Method for VD refining of molten steel

Abstract

The invention relates to a molten steel VD refining method which comprises the following steps: carrying out VD refining on initial molten steel by using a refining agent to obtain target molten steel; wherein the raw materials of the refining agent comprise a calcium carbonate-containing material, the weight of the calcium carbonate-containing material is 83%-95% of the total weight of the refining agent, and the weight content of calcium carbonate in the calcium carbonate-containing material is greater than or equal to 85%. According to the method, the refining agent is added in the VD refining process, the molten steel is desulfurized and the inclusions are promoted to quickly float upwards under the intense stirring effect of CO2 generated through decomposition of the refining agent, and the target molten steel meets the following indexes that the S content is not higher than 5 ppm, the total content of the inclusions is not higher than 1.0 grade, and the monomer size of the inclusions is smaller than 10 micrometers.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, and in particular to a method for VD refining of molten steel. Background Technology

[0002] For steel grades requiring deep desulfurization, deep degassing, and high standards for the content and size of non-metallic inclusions, VD vacuum degassing refining (the process of placing a ladle filled with molten steel in a vacuum chamber for degassing) offers advantages over LF refining furnaces in terms of shorter processing time and better inclusion removal efficiency. The quicklime (mainly CaO) used in traditional steelmaking refining processes differs significantly from the CaO generated by the decomposition of limestone in high-temperature molten pools. Traditional steelmaking quicklime is produced by burning limestone, dolomite, etc., in a kiln. During heating, porous, highly reactive CaO is initially formed. Upon further heating, the CaO recrystallizes, increasing its density and decreasing its activity.

[0003] Therefore, the quicklime used in traditional steelmaking refining processes has relatively low activity, so its desulfurization and inclusion removal effects are not significant. Summary of the Invention

[0004] This application provides a method for VD refining of molten steel to solve the technical problem of how to improve the cleanliness of steel.

[0005] In a first aspect, this application provides a method for VD refining of molten steel, the method comprising:

[0006] The initial molten steel is refined using a refining agent via VD refining to obtain the target molten steel; wherein...

[0007] The raw materials for the refining agent include calcium carbonate-containing materials, wherein the weight of the calcium carbonate-containing materials is 83% to 95% of the total weight of the refining agent, and the weight content of calcium carbonate in the calcium carbonate-containing materials is ≥85%.

[0008] Optionally, the calcium carbonate-containing material includes at least one of the following: pure calcium carbonate or limestone.

[0009] Optionally, the raw materials for the refining agent may also include a co-solvent and a binder.

[0010] Optionally, the co-solvent includes at least one of the following: fluorite, sodium fluoride, cryolite; and / or,

[0011] The binder includes at least one of the following: clay, ordinary cement, bentonite, and water glass.

[0012] Optionally, the weight of the co-solvent is 4% to 12% of the weight of the refining agent, and the weight of the binder is 1% to 5% of the weight of the refining agent.

[0013] Optionally, the process parameters for VD refining include: vacuum degree ≤67Pa, refining time 10min~25min, and argon flow rate 0.1m³. 3 / min~0.5m 3 / min, with an argon supply pressure of 0.1MPa~0.35MPa.

[0014] Optionally, the refining agent is 3 kg to 6.5 kg relative to 1 t of molten steel.

[0015] Optionally, the refining agent is added to the initial molten steel in 3 to 5 batches, with an interval of 1 to 3 minutes between each batch.

[0016] Optionally, the raw materials for the refining agent include calcium carbonate-containing materials, including:

[0017] The raw materials for the refining agent include materials containing calcium carbonate; wherein,

[0018] The method for preparing the refining agent includes the following:

[0019] The calcium carbonate-containing material, co-solvent, and binder are mixed, and then the mixture is first dried.

[0020] The first dried mixture is shaped, and then the shaped mixture is subjected to a second drying to obtain a refining agent; wherein...

[0021] The process parameters for the first drying process include: a temperature of 200℃~230℃ and a time of 5h~8h;

[0022] The process parameters for the second drying process include: a temperature of 100℃~125℃ and a time of 16h~20h.

[0023] Optionally, the target molten steel meets the following criteria: S content not higher than 5 ppm, total inclusion content not higher than grade 1.0, and inclusion individual size less than 10 μm.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] The method for VD refining of molten steel provided in this application includes: using a refining agent to perform VD refining on initial molten steel to obtain target molten steel; wherein the raw material of the refining agent includes a material containing calcium carbonate, the weight of the material containing calcium carbonate is 83% to 95% of the total weight of the refining agent, and the weight content of calcium carbonate in the material containing calcium carbonate is ≥85%. The initial molten steel is refined using calcium carbonate-containing materials through VD refining. During the refining process, limestone is rapidly calcined in the molten steel under high temperatures, resulting in a strong tendency for the surface calcium carbonate to decompose. The decomposition process generates a large amount of CO2, which rapidly breaks down and cracks the limestone, increasing its specific surface area. The resulting lime has characteristics such as small grain size, high activity, and high porosity. As refining progresses, the limestone undergoes simultaneous smelting and cracking, ensuring a complete and efficient reaction. The high-temperature decomposition of CaCO3 breaks down the high-melting-point 2CaO·SiO2 slag shell, promoting the steel-slag reaction. The large amount of CO2 generated after CaCO3 decomposition thoroughly agitates the molten steel. As CO2 bubbles rapidly rise within the ladle, they continuously capture high-melting-point inclusions in the molten steel. Impurities, under the upward buoyancy of the bubbles, quickly enter the slag layer on the surface of the molten steel and are adsorbed, effectively removing inclusions and purifying the molten steel. The CO2 bubbles generated by the decomposition of CaCO3 are small, diffusely distributed, and numerous, exerting a strong stirring effect on the molten steel. The stirring force generated by the generation, expansion, and upward movement of CO2 gas is far greater than the stirring effect generated by bottom-blown gas impacting the molten pool surface, thus aiding in desulfurization and inclusion flotation. Simultaneously, the calcium carbonate-containing material constitutes 83%–95% of the refining agent's weight, and the calcium carbonate content in the material is ≥85%, enhancing the refining agent's reaction efficiency for desulfurization and inclusion removal, thereby improving the desulfurization and inclusion removal effect on the molten steel. Therefore, using limestone (CaCO3) as the main raw material in a VD refining agent to replace the traditional quicklime (CaO) refining agent can achieve deep desulfurization and efficient removal of non-metallic inclusions. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart of a method for VD refining of molten steel provided in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0031] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] In lime production, calcination temperatures higher than the decomposition temperature of limestone (typically 1000–1150℃) are used due to requirements for productivity and other factors. Ensuring thorough calcination inevitably reduces the activity of the outer CaO layer. In steelmaking refining, the ideal situation is to expose the newly formed, highly active CaO to the reaction front to accelerate lime dissolution into slag, thus maximizing its refining effect. Furthermore, during traditional quicklime slag formation, a high-melting-point 2CaO·SiO2 slag shell forms on the lime surface, becoming a limiting factor hindering the dissolution and reaction of quicklime.

[0034] High-temperature decomposition reaction formula of limestone:

[0035]

[0036] Thermodynamic calculations show that the decomposition temperature of CaCO3 is around 896℃. If we extend the temperature range to 1400-1600℃ during the refining process according to equation (1), the temperature is much higher than the decomposition temperature. Temperatures can reach -72796 to -101715 J / mol, and the decomposition tendency of calcium carbonate in the surface layer is very strong after rapid heating. According to publicly available literature, the decomposition time of limestone within the refining temperature range is about 5 minutes, which has little impact on the refining cycle.

[0037] Under high-temperature conditions, rapid calcination of limestone produces a micro-explosive fracturing effect during decomposition. A large amount of CO2 overflowing from the surface layer rapidly fragments and cracks the limestone, increasing its specific surface area. The resulting lime is characterized by small grains, high activity, and high porosity. Furthermore, the high-temperature decomposition of CaCO3 breaks down the high-melting-point 2CaO·SiO2 slag shell, promoting the steel-slag reaction. After CaCO3 decomposition, CO2 bubbles circulate with the molten steel in the VD furnace and enter the ladle. These bubbles rise rapidly within the ladle, continuously capturing high-melting-point inclusions in the molten steel. Under the upward buoyancy of the bubbles, these inclusions quickly enter the slag layer on the surface of the molten steel and are adsorbed, thus efficiently removing inclusions and purifying the molten steel. Moreover, the CO2 bubbles produced by the decomposition of CaCO3 are very small, diffusely distributed, and numerous, which have a strong stirring effect on the molten steel. The stirring force generated by the generation, expansion and floating of CO2 gas will be much greater than the stirring effect generated by the bottom blowing gas impacting the surface of the molten pool, which helps desulfurization and the floating of inclusions, and achieves deep desulfurization and efficient removal of non-metallic inclusions.

[0038] Currently, whether for deep decarburization to increase decarburization rate or deep desulfurization to remove inclusions, CaCO3 is commonly used in RH refining furnaces, but research on its application in VD refining is unreported. VD and RH refining furnaces differ significantly. Compared to the smaller immersion tube area of ​​an RH furnace, the reaction interface in a VD refining furnace is larger, resulting in more intense stirring and a more complete reaction between slag and steel, leading to significant improvements. Therefore, in its first aspect, this application provides a method for VD refining molten steel. Figure 1 A schematic flow chart of a method for VD refining of molten steel provided in this application embodiment; please refer to Figure 1 The method includes:

[0039] S1. The initial molten steel is refined using a refining agent via VD refining to obtain the target molten steel; wherein...

[0040] The raw materials for the refining agent include calcium carbonate-containing materials, wherein the weight of the calcium carbonate-containing materials is 83% to 95% of the total weight of the refining agent, and the weight content of calcium carbonate in the calcium carbonate-containing materials is ≥85%.

[0041] In this embodiment, calcium carbonate-containing materials are used to perform VD refining on the initial molten steel. During the refining process, limestone is rapidly calcined in the molten steel under high-temperature conditions, resulting in a strong tendency for the surface calcium carbonate to decompose. The decomposition process generates a large amount of CO2 that rapidly breaks down and cracks the limestone, increasing its specific surface area. The resulting lime has characteristics such as small grain size, high activity, and high porosity. As refining progresses, the limestone undergoes simultaneous smelting and cracking, ensuring a thorough and efficient reaction. The high-temperature decomposition of CaCO3 breaks down the high-melting-point 2CaO·SiO2 slag shell, promoting the steel-slag reaction. The large amount of CO2 generated after CaCO3 decomposition thoroughly stirs the molten steel. As CO2 bubbles rapidly rise within the ladle, they continuously capture high-melting-point inclusions in the molten steel. The inclusions, under the upward buoyancy of the bubbles, quickly enter the slag layer on the surface of the molten steel and are adsorbed, effectively removing inclusions and purifying the molten steel. The CO2 bubbles generated by the decomposition of CaCO3 are small, diffusely distributed, and numerous, exerting a strong stirring effect on the molten steel. The stirring force generated by the generation, expansion, and upward movement of CO2 gas is far greater than the stirring effect generated by the bottom-blown gas impacting the molten pool surface, which helps in desulfurization and inclusion flotation. Simultaneously, ensuring that the weight of the calcium carbonate-containing material is 83%–95% of the total weight of the refining agent, and that the calcium carbonate content in the calcium carbonate-containing material is ≥85% by weight, enhances the refining agent's reaction efficiency for desulfurization and inclusion removal, thereby improving the desulfurization and inclusion removal effect on the molten steel. Therefore, using limestone (CaCO3) as the main raw material as a VD refining agent to replace the traditional quicklime (CaO) refining agent can achieve deep desulfurization and efficient removal of non-metallic inclusions. For example, the weight of the calcium carbonate-containing material can be 83%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc., of the total weight of the refining agent, and the weight content of calcium carbonate in the calcium carbonate-containing material can be 85%, 86%, 87%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0042] In some embodiments, the calcium carbonate-containing material includes at least one of the following: pure calcium carbonate and limestone.

[0043] In the embodiments of this application, the calcium carbonate-containing material can be one or more of pure calcium carbonate and limestone.

[0044] In some embodiments, the raw materials for the refining agent also include a co-solvent and a binder.

[0045] In this embodiment, the refining agent plays a decisive role in deep desulfurization and inclusion removal through its rapid decomposition at high temperatures. The raw materials for the refining agent also include a co-solvent and a binder. The co-solvent promotes the decomposition reaction of the refining agent, improves its flowability, wettability, stability, and uniformity, and enhances its density, hardness, and strength. The binder, through its adhesive properties, tightly bonds the refining agent and co-solvent, forming a stable bond and enhancing its bonding strength, durability, and ease of use. Therefore, the main component undergoing the chemical reaction in the refining agent is the refining agent itself, while the co-solvent and binder serve as auxiliary components, promoting the reaction, improving uniformity, increasing bonding strength, and enhancing stability in use.

[0046] In some embodiments, the co-solvent includes at least one of the following: fluorite, sodium fluoride, cryolite; and / or,

[0047] The binder includes at least one of the following: clay, ordinary cement, bentonite, and water glass.

[0048] In some embodiments, the co-solvent can be one or more of fluorite, sodium fluoride, and cryolite, and the binder can be one or more of clay, ordinary cement, bentonite, and water glass.

[0049] In some embodiments, the weight of the co-solvent is 4% to 12% of the weight of the refining agent, and the weight of the binder is 1% to 5% of the weight of the refining agent.

[0050] In the embodiments of this application, the weight of the co-solvent can be 4% to 12% of the weight of the refining agent, which can maximize the co-solvent's role in promoting the reaction and improving flowability, while ensuring the stability of the refining agent. The weight of the binder can be 1% to 5% of the weight of the refining agent, which can fully achieve its adhesive properties, ensure the strength of the refining agent, and prevent cracking. For example, the weight of the co-solvent can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc., of the weight of the refining agent; the weight of the binder can be 1%, 2%, 3%, 4%, 5%, etc., of the weight of the refining agent.

[0051] In some embodiments, the process parameters for VD refining include: a vacuum degree of ≤67 Pa, a refining time of 10 min to 25 min, and an argon flow rate of 0.1 m³ / min. 3 / min~0.5m 3 / min, with an argon supply pressure of 0.1MPa~0.35MPa.

[0052] In this embodiment, by adjusting the process parameters of VD refining, combined with the effects of the aforementioned refining agent, deep desulfurization and efficient removal of non-metallic inclusions are achieved. For example, the vacuum degree can be 67 Pa, 66 Pa, 65 Pa, 64 Pa, etc.; the refining time can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 25 min, etc.; and the argon flow rate can be 0.1 m³ / min. 3 / min, 0.2m 3 / min, 0.3m 3 / min, 0.4m 3 / min, 0.5m 3 / min, etc.; the argon supply pressure can be 0.1MPa, 0.15MPa, 0.2MPa, 0.25MPa, 0.3MPa, 0.35MPa, etc.

[0053] In some embodiments, the refining agent is 3 kg to 6.5 kg relative to 1 t of molten steel.

[0054] In this embodiment, the refining agent is 3 kg to 6.5 kg relative to 1 ton of molten steel, maximizing the desulfurization and inclusion removal effects of the refining agent. For example, the refining agent can be 3 kg, 3.5 kg, 4 kg, 4.5 kg, 5 kg, 5.5 kg, 6 kg, 6.5 kg, etc., relative to 1 ton of molten steel.

[0055] In some embodiments, the refining agent is added to the initial molten steel in 3 to 5 batches, with an interval of 1 to 3 minutes between each batch.

[0056] In this embodiment, the refining agent can be added to the initial molten steel in 3 to 5 batches, with an interval of 1 to 3 minutes between each batch. This allows the refining agent sufficient time and space to exert its desulfurization and inclusion removal effects. After being added in 3 to 5 batches, the refining agent is generally carried to the bottom of the ladle within approximately 1 to 3 minutes due to the mass transfer effect of the flowing molten steel. The highly active CaO and a large amount of CO2 bubbles generated by the high-temperature decomposition of the refining agent in the VD furnace cause the refining agent to burst due to gas expansion, inducing strong circulation within the molten steel. This significantly improves the stirring of the molten pool, the deep desulfurization rate, and the rapid removal of inclusions. The strong cracking effect of limestone also enhances the emulsification and activity of lime, achieving a superior refining effect. For example, the refining agent can be added to the initial molten steel in 3, 4, or 5 batches, with intervals of 1 minute, 2 minutes, or 3 minutes between each batch.

[0057] The above-mentioned VD refining method for molten steel specifically includes: adding a refining agent during the VD refining process, utilizing the strong stirring effect of the CO2 generated by its decomposition to desulfurize the molten steel and promote the rapid floating of inclusions. 1) After slagging, composition, and temperature adjustment are completed in the ladle furnace, the molten steel is lifted from the ladle furnace station and transported to the ladle support seat where the VD is located in the vacuum tank; 2) Argon gas is turned on from the bottom of the ladle. After temperature measurement and sampling, the vacuum tank cover is moved to the top of the vacuum tank and lowered onto the flange surface at the top of the vacuum tank body. The steam jet pump is started; 3) When the vacuum degree is ≤67Pa, the argon supply intensity is adjusted, and the VD refining agent is added through the feed pipe connected to the high-level silo. The amount added per ton of steel is 3Kg~6.5Kg. To reduce the temperature drop during the refining process and to make the refining agent slag quickly, the refining agent is added in 3~5 batches, with an interval of 1min~3min between each batch. The argon flow rate is controlled at 0.1m³. 3 / min~0.5m 3 The argon supply rate is maintained at a pressure between 0.1 MPa and 0.35 MPa. Refining is carried out for 10 to 25 minutes at a vacuum level ≤67 Pa. After completing the vacuum refining task, nitrogen is supplied to break the vacuum. Once atmospheric pressure is reached, the vacuum tank lid is raised and removed. After adjusting the argon supply intensity, temperature measurement and sampling are performed.

[0058] In some embodiments, the raw material for the refining agent includes calcium carbonate-containing materials, including:

[0059] The raw materials for the refining agent include materials containing calcium carbonate; wherein,

[0060] The method for preparing the refining agent includes the following:

[0061] The calcium carbonate-containing material, co-solvent, and binder are mixed, and then the mixture is first dried.

[0062] The first dried mixture is shaped, and then the shaped mixture is subjected to a second drying to obtain a refining agent; wherein...

[0063] The process parameters for the first drying process include: a temperature of 200℃~230℃ and a time of 5h~8h;

[0064] The process parameters for the second drying process include: a temperature of 100℃~125℃ and a time of 16h~20h.

[0065] In this embodiment, the purpose of the first drying is to remove excess moisture from the raw materials; the purpose of the second drying is that the refining agent absorbs moisture from the air during the processing and forming process, and adding it to the molten steel will cause hydrogenation, so a second drying is necessary. For example, the process parameters for the first drying can include temperatures of 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, etc., and times of 5h, 6h, 7h, 8h, etc.; the process parameters for the second drying can include temperatures of 100℃, 103℃, 105℃, 107℃, 110℃, 113℃, 115℃, 118℃, 120℃, 123℃, 125℃, etc., and times of 5h, 6h, 7h, 8h, etc. The refining agent has a particle size of 10.8cm to 12cm and a single weight of more than 1.4kg to 1.9kg. Generally, 15 to 20 refining agents are stored in one packaging bag, weighing about 21kg to 38kg.

[0066] In some embodiments, the target molten steel meets the following criteria: sulfur content not higher than 5 ppm, total inclusion content not higher than grade 1.0, and inclusion individual size less than 10 μm.

[0067] In the embodiments of this application, the above-mentioned VD refining method for molten steel is suitable for the refining production process of various low-alloy high-strength steels (steel grades that require extremely low [S]) and special steels with high purity requirements. It achieves the goal of refining molten steel with an S content of no more than 5 ppm, an overall inclusion content of no more than grade 1.0, and an inclusion individual size of less than 10 μm within 15 to 25 minutes, thereby realizing the production of low-cost, high-efficiency, and high-purity steel.

[0068] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0069] Example 1

[0070] 1. Preparation of refining agent:

[0071] 1) Ingredients: The weight ratio of each component is 83% limestone, 12% fluorite, and 5% clay; the calcium carbonate in the limestone is 95% by weight.

[0072] 2) Preparation: First, the limestone (CaCO3) is crushed to a particle size of 200 mesh (0.01-0.5mm). Then, the components of the raw materials are added to a mixer in proportion and mixed thoroughly for 1 hour. After mixing, the mixture is dried at 220℃ for 6 hours. Then, it is pressed into 10.8-12cm blocks of special refining agent using a briquetting machine. After the special refining agent is formed, it is dried again at 110℃ for 18 hours. After cooling, it is packed into high-density, high-strength moisture-proof bags, each weighing 21-38kg. The packaging must be sealed well to prevent moisture and should be used within 90 days from the date of production.

[0073] 2. A method for VD refining of molten steel (addition of refining agents)

[0074] 1) After the molten steel has completed slag formation, composition and temperature adjustment in the ladle furnace, it is lifted from the ladle furnace station and transported to the ladle support seat where the VD is located in the vacuum vessel;

[0075] 2) Connect the bottom blowing argon gas in the ladle. After completing the temperature measurement and sampling, move the vacuum tank cover to the top of the vacuum tank and lower it to the flange face at the top of the vacuum tank. Start the steam jet pump.

[0076] 3) At a vacuum of 67 Pa, adjust the argon supply intensity to 0.3 m. 3 The refining agent is added at a rate of 5 kg per ton of steel via a feed pipe connected to the high-level silo. To minimize temperature drop during refining and facilitate rapid slag formation of the special refining agent, it is added in three batches, with a 3-minute interval between each batch. Refining is carried out at a vacuum of 67 Pa for 23 minutes. After completing the vacuum refining process, nitrogen is supplied to break the vacuum, and once atmospheric pressure is reached, the vacuum tank lid is raised and removed. After adjusting the argon supply intensity, temperature measurement and sampling are performed.

[0077] Comparative Example 1

[0078] Based on the disclosed content of the embodiments, the difference between Comparative Example 1 and Example 1 is that the refining agent is quicklime (CaO).

[0079] The smelting effects of Example 1 and Comparative Example 1 were tested, and the test results are shown in Table 1.

[0080] Table 1. Test results of Example 1 and Comparative Example 1

[0081] Serial Number S content at the end of refining Refining End Impurity Level Inclusion unit size Example 1 4ppm Level 1.0 ≤7μm Comparative Example 1 10ppm Level 1.5 10μm~28μm

[0082] Example 2

[0083] 1. Preparation of refining agent:

[0084] 1) Ingredients: The weight ratio of each component is 89% limestone, 6% fluorite, 2% sodium fluoride, and 3% bentonite; the calcium carbonate in the limestone is 90% by weight.

[0085] 2) Preparation: First, the limestone (CaCO3) is crushed to a particle size of 200 mesh (0.01-0.5mm). Then, the components of the raw materials are added to a mixer in proportion and mixed thoroughly for 1.5 hours. After mixing, the mixture is dried at 200℃ for 5 hours. Then, it is pressed into 10.8-12cm blocks of special refining agent using a briquetting machine. After the special refining agent is formed, it is dried again at 100℃ for 20 hours. After cooling, it is packed into high-density, high-strength moisture-proof bags, each weighing 21-38kg. The packaging must be sealed well to prevent moisture and should be used within 90 days from the date of production.

[0086] 2. A method for VD refining of molten steel (addition of refining agents)

[0087] 1) After the molten steel has completed slag formation, composition and temperature adjustment in the ladle furnace, it is lifted from the ladle furnace station and transported to the ladle support seat where the VD is located in the vacuum vessel;

[0088] 2) Connect the bottom blowing argon gas in the ladle. After completing the temperature measurement and sampling, move the vacuum tank cover to the top of the vacuum tank and lower it to the flange face at the top of the vacuum tank. Start the steam jet pump.

[0089] 3) At a vacuum of 67 Pa, adjust the argon supply intensity to 0.4 m. 3 The refining agent is added at a rate of 4.5 kg per ton of steel via a feed pipe connected to the high-level silo. To minimize temperature drop during refining and facilitate rapid slag formation of the special refining agent, it is added in three batches, with a 3-minute interval between each batch. Refining is carried out at a vacuum of 67 Pa for 22 minutes. After completing the vacuum refining process, nitrogen is supplied to break the vacuum, and once atmospheric pressure is reached, the vacuum tank lid is raised and removed. After adjusting the argon supply intensity, temperature measurement and sampling are performed.

[0090] Comparative Example 2

[0091] Based on the disclosure in Example 2, the difference between Comparative Example 2 and Example 2 is that the refining agent is quicklime (CaO).

[0092] The smelting effects of Example 2 and Comparative Example 2 were tested, and the test results are shown in Table 1.

[0093] Table 2. Test results of Example 2 and Comparative Example 2

[0094] Serial Number S content at the end of refining Refining End Impurity Level Inclusion unit size Example 2 5ppm Level 1.0 ≤8μm Comparative Example 2 13ppm Level 1.5 10μm~31μm

[0095] Example 3

[0096] 1. Preparation of refining agent:

[0097] 1) Ingredients: The weight ratio of each component is 95% limestone (CaCO3), 3% cryolite, 1% clay, and 1% ordinary cement; the calcium carbonate in the limestone is 93% by weight.

[0098] 2) Preparation: First, the limestone (CaCO3) is crushed to a particle size of 200 mesh (0.01-0.5mm). Then, the components of the raw materials are added to a mixer in proportion and mixed thoroughly for 2 hours. After mixing, the mixture is dried at 220℃ for 5.5 hours. Then, it is pressed into 10.8-12cm blocks of special refining agent using a briquetting machine. After the special refining agent is formed, it is dried again at 120℃ for 19 hours. After cooling, it is packed into high-density, high-strength moisture-proof bags, each weighing 21-38kg. The packaging must be sealed well to prevent moisture and should be used within 90 days from the date of production.

[0099] 2. A method for VD refining of molten steel (addition of refining agents)

[0100] 1) After the molten steel has completed slag formation, composition and temperature adjustment in the ladle furnace, it is lifted from the ladle furnace station and transported to the ladle support seat where the VD is located in the vacuum vessel;

[0101] 2) Connect the bottom blowing argon gas in the ladle. After completing the temperature measurement and sampling, move the vacuum tank cover to the top of the vacuum tank and lower it to the flange surface at the top of the vacuum tank. Start the steam jet pump.

[0102] 3) At a vacuum of 67 Pa, adjust the argon supply intensity to 0.45 m. 3 The refining agent is added at a rate of 4.8 kg per ton of steel via a feed pipe connected to the high-level silo. To minimize temperature drop during refining and facilitate rapid slag formation of the special refining agent, it is added in three batches, with a 2-minute interval between each batch. Refining is carried out at a vacuum of 67 Pa for 20 minutes. After completing the vacuum refining process, nitrogen is supplied to break the vacuum, and once atmospheric pressure is reached, the vacuum tank lid is raised and removed. After adjusting the argon supply intensity, temperature measurement and sampling are performed.

[0103] Comparative Example 3

[0104] Based on the disclosure in Example 3, the difference between Comparative Example 3 and Example 3 is that the refining agent is quicklime (CaO).

[0105] The smelting effects of Example 3 and Comparative Example 3 were tested, and the test results are shown in Table 1.

[0106] Table 3. Test results of Example 3 and Comparative Example 3

[0107] Serial Number S content at the end of desulfurization Refining End Impurity Level Inclusion unit size Example 3 3.5ppm Level 0.5 ≤5μm Comparative Example 3 9.5ppm Level 1.0 10μm~18μm

[0108] One or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0109] 1) The VD refining method for molten steel provided in this application is simple, convenient and easy to operate, and requires no additional auxiliary equipment;

[0110] 2) By adding refining agents during the VD refining process, the desulfurization reaction speed is accelerated, which can shorten the normal desulfurization reaction time of VD by at least 2 to 3 minutes;

[0111] 3) By adding refining agent during the VD refining process, the desulfurization effect is good and the inclusion removal rate is high. The S content of molten steel is not higher than 5 ppm within 15 to 25 minutes of refining, the total inclusion content is not higher than grade 1.0, and the size of the individual inclusions is less than 10 μm.

[0112] 4) Although the steel liquid VD refining method provided in this application has a certain temperature drop, due to the reasonable arrangement of the feeding process and the full reaction, it saves the time for normal VD desulfurization and inclusion flotation, and at the same time solves the problem of deep desulfurization and efficient removal of non-metallic inclusions, with ideal overall effect.

[0113] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for VD refining of molten steel, characterized in that, The method includes: The initial molten steel is refined using a refining agent via VD refining to obtain the target molten steel; wherein... The raw materials for the refining agent include calcium carbonate-containing materials, wherein the weight of the calcium carbonate-containing materials is 83% to 95% of the total weight of the refining agent, and the weight content of calcium carbonate in the calcium carbonate-containing materials is ≥85%.

2. The method according to claim 1, characterized in that, The calcium carbonate-containing material includes at least one of the following: pure calcium carbonate and limestone.

3. The method according to claim 1, characterized in that, The raw materials for the refining agent also include a co-solvent and a binder.

4. The method according to claim 3, characterized in that, The co-solvent includes at least one of the following: fluorite, sodium fluoride, cryolite; and / or, The binder includes at least one of the following: clay, ordinary cement, bentonite, and water glass.

5. The method according to claim 3, characterized in that, The weight of the co-solvent is 4% to 12% of the weight of the refining agent, and the weight of the binder is 1% to 5% of the weight of the refining agent.

6. The method according to claim 1, characterized in that, The VD refining process parameters include: vacuum degree ≤67Pa, refining time 10min~25min, and argon flow rate 0.1m³ / min. 3 / min~0.5m 3 / min, with an argon supply pressure of 0.1MPa~0.35MPa.

7. The method according to claim 1, characterized in that, The refining agent is 3 kg to 6.5 kg relative to 1 ton of molten steel.

8. The method according to claim 1, characterized in that, The refining agent is added to the initial molten steel in 3 to 5 batches, with an interval of 1 to 3 minutes between each batch.

9. The method according to claim 1, characterized in that, The raw materials for the refining agent include calcium carbonate-containing materials, including: The raw materials for the refining agent include materials containing calcium carbonate; wherein, The method for preparing the refining agent includes the following: The calcium carbonate-containing material, co-solvent, and binder are mixed, and then the mixture is first dried. The first dried mixture is shaped, and then the shaped mixture is subjected to a second drying to obtain a refining agent; wherein... The process parameters for the first drying process include: a temperature of 200℃~230℃ and a time of 5h~8h; The process parameters for the second drying process include: a temperature of 100℃~125℃ and a time of 16h~20h.

10. The method according to claim 1, characterized in that, The target molten steel meets the following criteria: sulfur content not higher than 5 ppm, total inclusion content not higher than grade 1.0, and inclusion individual size less than 10 μm.

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