Low temperature preannealing production method for grain oriented silicon steel

Abstract

The application discloses a low-temperature pre-annealing production method of oriented silicon steel, and realizes the low-temperature pre-annealing production method by using a low-temperature pre-annealing furnace, and comprises the following steps: step 1, a vertical steel coil (4) is arranged in a furnace body (1) through a sealing device (3), a heating system (2) is used for heating the furnace temperature in the furnace body from normal temperature to a first temperature, the first temperature is greater than or equal to an MgO dehydration temperature, the furnace temperature is less than or equal to 950 DEG C, water in an MgO coating on a surface of the vertical steel coil is decomposed and discharged, and a cold spot (41) of the vertical steel coil reaches a temperature higher than the MgO dehydration temperature; and step 2, after the low-temperature pre-annealing is completed, a temperature difference between the cold spot and a hot spot (42) of the vertical steel coil is not more than a temperature difference threshold value, and subsequent high-temperature annealing production is carried out on the vertical steel coil. The application can break through the capacity limitation of a conventional high-temperature annealing process, greatly improves the yield on the basis of guaranteeing the production quality, and simultaneously improves the problem of poor production and process flexibility of the high-temperature annealing process.

Description

Technical Field

[0001] This invention relates to a production process for grain-oriented silicon steel, and more particularly to a low-temperature pre-annealing production method for grain-oriented silicon steel. Background Technology

[0002] Grain-oriented silicon steel is an indispensable soft magnetic material in the power and defense industries. The core technology of grain-oriented silicon steel utilizes fine, dispersed second-phase particles to suppress the normal growth of primary recrystallized grains, and leverages the interfacial energy difference between grains with different orientations to complete secondary recrystallization during high-temperature annealing, forming a sharp Goss texture. Besides secondary recrystallization, the metallurgical purpose of high-temperature annealing also includes: allowing the MgO coating on the steel plate surface to chemically react with the SiO2 in the surface oxide film to form a Mg2SiO4 underlayer. This underlayer can both combine with the insulating coating to improve the product's insulation performance and prevent inhibitors such as AlN from being oxidized or nitrided during high-temperature annealing, thus preventing the loss or reduction of their inhibitory effect; and purifying the steel plate by holding it at approximately 1200℃ for an extended period to remove excess S, N, and other impurities.

[0003] The existing high-temperature annealing process for grain-oriented silicon steel includes five stages: primary heating, low-temperature holding, secondary heating, high-temperature holding, and cooling. In the primary heating stage, the decarburized steel coil is flipped from a horizontal coil to a vertical coil and loaded into the furnace. Nitrogen or a hydrogen-nitrogen mixture containing a certain proportion of hydrogen replaces the air, heating the coil to 350–450°C, at which point the bound water (MgOH)2 in the MgO coating on the strip surface begins to decompose. The low-temperature holding stage removes free and bound water from the MgO, reducing the temperature difference between hot and cold spots. The secondary heating stage involves heating at a certain rate, forming a magnesium silicate underlayer and promoting secondary recrystallization. The high-temperature holding stage, after secondary recrystallization and the formation of the underlayer, involves holding at approximately 1200°C for about 20 hours to remove impurities and eliminate magnetic aging issues. The cooling stage involves cooling the steel coil to approximately 300°C before unloading from the furnace. The entire high-temperature annealing process takes 6–8 days, which is relatively long.

[0004] Existing high-temperature annealing equipment for grain-oriented silicon steel includes bell-type annealing furnaces, annular annealing furnaces, and tunnel annealing furnaces. Bell-type annealing furnaces have low production efficiency and high energy consumption, making them unsuitable for large-scale production. While annular and tunnel annealing furnaces can increase annual production capacity to some extent, their capacity is relatively fixed and difficult to increase effectively after construction due to limitations imposed by physical conditions such as loading capacity and heating zones; they also suffer from poor production and process flexibility and inconsistent quality.

[0005] Chinese invention patent ZL201610678352.1 discloses a tunnel-type continuous high-temperature annealing process for grain-oriented silicon steel, achieving continuous annealing production of grain-oriented silicon steel: The process involves loading the furnace, moving a trolley loaded with steel coils to the furnace inlet via auxiliary rails, and then pushing the trolley into the furnace for annealing using hydraulic pushers. After cooling and unloading, the grain-oriented silicon steel is purged with protective gas throughout the sealed hood of the entire annealing furnace. The process then involves unloading, repairing the trolley, and repeating the above steps to achieve continuous annealing. However, this high-temperature annealing process uses a tunnel-type annealing furnace. Once built, its production capacity is limited by physical conditions such as loading capacity and heating zones, making it difficult to significantly increase production capacity. Furthermore, it suffers from poor production and process flexibility, and inconsistent quality. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature pre-annealing production method for grain-oriented silicon steel. This low-temperature annealing production method is achieved by adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace, which can overcome the capacity limitations of conventional high-temperature annealing processes, significantly increase output while ensuring production quality, and improve the problem of poor production and process flexibility in the high-temperature annealing process.

[0007] This invention is implemented as follows:

[0008] A method for producing oriented silicon steel by low-temperature pre-annealing, wherein the low-temperature pre-annealing production method is implemented by a low-temperature pre-annealing furnace, the low-temperature pre-annealing furnace includes a furnace body, a heating system disposed on the inner wall of the furnace body, and a number of sealing devices arranged in the furnace body, wherein a vertical steel coil is disposed in the sealing device, and the surface of the strip steel of the vertical steel coil is coated with an MgO coating.

[0009] The low-temperature pre-annealing production method for the grain-oriented silicon steel includes the following steps:

[0010] Step 1: The vertical steel coil is placed in the furnace body through a sealing device. The furnace temperature inside the furnace body is heated from room temperature to a first temperature through the heating system. The first temperature is ≥ MgO dehydration temperature and the furnace temperature is ≤ 950℃. This causes the water in the MgO coating on the surface of the vertical steel coil to decompose and be discharged, and the cold point temperature of the vertical steel coil reaches above the MgO dehydration temperature.

[0011] Step 2: After the low-temperature pre-annealing is completed, the temperature difference between the cold point and the hot point of the vertical steel coil does not exceed the temperature difference threshold. The vertical steel coil will then undergo subsequent high-temperature annealing production.

[0012] In step 1, the heating system can be either single-stage heating or multi-stage heating. After single-stage heating, the furnace temperature is raised to the first temperature by heat preservation or cooling. During multi-stage heating, the furnace temperature is raised to the first temperature by heat preservation or cooling.

[0013] In step 1, the dehydration temperature of MgO is in the range of ≥210℃, and the first temperature range is 210-950℃.

[0014] The range of the first temperature is 300-950℃.

[0015] In step 1, the cold spot of the vertical steel coil is located at the intersection of the centerline of the coil thickness and the centerline of the coil height, and the cold spot temperature of the vertical steel coil is ≥210℃.

[0016] The cold point temperature of the vertical steel coil is ≥300℃.

[0017] In step 2, the temperature difference threshold between the cold and hot points of the vertical steel coil is ≤350℃.

[0018] The annual production capacity Q of the low-temperature pre-annealing process is mentioned. 预 for:

[0019] Wherein, Q0 is the annual production capacity of vertical steel coils without low-temperature pre-annealing, H0 is the minimum moving cycle of vertical steel coils without low-temperature pre-annealing in the high-temperature annealing furnace, and H1 is the minimum moving cycle of vertical steel coils with low-temperature pre-annealing in the high-temperature annealing furnace.

[0020] During the low-temperature pre-annealing process, a protective gas is introduced into each sealing device. The protective gas is a non-oxidizing atmosphere.

[0021] The total production time for the low-temperature pre-annealing process is less than 60 hours.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. By adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace for annealing, this invention ensures more thorough decomposition and removal of water from the MgO coating at different locations on the steel coil, resulting in better uniformity of steel coil quality and magnetic properties. On the other hand, it solves the bottleneck problem of current high-temperature annealing furnaces, which are limited by physical conditions such as loading capacity and heating zones, without requiring high investment, thus significantly increasing production capacity.

[0024] 2. This invention adds a low-temperature pre-annealing furnace before the high-temperature annealing furnace for annealing. On the one hand, this facilitates flexible process adjustments for different thicknesses, widths, and other specifications during the low-temperature pre-annealing furnace stage, thereby further improving product quality. On the other hand, since some processes are completed in the low-temperature pre-annealing furnace, it increases the possibility and flexibility for subsequent high-temperature annealing adjustments. For example, it can significantly reduce the minimum moving cycle of steel coils and extend the cooling time in conventional high-temperature annealing processes, thereby reducing the occurrence of waviness defects, improving the process flexibility of conventional high-temperature annealing processes, and more flexibly matching the production capacity of the preceding and following processes.

[0025] This invention achieves its purpose by adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace. This significantly breaks through the capacity limitations of conventional high-temperature annealing processes, increases output and production efficiency while ensuring and further improving product quality, and addresses the issues of poor production and process flexibility in the high-temperature annealing process. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of the low-temperature pre-annealing furnace used in the low-temperature pre-annealing production method of the oriented silicon steel of this invention.

[0027] Figure 2 yes Figure 1 A cross-sectional view of a neutral steel coil;

[0028] Figure 3 This is a schematic diagram of the weight loss curves of three MgO coatings on oriented silicon steel used in the low-temperature pre-annealing production method of oriented silicon steel of the present invention.

[0029] Figure 4 This is a temperature-time curve diagram of six heating methods in the heating system of the low-temperature pre-annealing production method of oriented silicon steel of the present invention.

[0030] In the diagram, 1 is the furnace body, 2 is the heating system, 3 is the sealing device, 4 is the vertical steel coil, 41 is the cold point, and 42 is the hot point. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] A method for producing grain-oriented silicon steel using low-temperature pre-annealing, wherein the low-temperature pre-annealing is achieved by adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace. Please refer to the appendix. Figure 1The low-temperature pre-annealing furnace includes a furnace body 1, a heating system 2 installed on the inner wall of the furnace body 1, and several sealing devices 3 arranged in a matrix or other form within the furnace body 1. Grain-oriented silicon steel is wound into vertical steel coils 4 and placed within the sealing devices 3. The surface of the vertical steel coils 4 is coated with an MgO coating. The sealing devices 3 can be moved or fixed within the furnace body 1 for heating, ensuring uniform heating of each vertical steel coil 4. Each sealing device 3 can hold one vertical steel coil 4, or multiple vertical steel coils 4 can be stacked longitudinally. This allows vertical steel coils 4 of different specifications of grain-oriented silicon steel to be arranged in layers or rows within the furnace body 1 and simultaneously subjected to low-temperature pre-annealing treatment. This provides greater flexibility in the configuration of grain-oriented silicon steel. This invention is applicable to all specifications of grain-oriented silicon steel and other products requiring annealing processes.

[0033] The vertical steel coil 4 has an MgO coating on its surface before high-temperature annealing. The MgO coating contains a certain mass fraction of free water and chemically bound water. The primary heating section and low-temperature holding section of the conventional high-temperature annealing process are mainly for removing moisture from the MgO coating. By adding a low-temperature pre-annealing furnace, the moisture in the MgO coating can be effectively removed, thus making the conventional high-temperature annealing process more flexible in its configuration.

[0034] Please see the appendix Figure 1 and attached Figure 2 The low-temperature pre-annealing production method of the oriented silicon steel includes the following steps:

[0035] Step 1: Several vertical steel coils 4 are arranged inside the furnace body 1 through the sealing device 3. The furnace temperature inside the furnace body 1 is heated from room temperature to a first temperature, where the first temperature is ≥ the MgO dehydration temperature and the furnace temperature is ≤ 950℃. This causes the water in the MgO coating on the surface of the vertical steel coils 4 to decompose and be discharged, and the cold point 41 temperature of the vertical steel coils 4 reaches above the MgO dehydration temperature. Currently, through testing, the weight loss curves of the MgO coating commonly used in three types of oriented silicon steel are shown in the attached figure. Figure 3 As shown. (From the appendix) Figure 3 It can be seen that below 200℃, the weight loss of the MgO coating mainly comes from the diffusion of free water in MgO; around 210℃, the chemically bound water in MgO begins to decompose and diffuse, and the decomposition rate gradually increases with temperature; between 300-550℃, the decomposition rate of chemically bound water is at a relatively high level, and as the temperature further increases, the decomposition rate gradually decreases because most of the chemically bound water in MgO has already decomposed. Therefore, to ensure that the decomposition rate of chemically bound water in MgO remains at a high level, the vertical steel coil 4 needs to be kept in the temperature range of 300-550℃ for a period of time to ensure that the chemically bound water in the MgO coating on the strip surface at different locations of the vertical steel coil 4 decomposes quickly, and that the decomposed water can diffuse completely from the end face of the vertical steel coil 4 through the interlayer air gap.

[0036] In step 1, the heating process of heating system 2 can be carried out using either single-stage heating or segmented heating. Heating can also be combined with heat preservation and cooling processes. For example, please refer to the appendix. Figure 4 The diagram, from left to right, illustrates six heating methods: single heating, segmented heating, single heating + holding + cooling, segmented heating + cooling, heating + holding + heating + holding, and heating + holding + cooling + holding. The heating rate for each step can be adjusted according to the required heating temperature and time to achieve the designed furnace temperature. Different heating methods allow for the decomposition and removal of water from the MgO coating on the strip surface, ensuring that the cold point 41 of the vertical steel coil 4 reaches above the MgO dehydration temperature as quickly as possible. Simultaneously, the temperature difference between the cold point 41 and the hot point 42 of the vertical steel coil 4 is controlled within a certain temperature difference threshold range. For example, at the end of the low-temperature pre-annealing process, the temperature of the hot point 42 minus the temperature of the cold point 41 should be ≤350℃.

[0037] During the pre-annealing process of heating and holding the vertical steel coil 4, the moisture in the MgO coating on the strip surface of the vertical steel coil 4 is completely or partially discharged. The degree of moisture discharge in the MgO coating on the strip surface of the vertical steel coil 4 can be controlled according to the process adjustment requirements of subsequent high-temperature annealing production. The degree of moisture discharge in the MgO coating on the strip surface of the vertical steel coil 4 can be roughly understood by dew point measurement. When the dew point is <0℃, it can be considered that the moisture in the MgO coating in the steel coil has been completely decomposed and discharged, which is beneficial to shortening the annealing cycle and optimizing the annealing process in subsequent high-temperature annealing production.

[0038] Depending on the MgO coating, the MgO dehydration temperature range is typically ≥210℃. Therefore, the first temperature can be in the range of 210-950℃. To reduce the difference in drainage and quality between the cold point 41 and the hot point 42 in the vertical steel coil 4, the preferred first temperature range is 300-950℃. If the first temperature is below 300℃, the cold point 41 of the vertical steel coil 4 will require a longer time to reach 210℃, which is the minimum threshold for MgO dehydration temperature. This results in poor drainage of the MgO coating near the cold point 41, and a significant difference in atmosphere between the cold point 41 and the hot point 42, making the advantages in production capacity, energy consumption, and product quality improvement less obvious.

[0039] Please see the appendix Figure 2The cold point 41 of the vertical steel coil 4 is located near the intersection of the coil thickness centerline and the coil height centerline. The temperature of the cold point 41 of the vertical steel coil 4 is ≥210℃, preferably ≥300℃. The top outer edge of the vertical steel coil 4 is the hot point 42. During the heating process of the vertical steel coil 4, the temperature difference between different positions is large. The heat transfer between layers of the vertical steel coil 4 is hindered by the MgO coating, resulting in a large thermal resistance. Therefore, the main heat conduction of the vertical steel coil 4 is through the upper and lower end faces. The greater the heat conduction of the upper and lower end faces, the more uniform the temperature distribution within the strip. The heating rate is faster closer to the upper outer ring, and the heating rate is slowest in the middle of the steel coil. Appropriate heat preservation can reduce the temperature difference between the cold point 41 and the hot point 42 of the vertical steel coil 4. The uniformity of the atmosphere of the entire vertical steel coil 4 is better, which can reduce the differences in product quality and magnetic properties of the vertical steel coil 4 at different positions.

[0040] Submerged thermocouples were used to measure the cold point 41 and hot point 42 of the vertical steel coil 4 after decarburization annealing. The coil was then subjected to high-temperature annealing in a ring furnace, and the temperature changes of the cold point 41 and hot point 42 were recorded. The results showed that the furnace reached 700℃ after 6.0 hours of high-temperature annealing. At this point, the temperature of hot point 42 was 330℃, and the temperature of cold point 41 was 145℃, with a temperature difference of 185℃ between them. After holding at 700℃ for 2.5 hours, the temperature difference between cold point 41 and hot point 42 reached its maximum of 215℃, with the temperature of hot point 42 at 435℃ and the temperature of cold point 41 at 220℃. Subsequently, the temperature difference between cold point 41 and hot point 42 gradually decreased. After holding at 700℃ for 6 hours, the temperature of cold point 41 reached 300℃. After holding at 700℃ for 24 hours, the temperature of hot spot 42 reached 695℃, and the temperature of cold spot 41 reached 585℃, reducing the temperature difference between cold spot 41 and hot spot 42 to 110℃. Based on the above temperature measurement results, to ensure that the temperature of different positions of the vertical steel coil 4 (including cold spot 41 and hot spot 42) can be maintained within the temperature range of rapid MgO decomposition, i.e., between 300-550℃, while the temperature difference between cold spot 41 and hot spot 42 should not be too large, during low-temperature pre-annealing production, the furnace temperature needs to be maintained between 400-800℃ for a period of time to reduce the temperature difference between cold spot 41 and hot spot 42, thereby improving the final product quality and shortening the time required for the subsequent high-temperature annealing process, thus giving the subsequent high-temperature annealing process greater configuration flexibility.

[0041] Step 2: After the low-temperature pre-annealing is completed, the temperature difference between the cold point and the hot point of the vertical steel coil 4 does not exceed the temperature difference threshold. The vertical steel coil 4 will then undergo subsequent high-temperature annealing production.

[0042] During the low-temperature pre-annealing process, a protective gas can be introduced into each sealing device 3 as needed. The protective gas is a non-oxidizing atmosphere such as nitrogen, helium, or a nitrogen-hydrogen mixture. This can prevent the vertical steel coil 4 from oxidizing during the low-temperature pre-annealing process, which would affect the formation of the magnesium silicate underlayer during high-temperature annealing and the final product quality.

[0043] The grain-oriented silicon steel is heated at high temperature in a non-oxidizing atmosphere within the sealing device 3 to prevent oxidation of the steel coil, which would affect the formation of the magnesium silicate underlayer. This allows the magnesium silicate underlayer to maintain its process stability during secondary recrystallization, further ensuring the quality of the finished product.

[0044] Preferably, the total production time of the low-temperature pre-annealing is less than 60 hours, which can match the annual production capacity of high-temperature annealing and give full play to the production capacity improvement advantage of low-temperature pre-annealing. At the same time, it can ensure the water decomposition and discharge of the MgO coating of oriented silicon steel, and avoid the secondary oxidation of oriented silicon steel, which would affect product quality and waste energy. This reduces production costs and improves quality to a certain extent.

[0045] The low-temperature pre-annealing process can also employ prolonged low-temperature heating to achieve the technical effect of water decomposition and removal from the MgO coating of grain-oriented silicon steel. However, this method will extend the total pre-annealing production time and increase energy costs to some extent. To match the annual output of the preceding and following processes, it may be necessary to increase the number of pre-annealing furnaces, which will not be elaborated here. In actual production, the form and process of low-temperature pre-annealing can be selected according to needs.

[0046] When the vertical steel coil 4 is produced using low-temperature pre-annealing, the annual production capacity of the low-temperature pre-annealing process needs to match the annual production capacity of the subsequent high-temperature annealing process using annular annealing furnaces or tunnel annealing furnaces. The annual production capacity Q of the low-temperature pre-annealing furnace is... 预 for:

[0047] Wherein, Q0 is the annual production capacity of vertical steel coil 4 without low-temperature pre-annealing and high-temperature annealing, H0 is the minimum moving cycle of vertical steel coil 4 without low-temperature pre-annealing in the high-temperature annealing furnace, and H1 is the minimum moving cycle of vertical steel coil 4 after low-temperature pre-annealing in the high-temperature annealing furnace. H1 can be obtained based on the number of steel coil rows in the high-temperature annealing furnace and actual production experience. Without affecting product quality and magnetic properties, H1 can be significantly shorter than H0.

[0048] Example 1:

[0049] This embodiment is used to produce oriented silicon steel with a thickness of 0.23mm and a width of 900-1300mm. The oriented silicon steel is produced by conventional production methods before high-temperature annealing, namely, smelting in a converter or electric furnace, continuous casting into slabs, slab heating, hot rolling, hot-rolled plate annealing, cold rolling, decarburization annealing, nitriding treatment, and coating with MgO coating.

[0050] The process of low-temperature pre-annealing is as follows:

[0051] Step 1: The furnace temperature inside the furnace body 1 is heated from room temperature to 700℃ at a rate of 50℃ / h through the heating system 2, and then held at 700℃ for 20h to decompose and remove the water in the MgO coating on the surface of the vertical steel coil 4.

[0052] The furnace temperature inside the furnace body 1 is heated from 700℃ to 800℃ at a rate of 15℃ / h by the heating system 2, and then held at 800℃, which further increases the hot spot temperature of the vertical steel coil 4 and makes the cold spot temperature 41 of the vertical steel coil 4 reach above 350℃.

[0053] During the low-temperature pre-annealing process, 100% nitrogen gas is introduced into each sealing device 3 as a protective gas.

[0054] Step 2: In this embodiment, the total production time of low-temperature pre-annealing is 34 hours. The temperature difference between the cold point 41 and the hot point 42 of the vertical steel coil 4 is controlled within 350°C. Then, the vertical steel coil 4 is subjected to the subsequent high-temperature annealing process in the ring furnace.

[0055] The high-temperature annealing process is as follows: 120 vertical steel coils 4 of oriented silicon steel are arranged in 60 columns in 60 sealing devices 3, with 2 vertical steel coils 4 arranged longitudinally in each sealing device 3, and the average coil weight is 18.5 tons.

[0056] After low-temperature pre-annealing in this embodiment, the minimum moving cycle of the vertical steel coil 4 during high-temperature annealing can be reduced from H0 = 3h to H1 = 2.2h. The annual production capacity of the vertical steel coil 4 without low-temperature pre-annealing is Q0 = 108,000 tons during high-temperature annealing. Therefore, the annual production capacity after low-temperature pre-annealing is Q0 = 108,000 tons. 预 for: The capacity increased by 39,000 tons, and the quality, waviness, and magnetic properties of the oriented silicon steel produced were better.

[0057] Examples 2-8:

[0058] This embodiment is used to produce oriented silicon steel with a thickness of 0.23mm and a width of 900-1300mm. The oriented silicon steel is produced by conventional production methods before high-temperature annealing, namely, smelting in a converter or electric furnace, continuous casting into slabs, slab heating, hot rolling, hot-rolled plate annealing, cold rolling, decarburization annealing, nitriding treatment, and coating with MgO coating.

[0059] The process of low-temperature pre-annealing is as follows:

[0060] The furnace temperature inside the furnace body 1 is heated from room temperature to a first temperature by the heating system 2. During the low-temperature pre-annealing production process, 100% nitrogen gas is introduced into each sealing device 3 as a protective gas. The low-temperature pre-annealing production process of Examples 2-8 is shown in Table 1. The annual production capacity and result indicators of the low-temperature pre-annealing production of Examples 2-8 are shown in Table 2. Among them, Comparative Example 1 is the annual production capacity and result indicators of the vertical steel coil 4 that has not undergone low-temperature pre-annealing production.

[0061] Table 1. Low-temperature pre-annealing production process of Examples 2-8

[0062]

[0063]

[0064] Table 2. Annual production capacity and results indicators for low-temperature pre-annealing corresponding to Examples 2-8.

[0065]

[0066] The high-temperature annealing process is as follows: 120 vertical steel coils 4 of oriented silicon steel are arranged in 60 columns in 60 sealing devices 3, with 2 vertical steel coils 4 arranged longitudinally in each sealing device 3, and the average coil weight is 18.5 tons.

[0067] As shown in Tables 1 and 2, Examples 2-8 employed different heating methods for low-temperature pre-annealing production. Multiple heating methods were used during the low-temperature pre-annealing process to ensure that the cold point 41 temperature of the vertical steel coil 4 was ≥300℃, and the temperature difference between the cold point 41 and hot point 42 of the vertical steel coil 4 was ≤350℃. This resulted in good quality, waviness, and uniformity of magnetic properties in the final product. Furthermore, the production time for the vertical steel coil 4 in the subsequent high-temperature annealing furnace could be significantly shortened, allowing for more flexible process adjustments. Specifically, the minimum moving cycle of the high-temperature annealing furnace could be reduced from H0 = 3h in Comparative Example 1 to H1 = 2.4h in this example. The annual production capacity of the vertical steel coil 4 produced without low-temperature pre-annealing was Q0 = 108,000 tons. Therefore, the annual production capacity Q0 after using the low-temperature pre-annealing furnace was significantly higher. 预 for: 10,000 tons, increasing annual production capacity by 25%.

[0068] Examples 9-11:

[0069] This embodiment is used to produce oriented silicon steel with a thickness of 0.23mm and a width of 900-1300mm. The oriented silicon steel is produced by conventional production methods before high-temperature annealing, namely, smelting in a converter or electric furnace, continuous casting into slabs, slab heating, hot rolling, hot-rolled plate annealing, cold rolling, decarburization annealing, nitriding treatment, and coating with MgO coating.

[0070] The furnace temperature inside the furnace body 1 is heated to the first temperature by the heating system 2. During the low-temperature pre-annealing production process, protective gas can be introduced into each sealing device 3. The low-temperature pre-annealing production process of Examples 9-11 is shown in Table 3, and the annual production capacity and result indicators of the low-temperature pre-annealing production corresponding to Examples 9-11 are shown in Table 4.

[0071] Table 3 Low-temperature pre-annealing production process of Examples 9-11

[0072]

[0073] Table 4. Annual production capacity and results indicators for low-temperature pre-annealing corresponding to Examples 9-11.

[0074]

[0075] As shown in Tables 3 and 4, although the heating methods differ in Examples 9-11, the cold point 41 temperature of the vertical steel coil 4 is ≥300℃, and the temperature difference between the cold point 41 and the hot point 41 temperature is ≤350℃. The atmosphere inside the sealing device 3 is non-oxidizing, and the final product quality and magnetic properties meet the requirements. Furthermore, after low-temperature pre-annealing, the production time of the vertical steel coil 4 in the subsequent high-temperature annealing furnace can be significantly shortened, providing flexibility in process adjustments. The final product quality, waviness, and magnetic properties meet the requirements. Simultaneously, the minimum moving cycle of the high-temperature annealing furnace can be reduced from H0 = 3h to H1 = 2.5h. The annual production capacity of the vertical steel coil 4 without low-temperature pre-annealing is Q0 = 108,000 tons. Therefore, the annual production capacity after using the low-temperature pre-annealing furnace is Q... 预 for: 10,000 tons, increasing annual production capacity by 20%.

[0076] Examples 12-16:

[0077] This embodiment is used to produce the following specifications: First type of oriented silicon steel with a thickness of 0.3mm and a width of 900-1300mm; second type with a thickness of 0.23mm and a width of 900-1300mm; third type with a thickness of 0.2mm and a width of 900-1300mm; and fourth type with a thickness of 0.18mm and a width of 900-1300mm. The oriented silicon steel is produced using conventional methods before high-temperature annealing, namely, converter or electric furnace smelting, continuous casting into slabs, slab heating, hot rolling, hot-rolled plate annealing, cold rolling, decarburization annealing, nitriding treatment, and MgO coating.

[0078] The furnace temperature inside the furnace body 1 is heated to the first temperature by the heating system 2. During the low-temperature pre-annealing process, 100% nitrogen gas is introduced into each sealing device 3 as a protective gas.

[0079] The low-temperature pre-annealing production process of Examples 12-16 is shown in Table 5. The annual production capacity and result indicators of the low-temperature pre-annealing production of Examples 12-16 are shown in Table 6. Among them, Comparative Examples 2-4 are the annual production capacity and result indicators of vertical steel coils 4 that have not undergone low-temperature pre-annealing production.

[0080] Table 5. Low-temperature pre-annealing production process of Examples 12-16

[0081]

[0082]

[0083] Table 6. Annual production capacity and results indicators for low-temperature pre-annealing corresponding to Examples 12-16.

[0084]

[0085] As shown in Tables 5 and 6, Examples 12-15, using different heating methods for low-temperature pre-annealing, achieved product quality and magnetic properties that met requirements for different thicknesses. In Example 15, minor defects existed in product quality and magnetic properties. Example 16, by adjusting the low-temperature pre-annealing furnace process, further improved product quality and magnetic properties compared to Example 15. Adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace compensates for the lack of flexibility in the subsequent high-temperature annealing process due to the flexibility of the pre-annealing furnace's process. Furthermore, adding a low-temperature pre-annealing furnace before the high-temperature annealing furnace increases the adjustable range of the high-temperature annealing furnace process, allowing for the satisfaction of different thicknesses and product quality and magnetic properties. Simultaneously, annual production capacity increased from 116,000 tons to 162,000 tons, a 40% increase.

[0086] Examples 17-21:

[0087] This embodiment is used to produce oriented silicon steel with a thickness of 0.35mm and a width of 900-1300mm. The oriented silicon steel is produced by conventional production methods before high-temperature annealing, namely, converter or electric furnace smelting, continuous casting into slabs, slab heating, hot rolling, hot-rolled plate annealing, cold rolling, decarburization annealing, nitriding treatment, and MgO coating.

[0088] The furnace temperature inside the furnace body 1 is heated to the first temperature by the heating system 2. During the low-temperature pre-annealing production process, 100% nitrogen gas is introduced into each sealing device 3 as a protective gas.

[0089] The low-temperature pre-annealing production process of Examples 17-21 is shown in Table 7, and the annual production capacity and result indicators of the low-temperature pre-annealing production corresponding to Examples 17-21 are shown in Table 8.

[0090] Table 7 Low-temperature pre-annealing production process of Examples 17-21

[0091]

[0092] Table 8. Annual production capacity and results indicators for low-temperature pre-annealing corresponding to Examples 17-21.

[0093]

[0094]

[0095] As shown in Tables 7 and 8, Examples 17-21, using different heating methods and furnace types for low-temperature pre-annealing, consistently achieved product quality and magnetic properties that met requirements. After low-temperature pre-annealing, the vertical steel coils underwent subsequent high-temperature annealing in various furnace types, including annular furnaces and tunnel furnaces. Compared to conventional high-temperature annealing methods, this significantly increased production capacity, raising the annual capacity to 162,000 tons, while maintaining good final product quality, waviness, and magnetic properties.

[0096] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., 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 producing grain-oriented silicon steel using low-temperature pre-annealing, characterized in that: The low-temperature pre-annealing production method is implemented using a low-temperature pre-annealing furnace. The low-temperature pre-annealing furnace includes a furnace body (1), a heating system (2) installed in the furnace body (1), and several sealing devices (3) arranged in the furnace body (1). The vertical steel coil (4) is installed in the sealing device (3), and the surface of the strip steel of the vertical steel coil (4) is coated with MgO coating. The low-temperature pre-annealing production method for the grain-oriented silicon steel includes the following steps: Step 1: The vertical steel coil (4) is placed in the furnace body (1) through the sealing device (3). The furnace temperature in the furnace body (1) is heated from room temperature to the first temperature through the heating system (2). The first temperature is ≥ MgO dehydration temperature and the furnace temperature is ≤ 950℃, so that the water in the MgO coating on the surface of the vertical steel coil (4) is decomposed and discharged, and the cold point (41) temperature of the vertical steel coil (4) reaches above the MgO dehydration temperature. Step 2: After the low-temperature pre-annealing is completed, the temperature difference between the cold point (41) and the hot point (42) of the vertical steel coil (4) does not exceed the temperature difference threshold, and the vertical steel coil (4) is then subjected to subsequent high-temperature annealing production. In step 1, the heating system (2) is heated either in one phase or in stages; after the first heating, the furnace temperature is controlled to the first temperature by heat preservation or cooling; during the staged heating process, the furnace temperature is controlled to the first temperature by heat preservation or cooling. In step 1, the dehydration temperature of MgO is in the range of ≥210℃, and the first temperature range is 210-950℃; In step 1, the cold spot (41) of the vertical steel coil (4) is located at the intersection of the thickness centerline and the height centerline of the steel coil, and the temperature of the cold spot (41) of the vertical steel coil (4) is ≥210℃; the top outer edge of the vertical steel coil (4) is the hot spot (42).

2. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: The range of the first temperature is 300-950℃.

3. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: The cold point (41) temperature of the vertical steel coil (4) is ≥300℃.

4. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: In step 2, the temperature difference threshold between the cold spot (41) and the hot spot (42) of the vertical steel coil (4) is ≤350℃.

5. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: The annual production capacity Q of the low-temperature pre-annealing process is mentioned. 预 for: ; Wherein, Q0 is the annual production capacity of vertical steel coils (4) without low-temperature pre-annealing, in ten thousand tons; H0 is the minimum moving cycle of vertical steel coils (4) without low-temperature pre-annealing in the high-temperature annealing furnace, in hours; H1 is the minimum moving cycle of vertical steel coils (4) after low-temperature pre-annealing in the high-temperature annealing furnace, in hours; Q 预 Annual production capacity for low-temperature pre-annealing, in 10,000 tons.

6. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: in During the low-temperature pre-annealing process, a protective gas is introduced into each sealing device (3). The protective gas is a non-oxidizing atmosphere.

7. The low-temperature pre-annealing production method for grain-oriented silicon steel according to claim 1, characterized in that: The total production time for the low-temperature pre-annealing process is less than 60 hours.

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