Flux for semi-steel making and method for slagging

Abstract

The application provides a flux for semi-steel smelting and a slagging method thereof, and belongs to the technical field of metallurgy. The flux for semi-steel smelting is characterized by the following composition: SiO2: 30-36%, MgO: 30-36%, Fe2O3: 10-20%, CaO: 1-5%, MnO: 1-2%, P: 0.001-0.01%, S: 0.001-0.01%, and the rest is inevitable impurities. The flux for semi-steel smelting and the slagging method thereof have good activity, improve the dephosphorization and desulfurization capacity of the steel smelting slag, and have good social and economic benefits.

Description

Technical Field

[0001] This invention relates to a flux for semi-steelmaking and its slag-forming method, belonging to the field of metallurgical technology. Background Technology

[0002] Converter slag is a multi-component system, containing not only CaO, SiO2, and FeO, but also MnO, Al2O3, and MgO, making it a complex multi-component system. This complexity contributes to a lower slag melting point, faster slag formation, and reduced mid-term re-drying. Semi-steelmaking in the Panxi region has its unique characteristics. The semi-steel contains trace amounts of Si and Mn, necessitating the addition of SiO2-containing auxiliary slag-forming materials and increasing the oxygen lance position to raise the FeO content in the slag during the smelting process, thus promoting lime melting. The simple composition of added raw materials such as quartz sand makes initial slag formation difficult. Furthermore, the vanadium extraction process in Panxi semi-steel significantly reduces carbon content, resulting in insufficient heat for steelmaking, further complicating slag formation. To extend the lifespan of steelmaking converters, slag splashing protection technology is often employed. This technology requires controlling the final slag composition within a suitable range, ensuring appropriate slag melting point and viscosity to meet the requirements of converter slag splashing protection.

[0003] Currently, the fluxes used in production mainly include the following: fluxes with CaF2 as the main component; bauxite-based fluxes (using iron bauxite, aluminum bauxite, and other bauxite as main raw materials) with Al2O3 as the main component; and scale-based fluxes (using iron scale, iron ore, and iron slag as main raw materials) with FeO as the main component. Fluorite is a commonly used slag-forming flux. Its main component, CaF2, has a low melting point and can significantly lower the melting point of CaO. However, fluorite releases harmful sulfur dioxide (F) during steelmaking. - Fluorite is an element that causes environmental pollution. Furthermore, it severely corrodes the converter lining; therefore, its use as a flux has been banned. The common problems with the aforementioned fluxes include severe lining corrosion, environmental pollution, insignificant slagging effect, large temperature drop in molten steel, short fluxing time, and inability to sustain slagging.

[0004] CN1291657A discloses a converter slag-forming flux and a slag-forming process. The flux is composed of bauxite with the following components: Al₂O₃ ≥ 45%, SiO₂ ≤ 30%, Fe₂O₃ 7–18%, and the balance being impurities such as CaO, MgO, TiO₂, P, and S. The particle size of this bauxite is 5–30 mm, and the amount used depends on the steel grade being refined and the silicon content of the molten iron, ranging from 1.6–9 kg bauxite / ton of steel. This method has the following drawbacks: while bauxite-based fluxes provide relatively stable slag-forming effects, they also cause severe erosion of the furnace lining and have an insignificant slag-forming effect.

[0005] CN1298028A discloses a converter steelmaking cooling and fluxing agent. This fluxing agent is an iron-scale fluxing agent with FeO as the main component, consisting of 70-90% iron scale, 5-25% ironmaking sludge, and 1-5% binder. The raw materials are crushed, prepared, mixed, and pressed into balls. This method has the following drawbacks: while the iron-scale fluxing agent has a significant slag-forming effect, it also causes severe erosion of the furnace lining, a large temperature drop in the molten steel, and a short fluxing time that cannot sustain slag formation. Summary of the Invention

[0006] The first technical problem solved by this invention is to provide a flux for semi-steelmaking.

[0007] A flux for semi-steelmaking is characterized by the following composition, by mass percentage: SiO2: 30-36%, MgO: 30-36%, Fe2O3: 10-20%, CaO: 1-5%, MnO: 1-2%, P: 0.001-0.01%, S: 0.001-0.01%, with the remainder being unavoidable impurities.

[0008] The flux used in semi-steelmaking has a melting point of 1300–1365°C.

[0009] The flux used in semi-steelmaking is a natural ore rich in both SiO2 and MgO, and the natural ore is magnesium olivine.

[0010] The second technical problem solved by this invention is to provide a method for slag formation using flux in semi-steelmaking, comprising the following steps:

[0011] a. Mechanically crush large pieces of semi-steel using flux to process them into blocks with a particle size of 10-80mm;

[0012] b. After the steel is tapped from the converter and slag splashing is performed to protect the furnace, the flux, i.e., 14-17 kg / t steel, is added at once from the high-level silo of the converter.

[0013] c. Introduce semi-molten steel and scrap steel to begin oxygen blowing for steelmaking, with an oxygen flow rate of 30000 Nm³. 3 / h;

[0014] d. When starting the blowing process, add two-thirds of the total lime usage, i.e., 12-19 kg / t of steel, into the converter. The remaining one-third of the lime is added in batches during the smelting process.

[0015] Step b helps to rapidly melt the flux.

[0016] The semi-molten steel in step c has the following composition by mass percentage: C: 3.2-4.1%, Si: 0.015-0.030%, Mn: 0.02-0.04%, P: 0.06-0.08%, S: ≤0.015%.

[0017] In step c, the temperature of the semi-steel molten steel and scrap steel entering the furnace is 1250–1360℃.

[0018] In step d, two-thirds of the total lime usage, i.e., 12-19 kg / t steel, is added to the converter to meet the requirements for dephosphorization of the converter slag.

[0019] In step d, the remaining one-third of the lime is added in batches during the smelting process, so that the lime is added when the slag is relatively active, in order to ensure sufficient fluidity and desulfurization and dephosphorization capabilities.

[0020] In step d, compared with the conventional process, the amount of lime used is reduced by 0.77-3.5 kg / t steel; because the magnesium olivine flux contains a large amount of magnesium oxide, it can ensure that the MgO mass percentage content in the converter slag is 10-12% to meet the requirements of furnace protection; compared with the conventional process, the amount of high-magnesium lime used is reduced by 9-14 kg / t steel; because the magnesium olivine flux contains a large amount of silicon dioxide, it can ensure the SiO2 content requirement in the converter slag, thereby meeting the needs of converter slag making and steelmaking dephosphorization; compared with the conventional process, the amount of composite slag or quartz sand used is reduced by 9-14 kg / t steel.

[0021] In step d, the initial slag basicity is controlled between 2.0 and 3.0, and the final slag basicity is controlled between 3.0 and 4.0.

[0022] The oxygen lance nozzle is positioned 1.4–2 m from the molten metal surface in the basic lance position, 1.4–1.8 m from the blowing lance position, 2 m from the initial blowing lance position, and 1.4 m from the carbon pulling lance position, ensuring that the slag has good fluidity to achieve rapid dephosphorization.

[0023] Among them, slag arrives 2.5 minutes after the start of blowing, which is 1 minute shorter than the slag arrival time of conventional semi-steel converter steelmaking. The slag is active and the process does not dry out or splash.

[0024] The beneficial effects of this invention are:

[0025] 1. The flux for semi-steelmaking and its slag-forming method provided by this invention use natural ore as flux in the converter. The ore has good activity and reacts quickly. Only one raw material, magnesium olivine, is used to replace two semi-steelmaking raw materials, namely high-magnesium lime and composite slag-forming agent, which greatly reduces the amount of steelmaking auxiliary materials by 4 to 9 kg / t steel.

[0026] 2. The flux for semi-steelmaking and its slag-forming method provided by this invention have extremely low phosphorus and sulfur content in the magnesium olivine natural ore, which improves the dephosphorization and desulfurization capacity of steelmaking slag and has good social and economic benefits. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the embodiments, conventional conditions apply.

[0028] Example 1

[0029] HRB400E steel was smelted in a new 120-ton converter at a steel plant. The actual weight of the semi-finished steel charged into the furnace was 130.6t, the weight of the scrap steel was 7t, and the weight of the tapped steel was 130.72t. The composition and temperature of the semi-finished steel are shown in Table 1; the actual amount of auxiliary materials added and the amount of oxygen blown are shown in Table 2; and the composition and tapping temperature of the tapped steel are shown in Table 3.

[0030] Table 1. Composition (%) and furnace inlet temperature (°C) of semi-finished steel

[0031] C Si Mn P S Furnace temperature Semi-steel molten steel 3.7 0.02 0.03 0.074 0.010 1320

[0032] Table 2 Actual addition amount (kg) and actual oxygen blowing amount (m³) of auxiliary materials for semi-steelmaking 3 )

[0033] lime Magnesium olivine Oxygen blowing volume 2500 2000 6210

[0034] Table 3. Composition (%) and tapping temperature (°C) of molten steel.

[0035] C Si Mn P S tapping temperature Molten steel tapping 0.055 0.015 0.023 0.015 0.008 1685

[0036] After the steel was tapped from the converter and slag splashing was performed for furnace protection, all 2000 kg of natural magnesium olivine ore was added at once from the high-level silo of the converter. After the blowing operation began, two-thirds of the total lime (2500 kg) was added to the converter, and the remaining one-third was added in 3-4 batches. Slag arrived 2 minutes and 30 seconds after the blowing operation began, which was 60 seconds earlier than the conventional operation using composite slag-forming agents and high-magnesium lime. The slag was active and had strong dephosphorization and desulfurization capabilities. After tapping, the conventional slag splashing process was used for furnace protection, resulting in good slag adhesion on the furnace walls.

[0037] The slag basicity of the final slag produced in this furnace was 3.5, the total iron content in the final slag was 18.88%, and the oxygen activity was 500 ppm. Good results were achieved.

[0038] Example 2

[0039] A steel plant is smelting Q235 steel in a new 120-ton converter. The actual weight of the semi-finished steel charged into the furnace was 140 tons, the weight of the scrap steel was 5 tons, and the weight of the tapped steel was 136.3 tons. The composition and temperature of the semi-finished steel are shown in Table 4; the actual amount of auxiliary materials added and the amount of oxygen blown are shown in Table 5; and the composition and tapping temperature of the tapped steel are shown in Table 6.

[0040] Table 4. Composition (%) and furnace inlet temperature (°C) of semi-finished steel

[0041] C Si Mn P S Furnace temperature Semi-steel molten steel 3.95 0.021 0.041 0.07 0.015 1300

[0042] Table 5 Actual addition amount (kg) and actual oxygen blowing amount (m³) of auxiliary materials for semi-steelmaking 3 )

[0043] lime Magnesium olivine Oxygen blowing volume 2800 2200 6400

[0044] Table 6. Composition (%) and tapping temperature (°C) of molten steel.

[0045] C Si Mn P S tapping temperature Molten steel tapping 0.069 0.02 0.035 0.017 0.011 1682

[0046] After the steel was tapped from the converter and slag splashing was performed for furnace protection, all 2200 kg of natural magnesium olivine ore was added at once from the high-level silo of the converter. After the blowing operation began, two-thirds of the total lime (2800 kg) was added to the converter, and the remaining one-third was added in 3-4 batches. Slag arrived 2 minutes and 40 seconds after the blowing operation began, which was 50 seconds earlier than the conventional operation using composite slag-forming agents and high-magnesium lime. The slag was active and had strong dephosphorization and desulfurization capabilities. After tapping, the conventional slag splashing process was used for furnace protection, resulting in good slag adhesion on the furnace walls.

[0047] The slag basicity of this furnace was 3.6, the total iron content in the slag was 19.89%, and the oxygen activity was 450 ppm. Good results were achieved.

[0048] Comparative Example 1

[0049] YQ450 steel was smelted in a new 120-ton converter at a steel plant. The actual weight of the semi-finished steel charged into the furnace was 133 tons, the weight of the scrap steel was 10 tons, and the weight of the tapped steel was 134.42 tons. The composition and temperature of the semi-finished steel are shown in Table 7; the actual amount of auxiliary materials added and the amount of oxygen blown are shown in Table 8; and the composition and tapping temperature of the tapped steel are shown in Table 9.

[0050] Table 7. Composition (%) and furnace inlet temperature (°C) of semi-finished steel

[0051] C Si Mn P S Furnace temperature Semi-steel molten steel 3.88 0.02 0.025 0.072 0.015 1360

[0052] Table 8 Actual addition amount (kg) and actual oxygen blowing amount (m³) of auxiliary materials for semi-steelmaking 3 )

[0053] lime High magnesium lime acidic composite slag Ladle slag Oxygen blowing volume 2750 2500 1500 1045 6600

[0054] Table 9. Composition (%) and tapping temperature (°C) of molten steel.

[0055] C Si Mn P S tapping temperature Molten steel tapping 0.078 0.023 0.035 0.012 0.011 1690

[0056] When the smelting process begins, 1045 kg of ladle slag, 1833 kg of lime, 1667 kg of high-magnesium lime, and 1500 kg of acidic composite slag are added to the converter. The slag arrives 4 minutes and 35 seconds after the start of the blowing process. The basicity of the final slag from this smelting process is 3.93, the total iron content in the final slag is 21%, and the oxygen activity is 500 ppm.

[0057] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading the specification of the present invention, those skilled in the art may make some modifications or improvements based on the present invention, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. Fluxed slagging process for semi-steel steelmaking, characterized in that, It comprises the following steps: a. mechanically crushing the large semi-steel smelting flux into blocks with a particle size of 10-80 mm; wherein the flux composition is, in mass percentage, SiO2: 30-36%, MgO: 30-36%, Fe2O3: 10-20%, CaO: 1-5%, MnO: 1-2%, P: 0.001-0.01%, S: 0.001-0.01%, and the rest is inevitable impurities; b. after the converter is finished and the slag splashing is completed, the flux is added once from the high-position stock bin of the converter at 14-17 kg / t of steel; c. The semi-steel iron melt and scrap steel start oxygen blowing, the oxygen flow is 30000Nm 3 / h; the semi-steel iron melt is composed of: in terms of mass percentage, C: 3.2-4.1%, Si: 0.015-0.030%, Mn: 0.02-0.04%, P: 0.06-0.08%, S: ≤0.015%; d. two-thirds of the total lime amount, i.e. 12-19 kg / t of steel, is added to the converter, and the remaining one-third of the lime is added in batches during the smelting process.

2. The semi-steel steelmaking fluxing-slagging method according to claim 1, characterized by, The semi-steel smelting flux has a melting point of 1300-1365℃.

3. The semi-steel steelmaking fluxing agent slagging method according to claim 2, characterized by, The oxygen lance nozzle is 1.4-2 m from the metal liquid surface of the molten bath, the blowing lance position is 1.4-1.8 m, the blowing opening position is 2 m, and the carbon pulling lance position is 1.4 m.

4. The semi-steel steelmaking fluxing agent slagging method according to claim 3, characterized by, The semi-steel and scrap steel in step c have an inlet temperature of 1250-1360℃.

5. The semi-steel steelmaking fluxing agent slagging method according to claim 3, characterized by, In step d, the initial slag basicity is controlled at 2.0-3.0, and the final slag basicity is controlled at 3.0-4.0.