Three-way argon flow control method for ultra-low carbon steel continuous casting tundish

Abstract

This invention discloses a method for controlling the flow rate of three argon gases in the tundish of ultra-low carbon steel continuous casting. After the casting process reaches the target casting speed, the flow rates of the three argon gases are controlled according to the cross-sectional dimensions of the crystallizer: for crystallizer cross-sections ≤1300mm, the flow rate of argon gas to the stopper rod is controlled at 4-5 L / min, the flow rate of argon gas to the inlet is controlled at 3-4 L / min, and the flow rate of argon gas between plates is controlled at 5-7 L / min; for crystallizer cross-sections 1300-1500mm, the flow rate of argon gas to the stopper rod is controlled at 5-6 L / min, the flow rate of argon gas to the inlet is controlled at 4-5 L / min, and the flow rate of argon gas between plates is controlled at 6-8 L / min; for crystallizer cross-sections ≥1500mm, the flow rate of argon gas to the stopper rod is controlled at 6-7 L / min, the flow rate of argon gas to the inlet is controlled at 5-6 L / min, and the flow rate of argon gas between plates is controlled at 7-9 L / min. This method, through reasonable control of the three-way argon flow in the tundish, minimizes fluctuations in the molten steel surface in the crystallizer, effectively improving the casting stability of ultra-low carbon steel continuous casting, enhancing the cleanliness of the submerged entry nozzle and molten steel, significantly reducing inclusion defects in the billet, and effectively ensuring the castability and quality of the molten steel.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, and in particular to a method for controlling the flow rate of three argon gases in the tundish of ultra-low carbon steel continuous casting. Background Technology

[0002] As the last metallurgical vessel in the continuous casting process, the tundish uses three argon streams. Argon is mainly introduced into the tundish stopper, the top nozzle, and between the plates to prevent secondary oxidation during the pouring of molten steel. At the same time, the formation of argon bubbles changes the flow behavior of the molten steel, and the collision adhesion and wake carry-over effects effectively remove inclusions from the molten steel.

[0003] Ultra-low carbon steels with [C] ≤ 30ppm, such as IF steel and steel used in automotive outer panels, have stringent requirements for the purity of molten steel. Because [Al] in the steel is prone to secondary oxidation, forming inclusions such as Al2O3, these inclusions accumulate at the stopper rod head and the inner wall of the immersion nozzle, leading to defects such as dots and lines on the surface of hot-rolled and cold-rolled sheets in subsequent processes. Therefore, preventing secondary oxidation and aggregation during the pouring of molten steel in the tundish, ensuring the floating of small inclusion particles in the molten steel, and preventing large inclusion particles formed by nozzle blockage are of great significance for improving the quality of cast billets.

[0004] Chinese patent application CN117340209A discloses a method and system for controlling surface defects in automotive outer panels. This method adjusts the flow rates of three argon gas channels in the tundish based on liquid level fluctuations and replaces the submerged entry nozzle based on the rising trend of the stopper rod or liquid level fluctuations. However, its control values ​​are fixed and do not differentiate based on different cross-sections, nor does it provide detailed explanations of the control process. Chinese patent application CN119747635A discloses a continuous casting method for improving liquid level fluctuations in ultra-low carbon IF steel crystallizers. It uses a three-channel argon gas flow rate of 3.0–5.5 L / min for the stopper rod, 3.5–6.5 L / min for the upper nozzle, and 5.0–9.5 L / min for the argon flow at the inter-plate argon gap. This method also lacks detailed classification based on cross-sections and does not mention the different argon flow rates for the stopper rod and upper nozzle, nor the specific control process, making its applicability limited. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for controlling the flow rate of three argon gases in the tundish of ultra-low carbon steel continuous casting, so as to effectively improve the casting stability of ultra-low carbon steel continuous casting.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: after the casting process reaches the target casting speed, the flow rate of three argon gases is controlled according to the cross-sectional size of the crystallizer: the cross-section of the crystallizer is ≤1300mm, and the flow rate of argon gas in the stopper rod is controlled at 4-5L / min, the flow rate of argon gas in the upper water inlet is 3-4L / min, and the flow rate of argon gas between the plates is 5-7L / min. The crystallizer has a cross-section of 1300-1500 mm, and the argon flow rate is controlled at 5-6 L / min for the stopper rod, 4-5 L / min for the upper water inlet, and 6-8 L / min for the interplate. The crystallizer has a cross-section ≥1500mm, and the argon flow rate is controlled at 6-7L / min for the stopper rod, 5-6L / min for the upper water inlet, and 7-9L / min for the interplate.

[0007] Furthermore, after the target casting speed is reached during the casting process, the argon back pressure of the stopper rod and the argon back pressure of the upper water inlet are both controlled at 0.2-0.5 MPa, and the argon back pressure between the plates is ≥0.1 MPa.

[0008] Furthermore, the argon flow rate of the stopper rod is 0.5 to 1.5 L / min greater than the argon flow rate of the inlet.

[0009] Furthermore, during the continuous casting ladle baking process, the argon flow rate of the stopper rod is controlled at 6-7 L / min, the argon flow rate of the upper water inlet is controlled at 5-6 L / min, and the argon flow rate between plates is controlled at 7-9 L / min; during the casting process, the argon flow rate of the stopper rod is controlled at 4-5 L / min, the argon flow rate of the upper water inlet is controlled at 3-4 L / min, and the argon flow rate between plates is controlled at 5-7 L / min.

[0010] Furthermore, in each consecutive furnace run, the argon flow rate at the stopper rod and the argon flow rate at the water inlet are increased by 0.1–0.15 L / min compared to the previous furnace run.

[0011] The beneficial effects of adopting the above technical solution are as follows: By rationally controlling the flow rate of argon gas in the three channels of the tundish, the liquid level of the molten steel in the crystallizer is stable and fluctuates little, which effectively improves the casting stability of ultra-low carbon steel continuous casting, enhances the cleanliness of the submerged entry nozzle and molten steel, and significantly reduces the inclusion defects in the billet. The incidence of inclusion defects in the billet is reduced from 5.6% in the conventional method to below 2.6%. The continuous casting stability of the present invention is good, and the submerged entry nozzle is clean, which effectively ensures the castability of continuous casting and the quality of molten steel. Attached Figure Description

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0013] Figure 1 This is a graph showing the fluctuation of the molten steel level in the continuous casting crystallizer of Example 1. Figure 2 This is a clean morphology diagram of the cylindrical area between the submerged nozzle plates of the tundish in continuous casting, which was replaced at the end of the fourth heat of the continuous casting process in Example 1. Figure 3 This is a clean morphology diagram of the submerged nozzle outlet of the continuous casting tundish that was replaced at the end of the fourth heat of the continuous casting process in Example 1. Figure 4This is a graph showing the fluctuation of the molten steel level in the continuous casting crystallizer of Example 2; Figure 5 This is a clean morphology diagram of the cylindrical area between the submerged nozzle plates of the continuous casting tundish that was replaced at the end of the 4th heat of the continuous casting process in Example 2. Figure 6 This is a clean morphology diagram of the submerged nozzle outlet of the continuous casting tundish that was replaced at the end of the fourth heat of the continuous casting process in Example 2. Figure 7 This is a graph showing the fluctuation of the molten steel level in the continuous casting crystallizer of Example 3; Figure 8 This is a clean morphology diagram of the cylindrical area between the submerged nozzle plates of the continuous casting tundish that was replaced at the end of the fourth heat of the continuous casting process in Example 3. Figure 9 This is a clean morphology diagram of the submersible nozzle outlet of the continuous casting tundish that was replaced at the end of the fourth heat of the continuous casting process in Example 3. Detailed Implementation

[0014] The method for controlling the three-channel argon gas flow in the tundish of ultra-low carbon steel continuous casting includes the following steps: (1) Continuous casting ladle baking stage: control the argon flow rate of stopper rod 6-7L / min, the argon flow rate of water inlet 5-6L / min, and the argon flow rate of plate inter-plate 7-9L / min; during this process, the argon flow rate of the three channels is controlled at a high flow rate, which can effectively prevent secondary oxidation of refractory materials such as stopper rod and water inlet during high-temperature ladle baking.

[0015] (2) Stage of increasing casting speed: When the baking is finished and the casting is ready to start, control the argon flow rate of the stopper rod to 4-5 L / min, the argon flow rate of the upper water inlet to 3-4 L / min, and the argon flow rate of the plate to 5-7 L / min. The continuous casting machine starts casting normally and increases casting speed.

[0016] (3) Stable casting speed stage: After the casting process reaches the target casting speed, control the argon back pressure of the stopper rod and the argon back pressure of the upper nozzle to be 0.2-0.5 MPa, and the argon back pressure between plates to be ≥0.1 MPa. Always ensure that the argon flow rate of the stopper rod is 0.5-1.5 L / min greater than the argon flow rate of the upper nozzle. For small cross sections, control at the lower limit and for large cross sections, control at the upper limit. In order to avoid inclusion defects caused by the adhesion and accumulation of inclusions on the stopper rod head and the inner wall of the nozzle falling into the molten steel, adjust the three argon flow rates immediately after reaching the target casting speed. According to the cross-sectional size of the crystallizer, control the three argon flow rates of the first furnace as follows: If the cross-sectional size of the crystallizer is ≤1300 mm, then control the argon flow rate of the stopper rod to be 4-5 L / min, the argon flow rate of the upper nozzle to be 3-4 L / min, and the argon flow rate between plates to be 5-7 L / min. If the cross-section of the crystallizer is 1300-1500mm, then the argon flow rate of the stopper rod is controlled at 5-6L / min, the argon flow rate of the upper water inlet is 4-5L / min, and the argon flow rate between the plates is 6-8L / min. If the cross-section of the crystallizer is ≥1500mm, the argon flow rate of the stopper rod is controlled at 6-7L / min, the argon flow rate of the upper water inlet is 5-6L / min, and the argon flow rate between the plates is 7-9L / min.

[0017] During consecutive furnace runs, in the stable phase of the furnace run, the argon flow rate of the three gas channels is increased by 0.1 to 0.15 L / min for the stopper rod and 0.1 to 0.15 L / min for the inlet gas flow rate compared to the previous furnace run.

[0018] If the submerged nozzle is replaced, the argon flow rate and back pressure of the three argon channels in the first furnace after the replacement will be controlled according to the argon flow rate of the three argon channels before the replacement of the submerged nozzle.

[0019] When the cross-section of the crystallizer is close to the lower limit of the cross-section range, the flow rate is controlled according to the lower limit; when the cross-section of the crystallizer is close to the upper limit of the cross-section range, the flow rate is controlled according to the upper limit.

[0020] When adjusting the argon flow rate, first adjust the argon flow rate at the top of the tundish to ensure slight bubbling and churning of the molten steel surface around the submerged entry nozzle, controlling the bubble diameter to 5-10 mm; then adjust the stopper rod argon flow rate to be 0.5-1.5 L / min greater than the top of the tundish argon flow rate, so that slight bubbling and churning of the molten steel surface at a distance of 150-200 mm from both sides of the submerged entry nozzle, controlling the bubble diameter to 5-10 mm; finally, adjust the argon flow rate between the plates.

[0021] Example 1: The working process of the three-channel argon flow control method for producing ultra-low carbon steel DC06 with a crystallizer cross-section of 1300mm is as follows: First, during the preheating of the tundish before the continuous casting of ultra-low carbon steel DC06, the three argon flow switches in the tundish were turned on, and the flow rates were all set to maximum: 7 L / min for the stopper rod, 6 L / min for the inlet, and 9 L / min for the interplate. After the preheating was completed and casting was about to begin, the three argon flow rates were adjusted to minimum: 4 L / min for the stopper rod, 3 L / min for the inlet, and 5 L / min for the interplate. The continuous casting machine then started casting normally.

[0022] When the casting speed of the continuous casting machine is increased from 0 m / min to 0.8 m / min, the flow rates of the three argon gas lines are quickly adjusted. First, the argon gas flow rate at the top nozzle is adjusted to 4 L / min and the back pressure to 0.2 MPa to ensure that the surface of the molten steel in the mold around the submerged entry nozzle is slightly bubbling and churning. Second, the argon gas flow rate at the stopper rod is adjusted to 5 L / min and the back pressure to 0.2 MPa, with a bubble diameter of 5 mm, to ensure that the surface of the molten steel in the mold at a distance of 150-200 mm from both sides of the submerged entry nozzle is slightly bubbling and churning, with a bubble diameter of 5 mm. Finally, the argon gas flow rate is adjusted to 7 L / min and the back pressure to 0.1 MPa.

[0023] When casting the second heat, the argon gas flow rate to the stopper rod was increased to 5.1 L / min and the flow rate to the top inlet to 4.1 L / min. Subsequently, as the number of consecutive heats increased, the argon gas flow rates to the stopper rod and top inlet were increased by 0.1 L / min for each additional heat. At the end of the casting cycle, the liquid level in the crystallizer for the entire cycle was as follows: Figure 1 As shown, the morphology of the 4th furnace after the replacement of the submersible nozzle is as follows. Figure 2 , Figure 3 The level of cleanliness shown.

[0024] Example 2: The working process of the three-channel argon flow control method for producing ultra-low carbon steel DC04 with a crystallizer cross-section of 1400mm is as follows: First, during the preheating of the tundish before the continuous casting of ultra-low carbon steel DC04, the three argon flow switches in the tundish were turned on, and the flow rates were all set to maximum: 6 L / min for the stopper rod, 5 L / min for the inlet, and 9 L / min for the interplate. After the preheating was completed and casting was about to begin, the three argon flow rates were adjusted to minimum: 4 L / min for the stopper rod, 3 L / min for the inlet, and 5 L / min for the interplate. The continuous casting machine then started casting normally.

[0025] When the casting speed of the continuous casting machine is increased from 0 m / min to 0.8 m / min, the flow rates of the three argon gas lines are quickly adjusted. First, the argon gas flow rate at the upper nozzle is adjusted to 4.5 L / min and the back pressure to 0.3 MPa to ensure that the surface of the molten steel in the mold around the submerged entry nozzle is slightly bubbling and churning, with a bubble diameter of 8 mm. Next, the argon gas flow rate at the stopper rod is adjusted to 5.5 L / min and the back pressure to 0.3 MPa to ensure that the surface of the molten steel in the mold at a distance of 150-200 mm from both sides of the submerged entry nozzle is slightly bubbling and churning, with a bubble diameter of 8 mm. Finally, the argon gas flow rate is adjusted to 6.5 L / min and the back pressure to 0.1 MPa.

[0026] When casting the second heat, the argon gas flow rate to the stopper rod was increased to 5.6 L / min and the flow rate to the top inlet to 4.6 L / min. Subsequently, as the number of consecutive heats increased, the argon gas flow rates to the stopper rod and top inlet were increased by 0.12 L / min for each additional heat. At the end of the casting cycle, the liquid level in the crystallizer for the entire cycle is shown below. Figure 4 As shown, the morphology of the 4th furnace after the replacement of the submerged nozzle is as follows. Figure 5 , 6 The level of cleanliness shown.

[0027] Example 3: The working process of the three-channel argon flow control method for producing ultra-low carbon steel DC03 with a crystallizer cross-section of 1500mm is as follows: First, during the preheating of the tundish before the continuous casting of ultra-low carbon steel DC03, the three argon flow switches in the tundish were turned on, and the flow rates were all set to maximum: 7 L / min for the stopper rod, 6 L / min for the inlet, and 9 L / min for the interplate. After the preheating was completed and casting was about to begin, the three argon flow rates were adjusted to minimum: 5 L / min for the stopper rod, 4 L / min for the inlet, and 7 L / min for the interplate. The continuous casting machine then started casting normally.

[0028] When the casting speed of the continuous casting machine is increased from 0 m / min to 0.8 m / min, the flow rates of the three argon gas lines are quickly adjusted. First, the argon gas flow rate at the top nozzle is adjusted to 5 L / min and the back pressure to 0.5 MPa to ensure that the surface of the molten steel in the mold around the submerged entry nozzle is slightly bubbling and churning, with a bubble diameter of 10 mm. Next, the argon gas flow rate at the stopper rod is adjusted to 6 L / min and the back pressure to 0.5 MPa to ensure that the surface of the molten steel in the mold at a distance of 150-200 mm from both sides of the submerged entry nozzle is slightly bubbling and churning, with a bubble diameter of 10 mm. Finally, the argon gas flow rate is adjusted to 7 L / min and the back pressure to 0.1 MPa.

[0029] When casting the second heat, the argon gas flow rate to the stopper rod was increased to 6.1 L / min and the flow rate to the top inlet to 5.1 L / min. Subsequently, as the number of consecutive heats increased, the argon gas flow rates to the stopper rod and top inlet were increased by 0.15 L / min for each additional heat. At the end of the casting cycle, the liquid level in the crystallizer for the entire cycle is shown below. Figure 7 As shown, the morphology of the 4th furnace after the replacement of the submerged nozzle is as follows. Figure 8 , 9 The level of cleanliness shown.

Claims

1. A method for controlling the flow rate of three-channel argon gas in a tundish for continuous casting of ultra-low carbon steel, characterized in that, After the casting process reaches the target casting speed, the flow rate of three argon gases is controlled according to the cross-sectional size of the crystallizer: for crystallizer cross-sections ≤1300mm, the flow rate of argon gas to the stopper rod is controlled at 4-5L / min, the flow rate of argon gas to the upper water inlet is controlled at 3-4L / min, and the flow rate of argon gas between plates is controlled at 5-7L / min. The crystallizer has a cross-section of 1300-1500 mm, and the argon flow rate is controlled at 5-6 L / min for the stopper rod, 4-5 L / min for the upper water inlet, and 6-8 L / min for the interplate. The cross-section of the crystallizer is ≥1500mm, and the argon flow rate of the stopper rod is controlled at 6-7L / min, the argon flow rate of the upper water inlet is 5-6L / min, and the argon flow rate between the plates is 7-9L / min. After the target casting speed is reached during the casting process, the argon back pressure of the stopper rod and the argon back pressure of the upper water inlet are both controlled at 0.2-0.5 MPa, and the argon back pressure between the plates is ≥0.1 MPa. The argon flow rate of the stopper rod is 0.5 to 1.5 L / min greater than the argon flow rate of the inlet.

2. The method for controlling the flow rate of three-channel argon gas in the tundish of ultra-low carbon steel continuous casting according to claim 1, characterized in that: During continuous casting ladle baking, control the argon flow rate of the stopper rod to 6-7 L / min, the argon flow rate of the top nozzle to 5-6 L / min, and the argon flow rate between plates to 7-9 L / min; during casting start, control the argon flow rate of the stopper rod to 4-5 L / min, the argon flow rate of the top nozzle to 3-4 L / min, and the argon flow rate between plates to 5-7 L / min.

3. A method for controlling the flow rate of three-channel argon gas in a tundish for continuous casting of ultra-low carbon steel according to claim 1 or 2, characterized in that: For each consecutive furnace run, the argon flow rate at the stopper rod and the argon flow rate at the water inlet are increased by 0.1–0.15 L / min compared to the previous run.

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