A short-process prepared high-purity stainless steel billet and a preparation method thereof

Abstract

The application provides a short-process prepared high-purity stainless steel billet and a preparation method thereof, and belongs to the technical field of stainless steel smelting.The application obtains molten steel with w(T.O) below 45ppm and a billet with w(T.O) below 50ppm through a middle-frequency induction furnace scrap smelting-AOD furnace molten steel deoxidation mixing and pouring-LF furnace refining-continuous casting.The application reduces the content of inclusions and residual elements in the LF refined molten steel and the billet through a strict deslagging process of the middle-frequency induction furnace, full-process argon blowing and deoxidation slag washing process of the middle-frequency induction furnace molten steel tapping, full-process argon blowing and deoxidation process of the AOD furnace molten steel tapping, full-process argon blowing and stirring of the mixing and pouring molten steel, optimization of the mixing and pouring molten steel LF furnace refining slag system, calcium treatment of the refined molten steel and improvement of the soft blowing process, continuous casting slag control process, protective pouring process and crystallizer flow field optimization, improves the billet quality, and has important significance for popularizing and applying a low-cost high-quality short-process stainless steel smelting process.

Description

Technical Field

[0001] This invention relates to the field of stainless steel smelting technology, and in particular to a short-process preparation method for high-purity stainless steel billets. Background Technology

[0002] Stainless steel has a wide range of applications, playing an important role not only in aviation, shipbuilding, and petrochemical industries, but also in transportation, kitchenware, home appliances, and construction equipment. Over the past few decades, with my country's rapid economic development, the country's steel production, especially stainless steel production and consumption, has also increased rapidly.

[0003] Currently, the lowest-cost long-process stainless steel smelting requires mineral processing, sintering, blast furnace smelting, AOD furnace smelting, and LF furnace refining to obtain qualified molten steel. This process is lengthy and significantly more expensive than the short-process molten steel smelting using a medium-frequency induction furnace + LF furnace. However, the traditional short-process stainless steel smelting using a medium-frequency induction furnace + LF furnace has high levels of harmful residual elements such as Zn and Sn, as well as inclusions, making it impossible to guarantee the quality of continuously cast billets.

[0004] Therefore, developing new short-process technologies to improve product quality and reduce production costs has become a key factor for the survival and development of stainless steel enterprises. Summary of the Invention

[0005] The purpose of this invention is to provide a short-process preparation method for high-purity stainless steel billets and to reduce the production cost of stainless steel smelting.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a short-process method for preparing high-purity stainless steel billets, comprising the following steps:

[0008] (1) Medium frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium frequency induction furnace in batches for melting, slag is removed, and molten steel is obtained by medium frequency induction furnace smelting. The ladle is hoisted into the ladle car and the steel is discharged into the ladle.

[0009] (2) Deoxidation and mixing of AOD furnace molten steel: The ladle car containing molten steel from the medium frequency induction furnace is driven into the AOD furnace, and the molten steel from the AOD furnace is discharged into the ladle containing molten steel from the medium frequency induction furnace for mixing.

[0010] (3) LF furnace steel refining: The molten steel after mixing in step (2) is transferred to the refining station, and deoxidizing and slag-forming materials such as ferrosilicon powder, lime, and fluorite are added. After refining, the steel is fed into the silicon-calcium wire and soft blowing is performed to obtain qualified molten steel. The molten steel is then continuously cast to obtain high-purity stainless steel billets.

[0011] Further, in step (1), the temperature of the molten steel after melting is 1610-1630℃. The slag removal process is performed to remove the slag from the medium-frequency induction furnace until the molten steel is exposed. Before the ladle car enters the medium-frequency induction furnace, 3-5 kg ​​of metallurgical lime is added to the bottom of the ladle per ton of steel. The argon gas pipe is connected. When tapping the steel, 0.5-1.0 kg of silicon-aluminum-iron and 1.0-1.5 kg of silicon-calcium-barium are added to the steel flow per ton of steel. Argon blowing and stirring are carried out throughout the process to achieve the deoxidation and slag washing process of the molten steel.

[0012] Furthermore, the temperature of the molten steel smelted in the AOD furnace in step (2) is 1580-1620℃. Before the molten steel from the AOD furnace is tapped into the ladle and mixed with the molten steel containing medium-frequency steel, a 300-500mm thick layer of AOD furnace reducing slag needs to be added to the ladle to prepare the LF furnace for slag formation in advance.

[0013] Further, in step (2), the ladle car containing molten steel from the medium-frequency induction furnace is driven into the AOD furnace. Argon gas is turned on 5 to 10 minutes before the molten steel from the AOD furnace is tapped. The mass ratio of the molten steel from the AOD furnace to the molten steel smelted in the medium-frequency induction furnace is 1:0.9 to 1.2. When tapping the steel, 0.5 to 1.0 kg of silicon-aluminum-iron and 1.0 to 1.5 kg of silicon-calcium-barium are added per ton of steel along the steel flow. Argon is blown and stirred throughout the tapping and mixing process.

[0014] Furthermore, before the mixed-fluid molten steel enters the LF refining station as described in step (3), argon must be continuously blown; after the mixed-fluid molten steel enters the LF refining station, ferrosilicon powder, lime, fluorite and other deoxidizing slag-forming materials are added according to the slag color and slag fluidity. When the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the refined molten steel are adjusted according to the analysis results. When the temperature and composition meet the requirements, the silicon-calcium wire is fed in for inclusion modification treatment.

[0015] Further, after the temperature of the refined molten steel in step (3) exceeds the liquidus temperature by 50-70°C, a calcium wire with a length of 100-200m is fed in at a speed of 3-4m / s; after feeding the calcium wire, soft blowing argon is performed for 10-15 minutes, and the w(TO) in the LF molten steel is controlled below 45ppm.

[0016] Furthermore, during continuous casting in step (3), argon blowing protection is performed on the long nozzle, stopper rod, slide plate, and other parts of the ladle. The argon blowing protection flow rates are 10-15 L / min, 3-5 L / min, and 2-3 L / min, respectively. The insertion depth of the SEN (submersible nozzle) is adjusted to 150-180 mm, the nozzle outlet angle is 5-8°, the temperature difference between the inlet and outlet water of the crystallizer is 7-9°, and the w(TO) in the billet is controlled below 50 ppm.

[0017] The present invention also provides a high-purity stainless steel billet prepared by the above preparation method.

[0018] This invention effectively reduces the content of inclusions and residual elements in LF refined steel and billets through strict slag removal process of molten steel in medium-frequency induction furnace, argon blowing and deoxidation slag washing process throughout the tapping process of molten steel in medium-frequency induction furnace, argon blowing and deoxidation process throughout the tapping process of molten steel in AOD furnace, argon blowing and stirring process throughout the entry of mixed-flow molten steel, optimization of the slag system for refining molten steel in LF furnace, improvement of calcium treatment and soft blowing process, slag control process for continuous casting, protective casting process, and optimization of the flow field of the crystallizer. It further improves the quality of cast billets and is of great significance for promoting the application of low-cost, high-quality short-process stainless steel smelting technology. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the short-process preparation of high-purity stainless steel billets according to the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below. These embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the art or in the product manual.

[0021] Methods for preparing high-purity stainless steel billets, such as... Figure 1 As shown, it includes the following steps:

[0022] S1: Medium-frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium-frequency induction furnace in batches for melting. When the temperature of the molten steel reaches 1610-1630℃, a slag removal process is performed to remove the slag from the medium-frequency induction furnace until the molten steel is exposed. Before the ladle car enters the medium-frequency induction furnace, 3-5 kg ​​of metallurgical lime is added to the bottom of the ladle per ton of steel. The argon gas pipe is connected. When tapping the steel, 0.5-1.0 kg of silicon-aluminum-iron and 1.0-1.5 kg of silicon-calcium-barium deoxidizer alloys are added per ton of steel along the steel flow. Argon blowing and stirring are carried out throughout the process to achieve steel deoxidation and slag washing.

[0023] S2: AOD furnace molten steel deoxidation and mixing: The ladle car containing molten steel from the medium-frequency induction furnace is driven into the AOD furnace. Argon gas is turned on 5-10 minutes before the AOD furnace taps the steel. The molten steel from the AOD furnace is poured into the ladle containing molten steel from the medium-frequency induction furnace for mixing. The mixing is stopped after half of the molten steel from the AOD furnace has been tapped. The remaining molten steel is mixed with the next ladle of molten steel from the medium-frequency induction furnace. When tapping the steel, 0.5-1.0 kg of silicon-aluminum-iron and 1.0-1.5 kg of silicon-calcium-barium deoxidation alloys are added per ton of steel for deoxidation.

[0024] S3: Mixing of Molten Steel: The ladle containing molten steel from the medium-frequency induction furnace is hoisted to the AOD furnace and argon gas is connected. The molten steel from one AOD furnace is mixed into the molten steel from two medium-frequency induction furnaces in two separate batches. The first batch of molten steel from the medium-frequency induction furnace automatically introduces reducing slag during tapping from the AOD furnace, thus pre-slagring the LF furnace. For the second batch of molten steel from the medium-frequency induction furnace, reducing slag from the AOD furnace is added before tapping from the AOD furnace to pre-slagred the LF furnace. After mixing the AOD furnace steel and the medium-frequency induction furnace steel, if there is space in the LF furnace, the steel is immediately transferred in. If there is no space, the ladle is hoisted to the ground and connected to an argon gas pipe to continue blowing argon gas until the ladle is transported to the LF furnace.

[0025] S4: LF furnace steel refining: After the molten steel enters the station, ferrosilicon powder, lime, fluorite and other materials are added according to the slag color and slag fluidity. When the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the molten steel are adjusted according to the analysis results. When the temperature and composition meet the requirements, the silicon-calcium wire is fed in for inclusion modification treatment. After feeding the calcium wire, soft argon blowing is performed for 10 to 15 minutes and then it is hoisted into the continuous casting for pouring.

[0026] S5: Mixed-flow molten steel continuous casting: Strictly implement the slag inspection system from ladle to tundish, minimize the amount of slag entrapped into the tundish, implement argon blowing protection casting measures for long nozzles, stoppers, slide plates, etc. in the ladle, reduce the amount of inclusions generated by secondary oxidation of molten steel, and optimize the flow field structure by adjusting the SEN (submerged entry nozzle insertion depth and nozzle outlet inclination angle) and the temperature difference between the inlet and outlet water of the crystallizer to prevent slag entrapment.

[0027] Example 1

[0028] Preparation of high-purity stainless steel billets:

[0029] Medium-frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium-frequency induction furnace in batches for melting, yielding 30 tons of molten steel. Once the molten steel reaches 1610℃, a strict slag removal process is implemented, removing the slag from the medium-frequency induction furnace until the molten steel is exposed. Before driving the ladle car into the medium-frequency induction furnace, 3 kg of metallurgical lime is added to the bottom of the ladle for every ton of steel, totaling 90 kg of metallurgical lime. The argon gas pipe is then connected. During tapping, 0.5 kg of ferrosilicon (aluminum silicon) is added per ton of steel (totaling 15 kg of ferrosilicon), and 1 kg of barium silicate (calcium silicate) is added per ton of steel (totaling 30 kg of barium silicate) for deoxidation. Argon blowing and stirring are carried out throughout the process to achieve steel deoxidation and slag washing.

[0030] AOD furnace deoxidation and mixing: A ladle car containing molten steel from an induction furnace is driven into the AOD furnace. Each AOD furnace produces 70 tons of molten steel. Argon gas is introduced 5 minutes before tapping. When the composition of the AOD furnace molten steel meets the company's internal control requirements and the molten steel temperature reaches 1580℃, the reducing slag from the AOD furnace molten steel is first added to the ladle containing the induction furnace molten steel to a thickness of 400mm. Then, the ladle car is driven out and the ladle is lifted out. Another ladle containing induction furnace molten steel is lifted into the ladle car. After the ladle is connected to argon gas, the ladle car is driven into the AOD furnace. The AOD furnace molten steel is tapped into the ladle containing the induction furnace molten steel for mixing. The process stops when half (approximately 35 tons) of AOD furnace molten steel has been tapped. The thickness of the reducing slag automatically introduced into the ladle by the AOD furnace molten steel is controlled to be approximately 350mm. The remaining AOD molten steel is then mixed with the 30 tons of induction furnace molten steel that has already had reducing slag added. During tapping from the AOD furnace, 0.5 kg of ferrosilicon (a total of 17.5 kg) and 1 kg of barium silicate (a total of 35 kg) are added per ton of steel along the flow for deoxidation. Argon is blown and stirred throughout the tapping process to ensure good kinetic conditions for steel deoxidation and slag washing. If there is no empty space in the LF furnace after mixing, the ladle is hoisted to the ground and connected to an argon gas pipe to continue argon blowing. Once there is empty space in the LF furnace, the ladle is transported there.

[0031] LF furnace steel refining: After the molten steel enters the station, deoxidizing and slag-forming materials such as ferrosilicon powder, lime, and fluorite are added according to the slag color and fluidity. When the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the molten steel are adjusted according to the analysis results. When the temperature reaches 1595℃ (50℃ above the liquidus temperature) and the composition meets the internal control standard requirements for stainless steel, 100m of calcium-silicon wire is fed in at a speed of 3m / s for inclusion modification treatment. After feeding the calcium wire, argon is blown softly for 10 minutes. Through sampling analysis, the maximum w(TO) in the LF furnace molten steel is 43ppm.

[0032] For mixed-flow continuous casting of molten steel: the slag detection system from the ladle to the tundish was adjusted to the sensitive setting to reduce the amount of slag entrapped into the tundish. The argon blowing flow rates for the ladle long nozzle, stopper rod, and slide plate were adjusted to 10 L / min, 3 L / min, and 2 L / min, respectively, to ensure that air was not adsorbed during casting, thereby reducing the amount of inclusions generated by secondary oxidation of the molten steel. The insertion depth of the SEN (submerged entry nozzle) was adjusted to 150 mm, the nozzle outlet angle was set to 5°, and the temperature difference between the inlet and outlet water of the crystallizer was adjusted to 7° to optimize the flow field structure and prevent slag entrapment. Analysis of five billet samples showed that the w(TO) content in the continuously cast billets was below 49 ppm.

[0033] Example 2

[0034] Preparation of high-purity stainless steel billets:

[0035] Medium-frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium-frequency induction furnace in batches for melting, yielding 30 tons of molten steel. Once the molten steel reaches 1620℃, a strict slag removal process is implemented, removing the slag from the medium-frequency induction furnace until the molten steel is exposed. Before the ladle car enters the medium-frequency induction furnace, 4 kg of metallurgical lime is added to the bottom of the ladle for every ton of steel, totaling 120 kg. The argon gas pipe is then connected. During tapping, 0.75 kg of ferrosilicon (22.5 kg total) and 1.25 kg of barium silicate (37.5 kg total) are added per ton of steel along the steel flow for deoxidation. Argon blowing and stirring are carried out throughout the process to achieve steel deoxidation and slag washing.

[0036] AOD furnace deoxidation and mixing: A ladle car containing molten steel from an induction furnace is driven into the AOD furnace. Each AOD furnace produces 70 tons of molten steel. Argon gas is introduced 7 minutes before tapping. When the composition of the AOD furnace molten steel meets the company's internal control requirements and the molten steel temperature reaches 1605℃, the reducing slag from the AOD furnace molten steel is first added to the ladle containing the induction furnace molten steel to a thickness of 400mm. Then, the ladle car is driven out and the ladle is lifted out. Another ladle containing induction furnace molten steel is lifted into the ladle car. After the ladle is connected to argon gas, the ladle car is driven into the AOD furnace. AOD furnace molten steel is tapped into the ladle containing induction furnace molten steel for mixing. The process stops when half (approximately 35 tons) of AOD furnace molten steel has been tapped, controlling the thickness of the reducing slag brought into the ladle from the AOD furnace to approximately 400mm. The remaining AOD molten steel is then mixed with the 30 tons of induction furnace molten steel that already had reducing slag added. During tapping from the AOD furnace, 0.75 kg of ferrosilicon (26.25 kg total) and 1.25 kg of barium silicate (43.75 kg total) are added per ton of steel along the flow for deoxidation. Argon is blown throughout the tapping process to ensure optimal kinetic conditions for steel deoxidation and slag washing. If there is no empty space in the LF furnace after mixing, the ladle is hoisted to the ground and connected to an argon gas pipe for continued argon blowing. Once there is empty space in the LF furnace, the ladle is transported there.

[0037] LF furnace steel refining: After the molten steel enters the station, based on the slag color, ferrosilicon powder, lime, fluorite and other deoxidizing and slag-forming materials, when the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the molten steel are adjusted according to the analysis results. When the temperature reaches 1609℃ (59℃ above the liquidus temperature) and the composition meets the internal control standard requirements for stainless steel, 150m of silicon-calcium wire is fed in at a speed of 3.5m / s to carry out inclusion modification treatment. After feeding the calcium wire, soft argon blowing is performed for 13 minutes. Through sampling analysis, the maximum w(TO) in the LF furnace molten steel is 37ppm.

[0038] For mixed-flow continuous casting of molten steel: the slag detection system from the ladle to the tundish was adjusted to the sensitive setting to reduce the amount of slag entrapped into the tundish. The argon blowing flow rates for the ladle long nozzle, stopper rod, and slide plate were adjusted to 12L / min, 4L / min, and 3L / min, respectively, to ensure that air was not adsorbed during casting, thereby reducing the amount of inclusions generated by secondary oxidation of the molten steel. The insertion depth of the SEN (submerged entry nozzle) was adjusted to 165mm, the nozzle outlet angle was adjusted to 6.5°, and the temperature difference between the inlet and outlet water of the crystallizer was adjusted to 8℃ to optimize the flow field structure and prevent slag entrapment. Analysis of five billet samples showed that the w(TO) content in the continuously cast billets was below 46ppm.

[0039] Example 3

[0040] Preparation of high-purity stainless steel billets:

[0041] Medium-frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium-frequency induction furnace in batches for melting, yielding 30 tons of molten steel. Once the molten steel reaches 1630℃, a strict slag removal process is implemented, removing the slag from the medium-frequency induction furnace until the molten steel is exposed. Before the ladle car enters the medium-frequency induction furnace, 5 kg of metallurgical lime is added to the bottom of the ladle for every ton of steel, totaling 150 kg. The argon gas pipe is then connected. During tapping, 1 kg of ferrosilicon (30 kg total) and 1.5 kg of barium silicate (45 kg total) are added per ton of steel along the steel flow for deoxidation. Argon blowing and stirring are carried out throughout the process to achieve steel deoxidation and slag washing.

[0042] AOD furnace deoxidation and mixing: A ladle car containing molten steel from an induction furnace is driven into the AOD furnace. Each AOD furnace produces 70 tons of molten steel. Argon gas is introduced 10 minutes before tapping. When the composition of the AOD furnace molten steel meets the company's internal control requirements and the molten steel temperature reaches 1615℃, the reducing slag from the AOD furnace molten steel is first added to the ladle containing the induction furnace molten steel to a thickness of approximately 500mm. Then, the ladle car is driven out and the ladle is lifted out. Another ladle containing induction furnace molten steel is lifted into the ladle car. After the ladle is connected to argon gas, the ladle car is driven into the AOD furnace. AOD furnace molten steel is tapped into the ladle containing induction furnace molten steel for mixing. The process stops when half (approximately 35 tons) of AOD furnace molten steel has been tapped, controlling the thickness of the reducing slag brought into the ladle from the AOD furnace to approximately 500mm. The remaining AOD molten steel is then mixed with the 30 tons of induction furnace molten steel that already had reducing slag added. During tapping, 1 kg of ferrosilicon (35 kg total) and 1.5 kg of barium silicate (52.5 kg total) are added per ton of steel along the steel flow for deoxidation. Argon is blown and stirred throughout the tapping process to ensure good kinetic conditions for steel deoxidation and slag washing. If there is no empty space in the LF furnace after mixing, the ladle is hoisted to the ground and connected to an argon gas pipe to continue argon blowing. Once there is empty space in the LF furnace, the ladle is transported there.

[0043] LF furnace steel refining: After the molten steel enters the station, deoxidizing and slag-forming materials such as ferrosilicon powder, lime, and fluorite are added according to the slag color and fluidity. When the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the molten steel are adjusted according to the analysis results. When the temperature reaches 1610℃ (65℃ above the liquidus temperature) and the composition meets the internal control standard requirements for stainless steel, 200m of calcium-silicon wire is fed in at a speed of 4m / s for inclusion modification treatment. After feeding the calcium wire, argon is blown softly for 15 minutes. Through sampling analysis, the maximum w(TO) in the LF furnace molten steel is 30ppm.

[0044] For mixed-flow continuous casting of molten steel: the slag detection system from the ladle to the tundish was adjusted to the sensitive setting to reduce the amount of slag entrapped into the tundish. The argon blowing flow rates for the ladle long nozzle, stopper rod, and slide plate were adjusted to 14 L / min, 5 L / min, and 3 L / min, respectively, to ensure that air was not adsorbed during casting, thereby reducing the amount of inclusions generated by secondary oxidation of the molten steel. The insertion depth of the SEN (submerged entry nozzle) was adjusted to 180 mm, the nozzle outlet angle was adjusted to 8°, and the temperature difference between the inlet and outlet water of the crystallizer was adjusted to 9° to optimize the flow field structure and prevent slag entrapment. Analysis of five billet samples showed that the w(TO) content in the continuously cast billets was below 36 ppm.

[0045] Data testing was performed on the technical solutions and products in Examples 1 to 3, and the results are shown in Table 1.

[0046] Table 1. Purity of molten steel after mixed rinsing

[0047]

[0048] This invention can prepare high-purity stainless steel billets by mixing molten steel from a medium-frequency induction furnace and molten steel from an AOD furnace. Since the medium-frequency induction furnace uses scrap steel for molten steel smelting, the process is shorter and the cost is significantly lower than that of the AOD furnace. Through the optimization of the above-mentioned processes of molten steel from the medium-frequency induction furnace and molten steel from the AOD furnace, the argon blowing and stirring throughout the mixing process, the LF refining and continuous casting process optimization, the production cost can be effectively reduced and the quality of the steel billets can be guaranteed. This is of great significance for improving the competitiveness of stainless steel production enterprises and promoting the technological development of short-process high-quality molten steel smelting.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity stainless steel billets using a short-process method, characterized in that, Includes the following steps: (1) Medium frequency induction furnace smelting: Stainless steel scrap is hoisted into the medium frequency induction furnace in batches for melting, slag is removed, and molten steel is obtained by medium frequency induction furnace smelting. The ladle is hoisted into the ladle car and the steel is discharged into the ladle. (2) Deoxidation and mixing of AOD furnace molten steel: The ladle car containing molten steel from the medium frequency induction furnace is driven into the AOD furnace, and the molten steel from the AOD furnace is discharged into the ladle containing molten steel from the medium frequency induction furnace for mixing. (3) LF furnace steel refining: The molten steel after mixing in step (2) is transferred to the refining station, and ferrosilicon powder, lime, and fluorite deoxidation and slag-forming materials are added. After refining, it is fed into the silicon-calcium wire and soft blowing is performed to obtain qualified molten steel. The molten steel is then continuously cast to obtain high-purity stainless steel billets. The temperature of the molten steel smelted in the AOD furnace in step (2) is 1580~1620℃. Before the molten steel from the AOD furnace is mixed with the molten steel containing medium frequency steel in the ladle each time it is tapped, a 300~500mm thick layer of AOD furnace reducing slag needs to be added to the ladle to prepare slag for the LF furnace in advance. In step (2), the ladle car containing molten steel from the medium-frequency induction furnace is driven into the AOD furnace. Argon gas is introduced 5-10 minutes before the molten steel from the AOD furnace is tapped. The mass ratio of the molten steel from the AOD furnace to the molten steel smelted in the medium-frequency induction furnace is 1:0.9-1.

2. When tapping the steel, 0.5-1.0 kg of ferrosilicon and 1.0-1.5 kg of barium silicate are added per ton of steel along the steel flow. Argon is blown and stirred throughout the tapping and mixing process. Before the mixed-fluid molten steel enters the LF refining station, argon must be continuously blown. After the mixed-fluid molten steel enters the LF refining station, ferrosilicon powder, lime, and fluorite deoxidizing slag-forming materials are added according to the slag color and slag fluidity. When the slag turns white and has good fluidity, temperature measurement and sampling analysis are carried out. The temperature and composition of the refined molten steel are adjusted according to the analysis results. When the temperature and composition meet the requirements, the silicon-calcium wire is fed in for inclusion modification treatment. After the temperature of the refined molten steel in step (3) exceeds the liquidus temperature by 50~70℃, a calcium wire with a length of 100~200m is fed in at a speed of 3~4m / s; after feeding the calcium wire, soft blowing argon for 10~15 minutes is performed, and the w(TO) in the molten steel leaving the LF station is controlled below 45ppm.

2. The preparation method according to claim 1, characterized in that, The temperature of the molten steel in step (1) is 1610~1630℃. A strict slag removal process is performed to remove the slag from the medium-frequency induction furnace until the molten steel is exposed. Before the ladle car enters the medium-frequency induction furnace, 3~5kg of metallurgical lime is added to the bottom of the ladle per ton of steel. The argon gas pipe is connected. When tapping the steel, 0.5~1.0kg of silicon-aluminum-iron and 1.0~1.5kg of silicon-calcium-barium are added to the steel flow per ton of steel. Argon blowing and stirring are carried out throughout the process to achieve the deoxidation and slag washing process of the molten steel.

3. The preparation method according to claim 1, characterized in that, In step (3), during continuous casting, argon blowing protection is performed on the long nozzle, stopper rod, and slide plate of the ladle. The argon blowing protection flow rates are 10~15L / min, 3~5L / min, and 2~3L / min, respectively. The insertion depth of the SEN submersible nozzle is adjusted to 150~180mm, the nozzle outlet angle is 5~8°, the temperature difference between the inlet and outlet water of the crystallizer is 7~9℃, and the w(TO) in the billet is controlled below 50ppm.

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