A steelmaking production method for reducing the hole defect rate of high-grade non-oriented silicon steel cold rolling

Abstract

The application discloses a steelmaking production method for reducing hole defect rate of high-grade non-oriented silicon steel cold-rolled plate, and belongs to the technical field of steel smelting. The method first carries out forced modification of slag in the converter tapping process, and sequentially adds special-grade lime and molten steel refining agent; then, after the decarburization of RH vacuum treatment is completed, deoxidation alloying is carried out, and desulfurizing agent is added in batches; finally, according to the adding amount and timing of alloy and desulfurizing agent, the RH net circulation time is dynamically adjusted, and the required time is determined through a calculation formula based on the adding amount of alloy and desulfurizing agent. Through fine control of top slag modification, desulfurization process and RH circulation time, the application realizes efficient removal and morphology optimization of inclusions in the steel, thereby significantly reducing the hole defect rate of the cold-rolled plate. The hole defect rate of the high-grade non-oriented silicon steel cold-rolled plate produced by the method is less than 3.5% due to the inclusions in the steelmaking.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a steelmaking production method for reducing the porosity defect rate of cold-rolled high-grade non-oriented silicon steel. Background Technology

[0002] Non-oriented silicon steel is a key soft magnetic material used in the manufacture of small and medium-sized motors, household appliances, power tools, large generators, and drive motors for new energy vehicles. High-grade non-oriented silicon steel, due to its excellent magnetic properties and low iron loss characteristics, can significantly improve motor energy efficiency, and its market demand continues to expand against the backdrop of industrial upgrading and the rapid growth of the new energy vehicle industry.

[0003] However, the production process of high-grade non-oriented silicon steel is complex, requiring extremely high control over the purity of molten steel and the morphology and size of inclusions. Non-metallic inclusions in steel can disrupt the continuity of the matrix, reduce the plasticity and toughness of the material, and easily cause porosity defects during subsequent cold rolling, seriously affecting the yield and product quality. In actual production, the quantity, size, and distribution of inclusions in molten steel are directly affected by the top slag modification effect in the steelmaking process and the method and timing of adding desulfurizing agent during RH refining. In particular, the desulfurizing agent addition strategy is generally adopted by adding it all at once after alloying. This may not only lead to insufficient desulfurization reaction, but also cause a large number of newly generated inclusions to remain in the molten steel due to insufficient floating time. At the same time, the RH net circulation time is usually a fixed value, which fails to be linked with the amount of alloying and desulfurizing agent added in different heats, resulting in either insufficient circulation causing substandard purity or excessive circulation causing energy waste and reduced production efficiency. These problems result in a persistently high rate of void defects in high-grade non-oriented silicon steel cold-rolled sheets, severely impacting product yield and reliability in high-end applications.

[0004] Therefore, developing a steelmaking production method that can effectively reduce the porosity defect rate of cold-rolled high-grade non-oriented silicon steel is of great significance for improving the product quality and yield of high-grade non-oriented silicon steel. Summary of the Invention

[0005] The purpose of this invention is to provide a steelmaking method for reducing the porosity defect rate of cold-rolled high-grade non-oriented silicon steel. By finely controlling the top slag modification, desulfurization process and RH cycle time, the number of inclusions in the steel is reduced and the inclusions are promoted to float, thereby achieving efficient removal of inclusions in the steel, improving the quality of the cast billet, and reducing the porosity of cold-rolled coils.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A steelmaking method for reducing the porosity defect rate in cold-rolled high-grade non-oriented silicon steel includes the following steps: (1) After the converter smelting is completed, the slag entering the ladle from the converter is forcibly modified during the tapping process. First, after the tapping amount reaches two-thirds, 200-350 kg / heat of special grade lime is added to the surface of the molten steel in the ladle, and then 150-300 kg / heat of steel refining agent is added after the tapping is completed. (2) Subsequently, the molten steel is sent to the RH station for vacuum treatment. After decarburization, it is deoxidized and then alloyed, and desulfurizing agent is added in batches according to the composition of the molten steel. (3) Dynamically control the net RH cycle time: Based on the amount of alloy and desulfurizer added in step (2), determine and execute the net cycle time, specifically as follows: When materials are added in batches, the net circulation time after the first batch is added is t1 (min), and the net circulation time after the second batch is added is not less than t2 (min), where: t1 = 1 × A + 2.5 × B; t2 = 1 × A' + 2.5 × B' + 6; In the formula, A and A' represent the total weight of the alloy added in the first and second batches, respectively, in tons; B and B' represent the total weight of the desulfurizer added in the first and second batches, respectively, in tons.

[0007] This dynamic control model is the core innovative technology of this invention. Traditional industry practices typically use a fixed net cycle time, lacking a technology for dynamically quantifying and calculating cycle time based on alloy and desulfurizer dosages. This invention, for the first time, proposes a weighted calculation formula based on alloy and desulfurizer dosages, establishing a quantitative relationship between material addition and required cycle time. This solves the problem of unstable purity control or excessive energy consumption caused by a "one-size-fits-all" approach to cycle time in traditional processes. The application of this model directly reduces the porosity defect rate of cold-rolled steel sheets from 10.00% in existing technologies to below 3.50%. This model is a specific process parameter control method specifically designed to reduce porosity defects.

[0008] Furthermore, in step (1), the premium lime comprises the following components by mass percentage: CaO ≥ 92.0%, SiO2 ≤ 1.5%, S ≤ 0.020%, loss on ignition ≤ 2%, and lime activity ≥ 360.

[0009] Furthermore, in step (1), the refining agent comprises the following components by mass percentage: Al: 20-35%, Al2O3: 25-35%, CaO: 20-40%, SiO2 < 5.0%, MgO: 2-6%, S < 0.05%, N < 0.005%.

[0010] Furthermore, in step (2), the desulfurizing agent comprises the following components, by mass percentage: CaF2≥25%, CaO:50~65%, SiO2<3.5%, S<0.020%, TC<0.15%.

[0011] Furthermore, in step (2), the specific order of adding the desulfurizing agent in batches is as follows: the first batch of desulfurizing agent is added according to the initial S content of the molten steel and the amount of alloy added, wherein the coarse alloying adjustment ensures that the content of Si, Als and Mn components is above 90% of the target composition; after fine adjustment of the alloy element composition, the second batch of desulfurizing agent is added according to the S content in the steel, at which time it is ensured that each alloy element has reached the target composition.

[0012] Furthermore, in step (2), the desulfurizing agent is added at the following time: after deoxidation, the alloy is added first and then the desulfurizing agent is added. The first batch of desulfurizing agent is added at a rate of ≤10 kg / t steel for deep desulfurization. The second batch of desulfurizing agent is added or not added depending on the S content in the steel. When added, the amount is ≤3 kg / t steel for final sulfur control.

[0013] Furthermore, in step (2), after adding the desulfurizing agent, the RH argon gas circulation flow rate is set to 120-130 m³ / h. 3 / h.

[0014] Furthermore, the chemical composition of the high-grade non-oriented silicon steel, by mass percentage, includes: C≤0.0030%, Si: 2.50~3.50%, Mn: 0.15~0.60%, P≤0.020%, S≤0.0020%, Als: 0.50~1.00%, N≤0.0030%, Ti≤0.0030%, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, the high-grade non-oriented silicon steel cold-rolled sheet produced by the method has a void defect rate induced by steelmaking inclusions of less than 3.5%.

[0016] This invention utilizes a 20-roll mill to produce high-grade non-oriented silicon steel. This mill has a large reduction and high elongation, making it easy for tiny inclusions inside the billet to tear and form holes during cold rolling. Simultaneously, the intrusion of rolls, guide plates, and foreign objects can create rolling-related holes. These two types of holes exhibit distinct and distinguishable morphological, distribution, and microstructure characteristics. Through a four-level determination using "online periodic distribution screening + macroscopic morphology + metallography + energy dispersive spectroscopy," the two types of holes can be 100% differentiated. Only holes induced by steelmaking inclusions are included in the statistics. The hole defect rate is calculated as: (Number of rolls with hole defects induced by steelmaking inclusions ÷ Total number of rolls after annealing in the corresponding heat (or casting)) × 100%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses the slag modification technology of "super lime + refining agent" to quickly transform the high oxidizing slag brought by converter steelmaking into a low oxidizing and high sulfur capacity alkaline refining slag, thereby controlling the sulfur return of molten steel from the source and creating favorable conditions for subsequent deep desulfurization and adsorption of non-metallic inclusions.

[0018] (2) The present invention adopts a desulfurization process with precise timing and batch addition of desulfurizing agent with specific components to ensure efficient desulfurization and prevent the introduction of new impurities.

[0019] (3) This invention pioneers a dynamic and quantitative RH net circulation time control model, solving the problem of "one-size-fits-all" circulation time in traditional processes. It achieves "on-demand allocation" and "process optimization." The more materials added, the more stirring energy, entrained gas, and potentially newly formed inclusions are generated, requiring a longer circulation time for them to fully react, homogenize, and float to the surface for removal. This model scientifically quantifies process parameters, ensuring that each treatment has sufficient, but not excessive, circulation time to guarantee the purity and compositional uniformity of the molten steel. This is a key breakthrough in ensuring product quality stability. Under the premise of ensuring treatment effect, unnecessary energy consumption and time waste can be avoided.

[0020] (4) This invention eliminates the conditions for the formation of pores to the greatest extent possible from the root of steelmaking through systematic purity control, inclusion modification and process stability assurance. As a result, the pore defect rate of high grade non-oriented silicon steel cold-rolled plates caused by steelmaking inclusions is significantly reduced to below 3.5%, which greatly improves product quality, yield and magnetic performance reliability of the final product. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0022] The technical solution and effects of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0023] This embodiment introduces a steelmaking method for reducing the porosity defect rate in cold-rolled high-grade non-oriented silicon steel, specifically referring to... Figure 1 As shown, it includes the following steps: In this embodiment, the steel grade produced is W310, with the following composition range: C: ≤0.0030%, Si: 3.00%~3.20%, Mn: 0.40%~0.60%, P: ≤0.020%, S: ≤0.0020%, Als: 0.60%~1.00%, N≤0.0030%, Ti≤0.0030%, and the remainder is Fe and unavoidable impurities.

[0024] (2) The nominal capacity of the RH station in this embodiment is 170 t. After the converter smelting is completed, top slag is added during the tapping process for forced modification. After the tapping amount reaches two-thirds, 220 kg / heat of special grade lime (CaO: 93.8%, SiO2: 1.0%, S: 0.018%, loss on ignition: 1.5%, lime activity: 382) is added. After the tapping is completed, 180 kg / heat of steel refining agent (Al: 27.25%, Al2O3: 30.13%, CaO: 33.50%, SiO2: 3.97%, MgO: 4.52%, S: 0.02%, N: 0.004%) is added.

[0025] (3) Subsequently, the molten steel is sent to the RH station for vacuum treatment. After decarburization, the S content of the molten steel is measured to be 0.0025%. First, aluminum particles are added for deoxidation. The target values ​​of Si content in the steel are 3.10%, Al content 0.70%, and Mn content 0.50%. The alloy rough adjustment is controlled at more than 90% of the target composition. Then, 7.15 t of special silicon A (Si: 76.1%, Ti: 0.009%, P: 0.009%, S: 0.004%, C: 0.011%, Al: 0.01%, the rest is Fe and unavoidable impurities) is added for Si alloying, 1.47 t of aluminum particles (aluminum content 98.5%, the rest is iron and unavoidable impurities) is added for Al alloying, and 0.75 t of metallic manganese is added for Mn alloying. The above alloy increases sulfur content by approximately 0.0003%, resulting in an S content of approximately 0.0028% in the molten steel. The first batch of desulfurizing agent (CaF2: 28.59%, CaO: 62.83%, SiO2: 3.15%, S: 0.016%, TC: 0.14%) is added at 0.68 t (4 kg / t steel) for deep desulfurization. The RH argon circulation flow rate is set to 120 m³ / t. 3 / h.

[0026] (4) After the above alloy and desulfurizing agent are added, the molten steel is circulated. The amount of alloy added is 9.37 t, the amount of desulfurizing agent added is 0.68 t, and the net circulation time is t1 = 1 × 9.37 + 2.5 × 0.68 = 11 min.

[0027] (5) The sample test showed that the Si content in the steel was 3.00%, the Al content was 0.63%, the Mn content was 0.46%, and the S content was 0.0021%. According to the composition range requirements, 0.33 t of special silicon A and 0.12 t of aluminum granules were added, and 0.30 t of the second batch of desulfurizing agent (1.76 kg / t steel) was added for final desulfurization.

[0028] (6) After the second batch of alloy and desulfurizing agent is added, the molten steel is circulated. The amount of alloy added is 0.45t, the amount of desulfurizing agent added is 0.30t, the net circulation time t2≥1×0.45+2.5×0.30+6=7.2 min, and the actual net circulation time is 9 min.

[0029] (7) The composition of the slab in this furnace is C: 0.0021%, Si: 3.15%, Mn: 0.46%, P: 0.015%, S: 0.0018%, Als: 0.68%, N: 0.0027%, Ti: 0.0022%, which meets the requirements of W310.

[0030] (8) The number of high-grade non-oriented silicon steel coils with void defects induced by steelmaking inclusions in this furnace is 0, so the void defect rate is 0.00%. Example 2

[0031] This embodiment introduces a steelmaking method for reducing the porosity defect rate in cold-rolled high-grade non-oriented silicon steel, specifically referring to... Figure 1 As shown.

[0032] (1) The steel produced in this embodiment is W350, with the following composition range: C: ≤0.0030%, Si: 2.50%~2.70%, Mn: 0.20%~0.40%, P: ≤0.020%, S: ≤0.0020%, Als: 0.50%~0.70%, N≤0.0030%, Ti≤0.0030%, and the remainder is Fe and unavoidable impurities. Example 2 describes the smelting process control for one casting (6 heats).

[0033] (2) The nominal capacity of the RH station in this embodiment is 170 t. After the converter smelting is completed, top slag is added during the tapping process for forced modification. After the tapping amount reaches two-thirds, 250 kg / heat of special grade lime (CaO: 93.0%, SiO2: 0.8%, S: 0.019%, loss on ignition: 1.6%, lime activity: 374) is added. After the tapping is completed, 200 kg / heat of steel refining agent (Al: 29.50%, Al2O3: 27.63%, CaO: 35.15%, SiO2: 3.20%, MgO: 4.12%, S: 0.02%, N: 0.003%) is added.

[0034] (3) Subsequently, the molten steel was sent to the RH station for vacuum treatment. After decarburization, the S content of the molten steel in each furnace was measured as shown in Table 1. First, aluminum particles were added for deoxidation. The target Si content, Al content, and Mn content in the steel were controlled at 2.60%, 0.60%, and 0.30%, respectively. The alloy rough adjustment was controlled at more than 90% of the target composition. 5.80 t of special silicon A (Si: 75.7%, Ti: 0.009%, P: 0.009%, S: 0.005%, C: 0.009%, Al: 0.01%, with the remainder being Fe and unavoidable impurities) was added for Si alloying, 1.30 t of aluminum particles (aluminum content 98.5%, with the remainder being iron and unavoidable impurities) was added for Al alloying, and 0.40 t of metallic manganese (Mn: 99.7%, C: 0.03%, S: 0.04%, with the remainder being iron and unavoidable impurities) was added for Mn alloying. The above alloys have a sulfur content of 0.0003%. The first batch of desulfurizing agent (CaF2: 27.36%, CaO: 63.52%, SiO2: 3.39%, S: 0.017%, TC: 0.13%) is added in the amounts shown in Table 1. This is used for deep desulfurization, with the RH argon ring flow rate set at 125 m³ / h. 3 / h.

[0035] (4) After the above alloys and desulfurizing agents are added, the molten steel is circulated. The amount of alloy added is 7.50 t. The net circulation time t1 of each furnace is calculated according to the formula t1. See Table 1.

[0036] (5) Take samples to test the composition of molten steel and add alloy additives to fine-tune the composition of each element. According to the detected S content and the amount of alloy additives added, add the second batch of desulfurizing agent (see Table 1 for the specific amount added) for final desulfurization.

[0037] (6) After the second batch of alloy additives and desulfurizers are added, the molten steel net circulation begins. The lower limit of the net circulation time t2 for each furnace and the actual value are shown in Table 1 according to the t2 calculation formula.

[0038] (7) The composition of steel slabs for each furnace is shown in Table 2 and meets the requirements of W350.

[0039] (8) The total number of coils of high-grade non-oriented silicon steel after annealing in this casting batch of 6 heats is 174. The number of coils with void defects induced by steelmaking inclusions is 4, so the void defect rate is 2.30%.

[0040] Table 1. Feeding details and calculation parameters for each furnace run.

[0041] Table 2. Composition of steel slabs from each furnace (wt%) Comparative Example 1

[0042] This comparative example illustrates the conventional steelmaking method for high-grade non-oriented silicon steel, as follows: (1) In the traditional process, the steel grade W310 is produced with the following composition range: C: ≤0.0030%, Si: 3.00%~3.20%, Mn: 0.40%~0.60%, P: ≤0.020%, S: ≤0.0020%, Als: 0.60%~1.00%, N≤0.0030%, Ti≤0.0030%, and the remainder is Fe and unavoidable impurities.

[0043] (2) The nominal capacity of the RH station in this embodiment is 170 t. After the converter smelting is completed, top slag is added during the tapping process for forced modification. After the tapping amount reaches two-thirds, 220 kg / heat of special grade lime (CaO: 93.2%, SiO2: 0.8%, S: 0.018%, loss on ignition: 1.5%, lime activity: 369) is added. After the tapping is completed, 180 kg / heat of steel refining agent (Al: 26.31%, Al2O3: 31.48%, CaO: 33.72%, SiO2: 3.46%, MgO: 4.73%, S: 0.03%, N: 0.004%) is added.

[0044] (3) Subsequently, the molten steel was sent to the RH station for vacuum treatment. After decarburization, the S content of the molten steel was measured to be 0.0024%. First, aluminum particles were added for deoxidation. The Si content in the steel was 3.10%, the Al content was 0.70%, and the Mn content was 0.50%. The alloy roughing was controlled to be above 90% of the target composition. 7.20 t of special silicon A (Si: 75.6%, Ti: 0.008%, P: 0.008%, S: 0.004%, C: 0.009%, Al: 0.01%, the remainder being Fe and unavoidable impurities) was added for Si alloying, 1.52 t of aluminum particles (aluminum content 98.5%, the remainder being iron and unavoidable impurities) was added for Al alloying, and 0.75 t of metallic manganese was added for Mn alloying. The above alloys increased sulfur by about 0.0003%. After the alloys were added, the system was circulated for 10 min.

[0045] (4) The composition of each element was fine-tuned by adding a second batch of alloy additives to the sample according to its composition. The S content in the steel was 0.0027%, and the total amount of the second batch of alloy additives added was 0.45 t. At the same time, according to the S content in the steel, 5.0 kg / t of desulfurizing agent (CaF2: 27.82%, CaO: 63.17%, SiO2: 3.27%, S: 0.017%, TC: 0.13%) was added at once. After adding the desulfurizing agent, the net circulation time was 9 min.

[0046] (5) After adding the desulfurizing agent, the RH argon circulation flow rate is set to 120 m³ / h. 3 / h.

[0047] (6) The composition of the slab in this furnace is C: 0.0023%, Si: 3.11%, Mn: 0.48%, P: 0.013%, S: 0.0018%, Als: 0.71%, N: 0.0025%, Ti: 0.0025%, which meets the requirements of W310.

[0048] (7) The total number of coils of high-grade non-oriented silicon steel after annealing in this furnace is 30. The number of coils with void defects induced by steelmaking inclusions is 3, so the void defect rate is 10.00%.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A steelmaking method for reducing the porosity defect rate in cold-rolled high-grade non-oriented silicon steel, characterized in that, Includes the following steps: (1) After the converter smelting is completed, the slag entering the ladle from the converter is forcibly modified during the tapping process. First, after the tapping amount reaches two-thirds, 200-350 kg / heat of special grade lime is added to the surface of the molten steel in the ladle, and then 150-300 kg / heat of steel refining agent is added after the tapping is completed. (2) Subsequently, the molten steel is sent to the RH station for vacuum treatment. After decarburization, it is deoxidized and then alloyed, and desulfurizing agent is added in batches according to the composition of the molten steel. (3) Dynamically control the net RH cycle time: Determine and execute the net cycle time based on the amount of alloy and desulfurizer added in step (2).

2. The method according to claim 1, characterized in that, In step (1), the extra-grade lime comprises the following components by mass percentage: CaO ≥ 92.0%, SiO2 ≤ 1.5%, S ≤ 0.020%, loss on ignition ≤ 2%, and lime activity ≥ 360.

3. The method according to claim 1, characterized in that, In step (1), the refining agent comprises the following components by mass percentage: Al: 20-35%, Al2O3: 25-35%, CaO: 20-40%, SiO2 < 5.0%, MgO: 2-6%, S < 0.05%, N < 0.005%.

4. The method according to claim 1, characterized in that, In step (2), the desulfurizing agent includes the following components, by mass percentage: CaF2≥25%, CaO:50~65%, SiO2<3.5%, S<0.020%, TC<0.15%.

5. The method according to claim 1, characterized in that, In step (2), the specific order of adding desulfurizing agent in batches is as follows: the first batch of desulfurizing agent is added according to the initial S content of the molten steel and the amount of alloy added, wherein the coarse alloying adjustment ensures that the content of Si, Als and Mn components is above 90% of the target composition; after fine adjustment of the alloy element composition, the second batch of desulfurizing agent is added according to the S content in the steel, at which time it is ensured that each alloy element has reached the target composition.

6. The method according to claim 5, characterized in that, In step (2), the desulfurizing agent is added after deoxidation is completed, the alloy is added first and then the desulfurizing agent is added. The first batch of desulfurizing agent is added at ≤10 kg / t steel for deep desulfurization. The second batch of desulfurizing agent is added or not added according to the S content in the steel. When added, the amount is ≤3 kg / t steel for final sulfur control.

7. The method according to claim 1, characterized in that, In step (2), after adding the desulfurizing agent, the RH argon gas circulation flow rate is set to 120-130 m³ / h. 3 / h.

8. The method according to claim 1, characterized in that, The method for determining the net cycle time in step (3) is as follows: When materials are added in batches, the net circulation time after the first batch is added is t1 (min), and the net circulation time after the second batch is added is not less than t2 (min), where: t1 = 1 × A + 2.5 × B; t2 = 1 × A' + 2.5 × B' + 6; In the formula, A and A' represent the total weight of the alloy added in the first and second batches, respectively, in tons; B and B' represent the total weight of the desulfurizer added in the first and second batches, respectively, in tons.

9. The method according to claim 1, characterized in that, The chemical composition of the high-grade non-oriented silicon steel, by mass percentage, includes: C≤0.0030%, Si: 2.50~3.50%, Mn: 0.15~0.60%, P≤0.020%, S≤0.0020%, Als: 0.50~1.00%, N≤0.0030%, Ti≤0.0030%, with the remainder being Fe and unavoidable impurities.

10. The method according to claim 1, characterized in that, The high-grade non-oriented silicon steel cold-rolled sheet produced by the method has a porosity of less than 3.5% due to inclusions induced during steelmaking.

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