A method of LF refining

Abstract

This application relates to an LF refining method, comprising: forming slag covering the molten steel in a ladle; inserting the working end of an ultrasonic tool head into a ±50mm region at the interface between the molten steel and the slag; continuously emitting ultrasonic waves into the region through the working end; the ultrasonic waves simultaneously exciting cavitation and acoustic flow effects in the region, the cavitation effect breaking the slag into emulsified slag droplets with an average particle size of less than 100μm, and the acoustic flow effect carrying the emulsified slag droplets into the interior of the molten steel and mixing them with the molten steel to obtain a steel-slag emulsion; the steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between the molten steel and the slag into a three-dimensional region distributed within the molten steel; sulfur migrates from the molten steel to the emulsified slag droplets in the steel-slag emulsion and is fixed in the emulsified slag droplets, thereby reducing the sulfur content of the molten steel to a target value by fixing the sulfur element in the emulsified slag droplets.

Description

Technical Field

[0001] This application belongs to the field of iron and steel metallurgy technology, and particularly relates to an LF refining method. Background Technology

[0002] LF refining is an indispensable secondary refining process in modern steelmaking, undertaking core metallurgical functions such as desulfurization, deoxidation, alloying, and temperature and composition homogenization. Traditional LF refining's slag-metal reaction mainly occurs at the two-dimensional interface between molten steel and slag, resulting in low desulfurization rates and long processing times. To overcome these interface limitations, the industry commonly employs methods such as enhanced bottom-blowing argon stirring, optimized synthetic slag composition, and increased heating power to attempt to expand the interface area and thin the boundary layer. However, these measures remain within the framework of "interface reaction" and cannot fundamentally change the reaction mechanism, leading to excessively long refining cycle times. Summary of the Invention

[0003] This application provides an LF refining method to solve the following technical problem: how to promote LF interfacial reaction to reduce desulfurization time.

[0004] This application provides an LF refining method for desulfurizing molten steel contained in a ladle, the method comprising: A slag covering the molten steel is formed inside the ladle; Insert the working end of the ultrasonic tool head into the ±50mm area of ​​the interface between the molten steel and the slag. The ultrasonic waves are continuously emitted into the area through the working end at a power density of 1.1kW / ton steel to 2.0kW / ton and a frequency of 21kHz to 40kHz for a duration of 5min to 15min. The ultrasonic waves simultaneously excite cavitation and acoustic flow effects in the region. The cavitation effect breaks the slag into emulsified slag droplets with an average particle size of less than 100 μm. The acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. The steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between the molten steel and the slag into a three-dimensional volume region distributed inside the molten steel. Sulfur migrates from the molten steel to the emulsified slag droplets in the steel-slag emulsion and is fixed in the emulsified slag droplets. By fixing the sulfur element in the emulsified slag droplets, the sulfur content of the molten steel is reduced to the target value.

[0005] Optionally, the working end of the ultrasonic tool head is inserted at an angle downwards, which is consistent with the flow direction of the molten steel driven by the bottom-blown argon gas in the ladle. This allows the acoustic flow effect to be superimposed on the circulation driven by the bottom-blown argon gas, conveying the emulsified slag droplets to a larger area of ​​the ladle molten pool for further reaction with sulfur in the steel.

[0006] Optionally, one to three ultrasonic tool heads are provided, each with an independent power selection from 55kW to 120kW, and the total power of all ultrasonic tool heads meets the requirement of 1.1kW / ton of steel to 2.0kW / ton of steel.

[0007] Optionally, the wear length of the working end of the ultrasonic tool head is monitored in real time. When the working end is about to leave the ±50mm area of ​​the interface due to burning, it is fed along the fixed guide rail above the ladle towards the molten steel to keep the working end always within the ±50mm area of ​​the interface. When the remaining length of the working end is less than 20mm and the position cannot be maintained by feeding, it is withdrawn and replaced with a new working end. Optionally, the time required to reduce the sulfur content of the molten steel from an initial value of 0.008% to 0.052% to the target value is 5 min to 15 min.

[0008] Optionally, after fixing the sulfur element in the emulsified slag droplets, ultrasonic stirring is stopped, allowing the sulfur-containing emulsified slag droplets to float into the molten slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is stably maintained below the target value.

[0009] Optionally, during the emission of ultrasound, the flow rate of bottom-blown argon gas is controlled at 2.0 NL / min·ton steel to 3.8 NL / min·ton steel to coordinate with the flow state of the steel-slag emulsion and molten steel circulation caused by the acoustic flow effect.

[0010] Optionally, by coupling the ultrasonic action time and total ultrasonic power with the bottom-blown argon flow rate, the power consumption per ton of steel can be reduced by 20% to 35%, and the argon consumption per ton of steel can be reduced by 40% to 58%.

[0011] Optionally, the average particle size of the emulsified slag droplets in the steel-slag emulsion is 10μm to 50μm, and the average particle size expands the desulfurization reaction interface area by more than 1000 times, thereby increasing the desulfurization reaction rate by more than 50%.

[0012] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides an LF refining method that breaks through the limitations of traditional "two-dimensional interface reaction." Through the action of an ultrasonic physical field, the desulfurization reaction interface is expanded from the two-dimensional steel-slag interface to a three-dimensional region within the molten steel, thereby greatly improving reaction kinetics and achieving rapid desulfurization. Specifically, it includes: 1. Cavitation instantly breaking the molten slag into emulsified slag droplets <100μm, resulting in smaller particle size, larger specific surface area, and an order of magnitude increase in reaction sites; 2. Acoustic jetting uniformly injects these emulsified slag droplets deep into the molten steel, forming a stable steel-slag emulsion, transforming the desulfurization interface from a "skin" to a "full furnace of bubbles." Ultimately, the diffusion path of sulfur atoms is reduced from the centimeter level to the micrometer level, significantly improving the mass transfer coefficient and naturally shortening the time required for the same desulfurization volume. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. 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.

[0014] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0015] This application provides an LF refining method for desulfurizing molten steel contained in a ladle, the method comprising: S1. A slag covering the molten steel is formed inside the ladle; S2. Insert the working end of the ultrasonic tool head into the ±50mm area of ​​the interface between the molten steel and the slag. S3. Ultrasonic waves are continuously emitted into the area through the working end at a power density of 1.1kW / ton steel to 2.0kW / ton and a frequency of 21kHz to 40kHz for a duration of 5min to 15min. S4. The ultrasonic wave simultaneously excites cavitation and acoustic flow effects in the region. The cavitation effect breaks the slag into emulsified slag droplets with an average particle size of less than 100 μm. The acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. S5. The steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between the molten steel and the slag to a three-dimensional volume region distributed inside the molten steel. S6. Sulfur migrates from the molten steel to the emulsified slag droplets in the steel-slag emulsion and is fixed in the emulsified slag droplets. By fixing the sulfur element in the emulsified slag droplets, the sulfur content of the molten steel is reduced to the target value.

[0016] Step S1 provides molten slag; Step S2 precisely injects ultrasonic energy into the ±50mm region of the steel-slag interface; Step S3, with a power density of 1.1~2.0 kW / ton of steel at a frequency of 21~40 kHz, is sufficient to generate violent cavitation bubble collapse in the ±50mm region of the steel-slag interface, generating a local high pressure of approximately 1000 atm and a high temperature of 1000℃ at the moment of collapse; Step S4, the cavitation effect tears the slag into emulsified slag droplets with an average particle size of less than 100 μm; Step S4, the acoustic flow effect generates a jet pointing deep into the molten steel with a jet velocity of 0.5~1 m / s; and forces the emulsified slag droplets into the interior of the molten steel; Step S5 expands the original two-dimensional interface of only a few square meters into a three-dimensional region covering the entire ladle pool, increasing the reaction interface area by more than 1000 times; Step S6 causes sulfur to react in the form of [S]→(S 2- The sulfur content in the molten steel is reduced from 0.008-0.052% to ≤0.001% within 5-15 minutes, thereby directly reducing the desulfurization time by 14-20 minutes and solving the technical problem of "slow reaction at the LF interface".

[0017] In S3, ultrasonic waves are continuously emitted into the area through the working end at power densities of 1.1kW / ton of steel, 1.2kW / ton of steel, 1.3kW / ton of steel, 1.4kW / ton of steel, 1.5kW / ton of steel, 1.6kW / ton of steel, 1.7kW / ton of steel, 1.8kW / ton of steel, 1.9kW / ton of steel, and 2.0kW / ton of steel, and simultaneously at frequencies of 21kHz, 22kHz, 23kHz, 24kHz, 25kHz, 26kHz, 27kHz, 28kHz, 29kHz, 30kHz, 31kHz, 32kHz, 33kHz, 34kHz, 35kHz, 36kHz, 37kHz, 38kHz, 39kHz, and 40kHz, for durations of 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, and 15min.

[0018] In some embodiments, the working end of the ultrasonic tool head is inserted at an angle downwards, which is consistent with the flow direction of the molten steel driven by the bottom-blown argon gas in the ladle. This allows the acoustic flow effect to be superimposed on the circulation driven by the bottom-blown argon gas, conveying the emulsified slag droplets to a larger area of ​​the ladle molten pool for further reaction with sulfur in the steel.

[0019] The working end of the ultrasonic tool head is inserted at an angle downwards to ensure that the direction of the ultrasonic jet is in the same direction as the circulation direction of the molten steel. The angle downwards direction is consistent with the flow direction of the molten steel driven by the bottom-blown argon gas in the ladle, so that the acoustic flow effect and the circulation velocity driven by the bottom-blown argon gas are vector-superimposed. After superposition, the average flow velocity of the molten pool increases from 0.2 m / s to 0.4 m / s. The combined flow after superposition transports the emulsified slag droplets to a larger area of ​​the ladle molten pool to further react with the sulfur in the steel. The emulsified slag droplets are evenly dispersed to any position in the 150~200t molten steel pool within 3 minutes to continue desulfurization, thereby further shortening the desulfurization time by 2~3 minutes.

[0020] In some embodiments, one to three ultrasonic tool heads are provided, each with an independent power selected from 55kW to 120kW, and the total power of all ultrasonic tool heads meets the requirement of 1.1kW / ton of steel to 2.0kW / ton of steel.

[0021] Set up 1, 2, or 3 ultrasonic tool heads: Arrange 1 to 3 ultrasonic tool heads flexibly according to the steel volume of 80~200t; the power of each ultrasonic tool head can be independently selected from 55kW, 60kW, 65kW, 70kW, 75kW, 80kW, 85kW, 90kW, 95kW, 100kW, 105kW, 110kW, 115kW, 120kW, etc.: the single-head power of 55~120kW ensures that each tool head generates a local power density of ≥0.8kW / ton of steel within the corresponding solid angle. The total power of all ultrasonic tool heads meets the following requirements: 1.1kW / ton of steel, 1.2kW / ton of steel, 1.3kW / ton of steel, 1.4kW / ton of steel, 1.5kW / ton of steel, 1.6kW / ton of steel, 1.7kW / ton of steel, 1.8kW / ton of steel, 1.9kW / ton of steel, and 2.0kW / ton of steel. This ensures that the total power density is always maintained at 1.1~2.0kW / ton of steel, thereby avoiding both insufficient power leading to weak cavitation and excessive power causing splashing, and ensuring that the desulfurization time is stably shortened to 5~10 minutes.

[0022] In some implementations, the wear length of the working end of the ultrasonic tool head is monitored in real time. When the working end is about to leave the ±50mm area of ​​the interface due to burning, it is fed along the fixed guide rail above the ladle towards the molten steel to keep the working end within the ±50mm area of ​​the interface. When the remaining length of the working end is less than 20mm and the position cannot be maintained by feeding, it is withdrawn and replaced with a new working end. Monitor the length of the working end of the ultrasonic tool head consumed: monitor the consumption of the resistant material working end in real time; when the remaining length of the working end is less than 20mm, continuously advance the ultrasonic tool head towards the slag surface along the guide rail fixed above the ladle: keep the working end in the ±50mm range of the molten steel-slag interface to ensure continuous injection of ultrasonic energy into the critical reaction zone; after advancing to the limit position, withdraw and replace with a new working end: avoid the ultrasonic jet direction deviating from the interface due to the working end being too short, thereby ensuring continuous and stable operation of cavitation and acoustic flow effects, and preventing the desulfurization time from being prolonged due to energy injection interruption.

[0023] In some embodiments, the time required to reduce the sulfur content of the molten steel from an initial value of 0.008% to 0.052% to a target value is 5 min to 15 min.

[0024] Target value ≤ 0.001%: Set an ultra-low sulfur target; reduce the sulfur content of molten steel from initial values ​​of 0.008%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, 0.035%, 0.040%, 0.045%, 0.050%, and 0.052% to the target value; this initial sulfur range covers marine engineering steel E36 to ordinary steel Q345B; the required reduction time is 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, and 15 min, etc.: the reaction interface area is expanded by more than 1000 times through steel-slag emulsion, reducing the desulfurization rate constant k_S from 0.002 min. -1 Increased to 0.01 min -1 This reduces the desulfurization time from the conventional 25 minutes to 5-15 minutes, directly solving the technical problem of "slow LF interface reaction".

[0025] In some embodiments, after the sulfur element is fixed in the emulsified slag droplets, ultrasonic stirring is stopped, allowing the sulfur-containing emulsified slag droplets to float into the molten slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is stably maintained below the target value.

[0026] After fixing sulfur in the emulsified slag droplets, ultrasonic stirring is stopped, and the sulfur-containing emulsified slag droplets float into the molten slag layer. Utilizing the density difference between the emulsified slag droplets and molten steel, the sulfur-containing emulsified slag droplets with an average particle size of 10~50μm float upwards at a speed of 0.5~1cm / s. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is stably maintained below the target value. The sulfur element is permanently transferred to the molten slag layer, preventing sulfur reversion, thereby ensuring that the sulfur content of the molten steel remains ≤0.001% in the subsequent casting stage, avoiding secondary refining, and further reducing the total processing time.

[0027] In some embodiments, during the emission of ultrasound, the bottom-blown argon flow rate is controlled at 2.0 NL / min·ton of steel to 3.8 NL / min·ton of steel to coordinate with the flow state of the steel-slag emulsion (a mixture of emulsified slag droplets and molten steel) and the large-scale circulation of molten steel caused by the acoustic flow effect.

[0028] During the ultrasonic emission, the bottom-blown argon flow rate is controlled at 2.0 NL / min·ton steel, 2.1 NL / min·ton steel, 2.2 NL / min·ton steel, 2.3 NL / min·ton steel, 2.4 NL / min·ton steel, 2.5 NL / min·ton steel, 2.6 NL / min·ton steel, 2.7 NL / min·ton steel, ..., 3.8 NL / min·ton steel. Maintaining the argon flow rate within the range of 2.0~3.8 NL / min·ton steel prevents rapid aggregation of emulsion slag droplets while avoiding excessive stirring that could cause slag entrapment. The bottom-blown argon flow rate, in conjunction with the acoustic flow effect, maintains the suspension of the steel-slag emulsion, ensuring that emulsion slag droplets with an average particle size of 10~50 μm remain suspended for ≥5 min. This guarantees the complete completion of the desulfurization reaction, avoids repeated electric heating, and directly reduces the desulfurization time by 2~3 min.

[0029] In some implementations, by coupling the ultrasonic action time and total ultrasonic power with the bottom-blown argon flow rate, the power consumption per ton of steel can be reduced by 20% to 35%, and the argon consumption per ton of steel can be reduced by 40% to 58%.

[0030] By coupling and controlling the ultrasonic action time and total ultrasonic power with the bottom-blowing argon flow rate: within a 5-10 minute ultrasonic action time, the total power of 1.1-2.0 kW / ton of steel and the argon flow rate of 2.0-3.8 NL / min·ton of steel are simultaneously optimized; the power consumption per ton of steel is reduced by 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, and 35%; thus reducing the LF heating time from 25 minutes... The time required for desulfurization is shortened to 8 minutes, thereby reducing the power consumption per ton of steel by 20-35%; the argon consumption per ton of steel is reduced by 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, and 58%; the cumulative argon consumption is reduced from 0.12 Nm3 / t to 0.05 Nm3 / t, a reduction of 40-58%, saving energy and shortening auxiliary time, indirectly reducing the total desulfurization cycle.

[0031] In some embodiments, the average particle size of the emulsified slag droplets in the steel-slag emulsion is 10 μm to 50 μm, and the average particle size expands the desulfurization reaction interface area by more than 1,000 times, thereby increasing the desulfurization reaction rate by more than 50%.

[0032] The average particle size of the emulsified slag droplets in the steel-slag emulsion is 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, and 50μm. The 10~50μm emulsified slag droplets increase the interfacial area per unit volume from 0.05m² / cm³ to 50m² / cm³; the average particle size expands the desulfurization reaction interfacial area by 1000 times, 1100 times, 1200 times, 1300 times, 1400 times, 1500 times, 1600 times, and 1700 times, respectively. 1800 times, 1900 times, 2000 times: Increase the interfacial area by 1000 to 2000 times; The increased interfacial area increases the desulfurization reaction rate by 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% respectively; Increase the desulfurization rate constant k_S by more than 50% respectively, thereby reducing the desulfurization time from 20 minutes to 5 to 10 minutes under the same sulfur distribution ratio, directly solving the technical problem of "slow LF interface reaction".

[0033] 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 industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0034] I. Implementation Examples Example 1 A slag covering the molten steel is formed in a 150t ladle, with an FeO mass fraction of 0.8%. Insert the working ends of the three ultrasonic tool heads into the interface between the molten steel and the slag, which is 30mm in diameter. Ultrasonic waves are continuously emitted into the area through each working end at a power density of 1.1 kW / ton of steel and a frequency of 25 kHz for a duration of 8 minutes. The ultrasound simultaneously excites cavitation and acoustic flow effects in the region. The cavitation effect breaks the molten slag into emulsified slag droplets with an average particle size of 45 μm, while the acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. Steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between molten steel and slag to a three-dimensional volume region distributed inside the molten steel. Sulfur migrates from molten steel to the emulsified slag droplets in the steel-slag emulsion and remains in the emulsified slag droplets; Stop ultrasonic stirring to allow sulfur-containing emulsified slag droplets to float to the slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is kept stable below the target value. During the ultrasonic emission, the bottom-blown argon flow rate is controlled at 2.2 NL / min·ton steel; By coupling and controlling the ultrasonic action time and total ultrasonic power with the bottom-blowing argon flow rate, the power consumption per ton of steel is reduced by 25%, and the argon consumption per ton of steel is reduced by 40%. The average particle size of the emulsified slag droplets in the steel-slag emulsion is 45 μm. This average particle size expands the desulfurization reaction interface area by 1500 times, thereby increasing the desulfurization reaction rate by 75%.

[0035] Example 2 A slag covering the molten steel is formed in a 200t ladle, with an FeO mass fraction of 0.6%. Insert the working ends of the three ultrasonic tool heads into the interface between the molten steel and the slag. 20mm area; Ultrasonic waves are continuously emitted into the area through each working end at a power density of 1.8 kW / ton of steel and a frequency of 30 kHz for a duration of 6 minutes. The ultrasound simultaneously excites cavitation and acoustic flow effects in the region. The cavitation effect breaks the molten slag into emulsified slag droplets with an average particle size of 25 μm, while the acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. Steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between molten steel and slag to a three-dimensional volume region distributed inside the molten steel. Sulfur migrates from molten steel into the emulsion slag droplets in the steel-slag emulsion and is fixed within the droplets; Stop ultrasonic stirring to allow sulfur-containing emulsified slag droplets to float to the slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is kept stable below the target value. During the ultrasonic emission, the bottom-blown argon flow rate is controlled at 2.5 NL / min·ton steel; By coupling and controlling the ultrasonic action time and total ultrasonic power with the bottom-blowing argon flow rate, the power consumption per ton of steel is reduced by 32%, and the argon consumption per ton of steel is reduced by 53%. The average particle size of the emulsified slag droplets in the steel-slag emulsion is 25 μm. This average particle size expands the desulfurization reaction interface area by 2000 times, thereby increasing the desulfurization reaction rate by 100%.

[0036] Example 3 A slag covering the molten steel is formed in an 80t ladle, with an FeO mass fraction of 0.9%. Insert the working end of one ultrasonic tool head into the interface between molten steel and slag +40mm area; Ultrasonic waves are continuously emitted into the area through the working end at a power density of 1.5 kW / ton of steel and a frequency of 30 kHz for a duration of 5 minutes. The ultrasound simultaneously excites cavitation and acoustic flow effects in the region. The cavitation effect breaks the molten slag into emulsified slag droplets with an average particle size of 35 μm, while the acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. Steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between molten steel and slag to a three-dimensional volume region distributed inside the molten steel. Sulfur migrates from molten steel into the emulsion slag droplets in the steel-slag emulsion and is fixed within the droplets; Stop ultrasonic stirring to allow sulfur-containing emulsified slag droplets to float to the slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is kept stable below the target value. During the ultrasonic emission, the bottom-blown argon flow rate is controlled at 2.4 NL / min·ton steel; By coupling and controlling the ultrasonic action time and total ultrasonic power with the bottom-blowing argon flow rate, the power consumption per ton of steel is reduced by 35%, and the argon consumption per ton of steel is reduced by 58%. The average particle size of the emulsified slag droplets in the steel-slag emulsion is 35 μm. This average particle size expands the desulfurization reaction interface area by 1800 times, thereby increasing the desulfurization reaction rate by 90%.

[0037] II. Comparative Example Comparative Example 1 A slag covering the molten steel is formed in a 150t ladle, with an FeO mass fraction of 0.8%. Do not insert the ultrasonic tool head, and do not emit ultrasonic waves into the interface area between molten steel and slag; The bottom-blown argon flow rate was controlled at 2.2 NL / min·ton of steel, and stirring was continued for 22 min. The desulfurization reaction interface maintains a two-dimensional interface between molten steel and slag. Sulfur migrates from molten steel to slag; The time required to reduce the sulfur content of molten steel from 0.024% to 0.0025% is 22 minutes; The electricity consumption per ton of steel was 133% of that in Example 1, and the argon gas consumption per ton of steel was 167% of that in Example 1.

[0038] Comparative Example 2 A slag covering the molten steel is formed in a 200t ladle, with an FeO mass fraction of 0.6%. Do not insert the ultrasonic tool head, and do not emit ultrasonic waves into the interface area between molten steel and slag; The bottom-blown argon flow rate was controlled at 2.5 NL / min·ton of steel, and stirring was continued for 25 minutes. The desulfurization reaction interface maintains a two-dimensional interface between molten steel and slag. Sulfur migrates from molten steel to slag; The time required to reduce the sulfur content of molten steel from 0.012% to 0.0006% is 25 minutes; The electricity consumption per ton of steel was 147% of that in Example 2, and the argon gas consumption per ton of steel was 213% of that in Example 2.

[0039] III. Results Data Experimental methods for evaluating results: Sulfur content determination: According to GB / T223.85-2009, molten steel samples were taken from each furnace before and after the ultrasonic wave was emitted, and the sulfur content was determined by an infrared carbon-sulfur analyzer. The average value was calculated from the three measurements. Electricity consumption measurement: The cumulative electricity consumption from the start of power-on to the moment of power-off is recorded using a smart meter on the high-pressure side of the LF furnace. The electricity consumption per ton of steel is obtained by dividing the cumulative electricity consumption by the weight of the molten steel. Argon consumption measurement: The cumulative volume is recorded using a bottom-blowing branch gas mass flow meter, and divided by the weight of molten steel to obtain the argon consumption per ton of steel; Determination of average particle size of emulsion slag droplets: Immediately after the ultrasonic treatment, a steel-slag emulsion sample was quickly taken with a quartz tube, quenched with water, and the particle size distribution was measured with a laser particle size analyzer. The D50 value was taken as the average particle size. Calculation of the increase in desulfurization rate: Based on the comparative example, the formula is: Desulfurization rate increase / % = (Comparative example desulfurization time) Calculate and round down the desulfurization time of the example (desulfurization time of the example) / the desulfurization time of the comparative example (desulfurization time of the comparative example) × 100%.

[0040] Table 1. Results data for both the examples and comparative examples.

[0041] As shown in Table 1, the inventiveness of this application's technical solution compared to the prior art is mainly reflected in: 1. Under the same initial sulfur content of 0.024% and the same target sulfur content of ≤0.0025%, the technical solution of this application shortens the desulfurization time from 22 min in Comparative Example 1 to 8 min in Example 1, and shortens the single treatment time by 14 min, which is 63.6%. This breaks through the inherent bottleneck of "20 min+" in LF refining for the first time and forms a new paradigm of 5-10 min ultra-low sulfur refining.

[0042] 2. At a steel ladle capacity of 150t, the power consumption per ton of steel in Example 1 was reduced to 0.75kWh, a 25% decrease compared to 1.00kWh in Comparative Example 1; the argon consumption per ton of steel was reduced to 0.048Nm³. 3 Compared to 0.080 Nm3 in Comparative Example 1, it is reduced by 40%, achieving a simultaneous decrease in the "time-energy consumption" hyperbola, thus resolving the long-standing contradiction that the acceleration of traditional LF inevitably increases energy consumption.

[0043] 3. By expanding the desulfurization reaction interface from a two-dimensional interface to a three-dimensional volume region and breaking the average particle size of the emulsion slag droplets to 45μm, the reaction interface area is increased by 1500 times, and the desulfurization rate is increased by 75%. For the first time, "micron-level emulsion reaction" replaces "macroscopic interface reaction", breaking through the physical limit of interface area.

[0044] 4. By coupling and controlling four parameters—ultrasonic power density, ultrasonic frequency, ultrasonic action time, and bottom-blowing argon flow rate—a repeatable and reproducible quantitative process window is formed, enabling a 200t steel ladle to complete deep desulfurization from 0.012% to 0.0006% within 6 minutes, achieving a power consumption of 0.68 kWh per ton of steel and an argon consumption of 0.042 Nm³ per ton of steel. 3 The extreme value record laid the foundation for engineering.

[0045] 5. Within the full range of different ladle capacities of 80–200t, different initial sulfur contents of 0.052–0.012%, and different target sulfur contents of 0.010–0.0006%, the examples can stably control the desulfurization time within 5–8 minutes, with a sulfur content accuracy of ±0.0002%. This is the first time that a robust process with "capacity-composition-time" decoupling has been achieved, and it has the universality to replace traditional LF refining.

[0046] 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. An LF refining method for desulfurizing molten steel contained in a ladle, characterized in that, The method includes: A slag covering the molten steel is formed inside the ladle; Insert the working end of the ultrasonic tool head into the ±50mm area of ​​the interface between the molten steel and the slag. The ultrasonic waves are continuously emitted into the area through the working end at a power density of 1.1kW / ton steel to 2.0kW / ton and a frequency of 21kHz to 40kHz for a duration of 5min to 15min. The ultrasonic waves simultaneously excite cavitation and acoustic flow effects in the region. The cavitation effect breaks the slag into emulsified slag droplets with an average particle size of less than 100 μm. The acoustic flow effect carries the emulsified slag droplets into the interior of the molten steel and mixes them with the molten steel to obtain a steel-slag emulsion. The steel-slag emulsion expands the desulfurization reaction interface from a two-dimensional interface between the molten steel and the slag into a three-dimensional volume region distributed inside the molten steel. Sulfur migrates from the molten steel to the emulsified slag droplets in the steel-slag emulsion and is fixed in the emulsified slag droplets. By fixing the sulfur element in the emulsified slag droplets, the sulfur content of the molten steel is reduced to the target value.

2. The LF refining method according to claim 1, characterized in that, The working end of the ultrasonic tool head is inserted at an angle downwards, which is consistent with the flow direction of the molten steel driven by the bottom-blown argon gas in the ladle. This allows the acoustic flow effect to be superimposed on the circulation driven by the bottom-blown argon gas, transporting the emulsified slag droplets to a larger area of ​​the ladle molten pool for further reaction with sulfur in the steel.

3. The LF refining method according to claim 1, characterized in that, Set up 1 to 3 ultrasonic tool heads, each with an independent power range of 55kW to 120kW, and the total power of all ultrasonic tool heads should meet the requirements of 1.1kW / ton of steel to 2.0kW / ton of steel.

4. The LF refining method according to claim 1, characterized in that, The wear length of the working end of the ultrasonic tool head is monitored in real time. When the working end is about to leave the ±50mm area of ​​the interface due to burning, it is fed along the fixed guide rail above the ladle towards the molten steel to keep the working end always within the ±50mm area of ​​the interface. When the remaining length of the working end is less than 20mm and the position cannot be maintained by feeding, it is withdrawn and replaced with a new working end.

5. The LF refining method according to claim 1, characterized in that, The time required to reduce the sulfur content of the molten steel from the initial value of 0.008% to 0.052% to the target value is 5 min to 15 min.

6. The LF refining method according to claim 1, characterized in that, After fixing the sulfur element in the emulsified slag droplets, ultrasonic stirring is stopped, allowing the sulfur-containing emulsified slag droplets to float into the molten slag layer. By removing the sulfur-containing emulsified slag droplets from the interior of the molten steel, the sulfur content of the molten steel is stably maintained below the target value.

7. The LF refining method according to claim 1, characterized in that, During the emission of ultrasound, the flow rate of bottom-blown argon gas is controlled at 2.0 NL / min·ton steel to 3.8 NL / min·ton steel to coordinate with the flow state of the steel-slag emulsion and molten steel circulation caused by the acoustic flow effect.

8. The LF refining method according to claim 1, characterized in that, By coupling and controlling the ultrasonic action time and total ultrasonic power with the bottom-blown argon flow rate, the power consumption per ton of steel can be reduced by 20% to 35%, and the argon consumption per ton of steel can be reduced by 40% to 58%.

9. The LF refining method according to claim 1, characterized in that, The average particle size of the emulsified slag droplets in the steel-slag emulsion is 10μm to 50μm. This average particle size expands the desulfurization reaction interface area by more than 1000 times, thereby increasing the desulfurization reaction rate by more than 50%.

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