Molten steel cleanliness intelligent optimization method based on dynamic alkalinity regulation and control and multi-modal slag system design process

Abstract

The invention discloses an intelligent molten steel cleanliness optimization method based on dynamic alkalinity regulation and control and a multi-modal slag system design process, and belongs to the technical field of ferrous metallurgy refining. The invention innovatively provides a staged variable slag system control method. According to the method, high-alkalinity slag is adopted in the early stage of refining to achieve deep deoxidation and control over the number of inclusions; in the later stage of refining, a specific composite slag modifier is added to change a slag separation system into medium alkalinity, inclusion polymerization adsorption and component plasticization are promoted, and the technical effects that the number of inclusions is reduced by more than or equal to 60%, the number of large-particle inclusions (larger than 50 microns) is reduced by more than or equal to 80% and the total oxygen content is smaller than or equal to 8 ppm are achieved by accurately controlling the refining time progress, argon stirring parameters and a temperature system. And meanwhile, the rating of B-class and D-class inclusions is stably controlled to be lower than 0.5 grade.

Description

Technical Field

[0001] This invention relates to the field of steel metallurgical refining technology, and in particular to an intelligent optimization method for the cleanliness of molten steel based on dynamic alkalinity control and a multimodal slag system design process. Background Technology

[0002] In high-end steel production, the control of non-metallic inclusions is a core factor determining product quality. Inclusions not only reduce the mechanical properties and fatigue strength of steel, but also lead to surface defects in cold-rolled sheets. Refining slag, as a key medium for regulating the cleanliness of molten steel, directly affects the composition, morphology, and size distribution of inclusions through slag-steel interface reactions.

[0003] The following key technical defects exist in the current LF refining process regarding inclusion control: ① Monolithic basicity control: Traditional processes use a slag system with a fixed basicity (high or low) throughout the entire refining process. While high-basicity slag is beneficial for deoxidation, it easily leads to slag viscosity and difficulty in inclusion flotation; low-basicity slag, although having good fluidity, has insufficient deoxidation capacity and easily generates new alumina inclusions. ② Low dispersion efficiency of slag conditioners: Existing slag conditioners are mostly dense particles or powders, which easily agglomerate and dissolve unevenly after being added to molten steel, resulting in large fluctuations in slag composition and making it impossible to accurately control the inclusion modification effect. ③ Incomplete inclusion modification: Traditional calcium treatment only achieves inclusion modification through calcium feeding lines, but it does not combine early deoxidation with later soft blowing processes for coordinated control, easily leading to recrystallization or large particle formation of calcium aluminate inclusions. Therefore, the current LF refining process faces the industry challenge of failing to simultaneously achieve efficient inclusion removal and plasticity control.

[0004] To address the aforementioned issues, there is an urgent need in this field to develop a method that can dynamically match the requirements of each refining stage and precisely control the characteristics of refining slag, so as to significantly reduce the number of inclusions in molten steel, effectively plasticize their morphology, and comprehensively improve the cleanliness of molten steel and the performance of the final product. Summary of the Invention

[0005] This invention addresses the aforementioned problems by providing an intelligent optimization method for molten steel cleanliness based on dynamic basicity control and a multimodal slag system design process. Specifically, it addresses the difficulty of removing inclusions using existing refining variable slag systems by innovatively proposing a staged variable slag system control method: In the early refining stage, high-basicity slag (CaO / SiO2=12-17) is used to achieve deep deoxidation and control the number of inclusions; in the later refining stage, a specific composite slag conditioner is added to change the slag system to medium basicity (CaO / SiO2=3.5-4.5), promoting inclusion polymerization and adsorption, and component plasticization. Through precise control of the refining time, argon stirring parameters, and temperature regime, the invention achieves a reduction of inclusion quantity ≥60%, a reduction of large-particle inclusions (>50μm) ≥80%, and a total oxygen content ≤8ppm, while simultaneously ensuring that the ratings of Class B and Class D inclusions are stably controlled below 0.5.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, this invention provides a method for intelligently optimizing the cleanliness of molten steel based on dynamic alkalinity control, comprising the following steps: (1) Early stage of refining: In the first 0-35 minutes of LF refining, the molten steel is deeply deoxidized by using ultra-high basicity slag and high frequency pulse argon stirring mode to ensure uniform mixing of the molten pool and initial floating of inclusions; the basicity R (CaO / SiO2) of the ultra-high basicity slag is controlled at 12-17. (2) Slag transformation period: When the refining process reaches 35-40 minutes, add the composite slag conditioner and disperse it with ultrasonic waves to ensure that the slag conditioner is uniformly melted and avoid secondary oxidation caused by local component fluctuations; (3) Refining stage: After the slag transformation period, the molten steel is plasticized by using medium basicity slag and low frequency steady-state argon stirring mode, and the temperature of the molten steel is controlled at 1590±5℃; the basicity R (CaO / SiO2) of the medium basicity slag is controlled at 3.5-4.5; (4) Soft blowing purification and inclusion modification stage: After the late refining stage, calcium wire is fed in to perform soft blowing argon treatment on the molten steel in stages. After the soft blowing is completed, the molten steel is calmed. In step (1), the mass fraction composition of the ultra-high alkalinity slag includes: CaO 50-55%, SiO2 1-6%, MgO 4-8%, Al2O3 30-35%, FeO+MnO < 1.0%; The argon flow rate of the high-frequency pulsed argon stirring mode is 600-800 L / min, and the pulse frequency is 2 Hz.

[0007] In step (1), lime is added in batches to form slag. The amount of lime added in the first batch is ≥1t, and the total amount of lime added is ≥1.2t. The molten steel is deoxidized by aluminum blocks. After deoxidation by aluminum blocks, the acid-soluble aluminum [Al] in the molten steel is controlled to be 0.100-0.120%.

[0008] In step (2), the composite slag conditioner includes a porous slag carrier and an active component loaded on the porous slag carrier; the active component includes, by mass fraction: Al 45-60%, CaO 15-20%, Si2O3 2-3%, MgO 0.3-1%.

[0009] In step (2), the amount of the composite slag conditioner added is 1.5-1.7 kg / ton of molten steel; the proportion of the porous slag carrier with a particle size in the range of 0.5-5 mm is ≥80%, and the porosity is ≥40%.

[0010] In step (3), the w(CaO) / w(Al2O3) ratio in the medium-alkalinity slag is controlled at 1.4-1.7 to ensure the slag system's ability to adsorb and modify inclusions; in the low-frequency steady-state argon stirring mode, the argon flow rate is 200-400 L / min and the pulse frequency is 0.5 Hz. The low-frequency steady-state argon stirring mode is used to reduce molten pool disturbance and prevent the re-dissolution of floating inclusions.

[0011] The temperature of molten steel is precisely controlled at 1590±5℃ to ensure stable slag fluidity and reaction kinetics of inclusions.

[0012] In step (4), after the calcium wire is fed in, the calcium aluminate inclusions in the molten steel are modified into low-melting-point calcium aluminate with a melting point ≤1350℃; the total time of the staged soft blowing of argon gas is ≥25 minutes, the argon gas flow rate is 300-350 L / min for the first 10 minutes (to promote the polymerization of inclusions), and the argon gas flow rate is 150-200 L / min for the subsequent time (to ensure that the inclusions float smoothly).

[0013] After soft blowing, the molten steel is calmed for ≥20 minutes to further reduce residual inclusions in the steel.

[0014] This invention employs an online spectral monitoring system to analyze the composition of refining slag (such as the content of CaO, SiO2, and Al2O3) in real time, and dynamically adjusts the amount and timing of slag conditioning agent addition through a feedback model to ensure that the slag system characteristics change according to a preset curve.

[0015] In a second aspect, the present invention provides the application of the above method in the preparation of high-purity steel grades.

[0016] In a third aspect, the present invention provides a high-purity steel product, which is smelted using the above-described method.

[0017] The technical solution of this invention can achieve the following technical effects: (1) The number of inclusions is significantly reduced: the total number of inclusions in the steel is reduced by ≥62%, and the number of large particle inclusions (particle size > 50 μm) is reduced by ≥88%; (2) Improved cleanliness of molten steel: The total oxygen content of molten steel is ≤6.5ppm, meeting the cleanliness requirements of high-end steel; (3) Inclusion morphology optimization: The inclusion rating of Class B (alumina) and Class D (sulfide) inclusions is stably controlled below 0.5. The inclusions are low melting point CaO-Al2O3-SiO2-Na2O quaternary system (Al2O3 content reduced to 40-50%), which are easy to deform during rolling. (4) Improved product performance: The fatigue life of steel is increased by 166%, meeting the needs of high-end products such as wear-resistant steel and high-strength steel; (5) Process stability: The slag system transformation process is stable (transformation time ≤ 10 min), there is no secondary oxidation phenomenon, and the production efficiency is more than 30% higher than that of the traditional dual slag process. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] The specific embodiments of the present invention will be described in further detail below with reference to examples. The following detailed descriptions are illustrative and intended to provide further explanation of this application, rather than limiting the scope of the invention.

[0020] Example 1: Production of BIS450 wear-resistant steel plates using a 130-ton refining furnace 1. Raw material conditions: Initial composition of molten steel (mass fraction): [C]=0.19%, [S]=0.018%, [P]=0.012%, [Mn]=1.25%, molten steel mass 130t.

[0021] 2. Control of process parameters at each stage (1) Early stage of refining (0-35 min) Slag-making operation: Add 2.6t of lime (1t initially, the remaining 1.6t added in two batches at 10min intervals) and 0.4t of calcium carbide (used to adjust the FeO content in the slag). Actual composition of slag: CaO 52.3%, SiO2 3.8%, Al2O3 32.7%, MgO 6.2%, FeO+MnO=0.8%, alkalinity R=13.76; Deoxidation and stirring: Add 150 kg of aluminum blocks and control the [Al] of the molten steel to 0.115%; use high-frequency pulsed argon gas for stirring, with a flow rate of 700 L / min and a pulse frequency of 2 Hz.

[0022] (2) Slag formation period (at 35 min) Addition of slag conditioner: Add 210 kg of porous composite slag conditioner (porous slag carrier loaded with Al 52%, CaO 18%, Si2O3 2.5%, MgO coating 0.5%). Ultrasonic assistance: Turn on the ultrasonic dispersion device, frequency 20kHz, power 500W, for 10 minutes.

[0023] (3) Refining stage (35-65 min) The adjusted slag composition is as follows: CaO 48.1%, SiO2 12.5%, Al2O3 35.2%, MgO 4.2%, basicity R=3.85, w(CaO) / w(Al2O3)=1.37; Stirring and temperature control: Argon gas is switched to low-frequency steady-state mode, with a flow rate of 300 L / min and a pulse frequency of 0.5 Hz; the molten steel temperature is controlled at 1590 ± 5 ℃.

[0024] (4) Soft blowing purification and impurity modification stage (65-95 min) Calcium line feeding and soft blowing: Feed 80m of calcium line (calcium line purity ≥98%); argon gas is controlled in stages during soft blowing: 320L / min for the first 10min, and 180L / min for the subsequent time; Calming treatment: After soft blowing, the molten steel is calmed for 25 minutes.

[0025] 3. Implementation effect evaluation The quantity and level of inclusions were tested in accordance with GB / T 18876.2-2024 standard.

[0026] Inclusion count: 68 inclusions / mm in the steel during LF refining. 2 When displaced, the number drops to 26 / mm. 2 , a reduction of 62%; Large particle inclusions: The number of inclusions with a particle size ≥50μm decreased from 8 per 100g of steel to 1 per 100g of steel, a reduction of 88%; Class D inclusions (grade): 0.5; Total oxygen content: The total oxygen content of the molten steel is 6.3 ppm; Melting point of inclusions: determined by differential scanning calorimetry (DSC), the melting point of inclusions is ≤1350℃; Product performance: BIS450 wear-resistant steel plate has a Brinell hardness ≥450HBW and an impact toughness (-40℃) ≥32J / cm. 2 Fatigue life: 5.6 × 10⁻⁶ 7 Secondly, the fatigue life is increased by 166% compared with products made by traditional processes.

[0027] Comparative Example 1: Comparative Example 1 uses a single high-alkalinity slag process (R=15). Process characteristics: Compared with the preparation method of Example 1, Comparative Example 1 uses high basicity slag throughout the process (CaO 52.3%, SiO2 3.8%, Al2O3 32.7%, MgO 6.2%, FeO+MnO=0.8%, basicity R=13.76), without slag change stage, and the stirring mode is a single steady-state argon gas (500L / min). Testing revealed that the inclusions in the steel prepared in Comparative Example 1 were mainly pure Al2O3 (content > 90%), with a melting point > 1600℃, and were clustered. The number of large inclusion particles ≥ 50 μm decreased by only 45%, and the D-class inclusion (grade) was 1.5. The total oxygen content was 8.9 ppm, and the fatigue life was 2.1 × 10⁻⁶. 7 Second-rate.

[0028] Comparative Example 2: Comparative Example 2 uses a single medium-alkalinity slag process (R=3.85). Process characteristics: Compared with the preparation method of Example 1, Comparative Example 2 uses medium-alkalinity slag (CaO 48.1%, SiO2 12.5%, Al2O3 35.2%, MgO 4.2%, alkalinity R=3.85) throughout the process, without slag change stage, and the stirring mode is a single steady-state argon gas (500L / min). Testing showed that the number of large inclusions ≥50μm in the steel prepared in Comparative Example 2 was reduced by 40%, with Class D inclusions (grade): 1.7; total oxygen content: 10.2 ppm; and fatigue life: 1.8 × 10⁻⁶. 7 Second-rate.

[0029] In summary, the method of the present invention can significantly reduce the total oxygen content and the number of inclusions in molten steel, improve the fatigue life of steel, and achieve a cleanliness stability far superior to the traditional single-basicity slag process, making it more suitable for the production requirements of high-cleanliness steel.

[0030] The above description is merely a preferred embodiment of this application and is not intended to limit the application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications made within the spirit and principles of this application are not permitted. Equivalent substitutions and improvements should all be included within the scope of protection of this application.

Claims

1. A method for intelligent optimization of steel molten cleanliness based on dynamic alkalinity control, characterized in that, Includes the following steps: (1) Early stage of refining: In the first 0-35 minutes of LF refining, the molten steel is deeply deoxidized by using ultra-high basicity slag and high frequency pulse argon stirring mode; the basicity R of the ultra-high basicity slag is controlled at 12-17; (2) Slag transformation period: When the refining process reaches 35-40 minutes, add the composite slag conditioner and perform ultrasonic dispersion; (3) Refining stage: After the slag transformation period, the molten steel is plasticized by using medium basicity slag and low frequency steady-state argon stirring mode, and the temperature of the molten steel is controlled at 1590±5℃; the basicity R of the medium basicity slag is controlled at 3.5-4.

5. (4) Soft blowing purification and inclusion modification stage: After the late refining stage, calcium wire is fed in to perform soft blowing argon treatment on the molten steel in stages. After the soft blowing is completed, the molten steel is calmed.

2. The method according to claim 1, characterized in that, In step (1), the mass fraction composition of the ultra-high alkalinity slag includes: CaO 50-55%, SiO2 1-6%, MgO 4-8%, Al2O3 30-35%, FeO+MnO < 1.0%; The argon flow rate of the high-frequency pulsed argon stirring mode is 600-800 L / min, and the pulse frequency is 2 Hz.

3. The method according to claim 1, characterized in that, In step (1), lime is added in batches to form slag. The amount of lime added in the first batch is ≥1t, and the total amount of lime added is ≥1.2t. The molten steel is deoxidized by aluminum blocks. After deoxidation by aluminum blocks, the acid soluble aluminum in the molten steel is controlled to be 0.100-0.120%.

4. The method according to claim 1, characterized in that, In step (2), the composite slag conditioner includes a porous slag carrier and an active component loaded on the porous slag carrier; the active component includes, by mass fraction: Al 45-60%, CaO 15-20%, Si2O3 2-3%, MgO 0.3-1%.

5. The method according to claim 4, characterized in that, In step (2), the amount of the composite slag conditioner added is 1.5-1.7 kg / ton of molten steel; the proportion of the porous slag carrier with a particle size in the range of 0.5-5 mm is ≥80%, and the porosity is ≥40%.

6. The method according to claim 1, characterized in that, In step (3), the w(CaO) / w(Al2O3) ratio in the medium alkalinity slag is controlled at 1.4-1.7; the argon flow rate in the low-frequency steady-state argon stirring mode is 200-400 L / min, and the pulse frequency is 0.5 Hz.

7. The method according to claim 1, characterized in that, In step (4), after the calcium wire is fed in, the calcium aluminate inclusions in the molten steel are modified into low-melting-point calcium aluminate with a melting point ≤1350℃; the total time of the staged soft blowing of argon is ≥25 minutes, the argon flow rate is 300-350 L / min for the first 10 minutes, and the argon flow rate is 150-200 L / min for the subsequent time.

8. The application of the method according to any one of claims 1-7 in the preparation of high-purity steel grades.

9. A high-cleanliness steel product, characterized in that, The high-purity steel product is smelted using the method described in any one of claims 1-7.