Method for improving slab quality by complex electromagnetic stirring and application thereof

Abstract

A method for improving slab quality using composite electromagnetic stirring and its application are disclosed. The method involves stirring the upper part of the crystallizer and braking the lower part, with braking achieved using a stable constant magnetic field generated by direct current. Stirring in the upper part of the crystallizer refreshes the protective slag, promotes the adsorption of inclusions, and washes away bubbles and inclusions trapped in the solidified slab shell. Braking the lower part of the crystallizer reduces the impact depth. Furthermore, the electromagnetic stirring device employs two copper plates joined together using superconducting magnets, addressing the problem of significant rigid deformation that often occurs with copper plate electromagnetic stirrers in large-section crystallizers.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, specifically to a method for improving slab quality through composite electromagnetic stirring and its application. Background Technology

[0002] In continuous casting, fluctuations in the flow rate typically lead to the entrapment of mold flux. Furthermore, the use of vertically curved continuous casting machines with long vertical sections can cause excessive impact depth, resulting in insufficient inclusion flotation. Existing companies employ electromagnetic stirring technology in the mold to agitate inclusions within the flow field, aiming to clean and remove inclusions trapped in the solidified billet shell. However, in continuous casting, because the mold is generally vertical, molten steel can carry inclusions deep into the liquid core, causing insufficient flotation. Therefore, addressing the problem of insufficient inclusion flotation requires in-depth research.

[0003] Chinese patent CN113000800B discloses a method for improving the surface and subsurface quality of slabs using electromagnetic stirring. In this method, continuous casting employs electromagnetic stirring in the crystallizer, with the center of the electromagnetic stirrer positioned 90-110 mm below the meniscus of the molten steel. Based on the characteristics of the steel grade and the magnitude of the electromagnetic force for different stirring parameters, corresponding electromagnetic stirring parameters are matched for different C-content steel grades and slab widths. Furthermore, by installing current transformers on the lines transmitting these parameters and limiting the thickness of the copper plating on the upper copper plate of the crystallizer, interference from the electromagnetic signals released by the stirrer on the crystallizer's liquid level detector is reduced. This maximizes the metallurgical effect of the electromagnetic stirrer, reducing the incidence of longitudinal cracks on the slab surface and the number of subsurface non-metallic inclusions and bubbles. The defect rate of the finished slab surface is controlled below 0.45%.

[0004] Chinese patent CN105728679B discloses a meniscus electromagnetic stirring system and method for continuous casting of square and round billets with magnetic shielding and multiple modes. The system includes a meniscus electromagnetic stirrer and a frequency conversion power supply control system. By changing the phase sequence and phase angle of the current in the coil, a meniscus electromagnetic stirring mode or a crystallizer stirring mode can be realized. The meniscus electromagnetic stirring mode includes two sub-modes: one that allows the molten steel to form a single circulation zone and the other that allows it to form a single-double circulation zone. For steel grades with high internal quality requirements, the crystallizer stirring mode is selected for stirring, while for steel grades with high surface and subsurface quality requirements, the meniscus electromagnetic stirring mode is selected for stirring.

[0005] Chinese patent CN108500227A discloses an electromagnetic control method for the flow field of a crystallizer used in slab continuous casting production. Addressing the issue of impact depth, it employs multiple electromagnetic stirrers to control the flow field. These electromagnetic stirrers are traveling wave magnetic field generators, with one installed in the upper region of the wide face of the crystallizer and another in the lower region of the narrow face. The upper electromagnetic stirrer is installed between the upper edge of the nozzle outlet and the meniscus, while the lower electromagnetic stirrer is installed below the impact point between the flow stream from the nozzle side hole and the narrow face. The intersection point of the upper edge of the lower electromagnetic stirrer core and a straight line drawn from the upper edge of the nozzle outlet at the nozzle outlet angle with the narrow face of the crystallizer is at the same height. The stirring coil's stirring direction is from bottom to top, opposite to the direction of the lower circulating flow along the narrow side, thus weakening the impact depth of the lower circulating flow.

[0006] Currently, there is a consensus in the industry to perform stirring in the upper part of the crystallizer, while stirring in the lower part to reduce the impact depth requires further development of solutions. However, with the increasing size of continuous casting machines, the addition of copper plate stirrers to large-sized crystallizers will result in significant rigid deformation. How to address the deformation of the copper plates in large-sized crystallizers, maintain their rigidity, and sustain a certain stirring flow field requires further solutions. Summary of the Invention

[0007] The purpose of this invention is to provide a method for improving the quality of slabs by composite electromagnetic stirring and its application, which removes inclusions, reduces the impact depth of inclusions, and solves the problem of large rigid deformation that easily occurs in the stirring of large cross-section crystallizers by electromagnetic stirrers on copper plates.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for improving slab quality through composite electromagnetic stirring involves installing electromagnetic stirring devices and DC electromagnetic braking devices above and below the crystallizer to form a composite electromagnetic field; wherein...

[0010] The electromagnetic stirring device is set on the crystallizer at the corresponding water inlet position. The upper end of the electromagnetic stirring device is flush with the upper end of the copper plate of the crystallizer, and the lower end of the electromagnetic stirring device is flush with the discharge hole of the water inlet inserted into the crystallizer. The electromagnetic stirring current is 300-700A. The water inlet insertion depth is used as the distance standard d, where d = 50-150mm.

[0011] The DC electromagnetic braking device is located at the bottom of the crystallizer, and the distance between the bottom of the DC electromagnetic braking device and the surface of the molten metal in the crystallizer is 4d; the height of the DC electromagnetic braking device is 4 / 3d, and the electromagnetic braking magnetic field strength is 0.1~0.5T.

[0012] Preferably, the electromagnetic stirring device includes two copper plates spliced ​​together with ultra-thin superconducting magnet sheets with a thickness of 0.2 to 0.5 mm, and coils and iron cores distributed on both sides of the copper plates. The two copper plates are connected by superconducting magnets, and the coils are externally connected to a three-phase AC power supply.

[0013] Preferably, the main components of the superconducting magnet include Ni: 85-92wt%, Nb: 0.03-0.05wt%, C: 0.02-0.05wt%, with the remainder being Fe and unavoidable impurities.

[0014] Preferably, the DC electromagnetic braking device includes an iron core and a coil wound on it, the coil being connected to a DC power supply.

[0015] The smelting of ultra-low carbon aluminum-killed steel includes the following steps: hot metal pretreatment and desulfurization, converter smelting, RH refining, and continuous casting. During the continuous casting process, the above-mentioned composite electromagnetic stirring method for improving slab quality is used to perform composite stirring and braking of the molten steel according to the width of the crystallizer and the casting speed.

[0016] The electromagnetic stirring current is set according to the pulling speed and the width of the crystallizer:

[0017] When the pulling speed is 0.6–1.5 m / min, the crystallizer width is 700–1200 mm, and the electromagnetic stirring current is 500–700 A; when the crystallizer width is 1201–1700 mm, the electromagnetic stirring current is 400–500 A; when the crystallizer width is 1701–2400 mm, the electromagnetic stirring current is 300–400 A.

[0018] When the pulling speed is 1.5–2.0 m / min, the crystallizer width is 700–1200 mm, and the electromagnetic stirring current is 400–500 A; when the crystallizer width is 1201–1700 mm, the electromagnetic stirring current is 350–400 A; when the crystallizer width is 1701–2400 mm, the electromagnetic stirring current is 300–350 A.

[0019] When the pulling speed is greater than 2.0 m / min, the width of the crystallizer is 700-2400 mm, and the electromagnetic stirring current is 300-350 A;

[0020] The strength of the electromagnetic braking magnetic field is set according to the pulling speed and the width of the crystallizer:

[0021] When the pulling speed is 0.6–1.5 m / min, the crystallizer width is 700–1200 mm, and the electromagnetic braking magnetic field strength is 0.2–0.3 T; when the crystallizer width is 1201–1700 mm, the electromagnetic braking magnetic field strength is 0.1–0.3 T; when the crystallizer width is 1701–2400 mm, the electromagnetic braking magnetic field strength is 0.1–0.2 T.

[0022] When the pulling speed is 1.5–2.0 m / min, the crystallizer width is 700–1200 mm, and the electromagnetic braking magnetic field strength is 0.3–0.4 T; when the crystallizer width is 1201–1700 mm, the electromagnetic braking magnetic field strength is 0.2–0.4 T; when the crystallizer width is 1701–2400 mm, the electromagnetic braking magnetic field strength is 0.2–0.3 T.

[0023] When the pulling speed is greater than 2.0 m / min, the crystallizer width is 700-1200 mm and the electromagnetic braking magnetic field strength is 0.4-0.5 T; the crystallizer width is 1201-1700 mm and the electromagnetic braking magnetic field strength is 0.3-0.4 T; the crystallizer width is 1701-2400 mm and the electromagnetic braking magnetic field strength is 0.2-0.3 T.

[0024] Preferably, the ultra-low carbon aluminum-killed steel composition by weight percentage is: C: 0.0005~0.0040wt%, Si≤0.20wt%, Mn: 0.05~0.15wt%, Al: 0.025~0.080wt%, S≤0.020%, P≤0.020wt%, TO≤0.0030wt%, with the remainder including Fe and unavoidable impurities.

[0025] Preferably, the converter shut-off temperature is 1600-1650℃, the shut-off free oxygen content is 300-700ppm, and the shut-off carbon content is 0.020%-0.035%.

[0026] Preferably, 150-700 kg of lime is added during the tapping process of the converter, and 100-400 kg of aluminum slag is added after tapping is completed.

[0027] Preferably, after refining and measuring oxygen at a constant temperature, a vacuum cycle is performed for 10-15 minutes to carry out decarburization; after decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after 2-4 minutes of deoxidation.

[0028] Preferably, during the continuous casting process, argon gas is used for protective casting, the argon seal flow rate of the long nozzle is 10-20 L / h, the continuous casting speed is 0.7-2.0 m / min, and the width of the continuous casting crystallizer is 750-2400 mm.

[0029] In continuous casting production, a combined stirring method is used, employing upper electromagnetic stirring and lower DC electromagnetic braking, depending on the cross-sectional conditions and casting speed. This method involves stirring the upper part of the mold and braking the lower part, with braking utilizing a stable constant magnetic field generated by DC current. Upper stirring in the mold refreshes the protective slag, promoting inclusion adsorption and flushing out bubbles and inclusions trapped in the solidified billet shell. Lower braking reduces the impact depth.

[0030] The insertion depth of the sprue is used as the standard distance d. The range from the molten metal surface to 3d from the molten metal surface constitutes the upper and lower circulating flow field. The distance from below the meniscus to 2 / 3d of the sprue is the effective range of the electromagnetic stirring. The effective range of the electromagnetic stirring is the middle position of the sprue outlet in the flow field. The effective range of the electromagnetic stirring is slightly larger than the electromagnetic stirring coil because there is an electromagnetically induced magnetic field outside the coil. The distance d is limited by the electromagnetic braking rectifier power supply and process design. The distance in this invention is adjusted between 50-150mm based on the rectifier power supply manufacturing capability and actual operating conditions.

[0031] The DC electromagnetic braking range is below the flow field of the crystallizer. The distance between the DC electromagnetic braking device and the surface of the molten metal is 4d, and the height of the DC electromagnetic braking device is 4 / 3d, forming a composite electromagnetic field of electromagnetic stirring and DC electromagnetic braking.

[0032] The electromagnetic stirring current ranges from 300 to 700 A, and the DC electromagnetic braking magnetic field strength ranges from 0.1 to 0.5 T. Currently, there are no successful precedents in China for combining electromagnetic stirring and electromagnetic braking. Water simulation calculations show that within the conventional electromagnetic stirring current range of 300 to 700 A, an electromagnetic braking magnetic field strength of no more than 0.5 T is suitable. Considering metallurgical effects, manufacturing costs, and actual flow field effects, this parameter setting will maximize the effectiveness of electromagnetic stirring and DC electromagnetic braking. If the electromagnetic braking magnetic field strength is less than 0.1 T, the braking current is too small, resulting in no braking effect. If the electromagnetic braking magnetic field strength is too large, it will cause liquid surface backflow, affecting the stability of the crystallizer's liquid surface. The electromagnetic stirring current and electromagnetic braking magnetic field strength are dynamically set according to the pulling speed and crystallizer width. The electromagnetic stirring current is adjusted according to the principle of appropriately reducing it at high pulling speeds and appropriately reducing it for large cross-sections; the electromagnetic braking magnetic field strength is adjusted according to the principle of requiring a small magnetic induction intensity at low pulling speeds and a large induction intensity at high pulling speeds.

[0033] The electromagnetic stirring device is formed by an iron core and coil wound around a copper plate. In actual production, if the crystallizer is large, deformation can cause significant deformation of the copper plate, resulting in excessive deflection. Once the copper plate deforms, the magnetic field generated by the electromagnetic stirring of the crystallizer will change significantly, failing to achieve optimal metallurgical results. To address the issue of significant rigid deformation in large-section crystallizers, this invention employs a two-section structure. The electromagnetic stirring device uses two copper plates joined together, solving the problem of insufficient rigidity. Furthermore, calculations show that even with a gap between the two copper plates, a traveling wave magnetic field for rotational stirring is still formed, demonstrating… Figure 4When the copper plates are spaced apart, the magnetic field weakens in the middle. To solve this problem, an ultra-thin superconducting magnet is used to connect the two copper plates. This not only solves the problem of copper plate deformation caused by insufficient rigidity of the large-size stirrer, but also creates a safe and stable flow field in the upper stirring process. Because an electromagnetic brake is installed below, upper stirring and lower braking can be achieved simultaneously. Preferably, the superconductor is smelted in an induction furnace, and its main components include: Ni: 85-92wt%, Nb: 0.03-0.05wt%, C: 0.02-0.05wt%, with the remainder being Fe and unavoidable impurities.

[0034] The specific implementation of the electromagnetic stirring device takes into account the saturation of the iron core and the winding of the coil. In the conventional production process of electromagnetic stirrers for crystallizers, the length of the copper plate limits the effective increase in the number of coil windings. This invention, by splicing two copper plates together, provides space for coil winding, resulting in a greater magnetic field strength. This solves the problem of copper plate deformation encountered during the winding of coils to form electromagnetic stirrers for large-sized crystallizers. Large-sized crystallizers require a larger number of electromagnetic stirring coils to be formed on the electromagnetic stirring device. This invention preferably uses six coils on one side (a total of 18 windings), with AC-1BA-1CB-1 as a single pole pair for power supply to form a traveling wave magnetic field. If the crystallizer size is even larger, nine coils can be formed on one side of the electromagnetic stirring device. However, its longitude and the stability of the equipment will no longer exist. Of course, for small-sized crystallizers, fewer coils can be used, for example, a design of three coils on one side, resulting in 18 peak values ​​across the three pole pairs, with a minimum value between the two peak values. This is because the magnetic field generated by the electromagnetic stirring device is strong at the tooth surface of the yoke and weaker at the tooth grooves. Because the tooth spacing of the yoke is equal, the spacing between adjacent peaks and minimums is also equal. Looking at the magnetic field curves of each pair of poles individually, it can be observed that the peak magnetic field at the center of each pair is always lower than its adjacent peak. This is because each pair of poles is connected in an A-CB-AC-B configuration, with magnetic field lines running from A to -A, C to -C, and B to -B. There is a region in the central area with opposite magnetic field directions, resulting in mutual cancellation and a weaker magnetic field at this point.

[0035] The above-mentioned composite electromagnetic stirring method for improving slab quality control is used in the smelting method of ultra-low carbon aluminum killed steel. The specific steps include: hot metal pretreatment and desulfurization, converter smelting, RH refining, and continuous casting. During the continuous casting process, the composite electromagnetic stirring method for improving slab quality control is used to perform composite stirring and braking of the molten steel according to the cross-sectional conditions and casting speed.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention utilizes electromagnetic stirring in the upper part of the crystallizer and DC electromagnetic braking in the lower part during continuous casting production. This prevents inclusions and air bubbles from being trapped in the solidified billet shell, and also avoids insufficient floating of inclusions due to excessive impact depth. It can be widely used in continuous steel casting processes to reduce inclusions, improve slab quality, further reduce steel modification, and enhance enterprise efficiency. While electromagnetic stirring within the crystallizer is a mature technology, combining electromagnetic stirring and electromagnetic braking has not yet been successfully implemented.

[0038] This invention addresses the problem of significant deformation of copper plates in large-size crystallizers when electromagnetic stirring is required, caused by the excessive number of coils on the copper plates. The electromagnetic stirring device of this invention uses two spliced ​​copper plates connected by a superconducting magnet. This not only solves the problem of copper plate deformation due to insufficient rigidity in large-size stirrers but also ensures a safe and stable flow field in the upper part of the crystallizer, without affecting the DC electromagnetic brake located below, thus forming a stable upper stirring and lower braking mode. Attached Figure Description

[0039] Figure 1 This is a schematic diagram showing the range of action of electromagnetic stirring and electromagnetic braking in an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram of the surface protective slag entrainment index for a crystallizer with only electromagnetic stirring.

[0041] Figure 3 This is a schematic diagram of the protective slag entrainment index using the electromagnetic stirring + electromagnetic braking method of the present invention.

[0042] Figure 4 This is a schematic diagram showing the change in the electromagnetic stirring magnetic field when two separating copper plates are used. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0044] See Figure 1 The diagram illustrates the combined stirring range of the method for improving slab quality using composite electromagnetic stirring as described in this invention.

[0045] An electromagnetic stirring device 2 and a DC electromagnetic braking device 3 are installed above and below the crystallizer 1 to form a composite electromagnetic field; wherein...

[0046] The electromagnetic stirring device 2 is set on the crystallizer 1 at the position corresponding to the water inlet 4. The upper end of the electromagnetic stirring device 2 is flush with the upper end of the copper plate of the crystal 1, and the lower end of the electromagnetic stirring device 2 is flush with the discharge hole 41 of the water inlet 4 inserted into the crystallizer 1. The insertion depth of the water inlet 4 is used as the distance standard d, where d = 50~150mm.

[0047] The DC electromagnetic braking device 3 is installed at the lower part of the crystallizer 1. The distance between the lower end of the DC electromagnetic braking device 3 and the metal liquid surface inside the crystallizer 1 is 4d; the height of the DC electromagnetic braking device 3 is 4 / 3d.

[0048] The electromagnetic stirring device 2 includes two copper plates spliced ​​together with ultra-thin superconducting magnet sheets with a thickness of 0.2 to 0.5 mm, as well as coils and iron cores distributed on both sides of the copper plates. The two copper plates are connected by superconducting magnets, and the coils are externally connected to a three-phase AC power supply.

[0049] Preferably, the main components of the superconducting magnet include Ni: 85-92wt%, Nb: 0.03-0.05wt%, C: 0.02-0.05wt%, with the remainder being Fe and unavoidable impurities.

[0050] Preferably, the DC electromagnetic braking device includes an iron core and a coil wound on it, the coil being connected to a DC power supply.

[0051] Figure 4 The diagram shows the change of the electromagnetic stirring magnetic field when two separating copper plates are used in the electromagnetic stirring device 2. The separating copper plates 21 are set on both sides of the crystallizer 1. As can be seen from the figure, a rotating stirring traveling wave magnetic field is still formed during the stirring process.

[0052] Example 1

[0053] The specific implementation steps for the smelting method of ultra-low carbon aluminum-killed steel are as follows:

[0054] (1) The conventional production process is adopted, which is hot metal pretreatment desulfurization, converter smelting, RH refining and continuous casting. The steel produced has the following composition by weight percentage: C: 0.0015%, Si≤0.20%, Mn: 0.06%, Al: between 0.025%, S≤0.020%, P≤0.020%, TO≤0.0030%.

[0055] (2) Production process parameters:

[0056] The converter's shut-off temperature is 1620℃, the free oxygen content at shut-off is 400ppm, and the carbon content at shut-off is 0.035%. 300kg of lime is added during the tapping process, and 200kg of aluminum slag is added after tapping.

[0057] After refining and oxygen measurement at a constant temperature, a 15-minute vacuum circulation process is performed for decarbonization.

[0058] After decarburization, aluminum is added for deoxidation, and alloying is carried out after 2 minutes of deoxidation.

[0059] During the continuous casting process, argon gas is used for protective casting, the argon seal flow rate of the long nozzle is 20L / h, the continuous casting speed is 1.2m / min, and the width of the continuous casting crystallizer is 1100mm.

[0060] During continuous casting, composite stirring is carried out according to the cross-sectional conditions and casting speed. Electromagnetic stirring is performed at the sprue position of the crystallizer by using a composite electromagnetic field of electromagnetic stirring device and DC electromagnetic braking device, while DC electromagnetic braking is performed at the bottom of the crystallizer. The electromagnetic stirring current is 700A. The sprue insertion depth is used as the distance standard d. The range from the metal liquid surface to 3d from the metal liquid surface is the upper and lower circulating flow field. The electromagnetic braking magnetic field strength is 0.2T.

[0061] The final results showed that the defect rate of cold-rolled steel was reduced from 5.0% to 2.0%, a reduction of 60%. This achieved good results.

[0062] Example 2

[0063] The specific implementation steps for the smelting method of ultra-low carbon aluminum-killed steel are as follows:

[0064] (1) The conventional production process is adopted, which is hot metal pretreatment desulfurization, converter smelting, RH fine treatment and continuous casting. The weight percentage composition of the produced steel is: C ≤ 0.0025%, Si ≤ 0.10%, Mn ≤ 0.85%, Al ≤ 0.065%, S ≤ 0.010%, P ≤ 0.015%, TO ≤ 0.0019%.

[0065] (2) Production process parameters;

[0066] The converter's shut-off temperature is 1640℃, the free oxygen content at shut-off is 600ppm, and the carbon content at shut-off is 0.045%. 500kg of lime is added during the tapping process, and 450kg of aluminum slag is added after tapping.

[0067] After refining and oxygen measurement at a constant temperature, a 10-minute vacuum circulation process is performed for decarbonization.

[0068] After decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after 3 minutes of deoxidation.

[0069] During the continuous casting process, argon gas is used for protective casting, with an argon seal flow rate of 40L / h at the long nozzle, a casting speed of 1.6m / min, and a continuous casting crystallizer width of 1600mm.

[0070] During continuous casting, composite stirring is carried out according to the cross-sectional conditions and casting speed. Electromagnetic stirring and DC electromagnetic braking are combined to form a composite electromagnetic field. Electromagnetic stirring is performed at the sprue of the crystallizer, and DC electromagnetic braking is performed at the bottom of the crystallizer. The electromagnetic stirring current is 400A. The sprue insertion depth is used as the distance standard d. The range from the metal liquid surface to 3d from the metal liquid surface is the upper and lower circulating flow field. The electromagnetic braking magnetic field strength is 0.3T.

[0071] The final result showed that the proportion of defects in cold rolling decreased from the usual 5.0% to 2.5% in this heat, a reduction of 50%. This achieved good results.

[0072] Example 3

[0073] The specific implementation steps for the smelting method of ultra-low carbon aluminum-killed steel are as follows:

[0074] (1) The conventional production process is adopted, which is hot metal pretreatment desulfurization, converter smelting, RH refining, and continuous casting. The weight percentage composition of the produced steel is: C ≤ 0.0030%, Si ≤ 0.12%, Mn ≤ 0.75%, Al ≤ 0.055%, S ≤ 0.012%, P ≤ 0.013%, and TO ≤ 0.0021%.

[0075] (2) Production process parameters;

[0076] The converter's shut-off temperature is 1650℃, the free oxygen content at shut-off is 700ppm, and the carbon content at shut-off is 0.035%. 600kg of lime is added during the tapping process, and 350kg of aluminum slag is added after tapping.

[0077] After refining and oxygen measurement at a constant temperature, a 10-minute vacuum circulation process is performed for decarbonization.

[0078] After decarburization, metallic aluminum is added for deoxidation, and alloying is carried out after 3 minutes of deoxidation.

[0079] During the continuous casting process, argon gas is used for protective casting, with an argon seal flow rate of 40L / h at the long nozzle, a casting speed of 2.5m / min, and a continuous casting crystallizer width of 2200mm.

[0080] During continuous casting, composite stirring is carried out according to the cross-sectional conditions and casting speed. Electromagnetic stirring is performed at the sprue position of the crystallizer by using a composite electromagnetic field of electromagnetic stirring device and DC electromagnetic braking device, while DC electromagnetic braking is performed at the bottom of the crystallizer. The electromagnetic stirring current is 300A. The sprue insertion depth is used as the distance standard d. The range from the metal liquid surface to 3d from the metal liquid surface is the upper and lower circulating flow field. The electromagnetic braking magnetic field strength is 0.3T.

[0081] The final result showed that the proportion of defects in cold rolling decreased from the usual 5.0% to 2.5% in this heat, a reduction of 50%. This achieved good results.

[0082] The difference between the comparative example and Example 1 is that electromagnetic braking was not performed at the bottom of the crystallizer.

[0083] Figure 2 It is the entrainment index of the protective slag on the surface of a crystallizer that is stirred without electromagnetic braking.

[0084] Figure 3 It is the entrainment index of the protective slag on the surface of the crystallizer in Embodiment 1 of the present invention, which is characterized by electromagnetic stirring and electromagnetic braking.

[0085] from Figure 2 and Figure 3 look, Figure 2 The slag index is relatively high. Figure 3 After implementation under an electromagnetic braking magnetic field strength of 0.2T, the slag entrainment index was significantly reduced.

Claims

1. A method for smelting ultra-low carbon aluminum-killed steel, characterized in that, The specific steps include: hot metal pretreatment and desulfurization, converter smelting, RH refining, and continuous casting; electromagnetic stirring devices and DC electromagnetic braking devices are installed above and below the crystallizer to form a composite electromagnetic field; among which... The electromagnetic stirring device is set on the crystallizer at the corresponding water inlet position. The upper end of the electromagnetic stirring device is flush with the upper end of the copper plate of the crystallizer, and the lower end of the electromagnetic stirring device is flush with the discharge hole of the water inlet inserted into the crystallizer. The electromagnetic stirring current is 300~700A. The water inlet insertion depth is used as the distance standard d, where d=50~150mm. The DC electromagnetic braking device is installed at the bottom of the crystallizer, and the distance between the bottom of the DC electromagnetic braking device and the surface of the molten metal in the crystallizer is 4d; the height of the DC electromagnetic braking device is 4 / 3d, and the electromagnetic braking magnetic field strength is 0.1~0.5T; During the continuous casting process, the molten steel is subjected to compound stirring and braking according to the width of the crystallizer and the casting speed. The electromagnetic stirring current is set according to the pulling speed and the width of the crystallizer: When the pulling speed is 0.6~1.5m / min, the crystallizer width is 700~1200mm and the electromagnetic stirring current is 500~700A; when the crystallizer width is 1201~1700mm, the electromagnetic stirring current is 400~500A; when the crystallizer width is 1701~2400mm, the electromagnetic stirring current is 300~400A. When the pulling speed is 1.5~2.0m / min, the crystallizer width is 700~1200mm and the electromagnetic stirring current is 400~500A; when the crystallizer width is 1201~1700mm, the electromagnetic stirring current is 350~400A; when the crystallizer width is 1701~2400mm, the electromagnetic stirring current is 300~350A. When the pulling speed is greater than 2.0 m / min, the crystallizer width is 700~2400 mm, and the electromagnetic stirring current is 300~350 A; The strength of the electromagnetic braking magnetic field is set according to the pulling speed and the width of the crystallizer: When the pulling speed is 0.6~1.5m / min, the crystallizer width is 700~1200mm and the electromagnetic braking magnetic field strength is 0.2~0.3T; when the crystallizer width is 1201~1700mm, the electromagnetic braking magnetic field strength is 0.1~0.3T; when the crystallizer width is 1701~2400mm, the electromagnetic braking magnetic field strength is 0.1~0.2T. When the pulling speed is 1.5~2.0m / min, the crystallizer width is 700~1200mm and the electromagnetic braking magnetic field strength is 0.3~0.4T; when the crystallizer width is 1201~1700mm, the electromagnetic braking magnetic field strength is 0.2~0.4T; when the crystallizer width is 1701~2400mm, the electromagnetic braking magnetic field strength is 0.2~0.3T. When the pulling speed is greater than 2.0 m / min, the crystallizer width is 700~1200 mm and the electromagnetic braking magnetic field strength is 0.4~0.5T; the crystallizer width is 1201~1700 mm and the electromagnetic braking magnetic field strength is 0.3~0.4T; the crystallizer width is 1701~2400 mm and the electromagnetic braking magnetic field strength is 0.2~0.3T.

2. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, The weight percentage composition of ultra-low carbon aluminum-killed steel is as follows: C: 0.0005~0.0040%, Si≤0.20%, Mn: 0.05~0.15%, Al: 0.025~0.080%, S≤0.020%, P≤0.020%, TO≤0.0030%, with the remainder including Fe and unavoidable impurities.

3. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, The converter shutdown temperature is 1600~1650℃, the free oxygen content during shutdown is 300~700ppm, and the carbon content during shutdown is 0.020~0.035%.

4. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, During the tapping process of the converter, 150-700 kg of lime is added, and after tapping, 100-400 kg of aluminum slag is added.

5. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, After RH refining and constant temperature oxygen measurement, vacuum circulation is performed for 10-15 minutes for decarburization. After decarburization, metallic aluminum is added for deoxidation, and alloying is performed after 2-4 minutes of deoxidation.

6. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, During the continuous casting process, argon gas is used for protection during casting. The argon seal flow rate at the long nozzle is 10~20L / h, the continuous casting speed is 0.7~2.0m / min, and the width of the continuous casting crystallizer is 750~2400mm.

7. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, The electromagnetic stirring device includes two copper plates spliced ​​together with ultra-thin superconducting magnet sheets with a thickness of 0.2~0.5mm, as well as coils and iron cores distributed on both sides of the copper plates. The two copper plates are connected by superconducting magnets, and the coils are externally connected to a three-phase AC power supply.

8. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 7, characterized in that, The superconducting magnet mainly consists of Ni: 85-92 wt%, Nb: 0.03-0.05 wt%, C: 0.02-0.05 wt%, with the remainder being Fe and unavoidable impurities.

9. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 1, characterized in that, The DC electromagnetic braking device includes an iron core and a coil wound on it, the coil being connected to a DC power supply.

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