Casting method for continuous casting

Abstract

The invention relates to the technical field of continuous casting production, and discloses a continuous casting casting method which comprises the following steps: manufacturing a tundish by adopting a refractory material with high fire resistance and high strength; the baking temperature of the tundish is controlled to be consistent with the molten steel casting temperature; if the degree of superheat of the molten steel is 20-40 DEG C, continuous casting operation is carried out, otherwise, continuous casting process parameters including the pulling speed and the secondary cooling water amount are adjusted according to the degree of superheat of the molten steel. According to the continuous casting method, the superheat degree of the molten steel can be effectively controlled, the problem of poor casting blank quality caused by high superheat degree of the first ladle during casting is reduced, the power consumption for heating the molten steel is reduced, and the production efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting production, in particular, to a continuous casting starting method. BACKGROUND

[0002] In continuous casting production, the superheat of molten steel directly affects the continuous casting process parameters, the surface quality of the casting blank, the blank shell thickness, the dendrite spacing size and the internal quality of the casting blank. If the superheat is too large, the solidification time of the casting blank with the same section is long, the element segregation is large, the center segregation level is high, the casting blank shell is thin, and surface cracks or induced pulling leaks are easily formed. The surface layer dendrite is thick, and the tendency of forming intermediate cracks at the position of the secondary cooling zone is increased. If the superheat is too small, the viscosity of the molten steel is large, and the fluidity is poor, which is not conducive to the floating of inclusions, the water nozzle is easily blocked or even frozen during the continuous casting process, and porosity and shrinkage holes are easily produced in the continuous casting blank. The role of the tundish is to accept the molten steel from the ladle, and it plays an important role in realizing the continuous production of the steelmaking process. However, a higher superheat of the molten steel will increase the refractory consumption of the entire steelmaking process, increase the number and size of inclusions in the molten steel, and at the same time, reduce the casting speed and production efficiency. A lower superheat will increase the production risk of low casting starting rate and "frozen eye" pouring. Therefore, the superheat of the molten steel has an important influence on the continuous casting process parameters, the surface quality of the casting blank, the blank shell thickness, the dendrite spacing size and the internal quality of the casting blank, and the superheat of the molten steel in the tundish needs to be accurately controlled.

[0003] In order to reduce the process temperature loss and temperature fluctuation, and control the superheat of the molten steel within a suitable range, common measures include covering the ladle and the tundish with insulation agents, roasting the ladle and the tundish, covering the ladle or the tundish, cooling the scrap blank, plasma heating of the tundish, electromagnetic induction heating of the tundish, etc. However, these measures all have defects, such as long-term cooling affecting the continuity of production and reducing production efficiency; if the scrap blank is not surface treated or roasted, it will increase the phenomenon of excessive oxide inclusions in the steel and hydrogen embrittlement; the passage of inert gas can reduce the temperature, but increases the cost. Therefore, it is necessary to improve the quality of the tundish refractory, ensure that the temperature of the tundish roasting and the starting temperature of the molten steel are consistent, reduce the poor casting blank quality caused by high superheat of the first package during starting, and reduce the power consumption of the molten steel heating.

[0004] To overcome the above technical problems, the patent application with publication number CN108907130A discloses a method for automatic casting of a thin slab continuous casting machine. The method realizes automatic casting by preheating the tundish, controlling the superheat degree of the molten steel in the tundish, and controlling the molten steel level. Although the method improves the automation degree of continuous casting production, it still has problems of poor quality of tundish refractory, inconsistency between the tundish baking temperature and the molten steel casting temperature, and high superheat degree of the molten steel. The patent application with publication number CN117696845A discloses a method for casting of a medium-thick slab continuous casting machine. The method improves the stability of the continuous casting process by using slab continuous casting, full-process protective casting, and controlling the high superheat degree of the molten steel in the tundish. Although the method improves the stability of the continuous casting process, it still has problems of poor quality of tundish refractory, inconsistency between the tundish baking temperature and the molten steel casting temperature, and high superheat degree of the molten steel. Therefore, the existing technology has the following disadvantages: 1. Poor quality of tundish refractory, resulting in high superheat degree of the molten steel and affecting the quality of the cast slab; 2. Inconsistency between the tundish baking temperature and the molten steel casting temperature, resulting in high superheat degree of the molten steel and affecting the quality of the cast slab; 3. High superheat degree of the molten steel increases the power consumption for heating the molten steel; 4. Long-time cooling affects the production continuity and reduces the production efficiency; the waste material is not subjected to surface treatment or baking, increasing the phenomena of excessive oxide inclusions in the steel and hydrogen embrittlement; the inert gas passage can reduce the temperature, but increases the cost; 5. The superheat degree of the molten steel cannot be effectively controlled, resulting in long solidification time of the cast slab with the same cross section, large element segregation, high center segregation grade, thin cast slab shell, easy formation of surface cracks or induced leakage, and increased tendency of intermediate cracks in the two-cooling zone position. SUMMARY

[0005] The purpose of the present application is to overcome the problems of poor quality of tundish refractory, inconsistency between the tundish baking temperature and the molten steel casting temperature, high superheat degree of the molten steel, and increased power consumption for heating the molten steel in the existing technology, and to provide a continuous casting casting method that can effectively control the superheat degree of the molten steel, reduce the problem of poor quality of the cast slab caused by high superheat degree of the first package in the casting process, reduce the power consumption for heating the molten steel, and greatly improve the production efficiency.

[0006] To achieve the above purpose, the present application provides a continuous casting casting method, which comprises: manufacturing the tundish by using high-refractory and high-strength refractory material; controlling the tundish baking temperature to be consistent with the molten steel casting temperature; If the superheat of the molten steel is 20℃-40℃, then the continuous casting start-up operation is carried out; otherwise, the continuous casting process parameters, including casting speed and secondary cooling water volume, are adjusted according to the superheat of the molten steel.

[0007] Preferably, the intermediate ladle is manufactured using high-refractory and high-strength refractory materials, including manufacturing the intermediate ladle using high-alumina refractory materials and subjecting the intermediate ladle to high-temperature sintering.

[0008] Preferably, the use of high-refractory and high-strength refractory materials to manufacture the tundish also includes the use of refractory castables for maintenance of the tundish.

[0009] Preferably, the high-refractory and high-strength refractory material is a high-alumina brick or a high-alumina castable.

[0010] Preferably, the alumina content in the high-alumina bricks or high-alumina castables is 70%-90%.

[0011] Preferably, the intermediate batch is baked at 1500℃-1650℃ for 5-6 hours.

[0012] Preferably, the maintenance of the tundish includes applying refractory castable to the inner wall of the tundish before each pouring, with a coating thickness of 10-20 mm.

[0013] Preferably, controlling the tundish baking temperature to be consistent with the molten steel pouring temperature includes: Infrared thermometers are used to detect the temperature of the tundish, and the target baking temperature of the tundish is set according to the initial pouring temperature of the molten steel. Adjust the heating element of the intermediate bread to bring the intermediate bread to the target baking temperature.

[0014] Preferably, adjusting the continuous casting process parameters according to the superheat of the molten steel includes: When the molten steel is overheated, reduce the casting speed and increase the amount of secondary cooling water. When the superheat of molten steel is too low, increase the casting speed and reduce the amount of secondary cooling water. A high-superheat casting process is used to control the upper limit of nitrogen content in steel and avoid the large-scale generation of TiN in the tundish. The process employs an air curtain baffle and argon blowing on the liquid surface of the tundish, along with full-process protective sleeve casting, and removes some inclusions from the molten steel by microbubbles rising to the surface. The billet is subjected to end-solidation pressure reduction and end-solidation strong cooling to improve the center segregation index and carbon segregation index.

[0015] Preferably, when the superheat of the molten steel is too high, the casting speed is reduced to 0.22-0.26 m / min, and the secondary cooling water volume is increased to improve the cooling intensity of the crystallizer to 4000 L / min; when the superheat of the molten steel is too low, the casting speed is increased to 0.02-0.04 m / min to reduce the temperature drop; the nitrogen content in the steel is controlled to an upper limit of 80 ppm by using a high superheat casting process, and the billet is subjected to a 10-20 mm reduction at the end of solidification and strong cooling at the end of solidification.

[0016] According to the above technical solution, a tundish is manufactured using high-refractory, high-strength refractory materials. The tundish baking temperature is then controlled to match the initial pouring temperature of the molten steel. If the superheat of the molten steel is between 20°C and 40°C, continuous casting is performed. Otherwise, the continuous casting process parameters, including casting speed and secondary cooling water volume, are adjusted based on the superheat of the molten steel. This effectively controls the superheat of the molten steel, reducing the problem of poor billet quality caused by high superheat in the first pour, while also reducing the electricity consumption for heating the molten steel and improving production efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a continuous casting start-up method according to one embodiment of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] In this invention, unless otherwise stated, directional terms such as "inner wall" in the terminology represent only the orientation of the term in its normal use or are common terms understood by those skilled in the art, and should not be regarded as a limitation on the term.

[0020] See Figure 1 The present invention provides a continuous casting start-up method, which includes: The intermediate ladle is manufactured using high-refractory and high-strength refractory materials; The baking temperature of the tundish is controlled to be consistent with the initial pouring temperature of the molten steel. If the superheat of the molten steel is 20℃-40℃, then the continuous casting start operation is carried out; otherwise, the continuous casting process parameters, including casting speed and secondary cooling water volume, are adjusted according to the superheat of the molten steel.

[0021] Through the above technical solutions, in order to improve the quality of tundish refractory materials, high-refractory and high-strength refractory materials are used to manufacture the tundish, thereby improving the service life and heat resistance of the tundish. In order to avoid excessive or insufficient superheat of the molten steel, the baking temperature of the tundish is controlled to ensure that the baking temperature of the tundish is consistent with the initial pouring temperature of the molten steel. Next, it is determined whether the superheat of the molten steel is within a reasonable range (20℃-40℃). If so, the continuous casting initial pouring operation is carried out. Otherwise, the continuous casting process parameters, including the casting speed and the secondary cooling water volume, are adjusted according to the superheat of the molten steel.

[0022] Specifically, in this embodiment, it is preferable to use high-refractory, high-strength refractory materials to manufacture the tundish, including high-alumina refractory materials, and then subject the tundish to high-temperature sintering. The resulting tundish exhibits higher refractoriness and is less prone to softening or melting during prolonged contact with molten steel at high temperatures. Furthermore, high-alumina materials offer strong resistance to chemical corrosion from molten steel and slag, reducing the formation of low-melting-point substances and extending service life. High-temperature sintering of the tundish further strengthens the internal particle structure, reducing porosity and preventing cracking due to thermal expansion during use. Simultaneously, a dense surface layer forms after sintering, further hindering slag penetration and enhancing corrosion resistance.

[0023] In this embodiment, to further extend the service life of the tundish, it is preferable to use high-refractory, high-strength refractory materials to manufacture the tundish, and this also includes the use of refractory castables for maintenance. Because the bottom, impact zone, and slag line of the tundish are subject to long-term scouring by molten steel and slag erosion, they are prone to localized damage. Refractory castables can be quickly repaired, avoiding complete replacement, saving costs and reducing furnace downtime. The castables are easy to apply, harden quickly, significantly shorten the maintenance cycle, and improve continuous casting efficiency.

[0024] In this embodiment, considering factors such as refractory performance, mechanical strength, chemical stability, and economy, high-alumina bricks or high-alumina castables are preferred as high-refractory materials with high refractory and high strength. High-alumina bricks or high-alumina castables possess high-temperature resistance far exceeding that of ordinary clay bricks, enabling them to withstand high-temperature molten steel for extended periods. Furthermore, they exhibit good volume stability at high temperatures, resisting softening or deformation and preventing collapse of the tundish lining. Simultaneously, high-alumina bricks or high-alumina castables have a dense structure, excellent room-temperature compressive strength and high-temperature flexural strength, resisting the impact of molten steel in the impact zone, slag flow friction, and mechanical damage during the cleaning of residual steel.

[0025] In this embodiment, in order to significantly improve the refractoriness, it is preferred that the alumina content in the high-alumina bricks or high-alumina castables is 70%-90%.

[0026] In one specific implementation, in order to improve the strength and density of the intermediate package, it is preferable to bake the intermediate package at a high temperature of 1500℃-1650℃ for 5-6 hours.

[0027] In addition, to facilitate maintenance of the tundish and extend its service life, it is preferable to maintain the tundish by applying refractory castable to the inner wall of the tundish before each pouring, with a coating thickness of 10-20mm.

[0028] The above-mentioned control of the tundish baking temperature to be consistent with the molten steel pouring temperature includes: Infrared thermometers are used to detect the temperature of the tundish, and the target baking temperature of the tundish is set according to the initial pouring temperature of the molten steel. Adjust the heating device of the tundish to bring the tundish temperature to the target baking temperature (if the initial pouring temperature of molten steel is 1550℃, the target baking temperature of the tundish is set to 1540℃-1560℃). This adjustment process can be carried out by heating the tundish with electric heating or gas heating.

[0029] In this embodiment, the preferred method for adjusting the continuous casting process parameters based on the superheat of the molten steel includes: When the molten steel is overheated, reduce the casting speed and increase the amount of secondary cooling water. When the superheat of molten steel is too low, increase the casting speed and reduce the amount of secondary cooling water. A high-superheat casting process is used to control the upper limit of nitrogen content in steel and avoid the large-scale generation of TiN in the tundish. The process employs an air curtain baffle and argon blowing on the liquid surface of the tundish, along with full-process protective sleeve casting. Microbubbles are used to remove some inclusions from the molten steel, reducing secondary inclusions. The billet is subjected to end-solidation pressure reduction and end-solidation strong cooling to improve the center segregation index and carbon segregation index.

[0030] Specifically, when the molten steel is excessively superheated, the casting speed is reduced to 0.22-0.26 m / min, and the secondary cooling water flow is increased to enhance the crystallizer cooling intensity to 4000 L / min, preventing steel leakage caused by a thin billet shell. When the molten steel is excessively superheated, the casting speed is increased to 0.02-0.04 m / min to reduce the temperature drop and prevent nozzle blockage. A high superheat casting process is used to control the nitrogen content in the steel to an upper limit of 80 ppm, preventing the excessive formation of TiN in the tundish and thus avoiding nozzle blockage. The billet is subjected to a 10-20 mm reduction at the end of solidification and strong cooling at the end of solidification to improve the center segregation index and carbon segregation index.

[0031] In summary, the continuous casting method provided by this invention improves the quality of refractory material in the tundish, ensures that the tundish baking temperature is consistent with the molten steel pouring temperature, effectively controls the superheat of the molten steel, and reduces the problem of poor billet quality caused by high superheat in the first pour. Secondly, it reduces the power consumption for heating the molten steel, improving production efficiency. Furthermore, it avoids the problem of prolonged cooling affecting production continuity, prevents excessive oxide inclusions and hydrogen embrittlement in the steel due to scrap billets, and eliminates the need for inert gas, thus reducing costs. In addition, it effectively controls the superheat of the molten steel, avoiding problems such as long solidification time, large elemental segregation, and high central segregation levels in billets with the same cross-section; it avoids the problem of thin billet shells easily forming surface cracks or inducing pull-out; and it avoids the increased tendency for coarse surface dendrites to form central cracks in the secondary cooling zone, achieving multiple benefits.

[0032] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A continuous casting start-up method, characterized in that, The continuous casting start-up method includes: The intermediate ladle is manufactured using high-refractory and high-strength refractory materials; The baking temperature of the tundish is controlled to be consistent with the initial pouring temperature of the molten steel. If the superheat of the molten steel is 20℃-40℃, then the continuous casting start operation is carried out; otherwise, the continuous casting process parameters, including casting speed and secondary cooling water volume, are adjusted according to the superheat of the molten steel.

2. The continuous casting start-up method according to claim 1, characterized in that, The process of manufacturing the intermediate ladle using high-refractory and high-strength refractory materials includes manufacturing the intermediate ladle using high-alumina refractory materials and sintering the intermediate ladle at high temperature.

3. The continuous casting start-up method according to claim 2, characterized in that, The use of high-refractory and high-strength refractory materials to manufacture tundishes also includes the use of refractory castables for the maintenance of tundishes.

4. The continuous casting start-up method according to any one of claims 1-3, characterized in that, The high-refractory, high-strength refractory material is a high-alumina brick or a high-alumina castable.

5. The continuous casting start-up method according to claim 4, characterized in that, The alumina content in the high-alumina brick or the high-alumina castable is 70%-90%.

6. The continuous casting start-up method according to claim 2, characterized in that, The intermediate batch is baked at 1500℃-1650℃ for 5-6 hours.

7. The continuous casting start-up method according to claim 3, characterized in that, The maintenance of the tundish includes applying refractory castable to the inner wall of the tundish before each pouring, with a coating thickness of 10-20mm.

8. The continuous casting start-up method according to claim 1, characterized in that, The step of controlling the tundish baking temperature to be consistent with the molten steel pouring temperature includes: Infrared thermometers are used to detect the temperature of the tundish, and the target baking temperature of the tundish is set according to the initial pouring temperature of the molten steel. Adjust the heating element of the intermediate bread to bring the intermediate bread to the target baking temperature.

9. The continuous casting start-up method according to claim 1, characterized in that, The adjustment of continuous casting process parameters based on the superheat of molten steel includes: When the molten steel is overheated, reduce the casting speed and increase the amount of secondary cooling water. When the superheat of molten steel is too low, increase the casting speed and reduce the amount of secondary cooling water. A high-superheat casting process is used to control the upper limit of nitrogen content in steel and avoid the large-scale generation of TiN in the tundish. The process employs an air curtain baffle and argon blowing on the liquid surface of the tundish, along with full-process protective sleeve casting, and removes some inclusions from the molten steel by microbubbles rising to the surface. The billet is subjected to end-solidation pressure reduction and end-solidation strong cooling to improve the center segregation index and carbon segregation index.

10. The continuous casting start-up method according to claim 9, characterized in that, When the molten steel is too overheated, the casting speed is reduced to 0.22-0.26 m / min, and the secondary cooling water flow is increased to improve the cooling intensity of the crystallizer to 4000 L / min; when the molten steel is too underheated, the casting speed is increased to 0.02-0.04 m / min to reduce the temperature drop. The nitrogen content in the steel is controlled to an upper limit of 80ppm by using a high superheat casting process, and the billet is subjected to a 10-20mm reduction at the end of solidification and strong cooling at the end of solidification.

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