A continuous casting method for improving the purity of a single flow slab steel

Abstract

The application discloses a continuous casting method for improving the purity of single-flow slab steel liquid, and the steel liquid height in a tundish is controlled to be 1000mm, two dam walls including a first dam wall and a second dam wall are arranged in the tundish, the thickness of the first dam wall and the second dam wall is 80mm-100mm, the first dam wall and the second dam wall divide the tundish into an impact area, a purification area and a pouring area, and the volume ratio of the three areas is 2:3:3; the impact area is provided with a flow stabilizer for restraining the flow of the steel liquid entering the impact area; and the pouring area is provided with a nozzle. The application comprises the matching of the tundish structure design and the tundish covering agent, realizes the sufficient floating of the inclusions in the tundish, the contact of the inclusions with the tundish covering agent, and the final entering of the inclusions into the tundish covering agent, and realizes the purification of the steel liquid in the tundish.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, and in particular to a continuous casting method for improving the purity of molten steel in a single-strand slab. Background Technology

[0002] The tundish is an intermediate container between the ladle and the crystallizer. The purpose of using the tundish is to reduce the static pressure of the molten steel, stabilize the steel flow, and reduce the impact and agitation of the molten steel in the crystallizer. While the molten steel remains in the tundish, non-metallic inclusions have a chance to float to the surface. In multi-strand continuous casting machines, the tundish can distribute molten steel to each crystallizer. In multi-heat continuous casting, the tundish can store a certain amount of molten steel to ensure continued casting when changing ladles. In continuous casting, the tundish is also a crucial location for fine-tuning and homogenizing the temperature and composition of the molten steel before it enters the crystallizer. Therefore, creating a reasonable flow field within the tundish not only promotes the full floating of inclusions but also creates favorable conditions for temperature and composition homogenization. The main function of the tundish is to ensure the intermediate storage and reasonable distribution of molten steel between the ladle and the crystallizer during continuous casting. Therefore, the solidification conditions of the continuously cast steel in the crystallizer and the final product quality are significantly related to the tundish process. The tundish also acts as a refining reactor, performing additional metallurgical functions.

[0003] The tundish in continuous casting is not only a buffer vessel for stabilizing pressure, distributing molten steel, and ensuring continuous pouring, but also a key piece of equipment for ensuring the quality of the cast billet. Tundish covering agent is one of the important auxiliary materials in the continuous casting production process. The tundish covering agent needs to have functions such as heat insulation, reducing heat loss, isolating air, preventing secondary oxidation of the molten steel, and absorbing inclusions that float to the surface of the molten steel.

[0004] The tundish, as the final container before solidification of molten steel, plays a crucial role in the quality of the cast billet. Since inclusions in molten steel have difficulty floating after entering the crystallizer, and the molten steel in the tundish has many opportunities to come into contact with non-metallic materials during the casting process, how to remove inclusions in the tundish has become a core issue.

[0005] Therefore, it is necessary to develop new continuous casting methods to improve the purity of molten steel. Summary of the Invention

[0006] Purpose of the invention: To address the shortcomings and defects of existing technologies, this invention provides a continuous casting method for improving the purity of molten steel in a single-strand slab. This method includes matching the tundish structure design with the tundish covering agent to ensure that inclusions in the tundish float to the surface and, upon contact with the tundish covering agent, ultimately enter the covering agent, thereby purifying the molten steel within the tundish.

[0007] Technical Solution: The present invention provides a continuous casting method for improving the purity of molten steel in a single-strand slab, characterized in that: the height of molten steel in the tundish is controlled at 1000mm; the tundish is equipped with two baffles, including a first baffle and a second baffle, the thickness of which is 80mm-100mm; the first baffle and the second baffle divide the tundish into an impact zone, a purification zone, and a casting zone, with a volume ratio of 2:3:3; the impact zone is equipped with a flow stabilizer to constrain the flow of molten steel entering the impact zone; the casting zone is equipped with a gate.

[0008] Specifically, the center lines of the fourth and fifth through holes of the first retaining wall between the impact zone and the purification zone are 100mm-150mm from the bottom of the tundish, the center lines of the third and fifth through holes are 100mm-150mm from the side wall of the tundish, the diameter of the through holes is 60mm-80mm, the horizontal inclination angle α of the through holes is 20°-30°, and the vertical inclination angle β of the through holes is 20°-30°.

[0009] Furthermore, the number of through holes is 3-5, arranged in 1 row or 2 rows.

[0010] Furthermore, the number of through holes is 5, including a first through hole, a second through hole, a third through hole, a fourth through hole and a fifth through hole. The first through hole, the second through hole and the third through hole are located in the first row, and the fourth through hole and the fifth through hole are located in the second row. The distance between the two rows is 150mm.

[0011] Specifically, the distance between the center lines of the fourth and fifth through holes of the second retaining wall between the purification zone and the casting zone and the bottom of the tundish is 150mm-200mm, the distance between the center lines of the third and fifth through holes and the side wall of the tundish is 150mm-200mm, the diameter of the through holes is 60mm-80mm, the horizontal inclination angle α of the through holes is 15°-25°, and the vertical inclination angle β of the through holes is 15°-25°.

[0012] Furthermore, the number of through holes is 3-5, arranged in 1 row or 2 rows.

[0013] Furthermore, the number of through holes is 5, including a first through hole, a second through hole, a third through hole, a fourth through hole and a fifth through hole. The first through hole, the second through hole and the third through hole are located in the first row, and the fourth through hole and the fifth through hole are located in the second row. The distance between the two rows is 150mm.

[0014] The molten steel surface is in contact with the covering agent, which comprises the following components in the following mass percentages: CaO: 45%-55%, Al2O3: 35%-45%, MgO: 4%-8%, C: 0.5%-2%, and the remainder is Na2O+K2O.

[0015] The covering agent has a melting temperature of 1300℃-1350℃ and a viscosity of 0.6 Pa·s-1.0 Pa·s at 1400℃. The thickness of the covering agent in the intermediate ladle is 30mm-50mm.

[0016] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention sets up two baffles in the tundish of single-strand slab continuous casting, dividing the tundish into three zones: an impact zone, a purification zone, and a casting zone. Guide holes are set at different heights of the baffles. The diameter and angle of these guide holes allow the steel flow to collide with the inner wall of the tundish near the steel / coating agent interface in the purification and casting zones, generating horizontal rotating flow. This increases the contact time between the steel and the coating agent, increasing the chance of inclusion removal. Simultaneously, the steel flow near the steel / coating agent interface generates a spiral downward flow under gravity, entering the purification and casting zones respectively through the guide holes in the baffles. By rationally designing the chemical composition, melting temperature, viscosity, and dosage of the coating agent, the coating agent's ability to absorb inclusions is improved, thus increasing the purity of the continuously cast steel. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention;

[0018] Figure 2 This is a structural schematic diagram of the first retaining wall of the present invention, wherein the left side is a structural schematic diagram of the through steel hole; the middle part is a structural schematic diagram of the first retaining wall at a horizontal angle; and the right side is a structural schematic diagram of the first retaining wall at a vertical angle.

[0019] Figure 3 This is a structural schematic diagram of the second retaining wall of the present invention, wherein the left side is a structural schematic diagram of the through steel hole; the middle part is a structural schematic diagram of the second retaining wall at a horizontal angle; and the right side is a structural schematic diagram of the second retaining wall at a vertical angle.

[0020] In the diagram, 1 is the impact zone; 2 is the purification zone; 3 is the casting zone; 4 is the flow stabilizer; 5 is the water inlet; 6 is the first retaining wall; 7 is the second retaining wall; 8 is the first through-hole; 9 is the second through-hole; 10 is the third through-hole; 11 is the fourth through-hole; and 12 is the fifth through-hole. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1:

[0023] In this embodiment, the molten steel height in the tundish is 1000mm. The tundish is equipped with two baffles, each 80mm thick, dividing it into three zones: an impact zone, a purification zone, and a casting zone, with a volume ratio of 2:3:3. A flow stabilizer is installed in the impact zone to constrain the flow of molten steel entering it. The through-holes in the baffles of the impact and purification zones are 100mm from the bottom and sidewall of the tundish; the through-hole diameter is 60mm, and there are five through-holes with horizontal inclination angles α1-α5 of 20°, 25°, 30°, 25°, and 30° respectively; and vertical inclination angles β1-β5 of 20°, 20°, 20°, 30°, and 30° respectively. The outlet holes are arranged in two rows (with a row spacing of 150mm). The steel passage holes of the retaining walls in the purification zone and the casting zone are 150mm from the bottom of the tundish and 150mm from the side wall of the tundish; the diameter of the steel passage holes is 60mm, and there are 5 steel passage holes. The horizontal inclination angles α1-α5 are 15°, 20°, 25°, 20°, and 25° respectively; the vertical inclination angles β1-β5 are 15°, 15°, 15°, 25°, and 25° respectively. There are 2 rows of steel outlet holes (the spacing between the 2 rows is 150mm).

[0024] The covering agent in contact with the molten steel surface comprises the following components by mass percentage: CaO: 45%, Al₂O₃: 45%, MgO: 4%, C: 2%, with the remainder being Na₂O + K₂O, and the sum of all components being 100%. The melting temperature of the covering agent is 1300℃, and its viscosity at 1400℃ is 0.6 Pa·s. The thickness of the covering agent inside the tundish is 50 mm.

[0025] The test results showed that the coarse inclusions in the board were grade 0, the fine inclusions in category A were grade 0, the fine inclusions in category B were grade 0.5, the fine inclusions in category C were grade 0, the fine inclusions in category D were grade 0, and the fine inclusions in category Ds were grade 0. The sum of the fine inclusions A+B+C+D equals grade 0.5.

[0026] Example 2:

[0027] In this embodiment, the molten steel height in the tundish is 1000mm. The tundish is equipped with two baffles, each 100mm thick, dividing it into three zones: an impact zone, a purification zone, and a casting zone, with a volume ratio of 2:3:3. A flow stabilizer is installed in the impact zone to constrain the flow of molten steel entering it. The through-holes in the baffles of the impact and purification zones are 150mm from the bottom of the tundish and 150mm from the side wall of the tundish; the through-hole diameter is 80mm, and there are three through-holes with horizontal inclination angles α1-α3 of 20°, 25°, and 30° respectively; and vertical inclination angles β1-β3 of 20°, 20°, and 20° respectively. There is one row of outlet holes. The steel passage holes of the retaining walls in the purification zone and the casting zone are 200mm from the bottom of the tundish and 200mm from the side wall of the tundish; the diameter of the steel passage holes is 80mm, and there are 3 steel passage holes. The horizontal inclination angles α1-α3 are 15°, 20°, and 25° respectively; the vertical inclination angles β1-β3 are 15°, 15°, and 15° respectively, and there is one row of steel outlet holes.

[0028] The covering agent in contact with the molten steel surface comprises the following components by mass percentage: CaO: 55%, Al₂O₃: 35%, MgO: 8%, C: 0.5%, with the remainder being Na₂O + K₂O, totaling 100%. The melting temperature of the covering agent is 1350℃, and its viscosity at 1400℃ is 1.0 Pa·s. The thickness of the covering agent inside the tundish is 30 mm.

[0029] The test results showed that the coarse inclusions in the board were grade 0, the fine inclusions in category A were grade 0, the fine inclusions in category B were grade 0.5, the fine inclusions in category C were grade 0, the fine inclusions in category D were grade 0, and the fine inclusions in category Ds were grade 0.5. The sum of the fine inclusions A + B + C + D = grade 1.

[0030] Example 3:

[0031] In this embodiment, the molten steel height in the tundish is 1000mm. The tundish is equipped with two baffles, each 100mm thick, dividing it into three zones: an impact zone, a purification zone, and a casting zone, with a volume ratio of 2:3:3. A flow stabilizer is installed in the impact zone to constrain the flow of molten steel entering it. The through-holes in the baffles of the impact and purification zones are 120mm from the bottom and sidewall of the tundish; the through-hole diameter is 70mm, and there are three through-holes with horizontal inclination angles α1-α3 of 20°, 25°, and 30° respectively; and vertical inclination angles β1-β3 of 20°, 20°, and 20° respectively. There is one row of outlet holes. The steel passage holes of the retaining walls in the purification zone and the casting zone are 180mm from the bottom of the tundish and 180mm from the side wall of the tundish; the diameter of the steel passage holes is 70mm, and there are 3 steel passage holes. The horizontal inclination angles α1-α3 are 15°, 20°, and 25° respectively; the vertical inclination angles β1-β3 are 15°, 15°, and 15° respectively, and there is one row of steel outlet holes.

[0032] The covering agent in contact with the molten steel surface comprises the following components by mass percentage: CaO: 50%, Al₂O₃: 32%, MgO: 5%, C: 1.5%, with the remainder being Na₂O + K₂O, totaling 100%. The melting temperature of the covering agent is 1320℃, and its viscosity at 1400℃ is 0.8 Pa·s. The thickness of the covering agent inside the tundish is 40 mm.

[0033] The test results showed that the coarse inclusions in the board were grade 0, the fine inclusions in category A were grade 0, the fine inclusions in category B were grade 0.5, the fine inclusions in category C were grade 0, the fine inclusions in category D were grade 0, and the fine inclusions in category Ds were grade 0.5. The sum of the fine inclusions A + B + C + D = grade 1.

[0034] This invention extends the average residence time of molten steel in the tundish, allowing non-metallic inclusions to float sufficiently, thus improving the cleanliness of the molten steel and the quality of the cast billet. It also increases the piston flow area within the tundish, reducing the dead zone volume fraction. Furthermore, it ensures that the tundish can distribute molten steel more evenly to each nozzle, resulting in similar average residence time and temperature at each nozzle. Simultaneously, it controls the flow at the steel-slag interface within the tundish to prevent slag covering the tundish surface from being drawn into the molten steel and affecting its purity.

[0035] This invention incorporates two baffles in a single-strand slab continuous casting tundish, dividing it into three zones: an impact zone, a purification zone, and a casting zone. Guide holes are installed at different heights along the baffles. The diameter and angle of these holes allow the molten steel to collide with the tundish wall near the molten steel / coating agent interface in both the purification and casting zones, creating a horizontal, rotating flow. This increases the contact time between the molten steel and the coating agent, enhancing the removal of inclusions. Simultaneously, the molten steel near the interface, under gravity, spirals downwards, flowing through the guide holes in the baffles into the purification and casting zones respectively. By rationally designing the chemical composition, melting temperature, viscosity, and dosage of the coating agent, the agent's ability to absorb inclusions is improved, thereby enhancing the purity of the continuously cast steel.

Claims

1. A continuous casting method for improving the purity of molten steel in a single-strand slab, characterized in that: The molten steel height in the tundish is controlled at 1000mm. The tundish is equipped with two baffles, including a first baffle (6) and a second baffle (7). The thickness of the first baffle (6) and the second baffle (7) is 80mm-100mm. The first baffle (6) and the second baffle (7) divide the tundish into an impact zone (1), a purification zone (2), and a casting zone (3). The volume ratio of the three zones is 2:3:

3. The impact zone (1) is equipped with a flow stabilizer (4) to constrain the flow of molten steel entering the impact zone. The casting zone (3) is equipped with a sprue (5). The first baffle (6) and the second baffle (7) are... All retaining walls (7) are provided with through holes; the number of through holes is 5, including a first through hole (8), a second through hole (9), a third through hole (10), a fourth through hole (11), and a fifth through hole (12). The first through hole (8), the second through hole (9), and the third through hole (10) are located in the first row, and the fourth through hole (11) and the fifth through hole (12) are located in the second row. The distance between the two rows is 150mm; the fourth through hole (11) and the fifth through hole (12) of the first retaining wall (6) between the impact zone (1) and the purification zone (2) are provided with through holes. The centerline is 100mm-150mm from the bottom of the tundish. The centerlines of the third through hole (10) and the fifth through hole (12) are 100mm-150mm from the side wall of the tundish. The diameter of the through hole is 60mm-80mm. The horizontal inclination angle α of the through hole is 20°-30°, and the vertical inclination angle β of the through hole is 20°-30°. The centerlines of the fourth through hole (11) and the fifth through hole (12) of the second retaining wall (7) between the purification zone (2) and the casting zone (3) are 150mm-200mm from the bottom of the tundish. mm, the center line of the third through hole (10) and the fifth through hole (12) is 150mm-200mm away from the side wall of the tundish, the diameter of the through hole is 60mm-80mm, the horizontal inclination angle α of the through hole is 15°-25°, and the vertical inclination angle β of the through hole is 15°-25°; the liquid surface of the molten steel is in contact with the covering agent, which includes the following components in the following mass percentages: CaO: 45%-55%, Al2O3: 35%-45%, MgO: 4%-8%, C: 0.5%-2%, and the remainder is Na2O+K2O.

2. The continuous casting method for improving the purity of molten steel in a single-strand slab according to claim 1, characterized in that: The melting temperature of the covering agent is 1300℃-1350℃, and the viscosity at 1400℃ is 0.6 Pa·s-1.0 Pa·s. The thickness of the covering agent in the intermediate ladle is 30mm-50mm.

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