High-grade non-oriented silicon steel and method for producing high-grade non-oriented silicon steel

Abstract

The application discloses a high-grade non-oriented silicon steel and a production method thereof. In the non-oriented silicon steel, Si is 2.5-3.5%, Al is 0.5-1.5%, and Mn is 0.2-0.8%. The production method comprises sequentially performed continuous casting, hot rolling, normalizing, cold rolling, annealing and coating processes. In the continuous casting process, the proportion of columnar crystals in the continuously cast billet is controlled to be 50-80%. In the hot rolling process, the final rolling temperature of rough rolling is 980-1020 DEG C, and the final rolling temperature of finish rolling is 860-900 DEG C. The rough rolling comprises even pass rough rolling and odd pass rough rolling. The working rolls of the rough rolling mill used in the odd pass rough rolling have an upper roll with a linear speed of u1 and a lower roll with a linear speed of u2. The working rolls of the rough rolling mill used in the even pass rough rolling have an upper roll with a linear speed of u3 and a lower roll with a linear speed of u4. u1>u2 and u3<u4, or u1<u2 and u3>u4.

Description

Technical Field

[0001] The present application belongs to the technical field of iron and steel material preparation, and specifically relates to a high-grade non-oriented silicon steel and a production method of high-grade non-oriented silicon steel. Background Art

[0002] High-grade non-oriented silicon steel is a key material for manufacturing cores of power equipment such as high-efficiency motors and large generator units. Its iron loss value directly determines the operating efficiency of the motor. Therefore, reducing the iron loss of high-grade non-oriented silicon steel is an effective way to improve motor energy efficiency.

[0003] To reduce iron loss, an alloying scheme that increases the content of silicon (Si) and aluminum (Al) is usually adopted. Si and Al elements can significantly increase the electrical resistivity of the material, thereby reducing eddy current loss and achieving the purpose of lowering iron loss. However, with the increase of Si and Al content, the difficulty of hot rolling and cold rolling production of high-grade non-oriented silicon steel increases sharply. Especially during hot rolling, serrated edge cracks are prone to occur at the edge of the strip steel, and this defect will further expand in the subsequent cold rolling process, causing edge cracks or even strip breakage, which seriously restricts the continuous and stable production of high-grade non-oriented silicon steel. Therefore, how to improve the hot-rolled edge quality of high-grade non-oriented silicon steel on the premise of ensuring low iron loss performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of the present application is to provide a high-grade non-oriented silicon steel and a production method of high-grade non-oriented silicon steel.

[0005] To achieve one of the above purposes of the present application, one embodiment of the present application provides a production method of high-grade non-oriented silicon steel, wherein the chemical composition of the non-oriented silicon steel, by mass percentage, comprises: 2.5~3.5% of Si, 0.5~1.5% of Al, 0.2~0.8% of Mn; the production method comprises sequentially performed continuous casting, hot rolling, normalization, cold rolling, annealing and coating processes;

[0006] In the continuous casting process, the proportion of columnar crystals in the continuous casting billet obtained by the continuous casting process is controlled to be 50~80%; The hot rolling process comprises rough rolling and finish rolling performed sequentially, the finish rolling temperature of rough rolling is 980~1020°C, and the finish rolling temperature of finish rolling is 860~900°C; Rough rolling comprises even-pass rough rolling; among the work rolls of the roughing mill adopted for odd-pass rough rolling, the linear velocity of the upper work roll is u1, and the linear velocity of the lower work roll is u2; among the work rolls of the roughing mill adopted for even-pass rough rolling, the linear velocity of the upper work roll is u3, and the linear velocity of the lower work roll is u4; Wherein, u1>u2 and u3<u4; or u1<u2 and u3>u4.

[0007] As a further improvement of an embodiment of the present application, u1>u2, u3<u4, u1 / u2=1.05~1.10, u4 / u3=1.05~1.10; Alternatively, u1<u2, u3>u4, u2 / u1=1.05~1.10, u3 / u4=1.05~1.10 As a further improvement of an embodiment of the present application, u1=u4, u2=u3.

[0008] As a further improvement of an embodiment of the present application, among the work rolls of the roughing mill adopted for rough rolling in odd passes, the diameter of the upper roll is D1, and the diameter of the lower roll is D2; among the work rolls of the roughing mill adopted for rough rolling in even passes, the diameter of the upper roll is D3, and the diameter of the lower roll is D4; Wherein, D1>D2, D3<D4; or, D1<D2, D3>D4.

[0009] As a further improvement of an embodiment of the present application, D1>D2, D3<D4, D1 / D2=1.05~1.10, D4 / D3=1.05~1.10; Alternatively, D1<D2, D3>D4, D2 / D1=1.05~1.10, D3 / D4=1.05~1.10.

[0010] As a further improvement of an embodiment of the present application, D1=D4, D2=D3.

[0011] As a further improvement of an embodiment of the present application, the rotating speeds of the upper work roll and the lower work roll of each roughing mill are the same.

[0012] As a further improvement of an embodiment of the present application, rough rolling adopts a reversible roughing mill train, the reversible roughing mill train comprises an R1 roughing mill and an R2 roughing mill arranged in sequence, the R1 roughing mill performs rough rolling in odd passes, and the R2 roughing mill performs rough rolling in even passes.

[0013] As a further improvement of an embodiment of the present application, the reduction rate of each rough rolling pass is 32~38%, and the reduction rate of each finish rolling pass is 30~38%.

[0014] As a further improvement of an embodiment of the present application, in the hot rolling process, the coiling temperature is 600~680°C.

[0015] As a further improvement of an embodiment of the present application, in the normalizing process, the temperature of the soaking section for normalizing is 920~970°C, and the normalizing time is 2~3min.

[0016] As a further improvement of an embodiment of the present application, in the annealing and coating process, the annealing temperature is 950~1050°C, and the annealing time is 50~80s.

[0017] As a further improvement of one embodiment of this application, the chemical composition of the high-grade non-oriented silicon steel, by mass percentage, further includes: C≤0.0025%, Nb≤0.002%, V≤0.002%, Ti≤0.002%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.002%, S≤0.0015%, P 0.03~0.05%, with the remainder being Fe and unavoidable impurities.

[0018] As a further improvement of one embodiment of this application, in the continuous casting process, electromagnetic stirring is controlled at the end of solidification, while electromagnetic stirring is not performed in the crystallizer.

[0019] As a further improvement of one embodiment of this application, in the continuous casting process, the thickness h of the billet shell at the outlet of the crystallizer is controlled to be ≥8Si+10Al+9Mn.

[0020] As a further improvement to one embodiment of this application, in the continuous casting process, the cooling water flow rate of the wide side of the crystallizer is controlled to be 2500~4500 L / min, the cooling water flow rate of the narrow side is controlled to be 400~700 L / min, the crystallizer inlet water temperature is controlled to be 28~35℃, the inlet and outlet water temperature difference is controlled to be 6~10℃, and the average heat flux density of the crystallizer is controlled to be 1200~2000 kW / m³. 2 .

[0021] As a further improvement of one embodiment of this application, the cooling rate of the second cooling zone in the continuous casting process is controlled to gradually decrease along the foot roll section, sector sections 1 to 4, and sector sections 5 to 12. Specifically, the cooling rate of the foot roll section is controlled to be 3 to 10 °C / s, the cooling rate of sector sections 1 to 4 is controlled to be 0.5 to 8 °C / s, and the cooling rate of sector sections 5 to 12 is controlled to be 0.2 to 1.5 °C / s.

[0022] As a further improvement of one embodiment of this application, in the continuous casting process, the specific water volume of the foot roll section is controlled to be 1.2~2.5L / kg, the cooling water volume of the wide face is 260~600L / min, and the cooling water volume of the narrow face is 50~125L / min; The specific water content of the first to fourth fan-shaped sections is controlled at 0.8 to 1.5 L / kg, and the surface temperature of the billet is 1000 to 1100℃; The specific water content of the 5th to 12th segments of the sector is controlled at 0.3 to 0.8 L / kg; Control the straightening temperature to >950℃.

[0023] As a further improvement of one embodiment of this application, in the continuous casting process, the continuous casting speed v, the target thickness δ of the continuous casting billet and the target width w are controlled to satisfy 0.21-0.005×(Si+Al)≤v×δ×w≤0.22-0.003×(Si+Al), and v×δ×w is negatively correlated with Si+Al, where the unit of v is m / min, the unit of δ is m and the unit of w is m.

[0024] As a further improvement of one embodiment of this application, 0.7m / min≤v≤1.2m / min, 0.18m≤δ≤0.25m, and 1.0m≤w≤1.3m.

[0025] To achieve one of the above-mentioned objectives, one embodiment of this application provides a high-grade non-oriented silicon steel, which is prepared using the production method of high-grade non-oriented silicon steel as described above.

[0026] Compared with the prior art, the beneficial effects of this application include: This application relates to high-grade non-oriented silicon steel and its production method. Specifically, for high-grade non-oriented silicon steel with high Si and Al content, the proportion of columnar crystals in the continuously cast slab is controlled to 50-80%. Utilizing the high high-temperature strength of columnar crystals along their growth direction, the high-temperature strength of the continuously cast slab is improved, effectively resisting the hydrostatic pressure of molten steel, reducing the risk of bulging deformation, and thus effectively reducing serrated edge cracks during subsequent hot rolling. Furthermore, during the roughing process in hot rolling, the slab is asynchronously rolled by using different linear speeds of the upper and lower work rolls of each roughing mill. By setting the odd and even number of high-speed work rolls to opposite vertical positions, alternating reciprocating shear deformation is generated in the thickness direction of the slab, breaking the columnar crystals on the upper and lower surfaces of the slab. Combined with the high-temperature finishing rolling during finishing, the broken columnar crystals undergo sufficient dynamic recrystallization, thus obtaining a fine and uniform equiaxed crystal structure in the hot rolling stage. This blocks the hereditary effect of a large proportion of columnar crystals, thereby avoiding corrugated defects during cold rolling. It also greatly reduces the occurrence of cold rolling edge cracks and cold rolling strip breaks, and avoids billet bending and warping caused by asynchronous rolling in one direction. Detailed Implementation

[0027] The present application will be described in detail below with reference to specific embodiments. However, these embodiments do not limit the present application, and structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are all included within the protection scope of the present application.

[0028] The present application studies the problem that high-grade non-oriented silicon steel with high Si and Al contents is prone to cracking during hot rolling, and finds that high contents of Si and Al significantly reduce the high-temperature thermal conductivity and high-temperature strength of steel, which slows down heat export during solidification, resulting in slow growth and insufficient strength of the initial slab shell during solidification of the billet in the continuous casting process, and the billet is prone to bulging deformation under the action of static pressure of molten steel. Bulging deformation induces internal stress at the edge of the billet, and the internal stress induces abnormal growth of columnar crystals at the edge of the billet during high-temperature heating, and uneven plastic deformation occurs at the edge of the billet during hot rolling, thereby forming jagged edge cracks.

[0029] In view of this, an embodiment of the present application provides a production method of high-grade non-oriented silicon steel and a high-grade non-oriented silicon steel prepared by the production method.

[0030] The chemical components of the high-grade non-oriented silicon steel, calculated by mass percentage, comprise: 2.5~3.5% of Si, 0.5~1.5% of Al, and 0.2~0.8% of Mn.

[0031] The production method comprises continuous casting, hot rolling, normalizing, cold rolling, annealing and coating processes performed in sequence.

[0032] In the continuous casting process, the proportion of columnar crystals in the continuous casting billet obtained in the continuous casting process is controlled to be 50~80%. In this way, by utilizing the characteristic that columnar crystals have higher high-temperature strength along the growth direction, the high-temperature strength of the continuous casting billet can be improved, thereby effectively resisting the static pressure of molten steel, reducing the risk of bulging deformation, and further effectively reducing the occurrence of jagged edge cracks during subsequent hot rolling.

[0033] However, columnar crystals have a specific crystallographic orientation (usually <100> direction). In the subsequent hot rolling process, if the columnar crystals are not sufficiently broken, their orientation information will be inherited to the hot-rolled strip, and form areas with concentrated micro-orientation after cold rolling and annealing, which is macroscopically manifested as corrugated surface defects, affecting the product quality of the finished strip.

[0034] To solve this problem, the hot rolling process in the present embodiment comprises rough rolling and finish rolling performed sequentially, the finish rolling temperature of rough rolling is 980~1020°C, and the finish rolling temperature of finish rolling is 860~900°C.

[0035] The rough rolling comprises even-numbered rough rolling passes. Among the work rolls of the roughing mill adopted for odd-numbered rough rolling passes, the linear velocity of the upper work roll is u1, and the linear velocity of the lower work roll is u2; among the work rolls of the roughing mill adopted for even-numbered rough rolling passes, the linear velocity of the upper work roll is u3, and the linear velocity of the lower work roll is u4. Wherein, u1>u2 and u3<u4; or u1<u2 and u3>u4.

[0036] In other words, the upper and lower rolls of each roughing mill have different linear velocities, thus performing asynchronous rolling on the slab. Furthermore, the upper and lower positions of the high-speed work rolls in odd and even passes are opposite. That is, when the linear velocity of the upper roll of the work roll in odd passes is greater than that of the lower roll, the linear velocity of the upper roll of the work roll in even passes is less than that of the lower roll; conversely, the linear velocity of the upper roll of the work roll in odd passes is less than that of the lower roll, while the linear velocity of the upper roll of the work roll in even passes is greater than that of the lower roll.

[0037] Thus, this application targets high-grade non-oriented silicon steel with high Si and Al content, controlling the proportion of columnar crystals in the continuously cast billet to 50-80%. Utilizing the high high-temperature strength of columnar crystals along their growth direction, the high-temperature strength of the continuously cast billet is improved, effectively resisting the static pressure of molten steel, reducing the risk of bulging deformation, and consequently effectively reducing serrated edge cracks during subsequent hot rolling. Furthermore, during the roughing process of hot rolling, the slab is asynchronously rolled by using different linear speeds of the upper and lower work rolls of each roughing mill, and large linear speeds of odd and even passes are set. The speed work rolls are positioned in opposite directions, resulting in alternating reciprocating shear deformation in the thickness direction of the slab. This breaks down the columnar crystals on the upper and lower surfaces of the slab. Combined with the high-temperature finishing rolling during finishing, the broken columnar crystals undergo sufficient dynamic recrystallization, thus obtaining a fine and uniform equiaxed crystal structure during the hot rolling stage. This blocks the hereditary effect of a large proportion of columnar crystals, thereby avoiding corrugated defects during cold rolling. It also greatly reduces the occurrence of cold rolling edge cracks and cold rolling strip breaks, and avoids billet bending and warping caused by asynchronous rolling in one direction.

[0038] In a preferred embodiment, the ratio of the diameter of the work roll with a higher linear velocity to the linear velocity of the work roll with a lower linear velocity in each work roll is 1.05 to 1.10. This not only creates a stable linear velocity difference, but this level of shear deformation effectively breaks down the columnar crystal structure on the slab surface. Furthermore, by generating alternating reciprocating shear deformation in the thickness direction of the slab through odd and even passes, the flatness of the intermediate slab obtained from rough rolling is ensured.

[0039] Specifically, in one embodiment, in the work rolls of the roughing mill used for odd-numbered passes, the linear velocity u1 of the upper roll is greater than the linear velocity u2 of the lower roll; in the work rolls of the roughing mill used for even-numbered passes, the linear velocity u3 of the upper roll is less than the linear velocity u4 of the lower roll.

[0040] Furthermore, u1 / u2 = 1.05~1.10, u4 / u3 = 1.05~1.10.

[0041] In another embodiment, it may also be configured that: in the work rolls of the roughing mill adopted for roughing in odd passes, the linear speed of the upper roll u1<the linear speed of the lower roll u2; in the work rolls of the roughing mill adopted for roughing in even passes, the linear speed of the upper roll u3>the linear speed of the lower roll u4.

[0042] Further, u2 / u1=1.05~1.10, and u3 / u4=1.05~1.10.

[0043] In a preferred embodiment, u1=u4 and u2=u3. That is, the linear speed of the upper work roll of the roughing mill for odd roughing passes is the same as the linear speed of the lower work roll of the roughing mill for even roughing passes, and the linear speed of the lower work roll of the roughing mill for odd roughing passes is the same as the linear speed of the upper work roll of the roughing mill for even roughing passes. In this way, the problem of poor flatness of the intermediate slab caused by asynchronous rolling can be avoided.

[0044] In an embodiment, in the work rolls of the roughing mill adopted for roughing in odd passes, the diameter of the upper roll is D1, and the diameter of the lower roll is D4; in the work rolls of the roughing mill adopted for roughing in even passes, the diameter of the upper roll is D3, and the diameter of the lower roll is D4. Wherein, D1>D2 and D3<D4; or D1<D2 and D3>D4. That is, the diameters of the upper and lower work rolls of each roughing mill are different, so that the linear speeds of the upper and lower work rolls are different, so as to realize asynchronous rolling of the slab, and the upper and lower positions of the large-diameter work rolls for odd and even passes are opposite. That is, when the large-diameter work roll for odd passes is the upper roll and the small-diameter work roll is the lower roll, the large-diameter work roll for even passes is the lower roll and the small-diameter work roll is the upper roll. In addition, the arrangement and control of the work rolls of the roughing mill can be simplified, the production difficulty is reduced, and the production cost is saved.

[0045] In a preferred embodiment, for each work roll, the ratio of the diameter of the larger-diameter work roll to the diameter of the smaller-diameter work roll is 1.05~1.10.

[0046] Specifically, in an embodiment, in the work rolls of the roughing mill adopted for roughing in odd passes, the diameter of the upper roll D1>the diameter of the lower roll D2; in the work rolls of the roughing mill adopted for roughing in even passes, the diameter of the upper roll D3<the diameter of the lower roll D4.

[0047] Further, D1 / D2=1.05~1.10, and D4 / D3=1.05~1.10.

[0048] In another embodiment, it may also be configured that: in the work rolls of the roughing mill adopted for roughing in odd passes, the diameter of the upper roll D1<the diameter of the lower roll D2; in the work rolls of the roughing mill adopted for roughing in even passes, the diameter of the upper roll D3>the diameter of the lower roll D4.

[0049] Furthermore, D2 / D1 = 1.05~1.10, D3 / D4 = 1.05~1.10.

[0050] In a preferred embodiment, D1=D4, D2=D3. That is, the diameter of the upper roll of the work roll in the odd-numbered roughing mill is the same as the diameter of the lower roll of the work roll in the even-numbered roughing mill, and the diameter of the lower roll of the work roll in the odd-numbered roughing mill is the same as the diameter of the upper roll of the work roll in the even-numbered roughing mill. This avoids the problem of poor flatness of the intermediate billet caused by asynchronous rolling.

[0051] In one embodiment, the upper and lower rolls of each roughing mill rotate at the same speed. Thus, by simply setting the diameters of the upper and lower rolls to be different, the linear velocities of the upper and lower rolls can be made different, achieving asynchronous rolling.

[0052] In one embodiment, a reversible roughing mill unit is used for roughing. This unit includes two sequentially arranged roughing mills, R1 and R2. R1 performs odd-numbered passes, while R2 performs even-numbered passes. For example, if the roughing process involves six passes, R1 performs passes 1, 3, and 5, and R2 performs passes 2, 4, and 6. Alternatively, the number of passes can be rationally arranged based on the target thickness of the intermediate billet obtained from the roughing process, such as even-numbered passes like 2, 4, or 8.

[0053] Thus, by setting up the R1 and R2 double stands, the odd and even passes of roughing can produce shear deformation in opposite directions in the slab thickness direction, realizing alternating asynchronous rolling and ensuring the flatness of the intermediate slab obtained from roughing.

[0054] In one embodiment, the reduction rate per pass of roughing rolling is 32-38%, and the reduction rate per pass of finishing rolling is 30-38%.

[0055] The thickness of the intermediate billet obtained from rough rolling is 40~45mm, and the thickness of the hot-rolled strip obtained after finishing rolling is 2.0~2.4mm.

[0056] In one embodiment, finishing rolling is performed using a seven-stand finishing mill.

[0057] In the hot rolling process, the coiling temperature is 600~680℃.

[0058] In one embodiment, the hot rolling process further includes heating prior to rough rolling, during which the continuously cast billet is fed into a heating furnace for heating. The homogenization temperature is 1050~1250°C, and the heating time is 180~220 min.

[0059] In one embodiment, the hot rolling process further includes laminar cooling after finishing rolling, and the hot-rolled strip is coiled after cooling to obtain a hot-rolled coil.

[0060] In one embodiment, the thickness δ of the continuously cast billet obtained from the continuous casting process is 0.18~0.25m, that is, δ is 180~250mm.

[0061] In one embodiment, during the normalizing process, the temperature of the soaking zone is 920~970°C, and the normalizing time is 2~3 minutes. High-temperature normalizing can effectively improve the inhomogeneity of the microstructure and texture of hot-rolled strip steel, and further reduce the corrugated defects on the surface of the strip steel after subsequent cold rolling and annealing.

[0062] In one embodiment, the production method of high-grade non-oriented silicon steel further includes shot blasting and pickling between the normalizing and cold rolling processes. Shot blasting and pickling can remove the oxide scale from the surface of the strip steel.

[0063] In one embodiment, during the annealing and coating process, the annealing temperature is 950~1050°C and the annealing time is 50~80s.

[0064] The annealing is carried out in a protective atmosphere, which is a mixture of 20% H2 and 80% N2.

[0065] The coating process involves applying an insulating coating to the surface of cold-rolled strip steel to obtain a finished non-oriented silicon steel product.

[0066] An embodiment of this application also provides a high-grade non-oriented silicon steel, the chemical composition of which, by mass percentage, further includes: C≤0.0025%, Si 2.5~3.5%, Al 0.5~1.5%, Mn 0.2~0.8%, Nb≤0.002%, V≤0.002%, Ti≤0.002%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.002%, S≤0.0015%, P0.03~0.05%, with the remainder being Fe and unavoidable impurities.

[0067] This high-grade non-oriented silicon steel is manufactured using the production method for high-grade non-oriented silicon steel as described above. The surface of this non-oriented silicon steel is free of corrugated defects.

[0068] In one embodiment, the chemical composition of the high-grade non-oriented silicon steel, by mass percentage, includes: C≤0.0025%, Si 2.5~3.5%, Al 0.5~1.5%, Mn 0.2~0.8%, Nb≤0.002%, V≤0.002%, Ti≤0.002%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, N≤0.002%, S≤0.0015%, P 0.03~0.05%, with the remainder being Fe and unavoidable impurities.

[0069] The role and mechanism of each element in the above chemical composition are introduced below.

[0070] C: In non-oriented silicon steel, C is generally considered to be a harmful element. An increase in C content will lead to fine grains, high iron loss, poor magnetic properties, and magnetic aging problems in the finished product. Therefore, it is generally better to control the C content as low as possible. In this embodiment, the C content is controlled at 0.0025% or below.

[0071] Si is an effective additive element for improving the resistivity of electromagnetic steel sheets and reducing iron loss. It can also effectively improve the strength of steel strips. In this embodiment, the Si content (by mass percentage) is controlled at 2.5-3.5% to effectively reduce iron loss and meet the requirements of high-grade non-oriented silicon steel.

[0072] Al is also an effective additive element for improving the resistivity of electromagnetic steel plates and reducing iron loss. If its content is too high, it will reduce the magnetic induction intensity and significantly increase the brittleness of the steel plate, increasing the difficulty of processing such as cold rolling. If its content is too low, it will lead to excessively low resistivity and fine precipitation of nitrides such as AlN, making it difficult for the grains to grow sufficiently and failing to meet the requirements of low iron loss. Therefore, in this invention, the content of Als (i.e., acid-soluble aluminum) is controlled at 0.5~1.5%.

[0073] Mn can increase the resistivity of materials and reduce iron loss. Mn readily reacts with S to form MnS. Adding an appropriate amount of Mn can suppress the hot brittleness caused by S. In this embodiment, Mn is added and the Mn content (by mass percentage) is controlled to be 0.2-0.8%.

[0074] Nb, V, and Ti: Nb, V, and Ti are carbide and nitride forming elements, and also major impurity elements. Carbides and nitrides in non-oriented silicon steel can form fine precipitates that hinder grain growth during annealing, worsen the magnetic properties of the non-oriented silicon steel, and lead to increased iron loss and decreased magnetic induction. Therefore, their content is controlled to not exceed 0.002%.

[0075] Cr, Ni, Cu: Adding Cr, Ni, and Cu to non-oriented silicon steel can improve its strength, but it will also increase iron loss and reduce magnetic induction. Therefore, their content is controlled to not exceed 0.03%.

[0076] N: It is also an important component of inclusions in steel. The AlN formed in the billet will dissolve in large quantities during the hot rolling process and then disperse and precipitate during the hot working process. It will hinder the growth of grains during the annealing process of the finished product and reduce the magnetism of the finished product. Therefore, its content should be controlled to N≤0.002%.

[0077] S: is a harmful element and an important component of inclusions in steel. In particular, when the billet is heated before hot rolling, a large amount of MnS precipitates in the steel will dissolve and then disperse during the hot working process. This will hinder the growth of grains during the annealing process of the finished product and reduce the magnetism of the finished product. Therefore, an increase in its content will lead to a decrease in magnetic induction intensity and an increase in iron loss. In this embodiment, in order to avoid the precipitation of fine MnS during hot rolling, the content of S (by mass percentage) is controlled to be ≤0.0015%.

[0078] P: It can effectively improve iron loss. Its content can effectively improve the strength of steel strip and improve stamping performance. However, for high-grade non-oriented silicon, P exceeding 0.05% will significantly deteriorate the cold rollability of steel. In this embodiment, in order to further improve the yield strength of non-oriented silicon steel products and meet the actual use requirements of high-speed motors, it is more preferable that the P content is controlled at 0.03~0.05%.

[0079] One embodiment of this application also provides a method for controlling the proportion of columnar crystals in a continuously cast billet.

[0080] The proportion of columnar crystals in the continuously cast billet obtained from the continuous casting process can be controlled to be 50-80% through the method of controlling the proportion of columnar crystals in the continuously cast billet.

[0081] The control method includes: Determine the initial value of electromagnetic stirring intensity at the solidification end of the continuous casting process; Real-time monitoring of the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process. m And based on the monitored columnar crystal ratio R m Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. m Adjust to the target value.

[0082] When the electromagnetic stirring intensity at the end of solidification is high, it can interrupt the growth of columnar crystals, break up coarse dendrites and disperse them, making them new equiaxed crystal nuclei, thereby increasing the proportion of equiaxed crystals and decreasing the proportion of columnar crystals; conversely, when the electromagnetic stirring intensity at the end of solidification is low, the proportion of equiaxed crystals decreases and the proportion of columnar crystals increases.

[0083] Thus, by real-time monitoring of the proportion R of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process... mAnd based on the monitored columnar crystal ratio R m Adjusting the intensity of electromagnetic stirring at the end of solidification can effectively regulate the ratio of columnar crystals and equiaxed crystals in the billet, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, so that the proportion of columnar crystals in the billet formed at the end of solidification reaches the target value.

[0084] The electromagnetic stirring intensity parameter includes at least one of the electromagnetic stirring current and the electromagnetic stirring frequency. In other words, the electromagnetic stirring intensity can be adjusted by regulating at least one of the electromagnetic stirring current and the electromagnetic stirring frequency.

[0085] One embodiment of this application also provides a continuous casting apparatus, which includes a continuous casting machine and a control system.

[0086] The continuous casting process is carried out using continuous casting equipment.

[0087] A continuous casting machine includes a rotary table, tundish, crystallizer, sector section, and straightening machine.

[0088] The rotary table can rotate 180 degrees, moving the ladle to the pouring position to enable continuous pouring of multiple heats of molten steel. The tundish, located below the ladle, serves as a crucial transition vessel, buffering the molten steel, stabilizing the flow rate, and providing time for impurities (such as slag) to rise and purify the steel. The crystallizer initially solidifies the molten steel to form a billet shell. The fan-shaped section supports and further cools the billet exiting the crystallizer. The straightening machine pulls out and straightens the billet.

[0089] The fan-shaped section forms the secondary cooling zone in the continuous casting process, meaning that the billet undergoes secondary cooling in the fan-shaped section. The solidification end is part of the secondary cooling zone.

[0090] The sector segment includes the foot roller segment (i.e., sector segment 0) arranged sequentially from the crystallizer to the straightening machine, as well as sector segments 1 to 12.

[0091] The control system is connected to the continuous casting machine and is used to obtain the proportion R of columnar crystals in the billet formed at the monitored solidification endpoint. m And based on the monitored columnar crystal ratio R m Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. m Adjust to the target value.

[0092] In one embodiment, the electromagnetic stirring intensity parameter includes the electromagnetic stirring current.

[0093] The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value I0 of the electromagnetic stirring current at the solidification end of the continuous casting process.

[0094] The adjustment of the electromagnetic stirring intensity at the solidification end based on the monitored columnar crystal ratio includes: The electromagnetic stirring current I at the end of solidification is adjusted according to the monitored columnar crystal ratio.

[0095] Thus, by adjusting the electromagnetic stirring current I at the end of solidification, the electromagnetic stirring intensity at the end of solidification can be adjusted, thereby achieving dynamic adjustment of the proportion of columnar crystals in the billet formed at the end of solidification, and the adjustment efficiency is relatively high.

[0096] In one embodiment, adjusting the electromagnetic stirring current I at the solidification end according to the monitored columnar crystal ratio includes: Based on the monitored columnar crystal ratio R m The target value of columnar crystal ratio R is used to calculate the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification using a PID algorithm. The electromagnetic stirring current I at the end of solidification is adjusted according to the calculated adjustment amount ΔI.

[0097] Thus, by monitoring the columnar crystal ratio R m Compared with the target value for the proportion of columnar crystals, if R m If the value is lower than the target value, it indicates that the proportion of columnar crystals is insufficient and the proportion of equiaxed crystals is too high. In this case, the electromagnetic stirring current should be reduced to decrease the electromagnetic stirring intensity and promote the development of columnar crystals; if R m If the value is higher than the target value, it indicates that the proportion of columnar crystals is too high. In this case, the electromagnetic stirring current needs to be increased to increase the electromagnetic stirring intensity and promote equiaxed crystal nucleation; if R m If the target value is met, the current electromagnetic stirring parameters are maintained.

[0098] The PID algorithm, also known as the proportional-integral-derivative control algorithm, calculates a control output based on the error between the target value and the current value, thereby quickly and stably reaching the target value.

[0099] The proportion R of columnar crystals based on monitoring m Given the target value R for the proportion of columnar crystals, the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification is calculated using a PID algorithm, including: Based on the monitored columnar crystal ratio R m The deviation value e(t) between the target value R of columnar crystal ratio is used to calculate the adjustment amount ΔI of the electromagnetic stirring current at the end of solidification using a PID algorithm. Where ΔI(t)=K p ·e(t)+K i ·∫e(t)dt+K d ·de(t) / dt, e(t)=RR m .

[0100] Thus, based on the currently monitored columnar crystal ratio R m and the deviation between the columnar crystal ratio and the target value R, the change in deviation, and the change rate of the deviation change, the adjustment amount ΔI(t) of the electromagnetic stirring current at the solidification end is calculated, so that the electromagnetic stirring current can be adjusted smoothly and stably in the direction that makes the columnar crystal ratio reach the target value R.

[0101] In one embodiment, K p = 0.5~1.5, K i = 0.05~0.15, K d = 0.02~0.08.

[0102] In one embodiment, the target value R of the columnar crystal ratio is R1~R2, that is, the target value of the columnar crystal ratio is an interval range.

[0103] Thus, when the monitored columnar crystal ratio R m < R1, the calculation is performed based on R1 as the target columnar crystal ratio, e(t)=R1-R m .

[0104] When the monitored columnar crystal ratio R m > R2, the calculation is performed based on R2 as the target columnar crystal ratio, e(t)=R2-R m .

[0105] When the monitored columnar crystal ratio R m is within the range of R1~R2, the electromagnetic stirring current at the solidification end remains unchanged.

[0106] That is, when the monitored columnar crystal ratio R m is not within the target range, calculation and adjustment are performed by taking the endpoint value of the target range closest to the monitored columnar crystal ratio R m as the target value.

[0107] In one embodiment, the electromagnetic stirring intensity parameter further comprises electromagnetic stirring frequency.

[0108] The determining the initial value of electromagnetic stirring intensity at the solidification end in the continuous casting process further comprises: determining the electromagnetic stirring frequency at the solidification end in the continuous casting process to be 3~7 Hz.

[0109] In this way, it is not necessary to adjust the electromagnetic stirring frequency at the solidification end, thereby simplifying the control method and saving costs.

[0110] In another embodiment, the electromagnetic stirring intensity parameter comprises electromagnetic stirring current.

[0111] The determination of the initial value of the electromagnetic stirring intensity at the solidification end of the continuous casting process includes: Determine the initial value f0 of the electromagnetic stirring frequency at the solidification end of the continuous casting process.

[0112] The proportion R of columnar crystals as monitored m Adjusting the intensity of electromagnetic stirring at the end of solidification includes: Based on the monitored columnar crystal ratio R m Adjust the electromagnetic stirring frequency f at the end of solidification.

[0113] Thus, by adjusting the electromagnetic stirring frequency f at the end of solidification, the intensity of electromagnetic stirring at the end of solidification can be fine-tuned, thereby fine-tuning the proportion of columnar crystals in the billet.

[0114] The initial value f0 of the electromagnetic stirring frequency at the end of solidification is 3~7Hz.

[0115] In one embodiment, determining the initial value I0 of the electromagnetic stirring current at the end of solidification in the continuous casting process includes: The preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content of the molten steel. y ; Determine the preset value I of the electromagnetic stirring current at the end of solidification. y I0 is the initial value of the electromagnetic stirring current at the end of solidification.

[0116] In this way, the electromagnetic stirring current at the end of solidification can be determined based on the influence of alloying elements in molten steel on columnar and equiaxed crystals during the solidification process of the billet, which is beneficial to control the proportion of columnar crystals in the billet formed at the end of solidification.

[0117] In one embodiment, the preset value I of the electromagnetic stirring current at the solidification end is calculated based on the alloy element content in the molten steel. y include: The preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y .

[0118] Since Si and Al significantly reduce the high-temperature thermal conductivity of steel, which is beneficial to the development of columnar crystals during solidification, and Mn can refine the solidification structure and promote the formation of equiaxed crystals, the preset value of the electromagnetic stirring current I at the end of solidification is calculated based on the Si, Al, and Mn element content in the molten steel. y This is to ensure that the proportion of columnar crystals in the billet formed at the solidification endpoint reaches the target value.

[0119] In one embodiment, I y=300 + 30 × Si + 20 × Al + 10 × Mn, where the element symbols represent the mass percentage of the corresponding element. Thus, the influence of Si, Al, and Mn alloying elements on heat transfer efficiency during solidification can be quantified into the control of the electromagnetic stirring current, thereby achieving control over the proportion of columnar crystals.

[0120] In one embodiment, determining the initial value I0 of the electromagnetic stirring current at the solidification end of the continuous casting process further includes: The initial value adjustment amount ΔI0 of the electromagnetic stirring current at the end of solidification is determined based on the fluctuation amount Δv of the continuous casting speed, the fluctuation amount ΔT of the superheat of the molten steel, and the fluctuation amount ΔC of the alloy element content in the molten steel. Determine the preset value I of the electromagnetic stirring current at the end of solidification. y The sum of the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification and the initial value adjustment ΔI0 of the electromagnetic stirring current at the end of solidification is the initial value I0 of the electromagnetic stirring current at the end of solidification.

[0121] Because the temperature and alloy element content of different batches of molten steel will fluctuate during the continuous casting process, and the casting speed will also fluctuate, it is necessary to adjust the initial value of the electromagnetic stirring current at the solidification end according to the different batches of molten steel poured during the continuous casting process and the actual casting speed, so as to make the proportion of columnar crystals in the continuously cast billet reach the target value and have universal applicability.

[0122] In one embodiment, the initial value adjustment amount of the electromagnetic stirring current at the end of solidification is ΔI0=k. v ·Δv+k T ·ΔT+k C ·ΔC; Where, Δv=v m -v0, v m v0 is the measured value of the continuous casting speed, and v0 is the preset value of the continuous casting speed. m Both v0 and v0 are in m / min. ΔT=T m -T0, T m T0 is the measured value of the superheat of molten steel, and T0 is the preset value of the superheat of molten steel. m The units for T0 are both °C; ΔC=C m -C0,C m C0 is the measured sum of the Si, Al, and Mn element contents in the molten steel, and C0 is the preset sum of the Si, Al, and Mn element contents in the molten steel. m Both C0 and C0 are in units of %.

[0123] In other words, in the above formula, v m v0, T m T0, C mBoth C0 and C0 are calculated by substituting the values ​​into the units listed above.

[0124] Where, k v k is the coefficient of variation of continuous casting speed. T k is the coefficient of change in superheat of molten steel. C This is the coefficient of variation of the alloying element content in molten steel.

[0125] k v For 100~200, k T For 8~15, k C It is 20~30.

[0126] In one implementation, k v k T k C The value was determined by linear regression with the electromagnetic stirring current value at the end of solidification.

[0127] In one embodiment, the proportion of columnar crystals in the billet formed at the solidification endpoint during the real-time monitoring of the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint is determined by X-ray detection.

[0128] The solidification structure of the billet formed at the solidification endpoint, i.e., the continuously cast billet, includes a fine-grained surface region, a columnar grain region, and a central equiaxed grain region. Their distribution and morphology determine the internal uniformity and density of the continuously cast billet, directly affecting the material's mechanical properties. Due to their regular crystal structure and consistent grain orientation, the columnar grain region exhibits measurable differences in X-ray scattering and absorption characteristics compared to the equiaxed grain region.

[0129] X-ray inspection technology utilizes the attenuation characteristics of X-rays as they penetrate matter to obtain internal information about the object being inspected. After X-rays penetrate a continuously cast billet, columnar crystal regions, due to their large grain size, low grain boundary density, and strong crystallographic orientation consistency, exhibit relatively high X-ray transmittance and appear as brighter areas on the detector. Conversely, equiaxed crystal regions, with their fine grains, high grain boundary density, and random orientation, experience stronger X-ray scattering and absorption, resulting in relatively lower transmittance and appearing as darker areas. This difference in brightness forms the material basis for distinguishing between columnar and equiaxed crystals.

[0130] In one embodiment, the continuous casting equipment further includes an online X-ray inspection system. The control system is connected to the online X-ray inspection system and is used to obtain the proportion R of columnar crystals in the billet formed at the solidification endpoint detected by the online X-ray inspection system. m .

[0131] X-ray inspection is performed using an online X-ray inspection system.

[0132] The X-ray online inspection system includes: An X-ray source that emits X-rays at an energy of 150-450 kV; A detector array is located on the side of the billet away from the X-ray source to receive transmitted signals; A collimator, placed between the X-ray source and the detector array, collimates the X-rays emitted by the X-ray source to form a narrow beam of scanning rays, thereby reducing scattering interference. The image processing and control system acquires signals received by the detector array in real time, performs image reconstruction and columnar crystal ratio recognition calculation, and transmits the calculation results to the control system to adjust the electromagnetic stirring intensity at the solidification end.

[0133] The energy emitted by the X-ray source can be automatically adjusted according to the thickness of the billet.

[0134] The detector array can employ high-sensitivity linear or area array detectors. For example, amorphous silicon planar detectors, CdTe semiconductor detectors, or CdZnTe semiconductor detectors.

[0135] Specifically, when X-rays pass through a continuously cast billet, their intensity follows the Lambert-Beer attenuation law: .

[0136] Where I is the intensity of the transmitted X-rays, I0 is the intensity of the incident X-rays, and μ is the linear attenuation coefficient, with units of cm. -1 μ reflects the absorption capacity of the medium (such as columnar crystals or equiaxed crystals) for X-rays; x is the path length of X-rays propagating in the medium, in cm.

[0137] A detector array acquires X-ray grayscale images of the cross-section of the continuously cast billet. After filtering, noise reduction, and contrast enhancement, a clear image of the solidification structure is obtained. Edge detection operators such as the Canny and Sobel operators are used to extract grayscale abrupt boundary changes and automatically delineate the inner contour lines of columnar crystal regions, thereby identifying the columnar crystal regions. Then, the pixel area of ​​the columnar crystal region is calculated, and the ratio of the pixel area of ​​the columnar crystal region to the total pixel area of ​​the cross-section is the columnar crystal area ratio R. Based on the low-magnification imaging principle of the solidification structure of the continuously cast billet, the area ratio of the columnar crystal region can be directly equivalent to the volume ratio of the columnar crystals, and is fed back to the control system as a feedback quantity for the image processing and control system.

[0138] In one embodiment, X-ray detection performs cross-sectional scanning and proportion calculation every 5 to 30 seconds to achieve continuous online monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint.

[0139] Specifically, the X-ray online detection system can use fan-shaped beamline scanning or multi-source array static scanning to perform scanning, with a detection frequency of 5 to 30 seconds per scan.

[0140] In another embodiment, the real-time monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint during the continuous casting process includes: The proportion of columnar crystals in the billet formed at the solidification endpoint is detected by ultrasonic testing.

[0141] The significant difference in grain size between columnar and equiaxed crystals affects the scattering and attenuation of ultrasound waves. Columnar crystals have large, uniformly oriented grains, resulting in lower ultrasound attenuation, higher echo amplitude, and narrower frequency distribution. In contrast, equiaxed crystals have small, randomly oriented grains, resulting in greater ultrasound attenuation, lower echo amplitude, and wider frequency distribution.

[0142] By propagating ultrasound in the billet, reflection and scattering occur when it encounters the boundary between columnar and equiaxed crystal regions. Based on the echo time-domain signal, the proportion of columnar crystals in the billet formed at the solidification endpoint can be detected.

[0143] In one embodiment, the continuous casting equipment further includes an online ultrasonic detection system. The control system is connected to the online ultrasonic detection system and is used to acquire the proportion R of columnar crystals in the billet formed at the solidification endpoint detected by the online ultrasonic detection system. m .

[0144] Ultrasonic testing is performed using an online ultrasonic testing system.

[0145] The ultrasonic online testing system includes: An electromagnetic ultrasonic transducer (EMAT) includes a high-frequency coil and a bias magnetic field system. The high-frequency coil includes a transmitting coil and a receiving coil.

[0146] An ultrasonic pulse transmitting and receiving system is used to generate high-voltage pulses to excite the EMAT to transmit ultrasonic waves and to receive the echo signals.

[0147] The signal processing unit is used to amplify, filter, perform analog-to-digital conversion, analyze the spectrum, extract features, and classify patterns in the echo signal.

[0148] The control system interface will use the calculated columnar crystal ratio R m Feedback is sent to the control system to adjust the intensity of electromagnetic stirring at the end of solidification.

[0149] Among them, the electromagnetic ultrasonic transducer (EMAT) performs non-contact detection by using non-contact electromagnetic induction to excite and receive ultrasonic transverse waves, which can operate without coupling agent and can operate in high-temperature environments.

[0150] The working principle of EMAT is based on electromagnetic acoustic transduction. When a high-frequency current passes through the high-frequency coil, the resulting alternating magnetic field induces eddy currents on the surface of the billet. The eddy currents interact with the bias static magnetic field to generate Lorentz force, thereby exciting high-frequency elastic waves (transverse or longitudinal waves) inside the billet. The high-frequency elastic waves propagate in the billet and are reflected and scattered when they encounter the microstructure boundaries of columnar and equiaxed crystal regions. The echo signal is received by EMAT.

[0151] An electromagnetic ultrasonic transducer (EMAT) can be installed at the exit of the fan-shaped section of the secondary cooling zone of a continuous casting machine. By installing at least one EMAT probe in the width direction of the billet, the echo signal can be detected.

[0152] In one embodiment, ultrasonic detection performs scanning and proportion calculation every 10 to 20 seconds to achieve continuous online monitoring of the proportion of columnar crystals in the billet formed at the solidification endpoint.

[0153] In one embodiment, the control method further includes: The X-ray or ultrasonic testing is calibrated using a low-magnification acid immersion method.

[0154] Specifically, when changing steel grades or at the beginning of each casting, a sample of the billet at the end of solidification is taken. After low-magnification acid etching, the solidification structure (including fine-grained region, columnar region, and equiaxed region) is observed. By comparing the boundary of the columnar region measured by X-ray detection or ultrasonic detection with the boundary of the columnar region in the low-magnification acid etching photograph, a calibration curve is established to calibrate the X-ray detection or ultrasonic detection.

[0155] In one embodiment, during the continuous casting process, electromagnetic stirring is performed at the end of solidification, while the crystallizer is not subjected to electromagnetic stirring. This avoids the expansion of the equiaxed crystal zone, thus promoting an increase in the proportion of columnar crystals.

[0156] In one embodiment, during the continuous casting process, electromagnetic stirring is not performed in the secondary cooling zone except at the end of solidification, in order to prevent the expansion of the equiaxed crystal zone and thus facilitate an increase in the proportion of columnar crystals.

[0157] In one embodiment, electromagnetic stirring is performed only at the end of the solidification process during continuous casting.

[0158] In high-grade non-oriented silicon steel, Si and Al are the core elements for improving resistivity and reducing iron loss. However, increasing the Si and Al content will significantly reduce the high-temperature thermal conductivity of the molten steel, thereby reducing the initial solidified shell thickness of the continuously cast billet. Mn, on the other hand, affects the width of the solidification two-phase region and the high-temperature strength of the billet shell.

[0159] In one embodiment, during the continuous casting process, the billet shell thickness h at the outlet of the crystallizer is controlled to be ≥8Si+10Al+9Mn. Thus, on the one hand, controlling the billet shell thickness at the crystallizer outlet based on the Si, Al, and Mn contents not only ensures the initial solidified shell thickness of the continuously cast billet, correspondingly reducing the bulging on the billet's wide face, and preventing bulging deformation in the secondary cooling zone, thereby avoiding abnormal growth of ferrite columnar crystals induced by the internal stress of bulging, thus reducing serrated edge crack defects in hot-rolled plates, lowering the difficulty of hot rolling, and reducing waste caused by edge trimming, but also lays the foundation for controlling a large proportion of columnar crystals and can cope with the preparation of non-oriented silicon steel with various compositional variations. On the other hand, this allows for the pre-determination of the minimum required initial solidified shell thickness of the continuously cast billet, and the targeted adjustment of the crystallizer's cooling intensity, such as cooling water flow rate and velocity, to control the initial solidified shell thickness of the continuously cast billet.

[0160] It is understandable that the element symbols in the formula represent the mass percentage of the corresponding element. For example, the mass fraction of Si [Si] means that the mass percentage of Si in molten steel is 2.5%, so the Si in the formula is calculated by substituting 2.5. In addition, the mass percentage of Si, Al, or Mn in the molten steel can be obtained by testing the molten steel poured during continuous casting (or the molten steel at the end of the steelmaking process).

[0161] In one embodiment, during the continuous casting process, the cooling water flow rate of the wide face of the crystallizer is controlled at 2500~4500 L / min, the cooling water flow rate of the narrow face is controlled at 400~700 L / min, the crystallizer inlet water temperature is controlled at 28~35℃, the inlet and outlet water temperature difference is controlled at 6~10℃, and the average heat flux density of the crystallizer is controlled at 1200~2000 kW / m³. 2 By controlling the cooling water flow rate and inlet / outlet water temperature of the crystallizer, the initial solidified shell thickness of the continuously cast billet can be effectively increased.

[0162] In one embodiment, during the continuous casting process, the cooling rate of the secondary cooling zone is controlled to gradually decrease along the foot roll section, sector sections 1-4, and sector sections 5-12. That is, the cooling rate of sector sections 1-4 is lower than that of the foot roll section, and the cooling rate of sector sections 5-12 is lower than that of sector sections 1-4. Thus, using a higher cooling rate in the foot roll section promotes rapid shell thickening and prevents bulging deformation; in sector sections 1-4, the billet still has a relatively thick liquid core, and maintaining a certain cooling rate can maintain a certain cooling intensity to synergistically increase the proportion of columnar crystals; in sector sections 5-12, the billet is about to completely solidify, and appropriately reducing the cooling rate can prevent cracks caused by thermal stress.

[0163] The cooling rate of the foot roller section is controlled at 3~10℃ / s, the cooling rate of the first to fourth fan-shaped sections is 0.5~8℃ / s, and the cooling rate of the fifth to twelfth fan-shaped sections is 0.2~1.5℃ / s.

[0164] Furthermore, the cooling rate of sector segments 1 to 4 gradually decreases from segment 1 to segment 4. Specifically, the cooling rate of sector segment 1 is 2~8℃ / s, and the cooling rate of sector segment 4 is 0.5~3℃ / s.

[0165] In one embodiment, during the continuous casting process, the specific water content of the foot roll section is controlled at 1.2~2.5 L / kg, the cooling water volume of the wide section is 260~600 L / min, and the cooling water volume of the narrow section is 50~125 L / min; the specific water content of the first to fourth fan-shaped sections is controlled at 0.8~1.5 L / kg, and the surface temperature of the billet is controlled at 1000~1100℃; the specific water content of the fifth to 12th fan-shaped sections is controlled at 0.3~0.8 L / kg; and the straightening temperature of the billet at the straightening machine is controlled to be >950℃ to avoid the brittle zone. By controlling these parameters, the cooling rate and cooling rhythm of the secondary cooling zone can be controlled to achieve control over the columnar crystal ratio of the continuously cast billet.

[0166] In one embodiment, during the continuous casting process, the surface cooling rate of the billet along its length is controlled to be <150°C / m.

[0167] In one embodiment, during the continuous casting process, the continuous casting speed v, the target thickness δ of the continuous casting billet, and the target width w are controlled to satisfy 0.21-0.005×(Si+Al)≤v×δ×w≤0.22-0.003×(Si+Al), and v×δ×w is negatively correlated with Si+Al, where the units of v are m / min, δ are m, and w are m.

[0168] Thus, by controlling the continuous casting speed *v*, the initial solidified shell thickness of the continuously cast billet can be increased (i.e., the shell thickness of the billet when it leaves the crystallizer), correspondingly reducing the bulge on the wide side of the billet. This avoids the abnormal growth of columnar ferrite crystals induced by the internal stress of the bulge, thereby reducing the serrated edge crack defect in hot-rolled plates. This production method also avoids a series of derivative problems such as lowering the heating temperature, increasing the difficulty of hot rolling, and waste caused by edge trimming. When the Si+Al content is high, the casting speed is controlled to be lower to prolong the solidification time and promote columnar crystal development.

[0169] Among them, 0.7m / min≤v≤1.2m / min, 0.18m≤δ≤0.25m, and 1.0m≤w≤1.3m.

[0170] In one embodiment, the superheat of the molten steel in the continuous casting process is 10~15°C, thereby controlling the thickness of the billet shell at the outlet of the crystallizer.

[0171] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application, and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

[0172] The beneficial effects of this application will be further illustrated below through specific embodiments 1-2 and comparative examples 1-3. Both embodiments employ the longitudinal thickness fluctuation control method for strip steel described in this application for cold continuous rolling. Of course, these two embodiments are only a part of the numerous variations contained in this application, and not all of them.

[0173] Example 1 The chemical composition of the non-oriented silicon steel in this embodiment, by mass percentage, includes: C 0.0022%, Si 3.0%, Al 1.0%, Mn 0.5%, Nb 0.0012%, V 0.0009%, Ti 0.0011%, Cr 0.013%, Ni 0.011%, Cu 0.021%, N 0.0011%, S 0.0009%, P 0.035%, with the remainder being Fe and unavoidable impurities.

[0174] The production method of this non-oriented silicon steel includes the following steps.

[0175] (1) Continuous casting Molten steel is fed into a continuous casting machine for casting. The superheat of the molten steel is 13°C, and it is continuously cast into a continuous casting billet with a thickness δ of 220 mm and a width w of 1.01 m.

[0176] The cooling water flow rate of the wide face of the crystallizer is 4000 L / min, and the cooling water flow rate of the narrow face is 580 L / min. The inlet water temperature of the crystallizer is 28~35℃, the inlet and outlet water temperature difference is 6~10℃, and the average heat flux density of the crystallizer is 1800 kW / m³. 2 The thickness h of the billet shell at the outlet of the crystallizer is 39.2 mm.

[0177] The continuous casting speed v is 0.9 m / min.

[0178] Within the second cooling zone, the surface cooling rate of the billet along its length is <150℃ / m. Specifically, the specific water volume of the foot roll section is 2.0L / kg, the wide-face cooling water volume is 550L / min, the narrow-face cooling water volume is 100L / min, and the cooling rate of the foot roll section is 8℃ / s; the specific water volume of sector sections 1-4 is 1.3L / kg, the surface temperature of the billet is 1000~1100℃, and the cooling rate of sector sections 1-4 is 6℃ / s; the specific water volume of sector sections 5-12 is 0.7L / kg, and the cooling rate of sector sections 5-12 is 1.3℃ / s; the straightening temperature of the billet at the tension leveler is 980℃.

[0179] Electromagnetic stirring is performed only at the end of the solidification zone in the secondary cooling zone, while electromagnetic stirring is not performed in the crystallizer, and electromagnetic stirring is not performed in the secondary cooling zone except at the end of the solidification zone.

[0180] First, the initial value of the electromagnetic stirring intensity at the end of solidification was determined to be 410A, and the electromagnetic stirring frequency at the end of solidification was determined to be 7Hz. The proportion R of columnar crystals in the billet formed at the solidification endpoint was monitored in real time using X-rays. m And based on the monitored columnar crystal ratio R m Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. m Adjusted to 68%.

[0181] (2) Hot rolling The continuously cast billet obtained from the continuous casting process is heated and then subjected to rough rolling, finish rolling and cooling in sequence to obtain hot-rolled strip steel with a thickness of 2.3 mm.

[0182] During heating, the continuously cast billet is fed into the heating furnace. The homogenization temperature is 1100℃, and the heating time is 220 minutes.

[0183] The roughing process employs a reversible roughing mill unit with six passes. This unit comprises two sequentially arranged roughing mills: R1 and R2. R1 performs passes 1, 3, and 5, while R2 performs passes 2, 4, and 6. In the R1 roughing mill, the ratio of the lower roll diameter D2 to the upper roll diameter D1 is 1.05; similarly, in the R2 roughing mill, the ratio of the upper roll diameter D3 to the lower roll diameter D4 is 1.05. The upper and lower rolls of both the R1 and R2 roughing mills rotate at the same speed.

[0184] The reduction rate per pass in the roughing mill is 35%, and the final rolling temperature is 1000℃. The thickness of the intermediate billet obtained from the roughing mill is 43mm.

[0185] The finishing mill is a seven-stand mill. The reduction rate for each pass in the finishing mill is 32%, and the final rolling temperature is 880℃.

[0186] The hot-rolled strip obtained from finishing rolling is then subjected to laminar flow cooling and then coiled at a coiling temperature of 650℃.

[0187] (3) Normalization The temperature of the soaking zone for normalization was 950℃, and the normalization time was 3 minutes.

[0188] (4) Shot blasting and pickling (5) Cold rolling After five rolling passes, it is rolled into cold-rolled strip steel with a thickness of 0.20 mm.

[0189] (6) Annealing and coating Annealing was carried out in a protective atmosphere consisting of a mixture of 20% H2 and 80% N2. The annealing temperature was 980℃ and the annealing time was 60s.

[0190] An insulating coating is then applied to the surface of the strip steel to obtain the finished non-oriented silicon steel product.

[0191] In the production process of non-oriented silicon steel in this embodiment, there are no edge cracks during hot rolling, no edge cracks or strip breaks during cold rolling, and the final non-oriented silicon steel product is free of corrugated defects.

[0192] Example 2 The chemical composition of the non-oriented silicon steel in this embodiment, by mass percentage, includes: C 0.0020%, Si 2.7%, Al 0.8%, Mn 0.4%, Nb 0.0012%, V 0.0011%, Ti 0.0009%, Cr 0.015%, Ni 0.013%, Cu 0.017%, N 0.0012%, S 0.0009%, P 0.041%, with the remainder being Fe and unavoidable impurities.

[0193] The production method of this non-oriented silicon steel includes the following steps.

[0194] (1) Continuous casting Molten steel is fed into a continuous casting machine for casting. The superheat of the molten steel is 12°C, and it is continuously cast into a continuous casting billet with a thickness δ of 220 mm and a width w of 1.05 m.

[0195] The cooling water flow rate of the wide face of the crystallizer is 3500 L / min, and the cooling water flow rate of the narrow face is 550 L / min. The inlet water temperature of the crystallizer is 28~35℃, the inlet and outlet water temperature difference is 6~10℃, and the average heat flux density of the crystallizer is 1800 kW / m³. 2 The thickness h of the billet shell at the outlet of the crystallizer is 40 mm.

[0196] The continuous casting speed v is 0.87 m / min.

[0197] Within the secondary cooling zone, the surface cooling rate of the billet along its length is <150℃ / m. Specifically, the specific water volume of the foot roll section is 2.3L / kg, the cooling water volume of the wide face is 450L / min, the cooling water volume of the narrow face is 120L / min, and the cooling rate of the foot roll section is 8℃ / s; the specific water volume of sector sections 1-4 is 1.4L / kg, the surface temperature of the billet is 1000~1100℃, and the cooling rate of sector sections 1-4 is 6℃ / s; the specific water volume of sector sections 5-12 is 0.7L / kg, and the cooling rate of sector sections 5-12 is 1.3℃ / s; the straightening temperature of the billet at the tension leveler is 970℃.

[0198] Electromagnetic stirring is performed only at the end of the solidification zone in the secondary cooling zone, while electromagnetic stirring is not performed in the crystallizer, and electromagnetic stirring is not performed in the secondary cooling zone except at the end of the solidification zone.

[0199] First, the initial value of the electromagnetic stirring intensity at the end of solidification was determined to be 415A, and the electromagnetic stirring frequency at the end of solidification was determined to be 6Hz. The proportion R of columnar crystals in the billet formed at the solidification endpoint was monitored in real time using X-rays. m And based on the monitored columnar crystal ratio R m Adjust the intensity of electromagnetic stirring at the end of solidification to reduce the proportion R of columnar crystals in the billet formed at the solidification endpoint. m Adjusted to 58%.

[0200] (2) Hot rolling The continuously cast billet obtained from the continuous casting process is heated and then subjected to rough rolling, finish rolling and cooling in sequence to obtain hot-rolled strip steel with a thickness of 2.3 mm.

[0201] During heating, the continuously cast billet is fed into the heating furnace. The homogenization temperature is 1100℃, and the heating time is 220 minutes.

[0202] The roughing process employs a reversible roughing mill unit with six passes. This unit comprises two sequentially arranged roughing mills: R1 and R2. R1 performs passes 1, 3, and 5, while R2 performs passes 2, 4, and 6. In the R1 roughing mill, the ratio of the lower roll diameter D2 to the upper roll diameter D1 is 1.08; similarly, in the R2 roughing mill, the ratio of the upper roll diameter D3 to the lower roll diameter D4 is 1.08. The upper and lower rolls of both the R1 and R2 roughing mills rotate at the same speed.

[0203] The reduction rate per pass in the roughing mill is 35%, and the final rolling temperature is 990℃. The thickness of the intermediate billet obtained from the roughing mill is 42mm.

[0204] The finishing mill is a seven-stand mill. The reduction rate for each pass in the finishing mill is 32%, and the final rolling temperature is 870℃.

[0205] The hot-rolled strip obtained from finishing rolling is then subjected to laminar flow cooling and then coiled at a coiling temperature of 650℃.

[0206] (3) Normalization The temperature of the soaking zone for normalization was 950℃, and the normalization time was 2.2 min.

[0207] (4) Shot blasting and pickling (5) Cold rolling After five rolling passes, it is rolled into cold-rolled strip steel with a thickness of 0.20 mm.

[0208] (6) Annealing and coating Annealing was carried out in a protective atmosphere consisting of a mixture of 20% H2 and 80% N2. The annealing temperature was 980℃ and the annealing time was 60s.

[0209] An insulating coating is then applied to the surface of the strip steel to obtain the finished non-oriented silicon steel product.

[0210] In the production process of non-oriented silicon steel in this embodiment, there are no edge cracks during hot rolling, no edge cracks or strip breaks during cold rolling, and the final non-oriented silicon steel product is free of corrugated defects.

[0211] Comparative Example 1 Comparative Example 1 and Example 1 are identical in all processes except for the continuous casting process, and will not be described again here. The following only introduces the differences.

[0212] In this comparative example, the proportion of columnar crystals in the billet formed at the end of the continuous casting process was 35%, and the proportion of columnar crystals was not monitored and controlled in real time. The proportion of columnar crystals was obtained by testing with the traditional low-magnification acid leaching method after the continuous casting process was completed.

[0213] In this comparative example, the continuously cast billet obtained by continuous casting had severe bulging, and the edge cracking rate during hot rolling was as high as 28%, which led to the inability to produce normally in the future.

[0214] Comparative Example 2 Comparative Example 2 is identical to Example 1 except for the continuous casting process, and will not be described again here. The following only introduces the differences.

[0215] In this comparative example, the proportion of columnar crystals in the billet formed at the end of the continuous casting process was 88%, and the proportion of columnar crystals was not monitored and controlled in real time. The proportion of columnar crystals was obtained by testing with the traditional low-magnification acid leaching method after the continuous casting process was completed.

[0216] The comparative example showed no edge cracks during hot rolling, but the final silicon steel product had obvious corrugated defects on its surface.

[0217] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is the hot rolling process; all other processes are the same and will not be described again here. The following description focuses only on the hot rolling process.

[0218] (2) Hot rolling The continuously cast billet obtained from the continuous casting process is heated and then subjected to rough rolling, finish rolling and cooling in sequence to obtain hot-rolled strip steel with a thickness of 2.3 mm.

[0219] During heating, the continuously cast billet is fed into the heating furnace. The homogenization temperature is 1100℃, and the heating time is 220 minutes.

[0220] The roughing process employs a reversible roughing mill unit with six passes. This unit comprises two sequentially arranged roughing mills: R1 and R2. R1 performs passes 1, 3, and 5, while R2 performs passes 2, 4, and 6. The upper and lower work rolls of the R1 roughing mill have the same diameter and rotational speed; similarly, the upper and lower work rolls of the R2 roughing mill also have the same diameter and rotational speed.

[0221] The reduction rate per pass in the roughing mill is 35%, and the final rolling temperature is 1000℃. The thickness of the intermediate billet obtained from the roughing mill is 42mm.

[0222] The finishing mill is a seven-stand mill. The reduction rate for each pass in the finishing mill is 32%, and the final rolling temperature is 830℃.

[0223] The hot-rolled strip obtained from finishing rolling is then subjected to laminar flow cooling and then coiled at a coiling temperature of 650℃.

[0224] The comparative example showed no edge cracks during hot rolling, but the final silicon steel product had obvious corrugated defects on its surface.

[0225] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for producing high-grade non-oriented silicon steel, characterized in that, In terms of mass percentage, the chemical composition of the non-oriented silicon steel comprises: Si 2.5~3.5%, Al 0.5~1.5%, Mn 0.2~0.8%; the production method comprises continuous casting, hot rolling, normalization, cold rolling, annealing and coating processes performed in sequence; In the continuous casting process, the proportion of columnar crystals in the continuous casting billet obtained by the continuous casting process is controlled to be 50~80%; The hot rolling process comprises rough rolling and finish rolling performed successively, the finish rolling temperature of rough rolling is 980~1020°C, and the finish rolling temperature of finish rolling is 860~900°C; The rough rolling comprises even-pass rough rolling; in the work rolls of the roughing mill adopted for odd-pass rough rolling, the linear velocity of the upper roll is u1, and the linear velocity of the lower roll is u4; in the work rolls of the roughing mill adopted for even-pass rough rolling, the linear velocity of the upper roll is u3, and the linear velocity of the lower roll is u4; wherein u1>u2, u3<u4, u1 / u2=1.05~1.10, u4 / u3=1.05~1.10; or u1<u2, u3>u4, u2 / u1=1.05~1.10, u3 / u4=1.05~1.

10.

2. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, u1=u4, u2=u3.

3. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, In the work rolls of the roughing mill adopted for odd-pass rough rolling, the diameter of the upper roll is D1, and the diameter of the lower roll is D2; in the work rolls of the roughing mill adopted for even-pass rough rolling, the diameter of the upper roll is D3, and the diameter of the lower roll is D4; wherein D1>D2, D3<D4; or D1<D2, D3>D4.

4. The production method of high-grade non-oriented silicon steel according to claim 3, characterized in that D1>D2, D3<D4, D1 / D2=1.05~1.10, D4 / D3=1.05~1.10; or D1<D2, D3>D4, D2 / D1=1.05~1.10, D3 / D4=1.05~1.

10.

5. The method for producing high-grade non-oriented silicon steel according to claim 3, characterized in that, D1=D4, D2=D3.

6. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, the rotating speeds of the upper roll and the lower roll of the work rolls of each roughing mill are the same.

7. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, Rough rolling adopts a reversible roughing mill train, the reversible roughing mill train comprises an R1 roughing mill and an R2 roughing mill arranged in sequence, the R1 roughing mill performs odd-pass rough rolling, and the R2 roughing mill performs even-pass rough rolling.

8. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, the reduction ratio per pass in rough rolling is 32~38%, and the reduction ratio per pass in finish rolling is 30~38%.

9. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, In the hot rolling process, the coiling temperature is 600~680°C.

10. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, In the normalization process, the temperature of the soaking section for normalization is 920~970°C, and the normalization time is 2~3min.

11. The method for producing high-grade non-oriented silicon steel according to claim 1, characterized in that, In the annealing and coating process, the annealing temperature is 950~1050°C, and the annealing time is 50~80s.

12. A high-grade non-oriented silicon steel, characterized in that, The high-grade non-oriented silicon steel is prepared by the production method of high-grade non-oriented silicon steel according to any one of claims 1~11.