A method for reducing iron loss in converter end-point slag

Abstract

The application relates to a method for reducing iron loss in converter end-point slag and belongs to the technical field of steel smelting. The method is characterized in that CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag systems with specific components are added at different stages of converter smelting to perform slagging, so that the slag systems can maintain good fluidity and dephosphorization effect at different temperatures. Meanwhile, the slag-steel interfacial tension is controlled to promote effective separation of the slag-steel and reduce the residual metal iron in the slag. In addition, the top blowing oxygen flow, bottom blowing gas flow and oxygen lance position are dynamically adjusted according to different temperature stages of the converter smelting, so that the molten pool stirring and slag-steel reaction kinetics are optimized. The method successfully realizes double reduction of T.Fe and M.Fe in the converter end-point slag, breaks through the limitation that T.Fe and M.Fe are in a trade-off relationship in the traditional slag system, and significantly reduces the iron loss.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, and in particular to a method for reducing iron loss in converter slag at the end point. Background Technology

[0002] Traditional converter steelmaking processes primarily rely on the CaO-FeO-SiO2 slag system. However, this slag system presents significant problems in the mid-to-late stages of converter smelting, namely, increased melting point, decreased fluidity, and reduced lime melting rate. These issues severely limit the efficiency of converter smelting. Specifically, because this slag system heavily relies on increasing the FeO content to improve fluidity, this often results in excessively high FeO content in the final converter slag. Before deep decarburization in steelmaking, although the relatively low temperature is favorable for the thermodynamic conditions of dephosphorization, the deterioration of slag fluidity in the mid-to-late stages of smelting kinetically restricts the dephosphorization reaction. Consequently, to ensure the molten pool temperature and the final phosphorus content of the molten steel, the molten steel is often in a hyperoxidized state at the end of steelmaking. This not only leads to a decrease in steel purity (resulting in a large number of endogenous inclusions during subsequent deoxidation) but also significantly increases iron loss. To achieve efficient smelting, two key conditions need to be met: first, deep dephosphorization must be achieved in the early stages of steelmaking, and the phosphorus load must be low ([P]≤0.02%) during the later decarburization period; second, the slag must maintain good fluidity under low FeO content conditions. However, existing technologies struggle to meet both conditions simultaneously. In particular, with the increase in the scrap ratio, the converter pool heat becomes insufficient, further deteriorating the slag fluidity, leading to a decrease in dephosphorization efficiency and an increase in lime consumption. To increase the converter pool temperature, the traditional approach is to add a large amount of heat-generating agent and adopt low-carbon-pulling operation. However, this further increases the T.Fe (total iron) content at the converter endpoint, while simultaneously worsening the slag-metal separation effect, increasing the M.Fe (metallic iron) content, and increasing overall iron loss.

[0003] Traditional methods to improve the fluidity and lower the melting point of steelmaking slag include adding fluorite or generating calcium ferrite. However, the use of fluorite has drawbacks such as short slag-forming duration, increased furnace lining erosion, and environmental pollution from fluoride emissions. Calcium ferrite generation mainly relies on high-temperature pre-melting, which has limited capacity and high production costs, making it difficult to widely apply in steel enterprises. To address the shortcomings of existing technologies, some related technical solutions have been proposed, but these solutions either focus on reducing the total iron (T.Fe) content or the total iron (M.Fe) content in the final slag of the converter, but cannot simultaneously reduce both, thus failing to maximize the reduction of iron loss in the slag. Therefore, developing a method that can simultaneously reduce the T.Fe and M.Fe content in the final slag of the converter to maximize the reduction of iron loss in the slag has become an urgent technical challenge. Summary of the Invention

[0004] This application provides a method for reducing iron loss in converter terminal slag to solve the following technical problem: how to simultaneously reduce the content of T.Fe and M.Fe in converter terminal slag. This application provides a method for reducing iron loss in converter terminal slag, the method comprising: At different stages of converter smelting, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation, and the slag-steel interfacial tension in the molten steel is controlled to reduce T.Fe and M.Fe in the final slag of the converter; among which, The melting point of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is <1300℃; At 1450℃, the viscosity of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is ≤1.2 Pa•s; The slag-steel interfacial tension is 0.3 N / m to 0.8 N / m.

[0005] Optionally, when the converter smelting temperature is ≤1400℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 35%~40%, FeO: 25%~30%, MgO: 1%~5%, SiO2: 15%~20%, Al2O3: 3%~5%.

[0006] Optionally, when the converter smelting temperature is ≤1400℃, the converter smelting satisfies the following condition: top-blown oxygen flow rate is 100m³ / h. 3 / h / t·Steel~200m 3 / h / t·steel, bottom blowing gas flow rate is 400m³ / h 3 / h / t·steel~500m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~200mm.

[0007] Optionally, when the converter smelting temperature is 1400℃~1500℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40%~45%, FeO: 15%~20%, MgO: 5%~8%, SiO2: 10%~12%, Al2O3: 2%~4%.

[0008] Optionally, when the converter smelting temperature is 1400℃~1500℃, the converter smelting satisfies the following condition: top-blown oxygen flow rate is 200m³ / h. 3 / h / t·Steel~250m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 180mm~250mm.

[0009] Optionally, 1 to 3 minutes before the end of the converter smelting, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40% to 45%, FeO: 8% to 12%, MgO: 6% to 8%, SiO2: 10% to 12%, and Al2O3: 3% to 5%.

[0010] Optionally, 1 to 3 minutes before the end of the converter smelting process, the converter smelting meets the following condition: the top-blown oxygen flow rate is 80 m³ / min. 3 / h / t·Steel ~120m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~170mm.

[0011] Optionally, the slag-forming process further includes adding lime and dolomite to the molten steel, wherein the lime has a particle size of 5 mm to 30 mm, the total mass of the lime is 60 kg / t steel to 80 kg / t steel, and the melting rate of the lime is ≥1.5 g / min.

[0012] Optionally, within 1 minute after the start of the converter smelting, the first batch of lime is added, wherein the mass of the first batch of lime is 40% to 60% of the total mass of the lime.

[0013] Optionally, the dolomite is added 2 to 3 minutes after the start of the converter smelting, wherein the mass of the dolomite is 15 kg / t steel to 25 kg / t steel.

[0014] Optionally, after the converter smelting is completed, the lance is pressed down for 30 to 35 seconds.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for reducing iron loss in converter terminal slag, the method comprising: During different stages of converter smelting, a specific ratio of CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is selectively added to the molten steel for slag formation based on changes in furnace temperature. This slag system is carefully designed to maintain a low melting point, good fluidity, and efficient lime dissolution capacity at different temperatures, thereby optimizing dephosphorization. By precisely controlling the slag-steel interfacial tension in the molten steel, the wettability between slag and steel is improved. This measure helps promote effective slag-steel separation, reduces the residue of metallic iron in the slag, and thus lowers the M.Fe content. Based on different temperature stages of converter smelting, key process parameters such as top-blown oxygen flow rate, bottom-blown gas flow rate, and oxygen lance position are flexibly adjusted. This dynamic matching strategy optimizes the stirring effect of the molten pool and the kinetics of the slag-steel reaction, providing strong support for the simultaneous reduction of T.Fe and M.Fe. During the slag-forming process, a strategy of adding lime in batches was adopted, with strict control over the lime particle size and timing of addition to ensure rapid dissolution and optimal effect. This measure not only improved lime utilization but also helped maintain slag stability and fluidity. At the end of converter smelting, the oxygen lance position was kept unchanged, and a brief lance-pressing operation was performed to further promote slag-steel separation and reduce iron loss. By implementing the above methods, this application ultimately achieved the dual goals of reducing T.Fe and M.Fe, overcoming the contradiction of the inverse relationship between T.Fe and M.Fe in traditional slag systems, and maximizing the reduction of iron loss. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart illustrating a method for reducing iron loss in converter slag at the end of a converter process, as provided in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] Figure 1 This is a schematic flowchart illustrating a method for reducing iron loss in converter slag at the end of a converter process, as provided in an embodiment of this application.

[0022] Please see Figure 1 This application provides a method for reducing iron loss in converter terminal slag, the method comprising: At different stages of converter smelting, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation, and the slag-steel interfacial tension in the molten steel is controlled to reduce T.Fe and M.Fe in the final slag of the converter; among which, The melting point of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is <1300℃; At 1450℃, the viscosity of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is ≤1.2 Pa•s; The slag-steel interfacial tension is 0.3 N / m to 0.8 N / m.

[0023] Different CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag systems with low melting points, good fluidity, and high lime melting efficiency are used at different converter smelting stages. The specific slag system composition is adjusted according to the smelting stage to ensure good fluidity and dephosphorization effect at different temperatures. T.Fe (total iron content) is the total iron content of iron element in the converter final slag, specifically referring to the total amount of total iron contained in the slag in the undersize material during testing, including iron oxide (FeO, Fe2O3), ferrous oxide (FeO), elemental iron (Fe), and other iron compounds. M.Fe (metallic iron content) specifically refers to the metallic iron content in the oversize material during testing.

[0024] The proportions of each component in the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system are adjusted at different smelting stages, but the slag system as a whole maintains a melting point below 1300℃. A slag system with a melting point below 1300℃ has better fluidity and lime dissolution efficiency, which helps improve smelting efficiency and steel quality. Simultaneously, a slag system with a melting point below 1300℃ also helps reduce the T.Fe and M.Fe content in the final slag at the converter endpoint, thereby maximizing the reduction of iron loss in the slag. For example, the melting points of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system can be 1250℃, 1260℃, 1270℃, 1280℃, 1290℃, etc.

[0025] Viscosity is a physical quantity that measures the magnitude of internal friction in a fluid; the lower the viscosity, the better the fluid's flowability. In converter steelmaking, good slag flowability facilitates mass exchange and reactions at the slag-steel interface, thereby improving smelting efficiency. By controlling the viscosity of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system at 1450℃ to ≤1.2 Pa•s, good slag flowability can be ensured during smelting, which is beneficial for dephosphorization, desulfurization, and other reactions. Furthermore, iron loss in the slag is an important economic indicator in converter steelmaking; a slag system with a viscosity ≤1.2 Pa•s helps reduce the retention of iron beads in the slag, thus reducing iron loss. For example, the viscosity of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system can be 0.8 Pa•s, 0.9 Pa•s, 1.0 Pa•s, 1.1 Pa•s, 1.2 Pa•s, etc.

[0026] Slag-steel interfacial tension refers to the interfacial tension between slag and molten steel during converter smelting. The magnitude of the interfacial tension directly affects the slag-steel separation effect, and thus the amount of iron loss. In converter smelting, good slag-steel separation is key to reducing iron loss. If the slag-steel interfacial tension is too high, the slag and molten steel are difficult to separate, resulting in iron beads being encapsulated by the slag, increasing iron loss. If the interfacial tension is too low, although slag and steel are easy to separate, it may affect the slag's fluidity and dephosphorization effect. Therefore, controlling the slag-steel interfacial tension to a suitable range is of great significance for reducing iron loss. In the embodiments of this application, during the converter smelting process, an Al2O3-CaO-MgO composite additive can be added in a timely manner according to different smelting temperatures to control the slag-steel interfacial tension to the range of 0.3 N / m to 0.8 N / m. The amount of Al2O3-CaO-MgO composite additive added can be 3% to 10% of the total mass of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system. A slag-steel interfacial tension of 0.3 N / m to 0.8 N / m helps improve the wettability between slag and steel, promotes slag-steel separation, and reduces the residue of metallic iron in the slag. For example, the slag-steel interfacial tension can be 0.3 N / m, 0.4 N / m, 0.5 N / m, 0.6 N / m, 0.7 N / m, 0.8 N / m, etc.

[0027] In some embodiments, when the converter smelting temperature is ≤1400℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 35%~40%, FeO: 25%~30%, MgO: 1%~5%, SiO2: 15%~20%, Al2O3: 3%~5%.

[0028] In the early stages of smelting, the furnace temperature is ≤1400℃, and the thermodynamic conditions are favorable for the dephosphorization reaction. The high FeO content (25%–30%) in the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system helps improve the oxidizing properties of the slag, thereby promoting the dephosphorization reaction. Simultaneously, CaO, as the main alkaline oxide, can combine with phosphorus oxides to form stable calcium phosphate, further promoting dephosphorization. The slag system design also considers the melting efficiency of lime. By optimizing the proportions of CaO, FeO, and MgO, the lime maintains a high melting rate (≥1.5 g / min) even at temperatures ≤1400℃, thus accelerating slag formation and improving smelting efficiency. The melting point of this slag system is below 1300℃, and the viscosity at 1450℃ is no higher than 1.2 Pa•s, giving the slag good fluidity. Good fluidity facilitates the dephosphorization reaction, as it mainly occurs at the slag-steel interface. Fluid slag with good fluidity can better contact the molten steel, improving dephosphorization efficiency.

[0029] In some embodiments, when the converter smelting temperature is ≤1400℃, the converter smelting satisfies the following condition: top-blown oxygen flow rate is 100m³ / h. 3 / h / t·Steel~200m 3 / h / t·steel, bottom blowing gas flow rate is 400m³ / h 3 / h / t·steel~500m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~200mm.

[0030] In the early stage of smelting, the furnace temperature is ≤1400℃. At this stage, the temperature is relatively low, and the main tasks are slag formation and improving the initial dephosphorization rate. Therefore, the oxygen flow rate should not be too high to avoid affecting slag formation and dephosphorization efficiency. The top-blown oxygen flow rate is 100 m³ / h. 3 / h / t·Steel~200m 3 / h / t·steel helps promote in-furnace chemical reactions, especially the slag formation process, allowing slag-forming materials such as lime to melt more quickly and creating a slag environment conducive to dephosphorization. For example, when the converter smelting temperature is ≤1400℃, the top-blown oxygen flow rate can be 100m³ / h. 3 / h / t·steel, 120m 3 / h / t·steel, 140m 3 / h / t·steel, 160m 3 / h / t·steel, 180m 3 / h / t·steel, 200m 3 / h / t·steel, etc. Bottom-blown gas (such as nitrogen or argon) is mainly used to stir the molten pool, promote slag-steel interface reactions, and increase the lime melting rate. The bottom-blown gas flow rate is 400m³ / h. 3 / h / t·steel~500m 3 / h / t·steel can enhance furnace stirring, promote slag-steel interface reaction, and facilitate phosphorus removal, while preventing premature slag solidification and maintaining its fluidity. For example, when the converter smelting temperature is ≤1400℃, the bottom-blown gas flow rate can be 400m³ / h. 3 / h / t·steel, 420m 3 / h / t·steel, 440m 3 / h / t·steel, 460m 3 / h / t·steel, 480m 3 / h / t·steel, 500m 3 / h / t·steel, etc.

[0031] At the initial stage of the smelting reaction, the furnace temperature is relatively low (≤1400℃). To promote rapid lime melting and efficient early dephosphorization, the oxygen lance needs to be kept close to the molten steel surface. A distance of 160mm to 200mm between the oxygen lance and the molten steel surface enhances the impact of the oxygen jet on the molten pool, improves the stirring effect, and thus facilitates lime melting and dephosphorization. Simultaneously, this ensures sufficient contact between the oxygen and the molten iron and slag in the pool, improving oxygen utilization. For example, when the converter smelting temperature is ≤1400℃, the distance between the oxygen lance and the molten steel surface can be 160mm, 170mm, 180mm, 190mm, 200mm, etc.

[0032] In some embodiments, when the converter smelting temperature is 1400℃~1500℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40%~45%, FeO: 15%~20%, MgO: 5%~8%, SiO2: 10%~12%, Al2O3: 2%~4%.

[0033] As smelting progresses and temperatures rise, the slag composition needs to be adjusted to maintain good fluidity and dephosphorization efficiency. Reducing the FeO content helps decrease iron loss in the later stages, while increasing the CaO and MgO content enhances the basicity and stability of the slag system.

[0034] In some embodiments, when the converter smelting temperature is 1400℃~1500℃, the converter smelting satisfies the following condition: the top-blown oxygen flow rate is 200m³ / h. 3 / h / t·Steel~250m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 180mm~250mm.

[0035] As smelting progresses, the furnace temperature gradually rises to 1400℃~1500℃, the slag fluidity increases, and the dephosphorization reaction enters its main stage. At this time, appropriately increasing the distance between the oxygen lance and the molten steel surface to 180mm~250mm can prevent the oxygen jet from causing excessive impact on the molten pool, thus preventing molten pool splashing and excessive slag foaming. Simultaneously, an oxygen lance distance of 180mm~250mm still ensures effective contact between oxygen and the molten pool, meeting the requirements of the smelting reaction. Furthermore, increasing the oxygen lance distance to 180mm~250mm also helps control the temperature distribution of the molten pool, avoiding localized overheating. For example, when the converter smelting temperature is 1400℃~1500℃, the distance between the oxygen lance and the molten steel surface can be 180mm, 190mm, 200mm, 210mm, 220mm, 230mm, 240mm, 250mm, etc.

[0036] When the converter smelting temperature is 1400℃~1500℃, the top-blown oxygen flow rate is increased to 200m³. 3 / h / t·Steel~250m 3 / h / t·steel. This is because as the temperature increases, the smelting reaction intensifies, requiring more oxygen to support reactions such as decarburization and dephosphorization. For example, when the converter smelting temperature is 1400℃~1500℃, the top-blown oxygen flow rate can be 200m³ / h. 3 / h / t·steel, 210m 3 / h / t·steel, 220m 3 / h / t·steel, 230m 3 / h / t·steel, 240m 3 / h / t·steel, 250m 3 / h / t·steel, etc. Bottom-blown gas flow rate increased to 500m³. 3 / h / t·Steel~800m 3 This helps to further stir the molten pool, improve reaction efficiency, and also helps to control the slag temperature and composition. For example, when the converter smelting temperature is 1400℃~1500℃, the bottom-blown gas flow rate can be 500m³ / h / t·steel. 3 / h / t·steel, 550m 3 / h / t·steel, 600m 3 / h / t·steel, 650m 3 / h / t·steel, 700m 3 / h / t·steel, 750m 3 / h / t·steel, 800m 3 / h / t·steel, etc.

[0037] In some embodiments, 1 to 3 minutes before the end of the converter smelting, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40% to 45%, FeO: 8% to 12%, MgO: 6% to 8%, SiO2: 10% to 12%, and Al2O3: 3% to 5%.

[0038] Near the end of the converter smelting process, by further reducing the FeO content to 8%–12% and combining this with precise control of other components, the total Fe (T.Fe) and total Fe (M.Fe) in the final converter slag are simultaneously reduced. The addition of MgO and Al2O3 helps optimize the physical properties of the slag system, such as viscosity and interfacial tension, thereby promoting slag-steel separation and reducing iron loss.

[0039] In some embodiments, 1 to 3 minutes before the end of the converter smelting process, the converter smelting meets the following condition: the top-blown oxygen flow rate is 80 m³ / min. 3 / h / t·Steel ~120m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~170mm.

[0040] Near the end of the smelting process, precise control of smelting conditions is crucial to ensure the quality and final composition of the molten steel. At this stage, adjusting the oxygen lance distance from the molten steel surface to 160mm–170mm enhances the stirring effect of the oxygen jet on the molten pool, promoting thorough separation of the molten steel from the slag and reducing iron loss in the final slag. Simultaneously, this 160mm–170mm distance also helps control the temperature and composition of the molten pool, ensuring the accuracy of the smelting endpoint. For example, 1–3 minutes before the endpoint of converter smelting, the oxygen lance distance from the molten steel surface can be 160mm, 162mm, 164mm, 166mm, 168mm, or 170mm.

[0041] Near the end of the converter smelting process, the oxygen flow rate needs to be reduced to prevent over-oxidation of the molten steel, while ensuring the stability of the molten pool temperature and composition. The top-blown oxygen flow rate is reduced to 80 m³ / h. 3 / h / t·Steel ~120m 3 / h / t·steel. Bottom-blown gas flow rate is 500m³ / h. 3 / h / t·Steel~800m 3 Maintaining a stable steel flow rate ( / h / t) helps sustain the stirring of the molten pool, promotes slag-steel separation, and reduces iron loss in the final slag. For example, the top-blown oxygen flow rate can be 80 m³ / h / t during the final 1-3 minutes of converter smelting. 3 / h / t·steel, 90m 3 / h / t·steel, 100m 3 / h / t·steel, 110m 3 / h / t·steel, 120m 3 / h / t·steel, etc.; bottom blowing gas flow rate can be 500m³ / h. 3 / h / t·steel, 550m 3 / h / t·steel, 600m 3 / h / t·steel, 650m 3 / h / t·steel, 700m 3 / h / t·steel, 750m 3 / h / t·steel, 800m 3 / h / t·steel, etc.

[0042] In some embodiments, the slag formation further includes adding lime and dolomite to the molten steel, wherein the lime has a particle size of 5 mm to 30 mm, the total mass of the lime is 60 kg / t steel to 80 kg / t steel, and the melting rate of the lime is ≥1.5 g / min.

[0043] Lime (primarily CaO) plays a crucial role in converter smelting, regulating slag basicity and promoting dephosphorization and desulfurization. Through reaction with other components in the slag (such as SiO2 and FeO), lime can also form slag with a low melting point and good fluidity, which is beneficial to the smelting process. Using lime with a particle size range of 5mm to 30mm ensures that the lime melting rate reaches or exceeds 1.5g / min during slag formation, a key factor in achieving efficient smelting and reducing iron loss. The 5mm to 30mm lime particle size also contributes to the formation of good slag during converter smelting, promoting dephosphorization and other smelting reactions, thereby improving smelting efficiency and steel quality. For example, lime particle sizes can be 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, etc.

[0044] Using the aforementioned CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, the lime melting rate is ≥1.5 g / min. This means that during the smelting process, lime can rapidly melt and participate in the formation of the slag phase, improving the basicity and dephosphorization capacity of the slag system. The increased lime melting efficiency also means that less lime can be consumed to achieve the same dephosphorization effect within the same smelting time, thereby reducing production costs and energy consumption. For example, the lime melting rate can be 1.5 g / min, 1.6 g / min, 1.7 g / min, 1.8 g / min, 1.9 g / min, 2.0 g / min, etc.

[0045] In some embodiments, the first batch of lime is added within 1 minute after the start of the converter smelting, the mass of the first batch of lime being 40% to 60% of the total mass of the lime.

[0046] The first batch of lime is added within one minute of the start of converter smelting. This timing is chosen because the initial smelting stage requires the rapid formation of slag with a certain degree of alkalinity and fluidity to promote the dephosphorization reaction. Early addition of lime accelerates slag formation and increases its alkalinity, thus facilitating dephosphorization.

[0047] The initial batch of lime should comprise 40% to 60% of the total lime mass. This proportion is chosen based on the lime's melting rate and the required slag formation during the smelting process. Maintaining an initial lime mass of 40% to 60% ensures sufficient basicity in the slag while avoiding excessive lime that could increase slag viscosity and hinder smelting. This 40% to 60% range provides flexibility, allowing adjustments based on specific smelting conditions (such as iron composition, temperature, and smelting time) to achieve optimal smelting results. After adding the initial batch of lime, the remaining lime and other slag-forming materials can be added as needed, depending on the smelting progress and slag condition.

[0048] In some embodiments, the dolomite is added 2 to 3 minutes after the start of the converter smelting, wherein the mass of the dolomite is 15 kg / t steel to 25 kg / t steel.

[0049] Dolomite is added 2-3 minutes after the start of smelting. This timing is based on considerations of chemical reaction kinetics and thermodynamics during converter smelting. In the initial stage of converter smelting, the main tasks are rapid slag formation and improving the initial dephosphorization rate. At this time, slag-forming agents such as lime are added to create a suitable slag environment. As smelting progresses, the furnace temperature gradually increases, and the slag's fluidity and chemical properties also change. Adding dolomite 2-3 minutes after the start of smelting ensures that the dolomite fully dissolves in the slag and functions effectively, while avoiding premature hardening of the slag due to early addition or incomplete reaction due to late addition.

[0050] In some embodiments, after the converter smelting is completed, the lance is pressed for 30 to 35 seconds.

[0051] In converter steelmaking, "lance pressing" refers to the operation of keeping the oxygen lance stationary above the molten steel surface after the normal operation of converter smelting has ended. In this embodiment, the lance is pressed for 30-35 seconds instead of being immediately lifted. This is intended to create a stable stirring environment in the molten pool, promote the slag-steel interface reaction, reduce the mechanical entrainment of metallic iron beads in the slag, and promote the reduction reaction of FeO: FeO + C → Fe + CO↑.

[0052] The method for reducing iron loss in converter slag provided in this application can be applied to converter steelmaking processes with a nominal capacity of 80t to 350t.

[0053] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0054] Example 1 An industrial experiment was conducted in a converter at a steel plant. The converter had a capacity of 100 tons and produced high-end automotive steel. Methods to reduce iron loss in the slag at the converter's endpoint included: A CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system was added to molten steel at different smelting stages for slag formation. The slag system had a melting point of 1290℃, a viscosity of 1.2 Pa•s, and an interfacial tension of 0.8 N / m between the slag and steel. Lime and dolomite were added to the molten steel, with the lime having a particle size of 5 mm and a total mass of 60 kg / t·steel. The lime had a melting rate of 1.5 g / min.

[0055] When the converter smelting temperature is ≤1400℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 35%, FeO: 25%, MgO: 5%, SiO2: 20%, Al2O3: 5%. The top-blown oxygen flow rate is 100 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 400m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm.

[0056] Within 1 minute after the start of converter smelting, the first batch of lime is added, with a mass of 40% of the total mass of lime. 2 to 3 minutes after the start of converter smelting, the dolomite is added, with a mass of 15 kg / t steel.

[0057] When the converter smelting temperature is 1400℃~1500℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 40%, FeO: 20%, MgO: 8%, SiO2: 12%, Al2O3: 4%. The top-blown oxygen flow rate is 200 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 250mm.

[0058] One to three minutes before the end of the converter smelting process, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 40%, FeO: 8%, MgO: 8%, SiO2: 12%, and Al2O3: 3%. The top-blown oxygen flow rate is 80 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm.

[0059] After the converter smelting is completed, press the lance for 30 seconds.

[0060] By adding the aforementioned CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, which has a low melting point, good fluidity, and high lime melting efficiency, and by controlling the slag-steel interfacial tension and optimizing the steelmaking process, the final slag T.Fe and M.Fe at the converter endpoint are reduced, thereby maximizing the reduction of iron loss in the slag. The final slag T.Fe at the converter endpoint is reduced to 12%, and the final slag M.Fe at the converter endpoint is reduced to 1%, achieving a total reduction of 13% for the sum of final slag T.Fe and M.Fe.

[0061] Example 2 An industrial experiment was conducted in a converter at a steel plant. The converter had a capacity of 200 tons and produced high-end automotive steel. Methods to reduce iron loss in the slag at the converter's endpoint included: A CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system was added to molten steel at different smelting stages for slag formation. The slag system had a melting point of 1250℃, a viscosity of 1.0 Pa•s, and an interfacial tension of 0.6 N / m between the slag and steel. Lime and dolomite were added to the molten steel, with the lime having a particle size of 20 mm and a total mass of 70 kg / t·steel. The lime had a melting rate of 1.8 g / min.

[0062] When the converter smelting temperature is ≤1400℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 38%, FeO: 28%, MgO: 3%, SiO2: 18%, Al2O3: 4%. The top-blown oxygen flow rate is 150 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 450m³ 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 180mm.

[0063] Within 1 minute after the start of converter smelting, the first batch of lime is added, with a mass of 40% of the total mass of lime. 2 to 3 minutes after the start of converter smelting, the dolomite is added, with a mass of 20 kg / t steel.

[0064] When the converter smelting temperature is 1400℃~1500℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 42%, FeO: 18%, MgO: 7%, SiO2: 11%, Al2O3: 3%. The top-blown oxygen flow rate is 220 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 600m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 200mm.

[0065] One to three minutes before the end of the converter smelting process, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 42%, FeO: 10%, MgO: 7%, SiO2: 11%, Al2O3: 4%. The top-blown oxygen flow rate is 100 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 600m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 165mm.

[0066] After the converter smelting is completed, press the lance for 32 seconds.

[0067] By adding the aforementioned CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, which has a low melting point, good fluidity, and high lime melting efficiency, and by controlling the slag-steel interfacial tension and optimizing the steelmaking process, the final slag T.Fe and M.Fe at the converter endpoint are reduced, thereby maximizing the reduction of iron loss in the slag. The final slag T.Fe at the converter endpoint is reduced to 10%, and the final slag M.Fe at the converter endpoint is reduced to 0.5%, achieving a total reduction of 10.5% for the sum of final slag T.Fe and M.Fe.

[0068] Example 3 An industrial experiment was conducted in a converter at a steel plant. The converter had a capacity of 300 tons and produced high-end automotive steel. Methods to reduce iron loss in the slag at the converter's endpoint included: A CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system was added to molten steel at different smelting stages for slag formation. The slag system had a melting point of 1100℃, a viscosity of 0.8 Pa•s, and an interfacial tension of 0.4 N / m between the slag and steel. Lime and dolomite were added to the molten steel, wherein the lime had a particle size of 30 mm, the total mass of the lime was 80 kg / t·steel, and the melting rate of the lime was 2.5 g / min.

[0069] When the converter smelting temperature is ≤1400℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 40%, FeO: 30%, MgO: 1%, SiO2: 20%, Al2O3: 5%. The top-blown oxygen flow rate is 200 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 200mm.

[0070] Within 1 minute after the start of converter smelting, the first batch of lime is added, with a mass of 60% of the total mass of lime. 2 to 3 minutes after the start of converter smelting, the dolomite is added, with a mass of 25 kg / t steel.

[0071] When the converter smelting temperature is 1400℃~1500℃, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 45%, FeO: 20%, MgO: 8%, SiO2: 12%, Al2O3: 2%. The top-blown oxygen flow rate is 250 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 800m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 180mm.

[0072] One to three minutes before the end of the converter smelting process, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system includes: CaO: 45%, FeO: 12%, MgO: 6%, SiO2: 12%, Al2O3: 5%. The top-blown oxygen flow rate is 120 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 800m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 170mm.

[0073] After the converter smelting is completed, press the lance for 35 seconds.

[0074] By adding the aforementioned CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, which has a low melting point, good fluidity, and high lime melting efficiency, and by controlling the slag-steel interfacial tension and optimizing the steelmaking process, the final slag T.Fe and M.Fe at the converter endpoint are reduced, thereby maximizing the reduction of iron loss in the slag. The final slag T.Fe at the converter endpoint is reduced to 9.7%, and the final slag M.Fe at the converter endpoint is reduced to 0.1%, achieving a total reduction of 9.8% for the sum of final slag T.Fe and M.Fe.

[0075] Comparative Example 1 An industrial experiment was conducted in a converter at a steel plant. The converter had a capacity of 300 tons and produced high-end automotive steel. Methods to reduce iron loss in the slag at the converter's endpoint included: A CaO-FeO-MgO-SiO2-based steelmaking slag system was added to molten steel at different smelting stages for slag formation. The slag system had a melting point of 1420℃, a viscosity of 2 Pa•s, and an interfacial tension of 2 N / m between the slag and steel. Lime and dolomite were added to the molten steel, wherein the lime had a particle size of 30 mm, the total mass of the lime was 80 kg / t·steel, and the melting rate of the lime was 0.5 g / min.

[0076] When the converter smelting temperature is ≤1400℃, a CaO-FeO-MgO-SiO2-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-based steelmaking slag system includes: CaO: 50%, FeO: 30%, MgO: 5%, SiO2: 15%, and the top-blown oxygen flow rate is 100 m³ / h. 3 / h / t·steel, bottom-blown gas flow rate is 200m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 200mm.

[0077] Within 1 minute after the start of converter smelting, the first batch of lime is added, with a mass of 40% of the total mass of lime. 2 to 3 minutes after the start of converter smelting, the dolomite is added, with a mass of 15 kg / t steel.

[0078] When the converter smelting temperature is 1400℃~1500℃, a CaO-FeO-MgO-SiO2-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-based steelmaking slag system includes: CaO: 45%, FeO: 20%, MgO: 10%, SiO2: 20%. The top-blown oxygen flow rate is 150 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 300m³ 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 200mm.

[0079] One to three minutes before the end of the converter smelting process, a CaO-FeO-MgO-SiO2-based steelmaking slag system is added to the molten steel for slag formation. The composition of the CaO-FeO-MgO-SiO2-based steelmaking slag system includes: CaO: 50%, FeO: 25%, MgO: 5%, and SiO2: 20%. The top-blown oxygen flow rate is 100 m³ / h. 3 / h / t·steel, bottom blowing gas flow rate is 400m³ / h 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 200mm.

[0080] By adding the aforementioned CaO-FeO-MgO-SiO2-based steelmaking slag system and controlling the steelmaking process, the final slag T.Fe and M.Fe at the converter endpoint are both high, resulting in large iron loss. The final slag T.Fe at the converter endpoint is 19.7%, while the final slag M.Fe at the converter endpoint is 3%, thus reducing the total T.Fe + M.Fe of the final slag to 22.7%.

[0081] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The use of slag in this invention reduces reliance on harmful additives such as fluorite, thus lowering environmental pollution from fluoride emissions. Simultaneously, by increasing the lime melting rate and smelting efficiency, production costs are reduced, improving economic benefits.

[0082] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for reducing iron loss in converter terminal slag, the method comprising: At different stages of converter smelting, a CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is added to the molten steel for slag formation, and the slag-steel interfacial tension in the molten steel is controlled to reduce T.Fe and M.Fe in the final slag of the converter; among which, The melting point of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is <1300℃; At 1450℃, the viscosity of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system is ≤1.2 Pa•s; The slag-steel interfacial tension is 0.3 N / m to 0.8 N / m.

2. The method according to claim 1, characterized in that, When the converter smelting temperature is ≤1400℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 35%~40%, FeO: 25%~30%, MgO: 1%~5%, SiO2: 15%~20%, Al2O3: 3%~5%.

3. The method according to claim 2, characterized in that, When the temperature of the converter smelting is ≤1400℃, the converter smelting satisfies the following condition: the top-blown oxygen flow rate is 100m³ / h. 3 / h / t·Steel~200m 3 / h / t·steel, bottom blowing gas flow rate is 400m³ / h 3 / h / t·steel~500m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~200mm.

4. The method according to claim 1, characterized in that, When the converter smelting temperature is 1400℃~1500℃, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40%~45%, FeO: 15%~20%, MgO: 5%~8%, SiO2: 10%~12%, Al2O3: 2%~4%.

5. The method according to claim 4, characterized in that, When the converter smelting temperature is 1400℃~1500℃, the converter smelting meets the following requirement: top-blown oxygen flow rate is 200m³ / h. 3 / h / t·Steel~250m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 180mm~250mm.

6. The method according to claim 1, characterized in that, In the 1-3 minutes before the end of the converter smelting, the composition of the CaO-FeO-MgO-SiO2-Al2O3-based steelmaking slag system, by mass fraction, includes: CaO: 40%-45%, FeO: 8%-12%, MgO: 6%-8%, SiO2: 10%-12%, Al2O3: 3%-5%.

7. The method according to claim 6, characterized in that, During the 1-3 minute period before the end of the converter smelting process, the converter smelting meets the following condition: the top-blown oxygen flow rate is 80 m³ / min. 3 / h / t·Steel ~120m 3 / h / t·steel, bottom blowing gas flow rate is 500m³ / h 3 / h / t·Steel~800m 3 / h / t·steel, the distance between the oxygen lance and the surface of the molten steel is 160mm~170mm.

8. The method according to claim 1, characterized in that, The slag-making process also includes adding lime and dolomite to the molten steel. The lime has a particle size of 5 mm to 30 mm, a total mass of 60 kg / t steel to 80 kg / t steel, and a melting rate of ≥1.5 g / min.

9. The method according to claim 8, characterized in that, Within 1 minute of the start of the converter smelting, the first batch of lime is added, the mass of which is 40% to 60% of the total mass of the lime; and / or, The dolomite is added 2 to 3 minutes after the start of the converter smelting, and the mass of the dolomite is 15 kg / t steel to 25 kg / t steel.

10. The method according to claim 1, characterized in that, After the converter smelting is completed, press the lance for 30 to 35 seconds.

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