This ratio ensures the excellent oxygen barrier and heat insulation effect of the upper covering agent while providing sufficient space for the adsorption of impurities and the diffusion deoxygenation reaction zone for the lower covering agent, thus achieving synergistic effects of the two covering agents.

[0029] Addition of diffusion deoxidizer: After the continuous casting enters the stable and balanced pouring stage, and the casting speed, molten steel temperature and liquid level are stable, add diffusion deoxidizer evenly to the surface of the double-layer covering agent in the tundish. The addition amount is 0.01 kg per ton of molten steel. The diffusion deoxidizer is an aluminum-calcium alloy with a density of 2.4 g / cm³. 3 The density is between that of the upper acidic covering agent and the lower alkaline covering agent; its chemical composition, by mass percentage, is 15% Ca, 84.5% Al, and 0.5% other elements. This density allows the aluminum-calcium alloy, after being added, to smoothly pass through the low-density upper acidic covering agent under gravity and enter the lower alkaline covering agent. Under the balance of buoyancy and gravity, it remains stably suspended in the lower covering agent, neither too dense to sink into the molten steel and introduce endogenous inclusions, nor too dense to float to the upper covering agent and lose its deoxidizing effect. It is precisely positioned in the deoxidation reaction zone near the steel-slag interface. (Some aluminum-calcium alloy may reach the interface between the upper and lower covering agents and the steel-slag interface, but this does not affect the diffusion deoxidation effect).

[0030] Throughout the continuous casting cycle, the stratification of the double-layer covering agent on the surface of the molten steel in the tundish is monitored in real time. Based on the consumption of the covering agent, an upper layer of acidic covering agent and a lower layer of alkaline covering agent are replenished synchronously in the original proportion to maintain the stability of the double-layer structure. Diffusion deoxidizer is added in batches according to the continuous casting duration and the tonnage of the molten steel, ensuring its continuous suspension and stable reaction within the lower layer of alkaline covering agent. Through the continuous diffusion deoxidation reaction between the suspended aluminum-calcium alloy and oxidizing components such as FeO in the lower layer of covering agent, the oxygen activity of the slag phase is continuously reduced, disrupting the oxygen balance at the steel-slag interface. This allows oxygen in the molten steel to continuously diffuse into the slag phase, achieving indirect deep deoxidation of the molten steel. Simultaneously, the lower layer of alkaline covering agent continuously adsorbs non-metallic inclusions floating in the molten steel, inhibiting secondary oxygenation throughout the process and resulting in highly clean molten steel.

[0031] Continuous casting: The high-purity molten steel in the tundish is stably fed into the crystallizer, and continuous casting is completed according to the conventional continuous casting process for bearing steel. After cooling, the steel is demolded to obtain the continuous casting billet of bearing steel.

[0032] In this embodiment, the total oxygen content of the molten steel in the diffusion deoxidation furnace is 4.8 × 10⁻⁶. -6 This is significantly lower than the 6.2 × 10⁻⁶ in the control group (non-diffusion deoxidation furnace). -6The oxygen content in the molten steel decreased by 22.6%; the number and size of non-metallic inclusions in the steel were significantly reduced, and the cleanliness level of the bearing steel was greatly improved.

[0033] Example 2: Continuous casting production of gear steel The specific implementation steps are as follows: Pre-smelting process: The process involves conventional electric furnace smelting, LF refining, and VD vacuum treatment, followed by transfer to the continuous casting station.

[0034] Construction of double-layer covering agent: During the continuous casting process, after the molten steel surface in the tundish stabilizes, the lower layer of alkaline covering agent is first evenly added to the surface of the molten steel, and then the upper layer of acidic covering agent is added. The stable upper and lower layer double-layer covering agent structure is formed by relying on the density difference. The upper acidic covering agent has a hollow spherical structure and a density of 1.1 g / cm³. 3 The chemical composition, by mass percentage, is SiO2: 55%, CaO: 25%, Al2O3: 5%, MgO: 5%, with the remainder being flux and unavoidable impurities. The optimized composition further enhances the low-temperature spreadability of the covering agent, allowing it to quickly cover the molten steel surface in the initial casting stage, preventing secondary oxidation of the molten steel during this phase. It also adapts to the low-temperature casting process of gear steel continuous casting, reducing the temperature drop of the molten steel and ensuring the stability of the continuous casting process.

[0035] The liquid phase density of the lower alkaline covering agent is 2.7 g / cm³. 3 It has a significantly higher content than the upper layer of acidic covering agent, allowing for stable direct contact with the molten steel surface. Its chemical composition, by mass percentage, is CaO: 50%, Al2O3: 25%, SiO2: 8%, MgO: 8%, with the remainder being flux and unavoidable impurities. The optimized CaO to Al2O3 ratio enhances the adsorption capacity for complex inclusions in gear steel, making it suitable for continuous casting of gear steel and ensuring the efficient and stable diffusion deoxidation reaction.

[0036] The upper layer of acidic covering agent is 6mm thick, and the lower layer of alkaline covering agent is 18mm thick, with a thickness ratio of 1:3. This is suitable for the long continuous casting cycle of gear steel and ensures the stability of oxygen isolation, heat preservation, and inclusion adsorption effects throughout the entire cycle.

[0037] Addition of diffusion deoxidizer: After the continuous casting enters the stable equilibrium pouring stage, add aluminum-calcium alloy diffusion deoxidizer evenly to the surface of the double-layer covering agent. The addition amount is 0.15 kg per ton of molten steel. The diffusion deoxidizer is an aluminum-calcium alloy with a density of 2.6 g / cm³. 3It has a density between that of the upper and lower covering agents; by mass percentage, its chemical composition is 30% Ca, 65% Al, and 5% other elements. Increasing the calcium content can further optimize the melting point and fluidity of the deoxidation products, improve the efficiency of diffusion deoxidation reaction, and at the same time adapt to the Al2O3 content of the lower covering agent, ensuring the stable suspension and continuous reaction of the deoxidizer in the lower covering agent.

[0038] Throughout the continuous casting process, the layered structure of the double-layer covering agent is maintained stably. For each heat of molten steel poured, a corresponding proportion of covering agent and diffusion deoxidizer is added simultaneously to ensure the continuity of the diffusion deoxidation effect. The diffusion deoxidizer continuously removes oxidizing components from the slag, indirectly reducing the oxygen content of the molten steel. Simultaneously, the lower alkaline covering agent continuously adsorbs floating composite inclusions in the molten steel, preventing inclusions from remaining in the steel and affecting its impact toughness and fatigue properties, resulting in high-purity gear steel molten steel.

[0039] Continuous casting: High-purity molten steel is fed into a crystallizer and continuously poured according to the conventional continuous casting process for gear steel. After cooling and demolding, a continuous casting billet of gear steel is obtained.

[0040] In this embodiment, the total oxygen content of the molten steel in the diffusion deoxidation furnace is 6.2 × 10⁻⁶. -6 This is significantly lower than the 8.3 × 10⁻⁶ for the control group (non-diffusion deoxidation furnace). -6 The oxygen content in the molten steel decreased by 25.3%; the number of non-metallic inclusions in the steel was significantly reduced, large inclusions were completely removed, and the impact toughness and contact fatigue life of the steel were significantly improved.

[0041] The comparison and verification between the above comparative examples and the two sets of embodiments clearly show that: The high-cleanliness steel production method of this application using tundish diffusion deoxidation achieves a synergistic effect of "upper acidic covering agent for oxygen isolation and heat preservation, and lower alkaline covering agent for adsorbing inclusions" through a double-layer functionalized covering agent structure design, thereby inhibiting secondary oxidation and oxygenation of molten steel during continuous casting from the source. Through a diffusion deoxidizer design with precise density matching, the deoxidizer is stably suspended in the lower alkaline covering agent, achieving efficient and continuous diffusion deoxidation. This method neither introduces endogenous inclusions into the molten steel nor fails to stably reduce the oxygen activity of the slag phase, thereby indirectly achieving deep deoxidation of the molten steel.

[0042] The proposed solution requires no modification to the existing continuous casting production line. The process is simple and controllable, and is not limited by the shape of the tundish or the type of steel. It can be stably adapted to the continuous casting production of various high-end clean steels such as bearing steel and gear steel. Without changing the original main smelting process, it can stably reduce the oxygen content of the molten steel, significantly reduce non-metallic inclusions in the steel, and effectively improve the cleanliness of the steel.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for producing high-cleanliness steel using tundish diffusion deoxidation, characterized in that, Includes the following steps: Step S1: During the continuous casting process, a lower layer of alkaline covering agent and an upper layer of acidic covering agent are sequentially added to the surface of the molten steel in the tundish. The density difference between the two covering agents is used to form a stable double-layer covering agent structure on the surface of the molten steel. The density of the upper acidic covering agent is lower than that of the lower alkaline covering agent. Step S2: During continuous casting and balanced pouring, a diffusion deoxidizer with a density between the upper and lower layers of the covering agent is added to the double-layer covering agent, so that the diffusion deoxidizer passes through the upper acidic covering agent and is stably suspended in the lower alkaline covering agent. Step S3: Throughout the continuous casting process, the layered structure of the double-layer covering agent and the suspension state of the diffusion deoxidizer are maintained. The oxygen activity of the lower layer covering agent is continuously reduced by the diffusion deoxidizer, while the non-metallic inclusions floating on the molten steel are adsorbed by the lower alkaline covering agent to obtain high-cleanliness molten steel. Step S4: The high-purity molten steel is fed into the crystallizer for continuous casting to obtain a high-purity steel billet.

2. The method for producing high-cleanliness steel using tundish diffusion deoxidation according to claim 1, characterized in that, The upper acidic covering agent has a hollow spherical structure with a density of 0.9-1.2 g / cm³. 3 .

3. The method for producing high-cleanliness steel using tundish diffusion deoxidation according to claim 2, characterized in that, The chemical composition of the upper acidic covering agent, by mass percentage, includes 50%≤SiO2≤75%; 5%≤CaO≤25%; Al2O3≤5%; MgO≤5%; Fe2O3≤1.5%, with the remainder being flux and unavoidable impurities.

4. The method for producing high-cleanliness steel using tundish diffusion deoxidation according to claim 1, characterized in that, The liquid phase density of the lower alkaline covering agent is 2.5-2.8 g / cm³. 3 .

5. The method for producing high-cleanliness steel using tundish diffusion deoxidation according to claim 4, characterized in that, The lower alkaline covering agent, by mass percentage, comprises 20%≤Al2O3≤50%; SiO2≤6%; 35%≤CaO≤55%; MgO≤8%; Fe2O3≤1.5%, with the remainder being flux and unavoidable impurities.

6. The method for producing high-cleanliness steel by tundish diffusion deoxidation according to claim 1, characterized in that, The thickness ratio of the upper acidic covering agent to the lower alkaline covering agent is 1:2 to 1:

4.

7. The method for producing high-purity steel using tundish diffusion deoxidation according to claim 1, characterized in that, The diffusion deoxidizer is an aluminum-calcium alloy with a density of 2.25-2.70 g / cm³. 3 By mass percentage, its calcium content is 0%-40%, with the remainder being aluminum and unavoidable impurities.