A slagging dephosphorizing agent for converter steelmaking

Abstract

The application discloses a converter steelmaking slagging dephosphorization agent and relates to the technical field of steel smelting. The dephosphorization agent is composed of a dense core and a porous shell coated on the outer surface of the dense core, and the whole is in a spherical core-shell structure; the mass ratio of the porous shell to the dense core is 3:7-4:6; the porous shell is a low-temperature calcined porous structure and is composed of the following components in percentage by mass: iron oxide scale 40-55%, fluorine-free composite fluxing agent 18-33%, light calcined magnesia powder 5-10% and interfacial activator 2-5%; the dense core is a high-pressure formed dense structure and is composed of the following components in percentage by mass: active lime 60-70%, converter steel slag powder 15-25%, alumina powder 5-8% and cerium oxide 2-4%; the application realizes efficient dephosphorization in the whole converter cycle through the core-shell hierarchical gradient release structure, the B-Ti-Li fluorine-free fluxing system and the double-component interfacial activation cooperation, and the fluorine-free environmental protection, furnace lining protection and cost optimization are considered.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, specifically to a slag dephosphorizing agent for converter steelmaking. Background Technology

[0002] In converter steelmaking, dephosphorization is one of the core metallurgical tasks, and its efficiency directly affects the final steel quality and smelting costs. Currently, the mainstream slag-forming dephosphorization system in the industry uses lime as the main alkaline component and fluorite (CaF2) as the core flux. This system has revealed three common bottlenecks in long-term industrial application:

[0003] Firstly, the delayed slag formation leads to low dephosphorization efficiency in the early stages. Lime has a melting point as high as 2572℃, and its dissolution rate is slow in the early stages of blowing (1200~1400℃). The slag basicity rises slowly, and the dephosphorization rate in the early stages is only 30%~40%. A large amount of phosphorus remains in the middle and late stages of blowing, and it is easy to revert to phosphorus as the temperature of the molten steel increases, which increases the difficulty of deep dephosphorization.

[0004] Secondly, the reliance on fluorite creates a dual contradiction between environmental protection and furnace lining protection. Although fluorite, as a traditional flux, has a significant slag-forming effect, fluoride ions can severely corrode the magnesia-carbon furnace lining, shortening the furnace life. At the same time, the treatment cost of fluorine-containing waste gas and wastewater is high, and environmental pressure continues to increase with the improvement of industry standards. Fluorine-free slag has become an inevitable development trend in the steel industry.

[0005] Third, the simultaneous release of components leads to poor matching of dephosphorization throughout the entire cycle. In conventional composite dephosphorizing agents, all components are introduced into the slag simultaneously at one time. When the oxidizing properties are insufficient in the early stage of blowing, the high-basicity components are prone to agglomeration, causing the slag to dry out again. When the basicity reaches the standard in the later stage of blowing, the oxidizing properties of the slag have decreased significantly. The thermodynamic and kinetic conditions for dephosphorization cannot be matched throughout the entire process, which limits the further improvement of dephosphorization efficiency.

[0006] Existing technologies for fluorine-free dephosphorizing agents mostly focus on replacing single fluxing components or simple component blends. These technologies generally suffer from insufficient fluxing effect, decreased dephosphorizing efficiency, and exacerbated furnace lining erosion. They fail to address industry pain points through a multi-dimensional approach that integrates structural design, chemical systems, and kinetic enhancement. Some solutions only improve oxidizing properties using iron oxides and manganese ore, resulting in limited low-temperature fluxing effects and prolonged slag formation time. Others use single boron-based fluxes, which, while lowering the melting point, exacerbate furnace lining erosion and result in insufficient dephosphorizing kinetics in the mid-to-late stages. Still others use composite dephosphorizing agents without structural gradation design, leading to a mismatch between component release rhythms and the blowing cycle, making it difficult to achieve efficient dephosphorization throughout the entire cycle. The real problem in promoting fluorine-free slag systems is not the lack of alternatives to fluorite, but rather how to maintain or even improve smelting performance after substitution while simultaneously protecting the furnace lining. Summary of the Invention

[0007] The purpose of this invention is to provide a slag dephosphorizing agent for converter steelmaking, in order to solve the problems of high pollution caused by fluorite dependence in existing dephosphorizing agents and low slag efficiency after fluorine-free substitution.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] According to the first aspect of this disclosure, a slag dephosphorizing agent for converter steelmaking is proposed. The dephosphorizing agent is composed of a dense core and a porous shell covering the outer surface of the dense core. The overall structure is a spherical core-shell structure with an overall particle size of 21-30 mm. The mass ratio of the porous shell to the dense core is 3:7-4:6.

[0010] The porous shell is a porous structure formed by low-temperature sintering, with a porosity of 25% to 35%, and is composed of the following components by mass percentage: 40% to 55% iron oxide scale, 18% to 33% fluorine-free composite flux, 5% to 10% lightly calcined magnesium oxide powder, and 2% to 5% interface activator;

[0011] The dense core is a high-pressure formed dense structure with a density ≥85% and a porosity ≤10%, and is composed of the following components by mass percentage: 60%–70% active lime, 15%–25% converter steel slag powder, 5%–8% alumina powder, and 2%–4% cerium oxide.

[0012] Furthermore, the fluorine-free composite flux is composed of borax and ilmenite mixed in a mass ratio of 2:1 to 1.5:1; the interface activator is lithium carbonate.

[0013] Furthermore, the total iron content of the iron oxide scale is ≥70%, of which Fe2O3 accounts for ≥60% of the total iron content; the MgO content of the lightly calcined magnesium oxide powder is ≥90%.

[0014] Furthermore, the active lime contains ≥92% CaO by mass and ≥300mL of activity; the converter steel slag powder has an alkalinity ≥3.0, a free CaO content ≥8% by mass, and a particle size of 200 mesh.

[0015] Furthermore, the thickness of the porous outer shell is 3-5 mm; the particle size of the dense core is 15-20 mm; and the compressive strength of the dephosphorizing agent product is ≥50 N / ball.

[0016] According to the second aspect of this disclosure, a method for preparing a slag dephosphorizing agent for converter steelmaking is also provided, for use in preparing the first aspect of this disclosure, comprising the following steps:

[0017] S1. Weigh each raw material according to the formula for dense core, dry grind until the 200 mesh passing rate is ≥90%, add bentonite binder and mix evenly, press into pellets under 15-20MPa pressure, and dry at 180-200℃ to obtain dense core green pellets.

[0018] S2. Weigh each raw material according to the porous shell formula, dry grind until the 180 mesh passing rate is ≥85%, add water glass binder and mix evenly to obtain coating powder; place the dense core green balls in a disc granulator, spray atomized water while rolling and add coating powder in batches to form green balls with shells.

[0019] S3. The coated green pellets are heated to 800-900℃ and roasted. After natural cooling, they are sieved to obtain the finished dephosphorizing agent.

[0020] Furthermore, in step S1, the amount of bentonite binder added is 3% to 5% of the total mass of the core powder, and the drying time is 2 hours.

[0021] Further, in step S2, the amount of water glass binder added is 2% to 4% of the total mass of the shell powder, the tilt angle of the disc granulator is 45° to 50°, the rotation speed is 20 to 25 r / min, and the coating time is 15 to 20 min, forming a porous shell sphere with a thickness of 3 to 5 mm outside the core.

[0022] Furthermore, in step S3, the heating rate of the calcination is 5°C / min, and the holding time is 1.5h.

[0023] Compared with existing technologies, the present invention provides a slag-forming dephosphorizing agent for converter steelmaking. This agent organically integrates a core-shell hierarchical structure design, a B-Ti-Li multi-element fluorine-free fluxing system, and a Li2O-CeO2 bi-component interface activation, achieving highly efficient dephosphorization throughout the converter blowing cycle. Utilizing the gradient release characteristics of the core-shell structure, the outer shell rapidly forms slag at low temperatures, while the core releases alkali at a uniform rate, precisely matching the dephosphorization requirements at each stage, resulting in a high overall dephosphorization rate. Furthermore, the fluorine-free fluxing system completely replaces fluorite, and the simultaneous introduction of MgO furnace protection components counteracts low-melting-point slag erosion, effectively extending furnace life compared to conventional fluorine-free systems. Its bi-component interface regulation enhances dephosphorization kinetics from both interfacial and bulk mass transfer dimensions, effectively improving the phosphorus mass transfer system and shortening slag-forming time. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0025] Figure 1The flowchart illustrates the preparation method of the slag dephosphorizing agent for converter steelmaking provided by this invention. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] Example 1:

[0028] The slag dephosphorizing agent for converter steelmaking in this embodiment has an overall particle size of 21-25 mm and a porous outer shell to dense core mass ratio of 3:7. The porous outer shell is 3 mm thick with a porosity of 28%, and its mass percentage composition is: 50% iron oxide scale, 30% fluorine-free composite flux, 12% light-burned magnesia powder, and 8% lithium carbonate; wherein the fluorine-free composite flux contains borax and ilmenite in a mass ratio of 2:1. The dense core has a particle size of 15 mm, a density of 88%, and a porosity of 8%, and its mass percentage composition is: 65% active lime, 22% converter steel slag powder, 8% alumina powder, and 5% cerium oxide.

[0029] The iron oxide scale contains 72% total iron, of which Fe2O3 accounts for 65% of the total iron. The iron oxide scale is the main component in the outer shell that provides the oxidizing power required for dephosphorization. At the same time, the composite oxide formed by the scale and flux has a low melting point and forms the matrix of the low-temperature slag.

[0030] The fluorine-free composite flux is composed of borax and ilmenite in a mass ratio of 1.8:1. Based on the total mass of the porous shell, the borax content is 16%, and the ilmenite content is 12%. The borax is industrial-grade sodium tetraborate decahydrate, with the chemical formula Na₂B₄O₇·10H₂O. It melts at approximately 740℃ to form a borate glass phase, which can rapidly dissolve surrounding oxides and is the core component for initiating low-temperature slag formation. The ilmenite contains 48% TiO₂ and 33% total iron. TiO₂ forms a low-melting-point eutectic phase with CaO and FeO below 1200℃, synergistically enhancing the fluxing effect with borax while supplementing iron. The blend of borax and ilmenite achieves a connection and expansion of the melting temperature range, allowing the shell to maintain high active melting capacity continuously within the range of 1100–1250℃, resulting in a fluxing effect superior to either component used alone.

[0031] The MgO content in the lightly calcined magnesia powder is 92%. It is introduced into the slag in the early stage of blowing to maintain the MgO content in the slag at 6% to 8%. By inhibiting the slag's tendency to dissolve MgO in the magnesia-carbon bricks, the erosion of the furnace lining by the low-melting-point slag system is reduced.

[0032] Lithium carbonate: Contains 99% Li₂CO₃, which decomposes at low temperatures to form Li₂O. Li₂O is a strongly basic network modifier that can significantly disrupt the silicon-oxygen complex anionic network in the slag, reducing slag viscosity; simultaneously, Li… +It accumulates at the steel-slag interface, reducing interfacial tension by more than 20%, and increases the mass transfer coefficient of phosphorus from molten steel to slag by more than 30%, thus accelerating the dephosphorization reaction from a kinetic perspective.

[0033] Furthermore, within its dense core, the active lime contains 94% CaO and has an activity level of 320 mL. Active lime possesses high reactivity and rapid dissolution characteristics, making it a core alkaline component providing the high alkalinity required for dephosphorization.

[0034] Converter slag powder: basicity 3.2, free CaO content 10%, all particles pass through a 200-mesh sieve. Converter slag powder realizes the resource utilization of metallurgical solid waste. The free CaO can replenish the basicity, while the already formed mineral phases such as dicalcium silicate and tricalcium silicate can serve as heterogeneous nucleation cores for the dephosphorization product calcium phosphate, reducing the nucleation barrier for calcium phosphate precipitation, promoting the rapid precipitation of dephosphorization products from the slag, and continuously shifting the reaction equilibrium in the positive direction.

[0035] Alumina powder: Al2O3 content is 99%. During the mid-stage of blowing, when the slag basicity continues to rise, Al2O3 preferentially forms a low-melting-point calcium aluminum feldspar phase with CaO and SiO2 in the slag, which destroys the dense network structure formed by dicalcium silicate under high basicity conditions, effectively preventing the slag viscosity from rising sharply and the phenomenon of re-drying, and ensuring the continuous dissolution channel of the dense core lime.

[0036] Cerium oxide plays a dual role: firstly, CeO2 combines with the phosphate ions generated during dephosphorization to form a cerium phosphate composite phase with superior high-temperature stability compared to tricalcium phosphate, thus thermodynamically locking in phosphorus and inhibiting phosphorus reversion under the high-temperature conditions at the end of the blowing process; secondly, Ce... 4+ As a high-valence cation, it can effectively break the complex silicon-oxygen network structure in slag, reduce the viscosity of the slag bulk, optimize the mass transfer conditions of the molten pool in the middle and later stages, and form a bi-component synergistic activation effect with Li2O in the shell.

[0037] The preparation method is as follows:

[0038] S1. Core high-pressure molding: Weigh all the raw materials of the core according to the formula, ball mill for 2.5 hours, and the 200 mesh passing rate is 92%; add 4% of the total mass of the core powder as bentonite binder and mix evenly, press into φ15mm pellets under 18MPa pressure, and dry at 200℃ for 2 hours to obtain dense core green pellets.

[0039] S2. Disc coating granulation: Weigh the raw materials for the outer shell according to the formula, ball mill them to 180 mesh with a passing rate of 88%, add water glass binder accounting for 3% of the total mass of the outer shell powder and mix evenly; place the core green balls in a disc granulator, tilt at 45°, rotate at 22 r / min, spray in atomized water and add coating powder in batches, coat for 18 min to obtain green balls with outer shell and outer shell thickness of 3 mm.

[0040] S3. Low-temperature calcination and curing: Heat to 850℃ at 5℃ / min, hold for 1.5h, and after natural cooling, sieve to obtain the finished product. The compressive strength of the finished product is 58N / ball.

[0041] The dephosphorizing agent in this embodiment is compatible with conventional top and bottom blowing converter steelmaking processes, requiring no equipment modifications.

[0042] Taking the smelting of ordinary carbon steel in a 120t top-and-bottom combined blowing converter as an example, the initial phosphorus content of the molten iron is 0.105%, and the final target phosphorus content is ≤0.015%. Before blowing begins, the dephosphorizing agent of this embodiment is added to the converter along with the scrap steel and molten iron, with an addition amount of 18kg / t steel.

[0043] The mechanism of action of dephosphorizing agents throughout the entire blowing cycle can be divided into three stages:

[0044] Phase 1: Early Stage of Blowing (0–5 min, molten pool temperature 1200–1400℃): The porous outer shell rapidly absorbs heat and heats up due to its high porosity and large specific surface area. Borax melts first at approximately 740℃, forming a liquid borate phase and rapidly dissolving iron oxide scale and ilmenite, forming a low-melting-point slag of FeO-TiO2-B2O3 at around 1200℃. This slag system has a melting point of only about 1180–1250℃, achieving low-temperature and rapid slag formation without the need for fluorite. The FeO content in the slag reaches 28%–32% within the first 5 min, providing ample oxidizing conditions for dephosphorization. Li2O simultaneously enters the slag phase, reducing the steel-slag interfacial tension and accelerating phosphorus mass transfer, achieving a dephosphorization rate of 50% in the early stage. MgO in the outer shell also dissolves simultaneously, maintaining the MgO content in the slag at around 7%, protecting the furnace lining.

[0045] Phase Two: Mid-stage of blowing (5–12 min, molten pool temperature 1400–1600℃): The outer shell has completely melted, and the slag gradually penetrates inward through the micropores on the surface of the core. The dense core begins to dissolve slowly and uniformly, continuously releasing CaO into the slag. The slag basicity gradually increases from 2.2 in the early stage to 3.3, achieving gradient alkali increase and avoiding slag re-drying and lime agglomeration caused by concentrated lime addition in traditional processes. Alumina powder reacts with CaO and SiO2 to form a calcium aluminum feldspar phase, ensuring the fluidity of the slag under high basicity. Calcium silicate minerals in converter steel slag powder provide a large number of heterogeneous nucleation sites, promoting the rapid precipitation and growth of dephosphorization products 3CaO·P2O5. CeO2 combines with phosphate to form a stable CePO4 composite phase, while simultaneously breaking up the silica-oxygen network to reduce slag viscosity. By the end of this stage, the total dephosphorization rate reaches 88%.

[0046] Stage 3: Late stage of blowing (12 minutes to the endpoint, endpoint temperature approximately 1650℃): The dense core has been almost completely dissolved, the slag basicity is stable at 3.5, and the FeO content remains at around 18%. The high-temperature stable phosphate phase locked by CeO2 and the appropriate slag viscosity regulated by MgO work together to maintain a high phosphorus capacity in the slag at the endpoint high temperature, effectively inhibiting phosphorus reversion. The endpoint test showed that the phosphorus content of the molten steel was 0.012%, and the phosphorus reversion rate was only 2.5%.

[0047] This embodiment eliminates the use of fluorite throughout the entire process, thus removing fluorine pollution at its source. Simultaneously, the accelerated slag formation speed shortens the smelting cycle by approximately 2 minutes, improving converter operation efficiency.

[0048] Example 2:

[0049] The dephosphorizing agent for converter steelmaking in this embodiment has an overall particle size of 25-30 mm and a porous outer shell to dense core mass ratio of 4:6. The porous outer shell is 5 mm thick with a porosity of 32%, and its mass percentage composition is: 45% iron oxide scale, 33% fluorine-free composite flux, 15% light-burned magnesia powder, and 7% lithium carbonate; wherein the fluorine-free composite flux contains borax and ilmenite in a mass ratio of 1.5:1. The dense core has a particle size of 18 mm, a density of 86%, and a porosity of 9%, and its mass percentage composition is: 70% active lime, 18% converter steel slag powder, 7% alumina powder, and 5% cerium oxide.

[0050] The preparation method is as follows:

[0051] S1. Core High-Pressure Molding: Weigh all the raw materials for the core according to the formula, ball mill for 2 hours, and the 200-mesh passing rate is 91%; add 3.5% bentonite binder of the total mass of the core powder and mix evenly, press into φ18mm pellets under 16MPa pressure, and dry at 190℃ for 2 hours to obtain dense core green pellets.

[0052] S2. Disc Coating Granulation: Weigh all the raw materials for the outer shell according to the formula, ball mill them to 180 mesh with a passing rate of 86%, add water glass binder accounting for 2.5% of the total mass of the outer shell powder and mix evenly; place the core green balls in a disc granulator, tilt at 50°, rotate at 20 r / min, spray in atomized water and add coating powder in batches, coat for 20 min to obtain green balls with outer shell and outer shell thickness of 5 mm.

[0053] S3. Low-temperature calcination and curing: Heat to 800℃ at 5℃ / min, hold for 1.5h, and after natural cooling, sieve to obtain the finished product. The compressive strength of the finished product is 52N / ball.

[0054] Example 3:

[0055] The slag dephosphorizing agent for converter steelmaking in this embodiment has an overall particle size of 23-27 mm and a porous outer shell to dense core mass ratio of 3.5:6.5. The porous outer shell is 4 mm thick with a porosity of 30%, and its mass percentage composition is: 55% iron oxide scale, 25% fluorine-free composite flux, 13% light-burned magnesia powder, and 7% lithium carbonate; wherein the fluorine-free composite flux contains borax and ilmenite in a mass ratio of 1.8:1. The dense core has a particle size of 16 mm, a density of 90%, and a porosity of 7%, and its mass percentage composition is: 62% active lime, 25% converter steel slag powder, 8% alumina powder, and 5% cerium oxide.

[0056] The preparation method is as follows:

[0057] S1. Core High-Pressure Molding: Weigh all the raw materials for the core according to the formula, ball mill for 3 hours, and the 200-mesh pass rate is 93%; add 5% bentonite binder of the total mass of the core powder and mix evenly, press into φ16mm pellets under 20MPa pressure, and dry at 180℃ for 2 hours to obtain dense core green pellets.

[0058] S2. Disc Coating Granulation: Weigh all the raw materials for the outer shell according to the formula, ball mill them to 180 mesh with a passing rate of 90%, add 4% water glass binder of the total mass of the outer shell powder and mix evenly; place the core green balls in a disc granulator, tilt at 48°, rotate at 25 r / min, spray in atomized water and add coating powder in batches, coat for 15 min to obtain green balls with outer shell and outer shell thickness of 4 mm.

[0059] S3. Low-temperature calcination and curing: Heat to 900℃ at 5℃ / min, hold for 1.5h, and after natural cooling, sieve to obtain the finished product. The compressive strength of the finished product is 65N / ball.

[0060] Comparative Example 1:

[0061] The traditional lime-fluorite slag-forming system consists of 85% active lime and 15% fluorite. It is a physical mixture of conventional lime particles and fluorite particles without a core-shell structure.

[0062] Comparative Example 2:

[0063] The common fluorine-free composite dephosphorizing agent has the same total composition as in Example 1. All raw materials are mixed evenly and then directly pressed into spheres, without a core-shell layered structure. The preparation process is to press the spheres once and then calcine them at 900°C for curing.

[0064] Experimental comparison:

[0065] The above-described Examples 1, 2, and 3, along with Comparative Examples 1 and 2, were subjected to industrial trials on a 120t top-and-bottom combined blowing converter. The initial phosphorus content of the molten iron was 0.10%–0.12%, the final temperature was controlled at 1650±20℃, and the amount of dephosphorizing agent added was 20 kg / t steel. The test results are shown in the table below:

[0066] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Initial slag formation time (min) 3.2 2.8 3.0 5.5 4.8 Initial phosphorus removal rate (%) 52 55 53 35 41 Total dephosphorization rate (%) 93.5 94.2 93.8 84.3 86.7 Final phosphorus recovery rate (%) 2.2 1.8 2.0 6.5 5.2 Furnace lining erosion rate (mm / furnace) 0.11 0.10 0.11 0.15 0.18

[0067] The experimental results show that:

[0068] The slag formation time in this embodiment is significantly shorter than that in the two comparative examples, and the dephosphorization rate in the early stage is increased by 10-20 percentage points, verifying the low-temperature rapid slag formation effect of the B-Ti-Li fluorine-free system and the pre-dephosphorization advantage of the core-shell structure; the total dephosphorization rate can reach more than 93%, which is more than 9 percentage points higher than that of the traditional system, and the phosphorus recovery rate is controlled within 2.5%, which is much lower than that of the comparative examples, proving the effectiveness of the gradient dephosphorization design and the phosphorus stabilization effect of CeO2;

[0069] Furthermore, the erosion rate of the furnace lining in this invention is significantly lower than that of the traditional fluorite system and the ordinary fluorine-free system, proving that the MgO furnace protection component effectively counteracts the erosion of low-melting-point slag and achieves synergy between fluorine-free slag and furnace lining protection. By comparing Example 1 and Comparative Example 2, it can be seen that, under the condition that the total composition is completely consistent, the dephosphorization effect of the core-shell layered structure is significantly better than that of the homogeneous mixed structure, proving that the core-shell physical structure design of this invention is not a simple superposition of components, but achieves an essential improvement in performance through functional grading and rhythm regulation.

[0070] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A slag dephosphorizing agent for converter steelmaking, characterized in that, The dephosphorizing agent consists of a dense core and a porous shell covering the outer surface of the dense core, forming a spherical core-shell structure with an overall particle size of 21-30 mm. The mass ratio of the porous shell to the dense core is 3:7-4:

6. The porous shell is a porous structure formed by low-temperature sintering, with a porosity of 25% to 35%, and is composed of the following components by mass percentage: 40% to 55% iron oxide scale, 18% to 33% fluorine-free composite flux, 5% to 10% lightly calcined magnesium oxide powder, and 2% to 5% interface activator; The dense core is a high-pressure formed dense structure with a density ≥85% and a porosity ≤10%, and is composed of the following components by mass percentage: 60%–70% active lime, 15%–25% converter steel slag powder, 5%–8% alumina powder, and 2%–4% cerium oxide.

2. The slag dephosphorizing agent for converter steelmaking according to claim 1, characterized in that, The fluorine-free composite flux is composed of borax and ilmenite mixed in a mass ratio of 2:1 to 1.5:1; the interface activator is lithium carbonate.

3. The slag dephosphorizing agent for converter steelmaking according to claim 1, characterized in that, The total iron content of the iron oxide scale is ≥70%, of which Fe2O3 accounts for ≥60% of the total iron content; the MgO content in the lightly calcined magnesium oxide powder is ≥90%.

4. The slag dephosphorizing agent for converter steelmaking according to claim 1, characterized in that, The active lime has a CaO content of ≥92% and an activity of ≥300mL; the converter steel slag powder has an alkalinity of ≥3.0, a free CaO content of ≥8%, and a particle size of 200 mesh.

5. The slag dephosphorizing agent for converter steelmaking according to claim 1, characterized in that, The thickness of the porous outer shell is 3-5 mm; the particle size of the dense core is 15-20 mm; and the compressive strength of the dephosphorizing agent product is ≥50 N / ball.

6. A method for preparing a slag-reducing dephosphorizing agent for converter steelmaking, used to prepare the slag-reducing dephosphorizing agent as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh each raw material according to the formula for dense core, dry grind until the 200 mesh passing rate is ≥90%, add bentonite binder and mix evenly, press into pellets under 15-20MPa pressure, and dry at 180-200℃ to obtain dense core green pellets. S2. Weigh each raw material according to the porous shell formula, dry grind until the 180 mesh passing rate is ≥85%, add water glass binder and mix evenly to obtain coating powder; place the dense core green balls in a disc granulator, spray atomized water while rolling and add coating powder in batches to form green balls with shells. S3. The coated green pellets are heated to 800-900℃ and roasted. After natural cooling, they are sieved to obtain the finished dephosphorizing agent.

7. The method for preparing a slag dephosphorizing agent for converter steelmaking according to claim 6, characterized in that, In step S1, the amount of bentonite binder added is 3% to 5% of the total mass of the core powder, and the drying time is 2 hours.

8. The method for preparing a slag dephosphorizing agent for converter steelmaking according to claim 6, characterized in that, In step S2, the amount of water glass binder added is 2% to 4% of the total mass of the shell powder, the tilt angle of the disc granulator is 45° to 50°, the rotation speed is 20 to 25 r / min, and the coating time is 15 to 20 min, forming a porous shell sphere with a thickness of 3 to 5 mm outside the core.

9. The method for preparing a slag dephosphorizing agent for converter steelmaking according to claim 6, characterized in that, In step S3, the heating rate of the calcination is 5°C / min, and the holding time is 1.5h.

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