Dephosphorization slag system and dephosphorization method for smelting high-quality steel through electric arc furnace with high scrap ratio

Abstract

The invention relates to a dephosphorization slag system for smelting high-quality steel by an electric arc furnace with a high scrap ratio and a dephosphorization method, belongs to the field of steel making of the electric arc furnace in ferrous metallurgy, and solves the contradiction between the dephosphorization difficulty of the electric arc furnace and the requirements of low phosphorus content and high cleanliness of the high-quality steel in the prior art. The method has important significance in promoting large-scale efficient production of the green low-carbon high-quality steel and improving international market competitiveness. The dephosphorization slag system for smelting the high-quality steel by the electric furnace with the high scrap steel ratio is realized and comprises the following components in percentage by mass: 24 to 31 weight percent of FeO, 2 to 6 weight percent of MgO, 44 to 56 weight percent of CaO, 14 to 21 weight percent of SiO2 and 2.4 to 3.1 weight percent of R. The alkalinity R is the mass ratio of the component CaO to the component SiO2; and the balance of 1-5% by mass of the metal oxide. According to the technical scheme, the quality of the molten steel is improved, the high-quality steel is finally obtained, the phosphorus content in the molten steel smelted through the electric furnace is reduced to 0.01 wt% or below, and an example is provided for smelting the high-quality steel through the electric furnace with the high scrap steel ratio.

Description

Technical Field

[0001] This invention relates to the field of electric arc furnace steelmaking in iron and steel metallurgy, and particularly to a high-phosphorus capacity dephosphorization slag system and dephosphorization method for high-quality steel smelting in electric arc furnaces. Background Technology

[0002] my country is a major steel producer. As a typical iron-coal chemical production process within the industrial sector, the steel industry is a major emitter of CO2. Currently, many countries have formulated and implemented relevant policies and regulations to address carbon emissions. These measures not only exert external pressure on the steel industry to reduce emissions but also create an urgent requirement for it to achieve green and low-carbon smelting. Against this backdrop, how to design high-quality steel suitable for green and low-carbon processes, thereby enhancing the market competitiveness of steel products, has become a significant challenge and an urgent issue for the steel industry. Establishing green, high-quality steel production lines is the trend, and solving the problems of the electric arc furnace steelmaking process is a key link.

[0003] Compared to converter steelmaking, high scrap ratio electric arc furnace (EAF) steelmaking presents a challenge due to the characteristics of its raw materials, processes, and equipment. EAFs face a contradiction between the difficulty of dephosphorization and the requirement for low phosphorus content and high cleanliness in high-quality steel. Traditional EAFs typically require multiple slag-making and slag-removal operations when smelting low-phosphorus steel, resulting in longer smelting cycles and larger slag volumes. This is extremely detrimental to large-scale, efficient smelting of high-quality steel and hinders the development of low-carbon, green, high-quality steel.

[0004] For general steel grades, the phosphorus content is typically required to be no more than 0.020 wt%, but for high-quality steel, the phosphorus content needs to be controlled below 0.010 wt%. Currently, the main method for achieving a low final phosphorus content is through converter long-process smelting technology, thus meeting the phosphorus content requirements for high-quality steels such as high-end automotive steel and high-grade pipeline steel. However, this process has high carbon emissions. In contrast, electric arc furnace smelting processes using high scrap ratios or even all scrap steel help reduce carbon emissions. However, high scrap ratio electric arc furnace smelting processes result in large fluctuations in phosphorus content after melting and cleaning. Furthermore, the low carbon content, high viscosity of the molten steel, and lack of CO reaction lead to poor molten pool kinetics. The slag system used in traditional electric arc furnace dephosphorization processes has a final slag phosphorus content of only 1–3 wt%, and the final phosphorus content can usually only be controlled below 0.020 wt%, making it difficult to further reduce it to meet the production requirements of high-quality steel. Summary of the Invention

[0005] Based on the above analysis, this invention relates to a dephosphorization slag system and dephosphorization method for high-quality steel smelting in an electric arc furnace with a high scrap ratio, which is used to solve the contradiction between the existing difficulties in dephosphorization in electric arc furnaces and the requirement for low phosphorus content and high cleanliness of high-quality steel, and to realize the production of high-quality steel under the condition of high scrap ratio in electric arc furnace.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] On one hand, the present invention provides a dephosphorization slag system for high-quality steel smelting in an electric arc furnace with a high scrap ratio, the components of which, by mass percentage, include: 24-31 wt% FeO, 2-6 wt% MgO, 44-56 wt% CaO, 14-21 wt% SiO2, and 1-5 wt% balance metal oxides.

[0008] Furthermore, the alkalinity R of the dephosphorization slag system is 2.5-3, where R is the mass ratio of component CaO to component SiO2.

[0009] Furthermore, the remaining metal oxides include Al2O3, MnO, and Cr2O3.

[0010] Preferably, the components, by mass percentage, include: 25-30 wt% FeO, 3-5 wt% MgO, 45-55 wt% CaO, 15-20 wt% SiO2; and 1-5 wt% balance metal oxides.

[0011] Furthermore, the alkalinity R of the dephosphorization slag system is 2.5-3, where R is the mass ratio of component CaO to component SiO2.

[0012] Furthermore, the remaining metal oxides include Al2O3, MnO, and Cr2O3.

[0013] On the other hand, the present invention provides a method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions, the specific steps of which are as follows:

[0014] Step S1: Add furnace charge into the electric arc furnace;

[0015] Step S2: Slag formation and dephosphorization;

[0016] Step S3: Smelting ends and steel is tapped.

[0017] Furthermore, in step S1, the furnace charge is: scrap steel mixed with molten iron and dephosphorized slag, wherein the mass ratio of scrap steel in the molten iron is 80-100 wt%.

[0018] Furthermore, in step S2, slag formation and dephosphorization are carried out in two stages.

[0019] Furthermore, in step S2, the timing of slag formation and dephosphorization is as follows: slag formation and dephosphorization during the melting period of scrap steel when the arc is ignited by electric current.

[0020] Furthermore, in step S2, the timing of secondary slag formation and dephosphorization is as follows: slag removal is performed in the middle and late stages of melting; secondary slag formation and dephosphorization are performed after the furnace is cleared.

[0021] Furthermore, in step S2, oxygen is injected to aid melting during slag formation and dephosphorization. Simultaneously, oxygen, as an essential oxidant for the dephosphorization reaction, enters the furnace to participate in the dephosphorization reaction. The injected oxygen flow rate is 1.2-1.4 Nm³. 3 / t.

[0022] Furthermore, in step S2, an appropriate amount of carbon powder is sprayed, and the particle size of the carbon powder is set to 2-4 mm.

[0023] Furthermore, in step S3, after the phosphorus content in the molten steel is reduced to the target value, it undergoes subsequent production process to achieve the production of high-quality low-phosphorus steel.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] (1) The dephosphorization slag system of the present invention reduces the phosphorus content in the molten steel produced by electric arc furnace to below 0.01 wt%, providing an example for high scrap ratio electric arc furnace smelting of high-quality steel.

[0026] (2) The dephosphorization slag system of the present invention has good dephosphorization effect and requires fewer slag-forming times, only two slag-forming dephosphorization steps are needed. The smelting cycle is controlled within 45 minutes, which shortens the smelting cycle.

[0027] (3) The dephosphorization slag system of the present invention makes the dephosphorization effect of electric arc furnace under high scrap steel ratio conditions better and improves the dephosphorization rate of electric arc furnace.

[0028] (4) The dephosphorization slag system of the present invention does not contain slag-forming agents such as fluorite, which saves production costs and avoids environmental pollution.

[0029] (5) The dephosphorization slag system of the present invention is suitable for use in electric arc furnace smelting of high quality steel under high scrap steel ratio conditions, while most other electric arc furnace slag systems are suitable for electric arc furnace smelting of high quality steel under high iron-to-water ratio conditions.

[0030] (6) The dephosphorization slag system of the present invention is suitable for use in electric arc furnace smelting of low-phosphorus high-quality steel. Most other electric arc furnace slag systems are suitable for electric arc furnace smelting of high-carbon steel, rebar and other ordinary steel grades with low phosphorus content requirements.

[0031] (7) The method of dephosphorizing high-quality steel smelting in electric arc furnace under high scrap ratio and low carbon conditions of the present invention effectively solves the contradiction between the difficulty of dephosphorizing in electric arc furnace and the requirement of low phosphorus content and high cleanliness of high-quality steel, solves the problem of efficient dephosphorization, thereby improving the quality of molten steel, saving production components, and increasing the economic benefits of steel enterprises.

[0032] (8) The method of dephosphorizing high-quality steel smelting in electric arc furnace under high scrap ratio and low carbon conditions of the present invention is adopted. Slag discharge operation is carried out in the later stage of dephosphorization melting to prevent phosphorus reversion.

[0033] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained through the specific points highlighted in the description. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0035] Compared to converter steelmaking, high scrap ratio electric arc furnace (EAF) steelmaking presents a challenge due to the characteristics of its raw materials, processes, and equipment. EAFs face a contradiction between the difficulty of dephosphorization and the requirement for low phosphorus content and high cleanliness in high-quality steel. Traditional EAFs typically require multiple slag-making and slag-removal operations when smelting low-phosphorus steel, resulting in longer smelting cycles and larger slag volumes. This is extremely detrimental to large-scale, efficient smelting of high-quality steel and hinders the development of low-carbon, green, high-quality steel.

[0036] For general steel grades, the phosphorus content is typically required to be no more than 0.020 wt%, but for high-quality steel, the phosphorus content needs to be controlled below 0.010 wt%. Currently, the main method for achieving a low final phosphorus content is through converter long-process smelting technology, thus meeting the phosphorus content requirements for high-quality steels such as high-end automotive steel and high-grade pipeline steel. However, this process has high carbon emissions. In contrast, electric arc furnace smelting processes using high scrap ratios or even all scrap steel help reduce carbon emissions. However, high scrap ratio electric arc furnace smelting processes result in large fluctuations in phosphorus content after melting and cleaning. Furthermore, the low carbon content, high viscosity of the molten steel, and lack of CO reaction lead to poor molten pool kinetics. The slag system used in traditional electric arc furnace dephosphorization processes has a final slag phosphorus content of 1–3 wt%, and the final phosphorus content can usually only be controlled below 0.020 wt%, making it difficult to further reduce it to meet the production requirements of high-quality steel.

[0037] Based on the above analysis, this invention provides a dephosphorization slag system for high-scrap-ratio electric arc furnace (EAF) smelting of high-quality steel, and a dephosphorization method for EAF smelting of high-quality steel under high scrap-ratio and low-carbon conditions. This addresses the contradiction between the difficulties in dephosphorization in existing EAFs and the requirement for low phosphorus content and high cleanliness in high-quality steel, enabling the production of high-quality steel under high scrap-ratio EAF conditions. This invention resolves the contradiction between the difficulties in dephosphorization in high scrap-ratio EAFs and the requirement for low phosphorus content and high cleanliness in high-quality steel, and is of great significance for promoting the large-scale and efficient production of green, low-carbon, high-quality steel and enhancing its competitiveness in the international market.

[0038] This invention is mainly achieved through the following technical solutions:

[0039] On one hand, the present invention provides a dephosphorization slag system for high-quality steel smelting in an electric arc furnace with a high scrap ratio, the components of which, by mass percentage, include: 24-31 wt% FeO, 2-6 wt% MgO, 44-56 wt% CaO, 14-21 wt% SiO2, 2.4-3.1R, and 1-5 wt% balance metal oxides.

[0040] Furthermore, the alkalinity R of the dephosphorization slag system is 2.5-3, where R is the mass ratio of component CaO to component SiO2.

[0041] Furthermore, the remaining metal oxides include Al2O3, MnO, and Cr2O3.

[0042] The slag components are formulated by mass fraction. Among them, alkaline oxides such as MgO and MnO reduce the erosion of the furnace lining by the slag, the specific range of FeO content ensures the oxidizing properties of the slag, and the specific range of CaO and SiO2 content ensures the alkalinity of the slag, which is the key to the slag's dephosphorization ability.

[0043] CaO combines with oxidized P2O5 to form stable calcium phosphate (3CaO·P2O5 or 4CaO·P2O5), which is the final outcome of the dephosphorization reaction. It provides basicity: It is the molecule of slag basicity (R = CaO / SiO2), and high basicity is a prerequisite for high phosphorus capacity. If the content is insufficient, the basicity is insufficient, the dephosphorization reaction cannot proceed to completion, and the final phosphorus content will inevitably exceed the standard. If the content is too high, the slag melting point increases significantly, leading to difficulties in slag formation.

[0044] FeO oxidizes [P] in molten steel to (P₂O₅), which is the first step in the dephosphorization reaction. It forms low-melting-point calcium ferrite with CaO, which is crucial for ensuring the low melting point and good fluidity of the slag system. If the FeO content is too low, phosphorus cannot be fully oxidized, resulting in insufficient driving force for the dephosphorization reaction. Excessive FeO will dilute the CaO concentration in the slag and, to some extent, reduce the phosphorus capacity of the slag, thereby reducing the slag's dephosphorization capacity.

[0045] SiO2: Reacts with CaO to form calcium silicate, constituting the matrix of slag. Basicity regulator: As the denominator in the basicity formula, its content directly determines the basicity R of the slag. If the content is too low, it will lead to difficulties in slag formation. If the content is too high, the basicity (R) will decrease significantly, the phosphorus capacity of the slag will drop sharply, and the dephosphorization capacity will be lost.

[0046] MgO: An appropriate amount of MgO can prevent the slag from becoming too thin at high temperatures, helping to maintain the stability of the foamed slag. Excessive MgO will raise the slag melting point, reduce its fluidity, and make it "viscous," which is detrimental to slag formation and mass transfer, thus ruining the foaming effect. Too little MgO will cause erosion of the furnace lining, increasing furnace lining maintenance costs.

[0047] Cr2O3 can optimize slag composition, promote phosphorus oxidation, and reduce phosphorus reversion. Al2O3 lowers the slag melting point and improves slag fluidity. MnO acts as a flux to improve slag fluidity; all three metal oxides contribute to dephosphorization. Al2O3, MnO, and Cr2O3 can be added in any ratio, with their mass percentage in the dephosphorizing slag system controlled at 1-5 wt%. Excessive or insufficient total amount of the remaining metal oxides can negatively impact the carefully designed slag system, altering its physicochemical properties and causing the melting point and viscosity to deviate from the optimal range, resulting in unstable dephosphorization. Maintaining the mass percentage of Al2O3, MnO, and Cr2O3 within the dephosphorizing slag system within 1-5 wt% allows them to exert their beneficial dephosphorization effects.

[0048] Preferably, in the balance of metal oxides, the aluminum oxide content is controlled between 2-4 wt%, and the manganese oxide content is controlled between 0.9-2.5 wt%.

[0049] This invention achieves a precise design of the "chemical reaction system" of the dephosphorization slag system by strictly controlling the composition and content of the components and leveraging the synergistic effect between them. Deviating from the design will disrupt its internal balance, potentially leading to a series of chain reactions such as "increased melting point, failure of foamed slag, and decreased phosphorus capacity." The dephosphorization slag system of this invention enables excellent dephosphorization performance even under harsh conditions with high scrap steel ratios.

[0050] Preferably, the components, by mass percentage, include: 25-30 wt% FeO, 3-5 wt% MgO, 45-55 wt% CaO, 15-20 wt% SiO2, with the remainder being 1-5 wt% metal oxides.

[0051] Furthermore, R is 2.5-3, where R is the mass ratio of component CaO to component SiO2.

[0052] For example, in the dephosphorization slag system, the mass percentage of FeO is 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, and 31wt%; the mass percentage of MgO is 2wt%, 3wt%, 4wt%, 5wt%, and 6wt%; the mass percentage of CaO is 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%, 54wt%, 55wt%, and 56wt%; and the mass percentage of SiO2 is 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, and 21wt%.

[0053] This dephosphorization slag system is a specific component and performance dephosphorization slag system with good low melting point and foaming effect. The melting point range of the dephosphorization slag system of this invention is 1470-1510 degrees Celsius.

[0054] The slag system of this invention is a high-performance, specialized, and green slag system designed to achieve the goal of "ultra-low phosphorus" under the premise of "fluorine-free" by precise proportion of "high FeO and high alkalinity" and under the conditions of "high scrap steel ratio and weak stirring".

[0055] The dephosphorization slag system of the present invention has the following characteristics:

[0056] (1) Fluorine-free, i.e., free of calcium fluoride. In traditional slag systems, calcium fluoride is added in large quantities due to its property of significantly lowering the melting point of slag, resulting in environmental pollution. This invention achieves this by utilizing specific alkalinity and appropriate amounts of alumina and manganese oxide.

[0057] (2) This slag system has good fluidity, low melting point, and strong dephosphorization ability. Experimental results show that it is suitable for electric furnace dephosphorization under conditions of high scrap ratio and low carbon.

[0058] The dephosphorization slag system of this invention achieves a low melting point through alkalinity control and the addition of components such as alumina and manganese oxide. This results in a low-melting-point slag system that is neither too sticky nor too thin. By combining the low melting point with injected carbon powder, a carbon-oxygen reaction occurs in the molten pool to generate CO bubbles. The combination of the two allows the CO bubbles to escape from the slag, resulting in a "foam slag" effect. The foam slag increases the contact reaction area between the slag and the molten steel, thereby improving the dephosphorization effect.

[0059] During the scrap steel melting period, the molten pool temperature is low. If the slag cannot melt, the dephosphorization reaction is impossible. The low melting point of the dephosphorization slag system of this invention ensures that liquid active slag can be rapidly formed at low temperatures, capturing and oxidizing [P] in the molten steel immediately, making full use of the favorable thermodynamic conditions for the dephosphorization reaction at low temperatures. This is the first and decisive step in achieving efficient dephosphorization. The foaming slag effect causes the slag volume to expand several times, greatly increasing the steel-slag reaction contact area, allowing phosphorus to be transferred from the molten steel to the slag more quickly. The foaming process itself forms the most effective mechanical stirring for the molten pool. The generation and rising of CO bubbles violently agitate the molten steel and slag, greatly improving the reaction kinetics, solving the core problem of "viscous and slow mass transfer" in high scrap steel ratio molten pools, and ensuring that the dephosphorization reaction can still proceed rapidly even at higher temperatures in the later stages.

[0060] R represents basicity. If the basicity is too high, more CaO will be used, leading to material waste and causing the slag to easily clump, resulting in poor dephosphorization. If the basicity is too low, there will be insufficient dephosphorizing agent, resulting in poor dephosphorization and failure to meet the final phosphorus requirements for high-quality steel.

[0061] On the other hand, the present invention also provides a method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions, comprising the following steps:

[0062] Step S1: Scrap steel is added using a horizontal vibration continuous feeding method, and furnace charge is added into the electric arc furnace;

[0063] Step S2: Slag formation and dephosphorization;

[0064] Step S3: Smelting ends and steel is tapped.

[0065] In step S1, the addition of high scrap steel ratio furnace charge specifically involves: adding scrap steel to molten iron and dephosphorization slag system, with the mass ratio of scrap steel in the molten iron being 80-100 wt%.

[0066] Compared to traditional converter steelmaking, which uses only molten iron without scrap and has a high carbon content, this invention uses molten iron with a lower content and consequently a lower carbon content. The lower carbon content, higher viscosity of the molten steel, and lack of CO reaction result in unfavorable molten pool kinetics.

[0067] Furthermore, the scrap steel is uniformly cut and preheated before being added.

[0068] Furthermore, the scrap steel is fed into the electric arc furnace using a horizontal vibration continuous feeding method.

[0069] The electric arc furnace adopts the following power supply system: 90-100MVA during the arc ignition period, 95-105MVA during the melting period, and 90-100MVA during the melting and heating period. The melting and heating rates are adjusted in a timely manner according to the oxidation rate of the elements.

[0070] Step S2 includes two slag-forming dephosphorization processes. The first slag-forming process uses 38-42 kg / t of steel, and the second slag-forming process uses 33-37 kg / t of steel. For example, the first slag-forming processes use 38 kg / t of steel, 39 kg / t of steel, 40 kg / t of steel, 41 kg / t of steel, and 42 kg / t of steel; the second slag-forming processes use 33 kg / t of steel, 34 kg / t of steel, 35 kg / t of steel, 36 kg / t of steel, and 37 kg / t of steel.

[0071] Furthermore, the timing of slag formation and dephosphorization is as follows: slag formation and dephosphorization during the melting period of scrap steel; during the melting period of electric arc furnace steelmaking, the temperature of the molten pool is relatively low, providing better thermodynamic conditions for dephosphorization. Slag formation and dephosphorization during the melting period can transfer a large amount of phosphorus from the molten steel into the slag.

[0072] Furthermore, the timing of secondary slag dephosphorization is as follows: slag removal is performed during the mid-to-late stages of melting; secondary slag dephosphorization is then carried out after the furnace is completely cleared. As the dephosphorization reaction proceeds, the FeO content in the slag gradually decreases. To avoid phosphorus reversion, slag removal is performed during the mid-to-late stages of melting. Secondary slag dephosphorization can ensure that the final phosphorus content of the high-quality steel produced reaches a low level, meeting the allowable value for ultra-low phosphorus steel specifications.

[0073] In step S2, the dephosphorization slag system with the above-mentioned specific components and properties is selected. The dephosphorization slag of the electric arc furnace uses the above-mentioned high scrap steel ratio electric arc furnace smelting high-quality steel dephosphorization slag system, while taking into account the stirring of the molten steel.

[0074] Furthermore, scrap steel is added during the initial melting stage to form slag. Simultaneously, dephosphorization slag is added, and oxygen is injected to aid melting. On the other hand, oxygen, as an essential oxidant for the dephosphorization reaction, enters the furnace to participate in the dephosphorization process, enhancing the dephosphorization effect. At this stage, the molten pool temperature is low, and the thermodynamic conditions for dephosphorization are favorable, making it the main stage of dephosphorization.

[0075] Furthermore, during a single slag-forming process, the oxygen injection flow rate is 1.2-1.4 Nm³. 3 / t, while ensuring dephosphorization efficiency, strengthen the stirring of the molten pool and shorten the smelting time.

[0076] Furthermore, during the slag-forming process, carbon powder is injected at a rate of 27-31 kg / t of steel, such as 27 kg / t, 28 kg / t, 29 kg / t, 30 kg / t, and 31 kg / t. The dosage fluctuates depending on the foaming effect of the slag. Once the desired foaming effect is achieved, carbon injection is stopped, and the carbon powder particle size is set to 2-4 mm. Simultaneously, the screen aperture of the carbon powder injection gun is increased accordingly. This ensures smooth powder injection, prolongs the foaming slag maintenance time, provides insulation to prevent nitriding of the molten steel, and enhances the smelting effect. Currently, the particle size of carbon powder injected into electric furnaces is generally required to be 0.5–3 mm. However, for the slag to foam, the carbon powder particle size should be greater than 2 mm. This allows for better reaction with FeO in the slag to generate CO and maintain it for a certain period. Too fine or too coarse a particle size is detrimental. This invention sets the carbon powder particle size to 2-4 mm and increases the screen mesh size, which ensures smooth powder spraying and prolongs the foam slag maintenance time, achieving good metallurgical results.

[0077] Furthermore, slag removal is performed in the later stages of melting to prevent phosphorus reversion in the molten steel. After the furnace is cleared, secondary slag formation and dephosphorization are carried out. During this stage, the molten pool temperature is high and the carbon-oxygen reaction is intense. Maintaining the basicity and oxidizing properties of the slag is crucial to ensure its dephosphorization capacity, thereby reducing the phosphorus content in the molten steel to a low level.

[0078] Furthermore, during the secondary slag formation process, the oxygen injection flow rate is 1.2-1.4 Nm³. 3 / t, while ensuring dephosphorization efficiency, strengthen the stirring of the molten pool and shorten the smelting time. Inject carbon powder at a rate of 27-31 kg / t steel, such as 27 kg / t steel, 28 kg / t steel, 29 kg / t steel, 30 kg / t steel, and 31 kg / t steel; set the carbon powder particle size to 2-4 mm, and at the same time increase the screen mesh size accordingly to ensure smooth powder injection and prolong the foam slag maintenance time, keep the heat insulated from the air to prevent nitriding of the molten steel, and enhance the metallurgical effect.

[0079] In step S3, after the phosphorus content in the molten steel is reduced to the target value, the temperature and composition of the molten steel are adjusted to meet the requirements for high-quality steel smelting and tapping. The molten steel is tapped from the electric arc furnace and then processed through subsequent production processes to achieve the production of high-quality low-phosphorus steel.

[0080] Furthermore, the electric arc furnace smelting cycle is controlled within 45 minutes. The dephosphorization slag system of this invention exhibits good dephosphorization effect, requires fewer slag formations, and achieves dephosphorization through two slag formations. The smelting cycle is controlled within 45 minutes, thus shortening the smelting period. Simultaneously, the phosphorus content in the molten steel smelted in the electric arc furnace can be reduced to below 0.01 wt%.

[0081] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0082] Example 1

[0083] This embodiment uses a 150t electric arc furnace to smelt high-quality automotive sheet steel (the finished steel must have a phosphorus content of P < 0.015%). The specific implementation steps are as follows:

[0084] S1: Adding furnace charge into the electric arc furnace

[0085] The furnace charge ratio, by mass percentage, is 80 wt% scrap steel and 20 wt% molten iron, wherein the scrap steel has been uniformly cut and preheated; the composition of the dephosphorized slag is shown in Table 1. Scrap steel is added using a horizontal vibrating continuous feeding method. The electric arc furnace operates under the following power supply system: 96 MVA during the arc ignition phase, 100 MVA during the melting phase, and 95 MVA during the melting and heating phase. The melting and heating rates are adjusted as needed based on the oxidation rate of the elements.

[0086] S2: Slag Forming and Dephosphorization

[0087] The dephosphorization process involves two stages of slag formation. First, scrap steel is added during the melting period for slag formation at a rate of 38 kg / t of steel, while oxygen is simultaneously injected at a flow rate of 1.3 Nm³. 3 / t; 29kg / t of carbon powder is injected into the steel, with the carbon powder particle size set to 3mm. The screen mesh size is increased accordingly to ensure smooth powder injection and prolong the foam slag maintenance time. Insulation and air isolation prevent nitriding of the molten steel and enhance metallurgical effects. Slag removal is performed in the middle and late stages of melting to prevent phosphorus reversion in the molten steel. After the molten steel is cleared in the furnace, secondary slag formation is carried out, with 37kg / t of slag-forming material added. The composition of the dephosphorized slag is shown in Table 1, with a basicity R of 2.5. Oxygen is injected simultaneously with the addition of slag-forming material at a flow rate of 1.3 Nm³. 3 / t; Injecting carbon powder at 29kg / t steel, setting the carbon powder particle size to 3mm, and correspondingly increasing the screen aperture to ensure smooth powder injection and extend the foam slag maintenance time, heat preservation and air isolation to prevent nitriding of molten steel, and enhance metallurgical effect.

[0088] S3: Steel tapping after smelting.

[0089] Samples were taken before tapping from the electric arc furnace, and the chemical composition of the final steel produced by the electric arc furnace smelting is shown in Table 2. Under high scrap ratio and low carbon conditions, the phosphorus content of the steel smelted by the electric arc furnace was 0.009 wt%, meeting the phosphorus content requirements for high-quality automotive sheet steel. After the phosphorus content in the molten steel decreased to the target value, the molten steel was tapped from the electric arc furnace. The molten steel underwent subsequent processing to achieve the production of high-quality automotive sheet steel.

[0090] Table 1. Composition of dephosphorization slag from electric arc furnace, by mass fraction (wt%)

[0091]

[0092] Note: The dephosphorization slag has a melting point of 1500℃ and an alkalinity of 2.5.

[0093] Table 2 Chemical composition (wt%) of steel produced at the end of electric arc furnace smelting

[0094]

[0095] Example 2

[0096] This embodiment uses a 150t electric arc furnace to smelt high-quality galvanized steel sheets (the finished steel must have a phosphorus content of P < 0.01%). The specific implementation steps are as follows:

[0097] S1: Adding furnace charge into the electric arc furnace

[0098] The furnace charge ratio, by mass percentage, is: 90 wt% scrap steel and 10 wt% molten iron, wherein the scrap steel has been uniformly cut and preheated; the composition of the dephosphorized slag is shown in Table 3, and the basicity R is 2.5. Scrap steel is added using a horizontal vibrating continuous feeding method.

[0099] The electric arc furnace adopts the following power supply system: 90MVA during the arc ignition period, 105MVA during the melting period, and 90MVA during the melting and heating period. The melting and heating rates are adjusted in a timely manner according to the oxidation rate of the elements.

[0100] S2: Slag Forming and Dephosphorization

[0101] The dephosphorization process involves two stages of slag formation. First, slag is formed during the melting period using scrap steel at a rate of 40 kg / t of steel, while oxygen is simultaneously injected at a flow rate of 1.2 Nm³. 3 / t; 29kg / t of carbon powder is injected into the steel, with the carbon powder particle size set to 2mm. The screen mesh size is increased accordingly to ensure smooth powder injection and extend the foam slag maintenance time. Insulation and air isolation prevent nitriding of the molten steel and enhance metallurgical effects. Slag removal is performed in the middle and late stages of melting to prevent phosphorus reversion in the molten steel. After the molten steel is cleared in the furnace, secondary slag formation is carried out, with 35kg / t of slag-forming material added. The composition of the dephosphorized slag is shown in Table 3. Oxygen is injected simultaneously with the slag-forming material, with an oxygen flow rate of 1.2 Nm³. 3 / t; Injecting carbon powder at 29kg / t steel, setting the carbon powder particle size to 2mm, and correspondingly increasing the screen aperture to ensure smooth powder injection and extend the foam slag maintenance time, heat preservation and air isolation to prevent nitriding of molten steel, and enhance metallurgical effect.

[0102] S3: Steel tapping after smelting.

[0103] Samples were taken before tapping from the electric arc furnace, and the chemical composition of the final steel produced by the electric arc furnace smelting is shown in Table 4. Under the conditions of high scrap ratio and low carbon, the phosphorus content of the steel smelted by the electric arc furnace was 0.007 wt%, which met the phosphorus content requirements for high-quality silicon steel. After the phosphorus content in the molten steel decreased to the target value, the molten steel was tapped from the electric arc furnace. The molten steel underwent subsequent processing to achieve the production of high-quality silicon steel.

[0104] Table 3. Composition of dephosphorization slag from electric arc furnace, mass fraction (wt%)

[0105]

[0106] Note: The dephosphorization slag has a melting point of 1480℃ and an alkalinity of 2.5.

[0107] Table 4 Chemical composition (wt%) of steel at the end point of electric arc furnace smelting

[0108]

[0109] Example 3

[0110] This embodiment uses a 150t electric arc furnace to smelt high-quality pipeline steel (the finished steel must have a phosphorus content of P < 0.01%). The specific implementation steps are as follows:

[0111] S1: Adding furnace charge into the electric arc furnace

[0112] The furnace charge ratio, by mass percentage, is: 100 wt% scrap steel and 0 wt% molten iron, wherein the scrap steel has been uniformly cut and preheated; the composition of the dephosphorized slag is shown in Table 5, with a basicity R of 3. Scrap steel is added using a horizontal vibrating continuous feeding method. The electric arc furnace operates under the following power supply system: 100 MVA during the arc ignition phase, 105 MVA during the melting phase, and 100 MVA during the clearing and heating phase. The melting and heating rates are adjusted as needed based on the oxidation rate of the elements.

[0113] S2: Slag Forming and Dephosphorization

[0114] The dephosphorization process involves two stages of slag formation. First, scrap steel is added during the melting period for slag formation at a rate of 38 kg / t of steel, while oxygen is simultaneously injected at a flow rate of 1.4 Nm³. 3 / t; 33kg / t of carbon powder is injected into the steel, with the carbon powder particle size set to 4mm. The screen mesh size is increased accordingly to ensure smooth powder injection and prolong the foam slag maintenance time. Insulation and air isolation prevent nitriding of the molten steel and enhance metallurgical effects. Slag removal is performed in the middle and late stages of melting to prevent phosphorus reversion in the molten steel. After the molten steel is cleared in the furnace, secondary slag formation is carried out by adding 35kg / t of slag-forming material. The composition of the dephosphorized slag is shown in Table 5. Oxygen is injected simultaneously with the slag-forming material, with an oxygen flow rate of 1.4 Nm³. 3 / t; Injecting carbon powder at 29kg / t steel, setting the carbon powder particle size to 4mm, and correspondingly increasing the screen aperture to ensure smooth powder injection and extend the foam slag maintenance time, heat preservation and air isolation to prevent nitriding of molten steel, and enhance metallurgical effect.

[0115] S3: Steel tapping after smelting.

[0116] Samples were taken before tapping from the electric arc furnace, and the chemical composition of the final steel produced by the electric arc furnace smelting is shown in Table 4. Under high scrap ratio and low carbon conditions, the phosphorus content of the steel smelted by the electric arc furnace was 0.005 wt%, meeting the phosphorus content requirements for high-quality pipeline steel. After the phosphorus content in the molten steel decreased to the target value, the molten steel was tapped from the electric arc furnace. The molten steel underwent subsequent processing to achieve the production of high-quality pipeline steel.

[0117] Table 5. Composition of dephosphorization slag from electric arc furnace, mass fraction (wt%)

[0118]

[0119] Note: The dephosphorization slag has a melting point of 1490℃ and an alkalinity of 3.

[0120] Table 6 Chemical composition (wt%) of steel produced at the end of electric arc furnace smelting

[0121]

[0122] Comparative Example 1

[0123] The dephosphorization method in this comparative example is similar to that in Example 1, except that the dephosphorization slag system uses a lower alkalinity than the slag system used in this invention.

[0124] Table 7. Composition (wt%) of dephosphorization slag from electric arc furnace

[0125]

[0126] Note: The dephosphorization slag has a melting point of 1500℃ and a fluidity alkalinity of 1.6.

[0127] Table 8 Chemical composition (wt%) of steel produced at the end of electric arc furnace smelting

[0128]

[0129] Comparative Example 2

[0130] The dephosphorization method in this comparative example is similar to that in Example 1, except that only one slag-forming dephosphorization is performed, without slag discharge operation and subsequent secondary slag-forming dephosphorization.

[0131] Table 9. Composition of dephosphorization slag from electric arc furnace, mass fraction (wt%)

[0132]

[0133] Note: The dephosphorization slag has a melting point of 1500℃ and an alkalinity of 2.5.

[0134] Table 10 Chemical composition (wt%) of steel produced at the final stage of electric arc furnace smelting

[0135]

[0136] Comparative Example 3

[0137] The dephosphorization method in this comparative example is similar to that in Example 1, except that the oxygen flow rate in step S2 is 1 Nm³. 3 / t.

[0138] Table 9. Composition of dephosphorization slag from electric arc furnace, mass fraction (wt%)

[0139]

[0140] Note: The dephosphorization slag has a melting point of 1500℃ and an alkalinity of 2.5.

[0141] Table 10 Chemical composition (wt%) of steel produced at the final stage of electric arc furnace smelting

[0142]

[0143] Comparative Example 4

[0144] The dephosphorization method in this comparative example is similar to that in Example 1, except that in step S2, an appropriate amount of carbon powder is injected and the particle size of the carbon powder is set to 1 mm.

[0145] Table 11. Composition of dephosphorization slag from electric arc furnace, mass fraction (wt%)

[0146]

[0147] Note: The dephosphorization slag has a melting point of 1500℃ and an alkalinity of 2.5.

[0148] Table 12 Chemical composition (wt%) of steel at the end point of electric arc furnace smelting

[0149]

[0150] By comparing Example 1 and Comparative Example 1, it was found that the dephosphorization efficiency of Comparative Example 1 was poor because the alkalinity R = 1.6, which is lower than the 2.4-3.1R of the present invention. The dephosphorization capacity was insufficient, resulting in poor dephosphorization effect, excessive final phosphorus content, and failure to meet the final phosphorus requirements of high-quality steel.

[0151] By comparing Example 1 and Comparative Example 2, Comparative Example 2 only performed one slag discharge dephosphorization, without subsequent slag discharge and secondary slag formation dephosphorization, which carries the risk of phosphorus reversion. Without the addition of new slag system to regain efficient dephosphorization capacity, the dephosphorization effect is poor, the final phosphorus content exceeds the standard, and it does not meet the final phosphorus requirements for high-quality steel.

[0152] By comparing Example 1 and Comparative Example 3, the oxygen flow rate of Comparative Example 3 was 1 Nm³. 3 / t, less than the oxygen flow rate of the present invention, which is 1.2-1.4 Nm. 3 The reduced phosphorus content ( / t) resulted in insufficient oxidizing capacity during injection, preventing effective phosphorus oxidation and hindering the dephosphorization reaction. Consequently, the final phosphorus content exceeded the standard, failing to meet the final phosphorus requirements for high-quality steel.

[0153] By comparing Example 1 and Comparative Example 4, the carbon powder particle size in Comparative Example 4 was set to 1 mm, which is smaller than the carbon powder particle size set to 2-4 mm in this invention. If the particle size of the injected carbon powder is too small, a large amount of CO gas may be generated and escape rapidly, forming large and fragile bubbles that cannot form dense and stable foam slag, resulting in excessive phosphorus content at the end point and failing to meet the phosphorus requirements for high-quality steel.

[0154] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A dephosphorization slag system for high-scrap-ratio electric arc furnace smelting of high-quality steel, characterized in that, The components, by mass percentage, include: 24-31 wt% FeO, 2-6 wt% MgO, 44-56 wt% CaO, 14-21 wt% SiO2; and 1-5 wt% balance metal oxides.

2. The dephosphorization slag system for high-scrap-ratio electric arc furnace smelting of high-quality steel according to claim 1, characterized in that, The alkalinity R of the dephosphorization slag system is 2.5-3, where R is the mass ratio of component CaO to component SiO2.

3. The dephosphorization slag system for high-scrap-ratio electric arc furnace smelting of high-quality steel according to claim 1, characterized in that, The remaining metal oxides include Al2O3, MnO and Cr2O3.

4. A method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions, characterized in that, The specific steps are as follows: Step S1: Add furnace charge into the electric arc furnace; Step S2: Slag formation and dephosphorization; Step S3: Smelting ends and steel is tapped.

5. The method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions according to claim 4, characterized in that, In step S1, the furnace charge is: scrap steel mixed with molten iron and dephosphorized slag, wherein the mass ratio of scrap steel in the molten iron is 80-100 wt%.

6. The method for dephosphorizing high-quality steel smelting in an electric arc furnace under high scrap ratio and low carbon conditions according to claim 4, characterized in that, In step S2, slag formation and dephosphorization are carried out in two stages.

7. The method for dephosphorizing high-quality steel smelting in an electric arc furnace under high scrap ratio and low carbon conditions according to claim 4, characterized in that, In step S2, the timing of slag formation and dephosphorization is as follows: slag formation and dephosphorization during the melting period of scrap steel when the arc is ignited by electric current.

8. The method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions according to claim 4, characterized in that, In step S2, the timing of secondary slag formation and dephosphorization is as follows: slag removal is performed in the middle and late stages of melting; secondary slag formation and dephosphorization are performed after the furnace is cleared.

9. The method for dephosphorizing high-quality steel smelting in an electric arc furnace under high scrap ratio and low carbon conditions according to claim 4, characterized in that, In step S2, oxygen is injected to aid melting during slag formation and dephosphorization. Simultaneously, oxygen, as an essential oxidant for the dephosphorization reaction, enters the furnace to participate in the dephosphorization reaction. The injected oxygen flow rate is 1.2-1.4 Nm³. 3 / t.

10. The method for dephosphorizing high-quality steel smelted in an electric arc furnace under high scrap ratio and low carbon conditions according to any one of claims 4-9, characterized in that, In step S2, carbon powder is sprayed, and the particle size of the carbon powder is 2-4 mm.

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