A method for controlling the width of an oriented silicon steel slab having a silicon content of 3.0-3.5%

Abstract

The present application relates to a kind of method for controlling the width of oriented silicon steel slab with silicon content of 3.0%-3.5%, belonging to the technical field of iron and steel metallurgy.The method of the present application comprises the following steps: S1, pouring the molten steel of oriented silicon steel with silicon content of 3.0%-3.5% in a ladle;S2, the molten steel after ladle pouring in S1 is poured into a tundish through argon sealing and long nozzle protection, and tundish pouring is carried out;S3, the molten steel after tundish pouring in S2 is poured into a mold through a submerged entry nozzle, and primary cooling is carried out;S4, the slab after primary cooling in S3 is removed from the mold and sent to a fan-shaped section, secondary cooling is carried out, and the fan-shaped section is removed.The method of the present application controls the heat flux of the mold by the amount of cooling water in the mold and the composition of the protective slag, which can increase the shell thickness of the oriented silicon steel slab with Si content of 3.0%-3.5% out of the mold, reduce the slab width, stabilize the slab width more timely and efficiently, improve the slab width qualification rate, and improve the edge quality of the finished product.The method of the present application can stabilize the slab width to ≤20mm, reduce the cutting loss, reduce the production cost, and improve the edge quality of the oriented silicon steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for controlling the width of oriented silicon steel slabs with a silicon content of 3.0%-3.5%. Background Technology

[0002] When oriented silicon steel with a silicon content of 3.0%-3.5% and a qualified smelting composition is cast into slabs via continuous casting, the high silicon content results in poor thermal conductivity, a wide solid-liquid phase range, and slow solidification. This leads to a thin slab shell exiting the continuous casting mold, weak resistance to deformation of the molten steel, and easy widening after exiting the mold. During solidification, this steel directly transforms from liquid to ferrite without undergoing austenitic phase transformation, resulting in coarse grains and low high-temperature strength of the slab. Under the force of the straightening rollers in the fan-shaped section of the slab continuous casting, high-temperature creep widening occurs. For these two reasons, the slab width (actual measured width - target width) can reach 20mm-100mm, resulting in poor slab width accuracy, low pass rate, and seriously affecting the reusability of subsequent processing steps. Smaller and more stable slab width deviations can significantly improve the width control accuracy and edge quality of the finished product after rolling.

[0003] Currently, steel mills mainly use two methods to control the width of grain-oriented silicon steel slabs with a silicon content of 3.0%-3.5%. One method involves installing a high-precision slab width measuring device at the exit roll to measure the slab width and then adjusting the tundish temperature, cooling, and casting speed based on the measured value. For example, the paper "Factors Affecting the Width of Ferritic Stainless Steel Slabs and Control Measures" introduces that many factors, such as casting speed, temperature, and secondary cooling strength, have a significant impact on slab width. While adjusting casting speed, temperature, and cooling can control slab width, frequent adjustments to these process factors can also lead to slab temperature deterioration, cracking, and slag curling. Furthermore, this method of controlling slab width is severely lagging and results in a low width qualification rate. The other method, as described in patent CN 114951577, involves... A discloses a method for controlling the width of continuously cast slabs. This method determines the slab width by calculating the difference between the theoretical and actual tensile forces of the slab at the target width. The slab width is then adjusted by adjusting the secondary cooling intensity. However, this method suffers from a lag in control. Due to the long secondary cooling zone, increasing or decreasing the secondary cooling intensity can lead to a large wedge shape in the slab within the fan-shaped section and a low width qualification rate. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of large width expansion and low slab width qualification rate of oriented silicon steel slabs with silicon content of 3.0%-3.5% in the continuous casting production process in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a method for controlling the width of oriented silicon steel slabs with a silicon content of 3.0%-3.5%. By controlling the speed at which the slab is removed from the crystallizer, the temperature of the tundish pouring, and the secondary cooling process during production, the internal and external quality of the slab is stabilized. The internal and external crack defect rate of the slab is zero, and the central segregation and central porosity of the slab are both ≤C-class 0.5 level, with the equiaxed crystal ratio stabilized between 55% and 65%. By controlling the heat flux of the crystallizer, the slab width expansion is reduced quickly and effectively.

[0006] The purpose of this invention is to provide a method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5%, comprising the following steps:

[0007] S1. Ladle pouring of oriented silicon steel molten steel with a silicon content of 3.0%-3.5%;

[0008] The molten steel poured into the ladle in S2 and S1 is then poured into the tundish through argon gas sealing and long nozzle protection for tundish pouring;

[0009] In S3 and S2, the molten steel poured through the tundish enters the crystallizer through an immersion nozzle for primary cooling.

[0010] After initial cooling in S4 and S3, the slabs are removed from the crystallizer and sent to the fan-shaped section for secondary cooling before being removed from the fan-shaped section.

[0011] In one embodiment of the present invention, in S1, the elemental composition and mass percentage of the oriented silicon steel melt with a silicon content of 3.0%-3.5% are as follows: Si 3.0%-3.5%, C 0.030%-0.045%, Mn 0.18%-0.23%, P 0-0.015%, S 0.006%-0.010%, N 0.0080%-0.0120%, with the balance being other unavoidable impurities and iron.

[0012] In one embodiment of the present invention, in S1, the temperature of the ladle casting is 1555℃-1565℃.

[0013] In one embodiment of the present invention, in S2, the tundish pouring is carried out under the protection of argon gas and a covering agent to ensure that there is no exposed surface of the molten steel, isolates it from air, and avoids secondary oxidation; the temperature of the tundish pouring is 1525℃-1540℃; the temperature of the tundish pouring is an important factor affecting the solidification of molten steel in the slab crystallizer. The higher the temperature, the slower the solidification of the slab shell, the thinner the shell exiting the crystallizer, and the wider the slab; however, the temperature cannot be lower than the target range. If the temperature is too low, it will lead to poor fluidity of the molten steel, affecting the smooth pouring process or causing production interruption.

[0014] In one embodiment of the present invention, the raw material composition and mass percentage of the covering agent are: SiO2 42.18%, MgO 1.38%, CaO 43.79%, Fe2O3 0.96%, Al2O3 9.29%, C 0.57%, with the balance being water, ash, and other unavoidable impurities. The function of the covering agent is to isolate air, prevent secondary oxidation, and absorb inclusions in the molten steel.

[0015] In one embodiment of the present invention, in S3, the crystallizer is composed of a copper plate with a cooling water tank; the long side of the crystallizer has a specification of (700mm-1300mm)×900mm, and the short side has a specification of 200mm×900mm.

[0016] In one embodiment of the present invention, during the first cooling process in S3, the cooling water flow rate along the long side of the crystallizer is 3820 L / min-3870 L / min, and the cooling water flow rate along the short side is 560 L / min-580 L / min. The main function of the cooling water is to remove the heat from the molten steel in the slab crystallizer, thus forming a uniform solidified shell. If the water flow rate is too low, the cooling water will boil, failing to remove the heat from the molten steel inside the crystallizer. This results in a thinner shell exiting the crystallizer, increased billet width, and even production accidents such as steel leakage due to an excessively thin shell. If the water flow rate is too high, the shell inside the slab crystallizer will shrink significantly due to cooling, easily causing cracks and affecting product quality.

[0017] In one embodiment of the present invention, during S3, the surface of the molten steel is covered with a protective slag to ensure that the heat flux along the long side of the crystallizer is 1.35 MW / m. 2 -1.62MW / M 2 The heat flux on the short side is 1.20 MW / m. 2 -1.45MW / M 2 The protective slag serves as a lubricant and heat transfer agent. Heat flux is the heat carried away by the cooling water in the crystallizer; it is a combined result of primary cooling and heat transfer controlled by the protective slag. Low heat flux indicates poor heat transfer efficiency of the protective slag and severe slab widening; high heat flux increases thermal stress on the slab surface, making it prone to cracking defects.

[0018] In one embodiment of the present invention, the raw material composition and mass percentage of the protective slag are as follows: SiO2 38%-42%, Al2O3 1.0%-3.0%, Fe2O3 0.5%-0.8%, CaO 29%-35%, MgO 2.0%-5.0%, R2O 8.0%-10.0%, F 6.0%-8.0%, with the balance being water and other unavoidable impurities; the R2O is an alkaline oxide; further, the R2O is Na2O. Using this protective slag can ensure a reasonable slag film thickness and a reasonable ratio of crystalline to glassy states under the same primary cooling conditions, controlling the heat flux of the crystallizer within the standard range.

[0019] In one embodiment of the present invention, in S4, the slab is removed from the crystallizer by a stretch leveler. The target stretch speed of the stretch leveler is 0.80 m / min-1.10 m / min. If the stretch speed is too low, not only will the production efficiency be low, but the service life of the stretch leveler rollers and bearings will also be reduced. If the stretch speed is too high, the slab is prone to surface cracks and internal cracks.

[0020] In one embodiment of the present invention, in S4, the specific water volume for secondary cooling is 0.75L / kg-0.85L / kg, and the temperature after secondary cooling is 600℃-800℃. A low specific water volume results in a high billet temperature, causing overheating of the straightening roll surface and reducing its service life. It also causes the billet to widen and solidify during secondary cooling. Conversely, a high specific water volume results in a low billet surface temperature, increasing gas consumption and production costs during subsequent hot rolling. The secondary cooling temperature is controlled by spraying water after rationally calculating the specific water volume using air-water atomizing nozzles arranged along the width and length of the billet and a two-stage water distribution model system.

[0021] The technical solution of the present invention has the following advantages compared with the prior art:

[0022] (1) The slab width of the method described in this invention decreases as the heat flux of the crystallizer increases, and the slab width is significantly reduced by reasonably controlling the heat flux of the crystallizer while ensuring the internal and external quality of the slab.

[0023] (2) The method described in this invention controls the slab width expansion problem from the source of slab forming (crystallizer), and has the advantages of being direct, efficient, precise in width control, and requiring no changes in processing equipment, processes, or operations, and is simple to operate.

[0024] (3) The method described in this invention controls the heat flux of the crystallizer by controlling the cooling water volume and the composition of the protective slag, which can increase the shell thickness of the oriented silicon steel slab with Si content of 3.0%-3.5% exiting the crystallizer, reduce the slab widening, stabilize the slab widening more timely and quickly, improve the slab width qualification rate, and improve the edge quality of the finished product.

[0025] (4) The method described in this invention can stabilize the slab width to ≤20mm, reduce cutting damage, lower production costs, and improve the edge quality of oriented silicon steel. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0027] Figure 1 This is a heat flux diagram of the long and short sides of the crystallizer in Embodiment 1 of the present invention;

[0028] Figure 2 This is a broadening diagram of the oriented silicon steel slab with a Si content of 3.0%-3.5% in Example 1 of the present invention;

[0029] Figure 3 This is a heat flux diagram of the long and short sides of the crystallizer in Comparative Example 1 of the present invention;

[0030] Figure 4 This is a broadening diagram of the oriented silicon steel slab with a Si content of 3.0%-3.5% in Comparative Example 1 of the present invention;

[0031] Figure 5 The diagram shows the heat flux of the long and short sides of the crystallizer in Embodiment 1 and Comparative Example 1 of the present invention.

[0032] Figure 6 This is a broadening diagram of the oriented silicon steel slab with a Si content of 3.0%-3.5% in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0034] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0036] In this invention, unless otherwise stated, when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of the said feature, integral, step, or operation, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, or combinations thereof.

[0037] In this invention, unless otherwise stated, the speed at which the slab is removed from the crystallizer by the stretch leveler in the embodiments and comparative examples is achieved by the stretch leveler consisting of 7 pairs of rollers and the corresponding PLC control system.

[0038] In this invention, unless otherwise stated, the raw material composition and mass percentage of the covering agent used in the examples and comparative examples are as follows: SiO2 42.18%, MgO 1.38%, CaO 43.79%, Fe2O3 0.96%, Al2O3 9.29%, C 0.57%, with the balance being water, ash and other unavoidable impurities.

[0039] In this invention, unless otherwise stated, the crystallizer used in the embodiments and comparative examples is composed of a copper plate with a cooling water tank. The long side of the crystallizer has a size of 1030mm × 900mm, and the short side has a size of 200mm × 900mm.

[0040] In this invention, unless otherwise stated, secondary cooling in the embodiments and comparative examples is achieved by a two-stage water distribution model system consisting of air-water atomizing nozzles arranged along the width and length of the slab.

[0041] Example 1

[0042] The method for controlling the width of oriented silicon steel slabs with a silicon content of 3.0%-3.5% according to the present invention specifically includes the following steps:

[0043] S1. Ladle Casting: 150 tons of oriented silicon steel molten steel with a silicon content of 3.0%-3.5% (the elemental composition and mass percentage of the molten steel are: Si 3.17%, C 0.0333%, Mn 0.21%, P 0.0091%, S 0.0077%, N 0.0098%, with the balance being other unavoidable impurities and iron) are hoisted to the continuous casting ladle turret for ladle casting. A total of 10 heats are cast, and the temperature of each heat is shown in Table 1.

[0044] Table 1

[0045] Furnace number 09401 09402 09403 09404 09405 09406 09408 09409 09410 09411 Temperature / °C 1560 1561 1560 1558 1560 1556 1559 1560 1562 1563

[0046] S2. Tundish Casting: After ladle casting, the molten steel is poured into the tundish through an argon gas seal and long nozzle protection. Then, it is poured into the tundish under argon gas protection (argon flow rate of 120 L / min) and 300 kg of covering agent protection. A total of 10 heats are poured. The temperature of each heat in the tundish is shown in Table 2.

[0047] Table 2

[0048] Furnace number 09401 09402 09403 09404 09405 09406 09408 09409 09410 09411 Temperature / °C 1536 1531 1530 1527 1530 1527 1535 1534 1532 1535

[0049] S3. Primary Cooling of the Crystallizer: After being poured from the tundish, the molten steel enters the crystallizer through an immersion nozzle. Each furnace of molten steel is covered with 40 kg of protective slag. Water is circulated through the copper plates of the crystallizer for primary cooling. During primary cooling, the cooling water flow rate along the long side of the crystallizer is 3852 L / min, and along the short side it is 576 L / min. The raw material composition and mass percentage of the protective slag are: SiO2 39.9%, Al2O3 1.5%, Fe2O3 0.58%, CaO 33.8%, MgO 3.89%, Na2O 8.21%, F 7.5%, with the balance being water and other unavoidable impurities. The heat flux along the long and short sides of the crystallizer is as follows: Figure 1 As shown;

[0050] S4. Secondary cooling of the sector section: After primary cooling, the slab is removed from the crystallizer by a straightening machine (target straightening speed is constant at 0.95m / min) and sent to the sector section for secondary cooling (the specific water volume for secondary cooling is 0.81L / kg). It is cooled to 726℃ and then removed from the sector section.

[0051] S5. Width Measurement Inspection: The slab removed from the sector section enters the slab inspection process. The actual width of the slab is measured using a laser width measuring instrument, and the slab width spread is calculated as (actual width - target slab width). The result is as follows: Figure 2 As shown, the width of each slab is less than 20mm.

[0052] Comparative Example 1

[0053] S1. Ladle Casting: 150 tons of oriented silicon steel molten steel with a silicon content of 3.0%-3.5% (the elemental composition and mass percentage of the molten steel are: Si 3.15%, C 0.0334%, Mn 0.20%, P 0.0098%, S 0.0078%, N 0.0095%, with the balance being other unavoidable impurities and iron) are hoisted to the continuous casting ladle turret for ladle casting. A total of 10 heats are cast, and the temperature of each heat is shown in Table 3.

[0054] Table 3

[0055] Furnace number 09367 09368 09369 09370 09371 09372 09373 09374 09375 09376 Temperature / °C 1565 1561 1561 1563 1558 1563 1562 1565 1561 1557

[0056] S2. Tundish Casting: After ladle casting, the molten steel is poured into the tundish through an argon gas seal and long nozzle protection. Then, it is poured into the tundish under argon gas protection (argon flow rate of 122 L / min) and 300 kg of covering agent protection. A total of 10 heats are poured. The temperature of each heat in the tundish is shown in Table 4.

[0057] Table 4

[0058]

[0059]

[0060] S3. Primary Cooling of the Crystallizer: After being poured from the tundish, the molten steel enters the crystallizer through an immersion nozzle. Each furnace of molten steel is covered with 40 kg of protective slag. Water is circulated through the copper plates of the crystallizer for primary cooling. During primary cooling, the cooling water flow rate along the long side of the crystallizer is 3855 L / min, and along the short side it is 578 L / min. The raw material composition and mass percentage of the protective slag are: SiO2 39.8%, Al2O3 5.06%, Fe2O3 0.51%, CaO 27.8%, MgO 3.49%, Na2O 11.21%, F 2.98%, with the balance being water and other unavoidable impurities. The heat flux along the long and short sides of the crystallizer is as follows: Figure 3 As shown;

[0061] S4. Secondary cooling of the sector section: After primary cooling, the slab is removed from the crystallizer by a straightening machine (target straightening speed is constant at 0.95m / min) and sent to the sector section for secondary cooling (the specific water volume for secondary cooling is 0.83L / kg). It is cooled to 723℃ and then removed from the sector section.

[0062] S5. Width Measurement Inspection: The slab removed from the sector section enters the slab inspection process. The actual width of the slab is measured using a laser width measuring instrument, and the slab width spread is calculated as (actual width - target slab width). The result is as follows: Figure 4 As shown, the width of each slab is greater than 20mm.

[0063] The heat flux of the long and short sides of the crystallizers in Example 1 and Comparative Example 1 was compared, and the results are as follows: Figure 5 As shown. From Figure 5 It can be seen that the thermal flux along the long side of the crystallizer in Example 1 is 1.4 MW / M. 2 -1.6MW / M 2 The average heat flux along the longer side is 1.480 MW / m². 2 The short-side heat flux is 1.2 MW / m². 2 -1.4MW / M 2 The average heat flux over the short side is 1.331 MW / m². 2 The heat flux along the long side of the crystallizer in Comparative Example 1 is 1.2 MW / m². 2 -1.8MW / M 2 The average heat flux along the longer side is 1.362 MW / m². 2 The short-side heat flux is 1.1 MW / m². 2 -1.4MW / M2 The average heat flux over the short side is 1.235 MW / m². 2 Example 1: The heat flux of the long and short sides of the crystallizer increased by 0.12 MW / m² compared to the comparative example. 2 and 0.10MW / M 2 According to thermal balance calculations, the thickness of the slab shell of the crystallizer in Example 1 increased by 1.67 mm compared to Comparative Example 1.

[0064] The width expansion of the grain-oriented silicon steel slabs with Si content of 3.0%-3.5% in Example 1 and Comparative Example 1 was compared, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that the slab width of Example 1 is about 10 mm smaller than that of Comparative Example 1, and it is more stable.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5%, characterized in that, Includes the following steps: S1. Ladle pouring of oriented silicon steel molten steel with a silicon content of 3.0%-3.5%; The molten steel poured into the ladle in S2 and S1 is then poured into the tundish through argon gas sealing and long nozzle protection for tundish pouring; After being poured from the tundish in S3 and S2, the molten steel enters the crystallizer through an immersion nozzle for primary cooling. During this primary cooling process, the cooling water flow rate along the long side of the crystallizer is 3820 L / min-3870 L / min, and the cooling water flow rate along the short side is 560 L / min-580 L / min. During this primary cooling process, the surface of the molten steel is covered with a protective slag. The raw material composition and mass percentage of the protective slag are as follows: SiO2 38%-42%, Al2O3 1.0%-3.0%, Fe2O3 0.5%-0.8%, CaO 29%-35%, MgO 2.0%-5.0%, R2O 8.0%-10.0%, F 6.0%-8.0%, with the balance being water and other unavoidable impurities. After initial cooling in S4 and S3, the slabs are removed from the crystallizer and fed into the fan-shaped section for secondary cooling before being removed from the fan-shaped section.

2. The method for controlling the width of grain-oriented silicon steel slabs with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S1, the elemental composition and mass percentage of the oriented silicon steel molten steel with a silicon content of 3.0%-3.5% are as follows: Si 3.0%-3.5%, C 0.030%-0.045%, Mn 0.18%-0.23%, P 0-0.015%, S 0.006%-0.010%, N 0.0080%-0.0120%, with the balance being other unavoidable impurities and iron.

3. The method for controlling the width of grain-oriented silicon steel slabs with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S1, the temperature at which the ladle is poured is 1555℃-1565℃.

4. The method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S2, the intermediate ladle pouring is carried out under the protection of argon gas and a covering agent, and the pouring temperature of the intermediate ladle is 1525℃-1540℃.

5. The method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S3, the crystallizer is composed of a copper plate with a cooling water tank; the long side of the crystallizer has a size of (700mm-1300mm)×900mm, and the short side has a size of 200mm×900mm.

6. The method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S3, during the primary cooling process, the surface of the molten steel is covered with a protective slag to ensure that the heat flux along the long side of the crystallizer is 1.35 MW / m. 2 -1.62MW / M 2 The heat flux on the short side is 1.20 MW / m. 2 -1.45MW / M 2 .

7. The method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S4, the slab is removed from the crystallizer by a stretch leveler with a target stretching speed of 0.80 m / min to 1.10 m / min.

8. The method for controlling the width of a grain-oriented silicon steel slab with a silicon content of 3.0%-3.5% according to claim 1, characterized in that, In S4, the specific water volume for the secondary cooling is 0.75L / kg-0.85L / kg, and the temperature after secondary cooling is 600℃-800℃.

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