A refining method for reducing the aluminum content in aluminum-killed rare earth steel

Abstract

This invention relates to a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, belonging to the field of iron and steel metallurgical technology. It solves the technical problem of high risk of nozzle blockage during continuous casting when using aluminum deoxidation in existing rare earth steel refining processes. The refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel includes the following steps: Step S1: When tapping from the converter, aluminum and low-silicon barium ferroalloy are added to the molten steel for deoxidation, and lime, magnesia-containing, and alumina-containing slag are added to the slag surface; Step S2: When entering the LF ladle furnace, lime, barium oxide-containing, magnesia-containing, and sodium oxide-containing slag are added to the slag surface to create white slag; aluminum particles and low-silicon barium ferroalloy are added simultaneously for deoxidation, and alloying is performed during the middle stage of white slag formation; after white slag formation, soft blowing treatment is performed; Step S3: During RH vacuum degassing refining, no alloy is added, and rare earth ferroalloy is added at the end of the vacuum treatment, and soft blowing is performed when exiting the RH furnace. This invention achieves the purpose of suppressing nozzle turbulence and reduces the frequency of nozzle replacement.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel. Background Technology

[0002] Rare earth elements in steel play various roles, including modifying inclusions, refining grains, improving high-temperature performance, enhancing corrosion resistance, and improving processing performance. However, rare earth elements have a strong affinity for oxygen, and when added during smelting, they are easily consumed in large quantities during deoxidation, resulting in low yields and hindering their full potential in steelmaking. Therefore, a large amount of metallic aluminum is currently added during the refining process of rare earth steel for deoxidation to ensure low-oxygen and low-sulfur conditions in the molten steel before the addition of rare earth elements. This also ensures that the aluminum content in the molten steel after refining is controlled between 0.04% and 0.06%. The disadvantage of this process is the high aluminum content in the molten steel. During subsequent continuous casting, this aluminum reacts with refractory materials and tundish covering agents, producing a large number of inclusions, causing nozzle blockage, and affecting the castability of the rare earth steel. In addition, the large amount of solid, high-melting-point Al2O3 inclusions produced by Al deoxidation are in the form of small clusters or chains with a wide size distribution. If the residual amount in the steel exceeds a certain limit, it will become the main harmful inclusion that degrades the performance of the steel. Therefore, this also increases the requirements for removing Al deoxidation products by flotation in the refining stage and increases the workload of refining.

[0003] Therefore, in the process of rare earth steel refining, how to ensure low sulfur and low oxygen conditions in molten steel while minimizing the aluminum content in the molten steel has become an urgent technical problem to be solved. Summary of the Invention

[0004] To address the above technical problems, this invention provides a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel. This method solves the technical problems that existing rare earth steel refining processes using aluminum deoxidation, while meeting the requirements of low oxygen and low sulfur in molten steel, also result in a high aluminum content, leading to a high risk of nozzle blockage during continuous casting and an increased probability of excessive alumina inclusions in the steel.

[0005] The objective of this invention is mainly achieved through the following technical solutions: This invention provides a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, comprising the following steps: Step S1: Use a converter for smelting. When tapping steel from the converter, add aluminum and low-silicon barium iron alloy to deoxidize the molten steel. Add lime, slag containing magnesium oxide and aluminum oxide to the slag surface. Step S2: After the steel is tapped from the converter, it is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, barium oxide, magnesium oxide and sodium oxide are added to the slag surface to make white slag. At the same time, aluminum particles and low silicon barium iron alloy are added to the molten steel for deoxidation. Alloying is carried out in the middle of the white slag making process. After the white slag making is completed, the molten steel is subjected to soft blowing treatment. Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

[0006] Furthermore, in step S1, when tapping the steel, the tapping temperature is ≥1620℃, and the carbon content of the tapped steel at the end of the blowing process is ≥0.08%, the phosphorus content is <0.010%, and the sulfur content is <0.01% by mass percentage.

[0007] Furthermore, the amount of aluminum added per ton of steel is (8.44×m / [%C]) kg, and the amount of barium added per ton of steel is (21.41×m / [%C]) kg, where m is the carbon-oxygen product and [%C] is the carbon content of the steel at the blowing endpoint; the amount of low-silicon barium-containing ferroalloy added is calculated by back-calculating based on the amount of barium added. In the low-silicon barium-ferroalloy, the mass percentage of silicon is less than 5%, the mass percentage of barium is more than 20%, and the remainder is iron and unavoidable impurities.

[0008] Furthermore, the aluminum content [Als] in the molten steel is controlled to be less than 0.015%.

[0009] Furthermore, in step S1, the lime contains no less than 85% CaO, the magnesium oxide slag contains more than 90% MgO, and the alumina slag contains no less than 80% Al2O3; the amount of lime added per ton of steel is 2.65~4.35 kg / t, the amount of magnesium oxide slag added is 1~3 kg / t, and the amount of bauxite added is 3.5~6.5 kg / t.

[0010] Furthermore, in step S2, the lime contains no less than 85% CaO, the barium oxide slag contains no less than 50% BaO, the magnesium oxide slag contains more than 90% MgO, and the sodium oxide slag contains no less than 90% Na2O. In each ton of steel, the following amounts are added: lime 8-15 kg / t, barium oxide slag 0.45-0.55 kg / t, magnesium oxide slag 0.45-0.55 kg / t, and sodium oxide slag 0.45-0.55 kg / t. 0.2-0.3 kg / t of aluminum granules and 0.5-0.76 kg / t of barium are added per ton of steel. The amount of low-silicon barium-containing ferroalloy added is calculated by back-calculating the amount of barium added. In the low-silicon barium-ferroalloy, the mass percentage of silicon is below 5%, the mass percentage of barium is above 20%, and the remainder is iron and unavoidable impurities.

[0011] Furthermore, in step S2, the stirring intensity of the bottom-blown argon gas in the ladle during the white slag formation stage is 0.008~0.013 Nm. 3 / (min·t), white slag formation time is 35~50 minutes; soft blowing treatment time is 20~30 minutes, and the bottom blowing gas stirring intensity of the ladle is 0.003~0.005 Nm. 3 Between / (min·t).

[0012] Furthermore, in step S2, the mass percentage composition of the molten steel after refining in the LF ladle furnace is as follows: [Als] < 0.020%, TO < 20 ppm, [S] < 0.0020%, [P] < 0.01%.

[0013] Furthermore, in step S3, the vacuum treatment time is 10-15 minutes; the soft blowing time is 3-5 minutes; and the stirring intensity of the bottom-blown gas in the ladle is 0.003-0.005 Nm. 3 Between / (min·t).

[0014] Furthermore, in step S3, the molten steel obtained from RH station has the following composition by mass percentage: [Als] < 0.015%, TO < 15ppm, [S] < 0.0020%, [P] < 0.01%, and [RE] 0.0020~0.02%.

[0015] Compared with the prior art, the present invention can achieve at least one of the following technical effects: (1) This invention first controls the tapping temperature to ≥1620℃, and the carbon content of the tapping steel at the end of the blowing process to ≥0.08%, phosphorus content to <0.010%, and sulfur content to <0.01%, so as to maintain a low dissolved oxygen content in the steel, as well as a sufficiently high tapping temperature and sufficiently low phosphorus and sulfur content. This reduces the deoxidation burden of converter tapping and LF furnace refining, and also reduces the tasks of raising the temperature, reducing sulfur and preventing phosphorus reversion in subsequent LF furnace refining. As a result, the total amount of deoxidizer added is effectively controlled, and over-refining in the LF furnace is eliminated. This achieves the goal of maintaining a favorable state of low aluminum, low oxygen, low sulfur and low phosphorus in the molten steel throughout the refining process.

[0016] (2) In the process of tapping steel in the converter, the present invention adopts the process of Al and Ba combined deoxidation. Compared with aluminum, barium has a stronger deoxidation ability and deoxidation efficiency. Moreover, after being added to the steel, the reaction is stable and it is not easy to splash. This further reduces the amount of Al used, and even the total amount of deoxidizer, which further improves the deoxidation efficiency. Ultimately, it reduces the aluminum content in the molten steel ([Als] < 0.015%) and the absolute amount of alumina inclusions generated. In addition, it promotes the alumina generated to float into the slag in the form of BaO·Al2O3 composite inclusions, which further reduces the refining burden.

[0017] (3) This invention protects the molten steel from secondary oxidation by adding lime, magnesium oxide and alumina-containing slag material to the slag surface during the steel tapping process, thereby quickly forming a slag with refining capabilities and providing a sufficient reaction interface to create a good starting point for LF furnace refining.

[0018] (4) In this invention, when the LF ladle furnace enters the slag, lime, slag containing barium oxide, magnesium oxide, and sodium oxide are added to the slag surface to create white slag. This slag has properties such as high basicity, low melting point, and strong adsorption, while also protecting the furnace lining and promoting rapid slag formation. The purpose is to obtain molten steel with ultra-low sulfur, low oxygen, and high purity. Specifically, a large amount of lime (8-15 kg / t) provides high basicity, which is a direct guarantee for deep desulfurization, ensuring that the sulfur content of the final molten steel is below 20 ppm; the SiO2 content is strictly controlled within the range of 3-10%, eliminating the risk of "silicon reversion" and ensuring the accuracy of the silicon composition of the molten steel. The addition of functional slag materials in trace amounts is crucial: BaO, as a strong alkaline flux, significantly lowers the melting point and viscosity of the slag, accelerates slag formation and synergistically desulfurizes, as well as adsorbs deoxidation inclusions generated by Ba deoxidation; MgO aims to saturate the slag with MgO to match the magnesia-carbon brick lining, prevent erosion, and avoid external contamination; Na2O reduces the surface tension and viscosity of the slag, greatly promoting the polymerization, flotation, and absorption of micro-inclusions such as deoxidation products Al2O3, which is the core to obtaining low total oxygen content and clean molten steel. The total slag volume ensures sufficient slag layer coverage and reaction capacity, while moderately strong bottom blowing provides optimized kinetic conditions for all steel-slag interface reactions.

[0019] (5) In this invention, aluminum particles and low-silicon barium ferroalloy are added to the molten steel during the LF ladle furnace deoxidation process. High-purity aluminum particles serve as the main deoxidizer, rapidly reducing the oxygen activity of the molten steel and creating a strong reducing atmosphere for white slag formation. The low-silicon barium ferroalloy undertakes a dual mission: firstly, it works synergistically with aluminum to perform composite deoxidation, reducing the amount of aluminum used and generating lower-melting-point barium aluminate that is easier to float; secondly, it performs inclusion modification treatment, transforming the residual Al2O3 inclusions in the steel into low-melting-point, spherical liquid or plastic inclusions, thereby significantly reducing their harm to the steel's properties. The "low-silicon" requirement of the low-silicon barium ferroalloy ensures that the introduction of barium does not interfere with the control of the silicon composition of the molten steel.

[0020] (6) This invention is based on the fact that BaO generated by Ba deoxidation easily combines with Al2O3 to form large-sized, liquid composite inclusions BaO·Al2O3 at high temperatures. These inclusions readily aggregate and spheroidize in molten steel, forming larger spherical particles, which are then removed by flotation, following Stokes' law with extremely high efficiency, resulting in a significant reduction in Al2O3 inclusions in the steel. Therefore, the amount of deoxidizer used in converter tapping and LF furnace refining is designed according to the formation of composite inclusions BaO·Al2O3, i.e., Al removes 75% of the oxygen in the steel, and Ba removes 25% of the oxygen in the steel. The amount of Ba added is approximately 2.54 times that of Al added. Therefore, the design of the Al and Ba addition ratio is reasonable.

[0021] (7) The RH refining of the present invention does not add any alloys during vacuum treatment, creating an undisturbed environment to allow the carbon-oxygen reaction and degassing to proceed fully. This is the key to reducing the total oxygen (TO) depth to <15ppm and controlling the aluminum content [Als]. The 10-15 minute vacuum treatment time ensures an optimized window for the full removal of these gases and inclusions. At the end of the vacuum treatment, the oxygen and sulfur content of the molten steel is extremely low. At this time, the addition of rare earth iron alloy can accurately control the rare earth content [RE] within the range of 0.0020-0.02%. The 3-5 minute weak stirring and soft blowing after the RH leaves the station promotes the complete removal of fine inclusions generated during the vacuum period and rare earth modification, stabilizes the extremely low TO and inclusion levels, and prevents secondary oxidation of the molten steel. The entire process is interconnected, ultimately obtaining ultra-high purity molten steel with extremely low gas content and harmless inclusions.

[0022] (8) The method of the present invention yields rare earth steel with low oxygen (TO<15ppm), low sulfur ([S]<20ppm) and low aluminum content ([Als]<0.015%), which greatly reduces the amount of alumina inclusions in the steel, thereby suppressing the turbulence of the nozzle and reducing the frequency of nozzle replacement from once every 1800 tons of rare earth steel cast on average to once every 2800 tons of rare earth steel cast on average. Detailed Implementation

[0023] The following detailed description of a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, with reference to specific embodiments, is provided. These embodiments are for comparative and illustrative purposes only, and the present invention is not limited to these embodiments.

[0024] Studies have shown that barium (Ba) has a slightly lower deoxidizing capacity than calcium (Ca) but a stronger capacity than aluminum (Al), and its desulfurization capacity is comparable to that of calcium (Ca). It also possesses comprehensive advantages such as high density (3.59 g / cm³), high boiling point (1640℃), and low vapor pressure (0.034 MPa). However, compared to existing mature and efficient steelmaking processes such as aluminum deoxidation and calcium treatment, barium-containing deoxidizers are not the mainstream. Even when barium-containing deoxidizers are occasionally used, barium is usually not used as the primary deoxidizer alone, but rather as a component in composite deoxidizers, often combined with elements such as silicon, aluminum, and calcium, such as silicon-barium alloys, silicon-barium-aluminum alloys, silicon-calcium-barium alloys, and silicon-barium-calcium-aluminum alloys. Moreover, the mass percentage of barium in these alloys is usually below 20%, not a major component.

[0025] In view of this, the present invention applies barium as a major deoxidizer in the rare earth steel refining process, and proposes a refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, the method comprising the following steps: Step S1: Use a converter for smelting. When tapping steel from the converter, deoxidize the molten steel with aluminum and low-silicon barium iron alloy. Add lime, slag containing magnesium oxide and aluminum oxide to the slag surface. Step S2: After tapping from the converter, the steel is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, slag containing barium oxide, magnesium oxide, and sodium oxide are added to the slag surface to create white slag. Simultaneously, aluminum particles and low-silicon barium ferroalloy are added to the molten steel for deoxidation. Depending on the slag formation, these are added in small batches, multiple times; adding them all at once is prohibited. During the middle stage of white slag formation, the oxygen content in the steel has been reduced to a low level. At this time, alloying is carried out to fine-tune the steel composition. During the white slag formation stage, the bottom-blown gas stirring intensity in the ladle should not be less than 0.008 Nm. 3 / (min·t); Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

[0026] Specifically, in step S1, converter smelting, such as top-blown converter or top-and-bottom combined-blown converter, is carried out; the tapping temperature is controlled to be ≥1620℃, and the carbon content of the tapped steel at the end of the blowing process is ≥0.08%, phosphorus content is <0.010%, and sulfur content is <0.01% by mass percentage. The purity of aluminum is above 99%, and the amount of aluminum added per ton of steel is (8.44×m / [%C]) kg, where m is the carbon-oxygen product, ranging from 0.0018 to 0.0025, and [%C] is the carbon content of the tapped steel at the end of the blowing process. For example, if the carbon content is 0.08%, then [%C] is 0.08. In low-silicon barium iron alloys, the mass percentage of silicon is below 5%, the mass percentage of barium is above 20%, and the remainder is iron and unavoidable impurities. The amount of barium added per ton of steel is (21.41 × m / [%C]) kg, where m is the carbon-oxygen product, ranging from 0.0018 to 0.0025, and [%C] is the carbon content of the steel at the blowing endpoint. For example, if the carbon content is 0.08%, then [%C] is 0.08. The amount of barium added for low-silicon barium-containing ferroalloys is calculated by reverse calculation based on the amount of barium added. The aluminum content [Als] in the molten steel is controlled to be less than 0.015%.

[0027] It should be noted that in rare earth steel smelting, aluminum deoxidation is generally used when tapping steel from converter smelting. The amount of aluminum added is determined based on the oxygen content in the steel. For ease of operation, it is usually determined by referring to the carbon content of the steel tapped at the end of the blowing process. Moreover, to strictly control the oxygen content, an excessive amount of aluminum is usually added, such as 1.5 times the amount of aluminum required for deoxidation. This results in two problems: first, an increase in dissolved aluminum [Als] in the molten steel, increasing the risk of nozzle blockage during continuous casting; second, the formation of a large amount of solid, high-melting-point Al2O3 initial inclusions. These primary Al2O3 inclusions are in the form of small clusters or chains with a wide size distribution. If the residue in the steel exceeds the standard, they become the main harmful inclusions that deteriorate the steel's properties.

[0028] Compared to aluminum, barium has a stronger deoxidizing ability and efficiency. Furthermore, its reaction in steel is stable and less prone to splashing. It can also "modify and remove" already formed Al2O3. Specifically, BaO, generated during Ba deoxidation, readily combines with Al2O3 to form large-sized, high-temperature liquid composite inclusions, BaO·Al2O3. These inclusions readily aggregate and spheroidize in molten steel, forming larger spherical particles that float to the surface and are removed efficiently, following Stokes' law. This significantly reduces the amount of Al2O3 inclusions in the steel. In addition, since the vast majority of Ba-containing inclusions float to the surface, the residual amount of Ba in the inclusions is extremely low, reducing the risk of increased inclusion formation in the steel and further lowering the probability of composite inclusion formation. This reduces the uncertainty of the inclusions' impact on steel properties and improves process stability.

[0029] In summary, this invention first achieves the process objective of maintaining low dissolved oxygen levels in steel, as well as sufficiently high tapping temperatures and sufficiently low phosphorus and sulfur contents, by controlling the tapping temperature to ≥1620℃ and ensuring that the carbon content of the tapped steel at the blowing endpoint is ≥0.08%, phosphorus content is <0.010%, and sulfur content is <0.01%. This reduces the deoxidation burden on converter tapping and LF furnace refining, as well as the tasks of raising the temperature, reducing sulfur, and preventing phosphorus reversion in subsequent LF furnace refining. Consequently, the total amount of deoxidizer added is effectively controlled, and over-refining in the LF furnace is eliminated. This ensures that the molten steel maintains a favorable state of low aluminum, low oxygen, low sulfur, and low phosphorus throughout the entire refining process. Secondly, during the converter tapping process, the combined Al and Ba deoxidation process further reduces the amount of Al used, and even the total amount of deoxidizer, thereby further improving deoxidation efficiency. This ultimately reduces the aluminum content in the molten steel ([Als] < 0.015%) and the absolute amount of alumina inclusions generated. Furthermore, it promotes the alumina to float into the slag as BaO·Al2O3 composite inclusions, further reducing the burden on refining. Specifically, the amount of deoxidizer added is calculated based on normal deoxidation requirements, and the amounts of Al and Ba added are designed according to the formation of the BaO·Al2O3 composite inclusions. That is, Al removes 75% of the oxygen in the steel, and Ba removes 25%. The amount of Ba added is approximately 2.54 times the amount of Al added, thus yielding the above formula for calculating the amount of aluminum and barium added per ton of steel.

[0030] In step 1, lime, magnesium oxide-containing slag, and aluminum oxide-containing slag are added to the slag surface to form a pre-melted slag. The lime contains no less than 85% CaO, the magnesium oxide-containing slag contains more than 90% MgO, and the aluminum oxide-containing slag contains no less than 80% Al2O3. Specifically, the amount of lime added per ton of steel is 2.65~4.35 kg / t; the amount of magnesium oxide-containing slag, such as magnesia, is 1~3 kg / t; and the amount of bauxite is 3.5~6.5 kg / t. Based on mass percentage, the chemical composition of the pre-melted slag is CaO 25~35%, Al2O3 30~45%, MgO 10~25%, and SiO2 3~10%, with a pre-melted slag mass of approximately 7~14 kg / ton of steel.

[0031] It should be noted that the slag system produced after tapping from the converter must be pre-melted or semi-melted. Its function is to quickly form slag with refining capabilities, protect the molten steel from secondary oxidation, and create a good starting point for LF (sulfurized leaching). Lime provides CaO to ensure that the slag has a certain basicity and desulfurization capacity; magnesia provides MgO, mainly to protect the furnace lining; bauxite provides Al2O3 to form a low-melting-point compound 12CaO·7Al2O3 with CaO, lowering the melting point of the slag system and balancing with [Al] in the molten steel, adsorbing Al2O3 inclusions produced by aluminum deoxidation; the addition of these three materials will introduce a small amount of SiO2, which can adjust the basicity and fluidity of the slag system. When the amount of lime added per ton of steel is 2.65~4.35 kg / t, the amount of magnesia added is 1~3 kg / t, and the amount of bauxite added is 3.5~6.5 kg / t, the final slag system formed is a quaternary slag system with CaO 25~30%, Al2O3 30~40%, MgO 10~25%, and SiO2 3~5%. In the CaO-Al2O3-MgO ternary phase diagram, the composition range is located in the low melting point region (about 1400~1550℃). The addition of SiO2 will further lower the melting point, resulting in a moderate melting point that can be pre-melted. The total amount added is about 7~14 kg / ton of steel, which is sufficient to form a slag layer with a thickness of 50~110 mm, which plays a role in heat preservation, air isolation, and providing a sufficient reaction interface.

[0032] In step S2, when the LF ladle furnace is filled with steel, lime, barium oxide, magnesium oxide, and sodium oxide slag are added to the slag surface to create white slag. Specifically, the lime contains no less than 85% CaO, the barium oxide slag contains no less than 50% BaO, the magnesium oxide slag contains more than 90% MgO, and the sodium oxide slag contains no less than 90% Na2O. For example, the amount of lime added per ton of steel is 8-15 kg / t; the amount of barium oxide slag added is 0.45-0.55 kg / t; the amount of magnesium oxide slag, such as magnesia, is 0.45-0.55 kg / t; and the amount of sodium oxide slag added is 0.45-0.55 kg / t. Simultaneously, aluminum particles and low-silicon barium ferroalloy are added to the molten steel for deoxidation. The purity of the aluminum particles is above 99%, and the mass percentage of silicon in the low-silicon barium ferroalloy is below 5%, the mass percentage of barium is above 20%, and the remainder is iron and unavoidable impurities. Specifically, 0.2~0.3 kg / t of aluminum granules and 0.5~0.76 kg / t of barium are added to each ton of steel. The amount of low-silicon barium-containing iron alloy added is calculated by reverse calculation based on the amount of barium added.

[0033] Based on mass percentage, the composition of the white slag is in the range of BaO 3~10%, CaO 30~45%, SiO2 3~10%, MgO 15~30%, Na2O3 3~10%, and Al2O3 10~25%. During the production of white slag, the bottom-blown argon gas stirring intensity in the ladle is 0.008~0.013 Nm. 3 / (min·t), white slag production time 35~50 minutes.

[0034] After the white slag formation is completed, the molten steel undergoes soft blowing treatment for 20-30 minutes, with the bottom-blown gas stirring intensity in the ladle ranging from 0.003 to 0.005 Nm. 3 Between / (min·t).

[0035] The composition of molten steel after refining in the LF ladle furnace was controlled as follows: [Als] < 0.020%, TO < 20 ppm, [S] < 0.0020%, [P] < 0.01%.

[0036] It should be noted that the white slag produced by the LF furnace refining process possesses properties such as high basicity, low melting point, and strong adsorption, while also protecting the furnace lining and promoting rapid slag formation. Its purpose is to obtain ultra-low sulfur, low oxygen, and high-purity molten steel. Specifically, in terms of white slag design, a large amount of lime (8-15 kg / t) provides high basicity, directly ensuring deep desulfurization and guaranteeing that the final sulfur content of the molten steel is below 20 ppm; strict control of SiO2 content within the range of 3-10% eliminates the risk of "silicon reversion" and ensures the accuracy of the silicon composition in the molten steel. The addition of functional slag materials in trace amounts is crucial: BaO, as a strong alkaline flux, significantly reduces the melting point and viscosity of the slag, accelerates slag formation and synergistically desulfurizes, as well as adsorbs deoxidation inclusions generated by Ba deoxidation; MgO aims to saturate the slag with MgO to match the magnesia-carbon brick lining, prevent erosion, and avoid external contamination; Na2O reduces the surface tension and viscosity of the slag, greatly promoting the polymerization, flotation, and absorption of micro-inclusions such as deoxidation products Al2O3, which is the core to obtaining low total oxygen content and clean molten steel. The total slag volume ensures sufficient slag layer coverage and reaction capacity, while moderately strong bottom blowing agitation (0.008-0.013 Nm³ / (min·t)) provides optimized kinetic conditions for all steel-slag interface reactions.

[0037] In terms of deoxidation design, high-purity aluminum particles serve as the primary deoxidizer, rapidly reducing the oxygen activity of molten steel and creating a strong reducing atmosphere for white slag formation. Low-silicon barium-iron alloy undertakes a dual mission: first, it works synergistically with aluminum for composite deoxidation, reducing aluminum usage and generating lower-melting-point barium aluminate that floats more easily; second, it performs inclusion modification treatment, transforming residual Al2O3 inclusions in the steel into low-melting-point, spherical liquid or plastic inclusions, thus significantly reducing their detrimental effects on steel properties. Its "low-silicon" requirement ensures that the introduction of barium does not interfere with the control of silicon content in the molten steel. The aluminum content meets the requirements for deoxidation and aluminum content control, while the barium content meets the minimum effective amount for inclusion modification treatment. Ultimately, through the optimization of the slag system's physicochemical properties and the combination of composite deoxidation / modification technology, a high-performance white slag conforming to rare earth weathering steel was designed. Specifically, the addition amounts of Al and Ba are designed according to the deoxidation process to form the composite inclusion BaO·Al2O3. That is, Al removes 75% of the oxygen in the steel, and Ba removes 25% of the oxygen in the steel. The amount of Ba added is about 2.54 times that of Al.

[0038] In step S3, during RH vacuum degassing and refining, no alloys are added, and the vacuum treatment time is 10-15 minutes. At the end of the vacuum treatment, a rare earth iron alloy is added, such as one or more of cerium iron alloy, lanthanum iron alloy, and yttrium iron alloy. When the RH exits the station, the ladle soft blowing time is 3-5 minutes, and the bottom blowing gas stirring intensity is 0.003-0.005 Nm. 3 Between / (min·t).

[0039] The molten steel obtained from RH station has the following composition by mass percentage: [Als] < 0.015%, TO < 15ppm, [S] < 0.0020%, [P] < 0.01%, and [RE] 0.0020~0.02%.

[0040] It should be noted that the RH refining process is designed strictly according to the principle of "ultimate purification first, then precise fine-tuning," with each step closely aligned with the goal of achieving ultra-high cleanliness in the final molten steel. No alloys are added during vacuum treatment to create an undisturbed environment, allowing the carbon-oxygen reaction and degassing to proceed fully. This is crucial for reducing total oxygen (TO) to <15ppm and controlling aluminum content [Als]. The 10-15 minute vacuum treatment time is an optimized window to ensure the thorough removal of these gases and inclusions. Rare earth ferroalloys are added only at the end of the vacuum treatment because the oxygen and sulfur content in the molten steel is already extremely low. The main role of rare earths shifts from deoxidation and desulfurization to inclusion morphology control. Rare earths can react with residual sulfur and oxygen to form harmless spherical compounds, thereby precisely controlling the rare earth content [RE] within the range of 0.0020-0.02%. Finally, the 3-5 minutes of gentle stirring and soft blowing (0.003-0.005 Nm³ / (min·t)) after the RH exits the station is the ultimate guarantee of purification. It promotes the complete removal of fine inclusions generated during the vacuum period and rare earth transformation, stabilizes extremely low TO and inclusion levels, and prevents secondary oxidation of the molten steel. The entire process is interconnected, aiming to lock in and enhance the results of vacuum purification, ultimately obtaining ultra-high purity molten steel with extremely low gas content and harmless inclusions.

[0041] Through the above treatment, rare earth steel with low oxygen (TO<15ppm), low sulfur ([S]<20ppm) and low aluminum content ([Als]<0.015%) is obtained, which greatly reduces the amount of alumina inclusions in the steel, thereby suppressing the turbulence of the nozzle and reducing the frequency of nozzle replacement from once every 1800 tons of rare earth steel cast on average to once every 2800 tons of rare earth steel cast on average.

[0042] Example 1 A refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, the method comprising the following steps: The composition range of rare earth steel, based on mass percentage, is as follows: C: 0.10~0.16%, Si: 0.1~0.3%, Mn: 0.5~0.9%, [Als]<0.015%, S<0.0020%, P<0.01%, TO<15ppm, N≤0.005%, Cu: 0.25~0.55%, Cr: 0.40~0.80%, Ni≤0.65%, Ce: 0.0020~0.02%.

[0043] Step S1: Smelting is carried out using a 100-ton converter. When tapping steel from the converter, aluminum and low-silicon barium iron alloy are used to deoxidize the molten steel. Lime, slag containing magnesium oxide and aluminum oxide are added to the slag surface. The tapping temperature was 1625℃, and the final tapping steel contained 0.08% carbon, 0.008% phosphorus, and 0.006% sulfur. The aluminum purity was above 99%, and the amount of aluminum added per ton of steel was (8.44 × m / [%C]) kg, totaling 21.1 kg, where m is the carbon-oxygen product of 0.0020. The low-silicon barium ferroalloy contained 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. The amount of barium added per ton of steel was (21.41 × m / [%C]) kg, totaling 53.53 kg, where m is the carbon-oxygen product of 0.0020; the amount of barium added to the low-silicon barium ferroalloy was calculated by reverse calculation based on the amount of barium added, resulting in 267.63 kg. The aluminum content in the molten steel was 0.013%.

[0044] Lime, magnesium oxide-containing slag, and aluminum oxide-containing slag are added to the slag surface to form a pre-melted slag. The lime contains no less than 85% CaO, the magnesium oxide-containing slag contains more than 90% MgO, and the aluminum oxide-containing slag contains no less than 80% Al2O3. The amount of lime added is 265 kg, the amount of magnesia added is 100 kg, and the amount of bauxite added is 350 kg. Based on mass percentage, the chemical composition of the pre-melted slag is 30% CaO, 40% Al2O3, 22% MgO, and 8% SiO2, with a total mass of 715 kg.

[0045] Step S2: After tapping from the converter, the steel is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, slag containing barium oxide, magnesium oxide, and sodium oxide are added to the slag surface to create white slag. Simultaneously, aluminum particles and low-silicon barium-iron alloy are added to the molten steel for deoxidation. Depending on the slag formation, these are added in small batches, not all at once. During the middle stage of the LF white slag formation, the oxygen content in the steel has been reduced to a low level. At this point, alloying is carried out by adding Si, Cu, Cr, and Ni to fine-tune the steel composition. The bottom-blowing gas stirring intensity during the white slag formation stage is 0.008 Nm. 3 / (min·t); When the LF ladle furnace receives slag, lime, barium oxide-containing slag, magnesium oxide-containing slag, and sodium oxide-containing slag are added to the slag surface to create white slag. Specifically, the lime must contain at least 85% CaO, the barium oxide-containing slag must contain at least 50% BaO, the magnesium oxide-containing slag must contain more than 90% MgO, and the sodium oxide-containing slag must contain at least 90% Na₂O. The amounts added are: 800 kg of lime, 45 kg of barium oxide-containing slag, 45 kg of magnesia, and 45 kg of sodium oxide-containing slag. Simultaneously, aluminum granules and low-silicon barium ferroalloy are added to the molten steel for deoxidation. The aluminum granules must have a purity of over 99%, and the low-silicon barium ferroalloy must contain 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. 20 kg of aluminum granules and 50 kg of barium are added, and the amount of low-silicon barium ferroalloy added is calculated by reverse calculation based on the amount of barium added, resulting in 250 kg.

[0046] Based on mass percentage, the composition of the white slag is BaO 5%, CaO 40%, SiO2 10%, MgO 25%, Na2O 35%, and Al2O3 15%. During the production of the white slag, the bottom-blown argon gas stirring intensity in the ladle is 0.008 Nm. 3 / (min·t), white slag production time 35 minutes.

[0047] After the white slag formation is completed, the molten steel undergoes soft blowing treatment for 20 minutes, with the bottom-blown gas stirring intensity at 0.003 Nm. 3 / (min·t).

[0048] The composition of molten steel after refining in the LF ladle furnace is as follows: [Als] 0.016%, TO 15ppm, [S] 0.0015%, [P] 0.008%.

[0049] Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

[0050] The vacuum treatment time is 10 minutes. At the end of the vacuum treatment, 200 kg of ferrocerium alloy containing 20% ​​cerium (particle size 50-200 mm) is added. The ladle soft-blowing time at RH outlet is 3 minutes, and the bottom-blowing gas stirring intensity is 0.003 Nm. 3 / (min·t).

[0051] The molten steel obtained from RH station has the following composition by mass percentage: [Als] 0.013%, TO 12ppm, [S] <0.0013%, [P] 0.008%, [Ce] 0.015%.

[0052] After leaving the RH station, continuous casting is carried out, and 2800 tons of rare earth steel are continuously cast with a replacement nozzle.

[0053] Example 2 A refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, the method comprising the following steps: The composition range of rare earth steel, based on mass percentage, is as follows: C: 0.10~0.16%, Si: 0.1~0.3%, Mn: 0.5~0.9%, [Als]<0.015%, S<0.0020%, P<0.01%, TO<15ppm, N≤0.005%, Cu: 0.25~0.55%, Cr: 0.40~0.80%, Ni≤0.65%, La: 0.0020~0.02%.

[0054] Step S1: Smelting is carried out using a 150-ton converter. When tapping steel from the converter, aluminum and low-silicon barium iron alloy are used to deoxidize the molten steel. Lime, slag containing magnesium oxide and aluminum oxide are added to the slag surface. The tapping temperature was 1625℃, and the final tapping steel contained 0.10% carbon, 0.008% phosphorus, and 0.005% sulfur. The aluminum purity was above 99%, and the amount of aluminum added per ton of steel was (8.44 × m / [%C]) kg, totaling 25.32 kg, where m is the carbon-oxygen product of 0.0020. The low-silicon barium ferroalloy contained 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. The amount of barium added per ton of steel was (21.41 × m / [%C]) kg, totaling 64.23 kg, where m is the carbon-oxygen product of 0.0020; the amount of barium added to the low-silicon barium ferroalloy was calculated by reverse calculation based on the amount of barium added, resulting in 321.15 kg. The aluminum content in the molten steel was 0.014%.

[0055] Lime, magnesium oxide-containing slag, and aluminum oxide-containing slag are added to the slag surface to form a pre-melted slag. The lime contains no less than 85% CaO, the magnesium oxide-containing slag contains more than 90% MgO, and the aluminum oxide-containing slag contains no less than 80% Al2O3. The amount of lime added is 653 kg, the amount of magnesia added is 450 kg, and the amount of bauxite added is 975 kg. Based on mass percentage, the chemical composition of the pre-melted slag is 32% CaO, 42% Al2O3, 18% MgO, and 28% SiO2, with a total mass of 2078 kg.

[0056] Step S2: After tapping from the converter, the steel is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, slag containing barium oxide, magnesium oxide, and sodium oxide are added to the slag surface to create white slag. Simultaneously, aluminum particles and low-silicon barium-iron alloy are added to the molten steel for deoxidation, in small batches and multiple batches depending on the slag formation. During the middle stage of LF white slag formation, the oxygen content in the steel has been reduced to a low level. At this point, alloying is carried out by adding Si, Cu, Cr, and Ni to fine-tune the steel composition. The bottom-blowing gas stirring intensity during the white slag formation stage is 0.013 Nm. 3 / (min·t); When the LF ladle furnace receives slag, lime, barium oxide-containing slag, magnesium oxide-containing slag, and sodium oxide-containing slag are added to the slag surface to create white slag. Specifically, the lime must contain at least 85% CaO, the barium oxide-containing slag must contain at least 50% BaO, the magnesium oxide-containing slag must contain more than 90% MgO, and the sodium oxide-containing slag must contain at least 90% Na₂O. The amounts added are: 2250 kg of lime, 82.5 kg of barium oxide-containing slag, 82.5 kg of magnesia, and 82.5 kg of sodium oxide-containing slag. Simultaneously, aluminum granules and low-silicon barium ferroalloy are added to the molten steel for deoxidation. The aluminum granules must have a purity of over 99%, and the low-silicon barium ferroalloy must contain 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. 45 kg of aluminum granules and 114 kg of barium are added. The amount of low-silicon barium ferroalloy added is calculated by reverse calculation based on the amount of barium added, resulting in 570 kg.

[0057] Based on mass percentage, the composition of the white slag is BaO 8%, CaO 40%, SiO 28%, MgO 12%, Na 2O 38%, and Al 2O 3 24%. During the production of the white slag, the bottom-blown argon gas stirring intensity in the ladle is 0.008 Nm. 3 / (min·t), white slag production time 50 minutes.

[0058] After the white slag formation is completed, the molten steel undergoes soft blowing treatment for 30 minutes, with the bottom-blown gas stirring intensity at 0.005 Nm. 3 / (min·t).

[0059] The composition of molten steel after refining in the LF ladle furnace is as follows: [Als] 0.018%, TO 17ppm, [S] 0.0016%, [P] 0.009%.

[0060] Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

[0061] Vacuum treatment time is 15 minutes. At the end of vacuum treatment, add 300 kg of lanthanum-iron alloy containing 30% lanthanum, with a particle size of 50-200 mm. When leaving the RH station, the ladle soft blowing time is 5 minutes, and the bottom blowing gas stirring intensity is 0.005 Nm. 3 / (min·t).

[0062] The molten steel obtained from RH station has the following composition by mass percentage: [Als] 0.013%, TO 13ppm, [S] 0.0014%, [P] 0.009%, and [La] 0.018%.

[0063] After leaving the RH station, continuous casting is carried out, and the nozzle is replaced once for every 3,000 tons of rare earth steel produced.

[0064] Example 3 A refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, the method comprising the following steps: The composition range of rare earth steel, based on mass percentage, is as follows: C: 0.10~0.16%, Si: 0.1~0.3%, Mn: 0.5~0.9%, [Als]<0.015%, S<0.0020%, P<0.01%, TO<15ppm, N≤0.005%, Cu: 0.25~0.55%, Cr: 0.40~0.80%, Ni≤0.65%, Ce: 0.0020~0.02%.

[0065] Step S1: Smelting is carried out in a 260-ton converter. When tapping steel from the converter, aluminum and low-silicon barium iron alloy are used to deoxidize the molten steel. Lime, slag containing magnesium oxide and aluminum oxide are added to the slag surface. The tapping temperature was 1630℃, and the final tapping steel contained 0.12% carbon, 0.007% phosphorus, and 0.005% sulfur. The aluminum purity was above 99%, and the amount of aluminum added per ton of steel was (8.44 × m / [%C]) kg, totaling 36.57 kg, where m is the carbon-oxygen product of 0.0020. The low-silicon barium ferroalloy contained 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. The amount of barium added per ton of steel was (21.41 × m / [%C]) kg, totaling 92.78 kg, where m is the carbon-oxygen product of 0.0020. The amount of barium added to the low-silicon barium ferroalloy was calculated by reverse calculation based on the amount of barium added, resulting in 463.88 kg. The aluminum content in the molten steel was 0.012%.

[0066] Lime, magnesium oxide-containing slag, and aluminum oxide-containing slag are added to the slag surface to form a pre-melted slag. The lime contains no less than 85% CaO, the magnesium oxide-containing slag contains more than 90% MgO, and the aluminum oxide-containing slag contains no less than 80% Al2O3. The amount of lime added is 910 kg, the amount of magnesia added is 520 kg, and the amount of bauxite added is 1300 kg. Based on mass percentage, the chemical composition of the pre-melted slag is CaO 35%, Al2O3 43%, MgO 15%, and SiO2 7%, with a total mass of approximately 2730 kg.

[0067] Step S2: After tapping from the converter, the steel is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, slag containing barium oxide, magnesium oxide, and sodium oxide are added to the slag surface to create white slag. Simultaneously, aluminum particles and low-silicon barium-iron alloy are added to the molten steel for deoxidation. Depending on the slag formation, these are added in small batches, not all at once. During the middle stage of the LF white slag formation, the oxygen content in the steel has been reduced to a low level. At this point, alloying is carried out by adding Si, Cu, Cr, and Ni to fine-tune the steel composition. During the white slag formation stage, the bottom-blown gas stirring intensity in the ladle is 0.010 Nm.3 / (min·t); When the LF ladle furnace receives slag, lime, barium oxide-containing slag, magnesium oxide-containing slag, and sodium oxide-containing slag are added to the slag surface to create white slag. Specifically, the lime must contain at least 85% CaO, the barium oxide-containing slag must contain at least 50% BaO, the magnesium oxide-containing slag must contain more than 90% MgO, and the sodium oxide-containing slag must contain at least 90% Na₂O. The amounts added are: 2990 kg of lime, 130 kg of barium oxide-containing slag, 130 kg of magnesia, and 130 kg of sodium oxide-containing slag. Simultaneously, aluminum granules and low-silicon barium ferroalloy are added to the molten steel for deoxidation. The aluminum granules must have a purity of over 99%, and the low-silicon barium ferroalloy must contain 5% silicon and 20% barium by mass, with the remainder being iron and unavoidable impurities. 65 kg of aluminum granules and 164 kg of barium are added. The amount of low-silicon barium ferroalloy added is calculated by reverse calculation based on the amount of barium added, resulting in 820 kg.

[0068] Based on mass percentage, the composition of the white slag is BaO 6%, CaO 38%, SiO 29%, MgO 18%, Na 2O 38%, and Al 2O 3 21%. During the production of the white slag, the bottom-blown argon gas stirring intensity in the ladle is 0.010 Nm. 3 / (min·t), white slag production time 38 minutes.

[0069] After the white slag formation is completed, the molten steel undergoes soft blowing treatment for 25 minutes, with the bottom-blown gas stirring intensity at 0.004 Nm. 3 Between / (min·t).

[0070] The composition of molten steel after refining in the LF ladle furnace is as follows: [Als] 0.015%, TO 18ppm, [S] 0.0015%, [P] 0.008%.

[0071] Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

[0072] The vacuum treatment time was 13 minutes. At the end of the vacuum treatment, 520 kg of ferrocerium alloy containing 30% cerium was added. The ladle soft-blowing time at RH discharge was 4 minutes, and the bottom-blowing gas stirring intensity was 0.004 Nm. 3 / (min·t).

[0073] The molten steel obtained from RH station has the following composition by mass percentage: [Als] 0.012%, TO 13ppm, [S] <0.0012%, [P] 0.008%, [Ce] 0.018%.

[0074] After leaving the RH station, continuous casting is carried out, and 2860 tons of rare earth steel are continuously cast with a replacement nozzle.

[0075] Comparative Example A refining method for aluminum deoxidized rare earth steel, the steel composition of which is exactly the same as that in Example 1.

[0076] Step S1: A 100-ton converter is used for smelting. The tapping endpoint control is exactly the same as in Example 1. The difference is that the tapping process uses full aluminum deoxidation. The amount of aluminum added per ton of steel is (17×m / [%C]) kg, for a total of 42.5 kg. In the formula, m is the carbon-oxygen product of 0.0020, and the aluminum content [Als] in the molten steel is 0.04%. Conventional ladle covering agent is added during the tapping process.

[0077] Step S2: After tapping from the converter, the steel is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, magnesia-containing slag, and fluorite are added to the slag surface to create white slag. Simultaneously, aluminum particles are added to the molten steel for deoxidation. The amount of lime added is 800 kg, magnesia 45 kg, fluorite 45 kg, and aluminum particles 50 kg. The remaining process steps and parameters are exactly the same as in Example 1.

[0078] The composition of molten steel after refining in the LF ladle furnace is as follows: [Als] 0.05%, TO 20ppm, [S] 0.0015%, [P] 0.008%.

[0079] Step S3, after refining in the LF ladle furnace, is followed by vacuum degassing and refining in the RH furnace. The specific process parameters are exactly the same as in Example 1.

[0080] The molten steel obtained from RH station has the following composition by mass percentage: [Als] 0.048%, TO 16ppm, [S] <0.0013%, [P] 0.008%, [Ce] 0.015%.

[0081] After leaving the RH station, continuous casting is carried out, and 1800 tons of rare earth steel are continuously cast with a replacement nozzle.

[0082] 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 changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A refining method for reducing the aluminum content in aluminum-deoxidized rare earth steel, characterized in that, The method includes the following steps: Step S1: Use a converter for smelting. When tapping steel from the converter, add aluminum and low-silicon barium iron alloy to deoxidize the molten steel. Add lime, slag containing magnesium oxide and aluminum oxide to the slag surface. Step S2: After the steel is tapped from the converter, it is refined in the LF ladle furnace. When the steel enters the LF ladle furnace, lime, barium oxide, magnesium oxide and sodium oxide are added to the slag surface to make white slag. At the same time, aluminum particles and low silicon barium iron alloy are added to the molten steel for deoxidation. Alloying is carried out in the middle of the white slag making process. After the white slag making is completed, the molten steel is subjected to soft blowing treatment. Step S3: After refining in the LF ladle furnace, the steel is then degassed and refined in the RH vacuum degassing furnace. No alloys are added during the RH vacuum degassing process. Rare earth iron alloys are added at the end of the vacuum treatment. The steel is then soft-blown when leaving the RH station.

2. The method according to claim 1, characterized in that, In step S1, the tapping temperature is ≥1620℃, and the carbon content of the tapped steel at the blowing endpoint is ≥0.08%, phosphorus content is <0.010%, and sulfur content is <0.01% by mass percentage.

3. The method according to claim 2, characterized in that, The amount of aluminum added per ton of steel is (8.44×m / [%C]) kg, and the amount of barium added per ton of steel is (21.41×m / [%C]) kg, where m is the carbon-oxygen product and [%C] is the carbon content of the steel at the blowing endpoint; the amount of the low-silicon barium-containing iron alloy added is calculated by back-calculating based on the amount of barium added, and the mass percentage of silicon in the low-silicon barium-iron alloy is less than 5%, the mass percentage of barium is more than 20%, and the remainder is iron and unavoidable impurities.

4. The method according to claim 3, characterized in that, The aluminum content [Als] in the molten steel should be controlled to be less than 0.015%.

5. The method according to claim 1, characterized in that, In step S1, the lime contains no less than 85% CaO, the magnesium oxide slag contains more than 90% MgO, and the alumina slag contains no less than 80% Al2O3; the amount of lime added per ton of steel is 2.65~4.35 kg / t, the amount of magnesium oxide slag added is 1~3 kg / t, and the amount of bauxite added is 3.5~6.5 kg / t.

6. The method according to claim 1, characterized in that, In step S2, the lime contains no less than 85% CaO, the barium oxide-containing slag contains no less than 50% BaO, the magnesium oxide-containing slag contains more than 90% MgO, and the sodium oxide-containing slag contains no less than 90% Na2O. In each ton of steel, the amount of lime added is 8-15 kg / t, the amount of barium oxide-containing slag added is 0.45-0.55 kg / t, the amount of magnesium oxide-containing slag added is 0.45-0.55 kg / t, and the amount of sodium oxide-containing slag added is 0.45-0.55 kg / t. In each ton of steel, 0.2-0.3 kg / t of aluminum granules are added, and 0.5-0.76 kg / t of barium is added. The amount of low-silicon barium-containing ferroalloy added is calculated by back-calculating the amount of barium added. In the low-silicon barium-ferroalloy, the mass percentage of silicon is less than 5%, the mass percentage of barium is more than 20%, and the remainder is iron and unavoidable impurities.

7. The method according to claim 1, characterized in that, In step S2, the stirring intensity of the bottom-blown argon gas in the ladle during the white slag formation stage is 0.008~0.013 Nm. 3 / (min·t), the white slag formation time is 35~50 minutes; the soft blowing treatment time is 20~30 minutes, and the bottom blowing gas stirring intensity of the ladle is 0.003~0.005 Nm. 3 Between / (min·t).

8. The method according to claim 1, characterized in that, In step S2, the mass percentage composition of the molten steel refined in the LF ladle furnace is as follows: [Als] < 0.020%, TO < 20 ppm, [S] < 0.0020%, [P] < 0.01%.

9. The method according to claim 1, characterized in that, In step S3, the vacuum treatment time is 10-15 minutes; the soft blowing time is 3-5 minutes; and the stirring intensity of the bottom-blown gas in the ladle is 0.003-0.005 Nm. 3 Between / (min·t).

10. The method according to claim 1, characterized in that, In step S3, the molten steel obtained from the RH station has the following composition by mass percentage: [Als] < 0.015%, TO < 15ppm, [S] < 0.0020%, [P] < 0.01%, and [RE] 0.0020~0.02%.