A method for producing an industrial pure iron

Abstract

This invention belongs to the field of metallurgical technology, specifically relating to a method for preparing industrial pure iron. The composition of this industrial pure iron, calculated by weight percentage, is: [C]≤0.01%, [Si]≤0.01%, [Mn]≤0.05%, [P]≤0.01%, [S]≤0.010%, [Al]: 0.03~0.05%, total oxygen ≤0.005%, with the remainder being Fe. By adding an oxygen barrier, calcium carbide, and aluminum granules to the LF refining furnace to create white slag, it is possible to achieve slag FeO≤1% while controlling the oxygen content of the molten steel at 0.05~0.09%, ensuring the decarburization requirements under non-oxygen blowing conditions in the RH furnace. After decarburization in the RH furnace, aluminum is added to remove oxygen from the molten steel, ultimately ensuring that the slag FeO content is controlled below 2%, enabling the smooth casting of small square billets containing aluminum steel.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and specifically relates to a method for preparing industrial pure iron. Background Technology

[0002] Industrial pure iron is a metallic material with very low carbon content. Its chemical composition is mainly iron, and the lower the levels of other alloying elements, the better. The room temperature microstructure of industrial pure iron is predominantly ferrite, characterized by its softness, high toughness, good ductility, and excellent electromagnetic properties, giving it an increasingly widespread market position. The smelting process for industrial pure iron is as follows: pre-desulfurization of molten iron → converter → LF refining furnace → RH vacuum treatment → continuous casting. Typically, oxygen blowing for decarburization and aluminum deoxidation is performed under RH vacuum conditions, followed by soft blowing after vacuum breaking, and then standing for at least 12 minutes (patent CN113512619A); or oxygen blowing for decarburization and aluminum deoxidation is performed under RH vacuum conditions with the addition of a 40Al modifier (patent CN113774277A), resulting in a longer RH process cycle. For converters, the final oxygen content of molten steel is 0.05-0.1%. LF furnaces only heat the steel without deoxidation, thus avoiding white slag formation. RH furnaces do not perform oxygen blowing; they rely solely on the inherent oxygen content of the molten steel for decarburization. After decarburization, aluminum is used to remove residual oxygen, followed by the addition of a slag modifier to the slag surface. However, in RH furnaces, slag modification is less effective due to slag crusting, resulting in a total iron content of approximately 10% after modification. During continuous casting, iron oxide in the slag reacts with Al in the molten steel to generate large amounts of Al2O3, causing blockage and clogging of the crystallizer nozzle and ladle nozzle. Furthermore, the cast billets have high inclusion and total oxygen content, failing to meet composition requirements.

[0003] Patent CN102978505A discloses a smelting method for high-strength IF steel. After tapping from the converter, a medium-carbon ferromanganese alloy is added, along with fine-grained quicklime and a slow-release deoxidizer containing 40%–50% metallic aluminum to modify the slag. The RH treatment utilizes the reaction of free oxygen in the molten steel with carbon for deep decarburization. After decarburization and void breaking, a slow-release deoxidizer is added to further modify the slag. Ultimately, the FeO content in the RH-exit slag can be controlled below 10%, meeting the casting requirements for slab automotive steel sheets. However, billet continuous casting machines require even lower FeO content in the furnace, making this patented method unsuitable.

[0004] Patent CN111518988A discloses a method for modifying refining slag of ultra-low carbon steel. After converter smelting, the steel is tapped, and small-particle quicklime and a first slow-release deoxidizer containing 55%–65% by mass of metallic aluminum are added during the tapping process to obtain the first modified slag. After decarburizing the steel with the first modified slag in an RH furnace, a second slow-release deoxidizer containing 40%–50% by mass of metallic aluminum is added to the slag surface, and the ladle is covered. Gas and oxygen are injected from inside the ladle cover to burn the slag surface and promote slag formation. Finally, after RH treatment, the FeO content in the refining slag can be stably controlled below 3%. This patented technology requires additional modification to the ladle cover to enable heating, and the process is complex.

[0005] Patent CN111893245A discloses a modifier for ultra-low carbon steel refining slag and its modification method. For ultra-low carbon steel smelting, the tapping temperature is controlled at 1680–1700℃, the carbon content at 0.03–0.05%, and the oxygen content at 0.05–0.075%. The tapping process uses a sliding plate to block slag. After tapping, the molten steel is transferred to the RH (refining and annealing) station without adding any slag-forming materials. The RH treatment process utilizes oxygen in the molten steel for decarburization, followed by the addition of aluminum shot for deoxidation. After deoxidation, a modifier is added to prevent oxygen from the slag from transferring to the molten steel. Then, other alloys are added for alloying, followed by pure circulation for 6–10 minutes to break up air pockets. After vacuum breaking up the air pockets, the molten steel is then calmed for 25–40 minutes before being cast onto the continuous casting platform. The patented modifier is spherical, with an aluminum-iron alloy core and a mixed slag outer layer. The aluminum-iron alloy contains 38-42% aluminum and accounts for 20-30% of the modifier's weight. The mixed slag contains CaO, Al2O3, MgO, and SiO2, with CaO accounting for 60-65% by weight, Al2O3 for 25-30%, MgO for 5-8%, and SiO2 for 2-5%. After cold pressing, the modifier has a diameter of 5-10 cm and a density of 3.5-4.0 kg / m³. 3The modifier is added to the molten steel in the vacuum chamber through a silo during the RH treatment process. Utilizing the kinetic energy of the circulating molten steel and the density difference between the modifier and the molten steel, the modifier forms an isolation layer between the molten steel and the slag. This prevents the highly oxidizing refining slag from directly contacting the molten steel, thus preventing secondary oxidation of the molten steel. Furthermore, the slag components in the isolation layer have a good ability to adsorb Al2O3 inclusions, improving the cleanliness of the molten steel. The modified agent in this patent has a spherical structure with an aluminum-iron alloy core and a mixed slag material on the outside. By adding the modified agent to the steel-slag interface, the aluminum element in the modified agent is used to prevent oxygen transfer from the slag to the molten steel. When added to the RH (reverse osmosis) stage, the modified agent floats to the slag-metal interface. It is speculated that the iron in the modified agent is mainly used to adjust the density. When the slag modified agent is added at the RH stage, it reacts with the oxidizing substances in the slag after reaching the slag-metal interface, producing a large amount of aluminum oxide. Finally, the oxygen in the slag is removed to below 3%. In order to ensure the cleanliness of the molten steel, it needs to be left to stand for 25-40 minutes after the RH stage treatment to allow the slag and modified agent to react fully. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing industrial pure iron by aluminum deoxidation. Through the slag modification technology of the LF treatment process, the refining slag is deoxidized to produce white slag while ensuring that the molten steel contains a certain oxygen content. Furthermore, RH does not require oxygen blowing treatment. After decarburization, the FeO content of the slag can be controlled within 2%, allowing for smooth continuous casting, and the total oxygen content of the billet can be controlled within 50ppm.

[0007] This invention provides a method for preparing industrial pure iron from aluminum deoxidation. The composition of this industrial pure iron, by weight percentage, is: [C]≤0.01%, [Si]≤0.01%, [Mn]≤0.05%, [P]≤0.01%, [S]≤0.010%, [Al]0.03~0.05%, total oxygen ≤0.005%, and the remainder being Fe. This invention achieves low oxidizing properties in the slag during refining in a refining furnace while ensuring a certain oxygen content in the molten steel, meeting the requirements for RH decarburization. Furthermore, the oxygen content of the slag can be controlled below 2% after RH treatment, improving the castability of the molten steel.

[0008] The specific methods, steps, and process parameters are as follows:

[0009] The specific operating steps for 120t converter smelting are as follows: KR hot metal desulfurization → BOF smelting → LF refining slag modification → RH decarburization and deoxidation → continuous casting.

[0010] Step 1: Desulfurize KR molten iron. After desulfurization, the sulfur content of the molten iron should be controlled below 0.001%.

[0011] Step two, BOF smelting: The converter smelting adopts a desulfurized molten iron + clean scrap steel smelting method. The molten iron ratio is controlled at 75%–90%, the scrap steel ratio is controlled at 10%–25%, the manganese content of the molten iron is required to be ≤0.35%, and the manganese content of the scrap steel is required to be ≤0.35%. The double slag method is adopted. The temperature of the molten pool is controlled at 1300–1400℃ during the first slag pouring, while the slag basicity is controlled at 1.0–1.5, and the slag MgO is controlled at 10–15%. The blowing end temperature is controlled at 1620–1650℃, and the end composition is controlled at [C]≤ 0.05%, [Mn]≤0.05%, [P]≤0.015%, [S]≤0.01%, [O]: 0.06~0.1%, the final slag composition at the blowing point is: CaO: 30%~45%, MgO: 10%~20%, SiO2: 10%~20%, FeO: 12%~25%, MnO: 5%~10%, and some unavoidable impurities; no deoxidizer or alloy is added during the tapping process, only 500kg of lime and 200kg of fluorite are added, and a dual-stage operation of slide plate + slag stopper is adopted;

[0012] Step 3, LF refining: The composition of the slag arriving at the LF station is controlled as follows: CaO: 40%–50%, CaF2: 10%–20%, MgO: 3%–10%, SiO2: 3%–5%, FeO: 10%–20%, MnO: 1%–3%, and some unavoidable impurities. After the molten steel arrives at the refining station, it is heated by electricity, and the temperature is controlled at 1640–1680℃. Then, an oxygen barrier, calcium carbide, and aluminum granules are added to modify the slag. The composition of the slag after tempering is: CaO: 55%–65%, CaF2: 8–15%, MgO: 3%–5%, SiO2: 3%–5%, FeO≤1%, MnO: 1%–3%, Al2O3: 5–10%, and some unavoidable impurities; the composition of the molten steel is [C]≤0.05%, [Mn]≤0.05%, [P]≤0.015%, [S]≤0.01%, [O]0.05–0.09%;

[0013] Step 4: RH decarburization and deoxidation. The RH arrival temperature is controlled at 1630-1660℃. After the molten steel arrives at the RH, it undergoes cyclic decarburization treatment, using argon as the lifting gas, with the vacuum degree controlled below 133Pa. After decarburization, the oxygen content is determined, requiring the carbon content of the molten steel to be ≤0.002%. Based on the oxygen determination results, aluminum particles are added for deoxidation treatment. After deoxidation, the aluminum content of the molten steel is controlled at 0.03-0.05%, and the oxygen content is ≤0.0015%. After breaking the vacuum, a low-carbon ladle covering agent with a carbon content ≤2% is added.

[0014] Step 5, continuous casting. The continuous casting process uses a 160mm×160mm cross-section and adopts protective casting. The continuous casting tundish uses an integral coated stopper rod tundish. The tundish is baked to 1050~1150℃, and the casting speed is controlled at 2.0~2.5m / min. The crystallizer adopts electromagnetic stirring and non-sinusoidal vibration mode. The secondary cooling adopts air mist cooling and weak cooling water supply. The continuous casting process uses a low carbon tundish covering agent with a carbon content ≤2% and an ultra-low carbon protective slag with a carbon content ≤8%.

[0015] Furthermore, as a preferred option, the slag modification method described in step three is as follows: First, the bottom blowing flow rate of the ladle is turned to the anti-clogging mode, and the bottom blowing flow rate is controlled at 50-100 L / min to reduce the slag-metal reaction; then, an oxygen barrier agent is added evenly into the ladle, with an addition amount of 200-500 kg. The oxygen barrier agent can prevent the molten steel from transferring oxygen to the slag; finally, 50-100 kg of calcium carbide and 30-60 kg of aluminum granules are added to create white slag and remove oxygen from the slag.

[0016] Furthermore, as a preferred embodiment, the oxygen barrier is prepared by first uniformly mixing aluminum powder and lime powder, then forming spheres, and finally coating the outside with a layer of iron sheet; the composition of the oxygen barrier is CaO: 20-40%, Al: 10-20%, Fe: 40-60%, and some unavoidable impurities; the particle size of the oxygen barrier is controlled at 20-40 mm, and the density is controlled at 4.5-5.5 g / cm³. 3 .

[0017] Furthermore, preferably, the argon flow rate for the cyclic decarburization in step four is 100–150 Nm³. 3 / h, with the cycle time controlled between 3 and 8 minutes.

[0018] Furthermore, as a preferred embodiment, after decarburization in step four, aluminum granules are added according to the oxygen content of the molten steel. When the oxygen content of the molten steel is ≤0.01%, 65-75 kg of aluminum granules are added; when the oxygen content of the molten steel is 0.01-0.02%, 80-90 kg of aluminum granules are added; when the oxygen content of the molten steel is 0.02-0.03%, 95-105 kg of aluminum granules are added.

[0019] Furthermore, as a preferred embodiment, after the RH treatment in step four, the slag composition is CaO: 45%–60%, CaF2: 5–10%, MgO: 3%–8%, SiO2: 2%–5%, FeO: ≤2%, Al2O3: 25–40%, and some unavoidable impurities.

[0020] Furthermore, as a preferred embodiment, the electromagnetic stirring current of the crystallizer in step five is 120-180A, and the frequency is 2.2-2.8Hz; the crystallizer amplitude is controlled at -2.5-2.5mm, and the frequency is controlled at 130+40Vopm.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The structure of the oxygen barrier of the present invention is that aluminum and calcium oxide are pressed into spheres, and then coated with iron sheet on the outside. The oxygen barrier is added during the refining process, and its density is 4.5–5.5 g / cm³. 3 Between the slag and molten steel, an oxygen barrier is added. After melting, the oxygen barrier disperses and settles between the slag and molten steel. The outermost layer of iron in the oxygen barrier melts into molten iron, and due to its density, this molten iron is closer to the molten steel, forming the first barrier against oxygen transfer from the molten steel. The aluminum in the oxygen barrier reacts with some of the oxygen transferred through the molten iron to form Al₂O₃, becoming the second barrier. The generated Al₂O₃ reacts with CaO in the oxygen barrier to form a low-melting-point liquid calcium aluminate. This liquid phase, closest to the slag layer, further prevents oxygen transfer from the molten steel to the slag, becoming the third barrier. Therefore, the refining process effectively prevents oxygen transfer from the molten steel to the slag.

[0023] 2. While ensuring the oxygen transfer from molten steel to the slag is blocked, a combination of calcium carbide and aluminum granules is used to remove oxygen from the slag surface. The main component of calcium carbide is CaC2, which can react with FeO in the slag as follows: CaC2 + 3FeO = CaO + 2CO + 3Fe. The CO gas generated in the reaction can stir the slag during the dispersion process, promoting the deoxidation reaction. The generated CaO is beneficial for the formation of white slag. After adding aluminum granules, the FeO content in the slag can be kept below 1%, and the oxygen content in the molten steel can be controlled between 0.05% and 0.09%, thus meeting the decarburization requirements under RH without oxygen blowing.

[0024] 3. The oxygen barrier agent is made into a size of 20-40mm and is added in a specific amount. It can also play an oxygen barrier role during the RH treatment process, and always maintain the ability to prevent the transfer of oxygen from the molten steel to the slag. After the RH decarburization is completed, aluminum is added to remove oxygen from the molten steel. Finally, it can ensure that the FeO content in the slag is controlled within 2%, so as to achieve the smooth casting of aluminum-containing steel in small square billets. Attached image description:

[0025] Figure 1 Example 3 shows the double-ladle casting curve;

[0026] Figure 2 To compare the single-ladle casting curve of Example 2. Detailed Implementation

[0027] Example 1 (First Furnace Casting)

[0028] 1. Desulfurization of molten iron

[0029] The composition of the desulfurized molten iron is: [Si] 0.35%, [Mn] 0.28%, [P] 0.13%, [S] 0.0002%, and the temperature of the molten iron is 1382℃.

[0030] 2. 120t converter smelting

[0031] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.25%, a manganese content of 0.25%, a phosphorus content of 0.02%, and a sulfur content of 0.01%.

[0032] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.6 min, slag basicity 1.3, temperature 1360℃; Slag dumping: 80% slag dumping; Second blowing: oxygen blowing time 6.5 min.

[0033] Endpoint: Final slag composition: CaO: 38.5%, MgO: 15.5%, SiO2: 12.7%, FeO: 18.9%, MnO: 6.5%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.04%, [Si] 0.002%, [Mn] 0.036%, [P] 0.008%, [S] 0.008%, free [O] 0.075%, endpoint temperature 1640℃.

[0034] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0035] 3. LF refining,

[0036] Arrival: Molten steel temperature 1580℃; Slag composition: CaO: 46.8%, CaF2: 16.2%, MgO: 5.6%, SiO2: 3.8%, FeO: 16.7%, MnO: 2.3%, and some unavoidable impurities.

[0037] Slag modification: Electricity is applied to raise the temperature. During the energizing process, the argon flow rate for bottom blowing from the ladle is controlled at 300 L / min. The energizing is stopped when the temperature reaches 1675℃. Oxygen content is determined, with the free oxygen in the molten steel at 0.071%. The bottom blowing flow rate is then increased to 60 L / min. 220 kg of oxygen barrier agent is evenly added to the ladle. The oxygen barrier agent consists of CaO: 28%, Al: 12%, Fe: 58%, and some unavoidable impurities. The particle size of the oxygen barrier agent is controlled at 20–40 mm, and the density is controlled at 5.2 g / cm³. 3 Two minutes later, 80 kg of calcium carbide and 45 kg of aluminum granules were added to the slag surface; the slag was discharged from the station after turning white.

[0038] Outgoing: Molten steel temperature 1659℃; Slag composition: CaO: 61.7%, CaF2: 13.6%, MgO: 4.2%, SiO2: 3.6%, FeO≤0.5%, MnO: 1.7%, Al2O3: 6.2%, and some unavoidable impurities; Molten steel composition: [C] 0.036%, [Si] 0.003%, [Mn]≤0.032%, [P]≤0.007%, [S]≤0.008%, Free [O] 0.063%.

[0039] 4. RH decarbonization and deoxidation

[0040] Arrival: After RH arrives at the station, temperature and oxygen levels are measured. The molten steel temperature is 1652℃, and the free oxygen content in the molten steel is 0.062%.

[0041] Decarburization: The process is carried out under a vacuum of 120 Pa, using argon as the booster gas at a flow rate of 120 Nm³. 3 After circulating for 5 minutes, the steel composition was measured as follows: [C] 0.001%, [Si] 0.003%, [Mn] 0.030%, [P] 0.008%, [S] 0.008%, and free [O] 0.026%.

[0042] Deoxidation: After decarburization, maintain the vacuum level and add 98 kg of aluminum granules. After circulating for 5 minutes, take a sample. The composition of the molten steel is [C] 0.001%, [Si] 0.004%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.032%, and free [O] 0.0012%. After deoxidation, continue circulating for 5 minutes to terminate the vacuum.

[0043] The ladle temperature is 1608℃, and a low-carbon ladle covering agent (carbon content ≤2%) is added to the surface of the molten steel; the slag composition is CaO: 50.3%, CaF2: 6.7%, MgO: 4.1%, SiO2: 3.5%, FeO: 1.1%, Al2O3: 32.1%, and some unavoidable impurities; the molten steel composition (as before) is: [C] 0.001%, [Si] 0.004%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.032%, and free [O] 0.0012%.

[0044] 5. Continuous casting: The continuous casting process uses a 160mm×160mm cross-section. The tundish is an integral coated stopper rod tundish, which is baked to 1130℃. This is the first casting batch, with superheat controlled at 43℃ and casting speed controlled at 2.2m / min. The crystallizer uses electromagnetic stirring and non-sinusoidal vibration mode. The electromagnetic stirring current of the crystallizer is 150A and the frequency is 2.5Hz. The crystallizer amplitude is controlled within ±2.5mm and the frequency is controlled at 130+40Vopm. The secondary cooling uses air mist cooling with weak cooling water supply. The continuous casting process uses a low-carbon tundish covering agent with a carbon content ≤2% and an ultra-low-carbon protective slag with a carbon content ≤8%.

[0045] The finished steel composition is: [C] 0.002%, [Si] 0.004%, [Mn] 0.032%, [P] 0.008%, [S] 0.008%, [Al] 0.032%, total oxygen 0.0026%, and the remainder is iron.

[0046] Example 2 (Second Batch)

[0047] 1. Desulfurization of molten iron

[0048] The composition of the desulfurized molten iron is: [Si] 0.42%, [Mn] 0.32%, [P] 0.14%, [S] 0.0002%, and the temperature of the molten iron is 1392℃.

[0049] 2. 120t converter smelting

[0050] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.29%, a manganese content of 0.28%, a phosphorus content of 0.012%, and a sulfur content of 0.01%.

[0051] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.8 min, slag basicity 1.2, temperature 1350℃; Slag dumping: 82% slag dumping; Second blowing: oxygen blowing time 6.7 min.

[0052] Endpoint: Final slag composition: CaO: 41.2%, MgO: 14.5%, SiO2: 13.3%, FeO: 20.3%, MnO: 6.7%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.037%, [Si] 0.003%, [Mn] 0.039%, [P] 0.007%, [S] 0.007%, free [O] 0.082%, endpoint temperature 1631℃.

[0053] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0054] 3. LF refining,

[0055] Arrival: Molten steel temperature 1571℃; Slag composition: CaO: 47.9%, CaF2: 15.4%, MgO: 5.3%, SiO2: 4.2%, FeO: 17.2%, MnO: 2.1%, and some unavoidable impurities.

[0056] Slag modification: Electricity is applied to raise the temperature, with the bottom blowing flow rate of the ladle controlled at 300 L / min during the energizing process. The energizing is stopped when the temperature reaches 1660℃. Oxygen content is determined, with the free oxygen content in the molten steel at 0.075%. The bottom blowing flow rate is then increased to 60 L / min. 310 kg of oxygen barrier agent is evenly added to the ladle. The composition of the oxygen barrier agent is CaO: 35%, Al: 10%, Fe: 54%, and some unavoidable impurities. The particle size of the oxygen barrier agent is controlled at 20–40 mm, and the density is controlled at 5.1 g / cm³. 3 Two minutes later, 85 kg of calcium carbide and 48 kg of aluminum granules were added to the slag surface; the slag was discharged from the station after turning white.

[0057] Outgoing: Molten steel temperature 1645℃; Slag composition: CaO: 62.5%, CaF2: 13.1%, MgO: 3.9%, SiO2: 3.2%, FeO: 0.6%, MnO: 1.8%, Al2O3: 7.1%, and some unavoidable impurities; Molten steel composition: [C] 0.032%, [Si] 0.003%, [Mn] ≤0.034%, [P] ≤0.007%, [S] ≤0.008%, Free [O] 0.068%.

[0058] 4. RH decarbonization and deoxidation

[0059] Arrival: After RH arrives at the station, temperature and oxygen levels are measured. The molten steel temperature is 1638℃, and the free oxygen content in the molten steel is 0.066%.

[0060] Decarburization: The process was carried out under a vacuum of 102 Pa, using argon as the booster gas at a flow rate of 120 Nm³. 3 After circulating for 5 minutes, the steel composition was measured as follows: [C] 0.001%, [Si] 0.003%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, and free [O] 0.028%.

[0061] Deoxidation: After decarburization, maintain the vacuum level and add 102 kg of aluminum granules. After circulating for 5 minutes, take a sample. The composition of the molten steel is [C] 0.001%, [Si] 0.003%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.036%, and free [O] 0.0011%. After deoxidation, continue circulating for 5 minutes to terminate the vacuum.

[0062] Leaving the station: The exit temperature is 1601℃, and a low-carbon ladle covering agent (carbon content ≤2%) is added to the surface of the molten steel. The RH exit slag composition is CaO: 50.8%, CaF2: 5.8%, MgO: 3.9%, SiO2: 2.7%, FeO: 1.3%, Al2O3: 34.2%, and some unavoidable impurities; the molten steel composition is [C] 0.001%, [Si] 0.003%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.036%, and free [O] 0.0011%.

[0063] 5. Continuous casting: This is the second casting in the cycle. The superheat is controlled at 36℃, and the casting speed is controlled at 2.2m / min. The crystallizer adopts electromagnetic stirring and non-sinusoidal vibration mode. The electromagnetic stirring current of the crystallizer is 150A and the frequency is 2.5Hz. The crystallizer amplitude is controlled within ±2.5mm and the frequency is controlled within 130+40Vopm. The secondary cooling adopts air mist cooling and weak cooling water supply. The continuous casting process uses low carbon ladle covering agent with carbon content ≤2% and ultra-low carbon protective slag with carbon content ≤8%.

[0064] The finished steel composition is [C] 0.002%, [Si] 0.003%, [Mn] 0.032%, [P] 0.008%, [S] 0.008%, [Al] 0.036%, total oxygen 0.0023%, and the remainder is iron.

[0065] Example 3 (Sixth consecutive casting)

[0066] 1. Desulfurization of molten iron

[0067] The composition of the desulfurized molten iron is: [Si] 0.28%, [Mn] 0.30%, [P] 0.135%, [S] 0.0002%, and the temperature of the molten iron is 1377℃.

[0068] 2. 120t converter smelting,

[0069] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.25%, a manganese content of 0.27%, a phosphorus content of 0.016%, and a sulfur content of 0.012%.

[0070] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.9 min, slag basicity 1.2, temperature 1361℃; Slag dumping: 85% slag dumping; Second blowing: oxygen blowing time 6.9 min.

[0071] Endpoint: Final slag composition: CaO: 41.7%, MgO: 16.2%, SiO2: 12.3%, FeO: 19.5%, MnO: 6.2%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.046%, [Si] 0.002%, [Mn] 0.042%, [P] 0.006%, [S] 0.008%, free [O] 0.071%, endpoint temperature 1626℃.

[0072] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0073] 3. LF refining,

[0074] Arrival: Molten steel temperature 1565℃; Slag composition: CaO: 48.6%, CaF2: 16.9%, MgO: 5.1%, SiO2: 4.3%, FeO: 16.2%, MnO: 1.8%, and some unavoidable impurities.

[0075] Slag modification: Electricity is applied to raise the temperature, with the bottom blowing flow rate of the ladle controlled at 300 L / min during the energizing process. The energizing is stopped when the temperature reaches 1655℃. Oxygen content is determined, with the free oxygen in the molten steel at 0.069%. The bottom blowing flow rate is then increased to 60 L / min. 380 kg of oxygen barrier agent is evenly added to the ladle. The composition of the oxygen barrier agent is CaO: 31%, Al: 11%, Fe: 57%, and some unavoidable impurities. The particle size of the oxygen barrier agent is controlled at 20–40 mm, and the density is controlled at 4.9 g / cm³. 3 Two minutes later, 80 kg of calcium carbide and 43 kg of aluminum granules were added to the slag surface; the slag was discharged from the station after turning white.

[0076] Outgoing: Molten steel temperature 1640℃; Slag composition: CaO: 61.5%, CaF2: 12.9%, MgO: 3.9%, SiO2: 3.5%, FeO: 0.7%, MnO: 1.9%, Al2O3: 7.3%, and some unavoidable impurities; Molten steel composition: [C] 0.044%, [Si] 0.003%, [Mn] ≤0.040%, [P] ≤0.005%, [S] ≤0.008%, Free [O] 0.064%.

[0077] 4. RH decarbonization and deoxidation

[0078] Arrival: After RH arrives at the station, temperature and oxygen levels are measured. The molten steel temperature is 1632℃, and the free oxygen content in the molten steel is 0.062%.

[0079] Decarburization: The process is carried out under a vacuum of 120 Pa, using argon as the booster gas at a flow rate of 120 Nm³. 3After circulating for 5 minutes at a time, a sample was taken. The composition of the molten steel was [C] 0.001%, [Si] 0.003%, [Mn] 0.039%, [P] 0.006%, [S] 0.008%, and [O] 0.016%.

[0080] Deoxidation: After decarburization, maintain the vacuum level and add 86 kg of aluminum granules. After circulating for 5 minutes, take a sample. The composition of the molten steel is [C] 0.001%, [Si] 0.003%, [Mn] 0.038%, [P] 0.006%, [S] 0.008%, [Al] 0.040%, and free [O] 0.0012%. After deoxidation, continue circulating for 5 minutes to terminate the vacuum.

[0081] The molten steel leaving the station has a temperature of 1590℃, and a low-carbon ladle covering agent (carbon content ≤2%) is added to the surface of the molten steel. The RH slag leaving the station consists of CaO: 49.6%, CaF2: 6.2%, MgO: 4.1%, SiO2: 3.1%, FeO: 1.0%, Al2O3: 33.4%, and some unavoidable impurities. The molten steel consists of [C] 0.001%, [Si] 0.003%, [Mn] 0.038%, [P] 0.006%, [S] 0.008%, [Al] 0.040%, and free [O] 0.0012%.

[0082] 4. Continuous casting: The continuous casting process uses a 160mm×160mm cross-section. This is the sixth continuous casting. The superheat is controlled at 30℃, and the casting speed is controlled at 2.2m / min. The crystallizer adopts electromagnetic stirring and non-sinusoidal vibration mode. The electromagnetic stirring current of the crystallizer is 150A and the frequency is 2.5Hz. The crystallizer amplitude is controlled within ±2.5mm and the frequency is controlled at 130+40Vopm. The secondary cooling adopts air mist cooling and weak cooling water supply. The continuous casting process uses low carbon ladle covering agent with a carbon content ≤2% and ultra-low carbon protective slag with a carbon content ≤8%.

[0083] The finished steel composition is: [C] 0.002%, [Si] 0.003%, [Mn] 0.038%, [P] 0.006%, [S] 0.008%, [Al] 0.040%, total oxygen 0.0025%, and the remainder is iron.

[0084] Figure 1 The casting curve for this casting cycle is shown. There were 8 consecutive casting heats, and the continuous casting process used a double-tundish method, with 5 streams per tundish, for a total of 10 streams. This indicates that the continuous casting curve is stable.

[0085] Comparative Example 1

[0086] The refining furnace does not use an oxygen barrier agent and directly uses calcium carbide and aluminum granules to make slag. When the refining slag turns into white slag, the free [O] in the molten steel is 0.008%, which cannot meet the decarburization requirements, and the smelting fails.

[0087] 1. Desulfurization of molten iron

[0088] The composition of the desulfurized molten iron is: [Si] 0.36%, [Mn] 0.27%, [P] 0.133%, [S] 0.0002%, and the temperature of the molten iron is 1383℃.

[0089] 2. 120t converter smelting

[0090] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.26%, a manganese content of 0.26%, a phosphorus content of 0.018%, and a sulfur content of 0.008%.

[0091] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.6 min, slag basicity 1.2, temperature 1356℃; Slag dumping: 81% of the slag is dumped; Second blowing: oxygen blowing time 6.6 min.

[0092] Endpoint: Final slag composition: CaO: 38.8%, MgO: 15.7%, SiO2: 12.9%, FeO: 18.5%, MnO: 6.6%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.039%, [Si] 0.002%, [Mn] 0.035%, [P] 0.007%, [S] 0.007%, [O] 0.078%, Endpoint temperature 1642℃.

[0093] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0094] 3. LF Refining

[0095] Arrival: Molten steel temperature 1582℃; Slag composition: CaO: 46.9%, CaF2: 15.8%, MgO: 5.7%, SiO2: 3.6%, FeO: 17.2%, MnO: 2.5%, and some unavoidable impurities.

[0096] Slag modification: Power is applied to raise the temperature. During the power-on process, the bottom blowing flow rate of the ladle is controlled at 300L / min. Power is applied to stop when the temperature reaches 1670℃. Oxygen is constant, and the free [O] in the molten steel is 0.075%. Then the bottom blowing flow rate is increased to 60L / min. After 2 minutes, 90kg of calcium carbide and 75kg of aluminum granules are added to the slag surface. The slag does not turn white. Then 50kg of calcium carbide and 50kg of aluminum granules are added again, and the slag turns white. Temperature sampling: molten steel temperature 1657℃; slag composition: CaO: 46.8%, CaF2: 11.2%, MgO: 3.7%, SiO2: 2.1%, FeO: 0.6%, MnO: 1.7%, Al2O3: 28.3%, and some unavoidable impurities; molten steel composition: [C] 0.036%, [Si] 0.012%, [Mn] ≤0.036%, [P] ≤0.007%, [S] ≤0.005%, free [O] 0.008%. The oxygen content of the molten steel was too low, and slag modification failed.

[0097] Comparative Example 2

[0098] The refining furnace does not use an oxygen barrier agent, but directly uses calcium carbide and aluminum granules to make slag. Under the condition of ensuring the oxidizing properties of molten steel, the refining slag cannot be made into white slag. The FeO content of the slag leaving the refining station is high. The oxidizing properties of the slag are high after RH treatment. After casting two heats in continuous casting, the nozzle is blocked and solidified.

[0099] 1. Desulfurization of molten iron

[0100] The composition of the desulfurized molten iron is: [Si] 0.34%, [Mn] 0.25%, [P] 0.132%, [S] 0.0002%, and the temperature of the molten iron is 1380℃.

[0101] 2. 120t converter smelting

[0102] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.25%, a manganese content of 0.26%, a phosphorus content of 0.019%, and a sulfur content of 0.009%.

[0103] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.7 min, slag basicity 1.23, temperature 1352℃; Slag dumping: 83% slag dumping; Second blowing: oxygen blowing time 6.8 min.

[0104] Endpoint: Final slag composition: CaO: 38.2%, MgO: 15.9%, SiO2: 12.5%, FeO: 18.8%, MnO: 6.7%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.035%, [Si] 0.002%, [Mn] 0.036%, [P] 0.006%, [S] 0.007%, free [O] 0.075%, endpoint temperature 1636℃.

[0105] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0106] 3. LF refining,

[0107] Arrival: Molten steel temperature 1577℃; Slag composition: CaO: 47.1%, CaF2: 15.5%, MgO: 6.1%, SiO2: 3.2%, FeO: 16.5%, MnO: 2.5%, and some unavoidable impurities.

[0108] Slag modification: Power is applied to raise the temperature. During the power application process, the bottom blowing flow rate of the ladle is controlled at 300L / min. Power is applied to raise the temperature to 1670℃ and then stopped. Oxygen is constant, and the free oxygen content of the molten steel is 0.072%. Then the bottom blowing flow rate is increased to 60L / min. After 2 minutes, 90kg of calcium carbide and 90kg of aluminum granules are added to the slag surface. The slag is light gray.

[0109] Outgoing: Molten steel temperature 1656℃; Slag composition: CaO: 56.2%, CaF2: 14.6%, MgO: 4.72%, SiO2: 3.5%, FeO: 12.8%, MnO: 1.7%, Al2O3: 3.8%, and some unavoidable impurities; Molten steel composition: [C] 0.036%, [Si] 0.003%, [Mn] ≤0.032%, [P] ≤0.007%, [S] ≤0.008%, Free [O] 0.052%.

[0110] 4. RH decarbonization and deoxidation

[0111] Arrival: After RH arrives at the station, temperature and oxygen levels are measured. The molten steel temperature is 1652℃, and the free oxygen content in the molten steel is 0.050%.

[0112] Decarburization: The process is carried out under a vacuum of 120 Pa, using argon as the booster gas at a flow rate of 120 Nm³. 3 After circulating for 5 minutes at a time, a sample was taken. The composition of the molten steel was [C] 0.001%, [Si] 0.003%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, and free [O] 0.019%.

[0113] Deoxidation: After decarburization, maintain the vacuum level and add 88 kg of aluminum granules. After circulating for 5 minutes, take a sample. The composition of the molten steel is [C] 0.001%, [Si] 0.004%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.038%, and free [O] 0.0010%. After deoxidation, continue circulating for 5 minutes to terminate the vacuum.

[0114] The ladle temperature is 1608℃, and a low-carbon ladle covering agent (carbon content ≤2%) is added to the surface of the molten steel; the slag composition is CaO: 43.6%, CaF2: 5.8%, MgO: 4.5%, SiO2: 3.3%, FeO: 12.1%, Al2O3: 25.8%, and some unavoidable impurities; the molten steel composition is: [C] 0.001%, [Si] 0.004%, [Mn] 0.032%, [P] 0.007%, [S] 0.008%, [Al] 0.035%, and free [O] 0.0010%.

[0115] 5. Continuous casting: The continuous casting process uses a 160mm×160mm cross-section. The tundish is an integral coated stopper rod tundish, which is baked to 1130℃, and the casting speed is controlled at 2.2m / min. The crystallizer adopts electromagnetic stirring and non-sinusoidal vibration mode. The electromagnetic stirring current of the crystallizer is 150A and the frequency is 2.5Hz. The crystallizer amplitude is controlled within ±2.5mm and the frequency is controlled within 130+40Vopm. The secondary cooling adopts air mist cooling and weak cooling water supply. The continuous casting process uses a low-carbon tundish covering agent with a carbon content ≤2% and an ultra-low carbon protective slag with a carbon content ≤8%.

[0116] The finished steel composition is: [C] 0.002%, [Si] 0.004%, [Mn] 0.032%, [P] 0.008%, [S] 0.008%, [Al] 0.009%, total oxygen 0.012%, and the remainder is iron. The total oxygen and aluminum content of the molten steel exceeds the requirements of the agreement.

[0117] The molten steel produced by the method in Comparative Example 2 was used for casting, employing a single ladle casting process with a total of 5 pours. Due to nozzle blockage, only two heats were cast, and the casting curves are as follows. Figure 2 As shown in the figure, the casting curve fluctuates greatly and cannot achieve the stable curve of the present invention.

[0118] Comparative Example 3

[0119] Adding the oxygen barrier substances in batches directly failed to achieve the desired oxygen barrier effect, resulting in failure to produce white slag. Subsequently, aluminum granules and calcium carbide were added to produce white slag, and it was found that the oxygen content of the molten steel was basically removed.

[0120] 1. Desulfurization of molten iron

[0121] The composition of the desulfurized molten iron is: [Si] 0.42%, [Mn] 0.30%, [P] 0.142%, [S] 0.0002%, and the temperature of the molten iron is 1395℃.

[0122] 2. 120t converter smelting

[0123] Raw materials: 110t of molten iron + 20t of clean scrap steel are used as raw materials for smelting. The scrap steel has a silicon content of 0.28%, a manganese content of 0.29%, a phosphorus content of 0.015%, and a sulfur content of 0.012%.

[0124] Smelting process: The double slag method is adopted; First blowing: oxygen blowing time 5.8 min, slag basicity 1.23, temperature 1352℃; Slag dumping: 82% slag dumping; Second blowing: oxygen blowing time 6.8 min.

[0125] Endpoint: Final slag composition: CaO: 41.5%, MgO: 14.3%, SiO2: 13.1%, FeO: 20.8%, MnO: 6.6%, and some unavoidable impurities; Endpoint molten steel composition: [C] 0.036%, [Si] 0.002%, [Mn] 0.038%, [P] 0.0072%, [S] 0.0071%, free [O] 0.081%, endpoint temperature 1635℃.

[0126] Steel tapping: 500 kg of lime and 200 kg of fluorite are added during the tapping process, and a dual-stage operation of sliding plate and slag stopper is adopted.

[0127] 3. LF refining,

[0128] Arrival: Molten steel temperature 1573℃; Slag composition: CaO: 47.2%, CaF2: 15.6%, MgO: 5.6%, SiO2: 4.5%, FeO: 17.1%, MnO: 2.2%, and some unavoidable impurities.

[0129] Slag modification: Electricity was applied to raise the temperature, with the bottom blowing flow rate of the ladle controlled at 300 L / min during the process. Electricity was stopped when the temperature reached 1660℃. Oxygen content was determined, with the free oxygen content in the molten steel at 0.074%. The bottom blowing flow rate was then increased to 60 L / min. 171 kg of iron sheet, 31 kg of aluminum blocks, and 120 kg of lime were evenly added to the ladle, with the particle size of the iron sheet, lime, and aluminum blocks controlled at 20–40 mm. After 2 minutes, 85 kg of calcium carbide and 48 kg of aluminum granules were added to the slag surface. The slag remained black, indicating failure to produce white slag. Calcium carbide and aluminum granules were then added to further modify the slag until it turned white. Oxygen content was then determined, with the result showing an oxygen content of 0.002% in the molten steel. The oxygen in the molten steel was removed, and the experiment failed.

[0130] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing industrial pure iron, characterized in that, The industrial pure iron composition by weight percentage is: [C]≤0.01%, [Si]≤0.01%, [Mn]≤0.05%, [P]≤0.01%, [S]≤0.010%, [Al]0.03~0.05%, total oxygen≤0.005%, with the remainder being Fe. The industrial pure iron is prepared using a 120t converter smelting process: KR hot metal desulfurization → BOF smelting → LF refining slag modification → RH decarburization and deoxidation → continuous casting, specifically including the following steps: Step 1: Desulfurize KR molten iron. After desulfurization, the sulfur content of the molten iron must be controlled below 0.001%. Step two, BOF smelting: The converter smelting adopts a desulfurized molten iron + clean scrap steel smelting method, with the molten iron ratio controlled at 75%~90% and the scrap steel ratio controlled at 10%~25%. The manganese content of the molten iron and the scrap steel must be ≤0.35%. A double-slag method is used, with the temperature of the molten pool controlled at 1300~1400℃ during the first slag pour, while the slag basicity is controlled at 1.0~1.5, and the slag MgO is controlled at 10~15%. The final blowing temperature is controlled at 1620~1650℃, and the final composition is controlled at [C]≤ 0.05%, [Mn]≤0.05%, [P]≤0.015%, [S]≤0.01%, [O]: 0.06~0.1%, the final slag composition at the blowing point is: CaO: 30%~45%, MgO: 10%~20%, SiO2: 10%~20%, FeO: 12%~25%, MnO: 5%~10%, and some unavoidable impurities; no deoxidizer or alloy is added during the tapping process, only 500kg of lime and 200kg of fluorite are added, and a dual-stage operation of slide plate + slag stopper is adopted; Step 3, LF refining. The composition of the slag arriving at the LF station is controlled as follows: CaO: 40%~50%, CaF2: 10~20%, MgO: 3%~10%, SiO2: 3%~5%, FeO: 10%~20%, MnO: 1%~3%, and some unavoidable impurities. After the molten steel arrives at the refining station, it is heated by electricity, and the temperature is controlled at 1640~1680℃. Then, an oxygen barrier, calcium carbide, and aluminum granules are added to modify the slag. After modification, the slag composition is: CaO: 55%~65%, CaF2: 8~15%, MgO: 3%~5%, SiO2: 3%~5%, FeO ≤1%. The molten steel composition is: MnO: 1%~3%, Al2O3: 5%~10%, and some unavoidable impurities; the molten steel composition is: [C]≤0.05%, [Mn]≤0.05%, [P]≤0.015%, [S]≤0.01%, [O]0.05~0.09%; the oxygen barrier is made by first uniformly mixing aluminum powder and lime powder, then forming balls, and then coating them with a layer of iron sheet; the oxygen barrier composition is: CaO: 20~40%, Al: 10~20%, Fe: 40~60%, and some unavoidable impurities; the particle size of the oxygen barrier is controlled at 20~40mm, and the density is controlled at 4.5~5.5g / cm³. 3 ; Step 4: RH decarburization and deoxidation. The RH arrival temperature is controlled at 1630~1660℃. After the molten steel arrives at the RH, it undergoes circulating decarburization treatment, using argon as the lifting gas, with the vacuum degree controlled below 133Pa. After decarburization, oxygen content is determined, requiring the carbon content of the molten steel to be ≤0.002%. Based on the oxygen determination results, aluminum particles are added for deoxidation treatment. After deoxidation, the aluminum content of the molten steel is controlled at 0.03~0.05%, and the oxygen content is ≤0.0015%. After breaking the vacuum, a low-carbon ladle covering agent with a carbon content ≤2% is added. Step 5, continuous casting. The continuous casting process uses a 160mm×160mm cross-section and adopts protective casting. The continuous casting tundish adopts an integral coated stopper rod tundish. The tundish is baked to 1050~1150℃, and the casting speed is controlled at 2.0~2.5m / min. The crystallizer adopts electromagnetic stirring and non-sinusoidal vibration mode. The secondary cooling adopts air mist cooling and weak cooling water supply. The continuous casting process uses low carbon tundish covering agent with carbon content ≤2% and ultra-low carbon protective slag with carbon content ≤8%.

2. The method for preparing industrial pure iron according to claim 1, characterized in that, Step 3 describes the following modification process: First, the bottom blowing flow rate of the ladle is switched to anti-clogging mode, and the bottom blowing flow rate is controlled at 50~100L / min to reduce slag-metal reaction; then, an oxygen barrier agent is added evenly into the ladle, with an addition amount of 200~500kg. The oxygen barrier agent can prevent oxygen transfer from the molten steel to the slag; finally, 50~100kg of calcium carbide and 30~60kg of aluminum granules are added to create white slag and remove oxygen from the slag.

3. The method for preparing industrial pure iron according to claim 1, characterized in that, The argon flow rate for the cyclic decarburization in step four is 100~150 Nm. 3 / h, with the cycle time controlled between 3 and 8 minutes.

4. The method for preparing industrial pure iron according to claim 1, characterized in that, After decarburization in step four, aluminum granules are added according to the oxygen content of the molten steel. When the oxygen content of the molten steel is ≤0.01%, 65~75kg of aluminum granules are added; when 0.01% < oxygen content of the molten steel is ≤0.02%, 80~90kg of aluminum granules are added; when 0.02% < oxygen content of the molten steel is ≤0.03%, 95~105kg of aluminum granules are added.

5. The method for preparing industrial pure iron according to claim 1, characterized in that, After the RH treatment in step four is completed, the slag composition is CaO: 45%~60%, CaF2: 5~10%, MgO: 3%~8%, SiO2: 2%~5%, FeO: ≤2%, Al2O3: 25~40%, and some unavoidable impurities.

6. The method for preparing industrial pure iron according to claim 1, characterized in that, In step five, the electromagnetic stirring current of the crystallizer is 120~180A and the frequency is 2.2~2.8Hz; the crystallizer amplitude is controlled at -2.5~2.5mm and the frequency is controlled at 130+40Vopm.

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