A method for producing a large-size round billet of a power plant boiler pipe blank steel by continuous casting

Abstract

The application is a large-scale round billet continuous casting production method of SA-335P92 steel for ultra-supercritical power station boiler pipe blank, through a series of measures such as optimizing the continuous casting machine pouring, casting process parameters, optimizing the taper of the crystallizer, replacing the type of the crystallizer protecting slag, improving the ingot blocking mode, tundish pouring mode and the like, the problems such as the easy occurrence of pouring leakage and the longitudinal crack defects on the surface of the cast blank due to the large drawing resistance of the steel are successfully solved, the round billet continuous casting production process route of the steel is opened up, the utilization rate of the cast blank is improved, the product quality is improved, the production cost is reduced, and great economic benefits are created.

Description

Technical Field

[0001] This invention relates to a method for continuous casting of large-size round billets for power plant boiler tube blanks, specifically a method for continuous casting of SA-335P92 round billets for ultra-supercritical power plant boiler tube blanks with a diameter of φ690. Background Technology

[0002] SA-335P92 is a steel for ultra-supercritical power plant boilers, belonging to a new type of heat-resistant steel series. It is used to manufacture heat-receiving tubes such as reheaters and superheaters in high-pressure boilers, as well as boiler headers and steam ducts with metal wall temperatures ≤600℃. It is widely used in power plant boilers, petroleum and petrochemical industries. Its operating environment is harsh, with high requirements for the non-metallic inclusion content and ultrasonic testing of the finished product. Lower oxygen content is better, and the production process is quite difficult; continuous casting of large-section round billets is a particular challenge in the steel industry. Our plant originally used ingot casting for SA-335P92 steel, resulting in a low billet yield. In March 2015, our round billet continuous casting plant was completed and put into operation, providing the conditions for continuous casting production of SA-335P92. We then began trial production of SA-335P92 using continuous casting.

[0003] The purpose of this invention is to achieve stable continuous casting of φ690 round billets for power plant boiler tube billet steel SA-335P92, solve the problem of steel leakage during the continuous casting process, eliminate longitudinal crack defects on the billet surface and the problem of billet tipping upwards, open up the slow cooling process route for SA-335P92, and solve the problem of normal production organization being affected by the heat treatment process. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a method for continuous casting of large-size round billets for power plant boiler tube billets.

[0005] The purpose of this invention is achieved as follows: A method for continuous casting of large-size round billets for power plant boiler tube billets, including the following aspects: (1) changing the crystallizer before production, using a small-tapered crystallizer, and using a plum-petal crystallizer for the copper tube of the crystallizer; (2) material preparation, preparing special materials before production; (3) setting the process parameters for casting; (4) ingot sealing: optimizing the ingot sealing method, placing cold material, placing the casting cup in the center of the crystallizer, filling the groove connecting claw of the ingot head with steel bars, filling the outer arc side of the groove of the ingot head with springs, placing two short springs around the spring fixing iron ring, the springs and short springs together require 35-45kg, after the ingot sealing is completed, applying lubricating oil to the inner wall of the copper tube of the crystallizer, requiring sufficient and even application to ensure the lubrication effect of the billet shell; (5) ) Ladle opening operation: After the ladle molten steel arrives at the station, quickly organize the tundish fire stop, the tundish car is driven to the casting position, the ladle long nozzle is hung and argon blowing protection is started, the flow rate is 80-120L / min, the ladle long nozzle sealing gasket is replaced for each heat, the argon blowing time is guaranteed to be 2-3 minutes before the tundish is opened for casting, the casting process is argon blowing protection throughout the casting process, the argon flow rate on both sides is 250-350L / min, and the ladle is opened for casting; (6) After the ladle is opened for casting, when the tundish molten steel volume is ≥25t, organize the tundish to open for casting, control the tundish opening and emergence time, the emergence time is controlled at 60-90 seconds, the first 60 seconds are required to be medium flow, the flow rate is controlled at 7-8kg / s, the molten steel fills the head of the ingot, and then the flow is reduced to 4-5kg / s; (7) Tundish superheat and casting speed control. The overheating of the tundish in SA-335P92 is controlled at 30-40℃, which is 5℃ higher than other steel grades. The target drawing speed is 0.22-0.24m / min. (8) Adjust the pressing parameters of the straightening machine, increase the pressing force of the billet tail, keep the billet tail pressure of the straightening machines in groups 1-5 unchanged at 500-550kN, adjust the billet tail pressure of the straightening machines in groups 6-11 to 1000-1200kN, and cancel the straightening machine tracking after cutting the tail to group 7. Keep all straightening machines in the pressing state and do not lift them automatically. After the tail is cut out of the straightening machine in group 11, adjust the billet tail pressure value back to the normal value of 500-550kN; (9) Adjust the cutting parameters: Before cutting, set the cutting carbon equivalent parameter to a constant of 1.0-1.5 to ensure that iron powder is sprayed throughout the cutting process. Set the cutting length tolerance to a positive tolerance of 100-150mm. (10) Before cutting, set the frequency of the dust removal fan of the flame cutting machine to 40-50Hz. After cutting, adjust it back to 30-40Hz. (11) Slow cooling process: The hot billet is put into the pit for slow cooling. The slow cooling time is ≥36h. At the same time, it is required to slow cool until the surface temperature is <150℃ before leaving the pit.

[0006] (3) Setting the initial casting process parameters is as follows: ① Lower the liquid level in the crystallizer to 54-56%; ② Adjust the vibration parameters of the crystallizer to a frequency of 290-300 spm / m and an amplitude of 3.3-3.5 mm; ③ Lower the water flow rate in the crystallizer to 3650-3750 L / min; ④ Lower the initial casting speed to 0.11 m / min and an initial acceleration of 0.01-0.02 m / min. 2 The initial casting speed of the billet is 0.11 m / min; ⑤ Electromagnetic stirring settings: electromagnetic stirring current of the casting flow is 230-250 A, frequency is 2.0-2.5 Hz, and reversing time is 10-20 s; electromagnetic stirring current of the secondary cooling is 90-110 A, frequency is 1.8-2.2 Hz, and reversing time is 10-20 s; electromagnetic stirring current of the end is 380-410 A, frequency is 1.0-1.2 Hz, and reversing time is 10-20 s.

[0007] The beneficial effects of this invention are as follows: Through the above-described continuous casting process control methods, large-size round billet continuous casting production of SA-335P92 steel for ultra-supercritical power plant boiler tubes was successfully achieved, with a continuous casting cycle of 4 heats. The problem of steel leakage during ladle opening in continuous casting was solved. By optimizing process parameters and using specialized protective slag, the problem of longitudinal cracks on the billet surface was resolved. The problem of tail billet warping was solved by adjusting the straightening machine's pressure. The slow cooling process route for the billet was established, achieving stable continuous casting production, solving the problem of large core defects, and improving economic efficiency. Detailed Implementation

[0008] A method for continuous casting of large-scale round billets for power plant boiler tube billet steel: (1) Replace the crystallizer before production. Select a small-tapered crystallizer with a taper of 1.82% and select a plum blossom petal crystallizer for the copper tube of the crystallizer; (2) Prepare materials. Prepare special materials before production. Use SA-335P92 special materials. Select Xibao special protective slag with fast melting speed and low viscosity for the crystallizer protective slag. Select Luoyang Kefeng T-FZK13HB tundish covering agent with low melting point for the tundish covering agent.

[0009] (3) Setting the initial casting process parameters is as follows: ① Lower the liquid level in the crystallizer to 54-56%; ② Adjust the vibration parameters of the crystallizer to a frequency of 290-300 spm / m and an amplitude of 3.3-3.5 mm; ③ Lower the water flow rate in the crystallizer to 3650-3750 L / min; ④ Lower the initial casting speed to 0.11 m / min and an initial acceleration of 0.01-0.02 m / min. 2The initial casting speed of the billet is 0.11 m / min; ⑤ Electromagnetic stirring settings: electromagnetic stirring current of the casting flow is 230-250 A, frequency is 2.0-2.5 Hz, and reversing time is 20 s; electromagnetic stirring current of the secondary cooling is 90-110 A, frequency is 1.8-2.2 Hz, and reversing time is 20 s; electromagnetic stirring current of the end is 380-410 A, frequency is 1.0-1.2 Hz, and reversing time is 20 s.

[0010] (4) Ingot sealing: Optimize the ingot sealing method, place the cold material, place the pouring cup in the center of the crystallizer, fill the ingot head groove connecting claw head with steel bars, fill the outer arc side of the south end of the ingot head groove with springs, place two short springs around the spring fixing iron ring, the springs and short springs together require 35kg to ensure the cooling effect. After the ingot sealing is completed, apply lubricating oil to the inner wall of the copper tube of the crystallizer. It is required to apply enough and evenly to ensure the lubrication effect of the billet shell.

[0011] (5) Ladle start-up operation: After the ladle molten steel arrives at the station, quickly organize the tundish fire stop, drive the tundish car to the casting position, hang the ladle long nozzle and start argon blowing protection, the flow rate is 80-120L / min, the ladle long nozzle sealing gasket is replaced for each heat, ensure argon blowing time of 2-3 minutes before the tundish starts casting, argon blowing protection is carried out throughout the casting process, the argon flow rate on both sides is 250-350L / min, and start the ladle casting operation.

[0012] (6) After the tundish starts casting, wait until the tundish steel volume is ≥25t before starting casting in the tundish. Control the emergence time of the tundish during casting. The emergence time should be controlled between 60 and 90 seconds. The first 60 seconds should be in the middle of the flow, with the flow rate controlled at 7-8 kg / s. The molten steel should cover the head of the ingot. Then reduce the flow rate to 4-5 kg / s.

[0013] (7) Control of tundish overheating and casting speed. The tundish overheating of SA-335P92 is controlled at 30-40℃, which is 5℃ higher than other steel grades, and the target casting speed is 0.22-0.24m / min.

[0014] (8) Adjust the pressing parameters of the tension leveler to increase the pressing force of the billet tail. The billet tail pressure of the tension levelers in groups 1-5 remains unchanged at 500-550kN. The billet tail pressure of the tension levelers in groups 6-11 is adjusted to 1000-1200kN. After cutting the tail to group 7, the tension leveler tracking is canceled. All tension levelers are kept in the pressing state and do not automatically lift. After the tail is cut out of the tension leveler in group 11, the billet tail pressure value is adjusted back to the normal value of 500-550kN.

[0015] (9) Adjust cutting parameters: Before cutting, set the cutting carbon equivalent parameter to a constant of 1.0-1.5 to ensure that iron powder is sprayed throughout the cutting process. Set the cutting length tolerance to a positive tolerance of 100-150mm.

[0016] (10) Before cutting begins, set the frequency of the dust removal fan of the flame cutting machine to 45Hz, and after cutting ends, adjust it back to 40Hz.

[0017] (11) Slow cooling process: The hot billet is put into the pit for slow cooling after it is removed from the line. The slow cooling time is ≥36h, and it is required to be slow cooled to the surface temperature <150℃ before it is removed from the pit.

[0018] The specific implementation of the method of the present invention will be described in detail below with reference to the embodiments, but the specific implementation of the present invention is not limited to the following implementation examples.

[0019] 1. Replace the crystallizer before production. Select a small taper crystallizer with a taper of 1.82% and select a crystallizer with upper and lower plum blossom petal-shaped copper tubes.

[0020] 2. Optimize the start-up process parameters as follows: (1) Reduce the crystallizer liquid level setting from the normal setting value of 59-61% to 54-56%.

[0021] (2) Adjust the crystallizer vibration parameters, change the vibration frequency from 330-350spm / m to 290-300spm / m, and change the amplitude from 2.8-3.1mm to 3.3-3.5mm.

[0022] (3) Reduce the water flow rate of the crystallizer. Adjust the water flow rate of the crystallizer from the normal 3950-4050L / min to 3650-3750L / min.

[0023] (4) Reduce the initial pouring speed. The starting speed of the leveling machine remains unchanged at 0.11 m / min, and the starting acceleration is 0.01-0.02 m / min. 2 The initial casting speed of the billet was reduced from 0.12 m / min to 0.11 m / min.

[0024] (5) Optimize the ingot sealing method, place the cold material, place the pouring cup in the center of the crystallizer, fill the ingot head groove connecting claw head with steel bars, fill the outer arc side of the south end of the ingot head groove with springs, place two short springs around the spring fixing iron ring, the total springs need 35kg to ensure the cooling effect, after the ingot sealing is completed, apply lubricating oil to the inner wall of the copper tube of the crystallizer, and apply enough and evenly.

[0025] (6) Control the time of molten steel emergence from the tundish opening. The emergence time should be controlled between 60 and 90 seconds. The first 60 seconds should be in the middle of the flow, with the flow rate controlled at 7-8 kg / s, so that the molten steel can cover the head of the ingot. Then the flow rate should be reduced to 4-5 kg / s.

[0026] (7) Adjust the pressing parameters of the straightening machine, increase the pressing force of the billet tail, keep the billet tail pressure of the straightening machines in groups 1-5 unchanged, keep it at 500-550kN, adjust the billet tail pressure of the straightening machines in groups 6-11 to 1000-1200kN, after cutting the tail to group 7, cancel the tracking of the straightening machine, keep all straightening machines in the pressing state, do not lift automatically, after cutting the tail out of the straightening machine in group 11, adjust the billet tail pressure value back to the normal value of 500-550kN;

[0027] (8) Adjust the cutting parameters. Before cutting, set the cutting carbon equivalent parameter to a constant of 1.0-1.5 to ensure that iron powder is sprayed throughout the cutting process. Set the cutting length tolerance to +100-150mm to ensure the length.

[0028] (9) Before cutting begins, set the frequency of the dust removal fan of the flame cutting machine to 45Hz. After cutting, adjust it back to 40Hz to improve the dust removal system’s ability to collect flue gas. After cutting, adjust it back to the normal value. This flexible operation protects the environment and the on-site workers, while also saving energy consumption.

[0029] 3. Material preparation: Prepare special materials before production. Use SA-335P92 special material. Select Xibao special protective slag with fast melting speed and low viscosity for crystallizer protection slag. Select Luoyang Kefeng T-FZK13HB tundish covering agent with low melting point to prevent carbon increase in tundish.

[0030] 4. Tundish overheating and casting speed control. The tundish overheating of SA-335P92 is controlled at 30-40℃, which is 5℃ higher than other steel grades, and the target casting speed is 0.22-0.24m / min.

[0031] 5. Electromagnetic stirring settings: Casting flow electromagnetic stirring current 230-250A, frequency 2.0-2.5Hz, commutation time 20s; Secondary cooling electromagnetic stirring current 90-110A, frequency 1.8-2.2Hz, commutation time 20s; End electromagnetic stirring current 380-410A, frequency 1.0-1.2Hz, commutation time 20s.

[0032] On March 2, 2024, a four-stage continuous casting of Φ690 SA-335P92 billets using a single ladle was organized. Before casting, material preparation, process parameter settings, and process control were all strictly implemented according to the above measures. The casting process, including the initial casting, was normal, and the billet cutting process was normal. The low-magnification inspection results of the billets met the requirements.

[0033] Through the above measures, a total of 6 castings of SA-335P92 were organized from March to July 2024, producing a total of 24 heats with a qualified output of 1,700 tons. The casting and production processes were all normal, and the product quality was qualified. SA-335P92 steel for power plant boilers has achieved mass production.

[0034] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for continuous casting of large-size round billets for power plant boiler tube billets, characterized in that: Including the following aspects: (1) Replace the crystallizer before production. Select a small-tapered crystallizer and a plum-petal-shaped crystallizer for the copper tube of the crystallizer. (2) Material preparation: Prepare special materials before production; (3) Setting of pouring process parameters; (4) Ingot sealing: Optimize the ingot sealing method, place the cold material, place the pouring cup in the center of the crystallizer, fill the ingot head groove connecting claw head with steel bars, fill the outer arc side of the ingot head groove with springs, place two short springs around the spring fixing iron ring, the springs and short springs together require 35-45kg, after the ingot sealing is completed, apply lubricating oil to the inner wall of the copper tube of the crystallizer, it is required to apply enough and evenly to ensure the lubrication effect of the billet shell; (5) Ladle start-up operation: After the ladle molten steel arrives at the station, quickly organize the tundish to stop the flame. Move the tundish car to the casting position, hang the ladle long nozzle and start argon blowing protection. The flow rate is 80-120L / min. Replace the sealing gasket of the ladle long nozzle for each heat. Ensure argon blowing time of 2-3 minutes before starting the tundish. During the casting process, argon blowing protection is carried out throughout the casting process. The argon flow rate on both sides is 250-350L / min. Operate the ladle to start casting. (6) After the ladle is started to pour, when the amount of molten steel in the tundish is ≥25t, organize the tundish to start pouring. Control the emergence time of the tundish to start pouring. The emergence time should be controlled at 60-90 seconds. The first 60 seconds should be in the middle of the flow, and the flow rate should be controlled at 7-8kg / s. The molten steel should cover the head of the ingot. Then the flow rate should be reduced to 4-5kg / s. (7) Control of tundish overheating and casting speed: The tundish overheating of SA-335P92 is controlled at 30-40℃, which is 5℃ higher than other steel grades, and the target casting speed is 0.22-0.24m / min; (8) Adjust the pressing parameters of the tension leveler, increase the pressing force of the billet tail, keep the billet tail pressure of the tension levelers in groups 1-5 unchanged at 500-550kN, adjust the billet tail pressure of the tension levelers in groups 6-11 to 1000-1200kN, after cutting the tail to group 7, cancel the tension leveler tracking, keep all tension levelers in the pressing state and do not lift automatically, after cutting the tail out of the tension leveler in group 11, adjust the billet tail pressure value back to the normal value of 500-550kN; (9) Adjust cutting parameters: Before cutting, set the cutting carbon equivalent parameter to a constant of 1.0-1.5 to ensure that iron powder is sprayed throughout the cutting process. Set the cutting length tolerance to a positive tolerance of 100-150mm. (10) Before cutting begins, set the frequency of the dust removal fan of the flame cutting machine to 40-50Hz, and after cutting ends, adjust it back to 30-40Hz. (11) Slow cooling process: The hot billet is put into the pit for slow cooling after it is removed from the line. The slow cooling time is ≥36h, and it is required to be slow cooled to the surface temperature <150℃ before it is removed from the pit.

2. The method for continuous casting of large-size round billets for power plant boiler tube billets according to claim 1, characterized in that: (3) Setting the initial casting process parameters is as follows: ① Lower the liquid level in the crystallizer to 54-56%; ② Adjust the vibration parameters of the crystallizer to a frequency of 290-300 spm / m and an amplitude of 3.3-3.5 mm; ③ Lower the water flow rate in the crystallizer to 3650-3750 L / min; ④ Lower the initial casting speed to 0.11 m / min and an initial acceleration of 0.01-0.02 m / min. 2 The initial casting speed of the billet is 0.11 m / min; ⑤ Electromagnetic stirring settings: electromagnetic stirring current of the casting flow is 230-250 A, frequency is 2.0-2.5 Hz, and reversing time is 10-20 s; electromagnetic stirring current of the secondary cooling is 90-110 A, frequency is 1.8-2.2 Hz, and reversing time is 10-20 s; electromagnetic stirring current of the end is 380-410 A, frequency is 1.0-1.2 Hz, and reversing time is 10-20 s.