Method for improving hit rate of acid-soluble aluminum narrow component of oriented silicon steel and application

Abstract

The invention provides a method for improving the hit rate of acid-soluble aluminum narrow components of oriented silicon steel and application. Comprising the following steps that after an RH vacuum treatment procedure is completed and before continuous casting, the content of acid-soluble aluminum in molten steel is detected, if the content is lower than 0.020 wt%, aluminum is supplemented into a steel ladle, and the content of the acid-soluble aluminum is adjusted to be within the range of 0.020 wt%-0.035 wt%. According to the method, in a process window after RH vacuum treatment and before continuous casting, the content of acid-soluble aluminum (Als) is difficult to quickly, accurately and stably regulate and control to a target range of 0.020 wt%-0.035 wt%, so that the technical problems that the magnetic performance fluctuation of oriented silicon steel (especially high-magnetic-induction Hi-B steel) is large, the high-grade yield is low and the production cost is high are solved.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a method and its application for improving the narrow composition hit rate of acid-soluble aluminum in grain-oriented silicon steel. Background Technology

[0002] Electrical steel, as a core soft magnetic material in the power and electronics industries, is mainly divided into two categories: grain-oriented silicon steel and non-oriented silicon steel. Grain-oriented silicon steel, with its excellent magnetic properties along the rolling direction, is widely used in high-efficiency electrical equipment such as transformer cores. Based on production processes and magnetic performance levels, grain-oriented silicon steel can be further subdivided into low-temperature high-magnetic-induction grain-oriented silicon steel (Hi-B) and ordinary grain-oriented silicon steel (CGO). In the production of high-magnetic-induction grain-oriented silicon steel (Hi-B steel) using traditional processes (i.e., using AlN as the main inhibitor), acid-soluble aluminum (Als) plays a crucial role. Its content is one of the core factors determining the final product's magnetic properties (iron loss, magnetic induction) and microstructure. Its mechanism and impact are as follows: When the Als content in the steel is insufficient, a sufficient number and appropriately sized AlN inhibitor particles cannot be formed during subsequent heat treatment. The weakening of the inhibitor's effect leads to premature and disordered abnormal growth of the primary recrystallized grains during the high-temperature annealing stage, making it difficult to ultimately form a single, strong Gaussian texture. As a result, the final product exhibits reduced magnetic flux density and increased iron loss, failing to meet the performance requirements of high-grade Hi-B steel. Conversely, if the Al content is too high, coarse AlN particles or clusters are easily formed. These coarse particles have poor pinning effect on grain boundary migration and cannot effectively inhibit the normal growth of primary recrystallized grains, thus impairing the perfection of the Gaussian texture and leading to a deterioration in the product's magnetic properties.

[0003] Therefore, precisely controlling the acid-soluble aluminum (Als) content in molten steel within an extremely narrow range is a prerequisite for the stable production of high-magnetic-induction, low-iron-loss grain-oriented silicon steel. In actual large-scale industrial production, especially in the steel composition adjustment stage after RH vacuum treatment, achieving a high hit rate for narrow-component acid-soluble aluminum (Als) composition faces significant challenges due to fluctuations in multiple factors such as temperature, time, and alloy yield. Low Als composition hit rate directly leads to large fluctuations in product magnetic properties and low yield of high-grade steel, resulting in serious economic losses. Therefore, there is an urgent need to develop a method to stably control the acid-soluble aluminum content in molten steel to solve the industry bottleneck problem of low narrow-component hit rate, thereby significantly improving the production efficiency and product consistency of high-grade grain-oriented silicon steel. Summary of the Invention

[0004] The main objective of this invention is to provide a method and its application for improving the narrow content hit rate of acid-soluble aluminum in grain-oriented silicon steel. This aims to solve the technical problems in the prior art, where it is difficult to quickly, accurately, and stably control the acid-soluble aluminum (Als) content to the target range of 0.020wt%~0.035wt% within the process window after RH vacuum treatment and before continuous casting. This results in large fluctuations in the magnetic properties of grain-oriented silicon steel (especially high magnetic induction Hi-B steel), low yield of high-grade steel, and high production costs.

[0005] To achieve the above objectives, the present invention provides a method for improving the narrow content hit rate of acid-soluble aluminum in oriented silicon steel, comprising the following steps: after the RH vacuum treatment process is completed and before continuous casting, the acid-soluble aluminum content of the molten steel is detected. If the content is lower than 0.020wt%, aluminum is added to the ladle to adjust the acid-soluble aluminum content to the range of 0.020wt% to 0.035wt%.

[0006] 1. Under the above conditions, precise control of the acid-soluble aluminum content in molten steel is achieved through RH treatment followed by detection and immediate aluminum replenishment. Maintaining the acid-soluble aluminum content within the optimized narrow range of 0.020wt% to 0.035wt% significantly improves the component hit rate of acid-soluble aluminum during smelting. This avoids insufficient inhibitors due to excessively low aluminum content and prevents the precipitation of coarse AlN caused by excessively high aluminum content, thus providing a stable and consistent raw material foundation for subsequent processes.

[0007] 2. Acid-soluble aluminum is a key element in the formation of AlN inhibitors. Increasing and stabilizing acid-soluble aluminum within the aforementioned range ensures sufficient bonding between Al and nitrogen in the steel, resulting in a sufficient quantity of fine-sized, uniformly distributed AlN precipitates during hot rolling and subsequent annealing. These fine, dispersed AlN particles effectively pin grain boundaries, inhibiting abnormal grain growth during primary recrystallization, thereby significantly improving the magnetic induction intensity of grain-oriented silicon steel and reducing iron loss.

[0008] 3. This method sets the aluminum replenishment operation after RH treatment and before continuous casting. At this time, the molten steel has high cleanliness and uniform temperature, which is conducive to the rapid melting of aluminum and the homogenization of composition. This avoids the vacuum fluctuations and compositional interference that may be caused by aluminum replenishment during RH treatment, and also prevents structural defects in the billet caused by insufficient aluminum content during continuous casting. Therefore, this method is suitable for large-scale continuous production and can significantly improve the stability and consistency of magnetic properties of products from different heats and batches, thereby increasing the yield of high-grade grain-oriented silicon steel.

[0009] According to some embodiments of the present invention, the addition of aluminum to the ladle is carried out by the following steps: inserting an aluminum rod into the molten steel inside the ladle.

[0010] According to some embodiments of the present invention, the addition of aluminum to the ladle is carried out by the following steps: inserting an aluminum rod into the molten steel inside the ladle.

[0011] In this invention, a solid aluminum rod is directly inserted into the molten steel to replenish aluminum. The aluminum rod melts and dissolves rapidly in the high-temperature molten steel, and the aluminum element directly enters the molten steel body, avoiding problems such as residual cladding material, floating aluminum wire, or entanglement in slag that may occur with traditional wire feeding methods.

[0012] After an aluminum rod is inserted into molten steel, it creates a localized high-aluminum concentration zone within the molten area. Under the influence of bottom-blowing argon stirring in the ladle or natural convection via RH, aluminum rapidly diffuses throughout the molten steel pool. Compared to adding aluminum ingots or granules to the slag surface, the insertion method reduces aluminum oxidation loss in the slag and utilizes the strong convection of the molten steel itself to achieve rapid homogenization of aluminum. This shortens the settling time required for composition adjustment, facilitating seamless integration with subsequent continuous casting processes and improving production speed.

[0013] Because the aluminum rod is directly inserted into the molten steel, prolonged contact with the slag is avoided, reducing the risk of non-metallic inclusions formed due to the reaction of aluminum with unstable oxides in the slag. At the same time, this method avoids introducing additional refractory materials or cladding impurities into the molten steel, which helps maintain or improve the purity of the molten steel, crucial for the production of high-quality grain-oriented silicon steel.

[0014] When an aluminum rod is inserted into molten steel, its rapid melting is essentially a mass transfer process from aluminum atoms into the molten steel. Under the strong convection of the molten steel, the newly added aluminum atoms disperse rapidly and react with the dissolved nitrogen atoms in the steel, providing a sufficient aluminum source for the subsequent formation of AlN inhibitors. By precisely increasing the acid-soluble aluminum content to an optimized window of 0.020wt%–0.035wt%, a suitable activity product is ensured in the molten steel. During the subsequent solidification of the cast billet and the hot rolling process, this activity product condition is conducive to the precipitation of AlN from austenite in a fine, dispersed form. This results in excellent magnetic properties with high magnetic induction and low iron loss.

[0015] According to some embodiments of the present invention, the aluminum rod has a diameter of 50-80 mm, a length of 1500-2500 mm, and an insertion depth of 500-800 mm below the surface of the molten steel.

[0016] Under the above conditions, when inserted into molten steel at high temperatures, the aluminum rod rapidly absorbs heat and melts completely, avoiding instantaneous vaporization or premature melting due to an insufficient diameter, or uneven melting and residual unmelted aluminum pieces due to an excessively large diameter. With a length of 1500-2500mm, it provides sufficient aluminum mass for single-use replenishment, suitable for the aluminum adjustment needs of large-capacity ladles. This size combination allows the aluminum rod to continuously and stably release aluminum into the molten steel during the melting process, further improving and stabilizing the aluminum recovery rate at over 90%, ensuring the accuracy and predictability of the replenishment amount.

[0017] Setting the insertion depth of the aluminum rod to 500-800mm below the molten steel surface effectively avoids the risk of high-alumina areas near the slag-steel interface being drawn into the slag. This accelerates the macroscopic transport and microscopic diffusion of aluminum throughout the molten steel volume. The added aluminum allows the molten steel to achieve compositional stability within minutes, providing highly homogeneous steel for subsequent continuous casting processes and fundamentally improving compositional consistency within and between slabs.

[0018] Using aluminum bars of the aforementioned dimensions and insertion depth, the melting process has a controllable and minor impact on the temperature of the molten steel. Since the heat absorption and heating process of aluminum melting mainly occurs inside the aluminum bar and in the adjacent thin layer of molten steel, and the amount of aluminum added is relatively small compared to the total amount of molten steel (usually on the order of kilograms), the impact on the overall thermal balance of the ladle is minimal, and it will not cause significant fluctuations in the temperature of the molten steel.

[0019] The deeper insertion depth (500-800 mm) ensures that the melting process of the aluminum rod takes place entirely within the molten steel, maximizing the isolation of air and slag. The aluminum droplets are thoroughly mixed with the molten steel before rising to the slag, significantly reducing the likelihood and extent of their reaction with oxidizing components in the slag. This not only further improves the actual aluminum yield but also significantly reduces the risk of large inclusions formed due to secondary oxidation of aluminum.

[0020] According to some embodiments of the present invention, the aluminum rod is inserted into the molten steel via an extension inserter, the extension inserter comprising an aluminum rod sleeve and a fixing bolt, the aluminum rod sleeve for accommodating the aluminum rod, and the fixing bolt for fixing the aluminum rod inside the sleeve.

[0021] According to some embodiments of the present invention, the detection of the acid-soluble aluminum content is completed within 5 to 8 minutes after the RH vacuum treatment process, and an aluminum replenishment operation is performed within 2 minutes after the detection is completed.

[0022] According to some embodiments of the present invention, the aluminum replenishment operation is performed in an inert gas atmosphere.

[0023] According to some embodiments of the present invention, the aluminum content of the molten steel after aluminum supplementation is 0.022wt% to 0.032wt%.

[0024] Under the above conditions, the acid-soluble aluminum content was further precisely controlled within the range of 0.022wt% to 0.032wt%, providing the ideal aluminum source concentration for the precipitation of AlN inhibitors. This ensures the formation of sufficient quantity, fine size, and highly dispersed AlN particles in subsequent processes. This narrow compositional window is the optimal range determined by experimental and mechanistic studies. Within this range, the magnetic induction intensity of the product reaches its peak, while iron loss is minimized.

[0025] The present invention also provides an electrical steel, which is manufactured by the method described above for improving the narrow composition hit rate of acid-soluble aluminum in oriented silicon steel.

[0026] According to some embodiments of the present invention, the electrical steel includes oriented silicon steel, which includes low-temperature high-magnetic-induction oriented silicon steel and ordinary oriented silicon steel. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0029] To further illustrate the present invention, the following examples are provided: Example 1 A1. A 210-ton oxygen converter is used, with 170 tons of molten iron and 45 tons of scrap steel charged into the converter. The molten iron temperature is 1350℃. Conventional dephosphorization and decarburization blowing processes are used in the converter smelting process. After blowing, the steel is tapped. During the tapping process, lime and a small amount of synthetic slag are added to the ladle to improve the ladle slag system. In the later stage of tapping, ferrosilicon, ferromanganese and a small amount of aluminum blocks are added for pre-deoxidation treatment. The final steel temperature at the tapping point is controlled at 1620℃. A2. Ferrosilicon is added to the ladle containing molten steel during the tapping process. After tapping, the ladle is immediately covered and kept warm. It is then gently stirred with bottom-blown argon (flow rate of 30 NL / min, time of 5 min) to homogenize the composition and temperature. The ladle is then directly sent to the working position of the RH vacuum refining furnace. A3. The molten steel is circulated under vacuum conditions with the furnace pressure reduced to ≤5kPa. After the composition is adjusted upon entering the station, the pump is depressurized and nitrogen is added. The vacuum degree is reduced to 7.8Kpa. After A4.RH vacuum treatment, a sample is taken from the middle of the ladle, and the acid-soluble aluminum content is measured to be 0.016 wt%. When the acid-soluble aluminum content is found to be lower than the target lower limit of 0.020 wt%, an aluminum replenishment operation is performed within 2 minutes after the test: a metal aluminum rod with a diameter of 60 mm and a length of 2000 mm is inserted into the molten steel in the ladle to a depth of approximately 600 mm below the molten steel surface. The aluminum replenishment operation is carried out while the ladle is covered to prevent secondary oxidation of the molten steel. A5. After aluminum addition, the molten steel is allowed to stand for 6 minutes to allow the aluminum to fully dissolve and distribute evenly before being sent to the continuous casting process. Before continuous casting, a sample is taken again from the same location for testing, and the acid-soluble aluminum content is 0.025 wt%. In Example 1, after the RH vacuum treatment, a sample of molten steel was taken from the middle of the ladle, and the acid-soluble aluminum content was measured. The result was 0.016 wt%. After the aluminum replenishment operation was completed and the sample was allowed to stand for 6 minutes, a sample was taken again from the same sampling location before continuous casting, and the acid-soluble aluminum content was measured using the same detection method. The result was 0.025 wt%. Using an acid-soluble aluminum content of 0.020–0.035 wt% as the composition hit criterion, statistics were compiled on 50 heats of molten steel produced using the method of this example. Among them, the acid-soluble aluminum content of 46 heats fell within the above target range, and the narrow composition hit rate of acid-soluble aluminum reached 91%.

[0030] Meanwhile, online monitoring of inclusions in molten steel and macroscopic inspection of the continuously cast billet during the continuous casting process revealed no obvious aluminum oxide inclusion defects, indicating that this method can maintain the cleanliness of molten steel while ensuring the composition is accurate.

[0031] Example 2 A1. A 210-ton oxygen converter is used, with 175 tons of molten iron and 40 tons of scrap steel charged into the converter. The molten iron temperature is 1360℃. Conventional dephosphorization and decarburization blowing processes are used in the converter smelting process. After blowing, the steel is tapped. During the tapping process, lime and a small amount of synthetic slag are added to the ladle to improve the ladle slag system. A2. Ferrosilicon is added to the ladle containing molten steel during the tapping process. After tapping, the ladle is immediately covered and kept warm. It is then gently stirred with bottom-blown argon (flow rate of 30 NL / min, time of 5 min) to homogenize the composition and temperature. The ladle is then directly sent to the working position of the RH vacuum refining furnace. A3. The molten steel is circulated under vacuum conditions with the furnace pressure reduced to ≤5kPa. After the composition is adjusted upon entering the station, the pump is depressurized and nitrogen is added. The vacuum degree is reduced to 7.8Kpa. A4. Five minutes after the RH vacuum treatment is completed, the molten steel in the ladle is sampled and analyzed. The acid-soluble aluminum content of the molten steel is detected to be 0.018 wt%. When the acid-soluble aluminum content of the molten steel is detected to be lower than 0.020 wt%, an aluminum replenishment operation is carried out within 2 minutes after the test. A metal aluminum rod with a diameter of 70 mm and a length of 2200 mm is inserted into the molten steel in the ladle. The insertion depth of the aluminum rod is about 700 mm below the surface of the molten steel. A5. After aluminum replenishment, the molten steel was allowed to stand for another 7 minutes before being sent to the continuous casting process. After aluminum replenishment, the acid-soluble aluminum content of the molten steel was tested and found to be 0.028 wt%, which is within the target control range of 0.020 to 0.035 wt%. In Example 2, molten steel was sampled and analyzed 5 minutes after RH vacuum treatment. The acid-soluble aluminum content was determined using OES spectrophotometry, and the result was 0.018 wt%. After aluminum replenishment and a 7-minute settling period, a second sample was taken, and the acid-soluble aluminum content was 0.028 wt%. Using 60 consecutive heats of molten steel as a statistical sample, the results showed that the acid-soluble aluminum content in 55 heats remained consistently within the range of 0.022–0.032 wt%, achieving a 92% accuracy rate.

[0032] Testing of the magnetic properties of the finished grain-oriented silicon steel showed a significant improvement in product consistency compared to steel produced without this method.

[0033] Example 3 A1. A 210-ton oxygen converter is used, with 168 tons of molten iron and 47 tons of scrap steel charged into the converter at a temperature of 1345℃. After the converter blowing process, steel is tapped. During tapping, lime and refining slag are added to the ladle to adjust the ladle slag system. A2. Ferrosilicon is added to the ladle containing molten steel during the tapping process. After tapping, the ladle is immediately covered and kept warm. It is then gently stirred with bottom-blown argon (flow rate of 30 NL / min, time of 5 min) to homogenize the composition and temperature. The ladle is then directly sent to the working position of the RH vacuum refining furnace. A3. The molten steel is circulated under vacuum conditions with the furnace pressure reduced to ≤5kPa. After the composition is adjusted upon entering the station, the pump is depressurized and nitrogen is added. The vacuum degree is reduced to 7.8Kpa. A4. Seven minutes after the RH vacuum treatment is completed, the molten steel in the ladle is sampled and analyzed. The acid-soluble aluminum content of the molten steel is detected to be 0.015 wt%. When the acid-soluble aluminum content of the molten steel is detected to be lower than 0.020 wt%, aluminum replenishment is performed within 2 minutes after the detection is completed using an extension inserter. The extension inserter includes an aluminum rod sleeve and a fixing bolt. A metal aluminum rod with a diameter of 80 mm and a length of 2500 mm is fixed in the aluminum rod sleeve and inserted into the molten steel to a depth of about 800 mm below the surface of the molten steel. A5. After aluminum replenishment, the molten steel was allowed to stand for another 6 minutes before being sent to the continuous casting process. The acid-soluble aluminum content of the molten steel after aluminum replenishment was measured to be 0.030 wt%. In Example 3, a statistical analysis was performed on 45 heats of molten steel that were continuously supplemented with aluminum using an extended inserter. Among them, the acid-soluble aluminum content of 42 heats of molten steel was within the target range of 0.020 to 0.035 wt%, and the acid-soluble aluminum hit rate reached 93%.

[0034] Comparative Example 1 The only difference between this comparative example and Example 1 is the timing of aluminum replenishment; all other smelting conditions, aluminum rod specifications, insertion depth, and testing methods are the same as in Example 1.

[0035] Specifically, in Comparative Example 1, an aluminum rod with a diameter of 60 mm and a length of 2000 mm was inserted into the molten steel in the ladle before RH vacuum treatment. The insertion depth was 600 mm below the surface of the molten steel. After aluminum replenishment, the ladle entered the RH vacuum refining furnace for vacuum treatment, which lasted for 15 minutes.

[0036] A statistical analysis of 50 consecutive heats of molten steel revealed that only 34 heats had acid-soluble aluminum content within the target range, resulting in a narrow acid-soluble aluminum content hit rate of 68%. This indicates that when aluminum is added before RH vacuum treatment, significant aluminum loss occurs during subsequent vacuum treatment, making it difficult to achieve stable control of acid-soluble aluminum.

[0037] Comparative Example 2 The only difference between Comparative Example 2 and Example 3 is the insertion depth of the aluminum rod. All other process conditions, timing of aluminum replenishment, aluminum rod specifications, and testing methods are the same as in Example 3.

[0038] Statistical analysis of 45 consecutive heats of molten steel showed that the average acid-dissolved aluminum content was 0.024 wt%, with a fluctuation range of ±0.005 wt% between heats. Only 31 heats met the control requirement of 0.020–0.035 wt% for acid-dissolved aluminum content, resulting in a success rate of 69%. This indicates that when the aluminum rod insertion depth is insufficient, aluminum mainly melts in the upper layer of the molten steel, easily reacting with ladle slag and air, making it difficult to achieve stable narrow composition control.

[0039] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the specification and contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for improving the narrow composition hit rate of acid-soluble aluminum in grain-oriented silicon steel, characterized in that, Includes the following steps: After the RH vacuum treatment process is completed and before continuous casting, the acid-soluble aluminum content of the molten steel is tested. If the content is lower than 0.020wt%, aluminum is added to the ladle to adjust the acid-soluble aluminum content to the range of 0.020wt% to 0.035wt%.

2. The method according to claim 1, characterized in that, The process of adding aluminum to the ladle is carried out by the following steps: inserting an aluminum rod into the molten steel inside the ladle.

3. The method according to claim 1, characterized in that, The aluminum rod has a diameter of 50-80 mm, a length of 1500-2500 mm, and an insertion depth of 500-800 mm below the surface of the molten steel.

4. The method according to claim 1, characterized in that, The aluminum rod is inserted into the molten steel through an extension inserter, which includes an aluminum rod sleeve and a fixing bolt. The aluminum rod sleeve is used to accommodate the aluminum rod, and the fixing bolt is used to fix the aluminum rod inside the sleeve.

5. The method according to claim 1, characterized in that, The detection of the acid-soluble aluminum content is completed within 5 to 8 minutes after the RH vacuum treatment process, and the aluminum replenishment operation is performed within 2 minutes after the detection is completed.

6. The method according to claim 5, characterized in that, The aluminum replenishment operation is performed in an inert gas atmosphere.

7. The method according to claim 5, characterized in that, After aluminum supplementation, the acid-soluble aluminum content in the molten steel is 0.022wt% to 0.032wt%.

8. The method according to claim 5, characterized in that, The time interval between the completion of the aluminum replenishment operation and the continuous casting is 6-8 minutes.

9. An electrical steel, characterized in that, It is manufactured by the method described in any one of claims 1 to 8.

10. The method according to claim 9, characterized in that, The electrical steel includes grain-oriented silicon steel, which includes low-temperature high-magnetic-induction grain-oriented silicon steel and ordinary grain-oriented silicon steel.