Flux for semi-steel making and method for slagging

Abstract

This invention provides a flux for semi-steelmaking and its slag-forming method, belonging to the field of metallurgical technology. A flux for semi-steelmaking is characterized by the following composition by weight percentage: SiO2: 60-70%, MgO: 25-36%, Fe2O3: 1-10%, Al2O3: 1-5%, MnO: 1-2%, P: 0.001-0.01%, S: 0.001-0.01%, with the remainder being unavoidable impurities. The flux for semi-steelmaking and its slag-forming method used in this invention have good activity, improving the dephosphorization and desulfurization capabilities of steelmaking slag, and thus possessing significant socio-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] In converter steelmaking, to promote rapid lime melting and disrupt dicalcium silicate crystallization or delay crust formation, a large amount of materials that aid in slag formation are added during steelmaking. In the past, fluorite was commonly used for slag formation in converter steelmaking; however, because fluorite contains sulfur... - Fluoride ions are harmful to the human body and equipment, so people are researching various slag-removing materials to replace fluorite.

[0003] After vanadium extraction from molten iron in the Panxi region, the content of elements such as Si, Ti, and Mn in the semi-steel is almost zero, resulting in a simple converter slag system that is not conducive to rapid slag formation. In the semi-steelmaking process, slag formation accounts for approximately 20% in the early blowing stage, approximately 70% in the middle blowing stage, and approximately 10% during the entire blowing process. Therefore, it is necessary to add slag-forming elements to enable rapid slag formation in the converter semi-steelmaking process. Simultaneously, the properties of the final slag system often affect the effectiveness of converter slag splashing for furnace protection; therefore, it is necessary to control the MgO content in the final slag within a suitable range to obtain appropriate slag melting point and viscosity, thereby meeting the requirements for converter slag splashing for furnace protection.

[0004] CN1291657A discloses a converter slag-forming flux and its slag-forming process. The flux composition is: Al2O3 ≥ 45%, SiO2 ≤ 30%, Fe2O3 7-8%, with the balance being impurities such as CaO, MgO, TiO2, P, and S. The particle size is 5-30 mm, and the usage is 1.6-9 kg of bauxite per 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 insignificant slag-forming effects.

[0005] CN1298028A discloses a converter steelmaking cooling and fluxing agent. This flux is an iron-scale fluxing agent with FeO as the main component. The fluxing agent composition is: 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: 60-70%, MgO: 25-36%, Fe2O3: 1-10%, Al2O3: 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 talc.

[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., 7-12 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; wherein, the weight ratio of semi-steel molten steel to scrap steel is 12.5~14.5:0.4~1;

[0014] d. When starting the blowing process, add two-thirds of the total lime amount, i.e., 10-17 kg / t steel and 10-15 kg / t steel of high-magnesium lime, to the converter to meet the needs of dephosphorization of the converter slag. 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, lime is added when the slag is relatively active to ensure sufficient fluidity and desulfurization and dephosphorization capabilities.

[0019] In step d, compared with the conventional process, the amount of lime used is reduced by 1-2 kg / t of steel; because the talc flux contains a large amount of magnesium oxide, it can ensure that the MgO mass percentage content in the converter slag is 8-12% to meet the requirements of furnace protection; compared with the conventional process, the amount of high-magnesium lime used is reduced by 6-14 kg / t of steel; because the talc flux contains a large amount of silicon dioxide, it can ensure that the SiO2 content in the converter slag meets the requirements of converter slag making and steelmaking dephosphorization; compared with the conventional process, the amount of composite slag or quartz sand used is reduced by 5-10 kg / t of steel.

[0020] 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.

[0021] 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.

[0022] Among them, slag arrives 3 minutes after the start of blowing, which shortens the slag arrival time by 0.5 minutes compared with conventional semi-steel converter steelmaking. The slag is active and the process does not dry out or splash.

[0023] The beneficial effects of this invention are:

[0024] 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, talc, 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 3-6 kg / t steel.

[0025] 2. The flux for semi-steelmaking and its slag-forming method provided by this invention have extremely low phosphorus and sulfur content in natural talc ore, which improves the dephosphorization and desulfurization capacity of steelmaking slag and has good social and economic benefits. Detailed Implementation

[0026] 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.

[0027] Example 1

[0028] 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.

[0029] Table 1. Composition (%) and furnace inlet temperature (°C) of semi-finished steel.

[0030] C Si Mn P S Furnace temperature Semi-steel 3.7 0.02 0.03 0.074 0.010 1320

[0031] Table 2 Actual Addition Amount (kg) and Actual Oxygen Blowing Amount (m³) of Auxiliary Materials for Semi-Steelmaking 3 )

[0032] lime High magnesium lime talc Oxygen blowing volume 2793 1596 1330 6210

[0033] Table 3. Composition (%) and tapping temperature (°C) of molten steel.

[0034] C Si Mn P S tapping temperature Molten steel tapping 0.055 0.015 0.023 0.015 0.008 1685

[0035] After the steel was tapped from the converter and slag splashing was performed for furnace protection, all 1330 kg of natural talc ore was added at once from the high-level silo of the converter. After the blowing began, two-thirds of the total lime (2793 kg) and all of the high-magnesium lime were added to the converter. The remaining one-third of the lime was added in 3-4 batches. Slag arrived 2 minutes and 30 seconds after the blowing began, which is 30 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.

[0036] 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.

[0037] Example 2

[0038] 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.

[0039] Table 4. Composition (%) and furnace inlet temperature (°C) of semi-finished steel.

[0040] C Si Mn P S Furnace temperature Semi-steel molten steel 3.95 0.021 0.041 0.07 0.015 1300

[0041] Table 5 Actual Addition Amount (kg) and Actual Oxygen Blowing Amount (m³) of Auxiliary Materials for Semi-Steelmaking 3 )

[0042] lime High magnesium lime talc Oxygen blowing volume 2500 1600 1400 6400

[0043] Table 6. Composition (%) and tapping temperature (°C) of molten steel.

[0044] C Si Mn P S tapping temperature Molten steel tapping 0.069 0.02 0.035 0.017 0.011 1682

[0045] After the steel was tapped from the converter and slag splashing was performed for furnace protection, all 1400 kg of natural talc ore was added at once from the high-level silo of the converter. After the blowing began, two-thirds of the total lime volume (2500 kg) and all of the high-magnesium lime were added to the converter. The remaining one-third of the lime was added in 3-4 batches. Slag arrived 2 minutes and 15 seconds after the blowing began, which is 45 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.

[0046] 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.

[0047] Comparative Example 1

[0048] 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.

[0049] Table 7. Composition (%) and furnace inlet temperature (°C) of semi-finished steel.

[0050] C Si Mn P S Furnace temperature Semi-steel molten steel 3.88 0.02 0.025 0.072 0.015 1360

[0051] Table 8 Actual Addition Amount (kg) and Actual Oxygen Blowing Amount (m³) of Auxiliary Materials for Semi-Steelmaking 3 )

[0052] lime High magnesium lime acidic composite slag Ladle slag Oxygen blowing volume 2750 2500 1500 1045 6600

[0053] Table 9. Composition (%) and tapping temperature (°C) of molten steel.

[0054] C Si Mn P S tapping temperature Molten steel tapping 0.078 0.023 0.035 0.012 0.011 1690

[0055] 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.

[0056] 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. A method for slag formation using flux in semi-steelmaking after vanadium extraction from molten iron, characterized in that, Includes the following steps: a. Mechanically crush large pieces of semi-steel using flux to process them into blocks with a particle size of 10-80mm; b. After the steel is tapped from the converter and slag splashing is performed to protect the furnace, the flux is added in one go from the high-level silo of the converter at a rate of 7-12 kg / t of steel; wherein the flux is natural talc, and its composition, by mass percentage, is: SiO2: 60-70%, MgO: 25-36%, Fe2O3: 1-10%, Al2O3: 1-5%, MnO: 1-2%, P: 0.001-0.01%, S: 0.001-0.01%, with the remainder being unavoidable impurities; c. Introduce semi-molten steel and scrap steel to begin oxygen blowing for steelmaking, with an oxygen flow rate of 30000 Nm³. 3 / h; wherein, the weight ratio of semi-steel molten steel to scrap steel is 12.5~14.5:0.4~1; d. When starting the blowing process, add two-thirds of the total lime amount, i.e., 10-17 kg / t steel and 10-15 kg / t steel of high-magnesium lime, to the converter to meet the needs of dephosphorization of the converter slag. The remaining one-third of the lime is added in batches during the smelting process.

2. The method for slag formation using flux in semi-steelmaking after vanadium extraction from molten iron according to claim 1, characterized in that, The flux used in semi-steelmaking has a melting point of 1300–1365°C.

3. The method for slag formation using flux in semi-steelmaking after vanadium extraction from molten iron according to claim 1, characterized in that, 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 in the blowing lance position, 2 m in the initial blowing lance position, and 1.4 m in the carbon pulling lance position.

4. The method for slag formation using flux in semi-steelmaking after vanadium extraction from molten iron according to claim 1, characterized in that, The semi-molten steel described 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%.

5. The method for slag formation using flux in semi-steelmaking after vanadium extraction from molten iron according to claim 1, characterized in that, In step c, the temperature of the semi-steel and scrap steel entering the furnace is 1250–1360℃.

6. The method for fluxing and slag formation in semi-steelmaking after vanadium extraction from molten iron according to claim 1, characterized in that, In step d, the basicity of the initial slag is controlled at 2.0 to 3.0, and the basicity of the final slag is controlled at 3.0 to 4.0.