A method for control of precious alloying elements in the LF furnace refining process

Abstract

The application discloses a method for valuable alloy component control in a LF furnace refining process, and belongs to the technical field of iron and steel metallurgy, and the method comprises the following steps: tapping after judging that converter smelting is qualified, adding corresponding specifications of alloys, slag materials and deoxidizers according to corresponding steel type regulation requirements and measured oxygen content at the end, preliminarily completing deoxidation in advance, and pre-controlling Als content; confirming alloy, slag material and molten steel weight parameters before arriving at a station; stirring and desulfurizing by blowing a large amount of argon at the bottom; quickly forming white slag and controlling FeO to be below 0.5%; adding conventional alloys for coarse adjustment first, accurately adding Nb, V, Ni and Mo valuable alloys after temperature stabilization, and limiting an extreme control range; uniformly homogenizing by soft blowing with medium intensity; end point testing and fine adjustment. Through time sequence separation and extreme narrow window control, the valuable alloy yield is significantly improved, the alloy consumption cost is reduced, and the molten steel component stability is improved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for controlling the composition of precious alloys in the LF furnace refining process. Background Technology

[0002] With increasingly fierce competition in the steel industry, reducing alloy production costs and improving market competitiveness have become core demands for steel companies. In the traditional LF furnace refining process, to ensure the qualified performance of steel, precious alloying elements such as Nb (niobium), Mo (molybdenum), V (vanadium), and Ni (nickel) are added during the LF furnace refining process, and the amount added directly affects the production cost.

[0003] Under the current smelting process system, there are several technical challenges in controlling precious alloys that urgently need to be addressed: 1. Low precision in controlling alloying elements.

[0004] In traditional processes, the composition control of precious alloying elements such as Nb, V, and Ni is usually based on empirical estimation, lacking a systematic and precise calculation method. Because numerous factors affect alloy yield during LF refining (including oxygen content in molten steel, slag oxidizability, temperature, and stirring intensity), the actual yield of alloying elements fluctuates significantly. To ensure the finished product composition meets standards, operators often tend to add excessive amounts. 2. The precious alloys suffered severe burn damage.

[0005] Taking Nb-niobium iron as an example, existing processes suffer from severe oxidation and burn-off, significant compositional interference, and difficulty in control. Niobium is a strong carbide-forming element and readily reacts with oxygen at high temperatures to form Nb₂O₅, resulting in low effective yield. Vanadium, nickel, and other elements also exhibit varying degrees of oxidation and burn-off problems.

[0006] 3. Lack of extreme control strategies for precious alloys.

[0007] While existing literature contains studies on narrow composition control in LF furnaces, most of these studies focus on the control of conventional elements (such as C, Mn, and Alt), and lack systematic process methods for controlling the lower limit of expensive microalloying elements such as Nb, V, and Ni.

[0008] 4. The timing of alloy addition is unreasonable.

[0009] In traditional processes, desulfurization and alloying are carried out simultaneously. The high oxidizing properties of the slag severely affect the yield of precious alloys, resulting in the actual amount of alloy added being far higher than the theoretical calculation. Summary of the Invention

[0010] To address the problems of low precision in controlling the composition of precious alloys and unstable yield in existing technologies, which lead to high production costs, this invention provides a method for controlling the composition of precious alloys in the LF furnace refining process. This method precisely controls the composition of precious alloy elements such as Nb (niobium), Mo (molybdenum), V (vanadium), and Ni (nickel) within an extremely narrow range near the lower limit of the specification, thereby minimizing the amount of precious alloys added and achieving cost reduction and efficiency improvement.

[0011] To solve the above technical problems, the technical solution of the present invention is as follows: A method for controlling the composition of precious alloys in an LF furnace refining process, specifically including the following steps: S1. After the converter smelting endpoint is qualified, steel is tapped. According to the corresponding steel grade specifications and the actual oxygen content measured at the endpoint, alloys, slag materials and deoxidizers of the corresponding specifications are added to complete the preliminary deoxidation in advance. The Als of the molten steel after tapping is pre-controlled in the range of 0.010%-0.030%, leaving room for adjustment for subsequent deep slag formation and deoxidation in the LF furnace. S2. Before the ladle is transferred to the LF furnace station, three core parameters are confirmed: First, the types and weights of alloys, slag, and deoxidizers actually added during the converter tapping process are verified to ensure that the deviation from the planned value does not exceed ±2%; second, the actual test results of the converter post-furnace composition rapid test samples are retrieved to confirm that the initial main component content deviation is within the allowable range; third, the net weight data of the ladle after the converter tapping is completed is read to accurately calculate the actual total weight of molten steel, eliminating the deviation in molten steel quantity calculation caused by factors such as ladle sticking and slag retention. S3. Once the ladle is in place, the bottom blowing argon system is turned on immediately. A large flow of bottom blowing argon is used for stirring, and lime and fluorite slag-forming materials are added simultaneously. The binary basicity of the slag is precisely controlled to carry out desulfurization operation, reducing the total sulfur content of the molten steel to below 0.005%. No precious alloy raw materials are added during the entire desulfurization process. S4. Within the first ten minutes of entering the LF furnace station, more than 80% of the total slag-forming material is put in, and aluminum wire is put in batches. The aluminum wire is fed in synchronously throughout the process to achieve rapid white slag formation. When the molten steel sample was first extracted for composition testing, slag samples were collected simultaneously to observe the appearance of the slag. If the slag showed a blackened high oxidation characteristic, aluminum wire was added to strengthen the deoxidation of the slag phase until the slag turned into a bright white reducing state. Finally, the FeO mass ratio in the slag was controlled below 0.5%, the Als in the molten steel was stably controlled in the range of 0.020-0.040%, and the slag basicity was maintained in the high basicity reducing range of 4.5-8. S5. After the slag oxidation has stabilized to the target range, conventional alloys are added to complete the rough adjustment of the main composition of the molten steel. During this stage, precious alloying elements such as Nb, V, Ni, and Mo are not added to avoid unnecessary oxidation and burn-off of precious alloys in the early high oxidation environment. S6. Precise quantitative addition of precious alloys: After the conventional alloy composition is adjusted and the overall temperature of the molten steel is stabilized in the range of 1570-1580℃, Nb, V, Ni and Mo precious alloys are added, and the target limit control range of each element is strictly limited. S7. After all the precious alloys have been added, adjust the bottom-blown argon flow rate to a medium stirring intensity; S8. After the soft blowing and stirring is completed, the final sample of molten steel is extracted for full composition analysis. If the measured content of a certain precious alloy element is lower than the preset target control limit, the corresponding trace alloy replenishment amount is calculated according to the control rules of step S6 above. After replenishment, the mixture is stirred for a short time and then sampled again for confirmation. If the measured content of all elements falls within the preset limit control range, the LF refining process is directly ended and the continuous casting is arranged to leave the station.

[0012] The above scheme fundamentally changes the traditional mixed operation mode of desulfurization and alloying by constructing a strict time-sequential separation process system of pre-deoxidation-deep desulfurization-reducing white slag-conventional alloy coarse adjustment-precise precious alloy fine adjustment. It ensures that precious alloys are added only under the protection of a strong reducing atmosphere and high alkalinity slag system, thereby greatly suppressing oxidation loss. Combined with the extreme narrow window control strategy, it achieves the ultimate reduction of precious alloy consumption and composition accuracy.

[0013] Preferably, after the ladle is in place in step S3, the bottom blowing argon system is turned on immediately, and a large flow rate of 150-250 NL / min of bottom blowing argon is used for stirring. Lime and fluorite slag-forming materials are added simultaneously, and the binary basicity of the slag is precisely controlled to be R≥4.5. Strong stirring and desulfurization operation is carried out continuously for 8-12 minutes to reduce the total sulfur content of the molten steel to below 0.005%.

[0014] The above scheme enhances the mass transfer rate at the steel-slag interface by limiting the kinetic and thermodynamic conditions of high-flow-rate argon stirring and high-alkalinity slag formation, ensuring that the deep desulfurization task is completed within a short time window. This creates a pure, low-sulfur molten steel environment for the subsequent addition of precious alloys and avoids interference with alloy yield caused by repeated processing in the later stages due to incomplete desulfurization.

[0015] Preferably, after the deep desulfurization process in step S3 is completed, the FeO mass fraction in the slag must be confirmed to be ≤0.5% by rapid slag sampling before proceeding to the subsequent rapid white slag production process. If the test result exceeds this threshold, the deoxidation operation time is extended until the index meets the standard.

[0016] The above scheme establishes a rigid process quality control node based on the FeO content in the slag, preventing highly oxidizing slag from being carried into the next process, eliminating the risk of oxidation when adding precious alloys from the source, and ensuring the determinism and repeatability of process execution.

[0017] Preferably, in step S4, the aluminum wire is fed in 2-3 batches, with each batch containing 20-50 kg, and 45-60 kg of aluminum wire is fed in simultaneously throughout the process to achieve rapid white slag formation.

[0018] The above scheme adopts a composite deoxidation mode of batch addition + continuous wire feeding, which avoids the violent local overoxidation reaction and excessive temperature drop caused by adding a large amount of aluminum wire at once, and maintains a stable deoxidation potential in the molten pool through continuous feeding of aluminum wire, promoting the rapid flotation and removal of high melting point Al2O3 inclusions and the rapid white slag transformation of slag.

[0019] Preferably, the target limit control range for each element in step S6 is: The nitrogen (Nb) element content is controlled according to the lower limit of the steel grade specification plus (0.001-0.0023%), with the final target value ≤ lower limit of the specification plus 0.0023%. The V element is controlled according to the lower limit of the steel grade specification + (0.001-0.0028%), and the final target value is ≤ the lower limit of the specification + 0.0028%; Ni content is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value ≤ lower limit of the specification plus 0.020%. Mo is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value ≤ lower limit of the specification plus 0.020%. Before delivery, the delivery weight is accurately calculated based on the real-time molten steel weight, the current measured content of elements, and the stable yield parameters of the corresponding alloys. The yield of Nb niobium iron is preset to be above 90%, the yield of V alloy is preset to be above 92%, and the yield of Ni alloy is preset to be above 97%.

[0020] The above scheme sets differentiated limit-narrow window control targets and high-confidence yield benchmarks based on the differences in the physicochemical properties of different precious elements, making the calculation of alloy addition more scientific and accurate, and minimizing the consumption of ineffective alloys while ensuring the hit rate of composition.

[0021] Preferably, after all the precious alloys are added in step S7, the bottom-blown argon flow rate is adjusted to a medium stirring intensity of 200-300 NL / min, and soft argon stirring is performed for 5-8 minutes to promote the full melting and uniform distribution of the alloy.

[0022] The above scheme optimizes the stirring kinetics parameters during the alloying stage, ensuring rapid melting and homogenization of the alloy while avoiding the risks of secondary oxidation and slag entrapment caused by excessive stirring, thus ensuring the efficient dissolution and stable existence of precious alloys in molten steel.

[0023] The beneficial effects of this invention are: This invention precisely controls the addition of precious alloying elements such as Nb (niobium), Mo (molybdenum), V (vanadium), and Ni (nickel) within an extremely narrow range near the lower limit of the specification, avoiding the large margin reserved in traditional processes to ensure qualification. The amount of precious alloying added can be reduced by 5-10%, which directly translates into significant cost savings per ton of steel, resulting in a reduction of 50,000 to 150,000 yuan in cost per ton of steel.

[0024] This invention employs a process design that separates the desulfurization and alloying processes sequentially. Combined with stable control of molten steel Als within the 0.020%-0.040% range and the creation of a highly reducing white slag environment with basicity R≥4.5 and FeO≤0.5%, it fundamentally suppresses the burn-off of easily oxidized precious alloying elements such as Nb and V. The yield of niobium-iron can be stably maintained above 90%, vanadium above 92%, and nickel above 97%, far exceeding the yield levels of traditional processes. This further reduces ineffective alloy loss and solves the long-standing problem of yield fluctuations that has plagued the industry. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below based on specific embodiments. Example 1

[0027] like Figure 1 As shown, this embodiment provides a method for controlling the composition of precious alloys in the LF furnace refining process. This method constructs a strictly sequential separation process system encompassing pre-deoxidation, deep desulfurization, preparation of reducing white slag, coarse adjustment of conventional alloys, and fine adjustment of precious alloys. Specific process parameters can be further defined in subsequent embodiments based on the actual steel grade and equipment conditions. The method specifically includes the following steps: Step S1: After the converter smelting endpoint is qualified, the steel is tapped. According to the corresponding steel grade specifications and the actual oxygen content measured at the endpoint, the corresponding specifications of alloy, slag and deoxidizer are added to complete the preliminary deoxidation in advance. The Als of the molten steel after tapping is pre-controlled in the range of 0.010%-0.030%, leaving room for adjustment for the subsequent deep slag formation and deoxidation in the LF furnace.

[0028] This step involves performing pre-deoxidation simultaneously during the tapping process. The kinetic energy of the molten steel itself promotes rapid melting and mixing of the deoxidizer and slag, preventing the accumulation of all deoxidation work at the LF station. By controlling Al2O3 levels within the aforementioned range, the molten steel maintains a certain initial reducing potential, preventing secondary oxidation during transfer. Furthermore, it avoids excessive pre-deoxidation leading to high Al2O3 content in the initial LF slag, which could affect the slag formation rate. This lays the thermodynamic foundation for precise slag formation control within the LF furnace.

[0029] Step S2: Before the ladle is transferred to the LF furnace station, three core parameters are confirmed: First, the types and weights of alloys, slag, and deoxidizers actually added during the converter tapping process are checked to confirm that the deviation from the planned value does not exceed ±2%; second, the actual test results of the converter post-furnace composition quick test sample are retrieved to confirm that the initial main component content deviation is within the allowable range; third, the net weight data of the ladle after the converter tapping is completed is read to accurately calculate the actual total weight of molten steel and eliminate the deviation in molten steel quantity calculation caused by factors such as ladle sticking and slag retention.

[0030] This step forms the data foundation for implementing limit control of precious alloys. Because limit control strategies abandon the ample safety margins in composition found in traditional processes, any deviation in raw material measurement or misjudgment of molten steel quantity can be amplified into a risk of deviations in the finished product's composition. Through the above three confirmations, a precise material and quality traceability chain is established from the converter to the LF furnace, ensuring that all subsequent alloy addition calculations are based on real and reliable boundary conditions, rather than empirical estimates.

[0031] Step S3: Immediately after the ladle is in place, the bottom-blowing argon system is activated, using a high-flow-rate bottom-blowing argon gas of 150-250 NL / min for stirring. Lime and fluorite slag-forming materials are added simultaneously, and the binary basicity of the slag, R, is precisely controlled to be ≥4.5. Strong stirring and desulfurization are carried out continuously for 8-12 minutes to reduce the total sulfur content of the molten steel to below 0.005%. No precious alloy raw materials are added during the entire desulfurization process. After the deep desulfurization process is completed, the FeO mass fraction in the slag must be quickly tested by slag sampling to confirm that it is ≤0.5% before proceeding to the subsequent rapid white slag formation process. If the test result exceeds this threshold, the deoxidation operation time is extended until the index meets the standard.

[0032] This step, using a high-flow-rate bottom-blown argon gas, provides intense kinetic stirring conditions, accelerating mass transfer at the steel-slag interface to achieve rapid and deep desulfurization. More importantly, the addition of precious alloys such as Nb, V, Ni, and Mo is strictly prohibited at this stage. This is because the slag is not yet fully reduced and has relatively high oxidizing properties. Adding precious alloys prematurely can easily lead to oxidation and burn-off, resulting in a significant decrease in yield and unpredictable composition. Furthermore, after deep desulfurization, rapid sampling and testing are conducted to confirm whether the FeO mass fraction in the slag is ≤0.5%. This is because precious elements such as Nb and V have a very high affinity for oxygen. If slag with an FeO content higher than 0.5% is allowed to enter the alloying stage, the residual iron oxide will directly consume the precious alloys, leading to significant and unpredictable fluctuations in yield. Therefore, S3 is not only a desulfurization process but also a necessary pre-conditioning barrier to create a safe environment for the addition of precious alloys.

[0033] Step S4: Within the first ten minutes of entering the LF furnace station, more than 80% of the total slag-forming material is fed in. The aluminum wire is fed in 2-3 batches, with each batch containing 20-50kg. Simultaneously, 45-60kg of aluminum wire is fed in throughout the process to achieve rapid white slag formation. When the molten steel sample was extracted for the first time for composition testing, slag samples were collected simultaneously to observe the appearance of the slag. If the slag showed a blackened high oxidation characteristic, aluminum wire was added to strengthen the deoxidation of the slag phase until the slag turned into a bright white reducing state. Finally, the FeO mass ratio in the slag was controlled below 0.5%, the Als in the molten steel was stably controlled in the range of 0.020-0.040%, and the slag basicity was maintained in the high basicity reducing range of 4.5-8.

[0034] This step, through concentrated slag formation and a combined deoxidation process, rapidly transforms the slag from an oxidized to a reduced state. The change in slag color from black to white is a direct indication that the FeO content has decreased to a low level. Combined with the dual indicators of Als and basicity, this ensures that the entire molten pool is in a deeply deoxidized state. Only when the slag reaches the aforementioned reducing standard can the prerequisite for adding precious alloys be met; otherwise, residual iron oxide will continue to consume precious alloying elements. This rigid quality control point effectively prevents the risk of oxidation from being passed on.

[0035] Step S5: After the slag oxidation has stabilized to the target range, conventional alloys are added to coarsely adjust the main composition of the molten steel. During this stage, precious alloying elements such as Nb, V, Ni, and Mo are not added to avoid unnecessary oxidation and burn-off of these elements in the early high-oxidation environment. Although white slag formation has been completed in S4, the temperature and compositional uniformity of the molten pool still need further stabilization through conventional alloying. Conventional alloys (such as ferrosilicon and ferromanganese) are relatively inexpensive and less sensitive to oxygen than precious microalloying elements; their addition at this stage can assist in deoxidation and temperature regulation. Maintaining the prohibition of precious alloys is to utilize the conventional alloying process as a final buffer period to completely eliminate any potential localized oxidation fluctuations within the molten pool, ensuring that precious alloys are only added in an absolutely safe reducing atmosphere.

[0036] Step S6, Precise quantitative addition of precious alloys: After the conventional alloy composition is adjusted and the overall temperature of the molten steel is stabilized in the range of 1570-1580℃, Nb, V, Ni and Mo precious alloys are added, and the target limit control range of each element is strictly limited.

[0037] This step is the core execution link for achieving cost reduction and efficiency improvement. Adding the alloy after the conventional alloy has been adjusted and the temperature has stabilized is chosen because the thermodynamic state of the molten pool is most stable at this time, and the predictability of alloy melting and dissolution is highest. Strictly limiting the target limit control range means no longer using traditional upper or middle limits or empirical values ​​for batching, but rather controlling the composition within an extremely narrow window near the lower limit that meets performance requirements based on a precise yield model and real-time operating conditions. This precise addition strategy directly reduces ineffective alloy consumption, while relying on the stable reduction environment created by the aforementioned S1-S5 steps to ensure a high and stable yield.

[0038] Step S7: After all the precious alloys have been added, adjust the bottom-blown argon flow rate to a medium stirring intensity of 200-300 NL / min and stir with soft argon for 5-8 minutes to promote the full melting and uniform distribution of the alloy.

[0039] After the addition of precious alloys, the stirring intensity must strike a balance between homogenizing the composition and preventing secondary oxidation. Excessive stirring may increase the exposed surface area of ​​the molten steel, increasing the risk of nitrogen absorption and secondary oxidation, and destroying the carefully established reducing atmosphere. Insufficient stirring, on the other hand, will lead to uneven alloy melting and prolong the refining cycle. A moderate stirring intensity of 200-300 NL / min provides sufficient kinetic energy to promote rapid melting and diffusion of the precious alloys while maintaining complete slag coverage and protecting the purity of the molten steel.

[0040] Step S8: After soft blowing and stirring, extract the final sample of molten steel for full composition analysis. If the measured content of a certain precious alloying element is lower than the preset target control limit, calculate the corresponding trace alloying amount according to the control rules in step S6 above. After adding the alloying amount, stir and mix briefly before sampling again for confirmation. If the measured content of all elements falls within the preset limit control range, the LF refining process is directly terminated and continuous casting is arranged to proceed. This step constitutes a closed-loop feedback mechanism for process control. Due to the use of the limit control strategy, the composition error tolerance is extremely small, therefore, a precise fine-tuning procedure based on measured data must be established. The calculation of the addition amount still follows the limit control rules of S6, ensuring that even during remedial operations, there will be no deviation from the narrow window target due to excessive addition. If the composition is qualified, the steel is directly discharged, avoiding unnecessary over-refining, which is of great significance for shortening the LF processing cycle and releasing continuous casting capacity. Example 2

[0041] This embodiment, based on Embodiment 1, further details the control strategy and calculation model for the precise quantitative addition of precious alloys in step S6. Specifically: The target limit control range for each element in step S6 is as follows: The nitrogen (Nb) element content is controlled according to the lower limit of the steel grade specification plus (0.001-0.0023%), with the final target value ≤ lower limit of the specification plus 0.0023%. The V element is controlled according to the lower limit of the steel grade specification + (0.001-0.0028%), and the final target value is ≤ the lower limit of the specification + 0.0028%; Ni content is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value ≤ lower limit of the specification plus 0.020%. The molybdenum (Mo) content is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value being ≤ the lower limit of the specification plus 0.020%.

[0042] Specifically, Nb and V are strong carbide-forming elements with extremely high chemical reactivity. In molten steel, they readily combine with oxygen and nitrogen to form inclusions or carbonitride precipitates. Their effective content is extremely sensitive to the yield strength and toughness of steel. Excessive Nb or V not only leads to expensive alloy waste but may also cause performance instability due to coarsening of precipitates or fluctuations in solid solution content. Therefore, their increment window is strictly limited to an extremely narrow range of 0.001-0.0028%, retaining only the minimum safety margin required for performance verification. In contrast, Ni and Mo mainly function through solid solution strengthening mechanisms, have relatively stable chemical properties, and their contribution to performance is linear within a certain range. In addition, although Ni and Mo have high unit prices, the base amount added is usually large. An excessively narrow control window would significantly increase the difficulty of production control and the frequency of sampling. Therefore, their increment window is appropriately widened to 0.01-0.020%, ensuring the hit rate of composition while taking into account the robustness of process operation.

[0043] As a preferred method, the feed weight is precisely calculated before feed based on the real-time molten steel weight, the current measured element content, and the stable yield parameters of the corresponding alloys. The Nb niobium-iron yield is preset to be above 90%, the V alloy yield to be above 92%, and the Ni alloy yield to be above 97%. These preset yield values ​​are the key confidence basis for implementing limit control. They are not derived from empirical estimations but are stable values ​​obtained through statistical regression and thermodynamic equilibrium calculations based on a large amount of historical production data under the strongly reducing, high-alkalinity slag system environment (FeO ≤ 0.5%, R = 4.5–8, Als = 0.020–0.040%) established in Example 1. In traditional processes, due to the large fluctuations in slag oxidizability, Nb recovery often oscillates wildly between 75% and 85%, forcing operators to add excessive amounts at low recovery rates to avoid risks. However, under the sequential separation and rigid deoxidation system constructed in this invention, oxidation loss is systematically suppressed, and the variance of the recovery rate is significantly narrowed, making the preset Nb recovery rate of over 90% a repeatable engineering reality, thus providing reliable thermodynamic boundary conditions for precise batching. Example 3

[0044] This embodiment takes heat 26105166 of a certain factory, using steel grade X80-3 as an example. The steel grade is an alloy steel containing Nb, Ni, and Mo, with a molten steel weight of 170 tons. The specifications require a lower limit of 0.042% for Nb, 0.11% for Ni, and 0.09% for Mo. This is achieved by providing a method for controlling the composition of precious alloys in the LF furnace refining process, specifically including the following steps: S1. After the converter smelting endpoint is qualified, steel is tapped. According to the corresponding steel grade specifications and the actual oxygen content measured at the endpoint, alloys, slag materials and deoxidizers of the corresponding specifications are added to complete the preliminary deoxidation in advance and control the oxygen content of the tapped steel to 11ppm. After tapping, the Als of the molten steel is pre-controlled at 0.0268%, leaving room for adjustment for subsequent deep slag formation and deoxidation in the LF furnace. S2. Before the ladle is transferred to the LF furnace station, three core parameters are confirmed: First, the types and weights of alloys, slag, and deoxidizers actually added during the converter tapping process are verified to ensure that the deviation from the planned value does not exceed ±2%; second, the actual test results of the converter post-furnace composition rapid test samples are retrieved to confirm that the initial main component content deviation is within the allowable range; third, the net weight data of the ladle after the converter tapping is completed is read to accurately calculate the actual total weight of molten steel, eliminating the deviation in molten steel quantity calculation caused by factors such as ladle sticking and slag retention. S3. Immediately after the ladle is in place, the bottom-blowing argon system is activated, using a high-flow-rate (220 NL / min) bottom-blowing argon gas for stirring. Lime and fluorite slag-forming materials are added simultaneously, and the binary basicity of the slag is precisely controlled to R=6.6. A strong stirring desulfurization operation is performed continuously for 12 minutes to ensure that the potential interference of sulfur elements on the subsequent microalloying process is completely eliminated before entering the precious alloy addition process. The total sulfur content of the molten steel is reduced to below 0.0027%. No precious alloy raw materials are added during the entire desulfurization process. After the deep desulfurization process is completed, the slag is sampled and quickly tested. The slag sample test results show that the FeO mass fraction is 0.37%, which meets the rigid access condition of ≤0.5%, so it can be successfully transferred to the next process. S4. Within the first ten minutes of entering the LF furnace station, more than 80% of the total slag-forming material is fed in. The aluminum wire is fed in three batches, with each batch containing 30kg. This effectively suppresses the peak intensity of the reaction and makes the deoxidation exothermic more uniform and gradual. At the same time, 50kg of aluminum wire is fed in throughout the process to continuously and stably replenish the deoxidizer, maintain a constant low oxygen potential in the molten pool, and promote the polymerization, growth and rapid floating of high-melting-point inclusions. The synergistic effect of the two not only achieves the rapid white slag transformation of the slag, but also avoids the uncertainty caused by the subsequent dissolution behavior of precious alloys due to drastic temperature fluctuations. S5. After the slag oxidation has stabilized to the target range, conventional alloys are added to complete the rough adjustment of the main composition of the molten steel. During this stage, precious alloying elements such as Nb, V, Ni, and Mo are not added to avoid unnecessary oxidation and burn-off of precious alloys in the early high oxidation environment. S6. Precise Quantitative Addition of Precious Alloys: After the conventional alloy composition adjustment is completed and the overall temperature of the molten steel stabilizes at 1580℃, Nb, V, Ni, and Mo precious alloys are added. This implementation's steel grade specification requires a lower limit of 0.042% for Nb, 0.11% for Ni, and 0.09% for Mo. According to the limit control rules of this embodiment, the target limit control range for each element is strictly limited: The addition weights are precisely calculated based on real-time molten steel weight, current measured element content, and stable yield parameters of the corresponding alloys. Specifically, the target increments are: Nb 0.0420% (lower limit of the specification +0.0020%), Ni 0.128% (lower limit of the specification +0.11%), and Mo 0.106% (lower limit of the specification +0.018%). The steel is added in the following order: ferromolybdenum (containing 60% Mo, 95% yield), nickel plate (containing 99% Ni, 97% yield), and ferroniobium (containing 63% Nb, 95% yield). S7. After all the precious alloys have been added, adjust the bottom-blown argon flow rate to 200NL / min with a medium stirring intensity and stir with soft argon for 7 minutes to promote the full melting and uniform distribution of the alloy. S8. After the soft blowing and stirring is completed, the final sample of molten steel is extracted for full composition analysis. The measured Nb: 0.0435%, Ni: 0.123%, Mo: 0.106%, all within the target range, and the steel is discharged from the station.

[0045] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for controlling the composition of precious alloys in an LF furnace refining process, characterized in that, Specifically, the following steps are included: S1. After the converter smelting endpoint is qualified, steel is tapped. According to the corresponding steel grade specifications and the actual oxygen content measured at the endpoint, alloys, slag materials and deoxidizers of the corresponding specifications are added to complete the preliminary deoxidation in advance. The Als of the molten steel after tapping is pre-controlled in the range of 0.010%-0.030%, leaving room for adjustment for subsequent deep slag formation and deoxidation in the LF furnace. S2. Before the ladle is transferred to the LF furnace station, three core parameters are confirmed: First, the types and weights of alloys, slag, and deoxidizers actually added during the converter tapping process are verified to ensure that the deviation from the planned value does not exceed ±2%; second, the actual test results of the converter post-furnace composition rapid test samples are retrieved to confirm that the initial main component content deviation is within the allowable range; third, the net weight data of the ladle after the converter tapping is completed is read to accurately calculate the actual total weight of molten steel, eliminating the deviation in molten steel quantity calculation caused by factors such as ladle sticking and slag retention. S3. Once the ladle is in place, the bottom blowing argon system is turned on immediately. A large flow of bottom blowing argon is used for stirring, and lime and fluorite slag-forming materials are added simultaneously. The binary basicity of the slag is precisely controlled to carry out desulfurization operation, reducing the total sulfur content of the molten steel to below 0.005%. No precious alloy raw materials are added during the entire desulfurization process. S4. Within the first ten minutes of entering the LF furnace station, more than 80% of the total slag-forming material is put in, and aluminum wire is put in batches. The aluminum wire is fed in synchronously throughout the process to achieve rapid white slag formation. When the molten steel sample was first extracted for composition testing, slag samples were collected simultaneously to observe the appearance of the slag. If the slag showed a blackened high oxidation characteristic, aluminum wire was added to strengthen the deoxidation of the slag phase until the slag turned into a bright white reducing state. Finally, the FeO mass ratio in the slag was controlled below 0.5%, the Als in the molten steel was stably controlled in the range of 0.020-0.040%, and the slag basicity was maintained in the high basicity reducing range of 4.5-8. S5. After the slag oxidation has stabilized to the target range, conventional alloys are added to complete the rough adjustment of the main composition of the molten steel. During this stage, precious alloying elements such as Nb, V, Ni, and Mo are not added to avoid unnecessary oxidation and burn-off of precious alloys in the early high oxidation environment. S6. After the conventional alloy composition has been adjusted and the overall temperature of the molten steel has stabilized in the range of 1570-1580℃, Nb, V, Ni and Mo precious alloys are added, and the target limit control range of each element is strictly limited. S7. After all the precious alloys have been added, adjust the bottom-blown argon flow rate to a medium stirring intensity; S8. After the soft blowing and stirring is completed, the final sample of molten steel is extracted for full composition analysis. If the measured content of a certain precious alloy element is lower than the preset target control limit, the corresponding trace alloy addition amount is calculated according to the control rules of step S6 above. After the addition, the mixture is stirred for a short time and then sampled again for confirmation. If the measured content of all elements falls within the preset limit control range, the LF refining process is directly ended and the continuous casting is arranged to leave the station.

2. The method for controlling the composition of precious alloys in the LF furnace refining process according to claim 1, characterized in that, After the ladle is in place in step S3, the bottom blowing argon system is turned on immediately. A large flow rate of 150-250 NL / min of bottom blowing argon is used for stirring. Lime and fluorite slag-forming materials are added simultaneously. The binary basicity of the slag is precisely controlled to R≥4.

5. Strong stirring and desulfurization operation is carried out continuously for 8-12 minutes to reduce the total sulfur content of the molten steel to below 0.005%.

3. The method for controlling the composition of precious alloys in the LF furnace refining process according to claim 2, characterized in that, After the deep desulfurization process described in step S3 is completed, the FeO mass fraction in the slag must be confirmed to be ≤0.5% by rapid slag sampling before proceeding to the subsequent rapid white slag production process. If the test result exceeds this threshold, the deoxidation operation time will be extended until the index meets the standard.

4. The method for controlling the composition of precious alloys in the LF furnace refining process according to claim 1, characterized in that, In step S4, aluminum wire is fed in 2-3 batches, with each batch containing 20-50 kg. Simultaneously, 45-60 kg of aluminum wire is fed throughout the process to achieve rapid white slag formation.

5. The method for controlling the composition of precious alloys in the LF furnace refining process according to claim 1, characterized in that, The target limit control range for each element in step S6 is: The nitrogen (Nb) element content is controlled according to the lower limit of the steel grade specification plus (0.001-0.0023%), with the final target value ≤ lower limit of the specification plus 0.0023%. The V element is controlled according to the lower limit of the steel grade specification + (0.001-0.0028%), and the final target value is ≤ the lower limit of the specification + 0.0028%; Ni content is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value ≤ lower limit of the specification plus 0.020%. Mo is controlled at the lower limit of the steel grade specification plus (0.01-0.020%), with the final target value ≤ lower limit of the specification plus 0.020%. Before delivery, the delivery weight is accurately calculated based on the real-time molten steel weight, the current measured content of elements, and the stable yield parameters of the corresponding alloys. The yield of Nb niobium iron is preset to be above 90%, the yield of V alloy is preset to be above 92%, and the yield of Ni alloy is preset to be above 97%.

6. The method for controlling the composition of precious alloys in the LF furnace refining process according to claim 1, characterized in that, After all the precious alloys have been added in step S7, adjust the bottom-blown argon flow rate to a medium stirring intensity of 200-300 NL / min and stir with soft argon for 5-8 minutes to promote the full melting and uniform distribution of the alloy.

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