A production method for reducing gas bubbles in a conductive steel casting blank

Abstract

This invention belongs to the field of steelmaking technology, and particularly relates to a production method for reducing air bubbles in conductive steel billets. The method includes: Hot metal pretreatment: Mn content in the hot metal is ≤0.12%, desulfurized to below 0.002%; Converter: Clean scrap steel is selected, and the steel is tapped using a boiling process, with small-particle quicklime added during tapping to create slag; iron-containing materials are also added during tapping; LF (Leakage Fluidization): LF treatment uses both quicklime and bauxite slag, and argon blowing and stirring are performed after LF heating; before removal, a deoxidizer is used to cover the ladle; RH (Resin Refining): Deep vacuum treatment is employed, with aluminum granules used for quenching, and a deoxidizer is used to cover the ladle before removal; Continuous casting: Immersion casting in the tundish, with full-process protective casting, under light pressure throughout, and a constant casting speed of 1.4–1.6 m / min. The advantages are: A systematic production process is adopted, encompassing the entire process from converter to LF refining and RH vacuum treatment, achieving precise control of the gas content and oxygen level in the molten steel, fundamentally eliminating air bubble defects in the billets.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology, and in particular relates to a production method for reducing air bubbles in conductive steel billets. Background Technology

[0002] The chemical composition of conductive steel used to produce conductive steel wire, sheets, or bars is similar to that of industrial pure iron. A factory producing conductive steel uses a process route of BOF converter-LF refining-RH refining-CC continuous casting. The content of each component in this steel grade is extremely low, making steelmaking very difficult. Bubbles frequently form on the surface of the steel billets, affecting user performance. The main reason for this is improper steel modification. It is necessary to maximize the purification of the steel matrix and reduce the scattering of free electrons by solid solution impurities to obtain extremely high conductivity. However, this extreme pursuit of purity brings enormous technical challenges and quality control difficulties to the steelmaking process. The core difficulty lies in: Ultra-low carbon control and gas sensitivity: To stably control the carbon content below 0.0030%, the smelting process requires deep decarburization and extremely high vacuum treatment. This makes the molten steel highly susceptible to absorbing gases such as hydrogen (H) and nitrogen (N) from the atmosphere, refractory materials, or alloy materials. These gases are the main source of bubble defects in the cast billet.

[0003] The contradiction between deoxidation and inclusion control: The extremely low silicon and aluminum content means that traditional silicon and aluminum deoxidation processes cannot be used. Steel mills typically employ carbon deoxidation or special deoxidation processes, but the control of deoxidation products (such as CO gas) and the residual trace deoxidizing elements are crucial to the "modification" effect on the purity of molten steel. If the modification is improper, the residual oxygen (O) content in the molten steel will be too high, which will react with elements such as [C] and [H] at the solidification front to generate CO and H2O bubbles. These bubbles may grow using fine inclusions as nucleation sites and eventually be captured by the billet shell to form subcutaneous bubbles.

[0004] The process stability requirements are extremely high: at every stage of the converter, LF, RH and even continuous casting, any process fluctuation (such as improper oxygen control at the converter endpoint, poor slag condition during refining, substandard vacuum, failure of continuous casting protection pouring, etc.) may lead to an instantaneous increase in the content of gases ([N], [H], [O]), which greatly increases the risk of bubbles in the billet.

[0005] In actual production, the aforementioned difficulties have directly led to frequent subcutaneous bubble defects on the surface of continuously cast billets. These bubbles cannot be welded together during subsequent rolling processes, and will be exposed on the steel surface, forming defects such as hairline cracks, fissures, or peeling, which seriously affect the product yield, surface quality, and processing and use by end users. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a production method for reducing air bubbles in conductive steel billets, thereby reducing surface air bubble defects in conductive steel billets, ensuring stable production process, good castability, high component qualification rate, and improving rolling yield.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A production method for reducing air bubbles in conductive steel billets includes hot metal pretreatment, converter, LF refining, RH refining, and continuous casting, wherein: Hot metal pretreatment: The Mn content in the molten iron is ≤0.12% by mass, and it is desulfurized to below 0.002%. Converter process: Clean scrap steel is selected. The converter final temperature is 1620-1660℃, the final oxygen content is >700ppm, the final Mn content is ≤0.06%, and the final S content is ≤0.004%. The steel is tapped using boiling tapping. During the tapping process, 1.7-2.0 kg / t of fine-grained quicklime is added to form slag. At the same time, iron-containing materials are added during the tapping process. After tapping, the net clearance of the molten steel ladle is 600-800 mm. LF process: The LF treatment process uses two types of slag materials: quicklime and bauxite. The quicklime addition is 3-5 kg / t, and the bauxite addition is 0.6-1.1 kg / t. The LF process involves heating, followed by argon blowing and stirring for 3-8 minutes to keep the Mn content below 0.04%. Before unloading, the tank is covered with 0.3-0.6 kg / t of deoxidizer. RH process: RH treatment employs deep vacuum, with a vacuum degree ≤0.2kPa, decarburization time ≥15 minutes, and residual oxygen controlled at 260~350ppm. Aluminum granules are used for detergency, with the addition amount = constant oxygen value * 0.0013kg / t + (0.11~0.14)kg / t. The removed Als ≤0.013%, O ≤20ppm. Before removal, the tank is covered with 0.3~0.6kg / t of deoxidizer. Continuous casting process: The tundish baking time is 2-3 hours. The tundish is immersed in the casting process, and the entire process is protected during casting. The initial tundish covering agent is added evenly to the three holes of the first tank at a rate of 2.5-3.5 kg / t. The covering agent added to the tundish in subsequent tanks is more than 0.4 kg / t. The entire process is carried out under light pressure, with a stopper flow rate of 2 L / min-6 L / min and a top water inlet flow rate of 1 L / min-4 L / min. The molten layer thickness is 6 mm-12 mm. The tundish superheat is 20-35℃. The casting process is controlled at a constant casting speed of 1.4-1.6 m / min.

[0008] The scrap steel used is clean scrap steel, free of Ni, Cr, Cu, Mo elements and impurities.

[0009] The chemical composition of the iron-containing material, by mass percentage, includes: TFe ≥ 60%, FeO: 8%–15%, CaO: 10%–20%, SiO2: 3%–10%.

[0010] The chemical composition of the deoxidizer, by mass percentage, includes: Al: 47%–58%, CaO: 16%–28%, Al2O3: 14%–20%, and SiO2 ≤ 5%.

[0011] The chemical composition of the conductive steel, by mass percentage, includes: C≤0.0030%, Si≤0.007%, Mn≤0.045%, P≤0.018%, S≤0.005%, Als≤0.010%, with the remainder being iron and unavoidable impurities.

[0012] The particle size of the fine quicklime is 10mm to 40mm.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a systematic production process for ultra-low composition conductive steel, encompassing the entire process from converter refining to LF refining and RH vacuum treatment. This process achieves precise control over the gas content and oxygen level in the molten steel, fundamentally eliminating bubble defects in the cast billet. The invention's precise oxygen content control throughout the entire process, from high-oxygen converter tapping (>700ppm) to deep vacuum RH decarburization (residual oxygen 260-350ppm), and then to precisely quantified aluminum particle deoxidation, forms a systematic oxygen control path. This effectively avoids the risks of excessive composition due to over-deoxidation or bubble formation due to insufficient deoxidation.

[0014] This invention provides stable control over the molten steel composition, ensures smooth stopper opening during continuous casting, maintains good castability of the molten steel, stabilizes the production process, reduces operational difficulty, and guarantees qualified billet quality. The converter tapping process utilizes specific iron-containing materials (high FeO, CaO) and fine-grained quicklime, which effectively adsorbs inclusions and controls oxidation. The LF process employs a quicklime + bauxite slag system, effectively adsorbing Al2O3 inclusions. A uniform deoxidizer is used in the later stages of LF and RH processes during "capping" to form a protective layer and prevent secondary oxidation. Detailed Implementation

[0015] The present invention will now be described in detail, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0016] A method for reducing air bubbles in conductive steel billets, wherein the chemical composition of the conductive steel comprises, by mass percentage: C≤0.0030%, Si≤0.007%, Mn≤0.045%, P≤0.018%, S≤0.005%, Als≤0.010%.

[0017] Production process route: Hot metal pretreatment - converter - LF refining - RH refining - continuous casting, wherein: Hot metal pretreatment: Select molten iron with Mn ≤ 0.12% and desulfurize it to a S content below 0.002%; Converter process: Clean scrap steel is selected, free from useless elements and impurities such as Ni, Cr, Cu, and Mo, ensuring that the elements in the molten steel after converter smelting meet the requirements. The converter's final temperature is 1620-1660℃, which can control the Mn content in the molten steel to a low level, with final oxygen >700ppm and final Mn ≤0.06%, providing the necessary oxygen content for Mn removal in the subsequent LF process. The final sulfur content is ≤0.004%, and the steel is tapped by boiling. During the tapping process, 1.7-2.0 kg / t of fine-grained quicklime with a particle size of 10-40 mm is added to form slag. At the same time, iron-containing materials are added during the tapping process. The melted fine-grained quicklime and iron-containing materials become the top slag of the ladle. The top slag with this slag ratio has good adsorption capacity for inclusions and also has good Mn removal capacity. The net clearance of the molten steel ladle after tapping is 600-800 mm; the chemical composition of the iron-containing material by mass percentage includes: TFe≥60%, FeO: 8%-15%, CaO: 10%-20%, SiO2: 3%-10%.

[0018] LF process: The LF treatment process uses two types of slag materials: quicklime and bauxite. The quicklime addition is 3-5 kg / t, and the bauxite addition is 0.6-1.1 kg / t. The addition of refining slag materials plays a good role in raising the temperature and preventing secondary oxidation of the molten steel. The LF process involves raising the temperature, followed by argon blowing and stirring. The stirring time is controlled at 3-8 minutes to keep the Mn content below 0.04%. Before unloading, 0.3-0.6 kg / t of deoxidizer is used to cover the tank. The deoxidizing effect of the deoxidizer ensures that the oxidation of the top slag is controlled below 2%. The chemical composition of the deoxidizer, by mass percentage, includes: Al: 47%-58%, CaO: 16%-28%, Al2O3: 14%-20%, SiO2≤5%.

[0019] RH process: RH treatment employs deep vacuum processing, with a vacuum degree ≤0.2kPa, decarburization time ≥15 minutes, and residual oxygen controlled at 260~350ppm. Aluminum granules are used for quenching, with the addition amount = constant oxygen value * 0.0013kg / t + (0.11~0.14)kg / t. The removed Als ≤0.013%, O ≤20ppm. Precise control of the aluminum addition amount ensures that Al content does not exceed the standard while minimizing oxygen levels in the steel, guaranteeing a smooth casting process. Before removal, 0.3~0.6kg / t of deoxidizer is used to cover the vessel; the chemical composition of the deoxidizer, by mass percentage, includes: Al: 47%~58%, CaO: 16%~28%, Al2O3: 14%~20%, SiO2 ≤5%.

[0020] Continuous casting process: The tundish baking time is 2-3 hours. The tundish is immersed in the casting process, with full-process protective casting to ensure the molten surface is completely covered by the covering agent, preventing bubbling and churning. For the first casting, 2.5-3.5 kg / t of covering agent is evenly added to the three orifices of the first casting. Subsequent castings are adjusted based on surface coverage, with each subsequent casting adding at least 0.4 kg / t. The entire process is carried out under light pressure, with a stopper flow rate of 2-6 L / min and a top nozzle flow rate of 1-4 L / min. The stopper flow control minimizes argon bubble formation in the billet, and low argon gas control keeps bubbles in the billet at a very low level. The molten layer thickness is 6-12 mm; the tundish superheat is 20-35℃; and a constant casting speed is maintained during casting, controlled at 1.4-1.6 m / min.

[0021] The chemical composition of the covering agent, by mass percentage, includes: SiO2≤20%, CaO:25%~35%, MgO≤20%, Al2O3:15%~30%, TFe≤2%, and total C≤8%.

[0022] Example 1: Production methods to reduce air bubbles in conductive steel billets include the following production processes: Hot metal pretreatment: Molten iron with Mn content of 0.08% and S content of 0.001% after desulfurization; Converter process: Clean scrap steel is selected, free from useless elements and impurities such as Ni, Cr, Cu, and Mo. The converter final temperature is 1646℃, the final oxygen is 754ppm, the final Mn is 0.03%, and the final S is 0.0025%. The steel is tapped using boiling tapping. During the tapping process, 1.8kg / t of fine-grained quicklime is added to form slag. At the same time, 500kg of iron-containing material is added during the tapping process. After tapping, the net clearance of the molten steel ladle is 700mm.

[0023] LF process: During the LF treatment process, 4.2 kg / t of quicklime and 0.6 kg / t of bauxite are added; the LF is heated for 8 minutes, followed by argon blowing and stirring for 8 minutes; the Mn content in the steel is 0.014%; before being removed, 0.6 kg / t of deoxidizer is added to cover the tank.

[0024] RH process: RH treatment employs deep vacuum, with a vacuum degree ≤0.2kPa, decarburization time of 19 minutes, and residual oxygen controlled at 336ppm. Aluminum granules are used for detergency, with an addition amount of 157kg. The resulting Als and O concentrations are 0.011% and 16ppm, respectively. 0.4kg / t of deoxidizer is added to the tank before removal.

[0025] Continuous casting process: The tundish baking time is 2.5 hours. The tundish is immersed in the casting process, with full-process protective pouring. At the start, 3.0 kg / t of covering agent is evenly added to the three holes of the first ladle, maintained under light pressure throughout the process. The stopper flow rate is 2 L / min, and the top nozzle flow rate is 3 L / min. The molten layer thickness is 11 mm. The tundish superheat is 26℃. The pouring speed is constant at 1.5 m / min. The produced billet is bubble-free.

[0026] Example 2: Production methods to reduce air bubbles in conductive steel billets include the following production processes: Hot metal pretreatment: Molten iron with Mn content of 0.07% and S content of 0.001% after desulfurization; Converter process: Clean scrap steel is selected, free from useless elements and impurities such as Ni, Cr, Cu, and Mo. The converter final temperature is 1641℃, the final oxygen is 734ppm, the final Mn is 0.03%, and the final S is 0.0021%. The steel is tapped using boiling tapping. During the tapping process, 1.9kg / t of fine-grained quicklime is added to form slag. At the same time, 520kg of iron-containing materials are added during the tapping process. After tapping, the net clearance of the molten steel ladle is 700mm.

[0027] LF process: During the LF treatment process, 4.7 kg / t of quicklime and 0.8 kg / t of bauxite are added; the LF is heated for 9 minutes, followed by argon blowing and stirring for 7 minutes; the Mn content in the steel is 0.011%; before being removed, 0.4 kg / t of deoxidizer is added to cover the tank.

[0028] RH process: RH treatment employs deep vacuum, with a vacuum degree ≤0.2kPa, decarburization time of 21 minutes, and residual oxygen controlled at 321ppm. Aluminum granules are used for detergency, with an addition amount of 153kg. The resulting Als is 0.009%, and O is 12ppm. 0.5kg / t of deoxidizer is added to the tank before removal.

[0029] Continuous casting process: The tundish baking time is 2.5 hours. The tundish is immersed for initial pouring, with full-process protective pouring. At the start, 3.0 kg / t of covering agent is evenly added to the three holes of the first ladle, maintained under light pressure throughout the process. The stopper flow rate is 2 L / min, and the top nozzle flow rate is 2 L / min. The molten layer thickness is 12 mm. The tundish superheat is 28℃. The pouring speed is constant at 1.5 m / min. The produced billet is bubble-free.

[0030] Example 3: Production methods to reduce air bubbles in conductive steel billets include the following production processes: Hot metal pretreatment: Molten iron with Mn content of 0.10% and S content of 0.002% after desulfurization; Converter process: Clean scrap steel is selected, free from useless elements and impurities such as Ni, Cr, Cu, and Mo. The converter final temperature is 1638℃, the final oxygen is 773ppm, the final Mn is 0.03%, and the final S is 0.0029%. The steel is tapped using boiling tapping. During the tapping process, 1.8kg / t of fine-grained quicklime is added to form slag. At the same time, 510kg of iron-containing materials are added during the tapping process. After tapping, the net clearance of the molten steel ladle is 650mm.

[0031] LF process: During the LF treatment process, 3.9 kg / t of quicklime and 0.6 kg / t of bauxite are added; the LF is heated for 9 minutes, followed by argon blowing and stirring for 6 minutes; the Mn content in the steel is 0.018%; before being removed, 0.5 kg / t of deoxidizer is added to cover the tank.

[0032] RH process: RH treatment employs deep vacuum, with a vacuum degree ≤0.2kPa, decarburization time of 18 minutes, and residual oxygen controlled at 286ppm. Aluminum granules are used for detergency, with an addition amount of 151kg. The resulting Als is 0.012%, and O is 10ppm. 0.5kg / t of deoxidizer is added to the tank before removal.

[0033] Continuous casting process: The tundish baking time was 2.7 hours. The tundish was immersed for initial pouring, with full-process protective pouring. At the start, 3.0 kg / t of covering agent was evenly added to the three holes of the first ladle, maintained under light pressure throughout the process. The stopper flow rate was 3 L / min, and the top nozzle flow rate was 4 L / min. The molten layer thickness was 10 mm. The tundish superheat was 24℃. The pouring speed was constant at 1.6 m / min. The produced billet was bubble-free.

[0034] This invention employs a systematic production process for ultra-low composition conductive steel, encompassing the entire process from converter refining to RH vacuum treatment. This process achieves precise control over the gas content and oxygen level in the molten steel, keeping the oxygen content below 20 ppm. The continuous casting process utilizes low argon gas volume, reducing the number of bubbles on the billet surface from 50-70 per square meter to less than 5 per square meter, fundamentally eliminating bubble defects and ensuring fully qualified billet surface quality. This invention provides precise oxygen content control throughout the entire process, from high-oxygen tapping in the converter (>700 ppm) to deep vacuum decarburization in RH (residual oxygen 260-350 ppm), and then to precise quantitative aluminum particle deoxidation. This forms a systematic oxygen control path, effectively avoiding the risks of excessive composition due to over-deoxidation or bubble formation due to insufficient deoxidation.

Claims

1. A production method for reducing air bubbles in conductive steel billets, characterized in that, This includes hot metal pretreatment, converter, LF refining, RH refining, and continuous casting, among which: Hot metal pretreatment: The Mn content in the molten iron is ≤0.12% by mass, and it is desulfurized to below 0.002%. Converter process: Clean scrap steel is selected. The converter final temperature is 1620-1660℃, the final oxygen content is >700ppm, the final Mn content is ≤0.06%, and the final S content is ≤0.004%. The steel is tapped using boiling tapping. During the tapping process, 1.7-2.0 kg / t of fine-grained quicklime is added to form slag. At the same time, iron-containing materials are added during the tapping process. After tapping, the net clearance of the molten steel ladle is 600-800 mm. LF process: The LF treatment process uses two types of slag materials: quicklime and bauxite. The quicklime addition is 3-5 kg / t, and the bauxite addition is 0.6-1.1 kg / t. The LF process involves heating, followed by argon blowing and stirring for 3-8 minutes to keep the Mn content below 0.04%. Before unloading, the tank is covered with 0.3-0.6 kg / t of deoxidizer. RH process: RH is treated with deep vacuum, with a vacuum degree ≤0.2kPa, decarburization time ≥15 minutes, and residual oxygen controlled at 260~350ppm. Aluminum granules are used for sedation, with the addition amount = constant oxygen value * 0.0013kg / t + (0.11~0.14)kg / t. The removed Als ≤0.013% and O ≤20ppm. Before removal, the tank is covered with 0.3~0.6kg / t of deoxidizer. Continuous casting process: The tundish baking time is 2-3 hours. The tundish is immersed in the casting process, and the entire process is protected during casting. The initial tundish covering agent is added evenly to the three holes of the first tank at a rate of 2.5-3.5 kg / t. The covering agent added to the tundish in subsequent tanks is more than 0.4 kg / t. The entire process is carried out under light pressure, with a stopper flow rate of 2 L / min-6 L / min and a top water inlet flow rate of 1 L / min-4 L / min. The molten layer thickness is 6 mm-12 mm. The tundish superheat is 20-35℃. The casting process is controlled at a constant casting speed of 1.4-1.6 m / min.

2. The production method for reducing air bubbles in conductive steel billets according to claim 1, characterized in that, The scrap steel used is clean scrap steel, free of Ni, Cr, Cu, Mo elements and impurities.

3. The production method for reducing air bubbles in conductive steel billets according to claim 1, characterized in that, The chemical composition of the iron-containing material, by mass percentage, includes: TFe ≥ 60%, FeO: 8%–15%, CaO: 10%–20%, SiO2: 3%–10%.

4. The production method for reducing air bubbles in conductive steel billets according to claim 1, characterized in that, The chemical composition of the deoxidizer, by mass percentage, includes: Al: 47%–58%, CaO: 16%–28%, Al2O3: 14%–20%, and SiO2 ≤ 5%.

5. The production method for reducing air bubbles in conductive steel billets according to claim 1, characterized in that, The chemical composition of the conductive steel, by mass percentage, includes: C≤0.0030%, Si≤0.007%, Mn≤0.045%, P≤0.018%, S≤0.005%, Als≤0.010%, with the remainder being iron and unavoidable impurities.

6. The production method for reducing air bubbles in conductive steel billets according to claim 1, characterized in that, The particle size of the fine quicklime is 10mm to 40mm.