A high speed continuous casting process for producing AH36 steel 150mm x (2800-3200)mm ultra-wide slab

Abstract

The application discloses a high-pulling speed continuous casting process for producing AH36 steel 150mm*(2800-3200)mm ultra-wide slab, and belongs to the field of high-pulling speed continuous casting.The process flow is as follows: BOF-LF / VD refining furnace, ladle rotating platform, single-flow tundish, multi-hole submerged entry nozzle, on-line width-adjusting crystallizer, gas-water secondary cooling, air cooling and fire cutting stacking.The AH36 steel pulling speed is increased by 20%-60% in the application, the slab is qualified in terms of the macroscopic quality, the product has no quality dispute, the production potential of the caster is further released, the production cost and the CO2 emission per ton of steel are reduced, and the furnace-machine matching relationship is improved; after the AH36 steel pulling speed is increased, the production rhythm of the caster is accelerated, the production capacity in the same period is increased by 10%-62%, and the energy loss of a heating furnace and the like is reduced by about 18-25%; in addition, the application increases the AH36 steel continuous casting production efficiency of an enterprise, meets the quality requirements of customers on the steel for ship plates, improves the production automation level, improves the carbon emission control level, reduces the cost and increases the efficiency, and improves the competitiveness of the enterprise.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high-speed continuous casting, and relates to a high-speed continuous casting process for producing 150mm-thick AH36 ultra-wide slab. BACKGROUND

[0002] In recent years, the demand for high-value-added steel grades in the domestic and foreign markets has significantly increased, which promotes the pace of efficient and high-quality production of enterprises, and casting billet solidification defects, breakout accidents and the like seriously restrict the high-speed continuous casting production, therefore, it is increasingly important to design a corresponding high-speed continuous casting process according to the solidification characteristics of different steel grades.

[0003] The high-speed continuous casting technology aims to tap the limit of the capacity of continuous casting equipment, and has certain advantages in equipment space and manufacturing design, accessory and labor cost, energy and emission control level, process and quality stability and the like, and has a direct promoting effect on the development of the entire steel production process towards greenness, high efficiency and intelligence.

[0004] The high-speed continuous casting needs to ensure that the casting billet with better quality is produced and higher control level is achieved, therefore, new technologies and processes need to be developed to solve the technical problems such as non-uniform solidification billet shell, mold slag entrapment, large mold liquid level fluctuation, bulging and the like under the condition of high-speed continuous casting of slab.

[0005] A continuous casting process for producing 25Mn4 steel at high speed is disclosed in Chinese patent (2022108242677), and the obtained square round billet is qualified, which is different from the AH36 steel grade and the billet type of 150mm medium-thin slab described in the present patent. A small square billet continuous casting high-speed production method is proposed, which is mainly used for deformed steel with a cross section of 160-165mm, and the selection of various process parameters is biased towards the technical points of small cross section billet. A high-speed production method for hypoperitectic steel is disclosed, the carbon content of the steel grade is 0.10-0.12%, the solidification shrinkage coefficient of the molten steel is quite different from that of AH36, and the billet thickness is 230mm. The present patent produces 150mm medium-thin slab, and the emphasis of process parameters such as mold vibration and selection mode of protective slag under high speed is different; therefore, designing a corresponding high-speed continuous casting process for AH36 steel becomes the key to solving this problem. SUMMARY

[0006] The application aims to provide a high-speed continuous casting process for producing AH36 steel 150mmx(2800-3200)mm ultra-wide slab; the process flow is as follows: BOF-LF / VD refining furnace→ladle turret→single-flow tundish→multi-hole submerged entry nozzle→on-line width-adjusting mold→gas-water secondary cooling→air cooling→fire cutting and stacking.

[0007] The specific process includes:

[0008] (1): The converter and refining furnace produce qualified molten steel, which is transported to the rotary table by ladle, and is injected into the single-flow tundish through the long nozzle. The weight of the molten steel in the tundish casting process should not be less than 40 tons. The tundish covering agent is a high-alkalinity covering agent, and the casting temperature is (liquidus temperature + 20) ± 5℃. The amount of molten steel injected into the crystallizer is controlled by the stopper, and argon blowing is configured to prevent nozzle clogging. The molten steel is injected into the crystallizer through the submerged nozzle, and the water nozzle is inserted into the crystallizer liquid surface at a depth of 140-160mm;

[0009] (2): The casting machine pulling speed is 1.5-2.0m / min, and the total heat exchange of the crystallizer cooling water is 6.0-8.0MW; the crystallizer vibration adopts a non-sine vibration mode, the vibration frequency is 120-190 times / min, the vibration amplitude is 3-5mm, the skew rate is 0.1<α≤0.4, and the crystallizer liquid surface fluctuation is controlled within ±5mm;

[0010] The crystallizer has a hot flow detection, vibration friction force detection, liquid surface fluctuation detection and leakage prediction system;

[0011] (3): The secondary cooling zone adopts continuous bending and continuous straightening, which is composed of a foot roller section (1 row of wide face and 4 rows of narrow face of the support roller, integrated with the crystallizer), a bending section (fan-shaped section 0#), an arc section (fan-shaped sections 1-5#), a straightening section (fan-shaped sections 6-7#), and a horizontal section (fan-shaped section 8#). The secondary cooling zone is divided into 8 loops, of which loop 1W and 1N are the wide face and narrow face of the foot roller respectively, loops 2-3 are the bending section, loop 4 is arc sections 1# and 2#, loop 5 is arc sections 3# and 4#, loop 6 is arc section 5# and straightening section 6#, loop 7 is straightening section 7# and horizontal section 8#, and the total length of the secondary cooling zone is 16.8m;

[0012] (4): The secondary cooling uses dynamic heat detection and dynamic water distribution function, which can real-time predict the heat state of the solidification process, and adjust the water quantity according to the target surface temperature;

[0013] (5): The secondary cooling zone is subjected to electromagnetic stirring, and the installation position is the roller at the outlet of 2nd and 3rd sections, the current intensity is 460-480A, and the frequency is 8-11Hz;

[0014] (6): It has a dynamic soft reduction function at the solidification end, and the main execution interval is fan-shaped sections 5-8#, and the total reduction amount is 3-10mm;

[0015] (7): The slab is subjected to flame cutting, and after cutting, it is stacked and slowly cooled, or directly hot sent and hot charged.

[0016] Further, after the increase of the casting speed, the residence time of the molten steel in the tundish is reduced, the inclusions are not sufficiently floated, and the purity of the AH36 molten steel is reduced. Therefore, the basic tundish covering agent with the basicity of 1.8-2.5 is used to absorb the inclusions in the molten steel.

[0017] Further, the minimum tonnage when the tundish is replaced is not less than 30t.

[0018] Further, in order to prevent the clogging caused by the clogging of the inner wall of the nozzle at high casting speed, the stopper argon blowing technology is used. When the casting speed is 1.5m / min, the argon blowing amount is 0.45L / min, when the casting speed is 2.0m / min, the argon blowing amount is 0.72L / min, and in the casting speed range, the argon blowing amount is increased by 0.054L / min for each increase of 0.1m / min of the casting speed.

[0019] Further, the outlet of the submerged nozzle can be two holes, three holes, four holes, five holes, etc.

[0020] Further, the primary shell is prone to uneven growth when the slab thickness is thin and the width is large. When the casting speed is increased, the mold vibration frequency is proportional to the casting speed, that is, the vibration frequency f=72×casting speed V C +18, so as to reduce the depth of the slab vibration marks;

[0021] The mold heat flow detection system displays the heat flow density distribution of the four surfaces of the copper plate of the mold in real time, the vibration friction force detection calculates the friction force size when the mold is vibrated in real time, the liquid level fluctuation detection monitors the fluctuation frequency and amplitude of the upper surface of the mold in real time, and the leakage prediction system displays the temperature change rule of the thermocouple of the copper plate of the mold in real time. The above systems can alarm the abnormal working conditions when the key data exceeds the normal range.

[0022] Further, the dynamic water distribution model adopts a two-dimensional or three-dimensional algorithm, which can predict the shape of the solidification end of the slab width direction as U-shaped or W-shaped.

[0023] Further, for the large width of the cast slab, the gas-water spray cooling is used in the secondary cooling zone to achieve more uniform cooling effect. For the 150mm×(2800-3200)mm slab, the pressure after the valve is 0.2-0.3Mpa, and the secondary cooling water quantity is 0.4-1.2Kg / t of steel.

[0024] Further, two or more types of nozzles are used in the secondary cooling zone along the width direction of the cast slab, and are uniformly arranged above the wide surface of the cast slab, which can better cover the wide surface of the cast slab.

[0025] Take three as an example, wherein the most edge adopts a small flow nozzle (model A, water quantity is 30%-60% of the face nozzle), the secondary edge adopts a transition flow nozzle (model B, water quantity is 60%-90% of the face nozzle), and the face center region adopts a normal flow nozzle (model C, water quantity is 100%), which share a cooling loop.

[0026] Further, the dynamic soft reduction function can automatically adjust the reduction amount, reduction interval and reduction rate parameters according to the changes of steel grade, superheat, drawing speed and cooling conditions, wherein the reduction interval is the position of the center line solid phase rate of 0.5-1.0, and the whole range of covering U-shaped or W-shaped liquid core shape is considered, for the U-shaped liquid core, the solid phase rate at the center of the slab is used as the standard; for the W-shaped liquid core, the center solid phase rate at the 1 / 4-1 / 8 width of the slab is used as the standard.

[0027] Further, the stacking slow cooling time is 36h or more, or the entry temperature of the furnace under the hot charging condition is higher than 600℃.

[0028] Beneficial effects: compared with the prior art, the characteristics of the present application are: based on the technical achievements of the present application, the drawing speed of AH36 steel is increased by 20%-60%, the slab macrostructure quality is qualified, the product has no quality dispute, at the same time, the production potential of the caster is further released, the production cost and the CO2 emission per ton of steel are reduced, and the furnace-machine matching relationship is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic view of the nozzle arrangement in the width direction of the continuous casting billet in the embodiment of the present application;

[0030] Figure 2 is a schematic view of the slab cross-section segregation sampling in the embodiment of the present application. DETAILED DESCRIPTION

[0031] The present application will be further described below in combination with the drawings and embodiments.

[0032] As shown in the drawings, the high-speed continuous casting process for producing 150mm thick AH36 ultra-wide slab (high-speed continuous casting process for 150mm x (2800-3200) mm ultra-wide slab of AH36 steel) according to the present application, the difference between the continuous casting process and the conventional drawing speed lies in: full-process protection casting, the steel liquid weight in the pouring process is not less than 40 tons; the covering agent in the tundish adopts high-alkalinity covering agent, argon blowing is used for the stopper, a porous submerged nozzle is used, the number of nozzle holes is determined according to the slab width, and the number of holes is appropriately increased as the width increases.

[0033] The frequency of the crystallizer is increased with the increase of the casting speed in the range of 120-190 times / min. The heat flow, vibration friction, liquid level fluctuation detection system and leakage prediction system are simultaneously opened in the production process to ensure the uniform growth of the shell in the crystallizer. The fan-shaped segment layout suitable for straightening with liquid core is configured. The dynamic heat detection and dynamic water distribution system of the secondary cooling are used to predict the thermal state of the solidification process in real time, and the water quantity is adjusted according to the target surface temperature. The gas-water cooling is carried out at a specific valve pressure. A plurality of nozzles with different cooling effects are arranged in the width direction of the slab to ensure that the high-speed casting slab is more effectively cooled in the secondary cooling zone.

[0034] The dynamic soft reduction function at the solidification end is used in the fan-shaped segments 5-8#. The extrusion effect of the soft reduction is beneficial to the feeding of the liquid steel, and at the same time, the center solute enrichment is mixed with the surrounding mother liquor to complete the redistribution of solute elements and improve the internal quality of the slab. The specific production process is as follows:

[0035] (1) After the molten steel is refined by the BOF-LF / VD refining furnace, it is stored in the ladle and then injected into the tundish. After the pouring, the temperature of the molten steel in the tundish is controlled at (liquidus temperature + 20℃) ± 8℃. The molten steel is injected into the crystallizer through the multi-hole submerged nozzle, and the water nozzle is inserted into the crystallizer at a depth of 140-160 mm.

[0036] (2) The casting speed is 1.5-2.0 m / min, and the heat exchange capacity of the crystallizer cooling water is 6.0-8.0 MW. The heat exchange capacity increases by 0.4 MW for every 0.1 m / min increase in the casting speed. The crystallizer vibration adopts a non-sinusoidal vibration mode, the vibration frequency is 120-190 times / min, the amplitude is 4-5 mm, and the skew rate is 0.1<α≤0.4. When high-speed continuous casting is carried out, the crystallizer heat flow detection, vibration friction detection, liquid level fluctuation detection and leakage prediction systems are opened, and the liquid level fluctuation in the crystallizer is controlled within ±5 mm.

[0037] (3) The secondary cooling zone adopts continuous bending and straightening, which is composed of a foot roller section (1 row of wide face and 4 rows of narrow face, integrated with the crystallizer), a bending section (fan-shaped section 0#), an arc section (fan-shaped sections 1-5#), a straightening section (fan-shaped sections 6-7#) and a horizontal section (fan-shaped section 8#). The secondary cooling zone is divided into 8 loops, of which loop 1W and 1N are the wide face and narrow face of the foot roller respectively, loops 2-3 are the bending section, loop 4 is the arc section 1# and 2#, loop 5 is the arc section 3# and 4#, loop 6 is the arc section 5# and the straightening section 6#, loop 7 is the straightening section 7# and the horizontal section 8#, and the total length of the secondary cooling zone is 16.8 m.

[0038] (4) : The dynamic thermal detection and dynamic water distribution function are used in the secondary cooling to predict the thermal state of the solidification process in real time, and the water quantity is regulated according to the target surface temperature. Electromagnetic stirring is carried out in the secondary cooling zone, the installation position is the roller at the outlet of the 2nd and 3rd sections, the current intensity is 460-480 A, and the frequency is 8-11 Hz;

[0039] (5) : Dynamic soft reduction at the end of solidification is adopted, the main execution interval is the fan-shaped sections 5-8#, and the total reduction is in the range of 3-10 mm;

[0040] (6) : Flame cutting is carried out when the slab reaches the flame cutting point, and then the stack is slowly cooled or directly hot charged.

[0041] Further, after the drawing speed is increased, the residence time of the molten steel in the tundish is reduced, the inclusions are not fully floated, and the purity of the AH36 molten steel is reduced. The tundish covering agent adopts a covering agent with a basicity of 1.8-2.5 according to the chemical composition in Table 1 to fully absorb the inclusions in the molten steel in the tundish.

[0042] Table 1 Composition of tundish basicity covering agent

[0043]

[0044]

[0045] Note: R2O = Na2O + K2O + Li2O, basicity = (CaO + MgO) / (SiO2 + Al2O3).

[0046] Further, when the AH36 steel ultra-wide slab is produced at a high drawing speed, the minimum tonnage of the tundish changing process is not less than 30 t.

[0047] Further, the argon blowing amount of the stopper argon blowing technology is 0.45-0.72 L / min in the drawing speed range of 1.5-2.0 m / min, and the argon blowing amount is increased by 0.054 L / min for each increase of 0.1 m / min of the drawing speed.

[0048] Further, the submerged entry nozzle can adopt a multi-hole nozzle such as a two-hole, three-hole, four-hole, five-hole nozzle, etc.

[0049] Further, the mold vibration frequency is proportional to the drawing speed, that is, the vibration frequency f = 72 x drawing speed VC + 18, which is beneficial to reduce the slab vibration mark depth. The mold heat flow detection system displays the heat flow density distribution of the four surfaces of the mold copper plate in real time, the vibration friction force detection calculates the friction force size when the mold vibrates in real time, the liquid level fluctuation detection monitors the fluctuation frequency and amplitude of the molten steel surface of the mold in real time, and the leakage prediction system displays the temperature change law of the mold copper plate thermocouple in real time. The above systems can alarm abnormal working conditions when the key data exceeds the normal range.

[0050] Further, the dynamic water distribution model adopts two-dimensional or three-dimensional algorithm, which can predict the shape of the solidification end of the slab width direction as U type or W type.

[0051] Further, the secondary cooling zone adopts air-water spray cooling, and for the 150mm x (2800-3200) mm slab, the valve pressure is 0.2-0.3 MPa, and the secondary cooling specific water quantity is 0.4-1.2 Kg / t steel.

[0052] Further, the secondary cooling zone adopts two or more types of nozzles along the width direction of the casting slab, which are uniformly arranged above the width surface of the casting slab and can better cover the width surface of the slab. Taking three types as an example, the most edge part adopts a small flow nozzle (model A, water quantity is 30%-60% of the surface nozzle), the next edge part adopts a transition flow nozzle (model B, water quantity is 60%-90% of the surface nozzle), and the center area of the surface adopts a normal flow nozzle (model C, water quantity is 100%), which share a cooling circuit, as shown in Figure 1 .

[0053] Further, the dynamic soft reduction function can automatically adjust the reduction amount, reduction interval and reduction rate parameters according to the changes of steel grade, superheat, casting speed and cooling conditions, wherein the reduction interval is the position where the center line solid fraction is 0.5-1.0, and the whole range of U type or W type liquid core shape is considered, for U type liquid core, the solid fraction at the center of the slab is used as the reference. For W type liquid core, the center solid fraction at 1 / 4-1 / 8 width of the slab is used as the reference.

[0054] Further, the slab is stacked and slowly cooled for more than 36 hours after hot cutting, or the entry temperature is higher than 600°C under hot charging conditions.

[0055] According to the above method, the following provides a specific embodiment of high-speed production of AH36 steel 150mm x (2800-3200) mm ultra-wide slab.

[0056] The composition of AH36 steel, wt%, is shown in Table 2.

[0057] Table 2 AH36 steel composition

[0058]

[0059] The composition of the AH36 steel is shown in Table 2, which belongs to domestic ship steel material, and is mainly used for manufacturing hull structures of sea ships and inland river ships, and is usually high-quality carbon steel and high-quality low-alloy steel; certain strength, toughness, low-temperature corrosion resistance and welding performance are required. When such steel is produced at high speed and high quality, the purity of the molten steel is required to be high, in the application, the BOF-LF / VD furnace is used to refine the molten steel, and the composition of the covering agent of the tundish is adjusted, so as to reduce the inclusions in the molten steel, in addition, the stopper argon blowing technology is used to prevent the nozzle from being clogged at high speed, and the generated argon bubbles can also accelerate the floating of the inclusions; the submerged nozzle adopts a porous nozzle, the mold thermal flow detection, liquid level fluctuation detection and leakage prediction system are combined, the mold liquid level fluctuation is controlled within ±5mm, and the uniform growth of the shell and the safety thickness of the shell out of the mold are ensured, the specific fan-shaped section design, dynamic secondary cooling heat detection and target temperature water distribution are used, so that the casting blank does not have defects such as bulging or cracking in the subsequent bending, straightening and cooling process; the vibration frequency f=72*speed V C +18, the vibration frequency is increased with the increase of the speed, so as to reduce the negative stripping time and the vibration mark depth of the surface of the AH36 slab, and the real-time friction between the shell and the mold is detected by the mold vibration friction force, so as to ensure the good stripping effect of the mold and the shell in the vibration process. The gas-water cooling and the multi-type nozzle arrangement are used for uniform cooling in the width direction of the ultra-wide slab, so as to cope with the difference between the two-dimensional heat transfer of the slab corner and the one-dimensional heat transfer in the width direction. When the speed is high, the cooling speed of the casting blank is reduced, the liquid core of the casting blank becomes thin and long, and the dynamic soft reduction at the solidification end can strengthen the feeding of the molten steel and the solute homogenization.

[0060] Example 1

[0061] The process flow of the 150mm*2800mm slab of the AH36 steel produced at 1.9m / min is as follows: BOF-VD / LF refining furnace→ladle turret→single-flow tundish→porous submerged nozzle→online width-adjusting mold→gas-water secondary cooling→air cooling→fire cutting→stacking.

[0062] The AH36 molten steel is refined after converter, and the fluxing agent is added at the station to ensure that the molten steel composition meets the standard strictly at the station. The calcium treatment is performed before the molten steel is discharged, and the temperature is measured before the molten steel is discharged. The temperature of the molten steel discharged from the converter is specified to be 1540-1550℃. The temperature of the first ladle is increased by 12-15℃ based on the temperature of the molten steel discharged from the converter, and the temperature of the second ladle is increased by 6-8℃ based on the temperature of the molten steel discharged from the converter. The strict protection casting is adopted throughout the process to prevent the secondary oxidation of the molten steel. The long nozzle with an inner diameter of 99mm and the protection sleeve are used from the tundish to the intermediate ladle. After the casting is started, the covering agent with a basicity of 2 is added to the molten steel surface when the liquid level of the intermediate ladle is increased to 1150mm. The molten steel quantity injected into the mold is controlled by the opening degree of the high-alumina stopper. The deviation between the submerged nozzle and the center of the mold is 1.2mm. When the distance between the molten steel surface of the mold and the upper section is 70mm, the straightening machine and the mold are started. The starting speed is 0.4m / min. The speed is slowly increased after 45s. The low-carbon steel protection slag is added to the molten steel surface of the mold after the straightening machine is started for 60s. The mold surface is uniformly covered with the protection slag. The speed reaches 1.1m / min after 2min. The speed reaches 1.9m / min after 5m / min.

[0063] After the speed is stabilized, the mold surface fluctuation detection, the vibration friction detection, the heat flow detection and the leakage prediction system are started. The argon flow is gradually increased to 0.66L / min by the stopper blowing. The temperature of the copper plate thermocouple of the mold is basically constant. The heat exchange capacity is 7.2MW. There is no leakage prediction. The frequency of the non-sinusoidal vibration is 154 times / min. The amplitude is 4mm. The deviation rate is 0.2. There is no abnormality in the vibration friction detection. The three-hole submerged nozzle is used. The insertion depth of the submerged nozzle into the molten steel surface of the mold is 145mm. The fluctuation of the molten steel surface of the mold is stabilized within ±4mm. The fluctuation frequency of the molten steel surface of the mold is 0.04Hz.

[0064] The shell thickness of the billet discharged from the lower outlet of the mold is 17mm. The shell thickness of the narrow surface of the billet is 14mm. The secondary cooling is performed after the billet is discharged from the mold. The real-time dynamic heat detection and the dynamic water distribution system are synchronously operated. The air-water spray cooling is used. The pressure after the nozzle valve is 0.28Mpa. The nozzle height is 305mm. The spray angle is 98℃. The specific water quantity of the secondary cooling is 1.0L / kg. The shape of the solidification end of the slab in the width direction is U-shaped according to the two-dimensional algorithm.

[0065] The billet with the liquid core reaches the solidification end. The dynamic soft reduction is performed in the interval of the fan-shaped segments 6-7#. The reduction interval is the position with the center solid fraction of 0.7. The total reduction amount is 8mm.

[0066] The casting blank is completely solidified at 3.5 m from the fire cutting point, and is slowly cooled for 36 h after cutting and stacking.

[0067] The casting blank sample is eroded by hot hydrochloric acid on site, and is rated according to YB / 153-2015 "Acid Etching Inspection Method for Macrostructure and Defects of High-quality Structural Steel Continuous Casting Blank", the center shrinkage and center porosity are less than 0.5 level, and according to Figure 2 The sample preparation method is to drill the sample on the slab, and the center segregation ratio is 1.032 by infrared absorption method (GB / T20123-2006) to detect the steel chips, which meets the customer's requirements.

[0068] Example 2

[0069] The process flow for producing AH36 steel 150 mm x 3050 mm wide slab at a drawing speed of 1.8 m / min is: BOF-VD / LF refining furnace→140 t ladle→single flow tundish→two-hole submerged nozzle→online width adjustment mold→gas-water secondary cooling→air cooling→fire cutting and stacking.

[0070] The AH36 molten steel is transported from the converter to the LF refining furnace, and the fluxing agent is added after arrival to ensure that the composition of the molten steel meets the standard at the exit, calcium treatment is carried out before the exit and the temperature is measured at the exit, the exit temperature is 1549℃, strict protection casting is adopted throughout the process, the long nozzle with an inner diameter of 99 mm and the protection sleeve are used from the ladle to the tundish, when the liquid level of the tundish rises to 1200 mm, the covering agent with a basicity of 2.2 is added to the liquid surface, the temperature of the tundish is 1534℃, the submerged nozzle is centered with the mold, the deviation is 1.2 mm, and the drawing speed is 1.8 m / min.

[0071] The stopper is opened to blow argon, and the argon flow is gradually increased to 0.61 L / min at this time, the copper plate thermocouple temperature of the mold is basically kept constant, the heat exchange capacity of the mold is 6.8 MW, there is no warning of leakage, the non-sinusoidal vibration frequency is 148 times / min, the amplitude is 4 mm, the skew rate is 0.2, the friction detection of the mold vibration is normal, the four-hole submerged nozzle is used, the insertion depth of the submerged nozzle into the mold liquid surface is 150 mm, the mold liquid surface fluctuation is stable at ±5 mm, and the liquid surface fluctuation frequency is 0.07 Hz. The lowest tonnage during ladle change is 33 t.

[0072] The shell thickness of the strand out of the mold lower port reaches 17 mm in the wide surface and 15 mm in the narrow surface. After the strand out of the mold, the real-time dynamic thermal detection and the dynamic water distribution system are synchronously operated to realize the gas-water spray cooling. The pressure after the nozzle valve is 0.26 MPa, the nozzle height is 305 mm, the spray angle is 102 °, and the secondary cooling specific water quantity is 1.1 L / kg. The shape of the solidification end in the slab width direction is W type predicted by the two-dimensional algorithm. The current intensity of the electromagnetic stirring in the secondary cooling zone is 466 A, the frequency is 8 Hz, there are 6 nozzles in the slab width direction, the most edge is the A type small flow nozzle, the water quantity is 35% of the surface nozzle water quantity, the second edge is two B type transition flow nozzles, the water quantity is 70% of the surface nozzle water quantity, the surface center area is two C type normal nozzles, the water quantity is 100%, and one loop is used.

[0073] The strand with the liquid core reaches the solidification end, the dynamic soft reduction execution interval is the fan-shaped segments 5-6#, the reduction interval is the position where the solid phase rate is 0.6 at the slab 1 / 4-1 / 8 width, and the total reduction amount is 6 mm.

[0074] The cast slab is completely solidified when the solidification end is 3.2 m away from the fire cutting point, and is slowly cooled for 36 h after cutting and stacking.

[0075] The cast slab sample is eroded by hot hydrochloric acid on site, and the rating is performed according to YB / 153-2015 "Acid etching test method for macrostructure and defects of high-quality structural steel continuous casting blank". The center shrinkage hole and the center porosity are less than 0.5 level. According to YB / 153-2015 "Acid etching test method for macrostructure and defects of high-quality structural steel continuous casting blank", the center segregation ratio of the sample is 1.036. Figure 2 The sample is taken by drilling and sampling the slab, the steel chips are detected by infrared absorption method (GB / T20123-2006), and the center segregation ratio is 1.036.

[0076] Example 3

[0077] The process flow for producing the AH36 steel 150 mm x 3200 mm wide slab at a casting speed of 1.6 m / min is as follows: BOF-VD / LF refining furnace→148 t ladle→single flow tundish→two-hole submerged nozzle→online width adjustment mold→gas-water secondary cooling→air cooling→fire cutting and stacking.

[0078] The AH36 molten steel is transported from the converter to the LF refining furnace, and the fluxing agent is added after arriving at the station to ensure that the molten steel composition strictly meets the standard when leaving the station. The calcium treatment is performed before leaving the station, and the temperature is measured when leaving the station. The leaving temperature is 1554 °C. The whole process is strictly protected by casting. The long nozzle with an inner diameter of 99 mm and the protection sleeve are used from the ladle to the tundish. When the tundish liquid level rises to 1250 mm, the covering agent with an alkalinity of 1.8 is added to the molten steel surface. The tundish temperature is 1538 °C. The submerged nozzle is centered with the mold with a deviation of 1.3 mm. The casting speed is 1.6 m / min. The minimum tonnage during ladle changing is 36 t.

[0079] Turn on the stopper rod to purge argon, and gradually increase the argon flow rate to 0.50 L / min. At this time, the temperature of the thermocouple on the copper plate of the crystallizer remains basically constant, the average heat exchange of the crystallizer is 7.3 MW, there is no steel leakage warning, the non-sinusoidal vibration frequency is 133 times / min, the skewness is 0.3, the friction force detection during crystallizer vibration is normal, a five-hole immersion nozzle is used, inserted 153 mm below the liquid surface of the crystallizer, the liquid level fluctuation of the crystallizer is stable within ±3 mm, the liquid level fluctuation frequency is 0.06 Hz, and the minimum steel volume in the tundish during the ladle change is 35 t.

[0080] The billet shell thickness at the bottom of the crystallizer is 16mm on both the wide and narrow sides. It then undergoes secondary cooling, with real-time dynamic thermal monitoring and a dynamic water distribution system operating synchronously. Air-water spray cooling is used, with a nozzle valve pressure of 0.23 MPa, a nozzle height of 305mm, a spray angle of 105°, and a secondary cooling water flow rate of 1.2 L / kg. A two-dimensional algorithm predicts that the solidification end shape in the width direction of the billet will be W-shaped. The electromagnetic stirring current in the secondary cooling zone is 478A at a frequency of 9Hz. There are six nozzles along the width direction of the billet: nozzle A at the outermost edge with 37% of the water flow of the main nozzles; two nozzles B at the next outermost edge with 72% of the water flow of the main nozzles; and two nozzles C in the central area of ​​the main surface with 100% water flow, all sharing a single circuit.

[0081] When the liquid core of the billet reaches the end of solidification, the dynamic light reduction is executed in the sector section 7-8#, and the reduction range is the position with a solid phase of 0.5 at 1 / 4-1 / 8 width of the billet, with a total reduction of 8mm.

[0082] The billet solidifies completely 3.3m from the fire cutting point, is hot-sent and hot-charged, and enters the furnace at a temperature of 638℃.

[0083] On-site etching of the cast billet samples with hot hydrochloric acid was performed. The samples were graded according to YB / 153-2015 "Acid Etching Test Method for Low-Magnification Microstructure and Defects in High-Quality Structural Steel Continuously Cast Billets". The central shrinkage cavity and central porosity were both below grade 1. Furthermore, according to... Figure 2 The sample preparation method involves taking drill chips from the slab and detecting the steel chips using infrared absorption method (GB / T20123-2006). The center segregation ratio is 1.04.

[0084] AH36 steel is a typical low-alloy high-strength ship plate steel with excellent strength, toughness and weldability.

[0085] After the casting speed of AH36 steel is increased, the production pace of the casting machine is accelerated, and the capacity increases by 10% to 62% within the same cycle, while the energy consumption of heating furnaces and other equipment is reduced by about 18% to 25%.

[0086] The present application mainly applies high-alkalinity tundish covering agent, stopper argon blowing, crystallizer liquid surface heat flow detection system, liquid surface fluctuation detection system, vibration friction force detection system, non-sine vibration, dynamic secondary cooling water distribution, secondary cooling zone electromagnetic stirring, multi-type nozzle coordinated distribution and solidification end dynamic soft reduction technology to increase the drawing speed of 150mmx(2800-3200)mm AH36 slab to 1.5-2.0m / min.

[0087] The present application improves the continuous casting production efficiency of AH36 steel, meets the quality requirements of ship plate steel, and improves the production automation level, improves the carbon emission control level, and reduces the cost and increases the efficiency.

Claims

1. A high-speed continuous casting process for producing ultra-wide slabs of AH36 steel with a diameter of 150mm × (2800-3200)mm, characterized in that, Its process flow is as follows: BOF-LF / VD refining furnace → ladle rotary table → single-strand tundish → multi-hole submerged nozzle → online adjustable crystallizer → gas-water dual cooling → air cooling → fire cutting and stacking. The specific process steps are as follows: (1): The qualified molten steel produced by the converter and refining furnace is transported to the rotary table by steel ladle and injected into the single-strand tundish through the long nozzle; During the tundish casting process, the molten steel weight is ≥40t, the tundish covering agent is a high-alkalinity covering agent, the casting temperature is ±5℃, the amount of molten steel injected into the crystallizer is controlled by a stopper rod, argon blowing is configured by a stopper rod, and the molten steel is injected into the crystallizer through an immersion nozzle, with the nozzle inserted into the liquid surface of the crystallizer to a depth of 140-160mm. (2): The casting machine speed is 1.5-2.0m / min, the total heat exchange of the cooling water in the crystallizer is 6.0-8.0MW; the crystallizer vibration adopts a non-sinusoidal vibration mode, the vibration frequency is 120-190 times / min, the amplitude is 3-5mm, the skewness is 0.1<α≤0.4, and the fluctuation of the liquid surface in the crystallizer is controlled within ±5mm; (3): The second cooling zone adopts continuous bending and continuous straightening, and consists of a foot roller section, a bending section, an arc section, a straightening section and a horizontal section; The two cooling zones are divided into eight loops: loop 1W, loop 1N, loop 2, loop 3, loop 4, loop 5, loop 6, and loop 7. Among them, loops 1W and 1N are the wide and narrow sides of the foot roller, loops 2-3 are the bending section, loop 4 is the arc section 1# and 2#, loop 5 is the arc section 3# and 4#, loop 6 is the arc section 5# and the straightening section 6#, loop 7 is the straightening section 7# and the horizontal section 8#, and the total length of the two cooling zones is 16.8m; (4): The secondary cooling system uses dynamic thermal detection and dynamic water distribution functions to predict the thermal state of the solidification process in real time and adjust the water volume according to the target surface temperature. (5): Electromagnetic stirring is carried out in the second cooling zone with a current intensity of 460-480A and a frequency of 8-11Hz; (6): It has the function of dynamic light pressing at the end of solidification, the execution range is the sector segment 5-8#, and the total pressing amount is 3-10mm; (7): The slab is flame-cut, and after cutting, it is stacked and cooled slowly or hot-sent and loaded.

2. The high-speed continuous casting process for producing ultra-wide slabs of AH36 steel (150mm × (2800-3200)mm) according to claim 1, characterized in that, As the casting speed increases, the residence time of molten steel in the tundish decreases, so an alkaline tundish covering agent with a basicity of 1.8-2.5 is used. The minimum tonnage for intermediate package replacement is ≥30t.

3. The high-speed continuous casting process for producing ultra-wide slabs of AH36 steel (150mm × (2800-3200)mm) according to claim 1, characterized in that, When using the stopper rod argon blowing technology, the argon blowing rate is 0.45 L / min when the pulling speed is 1.5 m / min and 0.72 L / min when the pulling speed is 2.0 m / min. Within the pulling speed range, the argon blowing rate increases by 0.054 L / min for every 0.1 m / min increase in pulling speed.

4. The high-speed continuous casting process for producing ultra-wide slabs of AH36 steel (150mm × (2800-3200)mm) according to claim 1, characterized in that, The immersion nozzle outlet has one of two, three, four, or five holes.

5. The high-speed continuous casting process for producing 150mm × (2800-3200)mm ultra-wide slabs of AH36 steel according to claim 1, characterized in that, The crystallizer's vibration frequency is directly proportional to the pulling speed, i.e., the vibration frequency... f =72×pulling speed V C +18.

6. The high-speed continuous casting process for producing ultra-wide slabs of AH36 steel (150mm × (2800-3200)mm) according to claim 1, characterized in that, The dynamic water distribution model uses a two-dimensional or three-dimensional algorithm to predict whether the solidification end shape of the slab in the width direction is U-shaped or W-shaped.

7. The high-speed continuous casting process for producing 150mm × (2800-3200)mm ultra-wide slabs of AH36 steel according to claim 1, characterized in that, The secondary cooling zone uses air-water spray cooling to produce 150mm×(2800-3200)mm slabs, with a valve pressure of 0.2~0.3Mpa and a secondary cooling water volume of 0.4-1.2Kg / t steel; The secondary cooling zone employs two or more types of nozzles along the width of the billet, evenly arranged above the wide surface of the billet.

8. The high-speed continuous casting process for producing 150mm × (2800-3200)mm ultra-wide slabs of AH36 steel according to claim 1, characterized in that, The dynamic light reduction function can automatically adjust the reduction amount, reduction range, and reduction rate parameters according to changes in steel grade, superheat, drawing speed, and cooling conditions. The reduction range is the position where the solid fraction at the center line is 0.5-1.0, while also considering the full range of U-shaped or W-shaped liquid core shapes. For U-shaped liquid cores, the solid fraction at the center of the slab is used as the standard; for W-shaped liquid cores, the solid fraction at the center of the slab at 1 / 4 to 1 / 8 of its width is used as the standard.

9. The high-speed continuous casting process for producing ultra-wide slabs of AH36 steel (150mm × (2800-3200)mm) according to claim 1, characterized in that, The stacking slow cooling time is >36h, or the furnace temperature is higher than 600℃ under hot delivery and hot charging conditions.

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