Method for reducing recarburization during mixed casting of continuous casting sheet billet IF steel and low-carbon aluminum killed steel

Abstract

The invention discloses a method for reducing recarburization during mixed casting of IF steel and low-carbon aluminum killed steel of a continuous casting sheet billet in the technical field of continuous casting sheet billet production, which mainly comprises the following steps: before mixed casting of IF steel and low-carbon aluminum killed steel, controlling the amount of residual molten steel in a tundish to be 1 / 4-1 / 3 of the total capacity of the tundish; in the continuous casting process, it is ensured that the amount of molten steel in a tundish is controlled within the range; in the slab continuous casting process, the pulling speed of a continuous casting machine is controlled to range from 1.0 m / min to 0.8 m / min. According to the method, the amount of molten steel in the tundish is controlled to be 1 / 4-1 / 3 of the total capacity, so that the two kinds of molten steel cannot generate large carbon potential gradient in the tundish, carbon migration is reduced, the molten steel entering the tundish has enough buffer space, the recarburization risk caused by unstable flowing of the molten steel is reduced, the continuous casting pulling speed is controlled in cooperation, and the continuous casting quality is improved. The flowing-out speed of the molten steel can be reduced, carbon in air or casting powder caused by too fast flowing of the molten steel is avoided, and it is ensured that the carbon content of the molten steel is always within a controllable range in the whole mixed casting process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting slab production, and particularly relates to a method for reducing carbon pick-up when IF steel and low-carbon aluminum killed steel are mixed cast. BACKGROUND

[0002] In the process of continuous casting slab production, when IF steel and low-carbon aluminum killed steel are mixed cast, the problem of product degradation caused by carbon pick-up often occurs. Carbon pick-up seriously affects the quality and performance of steel, so that it cannot meet the corresponding standards and use requirements, and brings huge economic losses to enterprises. At present, the traditional production process lacks effective control means when dealing with the mixed casting of the two steel grades, and cannot accurately reduce the occurrence of carbon pick-up. There are many reasons for carbon pick-up, such as carbon in refractory materials penetrating into molten steel, carbon in protective slag dissolving into molten steel, carbon in molten steel flowing from the air, etc., but the most important reason is that the carbon content of low-carbon aluminum killed steel is usually slightly higher than that of IF steel. When the two molten steels meet in the tundish during the mixed casting process, carbon will diffuse from the aluminum killed steel with higher carbon potential to the IF steel with lower carbon potential, so that the carbon content of the IF steel increases. SUMMARY

[0003] In order to overcome the deficiency that carbon pick-up is easily caused when IF steel and low-carbon aluminum killed steel are mixed cast, the technical problem to be solved by the present application is to provide a method for reducing carbon pick-up when IF steel and low-carbon aluminum killed steel are mixed cast in continuous casting slab production.

[0004] The technical scheme adopted by the present application to solve the technical problem is: The method for reducing carbon pick-up when IF steel and low-carbon aluminum killed steel are mixed cast in continuous casting slab production controls the remaining amount of molten steel in the tundish to be between 1 / 4 and 1 / 3 of the total capacity of the tundish before the mixed casting of IF steel and low-carbon aluminum killed steel, and ensures that the amount of molten steel in the tundish is controlled within the range during continuous casting. During the process of slab continuous casting, the casting speed of the continuous casting machine is controlled to be between 1.0 m / min and 0.8 m / min, and the lower the speed, the closer to the lower limit of the control range of the amount of molten steel in the tundish.

[0005] Further, the liquid level sensor is used to monitor the liquid level of the molten steel in the tundish in real time during the continuous casting process, and the amount of molten steel in the tundish is calculated according to the liquid level.

[0006] Further, in the continuous casting control system, the continuous casting machine speed, the liquid level sensor and the calculation unit form a closed loop control chain, and the speed is adjusted according to the preset parameters and algorithms to ensure the balance between the speed and the amount of molten steel in the tundish.

[0007] The beneficial effects of the present application are: by controlling the amount of molten steel in the tundish between 1 / 4 and 1 / 3 of the total capacity, the two kinds of molten steel in the tundish will not produce a large carbon potential gradient, thereby reducing carbon migration, and also providing sufficient buffer space for the molten steel entering the tundish, thereby reducing the risk of carbon pickup caused by unstable molten steel flow, and cooperating with the control of the continuous casting speed, the molten steel flow rate can be slowed down, the carbon in the air or protective slag caused by too fast molten steel flow can be reduced, and the carbon content of the molten steel during the entire mixed pouring process can be ensured to be within a controllable range. DETAILED DESCRIPTION

[0008] The present application will be further described below in conjunction with examples.

[0009] In the slab continuous casting process, mixing pouring of IF steel and low-carbon aluminum killed steel is an effective means to improve slab quality. Because IF steel has excellent deep drawing performance and low aging property, but due to its extremely low carbon content and sensitivity to oxygen, problems such as carbon pickup, Al2O3 inclusions, nozzle clogging, and surface defects can easily occur during continuous casting. Low-carbon aluminum killed steel provides moderate carbon, Al deoxidizer, and good fluidity, which can inhibit carbon pickup, reduce Al2O3 inclusions, and improve pouring stability without significantly increasing carbon content. After mixing pouring of the two, the chemical composition, thermodynamic equilibrium, and fluid dynamic characteristics of the molten steel are more in line with the requirements of the continuous casting process, thereby realizing high-quality, low-defect IF steel continuous casting products. However, if the mixed pouring process is not properly controlled, the carbon in the aluminum killed steel will diffuse, and the carbon in the air or protective slag will be entrained into the molten steel, resulting in excessive carbon content of the molten steel and product degradation.

[0010] To solve the above problems, the present application provides a method for reducing carbon pickup during mixed pouring of continuous casting slab IF steel and low-carbon aluminum killed steel, which mainly controls the amount of remaining molten steel in the tundish to be between 1 / 4 and 1 / 3 of the total capacity of the tundish before mixing pouring of IF steel and low-carbon aluminum killed steel, and ensures that the amount of molten steel in the tundish is controlled within this range during continuous casting. During the slab continuous casting process, the casting speed of the continuous casting machine is controlled between 1.0 m / min and 0.8 m / min, and the lower the speed, the closer to the lower limit of the tundish molten steel amount control range. The control of the amount of molten steel in the tundish can be realized by monitoring the liquid level height of the molten steel in the tundish through the liquid level sensor installed in the tundish, and then converting the liquid level height to obtain the amount of molten steel in the tundish. In addition, in order to realize the linkage control of the continuous casting speed and the amount of molten steel in the tundish, the continuous casting control system can be composed of a closed loop control chain including the continuous casting machine speed, the liquid level sensor, and the calculation unit, and the continuous casting machine speed can be adjusted according to the preset parameters and algorithms, so that the continuous casting machine speed and the amount of molten steel in the tundish are always in a balanced state during the continuous casting process, and the carbon content of the molten steel during the entire mixed pouring process can be ensured to be within a controllable range.

[0011] The present application does not change the mixing ratio and temperature parameters of the existing mixed pouring process for IF steel and low-carbon aluminum killed steel, ensures that the composition of the molten steel meets the grade requirements, and only optimizes the control of the tundish molten steel quantity and the casting speed.

[0012] For the control of the tundish molten steel quantity, on the one hand, the total quantity of the two molten steels is controlled in a lower range, which can reduce the diffusion of carbon in the low-carbon aluminum killed steel to the IF steel caused by long-time mixing of the two molten steels; on the other hand, a small quantity of molten steel is beneficial to the control of molten steel flow, and unstable molten steel flow can easily cause large fluctuations in the surface of the molten steel, resulting in the gas being entrained into the molten steel, and at the same time, the stable interface between the molten steel and the protective slag is destroyed, so that the carbon in the slag layer is more easily absorbed by the molten steel. According to the long-term experience and a large number of tests in this field, the applicant has proved that controlling the remaining molten steel quantity in the tundish between 1 / 4 and 1 / 3 of the total capacity of the tundish can achieve good results in reducing carbon diffusion and ensuring stable molten steel flow.

[0013] For the control of the casting speed, the casting speed is a key parameter for balancing the two requirements of “scouring slag removal” and “homogenization diffusion”, and has a great influence on the forming quality of the slab. If the casting speed is too high, strong scouring will occur, resulting in an increase in the size of Al2O3 inclusions and slag inclusion, and a decrease in the cleanliness of the surface of the casting slab. If the casting speed is too low, fine Al2O3 clusters will be aggregated, and the production efficiency will be reduced. A reasonable casting speed enables the molten steel to have sufficient scouring effect to remove the slag layer that has been entrained, and has sufficient residence time to allow the two molten steels to fully diffuse in the tundish, so as to realize the homogenization of carbon, aluminum, titanium and other micro-alloy elements, while maintaining a low number of surface inclusions, meeting the requirements of ultra-low carbon and cleanliness of the IF steel. According to the long-term experience and a large number of tests in this field, the applicant has proved that controlling the casting speed of the continuous casting machine between 1.0 m / min and 0.8 m / min can meet the two requirements of “scouring slag removal” and “homogenization diffusion”. The lower the casting speed is, the closer it is to the lower limit of the control range of the tundish molten steel quantity, mainly to ensure the stability of the molten steel quantity in the tundish.

[0014] Embodiment: Taking a tundish with a total capacity of 60 tons as an example, the remaining molten steel quantity in the tundish is controlled between 15-20 tons before mixed pouring, the liquid level sensor detects that the liquid level is between 150-200 mm, and the liquid level is controlled in this range during the continuous casting process, and the casting speed of the continuous casting machine is stably controlled at about 0.8 m / min. According to the comparison test of multiple batches of continuous casting slabs, the control method of the present application can reduce the judgment amount by 50% compared with the traditional process (the tundish molten steel quantity is not specially managed, and the casting speed of the continuous casting machine is between 1.5 m / min and 1 m / min), which proves that by controlling the tundish molten steel quantity and the casting speed of the continuous casting machine, the carbon increase amount during the mixed pouring of the IF steel and the low-carbon aluminum killed steel can be limited, thereby improving the process stability of the continuous casting slab.

Claims

1. A method for reducing carbon gain when continuously cast slabs of IF steel and low-carbon aluminum-killed steel are mixed, characterized in that: Before mixing IF steel with low-carbon aluminum killed steel, the remaining molten steel in the tundish should be controlled between 1 / 4 and 1 / 3 of the total tundish capacity, and the molten steel in the tundish should be kept within this range during continuous casting. During the slab continuous casting process, the casting speed of the continuous casting machine should be controlled between 1.0 m / min and 0.8 m / min, and the casting speed should be lower as it gets closer to the lower limit of the molten steel control range in the tundish.

2. The method for reducing carbon gain when mixing IF steel and low-carbon aluminum-killed steel in continuously cast slabs as described in claim 1, characterized in that: During continuous casting, a liquid level sensor is used to monitor the liquid level of molten steel in the ladle in real time, and the amount of molten steel in the ladle is calculated based on the liquid level.

3. The method for reducing carbon gain when mixing IF steel and low-carbon aluminum-killed steel in continuously cast slabs as described in claim 2, characterized in that: In the continuous casting control system, the casting speed, liquid level sensor and computing unit are combined into a closed-loop control chain. The casting speed is adjusted according to preset parameters and algorithms to ensure the balance between the casting speed and the amount of molten steel in the ladle.