Method for improving slab quality through composite electromagnetic stirring and application of method

Abstract

According to the method for improving the slab quality through composite electromagnetic stirring and the application thereof, stirring is conducted on the upper portion of a crystallizer, braking is conducted on the lower portion of the crystallizer, and a stable constant magnetic field generated by direct current is adopted for braking. Stirring at the upper part of the crystallizer can update the casting powder, promote the casting powder to adsorb inclusions, and flush bubbles and inclusions captured by a solidified blank shell. The lower portion of the crystallizer is braked, and the impact depth can be reduced. Meanwhile, the electromagnetic stirring device adopts a mode of splicing two copper plates and is connected by using a superconducting magnet, so that the problem that a copper plate electromagnetic stirrer is easy to generate relatively large rigid deformation in the stirring process of a large-section crystallizer is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting, in particular to a method for improving slab quality by composite electromagnetic stirring and application thereof. BACKGROUND

[0002] In the continuous casting production process, general fluctuations will cause the wrapping of the mold powder. At the same time, due to the use of vertical bending type continuous casting machine, the vertical section is longer, which will cause the problem of insufficient floating of inclusions caused by too deep impact depth. The existing enterprises adopt mold electromagnetic stirring technology to stir the inclusions in the flow field, expecting to clean and remove the inclusions captured by the solidified shell. However, in the continuous casting production process, since the mold is generally vertical, the molten steel will bring the inclusions into the deep liquid core, causing insufficient floating, so how to solve the problem of insufficient floating of inclusions is a problem that needs to be further studied.

[0003] Chinese patent CN113000800B discloses a method for improving slab surface and subsurface quality by electromagnetic stirring. The continuous casting adopts mold electromagnetic stirring, and the center position of the electromagnetic stirrer corresponds to 90-110mm below the meniscus of the mold. According to the characteristics of the steel grade and the size of the electromagnetic force of different electromagnetic stirring parameters, the corresponding electromagnetic stirring parameters are matched for different C content steel grades and slab widths, and the current transformer and the limiting liquid level monitoring position to the thickness of the copper plate coating of the upper mouth of the mold are installed through the electromagnetic stirring parameter line of the electromagnetic stirrer to reduce the interference of the electromagnetic signal released by the electromagnetic stirrer on the mold liquid level detector, so as to fully exert the metallurgical effect of the electromagnetic stirrer, reduce the occurrence rate of longitudinal cracks on the slab surface, and the number of non-metallic inclusions and bubbles under the skin, and the surface defect judgment rate of the finished plate is controlled below 0.45%.

[0004] Chinese patent CN105728679B discloses a square round billet continuous casting meniscus electromagnetic stirring system and method with magnetic shielding and multi-mode. The system includes a meniscus electromagnetic stirrer and a variable frequency power supply control system. By changing the phase sequence and phase angle of the current in the coil, the meniscus electromagnetic stirring mode or the mold stirring mode is realized. The meniscus electromagnetic stirring mode includes two sub-modes of forming a single circulation zone and a single two-circulation zone for the molten steel respectively. For steel grades with higher internal quality requirements, the mold stirring mode is selected for stirring. For steel grades with higher surface and subsurface quality requirements, the meniscus electromagnetic stirring mode is selected for stirring.

[0005] Chinese patent CN108500227A is a kind of electromagnetic control method for crystallizer flow field of slab continuous casting production, also for the problem of impact depth, adopt multiple electromagnetic stirrers to control the crystallizer flow field, the electromagnetic stirrer is a traveling wave magnetic field generator, the upper region of the crystallizer wide surface and the lower region of the crystallizer narrow surface are respectively configured with electromagnetic stirrers, the upper electromagnetic stirrer is installed above the upper edge of the nozzle outlet to the meniscus, and the lower electromagnetic stirrer is installed below the impact point of the nozzle side hole discharge stream and the narrow surface. The upper edge of the lower electromagnetic stirrer core is at the same height as the intersection of the straight line made with the nozzle outlet upper edge as the starting point and the nozzle outlet angle as the angle with the crystallizer narrow surface, the stirring direction of the stirring coil is from bottom to top, opposite to the direction of the lower ring current along the narrow edge, for weakening the impact depth of the lower ring current stream.

[0006] From the current existing technology, it is generally recognized in the industry to stir in the upper part of the crystallizer, and to reduce the impact depth in the lower part, which needs to be further proposed. However, with the further increase of the size of the continuous casting machine, the additional copper plate stirrer of the large size crystallizer copper plate will cause large rigid deformation. How to solve the deformation of the large size crystallizer copper plate, maintain the rigidity of the copper plate and maintain a certain stirring flow field needs to be further solved. SUMMARY

[0007] The purpose of the present application is to provide a composite electromagnetic stirring method for improving slab quality and its application, to remove inclusions and reduce the impact depth of inclusions, while solving the problem of easy large rigid deformation of copper plate electromagnetic stirrer in large section crystallizer stirring.

[0008] To achieve the above purpose, the technical scheme of the present application is as follows:

[0009] A composite electromagnetic stirring method for improving slab quality, electromagnetic stirring devices and direct current electromagnetic braking devices are arranged above and below the crystallizer to form a composite electromagnetic field form; wherein,

[0010] The electromagnetic stirring device is arranged at the position corresponding to the nozzle on the crystallizer, the upper end of the electromagnetic stirring device is flush with the upper end of the crystallizer copper plate, and the lower end of the electromagnetic stirring device is flush with the discharge hole of the nozzle inserted into the crystallizer; the electromagnetic stirring current is 300-700 A; the nozzle insertion depth is taken as the distance standard d, d=50-150 mm;

[0011] The direct current electromagnetic braking device is arranged in the lower part of the crystallizer, the distance between the lower end of the direct current electromagnetic braking device and the metal liquid surface in the crystallizer is 4d; the height of the direct current electromagnetic braking device is 4 / 3d, and the electromagnetic braking magnetic field strength is 0.1-0.5T.

[0012] Preferably, the electromagnetic stirring device comprises two copper plates spliced by superconducting magnet plates with a thickness of 0.2-0.5 mm, and wire packages and iron cores distributed on both sides of the copper plates, the two copper plates are connected by superconducting magnets, and the wire packages are connected with a three-phase alternating current power supply.

[0013] Preferably, the superconducting magnet mainly comprises Ni: 85-92 wt%, Nb: 0.03-0.05 wt%, C: 0.02-0.05 wt%, and the rest is Fe and inevitable impurities.

[0014] Preferably, the direct current electromagnetic braking device comprises an iron core and a coil wound thereon, and the coil is connected with a direct current power supply.

[0015] The specific steps of smelting the ultra-low-carbon aluminum killed steel include: hot metal pretreatment desulphurization, converter smelting, RH refining, and continuous casting pouring; during the continuous casting pouring process, the molten steel is subjected to composite stirring and braking according to the width of the crystallizer and the casting speed by using the above-mentioned composite electromagnetic stirring method to improve the slab quality.

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

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

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

[0019] When the casting 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 electromagnetic braking magnetic field strength is set according to the casting speed and the width of the crystallizer.

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

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

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

[0024] Preferably, the composition of the ultra-low carbon aluminum killed steel is: C: 0.0005-0.0040 wt%, Si≤0.20 wt%, Mn: 0.05-0.15 wt%, Al: 0.025-0.080 wt%, S≤0.020%, P≤0.020 wt%, T.O≤0.0030 wt%, the rest including Fe and inevitable impurities.

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

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

[0027] Preferably, after the refining constant temperature oxygen measurement, 10-15 min vacuum circulation is carried out for decarburization treatment; after decarburization, metal aluminum is added for deoxidation, and after 2-4 min of deoxidation, alloying is carried out.

[0028] Preferably, during the continuous casting production process, argon protection pouring is adopted, the long nozzle argon sealing flow is 10-20 L / h, the continuous casting drawing speed is 0.7-2.0 m / min, and the continuous casting crystallizer width is 750-2400 mm.

[0029] During the continuous casting production process, according to the cross section and the drawing speed, the upper part is subjected to electromagnetic stirring, and the lower part is subjected to direct current electromagnetic braking composite stirring. The upper part of the crystallizer can be stirred, and the lower part of the crystallizer can be braked, and the braking adopts stable constant magnetic field generated by direct current. The upper part of the crystallizer can update the protective slag, promote the protective slag to absorb inclusions, and flush the bubbles and inclusions captured by the solidified shell. The lower part of the crystallizer is braked, which can reduce the impact depth.

[0030] The water gap insertion depth is taken as the distance standard d, the range from the liquid surface to the distance of 3d from the liquid surface is the flow field of the up and down circulation, the distance of 2 / 3d from below the meniscus is the action range of the electromagnetic stirring. The action range of the electromagnetic stirring is the middle position of the flow field of the water gap discharge hole. The action range of the electromagnetic stirring is slightly larger than the electromagnetic stirring coil because there is an electromagnetic induction magnetic field outside the coil. The d distance is subject to the electromagnetic braking rectifier power supply and the process design. The distance of the present application is adjusted between 50-150mm according to the manufacturing capacity of the rectifier power supply and the actual working condition.

[0031] The DC electromagnetic braking range is below the crystallizer flow field, the distance from the liquid surface below the DC electromagnetic braking device is 4d, the height of the DC electromagnetic braking device is 4 / 3d, forming the combined electromagnetic field form of the electromagnetic stirring and the DC electromagnetic braking.

[0032] The electromagnetic stirring current is 300-700A, and the DC electromagnetic braking magnetic field strength is 0.1-0.5T. There is no precedent for successfully combining electromagnetic stirring and electromagnetic braking in China at present. According to the water simulation calculation results, it is appropriate that the electromagnetic braking magnetic field is not greater than 0.5T in the range of 300-700A of the conventional electromagnetic stirring current, and the parameters are set to maximize the effects of the electromagnetic stirring and the DC electromagnetic braking by comprehensively considering the metallurgical effect, the cost of manufacturing, and the actual effect of the flow field. If the electromagnetic braking magnetic field strength is less than 0.1T, the braking current is too small and has no braking effect. If the electromagnetic braking magnetic field strength is too large, it will cause liquid surface recoil and affect the stability of the crystallizer liquid surface. According to the casting speed and the width of the crystallizer, the electromagnetic stirring current and the electromagnetic braking magnetic field strength are dynamically set. The electromagnetic stirring current is adjusted according to the principle of appropriately reducing the high casting speed and the large section. The electromagnetic braking magnetic field strength is adjusted according to the principle of small magnetic induction intensity for low casting speed and large induction intensity for high casting speed.

[0033] The electromagnetic stirring device is formed by winding the iron core and the coil on the copper plate. In the actual production process, if the size of the crystallizer is large, the copper plate will be deformed due to the deformation, and the middle deflection will be caused. Once the copper plate is deformed, the magnetic field generated by the electromagnetic stirring of the crystallizer will be greatly changed, and the good metallurgical effect cannot be achieved. At the same time, in order to solve the problem of large rigid deformation of the stirring of the large-section crystallizer, the electromagnetic stirring device of the present application adopts a two-section structure. The electromagnetic stirring device is spliced by two copper plates, which solves the problem of insufficient rigidity. At the same time, it is found through calculation that the rotating stirring traveling wave magnetic field is still formed under the condition that there is a gap between the two copper plates. It can be seen that Figure 4In the case that the copper plates have intervals, the magnetic field is weakened in the middle position, in order to solve this problem, the super thin sheet superconductive magnet is connected in the middle of the two copper plates, so that the problem of copper plate deformation caused by the insufficient rigidity of the large size stirrer is solved, and the upper stirring flow forms a safe and stable flow field, and since the electromagnetic brake is arranged below, the upper stirring and the lower braking can be realized at the same time. Preferably, the superconductor is smelted by an induction furnace, and the main components include: Ni: 85-92wt%, Nb: 0.03-0.05wt%, C: 0.02-0.05wt%, and the rest is Fe and inevitable impurities.

[0034] The specific implementation form of the electromagnetic stirring device considers the saturation of the iron core and the winding of the coil, and in the conventional production process of the crystallizer electromagnetic stirrer, the winding of the coil cannot be effectively increased due to the size of the copper plate. The two copper plates are spliced together, which can provide a winding space for the coil and provide greater magnetic field strength, solve the problem of copper plate deformation in the process of winding the coil to form an electromagnetic stirrer in a large size crystallizer, and more electromagnetic stirring coils can be formed on the electromagnetic stirring device for a large size crystallizer. The application preferably adopts a single-sided six-group coil (a total of 18 windings), AC-1BA-1CB-1 pair of poles form to supply power, to form a traveling wave magnetic field. If the size of the crystallizer is larger, 9 groups of coils can be formed on one side of the electromagnetic stirring device. However, at that time, the stability of the device will no longer exist. Of course, for small size crystallizers, the number of coils can be reduced, for example, a design of a single-sided 3-group coil is adopted, and a total of 18 peak values appear on three pairs of poles, and there is a minimum value between 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 weak at the tooth groove of the yoke. Since the tooth surfaces of the yoke are equal in distance, the distances between adjacent peak values and minimum values are also equal. When looking at each pair of pole magnetic field curve alone, it can be found that the magnetic field peak value at the center of each pair of poles is always lower than the adjacent magnetic field peak value, which is because the connection mode of each pair of poles is connected in the connection mode of A-CB-AC-B, the magnetic lines are from A to-A, C to-C, and B to-B, and there is a region with opposite magnetic field direction in the center region, which is offset, so the magnetic field here is relatively weak.

[0035] The super-low-carbon aluminum killed steel smelting method adopting the composite electromagnetic stirring method for improving slab quality control method comprises the following specific steps: hot metal pretreatment desulphurization, converter smelting, RH refining, and continuous casting pouring; in the continuous casting process, according to the cross section and the drawing speed, the composite electromagnetic stirring method for improving slab quality control method is used to composite stir and brake the molten steel.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] The present application is in the continuous casting production process, in the upper part of crystallizer electromagnetic stirring, crystallizer lower part of direct current electromagnetic braking, prevent crystallizer solidification shell capture inclusion and bubble, at the same time can avoid impact depth too deep caused by inclusion floating not fully, can be widely used in continuous casting steel production process, reduce inclusion, improve slab quality, further reduce the steel, enhance enterprise benefit. In the prior art, the electromagnetic stirring in the crystallizer is a mature process, but the combination of electromagnetic stirring and electromagnetic braking has not been successfully applied.

[0038] The present application is to solve the large size crystallizer needs to carry out electromagnetic stirring, because the copper plate needs to set too many coils, resulting in the copper plate deformation, the present application electromagnetic stirring device adopts two spliced copper plates, and the superconducting magnet is connected between the two copper plates, which not only solves the problem of copper plate deformation caused by insufficient rigidity of large size stirrer, but also forms a safe and stable flow field in the upper part of the crystallizer, and does not affect the lower part of the direct current electromagnetic brake, thereby forming a stable upper stirring and lower braking mode. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is the schematic diagram of the electromagnetic stirring and electromagnetic braking range in the embodiment of the present application.

[0040] Figure 2 It is the schematic diagram of the protective slag entrapment index of the crystallizer with single electromagnetic stirring.

[0041] Figure 3 It is the schematic diagram of the protective slag entrapment index of the crystallizer with electromagnetic stirring + electromagnetic braking of the present application.

[0042] Figure 4 It is the schematic diagram of the electromagnetic stirring magnetic field change when two separate copper plates are used. DETAILED DESCRIPTION

[0043] The present application will be further described below in combination with embodiments and drawings.

[0044] Referring to Figure 1 The composite stirring range diagram of the method for improving slab quality by composite electromagnetic stirring according to the present application is shown.

[0045] The electromagnetic stirring device 2 and the direct current electromagnetic braking device 3 are arranged on the upper and lower parts of the crystallizer 1, forming a composite electromagnetic field form; wherein,

[0046] The electromagnetic stirring device 2 is arranged at the position corresponding to the water gap 4 on the crystallizer 1, the upper end of the electromagnetic stirring device 2 is flush with the upper end of the copper plate of the crystallizer 1, and the lower end of the electromagnetic stirring device 2 is flush with the discharge hole 41 of the water gap 4 inserted into the crystallizer 1; the insertion depth of the water gap 4 is taken as the distance standard d, d = 50-150 mm;

[0047] The direct current electromagnetic braking device 3 is arranged at the lower part of the crystallizer 1, and the distance between the lower end of the direct current electromagnetic braking device 3 and the liquid metal surface in the crystallizer 1 is 4d; the height of the direct current electromagnetic braking device 3 is 4 / 3d.

[0048] The electromagnetic stirring device 2 comprises two copper plates spliced by superconducting magnet sheets with a thickness of 0.2-0.5mm, and wire packages and iron cores distributed on both sides of the copper plates, the two copper plates are connected by the superconducting magnet, and the wire packages are connected with three-phase alternating current 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%, and the rest is Fe and inevitable impurities.

[0050] Preferably, the direct current electromagnetic braking device comprises an iron core and a coil wound thereon, and the coil is connected with a direct current power supply.

[0051] Figure 4 The electromagnetic stirring magnetic field change schematic diagram when the electromagnetic stirring device 2 adopts two separated copper plates is shown in the figure, and it can be seen from the figure that a rotating stirring traveling wave magnetic field is still formed in the stirring process.

[0052] Example 1

[0053] The smelting method of the ultra-low carbon aluminum killed steel is as follows:

[0054] (1) The conventional production process is adopted, i.e. hot metal pretreatment desulfurization-converter smelting-RH refining-continuous casting pouring; the produced steel grade composition is as follows: C: 0.0015%, Si≤0.20%, Mn: 0.06%, Al: 0.025%, S≤0.020%, P≤0.020%, and T.O≤0.0030%.

[0055] (2) Production process parameters:

[0056] The converter blowing stop temperature is 1620℃, the blowing stop free oxygen content is 400ppm, and the blowing stop carbon content is 0.035%; 300kg of lime is added during the converter tapping process, and 200kg of aluminum slag is added after the tapping is completed;

[0057] After the refining temperature is measured, the oxygen is measured, and the vacuum circulation is performed for 15min to perform decarburization treatment;

[0058] After decarburization, metal aluminum is added for deoxidization, and alloying is performed after deoxidization for 2min;

[0059] In the continuous casting production process, argon protection casting is adopted, the argon sealing flow of long nozzle is 20 L / h, the continuous casting speed is 1.2 m / min, and the width of the continuous casting crystallizer is 1100 mm;

[0060] In the continuous casting production process, according to the cross-section and the drawing speed, composite stirring is carried out, the electromagnetic stirring device and the direct current electromagnetic braking device are used to form a composite electromagnetic field, electromagnetic stirring is carried out at the position of the crystallizer nozzle, and direct current electromagnetic braking is carried out at the lower part of the crystallizer; the size of the electromagnetic stirring current is 700 A; the nozzle insertion depth is used as the distance standard d, the range from the metal liquid surface to the metal liquid surface 3d is the flow field of the up and down circulation, and the electromagnetic braking magnetic field strength is 0.2T.

[0061] Finally, the proportion of defects of the cold-rolled steel is reduced from 5.0% to 2.0%, and the reduction rate reaches 60%. Good results have been achieved.

[0062] Example 2

[0063] The smelting method of the ultra-low-carbon aluminum killed steel is specifically implemented as follows:

[0064] (1) The conventional production process is adopted, that is, hot metal pretreatment desulfurization - converter smelting - RH fine - continuous casting pouring; the produced steel grade product composition is as follows: C is 0.0025%, Si is less than or equal to 0.10%, Mn is 0.85%, Al is 0.065%, S is less than or equal to 0.010%, P is less than or equal to 0.015%, and T.O is less than or equal to 0.0019%.

[0065] (2) Production process parameters

[0066] The converter blowing stop temperature is 1640℃, the blowing stop free oxygen content is 600ppm, and the blowing stop carbon content is 0.045%; 500kg of lime is added during the converter tapping process, and 450kg of aluminum slag is added after the tapping is completed;

[0067] After the refining temperature is measured, oxygen is measured, and then 10min vacuum circulation is carried out for decarburization treatment;

[0068] After decarburization, metal aluminum is added for deoxidization, and alloying is carried out after 3min deoxidization;

[0069] In the continuous casting production process, argon protection casting is adopted, the argon sealing flow of long nozzle is 20 L / h, the continuous casting speed is 1.2 m / min, and the width of the continuous casting crystallizer is 1100 mm;

[0070] In the continuous casting production process, according to the section condition and the drawing speed condition, composite stirring is carried out, through the electromagnetic stirring device and the direct current electromagnetic braking device composite electromagnetic field form, electromagnetic stirring is carried out at the position of the crystallizer water port, direct current electromagnetic braking is carried out at the lower part of the crystallizer; the electromagnetic stirring current size is 400A; the water port insertion depth is taken as the distance standard d, the range from the metal liquid surface to the distance of 3d from the metal liquid surface is the flow field of the up and down circulation, the electromagnetic braking magnetic field strength is 0.3T.

[0071] Finally, the proportion of cold rolling defects is reduced from 5.0% of the conventional to 2.5% of the current furnace, and the reduction is 50%. Good results are achieved.

[0072] Example 3

[0073] The smelting method of the ultra-low carbon aluminum killed steel is specifically implemented as follows:

[0074] (1) The conventional production process is adopted, that is, hot metal pretreatment desulfurization-converter smelting-RH fine-continuous casting pouring; the produced steel grade finished product composition is as follows: C is 0.0030%, Si is less than or equal to 0.12%, Mn is 0.75%, Al is 0.055%, S is less than or equal to 0.012%, P is less than or equal to 0.013%, and T.O is less than or equal to 0.0021%.

[0075] (2) Production process parameters

[0076] The converter stopping blowing temperature is 1650℃, the stopping blowing free oxygen content is 700ppm, and the stopping blowing carbon content is 0.035%; 600kg of lime is added during the converter tapping process, and 350kg of aluminum slag is added after the tapping is completed;

[0077] After the refining constant temperature oxygen measurement, 10min vacuum circulation is carried out for decarburization treatment;

[0078] After decarburization, metal aluminum is added for deoxidation, and alloying is carried out after 3min deoxidation;

[0079] In the continuous casting production process, argon protection pouring is adopted, the long water port argon sealing flow is 40L / h, the continuous casting drawing speed is 2.5m / min, and the continuous casting crystallizer width is 2200mm;

[0080] In the continuous casting production process, according to the section condition and the drawing speed condition, composite stirring is carried out, through the electromagnetic stirring device and the direct current electromagnetic braking device composite electromagnetic field form, electromagnetic stirring is carried out at the position of the crystallizer water port, direct current electromagnetic braking is carried out at the lower part of the crystallizer; the electromagnetic stirring current size is 400A; the water port insertion depth is taken as the distance standard d, the range from the metal liquid surface to the distance of 3d from the metal liquid surface is the flow field of the up and down circulation, the electromagnetic braking magnetic field strength is 0.3T.

[0081] The final result is that the proportion of cold rolling defects is reduced from 5.0% of the conventional method to 2.5% of the present method, which is reduced by 50%. Good results are achieved.

[0082] The difference between the comparative example and example 1 is that no electromagnetic braking is performed at the lower part of the crystallizer.

[0083] Figure 2 The surface protection slag entrainment index of the crystallizer of the comparative example is only stirring without electromagnetic braking.

[0084] Figure 3 The surface protection slag entrainment index of the crystallizer of example 1 is electromagnetic stirring + electromagnetic braking.

[0085] From Figure 2 and Figure 3 , the slag entrainment index of Figure 2 is higher, Figure 3 after the implementation of the 0.2T electromagnetic braking magnetic field strength, the slag entrainment index is significantly reduced.

Claims

1. A method for improving slab quality through composite electromagnetic stirring, characterized in that, Electromagnetic stirring devices and DC electromagnetic braking devices are installed above and below the crystallizer to form a composite electromagnetic field. The electromagnetic stirring device is set on the crystallizer at the position corresponding to the water inlet. The upper end of the electromagnetic stirring device is flush with the upper end of the copper plate of the crystal, 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 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.

2. The method for improving slab quality using composite electromagnetic stirring 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 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.

3. The method for improving slab quality by composite electromagnetic stirring as described in claim 2, characterized in that, The superconducting magnet mainly consists of Ni: 85-92wt%, Nb: 0.03-0.05wt%, C: 0.02-0.05wt%, with the remainder being Fe and unavoidable impurities.

4. The method for improving slab quality by composite electromagnetic stirring 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.

5. 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; during the continuous casting process, the molten steel is composite stirred and braked using the composite electromagnetic stirring method described in claim 1, 2, 3, or 4 to improve the slab quality, depending on 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 0.6–1.5 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. 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. 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; 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 0.6–1.5 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. 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. 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.

6. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 5, 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.

7. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 5, characterized in that, The converter shutdown temperature is 1600–1650℃, the free oxygen content during shutdown is 300–700 ppm, and the carbon content during shutdown is 0.020–0.035%.

8. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 5, 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.

9. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 5, 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.

10. The method for smelting ultra-low carbon aluminum-killed steel as described in claim 5, 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 10-20 L / h, the casting speed is 0.7-2.0 m / min, and the width of the continuous casting mold is 750-2400 mm.

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