Method for smelting low-phosphorus steel at low cost

Abstract

The invention discloses a low-cost method for smelting low-phosphorus steel. Converter charging: pouring a large ladle of residual molten steel and attached aluminum killed steel refining slag, waste steel and molten iron into a converter to obtain mixed molten iron, and preparing for smelting; and the mixed molten iron is subjected to blowing before deslagging, deslagging, blowing after deslagging and end point control, and the low-phosphorus steel is obtained. According to the method, an oxygen lance operation mode and a feeding mode are highly matched with the physical and chemical characteristics of the hot slag, and through accurate control of early-stage high-lance-position slagging and dephosphorization and later-stage low-lance-position uniform stirring, smooth operation of the whole smelting process and accurate hitting of an end point target are ensured, and the process matching performance is high. Refined hot slag of aluminum killed steel is recycled, an optimized converter double-slag operation process is combined, the using amount of a cooling agent and a slagging material is reduced, the tapping amount is increased, and on the premise that the cost of raw materials is reduced, the phosphorus content at the end point of the converter is stably controlled to be 0.010% or below.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and specifically to a low-cost method for smelting low-phosphorus steel. Background Technology

[0002] Phosphorus, a common harmful element in steel, severely deteriorates the low-temperature impact toughness of steel, leading to cold brittleness. It also negatively impacts the weldability and crack propagation resistance of steel. For key products such as high-end pipeline steel, offshore platform steel, and high-strength automotive steel, the phosphorus content in the steel must be stably controlled below 0.010%, or even reach an ultra-low level of 0.005%.

[0003] Currently, the mainstream technology for converter smelting of low-phosphorus steel is the double-slag method or the dual-slag method. The double-slag method involves removing high-phosphorus slag during the blowing process and then re-forming slag for deep dephosphorization. However, its challenge lies in balancing dephosphorization with temperature rise and controlling the properties of the final slag to prevent phosphorus reversion. Conventional double-slag processes consume large amounts of coolant (such as ore or sinter) and slag-forming materials (such as lime or dolomite), resulting in high production costs and difficulty in controlling process stability. Furthermore, the large amount of suitable-composition, high-temperature refining slag generated during the refining process in steel enterprises is usually treated as solid waste, causing resource waste and increasing environmental costs. For example, patent application number 202410792975.6 discloses a method for smelting low-phosphorus steel from high-phosphorus, low-silicon molten iron by adding silicon-killed steel LF refining slag to the molten iron for smelting. However, the silicon-killed steel LF refining slag has low basicity, making it difficult to smelt steel with even lower phosphorus content. Patent application number 202411932021.7 discloses a method for smelting ultra-low phosphorus steel. By utilizing refining slag for slag formation and optimizing slag formation, oxygen supply, temperature, and endpoint control, along with optimizing the bottom-blowing process, the method achieves stable production of ultra-low phosphorus steel without the need for a dual-process. Furthermore, the phosphorus content in the ultra-low phosphorus steel produced by this invention is consistently controlled below 0.003%. Although this patent adds aluminum-killed steel refining slag with higher basicity, this method requires the addition of more coolant and slag-forming materials, increasing smelting costs. Moreover, the amount of aluminum-killed steel refining slag added is relatively small, with a maximum of about 2 tons per furnace, resulting in limited cost reduction. Therefore, the industry urgently needs a low-cost converter smelting method that can fully utilize existing resources, reduce raw material consumption, and stably control the endpoint phosphorus content. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide a low-cost method for smelting low-phosphorus steel. This invention achieves stable control of the final phosphorus content at the converter endpoint below 0.010% by recycling the hot slag from aluminum-killed steel refining and combining it with an optimized converter dual-slag operation process, while reducing raw material costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a low-cost method for smelting low-phosphorus steel, comprising the following steps: (1) Converter charging The remaining molten steel from the ladle, along with the attached aluminum-killed steel refining slag, scrap steel, and molten iron, are all poured into the converter in preparation for smelting. (2) Blowing before slag removal Oxygen lance position: 1450~1550mm, oxygen pressure: 0.85~0.90 MPa; When the blowing time reaches 2.5 to 3.0 minutes, raise the oxygen lance position to 1600 to 1700 mm while keeping the oxygen pressure unchanged; When the blowing time reaches 4.0 to 5.0 min, raise the oxygen lance position to 1800 to 1900 mm again; When the total blowing time is 6-7 minutes, turn off the oxygen and lift the lance; (3) Pouring out the slag (4) After slag is poured out, the smelting process is carried out. The oxygen pressure is controlled at a relatively high constant lance position of 1550-1600 mm, and the oxygen pressure is controlled at 0.85-0.95 MPa. One minute before the finish line, lower the gun position to 1100-1200mm; (5) Endpoint control.

[0006] Preferably, in step (1), the mass ratio of the molten steel in the ladle to the aluminum-killed steel refining slag is 1:3.

[0007] Preferably, in step (1), the aluminum-killed steel refining slag comprises SiO2 ≤ 12%, Al2O3: 25%~40%, CaO ≥ 50%; and the basicity of the aluminum-killed steel refining slag is ≥ 4.5.

[0008] Preferably, in step (1), the mass of the scrap steel accounts for 3.5 to 12% of the total mass of the scrap steel and molten iron; the silicon content in the molten iron is ≤ 0.60%, and the phosphorus content is ≤ 0.150%.

[0009] Preferably, in step (1), the ratio of the total mass of the molten steel and the attached aluminum-killed steel refining slag in the ladle to the total mass of the scrap steel and molten iron is 8~15:140.

[0010] Preferably, in step (2), sinter is added in 1 to 2 batches within 1 to 3 minutes after the start of blowing, and the amount of sinter added is 7.0 to 15.0 kg / ton of molten steel.

[0011] Preferably, in step (4), after blowing for 30 seconds, 20.0-25.0 kg / ton of lime and 7.0-12.0 kg / ton of dolomite are added at once; sinter is added in batches, with an addition amount of 3.0-5.0 kg / ton of sinter, and all of it is added 3 minutes before the end.

[0012] Preferably, in step (5), the endpoint carbon content is 0.05% ~ 0.07%; the endpoint temperature is 1620℃ ~ 1635℃.

[0013] Preferably, the phosphorus content of the low-cost smelted low-phosphorus steel obtained by smelting is less than ≤0.010%.

[0014] A second aspect of the invention provides the application of the above-described method in reducing the amount of coolant and slag-forming material used and increasing the steel output.

[0015] The beneficial effects of this invention are: (1) This invention reuses the hot slag from refining as a high-quality slag-forming material for converter smelting, which greatly reduces the consumption of slag-forming agents such as lime. At the same time, it utilizes its physical heat to reduce smelting energy consumption and achieve cost reduction and efficiency improvement.

[0016] (2) This invention utilizes the high alkalinity of the refining hot slag to rapidly form a slag environment with strong dephosphorization capabilities in the early stage of blowing, achieving "early slag formation and early dephosphorization". Combined with the optimized dual-slag process, high-phosphorus slag is eliminated in time, and a low-phosphorus slag system is created for the final stage, effectively preventing phosphorus reversion and ensuring stable control of the final phosphorus content. The dephosphorization efficiency is high and the stability is good.

[0017] (3) The oxygen lance operation mode and feeding mode provided by the present invention are highly matched with the physicochemical properties of hot slag. Through the precise control of "high lance position for slag dephosphorization in the early stage and low lance position for uniform stirring in the later stage", the smooth operation of the entire smelting process and the precise hit of the final target are ensured, and the process matching is strong.

[0018] (4) This invention realizes the resource utilization of metallurgical solid waste, with significant environmental benefits, and is in line with the green and sustainable development direction of steel manufacturing. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0020] As introduced in the background section, aluminum-killed steel refining slag has a higher basicity than silicon-killed steel LF refining slag, which is more conducive to dephosphorization. However, the high Al2O3 content in aluminum-killed steel refining slag makes the molten steel more dilute, which makes it easier for the steel to splash during the smelting process, affecting the steel output and process control stability.

[0021] Therefore, the purpose of this invention is to provide a low-cost method for smelting low-phosphorus steel. This invention significantly increases the amount of aluminum-killed steel refining slag used, with a single furnace consumption of 6-12 tons, which facilitates "early slag formation and early dephosphorization," reduces the amount of coolant and slag-forming materials used, and achieves efficient dephosphorization. By adjusting the oxygen lance operation mode through pre-slag blowing and post-slag blowing, and through precise control of "high lance position for slag formation and dephosphorization in the early stage and low lance position for uniform stirring in the later stage," steel splashing is avoided, and the steel output is increased. By reducing the amount of coolant and slag-forming materials used and increasing the steel output, the smelting cost of low-phosphorus steel is reduced.

[0022] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0023] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0024] This invention provides a low-cost method for smelting low-phosphorus steel, comprising the following steps: 1. Collection and preparation of hot slag The aluminum-killed steel ladles, after the molten steel pouring is completed, are transferred to the iron slag bay using a transfer car. The remaining molten steel from ladles 4-7 and the attached refining slag are then poured into a single ladle for later use. The chemical composition of the aluminum-killed steel refining slag, by mass percentage, must meet the following requirements: SiO2 ≤ 12%, Al2O3: 25%–40%, CaO ≥ 50%, and basicity (CaO / SiO2) ≥ 4.5. This slag system possesses high basicity and high reactivity, making it an ideal dephosphorizing agent.

[0025] 2. Converter charging and initialization After the converter is slag splashed for furnace protection, all the final slag from the previous heat is completely drained. Then, scrap steel and molten iron are added. The scrap steel ratio is controlled between 3.5% and 12%; the molten iron composition requires a silicon content of ≤ 0.60% (Si) and a phosphorus content of ≤ 0.150%.

[0026] 3. Adding hot slag Pour the mixture of ladle residue and refining slag prepared in step 1 into the converter before blowing begins.

[0027] 4. Pre-slag blowing (first stage dephosphorization) Oxygen supply system: Oxygen lance position: 1450-1550mm, oxygen pressure: 0.85-0.90 MPa. The purpose is to achieve rapid ignition and temperature rise.

[0028] When the blowing time reaches 2.5–3.0 min, raise the oxygen lance position to 1600–1700 mm while maintaining the oxygen pressure. This "high lance position" mitigates the impact of the oxygen stream on the molten pool, increases the FeO content in the slag, and promotes slag formation and dephosphorization.

[0029] When the blowing reaches 4.0 to 5.0 minutes, the oxygen lance position is raised again to 1800 to 1900 mm to further enhance the foam slag and maximize the dephosphorization efficiency in the early stage.

[0030] When the total blowing time is 6-7 minutes, turn off the oxygen and lift the lance.

[0031] Adding ingredients system: Within 1–3 minutes after the start of blowing, sinter is added in 1–2 batches, with a total amount of 7.0–15.0 kg / ton of molten steel. The sinter acts as a coolant to control the excessively rapid temperature rise in the early stage, while also providing FeO to help adjust the fluidity and oxidizing properties of the slag.

[0032] 5. Discarding the slag After lifting the lance, pour out the high-phosphorus slag from the furnace.

[0033] 6. Slag removal followed by blowing (second stage dephosphorization and endpoint adjustment) Oxygen supply system: A relatively high constant lance position of 1550–1600 mm is adopted, and the oxygen pressure is controlled at 0.85–0.95 MPa. Maintaining a high lance position helps to maintain good oxidizing and foaming properties of the slag, continue dephosphorization, and inhibit phosphorus reversion.

[0034] One minute before the finish line, lower the lance position to 1100–1200 mm. Using a "low lance position" enhances the stirring of the molten pool at the finish line, ensuring uniform steel composition and temperature, promoting the decarburization reaction, and facilitating accurate hitting of the finish line.

[0035] Adding ingredients system: After blowing for 30 seconds, add 20.0-25.0 kg / ton of lime and 7.0-12.0 kg / ton of dolomite to quickly form a new slag system.

[0036] Depending on the temperature inside the furnace, sinter is added in batches for cooling, with each batch consisting of 3.0–5.0 kg / ton of molten steel, and all sinter is added 3 minutes before the end of the process.

[0037] 7. Endpoint Control Final carbon content: 0.05% ~ 0.07%; Final temperature: 1620℃ ~ 1635℃.

[0038] By precisely controlling the above process, the phosphorus content at the converter endpoint can be stably maintained at ≤0.010%.

[0039] Example The nominal capacity of the converter is 120t, and the target endpoint phosphorus content P ≤ 0.010%.

[0040] 1. Collect and mix the hot slag from the refining of aluminum killed steel from 5 heats. The composition of the refining slag system from the 5 heats is shown in Table 1. The weights of the hot slag from the 5 heats and the ladle residue are 2.23t, 2.35t, 2.36t, 2.20t, and 2.18t, respectively; among which, the hot slag from the refining of aluminum killed steel is approximately 8.5t, and the ladle residue is approximately 2.82t.

[0041] Table 1 2. After the converter slag splashes out, empty the slag completely and load in 15t of scrap steel and 125t of molten iron. Molten iron composition: Si=0.46%, P=0.136%.

[0042] 3. Pour the prepared hot slag mixture into the converter.

[0043] 4. Smelting process before slag removal: Start blowing oxygen: The blow gun position is 1530mm, and the oxygen pressure is 0.87 MPa.

[0044] Add 2226 kg of sintered ore when blowing for 1 min 20 s; add 1809 kg of sintered ore when blowing for 2 min 15 s.

[0045] After blowing for 3.0 minutes, raise the gun position to 1650mm.

[0046] After 5.0 minutes of blowing, the gun position was raised to 1820mm.

[0047] When the blowing process has lasted for 6.5 minutes, turn off the oxygen, lift the lance, and pour out the slag.

[0048] 5. After discarding the slag, begin the second stage of refining: The gun position is set at 1580mm and the oxygen pressure is 0.91 MPa.

[0049] After blowing for 30 seconds, add 2856 kg of lime and 1022 kg of dolomite at once.

[0050] Sintered ore was added in three batches at 9 min, 10 min, 11 min and 12 min, with weights of 500 kg, 480 kg, 560 kg and 558 kg respectively.

[0051] One minute before the finish line, lower the gun position to 1150mm.

[0052] The blowing process reached its endpoint after a total time of 15 minutes and 20 seconds. The endpoint carbon content was 0.062%, the endpoint temperature was 1628℃, and the endpoint phosphorus content was 0.0081%.

[0053] Comparative Example The difference from the embodiment is: 4. Pre-slag blowing process: Oxygen lance position: 1620mm (lance position refers to the distance between the oxygen lance nozzle and the molten pool surface), oxygen pressure controlled at 0.81Mpa; A batch of material was added: 400 Nm of material was blown. 3 2.232t of lime and 2.012t of sinter were added simultaneously. Second batch of material added: blown to 850Nm 3 Add 2,500 tons of lime and 2,300 tons of sinter at the same time; Lifting the gun: Blowing to 1550Nm 3 Then raise the oxygen lance position to 1700mm while keeping the oxygen pressure unchanged; Oxygen-free lance lifting: Blowing at 2800 Nm 3 Turn off the oxygen and lift the gun.

[0054] 5. Slag removal and blowing process: After slag removal, the lance position is kept constant at 1600mm in the early stage, and the oxygen pressure is controlled at 0.83Mpa. The lime is added in one go 30 seconds after the blowing starts, with the total amount added controlled at 3.500t. At the same time, 2.126t of dolomite is added in one go. The sinter is added evenly in 5 batches according to the temperature, with a total amount of 2.300t. The addition is completed 3 minutes before the end point. 1 minute before the end point, the lance position is lowered to 1200mm, and the oxygen pressure is controlled at 0.86Mpa until the lance is lifted at the end point.

[0055] Calculations were performed using one heat of low-phosphorus steel. The coolant and slag-forming materials used in the examples and comparative examples, as well as the steel output, were statistically analyzed. The results are shown in Table 2.

[0056] Table 2 As shown in Table 2, with the same amount of hot slag added during the refining of aluminum-killed steel, the comparative method requires more slag-forming material than the method in the example, and the steel output is less than that in the example. This indicates that the method of the present invention can reduce the amount of slag-forming material used and increase the steel output, thereby reducing the smelting cost of low-phosphorus steel.

[0057] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method of low cost smelting of low phosphorus steel, characterized in that, The method comprises the following steps: (1) ladle charging Pouring ladle residual molten steel, adhered aluminum killed steel refining slag, scrap steel and molten iron into a converter to prepare for smelting; (2) pre-deslagging blowing of mixed molten iron Opening blowing oxygen lance position: 1450-1550 mm, oxygen pressure: 0.85-0.90 MPa; When blowing for 2.5-3.0 min, the oxygen lance position is raised to 1600-1700 mm, and the oxygen pressure remains unchanged; When blowing for 4.0-5.0 min, the oxygen lance position is raised to 1800-1900 mm again; When the total blowing time is 6-7 min, oxygen is turned off and the lance is lifted; (3) deslagging (4) post-deslagging blowing A higher constant lance position of 1550-1600 mm is adopted, and the oxygen pressure is controlled at 0.85-0.95 MPa; 1 min before the end point, the lance position is lowered to 1100-1200 mm; (5) end point control.

2. The method of claim 1, wherein, In step (1), the mass ratio of the ladle residual molten steel to the aluminum killed steel refining slag is 1:

3.

3. The method of claim 1, wherein, In step (1), the aluminum killed steel refining slag comprises SiO2 ≤ 12%, Al2O3: 25%-40%, and CaO ≥ 50%; the basicity of the aluminum killed steel refining slag is ≥ 4.

5.

4. The method of claim 1, wherein, In step (1), the mass of the scrap steel accounts for 3.5-12% of the total mass of the scrap steel and the molten iron; the silicon content in the molten iron is ≤ 0.60%, and the phosphorus content is ≤ 0.150%.

5. The method of claim 1, wherein, In step (1), the ratio of the total mass of the ladle residual molten steel and the adhered aluminum killed steel refining slag to the total mass of the scrap steel and the molten iron is 8-15:

140.

6. The method of claim 1, wherein, In step (2), 1-2 batches of sinter are added within 1-3 min after the start of blowing, and the addition amount of the sinter is 7.0-15.0 kg / ton of molten steel.

7. The method of claim 1, wherein, In step (4), 20.0-25.0 kg / ton of molten steel of lime and 7.0-12.0 kg / ton of molten steel of dolomite are added at once after blowing for 30 seconds; sinter is added in batches, and the addition amount is 3.0-5.0 kg / ton of molten steel, and all of the sinter is added 3 min before the end point.

8. The method of claim 1, wherein, In step (5), the end point carbon content is 0.05%-0.07%, and the end point temperature is 1620°C-1635°C.

9. The method of claim 1, wherein, The phosphorus content of the low-cost smelted low-phosphorus steel obtained by the method is lower than ≤ 0.010%.

10. The method according to any one of claims 1-9 is used for reducing the amount of coolant and slagging material and increasing the steel tapping amount.

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