A method for substituting vanadium-nitrogen alloy with converter vanadium slag alloying in a steelmaking LF refining furnace

Abstract

The present application provides a kind of steelmaking LF refining furnace using converter vanadium slag alloying method to replace vanadium-nitrogen alloy, belong to steel smelting technical field;The present application includes the following steps: converter tapping process slag wash pre-desulfurization, LF refining furnace is added lime, fluorite, converter vanadium slag and reducing agent, creates high basicity reducing slag, and V2O5 is reduced into vanadium into molten steel;Nitrogen bottom blowing is used, and nitrogen content is increased to 0.012-0.025% by controlling the flow rate in promoting slag-steel reaction;According to the target vanadium content and initial vanadium content of steel grade, the amount of vanadium slag is calculated and controlled.The present application can replace expensive vanadium-nitrogen alloy with low-cost converter vanadium slag, vanadium absorption rate is 93-97%, reduces the cost per ton of steel, realizes the green and efficient recycling of vanadium resources, and has strong process compatibility, suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a method for using converter vanadium slag alloying to replace vanadium-nitrogen alloys in a steelmaking LF refining furnace. Background Technology

[0002] In the science of steel materials, microalloying technology is one of the important means to improve the comprehensive mechanical properties of steel. Vanadium, as an important microalloying element, has a significant effect on grain refinement and precipitation strengthening in steel. Vanadium carbonitride (V(C,N)) particles formed by the combination of vanadium with carbon and nitrogen elements in steel are dispersed and precipitated during hot working and cooling, which can effectively hinder grain growth and dislocation movement, thereby significantly improving the yield strength, tensile strength and wear resistance of steel, while maintaining good plasticity and toughness. Based on the above strengthening mechanism, vanadium-containing high-strength steel bars such as HRB400E, HRB500E, and T63E have been widely used in building structures, playing an important role in improving building safety and material utilization efficiency.

[0003] Currently, the mainstream process for industrial production of vanadium-containing steel is microalloying by adding vanadium-nitrogen alloy (V-N alloy). Vanadium-nitrogen alloy is an intermediate alloy in which vanadium and nitrogen are pre-alloyed, typically containing 75-80% vanadium and 10-18% nitrogen. The advantages of this process are: vanadium is added in alloy form, resulting in a stable absorption rate, usually above 90%; nitrogen exists in a combined state, leading to high nitrogen addition efficiency and strong controllability; and the amount of alloy used is relatively small, having little impact on the purity of the molten steel.

[0004] However, the production process of vanadium-nitrogen alloys is complex, requiring the mixing and pressing of V2O5, carbon black, and binder into blocks, followed by carbothermic reduction nitriding reaction under high temperature vacuum or protective atmosphere. This process is energy-intensive and time-consuming, resulting in high market prices. In the production of ordinary HRB400E and HRB500E series steels, the cost of vanadium-nitrogen alloys accounts for more than 20% of the total alloy cost, which restricts the product's market competitiveness.

[0005] On the other hand, with the advancement of comprehensive resource utilization technology and the deepening of the concept of circular economy, some steel companies have begun to focus on the internal recycling of vanadium resources. Taking the converter vanadium extraction process as an example, vanadium-containing molten iron undergoes selective oxidation in the converter, and the vanadium in the molten iron is oxidized and enters the slag to form converter vanadium slag. The V2O5 content in the above vanadium slag can reach 8-20%, which is a valuable secondary vanadium resource. After being processed by crushing, magnetic separation, and screening, the particle size of the converter vanadium slag can be controlled below 40mm, which meets the conditions for being added through the alloy feeding system of the LF refining furnace. At the same time, for production lines that are not equipped with KR mechanical stirring desulfurization devices, high-sulfur molten steel needs to undergo deep desulfurization treatment in the LF refining furnace. The above process requires the creation of a strong reducing slag atmosphere, which provides favorable thermodynamic and kinetic conditions for the reduction of vanadium in the vanadium slag.

[0006] However, there are a series of technical challenges in directly using converter vanadium slag for alloying in the existing technology: 1. The phase composition of converter vanadium slag is complex: Vanadium mainly exists in the spinel phase and silicate phase in converter vanadium slag. Among them, the vanadium in the spinel phase has stable chemical properties and is difficult to be reduced by conventional reducing agents. At the same time, the total iron content in the slag is as high as 15-30%, and the presence of iron oxides will preferentially consume the reducing agent and reduce the reduction efficiency of vanadium. 2. The reduction thermodynamic conditions of vanadium are harsh: The reduction of V2O5 to metallic vanadium requires an extremely strong reducing atmosphere and a sufficiently high temperature. The reduction process of V2O5 is: V2O5→V2O4→V2O3→VO→V. Among them, the reduction reaction from low-valence oxide to metallic vanadium requires a very low oxygen potential under standard conditions and can only be achieved under slag conditions with high basicity and low FeO content. 3. Nitrogen Supplementation: Vanadium-nitrogen alloys provide not only vanadium but also nitrogen. When converter vanadium slag is used to replace vanadium-nitrogen alloys, the nitrogen content in the steel will be significantly lower without additional measures. Nitrogen is an indispensable element in vanadium-containing steel. The presence of nitrogen can promote the precipitation of vanadium carbonitride, improve the precipitation strengthening effect, and reduce the amount of vanadium added. Studies have shown that for every 0.001% increase in nitrogen content in steel, 0.002-0.003% of vanadium can be saved. Therefore, how to accurately supplement nitrogen while reducing vanadium is the key to the success of the substitution process. 4. Difficulty in matching process parameters: The composition of converter vanadium slag fluctuates greatly, with V2O5 content fluctuating between 8-20% and FeO content also varying significantly. If there is a lack of a model for controlling the amount added, the vanadium content in the molten steel is likely to deviate from the target range, resulting in component scrap or alloy waste.

[0007] To address the aforementioned technical challenges, some studies have attempted to add vanadium slag directly into the ladle during the converter tapping process, utilizing the strong stirring during tapping for reduction. However, this method has low reduction efficiency, with vanadium absorption rate less than 50%, and easily causes phosphorus and sulfur reversion in the molten steel. Other studies have attempted to premix vanadium slag with reducing agents, press it into briquettes, and add it to the LF refining furnace, but the nitrogen replenishment problem has not been solved, making it difficult to meet the steel performance standards. There are also studies on using electric furnaces to reduce vanadium slag to prepare ferrovanadium, but these processes require specialized equipment, involve large investments, and have high energy consumption, making them unsuitable for widespread application in ordinary long-process steel plants.

[0008] Therefore, developing a converter vanadium slag utilization method that can be directly implemented on existing LF refining equipment, takes into account both vanadium reduction and nitrogen supplementation, and has high vanadium absorption rate and good economic benefits is of great practical significance and industrial value for reducing the production cost of vanadium-containing steel and realizing the efficient recycling of vanadium resources. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for using converter vanadium slag alloying to replace vanadium-nitrogen alloys in steelmaking LF refining furnaces. The aim is to replace expensive vanadium-nitrogen alloys with low-cost converter vanadium slag. Through a combination of processes including converter tapping pre-desulfurization, high-basicity reducing slag vanadium extraction, nitrogen bottom blowing for nitrogen enhancement, and dynamic and precise control, the production cost of vanadium-containing steel is significantly reduced while ensuring that the mechanical properties of the steel meet national standards, thereby achieving green, efficient, and circular utilization of vanadium resources.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for replacing vanadium-nitrogen alloying with converter vanadium slag alloying in a steelmaking LF refining furnace, through a synergistic process of vanadium extraction by converter vanadium slag reduction and nitrogen bottom blowing to increase nitrogen, simultaneously completes the alloying of vanadium and nitrogen in the LF refining furnace, specifically including the following steps: Step 1: Pre-desulfurization of slag from converter tapping: The purpose of this step is to reduce the initial sulfur content of the molten steel entering the LF furnace, creating favorable initial conditions for subsequent deep desulfurization and vanadium reduction, while also initially homogenizing the composition and temperature of the molten steel.

[0011] The final tapping temperature of the converter is controlled at 1640℃-1660℃. This temperature range is set based on the following considerations: if the temperature is too low, i.e., <1640℃, the molten steel has poor fluidity, slag-steel separation is difficult, and the pre-desulfurization efficiency is reduced; if the temperature is too high, i.e., >1660℃, the molten steel will have serious air absorption, the furnace lining will be eroded more, and the temperature drop during tapping will be too large, which is not conducive to the subsequent heating of the LF furnace.

[0012] During the tapping process, quicklime and fluorite are added to the ladle along with the steel flow. The amount of quicklime added is 2-6 kg / t of steel, and the amount of fluorite added is 0.3-1 kg / t of steel. Specifically, quicklime is mainly composed of CaO and is the basic raw material for desulfurization reaction. Fluorite is mainly composed of CaF2 and its function is to lower the melting point of slag, improve fluidity, and promote the kinetic conditions of desulfurization reaction. The amount of both added needs to be matched according to the sulfur content of the molten iron entering the furnace and the target sulfur content: the upper limit is used when the sulfur content is high, and the lower limit is used when the sulfur content is low.

[0013] Utilizing the powerful impact of the steel flow during tapping, and combined with the stirring effect of nitrogen blown into the bottom of the ladle, a state of vigorous steel-slag mixing is created, increasing the contact area between the steel and slag, and allowing the CaO in the slag to undergo a desulfurization reaction with the S in the molten steel: CaO + S + C = CaS + CO↑ The CaS generated by the reaction enters the slag phase, thereby reducing the sulfur content of the molten steel.

[0014] After tapping and before the ladle is hoisted to the LF furnace station, nitrogen is blown and stirred for another 5-8 minutes. This process can extend the slag-steel reaction time, further improve the desulfurization rate, and also uniformize the temperature of the molten steel, eliminating temperature stratification during tapping.

[0015] After this step, the sulfur content of molten steel can be reduced to 0.055-0.070%.

[0016] Step 2, Slag Formation and Reduction in the LF Refining Furnace: This step is used to create a strongly reducing slag atmosphere, reducing vanadium oxides in converter vanadium slag to metallic vanadium or low-valence vanadium oxides that can be absorbed by molten steel, thereby achieving vanadium alloying.

[0017] After the ladle carrying the pre-desulfurized molten steel enters the LF refining furnace, the initial feed plan is formulated based on the composition of the ladle sample at the converter's final stage. The initial feed includes: Lime: 3-8 kg / t steel, used to adjust the basicity of slag and provide a source of CaO; Fluorite: 1-2 kg / t steel, used to improve slag fluidity; Vanadium slag from converters: 3-10 kg / t steel, providing vanadium source.

[0018] After the initial material is added, the furnace is powered on and heated for 5-7 minutes. The purpose of heating is twofold: first, to promote the rapid melting of the slag and form a uniform slag layer; and second, to increase the temperature of the molten steel to provide sufficient thermodynamic driving force for the subsequent reduction reaction.

[0019] After heating for 5-7 minutes, the molten steel temperature typically reaches 1520℃-1550℃. At this point, the first sample is taken, including: analyzing the composition of the molten steel such as V, S, P, and Si, and the composition of the slag such as CaO, SiO2, FeO, and V2O5. Based on the analysis results of this second sample, dynamic adjustments are made. If the slag basicity is too low (CaO / SiO2<2), add lime; If the slag has poor fluidity, add fluorite; If the vanadium content in the molten steel is lower than the lower limit of the target value, add converter vanadium slag.

[0020] While adding feed, a reducing agent is added to the surface of the slag. The preferred reducing agent of this invention is a mixture of ferrosilicon powder and silicon-aluminum-barium, with a total addition amount of 0.3-1.0 kg / t steel. Specifically, silicon, aluminum, and barium are all strong deoxidizing elements. They react with FeO and MnO in the slag to reduce the oxidizing properties of the slag. At the same time, the above elements undergo a displacement reaction with V2O5 in the slag to reduce vanadium.

[0021] After adding the reducing agent, continue to heat the molten steel for 10-12 minutes to raise the temperature to 1580℃-1590℃. During the heating process, continue bottom blowing and stirring to promote the reduction reaction. At the same time, adjust the ratio of binary basicity (CaO / SiO2) of the slag to 2-3 by controlling the slag ratio.

[0022] The role of high-basicity slag is to improve the desulfurization capacity of slag, reduce the activity of SiO2, promote the above-mentioned reduction reaction to the right, and improve the fluidity of slag and the slag-steel separation performance.

[0023] On-site operators observe the appearance of the slag by picking through it: when the slag color gradually changes from black or dark gray to grayish-white and white, it indicates that the oxides such as FeO and MnO in the slag have been fully reduced, the reducing atmosphere is sufficient, and the vanadium reduction reaction is basically completed.

[0024] At this point, a second sample is taken, and after testing confirms that the composition of the molten steel and the slag meet the requirements, the molten steel is organized to leave the station. Before leaving the station, the sulfur content of the molten steel is controlled within 0.040%, which meets the requirements of most steel grades.

[0025] Step 3: Nitrogen increase in the LF refining furnace: The core objective of this step is to use nitrogen as a bottom-blowing gas source to add nitrogen to the steel while stirring it, thereby solving the problem of nitrogen-free vanadium slag in converters and achieving synergistic alloying of vanadium and nitrogen.

[0026] When converter vanadium slag completely replaces vanadium-nitrogen alloys, nitrogen is used as the bottom-blowing gas source throughout the LF refining furnace process. Nitrogen flow rate is controlled in stages according to different smelting stages: Slag washing stage: After adding the first batch of lime, fluorite and vanadium slag, adjust the bottom blowing nitrogen flow rate to 1000-1200 NL / min and continue for 3-5 minutes. The high flow rate stirring in this stage has two functions: first, to quickly melt the slag material and form a uniform slag layer; second, to promote mass transfer between slag and steel and accelerate the desulfurization reaction.

[0027] Heating stage: As the power is applied and the temperature rises, the bottom-blown nitrogen flow rate is adjusted to 500-800 NL / min. The stirring intensity at this stage needs to balance two factors: if the stirring is too weak, the slag-steel reaction will be insufficient and the vanadium reduction efficiency will be reduced; if the stirring is too strong, the steel surface will be exposed, the risk of secondary oxidation will increase, and the temperature drop will be accelerated. Specifically, 500-800 NL / min is the optimized flow rate range, which can ensure good slag-steel contact while avoiding excessive temperature drop and secondary oxidation.

[0028] Late refining stage: After the heating is completed and the slag turns into white slag, adjust the bottom blowing nitrogen flow rate to 200-400 NL / min and continue for 3-5 minutes to homogenize the composition and temperature of the molten steel, prepare for casting at the station, and increase nitrogen by contacting the molten steel with nitrogen.

[0029] By controlling the stirring time and flow rate, the nitrogen content of molten steel can be precisely controlled within the target range through the above steps.

[0030] When using converter vanadium slag to partially replace vanadium-nitrogen alloys, the gas source can be switched at different stages according to process requirements: argon gas can be used for stirring during the heating stage to avoid premature nitrogen addition leading to excessive nitrogen content; nitrogen gas is switched to the later refining stage for short-term weak stirring to add nitrogen and achieve precise fine-tuning of nitrogen content.

[0031] Through the above-mentioned graded control, the present invention can accurately control the nitrogen content of the molten steel leaving the station to 0.012-0.025%, which can cover the nitrogen content requirements of mainstream vanadium-containing steel grades such as HRB400E, HRB500E, and T63E, and has good universality.

[0032] Step 4: Precise control of vanadium slag dosage: This step is used to accurately calculate and dynamically correct the amount of vanadium slag added to the converter, ensuring the accuracy of the vanadium content in the molten steel. Specifically, it includes the following steps: First, the target vanadium content is determined based on the technical specifications of the steel grade; Secondly, the actual vanadium content of the molten steel before refining in the LF furnace is obtained, which can be obtained through the analysis of the final sample from the converter.

[0033] Then, the V2O5 content in the converter vanadium slag used is determined by X-ray fluorescence spectroscopy (XRF) or chemical titration.

[0034] Finally, the amount of vanadium slag added per ton of steel is calculated using the following formula: M 渣 = (V 目标 -V 初始 )×100 / (w V2O5 ×η×0.56) Where: M 渣 The amount of vanadium slag added per ton of steel, expressed in kg / t steel; V 目标 Target vanadium content for steel grade, in %; V 初始 Vanadium content of molten steel before refining in the LF furnace, in %; w V2O5 denoted as %; η is the vanadium absorption coefficient, ranging from 0.93 to 0.97, preferably 0.95; 0.56 is the mass fraction of vanadium in V2O5.

[0035] The vanadium absorption coefficient η is used to reflect the proportion of vanadium added to vanadium slag that can eventually enter the molten steel and be effectively utilized. This coefficient is affected by a variety of factors, including slag basicity, reducing agent dosage, stirring intensity, and temperature regime. Through a large number of industrial tests, this invention has determined that the stable range of η is 0.93-0.97, that is, under optimized process conditions, the vanadium absorption rate can reach 93-97%.

[0036] To prevent excessive slag from adversely affecting the refining process, this invention limits the total amount of converter vanadium slag to no more than 10 kg / t steel. Simultaneously, the increase in vanadium content in the molten steel (V) is controlled using the aforementioned formula. 目标 -V 初始 The concentration of vanadium slag is 0.020-0.050%, which ensures the effective utilization of vanadium slag and avoids problems such as phosphorus reversion and increased inclusions caused by excessive addition.

[0037] In practical operation, to ensure the accuracy of ingredient matching, this invention also establishes a dynamic correction mechanism: When adding for the first time, add 70-80% of the calculated amount; After the initial sample test results from step 2 are returned, calculate the supplementary amount based on the measured vanadium content of the initial sample using the following formula: M 补加 = (V 目标 -V 一次 )×W 钢 ×1000 / (w) V2O5 ×η×0.56) Where: M 补加 The amount of vanadium slag to be added, in kg; V 一次 The vanadium content of molten steel obtained from a single sample analysis is expressed in % (W). 钢 The total volume of molten steel is expressed in tons (t).

[0038] The aforementioned dynamic correction mechanism can effectively eliminate the influence of factors such as fluctuations in vanadium slag composition and absorption rate, ensuring that the final vanadium content in the molten steel strictly falls within the target range.

[0039] As a preferred technical solution of the present invention, in step 1, the final tapping temperature of the converter is 1645℃-1655℃, the amount of active lime added is 3-5kg / t steel, the amount of fluorite added is 0.5-0.8kg / t steel, and the nitrogen blowing and stirring time is 6-7min, so that the sulfur content of the molten steel is reduced to 0.055-0.065%.

[0040] As a preferred technical solution of the present invention, in step 2, the heating time after the first batch of material is added is preferably 6 minutes. The material replenishment operation is dynamically adjusted according to the vanadium content, sulfur content and slag alkalinity in the first sample. The timing of adding the reducing agent is preferably after the first sample is taken and before the heating continues.

[0041] As a preferred technical solution of the present invention, in step 2, the binary basicity of the slag, CaO / SiO2, is controlled at 2.5-2.8. When the slag color turns grayish-white or white, it indicates that the reducing atmosphere is sufficient and the vanadium reduction reaction is basically completed.

[0042] As a preferred technical solution of the present invention, in step 3, when converter vanadium slag is used to completely replace vanadium-nitrogen alloy, nitrogen is used as the bottom blowing gas source in the LF refining furnace throughout the process; when converter vanadium slag is used to partially replace vanadium-nitrogen alloy, argon can be used in the heating stage and nitrogen can be switched to nitrogen in the later stage of refining for nitrogen enrichment operation.

[0043] As a preferred technical solution of the present invention, in step 3, the correspondence between the bottom-blown nitrogen flow rate and the nitrogen content of molten steel is calibrated by online monitoring or offline testing, and the nitrogen content of molten steel leaving the station is controlled at 0.015-0.022%.

[0044] As a preferred technical solution of the present invention, in step 4, the vanadium absorption coefficient is calibrated through industrial tests, and its specific value is related to the slag alkalinity, the amount of reducing agent, and the stirring intensity, and is 0.95.

[0045] As a preferred technical solution of the present invention, in step 4, the calculation of the amount of vanadium slag added also includes the following correction step: dynamically correcting the amount of subsequent addition based on the vanadium content test results returned from the first sample.

[0046] As a preferred technical solution of the present invention, the converter vanadium slag is the slag produced during the vanadium extraction and smelting process in a converter. After crushing, magnetic separation and screening, its particle size is controlled at 5-40mm, the V2O5 content is 8-20%, the total iron content is 15-30%, and the moisture content is less than 1%.

[0047] As a preferred technical solution of the present invention, through the synergistic effect of steps 1 to 4, before leaving the LF refining furnace, the residual V2O5 content in the refining slag is reduced to below 0.005%, the phosphorus recovery of molten steel is controlled to below 0.003%, and the vanadium absorption rate is stabilized at 93-97%.

[0048] The beneficial effects of this invention are as follows: 1. This invention can utilize by-products generated during steel production, eliminating the intermediate steps of vanadium slag purification and alloy preparation, thus significantly reducing the alloy cost of vanadium-containing steel. At the same time, the utilization of converter vanadium slag can greatly reduce solid waste emissions and save slag treatment costs. 2. The present invention can be implemented based on existing LF refining furnace equipment without any equipment modification. The process operation is connected with the existing converter-continuous casting production process, which is convenient for large-scale promotion and application in the industry. It can be embedded into the existing production process without changing the original production rhythm or adding extra processes and equipment investment.

[0049] 3. This invention utilizes the synergistic effect of vanadium extraction from high-alkalinity reducing slag and nitrogen bottom blowing to increase nitrogen content. While efficiently reducing vanadium, nitrogen is added to the molten steel, thus solving the technical problem of nitrogen-free converter vanadium slag. Furthermore, the addition of vanadium and nitrogen can promote the precipitation of vanadium carbonitride, fully exert the microalloying strengthening effect, and ensure that the mechanical properties of the steel meet or even exceed national standards. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. The specific embodiments of this invention are only for explaining the invention and are not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0051] The vanadium slag used in the following examples all came from the vanadium extraction process of a steel company's converter. After crushing, magnetic separation, and screening, the particle size was controlled at 5-40 mm, and the moisture content was less than 1%. Its typical composition range is: V2O5 8-12%, TFe 18-25%, SiO2 12-18%, CaO 1-3%, MgO 2-5%, MnO 5-8%, P 0.05-0.15%, with the remainder being unavoidable impurities.

[0052] The vanadium slag used in the example has a V2O5 content of 10% (mass percentage).

[0053] Other raw materials such as quicklime (CaO≥85%), fluorite (CaF2≥80%), ferrosilicon powder (Si≥70%, particle size <3mm), and barium aluminum silicon (Si 40-50%, Al 8-12%, Ba 8-12%, particle size <5mm) are all commercially available products in the iron and steel metallurgy industry.

[0054] Regarding the testing methods: the composition of molten steel was analyzed using a direct-reading spectrometer; the composition of slag was analyzed using an X-ray fluorescence spectrometer (XRF); the nitrogen content in the steel was determined using an oxygen-nitrogen analyzer; and the temperature was determined using continuous temperature measurement or a rapid thermocouple.

[0055] Example 1 This embodiment describes the use of the method of the present invention to completely replace vanadium-nitrogen alloy with converter vanadium slag, producing HRB400E coiled rebar with a specification of Φ8-10mm. The specific steps are as follows: Step 1: Pre-desulfurization of slag from converter tapping: At the end of the converter smelting process, the molten steel temperature reached 1650℃, and the final sulfur content of the molten steel was 0.08%. During the tapping process, 5 kg / t of active lime and 0.8 kg / t of fluorite were added to the ladle along with the steel stream. Utilizing the impact force of the tapping steel stream, and with bottom blowing nitrogen gas continuously activated throughout the process for stirring at a flow rate of 800 NL / min, the high-basicity slag and molten steel were thoroughly mixed, achieving slag washing and pre-desulfurization. After tapping, before the ladle was hoisted to the LF furnace station, nitrogen gas was continuously blown and stirred for 7 minutes at a flow rate of approximately 400 NL / min. After this treatment, the sulfur content of the molten steel was reduced to 0.056%, the desulfurization rate reached 30%, and the outlet temperature was 1540℃.

[0056] Step 2, Slag Formation and Reduction in the LF Refining Furnace: After the molten steel enters the LF refining furnace, the first batch of materials is added according to the composition of the converter ladle sample: 5 kg / t steel of active lime, 1.5 kg / t steel of fluorite, and 3 kg / t steel of vanadium slag with a grade of 10%. After heating for 6 minutes, the temperature of the molten steel is 1530℃. The first steel sample and slag sample are taken for testing. The test results of the first sample are: S=0.042% and V=0.012% for molten steel, and the basicity of slag CaO / SiO2=2.2.

[0057] Based on the above results, in order to increase the slag basicity and continue to increase vanadium, 1 kg / t steel of active lime and 2 kg / t steel of converter vanadium slag were added in batches. At the same time, reducing agents were added to the slag surface, including 0.3 kg / t steel of ferrosilicon powder and 0.4 kg / t steel of silicon aluminum barium.

[0058] After adding the reducing agent, the power was continued to be applied for heating for another 10 minutes, and the temperature of the molten steel reached 1590℃. During this process, through the adjustment of the slag material in the early stage, the basicity of the slag was finally controlled at 2.7, forming a high-basicity white slag with good fluidity and strong reducing ability. After the operator picked and observed the slag and confirmed that the color of the slag was grayish-white, a sample was taken again and the molten steel was organized to leave the station. At this time, the sulfur content of the molten steel was controlled at 0.038%. This step successfully reduced V2O5 in the vanadium slag into vanadium element and entered the molten steel, increasing the vanadium content of the molten steel to 0.027%. After testing, the residual V2O5 content in the final refined slag was only 0.005%.

[0059] Step 3: Nitrogen increase in the LF refining furnace: In this embodiment, vanadium slag is used to replace 100% of the vanadium-nitrogen alloy. Nitrogen is used as the bottom-blowing gas source throughout the LF refining furnace process. After adding the first batch of lime, fluorite, and vanadium slag, the bottom-blowing nitrogen flow rate is adjusted to 1100 NL / min for strong stirring and slag washing for 4 minutes. During the heating process, the bottom-blowing nitrogen flow rate is adjusted to 500 NL / min to promote the slag-steel interface reaction and improve the reduction and absorption efficiency of vanadium. After heating is complete and the slag turns into white slag, the bottom-blowing nitrogen flow rate is reduced to 300 NL / min for weak stirring for 4 minutes to homogenize the composition and temperature while increasing nitrogen content. The ladle is then hoisted to the continuous casting machine for pouring. Testing showed that the nitrogen content of the molten steel leaving the station was 0.018%.

[0060] Step 4: Precise control of vanadium slag dosage: The internal control target vanadium content for HRB400E coiled rebar is 0.027%. Before entering the LF furnace, no vanadium-nitrogen alloy was added to the converter, and the vanadium content of the molten steel was 0.012%, which was brought in by residual vanadium in the molten iron. The V2O5 content in the vanadium slag used in the converter was 10%. Taking the vanadium absorption coefficient η=0.95, the amount of vanadium increase and the amount of vanadium slag to be added were calculated according to the formula. The required vanadium increase was 0.025%-0.030%, and the total amount of vanadium slag used did not exceed 5.4 kg / ton of steel. Considering that some vanadium slag had been melted and reduced before the first sample test, the first addition was based on the upper limit of the calculated amount, and 3 kg / ton of steel was added. After the results of the first sample were returned, it was calculated that about 2.5 kg / ton of steel still needed to be added. In fact, 2 kg / ton of steel was added in batches. Finally, the total amount of vanadium slag used was 5 kg / ton of steel, achieving precise control of the vanadium increase to 0.027%.

[0061] Effect Analysis: In this embodiment, vanadium slag from the converter completely replaced vanadium-nitrogen alloy, increasing the vanadium content in the molten steel to 0.027%, with a phosphorus recovery rate of only 0.001%, a nitrogen content in the molten steel reaching 0.018%, a V2O5 residue in the final slag of the refining process of 0.005%, and a vanadium absorption rate of 94%. The mechanical properties of the finished steel bars are: yield strength 455MPa, tensile strength 610MPa, and elongation after fracture 25%, meeting the requirements of GB / T1499.2 standard.

[0062] Example 2 This embodiment describes the use of the method of the present invention to completely replace vanadium-nitrogen alloy with converter vanadium slag, producing HRB400E rebar with a diameter of Φ18-25mm. The specific steps are as follows: Step 1: Pre-desulfurization of slag from converter tapping: The final temperature of the converter was 1640℃, and the sulfur content of the molten steel was 0.083%. During the tapping process, 5 kg / t of active lime and 0.8 kg / t of fluorite were added with the steel stream, along with bottom-blown nitrogen stirring. After tapping, nitrogen stirring was continued for 6 minutes. After treatment, the sulfur content of the molten steel was reduced to 0.058%, and the outlet temperature was 1535℃.

[0063] Step 2, Slag Formation and Reduction in the LF Refining Furnace: After the molten steel enters the LF furnace, the first batch of materials added are: 5 kg / t steel of lime, 1.5 kg / t steel of fluorite, and 4.6 kg / t steel of 10% vanadium slag. After heating for 6 minutes, a sample is taken. The initial sample has V=0.010% and S=0.045%. Based on the results of the initial sample, 1 kg / t steel of lime is added in batches, along with 0.3 kg / t steel of ferrosilicon powder and 0.4 kg / t steel of barium aluminum silicon reducing agent. The temperature is further increased for 11 minutes to 1590℃, and the slag basicity is controlled at 2.7 to form white slag. After sampling, the molten steel leaves the station with a sulfur content controlled at 0.037%, vanadium content increased to 0.032%, and V2O5 residue in the refining slag at 0.004%.

[0064] Step 3: Nitrogen increase in the LF refining furnace: Nitrogen bottom blowing was used throughout the process. After the first batch of material was added, the nitrogen flow rate was adjusted to 1100 NL / min and stirred for 4 minutes. During the heating process, the flow rate was adjusted to 600 NL / min. After the heating was completed and white slag was formed, the flow rate was reduced to 300 NL / min and stirred weakly for 4 minutes. The nitrogen content of the molten steel leaving the station was 0.019%.

[0065] Step 4: Precise control of vanadium slag dosage: The internal control target vanadium content of HRB400E rebar is 0.032%, and the V content before refining in the LF furnace is 0.010%. The required vanadium addition is 0.022%, and the calculated vanadium slag addition is 0.022×100 / (10×0.95×0.56)=4.13kg / t steel. The initial addition is 4.6kg / t steel, and no further large-scale addition is made based on the results of the first sample. The final total vanadium slag usage is approximately 4.6kg / t steel.

[0066] Effect Analysis: In this embodiment, vanadium slag from the converter is used to replace vanadium-nitrogen alloy 100%, vanadium content in molten steel is increased to 0.032%, phosphorus recovery is 0.002%, nitrogen content in molten steel is 0.019%, V2O5 residue in refining slag is 0.004%, and vanadium absorption rate is 95%. The mechanical properties of the finished steel bars are: yield strength 465MPa, tensile strength 620MPa, and elongation after fracture 24%, which meet the standard requirements.

[0067] Example 3 This embodiment demonstrates the use of the method of the present invention to partially replace vanadium-nitrogen alloy with converter vanadium slag to produce high-strength earthquake-resistant steel bars T63E with a specification of Φ22-25mm. The specific steps are as follows: Step 1: Pre-desulfurization and alloying of converter slag washing: The final temperature of the converter was 1660℃, and the final sulfur content of the molten steel was 0.090%. During the tapping process, 6 kg / t of active lime and 1 kg / t of fluorite were added with the steel stream. At the same time, in order to meet the high vanadium content requirements of T63E, some vanadium-nitrogen alloy was added with the steel stream for preliminary alloying. This was combined with bottom-blown nitrogen stirring, and nitrogen stirring continued for 7 minutes after tapping. After treatment, the sulfur content of the molten steel was reduced to 0.062%, and the tapping temperature was 1538℃. At this point, the vanadium content of the molten steel was 0.130% before LF refining, after preliminary vanadium addition.

[0068] Step 2, Slag Formation and Reduction in the LF Refining Furnace: After the molten steel enters the LF furnace, the first batch of materials added are: 7 kg / t steel of lime, 2 kg / t steel of fluorite, and 7.5 kg / t steel of 10% vanadium slag. After heating for 6 minutes, a sample is taken. The initial sample has V=0.150% and S=0.045%. Based on the composition of the initial sample, 2 kg / t steel of vanadium slag is added, along with 0.5 kg / t steel of ferrosilicon powder and 0.8 kg / t steel of barium aluminum silicon reducing agent. The temperature is continuously increased for 12 minutes to 1590℃, and the slag basicity is controlled at 2.8 to form white slag. After sampling, the molten steel is discharged from the station with the sulfur content controlled at 0.035%. This step successfully increased the vanadium content in the molten steel from 0.130% to 0.180%, and the residual V2O5 in the refining slag was only 0.001%.

[0069] Step 3: Argon / Nitrogen stirring in the LF refining furnace: T63E steel has high requirements for nitrogen content, and some vanadium-nitrogen alloy has been added to the converter. In order to accurately control the nitrogen content and avoid excessive nitrogen increase, this embodiment adopts a combined gas source mode: argon is used as the bottom blowing gas source in the early stage of LF refining, and the flow rate control is similar to that in embodiment 2; in the later stage of refining, after the composition and temperature are adjusted and the slag turns white, nitrogen is switched as the bottom blowing gas source, the flow rate is adjusted to 300NL / min, and weak stirring is carried out for 4 minutes to carry out precise nitrogen increase. The nitrogen content of the molten steel leaving the station is 0.022%.

[0070] Step 4: Precise control of vanadium slag dosage: The target vanadium content for T63E is 0.180%, and the V content before refining in the LF furnace is 0.130%, requiring a vanadium increase of 0.050% from vanadium slag. The amount of vanadium slag to be added is calculated using the formula: The amount of vanadium slag added per ton of steel = 0.050 × 100 / (10 × 0.95 × 0.56) = 9.4 kg / t steel The initial addition was 7.5 kg / t of steel. After the first sample (0.150%) was returned, the required additional amount was calculated as: (0.180-0.150)×100 / (10×0.95×0.56)=5.64 kg / t of steel. Considering that the vanadium slag added earlier was still reacting, an additional 2 kg / t of steel was actually added, bringing the final total amount to approximately 9.5 kg / t of steel, which was kept below 10 kg / t of steel.

[0071] Effect Analysis: In this embodiment, a combination of vanadium-nitrogen alloy and converter vanadium slag is used to produce high-strength steel. The use of vanadium slag achieves a vanadium increase of 0.050%, a phosphorus recovery of 0.003%, a nitrogen content of molten steel of 0.022%, a V2O5 residue of 0.001% in the refining slag, and a vanadium absorption rate of 96%. The mechanical properties of the finished steel bars are: yield strength of 630 MPa, tensile strength of 815 MPa, and total elongation at maximum force of 12%, which meets the requirements of T63E technical conditions.

[0072] Comparative Example 1 This comparative example uses a traditional process, namely, vanadium-nitrogen microalloying with vanadium-nitrogen alloy throughout the entire process, to produce HRB400EΦ8-10mm coiled screws.

[0073] During the converter tapping process, a vanadium-nitrogen alloy (grade FN-3, V 78%, N 16%) was added with the steel stream at a rate of 0.4 kg / t steel. Conventional white slag refining was carried out in the LF refining furnace, and argon was used as the bottom blowing gas. No nitrogen was deliberately added, and other process parameters remained the same as in Example 1.

[0074] Results: The vanadium content of the molten steel was 0.028%, the nitrogen content was 0.010%, and the total alloy cost was 17.5 yuan / ton higher than that of Example 1. The mechanical properties of the steel were comparable to those of Example 1.

[0075] Comparative Example 2 This comparative example attempts to directly replace vanadium-nitrogen alloy with converter vanadium slag, but does not employ the nitrogen bottom blowing nitrogen enhancement process of this invention to produce HRB400EΦ8-10mm coiled rebar.

[0076] The converter tapping and LF refining operations are basically the same as in Example 1, but the LF refining furnace uses argon as the bottom blowing gas source throughout the process and does not perform nitrogen addition operations. The amount of vanadium slag added is calculated according to the formula in Example 1.

[0077] Results: The vanadium content in the molten steel was 0.026%, meeting the target requirement; however, the nitrogen content in the molten steel was only 0.008%, which was significantly low; the mechanical properties of the finished steel bars were: yield strength 430 MPa, tensile strength 585 MPa, elongation after fracture 22%. The yield strength was slightly lower than the 400 MPa required by GB / T1499.2, and the performance did not meet the requirements; this indicates that simply replacing vanadium without supplementing nitrogen cannot achieve the vanadium-nitrogen composite strengthening effect.

[0078] Comparative Example 3 This comparative example attempted to replace vanadium-nitrogen alloy with converter vanadium slag, but failed to form a high-basicity reducing slag due to insufficient reducing agent addition, resulting in the production of HRB400E Φ8-10mm coiled rebar.

[0079] The converter tapping operation is the same as in Example 1. In the LF refining furnace, 3 kg / t steel of lime, 1 kg / t steel of fluorite, and 5 kg / t steel of vanadium slag are added. Only 0.1 kg / t steel of ferrosilicon powder is added as a reducing agent; no silicon, aluminum, or barium is added. The steel is then discharged from the station after being heated to 1590℃.

[0080] Results: The vanadium content in the molten steel was only 0.015%, far below the target value; the residual V2O5 content in the refining slag was as high as 0.12%, indicating that the vanadium reduction was insufficient and that vanadium-nitrogen alloy needed to be added later to adjust the composition, which would actually increase the cost.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in a steelmaking LF refining furnace, characterized in that, Includes the following steps: Step 1: Pre-desulfurization of slag washing at converter tapping: Control the final tapping temperature of the converter to 1640℃-1660℃. During tapping, add 2-6 kg / t steel of active lime and 0.3-1 kg / t steel of fluorite to the ladle. Use the impact force of the steel flow and bottom-blown nitrogen to stir the slag for washing. After tapping, continue to blow nitrogen and stir for 5-8 minutes to reduce the sulfur content of the molten steel by 20-35%. Step 2, Slag Formation and Reduction in the LF Refining Furnace: After the molten steel enters the LF refining furnace, the first batch of materials is added, which includes 3-8 kg / t steel of lime, 1-2 kg / t steel of fluorite, and 3-10 kg / t steel of converter vanadium slag. After heating for 5-7 minutes, a sample is taken. Based on the composition of the first sample, quicklime, fluorite, and converter vanadium slag are added in batches. At the same time, reducing agents ferrosilicon powder and barium silicate are added, with a total addition of 0.3-1.0 kg / t steel. The temperature is further increased for 10-12 minutes to 1580℃-1590℃. The binary basicity of the slag, CaO / SiO2 ratio, is adjusted to 2-3 to form a high-basicity reducing slag, which reduces V2O5 in the converter vanadium slag to soluble vanadium, which then enters the molten steel. Step 3: Nitrogen enhancement in the LF refining furnace: When using converter vanadium slag to completely or partially replace vanadium-nitrogen alloy, nitrogen is used as the bottom-blowing gas source in the LF refining furnace. After adding the first batch of material, the bottom-blowing nitrogen flow rate is controlled at 1000-1200 NL / min, with strong stirring for 3-5 minutes. During the heating process, the bottom-blowing nitrogen flow rate is controlled at 500-800 NL / min. After the slag turns into white slag after heating is completed, the bottom-blowing nitrogen flow rate is controlled at 200-400 NL / min, with weak stirring for 3-5 minutes, so that the nitrogen content of the molten steel is controlled at 0.012-0.025%. Step 4: Precise control of vanadium slag dosage: Based on the target vanadium content of the steel grade and the actual vanadium content of the molten steel before LF furnace refining, calculate and control the amount of converter vanadium slag added according to the following formula: Vanadium-containing slag addition per ton of steel (kg) = (target V content of steel grade - V content before LF furnace refining) × 100 / (V2O5 content of vanadium-containing slag × 0.95 × 0.56); Using the above formula, the vanadium content in molten steel can be controlled to be 0.020-0.050%, and the total amount of vanadium slag used in the converter should not exceed 10 kg / t of steel.

2. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1, characterized in that, In step 1, the final tapping temperature of the converter is 1645℃-1655℃, the amount of active lime added is 3-5 kg / t steel, the amount of fluorite added is 0.5-0.8 kg / t steel, and the nitrogen blowing and stirring time is 6-7 min, so that the sulfur content of the molten steel is reduced to 0.055-0.065%.

3. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloys in the steelmaking LF refining furnace according to claim 1, characterized in that, In step 2, the heating time after the first batch of material is added is 6-8 minutes. The material replenishment operation is dynamically adjusted according to the vanadium content, sulfur content and slag alkalinity in the first sample. The timing of adding the reducing agent is preferably after the first sample is taken and before the heating continues.

4. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1 or 3, characterized in that, In step 2, when the slag binary basicity CaO / SiO2 ratio is 2.5-2.8 and the slag color turns grayish-white or white, it indicates that the reducing atmosphere is sufficient and the vanadium reduction reaction is basically completed.

5. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1, characterized in that, In step 3: When converter vanadium slag is used to completely replace vanadium-nitrogen alloy, nitrogen is used as the bottom blowing gas source in the LF refining furnace throughout the entire process. When vanadium slag from a converter is used to partially replace vanadium-nitrogen alloys, the LF refining furnace can use argon gas during the heating stage and switch to nitrogen gas for nitrogen enrichment in the later stage of refining.

6. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1 or 5, characterized in that, In step 3, the relationship between the bottom-blown nitrogen flow rate and the nitrogen content of the molten steel is calibrated by online monitoring or offline testing, and the nitrogen content of the molten steel leaving the station is 0.015-0.022%.

7. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1, characterized in that, In step 4, the vanadium absorption coefficient is calibrated through industrial tests. Its specific value is related to the slag alkalinity, the amount of reducing agent, and the stirring intensity, and is between 0.95 and 1.

00.

8. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1 or 7, characterized in that, In step 4, the calculation of the vanadium slag addition amount also includes the following correction step: based on the vanadium content test results returned from the first sample, the subsequent addition amount is dynamically corrected, and the correction formula is: The amount of vanadium slag to be added (kg) = (target V content of steel grade, V content of primary sample) × total amount of molten steel (t) × 1000 / (V2O5 content in converter vanadium slag × vanadium absorption coefficient × 0.56).

9. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1, characterized in that, The converter vanadium slag is the slag produced during the vanadium extraction and smelting process in a converter. After crushing, magnetic separation, and screening, its particle size is 5-40mm, with a V2O5 content of 8-20%, a total iron content of 15-30%, and a moisture content of less than 1%.

10. The method for using converter vanadium slag alloying to replace vanadium-nitrogen alloying in the steelmaking LF refining furnace according to claim 1, characterized in that, Before leaving the LF refining furnace, the residual V2O5 content in the refining slag is reduced to below 0.005%, the phosphorus recovery rate of the molten steel is controlled to below 0.003%, and the vanadium absorption rate is stabilized at 93-97%.